Sponge rubber composition
US RE23697 E
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Reissued Aug. 4, 1953 V R UNITED STATES PA ENT OFFICE SPONGE RUBBER COMPOSITION No Drawing. Original No. 2,567,950, dated September 18, 1951. Serial No. 32,717, June 12, 1948.
Application for reissue September 8, 1952, Serial No. 308,500
Matter enclosed in heavy brackets I: II appears in the original patent but forms no part of this remote specification; matter printed in italics indicates the additions made by reissue.
- 2 This application is a continuation-impart of I g the application filed in the name of William R. Neoprene latex. an aqueous emulsion or Stauifer, Serial No. 770,109, filed August 22, 1947, neoprene r-ubber gm 100.-
and entitled Method and Apparatus for Mair.- ing sponge Rubber and now abandoned.
This invention relates to a sponge rubber com- Plasticizer, 30-1 (a vegetable oil) ..cc 1. Sensltizer, a 25% dispersion of sodium posm silicofluoride cc 2.3
on. It is an object of this invention to provide a 11 v composition for the manufacture of sponge rub- Natural latex. an aqueous dispersion of her hi h composition does not neces t using 10 natural rubber o, solid gasifying substances. Foaming agent, egg albumen cc-.. 2.5 11; 1 another object of this inven o o p Plasticizer, 30-1 2,5 ide a composition for the manu actur of 9 8 Activator, zinc oxide 2,0 rubber Produc s which does not equire t e u Sensitizer, a dispersion of sodium of autoclaves or closed molds. 15 silicofluoride 1 o It is still another object of this invention to provide a rubber foam without the use of heat. m Y
It is another object of the invention to pro- Natural latex. an aqueous dispersion of vide a composition useful for making rubber foam natural rubber ee 50, at the point desired, for instance within automo- 2o Nwprene latex. 1 0-2 087 cc 5o, bile bodies, in railway cars for sound installa- Plasticizalr cc 1, tion and other places of similar character and sensitize!" di persion of sodium then vuloanizing the foamed composition in silimfluoride cc 2,3 position- The foregoing mixtures are impregnated in a These objects of the invention are flccom- 215 closed container with nitrous oxide at from so plished by mixing latex under pressure with other suitable materials, including a plasticizer, to form the composition of the invention and releasing the pressure whereby a foam is formed, and then heating said foam to cure and stabilize it. More specifically, these objects of the invention are accomplished by producing a rubber foam by the use of nitrous oxide (N20). Unexpected results occur from the use of nitrous oxide in that the foaming takes place with a decrease in pressure upon the fluid rubber [latex] being impregnated with nitrous oxide; the foam obtained can then be vulcanized, whereby the sponge is obtained.
The addition of albumen tolatex facilitates foaming still more and also increases the stability ofthe foam. It has been found that .an amount of 2% albumen with regard to the [latex] fluid rubber is the optimal quantity in case a soft sponge is to be produced, while 5% albumen gives better results in the case of a hard sponge. Other foaming agents operative with satisfaction are proteins.
Examples of compounds The following are typical examples of compounds which I have successfully used.
In the case of neoprene latex, it is necessary to maintain the mixture at 40 to 41 F. This refrigeration effect permits the use of a dormant coagulant or gelling agent, such as sodium silicofluoride (NaiSiFa) or calcium formate;
to 250 pounds. A pressure of approximately 200 pounds has been found most desirable.
It is desirable to agitate the mixture after impregnation to bring about a thorough and uniform distribution of the gas in the latex.
As soon as the impregnated liquid is released, asthrough a hose nozzle, it immediately foams. The product so foaming is then subjected to heat of vulcanization either by infrared ray lamp, induction heating or by convection heating. A
sponge is formed thereby having a very fine bubble formation with the bubbles of gas interconnected. This gives a very strong and soft sponge of homogeneous character. It can be cast in very thick sections as well as thin sections and constitutes a mass production item which can be continuously produced.
The temperatureof vulcanization depends upon the type of rubber, its accelerators, etc. The time of vulcanization likewise varies. The problem involved in its solution is well-known in the rubber industry and needs no description here except that an oven temperature of from 200 to 250 F. has been found satisfactory. The length of time varies greatly.
