Method for producing a resin composition having a porous structure with independent porosities
09657153 ยท 2017-05-23
Assignee
Inventors
- Yohei Miyauchi (Inagi, JP)
- Naotake Sato (Sagamihara, JP)
- Yuichi Hashimoto (Tokyo, JP)
- Toshihiro Kikuchi (Yokohama, JP)
Cpc classification
C08L79/08
CHEMISTRY; METALLURGY
C08G73/10
CHEMISTRY; METALLURGY
G03G15/162
PHYSICS
C08J2205/044
CHEMISTRY; METALLURGY
C08J9/28
CHEMISTRY; METALLURGY
G03G15/2057
PHYSICS
C08L77/00
CHEMISTRY; METALLURGY
C08J2201/054
CHEMISTRY; METALLURGY
C08J9/286
CHEMISTRY; METALLURGY
C08J2205/052
CHEMISTRY; METALLURGY
International classification
C08J9/28
CHEMISTRY; METALLURGY
C08L79/08
CHEMISTRY; METALLURGY
C08J9/00
CHEMISTRY; METALLURGY
C08G73/10
CHEMISTRY; METALLURGY
C08L77/00
CHEMISTRY; METALLURGY
Abstract
An object of the present invention is to provide a porous material (resin composition) having high heat insulation properties, mechanical properties, and electrical properties by controlling function of a porous film by setting a porosity size, distribution of the porosity size, and a porosity ratio of the porous film in predetermined ranges. The resin composition according to the present invention is comprised of an engineering plastic having porous structure in which not less than 80% of a total porosity is comprised of independent porosities, a mean porosity size is not less than 0.01 m and not more than 0.9 m, and not less than 80% of the total porosity has a porosity size within 30% of the mean porosity size.
Claims
1. A method for producing a resin composition having a porous structure in which 80% to 94% of a total porosity is comprised of independent porosities, the independent porosities having walls having no opening between adjacent porosities, the method comprising: molding a resin solution having a viscosity of 10,000 cP to 1,000,000 cP; and removing a solvent of the resin solution by a phase separation method to perform porosification, wherein the porous structure has a mean porosity size of 0.01 m to 0.9 m, and wherein not less than 80% of the total porosity has a porosity size within 30% of the mean porosity size.
2. The method according to claim 1, wherein the resin solution comprises at least one selected from the group consisting of a polyimide, a polyamidoimide, a polyamide, a polyether imide, a polycarbonate, a polyether ether ketone, a polysulfone, and a polyether sulfone.
3. The method according to claim 1, wherein the resin solution contains 1% by weight to 30% by weight based thereon of a conductive controlling agent.
4. The method according to claim 1, wherein the porous structure has a porosity ratio from 10% to 90%.
5. The method according to claim 1, wherein the porous structure has a porosity ratio from 30% to 70%.
6. The method according to claim 1, wherein the porous structure has a porosity ratio from 60% to 70%.
7. The method according to claim 1, wherein the composition includes an inorganic substance that increases viscosity of a precursor of the resin solution.
8. The method according to claim 7, wherein the inorganic substance comprises at least one substance selected from the group consisting of lithium chloride, lithium bromide, and lithium oxalate.
9. The method according to claim 1, wherein the resin composition is a resin film, which is disposed between a substrate and a releasing layer.
10. The method according to claim 9, wherein the releasing layer has a thickness of 1 mm to 10 mm.
11. The method according to claim 9, wherein if the resin film has a macro void, a porosity size thereof is less than 10 m.
12. The method according to claim 9, wherein the resin film has a thickness of at least 120 m.
13. The method according to claim 1, wherein the viscosity of the resin solution is 94,000 cP to 500,000 cP.
14. The method according to claim 1, wherein the resin composition has a thermal conductivity of less than 0.1 W/m.Math.K, a compression resistance of less than 10%, and a thermal conductivity after compression of less than 0.1 W/m.Math.K.
15. The method according to claim 1, wherein the resin composition has a thermal conductivity of less than 0.05 W/m.Math.K.
16. The method according to claim 1, wherein not less than 91% of the total porosity has the porosity size within 30% of the mean porosity size.
17. The method according to claim 1, wherein the phase separation method comprises adjusting a solvent substitution rate.
18. The method according to claim 17, wherein the adjusting of the solvent substitution rate comprises adding a second solvent and a solidifying solvent, wherein the solidifying solvent is water, and wherein the second solvent is at least one selected from the group consisting of ethanol, methanol, propanol, acetone, and methyl ethyl ketone.
19. A for producing a resin composition having a porous structure in which 80% to 94% of a total porosity is comprised of independent porosities, the independent porosities having walls having no opening between adjacent porosities, the method comprising: molding a resin solution having a viscosity of 10,000 cP to 1,000,000 cP; and removing a solvent of the resin solution by a phase separation method, which comprises adjusting a solvent substitution rate, to perform porosification, wherein the porous structure has a mean porosity size of 0.01 m to 0.9 m, wherein not less than 80% of the total porosity has a porosity size within 30% of the mean porosity size, wherein the adjusting of the solvent substitution rate comprises adding a solidifying solvent and changing a temperature of the solidifying solvent, and wherein the solidifying solvent is water.
20. The method according to claim 1, wherein the phase separation method comprises adjusting a solidifying rate.
21. A method for producing a resin composition having a porous structure in which 80% to 94% of a total porosity is comprised of independent porosities, the independent porosities having walls having no opening between adjacent porosities, the method comprising: molding a resin solution having a viscosity of 10,000 cP to 1,000,000 cP; and removing a solvent of the resin solution by a phase separation method to perform porosification, wherein the porous structure has a mean porosity size of 0.01 m to 0.9 m, wherein not less than 80% of the total porosity has a porosity size within 30% of the mean porosity size, and wherein the phase separation method comprises casting the resin solution on a substrate to form a cast film and covering the cast film with a solvent substitution rate adjustment film.
22. The method according to claim 3, wherein the conductive controlling agent is at least one of carbon black and a metal oxide.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DESCRIPTION OF THE EMBODIMENTS
(15) In order to describe the present invention in detail, embodiments for implementing the invention will be shown below using the drawing. The embodiments individually disclosed are an example of actual usage of a resin composition as the present invention, a lamination film containing the resin composition, and an image forming apparatus that uses the lamination film as a component, but the present invention will not be limited to these.
(16) (Embodiments of the Present Invention)
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(18) From a viewpoint of mechanical properties, the porous structure of the resin composition in the present embodiment includes independent porosities whose spaces are separated by a resin wall of a curved surface. The porosities are independent of each other, and each have a wall made of a resin between the porosities. For that reason, it is expected that the entire resin composition will manifest a modulus of elasticity higher than that of a continuous porosity because of not only the modulus of elasticity of the resin but also an effect of gas pressure in the porosity. Formation of the independent porosities can reduce invasion of impurities produced in an image formation process into a porous layer, and can suppress manifestation of deterioration of the material and change in physical properties. Moreover, in the porous structure according to the present embodiment, the independent porosities occupy not less than 80% of the total porosity. Here, the independent porosity means a porosity in which the wall of the resin existing between the porosity and an adjacent porosity has no opening hole.
(19) The porosity size of the resin composition in the present embodiment is properly selected in the range of not less than 0.01 m and not more than 0.9 m. Form a viewpoint of heat insulation properties, the porosity size is preferably not more than a mean free path of air. At a porosity size of not more than the mean free path (65 nm in the case of the air), the thermal conductivity of the air included in the porosity is reduced, and the porosity can be regarded as vacuum. For that reason, the thermal conductivity is reduced as the entire the resin composition, and improvement in heat insulation properties can be expected. However, at a porosity size smaller than 0.01 m, the configuration is similar to a nonporous film, and therefore propagation by heat conduction in the porosities through the resin wall is increased. For that reason, the thermal conductivity is increased as the entire resin composition, making it difficult to use the resin composition as a heat insulating material. Moreover, the porosity size can be controlled by a viscosity of a solution as described later. However, in the case where it is going to realize a porosity size of not more than 0.01 m, the viscosity of the solution is very high, leading to difficulties in handling in film production.
(20) The porous structure of the resin composition according to the present invention also has a structure including no macro void having a porosity size of not less than 10 m. This is because when the macro voids are increased, the material easily deteriorates due to external physical change such as compression and tension. Preferably, no macro void is included for a relationship with a conductive controlling agent, as described later. Further, in the present invention, the mean porosity size of the resin composition is within the range of not less than 0.1 m and not more than 0.9 m. A method for measuring a porosity size in the present embodiment is not particularly limited. The conventional measuring method can be used, and mercury porosimetry and image analysis after SEM observation can be used.
(21) Further, in the present invention, not less than 80% of the total porosity includes a porosity size within 30% of the mean porosity size in the above-mentioned range.
(22) The porosity size is kept uniform, an external stress can be dispersed, and it is less likely to produce deterioration of the film or cracks by concentration of stress because not less than 80% of the total porosity includes a porosity size within 30% of the mean porosity size. Moreover, in the case where a material such as a filler is dispersed in the film, a uniform dispersion state is obtained and desired properties are easily manifested.
