United States Patent (19) (11) 3,904,558 Graham et al. (45) Sept. 9, 1975 54) PREPARATION OF LATEX FOAM Primary Examiner-Morton Foelak RUBBERS AND FILMS Attorney, Agent, or Firm-Stevens, Davis, Miller & 75 Inventors: Everett Steadman Graham; Ernest Mosher George Pole, both of Sarnia, Canada 73) Assignee: Polysar Limited, Sarnia, Canada 57 ABSTRACT An amine-sulfamate is added to a natural rubber latex (22) Filed: May 31, 1974 or a latex of a rubbery C-Co conjugated diene poly 21 Appl. No.: 474,962 mer in which the rubbery polymer particles are main tained in a dispersed state by an emulsifier which Related U.S. Application Data forms water-insoluble compounds on reaction with 63 Continuation-in-part of Ser. Nos. 372,502, June 22, zinc or cadmium ions to form a latex composition 1973, abandoned, and Ser. No. 372,521, June 22, which is suitable for use in the preparation of latex 1973, abandoned. foam rubbers and films. The composition is stable to storage at ambient temperatures for lengthy periods of 52 U.S. Cl...... 260/2.5 L; 260/2.5 H; 260/2.5 HB; time. To prepare the foam rubber, the amine-sulfa 260/4 R; 260/4 AR; 260/29.7 UA; 260/29.7 mate-containing latex is compounded with (1) a mate H; 260/723; 260/887; 260/890; 260/892; rial which supplies zinc or cadmium ions such as an 428/96; 428/315 oxide or carbonate of zinc or cadmium, (2) ammonia 51 Int. Cl... C08f 47/08; C08c 17/08; C08d 13/08 or a compound which releases ammonia on heating, 58) Field of Search.... 260/723, 724, 2.5 L, 29.7 P, (3) a vulcanization system for the rubbery polymer 260/29.6 MP, 29.7 UA, 29.7 H; 161/67, 159 and (4) other materials such as foaming agents, sensi tizing agents, antioxidants, fillers, thickeners, etc. as 56 References Cited required and then foamed, shaped and heated to cause M UNITED STATES PATENTS gelation, drying and vulcanization. A water soluble 3,645,926 2/1972 Dunlop............................. 260/2.5 L C-Cs alkyl or alkanol amine containing 1-5 amino 3,719,614 3/1973 Wright............................. 260/2.5 L groups can be substituted for part of the ammonia. By omitting the foaming step, films can be obtained. 10 Claims, No Drawings 3,904,558 2 PREPARATION OF LATEX FOAM RUBBERS AND hours. It is also known to use ammonium polyphos FELMS phates - see U.S. Pat. No. 3,719,614. However, these polyphosphate compounds have a low solubility in This application is a Continuation-in-Part of our water and also tend to settle out if the latex composi prior application Ser. No. 372,502 filed June 22, 1973 5 tions are stored without agitation. It is desirable to im and our prior application Ser. No. 372,521 filed June prove on the above-mentioned characteristics of the 22, 1973, both of which are now abandoned. prior known heat-gelling systems and products. BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION This invention relates to the preparation of foam rub- 10 It has now been found that when an amine-sulfamate bers and films from latices of rubbery polymers. More is added to a latex of a rubbery polymer in which the particularly, it relates to the means employed for gel rubbery polymer particles are maintained in a dis ling the wet latex composition on exposure to elevated persed state by the presence of adsorbed ions of a sus temperatures. pending agent which is capable of forming water In preparing latex foam rubber, a suitably com- 15 insoluble species on reaction with zinc and cadmium pounded latex composition is converted into a foam ions, there is obtained a latex composition of improved which is then shaped and heated to effect drying and suitability for use in the preparation of latex foam rub vulcanization of the rubbery polymer. Special means bers. The composition is stable to storage at ambient are used to prevent collapse of the cellular structure of temperatures for lengthy periods of time. To prepare the wet foam during the shaping and drying steps. Thus, 20 the foam rubber, the latex composition is compounded a foaming agent in the form of extra emulsifier is usu with (l) a material which supplies zinc or cadmium ally added to help in maintaining the foam structure ions such as an oxide or carbonate of zinc or cadmium, and to help in providing the required viscosity and cell (2) ammonia or a compound which releases ammonia size characteristics. Frequently, a gelling agent is also on heating, (3) a vulcanization system for the rubbery added to cause the dispersed rubber particles in the 25 polymer and (4) other materials such as gelation sensi latex to become associated as a continuous phase i.e. tizers, fillers, thickeners, foaming agents, antioxidants, to gel in the form of a three dimensional network. etc. as required, and