SI9420039A - Surface coating method - Google Patents

Abstract

A surface coating method is provided which can make an anticorrosive coating film having a high corrosion resistance with reduced man-hour and low costs. The method comprises coating a metal substrate with a bake-type metal anticorrosive composition containing a water-soluble chromate compound and zinc powder, baking the coated metal substrate, immediately followed by dipping the baked metal substrate into a liquid compositon either or both of a chromate compound and a resin monomer.

Description

SURFACE PROTECTION METHOD

The object of the invention is a surface protection method, more specifically a method for forming a protective film with high corrosion resistance on a metal surface.

Various protective compositions are known for use in the prevention of metal corrosion, e.g. steel. For example, JP 60-50228 (B) discloses a metallic anti-corrosion mixture containing chromium trioxide and metal, e.g. zinc or aluminum powder as a protective mixture with superior properties. Such a protective compound is commercially available under the Dacrodip brand.

Usually supplied to users, Dacrodip contains a combination of the first component, which mainly consists of chromium trioxide and water, with the second component, consisting of metal powder and low molecular weight oxohydroxyether such as e.g. propylene glycol, with additional host. When using Dacrodip, users mix the first component, the second component and the host, and apply a certain amount of the mixture to the metal substrate they want to protect. The amount of application is usually sufficient to protect the thickness of a few micrometers. Thereafter, the coated metal substrate may be heated for up to approx. 300 ° C to form a thin protective film.

This protective film has excellent corrosion resistance with salt water, but today even more resistance is required. In order to fulfill this requirement, the aforementioned security treatment, hereinafter referred to as the first protection process, is often followed by an additional chrome or protection process, called the second protection process. The second protection procedure, which follows the first one, enables the required corrosion protection to be achieved, but with this the number of operations is increased, since they can be duplicated, given that the first one covers protection, firing and cooling, and the second process also protection, firing and cooling. The problem is that processing time and costs go up a lot.

It is an object of the present invention to solve the aforementioned problem and to determine such a method of forming an anti-corrosion protective film on a metal surface that would have fewer processes and lower costs.

The first aspect of the present invention is a method of surface protection of a metal substrate with a burning metal anti-corrosion mixture containing a water-soluble chromium compound and zinc powder, and firing a protected metal substrate, followed immediately by immersion of the burning metal substrate in a liquid mixture containing the chromium compound and / or resin.

Another aspect of the present invention is the surface protection method as in the first aspect, whereby the calcined metal substrate is immersed in the aforementioned liquid mixture while maintaining the substrate temperature at 50 ° C or more.

A third aspect of the present invention is the surface protection method as in the first and second aspects, with diving being performed for 30 minutes or less.

io The corrosion-resistant metal corrosion mixture used in the present invention must contain a water-soluble chromium compound and zinc powder.

The water-soluble chromium compounds used in the method of the invention are not specifically specified, but all known, for example, chromic acid, a water-soluble metal salt of chromic acid such as e.g. calcium chromate and is magnesium chromate, and dichromate such as e.g. zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate and calcium dichromate.

The zinc powders used in the method of the invention may take any form. Zinc flakes are preferred, especially flakes of thickness 0.1-0.5 μηη and lengths up to 15 μιτ ». Zinc powder can be used in conjunction with aluminum powder.

The water content of the soluble chromium compound is in the range of 1-12%, preferably 2-8% by weight of the final mixture. The zinc powder content is in the range of 10-40%, preferably 15-30% by weight of the final mixture.

In addition to water-soluble chromium compound and zinc powder, the calcining metal anticorrosive compound may also contain boric acid and boric oxide, low molecular weight oxohydroxyether and pH regulator, humectant and / or organic solvent, if desired.

Of the boric acids, orthoboric acid is commercially available. If necessary, metabolic or tetraboronic acid may be used instead of or in combination with orthoboric acid. In case we use boric acid or. boric oxide, its proportion in the combustion metal anticorrosive mixture in the range of 10-75%, preferably 15-50% of the total weight of boric acid or. io of boron oxide and water-soluble chromium compound. Proportion of boric acid or. of boron oxide in such an area gives the mixture good anti-corrosion properties, both in salt and fresh water.

