JPH04176707A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve the frictional force on an ice snow road by constituting a tread part having a specific value of the average gas foam area of the surface from a specific kind of foamed rubber and polyamide group short fibers and arranging the polyamide group short fibers on the block surface and side surface of the tread part in a foamed rubber. CONSTITUTION:A tread part 13 is constituted of a polymer having a glass transition temperature from -60 to -20 deg.C, foamed rubber which has independent gas foams and contains the urethane group assisting agent having at most the equal quantity to the foaming agent compounding quantity and polyamide group short fibers 17 having a number average molecular weight of 5,000 or more. At this time, the polyamide short fibers 17 are arranged along the obverse surface (a) and side surface (b) of the block 16 of the tread part 13. The average gas foam area of a tread surface 10 is set to 100-5,000mum<2>, and the variation coefficient of each gas foam area is set to 0.5-0.8, and the gas foam occupation area rate is set to 1-4%.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to: - reducing frictional force (braking performance, driving performance) on icy roads, especially on ice, without impairing running performance on shipping routes (dry roads, wet roads); This invention relates to a pneumatic tire with improved frictional force and all-weather performance.

[Conventional technology]

Conventionally, when driving a car in winter in a snowy and cold region, safety on snowy and icy roads is ensured by using spiked tires with spikes driven into the tires or by attaching tire chains to the outer circumference of the tires. There is. However, tires equipped with spiked tires or tire chains are susceptible to road wear and damage, which becomes dust and causes pollution, posing a major environmental problem.

In order to solve these safety and environmental problems, studless tires that have braking and driving performance on snowy and icy roads without the use of spikes or chains are rapidly becoming popular.

As this studless tire, a tire using foamed rubber having closed cells in the tread portion is, for example,
It is disclosed in Japanese Patent Application Laid-open No. 2-283001 and Japanese Patent Application Laid-Open No. 63-90402. However, although these tires have good frictional force on icy and snowy roads, the hardness of the foamed rubber is low, so the edge effect and drainage effect of closed cells are insufficient, resulting in poor wear resistance and poor friction on ordinary roads (dry roads). There is a problem in that the driving performance on roads (roads, wet roads) is reduced.

In order to solve these problems, we conducted a thorough study on the development of frictional force in rubber on icy and snowy roads, and found that the frictional force of rubber on icy and snowy roads is due to the excavation frictional force caused by the edges of the rubber blocks and the frictional force caused by the rubber coming into contact with the ice surface. It was found that the adhesive friction force generated was the main cause. Therefore, it is desirable to have a rubber compound that makes maximum use of both of these two frictional forces.
In order to increase the edge effect, it is necessary to increase the rigidity of the rubber block in the tire circumferential direction to some extent, while in order to increase the adhesion force, it is necessary to decrease the rigidity in the direction perpendicular to the water surface, that is, in the radial direction of the rubber block.

Japanese Unexamined Patent Publication No. 63-89547 proposes adding short fibers to foamed rubber to increase the hardness of the tread portion to improve running performance on general roads. However, in this case, because the short fibers are randomly mixed into the foamed rubber, the block rigidity of the tread increases uniformly, and the block rigidity in the tire circumferential direction is greater than the block rigidity in the tire radial direction. Therefore, the so-called adhesion effect (the tread surface attaching to the ice surface and following the surface shape of the ice surface) does not occur. For this reason, there is a drawback that the frictional force on ice is not improved.

Furthermore, studless tires have poor handling performance on ordinary roads (dry roads, wet roads), and it has been found that the main reason for this is related to the glass transition temperature (Tg) of the polymer used. That is, since it is important that polymers used in tread compounds for studless tires do not lose their rubber elasticity even at low temperatures, it is thought that they need to have a low Tg. For this, for example, natural rubber (
NR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber with low styrene content (SBR)
etc. are commonly used as polymers for studless tires.

On the other hand, the frictional force of rubber on a dry or wet road is 0.
It largely depends on the loss tangent of the rubber near °C.
For this purpose, it is preferable to use a polymer whose viscoelastic temperature-dependent transition region is around 0° C., that is, a polymer with a high Tg.

