Thermoplastic resin composite and method of preparing the same

Abstract

Disclosed is a resin composite having improved tensile properties and a method of preparing the same. Particularly, the resin composite comprises a matrix resin and a reinforcement resin which are made of thermoplastic resin compositions.

Claims

1. A resin plastic composite, which is manufactured by a method comprising melting a reinforcement resin and a matrix resin; and impregnating the reinforcement resin into the matrix resin to form the resin composite, wherein the resin composite is prepared using a double belt press laminator comprises four or more sections having different temperature conditions where a first section is closest to the resin injection part of the laminator and a second section, a third and a fourth sections are located sequentially from the first section to the resin discharge part, wherein a temperature in the double belt press laminator decreases from the resin injection part to a resin discharge part of the laminator, and a temperature of the first section (T.sub.1) is in a range of about (T.sub.m−5) ° C. to (T.sub.m+5) ° C., a temperature of the second section (T.sub.2) is in a range of about (T.sub.m−70) ° C. to (T.sub.m−50) ° C., a temperature of the third section (T.sub.3) is in a range of about (T.sub.m−90) ° C. to (T.sub.m−80) ° C., and a temperature of the fourth section (T.sub.4) is in a range of about (T.sub.m−110) ° C. to (T.sub.m−90) ° C., as Tm being a melting temperature of the reinforcement resin, wherein a ratio of an interval between the double belts of laminator to a thickness of the laminated matrix resin and the reinforcement resin ranges from about 0.75 to about 0.95, and wherein the resin composite has specific gravity of about 0.880 to 0.900, a tensile modulus of about 0.80 to 1.1 Gpa, and a tensile strength of about 0.80 to 1.10 Mpa.

2. The resin plastic composite of claim 1, which is prepared in continuous process.

3. The resin plastic composite of claim 1, wherein the method further comprises recrystallizing the formed resin composite in the second section.

4. The resin plastic composite of claim 1, wherein the temperature of the second section (T.sub.2) is lowered by using a cooling apparatus positioned between the first and second sections.

5. The resin plastic composite of claim 4, wherein a cooling apparatus is installed between the first and second sections.

6. The resin plastic composite of claim 1, wherein the method further comprises laminating the matrix resin and the reinforcement resin before melting the reinforcement resin.

7. The resin plastic composite of claim 1, wherein the matrix resin is in a form of a film, and the reinforcement resin is in a form of a fiber or fabric.

8. The resin plastic composite of claim 1, wherein the matrix resin and the reinforcement resin have a melting temperature of about 130 to 165° C.

9. The resin plastic composite of claim 1, wherein the matrix resin and the reinforcement resin are each a thermoplastic resin comprising at least one selected from the group consisting of polyethylene, polypropylene, an acrylonitrile-butadiene-styrene (ABS) resin, polycarbonate, polyacetal, polyamide, polystyrene, and polyphenylene sulfide.

10. The resin plastic composite of claim 1, wherein the matrix resin and the reinforcement resin are polyolefin resin.

11. The resin plastic composite of claim 1, wherein each the first and second section of the laminator is driven by a separate roller.

12. The resin plastic composite of claim 6, wherein each section of the laminator is driven by a separate roller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates the physical properties of a thermoplastic resin composite depending on a compression temperature of the resin composite prepared by a conventional method.

(2) FIG. 2 illustrates the tensile properties of a thermoplastic resin composite depending on a cooling condition of the resin composite prepared by a conventional method.

(3) FIG. 3 illustrates an exemplary internal sections of an exemplary double belt press laminator used in an exemplary embodiment of the present invention.

(4) FIG. 4 is a graph showing changes in physical properties of an exemplary resin composite depending on compression temperature in an exemplary embodiment of the present invention.

(5) FIG. 5 is a graph showing changes in physical properties of an exemplary resin composite obtained by applying the recrystallization process in an exemplary embodiment of the present invention.

