USRE13667E - Fritz pfleumer - Google Patents

Description

UNITED STATES PATENT OFFICE.

FRITZ PFLEUMER, OF DRESDEN, GERMANY.

PROCESS OF MANUFACTURING VULCANIZED FROTH.

Specification of Reissued Letters Patent. Reissued Dec, 30, 1913 No Drawing. Original No. 1,038,950, dated September 17, 1912, Serial No. 640,640. Application for reissue filed November 12, 19:13.

To all whom it may concern Be it known that I, FRITZ PrLnUMER, a subject of the iiesiding at Dresden, Germany, have invented certain new and useful Improvements in processes of Manufacturing Vulcanlar su it is proposed bub les bycarrying ized Froth,

of which the following is a specification.

Processes of manufacturing elastic froth In the first-mentioned two German patents it is suggested to raise the froth or spongestructures by mixing into the india rubber chemicals yielding gases at the vulcanizing temperature. In the next-mentioned patent chemlcalswhich on coming in contact with the moist matter generate carbonic acid, and to use the thus produced gas as frothraising medium. In the processes of the other patents mentioned above an optional gas is brought into the mass by mechanical treatment as beating, stirring, kneading, shaking or centrifuging saidmass under an atmosphere of the respective gas, or by injecting the gas into the mass.

Processes of vulcanizing solid rubber articles under an atmosphere of a hot inert gas as nitrogen or carbon dioxid are described in the British Patent No. 7159/01 and United States Patent No. 661,177. In these processes it is intended to revent air eventually included by the rub er or the vapors of'the sulfur generated at the vulcanizin temperature from raising pores or out the vulcanization under pressure of said gases up to about 100 pounds er square inchor about 7 atmospheres, he gas-pressure thereby acting as mechanical counter-pressure against the raising of bubbles.

I have based my invention upon the observation that india rubber as well as gutta percha and balata are by no means homogeneous or impenetrable substances, but represent, so much as is known'at present, a reticular structure just visible under the best Emperor of Austria-Hungary,

to add to the glycerin-gelatin Serial No. 800,638.

microscopes, into which structure gas can penetrate or pass through it under certain conditions. (Literature: C. O..\ Veber, T he Chemistry of India Rubber, age 19, Wroblewskis conclusions 3, 5 an 11; page 78, line 6 and 11 to 18.)

A iece of raw rubber submitted in an autoc ave to a high pressure (from 80 to 300 atmospheres) of an optional gas, airnitro'gen etc.', on being relieved of the gas-pressure, shows a considerable increase of its bulk and a crackling, which originates from small bubbles burstin on the surface of the piece. On ceasing of t e crackling the rubber piece has regained almost its original volume. The thus treated piece on superficial inspection shows a great number of pores, obviously channels worked by the gas on its way into, and out of, the rubber piece. The eifect increases, if the rubber previously to its being subjected to high gas-pressure is soaked in about one quarter of its weight of any rubber solvent, for instance benzene. If, however, the rubber pieoe is kneaded together with from 2 to 10% of its weight of precipitated sulfur and the piece subjected under the above mentioned gas-pressures to the vulcanizing temperature, 135 to 145 (1., for about two hours, the piece on being relieved of the external gas-pressure does no more allow its contents of gas to escape, and consequently expands to a highly voluminous and regular froth in the cells of which the gas is permanently imprisoned. In this case the action of the gas upon the indie rubber is a directly opposite one to the action men- .tioned in the last cited, two specifications.

' Such highly compressed gas acts no more as counter-pressure against any raising of bubbles, but penetrates the'india rubber, filling up all the pores of the microscopic structure. V Experience teaches thatindia rubber in the heated state receives much more gas than it does in the cold state (m'de C. O. Weber, VVr..s conclusion 2), and this applies in enlarged proportions to guttapercha and balata. The heating, moreover, transfers to the material'that, plastic state of a tough liquid, which allows of the mass being drawn out into thin films, while vulcanization renders them sufficiently resistant to stand the stretching coincident to the expansion of the froth. In the stretched state the films are gas-tight in spite of the structure of the material. It must be considered an addi ion by or benzol, however, allows of conrubber that the natural structure of the material has the appearance of a sponge, the channels and walls of which are of smaller 'dimensions than the artificial froth structure forced upon thematerial by the described treatment.

It is not a condition of the process that the raw rubber should contain any solvent, weight vof one quarter of benzene siderably lower gas pressures being applied for making an equally voluminous froth than are required, when every solvent is recluded. More solvent on the other hand, has a destroying effect on the material, and renders the product of vulcanization inferior.

follows: Ten parts, by weight, of raw rubber are kneaded together with from onefifth to one part of tionally according previously to the kneading may be soaked in about two parts of benzene or benzol. In conjunction with the sulfur antimony pentasulfid, so-called golden sulfid may be employed advantageously. The thus cell in the interior of and the finished froth made dough is now formed into articles, the form of which is geometrically similar to the form therespective article is intended to have after transformation into froth.

