DE1905270B2 - Process for coating hollow bodies - Google Patents

Description

The electrophoretic coating of the inner and outer surfaces of hollow bodies is state of the art Technology. This coating takes place in one operation and before any further coating with coating agents other than electrophoresis, e.g. B. solvent-based primers or top coats. Process, the electrophoretic coating of the inner surfaces of hollow grains only after the outer surfaces of hollow bodies have been coated with electrophoretically non-depositable, insulating and water-insoluble coatings are known per se Make composition and the resulting advantages are not known.

According to W. Maisch, »The cavity coating in electrodeposition «, industrial painting company 1967, p. 4, paragraph 1, is the layer thickness in the cavity or on the inner surfaces of the hollow body not as big as on the outside of the object. Considerable differences in the layer thickness of the inside and outside The outer surfaces of hollow bodies in electrophoretic coating are also made of "metal surfaces", 1968, Issue 10, p. 302, Tables 1 and 2, can be seen.

It is also known that the electrophoretic coating of the inner surfaces of hollow bodies only takes place after the electrophoretic coating of the outer surfaces. Because throwing power or throwing power of electrophoresis coating agents in many cases for adequate coating of the inner surfaces of hollow bodies, e.g. B. Hollow profiles on automobile bodies. is not sufficient, either the protection of the inner surfaces \ of hollow bodies from the Installation in other parts or units, e.g. B. Automobile bodies. with non-electrophoresis coating agents. e.g. zinc dust paint. Spot welding color, required, or so-called auxiliary electrodes must be used for adequate coating the inner surfaces of hollow bodies are used, and / or they are recesses. Frcischnitte or Löc, necessary in the hollow bodies, which in general ^ after the electrophoretically. ^ coating, must be closed again and can affect the stability of the hollow body. It is also known that the extent of electrophoretic Coating of the inner surfaces of hollow bodies by a number of known criteria is dependent, e.g. B. from the so-called wet film resistance of the deposited layer: in the literature also as a film withstood a fresh film.

referred to as the electrical resistance of the deposited layer or as the layer conductivity. Even though numerous attempts to optimally formulate and use electrophoresis coating agents have been carried out, it has been shown that the fulfillment of the partially contradicting one another Criteria has encountered considerable difficulties in practice and none of the previously known Electrophoresis coating agent ideally meets all requirements (see "Metal surface",

1968, No. 10, pp. 300 to 302 "under 5 .. in particular S.? 01. right column, lines 38 and 39).

Compared to these known methods and attempts to improve the electrophoretic coating the inner surfaces of hollow bodies is a completely different way to according to the invention Solution to this problem.

The invention relates to a method for coating hollow bodies, which is characterized is that first the electrically conductive outer surfaces of hollow bodies with electrophoretically non-separable, insulating and water-insoluble Coating agents of known composition are provided to produce coatings and only then is the electrophoretic coating of the electrically conductive inner surfaces this hollow body is made with electrophoresis coating agents of known composition.

It is particularly advantageous to use degreased or degreased and phosphated or otherwise passivated metallic outer surfaces of hollow bodies initially electrostatically with a non-aqueous coating agent known composition, e.g. a primer based on alkyd resins or epoxy resin esters, but especially with powdery ones Coating agents z. B. based on epoxy resin to coat and this coating agent at least To condense further until water resistance or water insolubility in the film, z. B. by Air or oven drying, followed by the electrophoretic coating of the conductive inner surfaces this hollow body with water-thinnable coating agents of known composition and both coatings afterwards

subject to further condensation in the film. z. B. by temperature treatment.

The new process creates an electrical resistance on the outer surfaces of hollow bodies built up, which seriously exceeds all known wet film resistances of electrophoretically applied coatings is as shown in the table.

Tabel

paint layer
thickness Schichtlc ^: ifahigkeu Film resistance ■ cm 15th • Kl- " around Siemens cm ohm - iO- '^; ■ io- ^|; Αι !.) 3 pp 0.035 · K ") - ' ¹ 28.57 ■ 10- « BI.) 36 Ü.U12 · H) " ⁵ • 10-> - '20 C (I.) . * C 0.016 · ΙΟ " ⁶ 62.5 • 10 ~ ¹⁵ D (2.) 35 0.620 x 10 ^ß 1.62 • ίο- ¹⁵ E (3.) 40 > 1 lO ' ¹ ' - > 1 • ίο- · « F (4.) 40 2 · 10- ¹ · ' 2. G (5.) 1000 6 · ΙΟ- '· 6th H (6.) 260 1 · ΙΟ- '' ¹ 1

Explanations of the 1 table: _a

All paints were applied to degreased steel sheet. The specification of the layer conductivity or the film resistance relates in the case of the lacquers AB C and D ι electrophoresis coating agent) to the so-called wet film. or Γ ischen film, in the case of lacquers E, F. G and H (electrophoretically non-depositable coating agents) on the dry film.

1. The lacquers A. B and C are commercially available electrophoresis coating media and the values given are taken from "Metalloberfläche", 1968, p. 302. Table 1. The coatings are

Electrophoretically deposited for 2 minutes at 200VoIt.

