Patent GB-764605-A (GB)
Title: Production of polymeric-ª -chloroacrylate sheets
IPC: B29D7/01
Filed: 1954-05-27
Abstract: In a method of producing a polymeric a -chloroacrylate sheet there is supported in inclined position on a flat rigid member a casting cell composed of upper and lower flat cell walls edge-sealed and with peripheral spacers, the upper wall being relatively thin and flexible, the cell is filled through an opening in the upper part of the edge seal with enough liquid a -chloroacrylic acid ester monomer to fill the cell completely when the walls are parallel, a second flat rigid member is forced on the upper cell wall so that it is substantially parallel with the lower cell wall and the opening is sealed when the level of the monomer is adjacent to it.  A gas escape opening is provided in the top part of the edge seal when the flat rigid member has been forced on the cell wall.  The monomer is then subjected to gelling conditions, the two flat rigid members are removed, the thickness of the spacers is reduced to compensate for shrinkage during polymerization and the gell is subjected to further polymerizing conditions.  The preferred material for the cell walls is glass, though certain metals, woods and resinous materials may be used.  Suitable materials for the rigid members are plywood, metal and composition board.  A preferred inclination of the cell during filling is 1/2 in. to 2 in. for each 12 in. of cell length.  The casting cell is level during the polymerization step following the gelling of the monomer, to prevent warping, and its surfaces should be straight and not excessively curved.  The amount of monomer required to fill the casting cell is pre-calculated, and the opening through which it is poured is sealed immediately afterwards by a piece of filter paper coated with adhesive.  The gas escape may be a pin hole made in the edge seal, which is of paper, flexible tubing or other suitable material.  After the cell has been filled the top flat rigid member is placed in position and the two rigid members are drawn together, e.g. by spring clamps placed around the periphery of the casting cell.  The gas escape pin hole is then sealed in the same way as the filling hole.  The gelling conditions may include gentle heating, ultra violet irradiation, the use of a catalyst, e.g. dibutyl tin diacetate and/or di-tert-butyl peroxide, or all three, and the gelling and polymerizing conditions must be so controlled that overheating due to too rapid polymerization is avoided.  With catalysts as mentioned three hours at room temperature is sufficient for gelling, but longer periods, up to 48 hours, are required under some conditions.  To prevent premature gelling due to contact of the monomer with air, the cell may first be filled with an inert gas such as nitrogen.  The monomer is also preferably kept cool, e.g. at a temperature from 0 DEG  to -35 DEG C., up to the time of pouring. It may first be purified by careful fractional distillation, by P2O5 treatment and flask vacuum distillation, or by steam distillation from a dehydrohalogenation treatment.  The spacers between the cell plates must be such as to allow for shrinkage during subsequent polymerization, and it is preferred to use spacers of a material which may be melted before it takes place, a suitable alloy being 80 per cent Wood's metal and 20 per cent mercury which is melted by infra-red heating or by a short heating step in the oil bath which is used for the polymerization heating.  Preferably the spacers are wrapped in small bags of regenerated cellulose material to prevent contamination of the monomer and to provide sufficient space for them on melting. Polymerization takes place, with the rigid members removed, and may occupy 12 to 18 hours, although periods up to 6 days have been employed.  The invention is advantageous for methyl a -chloroacrylate and is useful for other esters of a -chloroacrylic acid mentioned in the Specification. Specification 758,136 is referred to.