Patent GB-617087-A (GB)
Title: Improvements in or relating to the manufacture of material for producing microporous articles
IPC: C08J9/26
Filed: 1946-03-04
Abstract: Solid stock moulding compositions suitable for manufacture of moulded microporous products consists of a vulcanisable natural rubber or rubber-like material and microscopic granules of a soluble filler which is unaffected by vulcanising and moulding and is removable by leaching thereafter.  It is prepared by dissolving the rubber in an evaporable solvent inert to the filler, mixing the filler therein in an amount proportional to the amount of rubber that gives contact of the granules after vulcanisation whilst leaving a continuous rubber phase, and then evaporating the solvent before any gravitational settlement of the granules occurs.  The mixing may be carried out under non-evaporating or evaporating conditions, in the latter case the rubber solution being maintained at a viscosity which ensures a thorough mix, e.g. by the introduction of additional solvent.  The solid stock is obtained by evaporation of the solvent from the mixture after casting in shallow trays or a tube may be built upon a core by repeated dipping and drying.  Preferably the filler granules do not exceed 100 mesh and the amount used is such as constitutes 42-74 per cent by volume of the moulded product.  In an example a rubbery butadiene-acrylonitrile copolymer is dissolved in a mixture of acetone, methyl ethyl ketone and toluene, sodium nitrate filler is added and the mixture beaten to a smooth slurry which is dried in shallow open moulds.  The dried cast product is stable and may be stored for future use.  When required it may be cut to fit the mould accurately.ALSO:Solid stock moulding compositions suitable for manufacture of moulded microporous products consists of a vulcanizable natural rubber or rubber-like material and microscopic granules of a soluble filler which is unaffected by vulcanizing and moulding and is removable by leaching thereafter.  it is prepared by dissolving the rubber in an evaporated solvent inert to the filler, mixing the filler therein in an amount proportional to the amount of rubber that gives contact of the granules after vulcanization whilst leaving a continuous rubber phase, and then evaporating the solvent before any gravitational settlement of the granules occurs.  The mixing may be carried out under non-evaporating or evaporating conditions, in the latter case the rubber solution being maintained at a viscosity which ensures a thorough mix, e.g. by adding additional solvent.  The solid stock is obtained by evaporation of the solvent from the mixture after casting in shallow trays or a tube may be built upon a core by repeated dipping and drying.  Preferably the filler granules do not exceed 100 mesh and the amount used is such as constitutes 42 - 74 per cent by volume of the moulded product.  In an example a rubbery butadiene-acrylonitrile copolymer is dissolved in a mixture of acetone, methyl ethyl ketone and toluene, sodium nitrate filler is added and the mixture beaten to a smooth slurry which is dried in shallow open moulds.  The dried cast product is stable and may be stored for future use.  When required it may be cut to fit the mould accurately.