CA2275415A1 - Paint and additive for cathodic electrophoretic dip-coating - Google Patents

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

' FILE, PM!-tN THUS AM~I'Bfa T~~ TRANSLATION
PAT 96482 12.10.1996 Electrodeposition coating material and additive for cathodic el.ectrodeposition coating The invention relates to a. process for preparing an electrodeposition coating material, to an electrodeposition coating material prepared by the process and to its use for improving edge coverage in connection with electrodeposition coating materials.
In electrodeposition coating, especially cathodic electrodeposition coating (C:ED), the process concerned is one which in recent years has been employed ever more frequently for the coating of electrically conductive articles, involving as it does the electrophoretic deposition on the surface to be coated of preferably water-thinnable synthetic resins which carry cationic groups. CED finds preferred application in connection with the priming of instrument casings and car bodies.
Electrodeposition baths suitable for said utilities are described, for example, in the following patent documents: US-3,799,854; US-3,984,299; US-4,031,050;
US-4,252,703; US-4,332,711; DE-31 08 073; DE-27 01 220;
DE-31 03 642; DE-32 15 891; EP-0 505 445; EP-0 074 634;
EP-0 358 221.

Resins which can be deposited electrically at the cathode are described, for example, in US-A 3,617,458.
These are crosslinkable coating compositions which deposit at the cathode. There coating compositions are derived from an unsaturated polymer, which contains amine groups and carboxyl groups, and an epoxidized material.
US-A 3,663,389 describes cationically electro-depositable compositions which are mixtures of certain amine-aldehyde condensates and a large number of cationic resinous materials, it being possible to prepare one of these materials by reacting an organic polyepoxide with a secondary amine and solubilizing with an acid.
US-A 3,640,926 discloses aqueous dispersions which can be deposited electrically at the cathode and which 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.
Epoxy-based and polyurethane-based binders for the use of binder dispersions and pigment pastes are disclosed, furthermore, in numerous embodiments. By way of example, reference may be made to DE-27 01 002, EP-A-261 385, EP-A-004 090 a:nd DE-C-36 30 667.
On the basis of good material yield and the substantial renunciation of organic solvents, CED offers great advantages over other prior art methods. A problem which has not been solved satisfactorily to date, however, is that of so-callE~d edge coverage, i . a . , the production of a uniform coating even over edges or, generally, sharp curvatures of the article to be coated. In fact, although the electrophoretic deposition of resin on the workpiece generally takes place within approximately uniform, sufficient coat thickness, the coating pul:Ls back in an undesirable manner from the edge regions and bend regions of the workpiece in the course of the subsequent stowing of the coating. In order to achieve crosslinking of the binders deposited during deposition coating it is in fact necessary to stove the coating film subsequently at temperatures of up to 180°C. During the heating of the coating film, however, it initially becomes liquid and at a certain temperature reaches its so-called viscosity minimum. Subsequently, as the temperature increases further, the viscosity of the applied coating material goes up again owing to the ensuing crosslinking of the binders. In the mobile phase in the region of the viscosity minimum, the effect then occurs that the coating film, owing to surface forces, flows away from the edges of the workpiece. This results in a decrease in the thickness of the coating film remaining on the edge, and in the worst case the edge is even exposed completely.
For these reasons various measures have been used in the attempt to raise the viscosity minimum so that the lowest level attained by the viscosity in the course of stowing is in any case sufficiently high to keep the flow away from the edges, as described, within tolerable limits. DE-43 32 014, for example, proposes achieving such an effect by using microgels in the electrodeposition coating material.
A disadvantage of the processes depicted, however, is that they are relatively expensive and complicated.
Furthermore, an increase in the edge coverage is accompanied by a deterioration in the leveling. This is because a uniform, smooth leveling of the electrodeposition coating film is brought about not least by virtue of the fact that, during stowing, the coating film liquefies and in doing so distributes itself in a uniform manner. The above-described raising of the viscosity minimum of the electrodeposition coating film therefore generally results in a deterioration in film leveling.

