Plastic sheet product offering matte appearance and method of preparation

Abstract

A plastic sheet product having a matte finish comprises a core layer of a thermoplastic polymer and at least one layer of a capstock composition which overlies, and is bonded to, at least one face of the core layer. The capstock composition comprises the same or different thermoplastic polymer and contains a plurality of discrete particles immiscible with and dispersed in the thermoplastic polymer of the capstock composition. The sheet product may be prepared by the co-extrusion of the thermoplastic polymer and the capstock composition, and in a particular embodiment, such co-extrusion may be conducted by means of a feedblock. In a particular embodiment, the thermoplastic polymer of the core layer and that of the capstock composition may be the same, such as in the instance of a methylmethacrylate-methylacrylate copolymer. Sheet products prepared in accordance with the invention exhibit improved post-processability and ease of surface maintenance, and may be fabricated into a variety of products including light diffusers, projection screens, and the like.

1 . A plastic sheet product having a matte finish comprising a core layer of a first thermoplastic polymer and at least one layer of a capstock composition overlying and bonded to at least one face of the core layer, said capstock composition comprising a second thermoplastic polymer having a refractive index and containing a plurality of discrete particles immiscible with, and dispersed in, the second thermoplastic polymer and having a refractive index, wherein the refractive index of the particles differs from the refractive index of the second thermoplastic polymer.  
   
   
       2 . The plastic sheet product of  claim 1  wherein the first thermoplastic polymer and the second thermoplastic polymer are independently selected from the group consisting of polyethylenes, polypropylenes, ethylene-propylene copolymers, ethylene-vinyl acetate copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl methylmethacrylate copolymers, ethylene-vinyl acetate-methyl methacrylate copolymers, polyvinyl chloride, methylmethacrylate-ethylacrylate copolymers acrylonitrile-styrene copolymers, polystyrenes, styrene-methylmethacrylate copolymers, polyethyl acrylates, polymethyl methacrylates, methylmethacrylate-methylacrylate copolymers, polyethylene terephthalates, polyamides, polycarbonates, polyurethanes and silicone resins.  
   
   
       3 . The plastic sheet product of  claim 1  wherein the first thermoplastic polymer and the second thermoplastic polymer are transparent.  
   
   
       4 . The plastic sheet product of  claim 1  wherein the second thermoplastic polymer is the same as the first thermoplastic polymer.  
   
   
       5 . The plastic product of  claim 3  wherein the second and the first thermoplastic polymer comprise a methyl methacrylate-methyl acrylate copolymer.  
   
   
       6 . The plastic sheet product of  claim 5 , wherein the copolymer comprises about 80 to about 98 wt. % methyl methacrylate and about 2 to about 20 wt. % methyl acrylate.  
   
   
       7 . The plastic sheet product of  claim 6 , wherein the copolymer comprises 93 to 97 wt. % methyl methacrylate and 3 to 7 wt. % methyl acrylate.  
   
   
       8 . The plastic sheet product of  claim 1 , wherein the capstock composition is bonded to only one face of the core layer.  
   
   
       9 . The plastic sheet product of  claim 1 , wherein the capstock composition is bonded to both faces of the core layer.  
   
   
       10 . The plastic sheet product of  claim 1 , wherein the first and second thermoplastic polymers have weight average molecular weights in the range of about 100,000 to about 175,000.  
   
   
       11 . The plastic sheet product of  claim 10 , wherein the first and second thermoplastic polymers have weight average molecular weights in the range of 125,000 to 150,000.  
   
   
       12 . The plastic sheet product of  claim 1 , wherein the core layer has a thickness of about 2 to about 13 mm and said at least one capstock layer has a thickness of about 10 to about 400 microns.  
   
   
       13 . The plastic sheet product of  claim 12 , wherein the core layer has a thickness of 4 to 10 mm and said at least one capstock layer has a thickness of 150 to 300 microns.  
   
   
       14 . The plastic sheet product of  claim 1 , wherein the particles have particle size diameters in the range of about 1 micron to about 60 microns.  
   
   
       15 . The plastic sheet product of  claim 14 , wherein the particles have particle size diameters in the range of 30 to 50 microns.  
   
