PROCESS FOR RENDERING AROMATIC POLYMERS RESISTANT TO DISCOLORATION

Abstract: Aromatic resins are rendered resistant to discoloration by surface treatment with a synergistic stabilizer combination of antioxidant and U.V. absorber.

Description: -1- Suromary PROCESS FOR RENDERING AROMATIC POLYMERS RESISTANT TO DISCOLORATION Background of the Invention This invention relates to aromatic resins and more particularly to a process for rendering aromatic resins resistant to discoloration by surface treatment with a syn¬ ergistic stabilizer combination of an antioxidant and an ultraviolet light, absorber. The vast majority of organic polymeric resins undergo some mode of degradation when exposed to the high energy photons of ultraviolet light. Further, oxygen, moisture and temperature have been shown to play an important role in many cases. The degradation manifests itself depending on the material in yellowing, discoloration, embrittle ent and other loss of physical - goperties. Aro¬ matic polymers such as bisphenol-A polycarbonates, polystyrene, ABS and the like are particularly subject to degradation by exposure to ultraviolet light. Not generally known, however, is the fact that these resins are also subject to discol¬ oration by photooxidation. Thus, the incorporation of both an antioxidant and an ultraviolet light absorber would be beneficial in inhibiting discoloration of these resins. Surprisingly, the combination is found to be synergistic when the resin is given a surface treatment of the combination in a suitable solvent. Thus, a solvent in which the resin is only partly soluble whereby it can diffuse into the surface of the resin without substantially degrading it enables one to use far less stabilizer than would be required if directly incorporated into the resin precursors as there is no substantial amount bound into the center of the 5 resin and consequently unavailable for protecting the resin. Further, by treating the surface of the resin in accordance with the invention, there is no degradation or impairment of the desirable resin properties caused by incorporation of the stabilizers. While surface treatment of aromatic resins 10 with protective ultraviolet light stabilizers ,has previously been accomplished, to applicant's knowledge it has not been previously suggested to combine an antioxidant and an ultra¬ violet light absorber to coat an aromatic resin and it is the provision of such a system to which this invention is 15 directed. Brief Summary of the Invention In accordance with the invention it has been found tj^t unusual protection against discoloration can be achieved for aromatic resins by coating with a stabilizer combination 20 of antioxidant and ultraviolet light absorber. By dipping or submerging the resin in a solvent containing the stab¬ ilizers in which the resin is only partly soluble or the solvent can diffuse into the surface of the resin without any substantial degradation, the stabilizers are easily 25 applied. The resin can then be dried to remove the solvent and is suitable for use in parts which are used outdoors or under exposure to ultraviolet light. Detailed Description of the Invention Aromatic resins which can be employed in the O /to W invention are those which are normally degraded by exposure to ultraviolet light. Typical resins include polycarbonate resins prepared by reacting a dihydric phenol such as bis¬ phenol-A (BPA) with a carbonate precursor such as phosgene which are disclosed in U.S. Patent No. 3,309,220. These polycarbonate resins which may be formed from mononuclear or- polynuclear aromatic compounds can also be formed from halo substituted dihydric phenols such as 1,1-dichloro- 2,2-bis(4-hydroxyphenyl)ethylene (BPC) . Other typical resins include styrene polymers such as polystyrene and ABS, polymers containing ether linkages such as poly(2,6-dimethyl- phenylene oxide) and polymer blends such as formed of 20 to 99% by weight of a polyphenylene ether which can be sub¬ stituted with alkyl groups of from 1 to 4 carbon atoms, e.g., poly(2,6-dimethylphenylene)oxide, and 1 to 807- of a styrene polymer such as polystyrene. The particular resin employed is not critical as the stabilizer combination is effective in protecting conventional aromatic resins. Any ultraviolet absorber can be used, such as, for example, benzophenone derivatives, such as 2-hydroxy- 4-methoxy-benzophenone, 2,4-dihydroxy-benzophenone, 2,2'- dihydroxy-4-methoxy-benzoρhenone, 2-hydroxy-4-n-octoxy- benzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-benzophenone, 2-hydroxy-4-methoxy- '-methylbenzophenone, benzotriazole derivatives, such as 2-(2'-hydroxy-5'-methylphenyl)-benzo¬ triazole, 2-(2'-hydroxy-5'-tert butylphenyl)-benzotriazole. 