The proportions in sizes of the pieces formed of the rubber dough on the one side piece on the other naturally depend on the quantity of gas the finished froth piece is intended to contain.

en vulcanized under a pressure of about 100 atmospheres the finished froth in the expanded and dry state contains about 9 parts by volume of gas in every one part of rubber, e., about 13 parts by volume of the rubber dough must be chosen for making a froth piece of 100 parts by volume. From this the linear proportions may be derived. If the solvent is left out, inorder to attain the above mentioned proportions of the volume, about 300 atmospheres gaspressure, gaged at the vulcanizing temperature, are required. 1 The shaping is carried out by either pressing the dough into molds, or for simple sectional pieces by squeezing the dough from a tubing machine-with a; mouthpiece of the required section into endless bars or rods.

The reception of gas may be considerably increased by mixing intofthe mass porous materials in a pulvei'fi'us state, for instance Kieselguhr, ground cork; bone-black, factice, etc. In this case besides the mass each grain into its pores receiving gas which on expansion leaves the grain forming one which the grain remains. The pieces are now vulcanized in an autoclave under high pressure of a gas. Nitrogen, carbon monoxid, eventually air'are vulcanized and contains no In practice the process is carried out as precipitated sulfur; op to the desired effect the suited to the purpose, while hydrogen and carbondioxid, so-called carbonic acid, are precluded from the technical application on account of their diffusing properties as well as oxygen on account of its oxidizing action on rubber. It is of course impossible to let steam-into an autoclave filled with gas under so high a pressure. The autoclave has therefore to be heated with steam from without. Also india rubber which is already of free sulfur, may be thus transformed into froth; it should, however, contain only small quantities'of other. admixtures in order to attain .a froth sufficiently gas-tight for the purpose in view. A small quantity of free sulfur is always present in soft vulcanized rubber, and generally sufiices to attain an additional vulcanization, which renders the froth raised stable. .Thus 91d motor-car tubes or waste of vulcanized sheets may directly be transformed into froth sheets, and

these worked up into inlayings for life-saving. dresses, heels, billiard cushions, sound proof mats for typewriters andv musical instruments, etc.

I From the fact that vulcanized material can be transformed into froth an alteration of the described process of making froth .from raw material may be derived in that direction that the raw material be vulcanized first without gas-pressure, and be placed .under gas-pressure afterward. In this case,

however, the material should be kept rather hot in order to'carry out vulcanization and froth raising in one uninterrupted operation. This optional way has the disadvantage .of the material being longer heated than in the process already described.

For many applications, as, for instance, cycle and motor-car tires the froth must contain its gas fillingunder a certain pressure. To subsequently compress rubber-froth that has'been expanded to the atmosphericpressure in order to make froth filled with gas under pressure would be a failure, as it is a matter of experience that the filmson recontraction lose their gas-tightness. Therefore the-froth already after vulcanization should not be expanded down to a lower pressure than is required for its application. This pressure amounts to from 2 to 3 at mospheres (28 to 42 pounds per square inch) for cycle tires and from 4% to 8 atmospheres (63 to 112 pounds per square-inch) for motor-car tires. Qne of the followin methods may be applied for making such 0th containing gas under pressure:

Raw material of high tensile strength is treated in the described manner, no solvent being applied. When the vulcanization is finished the articles are left under pressure for several hours so that the may cool out and regainth'eir original tensile strength previously to being expanded into froth.

more than 10% Part of the gas in the autoclave may be let out directly after vulcanization 'with the purpose of starting formation of the froth structure. The gas cooling out after vulc'aniz'ation its pressure further decreases.

2. Into the raw material, when being mixed with the ingredients, fibrous substances as, for instance, fibers of raw cotton, raw jute or raw hemp are kneaded. These fibers should be no longer than about an inch (5 mm.) otherwise they would conglobate into lumps. By the quantity of fibers admixed the pressure, at which further expansion ceases, may be fixed.

By means of these methods interchangeable tire cushions are made, which upon account of their being gas elastic and indestructible by punctures represent a suitable substitute for air-tubes. They do not expand so far on being dismounted from a worn-out cover as toinipede their being mounted under a new one.

Analogous to that described, the process is carried out with guttapercha and balata. These are kneaded with from 5 to 10% of precipitated sulfur, optionally with an addition of antimony pentasulfid. In the trade this chemical is to be had with an admixture of up to 50% of free sulfur, and 10% of it, containing 5% of the raw materials weight of free sulfur, give a grade of vulcanization best suited to the purpose. Also soft vulcanized guttapercha and balata may be trans formed into froth in the described manner. With this process one can also manufacture froth of hard rubber, hard guttapercha and I hard balata. To this end a dough containing from 30 to 50% of sulfur is used, the articles vulcanized under gas-pressure, and expanded when still hot. The vulcanization is continued on the expanded froth until the hard state is reached. The expansion'must be carried out on the hot froth as otherwise cork.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States is 1. A process for manufacturing vulcanized froth from material such as india-rubher, gutta-percha, or balata, consisting in hot vulcanizing raw or partly vulcanized material under such a high pressure of agas that the gas penetrates the structure of the material, and on partly or wholly releasing the external gas pressure raises the material into froth.

2. A process of manufacturing vulcanized froth from material such as india-rubber, gutta-percha or balata, consist-ing in hot vulcanizing raw or partly vulcanized material by keeping the thus treated material under high gas pressure, so that the gas penetrates the structure of the material until it is cooled, and afterward releasing it of the gas pressure in order to produce froth containing more than atmospheric pressure.

In testimony whereof I aflix my signature in presence of two witnesses.

B. H. CONNER, HAROLD B. SHARP.