JP2013100479A - Silica-styrene-butadiene rubber composite and manufacturing method thereof, rubber composition, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silica-styrene-butadiene rubber composite in which silica is minutely dispersed, and a manufacturing method thereof.SOLUTION: The silica-styrene-butadiene rubber composite is obtained from compounded latex prepared by mixing emulsion-polymerized styrene-butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and alkali.

Description

The present invention relates to a silica / styrene butadiene rubber composite, a method for producing the same, a rubber composition containing the composite, and a pneumatic tire using the same.

In order to reduce the fuel consumption of tires, it has been studied to add silica as a filler to obtain good low heat build-up, but silica has a silanol group on the surface and exhibits hydrophilicity. It is not easy to disperse uniformly in the rubber because it has a low affinity with rubber exhibiting good properties and also has strong self-aggregation.

As a method for dispersing silica in rubber, a method is known in which a silica slurry is added to natural rubber latex and stirred, and then an acid is added to solidify the rubber. According to this method, although the dispersibility of silica is improved as compared with the method of mixing rubber and silica in a dry state, the dispersibility is still not sufficient and there is a lot of silica loss.

Also, Patent Document 1 discloses a method for producing a composite by mixing fine particles silica produced from water glass with rubber latex in a liquid state, and proposes a production method using styrene butadiene rubber latex. is not. There is also room for improvement in terms of silica dispersibility and loss.

JP 2009-51955 A

An object of the present invention is to solve the above problems and to provide a silica / styrene butadiene rubber composite in which silica is finely dispersed and a method for producing the same. Another object of the present invention is to provide a rubber composition and a pneumatic tire using the composite.

In the preparation of a silica-styrene butadiene rubber composite in which silica is finely dispersed, in the method of adjusting the pH of the mixture of styrene butadiene rubber latex and silica slurry to the acidic side and solidifying, the rubber becomes a large block, and the silica becomes the rubber. Silica and rubber are separated due to insufficient incorporation. As a result, since silica becomes a large aggregate, a composite in which silica is uniformly finely dispersed cannot be obtained. In addition, due to the separation, the packing amount of silica is lowered, and silica loss occurs.

In this regard, as a result of various studies, the present inventors have found that silica and rubber are mixed by mixing a styrene butadiene rubber latex synthesized by emulsion polymerization in the presence of a combination of a surfactant and an alkali with a dispersion of fine particle silica. The present invention has been completed by finding that it is possible to coagulate in a state in which the above interaction is enhanced and the dispersibility of silica can be improved.

That is, the present invention is obtained from a blended latex prepared by mixing an emulsion-polymerized styrene butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and an alkali. The present invention relates to a silica / styrene butadiene rubber composite. Here, the alkali is preferably ammonia.

The present invention also includes a step 1 of preparing a compounded latex by mixing an emulsion-polymerized styrene butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and an alkali, and It is related with the manufacturing method of the said silica styrene butadiene rubber composite including the process 2 which adjusts the pH of the mixing | blending latex obtained at the said process 1 to 5-7, and solidifies.

The present invention also relates to a rubber composition containing the silica-styrene butadiene rubber composite. The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, using a compounded latex prepared by mixing an emulsion-polymerized styrene butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and an alkali. Therefore, a silica / styrene butadiene rubber composite in which silica is finely dispersed in the rubber component can be obtained. Further, loss of silica or styrene butadiene rubber during production can be suppressed.

The photograph which shows the state of the filtrate of the composite_body | complex of Example 1. FIG. The photograph which shows the state of the filtrate of the composite_body | complex of the comparative example 1.

<Silica-styrene butadiene rubber composite>
The silica / styrene butadiene rubber composite (silica / SBR composite) of the present invention is prepared by using an emulsion-polymerized styrene butadiene rubber latex (E-SBR latex) and an average particle diameter of 1 μm in the presence of a nonionic surfactant and an alkali. It is obtained from a blended latex prepared by mixing the following fine particle silica dispersion.

