Method for manufacturing pneumatic tires

Abstract

To provide a manufacturing method of a pneumatic tire, the method capable of curbing contamination of a white letter.SOLUTION: A manufacturing method of a pneumatic tire includes: a step of forming a green tire by disposing sidewall rubber of a first color outside a carcass in a tire axial direction in a sidewall, disposing different color rubber of a second color adjacent to outside the sidewall in the tire axial direction, and disposing cover rubber of the first color adjacent to outside the different color rubber in the tire axial direction; and a step of vulcanization-molding the green tire using a tire molding die having a recess for causing protrusion from a profile line of a tire outer surface by allowing the different color rubber and the cover rubber to flow in. A maximum thickness H of the different color rubber before the vulcanization-molding and a maximum protrusion height α of the different color rubber after the vulcanization-molding from the profile line satisfy a relation of α≤0.7H.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a pneumatic tire. [Background technology]

[0002] The sidewalls of tires are marked with marks such as letters, symbols, and figures. These marks may be white letters made of white rubber on the tire's original black background, and tires with such white letters are called white letter tires.

[0003] In the manufacture of a typical white letter tire, first, white rubber for forming the white letters is provided on the outer surface of the sidewall rubber, and a cover rubber layer made of black rubber is laminated on that surface to form an unvulcanized green tire. Then, during vulcanization molding of the green tire, the area where the white letters will be formed is raised by creating a depression in the mold, and the cover rubber layer in the raised area is scraped away to expose the white rubber, thereby forming the white letters made of white rubber (see Patent Document 1 below).

[0004] In white-letter tires, the black color of the sidewall rubber surrounding the white rubber can seep into the white letters over time, causing a poor appearance (hereinafter referred to as "white-letter contamination"). This contamination occurs early, especially in areas where the distance between the white letters and the outer edge of the white rubber is short. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-203227 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide a method for manufacturing a pneumatic tire that can suppress contamination of white letters. [Means for solving the problem]

[0007] A method for manufacturing a pneumatic tire according to the present disclosure includes the steps of: arranging a sidewall rubber of a first color on the axially outer side of a carcass in a sidewall; arranging a different-colored rubber of a second color adjacent to the axially outer side of the sidewall rubber; and arranging a cover rubber of the first color adjacent to the axially outer side of the different-colored rubber to form a green tire; and vulcanizing and molding the green tire using a tire mold having recesses into which the different-colored rubber and the cover rubber are introduced to raise the tire from a profile line on the outer surface of the tire. The maximum thickness H of the different color rubber before vulcanization molding and the maximum protruding height α of the different color rubber from the profile line after vulcanization molding satisfy the relationship α≦0.7H. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a main part of a pneumatic tire according to an embodiment of the present invention taken along a tire meridian plane; [Figure 2] Enlarged view of the pneumatic tire shown in Figure 1 [Figure 3] Cross-section of a sidewall component used in forming a green tire [Figure 4] Cross-sectional view of the main part of a green tire immediately after vulcanization molding DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a pneumatic tire and a method for manufacturing the same will be described below with reference to Figures 1 to 4. Note that in each figure, the dimensional ratios in the drawing do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match either.

[0010] <Configuration of pneumatic tires> 1 and 2, a pneumatic tire T according to this embodiment includes a pair of beads 1, 1 each having a bead core 1a, and a pair of sidewalls 2, 2 extending outward in the tire radial direction D2 from each bead 1. The pneumatic tire T also includes a tread 3 connected to outer ends of the pair of sidewalls 2, 2 in the tire radial direction D2. Although not shown, various grooves such as circumferential grooves and lug grooves that form a tread pattern are provided on the outer peripheral surface of the tread 3.

