JPS6332878B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing an electrolytically chromate-treated steel sheet as a material for adhesive cans, and the present invention relates to a method for producing an electrolytically chromate-treated steel sheet as a material for adhesive cans. The present invention aims to provide a method for manufacturing treated steel sheets. Electrolytic chromate-treated steel sheets are currently manufactured using two methods: a one-component method and a two-component method.
For example, the one-liquid method is JP-KOK No. 35-8207, JP-KOK No. 41-
As stated in Japanese Patent Publication No. 13008, Japanese Patent Publication No. 43-2768, and Japanese Patent Application Laid-Open No. 48-75432, relatively low concentration chromic acid (50 to 150 g/) is used as the main ingredient, and a small amount of auxiliary agent (aromatic disulfonic acid) is used as the main ingredient. In this method, a steel plate is electrolyzed cathodically in an aqueous solution containing chromium, sulfate, thiocyanate, fluoride) to simultaneously precipitate metallic chromium and hydrated chromium oxide. In addition, the two-liquid system is
No. 15155, Special Publication No. 1977-3517, Special Publication No. 1972-35172
As described in British Patent No. 939136, a steel plate is electrolyzed cathodically in an aqueous solution that uses relatively high concentration chromic acid (150 to 500 g/) as the main agent and contains small amounts of sulfate and fluoride as auxiliary agents. This is a method in which metal chromium plating is performed, followed by cathodic electrolysis in a low concentration chromic acid aqueous solution containing a small amount of auxiliary agent to precipitate hydrated chromium oxide. Electrolytic chromate-treated steel sheets manufactured by the method described above have excellent paint adhesion, and are sold in large quantities on the market as painted cans such as carbonated beverage cans and beer cans. Cans made of such electrolytic chromate-treated steel sheets cannot be joined with solder like tinplate, so the mirror seam method and Toyo seam method using nylon adhesive are used, and the joint is the first The structure is as shown in the figure. In the figure, 1 is a base steel plate, 2 is a metal chromium layer, 3 is a hydrated chromium oxide layer, 4 is a coating film, and 5 is an adhesive layer. In general, the joints of electrolytic chromate-treated steel sheet adhesive cans are
In the 90° beer method, the strength is approximately 6 kg/5 mm (0.17 mm DR-8 machine) at a tensile speed of 200 mm/min, and even though carbonated beverage cans served at room temperature or below are under internal pressure, It has such good paint adhesion that it does not cause damage to the shell due to broken joints. However, with conventional electrolytic chromate-treated steel plate adhesive cans, so-called hot-pack cans, in which the contents are heated and sterilized at 80 to 100°C and filled immediately, or
In retort cans that are sterilized in pressurized steam at temperatures above 100℃, the strength of the joints decreases over time, and the coating film deteriorates.
There were problems with aging resistance, retort resistance, and so-called secondary paint adhesion, such as the risk of peeling and fracture due to adhesion failure at the steel plate interface. This is one of the reasons why it is difficult to use electrolytically chromate-treated steel sheet adhesive cans for food cans and fruit juice cans. The present invention provides a method for producing an electrolytically chromate-treated steel sheet that improves the drawbacks of the conventional electrolytically chromate-treated steel sheet as described above and has excellent secondary paint adhesion. , by performing electrolytic chromate treatment or electrolytic chromate treatment after chrome plating, 30~
An electrolytically chromate-treated steel sheet having two layers of a metallic chromium layer of 200 mg/m ² and a hydrated chromium oxide layer with a chromium content of 5 to 30 mg/m ² on top of the metal chromium layer, and a polyacrylic PH containing acid or its alkali salt at a concentration of 0.3g/~10g/
The reason is that an aqueous solution of 2.0 to less than 5.0 is applied and then dried. The present inventors have completed the present invention by obtaining the following knowledge as a result of detailed study on the aging deterioration of paint adhesion in a high-temperature aqueous environment or steam return environment, that is, the aging deterioration of secondary paint adhesion. It is. The causes of deterioration of paint adhesion, that is, secondary paint adhesion, over time under the above conditions can be broadly classified into the following two points. A phenomenon in which an aqueous or non-aqueous solution penetrates the interface between the metal layer (base steel sheet and metal chromium layer) exposed on the surface of an electrolytically chromate-treated steel sheet and the paint film, reducing the adhesion at the metal-paint film interface. When an aqueous or non-aqueous solution penetrates the interface between the hydrated chromium oxide layer and the coating film, the hydrated chromium oxide
