阅读说明：本技术 橡胶组合物、硫化橡胶、轮胎、无钉防滑轮胎 (Rubber composition, vulcanized rubber, tire, studless tire ) 是由 川岛正宽 于 2018-03-20 设计创作，主要内容包括：本发明的橡胶组合物包含橡胶组分和A/B的比大于1的短纤维状树脂D1,其中对于垂直于长轴方向截取的截面,A为所述截面在其长径方向上的长度并且B为所述截面在垂直于所述长径方向的短径方向上的长度。吸水力大的硫化橡胶可以由所述橡胶组合物获得。本发明还提供吸水力大的硫化橡胶、具有优异的冰上性能的轮胎和具有优异的冰上性能的无钉防滑轮胎。(The rubber composition of the present invention comprises a rubber component and a short fiber-shaped resin D1 having an A/B ratio of more than 1, wherein for a cross section taken perpendicular to the long axis direction, A is the length of the cross section in the long diameter direction thereof and B is the length of the cross section in the short diameter direction perpendicular to the long diameter direction. Vulcanized rubbers having high water absorption can be obtained from the rubber composition. The present invention also provides a vulcanized rubber having a large water absorption capacity, a tire having excellent on-ice performance, and a studless tire having excellent on-ice performance.)

1. A rubber composition, comprising:

a rubber component, and

a short fiber-like resin having a ratio of a/B of more than 1, wherein a is a length of a cross section perpendicular to a long-axis direction thereof in a long-axis direction thereof and B is a length of the cross section in a short-axis direction perpendicular to the long-axis direction.

2. The rubber composition of claim 1, further comprising a blowing agent.

3. The rubber composition according to claim 1 or 2, wherein the short fiber-shaped resin is a composite resin including a hydrophilic resin and a coating layer that coats the hydrophilic resin, wherein the coating layer is formed of a resin having affinity with the rubber component.

4. The rubber composition according to claim 3, wherein the hydrophilic resin contains at least one selected from an oxygen atom, a nitrogen atom and a sulfur atom.

5. The rubber composition according to claim 3 or 4, wherein the resin having affinity with the rubber component is a low-melting resin having a melting point lower than the maximum vulcanization temperature of the rubber composition.

6. The rubber composition according to any one of claims 1 to 5, wherein the A/B ratio of the short fiber-shaped resin is 10 or less.

7. The rubber composition according to any one of claims 1 to 6, wherein the short fiber-shaped resin has an average length in a length direction of 0.1 to 500 mm.

8. The rubber composition according to any one of claims 1 to 7, wherein the short fiber-shaped resin is contained in an amount of 0.1 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

9. The rubber composition according to any one of claims 1 to 8, wherein the average area of the cross section of the short fiber-shaped resin is 0.000001 to 0.5mm²。

10. The rubber composition of any one of claims 3-9, wherein the hydrophilic resin comprises a hydrophilic polymer selected from the group consisting of-OH, -COOH, -OCOR (where R is alkyl), -NH₂At least one substituent of the group consisting of-NCO and-SH.

11. The rubber composition according to any one of claims 3 to 10, wherein the hydrophilic resin comprises at least one selected from the group consisting of an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly (meth) acrylic resin, a polyamide resin, an aliphatic polyamide-based resin, an aromatic polyamide-based resin, a polyester resin, a polyolefin resin, a polyvinyl alcohol-based resin, and an acrylic resin.

12. The rubber composition according to any one of claims 5 to 11, wherein the low-melting resin is a polyolefin-based resin.

13. The rubber composition according to claim 12, wherein the polyolefin-based resin comprises at least one selected from the group consisting of a polyethylene-based resin, a polypropylene-based resin, a polyolefin ionomer, and a maleic anhydride-modified α -polyolefin.

14. The rubber composition according to any one of claims 1 to 13, which is a rubber composition for a tread.

15. A vulcanized rubber obtained by vulcanizing the rubber composition according to any one of claims 1 to 14.

16. The vulcanized rubber according to claim 15, which has flat voids having a ratio of M/N of more than 1, wherein M is a length of a cross section perpendicular to a major axis direction in a major axis direction thereof and N is a length of the cross section perpendicular to the major axis direction in a minor axis direction thereof, and a ratio of the flat voids is half or more of the total voids.

17. The vulcanized rubber according to claim 15 or 16, wherein at least a part of the wall surface of the cavity is hydrophilized.

18. A tire comprising the vulcanized rubber according to any one of claims 15 to 17.

19. A studless tire comprising the vulcanized rubber according to any one of claims 15 to 17.

Technical Field

The present invention relates to a rubber composition, a vulcanized rubber, a tire and a studless tire.

Background

From the viewpoint of improving vehicle safety, various studies have been made so far in order to improve braking performance, driving performance, and the like of tires not only on dry road surfaces but also on various road surfaces such as wet road surfaces and ice and snow road surfaces. For example, in order to improve on-ice performance, a winter tire such as a studless tire is provided with a foamed rubber layer in a tire tread portion.

