JP2005281656A - Novel processing auxiliary for rubber and silica-compounded rubber composition containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel processing auxiliary for rubber for improving workability of a silica-containing unvulcanized rubber composition without loss of physical properties of the rubber in combination with the silica simultaneously together with improved releasability from a die in vulcanization. <P>SOLUTION: The processing auxiliary for rubber is composed of a decyltrialkoxysilane and/or a cyclohexylalkyldialkoxysilane. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a novel rubber processing aid that improves the processability of a silica-containing unvulcanized rubber composition and at the same time improves the mold releasability during vulcanization.

When silica is blended with rubber, it is necessary to reduce the viscosity of these compositions and ensure processability. In general, various plasticizers, softeners and the like are used, and further, processing aids composed of fatty acids, fatty acid esters, fatty acid amides, and fatty acid metal salts are often used in combination. In particular, fatty acid zinc salts and composites based on them are effective in reducing the viscosity of unvulcanized rubber compositions containing silica, and are used on a daily basis (see, for example, Non-Patent Document 1). However, when a processing aid composed of a fatty acid zinc salt is used, the unvulcanized rubber composition may adhere in the closed mixer or on an open roll, which may impair operability. In addition, the fatty acid zinc salt may be used in combination with other fatty acid metal salts to solve the above problems. However, processing aids mainly composed of these fatty acid metal salts are vulcanized rubber properties such as wear resistance. The amount of their use is limited regardless of whether the effect is excessive or insufficient. In addition, silica compounding has a problem with mold releasability during vulcanization and may be dealt with by using various external mold release agents, but external mold release agents are frequently applied to the mold. This is not preferable in terms of productivity. Therefore, an internally added mold release agent has been demanded, and the above fatty acid derivative has been recognized as having a temporary effect, but is insufficient in performance.
"The 55th Rubber Technology Symposium Text: Compounding Examination (Processing Aid) from Molding Process, Japan Rubber Association, 1998"

The problem to be solved by the present invention is to improve the processability of a silica-containing unvulcanized rubber composition without impairing the rubber physical properties in silica compounding, and at the same time, mold releasability during vulcanization, in view of the above-mentioned drawbacks of the prior art It is also to provide a new rubber processing aid having a function of improving.

（式中、Ｒ１及びＲ２は炭素数１〜４のアルキル基を示す。）
ジエン系ゴム１００重量部にシリカを１０〜８０重量部配合する時点で一般式（１）及び／又は一般式（２）で表されるオルガノシランを用いる。また、オルガノシランは反応を促すためにシリカと同時にゴムへ配合することが好ましく、更にシランカップリング剤を併用しても構わない。オルガノシランの添加量は０．５〜８重量部で、配合されるシリカ重量部の５〜１０重量％が好ましい。混練りによるシリカとオルガノシランの反応条件は、一般的にゴムへ用いられるシランカップリング剤の条件に準ずるが、８０〜１２０℃で２分以上の混練りを保持することが好ましい。As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, by using the organosilane compound represented by the general formula (1) and / or the general formula (2) at the stage of kneading rubber and silica, the above problems have been solved and the present invention has been completed.

(In the formula, R 1 and R 2 represent an alkyl group having 1 to 4 carbon atoms.)
The organosilane represented by the general formula (1) and / or the general formula (2) is used when 10 to 80 parts by weight of silica is added to 100 parts by weight of the diene rubber. Further, organosilane is preferably blended with rubber simultaneously with silica in order to promote the reaction, and a silane coupling agent may be used in combination. The addition amount of the organosilane is 0.5 to 8 parts by weight, and preferably 5 to 10% by weight based on the silica part by weight. The reaction conditions of silica and organosilane by kneading are generally the same as those of a silane coupling agent used for rubber, but it is preferable to maintain kneading for 2 minutes or more at 80 to 120 ° C.

The silica-containing rubber composition containing the organosilane represented by the general formula (1) and / or the general formula (2) can be processed and vulcanized without losing physical properties of the vulcanized rubber as compared with the conventional silica-containing rubber composition. It is clear and useful that the mold releasability at the time is excellent.

粘度が高いにもかかわらず、グリーン強度の低いＳＢＲ／シリカ配合は、バンバリー混合槽内やオープンロール上（特にバックロール）で付着しやすい。実施例１〜３のオルガノシランはＳＢＲ／シリカ配合の防着に寄与し、バンバリーやオープンロールの操作性を改善する。
次に未加硫ゴム物性試験の結果を表２に示す。

ムーニー粘度測定の結果より、オルガノシランを用いた実施例１〜３の何れも、脂肪酸亜鉛塩であるエクストンＬ−２を用いた比較例１より大幅に粘度が低下していることがわかる。また、スコーチタイム及び加硫速度については、加工助剤を用いていない比較例２よりも若干遅いものの、比較例１とほぼ同等な結果が得られている。
次に加硫時の金型離型抵抗（指数）の結果について表３に示す。