According to the study in the present invention, when the E-SBR latex and the fine particle silica dispersion are mixed in the presence of a nonionic surfactant, it does not coagulate even when an acid is added, but with a nonionic surfactant. By using together with alkali such as ammonia, the interaction between silica and rubber is enhanced, not only can the separation of silica and rubber and the aggregation of silica be suppressed, but also good coagulation properties can be obtained, so silica is uniformly finely dispersed. A complex can be prepared. The coagulation mechanism due to the addition of alkali is not necessarily clear, but it is presumed that coagulation proceeds as a result of effective effects of pH, the influence of charge by ammonium ions, and the like.

Moreover, the loss of silica or styrene butadiene rubber can be suppressed by preparing the composite in the presence of a nonionic surfactant and an alkali.

The composite is prepared, for example, by mixing E-SBR latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and an alkali to prepare a compounded latex, and It is obtained by a production method including the step 2 of adjusting the pH of the compounded latex obtained in the step 1 to 5 to 7 and coagulating it.

(Process 1)
In step 1, E-SBR latex is used. Here, pH of E-SBR latex becomes like this. Preferably it is 8.5 or more, More preferably, it is 9.5 or more. When the pH is less than 8.5, the E-SBR latex becomes unstable and tends to coagulate. The pH of the E-SBR latex is preferably 12 or less, more preferably 11 or less. If the pH exceeds 12, the E-SBR latex may be deteriorated.

E-SBR latex can be prepared by a conventionally known production method, and various commercially available products can also be used.
The E-SBR latex preferably has a rubber solid content of 10 to 70% by mass.

In step 1, a fine particle silica dispersion having an average particle size of 1 μm or less is used. That is, not a silica powder but a dispersion (slurry) in which silica having a specific particle diameter is dispersed in water is used. The fine particle silica contained in the dispersion is not particularly limited, and examples thereof include dry method silica (anhydrous silicic acid), wet method silica (hydrous silicic acid), and the wet method silica is used because there are many silanol groups. preferable. The fine particle silica may be used alone or in combination of two or more.

In the dispersion, the average particle size of the fine particle silica is preferably 1 μm or less, more preferably 0.05 μm or less. When it exceeds 1 μm, the fracture strength tends to be inferior. The average particle diameter is preferably 0.005 μm or more, more preferably 0.01 μm or more. If it is less than 0.005 μm, the fine-particle silica is strongly aggregated and may be difficult to disperse.

In this specification, transmission electron microscope (TEM) observation is used as a method for measuring the average particle size of the fine particle silica. Specifically, the microparticles are photographed with a transmission electron microscope. If the shape of the microparticles is spherical, the diameter of the sphere is the particle diameter, and if it is needle-shaped or rod-shaped, the minor diameter is the particle diameter. In this case, the average particle diameter from the center is defined as the particle diameter, and the average value of the particle diameters of 100 fine particles is defined as the average particle diameter.

In the above dispersion, the nitrogen adsorption specific surface area (N ₂ SA) of the fine particle silica by the BET method is preferably 40 m ² / g or more, more preferably 60 m ² / g or more, and still more preferably 140 m ² / g or more. If it is less than 40 m < ² > / g, there exists a tendency for fracture strength to be inferior. Further, the _N 2 SA is preferably 300 meters ² / g or less, 200 meters ² / g or less is more preferable. When it exceeds 300 m ² / g, the fine particle silica is strongly aggregated and may be difficult to disperse.
In addition, the nitrogen adsorption specific surface area by the BET method of a silica can be measured by the method based on ASTM D3037-81.

The fine particle silica dispersion can be produced by a known method and is not particularly limited. For example, the fine particle silica dispersion can be prepared by dispersing fine particle silica using a high-pressure homogenizer, an ultrasonic homogenizer, a colloid mill, or the like. Here, the content of the fine particle silica in the dispersion is not particularly limited, but is preferably 1 to 10% by mass from the viewpoint of uniform dispersibility in the dispersion (100% by mass).

In step 1, a nonionic surfactant is used. The nonionic surfactant is not particularly limited, and polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers, polyoxyethylene polypropylene alkyl ethers, polyoxyethylene polybutylene alkyl ethers; polyoxyethylenes such as polyoxyethylene alkenyl ethers Conventionally known ones such as alkylene alkenyl ethers; polyoxyethylene alkyl phenyl ethers; higher fatty acid alkanolamides can be used, and the polyoxyethylene group can increase the hydrogen bonding force with the silica surface. A nonionic surfactant having a hydrocarbon group as a group or a hydrophobic group can be preferably used.

