EP0946657A1

EP0946657A1 - Paint and additive for cathodic electrophoretic dip-coating

Info

Publication number: EP0946657A1
Application number: EP97953860A
Authority: EP
Inventors: Klaus Arlt; Walter Jouck; Guido Wilke; Udo Strauss; Wolfgang Bremser; Edwin Cramer
Original assignee: BASF Coatings GmbH
Current assignee: BASF Coatings GmbH
Priority date: 1996-12-18
Filing date: 1997-12-18
Publication date: 1999-10-06
Also published as: CA2275415A1; BR9714412A; JP2001506299A; DE19652884A1; KR20000057639A; WO1998027167A1

Abstract

The invention relates to a method for manufacturing paint for electrophoretic dip-coating made of aqueous binder dispersions. If needed, catalysts are added to these binder dispersions, as are one or several aldehydes of the general formula R-CH=0, or one or more compounds which release such aldehydes, R representing one hydrogen atom or an alcyl group with between 1 and 10 C atoms.

Description

Electrocoating and additive for cathodic electrocoating

The invention relates to a method for producing an electrocoat, an electrocoat produced by the process and its use to improve edge protection in electrocoats.

Electrocoating (KTL), in particular cathodic electrocoating, is an increasingly common method for coating electrically conductive objects in recent years, in which preferably water-thinnable, cationic group-bearing synthetic resins are deposited electrophoretically on the surface to be coated become. The KTL finds a preferred application in the priming of device housings and automobile bodies.

Electric immersion baths suitable for the purposes mentioned are e.g. described in the following patent documents: US-3,799,854; U.S. 3,984,299; U.S. 4,031,050; U.S. 4,252,703; U.S. 4,332,711; DE-31 08 073; DE-27 01 220; DE-31 03 642; DE-32 15 891; EP-0505 445; EP-0074634; EP-0358221.

Resins which can be electrodeposited on the cathode are described, for example, in US Pat. No. 3,617,458. It is a cross-linkable coating compound that is deposited on the cathode. These coating compositions are derived from an unsaturated polymer which contains amine groups and carboxyl groups and an epoxidized material. US Pat. No. 3,663,389 describes compositions which can be deposited electrically and electrically and which are mixtures of certain amine-aldehyde condensates and a large number of cationic resinous materials, one of these materials being reacted with an organic polyepoxide with a secondary amine and solubilizing with Acid can be produced.

From US Pat. No. 3,640,926, aqueous dispersions are known which can be deposited electrically on the cathode and consist of an epoxy resin ester, water and tertiary amino salts. The epoxy ester is the reaction product of glycidyl polyether and a basic unsaturated oleic acid. The amine salt is the reaction product of an aliphatic carboxylic acid and a tertiary amine.

Binder based on epoxy and polyurethane for the use of binder dispersions and pigment pastes are also known in numerous configurations. For example, reference is made to DE-27 01 002, EP-A-261 385, EP-A-004090 and DE-PS 3630 667.

The KTL offers great advantages over other state-of-the-art processes due to its good material yield and the fact that organic solvents are largely avoided. A problem that has not yet been solved satisfactorily, however, is the so-called edge protection, ie the generation of a uniform coating even over edges or generally sharp curvatures of the object to be painted. This is because the electrophoretic resin deposition on the workpiece is generally carried out with a sufficient layer thickness that is approximately the same everywhere, however, during the subsequent baking of the lacquer, the coating undesirably withdraws from the edges and kinks of the workpiece. In order to achieve the crosslinking of the binders deposited during dip coating, the lacquer layer must subsequently be baked at temperatures of up to 180 ° C. During the heating of the lacquer layer, however, it first becomes liquid and reaches its so-called minimum viscosity at a certain temperature. As the temperature continues to rise, the viscosity of the applied coating then increases again due to the crosslinking of the binders. In the thin liquid phase in the area of the viscosity minimum, the effect now occurs that the lacquer layer flows away from the edges of the workpiece due to interfacial forces. This reduces the thickness of the paint layer remaining on the edge, and in the worst case, the edge is even completely exposed.

