JPH04365606A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To secure the stable on-ice performance over a wide temperature range and the stable ice performance under all the using conditions up to the perfect abrasion, as for a neumatic tire for a vehicle ranging from small size to large size. CONSTITUTION:The foamed rubber which has independent gas foams having a foaming rate of 3-35% and contains 3-30wt. parts inorganic high hardness particles which each possess a Mohs's hardness of 1.5 deg.C or more and has an average particle diameter of 10-400mum and to which the processing for improving the affinity with rubber is applied, for 100wt. parts rubber portion are used for tread.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to pneumatic tires.
In particular, this invention relates to technology for improving the treads of pneumatic tires for vehicles used on icy and snowy roads, from small to large vehicles such as passenger cars, trucks, and buses.

0002

[Prior Art] When driving a car on a low-temperature road surface in winter, especially on a road surface where water or snow on the road surface has frozen and formed an icy surface, there is a gap between the tread rubber of the tires installed on the car and the ice surface. The frictional force is significantly lower than the frictional force on a normal, dry, non-icy road surface. Therefore, in order to drive safely on roads with icy surfaces, it is necessary to attach spiked tires to the car, or attach tire chains around the outer circumference of the tires to prevent the tread between the tire tread rubber and the icy surface. Frictional force is maintained so as not to become low.

However, when tires equipped with tire chains or spiked tires are installed on a car, when the car runs around a curve, starts suddenly, or suddenly stops, the spikes of the spiked tires or tire chains may touch the road surface. hurt,
A problem arises in that a portion of the damaged road surface is cut out and becomes powder, and when this road surface dries, the powder is blown up by the wind and scatters dust. In addition, when a car equipped with the spiked tires or tires with tire chains runs on a road, the spikes of the spiked tires or tire chains hit the road surface and generate noise.

[0004] In response to this, in recent years, techniques have been adopted in which improvements are made to the tread rubber itself in order to improve the frictional force. The first method is to foam the tread rubber by 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. Demonstrates high friction properties. This method has been incorporated into actual tire treads and is commercially available as studless tires. A method is also being considered in which various foreign substances (such as sand and natural substances such as rice husks) are mixed into the tread rubber, and these foreign substances fall off when the tire is running, thereby creating pores. This method has the same mechanism as foaming to increase friction on ice.

[0005] A second method is to mix various high-hardness materials into tread rubber and utilize the scratching effect of the high-hardness materials on the ice surface to achieve high friction of the tread rubber on ice. There is (Tokuko Sho 46-317
No. 32, JP-A No. 51-147803, Special Publication No. 5
6-52057). This method clearly uses a different mechanism from the first method to increase the friction of tread rubber on ice. In fact, in many cases, the more these high hardness materials are mixed in, the more the tread rubber tends to have high friction on ice.

[0006]

[Problems to be Solved by the Invention] Among the above-mentioned conventional techniques, the first one scratches the ice with the convex portions of the surface unevenness after foaming of Treo rubber or the removal of mixed foreign matter, and the concave portions absorb and discharge moisture on the ice surface. The disadvantage of method 1 is that the hardness of the rubber is relatively lower than that of the ice surface, so the scratching effect cannot be expected at low temperatures (usually below -3°C).

On the other hand, the second method, in which a high hardness material with a high scratching effect is mixed into the matrix rubber of the tread, has the disadvantage that the effect of improving performance on ice at around 0°C, where there is a lot of moisture, is small, and the high hardness material does not affect the rubber. Since it exists as a foreign substance with no affinity, there is a significant drop in friction resistance and fracture properties.

[0008] Since the actual ice surface temperature changes variously from daytime to nighttime, it is desirable to have a tire tread that exhibits more stable on-ice performance over a wide temperature range and that does not significantly reduce wear resistance and fracture properties. ing.

[0009] Another problem with pneumatic tires for running on ice is that compared to when the tire is new, at the final stage of running, the stiffness of the rubber increases over time and the pattern groove depth decreases, resulting in a decrease in on-ice performance. Met.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a pneumatic tire with a tread that exhibits stable on-ice performance over a wide temperature range and also exhibits more stable on-ice performance under all usage conditions up to complete wear. It's about doing.