Henry's law states that the mass of a. soluble gas that dissolves in a definite mass of liquid at a given'temperature is very nearly directed proportional to the partial pressure of the gas and is valid for gases that do not unite chemically with the solvent. This means that as the pressure increases, the amount. of dissolved gas increases proportionally. 7
Although nitrous oxide is the anhydride of hyponitrous acid, the breakdown of this acid is irreversible. It has therefore been i'ound that nitrous oxide does not chemically combine with water. V
Nitrous oxide has been incorporated into natural and synthetic latices and into mixtures of these fluid rubbers using pressures of from 100 p. s. i. to 300 p. s. i. A pressure of 80 p. s. i. on the nitrous oxide incorporated less gas than did 100 p. s. 1. However. the latices that is fluid rubbers may be also converted to foam by simply bubbling nitrous oxide through them under atmospheric pressure.
By way of contrast, carbon-dioxide has been tried and found undesirable because carbon dioxide, although considerably more soluble in water than nitrous oxide, reacts with water forming carbonic acid which coagulates latices.
Carbon dioxide under pressure of 100 p. s.- i. was bubbled through and inco porated in natural latex coniined in a closed vessel. After the latex was saturated with carbon dioxide, it was foamed by letting the carbon dioxide escape from the ves sel through a valve.
' Under these conditions, the foam contained curds of coagulated latex. Pipes and valves at-' tached to the pressure vessel were coated on the inside and at places almost clogged with this coagulated latex. About one third of the latex charge ooasulated in the bomb.
Carbon dioxide dissolves in water under pressure; carbonic acid has little or no eflect on either synthetic or natural latices. However, un-
4 latices are especially satisfactory. The polyvinyl chlorides as is known are vinyl esters termed in the trade as "Vinylite and are members of a class of resinous thermoplastics possessed of rubbery characteristics.
It will be understood that I desire to comprehend within my invention such modifications as may be necessary to adapt it to varying conditions and uses.
Having fully described my invention'what I claim as new and desire to secure by Letters Patent is:
1. A composition for producing sponge rubber comprising an aqueous dispersion of a rubber selected from the group of natural rubber, polychloroprene latex, polyvinyl chloride latex, polybutadiene latices and mixtures thereof, a small amount of a vegetable oil as a plasticizer, from substantially l to 2.3 percent of a heat sensitizer selected from the group consisting of sodium silioo fluoride and calcium formate, impregnated. with nitrous oxide at a pressure of from 80 to 250 lbs., said composition being maintained at approximately 40 to 41 F. and having the property to expand upon release from a container into a rubber foam.
2. The composition of claim 1 in which the :aqueous dispersion of rubber is natural rubber tex.
3. A composition for producing sponge rubber comprising an aqueous dispersion of a mixture comprising polyvinyl chloride, a small amount of vegetable oil as a plasticizer, from substantially 1 to 2.3% of a heat-sensitizer selected from .the group consisting of sodium silicojluoride and calcium jormate, impregnated with nitrous oxide der pressure, this weak acid can react with enough of the sodium hydroxide in synthetic latex or ammonium hydroxide in natural latex to cause coagulation. When carbon dioxide isbubbled through latex, enough of the stabilizing hydroxide is converted to the carbonate to cause coagulation. Thisunexpectedresultwiththeuseofnitr oxide has indicated that nitrous oxide is the only gas suitab1e'ior4oaming latices by releasing the pressure required to dissolve the gas in the latex.-
I have found that this foamed latex, after being injected into the mold and committed, can be cured in hot water or with steam or by the application oi infrared heat.
Therefore, nitrous oxide is the only common gas which is suitable for producing foamed latex becauseothercommoninertgasesaretooinsolubleinthelatex.
While natural as well as sypthetic rubbers or their mixtures are applicable for the invention, polychloroprene sold as neoprene, polyvinyl chlorides. polyvinylidene and polybutadiene to 41 F. and having the property to expand upon release from a container into a rubber loam.
WILLIAM R. STAUFFER.
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