Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-01-18
2002-06-11
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S156000, C524S493000, C524S519000, C524S527000, C524S834000
Reexamination Certificate
active
06403673
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to primer compositions that may be mixed with water and water-based adhesives to provide a range of primers and priming adhesive compositions for bond improvement between polymers of similar or dissimilar types. Compositions according to the present invention optionally include olefinically unsaturated monomers or oligomers for added bond strength after exposure to ultraviolet radiation. More particularly the present invention relates primarily to water-based dispersions of surface modifying components for enhancing bond formation between substrates, such as polyolefins, which are known for low interfacial bond strength. Priming adhesives of the present invention improve adhesive bonding between materials without the application of surface pre-treatments.
2. Background of the Invention
Adhesives provide a relatively rapid and convenient way for attaching one type of material to another. Over the years, development of adhesive systems has addressed ways to modify the strength of the adhesive bond between selected materials. Depending on the application, the adhesive of choice may include a pressure sensitive adhesive, a structural adhesive, a hot-melt adhesive or a repositionable adhesive. Regardless of the wide range of available adhesives, the surfaces of some commonly occurring polymer substrates still lack suitable adhesive affinity to form strong bonds with other materials, whether similar or dissimilar. Lack of bonding to surfaces with low adhesive affinity also affects the bonding and retention of surface coatings or printing inks that may be used for surface marking or decoration.
One solution to poor bond formation and poor retention of coatings and inks lies in the use of special treatments to change the condition of a surface by increasing its surface energy. Surface treatments for increased surface energy include oxidizing pretreatments or the use of adhesion promoters. Oxidizing pre-treatments include the use of flame, ultraviolet radiation, corona discharge, and chemical oxidizing agents and the like. Adhesion promoters include chemical compositions containing e.g. solutions of styrene-ethylene/butylene-styrene block copolymers or acrylate polymers in an organic solvent. These compositions improve the bonding of pressure sensitive adhesives and structural adhesives to polymer substrates.
Unfortunately, these methods for raising surface energy are not without problem. For example, chemical oxidizing agents are typically hazardous materials requiring special handling. Surface treatment using flame, corona discharge, etc. usually requires special equipment of a design more suited to sheet or film or web processing than to surface treatment of shaped articles.
Both oxidizing and adhesion promoter pre-treatments provide improvement in bond formation associated with low surface energy polymers such as polyethylene (PE), polypropylene (PP), ethylene-propylene-diene terpolymer (EPDM) and ethylene-alpha olefin copolymers. Substrates of this type may also include ethylene-vinyl acetate copolymers as representative of polymers that are substantially free from ethylenic unsaturation.
Polymeric substrates that have some degree of ethylenic unsaturation also benefit from the use of surface pre-treatments. It is known, for example, that rubbers comprising styrene/butadiene copolymers (SBR) require treatment with chlorinating agents including solutions of halogen donors such as trichloroisocyanuric acid, and N,N-dichlorobenzenesulfonamide, for improved bonding with adhesive bonding agents. Such halogen donors may be incorporated into primers or adhesives separately. The effectiveness of treatment by chlorination appears somewhat limited to substrates having a high level of ethylenic unsaturation such as polybutadiene, polyisoprene, natural rubber, styrene-butadiene copolymers, polychloroprene and the like. Also the addition of halogen donors reduces the stability of some adhesives, including polyurethane adhesives.
Further improvement in bonding to numerous types of substrates may be possible by abrading the surface of a substrate even before applying any pre-treatment. Mechanical means for surface roughening then represents a preliminary step to surface pre-treatments. Regardless of their effectiveness, pre-treatments represent an additional step in the process of manufacturing a product. Additional process steps incur additional time and expense and thereby add undesirable cost to a final product.
The development of primer pre-treatments, primarily in solvent, has yielded some improvement in adhesive bonding to low energy surfaces. U.S. Pat. No. 6,008,286, for example, provides compositions comprising mixtures of hydrocarbon polymers, halogen-substituted hydrocarbon polymers and substituted aliphatic isocyanates which, coated from solvent, improve the bond between low energy substrates and adhesives, coatings, printing inks and the like. Unfortunately the benefits of solvent-based primers are diminished by the need to limit volatile organic compounds (VOC) to a level that avoids health hazards and prevents environmental contamination.
Ultraviolet irradiation of solvent-based primers, including chlorinated polymers, may lead to modification of polyolefin surfaces. United States Patent No. U.S. Pat. No. 4,303,697 describes the use of a primer containing chlorinated polypropylene applied to the surface of a thermoplastic polyolefin. Subsequent exposure to ultraviolet radiation of the surface improves the adhesion of paint coatings. U.S. Pat. No. 4,859,540 compares the benefits of repeated exposure to low intensity ultraviolet radiation versus a single exposure to high intensity ultraviolet as a means for improving adhesion of solvent-based primers to both adhesives and substrates. Multiple exposures to low intensity ultraviolet radiation is time consuming and probably adds to processing costs.
The description of solvent-based primer solutions and water-based priming dispersions of chlorinated polymers provided by WO 98/05704 suggests that coating of such primers on a polyolefin surface, followed by exposure to ultraviolet radiation, improves adhesion to the polyolefin surface. Stabilizers for the water-based chlorinated polymer dispersions of WO 98/05704 include surfactants, emulsifiers, thickening agents and sodium hydroxide. These materials are moisture sensitive and require careful control in order to attain a strong and hydrolytically stable bond of the primer to either a low-energy substrate or an adhesive.
U.S. Pat. No. 5,446,083 describes a coating formulation comprising an aqueous dispersion including an olefinic unsaturated monomer and a solution of a chlorinated polyolefin in organic solvent. Stabilization of the dispersed phase, of the aqueous dispersion, requires the use of a surfactant. Unsaturated monomer in the dispersed phase becomes polymerized upon exposure to heat, ultraviolet radiation or electron beam radiation. This reference indicates lack of compatibility between chlorinated polyolefin compositions and film forming polymers including polyurethanes and acrylic polymers. To add further confusion, U.S. Pat. No. 5,446,083 teaches successful use of coatings containing chlorinated polyolefins in the presence of polymerizable acrylate monomers, suspension polymerized polyacrylates or mixtures thereof.
Solvent based or aqueous based thermosettable primers may be used, for bond improvement, without a flame or corona preliminary treatment. U.S. Pat. No. 6,001,469 describes primers and topcoats of this type used with e.g. thermoplastic polyolefins (TPO) and reaction injection molded polyurethane (RIM). These materials may be suitably cured on the substrate at temperatures in the region of 130° C. for 30 minutes. Similarly WIPO publication WO 94/28077 describes aqueous-based compositions requiring heat treatment at 130° C. for 40 minutes. It is known (see e.g. R. Ryntz in “Waterborne, High Solids Powder Coatings Symposium,” Univ. of Southern Mississippi 1995), that high temperature treatment may also
3M Innovative Properties Company
Ball Alan
Chernivec Gerald F.
Griswold Gary L.
Yoon Tae H.
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