US1909219A - Process of producing high-percent caoutchouc solutions - Google Patents

Description

llatented May l6, 1933 FFEQE RUDOLF OECKINGHAUS, OF METTMANN, GERMANY, ASSIGNOB T IMMALIN-WERKE OHEMISCl-IE FABRICK EISENDRATH G. M. B. 1-1., OF METTMANN, GERMANY rnoonss or rnonnorne iiieir-rnncnn'r GAOUTCHOUG soLU'rIoivs No Drawing. Application filed November 20, 1930, Serial No. 497,082, and in Germany August 26, 1930.

A characteristic property of caoutchouc is, that it will swell gradually in organic solvents such as ether,'benzine, benzene, chlorine, hydrocarbons, carbon disulfide and the like and together with such solvents will form thick, hardly movable jellies. This conversion will take place already at a caoutchouc content of only 2 to 5% and in dependence of the nature of the caoutchouc and the dissolving conditions. Such tumefactions will, however, turn more liquid when left to themselves for some time or heated, especially in the presence of light. It is also possible to produce thinly liquid caoutchouc solutions by masticizing or milling the caoutchouc for a relatively long period before the solvent is added in such a manner that the material is overmilled, i. e. the nerves of the same are destroyed. This treatment is especially effective when carried out at raised temperature. Another method consists in adding softening, high-boiling plasticizing agents to the caoutchouc during the rolling or milling operation. Suitable agents for this purpose are for instance tetrahydro naphthalene and the ester of this compound. It is, however, not possible by means of the methods hitherto known to produce solutions containing more than of caoutchouc. Further this result can only be obtained at high working expenses and the nerve system of the caoutchouc will be severely damaged through the treatment.

Now, according to the present invention caoutchouc solutions containing 15, and even of caoutchouc may be obtained in an exceedingly simple manner by adding an oxidizing agent, for instance nitric acid,to the solution. The caoutchouc solutions obtained by this treatment may be used for dipping, staining and spraying purposes. This effect of the oxidizing agents is very surprising, because strong nitric acid and ozone react violently with crude or vulcanized caoutchouc, whereby nitrosites respectively ozonides are formed. "When certain conditions with regard to the amount, the concentration and the duration of the action of the oxidizing agent are maintained it is,

however, in accordance with the present inlot is added.

vention possible to conduct the reaction in such a manner that the solubility of the caoutchouc or the fluidity of the caoutchouc solution is increased without any essential change in the nature or structure of the caoutchouc taking place.

Example 1 10 kg. of Ceylon-crepe or fine hard cure Pararubber are cut up into pieces of hand size and these pieces are filled into a container of suitable size, which is equipped with a cover and'an agitator (or a mastifier). Into this container now the fourto sixfold amount of an organic solvent is poured and the mass is stirred from time to time until a homogeneous, thick massis Example 2 This treatment differentiates from that described under Example 1 in that the nitric acid at once is added to the solvent. The effect of the acid may be neutralized at any desired moment by adding a substance of alkaline reaction.

The exact nature of the reaction between the nitric acid and the caoutchouc solution is not as yet positively known. Apparently the nitric acid reacts chemically with the solved caoutchouc and eventually also with the solvent, which is usually benzine which is well known as a solvent for caoutchouc or with the natural aromatic ingredient of the benzine. However this may be, the nitric acid as stated above is used during the reaction and therefore causes the more physical effect of the cleavage of the caoutchouc macro molecules. The process depends essentially upon the right proportion of the nitric acid used and the minimizing of the nitric acid to the point that only such cleavage of the caoutchouc macro molecules is obtained as to lower the viscosity without an appreciable loss of the nerve (of the original condition) of the caoutchouo.

It will be evident that such concentrated caoutchouc solutions of relatively low viscosity are of great practical importance. Said solutions may be employed in natural or filled state, for instance dyed with covering pigments. The dyed solutions may for instance be used for applying non-crumbling colored high-glaze coatings to articles of soft rubber, such as balls and toys.

The high-percent caoutchouc solutions according to the invention are especially valuable in the producing of coatings for articles of soft rubber which are subjected to severe mechanical strains, such as rubber boots and the like.

Suitably dyed high-percentage caoutchouc solutions may further be used with advan tage for producing durable colored coatings of high covering power for such rubber articles which must be sold at relatively low prices and therefore hitherto could not be dyed thoroughly and delivered in unobjectionable state. Such articles are for instance rubber heels, rubber soles, toys, rubber plates, rubber carpets, rubber mats and the like. Foot wear is an. article which is subject to the changes of the mode or fashion and especially the color of foot wear changes Very frequently. From an economical point of View it is therefore not advisable to dye the mass of the rubber heels in all the colors in which the shoes or the like are to be delivered. In this case the heels would become rather costly and it would be necessary to employ cheap material of low quality for the other parts of the shoes in order to be able to sell the same with profit at normal prices.

Now, according to the present invention it is possible to produce heels, soles and the like of a single, neutral color (for instance grey or black) and to coat said bodies with a durable coating of any desired color obtained from the said high-percent caoutchouc solutions.

The high-percent solutions according to the invention may also be used for repairing cracks and other defects in soft rubber articles. Hitherto such defects were remedied by attaching a thin rubber plate to the spot to be repaired by means of a solution poor in caoutchouc. The dried caoutchouc solution may of course be hardened in the usual manner by vulcanizing it in cold state.

The filled, non-filled, dyed or undyed high-percent caoutchouc solutions may also be used for producing articles which are dipped into or coated with caoutchouc. The working process is in this case much simpler than the processes hitherto used.

I claim:

1. A high percent oaoutchouc solution of low viscosity, comprising a solution of caoutchouc in an organic solvent and nitric acid in the proportion of from one to three percent of the acid with respect to the caoutchouc.

2. As a new composition of matter, the physical reaction product of a solution of caoutchouc in an organic solvent in the proportion of from 15 to 25 per cent of the caoutchouc with respect to the solvent and nitric acid in the proportion of from 1 to 3 percent of the acid with respect to the caoutchouc.

3. The herein described process of making a high percent caoutcliouc solution of low viscosity and adapted for use in dipping, spreading and spraying, and consisting in adding an organic solvent to a mass of pieces of rubber in the proportion of from about 15 to 25 per cent or the caoutchouc with re spect to the solvent, stirring such mixture until a homogeneous thick mass is formed, adding nitric acid to the mixture in the proportion of from 1 to 3 percent o1 the acid with respect to the caoutchouc content of. the mixture and stirring sutficiently to cause the mass to attain such consistency as to enable the mixture to be spread or stained.

In testimony whereof I aifix my signature.

RUDOLF OECKINGHAUS.