JPH02156096A - Material for very thin welded can having superior seam weldability, adhesion to coating material and corrosion resistant after coating - Google Patents

Abstract

PURPOSE:To obtain a material for a very thin welded can having satisfactory coatability and corrosion resistance after coating by leaving a specified amt. of unalloyed tin on each of both sides of a plated steel sheet of a specified thickness for a can corresponding to the inside and outside of the can and forming a specified amt. each of chromate coating layers. CONSTITUTION:Metallic tin unalloyed after coating and baking is left by 20-2,500mg/m<2> on one side of a plated steel sheet of 0.10-0.18mm thickness for a can corresponding to the inside of the can. Metallic tin unalloyed after coating and baking is left by 50-2,000mg/m<2> on the other side of the steel sheet corresponding to the outside of the can. Both sides of the steel sheet are then coated with chromate by 1-30mg/m<2> each (expressed in terms of Cr). A material for a very thin welded can having satisfactory coatability and corrosion resistance after coating can be obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a sheet with a thickness of 0.10 to 0.18 mm that has a coating structure with excellent seam weldability, paint adhesion, and post-painting corrosion resistance.
This relates to materials for ultra-thin welded cans.

(Prior Art) In recent years, the practical application of seam welding can manufacturing methods represented by the Sudronitsta method has rapidly progressed. This welding can-making method is different from the solder can-making method and the drawing and ironing can-making method, and because it allows cans to be made with a smaller amount of tin plating, the use of Sn-based coated steel sheets (hereinafter referred to as rLTs), which have a smaller amount of plating, has increased. There is.
LTS is used with baking paint applied to the inside and outside of the can to improve corrosion resistance.

Naturally, LTS for welded cans is required to have excellent seam weldability by electric resistance welding. Metallic tin (hereinafter referred to as 'free-5n') remaining after baking the paint is most effective in improving seam weldability, and the greater the amount of free-5n, the better the seam weldability. During paint baking, a portion of the Sn plating layer becomes alloyed with the plated original plate by thermal diffusion, and free-5n decreases, resulting in deterioration of seam weldability. Therefore, efforts are being made to develop materials for welded cans that can sufficiently secure frea-5n after baking the paint and at the same time exhibit good corrosion resistance and coating performance. For example, the following prior art is known.

■ A Nl plating layer of 30 to 1000 mg/a" and a Sn plating layer of 100 to 2000 mg/m2 are provided on the steel plate surface, and the amount of Cr equivalent is 2 with or without heat melting treatment (hereinafter referred to as "reflow treatment"). A method for forming a chromate film of ~20 mg/m' (Japanese Unexamined Patent Publication No. 57-2
No. 3091).

■ Apply Nl plating to a thickness of 0.001 to 0.05 μl1 (approximately 8.9 to 445 mg/m2) on the surface of the steel plate, then heat treat it in a reducing atmosphere to transfer part or all of the Ni plating layer into the steel base. After diffusion and penetration, the thickness is 0.01~
0.2 μm (approximately 73 to 1480 mg/m') Sn plating is removed by a flow treatment, followed by a chromate treatment (Japanese Patent Laid-Open No. 57-200592).

■ Weight ratio of Nl/Nl+Fa-0.02~0 on steel plate
．． Thickness 10-5000 people (approximately 8-4
900mg/+”) Fe-Ni alloy layer from 100 to 10
A method of providing a Sn plating layer of 00 mg/m' and performing reflow treatment to form a chromate treatment layer of 5 to 20 mg/m'' in terms of Cr (Japanese Unexamined Patent Publication No. 17099/1983).

In both of these methods, (a) an old or Ni-Fe alloy layer is provided as an intermediate base layer between the plating original plate and the Sn plating layer, and a uniform and dense Ni-5n-Fe alloy layer is formed by Snn plating soliflow treatment. (b) The formation of these uniform and dense alloy layers causes the Sn plating layer and the original plate to interact with each other during painting baking. The idea was to secure weldability and coating performance by providing a chromate film that improves coating performance by suppressing the heating diffusion reaction of Cr and by maintaining weldability and coating performance with an amount of Cr deposited within a range that does not impair weldability. It is an excellent material for welded cans.

(Problems to be Solved by the Invention) In recent years, with further progress in welding can manufacturing technology and reductions in can manufacturing costs, there has been a demand for thinner original plate materials.

In other words, the current plate thickness is 0.20 to 0.24 mm to 0.10 mm.
There is a need to develop a material for welded cans that is 18 mm thin and has excellent weldability, corrosion resistance, and coating performance.