Therefore, for high-performance tires that emphasize grip,
High styrene content SBR with high Tg is used.

Since the required items regarding the Tg of the polymer are different in this way, there is no tread compound that can achieve both grip power on ice and snow and grip power on dry and wet roads.

As described above, it is currently not possible to obtain a tire that satisfies not only ice and snow performance (frictional force on ice and snow roads) but also wear resistance and driving performance on ordinary roads.

However, there is a limit to the fiber length of the short fibers that are blended into this tread rubber, and when the fiber length of the short fibers becomes long, it becomes difficult to uniformly disperse them in the tread rubber, making it difficult to create a tread rubber composition with good processability. However, if the fiber length of the short fibers was too short, the orientation during extrusion molding would be insufficient, and the ice and snow performance could not be sufficiently improved.

[Problem to be solved by the invention]

An object of the present invention is to provide a pneumatic tire that has improved frictional force on icy and snowy roads without impairing running performance on dry or wet road surfaces.

[Means to solve the problem]

The pneumatic tire of the present invention has a tread portion made of foamed rubber having closed cells and a number average molecular weight of s, oo.

The foamed rubber contains a polymer having a glass transition temperature of -60°C to -20°C and a urea-based auxiliary agent in an amount less than the same amount as the amount of the blowing agent. , and the average bubble area on the surface of the tore nod is 1
00 to 5000 μm2, the coefficient of variation of each bubble area on the tread surface is 0.5 to 0.8, and the bubble occupation area ratio on the tread surface is 1% to 4%, and most of the polyamide short fibers are In the foamed rubber, the tread part is
It is characterized by being oriented along the surface and sides.

The present invention is a rubber compounded with short fibers in which when the short fibers blended into the rubber are arranged in one direction, the elastic modulus in the direction parallel to the arrangement increases, and the elastic modulus in the direction perpendicular to the arrangement hardly changes. This method takes advantage of the anisotropy of . That is, as the short fiber compounded rubber constituting the tread block, a compound rubber compounded with polyamide short fibers having a number average molecular weight of 5,000 or more is used, and by arranging the fibers parallel to the surface of the block, the tread block surface is By reducing the stiffness in the direction perpendicular to the road surface and increasing the stiffness in the direction parallel to the surface, this increases the circumferential stiffness of the tread block and increases its edge effect, while at the same time increasing the stiffness of the block in the direction perpendicular to the road surface. By lowering the radial rigidity, it is possible to improve the frictional force against the ice surface, the so-called adhesion frictional force.

In addition, polymers for the tread compound of standless tires include NR with a Tg of -60°C or less that can exhibit sufficient rubber elasticity even at low temperatures, BRl with a high cis bond component, or SBR with a low styrene content. It is widely used (Japanese Patent Application Laid-open Nos. 62-283001 and 63-90402). However, it is not preferable for the Tg to be too low for the tire's maneuverability on dry roads or rough roads. In other words, in order to improve the dynamic performance of tires, it is important to increase the frictional force with the road surface by increasing the hysteresis loss of the tread rubber, but the vibration frequency of the rubber during friction reaches several thousand hertz. Therefore, a high hysteresis loss can be achieved by increasing the loss tangent of about 10 Hz at a temperature several tens of degrees lower than the rubber temperature. In fact, tan δ at 0° C. is maximum in the viscoelastic temperature-dependent transition region of the loss tangent of the polymer region, which shows a good correlation with the braking friction force of the tire. The transition region generally has a temperature range of about 30°C on the high temperature side starting from the glass transition temperature, so if 0°C is included within this range, the loss tangent of the polymer will increase. Therefore, a polymer with a high Tg is good for driving performance on dry and wet roads, but since it is used at temperatures close to Tg on icy and snowy roads, it loses its rubber elasticity and hardens, resulting in less frictional force on ice and snow. The problem is that it is not.

Therefore, in order to prevent such a high Tg polymer from curing at low temperatures and maintain rubber elasticity, it is effective to include bubbles in the polymer, that is, to use foamed rubber.

Even if the amount of bubbles is extremely small, if a polymer with a high Tg is contained, the rubber elasticity will not be lost even at relatively low temperatures, and the performance necessary for a studless tire can be obtained.

