HUT74110A - Surface coating method - Google Patents

Description

EXTRACT ^ A-4a4á + Rated Serinfy Method for Coating a Surface Where the surface of a metal substrate is coated with a burnable type anti-corrosion composition. The process uses a composition comprising a water-soluble chromate compound and a zinc powder, heat-treating the coated metal substrate, and immersing the heat-treated metal substrate directly at chilled temperature in a liquid composition containing a compound and / or resin, where a second curing step is not used.

82939-7884 / VO / LZs

P 95 03769

By l

Representative:

Danubia Patent and Trademark Office Ltd.

Budapest

Surface Coating Procedure

Nippon Dacro Shamrock Co., Yokohama-shi, Kangawa-ken, JP

inventors:

NAKAZOATO Michiaki Yokohama-shi, Kangawa-ken, JP

SUGANO Kazuaki Yokohama-shi, Kangawa-ken, JP

Date of filing: 04/08/1994

Priority: 08-08-1993 (5-194940, JP)

International Application Number: PCT / JP94 / 01291

International Publication Number: WO 95/04843

82939-7884 / VO / LZs

P 95 03769 ··· • · ·

The present invention relates to a process for coating a surface, more particularly to a coating with a high corrosion resistance on a metal surface.

Numerous formulations are known for providing a corrosion protection coating for metals such as steel. JP 60-50 228 (B) discloses a composition having excellent properties as a metal corrosion inhibiting composition containing chromic anhydride and a metal powder such as zinc or aluminum powder. Such a coating composition is commercially available as Dacrodip.

Dacrodip, supplied to users, is usually a combination of a first component consisting of chromic anhydride and water and a second component consisting of a metal powder and a low molecular weight oxohydroxyether such as propylene glycol, which also contains a viscosity enhancing agent. In applying Dacrodip, the user mixes the first and second components and the viscosity enhancing agent, and applies a predetermined amount of mixture to the metal substrate to be coated. The amount applied usually allows for coatings of a few μιτι thickness. Subsequently, the coated metal substrate is heated to a temperature of 300 ° C for a predetermined time to form the coating.

The coating thus obtained provides excellent corrosion resistance to saline solutions, but recently there has been a demand for greater corrosion resistance. To meet this need, after the above operation, hereinafter referred to as the first coating step, a further step of the second coating step

82939-7884 / VO / LZs

P 95 03769 • · · · · · · ·

They perform a chromating or coating operation called · ···· * · ······· · ···. The second coating step after the first step provides the required corrosion resistance, but it almost doubles the number of operations since the first coating step includes coating, heat treatment and cooling, while the second coating step also includes coating, heat treatment and cooling. This significantly increases the duration and cost of treatment.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problem and to provide a process for producing a corrosion-protective coating on a metal surface at a reduced number of operating steps and at a lower cost.

Accordingly, the present invention provides a method for coating a surface comprising coating a metal substrate surface with a burnable metal corrosion inhibiting composition. The process of the present invention uses a composition comprising a water-soluble chromate compound and a zinc powder, heat-treating the coated metal substrate, and immersing the heat-treated metal substrate directly in a liquid composition containing the chromate compound and / or resin without using a second heat treatment step.

During the process of the invention, the immersion time is up to 30 minutes.

The burn type metal corrosion inhibitor composition of the present invention comprises a water soluble chromate compound and a zinc powder.

The process comprises chromic acid, a water-soluble chromate compound, a water-soluble salt thereof such as calcium chromate, magnesium chromate, and dichromate such as zinc dichromate, potassium 82939-7884 / VO / LZs.

P 95 03769 • · ·

4-dichromate, sodium dichromate, magnesium dichromate and calcium dichromate.

The zinc powder used in the process of the invention may be of any shape. The zinc powder preferably consists of flakes, in particular 0.1 to 0.5 µm in thickness and up to 15 µm in length. Zinc powder can also be used in combination with aluminum powder.

The amount of water-soluble chromate compound is from 1 to 12% by weight, preferably from 2 to 8% by weight, based on the total weight of the composition. The amount of zinc powder is 10-40% by weight, preferably 15-30% by weight, based on the total weight of the composition.

In addition to the water soluble chromate compound and the zinc powder, the burn type anti-corrosion composition may optionally contain boric acid or boric oxide, low molecular weight oxo-hydroxy ether and pH adjusting agent, wetting agent and water and / or organic solvent.

