JPS6337825B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new rubber composition for inner liners of tires, and more specifically, to inner liners, which are essential for increasing tire internal pressure or reducing tire weight in order to improve fuel efficiency of automobiles. The present invention relates to a rubber composition for an inner liner that simultaneously prevents the rubber layer from flowing in, that is, makes the rubber layer uniform and reduces air permeability. Recently, from the viewpoints of both fuel efficiency and weight reduction of automobiles, there has been a strong desire to reduce the rolling resistance of automobile tires, that is, to increase the internal tire pressure and reduce the weight of the tires. For this purpose, it is necessary not only to reduce the air permeability of the inner liner rubber of tubeless tires, but also to reduce the weight of the tire, that is, reduce the gauge of the inner liner rubber. However, conventional rubber compositions for inner liners of tubeless tires have mostly been diene rubbers, halogenated butyl rubbers, or mixtures thereof. In a rubber composition for an inner liner mainly made of diene rubber, such as natural rubber, the tensile stress of unvulcanized rubber is relatively high, but the air permeability is extremely high. Therefore, in order to reduce air permeability, it is necessary to increase the thickness of the inner liner rubber layer. However, increasing the gauge of the inner liner is contrary to reducing the weight of the tire, and furthermore is contrary to reducing rolling resistance. Additionally, it is a common practice to add inorganic fillers (e.g. clays, mica, calcium carbonate, etc.) to reduce the air permeability of diene rubber compositions, but in this case a large amount must be added. , which is unfavorable in terms of crack resistance. On the other hand, it is generally known that the use of halogenated butyl rubber reduces air permeability.
Therefore, halogenated butyl rubber alone or a blend of halogenated butyl rubber and diene rubber are used as the inner liner rubber for tubeless tires, but although the air permeability can be kept relatively low, the tensile stress of the unvulcanized rubber causes There is no big difference in terms of the rubber from the natural rubber mentioned above, so if the gauge is made thinner, the gauge stability of the inner liner rubber layer will deteriorate. In other words, when molding a tire, the inner liner rubber or carcass is made into a cylindrical shape, and a molding bladder applies large internal pressure to the crown part to inflate the tire into a toroidal shape. The pressure becomes very large and the stability of the gauge in the vicinity is poor. Furthermore, when the tire is vulcanized, a large internal pressure is similarly applied to the crown portion by the vulcanization bladder, so that the tire is inflated in the same manner as during molding. In the manufacturing process of such tires, reducing the gauge of the inner liner rubber layer is considered to be a necessary measure to reduce the weight of the tire, but even if the air permeability is low, the tensile stress of the unvulcanized rubber is small. Even these halogenated butyl rubbers cannot prevent the deterioration of air permeability. Furthermore, since the unvulcanized rubber has a low tensile stress, the inner liner layer may flow into the carcass coat, causing separation of the tire. Therefore, there is an urgent need to develop a rubber composition that has low air permeability and extremely high tensile stress of unvulcanized rubber for the inner liner rubber layer of tubeless tires. It is suitable for weight reduction.
Furthermore, it is necessary to have a well-balanced crack resistance. The present invention has been made in view of these circumstances, and it prevents the inner liner rubber layer from flowing in and reduces air permeability.
Another object of the present invention is to provide a rubber composition that does not impair flex scratch resistance. Therefore, the rubber composition for an inner liner of the present invention contains at least polynorbornene rubber and halogenated butyl rubber, and the amount of polynorbornene rubber is 5 to 45 parts by weight based on 100 parts by weight of the rubber component, and the halogenated butyl rubber amount of 5 to 80
Parts by weight. Hereinafter, the configuration of the present invention will be explained in detail. The polynorbornene rubber used in the present invention is known, and for example, the manufacturing method thereof is described in Japanese Patent Publication Nos. 47-13863 and 47-35800.
It is described in publications such as Japanese Patent Publication No. 48-35960. Furthermore, the halogenated butyl rubber used in the present invention is also known. The halogenated butyl rubber preferably contains 1.0 to 2.0% by weight of halogen atoms, and specifically, chlorinated butyl rubber (chlorine content 1.0 to 1.5% by weight), brominated butyl rubber (bromine-containing Amount 1.8~2.0
It is preferable to use % by weight) or a mixture thereof. The rubber composition of the present invention is composed of polynorbornene rubber and halogenated butyl rubber, and in this rubber composition, the amount of polynorbornene rubber is 5 to 45 parts by weight based on 100 parts by weight of the rubber component, and The amount of halogenated butyl rubber is 5 to 80 parts by weight per 100 parts by weight of the rubber component. When the amount of polynorbornene rubber is 5 parts by weight or less, as shown in Comparative Example 2 (0 parts by weight of polynorbornene rubber), the tensile stress of the unvulcanized rubber becomes small, and therefore the inner liner rubber layer flows into the carcass coat rubber, worsening the air permeability of the tire. Furthermore, if the amount of polynorbornene rubber exceeds 45 parts by weight, as shown in Comparative Example 3 below, the flex scratch resistance deteriorates, the durability as a tire decreases, and the tire becomes unusable. Therefore, in the present invention, the amount of polynorbornene rubber used must be within the above range. The halogenated butyl rubber used in the present invention may be chlorinated butyl rubber, brominated butyl rubber, or a mixture thereof in any proportion, but in order to achieve this purpose, the amount used is 5 to 80 parts by weight as described above. It must be. When the amount of halogenated butyl rubber is 80 parts by weight or more, the air permeability is good as shown in Comparative Example 4 below, but the tensile stress of the unvulcanized rubber is small, so the inner liner layer is not included in the carcass coat rubber. The air permeability of the tire deteriorates, and its durability also decreases. If the amount of halogenated butyl rubber is less than 5 parts by weight, use more than 45 parts by weight of polynorbornene rubber or add 50 parts by weight of other rubber components, such as diene rubber, to bring the total amount of rubber to 100 parts by weight. If polynorbornene rubber is used beyond the scope of the present invention, the flex scratch resistance will decrease as described above, and if a large amount of diene rubber etc. is used, the air resistance will decrease. Permeability decreases. Air resistance can be improved by adding up to 50 parts by weight of diene rubber such as natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, or a mixture thereof per 100 parts by weight of the total rubber to the above composition. Processability (ease of mixing and extrusion) and dimensional stability can be improved while maintaining permeability. In this case, the amount of diene rubber used must be 50 parts by weight or less per 100 parts by weight of the rubber component in the resulting rubber composition. If more than 50 parts by weight of diene rubber is blended, as shown in Comparative Example 1 (natural rubber is 100 parts by weight) below, although the tensile stress of the unvulcanized rubber is relatively large, the air permeability will deteriorate significantly. It is. For the rubber composition thus formed, which optionally contains diene rubber, reinforcing agents, fillers, anti-aging agents, vulcanization accelerators, vulcanizing agents, active materials, etc., which are used as ordinary rubber compounding agents, are added. Agents, softeners, plasticizers, adhesives, plasticizers, etc. may be added as appropriate. Examples and comparative examples are illustrated below. Examples 1 to 7, Comparative Examples 1 to 5 The physical properties of the rubber compositions having the formulations shown in Table 1 above were tested, and the results are shown in Table 1.

