Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1998-05-01
2001-02-13
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S393000, C427S393500, C427S393600, C427S407100, C427S408000, C427S409000, C427S412100, C528S044000, C524S591000, C524S839000, C524S840000
Reexamination Certificate
active
06187384
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to aqueous binder dispersions for preparing high-gloss coatings which are low in yellowing, comprising polyurethane alkyd resin components with a specific content and a specific combination of polyunsaturated fatty acid substituents as polymer side chains, and to their use as coating compositions, especially for wood and plastic.
BACKGROUND OF THE INVENTION
Aqueous polyurethane dispersions have long been known as binders in the preparation of coatings on metallic, mineral, wood or plastic substrates.
For example, polyurethane resin dispersions having a segment structure of the polymer backbone which leads to a two-phase or more-than-two-phase character and, associated therewith, to excellent elastic properties of the resins have been described (cf. e.g.: Dr. H.-P. Klein and Dr. M. Schwab, Kunstharz-Nachrichten 29, pages 38 to 42, 1993). In these dispersions, for example, long-chain polyether-, polyester- or polycarbonate-polyol units form the soft segments and urethane units, formed from diisocyanate, glycol and dihydroxycarboxylic acid, the hard segments.
Moreover, oxidatively drying polyurethane-alkyd resin hybrids are known, which carry unsaturated fatty acids as substituents and which are employed, in particular, in the field of corrosion protection.
DE-A 3901190 describes alkyd resins based on polyesterpolyols which are reacted with a 2,2-bis(hydroxymethyl)alkanecarboxylic acid and a diisocyanate component in a one-pot reaction so as to give a resin having a weight-average molecular weight Mw of from 10,000 to 70,000 daltons, an acid number of from 18 to 36 mg of KOH/g, which still contains free hydroxyl groups but no longer contains isocyanate groups, with from 45 to 100% of the carboxyl groups introduced into the resin being converted to carboxylate groups by addition of a base.
DE-A 4326270 embraces two-component polyurethane coating compositions, especially for the preparation of multicoat finishes in the automotive sector, which comprise aqueous dispersions of water-soluble or water-dispersible binders having isocyanate-reactive groups, as well as polyisocyanates as crosslinking components. Examples described of suitable binders are alkyd-free anionic polyesters, prepared from polyalcohols and polycarboxylic acids having hyroxyl numbers of between 10 and 200 mg of KOH/g, acid numbers of between 10 and 100 mg of KOH/g and number-average molecular weights Mn of between 1000 and 100,000 daltons.
DE-A 4328092 describes emulsifier-free aqueous coating compositions which contain as binder a combination of (A) a mixture of one or more water-dilutable polyurethane resins and/or alkyd-urethane resins, which may contain unsaturated fatty acid residues as substituents, with one or more water-dilutable (meth)acrylate copolymers, polyurethane resins and/or polyester resins, and (B) one or more amino resins and one or more blocked polyisocyanates. The binders described have acid numbers of between 10 and 100 mg of KOH/g, hydroxyl numbers of between 10 and 150 mg of KOH/g and number-average molecular weights of between 2000 and 10,000 daltons.
DE-A 4226243 describes water-dilutable coating compositions comprising (A) film-forming polymerpolyols in the form of aqueous dispersions of fatty acid-modified polyurethane resins and/or fatty acid-modified polyester resins (alkyd resins) with saturated and unsaturated fatty acid residues, and (B) polyisocyanates having more than one free isocyanate group, with or without the addition of one or more organic solvents and of the customary paint additives, such as pigments, fillers or rheological auxiliaries, as two-component coating compositions.
In the case of so-called do-it-yourself decorating paints, which are employed predominantly in the coating of wood, plastic or metal substrates, there is a need for low-solvent one-component systems which ensure rapid curing of the coating at room temperature. Moreover, such decorating paints should be low in yellowing, stable to weathering, mar-resistant and of high gloss, and should have a high resistance to water. In particular, the resistance to yellowing, which is essentially induced by oxidative processes, and the low solvent content in the coating material, which is required as a result of increasingly more restrictive environmental protection regulations, are of outstanding importance for decorating paints.
