Electroconductive elastomer composition and manufacturing method therefor

Abstract

There are provided: an electrically conductive thermoplastic elastomer composition which can be produced with higher productivity at lower costs by means of a simple arrangement and has excellent extrudability and a lower resistance required for a driving roller; a production method for the composition; a driving roller produced by employing the electrically conductive thermoplastic elastomer composition; and an image forming apparatus incorporating the driving roller. In the electrically conductive thermoplastic elastomer composition, 5 to 15 parts by mass of Ketjen black is finely dispersed in 100 parts by mass of a mixture of an ester type urethane thermoplastic elastomer and a plasticizer or in 100 parts by mass of a polyester thermoplastic elastomer. In the production method, the ingredient other than the Ketjen black is first kneaded, and then the Ketjen black is added to and further kneaded with the ingredient. The driving roller (1) is formed of the electrically conductive thermoplastic elastomer composition. The image forming apparatus incorporates the driving roller.

Claims

1. An electrically conductive thermoplastic elastomer composition essentially comprising: an ester type urethane thermoplastic elastomer E which comprises a molecule that contains a hard segment having a polyurethane structure and a soft segment having a polyester structure; a plasticizer P; and Ketjen black finely dispersed in a mixture of the ester type urethane thermoplastic elastomer and the plasticizer, the Ketjen black being present in an amount of not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer, wherein the ester type urethane thermoplastic elastomer E and the plasticizer P are present in a mass ratio E/P of E/P=70/30 to 85/15.

2. The electrically conductive thermoplastic elastomer composition according to claim 1, wherein the ester type urethane thermoplastic elastomer has a Durometer Type-A hardness of not lower than 69 degrees and not higher than 75 degrees.

3. The electrically conductive thermoplastic elastomer composition according to claim 1, wherein only the Ketjen black is present for imparting the ester type urethane thermoplastic elastomer E with electrical conductivity.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view showing the appearance of an exemplary driving roller according to one embodiment of the present invention.

(2) FIG. 2 is a diagram for explaining a method of measuring the roller resistance of the driving roller.

(3) FIG. 3 is a schematic diagram for explaining an apparatus to be used for measuring the frictional force of the driving roller with respect to a belt.

(4) FIG. 4 is a transmission electron microscope photograph showing the dispersion state of Ketjen black in a driving roller produced in Example 3.

(5) FIG. 5 is a transmission electron microscope photograph showing the dispersion state of Ketjen black in a driving roller produced in Comparative Example 3.

DESCRIPTION OF EMBODIMENTS

(6) <<Electrically Conductive Thermoplastic Elastomer Compositions>>

(7) An electrically conductive thermoplastic elastomer composition according to the present invention essentially contains: an ester type urethane thermoplastic elastomer; a plasticizer; and Ketjen black finely dispersed in a mixture of the ester type urethane thermoplastic elastomer and the plasticizer, the Ketjen black being present in an amount of not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer.

(8) Another electrically conductive thermoplastic elastomer composition according to the present invention essentially contains: a polyester thermoplastic elastomer; and Ketjen black finely dispersed in the polyester thermoplastic elastomer, the Ketjen black being present in an amount of not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the polyester thermoplastic elastomer.

(9) <Ester Type Urethane Thermoplastic Elastomer>

(10) Usable as the ester type urethane thermoplastic elastomer are various ester type urethane thermoplastic elastomers which each contain a hard segment having a polyurethane structure and a soft segment having a polyester structure in a molecule thereof, and have thermoplasticity that permits injection molding and elasticity that permits a driving roller to properly function.

(11) Particularly, the ester type urethane thermoplastic elastomer preferably has a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees as measured in conformity with Japanese Industrial Standards JIS K6253-3:2012 Rubber, vulcanized or thermoplasticDetermination of hardnessPart 3: Durometer method.

(12) If the hardness is lower than the aforementioned range, the driving roller is liable to have insufficient abrasion resistance. If the hardness is higher than the aforementioned range, the driving roller is liable to have a reduced frictional force with respect to a belt, suffering from slippage or the like.

