Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-02-23
2002-06-04
Truong, Duc (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S351000, C428S3550RA, C427S409000, C427S407100
Reexamination Certificate
active
06399191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to moisture resistant coated metal substrates. The metals are typically steel or other structural metals which are formed into piping or other metal fabricated parts which are subsequently exposed to the elements including, for example, moisture.
2. Description of Related Art
Coatings or polymeric layers on metal surfaces are generally known. The coatings may typically serve some kind of protective function to prevent the metal surface from degrading and/or to retain or keep liquids in/out of the fabricated metal element. In order to function properly, the coatings must adhere to the metal or metal surface.
Adhesive compositions are also known which form layers or coatings for multilayer elements to adhere, for example, non-polar material such as polyolefins to polar material or substrates such as metals. In particular, such adhesive compositions are utilized in multilayer elements for packaging food, liquids and the like. These adhesive compositions may contain various polyolefins selected from, for example, polyethylenes or polypropylenes, which are further reacted with a grafting reagent selected from a polar substance such as maleic anhydride. The post-grafted polymeric material and/or blends with ungrafted material is then utilized as an adhesive composition or film and is coextruded between structural and barrier layers to form a suitable package or bottle.
These adhesive compositions can further contain additional excipients or ingredients to provide additional performance characteristics to the polymeric film. For example, PCT publication WO 95/20487 discloses the addition of a tackifier to the particularly recited adhesive composition along with various other active ingredients which include a modified polypropylene, a crystalline ethylene copolymer and an elastomeric component. EPO 507,557 A1 discloses blends of polyethylenes; grafted polyethylenes and tackifiers for adhesion to EVOH and paper.
Other compositions are known which are utilized to bond to the surfaces of metal substrates. See, for example, U.S. Pat. No. 4,500,577 or Japanese patent 85023026. EPO 479 457 A1 discloses polyolefin compositions suitable for bonding to metals or polyamides or EVOH and to polyethylene to form layered pipes or multilayered structures. Blends of grafted HDPE and other polyolefins of different densities are described as particularly suitable for bonding to metal. There is no teaching of a tackifier in said composition. JP-89-74015 discloses pipe coating compositions containing certain modified polymers, non-crosslinked rubbers, elastomers and a tackifier selected from a terpene-phenol copolymeric resin; and asphalt.
U.S. Pat. No. 4,337,297 discloses a coextrudable thermoplastic composition comprising blends of a copolymer of ethylene with a lower alkyl acrylate or methacrylate or vinyl acetate; a chlorinated ethylene polymer and an optional tackifying resin.
EPO 091 807 B1 discloses a heat sealing tape composition for bonding heat-sealable belt shaped covering sheets which are wrapped around the joint portions of steel pipes to protect these joints. The heat sealing tape composition comprises a tape-substrate and a heat bonding layer consisting essentially of a) an ethylene propylene copolymer as described therein, b) a maleic modified polyethylene; c) a polyethylene; d) a tackifier and e) an inorganic filler. This tape is not bonded to metal but is, instead, bonded to the polymeric covering sheet.
U.S. Pat. No. 3,868,433 discloses hot melt adhesive compositions and further states that a typical class of hot melt adhesive compositions utilizes polyolefin polymers as the base or carrier material which is usually blended with other polymers and copolymers, resin tackifiers and with modifiers and additives. A serious short coming of these adhesives is their lack of strong adhesion to metals. This patent teaches one way to improve adhesion to metals is to add grafted or modified polyolefin components. However, there is only a single species actually disclosed—a 60/40 blend of a modified polypropylene grafted with 6 wt. % acrylic acid and an ethylene/propylene/diene monomer elastomer.
U.S. Pat. No. 3,492,372 discloses a hot melt adhesive composition comprising random ethylene/propylene copolymers and certain resin tackifiers and carrier polymers such as polyethylene or polypropylene wherein the composition does not include unsaturated elastomers susceptible to oxidation and degradation.
U.S. Pat. No. 4,670,349 discloses adhesive resin compositions comprising a) ethylene vinyl acetate copolymers or ethylene/alpha olefin random copolymers; b) modified polyethylene and c) a hydrogenated aromatic petroleum resin in which at least 70% of the aromatic ring is hydrogenated. There is no teaching of a metal substrate or said substrate with an adhesive layer.
U.S. Pat. No. 5,405,894 discloses a corrosion protection composition for the undercoating of motor vehicles which comprises a thermoplastic elastomeric block copolymer, a sulphonate of an alkaline earth metal, a tackifier resin and an optional plasticizer.
There is a continuous need for coatings and/or layers on metal surfaces which provide the necessary protective/barrier functions and which are durable and long lasting in terms of adherence properties. The present inventors have solved the problem of moisture penetration through protective adhesive coatings on metal surfaces by discovering a particularly effective adhesive coating composition which is durable, protective and with sufficient moisture barrier properties. This coating composition is applied to a metal substrate to form the coated metal substrate of the invention. The coating composition provides excellent corrosion resistance, environmental stress crack resistance and significantly improved resistance to disbondment in an aqueous or moist environment. The coating compositions having a particular class of tackifiers, the rosin esters and hydrogenated versions thereof, have significantly improved resistance to cathodic disbandment. Furthermore, the coating composition does not require elastomers, rubber, inorganic fillers or asphalt. In addition, the present composition does not require the addition of chlorinated polymers or copolymers of ethylene with vinyl acetate or lower alkyl acrylates or methacrylates.
BRIEF SUMMARY OF THE INVENTION
The present invention broadly relates to a coated metal substrate comprising:
(a) an adhesive coating composition consisting essentially of (i) a modified polyolefin optionally containing at least one additional modified or unmodified polyolefin and (ii) at least one tackifier; and
(b) a metal substrate; wherein, for element (a), the tackifier is present in a weight percentage relative to the combined weight of (i) plus (ii) of about 15 to 25% and the modified polyolefin also contains at least one additional unmodified polyolefin.
A method of improving the environmental stress crack resistance of a coating composition, comprising
(a) adding a tackifier to a metal coating composition comprising a modified polyolefin optionally containing at least one additional modified or unmodified polyolefin or to a non-metal coating composition comprising a modified polyolefin optionally containing at least one additional modified or unmodified polyolefin to form a composition consisting essentially of the modified polyolefin optionally containing at least one additional modified or unmodified polyolefin and the tackifier wherein said tackifier improves the environmental stress crack resistance of the coating composition according to ESTM D-1693.
DETAILED DESCRIPTION
As summarized above, the present invention relates to coated metal substrates having improved moisture disbandment properties as well as environmental stress crack resistance (“ESCR”). The addition of a tackifier to a modified polyolefin optionally blended with at least one unmodified polyolefin surprisingly led to an increase in ESCR when the opposite effect would be expected—a low molecular weight compound
Du Pont Canada Inc.
Truong Duc
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