The boronic acid is preferably commercially available orthoboric acid. Metabolic acid or tetrabic acid may be used in place of or in combination with orthoboric acid, if necessary. When used, the amount of boric acid and / or boric oxide in the burn type metal corrosion inhibitor composition is 10 to 75% by weight, preferably 15 to 50% by weight, based on the total weight of boric acid and / or boric oxide and water soluble chromate. The amount of boric acid and / or boric oxide present in the above range gives the composition high corrosion resistance in both salt and ordinary water.

The low molecular weight oxo-hydroxy ether may be glycol or a low molecular weight ether type polymer such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol

82939-7884 / VO / LZs

P 95 03769 ················································································ kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol kol These ethers may act as reducing agents for water-soluble chromate compounds, whereby the change induced in the chromate compound promotes the formation of a uniform corrosion protection coating as the ethers gradually exert their action by applying and burning a burnable type anti-corrosion composition.

In the case of highly acidic water soluble chromate compounds, a pH adjusting agent is effectively employed to maintain the pH of the mixed solution in the range of 3.0 to 6.0. Generally, such pH adjusting agent is an oxide or hydroxide of a metal, such as lithium, or a member of a periodic column of a cell having a serial number IIA or greater, such as strontium, calcium, barium, magnesium, zinc, cadmium and the like. The pH adjusting agent may, in optimum condition, maintain the shelf life of the burn type metal corrosion inhibiting composition by inhibiting the rapid reaction of zinc powder and acids in the liquid, which reduces adhesion of the coating and causes the coating to darken.

A wetting agent may be used to maintain the suspension and disperse the zinc powder, which may be a nonionic surfactant, especially an alkylphenol / polyethoxy adduct such as Nopco 1592 (manufactured by Diamond Shamrock Chemical Co.).

The burn type metal corrosion inhibitor composition used in the present invention may be prepared by:

82939-7884 / VO / LZs

P 95 03769 • ·· ·· The above components are mixed in a known manner, such as by a high speed mixer.

As a burn-type anti-corrosion composition of metal, a composition (commercially available as Dacrodip) which according to JP 60-50 228 (B) is a chromic anhydride, a metal such as zinc or aluminum, a metal oxide or a pH adjusting agent is preferred. hydroxide, a low molecular weight oxo-hydroxy ether such as polyglycol and a solvent.

Combustion-type metal corrosion inhibiting compositions supplied to users are typically a combination of a first component consisting of chromic anhydride and water and a second component consisting of a metal powder and a low molecular weight oxohydroxyether and a viscosity enhancing agent.

Immediately prior to use, the user mixes the first and second components and applies a predetermined amount of mixture to the metal substrate to be coated. The amount employed usually allows for a coating of a few µm thickness. Subsequently, the coated metal substrate is heated to a temperature of 300 ° C for a predetermined time to form the coating.

The metal substrate is not limited in size and shape and may be of any known metal. The process of the invention is particularly advantageous for inhibiting the corrosion of steel and is therefore frequently used on steel substrates. The process is preferably carried out by removing dust or grease from the surface of the substrate with an alkaline cleaning agent or a chlorinated solvent.

82939-7884 / VO / LZs

P 95 03769

A method of coating a metal burnable type with a metal corrosion inhibiting composition comprises applying the composition and firing as a process step.

The composition may be applied by any known means such as by brush, surface painting, spraying, high temperature spraying, air spraying, electrostatic coating, roller coating, spray coating, dipping, electrolytic deposition, spatula coating and the like. In the case of immersion coating, excess formulation may be removed by immersion by centrifugation or vibration.

Combustion is performed using a hot air circulation furnace (gas fired or electrically heated furnace), a far infrared furnace, an infrared furnace, a radio frequency induction furnace, or a combination thereof. The heat treatment is carried out at a temperature of at least 180 ° C for at least 0.2 seconds, preferably at least 200 ° C for at least 0.5 seconds, more preferably at least 260 ° C for at least 0.5 seconds.

If desired, the coating may be repeated.

The coating on the metal substrate is usually at least 1 µm, preferably at least 3 µm thick. This thickness is required for good corrosion resistance.

In the process of the present invention, the coated metal substrate is immersed immediately after heat treatment in a liquid composition containing a chromate compound and / or resin.

