Method of preparing thermoplastic resin, thermoplastic resin prepared therfrom and thermoplastic resin composition comprising the same

Abstract

The present invention relates to a method of preparing a thermoplastic resin, a thermoplastic resin prepared by the same, and a thermoplastic resin composition including the same. More specifically, the method of the present invention includes a step of performing acid coagulation of emulsion polymerization latex, a step of treating coagulated slurry with a base and performing dehydration, and a step of adding a metal salt and water to dehydrated wet powder to adjust pH to 9 or more. According to the present invention, the method may increase the productivity of a thermoplastic resin, and the thermoplastic resin prepared by the method has excellent mechanical strength, thermal stability, and appearance properties. In addition, when the thermoplastic resin of the present invention is used in coating, the thermoplastic resin has an effect of improving the adhesive strength and appearance quality of a coating film.

Claims

1. A method of preparing a thermoplastic resin, comprising: A) performing acid coagulation of emulsion polymerization latex; B) treating coagulated slurry with a base and performing dehydration; and C) adding a metal salt and water to dehydrated wet powder to adjust pH to 9 or more.

2. The method according to claim 1, wherein the emulsion polymerization latex is vinyl cyanide compound-conjugated diene-aromatic vinyl compound copolymer latex.

3. The method according to claim 1, wherein the acid coagulation comprises adding an acid comprising one or more selected from sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, and acetic acid.

4. The method according to claim 1, wherein the acid coagulant is contained in an amount of 0.5 to 4.0 parts by weight based on 100 parts by weight (based on solids) of the emulsion polymerization latex.

5. The method according to claim 1, wherein the base treatment is performed by adding and mixing a base with water to form a basic aqueous solution and adding the basic aqueous solution to the coagulated slurry.

6. The method according to claim 1, wherein the base comprises one or more selected from sodium hydroxide and potassium hydroxide.

7. The method according to claim 1, wherein the metal salt is contained in an amount of 0.05 to 0.5 parts by weight based on 100 parts by weight (based on solids) of the emulsion polymerization latex.

8. The method according to claim 1, wherein the water is contained in an amount of 230 to 570 parts by weight based on 100 parts by weight (based on solids) of the emulsion polymerization latex.

9. The method according to claim 1, wherein the metal salt comprises one or more selected from magnesium sulfate, magnesium chloride, calcium chloride, and aluminum sulfate.

10. The method according to claim 1, wherein the method further comprises aging the coagulated slurry at 85 to 95° C. for 2 to 20 minutes between step A and step B.

11. The method according to claim 1, wherein the method further comprises, after step C, dehydrating and drying the wet powder, pH of which has been adjusted to 9 or more, to obtain a thermoplastic resin powder.

12. A thermoplastic resin prepared by the method according to claim 1, wherein the thermoplastic resin has an oxidative induction time of 20 minutes or more.

13. A thermoplastic resin composition, comprising 10 to 60% by weight of the thermoplastic resin according to claim 12 and 40 to 90% by weight of an aromatic vinyl compound-vinyl cyanide compound copolymer.

14. The thermoplastic resin composition according to claim 13, wherein a “b” value of the thermoplastic resin composition measured using a color-difference meter (Color Quest II, Hunter Lab Co.) is 10 or less.

15. The thermoplastic resin composition according to claim 13, wherein plating adhesion of the thermoplastic resin composition is 15 N/cm or more.

Description

EXAMPLE AND COMPARATIVE EXAMPLES

Example 1

Preparation of Thermoplastic Resin Powder

(1) A) Acid Coagulation and Aging Step:

(2) 2.0 parts by weight of a 5 wt % sulfuric acid aqueous solution was added to 100 parts by weight of emulsion polymerization ABS resin latex (solids content of 45% by weight, average particle diameter of 3,400 Å) prepared according to Preparation Example 1. Then, coagulation was performed at 80° C. for 15 minutes, and aging was performed at 95° C. for 10 minutes.

(3) B) Base Treatment and Dehydration Step:

(4) 1.4 parts by weight of a 10 wt % sodium hydroxide aqueous solution was added to the aged latex and stirred for 10 minutes to perform base treatment. After base treatment, the base-treated slurry was placed in a centrifugal dehydrator, and the same amount of water as the base-treated slurry was added thereto. Then, dehydration was performed for 90 seconds to obtain a wet powder. The pH of the obtained wet powder was 11.

(5) C) Step of Adding Metal Salt and Water to Adjust pH:

(6) 400 parts by weight (based on solids) of water and 0.1 parts by weight of magnesium sulfate were added to the obtained wet powder to adjust pH to 9 or more. Specifically, the pH was 9.3.

