JP5217130B2 - Rubber composition for tire inner liner and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a tire inner liner. More specifically, the present invention provides a processability in an unvulcanized state or before vulcanization (hereinafter simply referred to as “vulcanization”) without impairing the barrier property and anti-aging property to a gas such as air after vulcanization. The present invention relates to a rubber composition for a tire inner liner, which is improved in the “formability before processing”.

  In general, a pneumatic tire is particularly required to have low gas permeability (or high gas barrier property) from the viewpoint of airtightness of a tire air chamber, and an inner liner provided on the inner surface of the pneumatic tire is high. A rubber composition mainly containing butyl rubber, halogenated butyl rubber or a combination thereof, which is required to have gas barrier properties and excellent in gas barrier properties, is often used for the production thereof. However, it is generally known that butyl rubber and halogenated butyl rubber are not very good in processability before vulcanization by rolling, extrusion, molding, etc. In order to improve the processability before vulcanization, the rubber composition It is common practice to add various plasticizers and softeners commonly used in the formulation of products. The names of plasticizers and softeners are generally properly used according to the purpose of use. However, since the functions are essentially the same and there is no clear distinction between them, plasticizers or softeners are described below. Those that exhibit the function of the agent are collectively referred to as a plasticizer.

  Examples of the plasticizer for rubber include, for example, those composed of an ester of a polyhydric alcohol, an aliphatic polyvalent carboxylic acid and an aliphatic monovalent carboxylic acid having substantially no hydroxyl group (Patent Document 1), and an aromatic process. Oils, naphthenic process oils, paraffinic process oils, natural plasticizers such as pine tar and palm oil, and phthalic acid derivatives such as dibutyl phthalate are known (Patent Document 2). Furthermore, it has been proposed to blend various aromatic carboxylic acid esters, aliphatic carboxylic acid esters and phosphate esters as plasticizers in rubber compositions based on diene rubbers such as natural rubber and butyl rubber. (Patent Documents 3 to 5). On the other hand, it has been proposed that a blend of phosphate is blended in a curing bladder composition as an antioxidant and an ozone cracking inhibitor (Patent Document 6), and an antioxidant or an antioxidant is added to a rubber composition for a tread. It has been proposed that phosphites are blended as (Patent Document 7).

  However, when the conventional plasticizer for rubber is used, the processability before vulcanization of the rubber composition is improved, but the gas barrier property after vulcanization is reduced, and the vulcanization of the rubber composition is reduced. When the amount of the plasticizer was decreased in order to maintain the gas barrier property at a high level later, the processability before vulcanization deteriorated.

JP 7-292154 A Japanese Patent Laid-Open No. 7-9807 JP 2002-36814 A JP 2002-52904 A JP 2002-114870 A JP-A-8-109285 JP 2002-3647 A

  As described above, various plasticizers for rubber are known, but in a rubber composition comprising butyl rubber, halogenated butyl rubber, or a combination thereof, the level is almost the same as when no plasticizer such as process oil is blended. To date, it has not been proposed to improve processability before vulcanization while maintaining gas barrier properties and aging resistance after vulcanization.

  Accordingly, an object of the present invention is to provide a rubber composition for a tire inner liner that has improved processability before vulcanization without impairing gas barrier properties and aging resistance after vulcanization.

  As a result of earnest research to solve the above problems, the present inventor has found that a rubber component containing 50% by weight or more of butyl rubber, halogenated butyl rubber or a combination thereof, and 3 to 20 parts by weight with respect to 100 parts by weight of the rubber component The rubber composition comprising the phosphoric acid ester of the present invention exhibits a good pre-vulcanization processability at the same level as when a conventional rubber plasticizer in the same proportion is used, and the plasticizer contains It has been found that gas barrier properties of almost the same level as when not blended are shown after vulcanization, and the present invention has been completed. Furthermore, the present inventors have surprisingly found that the rubber composition also exhibits excellent aging resistance after vulcanization.