However, when the above-mentioned known technology is applied to this thin material,
There has been a problem in that the suitable welding range in which sufficient welding strength and good appearance can be obtained is extremely narrow. This is a problem in that the molten metal jumps out before sufficient welding strength can be secured, particularly on the inner surface of the can (hereinafter referred to as "defeat"), resulting in deterioration of corrosion resistance and welding strength after painting.

In order to deal with this problem, the present invention has a plate thickness of 0.10 to 0.
It is an object of the present invention to provide a material for an ultra-thin welded can that has a sufficiently wide suitable welding range when an ultra-thin material of 18+aa+ is used, and exhibits good coating performance and corrosion resistance after coating.

(Means for Solving the Problems) As a result of the inventors' study on the appropriate surface coating composition of materials for welded cans, it was found that when an ultra-thin material with a plate thickness of 0.18111Q1 or less is applied to materials for welded cans, there is no scattering. It has been found that in order to ensure a wide suitable welding range in which sufficient welding strength can be obtained without occurrence of welding, it is necessary to reduce the contact resistance at the weld can material interface and material/material interface as much as possible. In particular, what is important here is that the diameter of the welding pole ring that contacts the inner surface of the can is limited to an extremely smaller diameter size than the diameter of the welding pole wheel that contacts the outer surface of the can due to the shape of the can body. The small diameter of the welding pole ring means that the contact area between the pole ring and the material is small, which restricts the current flow path during welding, and overcurrent during welding can cause splintering. In order to increase the contact area and reduce the contact resistance between materials for cans that are easy to weld, metal tin that is soft and has a low melting point, that is, fr.
It was found that the presence of ee-5n had the greatest effect.
The more free-5n there is, the better the weldability will be, but from an economical point of view, the amount of expensive tin must be reduced as much as possible, since the contact area with the welding pole ring is different between the inside and outside of the can. , each has an appropriate free-5n residual amount.

Furthermore, such fre
To ensure the amount of e-5n and exhibit good corrosion resistance, Nl
It is desirable to perform surface treatment for the system. By performing Ni-based surface treatment, a dense and uniform Ni-Fe-5n alloy layer is generated, which acts as a barrier layer when tin is alloyed during paint baking, and also exhibits excellent corrosion resistance. .

In addition, to ensure good painting performance and corrosion resistance after painting, fr
A chromate film must be provided on ee-5n, but since the chromate film is an insulator and the small amount of metallic chromium present has a high melting point, the chromate film is a negative factor for weldability. Therefore, the amount of chromate film needs to be regulated to the minimum necessary amount to ensure good coating performance and post-coating corrosion resistance.

As a result of detailed studies based on these ideas, the inventors of the present invention have developed a material for ultra-thin welded cans with excellent weldability, paintability, and post-painting corrosion resistance as a material for welded cans with a plate thickness of 0.10 to 0.18n+m. discovered that the material could be obtained.

The present invention has been made based on this knowledge, and its gist is as follows: 1) 200% of unalloyed metallic tin is coated on the surface equivalent to the inner surface of a can plated original plate having a thickness of 0.10 to 0.18 mm after baking the paint. ~2500mg/i'', unalloyed metallic tin after baking on the surface equivalent to the outer surface of the can is 50~2
Material for ultra-thin welded cans with excellent seam weldability, paint adhesion, and post-painting corrosion resistance, with a chromate film layer of 1 to 3 hg/m2 on both the inside and outside surfaces, with a residual amount of 000 mg/m2 2) Steel plate thickness After baking, a Ni-Fe-5n alloy layer or a Fe-5n alloy layer is present on the surface corresponding to the inner surface of a can plating original plate of 0.1θ to 0.18 mm, and on top of that is a Ni-Fe-5n alloy layer or a Fe-5n alloy layer with a thickness of 200 to 200 mm. 2500 mg/m" remained, while Ni-Fe remained on the surface equivalent to the outer surface of the can after baking
-5n alloy layer or Fe-5n alloy layer is present, and unalloyed metallic tin is present on it at 50 to 2000 mg/m
”remains, and furthermore, the amount of chromium attached on both the inside and outside is 1.
This is a material for ultra-thin welded cans that has a chromate coating layer of ~30 mg/m'' and has excellent seam weldability, paint adhesion, and post-painting corrosion resistance.

(For writing) The present invention will be explained in detail below.

