JPH04365607A - 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 pneumatic 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 resin which possesses a hardness of ASTM Shore D 40 deg. or more and an average diameter of 10-400mum and forms a polymer allay with rubber or the resin which is conjugation-cross- linked with rubber is 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. The foamed rubber has a certain foaming rate, and the matrix rubber is mixed with a special resin that has a specific hardness and particle size and is compatible with the matrix rubber.By making a certain area of the resin appear on the tread surface, it is more effective than rubber. It was discovered that a scratching effect can be obtained at low temperatures where the surface becomes hard, and that there is no deterioration in wear resistance and fracture properties due to detachment of the mixed resin, and the present invention has been completed.

That is, the pneumatic tire of the present invention has AS
A resin that forms a polymer alloy with rubber or a resin that co-crosslinks with rubber, which has a hardness of 40° or more as measured by TM Shore D and an average particle size of 10 to 400 μm, is added to 3 to 3 parts per 100 parts by weight of rubber. Contains 30 parts by weight, and 3
The tread is characterized by having a tread made of foamed rubber having closed cells with an expansion ratio of ~35%. The area of resin per 1cm2 of surface area of the above tread is all 1.6m
It becomes more than m2.

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 foaming ratio between 1 mm of the tread surface layer is made smaller than the average foaming ratio between 1 mm of the innermost tread layer.

[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),
ρ1 is the density of the foamed rubber (g/cm3), ρo is the density of the solid phase part of the foamed rubber (g/cm3), and ρg is the density of the gas part in the cells of the foamed rubber (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 calculated as follows: VS = {(ρo −ρ1 )−1}×100
(%) -----(2
) is almost equivalent to

At low temperatures, where the hardness of ice is higher than the hardness of rubber, in order to obtain a scratching effect, a resin that satisfies the following conditions is required as a high hardness material to be mixed into foamed rubber. That is, first, the hardness measured by ASTM Shore D is 40° or more. If the angle is less than 40°, a sufficient scratching effect cannot be obtained. The specific ASTM Shore D measurement method was based on JISK7215.

[0018] The average particle size of this resin is 10 to 400 μm.
If the thickness is less than 10 μm, no effect of improving on-ice performance will be observed, while if it exceeds 400 μm, the occurrence of groove bottom cracks will become a problem.

[0019] A high hardness material that satisfies these conditions is a rubber component.
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 resin on the tread surface will be too small even when the lightest resin is assumed, so it will not be effective in improving on-ice performance. I can't see it. In other words, after actually driving straight for 200 km, we measured the total area of resin appearing per 1 cm2 of tread surface area of the test tire using a microscope, and found that tires with a total resin area of 1.6 mm2 or more had sufficient on-ice performance. However, in order to obtain this total area, it is necessary to mix the resin in an amount of 3 parts by weight or more. 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 resin to be mixed forms a polymer alloy with the matrix rubber, or
Or it must be a resin that co-crosslinks with rubber. If it is not such a resin, the resin will separate from the matrix rubber during running, and although it will contribute to the formation of surface irregularities, the desired scratching effect will not be obtained, and the fracture characteristics and wear resistance of the tread rubber will be significantly reduced. do. As such a resin, a resin that directly penetrates into the matrix rubber network to form a polymer alloy or a resin that co-crosslinks with the matrix rubber may be selected, but if it is not such a resin, a co-crosslinkable resin may be selected. It is sufficient to use a material that has been surface-treated with a certain resin or crosslinking agent as appropriate.

[0021] Examples of resins that form polymer alloys as they are include ultra-high molecular weight polyester resins having a molecular weight of 1 million to 10 million, and examples of resins that co-crosslink as they are such as styrene-butadiene resins. On the other hand, polyethylene resins and polyamide resins can be made into polymer alloys by subjecting them to a predetermined heat treatment together with styrene-butadiene (20/80) or the like.

[0022] 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. Note that the high hardness resin used in the present invention is not limited to one type, but can be used in combination of two or more types.

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 layer of the tread is 1mm
This improvement objective can be achieved by setting the average expansion ratio between the tread surface layers to be higher than the average expansion ratio between 1 mm of the tread surface layer, 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.

[0024] 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.

[0025] This E' is the vulcanization condition: 160°C x 1
5 minutes, width 5m cut from a 2mm gauge slab sheet
A sample with a length of 20 mm and a length of 20 mm was measured using a spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under 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.

[0026]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. Table 1 below summarizes the properties of the resins used in the Examples and Comparative Examples of the present invention.

[0027]

[Table 1]

*As the affinity treatment for B, G
For Noryl 731J manufactured by E-Plastics and maleic anhydride-modified styrene-butadiene copolymer (Tuffprene 912 (trade name) (60/40) manufactured by Asahi Kasei Corporation),
A polymer alloy was formed from 1 phr of stearic acid, 1.5 phr of sulfur, and 3 phr of zinc white by co-rotating twin screw extrusion. Affinity processing in F, I and J is
Nylon (Toray, 6-
Nylon amylan CM1021) was coated with a resorcinol-formaldehyde condensate/rubber latex aqueous solution adhesive using a Henschel mixer such as Supermixer. The treatment in D was ultra-high molecular weight polyethylene resin, Asahi Kasei Sunfine U900.
B block copolymer Asaflex 80 60/4
0, 1 stearic acid, 3 ZnO, and 1.5 S were made into a polymer alloy using a twin-screw extruder in the same direction. In the treatment in E, 100 parts of 1,2-polybutadiene were dynamically crosslinked with 1 stearic acid, 3 ZnO 3, and 1.5 S in a co-directional twin-screw extruder. A PCM type extruder manufactured by Ikegai Iron Works was used as the co-directional twin-screw extruder, and the temperature for each treatment was 150°C in the feed section, the temperature at which each resin was sufficiently softened in the kneading section, and 200 - 200°C in the crosslinking section.
It was carried out at a temperature of 20°C.