(23) The porosity ratio in the resin composition is from not less than 10% and not more than 90%, and particularly preferably from not less than 30% and not more than 70%. At an excessively low porosity ratio, reduction in the thermal conductivity is suppressed so that heat insulation properties cannot be manifested. At an excessively high porosity ratio, the film having poor mechanical strength is obtained, making it difficult to use the film as an electrophotographic belt member. A method for measuring a porosity ratio in the present embodiment is not particularly limited. For example, the porosity ratio can be calculated with a density measurement method.
(24) The thermal conductivity of the porous layer can be reduced by properly determining the porosity size and the porosity ratio. For example, in the case of a polyimide material, the thermal conductivity of a nonporous film is approximately from 0.2 to 0.3 [W/mK]. On the other hand, the thermal conductivity can be reduced to approximately 0.03 to 0.1 [W/mK] by providing the porosities of the present invention, which have the independent porosities that occupy not less than 80% of the total porosity.
(25) The engineering plastic used for the present invention is a functional resin having a heat-resistant temperature of not less than 110 C. Here, the heat-resistant temperature refers to a temperature at which the resin can be continuously used without deforming nor deteriorating, for example, refers to a glass transition temperature.
(26) The resin composition including the engineering plastic used for the present invention includes a resin composition selected from the group consisting of polyimides, polyamidoimides, polyamides, polyether imides, polysulfones, polyether sulfones, polycarbonates, and polyether ether ketones or a combination thereof. These resin compositions are a material having high thermal resistance, mechanical properties, and solvent resistance.
(27) The present inventors considered an optimal configuration in case of using these materials as a transfer member or a fixing belt member for the electrophotographic image forming apparatus. As a result, it was found out that the porous structure in the range of the present invention can suppress deterioration of the material and change in physical properties in thermal and chemical environments to which the porous structure is exposed, and a film with high mechanical strength can be attained even if the porosity ratio is set to be high in order to improve heat insulation properties. Of these, thermosetting polyimides can be use suitably from a viewpoint of operability of the porosification method, control of the porosity form, thermal resistance, and mechanical strength.
(28) Hereinafter, a method for producing a resin composition according to the present invention will be described in detail.
(29) A method for producing a resin composition according to the present invention is a method for producing a resin composition having a porous structure in which not less than 80% of the total porosity includes the independent porosities. The method also includes molding an engineering plastic resin solution having a viscosity of not less than 10,000 cP and not more than 1,000,000 cP, and removing a solvent of the resin solution with a phase separation method to perform porosification.
(30) Production of the resin composition is preferably conducted using a phase separation method. A solution (resin solution) of a resin such as polyamic acid serving as a raw material is molded on a substrate. Subsequently, the substrate is immersed in a solidifying solvent to be porosified. A molded shape can be selected properly, and a method for cast molding a resin solution into a shape of a film is preferable. The state of the film changes (phase transition) by immersing the substrate in the solidifying solvent. This method is referred to as the phase separation method. Phase transition here means that a resin deposits as a solid by immersing a solution system in a solidifying solvent (poor solvent).
(31) When polyamic acid is used for the resin solution, a porous polyimide film can be obtained by further imidizing the resin after this porosification.
(32) Upon production of the porous film with the above-mentioned method, the porous film is preferably produced with the phase separation method by using the resin solution having a viscosity of not less than 10,000 cP and not more than 1,000,000 cP, and more preferably not less than 30,000 cP and not more than 500,000 cP. A resin having a low viscosity cannot suppress growth of the macro voids. Conversely, a resin having a high viscosity cannot be casted on the substrate with the casting method. Accordingly, film production is difficult.
(33) The viscosity of the solution can be increased or controlled by adding an inorganic salt to the resin solution.
(34) Here, as the inorganic salt, lithium chloride, lithium bromide, lithium oxalate and the like, are used suitably. Addition of the inorganic salt can improve the viscosity of the resin solution, and can suppress growth of the macro voids produced at the time of phase transition.
(35) The resin composition without macro voids can be obtained also by adjusting a solvent substitution rate.
(36) As a method, a cast film can be covered with a solvent substitution rate adjustment film to be immersed in the solidifying solvent, for example. Alternatively, without using the above-mentioned film, phase transition is conducted by adding the solvent used to dissolve the resin to the solidifying solvent, or by changing the temperature of the solidifying solvent, thereby, the solvent substitution rate can be changed so that the same effect as that of a solvent substitution adjustment material can be manifested.
(37) Here, a sheet-shape polymeric material having constant porosities is used as a solvent substitution adjustment film. Specifically, nonwoven fabrics and resin compositions including polyolefines, celluloses, and fluororesins are used suitably. Upon phase transition, by covering the cast film with the above-mentioned film, the substitution rate of the solvent of the resin solution and the solidifying solvent can be adjusted to obtain the resin composition having a uniform porosity size without macro voids.
(38) Moreover, the porosity size of the porous film can be controlled by changing the solidifying rate of the resin. Specifically, the porosity size can be reduced by making the solidifying rate faster, and the porosity size can be increased by making the solidifying rate slower. Accordingly, the porosity size can be properly controlled by changing the solidifying rate using the viscosity of the resin or the solvent substitution adjustment material.
(39) As a parameter to control the solidifying rate, a Gurley value of a sheet having porosities or the temperature of the solidifying solvent can be used, for example. Preferably, a value represented by a product of the Gurley value and the resin viscosity can be used as a factor that controls a porosity structure of the porous film. Examples of the solidifying solvent include water, alcohols (e.g., methanol, ethanol, propanol), hydrocarbons (e.g., hexane, cyclohexane, heptane), ketones (e.g., acetone, butanone, 2-butanone), and esters (e.g., ethyl acetate). Water is preferable from a viewpoint of simple operation and cost.
(40) Here, the porosity structure of the porous film can be controlled by controlling a phase separation state of the polymer solution at the time of phase transition. Specifically, the phase separation state can be controlled into a sea-island type or a spinodal type by properly changing the viscosity of the polymer solution, the concentration of the resin, and the solvent. By reflecting the phase separation state, the porous structure of the porous film can be changed. Also in the present invention, the phase separation structure can be controlled to produce the resin composition in which the independent porosities occupy not less than 80% of the total porosity.
(41) Polyamic acid can be imidized by a thermal imidization treatment or a chemical imidization treatment using such as acid anhydride. Thermal imidization is suitably used for simple operation. It is known that mechanical strength of the polyimide film greatly changes depending on heat treatment conditions. In the heat treatment in the present invention, the temperature may be increased at a constant rate, and preferably the heating temperature is increased stepwise. Specifically, the temperature can be increased for example, for 10 to 60 minutes from 80 C. to 120 C., for 10 to 60 minutes from 120 to 200 C., and for 10 to 60 minutes from 200 to 350 C.
(42) The porosity ratio can be controlled by adjusting the concentration of the resin in the resin solution. The porosity ratio can be properly reduced by increasing the concentration of the resin and reducing the concentration of the solvent in the solution. On the other hand, the porosity ratio can be properly increased by reducing the concentration of the resin and increasing the concentration of the solvent in the solution.
(43) A conductive controlling agent can be added to the porous layer when necessary to adjust resistance. As a method, a predetermined amount of the conductive controlling agent can be added to the resin solution and dispersed. Using the resin solution, the resistance is adjusted with the phase separation method.
(44) Dispersion can be conducted with a dispersing machine usually used. Specifically, a roll mill, a paint shaker, a bead mill and the like can be used.
(45) As the conductive controlling agent, substances usually used in this field can be used. For example, carbon black such as furnace black, thermal black, channel black, graphite, carbon nanotube, and the like can be used. Metal oxides such as tin oxide, antimony oxide, indium oxide, zinc oxide, indium zinc based oxides, and the like, and metals such as gold, silver, copper, nickel, and the like can also be used. Further, a conductive material may be formed by covering the surface of various inorganic substances (e.g., titanic acid based compounds such as potassium titanate, titanium dioxide, monoclinic titanium dioxide, and the like, calcium silicate such as wollastonite, xonotlite, and the like, amorphous silica, etc.) with the above-mentioned material.
(46) An ionic conducting agent such as quarternary ammonium salts, phosphoric esters, sulfonic acid salts, aliphatic polyhydric alcohols, and aliphatic alcohol sulfate salts can also be used.
(47) Of these, carbon black and metal oxide are preferable, and carbon black is particularly preferable. One kind of the conductive controlling agent can be used alone, or not less than two kinds thereof can be used in combination.
(48) Also from a viewpoint of control of the resistance, the porous structure without macro voids is preferable. Electric conduction is manifested when the conductive controlling agents approach each other. However, the conductive controlling agents are physically isolated if a porosity much larger than the particle size of the conductive controlling agent exists. Existence of such a large porosity causes a remarkably nonuniform dispersion state, leading to unstable control of conductivity. A uniform porosity size is also preferable. Such a uniform porosity size leads to uniform dispersion of the conductive controlling agent, and control of the conductivity can be performed with good repeatability.
