Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
2000-09-13
2001-10-30
Dawson, Robert (Department: 1712)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S502000, C204S507000, C523S404000, C525S382000, C528S228000
Reexamination Certificate
active
06309527
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermosetting resinous binder compositions, to their preparation, and to the use of these binder compositions in paints. The invention relates in particular to the use of these binder compositions in cathodic electrodeposition systems.
BACKGROUND OF THE INVENTION
Thermosetting resinous binder compositions, e.g., as used in paints, usually contain a cross-linking component. This cross-linking component reacts during stoving with the functional groups of the main resinous binder component, and the cross-linking provides a network which is insoluble and infusible, and therefore resistant to solvents and elevated temperatures.
In automotive industry, both solvent borne and water borne paints may be used, but the latter are preferred for environmental reasons. Nowadays a substantial part of the water borne paints, and those applied in electro-deposition systems (ED) in particular, are based on epoxy resins as binder. Such binder compositions are for instance used to provide automobiles with a base coating.
The presently used cathodic ED (CED) system is based on cationic hydroxyl-containing epoxy resin/amine adducts. The hydroxyl groups provide for the adhesion, whereas the amine groups render the adducts water-soluble and ensure deposition on the substrate acting as cathode. The system is based on an epoxy resin (e.g., a compound having an epoxy functionality greater than 1) as such resins have excellent stability during storage.
CED systems based on these adducts will contain a cross-linker and usually also a catalyst. Examples thereof include: (A) phenol-formaldehyde (PF) or amino-formaldehyde resins (both melamine-formaldehyde [MF] and urea-formaldehyde [UF] types) and a strong acid (as disclosed in U.S. Pat. No. 4,177,124); (B) non-acidic polyesters having more than one &bgr;-hydroxyl ester group per molecule and a metal salt (as disclosed in U.S. Pat. Nos. 4,332,711 and 4,362,847), and (C) partially blocked organic polyisocyanates (such as disclosed in UK patent 1,409,728, or in U.S. Pat. Nos. 3,947,338 and 3,947,339) and a metal salt. At present, the vast majority of CED systems is based on epoxy resin/amine adducts and partially blocked organic polyisocyanates in the presence of a metal salt.
The aforementioned CED systems (A) to (C) all provide very good corrosion resistance on bare steel; adequate bath stability and good ED characteristics. However, they also suffer from certain drawbacks. Thus, the system based on MF typically has a pH value of approximately 4.5 and is hence considered too acidic and corrosive for general application. The system based on the &bgr;-hydroxyl ester has to be cured at relatively high temperatures, say about 160 to 180° C. This system can therefore not be applied on articles composed of metal parts and plastic parts—which need to be conductive if these parts are also to be coated—as the plastic parts would deform during curing. Besides, the system results in high stoving losses due to the split-off of volatile organic compounds, and requires the presence of a metal salt—typically a lead salt—as catalyst. The latter is known to be an environmental hazard (C&EN Oct. 27, 1997 p. 43-54). The system based on blocked polyisocyanates has the same disadvantages as that based on the &bgr;-hydroxyl ester. In addition this cross-linker itself is cause for further concern due to its poisonous nature. Finally, in each of these “trans” reactions volatile organic compounds are released, which have to be trapped. Inadvertent condensation of these compounds during the curing may be detrimental to the appearance of the cured composition.
It would be desirable to have a thermosetting resinous binder composition that does not suffer from the aforementioned drawbacks, e.g., that is as versatile to apply as the aforementioned compositions, in particular by ED, that requires no environmentally hazardous or corrosive catalyst; is non-toxic; does not result in the release of volatile organic waste, and —importantly—allows cure at reduced temperatures (e.g., about 140° C. and below).
Although a combination of all of these properties is important, the final more so as it would allow coating conductive plastic parts, and articles of mixed composition.
SUMMARY OF THE INVENTION
The invention relates to thermosetting resinous binder compositions comprising a cationic resin (1) and a cross-linking agent (2), wherein the cationic resin (1) is an epoxy resin/amine adduct with on average more than one primary amine group, and the cross-linking agent (2) is a polyketone with on average more than one 1,4-dioxobutylene groups in the backbone.
The invention also relates to the preparation of these compositions, and their use in general and in CED more particularly.
DETAILED DESCRIPTION OF THE INVENTION
As stated, in the thermosetting resinous binder composition the epoxy resin/amine adduct and the polyketone have on average more than one primary amine group and more than one 1,4-dioxobutylene group, respectively, per molecule. This means that their average functionality is more than 1. The average functionality of at least one of the two components (i.e., primary amine group and 1,4-dioxobutylene group respectively) is preferably larger than 2. More preferably, the average functionality of both components is larger than 2. The epoxy resin/amine adduct has typically a functionality of at most 10. For a given chain length the functionality of a polyketone is at maximum if the polyketone has a perfectly alternating structure.
The reaction of both components occurs when both components are brought into contact, already at ambient temperature. Therefore, no or only marginal heating will suffice. Suitably, the components are reacted by heating to a temperature of 50 to 150° C., typically 120 to 140° C. Higher temperatures may be used, but are not required.
In general, the ratio of both components may depend on their functionality. Typically, the cationic resin and the cross-linking agent may be applied in a weight ratio of 100:1 to 1:100, although weight ratios of 50:1 to 1:50, particularly 20:1 to 1:20, e.g., 19:1 to 3:2 are preferred.
Component (1) of the composition, i.e., the cationic resin, may be a resinous saturated compound having a molecular weight of at least 300. When used in CED systems, it preferably has a molecular weight of at least 900, more preferably in the range of 2000 to 5000. Compounds having much higher molecular weights (40,000+) are not preferred as they will be difficult to dissolve.
In the context of this patent document the molecular weights unless otherwise indicated are number-average molecular weights.
Component (1) will ordinarily contain hydroxyl groups. Suitably, it has an alcoholic hydroxyl content in the range of 0.1 to 25 milliequivalents per gram, more suitably in the range of 1 to 20 meq/g. Outside this range, the composition may have difficulty adhering to, e.g., metal substrates or have difficulty in producing an acceptable and appealing coating. When applied in CED systems it preferably has a hydroxyl content in the range of 1.5 to 15 meq/g, more preferably in the range of 2 to 10 meq/g.
Although epoxy resin/amine adducts suitable as component (1) are not sold as such, their synthesis is known, e.g., in the aforementioned patent publications (GB-A-1,409,728 in particular), and in the European patent applications Nos. 25,555 and 212,483. For instance, component (1) may be produced by reacting an epoxy resin (3), with an “amine source” such as ammonia, a di- or polyfunctional compound having at least one temporarily blocked primary amine group, or a polyamine containing at least one primary amine group.
Suitable epoxy resins include resins produced (I) by reaction of epichlorohydrin with a polyol, with a polyacid (such as the diglycidyl ester of hexa-hydrophthalic acid) or a polyamine (e.g., tetraglycidated diaminodiphenylmethane); (II) by copolymerisation of glycidyl (meth)acrylate in an addition polymer (e.g., with styrene and/or (hydroxy)alkyl esters of (meth)acryl
Broekhuis Antonius Augustinus
Kooijmans Petrus Gerardus
Van Hek Jeffrey Roy
Aylward D.
Dawson Robert
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