EP0298968A1

EP0298968A1 - Aqueous electrophoretic painting baths for cathode electrophoretic painting and process for its performance

Info

Publication number: EP0298968A1
Application number: EP87901476A
Authority: EP
Inventors: Georg SCHÖN; Günter Ott; Michael Geist
Original assignee: BASF Lacke und Farben AG
Current assignee: BASF Farben und Fasern AG
Priority date: 1986-03-26
Filing date: 1987-03-07
Publication date: 1989-01-18
Also published as: KR880701268A; WO1987005922A1; ZA872011B; BR8707646A; US4944855A; ES2023374B3; AU7125287A; JPH01501943A; DE3771097D1; AU595596B2; EP0238920B1; ATE64934T1; CN1009109B; KR930007352B1; CA1300791C; DE3610183A1; EP0238920A1; JPH0357154B2; CN87102278A

Abstract

PCT No. PCT/EP87/00130 Sec. 371 Date Sep. 23, 1988 Sec. 102(e) Date Sep. 23, 1988 PCT Filed Mar. 7, 1987 PCT Pub. No. WO87/05922 PCT Pub. Date Oct. 8, 1987.The invention relates to aqueous electrocoating baths for cathodic paint deposition which contain, as cathodically depositable binders, modified epoxide-amine adducts and are prepared by reacting, in the presence of basic amine catalysts, (1) (A) polyepoxides with (B) compounds which contain, per molecule, one or more, preferably 2, hydroxyl groups bonded to aromatic and/or (cyclo)aliphatic molecular fragments, to form epoxide group-containing intermediates, and (2) by subsequently reacting these intermediates, if appropriate, with further conventional modifiers and finally with (C) primary and/or secondary (poly)amines or their salts and/or salts of tertiary amines, the resultant reaction products being neutralized with acids, if appropriate, dispersed in an aqueous medium and these dispersions further processed by well-known methods to form electrocoating baths. The electrocoating baths according to the invention are distinguished by the fact that the basic amine catalyst which catalyzes the reaction between the components (A) and (B) is neutralized, prior to further reaction of the intermediates formed from the components (A) and (B), with a Brönsted acid having a pKs value of the first stage of dissociation, measured at 20 DEG C., below 3.7, preferably below 3.5.

Description

Aqueous electrocoating baths for cathodic electrocoating and process for their production

0

The invention relates to aqueous electrodeposition coating baths for cathodic electrodeposition coating, which use modified epoxy as cathodically separable binders.

Aninaάucts contain and have been prepared by 5 (1) (A) polyepoxides and

(B) Compounds containing one or more, preferably 2, aromatic and / or (cyclo) aliphatic

Molecular fashions bound hydroxyl groups per

Contain molecule, _Q have been converted to epoxy group-containing intermediates in the presence of amine-based catalysts and

(2) these intermediates are subsequently reacted, if appropriate, with further customary modifiers and finally with 5 ^' (C) primary and / or secondary (poly) aenes or their salts and / or salts of tertiary amines, the reaction products thus obtained, if appropriate, with Acids neutralized, dispersed in an aqueous medium and these dispersions have been further processed into electrocoating baths by well-known methods.

Cationic electrodeposition coating is a coating process that is frequently used primarily for priming, _c in which water-thinnable synthetic resins bearing cationic groups are applied to electrically conductive bodies with the aid of direct current. Electrocoating baths of the type described above are disclosed, for example, in the following patent documents:

3,799,854, U.S. Patent 3,984,299, U.S. Patent 4,031,050, U.S. Patent

4,252,703, U.S. Patent 4,332,711 and DE Patent 3108073.

It is known that lacquer systems of this type can be used to achieve high-quality lacquers.

Unfortunately, the electrocoating baths in question undesirably also contain chloride ions, which, if they exceed a concentration limit dependent on several parameters (for example pH value of the electrocoating bath), corrode the electrocoating systems, in particular the anodes (for example pitting corrosion on stainless steel) - electrodes).