Low molecular weight oxohydroxyether can be a glycol or ether polymer of low molecular weight. It may be, for example, ethylene glycol, propylene is glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, diacetone alcohol, or members of like groups or mixtures thereof. These ethers can act as a reducing agent for a water-soluble chromium compound to be converted to a chromium compound and allow the formation of a uniform anti-corrosion protective film, since the ethers can act gradually while forming a protective film by applying and firing an anti-corrosion metal mixtures to prevent solvent boiling, etc.

The pH regulator is effectively used when the water-soluble chromium compound is strongly acidic and is used to regulate the pH of the mixed solution in the range 3.0-6.0 and is usually an oxide or hydroxide of a metal such as lithium or an element of the HA group and groups higher numbers such as strontium, calcium, barium, magnesium, zinc, cadmium, etc. The pH controller allows the stability of the storage of the calcining anti-corrosion mixture to be maintained in the optimum state, thus preventing the rapid reaction of zinc dust and acids in the liquid, which causes a decrease in the adhesion of the protective film and its darkening.

To aid in the suspension and dispersion of zinc powder, a moisturizing agent may be used, which may be a non-ionic surfactant, in particular an alkylphenol polyethoxy adduct, such as Nopco 1592 (trademark) manufactured by Diamond Shamrock Chemical Co.

The combustible metal anticorrosion mixture used in the present invention can be prepared by mixing the above-mentioned components in a known manner, for example by using a quick mixer.

Preferably, the is is (commercially available under the Dacrodip trademark) containing chromium anhydride, metal such as zinc or aluminum, pH regulator as a metal oxide or hydroxide, low molecular weight oxohydroxyether as an incendiary metal anticorrosion mixture. polyglycol and solvent, and is disclosed in patent J P 60-50228 (B).

Typically, this non-corrosive metal corrosion-resistant mixture is supplied to 20 users in combination with a first component, mainly containing chromium anhydride and water, with a second component containing low-molecular-weight metal powder and oxohydroxyether, and a host.

Users mix the first component, the second component and the host just before use, and then apply a certain amount of the mixture to the metal substrate they want to protect with a protective film. The amount of coating is usually sufficient to form the protective film a few micrometers or more in thickness. The protected metal substrate is then heated to a temperature of ca. 300 ° C to form a protective film on the metal substrate.

The metal substrate is not limited in size and shape and is already known. The method of the invention is particularly suitable for preventing the corrosion of steels and is therefore commonly used on steel substrates. It is recommended that the method is carried out after dust and grease have been removed from the substrate surface with an alkaline cleaner or chlorinated solvent.

The method of protecting a metal substrate with a burning metal anti-corrosion mixture consists of a mixture application process and a firing process.

is The application process can be carried out in a known manner, for example by painting, padding, spraying, hot spraying, air spraying, electrostatic application, roller application, canvas application, dipping, electrolysis, trowel application, etc.. In the case of diving, the excess mixture can be removed by centrifugation or vibration.

The firing process is carried out using a hot air circulation furnace (liquefied gas or electric furnace), remote infrared furnace, infrared furnace, radio frequency induction furnace, etc. or a combination of only 7 of these. The heat treatment is carried out at a temperature of 180 ° C or more for a period of at least 0.2 seconds, preferably at a temperature of 200 ° C or more for a period of at least 0.5 seconds, and more preferably at a temperature of 260 ° C or more and for a period of at least 0.5 seconds.

s The protection can be repeated if desired. The protective film made on a metal substrate is typically 1 pm or more thick, preferably 3 pm or more. This thickness is required for a more stable corrosion resistance.

According to the method according to the invention, the protected metal substrate is immediately immersed in a liquid mixture containing a chromium compound or a chromium compound after the firing process.

and resin.

The terms immersed immediately after the firing or firing process ... followed immediately by the immersion used herein mean that the metal substrate is immersed when it is not yet completely cooled. Diving is thus carried out before the substrate is completely cooled. The temperature of the submerged substrate may be 50 ° C or more, typically 50-350 ° C, preferably 100300 ° C. Especially if the temperature is in the range of 50-350 ° C, a nice protective film can be formed.

A liquid mixture containing a chromium compound or a chromium compound. the resin monomer may generally be one that can be applied and then dried to form a protective film.

