KR0143479B1 - Chromate solution - Google Patents

Abstract

The present invention relates to a coated chromate treatment solution used for the chromate treatment of zinc or zinc alloy plated steel sheet, and to the corrosion resistance of the steel sheet by adding a silane coupling agent so as to have an appropriate ratio range with colloidal silica among the components of the coated chromate treatment solution. It is an object of the present invention to provide a coated chromate treatment solution for producing chromate coatings, which satisfies characteristics such as electrical conductivity, surface appearance, and surface appearance, and is particularly excellent in fingerprint resistance and alkali degreasing resistance.

In the present invention for achieving the above object, in the coated chromate treatment solution, total chromium ion: 1 50 g / l, chromium trivalent ion ratio to the total chromium ion: 10 50%, colloidal silica: 20 120 g / l , Resin: 20 200 g / l, the sum of the colloidal silica and resin: 40 250 g / l, silane coupling agent: 0.2 1 and the rest of the colloidal silica content: the composition is composed of water, the pH is adjusted to 3 7 It is an object of the present invention to provide a coated chromate treatment solution for producing a chromate coating having excellent anti-fingerprint and alkali degreasing resistance.

Description

Coating type chromate treatment solution for producing chromate coating with excellent anti-fingerprint and alkali degreasing resistance

The present invention relates to a treatment solution used for the chromate treatment of zinc or zinc alloy plated steel sheet, and more particularly, to a treatment solution for forming a chromate coating having excellent anti-fingerprint resistance and alkali degreasing resistance.

Chromate treatment is widely used to improve the corrosion resistance of galvanized steel sheets having zinc, aluminum and a plating layer composed thereof. The chromate treatment is classified by the method of film formation determined by the composition of the treatment solution. As the chromate treatment solution, a chromate solution containing one or two or more sulfuric acid, hydrochloric acid, and nitric acid is used. The method of forming a film by redox reaction with a solution is called a reactive chromate treatment. The film is formed by using an aqueous solution of chromium ion which does not contain the strong acid and to which a colloidal material and an resin in an emulsion state are added. Dehydration condensation reaction between chromium compounds during drying as a reaction and a method of forming a film by using an inherent bonding force of a substance added as a film constituent are called coated chromate treatment.

In recent years, when the steel sheet is used for the use of home appliances such as computer shells, photocopiers, microwave ovens and automobile steel sheets, the film quality required is corrosion resistance of the steel sheet, anti-fingerprint adhesion (fingerprint resistance), electrical conductivity of the film, and surface appearance. , Weldability, electrical conductivity, water resistance, alkali resistance, etc., and it is difficult to satisfy all the film quality requirements of the steel sheet users as the reactive chromate treatment that has been conventionally treated, and even the coated chromate treatment requires the above quality. Treatment techniques are known that satisfy only a few of them.

Representative conventional techniques include proposals by Japanese Laid-Open Patent Publications 76-28538, 77-51032, 83-35682, 86-103086, 86-207579, 88-96286, 88-96277, and the like. These are methods of forming a coated chromate film and using a solution in which a resin and a silica oxide are added to or in the chromate treatment solution, respectively. Since the film formed by the method according to the proposed method contains resin and silica oxide as constituents, a thick film is produced at the same chromium deposition amount as compared with the conventional reactive chromate film, so that the plating layer protection effect by the chromate film is increased to improve corrosion resistance. In the case of weak binding force between chromium oxides or between chromium oxides and resins or silicates, the chromium component is eluted in the treatment solution during the degreasing and washing process at the demand value, resulting in deterioration of the coating properties. There is a risk that demand will shorten the life of the skim.

As a method of improving the water resistance and alkali degreasing property of the chromate coating, a method of polymerizing the chromate compound in the coating by dehydration condensation reaction is frequently used. In this case, the steel sheet needs to be heated to a high temperature of 200 ° C. or higher, so that There is a need for a dryer and there is a risk of changes in the mechanical properties of the steel sheet due to high temperature drying. As a well-known technique for improving this, there is a method using ultraviolet light for drying, but there is a problem that the resin is complicated and the resin which can be used is limited to an ultraviolet curable resin. There is a problem that can not be used when the hot air drying type of drying equipment.

