JP2853980B2 - Rubber composition for tire tread - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire tread, and more particularly to a vulcanizable silica-containing rubber composition for a tire tread, which has improved processability when unvulcanized. The rubber composition for a tire tread of the present invention,
For example, it is useful for cap treads, side treads, and undertreads. Here, "silica"
Is hydrated silicic acid, and refers to those having a nitrogen specific surface area of 50 to 300 m ² / g used for rubber, and “vulcanization” includes cross-linking by sulfur or peroxide. .

[0002]

2. Description of the Related Art Rubber compositions comprising silica mixed with various rubbers are known, and are used, for example, as rubber compositions for tire treads having low heat generation and excellent wear resistance.
However, tire treads containing silica have low rolling resistance and good grip on wet roads, but the viscosity of unvulcanized compounds increases, vulcanization delays, and the cohesion of the mixture decreases, resulting in poor productivity. was there. In particular, when silica and carbon are simply mixed at the same time, sufficient contact and reaction occur between carbon and rubber to promote sufficient mixing, but not sufficient with silica, causing poor dispersion of silica and causing sufficient silica characteristics. It was not alive. There have been various proposals for solving such a problem, but none of them is practically satisfactory.

For example, diethylene glycol or a fatty acid is added (for example, Rubber Industry Handbook <4th edition>, 517-
518, published in 1994), and addition of a metal carboxylate (for example, Tire Technology I)
International 1995, pp. 107-108), and treatment of silica with a silicone oil in advance (see, for example, JP-A-6-248116) has been proposed. I can not say. Furthermore, there is no method other than taking a method such as increasing the number of times of mixing for the occurrence of burns and a reduction in cohesion during mixing, and when mixing carbon and silica, Alternatively, the actual situation is that the mixing time and the number of times of mixing are increased.

[0004]

Accordingly, the present invention eliminates the above-mentioned problems of the prior art and substantially reduces the characteristics of the silica-containing vulcanizable rubber composition, for example, the characteristics such as low heat build-up and abrasion resistance. It is an object of the present invention to provide a silica-containing vulcanizable tire tread rubber composition in which the processability of an unvulcanized rubber composition is improved without impairing the rubber composition.

[0005]

According to the present invention, 100 parts by weight of a diene rubber, 2 to 80 parts by weight of carbon black, 5 to 80 parts by weight of silica, a silane coupling agent and formula (I):

Embedded image (Wherein, R ¹ independently represents a methyl group, an ethyl group or a phenyl group, R ² independently represents a hydrogen or an organic group, R ³ independently represents an alkyl group, and m represents 0 or an integer of 1 or more. Wherein n is an integer of 1 or more). A rubber composition for a tire tread comprising a polysiloxane having a number average molecular weight of 200 to 100,000 having a repeating unit of

According to a preferred embodiment of the present invention, there is provided a cap tread rubber composition for a tire in which the amounts of the polysiloxane and the silane coupling agent are in the following ranges. 0.5 ≦ (W _PS / W _SC ) ≦ 7 Silica content × 1% by weight ≦ W _PS + W _SC ≦ Silica content ×
40 wt% where W _PS : blending amount of polysiloxane (parts by weight)
W _SC : Compounding amount of silane coupling agent (parts by weight)

According to a preferred embodiment of the present invention, there is provided a tread rubber composition for a tire, wherein the rubber composition is mixed in a simultaneous step at a temperature of 120 ° C. or higher except for a vulcanization system.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure, operation and effect of the present invention will be described in detail. As described above, the tire tread containing silica has good vulcanization properties, but has a drawback that the workability in the unvulcanized state is poor. According to the findings of the present inventors, this is due to silanol groups (≡Si—OH) present on the silica surface, and a structure is formed in the rubber composition due to the cohesive force of the silanol groups to increase the viscosity. Or
An unvulcanized composition due to the phenomenon that vulcanization accelerators are adsorbed due to the polarity of the silanol group and vulcanization is delayed, or the cohesion of the mixture is reduced due to insufficient compatibility with the non-polar rubber. The workability of the steel is reduced. Further, a silane coupling agent is often used in combination with the silica-containing rubber composition to reinforce the rubber.However, a silanol group also exists in the inner cavity of the silica particles, and this is considered as a silane coupling agent. There is a problem that a large amount of the silane coupling agent must be blended because the reaction causes loss of the silane coupling agent and a reduction in the reinforcing effect. As in the prior art, when a polar substance such as diethylene glycol is added thereto, the phenomenon that a polar compounding agent such as a vulcanization accelerator is adsorbed can be prevented to some extent, but cannot be completely prevented, and a silane coupling agent or the like cannot be prevented. Neither was it possible to prevent substances that chemically bond with the silica particles from binding to the lumen.

