Patent GB-648859-A (GB)
Title: Improvements in or relating to the stiffening of shoes
IPC: A43B23/16
Filed: 1947-12-06
Abstract: A shoe stiffener comprises a thermoplastic resinous material which is plasticized sufficiently to be easily shaped at room temperature and a substance which, on heating and cooling, undergoes a change to stiffen the stiffener.  The thermoplastic resinous material is preferably a synthetic resin stiff at room temperature in the unplasticized state, examples being a vinyl chloride/vinyl acetate copolymer or a cellulose derivative, such as a cellulose ester or ether.  The substance which is mixed with this resin is from 5-75 per cent by weight of the resin and is preferably a compatible substance which acts to, at least in part, plasticize the resin and can be polymerized under heat to stiffen p  the stiffener.  It should contain the polymer-forming group >C=CH2, and at least one other polymer-forming olefinic group so separated therefrom that two double bonds do not form a conjugate system.  Examples are: (a) a divinyl or diallyl ester of a polybasic acid, e.g. diallyl phthalate; (b) an acrylic, or substituted acrylic ester of a polyhydric alcohol, e.g. polyethylene glycol 200 dimethacrylate; (c) a divinyl aromatic compound, e.g. divinyl benzene; and (d) a vinyl or allyl ester of an acid which already contains an olefinic double bond, e.g. acrylic or crotonic acid.  In addition, further substances may be added to the stiffener means, for example a further plasticizer (5-20 per cent by weight of the resin) to minimize brittleness of the stiffened stiffener, e.g. a high boiling point ester, e.g. trioctyl phosphate or tricresyl phosphate, or a synthetic elastomer.  Also a polymerization catalyst, e.g. benzoyl peroxide or di-t-butyl peroxide, and a mineral filler, e.g. titanium dioxide, may be included.  One method of forming the stiffener is to mill the substances together and to form sheets of appropriate thickness.  In this case the thermoplastic resin must have a softening point about 15 DEG  F. below that at which any polymerization will take place. Alternatively, a solvent may be used to assist milling or a solvent, e.g. acetone, may be used to dissolve the milled resin and polymerizing substance, the resultant solution being employed to impregnate a fabric base. Specification 595,140 is referred to.ALSO:Textile fabric for use as shoe stiffeners is impregnated with a thermoplastic resinous material which is plasticized sufficiently to be easily shaped at room temperature and a substance which on heating and cooling undergoes a change to stiffen the stiffener. The thermoplastic resin is preferably a synthetic resin which is stiff at room temperature in the unplasticized state, examples being a vinyl resin such as vinyl chloride/vinyl acetate copolymer or a cellulose derivative such as a cellulose ester or ether.  The substance which is mixed with this resin is from 5-75 per cent by weight of the resin and is preferably a compatible substance which acts to plasticize the resin and which can be polymerized under heat to stiffen the stiffener.  It should contain the polymer-forming group >C=CH2, and at least one other polymer-forming olefinic group so separated therefrom that two double bonds do not form a conjugate system. Examples are (a) a divinyl or diallyl ester of a polybasic acid (e.g. diallyl phthalate); (b) an acrylic, or substituted acrylic ester of polyhydric alcohol (e.g. polyethylene glycol 200 dimethacrylate); (c) a divinyl aromatic compound (e.g. divinyl benzene); and (d) vinyl or allyl ester of an acid which already contains an olefinic double bond (e.g. acrylic or crotonic acid).  In addition, further substances may be added to the stiffener means, for example a further plasticizer of 5-20 per cent by weight of the resin to minimize brittleness of the stiffened stiffener, e.g. a high boiling-point ester or a synthetic elastomer, e.g. trioctyl phosphate or tricresyl phosphate or a synthetic elastomer.  Also a polymerization catalyst, e.g. benzoyl peroxide or di-t-butyl peroxide, and a mineral filler, e.g. titanium dioxide, may be included.  One method of forming the stiffener is to mill the substances together and to form sheets of appropriate thickness. In this case the thermoplastic resin must have a softening point about 15 DEG  F. below that at which any polymerization will take place.  Alternatively, a solvent may be used to assist milling or a solvent, e.g. acetone, may be used to dissolve the milled resin and polymerizing substance, the resultant solution being employed to impregnate a fabric base.  Specification 595,140 is referred to.