CA2042134A1 - Low-solvent aqueous pigment paste, a method of manufacturing it, and use thereof - Google Patents

Abstract

A B S T R A C T

1. Aqueous pigment paste, manufacture and use thereof.

2.1 Prior-art pigment pastes have a high content of solvent. The aim is to prepare an aqueous pigment paste with a low solvent content.

2.2 The aqueous pigment paste contains one or more water-dispersible or water-soluble pigment paste resins based on an epoxy resin with an aromatic content of 20 to 70 wt.%, a number average molecular weight of 400 to 10000, a hydroxy number less than 150, at least one oxazolidine group per molecule and amino groups neutralised by acid and non-quaternised (component A), pigments, fillers and/or conventional lacquer adjuvants (component B) the weight ratio of A to B
being from 1 : 0.5 to 1 : 11, and 0 to 5 wt.% solvent and 25 to 75 wt.% water.

2.3 Aqueous pigment pastes for cathodic electrodeposition coating.

Description

2~4~ 3~

Herberts Gesellschaft mit beschrankter Haftung, Christbusch 25, 5600 Wuppertal 2, DE

Low-solvent aqueous pigment paste, a method of manufacturing it, and use thereof The invention relates to aqueous pigment pastes, more particularly for cathodic electrodeposition coating (German abbreviation KTL), the content of solvent in the paste formulation being particularly low.

~lectrodeposition coating is a known method of coating the surface of electrically conductive objects to improve their resistance to corrosion. The method is as follows: the article to be coated is immersed in an aqueous coating bath, connected as cathode to a d.c. source, and the lacquer is then coagulated and deposited on the surface of the material by the flow of current. The material is then physically liquefied by heating and chemical cross-linking is brought about, resulting in a homogeneous uniform surface on the substrate.

The deposition process can be influenced by various parameters. For example, the layer thickness can be increased by increasing the deposition voltage. Another possibility of increasing the layer thickness is by increasing the content of solvent in the bath, but this negatively influences other parameters such as the wrap-around. ~he solvent content of a cathodic electrodeposition bath must therefore be kept at a minimum.

Ano~her reason Eor keeping the solvent content low is that ultrafiltrate has to be reyularly withdrawn from an 20~21~

electrodeposition bath and dumped. The ultrafiltrate has to be disposed o-f, which is very difficult if it contains relatively high proportions of solvent. In order to reduce the solvent content of cathodic electrodeposition coatiny materials, an early transition was made to a two-component method. In this method the lacquer binder is produced in the form of an aqueous dispersion containing little organic solvent. The second solvent is an aqueous pigment paste consisting of solutions of paste binders, picfments, neutralising agents and other additives. Hitherto however it has been necessary to add considerable proportions of organic solvents to the aqueous pigment pastes in order to obtain advantageous viscosity and adequate stability. The solvents are therefore also added to the electrodeposition bath, resulting in the aforementioned problems. The two components are supplied separately by the manufacturer to the users of electrodeposition coatings, and are added to the cathodic electrodeposition tank.

EP-A-O 270 877 describes self cross-linking neutralisable cathodically deposited binders for pasting pigment formulations and comprising modified epoxy resins which are activated with polyphenols and amines and contain activated ester groups and/or blocked isocyanate groups. These pi~ment-paste binders are chemically incorporated in the KTL systems by cross-linking via the functional groups.
However, pigment pastes made with these binders have a low pigment-binder ratio. The resins are manufactured in the form of solutions containing 35% solvent.

EP~A-O 183 025 describes paste binders based on epoxy reslns with oxazolidine rings reacted thereon, and having a h:igh content of aliphatic structures, preferably over 50%.

~2~4 The aliphatic components are carbon chains containing more than three C atoms, e.g. fat-ty amines, fatty acids and/or oxyalkylene chains. These molecular components have advantages as regards the capacity of the resin to wet the pigments. Usually however they have the associated disadvantage of reduced protection against corrosion. This product is therefore unsuitable for many applications. 15~
organic solvents are added to these resins to produce pigment pastes which can be additionally diluted with water during manufacture. The solvent content is made even higher by the fact that the resins are in solution with organic solvents. This has inevitable disadvantages as regards the coating properties of the electrodeposition baths.

