JP2008030635A - Pneumatic tire and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire and its manufacturing method, which enhance braking performance on an ice by increasing an amount of moisture content capable of being sucked in a sipe. <P>SOLUTION: In the pneumatic tire relating to the present invention, a plurality of blocks 26 divided by a circumferential groove and a lateral groove, are formed on a tread part 16. The sipe 28 is formed on the block 26, and a hydrophilic film 32 is formed on a wall surface of the sipe 28. Since a contact angle of water relative to the hydrophilic film 32 thereby becomes an acute angle, when water stayed on the ice or the like is contacted with the hydrophilic film 32, water is sucked up in the sipe 28 by capillarity. Accordingly, an amount of moisture content to be sucked up in the sipe, i.e., a removal amount of water stayed on the ice is increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire in which a plurality of blocks having sipes are formed in a tread portion, and a method for manufacturing the same.

  In order to improve braking performance (braking performance) on ice, it has been conventionally performed to release water generated on ice to a sipe formed on a tread portion of a tire. However, since the amount of moisture that can be absorbed by sipes is not large, it is difficult to secure a sufficient escape route for water, particularly at temperatures where water is likely to be generated on the ice surface. For this reason, the tread portion is in a state of riding on the water film, and it may be difficult to sufficiently obtain the water absorption effect by the sipe.

  As a countermeasure, Patent Document 1 discloses disposing a fiber layer chip in a sipe and causing it to swell by absorbing water to serve as an edge. Patent Document 2 discloses that a part of a block wall forming a circumferential groove or a lateral groove is made of hydrophilic rubber.

  However, it is preferable that a pneumatic tire capable of obtaining a water absorption effect as compared with Patent Documents 1 and 2 is realized because braking performance on ice is further improved.

If the sipe volume is excessively increased in Patent Documents 1 and 2 in an attempt to increase the amount of water absorption, there is a problem in that the block rigidity is decreased and the water absorption performance is decreased. In Patent Documents 1 and 2, since the water absorption direction when the sipe abuts the road surface and absorbs water is opposite to the gravity direction, it is difficult to absorb water and there is a limit in terms of drainage.
JP-A-9-202116 JP 2001-287509 A

  In view of the above-described facts, an object of the present invention is to provide a pneumatic tire having improved braking performance on ice by increasing the amount of water that can be sucked into a sipe and a method for manufacturing the same.

  The present inventor has studied to increase the water absorption speed at the sipe. Then, when water is absorbed by the sipe, attention is paid to the fact that a phenomenon equivalent to the capillary phenomenon (capillary phenomenon) occurs between the sipe wall surfaces (hereinafter, in this specification, this phenomenon between flat plates such as sipe). The phenomenon is also called capillary phenomenon).

  In general, between flat plates separated by a narrow gap, when the flat plate surface in contact with water is hydrophilic, the water rises by capillary action as shown in FIG. The rising height h is expressed by the formula (1).

h = (2T cos θ) / ρgt (1)
Here, T is the surface tension of water, θ is the contact angle (angle between the free surface of water and the flat plate surface in contact with water), ρ is the density of water, g is the gravitational acceleration, and t is between the flat plates. Indicates a gap.

  In order to increase h, θ should be decreased or t should be decreased, and there is no other countermeasure. In the case of sipe, reducing t is reducing the sipe width, but there are many restrictions on reducing the sipe width.

  Therefore, the present inventor studied a countermeasure for reducing θ. Here, the inventor paid attention to the fact that θ is larger than 90 ° as shown in FIG. 9 because the rubber material constituting the sipe wall is conventionally water-repellent. Then, it was considered to make this θ smaller than 90 ° by making the sipe wall hydrophilic.

  As a result of intensive studies, the inventors have thought of applying a hydrophilic material to the sipe wall surface, and have further studied through repeated experiments to complete the present invention.

  According to the first aspect of the present invention, a plurality of blocks defined by the circumferential grooves and the lateral grooves are formed in the tread portion, at least one sipe is formed in the block, and at least a part of the wall surface of the sipe A hydrophilic film is formed.

  In the first aspect of the invention, when water staying on ice or the like touches the hydrophilic film, the water contact angle with the hydrophilic film becomes an acute angle, so that water is sucked into the sipe by capillary action. It is done. Therefore, it is possible to obtain a pneumatic tire with improved braking performance (friction characteristics) on ice by increasing the amount of water that can be sucked into the sipe, that is, the amount of water remaining on the ice.