The chromium compound contained in the liquid mixture may be the same as the water-soluble chromium compound contained in the burning metal anti-corrosion mixture. The type of chromium compound used in the dipping may be identical to or different from the water-soluble chromium compound used in the burning metal anti-corrosion mixture. Chromium compounds used in diving can be used individually or in combination.

As for the resin, it may be a water-soluble resin, a resin in an aqueous emulsion, or a resin in an aqueous suspension. Examples of resins are: acrylic resin, epoxy resin, phenolic resin, etc. Of these, acrylic resin is the most desirable.

The liquid mixture may contain a chromium compound without a resin, a resin without a chromium compound, or a chromium compound and a resin. In the method of the invention, a liquid mixture containing both a chromium compound and a resin is recommended. Liquid mixture containing both chromium compound and resin typically contains 0.1-50%, preferably 0.5-30% chromium compound by weight and typically 0.5-40%, preferably 0.5-20% resin by weight .

Chromium fluid, the product of Nippon is Dacro Shamrock K.K., under the trade name Dacromet # 100, and the resin protection agent under the trade name Dacromet LTX made by Nippon Dacro Shamrock K.K.

If the liquid mixture contains a solid ingredient, it should be adjusted to 0.5-90%, preferably 1-50% by weight. If the solid ingredient is in the range of 0.5-90% by weight, a protective film of good appearance and suitable thickness is obtained.

In the surface treatment method of the invention, the temperature of the liquid mixture is also important. If the temperature of the liquid mixture is too low, the cooling effect is too high for the protective film to form properly. However, if the temperature of the liquid mixture is too high, the liquid mixture itself may be degraded. The temperature of the liquid mixture may vary depending on the temperature of the metal substrate, which is preferably adjusted to the range of 5-95 ° C.

The metal substrate, which was calcined during the protection process, is immersed in the liquid mixture preferably for 20 minutes or less, usually for 0.1 seconds to 30 minutes, and preferably for 0.5 seconds to 5 minutes. If the immersion time is in the range of 0.1 seconds to 30 minutes, the protective film on the metal substrate can be formed completely, and the substrate temperature does not drop too much, so the drying effect of the firing during the protection process is not lost.

In the embodiment of the invention, after the immersion process, firing is usually no longer required. However, a simple drying process can be performed if desired.

The immersion process produces a protective film, typically 0.1 μηη or more thick, preferably 1 gm or more. The best film is 1gm is or more in thickness, as it offers a more stable corrosion resistance than the first film of protection.

The invention will now be explained below with a few examples, which do not limit it.

The evaluation of the protective films produced in the following cases was performed as follows:

1. Exterior appearance

The thinness and unevenness of the protective films were visually observed. The evaluation was divided into three criteria:

In ......................... very good

G ......................... good

P .......................... poor (Poor)

G-P ...................... slightly worse, not problematic

2. Anti-corrosive

After performing a composite cyclic corrosion test, the appearance of rust was visually observed. The evaluation was divided into three criteria:

In ........................ very good

G ........................ good

P ......................... poor (Poor)

G-P ..................... slightly worse, not problematic

3. The time it takes to process

The time (hours) required for processing was evaluated on the basis of the 1st comparative example. A M 10 steel screw (overall length 37mm; weight approx. 22g) was used as the test substrate, which was washed with solvent steam and sanded dry.

Example 1

In the process of protection, Dacrodip (trademark) was used as an incendiary metal anti-corrosion compound and was mixed according to the recipe.

In the immersion process, we used Dacromet # 100BL (Trademark; Black Chromium Liquid) as a liquid mixture containing a chromium compound, but not a resin. The Dacromet mixture is as follows:

Chromic acid approx. 4% by weight

Zinc powder approx. 20% by weight

The test substrate was immersed in Dacrodip, and excess Dacrodip on the substrate was removed by centrifugation. During the firing process, the test substrate was placed in an electric hot air circulation oven and heated to 300 ° C for 5 minutes. After the test substrate cooled to 290 ° C after removal from the io oven, it was immersed in Dacromet # 100BL, set to 50 ° C, extracted and dried after 1 second.

The amount of protective film adhered to the test substrate during the protection process was 100 mg / dm ² and the amount adhered during the immersion process was 50 mg / dm ² . After the dive was completed, the test substrate was evaluated as described above. The results are given in Table 1.