The method of producing two-component KTL baths is described e.g. in EP-A-107 088, EP-A-107 089 or EP-A-107 098, which also describe methods of prPparing pigment pastes. The pigment paste resins used therein, however, are produced on the basis of modified mono-epoxides with ~uaternised nitrogen atoms, and have the disadvantage that the lacquer systems have low dielectric strength.
Likewise, EP-A-270 877 describes manufacture of two-component KTL lacquers. As before, however, considerabl quantities of solvent are incorporated in the lacquer, which as before has unfavourable deposition properties.

The object of the invention is to prepare aqueous piqment pastes which are suitable for cathodic electrodeposition coating materials and contain only small quantities of organic solvents but have good stability, low viscosity and ar~ easy to handle.

This problem is solved by an aqueous pigment paste which contains water-dispersible or water-soluble pigment paste resin containing O to 15, preferably O to 10 wt.% of organic solvent relative to the non-volatile resin, and based on an epoxy resin having an aromatic content (calculated as phenylene groups) of 20 to 70 wt.%, relative to the non-volatile resin, a number average molecular weight (Mn) of 400 to 10000, a hydroxy number of < 150, at least one oxazolidine group per molecule and a content of neutralisable, non-quaternised amino groups which determine the dispersibility or solubility in water.
These neutralised paste binders, together with conventional pigments, additives, catalysts and/or adjuvants, can be used to make pigment paste which is soluble in storage and contains up to 5 wt.%, preferably up to 2 wt.% of solvent.
It could not have been anticipated that the possibility of manufacturing low-solvent pigment pastes stable in storage might be improved by an increased aromatic content and the absence of quaternary ammonium groups in the paste binder.
:
The pigment paste resins (paste binders) used in the pigment paste according to the invention are binders based on modi~ied epoxy resins containing at least one and preferably two epoxy groups, 50 - 100 mol % of the free epoxy groups being reacted with a primary-tertiary diamine, the excess epoxy groups having previously been optionally reacted with secondary or primary amines, and from 80 to 100 mol % o~ the secondary amino groups being reacted with a carbonyl compound to ~orm oxazolidine structures. These binders can then be converted into a solid dispersion by addin~ an acid, e.g. a low-molecular weight organic acid.

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The molecular weight of the modif ied epoxy resin should be 400 - 10000, preferably 600 - 4000. The hydroxyl number should be not more than L00 mg KOH/g. The product should have an aromatic content, calculated as phenylene groups, of 20 - 70~6, preferably 25 - 50%. The content of organic solvents, i~e. the solvent remaining after manufacture of the resin, should not exceed O - 10 wt . % of the non-volatile resin.

On average, the epoxy resins used have at least one and pref erably at least two epoxy groups per molecule . These products can easily be manufactured by modifying glycidyl ethers based on bisphenol A or novalaks with an epoxy equivalent weight between 200 and 1000. The resulting epoxy compounds can be cross-linked by aliphatic and/or aromatic bridges . Cross-linking can be brought about e . g.
by (poly) glycols, aliphatic dicarboxylic acids, secondary diamines, polyether diols, (poly)disulphides, polycaprolactone diols or secondary diamines.

Other epoxy groups can be reacted with monophenols such as octyl- or nonylphenol. Alternatively some of the epoxy groups can be reacted with monocarboxylic compounds~ The monocarboxylic compounds should be monocarboxylic acids containing more than eight carbon atoms, such as natural or synthetic fatty acids or semiesters of dicarboxylic acids with monoalcohols such as octanol or N-hydroxyalkyl oxazolidines. These reactions are brought about at elevated temperature until the acid number is below 3 mg KOH/g. In the manufacture of epoxy resins, the proportion o~ components containing aromatic groups is chosen to give the desired aromatic content.

