JP2020002322A - Rubber composition and pneumatic tire using the same - Google Patents

Abstract

To overcome a difficult item in the field that improves both of air permeable prevention performance and processability at same time under a state that a process oil is used for a tire compound as a processing aid generally, and processability can be enhanced, but air permeability is increased.SOLUTION: The above described problem is solved by a rubber composition comprising polyester of 5 to 32 pts.mass based on 100 pts.mass of a rubber component consisting of one or more kind of isobutylene rubber selected from a group consisting of butyl rubber, halogenate butyl rubber, and halide of an isobutylene-paramethylstyrene copolymer of 50 pts.mass to 100 pts.mass, and diene rubber of 0 pts.mass to 50 pts.mass.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition and a pneumatic tire using the same, and more particularly, to a rubber composition excellent in air permeation prevention performance and processability and a pneumatic tire using the same.

The inner surface of the tubeless pneumatic tire is provided with an inner liner mainly composed of isobutylene rubber having excellent air permeation prevention performance.
On the other hand, a process oil is generally used as a processing aid in a rubber composition for a tire. One of the roles of the process oil is to reduce the viscosity of the unvulcanized rubber and improve processability, such as sheeting. On the other hand, on the other hand, oil increases the mobility of the rubber and the air permeability increases accordingly, so that it is not desirable to use the oil in the rubber composition for the inner liner.
Thus, it is recognized in the art that it is difficult to improve both the air permeation prevention performance and the processability at the same time.

Patent Literature 1 below discloses a ricinoleic acid ester copolymer satisfying specific requirements. However, Patent Literature 1 does not disclose or suggest any technical idea of blending the ricinoleic acid ester copolymer in a rubber composition in a specific amount to enhance air permeation prevention performance and processability.
Patent Literature 2 below discloses a rubber composition in which a ricinoleic acid copolymer having a specific molecular weight is mixed with a diene rubber. However, even in the rubber composition disclosed in Patent Document 2, there is no disclosure or technical idea of blending the ricinoleic acid copolymer with the rubber composition in a specific amount to enhance air permeation prevention performance and processability. Not suggested.

International Publication WO2017 / 038734 pamphlet Japanese Patent No. 5458006

  Therefore, an object of the present invention is to provide a rubber composition excellent in air permeation prevention performance and processability, and a pneumatic tire using the same.

As a result of intensive studies, the present inventors have found that the above problems can be solved by blending a polyester in a specific amount with a diene rubber having a specific composition, and have completed the present invention.
That is, the present invention is as follows.

1. Butyl rubber, halogenated butyl rubber and one or more isobutylene rubbers selected from the group consisting of halides of isobutylene-paramethylstyrene copolymer are 50 parts by mass or more and 100 parts by mass or less, and diene rubbers are 0 parts by mass or more and 50 parts by mass or less. A rubber composition comprising 5-32 parts by mass of a polyester with respect to 100 parts by mass of a rubber component composed of not more than parts by mass.
2. 2. The rubber composition according to the above item 1, wherein the polyester is liquid at 23 ° C.
3. 3. The rubber composition according to the above 1 or 2, wherein the polyester has a weight average molecular weight of 10,000 to 150,000.
4. The rubber composition according to the above item 3, wherein a fatty acid having a hydroxyl group in a molecule is contained in a component of the polyester.
5. 5. The rubber composition according to the item 4, wherein the fatty acid having a hydroxyl group in the molecule is ricinoleic acid.
6. A pneumatic tire using the rubber composition according to any one of the above 1 to 5 for an inner liner.

The rubber composition of the present invention comprises 50 parts by mass or more and 100 parts by mass or less of at least one isobutylene rubber selected from the group consisting of butyl rubber, halogenated butyl rubber and a halide of isobutylene-paramethylstyrene copolymer, and a diene. The rubber composition is characterized by containing 5 to 32 parts by mass of a polyester with respect to 100 parts by mass of a rubber component comprising 0 to 50 parts by mass of a rubber, and a rubber composition having excellent air permeation prevention performance and processability. A pneumatic tire using the same can be provided.
The rubber composition of the present invention is particularly useful for inner liners of pneumatic tires because it can simultaneously enhance air permeation prevention performance and processability.