(6) FIG. 6 is a DSC graph showing changes in melting point of exemplary resin composites obtained in an exemplary embodiment of the present invention.

(7) FIG. 7 illustrates a main crystalline structure of polypropylene in an exemplary embodiment of the present invention.

(8) FIG. 8 illustrates exemplary configurations of polypropylene of exemplary resin composites obtained from XRD patterns in an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

(9) The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

(10) Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

(11) Hereinafter, a resin composite and a method for manufacturing the same according to various exemplary embodiments will be explained in detail.

(12) In one aspect, the present invention provides a resin composite having improved tensile properties, and the resin composite may comprise a matrix resin and a reinforcement resin. In particular, the matrix resin and the reinforcement resin may have same composition. In certain aspect, the resin composite of the present invention may comprise a thermoplastic resin composite, and be a self-reinforced resin composite.

(13) In another aspect, the present invention provides a method of preparing the above resin composite having improved tensile properties by controlling the process conditions such as a temperature, a pressure, and the like of each process.

(14) An exemplary embodiment of the present invention provides a self-reinforced thermoplastic resin composite having improved tensile properties, and a method of preparing the same.

(15) In addition, an exemplary embodiment of the present invention provides a method of preparing a thermoplastic resin composite using a double-belt press laminator, instead of a batch-typed discontinuous process, by controlling the process parameters and the optimal properties of a self-reinforced composite. In particular, the method may be performed in continuous process. Thus, the method of present invention can achieve an improvement in the physical properties and the productivity.

(16) In an exemplary embodiment, a self-reinforced thermoplastic composite may be prepared by using a double belt laminator with a higher productivity than the compression molding. In the related arts, the compression cooling process may be required for performing a recrystallization step after a melting step of thermoplastic resin. Thus, the temperature can be controlled to be suitable for each section of double-belt laminator, so as to produce the self-reinforced composite with excellent properties.

(17) A conventional laminating method using a double-belt laminator has been used largely for preparing the thermoplastic prepreg. The prepreg is a sheet-type product used as an intermediate material for producing the molded composite which may be prepared by using the matrix resin impregnated into the reinforcement fiber beforehand.

(18) As illustrated in FIG. 3, a double-belt typed heating/pressing apparatus may continuously apply the heat and the pressure on the thermoplastic prepreg by using a continuous metal belt positioned at upper and lower parts of the thermoplastic pregreg. The heating/pressing apparatus with double belt press type may be mainly used in a continuous process.

(19) The thermoplastic resin composite including the same thermoplastic resin composition of matrix resin and a reinforcement resin may have a different thermal stability from a thermoplastic prepreg which includes a carbon/glass fiber as a reinforcement material in the conventional art. Further, in a manufacturing process, the resin composite of the present invention may require a suitable temperature condition for preventing the physical properties from being deteriorated due to the heat shrinkage of the thermoplastic reinforcement material. Therefore, in the case that the conventional heating/pressing apparatus in double belt type and the manufacturing conditions applied for the prepreg preparation are used for the thermoplastic resin composite of the present invention, the physical properties of the reinforcement resin may be deteriorated due to shrinkage and melting of the reinforcement resin caused by heat.

(20) Accordingly, the method of preparing a resin composite according to an exemplary embodiment of the present invention may include melting a reinforcement resin and a matrix resin, and impregnating the reinforcement resin into the matrix resin. Preferably, the method may further include a recrystallizing step of the impregnated resin composite. In addition, before the melting and impregnating, the method may further include a laminating step of the matrix resin and the reinforcement resin.

(21) In the melting and impregnating steps, the laminated resins used for preparing the resin composite may be injected into inside of double belt laminator and the reinforcement resin may be melted and thus impregnated into the matrix resin by being applied with heat and pressure.

