CA2088805A1 - Coating compositions, a process for their production and their use for coating water-resistant substrates - Google Patents

Abstract

Mo-3851 LeA 28,894 COATING COMPOSITIONS, A PROCESS FOR THEIR PRODUCTION
AND THEIR USE FOR COATING WATER-RESISTANT SUBSTRATES
ABSTRACT OF THE DISCLOSURE
The present invention relates to an aqueous two-component coating composition wherein the binder contains a) a component which is dissolved and/or dispersed in water, has an average hydroxyl number of 15 to 200 mg KOH/g and contains a1) a polyol component having a content of 8 to 450 milliequivalents, per 100 g of component a1) solids, of chemically incorporated ammonium groups, -N=+ and containing one or more polyaddition, polymerization and/or polycondensation resins which are water-dilutable, contain hydroxyl groups and have a molecular weight (Mn) of at least 500 and a2) up to 10 wt%, based on the weight of component a1), of one or more reactive diluents which are water-soluble, have a molecular weight (Mn) below 500 and contain at least one isocyanate-reactive group, and b) a polyisocyanate component having an NCO content of 5 to 25 wt% and containing one or polyisocyanates which are emulsified in the aqueous solution and/or dispersion of hydroxyl group-containing component a), wherein components a) and b) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups of component b) to isocyanate-reactive groups of component a) of 0.5:1 to 5:1.
The present invention also relates to a process for the production of this coating composition and to their use for the production of coatings on water-resistant substrates.

Mo3851

Description

2 IL) ~ rj Mo-3851 L~A 28894-US
COATING COMPOSITIONS, A PROCESS FOR THEIR PRODUCTION
AND ~HEIR USE FOR COATING WATER-_ESISTANT SUBSTRATES
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a new aqueous coating composition containing a cationically modified polyol component dissslved and/or dispersed in water, optionally a reactive diluent and, emulsified therein~ a polyisocyanate component; a process for the production of this coating composition; and its use for the production of coatings on water-resistant substrates.
Description of the Prior Art Aqueous coating compositiors are gaining increasing importance for economic and ecological reasons. However, the replacement of conventional~ solvent-based coating compositions is proceeding more slowly than expected.
There are numerous reasons for this. Aqueous dispersions frequently still have processing disadvantages when compared to coating compositions dissolved in organic media. With aqueous solut;ons there is also the conflict between providing sufficient water dispersibility or solubility versus the contrary effect resulting therefrom of the lower resistance of the coatings to water. This is not a problem with coating compositions dissolved in organic solvents. In addition, there are also process;ng problems in this regard which result from the high viscosity of the aqueous coating compositions. These problems have previously been overcome by the use of organic auxiliary solvents. However, the amount of auxiliary solvent used in this conneotion is limited, since, otherwise, the ecological impact of the aqueous systems is lessened.

L~ 28 ~94-~S

2 ~

For this reason, in binder systems crosslinked with melamine resins ~U~ Patents 4 031 052, 4 171 294 and 4 276 210 and DE-OS 2 446 760 and 2 847 532), water-dilutable reactive diluents have previously been used. These resins have a favorable effect on the solubility properties of the polymer systems and are also incorporated ;n the coatings by melamine resin crosslinking. However, the reactivity of many aqueous melamine resins is so low that high crosslinking temperatures are requ;red such that the reactive diluents can escape from the coatings before crosslinking occurs.
Only recently have aqueous two-component polyurethane systems become known (DE-OS 3 829 587). In these systems the binder is based on a polyacrylate resin dissolved or dispersedin water in combination with a polyisocyanate containing free isocyanate groups emulsified in this dispersion or solution.
The systems are essentially solvent-freP, as is evident from the fact that the solvents used in the production of these polymer resins are removed before preparation of the aqueous composition. These known prior art systems may be used to produce high-grade coatings, which are comparable in their properties to coatings prepared from solvent-containing coating compositions of analogous structure.
It has now surprisingly been found that aqueous two-component polyurethane coating compositions in which the polyol co~ponent is cationically as opposed to anionically modified have a considerably longer pot life and are as suitable as analogous systems based on anionically modified polyhydroxyl compounds for the production of high-grade coatings. The coating compositions according to the invention, which are described in more detail below, have pot lives of at least 8 hours to as much as several days.

Mo3851 2 ~

SUMMARY OF THE INVENTION
The present inventlon relates to an aqueous two-component coating composition wherein the binder contains a) a component which is dissolved and/or dispersed in water, has an average hydroxyl number of 15 to 200 mg KOH/g and contains al) a polyol component having a content of 8 to 450 milliequival~nts, per 100 9 of component al) solids, of chemically incorporated ammonium groups, =N=+ and containing one or more polyaddit;on, polymerization and/or polycondensation resins which are water-dilutable, contain hydroxyl groups and have a molecular weight (Mn) of at least 500 and : a2) up to 10 wt%, based on the weight of component al), of one or more reactive diluents which are water-soluble, have a molecular weight ~Mn) below 500 ;~ and contain at least one isocyanate-reactive group, and b) a polyisocyanate component having an NCO content of 5 to 25 wt~o and containing one or polyisocyanates which are : 20 emulsified in the aqueous solution andfor dispersion of hydroxyl group-containing component a), ~:~ wherein components a) and b) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups of component b) to isocyanate-reactive groups of component a) ~f 0.5:1 to 5:1.
The present invention also relates to a process for the production of this coating composition and to their use for the production of coatings on water-resistant substrates.
; UETATLED DESCRIPTIOW OF T~IE INVENTION
Component a) has an average hydroxyl number of 15 to 200, preferably 40 to 160, mg KOH/g and preferably an average hydroxyl functional~ty of at least 2.5, more preferably at least 3. It contains of polyol component al) which has a molecular weiyht (Mn) greater than 500 or a mixture of polyol Mo3851 .:

