JP2008274166A - Rubber composition for pneumatic tire bead filler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a bead filler, which is improved in heat deterioration resistance and flexural fatigue resistance. <P>SOLUTION: The rubber composition for pneumatic tire bead filler is obtained by compounding together (A) a rubber component comprising at least one sulfur-vulcanizable diene rubber, (B) 20-130 pts.wt. of carbon black based on 100 pts.wt. of the rubber component A, (C) 0.1-30 pts.wt. of a phenolic thermosetting resin selected from a novolak-type phenolic resin and a novolak-type modified phenolic resin based on 100 pts.wt. of the rubber component A and (D) 0.5-10 pts.wt. of a sulfur donor-type crosslinking agent containing a structure represented by general formula (I): -[(CH<SB>2</SB>-CH<SB>2</SB>-O)<SB>m</SB>-CH<SB>2</SB>-CH<SB>2</SB>-S<SB>x</SB>]<SB>n</SB>- (wherein, m is an integer of 2-5; n is an integer of 10-350; and x is an integer of 3-6) based on 100 pts.wt. of the rubber component A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for a bead filler of a pneumatic tire to be mounted on a vehicle such as a passenger car, a truck, a bus, or a two-wheeled vehicle. More specifically, the present invention relates to a rubber composition for a bead filler of a pneumatic tire, which has improved heat aging resistance and bending fatigue resistance.

  The bead filler is a rubber member filled in a space generated when the carcass is wound around the bead wire, and is used to firmly fix the carcass to the bead and increase the rigidity of the entire bead portion. Therefore, the bead filler itself is required to have high rigidity. For example, in Patent Document 1 below, for the purpose of improving steering stability and reducing weight by gauge down, a novolac type phenol that becomes a high elastic modulus resin after thermosetting It has been proposed to increase the rigidity of the bead filler by forming a bead filler using a rubber composition in which a phenolic thermosetting resin such as a resin is mixed with rubber.

  However, when such a rubber composition is used as a bead filler, there is a problem in that the bending fatigue resistance of the bead filler decreases as the rigidity increases due to the addition of a phenolic thermosetting resin such as a novolac-type phenolic resin. was there.

JP 2002-105249 A

  Accordingly, an object of the present invention is to improve the bending fatigue resistance of a rubber composition for a bead filler in which a phenol-based thermosetting resin such as a novolac-type phenol resin is blended with rubber.

As a result of intensive studies to solve the above problems, the present inventors have found that a specific amount of carbon black and a phenol-based thermosetting resin selected from a novolac-type phenolic resin and a novolac-type modified phenolic resin have a specific amount. The following general formula (I):
_{- ((CH 2 -CH 2 -O} ) m -CH 2 -CH 2 -S x) n -
(In the formula, m represents an integer of 2 to 5, n represents an integer of 10 to 350, and x represents an integer of 3 to 6)
When the sulfur donor type | mold crosslinking agent containing the structure represented by this is mix | blended, while finding that bending-fatigue resistance improves and heat aging resistance, it came to complete this invention.

That is, according to the present invention,
(A) a rubber component containing at least one kind of sulfur vulcanizable diene rubber;
(B) 20 to 130 parts by weight of carbon black with respect to 100 parts by weight of the rubber component (A);
(C) a phenolic thermosetting resin selected from 0.1 to 30 parts by weight of a novolac-type phenolic resin and a novolac-type modified phenolic resin with respect to 100 parts by weight of the rubber component (A);
(D) 0.5 to 10 parts by weight of the following general formula (I) with respect to 100 parts by weight of the rubber component (A):
_{- ((CH 2 -CH 2 -O} ) m -CH 2 -CH 2 -S x) n -
(In the formula, m represents an integer of 2 to 5, n represents an integer of 10 to 350, and x represents an integer of 3 to 6)
A sulfur donor type cross-linking agent comprising a structure represented by:
A rubber composition for a bead filler of a pneumatic tire is provided.

  The rubber component (A) blended in the rubber composition for bead fillers of the present invention is composed of at least one diene rubber capable of sulfur vulcanization. Examples of the sulfur vulcanizable diene rubber include natural rubber (NR), styrene-butadiene copolymer rubber (SBR), polyisoprene rubber (IR), polybutadiene rubber (BR), acrylonitrile-butadiene copolymer. Examples include diene-based synthetic rubbers such as coalesced rubber (NBR) and chloroprene rubber (CR), and combinations of two or more thereof.