then foamed, shaped and heated These gelling agents are commonly classified into two to cause gelation, drying and vulcanization. The amine types, (1) the delayed action gelling systems in which sulfamates have high water solubility and do not settle the gelation takes place in a predetermined and con- 30 out when stored without agitation. Thus, the advan trollable time interval after the addition of the gelling tages of the present invention are attained by the use agent without any substantial change in temperature of an amine-sulfamate as the ammonium salt in the and (2) the heat gelling systems in which the latex is heat-gelling system. conditioned by sensitizing agents and the gelation is brought about by the application of heat. This classifi 35 DETAILED DESCRIPTION cation is somewhat arbitrary and is made solely for con The amine-sulfamates useful in this invention are venience since the delayed-action systems, as exempli those which hydrolyze in water when the temperature fied by sodium silicofluoride, have rates which are also is raised but which are characterized by little or no hy temperature dependent while the heat gelling systems, drolysis at ambient temperatures. The amine radical as exemplified by the zinc oxide-ammonia-ammonium 40 can be one derived from any amine which has a boiling salt systems, cause a slow destabilization and gelation point in the range of about -35°C to +300°C and pref at room temperature and thus are also time dependent. erably between about -35°C to +175°C. Examples of It is theorized that the chain of reactions initiated by the amines are ammonia, ammonium hydroxide, the C heating a foamed latex composition containing zinc ox - C alkyl and alkylene amines and the C - C alkanol ide, ammonia and an ammonium salt includes solubili 45 amines, such as ethyl amine, monoethanolamine, dieth zation of the zinc oxide by the ammonium salt so that anolamine, propyl amine, amyl amine, hexyl amine, the zinc oxide behaves as zinc hydroxide, the zinc ions monoisopropanolamine, diisopropanolamine, ethylene liberated by dissociation are complexed by the free am diamine and triethylene tetramine. Ammonium sulfa monia to form zinc-amine ions which in turn dissociate mate, along with the C - C3 alkanolamine sulfamates, to form amine ions and hydrated zinc ions. The resul are the preferred compounds with ammonium sulfa tant free zinc ions interact with the latex-stabilizing mate being most preferred. The amount of the amine component to form water-insoluble zinc derivatives sulfamate which may be used in the process of this in thus destabilizing the latex and causing gelation of the vention is in the range of 0.2-30 parts by weight per polymer particles into the cellular structure of the foam 100 parts by weight of uncompounded latex solids i rubber. With natural rubber latex, the zinc derivatives 55 when it is used with up to 5 parts of added non-reactive are probably zinc proteinates while with synthetic lati emulsifier. A non-reactive emulsifier is one which does ces they are believed to be zinc soaps. not react with zinc and cadmium ions to form water in In the zinc oxide-ammonia-ammonium salt heat gel soluble species. Examples of these emulsifiers are alkali ling systems, it is known to use as the ammonium salts, metal alkyl sulfates, sulfonates and sulfosuccinamates, ammonium chloride, nitrate, carbonate, sulfate, for 60 fatty alcohol polyethers, alkylene oxide-alkyl phenol mate and acetate - see Transactions of the Institution condensates, etc. In the absence of added non-reactive of the Rubber Industry, 23, 104 (1947) Leptit; ibid, 28, emulsifiers, the amount of amine-sulfamate required to 144 (1952) Kraay; ibid, 29, 160 (1953) Newnham and be used is reduced. Thus, with ammonium sulfamate British Pat. No. 391,511. However, latex compositions 65 the required amount is reduced to 0.2-8 parts and pref containing these systems have rather limited storage erably 0.5-5 parts. If less than 0.2 part is used, there stability at ambient temperature and may become un will be insufficient gelation and the foam structure may stable and grainy in appearance on standing several become coarse or collapse during the drying-curing 3,904,558 3. 4. step. Additionally, if a foam rubber is obtained, it will parts will give acceptable results within the above pH likely have a skin which forms wrinkle marks when the limitations. surface is bent into a concave shape. On the other The latices to which the heat-gelling system of the hand, if more than 8 parts of the ammonium sulfamate present invention may be applied are those in which the are used, the gelation takes place so rapidly that cracks rubbery polymer particles are stabilized i.e.