JPH09209171A - Laminated steel sheet for welding cans with excellent corrosion resistance, weldability, and laminate adhesion - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a laminated steel sheet for a welding can, which is excellent in laminate adhesion, high-speed weldability and corrosion resistance and can be manufactured at a relatively low cost. Kind Code: A1 A chemical conversion treatment layer having a granular tin portion dispersedly formed on a steel sheet surface without being subjected to molten tin treatment, and a metal chromium layer and a hydrated chromium oxide layer having a predetermined adhesion amount on an upper layer thereof. And further has a laminate film layer on the upper layer thereof, the granular tin portion is composed of a tin-iron alloy on the lower layer side and metallic tin on the upper layer side, and each of the granular tin portions has a number of 90% or more. The maximum thickness of the granular tin part is 0.8 μm or less, and the maximum thickness of the metallic tin on the upper layer side is 0.2 to 0.7 μm. 50% of the granular tin part satisfying these thicknesses is separated. The average particle size is 0.3 μm or more and less than 1.5 μm, and the coverage ratio of the steel plate surface of the granular tin portion satisfying the above thickness is 10% or more, and the coverage ratio of the steel plate surface not covered by the granular tin portion is 60%. That is all.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated steel sheet used as a material for a laminated welding can suitable for filling and storing various foods, beverages and the like.

[0002]

2. Description of the Related Art Conventionally, cans used for various foods and beverages have been coated with an epoxyphenol-based paint or the like in order to ensure corrosion resistance on the inside and outside of the can and aesthetic appearance on the outside. However, in recent years, a can laminated with a film of polyethylene terephthalate (PET) or the like has been developed and rapidly spread in view of a problem of environmental pollution due to an organic solvent discharged in a painting process and a need for improving corrosion resistance of contents. By the way, among laminated cans used for beverages and the like, a material (plated steel plate) used for a three-piece welded can for forming a can body by welding is required to have a plurality of performances such as weldability and laminate adhesion. . Further, recently, there is a strong need for cost reduction of cans, and the materials used for these cans are beginning to be required to undergo strong processing such as neck-in processing for the purpose of thinning gauges and reducing the amount of lids used.

However, the thin gauge material has a drawback that a welding defect is apt to occur due to excessive heat unless the fluctuation of the heat generation amount at the time of welding is sufficiently reduced. Therefore, in order to make the material thin, the weldability of the material itself is required. It needs to be improved more than ever before. Further, in order to perform the strong processing required to reduce the amount of the lid used, it is necessary to improve the adhesion between the material and the laminated film, since high adhesion of the laminated film is required in the material processing part. However, regarding the adhesion to the material, the laminated film behaves differently from the conventionally used epoxyphenol-based paint. This is because the laminated film has a high internal stress because it is thicker than the coating film, and the organic resin component of the adhesive portion is completely different from that of the paint.
Therefore, the optimum film structure on the material side suitable for lamination is also different from that of the epoxyphenol-based paint that has been used conventionally. Generally, the adhesiveness of the laminated film is inferior to that of the epoxyphenol-based paint, so that the surface-treated steel sheet is required to have high adhesiveness.

Conventionally, the following types of surface-treated steel plates for welding cans have been known. (a) A steel sheet in which a steel sheet is coated with a chromium plating layer and a hydrated chromium oxide layer, the chrome plating layer having a granular or discontinuous form, or a chromium hydrated oxide that is an electrically insulating layer. By thinning the material layer, a surface-treated steel sheet having improved weldability by reducing electric resistance during welding (JP-A-62-20529, JP-A-62-9)
9497, JP-A-63-35797, JP-A-62-63678, JP-A-61-281899.
(Japanese Patent Laid-Open No. 61-213399) (b) A tin-iron alloy layer formed by a molten tin treatment below the chemical conversion treatment layer consisting of a chromium plating layer and a chromium hydrate oxide layer. Alternatively, a surface-treated steel sheet having improved weldability by providing a plating layer formed of a tin-iron-nickel alloy layer and a continuous (flat plate) or discontinuous (or island-shaped) metal tin layer above it (special characteristics (Japanese Patent Publication No. 61-36595, Japanese Patent Publication No. 1-54437)

