CA1312165C

CA1312165C - Process for catalysing the cross-linking of cathodically depositable paint binders

Info

Publication number: CA1312165C
Application number: CA000575546A
Authority: CA
Inventors: Helmut Honig; Herbert Matzer; Georg Pampouchidis
Original assignee: Vianova Resins AG
Current assignee: Allnex Austria GmbH
Priority date: 1987-08-25
Filing date: 1988-08-24
Publication date: 1992-12-29
Anticipated expiration: 2009-12-29
Also published as: EP0304754B1; JPS6470573A; ES2052653T3; EP0304754A3; AT390275B; DE3876720D1; ATA211887A; EP0304754A2

Abstract

ABSTRACT OF THE DISCLOSURE

Process for catalyzing the crosslinking of cathodi-cally depositable paint binders based on resins containing ethylenic double bonds wherein before water is added to the binder, 0.01 to 2.0% by weight, based on the non-volatile binder content, preferably 0.1 to 2.0% by weight of iron-acetylacetonate, calculated as metal, is added to the resin binder and homogeneously mixed therewith. The iron cata-lyst provides rapid curing without use of lead components normally required and without impairing the quality of the crosslinked paint films.

Description

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F I E LD OF I NVE NT I ON

This invention relates to a process for catalyzing the crosslinking of cathodically depositable paint binders based on binder resins containing ethylenic double bonds.
More particularly, the invention relates to cathodically depositable paint binders containing resins having ethylenic double bonds catalyzed with iron-acetylacetonate.

~' BACKGROUND OF INVENTION

It is known that the crosslinking reaction of ca-thodically depositable paint binders which are crosslinked by transurethanization can be catalyzed by the use of metal compounds, thereby reducing the hardening temperature re-quired or shortening the stoving time. Thus, according to DE-OS 25 41 234, the acetates, naphthenates, oleates, chro-mates, phosphates, and the like of bismuth, lead, tin, iron, cobalt, nickel, aluminium, zinc, manganese, copper, zircon-ium, and the like are used for this purpose. Further, the addition of water-soluble metal salts to improve corrosion resistance is also known, According to DE-OS 24 57 437, water-soluble salts of cobalt, nickell cadmium, tin, antimony, zinc, or copper are used for this purpose. DE-OS 28 14 439 '~

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discloses water-soluble lead compounds, particularly lead acetate and lead lactate, added to an electrodeposition bath.

According to EP-A-12 463, the catalysts used for transesterification reactions are metal salts or metal com-plexes which are soluble in liquid hydrocarbons, such as the octoates or naphthenates of lead, zinc, calcium, barium, iron, and a large number of other metals. EP-A-82 214 dis-closes that octoates, naphthenates, borates or acetylaceton-ates o cobalt r copper, lead, nickel, and manganese when used as catalysts can be reàcted with the paint binder in order to prevent separation during ultra~iltration. Accord-ing to the prior art, paints based on these binders ars for-mulated with a certain amount of lead ions which are intro-duced either by using partially acid-soluble lead pigments or by adding soluble lead salts.

In practice, iron compounds are not added as cata-lysts in cathodically depositable paints since experience has shown that if any iron ions are accidentally ~ormed in the deposition system by the use o~ non-stainless steel parts (so-called instaIlation corrosion), they will cause the precipitated and stoved paint films to become extremely ' ` ~ 2151/US-3140 ~ 3121 ~

brittle. Surprisingly, it has now been found that iron-acetylacetonate exhibits a specific catalytic effect in the ~` crosslinking of cationic paint binders which contain poly-merizable ethylenic double bonds in the end or terminal position.
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SUMMARY OF INVENT ION
-The present invention, therefore, is directed to a process for catalyzing the crosslinking of cathodically depositable paint binders which contain polymerizable ethy-lenic double bonds in the end or terminal position, charac-terized in that before water is added to the binder, 0.01 to 2.0% by weight, based on the non-volatile binder content, preerably 0.1 to 2.0~ by weight of iron-acetylacetonate, calculated as the metal, is added to the resin binder and i5 homogeneously mixed therein.

The invention further relates to the cathodically depositable electrodeposition paint catalyzed with the iron-acetylacetonate.

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-~ The process of the present invention makes it possible to retain the good qualities of the paint films, particularly from the standpoint of rapid curing time and , ~
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corrosion resistance, while avoiding the environmentally undesirable lead content of binders and without the aid of anti-corrosion pigments. The corrosion tests on degreased steel panels are substantially improved in many cases by using the catalyst according to the present invention.

