Stock material or miscellaneous articles – Composite – Of polyamidoester
Patent
1997-10-06
2000-02-22
Acquah, Samuel A.
Stock material or miscellaneous articles
Composite
Of polyamidoester
525 56, 525 57, 525 58, 525 88, 525165, 525167, 525168, 525178, 525240, 525426, 525540, B32B 2700, C08F 1606
Patent
active
060278145
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a polyamide-based powder composition for coating metal substrates.
BACKGROUND OF THE INVENTION
Polyamides are commonly employed for coating metal substrates, especially because of their good mechanical properties such as abrasion resistance, impact strength and chemical inertness towards many products such as hydrocarbons, bases and inorganic acids.
The adhesiveness of polyamides to metals is known, however, to be insufficient, as a result of poor wetting ability of polyamides in a molten state. To overcome this shortcoming the metal substrate has been coated with an undercoat, called an adhesion primer, intended to ensure the mechanical bonding and anchoring of the polyamide powder. The adhesion primer which is employed is generally based on heat-curable resins and supplied in powder form or in solution or in suspension in organic or aqueous solvents. Additional plant must therefore be provided for the possible removal of the solvents and for curing the primer before the substrate which is thus clad is coated with the polyamide powder.
In addition, the curing and/or drying of the primer significantly lengthen the duration of the coating operations and hence their cost.
Mixtures of polyamides and of epoxy/sulphonamide resins which can be employed for coating metal substrates without employing an adhesion primer undercoat have been described in Patent EP 0 412 888. These mixtures of polyamide and of epoxy/sulphonamide resins in powder form can be applied to the substrate with an electrostatic gun. It then suffices to pass the substrate thus coated through an oven to obtain melting of the powder and a uniform coating. It is also possible to preheat the substrate above the melting point of the powder and to immerse it in a fluidized bed of the powder.
DESCRIPTION OF THE INVENTION
There has now been found another polyamide-based powder composition for coating metal substrates without an adhesion primer, which exhibits very good adhesiveness which is durable in time. The compositions of the invention also exhibit other advantages:
when the powder is applied with the gun, the coating does not fall off during the introduction and during the period in the oven;
a metal plate coated with a film resulting from the melting of the powder deposited on the substrate is slashed and then subjected to a saline mist and exhibits a limited corrosion growth;
good resistance to hot water, which makes it possible, for example, to make household water-heater coatings.
The present invention is a composition including (i) at least one polyamide and at least one copolymer (A) of ethylene with at least one comonomer chosen from unsaturated carboxylic acids, unsaturated carboxylic acid esters or vinyl esters of saturated carboxylic acids and (ii) being in powder form.
The compositions of the invention are intimate mixtures of polyamide and of copolymer (A), that is to say that each grain of the powder includes polyamide and copolymer (A).
Within the meaning of the invention the polyamide is intended to mean products of condensation of lactams, of amino acids or of diacids with diamines and, as a general rule, any polymer made up of units linked together by amide groups.
The polyamide advantageously has a melting temperature between 130 and 270.degree. C., like, for example, PA-6, PA-66, PA-6,66, PA-11, PA-12, PA-11,12 and PA-6,12.
Those advantageously employed are polyamide 11, which can be obtained by condensation of 11-aminoundecanoic acid or of lactam 11, and polyamide 12, which can be obtained by condensation of 12-aminododecanoic acid or of lactam 12. It is also possible to employ polyamides 12--12.
Polyamide is also intended to mean polymers which have polyamide blocks in their chain. These are, for example, polyetheresteramides made up of polyamide blocks and of polyether blocks linked by ester functional groups. U.S. Pat. No. 4,230,838 describes a possible preparation of these products. The polymerization of a lactam is performed in the presence of a diacid to obtain a po
REFERENCES:
patent: 4207410 (1980-06-01), Burzin et al.
patent: 4230838 (1980-10-01), Foy et al.
patent: 4248977 (1981-02-01), Wertz
patent: 5229458 (1993-07-01), Schimmel et al.
patent: 5409999 (1995-04-01), Merval et al.
PCT/FR95/001740 (WO 96/20979), European Search Report, Apr. 18, 1996.
Julien Olivier
Sage Jean-Marc
Tedoldi Arnaud
Werth Michael
Acquah Samuel A.
Elf Atochem S.A.
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