In the light of the known prior art, the object of the present invention is to achieve a considerable improvement in the edge coverage with a simple and cost-effective process for preparing the electrodeposition coating materials from aqueous binder dispersions.
This object is achieved in accordance with the invention by adding catalysts, if desired, to the binder dispersions comprising the electrodeposition coating material and adding one or more aldehydes of the formula R-CH=O or one or more compounds which donate such aldehydes, R being a hydrogen atom or an alkyl radical having 1-10 carbon atoms.
The aldehydes in question, accordingly, are not only aldehydes per se but also compounds which are able to donate aldehydes or aldehyde groups. The invention gives particular preference i=o the use of formaldehyde.
In one form which is particularly preferred in accordance with the invention, the aldehyde is added as a 35-45~ strength aldehyde solution. Solutions of this kind are obtainable commercially - in the case of the invention's preferred formaldehyde, for example, under the designation Formalin~. The level of aldehydes in the solution, or aldehyde donor compounds, is dependent on the intended use. In principle, however, the additives can consist of up to 100 aldehyde.
In one variant of the process of the invention, a mixture comprising one or more aldehydes of the formula R-CH=0 or one or more compounds which donate such aldehydes, R being a hydrogen atom or an alkyl radical having 1-10 carbon atoms, is prepared and stored separately from the electrodeposition coating material.
Where the electrodeposition coating material contains few or no compounds having amino groups, it is preferred first of all to prepare a mixture of organic compounds which do contain amino groups, preferably primary amino groups, and then to add the mixture to the binder or coating materi<~1.
The amino-containing compounds which can be employed in the context of the invention are preferably reactive with the aldehydes, i.e., they have primary or secondary amino groups. If reactive amino-containing compounds are indeed added, an improvement in the edge coverage is based on the following relationships. In the course of curing at relatively high temperatures, a deposited film undergoes a reduction in its viscosity, and does so before the crosslinking reaction has started or sufficiently advanced. As a result, the film runs undesirably away from the edges in the course of curing, owing to surface forces. The use of aldehydes and aldehyde-reactive amino-containing compounds, either an amino-containing binder or a different, additional, amino-containing compound, exerts an advantageous influence on the abovementioned time-dependent and/or temperature-dependent development of the viscosity in the course of curing. The amino-containing compound and thf~ aldehyde react with one another and the reaction product raises the viscosity of a deposited film in t:he initial phase of the temperature increase in the course of curing. However, this increase in viscosity is presumably only intermediate in nature, since as temperature increase advances there is apparently a reduction in viscosity (compared with the course of. viscosity when microgels, for example, are used) with the consequence of good leveling. This subsequent reduction in viscosity can probably be attributed to the fact that at a further increased temperature (and, .consequently, with further-advanced crosslinking) the :reaction product of amino-containing compound and aldehyde breaks down again. To this extent, curing takes place in the following phases: i) initial temperature increase for curing in the deposited film, with reaction between amino-containing compounds and aldehydes, or by means of a reaction product thereof, and viscosity increase relative to the same curing sequence without addition of aldehydes; ii) progressive curing or temperature increase in the deposited film, with reduction in viscosity relative to other, known viscosity-increasing measures; iii) final curing.
The mixture then, can be added to commercially customary deposition coating materials in an amount which can be controlled by the user. Preferably, the amounts are such that the aldehyde content in the electrodeposition coating material is from 50 to 1000 ppm, preferably from 200 to 500 ppm.
The addition of the aldehydes or aldehyde mixtures of the invention to electrodeposition coating materials has surprising, unforeseeab=Le positive effects on the edge coverage achieved. In connection with the evaluation of edge coverage' quality using customary, standardized test procedures (microscopic analysis;
climatic cycling test on phosphated metal panels:
VDA 621/415; salt spray tE:st (360 h): DIN50021 SS;
outdoor weathering with salt:: VDA 621/414), ratings in the region of 4 (within a ratings spectrum from 0 to 5) are obtained in accordance with the prior art, whereas with a deposition coating material according to the invention, using formaldehyde in the form of Formalin~, ratings in the region of 1 to 2 are always obtained.

