DE1621818B2 - Process for the production of coatings by electrocoating - Google Patents

Description

The invention relates to a method of manufacture of coatings on electrically conductive surfaces through the electrophoretic deposition of binders based on mixtures of acrylate resins, alkyd resins, maleinized oils or other resins that can be electrically precipitated from an aqueous medium and phenolic resins, the basic building blocks of the phenolic resin consist of polynuclear phenols.

It is known that lacquer-like coatings on electrically conductive surfaces by anodic or cathodic deposition of so-called one-component paints based on acrylate resins, Can produce alkyd resins or maleinized oils. Such paintwork does have have found widespread entry into technology, but they are not satisfactory increased demands, as z. B. in automobile construction on body primers with regard to adhesive strength, Corrosion resistance and impact resistance can be provided.

Attempts have therefore been made to improve the performance properties of such coatings by adding to improve crosslinkable urea, melamine or phenolic resins. These resins will work on their own not deposited electrically, but partly also precipitated, if in their presence acrylate resins, Alkyd resins or maleinized oils are deposited electrophoretically. The composition of the bath used for electrocoating is crucial for the quality of the generated paint coatings.

It has now been found that it is difficult to determine the weight ratio of the various resin components to be kept sufficiently constant in the immersion bath over a longer period of time. Preferred are the polar acrylate resins, alkyd resins or maleinized oils are deposited, so that with continued use of the immersion bath, an enrichment of the resins in the bath, which cannot be separated electrically by themselves takes place.

This disadvantage can be remedied by refilling an appropriate compensation varnish, however, this requires considerable analytical and technical effort. Also tend to the. very reactive urea, melamine and phenolic resins with prolonged residence time in the bath for premature undesirable crosslinking, which affects the quality the paint coatings and thus the service life of the immersion baths is significantly impaired. The dwell time the resin component in the immersion bath, which cannot be electrophoretically deposited by itself, is in extended to the same extent that the composition of the deposited paint binder differs from the of the bathroom differs.

It has now been found that the disadvantages mentioned can be avoided and high-quality electrodeposition coatings can be achieved by using a phenolic resin component, its phenolic building blocks consist mainly of polynuclear phenols. The subject of the present invention is thus a process for the production of coatings on electrically conductive surfaces by electrophoretic Separation of binders based on mixtures of acrylate resins, alkyd resins and / or maleinized oils and a phenol-formaldehyde condensate, optionally under Addition of other resins which can be separated out electrophoretically from an aqueous medium, in which the phenolic Basic building blocks of the phenol-formaldehyde condensate predominantly from polynuclear phenols exist.

In dipping baths, the mixtures of acrylate resins and the phenolic resins used according to the invention contained, the weight ratio of acrylate resins and phenol-formaldehyde condensates also remains constant over a longer period of time. The addition of such a phenolic resin acts in the same way, if, instead of acrylate resins, alkyd resins and / or maleinized oils, possibly together with others Electrophoretically separable resins are the main components of immersion baths.

The usual acrylate resin components can be used, especially aqueous solutions or aqueous solutions Dispersions of copolymers containing 10 to 95 percent by weight of an ester of acrylic acid or Methacrylic acid with a monohydric alcohol having 1 to 20 carbon atoms, 2 to 30 and in particular 3 to 20 percent by weight of at least one amide, alkyl amide, hydroxylalkyl amide, oxaalkyl amide or a hydroxyalkyl ester of acrylic acid and / or methacrylic acid in copolymerized form. If the resins are deposited cataphoretically, they also advantageously have 3 to 30, in particular 5 to 20 percent by weight of the units of a salt of an aminoalkyl ester and / or aminoalkylamide of acrylic acid and / or methacrylic acid and / or a basic nitrogen-containing five- or six-membered polymerized heterocyclic vinyl compound, they are deposited anaphoretically, see above they contain in particular units of 2 to 40 and in particular 2 to 15 percent by weight of an ethylenic unsaturated carboxylic acid with 3 to 6 carbon atoms in the form of its ammonium or amine salts.

