JP5741235B2 - Tire rubber composition containing polylactic acid or diene polymer modified with the same - Google Patents

Description

The present invention relates to a tire rubber composition containing polylactic acid or a diene polymer modified with the same. More particularly, while ensuring workability, rubber tire compounded with effectively used may polylactic acid or so modified diene polymer as one component such as a rubber composition for a tire which can improve a further physical properties Relates to the composition.

  Patent Document 1 describes a polymer alloy containing polylactic acid in an amount of about 50% by mass or more and containing a copolymer of polypropylene and D-lactic acid and a saccharide. When used under external force or at high temperature, the problem is that the characteristics are insufficient and the application is limited. In addition, it is also described that a compatibilizing agent such as a styrene-butadiene copolymer having an arbitrary structure is used in a ratio of 2 to 10 parts by weight with respect to 100 parts by weight of polylactic acid in polymer alloying.

  The performance required for automobile tires is diverse, and in particular, handling stability during high-speed driving, stability on wet roads, reduction of rolling resistance to reduce fuel consumption of automobiles, improvement of wear resistance, etc. .

  Conventionally, silica is widely used as a reinforcing filler in order to achieve both reduction in rolling resistance and stability on wet road surfaces. In order to improve the dispersibility of silica, methods such as increasing the mixing time or adding a large amount of silane coupling agent are generally known. However, if the mixing time is lengthened, the gel content increases too much and the rolling resistance is deteriorated. Moreover, when a lot of silane coupling agents are blended, the scorch time becomes too short, and the tread extrudability deteriorates.

  In order to reduce rolling resistance, the rubber composition used in the tread portion is reduced in the amount of reinforcing filler or the amount of oil that also contains a lubricating component. However, since such a rubber composition has fewer lubricating components, the viscosity of the rubber composition is increased, and processability such as mixing processability and extrusion processability is deteriorated. On the other hand, when the compounding amount of the reinforcing filler is reduced, it is difficult to increase the rubber hardness, and it becomes difficult to ensure the steering stability. Furthermore, since the elongation at break of rubber is small, a significant deterioration in workability is inevitable.

  Patent Document 2 discloses a composition in which polylactic acid particles and synthetic rubber particles are dispersed in an aqueous dispersion medium as an adhesive composition having sufficient adhesive strength even under high-temperature and high-humidity conditions and having excellent adhesion durability. As the synthetic rubber, a styrene-butadiene copolymer and the like are mentioned.

JP 2008-280474 A JP 2008-50414 A

An object of the present invention is a tire blended with polylactic acid or a diene polymer modified therewith, which can be used effectively as a component of a rubber composition for a tire that can further improve physical properties while ensuring processability It is to provide a rubber composition for use.

According to the present invention , a tire rubber in which 5 to 150 parts by weight of silica and 0.1 to 10 parts by weight of polylactic acid having a functional group capable of addition reaction with a double bond site of a diene polymer are blended with 100 parts by weight of a diene rubber. A composition is provided.

Further, according to the present invention, in a rubber composition in which 5 to 150 parts by weight of silica is blended with 100 parts by weight of diene rubber, 5 to 50 parts by weight of 100 parts by weight of diene rubber is a double bond site of the diene polymer. There is provided a rubber composition for a tire, which is modified with a polylactic acid having a functional group capable of undergoing an addition reaction with a modified diene polymer having a polylactic acid moiety.

  As described above, the performance required for automobile tires includes reduction of rolling resistance and stability on wet road surfaces. As a method for achieving both reduction of rolling resistance and stability on a wet road surface, silica is added as a reinforcing filler to the tire rubber composition. However, even if silica is added to the tire rubber composition, the dispersibility of the silica in the tire rubber composition is low, and even if a large amount of silica is added, the effect cannot be fully exhibited. Is seen.

  In the present invention, polylactic acid having a functional group exhibiting addition reactivity with the double bond site of the diene polymer, or polylactic acid having the reactive functional group and the double bond site of the diene polymer are added. By using a modified diene polymer having a polylactic acid moiety, in which polylactic acid is uniformly introduced into the diene polymer under mild reaction conditions, as a component of the tire rubber composition, silica is used for the tire rubber composition. It is possible to disperse uniformly in the inside. As a result, reduction of viscosity, pain effect, improvement of scorch property, improvement of workability, high hardness, improvement of elongation at break, low heat generation, improvement of lamborn wear, etc. are achieved. It is possible to achieve both stability on a wet road surface, and thereby achieve improvements in the functions and performance required for automobile tires.

