ACRYLONITRILE/STYRENE/ACRYLATE COPOLYMERS WITH IMPROVED STAIN RESISTANCE

Abstract: The invention provides acrylonitrile/styrene/acrylic compositions having advantageous staining and weathering properties. Compositions of the invention include an acrylonitrile-styrene-acrylic elastomer polymer and up to 5 percent by weight of at least one additive selected from the group consisting of nonionic fluorinated compounds, silicon-based polymers, and mixtures thereof.

Description: ACRYLONITRILE/STYRENE/ACRYLATE COPOLYMERS WITH IMPROVED STAIN RESISTANCE Description The present invention relates to acrylonitrile - styrene - acrylate (ASA) copolymers with improved stain-resistance and methods for improving the stain resistance of ASA copolymers. Acrylonitrile/styrene/acrylate (ASA) copolymers are weatherable, UV-resistant thermoplastic polymers that retain color and property stability in outdoor exposure. These copolymers have many applications in automotive, construction, and recreational mar- kets. For example, ASA copolymers are used in production of automotive body moldings, exterior and interior trim parts, bumper parts, pickup truck caps, and recreational vehicle components; in home siding and trim, gutters and downspouts, shutters, and window frames; and in swimming pool and pump components, outdoor furniture, bath tubs, shower stalls, and spas. In general, ASA copolymers are excellent candidates for fabricating articles that will be used outdoors because the copolymers exhibit good weathering properties. In some applications for which ASA copolymers are suitable, the formed article may be brought into contact with water, solvents, or other substances that might damage the surface of the article. For example, ASA copolymers are used for the fabrication of automotive grills such as the cowl vent grill below the windshield. One concern for a cowl vent grill is the resistance of the plastic to water and/or the chemicals in windshield washer solution or other products that may come into contact with the plastic grill. Products of concern including cleaning and polishing materials. Traditional ASA has been found to stain in such applications. Staining of ASA may also be observed in other ASA end use applications involving exposure to water or aqueous mixtures of other agents. For example, hot tub spas have been found to show stains. Pigments, dyestuffs, and water treatment chemicals have been suspected of contributing to the staining of ASA in these applications. "Staining", as used herein, includes discoloration, blushing, loss of gloss, weathering and/or whitening, which is perceived as a surface imperfection. Such staining or weathering typically results from exposure to water or mixtures of water and other agents such as chemicals, solvents, pigments and dyes. Staining can be manifested via the appearance of water spot-like marks on the polymer surface. Although staining can occur at any time, parts which have been exposed outdoors or weathered have been found to be more likely to show stains. The appearance of staining in weathered parts is highly disadvantageous, because many articles that may potentially be manufactured using ASA copolymers would likely come into contact with water or products containing the agents described above. Thus, it is highly desirable to produce ASA articles that are resistant to staining and other appearance problems that could develop during use. It has been discovered that ASA copolymer compositions that include certain fluorine- or silicon-based additives have a high degree of stain, spotting and weathering resistance. The compositions of the invention comprise both ASA copolymers and a fluorine or silicon-based additive, or a mixture of these additives, in an amount sufficient to improve the stain resistance of the composition. An effective amount is an amount that demonstrates a measurable or observable difference. The fluorine- based additive is a fluorinated compound, preferably a fluorosur- factant. The silicon-based additive is a polymeric silicon material, preferably a polysiloxane. Materials that are hydrophobic, nonionic compounds compounds that can migrate through the ASA matrix to the surface of the formed article are preferred. The ASA copolymers of the invention are known in the art and may be produced by known processes, for example, according to the methods described in U.S. Pat. Nos. 3,944,631; 4,111,876; 4,528,328; 4,537,933; 5,068,285; and 5 , 070, 142 , the disclosures of each being incorporated herein by reference. ASA