(22) As used herein, the term, “a reinforcement material for self-reinforced resin composite” means a resin in a broad meaning, and is distinguished from an inorganic fiber such as carbon fiber, glass fiber, and the like, as a reinforcement material in related art. In a preferred aspect, the reinforcement material for self-reinforced resin composite means a resin which has the same or similar physical properties of a matrix resin. For example, the self-reinforced property of reinforcement material may be determined by differential scanning calorimetry (DSC). When the composite made from the same resin composition of matrix and reinforcement material is analyzed by DSC analysis, the “self-reinforced” material may mean the materials characterized by a single melting temperature (T.sub.m) peak at a primary heating peak, instead of two different peaks.

(23) In the present invention, as the matrix resin and the reinforcement resin, all of the thermoplastic resin known in the art may be used, but are not particularly limited.

(24) In an exemplary embodiment of the present invention, the matrix resin may be in a form of a film, and the reinforcement resin may be in a form of a fiber or fabric. The matrix resin and the reinforcement resin may be thermoplastic resins having a melting temperature of about 130 to 165° C.

(25) The examples of the self-reinforced material can include a thermosetting resin such as an unsaturated polyester resin, a vinyl ester resin, an epoxy resin, a phenol resin or the like, and a thermoplastic resin such as polyethylene, polypropylene, an acrylonitrile-butadiene-styrene (ABS) resin, polycarbonate, polyacetal, polyamide, polystyrene, polyphenylene sulfide or the like. The reinforcement resin, as used herein, may be a resin having physical properties equal or similar to those of the matrix resin. The matrix resin and the reinforcement resin may be polyolefin resins such as homopolymers, heteropolymers, or copolymers including an aliphatic olefin having a C2 to C4 a repeating unit. Examples of the polyolefin resin may include polyethylene, polypropylene, a copolymer of polyethylene and polypropylene, and the like.

(26) The method of preparing a resin composite according to an exemplary embodiment of the present invention may include, by using a double belt press laminator divided into at least two different temperature sections: melting the reinforcement resin and the matrix resin; and impregnating the reinforcement resin into the matrix resin. Accordingly, at least two sections, for example, a first section and a second section, may be arranged sequentially from a resin injection part of the laminator to a resin discharge part thereof, and those sections may have a temperature gradient that is decreasing from the resin injection part of the laminator to the resin discharge part thereof.

(27) In the first section, the reinforcement resin may be melted and impregnated into the matrix resin. Particularly, the temperature of the first section (T.sub.1) disposed to be closest to the resin injection part may be in a range of about (T.sub.m−5)° C. to (T.sub.m+5)° C. as T.sub.m being a melting temperature of the reinforcement resin. When the temperature of the first section is lower than the predetermined range, for example, T.sub.1 is less than (T.sub.m−5)° C., the tensile modulus of elasticity by impregnation may deteriorate due to the heat deficiency. When the temperature of the first section is greater than the predetermined range, for example, T.sub.1 is greater than (T.sub.m+5)° C., the physical properties may deteriorate due to melting of the reinforcement material. Accordingly, it is preferable that the temperature of the first section (T.sub.1) is in a range of about (T.sub.m−5)° C. to (T.sub.m+5)° C.

(28) After the melting and impregnating of the reinforcement resin into the matrix resin, the method of preparing a thermoplastic resin composite according to an exemplary embodiment of the present invention may further include a step of recrystallizing the melted and impregnated resin composite in the second section. A temperature of a recrystallization section or the second section (T.sub.2) may be is in a range of about (Tc−5)° C. to (T.sub.c+5)° C. as T.sub.c represents a recrystallization temperature of the reinforcement resin, or in a range of −70° C. from the melting temperature (T.sub.m) of the reinforcement resin to −50° C. from T.sub.m, that is from about (T.sub.m−70)° C. to (T.sub.m−50)° C. The temperature of the recrystallization section may be determined by considering an effect of increased physical properties due to the crystalline structure of resin which is formed by heat treatment of resin at the recrystallization temperature after the melting. After recrystallization section, the resin may be cooled to form a shape. The recrystallization temperature may be measured for example, by Tc of DSC.

