Abstract:
Solid surface material is prepared from an extrudable composite material comprising a matrix of at least one acrylic resin and a filler dispersed in the matrix, said acrylic resin comprising an acrylic epoxy-ftmctional copolymer as a matrix resin crosslinked with a straight or branched chain aliphatic carboxylic acid or anhydride of such acid.

Description:
FIELD OF THE INVENTION 
     This invention is directed to producing thin sheets of extrudable acrylic compositions for solid surface applications having desired physical properties. More particularly, the invention is directed to improving the heat resistance of such materials. 
     DESCRIPTION OF THE RELATED ART 
     Artificial (or synthetic) marble can be considered as a general designation for various types of materials used as building products, such as bathroom vanity tops, sinks, shower stalls and kitchen counter tops, for example; furniture; sanitary use; lining materials; and stationary small articles. Artificial marbles encompass cultured marble, onyx and solid surface materials typically comprising some kind of resin matrix and either with or without a filler present in the resin matrix. Solid surface materials are typically filled resin materials. Corian®, sold by E. I. du Pont de Nemours and Company, Wilmington, Del., (DuPont), is a solid surface material comprising an acrylic matrix filled with alumina trihydrate (ATH). 
     While the prior art discloses many polymeric compositions containing fillers for various purposes, the solid surface market is non-differentiated with respect to heat resistance, and the problem of improving heat resistance has not been adequately addressed. Such compositions are not readily extrudable to form thin sheet material. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention there is provided solid surface material having improved heat resistance. The solid surface material comprises a crosslinked acrylic composite as a matrix and at least one filler dispersed in the matrix. In a preferred embodiment the matrix is selected from an epoxy functional copolymer such as poly (methyl methacrylate/glycidol methacrylate) and a diacid as the crosslinking agent. The filler is calcium carbonate or another filler commonly disclosed in the art. The compositions of this invention are readily extrudable to form thin sheet material which has high heat resistance. 
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention comprises acrylic composites that can be extruded into thin sheets, which are thermoformable , have high heat resistance and resistance to staining. Acrylic resins useful in the present invention are not specially limited as long as they include a cross-linkable component and can be formed into an acrylic solid surface material. Examples of useful acrylic resins include various kinds of conventional acrylic monomers, acrylic oligomers, vinyl monomers for copolymerization other than acrylic monomers, or oligomers. As the acrylic monomer, (meth)acrylic ester is preferred. Examples of (meth)acrylic ester include methyl (meth)acrylic ester, ethyl(meth)acrylic ester, butyl (meth)acrylic ester, 2-ethylhexyl (meth)acrylic ester, and benzyl (meth)acrylic ester. The acrylic resin has an epoxy functionality provided by copolymerization of the acrylic component with from about 8 to 35% by weight of glycidyl methacrylate, preferably from 10 to 20% by weight of glycidyl methacrylate, based on the weight of the acrylic resin. 
     The acrylic polymer matrix is crosslinked using a straight or branched chain, aliphatic dicarboxylic acid such as adipic, pimelic,suberic, azelaic, sebacic, undecanoic, and 1,12-dodecandioic acid in an amount from about 7 to 15% by weight of the acrylic polymer. Also useful are anhydrides of the acids such as decanedicarboxylic acid anhydride. 
     The ingredients are mixed at a low temperature to prevent cross linking, for example on a roll mill at temperatures from 75° to 140° C., extruded and thereafter cross linked at temperatures of 170° to 210° C. As just described cross linking can be accomplished by heating the reactants to a temperature above about 170° C. or by the addition of a small amount of a catalyst to speed up the reaction such as dibutyltin dilaurate or methyltriphenylphosphonium bromide in amounts from 0.05 to 1% by weight of the total mixture. Fillers useful in the present invention include, for example, calcium carbonate, barium sulfate, aluminum oxide, magnesium hydroxide, kaolin, or decorative agents, as a list that is not exhaustive and not intended to limit the invention. Fillers can be present in effective amounts from as low as about 20% by weight to about 75% by weight. Preferably, amounts from 30 to 60% by weight are used. 
     It is known to include in solid surface materials other additives such as pigments, dyes, flame retardant agents, parting agents, fluidizing agents, viscosity control agents, curing agents, antioxidants, toughening agents and color inhibitors. Additives to provide simulated granite are disclosed in U.S. Pat. No. 4,085,246. 
     Solid surface materials of this invention can be prepared by a continuous extrusion process using a multi-feeder twin-screw extruder equipped with vacuum and a sheet die of proper dimensions. The extruded sheets can be directly transferred either onto a double belt press or into an oven for curing. Light pressure may be needed for maintaining sheet gauge or profile during curing. The resulting solid surface material is thermoformable, i.e. reshapeable under controlled conditions of temperature and force which is useful in building product applications. 
     Heat Resistance Test Method 
     Heat resistance is determined by a “hot block test”. A metal block (a 800 g stainless steel cylinder of 2 inches (5.08 cm) diameter and 1⅞ inches (4.76 cm) height is heated with and internal cartridge heater and its temperature is controlled by a temperature controller. In the Examples below thin samples (thickness less than ¼ inch (0.6 cm) are laminated onto ¾ inch (1.9 cm) particle boards before the test. The metal block, which is heated to and maintained at a desired temperature (±2° C.), is placed on a sample surface for 5 minutes. The sample surface is then inspected for any visible (qualitative) change with an unaided eye. If a tested surface with a subtle surface change can still be refinished to the original look using light sanding, the sample is considered “Pass” at the test temperature. 
    