Measurement of the coating film produced by using the coating material of the invention, with formaldehyde, gave a film thickness at the edges of from 5 to 9 dun under conditions in which in the absence of formaldehyde the edge coverage is nil (film thickness =
0 um) . Even with the minimtun film thickness of 5 dun, therefore, the edge protection achieved was still sufficient for practical purposes.
In order to improve edge protection, the aldehydes or aldehyde mixtures of the invention, as described, can be added in principle to ,all commercially customary electrodeposition coating materials or binders.
Where the electrodeposition coating material contains no catalyst, accordingly, t:he catalyst can be added separately to the electrodeposition coating material.
The catalyst generally comprises metals, especially heavy metals, metal compounds, or mixtures. They can preferably be present as divalent cations in the electrodeposition coating material. The presence of lead has been found to be particularly advantageous in accordance with the invention. Mixtures containing lead, or compounds which donate lead cations, inter alia, are suitable here. The catalysts are added in amounts of from about 200 to 800 ppm, with particular preference 350-650 ppm, based on the electrodeposition coating material.
It should be noted here that lead is often present in pigments and under certain circumstances is therefore already present in the electrodeposition coating material. In this case, the added amounts of lead or other catalysts must be matched to the lead-containing substances already present :in the form of pigment. If desired, the addition of catalyst can be omitted if it is present in a suf:Eicient amount in the electrodeposition coating material.
In the case of the preparation process described it is essential to the invention that the electrodeposition coating material used comprises the required compounds having amino groups: for instance, in the form of binders having primary amino groups. It is, however, also possible to add the compounds which carry amino groups to the electrodeposition coating material separately. It is likewise possible first of all to mix these compounds with the aldehyde - as already described above - and then to add the reaction adduct produced in this mixture to the electrodeposition coating material.

PAT 96482 - 1:1 -Suitable electrodeposition coating materials include those which can be depo:>ited at the anode, but preferably those which can be deposited at the cathode.
Examples of anodically depositable electrodeposition binders and coating materials (AED), containing anionic groups, which can be employed in accordance with the invention are knov,rn and are described, for example, in DE-A-28 24 418. For example, they comprise binders based on polyesters, epoxy resin esters, poly(meth)acrylates, maleate oils or polybutadiene oils. The binders carry, for example, -COOH, -S03H
and/or P03H2 groups. Follovuing neutralization of at least some of the acidic groups, the resins can be transferred to the aqueous phase. The coating materials may also include commonly employed crosslinkers, examples being triazine resins, crosslinkers with transesterifiable and/or t:ransamidatable groups, or blocked polyisocyanates.
The cathodically depositablE~ synthetic resins present in the cathodically depositable electrodeposition coating materials can in principle comprise any aqueous cathodically depositable synthetic resin that is suitable for aqueous electrodeposition coating materials. Examples of binders and crosslinkers which can be employed in CED coating materials are described in EP-A-82 291, EP-p,-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-3,922,253.
These electrodeposition coating materials comprise preferably cationic, amine--modified epoxy resins as cathodically depositable synthetic resins. Synthetic resins of this kind are known and are described, for example, in DE-A-35 18 770, DE-A-35 18 732, EP-B-102 501, DE-A-27 01 002, US-A-4,104,147, EP-A-4090, EP-A-12 463, US-A.-4,031,050, US-A-3,922,253, US-A-4,101,486, US-A-4,038,,232 and US-A-4,017,438.
These patent documents also describe in detail the preparation of cationic, amine-modified epoxy resins.
By cationic, amine-modified epoxy resins are meant cationic reaction products o:E
(a) modified or unmodified polyepoxides and ((3) amines and, if desired, (y) polyols, polycarboxyl~_c acids, polyamines or polysulfides.
These cationic, amine-modii:ied epoxy resins can be prepared by reaction of components (a), ((3) and, if used, (y) along with subsequent protonation if required. However, it is ,also possible to react an unmodified polyepoxide with an amine and to carry out further modifications on the resultant amine-modified epoxy resin.
By polyepoxides are meant compounds which contain two or more epoxide groups in the molecule.
Particularly preferred components (a) are compounds which can be prepared by reacting (i) a diepoxide compound or a mixture of diepoxide compounds having an epoxide equivalent weight of less than 2000 with (ii) a phenol or thiol compound which reacts monofunctionally with respect to epoxide groups under the given reaction conditions, or a mixture of such compounds, components (i) and (ii) being employed in a molar ratio of from 10:1 to 1:1, preferably from 4:1 to 1.5:1, and the reaction of component (i) with component (ii) taking place at from 100 to 190°C in the presence or absence of a catalyst (cf. Dl~-A-35 18 770).