  Hereinafter, the present invention will be described in more detail.

(Rubber component)
The rubber component used in the present invention contains 50 to 100 parts by mass, preferably 70 to 100 parts by mass of an isobutylene rubber, when the whole rubber component is 100 parts by mass.
As the isobutylene-based rubber, any rubber used for the inner liner can be adopted, for example, butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), halogen of isobutylene-paramethylstyrene copolymer. (For example, bromide: Br-IPMS). Examples of commercially available isobutylene rubbers include Br-IIR, BROMOBUTYL2255 manufactured by ExxonMobil, and Br-IPMS, MDX90-10 manufactured by ExxonMobil Chemical.
The rubber component may contain an optional diene rubber in addition to the isobutylene rubber, if necessary. Examples of the diene rubber include, for example, natural rubber (NR). When the compounding ratio of the diene rubber exceeds 50 parts by mass, the air permeation prevention performance deteriorates.

(polyester)
The polyester used in the present invention is preferably liquid at room temperature (23 ° C.) from the viewpoint of the effects of the present invention, particularly from the viewpoint of improving processability (hereinafter, referred to as liquid polyester (A)).
The weight average molecular weight (GPC method) of the liquid polyester (A) is preferably from 10,000 to 150,000, more preferably from 10,000 to 30,000, from the viewpoint of the effects of the present invention, particularly from the viewpoint of improving processability. More preferred. Furthermore, from the viewpoint of further enhancing the air permeation prevention performance and processability, it is preferable that the fatty acid having a hydroxyl group in the molecule is included in the constituents thereof, and the fatty acid having the hydroxyl group in the molecule is ricinoleic acid. Is more preferred. Specifically, the liquid polyester (A) is particularly preferably a ricinoleic acid ester copolymer (A1).

(Risinoleate copolymer (A1))
The ricinoleic acid ester copolymer (A1) used in the present invention can be composed of a structural unit derived from ricinoleic acid and a monomer copolymerizable therewith.
In the present invention, the ricinoleic acid ester copolymer (A1) is composed of a structural unit (a) derived from ricinoleic acid, a structural unit (b) derived from an aliphatic dicarboxylic acid, and a diol having 2 to 10 carbon atoms. It is preferable to include a structural unit (c) derived therefrom.

  In the present invention, the structural unit (a) derived from ricinoleic acid (hereinafter sometimes simply referred to as “structural unit (a)”) refers to ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) or ricinol It is a structural unit derived from an acid derivative.

  Examples of the derivatives of ricinoleic acid include condensates of ricinoleic acid, esterified products of ricinoleic acid and carboxylic acids, esterified products of ricinoleic acid and alcohols (eg, methyl ricinoleate), and reaction products of ricinoleic acid and epoxy compounds Such as 12-hydroxystearic acid obtained by hydrogenating ricinoleic acid or a condensate thereof, or an esterified product of 12-hydroxystearic acid with a carboxylic acid or alcohol (eg, methyl 12-hydroxystearate) to give ricinoleic acid by a polymerization reaction. Various compounds giving the structural unit (a) derived therefrom are exemplified.

  As described above, since the derivative of ricinoleic acid also includes 12-hydroxystearic acid and its ester, the structural unit (a) in the present invention is specifically represented by the following formula (1) or It is a structural unit represented by the formula (2).

  Here, the ratio of the total of the structural units derived from 12-hydroxystearic acid and its ester derivative in the total structural units (a), that is, the structure represented by the above formula (2) in the total structural units (a) The ratio of the total of the units is not particularly limited, and the total of the structural units (a) derived from ricinoleic acid (ie, the structural unit represented by the above formula (1) and the structural unit represented by the above formula (2)) Is 100 mol%, the structural unit (a) derived from ricinoleic acid includes the structural unit represented by the above formula (1). Is preferred. In that sense, the ratio is preferably 0 to 80 mol%, and more preferably 0 to 60 mol%.