[0011] In each drawing, the tire axial direction D1 is a direction parallel to the tire rotation axis which is the rotation center of the pneumatic tire T, the tire radial direction D2 is a diameter direction of the pneumatic tire T, and the tire circumferential direction is a direction around the tire rotation axis. The tire equatorial plane S1 is a plane perpendicular to the tire rotation axis and is a plane located at the center of the tire axial direction D1 of the pneumatic tire T, and the tire meridian plane is a plane including the tire rotation axis and is a plane perpendicular to the tire equatorial plane S1.

[0012] In the tire axial direction D1, the inner side refers to the side closer to the tire equatorial plane S1, and the outer side refers to the side farther from the tire equatorial plane S1. In the tire radial direction D2, the inner side refers to the side closer to the tire rotational axis, and the outer side refers to the side farther from the tire rotational axis.

[0013] The pneumatic tire T includes a carcass 4 that is bridged between a pair of bead cores 1a, 1a, and an inner liner 5 that is disposed inside the carcass 4 and has an excellent function of preventing gas permeation in order to maintain air pressure. The carcass 4 and the inner liner 5 are disposed along the inner circumference of the tire, spanning the beads 1, sidewalls 2, and tread 3.

[0014] The tread 3 includes a tread rubber 3 a that comes into contact with the road surface, and a belt 3 b that is disposed between the tread rubber 3 a and the carcass 4 .

[0015] The bead 1 includes an annular bead core 1a made of a bundle of steel wires or the like coated with rubber, and a bead filler 1b with a triangular cross section that is located outside the bead core 1a in the tire radial direction D2. The bead 1 also includes a rubber pad 1c that is located outside the bead filler 1b in the tire axial direction D1 and covers the folded-up end of the carcass 4 from the outside in the tire axial direction D1. The bead 1 also includes a rim strip rubber 1d that is located outside the rubber pad 1c in the tire axial direction D1. A rim line 1e that protrudes from the outer surface is formed on the rim strip rubber 1d.

[0016] The sidewall 2 includes a sidewall rubber 2a disposed on the outer side of the carcass 4 in the tire axial direction D1. The sidewall rubber 2a is usually made of a black rubber composition (black rubber) containing carbon black as a reinforcing filler. That is, in this embodiment, black corresponds to the first color of the present invention.

[0017] The sidewall 2 includes a white rubber 6 arranged on the outside of the sidewall rubber 2a in the tire axial direction D1. That is, in this embodiment, white corresponds to the second color of the present invention, and the white rubber 6 corresponds to the different color rubber of the present invention. The sidewall 2 also includes a black cover rubber 7 arranged on the outside of the white rubber 6 in the tire axial direction D1. The white rubber 6 is arranged on the inside of the tire maximum width position 2b in the tire radial direction D2. Note that the white rubber 6 does not necessarily have to be arranged on both sidewalls 2, and may be arranged only on the side that will be on the outside of the vehicle when mounted on a vehicle.

[0018] The white rubber 6 does not contain carbon black as a reinforcing filler, but is made of a rubber composition containing fillers other than carbon black (i.e., non-carbon black fillers), such as silica, talc, clay, etc. The white rubber 6 is made of a rubber composition that is softer (has lower hardness) and has lower rigidity than the black rubber containing carbon black that constitutes the sidewall rubber 2a.

[0019] The white rubber 6 is covered with a cover rubber 7 made of a black rubber composition that is more ozone-resistant, fatigue-resistant, and cut-resistant than the white rubber 6. The white rubber 6 is exposed by scraping off the cover rubber 7 on the surface at protrusions 8 that are raised in correspondence with marks such as letters and symbols, thereby forming white letters 9 made of the white rubber 6.

[0020] <Manufacturing method of pneumatic tires> Next, a method for manufacturing the pneumatic tire T will be described with reference to FIGS.

[0021] The following method is an example of a typical method for manufacturing a pneumatic tire T. First, tire components including an inner liner 5, a carcass 4, a bead core 1a, a bead filler 1b, etc. are arranged in predetermined positions on a cylindrical building drum to form a cylindrical case, and the case is deformed into a toroidal shape and combined with separately formed tread rubber 3a, sidewall rubber 2a, etc. to form an unvulcanized green tire. The green tire is then vulcanized to manufacture the pneumatic tire T.