(13) Specific examples of the ester type urethane thermoplastic elastomer include ELASTORAN (registered trade name) series C80A (having a Durometer Type-A hardness of 802 degrees), S80A (having a Durometer Type-A hardness of 802 degrees), C60A10WN (having a Durometer Type-A hardness of 654 degrees and containing a plasticizer), C70A (having a Durometer Type-A hardness of 702 degrees), C70A10WN (having a Durometer Type-A hardness of 734 degrees and containing a plasticizer) and C70A11FG (having a Durometer Type-A hardness of 753 degrees) available from BASF Japan Co., Ltd., and MIRACTORAN (registered trade name) series E670 (having a Durometer Type-A hardness of 702 degrees) available from Nippon Miractoran Co., Ltd. These ester type urethane thermoplastic elastomers may be used alone or in combination.

(14) The ester type urethane thermoplastic elastomers described above may each have a Durometer Type-A hardness having an upper limit and/or a lower limit falling outside the range of not less than 60 degrees and not greater than 80 degrees, as long as the median of the Durometer Type-A hardness falls within this range.

(15) The ester type urethane thermoplastic elastomers without the note containing a plasticizer are supplied in a plasticizer-free state. On the other hand, the ester type urethane thermoplastic elastomers with the note containing a plasticizer are supplied in a plasticizer-containing state and, like the plasticizer-free ester type urethane thermoplastic elastomers, each provide an electrically conductive thermoplastic elastomer composition imparted with excellent extrudability by additionally blending the plasticizer in a mass ratio to be described later.

(16) <Plasticizer>

(17) Examples of the plasticizer include SANFLEX (registered trade name) series EB-200, EB-300 and EB-400 (polyethylene glycol dibenzoates) available from Sanyo Chemical Industries Ltd., BENZOFLEX (registered trade name) 9-88 (dipropylene glycol dibenzoate) available from Eastman Chemical Co., Ltd., bis(2-methoxyethyl) phthalate (DMEP) and tributoxyethyl phosphate (TBP), which may be used alone or in combination.

(18) <Mass Ratio>

(19) The mass ratio E/P of the ester type urethane thermoplastic elastomer E and the plasticizer P is preferably E/P=55/45 to 85/15, particularly preferably E/P=70/30 to 85/15.

(20) If the ratio E of the ester type urethane thermoplastic elastomer is less than the aforementioned range, the driving roller is liable to have insufficient abrasion resistance. If the ratio P of the plasticizer is less than the aforementioned range, the electrically conductive thermoplastic elastomer composition is liable to have lower extrudability, and the driving roller is liable to have a reduced frictional force with respect to the belt, suffering from slippage or the like.

(21) Where the ester type urethane thermoplastic elastomer preliminarily contains the plasticizer as described above, the amount of the plasticizer to be additionally blended is determined so that the mass ratio E/P between the solid content E of the ester type urethane thermoplastic elastomer (i.e., the amount E of the ester type urethane thermoplastic elastomer per se) and the total amount P of the plasticizer contained in the ester type urethane thermoplastic elastomer and the plasticizer to be additionally blended falls within the aforementioned range.

(22) <Polyester Thermoplastic Elastomer>

(23) Examples of the polyester thermoplastic elastomer include various polyester thermoplastic elastomers such as multi-block polymers each containing a hard segment of an aromatic polyester (polybutylene terephthalate or the like) having a higher melting point and a higher crystallinity and a soft segment of an amorphous polyether (polytetramethylene ether glycol or the like) having a glass transition temperature of not higher than about 70 C. These polyester thermoplastic elastomers may be used alone or in combination.

(24) Particularly, the polyester thermoplastic elastomer preferably has a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees as measured in conformity with the aforementioned JIS K6253-3:2012.

(25) If the hardness is lower than the aforementioned range, the driving roller is liable to have insufficient abrasion resistance. If the hardness is higher than the aforementioned range, the driving roller is liable to have a reduced frictional force with respect to the belt, suffering from slippage or the like.

(26) Specific examples of the polyester thermoplastic elastomer include HYTREL (registered trade name) series 3046 (having a Durometer Type-A hardness of 77 degrees), 3078 (having a Durometer Type-A hardness of 78 degrees), G3548L (having a Durometer Type-A hardness of 80 degrees), SB654 (having a Durometer Type-A hardness of 65 degrees), SB704 (having a Durometer Type-A hardness of 70 degrees), SB754 (having a Durometer Type-A hardness of 75 degrees) and SC753 (having a Durometer Type-A hardness of 75 degrees) available from Toray Du Pont Co., Ltd., and PELPRENE (registered trade name) series P30B (having a Durometer Type-A hardness of 71 degrees) available from Toyobo Co., Ltd. These polyester thermoplastic elastomers may be used alone or in combination.

