CA1263981A - Binders for cathodic electrocoating - Google Patents

Abstract

Abstract of the Disclosure: binders for cathodic electrocoating which are based on polyadducts/poly-condensates which carry basic nitrogen groups and are rendered water-dilutable by protonation with an acid, and one or more crosslinking agents for these polyadducts/
polycondensates, and their use.
These binders essentially consist of a mixture of (A) from 50 to 90% by weight of a polyadduct/polycon-densate which carries basic nitrogen groups and is obtainable by reacting (a) an adduct of a secondary amine and a polyepoxide compound, the adduct still containing free epoxide groups, with (b) a condensate which contains primary amino groups and is obtained from a primary diamine of not less than 4 carbon atoms and one or more mono-and/or dicarboxylic acids, one or more primary amino groups of the condensate (b) being used per free epoxide group of the adduct (a), and (B) from 10 to 50% by weight of a crosslinking agent which does not react with component (A) at room tem-perature but reacts with the latter at elevated tem-peratures with crosslinking.
The binders are useful for the cathodic electro-coating of electrically conductive substrates and as coating materials.

Description

t~
- 1 - 0.Z. 0062t0Z061 ~inders for cathodic electrocoating The presen~ invention relates to binders which are rendered water-dilutable by protonation with an acid and which are useful as coating ~aterials and for the preparation of cathodic electrocoating finishes.
German Published Application DE-AS 2~057,799 de-scribes a process for the cathodic electrophoretic de-position of a water-dispersed, ionic, organic resin which consists of a positively charged, amine-containing resin and a blocked, polyfunctional isocyanate.
European Patents 12,463 and 40,867 disclose heat-curable coating materials which undergo crosslinking via a transesterification reaction. The crosslinking agents used contain 3-hydroxy ester groups.
German Laid-Open Application DE-OS 2,737,375 dis-closed reaction products of polyepoxy resins with poly-amines which are reacted with not less than 2 moles of a monoepoxide or a Cg-C24-monocarboxylic acid per mole of adduct, monoepoxid~s being preferred. Aminoplasts and phenoplasts are used as crossl;nking agents.
German La;d-Open Application DE-OS 3,311,514 de-scribes urea condensates which are su;table as binder components in heat-curable finishes. In Example 6 of this application, a urea condensate is used together with a condensate of a hexamethylened;amine/polyepoxide adduct and a dimerized fatty acid for the preparation of a cath-odic e~ectrocoating finish which possesses very good mechanical and anticorrosion properties at a baking tem-perature a~ ~ow as 140C. The only disadvantages of this binder are the slight surface roughness and a small ten-dency to sedimentation in the electrocoating bath.
It is an object of the present ;nvention to over-co~e these disadvantages and retain the other~ise good ~roperties~ especially the bath pH of more than 7, which affords effective protection aga;nst plant corrosion.
~e have found that this object is achieved by the binder composition according to the invention.

, 3k~.'1

- 2 - o.~. Oa6Z/0~861 The present invention relates to a binder for cathodic electrocoating which is based on polyadducts/
polycondensates which contain basic nitrogen groups and are rendered water-dilutable by protonation with an acid S and one or more crosslinking agents for these polyadducts/
polycondendates, wherein the binder essentially consists of a mixture of (A) from S0 to 90% by weight of a polyadduct/polyconden-sate which carries basic nitrogen groups and is ob-tainable by reacting (a) an adduct of a secondary amine and polyepoxide compound, the adduct still containing free epoxide groups, with (b) a condensate which contains primary amino groups and is obtained from a primary diamine of not less than 4 carbon atoms and one or more nono-and/or dicarboxylic acids of not less than 6 carbon atoms, ~ith the proviso that one or more Z0 primary amino groups of the condensate (b) are used per free epoxide group of the adduct (a), and (~3 from 10 to 50% by weight of a crosslinking agent which does not react with component (A) at room temperature bu~ reacts with the latter at elevated temperatures with crosslinking.
Novel binders in which, for the preparation of component (b), the dimer fatty acid is used as the di' carboxyl~ic acid and/or the saturated or unsaturated fatty acid is used as the monocarboxylic acid are preferred.
Component (a) is PreferablY prepared using, as the secondary amine, a dialkylamine which contains 2 to 36 carbon atoms and may contain further funct;onal groups.
Preferred crosslinking agents (8) are polyvalent blocked isocyanates, aminoplast resins or phenoplast resins, polyam;nomethylated polyphenols, crosslinking agents ~hich undergo curing via esteraminolysis and/or transesterification, 12~;~'3~3....

