JPS6197342A - Rubber composition for covering steel cord - Google Patents

Abstract

PURPOSE:To lower viscosity in an unvulcanized state, to improve green strength, to reduce stickiness on rubber surface and to improve processability, by adding a specified compd. to a rubber compsn. contg. cobalt salt of an org. acid for covering steel cord. CONSTITUTION:In a rubber compsn. for covering steel cord, which contains 0.01-0.8pts.wt. (in terms of Co) organocobalt (e.g. cobalt caprylate) per 100pts. wt. rubber, 1-15wt% (per 100pts.wt. rubber) trans polyisoprene having a trans bond content of 50wt% or above is incorporated in the compsn. A high-quality rubber compsn. for covering steel cord, of which the viscosity is lowered in an unvulcanized state, the green strength is increased, the stickiness on a rubber surface is reduced, the viscosity at a processing temp. is lowered so as to facilitate processing in an unvulcanized state and no changes in physical properties after vulcanization occur can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a rubber composition for tires, particularly to a rubber composition for coating steel cords.

<Prior art>ilF'l automatic Φ, ■ As tires, steel radial tires are used for high speed and safety. -+ In steel tires, the rubber for the steel cord is specially formulated to improve stone contact between the rubber and the steel adhesion IS. That is, rubber compositions for adhesion to steel often contain cobalt salts such as naphthenic cobalt, cobalt octylate, and cobalt rosin acid as compounding agents for adhesion to steel.

However, these cobalt itaate compounding agents usually greatly increase the tackiness of unvulcanized rubber, making it difficult to work during cutting.

In addition, the rubber composition for covering steel cords has a relatively high r4
Normally, it is preferable to use rubber with a certain degree.

Carbon is often blended in a large amount, resulting in high viscosity and poor processability when unvulcanized. Moreover, F
Rubbers containing cobalt salts, such as those shown below, have low green strength (tensile strength when unvulcanized), so they are so-called "lack of stiffness".
This means that there are 11-11 problems with sexuality.

In other words, the rubber composition containing organic acid cobalt is suitable for public use.
Despite its high viscosity, iIIIF had a deficiency in that it had low green strength 1a and excessive tackiness, making it difficult to process.

<Purpose of the invention> The purpose of unreleased Ill is to reduce the unvulcanized viscosity of a rubber composition for steel cord W containing dibaltate 41, improve the green strength, and improve the rubber surface. By preventing excessive stickiness (overtar), processability can be improved without changing the physical properties of the rubber after vulcanization.
The object of the present invention is to provide a rubber composite bale for covering steel cord.

〈Introductory explanation of the invention〉 Such IJ targets can be achieved by I! according to the present invention described below. will be accomplished.

That is, in the present invention, a good cobalt isoate is added to a 100% rubber part with a cobalt element of 0.1 to 0.8.
To! In a rubber composition for coating a steel cord containing 11 parts.

lin rubber 100@FJ part is transformer bonding metal field 5
0 rk g% or more of 1-cadrane polyisoprene
The present invention provides a rubber composition for covering a steel cord, characterized in that the rubber composition for covering a steel cord contains 15% by weight. We investigated ways to improve the drawbacks of high viscosity during sulfurization, low green strength, excessive viscosity, and poor processability, and found that a rubber composition containing transpolyisoprene was effective in improving it. Ta.

Transpolyisoprene as used herein refers to an isoprene polymer containing 50% by weight or more of trans-bonding components.
In particular, it is preferable to use an isoprene polymer in which the trans bond component is 95% or more, and the average molecular weight is 10,000 to 300,000.If the trans bond component is less than 50@dark%, the effects of the present invention will not be achieved. - For example, clareisoprene trans polyisoprene TP-30
1 (average molecular weight 250,000, trans bond content 99% by weight)
67°C), etc. This transpolyisoprene is crystalline at room temperature and has a melting point of 67°C.
It is a sign.

It is also possible to use gutta-percha, which is a natural transpolyisoprene. When these transpolyisoprenes are added to a rubber composition, the rubber composition becomes hard due to its crystallinity at around room temperature, and its green strength increases. Moreover, due to its crystallinity, excessive stone formation can be reduced. On the other hand, since the processing temperature such as rolling is higher than room temperature and higher than that of transpolyisoprene, the crystals actually melt and lower the viscosity IW of the rubber composition.

Addition of transpolyisoprene to steel cord-coated rubber containing a relatively high carbon black content with cobalt content reduces viscosity at processing temperatures, while at room temperature increases green strength and prevents excessive tack. It was discovered that it has a suppressing effect.

