GRAFT COPOLYMER, METHOD OF PREPARING GRAFT COPOLYMER, THERMOPLASTIC RESIN COMPOSITION INCLUDING GRAFT COPOLYMER, AND MOLDED PART INCLUDING THERMOPLASTIC RESIN COMPOSITION

Abstract

The present invention relates to a graft copolymer having excellent thermal stability, a method of preparing the graft copolymer, a thermoplastic resin composition including the graft copolymer, and a molded part including the thermoplastic resin composition. According to the present invention, since the thermoplastic resin composition of the present invention includes the graft copolymer having excellent thermal stability, the thermoplastic resin composition and the molded part manufactured using the thermoplastic resin composition have excellent physical properties, such as impact strength, fluidity, and transparency. Furthermore, the degree of discoloration that may occur when the resin composition or the molded part is allowed to stay in an injection molding machine or stay at a high temperature for a long period of time may be reduced.

Claims

1. A graft copolymer, comprising: a conjugated diene rubber core; and a shell surrounding the rubber core, wherein the shell is obtained by graft-polymerizing a (meth)acrylic acid alkyl ester compound, an aromatic vinyl compound, and a vinyl cyanide compound, wherein, when the graft polymerization is performed, a metal salt of sorbic acid is added in an amount of 0.1 to 0.49 parts by weight based on 100 parts by weight of a total composition of the conjugated diene rubber core and the shell.

2. The graft copolymer according to claim 1, wherein the graft copolymer is obtained by polymerizing 100 parts by weight of a monomer mixture containing 40 to 60 parts by weight of the conjugated diene rubber core, 25 to 50 parts by weight of the (meth)acrylic acid alkyl ester compound, 5 to 25 parts by weight of the aromatic vinyl compound, and 1 to 15 parts by weight of the vinyl cyanide compound under reaction conditions in which 0.1 to 0.49 parts by weight of the metal salt of sorbic acid are added.

3. The graft copolymer according to claim 1, wherein the metal salt is one or more selected from a potassium salt and a sodium salt.

4. The graft copolymer according to claim 1, wherein the conjugated diene rubber core has an average particle diameter of 2,000 to 4,000 A.

5. The graft copolymer according to claim 1, wherein the shell has a weight average molecular weight of 80,000 to 300,000 g/mol.

6. A method of preparing a graft copolymer, comprising: a step of feeding 100 parts by weight of a monomer mixture containing 40 to 60 parts by weight of a conjugated diene rubber latex (based on solids), 25 to 50 parts by weight of a (meth)acrylic acid alkyl ester compound, 5 to 25 parts by weight of an aromatic vinyl compound, and 1 to 15 parts by weight of a vinyl cyanide compound; 0.1 to 3 parts by weight of an emulsifier; and 0.005 to 1 part by weight of an initiator into a reactor, and performing graft polymerization, wherein the emulsifier comprises a metal salt of sorbic acid.

7. The method according to claim 6, wherein the metal salt of sorbic acid is contained in an amount of 10 to 90% by weight based on a total weight of the emulsifier.

8. The method according to claim 6, wherein the metal salt is one or more selected from a potassium salt and a sodium salt.

9. The method according to claim 6, wherein, when the graft polymerization is performed, the (meth)acrylic acid alkyl ester compound, the aromatic vinyl compound, the vinyl cyanide compound, and the initiator are continuously fed into the reactor.

10. The method according to claim 6, wherein, when the graft polymerization is performed, 0.1 to 1 part by weight of a molecular weight modifier, 0.001 to 0.5 parts by weight of a redox initiator, or both are used.

11. The method according to claim 6, wherein a content of solidified substances contained in a graft copolymer latex generated after completion of the graft polymerization is 0.4% by weight or less.

12. A thermoplastic resin composition comprising 10 to 60% by weight of a graft copolymer prepared according to claim 6 and 40 to 90% by weight of a (meth)acrylic acid alkyl ester compound-aromatic vinyl compound-vinyl cyanide compound copolymer.

13. The thermoplastic resin composition according to claim 12, further comprising one or more additives selected from a stabilizer, a pigment, fuel, a reinforcing agent, an ultraviolet light absorber, an antioxidant, a coloring agent, a release agent, a lubricant, an antistatic agent, and a plasticizer.