GENERAL DESCRIPTION OF INVENTION

The binder resins which are particularly suitable for catalyzing according to the present invention are de-scribed, for example, in U.S. Patent Nos. 4,238,594;
4,320,220; 4,147,676, and 4,174,332; and in EP-A-30 692.
Paint binders based on polycondensation or polyaddition polymerization, more particularly binders based on modified epoxy resins which have double bonds present in an end or terminal position, such as binders where double bonds have been introduced by reacting resins which carry OH-groups with unsaturated monoisocyanates, e.g., reaction products of equimolar quantities of a diisocyanate and a hydroxyalkyl-(meth)acrylate, are particularly useful. The products har-den essentially by thermal polymerization.

The iron-acetylacetonate can be added to the binder as a 10 to 15~ solution in acetone. Preferably, the iron-'~. ", '' " ''.' .' ,~

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acetylacetonate is added to the binder as a powder together with the pigments and/or extenders, e.g., carbon black, alu-minium silicate and titanium dioxide, dispersed therein and the mixture ground. If desired, the catalyst can be added to a resinous mixing component or to a pigment paste con-taining a resinous dispersion medium before the resin com-ponent or binder (system) is diluted with water. The iron-acetylacetonate is added in a quantity, calculated as metal, of from 0.01 to 2~0% by weight, based on the non-volatile binder content. Preferably, the iron content is at least 0.1% by weight of metal, based on 100% resin solids.

The ormulation of cathodically depositable paints, the processing thereof, particularly by the electrodeposi-tion method, and the testing of the paint films are known to those skilled in the art.

PRESENTLY PREFERRED EMBODIMENTS

The examples which follow illustrate the invention without restricting its scope. All the quantities given in parts or percentages refer to units by weight, unless other-wise stated.

The resin binders used in the examples are binders as disclosed in AT-PS 353,369, corresponding to U.S. Patent ~,`; ~ ' .

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No. 4,174,332 issued November 13, 1979. These binders are cathodically depositable resin combinations having a double bond number of at least 0.8. The double bond number (DBn) is defined as the number of double bonds in the end and side positions for every 1000 molecular weight units. The number of basic groups per thousand molecular weight units is given by the BNz.

Binder Component (A) (Al) In a reaction vessel equipped with stirrer, ther-mometer, dropping funnel and reflux condenser, 1000 g of an epoxy resin based on bisphenol-A and epichlorohydrin, having an epoxy equivalent of about 500, are dissolved in 492 g of ethylglycol acetate at 60 to 70C. 0~2 9 hydroquinone and 144 g of acrylic acid are added, and the temperature is increased to 100 to 110C. The reaction is carried out at this temperature until an acid number of less than 5 mg KOH/g is obtained to provide a DBn value of 1.75. The reac-tion product is then mixed at 60 to 70C with 652 g of a 70%
solution in ethylglycol acetate of a basic monoisocyanate prepared from equimolar quantities of toluylene diisocyanate and dimethylethanolamine and reacted until an NCO-value of virtually zero is obtained. The binder has a DBn of 1.25 and a BNz of 1.1.

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(A2) 520 g of an epoxy resin based on bisphenol-A and epichlorohydrin, having an epoxy equivalent of about 260, are dissolved in 465 9 ethylglycol acetate and reacted as in (Al) with 564 g of a semiester of tetrahydrophthalic acid anhydride and hydroxyethyl methacrylate to provide a DBn of 1.85. The reaction product was further reacted with 750 g of the solution of a basic monoisocyanate as used in (Al) to provide a D~n of 1.24 and a BNz of 1.24.

Binder ComPonent (B) (Bl) In a reaction vessel fitted with stirrer, ther-mometer, dropping funnel and reflux condenser, 400 9 of an epoxy resin based on bisphenol-A and epichlorohydrin, having an epoxy equivalent o about 200, are dissolved in 172 g of ethylglycol acetate at 60 to 70C. Over a period of one hour 210 9 of diethanolàmine are added dropwise at 90 to 120C. The mixture is then heated to 150C and reacted for another hour. After this, the reaction product is reacted at 60 to 70C with 830 g of a 70~ solution in ethylglycol acetate of an unsaturated monoisocyanate prepared from equimolar quantities of toluylene diisocyanate and hydroxy-ethyl acrylate until an NCO-value of virtually zero is obtained. The binder has a DBn of 1.68 and a BNz of 1.68.
(B2) 500 g of an epoxy resin based on bisphenol-A and ~ ' .
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epichlorohydrin, having an epoxy equivalent of about 250, dissolved in 215 g of ethylglycol acetate, are reacted ac-cording to the procedure of (Bl) with 210 g of diethanola-mine and then reacted with 995 g of the monoisocyanate solution which is used in (Bl). The binder has a DBn of 1.71 and a BNz of 1.42.