More specifically, for example, in order to provide a pneumatic tire that further improves the water removal effect and greatly improves the on-ice performance as compared with the conventional art, it is disclosed that a pneumatic tire provided with a foam rubber layer on at least a face of a tire tread that actually keeps contact with a road surface is configured such that: the foamed rubber layer has independent cells (closed cells) with an average diameter of 40-50 μm and a foaming rate of 10-25%, and contains 1-15 parts by weight of short fibers per 100 parts by weight of the rubber component; and the short fibers have a length of 0.5 to 5.0mm, an average diameter of 40 to 50 μm, and a heat shrinkage at 170 ℃ of 8% or less (see, for example, PTL 1).

Reference list

Patent document

PTL 1：JP-A 10-24704

Disclosure of Invention

Problems to be solved by the invention

However, the cells formed by foaming involve a problem of insufficient water removal effect.

The present invention has an object to provide a rubber composition capable of obtaining a vulcanized rubber having a large water absorption capacity, a tire having excellent on-ice performance, and a studless tire having excellent on-ice performance, and an object of the present invention is to solve the above object.

Means for solving the problems

<1> a rubber composition comprising: a rubber component, and a short fiber-like resin having a ratio of A/B of more than 1, wherein A is a length of a cross section perpendicular to a long-axis direction thereof in a long-diameter direction and B is a length of the cross section in a short-diameter direction perpendicular to the long-diameter direction.

<2> the rubber composition as stated in <1>, which further comprises a foaming agent.

<3> the rubber composition as stated in <1> or <2>, wherein the short fiber-shaped resin is a composite resin comprising a hydrophilic resin and a coating layer coating the hydrophilic resin, wherein the coating layer is formed of a resin having affinity with the rubber component.

<4> the rubber composition as stated in <3>, wherein the hydrophilic resin contains at least one selected from the group consisting of an oxygen atom, a nitrogen atom and a sulfur atom.

<5> the rubber composition as stated in <3> or <4>, wherein the resin having affinity with the rubber component is a low-melting resin having a melting point lower than the maximum vulcanization temperature of the rubber composition.

<6> the rubber composition according to any one of <1> to <5>, wherein the short fiber-shaped resin has an A/B ratio of 10 or less.

<7> the rubber composition as stated in any one of <1> to <6>, wherein an average length of the short fiber-shaped resin in a length direction is 0.1 to 500 mm.

<8> the rubber composition as stated in any one of <1> to <7>, wherein the short fiber-shaped resin is contained in an amount of 0.1 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

<9>Such as<1>To<8>The rubber composition as described in any one of the above, wherein the short fiber-like resin has an average area of a cross section of 0.000001 to 0.5mm²。

<10>Such as<3>To<9>The rubber composition as described in any one of the above,wherein the hydrophilic resin comprises a hydrophilic group selected from the group consisting of-OH, -COOH, -OCOR (wherein R is alkyl), -NH₂At least one substituent of the group consisting of-NCO and-SH.

<11> the rubber composition according to any one of <3> to <10>, wherein the hydrophilic resin comprises at least one selected from the group consisting of an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly (meth) acrylic resin, a polyamide resin, an aliphatic polyamide-based resin, an aromatic polyamide-based resin, a polyester resin, a polyolefin resin, a polyvinyl alcohol-based resin, and an acrylic resin.

<12> the rubber composition according to any one of <5> to <11>, wherein the low-melting resin is a polyolefin-based resin.

<13> the rubber composition according to <12>, wherein the polyolefin-based resin comprises at least one selected from the group consisting of a polyethylene-based resin, a polypropylene-based resin, a polyolefin ionomer, and a maleic anhydride-modified α -polyolefin.

<14> the rubber composition according to any one of <1> to <13>, which is a rubber composition for a tread.

<15> a vulcanized rubber obtained by vulcanizing the rubber composition as stated in any one of <1> to <14 >.

<16> the vulcanized rubber according to <15>, which has flat voids having a ratio of M/N of more than 1, wherein M is a length of a cross section perpendicular to a major axis direction in a major axis direction thereof and N is a length of the cross section in a minor axis direction perpendicular to the major axis direction, and the ratio of the flat voids is at least half of the total voids.

<17> the vulcanized rubber according to <15> or <16>, wherein at least a part of the wall surface of the cavity is hydrophilized.

<18> a tire comprising the vulcanized rubber as described in any one of <15> to <17 >.

<19> a studless tire comprising the vulcanized rubber according to any one of <15> to <17 >.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, there can be provided a rubber composition which can give a vulcanized rubber having a large water absorption capacity, a tire excellent in on-ice performance, and a studless tire excellent in on-ice performance.

Drawings

Fig. 1 is a schematic view showing a short fiber-shaped resin contained in the rubber composition of the present invention.

Fig. 2 is a schematic view showing the shapes of a short fiber-shaped resin and a conventional short fiber-shaped resin contained in the rubber composition of the present invention, and the sectional shapes of voids derived from each of these resins.

FIG. 3 is a longitudinal sectional view of a die installed in a twin-screw extruder.

Fig. 4 is a longitudinal sectional view of a die installed in a twin-screw extruder.

Fig. 5 is a schematic diagram showing the cross-sectional shape of a void derived from a short fiber-shaped resin.

Fig. 6 is a schematic view showing the cross-sectional shape of an irregular void derived from a composite short fiber-shaped resin.

