DE1950014A1 - Latex preparations - Google Patents

Description

Attorney file 18 874 Jie / och

date

Monsanto Chemicals Limited London / England

"Latex preparations"

This xirfindung concerns latex preparations, in particular synthetic cis-polyisoprene latices and their use in the manufacture of vulcanized rubber articles.

Bynthetic cis - folyisoprene latex can be used in many cases as a full or partial replacement for

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natural rubber latex can be used. Although the polymer itself is basically the same as natural rubber, there are a number of differences between-the latices, and some codifications the processes used for the manufacture of articles from natural rubber latex, usually necessary when the natural latex is replaced by the synthetic one, even with such modifications it was still not possible to obtain the full properties of a vulcanizate from a natural one Rubber latex on one made of a synthetic cis-polyisoprene latex to transfer. For example, the codule of the latter is significantly lower and this is a disadvantage with certain submerged objects and with elastic threads.

In addition, the synthetic cis-PolyisopTenlatex W is more sensitive to slight changes in the process conditions than the natural rubber latex, in particular to the conditions in the manufacture of the compound fiber parts, which are added to the L & tex before vulcanization. Many of these ingredients, including, for example, the vulcanization accelerators such as the zinc dithiocarbamates and zinc-2-mercapto-benzothiazole, are water-insoluble materials and in order for them to be punctured satisfactorily; it is necessary

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to crush them to a very small particle size. this usually done by working in a "ball mill" in the presence of a surface active wittels, whereby the Duration of the i-iahiens and the type of surface-active means are often critical, ijicut sufficient grinding can for example ax production of Vulkanisaten zur.X'Olge have, aie have significantly lower tensile strengths and r, oduli than Vulkariisates that have been grown in less than optimal conditions. For the manufacture of items of equal choice ^ uality is there a precise control of the compound ;:; aterialica and their manufacture essential.

It has now been found that if the synthetic cisi olyisopx enlatex approach contains colloidal silica, changes in the fermentation conditions have a much smaller effect on the quality of the volatile matter. Colloidal Kieselei'de therefore works as a processing aid for the iiersLuiluiig of. vulcanized objects made of synthetic cis-irolyisoprene latex. ^ ie Zugaoe of colloidal silica to a synthetic cis-jrol ^ .isoprenlatex nat further, nütz_iene for many Verwe.ijuncszwecie V / MPACT because ^: i :: u: the module read Valkanisats wesentxica ^eri. This is an effect that is monitored independently of the vulcanization system, for example even where the Verwe :: ueto accelerator is water-soluble or a liquid and therefore a dispersion problem occurs.

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The present invention accordingly provides a preparation comprising a dispersion of colloidal silica in a synthetic cis polyisoprene latex.

Furthermore, it creates a method for producing a vulcanized object made of a synthetic polyisoprene latex, whereby colloidal gravel was added to the latex used.

Another object of the invention is a method for Improving the uniformity of, quality of objects, made from a synthetic cis-polyisoprene latex which contains water-insoluble Kornpound constituents, wherein a preparation that containing colloidal silica together with such compound ingredients is used.

A preparation of the invention can include up to, for example 30 parts by weight of silica per 100 parts by weight of cis-polyisoprene polymer, each on a dry weight basis, but normally no more than 20 parts Silica present in the same base material. For For many purposes, the optimal amount is in the range of 5 to 15 parts by weight of silica per 100 parts by weight of cis-polyisoprene— polymer.

The preparations of the invention can be obtained by mixing one

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synthetic cis-polyisoprene latex with dry egg? powdered Colloidal silica (generally 0.5 micron particle size not exceeding), if necessary after adding the wetting agent or dispersant to the latex that is normally in a synthetic cis-polyisoprene latex are present. Various grades of small particle size silica that are surface treated are available on the market are to facilitate dispersion in aqueous media and such are particularly suitable. Preferred preparations of the invention, however, are Geraische of synthetic cis-Polyisoprenlatiees with silica sols, im special ones with silica aquasols.

A variety of silica aquasol species are commercially available, from sols in which the average particle size, as determined by light diffraction, is 250 pounds or less, in some cases as little as "50 to 10,000 pounds, to sols in which the average particle size is 1000 pounds to 1500 Å is "The concentration of silica in the different sols can range from about 15 to 55 wt. % or more." It has been found that the effectiveness of the silica appears to increase for a given amount to the extent that as the particle size decreases and preferred sols are accordingly those with a lower average particle size «suitable

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Sols can be obtained by contacting a dilute alkali metal silicate solution with a cation exchange resin in the hydrogen form, then by heat stabilization of the initially formed silica solution are produced,

as for example in the British patent specification 64-5 703 it is described «Such brine normally contain residual alkali metal ions and have pH values in the range of 9.5 to 11.0. oilieiumdioxidsole with larger average particle sizes can be obtained by methods described in British patents 649 897 and 1 143 019 are described.