For these reasons, attempts have been made to increase the viscosity minimum with various measures, so that the smallest value of the viscosity reached during the baking is in any case so high that the described flow away from the edges is kept within tolerable limits. DE-43 32014 e.g. proposed to achieve such an effect by using microgels in the electrocoat.

A disadvantage of the described methods, however, is that they are relatively complex and complicated. Furthermore, an increase in the edge protection is accompanied by a deterioration in the course. This is because a uniform, smooth course of the electrocoat layer is not least produced by the fact that the lacquer layer liquefies during the baking and is evenly distributed in the process. The increase described the minimum viscosity of the electrocoat layer therefore generally results in a deterioration in the film flow.

Compared to the known prior art, the object of the present invention is to achieve a considerable improvement in edge protection with a simple and inexpensive method for producing electrocoat materials from aqueous binder dispersions.

According to the invention, this object is achieved in that catalysts are optionally added to the binder dispersions from the electrocoat material, and one or more aldehydes of the general formula R-CH = 0 or one or more compounds which split off aldehydes are added, where R is a hydrogen atom or a Alcyl radical with 1-10 C atoms.

Accordingly, aldehydes are not only suitable as such, but also those compounds which are able to split off aldehydes or aldehyde groups. The use of formaldehyde is particularly preferred according to the invention.

In a form which is particularly preferred according to the invention, the aldehyde is added as a 35-45% aldehyde solution. Such solutions are commercially available in the case of the invention according to preferred formaldehyde such as formalin under the name ^®. The content of the aldehydes in the solution or compounds which release aldehydes depends on the intended use. In principle, however, the additives can consist of up to 100% aldehyde. In a variant of the process according to the invention, a mixture comprising one or more aldehydes of the general formula R-CH = O or one or more compounds which split off such aldehydes is separated from the electrocoat material, where R is a hydrogen atom or an alcyl radical having 1-10 C atoms is manufactured and stocked. If the electrodeposition paint contains little or no compounds with amino groups, a mixture of organic compounds which contain amino groups, preferably primary amino groups, is preferably first prepared and then the mixture is added to the binder or paint.

The compounds containing amino groups which can be used in the context of the invention are preferably reactive with the aldehydes, ie have primary or secondary amino groups. If reactive amino lip-containing compounds are added, an improvement in edge protection is based on the following relationships. A deposited film lowers its viscosity during curing at a higher temperature, before the crosslinking reaction has started or has progressed sufficiently. As a result, the film interferes with the edges during curing due to interfacial forces. With the use of aldehydes and compounds containing amino groups reactive with aldehydes, whether it is a binder containing amino groups or a different additional compound containing amino groups, the time and temperature-dependent development of the viscosity mentioned during curing is advantageously influenced. The amino group-containing compound and the aldehyde react with one another and the reaction product increases the viscosity of a deposited film in the initial phase of the temperature increase in the course of the curing. However, this increase in viscosity is probably only an intermediate one, since, as the temperature increases, a reduction in viscosity (compared to the viscosity development when using, for example, microgels) occurs with the 5a

Result of a good course. This subsequent decrease in viscosity is probably due to the fact that the reaction product of a compound containing amino groups and aldehyde disintegrates again at a further elevated temperature (and consequently more advanced crosslinking). The curing takes place in the following phases: i) initial temperature increase for curing in the deposited film with reaction between compounds containing amino groups and aldehydes or through a reaction product thereof and viscosity increase compared to the same curing sequence, but without the addition of aldehydes, ii) progressive curing or Temperature increase in the deposited film with lower viscosity compared to other known viscosity-increasing measures, iii) final hardening.

The mixture can then be added to commercial dip lacquers in an amount that the user can control. The amounts are preferably adjusted so that the aldehyde content in the electrocoat material is between 50 to 1,000 ppm, preferably 200 to 500 ppm.

