JPS5962371A - Pretreatment of substrate for powder painting - Google Patents

Abstract

PURPOSE:To prevent the generation of the defective appearance occuring in the oozing of oil from the inside of the seam in the stage of stoving after powder painting, by degreasing and washing the substrate having the seam by using a solvent prior to alkali degreasing. CONSTITUTION:A substrate having a seam such as housing or the like is beforehand degreased and washed by using a chlorine solvent such as trichloroethylene or the like and is thereby subjected to a pretreatment for washing away the oil on the surface and in the seam. The substrate is then passed through an alkali degreasing stage and is then subjected to powder painting and baking after a chemical conversion treatment. The defective appearance occuring in the uneven paint coated film in electrostatic painting of powder and the oozing of the oil in the stage of baking is prevented by the above-mentioned pretreatment method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for pre-treating objects to be coated for powder coating, and in particular to a method for pre-treating objects to be coated that have seams such as casings.

The surface of the object to be powder coated is coated with phosphorus f'1 in advance.
21λ? 1 solution to form a chemical coating, which not only prevents rust on the metal surface but also improves the adhesion of the paint film.
The surface of the object to be coated is degreased for chemical conversion treatment to form a chemical conversion film.

Conventionally, this degreasing treatment has been carried out by cleaning the object to be coated with an alkaline degreasing liquid spray or tep, followed by water washing, surface conditioning, chemical conversion treatment, water washing, and drying. The body is painted and the painting is completed by baking. However, in the case of objects to be coated, such as casings that have joints due to assembly, it is difficult to sufficiently remove the oil that is inside the joints with the above-mentioned one-spray alkaline degreasing method. When heated in the firing process after body painting, there was a problem in that oil seeped from inside the seam area, resulting in poor painted appearance in that area.

One possible solution to this problem is to immerse the object to be coated in an alkaline degreasing solution during the alkaline degreasing process.
Since this method requires soaking the object for a long time, it is not suitable for coating lye/conversion including pre-treatment, and even with this long immersion, the oil inside the seam can be removed. Removal is far from complete.

When assembling the casing, etc., it is possible to avoid the presence of oil in the seams. However, in that case, in order to prevent the powder coating from blistering due to rust, pickling treatment is usually performed prior to the chemical conversion treatment in the pretreatment step. However, in the case of objects to be coated that have many seams, acid remains at the seams, resulting in the problem of blistering of the painted surface, and a corrosion-resistant device for pickling is also required.

On the other hand, in powder coating, by establishing a method for removing oil from inside the joints of objects to be coated in the pre-treatment process, it is possible to apply sufficient anti-corrosion oil at the manufacturing stage of the parts, and it is possible to manage parts and Assembling management becomes easier, the pickling process can be omitted from the pre-treatment process in painting, and the occurrence of defective products in painting is also prevented.

The present invention has been developed to meet these demands, and includes a pretreatment method in which a powder coated object is degreased with alkali and then chemically treated. This is a method for pre-treating objects to be coated for powder coating, which includes degreasing and cleaning.

Solvent used in the present invention (2) Since the main purpose is to remove rust preventive oil, any solvent can be used as long as it is suitable for this purpose and does not cause corrosion or other adverse effects on the object to be coated, but generally is used for degreasing and cleaning metal foils, and less flammable chlorinated solvents such as dichlorotyrene, ethane, perchlorethylene, etc. are used.

The degreasing method using a solvent can use a three-type steam cleaning machine that is generally used for degreasing metals and passes through a hot liquid bath, a cold liquid bath, and a steam bath in sequence, but in some cases, a hot liquid bath may be used. can be omitted.

In the method of the present invention, oil on the surface of the object to be coated is removed at least by immersion in a cold solvent, and oil inside the seam is also cleaned in a solvent vapor bath, so the coating film in electrostatic coating of powder is removed. For unevenness and oil oozing during the baking process J:
V) The appearance defects that occur are prevented.

Hereinafter, the pretreatment method and subsequent powder coating according to the present invention will be explained by way of examples.

FIG. 1 shows a process diagram of powder coating according to the present invention.

The object to be coated 1 is, for example, an outer casing of a public telephone set, and has a seam formed by joining two casings, an upper and a lower casing. The object to be coated, which is suspended on a hanger and transported by a chain conveyor, is first immersed in 1°1.1-1-IJ dichloroethane at room temperature in a cold liquid immersion cleaning tank in solvent cleaning step 2, and then in a steam cleaning tank. Exposure to the vapor phase (approximately 73° C.) above a boiling liquid of the same solvent. Next, the object 1 to be coated is sprayed with an alkaline degreasing liquid in an alkaline degreasing step 3. As the alkaline degreasing liquid, Fine Cleaner 4309 (trade name) manufactured by Nihon Vercalizing Co., Ltd. was used.