(49) The amount of the conductive controlling agent is determined properly such that 1 to 30% by weight of the above-mentioned conductive controlling agent is contained, and the volume resistivity of the porous layer is approximately 10.sup.7 to 10.sup.10 cm. Thereby, the toner can be efficiently transferred from the photoreceptor drum onto the belt. The conductivity cannot be manifested at a conductive controlling agent of not more than 1% by weight. Moreover, at a conductive controlling agent of not less than 30% by weight, an influence of the viscosity makes it difficult to realize uniform dispersion using a dispersing machine.
(50) Additionally, it is usually known that addition of the conductive controlling agent significantly increases the thermal conductivity. In the present invention, however, the thermal conductivity can be suppressed to be not more than 0.10 [W/mK] when the porosity ratio is at least 30% or larger even in the resin composition to which the conductive controlling agent is added to control the resistance. Heat is transmitted by free electrons of the conductive controlling agent in the polymeric material. On the other hand, in the porous body that includes a large amount of porosities per unit volume, increase in the thermal conductivity can be suppressed to be a value of not more than a constant value.
(51) In the present invention, the resin composition can have a structure in which on at least one surface of the resin composition, a releasing layer or a substrate is laminated, and an elastic layer is further laminated when necessary (see
(52) As the releasing layer 101, a fluororesin is used suitably. The kind of the fluororesin is not particularly limited. Examples of the fluororesin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), and tetrafluoroethylene-ethylenic copolymers (ETFE). The releasing layer 101 made of a fluororesin or a resin mainly containing the fluororesin can prevent a molten toner from adhering to the fixing belt so that a high-quality fixed image can be obtained.
(53) The releasing layer 101 (for example, a fluororesin layer) has a thickness of not less than 1 m and not more than 10 m, and particularly preferably not less than 3 m and not more than 7 m. An excessively small thickness of the lamination film 100 containing the resin composition 103 makes mechanical strength poor so that the material is likely to deteriorate due to cracks or scraping. Moreover, an excessively large thickness of the lamination film 100 increases the heat capacity of a surface layer so that thermal diffusion from the toner easily occurs. For this reason, it is impossible to heat only the toner efficiently.
(54) A conductive controlling agent can also be added to the releasing layer 101 when necessary. As the conductive controlling agent, the same conductive controlling agent as that added to the resin composition 103 can be added. Moreover, similarly to the case of the resin composition 103, the content of the conductive controlling agent is determined so that the volume resistivity may be in the range of 10.sup.7 to 10.sup.11 cm.
(55) Of the surfaces of the resin composition 103, the substrate 105 can be laminated on the surface having no releasing layer 101. The substrate 105 can be laminated by casting the resin solution on the substrate 105 and porosifying the resin solution in the phase separation method.
(56) At this time, in order to improve adhesion of the substrate 105 to the resin composition 103, the same resin as the porosified resin or a material having a chemical structure having affinity with the porosified resin is preferably used for the substrate 105. Further, the surface of the substrate 105 may be physically or chemically roughened to improve adhesion by an anchor effect.
(57) Moreover, the elastic layer 104 can be laminated between the resin composition 103 and the substrate 105 when necessary. As the elastic layer 104, heat-resistant silicone rubber, fluororubber, or mixture mainly containing these can be used suitably.
(58) In the resin composition of the present invention, the application and shape thereof can be properly selected according to the function. When a resin composition of polyimide is taken, for example, since the resin composition of polyimide has high heat resistance, low dielectric constant, chemical resistance, and high mechanical strength, the resin composition of polyimide can be used as an electrolyte membrane for fuel cells or a supporting substrate for an electronic material, and can also be used for a heatproof filter or a lightweight member for automobiles. The resin composition preferably has a belt-like shape particularly in the case where the resin composition is used for the fixing member for electrophotography as an insulating member. The resin composition is formed on a tubular or cylindrical substrate, and can be used as the fixing roller as it is.
(59) Particularly because the resin composition of the present invention has independent porosities 102 of a small porosity size, the resin composition of the present invention can be used as an insulating member that can suppress reduction of mechanical strength accompanied by porosification. The lamination film containing the resin composition of the present invention also has resistance against physical deformation applied to the material and exposure to chemical substances at the time of mass printing. Accordingly, the lamination film containing the resin composition of the present invention can be used as the electrophotographic transfer member, the fixing member, the member for transfer and fixing in the image fixing apparatus (system) that performs mass printing and/or high-speed printing.
(60) For example, the lamination film containing the resin composition of the present invention can be used for an image fixing apparatus having a simultaneous transfer and fixing system as illustrated in
(61) Moreover, in the present invention, toner transfer from a photoreceptor drum 206 can also be conducted because the resin composition 103 whose resistance is controlled is used. Transfer and fixing can be conducted with one belt material in the simultaneous transfer and fixing system, leading to space saving and reduction in cost.
(62) Hereinafter, an example of the fixing apparatus including a member for electrophotographic transfer and fixing in the present invention will be illustrated, but the fixing apparatus will not be limited to this.
(63) The apparatus illustrated in
(64) The apparatus illustrated in
(65) In addition, the porous film in the present invention can be used not only for the belt material but also for resin members at large such as organic photoreceptors and frames in the electrophotography field.
(66) Moreover, besides the electrophotography field, the porous film in the present invention can also be used for a covering material for electronic components and electric wire as a low dielectric constant material having high mechanical strength, or for structure members for transportation vehicles or aerospace industry and building materials as a lighter weight material or a heat insulating material. The porous film in the present invention can be potentially applied to processed components at large in which a heat resistant resin is used.
EXAMPLES
(67) Hereinafter, the present invention will be described in detail using Examples, but the present invention will not be limited to these.
(68) A porosity ratio is calculated in accordance with the following equation by measuring the thickness and weight of a porosity film cut into a 3 cm square. S designates an area of the porosity film, d designates the thickness thereof, w designates the weight of the porosity film, and D designates the density of polyimide.
Porosity ratio (%)=(D/w)(Sd)100
(69) Porosity size distribution (the size of a small porosity size and number distribution) and the ratio of independent porosities is calculated by using an image processing system (LUZEX AP, Nireco Corporation) based on an image obtained by observing the cross section of a porosity polyimide resin layer with a scanning electron microscope (SEM).
(70) A thermal conductivity is calculated by measuring a thermal diffusivity with a thermal diffusivity meter (FTC-1, Ulvac-Riko, Inc.) and integrating a density and a specific heat separately determined with the thermal diffusivity.
(71) With respect to polyimides and polyamide imide resins, a compression resistance is calculated from a ratio of thickness change before and after compression by compressing polyimide or a polyamide imide resin using a high precision hotpress (Tester Sangyo Co., Ltd.) under conditions of a pressure of 7 kgf/cm.sup.2, a compression temperature of 170 C., and a compression time of 4 hours. Moreover, with respect to polycarbonate resins, a compression resistance is calculated from a ratio of thickness change before and after compression by compressing a polycarbonate resin using a high precision hotpress (Tester Sangyo Co., Ltd.) under conditions of a pressure of 7 kgf/cm.sup.2, a treatment temperature of 70 C., and a compression time of 4 hours.
(72) An average surface roughness (Rz) is evaluated using a surface roughness measuring apparatus (SURF-CORDER SE3500, Kosaka Laboratory Ltd.).
(73) A viscosity is evaluated using a viscometer (a cone-and-plate rheometer MCR-300, Anton Paar GmbH).
(74) A surface resistance is evaluated using a sample box for super high resistance measurement (TR42, Advantest Corporation).
(75) A dielectric constant is evaluated with an LCR meter (HP4284A, Yokogawa-Hewlett-Packard Ltd.).
Example 1
(76) An N-methyl-pyrrolidone (NMP) solution (U-varnish-A, Ube Industries, Ltd., resin concentration of 20% by weight) of polyamic acid that is a polyimide precursor was prepared. Lithium chloride was added to the polyamic acid solution so that the concentration of lithium chloride might be 15% by weight, and was dissolved. The resin viscosity at this time was 120,000 cP. A polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m was prepared as a substrate, and the above-mentioned solution was casted on the substrate using a coater. Subsequently, the cast film was immersed in distilled water at room temperature for 5 minutes. The substrate was taken out from the water, and the obtained film was rinsed with distilled water.
(77) Adhering water was wiped off, and the film was put into a drying furnace. The film was dried at 80 C. for 1 hour. Subsequently, the temperature was raised to 150 C. at a heating rate of 10 C./min. After the film was heated at 150 C. for 30 minutes, the temperature was raised to 250 C. at a heating rate of 10 C./min. After the film was heated at 250 C. for 10 minutes, the temperature was raised to 350 C. at a heating rate of 10 C./min. Then, the film was heated at 350 C. for 10 minutes to produce a polyimide resin composition.
(78) The porosity form of the obtained film was examined. The mean porosity size thereof was 0.015 m. The number distribution was examined. Then, 81% of the total porosity was included in a size of 0.011 to 0.019 m. Moreover, the porosity ratio was measured. The porosity ratio was 65%, and the thickness of the obtained porous film was 180 m. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
(79) The properties of the porous film at the time of drying were examined. Then, the mean porosity size at the time of drying at 80 C. for 1 hour was 0.020 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.014 to 0.026 m. Moreover, the porosity ratio was measured. Then, the porosity ratio was 69%, and the thickness of the obtained porous film was 190 m. Moreover, the physical properties of the film when the film was heated at 250 C. for 10 minutes were examined. Then, the mean porosity size was 0.019 m. The number distribution was examined. Then, 83% of the total porosity was included in a size of 0.0133 to 0.0247 m. Moreover, the porosity ratio was measured. Then, the porosity ratio was 68%, and the thickness of the obtained porous film was 188 m.
