JPS5911000B2 - Manufacturing method of chromic acid treated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an electrolytically chromic acid treated steel sheet, particularly a steel sheet having metallic chromium in the lower layer and hydrated chromium oxide in the upper layer.

In recent years, electrolytic chromic acid-treated steel sheets (commonly known as tin-free steel; TFS) having the above-mentioned two-layer coating have been widely used as materials for adhesive cans in the fields of beer and carbonated beverages.

In the case of adhesive cans, the can body is formed by coating the surface with a paint mainly composed of epoxy resin or epoxy phenol resin and then bonding with nylon adhesive5. It had excellent performance as a can for low temperature storage. However, with the advent of so-called DI cans, which are formed by drawing and ironing, DI cans have been used in the field of beer and carbonated drinks due to their quality, stability, good appearance, and cost advantage. As a result, TFS adhesive cans have no choice but to contain beverages such as coffee and juice, or general foods.

In the case of these beverage cans or general foods, it is necessary to perform sterilization treatment when filling at high temperatures, and the filled cans are exposed to high temperatures of 90 to 130 degrees Celsius.
There is a risk that the strength of the adhesive may deteriorate, leading to damage to the can body. In the case of coffee, there are cases in which coffee is stored at around 70°C for long periods of time, especially in vending machines, and deterioration of the strength of the adhesive is a problem. Since deterioration of adhesive strength occurs at the steel plate-paint film interface rather than between the paint and adhesive, the quality performance of the electrolytic chromic acid treated steel sheet is most important. The present invention was discovered by studying various methods for manufacturing TFS with the aim of providing TFS with excellent paint adhesion under such heat sterilization conditions.

The present invention relates to a method for manufacturing an electrolytic chromium acid-treated steel sheet having metallic chromium in the lower layer and hydrated chromium oxide in the upper layer.
F as a weight ratio in a plating bath containing chromic acid as the main component.
Contains a fluorine compound that satisfies the relationship: /5≧20, and further contains a type A fluorine compound (NH4F, Na
Fluorine (FA) by F, HF, KF, NaHF2, NH4HF2) and B-type fluorinated polymer compound (Na2Si
F6, H2SiF6, 2SiF6, (NH4)2Si
F6, HBF4, NaBF4, KBF4, NH4BF4
) due to fluorine (FB) is FA/FB 1.0j 1-
(weight ratio) is characterized by electrolyzing in a plating bath containing the following relationship:

As is well known, the method for manufacturing electrolytic chromic acid treated steel sheets having metallic chromium in the lower layer and a hydrated chromium oxide film in the upper layer is as follows:
As seen in Japanese Patent Publication No. 41-13008, 0.1 to 0
．． A method in which an inorganic acid containing 3 f/t of sulfuric acid and 1.01 i/t or less of fluorine or a water-soluble salt thereof is added, or a method in which chromic anhydride 200 i/t and sulfate ion 0. 3f/t
, silicon ion 1.0tai, or Japanese patent 1862
In 21, chromic anhydride 100f/t, sulfuric acid 0.5
Plating baths such as No. 11 and boronic acid 111 are known.

In all of these inventions, sulfate ions are necessary as an essential component and are artificially added to the plating bath. Furthermore, no particular reason has been found to limit the type of fluorine compound. The present invention aims to improve the water resistance of hydrated oxides during high-temperature heat sterilization, while suppressing the eutectoid of sulfate groups in the film as much as possible.
We have discovered a plating bath composition that makes the structure of the oxide itself the most desirable.

The present invention will be explained in detail below.

The main feature of the plating bath of the present invention is that it is a so-called all-fluoride bath, and the most significant feature lies in the type and composition ratio of the fluorine compound added.

The main component of the plating bath is chromic anhydride, and its concentration range is preferably from 30 to 300 f/t, preferably from 60 to 2001i. If it is less than 30 f/t, it is unfavorable because of an increase in electrolytic voltage or a decrease in current efficiency, and if it is more than 300 f/t, there is a disadvantage that losses such as chromic acid being taken out by the steel plate are likely to occur.

