JPS5932557B2 - Manufacturing method of chromate-coated steel sheet for containers with excellent weldability and corrosion resistance after painting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a steel plate for a welded container suitable as a material for can manufacturing, and in particular a method for producing a steel plate for a welded container that has excellent weldability, performance after painting, and especially corrosion resistance after painting. It is related to.

In recent years, due to the diversification of can manufacturing methods, can manufacturing methods using electric resistance welding (for example, the Sudronik welding method) have significantly developed as a method for manufacturing cans.

The can-making material used in the can-making method must not only have excellent properties required for steel sheets for containers, such as corrosion resistance, workability, painting performance, and corrosion resistance after painting, but also have extremely good weldability. is required. Sn has traditionally been used as a material for containers.
Plated steel plate (tin plate) or electrolytic chromic acid treated steel plate (T
FS), but these container materials each have the following problems or drawbacks when used in the above-mentioned can manufacturing method. In other words, one of the important reasons for the development of the above-mentioned can manufacturing method is the reduction of can manufacturing costs, and it is difficult to say that tinplate material is necessarily an answer to the reduction of can manufacturing costs, and the can manufacturing method using the welding method In this case, an iron-tin alloy layer is formed in the heat affected zone near the weld, or Sn
Significant thermal oxidation of the surface causes performance problems such as discoloration of the appearance and deterioration of paint adhesion.

On the other hand, electrolytic chromic acid treated steel sheets (TFS) are superior in terms of economy and cost, but the coating of TFS is composed of a talomete coating consisting of metallic chromium and chromium oxide.

Therefore, as is known from the past, these metal chromium and chromate coatings are metals or oxides that are difficult to weld, so when welding is used to make cans, the strength of the welded part is often insufficient. . Furthermore, after performing Nl plating, a can making material consisting of a Ni plating layer and a chromate coating (Japanese Patent Publication No. 36-10064) or Ni plating is applied, which is cathodically treated in an aqueous solution of dichromic acid or a salt of chromic acid. A material for can making in which the Ni plating layer and the oxide film on the surface of the Ni plating layer are improved by cathodic treatment in an aqueous solution of potassium permanganate etc.
15252) is known.

However, as with these materials, the performance aimed at by the present invention could not be obtained simply by subjecting the Ni plating layer to chromate treatment by a known method. That is, in the known chromate treatment method, the adhesion of the paint is extremely good after painting, but
In a corrosion test simulating a corrosive environment in a can manufacturing container that is exposed to a corrosive aqueous solution for a long period of time after being painted, six blisters were observed on the coating surface due to the corrosive aqueous solution penetrating through the coating. The corrosion resistance after painting was significantly deteriorated, such as peeling of the paint film, and this tendency was even more severe in the defective areas of the paint film. Furthermore, the weldability by electric resistance welding after chromate treatment by this known method is not very good, and when the amount of coating is large, it is difficult to generate uniform weld nuggets and it is difficult to obtain sufficient welding strength. Also, even when the amount of coating is small, a uniform and good weld cannot be obtained, probably due to the influence of the highly hydrated chromate coating of the Cr-0H system, and weld defects often called "weld dust" occur in the weld. There was a tendency for this to occur, and the extravasation properties were not very good.

It is an object of the present invention to solve the above-mentioned problems and to provide an inexpensive method for manufacturing a steel sheet for containers that has sufficient performance to be used in a can-making method using electrical resistance contact.

That is, the present invention aims to provide a method for manufacturing a steel sheet for containers that is excellent in corrosion resistance, weldability, coating performance, and especially corrosion resistance after coating. As a result of various studies to improve the coating performance and weldability of these coatings, we have improved the chromate coating using a known method to form a chromate coating with fewer pinholes. In contrast, the soluble component F-
, Cr+6 ions are eluted, and colloidal Cr
The degree of oxation (Cr in the chromate film) promoted the dehydration and condensation reaction of the chromate film consisting of
It has been found that it is sufficient to form an appropriate amount of a difficult to tolerate chromate film with a high ratio of Cr-0 type oxo bonds to -0H type all bonds, that is, a low degree of hydration, on the surface of the Nl plating layer.