  Note that the direction in which the sipe extends is often the tire width direction, but the above effect can be observed even in other directions. For example, the sipe may extend along the tire circumferential direction.

  The invention according to claim 2 is characterized in that a contact angle of water with respect to the hydrophilic film is 80 ° or less. This makes it possible to absorb water until the inside of the sipe is completely filled with water.

  The invention according to claim 3 is characterized in that both ends of the sipe are open to the circumferential groove or the lateral groove.

  In the invention described in claim 3, as the water rises, the air in the sipe is expelled from both ends of the sipe to the circumferential groove. That is, since it is not necessary for water to rise in the sipe by overcoming the air pressure in the sipe, the water absorption amount and the water absorption speed are increased compared to a closed sipe in which both ends of the sipe are not opened in the circumferential groove. be able to.

  The invention according to claim 4 is characterized in that the hydrophilic film contains titanium oxide. Titanium oxide is a particularly hydrophilic material, so it is preferable in terms of the amount of water absorbed by the sipe and the rate of water absorption, and titanium oxide is easily available.

  The invention according to claim 5 is characterized in that the width of the sipe is 0.3 mm or more and 0.8 mm or less.

  This is because a sipe having a sipe width of less than 0.3 mm is difficult to manufacture, and when the sipe width is 0.9 mm or more, the effect of rising water due to capillary action is rapidly reduced.

  The invention according to claim 6 is a method for producing the pneumatic tire according to claim 1, wherein the hydrophilic film is formed by applying and solidifying a paint containing a hydrophilic substance on the wall surface of the sipe. Is formed.

  Thereby, the hydrophilic film can be formed by a simple operation after molding.

  The invention according to claim 7 is a method for producing the pneumatic tire according to claim 1, wherein a coating material containing a hydrophilic substance is applied to a surface of a blade constituting the mold and forming the sipe. The hydrophilic film is formed by solidifying the paint attached to the wall surface of the sipe by molding.

  Thereby, a hydrophilic film can be formed on the sipe wall surface when molding.

  The invention according to claim 8 is characterized in that the hydrophilic substance is titanium oxide. Titanium oxide is a particularly hydrophilic material, so it is preferable in terms of the amount of water absorbed by the sipe and the rate of water absorption, and titanium oxide is easily available.

  According to the present invention, a pneumatic tire with improved braking performance on ice can be manufactured by increasing the amount of water that can be sucked into the sipe.

  Hereinafter, embodiments will be described and embodiments of the present invention will be described. In the second and subsequent embodiments, the same components as those already described are denoted by the same reference numerals, and description thereof is omitted.

[First Embodiment]
First, the first embodiment will be described. As shown in FIG. 1, a pneumatic tire 10 according to the present embodiment includes a carcass 12 configured by one layer or a plurality of layers, each end portion of which is folded by a bead core 11.

  On the outer side in the tire radial direction of the crown portion 12C of the carcass 12, a belt layer 14 in which a plurality of (for example, two) belt plies are stacked is embedded.

  A tread portion 16 provided with a groove is formed on the outer side of the belt layer 14 in the tire radial direction. As shown in FIG. 2, the tread portion 16 is formed with a plurality of circumferential grooves (main grooves) 22 along the tire circumferential direction U on the tire equatorial plane CL and on both sides thereof. The tread portion 16 is formed with a plurality of lateral grooves 24 that intersect the tire circumferential direction U. In the present embodiment, the lateral groove 24 is formed along the tire width direction V. Both end portions of each lateral groove 24 communicate with the circumferential groove 22 or extend beyond the tread end T so as to be drained outward in the tire width direction.

  Here, the tread end means that a pneumatic tire is mounted on a standard rim specified in JATMA YEAR BOOK (2005 edition, Japan Automobile Tire Association Standard), and the maximum load in the applicable size and ply rating in JATMA YEAR BOOK. Fills 100% of the air pressure (maximum air pressure) corresponding to the capacity (internal pressure-load capacity correspondence table) as the internal pressure, and indicates the outermost contact portion in the tire width direction when the maximum load capacity is applied. In addition, when TRA standard and ETRTO standard are applied in a use place or a manufacturing place, it follows each standard.

