JPS6390403A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve resistance to ice and snow without impairing abrasion resistance and heat-generation durability by placing a foam rubber layer having closed cells in the thickness direction of a tread, and differentiating its foaming rate in the thickness direction and in the width direction of said tread. CONSTITUTION:A foam rubber layer 11 having closed cells is provided between both shoulders ranging over the whole thickness of a tread 3. In the foam rubber 12 constituting this foam rubber layer 11, the foaming rate Vs is differentiated between the outermost side part 11a and the innermost side part 11b, making the foaming rate Vs on the outermost side part 11a larger by more than 5% in the difference in foaming rate, than the foaming rate Vs on the innermost side part 11b. 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, and more specifically, to a pneumatic tire, which has sufficient wear resistance for practical use without impairing heat generation durability, and which has excellent drivability on icy and snowy roads. This invention relates to a pneumatic tire that has significantly improved braking performance, maneuverability, and ride comfort.

(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).
In order to ensure this, spiked tires with spike bins driven into the tread surface are often used. however,
Dust pollution caused by the scattering of these fine powders due to wear of spike bins and road wear, and damage to roads caused by spike bins has become a major social problem. In addition, the vibration riding comfort is also significantly deteriorated. In order to deal with these problems, studies have been made on regulating the amount of protrusion of the spike bottle, the number of spikes, and the material of the spike bottle, but this has not resulted in a fundamental solution to the social problem.

On the other hand, with regard to so-called studless tires that do not use spike pins, the pattern of the tire tread and the quality of the tread rubber have been studied, but there is a problem in that they cannot exhibit 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 U.S. Pat.
P 4,249.588. However, in Japanese Patent Publication No. 40-4641, synthetic rubber with a large hysteresis loss, such as high styrene rubber, is used for the tread rubber, which increases the glass transition temperature of the rubber, increases the hardness of the rubber at low temperatures, and increases the risk of ice and snow. This is not desirable in terms of ensuring performance. Also, US P4,
In 249.588, the tread rubber was heated to 25°C.
, compression characteristics (stress) at 50% compressive strain is 1 to 800 ps
However, it is not practical in terms of steering response unless the tread rubber of a pneumatic automobile tire is at least 400 ps i.

In addition, attempts have been made to improve the slipperiness on icy and snowy road surfaces by mixing granular materials such as sand, wire mesh sand, carborundum, and metal particles into the tread rubber, but the slipperiness is poor unless a large amount of granular materials are mixed in. There is a problem in that if it is not improved and is mixed in a large amount, the abrasion properties will be significantly deteriorated.

Furthermore, in Japanese Patent Application Laid-Open No. 60-68561, the present applicant has proposed a method for solving the above-mentioned problems. However, according to this method, a foamed rubber layer and a non-foamed rubber layer are laminated in the tread thickness direction, or the tread is divided in the tire width direction, in order to meet the various functions required of pneumatic tires. It must be placed in a suitable location. For this reason, there are problems in that the number of members prepared when manufacturing the tire increases and the number of man-hours during molding increases.

Therefore, the purpose of the present invention is to solve the above-mentioned problems of conventional spiked tires and studless tires, and to achieve both ice and snow performance, wear resistance, riding comfort, and heat generation durability of the tire, and to improve the coefficient of friction on ice of the tire. Particularly, the object of the present invention is to provide a pneumatic tire that has an improved coefficient of friction on wet ice at a temperature of about 0° C., is sufficiently durable for practical use, and has excellent productivity with fewer man-hours during its manufacture.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the inventors of the present invention have conducted various studies, and as a result, have improved the driving and braking performance of tires by using foamed rubber having closed cells in the tread. It has been found that the effect is particularly great on wet or frozen roads.

Further, when foamed rubber having closed cells is used for the tread, a soft ride is provided, but if the foaming rate of the foamed rubber is too high, the tire's handling performance and abrasion resistance are reduced. Therefore, the foaming rate of the foamed rubber of the tread is changed depending on the desired degree of tire performance. That is, if slip resistance and maneuverability are desired, the outside of the tread (
The foaming ratio of the foamed rubber on the side that contacts the road surface is increased to improve slip resistance, while the foaming ratio on the inside of the tread is lowered to maintain tread rigidity. Furthermore, if wear resistance and good vibration riding comfort are desired, the foaming rate of the foamed rubber on the outside of the tread may be reduced, and the foaming rate on the inside of the tread may be increased. Furthermore, the foaming rate of the foamed rubber is changed in response to the ground pressure distribution at the center and side edges (shoulders) of the tread, improving the tire's handling performance, heat generation, vibration comfort, rolling resistance, and braking. We have found that various functions such as gender can be improved.

In addition, a method for changing the foaming rate of foamed rubber with closed cells in the tread is that when an unvulcanized tire is vulcanized, there is It has been found that by applying a temperature gradient, it is possible to change the foaming rate of the inside and outside of the closed-cell foam rubber of a tread made of a single rubber composition.