- 3 - O.Z. 006Z/~2061 and urea condensates.
The present invention furthermore relates to the use of the novel binder which is rendered ~ater-dilutable by protonation with an acid, in the for0 of an aqueous dispersion which may contain pigments, organic solvents and/or furthPr assistants, as coating agents, an aqueous cathodic electrocoating bath which contains from S to 30% by weight of the novel binder and an article which is provided with a coating and is obtained by applying the novel binder or coating agent and carrying out baking.
Regarding the components of the novel binder, the following ~ay be stated specifically.
Component (A) is a poLyadduct/polycondensate which carries basic nitrogen groups and is obtainable by reace-ing components (a) and (b).
Component ~a) is an adduct of a secondary amine and a polyepoxide compound, the adduct still containing free epoxide groups.
The conventional glycidyl polyethers of polyhy-dricphenols can be used as polyepoxide co0pounds for the preparation of component (a). Examples of such polyhy-dricphenols are resorcinol, hydroquinone, p,p'-dihydroxy-phenylpropane (bisphenol A), p,p'-dihydroxybenzophenone, Z5 p,p'-dihydroxydiphenyl, p,p'-dihydroxydiphenylethane, bis-~2-hydroxynaphthyl)-methane, 1,5-dihydroxynaphthylene and novolaks. Bisphenol A is preferred. The polyphenols can be converted to the polyepoxides by reaction with an epi`ha~ohydrin, in part;cular epichlorohydrin. Polyepoxides having a lo~ molecular weight are formed when a large excess of an epihalohydrin is used, while those having a high ~olecular weight are obtained using a small amount of an epihalohydrin or by reacting a polyepoxide having ~ low molecular weight with a polyphenol. Diglycidyl ethers of bisphenol A, having an epoxide equivalent weight of about 180 - Z,S00, are preferably used for the pre-paration of the novel b;nders.