As such a nonionic surfactant, a compound represented by the following formula (I) can be suitably used from the viewpoint that the effect of the present invention can be obtained satisfactorily.
R ¹ —O— (EO) _x —H (I)
(In the formula (I), R ¹ represents an alkyl group having 3 to 50 carbon atoms or an alkenyl group having 3 to 50 carbon atoms. EO represents an oxyethylene group. The average added mole number x is 3 to 100. )

The number of carbon atoms of R ¹ is preferably 5-30, more preferably 8-20.
Said x becomes like this. Preferably it is 5-50, More preferably, it is 8-30.

In step 1, an alkali is used. Thereby, coagulation | solidification of a rubber component can fully advance and the silica * styrene butadiene rubber composite body which disperse | distributed the silica finely in a rubber component can be obtained. It does not specifically limit as an alkali, A conventionally well-known basic compound can be used, For example, ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium hydrogencarbonate, ammonium carbonate etc. are mentioned. Among these, ammonia is preferable because it has excellent coagulability and can provide a composite in which silica is uniformly dispersed.

In the mixing step of Step 1, E-SBR latex and a fine particle silica dispersion having an average particle diameter of 1 μm or less can be mixed by a known method in the presence of a nonionic surfactant and an alkali. E-SBR latex is put into a known stirring device such as a blender mill, and a method of dropping the fine particle silica dispersion, nonionic surfactant and alkali while stirring, or stirring the fine particle silica dispersion, Examples thereof include a method of dropping E-SBR latex, nonionic surfactant and alkali. By thoroughly stirring until a uniform dispersion is obtained, a compounded latex (mixed solution) can be prepared.

The pH of the compounded latex is preferably 9.0 or higher, more preferably 9.5 or higher. When the pH is less than 9.0, the compounded latex tends to be unstable. The pH of the compounded latex is preferably 12 or less, more preferably 11.5 or less. If the pH exceeds 12, the blended latex may be deteriorated.

In the mixing step, the fine particle silica dispersion is preferably mixed so that the fine particle silica is 5 to 150 parts by mass (in terms of SiO ₂ ) with respect to 100 parts by mass (solid content) of SBR. When the amount is less than 5 parts by mass, the amount of fine particle silica is small, and the effects of the present invention tend not to be obtained sufficiently. When it exceeds 150 parts by mass, the uniform dispersibility of silica tends to be lowered. The content of the fine particle silica is more preferably 30 parts by mass or more. The content is more preferably 100 parts by mass or less, still more preferably 70 parts by mass or less.

In the mixing step, the amount of the surfactant added is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass (solid content) of SBR. If the amount is less than 0.1 parts by mass, the amount of the nonionic surfactant is small, and the effects of the present invention tend not to be sufficiently obtained. When it exceeds 10 parts by mass, the nonionic surfactant tends to affect the deterioration of physical properties. There exists a tendency for the uniform dispersibility of a silica to fall. The added amount is more preferably 0.3 parts by mass or more. Moreover, this addition amount becomes like this. More preferably, it is 8 mass parts or less, More preferably, it is 6 mass parts or less.

In the mixing step, the amount of alkali added is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more with respect to 100 parts by mass (solid content) of SBR. The content is preferably 2.0 parts by mass or less, more preferably 1.2 parts by mass or less. Moreover, when using ammonia as said alkali, the addition amount of ammonia becomes like this. Preferably it is 0.1 mass part or more with respect to SBR100 mass part (solid content), More preferably, it is 0.2 mass part or more. The content is preferably 1.5 parts by mass or less, more preferably 1 part by mass or less. If the amount of alkali or ammonia added is less than the lower limit, the solidification property of the rubber is inferior, and the desired composite may not be obtained. When the upper limit is exceeded, the uniform dispersibility of silica tends to decrease.

When ammonia is used as the alkali, it is preferable to use ammonia water having a concentration of preferably 2 to 20% by mass (more preferably 5 to 15% by mass) from the viewpoint of obtaining good solidification properties.

The temperature and time of the mixing step are preferably 10 to 40 ° C. for 30 to 120 minutes, more preferably 15 to 30 ° C. for 45 to 90 minutes, from the viewpoint that a uniform blended latex can be prepared.