In the present invention, as a plating original plate for cans, the plate thickness is 0.10~
A 0.18 mm steel plate is used. There are no particular restrictions on the manufacturing method or material of the plated original plate, and it is manufactured through normal steel billet manufacturing processes such as hot rolling, pickling, cold rolling, annealing, and tempering. Furthermore, this plated original plate is manufactured using a manufacturing process that involves cold rolling, annealing, and re-cold rolling (i.e., 2CR method) depending on the required strength of the can body. A hardness of 65 to 71 is preferable from the viewpoint of flange workability in the process.

In the present invention, in the case of a thin plating plate with a thickness of 0.10 mm and no grooves, a sufficient can body can be obtained by using the pressure of the contents of the can, filling with nitrogen gas, or adding a can bead. It is difficult to ensure stable strength, and the plate thickness is 0.
It is 10 mm or more.

Further, when the plate thickness exceeds 0.18o+m, a welded can with good performance can be manufactured by using known technology. However, if the plate thickness is 0.18 mm or more, it will not be possible to reduce the weight of the can or reduce costs.
In the present invention, a plated original plate having a thickness of 0.111+ni or less is used. The present invention applies appropriate coating treatment to the surface of steel plates having these plate thicknesses, which has excellent weldability, paint adhesion, and paint corrosion resistance.

First, the effects of the coating structure that exhibits good weldability will be described. Weldability is evaluated to be better as the welding range is wider and there is no spatter, and sufficient welding strength is obtained. For this purpose, the amount of free-5n remaining after baking the paint is most effective, and the larger the amount, the better the weldability. The reason for this, that is, the effect of the amount of residual free-5n on weldability, is as follows.

a) Since tin metal is soft, the pressure applied from the pole during welding increases the contact area between poles/materials or between materials, reducing contact resistance and preventing local current concentration during welding. When the welding current is concentrated, local heat generation occurs in that area, causing spatter. In other words, free-5n prevents a loss from occurring.

b) Because tin metal has a low melting point, it easily melts due to the heat generated during welding, which increases the contact area between materials or between materials, reduces contact resistance, and reduces local current concentration during welding. To prevent.

Before the materials for welded cans are welded, the parts other than those corresponding to the welds are painted, and the paint is baked at a temperature of around 200°C for several minutes! ! ! A film is formed. During this coating baking process, a thermal diffusion reaction progresses at the interface between the tin plating layer and the isthmus, and the amount of free-3n decreases, resulting in deterioration of weldability. In other words, in order to ensure good weldability, an important point is how to secure the amount of free-sn that remains after baking the paint and immediately before welding. Especially 0.10
When considering the material design of a welding can material using an extremely thin original plate material of ~0.18 m1 and the minimum amount of Sn plating necessary from an economical point of view, the free-5n remaining after baking the paint dominates the weldability.

What is important here is that due to the shape of the can body, welding that contacts the inner surface of the can is performed inside the can, so its diameter must be smaller than the can diameter; Welding Extreme Theory is not subject to such regulations,
The diameter of the extreme theory can be set arbitrarily. In other words, the extreme diameter that contacts the inner surface of the can is regulated to be extremely smaller than the extreme diameter that contacts the outer surface of the can. The small diameter of the pole means that the contact area between the pole and the material is small, which restricts the current flow path during welding, and a local overcurrent flows during welding. Splashing that occurs during welding is directly caused by local heat generation caused by such overcurrent.

In particular, when making welded cans by electric resistance welding using ultra-thin steel plates of 0.10 to 0.18 mm as in the present invention, the small-diameter electrode on the inner side and the material surface are closer to each other than the surface corresponding to the outer surface. It is necessary to reduce the interfacial contact resistance and ensure a wide conduction path.

In other words, the welding current required to form a weld nugget at the interface of the steel plates where materials are overlapped in the welding process is:
The load is applied according to the total resistance including material/electrode contact resistance, material/material contact resistance and material resistance. This welding current is within an appropriate welding range that provides sufficient welding strength and at the same time does not cause damage to the formed weld nuggets.

This applied welding current provides the necessary amount of heat to form a weld nugget at the material/material interface, but when the material is an ultra-thin steel plate, the material surface is There is a problem in that it is extremely difficult to cool down. In particular, since the inner surface of the can has a smaller diameter, the amount of heat radiated by heat transfer to the inner surface of the can is smaller than that on the outer surface of the can, and the temperature of the material surface on the inner surface of the can tends to be higher than that on the outer surface of the can. As a result, the temperature of the material surface increases during welding, so when the material plate is thin, the contact resistance at the material interface increases,
Since a current higher than the welding current required to generate a weld nugget at the material/material interface is supplied, more spatter is generated than at the nugget, resulting in weld defects.

