Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-08-31
2002-08-13
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550BL, C428S343000, C428S518000
Reexamination Certificate
active
06432530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to solventless adhesives useful in applications requiring vinyl electrical tape. These adhesives and adhesive tapes provide excellent retention of adhesion properties, and strong anchorage to the plasticized vinyl backing.
2. Description of the Art
Electrical tapes, as well as tapes and adhesive sheets for other applications which require stretching, typically use a polyvinylchloride (vinyl) substrate, upon which the adhesive is coated. This material provides excellent mechanical properties such as elongation. Such vinyl materials are highly plasticized, with some containing up to 60% plasticizers. Typical plasticizers include relatively low-molecular weight oils such as epoxidized soybean oil (ESO), epoxidized linseed oil (ELO), diisononyl phthalate (DNP), diisooctyl phthalate (DOP), and the like.
Vinyl electrical tapes and sheets have traditionally been made by first applying a primer layer such as water based lattices to the vinyl. This primer helps to isolate the vinyl and its plasticizers from the adhesive while providing the required anchorage of these two (in principle) incompatible layers. The primer is dried in an oven. The adhesive layer is then coated from solution and dried in the oven. Such coating and drying operations require expensive ovens, and solvent recovery systems to avoid releasing solvent into the environment. However, this process does produce a high performance product.
It would be extremely advantageous to be able to produce such a vinyl backed tape by means of a solventless process to avoid the environmental and economic issues associated with the solvent process. However, conventional solventless processes have produced tapes having low anchorage of the adhesive to the vinyl backing. Such tapes invariably delaminate at the adhesive-vinyl interface. This is primarily caused by the migration of the plasticizers from the vinyl into the adhesive.
U.S. Pat. No. 5,500,293 discloses adhesives suitable for use in vinyl insulating tapes which comprise a blend of a polyisoprene homopolymer, a styrene-isoprene-styrene copolymer, a tackifying resin, and an end block reinforcing resin.
Japanese Kokai Publication Number 11-263947 discloses migration of plasticizer from vinyl backings to adhesive and resulting delamination. The document discloses a primer that comprises 10 to 150 parts by weight of a thermosetting compound, and a thermosetting initiator. Specifically, a three-dimensional network is disclosed with a thermal polymerization initiator that hardens the primer totally, and obstructs the movement of the plasticizer. The network contains an acrylate-type compound, a urethane acrylate oligomer or monomer, an epoxy acrylate, and a possible a polyester acrylate urethane. Exemplary thermosetting initiators are organic peroxide derivatives, and azo type polymerization initiators, preferable used with an amine polymerization promoter. The use of such a promoter indicates that the compounds are coated from solution.
Japanese Publication 11-263946 discloses an adhesive sheet having a vinyl substrate with a primer coated thereon, and an adhesive laminated to the primer. The primer has an ultraviolet curable compound and an ultraviolet curing initiator. Exemplary compounds include acrylates, urethane acrylates, urethane acrylate oligomers or monomers, epoxy acrylates, and polyester acrylate urethanes.
The present invention provides an primer, and a vinyl tape employing a primer, which does not exhibit adhesive delamination from the backing, but rather shows good adhesive anchorage to the vinyl, and wherein the adhesive is substantially immune to attack by the plasticizers in the backing.
SUMMARY OF THE INVENTION
The invention provides a solventless primer layer for use in an adhesive tape having a plasticized vinyl substrate. Specifically, the primer comprises at least one epoxidized conjugated diene monomer such as a polybutadiene polymers or styrene-butadiene copolymer having a minimum concentration of epoxidized units of about 3 percent.
The invention further provides an adhesive tape formed without the use of solvent comprising a polyvinyl chloride backing bearing on at least one major surface thereof a primer comprising at least one epoxidized conjugated diene polymer such as a butadiene polymer or an epoxidized styrene-butadiene copolymer having a minimum concentration of epoxidized units of at least about 3%.
In one embodiment of the invention, the primer layer comprises at least one compound useful as an ultraviolet (UV) initiator.
Preferred solventless tapes of the invention comprise an adhesive formulation coated onto the primer layer comprising a blend of a polyisoprene homopolymer, a styrene-isoprene-styrene copolymer, and at least one aliphatic tackifying resin.
As used herein, these terms have the following meanings.
1. The terms “vinyl” and “vinyl backing” refer to film forming polymers containing polyvinyl chloride used as substrates for adhesive compositions.
2. The term “primer layer” or “tie-layer” means a layer of a composition of an adhesive tape coated between the backing and an adhesive layer.
As used herein, all parts, percents, and ratios are by weight, unless specifically stated otherwise.
DETAILED DESCRIPTION OF THE INVENTION
Tapes of the invention comprise a vinyl backing, a primer layer, and at least one adhesive layer.
Primer layers of the invention comprise at least one epoxidized polymer formed from conjugated dienes, i.e., butadiene polymers, styrene-butadiene polymers, styrene-isoprene polymers, and butadiene copolymers of acrylonitrile. The double bonds remaining in these polymers and copolymers can be partially of almost completed epoxidized either by preformed peroxy acids or by in-situ methods using hydrogen peroxides and lower aliphatic acids. Performed peroxy acids yield more efficient conversion to oxirane groups with fewer unwanted side reactions. Generally, the unsaturated polymer must be a liquid of relatively low molecular weight or readily soluble in solvents suitable for carrying out epoxidation reactions. Useful epoxidized conjugated dienes have a minimum concentration of epoxidized units of at least about 3%.
Useful commercially available styrene-butadiene copolymers include epoxidized nonhydrogenated styrene-butadiene block copolymer, (e.g., Epofriend™ A1020, A1010, and A1005, Daicel Chemical Industries LTD, Osaka, Japan), and epoxidized hydrogenated styrene-butadiene (SB) block copolymers.
When SB copolymers are used, the styrene block can be formed from polymerization of compounds such as alpha-methylstyrene, p-tert-butylstyrene, p-methylstyrene, 4-n-propylstyrene, 2,4-dimethylstyrene, 3,5-diethylstyrene, 1,1-diphenyl-styrene, 2,4,6-trimethyl styrene, 4-cyclohexylstyrene, 3-methyl-5-n-hexyl styrene, and the like, and mixtures thereof. The double bonds in the backbone are derived from polymerization butadiene, 2,3-butadiene, and the like. The copolymerization weight ratio of the aromatic vinyl compound with respect to the butadiene is generally 5/95 to 70/30.
In one embodiment of the invention, the primer also includes an ultraviolet (UV) radiation photoinitiator. Such an initiator will crosslink the primer into a three dimensional network which may include chains from the substrate due to the presence of epoxidized chains (e.g., ELO, ESO) in the substrate. This initiator, when present, comprises up to about 10% preferably up to about 5% of the epoxidized units present. Useful UV initiators include sulfonium phosphate salts and sulfonium antimonate salts. Preferred initiators include triarylsulfonium hexafluorophosphate, triarylsulfonium hexafluoroantiomonate, and the like. In another embodiment of the invention, one or more thermal initiators may be used.
Preferred tapes of the invention comprise an adhesive formed from a blend of a polyisoprene homopolymer, a styrene-isoprene-styrene copolymer, and at least one aliphatic tackifying resin.
Polyisoprene homopolymers useful in such adhesive compositions include those comprised of cis- 1,4
Garcia-Ramirez Rafael
Mahoney David V.
Ward Steven O.
3M Innovative Properties Company
Dawson Robert
Fonseca Darla P.
Keehan Christopher M.
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