JP2008111109A - Rubber composition for tire inner liner and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition having a processability improved to be well-balanced before vulcanized, an air barrier property after vulcanized and an age resistance after vulcanized which is useful for manufacturing a tire inner liner. <P>SOLUTION: The rubber composition for the tire inner liner comprises: (A) a rubber component comprising 50 wt.% or more of one or more butyl-type rubbers selected from the group consisting of butyl rubbers and halogenated butyl rubbers; and (B) 3-20 pts.wt. of a process oil with respect to 100 pts.wt. of the above described rubber component (A), wherein the process oil is comprised of an aromatic hydrocarbon, a paraffinic hydrocarbon and a naphthenic hydrocarbon, and then the weight percentages of the carbons constituting the aromatic hydrocarbons C<SB>A</SB>, the carbons constituting the paraffinic hydrocarbons C<SB>p</SB>and the carbons constituting the naphthenic hydrocarbons C<SB>N</SB>in the process oil, as determined according to ASTM D2140, are respectively within a range as follows: 20 wt.%≤C<SB>A</SB>≤40 wt.%, 30 wt.%≤C<SB>p</SB>≤60 wt.%, and 20 wt.%≤C<SB>N</SB><30 wt.%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire inner liner. More specifically, the present invention relates to a rubber composition for a tire inner liner that improves the workability before vulcanization, the air barrier property after vulcanization, and the aging resistance after vulcanization in a well-balanced manner.

  In general, a pneumatic tire is particularly required to have low air permeability (or high air blocking 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 composed of a butyl rubber selected from butyl rubber and halogenated butyl rubber, which is required to have air barrier properties and excellent in air 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 that are 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.

  Various hydrocarbon plasticizers are known as rubber plasticizers added to rubber compositions for producing inner liners of pneumatic tires. For example, paraffin oil is used as the hydrocarbon plasticizer. (Patent Document 1), using one or more of naphthenic oil and paraffinic oil (Patent Document 2), using one or more of paraffinic oil and aroma oil (Patent Document 3). Proposed.

  However, when an inner liner is produced using a conventional plasticizer for rubber, it is possible to improve the workability before vulcanization, the air barrier property after vulcanization, and the aging resistance after vulcanization in a balanced manner. There wasn't.

JP-A-6-192508 JP 2002-88191 A Japanese Patent Laid-Open No. 2005-60442

  As described above, it is known to use various rubber plasticizers in the production of an inner liner of a pneumatic tire, but a rubber composition comprising a butyl rubber selected from the group consisting of butyl rubber and halogenated butyl rubber In the past, it has not been proposed to improve the workability before vulcanization, the air barrier property after vulcanization, and the aging resistance after vulcanization in a well-balanced manner.

  Accordingly, an object of the present invention is to provide a rubber composition for a tire inner liner that improves the workability before vulcanization, the air barrier property after vulcanization, and the aging resistance after vulcanization in a well-balanced manner. .

  As a result of diligent research to solve the above-mentioned problems, the present inventor has found that a rubber component containing 50% by weight or more of at least one butyl rubber selected from the group consisting of butyl rubber and halogenated butyl rubber has a specific ratio of aroma system When a specific amount of process oil composed of hydrocarbon, paraffinic hydrocarbon and naphthenic hydrocarbon is blended, the balance is improved and the processability before vulcanization, which is useful for the production of tire inner liners, and the air barrier after vulcanization are improved. The inventors have found that a rubber composition having aging resistance after vulcanization can be obtained, and have completed the present invention.

According to the present invention,
(A) a rubber component containing 50% by weight or more of at least one butyl rubber selected from the group consisting of butyl rubber and halogenated butyl rubber;
(B) 3 to 20 parts by weight of process oil with respect to 100 parts by weight of the rubber component (A),
A rubber composition for a tire inner liner, the process oil comprising an aromatic hydrocarbon, a paraffinic hydrocarbon, and a naphthenic hydrocarbon, and the aromatic carbonization in the process oil determined in accordance with ASTM D2140 hydrogen, paraffinic hydrocarbons and naphthenic constituting the hydrocarbon respectively C _a weight percentage of carbon, when expressed as C _P and C _N, is C _a, C _P and C _N, respectively, 20 wt% ≦ There is provided a rubber composition for a tire inner liner, wherein C _A ≦ 40 wt%, 30 wt% ≦ C _P ≦ 60 wt%, and 20 wt% ≦ C _N <30 wt%.