copolymers comprise at least a styrene-acrylonitrile copolymer matrix containing acrylic rubber particles. The styrene portion may comprise vinyl aromatic monomers selected from styrene and alkyl styrenes, such as alpha methyl styrene, p-methyl styrene, ethyl styrene, isopropyl styrene, and the like, and halogenated substi- tuted styrenes such as chlorostyrene and the like, and mixtures thereof. Copolymer matrices of acrylonitrile and alpha-methyl styrene are preferred. ASA copolymers are generally random amorphous terpolymer produced either by a mass copolymerization or emulsion copolymerization process or by grafting styrene-acrylo- nitrile to the acrylic elastomer backbone. The acrylic rubber particles may be, and preferably are, grafted to the styrene-acrylonitrile copolymer matrix. During the polymerization, the acrylic rubber particles may be grafted to the polystyrene/acrylonitrile (SAN) matrix by reaction of unsaturation remaining in the rubber or grafted to the SAN matrix after polymerization by a further unsaturation reaction of additional acrylic rubber particles with the polymerized SAN matrix. The ASA copolymer preferably has a weight average molecular weight, as measured against a polystyrene standard, of from about 50,000 to about 120,000. The acrylic rubber particles may be, and preferably are, at least partially crosslinked. In one embodiment of the invention, the ASA polymer may be made by first emulsion polymerization of an alkyl acrylate or methacrylate or mixtures thereof, with at least one crosslinking monomer to form a crosslinked acrylate elastomer, followed by emulsion polymerization of a mixture of the styrene monomer, the acrylonitrile, and the acrylate rubber. The sequence of the first two steps may be reversed, so that the acrylic elastomer is polymerized in the presence of the already- formed crosslinked styrene-acrylonitrile copolymer. In general, in forming the acrylic rubber, the acrylate and/or methacrylate monomers are chosen from alkyl acrylates and meth- acrylates having alkyl groups of Ci to Cι , preferably C to Cio- The C to Cβ alkyl acrylates and mixtures of these acrylates with other acrylates or methacrylates are preferred. Examples of useful acrylic monomers include, without limitation, ethyl acrylate, isopropyl acrylate, propyl acrylate, n-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 3-methyl-l-butyl acrylate, isobutyl acrylate, isodecyl acrylate, and the corresponding methacrylates. The crosslinking monomer is a polyethylenically unsaturated monomer, preferably a divinyl, diacrylate, triacrylate, or tetraacrylate monomer. The crosslinking monomers of the acrylic polymerizations preferably comprise from about 0.05 to about 10 percent, and most preferably 0.1 to 5 percent, by weight of the respective monomer mixtures. Examples of suitable crosslinking monomers include, without limitation, divinyl benzene, trimethylol triacrylate, allyl methacrylate, diallyl fumarate, diallyl aleate, 1,3-butylene dimethacrylate, diethylene dimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trime- thylolpropane triacrylate, diethylene glycol diacrylate, divinyl ether, diallyl phthalate, divinyl sorbitol, triethylene glycol dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, pentamethylene glycol diacrylate, glyceryl triacrylate, and the tetraacrylate ester of pentaerythritol . The emulsion polymerizations may be carried out in the manner usual for the art, for example with anionic, nonionic, or cationic emulsifiers in amounts of from about 0.5 to about 5% by weight of the emulsion. Conventional initiators and chain transfer agents may be employed, including, without limitation, hydrogen peroxide and organic peroxides and redox catalysts may be used. Initiators may be used in amounts of from about 0.005 to about 2 percent by weight, based on the weight of the monomers. The polymerization of styrene and acrylonitrile provides a hard matrix component. The preferred ratio of acrylonitrile to styrene is from about 1 to 3 acrylonitrile to about 1 to 7 styrene, by weight. The acrylonitrile-styrene matrix should be in the range of from about 20 to about 60 percent by weight of the ASA copolymer, preferably from about 20 to about 40 percent by weight of the ASA copolymer. Compositions with oc-methyl styrene are preferred. The ASA copolymer preferably comprises from about 5 to about 95 percent by weight of the acrylic elastomer, from 0 to about 35 percent by weight of the crosslinked styrene-acrylonitrile copolymer, and from about 