2 ~

component al) with up to 10 wt%, based on the weight of al), of a water-soluble reactlve diluent which has a molecular weight (Mn) below 500 and at least one group reactive towards isocyanate groups.
The aqueous solutions and/or dispersions of component a) preferably contain 65 to 400, more preferably 100 to 240, parts by weight of water per 100 parts by weight of component a).
Polyol component al) is selected from hydroxyl group-containing polyaddition, polycondensation and/or polymerization resins having a molecular weight (Mn) of at least 500, preferably 1500 to 5000; and a hydroxyl functionality of at least 2, preferably at least 3. Component a) contains at least a portion and preferably exclusively contains polyol components al) which have a content of incorporated ammonium groups, =N=++, which is sufficient to solubilize or disperse component al) in water. It is possible, although not generally preferred, to use mixtures of polyhydroxyl compounds which contain both cationically modified polyols and also ionically unmodified polyols, provided that the proportion of the cationically modified polyols is sufficient to ensure the dispersibility or the solubility of the total mixture. The content of chemically incorporated ammonium groups, =N=+, in polyol component al) is 8 to 450, - preferably 25 to 250, milliequivalents per 100 9 of solids.
Molecular weights (Mn) of less than 5000 are measured by vapor-pressure osmometry in dioxane and acetone, the low value being used when the values differed. Molecular weights (Mn) of greater than 5000 are determined by membrane osmometry in acetone.
The polyhydroxyl compounds of component al) may be catlonlcally modified by the incorporation of tertiary nitrogen atoms and their subsequent conversion to an ammonium grollp by neutralization with an acid or by quaternization with a quaterniziny agent.

Mo3851 Polyhydroxyl compounds suitable as component al) include polyaddition, polycondensation and/or polymerization products that satisfy the above requirements. These compounds often contain segments which have been formed by a polyaddition reaction in add;tion to segments which have been for~ed by a polycondensat;on reaction or a polymerization reaction.
Examples of compounds which can be used as component al) or as a part of component al3 or which can be converted by neutralization or quaternization into these compounds include:
i) Polyether polyols having incorporated tertiary nitrogen atoms which can be produced by the propoxylation and/or ethoxylation of starter molecules having amine nitrogen.
Such polyether polyols include the propoxylation and/or ethoxylation products of ammonia, ethanolamine, tr;ethanolamine, ethylenediamine and mixtures of these amines.
ii) Polyester or polyamide resins ha~ing ter~iary nitrogen atoms wh;ch are prepared by the polycondensation of multivalent and optionally monovalent starting components.
Known processes for the polycondensation of alcohols and carboxylic acids are described, e.g., in Rompp's Chemielexikon, vol. 1~ page 202, Frankh'sche Verlagsbuchhandlung, Stuttgart, 1966, and D.H. Solomon, The Chemistry of Organic Filmformers, pp. 75-101, John Wiley ~ Sons Inc., New York, 1967.
Starting materials for preparing the polycondensation resins include - alcohols having 1 to 6, preferably 2 to 4 hydroxyl groups and a molecular weight of 32 to 500, preferably 62 to 250, such as ethylene glycol, propylene glycol, butanediols, neopentyl glycols, cyclohexanedimethanols, 2-ethyl-1,3-propanediol, hexanediols, ether alcohols such as di- and triethylene glycols, ethoxylated bisphenols, perhydrogenated bisphenols, trimethylolekhane, trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, mannitol and sorbitol; and monohydric chain-termlnating alcohols such as methanol, propanol, butanol, cyclohexanol and benzyl alcohol;
Mo3851 2 ~ 5 - multivalent carboxylic acids or carboxylic acid anhydrides having a molecular weigh~ of 100 to 300, such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, ~rimellitic s anhydride, pyromellitic anhydride, maleic anhydride, adipic acid and succinic anhydride;
- aromatic or saturated aliphatic monocarboxylic acids such as benzoic acid, hexahydrobenzoic acid, butylbenzoic acid, coconut oil acids and ~ ethylhexanoic acid;
}o - olefinically unsaturated fatty acids and derivatives of olefinically unsaturated fatty acids such as the fatty acids of linseed oil, soya oil, tung oil, safflower oil, dehydrated castor oil, cottonseed oil, groundnut oil and tall oil;
synthetic olefinlcally unsaturated C12 - C22fatty acids; and derivatives obtained by conjugation~ isomerization or dimerization of these unsaturated fatty acids;
- the oils corresponding to the previously mentioned natural fatty acids such as linseed oil, soya oil, tung oil, safflower oil, dehydrated castor oil, cottonseed oil, groundnut oil, tall oil and castor oil; and ; - amines and/or alcohols having tertiar~y nitrogen atoms such : as N-methyldiethanolamine, N-methyldipropanolamine, N-butyldiethanolamine, N-butyldipropanolamine, N-stearyldiethanolamine, N-stearyldipropanolamine, triethanolamine, tripropanolamine, hydroxyethylmorpholine, 2-hydro~ypropylmorpholine, hydroxyethylpiperazine, 2-hydroxypropylpiperazine and alkoxylation productsofallthese amines and/or alcohols having a molecular weight ~Mn) of less than 3000.
iii) Polyols having urethane groups and tertiary nitroyen atoms which may be obtained in known manner from the conventional starting materials of polyurethane chemistry.
These polyurethanes may be prepared by reacting less than stoichiometric amounts of polyisocyanates with the previously mentioned, preferably at least difunctional, 10w molecular Mo3851 2 ~ 5 weight, starting components having ~ertiary nitrogen atoms and groups reactive towards isocyanate groups; polyester polyols having a molecular weight (Mn) of ?50 to 10,000, preferably 1000 to 5000, which may or may not contain ;ncorporated tertiary nitrogen atoms; polyether polyols having a molecular weight (Mn) of 250 to 10,000, preferably 1000 to 5000, which may or may not contain incorporated tertiary nitrogen atoms;
the previously mentioned polyhydric alcohols having a molecular weight of 62 to 250; and mixtures of these polyhydroxyl compounds. The nature and proportions of the reactants are chosen so that the urethane-modified polyhydroxyl compounds obtained satisfy the conditions previously set forth with regard to the content of tertiary nitrogen atoms, molecular weight and OH number.
Suitable polyisocyanates for the production of these resins include hexamethylene diisocyanate, isophorone diisocyanate, 4~4'-diisocyanatodicyclohexylmethane, 2,4 -and/or 2,6-diisocyanatotoluene and/or the isomeric or homologous polyisocyanates or polyisocyanate mixtures of the diphenylmethane series.
iv) Polyhydroxypolyacrylates prepared by the known copolymerization of olefinically unsaturated monomers wherein a portion of these ~onomers have alcoholic hydroxyl groups and a portion have tertiary nitrogen atoms incorporated therein.
Suitable monomers for the production of these polyacrylate resins include Cl-C8, preferably Cl-C2-alkyl methacrylates such as methyl or ethyl methacrylate; styrene; Cl-C8-alkyl acrylates such as methyl, ethyl, n-propyl, isopropyl, n-butyl, n-hexyl or n-octyl âcrylate; C2 C8-hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate (e.g., an isomer mixture obtained by the addition of propylene oxide to (meth)acrylic acid), 4-hydroxybutyl (meth)acrylate and mixtures of such monomers; vinyltoluenes; vinyl esters such as vinyl acetate; and monomers having tert-nitrogen atoms, e.g., such as the acrylate or methacrylate esters of alcohols having Mo3851 2~g~S

