Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1998-10-02
2001-04-10
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C528S272000, C528S302000, C528S303000, C528S306000, C528S308000, C522S060000, C522S093000
Reexamination Certificate
active
06214898
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention lies within the technical field of powder coatings intended for the coating of aluminium substrates.
More specifically, the present invention provides some new modified polyester resin/organic peroxide systems which are especially appropriate for the said type of coatings, which are a significant improvement over the systems currently employed in that they lack properties harmful to health and are economically more advantageous.
PRIOR ART
Powder coatings have been employed since the sixties, having flourished greatly as a result of technical and economic environmental considerations.
Powder coatings are dry, solid, film-forming coating formulations. In fact, powder coatings may be regarded as a paint once the coated substrate emerges from the curing or melting oven.
Powder coatings are typically formulated by combining the following ingredients:
Resin
Curing or hardening agent
Filler
Pigments or colorants
Other additives
The basic or defining ingredients of a particular coating are defined by the resin/hardening agent system.
The other ingredients are incorporated in accordance with the colour and appearance and the ultimate application for which the coating is intended.
Among the resins most extensively distributed worldwide, epoxy resins, polyester resins and acrylic resins may be mentioned.
Among typical curing agents, solid aliphatic amines (for example Dicyandiamide), solid amine derivatives, solid phenolic resins, solid anhydride compounds, solid blocked isocyanate adducts, solid polyepoxides (for example TGIC) and solid dicarboxylic acids may be mentioned.
Turning our attention now to the polyester resin, three types of system are mainly used:
Polyester/TGIC (triglycidyl isocyanurate)
Polyester/epoxy hybrids
Polyester/isocyanate (or urethane systems).
Of these systems, the polyester/TGIC system has been extensively developed in Europe, since it gives rise to coatings with very good properties for outdoor use, especially for the coating of metal substrates such as steel and aluminium, such as, for example, aluminium sections for windows and doors exposed to the weather.
The problem arising with these systems is the high toxicity of TGIC, a product of mutagenic character apart from being irritant to the skin and the mucosae, toxic on inhalation, and the like. These collective features compel the introduction of robust safety measures from the stand-point of the health of the workforce, the personnel having to be appropriately protected and to submit to the appropriate medical checks, thereby entailing substantial costs in addition to the already high cost of TGIC.
Accordingly, current research efforts are being directed towards replacing this polyester resin/TGIC system by other, less harmful and expensive systems.
These are precisely the reasons which have provided the incentive for the development and attainment of the present invention, in which new modified polyester resin/organic peroxide systems are proposed for powder coatings intended for the coating of aluminium supports which are going to be exposed to the weather.
There are numerous patents in which the use is described of organic peroxides as curing initiator for different types of resins, among which there may be mentioned JP 55027324 and JP 04227713 relating to polyester resins; JP 57209965A relating to polyolefin resins; US 4410680A and EP 503866A relating to epoxy resins; JP 52103427A relating to organopolysiloxane resins; and DE 2461416A relating to polyurethane resins.
In these patents, typical peroxides are employed, such as dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexene, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, benzoyl peroxide, p-chlorobenzoyl peroxide, t-butylperbenzoate, cyclohexanone peroxide, cumene hydroperoxide, t-butyl hydroperoxide, and the like.
With these systems, coatings of different qualities are obtained on very diverse types of substrates.
With reference more specifically to the case of polyester resins cured with organic peroxides, the following may be mentioned: JP 49128939, JP 49040348, JP 55025462, DE2332749, JP 54150440, JP 55027307, JP 56100870, JP 55003416, JP 54158440, JP 52150443, JP 49129725 and JP 49093425. In the majority of these patents, the addition of the peroxide takes place during the preparation of the copolymer or the production of the resin. Moreover, in the majority of cases, the coatings obtained from these systems are intended for the application to steel substrates.
According to JP 52250443, 54150440, 54158440, 55027307 and 56100870 a polyester powder contains a radical-generating agent together with a metal or metallic compound or together with a specific radical trapping compound or absorbed on finely divided inorganic powder.
JP-04/227713 describes polyesters prepared from saturated and unsaturated carboxylic acids, saturated and unsaturated alcohols and organic peroxides as curing agent, for example 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. The polyesters are useful for powder coating material. They cure rapidly at low temperature.
According to JP 55025462 a powder composition comprises an unsaturated polyester from aromatic dicarboxylic acid, a dihydroxypropane and a resin of unsaturated bonds and also a radical generator, e. g. cyclohexanoneperoxide. This composition may also comprise low molecular weight polyesters, pigments, a curing agent. The baking process proceeds at 140 to 240° C. for 3 to 14 minutes.
In JP 56060911 a powder paint composition contains an unsaturated polyester from unsaturated di-carboxyded acid and polyvalent alcohol, an organic peroxide as curing catalyst and/or a curing auxiliary catalyst. The composition is baked at 160 to 230° C. for 5 to 30 minutes.
SUMMARY OF THE INVENTION
Given the state of the art defined in the above paragraphs, new modified polyester resin/organic peroxide systems are proposed which overcome the drawbacks of toxicity and price presented by TGIC, which may be baked at lower temperature and shorter time and which are especially suitable for aluminium substrates.
DETAILED DESCRIPTION OF THE INVENTION
The present invention, relates to new modified polyester resin/organic peroxide systems for powder coatings, intended especially for the coating of aluminium substrates, and in particular for both decorative and protective coatings which are going to be subjected to the weather.
The present invention relates to coatings based on resin of unsaturated linear or branched polyesters of appropriate molecular weight, which can be crosslinked by the action of free radicals obtained by means of organic peroxides which permit the formulation of powder coatings with appropriate melt viscosity and a glass transition temperature above 40° C., with consequent chemical and physical stability on storage.
The polymers or resins for the present invention are hydroxylated or carboxylated polyesters which possess unsaturation in their chain, obtained by reacting polycarboxylic acids or anhydrides with polyhydroxylated alcohols. The unsaturation in the polyester may be obtained according to:
a) Use of olefinically unsaturated di- or polycarboxylic acids or anhydrides.
b) Use of acrylic or methacrylic acid and/or its esters as chain terminators of hydroxylated polyesters.
c) Use of allyl compounds and their derivatives as chain terminators of carboxylated polyesters.
d) Olefinically unsaturated polyesters modified with dicyclopentadiene.
The functional groups of the polymer permit the cross-linking of chains, by addition to its double bonds and via a free radical mechanism, the requisite free radicals having been obtained by decomposition of organic peroxides, either thermally or chemically. The terminal hydroxyl or carboxyl functions, which regulate the molecular weight of the polymer, likewise permit a dual crosslinking, with blocked isocyanates, amine resins, hydroxyalkylamides and aromatic or aliphatic epoxy resins.
The number average molecular weight Mn of the unsaturated binding agent or polymer o
Acquah Samuel A.
Herberts Gesellschaft mit beschrankter Haftung
Pillsbury & Winthrop LLP
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