Ammonium and Hydrazinum Hydrazine Sulfinates and Low Molecular Weight Derivatives Thereof as Blowing Agents for Synthetic Resins and Natural Rubber

0 United States Patent Office _ 2,803,688 Patented Aug. 20, 1957 1 2,803,688 AMMONIUM AND HYDRAZINIUM HYDRAZINE SULFINATES AND LOW MOLECULAR WEIGHT DERIVATIVES THEREOF AS BLOWING AGENTS SYNTHETIC RESINS. AND NATURAL RUB- Norman W. Dachs, Buffalo, N. Y., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Application October 10, 1952, Serial No. 314,200 13 Claims. (Cl. 260-724) My invention relates to improvements in blowing agents for the manufacture of porous rubber and plastic articles. Foamed articles of plastics or rubber are prepared by various means including solution of nitrogen under high pressures and subsequent release of the pressure. A simpler method is to incorporate in the rubber or plastic composition a suitable chemical agent which, on heating to vulcanization or molding temperatures, releases large quantities of gas and thus causes foaming of the com- position. Sodium bicarbonate has been widely used for this purpose but suffers several disadvantages. Uniform incorporation in the rubber or plastic is ditficult, because of the insolubility of sodium bicarbonate. Also, relatively large and non-uniform bubbles are usually formed which adversely affects the mechanical properties of the product. Blowing agents of organic structure such as benzene‘ sulfonyl hydrazide and p,p’-oxybis (benzene sulfonyl hydrazide) have been proposed which have the advantage of being relatively soluble in rubber and plastics so that their uniform incorporation is relatively easy, but they are expensive and relatively deficient in other require- ments. Thus, desirable supplementary properties in a blowing agent include ready solubility in rubber and plastics, the absence of discoloration of light colored materials, the absence of toxic or odorous residues, the absence of any effect on the cure of rubber and, for desir- able mechanical properties, the formation of fine uniform bubbles and the production of the maximum proportion of non-condensable gas per gram of the blowing agent. According to my invention, special advantages are obtained in the production in foamed form of polymeric materials having a visco-elastic stage by the use of a blowing agent selected from the class consisting of ammonium and hydrazinium hydrazine sulfinates and low molecular weight derivatives thereof. The blowing agents of my invention produce in general two to three times as much gas or more per gram as previously known blow- ing agents. The best of the known blowing agents pro- duces approximately 100-110 ml. of non-condensable gas per gram of agent decomposed at about 180° C. For example, one gram of dihydrazinium hydrazinedisulfinate produces as much as about 350 ml. of non-condensable gases per gram at 160° C. Thus, with this blowing agent less than one-third as much is. required to produce the same volume of gas. . The new blowing agents include, by way of example, diammonium hydrazine disulfinate (NH4—SO2——‘NH—NH—-S02--NH4) dihydrazinium hydrazine disulfinate (NH2——NHa——SO2—NH—N'H——SOz—-NH3-—NH2) ammonium hydrazinium hydrazine disulfinate (NH4-—-S02-NH—-NI-I-802-—NHa—NH_2) , l0 15 20 25 30 35 40 45 50 55 60 65 70 2 diammonium hydrazine carboxy sulfinate (NH4-—-S02-—-NH-—-NH——CO2—-NH4) dihydraziniurn hydrazine carboxy sulfinate ( NH2-—-NH3—-S02-—NH—-NH-—~CO2——NH3-—NH2) and the like. The blowing agents may be prepared by reaction of sulfur dioxide or of sulfur dioxide and carbon dioxide with hydrazine, ammonia and hydrazine or a mixture of hydrazine and an ammonium or hydrazinium derivative, advantageously in organic solution. The proportion of sulfur dioxide to hydrazine advantageously is adjusted to provide at least one sulfinate group linked to hydrazine, and the proportions of reactants are controlled to provide at least two additional ammonium or hydrazinium groups and an additional sulfinate or other gas forming linkage such as a carboxy group. The relative proportions of sulfur dioxide and carbon dioxide, where the latter is employed, may be varied from _100 percent sulfur dioxide designed to result in a disulfinate to about 50 percent sulfur dioxide designed to result in a monosulfinate. In addition to the ammonium, hydrazinium or mixed ammo- nium hydrazinium products, other basic nitrogen salts may be formed by employing ammonium or hydrazine deriva- tives such as the aminoguanidines or simple hydrazine derivatives such as methyl or dimethyl hydrazine. Thus it may be generally stated that the blowing agents of my invention can be generally described by the following formula: Y-—XO2-—NH——NH—-SO2——Y in which X represents either a carbon or a sulfur atom and Y represents either a hydrazinium or ammonium radical. ‘ Although the new blowing agents are technically inorganic materials they possess the advantage of com- patibility with the organic components of the rubber or plastic mixtures to be treated and decompose substantially to gaseous products with very little residue.. The new agents have excellent blowing activity and yet possess the chemical stability necessary for commercial handling. The new agents in general result in a different type of blow than that produced by agents evolving carbon diox- ide as the primary decomposition product. Instead of the carbon dioxide type blow, the new agents produce a char- acteristically nitrogen type blow provided at least one mole of sulfur dioxide is included in the molecule, and the products are characterized by the very fine pore, unicellular nature of the foamed products. Most of the organic blowing agents previously known evolve gas on heating to suitable temperatures, for exam- ple, 130 to 180° C. fairly rapidly at first. Subsequently the rate decreases as decomposition approaches comple- tion. It is a particular advantage of the new blowing agents that the non-condensable gases are evolved extremely rapidly at desirable vulcanization temperatures. Thus, to obtain 98.5 percent of the total amount of non-condensable gas practically available at 160° C. re- quires only 5 minutes with dihydrazinium hydrazine disulfinate but 50 minutes with p,p’-oxybis (benzene sulfonyl hydrazide). Shorter molding and vulcanization cycles are possible allowing the production of more articles per mold per hour. It is a further feature of the blowing agent of the present invention that the decrease in volume of gas per gram with decreasing temperatures is less than with previous agents. Thus at 135° C. my blowing agent liberates about 94 percent as much gas as at 166° C., whereas p,p’-oxybis (benzene sulfonyl hydrazide) liberates only about 46 percent as ‘much gas at 131° C. as at 160° C. It is thus possible to use lower temperatures which extends 2,803,688 3 mold life and. by shortening cooling periods, speeds sub- g'—~m?m1,4.j (‘Vi-°i"rtir~1~.