Patent GB-808679-A (GB)
Title: Method of shaping foamed rubber latex
IPC: B29C67/24
Filed: 1956-09-10
Abstract: <PICT:0808679/IV (a)/1> <PICT:0808679/IV (a)/2> <PICT:0808679/IV (a)/3> A method of continuously shaping foamed rubber comprises passing stiffened but ungelled foamed natural or synthetic rubber latex under a shaping means, gelling and vulcanizing the shaped mass. Foamed latex 11 is discharged through an opening 9 of a hopper 10 on to a sheet of fabric 6 fed from a roll 7 on to a conveyer belt 3 driven by rollers 4, 5.  A doctor blade 12 with arcuate cut-outs 13 shapes the moving rubber before it passes under a gelling chamber 19 and a curing chamber 20.  The fabric 6 bonds to the rubber.  The hopper 10 may be replaced by a transversely travelling hose.  The foamed latex may be further shaped by oscillating the doctor blade 12 transversely of the direction of movement of the latex, or another forming means may oscillate transversely to break the pattern formed by the doctor blade 12. Alternatively the doctor blade 12 may be used in conjunction with a shaped conveyer belt 16 (Fig. 3) to form another configuration of rubber.  The foamed rubber latex is compounded so that after shaping it is form-retaining until it is gelled and cured.  A preferred manner of compounding the latex is to add a primary stiffening agent prior to foaming, then to add a secondary stiffening agent after frothing to obtain the correct consistency for form-retention.  The primary stiffening agent may be selected from water-soluble proteins, such as soya bean protein, egg albumin, h moglobin, casein and gelatine, sodium alginate, ammonium alginate, locust bean gum, gum tragacanth and bean albumin.  These may be used singly or in combination.  The secondary stiffening agent may be an alkali polyacrylate such as sodium or ammonium polyacrylate, but other secondary stiffening agents such as carboxy-alkyl celluloses, e.g. carboxy-methyl cellulose or polyvinyl alcohol may be used.  In addition to the primary and secondary stiffening agents a heat-sensitive stiffening agent such as polyvinyl methyl ether may be used. Other heat-sensitive stiffening agents which may be used include the half amide of the reaction product of methyl vinyl ether and an anhydride such as maleic anhydride or ammonium maleamate as well as cellulose ethers such as methyl cellulose.  The synthetic rubber latex may be selected from aqueous emulsion polymerizates of various diene hydrocarbons such as butadiene - 1,3, methyl - 2 - butadiene - 1,3 (isoprene), 2,3 - dimethylbutadiene - 1,3, pentadiene - 1,3 (piperylene), and 2 - chlorobutadiene-1,3, or of a mixture of a diene hydrocarbon such as butadiene-1,3 and another polymerizable compound, especially a monomer containing a vinyl group, e.g. styrene, vinyl toluene, alpha-methyl styrene, and vinyl naphthalene, acrylic acid, methyl acrylate, methyl methacrylate acrylonitrile, methacrylonitrile and methacrylamide, methyl vinyl ether, methyl vinyl ketone, and vinylidene chloride. In one of the examples 100 parts of a latex of butadiene-styrene copolymer was compounded with minor amounts of potassium soap of castor oil, sodium rosinate, zinc diethyldithiocarbamate, zinc mercaptobenzothiazole, sulphur, commercial mixture of alkylated phenols and soya bean.  There was then added after frothing sodium polyacrylate, zinc oxide, diphenyl guanidine and potassium silico fluoride.