JPH0116260B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition for a tire bead filler that has low rigidity when unvulcanized but high dynamic modulus after vulcanization, excellent tire molding workability, and excellent properties at break. Conventionally, in order to increase the dynamic elastic modulus (hereinafter referred to as elastic modulus) of rubber compositions for bead fillers, large amounts of compounding agents such as carbon black, sulfur, and thermosetting resins have been added to rubber. It is certainly possible to increase the elastic modulus of a rubber composition by blending a large amount of carbon black into rubber, but this rubber composition tends to cause the rubber to clump during the processing process and increase the power load on the Banbury mixer. , the winding state on the roll is extremely poor and it is difficult to put it into practical use. On the other hand, the elastic modulus of rubber has been increased by adding a large amount of sulfur, but this rubber composition has a high sulfur content, so sulfur blooms during extrusion, making tire molding difficult. This is undesirable as it may cause a decrease in the yield of the product. Therefore, as a means to increase the elastic modulus of rubber while avoiding the addition of large amounts of sulfur and suppressing the amount of carbon black added to a practical level, thermosetting resins such as novolak-type phenolic resins and novolak-type modified phenolic resins have been developed. There are many examples of blending resins. However, in the case of a rubber composition containing a thermosetting resin and carbon black as described above, the mixing processability is alleviated to some extent by the thermosetting resin being softened by the heat generated during mixing, but it is difficult to process at room temperature. The disadvantage is that the unvulcanized rubber has high rigidity, making the tire molding workability very poor. Therefore, the self-adhesive ability, which is the essence of rubber, is lost, and the workability of bonding and bending the extrudates is significantly impaired. To improve these drawbacks, increasing the amount of process oil, using soft carbon black, or using liquid rubber without functional groups in the molecular chain can improve the extrusion processability of bead filler rubber and tire Although the molding workability has been improved, the current situation is that the elastic modulus or elongation of the rubber is not sufficient. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition for a tire bead filler that is excellent in various properties such as elastic modulus after vulcanization and tire molding workability. Therefore, the rubber composition of the present invention includes natural rubber,
At least one solid rubber selected from polyisoprene rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber, a diene liquid rubber having a functional group at the end of the molecule or within the molecule, a masked polyisocyanate, a novolak type phenolic resin, and/or or a novolak type modified phenolic resin, (1) the blending ratio of the solid rubber and the diene liquid rubber is 70/30 to 95/5 based on 100 parts by weight of rubber; (2) The ratio of the isocyanate equivalent of the masked polyisocyanate to the functional group equivalent in the diene liquid rubber is 0.5.
-2.0, and (3) the amount of the novolak type phenolic resin and/or novolak type modified phenolic resin is 5 to 25 parts by weight per 100 parts by weight of rubber.
Parts by weight. Hereinafter, the configuration of the present invention will be explained in detail. The natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber used in the present invention may be of any generally known type. In the present invention, at least one of these solid rubbers is used. The diene liquid rubber having a functional group at the end of the molecule or within the molecule used in the present invention is, for example, liquid polyisoprene rubber, liquid polybutadiene rubber, liquid styrene-butadiene copolymer rubber having a functional group at the end of the molecule or within the molecule. , a liquid acrylonitrile-butadiene copolymer rubber. Furthermore, examples of the functional group include a hydroxyl group, a carboxyl group, and an epoxy group. One or more types of this liquid rubber can be used. In the present invention, a masked polyisocyanate is used as a chain extender or crosslinking agent for the diene liquid rubber having a functional group at the end of the molecule or within the molecule. This is a compound that has two or more isocyanate groups in the same molecule and is obtained by temporarily inactivating the isocyanate groups. In other words, polyisocyanates are highly reactive and may be inconvenient to handle; in such cases, it is effective to temporarily protect the isocyanate groups, regenerate them as necessary, and use them for reactions. . Substances that mask polyisocyanates, that is, masking agents, include, for example, phenyl, alcohol, oxime,