The values in [Table] indicate the pure rubber content.
2) Air permeability = ASTM D814 = 56T.
3) Tensile stress of unvulcanized rubber An unvulcanized rubber sheet with a thickness of 2 mm was punched out into a JIS No. 1 dumbbell, a tensile test was conducted, and the 50 mm tensile stress at 25°C was measured.
4) Flex Scratch: Using a De Mattia type crack tester.
Examples 1 and 2 differ from Comparative Example 2 by replacing natural rubber with polynorbornene rubber. The air permeability of Example 1, in which 15 parts by weight of the natural rubber of Comparative Example 2 was replaced with polynorbornene rubber, was reduced by about 40%, and the tensile stress of the unvulcanized rubber was 3.4 times higher. This is a surprising result that cannot be obtained using halogenated butyl rubber alone. Example 2 shows the data when 5 parts by weight, which is the lower limit amount of polynorbornene rubber, was substituted.
In addition to the reduction in air permeability, the tensile stress of unvulcanized rubber is nearly double, which is data that cannot be obtained with halogenated butyl rubber. Example 3 is a case in which 20 parts by weight of the halogenated butyl rubber in Comparative Example 2 was replaced with polynorbornene rubber. Air permeability in this case is 50%
The tensile stress of the unvulcanized rubber is reduced by four times. In Example 4, the diene rubber of Example 3, natural rubber, was replaced with styrene-butadiene copolymer rubber, but the same effect as in Example 3 was obtained. In Example 5, the polynorbornene rubber of Example 3 was further increased by 20 parts by weight to 40 parts by weight, and the upper limit of polynorbornene rubber, that is,
It is close to 45 parts by weight. In this case, although the air permeability is significantly reduced, Example 1,
It does not decrease linearly like 2 and 3. However, the tensile stress of the unvulcanized rubber continues to increase linearly, and the flex crack resistance remains in a well-balanced state. Examples 6 and 7 show cases in which no diene rubber is included. As shown in Examples 1 to 5 above, when the composition ratios of polynorbornene rubber, halogenated butyl rubber, and diene rubber are limited, and when the composition ratios are as shown in Examples 6 to 7, The present invention makes it possible to create an inner liner rubber composition that exhibits remarkable effects on air permeability and tensile stress of unvulcanized rubber, and is also well-balanced in terms of flex crack resistance. Next, in order to prove the effectiveness of the present invention as a tire, a tubeless radial tire of size 155SR12 was created using steel cord for the belt portion and polyester cord for the carcass portion (product A of the present invention). This rubber composition for inner liner is
This is a formulation example of Example 1 in Table-1. In addition, the thickness of the inner liner rubber layer in this case is the normal thickness, but since it is used for high-pressure tires,
The initial air pressure was adjusted to 2.20Kg/cm ² .
The test results are shown in Table 2 below. As shown in Table 2, the thickness of the inner liner rubber composition of the product of the present invention is not much different from the thickness of the conventional product, but the product of the present invention has the highest air pressure retention rate.

[Table] In order to further prove the effectiveness of the present invention as a tire, tubeless radial tires of size 165SR13 were similarly made using steel cord for the belt part and polyester cord for the carcass part (invention products B and C). ). The rubber composition for inner liner in this case is the blending example of Examples 3 and 5 in Table-1. The thickness of the inner liner rubber layer of this tire is thinner than usual in order to reduce the weight of the tire. The test results are shown in Table 3 below. As shown in Table 3, the thickness of the rubber composition for inner liner of the product of the present invention shows less change in thickness compared to the conventional product of Comparative Example 2. This is due to the difference in the magnitude of the tensile stress of the unvulcanized rubber of the inner liner rubber composition of the present invention. The low air permeability of the rubber composition for an inner liner used in the product of the present invention, combined with the small change in gauge, results in a significantly high air pressure retention rate.

【table】

Claims (1)

[Claims] 1 Containing polynorbornene rubber and halogenated butyl rubber, the amount of polynorbornene rubber is 5 to 45 parts by weight and the amount of halogenated butyl rubber is 5 to 80 parts by weight per 100 parts by weight of the rubber component. A rubber composition for inner liners of tires.