The surface of the object to be coated in this process has already had its oil removed by solvent cleaning, but due to the spray effect of the warm alkaline degreasing solution at around 50°C, it can remove stains caused by inorganic substances that are insoluble in the solvent, such as metal cutting waste, polishing particles, etc. Dregs and other debris are removed. As a result, the surface of the coated object 1 has become clean,
In order to remove alkaline content, in the washing step 4, the material is washed with water using a water shower. In this case, there is a drain section between the alkaline degreasing process and the water washing process to avoid splashing of the washing water into the alkaline degreasing solution, and while being conveyed through that drain section, the water heated by the warm alkaline degreasing solution is transported through the drain section. The upper part of the object 1 to be coated dries as the liquid flows down, and this dry area causes uneven formation of the chemical conversion film in the subsequent chemical conversion treatment, so a mist is placed in the drain section of the object 1. spray 5
is installed to spray a mist of alkaline degreasing liquid to prevent the object being coated from drying out. The coated object 1 from which the alkali content has been completely removed in the water washing step 4 is then sprayed with a surface conditioner in the surface conditioning step 6. This surface conditioning is to form a uniformly dense chemical conversion film in the next chemical conversion treatment. For chemical conversion treatment using a zinc phosphate bath, a surface conditioning agent containing titanium is effective. Percolene Z (trade name) manufactured by Nippon Parkerizing Co., Ltd. is spray applied.

Next, in a chemical conversion treatment step 7, the object to be coated 1 is immersed in a zinc phosphate film conversion bath at a temperature of about 50°C. The film-forming acid bath used here is various or commercially available, but compared to the powder electrostatic coating employed in this example (l″t1
A good chemical conversion film could be obtained by using Bonderite 3004 (trade name) manufactured by Nippon Parriki Rising Co., Ltd. In addition, Chemicoat 1-428 or 556S (product name) manufactured by Chemicoat Co., Ltd. or Lascuff (manufactured by Teruko Kagaku Co., Ltd.)
502 (trade name) also gives a good chemical conversion film.

The object to be coated is immersed in the film-forming acid bath in the chemical conversion treatment step 7 for 4 minutes to form a uniform chemical conversion film, and then thoroughly washed with water in the washing step 8. The washed object 1 is dried at 140° C. for 20 minutes in a drying step 9.

The coated object 1 on which the zinc phosphate chemical conversion coating has been sufficiently dried through the above pretreatment process has +f,! ! , and is transported by a chain conveyor and introduced into the powder coating process 10. The coating was electrostatically coated with polyester powder paint.'+ (1; (=
By baking in the I furnace 11 at a temperature of 200° C. for 20 minutes, a coated product 12 with good appearance, adhesion, and corrosion resistance was obtained. This coated product 12 showed no appearance defects due to oil bleeding from the seams.

The coating film of the obtained painted product showed a value of 1 K, P 30 cm in the impact test according to the JISK540oB method, and was compliant with the Communication Equipment Industry Association Technical Standard (CES), Test Method for Painted Products M05.
Crosscut 100 in cross cut test A method according to 06-2
Medium peeling was 0, and 5% Na was also tested by salt spray test.
(As a result of continuous spraying of the 1 solution at 35° C. for 500 hours, the blistering from the scratch mark area was only 0.1 mm on one side, which was extremely good.

In the pretreatment method of the present invention, in the pretreatment step of the object to be coated,
By carrying out the degreasing process using a solvent every month, even the oil inside the seams is removed, so (1) it is possible to sufficiently apply rust-preventing oil to the rust-preventing pots during the manufacture of the casing, etc.;

(2) There is no need to remove rust by pickling during chemical conversion treatment, and there is no occurrence of defective products due to residual acid.

(3) Seizure of powder coating sometimes prevents poor appearance due to oil oozing out from inside the seams1, (4) Solvent degreasing can substantially remove oil from the object Therefore, the deterioration of the alkaline degreasing liquid is reduced and the service life of the alkaline degreasing liquid is extended.

It has many effects such as.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of a powder coating line including a pretreatment step according to the present invention. The correspondence between the main parts illustrated and the symbols is as follows. 1. Object to be coated, 2. Solvent cleaning process, 3. Alkaline degreasing process, 4. Water washing process, 5. Mist spray, 6. Surface conditioning process, 7. Chemical conversion treatment process, 8. Water washing process, 9.
・Drying process, 10... Powder coating process, 11... Burning oven,
12. Painted product applicant Katsura Atsuta, patent attorney representing Anritsu Electric Co., Ltd.

Claims (3)

[Claims] (1) A pretreatment method in which an object to be powder coated is subjected to alkaline degreasing and then chemical conversion treatment, characterized in that the object to be coated having seams is degreased and cleaned with a solvent before alkaline degreasing. Method for pre-treatment of objects to be painted. (2) The method according to claim (1), wherein a chlorinated solvent is used as the solvent. (3) The chlorinated solvent is trichlorethylene 7.1,1.
1-1-' The method according to claim (2), wherein in the J chloroethane extraction, barchlorethylene is used.