  As shown in FIG. 2, a large number of blocks 26 are formed in the tread portion 16 by the circumferential grooves 22 and the lateral grooves 24.

  As shown in FIGS. 2 and 3, each block 26 is formed with a sipe 28 along the lateral groove 24. Both ends of each sipe 28 are open to both side walls of the block and communicate with the circumferential groove 22, so that the so-called sipe 28 is an open sipe. In the present embodiment, one sipe 28 is formed for each block 26. In the present embodiment, the sipe 28 is formed along the tire width direction V.

  A hydrophilic film 32 is formed on the wall surface of the sipe 28. In the present embodiment, the hydrophilic film 32 is a film made of a water-soluble polymer. This water-soluble polymer has an HLB value of 8.

  In order to form the hydrophilic film 32, a film having an HLB value larger than 7 may be used. Here, the HLB value is Griffin's HLB (Hydrophilic-Lipophilic Balance) value.

  The HLB value is calculated by the following formula (2) by the Griffin method, where M is the molecular weight of the nonionic surfactant and Mw is the molecular weight of the hydrophilic portion.

HLB = 20Mw / M (2)
FIG. 4 shows an example of a hydrophobic coating material and a hydrophilic coating material. The smaller the HLB value is, the stronger the hydrophobicity, and the larger the HLB value is, the stronger the hydrophilicity.

  In order to form the hydrophilic film 32 on the wall surface of the sipe 28, a paint in which this water-soluble polymer is dissolved is manufactured in advance, and this paint is applied to the sipe wall surface after molding. The hydrophilic film 32 is formed by solidifying the applied film. Thereby, the hydrophilic film 32 can be formed by a simple operation after molding.

  In addition, if this water-soluble polymer is a substance that is not adversely affected by the temperature at the time of molding, the sipe wall surface in contact with the blade surface is applied by applying the above-mentioned paint to the surface of the blade constituting the mold and molding. A hydrophilic film 32 formed by solidifying the paint is formed. Thereby, the hydrophilic film 32 can be formed on the sipe wall surface when molding.

(Function, effect)
Hereinafter, an operation and effect when the pneumatic tire 10 according to the present embodiment is mounted on a vehicle and travels on an icy road surface will be described.

  As shown in FIG. 5, when the block 26 (26A to D) contacts the ice road surface S and the block 26 moves from the tire stepping side I to the tire kicking side K, a water film W is generated on the ice road surface S. is doing.

  Here, in this embodiment, since the hydrophilic film 32 is formed on the wall surface of the sipe 28, when the water forming the water film W touches the hydrophilic film 32, The contact angle becomes an acute angle. For this reason, water is sucked into the sipe 28 at a higher water absorption speed than before due to capillary action, and the amount of water absorbed by the sipe 28 is larger than before. Therefore, if a water film W is generated on the ice road surface S on the tire kicking side K, the water film W is sucked up to the sipe 28 at a high speed and removed from the ice road surface S. Thereby, the frictional force between the block 26 and the ice road surface S is increased on the tire kicking side K, so that the sliding of the block 26 with respect to the road surface is suppressed, and the braking performance (friction characteristics) is improved. This effect is particularly noticeable at temperatures near 0 ° C. where the amount of water generated is large.

  As described above, in this embodiment, the sipe wall surface becomes hydrophilic by forming the hydrophilic film 32 on the sipe wall surface that plays the role of drainage. For this reason, water absorption improves by a capillary phenomenon, and the brake performance on ice improves.

  Further, both ends of the sipe 28 are opened in the circumferential groove 22, and the sipe 28 is an open sipe. Therefore, the air in the sipe 28 is expelled from the both ends of the sipe 28 to the circumferential groove 22 as the water is absorbed. Therefore, the water absorption amount and the water absorption speed can be increased as compared with a closed sipe in which both ends of the sipe are not opened in the circumferential groove 22.

[Second Embodiment]
Next, a second embodiment will be described. In the present embodiment, as compared to the first embodiment, as shown in FIG. 6, a block 46 in which a sipe 48 that is a coulomb sipe is formed in place of the sipe 28 that is an open sipe is formed in the tread portion. A hydrophilic film 32 is formed on the wall surface of the sipe 48 as in the first embodiment.