According to the present invention,
(A) a rubber component containing 50% by weight or more of butyl rubber, halogenated butyl rubber or a combination thereof;
(B) 3 to 20 parts by weight of a phosphoric ester based on 100 parts by weight of the rubber component (A),
A rubber composition for a tire inner liner is provided.

  The rubber component (A) in the rubber composition for a tire inner liner of the present invention contains 50% by weight or more of butyl rubber, halogenated butyl rubber, or a combination thereof based on the total weight thereof. Commercially available butyl rubber and halogenated rubber can be used. Halogenated butyl rubber is, for example, chlorinated butyl rubber or brominated butyl rubber.

  In addition to butyl rubber, halogenated butyl rubber, or combinations thereof, rubbers that can be included in the rubber component include natural rubber, butadiene rubber, isoprene rubber, diene rubber such as styrene-butadiene rubber, and ethylene-propylene rubber. Examples include rubbers selected from non-diene rubbers. The rubber composition of the present invention may contain one or more of these in any proportion as long as the rubber component (A) contains butyl rubber, halogenated butyl rubber or a combination thereof in the above proportion. .

  The phosphate ester (B) used as a plasticizer in the rubber composition of the present invention is a phosphate triester. The phosphate ester preferably has a freezing point of -60 ° C to -20 ° C, more preferably a freezing point of -54 ° C to -35 ° C. Specific examples of phosphoric acid triesters include, for example, trimethyl phosphate (freezing point −70 ° C. or lower), triethyl phosphate (freezing point −56 ° C. or lower), tributyl phosphate (freezing point −80 ° C. or lower), tris phosphate (2 -Ethylhexyl) (freezing point -70 ° C or lower), Tris phosphate (butoxyethyl) (freezing point -70 ° C or lower), triphenyl phosphate (freezing point 48-50 ° C), tricresyl phosphate (freezing point -35 ° C), phosphoric acid Examples include trixylenyl (freezing point—15 ° C.), cresyl diphenyl phosphate (freezing point—30 ° C.), and 2-ethylhexyl diphenyl phosphate (freezing point—54 ° C.).

  The amount of the phosphoric ester (B) is 3 to 20 parts by weight, preferably 4 to 18 parts by weight per 100 parts by weight of the rubber component (A) containing 50% by weight or more of butyl rubber, halogenated butyl rubber or a combination thereof. is there. When the amount of the phosphate ester (B) is less than 3 parts by weight per 100 parts by weight of the rubber component (A), the processability before vulcanization cannot be sufficiently improved, and the rubber component ( A) When it exceeds 20 parts by weight per 100 parts by weight, the workability before vulcanization is improved, but the gas barrier property is lowered.

  In the rubber composition of the present invention, in addition to the rubber component (A) and the phosphoric ester (B), a reinforcing filler such as carbon black, gas barrier properties, which is generally blended in a rubber composition for tires. General use of various fillers such as clay and talc, which are generally known to improve the quality, stearic acid, vulcanization or crosslinking agent, vulcanization or crosslinking accelerator, anti-aging agent, etc. It can mix | blend in quantity.

  The rubber composition of the present invention can be produced by a general mixing or kneading method and operating conditions using a mixing or kneading apparatus such as a Banbury mixer or a kneader that is usually used for the production of a rubber composition. The rubber composition of the present invention is kneaded with a predetermined amount of the above components and other general compounding agents, or a rubber mixture (master batch) of specific components is prepared in advance and then mixed or kneaded with the predetermined components. Can be manufactured. After kneading the rubber composition of the present invention, the inner liner of the tire can be formed by making a desired thickness with a rolling mill or an extruder and cutting the rubber composition into an appropriate size.

  The invention is further illustrated by the following examples, but it goes without saying that the scope of the invention is not limited to these examples.