  The rubber component (A) in the rubber composition for a tire inner liner of the present invention contains at least one butyl rubber selected from the group consisting of 50% by weight or more of butyl rubber and halogenated butyl rubber based on the total weight thereof. . Commercially available butyl rubber and halogenated butyl rubber can be used. As the butyl rubber, halogenated butyl rubber is preferable. Examples of the halogenated butyl rubber include chlorinated butyl rubber and brominated butyl rubber.

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

The process oil (B) contained as a plasticizer in the rubber composition of the present invention is composed of an aromatic hydrocarbon, a paraffinic hydrocarbon, and a naphthenic hydrocarbon, and is an aroma based hydrocarbon determined in accordance with ASTM D2140. paraffinic hydrocarbons and naphthenic hydrocarbons constituting each C _a weight percentage of carbon, when expressed as C _P and C _N, C _a, C _P and C _N, respectively, 20 wt% ≦ C _a ≦ 40 wt%, 30 wt% ≦ C _P ≦ 60 wt%, 20 wt% ≦ C _N <30 wt%. Process oil (B) can consist of one process oil or a mixture of several process oils. When the process oil (B) is composed of a mixture of plural kinds of process oils, as long as C _A , C _P and C _N of the mixture of the process oils are within the predetermined range, the plural kinds of process oils C _A , C _P and C _N may be different from each other.

  Generally, a high-boiling petroleum fraction is used as a process oil for rubber. Depending on the chemical structure of the hydrocarbon, paraffinic hydrocarbons, which are chain saturated hydrocarbons, and naphthenic hydrocarbons, which are cyclic saturated hydrocarbons, are used. It is classified into hydrogen and aromatic hydrocarbons that are aromatic hydrocarbons. These hydrocarbons are generally distinguished by a numerical value known as a viscosity specific gravity constant (hereinafter referred to as “VGC”). Aromatic hydrocarbons have a VGC of 0.900 or more, and paraffinic carbonization. Hydrogen has a VGC of 0.790 to 0.849, and naphthenic hydrocarbons have a VGC of 0.850 to 0.899. According to an analysis method known as a ring analysis method such as ASTM D2140, from the values of VGC and refractive index, specific gravity, kinematic viscosity, etc. of the sample, paraffinic hydrocarbon, naphthenic hydrocarbon and aroma hydrocarbon of the sample The proportion (% by weight) of carbon that constitutes can be determined.

  The rubber composition of the present invention contains 3 to 20 parts by weight, preferably 7 to 18 parts by weight of the process oil (B) with respect to 100 parts by weight of the rubber component (A). When the amount of the process oil (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 the amount exceeds 20 parts by weight per 100 parts by weight, the workability before vulcanization is improved, but the air barrier property is lowered.

  In addition to the rubber component (A) and the process oil (B), the rubber composition of the present invention has a reinforcing filler such as carbon black, which is generally blended in a tire rubber composition, and air barrier properties. General amounts of various additives such as clays and talc, which are generally known to improve, stearic acid, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, anti-aging agents, etc. Can be blended.

  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 following examples further illustrate the invention, but it should be understood that it is not intended to limit the scope of the invention.

Preparation of rubber compositions of standard examples, Examples 1 to 8 and Comparative Examples 1 to 5 In the blending (parts by weight) shown in Table 1 below, components other than sulfur, a 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. The rubber composition of each example was prepared by compounding sulfur, a vulcanization accelerator and zinc oxide with 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) Butyl 268 (Nippon Butyl Co., Ltd.)
(3) Seast V (manufactured by Tokai Carbon Co., Ltd.)
(4) Industrial stearic acid (manufactured by NOF Corporation)
(5) Three types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
(6) Noxeller DM (Ouchi Shinsei Chemical Co., Ltd.)
(7) Powdered sulfur (made by Hosoi Chemical Co., Ltd.)
(8) Process oil P-100 (Fuji Kosan Co., Ltd.) (C _A = 5 wt%, C _P = 67 wt%, C _N = 28 wt%)
(9) Extract No. 4 S (manufactured by Showa Shell Sekiyu KK) (C _A = 28 wt%, C _P = 48 wt%, C _N = 24 wt%)
(10) AH24 (made by Idemitsu Kosan Co., Ltd.) (C _A = 44% by weight, C _P = 25% by weight, C _N = 31% by weight)
(11) Calsol 810 (manufactured by Calmet Oil) (C _A = 12 wt%, C _P = 40 wt%, C _N = 48 wt%)
(12) _A 1: 1 mixture by weight of process oil 1 and process oil 2 (C _A = 25 wt%, C _P = 46 wt%, C _N = 29 wt%)
(13) Weight ratio 34:66 mixture of process oil 1 and process oil 2 (C _A = 20 wt%, C _P = 55 wt%, C _N = 25 wt%)
(14) Process oil 1 and process oil 3 weight ratio 61:39 mixture (C _A = 20 wt%, C _P = 51 wt%, C _N = 29 wt%)
(15) Mixture ratio of process oil 2 and process oil 3 25:75 (C _A = 40 wt%, C _P = 31 wt%, C _N = 29 wt%)

