JP3228913B2 - Method for producing rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rubber composition used for a tire tread for a vehicle, and more particularly, to a method for measuring a change in dynamic viscoelastic tan δ at 0 ° C. and 40 ° C. while maintaining breaking strength. The present invention relates to a method for producing an enlarged rubber composition for a vehicle tire tread.

[0002]

2. Description of the Related Art Tires having high grip force on wet road surfaces (hereinafter referred to as "wetness") and low rolling resistance are required to improve the safety of running a vehicle and save energy. Compatibility is difficult because it is closely related to tan δ of dynamic viscoelasticity. For example, "Automotive Technology", Vol. As described on pages 3 and 8 (1989), the wettability correlates with tan δ around 0 ° C. and the rolling resistance correlates with tan δ around 40 ° C., and tan δ at a temperature close to that. There was a problem that the wettability deteriorated when trying to lower the resistance. Therefore 0
The tan δ at 40 ° C. is increased, and the tan δ at 40 ° C. is reduced, that is, (tan δ at 0 ° C.) ÷ (tan at 40 ° C.).
It is desirable to increase the temperature gradient of tan δ represented by δ). In general, when the amount of the reinforcing agent such as carbon black or white carbon is reduced, the temperature gradient of tan δ is increased, but the vulcanized rubber is lowered in breaking strength and hardness, which is not preferable as a rubber for tire tread.
Therefore, many techniques have been reported to improve wettability with low rolling resistance.

For example, JP-A-61-218404 and JP-A-4-325535 disclose the use of white carbon or a specific carbon black as a reinforcing agent added to a rubber composition. In Japanese Patent Application Laid-Open No. Hei 4 (1994), the use of raw rubber having modified molecular terminals is used.
JP-A-35654 proposes means for improving raw materials, such as adding a dinitrosamine compound or the like. Japanese Patent Application Laid-Open No. 6-32941 proposes means for improving the mixing method by devising it. However, although the improvement effect of these techniques can be seen to some extent, further improvement is desired to satisfy the required performance of the tire tread.

[0004] Further, Rubber Chem. Techn
ol. 47, 48 pages (1974), 50 volumes,
301 (1977), 61, 609 (198
8), Vol. 66, p. 276 (1993), reports that the rebound resilience varies depending on the combination of a master batch in which raw rubber and carbon black are mixed in advance and another raw rubber. However, it has not been clarified in these studies what is involved in the effect of tan δ on the temperature gradient.

JP-A-6-200083 proposes a method of vulcanizing a compound comprising a raw rubber having a low glass transition temperature (Tg) and then adding a raw rubber having a high Tg. In addition to the drawback that the viscosity increases, the material tends to burn during processing. In addition, there is a restriction that the high Tg raw material rubber must form a continuous (matrix) phase. The above must be done, which is disadvantageous for low rolling resistance.

[0006] In addition, the mixing of the rubber composition promotes the dispersion of carbon black and causes the breakdown of the structure, so that tan δ is reduced by kneading.
Japanese Patent Application Laid-Open No. 55-104343 discloses that 40
A method in which carbon black is added to and mixed with ６０60% by weight, and then the remaining raw rubber is added, but a large amount of carbon black needs to be added to a small amount of raw rubber, so that the viscosity of the master batch is reduced. It is very high, has the problem of processability, and has drawbacks limited to blends of BR and NR.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention is to provide a rubber composition for a tire tread having good wettability and low rolling resistance without losing the breaking strength by eliminating the above-mentioned problems of the prior art. It is an object of the present invention to provide a method for producing the same.

[0008]

According to the present invention, (A)
10 to 40 parts by weight of raw rubber having a glass transition temperature (Tg) of -40 ° C to -15 ° C, (B) viscoelastic raw rubber (A)
30 to 85 parts by weight of a raw rubber which is incompatible with the raw rubber (A) and has a Tg lower than that of the raw rubber (A) by 20 ° C. or more; and (C) a viscoelastically compatible raw rubber (A) and a raw rubber (B ) Is incompatible with the raw rubber (A) and has a Tg at a temperature equal to or lower than the Tg of the raw rubber (A).
In producing a rubber composition containing a total of 100 parts by weight of the raw rubbers (A), (B) and (C) containing 30 parts by weight and 30 to 60 parts by weight of the reinforcing agent, the raw rubbers (B) and ( C) and a reinforcing agent of 80% by weight or more of the total amount are mixed in an internal mixer at 150 to 200 ° C. for 10 seconds or more, and then the raw rubber (A) and the remaining reinforcing agent are added and mixed. A method of making a composition is provided.

