JPH03167008A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To enhance friction force especially against icy and snowy roads by forming main grooves and transverse grooves on the surface of a tread and respectively specifying the width of the transverse grooves, a groove area ratio and snow traction noise, as well as forming the tread part with specified foam rubber having closed cells. CONSTITUTION:In the tread surface 10, multiple main grooves 1 (1-1 to 1-3) extend to the direction of tire circumference E-E' and multiple transverse grooves 2 that mutually connect with respective main grooves 1 are respectively formed. And, respective settings of the width of respective transverse grooves 2 below 5mm, the groove area ratio of the surface 10 at 25%-40%, and snow traction index (STI) at 180-250 are performed. On the other hand, the tread part is formed with foam rubber having closed cells. Also, the foam rubber is formed blending an urea light auxiliary agent less than the same quantity against the blending quantity of a foaming agent, and respective settings at 0 deg.C of JIS hardness at 60-70, the average bubble area at 500-600mum<2>, the variation coefficient of respective bubble area at 0.5-0.8, and the bubble occupation area ratio at 10%-40% are performed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that can reduce frictional force (braking performance) on icy and snowy roads without impairing running performance on general roads (dry roads, wet roads). , drivability).

[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 turns into dust and causes pollution, posing a major environmental problem.

In order to solve these safety and environmental problems, straddle-less tires that do not use spikes or chains and have braking performance on snowy and icy roads are now rapidly becoming popular.

However, in conventional studless tires, the tread pattern formed on the tread surface of the tire is a kerf-based tread pattern, and snow tires (
Similar to snow road tires), the groove area ratio of the tread surface is 40.
% to about 50%, it exhibits maneuverability comparable to that of spiked tires on snowy roads, but its maneuverability on ice is insufficient. Therefore, if an attempt is made to lower the groove area ratio in order to improve the performance on ice, the performance on snow will decrease.

In order to improve the braking performance of such studless tires on icy roads, various proposals have been attempted in the past while keeping the groove area ratio at about 40% to 50%. For example, JP-A-55-135149, JP-A-58-19
As disclosed in Japanese Patent Application Laid-open No. 9203 and Japanese Patent Application Laid-open No. 137945/1983, by using a rubber composite sole containing a large amount of softener and plasticizer as tread rubber, the hardness at low temperatures is lowered and performance on ice is improved. There are known methods to improve this.

However, if a large amount of softener or plasticizer is added to lower the hardness at low temperatures, performance on ice is improved, but problems tend to occur in terms of reduced braking performance and steering stability on wet road surfaces.

As an alternative to these standless tires, there are tires that use foamed rubber in the tread. Tires using such foamed rubber are disclosed in, for example, Japanese Patent Application Laid-Open No. 62-283001.
This method is disclosed in Japanese Patent Application Laid-Open No. 63-90402. However, in these tires, the hardness of the foamed rubber is low, so the edge effect and drainage effect of closed cells are insufficient, and therefore the wear resistance and general road (dry road, wet road)
There is also the problem that the driving performance in the vehicle is degraded.

On the other hand, in order to improve these problems,
As described in Japanese Patent Application Laid-open No. 89547 and Japanese Patent Application Laid-Open No. 64-63401, short fibers are added to foamed rubber to increase the hardness of the tread part, and a part of the shoulder in the tresode part is reinforced. Efforts are being made to improve driving performance, but it is still insufficient.

As described above, although a certain degree of improvement in ice and snow performance has been recognized, at present no standless tire has been obtained that simultaneously satisfies wear resistance and running performance on ordinary roads.

[Problem to be solved by the invention]

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

[Means to solve the problem]

The pneumatic tire of the present invention is provided with a plurality of main grooves extending in the circumferential direction of the tire on the tresode surface, and with a lateral groove connecting the outermost main groove in the tire width direction and the tire ground contact edge, or in addition to the lateral groove, the main groove is provided with a plurality of main grooves extending in the circumferential direction of the tire. Horizontal grooves connecting each other are provided, the groove width of these lateral grooves is 5 am or less, the groove area ratio of the tread surface is 25% to 40%, the snow traction index (STI) is 180 to 250, and the tread portion is The foamed rubber is composed of a foamed rubber having closed cells, and the foamed rubber is blended with a urea-based auxiliary agent in an amount less than the same amount as the amount of the foaming agent blended, and the foamed rubber has a JIS hardness of 60 to 70 at 0°C. The average bubble area on the tread surface is 500~
6000 μm2, a coefficient of variation of the area of each bubble on the tread surface is 0.5 to 0.8, and a bubble occupation area ratio on the tread surface is 10% to 40%.