That is, when exposed to a corrosive aqueous solution under the coating, there is less corrosion of the Nl plating layer from the pinholes in the chromate coating, and there is less blistering of the coating that occurs due to the dissolution of soluble components from the chromate coating. As a chromate film, the welding current flows uniformly and is less likely to occur.
) F-/Cr+6 weight ratio (hereinafter abbreviated as ratio) is 1
To form a chromate film with a coating amount of 2 to 25 η/m'' in terms of Cr amount by cathodic treatment in an aqueous solution of chromate or dichromate containing F- consisting of /10 or less.

(2) F with a ratio of F-/Cr+6 of 1/10 or less
- A chromate film is formed by cathodic treatment in an aqueous solution of chromate or dichromate containing 2~
Immediately after forming 25~/m'', or after washing with water, further rinse with high temperature water of 65~100℃ and PH4 or higher.
．． Perform high temperature water treatment for 3-10 seconds.

etc. were found.

A first method of manufacturing a steel plate for a welded container according to the present invention to achieve the above object is to apply a thickness of 0.015 to 0.3 on the surface of the steel plate.
A 0μ Ni plating layer is applied, followed by an aqueous solution containing F with a ratio of F-/Cr+6 of 1/10 or less, and containing one or more of chromate and dichromate. The second feature is that a chromate film is applied in a chromate film with a coating amount of 2 to 25 TI1 g/M° in terms of Cr. 0.3 for high temperature water
It is characterized by immersion treatment for ~10 seconds.

The contents of the present invention will be explained in detail below.

Ni plating is carried out mainly for the purpose of improving corrosion resistance, and the plating means may be a normal electric nickel plating method.

The composition of the Ni plating bath, plating conditions, etc. are not particularly specified, but the current density is approximately 3 to 300 A/Dm'' and the plating temperature is 700 C or less. Examples of the composition of the Ni plating bath and plating conditions are as follows. In addition, in the present invention, the thickness of this Nl plating is defined as 0.015 to 0.3μ, but this means that if the thickness is thinner than the lower limit, the corrosion resistance will be insufficient and the Ni plating will have no meaning. The reason is that if this happens, the effect will be saturated and the cost will be disadvantageous.

Therefore, in the present invention, after Ni plating C, F- is added by weight to 1 of Cr+6 in chromate or dichromate.
Cathodic electrolysis treatment is carried out in an aqueous solution containing a ratio of 1/10 or less, preferably 1/40 or less, and the amount of
Either perform chromate treatment consisting of 25m9/M゜, or after this treatment, further chromate treatment at a temperature of PH4 or higher.
High-temperature water treatment for 0.3 to 10 seconds with high-temperature water of 5 to 100°C significantly improves weldability, corrosion resistance, and coating performance based on electrical resistance, especially post-coating corrosion resistance when exposed to corrosive aqueous solutions. It is improving. Therefore, as a method for forming a chromate film with the above structure, treatment in a chromate bath containing F- ions is necessary in order to obtain a chromate film that has few pinholes and is poorly soluble in corrosive aqueous solutions. .

If the amount of F- ions exceeds 1/10 of Cr+6 by weight in this treatment bath, the F- content in the chromate film will increase, and the heating process or high temperature in the coating process following cathodic treatment will increase. It cannot be removed even in the water treatment → heating process and deteriorates the performance after painting.
It is desirable to reduce the amount to 1/10 or less, preferably 1/40 or less. In addition, in the cathodic electrolytic treatment of the present invention, F-
A Cr+6-F series bath containing Cr+6-F is used, but the treatment conditions are It has a wide selection range and is industrially advantageous.

In other words, in a treatment bath consisting of chromate or dichromate and F-, the cathodic electrolytic treatment clearly does not cause the precipitation of a metallic Cr layer that can be measured at the current state of the art, and the chromate coating is A main coating is formed.

Therefore, compared to a treatment bath using CrO3, it is possible to select a wider range of electrolytic conditions, and it is advantageous because only the adjustment of the chromate film is required. Usually, the cathodic treatment is carried out at room temperature to 90°C and at a current density of 3 to 30 A/Dm'', preferably 5 to 15 A/Dm''.The chromates used in the present invention include ammonium chromate, ammonium chromate, Sodium chromate,
Potassium taromate and the like are used, and as the dichromate, ammonium dichromate, sodium dichromate, potassium dichromate, etc. are used.