(29) Since the temperature of the second section (T.sub.2) is less than that of the first section (T.sub.1), the temperature of the second section may be lowered by using a cooling apparatus located between the first and second sections. For example, a cooling unit of the belt may be installed between the first and second sections. In the cooling step, the resin composite may be cooled in a press state after the melting and impregnating steps, such that shrinkage of a fiber reinforcement material may be prevented. The cooling step can increase dimensional stability by preventing the reinforcement resin shrinkage and maintains the physical properties of the fiber reinforcement resin. The cooling temperature may be gradually lowered from the temperature of the melting and impregnating steps to room temperature.

(30) The double belt press laminator may be divided into at least two sections having the different temperature conditions, for example, the double belt press laminator may be divided into two, three, four, five portions, or the like. In an exemplary embodiment of the present invention, when the laminator has at least two sections, each section may be operated separately driven by separate rollers, and the temperature of each section may be controlled separately.

(31) As shown in FIG. 3, the double belt press laminator may include four or more sections having the different temperature conditions where the sections may be sequentially divided into a first section, a second section, a third section, and a fourth section located from the resin injection part of the laminator to the resin discharge part thereof. In particular, a temperature of the second section (T.sub.2) may be in a range of about (T.sub.m−70)° C. to (T.sub.m−50)° C., a temperature of the third section (T.sub.3) may be in a range of about (T.sub.m−90)° C. to (T.sub.m−80)° C., and a temperature of the fourth section (T.sub.4) may be in a range of about (T.sub.m−110)° C. to (T.sub.m−90)° C.

(32) In an exemplary embodiment of the present invention, the matrix resin and the reinforcement resin may be laminated before the melting and impregnating steps. In the laminating, the matrix resin and the reinforcement resin may be laminated in consideration of a thickness of a final product and be inserted into the double belts. The matrix resin and the reinforcement resin may be laminated in various combinations without limitation. For example, the matrix resin and the reinforcement resin may be staked in an order of the matrix resin, the reinforcement material and matrix resin.

(33) Preferably, the ratio of an interval between the double belts of the laminator to a total thickness of laminate stacked with the matrix resin and the reinforcement resin may be of about 0.75 to 0.95. The ratio may influence the physical properties of the resin composite. Since the decreased belt interval may increase the lamination pressure, the tensile stiffness of the resin composite may be increased. This change in the physical properties may be caused by increased impregnation rate due to the elevated pressure and by decreased air gap (increased specific gravity). When the ratio is less than the predetermined range, for example, less than about 0.75, the materials may not be uniformly laminated/compressed, such that a product may have non-even thickness and bad appearance. Meanwhile, a roll gap is greater than the predetermined range, for example, greater than about 0.95, the tensile modulus of elasticity may be excessively decreased.

(34) In the method of preparing the thermoplastic resin composite according to the present invention, the retention time of the resin in the laminator may be affected by various conditions, and thus may be suitably selected.

(35) The thermoplastic resin composite as described above or manufactured according to exemplary methods of the present invention may have improved tensile properties and specific gravity of about 0.880 to 0.900, tensile strength of about 0.80 to 1.10, and tensile modulus of about 0.80 to 1.1.

(36) The present invention provides the resin composite may the matrix and the reinforcement material which are selected from the thermoplastic resins, and the method of preparing the same to achieve the high productivity in the continuous process. The resin composite having substantially physical properties may be prepared by controlling process conditions such as a temperature, a pressure and the like. In addition, the resin composite may be widely used in various fields, for example, civil engineering and architectural fields, a transportation field such as vehicle materials, or the like, electronic and electric device fields, aviation and aerospace fields and the like.

EXAMPLE

(37) The present invention will be described in more detail through the following Examples, but the scope of the present invention is not limited to the following Examples.

