WO2014117693A1

WO2014117693A1 - Abrasive and method of preparing the same

Info

Publication number: WO2014117693A1
Application number: PCT/CN2014/071456
Authority: WO
Inventors: Xiaobin He; Xueyuan Zhu; Xianglei ZHOU
Original assignee: Shenzhen Byd Auto R&D Company Limited; Byd Company Limited
Priority date: 2013-01-30
Filing date: 2014-01-26
Publication date: 2014-08-07
Also published as: CN103965832B; CN103965832A

Abstract

An abrasive is provided. The abrasive contains a silicon carbide, an elastomer, a coupling agent and an auxiliary agent. The silicon carbide includes an end embedded in the elastomer and another end exposed out of the elastomer. A method for preparing an abrasive is also provided.

Description

ABRASIVE AND METHOD OF PREPARING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and benefits of Chinese Patent Application No. 201310034978.5, filed with the State Intellectual Property Office of P. R. C. on January 30, 2013, the entire content of which is incorporated herein by reference.

FIELD

Exemplary embodiments of the present disclosure relate generally to an abrasive and a method of preparing the abrasive.

BACKGROUND

As is well known, glasses become more and more widely used in mobile phones, especially in the screen of the smart phones. With the large-scale production of smart phones, requirements on the performances of a mobile phone screen are higher and higher nowadays. Therefore, glasses and process materials related to glass fabrication, such as abrasives, need to be high in quality and low in cost. Recently, the abrasive used for polishing glasses mainly includes Ce0₂ particles or SiC particles. However, Ce0₂ abrasive has a relatively high cost, and is hard to be recycled which will result some environmental problems. The conventional SiC abrasive has rather high hardness, which is easy to scratch the surface of the glass and the final yield for the glass is relatively low.

SUMMARY

Embodiments of the present disclosure seek to solve at least one of the problems existing in the prior art. Accordingly, an abrasive which has improved performances, lower cost and may not harm the environment is provided. Further, a method of preparing the abrasive is provided.

According to a first aspect of the present disclosure, an abrasive is provided. The abrasive comprises: a silicon carbide (SiC), an elastomer, a coupling agent and an auxiliary agent. The silicon carbide may include an end embedded in the elastomer and another end exposed out of the elastomer.

According to embodiments of the present disclosure, the abrasive contains both SiC and the elastomer, and one end of the SiC is embedded in the elastomer and another end of the SiC exposes out of the elastomer. Therefore, an action force generated by the abrasive during a polishing process may be buffered or reduced with the help of the elastomer. Therefore, scratches on a polished surface (for example, a glass surface) may be reduced or even avoided. In this way, deficiencies of the polished surface may be reduced or avoided. In addition, the abrasive may be recycled after use, so that the production for the abrasive may be low in cost and may not harm the environment. According to another aspect of the present disclosure, a method of preparing the abrasive is provided. The method may include the steps of: mixing silicon carbide and a coupling agent to form a first mixture; drying the first mixture to form a modified silicon carbide; mixing the modified silicon carbide with an elastomer and an auxiliary agent to form a second mixture; and melting, extruding and granulating the second mixture.

With the method according to embodiments of the present disclosure, the prepared abrasive may contain both SiC and the elastomer, and one end of SiC may be embedded in the elastomer and another end of the SiC may be exposed out of the elastomer. Therefore, an action force generated by the abrasive during a polishing process may be buffered or reduced with the help of the elastomer. Therefore, scratches on a polished surface (for example, a glass surface) may be reduced or even avoided. In this way, deficiencies of the polished surface may be reduced or avoided. In addition, the abrasive may be recycled after use, so that the method of preparing the abrasive may be low in cost and may not harm the environment.

Additional aspects and advantages of embodiments of present disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of embodiments of the present disclosure will become apparent and more readily appreciated from the following descriptions made with reference to the accompanying drawing, in which:

Fig. 1 is a flow chart showing a method for preparing an abrasive according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the present disclosure. The embodiments described herein are explanatory, illustrative, and used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions.

For the purpose of the present description and of the following claims, the definitions of the numerical ranges always include the extremes unless otherwise specified.

In addition, terms such as "first" and "second" are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.

According to an embodiment of the present disclosure, an abrasive is provided. The abrasive may contain silicon carbide (SiC), an elastomer, a coupling agent and an auxiliary agent. The silicon carbide may include an end embedded in the elastomer and another end exposed out of the elastomer.

