Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-17
2001-07-10
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S415000, C525S528000, C528S065000, C528S068000, C528S073000
Reexamination Certificate
active
06258875
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to aqueous dispersions of modified epoxy resins, which are suitable as binders for aqueous coating Compositions. They are particularly used in the preparation of primer and/or primer surfacer layers in vehicle and in industrial coating.
Aqueous dispersions of epoxy resins are known in the prior art.
DE-A-3643751 for example describes aqueous dispersions of epoxy resins, which are obtained by reaction of epoxy compounds having at least two epoxy groups per molecule with an aromatic polyol and a condensation product of an aliphatic polyol and of an epoxy compound.
In EP-A-610068 epoxy resins for aqueous epoxide/amine-systems are described, which contain 20-70 wt-% of an epoxy resin and 5-40 wt-% of a self-emulsive epoxy resin, whereby the latter is obtained by reaction of a urethane compound, prepared from a polyalkylene polyether polyol and a polyisocyanate in excess, with an epoxy compound having hydroxyl groups and an alkylphenol ethoxylate.
EP-A-346 742 describes water-dilutable epoxy resins, obtained by reaction of epoxy compounds having at least two epoxy groups per molecule with an aromatic polyol and a condensation product of an aliphatic polyol, an epoxy compound and a mono- or diisocyanate, whereby the condensation product is present in the epoxy resin at 3-15 wt-%.
Further, water-dilutable epoxy resins, which are reaction products of a diglycidyl ether of a dihydric phenol, a dihydric phenol, a diglycidyl ether of a polyoxyalkylene glycol and a diisocyanate, are disclosed in U.S. Pat. No. 4,399,242. Additionally the water-dilutable epoxy resin contains an aliphatic monoepoxide as a reaction diluent.
The mentioned aqueous dispersions of epoxy resins of the prior art can be used in coating compositions, for example in combination with polyamine curing agents in aqueous two-component coating compositions. It is, however, a disadvantage of the aforementioned dispersions of epoxy resins that as binder components in aqueous two-component coating compositions lead to coating formulations which do not have the same high level of quality as the corresponding solvent-based coating formulations. In particular the poor sandability of the obtained coatings has shown to be of considerable disadvantage in the wet as well as in the dry state. The over long drying times, in particular the insufficient through-drying and the unsatisfactory final hardness of the obtained coatings are likewise unfavourable. The adhesion to the substrate is also often unsatisfactory.
The object of the invention was therefore to provide aqueous dispersions of epoxy resins, which, in combination with cross-linking agents, in particular with amino-functional cross-linking agents, can be processed into coating compositions which give the coatings an excellent sandability in the wet as well as in particular in the dry state. The coating compositions should likewise be applicable without difficulty as thick layers and should result in coatings with a rapid through-drying and a good final hardness. A good adhesion to most varied substrates should be assured.
SUMMARY OF THE INVENTION
The invention provides an aqueous dispersion of modified epoxy resins with an epoxy equivalent weight of 250-10,000 and with a urethane and urea group content of 5-250 mmol based on 100 g solid content of the dispersion.
In another aspect, the invention provides an aqueous dispersion of modified epoxy resins with a urethane and urea group content of 5-250 mmol, based on 100 g solid content of the dispersion, containing at least one modified epoxy resin A) with an epoxy equivalent weight of 250-10,000, which epoxy resin is the reaction product of:
A1) 43.0-86.0 wt-% of at least one epoxy compound having at least 2 epoxy groups per molecule and an epoxy equivalent weight of 100 to 2000,
A2) 10.0-25.0 wt-% of at least one aromatic polyol,
A3) 2.0-12.0 wt-% of at least one aliphatic polyol and
A4) 2.0-20.0 wt-% of at least one polyisocyanate, wherein the percentages are relative to solid content and wherein the sum of the components A1), A2), A3) and A4) adds up to 100 wt-%.