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 the pneumatic tire of the present invention. In FIG. 1, the pneumatic tire A of the present invention has a pair of left and right bead portions 11. 11 and these bead portions 11. A pair of left and right sidewall portions 12 connected to 11. 12 and these sidewall portions 12. It consists of a tread portion 13 arranged between 12 and 12. A pair of left and right bead portions 11. A carcass layer l4 is installed between the carcass layers 11, and a belt layer 15 is arranged so as to surround the outer periphery of the carcass layer l4 in the tread portion l3. 10 is the tread surface.

(11 In the present invention, a plurality of leads extending in the tire circumferential direction are arranged in an annular manner on the tread surface. In FIGS. 2 and 3, the tread surface 10 includes
3 main grooves in I 1-1. 1-2. 1-3 are provided in an annular shape. This is to improve drainage.

Further, as shown in FIG. 2, the tresode surface 10 is provided with a lateral groove 2 that connects the outermost main tMl-2 or l-3 in the tire width direction and the tire ground contact edge. This is to improve braking performance during cornering and improve steering stability. Or, as shown in Figure 3, the main groove 1-2
Or, in addition to providing the lateral groove 2 that connects 1-3 and the tire ground contact end, between the main grooves (l-2 and 1-1.11 and 1
3) is provided with a lateral groove 2 connecting the two. This is to improve steering stability not only when cornering but also when driving straight.

The groove width of the horizontal groove 2 is 5 mm or less, preferably 2. 0
mm~3. It is in the range of 0xv. This is because if the groove width of the lateral grooves 2 exceeds 5 mm, it is undesirable in terms of tire noise. The depth of the lateral groove is not particularly limited as long as it is the depth of the lateral groove in a normal tire, but it is preferably 50% or less of the groove depth of the main groove 1-L 1-2.1-3. It is better.

Main groove 1-1. 1-2. Rib 5 separated by 1-3
(Fig. 2) or the bronc 7 (Figs. 2 and 3), thin cuts 4 called kerfs or sipes of any number and depth may be formed at appropriate intervals in the tire width direction. , as shown in the example of FIG. 1-2.
1-a and the sub-groove 3 having a groove width exceeding 2+n may be provided under the condition that it does not penetrate between the outermost main groove 1-2, 1-3 and the tire ground contact edge.

(2) In the present invention, the groove area ratio of the tread surface 10 is set to 25% to 40%, and the tread surface 10
Snow traction index (STl) of 180
~250.

Here, the groove area ratio is the ratio of the groove contact surface to the total area of the contact area (contact width x circumference) of the tread surface 10. In the present invention, this groove area ratio is set to 25% to 40%. If the groove area ratio is less than 25%, the tire's on-snow performance will deteriorate, and if it is more than 40%, the land area of the torso surface lO will decrease, which will prevent the esoge effect of the blossock and the 1.resodo part l3. This is because the edge effect of the closed-cell foam rubber is reduced, resulting in a reduction in performance on ice. For reference, conventional pneumatic tires for ice and snow roads have a groove area ratio of 40% to 50%. In the present invention, the groove area ratio is made smaller than before to improve on-ice performance, and to compensate for the resulting decrease in on-snow performance.
As will be described later, the tread portion l3 is made of foamed rubber having closed cells to suppress the deterioration.

In addition, in the present invention, the snow traction index (
STI) value is set at 180 to 250. here,
What is Snow Traction Index (STI)?
It is an index showing the on-snow performance level calculated from the length of the grooves and kerfs on the tread pattern surface, the depth in the cross-sectional direction of the tire and the depth of the grooves described in E Paper 820345, and is expressed by the following formula. .

STI = −6.8 + 2202ρ ++672
ρ! +7.60gIn the above formula, ρ1 is the sum of the projected lengths of the grooves in the tire cross-sectional direction (1/mW) in the total area of the tread surface contact area (contact width x circumference), and ρ2 is the total tread surface contact area (contact width x circumference). The sum (1/mm) of the projected length of the kerf in the tire cross-sectional direction (width x circumference), and Dg is the average groove depth (m).