According to embodiments of the present disclosure, with the application of the coupling agent (especially a silane coupling agent), abrasive grains of the abrasive may be partially embedded into the elastomer (such as thermoplastic polyurethanes (TPU)), for example, with one end embedded in the elastomer. In addition, the abrasive grains and the elastomer may be bridge connected to form an island structure under the action of the coupling agent. The island structure may provide a buffer action, which may further reduce or avoid scratches on a polished surface, such as a glass surface.

In one embodiment, based on the whole abrasive, based on the total weight of the abrasive, the SiC may amount to about 10% to about 40% by weight.

In one embodiment, based on the total weight of the abrasive, the elastomer may amount to about 55% to about 85% by weight. With the elastomer having the above weight content, the stability of abrasive may be ensured. Further, the efficiency and quality for the following polishing process may be improved.

In some embodiments of the present disclosure, based on the total weight of the abrasive, the coupling agent may amount to about 3% to about 5% by weight. Then the abrasive may have better performances and be suitable for use in various polishing processes.

In some embodiments of the present disclosure, based on the total weight of the abrasive, the auxiliary agent may amount to about 0.5% to about 2% by weight. Then the abrasive may have better performances and be suitable for use in various polishing processes.

In one embodiment of the present disclosure, the elastomer may contain at least one selected from the group consisting of: thermoplastic polyurethanes (TPUs), styrenes, olefin, vinyl chlorides, thermoplastic silicon copolymers and polyvinyl acetate.

In one embodiment of the present disclosure, the elastomer contains at least one selected from the group consisting of: TPU, thermoplastic polystyrene (TPS), thermoplastic polyolefm (TPO), thermoplastic polyvinyl chloride (TPE, TPVC, TCPE), thermoplastic silicon copolymers (TPSIV), ethylene vinyl acetate (EVA) polymers. In which, the thermoplastic polyurethane elastomer has a good abrasive resistance and a good resilience force.

In one embodiment, the elastomer may be TPU. The TPU has good wear resistance and resilience, then the abrasive may have better performances and be suitable for use in various polishing processes.

In one embodiment of the present disclosure, the weight-average molecular weight of the elastomer may range from 50000 to 80000.

In one embodiment of the present disclosure, in the abrasive, the weight-average molecular weight of TPU ranges from 50000 to 80000. With the weight-average molecular weight identified above, the abrasive may have a hardness which is suitable for polishing.

The inventors have found that, the prepared abrasive is relatively soft and not good for polishing, when the weight-average molecular weight of the elastomer (such as TPU) is smaller than 5000; while the prepared abrasive has rather low elasticity and is easy to scratch the polished surface, when the weight-average molecular weight of the elastomer (such as TPU) is larger than

80000.

In one embodiment of the present disclosure, the abrasive may have an average particle size in the range of 200 meshes to 400 meshes.

In one embodiment of the present disclosure, the abrasive may have an average particle size of 300 meshes.

The inventors have found that, when the average particle size of the abrasive is smaller than 200 meshes, particles of the abrasive are relative large, so that the surface to be polished is easy to be scratched during the polishing process. When the average particle size of the abrasive is larger than 400 meshes, particles of the abrasive may have a poor cutting performance, and then the abrasive is not suitable for polishing and may result in a poor polishing efficiency. In one embodiment of the present disclosure, the SiC may have an average particle size in the range of 3000 meshes to 8000 meshes.

In one embodiment of the present disclosure, the SiC may have an average particle size of 6000 meshes.

The inventors have found that, when the average particle size of the SiC is smaller than 3000 meshes, particles the abrasive are relatively large, so that the surface to be polished is easy to be scratched during the polishing process. When the average particle size of the SiC is larger than 8000 meshes, particles of the abrasive may have a poor cutting performance, and then the abrasive is not suitable for polishing and may result in a poor polishing efficiency.

According to one embodiment of the present disclosure, the auxiliary agent may contain a dispersant and an antioxidant.

According to another aspect of the present disclosure, a method of preparing an abrasive is provided. The method may include the following steps: mixing SiC and a coupling agent to form a first mixture; drying the first mixture to form a modified SiC; mixing the modified SiC with an elastomer and an auxiliary agent to form a second mixture; and melting, extruding and granulating the second mixture to get granulated particles.. The method may be used for preparing the abrasive identified above.