[0022] In manufacturing a white-letter tire, in the process of forming a green tire, a sidewall rubber 2a is arranged on the sidewall 2 outside the carcass 4 in the tire axial direction D1, a white rubber 6 is arranged adjacent to the outside of the sidewall rubber 2a in the tire axial direction D1, and a black cover rubber 7 is arranged adjacent to the outside of the white rubber 6 in the tire axial direction D1. At this time, the sidewall rubber 2a, the white rubber 6, and the cover rubber 7 are arranged as an integrated sidewall component 10 as shown in FIG. 3, for example. Such a sidewall component 10 may be formed by integrating the respective rubbers by extrusion molding, or by sequentially laminating the respective extrusion-molded rubbers. The sidewall component 10 is arranged on the sidewall 2 so that a first end 10a is connected to the tread rubber 3a and a second end 10b is connected to the rim strip rubber 1d.

[0023] The maximum thickness H of the white rubber 6 before vulcanization, i.e., in the state of the sidewall component 10 shown in Fig. 3, is preferably 5 mm or more, and more preferably 6 mm or more. If the maximum thickness H of the white rubber 6 is smaller than 5 mm, the minimum thickness γ (see Fig. 4) of the white rubber 6 after vulcanization becomes too small, making the white letters 9 more susceptible to contamination from the sidewall rubber 2a on the inside of the white rubber 6 in the tire axial direction D1.

[0024] Furthermore, the maximum thickness H of the white rubber 6 is preferably 9 mm or less, and more preferably 8 mm or less. If the maximum thickness H of the white rubber 6 is greater than 9 mm, the durability of the white rubber 6 after vulcanization molding may deteriorate.

[0025] Before vulcanization, i.e., in the state of the sidewall component 10 shown in Figure 3, the width A of the white rubber 6 in the tire radial direction D2 is preferably 75 mm or less, and more preferably 70 mm or less. If the width A of the white rubber 6 is greater than 75 mm, the outer end 6a (see Figure 4) of the white rubber 6 in the tire radial direction D2 after vulcanization may extend beyond the tire maximum width position 2b, which may increase the likelihood of cracks occurring in the white rubber 6. Furthermore, if the width A of the white rubber 6 is greater than 75 mm, the inner end 6b (see Figure 4) of the white rubber 6 in the tire radial direction D2 may come closer to the rim strip rubber 1d, which may reduce durability.

[0026] The width A of the white rubber 6 is preferably 55 mm or more, and more preferably 60 mm or more. If the width A of the white rubber 6 is smaller than 55 mm, in the white rubber 6 after vulcanization molding, the distance δ (see FIG. 4) between the raised portion 6c (the portion that becomes the white letters 9) and the outer end 6a and inner end 6b becomes too short, making the white letters 9 more susceptible to contamination from the sidewall rubber 2a on the outer and inner sides of the white rubber 6 in the tire radial direction D2.

[0027] The thickness H and width A of the white rubber 6 in the state of the sidewall part 10 were measured by cutting the part with a cutter knife or the like before forming the green tire.

[0028] FIG. 4 is a cross-sectional view of a main portion of a tire T1 (hereinafter also referred to as a vulcanized tire T1) immediately after a green tire has been vulcanized using a tire mold (not shown). The tire mold has recesses into which white rubber 6 and cover rubber 7 are poured to raise the tire outer surface from a profile line PL. The recesses in the tire mold form protrusions 8 on the outer surface of the vulcanized tire T1. Here, the profile line PL is the outline of the outer surface of the sidewall 2 excluding protrusions such as the protrusions 8 and rim protectors (not shown), and typically has a tire meridian cross-sectional shape defined by smoothly connecting multiple arcs. However, the profile line PL may be formed by a single arc, have a continuously changing radius of curvature, or include a straight line in part.