PAT 96482 - 1~4 -Further particularly preferred components (a) are compounds which can be prepared by polyaddition of a diepoxide compound and/or a mixture of diepoxide compounds, alone or together with at least one monoepoxide compound, which is conducted at from 100 to 195°C in the presence or absence of a catalyst and is initiated by a monofunctionally reacting initiator which carries alternatively an alcoholic OH group, a phenolic OH group or an SH group, to give an epoxy resin in which diepoxide compound and initiator are incorporated in a molar ratio of more than 2:1 to 10:1 (cf. DE-A-35 18 732).
Polyepoxides which can be employed to prepare the particularly preferred components (a) and also as components (a) themselves a.re polyphenol polyglycidyl ethers prepared from polyp:henols and epihalohydrins.
Polyphenols which can be employed are, for example, with very particular preference, bisphenol A and bisphenol F. Also suit=able, furthermore, are 4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)-ethane, 1,1-bis(4-hydroxyphenyl)isobutane, 2,2'-bis(4-hydroxy-tert-butylphenyl)propane, bis(2-hydroxy naphthyl)methane, 1,5-dihydroxynaphthalene and phenolic novolak resins.

Further suitable polyepoxides are polyglycidyl ethers of polyhydric alcohols such as, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and 2,2-bis(4-hydroxycyclohexyl)propane. It is also possible to employ polyglycidyl esters of polycarboxylic acids such as, for example, oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid and dimerized linoleic acid. Typical examples a.re glycidyl adipate and glycidyl phthalate.
Also suitable are hydant:oin epoxides, epoxidized polybutadiene, and polyepox:ide compounds obtained by epoxidizing an olefinically unsaturated aliphatic compound.
By modified polyepoxides are meant polyepoxides in which at least some of the reactive groups have been reacted with a modifying compound.
Examples of modifying compounds are the following:
- carboxyl-containing compounds, 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 dicar:boxylic acids of various chain lengths (e. g., adipic acid, sebacic acid, isophthalic acid or dimeric fatty acids), hydroxyalkylcarboxylic acids (e. g., lactic acid, dimethylolpropionic acid), and carboxyl-containing polyesters, or amino-containing compounds, such as diethylamine or ethylhexylamine or diamines having secondary amino groups, e.g., N,N'-dialkylalkylenediamines, such as dimethylethy:lenediamine, N,N'-dialkyl-polyoxyalkyleneamines, such as N,N'-dimethyl-polyoxypropylenediamine, cyanoalkylated alkylene-diamines, such as bis-N, N'-cyanoethylethylene-diamine, cyanoalkylat~sd polyoxyalkyleneamines, such as bis-N,N'-cyanoethylpolyoxypropylene-diamine, polyaminoamide;s, such as Versamides, for example, especially terminal-amino-containing reaction products of diamines (e. g., hexamethylenediamine), polycarboxylic acids, especially dimeric 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 esters of branched fatty acids, such as of Versat:ic acid, or hydroxyl-containing compounds, such a neopentyl glycol, bisethoxylated neopentyl glycol, neopentyl glycol hydroxypivalate, dimethylhydantoin-N,N'-diethanol, 1,6-hexanediol, 2,5-hexanediol, 1,4-bis(hydroxymethyl)cyclohexane, 1,1-iso-propylidenebis(p-phenoxy)-2-propanol, trimethylol-propane, pentaerythritol or amino alcohols, such as triethanolamine, methyldiethanolamine or hydroxyl-containing a:Lkyl ketimines, such as aminomethyl-1,3-propanediol methylisobutyl ketimine or tris(hydroxymethyl)aminomethane cyclohexanone ketimine, and also polyglycol ethers, polyesterpo:lyols, polyetherpolyols, polycaprolactonepolyols and polycaprolactampolyols of various functionality and molecular weights, or - saturated or unsaturated fatty acid methyl esters which are transesterified with hydroxyl groups of the epoxy resins in the presence of sodium methoxide.
Primary and/or secondary amines can be employed as component ( (3 ) .