Example 2
(80) Example 2 was conducted by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 108,000 cP.
(81) The mean porosity size of the independent porosity was 0.055 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.040 to 0.070 m. Moreover, the porosity ratio was 64%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 150 m.
Example 3
(82) Example 3 was conducted by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 96,000 cP.
(83) The mean porosity size of the independent porosity was 0.10 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.070 to 0.13 m. Moreover, the porosity ratio was 61%, and 80% of the total porosity was the independent porosity. The thickness of the obtained porous film was 125 m.
Example 4
(84) A polyimide resin composition was produced by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 78,000 cP.
(85) The mean porosity size of the independent porosity was 0.20 m. The number distribution was examined. Then, 83% of the total porosity was included in a size of 0.17 to 0.26 m. Moreover, the porosity ratio was 62%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 5
(86) A polyimide resin composition was produced by the same method as that in Example 1 except that the cast film casted on the substrate was covered with a solvent substitution adjustment material (U-Pore, a Gurley value of 210 sec/100 cc, Ube Industries, Ltd.), and was subjected to phase transition. The resin viscosity was 118,000 cP.
(87) The mean porosity size of the independent porosity was 0.20 m. The number distribution was examined. Then, 94% of the total porosity was included in a size of 0.17 to 0.26 m. Moreover, the porosity ratio was 63%, and 94% of the total porosity was the independent porosity. The thickness of the obtained porous film was 160 m.
Example 6
(88) Example 6 was conducted by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 69,000 cP.
(89) The mean porosity size of the independent porosity was 0.40 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.28 to 0.52 m. Moreover, the porosity ratio was 64%, and 82% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Example 7
(90) A polyimide resin composition was produced by the same method as that in Example 5 except that the amount of lithium chloride was adjusted so that the resin viscosity of the polyamic acid solution was 105,000 cP, and the cast film casted on the substrate was covered with a solvent substitution adjustment material (U-Pore, a Gurley value of 300 sec/100 cc, Ube Industries, Ltd.), and was subjected to phase transition.
(91) The mean porosity size of the independent porosity was 0.40 m. The number distribution was examined. Then, 93% of the total porosity was included in a size of 0.28 to 0.52 m. Moreover, the porosity ratio was 61%, and 95% of the total porosity was the independent porosity. The thickness of the obtained porous film was 150 m. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
Example 8
(92) Example 8 was conducted by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 59,000 cP.
(93) The mean porosity size of the independent porosity was 0.60 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.42 to 0.78 m. Moreover, the porosity ratio was 63%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Example 9
(94) Example 9 was conducted by the same method as that in Example 1 except that the amount of lithium chloride was adjusted so that the resin viscosity of polyamic acid was 39,000 cP.
(95) The mean porosity size of the independent porosity was 0.80 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.56 to 1.0 m. Moreover, the porosity ratio was 62%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Example 10
(96) A polyimide resin composition was produced by the same method as that in Example 7 except that the cast film was covered with a solvent substitution adjustment material (Poreflon Membrane, Gurley value: 330 sec/100 cc, Sumitomo Electric Fine Polymer, Inc.), and was subjected to phase transition.
(97) The mean porosity size of the independent porosity was 0.40 m. The number distribution was examined. Then, 91% of the total porosity was included in a size of 0.28 to 0.52 m. Moreover, the porosity ratio was 60%, and 93% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 11
(98) A polyimide resin composition was produced by the same method as that in Example 9 except that the cast film casted on the substrate was immersed in a solution of water/methanol=1/1 (% by volume). The resin viscosity was 41,000 cP.
(99) The mean porosity size of the independent porosity was 0.85 m. The number distribution was examined. Then, 88% of the total porosity was included in a size of 0.60 to 1.1 m. Moreover, the porosity ratio was 62%, and 86% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Example 12
(100) A polyimide resin composition was produced by the same method as that in Example 9 except that the cast film casted on the substrate was immersed in a solution of water/NMP=1/1 (% by volume). The resin viscosity was 40,000 cP.
(101) The mean porosity size of the independent porosity was 0.88 m. The number distribution was examined. Then, 86% of the total porosity was included in a size of 0.62 to 1.1 m. Moreover, the porosity ratio was 63%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 13
(102) A polyimide resin composition was produced by the same method as that in Example 9 except that the temperature of a solidifying solvent (water) was 70 C. The resin viscosity was 42,000 cP.
(103) The mean porosity size of the independent porosity was 0.90 m. The number distribution was examined. Then, 87% of the total porosity was included in a size of 0.63 to 1.17 m. Moreover, the porosity ratio was 61%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 135 m.
Example 14
(104) A polyimide resin composition was produced by the same method as that in Example 7 except that the resin concentration of polyamic acid was 30% by weight, and the amount of lithium chloride was adjusted so that the resin viscosity of the polyamic acid solution was 110,000 cP.
(105) The mean porosity size of the independent porosity was 0.45 m. The number distribution was examined. Then, 86% of the total porosity was included in a size of 0.32 to 0.59 m. Moreover, the porosity ratio was 21%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 15
(106) A polyimide resin composition was produced by the same method as that in Example 7 except that the resin concentration of polyamic acid was 25% by weight, and the amount of lithium chloride was adjusted so that the resin viscosity of the polyamic acid solution was 113,000 cP.
(107) The mean porosity size of the independent porosity was 0.45 m. The number distribution was examined. Then, 86% of the total porosity was included in a size of 0.32 to 0.59 m. Moreover, the porosity ratio was 32%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 16
(108) A polyimide resin composition was produced by the same method as that in Example 7 except that the resin concentration of polyamic acid was 15% by weight, and the amount of lithium chloride was adjusted so that the resin viscosity of the polyamic acid solution was 108,000 cP.
(109) The mean porosity size of the independent porosity was 0.48 m. The number distribution was examined. Then, 86% of the total porosity was included in a size of 0.34 to 0.62 m. Moreover, the porosity ratio was 74%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 17
(110) A polyimide resin composition was produced by the same method as that in Example 7 except that the resin concentration of polyamic acid was 10% by weight, and the amount of lithium chloride was adjusted so that the resin viscosity of the polyamic acid solution was 100,000 cP.
(111) The mean porosity size of the independent porosity was 0.50 m. The number distribution was examined. Then, 86% of the total porosity was included in a size of 0.35 to 0.65 m. Moreover, the porosity ratio was 85%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 130 m.
Example 18
(112) An N-methyl-pyrrolidone solution (HL-1210, Hitachi Chemical Co., Ltd.) of polyamidoimide was prepared. Lithium chloride was added to the solution so that the concentration of lithium chloride might be 10% by weight, and dissolved. The resin viscosity at this time was 69,000 cP. A polyimide material (Kapton, Du Pont-Toray Co., Ltd.) was prepared as a substrate, and the above-mentioned solution was casted on the substrate using a coater. Subsequently, the cast film was immersed in distilled water for 5 minutes. The substrate was taken out from the water, and the obtained film was rinsed with distilled water.
(113) Adhering water was wiped off, and the film was put into a drying furnace. After the film was dried at 80 C. for 1 hour, the temperature was raised to 150 C. at a heating rate of 10 C./min. After the film was heated at 150 C. for 30 minutes, the temperature was raised to 250 C. at a heating rate of 10 C./min. The film was heated at 250 C. for 10 minutes to produce a polyamide-imide resin composition.
(114) The mean porosity size was 0.30 m. The number distribution was examined. Then, 80% of the total porosity was included in a size of 0.21 to 0.39 m. Moreover, the porosity ratio was 67%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 120 m.
Comparative Example 1
(115) An N-methyl-pyrrolidone solution (HL-1210, Hitachi Chemical Co., Ltd.) of polyamidoimide was prepared. The resin concentration was 20% by weight, and the resin viscosity was 5,200 cP. A polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m was prepared as a substrate, and the above-mentioned solution was casted on the substrate using a coater. After casting, the cast film was immediately kept for 4 minutes in a container having a humidity of approximately 100% and a temperature of 50 C. Subsequently, the cast film was immersed in water and subjected to phase transition. The film was taken out from the water, and the obtained film was rinsed with distilled water.
(116) Adhering water was wiped off, and the film was dried under room temperature to obtain a polyamide-imide resin composition.
(117) The mean porosity size was 1.0 m. The number distribution was examined. Then, 68% of the total porosity was included in a size of 0.70 to 1.30 m. Moreover, the porosity ratio was 62%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 120 m.