According to embodiments of the present disclosure, the method applies a combination of the SiC and the elastomer, while in the prepared abrasive, one end of the SiC is embedded in the elastomer and another end of the SiC exposes out of the elastomer. In this way, the method is easy to operate, low in cost and high in production efficiency. In addition, with the method according to embodiments of the present disclosure, scratches on the surface to be polished may be greatly reduced or even avoided. With the abrasive prepared by the method according to embodiments of the present disclosure, the polishing process in which the abrasive is used may have an improved yield.

Referring to Fig. 1, in an embodiment, the method for preparing the abrasive may include the following steps slOl-104.

Step slOl : SiC and a coupling agent are mixed to form a first mixture.

Step sl02: the first mixture is dried to form a modified SiC.

Step si 03: the modified SiC is mixed with an elastomer and an auxiliary agent to form a second mixture. Step si 04: the second mixture is melted, extruded and granulated.

In one embodiment of the present disclosure, in the abrasive, the silicon carbide may include an end embedded in the elastomer and another end exposed out of the elastomer.

In some embodiments, the coupling agent may contain a silane coupling agent.

In one embodiment of the present disclosure, the method may further include steps of pulverizing and screening granulated particles. With the additive pulverizing and screening, abrasive grains having desired particle diameters may be separated out easily.

In one embodiment of the present disclosure, the extruding and granulating may be conducted under conditions that: a melting temperature ranges from about 160°C to about 220°C, a rotating speed of a main screw ranges from about 100 r/min to about 200 r/min, and a feeding speed ranges from about 10 r/min to about 30 r/min.

According to the embodiments of the present disclosure, the SiC may have an average particle size of 6000 meshes, and the prepared abrasive may have an average particle size of 300 meshes. The average particle size of the abrasive is obviously larger than that of the SiC, therefore the prepared abrasive may be recovered and reused in the method for preparing the abrasive. In some embodiments, the recovery rate for the abrasive may reach 60%. In this way, the method according to embodiments of the present disclosure may be environmental friendly and low in cost.

The present disclosure may be further explained by the embodiments in the following.

It will be understood that the features mentioned above and those still to be explained hereinafter may be used not only in the particular combination specified but also in other combinations or on their own, without departing from the scope of the present invention.

Embodiment 1

The present embodiment provides an abrasive and a method of preparing the abrasive.

1) Coupling

la) 5 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (al), and the solution (al) was stirred for 30 min.

lb) 20 weight parts of SiC (with an average particle size of 3000 meshes) were added into the solution (al) to form a solution (bl), and the solution (bl) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (bl) was dried to form a modified SiC. 2) Mixing, extruding and granulating

73 weight parts of thermoplastic silicon copolymer elastomer (with a weight-average molecular weight of 50000), 1 weight part of a dispersant, 1 weight part of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulatedunder the conditions that: the melting temperature of silicon copolymer elastomer & SiC mixture was 190°C; the rotating speed of the main screw of the extruder was 200 r/min; and the feeding speed was 16 r/min, obtaining granulated particles.

3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles Al having an average particle size of 300 meshes.

4) Screening

The abrasive particles Al were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles.

Embodiment 2

1) Coupling

la) 3 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (a2), and the solution (a2) was stirred for 30 min.

lb) 30 weight parts of SiC (with an average particle size of 5000 meshes) were added into the solution (a2) to form a solution (b2), and the solution (b2) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (b2) was dried to form a modified SiC.

2) Mixing, extruding and granulating

66 weight parts of polyvinyl acetate (with a weight-average molecular weight of 70000), 0.5 weight parts of a dispersant, 0.5 weight parts of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulated under the conditions that: the melting temperature of polyvinyl acetate & SiC mixture was 160°C; the rotating speed of the main screw of the extruder was 180 r/min; and the feeding speed was 10 r/min, obtaining granulated particles. 3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles A2 having an average particle size of 300 meshes.

4) Screening

The abrasive particles A2 were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles. Embodiment 3

1) Coupling

la) 5 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (a3), and the solution (a3) was stirred for 30 min.

lb) 25 weight parts of SiC (with an average particle size of 8000 meshes) were added into the solution (a3) to form a solution (b3), and the solution (b3) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (b3) was dried to form a modified SiC.

