KR0136168B1 - 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, which satisfies the corrosion resistance of the steel sheet, the electrical conductivity of the film, the anti-fingerprint resistance, and the alkali degreasing resistance by controlling the components of the chromate treatment solution. At the same time, to provide a chromate treatment solution for coating the chromate coating with excellent surface gloss, an object thereof.

In the present invention for achieving the above object, in the coated chromate treatment solution, total chromium ions: 1 to 50 g / l, chromium trivalent ions to total chromium ions: 10 to 50%, colloidal silica: 20 to 120 g / l, resin: 20 to 200 g / l, sum of the colloidal silica and numerical value: 40 to 250 g / l, titanate compound: 0.2 to 10 g / l and the rest: water, the pH of which is 3-7 It is an object of the present invention to provide a coated chromate treatment solution for producing chromate coating having excellent controlled anti-fingerprint, alkali degreasing resistance and surface gloss.

Description

Coating type chromate treatment solution for producing chromate coating having excellent anti-fingerprint, alkali degreasing resistance and surface gloss.

The present invention relates to a coated chromate treatment solution used for the chromate treatment of zinc or zinc alloy plated steel sheet, and more particularly, by adjusting the addition amount of colloidal silica and resin and adding a titanate compound as a resin curing agent. The present invention relates to a coated chromate treatment solution capable of producing a chromate coating having excellent moon resistance, alkali degreasing resistance and surface gloss.

In general, chromate treatment is required to improve the corrosion resistance of a plated steel sheet having a plating layer composed of zinc, aluminum, and the like. Such chromate treatment is classified into reaction type and coating type by the method of film formation determined by the composition of the treatment solution, and chromate treatment is performed using chromate solution containing one or two or more kinds of sulfuric acid, hydrochloric acid and nitric acid. As a film forming reaction, a method of forming a film by redox reaction between a workpiece and a solution is referred to as a reactive chromate treatment. A chromate treatment solution does not contain the strong acid and a colloidal material and an resin in an emulsion state. A coating type chromate treatment is called a method of forming a film by using an aqueous solution of added chromium ions and using a dehydration condensation reaction between chromium compounds and the inherent binding force of the material added to the film composition as a film forming reaction.

In order to use the chromate-treated zinc and zinc alloy plated steel sheet in the same way as above for home appliances such as computer shells, copiers, microwave ovens, and automobile steel sheets, the corrosion resistance of the steel sheet, anti-fingerprint adhesion (fingerprint resistance), and electrical conductivity of the film In addition to surface appearance, weldability, electrical conductivity, water resistance and alkali resistance, beautiful surface appearance characteristics such as surface gloss are required.

However, it has been difficult to satisfy all the film quality requirements of the steel sheet demands as the reactive chromate treatment that has been conventionally processed, and there are known methods that can satisfy only some of the above quality requirements even in the coated chromate treatment. have.

As a known technique for a film formation method by such a coating chromate treatment, Japanese Patent Laid-Open Nos. 76-28538, 77-51032, 83-35682, 86-103086, 86-207579, 88-96286, and 88-96277 And suggestions.

The above methods use a solution in which the resin and the silicon oxide are added to the chromate treatment solution, respectively, or together, and the film formed by this method contains the resin and the silica as a constituent, compared with the conventional reactive chromate coating. Since a thick film is produced at the same chromium adhesion amount, the plating layer protection effect by the chromate film is increased, and corrosion resistance is improved. However, if the binding strength between chromium oxides, chromium oxides and resins, or chromium oxides and silicates is weak, the chromium component is eluted in the treatment solution during degreasing at the demand price and washing process, resulting in deterioration of film characteristics and degreasing demand. There is a risk of a problem of shortening the life of the liquid.

Method of polymerizing chromium compounds in the film by dehydration condensation by solving the problems of deterioration of film properties and degreasing of the degreasing solution due to the elution of chromium components and improving the water resistance and alkali degreasing of the chromate film. This is mainly used. In this method, however, the steel sheet needs to be heated to a high temperature of 200 ° C. or higher, so a large capacity dryer is required, and there is a risk of changing the mechanical properties of the steel sheet due to high temperature drying. As a technique to improve this, there is a method of using Japanese Patent Application Publication No. 80-51032, which is a method of using ultraviolet light for drying steel sheet. In this method, there is a problem that the facility is complicated and the resin that can be used is limited to an ultraviolet curable resin. There is a problem that can not be used when having a hot air drying type drying equipment.