However, according to the present invention, since the polysiloxane having the repeating structural unit of the formula (I) is blended in the rubber composition, the alkoxysiloxane reacts with silanol groups to cover the surface of the silica particles. By solving all the problems of the prior art, it is possible to effectively suppress the increase in viscosity caused by the cohesive force and polarity of silanol groups and the wasteful consumption of polar additives such as vulcanization accelerators and silane coupling agents. it can.

The polysiloxane of the formula (I) blended in the rubber composition according to the present invention has an alkoxysilyl group which reacts with a silanol group as described above, and covers the surface of the silica particles to provide a lubricating effect. The size indicated, for example, the number average molecular weight is 200 to 100,000, preferably 500 to
It must be 50,000 polymers (or oligomers). Therefore, in the repeating unit of the above formula (I), the presence of the ≡Si—O—R ³ group is indispensable, and therefore, n is 1 or more, preferably 5 to 1000, and even if m is zero, However, there may be a hydrogen group or another organic group. Such a polysiloxane is a known substance and can be generally produced, for example, as follows.

The compound having the siloxane structure of the formula (I) is synthesized by reacting the corresponding polyalkyl hydrogen siloxane with an alcohol in the presence of a catalyst. As polyalkyl hydrogen siloxane,
The following can be exemplified.

[0012]

Embedded image

The alcohol includes methanol, ethanol, propanol, butanol, pentanol,
In addition to heptanol, octanol, octadecanol, phenol, benzyl alcohol, alcohols having an oxygen atom such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether can be exemplified. Examples of the carboxylic acid include acetic acid, propionic acid, palmitic acid, stearic acid, and myristic acid. Examples of the catalyst include chloroplatinic acid, a platinum-ether complex, a platinum-olefin complex, PdCl ₂
(PPh ₃ ) ₂ , RhCl ₂ (PPh ₃ ) ₂ tin octylate, zinc octylate, or an acid or base catalyst can be used.

As described above, the polysiloxane used in the present invention is not particularly limited in its terminal group, and is determined by the type of raw materials used in the production. Examples thereof include a trimethylsilyl group, a methyldiphenylsilyl group, and a trimethylsilyl group. An organic group other than the phenylsilyl group may be used.

In the formula (I), R ¹ represents a methyl group, an ethyl group or a phenyl group, R ² represents hydrogen or an organic group, and the organic group includes, for example, C 1
Examples include H ₃ , C ₂ H ₅ , a styrene residue, a divinylbenzene residue, a limonene residue, a butadiene residue, and an isoprene residue. R ³ is CH ₃ , C ₂ H
Examples thereof include an alkyl group having 1 to 36 carbon atoms such as ₅ .

The diene rubber compounded as a main component in the vulcanizable rubber composition according to the present invention may be any diene rubber conventionally compounded in various rubber compositions, such as natural rubber (NR). , Polyisoprene rubber (IR), various styrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers (BR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), and the like. These diene rubbers can be used alone or as an arbitrary blend. In addition, these diene rubbers can also be used by blending with ethylene-propylene copolymer rubber (EPR, EPDM) and the like.

The silane coupling agent used in the present invention can be any silane coupling agent conventionally used in combination with a silica filler. Typical examples include the following. Of these, bis- [3- (triethoxysilyl) -propyl] tetrasulfide is most preferred from the viewpoint of processability.

[0018]

Embedded image

The total amount of the polysiloxane and the silane coupling agent used in the present invention is 1 to 40% by weight, preferably 2 to 20% by weight based on the total amount of the silica and the silane coupling agent. (Polysiloxane / silane coupling agent) weight ratio is 0.5
-7, preferably 1-4. If the amount of the polysiloxane is too small, the desired effect cannot be obtained,
Conversely, if the amount is too large, the substance that does not bind to silica may exude from the vulcanized product, which is not preferable. On the other hand, if the amount of the silane coupling agent is too small, the desired effect cannot be obtained. On the other hand, if the amount is too large, burning (scorch) tends to occur in the mixing and extrusion steps, which is not preferable.

According to a preferred embodiment of the present invention, when silica and carbon black are mixed in the same step, sufficient contact / reaction occurs between the diene rubber and carbon black to promote the mixing. With rubber and silica, sufficient contact / reaction cannot be obtained due to the polarity of the silanol groups on the silica surface, causing cohesion during mixing, burning, etc., and also worsening the dispersion. Further, when silica and carbon black are separately mixed, for example, when silica is mixed in the first step (process) and carbon black and other compounding agents are added in the second process, the diene rubber in the second process is mixed. In some cases, sufficient mixing of carbon black is not promoted, and it may be difficult to obtain the original reinforcing properties of carbon black. However, as described above, according to the present invention, the addition of the silane coupling agent and the polysiloxane represented by the formula (I) results in cohesion at the same time in the simultaneous mixing, the burning is improved, and the dispersion proceeds. It is possible to obtain the same or better performance than when carbon is mixed in another step.