2) Mixing, extruding and granulating

69 weight parts of TPU (with a weight-average molecular weight of 50000), 0.5 weight parts of a dispersant, 0.5 weight parts of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulated under the conditions that: the melting temperature of TPU & SiC mixture was 220°C; the rotating speed of the main screw of the extruder was 100 r/min; and the feeding speed was 30 r/min, obtaining granulated particles.

3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles A3 having an average particle size of 300 meshes.

4) Screening

The abrasive particles A3 were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles.

Embodiment 4

1) Coupling

la) 4 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (a4), and the solution (a4) was stirred for 30 min.

lb) 10 weight parts of SiC (with an average particle size of 6000 meshes) were added into the solution (a4) to form a solution (b4), and the solution (b4) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (b4) was dried to form a modified SiC.

2) Mixing, extruding and granulating

85 weight parts of TPU (with a weight-average molecular weight of 80000), 0.5 weight parts of a dispersant, 0.5 weight parts of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulated under the conditions that: the melting temperature of TPU & SiC mixture was 200°C; the rotating speed of the main screw of the extruder was 150 r/min; and the feeding speed was 20 r/min, obtaining granulated particles.

3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles A4 having an average particle size of 300 meshes.

4) Screening

The abrasive particles A4 were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles.

Embodiment 5

1) Coupling

la) 3 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (a5), and the solution (a5) was stirred for 30 min. lb) 40 weight parts of SiC (with an average particle size of 4000 meshes) were added into the solution (a5) to form a solution (b5), and the solution (b5) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (b5) was dried to form a modified SiC.

2) Mixing, extruding and granulating

55 weight parts of TPU (with a weight-average molecular weight of 60000), 1 weight part of a dispersant, 1 weight part of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulated under the conditions that: the melting temperature of TPU & SiC mixture was 190°C; the rotating speed of the main screw of the extruder was 200 r/min; and the feeding speed was 16 r/min, obtaining granulated particles.

3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles A5 having an average particle size of 300 meshes.

4) Screening

The abrasive particles A5 were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles. Embodiment 6

1) Coupling

la) 3 weight parts of a silane coupling agent (KH570) were added into 95% ethyl alcohol to form a solution (a6), and the solution (a6) was stirred for 30 min.

lb) 40 weight parts of SiC (with an average particle size of 4000 meshes) were added into the solution (a6) to form a solution (b6), and the solution (b6) was stirred with a magnetic stirrer for 4 h. Then the stirred solution (b6) was dried to form a modified SiC.

2) Mixing, extruding and granulating

55 weight parts of styrene (with a weight-average molecular weight of 60000), 1 weight part of a dispersant, 1 weight part of an antioxidant and the modified SiC resulting from step lb) were mixed to form a mixture. Then the mixture was melted, extruded and granulated under the conditions that: the melting temperature of styrene & SiC mixture was 190°C; the rotating speed of the main screw of the extruder was 200 r/min; and the feeding speed was 16 r/min, obtaining granulated particles.

3) Pulverizing

The granulated particles were pulverized with a pulverizer cooled with liquid nitrogen (provided by GAOQIAO MACHINERY WORKS, Shanghai, -70°C) to form abrasive particles A6 having an average particle size of 300 meshes.

4) Screening

The abrasive particles A6 were screened with a 200 mesh sieve and a 400 mesh sieve, so that the particles having a D50 of about 300 meshes were collected and it prevented the removed SiC from mixing into the abrasive particles.

Comparative Embodiment 1

This comparative embodiment provides an abrasive in the prior art.

Cerium oxide (CP-2, commercially available from CHENGDU BEYONDCHEM CO., LTD, China) was provided as comparative abrasive CA1.

Comparative Embodiment 2

This comparative embodiment provides an abrasive in the prior art.

SiC (W1.5, commercially available from SHENZHEN LOLOYA.DIYTRADE CO., LTD, China) was provided as comparative abrasive CA2.

Embodiments 7-12

The abrasive particles A1-A6 were respectively mixed with water with an abrasive: water ratio of 1 :10 to form abrasive solutions. Corning gorilla glasses were polished with these abrasive solutions respectively under the conditions of: a rotating speed of 40 rpm, a pressure of 0.2 Mpa, and a polishing time of 3600. The polished glasses was clean, obtaining glass samples B1-B6.

