A METHOD FOR PREPARING THERMOPLASTIC RESIN HAVING EXCELLENT COLOR MATCHING PROPERTY, RESIDENT GLOSS AND WEATHER RESISTANCE

Abstract: The present invention relates to a method for preparing a weather resistant thermoplastic resin having excellent color matching properties and resident gloss. The method of the present invention comprises the steps of a) preparing a core rubber latex using alkyl acrylate monomers and aromatic vinyl monomers having a large refractive index, and b) grafting aromatic vinyl, vinyl cyan and methacrylate alkyl ester monomers using an oil soluble initiator.

Description: A METHOD FOR PREPARING THERMOPLASTIC RESIN HAVING EXCELLENT COLOR MATCHING PROPERTY, RESIDENT GLOSS AND WEATHER RESISTANCE BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to a method for preparing thermoplastic resin, and more particularly to a method for preparing weather resistant thermoplastic resin having excellent color matching properties and resident gloss. (b) Description of the Related Art Generally, ASA resin, a terpolymer consisting of acrylate-styrene- acrylonitrile, is prepared by grafting styrene and acrylonitrile compounds into acrylate rubber, and it is commonly used for outdoor electronic parts, building materials and sports goods due to its good properties including weather resistance, chemical resistance, processibility, etc. However, ASA resin is restrictively used for materials requiring colors such as red, yellow, green, etc., because during the preparation thereof, styrene and acrylonitrile compounds are not sufficiently grafted into acrylate rubber and bare acrylate rubber exist therein, thus color matching properties and resident gloss thereof are poor. Specifically, refractive indices of the compounds used to prepare ASA resin are 1.460 for butylacrylate, 1.518 for acrylonitrile and 1.590 for styrene. Thus, the difference between the refractive index of acrylate rubber that is used as a core and those of the compounds grafted therein is large. Therefore, ASA resin has poor color matching properties since it looks opaque and only the surface of the product prepared therefrom can be seen when color matching. In addition, since aqueous potassium persulfate (KPS) having good latex stability is used as an initiator in order to compensate for a decrease in the stability of acrylate rubber latex, and potassium persulfate limits improvement in grafting rate, the improvement in color matching properties and resident gloss is limited. Methods for preparing weather resistant ASA are disclosed in USP 3,426,101 , Japanese Patent Laid-open publication Nos. Hei 4-180949, and Hei 5-202264, Hei 7-316243, and German Patent Nos. 1260135 and 19,826,135, etc. Although these patents disclose methods for preparing ASA resin for improving weather resistance, impact resistance, etc., they do not disclose methods for improving color matching properties and resident gloss. As a method for improving color-matching properties, JP Patent No. 61-155516 discloses roll-mixing milling polybutadiene rubber for increasing color- matching properties with acrylate rubber. Although this method can improve color matching properties and impact resistance, double bonds of polybutadiene rubber remain in resin prepared by the method, thereby decreasing weather resistance of the resin. JP Patent No. 11-240925 discloses preparing resin with a multi-layered structure in order to minimize bare acrylate rubber. However, this method has defects in that the process is complicated and reaction time is long, which makes the method uneconomical. In addition, although USP 4,831 ,079 discloses using PMMA resin having excellent color matching properties, this method is uneconomical due to the use of expensive PMMA, and it has a limit in improving impact resistance. Accordingly, there is a need for a method for preparing weather resistance resin having excellent color matching properties and resident gloss. SUMMARY OF THE INVENTION As a result of various studies and experiments for solving these problems, the present inventors discovered that the color matching properties of ASA resin can be improved by introducing aromatic vinyl monomers having a comparatively high refractive index when preparing core rubber latex resin to increase the refractive index of a core rubber latex and by introducing methacrylate alkylester monomers when preparing graft ASA resin to decrease the refractive indices of grafted compounds, thereby making the refractive indices of core rubber latex and compounds grafted therein similar, and that color matching properties and resident gloss can be simultaneously improved by using an oil-soluble initiator instead of a water- soluble initiator. Accordingly, it is an object of the present invention to provide a method for preparing weather resistant resin having excellent color matching properties and resident gloss. In order to achieve the object, the present invention provides a method for preparing thermoplastic resin comprising the steps of a) preparing a core rubber latex using alkyl acrylate monomers and aromatic vinyl monomers having a high refractive index, and b) grafting aromatic vinyl, vinyl cyan and methacrylate alkyl ester monomers into the core rubber latex prepared in step a) using an oil soluble initiator. DETAILED DESCRIPTION AND THE PREFERRED EMBODIMENTS The present invention will now be explained in more detail. 