For tires intended for all-weather performance, it is necessary to increase the block rigidity of the tread, but foamed rubber alone cannot maintain rigidity at high temperatures. Only by controlling the stiffness anisotropy can it be possible to use compounds with low elastic modulus.

This means will be explained in detail below with reference to the drawings.

FIG. 1 is an explanatory half-sectional view in the meridian direction of an example of the pneumatic tire of the present invention. In FIG. 1, the pneumatic tire A of the present invention includes a pair of left and right bead portions IL 11, a pair of left and right sidewall portions 12.12 connected to these bead portions IL 11, and these sidewall portions 12.12.
It consists of a tread section 13 arranged between the two. A carcass layer 14 is installed between the pair of left and right bead portions 11.11, and a belt layer 15 is arranged to surround the outer periphery of the carcass layer 14 in the tread portion 13. 10 is the tread surface.

The constituent elements of the present invention will be explained in detail below.

(1) In the present invention, the tread portion 13 is composed of foamed rubber having closed cells and short polyamide fibers having a number average molecular weight of 5,000 or more. This foam rubber has a Tg of 160
It contains a polymer having a temperature of .degree. C. to -20.degree. C. and a urea-based auxiliary agent in an amount less than the same amount as the amount of blowing agent blended.

In order to improve grip on dry and wet roads, a polymer with a Tg of 160°C or higher is required.

Furthermore, if the Tg exceeds 120° C., it will become too hard even at room temperature, and the grip strength will actually decrease. Examples of polymers whose Tg falls within the range of -20°C include SBR with a high styrene content, SBR with a high vinyl content in butadiene, BR with a large vinyl content,
Examples include butyl rubber. The blending amount of these polymers is preferably 30 to 70 parts by weight based on 100 parts by weight of the total rubber content. If it is less than 30 parts by weight, performance on dry roads and wet roads will be poor, and 70! This is because if the temperature exceeds the amount, hardening occurs at low temperatures, resulting in insufficient grip on icy and snowy roads. the remaining 7
For 0 to 30 parts by weight, a diene rubber having a Tg of less than 160°C, such as NR, BR1 with a large cis component, and SBR with a low styrene content may be used.

Furthermore, in the present invention, foamed rubber with relatively high hardness is used for the tread portion 13 in order to improve the frictional force on icy and snowy road surfaces. In other words, the closed cells contained in foam rubber improve the edge effect and drainage effect, especially at 0°C.
It has a surprising effect on ice where there is a pseudo-liquid layer nearby. Furthermore, the conventional concept of improving ice and snow friction with low hardness at low temperatures does not apply to foamed rubber; in fact, making it a certain degree of hardness can significantly improve the edge effect and drainage effect brought about by closed cells in contact with the road surface. can. Furthermore, by making the hardness relatively high,
The block rigidity is improved, making it possible to maintain a high level of driving performance on general roads (dry roads and wet roads), which has been a weak point of conventional winter tires.

However, since the hardness of foamed rubber is significantly lower than that of non-foamed rubber, normally, in order to increase the hardness of foamed rubber, the hardness of the matrix rubber is significantly increased. - For boat fishing, adjustments are made such as significantly increasing the amount of reinforcing agents such as carbon blank, or significantly reducing the amount of softening agents such as oil, but this is not desirable as it will worsen workability and heat generation. . Therefore, in order to lower the decomposition temperature of the blowing agent,
As a result of our research focusing on the fact that urea-based auxiliary agents used in combination with foaming agents increase crosslink density, we found that adding urea-based auxiliary agents alone to a rubber composition increases hardness, but when combined with foaming agents, hardness increases. It was found that the effect was even greater when used in combination.

In other words, by blending a specific amount of urea-based auxiliary agent into the foaming agent, it is possible to suppress the decrease in hardness due to foaming and achieve a hardness comparable to that of non-foamed rubber, while also having a negative impact on processability, heat generation, etc. It is also 1i1 that it does not affect you! It has been certified. Furthermore, if a nitroso compound is selected as a blowing agent, formaldehyde will be generated during the decomposition reaction and give a strong irritating odor, so in this case as well, it is important to incorporate a urea-based auxiliary agent that accepts aldehyde. It is very effective from this point of view.