As described above, it is known that the tan δ of the vulcanized rubber is changed by changing the mixing method of the rubber composition. However, the inventors diligently studied the selection of the raw materials and the effect of the mixing method. As a result, three groups of raw rubbers (A), (B) and (C) having compatibility with a specific Tg and a reinforcing agent were mixed in a specific procedure to maintain the tan δ temperature while maintaining the breaking strength. We found that dependency can be increased. According to this method, there is also an advantage that the increase in viscosity of the master batch during mixing is small. The details will be described below.

When a part of the raw rubber and carbon black are mixed in advance and then the remaining raw rubber is added and mixed, it is known that carbon black tends to be unevenly distributed in the first raw rubber and tan δ changes. ing. See Rubber Chem. Techn
ol. Journal Vol. 61, p. 276 (1993) describes the effect of the mixing technique on the rebound resilience for a number of blends. Although this document does not disclose any relation to the Tg of the blended rubber, the present inventors have paid their own attention and converted the described rebound resilience into tan δ to organize the raw rubber with high Tg and low Tg. It is better to distribute carbon black unevenly in raw rubber with low Tg than to distribute carbon black evenly.
nδ was found to be low. However, some of the effects of carbon black move between the blend phases during the mixing process and the effect of the combination of the raw rubber,
The state of the temperature gradient between 0 ° C. and 40 ° C. did not lead to a unified interpretation.

Therefore, as a result of measuring and examining the viscoelastic compatibility of Tg and Tg of many combinations of raw rubber, tan δ at a certain degree of uneven distribution of carbon black was determined.
Is that the two types of raw rubbers are viscoelastically incompatible and the Tg of both are separated, and the Tg of the high Tg component is high.
It has been found that g increases as it approaches -20 ° C. Therefore, the effect is greater when the Tg of the two incompatible raw rubbers is as far apart as possible, and the difference is at least 2%.
It must be 0 ° C., preferably 35 ° C. or higher.

The term "viscoelastic incompatibility" as used herein means that when the temperature dependence of the viscoelasticity of the vulcanized rubber is measured, the tan δ peaks of both raw rubbers are observed separately. It is considered that this occurs when the raw rubbers are not completely mixed in the rubber composition and are separated into layers or islands having a size of several tens of nanometers or more and Tg is separated. Specifically, as shown in FIG.
The δ measurement values are displayed, and if there are two points sharing a tangent, it is understood that they are viscoelastically incompatible.

The present inventors have measured the viscoelasticity at 0 ° C. and 40 ° C., and have also described Rubber Chem. Technol.
Journal, Vol. 61, p. 609 (1988), to measure the uneven distribution of carbon black determined by a method for quantifying the raw rubber composition in unvulcanized rubber bound rubber (carbon gel). Was examined in detail. As a result, the effect of improving the temperature gradient of tan δ expressed by (change in temperature gradient of tan δ) ÷ (change in uneven distribution of carbon black) shows that carbon black is reduced when the Tg of the raw rubber having a high Tg component is −40 ° C. or lower. Even if it is unevenly distributed, the temperature gradient of tan δ is hardly improved.
It was found that the temperature rapidly increased at 30 ° C. or higher, and reached a maximum at around −10 ° C., but decreased again at higher temperatures.
It is not clear why the effect of improving the temperature gradient of tan δ is maximized at around −20 ° C. for the raw rubber having a high Tg component, but in general, ta is higher at 10-20 ° C. than the Tg of the raw rubber.
Since there is a maximum point of the nδ curve, it is considered that the improvement effect is maximized when the maximum point of tan δ is near the measurement point of 0 ° C.

However, in order to improve the temperature dependence of tan δ by unevenly distributing carbon black, two types of raw rubbers having mechanically different Tg are selected, and a raw material having a low Tg is selected in the first mixing step. If the rubber and carbon black are mixed in advance, and only the raw material rubber having a high Tg is added in the subsequent step, as described below, there are various industrial problems, so that it is suitable for a tire tread alone. A rubber composition cannot be obtained.

