Patent Application
20120285606
The present invention relates to a manufacturing method for pneumatic tire capable of suppressing generation of a bare near a sidewall rubber edge while improving durability.
Recently, a pneumatic tire is known to have an improved noise-property and ride comfort owing to omitting a bead-reinforcing layer disposed separately from a carcass so as to reduce a rigidity of a bead portion. However, this kind of pneumatic tire has a problem that a bare (b) is apt to arise on a tire surface of a bead portion (a) as shown in
The inventors of the present invention found that a sidewall rubber edge (e), which is the radially inner edge of a sidewall rubber (c), deforms under a pressure from a large compressional force between a very hard bead core (d) and a mold (f), so that a bare (b) generates during vulcanization as shown in
Then, the inventors of the present invention made a proposal in the patent document 1 of a manufacturing method for pneumatic tire as shown in
Patent document 1: Japanese Patent JP3367895.
However, the generation of the bare (b) of such a manufacturing method for pneumatic tire could be suppressed to some extent, but it was not enough; there was room for improvement.
Additionally, to absorb the compressional force during vulcanization, it was also suggested to turn-back an inner liner (i) disposed on the tire cavity surface (h) from the axially inside to the axially outside of the tire around the bead core (d) so as to enlarge a rubber thickness (w) of the bead portion (a). However, the inner liner (i) was formed of a rubber having an inferior adherence property, so that it was difficult to get a sufficient joining strength with a carcass (j) and a bead chafer (k) and the like; therefore, the durability of the bead portion (a) was apt to decrease.
It is therefore, in view of the above-mentioned problems, an object of the present invention to provide a manufacturing method for pneumatic tire capable of suppressing a bare arising near a sidewall rubber edge and improving durability. The present invention is based on arranging an insulation rubber having an adherence property superior to an inner liner between a carcass and an inner liner and turned up around a bead core, disposing a sidewall rubber edge more inward in the tire radial direction than the bead core, and terminating an outer edge of the turn-up part of the insulation rubber more outward in the tire radial direction than the sidewall rubber edge.
The present invention relates to a manufacturing method for pneumatic tire comprising a process for forming a raw cover of the tire, and a vulcanization process for vulcanization forming by inserting the raw cover into a mold.
The raw cover comprises
a carcass comprising a carcass ply having a turn-up part extending from a tread portion through a sidewall portion and turned up around a bead core of a bead portion,
a sidewall rubber disposed in an axial outside of the carcass and forming an outer surface of the sidewall portion,
a bead chafer connected with a radially inner edge of the sidewall rubber and disposed along a bead seat surface,
an inner liner made of an air impermeable rubber material and disposed in an inside of the carcass so as to form a tire cavity surface, and
an insulation rubber having an adherence property superior to the inner line comprising a main portion disposed between the carcass and the inner liner and extending from the tread portion through the sidewall portion to the bead portion, and a turn-up part connecting with this main portion and turned up around the bead core from the axially inside to the outside.
In the inserted state of the raw cover into the mold, a sidewall rubber edge, which is a boundary part between the sidewall rubber appearing on a surface of the raw cover outer surface and the bead chafer, is disposed more inward in the tire radial direction than a core inner point P1 where the raw cover outer surface intersects with a tire axial-directional line L1 passing through a radially inner edge of the bead core.
An outer edge of the turn-up part the insulation rubber extends between a turn-up part of the carcass ply and the sidewall rubber and terminates more outward in the tire radial direction than the sidewall rubber edge.
In such a manufacturing method for pneumatic tire, in an inserted state of the raw cover into the mold, a sidewall rubber edge, which is a boundary part between the above-mentioned sidewall rubber appearing on a surface of a raw cover outer surface and the bead chafer, is disposed more inward in the tire radial direction than a core inner point P1 where the raw cover outer surface intersects with a tire axial-directional line L1 passing through a radially inner edge of the above-mentioned bead core. Therefore, the sidewall edge is not forced by the large compressive force generated between the bead core and the mold during vulcanization; and the deformation of the sidewall rubber edge can be suppressed. Thus, the bare arising near the sidewall edge can be suppressed.