Therefore, when an ultra-thin steel plate with a thickness of 0.10 to 0.18 mm is used as a material for welded cans, it is necessary to have a coating structure that can reduce the contact resistance between the can inner surface and the weld polar axis interface. . As a result of various studies from these points of view, it is important to create a coating structure in which a large amount of soft, low-melting point free-5n can remain on the surface of the material corresponding to the inner surface of the can after the coating is baked.

By retaining a large amount of free-5n, a large contact area with the small-diameter electrode can be secured, and furthermore, even if the temperature of the material surface increases, the conductivity in the thickness direction of the material increases, so it is It is not necessary to supply a current higher than the current required for the nugget formation to be generated. To obtain this effect, the free-5n should be 200 to 2500 mg/m2 after baking the welded can material on the surface equivalent to the inside of the can, and the outside surface of the can. free-5n is 50 ~ after painting and baking on the corresponding surface
2,000 rng/m” remains.

The amount of free-5n remaining on the surface equivalent to the inner surface of the can is 2001
! In the case of 1 g/l112 without grooves, the contact resistance at the material/polar axis interface is high and good weldability cannot be ensured. Moreover, from the viewpoint of corrosion resistance, a small residual amount of free-5n means that the sacrificial anticorrosion effect decreases and the corrosion resistance deteriorates. On the other hand, when the free-5n residual amount exceeds 2500 mg/m2, the contact resistance at the material/polar axis interface is sufficiently reduced and good weldability can be ensured. Furthermore, sufficiently good corrosion resistance performance is ensured. However, when the amount of free-Sn remaining increases, the effect of reducing contact resistance and the effect of improving corrosion resistance become saturated, and the coating film hardness after painting is also soft, making it easy to be scratched during can manufacturing, so that corrosion resistance also deteriorates. As described above, an appropriate residual amount of free-5n that exhibits particularly good weldability on the inner surface of the can and does not cause deterioration of coating hardness is 200 to 25 QOmg/m''.

Next, since the extreme diameter on the surface equivalent to the outer surface of the can is larger than the extreme diameter on the inner surface, a large amount of free-5n residual is not required on the inner surface of the can. However, the residual amount of free-5n is 50
If it is less than 11 g/112, the contact resistance at the material/polar axis interface is large, and expulsion is likely to occur due to local heat generation, resulting in deterioration of weldability. Furthermore, from the perspective of rust resistance, free-
When the residual amount of free-5n decreases, the exposed area of the base metal increases, which is undesirable.On the other hand, when the residual amount of free-5n decreases
If it exceeds 0hg/a'', good weldability and rust resistance can be ensured, but the effects are saturated and there is no economic advantage.

Therefore, the appropriate amount of free-5n remaining on the outer surface of the can is 50 to 200 hg/m''.

As described above, the amount of tree-5n remaining after baking the paint has the greatest influence on the material for welded cans, which is extremely thin and exhibits good weldability. However, from the viewpoint of corrosion resistance, rust resistance, and economical aspects, it is desirable to perform appropriate surface treatment to ensure the amount of free-5n remaining after baking the paint with as little tin plating as possible.

Next, this appropriate base treatment will be explained in detail.

As an appropriate base treatment for the tin plating layer, Ni-Fe-5n
Ni-Fe with alloy layer or Fe-5n alloy layer applied
-5n alloy undercoating is particularly effective in providing good performance in areas where the amount of tin plating is low. Although it is preferable to perform Nf-Fe-5n alloy undercoating even in areas where there is a large amount of tin plating, there is not a very large difference in practical terms. Since no significant effect was observed in forming the alloy layer, Sn plating was applied directly to the plated original plate, and the Fa
-5n alloy layer is formed. In areas with a large amount of Sn plating, even the Fe-5n alloy layer is free-5n after baking the paint.
remains, ensuring good weldability, corrosion resistance,
Rust resistance is also good.

However, from an economic point of view, it is necessary to ensure good weldability, corrosion resistance, and rust resistance with as little tin plating as possible to save expensive tin.
Surface treatment of e-5n alloy is important.

These are three points for the purpose of providing a Ni-Fe-5n alloy layer as a base treatment for a tin plating layer.

■ Applying the Ni-Fe-5n alloy base treatment has the effect of suppressing heat diffusion between the tin plating layer and the base plate during paint baking, compared to the case where the Ni-Fe-5n alloy base treatment is not applied. , there is a large amount of unalloyed free-5n remaining.

As a result, since more free-5n, which is soft and has a low melting point, is present, the contact resistance at the material/extreme interface is reduced, making it easy to ensure good weldability. Furthermore, when the same amount of tin plating is applied, if the amount of free-5n remaining is large, the softness of the tin metal makes it easier to make cans, and excellent rust resistance can be obtained in the processed parts.