The carbon black (B) blended in the bead filler rubber composition of the present invention preferably has an adsorption specific surface area of cetyltrimethylammonium bromide (CTAB) of 20 to 150 m ² / g. When the CTAB adsorption specific surface area is less than 20 m ² / g, the rigidity is lowered, and when it exceeds 150 m ² / g, the dispersibility of the carbon black (B) itself is lowered, and as a result, the mixing processability is lowered. The compounding quantity of carbon black (B) is 20-130 weight part with respect to 100 weight part of rubber components (A), Preferably it is 60-100 weight part. If the blending amount of carbon black is less than 20 parts by weight with respect to 100 parts by weight of the rubber component (A), the rigidity decreases, and if it exceeds 130 parts by weight, the exothermic property deteriorates. The CTAB adsorption specific surface area is determined according to JIS K6217. In addition to carbon black, silica, clay, calcium carbonate, aluminum hydroxide, or the like may be blended as a reinforcing filler.

  The phenolic thermosetting resin (C) blended in the bead filler rubber composition of the present invention is a component used for imparting high rigidity to the rubber composition of the present invention, a novolac type phenolic resin, And a novolac modified phenolic resin obtained by modifying a novolac phenolic resin with oil. Examples of the oil used for modification of the novolak type phenol resin include rosin oil, tall oil, cashew oil, linoleic acid, oleic acid, and linolenic acid.

  In the rubber composition for bead filler of the present invention, the amount of the phenolic thermosetting resin (C) is 0.1 to 30 parts by weight, preferably 3 to 20 parts per 100 parts by weight of the rubber component (A). Parts by weight. When the blending amount of the phenol-based thermoplastic resin (C) is less than 0.1 parts by weight with respect to 100 parts by weight of the rubber component (A), the rigidity decreases, and when it exceeds 30 parts by weight, the elongation at break decreases. The novolac type phenolic resin is available from Sumitomo Bakelite Co., Ltd. under the trade name of Sumilite Resin PR-50235A, and the novolac type modified phenolic resin is available from Sumitomo Bakelite Co., Ltd. It is available. An amine-based crosslinking agent such as hexamethylenetetramine is typically blended in an amount of 0.1 to 15 parts by weight with respect to the phenol-based thermosetting resin (C).

  In the rubber composition for bead filler of the present invention, bending resistance is obtained by including 0.5 to 10 parts by weight of the sulfur donor type crosslinking agent represented by the above general formula (I) with respect to 100 parts by weight of the rubber component (A). Both fatigue and heat aging are improved.

Generally, in a crosslinked rubber, hardness and elastic modulus increase as the crosslinking density increases, while fatigue resistance and tensile strength increase to a certain crosslinking density, but decrease after reaching a peak. It has been known. The sulfur donor type cross-linking agent used in the present invention has a polysulfide part and a polyether part in the molecule, and the polysulfide part is thermally decomposed to release active reactive sulfur, thereby releasing active sulfur. It is believed that the later polyether group-containing residue can also function as a crosslinking agent. The released active sulfur forms many monosulfide bridges (-S-) and disulfide bridges (-S-S-) having high heat resistance between the rubber molecules, while the polyether group-containing residues are highly dynamic. It is considered that the durability of the crosslinked rubber, such as the heat aging resistance and the bending fatigue resistance, can be achieved because of its mechanical properties and heat resistance. For example, in the above general formula (I), when m is 2, the sulfur donor-type crosslinking agent is thermally decomposed during vulcanization, and in addition to the monosulfide and disulfide bridges, It is thought to form a bridge represented by — (CH ₂ —CH ₂ —O) ₂ —CH ₂ —CH ₂ —S—.

  The sulfur donor type cross-linking agent can be prepared by a known method, for example, the following reaction scheme (1):

It can be obtained by reacting polyethylene glycol dichloride and sulfur chloride as represented by Alternatively, the sulfur donor-type cross-linking agent is the following reaction scheme (2):

It can also be obtained by reacting polyethylene glycol dichloride with sodium polysulfide as represented by: Here, in the above reaction formula, m represents an integer of 2 to 5, n represents an integer of 10 to 350, and x represents an integer of 3 to 6. The compounding amount of the sulfur donor type crosslinking agent (D) is 0.5 to 10.0 parts by weight with respect to 100 parts by weight of the diene rubber as described above, preferably 0.5 to 5.0 parts by weight. is there. When the amount of the sulfur donor type crosslinking agent (D) is less than 0.5 parts by weight relative to 100 parts by weight of the rubber, the effect is small, and when it exceeds 10.0 parts by weight, the rubber composition obtained after vulcanization The hardness becomes too high, making it difficult to adjust the physical properties, and it is also uneconomical. In the above general formula (I), if m is less than 2, the bending fatigue resistance decreases. If m exceeds 5, the elastic modulus is lowered by decreasing the network chain density of the vulcanized rubber composition obtained after vulcanizing the rubber composition, and as a result, the rigidity is lowered. If n is less than 10, the volatility is high and handling is difficult, and if n exceeds 350, the compatibility decreases, which is not preferable. When x is less than 3, vulcanization is delayed, and when x exceeds 6, the elongation at break tends to decrease, which is not preferable.