1) Preparation of core rubber latex A core rubber latex is prepared through two steps of polymerization. In the first polymerization step, a crosslinked alkyl acrylate rubber is prepared using alkyl acrylate monomers and an ethyleneglycolmethacrylate crosslinking agent without using an emulsifier. In the second polymerization step, the rubber prepared in the first polymerization step is used as a seed, and alkyl acrylate, an emulsifier, a crosslinking agent, a grafting agent and aromatic vinyl monomers having a relatively high refractive index are introduced therein to make alkylacrylate rubber particles bigger to prepare rubber latex having a large diameter. The aromatic vinyl compound having a relatively high refractive index is used to increase the refractive index of the rubber latex to make it similar to the refractive indices of grafted monomers. The monomer predominantly used in the first polymerization step is preferably butylacrylate, and the contents thereof is preferably 0.5 to 5 wt parts per 100 wt parts of total monomers. Examples of the crosslinking agent include ethylglycoldimethacrylate, diethyleneglycoldimethacrylate, triethyleneglycoldimethacrylate, 1 ,3-butandioldimethacrylate, 1,6- hexanedioldimethacrylate, neopentylglycoldimethacrylate, trimethylolpropanetrimethacrylate, trimethylolmethanetriacryalte, etc., and the contents thereof is preferably 0.05 to 0.3 wt parts per 100 wt parts of total monomers. As an electrolyte, NaHC0 3 , Na 2 S 2 0 7 , K 2 C0 3 , etc. can be used, and the contents thereof is preferably 0.05 to 0.4 wt parts per 100 wt parts of total monomers. As a polymerization initiator, an inorganic or organic peroxide compound can be used, and a water soluble initiator or oil soluble initiator can be used. Examples of the initiator include water soluble initiators such as potassium persulfate, sodium persulfate and ammonium persulfate, and oil soluble initiators such as cumenehydroperoxide and benzoylperoxide. The contents of the polymerization initiator is preferably 0.05 to 0.2 wt parts per 100 wt parts of total monomers. The second polymerization step is conducted to make the diameter of rubber latex bigger using the rubber latex polymerized in the first step as a seed, and alkyl acrylate and aromatic vinyl monomers having relatively high refractive index are used in this step. Butylacrylate is preferably used as an alkyl acrylate, and styrene having a refractive index of approximately 1.590 is preferably used as an aromatic vinyl compound having a relatively high refractive index. 29 to 49 wt parts of butylacrylate and 1 to 7 wt parts of aromatic vinyl compound are preferably used per 100 wt parts of total monomers. As an emulsifier, carboxylate metal salt derivatives having a pH of 9 to 13 and carbon atoms of C12- 20, such as fatty acid metal salts, rosin acid metal salts, etc. can be used, and as a grafting agent, allylmethacrylate (AMA), triallylsocyanurate (TAIC), triallylamine (TAA), diallylamine (DAA), etc. can be used, and 0.01 to 0.07 wt parts of the emulsifier is preferably used per 100 wt parts of total monomers. The pH of the prepared core rubber latex is preferably 5 to 9, with a diameter of 2500 to 5000 A. 2) Preparation of graft ASA resin Weather resistant ASA resin is prepared by grafting an aromatic vinyl compound, vinyl cyan and methacrylate alkyl ester momoners into the core rubber latex prepared in 1). This process is characterized by mixing methacrylate alkyl ester monomers having a relatively low refractive index with the grafted aromatic vinyl and vinyl cyan monomers. Since this decreases the refractive index of the grafted monomers to make it similar to the refractive index of core rubber latex, color matching properties can be improved. In addition, this process is characterized by improving a grafting rate using an oil soluble initiator to improve color matching properties and resident gloss. Preferably, 10 to 50 wt parts of aromatic vinyl compound, 10 to 25 wt parts of vinyl cyan compound and 1 to 25 wt parts of methacrylate alkyl ester compound are used per 100 wt parts of total monomers. As a methacrylate alkyl ester, methylmethacrylate having a refractive index of approximately 1.490 is preferably used. Although each component can be added by a whole amount administration method, multi-stage divisional administration and continuous administration methods are preferable in order to minimize the production of coagulum. Examples of initiator include oil soluble peroxides such as cumenehydroperoxide (CHP), diisopropylbenzenehydroperoxide (DIPHP), etc. and oxidation-reduction catalyst such as sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate, dextrose, sodium pyrophosphate, sodium sulfite, etc. Tertiary dodecylmercaptan is preferably used as a molecular weight controlling agent, and examples of the emulsifier include rosin acid salts such as potassium rosin acid, sodium rosin acid, etc, fatty acid salts such as potassium oleate, sodium oleate, sodium stearate, and alkylarylsulfone salt, etc. The latex diameter of the prepared graft ASA resin is preferably 3500 to 6000 A, and the pH