In the case of uniform rubber inside, it is difficult to increase the frictional force of these air bubbles against the waterway surface and at the same time increase the edge effect of the tire tread block.In order to increase the edge effect, the circumferential rigidity of the block must be increased to a certain degree. Of course, in order to improve the so-called adhesive friction force, it is necessary to lower the radial rigidity of the block in the direction perpendicular to the road surface.

To this end, the present invention aims to improve the anisotropy of the rubber compounded with short fibers, that is, by arranging the short fibers mixed in the rubber in one direction, the modulus of elasticity in the direction perpendicular to the direction of arrangement is almost unchanged. However, this method utilizes the fact that the elastic modulus in the direction parallel to the arrangement direction is increased. In other words, by controlling the short fiber orientation direction of the short fiber compound rubber and arranging the fibers parallel to the surface of the rubber block, the stiffness in the direction perpendicular to the block surface is reduced, while the stiffness in the direction parallel to the surface is increased. Only then can the wedge effect and adhesive friction force be maximized.

In the present invention, the foamed rubber is made of a rubber composition containing a foaming agent and a urea-based auxiliary agent in an amount less than the same amount as the foaming agent. The amount of urea-based auxiliary agent is 30 to 9% of the blowing agent.
It is preferable to blend within the range of 0% by weight. If a urea-based auxiliary agent is not added, the hardness of foamed rubber will be significantly lower than that of non-foamed rubber, so it is necessary to significantly increase the amount of reinforcing agents such as carbon black or significantly reduce the amount of softeners such as oil. Adjustment is required, and processability and heat generation properties deteriorate. Moreover, when a blowing agent with a high decomposition temperature is used, it becomes difficult to manufacture tires at normal vulcanization temperatures.

In addition, if a urea-based auxiliary agent is added in an amount equal to or more than the amount of blowing agent, the effect of suppressing the decrease in hardness due to foaming becomes saturated, making it uneconomical, and depending on the blowing agent, the decomposition temperature may drop too much, resulting in , there is a risk that unvulcanized rubber may foam during the extrusion process.

In order to construct the tread portion of a pneumatic tire in the present invention with foamed rubber having closed cells, a foaming agent and a urea-based auxiliary agent are added to the rubber composition used for the tread portion, and vulcanization is performed using a normal tire manufacturing method. It depends on what you do. As the blowing agent in this case, any organic or inorganic blowing agent can be selected. For example, organic blowing agents include benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, azudicarbonamide, etc., and inorganic blowing agents include sodium bicarbonate, ammonium carbonate, ammonium nitrite, and are not particularly limited. As the urea-based auxiliary agent, a compound of urea and an anti-aggregation agent, an acidic substance for preventing moisture absorption, etc., or urea alone is used. Specifically, for example, Hydration Kasei Kogyo's Cellupace) M3
(urea + acidic substance), cell paste 5 (urea + acidic substance), and cell paste 101 (urea + anti-aggregation agent). In addition, compounding agents such as carbon black, softeners, processing aids, anti-aging agents, waxes, vulcanizing agents, and vulcanization accelerators may be added in appropriate amounts according to the practices in the industry. However, in order to obtain the tire of the present invention, the blowing agent is preferably blended in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the raw rubber. Furthermore, as a method to improve performance on ice and snow roads, and on sea routes, it is possible to further improve these performances by introducing a two-layer or three-layer tread structure such as the camp tread rubber/heath tread rubber structure. Therefore, it is preferable.

(2) The short fibers are polyamide short fibers with a number average molecular weight of 5,000 or more.

When the dispersibility of short fibers in tread rubber improves, the stability and processability of the tread rubber composition containing short fibers improves. The dispersibility of these short fibers into rubber increases as the average length of the short fibers increases or as their average diameter decreases, the fibers become more likely to become entangled with each other, forming clumps and dispersing uniformly. I can't. However, if the average length of the short fibers becomes too short, the orientation of the short fibers during extrusion will deteriorate. For this reason, it was common to use short fibers with an average diameter of 1 to 10 μm and an average length of 5,000 μm or less. In the present invention, the short fibers are made of polyamide with a number average molecular weight of 5.000 or more. By using short fibers, it is possible to obtain a Tore-Rad rubber composition that has improved dispersibility in the tread rubber and improved orientation during extrusion molding.