1+ of transpolyisoprene that uses 1+ person
8 is a combination of transpolyisoprene and other raw rubber 1,
When 4 is 100, it is 1-15%! +)%, preferably 3 to 10 ilF:J%. If transpolyisoprene is less than l iT (crystalline %), the infants of the present invention will be less likely to be present, and if it exceeds 15T (41%), it will cause stone formation (tuck).
The viscosity decreases too much, making it difficult to perform operations such as addition.

The other raw material rubber used in the present invention may be natural rubber, synthetic rubber, or a mixture thereof; in particular, natural rubber and/or synthetic cis-polyisoprene at 80% by weight.
Including the above, the remainder is preferably a diene rubber of BRlSBR, NBR, CR3.

Further, the rubber composition for coating steel cord used in the present invention contains 0.1 to 0.0% cobalt acetate per 100 weight 1111 parts of polymer (rubber) as a cobalt element.
The composition contains 6 parts of 8'kr. Further, the effects of the present invention are remarkable when the composition contains 50 parts or more of carbon black.

The method of kneading the additive of transpolyisoprene organic acid cobalt and the like into the raw rubber may be a threading method.

<Example> The present invention will be described in detail below using Examples.

(1162 Example 1) As a rubber composition for steel cord YQ, the compounded rubber polymers shown in Fig. 1, Fig. 2, and Fig. 3 were mixed with A', KM (NR'), and transpolyisoprene ([-trt). Seven samples were prepared with different stone content ratios and MI, and the changes in green strength J Ratac over the course of one summer and the Mooney electrostatic discharge were measured.

The green strength was measured using an autograph after punching out an unvulcanized rubber sheet using a JI53F paper cutter.

Also sticky 7. The evaluation of the properties was carried out using a Pikmatac meter (manufactured by Toyo Seihi) using a sample cut into 10 mm wide strips.
The peeling force was measured at a peeling speed of 1250 m/1n and a pressure bonding time of θ seconds.

The conclusion is shown in Figure iS1, Figures 2 and 3.

As can be seen from FIG. 1, as the transpolyisoprene content increases, the green strength at room temperature increases with the blade width. Furthermore, as seen from the wIJz diagram, the viscosity lr property decreases as the content of Tora 7 polyisoprene increases. However, if more than 20% by weight is added, the oral tackiness and irreversible tackiness will drop too much.As seen from No. 31N, the Mooney viscosity decreases as the trans-isoprene content; li increases.

(Example 2) No. 414 and No. 5 rubber compositions for coating steel cords
The polymers of the compounded rubber shown in Fig. 61N are cis-polyisoprene (IR) and trans-polyisoprene (t-IR).
The same measurements as in Example 1 were made by changing the content ratio of .

In Example 8 and Example 2, the same effect of the present invention as in Example 1 was observed.

Effects of the present invention> The present invention provides a steel cord coating rubber composition containing cobalt and relatively high carbon black content by adding a predetermined amount of transpolyisoprene to the steel cord coating rubber composition.
It lowers the viscosity when uncured, increases the green strength, reduces excessive stickiness on the rubber surface, and lowers the viscosity at processing temperature, making it extremely easy to process when uncured. A rubber composition for coating steel cords can be obtained in a large amount without changing the physical properties of the rubber after sulfurization.

[Brief explanation of the drawing]

Figure i1 is a graph showing the improvement in green strength by adding transpolyisoprene to natural rubber. Figure 3 is a graph showing the decrease in Mooney viscosity due to the addition of trans polyisoprene to natural rubber. FIG. 5 is a graph showing the change in green strength due to the addition of trans polyisoprene to polyisoprene rubber. FIG. 5 is a graph showing the change in tack over time due to the addition of trans polyisoprene to polyisoprene rubber. FIG. is a graph showing the decrease in Mooney viscosity due to the addition of trans-polyisoprene to polyisoprene rubber. Patent applicant: Yokohama Rubber Co., Ltd., agent, patent attorney: Nozomi Watanabe, patent attorney: Yo Ishii - FIG, 1 strain (@ l・) Tack value (9) FIG, 3 NR/1-IR<f4ra> FIG, 4 strain <S>

Claims (1)

[Claims] In a steel cord coating rubber composition containing 0.1 to 0.8 parts by weight of organic acid cobalt as an elemental cobalt amount based on 100 parts by weight of rubber, 100 parts by weight of the rubber has a trans bond content of 50% by weight or more. A rubber composition for coating a steel cord, characterized in that it contains 1 to 15% by weight of transpolyisoprene.