The disruptive chloride ions mainly come from the polyepoxides used as component (A) for the synthesis of the binders and contaminated with chlorine-containing by-products.

These by-products can e.g. contain the following structural elements:

CHoOH - <° 0> - 0-CH ₂ -CH-CH ₂ OH

Cl

The chlorine content of commercially available polyepoxides is between 0.15 and 0.5% due to the presence of such by-products.

DE-AS-2751498 describes that the addition of nitrate and / or nitrite ions in the electrocoating bath reduces the corrosion damage caused by the presence of the chloride ions.

This process, like the cleaning of the poly-epoxides contaminated with chlorine-containing by-products or the removal of the chloride ions from the finished aqueous electrocoat material, is not carried out in practice using known separation processes due to economic and / or technical difficulties. The object on which the present invention is based is to provide electrodeposition paint baths of the type described at the outset, which have lower chloride ion concentrations than the baths known in the prior art.

This object can surprisingly be achieved by providing electrocoating baths of the type described above, which are characterized in that the amine-based catalyst which catalyzes the reaction between components (A) and (B) before the further reaction of the components (A) and (B) Intermediates formed with a Bronsted acid, the pK value of the first dissociation stage measured at 20 ° C. which is below 3.7, preferably below 3.5, has been neutralized

The invention also relates to a process for the production of aqueous electrocoating baths for cathodic electrocoating, in which

(1) (A) polyepoxides and

(B) compounds which contain one or more, preferably 2, hydroxyl groups per molecule bound to aromatic and / or (cyclo) aliphatic molecular fragments, are converted to intermediate products containing epoxide groups in the presence of amine-based catalysts and

(2) these intermediates then, if necessary, with further customary modifiers and finally with

(C) primary and / or secondary (poly) amines or their salts and / or salts of tertiary amines are reacted, the reaction products thus obtained are optionally neutralized with acids, dispersed in an aqueous medium and these dispersions are further processed into electrocoating baths using well-known methods characterized in that the reaction between components (A) and (B) is catalytic amine-based catalyst prior to the further reaction of the intermediates formed from components (A) and (B) with a Bronsted acid whose pK value measured at 20 ° C. of the first dissociation stage is below 3.7, preferably below 3.5 lies, is neutralized.

To produce the electrodeposition coating baths according to the invention, the binder which can be deposited by cathodic treatment is produced in a predominantly organic manner by well-known methods

Synthesized existing reaction medium.

First of all, components (A) and (B) contain epoxy groups under amine-based catalysis

Intermediates manufactured.

All compounds whose molecules contain more than 1 epoxy group on average can be used as component (A). Preferred compounds are those which

Contain 2 epoxy groups in the molecule and a relatively low molecular weight of at most 750, preferred

400-500.

Particularly preferred epoxy compounds are polyglycidyl ethers of polyphenols made from polyphenols and epihalohydrins. Preferred as polyphenol

Bisphenol A can be used.

Polyglycidyl esters of polycarboxylic acids can also be used. Typical examples are glycidyl adipate and glycidyl phthalate.

Also suitable are hydantoin epoxides, epoxidized polybutadiene and polyepoxide compounds which are obtained by epoxidizing an olefinically unsaturated alicyclic compound.

Compounds are used as component (B) which contain one or more, preferably 2, hydroxyl groups per molecule bound to aromatic and / or (cyclo) aliphatic molecular fragments.