82939-7884 / VO / LZs

P 95 03769

The term "immersed immediately after heat treatment" as used herein means that the heat treated metal substrate is immersed in the liquid preparation until it has cooled completely. The temperature of the substrate to be submerged may be at least 50 ° C, usually 50-350 ° C, more preferably 100-300 ° C. If this temperature is in the range of 50 ° C to 350 ° C, a coating with a particularly good visual appearance can be produced.

The liquid composition containing the chromate compound and / or the resin monomer may generally be applied as a coating and then dried.

The chromate compound in the liquid composition may be the same as the water soluble chromate compound in the burn type metal corrosion inhibitor composition. However, the type of chromate compound used during immersion may be different from the type of water soluble chromate compound used in the burnable metal corrosion inhibitor composition. One or more chromate compounds may be used during the immersion.

The resin used in the process of the invention may be a water-soluble resin, a resin in aqueous emulsion or an aqueous suspension. Examples of suitable resins are acrylic resin, polyester resin, polyethylene resin, polyvinyl resin, epoxy resin, butadiene resin, mycelium resin, alkyd resin and phenolic resin. Acrylic resin is preferred among the listed resins.

The liquid composition may contain the chromate compound without the resin, the resin without the chromate compound, or the chromate compound and the resin together. According to the invention, a stream containing chromate compound and resin is preferred 82939-7884 / VO / LZs

P 95 03769 • ··· · · · · · · · · · · · · · · · · · · · · · · · ·

- 9 kitchen preparations. The liquid composition containing the chromate compound and the resin usually contains 0.1 to 50% by weight of the chromate compound and 0.5 to 40% by weight of the resin, preferably 0.5 to 30% by weight of the chromate compound and 0.5 to 20% by weight of the resin.

Preferred liquid formulations are Dacromet 100 (Nippon Dacro Shamrock K.K.) and Dacromet LTX (Resin Coating) (Nippon Dacro Shamrock K.K.).

If the liquid composition contains a solid, it is preferably present in an amount of 0.5 to 90% by weight, more preferably 0.1 to 50% by weight. If the solids content is in the range of 0.5 to 90% by weight, a coating with a good visual appearance and a suitable thickness can be obtained.

The temperature of the liquid composition may be important in the surface treatment process of the invention. If the temperature of the liquid preparation is too low, too much cooling will inhibit the formation of a suitable coating. If, on the other hand, the temperature of the liquid preparation is too high, it may itself be degraded. The temperature of the liquid composition may vary depending on the temperature of the metal substrate, and is usually set at 5 to 95 ° C.

Preferably, the cured metal substrate in the coating step is immersed in the liquid composition for a period of up to 20 minutes, typically from 0.1 seconds to 30 minutes, more preferably from 0.5 seconds to 5 minutes. If the immersion time is in the range of 0.1 seconds to 30 minutes, the coating may be completely formed on the metal substrate;

82939-7884 / VO / LZs

The temperature of the substrate P 95 03769 does not decrease too much, so the drying effect of the heat treatment of the coating step is not lost.

According to the invention, no heat treatment is generally required after the immersion step. However, simple drying may be carried out if desired.

During the immersion step, a coating of at least 0.1 µm, preferably at least 1 µm, is usually formed. Preferably, a coating of at least 1 µm thick is formed, as this enhances the corrosion resistance of the coating produced in the first coating step.

The invention is further illustrated by the following non-limiting examples.

The properties of the coatings prepared according to the examples were determined as follows.

1. Visual appearance

The thickness and uniformity of the coating were visually observed. The evaluation was carried out in the following classes:

V - very good

G - good

P - bad

G-P - weak, but not a problem in practice.

2. Corrosion resistance After complex cyclic corrosion testing, the presence of red rust was visually observed. The evaluation was carried out in the following classes:

82939-7884 / VO / LZs

P 95 03769

- 11V - very good

G - good

P - bad

G-P - weak, but not a problem in practice.

3. Time required for production

The time required for preparation was determined relative to Comparative Example 1.

Solvent vapor cleaned and dry ground (M 47) type M 10 molten steel stud was used as the substrate tested.

Example 1

In the coating step, a burnable type Dacrodip commercially available metal corrosion inhibitor formulation was used and mixed according to the specification. In the immersion step, Dacromet 100BL, a black chromating liquid, was used as a liquid composition containing chromate compound which was resin-free. The composition of Dacromet was as follows:

chromic acid 4% by weight zinc powder 20% by weight.