It was also discovered that by creating a temperature difference in the temperature of the vulcanization mold on the radially outer side of the tread in the width direction of the tread (in the axial direction of the tire), it was possible to change the expansion rate of foamed rubber with closed cells in the width direction of the tread. Ta.

Based on these results, the present inventors further conducted intensive research on the material and structure of foam rubber, the vulcanization method for tires, etc., and arrived at the present invention.

A pneumatic tire according to the present invention includes a tire case and a tread covering a crown portion of the case, wherein the tread has a foamed rubber layer in at least a portion of the thickness direction of the tread. , the foamed rubber layer mainly consists of foamed rubber having closed cells, and each portion of the foamed rubber has a mutually different foaming rate Vs in both or either of the tread thickness direction and the tread width direction. It is a feature.

Here, the tread thickness direction refers to a tire radial direction perpendicular to the tire rotation axis, and the tread width direction refers to a direction parallel to the tire rotation axis.

Further, it is desirable that the foamed rubber is a single compounded rubber composition.

Further, the rubber components in the rubber composition of the foamed rubber include natural rubber, diene rubber such as butadiene rubber, styrene-butadiene rubber, butyl rubber, ethylene propylene rubber, etc. used in the tread rubber of ordinary tires; Selected according to the desired performance.

Foaming agents in the rubber composition of the foamed rubber include, for example, azosicabonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, toluenesulfonylhydrazide derivatives, toluene-sulfonylhydrazide, toluenesulfonyl semihydrabide, Sodium carbonate, etc. are used.

In addition, the foaming rate Vs is calculated by the following formula: %formula%) where ρ1 is the density of the foamed rubber (Cg/cd), and ρ.

is the density (g/cn) of the rubber solid phase part of the foamed rubber, and ρ is the density (g/d) of the gas part in the cells of the foamed rubber.The foamed rubber has a rubber solid phase part and a rubber solid phase part. The density of the gas part, ρ9, is extremely small, close to zero, and is extremely lower than the density of the rubber solid phase, ρ1. Since it is small, formula (1) can be transformed into the following formula Vs=(ρ./p, -1) X100 (%)-・
- Almost equivalent to (2).

In the foaming rate Vs of the foam rubber of the tread, the foaming rate Vs
It is preferable that the difference between the maximum foaming rate and the minimum foaming rate is 5% or more. The reason why the amount is set at 5% or more is that if it is less than 5%, the difference in tire performance will not be clear and the effect of the present invention will not be sufficient.

(First Example, Comparative Example 1) Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing a first embodiment of a 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. 9 is an inner liner that covers the inside of the carcass portion 6.

The tread 3 has a foamed rubber layer 11 between both shoulders over at least a portion of the thickness of the tread 3, in this embodiment the entire thickness of the tread. The foam rubber layer 11 mainly consists of foam rubber 12 having closed cells.
has a single compounded rubber composition 1 shown below.

(Rubber compositions 1 and 2 for pre-produced rubber) (Units are parts by weight) (Rubber composition 1) <Rubber composition 2) Natural rubber 60.0 60.0 parts by weight Butadiene rubber 40.0 40.0"
Carbon black 70.0 70.0 〃
Process oil 30.0 30.0 〃
Wax 1.0 1.0 〃
Stearin M 2.0 2,0-Anti-aging agent 1.5 1.5 Zinc white
3.5 3.5 Vulcanization accelerator
1.5 1.5 Sulfur yellow
1.5 1.5 ” Foaming agent (dinitrosopentamethylenetetramine) 4.5 0〃 Pneumatic tires have the same structure as normal pneumatic radial tires, except that foamed rubber 12 is used for the tread 3, and the same An unvulcanized pneumatic tire (so-called Daleen tire) was molded.

The unvulcanized tire is inserted into a normal vulcanizing device, and the vulcanizing device lowers the temperature of the innermost part 11b of the tread of the unvulcanized tire to 1.
The temperature on the surface 3a side of the tread 3 was maintained at 60°C and 170°C, and vulcanization was carried out by heating and pressurizing for 10 minutes. This results in
The foamed rubber 12 of the tread 3 is foamed by the decomposition of the foaming agent to form closed cells. Since the temperature on the surface 3a side of the tread 3 is higher than the temperature on the innermost part 11b side of the tread, the foaming rate Vs on the surface 3a side of the tread 3 increases, and the foaming rate differs in each part of the tread 3 in the thickness direction. A foamed rubber having Vs is produced. That is, in the foamed rubber layer 11, in the thickness direction of the tread 3, the outermost part 11a is smaller than the innermost part 11b.
has a larger foaming rate VS (in the figure, black dots indicate closed cell 13
(more sunspots indicate higher foaming rate),
That is, foamed rubber having closed cells with mutually different expansion ratios Vs can be produced.

In manufacturing this pneumatic tire, only a single compounded rubber composition is used, so molding and manufacturing of the unvulcanized tire is simple, requires less man-hours, and has good tire productivity.

Next, a comparative example will be explained.