One problem is that even if an additional raw rubber is added to and mixed with a master batch in which the raw rubber and the reinforcing agent are previously mixed, the dispersion is not good. Originally, the raw rubbers are hardly mixed with each other, so that they are viscoelastically incompatible. However, since one raw rubber is partially bonded to the filler to form a three-dimensional structure, the raw rubbers are further hardly mixed. Therefore, even if measures such as prolonging the mixing time are taken, the breaking strength and wear resistance of the vulcanized rubber are reduced. Therefore, the present inventors have found that a possibility of avoiding this problem can be avoided by adding a small amount of raw rubber which is easily mixed with the raw rubber to be additionally mixed and does not impair the tan δ peak shape to the raw rubber of the master batch in advance. .

However, it is probably empirical what kind of raw rubber should be selected to improve the temperature dependency of tan δ and at the same time dispersibility of the raw rubber (A). Studies of the compatibility of two polymers according to theoretical formulas are described, for example, in Macrom.
As described in Olecule, Vol. 24, p. 4839 (1991), it is possible to some extent, but not enough, and using the three groups of raw rubbers (A), (B) and (C) as in the present invention. Predicting whether to maintain viscoelastic incompatibility is quite difficult.

The present inventors mixed a large number of raw rubbers having different Tg, measured their viscoelasticity, examined whether or not the combination was viscoelastically compatible. Raw rubber to be raw rubber (B) and (C),
When the raw rubber to be added to the additional mixing step is the raw rubber (A), it has been found that it is preferable to select from the following four combinations to achieve the object of the present invention (%
Indicates weight%).

1) The raw rubber (A) has a styrene content of 30.
The content of 1,2-bonded butadiene in the emulsion-polymerized SBR and / or butadiene portion is preferably 70% or less, preferably 10-70%, and the styrene content is represented by the following formula (1). Solution-polymerized SBR styrene content> 40- (1,2-bonded butadiene content) ÷ 3 --- (1) Raw rubber (B): NR and / or IR Raw rubber (C): styrene content 50% or less, Preferably 35-45% emulsion polymerization SBR and / or 1,2-bonded butadiene content is 70% or less, preferably 10-70%
And the styrene content is 15% or more, preferably 20 to 40.
% Solution polymerization SBR

2) Raw rubber (A): BR having a 1,2 bond butadiene content of 65% or more, preferably 65 to 85% and / or 1,2 bond butadiene content of 70% or more, preferably 70 to 85%. And a solution-polymerized SBR having a styrene content of 30% or less, preferably 5 to 20%. Raw material rubber (B): a styrene content of 35% or less, preferably 20 to 30%, and an emulsion-polymerized SBR and / or 1,2-bonded butadiene content. Is 40% or less, preferably 5 to 20%,
Solution polymerization SB having a styrene content of a value represented by the following formula (2)
R Styrene content <40- (1,2-bonded butadiene content) ÷ 3 --- (2) Raw rubber (C): BR and / or 1,2-bonded butadiene content of 65% or more, preferably 65 to 85%. 1,2-bonded butadiene content is 70% or more, preferably 10-70
%, The styrene content is 30% or less, preferably 5 to 20%.
% Solution polymerized SBR and / or NR and / or IR

3) Raw rubber (A): 1,2-bonded butadiene content is 65% or more, preferably 65-85% BR and / or styrene content is 30-50%, preferably 35
Emulsion polymerized SBR and / or 1,2-bonded butadiene content of 70% or more, preferably 70-85% and styrene content of 30% or less, preferably 5-20%, and 7,2-bonded butadiene content is 7
Solution-polymerized SBR having a styrene content of 0% or less, preferably 10 to 70%, and a value represented by the following formula (1) Styrene content> 40- (1,2-bonded butadiene content) ÷ 3 --- (1) Rubber (B): cis-1,4-bonded butadiene content 95
%, Preferably 97-99% BR and / or 1,
2-linked butadiene content of 10 to 50%, preferably 12
Raw material rubber (C): Emulsion polymerized SBR having a 1,2-bonded butadiene content of 65% or more, preferably 65-85% BR and / or styrene content of 50% or less, preferably 35-45% And / or a 1,2-bonded butadiene content of 70% or more, preferably 70-85%, and a styrene content of 30%
Hereinafter, preferably 10-20% of solution-polymerized SBR and / or
Or a solution-polymerized SBR having a 1,2-bonded butadiene content of 70% or less, preferably 10 to 70%, and a styrene content of a value represented by the following formula (1): styrene content> 40- (1,2-bonded butadiene content)} 3 --- (1)