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50 - 100% of the free epoxy groups in the modified resins can be reacted in the presence of an inert solvent with a primary-tertiary diamine, preferably N-N-dialkyl aminoalkyl amines. The remaining epoxy groups are reacted with primary and/or secondary amines. If primary and secondary amines are used, the secondary amines are preferably reacted in a first step, after which the primary amines (or optionally mixtures of primary amines) are reacted. No excess of amines should be left unless the excess amines are removed e.g. by distillation in vacuo. The amines can e.g. be alkyl and/or alkanol amines containing more than four C atoms. The mono-amines and diamines preferably react simultaneously at elevated temperature, e.g. from 70 to 80C.

The resulting secondary ~-hydroxyalkyl amino groups are then reacted with a carbonyl compound, e.g. an aldehyde compound, to form oxazolidine groups. Ths aldehydes used are aromatic or aliphatic, e.g. butanal or benzaldehyde, but are preferably formaldehyde. The water produced by the reaction i5 removed by azeotropic distillation. The number of oxazolidine groups is preferably at least one per molecule.

To improve the solubility, the binder must carry a sufficient number of amino groups. These should preferably not be quaternised; the binder should need to be neutralised with a suitable agent before beiny convertible to the aqueous phase. The nature and number of the amino groups also influences the basicity of the binder and the resulting KTL bath. This is a way of influencing the neutralisation and the pH.

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The behaviour of the piyment paste resins (paste binders) can be controlled via the number of hydroxyl groups, the number of oxazolidine groups or the number of urethane groups. For example an increased number of OH groups or other polar groups improves the solubility of the resin in water. The solubility can also be influenced via the number of neutralisable amino groups The viscosity of the paste binder is closely dependent on the molecular weight obtained. To ensure that the resin and paste has advantageous viscosity, the molecular weight of the binder must not be too high. On the other hand a low molecular weight results in low viscosity and low dielectric strenyth of the molecule and strongly influences the cross-linking density in the film of lacquer after it has been deposited and stoved.

Other modifications to the molecule can be made via the free secondary OH groups which occur, and which can be reacted e.g. with monoisocyanate groups such as masked isocyanates.

If other secondary amino groups are present they also react with the aforementioned functional groups. Optionally, other monoepoxy compounds can react with these reactive OH
groups.

In the manufacture 4f these paste binders, it may be necessary to add various quantities of solvents. In order to obtain the piyment paste with low solvent content accordiny to the invention, therefore, it may be necessary to remove these solvents, e.g. by distillation at normal pressure or in vacuo or by water-vapour distillation. The - 20~2~3~

solvents can be present individually or in mixtures~
Distillation can be brought abou-t during synthesis or at the end, before or after neutralisation of the resins with the acid. If the viscosity of the paste resins is low, lt may be unnecessary to add a solvent. The solvents can he those normally used in resin manufacture, more particularly solvents which do not react with epoxy resins or isocyanates, e.g. aliphatic or aromatic hydrocarbons such as xylene, aromatic mixtures known to the skilled addressee under the name Solvesso, toluene, esters such as butyl acetate, ethers, alcohols, ether alcohols such as methoxypropanol or ketones such as methyl isobu-tyl ketone.

If the viscosity of the binder is high, advantageously the resin is converted after neutralisation into an aqueous dispersion, optionally by heating. Optionally the solvent content of the aqueous dispersion can be lowered by azeotropi~ distillation.

The resulting paste resins or paste-resin dispersions have a good wetting capacity for pigments. They can be used to obtain a high piyment-binder ratio. The ratio by weight of paste resin (non-volatile resin) to the total weight of pigments, fillers and conventional lacquer adjuvants is 1 :
0.5 to 1 : 11.

