Patent Description:
<CIT> describes a tire having a decorative portion at a part of the outer surface thereof, and the decorative portion has a plurality of micro projections arranged therein. The micro projections can reduce reflection of light on the decorative portion, thereby increasing the degree of blackness of the decorative portion. Therefore, the contrast in brightness between the decorative portion and a non-decorative portion adjacent thereto can be enhanced. Accordingly, the visibility of the outer surface of the tire can be improved.

<CIT> and <CIT> disclose tires having indentations on its sidewall surface which respectively have several peak elements distributed and projecting from the bottom of the indentation.

A tire vulcanization mold for forming the above decorative portion includes a plurality of minute recesses corresponding to the micro projections. In such a tire vulcanization mold, fine pieces of rubber, dust, and the like are likely to be accumulated in the recesses as tire molding is performed repeatedly. Therefore, there has been a need to increase the frequency of cleaning of the mold in order to perform tire molding with the degree of blackness of the decorative portion maintained at an appropriate level.

The present invention has been made in view of the above circumstances, and a major object of the present disclosure is to provide: a tire vulcanization mold and a production method for a tire in which dirt is less likely to be accumulated in recesses provided in a molding surface.

The present invention is directed to a tire vulcanization mold including a molding surface for molding a tire during vulcanization molding according to claim <NUM>. The molding surface includes a first region in which a plurality of recesses for forming a plurality of projections on a surface of the tire are provided. In the first region, at least two of the recesses are arranged per mm<NUM>. Each of the recesses includes a side wall surface, a bottom surface, and a virtual recess central axis extending in a depth direction of the recess. In a cross-sectional view of the recess including the recess central axis, the bottom surface includes a bottom projection that projects outward in the depth direction. The side wall surface includes an arc-shaped surface that is smoothly connected to the bottom surface. The bottom projection includes a peak portion located on an outermost side in the depth direction of the recess, and a bottom projection side wall surface extending from the peak portion inward in the depth direction of the recess, the peak portion being disposed on the virtual recess central axis.

The present invention is also related to a method for producing a tire according to claim <NUM>, a tire according to claim <NUM> and a tire according to claim <NUM>.

In the tire vulcanization mold according to the present invention, dirt is less likely to be accumulated in the recesses. Therefore, an increase in the frequency of cleaning of the mold can be suppressed.

An embodiment of the present disclosure will be described below with reference to the accompanying drawings. <FIG> is a cross-sectional view of a tire vulcanization mold <NUM> according to the present embodiment (also simply referred to as a "mold"). As shown in <FIG>, the tire vulcanization mold <NUM> according to the present embodiment has a molding surface for forming an outer surface of an unvulcanized green tire <NUM>. The green tire <NUM> is pressed from the inside against the molding surface of the tire vulcanization mold <NUM> by an expanded bladder <NUM> while being heated in the tire vulcanization mold <NUM>. Accordingly, the green tire <NUM> is vulcanized and molded to obtain a tire.

<FIG> is a perspective view showing an example of a tire <NUM> vulcanized and molded using the tire vulcanization mold <NUM> according to the present disclosure. Although the tire <NUM> in <FIG> is for a passenger car, the tire vulcanization mold <NUM> according to the present disclosure is not limited to such a mode. The tire vulcanization mold <NUM> according to the present disclosure may be used for vulcanizing and molding a motorcycle tire or heavy-duty tire, for example.

As shown in <FIG>, the tire <NUM> has a visible outer surface <NUM>. The visible outer surface <NUM> is a surface that can be seen from the outside when the tire <NUM> is mounted on a rim (not shown). The tire <NUM> has a decorative region <NUM> (marked by dots in <FIG>) at a part of the outer surface <NUM>. The decorative region <NUM> is a region having a plurality of micro projections provided therein. For example, at least <NUM> micro projections, more particularly <NUM> to <NUM> micro projections, are disposed per mm<NUM> in the decorative region <NUM> of the present embodiment. Such micro projections can reduce reflection of light on the decorative region <NUM> to increase the degree of blackness of the decorative region <NUM>, thereby serving to improve the appearance of the tire <NUM>. The decorative region <NUM> of the present embodiment is, for example, provided at a sidewall portion <NUM>.

As shown in <FIG>, the tire vulcanization mold <NUM> according to the present embodiment includes a tread segment 1A, sidewall segments 1B, and bead rings 1C. In the present embodiment, a molding surface of the sidewall segment 1B can be used to form the decorative region <NUM> provided at the sidewall portion <NUM> of the tire <NUM>.