14. A molded part, wherein the molded part is manufactured by injection-molding the thermoplastic resin composition according to claim 12.

15. The molded part according to claim 14, wherein the molded part has a fluidity (220 C., load: 10 kg) of 10 to 20 g/10 min as measured according to ASTM D1238.

16. The molded part according to claim 14, wherein the molded part has an impact strength of 12.5 to 16 kgcm/cm as measured according to ASTM D256.

17. The molded part according to claim 14, wherein the molded part has a haze value of 2.0 or less as measured according to ASTM 1003.

18. The molded part according to claim 14, wherein, when discoloration degree (E) is measured under conditions wherein the molded part is allowed to stand at 250 C. for 15 minutes, the molded part has a discoloration degree (E) of 3.0 or less.

Description

EXAMPLE

Example 1: Preparation of Graft Copolymer

[0079] parts by weight of deionized water, 0.2 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.3 parts by weight of the potassium salt of sorbic acid as an emulsifier were added to 50 parts by weight (based on solids) of a large-diameter conjugated diene rubber latex seed having an average particle diameter of 3,000 . Then, 35 parts by weight of methyl methacrylate, parts by weight of styrene, 3 parts by weight of acrylonitrile, 0.5 parts by weight of t-dodecyl mercaptan, 0.048 parts by weight of sodium formaldehyde sulfoxylate, 0.012 parts by weight of ethylenediaminetetraacetic acid sodium, 0.001 parts by weight of ferrous sulfide, and 0.04 parts by weight of cumene hydroperoxide were continuously fed at 75 C. for 5 hours, and reacted. Thereafter, temperature was raised to 80 C., and the reaction products were aged for 1 hour, and the reaction was terminated. In this case, polymerization conversion rate was 98.8%, and the amount of solidified substances was 0.24% by weight.

Example 2

[0080] Except that 0.25 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.25 parts by weight of the potassium salt of sorbic acid as an emulsifier were fed, experiments were performed in the same manner as in Example 1.

Example 3

[0081] Except that 0.3 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.2 parts by weight of the potassium salt of sorbic acid as an emulsifier were fed, experiments were performed in the same manner as in Example 1.

Example 4

[0082] Except that 0.2 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.4 parts by weight of the potassium salt of sorbic acid as an emulsifier were fed, experiments were performed in the same manner as in Example 1.

Comparative Example 1

[0083] Except that 0.5 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid were fed instead of 0.2 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.3 parts by weight of the potassium salt of sorbic acid as an emulsifier, experiments were performed in the same manner as in Example 1.

Comparative Example 2

[0084] Except that 0.5 parts by weight of the potassium salt of sorbic acid were fed instead of 0.2 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.3 parts by weight of the potassium salt of sorbic acid as an emulsifier, experiments were performed in the same manner as in Example 1.

Comparative Example 3

[0085] Except that 0.2 parts by weight of the dipotassium salt of alkenyl (C16-18) succinic acid and 0.09 parts by weight of the potassium salt of sorbic acid as an emulsifier were fed, experiments were performed in the same manner as in Example 1.

Usage Example

Usage Examples 1 to 7: Preparation of Thermoplastic Resin Composition

[0086] 30 parts by weight of each of the graft copolymers prepared according to Examples 1 to 3 and Comparative Examples 1 and 3 were mixed with 70 parts by weight of a MSAN copolymer (LG Chem., XT500), 1 part by weight of a lubricant, and 0.2 parts by weight of an antioxidant using a mixer, and the mixture was extruded at 210 C. using a twin screw extruder to form pellets. The resin composition in the form of a pellet was subjected to injection molding at 210 C. to prepare specimens for measuring physical properties.

Test Example

[0087] Physical properties of the graft copolymer latexes prepared according to Examples and Comparative Examples and properties of the specimens prepared according to Usage Examples 1 to 7 were measured according to the following methods, and the results are shown in Table below.

[0088] Content of solidified substances (% by weight):

[0089] The content of solidified substances contained in the graft copolymer latex was calculated according to Equation 1 below.

Content of solidified substances={Weight of solidified substances formed in reactor (g)/total weight of rubber and monomers (g)}100 [Equation 1]

[0090] Transparency (haze): Haze values of specimens were measured according to ASTM 1003. As a haze value decreases, transparency increases.