In addition, the proposals described in JP-A-85-13079, 85-228682, 89-111883, 89-283382, and 89-225780 have been proposed to increase the specific gravity of chromium trivalent compounds in the coating composition of the above-described coated chromate treatment. Specifically, a method of coexisting chromium ions in a solution with chromium hexavalent ions and chromium trivalent ions and increasing the reactivity of the solution to reduce chromium hexavalent ions in the solution to chromium trivalent during film formation How to make it happen. The method of coexisting chromium hexavalent ions and chromium trivalent ions in the solution depends on a method of reducing chromium hexavalent by a reducing agent, which is a general technique, and for improving the reactivity of the solution, a reactivity enhancer such as phosphoric acid or fluorine compound is added.

In the conventional known art, the content of poorly water-soluble chromium trivalent compound increases and the water resistance of the film is improved, but the amount of chromium hexavalent compound in the film is relatively decreased, making it difficult to obtain a beautiful yellow color by chromium hexavalent ions. There is a problem in that corrosion resistance is deteriorated when the coating is damaged due to a decrease in self-healing effect caused by chromium hexavalent ions.

Korean patent applications 93-29655 and 93-29656 which the present inventors have filed are well-known techniques for easily improving the poor water solubility of chromate coatings. Korean Patent Application No. 93-29655 aims at forming a coating with excellent weldability, and 93-29656 is for forming a coating with excellent workability. The present invention relates to a technique for poorly solubilizing a chromium hexavalent compound in a film using a chromate treatment solution in which a strontium chromate compound having poor solubility in weak acid and weak alkali conditions is dissolved. In the present invention, compared to the known art, the amount of chromium trivalent compound and chromium hexavalent compound in the coating is formed in an appropriate ratio, and it has a beautiful yellow surface color, but it is sufficiently secured in the film's poor solubility under general steel sheet use conditions. However, there is a problem that the film is damaged under strong alkaline degreasing conditions.

Accordingly, the present inventors have conducted research and experiments to solve the above problems, and suggest the invention according to the results. The present invention has a proper ratio range with colloidal silica in the components of the coated chromate treatment solution. By adding the silane coupling agent, the coating type chromate treatment solution can be prepared that satisfies the characteristics of the corrosion resistance of the steel sheet, the electrical conductivity of the coating, the surface appearance, and at the same time produces a chromate coating having particularly excellent anti-fingerprint and alkali degreasing resistance. I would like to, but its purpose is.

Hereinafter, the present invention will be described.

In the coated chromate treatment solution, super chromium ion: 1 50 g / l, chromium trivalent ion ratio to the total chromium ion: 10 50%, colloidal silica: 20 120 g / l, resin: 20 200 g / l The sum of the colloidal silica and the resin: 40 250 g / L, the silane coupling agent: 0.2 1 with respect to the colloidal silica content and the remainder: water-based, anti-fingerprint and alkali degreasing resistance adjusted to 3 7 A coating type chromate treatment solution for producing excellent chromate coatings.

Hereinafter, the present invention will be described in more detail.

The total chromium ion in the chromate treatment solution according to the present invention is present in the solution as a chromium hexavalent compound and a chromium trivalent compound as main elements exerting the anticorrosive effect of the chromate coating. In the present invention, the total chromium ion in the solution as described above is preferably 1 50 g / L, because the total chromium ion is less than 1 g / L, and the adhesion amount of the chromium compound in the coating is small, so that the corrosion resistance is not satisfactory. This is because at 50 g / l or more, the specific gravity of the chromium compound in the coating is so large that the coating is easily colored yellow.

In this case, the chromium compound added to adjust the total chromium ion in the above range can satisfy sufficient performance if it is one or two or more selected from water-soluble chromate compounds of chromic acid and potassium dichromate, sodium dichromate and ammonium dichromate. In addition, when the chromate treatment solution is prepared by the method described in Korean Patent Application Nos. 93-29655 and 29656, strontium chromate, zinc chromate, and lead chromate compounds may also be used.