A phenomenon in which the adhesion of the paint film interface decreases. This phenomenon is much larger when comparing the rate of deterioration over time. Therefore, in order to improve the adhesion of the secondary paint, it is necessary to minimize the exposed area of the metal layer, that is, to increase the coverage of the hydrated chromium oxide layer, and then to improve the adhesion between the hydrated chromium oxide and the paint film. It is an essential requirement to further strengthen the In general, hydrated chromium oxide formed in the production of electrolytically chromate-treated steel sheets has the property of being easily dissolved in an electrolytic solution immediately after its formation. For this reason, in actual production lines, hydrated chromium oxide undergoes non-uniform dissolution in the electrolytic solution immediately after its formation, and the metal layer tends to be exposed. To improve this, the 1-liquid method, the 2-liquid method,
Regardless of the liquid method, an electrolytic solution for forming hydrated chromium oxide must be selected from a liquid system with as low solubility as possible. However, there is a natural limit to the improvement effect achieved by the coverage of the hydrated chromium oxide layer.
For further improvement, it is necessary to solve the above items. JP-A-53-58442 and JP-A-54-14885 as a proposal for improving the adhesion of secondary paint between hydrated chromium oxide and paint film.
There is a method of modifying the hydrated chromium oxide layer disclosed in JP-A-54-64034 and JP-A-54-89946, but the present inventors have conducted various studies from different viewpoints. , forming a hydrated chromium oxide layer adjusted to a specific amount, and further forming a third layer on top of it by a predetermined method to improve adhesion between the hydrated chromium oxide layer and the coating film. I have found that this is the most effective method. That is, a metal chromium layer is formed on a steel plate, a hydrated chromium oxide layer adjusted to a chromium content of 5 to 30 mg/m ² is formed on top of the metal chromium layer, and a solid concentration of polyacrylic acid or its alkali salt is 0.3 to 10 g. /Including PH2.5
By immersing or spraying in an aqueous solution of less than ~5.0 and then squeezing with a roll or gas squeezing method to form a third layer made of the organic polymer,
It has been discovered that excellent secondary paint adhesion can be obtained. A method of forming a third layer by applying a water-soluble polymer to an electrolytically chromate-treated steel sheet is already known, and is disclosed in Japanese Patent Publication No. 44-20848 and Japanese Patent Publication No. 44094-1973.
No., JP-A No. 50-59238, etc. Although these known techniques are effective in improving paint adhesion, the problem lies in the adhesion of the paint before and after processing the treated steel sheet, which is what is called primary paint adhesion. Therefore, the selection range of water-soluble polymers that can be applied is extremely wide. Also,
Japanese Patent Publication No. 44-20848 contains a water-soluble polymer and an inorganic ammonium salt of a water-soluble aliphatic saturated aldehyde, and requires the pH to be controlled at 5 to 12. Also, does Tokuko No. 51-44094 contain transition metal salts such as chromate at the same time as water-soluble polymers?
Or, in terms of liquid stability of water-soluble polymers, pH ~ 5 ~
It states the need to limit the number to 10. In addition, JP-A-1988
No. -59238 is a water-soluble polymer that has ammonium salts, ammonium, organic amines, organic amine salts, and polyhydric phenols added as stabilizers.
Needs to be maintained at ~5-10. All of these known techniques for improving primary paint adhesion require the inclusion of ammonium, amines, salts thereof, chromic acid or salts thereof, or other inorganic salts. In the case of the polyacrylic acid or its alkali salt of the present invention, as described below, the pH of the aqueous solution is important, and it has been found that setting the pH to the alkaline side as in the above-mentioned patents has a very negative effect. This characteristic will be explained below using polyacrylic acid, which is a representative example of the water-soluble organic polymer selected in this application, but this characteristic also applies to an alkali salt of polyacrylic acid. For 2 grand children, add 2g of polyacrylic acid/(PH3.5)
An electrolytic chromate-treated steel plate that had been immersed in an aqueous solution whose pH was adjusted with NH ₄ OH was coated and bonded in the same manner as in the example below, and then soaked in a 0.4% citric acid aqueous solution at 70°C for 10 minutes.
