CS208190B2 - Method of coating the hollow letal object - Google Patents

Description

(54) A method for coating a hollow metal article

The present invention relates to a method for coating hollow metal articles and is particularly suitable for coating car body parts.

In the coating of metal objects, it has been proposed to proceed by coating the outer side of the hollow metal object with a layer of electrically insulating coating and then electrophoretically coating its inner side; The advantage of this coating method is that the insulating coating layer provides a visible and corrosion-resistant coating on the visible exterior of the article and at the same time reduces the consumption of electrophoretic coating material, while the electrophoretic coating provides the necessary corrosion protection on the inner parts of the article which are otherwise difficult to coat.

This coating method is with ^! It is advantageous in terms of the quality of the article to be coated, but it has disadvantages from the manufacturing point of view, since additional and space-intensive devices for applying and curing each coating separately must be provided to form two separate coatings.

The need for separate curing equipment prior to) constitutes a further substantial increase in the energy consumed during a large number of curing operations; This disadvantage is further exacerbated by the need to build up a device for the removal of the vapors generated during each curing. The device for carrying out such a method is not only space-intensive and expensive in investment terms, but consumes 1 much energy to operate.

The purpose of the invention is to simplify the coating of hollow metal objects and to reduce the cost of its execution while maintaining the quality of the coatings.

An object of the invention is to provide a method for coating a hollow metal article in which an aqueous primer is sprayed onto predetermined surfaces of the article, the omitted surfaces are electrophoretically coated with the primer, but at least those surfaces of the object that are visible are coated. fires to cure the top layer.

The electrophoretic coating is carried out without prior complete or partial curing of the sprayed primer, after the electrophoretic coating at least partially heat-cures both the sprayed and electrophoretically applied primer, and then, after applying the topcoat, the paint coat completely cures as well as any incompletely cured primers.

The process according to the invention has the advantage that the water-sprayed primer used to even the surface does not cure at all or only partially before the electrophoretic coating, so that it can be dried at a relatively low temperature and thus with considerable energy savings compared to complete curing. In addition, the fumes generated by the drying process do not normally have to be burned or otherwise disposed of, thus saving energy again.

Some primers, which serve as corrosion protection and as a leveling spray sealant, can be applied to an incompletely dried surface. Thus, the preparation of the surface of the article prior to coating may be completed by rinsing in water, after which a coating is applied to compensate for surface irregularities on the surface of the article in an incomplete drying state.

Incomplete, drying of moisture means that the surface of the object is. completely free of surface water, but not perfectly dry as after curing. This incompletely dried state can be formed after rinsing with water either by blowing air under high pressure or by blowing hot air under low pressure.

This eliminates the need for perfect drying, which is usually carried out after the article has been rinsed with water before the primer is sprayed, saving both the space and equipment costs and the energy associated with its operation.

In practice, it has not yet been possible in practice to apply a primer suitable for leveling surface irregularities and irregularities on an object of complex shape, such as the bodywork, using fully automated spray gun devices that monitor the surface of the object. For example, in the case of bodywork, certain areas of the coating have to be “thickened” manually by spraying with an automatic spray gun.

The process according to the invention eliminates the need for manual spraying and the primer which protects against corrosion and at the same time forms a sealant leveling surface can be sprayed automatically. Since the sprayed primer is compatible with the electrophoretic primer applied to the desired appearance and function of the finished article, the electrophoretic primer serves to “strengthen” in those areas that have been unevenly coated with the automatic spray primer.

If the malfunction of the automatic spray gun would cause defects such as paint run-off and "curtains" in the sprayed primer, they can normally be removed with a spatula using a suitable solvent after partially curing the sprayed primer, since even spots on which bare metal or only a thin layer of primer remains, is then coated with a primer during electrophoresis.

When, after the electrophoretic application of the primer, spray paint is sprayed onto the article, which is also common in the prior art methods, the topcoat layer does not adhere sufficiently to the edges of the surfaces covered with the sprayed sealant to level the surface. putty in the form of separate droplets. In such cases, the mastic droplets in these marginal regions usually have to be scraped off to determine the adhesion and appearance of the topcoat. In contrast to the invention, the electrophoretic coating of the coating and, in some cases, watering the droplets of the sprayed primer and the topcoat has sufficient adhesion without the need for manual treatment.

Initial surface treatment involves the normal cleaning and application of a chemical conversion agent, for example zinc or ferric phosphate in the case of iron articles, and preferably, in particular in the case of bodywork, multiple spraying and immersion in a bath, each section of the respective equipment having both a spray station and a bath, which for practical reasons can be located in the same part of the working tunnel. In the case of automobile bodies, the depth of the bath should be so large as to immerse all the main body parts of the body which are susceptible to corrosion, and so that their chemical treatment is carried out in more manageable conditions than spraying alone. Secondary spraying should be performed at the outlet of each section to reliably remove any chemical residues and foam that might remain on the exterior surface of the bodywork after leaving the bath.