Example 2

The same procedures as in Case 1 were repeated, except for the following:

Dacromet LTX (branded; clear) containing resin, but not chromium compounds, was used as the liquid immersion mixture. After firing as part of the shielding process, the test substrate was immersed in Dacromet LTX (trademark; clear) when it was cooled to 250 ° C, then extracted and dried after 2 seconds.

The amount of protective film adhered to the test substrate during the shielding process was 100 mg / dm ² and the amount adhered to during the immersion process was 80 mg / dm ² . After completion of the dive, the test substrate was evaluated as described above. The results are given in Table 1.

Case 3 io The same procedures as in Case 1 were repeated, except for the following:

In the immersion process, we used Dacromet # 100 (trademark; chromium liquid) as the liquid mixture, which contained a chromium compound but not a resin. The diving time was 5 seconds.

The amount of protective film adhered to the test substrate was 100 mg / dm ² and the amount adhered during the immersion process was 50 mg / dm ² . After completion of the dive, the test substrate was evaluated as described above. The results are given in Table 1.

Example 4

The same procedures as in Example 1 were repeated, except for the following: The firing process was performed by heating the test substrate to 350 ° C in an electric hot air circulation oven and maintaining the substrate at this temperature for 5 minutes. After the removed substrate had cooled to 300 ° C from the furnace, it was immersed in a liquid mixture set to 95 ° C and extracted and dried after 5 seconds.

The amount of protective film adhered to the test substrate was 100 mg / dm ² and the amount adhered during the immersion process was 100 mg / dm ² . After completion of the dive, the test substrate was evaluated as described above. The results are given in Table 1.

Example 5

The same procedures as in Case 1 were repeated, except for the following:

When the test substrate, which was burned during the protection process and then removed from the electric hot air circulation furnace, cooled to 270 ° C, it was immersed in a liquid mixture set at 20 ° C after 0.5 seconds. pulled out and dried.

The amount of protective film adhered to the test substrate during the protection process was 100 mg / dm ² and the amount adhered during the immersion process was 30 mg / dm ² . After completion of the dive, the test substrate was evaluated as described above. The results are given in Table 1.

Example 6

The same procedures as in Example 1 were repeated except that the protection process was repeated twice, followed by the immersion process.

The amount of protective film adhered to the test substrate during the protection process was 200 mg / dm ² and the amount adhered during the immersion process was 100 mg / dm ² . After the dive was completed, the test substrate was evaluated as described above. The results are given in Table 1.

Example 7

The same procedures as in Case 1 were repeated, except for the following:

Dacromet is # 100BL (trademark; chromium liquid) was used as the liquid mixture in the immersion process, to which a 10% aqueous acrylic ester (manufactured by Showa Kobunshi KK) was added as a resin. The amount of protective film adhered to the test substrate during the protection process was 100 mg / dm ² and the amount adhered during the immersion process was 50 mg / dm ² . After completion of the dive, the test substrate was evaluated as described above. The results are given in Table 1.

1st comparative example

In the first protection process, Dacrodip was used as a burning metal corrosion-resistant compound, which was mixed according to the recipe. In another protection process, Dacromet 100BL (black chromium liquid) was used as the liquid mixture containing the chromium compound and / or the resin monomer.

The test substrate was immersed in Dacrodip and centrifugally removed excess Dacrodip on the substrate. The test substrate was then calcined by heating in an electric oven to circulate hot air to 300 ° C and maintained at the same temperature for 5 minutes. After removal from the oven, the test substrate was allowed to cool to room temperature.

In the same manner as in the first protection procedure, the test substrate was immersed in Dacromet # 100BL liquid mixture and the excess liquid mixture on the substrate was centrifugally removed. The test substrate was re-ignited by heating in an electric furnace to circulate hot air at

250 ° C and maintained at the same temperature for 5 minutes.

The amount of protective film adhered to the test substrate in the first protection process was 100 mg / dm ² and the amount adhered during the second protection process was 50 mg / dm ² .

After protection was completed, the test substrate was evaluated as described above. The results are given in Table 1.

2. comparative example

The same procedures as in Comparative Example 1 were repeated, except the following:

In the second protection process, we used Dacromet LTX (clear), which is a resin protective agent. The firing was performed in the second protection process by heating the test substrate in an electric oven to circulate hot air at 100 ° C and maintained at the same temperature for 5 minutes. After removal from the oven, the test substrate was allowed to cool to room temperature.