The amine should preferably be a water-soluble compound. Examples of such amines are mono- and PAT 96482 - lg -dialkylamines, such as methylamine, ethylamine, propylamine, butylamine, d_imethylamine, diethylamine, dipropylamine, methylbutylamine and the like. Likewise suitable are alkanolamines, such as methylethanolamine, diethanolamine and the like, for example. Also suitable are dialkylaminoalkylamines, such as, for example, dimethylaminoethylamine, diethylaminopropylamine, dimethylaminopropylamine and the like. It is also possible to employ amines which contain ketimine groups, such as, for example, the methyl isobutyl diketimine of diethylenetriamine. In the majority of cases use is made of amin~=s of low molecular mass, although it is also possib7_e to employ monoamines of higher molecular mass.
The amines may also include other groups as well, although these should not interfere with the reaction of the amine with the epoxide group and should also not lead to gelling of the reaction mixture.
It is preferred to employ secondary amines as component ((3) .
The charges required for water thinnability and electrodeposition can be generated by protonation with water-soluble acids (e. g., boric acid, formic acid, lactic acid, preferably acetic acid). A further possibility for introducing cationic groups is to react epoxide groups of component (a) with amine salts.
As component (y), use is made of polyols, polycarboxylic acids, polyaunines or polysulfides, or mixtures of these classes of substance. The polyols which are suitable include diols, triols and higher polymeric polyols, such as polyesterpolyols and polyetherpolyols. For further details and further examples of suitable components (y) reference may be made to EP-B2-301 293, especially page 4 line 31 to page 6 line 27.
The cathodically depositabl~~ synthetic resins present in the electrodeposition coating materials are generally either self-crossl.inking and/or are combined with a crosslinking agent: or with a mixture of crosslinking agents.
Self-crosslinkable synthetic' resins are obtainable by introducing into the synthetic-resin molecules reactive groups which react with one another under stowing conditions. For example, in hydroxyl- and amino-containing synthetic resins, blocked isocyanate groups can be introduced which deblock under stowing conditions and react with the hydroxyl and/or amino groups to form crosslinked coating films. Self-crosslinkable synthetic resins can be obtained, for example, by reacting a hydroxyl- and/or amino-containing synthetic resin with a partially blocked polyisocyanate containing on average one free NCO group per molecule.
The electrodeposition coating materials can in principle include any crosslinking agent suitable for electrodeposition coating materials, examples being phenolic resins, polyfunctional Mannich bases, melamine resins, benzoguanamine resins, blocked polyisocyanates, and compounds containing activated ester groups. The electrodeposition coating materials preferably comprise blocked polyisocyanates as crosslinking agents. The use of blocked polyisocyanates in electrodeposition coating materials comprising cathodically depositable synthetic resins has been known for a long time and is described in detail, inter alia, in the patent documents cited above, as for example in EP--B2-301 293, page 6 line 38 to page 7 line 21.
The electrodeposition coating materials of the invention are prepared by methods which are common knowledge. The cathodically depositable binders are synthesized by well-known methods (cf. e.g., DE-C-27 Ol 002 and the like;l in organic solvents. The binder solutions or disper~~ions obtained in this way are transferred in neutra:Lized form to an aqueous phase.
In addition to the components described above, the aqueous electrodeposition coating materials of the invention may also include further customary coatings constituents, such as, for .example, pigments, fillers, wetting agents, leveling agents, polymer microparticles, antifoams, anticrater additives, catalysts, etc.
The solids content of the electrodeposition coating materials of the invention is generally from 5 to 40, preferably from 10 to 40 and, with particular preference, from 20 to 40 percent by weight.
The nonvolatiles content of the electrodeposition coating materials of the invention comprises from ...
to ..., preferably from ... to ...~ by weight of an electrophoretically depositable binder or a mixture of electrophoretically depositable binders, from 0 to ..., preferably from ... to ...~ by weight of a crosslinking agent or a mixture of different crosslinking agents, and from ... to ..., preferably from ... to ...~ by weight of pigments and/or fi:Llers.