Moreover, the above-mentioned raw cover is provided with an insulation rubber comprising a main portion extending between the carcass and the inner liner from the tread portion through the sidewall portion to the bead portion, and a turn-up part connecting with this main portion and turned-up around the bead core form the axially inside to the axial outside of the tire. The outer edge of the turn-up part of the insulation rubber passes between a turn-up part of the carcass ply and the sidewall rubber and terminates more outward in the tire radial direction than the sidewall rubber edge. Therefore, the insulation rubber helps to increase a rubber thickness of the bead portion, and it can absorb the large compressive force generated between the bead core and the mold during vulcanization and can suppress a rigidity gap with the sidewall rubber edge. Therefore, the bare generation can be effectively suppressed.
Moreover, the insulation rubber has the adherence property superior to the inner liner and can joint with the carcass and the sidewall rubber solidly. Therefore, the joint strength with the carcass and the sidewall rubber can be sufficiently ensured, so that the durability of the bead portion is improved.
(b): the cross-sectional view thereof.
Hereinafter, an embodiment of the present invention will be described with referent to the drawings. The present invention relates to a manufacturing method for pneumatic tire comprising a process for forming a raw cover 2 of a tire, and a vulcanization process for vulcanization forming by inserting the raw cover 2 into a mold 3.
As shown in
The above-mentioned carcass 9 of the present embodiment is formed with a single carcass ply 9A turned-up and secured from the axially inside to the axially outside of the tire so as to wrap a bead apex rubber 8 around the above-mentioned bead core. That is to say, the carcass ply 9A comprises a main portion 9a extending from the tread portion 4 through the sidewall portion 5 to the bead core 7 of the bead portion 6, and a turn-up part 9b extending from this main portion 9a and turned-up around the bead core 7 from the axial inside to the axial outside of the tire. Moreover, the carcass ply 9A comprises a carcass cord made of an organic fiber cord such as polyester, nylon, rayon or the like, and is disposed after vulcanization to the carcass cord incline at an angle of from 75 to 90 degrees with respect to the tire equator C.
The above-mentioned belt layer 10 is formed by overlapping two belt plies, an inner belt ply 10A and an outer belt ply 10B, having a belt cord arranged and inclined at a small angle of from 10 to 40 degrees, for example, with respect to the tire equator c so that belt cords intersect one another. As a belt cord of the present embodiment, a steel cord is adopted, but also a highly elastic organic fiber cord such as aramid, rayon and the like can be adopted as required.
Moreover, the raw cover 2 of the present embodiment comprises a tread rubber 11 forming an outer surface 4A of the tread portion 4, a sidewall rubber 12 forming an outer surface 5A of the sidewall portion 5, a bead chafer 13 disposed along a bead seat surface 16, and an inner liner 14 forming a tire cavity surface 2i inside the carcass 9.
The above-mentioned tread rubber 11 is disposed outward the belt layer 10 in the radial direction of the tire. Moreover, a predetermined tread pattern is formed on the outer surface 4A of the tread rubber 11 by use of the mold 3.
The above-mentioned sidewall rubber 12 is disposed outside the carcass 9 in the axial direction of the tire. The sidewall rubber 12 of the present embodiment comprises a side base rubber 12a occupying a great part of the sidewall portion 5, and a clinch rubber 12b connected to the radially inner edge of the side base rubber 13a. This clinch rubber 12b is harder than the side base rubber 12a and has a short length.
The bead chafer 13 of the present embodiment, as shown in an enlarged view of
The above-mentioned hard rubber portion 17 comprises a basal part 17a extending along the bead seat surface 16, and an inside rising part 17i rising from the tire axially inner edge of this basal part 17a to the tire radial outside in a tapered manner. The cross-section of the hard rubber portion 17 is formed as a substantially L-shape in regard to
The above-mentioned canvas portion 18 comprises a basal piece 18a extending along the bead seat surface 16 while covering the basal part 17a, and an inner stand-piece 18i and an outer stand-piece 18o rising outwardly in the radial direction of the tire from both of the axially outer edges of this basal piece 18a. The inner stand-piece 18i covers the inside rising part 17i of the hard rubber portion 17. With this arrangement, the inner stand-piece 18i extends along the tire cavity surface 2i in the radial direction of the tire. Moreover, the outer stand-piece 18o extends between the carcass 9 and the sidewall rubber 12 around in the tire radial direction.
The above-mentioned inner liner 14 is formed in a toroidal shape arranged substantially between the bead portions 6 and 6 so as to keep the air in the tire cavity (I) as shown in
Moreover, the raw cover 2 of the present embodiment is provided with an insulation rubber 15. The insulation rubber 15 is disposed between the carcass 9 and the inner liner 14, and comprises a toroidal main portion 15A extending from the tread portion 4 through the sidewall portion 5 to the bead portion 6 and a turn-up part 15B connecting with the main portion 15A and turned-up around the bead core 7 from inside to outside in the axial direction of the tire.