4) Raw rubber (A): BR raw material having a 1,2-bonded butadiene content of 65% or more, preferably 65-85%. Raw rubber (B): cis-1,4-bonded butadiene content 95
%, Preferably 97-99% BR and / or 1,
2-linked butadiene content of 10 to 50%, preferably 12
２０20% BR Raw material rubber (C): BR and / or NR and / or IR having a 1,2 bond butadiene content of 65% or more, preferably 65 to 85%

In all of these four preferred combinations, the following is essential. That is, the raw rubber (A) has a Tg of -40 ° C to -15 ° C and the amount thereof is 1
It is necessary to be 0 to 40 parts by weight, preferably 15 to 30 parts by weight. If the Tg is less than -40 ° C, the effect of improving the temperature gradient of tan δ is small, and if it exceeds -15 ° C, the rubber hardness around 0 ° C increases, which is not practical as a tire tread. If the amount is less than 10 parts by weight, the effect of improving the temperature gradient of tan δ is inferior. If the amount exceeds 40 parts by weight, the viscosity of the masterbatch is increased and processability is poor.

The raw rubber (B) is viscoelastically incompatible with the raw rubber (A) and has a Tg of 20 from the Tg of the raw rubber (A).
C. or higher, preferably 35-60 C., low Tg rubber 30
It is necessary that the amount be from 85 to 85 parts by weight, preferably from 50 to 75 parts by weight. If it is compatible with the raw rubber (A), uneven distribution of the reinforcing agent does not occur, and if the temperature difference of Tg is smaller than 20 ° C., the effect of improving the temperature dependency of tan δ cannot be expected. 3
If the amount is less than 0 parts by weight, the processability is poor, and if it exceeds 85 parts by weight, the effect of improving the temperature dependency is poor.

The raw rubber (C) is viscoelastically compatible with the raw rubber (A), incompatible with the raw rubber (B), and at a temperature equal to or lower than the Tg of the raw rubber (A). It is necessary that the rubber has a Tg of 5 to 30 parts by weight, preferably 5 to 10 parts by weight. If the rubber is not compatible with the raw rubber (A) and is not incompatible with the raw rubber (B), the dispersibility of the rubber of the raw rubber (A) is reduced. Is less than 5 parts by weight, the dispersibility of the raw material rubber (A) is reduced.
The effect of improving the temperature gradient of nδ is reduced.

Another problem in mixing the high Tg raw rubber after the low Tg raw rubber and carbon black are mixed in advance is that the raw rubber (A) which is a high Tg component added later during the mixing. ), The carbon black partially migrates, so that uneven distribution may not occur sufficiently.
The effect of improving the temperature gradient of nδ is reduced. The reason is that the bond between the carbon black and the raw rubber molecules is not sufficiently formed in the first mixing step, and that the raw rubber added later has a higher affinity for the carbon black.

As confirmed by the amount of bound rubber produced, the bonding between the carbon black and the raw rubber molecules becomes stronger due to the heat during mixing, so that it is preferable to mix them at a high temperature.
To achieve the effect of the present invention, the temperature is mixed at 130 to 200 ° C, preferably 150 to 190 ° C. Mixing temperature 13
If the temperature is lower than 0 ° C., the bonding is insufficient. If the temperature is higher than 200 ° C., the strength of the vulcanized rubber is significantly reduced due to deterioration due to heat. In the mixing by the closed mixer, the temperature rises with the mixing time and the mixing temperature is not constant, but when the temperature reaches a predetermined temperature, the bonding of the raw rubber and the carbon black is completed in a short time of about 10 seconds. That is, as the first mixing step, the raw rubber (B), the raw rubber (C), and the reinforcing agent may be maintained in the required temperature range for at least 10 seconds in the closed mixer. Subsequent mixing of the raw material rubber (A) and the remaining reinforcing agent may be carried out by additionally adding the mixture into the mixer following the first mixing step, or by using a master batch in which the first mixture is discharged from the mixer and cooled. It may be performed by a mold mixer or an open roll.