The results of the adhesive strength obtained by performing a T-peel tensile test after being immersed for one day are shown. Figure 2b shows the case in which chromic acid was added to an aqueous solution of 2 g of polyacrylic acid, assuming that the chromic acid from the previous step was mixed into the treatment solution, and treatment was performed with treatment solutions of various chromic acid concentrations. The adhesive strength of the electrolytically chromate-treated steel sheet is shown, and the test method is the same as in case a above. As shown in Figure 2b, there is no effect when the amount of chromic acid is less than 1.0 g, and even when it is more than 1 g, polyacrylic acid Shows performance equivalent to that of a single sample. In this way, even if a second component such as chromic acid is mixed into the treatment liquid from the previous process, the same performance will be achieved as long as the pH is controlled. If hydrochloric acid is added instead of chromic acid and the PH is adjusted to the acid side, no deterioration in performance is observed, but by making the treatment solution strongly acidic, other properties of the electrolytic chromate-treated steel sheet may be affected. Considering the sub-effects, this is not industrially meaningful. In the present invention, regardless of the one-liquid method or the two-liquid method, the amount of hydrated chromium oxide in the electrolytic chromate treated steel sheet is 5 to 30 mg/m ² , preferably 8 to 30 mg/m 2 in terms of chromium content.
Controlled at 25mg/ ^m2 . Below 5mg/ ^m2 , the metal chromium layer is not uniformly covered with hydrated chromium oxide and the exposed area of the metal layer becomes large, resulting in poor secondary paint adhesion such as corrosion resistance, aging resistance, and retort resistance. Both genders are poor. Moreover, if it exceeds 30 mg/m ² , the hydrated chromium oxide layer is too thick, resulting in deterioration in appearance and deterioration in primary paint adhesion and secondary paint adhesion such as aging resistance and retort resistance, which is undesirable. . The thickness of the metallic chromium layer does not need to be particularly limited as long as it is the thickness used for ordinary electrolytic chromate treated steel sheets, but if it is less than 30mg/ ^m2 , problems will occur with corrosion resistance, etc., and if it is more than 200mg/ ^m2 , it will have poor workability. I don't like it because it's inferior. Next, a third organic polymer film is formed on this hydrated chromium oxide layer, but regardless of whether the method is a one-liquid method or a two-liquid method, this film still has a slight residual amount after the final cathodic electrolytic treatment and water washing. Electrolytic chromate-treated steel sheet wet with water, 0.3~10g/,
Preferably, it is formed by a treatment step of immersing or spraying in an aqueous solution containing 0.5 to 4 g of polyacrylic acid or an alkali salt thereof, and then uniformly coating and drying by roll squeezing or gas squeezing. In the case of the present invention, similar effects can be observed even if the present invention treatment is performed after cathodic electrolysis treatment, water washing, and drying, but as will be described later, the chelate reaction between the hydrated chromium oxide and the organic polymer is It is more effective to leave it slightly wet until after washing. The mechanism of action of forming the third layer made of organic polymer according to the present invention is considered as follows. The polyacrylic acid or its alkali salt of the present invention is a polymer having a large number of carboxylic acid groups within the molecule. Generally, carboxylic acid groups are known to undergo a chelate reaction with trivalent chromium, and it has been reported that they are used in all- and oxo-chromium paints. The hydrated chromium oxide of the electrolytically chromated steel sheet is composed of trivalent chromium, regardless of whether it is a one-component or two-component method, and this trivalent chromium causes a chelate reaction with the carboxylic acid group of the organic polymer. It is certain that a complex and tightly bonded film is formed. Regarding the concentration, if the concentration is less than 0.3g/, the absolute amount of carboxylic acid groups applied to the electrolytic chromate treated steel sheet will be small, and the uniformity of the formed film itself will be poor, resulting in poor aging resistance and retort resistance. The adhesion of the secondary paint, such as its properties, varies significantly due to minute changes in processing conditions. In addition, if 10 g / This is undesirable as it will actually impair the sex. In addition, since the third