Example 1: Preparation of Resin Composite

(38) In order to prepare a resin composite, a reinforcement resin fiber and a matrix resin were prepared. Specifically, a homopolypropylene resin (FR 150, Lotte Chemical, MI: 10, T.sub.m: 166° C., Mw: 230,000) was used as the reinforcement resin. A grey yarn was prepared by using the reinforcement resin and was weaved to for a fabric obtained by 1:1 plain weaving the fiber was used. A propylene/ethylene copolymer resin (MI: 25, T.sub.m: 130° C.) was manufactured in a film form and used as the matrix resin.

(39) In order to stack three layers which was sequentially composed of a fiber reinforcement material/a matrix/the fiber reinforcement material, the reinforcement resin and the matrix resin were mounted on a roll shaped unwinder, and sequentially laminated while being transported from the unwinder, such that the laminator of reinforcement resin and the matrix resin were inserted into a double belt press laminator. The simple stacked sample before being processing had a thickness of 0.56 mm, and the double belt laminator was operated at a belt speed of 8 mm/sec and a retention time of 150 seconds with a belt interval (roll gap) of 0.5 mm. The double belt press laminator included four divided sections, and a schematic view specifically indicating four sections of the double belt press is illustrated in FIG. 3. In the present Experiment, the four sections had the same belt temperature of T.sub.m−5° C., and a belt interval of 0.5 mm.

(40) As physical properties of a self-reinforced composite prepared by the method, specific gravity was measured according to ISO-1183, and tensile strength and tensile modulus of elasticity were measured according to ISO-527.

(41) As a result, the obtained self-reinforced composite had specific gravity of 0.874, tensile strength of 0.88, and tensile modulus of 0.30.

Example 2: Evaluation of Effect of Lamination Temperature

(42) As Example 1, a reinforcement resin and a matrix resin were prepared and a resin composite was prepared using a double belt laminator, except for the temperature of double belts laminator. That is, the belt temperature in first to fourth sections of double belt were equally set as four temperatures, such as (T.sub.m−10)° C., (T.sub.m−5)° C., T.sub.m, and (T.sub.m+5)° C. of a fiber reinforcement material, the melting temperature for Experiments 1 to 4.

(43) Specific gravity, tensile strength and tensile modulus of the self-reinforced composite prepared by the method were measured by the same method as Example 1, and the results were illustrated in the following Table 1 and FIG. 4. FIG. 4 is a graph illustrating the changes in physical properties depending on a double belt lamination temperature.

(44) TABLE-US-00001 TABLE 1 Classification Experiment 1 Experiment 2 Experiment 3 Experiment 4 Temperature (° C.) (T.sub.m−10) ° C. (T.sub.m−5) ° C. (T.sub.m+0) ° C. (T.sub.m+5) ° C. of four sections Specific Gravity 0.869 0.874 0.891 0.897 Tensile Strength 0.92 0.88 0.84 0.61 Tensile Modulus 0.33 0.30 0.66 1.02

(45) As illustrated in Table 1 and FIG. 4, in the case of increasing a processing temperature in a double belt press lamination process, tensile modulus of the obtained resin composite was increased, but tensile strength was decreased. The increased stiffness of the resin composite may be caused by increased impregnation rate and decreased air gap. In addition, the decreased tensile strength may be caused by decreased physical properties of the reinforcement material itself by melting of the reinforcement fiber. Therefore, by cooling the resin composite after applying heat to the melting of reinforcement material, the strength and stiffness must be maintained, with preventing deterioration of the physical properties of the reinforcement resin.

Example 3: Effect of Lamination Pressure

(46) As Example 1, a reinforcement resin and a matrix resin were prepared and a resin composite was prepared using a double belt laminator, except for the ratio of roll gap of double-belt laminator to the stacked resins. That is, the ratio of roll gap of double-belt laminator to the stacked resins was set to 0.71 (0.4 mm roll gap), 0.89 (0.5 mm roll gap), or 1.07 (0.6 mm roll gap).