Comparative Example 2
(118) An N-methyl-pyrrolidone (NMP) solution (U-varnish-A, Ube Industries, Ltd., the resin concentration of 20% by weight) of polyamic acid that is a polyimide precursor was prepared. The resin viscosity at this time was 7,200 cP. A polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m was prepared as a substrate, and the above-mentioned solution was casted on the substrate using a coater. After casting, the cast film was immediately kept for 3 minutes in a container having a humidity of approximately 100% and a temperature of 50 C. Subsequently, the cast film was immersed in water and subjected to phase transition. The film was taken out from the water, and the obtained film was rinsed with distilled water.
(119) Adhering water was wiped off, and the film was dried at 100 C. in a drying furnace. Subsequently, the film was dried for 60 minutes in a drying furnace of 260 C. to obtain a polyimide resin composition.
(120) The mean porosity size was 2.5 m. The number distribution was examined. Then, 69% of the total porosity was included in a size of 1.8 to 3.2 m. Moreover, the porosity ratio was 62%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 120 m.
Comparative Example 3
(121) An N-methyl-pyrrolidone (NMP) solution (U-varnish-A, Ube Industries, Ltd., the resin concentration of 20% by weight) of polyamic acid that is a polyimide precursor was prepared. A polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m was prepared as a substrate, and the above-mentioned solution was casted on the substrate using a coater. The cast film was covered with a solvent substitution adjustment material (U-pore, Ube Industries, Ltd.) having a Gurley value: 800 sec/100 cc, immersed in water, and subjected to phase transition. Then, the cast film was subjected to thermal imidization by the same method as that in Example 1 to produce a polyimide resin composition. The resin viscosity was 7,800 cP.
(122) The mean porosity size of the independent porosity was 13 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 9.1 to 17 m. Moreover, the porosity ratio was 64%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Comparative Example 4
(123) A polyimide resin composition was produced by the same method as that in Comparative Example 3 except that the cast film was immersed in a solution of water/NMP=1/1 (% by volume) without using any solvent substitution adjustment material. The resin viscosity was 7,500 cP.
(124) The mean porosity size of the independent porosity was 3.0 m. The number distribution was examined. Then, 87% of the total porosity was included in a size of 2.1 to 3.9 m. Moreover, the porosity ratio was 62%, and 87% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Comparative Example 5
(125) A polyimide resin composition was produced by the same method as that in Comparative Example 4 except that the cast film was immersed in a solution of water/methanol=1/1 (% by volume). The resin viscosity was 7,400 cP.
(126) The mean porosity size of the independent porosity was 3.2 m. The number distribution was examined. Then, 88% of the total porosity was included in a size of 2.2 to 4.1 m. Moreover, the porosity ratio was 61%, and 86% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Comparative Example 6
(127) A polyimide resin composition was produced by the same method as that in Comparative Example 3 except that phase transition was performed without using any solvent substitution adjustment material. The resin viscosity was 7,200 cP.
(128) The mean porosity size of the porosity was 5.2 m. The number distribution was examined. Then, 64% of the total porosity was included in a size of 3.6 to 6.7 m. Moreover, the porosity ratio was 65%, and 82% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
Comparative Example 7
(129) A polyimide resin composition was produced by the same method as that in Comparative Example 6 except that the temperature of a solidifying solvent (water) was 70 C. The resin viscosity was 7,100 cP.
(130) The mean porosity size of the porosity was 6.0 m. The number distribution was examined. Then, 81% of the total porosity was included in a size of 4.2 to 7.8 m. Moreover, the porosity ratio was 64%, and 64% of the total porosity was the independent porosity.
Comparative Example 8
(131) A polyimide resin composition was produced by the same method as that in Comparative Example 6 except that the resin concentration was 15% by weight. The resin viscosity was 6,200 cP.
(132) The mean porosity size of the porosity was 5.5 m. The number distribution was examined. Then, 64% of the total porosity was included in a size of 3.9 to 7.1 m. Moreover, the porosity ratio was 69%, and 62% of the total porosity was the independent porosity. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
Comparative Example 9
(133) A polyimide foamed sheet (UPILEX-FOAM BP021, Ube Industries, Ltd.) was prepared. The thickness was 500 m. The porosity ratio was 60%. The cross section of the polyimide foamed sheet was observed with the SEM. Then, as illustrated in
(134) Using the resin compositions (3 cm square) obtained from Examples 1 to 18 and Comparative Examples 1 to 9, the thermal conductivity, the compression resistance (ratio of thickness change before and after compression), and the thermal conductivity after compression were evaluated. The resin compositions were compressed using a press under conditions of a pressure 7 kgf/cm.sup.2, a compression temperature of 170 C., and compression time of 4 hours. Subsequently, the compression resistance was evaluated. Table 1 shows the result.
(135) TABLE-US-00001 TABLE 1 Solvent Thermal Porosity Porosity Porosity Resin substitution conductivity size Independent size ratio viscosity adjustment Thermal Compression after [m] porosity distribution [%] [cP] material conductivity resistance compression Example 1 0.015 ++ 81 65 120000 + +++ + Example 2 0.055 ++ 82 64 108000 ++ +++ ++ Example 3 0.10 ++ 82 61 96000 ++ +++ ++ Example 4 0.20 ++ 83 62 78000 ++ ++ ++ Example 5 0.20 ++ 94 63 118000 210 +++ +++ +++ [sec/100 cc] Example 6 0.40 ++ 82 64 69000 +++ ++ ++ Example 7 0.40 ++ 93 61 105000 300 +++ +++ +++ [sec/100 cc] Example 8 0.60 ++ 82 63 59000 ++ ++ ++ Example 9 0.80 ++ 82 62 39000 ++ ++ ++ Example 10 0.40 ++ 91 60 11000 330 +++ +++ +++ [sec/100 cc] Example 11 0.85 ++ 88 62 41000 ++ + ++ Example 12 0.88 ++ 86 63 40000 ++ + ++ Example 13 0.90 ++ 87 62 42000 ++ + ++ Example 14 0.45 ++ 86 21 110000 300 + +++ ++ [sec/100 cc] Example 15 0.45 ++ 86 32 113000 300 + +++ ++ [sec/100 cc] Example 16 0.48 ++ 86 74 108000 300 +++ + ++ [sec/100 cc] Example 17 0.50 ++ 86 85 100000 300 +++ + + [sec/100 cc] Example 18 0.30 ++ 80 67 69000 +++ ++ +++ Comparative 1.0 ++ 68 62 5200 ++ + Example 1 Comparative 2.5 ++ 69 62 7200 + + Example 2 Comparative 13 ++ 82 62 7800 800 + Example 3 [sec/100 cc] Comparative 3.0 ++ 87 62 7500 + + + Example 4 Comparative 3.2 ++ 88 61 7400 + + Example 5 Comparative 5.2 ++ 64 65 7100 + + Example 6 Comparative 6.0 + 81 64 7200 + + Example 7 Comparative 5.5 + 64 69 6200 + Example 8 Comparative continuous 60 +++ + Example 9 porosities
(136) In Examples 1 to 18 and Comparative Examples 1 to 9, the thermal conductivity, the compression resistance, and the thermal conductivity after compression were evaluated according to the criteria as follows:
(137) (The independent porosity: the ratio of the independent porosities based on the total porosity, ++: not less than 80%, +: not less than 60% and not more than 80%, and : less than 60%.)
(138) (The porosity size distribution: the proportion of the porosity having a porosity size within 30% of the mean porosity size based on the total porosity.)
(139) (The thermal conductivity [W/mK]: +++: <0.05, ++: 0.05<0.075, +: 0.075<0.1, and : not less than 0.1 [W/mK].)
(140) (The compression resistance: +++=less than 1%, ++=not less than 1% and less than 5%, +=not less than 5% and less than 10%, and =not less than 10%.)
(141) From Table 1, it turned out that a film having a smaller porosity size has a more preferable compression resistance. It also turned out that a film having a smaller porosity size has higher mechanical strength, and therefore reduction in thermal conductivity by compression can be suppressed in spite of the high porosity ratio of the film. It also turned out that a low porosity ratio leads to a high thermal conductivity, and conversely, a high porosity ratio lead to poor mechanical strength.
(142) On the other hand, the film having macro voids and continuous porosities had poor compression resistance, and therefore showed remarkable increase in the thermal conductivity by compression.
Example 19
(143) Carbon black (Denka Black, Denki Kagaku Kogyo K. K.) was added to N-methyl-pyrrolidone (NMP) solution (U-varnish-A, Ube Industries, Ltd., the resin concentration of 20% by weight) of polyamic acid so that the concentration of carbon black might be 5, 10, 15, 20, 25, and 30% by weight. Then, carbon black was dispersed in the resin solution using a roll mill dispersion machine (BR-100V, IMEX Co., Ltd.). Lithium chloride was added to each solution so that the concentration of lithium chloride might be 15% by weight. The dispersing solution was casted on a polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m, and the cast film was immersed in water (the viscosity of the resin solution containing 15% by weight of carbon black was 120,000 cP). The cast film was subjected to thermal imidization by the same method as that in Example 1 to obtain a polyimide resin composition containing carbon black.
(144) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.060 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.042 to 0.078 m. The porosity ratio was measured. Then, the porosity ratio was 66%, and 81% of the total porosity was the independent porosity. The thickness of the obtained film was 180 m.