■ Since the Ni-Fe-5n alloy layer is more uniform and dense than the Fe-5n alloy layer, the elution rate of the tin plating layer in the can contents is reduced, and for the same -free-Sn residual amount, When the Ni-Fe-5n alloy base treatment is applied, the sacrificial anticorrosion ability of tin metal is maintained for a long time, and the life of the can is extended. Furthermore, even if a defect occurs in the tin plating layer or paint film in the content that does not have sacrificial corrosion protection, or if a defect occurs in the tin plating layer or paint film on the outer surface, it will prevent the elution of iron. Improves corrosion resistance and rust resistance.

(2) The Ni-Fe-5n alloy layer is relatively hard. Therefore, the paint film is prevented from being scratched during can manufacturing or transportation of the can body, and even if scratches occur, the presence of the hard Ni-Fe-5n alloy layer prevents the scratches from reaching the steel base. It is difficult to stick to and improves corrosion and rust resistance after coating.

Although the method for forming an appropriate Ni-Fe-5n alloy layer having such effects is not particularly limited in the present invention, it is preferable to form it by the following method.

■ By electroplating, the old plating and Ni-
Fe alloy plating or Ni-5n alloy plating is applied,
The upper layer is tin-plated to obtain the coating structure of the present invention, and a Ni-Fe-5n alloy layer is formed by performing reflow treatment, or by using heat treatment during paint baking to form a Ni-Fe-5n alloy layer. Method of forming an alloy layer ■ Apply Ni plating, Ni-Fe alloy plating, or Ni-5n alloy plating to the surface of a steel plate by electroplating, then perform a diffusion treatment in a reducing atmosphere, and then add tin on top. Plating and reflow treatment to form a Ni-Fe-5n alloy layer, or heat treatment during coating baking to form a Ni-Fe-5n alloy layer.
A method such as forming an i-Fe-5n alloy layer is adopted.

In particular, when performing reflow treatment to form a Ni-Fe-5n alloy layer after providing a Ni-based base treatment layer and a tin plating layer, flux treatment is performed on the surface of the tin plating layer, and then tin metal 235-350℃ just above the melting point (232℃)
It is easily formed by heating and melting for about 1 to 10 seconds at a temperature range of . Furthermore, the appearance after reflow treatment is affected by the type of flux. To obtain an appearance with metallic luster, use a uniformly diluted solution of the tin plating bath as the flux, and to obtain a white matte appearance, use tap water, distilled water, or a tin plating bath at one time.
A solution diluted to 71O or less may be used.

When using a steel plate with a thickness of 0.10 to 1.18 mm as in the present invention, it is preferable to use an original plate manufactured by the 2CR method as described above in order to ensure can strength. Therefore, Since the Ni-based base treatment layer may be destroyed by the cold rolling of the annealing diffusion treatment, it is preferable as the base treatment to perform the plating treatment after 2CR rolling rather than the diffusion treatment method.

Furthermore, the thickness of the Ni-Fe-5n alloy layer depends on the temperature during reflow treatment, heating time, and the compositional plating amount of Nf plating, Ni-Fe alloy plating, and Nf-5n alloy plating layer applied as base treatment. , each can be adjusted arbitrarily. In addition, if reflow treatment is not performed, the heating conditions for paint baking are determined by the paint used, but the composition and amount of adhesion of the base treatment layer determines the Ni-F
The e-5n alloy layer can be adjusted arbitrarily.

The coating amount of the Nt4a-5n alloy layer is not particularly restricted, but in order to reduce pinholes in the alloy layer, form a dense alloy layer, and ensure good performance, it is 250 mg.
/m” or more, and hard Ni-Fe during can manufacturing.
In order to prevent cracks from occurring in the -Sn alloy layer and reaching the upper free-5n layer or the coating surface, it is desirable that the amount is 1000 mg/m' or less.

A Fe-Sn alloy layer is formed in areas with a large amount of Sn plating, but since the Fe-Sn alloy layer is coarser than the Ni-Fe-Sn alloy layer, the coating amount must be limited to ensure good performance. 400mg/m2 or more, and 1400m to prevent cranking during can manufacturing and to prevent deterioration of corrosion resistance.
A coating amount of less than g/+" is desirable.

Subsequently, the tin-plated layer of the steel plate with such a coating layer is subjected to chromate treatment for the purpose of improving paint adhesion and paint corrosion resistance. Prevents undercutting corrosion, which occurs when the paint passes through and progresses under the paint film, and improves the rust resistance of filamentous rust that occurs under the paint film during storage on the outside of the can, such as so-called filiform corrosion B. is very effective.