(27) <Ketjen Black>

(28) Usable as the Ketjen black are Ketjen blacks of various grades each including hollow shell particles and having a higher electrical conductivity.

(29) Specific examples of the Ketjen black include KETJEN BLACK EC300J (granular form), KETJEN BLACK EC600JD (granular form), CARBON ECP (powder obtained from KETJEN BLACK EC300J) and CARBON ECP600JD (powder obtained from KETJEN BLACK EC600JD) available from Lion Corporation. These Ketjen blacks may be used alone or in combination.

(30) The amount of the Ketjen black should be not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer or based on 100 parts by mass of the polyester thermoplastic elastomer.

(31) If the amount of the Ketjen black is less than the aforementioned range, it will be impossible to impart the electrically conductive thermoplastic elastomer composition with proper electrical conductivity even with the addition of the Ketjen black having excellent electrical conductivity, failing to sufficiently reduce the resistance of the driving roller to a resistance range suitable for the driving roller.

(32) If the amount of the Ketjen black is greater than the aforementioned range, on the other hand, the driving roller is liable to have a higher hardness and hence have a reduced frictional force with respect to the belt, suffering from slippage or the like.

(33) In consideration of the balance between the frictional force and the resistance of the driving roller, the amount of the Ketjen black is preferably not greater than 12 parts by mass within the aforementioned range.

(34) <Other Ingredients>

(35) As described above, the inventive electrically conductive thermoplastic elastomer composition preferably contains only the ester type urethane thermoplastic elastomer or the polyester thermoplastic elastomer as the base polymer for the driving roller, the Ketjen black for imparting the base polymer with electrical conductivity, and the plasticizer for improving the extrudability of the ester type urethane thermoplastic elastomer.

(36) In the present invention, however, other ingredients for imparting the electrically conductive thermoplastic elastomer composition with auxiliary functions other than the aforementioned function may be blended in the electrically conductive thermoplastic elastomer composition.

(37) <<Production Method for Electrically Conductive Thermoplastic Elastomer Composition>>

(38) In the inventive production method, a twin screw kneading extruder is used, which includes a kneading portion which kneads a material and extrudes the material in one direction, a main feeder which feeds an ingredient to the kneading portion, and aside feeder which feeds an ingredient to the kneading portion at a position downstream of the main feeder with respect to the material extruding direction.

(39) With the kneading portion being operated, the aforementioned ingredients other than the Ketjen black are preliminarily dry-blended, and fed into the kneading portion from the main feeder. While the ingredients are fed in the extruding direction and kneaded in the kneading portion, the Ketjen black is fed into the kneading portion from the side feeder and further kneaded with the previously kneaded ingredients.

(40) Through this two-step process, the inventive electrically conductive thermoplastic elastomer composition can be continuously efficiently produced by finely dispersing the Ketjen black in the ingredients while preventing the destruction of the structure of the Ketjen black and the flocculation of the Ketjen black.

(41) The electrically conductive thermoplastic elastomer composition thus produced is continuously extruded from a distal end of the kneading portion, and the resulting strand is continuously cooled, for example, through a strand cooling section and continuously pelletized by a pelletizer.

(42) <<Driving Roller>>

(43) FIG. 1 is a perspective view showing the appearance of an exemplary driving roller according to an embodiment of the present invention.

(44) Referring to FIG. 1, the driving roller 1 according to this embodiment includes a tubular body formed of the inventive electrically conductive thermoplastic elastomer composition and having a single layer structure, and a shaft 3 is inserted through and fixed to a center through-hole 2 of the tubular body.

(45) The driving roller 1 may be porous, but is preferably nonporous for improvement of durability and the like.

(46) The shaft 3 is a unitary member made of a metal such as aluminum, an aluminum alloy or a stainless steel.

(47) The shaft 3 is electrically connected to and mechanically fixed to the driving roller 1, for example, via an electrically conductive adhesive agent. Alternatively, a shaft having an outer diameter that is greater than the inner diameter of the through-hole 2 is used as the shaft 3, and press-inserted into the through-hole 2 to be electrically connected to and mechanically fixed to the driving roller 1. Thus, the shaft 3 and the driving roller 1 are unitarily rotatable.