(Process 2)
In step 2, the pH of the compounded latex obtained in step 1 is adjusted to 5-7 (preferably 6-7) and coagulated. When the pH is less than 5, silica dispersion tends to deteriorate. On the other hand, when the pH exceeds 7, coagulation does not proceed and silica dispersion tends to deteriorate.

As a method for adjusting the pH to 5 to 7 and coagulating the compounded latex, an acid is usually used, and the acid is coagulated by adding it to the compounded latex. Examples of the acid for coagulation include sulfuric acid, hydrochloric acid, formic acid, acetic acid and the like. It is preferable to perform the temperature of a coagulation process at 10-40 degreeC.

The obtained coagulated material (agglomerated rubber and agglomerate containing silica) is filtered and dried by a known method, and further dried and then kneaded with a biaxial roll, a banbury, etc., so that the fine particle silica is uniformly formed in the SBR matrix. A dispersed complex can be obtained.
The silica / SBR composite of the present invention may contain other components as long as the effects of the present invention are not impaired.

<Rubber composition>
The rubber composition of the present invention contains the silica / SBR composite. The silica / SBR composite can be used as a master batch. In the silica / SBR composite, since silica is uniformly dispersed in rubber, silica can be uniformly dispersed even in a rubber composition mixed with other components. Therefore, effective reinforcement can be expected.

In addition to the silica / SBR composite, the rubber composition of the present invention includes rubber components other than SBR generally used in the tire industry, fillers such as carbon black, silane coupling agents, zinc oxide, stearin. Various materials such as acid, anti-aging agent, sulfur, and vulcanization accelerator can be appropriately blended.

<Pneumatic tire>
The rubber composition of the present invention can be suitably used for a pneumatic tire. The pneumatic tire is manufactured by a normal method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of each member of the tire at an unvulcanized stage and molded by a normal method on a tire molding machine. After forming an unvulcanized tire by heating, the tire can be manufactured by heating and pressing in a vulcanizer.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
SBR (E-SBR latex): synthesized by a known method. (Styrene content: 23.5% by mass, rubber solid content concentration: 23% by mass, pH: 10.1)
Wet silica: Tokuyama USG manufactured by Tokuyama Corporation (average particle size: 20 nm, N ₂ SA: 170 m ² / g)
Nonionic surfactant: Huntsman Corp. of _{teric 16A29 (CH 3 (CH 2} ) 15 (OC 2 H 4) 29 -OH)
10% sulfuric acid: 10% by mass ammonia water manufactured by Wako Pure Chemical Industries, Ltd .: Silane coupling agent manufactured by Wako Pure Chemical Industries, Ltd .: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide manufactured by EVONIK-DEGUSSA )
Zinc Hana: Mitsui Mining & Mining Co., Ltd. Zinc Hana 2 types Stearic Acid: NOF Co., Ltd. Anti-aging Agent: Nouchi 6C (N- (1,3- Dimethylbutyl) -N′-phenyl-p-phenylenediamine)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Example 1>
(Preparation of silica dispersion)
85.5 g of pure water was added to 4.5 g of wet silica to prepare a 5% silica suspension, which was stirred and sonicated for 10 minutes to obtain a silica dispersion.

(Preparation of silica / SBR composite)
To 43.5 g of E-SBR latex, 90 g of silica dispersion, 0.5 g of surfactant and 0.5 g of 10% by mass ammonia water are added, and mixed and stirred at room temperature for 1 hour to obtain a blended latex having a pH of 9.8. It was. Subsequently, sulfuric acid was added at room temperature to adjust the pH to 6 to 7 to obtain a coagulated product. The obtained solidified product was filtered and dried to obtain silica / SBR composite 1.

<Example 2>
A silica / SBR composite 2 was obtained in the same manner as in Example 1 except that the surfactant was changed to 0.05 g.

<Comparative Examples 1-2>
In Comparative Example 1, a silica / SBR composite was obtained in the same manner as in Example except that 10% by mass of ammonia water was not added.
In Comparative Example 2, a silica / SBR composite was obtained in the same manner as in Example except that the surfactant was not added.

The following evaluation was performed using the obtained silica / SBR composite. The results are shown in Table 1.

(Filtration operation)
Regarding filtration operability in the preparation of the composite, it was evaluated whether aggregates were generated and filtration operation was possible.