Detailed Description

< rubber composition >

The rubber composition of the present invention comprises a rubber component and a short fiber-like resin having a ratio of a/B of more than 1, wherein a is a length of a cross section perpendicular to a long-axis direction thereof in a long-diameter direction and B is a length of the cross section in a short-diameter direction perpendicular to the long-diameter direction.

The rubber composition of the present invention is an unvulcanized rubber composition before vulcanization, and a vulcanized rubber is obtained by vulcanizing the rubber composition of the present invention.

"a short fiber-like resin having a ratio of a/B of more than 1, where a is a length of a cross section perpendicular to a long-axis direction thereof in a long-diameter direction and B is a length of the cross section in a short-diameter direction perpendicular to the long-diameter direction" is sometimes referred to as "flat resin".

In the case where the rubber composition contains a rubber component and a flat resin, a vulcanized rubber obtained by vulcanizing the rubber composition becomes large in water absorption force.

First, the geometric characteristics of the flat resin and the reason why the water absorption capacity of the vulcanized rubber becomes large when the rubber composition of the present invention contains the flat resin are described.

Fig. 1 is a schematic view showing an example of a short fiber-shaped resin contained in the rubber composition of the present invention.

Fig. 1 shows an elliptic cylindrical resin D1 (flat resin). The resin D1 has a section S perpendicular to the long axis direction b, and the distance in the long axis direction a having the longest diameter in the section S is referred to as a length a. In the cross section S, the distance in the short diameter direction perpendicular to the long diameter direction a of the cross section S is referred to as a length B.

When the length a of the major diameter of the cross section S is greater than 1 with respect to the length B of the minor diameter of the cross section S, i.e., a/B, the cross section S becomes elliptical. Although fig. 1 shows one whose sectional shape is an ellipse, the sectional shape is not particularly limited as long as a/B is greater than 1, and may be any of an ellipse, a rectangle, a polygon, and an irregular shape.

With respect to the resin conventionally used as the short fiber, the aspect ratio of the resin itself, that is, with respect to the resin D1, the ratio of C/a of the length C in the long axis direction b (the length of the short fiber-like resin in the longitudinal direction) to the length a of the long axis of the section S has been studied. However, in the present invention, attention is paid to the ratio of a/B of the length a of the major diameter to the length B of the minor diameter in the cross section S.

Details of the production method of the rubber composition are described later. However, when the rubber component and the flat resin are kneaded, the flat resin in the rubber composition is randomly oriented, and the long axis direction b of the short fiber-shaped resin D1 is oriented perpendicular to the surface of the vulcanized rubber, or the long axis direction b of the short fiber-shaped resin D1 is oriented parallel to the surface of the vulcanized rubber.

In consideration of the fact that the short-fiber-shaped resin D1 has a flat shape, even in the case where the long-axis direction b of the short-fiber-shaped resin D1 is oriented parallel to the surface of the vulcanized rubber, it can be considered that the long-axis direction a of the cross section S is oriented perpendicular to the surface of the vulcanized rubber, or is oriented parallel to the surface of the vulcanized rubber.

Such an orientation state of the short-fiber-shaped resin D1 can be confirmed by observing a cut surface obtained by cutting the vulcanized rubber using an optical microscope.

In the case where such a short fiber-shaped resin having a flat shape is contained in the rubber composition together with the rubber component, in a vulcanized rubber and a tire obtained by vulcanizing the rubber composition, the flat resin is easily contained, or voids derived from the flat resin are easily generated. For example, by using a resin having a melting point lower than the vulcanization temperature of the rubber composition as the short-fiber-shaped resin, the short-fiber-shaped resin is melted by vulcanization of the rubber composition, and thus voids derived from the resin are easily generated in the vulcanized rubber. Further, when the vulcanized rubber is rubbed against a road surface or the like, the short-fiber resin may peel off from the vulcanized rubber, thereby generating voids.

Now, the occurrence of tire slip on frozen road surfaces is mainly caused by the generation of a water film between ice on the road surface and the tire.

The cavity generated when the short fiber-shaped resin melts or peels off becomes a water path on the tire surface (particularly, tread), and carries a water film on the road surface into the cavity. As a result, the tire surface is brought into close contact with the icy road surface, so that the slip can be suppressed.

In the case where the short fiber-shaped resin is oriented on the surface of the vulcanized rubber so that the long axis direction thereof becomes perpendicular to the surface of the vulcanized rubber, in other words, in the case where the pillar (pilar) stands on the ground and a void is generated, even when the sectional shape orthogonal to the long axis direction of the short fiber-shaped resin is a perfect circle or an ellipse, the depth of the void is longer than the size of the width, and therefore, it can be considered that water absorption is easily caused due to the capillary phenomenon.

On the other hand, in the case where the short fiber-shaped resin is oriented on the surface of the vulcanized rubber so that the long axis direction thereof becomes parallel to the surface of the vulcanized rubber, in other words, in the case where the pillar is lying on the ground, it can be said that the water absorption force varies with the sectional shape orthogonal to the long axis direction of the short fiber-shaped resin.

Fig. 2 is a schematic view showing the shapes of a short fiber-shaped resin and a conventional short fiber-shaped resin contained in the rubber composition of the present invention, and the cross-sectional shapes of voids derived from each of these short fiber-shaped resins.

Fig. 2 shows the shapes of the short-fiber-like resins D1, D2, and D3 before being incorporated into the rubber composition, and voids D1, D2, and D3 derived from the short-fiber-like resins D1, D2, and D3. The voids D1, D2, and D3 are each voids generated on a cut surface e2 of a vulcanized rubber obtained by mixing each of short-fiber-shaped resins D1, D2, and D3 in a rubber composition and vulcanizing the mixture, followed by cutting. All of the short-fiber-shaped resins D1, D2, and D3 are those oriented in such a manner that the long-axis direction e1 of each of the short-fiber-shaped resins D1, D2, and D3 is parallel to the cut surface e2 of the vulcanized rubber. In addition, the shapes of the cavities D1, D2, and D3 shown in fig. 2 are cross-sectional shapes obtained by cutting cavities derived from the short-fiber-shaped resins D1, D2, and D3 in the direction orthogonal to the long-axis direction e1, respectively.

In fig. 2, short fiber-shaped resins D1 and D2 are short fiber-shaped resins (flat resins) in the present invention, and D3 is a resin of short fibers contained in a conventional rubber composition.

The resin of the short fiber contained in the conventional rubber composition has a perfectly circular sectional shape, and therefore, in the case where the resin D3 is oriented such that the long axis direction e1 is parallel to the surface of the vulcanized rubber, the sectional shape of the cavity is not changed.

In contrast, the short-fiber resin used in the present invention has a flat shape, and therefore, the long-diameter direction of the cross section is oriented perpendicular to the cut surface e2 of the vulcanized rubber like the short-fiber resin D1, or parallel to the cut surface e2 of the vulcanized rubber like the short-fiber resin D2.

In the short-fiber resin in which the major axis direction of the cross section is oriented perpendicular to the cut surface e2 of the vulcanized rubber like the short-fiber resin D1, when the cavity is formed, the depth of the cavity is easily increased with respect to the width of the cavity. In the cavity d1, water absorption due to capillary phenomenon acts, thereby improving water absorption compared to the conventional cavity d 3.

In the short-fiber-shaped resin in which the major-diameter direction of the cross section is oriented parallel to the cut surface e2 of the vulcanized rubber like the short-fiber-shaped resin D2, when the cavity is formed, the depth of the cavity is short with respect to the width of the cavity, and it is considered that the capillary phenomenon as in the cavity D1 does not work. However, it can be considered that the cavity 2 functions as a water path as in the conventional cavity d 3.

In view of the above, in the vulcanized rubber and the tire obtained by vulcanizing the rubber composition of the present invention, the cavity having a long depth with respect to the width of the cavity like the cavity d1 is formed on the surface of the vulcanized rubber or the tire surface, and therefore, it can be considered that the water absorption force is larger than that in the conventional vulcanized rubber and tire. Therefore, in the tire and the studless tire manufactured using the rubber composition of the present invention, it is considered that the water inrush absorption force on ice is improved due to the capillary phenomenon, thereby improving the on-ice performance.

The rubber composition, vulcanized rubber and tire of the present invention are described in detail below.

Unless otherwise stated, the description will be made while omitting symbols in the drawings.

[ rubber component ]

The rubber component used in the rubber composition of the present invention is not particularly limited, and in addition to the Natural Rubber (NR), synthetic rubbers such as polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), Chloroprene Rubber (CR), halogenated butyl rubber, and acrylonitrile-butadiene rubber (NBR) can be used. Among them, Natural Rubber (NR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR) are preferable. These rubber components may be used alone or in combination of two or more thereof.

[ short-fiber-like resin ]

The rubber composition of the present invention contains a short fiber-like resin having a ratio of a/B of more than 1, where a is the length of a cross section perpendicular to a long-axis direction in a long-diameter direction thereof and B is the length of the cross section in a short-diameter direction perpendicular to the long-diameter direction.

In the short-fiber resin (flat resin) of the present invention, as long as a/B is greater than 1, the shape and area of the cross section perpendicular to the long axis direction (cross section S in fig. 1) and the length in the long axis direction (length C in fig. 1) are not particularly limited. From the viewpoint of improving the water absorption of the vulcanized rubber, the flat resin is in a short fiber form.

Specifically, from the viewpoint of further improving the water absorption of the vulcanized rubber, the area of the cross section (cross section S in FIG. 1) perpendicular to the long axis direction of the flat resin is preferably 0.000001 to 0.5mm in terms of the average area²More preferably 0.00002 to 0.2mm²。

The shape of the cross section (cross section S in fig. 1) perpendicular to the long axis direction of the flat resin may be any of an oval shape, a triangular shape, a rectangular shape, a polygonal shape, and an irregular shape, but from the viewpoint of improving the water absorption capacity of the vulcanized rubber, an oval shape or a rectangular shape is preferable, and an oval shape is more preferable.

The length of the flat resin in the longitudinal direction (length C in FIG. 1) is preferably 0.1 to 500mm, more preferably 0.1 to 7mm, in average (average length of the short-fiber resin in the longitudinal direction).

When both the cross-sectional area and the length in the long axis direction of the flat resin fall within the above ranges, not only the water absorption of the vulcanized rubber is improved, but also the short fiber-like resins hardly become unnecessarily entangled with each other and are easily well dispersed in the rubber composition.

