US2378701A - Manufacture of articles from liquid dispersions - Google Patents

Description

e 19, 1945 E.-E.HABI B Em 2 378,7

. MANUFACTURE OF ARTICLES FROM LIQUID DISPERSIONS Filed Nov. 16, i945 layer of coagulont liquid conraininq acceleraror F|G 2 accelera'for 'solud'lon surface wcf wrfh accelenflor scalmrion FlG.4

warm Clll EMILE E. HABIB GORDON E. GOTT Inventors By Pit ntod June 19, 1945 2.37am I l I MANUFACTURE OF narrows msrunsrous moumqum Emile E. Habib' and Gordon ErGott, Arlington, Mass, assignors to Dewey and Almy (Chemical Company, North Cambridge, Mass, a oorpora= tion of Massachusetts Application November is, ices, Serial No. amass (cl. ia-ss) 3 Elaims.

' The present invention relates to the manufacture of hollow rubber objects and more particularly to the manufacture of large-size meteorological and radiosonde balloons by a coagulant dipping process.

Balloons of this recent past by a casting procedure. This was a slow process and save control difiiculties because of the sensitivity and lack of stability of the dispersion; These dimculties were avoided by the introduction of a coagulant dipping process in which the deposited layer of rubber is stripped from the dipping mold while it is still plastic and is subsequently inflated to the desired larger size.

This processis described in detail in our copend- 1 ing application Serial No. 510,442, filed on the same day as the present application.

This improved dipping type process was found to be applicable to natural latex dispersions only with the limitation that the dipping compound be used before the percentage of sulfur combined on the rubber hydrocarbon had risen to more than 0.45%, based on the dry weight of the hydrocarbon. If a natural latex dispersion in which the combined sulfur on the rubber hydrocarbon exceeds 0.45% is used, the freshly deposited gels can not be stretched enough to get them Oh the mold without tearing them. If they are allowed to drytype had been made until the and thus acquire'sufilcient strength for stripping,

then they can not be permanently enlarged enough by inflation because the material is no longer capable of sufilcient plastic flow. This characteristic of the process means ping bath must'be freshly prepared and used when not more than a few days old. For laboratory scale operation, this characteristic is not a serious handicap, but those skilled in the art will appreciate immediately the difificulties it causes when the Process is used on a factory scale.

It is the principal object of the present invention to overcome the dimculty described above; to provide a modification of the coagulant dipping process referred to above which will adapt it to efficient and economic factory scale operation; and to provide a means of preventing the combined' sulfur of the dipping bath from rising to an undesirable amount before the bath is used.

We have discovered a satisfactory procedure .for introducing .a sufficiently large amount of a vulcanization accelerator into the wet gels formed in the proces described in the application referred to above which will distribute the accelerator uniformly inthe gel without local concentrations which would produce non-uniform cure. This procedure is availed of to accomplish the objects of the invention by. omitting that, the d p-- the dipping compound the accelerawr,

the compound for dipping in the normal manner, and then introducing an accelerator into the formed objects. As a consequence of the absence of an accelerator from the compound, modern hish=speed accelerators may be used with the process and the compounds do not materially change in their combined sulfur content upon ageing and, therefore, need not be freshly prepared.

The invention will be more fully understood from a reference to the accompanying drawing.

in which Figure 1 is an elevation partly in section of the dipping mold after it has been'withdrawn from the dispersion withthe deposited gel layer on its "dispersion of natural latex and also make up a suitable coagulant compound. The following example illustrates compounds whioh'are suitable:

Parts by weight of solids Rubber latex (60% solids) 100.00 Potassium hydroxide 1.75 Zinc. stearate 1.00

Symmetrical di-beta-naphthyl para phenylene diamine 1.00 Formaldehyde condensation product of naphthalene sulphonic acid 0.24

Titanium dimride 1.00

, Sulphur 1.10

ingredients are added in the order stated.

The amount will vary with different latices; suficieni: shouldbe used to give the dispersion a viscosity suitable for dipping.

The coagulant has the following composition:

Bentonite 150 Water 900 Acetone 1,321 Calcium nitrate tetra hydrate 1,250 Glycerine Glacial acetic acid 37 A suitably shaped balloon mold l is dipped into the coagulant composition and then withdrawn,

forming on its surface a layer of coagulant l.

mold I together with the deposited gel layer B on: its surface is then immersed in ninth as shown in Figure 2 containing a suitable accelerator of vulcanization. The accelerator may be in solution or in suspension. For gels formed from the composition of Example 1, a suitable bath may be made by dissolving parts of potassium pentamethylene dithiocarbamate in 90 parts or water, and the mold should be held in the accelerator for about minutes. The mold is then withdrawn from the accelerator and the .gel layer I is stripped from its surface by stretching the neck of the gel and sliding it downwardly oil the form as shown in Figure 3. The gel layer is then placed on an inflating nozzle and blown up to the desired size as shown in Figure 4. .During the inflation it is found that the liquid accelerator is caused by the stretching of the gel material to be absorbed into the gel. The gel is then dried in inflat d condition as shown in Figure 4 and, when it has been dried, is deflated and heated in dry air at 212 F. to bring about vulcanization as shown in Figure 5. It is found that the vulcanization proceeds normallybecause of the presence of the accelerator which has been drawn into the gel during inflation.

It is essential that the step'of soaking the gel article in the accelerator be carried out before the article is inflated, because, in addition to absorption of accelerator into the gel during soaking, there is a relatively enormous absorption of accelerator into the gel as the gel is expanded during inflation. By inflating the latex from the mold, although we have found that the gels may be more conveniently handled and immersed while they are still on the molds.

It will be appreciated that the objects of the invention may be attained by including in the dipping bath only a small amount of accelerator, the particular amount depending upon plant conditions.

, The present invention, it will be appreciated, is equally applicable to the manufactureoi other objects than the meterological balloons selected as the specific exam le for purposes of disclosure. The present process may be used'in the manufacture of any rubber article which lends itself to production by the process of our copending application, Serial No. 510,442 (on which the present invention is an improvement).

-We claim:

1. The process of manufacturing rubber articles which comprises dipping a coagulant-coated mold into a. liquid dispersion of natural rubber compounded for vulcanization except that it is deficient in accelerator, withdrawing the mold article while wet with an accelerator solution from the dispersion with a deposit of rubber gel thereon, soaking the gel in a liquid containing an accelerator of vulcanization, expanding the gel while it is still plastic and thereafter drying and vulcanizing the gel.

2. The process of manufacturing rubber articles which comprises dipping a coagulant-coated mold into a liquid dispersion of natural rubber compounded for vulcanization except that it is deficient in accelerator, withdrawing the mold from the dispersion with a deposit of rubber gel thereon, immersing the'mold and gel in a liquid containing an accelerator of vulcanization, stripping the gel from the mold, expanding the gel while it is still plastic and thereafter drying and vulcanizing the gel. n

3. The process of manufacturing rubber articles which comprises dipping a coagulant-coated mold into a liquid dispersion of natural rubber compounded for vulcanization except that it is deficient in accelerator, withdrawing the mold from the dispersion with a deposit of rubber gel thereon, stripping the gel from the mold, soaking the gel in a liquid containing an accelerator of vulcanization, expanding the gel while it is still plastic, and thereafter drying and vulcanizing the gel.

Em E. HABB. GORDON E. GO'I'I'.

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