JPH04368205A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve the drivability, braking ability and maneuverability on an icy and snowy road without degrading the abrasion resistance of a pneumatic tire. CONSTITUTION:Foam rubber which has 3-100 pts.wt. of super macromolecule polyethlene whose molecule amount is more than 500,000 to rubber content 100 pts.wt. average grain diameter is 1-500mum, and separate bubble with 3-35% foaming rate is provided at a tread.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to pneumatic tires.
Specifically, the present invention relates to an all-season pneumatic tire that has significantly improved driving performance, braking performance, and maneuverability on icy and snowy roads without impairing summer handling performance and durability.

0002

BACKGROUND OF THE INVENTION In recent years, there has been an increasing demand for so-called all-season tires that can be used in the winter without having to change tires in the same way as in the summer. Such tires must have the same dry grip, wet grip, steering stability, durability, and fuel efficiency in winter as they do in summer, and also have sufficient driving and braking performance on ice and snow. is required. Traditionally, the tread rubber used in such tires has been required to have low hardness at low temperatures for summer tread rubber, so polymers with low glass transition points have been used, or polymers with low elastic modulus at low temperatures have been used. It is known to use softeners and plasticizers that can be maintained appropriately.

However, the former method has the problem that, due to the hysteresis characteristics of the polymer, although it exhibits reasonable performance in the freezing and snow temperature range, braking performance and maneuverability on wet and dry road surfaces are insufficient. The latter method is also disclosed in Japanese Patent Application Laid-open Nos. 135149-1982 and 1983-
No. 199203, Japanese Unexamined Patent Publication No. 1992-137945, etc., but in both methods, the abrasion resistance and durability when driving on ordinary roads are low, considering the degree of improvement in performance on ice and snow. Problems have been pointed out, such as the large negative impact it has on people.

On the other hand, the rubber compositions used in the conventional tire treads mentioned above generally include natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (
BR) and a blend thereof are selected as the base polymer, and in addition to this, fine-grained and highly reinforcing carbon black, vulcanizing agents such as sulfur, vulcanization accelerators, anti-aging agents, softeners, etc. Although it is a composite material to which rubber chemicals have been added, it can also be said to be a homogeneous material. Conventionally, in order to improve the performance required for tire treads, as mentioned above, constituent factors such as polymers, carbon black, and other rubber chemicals constituting such rubber compositions have been improved individually or in combination with each other. The main approach taken has been to deal with these issues by making related improvements, and as a result, improvements have been mainly investigated within the framework of homogeneous composite materials.

However, instead of using such a homogeneous rubber composition as a conventional tire performance improvement method, the rubber composition is made non-uniform, that is, domains within the average particle size range of about 0.1 to 1000 μm are incorporated into the rubber composition. formed into
A rubber composition with a non-uniform structure having a so-called sea-island structure,
It is also known that by changing the properties of the material that forms these domains and the number of parts filled, it is possible to improve the performance of tire treads using a different approach from controlling rubber physical properties within the framework of conventional homogeneous rubber. .

That is, in improving the physical properties of homogeneous rubber, for example, there are many cases where an antinomic relationship arises between grip performance and wear resistance performance, and there is a limit to improving both performances at the same time. On the other hand, in a heterogeneous rubber composition having a sea-island structure, it is possible to solve this problem by distributing the performance-improving factors between the domain part (island part) and the matrix part (sea part). Be expected.

However, when such a rubber composition with a heterogeneous structure is introduced, there is a chemical or physical interaction between the domain part and the matrix part, and it is not sufficient unless the domain part has reinforcing properties. However, the advantages of the heterogeneous structure are not realized, and the domain portion ends up acting as a nucleus of destruction for the matrix portion. Therefore, reinforcement of the domain portion is essential for controlling the physical properties of heterogeneous rubber. However, at present, very little research has been done on materials that form domain diameters of about 0.1 to 1000 μm and have sufficient reinforcing properties for the matrix portion.

Furthermore, in recent years, there has been a method of foaming tread rubber using an appropriate method to generate closed cells (Japanese Patent Laid-Open No. 6
3-89547). In other words, since the ice surface of the tread rubber obtained in this way is covered with a large number of pores, the water removal effect on the ice surface and the edge effect that scrapes off the ice due to the microscopic movement of the pores cause the ice surface to be easily removed. It exhibits high frictional properties. However, when foamed rubber is used for the tread, it cannot be said that the tire durability, such as wear resistance, is always at a satisfactory level.