thereof is preferably 8 to 1 1. The present invention will now be explained with reference to the following Examples. However, these are to illustrate the present invention and the present invention is not limited thereto. [Example 1] A) Preparation of core rubber latex 1 ) First polymierization step The following ingredients were introduced into a polymerization reactor under nitrogen atmosphere and the temperature was elevated to 70 ° C and then they were reacted for 1 hour. Ion-exchange water 70 wt parts Butylacrylate 2 wt parts Ethyleneglycoldimethacrylate (EDMA) 0.02 wt parts Sodium bicarbonate 0.1 wt parts Potassium persulfate (KPS) 0.04 wt parts 2) Second polymerization step All the following ingredients except potassium persulfate were mixed in a polymerization reactor, and then the product of the first polymerization step and a catalyst were continuously introduced therein at 70 ° C for 4 hours to conduct polymerization reaction. Ion exchange water 45 wt parts Sodium dioctylsulfosuccinate 0.5 wt parts Butylacrylate 38 wt parts Styrene 5 wt parts Ethyleneglycoldimethacrylate 0.12 wt parts Allyl methacrylate 0.04 wt parts Sodium bicarbonate 0.1 wt parts Potassium persulfate 0.06 wt parts The diameter of the obtained latex was 4000 A as measured by the dynamic laser-light scattering method using Nicomp (Model: 370HPL), the pH thereof was 8 and a polymerization conversion rate was 98%. B) Preparation of graft ASA resin All the following ingredients were mixed except a catalyst, diisopropylbenzenehydroperoxide. The mixture and the catalyst were continuously introduced in the rubber latex polymerization product prepared in A) at 70 ° C for 3 hours and polymerization reacted, and then reacted at 80 " Cfor another 1 hour in order to increase a polymerization conversion rate, and cooled to 60 ° C . Ion exchange water 63 wt parts Sodium dioctylsulfosuccinate 0.5 wt parts Styrene(SM) 17 wt parts Acrylonitrile(AN) 18 wt parts Methylmethacrylate 20 wt parts Tertiary dodecylmercaptan(TDDM) 0.3 wt parts Sodium ethylenediaminetetraacetate 0.1 wt parts Ferrous sulfate 0.005 wt parts Formaldehydesodiumsulfoxylate 0.23 wt parts Dioctylsulfosuccinate 0.25 wt parts Diisopropylenebenzenehydroperoxide(DIPHP) 0.4 wt parts The diameter of the polymerized latex was measured by the dynamic laser-light scattering method using Nicomp (Model: 370HPL), and the graft rate thereof was calculated by the following equation. [Equation] Graft rate (%) = the weight of grafted monomers/the weight of rubber X 100 The diameter of the polymerized latex was 4400 A, the pH thereof was 9.5, the polymerization conversion rate thereof was 99% and the graft rate thereof was 45%. The obtained latex was coagulated at 90 ° C with calcium chloride aqueous solution, dehydrated and dried to obtain ASA powder particles having weather resistance. B) Measurement of color matching properties and resident gloss of ASA resin To 45 wt parts of ASA resin powder prepared in B) and 55 wt parts of general SAN 92HR(LG Chemical product), 0.4 wt parts of activator, 0.3 wt parts of antioxidant, and 0.1 wt parts of photostabilizer were introduced and roll- mixing milled at 220 ° C using a double shaft extruder to prepare a pellet, and the pellet was injected again and the properties were measured. The properties were measured by the ASTM method, and the color matching property was observed with naked eyes by a 5 grade scale. 5 points is best level, and 1 point is poorest. In addition, resident gloss was estimated by standing the resin at 200 ° C in an extruder for 20 minutes to measure gloss . The impact resistance was 19, color matching property was 5 and resident gloss was 85. [Example 2] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that the amounts of styrene and methylmethacrylate used in B) were changed to 32 wt parts and 5 wt parts, respectively. As results of analyzing the resin, the graft rate was 48%, and a particle diameter was 4450 A. And, regarding the properties thereof, the impact resistance was 20, color matching property was 4, and resident gloss was 86. [Example 3] ■ ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that TAIC was used instead of EDMA in A). As results of analyzing the resin, the graft rate was 43 %, and particle diameter was approximately 4400 A. Regarding the properties, the impact resistance was 18, color matching property was 5, and resident gloss was 85. [Example 4] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that CHP was used instead of KPS in A). As results of analyzing the resin, the graft rate was 46% and the particle diameter was approximately 4450 A. Regarding the properties, the impact resistance was 18, color matching property was 5, and resident gloss was 86. [Example 5] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that DIPHP was used instead of KPS in A). As results of analyzing the resin, the graft rate was 46%, and particle diameter wa approximately 4500 A. Regarding the properties, the impact resistance was 18, color matching property was 5, and resident gloss was 86. [Example 6] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that sodium laurylsulfate was used as an emulsifier instead of sodiumdioctylsulfonate in B). As results of analyzing the resin, the graft