The pigment pastes according to the invention can contain various pigments and fillers known to the skilled addressee. The followiny are examples: aluminium or magnesium silicate, titanium dioxide, barium sulphate, carbon black, mica, finely dispersed silica micronised titanium dioxide with a particle size of 0.1 - 1 ~m, metallic pigments metal oxides, interference pigments, ~2~

organic or inorganic paint pigments, or lead or chromate pi~ments. These can be selected to influence e.g. the anti-corrosion properties, the flow properties, the colour shade and the mechanical propertiesO Various known polymer powders or organic microparticles can also be added as fillers, e.g. cross-linked or non-crosslinked olefinically polymerisable polymers such as polyacrylonitrile, (meth)acrylate homopolymers or copolymers, polyethylene powders; straight-chain or branched polyaddition polymers such as polyamide resins or polyurethane resins, or polycondensation resins such as polyesters, triazine formaldehyde reaction products or phenolic resin powders.
These powdered plastics, whether cross-linked or not cross-linked, ionic or non-ionic, reactive or non-reactive, can also be used to adjust the film properties, e.g. the levelling, the resistance to gravel or the density of the film.

Optionally other additives (conventional lacquer adjuvants) such as catalysts, wetting agents, anti-foam agents and/or levelling agents can be added.

The pigment pastes can be prepared as follows: the paste binder is neutralised with a suitable acid ancl then converted to the aqueous dispersion phase. The pigments and/or other additives can then be supplied. rrhe viscosity of the pigment paste is adjusted with water. Additives which are preferably soluble in the organic phase can also optionally be homogeneously mixed in the paste binder. The substance is then ground to the necessary particle Eineness in a conventional grin~er such as a pearl mill. The resulting pigmerlt pastes are stable in storage, have low viscosity, and have only a low solvent content.

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The resultiny pigment pastes are stable. They contain 0 to 5 wt.%, preferably only O to 2 wt.% of organic solvent and their viscosity is adjusted with water without substantial sedimentation of the non-volatile content. Conventional organic additives and admixtures can be homogeneously incorporated. No phase separation is observed. The non~
volatile content can be 20 to 75 wt.~, preferably 35 to 65 wt.%, and the resin content is preferably 3 to 35 wt.%.
The water content is 25 to 80 wt.%.

These pigment pastes have a low solvent content, as required for environmental reasons and sa~ety at work. The pigments are well wetted and the pastes are stable in storage. The viscosity properties are good and the intrinsic viscosity is only slight.

These pigment pastes can be used together with conventional known KTL binders to produce an electrodeposition coating bath in which conductive substrates such as metals can be cathodically coated and then stoved. Owing to the low solvent content, the coating properties of the bath are advantageous, i.e. a good wrap-around is obtained. The waste water also has a very low solvent content.

The invention will be explained in detail in the following examples. All percentages are by weight. The non-volatile substance (dry extract) was determined at 150C as per DIN
53 182.

Manufacture o~ paste resins:

~mE~le ~

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950 9 of an epoxy resin based on bisphenol A and corresponding to two epoxy equivalents was dissolved in 633 9 xylene and added at 60 - 70C to a mixture of 129 g 2-ethylhexylamine and ~17 g diethyl aminopropyl amine. The temperature was kept below 75C by cooling. After all the epoxy groups had been completely used up, 59 g of paraformaldehyde ~91%) was added to the batch. The mixture was heated until a continuous azeotropic circuit was obtained, for removing the reaction water from the batch.
At the end of the reaction the xylene in the batch was removed by distillation and the binder, after adding 70 mmol of acetic acid per 100 g non-volatile resin, was diluted with deionised water to a non-volatile content of 30~.

