Patent GB-687976-A (GB)
Title: Improved curing process for thermosetting resinous coatings
IPC: B05D3/04
Filed: 1950-10-13
Abstract: <PICT:0687976/IV (a)/1> Thermosetting resinous varnish binders or coatings, e.g. on electrical apparatus, are cured by exposure to the vapour of a liquid, boiling (at the pressure of the curing operation) at a temperature in the curing range and which is a non-solvent for the resin.  The latent heat of condensation of the vapour effects the curing.  Suitable varnishes mentioned are based on phenol aldehyde resins, oil-modified phenol aldehyde resins, alkyd resins, or allyl phthalate.  Vapours used may be of light mineral oil (10 per cent distilling at 340 DEG  C. and 90 per cent 350 DEG  C.) under reduced pressure to cause it to boil at 140-160 DEG  C., xylene, butyl stearate, tetrachloroethylene, or the naphthas (if desired with reduced pressure).  The article 1 with the coating to be cured (e.g. an electric coil) is placed on a perforated stand 4 in a tank 2 with cover 3.  Liquid 5 may be supplied by pipe 9 and drawn off by pipe 10 and is heated by pipes 6 in which heating fluid is circulated by pipes 7, 8.  Vapour fills tank 2 and excess passes to condenser 12 and receiver 13.  A vacuum pump (not shown) may be provided and vapour-sealed openings may permit resin-treated sheet material to be fed through the tank.  Examples are described of the curing of varnish - impregnated, paper-insulated coils, using phenol-formaldehyde varnish with vapours, at reduced pressure, of light mineral oil, or with such vapours followed by petroleum naphtha vapour; and using an oil-modified phenolic varnish with light oil vapour at reduced pressure.  A cycle of alternating high and low pressure is applied to the coils immersed in the varnish for impregnating them.  The electrical properties are compared with those of coils coated with a normally baked varnish. When two vapours are used in succession, the second may be one which would dissolve the uncured resin but does not dissolve the partially cured resin.ALSO:<PICT:0687976/III/1> Thermosetting resinous varnish binders or coatings, e.g. on electrical apparatus are cured by exposing to the vapour of a liquid, boiling (at the pressure of the curing operation), at a temperature in the curing range and which is a non-solvent for the resin.  The latent heat of condensation of the vapour effects the curing.  When the treated article reaches the temperature of the vapour, further condensation is only sufficient to replace heat of curing and of volatilisation of solvents and moisture from the coating.  Suitable varnishes mentioned are based on phenol aldehyde resins, oil modified phenol aldehyde resins, alkyd resins, or allyl phthalate.  Vapours used may be of light mineral oil (10 per cent distilling at 340 DEG C and 90 per cent at 350 DEG C), under reduced pressure to cause it to boil at 140-160 DEG C, xylene, butyl stearate, tetrachloroethylene, or the naphthas (if desired with reduced pressure).  The article 1 with the coating to be cured, e.g. an electric coil is placed on a perforated stand 4 in a tank 2 with cover 3.  Liquid 5 may be supplied by pipe 9 and drawn off by pipes 6 in which heating fluid is circulated by pipes 7, 8.  Vapour fills tank 2 and excess passes to condenser 12 and receiver 13.  A vacuum pump (not shown), may be provided and vapour-sealed openings may permit resin-treated sheet material to be fed through the tank. Examples are described of the curing of varnish impregnated, paper-insulated coils, using phenol-formaldehyde varnish with vapours at reduced pressure of light mineral oil, or with such vapours followed by petroleum naphtha vapour; and using an oil-modified phenolic varnish with light oil vapour at reduced pressure.  A cycle of alternating high and low pressure is applied to the coils immersed in the varnish for impregnating them.  The electrical properties are compared with those of coils coated with a normally baked varnish. When two vapours are used in succession, the second may be one which would dissolve the uncured resin but does not dissolve the partially cured resin.