Pigments are preferably incorporated in the form of a pigment paste into the aqueous binder solution or binder dispersion. The preparation of pigment pastes is common knowledge and need not be discussed further here (cf. D.H. Parker, Principles of Surface Coating Technology, Interscience Publishers, New York (1965) etc.).
To prepare the pigment pastes, epoxy-amine adducts containing quaternary ammonium groups, for example, are employed. Examples of suitable resins are also described, for example, in EP-A-183 025 and EP-A-469 497.
The pigment pastes can in principle comprise any pigments and/or fillers that are suitable for electrodeposition coating materials, examples being 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, chromiu~,m yellow, toluidyl red and iron oxides, and also anticorrosion pigments, such as, for example, zinc phosphate, lead silicate, or organic corrosion inhibitors.

Furthermore, the electrodeposition coating materials can also comprise customary additives, such as, for example, the homopolymers or copolymers of an alkyl vinyl ether that are described in EP-B2-301 293 (cf.
EP-B2-301 293, page 7 lines 21 to 51), polymer microparticles, anticrater agents, wetting agents, leveling agents, antifoams, catalysts and the like in customary amounts, preferably in amounts from ... to ...$ by weight, based on the overall weight of the electrodeposition coating material.
The electrodeposition coating materials of the invention can be used for coating electrically conductive substrates, where (1) the electrically conductive substrate is immersed in an aqueous electrodeposition coating material, (2) the substrate is connected as one electrode, (3) a film is deposited on the substrate by means of direct current, (4) the coated substrate is removed from the electrodeposition coating material, and (5) the deposited coating film is stowed.