   
       16 . The plastic sheet product of  claim 1 , wherein the particles are dispersed in the second thermoplastic polymer in an amount of about 4 to about 30 wt. %.  
   
   
       17 . The plastic sheet product of  claim 16 , wherein the particles are dispersed in the second thermoplastic polymer in an amount of 22 to 26 wt. %.  
   
   
       18 . The plastic sheet product of  claim 1 , wherein the refractive indices of the particles and the second thermoplastic polymer are in the range of about 1.40 to about 1.65.  
   
   
       19 . The plastic sheet product of  claim 18 , wherein the refractive indices of the particles and the second thermoplastic polymer are in the range of 1.49 to 1.55.  
   
   
       20 . The plastic sheet product of  claim 1 , wherein the refractive index of the particles differs from the refractive index of the second thermoplastic polymer by a value in the range of about 0.001 to about 0.030.  
   
   
       21 . The plastic sheet product of  claim 20 , wherein the refractive index of the particles differs from the refractive index of the second thermoplastic polymer by a value in the range of 0.005 to 0.020.  
   
   
       22 . The plastic sheet product of  claim 1 , wherein the particles are comprised of a polymer or a pigment.  
   
   
       23 . The plastic sheet product of  claim 22 , wherein the particles are comprised of a polymer selected from the group consisting of crosslinked polymethylmethacrylate, crosslinked polymethylmethacrylate modified with an acrylate or methacrylate monomer, crosslinked copolymers of methylmethacrylate and styrene, silicone resins and polyallyl methacrylates.  
   
   
       24 . The plastic sheet product of  claim 22 , wherein the pigment is selected from the group consisting of barium sulfate, silicon dioxide, aluminum oxide, aluminum hydroxide and calcium carbonate.  
   
   
       25 . The plastic sheet product of  claim 1 , wherein plastic sheet is formed by feedblock coextrusion of the core layer and the capstock composition.  
   
   
       26 . The plastic sheet product of  claim 6 , wherein the copolymer comprises methyl methacrylate in an amount of about 94 to 96 wt. %.  
   
   
       27 . The plastic sheet product of  claim 1  wherein the core layer has a thickness of about 5 to about 8 mm.  
   
   
       28 . The plastic sheet product of  claim 13  wherein one capstock layer has a thickness of from about 200 to about 275 microns.  
   
   
       29 . The plastic sheet product of  claim 16  wherein the particles immiscible in the second thermoplastic polymer are present in the amount of about 10 to 30 wt. %.  
   
   
       30 . The plastic sheet product of  claim 29  wherein the particles immiscible in the second thermoplastic polymer are present in the amount of about 18 to 28 wt. %.  
   
   
       31 . The plastic sheet product of  claim 14  wherein the particles have particle size diameters in the range of about 20 to about 80 microns.  
   
   
       32 . The plastic sheet product of  claim 31  wherein the particles have particle size diameters in the range of about 30 to about 50 microns.  
   
   
       33 . The plastic sheet product of  claim 1  wherein at least about half the particles have particle size diameters greater than about 30 microns and at least about half of the particles have particle size diameters less than about 50 microns in diameter.  
   
   
       34 . The plastic sheet product of  claim 21  wherein the difference in the refractive index values of the particles and the second thermoplastic polymer is about 0.015 to about 0.035.  
   
   
       35 . The plastic sheet product of  claim 1  having a Half Angle of from about 5° to about 10°.  
   
   
       36 . The plastic sheet product of  claim 1  having a Half Angle of from about 7° to about 9°.  
   
   
       37 . The plastic sheet product of  claim 1  having a Diffusion Factor may range from about 2 to about 10.  
   
   
       38 . The plastic sheet product of  claim 1  having a Diffusion Factor may range from about 3 to about 9.  
   
   
       39 . The plastic sheet product of  claim 1  having a Diffusion Factor may range from about 4 to about 7.  
   
   
       40 . The plastic sheet product of  claim 1  that when tested in accordance with the ASTM D 1003 “Test Method for Haze and Luminous Transmittance of Transparent Plastics” using a GretagMacBeth Color Eye-7000A spectrophotometer using Illuminant C and a 20° observer demonstrates transmission of light of at least about 92%.  
   