Further, these chromates and dichromates may be used in combination. The bath concentration of chromate or dichromate is not particularly specified, but is 5 to 150 f/11, preferably 2.
It is carried out at 0 to 120 y/l. Treatment bath concentration is 5t/t
In the following, it is difficult to form a uniform chromate film with a short treatment time, and bath changes are likely to occur due to the contamination of surface residues that have not been sufficiently removed by water washing on the surface of the Nl plating layer, which is not preferred. Moreover, if the concentration of the bath exceeds 1507/l, the effect will be saturated and the amount of dragout will increase, which is economically unfavorable. F] Use salts that dissolve in aqueous solutions such as chromates and dichromates such as NH4F, HF, NaF, and K2SiF6. The chromate film thus formed with the above structure has a Cr equivalent content of 2T! If it is 1 f/m'' or more, there will be few pinholes, and since it is composed of a hardly soluble chromate film, the corrosion resistance and performance after painting will be good.

Furthermore, this chromate film with a high degree of oxation, that is, a low degree of hydration, has excellent weldability, probably because the welding current flows uniformly. If it is less than 2~/m'', it will not be effective in improving corrosion resistance and performance after painting, especially improving corrosion resistance after painting.

However, if the amount of coating exceeds 25W19/m", corrosion resistance and performance after painting are excellent, but the welded part becomes dusty during electric resistance welding, and defects are more likely to occur in the welded part. Since uniform formation will not be achieved sufficiently and sufficient welding strength will not be obtained, it is necessary to limit the amount of the chromate film to less than 25 η/M.In other words, the amount of chromate film must be limited to 2 to 25 η/M in terms of Cr.
゜By forming a chromate film on the surface of the Nl plating layer, preferably in the range of 3 to 15 η/m, the welded part has no welding defects due to dust phenomenon and has sufficient welding strength with uniform nuggets formed. It is possible to obtain a steel plate for containers which has excellent welding properties and whose performance after painting does not deteriorate due to elution of the chromate film by the corrosive aqueous solution under the paint film.

Incidentally, in the cathodic electrolytic chromate treatment bath of the present invention, Cr+3 is naturally generated along with the electrolytic treatment, and Cr+3 is generated in the treatment bath.
Even if it is accumulated up to about 1/10 of the weight of 6, it will not affect the formation of a chromate film, so there are no particular restrictions.

Next, in the present invention, immediately after cathodic electrolytic treatment or after washing with water, the temperature is 65 to 100°C, preferably 75 to 95°C.
By treating with high-temperature water with a pH of 4 or more, preferably 6 to 9, the product is mainly composed of colloidal hydroxide, which inevitably contains small amounts of Cr+6 and F- ions. Modification of the chromate coating is carried out.

That is, the elution of F- ion, which is a soluble component contained in the talome film, the elution of Cr+6, and the elution of colloidal C
Due to the promotion of dehydration and condensation reaction of r+3 hydroxide, the soluble component (F-Cr+3) contained in the coating is extremely small, and the chromate coating has a high degree of oxation, that is, a low degree of hydration. be done. Furthermore, in the present invention, as described above, a chromate coating having a low content of soluble components and a high degree of oxo conversion has a coating amount of 2 to 25▼/m'' in terms of Cr content, preferably It is important to limit and configure the chromate coating to a range of 3 to 15 η/m.By using the above treatment method and limiting the amount of chromate coating, the chromate coating will have fewer pinholes and less F in the coating. −
Since the amount of ions and Cr+6 ions is small, the corrosion resistance of the steel sheet for containers of the present invention is good, and the chromate coating becomes poorly soluble when exposed to a corrosive aqueous solution, making it difficult for the chromate coating to evaporate under the coating. Alternatively, there is little elution of corrosion products from the Ni plating layer from the pinhole portions of the chromate coating, resulting in extremely excellent corrosion resistance after painting.

As described above, high-temperature water treatment after forming a chromate film by cathodic electrolysis treatment is absolutely necessary to elute F- ions and Cr+6 ions in the film and to promote dehydration and condensation reaction of colloidal Cr+3 hydroxide. The quality of the water in this high-temperature water treatment is important in order to elute and remove F- and Cr+6 from the chromate film in a short time.If the pH is less than 4, the elution of F- and Cr+6 is hindered and This is also undesirable because it re-permeates into the chromate coating from the treated aqueous solution. If the pH exceeds 10, there is a risk of dissolving the chromate film.
is 10 or less. In particular, in consideration of the elution rate, a pH range of 6 to 9 is most preferable, and the pH may be adjusted using ammonium carbonate, soda carbonate, or the like. In addition, if a cathode electrolytic bath is brought in to this high-temperature water, or Cr+6 is eluted from the chromate film,
The amount of anions contained in the treated aqueous solution is Cr+
6107/1, F-3y/l or less, and the pH satisfies the above range.Perhaps because exceeding this range prevents the elution of F- ions and Cr+6 from the chromate film. No longer satisfied with purpose.