  The structural unit (b) derived from an aliphatic dicarboxylic acid (hereinafter sometimes simply referred to as “structural unit (b)”) is derived from an aliphatic dicarboxylic acid or an aliphatic dicarboxylic acid ester. The structural unit (b) referred to in the present invention is specifically a structural unit having a structure in which -OH is removed from two carboxyl groups contained in an aliphatic dicarboxylic acid.

  The aliphatic dicarboxylic acid is not particularly limited as long as it does not have a reactive functional group, for example, a hydroxyl group in a system in which the ester polymerization reaction is performed, and may be a single type or a combination of two or more types. Specifically, malonic acid (3 carbon atoms), dimethyl malonic acid (5 carbon atoms), succinic acid (4 carbon atoms), glutaric acid (5 carbon atoms), adipic acid (6 carbon atoms) 2-methyladipic acid (C7), trimethyladipic acid (C9), pimelic acid (C7), 2,2-dimethylglutaric acid (C7), 3,3- Examples include diethylsuccinic acid (C8), suberic acid (C8), azelaic acid (C9), sebacic acid (C10) and the like. On the other hand, examples of the aliphatic dicarboxylic acid esters include various esters of the above aliphatic dicarboxylic acids.

  Of these, aliphatic dicarboxylic acids having 6 to 12 carbon atoms are preferred, and sebacic acid is particularly preferred.

  In the present specification, the monomer component corresponding to the structural unit (b), that is, the aliphatic dicarboxylic acid and the aliphatic dicarboxylic acid ester may be referred to as “aliphatic dicarboxylic acid component (b ′)”. .

  The structural unit (c) derived from a diol having 2 to 10 carbon atoms (hereinafter, may be simply referred to as “structural unit (c)”) is specifically, formally, having 2 to 10 carbon atoms. Is a structural unit having a structure in which -H is removed from two hydroxyl groups contained in the diol. As the diol having 2 to 10 carbon atoms, which leads to the structural unit (c), one kind may be used alone, or two or more kinds may be used in combination, and specific examples include the following compounds.

  Examples of the diol having 2 to 10 carbon atoms include aliphatic diols having 2 to 10 carbon atoms. Examples of such aliphatic diols include 1,2-ethanediol (ethylene glycol: having 2 carbon atoms), 1,3-propanediol (trimethylene glycol: having 3 carbon atoms), 1,2-propanediol ( Propylene glycol: 3 carbon atoms, 1,4-butanediol (tetramethylene glycol: 4 carbon atoms), 2,2-dimethylpropane-1,3-diol (neopentyl glycol: 5 carbon atoms), 1 1,6-hexanediol (hexamethylene glycol: carbon atoms 6), 1,8-octanediol (octamethylene glycol: carbon atoms 8), 1,9-nonanediol (nonamethylene glycol: carbon atoms 9), etc. Is mentioned.

  Among such aliphatic diols, side-chain alkyl group-containing glycols include 2-methyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-hexyl-1,3-propanediol, 2-hexyl-1,6-propanediol, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-n -Butyl-1,3-propanediol, 1,3-nonanediol, 2-methyl-1,8-octanediol, and the like.

  Among the above-mentioned diols, 1,4-butanediol is particularly preferred.

  The ricinoleic acid ester copolymer (A1) used in the present invention is preferably composed of only the above-mentioned structural units (a) to (c), but as long as the effects of the present invention are not inhibited, A structural unit that does not correspond to any of (a) to (c) (hereinafter, “other structural units”) may be further included. Other structural units include frangicarboxylic acids such as 2,5-furandicarboxylic acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, and the like. -Structural units derived from various dicarboxylic acids and carboxylic esters not corresponding to the aliphatic dicarboxylic acid component (b '), such as aromatic dicarboxylic acids such as methyl terephthalic acid and naphthalenedicarboxylic acid, and having 11 or more carbon atoms. Structural units derived from aliphatic diols, structural units derived from aromatic diols, trivalent or higher polyhydric alcohols such as trimethylolethane and glycerin, and trivalent or higher polyvalent carboxylic acids such as butanetricarboxylic acid and trimellitic acid Examples thereof include acids, oxydicarboxylic acids such as 4-hydroxyphthalic acid, and the like.

