Adhesive composition, resin material, rubber article and...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...

Reexamination Certificate

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C428S361000, C428S375000

Reexamination Certificate

active

06774172

ABSTRACT:

TECHNICAL FIELD
This invention relates to an adhesive composition, a resin material treated therewith, a rubber article reinforced by the resin material, and a pneumatic tire applied with the rubber article.
BACKGROUND ART
Since polyester fibers such as polyethylene terephthalate fiber and polyethylene naphthalate fiber and the like, and aromatic polyamide fibers possess a higher initial modulus and an excellent dimensional stability under heat, they are very useful in forms of filament, cord, cable, cord fabric, canvas and the like as a reinforcement for rubber articles such as a tire, a belt, an air spring, a rubber hose and the like.
However, these reinforcements are compact in their molecular structure and less in the number of functional groups on their resin surface, so that they hardly adhere to rubber with an adhesive composition comprising resorcin, formaldehyde and a rubber latex (hereinafter referred to as RFL) capable of well adhering a reinforcement such as nylon fiber and rayon fiber to rubber.
For this end, there have variously been proposed not only adhesive compositions but also adhering methods, treated fibers and the like in order to adhere synthetic fibers to rubber well.
DISCLOSURE OF THE INVENTION
As the adhering method, there are a one-bath treating adhering method and a two-bath treating adhering method. As the one-bath treating adhering method, there is a method wherein an adhesive composition obtained by mixing the RFL with a compound containing a chain structure made from methylene diphenyls in its molecule (adhesion improver) such as a condensate of phenol-formaldehyde obtained through novolak reaction (see WO 97/13818) is applied onto the cord.
This one-bath treating adhering method is less in the amount of the adhesive composition used and excellent in the raw material cost and production cost because the adhesive composition is applied onto the cord surface only once. And also, the adhesive composition is flexible, so that stress concentration and heat generation accompanied therewith are small, and the fatigue property of the cord is excellent. Therefore, it is effective in the application to general-purpose tires.
However, the adhesive composition includes a rubber latex, so that it reacts with sulfur migrated from adherend rubber to cause sulfur cross-linking, which renders the modulus of the adhesive layer high, while it shrinks to create strain stress at an interface between the fiber and the adhesive layer, leading to lower an adhesion force (see the aforementioned WO 97/13818).
As the temperature is raised, the sulfur crosslinking in the latex rubber changes from a polysulfide bond to a monosulfide bond, so that the crosslinking portion are shortened and the number of crosslinkings is increased accompanied therewith, and hence the shrinkage of the adhesive layer becomes large and the adhesion force considerably lowers. Thus, in non-general-purpose tires wherein the environmental temperature of the tire in the running at a high-temperature reaches, for example, 180° C. or higher, there is a possibility that the adhesion force in the high-temperature running of the tire becomes insufficient.
On the other hand, as the two-bath treating adhering method, there are a method wherein the surface of a fiber cord is firstly coated with an adhesive composition containing an epoxy compound and a blocked isocyanate and then coated with an adhesive composition containing the RFL, and the like.
The fiber cord treated by the two-bath treating adhering method becomes hard and the handling thereof is difficult in view of the production (see JP-A-06-173172). A rubber article reinforced therewith initially exhibits a high adhesion force even at a high temperature, but after it is used under a high temperature and a high strain, the degradation of adhesion and cord fatigue are violently caused and there is an inconvenience that the service life of the article is considerably reduced.
Since a high adhesion force is obtained just for a short time, however, if the above adhesion degradation and cord fatigue could be improved, such a method may be able to be applied to tires running at the high temperature and the like.
Recently, tire performances are improved, while strain or heat input to the cord through the rotation of the tire becomes severer. For example, it has been conventionally sufficient to ensure an adhesion performance up to about 190° C. during the running even in case of a racing tire (see “Tire Engineering for Driver”, p.182, line 3: Grand Prix Press Co. Ltd.; 1989).
Lately, run flat tires capable of running at a puncture state are noticed. In this tire, the heat generation due to the running at the puncture state is large, and particularly, the temperature becomes higher in local portions causing the concentration of strain stress, so that the temperature of the tire reinforcing cord easily causing the concentration of strain stress in view of its structure may reach a temperature thermally deforming the tire reinforcing cord made of polyester or nylon.
The thermal deformation condition of a resin material such as a polyester, a nylon or the like depends not only on the temperature but also on the strain. Namely, as the strain becomes large, creep deformation may be caused even at a temperature lower than its melting point.
Under such circumstances, the heat-resistant performance required in an adhesive for tire cords lies in a point that the adhesion state is kept up to a condition where the tire cord is thermally deformed by heat and strain. Although this condition differs depending upon the cord material, it is preferable that the adhesive layer is not peeled at least up to a temperature near 200° C.
In some cases, a rubber hardened by increasing a sulfur content is used as a reinforcing rubber for a tire. In the vicinity of such a reinforcing rubber, the amount of sulfur migrating from the reinforcing rubber into the adhesive layer is increased and strain deterioration produced by the sulfur crosslinking of the adhesive layer under a high heat may be increased.
From a viewpoint of the adhesion durability and fatigue property of cord under high strain in such a condition, the adhesion durability is insufficient in both of the adhesive compositions based on the above one-bath treating adhering method and two-bath treating adhering method.
Therefore, under a situation that the tire carcass material and the like of the run flat tire reach a high temperature during the running of the tire, there is no example of practically using polyester fiber, aromatic polyamide fiber, acrylic fiber or the like as a tire reinforcing fiber.
Moreover, the vulcanization is demanded to be carried out at a high temperature, for example, above 190° C. in order to improve the tire performances and also to shorten the process time even at the vulcanization step in the manufacture of rubber articles such as tires and so on, so that it is required to develop an adhesive composition endurable to thermal deterioration.
From the above view points, there is strongly demanded an adhesive composition having a good durability under high temperature and high strain.
The adhesive composition satisfying these demands is required to be high in the initial adhesion force and excellent in the following three performances. That is, (i) the adhesion property at a high temperature is high, (ii) the thermal deterioration of adhesion force at a high temperature is less, and (iii) the fatigue resistance of the cord under a high strain is good.
(i) Firstly, an adhesive composition having a high adhesion property at a high temperature is required to be high in the resistance to cohesive failure at the high temperature. The resistance to cohesive failure of the adhesive composition at the high temperature can be explained from a change of physical state of molecules reversibly changing through a temperature such as cohesive state of molecule and motion of molecular chain in the adhesive composition (see “Development and Application of Functional Adhesive” (the latter volume), p174; 1997; CMC)

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