tertiary nitrogen atoms, such as N,N-dimethylam;noethanol, and N-(2-hydroxyethyl)-morpholine or -p;perid;ne.
It is also possible to produee polyacrylate polyols having tertiary nitrogen atoms by the incorporation of the pneviously disclosed alcohols having ter~iary nitrogen atoms via urethane groups. This is accomplished by reacting a portion of the hydroxyl groups of a polyacrylate polyol with tertiary nitrogen-containing isocyanatourethanes. These isocyanatourethanes may be produced, for example, by reacting monohydric alcohols having tertiary nitrogen atoms with a large excess of diisocyanate and subsequently removing the unreacted excess diisocyanate by distillation.
Component al) may contain mixtures of the previously descr;bed polyhydroxyl compounds provided that the mixtures contain the required content of ammonium groups. The incorporated tertiary nitrogen atoms are converted into ammonium ions by neutralization or quaternization.
To achieve at least partial neutralization ~protonation), the incorporated basic tertiary nitrogen atoms are treated with aliphatic acids such as formic acid, acetic acld, propionic acid, lactic acid, malonir acid, malic acid7 tartaric acid, glyoxalic acid, methanesulphonic acid, oxalic acid, fumaric acid, succinic acid and adipic acid. These acids can be used as aqueous solution or anhydrous (e.g., methanesulphonic acid).
The neutralization may be carried out in bulk, in aqueous medium or in the inorganic phase. To produce an aqueous solution or dispersion of component al), it is often sufficient to mix the polyhydroxyl compounds having tertiary nitrogen atoms with an aqueous solution of an acid suitable for 3~ neutral katlon. lf it is desired to produce anhydrous polyhydroxyl compounds, then neutralization with an anhydrous acid such as methanesulphonic acid is preferrecl. In this way an anhydrous salt is formed which can later be dissolved c~r dispersed by simple stirring with water.

Mo3851 ~ 3 The use of water-miscible solvents, such as acetone, during neutralization is also poss;ble. In particular, acetone solut~ons of the at least partly neutralized polyhydroxyl compounds can simply be stirred with water and, if desired, the acetone can be removed by dlst~llat~on.
Suitable alkylating agents are known and include methyl chloride, methyl bromide, methyl iodide, dimethyl sulphate, diethyl sulphate, methyl p-toluenesulphonate and chloroacetamide. The alkylation reactlon can be carried out, for example, in the presence of solvents, such as acetone, acetonitrile, tert-butanol or ethyl acetate, at 20 to 100C
with subsequent removal of solvent. The alkylation san also advantageously be carried out in the presence of small amounts of polar, high-boiling solvents, for example, N-methyl pyrrolidone and the acetates of propylene glycol and glycerol as well as propyleneglycol-n-buty]etheracetate and propyleneglycol-methyletheracetate.
These solvents are not removed and serve as coalescing agents during the subsequent formation of coatings.
Optional polyol component a2), i.e., the reac~ive diluent, is selected from compounds which contain at least one, preferably 2 to 4, isocyanate-reactiv~ groups, are water-soluble and have a molecular weight (Mn) of less than 500, preferably less than 300.
Suitable monofunctional compounds include n-hexanol~
n-octanol and amides such as ~ caprolactam~ The preferred 2s compounds containing 2 to 4 isocyanate-r~active groups include ethylene glycol; propylene glycol; the isomeric butanediols, pentanediols, hexanediols, octanediols, polyethylene glycols and polypropylene glycols; glycerol; trimethylolpropane;
pentaerythritol; sorbltol; mannitol; the ethoxylation or propoxylation products of these hlgher-functional alcohols; and mixtures of these compounds.
Optional component a2) is present in an amount of up to 10 wt%, preferably up to 5 wt%, based on the weight of component al). ~he nature and proportions of the individual components Mo3851 2~3~