The process described above is known and has already been widely used for many years (compare also the above-cited patent document~~). The applied voltage can vary within a wide range and can, for example, be between 2 and 1000 V. Typically, however, voltages of between 50 and 500 V are employed. The current density is generally between about 10 and 100 A/m2. In the course of deposition the current density tends to drop.
As soon as the coating film has been deposited on the substrate, the coated substrate is removed from the electrodeposition coating material and rinsed.
Subsequently, the deposited coating film is stowed. The stowing temperatures are usually from 130 to 200°C, preferably from 150 to 180°C, and the duration of stowing is generally between 10 and 60 minutes, preferably between 15 and 30 minutes.
The process described above can be used in principle to coat any electrically conductive substrate. Examples of electrically conductive substrates are, in particular, substrates of metal, such as steel, aluminum, copper and the like. In particular, motor vehicle bodies and parts thereof are coated in accordance with the invention with the electrodeposition coating materials in question. The electrodeposition coating materials are preferably used for priming in the context of a multicoat paint system.
Using two examples, the text below describes the preparation of cathodic electrodeposition coating materials:
Example 1:
The example which follows :shows the preparation of a cationic resin comprising 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. A blocked isocyanate is added as crosslinker. This is followed by a reaction with a mixture of secondary amines. The resin is partially neutralized with lactic acid and is dispersed in water.
Ingredients Parts by weight Epikote 8281 682.4 Bisphenol A 198.4 Dianol 2652 252.7 Methyl isobutyl ketone 59.7 Benzyldimethylamine 3.7 Blocked isocyanate3 1011.3 Diketimine4 65.4 Methylethanolamine 59.7 1-Phenoxy-2-propanol 64.8 Lactic acid 88~ 60.9 Emulsifier mixtures 15.2 Demineralized water 3026.6 1 Liquid epoxy resin prepared by reacting bisphenol A
and epichlorohydrin, having an epoxide equivalent weight of 188 (Shell Chemicals) 2 Ethoxylated bisphenol A having an OH number of 222 (Akzo) 3 Polyurethane crosslin.ker prepared from diphenylmethane diisocyan<~te, where, of 6 moles of isocyanate, 4.3 are first reacted with butyldiglycol and the remaining 1.'7 mol are reacted with trimethylolpropane. The crosslinker is present in the form of an 80~ strength :solution in methyl isobutyl ketone and isobutanol (weight ratio 9:1) 4 Diketimine from the reaction of diethylenetriamine and methyl isobutyl ketone, 75~ strength in methyl isobutyl ketone 5 Mixture of 1 part of buty:Lglycol and 1 part tertiary acetylene glycol (Surfynol 104; Air Products) The Epikote 828, bisphenol A and Dianol 265 are heated to 130°C in a reactor under- nitrogen blanketing. Then 1.6 parts of the benzyldirnethylamine (catalyst) are added, and the reaction mixture is heated to 150°C, held between 150 and 190°C for about half an hour and then cooled to 140°C. Subsequently, the remainder of the benzyldimethylamine is added and the temperature is held at 140°C until, after about 2.5 h, an epoxide equivalent weight of 1120 is established. Directly thereafter, the polyurethanes crosslinker is added and the temperature is lowered i.o 100°C. Subsequently, the mixture of the secondary amines is added and the reaction is maintained at 1.15° for about 1 h until a viscosity of about 6 dPas is reached (50~ dilution in methoxypropanol, ICI cone and plate viscometer).
Following addition of the phenoxypropanol, the resin is dispersed in the water, in which the lactic acid and the emulsifier mixture are present in dissolved form.
The desired primary amino groups form from the ketimine adduct by hydrolysis.
Following this step, the :>olids content is 35~ but increases to 37~ after the low-boiling solvents have been stripped off.
The dispersion is characterized by a particle size of about 150 nm.

Example 2:
This example shows the preparation of an aqueous dispersion comprising a cathodically depositable synthetic resin and a crosslinker:
In a reactor, 589 parts of epoxy resin based on bisphenol A, having an epox:ide equivalent weight (EEW) of 188, together with 134 parts of bisphenol A and 108 parts of nonylphenol, a:re heated to 125°C under a nitrogen atmosphere and stirred for 10 minutes. The mixture is subsequently 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 the level of 851 g%eq. Then 723 parts of the crosslinker (80~ strength; blocked isocyanate, see Example 1) are added. Half an hour after the addition of the crosslinker, a mixt=ure of 21 parts of butyl glycol and 102 parts of sec,-butanol is added and the mixture is maintained at 95°C. Subsequently a mixture of 50 parts of methylethanolamine and 48 parts of precursor diketimine (cf. Example 1: diethylenetriamine diketimine in methyl isobutyl ketone) is introduced into the reactor. The reaction mixture warms up (exothermic reaction) and i.s held at 100°C. After a further half an hour, 1.5 parts of N,N-dimethyl-aminopropylamine are added to the reaction mixture.