On the other hand, other known techniques for coating chromate treatment include Japanese Patent Application Laid-Open No. 85-228682, 89-111883, 89-283382, 89-225780, and the like.

These methods relate to a method of increasing the specific gravity of chromium trivalent compounds in coating chromate-treated coating compositions. Specifically, a method and a solution in which chromium ions in a solution coexist with chromium hexavalent ions and chromium trivalent ions. It is to increase the reactivity of the chromium hexavalent ions in the solution to reduce the chromium trivalent during the film formation process.

The method of coexisting chromium hexavalent and trivalent ions in a double solution depends on a method of reducing chromium hexavalent by a reducing agent, which is a general technique, and a method of reducing chromium trivalent ions in solution to chromium trivalent during film formation. In order to improve the reactivity of the solution, a reactivity enhancer such as phosphoric acid or fluorine compound is added.

In this method, however, the water content of the chromium trivalent compound, which is a poorly water-soluble chromium compound, is increased, but the water resistance of the coating is improved, but the amount of the chromium hexavalent compound in the coating is relatively decreased to obtain a beautiful yellow color by the chromium hexa-ion. Difficult to reduce the self-healing effect of the chromium hexavalent ions has a problem that the corrosion resistance is deteriorated when the coating is damaged.

In order to easily improve the poor water solubility of the chromate coating, the present inventor has proposed the Republic of Korea Patent Application 93-29655 and 93-29656. Republic of Korea Patent Application 93-29655 is for forming a coating with excellent weldability, 93-29656 is for forming a coating with excellent workability, they dissolve strontium chromate compound having poor solubility in the conditions of weak acid and weak alkali A technique for poorly solubilizing a chromium hexavalent compound in a film using a chromate treatment solution. In these proposals, the amount of chromium trivalent compounds and chromium hexavalent compounds in the coating is set in an appropriate ratio compared to the known technologies, and the film has a beautiful yellow surface color, but the film is sufficiently insoluble in general steel sheet use conditions. Although there is an advantage, 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 based on the results, the present invention has been proposed. The present invention controls the components of the chromate treatment solution to control the corrosion resistance of the steel sheet, the electrical conductivity of the film, An object of the present invention is to provide a coated chromate treatment solution for producing chromate coatings that satisfies anti-fingerprint and alkali degreasing properties and has excellent surface gloss.

Hereinafter, the present invention will be described.

The present invention is a coating chromate treatment solution, the total chromium ion: 1-50g / l, the ratio of chromium trivalent ions to the total chromium ion: 10-50%, colloidal silica: 20-120g / l, resin: 20 -200 g / l, sum of numerical values with colloidal silica: 40-250 g / l, titanate compound: 0.2-10 g / l, and the remainder: water-resistant, alkali-resistant, alkali-adjusted to pH 3-7 The present invention relates to a coated chromate treatment solution for producing chromate coating having excellent degreasing property and surface gloss.

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 to 50 g / l because the adhesion amount of the chromium compound occupied in the coating is less than 1 g / l in the total chromium ion, 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.

At this time, 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.

As described above, however, when the film is formed using only chromium hexavalent ions provided by water-soluble chromium compounds such as chromic acid, sodium dichromate, potassium dichromate and ammonium dichromate, the chromium hexavalent ions exhibit a bright color. It is preferable to reduce the chromium trivalent ions to 10 to 50% of the total chromium ions by reducing the chromium trivalent ions.

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 types, the amount of reducing agents varies depending on the type in order to obtain the target chromium ion reduction ratio, but the added reducing agent is decomposed by the reducing reaction, so there is little effect on the solution performance.

In addition, in the present invention, as in the above-mentioned Korean Patent Application Nos. 93-29655 and 29656, some of the chromium hexavalent ions provided by the water-soluble chromium compound are used with poorly soluble chromium compounds such as strontium chromate, zinc chromate and lead chromate. To stabilize, and then the rest can be used by reducing the chromium trivalent ions using the reducing agent.

