Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Patent
1996-05-31
1998-11-03
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
528310, 528322, 528332, 528340, 525600, 525606, 524420, 524423, 524434, C08L 7700, C08G 7300
Patent
active
058309756
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a polyamide-based powder composition for coating metal substrates.
Polyamides are commonly employed for coating metal substrates, especially because of their good mechanical properties such as abrasion resistance, impact strength and their chemical inertness towards many products such as hydrocarbons, bases and inorganic acids.
It is known, however, that the adhesiveness of polyamides to metals is inadequate as a result of poor wettability of the polyamides in the molten state. To overcome this deficiency the metal support has been coated with an undercoat, called adhesion primer, intended to ensure the attachment and the mechanical bonding of the polyamide powder. In general the adhesion primer which is employed is based on heat-curable resins and is applied in powder form or in solution or in suspension in organic or aqueous solvents. Additional plant must therefore be provided for the contingent removal of the solvents and for baking the primer before the substrate thus clad is coated with the polyamide powder. In addition, the baking and/or drying of the primer result in a significant increase in the duration of the coating operations and hence their cost.
BACKGROUND ART
Mixtures or polyamides and of epoxy/sulphonamide resins which can be employed for coating metal substrates without employing an adhesion primer undercoat have been described in European Patent EP 0,412,288. These mixtures of polyamide and of epoxy/sulphonamide resins in powder form are applied with an electrostatic gun to the substrate. 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 dip it in a fluidized bed of the powder.
DISCLOSURE OF THE INVENTION
Another polyamide-based powder composition has now been found which may be used for coating metal substrates without any adhesion primer, which exhibits very good resistance to saline mist. According to the present invention there is provided a mixture which takes the form of powder comprising at least one polyamide and at least one polymer (A) containing hydroxyl functional groups and compatible with the polyamide.
Polyamide within the meaning of the invention 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 joined together by amide groups. Those advantageously employed are polyamide 11, which can be obtained by condensation of 11-aminododecanoic 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 joined 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 polyamide with carboxylic acid ends, and a polyether with hydroxyl ends is then added to it. The polyether is preferably polytetramethylene glycol, polypropylene glycol or polyethylene glycol. Other polymers which have polyamide blocks in their chain can be prepared according to U.S. Pat. No. 4,207,410. A lactam, a diacid and a polyether with hydroxyl ends are mixed in the presence of water and the temperature is maintained. A polymer is obtained which has polyamide blocks and polyether blocks mixed with diacid, all these components being joined by ester functional groups. It would not constitute a departure from the scope of the invention to employ a mixture of these polyamides.
The polymers (A) which have hydroxyl functional groups may be copolymers in which one of the monomers has at least one hydroxyl functional group, for example copolymers of ethylene and of vinyl alcohol (EVOH) or polymers
REFERENCES:
patent: 5409999 (1995-04-01), Merval et al.
patent: 5489667 (1996-02-01), Knipf et al.
Perraud Eric
Sage Jean Marc
Tedoldi Arnaud
Elf Atochem S.A.
Hampton-Hightower P.
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