Test Method (1) Ring Analysis According to ASTM D2140, aromatic hydrocarbons, paraffinic hydrocarbons and naphthenic hydrocarbons for process oils 1 to 8 used in the above standard examples, examples and comparative examples are constituted. Carbon weight percentages C _A , C _P and C _N were determined, respectively. The procedure for obtaining the values of C _A , C _P, and C _N defined in ASTM D2140 is summarized as follows.
First, the density d at 20 ° C. is obtained according to ASTM D1481 or D4052, and the value of this density d is converted to the specific gravity G at 15.6 ° C., and further, the density d at 37.8 ° C. according to ASTM D445. obtains a viscosity V (cSt), we obtain the refractive index n _D ²⁰ at 20 ° C. with sodium D line in compliance with ASTM D1218. Next, the obtained specific gravity G and kinematic viscosity V are expressed by the following formula:
VGC = (G + 0.0887-0.776loglog (10V-4)) / (1.082-0.72loglog (10V-4))
Into the viscosity specific gravity constant VGC, and the density d and the refractive index n _D ²⁰ are expressed by the following formula:
r _i = n _D ^20- (d / 2)
Substituting into, find r _i . Next, using the correlation diagram shown in FIG. 1 of ASTM D2140, the corresponding values of C _A , C _P and C _N are obtained from the values of VGC and r _i .
When the sample oil contains 0.8% or more of sulfur, the accuracy of the values of C _A , C _P and C _N obtained using the correlation diagram described in FIG. 1 of ASTM D2140 (hereinafter, “ (C _A before correction ”,“ C _p before correction ”, and“ C _N before correction ”) can be increased by correcting using the following equations.
C _N after correction = (C _A before correction) −S / 0.288
After the correction C _P = (before correction of C _P) -S / 0.216
C _A after correction = 100− (C _N + C _P )
In these formulas, S represents the sulfur content (% by weight) of the sample oil determined in accordance with ASTM D129.
The derivation of C _A , C _P and C _{N for} the following standard examples, examples and comparative examples is as follows: density d determined at 20 ° C. by the floating scale method according to JIS K2249 corresponding to ASTM D4052; Specific gravity G at 15.6 ° C. converted from density, kinematic viscosity V (cSt) determined at 37.8 ° C. using a Canon-Fenske viscometer according to JIS K2283 corresponding to ASTM D445, and ASTM D1218 The refractive index n _D ²⁰ determined at 20 ° C. using a refractometer type 3 manufactured by Atago Co., Ltd. in accordance with JIS C2101 corresponding to the above.

(2) 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. . 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.

(3) Mooney scorch index In accordance with JIS K6300, an L-shaped rotor (testing machine: SMV300J manufactured by Shimadzu Corporation) was used, and the time until the viscosity increased by 5 points at 125 ° C. was determined. The time obtained for the comparative example was expressed as an index value with the time obtained for the standard example being 100. The smaller the index, the shorter the scorch time and the easier it is to burn.

(4) Air permeability It was performed in accordance with “Test method for gas permeability of plastic film and sheet (Method A)” of JIS K7126. 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.

(5) 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 in accordance with JIS K6257 and heated to 120 ° C. It was heated in a set oven for 96 hours to accelerate aging. The elongation at break (tensile speed: 500 mm / min) of the specimen was measured before and after aging, and the following formula:
Residual rate 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 cutting | disconnection is large.

(6) Pneumatic pressure retention truck bus steel radial tire of tire size 11R22.5 14PR using the rubber compositions of the standard examples, Examples 1-8 and Comparative Examples 1-5 as sheets and using them as inner liners Was made. After setting the tire air pressure to 700 kPa for these tires, the tire was allowed to stand for 3 months at a room temperature of 21 ° C. under no load conditions, and the tire internal pressure was measured every 4 days. The initial value is P ₀ , the measured pressure is P _t , the elapsed days is t, and the α value is obtained by regressing the equation P _t / P ₀ = exp (−αt), and then the obtained α value And t = 30 were substituted into the formula: β = [1-exp (−αt)] × 100 to determine 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 8 and Comparative Examples 2, 3 and 5 was expressed as an index value when the standard example was 100. A smaller index value indicates better air pressure retention.