The manufacture of vulcanized items made from methods used in the latex formulations of the invention generally follow the working procedures used so far with synthetic cis-polyisoprene latex »although, as stated above, a slightly greater ability to move can be tolerated in the process conditions. The preparations of the invention, can be used to produce, for example cast! mimes, manufactured in the .dipping process Goods using simple! Dipping procedures, from ! Coagulation 'or heat-sensitized' lauching procedure and used to make extruded threads * "· Sulfur is normally used as a vulcanization agent and the preparation usually contains zinc oxide * Zu the examples of accelerators that can be used i belong to zinc salts from Hjli

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IJ, H-diethyIdithiocarbamic acid, N, IT-dibutyldithiocarbamic acid, H-ethyl-K-phenyldithiocarbamic acid and of 2-hercaptobenzothiazole, amine salts of H, N-substituted dithiocarbamic acids, for example Piperidincy U -Nhexyl-Ifhexylammiocarbamic acid N 'dibutyldithiocarbamate and thiuram sulfides, for example tetraraethylthiuram disulfide. The preparations may further contain other conventionally used ingredients such as dispersants, fillers and antioxidants. In addition, the preparation can contain a portion of a rubber latex other than synthetic cis-polyisoprene, for example natural rubber latex or ώβΚ latex.

The invention is illustrated by the following examples.

Example 1 -

The following batch formulations were made.

Dry weights I II

synthetic ice-polyisoprene latex

CCariflex IR 700) 1st floor 100

Hatriuinalkylnaphthalinsulfonat (Perminal BX)

Potassium oileate -

zinc oxide

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0.5 o, 5 0.5 0.5 2.0 2.0

Dry weights
I, ■ - II. 1.0. sulfur 1, - Zinc rvi ^ N-diethyldithiocarbamate (ZDC) 1, Zinc salt of 2-mercaptobenzothiazole
(ZMBT) 1, , 0 , 0 , 0

RZ5O B · - 5.0

Zinc oxide and sulfur were prepared as separate 50 ™ aqueous dispersions by mixing the solid powder in water containing 1 and 2 percent, respectively, based on the weight of the solid, β-naphthalenesulfonic acid / formaldehyde condensate as a wetting agent and 24 hours prior to use processed with a ball mill. Zinc N, N-diethyldithiocarbamate and zinc-2-benzothiazole mercaptide were mixed together in water containing 2% (based on the weight of the mixed zinc salts) β-naphthalenesulfonic acid / formaldehyde condensate. The dispersion produced dung for normal Verwen- Mk was processed 24 hours prior to their use with the ball mill. In a comparative experiment, the processing with the ball mill was omitted. RZ 50 B is a 50% solution of N ₁ N-dimethyicyclohexylammonium-N'-N'-dibutyldithiocarbamate in ethylene glycol monoethyl ether. The dispersions for incorporation into the latex were prepared by adding the solution to an equal volume of water with stirring.

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The silica sol for preparing the formulations of the invention containing 30 wt. # Silica having an average particle size was determined by light diffraction of 250% and a pH of 9 »5 to 10.0, and it was in an amount of 10 Parts by weight of silica are used per 100 parts by weight of cis-polyisoprene, each based on dry weight basis.

The formulations were prepared by adding the latex to the various dispersions with stirring until a uniform mixture was obtained, taking care to avoid entrapping air bubbles during mixing. Films were cast by pouring the preparations onto glass dish-shaped slides approximately 1.5 ^{mm deep.}

The gelation of the latex occurred during drying at room temperature and the gelled plates or films were then cured by heating in an oven, curing conditions of 25, 55 and 50 minutes at ⁰ 1QO O were used. There was no significant difference in curing and the results were therefore averaged. After the hardened films had been peeled off the glass, dumbbell model test pieces were cut from them to determine the physical properties in accordance with BS 903. A cis-polyisoprene latex preparation which the

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indicated above was identical, but no silica sol was used to make control test pieces.

The results obtained in Table I show in which Way the addition of colloidal silica to polyisoprene latex counteracts the effect of inadequate preparation or formation of the compound components.

Table I.

Accelerator system tensile strengths of

search items (kg / cm ^)

with without

Silica

ZMBT / ZDG - - '

Dispersion, with the ball mill

treated 1? 8 185

ZMBT / ZDC -

Dispersion, not ground 46 83

The inadequate preparation of the compound ingredients (i.e. oversized particle sizes) is also evident as poor surface finish on the vulcanized article. This effect also does not occur if colloidal silica is incorporated into the latex preparation, what by a visual comparison of the silica. holding test pieces can be determined with the controls.