[0011]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors have developed a method to improve the performance on ice at around 0°C, where the matrix rubber of the tread is melted on the ice surface and has a high moisture content. A foamed rubber with a foaming ratio is used, and special inorganic high-hardness particles having a specific hardness and particle size and having an affinity for the matrix rubber are mixed into the matrix rubber, so that the high-hardness particles appear in a certain area on the tread surface. It was discovered that by doing so, a scratching effect can be obtained at low temperatures where the ice surface is harder than rubber, and that there is no deterioration in wear resistance and fracture properties due to detachment of mixed particles, and in completing the present invention. It's arrived.

That is, the pneumatic tire of the present invention has a Mohs hardness of 1.5 degrees or more and an average particle size of 10 to 400 μm.
m, contains 3 to 30 parts by weight of inorganic high hardness particles whose surface has been treated to improve affinity with rubber, based on 100 parts by weight of rubber, and has closed cells with an expansion ratio of 3 to 35%. It is characterized by having a tread made of foamed rubber. The area of the high hardness particles per 1 cm 2 of surface area of the tread is all 1.6 mm 2 or more.

Further, in the tire tread of the present invention, in order to suppress the deterioration of on-ice performance until complete wear occurs, it is preferable that the expansion ratio of the rubber matrix is gradually increased from the tread surface toward the innermost layer. For this purpose, the average expansion ratio of the foamed rubber layer located within 1 mm from the tread surface is within a range of 0.5 to 1.5 mm from the innermost layer of the foamed rubber layer, which is in contact with the non-foamed rubber. smaller than the average foaming ratio.

[0014]

[Function] In the present invention, the foamed rubber has closed cells with an expansion ratio of 3 to 35% because it has a microscopic absorption and drainage effect by the pores when there is a lot of melted water on the ice surface at around 0℃. This is because such closed cells are essential in order to increase the size and exhibit excellent ice and snow performance. In addition to foaming, closed cells can also be created by mixing powder that has no affinity with the matrix rubber, such as rice husk, and separating it during running. No effect beyond foaming can be obtained in terms of performance on ice.

In addition, the foaming means can control the foaming ratio from the surface layer to the innermost layer of the tread, and can reduce changes in on-ice performance until complete wear. Select this. 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 determined by the following formula: Vs = {(ρo - ρg )/(ρ1 - ρg
)-1}×100 (%) ----- (1) where ρ1 is the density of foam rubber (g/cm3), ρ
o is the density of the solid phase part of the foam rubber (g/cm3), ρg
is the density of the gas part in the foam rubber bubbles (g/cm3)
It is. 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) is expressed as follows: Vs = {(ρo - ρ1 )-1} x 100
(%) -----
It is almost equivalent to (2).

At low temperatures, where the hardness of ice is higher than the hardness of rubber, inorganic particles that satisfy the following conditions are required as a high hardness material to be mixed into foamed rubber in order to obtain a scratching effect. That is, first, the Mohs hardness measured by a Mohs hardness tester is 1.5° or more. If it is less than 1.5°, a sufficient scratching effect cannot be obtained.

[0018] The average particle diameter of such high hardness particles is 10 to 40
0 μm, preferably within the range of 15 to 250 μm; if it is less than 10 μm, no improvement in performance on ice will be observed, while if it exceeds 400 μm, occurrence of groove bottom cracks will become a problem.

[0019] High hardness particles satisfying these conditions have a rubber content.
It must be blended in an amount of 3 to 30 parts by weight per 100 parts by weight, and if it is less than 3 parts by weight, the area occupied by the particles on the tread surface will be too small even when the lightest particles are assumed, resulting in poor performance improvement on ice. I can't see it. In other words, after actually driving straight for 200 km, we measured the total area of particles appearing per 1 cm2 of tread surface area of the test tire using a microscope, and found that tires with a total particle area of 1.6 mm2 or more had sufficient on-ice performance. However, in order to obtain this total area, 3 parts by weight or more of high hardness particles are required to be mixed. However, when more than 30 parts by weight is mixed in, the wear resistance is significantly reduced and the occurrence of groove bottom cracks becomes a problem.