On the other hand, when forming a film with a solution consisting of chromium ion, silica, and resin, which is a general coating type chromate treatment solution composition, it is possible to secure a certain amount of film characteristics under the conditions of use of steel sheet in the air, and also to Korean Patent Application No. 93-29655, When insoluble chromium salt proposed in 93-29656 is used and a small amount of silane coupling agent is added, a certain film water resistance is ensured, and there is no sudden film deterioration phenomenon in a humid atmosphere. Although there is no large film quality deterioration at, the film performance deteriorates under strong alkaline degreasing conditions.

The reason for this is that the resin, which acts as a binder in the coating, is not sufficiently cured and the resin is preferentially destroyed under strong alkaline degreasing conditions. In this case, an insoluble chromium compound is used and a silane coupler is used. When the adhesion between the resin and the silica is improved by the ring agent (Korean Patent Application Nos. 93-29655 and 93-29656), it is difficult to expect satisfactory alkali resistance.

In the present invention, in order to solve this problem, the addition amount and sum of the colloidal silica and the resin to a certain range as follows, and by adding a tinate compound as a curing agent of the resin to increase the bond strength of the film to strong alkali Even after degreasing, the resin is not destroyed so that excellent coating properties can be maintained.

Silica is a colloidal component that is effective in improving the corrosion resistance by removing the fine roughness of the coating layer by vaporizing the thickness of the coating layer to impart the corrosion resistance of the coated chromate coating and causing the corrosion product of the dense galvanized layer under the corrosive environment. Silica in the state is preferable and the amount is preferably limited to 20 to 120 g / L in terms of silica, for the following reasons. Corrosion resistance is insufficient when the addition amount of the colloidal silica is less than 20g / ℓ, over 120g / ℓ the hardness of the film is excessively increased, the film is easily damaged, the risk of corrosion resistance of the site subjected to processing such as bending steel sheet, drawing, etc. Because of this.

Resin is a component that prevents micro chemical adsorption of contaminants such as contaminants and perspiration 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. It is possible to obtain stable solution storage stability in the solution, so it is not greatly affected by the type such as vinyl, acrylic or / and styrene. The amount of such resin added is preferably 20 to 200 g / l in terms of nonvolatile content of the resin, for the following reasons.

When the amount of the resin is less than 20g / ℓ, the effect of the addition of the resin is almost not enough, the anti-fingerprint of the prepared film is insufficient, the curing of the resin is insufficient in 200g / ℓ or more, the resin is dissolved during strong alkali degreasing and alkali degreasing resistance This is because there is a risk of degradation.

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

In the present invention, it is preferable that the sum of the colloidal silica and the resin added to the solution is limited to 40 to 250 g / L, because the amount of the coating film prepared when the sum of the colloidal silica and the resin is 40 g / L or less This is because there is a risk of lack of fingerprint resistance, and the viscosity in the solution is increased at 250g / L or more, there is a problem that non-uniform coating is likely to occur when the solution is applied.

The titanate compound improves the alkali resistance of the film by curing the resin to increase the bond strength of the film, and improves the spreadability of the solution when the solution is applied to the surface of the steel sheet. It is preferable to limit the amount to 0.2 g / l W 10 g / l, for the following reason.

When the titanate compound is 0.2g / l or less, there is almost no effect of addition, so that there is almost no improvement in alkali resistance and surface gloss, and more than 10g / l, there is no further improvement in film properties, but solution stability is lowered and gelation of the solution occurs. This is because a phenomenon occurs.

At this time, it is assumed that the titanate compound improves the glossiness of the film because the resin resin particles are dissolved with each other while the resin is cured when the film is formed, thereby preventing surface irregularities caused by the fine emulsion particles.

As the titanate compound, an aqueous chelate titanate compound can obtain good solution stability without generating entanglement or the like during solution preparation, and it is preferable that the trade names Tyzor LA and Tyzor 131 manufactured by DuPont of the United States are used.