The substrate under investigation was immersed in Dacrodip, and the excess was removed by centrifugation. During the heat treatment phase, the test substrate was placed in an electrically heated air circulation oven, heated to 300 ° C and maintained at this temperature for 5 minutes. The substrate under test was removed from the oven and cooled to 290 ° C, looking for Dacromet 100BL at 50 ° C 82939-7884 / VO / LZs

P 95 03769 • · ···· • ·

- It was immersed in 12 products called petfood, and after 1 second it was removed and dried.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² and the weight of the coating adhering to the substrate in the dipping step was 50 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are as follows:

Table 1 summarizes.

Example 2

The procedure described in Example 1 was the following:

the liquid preparation for immersion was a clear formulation called Dacromet LTX, which contained resin but was free of chromate compound. After the heat treatment step of the coating step, the substrate under investigation was immersed in Dacromet LTX, cooled to 250 ° C, and removed and dried after 2 seconds.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² and the weight of the coating adhering to the substrate in the dipping step was 80 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are as follows:

Table 1 summarizes.

Example 3

The procedure of Example 1 was repeated with the following exception:

82939-7884 / VO / LZs

P 95 03769 • · · · · · · · ······························· ·

The 13 liquid formulations used in the immersion step were Dacromet 100, a chromating liquid containing chromate compound and free of resin. The immersion time was 5 seconds.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² and the weight of the coating adhering to the substrate in the dipping step was 50 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are as follows:

Table 1 summarizes.

Example 4

The procedure described in Example 1 was followed with the following exception:

in the coating step, the substrate under investigation was heated to 350 ° C in an electrically heated air circulation oven and maintained at this temperature for 5 minutes. The substrate, except the furnace, was cooled to 300 ° C, immersed in a liquid formulation set at 95 ° C, and after 5 seconds removed and dried.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² , while the weight of the coating adhering to the substrate during the immersion step was 100 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are as follows:

Table 1 summarizes.

Example 5

82939-7884 / VO / LZs

P 95 03769

The procedure described in Example 1 was carried out with the following exception:

the test substrate was heat treated in the coating step, then cooled to 270 ° C, except in an electrically heated air circulation oven, immersed in a liquid preparation at 20 ° C, then removed and dried after 0.5 seconds.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² , while the weight of the coating adhering to the substrate in the immersion step was 30 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are as follows:

Table 1 summarizes.

Example 6

The procedure of Example 1 was followed except that the coating step was repeated twice and then the dipping step was followed.

In the coating step, the weight of the coating adhering to the substrate under test was 200 mg / dm ² , while the weight of the coating adhering to the substrate in the dipping step was 100 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are summarized in Table 1.

Example 7

The procedure described in Example 1 was followed with the following exception:

in the immersion step, the liquid preparation was a Dacromet 100BL chromating liquid,

82939-7884 / VO / LZs

P 95 03769 • ··· ···

15 containing 10% aqueous acrylic ester as an added resin.

In the coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² and the weight of the coating adhering to the substrate in the dipping step was 50 mg / dm ² . The submerged test substrate was evaluated as described above. The test results are summarized in Table 1.

Comparative Example 1

In the first coating step, Dacrodip, a commercially available anti-corrosion metal composition, was used and mixed according to the manufacturer's specifications. In the second coating step, Dacromet 100BL (black chromating fluid) was used as a liquid formulation containing chromate compound and / or resin monomer.

The substrate under investigation was immersed in Dacrodip and excess was removed from the substrate by centrifugation. Subsequently, the test substrate was heated to 300 ° C in an electrically heated air circulation oven and maintained at this temperature for 5 minutes. The substrate under investigation, except the furnace, was allowed to cool to room temperature.

As with the first coating step, the test substrate was immersed in Dacromet 100BL, a liquid formulation, and the excess liquid formulation was removed from the substrate by centrifugation. The test substrate is then electrically heated by air circulation

82939-7884 / VO / LZs

P 95 03769 ···· ···

- Re-heat in 16 furnaces at 250 ° C for 5 minutes.

In the first coating step, the weight of the coating adhering to the substrate under test was 100 mg / dm ² , and in the second coating step, the weight of the adhesive coating was 50 mg / dm ² . The coated treated substrate was evaluated as described above. The test results are summarized in Table 1.