<FIG> is an enlarged perspective view of a molding surface <NUM> of the tire vulcanization mold <NUM>. The molding surface <NUM> of the tire vulcanization mold <NUM> includes a first region <NUM> in which a plurality of recesses <NUM> for forming a plurality of projections (micro projections) on the surface of a tire are provided. The tire <NUM> vulcanized and molded using the tire vulcanization mold <NUM> having the molding surface <NUM> has, on the outer surface thereof, a plurality of micro projections, each of which has a reverse shape of the recess <NUM>, and thus, has the decorative region <NUM> (shown in <FIG>).

In order to reliably reduce reflection of light on the decorative region <NUM>, preferably, the micro projections in the decorative region <NUM> are sufficiently small micro projections. Thus, in the first region <NUM> of the molding surface <NUM>, at least two recesses <NUM> are provided per mm<NUM>. Specifically, in the first region <NUM>, <NUM> to <NUM> recesses <NUM> are preferably provided per mm<NUM>. The number of recesses <NUM> per mm<NUM> can be calculated by dividing the number of recesses <NUM> completely included in a plane that is in the shape of a square with a side of <NUM> by <NUM>.

An end edge <NUM> which defines the recess <NUM> is preferably in the shape of a circle, for example. However, the present disclosure is not limited to such a mode. The end edge <NUM> of the recess <NUM> may have any of various shapes such as an ellipse, a rectangle, and a polygon.

<FIG> is a cross-sectional view of the recess <NUM>. As shown in <FIG>, each recess <NUM> includes a side wall surface <NUM>, a bottom surface <NUM>, and a virtual recess central axis 13c extending in the depth direction of the recess <NUM>. The recess central axis 13c means a virtual line that passes through the centroid of a plane surrounded by the end edge <NUM> of the recess <NUM> and extends in the depth direction of the recess <NUM>. In the present embodiment, the plane surrounded by the end edge <NUM> of the recess <NUM> is in the shape of a circle, through the center of which the recess central axis 13c passes.

In a cross-sectional view of the recess <NUM> including the recess central axis 13c, the bottom surface <NUM> includes a bottom projection <NUM> which projects outward in the depth direction. The side wall surface <NUM> includes an arc-shaped surface <NUM> that is smoothly connected to the bottom surface <NUM>. Due to the abovementioned configuration, dirt is less likely to be accumulated in the recesses <NUM> of the tire vulcanization mold <NUM> according to the present disclosure. Therefore, an increase in the frequency of cleaning of the mold can be suppressed. This may be attributed to a mechanism described below.

In conventional tire vulcanization molds, recesses have a relatively flat inner surface, and a bottom surface and a side wall surface thereof are connected such that a ridge is formed therebetween. Therefore, during vulcanization molding, it is difficult to separate rubber from the inner surface of the recess, so that fine pieces of rubber or dust, an oil component released from rubber, and the like are likely to be accumulated in the recess.

In contrast to this, in the present disclosure, as described above, the bottom surface <NUM> of the recess <NUM> has the bottom projection <NUM>, and the side wall surface <NUM> includes the arc-shaped surface <NUM>. Therefore, when the mold is separated from a tire, the separation of the rubber begins from the bottom projection <NUM>, and the rubber can be separated progressively from the bottom projection <NUM> along the side wall surface <NUM>. In particular, the side wall surface <NUM> includes the arc-shaped surface <NUM>, and therefore, tearing of the rubber during the progressive separation of the rubber can be effectively suppressed. It is inferred that such a mechanism can suppress accumulation of dirt in the recess.

A more detailed configuration of the present embodiment will be described below. It should be noted that each part described below illustrates a specific example of the present embodiment. Therefore, it is needless to say that the present disclosure can exhibit the abovementioned effect even in the case where parts described below are not included. In addition, even if any one of the parts described below is applied alone to the tire vulcanization mold according to the present disclosure having the abovementioned features, the performance of the tire vulcanization mold according to the present disclosure can be expected to be improved according to that part. Furthermore, if some of the parts described below are applied in combination, the performance of the tire vulcanization mold according to the present disclosure can be expected to be improved in a complex manner according to those parts.

An opening width W1 of the recess <NUM> is, for example, not greater than <NUM> and preferably <NUM> to <NUM>. A maximum depth d1 of the recess <NUM> is, for example, not greater than <NUM> and preferably <NUM> to <NUM>. However, the dimensions of the recess <NUM> are not limited to such a mode. Unless otherwise specified, the dimension of each portion of the recess <NUM> is a dimension measured when the tire vulcanization mold <NUM> is cooled to room temperature.