3~3~

- 4 - O.Z. 0062/02061 To prepare component (a), the polyepoxides are reacted with secondary amines. The ratio of the number of equivalents of epoxide groups to that of amino groups can vary within wide limits and is in general from 1.1:1 to 10:1, preferably from 1.4:1 to 3.3~ he reac~ion can be carried out in the presence or absence of a sol-vent. ~he reaction temperature and reaction time can be varied within certain limits and depends on the type of secondary amine used. For example, temperatures of from 20 to 200C are suitable, but it is advantageous to heat the mixture to SC to 150C in order to achie~e rapid reaction.
Suitable secondary amines for the preparation of component (a) are secondary monoamines, for example di-alkylamines of 2 to 36 carbon atoms, e.s. dimethylamineor diethylamine, alkylalkanolamines, e.g. methylethanol-amine, ~thylethanolamine or methylisoprpanolamine, and dialkanolamines, such as diethanolamine or diisopropanol-amine. The secondary monoamines may also contain further functional groups, provided that these do not interfere with the reaction of the secondary amines ~ith the poly-epoxides. The stated secondary monoamines can be em-ployed alone or as a mixture, and secondary diamines and, in a minor amount, for example up to 20 equivalent percent, based on the secondary amines, of primary/secondary or diprimary diamines may additionally be used.
To prepare componenc (b), primary diamines o~ not less than 4 carbon atoms are condensed with mono- and/or dicarboxyl ic acids of not less than 6 carbon atoms. Ex-amples of suitable diamines are 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane and 2-methyl-1,5-pen-tanediamine. Diamines containing ether groups, e.g.
4,9-dioxadodecane-1,12-diamine and 4,7~10-trioxatridecane-~,13-diamine, may also be used.
Exa~ples of suitable monocarboxylic acids are alpha-ethylhexanoic acid, isononanoic acid, caprylic acid, capric acid, stearic acid, linoleic acid, linolenic acid 1~3~3~3~
- S - O.Z. 0062/02061 and benzoic acid.
Examples of suitable dicarboxylic acids are adipic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, dodecanedicarboxylic acid and S preferably dimerized unsaturated C10-Cz4-fatty acids (dimer fatty acids"), e.g. Pripol~ 1014 from Unilever, and phthalic acid and terephthalic acid, as well as mix-tures of these carboxylic acids.
Although monocarboxylic acids may be employed alone, it is in general advantageous if dicarboxylic acids are concomitantly used. On the other hand, dicarboxylic acids can be used alone, this leading in many cases to excellent binders; however, it is often advantageous if minor amounts of monocarboxylic acids are also present~
The reaction of the diamines with the carboxylic acids is generally carried out at from 100 to 250C, pre-ferably from 150 to 200C~ To facilitate removal of the water formed during the condensation reaction, a solvent which is suitable as an entraining agent e.g. toluene or xylene, may be added. The carbo~ylic acids may also be used in the form of their esters. In this case, in-stead of water, an alcohol is eliminated during the con-densation. Instead of fatty acids, it is therefore also possible to use fats, i.e. the glycerol esters of the Z5 fatty acids. To prepare component (b), the primary di-amine and the carboxylic acids are used in amounts such that the ratio of the number of equivalents of NH2 to that of COOH is from about Z:1 to 10:1, preferably from Z;5:1 to 5:1~ The fact that, depending on the ratio of the numbers of equivalents employed, the product contains a larger or smaller amount of free diamine does not pre-sent problems and, on the contrary, may even be desirable in many cases.
Components (a) and (b) are reacted with one another in a ratio such that one or more primary amino groups of the condensate (b) are employed by a free epoxide group of the adduct (a). To limit the molecular weight, it is ~ ~39Bl - 6 - O.Z. 0062/02061 appropriate in most cases to use more than one primary amino group, e.g. from 1.05 to 1.5 primary amino groups, per free epoxide group of the adduct (a). The excess amount depends on the level of the desired molecular weight of ~A), which is about 500 - 13,000~ preferably about 1,500