Therefore, in the present invention, the short fibers have a shorter average length and a smaller average diameter, preferably within the range of an average length of 1 to 100 μm, an average diameter of 0.05 to 0.8 μm, and silane coupling. It is best to use one whose surface has been treated with a chemical agent.

Moreover, it is even more preferable that the short fibers have a melting point within the range of 150 to 260°C. When the number average molecular weight is less than the specified value, the fiber forming ability of the polyamide is poor (and the orientation is decreased due to low strength).

Polyamide staple fibers include nylon 6° and nylon 6.
Nylon such as 6.6 and nylon 610 can be used as an example. In addition, as a silane coupling agent,
T-aminopropyltrimethoxysilane can be cited as a representative example.

The polyamide short fibers surface-treated with this silane coupling agent are not directly blended into the tread rubber, but are added at a concentration of 5 to 100 parts by weight per 100 parts by weight of rubber components such as natural rubber.
It is preferable to prepare a masterbatch containing part by weight of the polyamide short fibers and blend the masterbatch into tread rubber. These short polyamide fibers are uniformly dispersed in a masterbatch, and are also uniformly dispersed when this masterbatch is blended into tread rubber. Moreover, they can be easily oriented by extrusion molding and exhibit anisotropy. .

In the present invention, when the polyamide short fibers have a non-circular cross-sectional shape such as flat, triangular or multi-lobed, the average diameter thereof refers to the total average value of the maximum diameter and the minimum diameter. Furthermore, the ratio of the average length l to the average diameter of the short fibers is 1/D
is preferably within the range of 10 to 1000.

(3) Most of the short polyamide fibers are oriented along the protrusion surface and side surfaces of the tread portion 13 in the foamed rubber.

The orientation of short polyamide fibers having a number average molecular weight of 5,000 is shown in FIGS. 2 and 3. FIG. 2 is an explanatory plan view of the tread and throat portion of an example of the pneumatic tire of the present invention, and FIG. 3 is a cross-sectional view taken along the line -2. Figures 2 and 3
As shown in the figure, the short fibers 17
Along the surface a and side surface of the hook 16 in the tire circumferential direction E
E' is oriented.

In order to obtain such orientation of the short fibers, the fact that short fibers having a certain length/diameter ratio tend to line up in the flow direction of the rubber, which is the matrices, is utilized. Such a tendency is also observed when the unvulcanized tread rubber flows along the mold due to the protrusions of the mold when the tire is vulcanized, resulting in short fibers being oriented along the mold protrusions and forming the tread. It will be oriented along the surface and sides of the block.

Blocks with short fibers oriented on the surface and sides have extremely high rigidity as a whole, but the elastic modulus is anisotropic in that the elastic modulus in the direction perpendicular to the orientation direction, that is, from the surface to the inside, is not so high. express sexuality. Because of the anisotropy of the elastic modulus of the block, it is possible to maintain steering stability at high temperatures in summer even when foamed rubber with low elasticity is used as in the present invention.

By orienting the polyamide short fibers along the surface and side surfaces of the tread block in this way, the rigidity of the tread block in the tire circumferential direction can be made larger than the tire radial direction rigidity. Therefore, an adhesion effect occurs and the frictional force on the ice improves.

(4) Average bubble area on the tread surface is 100 to 5ooo
Must be μ112.

The average cell area of foamed rubber is 100 to 5000 μl11
2 closed cells, preferably 50
It is 0 to 3000 μm2. If it is less than 100 p m", the improvement effect on ice and snow road performance is insufficient, and if it is less than 5000 μl1
This is because if it exceeds 12, wear resistance and running performance on ordinary roads will be significantly reduced.

(5) The coefficient of variation of each bubble area on the tread surface is 0.5~
Must be 0.8.