  When the total of the structural units (a), (b) and (c) is 100 mol%, the content of the structural unit (a) is 20 to 90 mol%, and the content of the structural unit (b) is 5 to 5 mol%. It is preferable that the content of the structural unit (c) is 40 to 40% by mol.

Further, the molar ratio ((b) / (c)) of the structural unit (b) and the structural unit (c) is preferably 0.9 to 1.1.
When other structural units are included, the total of the above structural units (a) to (c) and the other structural units is 100 mol%, and the other structural units are preferably 20 mol% or less, more preferably It is at most 10 mol%, particularly preferably at most 5 mol%.

The contents of the above structural units (a) to (c) and “other structural units” in the ricinoleic acid ester copolymer (A1) can be determined by an appropriate method such as NMR.
A method for producing the ricinoleic acid ester copolymer (A1) is known, and is disclosed, for example, in International Publication WO2017 / 038734.

  The ricinoleic acid ester copolymer (A1) used in the present invention is liquid at ordinary temperature and has a low viscosity with respect to the polymer constituting the matrix, so that it can be used as an alternative material to oils that are usually blended. In addition, when compounding oil, the compounding quantity can be 15 mass parts or less, preferably 7 mass parts or less, more preferably 2 mass parts or less with respect to 100 mass parts of rubber components.

  In the present invention, the amount of the polyester is 5 to 32 parts by mass, preferably 10 to 20 parts by mass, per 100 parts by mass of the rubber component. If the amount of the polyester is less than 5 parts by mass, the effect of the present invention cannot be obtained because the amount is too small. Conversely, if it exceeds 32 parts by mass, the air permeation prevention performance does not improve.

  In the rubber composition of the present invention, in addition to the components described above, a vulcanizing or crosslinking agent, a vulcanizing or crosslinking accelerator, carbon black, silica, various fillers such as plate-like inorganic filler, various oils, aging Inhibitors, plasticizers and the like, for example, various additives that are generally compounded in a rubber composition for a tire inner liner can be compounded, and such additives are kneaded by a general method to form a composition, Can be used to vulcanize or crosslink. The amounts of these additives may be conventional general amounts as long as the object of the present invention is not adversely affected.

  Further, the rubber composition of the present invention is suitable for producing a pneumatic tire according to a conventional method for producing a pneumatic tire, and is used as an inner liner because it can simultaneously improve air permeability and processability. Is good.

  Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Examples 1 to 7 and Comparative Examples 1 to 3
Preparation of Samples In the composition (parts by mass) shown in Table 1, the components other than the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 1.7-liter closed Banbury mixer, and the rubber was discharged outside the mixer and cooled to room temperature. I let it. Then, the rubber, the vulcanization accelerator and sulfur were added to the same Banbury mixer and further kneaded to obtain a rubber composition. Next, the obtained rubber composition was press-vulcanized in a predetermined mold at 170 ° C. for 10 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the following test methods.

Air permeation prevention performance: The air permeation coefficient at 70 ° C. was measured according to JIS K7126 A method. The results were expressed as an index with the value obtained in Comparative Example 1 as 100. A smaller index indicates better air permeation prevention performance. If the index is 95 or less, it can be determined that the composition has sufficient air permeation prevention performance.
Mooney viscosity _{(ML 1 + 4, 100 ℃} ): unvulcanized rubber composition, JIS K6300-1: according to 2013, was measured Mooney viscosity _{(ML 1 + 4, 100 ℃} ). The results were expressed as an index with the value of Comparative Example 1 taken as 100. The smaller the index is, the lower the viscosity of the rubber is, indicating that the processability is excellent. When the index is 105 or less, it can be determined that the material has practical workability.
Table 1 shows the results.