For the pneumatic tire of Comparative Example 1, the same unvulcanized tire was inserted into a vulcanizing device, and the temperature of the innermost part of the tread and the temperature of the surface of the tread were both maintained at 170°C, and the other conditions were the same. Vulcanized under vulcanization conditions.

Next, these pneumatic tires were tested for the foaming ratio Vs of the foamed rubber of the tread and tire performance (drum heat generation temperature, wear resistance performance, braking performance on ice) using the following test method, and will be explained.

The test results are shown in the table below.

(Test method) (1) Difference in foaming rate VsO of foamed rubber Block-shaped samples were cut out from the parts of the foamed rubber layer of the tread with the maximum and minimum foaming rates, and the density ρ
, (g/ad) was measured, and - the density ρ of non-foamed rubber (solid phase rubber) of a separately manufactured tire. was measured, and the foaming rate Vs was determined using the above formula (2).

In the first example, samples were cut out and measured from the outermost part 11a of the foamed rubber layer 11 as the part of the foamed rubber layer with the maximum expansion rate, and from the innermost part 11b of the foamed rubber layer 11 as the part with the minimum expansion rate. .

The cutout portions of these samples were determined from the temperature distribution of the vulcanization mold during vulcanization.

(2) Tread surface heat generation temperature test After filling the tire with the regular internal pressure, it was pressed against a drum testing machine with an outer diameter of 1°7ms and a speed of 1100k/H under the regular load and run for 3 hours, and the surface temperature of the center of the tread was measured. did.

(3) Wear resistance performance Two tires for each test were attached to the drive shaft of a passenger car with an exhaust of 1,500 cc and run on the concrete road surface of a test course at a predetermined speed.The amount of change in groove depth was measured, and the non-foaming The tire (comparative tire 2) was expressed as an index, with the value being 100. The larger the value, the better the wear resistance.

(4) Braking performance on ice Four test tires of each type were mounted on a passenger car with a displacement of t1500 cc, and the braking distance on ice at an outside temperature of -15°C was measured. Non-foamed tires (Comparative Example 2 are expressed as an index with the case of Comparative Example 2 set as 100. The smaller the value, the better the braking is.

(5) Ride comfort was evaluated by a test driver on a test course (road surface: gravel road, cobblestone joint circuit). The evaluation results were expressed as an index. Number 11 indicates that the larger the value, the better.

(This page, margins below)! As shown in the table, the test results show that the foaming ratio (3) of the outermost part of the foamed rubber layer is significantly higher than that of the innermost part, and the tire's braking performance on ice and riding comfort are significantly improved. In this way, by providing a difference in the foaming rate of the foamed rubber layer of the tread, tire performance can be significantly improved, and riding comfort performance can also be improved.

In addition, in the above-mentioned example, the foaming rate Vs of the foamed rubber layer
Although the case where the foaming rate Vs is large at the outermost part of the tread and small at the innermost part of the tread has been described, the present invention is not limited to this embodiment, and as in the second embodiment shown in FIG.
may be larger at the innermost part of the tread and smaller at the outermost part. Such pneumatic tires have excellent wear resistance and vibration riding comfort.

Further, as in the third embodiment shown in FIG. 3, the foaming rate Vs can be made larger at the center tlllc of the foamed rubber layer 11 of the tread 3 and smaller at the side edges lid.

That is, the foaming rate can be changed in accordance with the ground pressure distribution of the tread, thereby improving the tire's maneuverability, heat generation, riding comfort, rolling resistance, and braking performance.

(Effects) As explained above, according to the present invention, it is possible to significantly improve ice and snow performance such as braking performance, driveability, and maneuverability on ice and snow road surfaces without impairing wear resistance and heat generation durability. Riding comfort and rolling performance can be improved, and the number of parts during production is small, reducing the number of molding steps, and productivity can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing a first embodiment of a pneumatic tire according to the present invention. FIG. 2.3 is a partial sectional view showing a 2.3 embodiment of the present invention. 1...Pneumatic tire, 2...Case, 2a...Crown portion, 3...Tread, 3a...Surface, 5. ...Bead part, 6...Carcass part, 7...Belt part, 8...Side wall rubber, 9...Inner liner rubber, 11... Foamed rubber layer, 11a... Outermost part, 11b... Innermost part, 11C... Center part, lid... Side end portion, 12... Foamed rubber, 13... Closed cell.

Claims (3)

[Claims] (1) In a pneumatic tire comprising a tire case and a tread covering the crown of the case, the tread has a foamed rubber layer in at least a portion of the thickness direction of the tread, and the foamed rubber layer is the main layer. A pneumatic tire made of foamed rubber having closed cells, wherein each part of the foamed rubber has a different expansion rate Vs in both or either of the tread thickness direction and the tread width direction. . (2) The pneumatic tire according to claim 1, wherein the foamed rubber is a single compounded rubber composition. (3) Claim 1, wherein the foaming rate Vs is a difference between a maximum foaming rate and a minimum foaming rate of 5% or more.
Pneumatic tires listed in section.