5 to about 95 percent by weight of the uncrosslinked styrene-acrylonitrile copolymer matrix. The acrylic rubber particles may contain thermoplastic polymer occlusions, such as, for example, when mass polymerization is used to prepare the ASA copolymer. Suitable ASA copolymer materials are commercially available. Preferred among the commercial products is LURAN ® S 778T, commercially available from BASF Corporation, 3000 Continental Drive North, Mt. Olive, New Jersey 07828. Preferred fluorine-based additives are hydrophobic fluorosurfac- tants. Fluorosurfactants are characterized in that they have a hydrophobic portion -C n F 2n+ ι and a hydrophilic portion. The fluorosurfactant are preferably nonionic. An especially preferred fluorosurfactant has a fluorocarbyl radical with F(CFCF x ) n , wherein n is 3 to 8. The hydrophobic fluorosurfactants may be added to the ASA copolymer composition in amounts of up to about 0.5 percent by weight, preferably from about 0.005 to about 0.15 percent by weight, and particularly preferably from about 0.08 to about 0.12 percent by weight. Fluorosurfactants are available commer- cially, for example from DuPont Specialty Chemicals, Wilmington, Delaware, under the tradename ZONYL ® . Particularly preferred among these are ZONYL ® FSN 100 and FSO 100. Preferred silicon-based additives are silicone fluids and greases. Among these, polydimethylsiloxanes, polyphenylmethylsi- loxanes, and polydiphenylsiloxanes are especially useful. Particularly preferred are polyphenylmethylsiloxanes. The silicone materials of the invention may have viscosities of between about 50 and about 250,000 centistokes. It is particularly preferred to use polysiloxanes that have viscosities of from about 50,000 to about 150,000 centistokes. Such silicones are available commercially, for example from Dow Corning Corp., Midland, Michigan and General Electric, Scenectady, New York. Preferred among these is 710 Fluid, available from Dow Corning. The silicone materials may be added to the ASA copolymer composition in amounts of up to about 5 percent by weight, preferably from about 0.1 to about 3 percent by weight, and particularly preferably from about 0.1 to about 1 percent by weight. In addition to the ASA copolymer and the fluorine- or silicon- based additive, the ASA copolymer compositions of the invention may include further polymer components or additives. For example, the ASA copolymer may be blended with one or more different thermoplastic polymers, including, without limitation, blends with polystyrenes, polycarbonates, unmodified styrene-acrylonitrile copolymers, polyvinyl chloride, polymethylmethacrylate, and poly- esters such as polybutylene terephthalate and polyethylene terephthalate. Further additives that may be incorporated into the ASA copolymer compositions of the invention include, without limitation, hin- dered amine stabilizers (HALS) , benzotriazole UV absorbers, organic and inorganic pigments, dyes, and fillers, thermal stabilizers, antioxidants, lubricants, processing aids, and plasticizers such as phenyl dicarboxylic esters of C to Cn alcohols, such as di-octyl phthalate and di-isononyl phthalate. Pre- ferably, the compositions of the invention include from about 0.1 to about 1.0 percent by weight of a HALS or a mixture of HALS. The ASA compositions may be blended or compounded in any manner known in the art. For example, and without any limitation, poly- mer blends may be prepared by mixing in a single- or twin-screw extruder, milling in a roll mill or Banbury mixer at an elevated temperature, continuous melt blending, or by calendering. All such blend preparations may be preceded by mixing in, for example, a Herschel type mixer. Blending can be carried out in the same equipment being used to produce the final article, e.g., in a screw-type extruder. Alternatively, the blend may be pro- duced as pellets for later thermoforming by, for example, melt mixing or extrusion molding techniques. Compounding and pelletiz- ing may be done by any of various means known in the art. The compositions of the invention may be processed by any thermo- forming technique, for example by injection molding, compression molding, and extrusion molding techniques. Molding conditions may be the same as conditions usually employed for molding ASA copolymer compositions. Molding conditions for particular compounds and equipment may be optimized by straightforward test- ing according to the usual methods. The compositions of the invention may be used to advantageously