JPS6390402A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve resistance to ice and snow without impairing abrasion resisting performance and heat-generation durability by providing a specific foam rubber layer having a defined rate of volume to the whole volume of a tread on a tread surface side. CONSTITUTION:A foam rubber layer 10 having a volume more than 10% of the whole volume of a tread is formed on the surface part 3a of a tread 3. This foam rubber layer 10 has closed cells having a foaming rate of 5-50% and an average foam diameter of 5-150mum, while containing more than 20 per 1mm<2> unit area of closed cells each having a foam diameter of 30-200mum. Also, its dynamic modulus of elasticity is specified to, 3X10<7>-13X10<7>dyn/cm<2>. And, a low temp. softening agent of 2-20pts.wt. is blended with respect to a rubber ingredient of 100pts.wt. By this structure, resistance to ice and snow can be improved without impairing abrasion resistance and heat generation durability.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a pneumatic tire, specifically, a pneumatic tire that has sufficient wear resistance for practical use without impairing summer handling performance and heat generation durability, and that can be used on icy and snowy roads. This invention relates to a pneumatic tire that has significantly improved driving performance, braking performance, and maneuverability.

(Conventional technology and its problems) Conventional pneumatic tires have poor driving performance, braking performance, and maneuverability when driving on icy and snowy roads (hereinafter simply referred to as icy and snowy performance).
To ensure this, spiked tires with spike pins driven into the tread surface are often used. however,
Dust pollution caused by the scattering of these fine powders due to wear of spike pins and road wear, and damage to roads caused by spike pins has become a major social problem. In order to cope with these problems, studies have been made on regulating the amount of protrusion of the spike pins, the number of spike pins, and the material of the spike pins, but these have not fundamentally solved the social problems mentioned above.

On the other hand, tire trends and tread rubber quality have been studied for so-called studless tires that do not use spike bins, but there is a problem in that they cannot achieve the same ice and snow performance as spiked tires. In particular, for the tread rubber, a polymer with a low glass transition point is used to ensure rubber elasticity at low temperatures, and a softener with a low melting point is used to ensure the coefficient of friction with the road surface at low temperatures. Although its use is being considered, it has the problem of insufficient ice and snow performance.

In addition, tires using closed-cell rubber for the tread are disclosed in Japanese Patent Publication No. 40-4641 and US Pat.
P4,249.588 and Special Publication No. 56-15430
This is proposed in Publication No. 4. However,
In Publication No. 4641, synthetic rubber with a large hysteresis loss, such as high styrene rubber, is used in the tread, which increases the glass transition temperature of the rubber, increases the hardness of the rubber at low temperatures, and improves ice and snow performance. Undesirable. Additionally, US P4,249.588 specifies that tread rubber has a compressive property (stress) of 1 to 800 ps i at a temperature of 25°C and a compressive strain of 50%. However, it is not practical in terms of maneuverability unless it is at least 400 ps i. Furthermore, in Japanese Patent Application Laid-Open No. 56-154304, a lightweight tire is made by using foamed rubber to obtain the same hardness as non-foamed rubber, but this does not improve ice and snow performance.

Attempts have also been made to improve the slipperiness on icy and snowy roads by mixing granular materials such as sand, wire mesh sand, carborundum, and metal particles into the tread rubber. However, if a large amount is mixed in, there is a problem that the abrasion properties will be significantly deteriorated.

Additionally, efforts have been made to lower the hardness of trend rubber in order to improve braking performance on ice. In other words, efforts have been made to reduce the amount of reinforcing agent, reduce the crosslinking density of rubber, and increase the amount of oil softener. This causes problems such as permanent deformation, and increasing the amount of oil and softener increases the change in hardness of the rubber during driving and long-term use.

Therefore, an object of the present invention is to solve the problems of the conventional spiked tires and studless tires, and to achieve both ice and snow performance, wear resistance, maneuverability, and heat generation durability of the tire, and to improve the coefficient of friction on ice of the tire. In particular, it is an object of the present invention to provide a pneumatic tire that has an improved coefficient of friction on wet ice at a temperature around 0° C. and is sufficiently durable for practical use.

(Means for Solving the Problems) In order to solve the above problems, the present inventors conducted various studies and found that they used a polymer with a low glass transition point in the rubber layer of the tread, and created closed cells inside the rubber. It has been found that by including the rubber, the hardness of the entire trend rubber, that is, the entire composite of rubber and foam, can be reduced without reducing the crosslink density of the rubber itself. Furthermore, it has been found that by foaming a rubber having a high elastic modulus, an appropriate trend rubber hardness can be obtained due to the softening effect of the foaming gas. In addition, when a small amount of low-temperature softener is used in the tread rubber together with a foaming agent that forms closed cells through vulcanization, the dynamic elastic modulus and internal loss of the tread can be adjusted.
It has also been found that changes in the hardness of the rubber during long-term use can be reduced, thereby increasing the coefficient of friction on wet water surfaces and improving the braking performance, driving performance, and cornering performance of the tire on wet water surfaces. Based on these facts, we also conducted repeated studies from the structural aspect and arrived at the present invention.

That is, the pneumatic tire according to the present invention is a pneumatic tire comprising a tire case and a tread covering the crown portion of the case, in which the tread contains a rubber component of a polymer having a glass transition temperature of -60°C or lower. The tread is provided with a foamed rubber layer having a volume of at least 10% of the total volume of the tread on the front side of the tread, and the foamed rubber of the foamed rubber layer has an average cell diameter of 5 to 15 with a foaming ratio Vs of 5 to 50%.
It is characterized in that it contains closed cells with a diameter of 0 μm, and the foamed rubber contains 20 or more closed cells with a cell diameter of 30 to 200 μm per unit area. Further, the foamed rubber has a dynamic elastic modulus of 3×107 to 13×107 d
It is preferably yn/crA, more preferably 3XIO' to 8xlO'dyn/crl. Coconi dynamic elastic modulus 3 xio' ~13×107
dyn/- is 3 X 10' dyn/
If it is less than d, the maneuverability in summer will not be sufficient, and 13
This is because if it exceeds X 10' dyn/aA, the tread grip force on snowy and icy roads deteriorates.

Here, the rubber component contained in the tread is a polymer having a glass transition temperature of -60°C or lower, such as natural rubber, polyisopropylene rubber, polybutadiene rubber, butyl rubber, styrene-butadiene copolymer rubber containing low styrene, or Alternatively, it is a mixture of two or more of these polymers. The reason for this is that by using these polymers, the tread has sufficient rubber elasticity even at low temperatures.

In addition, the foam rubber layer has a small total area of the tread.
It is desirable to have a volume of 0% or more, preferably 10
The reason why the foamed rubber layer is made to have a volume of at least 10% or more of the total tread volume, which is 70% to 70%, more preferably 40 to 60%, is that if it is less than 10%, the effect of improving ice and snow performance is small.

Further, as a method of using a foamed rubber layer in the tread, the entire tread may be made of the foamed rubber layer (foamed rubber N100%).

In addition, the foaming rate Vs of the foamed rubber is expressed by the following formula (% formula %), where ρ is the density of the foamed rubber (g/cni), and ρ
. is the density of the rubber solid phase of foamed rubber (g/cffl), ρ
9 is the density (g/d) of the gas portion within the foamed rubber cells. Foamed rubber is composed of a rubber solid phase portion and a gas portion within the cavities (closed cells) formed by the rubber solid phase portion. The density ρ9 of the gas part is extremely small, close to a hollow atmosphere, and is extremely small compared to the density ρ1 of the rubber solid phase part, so equation (1) is expressed as the following equation Vs= (ρ./ρr −1) xloo (%)・
...It is almost equivalent to (2). Foaming rate Vs is 5~
A range of 50% is desirable, preferably 5-30%. The reason why the foaming rate Vs is set to 5 to 50% is that if it is less than 5%,
The flexibility of foamed rubber at low temperatures cannot be obtained, and if it exceeds 50%, the abrasion resistance decreases and the abrasion resistance on dry roads other than icy and snowy roads and wet roads is insufficient for practical use. It is from.

In addition, the average cell diameter of closed cells in foam rubber is 5 to 150.
μm is desirable, preferably 10 to 100 μm1 The reason why the average cell diameter of the closed cells of the foamed rubber is set to 5 to 150 μm is because if the average cell diameter is less than 5 μm, the effect of improving ice and snow performance will be small, and if the average cell diameter exceeds 150 μm, the Abrasion performance is significantly reduced, and the distortion recovery power of the foam rubber is also reduced, so-called fatigue resistance is reduced, which causes deformation of the tire block and clogging of the sipes during driving, reducing performance on snow. let In addition, cut resistance decreases and block chipping increases. Furthermore, it is difficult to obtain a stable shape during manufacturing.

Further, it is desirable that the foamed rubber contains 20 or more closed cells with a cell diameter of 30 to 120 μm per unit area 112, preferably 30 or more. Here, the number of closed cells per unit area of 1w2 is 20 or more.
This is because if it is less than 1, the unevenness caused by the closed cells on the rubber surface of the tread rubber that comes into contact with the icy and snowy road surface is insufficient, and the icy and snowy performance cannot be fully exhibited.

Further, the foamed rubber used for the tread of the pneumatic tire according to the present invention is formed by adding a foaming agent to a conventional rubber compound and heating and pressurizing the mixture according to a conventional tire manufacturing method. Examples of the blowing agent include azocabonamide, dinitroso-pentamethylene-tetraamine, azobisisobutyronitrile, benzenesulfonylhydrazide,
Resin microcapsules of high-boiling hydrocarbon compounds are used.

Further, it is preferable that the foamed rubber contains 2 to 20 parts by weight of a low temperature softener based on 0 parts by weight of the rubber component ICl.

This is because the dynamic elastic modulus and internal loss of the foamed rubber can be adjusted and the friction performance on ice can be improved.

Examples of low-temperature softeners include low-temperature plasticizers having a freezing point of 140°C or lower, namely dioctyl adipate (DOA);
Dioctyl phthalate (DOP), dioctyl sebacate (DO8), diethyl phthalate (DHP), diethyl phthalate (DEP), dioctyl abire) (D
OZ), dibutyl maleate (DBM), tributyl phosphate (TBP),) lyoctyl phosphate (TO
P), -, etc. are used.

The details will be explained below with reference to Examples, but the properties of the foamed rubber and the tire performance using the test tires were tested in the following manner.

Test method (1) Average cell diameter and foaming ratio Vs The average cell diameter of foam rubber is determined by cutting out a block-shaped sample from the foam rubber layer of the tread of a test tire, and taking a photograph of the cross section of the sample with an optical microscope at a magnification of 100 to 400. 20
The cell diameter of 0.9 or more closed cells was measured and expressed as an arithmetic mean value.

In addition, the foaming rate Vs of the foamed rubber is determined by measuring the density ρI (g/c-+d) of the block-shaped sample;
solid phase rubber) tread density ρ. is measured, and the formula (2
).

(2) Cell diameter and cell number of closed cells The cell diameter and cell number of closed cells of foam rubber are determined by cutting out a block-shaped sample from the foam rubber layer of the tread of a test tire, and taking a photograph of the cross section of the sample at a magnification of 100 to 400. Photograph the cells with an optical microscope and determine the diameter of the closed cells. Next, the number of closed cells having a diameter of 5 μm or more was measured over a total area of 4 squares or more, and the number of closed cells per unit area of 1 m 12 was calculated.

(3) Surface roughness and coefficient of friction on ice of foamed rubber As surface roughness that specifies minute irregularities on the rubber surface of foamed rubber,
The root mean square roughness (RMS) described in JXS Surface Roughness BO601) was used. In other words, foamed rubber is cut from the tread of a tire, and a stylus-type surface roughness meter (
(manufactured by Koita Research Institute) using the specified sample dimensions (length 101 m).
, width Ion, thickness 5 mm), radius R of the tip of the stylus = 2 μm
, measurement car 0.7 mN, measurement scanning length 2.5 mN, the sample surface is 0.5 R in the length direction of the sample.
A total of 10 measurements were taken at 10 intervals and averaged.

The coefficient of friction of foam rubber on ice, especially the coefficient of friction on ice in a wet state around 0°C, is determined by measuring the surface roughness of the sample surface (sample size, length 10
The forehead, 101 m wide, 5 fl thick) was brought into contact with ice, and measured using a Kyowa Interface Science side type dynamic and static friction coefficient needle. The measurement conditions were a load of 2 kg/ctA and a sliding speed of 10 f.
The test was carried out at a l/5eC1 atmosphere temperature of -2°C and a surface state approximated to a mirror surface.

(4) Dynamic modulus of elasticity and internal loss of foamed rubber The dynamic modulus of elasticity and internal loss of foamed rubber were determined from the foamed rubber layer of the tread of a test tire.
m, thickness 2°Cm), and using a dynamic elasticity needle (manufactured by Iwamoto Seisakusho ■), the temperature was 30°C, the frequency was 60Hz, and the amplitude strain was 1.
It was measured in %.

(5) Tread surface heat generation temperature test After filling the tire with the normal internal pressure, the drum outer diameter was 1.7
The sample was pressed against a normal indoor drum testing machine of 1,100 k/H1 with a normal load and run for 3 hours, and the surface temperature at the center of the trend was measured.

(6) Wear resistance performance Two tires for each test were attached to the drive shaft of a passenger car with an exhaust of 11,500 cc, and the tires were run on the concrete road surface of a test course at a predetermined speed. Measure the amount of change in groove depth,
The comparison tire was set as 100 and expressed as an index. The larger the value, the better the wear resistance performance.

(7) Braking performance on ice Four test tires of each type were mounted on a passenger car with a displacement of 1500 cc, and the braking distance was measured on ice at an outside temperature of -5°C. The comparison tire was expressed as an I index with the value being 100.

The smaller the value, the better the braking.

(8) - Steering stability performance on a ship's road surface Steering stability performance was evaluated using a 10-point evaluation method, in which a test vehicle was equipped with test tires and was run at a specified speed on a general paved road surface in the summer, and the steering performance and stability while driving were evaluated on a 10-point scale. The results were averaged and shown as + and - with Comparative Example 3 in Table 4 as a control (standard). +
indicates good and - indicates poor.

Embodiments of the present invention will be described below based on the drawings.

(1st to 5th Examples, Comparative Example 1.2) Figure 1.2 is a diagram showing a first example of the pneumatic tire according to the present invention.

First, the configuration will be explained. In FIG. 1, a pneumatic tire (tire size 165SR13) 1 has a tire case 2 and a tread 3 made of foamed rubber and covering a crown portion 2a of the case 2. The case 2 includes a pair of bead portions 5, a carcass portion 6 consisting of a rubberized cord arranged approximately radially between the bead portions 5,
It is comprised of a belt part 7 disposed substantially in the tire circumferential direction on the crown part of the carcass part 6, and sidewall rubber 8 covering both sides of the carcass part in the tire axial direction.

The tread 3 has a foam rubber layer 11 (indicated by a black dot in the figure) between both shoulder parts on the front surface 3a side of the tread 3, and the foam rubber layer 11 accounts for at least 10% of the total volume V of the tread 3. In this example, the volume is 100%, which is the same as the total volume of the trend. Foam rubber N10
is made of foamed rubber 11, and the foamed rubber 11 is a tread rubber composition (composition 3) as shown in Table 1, that is,
Contains a rubber component consisting of a polymer with a glass transition temperature of -60°C or lower (natural rubber (glass transition temperature -72°C) and polybutadiene rubber (glass transition temperature -100°C)),
In addition, ordinary compounding agents and blowing agents (dinitroso, etc.) are added to this.
It is molded according to a normal tire manufacturing method, and when heated and pressurized, it foams to form closed cells (indicated by black dots in the figure) 13.

(This page, hereafter blank) Foamed rubber 11 used in the first example is shown in Table 2 (Composition 3
), the foaming rate Vs is 12% and the average cell diameter is 24%.
It has 50 closed cells with a cell diameter of 30 to 200 μm per unit area lfl''.

Furthermore, the foamed rubber 11 has a wear coefficient on ice of 0°037 (surface roughness 2.3 RMS (μm)), which is larger than the normal one (0.01 to 0.02). The configuration and manufacturing method other than the tread 3 are the same as those of a normal pneumatic radial tire, and detailed explanations will be omitted.

Regarding the performance of the tire, the tread heat generation temperature was 59°C, the wear resistance was 90, and the braking performance on ice was 95, indicating good braking performance on ice.

Next, test tires (tire size 165 S R13)
Seven types (5 types of Examples, 2 types of Comparative Examples) were prepared, and the effects of the present invention were confirmed. Details are shown in Table 2.

The first embodiment is shown in FIG. 1 mentioned above.

In Examples 2 to 5 and Comparative Example 1.2, the tread 3
As shown in FIG.
~The foamed rubbers of the foamed rubber layers of Example 5 and Comparative Example 1.2 contained Compositions 4 to 7 and Composition 1.1 in Table 1, respectively.
2 was used, the amount of foaming agent blended was changed, and the physical properties of the foamed rubber were changed. Comparative example 1.2 has a bubble diameter of 30 to 200μ
This is a case where the number of closed cells in m is less than 20 per unit area of 1 m and 1 m and the surface roughness is insufficient. These test tires were the same as the first example except as described above.

The properties of the foamed rubber in these test tires were: average cell diameter,
The foaming rate Vs, the number of closed cells with a cell diameter of 30 to 200 μm, and the coefficient of friction on ice (Fig. 2) were measured by the above-mentioned test method. The coefficient of friction of tires on ice is particularly important at a temperature of 0°C.
As shown in Figure 2 (the numbers in the figure indicate the composition numbers), the wet state of the foam rubber compositions 3 to 7 used in Examples 1 to 5 on ice is important. The coefficient of friction is significantly improved compared to that of Composition 1.2 used in Comparative Example 1.2.

The performance of the test tires was tested using the above-mentioned test method for the heat generation temperature of the tread surface, wear resistance performance, and braking performance on ice.

The test results are shown in Table 2.

(This page, below in the margins) As is clear from these results, the first to
In the fifth example, compared to Comparative Example 1.2, the increase in heat generation temperature on the tread surface was slight, and the heat generation durability was sufficient.
In addition, wear resistance is ensured to be sufficient for practical use. Furthermore, braking performance on ice has been significantly improved. Furthermore, the driving performance and maneuverability on icy and snowy roads were also sufficient.

(6th to 8th Examples, Comparative Examples 3 to 5) Next, sixth to eighth embodiments will be described.

In Examples 6 to 8, the foamed rubber has the characteristics of the foamed rubber of the present invention and has a dynamic elastic modulus of 3×
107～13×107 dyn/an! This is the case when the range is .

In Examples 6 to 8 and Comparative Examples 3 to 5, compositions 8 to 13 shown in Table 3 were used as trending rubber compositions, respectively. Compositions 8 to 10 contain a blowing agent, and composition 11 contains a foaming agent.
-13 are cases where no blowing agent is blended. The configuration other than the trend is the same as the first embodiment (FIG. 1).

Table 3 The properties of the tread rubber are its foaming ratio Vs, dynamic elastic modulus, and coefficient of friction on ice.The performance of pneumatic tires using this tread rubber is determined by its braking performance on ice and steering stability in summer on general roads. was tested using the test method described above.

The test results are shown in Table 4 and Figure 3.4.

In Figure 3.4, the triangle marks represent the cases in which a foaming agent is added.
The black circles indicate the test results when no blowing agent is added. The numbers in the figure are the numbers of Examples and Comparative Examples.

(This page, margins below) Table 4 show.

The test results are as shown in Table 4 and Fig. 3.4. Examples 6 to 8 are made of foamed rubber having a predetermined foaming ratio Vs and a predetermined dynamic elastic modulus using a foaming agent in the tread rubber.
Compared to Comparative Examples 3 to 5, - the coefficient of friction on ice can be significantly improved while maintaining sufficient steering stability on the ship's road surface;
Braking performance on ice can be further significantly improved. In the case of Comparative Examples 3 to 5 (conventional formulations) that do not use a foaming agent, by decreasing the dynamic elastic modulus, the coefficient of friction on ice can be slightly increased (Comparative Example 5), but the steering stability performance (94) increases (decreases). So it's not practical.

(9th to 13th Examples, Comparative Examples 6 to 13) Next, 9th to 1st Examples
A third embodiment will be explained.

In Examples 9 to 13, the foamed rubber has the characteristics of the foamed rubber of the present invention (i.e., the composition of the tread rubber), and 2 parts of the low-temperature softener is added to 100 parts by weight of the rubber component.
This shows that the braking performance, driving performance, and cornering performance of the tire are further improved on a wet water surface when the content is 20 parts by weight.

First, it will be explained that when a low-temperature softener is used in combination with a foaming agent that forms closed cells by vulcanization in a tread, the dynamic elastic modulus and internal loss of the tread can be adjusted, thereby improving wet water surface performance.

Figure 5.6 shows the temperature dependence of the dynamic elastic modulus and internal loss of the tread rubber, respectively. These tests were conducted according to the test method described above. The solid line in FIG. 5 is a normal trend rubber that does not contain a foaming agent or a low-temperature softener, and the tread rubber that contains a small amount of a low-temperature softener is almost the same as this solid line.

- The dotted chain line is a tread rubber made of foamed rubber containing a foaming agent and having closed cells (does not contain a low-temperature softener).

From this, the dynamic elastic modulus of the tread rubber made of foamed rubber shifts downward. The solid line in FIG. 6 is normal trend rubber, and the tread rubber made of foamed rubber is almost the same as this solid line. The dotted line is tread rubber containing a low-temperature softener (no foaming agent). From this, the tread rubber containing a low-temperature softener shifts to the left (lower temperature side). Therefore, at the temperature indicated by arrow A, trend rubber made of foamed rubber can have a smaller dynamic elastic modulus and larger internal loss than tread rubber containing a low-temperature softener. Therefore, the wet water surface performance (friction performance on ice) of the tread improves, which is advantageous. On the other hand, tread rubber containing a low-temperature softener has a higher dynamic elastic modulus and lower internal loss than trend rubber made of foamed rubber, which is advantageous in terms of wear resistance.

From what has been explained above, by using a low-temperature softener and a foaming agent in combination, the wet water surface performance can be improved while maintaining wear resistance.

Next, 9th to 13th embodiments in which the above-described matters were applied to foamed rubber will be described.

In Examples 9 to 13 and Comparative Examples 6 to 13, the rubber compositions of the tread were Compositions 14 to 14 shown in Table 5, respectively.
26 was used. Composition 14.15 did not contain a blowing agent;
Compositions 16 to 26 are cases in which the blending amount of the blowing agent was changed sequentially. Also, composition 14.15.17.19.21
．． Compositions 23.25 and 16.18.20.22.24.26 are cases in which the content of the low-temperature softener was varied, and compositions 16.18.20.22.24.26 and 16.18.20.22.24.26 do not contain the low-temperature softener for comparison.

The configuration other than the tread is the same as the first embodiment (FIG. 1).

(This page, below in the margins) The properties of the tread rubber were tested for its foaming rate Vs, hardness at temperature θ°C, changes in hardness, and abrasion resistance.
Furthermore, the performance of pneumatic tires using this trend rubber was tested for braking performance on ice at temperatures around 0°C and around -20°C using the test method described above, and the test results are shown in Table 6.

(This page, blank space below) As shown in Table 6, the test results show that Examples 9 to 13 containing low-temperature softeners showed less decrease in hardness than Comparative Examples 6 to 13 (hardness during long-term use The changes are slight, and braking performance on ice has been significantly improved while maintaining sufficient wear resistance for practical use.

(Effects of the Invention) As explained above, according to the present invention, ice and snow performance such as braking performance, driveability, and maneuverability on ice and snow road surfaces can be significantly improved without impairing wear resistance and heat generation durability. be able to. Further, by adjusting the dynamic elastic modulus of the foam rubber within a predetermined range, braking performance on ice can be significantly improved while maintaining sufficient steering stability on ordinary roads.

Furthermore, by incorporating a low-temperature softener into the foamed rubber, the braking performance on ice can be further improved significantly.

[Brief explanation of the drawing]

