Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-11-14
2004-11-30
Dye, Rena (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S383000, C428S295100, C156S166000, C156S910000
Reexamination Certificate
active
06824871
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to (A) multifilament poly(p-phenylene-2,6-benzobisoxazole) (“PBO”) yarn or cord which is coated with a mixture of an epoxy resin with a vinyl pyridine-styrene-butadiene rubber latex (VPSBRL), the mixture referred to as a “subcoat”; the subcoated cord is then again coated by dipping in a conventional reaction product of a phenolic compound, an aldehyde donor and a latex, familiarly referred to generically as a “resorcinol-formaldehyde latex (RFL)”; and, (B) to a PBO-finishing process to make twice-coated yarn, in which process the epoxy-latex mixture is applied to PBO yarn which may have been given a spin-finish, or corona, or plasma treatment, yielding subcoated PBO yarn; and, the subcoated yarn is then again coated by dipping in a conventional RFL dip. The twice-coated yarn or cord has improved adhesion comparable to that provided by a coated poly(phenylenediamine terephthalamide) “aramid” yarn. Aramid is the generic name for fiber in which the fiber-forming substance is a long-chain synthetic aromatic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic linkages.
BACKGROUND OF THE INVENTION
The great strength of yarn or cord made from aramid fibers which have a crystalline surface has resulted in its widespread use to reinforce a variety of rubber articles in which adhesion is of paramount importance. The inherently poor bonding of vulcanized rubber to the surfaces of aramid fibers was overcome, over many years, by using several different processes many of which rely on a polyepoxide, or “epoxy” for brevity, subcoat followed by a RFL dip.
PBO yarn has higher strength and could deliver better performance than aramid yarn in reinforced tires, conveyor belts, drive belts and the like, if the inherently poor adhesive characteristics of the PBO yarn, due to low chemical reactivity and rigid surface structure, could be overcome. The outstanding flame resistance and thermal stability of the yarn is ideally suited for the manufacture of heat-resistant fabrics used to make high-pressure high-temperature resistant hose and protective clothing.
Because PBO fiber has a tensile modulus (T/mm
2
) nearly twice as high as that of aramid fiber it was believed that PBO yarn was ideally suited for use in reinforced sulfur-vulcanizable rubber if the yarn could be successfully coated with a coating which exhibited a comparable or better adhesion for rubber than which has been already achieved in aramid yarn.
The Problem
The surface characteristics of PBO yarn and the filaments from which it is made, are such that it is difficult to obtain substantially the same degree of adhesion with rubber as is currently obtained with aramid yarn. Of the many epoxy resins with which aramid, and some polyester yarns, may be effectively subcoated before each is topcoated with a conventional RFL dip, the aromatic polyglycidyl ethers are not sufficiently effective with PBO yarn. A subcoat for PBO yarn is to be found which has substantially the same adhesion to sulfur-vulcanized rubber as does successfully subcoated aramid yarn.
It is well known that an epoxy resin, both aliphatic and aromatic polyglycidyl ethers, is a highly effective subcoat for aramid fibers and it is unnecessary to combine the epoxy resin with a rubber latex of any kind. Moreover, as will be seen in Tables IV and V below for reinforcement by embedding and bonding twice-coated cord in the same two rubber compounds used in belts or plies, it was found that addition of a nitrile-butadiene rubber (“NBR”) latex to either an aliphatic or an aromatic polyglycidyl ether used in a subcoat for PBO cord, failed to provide adhesion comparable to that provided without the NBR latex in aramid cord.
Since it is also known that epoxy resins could be reinforced with PBO fibers as disclosed in U.S. Pat. No. 5,874,152 to Middelman, an obvious choice was to use an epoxy resin as a subcoat. However, as will be evident from tests presented hereafter, several epoxy resins provided reasonably good adhesion in sulfur-vulcanizable rubber when used as subcoats, followed by a RFL dip, but the adhesion to PBO yarn was far from a close match compared to the adhesion provided by aramid cord in sulfur-vulcanizable rubber. Not unexpectedly, it was found that aliphatic polyglycidyl ethers which are effective only in combination with a VPSBRL on PBO yarn, were also effective without the latex, on aramid fibers.
It is known, as disclosed in U.S. Pat. No. 6,077,606 to Gillick et al, that carbon yarn may be used to reinforce a rubber composition comprising VPSBRL in combination with resorcinol, formaldehyde and an acrylonitrile-butadiene copolymer, if the yarn is first impregnated with an aliphatic epoxy resin, but there was no reason to believe that the combination of the VPSBRL with the epoxy resin would provide an effective subcoat for the carbon yarn, or for any other yarn.
Rubber articles designed to withstand high stresses in use are typically reinforced with substantially inextensible yarn or cord derived from filamentary polyester, nylon, glass, graphite, ultra high molecular weight (UHMW) polyethylene, polypropylene, polyvinyl alcohol, aramid and the like, the last named being the current material of choice for high-performance rubber hose, belts, and tires, inter alia. In such articles, it is essential that the yarn or cord be firmly adhered, preferably cohesively bonded, to the rubber and remain effectively adhered even after the article has been repeatedly subjected to strains varying by orders of magnitude in use, because any separation and relative movement of the rubber and yarn or cords leads to abrasion therebetween and failure. When cord or yarn is cohesively bonded to rubber, pulling the yarn or cord out of the rubber results in the rubber being torn away so that it covers a major portion of the surface of the yarn or cord. Twice-coated PBO yarn is particularly desirable for reinforcing conveyor belts, drive belts and any of the rubbery portions of a tire, especially the tread and breaker plies.
SUMMARY OF THE INVENTION
PBO yarn from filaments which may be provided with an initial spin-finish, or a corona, or a plasma treatment, is first coated with a subcoat of a mixture of a slightly water-soluble epoxy resin with a vinyl pyridine-styrene-butadiene rubber latex (VPSBRL), then coated in a conventional RFL dip, to yield a twice-coated PBO yarn; this yarn provides adhesive strength in sulfur-vulcanizable rubber which is substantially the same or better than that provided by aramid yarn having the same physical dimensions and construction, in the same application. By “slightly water-soluble” is meant that the solubility of the epoxy resin in water at 23° C. is in the range from about 1% to 15% by weight. Acceptable bonding is indicated by cohesive failure, evidenced on a scale of (0) to (5) by rubber coverage of (5), and a peel force of at least 100 Newtons.
PBO yarn or cord adapted for the reinforcement of rubber articles has a surface coated with a mixture of VPSBRL such as 2-vinyl pyridine-SBR and an aliphatic polyglycidyl ether having a flash point greater than 150° C. with only enough OH-groups to be slightly water-soluble.
Though VPSBRL, used by itself as a subcoat, has substantially the same effect as water, irrespective of the solids content of the subcoat and how much solids is deposited on the yarn, it is found that using a subcoat in which the aliphatic polyglycidyl ether (solids) relative to the VPSBRL (solids) is present in a range from 1:3 to 3:1, the VPSBRL solids preferably being present in a minor proportion by weight; when the subcoated yarn or cord is adequately topcoated with RFL, the adhesion produced is comparable to that provided by a commercially used subcoat on aramid yarn similarly topcoated; preferably the VPSBRL solids are present in the range from about 30 to 95 parts by weight per 100 parts of aliphatic polyglycidyl ether solids deposited on the PBO yarn; the total solids of the deposited subcoat is in the range from about 10 ppm to 1% by weight, bas
Dye Rena
Gray J.
Hendricks Bruce J.
Lobo Alfred D.
The Goodyear Tire & Rubber Company
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