Patent GB-1368785-A (GB)
Title: Process and apparatus for forming laminates
IPC: C03C27/12
Filed: 1971-12-08
Abstract: 1368785 Laminating process and apparatus GLAVERBEL 8 Dec 1971 [3 March 1971] 57079/71 Heading B5N A process for forming a laminate by heating an assembly comprising at least two sheets 18, 19 of glass or of vitrocrystalline material formed by subjecting glass to a thermal treatment to induce the formation of one or more crystalline phases therein and an intervening thermoplastic layer 20 between the or each adjacent pair of sheets to soften or melt the thermoplastic layer(s) and subjecting the assembly to heat and pressure conditions to firmly bond the sheets by means of the thermoplastic layer(s) is characterized in that there is assembly means 17 which envelopes at least the edges thereof, to define with such edges, a space within which subatmospheric pressure can be created for subjecting the inter sheet spaces to suction at said edges, and that in a preliminary treatment stage before the assembly is subjected to said firm bonding conditions, the assembly is exposed to sub-atmospheric environmental pressure acting upon at least one of the main external faces of the assembly while the assembly is exposed to heat in a treatment chamber and the inter-sheet spaces are subjected to said suction produced by sub-atmospheric pressure within the spaces around the edges of the assembly. An apparatus for use in forming a laminate, comprises at least two chambers 2, 3, 4 into which an assembly of sheets 18, 19 for forming a laminate can be introduced in succession, at least one of the chambers 2 being associated with means, e.g. vacuum pump 14 for producing sub-atmospheric environmental pressure therein, means, e.g. roller conveyer 9 for conveying an assembly from one chamber to another, sealing means, e.g. endless flexible sealing tube 17 which is open at its inner periphery for enclosing the edges of an assembly to define a space around the edges and associated with means, e.g. vacuum pump 15 for producing a sub-atmospheric pressure in the space around the edges for subjecting the inter-sheet spaces to suction while the assembly is in a chamber at sub-atmospheric environmental pressure, and means for heating an assembly to a predetermined schedule. In the apparatus, the chambers 2, 3, 4 are formed by division of the enclosure 1 by partitions 5 and 6 respectively controlled by automatic mechanisms 7 and 8, the compartments 2 and 3 being provided with heating elements 10,11, 12 and 13. In operation of the apparatus, the sealing tube is fitted around the margin of the assembly which is placed on carriage 21 and conveyed into chamber 2 which is maintained by heating elements 10 and 11 at about 100‹C., the vacuum pump 14 being operated to reduce the environmental pressure to not more than 400 mm. of mercury, the pump 15 reducing the pressure within the tube 17 and 30 mm. of mercury, the assembly being progressively heated to 80‹ C. at which temperature the pre-bonding stage is commenced by increasing the environmental pressure within chamber 2 to atmospheric. When the assembly reaches a temperature of 100‹ C., the conduit 16 is disconnected from the tube 17 and the assembly subjected to atmospheric pressure, the partition 5 is then opened and the carriage and assembly moved into compartment 3 where the temperature of the assembly is raised by heating elements 12 and 13 to 140‹ C., the partition 6 then being opened and the assembly moved to chamber 4 where it is progressively cooled. Figure 3 shows an alternative means for forming the inter-sheet spaces, the means comprising an envelope 20 which encloses the whole assembly and is connected by line 26 to vacuum pump 27. The thermoplastic layer may be polyvinyl butyral, polyvinyl chloride, a polyolefine, an acrylic resin or a silane.