The addition of the aldehydes or aldehyde mixtures according to the invention to electrocoat materials leads to surprising, unforeseeable positive effects on the edge protection achieved. While according to the state of the art in the evaluation of edge protection quality using standard, standardized test methods (microscopic analysis; climate change test on phosphated sheets: VDA 621/415; salt spray fog test (360 h): DIN50021 SS; outdoor exposure to salt: VDA be achieved 621/414) scores ranging from 4 (with a score range of 0 to 5) can be consistently achieved with an inventive paint with the use of formaldehyde in the form of formalin ^® notes in the range 1 to 2 A measurement of the formaldehyde produced by using the paint according to the invention The lacquer layer provided a lacquer layer density of 5 to 9μm at the edges under conditions in which no edge coverage can be achieved without formaldehyde (layer thickness = O μm). Even with the minimum layer thickness of 5 μm, edge protection was achieved that was sufficient in practice.

The aldehydes or aldehyde mixtures according to the invention described can in principle be added to all commercially available electrocoat materials or binders to improve edge protection.

If the electrocoat does not contain a catalyst, this can accordingly be added separately to the electrocoat. These are generally metals, in particular heavy metals, metal-containing compounds or mixtures. These can preferably be present as divalent cations in the electrocoat material. According to the invention, the presence of lead has proven to be particularly advantageous. The following can be considered here: Mixtures containing lead or compounds releasing lead cations. The catalysts are added in amounts of about 200 to 800 ppm, particularly preferably 350-650 ppm, based on the electrocoat material.

It should be noted that lead is often contained in pigments and may therefore already be present in the electrocoat. In this case, the amounts of lead or other catalysts added must be matched to the lead-containing substances already present as a pigment. If necessary. the addition of the catalyst can be omitted if it is present in sufficient quantities in the electrocoating material. It is essential to the invention in the production process described that the electrocoat used contains the necessary compounds with amino groups, for example in the form of binders with primary amino groups. However, it is also possible to add the amino group-carrying compounds separately to the electrocoat material. It is also possible to first mix these compounds with the aldehyde - as already described above - and then to add the reaction adduct produced in this mixture to the electrocoating material.

Suitable electrocoating materials are both electrocoating materials which can be deposited on the anode, but preferably electrocoating materials which can be deposited on the cathode.

Examples of anodically depositable electrodeposition paint binders and paints (ATL) containing anionic groups which can be used according to the invention are known and are described, for example, in DE-A-28 24 418. These are, for example, binders based on polyesters, epoxy resin esters, poly (meth) acrylates, maleate oils or polybutadiene oils. The binders carry, for example, -COOH, -SO3H and / or P03H2 groups. After neutralization of at least some of the acidic groups, the resins can be converted into the water phase. The lacquers can also be crosslinkers commonly used, e.g. Contain triazine resins, crosslinkers with groups capable of transesterification and / or transamidation or blocked polyisocyanates.

In principle, the cathodically depositable electrocoat materials can contain any aqueous cathodically depositable synthetic resin suitable for aqueous electrocoat materials. examples for Binders and crosslinking agents which can be used in KTL lacquers are described in EP-A-82 291, EP-A-234 395, EP-A-209 857, EP-A-227 975, EP-A-178 531, EP-A-333 327, EP-A-310 971, EP-A-456 270, EP-A-261 385, EP-A-245 786, EP-A-414 199, EP -A-476 514, DE-A-33 24 211 and US-A-3,922253.

These electrocoat materials preferably contain cationic, amine-modified epoxy resins as cathodically depositable synthetic resins. Such synthetic resins are known and are described, for example, in DE-A-35 18 770, DE-A-35 18 732, EP-B-102501, DE-A-27 01 002, US-A-4,104,147, EP-A-4090 , EP-A-12463, US-A-4,03,050, US-A-3,922,253, US-A-4, 101,486, US-A-4,038,232 and US-A-4,017,438. The preparation of cationic, amine-modified epoxy resins is also described in detail in these patent documents.