As a result of investigating the shape and distribution of bubbles, it was found that the bubble distribution has a narrow distribution width, and that by optimizing the bubble shape and occupied area ratio, it is possible to simultaneously satisfy snow and ice road performance and -ship road performance. by.

Here, the coefficient of variation (K) of closed cells is determined according to the following formula.

K = S / is necessary. When this coefficient of variation (K) is less than 0.5, the performance on ice and snow roads and on ordinary roads deteriorates due to a decrease in the edge effect of air bubbles, and when it exceeds 0.8, the performance on ice and snow decreases due to a decrease in the drainage effect of air bubbles.

(6) The air bubble occupation area ratio on the tread surface is 1% to 4%.

The bubble occupation area ratio (foaming ratio) is preferably higher for snow and ice performance, and is 10% to 20% when used as a standless tire. However, when a tire having such a bubble occupation area ratio runs on a dry road surface, it wears out extremely quickly, and especially on a dry road surface in spring and summer, the tire wears out so fast that it can hardly be used. Although this is acceptable for a studless tire that is intended to be used only on snowy and icy roads in the winter, it is unacceptable for a tire with all-weather performance, and it cannot be improved by changing the composition such as the amount of carbon blank. The reason why a tread with a high bubble area ratio has excellent grip on ice and snow is that when the surface wears, internal air bubbles come out to the surface, which increases the roughness of the surface that comes into contact with ice and snow, and this roughness creates a water film on the ice and snow surface. This is due to the fact that the actual contact area increases.

On the other hand, when the purpose is to foam rubber so that the high Tg polymer does not lose its rubber elasticity even at low temperatures, as in the present invention, a low cell occupation area ratio may be sufficient; It appears even at an area ratio of 1%. Anything less than that is hardly considered to be effective.

Furthermore, if the bubble occupation area ratio exceeds 4%, wear on dry road surfaces will be extremely rapid, making it impossible to put it into practical use.

〔Example〕

Examples, Conventional Examples, and Comparative Examples 1 to 5 Various tires with a tire size of 185/70 R1385Q whose tread portions were configured with the formulation contents (parts by weight) shown in the table were prepared, and these Examples, Conventional Examples, and Comparative Examples 1 were prepared. The following evaluations were made for each of the seven types of tires listed below. The results are shown in the table.

The test vehicle used was a 1600cc FF vehicle.

...-4r ゛, 4' 1. Kei Pa: A test piece was cut from the tread part of each test tire, and after making it a flat surface, it was image-processed at 165x using a NEXUS 6400 manufactured by Aiki Research Institute. The average value of 10 samples was used for evaluation.

2 above: The vehicle was run on a water basin at an initial speed of 30 km/h, and the braking distance was measured and expressed as an index with the conventional tire (conventional example) set as 100. The larger the value, the better the braking.

J'4'' on tatami A passenger car was repeatedly braked on a 5% (2.9°) slope of a 5% (2.9°) slope on a smooth, compacted snow road surface by repeatedly braking with a passenger car. The pitching acceleration time was measured and expressed as an index compared to conventional tires. The larger the value, the better the drive performance.

A scolding at 'flI.

The tires were driven at an initial speed of 40 km/h on a water-sprayed asphalt road surface, and the braking distance was measured when the tires were braked.
It was expressed as an index as 0. The larger the value, the better the braking.

( ): After running 20,000 km on a dry road surface under the conditions of design regular load and air pressure specified by JATMA, the amount of wear of each tire was expressed as an index relative to the amount of wear of conventional tires.

The larger the value, the better the wear resistance.

・Young'(Block's Heart., 1.l) (MP
a): Samples were cut from the center and surface of the block from the tread part of each test tire in the radial direction relative to the tire rotational axis, and measured using a viscoelastic spectrometer manufactured by Toyo Seiki ■, with a length between chucks of 20n, A sample with a width of 5fi and a thickness of 2 days was tested at a frequency of 20Hz, an initial strain of 10%, a dynamic strain of ±2%,
Measurement was performed at a temperature of 0°C. The larger the value, the greater the rigidity.

(Margins below this page) Note: Styrene content: 14.1% by weight, vinyl content in butadiene portion: 30% by weight, Tg -56°C.