al) and a2) are chosen such that component a) has the required OH number and hydroxyl functionality.
Polyisocyanate component b) is selected from polyisocyanates having aliphatically, cycloaliphaticaliy, araliphatically and/or aromatically bound isocyanate groups which may optionally contain nonionic hydrophilic groups and/or cationic groups. The polyisocyanate is preferably liquid at room temperature. Solid polyisocyanates may also be used, but it is recommended that they be used with small amounts of lo solvents such as toluene, ethyl acetate, solvent naphtha, propylene glycol ether acetate, propylene glycol diacetate, d;propylene glycol diacetate~ N-methylpyrrolidone or ethylene glycol dimethyl ether.
Polyisocyanate component b3 preferably has a viscosity of 50 to 10,000, more preferably 50 to 1000 mPa.s at 23C. It is particularly preferred to use a polyisocyanate mixture having exclusively aliphatically and/or cycloal;phatically bound isocyanate groups, an average NCO functionality of 2.2 and 5.0 and a viscosity at 23aC of 50 to 5000 mPa.s.
Suitable polyisocyanates for use as component b) are polyisocyanates derivatives having aromatically or (cyclo)aliphatically bound isocyanate groups, preferably (cyclo~aliphatically bound isocyanate groups.
Polyisocyanates derivatives prepared from hexa~ethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI~ and/or 4,4'-bis-(isocyanatocyclohexyl)-methane are very suitable, especia71y those prepared exclusively fro~ hexamethylene diisocyanate. Polyisocyanate derivatives include polyisocyanates having biuret, urethane, 3~ uretdione and/or isocyanurate groups. These polyisocyanates are generally prepared from diisocyanates and are preferably subsequently treated to remove excess starting isocyanate in known Inanner, preferably by distillation, to a residual content of less than 0.5 wt%.

Mo3851 8 ~ ~

Preferred polyisocyanate derivatives include poly;socyanates which conta;n biuret groups, are prepared from hexamethylene diisocyanate in accordance with the processes described, e.g., in U.S. Patents 3,l24,605, 3,358,010, 3,903,126, 3,903,127, or 3,976,627, and contain mixtures of N,N',N"-tris-(6-;socyanatohexyl)biuret with minor amounts of its higher homolog; and polyisocyanates which contain isocyanura~e groups~ are prepared by the trimerization of hexamethylene diisocyanate in accordance with the process described, e.g., in U.S. Patent 4,324,879, and contain mixtures of N,N',N"-tris-(6-isocyanato-hexyl)-isocyanurate with minor amounts o~ its higher homolog. Especially preferred are polyisocyanates which contain uretdione and isocyanurate groups and are prepared by the catalytic oligomerization of hexamethylene diisocyanate in the presence of trialkyl-phosphines. Especia71y preferred are latter polyisocyanates having a viscosity of 50 to 500 mPa.s at 23C and an NCO
functionality of 2.2 to 5Ø
The less preferred aromatic polyisocyanates include polyisocyanate derivatives prepared from 2,4-diisocyanato-toluene or mixtures thereof with 2,6-diisocyanatotoluene or prepared fro~ 4,4'-diisocyanatodiphenylmethane or mixtures thereof with its isomers and/or higher homoloyues. The aromatic polyisocyanate derivatives in~lude those containing urethane groups which may be prepared by the reaction of excess amounts of 2,4-diisocyanatotoluene with polyhydric alcohols, such as trimethylolpropane, followed by removal by distillation of the unreacted excess diisocyanate. Other aromatic polyisocyanate derivatives include the trimers prepared from aromatic diisocyanates from which excess monomeric diisocyanates have preferably been removed by distillation follow~ng their production.
The use of hydrophilically modified polyisocyanates as component b) or as a portion of component b) is particularly preferred and is generally advantageous due to the additional Mo3851 emulsifying effect. Such hydrophilic mod1fication of the polyisocyanates can be carried out by reac~ing a portion of the isocyanate groups with monovalent polyether alcohols having ethylene oxide units, for example, the ethoxylation products of monomeric alkanols having 5 to 100 ethylene oxide units per molecule. These polyether alcohols and their production are described for example in DE-OS 3 521 618. Cationic modification of the polyisocyanates can also be carried out for example by reacting the polyisocyanates with a less than stoichiometric amount of an aminoalcohol containing at least one tertiary amino group, which is then subsequently converted with a suitable acid, such as anhydrous methanesulphonic acid, or by quaternization, into an ammonium group.
Especially suitable polyisocyanates b) ~ethosehaving~n NCO content of 5 to 30 wt%~ an NCO functionality of 2.2 to 5.0, and a content of incorporated ammonium groups, =N=+, of 10 to 250 m;lliequivalents per lOO g of polyisocyanate b). The use of such cationically modified polyisocyanates is especially advantageous because in this embodiment both the component a) 20 and the polyisocyanate component b) have incorporated cations.
This results in a synergism such that at a constant total concer.tration of cations, better emulsifiability of the overall system can be observed.
It is also possible to modify polyisocyanate component b) 25 so that itcont~ns both nonionic hydrophilic groups and cationic groups. It is also possible to use hydrophobic polyisocyanates without any hydrophilic modification. These polyisocyanates are also emulsifiable in the system since component a) can perform the function of an emulsifier for these polyiso-cyanates.
The coating compositions according to the invention mayalso contain the known auxiliary agents and additives from polyurethane coatings technology. Examples include pigments, antifoaming agents, levelling agents, dispersant aids for pigment distribution, thickeners, driers, extenders, catalysts Mo3851 3 ~