In the prior art, surface treatment of multi-metal bodies prior to electrophoretic coating is critical, and special procedures or phosphating solutions are necessary for the article to have an adequate final appearance. The bodies have main parts of steel and, some unstressed parts, such as doors and lids. trunks (aluminum spaces. Previously, aluminum parts had to be treated prior to fitting to the body and other surface preparation solutions had to be chosen to have either steel parts effect and no aluminum parts effect, or special phosphates were used which both steel and aluminum parts.

In the method according to the invention, a visible anticorrosion primer having a spray-on-putty properties is sprayed on the visible parts of the multi-metal bodies before the electrophoretic coating, so that in some cases different pretreatment for different metals or the use of special phosphates can be omitted.

For articles that are not intended for automobiles, especially when treatment requirements are not so high, cleaning without chemical surface treatment is often sufficient.

Upon preparation of the water-bathed surface, an incomplete dried surface is formed by turbulence by air entraining or by blowing with a hot air stream, especially in the case of bodies where a strong air stream could blow water droplets from the hollow parts onto the object surface.

The aqueous primer may be an epoxy resin coating to contain pigments to provide adequate corrosion protection.

In the case of bodywork, all visible external surfaces are covered with an anticorrosive and bonding primer.

These primers, which have been fired for about 20 minutes at a temperature of about 160 ° C, have found that partial curing can be performed at 110 ° C for 10 minutes and that the resulting vapors do not need to be burned or otherwise disposed of.

The electrophoretically applied primer may also be an aqueous epoxyester-based coating which is compatible with the sprayed coating and is applied, rinsed and cured by conventional methods. The flushing space or spaces must be arranged so that the inner inaccessible parts are rinsed as thoroughly as possible.

After curing, the gaps between the parts of the article to be made, such as the bodywork, are filled with a joint filler of a composition to cure when the topcoat is fired. Suitably, the filler should be of such a composition that a solidified layer is rapidly formed thereon at normal ambient temperature so that the adhesive filler does not smear the adhesive filler on the surface of the object if the curtains are wiped off with a solvent.

The topcoat layer may consist of a conventional liquid lacquer or powder coating which is applied electrostatically in a known manner. Final firing is carried out in the usual way at temperatures and for a time appropriate for the topcoat.

In order to coat the car bodies, the curing equipment must be equipped with a perfect combustion. the process to remove gases resulting from the degradation products of the primer and the electrophoretic primer. The combustion heat can be used, for example, for pretreatment to dry the sprayed primer. or · to burn the topcoat. This achieves further energy savings.

The invention will be further elucidated by means of examples.

He did

The mild steel automobile door was cleaned and subjected to pre-treatment by immersion in a zinc phosphate solution, then rinsed with demineralized water and the water removed by air blowing. An aqueous epoxy primer was sprayed onto the exterior surface of the door in a layer of about 37 to 40 µm.

After 10 minutes of evaporation at ambient temperature and drying at 110 ° C for a further 10 iminuites when the primer was not fully cured, the door was completely immersed in the bath and primed with an electro-theoretical coating. Throughout the interface between sprayed. the primer and electrophoretic primer had a film thickness of 25 μ, ηι ·. The door was then dried for 20 minutes at 160 ° C (real temperature for metal until both primers were fully cured. Then the door was sprayed with pigmented alkydmelamine car enamel in a layer of 55 to 70 μπι and baked at 150 ° C for 20 minutes (actual metal temperature) The door had a nice appearance and the coating layer had satisfactory properties as determined by accelerated aging tests.

Example 2

The whole procedure as in Example 1 was repeated using aluminum doors that had been pre-immersed in an oxychromate bath. Even such a modified door suited.

Example 3

The mild steel door was coated according to Example 1 except that the top layer was a pigmented acrylic powder that was fired at 18 ° C (metal temperature for 15 minutes).

Claims (1)

r D E D m E τ A method of coating a hollow metal article, in which an aqueous primer is sprayed onto predetermined surfaces of the article, the omitted surfaces are electrophoretically coated with a primer, at least those surfaces of the object which are visible are applied with a topcoat and fired to cure a top layer characterized by electrophoretic coating The invention is carried out without prior complete or partial curing of the sprayed primer, after electrophoretic coating at least partially heat-cured both the sprayed and electrophoretically applied primer, after which the topcoat is fully cured and possibly even incomplete cured primers.