Next, important conditions in the treatment of the present invention are the temperature of the water used in the treatment and the treatment time.

The temperature is 65°C to 100°C, preferably 75°C to 95°C.
It is ℃. Processing time should be between 0.3 seconds and 10 seconds. That is, in order to form a chromate film by the method of the present invention in a manner suitable for industrial production (or to form a chromate film in a short period of time, F- ions and Cr+6 from the above-mentioned chromate film)
In order to make the chromate leaching as short as possible, high-temperature treatment is naturally necessary, and in addition to increasing the degree of oxidation of the G chromate film, which is added to these elutions, the chromate film is exposed to a corrosive environment after painting. In some cases, it is absolutely necessary to make it poorly soluble. That is, if the temperature of the treated water is 65°C or less (well, perhaps because the elution of F- ions and Cr+6 is not sufficient within the above treatment time range, and the degree of oxo-ization of the chromate film is not sufficient, the purpose of the present invention is In addition, if the temperature of the treated water exceeds 100°C, it becomes uneconomical, and even if this water vapor comes into contact with the electrolytic chromate treated steel sheet, it is difficult to immediately turn into liquid water, so the chromate coating is removed. It is not preferable to raise the temperature of the treated aqueous solution to 100° C. or higher because the elution effect of water will be lost.

Regarding the processing time, unless the processing time is 0.3 seconds or more, the elution of F- ions from the chromate film and the Cr+
6 is not sufficiently eluted, the degree of oxo-ization of the chromate film is not sufficiently improved, and the desired effect of the present invention cannot be obtained.
In addition, a treatment time of 10 seconds or more is not industrially economical, and components that are easily eluted into the chromate film may be contained due to re-penetration of F-1 anions in the water used or other impurities contained in the water. The treatment time is limited to 10 seconds or less because of the adverse effects caused by the treatment.

The method of applying high-temperature water according to the present invention may be any of immersion treatment, spray treatment, and injection treatment using a mixture of hot water of high-temperature steam and low-temperature aqueous solution, as long as the above-mentioned conditions are satisfied. As described above, according to the steel plate for containers and the method for manufacturing the same of the present invention, the steel plate strip has 0.
A Ni plating layer with a thickness of 0.015 to 0.30 μm is applied to the surface, and a chromate coating with few pinholes and soluble components in the corrosive bath solution, with a high degree of oxation, and a low degree of hydration, in terms of Cr amount. Since the coating has a coating amount of 2 to 25 m/m, its weldability by electric resistance welding is good, and it also has excellent corrosion resistance and corrosion resistance after painting.

Therefore, the steel sheet for containers according to the present invention has suitable performance as a material for can manufacturing, does not cause any trouble even when can manufacturing is performed by electric resistance welding, and is advantageous in terms of cost. Next, examples of the present invention will be described.

A cold-rolled steel sheet for tinplate (temper grade T5) is subjected to conventional plating pretreatment (degreasing, pickling), and then Ni plating is applied using the electroplating method.
The surface was subjected to the cathodic electrolytic treatment and high temperature water treatment of the present invention.

Claims (1)

[Claims] 1 Ni with a thickness of 0.015 to 0.300μ on the surface of the steel plate
After plating, the weight ratio of F^-/Cr^+^6 is 1
/10 or less of chromate, dichromate, or more, by cathodic electrolysis treatment in an aqueous solution of 2 to 25 mg/m^2 of chromate in terms of Cr. A method for manufacturing chromate-coated steel sheets for containers that have excellent weldability and corrosion resistance after painting. 2 Ni with a thickness of 0.015 to 0.300μ on the surface of the steel plate
After plating, the weight ratio of F^-/Cr^+^6 is 1
Immediately after applying a chromate coating in an amount of 2 to 25 mg/m^2 in terms of Cr by cathodic electrolytic treatment in an aqueous solution of one or more of chromate and dichromate with a concentration of less than 10%. Or wash with water and further at a temperature of 65° to 100°C
A method for producing a chromate-coated steel sheet for containers having excellent weldability and corrosion resistance after painting, characterized by treating the steel sheet with high-temperature water having a pH of 4 or more for 0.3 to 10 seconds.