(7) D) Dehydration and Drying Step:

(8) The pH-controlled slurry was placed in a centrifugal dehydrator, and the same amount of water as the slurry was added thereto. Then, dehydration was performed for 90 seconds, followed by washing. Thereafter, drying was performed in a 90° C. hot air dryer for 30 minutes to obtain an ABS resin powder.

Comparative Example 1

(9) An ABS resin powder was obtained by the same method and under the same conditions as in Example 1, except that steps B and C were omitted.

Comparative Example 2

(10) An ABS resin powder was obtained by the same method and under the same conditions as in Example 1, except that magnesium sulfate was used instead of sulfuric acid as a coagulant, and steps B and C were omitted.

Comparative Example 3

(11) An ABS resin powder was obtained by the same method and under the same conditions as in Example 1, except that acid treatment in step C was performed by adding sulfuric acid instead of a metal salt, magnesium sulfate.

Comparative Example 4

(12) An ABS resin powder was obtained by the same method and under the same conditions as in Example 1, except that, in step C, the amount of water added with a metal salt was changed from 400 parts by weight to 900 parts by weight. In this case, when a metal salt and water were added in step C, pH was 8.2.

(13) Preparation of Thermoplastic Resin Composition

(14) 1.2 parts by weight of a lubricant and 0.2 parts by weight of an antioxidant are mixed with 100 parts by weight of a base resin containing 27% by weight of each of the ABS resin powders prepared in the examples and the comparative examples and 73% by weight of a styrene-acrylonitrile copolymer (LG Chem DP270 including a butadiene rubber polymer having an average particle diameter of 0.2 to 0.4 μm). Then, extrusion of the mixture was performed at 210° C. and 250 rpm, and an ABS resin composition pellet was prepared using a pelletizer. The prepared pellet was dried and injection-molded to obtain a specimen for measurement.

Test Example

(15) The physical properties of the thermoplastic resins and the thermoplastic resin compositions according to the examples and the comparative examples were measured by the following methods, and the results are shown in Table 1.

(16) Izod Impact Strength

(17) An injection specimen having a thickness of about 6.4 mm was prepared according to the method specified in ASTM D256, a notch was formed on the specimen, and impact strength (unit: kg.Math.cm/cm) was measured at room temperature (23° C.).

(18) Moisture Content

(19) When a thermoplastic resin powder was prepared, the moisture content of a wet powder obtained after the dehydration process of step D was measured using a HR83-P moisture analyzer (Mettler-Toledo Co., Switzerland). In this case, the weight change before and after drying was measured after complete drying at 150° C., and the weight loss was expressed as a percentage.

(20) Distortion-Temperature Under Heat (HDT)

(21) An injection specimen having a thickness of about 6.4 mm was prepared according to the method specified in ASTM D648, and distortion-temperature under heat (unit: ° C.) was measured under a load of 18.6 kg/cm.sup.2.

(22) Glossiness (Gloss, GU)

(23) The gloss of an injection specimen was measured at an angle of 45° using a Gloss meter according to the method specified in ASTM D528.

(24) Color and Whiteness (White Index, WI)

(25) The L, a, b, and whiteness index (WI) values of an injection specimen were measured using a color-difference meter (Color Quest II, Hunter Lab Co.). L, a, and b each indicate a value of a coordinate axis indicating a unique color. “L” has a value of 0 to 100. When an “L” value is close to 0, a specimen is black, and when an “L” value is close to 100, a specimen is white. “a” has a positive (+) or negative (−) value based on 0. A positive (+) “a” value indicates that a specimen is red, and a negative (−) “a” value indicates that a specimen is green. “b” has a positive (+) or negative (−) value based on 0. A positive (+) “b” value indicates that a specimen is yellow, and a negative (−) “b” value indicates that a specimen is blue. When a specimen has a positive “b” value, the absolute value of the “b” value is proportional to the degree of yellowing of the specimen.

(26) Plating Adhesion (Unit: N/cm)

(27) A specimen for measuring physical properties prepared by injection molding was etched using a chromic acid/sulfuric acid solution. Then, a conventional plating process was performed to obtain a plated specimen having a length of 100 mm, a width of 100 mm, and a thickness of 3 mm, on which a chromium plating film was formed. Thereafter, a 10 mm wide scratch was formed on the front surface of the plated specimen. Then, values were measured while peeling off the plating film by 80 mm in the vertical direction using a push-pull gauge, and the obtained values were averaged to calculate plating adhesion.