(C) By providing a granular metal tin layer discontinuously on the surface of a steel sheet without performing molten tin treatment, and by providing a chromium plating layer and a chromium hydrate oxide layer on top of it, tin at the time of paint baking is formed. Steel plate with suppressed alloying and improved weldability (Japanese Patent Laid-Open No. 60-67677) (d) The surface of the steel plate is plated with nickel, iron-nickel alloy or tin-iron alloy. Weldability, lubricity, paint adhesion by discontinuously providing a granular metal tin layer on the upper layer without performing molten tin treatment and further providing a chromium plating layer and a chromium hydrate oxide layer on the upper layer. Improved surface-treated steel sheet (JP-A-4-128387, JP-A-4-247897, JP-A-6-293)
(Publication 996)

However, when the surface-treated steel sheets of (a) to (d) above are applied to a laminated welding can, there are the following problems. First, the surface-treated steel sheet (a) is not suitable for high-speed can-making, which has high productivity in recent years, although it has excellent laminate adhesion but has poor high-speed weldability. In the surface-treated steel sheet of (b), the amount of chromium deposited in the chemical conversion treatment layer is 30 mg.
If it exceeds / m ² , there is a drawback that high-speed weldability becomes insufficient. Also, the amount of chromium deposited on the chemical conversion treatment layer is 30 m.
Even when it is less than g / m ² , when the lower layer side of the chemical conversion treatment layer is a continuous metal tin layer, the tin oxide formed on the surface layer of the metal tin layer hinders the adhesion of the laminate. Sufficient laminating adhesion cannot be obtained when performing strong processing such that the peripheral length in the vicinity of the can lid portion is reduced by 15% or more relative to the peripheral length of the can body in the processing. When the lower layer of the chemical conversion treatment layer is a discontinuous metal tin layer, the high melting point tin-
The iron alloy layer or the tin-iron-nickel alloy layer is thickly present. Therefore, in parts other than the metal tin layer, the chemical conversion treatment layer is formed on the high-melting-point thick alloy layer, so good laminate adhesion is obtained, but when the chromium adhesion amount of the chemical conversion treatment layer is small. However, the high speed weldability is inferior. On the other hand, if the metal tin coverage is increased to improve the high speed weldability, the laminate adhesion will be poor. Therefore, with this coating structure, it is difficult to achieve both high-speed weldability and high laminate adhesion.

The surface-treated steel sheet (c) is considered to be advantageous in terms of weldability and laminate adhesion because it has a granular metal tin layer formed without being subjected to molten tin treatment, but the disclosed film is disclosed. In terms of structure, it is not possible to obtain excellent high-speed weldability and laminate adhesion when applied to laminated welded cans, and in particular, it is inferior in high-speed weldability when the material is thin gauge and laminate adhesion during heavy processing. . In addition, the portion other than the granular metal tin layer has a coating structure in which the chemical conversion treatment layer is directly provided on the steel plate surface, and therefore, there is a drawback that the corrosion resistance of the plate end surface is poor. The surface-treated steel sheet of (d) is considered to be advantageous for laminate adhesion in that it has a granular metal tin layer formed without performing molten tin treatment. Laminate adhesion is not sufficient. In addition, since this surface-treated steel sheet is coated with an alloy layer on the surface of the steel sheet, it is considered to be excellent in rust resistance of the plate edge surface, etc. Since it has not been performed and the amount of chromium deposited on the chemical conversion treatment layer is very large, excellent high-speed weldability cannot be expected. Further, the surface-treated steel sheet plated with expensive nickel has the drawbacks that the number of plating steps increases and the coating cost also increases.

As described above, at present, it has excellent laminate adhesion, high-speed weldability, and corrosion resistance, which can cope with strong processing for the purpose of thinning the can material and reducing the amount of lid used. Laminated steel sheets for welding cans are not known. Therefore, an object of the present invention is to provide a laminated steel sheet for welding cans which has the above-mentioned various properties and can be manufactured at a relatively low cost.

[0009]

[Means for Solving the Problems] The inventors of the present invention have been excellent in laminate adhesion, high-speed weldability and corrosion resistance, and have made it possible to perform strong working for the purpose of thinning the can material and reducing the cost of the lid. We investigated the film structure of a laminated steel sheet for welding cans, and as a result, by combining a specific tin plating adhesion structure and coverage with a chromate layer and laminate film layer, high-speed weldability as a material for welding cans It was found that the laminate adhesion and the corrosion resistance can be remarkably improved while ensuring the above. The present invention has been made on the basis of such knowledge, and the characteristic configuration is as follows.