The affinity between the raw rubber and the reinforcing agent varies depending on the type of the raw rubber. For example, NR, IR and BR have a higher amount of double bonds in the molecule than SBR and thus have higher affinity with the reinforcing agent. The most effective is the introduction of a functional group called terminal modification. Terminal modification is described in, for example, JP-A-64-60.
As described in JP-A-604, an alkali metal or an alkaline earth metal at the synthetic end of a raw rubber molecule contains -CO-N <or-such as N-methyl-2-pyrrolidone in the molecule.
This is an operation of reacting with a compound having CS-N <bond. The higher the denaturation rate of the synthetic terminal, the more effective, usually 20%
The one with the above metamorphic rate is used. It is believed that the terminally modified raw rubber binds preferentially to the carbon black surface during mixing. Therefore, when the raw rubber (B) has a high affinity with the reinforcing agent, the reinforcing agent is less likely to be transferred to the additional raw rubber (A), but in the opposite case, the temperature of the first mixing step is increased to increase the bound rubber. If not sufficiently developed, the effects of the present invention may not be sufficiently exhibited. The present invention becomes more effective by using the terminal-modified rubber as the raw rubber (B).

As a reinforcing agent, carbon black is generally used. In the case of white carbon, the same raw rubber selection and mixing method as in the case of carbon black may be used. In the case of white carbon (silica), silane cups are generally used. Although a ring agent is used in combination, it is necessary to mix with the white carbon in the first mixing step in order to improve dispersibility and abrasion resistance. The compounding amount of the reinforcing agent is 30 to 60
If the amount is less than 30 parts by weight, the abrasion resistance is inferior. If the amount exceeds 60 parts by weight, the tan δ at 40 ° C. is increased by the method of the present invention, and the rolling resistance becomes inferior. Not preferred. When the raw rubbers (B) and (C) are mixed, it is necessary to mix at least 80% of the total amount of the reinforcing agent, and as the amount of the remaining reinforcing agent mixed with the raw rubber (A) increases, the tan δ increases. The effect of improving the temperature gradient is reduced.

The rubber composition of the present invention has the above (A),
In addition to the raw rubbers (B) and (C) and the essential components of the reinforcing agent, they are generally used in rubber compositions for tires such as sulfur, vulcanization accelerators, antioxidants, fillers, softeners and plasticizers. Various additives that have been blended can be blended, and the blending amounts and blending methods of such additives are not particularly limited, and general amounts and methods can be used.

[0030]

EXAMPLES The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

Examples 1 to 16 1) Raw materials The following commercial products were used as raw materials used in the following examples. (1) Solution polymerization BR: ZEON Nipol BR12
20, Tg = −102 ° C., cis-1,4-bonded butadiene content = 98% (2) Solution polymerization BR: Asahi Kasei Diene NF35R, T
g = -90 ° C., 1,2-bonded butadiene content = 13% (3) Natural rubber: TSR20, Tg = −73 ° C. (4) Solution polymerization SBR: Asahi Kasei Toughden 1000
R, Tg = -72 ° C., styrene content = 18%, 1,2-bonded butadiene content = 9% (5) Terminally modified solution-polymerized SBR: Nippon Zeon Nipol NS114, Tg = −47 ° C., styrene content = 2
3%, 1,2-bonded butadiene content = 37% (6) Solution polymerization SBR: Nippon Elastomer Sorprene 303, Tg = −33 ° C., styrene content = 47%,
1,2-bonded butadiene content = 29% (7) Emulsion polymerization SBR: Nippon Zeon Nipol 952
0, Tg = −32 ° C., styrene content = 38%, 1,2-bonded butadiene content = 14%, oil extended product with 37.5 parts by weight of aroma-based process oil added to 100 parts by weight of raw rubber (8) Terminal modification Solution polymerization SBR: Nippon Zeon Nipol NS116, Tg = -30 ° C, styrene content = 2
1%, 1,2-bonded butadiene content = 67% (9) Solution polymerization BR: Nippon Zeon Nipol BR12
40, Tg = −30 ° C., 1,2-bonded butadiene content = 7
0% (10) Carbon black, HAF (11) Zinc flower No. 3 (12) Industrial stearic acid (13) N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine (14) Micro Crystalline wax (15) Aroma-based process oil (16) Powder sulfur treated with 5% oil (17) Diphenylguanidine (18) N-cyclohexyl-2-benzothiazylsulfenamide Ingredients in Tables 1 to 5 Is shown in parts by weight.