Cationic reaction products are formed from cationic, amine-modified epoxy resins

(α) optionally modified polyepoxides and (ß) amines and optionally

(γ) polyols, polycarboxylic acids, polyamines or polysulfides

Roger that. These cationic, amine-modified epoxy resins can be prepared by reacting components (α), (β) and, if appropriate, (γ) and - if necessary - subsequent protonation. However, it is also possible to react an unmodified polyepoxide with an amine and to carry out further modifications on the amine-modified epoxy resin thus obtained. Polyepoxides are understood to mean compounds which contain two or more epoxy groups in the molecule.

Particularly preferred (α) components are compounds which can be prepared by reacting

(i) a diepoxide compound or a mixture of

Diepoxidverbindungen with an epoxy equivalent weight below 2000 with

(ii) a compound which reacts monofunctionally with respect to epoxy groups and contains a phenol or thiol group or a mixture of such compounds,

components (i) and (ii) being used in a molar ratio of 10: 1 to 1: 1, preferably 4: 1 to 1.5: 1, and the reaction of component (i) with component (ii) 100 to 190 ° C, optionally in the presence of a catalyst, is carried out (cf. DE-A-35 18 770).

Other particularly preferred (α) components are compounds which can be prepared by a starter which reacts at 100 to 195 ° C., optionally in the presence of a catalyst, by a monofunctional reactant which either contains an alcoholic OH group or a phenolic OH group. Group or an SH group, initiated polyaddition of a diepoxide compound and / or a mixture of diepoxide compounds, optionally together with at least one mono-epoxide compound 10 an epoxy resin in which the diepoxide compound and starter are installed in a molar ratio of greater than 2: 1 to 10: 1 (cf. DE-A-35 18732).

Polyepoxides which can be used for the production of the particularly preferred (α) components and also themselves as (α) components are polyglycidyl ethers of polyphenols prepared from polyphenols and epi-halohydrins. As polyphenols e.g. bisphenol A and bisphenol F are very particularly preferably used. In addition, 4,4'-dihydroxybenzophenone, bis (4-hydroxyphenyl) l, l-ethane, bis- (4-hydroxyphenyl) -l, l-isobutane, bis- (4-hydroxy-tertiary-butylphenyl) are also ) -2,2-propane, bis- (2-hydroxynaphthyl) methane, 1,5-di-hydroxynaphthalene and phenolic novolak resins.

Other suitable polyepoxides are polyglycidyl ethers of polyhydric alcohols, e.g. Ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and bis- (4-hydroxycyclohexyl) -2,2-propane. Polyglycidyl esters of polycarboxylic acids, e.g. Oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-nphthalinedicarboxylic acid and dimerized linoleic acid can be used. Typical examples are glycidyl adipate and glycidyl phthalate.

Hydantoine epoxides, epoxidized polybutadiene and polyepoxide compounds which are obtained by epoxidation of an olefinically unsaturated aliphatic compound are also suitable.

Modified polyepoxides are understood to mean polyepoxides in which at least some of the reactive groups have been reacted with a modifying compound. 11

Examples of modifying compounds are:

Compounds containing carboxyl groups, such as saturated or unsaturated monocarboxylic acids (e.g. benzoic acid, linseed oil fatty acid,

2-ethylhexanoic acid, versatic acid), aliphatic, cycloaliphatic and / or aromatic dicarboxylic acids of various chain lengths (e.g. adipic acid, sebacic acid, isophthalic acid or dimeric fatty acids), hydroxyalkyl carboxylic acids (e.g. lactic acid, dimethylolpropionic acid) and carboxyl-containing polyesters or

compounds containing amino groups, such as diethylamine or ethylhexylamine or diamines with secondary amino groups, e.g. N, N'-dialkylalkylenediamines, such as dimethylethylenediamine, N, N'-dialkylpolyoxyalkyleneamines, such as N, N'-dimethylpolyoxypropylenediamine, cyanoalkylated alkylenediamines, such as bis-N, N'-cyanoethylethylenediamine, cyanoalkylated polyoxyal -kylenamines, such as Bis-N, N'-