[1] At least one surface of the steel sheet has a granular tin portion formed without being subjected to molten tin treatment and dispersed on the steel sheet surface. The granular tin portion has an upper portion and the granular tin portion. A laminate having a chemical conversion treatment layer consisting of a metal chromium layer and a chromium hydrate oxide layer thereabove on the uncoated steel plate surface, and further covering at least a part of the chemical conversion treatment layer on the upper part of the chemical conversion treatment layer. A laminated steel sheet having a film layer, wherein the granular tin portion is composed of a tin-iron alloy on the lower layer side and metallic tin on the upper layer side, and 90% or more of each of the granular tin portions has a granular tin portion, Maximum thickness is 0.8 μm
Hereinafter, the thickness of the maximum thickness portion of the metal tin constituting the upper layer side is 0.2 to 0.7 μm, and the 50% separated average particle diameter of the granular tin portion satisfying the thickness of these maximum thickness portions is 0. 0.3 μm
The area ratio of the steel sheet surface not covered by the granular tin portion is 10% or more, and the area ratio of the steel sheet surface is not less than 1.5 μm and satisfies the thickness of the maximum thickness portion. 60% or more, the chemical conversion treatment layer, the chromium adhesion amount of the metal chromium layer is 5 mg / m ² or more, the chromium adhesion amount of the chromium hydrated oxide layer is 5 mg in terms of metal chromium.
/ M ² or more and less than 15 mg / m ² , and the total amount of chromium deposited on the metallic chromium layer and the chromium hydrate oxide layer is 1 in terms of metallic chromium.
Laminated steel sheet for welding cans having an excellent corrosion resistance, weldability and laminate adhesion, which is 0 to 30 mg / m ² .

[2] In the laminated steel sheet of [1] above,
The thickness of the tin-iron alloy forming the lower layer side of the granular tin portion is 0.0
A laminated steel sheet for welding cans having a corrosion resistance of 1 μm or more, excellent weldability and laminate adhesion. [3] The laminated steel sheet for a welding can according to the above [1] or [2], which has a chromium adhesion amount of 10 mg / m ² or more in the metal chromium layer and is excellent in corrosion resistance, weldability and laminate adhesion. [4] In the laminated steel sheet according to the above [1], [2] or [3], the laminate film layer has an adhesive layer and a biaxially stretched polyethylene terephthalate film layer from the lower layer side to improve corrosion resistance, weldability and laminate adhesion. Excellent laminated steel sheet for welding cans.

[5] In the laminated steel sheet according to the above [4],
A laminated steel sheet for a welding can having excellent corrosion resistance, weldability and laminate adhesion, in which the adhesive constituting the adhesive layer is a thermosetting epoxy resin adhesive. [6] In the laminated steel sheet according to the above [1], [2] or [3], the laminate film layer is a biaxially stretched polyethylene terephthalate film having at least one layer in which isophthalic acid is copolymerized on at least the surface to be adhered to the steel sheet. A laminated steel sheet for welding cans, which is made of a film and has excellent corrosion resistance, weldability, and laminate adhesion.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION High-speed weldability is required for materials for welding cans for beverage cans and food cans. However, when the welding speed is 80 m / min or more at the wire supply speed, the amount of heat input per unit area becomes high, so that melting defects called jetting due to the ejection of molten metal are likely to occur. Especially, plate thickness 0.19m
In the case of a thin gauge material of less than m, welding defects such as spatter and holes due to excessive heat generation due to heat input fluctuation are likely to occur. In order to solve such a problem, it is conventionally important to reduce the contact resistance between the material and the welding electrode in order to secure high-speed weldability. Therefore, the presence of metal tin, which is a low melting point metal, is effective. Under the premise, measures have been taken to ensure the necessary weldability by adjusting the amount of metallic tin.