The above-mentioned insulation rubber 15 is made of a rubber having an adherence property superior to the inner liner 14. The term “adherence property” here means an adherence between unvulcanized rubber materials. To develop the adherence property more than the inner liner 14, it is preferable for the insulation rubber 15 to adopt NR-based rubber in which natural rubber (NR) is compounded of not less than 60 parts by mass, more preferably not less than 80 parts by mass in rubber component 100 parts by mass, for example. Additionally, as the rest of the rubber polymer, isoprene rubber (IR) or butamoldne rubber (BR) is preferably adopted.
The above-mentioned main portion 15A of the insulation rubber 15 is arranged between the carcass 9 and the inner liner 14; therefore, the adherence property between them is improved. Moreover, as shown in
There are various kinds of the mold 3 which might be used, but
a tread shaping mold 3a enabling to form a tread pattern in the tread rubber 11, and
an upper piece 3b and a lower piece 3c disposed in both sides thereof and forming the sidewall portion 5 and the bead portion 6, enabling to move closely and separately in the axial direction of the tire.
In the tire manufacturing method of the present embodiment, in the inserted state of the raw cover 2 into the mold 3 as shown in
Moreover, in the tire manufacturing method of the present embodiment, an outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 terminates more outward in the tire radial direction than the sidewall rubber edge E. Therefore, the manufacturing method of the present embodiment, the sidewall rubber edge E is not forced by the large compressive force generated between the bead core 7 and the mold 3 during vulcanization; eventually, a large deformation caused by the bare arising near the sidewall rubber edge E can be suppressed.
Furthermore, in the manufacturing method of the present invention, owing to the insulation rubber 15, a rubber thickness W1 at the axial outside the bead core 7 can be increased. This helps to absorb preferably the large compressive force generated between the bead core 7 and the mold 3 during vulcanization. Moreover, the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 is disposed from the sidewall rubber edge E in the radial direction of the tire, so that a poor jointing owing to closing both of the end portions one another and a durability deterioration can be prevented, and the bare generation can be effectively prevented.
Moreover, since the insulation rubber 15 has the adherence property superior to the inner liner 14, it can solidly adhere together with the carcass 9 and the sidewall rubber 12. Therefore, the jointing strength with the carcass 9 and the sidewall rubber 12 can be sufficiently obtained so as to improve the durability of the bead portion 6.
Also, in the tire manufacturing method of the present embodiment, it is important to the identify positions of sidewall rubber edge E and of the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 in the inserted state of the raw cover 2 into the mold 3; however, it is not very important to identify the respective positions in the vulcanized pneumatic tire in view of the preventing the bare. Additionally, the sidewall rubber edge E and the outer edge 15Bo may vary the positions in the radial direction of the tire before and after vulcanization.
A radial length H1 between the sidewall rubber edge E and the tire axial-directional line L1 passing through the radially inner edge of the bead core 7 can be arbitrarily determined. When the radial length H1 is too small, a large compressional force acts in the sidewall rubber edge E, and the bare generation may be insufficiently suppressed. From the viewpoint of this, the length Hi is preferably not less than 1 mm, more preferably not less than 2 mm, furthermore preferably not less than 3 mm.
Moreover, the tire radial length H2 between the sidewall rubber edge E and the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 can be arbitrarily determined. When this length H2 is too small, the end of the sidewall rubber 12 comes close to the end of the insulation rubber 15, and the durability may decrease; however, when the length H2 is too large, the property does not improve in proportion to a mass increase of the tire. From the viewpoint of this, the length H2 is preferably not less than 5 mm, more preferably not less than 6 mm, furthermore preferably not less than 7 mm.
Moreover, the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 preferably extends more outwardly in the radial direction of the tire than a tire axial-directional line L2 passing through the radially outer edge of the bead core 7. With this arrangement, the insulation rubber 15 can cover the axial outside of the bead core 7 and can absorb the large compressive force generated between the bead core 7 and the mold 3 during vulcanization. Also, when an axial length H3 between the outer edge 15Bo of the insulation rubber 15 and the tire axial-directional line L2 is small, a strain concentrates near the outer edge 15Bo of the insulation rubber 15, and damage may begin from there. However, when the axial length H3 is too large, the property does not improve in proportion to a mass increase of the tire. From the viewpoint of this, the length H3 is preferably not less than 1 mm, more preferably not less than 2 mm, preferably not more than 10 mm.