However, in this way, when the film is formed only with chromium hexavalent ions provided by water-soluble chromium compounds such as chromic acid, sodium dichromate, potassium dichromate and ammonium dichromate, the chromium hexavalent ions have a bright color. It is preferable to reduce the chromium trivalent ions to 10 to 50% relative to the total chromium ions, for the following reasons.

If the chromium trivalent ions account for less than 10% of the total chromium ions, the proportion of chromium hexavalent compounds in the coating is high, resulting in severe staining of yellow compared to the amount of chromium deposit. This is because the formation of the solution becomes unstable and the risk of depositing or gelling is high.

In this case, the reducing agent used to reduce the chromate hexavalent ions in the solution to trivalent ions may be a compound such as alcohols, polyhydric alcohols, starch, starch, hydrogen peroxide and the like which are soluble in water. Since these reducing agents have different reducing capacities according to their type, the amount of reducing agent required to obtain a target chromium ion reduction ratio varies depending on the type, but since the added reducing agent is decomposed by the reducing reaction, there is little effect on the solution performance according to the type. .

Silica is a colloidal component that has the effect of improving the corrosion resistance by removing the fine roughness of the coating layer by increasing the thickness of the coating layer, thereby giving the rubbing resistance of the coated chromate coating, and causing the corrosion product of the dense galvanized layer under the corrosive environment. Silica in a state is preferable and the amount is preferably limited to 20 120 g / L in terms of silica, for the following reasons. If the addition amount of the colloidal silica is less than 20g / ℓ, the corrosion resistance is insufficient, 120g / ℓ or more, the hardness of the coating is excessively increased, the coating is easily damaged, the corrosion resistance of the processed portion when bending, drawing, etc. Because there is a risk of falling.

The resin prevents micro-chemically adsorbing foreign substances such as contaminants and sweat caused by silanol groups on the surface of silica, further improves fingerprint resistance, and also lowers the hardness of the coating to improve corrosion resistance of the processed part, and chromate treatment. As a component which can obtain stable solution storage stability in a solution, it does not have a big influence on the kind, such as vinyl type, an acryl type, and / or a styrene type. The amount of such a resin is preferably 20 200 g / l in terms of nonvolatile content of the resin, for the following reason.

If the amount of the resin is less than 20g / ℓ, the effect of the addition of the resin is hardly insufficient, the anti-fingerprint of the prepared film is insufficient, at 200g / ℓ or more the curing of the resin is insufficient, the resin is dissolved during strong alkali degreasing and alkali-resistant This is because there is a danger that intelligence will be degraded.

Since the resin is in an emulsified form in water, it can satisfy the properties required when added in the range limited in the present invention, but in order to ensure stable workability in the composition of the solution limited in the present invention, it is dispersed in a pH 3 7 range. It is more preferable to use an emulsion resin having stability because it can give a stable dispersed phase in preparing a solution.

It is preferable that the sum of the colloidal silica and the resin added to the solution is limited to 40 250 g / l, because the amount of the coating film produced is less when the sum of the colloidal silica and the resin is 40 g / l or less. This is because there is a risk of shortage, because the viscosity in the solution is more than 250g / ℓ because there is a problem that non-uniform coating is likely to occur when the solution is applied.

On the other hand, if the film is formed using the chromate treatment solution composed of the chromium ion, colloidal silica and resin only, it is possible to obtain some film characteristics under the condition of using the steel sheet in the air. There is a problem that the performance drops sharply.

This problem can be solved by Korean patent applications 93-29655 and 29656 which use an insoluble chromium salt and add a small amount of silane coupling agent.

That is, according to the Korean Patent Application Nos. 93-29655 and 29656, a certain degree of water resistance is ensured, and there is no sudden degradation of film quality in a humid atmosphere, and almost no water-soluble chromium hexavalent ions are eluted during alkali degreasing after steel sheet processing. Do not.