  Polylactic acid, in which a functional group capable of addition reaction with a double bond site of a diene polymer is introduced, is a typical polymer of biodegradable plastics, and polymerizes L-lactic acid synthesized from plant raw materials (such as corn). Poly-L-lactic acid. On the other hand, lactic acid obtained by a chemical synthesis method using ethylene as a starting material is D, L-lactic acid (racemic).

  Poly-L-lactic acid is actually produced by ring-opening polymerization of lactide, which is a cyclic dimer of lactic acid. When passing through lactide, lactic acid is melt polycondensed to synthesize low molecular weight polylactic acid. When this low molecular weight product is heated to high temperature, depolymerization occurs from the end, and the depolymerized product is purified to obtain lactide. However, lactide containing D-form is formed at the depolymerization stage, and the ratio of D / L can be arbitrarily changed by adjusting the type and amount of catalyst used, residence time, temperature and the like.

  Poly-L-lactic acid consisting only of L-lactic acid is a crystalline polymer with a melting point of 180 ° C and a glass transition temperature (Tg) of 60 ° C. The melting point is lowered by the random copolymerization of D-lactic acid. -The copolymer containing 12% lactic acid has a melting point of 140 ° C or lower and forms an almost amorphous polymer. In the present invention, polylactic acid having an L-lactic acid content of 85% or more and a melting point of 120 ° C. or more, preferably an L-lactic acid content of 90% by weight or more and a melting point of 140 ° C. or more is used.

  Also produced by a method of obtaining a high molecular weight polylactic acid by carrying out a dehydration polycondensation reaction in a solvent such as diphenyl ether and removing the water produced as an azeotrope with the solvent to advance the polymerization reaction. Things can also be used.

のn値として、2〜100、好ましくは2〜10程度のものが用いられる。 The molecular weight of polylactic acid used in the present invention is lactic acid units.

N value of 2 to 100, preferably about 2 to 10 is used.

  Such polylactic acid is introduced with a functional group capable of reacting with an additional double bond site of a diene polymer, for example, a terminal vinyl group derived from an acrylic group, a mercapto group, or a sulfide group. Examples of the compound having such a functional group include 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, 2,2′-dihydroxyethyl disulfide, 2,2′-dihydroxyethyl tetrasulfide, and the like. Preferably, a compound having a terminal hydroxyl group is used.

  These functional group-containing compounds are introduced into polylactic acid by ring-opening polymerization reaction in the presence of the functional group-containing compound when ring-opening polymerization of lactide, which is a cyclic dimer of lactic acid, to form polylactic acid. Is done. When the functional group-containing compound is a monohydroxy compound, the reaction is carried out in one stage. For example, in the case of a disulfide compound having a dihydroxy group, each dihydroxy group reacts with lactide. By reacting with a reducing agent such as trioctylphosphine or the like, a two-stage reaction is performed in which a disulfide bond is split and a compound having a mercapto group is formed.

  In this reaction, the functional group-containing compound is subjected to the reaction at a molar ratio of about 1/1 to 1/50, preferably about 1/1 to 1/5, with respect to lactide. If the functional group-containing compound is used in the reaction at a molar ratio lower than this, the final diene polymer will not be sufficiently modified with the polylactic acid moiety. On the other hand, when a functional group-containing compound is used in the reaction at a molar ratio higher than this, the number of functional groups capable of addition reaction with the double bond sites of the diene polymer contained in the polylactic acid becomes too large, and the diene polymer inherently This is unfavorable because it affects the physical properties.

  The ring-opening polymerization reaction of lactide in the presence of a functional group-containing compound is performed in the presence of a solvent, but is generally performed in the absence of a solvent. At that time, dioctyltin, dibutyltin dilaurate and the like are used as a reaction catalyst in a molar ratio of about 0.01 to 10%, preferably about 0.1 to 3% with respect to lactide.

  The ring-opening polymerization reaction is carried out at about 60 to 150 ° C. for about 1 to 24 hours. The obtained reaction mixture is dropped into hexane, for example, as an acetone solution, and divided into a hexane insoluble part and a hexane soluble part. The insoluble matter is again made into an acetone solution and purified by a reprecipitation method using hexane, so that a functional group capable of addition reaction with the double bond site of the diene polymer, for example, a terminal vinyl group derived from an acrylic group, a mercapto group, a sulfide group Etc. can be obtained.

