AU599777B2 - Method for the preparation of electrophoretic enamel coating materials, which can be deposited at the cathode - Google Patents

Description

applicant or Australian attorney (Signature) "SA$DERCOCK, SMITH BEADL.E THE COMMISSIONER OF PATENTS This form must be accompanied by either a provisional specification (Form 9 and true copy) or by a complete specification (Form 10 and true copy).

Pas/f COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

Form FOR OFFICE USE

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Application Number: Class Int. Class

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S I Lodged: tj Complete Specification-Lodged: Accepted: Published: Priority: Tb13 du,-wnent contains tbt ano~daients Weade nuder Seto 49, MWd to Correct tar printing, Related Art: Name of Applicant: Address of Applicant: Actual Inventor: TO BE COMPLETED BY APPLICANT HERBERTS GESELLSCHAFT MIT BESCHRANKTER HAFTUNG Christbusch 25, D-5600, Wuppertal 2, Federal Republic of Germany WOLFGANG KANN HANS-PETER PATZSCHKE ARMIN GOEBEL Address for Service: SANDERCOCK, SMITH BEADLE 207 Riversdale Road, Box 410) Hawthorn, Victoria, 3122 Complete Specification for the invention entitled: METHOD FOR THE PREPARATION OF ELECTROPHORETIC ENAMEL COATING MATERIALS, WHICH CAN BE DEPOSITED AT THE CATHODE The following statement is a full description of this invention, including the best method of performing it known to me:tQ- Methods for the preparation from water-dilutable basic resins and cross linking agents of aqueous coating materials, which can be deposited at the cathode, are known. The are prepared, for example, according to the teachings of the European Auslegeschrift 12 463, the German Auslege- S schrift 3,122,641, the German Auslegeschrift 3,436,345 and the German Auslegeschrift 2,603,666 in organic, water-soluble solvents. After the individual resin solutions are mixed, the amino groups are neutralized completely or partly with organic monocarboxylic acid and the product is subsequently diluted with water. A common disadvantage of this method \o is the relatively high proportion of organic §olvents in the coating material prepared. It generally amounts to 3 to 10% by weight for a solids content of the electrophoresis bath of 15 to 20% by weight; that is, the organic solvents may constitute 50 to 60% by weight of the solids content.

S \5 Summary of Invention It is an object of the invention to provide aqueous dispersions of coating materials, especially of electrophoretic enamel coating materials, which can be deposited at the cathode and which have a low organic solvents content. The type and quantity of solvent selected can be controlled precisely, so that reproducible control of the basin becomes

I

possible.

Detailed Descrption of Invention Surprisingly, it was discovered that this objective can be accomplished, by following a procedure for the preparation of the aqueous coating 2S material, in which a mixture of basic resin and cross-linking agent 1. is prepared in resin solvents, which are not or only partially miscible with water, 4* 4 4 4 2. the resin solution is neutralized completely or partially with acids, 3. an emulsion or dispersion is produced by addition of water, 4. the water-insoluble organic solvent is distilled azeotropically from the emulsion or dispersion, preferably completely or almost complete- 4 ly, and optionally, defined amounts of water-soluble and/or water-insoluble solvents, which can be used, for example, for controlling the electrophoretic coatings, are added once again.

o For the preparation of the mixtures in accordance with the above Step 1, 1 /o solutions of vehicles and cross-linking agents, for example, in the same or different resin solvents or organic solvents that are immiscible or only partially miscible with water, are mixed together. Preferably, the solutions are those that are obtained during the preparation of vehicles or cross-linking agents. Therefore, those solvents, which are suitable I J for the preparation of the mixtures used pursuant to the invention, are preferably used for the preparation of vehicles and or cross linking agents.

The selection of solvents is determined essentially by two factors, namely S. 2 o the capacity to dissolve the resin and the ability to be removed practically completely in admixture with water, for example, as an azeotropic mixture.

The capacity to dissolve can be estimated using the 3-dimensional dissolving parameters of C.M. Hansen Paint Techn. 42(1970), 660). To achieve good solubility, the solvent (mixture) should have approximately the same solubility parameter as the synthetic resin. The following parameters, for example, are preferred for a basic resin, which can be deposited at the cathode: -2dispersion forces: 60 about 7.0 to dipole interactions: 6 p about 3 to hydrogen bonds: 6 H about 2 to 7 Examples of suitable solvents accordingly are those, which i 1. have a molecular weight of 70 to 250 and a boiling point of to 270 0

C,

2. on the basis of their solubility properties, homogeneously dissolve the resin prepared (vehicle and/or cross linking agent), i if necessary, at an elevated temperature, S0 3. can be distilled practically completely from water and, especially with water, form an azeotrope with a boiling point, which in each case is below that of water and 4. are not very miscible with cold water or form two phases with water.

SPreferably, water-insoluble organic solvents are used, which form a ,l homogeneous resin solution (vehicle or cross linking agent) with a I solids content of 20 to 60% by weight.

St 1 Especially suitable are solvents with a molecular weight of 70 to 170 j and a boiling point of 80 to 150 0 C. The azeotropic mixture advisably boils between 550 and 100*C and especially between 70° and 98C at atmospheric pressure. A rather large lowering of the boiling point is obtained, if the boiling point of the solvent is close to 100 0 C. Soljvents, the concentration of which exceeds that of water in the azeotropic mixture, are removed more rapidly from the reaction vessels and are 2 -J therefore particularly suitable.

The various isomers of the following solvents, which are not very soluble in water, are examples of suitable solvents: -3vr-'

I

1. Aliphatic hydrocarbons with a molecular weight of 70 to 170 and a boiling point of 350 to 2200C, such as cyclohexane, n-hexane, isooctane, n-nonane, decane, etc.

2. Aromatic hydrocarbons with a molecular weight of 75 to 120 and a boiling point of 800 to 160°C, such as benzene, toluene, xylene, ethylbenzene, cumene, etc.

3. Alcohols with a molecular weight of 85 to 160 and a boiling point of 130* to 220°C, such as isobutanol, n-amyl alcohol, isoamyl alcohol, t-amyl alcohol, 1-hexanol, 2-ethylhexanol, cyclohexanol, etc.

o 4. Esters with a molecular weight of 90 to 150 and a boiling point of to 150 0 C, such as n-propyl acetate, isopropyl propionate, t-butyl acetate, pentyl acetate, hexyl acetate, cyclohexyl acetate, etc.

