Patent GB-1000633-A (GB)
Title: Resinous sheet materials
IPC: B32B27/00
Filed: 1962-05-04
Abstract: A brominated epoxy resin, e.g. the polyglycidyl ether of 2,2-bis(4-hydroxy-3,5-dibromophenyl) propane, is made by dissolving 1 mol. of brominated bis-phenol A in 6.4 mols. of epichlorhydrin, adding alcohol sodium hydroxide gradually with heating, refluxing, filtering off precipitated salt, and removing volatiles by distillation.  A solution of the resin, used to impregnate fibrous sheets subsequently laminated, has added to it a latent hardener, such as 4-41-diaminodiphenyl sulphone, a polycarboxylic acid anhydride such as pyromellitic dianhydride or methyl-endomethylene-tetrahydrophthalic anhydride, dicyandiamide, boron trifluoride-monoethylamine or a similar boron trifluoride complex, or a tertiary amine, whereby the sheets may be stored at ambient temperature before lamination under heat and pressure. The brominated resin may have admixed with it a proportion of non-brominated similar resin, or of a phenolic-modified epoxy resin.ALSO:A flexible resinous sheet, capable of lamination, after storage, with similar sheets, comprises a fibrous layer saturated with a solvent-free resin composition comprising a polyglycidyl ether of a polynuclear phenol having a number of bromine atoms attached directly to the nuclear C atoms, and a latent hardening agent for the resin, i.e. one which permits storage of the sheet at ambient temperatures and subsequent curing under heat and pressure.  The brominated resin may be used with one less brominated or free from bromine atoms, the bromine content of the resin preferably being within the range 10-16%.  The preferred brominated resin is polyglycidyl ether of 2, 2-bis (4-hydroxy-3, 5-dibromo-phenyl) propane, and the preferred added resin is the corresponding non-brominated compound or a similar material modified with phenolic resin.  The fibrous layer may comprise glass fibre cloth or mat, a web of glass yarns or rovings in substantial parallel alignment, or a mat of polyethylene terephthalate fibres containing fibres oriented by drawing, and unoriented films fused together at their crossing points.  Glass fibre layers are preferably pre-sized with a vinyl-silane or a chrome-complex material.  Latent hardening agents usable include 4-41 diaminodiphenyl sulphone, polycarboxylic acid anhydrides such as pyromellitie dianhydride and methylendomethylene-tetrahydro-phthalic anhydride, dicyandiamide, boron trifluoride-monoethylanime and similar complexes, and tertiary amines; these are preferably used in amounts within one half to twice the stoichiometric quantity.  In examples (a) glass cloth was dip-coated with a solution in acetone of a mixture of the above mentioned brominated and non-brominated resins together with latent hardening agent, and was then dried for 5 minutes in air and 13 minutes at 165 DEG C. and wound up for storage; subsequently nine sheets were stacked and heavily pressed at 165 DEG C.  (b) Seven sheets of glass cloth similarly impregnated and dried were stacked with a sheet of lighter weight impregnated glass cloth on each side, and a sheet of electrolytically deposited copper foil, oxidized and coated with a phenol-aldehyde/polyvinyl butyral adhesive on its underside was superposed; the stack was then laminated as in (a). (c) A solution in toluene and methanol of the above-mentioned brominated resin, a non-brominated resin/phenolic resin mixture, and a -methylbenzyldimethylamine was used to impregnate, with subsequent drying, sheets of glass cloth and webs of oriented, and non-oriented and fusion-bonded, polyethylene terephthalate fibres, and a stack containing seven of the latter sheets interleaved with six of the former was hot pressed into a laminate.  The laminated products are characterized by flexibility, flame retardancy, and good electrical insulating and satisfactory dielectric constant properties, and may be used in making printed circuits.  Pigments, dyes, and additional flame retardant agents such as antimony trioxide or organic or inorganic phosphates may be included in the resin compositions, at the expense of the electrical and physical properties of the laminates.