  Polylactic acid having these functional groups can be added to the double bond site of the diene polymer to introduce a polylactic acid site into the diene polymer. Examples of the diene polymer include styrene butadiene rubber, synthetic isoprene, butadiene rubber, butyl rubber, halogenated butyl rubber, and EPDM, and styrene butadiene rubber is preferably used. The styrene butadiene rubber may be either emulsion polymerization SBR (E-SBR) or anion polymerization SBR (S-SBR).

The reaction between the diene rubber and the functional group-containing polylactic acid is performed using a functional group-containing polylactic acid in a weight ratio of about 0.001 to 2, preferably about 0.001 to 0.1, based on the diene rubber. The reaction is carried out by addition reaction for about 0.5 to 24 hours at about 60 to 200 ° C. in the presence or absence of a solvent such as benzene. Actually, when a modified diene polymer is used as one component of the rubber composition for a tire, a weight ratio of about 0.01 is sufficient. However, in Reference Examples 3 to 4 described below, polylactic acid is introduced into SBR. The reaction is performed at a weight ratio of 1.170 or 1.207 for clarity.

The treatment after the completion of the reaction is, for example, dropping the reaction mixture solution into methanol to divide it into a methanol insoluble part and a methanol soluble part, making the methanol insoluble part a toluene solution again, and reprecipitation using acetone, methanol, etc. Obtained as a modified diene polymer having a polylactic acid moiety purified by the method.

  The polylactic acid having a functional group capable of addition reaction with the double bond site obtained as described above, more specifically a terminal vinyl group derived from an acrylic group, a mercapto group, a nitrone group, etc. is 100 weights of diene rubber. 5 to 150 parts by weight, preferably 20 to 120 parts by weight, more preferably 30 to 100 parts by weight, together with silica used, 0.1 to 10 parts by weight, preferably 1 to 7 parts by weight, more preferably Are used together at a ratio of 2 to 5 parts by weight to form a rubber composition for a tire.

  As the diene rubber used as the main component of the tire rubber composition, at least one kind of various synthetic rubbers as described above, natural rubber, or a blend rubber of synthetic rubber and natural rubber is used.

  There are two types of silica, wet and dry, depending on the synthesis method, and wet silica is preferably used for tire applications from the viewpoint of performance and cost. By using silica as a filler in the tread formulation of passenger car pneumatic tires, it is possible to achieve both high rolling resistance and high tire performance on wet surfaces without sacrificing wear resistance. In the present invention in which the specific blending agent is blended with the diene rubber, the abrasion resistance is improved.

  Silica used as a filler has poor affinity with rubber polymers, and in rubber, silica has the ability to generate hydrogen bonds through silanol groups and lower the dispersibility of silica in rubber. In order to improve the properties required for the above and the dispersibility with the diene rubber, the silane coupling agent is used in a proportion of 2 to 18% by weight, preferably 5 to 10% by weight, based on the silica weight. If the proportion of silane coupling agent used is less than this, the properties required of silica and dispersibility with diene rubber will not be fully exhibited, while if it is used in a proportion higher than this, workability will deteriorate. To come.

The silane coupling agent has a general formula
(R ′) _3-n (OR) _n SiR ″ SxR ″ Si (OR) _n (R ′) _3-n
R: an alkyl group having 1 to 3 carbon atoms
R ′: an alkyl group having 1 to 3 carbon atoms
R ″: an alkylene group having 1 to 5 carbon atoms
X: 2-4
n: 1 to 3
A polysulfide silane coupling agent having an alkoxysilyl group that reacts with a silanol group on the silica surface and a sulfur chain that reacts with a polymer is used. Specifically, for example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) ) Disulfide and the like are preferably used.

  When a predetermined amount of polylactic acid having an acrylic group as a functional group capable of addition reaction with a double bond site is blended in a diene rubber, not only improvement in workability and high hardness can be achieved, but also specified. By reducing the amount of silica within the range, the value of loss tangent tan δ (60 ° C.) is reduced, and low heat generation is also possible. When polylactic acid is used at a prescribed ratio or more, the value of tan δ (60 ° C.) is particularly increased (see Table 1 No. 4).