By forming such a romate film, the adhesion of the coating does not deteriorate over a long period of time, and good corrosion resistance and rust resistance are maintained.

In addition, the chromate film is highly effective in preventing blackening, that is, sulfide blackening, on the surface of steel sheets that occurs when foods containing sulfur compounds, such as fish meat and livestock products, are used. When used, it is highly effective in improving performance, but it is a negative factor in weldability. The chromate coating referred to here refers to two cases: one is a single coating of hydrated chromium oxide, that is, the original chromate coating, and the other is a coating consisting of two layers: a metallic chromium layer on the bottom layer and a hydrated chromium oxide layer on the top layer. pointing. Since the hydrated chromium oxide film is an electrical insulator, it has very high electrical resistance, and metallic chromium also has a high melting point and high electrical resistance, both of which are negative factors that deteriorate weldability.

Therefore, it is very important to have good coating performance and an appropriate amount of chromium that does not deteriorate practical weldability.In the present invention, the amount of chromium deposited is preferably 1 to 30 mg/m per side in terms of metallic chromium. is 5-2011g/l
It is 112.

That is, if the amount of chromium deposited is less than 1 tag/+2, it will not be effective in improving paint adhesion or preventing corrosion under the paint film such as undercutting corrosion.
It is desirable that the amount of chromium deposited is 30 g/m” or more.
If it exceeds "g/m", the contact resistance will increase significantly, failure will likely occur due to local heat generation, and weldability will deteriorate.

Therefore, the amount of chromium deposited is 30 mg/m2 or less, preferably 20 mg/m2 or less.

The chromate treatment may be carried out by any method such as immersion treatment with aqueous solutions of various sodium salts, potassium salts, and ammonium salts of chromic acid, spray treatment, electrolytic treatment, etc., but cathodic electrolytic treatment is particularly excellent. In particular, chromic acid contains so, "- ions, F- ions (including complex ions)
Alternatively, cathodic electrolytic treatment in an aqueous solution to which a mixture thereof is added is most excellent. The concentration of chromic acid is not particularly limited, but a range of 20 to 200 gin is sufficient.

The amount of anion added is 17300 to 1/25 of Cr”
Preferably, the best chromate coating is obtained between 17,200 and 175G. The amount of anion is 1/300 of Cr”
If it is less than 1725, it will not be possible to obtain a high-quality chromate film that is homogeneous and uniform and will greatly affect coating performance, and if it is more than 1725, the amount of anions incorporated into the formed chromate film will be large, which will affect coating performance, especially secondary paint adhesion. Sexuality deteriorates. The anions to be added are added to the chromic acid bath in the form of compounds such as sulfuric acid, chromium sulfate, ammonium fluoride, and sodium fluoride.

Although the bath temperature is not particularly limited, a range of 30 to 70°C is an appropriate temperature range from the viewpoint of workability. A cathode electrolytic current density of 5 to 100 A/dm' is sufficient.

The treatment time is set so that the amount of chromium deposited falls within the range of 1 to 30 mg/m'' shown above under any combination of the treatment conditions.

In particular, in the present invention, so4"- or F- ions are added to the chromic acid aqueous solution in the above range, and the current density is 50 to 100 A.
It is preferable to perform short-time processing of 0.2 sec or less at /dm'. Through this treatment, 55% of metallic chromium is deposited on the tin plating layer.
~15mg/m" is precipitated, and a two-layer chromate film consisting of a hydrated chromium oxide layer is formed on the upper layer. This hydrated chromium oxide layer can be formed by adjusting the immersion time in the aqueous solution after electrolytic treatment or by The coating amount is adjusted by dissolution treatment in chromic acid-anion treatment baths having different concentrations in a treatment tank provided.

By uniformly coating the surface of the tin-plated layer with this metallic chromium layer, the coating performance is significantly improved.In particular, the coating performance is further improved when reflow treatment is performed after tin plating and these chromate treatments are applied. When used as a material for containers, the metal chromium layer is exposed to corrosive environments containing aqueous solutions of organic acids such as citric acid. The effect of inhibiting the aqueous corrosive solution from reaching the tin metal surface is remarkable.