The compounds which can be considered as component (B) include both low and high molecular weight compounds. 1 Suitable low molecular weight (B) components consist of phenolic, aliphatic and / or alicyclic polyfunctional alcohols with a molecular weight below

_ 350. b

Examples include:

Diols, such as ethylene glycol, dipropylene glycol, triglycol,

1, 2-propanediol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propy_W. , 3-propanediol, 1, 2-butanediol,

1,4-butanediol, 2-ethyl-l, 4-butanediol, butene-2-diol-l, 4,

1,2-pentanediol, 1,5-pentanediol, 3-methyl-l, 5-pentanediol,

1,6-hexanediol, 2-hydroxyethyl hydroxyacetate, 2,2-dimethyl

3-hydroxypropyl-2,2-di ethyl hydroxypropionate, 4,4'-ethylene-biscyclohexanol and 4,4'-isopropylidene-biscyclohexanol. 5

Some preferred diols are 2,2-dimethyl-1,3-propanediol and 3-methyl-1,5-pentanediol.

Examples of higher molecular weight (B) components are polyester polyols, polyether polyols or polycaprolactone polyols of different functionality and molecular weights.

Polyalkylene ether polyols suitable for component Bj correspond to the general formula:

in which R = hydrogen or a lower alkyl radical, 0 optionally with different substituents, n = 2-6 and m = 3-50 or even higher. Examples are poly (oxytetra-methylene) glycols and poly (oxyethylene) glycols.

The preferred polyalkylene ether polyols are poly (oxytetra-5 methylene) glycols with a molecular weight in the range of 350-1000. Polyester polyols can also be used as (B) components. You can go through the polyester polyols

Polyesterification of organic polycarboxylic acids or their anhydrides with organic polyols which contain primary 5 hydroxyl groups. The polycarboxylic acids and the polyols are usually aliphatic or aromatic dicarboxylic acids and diols.

The diols used to make the polyester

10 include alkylene glycols such as ethylene glycol, butylene glycol,

Neopentyl glycol and other glycols such as cyclohexanedimethanol.

The acid component of the polyester consists of the first

15 line of low molecular weight carboxylic acids or their

Anhydrides with 2-18 carbon atoms in the molecule. Suitable acids are, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid and glutaric acid.

20 ssääuurree .. AAnnsstteellllee ddiieesseerr SSääuurreenn kköönnnneenn aauucchh their anhydrides, if they exist, are used

It is also possible to use polyester polyols derived from

Derive lactones, use as component (B). This

25 products are obtained by reacting a £ -caprolactone with a polyol. Such products are described in U.S. Patent 3,169,945.

The polylactone polyols that qn

° are characterized by the presence of a terminal hydroxyl group and by recurring polyester fractions which are derived from the lactone. These recurring molecular parts can be of the formula

35 9 - (CHR) n - CH ₂ 0 correspond in which n is at least 4, preferably 4-6, and the substituent is hydrogen, an alkyl radical

Is cycloalkyl or an alkoxy.

In principle, all amine-based catalysts can contain one or more basic nitrogen atoms

Connections are used.

Preferably tertiary amines such as e.g. N, N-dimethylbenzylamine, tributylamine, dimethylcyclohexylamine and

Dimethyl-C ₁₂ / C. ^Amine ( ^C ₁₂ ^/ ' ^C 14 ^{s is for an} aliphatic chain containing ^{12-14 c} atoms) was used.

The amine-based catalyst is generally used in an amount of 0.1-2% by weight, based on the intermediate product formed from components (A) and (B).

In the method according to the invention for producing the electrocoating baths according to the invention,

Contrary to the prior art - the amine-based catalyst catalyzing the reaction of components (A) and (B) before the further reaction of the intermediates formed from components (A) and (B) with a

Bronsted acid neutralized.

The a inbasic catalyst can be neutralized before the reaction of components (A) and (B) or in the course of the reaction between components (A) and (B).

In one embodiment of the invention, the amine-based catalyst is switched off within the time interval between the onset of the reaction between components (A) and (B) and the completion of the reaction between components (A) and (B) the epoxy group-containing intermediates formed by components (A) and (B) by adding a sufficient amount neutralized with a suitable Bronsted acid. As a result, chloride ion concentrations are achieved which are lower than the chloride ion concentrations to be found in comparable electrodeposition coating baths according to the invention.

