Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-10-29
2001-06-26
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C524S425000, C428S323000, C428S457000, C428S458000, C428S474400
Reexamination Certificate
active
06251515
ABSTRACT:
TABLE OF CONTENTS
1. Background of The Invention
1.1 Technical Field
1.2 Description of Related Art
2. Description of The Invention
3. Description of The Preferred Embodiments
4. Claims
5. Abstract of The Disclosure
1. BACKGROUND OF THE INVENTION
1.1 Technical Field
The invention relates to powder self-adhesive compositions with improved resistance to creep, based on thermoplastic and/or heat-curable resins for coating metal substrates.
1.2 Description of Related Art
Polyamide, polyolefin, polyester and/or polyurethane resins are commonly employed for coating metal substrates, especially because of their good. mechanical properties such as abrasion resistance and impact strength and their chemical inertness towards many products such as hydrocarbons, bases and inorganic acids.
However, it is known that the adhesiveness of these resins to metals is generally inadequate because, for example, of poor wettability. To overcome this defect, the metal support is coated with an undercoat, called adhesion primer, to ensure the bonding and the mechanical anchoring of the polyamide powder. In general, the adhesion primer employed is based on heat-curable resins and is applied in the form of powder, in solution or in suspension in organic or aqueous solvents. Provision must therefore be made for additional facilities for possible removal of the solvents and for curing the primer before the coating of the substrate thus clad with the polyamide powder. In addition, curing and/or drying the primer significantly increases the duration of the coating operations, and hence their cost.
Given the above-mentioned disadvantages, it is increasingly being preferred to eliminate the adhesion primer and to improve the direct adhesion of the coating to the substrate.
Thus, in European Patent Application No. EP 412 888 there is described mixtures of polyamides and of epoxy/sulfonamide resins which can be employed for coating metal substrates without employing any adhesion primer. These mixtures of polyamide and of epoxy/sulfonamide resins in powder form can be applied onto the substrate with an electrostatic gun. It then suffices to introduce the substrate thus clad into an oven to obtain melting of the powder and a uniform coating. The substrate can also be preheated above the melting point of the powder and immersed in a fluidized bed of the powder.
PCT International Patent Application No. PCT/FR95/01740 discloses pulverulent compositions based on polyamide, on ethylene copolymers and on unsaturated carboxylic acids or their vinyl or other esters, and, optionally, on copolymer of ethylene and vinyl alcohol. However, the adhesion of such existing coatings which are applied without a primer is still inferior to that of the coatings with a primer, especially where resistance to creep is concerned.
2. Description of the Invention
The applicants have now found anticreep additives for self-adhesive powder compositions, i.e. those which are intended to coat metal substrates without any adhesion primer.
The anticreep additives of the invention improve the creep resistance of the self-adhesive compositions into which they are incorporated, so that the creep resistance of the coating films which are applied without any primer approaches that of the coating films applied over a primer. The anticreep additives are precipitated calcium carbonates (PCC), which, when uncoated, have specific (BET) surface area of from about 7 m
2
/g to about 12 m
2
/g, measured according to ISO standard 9277, and free-flow apparent specific weight of from about 130 g/l to about 180 g/l and, preferably, equal to approximately 150 g/l, measured according to ISO standard 903.
The compositions of the invention are intimate mixtures based on the resins and the anticreep additives described above.
The resins or polymers of the coating compositions may be thermoplastic resins or heat-curable resins. By way of example of thermoplastic resins, there may be mentioned polyolefins such as PE (polyethylene), PP (polypropylene) and their copolymers or blends; PVC (polyvinyl chloride); and aliphatic, cycloaliphatic and/or aromatic polyamides such as PA-11, PA-12, PA-12,12, PA-6, PA-6,6, PA-6,12 and polyamide-based thermoplastic elastomers, used alone, mixed and/or copolymerized.
By way of example of heat-curable resins, there may be mentioned epoxy resins, epoxy/phenolic resins and epoxy/polyester hybrids.
The acrylic, polyester and polyurethane resins which are also suitable may be either thermoplastic or heat-curable.
Polyesters are intended to mean the resins originating from condensation reactions between mono- and polyfunctional acids with anhydrides, polyols or esters.
Epoxy resins are intended to mean the products originating from the chemistry of the diglycidyl ethers of bisphenol A, which are also called BADGE, and the products originating from the chemistry of the glycidyl ether of novolac resins. The BADGE resins employed have molecular weights of, generally, from about 600 g/mol to about 6,000 g/mol.
The coating compositions according to the invention may contain one or several of the resins listed above and also other resins or polymers improving, for example, adhesion, such as the epoxy/sulfonamide resins described in European Patent Application No. EP 412 888, the resins obtained by polycondensation of aromatic sulfonamide compounds and of aldehydes and/or dicarboxylic acids, described in European Patent Application No. EP 290 342, copolymers of ethylene and unsaturated carboxylic acids or their vinyl or other esters, and, optionally, copolymers of ethylene and vinyl alcohol which are described in PCT/FR95/01740.
Besides the resins and the anticreep additives indicated above, the coating compositions according to the invention may contain various additives and/or fillers such as pigments or dyes, anticratering, reducing and antioxidant agents, reinforcing fillers, and the like as follows:
antioxidants such as copper iodide combined with potassium iodide, phenol derivatives and hindered amines,
fluidizing agents,
reinforcing and nucleating fillers such as dolomite, calcium carbonates (other than the anticreep additives according to the invention) and/or magnesium carbonates, quartz, boron nitride, the kaolin sold under the trade name FRANTEX®, wollastonite, titanium dioxide, ballotini, talc, mica, which are sold under the names DOLOMIE® (calcium magnesium carbonate), PLASTORIT (a mixture of quartz, mica and chlorite), MINEX® (feldspar) and carbon black,
UV stabilizers such as resorcinol derivatives, benzotriazoles and salicylates,
anticratering agents or spreading agents,
pigments such as titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum disulfide, aluminum flakes, iron oxide, zinc oxide and organic pigments like phthalocyanine and anthraquinone derivatives.
Into the compositions of the invention may be incorporated additives chosen especially from those described above and whose respective proportions remain within the limits usually encountered in the field of the powder compositions for the coating of substrates, especially metallic substrates. In general, up to 100% by weight of additives are incorporated, that is, these fillers may represent the same weight as the quantity of resin(s).
These additives can be incorporated into the compositions of the invention by any means. The above compositions may be obtained in a known manner by any technique for mixing the constituents in the molten state, such as extrusion or compounding on a single-screw or twin-screw extruder or on a co-kneader, or by any continuous or noncontinuous technique as, for example, with the aid of an internal mixer.
In general, the particle size of the powders in accordance with the invention may be between about 5 &mgr;m and about 1 mm.
A first process for obtaining powder compositions according to the invention consists of kneading, in the molten state, resin(s), anticreep additive(s) and other possible additive(s) and/or filler(s) in a kneader of suitable type. The kneading temperature may be between about 150° C. and about 300° C. and
Douais Patrick
Juhue Didier
Julien Olivier
Werth Michael
Nakarani D. S.
Paulraj Christopher
Pennie & Edmonds LLP
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