Furthermore, in the present invention, the inorganic high hardness particles to be mixed must be treated to improve their affinity with the matrix rubber. If such particles are not used, the particles will separate from the matrix rubber during running and contribute to the formation of surface irregularities, but the desired scratching effect will not be obtained sufficiently, and the fracture characteristics and wear resistance of the tread rubber will be affected. Significantly decreased.

[0021] As a treatment method for improving affinity that can be used in the present invention, there may be mentioned a treatment method in which the surfaces of the particles are coated with an adhesive capable of firmly adhering to the matrix rubber and the other particles. Alternatively, instead of using an adhesive, a treatment method may be used in which brass, copper, or cobalt is deposited on the surface of high-hardness particles by plating, plasma treatment, sputtering, or the like. In this case, stronger adhesive strength can be obtained by, for example, making the rubber material that forms the matrix a high-sulfur compound.

It is also effective to coat the high hardness particles with an adhesive rubber material. In this case, even if the adhesive rubber material is a matrix rubber material,
Rubber materials with different formulations may be used. When using a rubber material having a different composition from that of the matrix rubber material, latex, emulsion, or thermoplastic rubber can be used as the rubber component in addition to general solid rubber. When these adhesive rubber materials have a high viscosity, a suitable solvent may be added and applied as a solvent to the high hardness particles.

Furthermore, it is also extremely effective to coat the high hardness particles with a resin. In this case, the resins include styrene-butadiene resin, polyester, hydroxide polyester, polyether polyol, polycaprolactone-polyol, hydroxide polyester-polyisocyanate, epoxy resin, acrylic resin, ethylene-vinyl acetate, phenolic resin, tolylene resin, Effective examples include isocyanate, glycidyl ether of bisphenol A, polysiloxane, silicone resin, PVA (polyvinyl alcohol), PMMA (polymethyl methacrylate), polyvinyl acetate, polyacrylic acid, pitch, methyl methacrylate, and styrene.

In addition, it is also effective to coat the surface of the highly hard particles with a resin having shape memory properties such as polynorbornene thermoplastic rubber. These resins can be used at low temperatures (
It firmly fixes high-hardness particles at high temperatures (freezing temperature), and softens at high temperatures and becomes compatible with the matrix rubber material, resulting in a significant improvement effect. Furthermore, surface treatment of high-hardness particles with a silane-based, titanate-based, chromium-based, or aluminum-based coupling agent, polyalkylene oxide, or the like is also effective in improving adhesion to the matrix rubber material.

When coating inorganic high-hardness particles with an adhesive rubber material or resin as described above, in order to form a co-crosslink with the matrix rubber, the adhesive rubber or resin is coated with a vulcanization accelerator commonly used in rubber compositions. Further improvement in affinity can be expected by incorporating agents. Note that the above-mentioned various treatment methods may be performed alone or in combination of two or more types, that is, a coating layer may be formed using two or more types of materials.

[0026] The material of the inorganic high-hardness particles is not limited in any way as long as it satisfies the above-mentioned hardness and average particle size, but specifically Al2O3, ZnO, TiO2,
Ceramics such as SiC, Si, C, SiO2, ferrite, zirconia, MgO, Fe, Co, Al,
Metals such as Ca, Mg, Na, Cu, Cr, alloys made of these metals, brass, stainless steel, etc., as well as nitrides, oxides, hydroxides, carbonates, silicates, sulfates of these metals, Others include glass, carbon, carbon random, mica, zeolite, kaolin, asbestos,
Examples include montmorillonite, bentonite, graphite, and silica, which are used in the present invention after being subjected to the above-mentioned affinity improvement treatment.

Particularly preferable combinations of inorganic high-hardness particles and surface treatment include plasma-treated mesoface carbon, a carbonaceous powder obtained by heat-treating coal tar pitch, and quartz powder or alumina with styrene-butadiene resin. Examples include those surface-treated with a triazine-based vulcanization accelerator.