Cyanoethyl polyoxypropylene diamine, polyaminoamides, e.g. Versamides, especially reaction products containing terminal amino groups from diamines (eg hexamethylendiamine), polycarboxylic acids, especially dimer fatty acids and monocarboxylic acids, especially fatty acids, or the reaction product of one mole of diaminohexane with two moles of monoglycidyl ether or monoglycidyl ester, especially glycidyl acid ester, of branched fat fatty acid like versatic acid, or

compounds containing hydroxyl groups, such as neopentyl glycol, bisethoxylated neopentyl glycol, hydroxypivalic acid neopentyl glycol ester, di- 12 methylhydantoin-N, N'-diethanol, 1,6-hexanediol, 2,5-hexanediol, 1,4-bis (hydroxymethyl) cyclohexane, 1,1-isopropylidene-bis- (p-phenoxy) -2-propanol, trimethylolpropane, pentaerythritol or amino alcohols, such as triethanolamine, methyldiethanolamine or hydroxyl group-containing alkylketimines, such as aminomethylpropanediol-1, 3-methylisobutylketimine or tris (hydroximethyl) aminomethancyclohexanonketol ether, as well as polyether polyol polyol polyols caprolactone polyols, polycaprolactam polyols various

Functionality and molecular weights or

saturated or unsaturated fatty acid methyl esters which are transesterified in the presence of sodium methylate with hydroxyl groups of the epoxy resins.

Primary and / or secondary amines can be used as component (β).

The amine should preferably be a water-soluble compound. Examples of such amines are mono- and dialkylamines, such as methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, methylbutylamine and the like. Alkanolamines, such as e.g. Methylethanolamine, diethanolamine and the like. Furthermore, dialkylaminoalkylamines such as e.g. Dimethylaminoethylamine,

Diethylaminopropylamine, dimethylaminopropylamine and the like. Suitable. Amines containing ketimine groups, such as, for example, methylisobutyldiketimine of diethylenetriamine, can also be used. Low molecular weight amines are used in most cases, but it is also possible to use high molecular weight monoamines. 13

The amines can also contain other groups, but these should not interfere with the reaction of the amine with the epoxy group and should not lead to gelation of the reaction mixture.

Secondary amines are preferably used as the (β) component.

The charges required for water dilutability and electrical separation can be generated by protonation with water-soluble acids (e.g. boric acid, formic acid, lactic acid, preferably acetic acid). Another possibility for introducing cationic groups is to react epoxy groups of component (α) with amine salts.

Polyols, polycarboxylic acids, polyamines or polysulfides or mixtures of these classes of substances are used as component (γ). The polyols in question include diols, triols and higher polymeric polyols such as polyester polyols and polyether polyols. With regard to further details and further examples of suitable components (γ), reference is made to EP-B2-301 293, in particular on page 4, line 31, to page 6, line 27.

The cathodically depositable synthetic resins contained in the electrocoat materials are generally either self-crosslinking and / or are combined with a crosslinking agent or a mixture of crosslinking agents. 14

Self-crosslinkable synthetic resins can be obtained by introducing reactive groups into the synthetic resin molecules, which react with one another under baking conditions. For example, blocked isocyanate groups can be introduced into synthetic resins containing hydroxyl and / or amino groups, which block under firing conditions and react with the hydroxyl or amino groups to form crosslinked coating films. Self-crosslinkable synthetic resins can be obtained, for example, by reacting a synthetic resin containing hydroxyl and / or amino groups with a partially blocked polyisocyanate, which on average contains one free NCO group per molecule.