The ~inaer had the follo~ing characteristics:

Aromatic content approx. 39%
Mn approx. 1200 Residual solvent approx. 1%
; OH number approx. 90 mg XOH/g non-volatile resin Example 2 259 g of an oxazolidine made from 61 g monoethanolamine, and 186 g of 2-ethylhexyl glycidyl ether and 33 g paraformaldehyde (91%) were reacted with 148 g phthalic acid anhydride at 60C until the acid number corresponded to a semle.ster. Next, 380 g of an epoxy resin based on bisphenal A (corresponding to two epoxy equivalents) were added to the batch ancl the mixture was kept at 60C until all the carboxyl groups had been completely used up. After 2B~2134 adding ~00 g toluene and 102 g dimethyl aminopropyl amine the reaction was continued via the free epoxy groups at 70 - 75C. Next, 33 g paraformaldehyde (33 %) were added and the water produced by the reaction was azeotropically removed. At the end of this reaction step, 304 g of a toluylene diisocyanate semi-blocked with 2-ethyl hexanol was added and the mixture was kept at 70C for 1 hour.

Conversion to a low-solvent binder was brought about after removal of the toluene by distillation, addition of 50 mmol lactic acid/100 parts non-volatile resin and dilutlon with deionised water to a non-volatile content of 35~.
. , Characteristics of the binder:

Aromatic content apprcx. 26%
Mn approx. 1200 Residual solvent approx. 1.5%
OH number approx. 10 mg KOH/g non-volatile resin ':
Exam~le 3 ~00 g of a polyoxyalkylene diamine with an average molecular weight of 400 was reacted in 1000 g methoxypropanol with 368 g dodecenoxyd and 1900 g of an epoxy resin based on bisphenol A (epoxy equivalent about 475) at 100C until the amount of epoxy groups stoichiometrically corresponded to the active amino hydrogen atoms. Next, 260 g diethyl aminopropyl amine was added at 70C and the reaction was continued until all the epoxy groups were completely used up. The reaction was continued by azeotropic removal of the water, after adding 2~ L3~

66 g o~ paraformaldehyde 91~ and methyl ethyl ketone as an entrainer. ~t the end of the reaction the mixture of methoxypropanol and methyl isobutyl ketone was removed by distillation and the binder was neutralised with 40 mmol of acetic acid per 100 parts of non-volatile resin. The solution was adjusted with deionised water to a non-volatile content of about 40%.

Characteristi~s of the binder:

Aromatic content approx. 32%
Mn approx. 3000 Residaul solvent approx. 4%
OH number approx. 150 mg KOH/g non-volatile resin Manufacture of pigment pastes:

Example 4 143 g of a commercial aluminium silicate powder/ 10 g carbon black, 16 g pyrogenic silica and 8 g dibutyl tin oxide powder were added to 175 g of a paste resin dispersion as per Example 1 (30%) in a high-speed agitator.
The non-volatile content was adjusted to about 44% with 480 g completely demineralised water and the mixture was ground in a pearl mill, producing a stable pigment paste containing 1% of solvent.

Example 5 27~ y o~ a paste resin as per Example 2 (35% in water) was mixed with 10 g a~ a commercial wetting ayent (Sur~ynol~, '~4'2~3~

~ 15 -25 g lead silicate, 355 g aluminium silicate and 5 g carbon black in a high-speed agitator. 340 g of completely demineralised water was then added to adjust the viscosity.
The mixture was ground to the required particle fineness in a pearl mill. Optionally the viscosity in storage can be subsequently adjusted with water. The solvent content was about 1~.

Example 6 25 g dibutyl tin oxide powder, 30 g lead silicate powder, 5 g carbon black and 440 g titanium dioxide as per Example 1 were mixed w.ith 178 g of a resin dispersion as per Example 3 containing 1 g acetic acid (100%) and the viscosity was adjusted with about 320 g of completely demineralised water, after which the mixture was ground in a pearl mill.
The resulting pigment paste was stable and had a solvent content of about 1%.

Production of stable cathodic electrodeposition baths:

A. Production of binder dispersions ExamPle 7 As per EP 12 463, 391 g o~ diethanolamine, 189 g of 3-tN,N-di-methylamino)-propylamine and 1147 g of an adduct of 2 mol hexane diamine-1,6 and 4 mol glycidyl ester of versatic acid (Cadura~ E 10 by Shell) were added to 5273 g of bisphenol A epoxy resin tepoxy equivalent weight about 475) in 3000 g ethoxypropanol. The reaction mixture was kept at 85 to 90C with agitation ~or 4 hours and then at 120C ~or 1 hour, followed by dilution with ethoxypropanol to a non-volatile content o~ 60%.