for the isocyanate addition reaction, and less preferably solvents that are not incorporated in the film.
To produce the coating composi~ions, the polyisocyanate component b~ is emulsified into the aqueous solution or dispersion of component al). Component a2) can be stirred into the system before or after the addition of polyisocyanate component b). The intermixing can be carried out simply by stirring at room temperature. The amount of polyisocyanate component b) is selected to provide an equivalent ratio of isocyanate groups of component b) to isocyanate-reactive groups of components a) of 0.5:1 to 5:1, preferably 0.8:1 to 3:1.
Components a) and b) are also preferably selected to provide an average functionality for these components with regard to the isocyanate addition reaction of at least 2.5 groups/mole.
If emulsifiable polyisocyanates are used, the coating compositions may also be prepared by emulsifyiny the polyiso-cyanates in water and then mix;ng them with the cationic polyhydroxyl compound. The reactive diluent may optionally be added in a final stage.
The ~ptional auxiliary agents and addi~ives are incorporated into the system by stirring, preferably before the addition of polyisocyanate component b).
The present invention makes available for the first time, aqueous cationic two-component polyurethane coating compositions which cure to high-quality crosslinked coatings.
This is due to the fact that the binder components a) and b) are essentially branched substances which cure to h1ghly crossiinked systems and are neither soluble nor dispersible in water after the components have reacted. Accordlngly, the cuating compos~tions according to the invention having only a ~nite pot life such that they yel after a certain time period.
The fundamental advantage of the systems according to the inventlon over corresponding anionically modified systems is to that the pot life ls considerably extended. In addition to the ecological advantages of these new coating compositions and the Mo3851 improvements in processing viscosity and flow properties, there is the additional ability to alter the coatings properties through the choice of the reactive diluent. Thus, brittle coatings can be adjusted to be more flexible by the appropriate s choice of the reaotive diluent, it is known that long chain diols have a flexibilizing effect.
In a binder sys$em with a relatively low crosslinking density, harder and more resistant coatings can be produced through the use of tri- or polyfunctional reactive diluents.
The coatings may be cured either at r~om temperature or at elevated temperatures. The choice of the reactive diluents depends upon both the reactivity of the polyisocyanates and/or the catalysis, and on the curing condit;ons. More volatile reactive diluents should preferably be used when the composition is cured at room temperature or slightly elevated temperature. At higher stoving temperatures and long crosslinking times, the use of less volatile reactive diluents is recommended.
The aqueous binder systems according to the invention are suitable for coating any water-resistant substrates, especially for the production of air- or heat-drying coatings on wood, concrete, masonry or metallic substrates. They are also suitable for the corrosion protection of metals, such as steel, and as automotive coatings, especially as cationic primers.
The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES
PolYhYdroxvl Com~ounds 3~ PlY~_er 1 A poly(neopentyl glycol adipate) having a molecular weight (Mn) of 1000 A poly(1,6-hexanediol/neopentyl glycol adipate) having a molecular weight (Mn) of 1700. (Weight ratio of diols - 3:2).
Mo38S1 ~3,~9~

PolYester 3 A polyethylene glycol adipate haYiny a molecular weight (Mn) of 1750.
Polyether 1 A monohydric polyether alcohol having a molecular weight of 2150 and prepared by the alkoxylation of n-bukanol using a mixture of ethylene oxide and propylene oxide at a weight ratio of EO:P0 = 4-1.
Polvether 2 A monofunctional ethylene ox;de polyether having a molecular weight of 1210 and prepared by the ethoxylation of 3-ethyl-3-hydroxymethyloxetane.
Polvisocyanates PolyisocYanate 1 15 g of Polyether 2 and 15 9 of hydroxyethylmorpholine were added with stirring at 50C to 250 g of a 70% solution of isophorone diisocyanate trimer in Solvesso 100 solvent. rhe mixture was heated to 100C and ma;ntained at that temperature for 2 hours. After coolin~ to 80C, the m;xture was catalyzed with 3 drops of tin octanoate, held for 30 minutes at ~his temperature and dissolved at a concentration of 60% in 61.6 g of methoxypropyl acetate. Finally, at 50C~ the product was alkylated with 10.15 g of dimethyl sulphate in 90 g of methoxypropyl acetate. After 1 hour the product was cooled to room temperature. A 50% solution of a water-dispersible cationic polyisocyanate resin having an NC0 content of 10~2%
was obtained.
PolYisocYanate 2 37.5 g of Polyether 2 were added with stirring at 50C to 300 g of a 50% solution of isophorone diisocyanate trimer in propylene glycol diacetate. The mixture was heated to 100C
and maintained at that temperature for 2 hours. After cooling to 80C, the mixture was catalyzed with 1 drop of tin octanoate dissolved in 3.4 g of propylene glycol diacetate. The mixture was kepk for 2 hours at this temperature and then cooled to Mo3851 2 ~