In principle, the electrocoat materials can be any crosslinking agent suitable for electrocoat materials, e.g. Phenoplasts, polyfunctional Mannich bases, melamine resins, benzoguanamine resins, blocked polyisocyanates and compounds containing activated ester groups. The electrocoat materials preferably contain blocked polyisocyanates as crosslinking agents. The use of blocked polyisocyanates in electrodeposition paints containing cathodically depositable resins has long been known and is also described in detail in the patent documents cited above, for example in EP-B2-301 293, page 6, line 38, to page 7, line 21.

The electrocoat materials of the invention are produced by generally well-known methods. The synthesis of the cathodically depositable

Binder is carried out according to well-known methods (see, for example, DE-C-27 01 002 and others) in organic solvents. The binder solutions thus obtained 15 or dispersions are converted into an aqueous phase in neutralized form.

In addition to the components described above, the aqueous electrodeposition paints according to the invention can also contain other customary paint constituents, e.g. Contain pigments, fillers, wetting agents, leveling agents, polymer microparticles, anti-foaming agents, anti-crater additives, catalysts, etc.

The solids content of the electrocoating materials of the invention is generally 5 to 40, preferably 10 to 40, particularly preferably 20 to 40, percent by weight.

The non-volatile fraction of the electrocoat materials of the invention consists of up to, preferably up to,% by weight of an electrophoretically depositable binder or a mixture of electrophoretically depositable binders, 0 to, preferably up to,% by weight of a crosslinking agent or a mixture of different crosslinking agents and up to , preferably up to% by weight of pigments and / or fillers.

Pigments are preferably incorporated in the form of a pigment paste in the aqueous binder solution or binder dispersion. The production of pigment pastes is generally known and does not need to be explained in more detail here (see D.H. Parker, Principles of Surface Coating Technology, Intersience Publishers, New York (1965) etc.).

For example, epoxy-amine adducts containing quaternary ammonium groups are used to produce the pigment pastes. Examples 16 for suitable resins are also described, for example, in EP-A-183 025 and EP-A-469 497.

In principle, the pigment pastes can contain all pigments and / or fillers suitable for electrocoating, for example Titanium dioxide, zinc oxide, antimony oxide, lead sulfate, lead carbonate, barium carbonate, porcelain, clay, potassium carbonate, aluminum silicate, silicon dioxide, magnesium carbonate and magnesium silicate, cadmium yellow, cadmium red, carbon black, phthalocyanine blue, chrome yellow, toluidyl red and iron oxides as well as anti-corrosion pigments, e.g. Zinc phosphate, lead silicate, or organic corrosion inhibitors.

Furthermore, the electrocoat materials can also contain conventional additives, such as e.g. the homo- or copolymers of an alkyl vinyl ether described in EP-B2-301 293 (see EP-B2-301 293, page 7, lines 21 to 51), polymer microparticles, anti-cratering agents, wetting agents, leveling agents, anti-foaming agents, catalysts and others. in conventional amounts, preferably in amounts of up to% by weight, based on the total weight of the electrocoat material.

The electrocoat materials of the invention can be used for painting electrically conductive substrates in which

(1) the electrically conductive substrate is immersed in an aqueous electrodeposition paint,

(2) the substrate is switched as an electrode,

(3) a film is deposited on the substrate by direct current, 17

(4) the painted substrate is removed from the electrocoat and

(5) the deposited paint film is baked.

The method described above is known and has been used on a large scale for several years (see also the patent documents cited above). The applied voltage can vary over a wide range and can be, for example, between 2 and 1000 V. Typically, however, voltages between 5o and 500 V are used.

The current density is usually between about 10 and 100 A / m ^. In the course of the deposition, the current density tends to drop. As soon as the paint film is deposited on the substrate, the painted substrate is removed from the electrocoating paint and rinsed off. The deposited paint film is then burned in. The stoving temperatures are usually 130 to 200 ° C., preferably 150 to 180 ° C. and the stoving time is generally between 10 and 60 min., Preferably between 15 and 30 min.