  In addition, when polylactic acid having a mercapto group as a functional group capable of addition reaction with a double bond site is blended with a diene rubber, the viscosity, the Pain effect are reduced, the scorch property is improved, and the low temperature tanδ (0 ° C) is reduced. Up, improvement of the Lambourn wear, etc. are achieved, and by reducing the amount of silica within the specified range, the hardness is equivalent and the workability can be further improved. If polylactic acid is used at a specified ratio or more, the vulcanization rate will be slow (see Table 2, No. 4).

  Furthermore, in a rubber composition in which 5 to 150 parts by weight of silica, preferably 20 to 120 parts by weight, more preferably 30 to 100 parts by weight are blended with 100 parts by weight of diene rubber, 5 to 100 parts by weight of diene rubber In the rubber composition for tires substituted with 50 parts by weight, preferably 10 to 40 parts by weight, more preferably 20 to 30 parts by weight of a modified diene polymer having a polylactic acid moiety, the hardness is increased and the elongation at break is increased. Improvement and reduction in tan δ (60 ° C.) are achieved, and the value of tan δ (60 ° C.) allows further reduction even when the amount of silica is reduced within a specified range. The prescribed substitution ratio is necessary to obtain a desired improvement effect, and if the substitution ratio is less than this, the desired improvement effect is not achieved. Become.

  In the silica-containing diene rubber composition containing the above components as essential components, an acid mixture generally used as a rubber compounding agent, for example, a reinforcing agent or a filler represented by carbon black, a diene Depending on the type of rubber, vulcanizing agents such as sulfur, vulcanizing accelerators such as thiazole, sulfenamide, guanidine and thiuram, processing aids such as stearic acid, paraffin wax and aroma oil, anti-aging An agent, a plasticizer, and the like are appropriately mixed and used.

  The composition is prepared by mixing other compounding ingredients excluding vulcanizing system components for about 1 to 10 minutes using a closed Banbury mixer, etc., and releasing these mixtures outside the mixer to cool to room temperature. Thereafter, the vulcanized components are blended using a Banbury mixer, an open roll or the like and mixed to produce a desired silica-blended diene rubber composition.

  The silica-containing diene rubber composition produced in this manner is extruded into a tread shape of a pneumatic tire, and is bonded to the casing portion by a normal method on a tire molding machine to form an unvulcanized tire. This can be pressurized and heated in a vulcanizer to obtain a pneumatic tire having a tread portion and the like formed from this composition. The tread portion may be any of a cap tread, an under tread, a side tread, etc., and can be applied to a carcass coat, a rim cushion, or the like.

  Next, the present invention will be described with reference to examples.

Reference Example 1 (Production of polylactic acid having an acrylic group)
Dioctyltin 0.810 g (2.0 mmol) was added to a mixture of 2-hydroxyethyl acrylate CH ₂ = CHCOOCH ₂ CH ₂ OH 16.2 g (140 mmol) and lactide (Musashino Chemical Laboratory) 60.3 g (418 mmol), and 100 The mixture was stirred at 0 ° C. for 3 hours and then cooled. The reaction mixture was dissolved in 30 ml of acetone, and the solution was dropped into 500 ml of hexane to separate into a hexane insoluble part and a hexane soluble part. The hexane-insoluble part was dissolved again in acetone and purified by a reprecipitation method using hexane to obtain 72.8 g (yield 95%) of a brown viscous liquid.

The reaction product was confirmed by NMR analysis to be polylactic acid having an acrylic group (n = 6).
¹ HNMR (CDCl ₃ , 20 ° C.) δ: 6.4 (d)
6.1 (m)
5.9 (d)
5.3 to 5.1 (m)
4.5 to 4.2 (m)
2.8-2.3 (br)
1.7-1.4 (m)

Reference Example 2 (Production of polylactic acid having a mercapto group)
(1) 2,2′-dihydroxyethyl disulfide 0.880 g (2.2 mmol) of dioctyltin was added to a mixture of 7.17 g (46.5 mmol) of HOCH ₂ CH ₂ SSCH ₂ CH ₂ OH and 40.2 g (279 mmol) of lactide, The mixture was stirred at 0 ° C. for 3 hours and then cooled. The reaction mixture was dissolved in 30 ml of acetone, and the solution was dropped into 500 ml of hexane to separate into a hexane insoluble part and a hexane soluble part. The hexane-insoluble part was dissolved again in acetone and purified by a reprecipitation method using hexane to obtain 42.8 g (yield 90%) of a brown viscous liquid.