(The state of the filtrate (silica / SBR loss))
Regarding the loss of silica and SBR, the state of the filtrate after filtration was observed and evaluated according to the following criteria.
Transparent or translucent: There is almost no loss.
Cloudiness: There are many losses.

(Sample after drying (silica / SBR composite))
The silica dispersibility in the sample after drying was visually evaluated according to the following criteria.
Translucent: Good dispersibility of silica.
Opaque: The dispersibility of silica is poor.

In the examples using 10% by mass aqueous ammonia and surfactant, aggregates were formed and the filterability was good, whereas in the comparative example, the solid content could not be recovered by filtration. Moreover, although the state of the filtrate of an Example was transparent and there was almost no loss of silica and SBR, in the comparative example, it became cloudy and there were many losses (FIGS. 1, 2).

About the sample after drying, in the Example, it turned out that a sample is translucent and the silica is disperse | distributing uniformly. In the comparative example, the sample was opaque and the dispersibility of the silica was inferior to that of the example.

<Examples 3 to 4 and Comparative Example 3>
According to the formulation shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 15 minutes to obtain a vulcanized product. The obtained vulcanizates were evaluated by the following methods, and the results are shown in Table 2.

(Rolling resistance)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each compound (vulcanized product) was measured under the conditions of a temperature of 50 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The tan δ of the rubber test piece of Comparative Example 3 was set to 100, and each compounding was expressed as an index (rolling resistance index) by the following formula. The larger the index, the better the rolling resistance characteristics (low fuel consumption).
(Rolling resistance index) = (tan δ of Comparative Example 3) / (tan δ of each formulation) × 100

(Abrasion test)
Using a Lambourn abrasion tester, the Lambourn abrasion amount was measured under the conditions of a temperature of 20 ° C., a slip ratio of 20% and a test time of 2 minutes. Further, the volume loss amount was calculated from the measured amount of lamborn wear, the volume loss amount of the rubber test piece of Comparative Example 3 was set to 100, and each compounding was indicated by an index according to the following calculation formula (wear resistance index). It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (Volume loss amount of Comparative Example 3) / (Volume loss amount of each formulation) × 100

(Breaking strength / elongation at break)
A vulcanized product was used to prepare a No. 3 dumbbell-shaped rubber test piece and subjected to a tensile test according to JIS K6251 “vulcanized rubber and thermoplastic rubber-Determination of tensile properties”, breaking strength (TB), breaking The time elongation (EB) was measured. TB and EB of the rubber test piece of Comparative Example 3 were set to 100, and each compounding was indicated by an index by the following calculation formula. It shows that it is excellent in reinforcement property, so that TB index is large, and it is excellent in crack resistance, so that EB index is large.
(TB index) = (TB of each formulation) / (TB of Comparative Example 3) × 100
(EB index) = (EB of each formulation) / (EB of Comparative Example 3) × 100

Formulations of Examples 3 to 4 using a silica / SBR composite prepared from a blended latex prepared by mixing an E-SBR latex and a fine particle silica dispersion in the presence of a nonionic surfactant and an alkali The rubber was obtained in a well-balanced manner with high fuel economy, wear resistance, breaking strength and elongation at break as compared with Comparative Example 3 prepared by kneading SBR, silica and the like. In particular, in Example 4 in which the amount of the surfactant was reduced at the time of producing the composite, a more remarkable effect was obtained.

Claims (5)

A silica / styrene butadiene rubber composite obtained from a compounded latex prepared by mixing an emulsion-polymerized styrene butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less in the presence of a nonionic surfactant and an alkali. body. The silica / styrene butadiene rubber composite according to claim 1, wherein the alkali is ammonia. In the presence of a nonionic surfactant and an alkali, the emulsion-polymerized styrene butadiene rubber latex and a fine particle silica dispersion having an average particle size of 1 μm or less are mixed to prepare a compounded latex, and obtained in the step 1 above. The method for producing a silica / styrene butadiene rubber composite according to claim 1 or 2, comprising a step 2 of adjusting and coagulating the pH of the obtained blended latex to 5 to 7. A rubber composition comprising the silica / styrene butadiene rubber composite according to claim 1. A pneumatic tire produced using the rubber composition according to claim 4.