Due to its characteristics, the fluorine compounds added next are NH4F, N
aF, HF, KF, NaHF2, KHF2, NH4゛ as A type compound, Na2SiF6, H2SiF6, K2Si
F6, (NH4)2SiF6, HBF4, NaBF4,
KBF4 and NH4BF4 are classified as class B compounds.

Class A compounds have a high degree of ionization and exist as relatively small ions in the bath, and when used alone with chromic acid, high current efficiency can be obtained, but hydrated chromium oxide is very thin and only 10111! /A (C, as a quantity) can only be obtained. On the other hand, the degree of ionization of the B-type compound is lower than that of the A-type compound, and it exists as a relatively large ion in the bath. In the case of this type B compound, the characteristics are different from those of the type A compound, and when used alone with chromic acid, the current efficiency is low and it is disadvantageous for the precipitation of metallic chromium, but it is desirable to secure a large amount of hydrated chromium oxide. It has excellent properties in some cases. ．． The present invention relates to a manufacturing method for obtaining a two-layer film of metallic chromium in the lower layer and hydrated chromium oxide in the upper layer, which combines the characteristics of the above-mentioned type A compound and type B compound,
The objective is to obtain TFS with good current efficiency and good paint adhesion under heat sterilization conditions.

In the present invention, fluorine added as a type A compound is FA (weight), and fluorine added as a type B compound is F
If B (weight) is displayed, FA/FB must satisfy 1.0.

When FA is higher than FB, the amount of hydrated chromium oxide decreases, and in the wet state before drying, a hydrated chromium oxide film that easily peels off due to friction with rolls or collision with washing spray water, etc., becomes uniform on the steel plate surface. A good covering cannot be expected. If FA/FB≦1.0 is satisfied, this problem will disappear and it will be easy to ensure the amount of hydrated chromium oxide. F.A.
If there are a large number of FBs, for example, FA/FB=0.
In a case like No. 10, the amount of hydrated chromium oxide deposited is sufficient, but the current efficiency decreases by about 8 to 15%, which is not preferable in terms of current efficiency. FA/FB to ensure current efficiency
is preferably within the range of 0.20 to 1.0. On the other hand, regarding the problem of sulfuric acid groups in plating baths, even if sulfuric acid groups are not artificially added to plating baths, they may be present as impurities in chromic acid or brought in from pre-treatment. This means that around 100 ppm of sulfuric acid groups are present therein.

Further, a small amount of sulfuric acid group may be added to improve current efficiency. In this way, the sulfate groups present in the plating bath eutectoid in the hydrated chromium oxide during electrolysis, but it is necessary to minimize the amount of eutectoid sulfate groups to prevent deterioration of paint adhesion during high temperature sterilization. be. For that purpose, F/S≧2 in the bath
It has been found that it is necessary to satisfy 0 (as a weight ratio). If F/S≧20, the amount of eutectoid sulfate groups will be at the lowest level, resulting in excellent adhesion. Also, the total amount of fluorine compounds added is 2 to 6 to chromic acid.
By keeping the amount within this range, it is possible to obtain a hydrated chromium oxide film having good high temperature water resistance and excellent adhesion performance.

In addition, the hydrated chromium oxide film obtained by the present invention has a low content of sulfuric acid groups and is structurally difficult to dissolve in acids and alkalis. It is possible to obtain a steel plate with better performance, especially excellent rust resistance.

Therefore, it is not only applicable to adhesive can bodies, but also various can lids, miscellaneous cans, etc.
It can be applied to 5 gallon cans, etc.

The film structure in the present invention consists of metallic chromium in the lower layer and hydrated chromium oxide in the upper layer, but the hydrated chromium oxide film in the upper layer means crystalline and/or amorphous chromium oxide. . Examples of the present invention will be described below.

Example 1 1 Electrolytic treatment method The ratio of fluorine FA from the type A fluorine compound and fluorine FB from the type B fluorine compound is FA/FB (weight ratio) = 0.6
7 Performance test The electrolytically treated sample (plate thickness 0.17) was tested at 5? Xl5Of
Cut into 1B pieces and glue with nylon 66 at 200°C.
The adhesive is melt-pressed for 0 seconds and has a final adhesive thickness of 50 μm.

The thus bonded sample was immersed in a 0.4% citric acid solution, heated in an autoclave, and kept at 110° C. for 8 hours.

