Process of forming a multi-ply laminate

Abstract

When forming a multi-ply laminate having at least one thermoplastic structural ply forming an outer ply of the laminate, known processes comprise degassing and bonding steps during which gas is removed from between assembled structural plies of the laminate and the plies are heated to cause them to bond together while a moulding plate is in contact with the or each exposed thermoplastic ply. In order to reduce or eliminate optical distortion in the laminate, which may be adapted to constitute a vehicle windshield, during the degassing step, the assembled plies are subjected to a sub-atmospheric environmental pressure having an absolute valve of 150 mm Hg or less while the inter-ply space or spaces are subjected to a sub-atmospheric pressure at the edges of the assembly to degas the assembly, said edge pressure and said environmental pressure are maintained at such values as to give rise to a separation of the plies which is attributable to the mean inter-ply gas pressure being higher than the environmental pressure while the assembly of plies is heated to a temperature below that at which effective adherence commences between the thermoplastic material and an adjacent ply, the degassed assembly remains subject to sub-atmospheric edge pressure while its temperature is increased past the temperature at which said effective adherence commences and the assembly is then subjected to a bonding step in which heat and pressure conditions are such as to cause the plies to bond firmly together.

Dependencies are inferred from the claim text.