However, in the case of a laminated welded can, there is a problem that when the amount of metallic tin increases, the tin coating area increases and sufficient laminating strength cannot be obtained. Therefore, only by applying the mosaic structure (tin plating deposition structure having a granular or discontinuous metal tin layer) composed of the alloy layer-metal tin layer or the steel plate surface-metal tin layer that has been conventionally adopted, the surface for a laminated welding can can be applied. It is not possible to satisfy both the high-speed weldability and the laminate adhesion required for a treated steel sheet, particularly a thin gauge material having a sheet thickness of less than 0.19 mm. Based on such a current situation, the present inventors presume a tin layer in which a part of tin is projected in a granular shape, or a tin plating adhesion structure in which tin is dispersed in a granular shape and adhered to the steel plate surface, in the vicinity of the can lid portion. Includes laminate adhesion and plate thickness of less than 0.19 mm that can withstand neck-in processing that reduces the perimeter of the can by 15% or more than the perimeter of the can body (hereinafter, this reduction rate is referred to as "processing rate"). We investigated and investigated the coating structure that is compatible with the high-speed weldability of steel sheets of various thicknesses.
The facts found as a result are described below.

(A) When a laminated film containing polyethylene terephthalate (PET) as a main component for a beverage can or a food can is adhered, the thickness of the tin-iron alloy layer formed by heating at the time of adhering is about 0. It was found to be about 0.05 μm, and the thickness of the tin-iron alloy layer formed in the can manufacturing process was about 0.06 to 0.1 μm even if the heating process by welding repair was included. On the other hand, in a surface-treated steel sheet having a tin-plated layer with granular metallic tin formed on the steel sheet surface, in order to improve the weldability by reducing the contact resistance, the metallic tin in the granular tin portion after lamination baking should be kept constant. It is necessary that the thickness is equal to or more than the thickness, specifically, the plate thickness is 0.
Even in the case of a steel plate of less than 19 mm, by setting the thickness of the metallic tin in the granular tin portion after lamination baking to 0.2 μm or more, the metallic tin is pushed out by the pressure of the electrode, and the contact resistance between the material and the electrode is increased. It has been found that it can be significantly reduced. Therefore, in consideration of the thickness of the tin-iron alloy layer formed in the above-described laminating and bonding step, the plate thickness is 0.
The thickness of the granular tin layer portion (thickness of the maximum thickness portion) of the laminated steel sheet required to obtain good high-speed weldability in the steel sheet of less than 19 mm is 0.3 μm or more, which results in the above-mentioned requirement for the upper layer side. The granular tin portion may have a thickness of metallic tin remaining.

(B) Further, it was found that the 50% separated average grain size of each grain of the granular tin portion having the above-mentioned thickness and the total coverage of the steel sheet surface have a great influence on the high speed weldability. It was Specifically, the 50% separated average particle diameter of each granular tin portion having the above thickness is too large (1.
(5 μm or more) If the dispersibility of the granular tin portion is insufficient, or if the area coverage of the steel sheet surface by the granular tin portion having the above-mentioned thickness is 10% or less, the portion other than the granular tin portion causes Significant adverse effect on weldability, especially plate thickness 0.1
The high-speed weldability of steel plates with a diameter of less than 9 mm is significantly reduced. Here, the 50% separated average particle size of the granular tin part means that when the diameter of the granular tin part when observed from the top of the plate is defined as a circular diameter having the same area as the granular tin part, the particle size of the granular tin part is Taking the diameter distribution, it refers to the specific grain size when the cumulative coating area of the steel sheet surface with the granular tin portion having the specific grain size is 50% of the coating area with all the granular tin portions. The area of each granular tin portion is obtained by observation with a scanning electron microscope, and the diameter of a circle having the same area as this is taken as the diameter of each granular tin portion. (c) It was found that flat parts other than the granular tin part do not contribute to high-speed weldability. However, high-speed weldability is greatly impaired depending on the formation of an alloy layer such as a tin-iron alloy, which is a high melting point alloy, or the structure of the chemical conversion treatment layer on this flat portion.

On the other hand, the presence of a flat portion other than the granular tin portion is indispensable for obtaining excellent laminate adhesion, and this portion is formed into a film structure in which a chemical conversion treatment layer is directly formed on the steel plate surface. A high degree of laminate adhesion is ensured. Therefore, in order to obtain excellent laminate adhesion, it is necessary to secure a sufficient area ratio of the steel plate surface that is not covered with the granular tin portion. Specifically, the area ratio is 60%.
It is necessary to be above. (d) Since the chemical conversion treatment layer is composed of a high melting point metallic chromium layer and an upper chromium hydrate oxide layer which is an insulating material, it has a great influence on the high-speed weldability. The hydrated chromium oxide layer has a reduced hydration degree due to a dehydration reaction due to heating during lamination, but remains present even after lamination, and the amount of adhered metal chromium does not change. Chromium hydrate oxide layer, which is an insulating layer, has a chromium adhesion of 15 mg in terms of metallic chromium.
/ M ² or less and the amount of chromium deposited on the entire chemical conversion treatment layer is 30 mg / m ² or less in terms of metallic chromium, which is essential for ensuring high-speed weldability.