After performing such retort treatment, the sample was peeled off in a T-shape at a 200Wr1ILA surface p tensile speed using a normal tensile tester, and the tensile strength (T-Peet
strength) was measured.

FIG. 1 is a diagram showing a comparison of adhesive strength between the conventional method and the method of the present invention. Example 2I Electrolytic treatment method a Bath composition Electrolytic conditions Performance test Electrolytically treated sample (plate thickness 0.17Fm) was heated to 5#MX15
Cut to 0Fm and heat at 200℃ using nylon 66 as adhesive.
The adhesive was melted and pressed for 60 seconds to a final adhesive thickness of 50 μm.

The thus bonded sample was immersed in a 0.4% citric acid solution, heated in an autoclave, and kept at 110° C. for 8 hours.

After performing such retort treatment, the sample was peeled off in a T-shape using a normal tensile testing machine at a tensile speed of 200 m of oil, and the tensile strength at that time (T-Peet strength) was measured.
was measured (see Figure 2).

Figure 2 is a diagram showing the relationship between K/S in the bath and adhesive strength.
Example 3 I electrolytic treatment method a Bath composition The fluorine compounds were FA (tai) with a type A fluorine compound at a F/S weight ratio of 50 in the bath, and FB (f) with a type B fluorine compound.
/t) and a FA/FB weight ratio of 0.25, a bath having the composition shown in the table below was prepared.

Performance test Electrolytically treated sample (plate thickness 0.1711) was 5fWn x 1
Cut into 50m lengths and heat at 200℃ using nylon 66 as adhesive.
The adhesive was melted and pressed for 60 seconds to a final adhesive thickness of 50 μm.

The thus bonded sample was immersed in a 0.4% citric acid solution, heated in an autoclave, and kept at 110° C. for 10 hours.

After performing such retort treatment, the test temperature was 200r1m/Ml using a normal tensile tester.

The sample was peeled off in a T-shape at a tensile speed of
(see figure). FIG. 3 is a diagram showing the adhesive strength of various fluorine compound added baths. Example 4 Cr031501. Cr3+1.21, SO4O. 2l
7/T. NaFl. 8f/T. HBF44. Electrolytic treatment (55°C 50 coulombs/D) in a plating bath containing Oll
d) Apply epoxy/phenol paint 45K9/D to one side of the chromic acid treated steel plate, and apply melamine paint 707A/D to the other side, then apply 5K so that the melamine paint-applied side becomes the outside surface of the can. After creating the No. 1 can lid and seaming the can lid, heat the lid at 40°C to determine the tendency for rust to occur in the seamed part.
85#) were stored in a constant temperature and humidity chamber at RH, and the rust occurrence tendency was compared.

As a comparison material, a chromic acid treated steel sheet obtained from the following plating bath was used. 1Cr0390I, Cr3+1.0f/T
,SO4O.

8l2CrO3l5Ol, Cr33l. 2l, SO4O
．． 3l, NaSiF64.5l As a result, the can lid made from the chromic acid treated steel plate according to the present invention showed no rusting for more than one month, whereas the comparative materials 1 and ? In all cases, rust was observed within 20 days from the defective parts of the coating film that were generated during the seaming process.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a comparison of adhesive strength between the conventional method and the method of the present invention.

Claims (1)

[Claims] 1. In the manufacturing method of electrolytic chromic acid treated steel sheet having metallic chromium in the lower layer and hydrated chromium oxide in the upper layer, F/S ≥ 20 (as a weight ratio) in a plating bath mainly composed of chromic acid.
Contains a fluorine compound that satisfies the following relationship, and further contains a type A fluorine compound (NH_4F, NaF, HF, KF, NaHF_4F, NaF, HF, KF, NaHF_
2. Fluorine F_ by KHF_2, NH_4HF_2)
A and B type fluorine compounds (Na_2SiF_6, H_2S
iF_6, K_2SiF_6, (NH_4)_2SiF
_6, HBF_4, NaBF_4, KBF_4, NH_
4BF_4) Fluorine F_B or F_A/F_B≦1
．． A method for producing a chromic acid-treated steel sheet, which is characterized by electrolyzing in a plating bath containing plating baths that satisfy the relationship: 0 (weight ratio).