In principle, all electrically conductive substrates can be coated with the method described above. In particular, substrates made of metal such as steel, aluminum, copper and the like are mentioned as examples of electrically conductive substrates. In particular, motor vehicle bodies and their parts are coated according to the invention with the electrocoat materials in question. The electrodeposition paints are preferably used for priming in the context of a multi-layer coating. 18th

The following describes the production of cathodic electrocoat materials using two examples:

example 1

The following example shows the preparation of a cationic resin containing primary amino groups. Bisphenol A, bisphenol A diglycidyl ether and a bisphenol A-ethylene oxide adduct are heated together and form a modified polyepoxy resin. For this purpose, a blocked isocyanate is given as a crosslinker. A reaction with a mixture of secondary amines then takes place. The resin is partially neutralized with lactic acid and dispersed in water.

Reactants by weight of Epikote 828 ¹ 682.4

Bisphenol A 198.4

Dianol 265 ² 252.7

Methyl isobutyl ketone 59.7

Benzyldimethylamine 3.7 Blocked isocyanate ³ 1011.3

Diketimine ⁴ 65.4

Methylethanolamine 59.7

1-phenoxy-2-propanol 64.8

Lactic acid 88% 60.9

Emulsifier mixture ⁵ 15.2

Demineralized water 3026.6 19

Liquid epoxy resin made by reaction of bisphenol A and epichlorohydrin with an epoxide equivalent weight of 188 (Shell Chemicals)

² ethoxylated bisphenol A with an OH number of 222 (Akzo)

Polyurethane crosslinker made from diphenylmethane diisocyanate, in which 4.3 of 6 moles of isocyanate are first reacted with butyl diglycol and the remaining 1.7 moles with trimethylol propane. The crosslinker is in an 80% solution of methyl isobutyl ketone and

Isobutanol (weight ratio 9: 1) before

⁴ diketimine from the reaction of diethylene triamine and methyl isobutyl ketone, 75% in methyl isobutyl ketone

Mixture of 1 part butyl glycol and 1 part of a tertiary acetylene glycol (Surfynol 104; Air Products)

The Epikote 828, bisphenol A and Dianol 265 are heated to 130 ° C. in a reactor with nitrogen blanketing. Then 1.6 parts of the benzyldimethylamine (catalyst) are added, the reaction mixture is heated to 150 ° C. and kept between 150 ° and 190 ° C. for about half an hour and then cooled down to 140 ° C. The remaining amount of benzyldimethylamine is then added and the temperature is kept at 140 ° until an epoxy equivalent weight of 1120 is established after about 2.5 h. Immediately afterwards, the polyurethane crosslinker is added and the temperature is reduced to 100.degree. The mixture of secondary amines is then added and the reaction is held at 115 ° for about 1 h, 20 until a viscosity of approx. 6 dPas is reached (50% solution in methoxypropanol, ICI cone-plate viscometer). After the phenoxypropanol has been added, the resin is dispersed in the water in which the lactic acid and the emulsifier mixture are dissolved. The desired primary amino groups are formed from the ketimine adduct by hydrolysis.

The solid is 35% after this step, increases after

Stripping the low-boiling solvent to 37%.

The dispersion is characterized by a particle size of approx. 150 nm.

Example 2

This example shows the preparation of an aqueous dispersion which contains a cathodically depositable synthetic resin and a crosslinking agent:

589 parts of epoxy resin based on bisphenol A with an epoxy equivalent weight (EEW) of 188 together with 134 parts of bisphenol A and 108 parts of nonylphenol are heated in a reactor to 125 ° C. under a nitrogen atmosphere and stirred for 10 minutes. The mixture is then heated to 130 ° C. and 2.3 parts of N, N-dimethylbenzylamine are added. The reaction mixture is held at this temperature until the EEW has reached a value of 851 g / eq. Now 723 parts of the crosslinker (80%; blocked isocyanate, see Example 1) are added. Half a hour after the addition of crosslinking agent, a mixture of 21 parts of butylglycol and 102 parts of sec-butanol is added and the mixture is kept at 95.degree. A mixture of 50 parts of methylethanolamine and 48 parts of the precursor diketimine (cf. Example 1: diethylene triamine diketimine in methyl isobutyl ketone) is then added to the reactor. The reaction mixture heats up (exothermic reaction) and is kept at 100.degree. After another half an hour, 15 parts of N, N- 21

Dimethylaminopropylamine to the reaction mixture. Half an hour after the start of the addition, 93 parts of Plastilit 3060 (propylene glycol compound, BASF), 52 parts of propylene glycol phenyl ether and 20 parts of sec-butanol are added.