The reaction product was confirmed to be polylactic acid (n = 6) having a disulfide group by NMR analysis.
¹ HNMR (CDCl ₃ , 20 ° C.) δ: 5.3 to 5.1 (m)
4.5 to 4.3 (m)
2.9 (m)
2.2 to 1.7 (br)
1.6-1.4 (m)

(2) 31.9 g (31.3 mmol) of polylactic acid having a disulfide group obtained in (1) above was dissolved in 50 ml of ethyl acetate, and trioctylphosphine P (C ₈ H ₁₇ ) ₃ 11.6 g ( 31.3 mmol) was added and stirred at room temperature for 1 day. The reaction solution was dropped into 500 ml of hexane, and separated into a hexane insoluble part and a hexane soluble part. The hexane-insoluble part was again dissolved in acetone and purified by a reprecipitation method using hexane to obtain 28.7 g (yield 91%) of a brown viscous liquid.

The reaction product was confirmed to be polylactic acid (n = 6) having a mercapto group by NMR analysis.
¹ HNMR (CDCl ₃ , 20 ° C.) δ: 5.3 to 5.1 (m)
4.3 (m)
4.2 (m)
2.8 (m)
2.2 to 1.7 (br)
1.6-1.4 (m)

Reference Example 3 (Modification of SBR using polylactic acid having an acrylic group)
2.74 g of acrylic acid-containing polylactic acid obtained in Example 1 was added to a solution prepared by dissolving 2.35 g of SBR (Nippon ZEON product A1326) in 40 ml of toluene, and the mixture was stirred for 1 day under reflux conditions and then cooled. The reaction mixture solution was dropped into 300 ml of methanol and separated into a methanol-insoluble part and a methanol-soluble part. The methanol-insoluble part was again dissolved in toluene and purified by a reprecipitation method using acetone to obtain 2.27 g of a reaction product as a white solid.

The reaction product was confirmed by NMR analysis to be an SBR-modified product in which the terminal vinyl group of acrylic group-containing polylactic acid was added to the SBR double bond.
¹ HNMR (CDCl ₃ , 20 ° C.) δ: 7.3 to 7.2 (br)
7.2 to 6.9 (br)
5.7-5.1 (br)
5.0 ~ 4.9 (br)
4.4〜4.2 (br)
2.7 ~ 2.4 (br)
2.4-0.8 (br)

Reference Example 4 (SBR modification using polylactic acid having a mercapto group)
3.26 g of the mercapto group-containing polylactic acid obtained in Example 2 was added to a solution obtained by dissolving 2.70 g of SBR (Nippon ZEON product A1326) in 40 ml of toluene, and the mixture was stirred at 80 ° C. for 1 day and then cooled. The reaction mixture solution was dropped into 300 ml of methanol and separated into a methanol-insoluble part and a methanol-soluble part. The methanol-insoluble part was again dissolved in toluene and purified by a reprecipitation method using methanol to obtain 4.42 g of a reaction product as a white solid.

The reaction product was confirmed by NMR analysis to be a modified SBR product in which the terminal mercapto group of mercapto group-containing polylactic acid was added to the double bond of SBR.
¹ HNMR (CDCl ₃ , 20 ° C.) δ: 7.3 to 7.2 (br)
7.2 to 6.9 (br)
5.7-5.1 (br)
5.0 ~ 4.0 (br)
4.5-4.1 (br)
2.8-2.4 (br)
2.3 ~ 0.6 (br)

Example 1
SBR (Nippon Zeon product Nipol NS460; 37.5 parts by weight oil exhibition) 96.3 parts by weight Butadiene rubber (Nippon Zeon product BR1220) 30.0 0.0
Silica (Evonik Degussa product Ultrasil 7000GR) (predetermined amount)
Carbon black (Tokai carbon product seast 6; N ₂ SA 119m ² / g) (predetermined amount)
Silane coupling agent (Evonik Degussa Si69) (predetermined amount)
Polylactic acid having an acrylic group obtained in Reference Example 1 (predetermined amount)
Zinc oxide (Zondox Chemical Products Zinc Oxide 3 types) 3 〃
Stearic acid (Japanese oil and fat product beads stearic acid) 2 〃
Anti-aging agent (Flexis product 6PPD) 3 〃
Aroma oil (Showa Shell Product Extract No. 4 S) 10 〃
Sulfur (Tsurumi Chemical Co., Ltd., Jinhua Indian Oil Fine Powdered Sulfur) 2〃
Vulcanization accelerator (Ouchi Emerging Chemical Industry Noxeller CZ-G) 2
Vulcanization accelerator (Sumitomo Chemical product Soxinol DG) 1 〃

