SE526172C2 - Method of treating a surface - Google Patents

Abstract

The invention concerns a method for treating a surface of aluminum or aluminum alloy. The method is characterized by a new combination of pretreatment and surface coating. The surface (1) intended for treatment is pretreated by means of anodization and coated with epoxy phenol adhesive primer. The pretreated surface is then sprayed with epoxy material in powder form with particle size in the 15 - 25 mu m range. The powder-coated surface is heated to the curing temperature of the epoxy material, 115 - 130 DEG C, whereupon the epoxy material is caused to cure.

Description

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O 0 0 0 0 uno 09000 2 chromates to compare with the 20% share included in the conventional primer. Furthermore, the total coating thickness can be reduced by about one third compared to when using a conventional paint system, which provides a weight saving that is valuable in the floor plan industry.

The proposed method of coating is also better in terms of resistance to chemical reactions, shocks and adhesion properties compared to the conventional method. As a result, a significant extension of the operating time can be expected.

Tests carried out have shown that the throughput time during manufacture is reduced by at least 50% compared to what is the case with the conventional method.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows conventional surface coating according to the prior art Figure 2 shows surface coating by means of the inventive combination of primer treatment and powder application.

DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows an aluminum surface 1 with a surface coating according to conventional technology.

The aluminum surface is in a first layer 2 chromic acid anodized with a layer thickness in the order of 2-5 μm. In the case of conventional surface treatment techniques, a primer layer 3 has a thickness of the order of 15-25 μm. The final coating is done in two to four steps with a resulting layer 4 in the order of 40-60 μm. A problem with conventional technology is that this technology is forced to use a large amount of environmentally hazardous solvents. Layers 2-4 must also be made relatively thick, which leads to an undesirably high weight in the eye plane context.

Figure 2 shows a surface coated in accordance with the new method of surface coating. An aluminum surface 1 has been anodized with a phosphoric acid and provided with a coating 6 of primer with a thickness of 5 - 10 μm. The technique for this pre-treatment is a well-known process that is currently used in surface treatment before metal gluing and spray needling.

Before coating the primer and coating the epoxy material in powder form, the articles intended for the coating must be anodized. This is preferably done in a process of b) phosphoric acid anodizing. The dimension of the conductor and the number of contact points are adapted to the material and article. The various articles are mounted on holders so that the treatment bath and rinsing water come into contact with all surfaces. The articles are anodized in 100-120 g / l phosphoric acid at a temperature of 22-28 ° C and at a voltage of 15 IV. The voltage is kept constant for a certain period of time, which can be in the order of 20-25 minutes.

The articles are then removed from the anodizing bath and rinsed. The article is then thoroughly dried, after which inspection is performed of the formed anodizing layer 5.

Within about three days after completion of anode oxidation and subsequent drying, the adhesive primer should be applied. The adhesive primer is used as an adhesion promoter and corrosion protection. Preferred primers consist mainly of epoxy and phenol, possibly with the addition of strontium chromate as corrosion inhibitor. The primer treatment is preferably carried out immediately after surface treatment or alternatively no later than within two hours - when stored in a clean room within 72 hours. Application of primer is via spraying. If the resulting primer layer 6 after spraying is thinner than desired, a second layer can be applied before curing to increase the thickness.

After application, the primer should dry at room temperature. Thereafter, the primer layer is cured at temperatures in the range of 110 - 135 ° C for 60-120 minutes, alternatively 80-90 ° for 24 hours.

The time between primer application and curing should not exceed 120 hours.

The thickness of the primer layer 6 should preferably be in the order of 5 - 10 μm.

Thicker primer layers are of course also possible; however, the use of thicker layers reduces one of the great advantages of the invention where the new surface treatment method makes it possible to reduce solvent emissions by reducing the thickness of the primer layer.

Coating of the phosphoric acid anodized and adhesive primer treated articles is done by means of a one-component epoxy powder coating. This powder coating should not be used on articles exposed to direct sunlight but is primarily intended for use inside the eye plane. In a preferred embodiment of the invention, a powder coating is used where the powder consists of epoxy particles with a very low particle size, 15 - 25 tm. The powder 10 “l» J k / \ -Q en ro 4 is used as it is delivered and does not undergo any further processing before the powder application on the current article.

The application takes place by electrostatic application of the powder. The article is grounded and the particles in the powder are charged, after which the powder is sprayed against the article. After application, the lacquered surface is allowed to harden for about 30 minutes at temperatures in the range 115 - l35 ° C. The powder coating is made in a layer 7 with a thickness of 40 - 50 μm. The thickness of the layer 7 can of course be varied within the scope of the invention; since the weight aspect is important in the pl planing industry, however, layer 7 should be kept as thin as is deemed possible.

Claims (1)

10 15 'Éï f »17 2 šïïi jQ-: Iäíš 5 PATENTKRAV Method for treating a surface (1) of aluminum or aluminum alloy characterized by the following steps in combination: the surface is dry-treated by anode oxidation and coated with a primer of epoxyphenol, the pretreated surface is sprayed with epoxy material in powder form with a particle size in a range 15 - 25 pm, the surface is heated to the curing temperature of the epoxy material 115 - 130 ° C, whereby the epoxy material melts and is caused to cure. Method according to claim 1, wherein the powder coating is made in a layer (7) with a thickness of 30-50 μm. A method according to any one of the preceding claims, wherein the primer layer (6) is given a thickness in the range 5 - 10 μm. A method according to claim 3, wherein the anodizing is done with phosphoric acid. Method according to one of the preceding claims, wherein the surface treatment is carried out on shaped and machined sheet metal articles such as frames and spools. Method according to one of Claims 1 to 4, in which the surface treatment is carried out on machined articles such as molds and castings. 0 00000: