JPH02155806A - Heavy duty pneumatic tire - Google Patents

Abstract

PURPOSE:To enhance the on-ice running characteristics by forming a heavy duty pneumatic tire with the ground contacting pressure exceeding a specified value which tire has a tread equipped with an outer layer part having a specific vol.% and consisting of foamed rubber whose rate of foaming, bubble dia., bubble density, and hardness are as specified. CONSTITUTION:In a heavy duty pneumatic tire 1 whose mean ground contacting pressure of tread 3 exceeds 4kg/cm<2>, the tread 3 is composed of an inner layer 3B consisting of normal rubber with low heat emission and an outer layer 3A consisting of foamed rubber, wherein the volume of the outer layer 3A shall be set to over 10% of the total volume of tread 3. The foamed rubber constituting the outer layer 3A shall have a hardness of 45-70 deg., a rate of foaming Vs of 5-50%, a mean bubble dia. of 5-150mum, wherein the bubbles shall be independent, and further more than 20 independent bubbles of 30-200mum in dia. shall be contained per unit area 1mm<2>. Thus the on-ice running characteristic can be enhanced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a heavy-duty pneumatic tire, and more specifically, to a pneumatic tire for heavy loads. Significantly improves performance,
The present invention relates to improvements in driving performance, braking performance, performance on ice, and other performance on ice and snow during winter, particularly to a pneumatic tire for heavy loads that has significantly improved performance on ice.

(Prior Art) In general, pneumatic tires that run on icy roads in the winter and paved roads in the summer are used in passenger car tires to avoid dust pollution caused by road wear and damage caused by spike pins or chains. So-called studless tires, which do not use spike pins, are used.

For studless tires, consideration has been given to the Tresoto pattern and the rubber quality of the tread.In particular, for the rubber quality of the tread, performance on ice has been improved by using Trendcom, which has a low hardness Hd and is made of polybutadiene rubber with a low glass transition point Tg. ”

In addition, by using rubber made of a polymer with a low glass transition point Tg for the tread, and using foamed rubber containing closed cells inside the rubber, the hardness of the entire tread rubber is reduced and the performance on ice is significantly improved. ing.

(Problem to be Solved by the Invention) However, in large, heavy-duty pneumatic tires with high ground contact pressure of the tread, ice easily melts due to the high ground contact pressure, forming a water film and reducing the coefficient of friction μ on the ice. For this reason, for example, a Toresoto made of rubber with a low glass transition point Tg and low hardness Hd has a considerable effect on ice performance for small pneumatic tires, but is significantly effective for large heavy-duty pneumatic tires. The problem is that performance cannot be improved.

Furthermore, by using foamed rubber containing closed cells in the tread, large heavy-duty pneumatic tires can significantly improve their on-ice performance, but when running on dry, wet, and icy roads for long periods of time, l. There is a problem that the red rubber wears quickly and does not have sufficient wear resistance.

In addition, when 1-red rubber with low hardness Hd is used in large, heavy-duty pneumatic tires, the average ground pressure of the tore soto is large, causing permanent distortion, or so-called sagging, in the trend blocks (ridges), resulting in poor durability. There is also the problem that there are not enough.

Therefore, the present invention combines an appropriate amount of highly reinforcing carbon black suitable for the foamed rubber of the tread of large pneumatic tires with high ground pressure, thereby significantly improving ice and snow performance, especially performance on ice, and significantly improving wear resistance. The purpose of the present invention is to provide a pneumatic tire for heavy loads.

(Another Means to Solve the Problem) The present inventors have investigated the rubber compounding and physical properties of the foamed rubber, as well as the tire's durability, abrasion resistance, and on-ice performance in foamed rubber used for the tread of large, heavy-duty pneumatic tires. We conducted various studies on the relationship between As a result, the tire tread blocks (ridges) are prevented from becoming sagging,
In order to improve the hardness of the entire tread and maintain wear resistance, we have found that a specific formulation containing an appropriate amount of highly reinforcing carbon is effective.

The inventors of the present invention further carried out intensive tests a.1 and reached the following conclusion.

That is, the heavy-duty pneumatic tire according to the present invention has a tire case and a tread covering the crown part of the case, and the average ground contact pressure of the tread is 4 kg/c.
A pneumatic tire for heavy loads with an FF of 1 or more, comprising an outer layer portion having a volume of at least 10% of the total volume of the tread on the outside of the tread, and an inner layer portion inside the outer layer portion, the outer layer portion being made of foamed rubber, The foam rubber has a foaming rate Vs
having closed cells with an average cell diameter of 5 to 150 μm in a range of 5 to 50%, and having 20 or more closed cells with a cell diameter of 30 to 200 μm per unit area of 1 mm, and
The hardness of the foamed rubber is 45 to 70 degrees. In addition, the foamed rubber has a cecyltrimethylammonium bromide adsorption specific surface area (CTAB) of 130 nτ/g or more and a compressed dibutyl phthalate oil absorption (24M4DBP) of 100 mj2/1 per 100 parts by weight of the rubber component.
It is preferable that 30 to 80 parts by weight of carbon black of 00 g or more is blended.

Here, pneumatic tires for heavy loads include pneumatic tires for light trunks, pneumatic tires for trucks and lotuses,
This refers to retreaded light trunk pneumatic tires and retreaded 1-rank lotus pneumatic tires.

Further, the reason why the average ground pressure is set to be 4 kg/c+a or more is because the effect of the present invention cannot be fully exhibited if it is less than 4 kg/cII1.

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

Further, the hardness Hd of the foamed rubber is desirably 45° to 70°, preferably 506° to 70°, and more preferably 54° to 70°. The reason why the hardness Hd is 45° to 70° is because if the hardness is less than 45°, the wear resistance deteriorates and the tread becomes sagging. If the angle exceeds 70°, the tread becomes too hard, resulting in poor workability and poor heat generation. The higher the hardness of the foam rubber (1-1 d), the more the bubbles will not collapse even under high ground pressure, and the better the performance on ice will be. Here, the hardness Hd is measured at room temperature in accordance with JIS K2SO3.

In addition, the highly reinforcing carbon black blended into foamed rubber has a specific surface area for adsorption of cecyltrimethylammonium bromide (hereinafter simply referred to as CTAB) of 130 ffl/g.
With the above, the compressed dibutyl phthalate-1 oil absorption amount (hereinafter simply referred to as 24M4DBP) is 100mff1/100g
It is preferable to have the above characteristics.

If the value is less than these values, the effects of the present invention cannot be sufficiently obtained. Here, the value of CTAB and the value of 24M4DBP are:
American Standard ASTM D3765-85 and D, respectively
This test was carried out in accordance with the test method of No. 3493-85.

Further, the amount of highly reinforcing carbon is preferably 30 to 80 parts by weight, more preferably 45 to 65 parts by weight, based on 100 parts by weight of the rubber component. Here, the reason why the amount is 30 to 80 parts by weight is because if the amount is less than 30 parts, the abrasion resistance deteriorates and sag occurs. This is because if the amount exceeds 80 parts by weight, workability and heat generation properties will deteriorate. By using the highly reinforcing carbon black in the specified weight part range, the abrasion resistance and setting property of the foamed rubber are significantly improved.

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

In addition, the foaming rate Vs of the foamed rubber is expressed by the following formula 7% (1), where ρ1 is the density of the foamed rubber (g/cII, ρ0
is the density (g/c%) of the rubber solid phase part of the foamed rubber.

The foaming rate Vs is desirably in the range of 5 to 50%, preferably 5 to 30%. The reason why the foaming ratio Vs is set to 5 to 50% is that if it is less than 5%, the foamed rubber will not have the flexibility at low temperatures, and if it exceeds 50%, the abrasion resistance will decrease and This is because the wear resistance on dry road surfaces other than road surfaces is insufficient for practical purposes.

In addition, the average cell diameter of closed cells in foam rubber is 5 to 150μ.
m is desirable, preferably 1O to 1100Ij. The reason why the average cell diameter of the closed cells of the foam rubber is set to 5 to 150 μm is that if it is less than 5 μm, the effect of improving ice and snow performance is small, and if the average cell diameter exceeds 150 μm, the wear resistance performance will be significantly reduced. The strain resilience of foamed rubber decreases, so-called fatigue resistance decreases, which causes deformation of tire blocks and clogging of sipes during driving, reducing performance on snow. 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 200 μm per mm 2 of unit area, preferably 30 or more. The reason why the number of closed cells is set to be 20 or more per unit area lInIn2 is that if the number of closed cells is less than 20, 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 will not be sufficient and the icy and snow performance will not be fully demonstrated. It's for a reason.

Furthermore, the foamed rubber used for the tread of the heavy-duty pneumatic tire according to the present invention is prepared by adding a foaming agent to a normal rubber compound containing a specific carbon black in a specific weight part and heating it according to a normal tire manufacturing method. Formed when pressed. As the blowing agent, for example, a system using dinitrosopentamethylenetetraamine in combination with urea, a benzenesulfonyl hydrazide derivative, especially oxybishenzenesulfonylhydrazide, etc. are preferable as a blowing agent in consideration of manufacturing processability.

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

Test M bean (1) Average cell diameter and foaming rate Vs The average cell diameter of foam rubber is test type A. 1- Cut a block-shaped sample from red foam rubber, and take a photograph of the test cross section at a magnification of 100 to 400 optical. Photographed with a microscope, 20
The cell diameter of zero 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 cutting the block-shaped sample into a thin piece with a thickness of 2 mmμ, leaving it for one week after vulcanization to stabilize it, and then measuring the density ρ, (g/c+fl). (same phase rubber) tread was measured and calculated using the above formula (1).

(2) Cell diameter and cell number of closed cells Cell diameter and cell number of closed cells of foam rubber: Cut a slit-shaped sample from the foam rubber of the tread of a test tire, and take a photograph of the cross section of the sample at a magnification of 100 to 400. image with an optical microscope and determine the bubble diameter of closed cells. Next, the number of closed cells with a diameter of 5 μm or more was measured over a total area of 4 mm or more, and the unit area of closed cells was
The number of bubbles (pieces) per 2 was calculated.

(3) Wear resistance performance Ten tires for each test were mounted on all axles of a truck with a load of IQTON LJ, and after traveling approximately 20,000 km, the traveling distance per 1 mm was determined from the average value of the groove depth. However, with regard to regenerated tie 1, tests were conducted by attaching it to the drive shaft and free shaft. The tire of Comparative Example 1 was set as 100 and expressed as an index. The larger the value, the better the wear resistance performance.

(4) Braking performance on ice Ten test tires of each type were attached to a trunk carrying a load of 10 TON7, and the braking distance was measured on ice at an outside temperature of -5°C. The tire of Comparative Example 1 was set as 100 and expressed as an index. The smaller the value, the better the braking.

(Examples 1 to 8, Comparative Examples 1 to 5) Figures 1 and 2 are views showing a first example of the pneumatic evening ear for heavy loads according to the present invention.

First, the configuration will be explained. In Figure 1, 1 is a pneumatic tire for heavy loads (Tie N. Seiz/LO.OO
R20 14PR) and is a radial tire for I rank Hass. A pneumatic tire for heavy loads (hereinafter simply referred to as a pneumatic tire) 1 consists of a tire case (
2 (indicated by the dashed dotted line) and L/Red 3 covering the crown portion 2a of the case 2. The case 2 includes a carcass part 6 made of rubberized cords arranged in a radial direction between the pair of parts 5 and a belt part arranged in a substantially circumferential direction so as to intersect with each other at the crown part of the carcass part 6. 7. Sidewalls 8 are provided on both outer sides of the carcass portion of the case 2 in the axial direction of the tire.

The tread 3 has an outer layer portion 3A that contacts the road surface on the outside of the tread 3, and an inner portion 3 on the inside of the outer layer portion 3.

It has The volume of the outer layer portion 3A is 60% of the total volume of the tread 3.

The average ground pressure of the tread 3 is about 7.5 kg/cfl when a regular load is applied to a heavy-duty pneumatic tire.

The outer layer 3A of the L/Red 3 is made of foamed rubber (indicated by dots in the figure) 11, and the hardness of the foamed rubber 11 is H.
d is 45-70. The inner part 3B is made of ordinary rubber with low heat generation property, and the side wall 8 is made of ordinary glue rubber with excellent bending resistance.

Foamed rubber 11 was made by blending the rubber composition shown in Example 1 in the following table, and the blend had a glass transition temperature of -60'
The highly reinforcing carbon blank according to the present invention, which contains a rubber component consisting of natural rubber and polybutadiene rubber having C or less, a normal rubber compounding agent, and a blowing agent (
oxybisbenzenesulfonyl hydrazide). Then, when it is molded according to a normal tire manufacturing method and heated and pressurized, it foams to form closed cells 13.

The foaming rate Vs, average cell diameter, and number of closed cells with a cell diameter of 30 to 200 μrn of the foamed rubber 11 are shown at the bottom of the following table.
The structure and manufacturing method other than the tread 3 are the same as those of a normal heavy-duty pneumatic tire, and detailed explanations will be omitted.

In the heavy-duty pneumatic tires of Examples 2 to 8 and Comparative Examples 1 to 5 shown in the following table, the foamed rubber 11 of the outer layer 3A of the tread 3 in the first example was replaced with the Examples and Comparative Examples shown in the following table. A foamed rubber and a non-foamed rubber made from the rubber composition of the example were used, and the other aspects were the same as in the first example.

(This page, hereafter in the margin) Next, performance test results of the heavy-duty pneumatic tire according to the present invention will be described.

The heavy-duty pneumatic tires of Examples and Comparative Examples shown in the preceding table were tested for wear resistance and performance on ice based on the above-mentioned test method. The test results are shown at the bottom of the table above.

In addition, as a result of investigating the performance in summer and the performance in winter other than those mentioned above, the performance was found to be sufficient. In addition, there was no tread wear or the like, and the durability was sufficient.

As shown in the test results in the previous table, the example in which the foamed rubber used in the present invention was combined with the optimal amount of highly reinforcing carbon black had significantly improved wear resistance and on-ice performance compared to the comparative example. are doing.

Next, a ninth embodiment of the present invention will be described.

FIG. 3 is a diagram of a tire 21 showing a ninth embodiment of the heavy-duty pneumatic tire according to the present invention, and the same components as in the first embodiment are given the same reference numerals.

In the ninth example, the outer layer portion 23A of the tread 3 does not form the groove bottom portion 15a of the groove 15 provided in the tread 3, and the foamed rubber 11 (the rubber composition of the third example) of the outer layer portion 23A is (used) is placed thinly on the outside, and the non-foamed rubber of the inner layer 23B is placed on the groove bottom 15a. As a result, it is possible to significantly improve group cracks, rib tear failures, and lack of wear resistance that may occur at the groove bottom 15a and the vicinity thereof under harsh operating conditions or during long-term use including refurbishment. can. Of course, what is shown in the ninth embodiment can also be applied to the second to eighth embodiments described above.

(Effects) As explained above, according to the present invention, large pneumatic tires with high ground pressure, that is, pneumatic radial tires for trucks and lotuses, pneumatic conventional bias tires for trucks and lotuses, and high-load In all types of tires, including radial tires for small trucks, small bias tires for heavy loads, and tires for retreading them, combining an appropriate amount of highly reinforcing carbon black suitable for the foamed rubber of the tread improves ice and snow performance, especially on ice. In addition to significantly improving wear resistance, it also significantly improves wear resistance. Furthermore, by suitably arranging the foamed rubber, the above-mentioned performance can be sufficiently maintained even under severe usage conditions and during long-term use.

[Brief explanation of the drawing]

1.2 are diagrams showing a first embodiment of a heavy-duty pneumatic tire according to the present invention, FIG. 1 is a partial cross-sectional view thereof, and FIG. 2 is an enlarged cross-sectional view of a main part thereof. FIG. 3 is an enlarged sectional view of the main part of the ninth embodiment. 1.21...Pneumatic tires for heavy loads, 2...
...Case, 3...Tread, 3A, 23A...Outer layer part, 3,. 23. ...Inner layer part, 11 ... Foamed rubber, 13 ... Closed cell, 15 ... Groove.

Claims (2)

[Claims] (1) It has a tire case and a tread that covers the crown of the case, and the average ground pressure of the tread is 4 kg/
A heavy-duty pneumatic tire of cm^2 or more, comprising an outer layer portion having a volume of at least 10% of the total volume of the tread on the outside of the tread, and an inner layer portion inside the outer layer portion,
The outer layer portion is made of foamed rubber, and the foamed rubber has a foaming rate of V.
It has closed cells with an average cell diameter of 5 to 150 μm in the range of s5 to 50%, and has 20 or more closed cells with a cell diameter of 30 to 200 μm per unit area of 1 mm^2, and the hardness of the foamed rubber is 45 to 50%. A heavy-duty pneumatic tire characterized by a 70° angle. (2) Foamed rubber has a specific surface area (CT
AB) is 130m^2/g or more, compressed dibutyl phthalate oil absorption (24M4DBP) is 100ml/100g
The pneumatic tire for heavy loads according to claim 1, which contains 30 to 80 parts by weight of the above carbon black.