The modified epoxy resins A) comprise an epoxy equivalent weight of 250-10,000, preferably of 450-2500, in particular preferably of 350-1500. The modified epoxy resins A) preferably comprise cross-linked parts, preferably in amounts of 0.5-50 wt-% (based on the solid content; determined as the insoluble part in tetrahydrofurane).
The aqueous dispersions of the modified epoxy resins have a urethane and urea group content of 5-250 mmol, preferably of 10-150 mmol, based on 100 g solid content of the dispersion. The solid content of the dispersion is thereby composed of the solid resin content of the epoxy resin prepared from the components A1), A2), A3) and A4) and of the solid content of the by-products formed in the reaction of the components A1), A2), A3) and A4).
The epoxy compounds A1) are polyepoxides with an average of at least 2 epoxy groups per molecule. These epoxy compounds can be saturated, unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and, optionally can also comprise hydroxyl groups. They can also comprise substituents, such as, for example, alkyl or aryl substituents or ether groups.
The epoxy compounds A1) preferably comprise polyglycidyl ethers based on polyhydric, preferably dihydric alcohols, phenols, hydrogenation products of these phenols and/or of novolaks (reaction products of mono- or polyhydric phenols with aldehydes, in particular with formaldehyde in the presence of acid catalysts). The preferred epoxy equivalent weights of these epoxy compounds are between 160-500. Examples of polyhydric phenols are resorcin, hydroquinone, 2,2-bis-(4-hydroxyphenyl)propane (bisphenol A), dihydroxydiphenylmethane (bisphenol F, optionally mixtures of isomers), 4,4′-dihydroxy-3,3′-dimethyldiphenylpropane, 4,4′-dihydroxydiphenyl, 4,4′-dihydroxydiphenylcyclohexane, 4,4′-dihydroxybenzophenol, bis-(4-hydroxyphenyl)-1,1-ethane, 1,5-dihydroxynaphthalene.
Polyglycidyl ethers of polyhydric alcohols are likewise suitable. Examples of polyhydric alcohols are ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propylene glycol, polyoxypropylene glycols, 1,4-butylene glycol, 1,5-pentane diol, 1,6-hexane diol, glycerin, bis-(4-hydroxycyclohexyl)-2,2-propane. Polyglycidyl esters of polycarboxylic acids, which are obtained by reaction of for example epichlorhydrine with an aliphatic, aromatic or cycloaliphatic polycarboxylic acid, can also be used. Examples of polyglycidyl esters of polycarboxylic acids are diglycidyl esters of adipic acid, diglycidyl esters of phthalic acid and diglycidyl esters of hexahydrophthalic acid.
Mixtures of several epoxy compounds A1) can be used.
Polyglycidyl ethers of bisphenol A are preferably used.
The aromatic polyols A2) are preferably the aromatic hydroxyl group-containing compounds mentioned already above in the description of the components A1). These are for example polyhydric, preferably dihydric phenols, halogenation products thereof and/or novolaks. Preferably the OH-groups are bonded directly to the aromatic ring. It is particularly preferred to use bisphenol A.
The aliphatic polyols A3) comprise polyols selected from the group of polyacrylates, polyesters, polyethers, polycarbonates and polyurethane polyols. The aliphatic polyols are provided, in a manner known to the person skilled in the art, with a hydrophilic group assuring sufficient water-dilutability. Preferably polyether polyols are used as the aliphatic polyols A3). They can comprise for example polyether polyols with average weight molecular weights Mw of 600-12,000 g/mol, preferably of 2000-8000 g/mol and OH-numbers of for example 10-200 mg KOH/g, preferably of 15-100 mg KOH/g. The aliphatic polyols have preferably only terminal primary OH-groups. Examples of the preferred polyether polyols are polyethylene, polypropylene, polybutylene glycols and block copolymers of ethylene oxide and propylene oxide. Mixtures of the polyalkylene glycols can be used. Polyethy
Awokola Morenike Gisela
Beyers Heike
Vogt-Birnbrich Bettina
Aylward D.
Dawson Robert
E. I. Du Pont de Nemours and Company
Tessari Joseph A.
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