    
     Additional features of the invention are illustrated by the following Examples, in which parts and percentages are by weight unless otherwise indicated. 
     EXAMPLES 1-15 
     Acrylic composites having compositions specified in Table 1 which follows were prepared by compounding the resins, fillers and additives on a 2 inch (5.08 cm) two-roll (can be various dimensions) mill at temperatures between 75 and 140° C. The particular temperature was selected so that no crosslinking reaction would take place within the processing time frame. The compounded materials were placed in a press at 170-210° C. for the crosslinking reaction. 
     The examples demonstrate that the epoxy-acid crosslink system of this invention dramatically improve the heat resistance of the acrylic compositions. The surface of some materials does not exhibit swelling or blistering even at 300° C. using the hot block test. Most of the yellowed surfaces after a hot block test at 270° C. can still be refinished by light sanding to their original color. For comparison, a 50% CaCO 3  filled homo-polymethylmethacrylate of molecular weight 100,000 (weight average) composite, made by a conventional extrusion process, exhibited severe surface blistering and melting under the hot block test at 180° C. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Heat Resistance Data of Representative Examples 
               
             
          
           
               
                 Formulation (percent on total weight) 
                   
               
             
          
           
               
                   
                   
                   
                   
                 Catalyst &amp; 
                 Hot Block Test 
               
               
                 # 
                 Polymer 
                 Crosslinker 
                 Filler 
                 Additive 
                 Observation 
               
               
                   
               
             
          
           
               
                 1 
                 40% 
                 20% 
                 40% 
                 0.08% 
                 200° C. - yellowing; no 
               
               
                   
                 RCP28170 
                 VXL1381 
                 CaCO3-8105C 
                 MTPPB 
                 swelling; no blistering 
               
               
                 2 
                 40% 
                 20% 
                 40% 
                 0.12% 
                 230° C. - yellowing; no 
               
               
                   
                 RCP28170 
                 VXL1381 
                 Talc 9101 
                 MTPPB 
                 swelling; no blistering 
               
               
                 3 
                 43% 
                 6.5% 
                 50% 
                 0.09% T12 
                 250° C.-yellowing; no 
               
               
                   
                 RCP28170 
                 DDDA 
                 CaCO3-8105C 
                   
                 Swelling; no blistering 
               
               
                 4 
                 6% 
                 3.5% 
                 50% 
                 0.05% T12 
                 250° C. - light yellowing; 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 CaCO3-8105C 
                   
                 no swelling; no blistering 
               
               
                 5 
                 46% 
                 3.5% 
                 50% 
                 0.05% T12; 
                 250° C. - very light 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 CaCO3-8105C 
                 0.05% 
                 yellowing; no swelling; no 
               
               
                   
                   
                   