- 5,000. When condensates (b) possessing primary amino groups and containing a large amount of monocarboxylic acids are used, the excess of primary amino groups over epoxide groups can of course be chosen to be smaller than in the case of condensates which contain exclusively or predominantly dicarboxylic acids.
The reaction of components (a) and (b) can be carried out at room temperature; however, it is advan-tageous to choose a higher temperature of up to about 150C, preferably up to about 120C, ;n order to ac-ceLerate the reaction. A reaction time of Z hours at from 70 to 90C is generally sufficient.
Suitable componQnts t~) are essentially any cross-linking agents which can be used in cathodic electrocoa-ting finishes.
Examples of suitable crosslinking agents (8) areaminoplast resins, such as urea/formaldehyde resins, mel-amine resins or benzoguanam;no resins, blocked ;socyanate crosslinking agents, crosslinking agents which undergo curing v;a esteraminolysis and/or transesterification and contain on average not less than two activated ester groups per molecule, e.g. ~-hydroxyalkyl ester crosslinking agents according to European Patent 40,867 and carbalkoxy-methyl ester crosslinking agents according to German Patent Application P 32 33 139.8, and urea condensates as de-scribed~in German Laid-Open Application DOS 3,311,514.
The ratio of components (A) and (B) depends on the type and number of groups capable of undergoing crosslink-irng in the two components. In general, a ratio of (A) to (~) of fro0 1:1 to 9:1, preferably from 1:1 to 5:1, par-ticularly preferably from 1.5:1 to 4:1, is used.
To prepare coating materials, further substances, ~39S~3~
- 7 - O.Z. 0062/~2061 such as pig~ents, assistants, solvents and curing cata-lysts can be added to the binder.
The coating materials prepared in this manner can be applied to substrates such as wood, glass, plastic or S metal by conventional methods, such a~ spraying, immersion, ~asting or knife coating.
The coatings are cured at from 80 to 220C for from 40 to 3 minutes, depending on the type of cross-linking agent.
After protonation with an acid, the novel binders are water-dilutable and can be applied not only in a con-ventional manner but also by cathodic electrocoating.
This procedure can be used to coat electrically conduc-tive substrates, such as metal articles or sheets of brass, copper, zinc, aluminum, iron or steel, which may or may not be chemically pretreated, e.g. phosphatized.
The binders can be protonated using inoran;c or organic acids. Formic ac;d, acetic acid, propionic acid, lactic acid and phosphoric acid are suitable for this purpose.
For cathodic electrocoating, the solids content of the electrocoating bath is generally brought to S - 45, preferably 10 - 30X by weight. Deposition is usually ef-fected at from 15 to 40C for from 30 to 360 seconds.
The pH of the bath is generally brought to 4.5 - 9.0, preferably 5.0 - 8.0, particularly preferably 6.8 - 8Ø
The deposition voltage is set at 50 - 500 volt. The ar-ticle to be coated is made the cathode, and the deposited film is baked at temperatures higher than 9ûC.
Preparation of component (A) , Component (A 1):
First, a condensate (b1) was prepared. To do this, 5,800 9 of hexamethylenediamine, 7,Z50 9 of a dimer fatty acid (Pripol~ 1014 from Unichema) and 1,400 9 of linseed oil fatty acid was slowly heated to 195C in a laboratory kettle, and water formed during this procedure (540 9) was distilled off~ The mixture was cooled to ~ i39~
- 8 - O.Z. 0062/02061 100C and then brought to a solids content of 70~ by iweight ~ith 5961 9 of tol~ene. The product had an amine number of 197 (mg of ~OH/g).
In a second vessel, an adduct (a1~ was first pre-pared from a seGondary amine and a polyepoxide compound.
To do this, 15 equivalents of a diglycidyl ether based on bisphenol A and epichlorohydrin, having an equivalent weight of 485 (Epikote~ 10001 from Shell), were dissolved in a solvent mixture consisting of 1û39 g of toluene and 103~ g of isobutanol, with heating. The 70~ strengt~ by weight solution formed was cooled to 60C, and 300.4 9 of methylethanolamine and 128 9 of isobutanol were added.
The temperature increased to 78C in the course of 5 minutes. After this time, 1850 9 of the condensate (b1) were added, and the mixture was heated at 80C for 2 hours~ The product had a viscosity of 2300 mPa.s, rneasured at 75C with a plate and cone v;scometer from ~pprecht.
Component (A 2):
The procedure described for the preparation of ZO (b1) was followed, except that the 14QO g of linseed oil fatty acid were replaced by an additional 1450 g of dimer fatty acid (Pripol 1014). The resulting product (b2) had an amine number of 190 and a solids content of 70X by we;ght, free hexamethylenediam;ne being calculated as a solid.
In a separate vessel 1589 9 of diglycidyl ether, having an epoxide equivalent weight of 535 and prepared from bisphenol A and epichlorohydrin, were dissoLved in 731.3 9 of isobutanol. 117.4 9 of ethylethanolamine were added at 60C, the temperature being kept at 70C for 45 minutes by initially cooling and subsequently heating.
The product is referred to below as adduct (a2). In an-other vessel 312.4 g of the amidoamine (b2) were initially t~aken and heated to 80C. 1108 9 of (a2) were then added in the course of 30 minutes, and the mixture was kept at 80C for a further 2 hours. The product had a solids content of 70~ by weight and a viscosity of 3,400 ~ 3~ ~
- 9 - O.Z. 0062/02061 mPa.s, measured at 75C using a plate and cone viscometer.
Component (A 3):
First, a condensate of a diamine and a carboxylic acid was prepared as described for component (A 1). In-stead of hexamethylenediamine, 2-methylpentamethylene-1,5-diamine was employed. The product (b3) had an amine number of 195 (mg of KOH/g).
In another vessel, 723 9 of a diglycidyl ether ob-tained from bisphenol A and epichlorohydrin (Epikote 1001 from Shell) were dissolved in 367 g of i-sobutanol, and 63 g of diethanolamine were added at 70C. The te~-perature was kept at 70C for 90 minutes by initially cooling and subsequently heating. Z82.7 9 of the con-densate (b3) were initially taken in a glass flask, and the above adduct was added in the course of 5 minutes at 80C, the temperature being kept at the stated vaLue by external cooling. Shortly after the end of the add;tion, the exothermic reaction died down and it was necessary to supply heat in order to keep the temperature at 80C.
Z0 After 2 hours at 80C, the product had a viscosity of 880 mPa.s, measured at 100C.
Component (A 4):
In a glass vessel, 737.6 9 of an aromatic epoxy resin based on bisphenoL A and having an epoxide equiva-lent weight of 189 (Araldite~ GY 2600 from Ciba-Geigy), 178 9 of bisphenol A and 0.24 9 of triphenylphosphine were heated to 130C while stirring, and kept at this temperature for 3 hours. After cooling, the mixture was diluted with 196.2 g of isobutanol and 196.2 9 of toluene.
The epoxide value of the solution was 0.181 (equivalents of epoxide/100 9). A mixture of 71.1 9 of methylethanol-a~ine and 23.7 9 of water was added at 65C. The tem-perature increased to ssQc in the course of S minutes.
After this time, 443.5 g of the condensate (b1) were rapidly added and the mixture was kept at 80C for 2 hours.