As this STI increases, the snow performance of the tire improves, but if it becomes too large, the rigidity decreases and the dry performance (dry road running performance) decreases.On the other hand, if the STI increases
If the value becomes small, good on-ice performance will not be achieved.

In the present invention, if this STI is smaller than 180, fully satisfactory on-snow performance cannot be obtained;
If it exceeds 50, the dry performance of the tire will deteriorate. The tire of the present invention that satisfies these requirements has a tresode surface with a large number of land areas and a lower groove surface reliability than that of a typical studless tire. The present invention improves the energy effect of the lateral grooves 2 by providing narrow lateral grooves 2 of 5 mm or less on the tread surface, and also improves independence by using foamed rubber in the tread portion, which has many land areas. It can be said that the edge effect and drainage effect of the bubbles are enhanced to effectively remove the thin water film on the icy and snowy road surface, resulting in a significant improvement in the icy and snowy performance.

(3) Furthermore, in the present invention, the tread portion 13 is made of foamed rubber having closed cells. This foamed rubber contains a urea-based auxiliary agent in an amount less than the same amount as the foaming agent.

The inventors of the present invention have conducted extensive research to improve the frictional force on icy and snowy roads, which has been difficult to achieve with conventional technology. The inventors have discovered that the above goals can be achieved using the following methods, and have arrived at the present invention.

That is, it has been found that the closed cells contained in the foamed rubber improve the edge effect and drainage effect, and have a surprising effect especially on ice where a pseudo liquid layer exists at around 0°C. Furthermore, the conventional idea that low hardness improves ice and snow friction at low temperatures does not apply to foamed rubber; rather, increasing the hardness to a certain degree significantly improves the edge effect and drainage effect brought about by the closed cells in contact with the road surface. I found out the truth. In addition, the relatively high hardness improves the tire's tire stiffness and maintains a high level of driving performance on general roads (dry roads and wet roads), which was 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 matrix rubber is significantly increased. Generally, adjustments are made such as significantly increasing the amount of reinforcing agent such as carbon black or significantly reducing the amount of softening agent such as oil, but this is not preferable because processability, heat generation properties, etc. will deteriorate. Therefore, in order to lower the decomposition temperature of the blowing agent, the present inventors conducted various studies focusing on the fact that the urea-based auxiliary agent, which is often used in combination with the blowing agent, increases the crosslink density. As a result of this study, it was found that although the hardness increases even when a urea-based auxiliary agent is blended alone into a rubber composition, the effect is further enhanced when used in combination with a foaming agent. In other words, it was discovered that by adding a specific amount of urea-based auxiliary agent to the foaming agent, the decrease in hardness due to foaming could be suppressed and the hardness could be made to be comparable to that of non-foamed rubber, while also having negative effects on processability, heat generation, etc. It was also confirmed that there was no effect on Furthermore, if a nitroso compound is selected as the blowing agent, formaldehyde will be produced during the decomposition reaction and give a strong pungent odor, so in this case as well, it is difficult to incorporate a urea-based auxiliary agent that accepts aldehyde. It is very effective from a sexual perspective.

After obtaining this knowledge, the present inventors repeatedly studied the distribution state of bubbles, the tresode pattern, etc., and arrived at the present invention.

In the present invention, the foamed rubber is obtained by adding a foaming agent to a normal rubber composition, and further adding a urea-based auxiliary agent in an amount less than the same amount as the amount of the foaming agent.

Preferably, a urea-based auxiliary agent is blended in an amount of 30 to 90% by weight based on the amount of the blowing agent. 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, which deteriorates processability and heat generation properties, and furthermore, 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 the 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. There is a risk that unvulcanized rubber may foam during the mixing and extrusion process.In order to construct the tread portion of a pneumatic tire in the present invention with foamed rubber having closed cells, the rubber assembly or material used for the tread portion is usually It is sufficient to add a foaming agent and a urea-based auxiliary agent and perform vulcanization by a normal tire manufacturing method.