(E) When welding beverage cans and the like, it is necessary to avoid mixing of foreign matter into the cans, but the thickness of the granular tin portion (the thickness of the maximum thickness portion) exceeds 0.8 μm, or When the thickness of the metal tin (the thickness of the maximum thickness portion) constituting the upper layer side of the tin portion exceeds 0.7 μm, the tin layer is formed by friction with the plate conveying system such as the Z bar arranged immediately before the welding machine. Peeling becomes noticeable, causing a problem that the peeled tin powder mixes in the can,
It is virtually impossible to use as a can material. Further, the thickness of the tin-iron alloy forming the lower layer side of the granular tin portion is 0.01 μm.
If it is less than m, peeling of tin is likely to occur. (f) The metal chromium layer constituting the chemical conversion treatment layer has a great influence on the laminate adhesion by suppressing the oxidation of the metal tin on the lower layer side and enhancing the adhesion between the chromium hydrate oxide layer and the metal tin. . To ensure sufficient laminate adhesion (adhesion similar to that obtained with thin plating tints that are generally used at present), the chromium adhesion amount of the metal chromium layer should be 5 mg / m ² or more. Need to Further, in order to secure sufficient laminate adhesion in the neck-in processing in which the processing rate is 15% or more, the chromium adhesion amount of the metal chromium layer needs to be 10 mg / m ² or more.

(G) As described above, the adhesion of the laminate is deteriorated by the tin oxide unavoidably formed on the surface of the metallic tin. Therefore, as a method of forming the granular tin portion, it is necessary to avoid performing a molten tin treatment such as a reflow treatment that produces a large amount of tin oxide. (h) Corrosion resistance is also an important performance for can materials, especially the corrosion resistance of the part not covered by the granular tin part is a problem.
The corrosion resistance of this portion is greatly affected by the coating state of the chemical conversion treatment layer. If the total amount of chromium deposited on the chemical conversion treatment layer formed in this portion is less than 10 mg / m ^{2 in} terms of metallic chromium, sufficient corrosion resistance cannot be obtained. In particular, the amount of chromium deposited on the hydrated chromium oxide layer is converted to metallic chromium. If it is not secured at 5 mg / m ² or more, sufficient corrosion resistance cannot be obtained and rust will occur during plate storage.

(I) The surface appearance of the material, especially the brightness of the plate surface, is an important element as a can material because it affects the color tone of the can appearance after lamination. The particle size of each granular tin part is 50% separated average. When the particle size is less than 0.3 μm, a light absorption phenomenon occurs when the thickness of the granular tin portion (thickness of the maximum thickness portion) required to secure the weldability as described above is secured, and the entire plate becomes dark. Therefore, it is not preferable. (j) The above-mentioned conditions regarding the thickness of the granular tin portion (including the "thickness of tin-iron alloy on the lower layer side of the granular tin portion") must be satisfied by the majority of the formed granular tin portions. More specifically, 90% or more of the total number of granular tin portions need to satisfy the above-mentioned thickness condition.

(K) The laminated film is preferably composed mainly of polyethylene terephthalate (hereinafter referred to as PET) in consideration of its use in beverages and foods. Among them, the stability of the shape and the adhesiveness are preferable. From the viewpoint, it is preferable to use a film containing, as a main component, a low-orientation biaxially-stretched PET that is three times in the longitudinal direction and three times in the lateral direction. Further, when laminating the film, it is preferable that the film is laminated via an adhesive layer, or at least a film obtained by copolymerizing isophthalic acid is heat-fused on the surface to be adhered to the steel plate. As the adhesive, it is preferable to use an adhesive having an adhesion temperature of 200 ° C. or higher and less than 232 ° C., which is the melting point of tin, for example, a thermosetting epoxy resin-based adhesive having a curing temperature in such a temperature range. . By thus providing the laminated film layer of the biaxially stretched PET film, a synergistic effect with the coating structure having the granular tin of the present invention (anchor effect by the granular tin portion)
As a result, particularly excellent laminate adhesion, that is, sufficient laminate adhesion can be obtained even in neck-in processing with a processing rate of 15% or more.