(48) For production of the driving roller 1, the inventive electrically conductive thermoplastic elastomer composition is extruded into a tubular body by means of an extruder, and the tubular body is cooled and cut to a predetermined length. As required, the tubular body is polished to a predetermined outer diameter.

(49) The shaft 3 may be inserted into and fixed to the through-hole 2 at any time between the end of the cutting of the tubular body and the end of the polishing.

(50) However, the tubular body is preferably polished with the shaft 3 inserted through the through-hole 2 after the cutting. Further, the tubular body may be polished while being rotated about the shaft 3. This improves the working efficiency in the polishing, and suppresses deflection of an outer peripheral surface 4 of the driving roller 1.

(51) As described above, the shaft 3 having an outer diameter that is greater than the inner diameter of the through-hole 2 is press-inserted through the through-hole 2. Alternatively, the shaft 3 may be inserted through the through-hole 2 with the intervention of the electrically conductive adhesive agent.

(52) In the former case, the electrical connection and the mechanical fixing are achieved simultaneously with the press insertion.

(53) The Durometer Type-A hardness of the driving roller 1 is limited to a range of not lower than 60 degrees and not higher than 80 degrees.

(54) If the hardness is lower than the aforementioned range, the driving roller is liable to have insufficient abrasion resistance. If the hardness is higher than the aforementioned range, the driving roller is liable to have a reduced frictional force with respect to the belt, suffering from slippage or the like.

(55) <Measurement of Roller Resistance>

(56) FIG. 2 is a diagram for explaining how to measure the roller resistance of the driving roller 1.

(57) Referring to FIGS. 1 and 2, the roller resistance of the driving roller 1 is measured in the following manner.

(58) An aluminum drum 5 rotatable at a constant rotation speed is prepared, and the outer peripheral surface 4 of the driving roller 1 to be subjected to the measurement of the roller resistance is brought into contact with an outer peripheral surface 6 of the aluminum drum 5 from above.

(59) A DC power source 7 and a resistor 8 are connected in series between the shaft 3 of the driving roller 1 and the aluminum drum 5 to provide a measurement circuit 9. The DC power source 7 is connected to the shaft 3 at its negative terminal, and connected to the resistor 8 at its positive terminal. The resistor 8 has a resistance r of 100.

(60) Subsequently, a load F of 450 gf (=4.41 N) is applied to each of opposite end portions of the shaft 3 to bring the driving roller 1 into press contact with the aluminum drum 5 and, in this state, a detection voltage V applied to the resistor 8 is measured by applying an application voltage E of DC 50 V from the DC power source 7 between the shaft 3 and the aluminum drum 5 while rotating the aluminum drum 5 (at a rotation speed of 40 rpm).

(61) The roller resistance R of the driving roller 1 is basically determined from the following expression (1) based on the detection voltage V and the application voltage E (=50 V):
R=rE/(Vr)(1)
However, the term r in the denominator of the expression (1) is negligible, so that the roller resistance of the driving roller 1 is expressed by a value determined from the following expression (1) in the present invention:
R=rE/V(1)

(62) The measurement is performed in an ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551%.

(63) <Measurement of Frictional Force>

(64) FIG. 3 is a schematic diagram for explaining an apparatus to be used for measuring the friction coefficient of the driving roller with respect to a belt.

(65) Referring to FIG. 3, the frictional force of the driving roller 1 is determined based on a friction coefficient measured by a measurement method in conformity with the Oiler belt system by means of the above apparatus.

(66) First, the driving roller 1 is held so as to be rotatable in a direction indicated by a two-dot-and-dash line in FIG. 3 with a center axis 10 of the shaft 3 kept horizontal. Further, a load meter 11 is provided near the driving roller 1 as spaced a predetermined distance from the center axis 10 of the driving roller 1.

(67) Then, a belt 13 is brought into contact with a portion of the outer peripheral surface 4 of the driving roller 1 defined by a center angle (degree) about the center axis 10 with a weight 12 attached to one of opposite ends thereof and suspended below the driving roller 1 and with the other end thereof connected to the load meter 11.