make automotive vehicle components such as cowl vent grills and the like as well as construction components, parts for outdoor articles and articles exposed to water such as tubs, showers, and spas. The invention is illustrated by the following examples. The examples are merely illustrative and do not in any way limit the scope of the invention as described and claimed. All parts are parts by weight unless otherwise noted. EXAMPLE 1 The present invention was testing according to Ford Motor Company Test Procedure No. 84-52509. A commercially available ASA from BASF Corporation, LURAN ® S 778T, was employed as the ASA with a standard UV stabilizer package. The same material without the standard UV stabilizer package was used as the ASA without UV stabilizer. All samples contained carbon black according to BASF Corporation's Color Code BLK-31261. Varying amounts of the fluoro surfactant or silicone-containing additives of the invention were added to the identified ASA. The ingredients of the composition were mixed in a Herschel-type mixer and subsequently compounded in a twin screw 40mm extruder. Sample plaques were made out of the samples below using standard injection molding techniques. After a 24 hour ambient aging period, the plaques where placed in a Xenon Arc Weatherometer per SAE J1960 procedure. After 2500 kJ/m 2 , the following staining tests were performed. TABLE 1 1 = 1/2 OF STANDARD UV PACKAGE 2 = CARBON BLACK INTRODUCED VIA MASTERBATCH CONCENTRATE RATHER THAN EXTRUSION. TABLE 2 OBSERVATIONS TAKEN WHILE SPOTS WERE ON TEST PANEL using a pipette, one spot each of Ford Motor Company commercially available windshield washer fluid, windshield washer fluid with rubber tubbing extract, and windshield washer fluid with nylon tubing extract, was dropped on a prepared sample panel. The appearance of the pipetted liquid spot was observed after three (3) minutes. TABLE 3 OBSERVATIONS OF PANEL APPEARANCE SUBSEQUENT TO REMOVAL OF SPOT AND 15-SECOND RINSE WITH WARM WATER FOLLOWED BY DRYING After concluding the observations set forth in Table 1, the panels were rinsed off under warm water and dried with compressed nitrogen. The surfaces were then examined for staining and spotting. Grading Scale: 0 represents significant white residue; 10 represents no observable residue. It can be seen that the compositions of the invention offer advantages with respect to staining and spotting resistance. The invention has been described in detail with reference to preferred embodiments thereof. It should be understood, however, that variations and modifications can be made within the spirit and scope of the invention and of the following claims.

Claims: Claims 1. A composition comprising an acrylonitrile-styrene-acrylic elastomer polymer and up to 5 percent by weight of at least one additive selected from the group consisting of nonionic fluorinated compounds, silicon-based polymers, and mixtures thereof . 2. A composition according to claim 1, wherein said additive is selected from the group consisting of fluorosurfactants, polydimethylsiloxanes, polymethylphenylsiloxanes, poly- diphenylsiloxanes, and mixtures thereof. 3. A composition according to claim 1, wherein said additive is a fluorosurfactant. 4. A composition according to claim 3, wherein said fluorosurfactant comprises from about 0.005 to about 0.5 weight percent of the composition. 5. A composition according to claim 3, wherein said fluorosurfactant is an ethoxylate fluorocarbon, wherein the fluoro- carbyl radical has a structure F(CF 2 CF ) n , wherein n is 3 to 8. 6. A composition according to claim 1, wherein said additive is a polysiloxane. 7. A composition according to claim 6, wherein said polysiloxane comprises from about 0.1 to about 5 weight percent of the composition. 8. A composition according to claim 1, further comprising a thermoplastic polycarbonate and mixtures thereof. 9. A cowl vent grill formed from the composition according to claim 1. 10. A method of improving the stain resistance of an acrylonitrile-styrene-acrylic elastomer copolymer composition, comprising the steps of: A) forming an acrylonitrile-styrene-acrylic elastomer copolymer; B) blending with the acrylonitrile-styrene-acrylic elastomer copolymer at least one additive selected from the group consisting of fluorinated compounds, silicon-based polymers, and mixtures thereof.

Inventors: KOGOWSKI GARY, KOGOWSKI, GARY
Applicants: BASF CORP, BASF CORPORATION
Application year: 1998
Main classification: C08L33
IPC codes: C08K5, C08L25, C08L33, C08L101