In the present invention, one type of high-hardness particles subjected to such surface treatment may be used alone, or two types of high-hardness particles having different materials, particle sizes, hardnesses, surface treatments, etc. may be used. The above may be combined.

[0029] By combining a high hardness resin that satisfies the above conditions with the above-mentioned foamed rubber, more stable performance on ice can be obtained from ice at around 0°C to extremely low temperature ice.

By gradually increasing the foaming ratio of the matrix rubber from the tread surface layer toward the innermost layer, the on-ice performance of the matrix rubber itself can be gradually increased toward the innermost layer, but on the other hand, the rigidity decreases. . By balancing this phenomenon with the hardening of the rubber over time, the increase in rigidity due to the decrease in groove depth, and the decrease in performance on ice,
It is possible to improve on-ice performance to be more stable until complete wear occurs. In other words, the innermost foamed rubber layer of the tread is 0.5 to 1.5mm from the surface in contact with the non-foamed rubber.
This improvement objective can be achieved by setting the average expansion ratio within the range of 1 mm higher than the average expansion ratio of the foamed rubber layer within 1 mm from the tread surface, and it is particularly preferable if the difference is 2% or more. Such control of the expansion ratio is possible by appropriately selecting the temperature on the tire mold side and the temperature on the bladder side during vulcanization.

[0031] There are no particular restrictions on the blending of the matrix rubber, and general rubber compositions can be used. That is, it is possible to use a rubber composition in which various fillers, oils, vulcanizing agents, etc. are appropriately blended with the rubber component, but it is necessary to set the hardness at low temperatures to be low to increase the actual contact area with ice.
The elastic modulus (E') at room temperature is 3 x 107 to 20 x 107 d, in order to obtain a scratching effect near ℃ and to balance other performances such as wear resistance and handling stability.
It is preferable to set it within yn/cm2.

[0032] This E' is determined by the vulcanization condition of 160°C x 1
Width 5mm cut from a 5 minute gauge 2mm slab sheet
A sample with a length of 20 mm was measured using a spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the conditions of an initial load of 150 g, a dynamic strain of 2%, a frequency of 50 Hz, and a set temperature of 25°C.

[0033]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Table 1 below summarizes the characteristics of the inorganic high hardness particles used in the Examples and Comparative Examples of the present invention.

[0034]

[Table 1]

In the table, A and B are both quartz powder resins, but while A is untreated, B is treated with a resin and a vulcanization accelerator to improve its affinity with rubber. A was used as a comparative example, and B was used as an example. C is a mesoface carbon produced from quartz that was subjected to plasma treatment, and D is a carbon that was subjected to the same treatment as alumina B, and both were used as examples. E to G are particles that do not meet the requirements of the present invention in terms of hardness or particle size, and were used as comparative examples.

Tables 2 and 3 show the formulation of the foamed rubber matrix combined with the inorganic high hardness particles shown in Table 1 (
(parts by weight), the vulcanized physical properties of the resulting particle-containing foamed rubber, and the tire performance when the foamed rubber is applied to a tire tread. Specifically, in Table 2, changes in the presence or absence of affinity improvement treatment, particle hardness, and type of blowing agent were investigated, and in Table 3, changes in particle blending amount, particle size, and expansion ratio were investigated.

[0037]

[Table 2]

[0038]

[Table 3]

The following was confirmed from Tables 2 and 3. Similar to Comparative Example 1, which contained only foamed rubber with no high-hardness particles mixed in, Comparative Example 2, which contained Particle A that had not been treated to improve its affinity with rubber, showed no improvement in on-ice performance. The same was true for Comparative Example 3 in which particles E having a Mohs hardness of less than 1.5 degrees were blended.

On the other hand, in Examples 1 to 3 using particles B, C, and D that were treated to improve their affinity with rubber, -2
In addition to the effect of improving the on-ice braking performance index at °C, the improvement effect is particularly remarkable at -10 °C, which is highly dependent on the scratching effect. In Examples 4 and 5, the type of blowing agent was
Further, in Example 6, the formulation of the matrix rubber was changed, and the performance on ice was improved in both cases compared to Comparative Example 1.