(68) Subsequently, a load P (N) occurring when the driving roller 1 is rotated at a predetermined speed in the direction indicated by the two-dot-and-dash line is measured by means of the load meter 11, and the friction coefficient is calculated based on the measured load P (N), the load W (N) of the weight 12 and the center angle (degree) from the following expression (2):
=(1/)ln(P/W)(2)

(69) Then, the frictional force F (N) is determined based on the measured load P (N) and the friction coefficient () from the following expression (3):
F(N)=P(3)

(70) The measurement is performed in the ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551%.

(71) <<Image Forming Apparatus>>

(72) An image forming apparatus according to the present invention is characterized in that the inventive driving roller 1 is incorporated, for example, in association with a sheet feed belt, a transfer belt, an intermediate transfer belt or the like.

(73) Examples of the inventive image forming apparatus include electrophotographic image forming apparatuses such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine and a printer-copier-facsimile multifunction machine.

EXAMPLES

Example 1

(74) (Production of Electrically Conductive Thermoplastic Elastomer Composition)

(75) With the use of a tumbler, 80 parts by mass of an ester type urethane thermoplastic elastomer (ELASTORAN C70A having a Durometer Type-A hardness of 70 degrees and available from BASF Japan Co., Ltd.) and 20 parts by mass of dipropylene glycol dibenzoate (BENZOFLEX 9-88 available from Eastman Chemical Co., Ltd.) as a plasticizer were dry-blended.

(76) The mass ratio E/P of the ester type urethane thermoplastic elastomer E and the plasticizer P was 80/20.

(77) A twin screw kneading extruder (HTM-38 available from Aibeck Co., Ltd.) including a kneading portion which kneads a material and extrudes the material in one direction, a main feeder which feeds an ingredient to the kneading portion, and a side feeder which feeds an ingredient to the kneading portion at a position downstream of the main feeder with respect to the material extruding direction was prepared. A mixture obtained by the dry blending was fed into the kneading portion of the twin screw kneading extruder from the main feeder.

(78) While the mixture was fed in the extruding direction and kneaded in the kneading portion, Ketjen black (EC600JD available from Lion Corporation) was fed into the kneading portion from the side feeder and further kneaded with the previously kneaded mixture. Thus, an electrically conductive thermoplastic elastomer composition was produced.

(79) The amount of the Ketjen black was 5 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer.

(80) The electrically conductive thermoplastic elastomer composition thus produced was continuously extruded from a distal end of the kneading portion, and the resulting strand was continuously cooled through a strand cooling section and continuously pelletized by a pelletizer.

(81) (Production of Driving Roller 1)

(82) The resulting pellets were fed into a 50 short axis extruder (available from Kasamatsukako Laboratory Co., Ltd.), and the resulting melt was extruded into a tubular body having an inner diameter of 19 mm and a wall thickness of 1.0 mm. Then, the tubular body was cut to a predetermined length, and an aluminum shaft 3 having an outer diameter of 20 mm was press-inserted into a through-hole 2 of the tubular body. In turn, an outer peripheral surface 4 of the tubular body was polished to a wall thickness of 0.5 mm. Thus, a driving roller 1 with the shaft 3 electrically connected and mechanically fixed thereto as shown in FIG. 1 was produced.

Examples 2 and 3 and Comparative Examples 1 and 2

(83) Electrically conductive thermoplastic elastomer compositions were produced in substantially the same manner as in Example 1, except that the amount of the Ketjen black was 3 parts by mass (Comparative Example 1), 7 parts by mass (Example 2), 15 parts by mass (Example 3) and 20 parts by mass (Comparative Example 2) based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer. Then, driving rollers 1 each having the same configuration and the same dimensions as in Example 1 were produced in the same manner as in Example 1 by using the electrically conductive thermoplastic elastomer compositions thus produced.

(84) The mass ratio E/P of the ester type urethane thermoplastic elastomer E and the plasticizer P was 80/20.

Comparative Example 3

(85) An electrically conductive thermoplastic elastomer composition was produced in substantially the same manner as in Example 1, except that the Ketjen black was dry-blended with the ester type urethane thermoplastic elastomer and the plasticizer with the use of the tumbler in a single step, and the resulting mixture was fed into the kneading portion from the main feeder without the use of the second feeder and further kneaded. Then, a driving roller 1 having the same configuration and the same dimensions as in Example 1 was produced in the same manner as in Example 1 by using the electrically conductive thermoplastic elastomer composition thus produced.