SUMMARY OF THE INVENTION
It has surprisingly been found that paint binders based on alkyd resin, with a specific combination of unsaturated fatty acids each containing at least two double bonds in the carbon chain, in the alkyd component of the paint binder, together with a reduced solvent content in the binder component, achieve these objects outstandingly.
The novel one-component coating materials comprise binders BM consisting essentially of a polyurethane alkyd resin component (A) composed of:
(a) from 5 to 50% by weight of a mixture of:
(a1) from 90 to 30 parts by weight of an unsaturated C6 to C30 fatty acid containing at least two nonconjugated double bonds, and
(a2) from 10 to 70 parts by weight of an unsaturated C6 to C30 fatty acid containing at least two conjugated double bonds as esterified polymer side chains of the polyurethane alkyd resin component (A) and
(b) from 95 to 50% by weight of polyurethane units as polymer main chains of the polyurethane alkyd resin component (A).
The mixture (a) preferably consists of from 80 to 50 parts by weight of (a1) and, correspondingly, from 20 to 50 parts by weight of (a2), particularly preferably of from 80 to 60 parts by weight of (a1) and, correspondingly, from 20 to 40 parts by weight of (a2).
In a particularly preferably embodiment of the invention, linoleic acid is employed as component (a1) and C18 conjuene fatty acid as component (a2).
For the synthesis of the polyurethane units (b) it is preferable to employ polyesterpolyols (b1) which as alcohol units (b11) preferably contain aliphatic, cycloaliphatic and/or araliphatic alcohols having per molecule 1-6 hydroxyl groups attached to nonaromatic carbon atoms, and as acid units (b12) preferably contain aliphatic, cycloaliphatic saturated or unsaturated and/or aromatic polybasic carboxylic acids, preferably di-, tri- and tetracarboxylic acids or their anhydrides or esters. The polyesterpolyols preferably possess acid numbers of between 1 and 10 mg of KOH/g, particularly preferably between 2 and 5 mg of KOH/g, and preferably hydroxyl numbers of between 100 and 250 mg of KOH/g, particularly preferably between 140 and 160 mg of KOH/g.
Preferred polyisocyanates (b2) for the introduction of the urethane groups into the polyester main chain have 4 to 25 carbon atoms and 2 to 4 isocyanate groups per molecule.
The polyurethane alkyd resin components (A) preferably have acid numbers of between 15 and 40 mg of KOH/g, particularly preferably between 20 and 30 mg of KOH/g, and preferably hydroxyl numbers of between 90 and 150 mg of KOH/g, particularly preferably between 100 and 130 mg of KOH/g. The content of urethane groups in the polyurethane alkyd resin components (A) is preferably between 5 and 15% by weight based on (A), particularly preferably between 5 and 10% by weight.
The aqueous binder dispersions BM preferably contain less than 2% by weight of solvents, particularly preferably less than 1% by weight based on the binder dispersion BM.
Furthermore, the aqueous binder dispersions BM may contain between 0 and 20% by weight, preferably between 0 and 10% by weight, based on (A), of additional crosslinking components (B), which are preferably able to react at room temperature with the excess hydroxyl and/or carboxyl groups of the polyurethane alkyd resin component (A).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The Components of Polyurethane Alkyd Resin Component (A)
The mixture (a) which makes up the polymer side chains, consisting of unsaturated fatty acids (a1) having at least two nonconjugated double bonds and unsaturated fatty acids (a2) having at least two conjugated double bonds, is present in proportions of from 5 to 50% by weight,
Grapatin Dittmar
Rink Heinz-Peter
Wilke Guido
BASF Coatings AG
Cameron Erma
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