Half an hour after the commencement of the addition, 93 parts of Plastilit 3060 (propylene glycol compound from BASF), 52 parts of prc>pylene glycol phenyl ether and 20 parts of sec-butanol .are added.
The mixture is cooled to 80°C and, after 10 minutes more, 1327 parts of the reaction mixture are transferred to a dispersing vessel. In that vessel, 45 parts of lactic acid (88~ strength in water) in 728 parts of deionized wat~=r are added in portions, with stirring. The mixture is subsequently homogenized for 20 minutes before being diluted further with an additional 1400 parts of deionized water in small portions.
The dispersion has the following characteristics:
Solids content: 30~ (1 h at 130°C) Base content: 0.68 milliequivalent/g solids Acid content: 0.3'7 milliequivalent/g solids Example 3 300 ppm of formaldehyde in the form of the commercially customary 37~ strength Formalin solution are added to a cathodically depositable electrodeposition bath in accordance with Examples 1 and 2, and stirred in for between 2 and 20 h. Following the reaction time, bright steel panels ST 1405 and phosphated steel panels Bo 25 are subjected to deposition and stowing in the customary manner.
The edge coverage can be determined using an edge quality measuring instrument. The isolation ability of the edge from an untreated C:ED bath is 10-20~. Through the addition of formaldehyde, this figure increases to about 90~, i.e., the edge is almost fully covered. This is confirmed by the ASTM corrosion test. ST 1405 panels were exposed for 360 h and showed an improvement in edge corrosion rating from 5 to 1-2.
Example 4;
In a procedure similar to that of Example 3, the same cathodically depositable electrodeposition coating material is admixed with 500 ppm of a hemiacetal formed from formaldehyde and urea or butanediol, and deposition is carried out following the reaction time of one day. In the weakly acidic medium, the hemiacetal is cleaved and reactive formaldehyde is liberated.
Similar results are obtained. An edge quality figure of 90-100 is obtained. In addition, the ASTM corrosion ratings at the edge are improved from 5 to 1.

Claims (11)

Claims

1. A process for preparing electrodeposition coating materials from aqueous binder dispersions, which comprises adding cata7_ysts, if desired, to the binder dispersions comprising the electrode-position coating mater_Lal and adding one or more aldehydes of the formula R-CH=O or one or more compounds which donate such aldehydes, R being a hydrogen atom or an alkyl radical having 1-10 carbon atoms.

2. The process as claimed in claim 1, wherein the binder dispersions or the electrodeposition coating material comprise or comprises organic compounds having amino groups, preferably primary amino groups.

3. The process as claimed in claim 1 or 2, wherein first of all a mixture of organic compounds containing amino groups, preferably primary amino groups, is prepared and then the mixture is added to the binder or coating material.

4. The process as claimed in one of claims 1 to 3, wherein the aldehyde employed is formaldehyde.

5. The process as claimed. in one of claims 1 to 4, wherein the binder or electrodeposition coating material comprises amine-modified epoxy resins.

6. The process as claimed in one of claims 1 to 6, wherein catalysts are employed which comprise metals, metal compounds, or mixtures.

7. The process as claimed in either of claims 5 and 6, wherein the catalysts in the electrodeposition coating material are in the form of cations, preferably in the form of divalent cations.

8. The process as claimed in claim 7, wherein the catalysts are employed in amounts such that the cations are present in concentrations of from 200 to 800 ppm, preferably from 350 to 650 ppm, in the electrodeposition coating material.

9. The process as claimed in one of claims 5 to 8, wherein the additive is added in amounts such that the electrodeposition coating material contains from 50 to 1000 ppm, preferably from 200 to 500 ppm, of aldehyde.

10. An electrodeposition coating material giving improved edge coverage', which is prepared in a process as claimed in one of claims 1 to 9.

11. The use of the electrodeposition coating material as claimed in claim 10 as an edge protector.