A particularly preferred embodiment of the invention is that the amine-based catalyst has been neutralized before the reaction of components (A) and (B), i.e. the implementation between the

Components (A) and (3) with a salt from the

Neutralization used Brönsted acid and the amine-based catalyst catalyzed. This procedure provides particularly low chloride ion contents.

As a result of the measures described above, the electrocoating baths produced by the process according to the invention have a chloride ion content which is significantly lower than that found in comparable electrocoating baths, in the manufacture of which the measure according to the invention has not been carried out ... .

It is surprising and was in no way foreseeable that electro-dip lacquer baths with a reduced chloride ion content can be produced with the aid of the measures according to the invention.

Brönsted acids are substances that can give off protons.

When selecting the Bronsted acid to be used to neutralize the amine-based catalyst which catalyzes the reaction between components (A) and (B), care must be taken that the extent of the reduction in chloride ion concentration also depends on the strength of the one used

Acid dependent 1 The pK value of the first dissociation stage of the acids used, measured at 20 C, should be below 3.7, preferably below 3.5, very particularly preferably below 3.1. (For a definition of the pK value, see e.g. Organikum, VEB German Publishing House of Sciences, Berlin 1974, page 150 f.)

Examples of suitable Bronsted acids are benzenesulfonic sulfonic acid, p-toluene sulfonic acid, o-nitrobenzoic acid, salicylic acid and _1Q called phosphoric acid.

Very particularly low chloride ion concentrations can be achieved when using salicylic acid.

, _ Preferably 1.0-1.5 equivalents of acid are used on 1 equivalent of basic nitrogen.

The reaction between components (A) and (B) is preferred at temperatures between 100 and 190 ° C

_ΛΛ between 115 and 185 C. 20th

After the neutralization of the amine-based catalyst has taken place, the intermediate products containing epoxide groups, which are formed from components (A) and (B), are reacted with other customary modifiers, which do not require amine-based catalysis, and then with component (C).

As component (C) primary and / or secondary

Amines or their salts and / or salts of tertiary 30th

Amines are used, the secondary amines being particularly preferred components (C).

The amine should preferably be a water-soluble compound. Examples of such amines are mono- and dialkylamines, such as methylamine, ethylamine, propyla in, butylamine,

Dimethylamine, diethylamine, dipropylamine, methylbutylamine and the like Alkanols such as, for example, are also suitable Methylethanolamine, diethanolamine and the like Furthermore, dialkylaminoalkylamines such as dimethylaminoethylamine, diethylaminopropylamine, dimethylaminopropylamine and the like. suitable.

Low molecular weight amines are used in most cases, but it is also possible to use high molecular weight amines

Apply monoamines.

Polyamines with primary and secondary amino groups can be reacted with the epoxy groups in the form of their ketimines. The ketimines are prepared from the polyamines in a known manner.

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.

The charges required for water dilutability and electrical deposition can be protonized with water-soluble acids (e.g. formic acid, lactic acid,

Propionic acid) or by reaction of the oxirane groups with salts of an amine.

The salt of a tertiary amine can be used as the salt of an amine.

The amine portion of the amine acid salt is an amine which can be unsubstituted or substituted as in the case of the hydroxylamine, these substituents should not interfere with the reaction of the amine acid salt with the polyepoxide and the reaction mixture should not gel. Preferred amines are tertiary amines, such as dimethylethanolamine, triethylamine, triisopropylamine and the like. Examples of other suitable amines are given in U.S. Patent 3,839,252 at column 5 line 3 through column 7 line 42. The reaction between amines and compounds containing epoxide groups often starts when the reactants are mixed. Depending on the desired course of the reaction - especially to complete the implementation -

5 it is recommended to set the reaction temperature to 50-

150 C to increase.

The binders prepared by the process described in detail above are further processed into aqueous electrocoating baths using well-known methods.

The electrocoating baths according to the invention can e.g. usual additives such as Crosslinker, coalescing solution

15 agents, pigments, surface-active agents, cross-linking catalysts, antioxidants, fillers, antifoams, etc. contain.