Examples include lactams, organic acid esters, amines, amides, imides, active methylene compounds, acidic sodium sulfite, hydrogen cyanide, and boric acid. Polyisocyanates include, for example, aliphatic polyisocyanates such as tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, 1,3- and 1,4-xylene diisocyanate, and ω,ω′-diisocyanate. Alicycles such as 1,2-dimethylcyclohexane, 1-methylcyclohexane-2,4- and 2,6-diisocyanate, 1,3- and 1,4-cyclohexyl diisocyanate, methylenebis(4-cyclohexylisocyanate), isophorone diisocyanate, etc. formula polyisocyanate,
2,4- and -2,6-tolylene diisocyanate, 5-chloro-2,4-tolylene diisocyanate, diphenyl-4,4'-diisocyanate, meta- and paraphenylene diisocyanate, 1,4-, 1,5 -, 2,6- and 2,7
-naphthalene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenyldimethylmethane-4,4'-diisocyanate, diphenyl ether-4,4'-diisocyanate, 3,
These are aromatic polyisocyanates such as 3'-dimethyldiphenyl-4,4' diisocyanate and polymethylene polyphenyl polyisocyanate. Further, in the present invention, a novolak type phenolic resin and/or a novolak type modified phenolic resin is used as the thermosetting resin. Examples of novolak type phenolic resin include novolak type phenolic resin, novolak type cresol resin,
Novolac-type resorcinol resin, etc.
Novolac-type modified phenolic resins include novolac-type phenolic resins modified with oils such as rosin oil, tall oil, cashew oil, linoleic acid, oleic acid, and linoleic acid, or novolac-type phenolic resins modified with aromatic hydrocarbons such as xylene and mesitylene. From the viewpoint of physical properties, it is preferable to use type phenolic resins and novolak type phenolic resins modified with rubber such as nitrile rubber. The novolak type phenolic resin and the novolak type modified phenolic resin can be used alone or as a mixture of two or more. The rubber composition of the present invention is formed by blending at least one of the solid rubbers, the diene liquid rubber, the masked polyisocyanate, and the thermosetting resin. For this combination,
The blending ratio of the solid rubber and the diene liquid rubber is 70/30 to 95/5 per 100 parts by weight of rubber, and the isocyanate equivalent of the masked polyisocyanate is based on the functional group equivalent in the diene liquid rubber. The ratio is 0.5 to 2.0, and the amount of the thermosetting resin is 5 to 25 parts by weight per 100 parts by weight of rubber.
Each component must be blended in parts by weight. It should be noted that if it is blended outside this range, the desired rubber composition cannot be obtained. In addition, the present invention utilizes liquid rubber that takes advantage of the characteristics of liquid rubber to reduce Mooney viscosity or green strength when unvulcanized, and has a functional group at the end of the molecular chain or within the molecular chain that can become a crosslinked structure when vulcanized. If a chain extender or crosslinker is used,
Even if a rubber composition contains a large amount of novolak-type phenolic resin, etc., it becomes sufficiently soft and has improved processability when unvulcanized, and when vulcanized, it not only hardens the resin but also hardens the functional groups and isocyanate of the liquid rubber. This was based on the findings from intensive research that the reaction between the groups occurs effectively, resulting in an increase in elastic modulus and elongation. The rubber composition formed as described above may contain a curing agent for a thermosetting resin, carbon black, sulfur, a vulcanization aid, an anti-aging agent, a process oil, a tackifier, etc., as necessary. It can be blended within a range that does not impair the elastic modulus, elongation at break, and green strength. The present invention will be specifically explained below with reference to Examples, in which the proportions of ingredients in the Examples mean parts by weight. Example Each component was mixed according to the formulation shown in Tables 1 and 2 below. This mixing is carried out by kneading as usual in a B-type Banbury mixer (capacity 1.7), and the various rubber compositions obtained are mixed.
A vulcanized rubber sheet with a thickness of 2 mm was prepared by press vulcanization at 1600°C for 20 minutes. Using this rubber sheet, the dynamic elastic modulus was measured using a tensile viscoelastic spectrometer manufactured by Iwamoto Seisakusho at a frequency of 20 Hz and a rectangular sample with a length of 20 mm and a width of 5 mm at an initial strain of 5%. Measurements were made under conditions of 2% strain and room temperature. As an indicator of the rigidity of unvulcanized rubber, a 2 mm thick unvulcanized rubber sheet was punched out into a JIS No. 1 dumbbell, a tensile test was performed, and the 25% tensile stress at room temperature was measured. In order to significantly improve tire performance, the dynamic elastic modulus of the bead filler rubber composition under the above conditions must be 500 kg/cm ² or more, and the elongation must be 150%.
In order to improve the tire molding workability, it is necessary that the 25% tensile stress of the unvulcanized rubber be 15 kg/cm ² or less, and the rubber composition of the present invention has these properties as shown below. It's satisfying like that.