Example 20
(145) A resin composition containing carbon black was obtained by the same method as that in Example 19 except that the amount of lithium chloride was adjusted so that the resin viscosity was adjusted (the viscosity of the resin solution containing 15% by weight of carbon black was 94,000 cP).
(146) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.25 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.18 to 0.32 m. The porosity ratio was measured. Then, the porosity ratio was 65%, and 82% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Example 21
(147) A resin composition was produced by the same method as that in Example 19 except that the cast film was covered with a solvent substitution adjustment material (U-pore, a Gurley value: 210 sec/100 cc, Ube Industries, Ltd.), and subjected to phase transition. The viscosity of the polyamic acid resin solution containing 15% by weight of carbon black was 123,000 cP.
(148) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.28 m. The number distribution was examined. Then, 92% of the total porosity was included in a size of 0.20 to 0.36 m. The porosity ratio was measured. Then, the porosity ratio was from 65 to 69%, and 93% of the total porosity was the independent porosity. Each thickness of the obtained films was 180 m.
Example 22
(149) A resin composition containing carbon black was obtained by the same method as that in Example 19 except that the amount of lithium chloride was adjusted so that the resin viscosity was adjusted (the viscosity of the resin solution containing 15% by weight of carbon black was 60,000 cP).
(150) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.53 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.37 to 0.69 m. The porosity ratio was measured. Then, the porosity ratio was 65%, and 81% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Example 23
(151) A resin composition was produced by the same method as that in Example 22 except that the cast film was covered with a solvent substitution adjustment material (U-pore, a Gurley value: 410 sec/100 cc, Ube Industries, Ltd.), and subjected to phase transition. The viscosity of the polyamic acid resin solution containing 15% by weight of carbon black was 108,000 cP.
(152) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.72 m. The number distribution was examined. Then, 92% of the total porosity was included in a size of 0.50 to 0.93 m. The porosity ratio was measured. Then, the porosity ratio was 64%, and 90% of the total porosity was the independent porosity. The thickness of the obtained film was 170 m.
Example 24
(153) A resin composition containing carbon black was obtained by the same method as that in Example 19 except that the amount of lithium chloride was adjusted so that the resin viscosity was adjusted (the viscosity of the resin solution containing 15% by weight of carbon black was 39,000 cP).
(154) The mean porosity size of the resin composition containing 15% by weight of carbon black was 0.90 m. The number distribution was examined. Then, 84% of the total porosity was included in a size of 0.63 to 1.17 m. The porosity ratio was measured. Then, the porosity ratio was 65%, and 81% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 10
(155) Carbon black (Denka Black, Denki Kagaku Kogyo K. K.) was added to N-methyl-pyrrolidone solution (HL-1210, Hitachi Chemical Co., Ltd., 20% by weight, 4,800 cP) of polyamidoimide so that the concentration of carbon black might be 5, 10, 15, 20, 25, and 30% by weight. Then, carbon black was dispersed in the resin solution using a roll mill dispersion machine (BR-100V, IMEX Co., Ltd.).
(156) The dispersing solution was casted on a polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m. The cast film was kept for 4 minutes in a container having a humidity of approximately 100% and a temperature of 50 C. Subsequently, the cast film was immersed in water and subjected to phase transition. The film was taken out from the water, and subjected to air drying at room temperature to obtain a resin composition of polyamidoimide. The viscosity of the resin solution containing 15% by weight of carbon black was 6,900 cP.
(157) The mean porosity size of the resin composition containing 15% by weight of carbon black was 1.0 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.70 to 1.3 m. The porosity ratio was measured. Then, the porosity ratio was 63%, and 67% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 11
(158) Carbon black (Denka Black, Denki Kagaku Kogyo K. K.) was added to N-methyl-pyrrolidone (NMP) solution (U-varnish-A, Ube Industries, Ltd., the resin concentration of 20% by weight) of polyamic acid that is a polyimide precursor so that the concentration of carbon black might be 5, 10, 15, 20, 25, and 30% by weight. Then, carbon black was dispersed in the resin solution using a roll mill dispersion machine (BR-100V, IMEX Co., Ltd.).
(159) The dispersing solution was casted on a polyimide material (Kapton, Du Pont-Toray Co., Ltd.) having a thickness of 120 m. The cast film was kept for 3 minutes in a container having a humidity of approximately 100% and a temperature of 50 C., and subsequently was immersed in water. The cast film was taken out from the water, and dried at 100 C. Subsequently, the film was dried for 60 minutes in a 260 C. drying furnace to obtain a resin composition containing carbon black. The viscosity of the resin solution containing 15% by weight of carbon black was 8,200 cP.
(160) The mean porosity size of the resin composition containing 15% by weight of carbon black was 3.2 m. The number distribution was examined. Then, 69% of the total porosity was included in a size of 2.2 to 4.2 m. The porosity ratio was measured. Then, the porosity ratio was 63%, and 83% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 12
(161) A resin composition containing carbon black was obtained by the same method as that in Example 19 except that the cast film made of the dispersion liquid of carbon black in Comparative Example 11 (the viscosity of the resin solution when 15% by weight of carbon black was contained was 8,200 cP) was covered with a solvent substitution adjustment material (U-pore, a Gurley value: 800 sec/100 cc, Ube Industries, Ltd.), and was subjected to phase transition.
(162) The mean porosity size of the resin composition containing 15% by weight of carbon black was 15 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 11 to 19 m. The porosity ratio was measured. Then, the porosity ratio was 61%, and 82% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 13
(163) A resin composition containing carbon black was obtained by the same method as that in Comparative Example 12 except that the cast film was subjected to phase transition without covering the cast film with any solvent substitution adjustment material. The viscosity of the resin solution when 15% by weight of carbon black was contained was 9,000 cP.
(164) The mean porosity size of the obtained film was 6.8 m. The number distribution was examined. Then, 64% of the total porosity was included in a size of 0.65 to 1.2 m. The porosity ratio was measured. Then, the porosity ratio was 62%, and 63% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 14
(165) A resin composition containing carbon black was obtained by the same method as that in Comparative Example 13 except that the temperature of the solidifying solvent (water) was 70 C. The viscosity of the resin solution when 15% by weight of carbon black was contained was 8,500 cP.
(166) The mean porosity size of the obtained film was 7.4 m. The number distribution was examined. Then, 81% of the total porosity was included in a size of 5.2 to 9.6 m. The porosity ratio was measured. Then, the porosity ratio was 64%, and 63% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 15
(167) A resin composition containing carbon black was obtained by the same method as that in Comparative Example 13 except that the resin concentration was 16% by weight. The viscosity of the resin solution containing 15% by weight of carbon black was 5,700 cP.
(168) The mean porosity size of the obtained film was 7.9 m. The number distribution was examined. Then, 61% of the total porosity was included in a size of 5.5 to 10 m. The porosity ratio was measured. Then, the porosity ratio was 69%, and 83% of the total porosity was the independent porosity. The thickness of the obtained film was 150 m.
Comparative Example 16
(169) Production of a resin composition containing carbon black by the same method as that in Comparative Example 13 except that the carbon black concentration was 35% by weight was tried. However, carbon black could not be dispersed so that the film could not be formed.
Comparative Example 17
(170) A resin composition containing carbon black was obtained by the same method as that in Comparative Example 13 except that the carbon black concentration was 0.5% by weight. However, the resistance of the obtained film was not reduced.
(171) The electrical properties of the porous films were examined using Examples 19 to 24 and Comparative Examples 10 to 17. Table 2 shows the result.
(172) The thermal conductivity, the compression resistance, and dielectric breakdown were evaluated using the films containing 15% by weight of carbon black in the resin composition according to Examples 19 to 24 and Comparative Examples 10 to 17.
(173) TABLE-US-00002 TABLE 2 Solvent Porosity Porosity Porosity Resin substitution size Independent size ratio viscosity adjustment Thermal Compression Control of Dielectric [m] porosity distribution [%] [cP] material conductivity resistance resistance breakdown Example 19 0.060 ++ 82 66 120000 + +++ + ++ Example 20 0.25 ++ 82 65 94000 ++ +++ + ++ Example 21 0.28 ++ 92 65 123000 210 ++ +++ ++ ++ [sec/100 cc] Example 22 0.53 ++ 82 65 60000 ++ +++ + ++ Example 23 0.72 ++ 92 64 108000 410 ++ +++ ++ ++ [sec/100 cc] Example 24 0.90 ++ 84 65 39000 + ++ ++ ++ Comparative 1.0 ++ 67 63 6900 + ++ Example 10 Comparative 3.2 ++ 69 63 8200 ++ Example 11 Comparative 15 ++ 82 64 8200 800 + Example 12 [sec/100 cc] Comparative 6.8 + 64 62 9000 + Example 13 Comparative 7.4 + 81 64 8500 + + Example 14 Comparative 7.9 ++ 61 69 5700 + + Example 15 Comparative Example 16 Comparative Example 17
(174) In Examples 19 to 24 and Comparative Examples 10 to 17, according to the criteria as follows, the thermal conductivity, the compression resistance (the ratio of thickness change before and after compression), the control of resistance (in a plot (percolation curve) of the resistance and the amount of carbon black (CB), an inclination when the amounts of CB corresponding to 10.sup.6 cm and 10.sup.14 cm were a denominator and common logarithms of the resistance (10.sup.6 cm and 10.sup.14 cm) were a numerator), and the dielectric breakdown (a voltage of 300 V was applied to the film for 1 minute) were evaluated.