Ethers with a molecular weight of 74 to 150 and a boiling point of Itoo o 39* to 150 0 C, such as methyl n-propyl ether, ethyl n-propyl ether, diisopropyl ether, methyl isobutyl ether, diisobutyl ether, di-nbutyl ether, diethylene glycol di-t-butyl ether, etc.

6. Ketones with a molecular weight of 80 to 150 and a boiling pint of 800 to 170 0 C, such as methyl n-propyl ketone, methyl isopropyl ketone, ethyl isopropyl ketone, diisopropyl ketone, methyl isobutyl ,o ketone, ethyl n-butyl ketone, di-isobutyl ketone, methyl isoamyl ketone, cyclohexane, etc.

I 7. Halogenated hydrocarbons with a molecular weight of 115 to 170 and a boiling point of 60 to 150 0 C, such as chloroform, carbon tetrachloride, d.ichloroethane, trichloroethane, trichloroethylene, tetra- I 2 J chloroethane, tetrachloroethylene, chlorobenzene, etc.

Basically, the solvents can be used individually or, for solubility reasons, in admixtures. Generally, aliphatic hydrocarbons are added only as diluents, because they do not have adequate solution properties for the resins (vehicle and cross linking agent).

So that the solvents, which are distilled off, can be reused without problems, the use of only one solvent is preferred for the basic resin and the cross linking agent.

-4- I I I

__J

Solvents with active hydrogens, such as alcohols, generally cannot be used to dissolve or prepare vehicles and cross linking agents, because they lead to undesirable side reactions. When esters are used, it should be kept in mind that they transamidate with amines and can be saponified by water. By these means, basic amino groups of the basic resin, which are important for the water solubility, are lost or acids, which lead to interference with the electrical properties and, associated therewith, to poor surface qualities, accumulate in the vehicle.

Preferred solvents are ethers such as di-n-butyl ether, ketones such as y o methyl isobutyl ketone and especially aromatic hydrocarbons such as xylene.

o o o It is adequate if the basic resin or the cross-linking agent is soluble in the solvent only at elevated temperatures. For example, the basic resins generally dissolve in aromatic hydrocarbons only at an elevated temperature and solidify on cooling.

0 o 0 The basic vehicle is neutralized with acids completely or partially in the solution in the organic solvent preferably after it is mixed with the solution of the cross linking agent. Typical examples of acids are formic acid, lactic acid, acetic acid, propionic acid, citric acid, o malonic acid, acrylic acid, phosphoric acid or alkylphosphoric acid.

Monobasic, low molecular weight organic carboxylic acids are preferred.

The neutralization is carried out to achieve dispersibility of the basic resins. Sufficient acid is therefore added, so that a stable emulsion of the basic resin is formed in the presence of the cross linking agent.

24 An excess of acid, that is, a degree of neutralization of more than 100%, is advisably avoided. An MEQ value (milliequivalents of acid per 100 g of solid resin) of 15 to 50 is preferred. The MEQ value should be as low as possible, so that the highest possible deposition equivalent jZ .4 is achieved during the later deposition of the coating material.

The neutralization is carried out especially after the solutions of basic resin and cross linking agent are mixed.

A dispersion with a solids content of 15 to 60% by weight is subsequent- SJf ly prepared from the neutralized mixture of the solutions of basic resin and cross linking agent by the gradual, slow addition of fully deionized water., A system, which can be distilled well, is selected within the above values for MEQ and solids content. The upper limit of the MEQ value is selected so that the dispersion does not become too thick, the S o lower limit, so that solubility difficulties do not arise on further i dilution with water. The upper limit of the solids content is selected so that the dispersion formed is once again not too thick, as other'wise there is danger of scorching at the heated walls. The lower limit is selected so as to avoid an excessive tendency to foam during distilla- I tion. It has turned out that the preferred range for the MEQ values is to 30; preferred values for the solids content are between 25 and I 40% by weight.

The quantitative ratio of organic solvent to water advisably is selected so that the organic solvent can be removed as completely as possible or j o so that an azeotropic mixture can be formed. During the distillation that must be carried out, a mixture of constant composition comes over at first. This mixture corresponds to the azeotrope minimum, because it has the lowest boiling point. If sufficient water is present or if water is present in excess relative to the composition of the solventwater azeotrope, the organic solvent is removed from the batch. Advisably, the distillation is carried out in a cyclic system, that is, provisions are made to ensure that the water, which is distilled off, is separated from the organic solvent and allowed to flow back continuously into the reaction vessel. If the relative density of the solvent is 3 0 less than 1, the water is returned to the cycle from the lower phase, if the relative density is above 1, the water is returned from the upper -6- 1 O I^ Cl~iCnrpu~*r.r L I- 1'Yphase. The distillation is continued until organic solvent no longer separates.

If there is danger of saponification or of an unwanted reaction between the basic resin and the cross linking agent, the process can also be J carried out under vacuum at lower temperatures, such as 40°C. In so doing, it should be noted the conditions for the formation of an azeotropic mixture may change due to the fact that the partial vapor pressures vary differently with pressure.

The distillation cycle can also be carried out in the form of a steam distillation. The carrier steam ensures a particularly vigorous mixing o of the material to be distilled and, with that, drives the last traces ;i of solvent particularly thoroughly from the reaction mixture. It prevents foaming, which frequently is bothersome, and, at the same time, acts as a protective gas.

j Preferably, the organic solvent, which is immiscible or only partially miscible with water, is distilled off completely or at least almost completely during the azeotropic distillation. The possibility then arises of adjusting the solvent content subsequently, as desired, by the addition of certain selected solvents or solvent amounts.

I o As basic vehicles, the amine epoxide resins, which contain primary, secondary and tertiary amino groups that are known or customary in this field of technology and which have an amine number of 30 to 150 (mg KOH per g of solid resin) or 0.5 to 2.7 milliequivalents of cationic groups per gram of solid resin and a hydroxyl number of 50 to 500 or 0.9 to 8.9 t f milliequivalents of hydroxyl groups per gram of solid resin, are preferred. The upper limit of the amine number preferably is 120 and especially 100 and the lower limit preferably is 45 and especially 70. If the amine number is too low, the solubility is too low or an acid pH develops in the electrophoresis bath due to an excessive degree of neuo tralization. If the amine number is too high, the adhesion of the de- -7- 1 r -v **rw 'i a 1 posited film is poor or a choppy surface is formed with layers of different thickness. The hydroxyl groups present in the molecule are essential for the cross linking reactions that take place during baking.