  In the bead filler rubber composition of the present invention, in addition to the above components, stearic acid, a vulcanization or cross-linking agent, a vulcanization or cross-linking accelerator, an antiaging agent, a plasticizer, which are generally blended in the rubber composition. Various compounding agents such as an agent and a coupling agent can be blended.

  The rubber composition for bead filler according to the present invention is 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 blending the rubber composition. Can do.

  The present invention will be described in more detail with reference to the following examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited to these examples.

Comparative Examples 1-2 and Examples 1-2
The formulations used in the preparation of the rubber compositions of Comparative Examples 1-2 and Examples 1-2 are as shown in Table 1 below. In addition, the unit of the compounding quantity shown by Table 1 is a weight part.

In accordance with the composition of Table 1 above, using a 1.7 liter closed Banbury mixer, components other than the crosslinking agent, vulcanization accelerator and sulfur were mixed for 5 minutes, released from the mixer at 150 ° C., and then opened roll Crosslinking agents, vulcanization accelerators and sulfur were mixed to obtain rubber compositions of Comparative Examples and Examples. The obtained rubber composition was press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare test pieces, and the following tests were performed. In addition, as a crosslinking agent according to the said general formula (I) of this invention, following formula:
_{HS - ((CH 2 CH 2} O) m -CH 2 CH 2 -S x) n - (CH 2 CH 2 O) m -CH 2 CH 2 -SH
(Where m is 2, n is 200, and x is 4). This crosslinking agent was prepared according to the following synthesis method.

Method for synthesizing crosslinking agent Into a 200 ml three-necked flask, 87 ml of a 33% aqueous solution of sodium trithiocarbonate was added, and while maintaining the liquid temperature at 25 ° C., triethylene glycol dichloride was added dropwise at 25 ° C. Stir for about 5 hours. The reaction mixture is cooled, unreacted triethylene glycol is extracted with toluene, transferred to the toluene layer, and then the aqueous layer is acidified with 50% aqueous sulfuric acid. Thereafter, this aqueous layer was extracted with toluene, toluene was distilled off from the extract under reduced pressure, a benzene solution of sulfur chloride was gradually added at a temperature of 5 to 30 ° C., and the mixture was stirred at the same temperature for 24 hours. Neutralize with The aqueous layer is removed, and only the benzene layer is distilled to obtain a viscous light yellow liquid. The reaction scheme in this synthesis method is as follows.

  This synthesis method uses triethylene glycol dichloride and sodium trithiocarbonate as raw materials, and the final step of this synthesis method follows the above reaction scheme (1).

Test method (1) Hardness (Hs) and hardness change rate (Hs change rate)
In accordance with JIS K6253, the hardness (Hs) was measured at 23 ° C. by a type A durometer hardness test.
The test sample was heat-aged in a gear oven at a temperature of 80 ° C. for 96 hours, cooled to 23 ° C., measured for hardness in the same manner as described above, and the rate of change in hardness (%) relative to the hardness before aging (100 × after aging). Hardness / hardness before aging) (hereinafter referred to as “Hs change rate”). The measurement results are displayed as an index with the value of Comparative Example 1 being 100. The higher the hardness (Hs) value, the higher the altitude. Hs change rate shows that heat resistance aging property is excellent, so that the numerical value is small.
(2) Bending fatigue resistance A bending crack growth test was conducted according to JIS K6260. A 2 mm long scratch was made in the center of the test sample in advance, bent at 23 ° C. with a stroke of 10 mm, 300 times per minute, a total of 100,000 times, the crack length was measured, and the crack growth was bent fatigue. As evaluated. As the measurement results, the reciprocal of the crack length was obtained, and the value of the comparative example was set to 100 and displayed as an index. It shows that it is excellent in bending fatigue resistance, so that a numerical value is large.
(3) Elongation at break The elongation at break was measured at a temperature of 23 ° C. according to JIS K6251. The measurement results are indicated by an index with the elongation at break of Comparative Example 1 as 100. It shows that breaking elongation is so large that a numerical value is large.

  From the above test results, it can be seen that the bead filler rubber composition of the present invention improves both the bending fatigue resistance and the heat aging resistance.

Claims (1)

(A) a rubber component containing at least one kind of sulfur vulcanizable diene rubber;
(B) 20 to 130 parts by weight of carbon black with respect to 100 parts by weight of the rubber component (A);
(C) a phenolic thermosetting resin selected from 0.1 to 30 parts by weight of a novolac-type phenolic resin and a novolac-type modified phenolic resin with respect to 100 parts by weight of the rubber component (A);
(D) 0.5 to 10 parts by weight of the following general formula (I) with respect to 100 parts by weight of the rubber component (A):
_{- ((CH 2 -CH 2 -O} ) m -CH 2 -CH 2 -S x) n -
(In the formula, m represents an integer of 2 to 5, n represents an integer of 10 to 350, and x represents an integer of 3 to 6)
A sulfur donor type cross-linking agent comprising a structure represented by:
A rubber composition for a bead filler of a pneumatic tire.