In the rubber composition according to the present invention, in addition to the above essential components, carbon black, a vulcanizing or crosslinking agent,
Various additives commonly used for tires such as vulcanization or crosslinking accelerators, various oils, anti-aging agents, reinforcing agents, fillers, plasticizers, softeners, and other general rubbers may be compounded. Can be kneaded in the usual way,
It can be vulcanized to a composition and used to vulcanize or crosslink. The compounding amounts of these additives can also be conventional general compounding amounts as long as they do not contradict the object of the present invention.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to standard examples, examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited to these examples.

Various polysiloxanes represented by the general formula (I)
Was synthesized by the following general method.Polysiloxane 1 Polymethyl hydrogen siloxane (KF99, Shin-Etsu
Mix 200 g of methanol and 85 g of methanol
40% of 1% chloroplatinic acid isopropyl alcohol solution
In addition, the mixture was reacted at 80 ° C. for 10 hours to synthesize. This compound
The estimated structure is as follows in the formula (I). R¹= CH_Three, R^Two= H, R^Three= CH_Three, M: n = 2
1:79, m + n = 30 Polysiloxane 2 Polymethyl hydrogen siloxane (KF99, Shin-Etsu
200 g of ethanol and 120 g of ethanol,
40 μl of 1% chloroplatinic acid isopropyl alcohol solution
It was added and reacted at 80 ° C. for 10 hours to synthesize. This compound
Is as follows. R¹= CH_Three, R^Two= H, R^Three= C_TwoH_Five, M: n = 2
1:79, (m + n) = 30

The following commercially available products were used as the other components in the following standard examples, examples and comparative examples. Natural rubber: RSS # 1 SBR (NS116): Nipol NS116 (Zeon Japan) SBR (NP9528): Nipol 9528 (Zeon Japan) SBR (NP1530): Nipol 1530 (Zeon Japan) BR (NP1220): Nipol BR1220L (Nihon Zeon) Silica: Nipsil AQ (Nippon Silica) Silane coupling agent: Si69 (Dexa) (chemical name:
Bis- [3- (triethoxysilyl) -propyl] tetrasulfide) Carbon Black 1: Seast KH (Tokai Carbon) Carbon Black 2: Seat 9M (Tokai Carbon)

Powdered sulfur: 5% oil-treated powdered sulfur Antioxidant 6C: N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine Aroma oil: Aromatic process oil Vulcanization accelerator CZ : N-cyclohexyl-2-benzothiazylsulfenamide Vulcanization accelerator DPG: diphenylguanidine Zinc oxide: Zinc flower No. 3 Stearic acid: Industrial stearic acid

Preparation of Sample The vulcanization accelerator and components other than sulfur were kneaded for 3 to 5 minutes in a 1.8-liter closed mixer, and the vulcanization accelerator was added to the masterbatch released when the temperature reached 165 ± 5 ° C. And sulfur were kneaded with an 8-inch open roll to obtain a rubber composition. In the case of two-step mixing, the first step is to knead the mixture in a 1.8-liter closed mixer for 3 to 4 minutes, and the masterbatch released when the temperature reaches 150 ± 5 ° C is mixed with the remaining components in the second step to 1.8. The mixture is kneaded for 3 to 5 minutes with a 1 liter closed mixer, and the vulcanization accelerator and sulfur are kneaded with an 8-inch open roll into the second step master batch released when the temperature reaches 165 ± 5 ° C. to obtain a rubber composition. Was. The unvulcanized physical properties of the obtained rubber composition were measured. Next, the composition was press-vulcanized in a 15 × 15 × 0.2 cm mold at 160 ° C. for 20 minutes to prepare a target test piece, and the vulcanization properties were evaluated.

The test methods for the unvulcanized and vulcanized properties of the compositions obtained in each example are as follows. Unvulcanized physical properties 1) Unity with a mixer: Evaluated by unity of the master batch at the time of release from the mixer. However, in the case of two steps, the evaluation is for the second step master batch. ◎: There is almost no powder that has been incorporated into a lump and has not been incorporated into rubber. …: Powders that are collected in a lump but not incorporated in rubber are occasionally found. X: Small pieces of loose rubber to which powder has adhered can be seen. 2) Mooney viscosity: 10 based on JIS K 6300
It was measured at 0 ° C. 3) Vulcanization rate: 160 ° C. based on JIS K 6300
The time to reach 95% vulcanization was measured at. 4) Scorch time: 12 based on JIS K 6300
The time at which the viscosity increased by 5 points at 5 ° C. was measured.