Production of rubber compositions of standard examples, examples 1 to 6 and comparative examples 1 to 4 In the composition (parts by weight) shown in Table 1 below, the components excluding sulfur, vulcanization accelerator and zinc oxide were adjusted to 60 ° C. The resulting BB-2 mixer was kneaded for 3 to 5 minutes at a rotation speed of 30 rpm, and the kneaded product was discharged at 110 ° C. Each rubber composition was prepared by blending sulfur and a vulcanization accelerator in an open roll. Each rubber composition obtained was formed into the shape required for the following tests except for the Mooney viscosity test, and vulcanized at 150 ° C. for 30 minutes.

註:
(1) Bromobutyl 2255 (Nippon Butyl Co., Ltd.)
(2) Seast V (manufactured by Tokai Carbon Co., Ltd.)
(3) Industrial stearic acid (manufactured by NOF Corporation)
(4) Three types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
(5) Noxeller DM (Ouchi Shinsei Chemical Co., Ltd.)
(6) Powdered sulfur (manufactured by Hosoi Chemical Co., Ltd.)
(7) Process oil P-100 (paraffinic hydrocarbon oil manufactured by Fuji Kosan Co., Ltd.)
(8) tricresyl phosphate (manufactured by Daihachi Chemical Industry Co., Ltd.), freezing point -35 ° C
(9) 2-ethylhexyl diphenyl phosphate (manufactured by Daihachi Chemical Industry Co., Ltd.), freezing point -54 ° C
(10) Tris phosphate (butoxyethyl) (manufactured by Daihachi Chemical Industry Co., Ltd.), freezing point of −70 ° C. or less (11) Trixylenyl phosphate (manufactured by Daihachi Chemical Industry Co., Ltd.), freezing point of −15 ° C.
(12) Dibutyl phthalate (manufactured by Daihachi Chemical Industry Co., Ltd.), freezing point -35 ° C

Test method 1) Mooney viscosity In accordance with JIS K6300, Mooney viscosity was measured using an L-shaped rotor (tester: SMV300J manufactured by Shimadzu Corporation) at a preheating time of 1 minute, a rotor rotation time of 4 minutes, and a temperature of 100 ° C. did. The Mooney viscosity is an index of processability before vulcanization of the rubber composition, and a small Mooney viscosity value means that the viscosity before vulcanization is low and the processability is excellent.

2) Air permeability It was performed in accordance with JIS K7126 “Plastic film and sheet gas permeability test method (Method A)”. The gas used for the test was air (nitrogen: oxygen = about 8: 2), and the test temperature was 30 ° C. The results are shown as index values with the air permeability coefficient of the standard example as 100. The smaller this value, the lower the air permeability, that is, the better the air barrier property.

3) Aging resistance A test piece having a size of 15 cm × 15 cm × 0.2 cm is produced by press vulcanization with a mold, and the test piece is filled with air and set at 120 ° C. in accordance with JIS K6257. In a heated oven for 96 hours and accelerated aging. The elongation at break (tensile speed: 500 mm / min) of the test piece was measured before and after aging, and the following formula:
Residual ratio of elongation at cutting (%) = (Elongation at cutting after aging) / (Elongation at cutting before aging) × 100
Accordingly, the residual ratio (%) of elongation at break was determined. It shows that it is excellent by aging resistance, so that the value of the residual rate of elongation at the time of a cutting | disconnection is large.

4) Air pressure retention property A truck bus steel radial tire having a tire size of 11R22.5 14PR in which the rubber compositions of the standard examples, Examples 1 to 6 and Comparative Examples 1 to 4 were processed into a sheet shape and used as an inner liner. Produced. For these tires, after setting the tire air pressure to 700 kPa, the tire was allowed to stand for 3 months at a room temperature of 21 ° C. under no load condition, and the tire internal pressure was measured every 4 days. The initial pressure was P ₀ , and the measured pressure was P _t The α value is obtained by regressing the equation P _t / P ₀ = exp (−αt), where t is the elapsed days, and then the obtained α value and t = 30 are expressed by the equation: β = [1-exp (−αt)] × 100 was substituted for the air pressure reduction rate per month, and this air pressure reduction rate was used as an index representing air pressure retention. The air pressure retention of Examples 1 to 3 and Comparative Example 3 was expressed as an index value when the standard example was 100. A smaller index value indicates better air pressure retention. The rubber compositions of Comparative Examples 1 and 3 were not tested for air pressure retention because the tires could not be produced because the Mooney viscosity was high, making it difficult to roll into sheets.