  According to the test methods of (2) to (6) above, the rubber compositions of the standard examples, Examples 1 to 8 and Comparative Examples 1 to 5 were tested. The test results are shown in Table 2 below. The rubber compositions of Comparative Examples 1 and 4 were not tested for air pressure retention because the tires could not be produced because the Mooney viscosity was high and it was difficult to roll into sheets.

As can be seen from the results shown in Table 2, it was found that process oil 1 with C _A = 5 wt%, C _P = 67 wt% and C _N = 28 wt% was not used when determined by ring analysis. Except for the comparative example 1 having the same composition as the standard example, the air barrier property was greatly improved, but the Mooney viscosity increased significantly, and this significant increase in Mooney viscosity was so high that the sheet could not be rolled. Brought down. Example 1, in which 7 parts by weight of process oil 2 was blended with 100 parts by weight of the rubber component, showed a Mooney viscosity and Mooney scorch index that were almost the same as those of the standard example, and improved air barrier properties and tire pressure retention, Aging resistance was also improved. In Example 2 in which 4 parts by weight of process oil 2 was blended with 100 parts by weight of the rubber component, the Mooney viscosity increased slightly and the Mooney scorch index decreased slightly compared to Example 1, but changes in these viscosity characteristics were This was an acceptable range for processing, the air barrier property and the tire air pressure retention property were further improved, and the aging resistance was substantially the same as in Example 1. In Example 3 in which 18 parts by weight of process oil 2 is blended with 100 parts by weight of the rubber component, the Mooney viscosity is significantly lower than in Example 1, the Mooney scorch index is greatly increased, and the processing becomes easier. In addition, the air barrier property, the tire air pressure retention property and the aging resistance were improved as compared with the standard example. In Comparative Example 2 in which C _A % and C _N % exceed the range of the present invention and C _P % falls, the air barrier property, tire air pressure retention and aging resistance are improved as compared with the standard example. More than the Mooney scorch index, the workability decreased. In Comparative Example 3, in which C _A % is lower than C _N % and C _N % is higher than the range of the present invention, the air barrier property and the tire air pressure retention are improved as compared with the standard example, and the Mooney viscosity is almost the same as the standard example. However, the Mooney scorch index increased and the workability improved, but the aging resistance decreased. _A mixture obtained by mixing process oil 1 and process oil 3 at a weight ratio of 1: 1 (C _A = 25 wt%, C _P = 46 wt%, C _N = 29 wt%) and Example 1 was used. When blended in the same amount (Example 4), the same effect as in Example 1 was obtained. As in Example 4, a mixture of process oils obtained by mixing a plurality of types of process oils, wherein C _A , C _P and C _N each have a value within the scope of the present invention. When blended in the same amount as in Example 1 (Examples 5 to 8), the same effect as in Example 1 was obtained. In Comparative Example 4 in which an amount of process oil less than the range of the present invention was blended, the Mooney viscosity increased significantly, the Mooney scorch index decreased, and the processability decreased. In Comparative Example 5 in which a larger amount of process oil than the range of the present invention was blended, the aging resistance was lowered, and the air barrier property and the air pressure retention property were hardly improved.

Claims (5)

(A) a rubber component containing 50% by weight or more of at least one butyl rubber selected from the group consisting of butyl rubber and halogenated butyl rubber;
(B) 3 to 20 parts by weight of process oil with respect to 100 parts by weight of the rubber component (A),
A rubber composition for tire inner liners, wherein the process oil comprises an aromatic hydrocarbon, a paraffinic hydrocarbon, and a naphthenic hydrocarbon, and the aromatic carbonization in the process oil determined in accordance with ASTM D2140 hydrogen, paraffinic hydrocarbons and naphthenic constituting the hydrocarbon respectively C _a weight percentage of carbon, when expressed as C _P and C _N, is C _a, C _P and C _N, respectively, 20 wt% ≦ _A rubber composition for a tire inner liner, wherein C _A ≦ 40 wt%, 30 wt% ≦ C _P ≦ 60 wt%, 20 wt% ≦ C _N <30 wt%. When the process oil (B) is composed of one process oil or a mixture of a plurality of process oils, and the process oil (B) is composed of a mixture of a plurality of process oils, The rubber composition for a tire inner liner according to claim 1, wherein C _A , C _P and C _N are each within the predetermined range according to claim 1.   The rubber composition for a tire inner liner according to claim 1 or 2, wherein the at least one butyl rubber is a halogenated rubber.   The rubber composition for a tire inner liner according to any one of claims 1 to 3, wherein the rubber component comprises only a butyl rubber.   A pneumatic tire comprising a tire inner liner manufactured using the rubber composition for a tire inner liner according to any one of claims 1 to 4.