There are at least 2 and preferably at least 4 hydroxyl groups per mole- J cule. An upper limit to the hydroxyl number of 400 and especially of 300 is preferred. The lower limit of the hydroxyl number preferably is 100 and especially 150. If the hydroxyl number is too low, films, which are still soluble in organic solvents such as acetone or methyl ethyl ketone, are formed during the cross linking reaction. On the other o hand, if the hydroxyl number is too high, the film becomes too brittle and possibly also remains too hydrophilic.

The chemical structure of the aminoepoxide resin and its properties can be varied within wide limits, for example, by o00 0 the choice of epoxide resin and amine, 0 the number of amino and hydroxyl groups, the molecular weight and molecular ratio of basic resin and cross linker 4 the ratio of hard to soft molecule segments..

4 4 Resins, which contain epoxide groups, preferably terminal 1,2-epoxide 2 o groups, are polyglycidyl ethers, polyglycidyl amines or polyhydrocarbons containing epoxide groups, with an average molecular weight of 140 4,000 and an epoxide equivalent weight of 70 to 2,600. There may be to 8 and preferably 1.8 to 3 epoxide groups per molecule. Suitable polyepoxide resins are, for example, compounds having the idealized J formula

O-CH

2 ^CH CH 2 -8-

I.;A

7- in which D represents a multifunctional, preferably difunctional alcohol, phenol, amine or corresponding heterocyclic compounds and n represents a number from 2 to 6, preferably 2.

Especially preferred is the use of polyglycidyl ethers, which contain about two 1,2-epoxide molecule groups per molecule, with an average molecular weight of about 300 to 1,500 and an epoxide equivalent weight of about 170 to 1,000 and especially of 180 to 500.

Oo They are prepared, for example, by the reaction of epihalogenhydrins or methylepihalogenhydrins, preferably epichlorohydrin with dihydric phenols. In this reaction, it is possible to adjust the molecular weight by the choice of the molar ratios and by the addition of suitable basic catalysts, such as ammonium and phosphonium salts. Formula 2 includes resins of, for example, the following formula S^o:o CH2-CH-CH2-0-R". -CH2-CH-CH2-0-R -C C-CH2 0 OH 0 in which o 0 to 2 and R" preferably is a bisphenol group of the following structure: H, OH -R wherein Y -CH 2

-C(CH

3 2

-SO

2 -C(CC1 3 2 The -9-

V

i I -r;rcoaromatic rings may have halogen or alkyl substituents.

Typical dihydric phenols are hydroquinone, resorcinol, naphthalene, p,p'-dihydroxydiphenylpropane, p,p'-dihydroxybenzophenone, p, p'-dihydroxydiphenylmethane, p,p'-dihydroxydiphenylethane, p,p'-dihydroxy-di-t-butyl-propane or bis(2-hydroxynaphthyl)methane.

Technical mixtures, such as p,p'-dihydroxydiphenylpropane, especially the isomers containing small amounts of the or the 4,2'isomers are preferred. The epoxide resins described may also be completely or partially hydrogenated like, for example, 1,4'-bis(-2,3'o epoxypropoxy)cyclohexane or used in mixtures, the components of which have different structures or molecular weights. They may also be modii fied by reactions with polyalcohols, preferably long-chain diols, such I as 1,4-butanediol or 1,6-hexanediol in the presence of suitable catai 'lysts, such as the BF 3 complexes.

/N Polyglycidyl ethers of multihydric alcohols are also suitable. They are characterized by the following general formula, which is a special case of the above general Formula

CH

2 -CH-CH-O-(CHR) CH 2

CH--CH

2- 0 0 in which R hydrogen or a low molecular weight alkyl group optionally .o having different substituents, preferably -CH 3 and p 2 to 15. Typical examples of this are the reaction products of epichlorohydrin and ethylene glycol, 1,3-propylene glycol,1,4-butanediol, 2-ethyl-1,6-hexanediol, and also compounds such as 1,2,6-hexanetriol or bis-(4-hydroxycyclohexyl)-2,2-propane. Suitable polyglycidyl ethers may SJ, also correspond to the formula S C CH 2 -CH2- 0-(CHR) -CH H-CH2 2 2 0(CHR)rO CH 2

HCH

2 q 0 which also is a special case of the general Formula and in which R has the same meaning as above and r 2 to 6 and q 1 to 20. Typical examples of this are the reaction products of epichlorohydrin and ethylr 4 ene glycol, 1,2-propylene glycol or 1,2-butylene glycol and the polyethers obtained therefrom such as polyethyleneglycols, polypropyleneglycols or polybutyleneglycols with different molecular weights.

Formula also covers heterocyclic polyepoxide compounds, which may likewise by used, such as 1,3-diglycidyl-5,5-dimethylhydantoin or tri- 0 glycidyl isocyanurate. Polyglycidyl ethers of phenolic novolak resins constitute a different class of suitable polyepoxides. They are con- I densed by the action of formaldehyde on phenols under acidic conditions S at a molar ratio of 1 0.5 to 0.8 and subsequently reacted with epichlorohydrin. They have an epoxide equivalent weight of 150 to 300 and I preferably of 170 to 210 and contain about 2 to 4 glycidyl groups per molecule. It should be taken into consideration that resins of this system generally have a higher average molecular weight, for example, between 474 and 3,000, As polyepoxides, it is also possible to use polyglycidyl ethers of poly- SLo amines such as N,N-diglycidylaniline or N,N,N',N'-tetraglycidyl-4,4'diaminodiphenylmethane or epoxidized aminomethyldiphenyloxides. Polyglycidyl ethers, which do not contain any additional amino groups, are preferred for the method of the invention.

Epoxide resins are also understood to include aliphatic or cycloali- Sphatic hydrocarbons, which have no ester groups, contain epoxide groups -11- 4 -it. V WV: 0*_ and are prepared by epoxidizing with per acids. Examples are epoxidized polybutadiene oils, vinylcyclohexene dioxide or bis(2,3-epoxycyclopentyl)ether.