  According to these test methods, the rubber compositions of the above-mentioned standard examples, examples and comparative examples were tested. The test results are shown in Table 2 below.

  As can be seen from the results in Table 2, the rubbers of Examples 1 and 3 containing 7 parts by weight and 18 parts by weight of tricresyl phosphate (freezing point -35 ° C.) per 100 parts by weight of the rubber component (brominated butyl rubber), respectively. The rubber composition of Example 4 in which 7 parts by weight of the composition and 2-ethylhexyldiphenyl phosphate (freezing point -54 ° C.) was blended with respect to 100 parts by weight of the rubber component was compared with a standard example using process oil as a plasticizer. Thus, approximately the same level of Mooney viscosity was achieved, improving air permeability, aging resistance and air pressure retention. Moreover, the rubber composition of Example 2 which mix | blended 4 weight part of tricresyl phosphate (freezing point -35 degreeC) with respect to 100 weight part of rubber components, respectively, and trixylenyl phosphate (freezing point -15 degreeC) were set to 100 weight part of rubber components. On the other hand, in the rubber composition of Example 6 blended with 7 parts by weight, the Mooney viscosity increases as compared with the standard example, but this increase in Mooney viscosity results in a decrease in workability that cannot be rolled into a sheet. Rather, it is within an acceptable range, and the effect of improving aging resistance and air pressure retention, particularly the effect of improving air pressure retention is great. In the rubber composition of Example 5 in which 7 parts by weight of tris (butoxyethyl) phosphate (freezing point of −70 ° C. or less) was blended with respect to 100 parts by weight of the rubber component, the Mooney viscosity was almost the same level as the standard example. The air permeability, aging resistance, and air pressure retention were improved, but the degree of improvement in air permeability and air pressure retention was smaller than in Examples 1-4. On the other hand, in the rubber composition of Comparative Example 1 in which no plasticizer was blended, the air permeability and aging resistance were improved as compared with the standard example, but the Mooney viscosity was greatly increased. The large increase resulted in a decrease in workability that could not be rolled into a sheet. Moreover, in the rubber composition of Comparative Example 2 in which 7 parts by weight of dibutyl phthalate (freezing point -35 ° C.), which is an aromatic carboxylate compound, is blended with respect to 100 parts by weight of the rubber component, compared with the standard example, Although Mooney viscosity, air permeability, and air pressure retention were almost the same level, the aging resistance was considerably inferior. Further, in the rubber composition of Comparative Example 3 containing 2 parts by weight of tricresyl phosphate per 100 parts by weight of the rubber component, the air permeability and aging resistance are improved as compared with the standard example, but the rubber composition of Comparative Example 1 is improved. Like the product, the Mooney viscosity increased significantly, and this significant increase in Mooney viscosity resulted in a decrease in workability that could not be rolled into a sheet. In the rubber composition of Comparative Example 4 containing 21 parts by weight of tricresyl phosphate per 100 parts by weight of the rubber component, the Mooney viscosity is reduced as compared with the standard example, but the air permeability, aging resistance and air pressure retention are It was almost the same level.

Claims (2)

(A) a rubber component containing 50% by weight or more of halogenated butyl rubber;
(B) 3 to 20 parts by weight of a phosphate ester having a freezing point of −60 ° C. to −20 ° C. with respect to 100 parts by weight of the rubber component (A),
A rubber composition for a tire inner liner, comprising: A pneumatic tire using the rubber composition for a tire inner liner according to claim 1 as a tire inner liner.