NZ213346A

NZ213346A - Radial tyre with sulphur- and cobalt salt-containing rubber compound as inner layer

Info

Publication number: NZ213346A
Application number: NZ21334685A
Authority: NZ
Inventors: Fukumoto Takahiro
Original assignee: Sumitomo Rubber Ind
Priority date: 1984-09-03
Filing date: 1985-09-03
Publication date: 1988-04-29
Also published as: JPS6160302A

Description

21334 Priority Date(s): Complete Specification Filed: 3.. f!. K*?. Class: g£pC%/08 Publication Date: .. ,2.-9. ARB.19?? P.O. Journal, No: ... .-/.v? F?77.

PATENTS FORM NO. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION STEEL CARCASS RADIAL TIRE HAVING TWO-LAYER LINER LAYER WE, SUMITOMO RUBBER INDUSTRIES, LTD of No. 1-1, Tsutsuicho 1-chome, Chuo-ku, Kobe-shi, Hyogo, Japan, a Japanese company, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement S3 "s » i ■ . ' ' <2> \ O v^,1 ,• ••■'>•' •■ ^«v«w.. - viFy?~fTv^ yr*ry?r<y?-r*rf, ■■ ,-v*f v • 2 1334 6 k This invention relates to a pneumatic radial tire with a carcass employing metal cords and more particularly to a compound of rubber for use as an inner liner layer, wherein adhesion between the carcass and the inner liner layer of the radial tire for a heavy vehicle is increased so as to improve the life of the tire.

Tires for use in heavy vehicles, such as trucks and buses, and carrying a heavy load under severe operating conditions are often equipped with a carcass composed of steel cords and a belt layer. There are two kinds of radial tires for heavy cars, namely, a tire with a tube and a tubeless one. The tire of either kind is normally equipped with an inner liner layer arranged over the whole inside surface thereof. The inner liner layer for the tire with a tube is used to protect the carcass ply layer and the tube, whereas for the tubeless tire it is used as a sealing material for preventing air within the tire from penetrating into the carcass. Heat resistant synthetic -I 1 | rubber or rubber containing less sulfur is normally used in the inner liner layer to prevent itself from being deteriorated by intense heat transmitted from the bladder * j when the tire is vulcanized. However, because the use of f I the heat resistant synthetic rubber poses a problem in that its tackiness and processability are reduced, another liner layer mostly prepared from natural rubber is added to the carcass ply side so as to provide a two-layer construction. When the inner liner layer is pressed 7 21334 6 against the carcass ply side by the vulcanizing pressure as the tire thus constructed is vulcanized, the metal carcass cords and the inner liner layer may contact each other, causing defective adhesion between them, and this may shorten the durability and life of the tire to a large extent.

An object of the present invention is to provide a durable radial tire by preventing, or at least obviating, a reduction in adhesion between the inner liner layer and the metal carcass cords caused by contact of the former with the latter when the tire is vulcanized.

The pneumatic radial tire according to the present invention comprises a pair of left- and right-hand beads, side walls respectively externally extending in the radial direction of the beads, a tread portion astriding the side walls, a carcass composed of metal cords practically extending in the radial direction and a belt layer = * :? 1 arranged on the outside of the carcass within the crown i J itself and is characterized in that an inner liner layer i ■* (^j is arranged over the whole inside surface of the tire, the k £ inner liner layer being composed of an inner layer of the f $ liner layer on the carcass ply side on the inside of said carcass and an innermost layer of the liner layer on the \ r inside surface of the tire and the inner layer of the liner layer is a compound of rubber having good adhesion properties with steel cords, said compound containing 2-8 parts by weight of sulphur and 0.5-5 parts by weight of organic acid cobalt salt per 100 parts by weight of rubber.

The inner liner layer according to the present invention consists of two layers and the inner layer of the liner layer on the carcass side must contain 2-8 parts by weight of sulfur and 0.5-5 parts by weight of organic acid cobalt salt per 100 parts by weight of rubber. The rubber used for the inner layer of the liner layer in that case is mainly composed of natural rubber accounting for at least 50% of the total, the rest being butadiene rubber and SBR. As for the 2-8 parts by weight of sulfur per 100 parts by weight of rubber, less than 2 parts by weight of sulfur will make insufficient adhesion between carcass cords and rubber, whereas more than 8 parts by weight of sulfur will fail to prevent the heat-deterioration of a tire at the time of its vulcanization. Less than 0.5 part, instead of 0.5-5 parts, by weight of organic acid cobalt salt, for instance, naphtene acid cobalt will make insufficient the adhesion of steel cords, whereas more than 5 parts by weight of such cobalt will result in increased production cost though the adhesion will be unchanged. On the other hand, the innermost layer of the liner layer must mainly be composed of halogen butyl rubber accounting for at least 50% of the total and a proper amount of rubber such as NR and BR so that the compound may be unpermeable to air.

The thickness of the inner layer of the liner layer should range from 0.2mm to 3mm and, if it is less than 0.2mm, the carcass ply cords may come in contact with the innermost layer of the liner layer at the time of the vulcanization of a tire, thus reducing the adhesion therebetween. On the other hand, if the thickness exceeds 3mm, it will increase only the weight of a tire and accordingly make the tire uneconomical. The thickness of the innermost layer of the liner layer should range from 0.3mm to 3mm and, if it is less than 0.3mm, the non-permeability thereof will be insufficient, whereas the diadvantage will become greater if it exceeds 3mm, because heat generation is amplified.

Brief Description of the Drawings Fig. 1 is a cross sectional view of the left half of a tire embodying the present invention.

Fig. 2 is a partially enlarged view of Fig. 1.

Reference characters: T...tire, l...bead, 2...side walls, 3...tread, 4...carcass, 5...inner liner layer, 5b...inner layer of liner layer, 5a...innermost layer of liner layer, and 6...belt layer.

Working Examples: There were prepared radial tires fcr heavy vehicles by way of trial, the tires being 1000R20 and 11R22.5 in size and having the cross sectional structure of Fig. 1. The tire T in Fig. 1 comprises a pair of left- and right-hand beads 1, side walls 2 respectively extending from the beads in the radial direction, a tread 3 astriding the side walls, a carcass 4 provided with metal cords practically extending from one bead to the other in the radial direction, a belt layer 6 on the outside of the carcass within the crown thereof, and an inner liner layer 5 arranged over the whole inside surface of the tire and adjacent to the carcass 4. The inner liner layer 5 consists of an inner layer of the liner layer 5b on the carcass side and an innermost layer of the liner layer 5a. The durability life of tires having an inner liner layer consisting of an inner layer and an innermost layer using the combinations of compounds shown in Table 1 was evaluated.

Table 2 shows the results evaluated.

Table 1 (Part by Weight) Compound A B C D NR 50 100 100 BR 50 - - - Chloro butyl rubber - HAF 40 - 50 50 GPF - Aromatic oil 3 3 2 2 Age resister - - 1 1 (Note 1) Stearin acid 1 1 1 1 Flowers of zinc 3 3 6 6 Napthene acid cobalt - - - 2 (Note 2) Sulfur 2 0.5 Accelerator 1 1 1 1 (Note 3) Note 1: 2. 2.2-trimethyl-l. 2 dihydro-quinolin polymer. Note 2: Containing 9.2% of cobalt.

Note 3: For compounds A and B, N-cyclo-hexyl-2-benzothiazolylsulfenamide. For compounds C and D, N, N-dicychlohexyl-2-benzothiazolylsulfenamide. r-*. 1! ^ /'i_. 1 . ■ ' The tires manufactured by way of trial were subjected to a durability test by leaving them in an oven heated to 70°C with 90% humidity for one week first and made to travel until they are damaged (separation of the shoulder portion) through the drum test method under test conditions including an internal pressure of 5kg/cm^ and load of 3.5 t at a speed of 40km/h.

The distance covered by each of the examples of the present invention proved excellent durability life.

As set forth above, a two-layer construction is employed for the inner liner layer according to the present invention and a rubber compound excellent in adhesion to metal carcass cords is used for the inner layer of the liner layer on the carcass side, so that not only adhesion between the metal cords and the rubber but also the durability life of the tire has been improved.

Although this invention has been described by way of example and with reference to a possible embodiment thereof, it is to be understood that modifications and improvements may be made thereto without departing from the scope of the invention as defined in the appended claims. 213346

Claims

WHAT WE CLAIM IS:

1. A pneumatic radial tire comprising a pair of left- and right-hand beads, side walls respectively externally extending in the radial direction of the beads, a tread portion astriding the side walls, a carcass composed of metal cords practically extending in the radial direction and a belt layer arranged on the outside of the carcass within the crown thereof, characterized in that an inner liner layer is arranged over the whole inside surface of the tire, said inner liner layer being composed of an inner layer of the inner liner layer on the carcass ply side on the inside of said carcass and an innermost layer inner liner layer on the inside surface of the tire, and said inner liner layer is a compound of rubber having good adhesion properties with steel cords, said compound containing 2-8 parts by weight of sulfur and 0.5-5 parts by weight of organic acid cobalt salt per 100 parts by weight of rubber.

2. A tire as claimed in claim 1 wherein said rubber comprises at least 50% of natural rubber by weight, together with butadiene rubber and SBR.

3. A tire as claimed in claim 1 or claim 2 wherein the innermost layer of the inner liner layer is impermeable to air and comprises at least 50% of halogen butyl rul by weight together with NR and BR rubber.

4. A tire as claimed in any one of the prece claims wherein the thickness of the inner layer of - 9 - 213346 inner liner layer is between 0.2mm and 3mm.

5. A tire as claimed in any one of the preceding claims wherein the thickness of the innermost layer of the inner liner layer is between 0.3mm and 3mm.

6. A tire as claimed in claim 1 having an inner liner layer substantially as herein described with reference to any one of examples A, B, C or D.

7. A tire as claimed in claim 1'substantially as herein described with reference to'the accompanying drawings. SUMITOMO RUBBER INDUSTRIES, LTD By its attorneys Baldwin Son & Care