  In the present embodiment, when the sipe 48 absorbs water, the water needs to rise over the pressure of the air in the sipe 48, but the braking performance on ice is improved as compared with the prior art.

[Third Embodiment]
Next, a third embodiment will be described. In the present embodiment, as compared with the first embodiment, as shown in FIG. 7, a hydrophilic film 52 made of titanium oxide is formed on the wall surface of the sipe 58 instead of the hydrophilic film 32. For this reason, the HLB value of the hydrophilic film 52 is 10, which is higher than that of the hydrophilic film 32. Titanium oxide also functions as a photocatalyst. The shape of the sipe 58 is the same as the sipe 28 described in the first embodiment.

  Titanium oxide is a material having particularly strong hydrophilicity, and therefore is preferable from the viewpoint of the amount of water absorbed by the sipe and the water absorption speed. In this embodiment, the contact angle of water with the hydrophilic film 52 is 80 ° or less. Therefore, it is easy to absorb water until the inside of the sipe is completely filled with water, and the braking performance on ice is improved as compared with the first embodiment. Titanium oxide is an easily available material.

  In order to form the hydrophilic film 52 on the wall surface of the sipe 58, a paint containing this titanium oxide is manufactured in advance, and this paint is applied to the sipe wall surface after molding. When the applied film is solidified, a hydrophilic film 52 made of titanium oxide is formed. Thereby, the hydrophilic film | membrane 52 can be formed by a simple operation | work after molding. The hydrophilic film 52 formed by solidifying the paint may be formed on the sipe wall surface in contact with the blade surface by applying the paint to the surface of the blade constituting the mold and molding. Thereby, the hydrophilic film | membrane 52 can be formed in a sipe wall surface at the time of shaping | molding.

<Test example>
In order to confirm the effect of the present invention, the present inventor made four examples of pneumatic tires according to the present invention (hereinafter referred to as tires of Examples 1 to 4) and an example of conventional pneumatic tires (FIG. 10). 11, hereinafter referred to as a conventional tire), the braking performance was tested on an icy road to evaluate the braking performance. The tire of Example 1 and the tire of Example 3 are both examples of the pneumatic tire according to the first embodiment, and the tire of Example 2 is an example of the pneumatic tire according to the second embodiment. The tire 4 is an example of a pneumatic tire according to the third embodiment. The conventional tire is a tire in which the hydrophilic film 32 is not formed on the wall surface of the sipe 28 in the block 86 formed in the tread portion in the tire of the first embodiment. Table 1 shows the tire conditions for each tire.

Regarding the block dimensions, in the tire of Example 1, as shown in FIG. 3, the tire circumferential direction length L is 25 mm, the tire width direction length M is 20 mm, and the tire radial direction depth (block height) H is 10 mm. It was. For the tires of Examples 2 to 4 and the tire of the conventional example, the block dimensions (L, M, and H values) were the same as those of the tire of Example 1.

  As shown in FIG. 3, the sipe depth h was 6 mm in the tire of Example 1. The sipe depth h was the same in the tires of Examples 2 to 4 and the tire of the conventional example (see FIG. 10). As shown in Table 1, the sipe width t was 0.4 mm for the tires of Examples 1, 2, 4 and the conventional tire, and 0.9 mm for the tire of Example 3. The sipe length d is the same as the length M in the tire width direction of the block in the tires of Examples 1, 2, and 4 and the conventional tire. In the tire of Example 2, the sipe length d was 15 mm.

  In this test example, for all tires, the tire size was set to 195 / 65R15, the tire was mounted on a regular rim, the internal pressure was set to 200 kPa, and the test was performed by running the vehicle in a state where it was attached to a passenger car and loaded with a regular load. Here, “regular rim” means, for example, a standard rim in an applicable size defined in the 2005 YEAR BOOK issued by JATMA. “Regular load” similarly refers to the 2005 YEAR issued by JATMA. It refers to the maximum load at the applicable size and ply rating specified in BOOK.

  In this test example, the braking distance from the initial speed of 40 km / h until full braking was applied to the stationary state was measured, and the average deceleration was calculated from the initial speed and the braking distance. And the evaluation index | exponent based on the average deceleration of the tire of a prior art example was set to 100, and the evaluation index | exponent used as relative evaluation about the tire of Examples 1-4 was computed. The evaluation results are also shown in Table 1.