rate was 45%, and particle diameter was approximately 4450 A. Regarding the properties, the impact resistance was 18, color matching property was 5 and resident gloss was 86. [Example 7] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that CHP was used as a catalyst instead of DIPHP in B). As results of analyzing the resin, the graft rate was 45%, and particle diameter was approximately 4400 A. Regarding the properties, the impact resistance was 19, color matching property was 5 and resident gloss was 85. [Comparative Example 1] ASA resin was prepared and the properties thereof were measure by the same method as in Example 1 , except that 5 wt parts of styrene were not used in the second step of A) process, and the amount of styrene in B) process increased from 17 wt parts to 22 wt parts. As results of analyzing the resin, the graft rate was 45%, and particle diameter was approximately 4300 A. Regarding the ' properties thereof, the impact resistance was 20, color matching property was 3, which is not good, and resident gloss was 86. [Comparative Example 2] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that 20 wt parts of methylmethacrylate were not used, and instead the amount of styrene increased from 17 wt parts to 37 wt parts in B) process. As results of analyzing the resin, the graft rate was 50%, and particle diameter was approximately 4600 A. Regarding the properties, the impact resistance was 21 , color matching property was 2, which is quite poor, and resident gloss was 87. [Comparative Example 3] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that 5 wt parts of styrene in the second step of A) process and 20 wt parts of methylmethacrylate in B) process were not used, and instead the amount of styrene in B) process increased from 17 wt parts to 42 wt parts. As results of analyzing the resin, the graft rate was 51 %, and particle diameter was approximately 4650 A. Regarding the properties thereof, the impact resistance was 21 , color matching property was 1 , which is poor, and resident gloss was 86. [Comparative Example 4] ASA resin was prepared and the properties thereof were measured by the same method as in Example 1 , except that KPS catalyst was used instead of DIPHP in B) process. As results of analyzing the resin, the graft rate was 36%, and particle diameter was approximately 4100 A. Regarding the properties, the impact resistance was 16, color matching property was 2, which is quite poor, and resident gloss was 65. As explained, the resin of the present invention has improved color matching properties since the refractive indexes of rubber latex and the compounds grafted thereto are made similar and colors look deep if color matched, and it simultaneously has improved color matching properties and resident gloss due to the use of an oil soluble catalyst instead of a water soluble initiator in the grafting step.

Claims: WHAT IS CLAIMED IS: 1. A method for preparing a weather resistant thermoplastic resin having excellent color matching properties and resident gloss comprising the steps of: a) preparing a core rubber latex using alkyl acrylate monomers and aromatic vinyl monomers having a large refractive index; and b) grafting aromatic vinyl compound, vinyl cyan compound and methacrylate alkyl ester compound monomers into the core rubber latex prepared in step a). 2. The method for preparing the thermoplastic resin according to claim 1 , wherein in step a), 30 to 50 wt parts of alkylacrylate and 1 to 7 wt parts of aromatic vinyl monomers having large refractive indexes are used, and in step b), 10 to 50 wt parts of aromatic vinyl monomers, 10 to 25 wt parts of vinyl cyan monomers and 1 to 25 wt parts of alkyl ester monomers are used. 3. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the core rubber latex prepared in step a) has a particle diameter of 2500 to 5000 A, and a pH of 5 to 9. 4. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the graft ASA resin prepared in step b) has a particle diameter of 3500 to 6000 A, and a pH of 8 to 11. 5. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the alkylacrylate is butylacrylate or a derivative thereof. 6. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the aromatic vinyl compound having a large refractive index used in step a) is styrene or a derivative thereof. 7. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the aromatic vinyl compound used in step b) is styrene or a derivative thereof. 8. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the vinyl cyan compound is acrylonitrile or a derivative thereof. 9. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the methacrylate alkyl ester is methylmethacrylate or a derivative thereof. 10. The method for preparing the thermoplastic resin according to claim 1 or 2, wherein the oil soluble initiator is diisopropylbenzene hydroperoxide or cumene hydroperoxide.

Inventors: AHN TAE-BIN, LEE CHAN-HONG, SHIN YANG-HYUN, YOO KEUN-HOON, AHN, TAE-BIN, LEE, CHAN-HONG, SHIN, YANG-HYUN, YOO, KEUN-HOON
Applicants: AHN TAE BIN, LEE CHAN HONG, LG CHEMICAL LTD, SHIN YANG HYUN, YOO KEUN HOON, AHN, TAE-BIN, LEE, CHAN-HONG, LG CHEMICAL CO., LTD., SHIN, YANG-HYUN, YOO, KEUN-HOON
Application year: 2001
Main classification: C08F291
IPC codes: C08F4, C08F265