(28) Oxidative Induction Time (OIT)

(29) The oxidative induction time of the ABS resin powder prepared as described above was measured using differential scanning calorimetry (DSC) according to ASTM D3895. Specifically, under an isothermal condition of 190° C., time (Unit: minute) at which oxidation occurs was measured while 50 ml of oxygen per minute was supplied to the ABS resin powder.

(30) TABLE-US-00001 TABLE 1 Examples Comparative Examples Classification 1 2 3 1 2 3 4 Coagulant Sulfuric Sulfuric Sulfuric Sulfuric Magnesium Sulfuric Sulfuric type acid acid acid acid sulfate acid acid Presence ∘ ∘ ∘ x x ∘ ∘ or absence of base treatment Presence Magnesium Magnesium Magnesium x x Sulfuric Magnesium or absence sulfate sulfate sulfate acid sulfate of acid or metal salt treatment pH in step 9.3 10.1 10.9 — — — 8.2 C Measurement results of physical properties Impact 17.2 17.2 17.3 17.1 17.2 17.3 17.2 strength [unit: kg .Math. cm/cm] Moisture 21.11 21.24 21.16 21.01 33.52 20.87 20.98 content [% by weight] HDT [° C.] 105.9 105.8 150.9 104.5 105.7 105.7 105.9 Glossiness 89.1 89.2 89.0 84.1 88.0 85.3 89.0 [unit: GU] b value 9.43 9.45 9.45 14.46 11.46 13.01 9.46 Whiteness 48.5 48.6 48.6 41.5 48.0 47.1 48.6 Plating 16.9 16.8 16.9 13.6 16.2 13.5 16.8 adhesion [N/cm] OIT [min.] 28.3 28.8 28.5 27.1 13.2 26.1 10.3

(31) Referring to Table 1, the moisture content of the resin powder of Examples 1 to 3 according to the method of preparing a thermoplastic resin of the present invention is similar to that of the resin powder of Comparative Example 1 in which coagulation is performed using sulfuric acid. These results indicate that the method of the present invention may increase the productivity of a thermoplastic resin powder. In addition, in the case of the thermoplastic resin compositions of Examples 1 to 3, the impact strength remains high, the heat resistance is slightly higher than that of the composition of Comparative Example 1, and the gloss and whiteness are the same as those of the composition of Comparative Example 2 in which a metal salt coagulant is used, indicating that the appearance quality of the thermoplastic resin composition of the present invention is excellent. That is, the present invention may solve the problems that occur in conventional acid coagulation and metal salt coagulation, and the resin composition of the present invention may satisfy productivity, impact strength, heat resistance, gloss, and whiteness. As shown in Table 1, in Examples 1 to 3, it can be confirmed that OIT is high while the “b” value is low. Both of these physical properties are related to the thermal stability of a material. When a thermoplastic resin composition is prepared according to the present invention, the thermal stability of the resin composition may be greatly improved. For reference, the “b” value is one of color values measured using a color-difference meter. When a composition has a positive “b” value, the absolute value of the “b” value is proportional to the degree of yellowing of the composition. Accordingly, it can be seen that the compositions of Examples 1 to 3 are less discolored due to heat in a high-temperature process and/or a molding process. In addition, OIT indicates time at which a material is oxidized under conditions that the material can be oxidized. As the OIT value increases, the thermal stability and oxidation resistance of a material increase. Accordingly, it can be seen that the thermal stability of the compositions of Examples 1 to 3 is excellent.

(32) In addition, in the case of Examples 1 to 3, the adhesive strength of the coating films is very high, and plating defects such as swelling of a plating film and unplating are not observed. Therefore, the thermoplastic resin and the resin composition according to the present invention may improve the efficiency of a coating process and may greatly improve the appearance quality of a coating product.

(33) On the other hand, in the case of Comparative Example 1, since base treatment and metal salt treatment are omitted, the gloss and whiteness are low resulting in deterioration in the appearance quality. In addition, due to the high “b” value, the thermal stability is low as compared with Example 1, and the coating properties are not improved.

(34) In addition, in the case of Comparative Example 2, since a metal salt, magnesium sulfate, is used in a coagulation process, the moisture content is very increased, thereby lowering the productivity. In addition, due to high OIT, the thermal stability and oxidation resistance are poor.

(35) In addition, in the case of Comparative Example 3, since an acid is added instead of a metal salt, the gloss, “b” value, whiteness, and OIT are very low as compared with examples, and the plating adhesion is very low.

(36) In addition, in the case of Comparative Example 4 in which the metal salt treatment step is performed as in Example 1, but pH in this step is out of the range of the present invention, OIT is very low as compared with Example 1, and the thermal stability and oxidation resistance are very low.