In the present embodiment, since the bottom surface <NUM> has the bottom projection <NUM>, a portion where the recess <NUM> is deepest (hereinafter, sometimes referred to as a deepest portion <NUM>) is provided around the bottom projection <NUM>. In a plan view (not shown) of the recess <NUM>, the deepest portion <NUM> has an annular shape, and the bottom surface <NUM> corresponds to a region surrounded by the annular deepest portion <NUM>. In the cross-sectional view of the recess <NUM> shown in <FIG>, the deepest portion <NUM> is substantially represented by a dot, and the bottom surface <NUM> is composed of the outer surface of the bottom projection <NUM>. In addition, the arc-shaped surface <NUM> is connected to the deepest portion <NUM>. In another embodiment, the deepest portion <NUM> may include a flat portion. That is, the deepest portion <NUM> may be composed of a flat portion provided between the side wall surface <NUM> and the bottom projection <NUM>. In this case, the outer surface of the bottom projection <NUM> and the flat portion that is the deepest portion <NUM> constitute the bottom surface <NUM>.

The side wall surface <NUM> extends from the end edge <NUM> of the recess <NUM> so as to be inclined, for example. An angle θ1 of the side wall surface <NUM> with respect to the depth direction of the recess <NUM> is, for example, <NUM> to <NUM>° and preferably <NUM> to <NUM>°. Therefore, reflection of light on the formed decorative region <NUM> is further suppressed.

From the viewpoint of exhibiting the abovementioned effect while ensuring a sufficient volume of the micro projection formed by the recess <NUM>, the arc-shaped surface <NUM> of the side wall surface <NUM> has a radius of curvature r1 of not less than <NUM> and more preferably not less than <NUM>, and preferably not greater than <NUM> and more preferably not greater than <NUM>.

In the cross-sectional view, the bottom projection <NUM> includes a peak portion 25t that is located on the outermost side in the depth direction of the recess <NUM>, and a bottom projection side wall surface <NUM> that extends from the peak portion 25t inward in the depth direction of the recess <NUM>. The peak portion 25t is disposed on the recess central axis 13c. The peak portion 25t of the present embodiment has a pointed shape that has substantially no flat surface. However, the peak portion 25t may include a small flat surface.

The bottom projection side wall surface <NUM> is preferably in the shape of an arc-shaped curve that is convex toward the recess central axis 13c. The arc-shaped curve has a radius of curvature r2 of not less than <NUM> and more preferably not less than <NUM>, and preferably not greater than <NUM> and more preferably not greater than <NUM>. In a more preferable mode, the radius of curvature r2 is equal to the radius of curvature r1 of the arc-shaped surface <NUM> of the side wall surface <NUM>. As a result, in the cross-sectional view, the profiles of the arc-shaped surface <NUM> of the side wall surface <NUM> and the outer surface of the bottom projection <NUM> preferably form a single arc. Such a bottom projection side wall surface <NUM> can effectively suppress accumulation of dirt in the recess <NUM>.

If the bottom projection <NUM> is small, there is a possibility that the abovementioned effect is not sufficiently obtained. On the other hand, if the bottom projection <NUM> is large, there is a possibility that the bottom projection <NUM> itself is chipped off. From such a viewpoint, a height h1 of the bottom projection <NUM> is, for example, not greater than <NUM>% and preferably <NUM> to <NUM>% of the depth d1 of the recess <NUM>. Specifically, the height h1 of the bottom projection <NUM> is preferably not less than <NUM> and more preferably not less than <NUM>, and preferably not greater than <NUM> and more preferably not greater than <NUM>.

From the same viewpoint, a width W2 of the bottom projection <NUM> is preferably not less than <NUM>% and more preferably not less than <NUM>%, and preferably not greater than <NUM>% and more preferably not greater than <NUM>%, of the opening width W1 of the recess <NUM>.

In a more preferable mode, each recess <NUM> preferably has a shape that is symmetric about the recess central axis 13c, as a result of having the abovementioned structure. Accordingly, accumulation of dirt in the recess <NUM> can be further suppressed.

<FIG> are each a cross-sectional view of a recess <NUM> according to another embodiment of the present disclosure. In the embodiments shown in <FIG>, the angle θ1 of the side wall surface <NUM> of the recess <NUM> is set to be greater than that of the embodiment shown in <FIG>. In the embodiment shown in <FIG>, the angle θ1 is <NUM>°, and the angle between the two side wall surfaces <NUM> in the cross-sectional view is <NUM>°. In the embodiment shown in <FIG>, the angle θ1 is <NUM>°, and the angle between the two side wall surfaces <NUM> in the cross-sectional view is <NUM>°. Even in such embodiments, accumulation of dirt in the recess <NUM> can be effectively suppressed.

<FIG> is a cross-sectional view taken during formation of the recess <NUM> on the molding surface <NUM>. As shown in <FIG>, the recess <NUM> according to the present disclosure can be formed, for example, using a small drill <NUM> attached to a radial drilling machine. Specifically, the small drill <NUM> has a tip surface <NUM> corresponding to the side wall surface <NUM> of the recess <NUM>, and is caused to revolve about the peak portion 25t of the bottom projection <NUM> to form the recess <NUM>, so that the above-described recess <NUM> having the bottom projection <NUM> is obtained.