room temperature. A 55% solution of a water-dispersible polyisocyanate resin was obtained having an NC0 content of 13.0% and a YiSCosity of 370 mPa.s/23C.
PolyisocYanate 3 The preparation of Polyisocyanate 2 was repeated except that the amount of propylene glycol diacetate was reduced to provide a 60% solution having an NC0 content of 13.0% and a viscosity 780 mPa.s/23C.
PolyisocYanate 4 lo 132 9 of a polyethylene oxide alcohol having a molecular weight of 350 and prepared by the ethoxylation of methyl glycol were added with stirring to 750 9 of a hexamethylene diisocyanate trimer having an NC0 content of ~1.5%. The mixture was heated to 11~C and maintained for 2.5 hours at that temperature. After cooling, a colorless resin having an NC0 content of 16.7% was obtained.
PolYisocvanate 5 A hydrophilically modified polyisocyanate having an NC0 content of 18.4% and was prepared accord;ng to Example 1 of U.S, Patent 4,663,377 by reactiny a hexamethylene diisocyanate trimer having an NC0 content of of 21.6% with an ethoxylated n-butanol having a molecular weight 1145.
PreE3~cation of aq~ us dispersions ali of_cationically modified polYhYdroxYl comPounds Example 1 123.8 9 (0.472 moles) of 4,4'-diisocyanatodicyclohexyl-methane (technical mixture of isomers) were added ak 50C to 157.5 g ~0.157 moles) of polyester 1 and 18.74 g (0.157 moles) of N-methyldiethanolamine. The mixture was heated to 100C and that temperature was maintained for 2 hours. The mixture was then dissolved in 253 ml of ~ acetone and the NC0 content was determined. At 30C, 29.6 9 (0.281 moles) of diethanolalnine were added and the mixture was then stirred for 10 minutes and neutralized with 11.34 9 of (00126 moles) of DL-lactic acid.
After 5 minutes the product was dispersed with 775 ml of water Mo3851 2~3~8~

and the solvent was then distilled off under vacuum. A fine particle size dispersion was obtained which had a solids content of 30% and a pH of 5. The solids had an OH number of B7 and contained 41 meq. (milliequivalents) of ammonium nitrogen per 100 9.
ExamPle 2 115.1 9 (0.439 moles) of 4~4'-diisocyalnatodicyclohexyl-methane ~technical mixture of isomers) were added at 50C7 to 165.2 g (0.165 moles~ of polyester 1 and 19.7 g (0.165 moles) of N-methyldiethanolamine. The mixture was heated to 100C
and that temperature was rnainta;ned for 2 hours. The mixture was then dissolved in 253 ml of acetone and the NCO con~ent was determined. At 30~C, 17.9 9 (0.170 moles) of diethanolamine and 1.6 g (0.001 moles) of isophoronediamine were added and the mixture was then stirred for 10 minutes and neutralized with 12 g (0,104 moles) of 85% phosphoric acid. After 5 minutes the product was dispersed with 780 ml of water and the solvent was then distilled off under vacuum. A fine particle size dispersion was obtained which had a solids content of 31.7% and a pH of 4.7. The solids had an OH number of 57 and contained 44.8 meq, of ammonium nitrogen per 100 9.
ExamPle 3 115.1 9 (0.439 moles) of 4,4'-diisocyanatodicyclohexyl-methane (technical mixture of isomers) were added at 50QC to 2 165.2 g (0.165 moles) of polyester 1 and 19.7 9 (0.165 moles) of N-methyldiethanolamine. The mixture was heated to lOO~C and that temperature was maintained for 2 hours. The product was then dissolved in 253 ml of acetone and the NCO content was determined. At 30C, 19.2 g (0.183 moles) of diethanolamine were added and the mixture was then stirred for 10 minutes and neutralized with 13.4 9 (0.149 moles) of DL-lactic acid dissolved in 20 ml of water. After 5 minutes the product was dispersed with 760 ml of water and the solvent was then distilled off under vacuum. A fine particle size dispersion was obtained which had a solids content of 32.4% and a pH of Mo3851 - 18 ^
4.7. The solids had an OH number of 63 and contained 44.7 meq.
of ammonium nitrogen per 100 9.
Example 4 81.5 g ~0.311 moles) of 4,4'-diisocyanatodicyclohexyl-methane (technical mixture of isomers) were added at 50C to ~04.6 g (0.117 moles) of ?olyester 3 and 13.9 9 (0.117 moles) of N-methyldiethanolamine. The mixture was heated to 100C
and that temperature was maintained for 3 hours. The product was then dissolved in 253 ml of aceto"e and the NCO content o was determined. At 30C, 12.4 9 (0.118 moles) of diethanolamine were added and the mixture was then stirred for 10 minutes and neutralized with 9.5 g (0.105 moles) of DL-lactic acid dissolved in 20 ml of water. After 5 minutes, the product was dispersed with 750 ml of water and the solvent was then distilled off under vacuum. A fine particle size dispersion which had a solids content of 33.1% and a pH of 5.6.
The solids had an OH number of 41 and contained 32 meq. of ammonium nitrogen per 100 g.
Example 5 318.5 g o~ n-butyl acetate were charged and a nitrogen purge was applied to a 3-liter stirred flask having a flat blade paddle agitator, reflux condenser and thermometer as well as a gas inlet and outlet. The flask was then heated to an internal temperature of 110C. Subsequently, over the course of 6 hours, a monomer mixture of 344 g of 2-hydroxyethyl methacrylate, 600 g of n-butyl acrylate, 346 g of methyl methacrylate and lSO g of 2-(N-dimethylamino)ethyl methacrylate as well as an initiator solution of 50 g of isobutyronitrile in 763 g of n-butyl acetate were charged at a constant rate to the flask. The flask was then cooled to an internal temperature of 100C and the mixture reactivated w;th an init;ator solution of 10 g of t-butyl per-2-ethylhexanoate in 94 g of n-butyl acetate. Stirring was continued for a further 4 hours. The polymer solution was subsequently combined with a solution of 34 g of acetic acid in 3300 g of deionized water. Afterwards, Mo3851 2 ~