2. Varnish D is an electrophoresis coating agent made from 120 parts of an aqueous alkyd resin solution, the composition and preparation of which are described below, and 20 parts of a water-soluble, commercially available hexamethylolmelamine derivative, pigmented in proportion

3: 4 with titanium dioxide, diluted with demineralized water to a solids content of 15 ⁰ O and adjusted with triethylamine to a pH value of 7.6, whereupon the electrophoresis was deposited for 2 minutes at 80 volts.

50

Composition and preparation of the aqueous alkyd resin solution:

100 parts of phthalic anhydride, 84 parts of a commercially available dimeric fatty acid and 84 parts of trimethylolpropane are reacted in a conventional esterification plant at 220.degree. C. up to an acid number of 55. After cooling below 100 ^° C., 70 parts of the alkyd resin obtained are diluted with 16 parts of isobutanol and 14 parts of triethylamine are added.

3. Lacquer E is a commercially available alkyd / melamine resin lacquer in a ratio of 70 parts of fatty acid-modified, non-drying alkyd resin containing hydroxyl groups: 30 parts of commercially available hexamethylol melamine ether, catalyzed with 0.5% p-toluenesulphonic acid, based on the binder, pigmented in a ratio of 2 parts binder: 1 part titanium dioxide Rutile, baked at 120 C for 15 minutes after application.

4. Lacquer F is a polyurethane lacquer, pigmented in a ratio of 2 parts binder! : 1 part titanium dioxide rutile, air-dried for 24 hours after application.

5. Lacquer G is a cold-curing solvent-based agent Varnish based on an unsaturated polyester and styrene. The values given are the Paperback »Bayer-Kunststoffe ·. 2. Auflaue. October 1959. S.'ZIZ and 213. under > -Leguval K 25 R-: removed.

6. Lacquer H is a powdery coating material based on epoxy resin, which is baked at 170 ° C for 30 minutes after application.

The new process results in the Outer surfaces of hollow bodies have a very high electrical resistance, which is the wet film resistance known electrophoresis coatings by multiple powers of ten and so to one extraordinary improvement of the electrophoretic coating of the inner surfaces of hollow bodies leads or even only without the application of additional measures, e.g. B. Use of auxiliary electrodes. Making holes possible. The advantages of the new process for coating the inner guards of hollow bodies are therefore unambiguous. But also with regard to the coating the outer surfaces of hollow bodies show the new process compared to the electrophoretic coating remarkable qualitative, procedural, economic and environmental protection improving benefits. These advantages are that of the electrophoretic coating Occurring partial destruction of zinc phosphate layers as a substrate is avoided (see e.g. "Metal surface".! 968, p. 300 under 4.), the lacquer losses of the electrophoresis coating agent described in "Metalloberfläche", 1968, pp. 302/303 under 6 be reduced or when using solvent-free coating agents such. B. powdery Coating agent, not required, very high layer thicknesses can be achieved in one operation and there is practically no water or air pollution when using powder-form coating agents. The new process also has the disadvantage of electrophoretic coating of Outer surfaces of large-area hollow bodies, e.g. automobile bodies, which consists in that according to the present At the technical level, the electrophoresis body plunge pool, which is open at the top, is currently on the most exposed areas of automobile bodies, namely bonnet, roof, trunk lid, neither a uniform nor the same layer thickness as on vertical surfaces or on the floor pan of bodies due to the decreasing electric field with the distance from the pool wall, avoided while the electrophoretic coating of the inner surfaces of hollow bodies such as Car bodies is decisively improved.

The extraordinary advantages of the new process can be seen in the painting of hollow bodies, the outer surfaces of which are currently still receiving a three- or four-layer paint structure, e.g. B. Automobile bodies, since according to the new process all layers are covered by two or even just one Layer of appropriate thickness can be replaced,

e.g. by powder or other solvent-free Coating agents, e.g. B. unsaturated polyester dissolved in monomeric or oligomeric vinyl compounds, e.g. B. styrene. Acrylic acid ester.

The consistent application of the new process therefore means painting the outer surfaces of hollow bodies, e.g. B. car bodies, with only one shift and in a single operation, being the primer of the inner surfaces of hollow bodies only takes place after painting, as was previously the opinion. that a Grundierup.g must always be done before painting.

The table and examples show the general Validity of the new procedure, regardless of the composition of the train materials used.

The ir. The explanations for the table and the parts given in the examples are parts by weight.

Claims (4)

Patent claims: 1. A method for coating hollow bodies, characterized in that first the electrically conductive outer surfaces of the hollow bodies with electrophoretically non-separable, however, insulating and water-insoluble coatings are provided coating agents of a composition known per se and then the electrophoretic coating of the electrically conductive inner surfaces this hollow body with electrophoresis coating agents of known composition is carried out. 2. The method according to claim 1, characterized in that that the outer surfaces of the hollow body initially electrostatically with coating agents are coated per se known composition, the coating agent at least are further condensed until they are insoluble in water, then the electrically conductive ones Inner surfaces with water-thinnable coating agents of known composition electrophoretically coated and the coatings subjected to further condensation will. 3. The method according to claim 2, characterized in that that the outer surfaces of the hollow bodies are electrostatically coated with powder! Coating media Coated per se known composition and a temperature treatment be subjected. 4. The method according to claim 3, characterized in that that powdery coating agents are based on a known composition used by epoxy resins.