The advantages that can be achieved with the invention are

20 that electro-dip lacquer baths of the type described above can be provided by a technically very simple process, which compared to comparable dip lacquer baths not produced by the method according to the invention have a lower chloride ion concentration.

25 concentration and thus less corrosivity.

The invention is explained in more detail in the following examples. All information on parts and percentages qn are weight data unless expressly stated otherwise.

35 example 1

Preparation of a binder according to DE-PS-3108073, Example 2.

1093 parts of Araldit GY 2600 are in a reaction vessel

(Epoxy equivalent weight EEW = 188, epoxy resin based on bisphenol A from Ciba-Geigy), 151 parts of eopentylglycol and 4.9 parts of dimethylbenzylamine. The temperature is raised to 131 ° C and held until an EEW of 415 is reached. Then 398 parts of Capa 200 (see Example 4) and a further 3.8 parts of dimethylbenzylamine are added. The temperature is kept at 131 ° C. until an EEW of 1050 is reached. 1274 parts of the crosslinking agent (see Example 4) and 112 parts of the diketi ins also mentioned in Example 4 and 86 parts of N-methylethanolamine are then added and the temperature is kept at 112 ° C. for 1 hour. Then 155 parts of phenoxypropanol and 40 parts of methoxypropanol are mixed in and mixed in for 15 minutes. This resin solution is dispersed in 3247 parts of water, 23.5 parts of glacial acetic acid and 21 parts of the emulsifier mixture (see Example 4).

The low-boiling solvents are then removed in vacuo and a solids content of 35% is established.

The argento etrically determined chloride content of this dispersion is 127 ppm chloride.

Example 2

Example 1 is repeated, but 12.5 parts of salicylic acid are added 45 minutes before the EEW of 1030 is reached. The reaction is then terminated as described above.

The argentometric chloride determination gives a value of less than 80 ppm chloride for this dispersion. At sp ι • e, l 3

Example 1 is repeated, except that the salt of 4.9 parts of dimethylbenzylamine and 5.3 parts of salicylic acid with the epoxy resin and the neopentyl glycol is initially introduced for catalysis. Likewise, instead of the 3.8 parts

Dimethylbenzylamine to catalyze the incorporation of Capa

200 the salt from 3.8 parts of dimethylbenzylamine and 4.1

Parts of salicylic acid added.

The argentometric chloride determination gives a value of less than 55 ppm chloride for these dispersions.

1

Example 4

Production of a binder according to EP 70 550, example B

Weight (g)

⁵ - Epikote 829 ¹⁾ 727.6

- Capa 200 ² ^ 268, 4th

- xylene 36, 1

Bisphenol A 197.8

- Dimethylbenzylamine 3.8 1-0 - Isocyanate crosslinker 901.3

- Diketimine from MIBK and diethylenetriamine 75% in MIBK 73.4

- N-methylethanolamine 59.1

Hexylglycol 76.5

15 - acetic acid 33.5

- Emulsifier mixture 4) 29.4

- Deionized ^' -. ^' asser 1793.1

1) Epoxy resin from Shell Chemie, epoxy equivalent 188 20 2) Polyester diol from Interox Chemical

3) Isocyanate crosslinker based on tolylene diisocyanate with butyl glycol capping and reaction with trimethylol propane in a ratio of 3: 1, dissolved in a mixture of MIBK and n-butanol (9: 1) to a solids content of 70%. 254) Emulsifier mixture based on Geigy Amin C (Geigy Industrial Chemicals) 120 parts, Surfynol 104 (Air Products and Chemicals) 120 parts, butylglycol 120 parts and 221 parts deionized water with 19 parts glacial acetic acid. 30

MIBK = methyl isobutyl ketone

Manufacturing instructions

Epikote 829, Capa 200 and xylene are placed in a reaction vessel and placed under N _? - Shielding gas heated to 210 ° C. Water is then removed from the circuit for half an hour. Then the mixture is cooled to 150 ° C. and bisphenol A is added 1 and 1.6 parts of dimethylbenzylamine. The mixture is then heated to 180 ° C. and kept at this temperature for half an hour.