The results given in Table II show the by adding coludal silica to the polyiso-

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Table II '

Accelerator system? OO ^ module (kg / cm)

without with silica

ZMBT / ZDC dispersion, ■ -.,

Ball mill treated 30 54

RZ 50 B - 28 54

Example 2

This example illustrates the effects of colloidal silica as a process aid in a heat-sensitive gelling system.

The basic batch was the same as batch II in Example 1. Polyvinylinethyl ether was added to a heat-sensitive gelling agent in an amount of 3 parts by weight per 100 parts by weight of cis-polyisoprene (based on dry weight). A silica sol was added to part of the mixture thus obtained, as described in Example 1, with formation of 10 parts by weight of silica per 100 parts by weight of cis-polyisoprene, in each case on a dry weight basis. The other part of the mixture was used without silica. Films were cast as in the previous example and gelled in one äaü they heat a jet which formed a temperature of 11O ⁰ C, exposing 4 Hinuten. The samples were cured with different times and

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determines the physical properties of the vulcanizates, The results are summarized in the following table. "

35 without Silica 35 with 60 Curing time min.,
at 100 ^° C 161 55 60 ' 121 55 114 Tensile strength kg / cm 8th 100 80 11th 128 11th 300 / J Iiodul kg / cm ² 31 6th - 42 10 36 7Ou '^ module kg / cm ² 910 20th 13th • ö80 37 880 Elongation to break ^: /> 920 950 880

The presence of colloidal silica in the batch gives a large increase in modulus and markedly reduces the effect of overcuring that is common to many factory drying processes is inevitable.

Example 3

This example illustrates the improvement in the uniformity of physical properties that is achieved by adding colloidal silica to a synthetic cis- ^ oiyisoprenlätexansa / cz. incorporated.

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The basic approach, the same as liasis preparation I of Example 1, and the silica sol was also the same, as used in Example 1; It was in two Amounts used, whereby one got approaches that 5 resp. 10 parts by weight of silica per 100 parts by weight of cis-polyisoprene polymer, each on a dry weight basis. A basic approach, water like water which is introduced with the silica sol in the other batches was used as a control.

Films were cast by pouring the preparations onto dish-like glass slides approximately 1.5 mm deep. The latex was gelled during drying at room temperature and the gelled films were then ^{cured by heating at 120 °} C. in a drying cabinet for 30 minutes. After the hardened films were peeled off the glass, dumbbell test pieces were cut from the film to determine the physical properties according to Bfc> 903.

The distribution of the moduli, elongations to break and tensile strengths in the control and the samples containing 5 and 10 wt.% Of silica contained, the accompanying drawings are illustrated in the histograms. The results were obtained with 40 samples each. The histograms

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clearly show a reduction in the variability of the Results and the shift to higher values for tensile strength and elongation to break for specimens that Contains silica.

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Claims (1)

Patent claims: 1. Preparation characterized in that it is a dispersion of colloidal silica in a synthetic cis-J / olyisopron latex. 2. Preparation geniä'ls claim 1, characterized in that daii the preparation a mixture of a synthetic cisi-olysoprene latex and a silica aquasol. 3. Preparation according to claim 2, characterized in that dais the average particle diameter of the silica from 50 to 250 S is «, 4. Preparation according to one of claims 1 to 3 characterized characterized in that they contain up to 20 parts by weight of silica per 10 parts by weight of ice-polyisoprene polymer, each including the '! 5. Preparation geniäis claim ^ f characterized that it contains 5 parts by weight of silica. ο. Preparation according to claim 1, essentially as in one of Examples 1 and 2 described. 7. Procedure for the production of a vulcanized 00 98 37/207 8 BATH Stand made of a synthetic polyisoprene latex characterized in that the latex used is colloidal silica contains. 8. The method according to claim 7, characterized in that
that the latex containing the colloidal silica is a preparation according to one of claims 2 to 5. Claim 7> described 9 · A method according to i ^m substantially as described in any of Examples 1 and 2. FIG. 10. Vulcanized item, provided that it is after a process according to any one of claims 7 to 9 was obtained. 11. Process for improving the constancy of the quality of objects made from a synthetic cis-Polyisoprerilatexzuöereitüng, which contains water-insoluble Korapound constituents are manufactured, characterized in that, you can add colloidal silica to a preparation to Golchen contains compound ingredients. ■ ■ ..'- 12. The method according to claim 11 characterized in that
since the approach is a preparation according to one of claims 2 to 5, the water-insoluble compound constituents contains. ■ ORIGINAL BATHROOM 009837/2078 ~ ¹⁷ ~ 19500U 15 · Method according to one of claims 11 and 12 thereby characterized in that the compound ingredients include sulfur, zinc oxide and a vulcanization accelerator. 14. The method according to claim 13, characterized in that that the vulcanization accelerator zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc-2-benzothiazole mercaptide or a mixture of such zinc salts. 15 · The method according to claim 11 essentially as in Example 3 described. 009837/2078 Blank page