Amino groups are advisably introduced by addition of NH-reactive com- J pounds to the epoxide groups. The reaction therefore takes place approximately at the equivalence ratio, optionally with a small excess of epoxide groups to compensate for the consumption by side reactions or to ensure complete incorporation of the amines. Primary amines react with two epoxide groups and, in so doing, lead to chain elongation. The D reaction of the amines commences already at room temperature and generl ally is exothermic. For stability reasons, it should be made certain that no epoxide groups are present any more at the end of the reaction i by increasing the temperature of the reaction to 50° to 150 0 C and pre- Sferably to 600 to 85 0 C. All the amines in the mixture can be reacted simultaneously with the epoxide groups or the reaction can be carried jout in stepwise fashion, that is, one or several basic epoxide groupcontaining intermediates can be synthesized in different se ances.

j Amines of the following groups are advisably selected for the reaction I with the epoxide resins: ao 1. Mono- or di-hydroxyalkylamines of the general formula: H-N-R -OH

-OH)

2

R

I wherein -R -H or an alkyl group, preferably methyl or ethyl, and an alkylene group with 2 to 8 carbon atori, pieferably ethylene or propylene.

-12f Amines of this type improve the reactivity of the basic resin by means of their preferred primary hydroxyl groups. Typical examples of this are aminoethanol, N-methyl-aminoethanol, N-ethyl-aminoethanol, diethanolamine, aminoisopropanol, N-methyl-aminoisopropanol, N-methyl-amino-npropanol, N-ethyl-aminoisopropanol, diisopropanolamine, etc.

2. N,N-dialkyl-aminoalkylamine of the general formula H-N-R'-NR HN-(R' -N %Rl@ 2

R

wherein -R H or R" ai alkylene group with 2 to 8 carbon atoms, preferably ethylene or propylene an alkyl group, preferably methyl or ethyl.

Because of the dialkylamino group, amines of this type improve the basicity and thus the solubility of the basic resin. Suitable examples of this type of amine are N-dimethylaminoethylamine, N.-diethyl-N'-methylaminopropylamine, diethylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine, dimethylaminoneopentylamine, etc.

3. Long-chain secondary diamines, which elongate the chain, are used for elastification and have the general formula .:L0 H-N-RO -N-H R R wherein -13- A- -4_ -R is an alkyl group or a hydroxyalkyl group with 1 to 18 carbon atoms and is an alkylene group or alkyleneoxy group with 2 to 12 carbon atoms and preferably 4 to 8 carbon atoms.

J The secondary diamine can also be synthesized by the reaction of the appropriate primary alkylenediamine with glycidyl ethers or glycidyl esters. Typical examples are N,N'-dialkyl-diaminoalkane such as N,N'onoo dimethyl-diamino-hexane or preferably the product of the reaction beo. tween hexanediamine and 2 moles of Cardura E, the glycidyl ester of C oo Versatic acid. The chain can be elongated and elasticized with formation of urea groups by reacting 2 molecules of the secondary diamines described above with 1 mole of diisocyanate. The secondary diamine may S,,S also have an asymmetric structure, in which case the 2 substituents are not the same. For example, the diamine may be a reaction product of Nhydroxyethyl-ethylenediamine or N-dimethylaminoethyl-propylenediamine o with Cardura E.

To modify the epoxide resins further, it is also possible to use primary 4o4 monoalkylamines and/or preferably secondary dialkylamines, such as diethylamine, n-octylamine, N-methyl-N-ethylhexylamine, didodecylamine or o methoxypropylamine.

jo If aminoepoxide resins are linked together with diisocyanates or isocyanate group-containing prepolymers, there is a molecular enlargement with formation of urethane groups. If, prior to being linked together, epoxide resins with OH groups are reacted with amines, there is an increase J in the epoxide resin functionality, which must be taken into considerai tion in the further reaction to avoid gelation.

The organic polyisocyanates have an average molecular weight of 112 to 5,000 and preferably of 140 to 1,000 and, advisably, an average isocynate functionality of 2 to 8. Polyisocyanates are, for example, -14- 4 compounds of the idealized formula E(N=C=O)s in which E represents an aromatic hydrocarbon group with a total of 6 to carbon atoms that is optionally substituted with one or several alkyl groups or has methylene bridges, an aliphatic hydrocarbon group with 2 to 18 and preferably 6 to 10 carbon atoms, a cyclic hydrocarbon group with 6 to 15 carbon atoms or a heterocyclic ring and 1 0 s represents a number frown 2 to 4 and preferably from 2 to 3.

Typical examples of such polyisocyanates are propylene diisocyanate, ethylene diisocyanate, di methyl ethylene diisocyanate, trimethylene diisocyanate, tetramethylene di isocyanate, pentamethylene dlisocyanate, kexamethylene diisocyanate, trimethylhexane dilsocyanate, 1, 12-dodecane i. dilsocyanate, 1,18-octadecane diisocyanate, cyclopentane dilsocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, as well as mixtures of these isomers, methyl'cyclohexane diisocyanate, m- or p-tetramethylxylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, perhydro-2,4'- and/or iphenyl methane diisoo cyanate, 1,3- and 1,4-phenylene dlisocyanate, 2.4- and 2,6-toluylene diisocyanate, as well as any mixtures of these isomers, xylylene diisocyaiiate, diphenylmethane-2,4'- and/or -4,4'-diisocyanate, and/or 3, 4-dilisocyanato-4-methyldi phenylmethane, bisphenylene dii socyanate, 1. 5-naphthylene dilsocyanate, 4,4',4"-trlphenylmethene tri isocyanate, S2, 2' 4, 4'-tetral socyanato-5, 5'-di methyl tri phenyl methane, diphenyl tetraisocyanate or naphthyl tetra isocyanate. Mixed aliphatic and aromatic compounds are also suitable. Especially preferred are dilsocyanates.

which are produced on an industrial scale, such as toluylene diisocyanate, hexane diisocyanatc. isophorone diisocyanate or dicyclohexylmethane diisocyanate.

Aside from the low molecular weight polyisocyanates mentioned by way of example, it is also possible to use higher molecular weight isocyanate polymers based on urethane-free polyisocyanates and higher molecular weight polyhydroxy compounds as polyisocyanate components. Both of these are known in polyurethane chemistry. Advisably n 1 moles of the diisocyanates described above are reacted for this purpose with n moles of a compound, which is difunctional with respect to isocyanate, at temperatures advisably of 500 to 120 0 C in the melt or in the presence of S/ inert solvents, which may be low molecular weight as well as high molecular weight with a molecular weight of 62 to 5,000 and preferably of to 1,000. If an excess of diisocyanate is used, the excess diisocyanate must be distilled off. Low molecular weight dialcohols are advisably defined as the different isomers of linear, branched and cyclic hydro- /J4 carbon compounds with 2 to 20 carbon atoms and two secondary and/or primary hydroxyl groups. Typical examples of this are 1,4-butanediol, 1,6-hexanediol, trimethylhexanediol, bis(hydroxymethyl)cyclohexane, neopentyl glycol, neopentyl glycol hydroxypivalate, N-methyl-diethanolamine or bis-ethoxylated bisphenol A. Suitable higher molecular weight 2 0 polyhydroxy compounds are the polyester diols, polycaprolactone diols, polycaprolactam diols and polyglycol ether diols, which are known from polyurethane chemistry. It is also possible to use long-chain primary I and secondary diamines, such as 1,6-hexanediamine, adducts of 2 moles of glycidyl ether or glycidyl ester and hexane diamine, N,N'-cyanoethyla J ethylenediamine or bis-N,N'-cyanoethylpolyoxypropylenediamine.

Diiocyanates are preferably used for the reaction of the invention. Polydiisocyanates of high functionality, similar to those used later on in the specifications of the cross linking agent, may also be used, if they are defunctionalized by suitable monofunctional compounds to a diisocyanate. Monoalcohols or monoamines of different chain length are used for this purpose, such as n-butanol, isodecanol or di(ethylhexyl)amine or also the compounds described later on as capping agents. Depending on the nature of the group, the organic groups, which are introduced, either are retained as elasticizing agents or, due splitting off of the protective group, lead to a self cross linking vehicle.

The above-described, amino group-containing synthetic resins vehicles I which,are cross linked by extraneous agents, are used together with cross linking agents, which are referred to in the following as component In accordance with the st ate of the art, 50 to 95% by weight of synthetic resin vehicle and 50 to 5% by weight of cross linking agent are used, based on the solid resin. The preferred ratio of mixing o components and lies between 90 to 10 and 60 to 40 and is determined empirically from optimally attainable application properties at the given stoving temperature. As cross linking agents, blocked polyisocyanates or resins with transesterifiable ester groups are used. The cross linking agent advisably has an average molecular weight (Mn) of S/ about 250 to 5,000 and especially of 500 to 3,000. Components and can be mixed in the cold or upon being heated and may optionally be precondensed, especially at elevated temperatures. For such a precondensation, the components and react to some extent with one l another without losing the ability to be cured by the action of heat or o the property of being made water-soluble by protonization with acids.

As component B, completely blocked polyisocyanates are preferably used, which optionally contain conventional catalysts. For special purposes, it may advantageous to dilute the blocked polyisocyanates with suitable formaldehyde condensation resins or transesterifiable polyesters.

S4 The polyisocyanates and/or isocyanate group-containing prepolymers, used as cross linking agents, are the same as those already described earlier. They differ, however, owing to the fact that, on the average, they make available for the cross linking reaction more than two reactive isocyanate groups per molecules, which are blocked by protective 2 o groups. For example, mixtures of trifunctional and/or higher functional polyisocyanates with difunctional isocyanate group-containing prepoly- -17-

-I

mers can be used.

The equivalent ratio of primary or secondary amino groups and hydroxyl groups of component A to the blocked isocyanate groups of component B falls within the range of 1 0.1 to 1.5 and preferably of 1 0.7 to J 1.2 and especially of 1 1.

Polyisocyanates are capped or blocked, if they do not react with the active hydrogen atoms of the base resin (hydroxyl groups or amine hydro- Sgen groups) at normal storage temperature. If, however, the coated object is heated to a temperature high enough to terminate the capping S. of the isocynate, the coating is cross linked or cured into a protective, insoluble film. As capped isocyanates, any isocyanates may be used, the isocyanate groups of which have been reacted with a compound, which reacts with active hydrogen at an elevated temperature, usually between about 90* and 200°C. Blocked polyisocyanates are prepared, for /f example, by reacting a multifunctional isocyanate with at least a stochiometric amount of a monofunctional compound containing active hydrogen (Zeretwinoff reaction), advisably at temperatures of 50° to If necessary, conventional catalysts, for example, basic catalysts such as tertiary amines or small amounts of tin salts, such as tin dibutyl .o dilaurate, can be added. The isocyanate group is protected in this manner at :oom temperature against reaction with water or alcohols. It splits off once again at stoving temperatures of less than 210 0 C, preferably of less than 190°C and especially of less than 180°C and, on the other hand, of greater than 110 0 C, preferably of greater than 140°C and 3.2 especially of greater than 150 0 C, so that the isocyanate group, which becomes free, can react with the basic resin.

As polyisocyanates, the so-called "lacquer polyisocyanates", which can be prepared from known diisocyanates, are particularly suitable. For example, tris-(6-isocyanatohexyl)-biuret is formed from hexane diiso- So cyanate and water. The trimerization of hexane diisocyanate results in the formation of tris-(6-isocyanatohexyl) isocyanurate, possibly in -18-

I

admixture with its higher homologues, as well as additional polyisocyanates, which have isocyanurate groups and are synthesized from isophorone diisocyanates, diisocyanatotoluene and hexamethylene diisocyanate. Polyisocyanates, which have urethane groups, can also be used j' very well. They are obtained, for example, by the reaction of excess amounts of 2,4-diisocyanatotoluene with simple multihydric alcohols with a molecular weight of 63 to 300, especially trimethylolpropane, optionally after distillative removal of the unreacted excess diisocyanate.

Blocked triisocyanates or blocked higher molecular weight reaction prodo /o ucts of triisocyanates with dialcohols are especially preferred. This reaction is carried out at approximately the following molar ratios: triisocyanate diol protective group 3y (y 1) (y y o o being 1 to 6 and preferably 2 to 3. Compounds, which block the isocyao nates, contain only a single amine, amide, imide, lactam, thio or hydroxyl group. In general, volatile, active hydrogen-containing como 0 pounds with a low molecular weight of preferably not more than 300 and especially of not more than 200 are used. For example, aliphatic or 0 6 o a o o cycloaliphatic alcohols, such as n-butanol, 2-ethylhexanol, cyclohexanol, phenols, t-butylphenols, dialkylaminoalcohols such as dimethyl- 2 o aminoethanol, oximes such as methyl ethyl ketoxime, lactams such as ecaprolactam or 2-pyrollidone, imides such as phthalimide or N-hydroxymaleimide, hydroxyalkyl esters, malonates or acetoacetates, have proven their value. However, 0-hydroxyglycols or 0-hydroxyglycol ethers and glycol amides are also recommended. Oximes and lactones are of partic- S A ular interest as capping agents, because the polyisocyanates, capped with these, react at relatively low temperatures. More than one type of protective group, preferably ones with different reactivity, can also be used for blocking.

The blocked polyisocyanate (component B) is generally emulsified stably 3 into the aqueous dispersion by the neutralized aminoepoxide resin. If it is present in relatively high amounts, it is, however, useful to incorporate basic nitrogen atoms into the blocked polyisocyanate. This is accomplished, for example, by the reaction of the isocyanates with -19- I9if .t polyalcohols containing tertiary amino groups, such as N-methyldiethanolamine, triethanolamine or polyamines having tertiary amino groups, such as 3-(methyl)-3-(2-aminoethyl)-aminopropylamine. In this case, there is an increase in molecular weight. The isocyanate group can also Jf be blocked with monofunctional compounds with tertiary amino groups.

For this purpose, compounds such as N-dialkyl-aminoalcohols, for example, dimethylaminoethanol or N,N-dialkyl-alkylenediamines, for example, dimethylaminopropylamine or N,N-diethyl-N'-methyl-l,3-ethanediamine can be used.

/o The cross linking of the aminoepoxide resins with blocked polyisocyanates may be accelerated by addition of 0.01 to 2% by weight and especially 0.5% to 1% by weight, based on the solid resin, of catalysts, such as strongly basic tertiary amines and/or active metal compounds. A special, sometimes synergistic effect is achieved by the combination of the basic medium of the deposited resins and the metal salts of bismuth, lead, cobalt, iron, antimony and/or tin-II and tin-IV compounds. Especially preferred are catalysts such as iron-III acetylacetonate, zinc acetylacetonate, tin dibutyl dilaurate, di-n-butyl tin oxide, dibutyl din dioctyl maleate, tin octoate, tin oleate, tetrabutyl titanate and/or a o cobalt 2-ethylhexanoate. Preferred are catalysts, which are only conditionally soluble in the EC bath and are deposited electrophoretically in finely dispersed form with the enamel and can be distributed uniformly on stoving without flow disorders. If there are unsaturated double bonds in the resin, the usual metal siccatives may also ba added, optionally in emulsion form, to improve the curing properties.

Resins with transesterifiable ester groups contain terminal or lateral, Sesterified carboxyl groups, which are largely stable in the neutral, Saqleous medium, but react in the basic medium of the deposited film at temperatures above about 140°C with one or several hydroxy- and/or 3 o amino-group-containing synthetic resin vehicles (Component In so doing, the transesterifiable ester groups esterify or amidate the hydroxy or primary amino groups of the synthetic resin vehicle the o.TL, more volatile "alcoholic protective" group being split off. Essentially all terminal or lateral carboxyl groups should be esterified with alcohol, which is volatile under stoving conditions. To avoid migration of polyester to the anode, care should be taken to ensure that the polyes- S ter has an acid number of less than 20, preferably less than 10 and especially less than 3.

The reactivity of the esters is increased by a suitable chemical structure, for example, by increasing the electrophilic activity of the carboxyl group or by a negative inductive effect on the alcohol group.

o Primary, secondary and tertiary carboxyl groups are capable of transesterifying. Primary carboxyl groups are preferred because of their highi er reactivity.

The transesterification is supported by the volatility of the lower molecular weight linear or branched primary monoalcohols or by 1,2-glycols, which are optionally substituted by ether or ester groups. In the literature, a series of ester group-containing cross linking agents are described, which are used for the transesterification with OH groups and/or the transamidation with NH 2 groups.

For example, a carboxyl group-containing polyester is described as cross Z o linking agent, the carboxyl groups of which are blocked by optionally substituted 1,2-glycols with formation of a-hydroxy compounds:

R

Resi CO-CH2-CH-R' 0 OH n the 1,2-glycols used are advisably substituted by saturated or unsatu- -21- 4a -1: L S rated alkyl, ether, ester or amide groups, that is, R' represents R, -CH2OH, -CH 2

-CH

2 COOR, -CH 2 HNCOR, in which n is at least 2 and preferably 3 to 10. R is a linear or branched alkyl group with 1 to carbon atoms. Such cross linking agents are described in the European Auslegeschrift 012 463 and the German Auslegeschrift 3,103,642, for example, as the reaction product of trimellitic anhydride with CARDURA

E

R

the glycidyl ester of VERSATIC ACID(R) Other cross linking agents are prepared by the transesterification of alkyl dicarboxylates with polyalcohols. Particularly reactive have S/a proven to be resins of the following general formula: I Resirt -C-X-C-0-R f II II I\ 0 0 n

I,

wherein n is at least 2 and preferably has a value of 3 to 10, X repre- II sents a -CH 2

-CH

2

-CH

2 or -CH=CH- group and R a linear or branched alkyl group with 1 to 8 and preferably 1 or 2 carbon atoms. In the /J simplest case, this cross linking agent is a reaction product of trij methylolpropane and dimethyl malonate, as described in the European Auslegeschrift 082 291.

Other cross linking agents, capable of transesterifying, are obtained by the Michael addition of alkyl acetoacetate or dialkyl malonate to the 0 o resin with double bonds, which are activated by CO groups: -22- R 's Resin-. -CH2-CH2-CH 0 COOR n in which R" represents -COOR, -CO-R or -CN and n has a value of least 2 and preferably of 3 to 10. In the simples case, these resins are prepared from .f butanediol diacrylate and an ester of acetoacetic acid or from the toluylene diisocyanate/hydroxyalkyl (meth)acrylate adduct and dialkyl malonate, as described in the German Auslegeschrift 3,315,469. The Michael addition can be carried out stochiometrically or also with excess double S. bonds.

i /o The cross linking of Components and may optionally be accelerated by addition of strongly basic tertiary amines and/or active metal compounds. A special, sometimes synergistic effect is achieved by the combination of the basic medium of the deposited basic amino resin and the metal catalysts.

Generally, a higher catalyst content is required for the catalysis of the transesterification procedure than for the transesterification of SComponent with the blocked polyisocyanate. On the whole, the content of such catalysts falls with the range of about 0.5% to 5% by weight of metal, based on the total weight of Components and Iz o Those skilled in the art can easily ascertain the exact quantitative ratio, taking into consideration the state of the art. As catalysts, advisably metal oxides, metal salts or metal complexes of univalent or multivalent metals are used. After salt formation with, for example, 2ethylhexanoic acid or napthenic acid, they are generally dissolved in S( aliphatic and aromatic hydrocarbons. These solutions are emulsified -23into the electrophoresis bath. A different possible method is to form the complex of the metals with acetylacetonate, dicyclopentadiene, 8hydroxyquinoline, 4-methylcatechol and/or 2,5-dimercapto-1,2,4-thiodiazol. Examples of suitable catalysts are antimony trioxide, tri-n-butyl Stin oxide, tin dibutyl dilaurate, lead octoate, iron-Ill acetylacetonate or the reaction product of zinc oxide and 8-hydroxyquinoline. The metal catalysts may also be dispersed in in finely distributed form as pigments such as lead silicate. Water-dilutable metal salts are also suitable as transesterification catalysts, if the metal is deposited as a o compound or complex in finely distributed form with the enamel. Preferred are catalysts, which are not very soluble in the ET bath and which, after electrophoretic deposition, are distributed uniformly in the deposited film during stoving.

Stable, practically solvent-free, aqueous vehicle S dispersions can be prepared by azeotropic distillation of the water-insoluble solvent with water according to the method of the invention. Defined amounts of solvents may be added once again to such a vehicle to improve leveling or to influence layer thickness. The organic solvent content S2- should be kept as low as possible, for example, below 5% and preferably below 3% by weight in the electrophoresis bath.

Alcohols, glycol ethers and ketoalcohols, but also aliphatic and/or aromatic hydrocarbons of different chain length can be used as solvent.

In choosing a solvent, it must be taken into consideration that the 2-S cross linking agent is not soluble in water and that the presence of suitable solvents may facilitate and stabilize the dispersing process.

As the solvent content is increased, the throwing power becomes worse, the thickness of the deposited layer increases and excessive coating may result. In this connection, water-insoluble solvents have a stronger S effect than water-soluble ones. To improve leveling and to lower layer resistance, it is also possible to add some water-insoluble, high-boil- -24r I- ~au u"~"'~"*rlli*,arnr;rri -3a~nrra~ ing solvent, such as hexylene glycol, phenoxyethanol, ethylhexanol, isodecanol or 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate.

To balance the application properties, it is frequently advisable to add to the dispersion of Components and an additional 30% by weight J of a different vehicle system. For this purpose, for example, unsaturated aminoepoxide resins from the German Patent 2,707,405 or aminoacrylate resins from the German Patent 3,628,121 are used.

To prepare coatings or enamels from the dispersions of vehicles prepared 9 pursuant to the invention, it is possible to disperse in pigments, filoo lers, corrosion inhibitors and/or conventional enamel auxiliaries in the usual manner at a suitable place in the manufacturing process.

Ii After dilution with water, the solids content of the coating material of S the invention advisably is 5 to 60% by weight. By adjusting the enamel to a higher solids content of 25 to 50% by weight and preferably of I to 40% by weight, water-dilutable stoving enamels are obtained, which can be applied on the object to be enameled by immersion, spraying, rolling, etc. On the other hand, if the coating material is diluted to to 30% by weight and preferably 10 to 20% by weight, the enamel is suitable for electrophoretic deposition. The bath is stirred constantly S. o in order to maintain a uniform temperature at the cathode surface and to prevent settling of the insoluble components of the dispersion, such as 1 pigments. The pH of the enamel generally is between 4.0 and 8.0 and preferably between 6.0 and 7.5. If the pH is too low, an attack by the acid on the iron of the basin, pipelines and pumps must be expected.

JV Advisably, the electrophoretic deposition is carried out at least 24 hours after the bath is prepared. Advisably, there is continuous stirring during this period in order to obtain a uniform distribution. As anode, electrically conductive, noncorroding electrodes of, for example, stainless steel or graphite are used. The object, which is to be coated 3 o at the anode, and the anode are immersed in an aqueous bath, in the manner known for electrophoretic deposition. All metallically conductt. e ing workpieces may be coated, such as copper, aluminum, tin, zinc, iron and alloys of these metals. During the deposition, the bath is advisably maintained at a temperature of about 150 to 35 0 C. The solids content, the deposition temperature and time, as well as the voltage are j" selected so that a coating of the desired thickness is obtained after rinsing with ultrafiltrate and/or water and baking at temperatures of 1300 to 230C. For example, the thickness of the coating increases as I the coating time and 'the deposition voltage increase. If an electric i current is applied with a voltage of advisably 50 to 500 volt between i /o the metallically conductive workpiece and a counter-electrode, the water-dilutable basic resin is coagulated at the cathode. At the same time, it transports the water-insoluble cross linking agent, the pigments, the catalysts, etc. During this process, the ratio of pigment to synthetic resin vehicle may change in the deposited film in favor of the pigment. At the same time, the concentration of water and of the a'id used for the neutralization increase in the bath. Therefore, for refilling the bath, concentrated enamels must be used, which compensate for this shift by a modified quantitative ratio. This correction can also Sbe made with suitable equipment using, for example, an electrodialysis .o method or ultrafiltration.

Pursuant to the invention, it is also possible to prepare a concentrated vehicle with a solids content of, for example, 85 to 60% by weight, which must then be diluted with water. Such a concentrated vehicle can be pigmented in the usual manner with a ball mill, a three-roll mill or .4 a pearl mill. For this purpose, the usual pigments, which are described, for example, in DIN 55 944, fillers, corrosion inhibitors and paint auxiliaries such as anticrater agents, leveling agents or antifoaming agents, may be used. Naturally, materials are selected, which do not enter into any interfering reactions with wnter in an acidic to So neutral medium, do not introduce any extraneous, water-soluble ions and which precipitate on aging in such a form, that they can be r-.ispended by stirring. The enamels are especially suitable for the electrophoretic enameling of metals and provide aqueous, practically solvent-free -26- I-I- p dispersions, which may contain exactly defined solvent additions.