As acrylate resin components in the invention Processes have proven particularly useful: water-soluble salts made from at least one water-soluble salt tertiary amine and at least one copolymer

3 4

A. an alkyl ester from an α-ethylenically unge resin components and with rapid throughput of the saturated monocarboxylic acid with 3 to 6 carbon phenolic resin, the high quality of the material atoms and an aliphatic alcohol with paints obtained remains even over a long 1 to 20 and in particular 1 to 8 carbon atoms, duration of use of the immersion bath preserved,
in particular the esters of acrylic acid and / or 5 The bisphenol A-formaldehyde condensate used in Examples 1 to 4 below ver-methacrylic acid and methanol, ethanol, butanols and / or octanols were prepared as follows:

570 parts by weight of 2,2-bis (p-hydroxyphenyl) propane

B. a «-äthylenisch unsaturated free mono- (bisphenol A) (2.5 mol), 375 parts by weight of 40 ° / ₀ ige or dicarboxylic acid with 3 to 6 carbon atoms, io aqueous formaldehyde solution (5.0 mol) and 56 particular Acrylic acid and / or methacrylic parts by weight of dimethylethanolamine (0.63 mol) are acidic and stirred at 50 ° C. for 5 hours. Then you get

a viscous aqueous solution, the resin content of which is 71

C. at least one derivative of an α-ethylene weight percent is. The production of the unsaturated carboxylic acid, the phenol -formaldehyde copolymerizable C - C double bond condensate used in addition to the same experiment, was carried out in an analogous manner,
at least one reactive free hydroxyl or that contains N- (hydroxymethyl) amide group or N- (alkoxy- used phenol or bisphenol A was radioactive methyl) amide group for the production of the phenolic resin component. This made it possible to do this in the immersion bath

20 existing weight ratio of the acrylate

D. further ethylenically unsaturated polymerizing resin to the phenolic resin component after any number of baren comonomers, z. B. styrene and its repeated electrophoretic precoating derivatives, vinyl esters, acrylonitrile and methangones to be determined with great accuracy,
acrylonitrile, butadiene, etc. The phenolic resin used in Example 5 was in

25 obtained in a similar manner. 70 parts by weight a, a '- (p-Hy-

As alkyd resins in the process according to the invention (droxyphenyl) -p-di-isopropylbenzene (0.20 mol), 50 Ge

can e.g. B. use the weight parts for these purposes 40 ° / ₀ aqueous formaldehyde solution

known commercial condensation products (0.67 mol), 10 parts by weight of dimethylethanolamine

of polybasic organic acids and more- (0.11 mol) and 80 parts by weight of isopropanol

Valuable alcohols, optionally modified at 3 ° at 80 ° C for 5 hours. After that it will

Fatty acids and fatty acid glycerides that have an acid number isopropanol from the now water-compatible substance

have between 30 and 150, especially those mixed by distillation in vacuo. The solid content

the solution obtained by salt formation with ammonia or amines is 74%.
have been converted into the water-soluble or easily water-dispersible state. 35

Adducts from comparative experiment 1
Maleic anhydride or fumaric acid on multiple

unsaturated oils with conjugated or non-conjugated A commercially available acrylate resin, in the form of

Gated double bonds understood, where in the water-soluble amine salt of a copolymer '

Adduct is the weight ratio of the oil content to the 40 of 85 weight percent acrylic acid n-butyl ester, 5 Ge

Maleic anhydride or fumaric acid content min- weight percent N-methylol methacrylamide and 10 wt.

is at least 70:30 and the free carboxyl groups weight percent acrylic acid is in weight ratio

of the adduct with monovalent or polyvalent Aiko- 70:30 with the radioactively labeled water-soluble

pick with 1 to 10 carbon atoms partially mixed with phenol-formaldehyde resin and in as much

can be estert. In place of the adducts from undissolved water, that the solids content, based on

Saturated oils can also add corresponding adducts to the resin mixture, 10 percent by weight. In

from free, unsaturated fatty acids can be used. 1 mm thick iron sheets are built into this bath.