butyl acetate together with water was distilled off azeotropically, and the residue adjusted with fresh deionized water to a concentration of 37.0 wt%. The pH value of this dispersion was 5.~, the viscosity was 13,900 mPa.s (structurally viscous behavior) and the aver~ge particle diameter measured by laser correlation spectroscopy was 195 nm.
Films cast on glass plates, after drying at room temperature, were clear and elastic.
Coatinq Exam~
Comparative ExamDle 1 A 30% dispersion of an ionically modified hydroxyl group-contain;ng polyacrylate res;n (hydroxyl group content of the dispersion: 1.2%) was mixed with a hydrophobic, isocyanurate-group-containing polyisocyanate prepared from hexamethylene diisocyanate and haviny an NCO content of 19.8% using a disperser ~NCO/OH equivalent ratio = 0.25:1) and the resulting mixture was applied to a glass support. The pot life of the coating mixture as well as the mechanical and physical properties of the resulting coating are set forth in Table 1.
ComParative ExamPles 2 to 4 ComparatiYe Example 1 was repeated with the exception that the NCO/OH e~uivalent ratios for Comparison Examples 2, 3, and 4 were 0.5:1, 0.75:1 and 1:1, respectively. The pot lives of the coating mixtures as well as the mechanical and phys;cal properties of the resulting coatings are set forth in Table 1.
Comparative Examples 5 and 6 Comparative Example 1 was repeated with the except;on that the NCO/OH equivalent ratios for Comparison Examples 5 and 6 were 2:1 and 3:1, respectively. The pot lives of the coating mixtures as well as the mechanical and physical properties of the resulting coatings are set forth in Table 1.
Coa~g Examples 1 to 4 The OH group-containing cationic polyurethane of Example 3 was mixed with each of Polyisocyanates 1~ 2~ 4 and 5 at an NCO/OH equivalent ratio of 0.25:1 using a disperser, and the Mo3851 2~8~5 resulting mixtures were applied to glass supports to prepare coat~ngs. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 2.
Coatinq Examples 5 to 7 The cationic water-dilutable resins of Examples 3, 2 and 1 were mixed with Polyisocyanate 3 ~30% in water) at an NCO/OH
equivalent ratio of O.S:l using a disperser and the resulting mixtures were applied to glass supports to prepare coatings.
The pot lives oF the coating mixture and the mechanical and physical properties of the resulting coatings are set forth in Table 3.
Coatinq ExamDles 8 to 10 Coating Examples 5 to 7 were repeated with the exception that the NCO/OH equivalent ratio was 0.75:1. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 3.
Coatinq Examples 11 to 13 Coating Examples 5 to 7 were repeated with the exception that the NCO/OH equivalent ratio was O 1. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 3.
Coatinq Examples 14 and 15 The OH group-containing cationic polyurethanes of Examples 2 and 3 were each mixed with Polyisocyanate 3 ~30% in water) at an NCO/OH equivalent ratio of 2:1 using a disperser and the resulting mixtures were applied to glass supports to prepare coatings. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 3.
Coatin~LExamPles 16 and 17 Coating Examples 14 and 15 were repeated with the exception that the NCO/OH equivalent ratlo was 3:1. The pot lives of the coating mlxtures and the mechanical and physical properties of the resulting coatings are set Forth ln Table 3.
Mo3851 2~3~

~, Çoatinq ExamPles 18 and 19 Coating Examples 14 and 15 were repeated with the exception that the NCO/OH equivalent ratio was 4:1. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 3.
Coatinq ExamPles 20_and 21 The OH group-containing cationic polyurethanes of Examples 2 and 3 were each mixed with Polyisocyanate 4 530% in water) at an NCO/OH equ;valent ratio of 0.75:1 usint~ a disperser and the result;ng mixtures were applied to glass supports to prepare coatings. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 4.
Coatinq Examples 22 and 23 Coating Examples 20 and 21 ~ere repeated with the exception that the NCO/OH equivalent ratio was 1:1. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 4.
Coati~ Examples 24_and 25 Coa~ing Examples 20 and 21 were repeated with the except;on that the NCO~OH equivalent ratio was 2:1. The pot lives of the coating mixtures and the mechanical and physical properties of the result;ng coat;ngs are set forth in Table 4.
Ooat;nq Examples 26 and 27 Coating Examples 20 and 21 were repeated with thP
exception that the NCO/OH equ;valent rat;o was 3:1. The pot lives of the coat;ng mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 4.
Coat;ngLE_amples 28 and 29 Coating Examples 20 and 21 were repeated with the exception that the NCO/OH equivalent ratio was 4:1. The pot lives of the coating mixtures and the mechanical and physical properties of the resulting coatings are set forth in Table 4.