The ratio of the metal chromium layer to the hydrated chromium oxide layer in the two-layer chromate coating is 0.
The range of 6≦hydrated chromium oxide/metallic chromium≦3 is preferable, that is, if the amount of hydrated chromium oxide is small relative to metal chromium, the uniform coverage of the hydrated chromium oxide layer on the metal chromium layer will be poor. , paint adhesion tends to deteriorate. On the other hand, if the hydrated chromium oxide layer is larger than the metal chromium layer, the anions and Cr ions contained in the hydrated chromium oxide layer will increase, and these ions will elute when exposed to a high temperature environment after painting. This is undesirable because minute blisters (so-called blisters) are likely to rust under the paint film.Therefore, it is preferable to set the composition ratio of hydrated chromium oxide to metallic chromium in the range of 0.6 to 3 as described above. .

[Example] Examples of the present invention will be described below, and the results are shown in Table 1.

The plated original plate, which has been adjusted to a specified thickness by cold rolling or rolling twice after annealing, is electrolytically degreased in 5% caustic soda, washed with water, electrolytically pickled in 10% sulfuric acid, and after surface activation, the base plate is prepared as necessary. processed. ■- When performing surface treatment
Ni plating under the conditions shown in (a), (0), and (8), respectively.
Ni-Fe alloy plating and Nf-5n alloy plating were performed. In addition, heat diffusion treatment is performed after cold rolling ■-(A), (B), (
After various surface treatments were performed under the conditions shown in 8), thermal diffusion treatment was performed under the annealing conditions shown in ①-(d).

After various surface treatments, tin plating was performed under the conditions shown in (2), followed by reflow treatment if necessary. And ■-
A chromate film was produced using the treatment baths shown in (1) to (0).

■Various base treatment conditions (a) Ni plating base treatment plating bath composition NiSO4/6H2ONiC text 2/6
Day 20 H, BO.

Plating bath temperature 50℃ 250g / 50g / vertical 25g / alternating current density 1 to 20A / d+a'' (Electrolysis time is adjusted according to the amount of Ni plating) (b) Ni-Fe alloy plating base treatment Plating bath composition NiSO4 6H2O N*C9t・66H2 O75/1 140 gel FeSO4・7Hz0 70-170g/fi (changed according to alloy composition) H, BO.

(8) (Ni-5n) Alloy plating base treatment Plating bath composition Snr: 1x NIC 2/6H2O N) 1. HF2 plating bath temperature 50℃ 40g/50g/1 300g/55g/1 Flow density 2~30^/dm" (Electrolysis time is adjusted according to the amount of Ni-5n alloy plating) (:) Heat diffusion conditions Various bases After treatment, heat diffusion treatment was performed under the conditions shown in the figure.

Annealing temperature Annealing time Gas atmosphere '550-700℃ 20-80sec 2-8% hydrogen + 92-98% nitrogen + inevitable impurities ■Tin plating conditions Plating bath composition Tin sulfate additive Plating bath temperature 50℃ Current density 15-25＾ /d112 ■Chromate treatment bath ■Crys 100g/1 so4'-o, 6g/cross ■Na2Cr20y 24g/l pH4,5 Q Crys 80g/1 504'-o, osg/also NazSfFa 2. Sg/l NH4F 0.5g/12 The above treated materials are shown below (^) ~ ()I)20
-30g/1 1 to 5g/2 items were carried out and the performance was evaluated.

(A) Measurement of contact resistance The contact resistance value, which has a large effect on seam weldability, was measured using a spot welder with a CF type electrode. The test piece for measurement is 205℃ x 10m1n, assuming paint baking.
Baking was performed three times, and the test piece was set so that the inner and outer sides of the can were in contact at the material/material interface.

The method for measuring static resistance using a CF type electrode is shown below. The electrode used is made of chromium copper and has a tip diameter of 4.5 mm.

Two test pieces were placed between the electrodes, and a low current of IA was applied between the electrodes under a pressurized state of 200 kgf using an air cylinder.
The cold static resistance was determined by measuring the voltage drop between the steel plates with a nanovoltmeter.

CB) Seam weldability test piece was prepared at 205℃ x 10m1 assuming paint burning.
Baking was performed three times, and seam weldability was evaluated under the following welding conditions.

Welding was performed by changing the current under the conditions of lap thickness 0.5a+m, pressurizing force 45kgf, and welding speed 420 cans/win, and the minimum current value and "splash" that can obtain sufficient welding strength were determined.
The evaluation was made comprehensively based on the width of the appropriate current range, which is the maximum current value at which welding defects begin to become noticeable, and the situation in which welding defects occur.

(C) Paint film hardness test In order to evaluate the extent of scratches on the paint film on the outer surface of the can, clear lacquer was applied at 40 ffig/dm2 on the surface corresponding to the outer surface of the can, and dried and cured at 180 t x 10 m1n.