The production of the above-mentioned acrylate resins, alkyd, depends on which are connected as anode. The Ab-

Resins and maleinized oils is not the subject of the separation of the lacquer binding agent on these sheets

present invention. 50 takes place under one for a period of 2 minutes

As phenol-formaldehyde condensation resins, direct voltage of 100 volts at 25 ° C. There will be

The 30 coating processes are carried out one after the other in a manner known per se for paint purposes,

produced, as far as their phenolic basic building blocks. After every 5 coating processes, the

a sample of its radioactivity is predominantly and preferably completely taken from flour bath

consist of pithy phenols. Suitable multi-core 55 (phenolic resin content) and total resin content analytically

Phenols are mainly polyhydric phenols, which are determined.

optionally also carrying further substituents The results are given in Table I, where the

Phenolic nuclei by z. B. alkylidene, sulfone or percentages percentages by weight of phenolic resin

Ether groups are connected. Except for the total resin content in the immersion bath, preference is given to phenols of the bisphenol A structure type and their ^6o
Homologues such as «,« '- (p-hydroxyphenyl) -p-di-

isopropylbenzene. example 1

The properties of the according to the invention

The method obtained paint coatings with regard to corrosion is carried out as indicated in the comparative experiment

tensile strength, adhesive strength, elasticity and over- ⁶ S drive, but as a phenolic resin component the radio-

surface quality are very good. Because the electro-actively labeled condensation product of bisphenol

phoretic separation from an immersion bath with A and formaldehyde is used. The results shows

a constant relation between the individual table I.

Table I. Table U

Number of coated sheets
0 5 10 15 20 25 30 resin combination

% Phenolic resin 30.0 34.5 39.7 49.8 61.4 73.7 84.8 according to comparative test 1

% Phenolic resin 30.0 30.3 31.2 31.9 32.6 33.4 33.9 according to Example 1

The result according to Example 1 shows that even after numerous repetitions of the electrophoretic deposition only a negligible change in the resin composition in the Dip takes place.

B is ρ ie 1 e 2 to 5
and comparative experiment 2

In dipping baths with the resin combinations given in Table II, sheets are coated one after the other, as indicated. The sheet metal after the first and the sheet metal after the 30th coating is removed from the immersion bath, rinsed with water and baked ^{at 170 ° C. for 20 minutes.} The coatings obtained in this way have the properties given in Table II.

Paint layer 1st sheet

Paint layer 30. Sheet metal

Example 2
70% acrylic resin + 30% bisphenol A formaldehyde condensate

Comparative experiment 2 70% acrylate resin + 30% phenol-formaldehyde condensate

Example 3

90% alkyd resin + 10% bisphenol A formaldehyde condensate

Example 4
90% maleinized linseed oil +

10% bisphenol A formaldehyde condensate

smooth, flawless

smooth, flawless

smooth, flawless

smooth, flawless

Example 5

70% acrylate resin + 30% «,« '- (p-hydroxyphenyl) -p-di-isopropyl- benzene-formaldehyde condensate

smooth, flawless

smooth, flawless

inhomogeneous, unusable

smooth, flawless

smooth, flawless

smooth, flawless

Claims (1)

Claim: Process for the production of coatings on electrically conductive surfaces by electrophoretic Separation of binders based on mixtures of acrylate resins, alkyd resins and / or maleinized oils and a phenol-formaldehyde condensate, optionally with the addition of others electrophoretically Resins separable from an aqueous medium, characterized in that as phenolic The basic building blocks of the phenol-formaldehyde condensate are predominantly multi-grain phenols be used.