Comparative Embodiments 3-4

The comparative abrasives CAl-2 were subjected to a polishing process substantially the same as that in Embodiments 7-12, and glass samples CB1 and CB2 were obtained. Tests

Appearance

The surface of each of the samples B1-B6, CBl and CB2 was observed with an optical microscope under a magnification value of 100. The results on the appearance were recorded in Table 1.

Roughness

The surface of each of the samples B1-B6, CBl and CB2 was illuminated with a monochromatic light, and the interference light generated from the surface of each of the samples B1-B6, CBl and CB2 were tested. Then the roughness Ra of each sample was calculated based on the interference light. Normally accepted products have a Ra ranging from about 0.005 μιη to about 0.009 μιη.

Polishing Time

The polishing time of each of the samples B1-B6, CBl and CB2 during the polishing process were recorded in Table 1.

Table 1

Referring to Table 1, it can be seen that the surface of the glass polished by the abrasives prepared according to the embodiments of the present disclosure has minor or no scratches. The polishing effect of cerium oxide was fine, but the polishing effect of pure SiC abrasive was rather bad. It can be concluded that, the polishing effect of the abrasive according to embodiments of the present disclosure is better than that of the pure SiC abrasive. As cerium oxide is much more expensive (10 times of the cost of) than the abrasive, thus the abrasive according to embodiments of the present disclosure is more cost effective than cerium oxide.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment", "another example," "an example," "a specific example," or "some examples," means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as "in some embodiments," "in one embodiment", "in an embodiment", "in another example," "in an example," "in a specific example," or "in some examples," in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments cannot be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present disclosure.

Claims

What is claimed is:

1. An abrasive comprising:

a silicon carbide;

an elastomer;

a coupling agent; and

an auxiliary agent,

wherein the silicon carbide includes an end embedded in the elastomer and another end exposed out of the elastomer.

2. The abrasive according to claim 1, wherein based on the total weight of the abrasive, the silicon carbide amounts to about 10% to about 40% by weight.

3. The abrasive according to claim 1 or 2, wherein based on the total weight of the abrasive, the elastomer amounts to about 55% to about 85% by weight.

4. The abrasive according to any one of claims 1-3, wherein based on the total weight of the abrasive, the coupling agent amounts to about 3% to about 5% by weight.

5. The abrasive according to any one of claims 1-4, wherein based on the total weight of the abrasive, the auxiliary agent amounts to about 0.5% to about 2% by weight.

6. The abrasive according to any one of claims 1-5, wherein the elastomer comprises at least one selected from the group consisting of: thermoplastic polyurethanes, styrenes, olefin, vinyl chlorides, thermoplastic silicon copolymers and polyvinyl acetate.

7. The abrasive according to claim 6, wherein the elastomer is thermoplastic polyurethanes.

8. The abrasive according to any one of claims 1-7, wherein the weight-average molecular weight of the elastomer ranges from 50000 to 80000.

9. The abrasive according to any one of claims 1-8, wherein the abrasive has an average particle size in the range of 200 meshes to 400 meshes.

10. The abrasive according to any one of claims 1-9, wherein the silicon carbide has an average particle size in the range of 3000 meshes to 8000 meshes.

11. The abrasive according to any one of claims 1-10, wherein the auxiliary agent comprises a dispersant and an antioxidant.

12. A method for preparing an abrasive, comprising the steps of:

mixing silicon carbide and a coupling agent to form a first mixture;

drying the first mixture to form a modified silicon carbide; mixing the modified silicon carbide with an elastomer and an auxiliary agent to form a second mixture; and

melting, extruding and granulating the second mixture to get granulated particles.

13. The method according to claim 12, wherein in the abrasive, the silicon carbide includes an end embedded in the elastomer and another end exposed out of the elastomer.

14. The method according to claim 12 or 13, wherein the coupling agent comprises a silane coupling agent.

15. The method according to any one of claims 12-14, further comprising steps of pulverizing and screening granulated particles.

16. The method according to any one of claims 12-15, wherein the melting, extruding and granulating are conducted under conditions that: a melting temperature ranges from about 160°C to about 220°C, a rotating speed of a main screw ranges from about 100 r/min to about 200 r/min, and a feeding speed ranges from about 10 r/min to about 30 r/min.