Aminoepoxide Resin Xylene (1,200 g) and 2,125 g of a polyglycidyl ether based on bisphenol A, with an epoxide equivalent weight of 482, are heated to 400 to 500C under an inert gas and reacted consecutively first with 149.2 g of diethanolamine and then with a mixture of 72.4 g of dimethylaminopropylamine and 452.8 of a adduct, which was prepared from 1 mole of hexanediamine and 2 moles of Cardura E, a glycidyl ester of Versatic acid.

Within 2 hours, the temperature is raised to 1100 to 120°C and then /o maintained for 3 hours. After this time, the epoxide content is zero and the amine number is 86 (mg of KOH per g of solid resin).

Solid content: 69% by weight (after warming to 180°C for 30 minutes).

The resinis processed further at an elevated temperature.

Transesterifiable Cross Linking Agent l/ Under an atmosphere of an inert gas, 1248 g of a -lycidyl ester of Versatic acid (Cardura E) is heated to 1000C and then added in several portions with good stirring to 460.8 g of trimellitic anhydride. Utilizing the exothermic reaction, the temperature is raised to 195*C.

When the resin is clear, the temperature is lowered to 145°C and 1.8 mL Z o of benzyldimethylamine is added as catalyst. After an acid number of 1 (mg KOH per gram of solid resin) is reached, the temperature is lowered to 100C and the product is diluted with 475 g of xylene.

Solids content: 76.7% by weight (30 minutes at 180°C).

Blocked Polyisocyanate aJ While excluding moisture under a blanket of a dry inert gas, 1,440 g 6f a reaction product of 1 mole of trimethylolpropane and 3 moles of toluylene diisocyanate (Desmodur which is dissolved in ethyl acetate to form a 75%'solution, is heated to 80°C with good stirring. Over a pe- -27- .e -r ^'i riod of an hour, 600 g of ethylhexanol are added. During this time, the temperature should not increase significantly further. The temperature is maintained at 80°C for 2 hours, during which time the isocyanate number falls to zero. The product is subsequently diluted with 408 g of S xylene and the ethyl acetate is distilled off completely at 47 solids content: 78.6% by weight Viscosity: 211 mPas (after dilution to 50% by weight with xylene) at Example 1 0 Aminoepoxide resin (1765 g) is mixed with 322 g of transesterifiable cross linking agent, whereupon 90 g of glacial acetic acid and 2285 g completely deionized water are added to form a viscous, homogeneous solution is prepared at 50 0 C. The xylene is azeotroped off under vacuum at a temperature of 40° to 50°C using a separator, which permits the -j water that has been separated out to run back into the reaction vessel.

Finally, the product is diluted with 670 g of water.

Solids content: 37% by weight (30 minutes at 180 0

C)

MEQ value 35 (milliequivalents of acid per 100 g of solid resin) A low-viscosity, storage-stable dispersion results, which still contains ;i o an approximately 0.5% residue of xylene.

Example 2 An aminoepoxide resin (1765 g) is mixed with 509 g of blocked polyisocyanate. After addition of 54 g of lactic acid and 2297 g of fully deionized water, a homogeneous solution is prepared, which is viscous at 2 50C,. The xylene is azeotroped off under vacuum at a temperature of about 50°C using a separator, which permits the water that has been separated out to run back into the reaction vessel. Finally, the product is diluted with 670 g of water.

Solids content: 35.2% by weight (30 minutes at 180 0

C)

3 o MEQ value 25.7 -28- 'I1 Example 3 An aminoepoxide resin (1765 g) is mixed with 483 g of blocked polyisocyanate and 26 g of transesterifiable cross linking agent. After addition of 44 g of lactic acid and 2294 g of fully deionized water, a homogeneous solution is prepared, which is viscous at 50 0 C. The xylene is azeotroped off under vacuum at a temperature of about 50°C using a separator, which permits the water that has been separated, out to run back into the reaction vessel. Finally, the product is diluted with 660 g of water.

0, "o Solids content: 36% by weight (30 minutes at 180*C) MEQ value 21 The aqueous emulsions, obtained in Examples 2 and 3 above, have a low viscosity and can be stored unchanged for several months. Enamels, which are deposited well, can be prepared from-them in the usual manner -lf using conventional additives.

The claims form part of the disclosure of this specification.

Claims (4)

1. Method for the preparation of an electrophoretic enamel coating mate- Srial, which can be deposited at the cathode, has a low solvent con- 3tent and contains pigments, fillers and conventional auxiliaries, by preparing a basic vehicle system in a solvent, a cross linking system 4y in a solvent, mixing the two systems, neutralizing and diluting with I water, wherein a) the basic vehicle system is prepared in an organic solvent, which is immiscible or only partly miscible with water, Sb) the cross linking system is prepared in a solvent, which is immis- L, cible or only partly miscible with water, c) the systems obtained in a) and b) are mixed and, if necessary, precondensed, /3 d) the solution obtained in c) is neutralized completely or partly S with acids and the water is added with formation of a dispersion or an emulsion, e) the organic solvent, which is immiscible or only partly miscible 7 with water, is azeotropically distilled off from this dispersion l/ or emulsion, and 1 f) if required for the control of the property, necessary water-solu- ble and/or water-insoluble solvents are added in defined amounts, as well as, optionally, pigments, fillers and/or conventional R enamel auxiliaries.

2. The method of Claim 1, wherein the same organic solvent, which is not 30 __T f I rr -31 or only partially miscible with water, is used for the preparation of a) and b).

3. A method for the preparation of an electrophoretic enamel coating material, substantially as herein described.

4. A coating produced by the method of any one of claims 1 to 3. A coating substantially as herein described. b. The articles, things, parts, elements, steps, features methods, processes, compounds and compositio erred to D or indicated in the specifica -and/or claims of the application indivi y or collectively, and any and all combi ans of any two or more of such. DATED THIS 13th April, 1988 'SANDERCOCK, SMITH BEADLE Fellows Institute of Patent Attorneys of Australia. Patent Attorneys for the Applicant HERBERTS GESELLSCHAFT MIT BESCHRANKTER HAFTUNG or% 4