                   
                 IRGAFOS168 
                 blistering 
               
               
                 6 
                 6% 
                 3.5% 
                 50% 
                 0.05% T12; 
                 250° C. - almost invisible 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 CaCO3-8105C 
                 0.05% 
                 yellowing; no swelling; no 
               
               
                   
                   
                   
                   
                 IRGANOX 
                 blistering 
               
               
                   
                   
                   
                   
                 1076 
               
               
                 7 
                 39% 
                 2.9% 
                 58% 
                 0.05% 
                 220° C. - no visible change 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 ATH 
                 IRGANOX 
               
               
                   
                   
                   
                   
                 1076 
               
               
                 8 
                 33% 
                 2.4% 
                 51% ATH; 
                 0.05% 
                 220° C. - no visible change 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 14% 
                 IRGANOX 
               
               
                   
                   
                   
                 SSChrunchie 
                 1076 
               
               
                 9 
                 7% 
                 2.8% 
                 50% 
                 0.05% T12 
                 270° C. - light yellowing; 
               
               
                   
                 Almatex PD9200 
                 Adipic 
                 CaCO3-8105C 
                   
                 no swelling; no blistering 
               
               
                   
                   
                 Acid 
                   
               
               
                 10 
                 47% RCP28170 
                 3.8% 
                 49% 
                 0.05% T12 
                 200° C. - light swelling; 
               
               
                   
                   
                 Adipic 
                 CaCO3-8105C 
                   
                 internal air bubbling; no 
               
               
                   
                   
                 Acid 
                   
                   
                 Blistering 
               
               
                 11 
                 48% 
                 3.0% 
                 49% 
                 0.05% 
                 270° C. - light yellowing; 
               
               
                   
                 Almatex PD9200 
                 DDDA 
                 CaCO3-8105C 
                 IRGANOX 
                 no swelling; no blistering 
               
               
                   
                   
                   
                   
                 1076 
               
               
                 12 
                 47% 
                 3.9% 
                 49% 
                   
                 250° C. - light yellowing; 
               
               
                   
                 Almatex PD6100 
                 DDDA 
                 CaCO3-8105C 
                   
                 no swelling; no blistering 
               
               
                 13 
                 48% 
                 2.1% 
                 50% 
                 — 
                 230° C. - swelling; internal 
               
               
                   
                 Almatex PD6100 
                 Adipic 
                 CaCO3-8105C 
                   
                 air bubbling; no blistering 
               
               
                   
                   
                 Acid 
               
               
                 14 
                 45.5% 
                 4.5% 
                 50% 
                   
                 200° C. - swelling; internal 
               
               
                   
                 RCP28222 
                 DDDA 
                 CaCO3-81O5C 
                   
                 air bubbling; 
               
               
                   
                   
                   
                   
                   
                 inhomogeneous 
               
               
                 15 
                 46% 
                 3.0% 
                 51% 
                   
                 200° C. - swelling; internal 
               
               
                   
                 RCP28222 
                 Adipic 
                 CaCO3-8105C 
                   
                 air bubbling; 
               
               
                   
                   
                 Acid 
                   
                   
                 inhomogeneous 
               
               
                   
               
             
          
         
       
     
     In the table above the various words and codes have the following meanings: RCP28170=copoly(MMA/22%GMA) mw˜11,000-15,000; RCP 28222=Co-poly(MMA/10%GMA) mw˜8000; VXL1381=decanedicarboxylic acid anhydride (Hoechst Co.); MTPPB=methyltriphenylphosphonium bromide (Aldrich Co.); DDDA=1.12-Dodecanedioic acid; Almatex PD9200=Co-poly(MMA/22%GMA) mw˜11000-15000 (Anderson Development Co.); Almatex 6100=Co-poly(MMA/I5%GMA) mw˜12000-15000 (Anderson Development Co.); T12=Dibutyltin dilaurate (Air Products Co.); Irganox® (Ciba Geigy Corp.) 1076=Octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate; IRGAFOS® 168(Ciba Geigy Corp.)=Tris(2,4-di-tert-butylphenyl)phosphite; SS-Crunchie=Corian® ground particles (DuPont Corian®); ATH=Aluminum Trihydrate (Alcoa); MMA=methylmethacrylate; GMA=glycidyl methacrylate.