Coating processes – With post-treatment of coating or coating material – Solid treating member or material contacts coating
Reexamination Certificate
2002-12-16
2004-06-15
Tucker, Philip (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Solid treating member or material contacts coating
C428S419000, C523S440000, C523S443000, C523S466000, C525S523000, C525S524000
Reexamination Certificate
active
06749896
ABSTRACT:
The present invention relates to a novel, self-crosslinking powder coating material based on epoxy resins and to its use to coat shaped parts.
Powder coating materials based on epoxy resin are known from European Patent Applications EP 0 509 392 A 1, EP 0 509 393 A 1, EP 0 322 827 A 1 or EP 0 517 536 A 1, from U.S. Pat. Nos. 5,055,524 or 4,849,283, or from the company publications Coatings Partner, The magazine of BASF, Powder Coatings Special, {fraction (1/2000)}, or BASF Coatings AG “Pulverlacke, Pulverlacke für industrielle Anwendungen” [Powder coating materials, powder coatings for industrial applications], January 2000. The systems in question are externally crosslinking systems, i.e., the epoxy resins are crosslinked using hardeners, such as phenolic or amine hardeners or bicyclic guanidines.
Externally crosslinking describes coating materials in which one type of complementary reactive functional groups is present in the binder and another kind is present in a hardener or crosslinking agent. The complementary reactive functional groups are able to react with one another and so construct a three-dimensional network. In contrast, the term “self-crosslinking” denotes the capacity of a binder to enter into crosslinking reactions with itself. A prerequisite for this is that both kinds of complementary reactive groups required for crosslinking are already present in the binders, or that there is one kind of reactive functional groups present that is able to react “with itself”. For further details, reference is made to Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “Curing”, pages 274 to 276, especially page 275, bottom.
Shaped parts, especially engine blocks for motor vehicles of all kinds, are increasingly being coated, for reasons both of aesthetics and corrosion protection. Since powder coating materials are solvent-free, easy to apply, and easy to recover as overspray, and the corresponding powder coatings have good mechanical properties and firm adhesion to the substrate, and also offer very good corrosion protection, they are increasingly being used for this utility.
The engine block blanks are usually coated while still in the iron works and are subsequently machined by milling and/or drilling. The heat produced in the course of these operations softens the customary and known powder coatings, making it impossible to produce defined cuts and bores. Moreover, owing to the thermal/mechanical load, the powder coatings form greasy, gluelike polymer melts which cause sticking of the tools and are very difficult to remove. Increasing the density of crosslinking is generally no solution, since the associated embrittlement of the powder coatings can cause them to flake in the course of subsequent machining.
It is an object of the present invention to find a new self-crosslinking powder coating material from which the disadvantages of the prior art are absent and which instead can be prepared in a simple manner from readily available starting compounds and gives powder coatings which, while retaining all of the other advantageous performance properties, are cuttable, millable and drillable and, as a consequence, are highly suitable for the coating of shaped parts, especially engine blocks, which require subsequent machining.
Accordingly, we have found the novel self-crosslinking powder coating material which comprises
(A) up to 50% by weight, based on the powder coating material, of a mixture of
(A1) at least one epoxy resin with an epoxy equivalent weight (EEW) <800 g,
(A2) at least one epoxy resin with an epoxy equivalent weight (EEW) of from 800 to 1500 g, and
(A3) at least one epoxy resin with an epoxy equivalent weight (EEW) >1500 g,
and
(B) at least 50% by weight, based on the powder coating material, of at least one filler
and which is referred to below as “powder coating material of the invention”.
Further subjects of the invention will emerge from the description.
In the light of the prior art, it was surprising and unforeseeable by the skilled worker that the powder coating material of the invention would be able to solve the problem on which the present invention is based. On the contrary, the expectation was that the powder coatings of the invention, like the customary and known powder coatings based on epoxy resin, would not be cuttable, millable or drillable but instead, owing to the thermal/mechanical load in the course of machining, would likewise give greasy, gluelike polymer melts which are very difficult to remove.
The first constituent, essential to the invention, of the powder coating material of the invention is the mixture (A) of epoxy resins which has self-crosslinking properties.
The amount of the epoxy resin mixture (A) in the powder coating material of the invention, based on the powder coating material, is up to 50% by weight. It is preferably from 20 to 49, more preferably from 25 to 48, with particular preference from 30 to 47, with very particular preference from 35 to 46, and in particular from 40 to 45% by weight.
Suitable epoxy resins are, fundamentally, all epoxy resins which have the epoxide equivalent weights (EEW) described below and are self-crosslinking in combination with one another. Particularly advantageous epoxy resins are linear epoxy resins which are bifunctional in respect of the epoxide groups and are based on aromatic diphenols, preferably bisphenol A and F, especially bisphenol A. They are used with particular preference in accordance with the invention.
In accordance with the invention, the epoxy resin mixture (A) comprises at least one epoxy resin (A1) with an EEW of <800, preferably <750, more preferably <700, and in particular <650 g. The amount of (A1) in the mixture (A) may vary widely. Based on (A), it is preferably from 10 to 40, more preferably from 12 to 39, with particular preference from 14 to 38, with very particular preference from 18 to 37, and in particular from 20 to 36% by weight.
In accordance with the invention, the epoxy resin mixture (A) further comprises at least one epoxy resin (A2) with an EEW of from 800 to 1500, preferably from 800 to 1300, with particular preference from 800 to 1100, with very particular preference from 800 to 1000, and in particular from 800 to 900 g. The amount of (A2) in the mixture (A) may vary widely. Based on (A), it is preferably from 40 to 75, more preferably from 42 to 73, with particular preference from 44 to 70, with very. particular preference from 46 to 68, and in particular from 50 to 65% by weight.
In accordance with the invention, the epoxy resin mixture (A) further comprises at least one epoxy resin (A3) with an EEW of >1500, preferably from 800 to 1300, with particular preference from 800 to 1100, with very particular preference from 800 to 1000, and in particular from 800 to 900 g. The amount of (A3) in the mixture (A) may vary widely. Based on (A), it is preferably from 5 to 15, more preferably from 6 to 14, with particular preference from 7 to 13, with very particular preference from 8 to 12, and in particular from 8.5 to 11.5% by weight.
In the powder coating materials of the invention, the percentages by weight stated above for the epoxy resins (A1), (A2) and (A3) add up in each case to 100% by weight.
The epoxy resins (A1), (A2) and (A3) are compounds which are known per se and are marketed, for example, by the companies Dow Chemical, Shell Chemie, or Ciba Specialty Chemical.
As a further constituent essential to the invention, the powder coating material of the invention comprises at least one filler (B). Suitable fillers (B) are, in principle, all organic and inorganic, especially inorganic, fillers, as described, for example, in Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “Fillers”, pages 250 to 252, and which do not exhibit any melting and/or decomposition during the machining of the shaped parts.
The fillers (B) preferably have a density of from 0.8 to 3.6, more preferably from 0.9 to 3.4, with particular preference from 1.0 to 3.2, and in parti
Boysen Rolf
Hilger Christoph
Rademacher Josef
Riestenpatt Helmut
Vietze Carsten
Aylward D.
Tucker Philip
LandOfFree
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