  Among the above components, each component excluding sulfur and vulcanization accelerator is mixed for 5 minutes using a 7L closed Banbury mixer, the rubber mixture is discharged outside the mixer and cooled to room temperature, and then the same Banbury. Using a mixer, sulfur and a vulcanization accelerator were blended and mixed. The obtained rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a desired test piece.

With respect to this rubber composition and test piece, the following items were measured and indicated by an index where No. 1 containing no modified polylactic acid was 100.
Viscosity: Measured at 100 ° C according to JIS K6300
The smaller the index is, the lower the viscosity is. Payne effect: Unvulcanized rubber composition is vulcanized at 160 ° C for 20 minutes, strain 0.28 ~
The strain shear stress G 'up to 30.0% was measured and the difference was displayed as an index.
The larger the index, the better the silica dispersibility.
20 ℃ hardness: Measured at 20 ℃ according to JIS K6253
The larger the index, the higher the hardness.
tanδ: Tensile deformation strain rate of 10 ± 2% using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho
, Measured under conditions of frequency 20Hz, temperature 0 ℃ and 60 ℃
The higher the index, the higher the tanδ that is the index of exothermicity.

The above measurement results are shown in the following Table 1 together with the amount of each component (unit: parts by weight) used in a predetermined amount.
Table 1
No.1 No.2 No.3 No.4 No.5 No.6
[Rubber composition component]
Silica 70 70 70 70 64 62
Carbon black 5 5 5 5 5 5
Silane coupling agent 7.0 7.0 7.0 7.0 6.4 6.2
Acrylic group-containing polylactic acid − 2.0 5.0 15.0 2.0 5.0
〔Measurement result〕
Viscosity 100 95 90 86 90 83
Payne effect 100 93 88 84 91 84
20 ° C hardness 100 104 108 110 101 105
tanδ
0 ° C 100 101 102 104 105 105
60 ° C 100 99 98 103 94 92

From the above results, the following can be said.
(1) From the results of Examples Nos. 2 to 3, by adding polylactic acid having an acrylic group, the viscosity, the Payne effect are reduced, the hardness is increased, and tanδ is maintained at the same level or slightly improved It can be seen that the processability can be improved.
(2) By comparing the results of Nos. 5-6 and Nos. 2-3, which are both examples, it is possible to increase the hardness and reduce tan δ (60 ° C) by reducing the amount of silica blended, that is, It can be seen that the workability can be improved, the hardness can be increased, and the heat generation can be reduced.

Example 2
SBR (Nipol NS460) 96.3 parts by weight Butadiene rubber (BR1220) 30.0 〃
Silica (Ultrasil 7000GR) (predetermined amount)
Carbon black (Seast 6) (predetermined amount)
Silane coupling agent (Si69) (predetermined amount)
Polylactic acid having a mercapto group obtained in Reference Example 2 (predetermined amount)
Zinc oxide (3 types of zinc oxide) 3 〃
Stearic acid (bead stearic acid) 2 〃
Anti-aging agent (6PPD) 3 〃
Aroma oil (Extract No. 4 S) 10 〃
Sulfur (fine powder sulfur with Jinhua seal oil) 2 2
Vulcanization accelerator (Noxeller CZ-G) 2 〃
Vulcanization accelerator (Soxinol DG) 1 〃

Vulcanization and measurement were performed in the same manner as in Example 1 using the above components. The obtained measurement results are shown in the following Table 2 together with the amount of each component (unit: parts by weight) used in a predetermined amount. In addition, the following measurement items were added as measurement items.
Mooney scorch: Measured at 120 ° C according to JIS K6300
The larger the index is, the slower the scorch is. Lambourne wear: Using a lambourne wear tester manufactured by Iwamoto Seisakusho, the load is 5 kg (49 N),
Measured under conditions of slip rate 25%, time 4 minutes, room temperature,
The weight loss was shown as an index.
The larger the index, the better the wear resistance.
Table 2
No.1 No.2 No.3 No.4 No.5
[Rubber composition component]
Silica 80 80 80 80 75
Carbon black 5 5 5 5 5
Silane coupling agent 8.0 8.0 8.0 8.0 7.5
Mercapto group-containing polylactic acid-2.0 5.0 15.0 5.0
〔Measurement result〕
Viscosity 100 89 84 80 82
Mooney Scorch 100 130 140 155 140
Pain effect 100 73 70 68 68
20 ° C hardness 100 100 101 102 100
tanδ (0 ° C) 100 106 108 110 110
Lambourne wear 100 127 130 129 128