(47) Specific gravity, tensile strength and tensile modulus of the self-reinforced composite prepared by the method were measured by the same method as Example 1, and the results were illustrated in Table 2. In the appearance evaluation in the following Table 2, when the arrangement of the woven fiber was not deformed and the thickness change and the fiber arrangement defect due to bending or folding in the processing, the appearance was evaluated as the term “good” state.

(48) TABLE-US-00002 TABLE 2 Classification Experiment 5 Experiment 6 Experiment 7 Roll Gap (mm) 0.71 0.89 1.07 Specific Gravity 0.885 0.874 0.869 Tensile Strength 1.17 0.88 0.65 Tensile Modulus 0.70 0.30 0.14 Appearance Wrinkle Pattern Good Good (Defective)

(49) The present Example was performed to test a change in physical properties of the obtained resin composite depending on an increased lamination pressure. When the decreased belt interval was set to increase the lamination pressure, tensile stiffness of the obtained resin composite was increased. This change in the physical properties was caused by improved impregnation rate due to the pressure increase and air gap decrease, in other words, due to an increase in specific gravity. When the ratio of roll gap to the thickness of stacked materials was 0.71, the materials were not uniformly laminated and/or compressed, such that a thickness of a product was not uniform, and the appearance was not good. Therefore, it is preferable that the ratio of the roll gap to the thickness of stacked materials is 75% or greater. In the case in which the ratio of roll gap to the thickness of stacked materials was 1.07, tensile modulus of elasticity was excessively decreased.

Example 4: Effect of Retention Time of Resin in Belt

(50) As Example 1, a reinforcement resin and a matrix resin were prepared and a resin composite was prepared using a double belt laminator, except for a retention time of the resin in a belt. That is, a retention time of the resin in a belt was set to 150 seconds and 470 seconds.

(51) Specific gravity, tensile strength and tensile modulus of elasticity for the self-reinforced composite prepared by the method were measured by the same method as Example 1, and the results were illustrated in the following Table 3. When the woven state of the fiber reinforcement resin and the constant pattern were maintained after a double belt lamination process, the state was determined as good state. When the starting materials were overlapped or melted, so as to generating wrinkles, the state was determined as bad state.

(52) Specific gravity, tensile strength and tensile modulus of the resin composite were measured, and the experimental results were illustrated in the following Table 3.

(53) TABLE-US-00003 TABLE 3 Classification Example 1 Experiment 8 Retention Time 150 sec 470 sec Specific Gravity 0.874 0.895 Tensile Strength 0.90 0.74 Tensile Modulus 0.30 1.13

(54) In the case of increasing the retention time in the belt in a lamination process using a double belt press, tensile stiffness of the obtained resin composite was increased, but tensile strength thereof was decreased. These changes in the physical properties of the resin composite were caused by an increased energy amount applied on the sample. When the retention time was excessively short, the processing energy was not sufficiently transferred, so as to deteriorate the physical properties of resin composite. When the retention time was excessively long, the tensile strength of the reinforcement material was decreased due to shrinkage and melting by heat.

Example 5: Effect of Cooling Process (Recrystallization Section)

(55) As Example 1, a reinforcement resin and a matrix resin were prepared and a resin composite was prepared using a double belt laminator, except that the temperature in each section of FIG. 3 was set differently as Experiments 9 to 12.

(56) The temperatures of four sections were equally set in Experiment 9. In Experiments 10 to 12, the temperatures of the first to fourth sections were differently set with the temperature gradient being from the highest temperature at the closest section to the resin injection part of the laminator to the lowest temperature at the closest section to the resin discharge part. In addition, a retention time in each section was equally set. The temperature conditions in Experiments 9-12 were summarized in the following Table 4.