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- 10 - O.Z. 0062/02061 Preparation of components (~):
Component (9 1):
504 9 of trimerized hexamethylene diisocyanate were dissolved in 382 9 of methyl isobutyl ke~one. 388 9 of dibutylamine were added dropwise at 70C, ~hile cool-ing. Stirring was continued until the isocyanate value was close to zero. The product had a solids content of 70~ ~y weight.
Component (9 2):
67 9 of trimethylolpropane, 550.8 9 of urea and 2322 9 of di-n-butylamine were ;nitially taken. The in-ternal pressure was brought to 4 bar with nitrogen, and the temperature was increased to 140C, while stirring.
The internal pressure was kept constant at 4 bar. After about 0.5 hour, the internal temperature was increased to 165C, and 522 9 of hexamethylenediamine were forced ;nto the kettle with nitrogen in the course of 1 hour.
After the end of the addition, the mi~ture was heated to Z10C, the internal pressure still being maintained at 4 bar. After a total reaction time of 8 hours, the mix-ture was cooled to about 190C, the pressure was let down and excess di-n-butylamine was distilled off. Thereafter, the mixture was cooled to 100C and diluted with methyl isobutyl ketone so that a colorless to slightly yellowish Z5 liquid having a solids content of 80% by weight was formed.
Component (~ 3):
The polyester from Example IId) of European Patent 40,867 was prepared, the saicl polyester undergoing cross-linking via transesterification.
. 30 EXAMPLES 1 TO 6:
Preparation of dispersions:
Components (A) and t8) were mixed in the stated ratios~ and 10X strength by weight acetic acid was added.
~he dispersion was then prepared by slo~ly adding water, with stirring.