* 1: Br-IIR (BROMOBUTYL2255 manufactured by ExxonMobil)
* 2: Br-IPMS (MDX90-10 manufactured by ExxonMobil Chemical Company)
* 3: Carbon black (Niteron #G manufactured by Shin Nikka Carbon Co., Ltd., nitrogen adsorption specific surface area (N ₂ SA) = 30 m ² / g)
* 4: Process oil (Diana Process Oil NH-60 manufactured by Idemitsu Kosan Co., Ltd.)
* 5: Ricinoleic acid ester copolymer 1 (copolymer of ricinoleic acid, sebacic acid and 1,4-butanediol, synthesized by the method disclosed in International Publication WO2017 / 038734; weight-average molecular weight = 20,000)
* 6: Ricinoleic acid ester copolymer 2 (copolymer composed of ricinoleic acid, sebacic acid and 1,4-butanediol, synthesized by the method disclosed in International Publication WO2017 / 038734; weight-average molecular weight = 100,000)
* 7: Sulfur (Mikulon OT-20 manufactured by Shikoku Chemical Industry Co., Ltd.)
* 8: Vulcanization accelerator (SANTOCURE CBS manufactured by FLEXSYS)

As is clear from Table 1 above, the rubber compositions prepared in Examples 1 to 5 contained 50 to 100 parts by mass of an isobutylene-based rubber and 100 parts by mass of the rubber component, and contained polyester. Since it was blended in the range of 5 to 32 parts by mass, it can be seen that the air permeation prevention performance and the processability can be simultaneously improved as compared with the rubber composition of Comparative Example 1 in which polyester was not blended.
In Example 1, 5 parts by weight of the polyester was blended in comparison with the composition of Comparative Example 1, and the blending amount of the process oil was reduced by 3 parts by weight. Thereby, the air permeation prevention performance is improved as compared with Comparative Example 1.
Example 2 is an example in which 32 parts by mass of polyester was blended with 100 parts by mass of the rubber component, and the air permeation prevention performance and processability were significantly improved.
Example 3 is an example in which the viscosity was adjusted to the same level as Comparative Example 1, and the air permeation prevention performance was improved by about 20% compared to Comparative Example 1.
Example 4 is an example in which a polyester having a weight-average molecular weight of 100,000 was used, and the air permeation prevention performance was improved while showing practically sufficient workability.
Example 5 is an example in which the composition of the isobutylene-based rubber was changed from Examples 1 to 4, and it can be seen that the air permeation prevention performance and the processability can be simultaneously improved.
In Example 6, 10 parts by weight of polyester was blended compared to the composition of Comparative Example 1, and the blending amount of process oil was reduced by 7 parts by weight. Even when the process oil is significantly reduced, the air permeation prevention performance is improved while maintaining the processability.
In Example 7, 8 parts by mass of the polyester was blended compared with the composition of Comparative Example 3, and the blending amount of the process oil was reduced by 5 parts by mass. As in Example 6, even when the amount of the process oil is significantly reduced, the air permeation prevention performance is improved while maintaining the workability.
On the other hand, in Comparative Example 2, since the blending amount of the polyester exceeds the upper limit specified in the present invention, no improvement in air permeation prevention performance is observed.
Comparative Example 3 is an example in which the same isobutylene rubber composition as in Example 5 was employed. Since the process oil was blended without blending the polyester, the air permeation prevention performance was deteriorated as compared with Example 5. ing.

Claims (6)

  Butyl rubber, halogenated butyl rubber and one or more isobutylene rubbers selected from the group consisting of halides of isobutylene-paramethylstyrene copolymer are 50 parts by mass or more and 100 parts by mass or less, and diene rubbers are 0 parts by mass or more and 50 parts by mass or less. A rubber composition comprising 5-32 parts by mass of a polyester with respect to 100 parts by mass of a rubber component composed of not more than parts by mass.   The rubber composition according to claim 1, wherein the polyester is liquid at 23 ° C.   3. The rubber composition according to claim 1, wherein the polyester has a weight average molecular weight of 10,000 to 150,000.   The rubber composition according to claim 3, wherein a fatty acid having a hydroxyl group in a molecule is contained in a component of the polyester.   The rubber composition according to claim 4, wherein the fatty acid having a hydroxyl group in the molecule is ricinoleic acid.   A pneumatic tire using the rubber composition according to any one of claims 1 to 5 for an inner liner.