   
       41 . The plastic sheet product of  claim 1  that when tested in accordance with ASTM D 523 “Test Method for Specular Gloss” using BYK-Gardner micro-TRI-gloss (20°, 60° and 85°) with a black felt backing demonstrates gloss at 20° of about 0.5 to 1.0, demonstrates gloss at 60° of about 5 to about 7, and demonstrate gloss at 85° of about 1 to about 6.  
   
   
       42 . A plastic sheet product having a matte finish and improved abrasion resistance and weathering comprising a core layer of a first thermoplastic polymer and at least one layer of a capstock composition overlying and bonded to at least one face of the core layer, said capstock composition comprising a second thermoplastic polymer and containing a plurality of discrete particles immiscible with, and dispersed in, the second thermoplastic polymer, the discrete particles having a diameter between 20 and 80 microns, and being dispersed in the second thermoplastic polymer in an amount of about 1 to about 30% by weight, and said capstock composition having a thickness of from 150 to 400 microns.  
   
   
       43 . A plastic sheet product having a matte finish and improved abrasion resistance and weathering comprising a core layer of a first thermoplastic polymer and two layers of a capstock composition overlying and bonded to both top and bottom faces of the core layer, said capstock composition comprising a second thermoplastic polymer and containing a plurality of discrete particles immiscible with, and dispersed in, the second thermoplastic polymer, the discrete particles having a diameter between 20 and 80 microns, and being dispersed in the second thermoplastic polymer in an amount of about 1 to about 30% by weight, and said capstock composition having a thickness of from 150 to 400 microns.  
   
   
       44 . The plastic sheet product of  claim 42  wherein the first thermoplastic polymer and the second thermoplastic polymer are independently selected from the group consisting of polyethylenes, polypropylenes, ethylene-propylene copolymers, ethylene vinyl acetate copolymers, ethylene methacrylate copolymers, ethylene-ethacrylate copolymers, ethylene-methylmethacrylate copolymers, ethylene vinyl acetate methylmethacrylate copolymers, polyvinyl chloride, acrylonitrile-styrene copolymers, polystyrenes, styrene methylmethacrylate copolymers, polyethylene acrylates, polymethylmethacrylates, methylmethacrylate copolymers, polyethylene terepthalates, polyamides, polycarbonates, polyurethanes, and silicone resins.  
   
   
       45 . The plastic sheet product of  claim 42  wherein the capstock composition is bonded to only one face of the core.  
   
   
       46 . The plastic sheet products of  claim 42  wherein the first and second thermoplastic polymers comprise a methylmethacrylate copolymer.  
   
   
       47 . The plastic sheet product of  claim 42  wherein the core layer has a thickness of 1.5 to 13 mm.  
   
   
       48 . The plastic sheet product of  claim 42  wherein the particles are dispersed in the second thermoplastic polymer in an amount of 22 to 26% by weight.  
   
   
       49 . The plastic sheet product of  claim 42  wherein the particles are comprised of spherical, crosslinked, polymeric beads 20-80 microns in diameter.  
   
   
       50 . The plastic sheet product of  claim 42  wherein the first thermoplastic polymer and the second thermoplastic polymer are transparent.  
   
   
       51 . The plastic sheet product of  claim 42  wherein the second thermoplastic polymer is the same as the first thermoplastic polymer.  
   
   
       52 . The plastic sheet product of  claim 43  wherein the first and the second thermoplastic polymer comprise a copolymer of methyl methacrylate and methyl acrylate.  
   
   
       53 . The plastic sheet product of  claim 42  wherein the copolymer comprises about 80 to about 98 wt. % methyl methacrylate and from about 2 to about 20 wt. % methyl acrylate.  
   
   
       54 . The plastic sheet product of  claim 53  wherein the copolymer comprises 93% to 97% by weight methyl methacrylate and 3% to 7% by weight methyl acrylate.  
   
   
       55 . The plastic sheet product of  claim 42  wherein the first and second thermoplastic polymers have weight average molecular weights in the range of 125,000 to 150,000.  
   
   
       56 . The plastic sheet product of  claim 43  wherein the core layer has a thickness of about 2 to about 13 mm.  
   
   
       57 . The plastic sheet product of  claim 42  wherein the core layer has a thickness of about 4 to 10 mm.  
   
   
       58 . The plastic sheet product of  claim 42  wherein the particles have particle size diameters in the range of 30 to 50 microns.  
   