The average area of a cross section (cross section S in fig. 1) perpendicular to the long axis direction of the flat resin and the average length of the flat resin in the long axis direction (length C in fig. 1) are each an average value of 100 resins selected at random. In addition, the length A, the length B and the length C of the flat resin can be each measured by observing the resin using an optical microscope of 20 to 400 times.

From the viewpoint of further improving the water absorption of the vulcanized rubber, A/B is preferably 1.5 or more, more preferably 2.0 or more. Although the upper limit of A/B is not particularly limited, it is difficult to produce a resin whose A/B is greater than 10 among resins having short fibers of the above-mentioned preferred cross-sectional area. Therefore, a/B is preferably 10 or less, and from the viewpoint of further improving the water absorption of the vulcanized rubber, a/B is more preferably 5 or less.

From the viewpoint of further improving the water absorption of the vulcanized rubber, the length A of the flat resin is preferably 0.001 to 2mm, more preferably 0.005 to 0.5mm, on average, per 100 resins.

The ratio C/A of the length of the flat resin in the long axis direction (length C in FIG. 1) to the length A of the long diameter of the cross section of the flat resin is usually 10 to 4,000, and preferably 50 to 2,000.

The content of the flat resin in the rubber composition of the present invention is preferably 0.1 part by mass or more with respect to 100 parts by mass of the rubber component from the viewpoint of improving the water absorption capacity of the vulcanized rubber and improving good water drainage due to the formed voids, and is preferably 100 parts by mass or less from the viewpoint of maintaining the durability of the vulcanized rubber. From the same viewpoint, the content of the flat resin is more preferably 0.1 to 50 parts by mass with respect to 100 parts by mass of the rubber component.

(composite resin)

The flat resin is preferably a composite resin including a hydrophilic resin and a coating layer covering the hydrophilic resin, wherein the coating layer is formed of a resin having affinity with the rubber component. That is, it is preferable that the flat resin is a composite resin including a hydrophilic resin as a core material and a coating layer that coats the hydrophilic resin as the core material, the coating layer being formed of a resin having affinity with the rubber component.

In the case where the flat resin has such a constitution, it is considered that the flat resin is easily dispersed in the rubber composition and adheres in a film-like form to a part or all of the wall surface of the cavity derived from the flat resin formed in the vulcanized rubber. Therefore, at least a part of the wall surface of the cavity is easily hydrophilized. As a result, it is considered that water easily enters the cavity, and thus the water absorption force due to the capillary phenomenon becomes much larger.

As described previously, when a resin having a melting point lower than the vulcanization temperature of the rubber composition is used as the flat resin (short fiber-like resin) and the flat resin is melted by vulcanization of the rubber composition, or when the vulcanized rubber is rubbed by a road surface or the like and the flat resin is peeled off from the vulcanized rubber, voids of the vulcanized rubber are generated. Regarding the cavity generated when the vulcanized rubber is rubbed by a road surface or the like and the flat resin is peeled off from the vulcanized rubber, the cavity of the vulcanized rubber and the tire is preferably a cavity generated when a composite resin in which the flat resin contains a hydrophilic resin is melted, in view of the fact that the wall surface of the cavity is hardly hydrophilized.

The hydrophilic resin and the resin having affinity with the rubber component are described below.

[ hydrophilic resin ]

The hydrophilic resin is a resin having a contact angle with water of 5 to 80 degrees.

The contact angle to water of the hydrophilic resin can be determined by: preparing a test piece obtained by molding a hydrophilic resin into a smooth plate-like form; using an automatic contact angle meter DM-301 manufactured by Kyowa Interface Science co., ltd.; dropping water on the surface of the test piece under the conditions of 25 ℃ and 55% of relative humidity; immediately thereafter, when viewed from the front side, the angle formed by the straight line of the test piece surface and the tangent line of the water droplet surface was measured.

Examples of the hydrophilic resin include resins having a hydrophilic group in the molecule thereof. Specifically, a resin containing at least one selected from an oxygen atom, a nitrogen atom and a sulfur atom is preferable. For example, compounds containing a group selected from the group consisting of-OH, -COOH, -OCOR (wherein R is alkyl), -NH₂A resin having at least one substituent selected from the group consisting of-NCO and-SH. Among these substituents, -OH, -COOH, -OCOR, -NH₂and-NCO is preferred.

As described above, although it is preferable that the hydrophilic resin has a small contact angle with water and has hydrophilicity with water, the hydrophilic resin is preferably insoluble in water.

In the case where the hydrophilic resin is insoluble in water, when water adheres to the surface of the vulcanized rubber and the surface of the tire, the hydrophilic resin can be prevented from being melted into water, and the water absorption force originating from the voids of the flat resin can be maintained.

As such a hydrophilic resin which has a large contact angle with water and is on the other hand insoluble in water, more specifically, an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly (meth) acrylic acid resin or an ester resin thereof, a polyamide resin, a polyethylene glycol resin, a carboxyvinyl copolymer, a styrene-maleic acid copolymer, a polyvinylpyrrolidone resin, a vinylpyrrolidone-vinyl acetate copolymer and mercaptoethanol are cited.

