Coating processes – Particles – flakes – or granules coated or encapsulated – Inorganic base
Reexamination Certificate
2002-10-03
2004-01-20
Wilson, D. R. (Department: 1713)
Coating processes
Particles, flakes, or granules coated or encapsulated
Inorganic base
C428S461000, C525S196000, C525S221000, C525S363000, C525S367000, C525S368000, C525S369000, C525S371000, C525S919000, C525S934000
Reexamination Certificate
active
06680082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to mixed-metal neutralized alpha-olefin/carboxylic acid copolymer powder coating materials for coating and protecting metal objects.
2. Description of Related Art
Thermoset powder coatings for materials or objects of metal are known. The success of powder coating in coatings of metals is mainly due to their functional and/or decorative performance as well as the reduction or elimination of noxious by-products in the production of coated substrates. Powder coatings are utilized for either decorative purposes or protective purposes. For the former, color, gloss, and appearance may be the primary attributes. Most decorative coatings are thin coatings mainly using thermoset coatings. For protective purposes, the coatings should have longevity, corrosion protection, impact resistance properties and serve as insulation. In this latter role, the coatings should be thick and can be applied in powder form.
The bulk of powder coatings are thermoset coatings. These coatings typically chemically react during baking to form a polymer network that will generally not remelt. Materials utilized in thermoset powder coatings include epoxies, polyesters and acrylics. Crosslinking agents typically employed include amines, anhydrides and isocyanates.
Thermoplastic resins, on the other hand, are generally of high molecular weight and require relatively high temperatures to achieve melt and flow during coating. However, the molecular weight and melt viscosity remain constant during the coating procedure so that the polymer can be easily remelted for easy repair or touch-up. Typical thermoplastic coating polymers include polyamides, polyolefins, plasticized PVC, polyester and poly (vinylidene fluoride), and ionomers.
U.S. Pat. No. 4,056,653 disclosed a process to make spherical ionomer particles having an average diameter of 10 to 100 microns. U.S. Pat. No. 5,344,883 discloses a polymer powder coating composition which comprises a low molecular weight ionomer to be added to polymer resin powder coating to reduce gloss. JP017145271-A discloses a composition for powder coating having an average particle size of up to 300 microns, comprising an ethylene/unsaturated carboxylic acid copolymer containing 5-15 wt. % unsaturated carboxylic acid or its salt with 0.3-5.0 wt. % of a phthalate type plasticizer compound. EP O 798 053 A1 discloses a process for forming a coating of a thermoplastic polymer powder on a hollow object formed of a low electrically conductive material. While some of the above patents disclose powder coating compositions with an ionomer and additional excipients, none disclose a mixed metal ionomeric powder coating composition for coating metal substrates.
U.S. Pat. No. 5,320,905 teaches certain ethylene carboxylic acid resins prepared from a copolymer having about 85 to about 50 weight percent olefin such as ethylene and about 15 to about 50 weight percent of at least one alpha, beta-ethylenically unsaturated carboxylic acid and at least one cationic metal compound or complex to form a salt which is ultimately made into fine particles or powders.
U.S. Pat. No. 4,440,908 teaches the preparation of certain powders of thermoplastic resins made from polyethylene or ethylene vinyl acetate copolymer. U.S. Pat. No. 4,481,239 teaches a process for coating metallic substrates with heat hardenable synthetic resins. Neutralized ethylene acid copolymers are additionally disclosed in, for example, U.S. Pat. No. 3,264,272 wherein it describes that these copolymers may be neutralized with one or more metal ions.
High molecular weight ionomer blends having different metals including sodium/zinc combinations are described in U.S. Pat. No. 4,911,451 or WO 94/01469 or EP 0 443 706 A2. However, the properties required for golf ball applications do not necessarily relate to those properties required for the functional or aesthetic application of material to metal surfaces.
Historically, many thermoplastic resins have been evaluated in powder coating applications, but few have the proper combination of physical and mechanical properties, stability, and melt viscosity. For attaining functional performance and longevity, an ideal thermoplastic polymer should have low density, high mechanical strength and good surface hardness (independent of humidity), high impact strength, scratch resistance and abrasion resistance, low water adsorption, good adhesion to metals, good resistance to chemicals in general, and weatherability.
There has been some difficulty, before the present invention, achieving both functional performance and application performance in a metal powder coating. While neutralization of ethylene acid copolymers may provide some benefits in terms of physical properties, it can actually negatively impact their use as powder coatings. For example, high hardness and stiffness and excellent scratch and abrasion resistance are “desirable” properties associated with salts of ethylene acid copolymers (neutralized copolymers) but these compounds also have reduced adhesion, high viscosity, vulnerability to weathering and water adsorption and are more prone to react with additives such as pigments.
There remains a need, therefore, for a thermoplastic polymer powder coating composition, which functions well as a metal coating and/or metal primer coating and is easy to produce and apply to the metal as corrosion protection, while also having an appropriate balance of properties. A powder coating with all the physical advantages associated with a neutralized ethylene acid copolymer is needed that also provides suitable adhesion to metals, good weatherability etc.
It has now been found that it is possible to obtain adhesive, protective and appearance qualities in a powder composition based on a thermoplastic polymer containing an ethylene acid mixed metal salt resin.
BRIEF SUMMARY OF THE INVENTION
The present invention comprises a process for preparing a powder coating material for protecting metal objects, comprising a neutralized ethylene acid copolymer resin having high adhesion to metal, high stiffness, hardness and toughness, low melt viscosity and high processability.
The present inventors have found, heretofore, it has been difficult to obtain a neutralized ethylene acid copolymer resin with a balanced set of properties which takes advantage of known characteristics of neutralized ethylene acid copolymers such as high toughness, abrasion resistance, chemical resistance, high hardness and high stiffness but which also have adequate adhesion to metal, high melt flow, weathering capability and low water adsorption properties and non-interaction with additives. High acid content and high neutralization ethylene acid copolymers are known to have excellent hardness and stiffness properties but they are also known to have poor adhesion qualities, low melt flow, water absorption properties and poor weathering properties. The inventors have discovered a combination of neutralized ethylene acid copolymers that have all the advantages generally associated with high molecular weight forms of these copolymers while also having properties which are suitable for metal coating applications.
The present invention, in particular, comprises a new physical form, a powder of a neutralized ethylene acid copolymer of mixed metal cations which provides a combination of properties for metal coating applications including strong adhesion to metal, high stiffness, hardness and toughness, low melt viscosity and ease of manufacture. The preferred metals are selected from sodium, zinc and lithium and the preferred mixed metals for neutralization are selected from Zn/Na, Zn/Mg, Zn/Ca and Zn/Li.
There is further provided according to the present invention, a coated metal substrate comprising a metal layer where the metal may be iron, steel or aluminum or other known metals or alloys, a primer coating of the metal-coating composition described above, and an optional outer coating, over the primer, of polyethylene or polypropylene or an ethylene acrylic ac
Chou Richard Tien-Hua
Kelly Mark Bernard
Dobson Kevin S.
E. I. du Pont de Nemours and Company
Wilson D. R.
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