Fig. 1.2 shows a first embodiment of the pneumatic tire according to the present invention, Fig. 1 is a partial sectional view thereof, Fig. 2 is a graph showing the coefficient of friction on ice of the foam rubber, and Fig. 2 is a graph showing the coefficient of friction on ice of the foamed rubber. Figure 3.4 is a diagram showing the performance of Examples 6 to 8 of the present invention, Figure 3 is a graph showing the relationship between the coefficient of friction on ice and the dynamic modulus of elasticity, and Figure 4 is the coefficient of friction on ice. It is a graph which shows the relationship between and foaming rate. Figure 5.6 is a diagram showing the principle when the foamed rubber of the present invention contains a low-temperature softener, and Figure 5.6 shows the relationship between its dynamic elastic modulus, internal loss, and temperature, respectively. It is a graph. ■...Pneumatic tire, 2...Case, 2a...Crown part of case, 3...
Tread, 3a...Tread surface, 5...Bead part, 6...Carcass part, 7...Belt part, 8... -Side wall rubber, 9... Shoulder portion, 10... Foamed rubber layer, 11... Foamed rubber, 13... Closed cell. Figure 1 Figure 2 &? *i-: (RMS) pv- Fig. 3 Fig. 4 Discovery rate Vs (%) Fig. 5 ・1 gain - 1 degree -6□ Fig. 6 Low temperature - Temperature - Advocate procedure master's official seal ) 1. Indication of the case Japanese Patent Application No. 61-235921 2. Name of the invention Pneumatic tire 3. Person making the amendment Relationship to the case Patent applicant address 10-1 Kyobashi-chome, Chuo-ku, Tokyo Name (52)
7) Brideston Co., Ltd. 4, Agent 151 Address 2-6-9-5 Yoyogi, Shibuya-ku, Tokyo, "Detailed description of the invention" column and "Brief description of drawings" column of the specification subject to amendment and drawings. 6. Contents of amendment (1) In the first line of page 16 of the specification, “foamed rubber layer 11 (
"Indicated by black dots in the figure" is replaced by "foamed rubber layer 10 (
The figures are shown with black dots.'' (2) In the second line of page 16, the phrase "foamed rubber layer 11" is corrected to "foamed rubber layer 10." (3) Add the following text and table between the 5th and 6th lines of page 33. (Example 14.15, Comparative Example 14) Next, the 14th.
Embodiment 15 will be explained. Examples 14 and 15 show that the pneumatic tire according to the present invention can be applied to large tires, such as pneumatic tires for trucks and buses. First, a fourteenth embodiment will be described. In Figure 7, 21 is tire size 10.0OR20
This is a 14PR pneumatic tire for heavy loads. In the pneumatic tire 21, the same components as in the first embodiment are given the same reference numerals, and only necessary parts will be described. The structure other than the tread 3 is a normal pneumatic tire for trucks and buses. The carcass part 6 of the case 2 is made of rubber-coated steel cords arranged in the radial direction, and the belt part 7 has four belt layers made of rubber-coated steel cords. The tread 3 is provided with a foamed rubber layer 10 having a volume of 10% or more of the total volume V of the tread 3 on the front side 3a of the trend 3. The foamed rubber layer 10 is made of foamed rubber 11, and the foamed rubber layer 1 contains a tread rubber composition 27 containing the foaming agent shown in Table 7, and is molded by a normal tire manufacturing method as in the first example. Then, it is heated and pressurized to foam and form closed cells 13. Next, a fifteenth example is a case in which the foamed rubber 11 is made of a rubber composition 28 containing a foaming agent shown in Table 7 in the fourteenth example. In addition, in Comparative Example 14, the tread was
This is the case with the trendy rubber composition 29 used in ordinary truck and bus tires shown in Table 7. (This page, blank space below) Table 7 Table 8 ■ *1.2 was tested according to JIS K6301. *3 was tested using a normal Lambourn rubber abrasion tester. The properties of the tore throat rubber used in Examples 14 and 15 and Comparative Example 14 are shown in Table 8. Regarding the performance of pneumatic tires using these tread rubbers, the braking performance on ice was tested at temperatures around 0°C and -20°C in the same manner as described above. As shown in Table 8, the test results show that the 14.15th example maintains sufficient wear resistance for practical use and significantly improves the braking performance on ice compared to the comparative example. There is. (4) On page 34, line 7, next to ``This is a graph.'' ``Figure 7 is a partial sectional view showing a 14th embodiment of a pneumatic tire according to the present invention.'' Add. (5) In the 8th line of page 34, the statement ``1...Pneumatic tire,'' is corrected to rL21...Pneumatic tire.'' (6) Add Figure 7 of the drawings as attached. that's all

Claims (3)

[Claims] (1) In a pneumatic tire comprising a tire case and a tread covering the crown portion of the case, the tread has a foamed rubber layer on the front side of the tread having a volume of at least 10% or more of the total volume of the tread. , the foamed rubber layer is made of foamed rubber containing a rubber component of a polymer having a glass transition temperature of -60°C or lower, and the foamed rubber has an expansion rate of Vs5.
A pneumatic tire characterized by having closed cells having an average cell diameter of 5 to 150 μm within a range of 50% and 20 or more closed cells having an individual cell diameter of 30 to 200 μm per unit area of 1 mm^2. (2) The foamed rubber has a dynamic elastic modulus of 3×10^7 to 13×
The pneumatic tire according to claim 1, which has a particle diameter of 10^7 dyn/cm^2. (3) The pneumatic tire according to claim 1, wherein the foamed rubber contains 2 to 20 parts by weight of a low temperature softener per 100 parts by weight of the rubber component.