2) Preparation of Rubber Composition The first mixing step (first step) is as follows: raw rubber (B), raw rubber (C), carbon black, zinc oxide, stearic acid, antioxidant, wax, process oil Was mixed in a 1.8 liter closed mixer for 3-5 minutes. The raw material at room temperature was put into a closed mixer, and was discharged when the temperature reached a predetermined temperature due to the heat generated by mixing. The raw material was formed into a sheet-shaped master batch by an 8-inch open roll. The release temperature was controlled at 110 ° C. only for Comparative Example 5, and at 165 ° C. for the others.

In the additional mixing step (second step), the masterbatch and the raw rubber (A) were charged into a 1.8-liter closed mixer, mixed for 2 minutes, discharged, and then sulfur-free with an 8-inch open roll. A vulcanization accelerator was added and kneaded to obtain a rubber composition. The release temperature was 115-125 ° C. When the raw rubber (A) was not used, only the master batch was remixed in a closed mixer, and sulfur and a vulcanization accelerator were added and kneaded with an open roll to obtain a rubber composition.

3) Measurement of Physical Properties of Vulcanized Rubber The obtained rubber composition was pressure-vulcanized at 160 ° C. for 20 minutes in a mold of 15 × 15 × 0.2 cm to prepare a rubber sheet.
The breaking strength was measured with a dumbbell-shaped No. 3 shape based on JIS K6251, and the value was indicated in MPa. 0 ° C and 40 ° C t
anδ is a rectangular sample, 20Hz, 10 ± 2%
Was measured in the elongation deformation mode.

Table I shows the results obtained when (3) NR, (5) terminal-modified solution polymerization SBR, and (8) terminal-modified solution polymerization SBR were used as the raw material rubber, and (5) terminal-modified solution polymerization SBR and (8) The terminally modified solution polymerized SBR is compatible with (3) N
R is incompatible with both of these SBRs. In Example 4 (Example) and Example 5 (Comparative Example), the raw rubber (A) was (8) terminal-modified solution-polymerized SBR, the raw rubber (B) was (3) NR,
The raw rubber (C) corresponds to (5) terminal-modified solution polymerization SBR.

The temperature gradient of tan δ in Example 1 (standard example) in which all of the raw rubbers (A), (B) and (C) were charged in one step was 2.57, whereas the NR was two steps. In Example 2 (standard example), the temperature gradient was slightly improved to 2.66 because the dispersion of carbon black proceeded. In Example 3 (Comparative Example) in which NR and carbon black were mixed in the first step and then two types of SBR were added in the second step, the temperature gradient was 3.
Although it is greatly improved to 00, there is a disadvantage that the breaking strength is reduced. On the other hand, in Example 4 (Example) of the present invention in which 10 parts by weight of (4) solution-polymerized SBR was mixed together with (3) NR in the first step, recovery of the breaking strength was maintained while maintaining a large tan δ temperature gradient. Are seen, showing favorable rubber properties for the tire tread. In addition, the first compound having the same composition as in Example 4 (Example) was used.
Example 5 when process temperature is reduced from 165 ° C to 110 ° C
As shown in (Comparative Example), the temperature gradient decreases.

[0037]

[Table 1]

Table II shows an example in which (4) solution-polymerized SBR and (9) solution-polymerized BR are used as raw rubbers, and (4) solution-polymerized SBR and (9) solution-polymerized BR are incompatible. Example 7
In Example, the raw material rubber (A) was (9) solution polymerized BR,
The raw rubber (B) corresponds to (4) solution polymerization SBR, and the raw rubber (C) corresponds to (9) solution polymerization BR. While the temperature gradient of tan δ of Example 6 (standard example) is 1.73, 10 parts by weight of (9) solution polymerization BR is added in the first step, and 30 parts by weight is added in the second step. Example 7 with additional input
In Example, the temperature gradient is improved to 1.91.