[0029] By buffing the tips of the projections 8, the white rubber 6 is exposed, and a pneumatic tire T can be manufactured in which white letters 9 are formed on the sidewall 2. The surface to be buffed is, for example, the surface indicated by the dashed line in FIG. 4.

[0030] The maximum protrusion height α of the white rubber 6 from the profile line PL after vulcanization molding is preferably 2 mm or more. If the maximum protrusion height α of the white rubber 6 is less than 2 mm, buffing becomes difficult and the appearance of the formed white letters 9 is poor. In this embodiment, the maximum protrusion height α of the white rubber 6 is set to 4 mm, and the protrusion height of the white rubber 6 by buffing is set to 2 mm.

[0031] The maximum thickness H of the white rubber 6 before vulcanization and the maximum protrusion height α of the white rubber 6 from the profile line PL after vulcanization satisfy the relationship α≦0.7H. Preferably, the relationship α≦0.6H is satisfied. If α is greater than 0.7H, a large amount of the white rubber 6 flows into the protrusion 8, which reduces the minimum thickness γ and shortens the distance δ, making it easier for contamination of the white letters 9 from the sidewall rubber 2a around the white rubber 6 to occur early.

[0032] It is also preferable to satisfy the relationship α≧0.5H. If α is smaller than 0.5H, buffing becomes difficult and the appearance of the white letters 9 formed tends to be poor.

[0033] The minimum thickness γ of the white rubber 6 after vulcanization molding is preferably 5 mm or more, and more preferably 6 mm or more. If the minimum thickness γ is less than 5 mm, contamination of the white letters 9 from the sidewall rubber 2a on the inside of the white rubber 6 in the tire axial direction D1 is likely to occur.

[0034] The width A of the white rubber 6 in the tire radial direction D2 before vulcanization and the maximum height β of the raised portions 6c of the white rubber 6 in the tire radial direction D2 after vulcanization satisfy the relationship β≦0.6A. Preferably, they satisfy the relationship β≦0.5A. If β is greater than 0.6A, the aforementioned distance δ becomes too short, making it easier for contamination of the white letters 9 from the sidewall rubber 2a on the outer and inner sides of the white rubber 6 in the tire radial direction D2. Note that, when multiple protrusions 8 are formed, the maximum height β in the tire radial direction D2 of the raised portions 6c of the white rubber 6 after vulcanization is the distance in the tire radial direction D2 between the outermost end of the white rubber 6 in the tire radial direction at the outermost protrusion 8 in the tire radial direction D2 and the innermost end of the white rubber 6 in the tire radial direction at the innermost protrusion 8 in the tire radial direction D2. In other words, the maximum height β is also the character height of the white letters 9 in the tire radial direction D2 when the pneumatic tire T is viewed axially.

[0035] The maximum height β of the raised portion 6c of the white rubber 6 in the tire radial direction D2 after vulcanization is preferably 20 mm or more, and more preferably 30 mm or more. The pneumatic tire T according to this embodiment is intended for use as a truck or bus tire, and the maximum height β is, for example, 30 mm.

[0036] It is also preferable to satisfy the relationship β≧0.4 A. If β is smaller than 0.4 A, the appearance of the formed white letters 9 tends to deteriorate.

[0037] In the white rubber 6 after vulcanization molding, the distance δ between the raised portion 6c (portion that becomes the white letters 9) and the outer end 6a and inner end 6b in the tire radial direction D2 is preferably 5 mm or more, and more preferably 8 mm or more. If the distance δ is shorter than 5 mm, the white letters 9 are more likely to be contaminated by the sidewall rubber 2a on the outer and inner sides of the white rubber 6 in the tire radial direction D2.