【table】

【table】

[Table] Regarding Table 1: Normally, novolac type phenolic resin is used in the rubber industry to increase the elastic modulus of rubber, but large amounts of it are blended into bead filler rubber, which is one of the parts of tires. There is a need. However, when a large amount of these resins is blended, the compatibility with the rubber becomes poor, and the cohesive force between the resin molecules is large, so the stiffness of the unvulcanized rubber, that is, the 25% tensile stress, is lower than normal. It becomes significantly larger than that of the rubber composition (Comparative Example 1). A rubber composition having a tensile stress 25% higher than that of unvulcanized rubber is disadvantageous in terms of processing. In other words, the load on the tuber or rolls increases during extrusion, which not only frequently causes damage to the extruder nozzle and breakage of the roll cap, but also reduces work speed during tire molding, resulting in poor productivity.
Furthermore, product defects occur due to blooms of sulfur and the like. Therefore, in order to reduce the 25% tensile stress of unvulcanized rubber, it is possible to use liquid rubber, but liquid rubber does not have a functional group in its molecular chain, or even if it has a functional group, it cannot be used with a chain extender or crosslinking agent. Although the 25% tensile stress of unvulcanized rubber is smaller in a rubber composition without compounding, two terminal free chains remain per liquid rubber molecule.
It does not contribute to rubber elasticity, makes the vulcanizate brittle, and reduces elongation at break (Comparative Examples 2 and 3). As shown in Examples 1 to 3, when the amount of liquid polybutadiene rubber having a hydroxyl group at the end of the molecular chain was increased to 5, 10, and 20 parts by weight, the tensile stress of unvulcanized rubber decreased by 25%. Of course, the elastic modulus also improves and elongation increases. This is because liquid rubber molecules are chain-extended and cross-linked by a polyisocyanate masked by a chain extender or cross-linker, i.e., phenyl, eliminating free end chains and increasing the elastic modulus to create a rubber network. ,
This is because it results in increased elongation. If the amount of liquid rubber blended is less than 5 parts by weight, it is undesirable in terms of the 25% tensile stress of unvulcanized rubber, and 30%
If the amount exceeds 1 part by weight, the extrudate tends to bleed if left for several days, which is unfavorable in terms of tire quality. If the amount of novolak type phenolic resin and/or novolak type modified phenolic resin is 5 parts by weight or less, it will not contribute to improving the elastic modulus (Comparative Example 4). Furthermore, when the amount exceeds 25 parts by weight, the elastic modulus increases significantly, but as a reaction, for example, even if the above-mentioned liquid rubber is mixed in an amount close to the upper limit, the 25% tensile stress of the unvulcanized rubber becomes large, and when used (Comparative Example 5). In Examples 4 to 6, natural rubber was blended with styrene-butadiene copolymer rubber, polybutadiene rubber, and polyisoprene rubber as the solid rubber, and hydroxyl-terminated liquid polybutadiene rubber was used as the liquid rubber. , elastic modulus, elongation, and 25% tensile stress of unvulcanized rubber. Regarding Table 2: Examples 7 to 10 are cases where hydroxyl group-terminated liquid polyisoprene rubber, hydroxyl group-terminated intramolecular epoxidized liquid polybutadiene rubber, carboxyl group-terminated liquid polybutadiene rubber, and epoxy group-terminated liquid polybutadiene rubber were compounded as liquid rubbers. The ratio of the isocyanate group equivalent to the functional group equivalent in the liquid rubber component is 1.0. The liquid rubber with the most remarkable increase in elastic modulus is hydroxyl-terminated and epoxidized polybutadiene rubber. This is because epoxy has high rigidity. The chain extender or crosslinking agent in Example 11 is a polyisocyanate when the masking agent is alcohol, and exhibits similar effects if the equivalent ratio is within the range of the present invention. Comparative Example 6 is a case where the masked polyisocyanate is blended in an equivalent ratio exceeding the range of the present invention, and although the elastic modulus and the 25% tensile stress of unvulcanized rubber are satisfied, the elongation is significantly reduced. Next, as shown in the drawing, the rubber composition of the present invention was used in the bead filler 4 of a tire (tire size 185 SR14), and the cornering power, which is one of the indicators of steering stability, was measured and the bead section was measured indoors. A durability test was conducted. The results are shown in Table 3 below. In addition, in the figure, 1
2 represents the folded end of the carcass, 2 represents the sidewall portion of the tire, 3 represents the carcass, 5 represents the bead wire, 6 represents the belt layer, R represents the rim, and R' represents the rim flange.