(86) The mass ratio E/P of the ester type urethane thermoplastic elastomer E and the plasticizer P was 80/20. The amount of the Ketjen black was 12 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer.

Example 4

(87) An electrically conductive thermoplastic elastomer composition was produced in substantially the same manner as in Example 1, except that a polyester thermoplastic elastomer (HYTREL 3046 having a Durometer Type-A hardness of 77 degrees and available from Toray Du Pont Co., Ltd.) was used instead of the ester type urethane thermoplastic elastomer and the plasticizer. Then, a driving roller 1 having the same configuration and the same dimensions as in Example 1 was produced in the same manner as in Example 1 by using the electrically conductive thermoplastic elastomer composition thus produced.

(88) The amount of the Ketjen black was 7 parts by mass based on 100 parts by mass of the polyester thermoplastic elastomer.

Comparative Example 4

(89) An electrically conductive thermoplastic elastomer composition was produced in substantially the same manner as in Example 1, except that a polyester thermoplastic elastomer (HYTREL 4047 having a Durometer Type-A hardness of 88 degrees and available from Toray Du Pont Co., Ltd.) was used instead of the ester type urethane thermoplastic elastomer and the plasticizer. Then, a driving roller 1 having the same configuration and the same dimensions as in Example 1 was produced in the same manner as in Example 1 by using the electrically conductive thermoplastic elastomer composition thus produced.

(90) The amount of the Ketjen black was 7 parts by mass based on 100 parts by mass of the polyester thermoplastic elastomer.

(91) <Measurement of Hardness>

(92) The Durometer Type-A hardness of each of the driving rollers 1 produced in Examples and Comparative Examples was measured in conformity with Japanese Industrial Standards JIS K6253-3:2012 Rubber, vulcanized or thermoplasticDetermination of hardnessPart 3: Durometer method in an ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551%.

(93) A driving roller having a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees was rated as acceptable (), and a driving roller having a Durometer Type-A hardness falling outside this range was rated as unacceptable ().

(94) <Evaluation for Extrudability>

(95) The pelletized electrically conductive thermoplastic elastomer compositions produced in Examples and Comparative Examples were each evaluated for extrudability based on measurement of a maximum line speed that permitted stable continuous extrusion of the electrically conductive thermoplastic elastomer composition into the tubular body having the aforementioned dimensions.

(96) An electrically conductive thermoplastic elastomer composition that achieved stable extrusion at a line speed of not lower than 4 m/min was rated as excellent (), and an electrically conductive thermoplastic elastomer composition that achieved stable extrusion at a line speed of not lower than 2 m/min but failed to achieve stable extrusion at a line speed of not lower than 4 m/min was rated as acceptable (). An electrically conductive thermoplastic elastomer composition that failed to achieve stable extrusion even at a line speed of lower than 2 m/min was rated as unacceptable ().

(97) <Evaluation for Abrasion Resistance>

(98) The driving rollers 1 produced in Examples and Comparative Examples were each incorporated in a color laser multifunction machine (Satera (registered trade name) MF8280Cw available from Canon Inc.) together with an original polyimide transfer belt. After 150000 paper sheets were successively passed through the color laser multifunction machine, a driving roller 1 having an outer diameter change of not greater than 0.03 mm was rated as acceptable (), and a driving roller 1 having an outer diameter change of greater than 0.03 mm was rated as unacceptable (). The evaluation was performed in the ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551%.

(99) <Measurement of Frictional Force>

(100) The friction coefficient of each of the driving rollers 1 produced in Examples and Comparative Examples was measured in the ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551% by the aforementioned measurement method, and the frictional force F of the driving roller 1 with respect to the belt was determined based on the friction coefficient thus measured.

(101) The belt was the same transfer belt as used for the abrasion resistance evaluation.

(102) A driving roller having a frictional force F of not less than 10 N was rated as acceptable (), and a driving roller having a frictional force F of less than 10 N was rated as unacceptable ().

(103) <Measurement of Roller Resistance>

(104) The roller resistance of each of the driving rollers 1 produced in Examples and Comparative Examples was measured in the ordinary temperature and ordinary humidity environment at a temperature of 231 C. at a relative humidity of 551% by the aforementioned measurement method.