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Example 8 2262 g of epoxy resin based on bisphenol A (epoxy equivalent weight about 260~ was dissolved in 2023 g diethylane glycol dimethyl ether at 60 to 70C and, after adding 0.8 g hydroquinone and 2453 g of a semiester of tetrahydrophthalic acid anhydride and hydroxymethyl methacrylate, was kept at 100 to 110C until the acid number had fallen below 3 mg KOH/g. The reaction product was then reacted with 3262 g of a 70% solution of a monocyanate from toluylene diisocyanate and dimethyl ethanolamine (molar ratio 1 : 1) in diethylene glycol dimethyl ether until the NCO value was zero.

Example 9 228 parts of bisphenol A (1 mol) was reacted with 260 parts of diethyl aminopropyl amine (2 mols) and 66 parts of para-formaldehyde (91%; 2 mols) in the presence of 130 parts toluene azeotropic entrainer until 42 parts of reaction water had been separated~ After 152 parts of dimethylene glycol dimethyl ether had been added and the product had been cooled to 30C, 608 parts (2 mols) of a tol.uylene diisocyanate semi-blocked with 2-ethyl hexanol were added within 45 minutes. After an NCO value of practically zero had been reached, 1400 parts of the solution were mixed with a solution of 190 parts of an epoxy resin based on bisphenol A (epoxy equivalent weight about 190~ and 250 parts by weight (1 mol) of a ylycidyl ester of a saturated tertiary C9 to C11 monocarboxylic acid in 389 parts of dlethyle.ne glycol dimethyl ether, and reacted at 95C to 100C until the epoxy value wa~ zero. The binder was 20~ 3~

easily soluble in water after adding 40 mmol/100 g non-volatile formic acid (S0%). The non-volatile content was adjusted to 35%.

Exam~le 10 768 g of trimellitic a~id anhydride and 2000 g of a glycidyl ester of a branched tertiary C10 monocarboxylic acid (Cadura~ E 10) were carefully heated with agitation to 190C, during which an exothermic reaction began above 90C. The reaction material was cooled to 140C and 2075 g o N.N-dimethyl benzylamine was added. The reaction material was kept at 145C until the acid number fell below 3 mg KOH/g. An additional calculated quantity of Cadura~ E
10 was added when necessary. The reaction product was diluted with 2-butoxyethanol to a non-volatile content of 80%.

Example 11 160 g caprolactam was slo~ly added at 70C and with agitation to 431 g of a solution (75% in ethyl acetate) of a reaction product of 3 mol toluylene diisoyanate and 1 mol trimethylol propane (Desmodur L~ ). The reaction mixture was then kept at 70C until the NCO content had fallen practically to 7ero. Next, 2-butyoxyethanol (204 g) was added and the ethyl acetate was distilled of over a column until the non-volatile content was 70%.

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1000 g o~ a resln as per Example 8 and 500 g as per Example 7 were mixed and then distilled in vacuo to about 85% non-2 al4213~

volatile. Next, 45 mmol/100 g non-volatile formic acid (50%) were added with heating, followed by dilution to about 33% non-volatile with completely demineralised water.

Example 13 1050 g resin as per Example 7, 225 g as per Example 10 and 130 g as per Example 11 were mixed and 50 mmol/100 g non-volatile acetic acid (100%) were added, followed by dilution to about 20~ non-volatile with completely demineralised water. 30% by volume of ultrafiltrate were withdrawn from the resulting clear lacquer in an ultrafiltration device. The non-~olatile content was then about 30%.

B. Production of the baths Exam~le 14 /

515 g of a dispersion as per Example 13 were diluted with 345 g of completely demineralised water. 140 g of a pigment paste as per Example 14 were added to the mixture with agitation. After thorough homogenisation, degreased steel sheets were coated with the lacquer and stoved at 180C for 30 minutes. Smooth KTL films were obtained.

