| 摘要 |
1,081,689. Rigid polymeric sheets; blackboards. IMPERIAL CHEMICAL INDUSTRIES Ltd. Dec. 1, 1965 [Dec. 29, 1964], No. 52651/64. Heading B5A. [Also in Division B6] Rigid sheets of organic polymer suitable for use as blackboards are made by introducing into a flat casting cell a polymerizable liquid comprising a monomer containing a single CH 2 = C< group per molecule, and containing in suspension insoluble particles having a hardness of at least 3 on the Mohs' scale, preferably 600.-9, a concentration of from 0À02 to 2 cu. ins., preferably 0À1 to 0À5, in bulk form per sq. ft. of surface of the sheet formed in the cell, and a maximum linear dimension of 2-1000 Á, preferably 10-100 Á, supporting said cell in a horizontal position whereby said particles settle towards the lower casting surface which is a matt surface to form a concentrated layer adjacent thereto, and polymerizing the liquid in this position. The monomer may be methyl methacrylate or a mixture of at least 60% thereof with a copolymerizable compound containing a single ethylenically unsaturated group per molecule. The liquid may be in the form of a syrup consisting of a solution of the polymer in the monomer, and may have a viscosity of 0À1 to 10 poises, or may also contain up to 7% by wt. of a copolymerizable monomer containing at least two groups/molecule, to make the material less thermoplastic. The solid particles may be glass powder, pumice powder, silica powder, fine white sand, aluminium oxide, emery, garnet, silicon carbide or slate powder, and the refractive index thereof of the sodium D line preferably does not differ from that of the polymer by greater than 0À3. A small amount of dyestuff and/or pigment may be included in the liquid to impart desired colouring to the sheet. |