As mentioned above, no matter which conventional technology is used, performance on ice and snow at relatively low temperatures below -5°C (so-called dry-on-ice) and wet conditions around 0°C (so-called It has been extremely difficult to obtain a sufficient coefficient of friction and improve driving performance, braking performance, and maneuverability in general while achieving both performance on ice and snow (wet on ice).

0010

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned difficulties and to provide a pneumatic pump which improves driving performance, braking performance, and maneuverability on icy and snowy roads without impairing maneuverability and durability in summer. The object of the present invention is to provide a tire that has improved driving performance, braking performance, and maneuverability on wet icy and snowy roads as described above without reducing wear resistance. .

[0011]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors have developed a foamed rubber containing ultra-high molecular weight polyethylene having a specific particle size and having a specific expansion ratio. The inventors have discovered that the above object can be achieved by using it in a tread, and have completed the present invention. That is, the pneumatic tire of the present invention contains ultra-high molecular weight polyethylene with a molecular weight of 500,000 or more and an average particle size of 1 to 500 μm per 100 parts by weight of rubber.
The tread is characterized in that the tread is equipped with foamed rubber containing 100 parts by weight of closed cells with an expansion ratio of 3 to 35%.

In the present invention, the ultra-high molecular weight polyethylene having a molecular weight of 500,000 or more means that the intrinsic viscosity [η] of the decalin solvent at 135° C. is 4.5 dl/g or more. However, it is preferably 35 dl/g or less. The intrinsic viscosity of ultra-high molecular weight polyethylene is 35 dl/g
This is because it is difficult to industrially produce anything exceeding this amount. The ultra-high molecular weight polyethylene powder is, for example, the product name HIZEX MILLION 240M (registered trademark) (manufactured by Mitsui Petrochemical Industries, Ltd., [η] = 16.5 dl/g).
) and product name Hi-ZEX Million 145M (registered trademark) (manufactured by Mitsui Chemicals, Ltd., [η] = 8.20 dl
/g). By the way, the intrinsic viscosity [η] of general-purpose polyethylene is about 2.6 dl/g.

[0013] In the pneumatic tire of the present invention, the ultra-high molecular weight polyethylene forms domains in the tread rubber as a matrix that are harder than the tread rubber. It is thought that the ultra-high molecular weight polyethylene as a domain and the rubber as a matrix are chemically bonded by radical generation from the ultra-high molecular weight polyethylene and rubber during kneading. Therefore, in the rubber composition of the present invention having a heterogeneous structure, the domain part has reinforcing properties with respect to the matrix part, the two are sufficiently bonded together, and the domain part has a higher hardness than the matrix part. Since it has a modulus of elasticity of
The following three performance improvements are possible as domain formation effects.

[0014] First, the existence of such a domain
It is possible to improve the wear resistance of the tire tread surface by changing the dynamic behavior of the tire tread surface in response to external forces and appropriately controlling the hardness, elastic modulus, and filling amount of the domain portion. can. Second, in such composite rubber compositions, it is known that by increasing the hardness and elastic modulus of the domain portion, the hardness and elastic modulus of the entire heterogeneous structure rubber composition can be increased. This increases the block rigidity in the pattern of the tread portion of the tire tread, and as a result, for example, grip performance in dry conditions can be improved. Thirdly, due to the presence of such domain parts, surface irregularities on the order of the domain diameter are formed on the surface of the tread part of the tire tread, and these irregularities have a drainage effect similar to the surface grooves formed by the above-mentioned pattern. The wet skid resistance of the tire is improved. In addition, the effect of improving drainage performance and block rigidity also makes it possible to improve these performances on ice and snow.

If the molecular weight of such ultra-high molecular weight polyethylene is less than 500,000, melt flow may occur during kneading, and a heterogeneous structure may not be created. In addition, even when domain portions are formed, the hardness of the domain portions may be lower than that of the matrix. This is not preferable because the rubber hardness comparison is insufficient and sufficient improvement effects are not seen in each performance of the tire. Furthermore, if the number of parts filled with ultra-high molecular weight polyethylene is less than 3 parts by weight per 100 parts by weight of the raw material rubber, both the improvement of block rigidity and the formation of surface irregularities will be insufficient, so grip properties and wet skid resistance will be particularly affected. Improvement will be insufficient. On the other hand, if it is filled in an amount exceeding 100 parts by weight, the balance between the reinforcing effect of the ultra-high molecular weight polyethylene and its function as fracture cores will be lost, and the wear resistance will particularly deteriorate, which is not preferable. Furthermore, if the average particle diameter of the ultra-high molecular weight polyethylene particles is less than 1 μm, the ice and snow performance of the tire will not be sufficient. On the other hand, if the average particle size exceeds 500 μm, this is not good because the wear resistance of the tread using foamed rubber will decrease.