<FIG> is a cross-sectional view taken during formation of the recess <NUM> on the molding surface <NUM> in another embodiment different from that of <FIG>. <FIG> illustrates a cross-sectional shape of a tip portion <NUM> of a small drill <NUM>. As shown in <FIG>, in the present embodiment, an outer surface <NUM> of the tip portion <NUM> of the small drill <NUM> has an indentation corresponding to the bottom projection <NUM>. The recess <NUM> according to the present disclosure can be obtained by machining the molding surface <NUM> of the tire vulcanization mold <NUM> using such a small drill <NUM>.

The tire vulcanization mold <NUM> according to the present disclosure is applied to a known production method for a tire. In a tire production method including the step of vulcanizing and molding a tire using the tire vulcanization mold <NUM> according to the present disclosure, dirt is less likely to be accumulated in the recesses <NUM> of the tire vulcanization mold <NUM>, and therefore, an increase in the frequency of cleaning of the mold can be suppressed.

As shown in <FIG>, a tire vulcanized and molded using the tire vulcanization mold <NUM> according to the present disclosure has a plurality of micro projections formed in the decorative region <NUM> so as to each have a reverse shape of the recess <NUM>. <FIG> is an enlarged perspective view of one of micro projections <NUM> provided on the outer surface of a tire. As shown in <FIG>, the micro projection <NUM> includes a side surface <NUM>, a projection peak portion <NUM>, and a virtual micro projection central axis 33c. The side surface <NUM> of the micro projection <NUM> has a shape corresponding to the side wall surface <NUM> of the recess <NUM>. The projection peak portion <NUM> of the micro projection <NUM> has a shape corresponding to the bottom surface <NUM> of the recess <NUM>.

In a cross-sectional view of the micro projection including the micro projection central axis 33c, the projection peak portion <NUM> includes a peak recess <NUM> that is recessed inward in the height direction of the micro projection <NUM>. In addition, the side surface <NUM> of the micro projection <NUM> has an arc-shaped surface <NUM> that is smoothly connected to the projection peak portion <NUM>. Such a micro projection <NUM> can further suppress reflection of light, thereby serving to improve the appearance of the tire.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the illustrated embodiments, and various modifications can be made to practice the present disclosure.

In order to verify the effects of the present disclosure, tires were produced as examples using a tire vulcanization mold having recesses shown in <FIG>. As a comparative example, a tire was produced using a tire vulcanization mold having recesses a shown in <FIG>. In each recess a of the comparative example, a side wall surface b and a bottom surface c are connected via a ridge d. The dimensions of the recesses of the comparative example and the examples are as follows.

It should be noted that the dimensions of Examples <NUM> and <NUM> other than the abovementioned dimensions are the same as those of Example <NUM>.

A plurality of tires were produced using the tire vulcanization molds of the comparative example and Examples <NUM> to <NUM> without cleaning the molds in the middle of production, and the degree of blackness L* of the decorative region of each tire was measured using a color difference meter. The degree of blackness L* was measured in accordance with lightness defined in JIS Z8721. The smaller the degree of blackness L*, the lower the lightness of black, which is more preferable for the decorative region of a tire.

<FIG> shows a relationship between the number N of produced tires and the degree of blackness L* in the comparative example and Examples <NUM> to <NUM>. In <FIG>, graphs g1 to g3 correspond to Examples <NUM> to <NUM>, and a graph g4 corresponds to the comparative example.

Claim 1:
A tire vulcanization mold (<NUM>) comprising:
a molding surface (<NUM>) for molding a tire (<NUM>) during vulcanization molding, wherein
the molding surface (<NUM>) includes a first region (<NUM>) in which a plurality of recesses (<NUM>) for forming a plurality of projections (<NUM>) on a surface of the tire (<NUM>) are provided,
in the first region (<NUM>), at least two of the recesses (<NUM>) are arranged per mm<NUM>,
each of the recesses (<NUM>) includes a side wall surface (<NUM>), a bottom surface (<NUM>), and a virtual recess central axis (13c) extending in a depth direction of the recess (<NUM>), and
in a cross-sectional view of the recess (<NUM>) including the virtual recess central axis (13c),
the bottom surface (<NUM>) includes a bottom projection (<NUM>) projecting outward in the depth direction,
the side wall surface (<NUM>) includes an arc-shaped surface (<NUM>) smoothly connected to the bottom surface (<NUM>), and
the bottom projection (<NUM>) includes a peak portion (25t) located on an outermost side in the depth direction of the recess (<NUM>), and a bottom projection side wall surface (<NUM>) extending from the peak portion (25t) inward in the depth direction of the recess (<NUM>), the peak portion (25t) being disposed on the virtual recess central axis (13c).