Patent GB-580822-A (GB)
Title: Improvements relating to the application of coating compositions to sheet materials
IPC: D06N3/06
Filed: 1944-04-06
Abstract: Coating compositions for applying to sheet material such as textile fabrics comprise at least one higher polymer in a finely divided state, or in a state of reduced cohesion if preplasticized material is used, mixed with at least one lower polymer (the two polymers belonging to the same homologous series or being mutually soluble or compatible) and any necessary fillers, plasticizers or compounding agents, the mixture being applied either by means of a volatile solvent for the lower polymer in which the higher polymer remains dispersed undissolved, or by means of heat and pressure sufficient to cause plastic flow of the lower polymer but insufficient fully to gelatinize or soften the higher polymer, the coated material being finally subjected to a heat treatment sufficient to soften both polymers. The lower polymer may comprise 15-80 per cent. and the higher polymer 85-20 per cent. by weight of the mixture although proportions of 20-45 per cent. and 80-55 per cent. respectively are preferred.  In one example, polyvinyl chloride-acetate having a molecular weight of 24000 and a similar polymer having a M.W. of 10,000 are mixed with tricresyl phosphate, dibutyl phosphate, castor oil, zinc oxide, lithopone, china clay and colouring matter. Methylisobutylketone may be the solvent used for spreading, or alternatively the mixture is worked without a solvent at 40-50 DEG C. The final heat cure is at 145 DEG C. for 1 hour. In a second example, polyvinyl chloride and polymethylmethacrylate are mixed with plasticizers, calcium stearate, whiting, talcum and colouring matter, and applied at 95 DEG C. without a solvent to fabric to produce leather cloth.  A final stoving at 150 DEG C. is given.  In preparing the compositions either a wet or dry method may be used.  In the former, the lower polymer is dissolved in a solvent and the other constituents mixed in a paste and stirred in with a mechanical mixer. In the dry method, the materials are mixed and sheeted in a rubber mixing mill at the suitable temperature.  When the higher polymer is in its preplasticized form it is reduced in cohesion by mechanical working as the temperature is gradually reduced.  In an example, polyvinyl chloride-acetate is mixed with china clay after treatment in the sheeting mill at 120 DEG C., the machine being cooled whilst still masticating the sheet over a period of 20 to 30 minutes.  A separate batch of polymethyl methacrylate is made and the first batch returned to the mill, the two being blended together at 70 DEG C. until smooth.  The composition may be applied by means of a solvent such as butyl acetate, and the cohesion restored to the polymer by heat treatment at 150 DEG C.  A composition containing two each of the higher and lower polymers comprises polyvinyl chloride (mol weight 18,000), polyvinyl chloride acetate (mol weight 24,000), polyvinyl chloride acetate (mol weight 6,000) plasticized with 30 per cent. dibutyl phthalate, polymethyl methacrylate containing 50 per cent. dibutyl phthalate. dibutyl phthalate, ethyl palmitate, lead stearate and colouring matter.ALSO:Coating compositions for applying to sheet material such as textile fabrics comprises at least one higher polymer in a finely divided state, or in a state of reduced cohesion if preplasticised material is used, mixed with at least one lower polymer (the two polymers belonging to the same homologous series or being mutually soluble or compatible) and any necessary fillers, plasticisers or compounding agents, the mixture being applied either by means of a volatile solvent for the lower polymer in which the higher polymer remains dispersed undissolved, or by means of heat and pressure sufficient to cause plastic flow of the lower polymer but insufficient fully to gelatinize or soften the higher polymer, the coated material being finally subjected to a heat treatment sufficient to soften both polymers. The lower polymer may comprise 15-80 per cent and the higher polymer 85-20 per cent by weight of the mixture although proportions of 20-45 per cent and 80-55 per cent respectively are preferred.  In one example, polyvinyl chloride-acetate having a molecular weight of 24,000 and a similar polymer having a molecular weight of 10,000 are mixed with tricresyl phosphate, dibutyl phosphate, castor oil, zinc oxide, lithopone, china clay and colouring matter.  Methyl isobutyl ketone may be the solvent used for spreading or alternatively the mixture is worked without a solvent at 40-50 DEG  C.  The final heat cure is at 145 DEG C. for 1 hour.  In a second example, polyvinyl chloride and polymethylmethacrylate are mixed with plasticisers, calcium stearate, whiting, talcum and colouring matter, and applied at 95 DEG  C. without a solvent to fabric to produce leather cloth.  A final stoving at 150 DEG  C. is given.  In preparing the compositions either a wet or a dry method may be used.  In the former, the lower polymer is dissolved in a solvent and the other constituents mixed in a paste and stirred in with a mechanical mixer.  In the dry method, the materials are mixed and sheeted in a rubber mixing mill at the suitable temperature.  When the higher polymer is in its pre-plasticised form, it is reduced in cohesion by mechanical working as the temperature is gradually reduced.  In an example, polyvinyl chloride-acetate is mixed with china clay after treatment in the sheeting mill at 120 DEG  C., the machine being cooled whilst still masticating the sheet over a period of 20 to 30 minutes.  A separate batch of polymethyl methacrylate is made and the first batch returned to the mill, the two being blended together at 70 DEG  C. until smooth.  The composition may be applied by means of a solvent such as butyl acetate, and the cohesion restored to the polymer by heat treatment at 150 DEG  C.  A composition containing two each of the higher and lower polymers comprises polyvinyl chloride (mol. weight 18,000), polyvinyl chloride-acetate (mol. weight 24,000), polyvinyl chloride-acetate (mol. weight 6,000) plasticised with 30 per cent dibutyl phthalate, polymethyl methacrylate containing 50 per cent dibutyl phthalate, dibutyl phthalate, ethyl palmitate, lead stearate and colouring matter.