Then it is cooled to 130 ° C. and the remaining amount of dimethylbenzene is added. Then keep the temperature for 2 1/2

Hours, then the isocyanate crosslinker, the diketi in and N-methylethanolamine are added and the temperature is then kept at 110 ° C. for half an hour. The hexylglycol is then added. The reaction mixture is then in the

, _n contains deionized water, glacial acetic acid and emulsifier mixture. A vacuum is then applied in order to remove the volatile organic solvents. A solids content of 36% is set.

. _ In this dispersion the chloride content is now determined argento yellow. It is 63 ppm chloride.

Example 5 (comparative example)

Experiment 1 is repeated, except that 4.8 g of glacial acetic acid are added to the reaction mixture half an hour before the crosslinker is added. The process is then continued as described above.

25 The argentometric determination of chloride gives a value of 63 ppm chloride for this dispersion.

30

35

Claims

1 Claims 5 _ 1. Aqueous electrocoating baths for cathodic electrocoating, which contain modified epoxy-amine adducts as cathodically depositable binders and have been produced by (1) (A) polyepoxides and (B) compounds which contain one or more , preferably 2, hydroxyl groups bound to aromatic and / or (cyclo) aliphatic molecule fragments per molecule, have been converted into epoxide group-containing intermediates in the presence of amine-based catalysts and (2) these intermediates are then optionally mixed with other customary modifiers and closing Lich reacted with (C) primary and / or secondary (poly) amines or their salts and / or salts of tertiary amines, the reaction products thus obtained are neutralized, if necessary, with acids, dispersed in an aqueous medium and this dispersion according to 5 well-known methods have been further processed to form electrocoating baths, characterized in that the amine-basic catalyst catalyzing the reaction between components (A) and (B) is reacted before the further reaction of the intermediate products formed from components (A) and (B) with a Brönsted acid whose concentration is at 20 C measured pK value of the first dissociation stage is below 3.7, preferably below 3.5, has been neutralized. 5 A process for producing aqueous electrocoating baths for cathodic electrocoating, in which

(1) (A) Polyepoxides and

(B) Compounds which contain one or more, preferably 2, hydroxyl groups per molecule bound to aromatic and/or (cyclo)aliphatic molecule fragments, are converted into intermediate products containing epoxide groups in the presence of amine-based catalysts and

(2) these intermediate products are then optionally mixed with other customary modifying agents and finally with

(C) primary and/or secondary (poly)amines or their salts and/or tertiary salts

Amines are implemented, the reaction products thus obtained are optionally neutralized with acid, dispersed in an aqueous medium and this dispersion is further processed into electrocoating baths using well-known methods, characterized in that the amine-based catalyst catalyzing the reaction between components (A) and (B). before the further reaction of the intermediate products formed from components (A) and (B) with a

Brönsted acid, whose pK value of the first dissociation stage measured at 20 C is below 3.7, preferably below 3.5, is neutralized.

3. Aqueous electrocoating baths or process according to one of claims 1 to 2, characterized in that the amine-based catalyst catalyzing the reaction between components (A) and (B) is neutralized before the reaction of components (A) and (B). has been or will be, i.e. the reaction between components (A) and (B) has been or will be catalyzed with a salt of the Brönsted acid used for neutralization and the amine-based catalyst.

4. Aqueous electrocoating baths or process according to one of claims 1 to 3, characterized in that the Brönsted acid used to neutralize the amine-based catalyst catalyzing the reaction between components (A) and (B) has a pK measured at around 2200 ° CC -Value that is below 3.1.

5. Aqueous electrocoating baths or process according to claim 4, characterized in that salicylic acid is used as the acid to neutralize the amine-based catalyst catalyzing the reaction between components (A) and (B).