[0039]

[Table 2]

Table III shows an example in which (3) NR and (8) terminal-modified solution-polymerized SBR were used as raw material rubbers.
And (8) Terminally modified solution polymerized SBR are incompatible. In Example 10 (Example), the raw rubber (A) corresponds to (8) terminal modified solution polymerization SBR, the raw rubber (B) corresponds to (3) NR, and the raw rubber (C) corresponds to (8) terminal modified solution polymerization SBR. .

In order to make the composition ratio of the raw rubber the same in the first step and the second step, (3) 21 parts by weight of NR and (8) 9 parts by weight of terminal modified solution polymerization SBR were additionally added in the second step. The temperature gradient of tan δ in Example 8 (standard example) was 3.35. On the other hand, the same 30 parts by weight but high Tg (8)
Example 9 where terminal-modified solution polymerization SBR was additionally added in the second step
In Comparative Example, although the temperature gradient was improved to 3.74, the breaking strength was reduced. Thus, it is not important that the raw rubber is put into separate steps, but it is incompatible and has a high Tg.
It is easily understood that adding the raw material rubber in the second step improves the temperature gradient.

Example 10 (Example) aims at lowering the breaking strength while maintaining the effect of improving the temperature gradient.
By adding the weight part (8) of the terminally modified solution polymerized SBR to the first step, the dispersibility of the raw rubber added in the second step is improved, and the breaking strength is improved as compared with Example 9 (Comparative Example). The temperature gradient is 3.62, which is higher than Example 8 (standard example).

[0043]

[Table 3]

Table IV shows examples in which (1) solution-polymerized BR and (6) solution-polymerized SBR were used as raw rubbers, and (1) solution-polymerized BR and (6) solution-polymerized SBR are incompatible. In Example 12 (Example), the raw rubber (A) is (6) solution polymerized S
BR and raw rubber (B) correspond to (1) solution polymerization BR, and raw rubber (C) corresponds to (6) solution polymerization SBR. In the second step, Example 12 (Example) of the present invention was compared to Example 11 (Comparative Example) in which 25 parts by weight of low-Tg (1) solution-polymerized BR was additionally added.
It can be seen that the temperature dependence of anδ is large.

[0045]

[Table 4]

Table V confirms the invention with another raw rubber. The combination of the incompatible (2) solution-polymerized BR and (7) emulsion-polymerized SBR has an improved temperature gradient in Example 14 (Example) as compared to Example 13 (Standard), and also has an incompatible (2) Solution polymerization BR and (9) Solution polymerization BR
In the combination of Example 16, the temperature gradient is improved in Example 16 (Example) as compared with Example 15 (Standard Example).

[0047]

[Table 5]

[0048]

As is clear from the results of Tables I to V, the rubber composition obtained by the production method of the present invention has a feature that tan δ at 0 ° C. is high and tan δ at 40 ° C. is low while maintaining the breaking strength. When used for a tire tread, running durability, high grip force on a wet road surface and low rolling resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the temperature of a rubber composition composed of two types of raw rubber and the logarithmic value of tan δ in a viscoelastic incompatible state.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-104343 (JP, A) JP-A-61-225226 (JP, A) JP-A-61-162536 (JP, A) JP-A 63-162536 108043 (JP, A) JP-A-57-87442 (JP, A) JP-A-57-70137 (JP, A) JP-A-57-70136 (JP, A) JP-A-60-99248 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 9/00 C08L 7/00 C08K 3/04 C08J 3/20

Claims (1)

(57) [Claims] (A) a glass transition temperature (Tg) of -40;
10 to 40 parts by weight of raw rubber at -15 ° C, (B) raw rubber 30- which is viscoelastically incompatible with raw rubber (A) and has a Tg lower than that of raw rubber (A) by 20 ° C or more. 8
5 parts by weight and (C) a Tg at a temperature which is viscoelastically compatible with the raw rubber (A), incompatible with the raw rubber (B), and equal to or lower than the Tg of the raw rubber (A). In producing a rubber composition containing a total of 100 parts by weight of the raw rubbers (A), (B) and (C) containing 5 to 30 parts by weight of a raw rubber and 30 to 60 parts by weight of a reinforcing agent, After mixing (B) and (C) with a reinforcing agent of 80% by weight or more of the total amount in a closed mixer at 150 to 200 ° C for 10 seconds or more, the raw rubber (A) and the remaining reinforcing agent are added. A method for producing a rubber composition, which comprises mixing.