Next, in Comparative Example 4 shown in Table 3, no inorganic particles are mixed in, whereas in Comparative Example 5, suitable high hardness particles are blended, but the blended amount is less than 3 parts by weight. Therefore, the particle appearance rate (total particle surface area per 1 cm2 of tread surface area m) that correlates with the scratching effect on ice
m2) has not reached the 1.6% required to improve on-ice performance.

On the other hand, in Examples 7, 8, 9 and Comparative Example 6, when the particle appearance rate was 1.6% or more, the particle appearance rate increased proportionally as the amount of particles added increased, and the performance on ice also decreased. Improvements are observed in correlation with this. However, Comparative Example 6 was unsuitable for practical use because the particle content exceeded 30 parts by weight, which caused groove bottom cracks and a significant drop in wear resistance.

The amount of particles in Comparative Example 11 is the same as that in Example 8, but since the particles in Comparative Example 11 were not treated to improve their affinity with rubber, most of them separated from the matrix rubber and particles appeared. The rate reached 1.6%, and no improvement in on-ice performance was observed. In this way, it can be seen that the particle appearance rate correlates with the amount of particles blended and the affinity with the rubber, and correlates well with the performance on ice.

[0044] The particles used in Comparative Example 7 had an average particle size of 10 μm.
Since the particles were too small (less than m), no improvement effect on on-ice performance was observed, and the particles used in Comparative Example 8 were too large in particle size, so there were problems with groove bottom cracks and wear resistance.

In Comparative Examples 9 and 10, the foaming ratio was investigated. Comparative Example 9 had a foaming ratio of less than 3%, and the effect of improving performance on ice was significantly inferior to that of Example 8, which had a foaming ratio of 20%. On the other hand, Comparative Example 10, in which the expansion ratio exceeded 35%, had problems with groove bottom cracks and wear resistance, and could not be put to practical use.

Table 4 shows how the foaming ratio of the matrix rubber is gradually increased from the tread surface toward the innermost layer, and how this gradual increase suppresses the deterioration of the on-ice performance until the tread is completely worn out.

[0047]

In Examples 10 and 11, the average expansion ratio of the innermost layer of the tread was equal to or smaller than that of the surface layer of the tire, which was cured with the mold side temperature higher than the bladder side temperature, so that the tread did not wear completely. A decline in on-ice performance was seen.

On the other hand, in Example 12, by making the vulcanization temperature on the mold side and the bladder side the same, the foaming ratio of the innermost layer was about 2% larger than that of the surface layer, and as a result, the performance on ice was improved. The decline was suppressed. In addition, in Example 13, by raising the vulcanization temperature on the bladder side than on the mold side, the difference in average foaming ratio between 1 mm of the innermost layer and 1 mm of the surface layer expanded to 6%, and as a result, complete wear occurred. The deterioration in on-ice performance has completely disappeared. Therefore, by changing the vulcanization conditions in combination with foaming, it becomes possible to freely control the balance of on-ice performance in the early and late stages of running.

[0050]

Effects of the Invention As detailed above, a pneumatic tire using a tread combining a foamed rubber matrix according to the present invention and inorganic high hardness particles treated to improve compatibility with the foamed rubber matrix can be used under all conditions of use. A remarkable improvement effect was observed in the on-ice performance, and the wear resistance and groove bottom cracks were within the range of no practical problems.

Claims (2)

[Claims] Claim 1: Inorganic high hardness particles with a Mohs hardness of 1.5 degrees or more, an average particle size of 10 to 400 μm, and whose surface has been treated to improve affinity with rubber, per 100 parts by weight of rubber. 1. A pneumatic tire, characterized in that the tread is equipped with foamed rubber containing 3 to 30 parts by weight of closed cells with an expansion ratio of 3 to 35%. 2. A layer in which the average expansion ratio of the foamed rubber layer located within 1 mm from the surface of the tread is within a range of 0.5 to 1.5 mm from the surface of the innermost layer of the foamed rubber that is in contact with the non-foamed rubber. The pneumatic tire according to claim 1, which has a smaller average expansion ratio than the average expansion ratio.