2-(2'-hydroxy-3'-methyl-5'-cyclohexlphenyl)-benzotriazole, 2-(2'-hydroxy-3' , 5'-dimethylphenyl)-benzotriazole, 2-(2'- hydroxy-5'-tert-butylphenyl)-5-chloro-benzotriazole, 2-(2'-hydroxy-3' ,5'-di-tert-butylphenyl)-benzotriazole, 2(2'- 5 - hydroxy-5'-tert-ociyphenyl)-benzotriazole and derivatives of crotonic acid, such as α-cyano-f_-methyl-β-(p-methoxyphenyl)- crotonic acid methyl ester, α-cyano-$-(N-2-methyl-indolinyl)- crotonic acid methyl ester and the like. It is to be under¬ stood that the invention is applicable to any ultraviolet 10 absorber and that any one or combination of -absorbers can be used in accordance with this invention. Any antioxidant can be used, such as, for example, 2,6-di-tert-butyl-p-cresol, 2,2'-methylene bis(4-methyl-6- tert-butyl-phenol) , 4,4'-butylidene bis(6-tert-butyl-m- 15 cresol) , 1,1,3-tris(2'-methyl- '-hydroxy-5'-1ert-butyl-phen 1) butane, 4,4'-methylene bis(2,6-di-tert-butylρhenol), octadecyl 3-(3' ,5'-di-tert-butyl-4'-hydroxy-phenyl)propionate, 2,6- di-(1-methylheptadecyl) -cresol, 1,3,5-trimethyl-2, ,6-tris (3 1 ,5'-di-tert-butyl- '-hydroxybenzyl)benzene, tetrakis[methylene 20 3-(3' ,5'-di-tert-butyl- '-hydroxyphenyl)propionate]methane, 4,4'-cyclohexylidene-bis(2-cyclohexyl-phenol), 3,5-di-tert- butyl-4-hydroxyhydrocinnamic acid triester of 1,3,5-tris (2-hydroxyethyl-s-triazine-2,4,6-(1H,3H,5H)-trione, and the like. Similarly to the ultraviolet absorber, any 25 antioxidant can be employed either alone or in combination in accordance with this invention. The amount of ultraviolet light absorber and antioxidant employed will depend upon the particular stabilizer, OM the resin,.and solvent employed but generally an absorber concentration in the solvent from about 0.5 to about 207. and an antioxidant from about 0.1% to about 5%. by weight is sufficient. Solvents which can be employed are those which will not decompose either the stabilizers or the resin but which will diffuse into at least the surface of the polymer so as to deposit the stabilizers. Typical solvents include aromatic, chloroaromatic and chloroaliphatic solvents. The particular solvent will depend upon the resin but exemplary of suitable solvents are methylene chloride, chloroform, toluene, benzene, tetrahydrofuran, chlorobenzene, and dichlorobenzene ^ . The solvent is employed in an amount sufficient to contain the stabilizers and provide a vehicle for submerging or coating the resin. Typically, an immersion time of no more than about 5 to 15 seconds is sufficient to impregnate the resin and the solvent can be easily evap¬ orated at room temperature in a period of between about 1/2 hour and about 24 hours. The following examples will serve to illustrate the invention and preferred embodiments thereof. All parts and percentages in said examples and elsewhere in the specificat¬ ion and claims are by weight unless otherwise specified. EXAMPLES Molded chips (2" x 2" x 1/8") of the copolycarbonate of BPC (85 pts) and BPA (15 pts) of the type described in Polish Patent 48,893 containing a mold stabilizer and formed by injection molding were dipped for 10 seconds in ethylene dichloride containing a stab¬ ilizer in the amount indicated (infra) and tested under accelerated weather conditions with a QUV cyclic ultraviolet weather tester (Q-Panel Co.) maintained on a 4 hr light/ 5 dark cycle at full humidity. After exposure, the weathered chips were assessed for discoloration by measuring their yellowness index, YI, according to ASTM method D1925. The results are shown in the following Table I wherein it can be seen that the combination of antioxidant 10 and U.V. absorber is far more effective than either one alone in inhibiting discoloration. In fact, the resins having a yellowness index change (ΔYI) of less than "-3 exhibit no discoloration discernable to the naked eye. - j OMP t. WVVI IPΪ TABLE I Coating System I∑E≤. YI (initial) ΔYI (144 hrs.) None __. 