Among them, at least one selected from the group consisting of an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly (meth) acrylic resin, a polyamide resin, an aliphatic polyamide-based resin, an aromatic polyamide-based resin, a polyester resin, a polyolefin resin, a polyvinyl alcohol-based resin, and an acrylic resin is preferable, and an ethylene-vinyl alcohol copolymer is more preferable.

[ resin having affinity with rubber component ]

The resin having affinity with the rubber component means a resin having a solubility parameter (SP value) close to the SP value of the rubber component contained in the rubber composition. The closer the SP values to each other, the higher the affinity, and the two are easily compatible with each other.

As for the SP value difference, the difference (| SP1-SP2|) between the SP value of the rubber component (SP1) and the SP value of the resin (SP2) is preferably 2.0MPa^1/2The following.

The respective SP values of the rubber component and the resin can be calculated according to the Fedors method.

The resin having affinity with the rubber component is preferably a low-melting resin having a melting point lower than the maximum vulcanization temperature of the rubber composition.

In the case where the flat resin includes such a coating layer, it is possible to exhibit good affinity with the rubber component in the vicinity of the composite resin while effectively maintaining the affinity with water possessed by the hydrophilic resin itself.

In the case where the flat resin includes the coating layer, when the rubber composition contains the foaming agent, the hydrophilic resin which is difficult to melt during vulcanization is supplemented, whereby the formation of the cavity derived from the composite resin can be promoted. That is, when the vulcanized rubber is formed by ensuring good dispersion of the composite resin in the rubber composition, the water-draining effect due to the hydrophilic resin can be sufficiently exhibited while the function as a water-draining groove due to the voids derived from the composite resin can be sufficiently exhibited.

In the case where the low-melting resin is melted during vulcanization of the rubber composition, a coating layer of inherent fluidity is formed and adhesion between the rubber and the composite resin is facilitated, whereby a tire imparted with good water drainage and durability can be easily realized.

Although the thickness of the coating layer may vary depending on the content of the hydrophilic resin in the rubber composition, the average diameter of the composite resin, etc., it is usually 0.001 to 10 μm, and preferably 0.001 to 5 μm. In the case where the thickness of the coating layer falls within the above range, a synergistic effect between the void generated by hydrophilization of the wall surface and the capillary phenomenon is easily obtained.

The coating layer of the composite resin may be formed over the entire surface of the hydrophilic resin or may be formed on a part of the surface of the hydrophilic resin. Specifically, the coating layer is preferably formed in a proportion occupying at least 50% of the total surface area of the composite resin.

The low-melting resin is a resin having a melting point lower than the maximum vulcanization temperature of the rubber composition, and the maximum vulcanization temperature refers to the maximum temperature reached by the rubber composition during vulcanization of the rubber composition. For example, in the case of mold vulcanization, it refers to the maximum temperature reached by the rubber composition during the time the rubber composition is allowed to enter the mold and is cooled after it is removed from the mold. The maximum vulcanization temperature can be measured, for example, by embedding a thermocouple or the like in the rubber composition.

The upper limit of the melting point of the low-melting-point resin is not particularly limited, but is preferably selected in consideration of the above points. In general, the melting point of the low-melting resin is preferably 10 ℃ or more lower than the maximum vulcanization temperature of the rubber composition, and more preferably 20 ℃ or more lower. Although the industrial vulcanization temperature of the rubber composition is usually at most about 190 ℃, for example, in the case where the maximum vulcanization temperature is set to 190 ℃, the melting point of the low-melting resin is usually selected in the range of 190 ℃ or less, and it is preferably 180 ℃ or less, more preferably 170 ℃ or less.

The melting point of the flat resin can be measured using a melting point measuring apparatus or the like known per se, and for example, a melting peak temperature measured using a differential scanning calorimetry (DSC measurement) apparatus can be employed as the melting point.

Specifically, the low-melting resin is preferably a resin in which the amount of the polar component is 50 mass% or less with respect to all components in the low-melting resin, and is more preferably a polyolefin-based resin. In the case where the low-melting resin is a resin in which the amount of the polar component falls within the above range with respect to all the components, the aforementioned low-melting resin has not only an appropriate SP value difference from the rubber component but also a melting point appropriately lower than the maximum vulcanization temperature, and can sufficiently ensure good affinity with the rubber component. Further, in the case where the rubber composition contains a foaming agent, the covering layer is easily melted during vulcanization, whereby foaming of the vulcanized rubber can be promoted.

Therefore, the dispersibility of the composite resin in the rubber composition is improved, and voids derived from the composite resin are easily formed.

The polyolefin resin may be branched or linear. The polyolefin resin may be an ionomer resin formed of an ethylene-methacrylic acid copolymer intermolecularly crosslinked with a metal ion. Specifically, examples thereof include polyethylene, polypropylene, polybutene, polystyrene, ethylene-propylene copolymers, ethylene-methacrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene/propylene/diene terpolymers, ethylene/vinyl acetate copolymers, and ionomer resins thereof. The polyolefin resin may be a modified resin which has been modified with maleic anhydride or the like. These may be used alone or in combination of two or more thereof.

Among them, the polyolefin-based resin as the low melting point resin preferably includes at least one selected from the group consisting of a polyethylene-based resin, a polypropylene-based resin, a polyolefin ionomer, and a maleic anhydride-modified α -polyolefin.