ίο In the first protection process, the amount of protective film adhered to the test substrate was 100 mg / dm ² . The amount adhered during the second protection process was 80 mg / dm ² . After the protection was completed, the substrate was evaluated as described above. The results are given in Table 1.

3. comparative example

The same procedures as in Case 1 were repeated, with the exception that no other protection procedure was performed.

The amount of protective film adhered to the test substrate was 100 mg / dm ² . After protection was completed, the test substrate was evaluated as described above. The results are given in Table 1.

4. Comparative Example

The same protection procedure as in case 6 was repeated twice, except that the second procedure was not performed.

The amount of protective film adhered to the test substrate 5 was 200 mg / dm ² . After protection was completed, the test substrate was evaluated as described above. The results are given in Table 1.

Table 1

External appearance Corrosion resistance The time it takes to process Example 1 V Mr 6 Example 2 V G-P 6 Example 3 V Mr 6 Example 4 v Mr 6 Example 5 v Mr 6 Example 6 v V 11 Example 7 v Mr 6 1. Compare. example P G-P 10 2. Compare. example P G-P 9 3. Compare. example P P 5 4. Compare. example Mr Mr 10

With conventional surface protection methods, a drying apparatus is required in the immersion process, thus consuming many working hours and operating time. The surface protection method of the invention can, however, be omitted from the drying process in the protection process by utilizing the high temperature obtained by the metal substrate in the firing process. Therefore, the surface protection method of the invention can simplify the apparatus and shorten the operating time. The method of the invention is therefore not only efficient in the industry, but also contributes to energy saving and environmental protection.

For:

NIPPON DACRO

SHAMROCK CO., LTD.

Claims (17)

PATENT APPLICATIONS 5 1. Surface protection method, characterized in that it covers the protection of the surface of a metal substrate with a burning metal anti-corrosion mixture containing a water-soluble chromium compound and zinc powder, burning a protected metal substrate, followed immediately by the immersion of a burning metal substrate in a liquid a mixture containing either a chromium compound or a resin or both. 2. Surface protection method according to claim 1, characterized in that the surface-protected metal substrate is immersed in a liquid mixture and the substrate has a maintained temperature of 50 ° C or higher. 3. The method of surface protection according to claim 1, wherein the metal substrate is steel. A surface protection method according to claim 1, characterized in that the water-soluble chromium compound is chromic acid or the water-soluble metal salt of chromic acid, such as e.g. calcium chromate, 5 magnesium chromate, zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate or calcium dichromate. 5. Surface protection method according to claim 1, characterized in that the zinc powder is flake-shaped. 6. Surface protection method according to claim 1, characterized in that the flakes have a thickness of 0.1-0.5 μηη and a length of up to 15 μηη. 7. Surface protection method according to claim 1, characterized in that the zinc powder is used together with the aluminum powder. 20 A surface protection method according to claim 1, characterized in that the proportion of water-soluble chromate is in the range of 1-12% by weight of the mixture. 9. Surface protection method according to claim 1, characterized in that 5 that the water-soluble chromate content is in the range of 1-8% by weight of the mixture. 10. Surface protection method according to claim 1, characterized in that the zinc dust content is in the range of 10-40% by weight of the mixture. Surface protection method according to claim 1, characterized in that the zinc dust content is in the range of 15-30% by weight of the mixture. A surface protection method according to claim 1, characterized in that the calcining metal anti-corrosion mixture also contains boric acid or. boron oxide, low molecular weight oxohydroxymeter, regulator 20 pH, moisturizer and / or organic solvent. 13. Surface protection method according to claim 12, characterized in that the boric acid is orthoboric acid, metaboric acid and / or tetraboric acid. A surface protection method according to claim 12, characterized in that the low molecular weight oxohydroxyether is glycol or a low molecular weight ether polymer thereof. 15. Surface protection method according to claim 14, characterized in that the low molecular weight oxohydroxyether is ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and is tripropylene glycol, diacetone alcohol or members of similar groups or mixtures thereof. 16. Surface protection method according to claim 1, characterized in that 20, after which the calcined metal substrate is immersed in the liquid mixture for 30 minutes or less. A surface protection method according to claim 2, characterized in that the calcined metal substrate is immersed in the liquid mixture for 30 minutes or less.