  The evaluation results in Table 1 indicate that the larger the evaluation index, the higher the performance on ice, that is, the shorter the braking distance and the better the braking performance. As can be seen from Table 1, in the tires of Examples 1 to 4, the evaluation index was higher than that of the conventional tire, and it was found that the braking performance on ice was improved.

  Therefore, in the tire of the conventional example, as shown in FIG. 11, since the amount of water that can be absorbed by the sipe 88 is small, the water film W between the block 86 (86A to D) and the icy road surface S on the tire kicking side K. However, in the tires of Examples 1 to 4, it was found that the water film W could be removed more than in the conventional tire.

  Further, in this test example, the evaluation index of the tire of Example 1 is higher than that of the tire of Example 3, and it was found that the sipe width is preferably 0.4 mm rather than 0.9 mm.

  Further, in this test example, the tire of Example 4 had the highest evaluation index, and it was found that the hydrophilic film was preferably composed of titanium oxide rather than composed of a water-soluble polymer.

  In this test example, it was also confirmed that when a hydrophilic film having a contact angle θ of 80 ° or less was formed, water was completely filled in the sipe when the sipe width t was 0.4 mm.

  The embodiments of the present invention have been described above with reference to the embodiments. However, these embodiments are merely examples, and various modifications can be made without departing from the scope of the invention. It goes without saying that the scope of rights of the present invention is not limited to these embodiments.

It is tire radial direction sectional drawing of the pneumatic tire which concerns on 1st Embodiment. It is explanatory drawing which shows the block arrangement of the tread part of the pneumatic tire which concerns on 1st Embodiment in a planar state. It is a perspective view of the block which constitutes the tread part of the pneumatic tire concerning a 1st embodiment (state where a block is located in the upper part of a tire). It is explanatory drawing which shows the example of an HLB value. In a 1st embodiment, it is a typical partial side sectional view showing that a pneumatic tire rolls on an icy road surface. It is a perspective view of the block which constitutes the tread part of the pneumatic tire concerning a 2nd embodiment (state where a block is located in the upper part of a tire). It is a perspective view of the block which constitutes the tread part of the pneumatic tire concerning a 3rd embodiment (state where a block is located in the upper part of a tire). It is side surface sectional drawing which shows that water rises by a capillary phenomenon with two hydrophilic flat plates. It is side surface sectional drawing which shows that water falls by capillary action with two hydrophobic flat plates. It is a perspective view of the block which comprises the tread part of the conventional pneumatic tire (state in which a block is located above a tire). It is a typical partial side sectional view showing that a conventional pneumatic tire rolls on an icy road surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pneumatic tire 16 Tread part 22 Circumferential groove 24 Horizontal groove 26A-D Block 28 Sipe 32 Hydrophilic membrane 46 Block 48 Sipe 52 Hydrophilic membrane 58 Sipe 86 Block 88 Sipe

Claims (8)

A plurality of blocks defined by the circumferential groove and the lateral groove are formed in the tread portion,
At least one sipe is formed in the block,
A pneumatic tire, wherein a hydrophilic film is formed on at least a part of the wall surface of the sipe.   The pneumatic tire according to claim 1, wherein a contact angle of water with respect to the hydrophilic film is 80 ° or less.   The pneumatic tire according to claim 1 or 2, wherein both ends of the sipe are opened in the circumferential groove or the lateral groove.   The pneumatic tire according to claim 1, wherein the hydrophilic film contains titanium oxide.   The pneumatic tire according to any one of claims 1 to 4, wherein a width of the sipe is 0.3 mm or more and 0.8 mm or less. A method for manufacturing the pneumatic tire according to claim 1,
A method for producing a pneumatic tire, wherein the hydrophilic film is formed by applying and solidifying a paint containing a hydrophilic substance on a wall surface of the sipe. A method of manufacturing the pneumatic tire according to claim 1,
By applying a coating material containing a hydrophilic substance on the surface of the blade constituting the mold and forming the sipe and molding it, the coating material adhering to the wall surface of the sipe is solidified to form the hydrophilic film. A method for producing a pneumatic tire, characterized in that   The method for manufacturing a pneumatic tire according to claim 6 or 7, wherein the hydrophilic substance is titanium oxide.