DE2041656A1 - Coating mixes - Google Patents

Description

PATENT LAWYERS

formerly Dr. D. Thomsen Dipi.-mg. H. Tiedtke

. G. Buehling

. W. Weinkauff

MUNICH 2 VALLEY 33

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FRANKFURT (?.; A. H) 50 FUCHSHOHL 71 TEL. 0611/51 «66

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8000 Munich 2

T 3791 / case PV. 22151

Imperial Chemical Industries Limited London / Great Britain

Coating mixtures

The invention relates to coating mixtures or masses, especially water-based coating masses, and the use of such coating masses in electro-coating processes.

It is known, for example from British patent specification 1 030 425, that water-based paints for use in electrocoating processes should have a pigment volume concentration which is low in relation to that which is usually present in coating compositions which are produced after older processes, e.g. dipping and spraying, In the case of black coating compounds, it is obvious that carbon black is used as the pigment because of its effectiveness as a pigment

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is known at low pigment volume concentrations.

According to the invention, however, it was found that coating compositions based on water, pigmented with carbon black can result in a rough surface finish when applied by electrocoating processes especially when applied to metallic iron that has been pretreated with zinc phosphate. This is going on returned the soot, which in some way causes the oxygen released at the cathodic object to fall Formation of larger bubbles is electroplated, these larger bubbles upon reaching the surface of the coated Films of the coating compound leave behind craters which are not adequately filled by the backflow of the coating film will.

In accordance with the invention it has been found that both a smoother surface finish and improved corrosion resistance can be achieved by using a particular type of pigmentation. According to the invention, an aqueous-based pigmented coating composition for use in electro-coating processes is provided for the production of black coatings on objects , the coating composition containing a mixture of two complementary colored pigments. In terms of the general principles of color aaching, we are familiar with suitable colors

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to use.

Preferably at least one of the pigments is inorganic; in a preferred combination, one is Pigments one inorganic red or brown simple iron oxide pigment and the other an organic blue copper phthalocyanine pigment. Alternatively, both blue and green phthalocyanine pigments can be used mixed. Such organic pigments are commercially available under the trademark "Monastral".

The relative amounts in which the two complementary pigments are used depend on their coloring power and the precise black shade desired, whereby the Black may have a brownish, bluish, greenish or other shade «In the present context the term "black" is intended to mean a neutral color with a Munsell value not greater than 2, preferably not greater than 1, and a color purity or color intensity of no greater than 1, preferably no greater than 0.5, describe.

The pigment volume concentration in the black coating composition is preferably not more than 20%.

In addition to the complementary pigments, the coating compound 109810/2154

Contain anti-corrosive pigments with little coloring power, e.g. lead chromate and lead silica chromate.

The mass can also contain a corrosion inhibitor, e.g. a soluble chromate, and anti-precipitating agents such as bentonite and montmorillonite clays.

The resins used in the composition as film formers can be those for use in electrocoating compositions are suitable, e.g. epoxy ester, alkyd / phenolic and Acrylic resins, maleinized oils and maleinized oils modified with styrene.

Resins particularly suitable for use in accordance with the invention are disclosed in British Patent Specification 1,069,841; They are made by adding a poly oil with at least three hydroxyl groups per molecule and one Molecular weight of at least 500 with a drying oil fatty acid is at least partially esterified and the resulting drying oil ester with maleinized fatty acid further is esterified. The resin is preferably an epoxy ester resin obtained by esterification of a condensation product of diphe-nylolpropane and epichlorohydrin was made with the listed fatty acids.

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Mixtures of any of the resins listed above can be used. The resins can also modified or extended with smaller amounts of certain resins, e.g. with crosslinking resins such as melamine / Formaldehyde resins.

The following are typical combinations of pigments indicated, which are suitable for use according to the invention, the values being the volume concentration in the Specify the coating weight of the pigment used and the other additives, expressed as a percentage of the total volume of the non-volatile material in the mass:

Ground brown red "Monastral" - lead silicone

- iron oxide iron oxide blue chromate bentonite

1. 2.38

2. 1.5

3. 3.23

4. -. 1.5

When dispersed in an epoxy ester containing carboxyl groups, partially neutralized with a base such as potassium hydroxide, dispersed in water and applied to an object made of metallic iron treated with zinc phosphate using an electrocoating process, these pigment combinations provide a smooth, semi-glossy black coating with an improved coating Corrosion resistance.

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2.83 0.645 0.155 2.83 0.645 0.155 1.53 - 0.13 4.5 _ 0.1

2OA1656

Similar results were obtained as the epoxy ester by a carboxyl group-containing alkyd / phenolic resin or acrylic resin has been replaced.

The invention is illustrated below by way of example. explained in more detail.

example

It became a pigmented aqueous coating (A) with a total solids content of 10% by weight on the basis an epoxy ester resin prepared according to Example 10 of British Patent 1,069,841, but with 60% of the Acid groups in the resin had been neutralized with potassium hydroxide instead of diethanolamine. The pigmentation corresponded to compound 1 in the table above; in the mass 400 parts per million potassium chromate before as a corrosion inhibitor.

A similar composition (B) was prepared with the pigment volume concentration the same as that of the above composition (A), but the mixture became .from brown ferric oxide and "Monastral" blue by the same Replaced volume of commercially available soot from plants.

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There were separate steel plates or steel panels coated with zinc phosphate at pH 7.8 and 200V electrocoated with the above compositions and heated at 163 ° C for 45 minutes to produce black films with a To produce strength of 20 ai. The pH of the coating bath was held essentially constant by the method described in British Patent 1,106,979. With the panels or panels coated with the compound (A) were smooth and semi-glossy, while one coated with a compound (B) Plate or a panel covered with it had a mottled and textured surface.

The coated panels were scribed to bare metal and subjected to a salt spray for 336 hours (ASTM B 117/64). A plate or a panel coated with the compound (A) showed one Loss of adhesion of up to 2 mm from the end of the crack, while a plate or one coated with the compound (B) Panel showed an adhesion loss of up to 8 mm from the end of the crack.

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Claims (8)

Claims 1. Aqueous-based pigmented coating mixture for electro-coating processes for the production of black coatings on objects, characterized by a content of a pigment device made up of two complementary colored pigments. 2. Mixture according to claim 1, wherein at least one of the pigments in the pigment mixture is inorganic. 3. Mixture according to one of the preceding claims, characterized in that a red or in the pigment mixture brown iron oxide and a blue copper phthalocyanine pigment is included. 4. Mixture according to one of the preceding claims, marked by a. Composition resulting in a black overlay with a Munsell value not greater than 1 and a color intensity (chroma) value not greater than 0.5. 5. Mixture according to one of the preceding claims, characterized by a pigment volume concentration up to 20%. 109810/2154 2041658 6. Mixture according to one of the preceding claims, characterized in that it contains an anti-corrosive pigment of low coloring power. 7. Mdsching according to one of the preceding claims, characterized in that it contains a corrosion inhibitor. 8. Mixture according to one of the preceding claims, characterized in that it uses an epoxy ester resin as a film former contains. 1 09810/21