Moreover, the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15 preferably terminates more outward in the tire radial direction than the outer edge 18t of the outer stand-piece 18o of the bead chafer 13. This helps to prevent from creating a rigidity difference owing to closing both of the outer edges one another. To certainly prevent such a rigidity difference, a radial length H4 between the outer edge 15Bo of the insulation rubber 15 and the outer edge 18t of the outer stand-piece 18o is preferably not less than 1 mm, moreover preferably not less than 2 mm. Also, the outer edge 18t of the outer stand-piece 18o is preferably disposed more outward in the tire radial direction than the tire axial-directional line L2 passing through the outer edge of the bead core 7.
Moreover, the thickness w2 of the insulation rubber 15 can be also arbitrarily determined. When the thickness W2 is too small, the large compressive force generated between the bead core 7 and the mold 3 during vulcanization may be insufficiently absorbed. However, when the thickness w2 is too large, in the outer edge 15Bo of the turn-up part 15B of the insulation rubber 15, unevenness generates in the sidewall portion 5, and a new bare may arise. From the viewpoint of this, the thickness w2 of the insulation rubber 15 is preferably not less than 0.5 mm, moreover preferably not less than 0.7 mm; additionally, preferably not more than 1.5 mm, more preferably not more than 1.3 mm.
Moreover, when a complex modulus E*1 of the insulation rubber 15 is small, the compressional force generated between the bead core 7 and the mold 3 during vulcanization may be insufficiently absorbed. However, when the complex modulus E*1 becomes large, the compressional force is not absorbed but transmitted to the sidewall rubber 12 and may cause a bare. In terms of this, the complex modulus E*1 of the insulation rubber 15 is preferably not less than 0.3 times, more preferably not less than 0.5 times of the complex modulus E*2 of the clinch rubber 12b; additionally, preferably not more than 1.0 times, more preferably not more than 0.8 times of the complex modulus E*2 of the clinch rubber 12b.
The complex moduli E*1 and E*2 are measured by use of a viscoelastic spectrometer manufactured by K. K. Iwamoto seisakusyo, according to the prescription of JIS-K6394, under a condition of a temperature of 70° C., a frequency of 10 Hz, an initial tension strain of 10%, and an amplitude of dynamic strain of ±1%.
The sidewall rubber 12 of the present embodiment is formed in an extruded-compact-style. Incidentally, in the present invention, the sidewall rubber 12 may be formed by way of winding spirally an unvulcanised rubber strip G in a ribbon fashion around the tire rotational axis, so-called in the strip winding method, as shown in
In such a strip winding method, the sidewall rubber 12 is formed by directly winding the rubber strip G on the carcass ply 9A and the outside of the turn-up part 15B of the insulation rubber 15. In the rubber strip G of this example, the clinch rubber 12b and the side base rubber 12a are wound from the sidewall rubber edge E toward the outside in the radial direction of the tire in order of precedence.
In the sidewall rubber 12 formed in this strip winding method, the sidewall rubber edge E can be disposed more inward in the tire radial direction than the core inner point P1, and the sidewall rubber 12 can be accurately formed.
Although the especially preferred embodiments of the present invention have been described in detail, needless to say, the invention is not limited to the above-mentioned concrete embodiments, and various modifications can be made.
A raw cover (tire size: 195/65R15) having a basic structure shown in
The test processes were as follows.
A thousand of each of the above-mentioned raw covers were formed in vulcanization by use of a mold, and a bare arising in a sidewall edge was checked up with the naked eye. Evaluation was made for a bare incidence; and the smaller the numeric values were, the more favorable it was.
A vulcanized tire mounted on a rim having a size of 15×63 was rolled on a drum tester under a condition of an internal pressure 200 kPa, a longitudinal load of 8.16 kN, and at a speed of 65 km/h; and a running time that elapsed before generation of a damage in the bead portion was measured. The results were displayed using indices with comparative Example 1 being 100. The larger the numeric value was, the more favorable the durability was.
The test results and the like are shown in Table 1. In Table 1, regarding lengths H1 to H4, a dimension shown in
For the test result, it was confirmed that the manufacturing method for pneumatic tire of the invention shown in Examples enabled a suppression of the bare arising near the sidewall rubber edge and an improvement of the durability.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-039118 | Feb 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/053897 | 2/23/2011 | WO | 00 | 7/20/2012 |