(175) (The independent porosity: the ratio of the independent porosities based on the total porosity, ++: not less than 80%, +: not less than 60% and not more than 80%, and : less than 60%.)
(176) (The porosity size distribution: the proportion of the porosity having a porosity size within 30% of the mean porosity size based on the total porosity.)
(177) (The thermal conductivity [W/mK]: +++: <0.05, ++: 0.05<0.075, +: 0.075<0.1, and : not less than 0.1 [W/mK].)
(178) (The compression resistance: +++=less than 1%, ++=not less than 1% and less than 5%, +=not less than 5% and less than 10%, and =not less than 10%.)
(179) (The control of resistance: ++: less than 1.5, +: not less than 1.5 and less than 2.0, and : not less than 2.0.)
(180) (The dielectric breakdown: ++=no breakdown, =breakdown.)
(181) From Table 2, in the case where the porosity size was large or the porosity size distribution was wide, namely, in the case of poor uniformity of the porosities, carbon black was nonuniformly dispersed. This caused rapid resistance change, resulting in difficulties to control the resistance according to the amount of carbon black. Further, the dielectric breakdown has occurred because of portions where carbon black nonuniformly existed. On the other hand, the films having the independent porosities of Examples 19 to 24 showed improvement in the compression resistance because the films contain carbon black, in addition to good thermal conductivity and good control of the resistance.
Example 25
(182) PFA was laminated on the resin composition obtained in Example 5. Lamination was conducted by applying PFA dispersion (510CL, Du Pont-Mitsui Fluorochemicals Company, Ltd.) on the resin composition with a spray injection apparatus, and heating the product for 10 minutes at 350 C. The thickness of the PFA was measured. Then, the thickness thereof was 5 m. The surface roughness Rz was 0.5 m. The cross section thereof was observed with the SEM. Then, the cross section had that as illustrated in
Example 26
(183) The PFA was laminated on the resin composition obtained in Example 8 by the same method as that in Example 25. Lamination was conducted by applying the PFA dispersion on the resin composition with the spray injection apparatus, and heating the product for 10 minutes at 350 C. The thickness of the PFA was measured. Then, the thickness thereof was 6 m. The surface roughness Rz was 0.6 m.
Comparative Example 18
(184) The PFA was laminated on the resin composition obtained in Comparative Example 2 by the same method as that in Example 25. The thickness of the PFA was measured. Then, the thickness thereof was 6 m. The surface roughness Rz was measured. Then, the surface roughness Rz was 0.9 m.
(185) A fixing test was conducted using the resin compositions according to Examples 25 and 26 and Comparative Example 18. First, a toner was transferred onto the resin composition using image press C1 (Canon, Inc.). In the fixing test, the film having the transferred toner was fixed on an aluminum stage, and heated with a halogen lamp of 800 W for 100 msec. Subsequently, the stage was moved at a rate of 360 mm/sec, and fixing to a medium after 100 msec was considered. It is configured such that the medium is fixed to an aluminum roller around which an elastic rubber is wrapped, to form a nip portion with the aluminum stage. Fixing was performed at a pressure at the nip portion of 10 kgf/cm.sup.2 and pressurization time of 10 msec. Table 3 shows the result.
(186) TABLE-US-00003 TABLE 3 Thermal conductivity Coverage Example 25 +++ ++ Example 26 ++ + Comparative + Example 18
(187) In Examples 25 to 26 and Comparative Example 18, the thermal conductivity and the coverage were evaluated according to the criteria as follows.
(188) (The thermal conductivity [W/mK]: +++: <0.05, ++: 0.05<0.075, +: 0.075<0.1, and : not less than 0.1 [W/mK].)
(189) (The coverage: evaluated as a toner residual ratio on a medium when a fixed object was bent crosswise and the printed matter was scrubbed with a brass around which a silbond sheet was wrapped; ++=the toner residual ratio after the test is not less than 75%, +=the toner residual ratio is not less than 50% and less than 75%, and =the toner residual ratio is less than 50%.)
(190) In Example 25, the thermal conductivity of the lamination film is low, and reduction in the toner temperature during conveyance is suppressed. It turned out that, for that reason, the toner is kept molten until the toner is fixed onto the medium so that the toner is firmly fixed onto the medium. On the other hand, in Comparative Example 18, the toner temperature was reduced during conveyance due to the high thermal conductivity of the lamination film. For that reason, the toner solidified at the time of nip, and poor fixing occurred.
Example 27
(191) As a substrate for a fixing belt, a conductive polyimide sheet formed into an endless belt shape having a perimeter length of 500 mm and having a thickness of 125 m was fixed to a tubular cylinder having an inner diameter of 30 mm and a length of 500 mm. An NMP (the resin concentration of 20% by weight) solution of polyamic acid was uniformly applied onto an outer circumferential surface of the polyimide sheet with dip coating, the NMP solution containing 15% by weight of lithium chloride and 15% by weight of carbon black (Denka Black, Denki Kagaku Kogyo K. K.) and having the viscosity (120,000 cP) adjusted according to the amount of lithium chloride. Next, the coating film was covered with a solvent substitution adjustment material (U-pore, a Gurley value: 210 sec/100 cc, Ube Industries, Ltd.), and the tubular cylinder was immersed in water for 20 minutes.
(192) Next, the applied solvent substitution adjustment material was peeled off. Adhering water was wiped off, and the film was put into a drying furnace. After the film was dried at 80 C. for 1 hour, the temperature was raised to 150 C. at a temperature raising rate of 10 C./min. After the film was heated at 150 C. for 30 minutes, the temperature was raised to 250 C. at a temperature raising rate of 10 C./min. After the film was heated at 250 C. for 10 minutes, the temperature was raised to 350 C. at a temperature raising rate of 10 C./min. The, the film was heated for 10 minutes at 350 C. to produce a polyimide resin composition.
(193) The mean porosity size was 0.20 m. The number distribution was examined. Then, 90% of the total porosity was included in a size of 0.14 to 0.26 m. The porosity ratio was 65%, and 90% of the total porosity was the independent porosity. Moreover, the thickness was 150 m.
(194) The PFA dispersion was applied onto the thus-obtained endless sheet of porosity polyimide using a spray gun. The PFA dispersion was applied onto the resin composition surface thereof. A lamination film made of the PFA was obtained by heating at 350 C. for 10 minutes. The thickness of the PFA was 5 m. The surface roughness (Rz) was 0.9 m.
Example 28
(195) An endless fixing belt was produced by the same method as that in Example 27 except that the amount of lithium chloride was adjusted so that the resin viscosity was 65,000 cP, and the film was subjected to phase transition without covering the film with any solvent substitution adjustment material. The mean porosity size of the porous layer was 0.80 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 0.56 to 1.0 m. The porosity ratio was 65%, and 87% of the total porosity was the independent porosity. Moreover, the thickness was 140 m. Application of the PFA onto the resin composition was conducted in the same manner as in Example 27. The thickness of the PFA was 7 m. The surface roughness (Rz) was 0.8 m.
Comparative Example 19
(196) An endless fixing belt was produced by the same method as that in Example 27 except that lithium chloride was not added, and the film was immersed in water without covering the film with any solvent substitution adjustment material. The mean porosity size of the porous layer was 4.8 m. The number distribution was examined. Then, 62% of the total porosity was included in a size of 3.4 to 6.2 m. The porosity ratio was 65%, and 65% of the total porosity was the independent porosity. Application of the PFA onto the resin composition was conducted in the same manner as in Example 27. The thickness of the PFA was 7 m. The surface roughness (Rz) was 0.8 m.
Comparative Example 20
(197) The polyimide foamed sheet shown in Comparative Example 9 and containing carbon black in a concentration of 15% by weight was attached onto the conductive polyimide sheet described in Example 27. The PFA was laminated thereon according to the method described in Example 27. The thickness of the PFA was 7 m. The surface roughness (Rz) was 0.7 m.
(198) Subsequently, the fixing belts obtained in Examples 27 and 28 and Comparative Examples 19 and 20 each were assembled into the fixing apparatus illustrated in
(199) 1) Fixed image
(200) 2) Fixing of the toner onto the fixing belt
(201) The fixed image and fixing of the toner onto the fixing belt were evaluated by ranking. The rank is from 1 to 5, and it is shown that a larger rank is better. Moreover, an OK level is rank 3 or more.
(202) TABLE-US-00004 TABLE 4 Number of sheets Fixing passed through Fixed image of toner Example 27 100K-OK 4 5 Example 28 100K-OK 3 4 Comparative 30K-NG 2 4 Example 19 Comparative 100K-NG Not fixed from beginning 1 Example 20
(203) From Table 4, it turns out that in the belt member containing the porous film having a small thermal conductivity and a high compression resistance, good fixing is also performed in continuous printing, and the toner is not fixed to the belt.