(105) A driving roller having a roller resistance of not greater than 10.sup.5 level was rated as acceptable (), and a driving roller having a roller resistance of greater than 10.sup.5 level was rated as unacceptable ().

(106) <Evaluation for Dispersion State>

(107) The driving rollers 1 produced in Examples and Comparative Examples were each evaluated for Ketjen black dispersion state based on a transmission electron microscope (TEM) photograph.

(108) FIG. 4 is a TEM photograph showing the Ketjen black dispersion state of the driving roller produced in Example 3, and FIG. 5 is a TEM photograph showing the Ketjen black dispersion state of the driving roller produced in Comparative Example 3.

(109) Comparison between the results for Example 3 (FIG. 4) and Comparative Example 3 (FIG. 5) indicates that, where the Ketjen black was later added to the elastomer from the side feeder and kneaded with the elastomer, the Ketjen black was more homogeneously and finely dispersed in the elastomer without flocculation.

(110) A driving roller having substantially the same fine dispersion state as in FIG. 4 was rated as acceptable (), and a driving roller having substantially the same flocculation state as in FIG. 5 was rated as unacceptable ().

(111) The results are shown in Tables 1 and 2.

(112) TABLE-US-00001 TABLE 1 Comparative Example 1 Example 1 Example 2 Example 3 Parts by mass Ester type urethane thermoplastic elastomer 80 80 80 80 Polyester thermoplastic elastomer 78 degrees 88 degrees Plasticizer 20 20 20 20 Ketjen black 3 5 7 15 Kneading step Two-step Two-step Two-step Two-step Evaluation Type-A hardness (degree) 67 69 70 75 Rating Extrudability Abrasion resistance Frictional force F (N) 28 26 23 13 Rating Roller resistance () 10.sup.6 level 10.sup.5 level 10.sup.5 level 10.sup.4 level Rating x Dispersion state

(113) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example 2 Example 3 Example 4 Example 4 Parts by weight Ester type urethane thermoplastic elastomer 80 80 Polyester thermoplastic elastomer 78 degrees 100 88 degrees 100 Plasticizer 20 20 Ketjen black 20 12 7 7 Kneading step Two-step Single-step Two-step Two-step Evaluation Type-A hardness (degree) 83 72 80 92 Rating X X Extrudability Abrasion resistance Frictional force F (N) 9 13 11 5 Rating X X Roller resistance () 10.sup.3 level 10.sup.7 level 10.sup.5 level 10.sup.5 level Rating X Dispersion state X

(114) The results for Comparative Example 3 in Table 2 indicate that, where the Ketjen black is kneaded together with the other ingredients by the single-step process, it is impossible to finely disperse the Ketjen black in the ingredients and hence to sufficiently reduce the resistance of the driving roller.

(115) In contrast, the results for Examples 1 to 4 in Tables 1 and 2 indicate that, where the ingredients other than the Ketjen black are first kneaded together and then the Ketjen black is added to and further kneaded with the other ingredients by the two-step process, it is possible to finely disperse the Ketjen black in the ingredients and hence to sufficiently reduce the resistance of the driving roller.

(116) The results for Examples 1 to 3 and Comparative Examples 1 and 2 indicate that, where the ester type urethane thermoplastic elastomer and the plasticizer are used in combination, the amount of the Ketjen black should be not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the mixture of the ester type urethane thermoplastic elastomer and the plasticizer in order to sufficiently reduce the resistance of the driving roller while imparting the driving roller with a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees and hence with sufficient frictional force.

(117) The results for Example 4 and Comparative Example 4 indicate that, where the polyester thermoplastic elastomer is used, the amount of the Ketjen black should be not less than 5 parts by mass and not greater than 15 parts by mass based on 100 parts by mass of the polyester thermoplastic elastomer in order to provide the aforementioned effects and, particularly, the polyester thermoplastic elastomer preferably has a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees in order to impart the driving roller with a Durometer Type-A hardness of not lower than 60 degrees and not higher than 80 degrees and hence with sufficient frictional force.

REFERENCE SIGNS LIST

(118) 1: Driving roller 2: Through-hole 3: Shaft 4: Outer peripheral surface 5: Aluminum drum 6: Outer peripheral surface 7: DC power source 8: Resistor 9: Measurement circuit f: Load V: Detection voltage 10: Center axis 11: Load meter 12: Weight 13: Belt P: Load W: Load : Center angle