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, and the plating layer is dissolved by the reaction between the solution and the plating layer and accumulated in the solution. Therefore, the increase in the amount of zinc ions in the solution increases the risk of gelation of the solution. Also, when the pH of the solution rises to 7 or higher, the solution stability decreases due to precipitation of chromium trivalent ions in the solution. Because there is.

The pH of the solution controlled in the above range can satisfy the required range of pH by appropriately selecting the type and amount of chromium compound used, and also the quality of weak alkali compounds such as phosphoric acid, acetic acid, and weak alkali compounds such as ammonia water. It is okay because it does not cause a problem.

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 a 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. The colloidal silica, resin and titanate compound were mixed in this 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 by using a roll coater, and then dried at a temperature of 120 ° C. for 30 seconds to produce a chromate steel sheet and to be rubbed with the chromate steel sheet. , 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 1 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 was less than 96 hours × 96 hours to 120 hours △ spraying the brine according to the method described in Japanese test standard JIS 2371 until the traces of white rust of the galvanized layer appeared on the plating surface , 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. Surface gloss was evaluated by measuring the gloss meter by the incident and reflection angle of 60 °. The glossiness of the chromate-treated steel sheet was largely influenced by the glossiness of the zinc plated layer before the chromate treatment, and thus evaluated by the difference in the glossiness before and after the chromate treatment. In other words, when the glossiness decreases by 5 or more by chromate treatment, the change in the glossiness is indicated by Δ in the range of −5 to 5 and the case where the glossiness is improved by 5 or more.

○: excellent, △: normal, ×: poor

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) has a problem in that there is no problem in film quality when the titanate compound is added in a large amount, but the solution is changed to a gel state after a long time after solution preparation. Comparative Example (7) had a problem in that the addition of less titanate compound was insufficient in corrosion resistance and in alkali degreasing, and the surface gloss was reduced by chromate treatment. Comparative Example (8) is a case where the addition amount and the sum of colloidal silica and resin are small, and the addition amount of titanate compound is also slightly smaller than the limited range of the present invention at about 0.1 g / L, and the coating amount is small, resulting in insufficient corrosion resistance and fingerprint resistance. The addition of the titanate compound improved the glossiness deterioration due to chromate treatment, showing a similar level of glossiness of the coated steel sheet itself. 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 chromium trivalent compound may be precipitated during the storage of the solution, indicating a problem in the stability of the solution.

Inventive examples (a-i) satisfying the scope of the present invention in half namely showed excellent performances in surface appearance, corrosion resistance, fingerprint resistance and alkali resistance, depending on the composition of the solution, but all showed excellent performance. It can be seen that the glossiness increased by 5 or more was improved by treatment.

As described above, the present invention is applied to the coating of the galvanized steel sheet by producing a coated chromate treatment solution by appropriately adjusting the addition amount and combination of colloidal silica and resin and the addition amount of the curing agent titanate compound among the components of the solution. When applied to the type chromate treatment, the adhesion between the film components is increased, so that there is almost no damage to the film even in strong alkaline degreasing liquid, and zinc having a chromate film having excellent alkali degreasing, anti-fingerprint, corrosion resistance, alkali degreasing resistance and gloss is excellent. It is possible to improve the quality of the product by easily manufacturing the coated steel sheet.

Claims (3)

In the coated chromate treatment solution, total chromium ions: 1 to 50 g / l, chromium trivalent ions to total chromium ions: 10 to 50%, colloidal silica: 20 to 120 g / l, resin: 20 to 200 g / l, sum of the colloidal silica and resin: 40 to 250 g / l, titanate compound: 0.2 to 10 g / l and the remainder: composed of water, its pH is adjusted to 3 to 7 Coating type chromate treatment solution for producing chromate coating with excellent alkali degreasing and surface gloss. 2. The coated chromate treatment for producing chromate coatings having excellent fingerprint resistance, alkali degreasing resistance and surface gloss according to claim 1, wherein the resin is at least one selected from the group consisting of vinyl, acryl and styrene. solution. The coated chromate treatment solution for producing chromate coatings having excellent anti-fingerprint, alkali degreasing resistance and surface gloss according to claim 1, wherein the titanate compound is an aqueous chelate type compound.