The mixture is cooled to 80 ° C. and, after a further 10 min, 1327 parts of the reaction mixture are transferred to a dispersion vessel. 45 parts of lactic acid (88% strength in water) in 728 parts of deionized water are added in portions with stirring. The mixture is then homogenized for 20 minutes before further dilution in small portions with a further 1400 parts of deionized water.

The dispersion has the following key figures:

Solids content: 30% (1 hour at 130 ° C.) Base content: 0.68 milliequivalents / g solids

Acidity: 0.37 milliequivalents / g solid

Example 3

300 ppm of formaldehyde in the form of the commercially available 37% formalin solution are added to a cathodically depositable electrodeposition bath according to Examples 1 and 2 and the mixture is stirred in for between 2 and 20 hours. After the reaction time, bare steel sheets ST 1405 and phosphated steel sheets Bo 25 are deposited and burned in as usual.

The edge coverage can be determined with an edge quality measuring device. The insulation ability of the edge from an untreated KTL- 22

Bad is 10-20%. Due to the addition of formaldehyde, this value increases to approx. 90%, i.e. the edge is almost completely covered. This is confirmed by the corrosion test according to ASTM. ST 1405 sheets were loaded for 360 h and showed an edge corrosion improvement from grade 5 to 1-2.

Example 4:

Analogously to Example 3, the same cathodically depositable ET varnish is mixed with 500 ppm of a hemavetal of formaldehyde and urea or butanediol and deposited after the reaction time of one day. The hemiacetal is cleaved in the weakly acidic medium and reactive formaldehyde is released. Similar results are obtained. An edge quality factor of 90-100% is obtained. The corrosion values according to ASTM on the edge are also improved from grade 5 to 1.

Claims

23 claims

1. Process for the production of electrocoating materials from aqueous binder dispersions, that is, that the

Binder dispersions from the electrocoat material are optionally added to catalysts, and one or more aldehydes of the general formula R-CH = 0 or one or more compounds which split off such aldehydes are added, where R is a hydrogen atom or an alcyl radical having 1-10 C atoms is.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the binder dispersions or the electrocoat organic compounds with amino groups, preferably primary

Contains amino groups.

3. The method according to claim 1 or 2, characterized gekennzeichn et that first a mixture of organic compounds, the amino groups, preferably primary

Contain amino groups, prepared and then the mixture is added to the binder or paint.

4. The method according to any one of claims 1 to 3, d a d u r c h g e k e n n z e i c h n e t that as Aldeyhd

Formaldehyde is used. 24

5. The method according to any one of claims 1 to 4, characterized in that the binder or the electrocoating material contain amine-modified epoxy resins.

6. The method according to any one of claims 1 to 6, characterized in that catalysts are used which contain metals, metal-containing compounds or mixtures.

7. The method according to any one of claims 5 or 6, characterized in that the catalysts are present in the electrocoating material in the form of cations, preferably in the form of divalent cations.

8. The method according to claim 7, so that the catalysts are used in such amounts that the cations are present in concentrations of 200 to 800 ppm, preferably 350 to 650 ppm, in the electrocoating material.

9. The method according to any one of claims 5 to 8, characterized in that the additive is added in such amounts that the electrocoat contains up to 50 to 1,000 ppm, preferably 200 to 500 ppm, of aldehyde. 25th

10. electrocoat with improved edge protection, characterized in that it is produced in a method according to any one of claims 1 to 9.

11. Use of the electrocoat material according to claim 10 as edge protection.