However, the above suggestion cannot exhibit sufficient performance under strong alkaline degreasing conditions. The reason for this is that the addition amount of the silane coupling agent is small, and the bonding force of the emulsion resin and the colloidal silica advances with the silane coupling agent, but the extent thereof is not sufficient.

In other words, the resin that acts as a binder in the coating is not sufficiently cured, and it is presumed that in strong alkaline degreasing conditions, the resin in the unbonded portion is preferentially destroyed by the silane coupling agent, thereby damaging the coating. It is difficult to expect sufficient alkali resistance even when the chromium compound is used and the adhesion between the resin and silica is improved by the silane coupling agent (Korean Patent Application Nos. 93-29655 and 93-29656).

In the present invention, in order to solve this problem, the addition amount and the sum of the colloidal silica and resin of the coated chromate treatment solution to be within a certain range, and the silane coupling agent in a certain ratio range to the addition amount of the colloidal silica It is possible to maintain the excellent film properties in which the chromium component is not eluted because the resin is not destroyed during strong alkali degreasing by increasing the bonding strength of the film by adding to.

The silane coupling agent is a component that improves alkali degreasing resistance of the film by curing the resin to increase the bond strength of the film, and the amount of the silane coupling agent is preferably 0.2 to 1 with respect to the content of the colloidal silica. The reason is as follows.

When the addition ratio of the silane coupling agent is 0.2 or less, the addition amount of the silane coupling agent is too small, so that the effect of addition is not large, and when it is 1 or more, the addition amount of the silane coupling agent is excessive and does not react with silica and remains in the solution. This is because it causes a problem of lowering stability.

When such a silane coupling agent has an amine group as an organic functional group, there is a problem that entanglement or the like occurs during solution preparation, which makes it difficult to use. However, if the organic functional group is one type of silane coupling agent selected from the group consisting of vinyl group, chloropropyl group, epoxy group, methacrylate group and mercapto group, it is excellent in solution stability and the same film property can be obtained regardless of the type. You may.

The pH of the coated chromate treatment solution having the above composition is preferably in the range of 3 to 7, because the pH of the solution is 3 or less, the reaction between the solution and the plating layer increases and is dissolved from the plating layer and is accumulated in the solution. This is because there is a risk of gelation of the solution due to the heavy weight of the amount of zinc ions, and when the pH of the solution reaches 7 or more, the solution stability decreases due to precipitation of chromium trivalent ions in the solution to form a hydrate. .

The pH of the solution adjusted to the above range can satisfy the required range of pH by appropriately selecting the type and amount of the chromium compound used, and the quality problem even when using weak acids such as phosphoric acid and acetic acid and weak alkali compounds such as ammonia water. It does not cause any problem.

As described above, when the addition amount of the appropriate resin and silica proposed in the present invention and the addition solution of the silane coupling agent having an appropriate ratio with silica are used, the bonding strength between the film components is increased, and the damage of the film is hardly achieved even in the strong alkali degreasing solution. Almost no elution of chromium ions can be achieved. Especially, even when only water-soluble chromium compounds are used, excellent alkali degreasing resistance and water resistance can be ensured even when water-soluble chromium compounds are used (Korean Patent Application Nos. 93-29655 and 29656). It works.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

A high concentration chromium hexavalent ion aqueous solution was prepared using 200 g / l chromic anhydride solution, and a high concentration chromium ion aqueous solution containing chromium trivalent ions and chromium hexavalent ions was prepared by adding a reducing agent. Here, colloidal silica, a silane coupling agent, and a resin were mixed in order, and finally water was mixed to prepare a chromate treatment solution having the composition shown in Table 1 below.

The solution of Table 1 was coated on the surface of the galvanized steel sheet having a coating amount of 20 g / m2 per side using a roll coater, and then dried at a temperature of 120 ° C. for 30 seconds to prepare a chromate steel sheet and to obtain , Alkali degreasing and corrosion resistance was evaluated and the results are shown in Table 2 below.

At this time, the solution stability was evaluated by visually seeing the state after one month after the solution was prepared to evaluate the layer separation phenomenon, coagulation phenomenon and the like. Solution coating workability visually evaluated the state that the solution is applied during the roll coating operation. The total coating amount was evaluated by gravimetric method after the film was prepared. Corrosion resistance is less than 96 hours × 96 hours 120 hours as the salt spray time required until the traces of white rust of the galvanized layer on the surface of the coating by spraying brine in accordance with the method described in Japanese test standard JIS 2371 , 120 hours or more.

At this time, a part of the specimen was drawn to evaluate the corrosion resistance of the machined part. Fingerprints were evaluated by visually measuring the degree of fingerprinting when contacted by hand. Alkali degreasing was film damage after immersion of the specimen for 2 minutes and 30 seconds in a strong alkaline degreasing solution heated to a temperature of 65 ° C. The condition was visually judged and evaluated.

As shown in Table 2, Comparative Example (1) showed a little yellow color when the chromium content and the chromium reduction ratio were small, and lacked the corrosion resistance. Comparative Example (2) has a problem that the surface is severely colored yellow when the chromium content and the chromium reduction ratio are high. In Comparative Example (3), the addition amount of colloidal silica was low, and the corrosion resistance was insufficient, and the alkali degreasing resistance of the film was insufficient when strong alkali degreasing. Comparative Example (4) had a high content of colloidal silica, but the corrosion resistance of the flat plate was good, but the corrosion resistance of the processed part was poor, the fingerprint resistance was insufficient, and the alkali degreasing resistance was insufficient. In Comparative Example (5), the amount of resin was small and the fingerprint resistance was insufficient. Comparative Example (6) is a case in which the amount of the silane coupling agent is added, there is no problem in the film quality, but there is a problem that the solution state is changed by the unreacted silane compound after a long time after the solution preparation. In Comparative Example (7), a small amount of silane coupling agent was added, and thus the corrosion resistance was insufficient and the alkali degreasing resistance was insufficient. In Comparative Example (8), when the amount of addition of colloidal silica and resin was small, the solid content (colloidal + resin) of the solution was insufficient, and the adhesion of the film was small, resulting in insufficient corrosion resistance and fingerprinting. Comparative Example (9) had a problem in that the film prepared by adding a large amount of resin and the sum of colloidal silica of the solution and the resin, that is, the solution coating property was deteriorated due to a large amount of solid content. Comparative Example (10) had a problem that the solution is gelling when the solution has a low pH when the solution is used for a long time. In Comparative Example (11), when the pH of the solution is high, the phenomenon of precipitation of the chromium trivalent compound occurs during storage of the solution, and it can be seen that there is a problem in the stability of the solution.

On the other hand, in the invention (1 9) satisfying the scope of the present invention, the surface appearance, corrosion resistance, anti-fingerprint resistance and alkali resistance, but some excellent superiority, but all showed excellent performance.

As described above, among the components of the solution of the present invention, a coating type chromate treatment solution is prepared by adding an appropriate amount of colloidal silica and a resin, a combination thereof, and a silane coupling agent in an appropriate ratio to colloidal silica. Therefore, when applied to the coated chromate treatment of the galvanized steel sheet, it is effective to improve the quality of the product by easily producing a galvanized steel sheet having an excellent alkali degreasing resistance and anti-fingerprint resistance, in particular, excellent corrosion resistance. .

Claims (2)

In the coated chromate treatment solution, super chromium ion: 1 50 g / l, chromium trivalent ion ratio to the total chromium ion: 10 50%, colloidal silica: 20 120 g / l, resin: 20 200 g / l, the colo Sum of Silica and Resin: 40 250 g / l, Silane Coupling Agent: Chromate and Alkaline Degreasing Resistance, which is composed of 0.2 1 and remainder: water relative to the colloidal silica content and whose pH is adjusted to 3 7 Coating type chromate treatment solution for film production. According to claim 1, wherein the silane coupling agent is an anti-fingerprint and alkali degreasing resistance, characterized in that the organic functional group is one selected from the group having a vinyl group, chloropropyl group, epoxy group, methacrylate group and mercapto group. Coating type chromate treatment solution for excellent chromate coating production.