, 3~
~ O.Z. 0062/02061 Dispersion Co~ponent Component 10~ strength ~ater of example (A) (8) by ~eight acetic acid 1695 9 (A 1) 260 9 (9 Z) 160 9 3121 9 2695 9 (A 1) 298 9 (0 1) 160 9 3083 9 369S g (A 2) 260 9 (~ 2) 160 g 3121 9 4*)695 9 (A 3) 208 9 (B ~) 180 9 3153 9 S695 9 (A 3) Z60 9 (a 2) 160 9 3121 9 6695 g (A 4) 260 9 (a 2~ 160 9 3121 9 *) before the addition of water, 15 9 of Lead octclate (24% by weight of Pb) were added Pigment paste:
168.7 9 of butylglycol, 600 g of water and 16.59 of acetic acid were added to 525.8 9 of component (A 1).
800 9 of titanium d;oxide, 11 9 of carbon black and S0 9 of basic lead silicate were then added, and the mixture was m;lled on a ball mill to a particle size of less than 9 ~m.
The solids content was then brought to 49% by weight with water.
Electrocoating baths:
.. ... .. ~ --764 9 of the pigment paste was added to each of the stirred dispersions. The baths were stirred for 120 hours at 28C. Coating films were deposited in the course of 120 seconds at the stated voltage onto zinc-phosphatized steel test panels which had been made the cathode, and the said f;lms were baked for 20 minutes at 170C. The table below shous the results of the coat-ing tes~.

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- 12 - 0 . Z . 0062/02061 _~
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V) C~
V~
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O
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Q O O O O O O C
~ ., L L L L L L L
. .~ O
S' ~ O O O O O O
1-- QlS ' ~ ~ , ~_ V~ C V
L c~ O O O O O O
~Q /0 O O O O C Q
U~ O I L U~ ~ L
L U ~ aJ
~IJ L L L L L L ~ C
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L
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u- :~ Z oo U~ ~ _. ~_ O
Q~ O
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., w ~ e L Q
C 1~5 W ~ ~ E
., 'Z L ~O C O Ul U~ O
L O ~1 ~ L 3 L L ~ l O
>~ ~ O O O OJ
~11 1~ LL E 1 _ O C
L 11~
~ ~ e U~
a~ .o ~ ~ ~ ~ ~ :: _ o o o o o o J O O ~ (~1 0 Nt~ C
O
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:1~`O`C U~ ~1 00 L
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Claims (7)

We claim:-

1. A binder for cathodic electrocoating which is based on polyadducts/polycondensates which carry basis nitrogen groups and are rendered water-dilutable by protonation with an acid, and one or more crosslink-ing agents for these polyadducts/polycondensates, essentially consisting of a mixture of (A) from 50 to 90% by weight of a polyadduct/poly-condensate which carries basic nitrogen groups and is obtainable by reacting (a) an adduct of a secondary amine and a poly-epoxide compound, the adduct still containing free epoxide groups, with (b) a condensate which contains primary amino groups and is obtained from a primary di-amine of not less than 4 carbon atoms and one or more mono- and/or dicarboxylic acids of not less than 6 carbon atoms, with the proviso that one or more primary amino groups of the condensate (b) are used per free epoxide group of the adduct (a), and (B) from 10 to 50% by weight of a crosslinking agent which does not react with component (A) at room temperature but reacts with the latter at ele-vated temperatures with crosslinking.

2. A binder as claimed in claim 1, wherein the dicar-boxylic acid used for the preparation of component (b) is a dimerized, unsaturated C10-C24-fatty acid ("dimer fatty acid").

3. A binder as claimed in claim 1, wherein the mono-carboxylic acid used for the preparation of component (b) is a saturated or unsaturated C8-C24-fatty acid.

4. A binder as claimed in claim 1, wherein a dialkylamine which contains 2 to 36 carbon atoms and may also con-tain functional groups is used as the secondary amine for the preparation of the adduct (a).

5. A binder as claimed in claim 1, wherein the crosslink-ing agent (3) is a polyvalent blocked isocyanate, an aminoplast resin or phenoplast resin,, a polyamino-methylated polyphenol, a crosslinking agent which undergoes curing via esteraminolysis and/or trans-esterification, or a urea condensate,.

6. An aqueous cathodic electrocoating bath containing from 5 to 30% by weight of a binder as claimed in claim 1.

7. An article which is provided with a coating and ob-tained using a binder as claimed in claim 1.