In order to manufacture a composite resin formed of a hydrophilic resin coated with a coating layer formed of a low-melting resin, the following method may be employed: the low-melting point resin and the hydrophilic resin are blended using a mixer mill, the blend is melt-spun to form an undrawn yarn, and the undrawn yarn is formed into a fibrous state while being thermally drawn.

The following methods may also be employed: the low-melting resin and the hydrophilic resin were blended using a twin-screw extruder provided with a die 1 as shown in fig. 3 or 4, and then formed into a state of a short fiber shape in the same manner. In this case, the hydrophilic resin and the low-melting resin are simultaneously extruded from the die outlet 2 and the die outlet 3, respectively, and then undrawn yarns are formed therefrom.

The amount of each of the low-melting resin and the hydrophilic resin to be charged into the mixer or hopper may vary depending on the length (length C in fig. 1), the cross-sectional area, and the like of the resulting composite resin, but the amount of the low-melting resin to be charged is 5 to 300 parts by mass, and preferably 10 to 150 parts by mass, relative to 100 parts by mass of the hydrophilic resin.

In the case where the low-melting resin and the hydrophilic resin are charged into the kneader or hopper in amounts falling within the above ranges, the coating layer is easily formed on the surface of the hydrophilic resin.

[ foaming agent ]

Preferably, the rubber composition of the present invention further comprises a foaming agent.

In the case where the rubber composition contains a foaming agent, the foaming agent generates cells in the vulcanized rubber, so that the vulcanized rubber can be formed into a foamed rubber. The foamed rubber has flexibility, and therefore, the tire surface using the vulcanized rubber is likely to come into close contact with an icy road surface. In addition, in the case where the cavity derived from the cells is generated by the cells on the surface of the vulcanized rubber and the surface of the tire, the cavity functions as a water path for draining water.

Further, by the gas generated by the foaming agent penetrating into the interior of the hydrophilic resin through the coating layer formed of the molten low-melting-point resin, it is possible to easily form the hollow having a shape associated with the shape of the composite resin, that is, a long shape. In the case where the voids having such a shape in association with the shape of the composite resin are present in the rubber, the water absorption force of the vulcanized rubber is improved, and the on-ice performance of the tire is excellent.

Specifically, examples of the blowing agent include azodicarbonamide (ADCA), Dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrene tetramine (dintrothionylenetetramine), benzenesulfonyl hydrazide derivatives, p '-oxybis-benzenesulfonyl hydrazide (OBSH), ammonium hydrogen carbonate capable of generating carbon dioxide, sodium hydrogen carbonate, ammonium carbonate, nitrososulfonyl azo compound capable of generating nitrogen, N' -dimethyl-N, N '-dinitrosophthalamide, toluenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, and p, p' -oxybis-benzenesulfonyl semicarbazide. Among them, azodicarbonamide (ADCA) and Dinitrosopentamethylenetetramine (DPT) are preferable from the viewpoint of production processability. These blowing agents may be used alone or in combination of two or more thereof.

Although the content of the foaming agent in the rubber composition is not particularly limited, it is preferably in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of the rubber component.

The foaming agent may be contained in the composite resin.

In the case where a foaming agent is used for the purpose of foaming the vulcanized rubber, it is preferable to use urea, zinc stearate, zinc benzenesulfinate, zinc oxide, or the like as a foaming aid in combination. These may be used alone or in combination of two or more thereof. By using the foaming aid in combination, the foaming reaction is promoted to improve the perfection of the reaction, whereby unnecessary deterioration with time can be suppressed.

In the vulcanized rubber obtained after vulcanizing the rubber composition containing the foaming agent, the foaming ratio is usually 1 to 50%, and preferably 5 to 40%. In the case of mixing a foaming agent, when the foaming ratio is too large, voids in the rubber surface become large, so that there is a fear that a sufficient ground contact area cannot be secured. However, as long as the foaming ratio falls within the above range, the amount of cells can be appropriately maintained while ensuring the formation of cells that effectively function as drainage channels, and therefore, the durability is hardly impaired. Here, the foaming ratio of the vulcanized rubber means an average foaming ratio Vs, specifically, it means a value calculated according to the following formula (I).

Vs＝(ρ₀/ρ₁-1)×100(％) (I)

In formula (I), ρ₁Shows the density (g/cm) of a vulcanized rubber (foamed rubber)³)，ρ₀Shows the density (g/cm) of a solid phase portion in a vulcanized rubber (foamed rubber)³)。

The foaming ratio determined according to formula (I) is a void ratio including not only voids of cells generated by foaming of the foaming agent but also voids generated when the flat resin is melted by vulcanization and voided.

In the rubber composition of the present invention, in addition to the foaming agent and the foaming aid, if necessary, together with a flat resin (preferably, a composite resin in which a hydrophilic resin is coated with a coating layer formed of a resin having affinity with the rubber component) within a range not impairing the object of the present invention, compounding agents generally used in the rubber industry, for example, fillers such as carbon black, softening agents, stearic acid, anti-aging agents, zinc oxide, vulcanization accelerators, vulcanizing agents and the like, may be appropriately selected and contained.