organic polymer film is an organic polymer, it must have the same basic constituents, have a large dispersion force, and contain carboxylic acid groups in the molecule. Since it has a large number of molecules, its adhesion is extremely strong, such as forming hydrogen bonds with the coating film. This third organic polymer film is interposed between the hydrated chromium oxide layer and the paint film, and the strong adhesion between the hydrated chromium oxide layer and the paint film improves the aging resistance. This has resulted in significant improvements in secondary paint adhesion such as retort resistance. Next, specific examples of the present invention will be described, but the content of the present invention is not limited to these examples only, and can be implemented in many embodiments according to the gist of the present invention. In other words, if the treatment of the present invention is applied, it is possible to obtain the excellent secondary paint adhesion shown in the examples, regardless of the manufacturing method of electrolytic chromate-treated steel sheets, such as the one-component method or the two-component method as described above. Needless to say. Comparative Example 1 Electrolytic chromate treated steel sheets with a metal chromium content of 100 mg/m ² and chromium content in the hydrated chromium oxide layer of 8, 15, and 23 mg/m ² were subjected to electrolytic chromate treatment using a TACA machine with a thickness of 0.23 mm. Examples 1 to 6 The treated steel sheets of Comparative Example 1 were immersed in an aqueous solution with a pH of 3.5 containing 0.3, 0.5, 1.0, 2.0, 4.0, and 10.0 g of polyacrylic acid, respectively, and then passed through a squeezing roll. , and then dried with hot air at 80°C. 40 to 60 mg/ ^dm2 of phenol epoxy paint was applied to each of the treated steel sheets of the comparative examples and examples above,
After baking at 210℃ for 10 minutes, cut into 5mm width
The painted surfaces of two mm-wide samples were glued together with a nylon adhesive and subjected to an accuracy test. The results are shown in the table below.

【table】

[Table] The various test methods in the table are as follows. Γ Primary paint adhesion T-peel tensile speed test showed that the tensile speed was 200
It was done at mm/min. Γ Secondary paint adhesion (a) Aging resistance The above T-peel tensile test was conducted after immersion in a 0.4% citric acid aqueous solution at 70°C for 10 days and 20 days. (b) Retort resistance test After being left in steam at 130°C for 3, 6, and 10 hours, the Tall tensile test was conducted. As shown in the table, the examples according to the present invention have almost the same primary paint adhesion as the comparative examples, but exhibit extremely superior performance in terms of aging resistance and retort resistance. It can be said that the paint adhesion has improved dramatically. As described above, the present invention covers the exposed metal surface on an electrolytically chromate-treated steel sheet having a two-layer structure of a metal chromium layer and a hydrated chromium oxide layer, and moreover, it is extremely firmly bonded to the hydrated chromium oxide layer and the coating film. By interposing an organic polymer film that can bond, electrolytic adhesive cans can be used to improve secondary paint adhesion, such as aging resistance and retort resistance, which are currently the biggest problems with electrolytic chromate-treated steel sheets. It is possible to obtain chromate-treated steel sheets, and has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of the adhesive part of the adhesive can, FIG. 2 a is a graph showing the relationship between adhesive strength and PH, and FIG. 2 b is a graph showing the relationship between the amount of Cro ₃ added and adhesive strength. In the figure, 1 is a base steel plate, 2 is a metal chromium layer, 3 is a hydrated chromium oxide layer, 4 is a coating film, and 5 is an adhesive layer.

Claims (1)

[Claims] 1 By electrolytically chromating a steel plate or electrolytically chromating it after chrome plating, a metallic chromium layer of 30 to 200 mg/m ² is formed on the surface of the steel plate, and 2.5 to 30 mg/m ² of hydrated chromium oxide in terms of the amount of chromium is formed on the surface of the steel plate. Obtaining an electrolytically chromated steel sheet having two layers of layers,
Secondary paint adhesion characterized by applying an aqueous solution containing polyacrylic acid or its alkali salt at a concentration of 0.3 g/~10 g/with a pH of less than 2.5 to 5.0 to the electrolytically chromate-treated steel sheet and drying the solution. A method for manufacturing electrolytic chromate-treated steel sheets for adhesive cans with excellent properties.