Example 29
(204) As a substrate for a fixing roller, a 400-m silicone rubber (TSE3033, Momentive Performance Materials, Inc.) was formed on an aluminum roller of 50 cm. Next, using a primer, porosity polyimide on which the thin film PFA was laminated described in Example 27 was attached on the silicone rubber to produce a fixing roller containing a porous layer.
Example 30
(205) A fixing roller containing a porous layer was produced by the same method as that in Example 29 except that porosity polyimide on which the thin film PFA was laminated described in Example 28 was used.
Comparative Example 21
(206) A fixing roller containing a porous layer was produced by the same method as that in Example 29 except that porosity polyimide on which the thin film PFA was laminated described in Comparative Example 19 was used.
(207) The fixing rollers obtained by Examples 29 and 30 and Comparative Example 21 each were assembled into the fixing apparatus illustrated in
(208) 1) Fixed image
(209) 2) Fixing of the toner onto the fixing belt
(210) The fixed image and fixing of the toner onto the fixing belt were evaluated by ranking. The rank is from 1 to 5, and it is shown that a larger rank is better. Moreover, an OK level is rank 3 or more.
(211) TABLE-US-00005 TABLE 5 Number of sheets passed through Fixed image Fixing of toner Example 29 120K-OK 4 5 Example 30 120K-OK 3 4 Comparative 30K-NG 2 2 Example 21
(212) From Table 5, it turns out that in the roller member containing the porous film having a small thermal conductivity and a high compression resistance, good fixing is also performed in continuous printing, and the toner is not fixed to the roller.
Example 31
(213) Polycarbonate (Z400, Mitsubishi Gas Chemical Company, Inc.) was dissolved in N-methyl pyrrolidone (NMP) of polyamic acid to prepare a solution of 20% by weight. Lithium chloride was added to this solution so that the concentration of lithium chloride might be 15% by weight, and dissolved. The viscosity of this solution was 105,000 cP. A polyester material (Teijin, Ltd.) was prepared as a substrate, and the polycarbonate solution was casted thereon using a coater. Subsequently, the cast film was immersed in distilled water for 5 minutes. The substrate was taken out from the water, and the obtained film was rinsed with distilled water.
(214) Adhering water was wiped off, and the film was put into a drying furnace to be dried at 80 C. for 1 hour. The porosity form of the obtained film was examined. As a result, the mean porosity size of the independent porosity was 0.015 m. With respect to the number distribution, 82% of the total porosity was included in a size of 0.011 to 0.020 m. Moreover, the porosity ratio was 65%, and the thickness of the obtained film was 70 m. The cross section of the film was observed with the SEM. As a result, the cross section had that as illustrated in
Example 32
(215) A polycarbonate resin composition was obtained by the same method as that in Example 31 except that when the cast film was immersed in water, the cast film was covered with a solvent substitution adjustment material (U-pore, a Gurley value: 210 sec/100 cc, Ube Industries, Ltd.) and was subjected to phase transition. The viscosity of the resin solution was 108,000 cP.
(216) The mean porosity size of the independent porosity was 0.20 m. With respect to the number distribution, 92% of the total porosity was included in a size of 0.14 to 0.26 m. Moreover, the porosity ratio was 64%, and 91% of the total porosity was the independent porosity. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
Example 33
(217) A polycarbonate resin composition was obtained by the same method as that in Example 31 except that the amount of lithium chloride was adjusted so that the resin viscosity of solution was 72,000 cP.
(218) The mean porosity size of the independent porosity was 0.50 m. With respect to the number distribution, 82% of the total porosity was included in a size of 0.35 to 0.65 m. Moreover, the porosity ratio was 61%, and 80% of the total porosity was the independent porosity.
Example 34
(219) A polycarbonate resin composition was obtained by the same method as that in Example 31 except that the amount of lithium chloride was adjusted so that the resin viscosity of solution was 39,000 cP.
(220) The mean porosity size of the independent porosity was 0.84 m. With respect to the number distribution, 82% of the total porosity was included in a size of 0.59 to 1.1 m. Moreover, the porosity ratio was 61%, and 80% of the total porosity was the independent porosity.
Comparative Example 22
(221) A polycarbonate resin composition was obtained by the same method as that in Example 31 except that the resin was casted without adding lithium chloride, and the cast film was kept for 2.5 minutes in a container having a humidity of approximately 100% and a temperature of 50 C. The viscosity of the resin solution was 7,600 cP.
(222) The mean porosity size of the independent porosity was 2.8 m. The number distribution was examined. Then, 65% of the total porosity was included in a size of 2.0 to 3.6 m. Moreover, the porosity ratio was 64%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Comparative Example 23
(223) A polycarbonate resin composition was produced by the same method as that in Example 31 except that lithium chloride was not added, and the cast film was covered with a solvent substitution adjustment material (a Gurley value: 800 sec/100 c, Ube Industries, Ltd.), and was subjected to phase transition. The viscosity of the solution was 7,600 cP.
(224) The mean porosity size of the independent porosity was 13 m. The number distribution was examined. Then, 82% of the total porosity was included in a size of 9.1 to 17 m. Moreover, the porosity ratio was 64%, and 81% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m.
Comparative Example 24
(225) A polycarbonate resin composition was produced by the same method as that in Comparative Example 23 except that the cast film was subjected to phase transition without covering the cast film with any solvent substitution adjustment material. The resin viscosity was 9,000 cP.
(226) The mean porosity size of the porosity was 5.0 m. The number distribution was examined. Then, 62% of the total porosity was included in a size of 3.5 to 6.5 m. Moreover, the porosity ratio was 65%, and 84% of the total porosity was the independent porosity. The thickness of the obtained porous film was 140 m. The cross section of the film was observed with the SEM. Then, the cross section had that illustrated in
Comparative Example 25
(227) A polycarbonate resin composition was produced by the same method as that in Comparative Example 24 except that the temperature of the solidifying solvent (water) was 70 C. The resin viscosity was 8,500 cP.
(228) The mean porosity size of the porosity was 6.0 m. The number distribution was examined. Then, 81% of the total porosity was included in a size of 4.2 to 7.8 m. Moreover, the porosity ratio was 64%, and 64% of the total porosity was the independent porosity.
Comparative Example 26
(229) A polycarbonate resin composition was produced by the same method as that in Comparative Example 24 except that the resin concentration was 18% by weight. The resin viscosity was 7,200 cP.
(230) The mean porosity size of the porosity was 5.3 m. The number distribution was examined. Then, 64% of the total porosity was included in a size of 3.7 to 6.9 m. Moreover, the porosity ratio was 69%, and 62% of the total porosity was the independent porosity.
(231) In Examples 31 to 34 and Comparative Examples 22 to 26, the thermal conductivity, the compression resistance (ratio of thickness change before and after compression), and the dielectric constant were evaluated according to the criteria as follows. Table 6 shows the evaluation result.
(232) TABLE-US-00006 TABLE 6 Solvent Porosity Porosity Porosity Resin substitution Dielectric size Independent size ratio viscosity adjustment Thermal Compression constant [m] porosity distribution [%] [cP] material conductivity resistance (10.sup.6 Hz) Example 31 0.015 ++ 82 65 105000 + +++ ++ Example 32 0.20 ++ 92 64 108000 210 +++ +++ ++ [sec/100 cc] Example 33 0.50 ++ 82 61 72000 ++ ++ ++ Example 34 0.84 ++ 82 61 58000 ++ ++ ++ Comparative 2.8 ++ 65 64 7600 + + ++ Example 22 Comparative 13 ++ 82 64 7600 800 + ++ Example 23 [sec/100 cc] Comparative 5.0 + 62 65 9000 + ++ Example 24 Comparative 6.0 + 81 64 8500 + + ++ Example 25 Comparative 5.3 ++ 64 69 7200 + + ++ Example 26
(233) (The thermal conductivity [W/mK]: +++: <0.05, ++: 0.05<0.075, +: 0.075<0.1, and : not less than 0.1 [W/mK].)
(234) (The compression resistance: +++=less than 1%, ++=not less than 1% and less than 5%, +=not less than 5% and less than 10%, and =not less than 10%.)
(235) (The dielectric constant [10.sup.6 Hz]: ++: less than 2.5, and : not less than 2.5.)
(236) From table 6, the porous films shown in Examples 31 to 34 are a film having small deterioration in mechanical properties and a low dielectric constant.
(237) (Evaluation of Film Properties)
(238) A relationship of film properties between the mean porosity size and porosity size distribution was evaluated.
(239) The thermal conductivity after compression was used as a film property parameter.
(240) Moreover,
(241) From the above-mentioned results, it turned out that the porous film having low thermal conductivity and high compression resistance can be obtained by setting the mean porosity size and porosity size distribution of the porosities in the ranges of the present invention (the mean porosity size is not less than 0.01 m and not more than 0.9 m, and not less than 80% of the total porosity has a porosity size within 30% of the mean porosity size.), and the porous film can be used suitably as a belt material in the present invention.
(242) While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
(243) This application claims priority from Japan Patent Application No. 2009-129726 filed on May 28, 2009, and the content thereof is cited as a part of this application.