[0038] As described above, the method for manufacturing a pneumatic tire according to this embodiment includes the steps of forming a green tire by arranging black sidewall rubber 2a on the outside of carcass 4 in sidewall 2 in the tire axial direction D1, arranging white rubber 6 adjacent to the sidewall rubber 2a on the outside of sidewall rubber 2a in the tire axial direction D1, and arranging black cover rubber 7 adjacent to the white rubber 6 on the outside of white rubber 6 in the tire axial direction D1, and vulcanizing the green tire using a tire molding die having recesses into which the white rubber 6 and cover rubber 7 are poured to raise the white rubber 6 from the profile line PL on the outer surface of the tire, and the maximum thickness H of the white rubber 6 before vulcanization and the maximum raised height α of the white rubber 6 from the profile line PL after vulcanization satisfy the relationship α≦0.7H.

[0039] According to this method for manufacturing a pneumatic tire, the minimum thickness γ and distance δ of the white rubber 6 after vulcanization molding can be sufficiently ensured, thereby suppressing contamination of the white letters 9 caused by the sidewall rubber 2a surrounding the white rubber 6.

[0040] Furthermore, in the manufacturing method of the pneumatic tire according to this embodiment, the width A in the tire radial direction D2 of the white rubber 6 before vulcanization molding and the maximum height β in the tire radial direction D2 of the raised portion 6c of the white rubber 6 after vulcanization molding satisfy the relationship β≦0.6A.

[0041] This configuration effectively prevents contamination of the white letters 9 caused by the sidewall rubbers 2a on the outer and inner sides of the white rubber 6 in the tire radial direction D2.

[0042] Furthermore, in the method for manufacturing a pneumatic tire according to this embodiment, the minimum thickness γ of the white rubber 6 after vulcanization molding is 5 mm or more.

[0043] This configuration effectively prevents contamination of the white letters 9 caused by the sidewall rubber 2a on the inside of the white rubber 6 in the tire axial direction D1.

[0044] Furthermore, in the manufacturing method of the pneumatic tire according to this embodiment, in the white rubber 6 after vulcanization molding, the distance δ between the raised portion 6c and the outer end 6a and inner end 6b of the white rubber 6 in the tire radial direction D2 is 5 mm or more.

[0045] This configuration effectively prevents contamination of the white letters 9 caused by the sidewall rubbers 2a on the outer and inner sides of the white rubber 6 in the tire radial direction D2.

[0046] The above-mentioned dimensional values, positional relationships, and magnitude relationships are measured when the pneumatic tire T is mounted on a regular rim, inflated to the regular internal pressure, and in a regular, unloaded state. For example, the tire maximum width position 2b is the position in the tire radial direction D2 of the position where the dimension in the tire axial direction D1, excluding structures such as patterns and letters protruding from the outer surface of the sidewall 2, is maximum when the pneumatic tire T is mounted on a regular rim, inflated to the regular internal pressure, and in a no-load state. The regular rim is a rim defined for each pneumatic tire T by a standard system including the standard on which the pneumatic tire T is based; for example, it is a standard rim in the case of JATMA, and a "Measuring Rim" in the cases of TRA and ETRTO.

[0047] The normal internal pressure is the air pressure determined for each pneumatic tire T by the standards on which the pneumatic tire T is based, and for truck and bus tires and light truck tires, it is the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. For passenger car tires, it is usually 180 kPa, but for tires labeled "Extra Load" or "Reinforced," it is 220 kPa.

[0048] The pneumatic tire T is not limited to the configurations of the above-described embodiments, and is not limited to the above-described effects. Furthermore, it goes without saying that various modifications can be made to the pneumatic tire T without departing from the spirit of the present invention. For example, it goes without saying that the configurations and methods of the above-described embodiments can be arbitrarily adopted and combined, and further, it goes without saying that one or more of the configurations and methods of the various modified examples described below can be arbitrarily selected and adopted in the configurations and methods of the above-described embodiments.

[0049] (1) In the manufacturing method of the pneumatic tire T according to the above embodiment, the width A of the white rubber 6 in the tire radial direction D2 before vulcanization and the maximum height β of the raised portion 6c of the white rubber 6 in the tire radial direction D2 after vulcanization satisfy the relationship β≦0.6A. However, the manufacturing method of the pneumatic tire T is not limited to this configuration. For example, by appropriately setting the maximum raised height α of the white rubber 6 after vulcanization, β can be made larger than 0.6A.