金型離型抵抗は任意の金型を用いて、各未加硫ゴム組成物を加硫した後、片面だけ金型を取り除き、現れた加硫ゴムを引張り試験機で引き剥がした時の剥離抵抗を測定した。加工助剤を用いていない比較例２に対して、脂肪酸亜鉛塩であるエクストンＬ−２を用いると、剥離抵抗が約１５％低下することが比較例１の結果にてわかる。しかし、効果としては充分とは言えない。一方、オルガノシランを用いた実施例１〜３の剥離抵抗は、比較例２と比較して４０％以上低下していることがわかり、効果として充分であると言える。
（加硫ゴム物性試験）
更に加硫ゴム物性を表４に示す。

比較例１の脂肪酸亜鉛塩は、シリカ配合の加硫ゴム物性に影響をもたらす。即ち、引張り物性において中間応力（特に１００〜３００％）の低下と最大応力及び伸びの増加が見られ、耐圧縮永久歪や動的発熱性等の特性に悪影響を与えることがわかる。これらの影響は脂肪酸亜鉛塩がゴム・ゴム間、ゴム・シリカ間でズレを生じさせやすくすることに起因すると考えられる。それに対し、各実施例で用いられているオルガノシランは、むしろブランクである比較例２に近い引張り物性を示し、実施例１及び３で用いたオルガノシランを併用することで、実施例２の結果の如く、比較例２のブランクに極めて近い物性を再現することができることは特筆すべき点である。更に各実施例の耐圧縮永久歪性や動的発熱性が、ブランクである比較例２以上の結果を示していることは、これら特定のオルガノシランがシランカップリング剤のカップリング反応及び加硫反応を妨げずに、混練り中にゴムへのシリカの分散を促し、更に未加硫ゴム組成物中のシリカの再凝集を抑制することで、シリカの分散を高度に保つことによるものと考える。EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, of course, this invention is not limited at all by this.
(Unvulcanized rubber physical property test)
Table 1 shows the formulation of S-SBR and the adhesion of the resulting unvulcanized rubber composition. The compounding kneading was performed using a Banbury mixer (FARREL BR type 1.7 l), and S-SBR, silica, zinc oxide, stearic acid, silane coupling agent, and organosilane were added all together and kneaded under predetermined conditions. . Thereafter, sulfur and a vulcanization accelerator were added with a 10-inch open roll, and various physical properties of the blend were measured.

Despite its high viscosity, SBR / silica blends with low green strength tend to adhere in Banbury mixing tanks and on open rolls (especially back rolls). The organosilanes of Examples 1 to 3 contribute to the prevention of SBR / silica blending and improve the operability of Banbury and open rolls.
Next, Table 2 shows the results of an unvulcanized rubber physical property test.

From the results of Mooney viscosity measurement, it can be seen that the viscosity of all of Examples 1 to 3 using organosilane is significantly lower than that of Comparative Example 1 using Exton L-2 which is a fatty acid zinc salt. Further, the scorch time and vulcanization rate were slightly slower than Comparative Example 2 in which no processing aid was used, but almost the same results as Comparative Example 1 were obtained.
Next, Table 3 shows the results of mold release resistance (index) during vulcanization.

Mold release resistance is the separation when each unvulcanized rubber composition is vulcanized using an arbitrary mold, the mold is removed only on one side, and the vulcanized rubber that appears is peeled off by a tensile tester. Resistance was measured. It can be seen from the results of Comparative Example 1 that the exfoliation resistance is reduced by about 15% when Exton L-2, which is a fatty acid zinc salt, is used compared to Comparative Example 2 in which no processing aid is used. However, it is not enough as an effect. On the other hand, it can be seen that the peel resistances of Examples 1 to 3 using organosilane are reduced by 40% or more compared to Comparative Example 2, which is sufficient as an effect.
(Vulcanized rubber property test)
Further, Table 4 shows the physical properties of vulcanized rubber.

The fatty acid zinc salt of Comparative Example 1 affects the physical properties of vulcanized rubber compounded with silica. That is, it can be seen that a decrease in intermediate stress (especially 100 to 300%) and an increase in maximum stress and elongation are observed in tensile physical properties, which adversely affect properties such as compression set resistance and dynamic exothermic property. These effects are thought to be caused by the fact that the fatty acid zinc salt tends to cause a gap between rubber and rubber and between rubber and silica. On the other hand, the organosilane used in each example shows a tensile physical property that is rather similar to that of the comparative example 2 that is a blank, and the results of the example 2 are obtained by using the organosilane used in the examples 1 and 3 together. As described above, it is a remarkable point that physical properties extremely close to those of the blank of Comparative Example 2 can be reproduced. Further, the compression set resistance and dynamic exothermic property of each example show the results of Comparative Example 2 or more, which is a blank. These specific organosilanes are used for coupling reaction and vulcanization of silane coupling agents. It is thought that the dispersion of the silica in the rubber during the kneading is promoted without impeding the reaction, and further the re-aggregation of the silica in the unvulcanized rubber composition is suppressed, thereby maintaining the dispersion of the silica at a high level. .

Claims (2)

A rubber processing aid comprising an organosilane compound represented by general formula (1) and / or general formula (2).

(In the formula, R 1 and R 2 represent an alkyl group having 1 to 4 carbon atoms.) A rubber composition comprising 10 to 80 parts by weight of silica and 0.5 to 8 parts by weight of the processing aid according to claim 1 with respect to 100 parts by weight of a diene rubber.