Vulcanized physical properties 1) Carbon / silica dispersed state: The vulcanized rubber was cut with a sharp blade, and the surface was visually observed and observed with an optical microscope (× 10).
0,400) and evaluated. …: Defective dispersion lump of carbon and silica (several 100 μm)
Diameter) and are evenly distributed. …: Several poorly dispersed masses of carbon and silica are scattered, but the others are dispersed to some extent. Δ: Dozens of poorly dispersed lumps of carbon and silica were observed, but the others were dispersed to some extent. C: Powder-like things can be seen from the cut surface, and countless defective lumps of carbon and silica are found. 2) 300% deformation stress, breaking strength, breaking elongation: JIS
3) tan δ: Measured with a rheograph solid manufactured by Toyo Seiki Seisakusho at 20 Hz, initial elongation 10%, dynamic strain 2% (sample width 5 mm, temperature 0) 4) Abrasion resistance: Measured with a Lambourn-type tester and displayed as an index of loss on wear Abrasion resistance (index) = [(weight loss on reference test piece) / (weight loss on each test piece) )] × 100 However, the reference test pieces were calculated as standard examples 1, 7 and 14 in Tables I to III, respectively.

Examples 1-2 (standard example), Examples 3-4 (example)
And Examples 5 to 6 (Comparative Examples) These examples show the evaluation results of the silane coupling agent, the polysiloxane, and the batch mixture in the NR and SBR systems. The formulations and results are shown in Table I.

[0030]

[Table 1]

Examples 7 to 9 (standard examples), Examples 10 to 12 (implementation
Example) and Example 13 (Comparative Example) These examples show the evaluation results of the silane coupling agent, the polysiloxane, and the batch mixing in the SBR system. The formulations and results are shown in Table III.

[0032]

[Table 2]

[0033]Examples 14 to 15 (standard examples), Examples 16 to 18
(Example) and Examples 19 to 20 (Comparative Examples) Examples of these are silane couplings in SBR systems.
Showing the evaluation results of the agent, polysiloxane and batch mixing
It is. The formulations and results are shown in Table III.

[0034]

[Table 3]

[0035]

As described above, according to the present invention, the rubber composition for a tire tread is mixed with a silane coupling agent and the polysiloxane of the formula (I) together with silica to prepare Examples 3 to 6 and Example 10. As shown in Examples 13 to 20, the processability of the unvulcanized rubber composition was improved, and the physical properties of the vulcanized rubber were equivalent or higher, and the silane coupling agent and the compound represented by the formula (I) When polysiloxane was added, Examples 3 to 4, Examples 10 to 12, and Examples 16 to 1
As shown in FIG. 8, even when silica and carbon are mixed in the same step, the dispersion state of carbon / silica is improved as compared with the case where they are separately mixed, and the same or higher physical properties are exhibited. Is improved in Comparative Examples 5 to 5.
6, it is clear when compared with Comparative Examples 13 and 19-20.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C08K 3:36 5:54) (C08L 9/00 83:06) (72) Inventor Tetsuji Kawamoe 2-1 Oiwake, Hiratsuka-shi, Kanagawa No. Yokohama Rubber Co., Ltd. Hiratsuka Works (56) References JP-A-6-248116 (JP, A) JP-A-62-48743 (JP, A) JP-A-57-172925 (JP, A) JP-A-8 −302070 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08L 7/00-21 / 02,23 / 16,83 / 00-83/16 C08K 3 / 04,3 / 36,5 / 54,13 / 02

Claims (3)

(57) [Claims] 1. A diene rubber (100 parts by weight), carbon black (2-80 parts by weight), silica (5-80 parts by weight), a silane coupling agent and a compound represented by the formula (I): (Wherein, R ¹ independently represents a methyl group, an ethyl group or a phenyl group, R ² independently represents a hydrogen or an organic group, R ³ independently represents an alkyl group , and m represents 0 or an integer of 1 or more. Wherein n is an integer of 1 or more). A rubber composition for a tire tread, comprising a polysiloxane having a number average molecular weight of 200 to 100,000 having a repeating unit represented by the following formula: 2. The amount of the polysiloxane and the silane coupling agent is in the following range: 0.5 ≦ (W _PS / W _SC ) ≦ 7 Silica loading × 1 wt% ≦ W _PS + W _SC ≦ Silica loading × 40 Wt% (wherein, W _PS : blending amount of polysiloxane (parts by weight), W
_The rubber composition for a tire tread according to claim 1, wherein _SC is a blending amount (part by weight) of a silane coupling agent. 3. The rubber composition for a tire tread according to claim 1, which is obtained by mixing a compound excluding a vulcanization system at a temperature of 120 ° C. or higher in a simultaneous step.