The vulcanized rubber obtained from the rubber composition of the present invention has high water absorption power, and when used for a tire, the water gushing on ice water absorption power of the vulcanized rubber is excellent. Therefore, the rubber composition of the present invention is suitable for a rubber composition for a tread.

< vulcanizates >

The vulcanized rubber of the present invention is a rubber prepared by vulcanizing the aforementioned rubber composition of the present invention.

Therefore, the vulcanized rubber of the present invention has a flat cavity as a cavity derived from a short-fiber-shaped resin with a ratio of M/N of more than 1, where M is the length of a cross section perpendicular to the long-axis direction in the long-diameter direction thereof and N is the length of the cross section in the short-diameter direction perpendicular to the long-diameter direction. When the vulcanized rubber has a flat cavity having an M/N ratio of more than 1, the water absorption capacity is excellent.

In the vulcanized rubber of the present invention, from the viewpoint of further improving the water absorption capacity, the proportion of the flat voids is preferably at least half of the total voids.

Fig. 5 is a schematic diagram showing the cross-sectional shape of a void derived from a short fiber-shaped resin.

Here, in fig. 1 for explaining the short fiber-shaped resin, when the short fiber-shaped resin is regarded as a flat cavity, the length M is a length corresponding to the length a, and the length N is a length corresponding to the length B. Preferred ranges of the length M, the length N and the ratio of M/N are the same as preferred ranges of the length A, the length B and the ratio of A/B of the short fiber-like resin, respectively.

A preferable range of the area of a cross section S' (corresponding to the surface of the cross section S of the short fiber-shaped resin in fig. 1) perpendicular to the flat cavity in the longitudinal direction is the same as the preferable range of the area of the cross section S. Although the shape of the cross section is not limited, it is preferably an ellipse. A preferable range of the average length of the flat hollow in the major axis direction (length corresponding to the length C of the short-fiber-shaped resin in fig. 1) is the same as the preferable range of the length C.

In fig. 5, when the ratio of the length M of the major diameter of the cross section S ' to the length N of the minor diameter of the cross section S ', i.e., M/N, is greater than 1, the cross section S ' becomes elliptical. The cross section of the void derived from the resin fiber is not limited to the elliptical void derived from a single resin fiber shown in fig. 5, and it may also be an irregular shape derived from a composite prepared by compositing a plurality of resin fibers. Specifically, a communication cavity is generated when 2 or more resin fibers are stacked and melted by kneading the rubber composition. Fig. 6 is a schematic view showing the cross-sectional shape of irregularly shaped voids derived from a composite short fiber-like resin. For the irregular holes shown in fig. 6, when the maximum length of the hole is defined as P and the minimum length in the width of the hole is defined as Q, the ratio of P/Q of P to Q only has to be larger than 1.

The shape of the cavity in the vulcanized rubber can be confirmed, for example, by: a block-shaped sample is cut out of vulcanized rubber, a photograph of a cross section of the sample is taken with an optical microscope at a magnification of 100 to 400, and the major axis and the minor axis of the cavity are measured. In addition, the proportion of flat voids can be calculated, for example, by regarding voids observed at three or more different positions in a field of view of 2mm × 3mm as a matrix (matrix) by using an optical microscope.

In addition, in the vulcanized rubber, it is preferable that at least a part of the wall surface of the cavity is hydrophilized. The voids of the vulcanized rubber are voids derived from the flat resin as described above, and as described with reference to fig. 1 and 2, the voids have a water absorption force due to a capillary phenomenon. Further, when at least a part of the wall surface of the cavity is hydrophilized, it is considered that the water absorption capacity becomes larger.

< tire and studless tire >

The tire and studless tire of the present invention comprise the vulcanized rubber of the present invention.

Therefore, the tire of the present invention and the studless tire each have a flat cavity with a ratio of M/N of more than 1, where M is the length of a section perpendicular to the long axis direction in the long diameter direction thereof and N is the length of a section perpendicular to the long axis direction in the short diameter direction thereof perpendicular to the long diameter direction. The ratio of the flat cavities of each of the tire and studless tire is preferably at least half of the total number of the cavities. Further, it is preferable that at least a part of the wall surface of the cavity is hydrophilized.

As described previously, since the vulcanized rubber of the present invention has a large water absorption force, even when a water film is developed on a road surface, water is taken into the tire due to a capillary phenomenon by the void derived from the flat resin formed on the tire surface, whereby occurrence of a slip can be prevented. In particular, the vulcanized rubber of the present invention is excellent in water-gushing absorption on ice. Therefore, the vulcanized rubber of the present invention is suitable for studless tires, and the studless tires are excellent in on-ice performance.

The tire can be obtained by using an unvulcanized rubber composition and vulcanizing it after molding according to the kind or member of the tire to be applied. Alternatively, the tyre may be obtained by: a precuring process is performed to obtain a semi-vulcanized rubber from an unvulcanized rubber composition at a time, which is molded, and further subjected to full-scale vulcanization. Among various members of the tire, the vulcanized rubber of the present invention is preferably applied to a tread member from the viewpoint that good water drainage and excellent breaking force resistance can be sufficiently exhibited. As the gas to be filled into the tire, in addition to normal air or air whose oxygen partial pressure has been adjusted, inert gases such as nitrogen, argon, and helium may be used.