[0091] Impact strength (kgcm/cm): Impact strength of specimens prepared in thickness was measured according to ASTM D256.

[0092] Fluidity (g/10 min): Fluidity was measured for 10 minutes according to ASTM D1238 under the conditions wherein a load of 10 kg was applied at 220 C.

[0093] Degree of discoloration during injection molding (E): using a color-difference meter (based on CIE Lab), L, a, and b values of a specimen were measured before the specimen was allowed to stand in an injection molding machine, and L, a, and b values of a specimen having the same size with the above-described specimen were measured after the specimen was allowed to stand in an injection molding machine at 250 C. for 15 minutes, and discoloration degree (E) can be calculated according to Equation 2 below.

E={square root over ((LL).sup.2+(aa).sup.2+(bb).sup.2)}[Equation 2]

[0094] Long-term storage stability at high temperature (E): Specimens were stored in an oven at 80 C. for 7 days, and then L, a, and b values of the specimens were measured using a color-difference meter (based on CIE Lab), and discoloration degree was calculated according to Equation 3 below.

E=((LL).sup.2+(aa).sup.2+(bb).sup.2) [Equation 3]

TABLE-US-00001 TABLE 1 Usage Usage Usage Usage Usage Usage Usage Example 5 Example 6 Example 7 Example 1 Example 2 Example 3 Example 4 Comparative Comparative Comparative Classification Example1 Example 2 Example 3 Example 4 Example 1 Example 2 Example 3 Dipotassium 0.2 0.25 0.3 0.2 0.5 0.2 salt of alkenyl succinic acid* Potassium 0.3 0.25 0.2 0.4 0.5 0.09 salt of sorbic acid* Content of 0.24 0.23 0.22 0.23 0.21 0.9 0.45 solidified substances [% by weight] Transparency 1.9 1.8 1.9 1.9 2.1 3.1 2.0 Impact 14.8 15 14.8 14.7 14.5 12 14.1 strength [kgcm/cm] Fluidity 17.5 17.6 18 17.5 18.1 16 17 [g/10 min] Discoloration 2.7 2.8 2.8 2.7 3.6 3.2 2.6 degree during injection molding (E) Long-term 0.43 0.46 0.47 0.43 0.8 0.7 0.41 storage stability at high temperature (E) (In Table 1, the numerical values shown in dipotassium salt of alkenyl succinic acid* and potassium salt of sorbic acid* represent the weight parts of each salt based on 100 parts by weight of the total composition of rubber and monomers fed when graft copolymers were prepared.)

[0095] As shown in Table 1, in the case of Examples 1 to 4 according to the present invention, in which the amount of alkenyl succinic acid dipotassium salt, a conventional emulsifier, was reduced, and sorbic acid potassium salt was additionally added as an emulsifier, compared with Comparative Example 1 in which only conventional emulsifier was used, the contents of solidified substances contained in graft copolymers were similar. These results indicate that, when sorbic acid potassium salt is mixed within a specific range, stability of the graft copolymer remains high.

[0096] In addition, compared with Usage Examples 5 to 7 not according to the present invention, in the case of the thermoplastic resin compositions (Usage Examples 1 to 4) including the graft copolymer according to the present invention, impact strength was kept in high and transparency was excellent. Also, the thermoplastic resin compositions of Usage Examples 1 to 4 exhibited a melt flow index suitable for processing and molding, and had very excellent thermal stability.

[0097] In addition, when an excess of sorbic acid potassium salt was included (Comparative Example 2), the content of solidified substances was 0.9% by weight, which indicated that stability of the latex was markedly reduced. Thus, physical properties, such as transparency, impact strength, and thermal stability, of the final resin composition were remarkably deteriorated due to decrease in stability of the latex.

[0098] In addition, in the case of Comparative Example 3, in which a small amount of sorbic acid potassium salt was used as compared with Examples 1 to 4, although physical properties, such as transparency, impact strength, and thermal stability, were similar in comparison with Examples according to the present invention, the content of solidified substances was increased about twice. These results indicate that the method used in Comparative Example 3 is not preferable in terms of latex stability and resin productivity.