In the table, A does not form either a polymer alloy or a co-crosslink with the matrix rubber, and is therefore unsuitable as the resin of the present invention. B, D, E and F are resins that co-crosslink with the matrix rubber through affinity treatment. C forms a polymer alloy with the matrix rubber as it is. G and H are resins that co-crosslink with the matrix rubber as they are, but G has a Shore D hardness of 4.
Since it is less than 0°, it cannot be used as the resin of the present invention. I and J each have an average particle diameter of 10 μm
Since it is less than 400 μm or more than 400 μm, it is still inappropriate as the resin of the present invention. K is the same as A,
Since the matrix rubber does not form any polymer alloy or co-crosslinking, it is unsuitable as the resin of the present invention.

Tables 2 and 3 show the formulation (parts by weight) of the foamed rubber matrix combined with the resin shown in Table 1.
In addition, the vulcanized physical properties of the obtained resin-containing foamed rubber and the tire performance when the foamed rubber is applied to a tire tread are shown. Specifically, in Table 2, changes in the type and hardness of the resin and in the type of foaming agent were examined, and in Table 3, changes in the amount of resin blended, particle size, and expansion ratio were examined.

[0031]

[Table 2]

*1 Azodicarbonamide *2
4,4'-oxybisbenzenesulfonyl hydrazide*
3 Dinitrosopentamethylenetetramine *4
Laboratory test vulcanization conditions 167℃×20kg/cm2*
5 Tested with size 165 R13 tires: After driving straight for 200 km, braking at a speed of 20 km/h (the smaller the index, the better)

[0033]

[Table 3]

The following was confirmed from Tables 2 and 3. Similar to Comparative Example 1, which contained only foamed rubber with no resin mixed in, Comparative Example 2, which contained Resin A, which has no affinity with rubber, showed no improvement in on-ice performance, only a decrease in fracture properties and abrasion resistance. was confirmed.

On the other hand, in Examples 1 to 5, in which resins B to F having an affinity for rubber were used, not only the on-ice braking index at -2°C was improved, but also the scratching effect dependence was improved. The improvement effect at high temperatures of -10°C is remarkable. Examples 6 and 7 are examples in which the type of blowing agent is changed, and Example 8 is an example in which the blend of matrix rubber is changed, and the performance on ice is improved in both cases compared to Comparative Example 1.

In Comparative Example 3 and Example 9, a styrene-butadiene resin having co-crosslinking properties with rubber was used;
Since the Shore D hardness of the resin was less than 40°, no improvement was seen in the effectiveness on ice.

Next, in Comparative Example 4 shown in Table 3, no resin was mixed at all, whereas in Comparative Example 5, a suitable resin was blended, but the blended amount was less than 3 parts by weight. It can be seen that the particle appearance rate (total particle surface area mm2 per 1 cm2 tread surface area), which is correlated with the scratching effect on ice, has not reached the 1.6% required to improve on-ice performance.

In contrast, Examples 10, 11, 12
In Comparative Example 6, the particle appearance rate increased in proportion to the increase in the amount of resin blended, and the performance on ice was also improved in correlation with this. However, in Comparative Example 6, since the amount of resin blended exceeded 30 parts by weight, groove bottom cracks occurred and the wear resistance performance deteriorated significantly, so it was not suitable for practical use.

The resin content of Comparative Example 11 is the same as that of Example 11, but since the resin of Comparative Example 11 has no affinity with rubber, most of it separates from the matrix rubber, resulting in a particle appearance rate of 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.

Since the particle size of Resin I used in Comparative Example 7 was too small, no improvement in performance on ice was observed, and in Comparative Example 8
Since the resin J used in the above was too large in particle size, 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 11, which had a foaming ratio of 25%. On the other hand, Comparative Example 10 where the expansion ratio exceeds 35%
had problems with groove bottom cracks and wear resistance, and was not usable for practical use.

Table 4 shows how gradually increasing the foaming ratio of the matrix rubber from the tread surface toward the innermost layer suppresses the deterioration of on-ice performance until complete tread wear.

[0043]

In Examples 13 and 14, 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 can be seen.

On the other hand, in Example 15, by making the vulcanization temperatures 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 16, by raising the vulcanization temperature on the bladder side than on the mold side, the difference in average foaming ratio between the innermost layer 1 mm and the surface layer 1 mm expanded to 6%, and as a result, the temperature on the ice until complete wear was The performance drop has almost 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.

[0046]

Effects of the Invention As detailed above, a pneumatic tire using a tread that combines a foamed rubber matrix according to the present invention and a high-hardness resin that has a high affinity with the foamed rubber matrix has outstanding on-ice performance under all usage conditions. The improvement effect was observed, and the wear resistance and groove bottom cracks were within the range of no practical problems.

Claims (1)

[Claims] Claim 1: 100 parts by weight of a resin that forms a polymer alloy with rubber or a resin that co-crosslinks with rubber and has a hardness measured by ASTM Shore D of 40° or more and an average particle size of 10 to 400 μm. 3-30 against
1. A pneumatic tire characterized in that the tread is provided with foamed rubber having closed cells containing parts by weight and an expansion ratio of 3 to 35%.