Subsequently, after adjusting the tip of pencil lead of various hardness to be flat, press it against the test piece at an angle of 45°, and hold it for 50 m.
A scratch test with a length of m was conducted.

(D) Base grain test Apply 55 mg/di' of epoxy phenol paint to the surface corresponding to the inner surface of the can of the test piece, and heat at 205°C x lomin.
Dry and harden. Further, a clear lacquer corresponding to the outer surface of the can was applied at a rate of 40 mg/dm2, and dried and cured at 180°C x lomin. Subsequently, scratches were made on each surface at 1 mm intervals to create a total of 100 base marks, and the tape was immediately peeled off, and the peeling status was evaluated.

(E) UCC (Undercutting Corrosion) Evaluation Test In order to evaluate the corrosion resistance after painting on the surface corresponding to the inner surface of the can, epoxy phenol for cans (phenol rich) was applied to the surface corresponding to the inner surface of the can! ! ! The material was applied at 50 mg/da2 per side, and baked at 205°C x 10ml, followed by dry baking at 180°C x 20ml. after that,
Make a scratch to reach the iron surface of the painted board, 1.5
% citric acid and 1.5% common salt in a test solution at 55° C. for 4 days in the open atmosphere. After the test was completed, the scratched area and flat area were immediately peeled off with tape, and the peeling status of the paint film near the scratched area, the pitting status of the scratch area, and the peeling status of the paint film on the flat area were determined and comprehensively evaluated.

(F) Apply the same coating as in (E) to the inner surface of the sulfurization-resistant blackening test can.
The test piece obtained by bending No. 1 was placed in a commercially available homogenized mackerel boiled in water, and subjected to retort treatment at 115° C. x 90 ml. After the test, the sulfide blackening status of the bent and flat parts was evaluated.

(G) Filiform corrosion test In order to evaluate the filiform rust on the surface corresponding to the outer surface of the can, 40 mg/dl12 of clear lacquer was applied and heated at 180℃
Qlin dry cured. Next, make a scratch that reaches the steel surface with a knife, spray with 5% salt water at 35℃ for 1 hour, immediately wash with water and dry, then dry at 25℃ and 85% relative humidity.
After being left for a week, the filamentous rust resistance was evaluated.

(H) Apply 55mg/dm' of epoxy phenol paint to the surface corresponding to the inner surface of the actual can test specimen, and apply it at 205℃ x 10mfn.
Dry and harden. Furthermore, clear lacquer was applied to the surface corresponding to the outer surface of the can at 40B/dm"i, and the temperature was 180℃ x 10m1.
It was dried and cured. Next, a can body was manufactured using a seam welding machine, the welded part was repaired with PVC sol resin, and after filling with orange juice and cola, a #25 tin can lid was wrapped around it and stored at 38℃ for 12 months. did. After the test, the contents were taken out and the amount of iron eluted and the corrosion status of the inner surface of the can (flat parts and welded parts) were observed and evaluated.

[Effects of the Invention] The present invention advantageously provides a material for ultra-thin welded cans that uses ultra-thin steel plates, has a sufficiently wide suitable welding range, and exhibits good painting performance and corrosion resistance after painting. This shows a remarkable effect.

4 others

Claims (1)

[Scope of Claims] 1. After baking the coating on the surface equivalent to the can inner surface of a plated original sheet for cans with a steel plate thickness of 0.10 to 0.18 mm, 200 to 2500 mg/m^2 of unalloyed metallic tin is added to the surface equivalent to the outer surface of the can. 50 to 200 unalloyed metal tin after painting baking
A pole with excellent seam weldability, paint adhesion, and post-painting corrosion resistance, with a chromate coating layer of 1 to 30 mg/m^2 in chromium equivalent on both the inner and outer surfaces, with a residual chromate content of 0 mg/m^2. Material for thin welded cans. 2. A Ni-Fe-Sn alloy layer or a Fe-Sn alloy layer is present on the surface corresponding to the inner surface of the can of a steel plate plate with a thickness of 0.10 to 0.18 mm after baking, and unalloyed metallic tin is present on the surface of the plated sheet for cans with a thickness of 0.10 to 0.18 mm. 200 to 2500 mg/m^2 remained, while Ni-Fe remained on the surface equivalent to the outer surface of the can after baking the paint.
- Sn alloy layer or Fe-Sn alloy layer is present, and unalloyed metallic tin is present on it at 50 to 2000 mg/m
An ultra-thin weld with excellent seam weldability, paint adhesion, and post-painting corrosion resistance, with a chromate coating layer on both the inner and outer surfaces with a chromate coating amount of 1 to 30 mg/m^2. Materials for cans.