(57) TABLE-US-00004 TABLE 4 Classi- Experiment Experiment Experiment Experiment fication 9 10 11 12 1st Section Tm +0 Tm −5 Tm +0 Tm +5 (° C.) 2nd Section Tm +0 Tm −65 Tm −65 Tm −65 (° C.) 3rd Section Tm +0 Tm −85 Tm −85 Tm −85 (° C.) 4th Section Tm +0 Tm −100 Tm −100 Tm −100 (° C.)

(58) Specific gravity, tensile strength and tensile modulus of the self-reinforced composite as Example 1, and the results were illustrated in Table 5.

(59) TABLE-US-00005 TABLE 5 Classi- Experiment Experiment Experiment Experiment fication 9 10 11 12 Specific 0.891 0.880 0.887 0.896 Gravity Tensile 0.84 1.00 1.07 1.00 Strength Tensile 0.66 0.83 0.91 1.00 Modulus

(60) In the case of performing a cooling process in the second to fourth sections after a heating process in the first section in FIG. 3, when the temperature of the first section (T.sub.1) was increased to T.sub.m±5° C., both of the tensile stiffness and tensile strength of the resin composite were increased. The causes of the physical properties changes of the resin composite was due to an increased melting and impregnation property of the matrix resin and/or reinforcement resin to the resin composite by increasing the temperature of the first section (T.sub.1). In addition, the additional melting and the decreased physical properties of reinforcement resin was prevented by cooling the material under the pressured state and the recrystallization of the composite.

(61) In Comparison of the results of Table 5 with those of Table 1, when the composite was prepared at the same temperature in all four sections, the higher melting temperature increased the specific gravity and tensile modulus of elasticity, but lowered the tensile strength. However, referring to Experiments 10 to 12 of Table 5, the higher melting temperature in the first section increased the specific gravity and tensile modulus, with maintaining the tensile strength. Specifically, in Experiment 2 of Table 1, the tensile strength was decreased and tensile modulus of elasticity was also excessively low (e.g. 0.30) at a temperature of (T.sub.m−5)° C. in the first section. However, in Experiment 10 of Table 5, both of the tensile strength and tensile modulus of elasticity were excellent.

(62) FIG. 5 is a graph showing changes in physical properties of an exemplary resin composite obtained by applying the recrystallization process in an exemplary embodiment of the present invention. The crystalline changes in the recrystallization section were summarized in the following Table 6 or FIGS. 6-8, which illustrated the changes in half width at various initial temperatures at the first section.

(63) TABLE-US-00006 TABLE 6 Experiment Experiment Experiment Experiment Half Width 8 9 10 11 6.9° 0.57 0.537 0.424 0.411 8.4° 0.545 0.537 0.455 0.447 9.1° 0.593 0.553 0.442 0.428 10.4°  0.473 0.603 0.215 0.395 10.8°  0.86 0.88 0.581 0.487

(64) FIG. 6 is a DSC graph showing the melting point change of the obtained resin composite. With respect to the starting materials of the composite before processing, the crystallinity and the melting temperature increased due to the heating and cooling treatment under the pressure, as the initial melting temperature increased.

(65) FIG. 7 illustrates the crystalline structures of the obtained resin composite. According to XRD graph of FIG. 8, as the initial melting temperature from the first section was increased before applying cooling under the pressure state, a XRD pattern approached to an alpha form, which is the most stable crystalline structure among crystalline structures of the resin illustrated in FIG. 7, and a half width was decreased. The decreased half width may indicate an increased crystallinity. In view of the results, as the initial melting temperature increased before applying cooling step under the pressure state, the tensile modulus of the composite increased. When the temperatures of all sections were equal, or when the temperature of the first section was lower than Tm−5° C., tensile modulus was decreased by the decreased impregnation due to a deficiency of heat. When the temperature of the first section was higher than Tm+5° C., the physical properties were deteriorated by the melting of the reinforcement material. Therefore, the temperature of the first section (T.sub.1) may be preferably in a range of about (T.sub.m−5)° C. to (T.sub.m+5)° C.