*2 Cis component 98%, Tg-103°C.

*3 Short fibers C: carbon short fibers, average length 5 μm, average diameter 1 μm0 Rate 4 short fibers F: surface treated with γ-aminopropyltrimethoxysilane, average length 30 μm, average diameter 0.3 μm
Master Hatch (Ube Industries ■), which contains 50 parts by weight of nylon 6 short fibers of 50% by weight per 100 parts by weight of natural rubber (NR).
Manufactured by UBE-FRR/NR) Hon 5 short fiber G...Aramid short fiber, average length 4,00
0 μm, average diameter 5 μm.

Umbrella 6 Foaming agent: dinitrosopentamethylenetetramine (Cellular D manufactured by Eiwa Kasei Kogyo ■).

N7 Urea-based auxiliary agent...Urea compound (5 in cell paste manufactured by Hydraulic Chemical Industry ■).

In the above table, the conventional example is a conventional studless tire, which does not contain foamed rubber and short fibers.

The example is a tire containing the foamed rubber and short polyamide fibers of the present invention, which can achieve both ice and snow performance and general performance.

Comparative Example 1 is a tire in which the foaming rate of the foamed rubber is increased in Example, and the area occupied by the bubbles on the tread surface is outside the range of the present invention, and the ice and snow performance and braking performance on wet road surfaces are good. It has very poor wear resistance and is not practical.

Comparative Example 2 is a tire in which the foamed rubber contains short nylon 6 fibers and uses a polymer with a low Tg, and has good ice and snow performance but poor performance on general roads.

In Comparative Example 4, the foamed rubber contained short aramid fibers, but the tire performance remained the same as in the conventional example, and the mixing processability was significantly reduced, making it practically impossible.

Comparative Example 3 is a tire containing short carbon fibers,
Ice and snow performance is not improved because the short fibers are randomly oriented in the rubber and the elastic modulus of the center and surface areas of the tread block are approximately the same.

〔Effect of the invention〕

As explained above, according to the present invention, the tread portion that comes into contact with the road surface is prepared by blending a specific proportion of a foaming agent and a urea-based auxiliary agent, as well as a polymer having a Tg of 160°C to -20°C. Foamed rubber with closed cells and number average molecular weight 5
,000 or more polyamide-based short fibers that are easily oriented by extrusion molding, the average cell area on the tread surface, the cell coefficient of variation, and the cell occupied area ratio are set within a specific range, and the short fibers are added to the tread part in foamed rubber. Since it is oriented along the block surface and side surfaces of the blocks, it is possible to significantly improve the frictional force on ice and snow roads without impairing running performance on shipping routes (dry roads, wet roads).

[Brief explanation of the drawing]

FIG. 1 is an explanatory half-sectional view in the meridian direction of an example of the pneumatic tire of the present invention, FIG. 2 is an explanatory plan view of the tread portion of an example of the pneumatic tire of the present invention, and FIG. FIG. 10...Tread surface, 11...Bead portion, 12.
...Side wall, 13...Tread section, 14...
- Carcass layer, 15... Heald layer, 16... Block, 17... Short fiber. Agent Patent Attorney Nobuo Ogawa −

Claims (2)

[Claims] (1) The tread portion is composed of foamed rubber having closed cells and short polyamide fibers having a number average molecular weight of 5,000 or more, and the foamed rubber has a glass transition temperature of -60°C to
Contains -20℃ polymer, contains less than the same amount of urea-based auxiliary agent with respect to the amount of foaming agent, and has an average cell area of 100 to 5,000 μm^2 on the tread surface, and the area of each cell on the tread surface. The coefficient of variation of is 0.5 to 0.8, and the bubble occupation area ratio on the tread surface is 1% to 4%,
Furthermore, a pneumatic tire in which most of the short polyamide fibers are oriented along the block surface and side surfaces of the tread portion in the foamed rubber. (2) The pneumatic tire according to claim (1), wherein the short polyamide fibers are surface-treated with a silane coupling agent, have an average diameter of 0.05 to 0.8 μm, and have an average length of 1 to 100 μm. .