GB664527A - Improvements in or relating to heat-hardenable phenol-formaldehyde resinous compositions - Google Patents

Abstract

Improved heat hardenable phenol-formaldehyde "A" stage resins suitable for use in impregnating paper, fabrics, wood, &c. for making laminates are obtained by condensing 1-1.8 mols. formaldehyde with 1 mol. of a mixture comprising phenol and a monobutyl phenol having two active nuclear positions, the proportions of phenol to mono butyl phenol being such that the total average active positions on the phenolic nuclei is between 2.3-2.8, the reaction being initiated under alkaline or acid conditions but being always completed under alkaline conditions. Improved plasticity of the resin is obtained by including in the mix a proportion of a dibutyl phenol free from other substituents and having one unsubstituted ortho or para reactive position. The proportion of dibutyl phenol should not exceed 0.35 mol. per mol. monobutyl phenol, which may be normal, iso, secondary, or tertiary. A ternary graph is given showing the preferred proportion of the phenolic mixtures which are 0.30-0.50 p-monobutyl phenol, 0.04-0.20 mols. o-monobutyl phenol, and 0.07-0.14 mols. dibutyl phenol per mol. phenol. Punching properties of the laminates are improved by including in the composition thermoplastic materials, e.g. polyvinyl acetate, cellulose acetate and ethyl cellulose or rosin. The compositions are dissolved in solvents, e.g. alcohols or ketones and improved impregnation is obtained by addition of water up to 10 per cent by weight of resin in solution. Conventional catalysts for making "A" stage resins are employed. Progressive reaction may be obtained by initiating the reaction with the slower acting phenols, e.g. the dibutyl phenols and then adding successively the faster reacting phenols and concluding with the addition of phenol itself. The "A" stage resins are dehydrated by decantation and distillation followed by neutralization before dissolution in solvents; they may be plasticized by addition of alkyl abietates, phthalates, tricresyl phosphate, &c. In examples: (1) A mixture of 47,8 parts phenol, 15.5 parts o-tert butyl phenol, 20 parts p-tert butyl phenol, 15 parts di-tert. butyl phenol and 64 parts 37 per cent formalin and 4.5 parts hexa was refluxed at 100 DEG C. for 1 hour, the resulting "A" stage resin was dehydrated to a water content of 3-5 per cent and the reaction continued until a product was obtained having a gelation speed of 180-300 seconds on a hot plate at 160 DEG C. This was dissolved in ethyl alcohol and used to impregnate rag paper which was dried and laminated. Varnishes were also made by dilution with water and addition of resin or polyvinyl acetate. Tables are given of (a) water absorption, (b) caustic absorption, (c) power factor, (d) dielectric constants, (e) loss factor, (f) impact strength, (g) bonding strength, (h) flexural strength, (g) hardness of the laminates obtained.