Melt-processable thermoplastic compositions
A melt-processable thermoplastic composition is described, which comprises a) 50-99.5 wt. % of a melt-processable thermoplastic polymer and b) 0.5-50 wt. % of a particulate polymer comprising the residues of a monomer mixture comprising 50-100 wt. % of MMA, at least 0-50% of an ethylenically unsaturated comonomer comprising at least one alkyl acrylate or methacrylate and 0-10 wt. % of a copolymerisable cross-linking monomer said particles having a maximum dimension of 5 mm. The compositions have reduced surface gloss and may be useful for forming building components or in any other application in which a low gloss surface is required. A method of making the composition and its uses, for example its use as a capstock material, are also described.
1. A method of forming a sheet of a melt-processable thermoplastic composition having a first surface and second opposite surface wherein said first surface exhibits a lower gloss than said second surface, the method comprising extruding a melt-processable thermoplastic composition comprising:
(a) 50-99.5 wt % of a melt-processable thermoplastic polymer; and
(b) 0.5 to 50 wt % of a particulate polymer comprising a homopolymer of methyl methacrylate or a copolymer comprising the residues of a monomer mixture comprising at least 50 wt % methyl methacrylate and up to 50 wt % of a copolymerisable acrylic comonomer comprising at least one alkyl acrylate or methacrylate and 0 to 10 wt % of a copolymerisable cross-linking monomer, said particles having a maximum dimension of 5 mm;
and calendaring the extruded thermoplastic composition with calendaring rolls to form said sheet, whereby said first surface of the sheet contacts said calendar rolls for a shorter period of time than said second surface.
2. A method as claimed in claim 1 wherein said particulate polymer further includes at least 0.1 wt % to 10 wt % of a copolymerisable cross-linking monomer.
3. A method as claimed in claim 2 wherein the particulate polymer comprises a copolymer formed from the residues of a monomer mixture comprising 70 to 95 wt % methyl methacrylate, 5 to 30 wt % of said copolymerisable acrylic comonomer and 0.1 to 5 wt % of said copolymerisable cross-linking monomer.
4. A method as claimed in claim 3 wherein said copolymerisable acrylic comonomer of the particulate polymer comprises at least one alkyl acrylate.
5. A method as claimed in claim 4 wherein said alkyl acrylate is selected from the group consisting of ethyl acrylate or butyl acrylate.
6. A method as claimed in claim 3 wherein said copolymerisable acrylic comonomer is present in an amount of at least 12 wt % and less than 18 wt % of said particulate polymer.
7. A method as claimed in claim 2 wherein said particulate polymer comprises a copolymer comprising 5 wt % and less than 20 wt % of said copolymerisable acrylic comonomer and at least 0.3 wt % and 1 wt % or less of said copolymerisable cross-linking monomer.
8. A method as claimed in claim 1 wherein the particulate polymer comprises a copolymer and said copolymerisable acrylic comonomer comprises at least one alkyl acrylate.
9. A method as claimed in claim 8 wherein said alkyl acrylate is selected from the group consisting of ethyl acrylate or butyl acrylate.
10. A method as claimed in claim 8 wherein said copolymerisable acrylic comonomer is present in an amount of at least 12 wt % and less than 18 wt % of said particulate polymer.
11. A method as claimed in claim 1 wherein said particles have a maximum dimension which is less than 1 mm.
12. A method as claimed in claim 1 wherein the weight average diameter of said particles of the particulate polymer is less than 500 μm as measured in accordance with ASTM D1921.
13. A method as claimed in claim 1 wherein the weight average diameter of said particles of the particulate polymer is greater than 150 μm as measured in accordance with ASTM D1921.
14. A method as claimed in claim 1 wherein at least 20 wt % of said particles of the particulate polymer are between 60 (250 μm) and 80 (177 μm) mesh.
15. A method as claimed in claim 3 wherein said particulate polymer comprises a copolymer formed from the residues of a monomer mixture comprising at least 79.9 wt % methyl methacrylate.
16. A method as claimed in claim 7 wherein said particulate polymer comprises a copolymer formed from the residues of a monomer mixture comprising at least 79.9 wt % methyl methacrylate.
17. A method as claimed in claim 1 wherein said particulate polymer is present in an amount of at least 3 wt % and less than 20 wt % of said melt-processable thermoplastic composition.
18. A method as claimed in claim 1 wherein the melt-processable thermoplastic polymer forms a matrix and is a polymethyl methacrylate homopolymer or a copolymer derived from a monomer mixture comprising at least 60 wt % methyl methacrylate and up to 40 wt % of at least one other copolymerisable alkyl acrylate or methacrylate.
19. A method as claimed in claim 7 wherein the melt-processable thermoplastic polymer forms a matrix and is a polymethyl methacrylate homopolymer or a copolymer derived from a monomer mixture comprising at least 60 wt % methyl methacrylate and up to 40 wt % of at least one other copolymerisable alkyl acrylate or methacrylate.
20. A method as claimed in claim 1 wherein the melt-processable thermoplastic composition is formed by mixing said melt-processable polymer and said particulate polymer by extrusion under conditions such that said particles of the particulate polymer are broken down.
21. A method as claimed in claim 1 wherein a surface of the sheet formed of said melt-processable thermoplastic composition has a surface gloss measured at 75° observation angle (according to ASTM D3679) of less than 65.