   
       59 . The plastic sheet product of  claim 43  wherein the particles are dispersed in the second thermoplastic polymer in an amount of about 22 to about 26% by weight.  
   
   
       60 . The plastic sheet product of  claim 42  wherein the refractive indices of the particles and the second thermoplastic polymer are in the range of about 1:40 to about 1:65.  
   
   
       61 . The plastic sheet product of  claim 60  wherein the refractive indices of the particles and the second thermoplastic polymer are in the range of about 1.49 to about 1.55.  
   
   
       62 . The plastic sheet product of  claim 42  wherein the refractive index of the particles differs from the refractive index of the second thermoplastic polymer by a value in the range of about 0.001 to about 0.030.  
   
   
       63 . The plastic sheet product of  claim 62  wherein the refractive index of the particles differs from the refractive index of the second thermoplastic polymer by a value in the range of 0.005 to 0.020.  
   
   
       64 . The plastic sheet product of  claim 42  wherein the particles are selected from the group consisting of a polymer, and a pigment.  
   
   
       65 . The plastic sheet product of  claim 64  wherein the particles are comprised of a polymer selected from the group consisting of crosslinked polymethylmethyacrylate, crosslinked polymethylmethacrylate modified with an acrylate or methacrylate monomer, crosslinked copolymers of methylmethacrylate and styrene, silicone resins, and polyallyl methacrylates.  
   
   
       66 . The plastic sheet product of  claim 42  wherein the plastic sheet is formed by feedblock coextrusion of the core layer and the capstock composition.  
   
   
       67 . The plastic sheet product of  claim 64  wherein the pigment is selected from the group consisting of barium sulfate, silicon dioxide, aluminum oxide, aluminum hydroxide and calcium carbonate.  
   
   
       68 . The plastic sheet product of  claim 53 , wherein the copolymer comprises methyl methacrylate in an amount of about 94 to 96 wt. %.  
   
   
       69 . The plastic sheet product of  claim 42  wherein the core layer has a thickness of about 5 to about 8 mm.  
   
   
       70 . The plastic sheet product of  claim 42  wherein one capstock layer has a thickness of from about 200 to about 275 microns.  
   
   
       71 . The plastic sheet product of  claim 42  wherein the particles immiscible in the second thermoplastic polymer are present in the amount of about 10 to 30 wt. %.  
   
   
       72 . The plastic sheet product of  claim 71  wherein the particles immiscible in the second thermoplastic polymer are present in the amount of about 18 to 28 wt. %.  
   
   
       73 . The plastic sheet product of  claim 42  wherein at least about half the particles have particle size diameters greater than about 30 microns and at least about half of the particles have particle size diameters less than about 50 microns in diameter.  
   
   
       74 . The plastic sheet product of  claim 62  wherein the difference in the refractive index values of the particles and the second thermoplastic polymer is about 0.015 to about 0.035.  
   
   
       75 . The plastic sheet product of  claim 42  having a Half Angle of from about 5° to about 10°.  
   
   
       76 . The plastic sheet product of  claim 42  having a Half Angle of from about 7° to about 9°.  
   
   
       77 . The plastic sheet product of  claim 42  having a Diffusion Factor ranging from about 2 to about 10.  
   
   
       78 . The plastic sheet product of  claim 77  having a Diffusion Factor ranging from about 3 to about 9.  
   
   
       79 . The plastic sheet product of  claim 78  having a Diffusion Factor ranging from about 4 to about 7.  
   
   
       80 . The plastic sheet product of  claim 42  that when tested in accordance with the ASTM D 1003 “Test Method for Haze and Luminous Transmittance of Transparent Plastics” using a GretagMacBeth Color Eye-7000A spectrophotometer using Illuminant C and a 2° observer demonstrates transmission of light of at least about 92%.  
   
   
       81 . The plastic sheet product of  claim 42  that when tested in accordance with ASTM D 523 “Test Method for Specular Gloss” using BYK-Gardner micro-TRI-gloss (20°, 60° and 85°) with a black felt backing demonstrates gloss at 20° of about 0.5 to 1.0, demonstrates gloss at 60° of about 5 to about 7, and demonstrate gloss at 85° of about 1 to about 6.