Comparative Example 2

The procedure described in Comparative Example 1 was repeated with the following exception:

The second coating step used was Dacromet LTX (clear), a resin-based coating agent. In the second coating step, the firing was carried out by heating the substrate under study in an electrically heated air circulation oven at 100 ° C for 5 minutes. The test substrate removed from the furnace was allowed to cool to room temperature.

In the first coating step, the weight of the coating adhering to the substrate under investigation was 100 mg / dm ² , and in the second coating step, the weight of the adhesive coating was 80 mg / dm ² . The coated substrate tested was evaluated as described above. The test results are summarized in Table 1.

Comparative Example 3

The procedure of Example 1 was followed except that the second coating step was omitted.

82939-7884 / VO / LZs

P 95 03769

The weight of the coating adhering to the substrate under investigation was 100 mg / dm ² . The coated treated substrate was evaluated as described above. The test results are summarized in Table 1.

Comparative Example 4

The procedure of Example 6 was followed except that the second coating step was omitted.

The weight of the coating adhering to the substrate tested was 200 mg / dm ² . The coated treated substrate was evaluated as described above. The test results are summarized in Table 1.

Table 1

Example visual appearance corrosion- resistance technological time needs First V G 6 Second V G-P 6 Third V G 6 4th V G 6 5th V G 6 6th V V 11 7th V G 6 1 * P G-P 10 2. ' P G-P 9 3. * P P 5 4. * G G 10

comparative example

82939-7884 / VO / LZs

P 95 03769 • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · «·

- 18 Conventional surface coating processes require drying equipment in the immersion step, resulting in higher labor and technological time requirements. The process of the invention, however, eliminates the drying step of the coating step by treating the metal substrate at high temperature during the heat treatment of the coating step. Therefore, the coating process of the present invention can simplify the equipment and shorten the technological time. The process of the present invention thus not only enhances industrial efficiency but also contributes to energy saving and environmental protection.

82939-7884 / VO / LZs

P 95 03769 ·· ···· ·· * ·· ·, »• · · · · · · · · • ··« · "· · · · ·· ···· ······ • _{4 you}

- 19 Patent claims

Claims (15)

CLAIMS 1. A method of coating a surface of a metal substrate with a burnable type anti-corrosion composition comprising a water-soluble chromate compound and a zinc powder composition, curing the coated metal substrate and directly treating the metal substrate with a temperature of at least 50 ° C. or immersed in a liquid composition comprising a resin, wherein a second heat treatment step after immersion is not used. 2. The process of claim 1, wherein the metal substrate is steel. 3. The process of claim 1 wherein the water-soluble chromate compound is chromic acid or a water-soluble metal salt such as calcium chromate, magnesium chromate, zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate or calcium. A process according to claim 1, characterized in that a flake-shaped zinc powder is used. A process according to claim 4 wherein the zinc powder is in the form of flakes of 0.1 to 0.5 µm thickness and up to 15 µm long. 6. A process according to claim 1, wherein the zinc powder is used in combination with aluminum powder. 82939-7884 / VO / LZs P 95 03769 • · · · · «··· ··· ································• The process according to claim 1, wherein the water-soluble chromate is used in an amount of from 1% to 12% by weight of the composition. 8. The process of claim 1 wherein the water-soluble chromate is 1-8% by weight of the composition. 9. The process of claim 1, wherein the zinc powder is present in an amount of from 10% to 40% by weight of the composition. The process of claim 1, wherein the zinc powder is present in an amount of from 15% to 30% by weight of the composition. 11. A process according to claim 1 wherein the composition is a burn type of boric acid or boron oxide, low molecular weight oxo-hydroxy ether, pH adjusting agent, wetting agent and / or organic solvent. The process according to claim 11, wherein the boric acid is orthoboric acid, metaboric acid and / or tetrabic acid. The process according to claim 11, wherein the low molecular weight oxohydroxyether is glycol or a low molecular weight ether type polymer derived therefrom. 82939-7884 / VO / LZs P 95 03769. · *. : ··· ......., ··. · ···. ί ··· ··· * · · · «A ···· ··· ·· e * 14. The process according to claim 13, wherein the low molecular weight oxohydroxyether is ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, diacetone alcohol, or a mixture thereof. The method of claim 1, wherein the cured metal substrate is immersed in the liquid composition for a period of up to 30 minutes. 'Κ. / Ι