In this case, the glass transition temperature of the foamed rubber should be such that the embrittlement temperature is 30° C. or less so that cracks do not occur during winter use. As the blowing agent, any organic or inorganic blowing agent can be selected. For example, organic blowing agents include benzenesulfonyl hydrazide, dinitrosopencumethylenetetramine, azodicarbonamide, 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. Specific examples include Cell Paste M3 (urea + acidic substance), Cell Base M5 (urea ten acidic substance), and Cell Paste 101 (urea ten agglomeration inhibitor) manufactured by Eiwa Kawei Industries. In addition, compounding agents such as carpon blank, softener, processing aid, anti-aging agent, wax, vulcanizing agent, and vulcanization accelerator may be added in appropriate amounts according to the practice 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.

1 5 Furthermore, as a method to improve performance on icy and snowy roads and on general roads, it is possible to further improve these performances by introducing a two-layer or three-layer tread structure such as camp tread rubber/base tread rubber structure. Therefore, it is preferable.

In the present invention, the foamed rubber having closed cells constituting the tread portion has the following requirements (1) to (2).

■ JIS hardness at 0°C is 60 to 70.

Here, JIS hardness refers to JIS-^ hardness.

The hardness of foamed rubber is JIS hardness at 0°C of 60 to 7.
It needs to be 0, preferably 63-68. If the JIS hardness at 0°C is less than 60, the edge effect of bubbles and drainage effect will be reduced, braking performance and driving performance on icy and snowy roads will be insufficient, and driving performance such as wear resistance and steering stability on ordinary roads will also be reduced. , undesirable. If it exceeds 70, performance on icy and snowy roads decreases due to a decrease in adhesive friction, which poses a practical problem.

1 6 ■ I・Red The average bubble area on the surface is 500-6000
Must be μm2.

The average cell area of the foamed rubber needs to be closed cells of 500 to 6000 μm2, preferably 1000 μm2.
~4000 μm2. If it is less than 500 μm2, the improvement effect on ice and snow road performance is insufficient;
This is because if it exceeds 2, wear resistance and running performance on general road surfaces will be significantly reduced.

■ The coefficient of variation of the area of each bubble on the tread surface is 0.5 to 0.
．． Must be 8.

As a result of investigating the shape and distribution of bubbles, we 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 general road performance. .

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

K = S/X 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 bubbles, and when it exceeds 0.8, the performance on ice and snow decreases due to a decrease in the drainage effect of bubbles.

(2) The bubble occupation area ratio on the surface of the tresode is 10% to 40%.

If it is less than 10%, the improvement effect on ice and snow road performance is small, and it is 40%.
This is because although the performance on icy and snowy roads is improved, the wear resistance and performance on ordinary roads are significantly reduced. The bubble occupation area ratio is expressed as the area ratio of the bubbles per unit area of the foamed rubber.

Examples and comparative examples are shown below.

Examples and Comparative Examples Various tires having the tread pattern shown in FIG. 2 and a tire size of 185/70 R13 85 (l) were prepared, and the following evaluations were performed on these tires.

The results are shown in Table 1. In addition, the width of the main groove is 8~l Q
m++, depth is 11 mm, horizontal groove depth is 9 mm
, Rikiichi 18 The depth of the hole was 8 mm. Also, the test car was 1600cc.
A FF car was used.

Average bubble area, coefficient of variation of bubbles, occupied area of bubbles: A test piece was cut out from the tread part of each test tire, flattened, and image processed at 165x magnification using a NEXUS 6400 manufactured by Kashiwagi Laboratory. The evaluation was based on the average value of the samples.

Dansai V Himen: A test piece was cut from the tresode part of each test tire, and J
The hardness at a temperature of 0° C. was measured according to the method specified in IS-K6301.

゛Braking on the upper road '4'': Driving on a water plate at an initial speed of 30km/h, the braking distance was measured and expressed as an index with conventional tires as 100. The higher the value, the better the braking. Show that something is true.

Performance in snow FIL: A test was carried out on a 5%l9 (2.9°) slope slope test on a smooth, compacted snow road by repeatedly braking a passenger car on a compacted snow road, and acceleration uphill over a 30m section using the zero starting method. The times were measured and expressed as an index compared to conventional tires. The larger the value, the better the drive performance.

Maneuverability (dry road surface): The feeling of each tire was scored by five test drivers using a 10-point system, and the results (average value) were expressed as an index relative to the conventional tire. The larger the value, the better the steering stability.

Wear resistance: 20% on a dry road surface under the design normal load and air pressure conditions stipulated by JATMA. After traveling OOOkm, the amount of wear on each tire was expressed as an index relative to the amount of wear on conventional tires.

The larger the value, the better the wear resistance.

(Margins below this page) 20 The following can be seen from Table 1.

(a) Example 1, Comparative Example 1 Example 1 in which the urea-based auxiliary agent is blended as specified in the present invention
In this case, the JIS-A hardness and foaming state were both as specified, and the tire performance was also superior to the conventional tire, whereas Comparative Example 1, which did not contain a urea-based auxiliary agent, met the JIS-A hardness and foaming state.
-A hardness decreases significantly and falls outside the range defined by the present invention. In order to bring the hardness within the range specified by the present invention, it is necessary to increase the amount of carbon plank or reduce the amount of oil, which is disadvantageous in terms of processability and heat generation.

Tbl Examples 1 to 3, Comparative Example 2 In Examples 1 to 3, in which the JIS-A hardness at 0°C is within the range specified by the present invention, not only the ice and snow performance is significantly improved compared to the conventional example, but also It also has excellent performance on public roads and wear resistance.

On the other hand, in Comparative Example 2, in which the hardness was outside the specifications of the present invention, it was found that not only the improvement effect on ice and snow performance was small, but also the performance on ordinary roads and abrasion resistance were significantly reduced.

(Cl Examples 1 to 3, Comparative Examples 3 and 4 Example 1 in which the average cell area and coefficient of variation are within the range specified in the present invention
-3, Comparative Example 3 where the average cell area is outside the specification of the present invention and Comparative Example 4 where the coefficient of variation is outside the specification of the present invention,
Although its performance and wear resistance on public roads are at a satisfactory level, it has the disadvantage of poor ice and snow performance.

(dl Example 4, Comparative Example 5 Example 4 where the bubble occupied area is within the range specified by the present invention
In Comparative Example 5, the tire performance is at the same or higher level than the conventional example, but the bubble occupation area ratio is outside the specification of the present invention.
In this case, although the ice and snow performance is improved, the performance on ordinary roads and the wear resistance are deteriorated, which is not preferable.

tel Examples 2 and 5, Comparative Example 6.7 Horizontal groove width, groove area ratio, and snow traction index (STI
) is within the range defined by the present invention, Examples 2 and 5 exhibit superior tire performance compared to the conventional example. On the other hand, in Comparative Example 6 in which the groove area ratio is outside the specification of the present invention, the on-snow performance is
In Comparative Example 7 in which Tr is outside the specification of the present invention, the wear resistance is
It turns out that each one is inferior.

〔Effect of the invention〕

As explained above, the pneumatic tire of the present invention uses a foamed rubber having closed cells prepared by blending a foaming agent and a urea-based auxiliary agent in a specific ratio as the rubber of the tresode portion that contacts the road surface. JIS hardness of rubber at O℃,
By setting the average bubble area, coefficient of variation of bubbles, and bubble occupation area ratio to specific ranges, and also specifying the tread pattern on the tread surface, it is possible to reduce the frictional force on icy and snowy roads without impairing running performance on ordinary roads (dry roads, wet roads). It becomes possible to make a significant improvement.

[Brief explanation of the drawing]

FIG. 1 is an explanatory half-sectional view in the meridian direction of the pneumatic tire of the present invention, and FIGS. 2 and 3 each show an example of the tresod pattern formed on the tread surface of the pneumatic tire of the present invention. FIG. 1-1, l-2. 1-3...Main groove, 2...
Horizontal groove, 3... Sub groove, 4... Notch, 5... Rib, 10... Tresod surface, 11... Bead part, 1
2...Side wall, 13...Tread part, l4
...Carcass layer.

Claims (1)

[Claims] A plurality of main grooves extending in the circumferential direction of the tire are provided on the tread surface, and a lateral groove is provided that connects the outermost main groove in the tire width direction and the tire ground contact edge, or in addition to the lateral groove, a lateral groove that connects the main grooves. The groove width of these horizontal grooves is 5 mm.
The groove area ratio on the tread surface is 25% to 40%,
Snow traction index (STI) from 180
250, and further, the tread portion is made of foamed rubber having closed cells, the foamed rubber is blended with a urea-based auxiliary agent in an amount less than the same amount as the amount of foaming agent blended, and the foamed rubber is
The JIS hardness at 0°C is 60 to 70, the average bubble area on the tread surface is 500 to 6000 mm^2, 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 A pneumatic tire characterized by having a pneumatic content of 10% to 40%.