Rubber components include natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, styrene-isoprene-butadiene terpolymer rubber, styrene-isoprene copolymer rubber, and isoprene-butadiene copolymer rubber. Polymer rubbers and the like can be mentioned, but are not particularly limited. In addition to the diene rubber and ultra-high molecular weight polyethylene, the composition disposed in the tread may also include other rubbers and compounding agents normally used in tread rubber, such as fillers, anti-aging agents, and vulcanizing agents. , a vulcanization accelerator may be included, and the types and amounts thereof are within the range normally used for tread rubber and are not particularly limited.

[0017] In the present invention, the tread rubber is 3 to 35
It was decided to have closed cells with a foaming ratio of 0°C.
This is because such closed cells are essential in order to increase the microscopic absorption and drainage effect of the pores and to exhibit excellent ice and snow performance when there is a large amount of melted water on the nearby ice surface. Foaming may be performed using a foaming agent or by high-pressure mixing of gas, but if the foaming ratio is less than 3%, the foaming effect will not be sufficient, while if it exceeds 35%, the tread rigidity may be insufficient. Therefore, the wear resistance deteriorates and the occurrence of groove bottom cracks increases.

Here, the foaming rate Vs of the foamed rubber is expressed by the following formula: Vs = {(ρo −ρg )/(ρ1 −ρg )−
1}×100 (%) ...(1) where ρ1 is the density of the foam rubber (g/cm3),
ρo is the density of the solid phase part of the foam rubber (g/cm3), ρ
g is the density of the gas part in the foam rubber cells (g/cm3
). Foamed rubber is composed of a solid phase portion and a cavity (closed cell) formed by the solid phase portion, that is, a gas portion within the cell. Since the density ρg of the gas part is extremely small, close to zero, and extremely small compared to the density ρ1 of the solid phase part, equation (1) can be expressed as %
) ... is almost equivalent to (2).

Furthermore, in the pneumatic tire of the present invention,
Foamed rubber blended with the above-mentioned ultra-high molecular weight polyethylene,
It may be provided only in the cap portion of the tread portion having a cap-base structure.

[0020]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Table 1 below shows the molecular weight and average particle size in the tread rubber of the ultra-high molecular weight polyethylene used in Examples and Comparative Examples. The average particle diameter of ultra-high molecular weight polyethylene in the tread rubber is determined by selecting 10 lots of tread rubber samples and calculating the diameter of 20 particles of ultra-high molecular weight polyethylene within the field of view of an optical microscope (longest diameter + shortest diameter). /2, the average particle size was calculated for each lot, and the arithmetic average of the average particle sizes of 10 lots was further calculated. Table 1 Table 2 shows the formulation (parts by weight) of the foamed rubber matrix combined with the ultra-high molecular weight polyethylene shown in Table 1.
In addition, the expansion ratio of the obtained particle-containing foamed rubber and the tire performance when the foamed rubber is applied to a tire tread are shown.

[0021]

[Table 2] As is clear from Table 2, in Example 1, which is the pneumatic tire of the present invention, the performance of both on-ice braking performance and steering stability was improved compared to Comparative Examples 1 to 5. There is.

[0022]

Effects of the Invention As explained above, the pneumatic tire of the present invention, in which a predetermined amount of ultra-high molecular weight polyethylene of a specific particle size is blended into a tread composition made of foamed rubber having a specific expansion ratio, has excellent wear resistance. Drivability, braking performance, and maneuverability on wet and dry icy and snowy road surfaces can be significantly improved without reducing performance.

Claims (2)

[Claims] [Claim 1] Average particle size 1 having a molecular weight of 500,000 or more
~500 μm ultra-high molecular weight polyethylene with rubber content 1
Contains 3 to 100 parts by weight per 00 parts by weight, and 3 to 100 parts by weight
A pneumatic tire characterized by having a tread made of foamed rubber having closed cells with an expansion ratio of 35%. 2. A pneumatic tire characterized in that the rubber composition according to claim 1 is disposed in a cap portion of a tread portion having a cap-base structure.