From the above results, the following can be said.
(1) From the results of Nos. 2 to 3 as examples, by blending a polylactic acid having a mercapto group, the viscosity, the pain effect is reduced, the scorch property is improved, and the value of the low temperature tan δ is increased. It can be seen that the lamborn wear is also good.
(2) By comparing the results of No. 5 and No. 3 which are both examples, it can be seen that by reducing the amount of silica, the hardness is equivalent and the workability can be further improved.

Example 3
SBR (Nipol NS460) (predetermined amount)
SBR (Nippon ZEON product Nipol NS616) (predetermined amount)
Silica (Ultrasil 7000GR) (predetermined amount)
Carbon black (Seast 6) 5 parts by weight Silane coupling agent (Si69) (predetermined amount)
Polylactic acid having a mercapto group obtained in Reference Example 4 (predetermined amount)
Modified SBR
Zinc oxide (3 types of zinc oxide) 3 〃
Stearic acid (bead stearic acid) 2 〃
Anti-aging agent (6PPD) 3 〃
Aroma oil (Extract No. 4 S) (predetermined amount)
Sulfur (fine powder sulfur with Jinhua seal oil) 2 2
Vulcanization accelerator (Noxeller CZ-G) 2 〃
Vulcanization accelerator (Soxinol DG) 1 〃

Vulcanization and measurement were performed in the same manner as in Example 1 using the above components. The obtained measurement results are shown in the following Table 3 together with the amount of each component (unit: parts by weight) used in a predetermined amount. In addition, the following measurement items were added as measurement items.
Elongation at break: In accordance with JIS K6251, a tensile test is performed at room temperature, and elongation at break
Sought
The larger the index, the higher the elongation at break
Table 3
No.1 No.2 No.3 No.4 No.5 No.6
[Rubber composition component]
SBR (Nipol NS460) 110.0 96.3 110.0 96.3 96.3 110.0
SBR (Nipol NS616) 20.0 30.0 − − − 20.0
Polylactic acid modified SBR − − 20.0 30.0 30.0 −
Silica 65 65 65 65 60 60
Silane coupling agent 6.5 6.5 6.5 6.5 6.0 6.0
Aroma oil 18 8 18 8 8 18
〔Measurement result〕
20 ° C hardness 100 100 102 102 100 95
Elongation at break 100 85 106 105 103 96
tanδ
0 ° C 100 104 100 105 106 102
60 ° C 100 105 98 99 94 98

From the above results, the following can be said.
(1) From the results of Nos. 3 to 4 as examples, by adding SBR modified with polylactic acid having a mercapto group, the hardness is increased, the elongation at break is improved, and the tan δ (60 ° C.) is decreased. It can be seen that the elongation at break is secured even when the amount of the modified SBR is increased.
(2) By comparing the results of No. 5 and No. 4 which are both examples, it can be seen that tan δ (60 ° C.) can be further reduced by reducing the amount of silica.
(3) From the result of Comparative Example No. 2, it is understood that the elongation at break decreases when the amount of unmodified SBR is increased.

Claims (4)

Rubber composition for tire comprising 100 parts by weight of diene rubber and 5 to 150 parts by weight of silica and 0.1 to 10 parts by weight of polylactic acid having a functional group capable of addition reaction with a double bond site of diene polymer . In a rubber composition in which 5 to 150 parts by weight of silica is blended with 100 parts by weight of diene rubber, 5 to 50 parts by weight of 100 parts by weight of diene rubber is a functional group capable of addition reaction with the double bond site of the diene polymer. A rubber composition for tires, which is substituted with a modified diene polymer having a polylactic acid moiety, which is modified with a polylactic acid having a polylactic acid. The rubber composition for a tire according to claim 1 or 2, which is used for forming a tread portion of a tire. An automotive pneumatic tire having a tread portion formed from the rubber composition for a tire according to claim 3.