Binder Combinations Binder combinations are prepared from components and proportions based on 100% resin solids by mixing binders at a temperature of not more than 70C as follows:
BM I : 100 parts (Al) + 33 parts (B2) BM II : 100 parts ~A2) + 30 parts (Bl) An iron-acetylacetonate catalyst is added to the resin and mixed thoroughly therein. Thereafter, the binder combinations are mixed with 40 millimole of acetic acid per 100 g o solid resin and diluted with water to give a solids content o~ 12~ by weight. The clear varnish is deposited onto phosphatized steel panels connected as the cathode of an electrodeposition system. A film is deposited having a dry film thickness of 20 to 22 microns.

The degree of crosslinking was tested after 24 hours' storage of the coated panels at ambient temperature _g_ , .. . ..

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using the so-called acetone test. The time shown is the maximum duration after which the paint film affected by a drop of acetone can still not be damaged using the finger-nail.
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The salt spray test was carried out in accordancewith ASTM B 117-64 on degreased steel panels which had not been pre-treated. After the time specified, there is corro-sive damage up to a width of about 2 mm, measured from the cross-shaped cut.

~ The stone-chipping resistance is tested by blasting ;~ sharp-edged steel shot (0.5 kg, 3 bar of compressed air) against the paint surface twice, and then applying and re-moving self-adhesive film. The remaining paint film adher-ing is given as a percentage of the total surface area.

The results of the tests are shown in the table which follows. Irrespective of the way in which the cata-lyst is added, i.e., either as a solution or as a solid substance with the pigment, virtually identical test results are obtained.

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Binder/StovingAcetone Test ( Clear Varnish ) Seconds Conditions% Iron as Iron-Acetylacetonate (Min/C) 0 0.2 0.5 1.0 2.0 about about over over BM I lS/160C 5 60 120 120 120 about over over over ____________________________________________________________ about about over about about over Salt Spray Test (Clear Varnish) Hours over over over _____ _________ ____________________________________________ over BM II 15~180C96 120 168 336 360 Stone-Chieping Resistance (Clear Varnish) %
BM I 15/180C60 ` 80 90 95 95 ____________________________________________________________ As will be apparent to one skilled in the art, various modif ications can be made within the scope of the aforesaid description . Such modif ications being within the ~~' 2151/US-3140 i31216~

ability of one skilled in the art form a part of the present : invention and are embraced by the appended claims.

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Claims

1. Process for catalyzing the crosslinking of cathodically depositable paint binders which contain poly-merizable ethylenic double bonds in a terminal position, characterized in that, before water is added to the binder, 0.01 to 2.0% by weight, based on the non-volatile binder con-tent, of iron-acetylacetonate, calculated as the metal, is added to the resin and is homogeneously mixed therein.

2. The process according to claim 1 wherein 0.1 to 2.0% by weight of the iron-acetylacetonate is added.

3. The process according to claim 1 or 2 wherein the iron-acetylacetonate is added in a solution in acetone.

4. The process according to claim 1 or 2 wherein the iron-acetylacetonate is added to the resin and dispersed therein as a solid substance together with the pigments and/or extenders.

5. The process according to claim 3 wherein the iron-acetylacetonate is mixed with a resinous mixing com-ponent or a pigment paste containing a resinous dispersion medium and in this form it is introduced into the binder.

6. The process according to claim 4 wherein the iron-acetylacetonate is mixed with a resinous mixing com-ponent or a pigment paste containing a resinous dispersion medium and in this form it is introduced into the binder.

7. A cathodically depositable electrodeposition paint comprising a paint binder containing polymerizable ethylenic double bonds and 0.01 to 2.0% by weight, based on the non-volatile binder content, of iron-acetylacetonate, calculated as the metal.

8. The paint binder according to claim 7 wherein the paint contains 0.1 to 2.0% by weight of iron-acetylace-tonate.