[Table] Test conditions Cornering power: Internal pressure 2.2Kg/cm ² speeds 10Kg/hr Load 00Kg Bead durability test: Internal pressure 2.2Kg/cm ² speeds 81Km/hr Load Starting from 100% load of the actual vehicle, 15% step-up for 4 hours The final load is 310%. In Table 3 above, the cornering power is expressed as a percentage based on the tire with symbol A (100%) (the larger the value, the better the steering stability). In addition, the durability test of the bead part was
I wrote the distance traveled until the bead part breaks, but
Those that exceeded 5000km were considered to have passed. These results show that Tire B, which uses the rubber composition of the present invention as a bead filler, is excellent in both handling stability and durability. As explained above, the rubber composition for bead filler of the present invention is composed of a solid rubber such as natural rubber, a diene liquid rubber having a functional group, a masked polyisocyanate, and a phenolic resin, so that when unvulcanized, The presence of the diene liquid rubber lowers the viscosity, lowers the rigidity, and improves processability (tire molding workability). Also, during vulcanization,
The mask of the masked polyisocyanate is removed by the heat during vulcanization, and its isocyanate groups react effectively with the functional groups of the diene liquid rubber, thereby increasing the dynamic elastic modulus and elongation. Therefore, after vulcanization, the dynamic elastic modulus increases, making it extremely hard, and the dynamic elastic modulus and elongation increasing, improving the physical properties at break. For this reason, the rubber composition for bead filler of the present invention can improve the tire molding workability before vulcanization, thereby contributing to the improvement of tire productivity. It becomes possible to improve the

[Brief explanation of drawings]

The figure is a partial cross-sectional view of the tire. 1... Tip of folded part of carcass, 2... Sidewall part of tire, 3... Carcass, 4... Bead filler, 5... Bead wire, 6... Belt layer, R... Rim, R'... Rim flange .

Claims (1)

[Claims] 1. At least one solid rubber selected from natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber, a diene liquid rubber having a functional group at the end of the molecule or within the molecule, a masked polyisocyanate, and a novolac rubber. type phenolic resin and/or novolac type modified phenolic resin, and the compounding ratio of the solid rubber and the diene liquid rubber is 100% rubber.
The weight part is 70/30 to 95/5, the ratio of the isocyanate equivalent of the masked polyisocyanate to the functional group equivalent in the diene liquid rubber is 0.5 to 2.0, and the novolak type phenolic resin and A rubber composition for a tire bead filler, characterized in that the amount of the novolak-type modified phenolic resin is 5 to 25 parts by weight based on 100 parts by weight of the rubber content.