Ex m le 15 465 g of a dispersion as per Example 12 was diluted with 400 g of completely demineralised water, followed by addition of 95 g of a pigment paste as per Example 5. The coating bath was adjuste.d with demineralised water to a non-vo].atile content of 19%. Metal substrates were coated ~2~

in the resulting KTL bath and then stoved. The baths were stable and gave conventional KTL films.

Rxample 16 550 g of a dispersion as per Example 9 was diluted with 79S
g of completely demineralised water, followed by addition of 155 g of a paste as per Example 60 The resulting KTL
bath was stable andhad the normal coatlng properties,

Claims (7)

1. An aqueous pigment paste without organic solvents or with a low content of organic solvents, containing:
A) one or more water-dispersible or water-soluble pigment paste resins based on an epoxy resin with an aromatic content (calculated as phenylene groups) of 20 to 70 wt.%, relative to the non-volatile resin, a number average molecular weight (?n) of 400 to 10000, a hydroxy number of ? 150, a content of at least one oxazolidine group per molecule and a content of amino groups neutralised by acid and not quaternised and determining the dispersibility or solubility in water, B) pigments and/or fillers and/or conventional lacquer adjuvants, components A and B being in the weight ratio of 1 : 0.5 to 1 : 11 and the non-volatile content of the aqueous paste, depending on the sum of components A and B, being 20 to 75 wt.%, C) 0 to 5 wt.% of solvent and, D) 25 to 75 wt.% of water, the percentages of components C and D each referring to the aforementioned aqueous pigment paste.

2. An aqueous pigment paste according to claim 1 in which the oxazolidine groups in the pigment paste resin and the neutralisable amino groups are obtainable by reacting 50-100% of the free epoxy groups of an epoxy resin containing at least one epoxy group per molecule with a primary-tertiary diamine, reacting the stoichiometrically excess epoxy groups with a primary or secondary amine and reacting - 100 mol.% of the secondary amino groups with a carbonyl compound to form oxazolidine structures

3. A method of producing the aqueous pigment pastes according to claim 1 or 2, characterised in that a pigment paste resin based on an epoxy resin with an aromatic content (calculated as phenylene groups) of 20 to 70 wt.%
relative to the non-volatile resin, a number average molecular weight (Mn) of 400 to 10000, a hydroxyl number of ? 150, a content of at least one oxazolidine group per molecule and a content of neutralised non-quaternised amino groups which, after neutralisation with acid, determine the dispersibility or solubility in water, the content of solvent being 0 to 10 wt.% relative to the epoxy resin, is neutralised with acid to form a dispersion or solution and then water is added, and pigments and/or fillers and catalysts and/or conventional lacquer adjuvants in a weight ratio of 1 : 0.5 to 1 : 11 are added to the resulting dispersion or solution and water is added until the total water content is 25 to 75 wt.% and the desired grinding viscosity is obtained, after which the substance is ground.

4. A method according to claim 3, characterised in that the epoxy resin is neutralised with 10 to 300 mmol acid per 100 g non-volatile resin.

5. A method according to claim 3 or 4, characterised in that the water-soluble pigment paste resin is obtained as follows:

a) an epoxy resin containing aromatic groups with an epoxy equivalent weight of 200 - 1000 and at least one epoxy group per molecule is reacted in a solvent with b) a primary-tertiary amine in a quantity such that 50-100 mol.%, of the free epoxy groups react, c) the stoichiometrically excess epoxy groups are reacted with primary and/or secondary amines, d) 80 to 100 mol.% of the secondary amino groups are reacted with a carbonyl group to give an oxazolidine structure and e) the solvent therein is removed until the content relative to the non-volatile resin is below 10 wt.%.

6. Use of the aqueous pigment pastes according to any of claims 1 to 5 in aqueous coating materials.

7. Use according to claim 6 in aqueous coating materials for cathodic electrodeposition coating.

T 31 775.WPF