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- 2~ -Coat;nq ExamDle 30 410.1 g of the cationically ~odified polyhydroxyl compound of Example 3, 2.8 9 of a commercial emulsifier (~5% aqueous solution of "Emulsifier WN"7 manufacturer: Bayer QG, Leverkusenj and 12 9 of a 5% aqueous solution oF a commercial thickener ~Borchigel DP 40, manufacturer: Gebr. Borchers AG) were mixed to prepare a p;gmented coating composition. 85 g of a commercial ;ron oxide pigment (Bayferrox 130 BM, ~anufacturer: Bayer AG) were dispersed in the mixture. 86.8 9 o of Polyisocyanate 2 were added to this forlnulation (NCO/OH
equivalent ratio 1:1). The coating compdsition was homogenized with a dissolver and applied to two glass supports.
One coating was cured at room temperature, while thP other was cured at 120~C.
Room temDerature curinq 120 C curinq/45 minutes Sand dry = 4 hours ~hrough dry ~ 16 hours Pendulum hardness = 100 sec Standing time > 2 days Gloss 6V = 90 Pendulum hardness = 2C seconds Gloss 60 = 91 Coating Example 31 A formulation was prepared as in Example 30. To this formulation was added 183.6 9 of Polyisocyanate 2, 1.34 9 of trimethylolpropane as reactive diluent and 51 g of water (NCO~OH equivalent ratio 1:1). A coated was prepared as described in Example 30 and cured at room temperature.
Sand dry = 5.5 hours Through dry - 16 hours Standing time >2 days Pendulum hardness = 20 seconds Gloss 60~ ~ 89 Co~tinq ExamPle 32 lOO g of the OH group-containing cationic resin of Example 5 were homogeneously mixed with 41 g of Polyisocyanate 2 (NCO/OH equivalent ratlo - 1`1) using a dissolver. The mixture was applied to a glass support and the coating properties were determined after curing for one week at room temperature.

Mo3851 2~3~

Sand dry lQO min Pendulum hardness (7 d) 161 sec Water resistance ~7 d~ O
White Spirit resistanee (7 dJ O
s Acetone resistanc~ (7 d) 3 The mixture had a working time oF more than 16 h and was being applied without difficulty after 24 h.
Coatinq_ xamDle 33 100 g of the OH group-containing cationic resin of Example o 5 were homogeneously mixed with 82 g of Polyisocyanate 2 (NCO/OH equivalent ratio - 2:1~ using a dissolver. The mixture was applied to a glass support and the coating properties were determined after curing for one week at room temperature.
- Sand dry 100 min Pendulum hardness (7 d) 179 sec Water resistance (7 d) White Splrit resistance (7 d) O
Acetone resistance (7 d) 3 The mixture had a working tim~ of more than 16 h and was applied without difficulty after 24 h.
Coating ExamPle 34 100 9 of the OH group-containing cationic resin of Example 5 were homogeneously mixed with 123 g of Polyisocyanate 2 (NCO/OH equivalent ratio - 3:1) using a dissolver. The mixture was applied to a glass support and the coating properties were determined after curing for one week at room temperature.
Sand dry 140 min Pendulum hardness (7 d) 176 sec Water resistance (7 d) O
Whlte Spirit resistance (7 d) O
Acetone resistance (7 d) 3 The mixture had a working time of more than 16 h and was applied without difficulty a~ter 24 h.
.
3s Mo3851 2~$~

Although the inven~ion has been described in detail in the foregoing for the purpose of illustra~ion, it is to be understood that such detail is solely for that purpose and that variations can be made ~herein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Mo3851

Claims (6)

1. An aqueous two-component coating composition wherein the binder comprises a) a component which is dissolved and/or dispersed in water, has an average hydroxyl number of 15 to 200 mg KOH/g and comprises a1) a polyol component having a content of 8 to 450 milliequivalents, per 100 g of component a1) solids, of chemically incorporated ammonium groups, =N=+ and containing one or more polyaddition, polymerization and/or polycondensation resins which are water-dilutable, contain hydroxyl groups and have a molecular weight (Mn) of at least 500 and a2) up to 10 wt%, based on the weight of component a1), of one or more reactive diluents which are water-soluble, have a molecular weight (Mn) below 500 and contain at least one isocyanate-reactive group, and b) a polyisocyanate component having an NCO content of 5 to 25 wt% and containing one or polyisocyanates which are emulsified in the aqueous solution and/or dispersion of hydroxyl group-containing component a), wherein components a) and b) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups of component b) to isocyanate-reactive groups of component a) of 0.5:1 to 5:1.

2. The coating composition of Claim 1 wherein the average functionality of components a) and b) in the context of the isocyanate addition reaction is at least 2.5 reactive groups/mole.

3. The coating composition of Claim 1 wherein said reactive diluent comprises a polyhydric alcohol which has a molecular weight of 62 to 300 and may contain ether and/or ester groups.

4. The coating composition of Claim 2 wherein said reactive diluent comprises a polyhydric alcohol which has a Mo3851 molecular weight of 62 to 300 and may contain ether and/or ester groups.
4. The coating composition of Claim 1 said polyisocyanates comprise polyisocyanate derivatives which contain non-ionic hydrophilic and/or cationic groups and have an average NCO functionality of 2.2 to 3.5.

5. A process for the preparation of the coating composition of Claim 1 which comprises incorporating any auxiliaries and additives into the solution or dispersion of polymer component a) and subsequently emulsifying polyisocyanate component by into the solution or dispersion of polyol component a).

6. A water-resistant substrate coated with the coating composition of Claim 1.

Mo3851