32.9 12.8 10.457. A' uvs 35.9 3.2 15.0%-B 2 uvs 37.5 3.7 27. C 3 AΘ 39.7 9.2 27. D 4c AO 56.0 5.4 10.457. A' + 27. D 4c Comb. 52.1 1.5 10.457. A' + 2% C 3 Comb. .33.2 2.2 157. B 2 + 27. D c Comb. 44.9 0.7 157. B 2 + 27. C 3 Comb. 34.4 1.1 Samples have slight hazy appearance increasing YI A 1 is 2(2'-hydroxy-5'-methylphenyl)benzotriazole 2 - B is 2(2'-hydroxy-5'-tert-octylphenyl)benzotriazole r 3 . 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester of - iS l p 3,5-tris(2-hydroxyethyl-s-triazine-2,4,6-(lH,3H,5H)- trione D is octadecyl 3-(3',5 * -di-ter_t-butyl-4'-hydroxy-phenyl)propionate Molded stabilized chips (2" x 2" x 1/8") of Lexan polycarbonate containing 0.3% of 2(2'-hydroxy-5'-methylphenyl) benzotriazole as a bulk stabilizer plus a mold stabilizer were dipped for 10 seconds in ethylene dichloride containing stabilizer in the amount indicated (infra) and exposed to a 400 watt clear mercury lamp and rotated in an exposure chamber so as to maintain a surface temperature for the chips of 110 β C. The results are shown in the following Table II wherein it can be seen that the comLination of antioxidant and U.V. absorber would permit the U.V. absorber to be employed in smaller concentrations. TABLE II YI ΔYI 10 Coating System Initial 526 Hrs. 1. None 1.0 . 22.8 2. EDC Only 1.8 22.6 3. 3% UVS-1 1.8 17.1 4. 3% UVS-1 + 1% AO* -1 2.9 13.1 15 5. 3% UVS-1 & 1% A0- -2 1.8 11.2 6. 3% UVS-1 & 1% A0- -3 1.8 10.3 EDC is Ethylene Dichloride . UVS-1 is 2(2'-hydroxy-5'-methylphenyl)benzotriazole A0-1 is 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester of 1,3,5-tris (2-hydroxyethyl)s-triazine-2,4,6 20 1H,3H,5H)-trione AO-2 is tris(2*,5'-di-tert-butyl-4'-hydroxylbenzyl) isocyanurate AO-3 is 2,6-di-tert-butyl-4-tert-nonylphenyl While the above examples are illustrative of the invention, those skilled in the art will appreciate that obvious modifications can be made without departing from the true scope of the invention and accordingly the invention is intended to be limited only by the appended claims.

Claims: C L A I M S 1. A process for treating an aromatic resin normally subject to discoloration upon exposure to air and ultraviolet' light which comprises the steps of submerging an air and ultraviolet light degradable aromatic resin in a bath for a 5 time sufficient to stabilize said resin, said bath compris¬ ing a solvent and a stabilizer combination of antioxidant and ultraviolet light absorber sufficient to inhibit discol¬ oration of said resin wherein said solvent can penetrate the surface of said resin to incorporate said stabilizer 10 combination without substantially degrading said resin. 2. The process of claim 1 wherein the resin is selected from bisphenol-A polycarbonate, l.l-dichloro-2,2- bis(4-hydroxyphenyl)ethylene polycarbonate, copolymer or of the former two blend, polystyrene, ABS; and poly(phenylene oxide) alone or 5 in combination with polystyrene. 3. The rocess of claim 1 wherein the resin is a ^ copolymer or blend of bisphenol-A polycarbonate and 1,1- dichloro-2,2-bis(4-hydroxyphenyl)ethylene polycarbonate. 4. The process of claim 1 wherein the ultraviolet light absorber is 2(2'-hydroxy-5.'-methylphenyl)benzotriazole. 5. The process of claim 1 wherein the ultraviolet light absorber is 2(2'-hydroxy-5'-tert-octylphenyl)benzo- triazole. 6. The process of claim 1 wherein the antioxidant is 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester of 1,3,5-tris(2-hydroxyethyl-s-triazine-2,4,6-(1H,3H,5H)- trione. 7. The process of claim 1 wherein the antioxidant is tris(3,5-di-tert-butyl-4-hydroxylbenzyl)isocyanurate. 8. The process of claim 1 wherein the antioxidant is 2,6-di-tert-butyl-4-tert-nonylphenol. 9. The-process of claim 3 wherein the ultraviolet light absorber is 2(2'-hydroxy-5'-methylphenyl)benzotria¬ zole. 10. The process of claim 3 wherein the ultraviolet light absorber is 2(2'-hydroxy-5'-tert-octylphenyl)-benzo- triazole. 11. The process of claim 3 wherein the antioxidant is octadecyl-3-(3' ,5'-di-tert-butyl-4'-hydroxyphenyl)propionate. 12. The process of claim 3 wherein the antioxidant is 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid triester of 1,3,5-tris(2-hydroxyethyl-s-triazine-2,4,6-(IH,3H,5H)-trione. @s

Inventors: FACTOR A
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1979
Main classification: C08K5
IPC codes: C08K5, C08L101