[0050] (2) In the manufacturing method of the pneumatic tire T according to the above embodiment, the minimum thickness γ of the white rubber 6 after vulcanization molding is 5 mm or more. However, the manufacturing method of the pneumatic tire T is not limited to this configuration.

[0051] (3) In the manufacturing method of the pneumatic tire T according to the above embodiment, in the white rubber 6 after vulcanization molding, the distance δ between the raised portion 6c and the outer end 6a and the inner end 6b in the tire radial direction D2 of the white rubber 6 is 5 mm or more. However, the manufacturing method of the pneumatic tire T is not limited to this configuration.

[0052] (4) In the manufacturing method of the pneumatic tire T according to the above embodiment, Fig. 1 and Fig. 2 show an example of a cross section of the pneumatic tire T, in which there are three protrusions 8, but this is not limited to this. Depending on the cutting position of the cross section of the pneumatic tire T, there may be one protrusion 8 or four or more protrusions 8.

[0053] (5) In the above embodiment, the white rubber 6 is given as an example of a different color rubber. However, the different color rubber may have a color different from the sidewall rubber 2a and the cover rubber 4, i.e., a color other than black. Typically, the different color rubber has a white color, but is not limited to this. [Explanation of symbols]

[0054] T...pneumatic tire, 1...bead, 2...sidewall, 2a...sidewall rubber, 2b...maximum tire width position, 3...tread, 4...carcass, 5...inner liner, 6...white rubber, 6a...outer end of white rubber in the tire radial direction, 6b...inner end of white rubber in the tire radial direction, 6c...raised portion of white rubber, 7...cover rubber, 8...protrusion, 9...white letter, 10...sidewall part, H...maximum thickness of white rubber before vulcanization molding, A...width of white rubber in the tire radial direction before vulcanization molding, PL...profile line, α...maximum raised height of white rubber from the profile line after vulcanization molding, β...maximum height of raised portion of white rubber in the tire radial direction, γ...minimum thickness of white rubber after vulcanization molding, δ...distance between raised portion of white rubber after vulcanization molding and outer and inner ends in the tire radial direction, D1...tire axial direction, D2...tire radial direction

Claims

1. The tire manufacturing method includes the steps of: forming a green tire by arranging a sidewall rubber of a first color on the axially outer side of a carcass in a sidewall; arranging a different-colored rubber of a second color adjacent to the axially outer side of the sidewall rubber; and arranging a cover rubber of the first color adjacent to the axially outer side of the different-colored rubber so as to cover the different-colored rubber; vulcanizing and molding the green tire using a tire molding die having a recess for allowing the different-colored rubber and the cover rubber to flow therein and protrude from a profile line on the outer surface of the tire; and buffing the tip of the protrusion formed by the recess to scrape off the cover rubber and expose the different-colored rubber. A method for manufacturing a pneumatic tire, wherein a maximum thickness H of the different color rubber before vulcanization molding and a maximum protrusion height α of the different color rubber from the profile line after vulcanization molding and before buffing satisfy the relationship 0.5H≦α≦0.7H.

2. 2. The method for manufacturing a pneumatic tire according to claim 1, wherein a width A in the tire radial direction of the different color rubber before vulcanization molding and a maximum height β in the tire radial direction of the raised portion of the different color rubber after vulcanization molding satisfy a relationship of β≦0.6A.

3. The method for manufacturing a pneumatic tire according to claim 1 or 2, wherein the different color rubber after vulcanization molding has a minimum thickness of 5 mm or more.

4. 4. The method for manufacturing a pneumatic tire according to claim 1, wherein the distance between the raised portion and the outer and inner ends of the different color rubber in the tire radial direction after vulcanization molding is 5 mm or more.

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