Subcoat for fiber adhesion

Details Subcoat for fiber adhesion Subcoat for fiber adhesion

2002-04-09

2004-03-09

Dixon, Merrick (Department: 1774)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S372200, C427S375000

Reexamination Certificate

active

06703077

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to adhesives and particularly to subcoats for bonding synthetic fibers, such as aramid, nylon and polyester fibers, to rubber. Such compositions may be used in manufacturing composite articles, for example tires, to bond reinforcement fibers to tire rubber compositions.
BACKGROUND OF THE INVENTION
In the manufacturing of rubber composites which include fiber reinforcement in the form of fibers, filaments or cords, close attention is given to the adhesion between the rubber matrix of the composite and the fibrous reinforcement.
Aramid fiber, for example, is a fiber used for tire reinforcement. Providing adhesion between aramid and rubber is very difficult due to the crystalline surface of the fiber. Hence a separate subcoat is necessary in order to form a reasonable bond between fiber and rubber. An epoxy adhesive subcoat followed with a resorcinol formaldehyde latex (RFL) dip provides good adhesion to sulfur cured rubber for aramid reinforcement.
U.S. Pat. No. 5,922,797, incorporated herein by reference, teaches the use of a latex adhesive for improving the adhesion between a rubber matrix and fibrous reinforcement.
U.S. Pat. No. 2,748,049 discloses an adhesive dip which is reported to strongly adhere to fabric and rubber, and which is further reported to be relatively flexible. This dip is made utilizing a latex of a copolymer of a conjugated diolefin monomer, such as butadiene, and an unsaturated aldehyde monomer, such as methacrolein.
In commercial practice, resorcinol-formaldehyde-latex (RFL) dips have been widely implemented by the tire industry for bonding synthetic fabrics to rubber. For instance, U.S. Pat. No. 3,525,703 discloses a water-based adhesive composition for bonding synthetic fiber material to rubber. The teachings of U.S. Pat. No. 3,525,703 specifically disclose the utilization of styrene-butadiene latex and vinylpyridine-styrene-butadiene latex in such water-based adhesive compositions.
U.S. Pat. No. 4,460,029, incorporated herein by reference, teaches the use of oxazoline polymerized in latex form for tire cord adhesion.
Nippon Shokubai Co., Ltd., has acquired U.S. Pat. No. 4,460,029, and has continued to develop oxazoline compositions. Product information on oxazolines has been published by Nippon Shokubai Co., Ltd., entitled “EPOCROS K-1000, K-2000 series”, whereby such publication is also incorporated herein by reference.
Epoxy subcoat used currently demonstrates excellent adhesion with good rubber coverage in all compounds.
Due to environmental concerns regarding epoxy material, there is an interest in finding an alternative subcoat material, if substantially equivalent adhesion is maintained.
Also, oxazoline polymer is known to provide much longer pot life in adhesive formulations than epoxies.
SUMMARY OF THE INVENTION
A composition comprising 1% to 4% solids oxazoline polymer, 0% to 4% alkylene glycol monoether, and 92% to 99% water is provided, wherein all percentages are by weight.
In an alternative embodiment, the composition may comprise (1) oxazoline polymer and (2) a latex which is comprised of (a) water, (b) an emulsifier and (c) a polymer.
Also provided is a process for adhering synthetic textile fibers to sulfur vulcanizable rubbers comprising the steps of (I) immersing said fibers in an aqueous dispersion which is comprised of (a) 1% to 4% by weight oxazoline polymer, (b) 0% to 4% alkylene glycol monoether and (c) 92% to 99% water to produce coated fibers; (II) drying the coated fibers to produce subcoated fibers; (III) subjecting the subcoated fibers to an RFL adhesive dip to produce dipped fibers; (IV) drying the dipped fibers to produce dried dipped fibers; (V) placing the dried dipped fibers in contact with a sulfur vulcanizable rubber; and (VI) curing the sulfur vulcanizable rubber while it is in contact with the dried dipped fibers.
Also provided is a composite article of rubber and fibers, wherein the fibers have distributed over surface portions thereof (a) oxazoline polymer; (b) an RFL adhesive; and (c) an in situ vulcanized rubber compound.
The fibers in the composite article may comprise, for example, polyester fibers and aramid fibers.
In a preferred embodiment, the composite article is a tire.
DETAILED DESCRIPTION OF THE INVENTION
Schuetz et al., in U.S. Pat. No. 4,460,029 teach the use of oxazoline in a water insoluble latex adhesive for improving adhesion between fiber reinforcement (especially filaments and cords) and rubber. According to the present invention, the inventors have modified a water soluble oxazoline polymer solution (without latex) provided by Nippon Shokubai by diluting the solution with water to provide a solution with a polymer solids content of 1% to 4%, and have used the diluted solution directly on substrate fibers as a subcoat (in place of an epoxy subcoat), prior to a resorcinol aldehyde latex (RFL) dip, to improve adhesion between the fibers and a rubber matrix in a composite in which the fibers may be used.
In one embodiment, the oxazoline polymer solution contains an alkylene glycol monoether solvent (WS-500). For environmental reasons, it is preferred that the oxazoline polymer be prepared without solvent, although compositions made with or without glycol monoether solvent show desirable results in the invention.
The diluted oxazoline polymer, when used as a subcoat on fibers, provides good adhesion to the types of rubber compositions described in U.S. Pat. No. 4,460,029.
Oxazoline polymers, EPOCROS WS-500 and WS-700, developed by Nippon Shokubai Co., Ltd., are water-soluble polymers containing pendant oxazoline groups which are designed for use as a crosslinker for carboxylated waterborne polymers.
Oxazoline reacts with functional groups such as carboxyl, acid anhydride, phenolic hydroxyl and phenolic thiol. The reaction of an oxazoline group with a carboxylic group is very effective. It can react rapidly with carboxylic groups above temperatures of 80 to 100 degrees C to form an amide ester.
Because of its high reactivity, the inventors speculated that the oxazoline crosslinker may have potential for use in an adhesive system for rubber reinforcement materials.
Early tests of the material provided by Nippon Shokubai did not show good results, and showed different degrees of effectiveness on different materials. Since some tests showed an over stiffening of the fiber, the inventors further speculated that a reduction of the solids content of adhesive would improve the results.
Oxazoline polymer WS-500 has a composition (% by wt) of polymer/PM/water 40/38/22, where PM is propylene glycol monomethylether. Although the inventors dilute the polymer to much lower solid level for subcoat applications, the presence of organic solvent could still affect the environment. Based on this concern, the inventors suggested, and Nippon Shokubai made an effort to produce a new oxazoline polymer (WS-700) which is free of volatile organic chemicals (VOC). WS-700 has a solid level of 24.1%. The weight per oxazoline equivalent (WPO) of WS-700 is 220 (gram solid /equivalent), the same as in WS-500.
In accordance with this invention, the cord or fabric to be treated is dipped for 1 to 5 seconds in the oxazoline polymer solution of the invention, followed by dipping in an RFL latex adhesive, and dried at a temperature within the range of about 75° C. to about 265° C. for about 0.5 minutes to about 5 minutes, and thereafter calendered into rubber and cured therewith. The drying step utilized will preferably be carried out by passing the cord through 2 or more drying ovens which are maintained at progressively higher temperatures. For instance, it is highly preferred to dry the cord by passing it through a first drying oven which is maintained at a temperature of about 250° F. (121° C.) to about 300° F. (149° C.) and then to pass it through a second oven which is maintained at a temperature which is within the range of about 350° F. (177° C.) to about 500° F. (260° C.). It should be appreciated that these temperatures are oven temperatures rather than the temperature of the c

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