Pneumatic tire, manufacturing device for pneumatic tire, and method of manufacturing pneumatic tire
A pneumatic tire that rotates about a center axis includes a tread rubber that comprises a contact patch; a groove provided in the tread rubber, the groove having an inner surface that includes a bottom surface and side surfaces that connect the bottom surface to the contact patch; and a coating film disposed covering at least a portion of the inner surface, the coating film reducing exposure of ultraviolet light to the inner surface.
1. A pneumatic tire that rotates about a center axis, the pneumatic tire comprising:
a tread rubber that comprises a contact patch;
a groove provided in the tread rubber, the groove comprising an inner surface that comprises a bottom surface and side surfaces that connect the bottom surface to the contact patch;
a wear indicator provided in the groove; and
a coating film disposed covering at least a portion of the inner surface, the coating film reducing exposure of ultraviolet light to the inner surface; wherein
the inner surface has a center line average surface roughness (Ra75) of from 1 μm to 100 μm,
the coating film has a thickness of from 5 μm to 120 μm,
the coating film is disposed covering the inner surface on the bottom surface side of an upper line of the wear indicator in a depth direction of the groove, and
the tread rubber is exposed at a region of the inner surface of the groove from an uppermost surface of wear indicator to the contact patch.
2. The pneumatic tire according to claim 1 , wherein the inner surface has a center line average surface roughness (Ra75) of from 1 μm to 2 μm, and the center line average surface roughness (Ra75) is measured with a laser-type non-contact surface roughness measuring device.
3. The pneumatic tire according to claim 1 , wherein the coating film has a thickness of from 20 μm to 60 μm.
4. The pneumatic tire according to claim 1 , wherein the coating film comprises a resin composition with urethane as a main component and a carbon black or a pigment.
5. The pneumatic tire according to claim 1 , wherein the coating film comprises a resin composition with urethane as a main component and at least one of: a benzotriazole-based ultraviolet light absorbing agent, a benzophenone-based ultraviolet light absorbing agent, a salicylate-based ultraviolet light absorbing agent, a cyanoacrylate-based ultraviolet light absorbing agent, a nickel-based ultraviolet light absorbing agent, a triazine-based ultraviolet light absorbing agent, or a hindered amine-based light stabilizer.
6. The pneumatic tire according to claim 1 , wherein the coating film comprises a resin composition with urethane as a main component and titanium oxide or zinc oxide.
7. The pneumatic tire according to claim 6 , wherein the resin composition has polycarbonate-based urethane as a main component.
8. The pneumatic tire according to claim 1 , further comprising a primer film with a water-based acrylic emulsion as a main component disposed between the inner surface and the coating film.
9. The pneumatic tire according to claim 1 , wherein the following conditions are satisfied:
H≥ 0.3 D , and
H/W≤ 5, where
H is a depth of the groove, W is a width of the groove, and D is a thickness of the tread rubber.
10. The pneumatic tire according to claim 1 , wherein the coating film is disposed covering the inner surface on a bottom surface side of positions located at 0.5H or inward of 0.5H from the contact patch in the depth direction of the groove, where H is a depth of the groove when the pneumatic tire is new.
11. The pneumatic tire according to claim 1 , wherein the coating film comprises a first coating film and a second coating film disposed adjacent to the first coating film with a gap portion therebetween.
12. The pneumatic tire according to claim 11 , wherein the groove comprises a main groove disposed in a tire circumferential direction; the first coating film and the second coating film are disposed in the main groove in the tire circumferential direction; and dimensions in the tire circumferential direction of the gap portion of the coating film located between the first coating film and the second coating film are less than dimensions in the tire circumferential direction of the first coating film and the second coating film.
13. The pneumatic tire according to claim 12 wherein the groove comprises a lug groove connected to the main groove; and the gap portion is disposed at an intersection portion where the main groove and the lug groove meet.
14. The pneumatic tire according to claim 11 , wherein the groove comprises a main groove disposed in a tire circumferential direction; the first coating film and the second coating film are disposed in the main groove in a tire width direction; and dimensions in the tire width direction of the gap portion of the coating film located between the first coating film and the second coating film are less than dimensions in the tire width direction of the first coating film and the second coating film.
15. The pneumatic tire according to claim 1 , wherein the coating film has a transmittance with respect to the ultraviolet light having wavelengths from 290 nm to 380 nm of 0.5 or less.