Patent GB-1254654-A (GB)
Title: Impregnating varnishes
IPC: C08L79/08
Filed: 1970-03-31
Abstract: 1,254,654. Laminates. MONSANTO CO. 31 March, 1970 [1 April, 1969], No. 15164/70. Heading B5N. [Also in Divisions B2, C3 and D1] Laminates are formed from glass-cloth impregnated with a polyimide-forming composition Q. The cloth is dipped into Q, passed through squeeze-rollers, and heated to volatilize some of the solvent and form B-stage resin. The treated cloth has good handleability and drape, and is easily cut. 12 layers of the treated cloth are then layed-up into a laminate by conventional vacuum-bag methods, placed in a press, and heated and cooled under vacuum and under pressure. Q may also be used for impregnating and laminating woven and non-woven fibres, e.g. glass, carbon, graphite, boron, high-silica glass fibres, quartz, or asbestos. Composition Q comprises, in parts by wt.: (i) polyimide-forming mixture M, 100; (ii) amorphous SiO 2  0À25-20; (iii) organic solvent system O comprising (A) aliphatic alcohol, 14- 1833. (B) non-polar solvent, 8-1100. (C) polar solvent, 3-367. Mixture M comprises an aromatic tetracarboxylic acid dialkyl ester E, the alkyl gps each containing 1-6 C atoms, and a polyamine P having # 2 primary -NH 2  gps per molecule; there may be from 70% molar excess of P to 10% molar excess of E. (A) contains 1- 6 C atoms and has b.p. 60-120‹ C. (B) has b.p. 35-372‹ C. (C) has b.p. 120-300‹ C. Ester E may be  where R 1  is a C 1-6  alkyl, and R is isopropylidene, -CO-, -CH 2 -, -SO 2 -, C 1-6  alkylene or alkylidene, C 6-16  arylene, -NH-, S, where R 4  and R 5  are each substituted or unsubstituted hydrocarbyl groups, or a direct bond; or a group formed by condensation of a -COOH gp attached to each aromatic ring with an at least difunctional compound. Polyamines P include H 2 N-R 2 -NH 2 , where R 2  is aromatic, C #2  aliphatic, cycloaliphatic, combination of aromatic and aliphatic, or heterocyclic, or bridged aromatic in which two aromatic groups are linked by R 3 , being C 1-6  alkylene, O, C 6-15  arylene, -NH-, S, -SO 2 -, -CO-, (F), (G) (H) or (I). P may contain 3-6 amino gps. Preferably P is melamine or a diamine, preferably aromatic. P may include a mixture of polyamines. The SiO 2  particles have surface-area 50-500 m.<SP>2</SP>/g., ultimate non-agglomerate particle size 0À001-0À1 Ám., and bulk density 0À5-20 lb./ft.<SP>3</SP> In agglomerate form the SiO 2  passes a 20 mesh screen U.S.S.S. R.I. is preferably 1À45-1À47. In Q, there may be 3- 80% wt. M. There may be 0À5-20 parts by wt. SiO 2 , but up to 50% of this quantity of SiO 2  may be replaced by glycerol, polyalkylene glycol, polyoxyethylene glycol, alkylphenol polyalkoxy alkanols, or the mono-laurates, monopalmitate, monostearate, trioleate, or tristearate of polyoxyethylene sorbitan. (B) may be an aromatic hydrocarbon, alkane, petroleum fraction, or a chlorohydrocarbon. (C) may be an N-alkyl or N,N-dialkyl amides, N-alkyl lactams, N,N-dimethylmethoxyacetamide, dimethyl sulphoxide, or formamide. (A), (B), and (C) may each be mixtures. Also present in Q may be fillers, e.g. metal, glass, ceramic and synthetic resin particles. Dyes, antioxidants, and stabilizers may be included.