The reasons for limiting the present invention based on the matters (a) to (k) described above are shown below. The laminated steel sheet for welded cans of the present invention has a granular tin portion formed on at least one surface of the steel sheet without the molten tin treatment and formed on the steel sheet surface in a dispersed form (distributed and formed). , Has a chemical conversion treatment layer consisting of a metallic chromium layer and a chromium hydrate oxide layer above it on the upper surface of the granular tin portion and on the steel plate surface not covered with the granular tin, and further on the upper surface of the chemical conversion treatment layer. It has a laminate film layer which covers at least one copy of a chemical conversion treatment layer. The granular tin portion has a lower layer side made of a tin-iron alloy and an upper layer side made of metallic tin. The surface of the steel plate to be tin-plated is usually degreased and pickled, and the granular tin portion is formed on such a steel plate base.

In the granular tin portion, the thickness of the maximum thickness portion of each of the granular tin portions, which is 90% or more of the total, is 0.8 μm or less, and the thickness of the maximum thickness portion of the metallic tin constituting the upper layer side is 0. .2-
It is 0.7 μm. Further, the particle size of the granular tin part satisfying such a thickness of the maximum thickness part is 0.
The coating area ratio of the steel sheet surface with the granular tin portion that is 3 μm or more and less than 1.5 μm and that satisfies the thickness of the maximum thickness portion is 10% or more. The thickness of the granular tin portion means the thickness from the steel plate surface to the upper surface of each granular tin portion (see FIGS. 1 and 2). If the thickness of the maximum thickness portion of metallic tin constituting the upper layer side of the granular tin portion is less than 0.2 μm, the contact resistance with the electrode cannot be sufficiently reduced, and satisfactory high-speed weldability cannot be obtained. On the other hand, the maximum thickness of granular tin is 0.8μ
If the thickness exceeds m or the thickness of the maximum thickness part of the metallic tin constituting the upper layer side of the granular tin part exceeds 0.7 μm, the granular tin may be peeled off during welding and the like.

Further, if the thickness of the tin-iron alloy constituting the lower layer side of the granular tin portion is less than 0.01 μm, the tin releasability tends to be poor. Therefore, the thickness of this tin-iron alloy is 0.01 μm.
The above is preferable. Further, the 50% separated average particle size of the granular tin part satisfying the thickness of the maximum thickness part is 0.3 μm.
If it is less than m, the color tone required for the can material is poor, while
When the thickness is 1.5 μm or more, the granular tin portion is flattened and the dispersibility of the granular tin portion becomes insufficient. Therefore, the effect of reducing the contact resistance due to the metal tin forming the upper layer of the granular tin portion being pushed by the welding electrode is reduced. It cannot be expected and the high speed weldability is poor.

The above-mentioned condition regarding the thickness of the granular tin portion (including the "thickness of the tin-iron alloy forming the lower layer side of the granular tin portion") is 90% or more of the formed granular tin portion. It is necessary to satisfy the number of the granular tin portions, and if the number of the granular tin portions satisfying the above conditions is less than 90% of the whole, excellent high-speed weldability cannot be obtained. Further, from the viewpoint of the releasability of granular tin during welding and the like, it is desirable that 99% or more of the total number of granular tin portions satisfy the above conditions regarding the thickness. Further, the coverage ratio of the steel sheet surface by the granular tin portion satisfying the above conditions regarding the thickness of the maximum thickness portion is 10%.
If it is less than the above range, the effect of improving the high-speed weldability using the granular tin portion cannot be sufficiently obtained. On the other hand, if the area ratio of the steel sheet surface not covered with the granular tin portion is less than 60%, sufficient laminate adhesion cannot be obtained. From the viewpoint of suppressing the formation of tin oxide that hinders the adhesion of the laminate, the granular tin portion needs to be formed without performing the molten tin treatment.

On the upper portion of the granular tin portion and on the surface of the steel sheet not covered with the granular tin portion, a chemical conversion treatment layer composed of a metallic chromium layer and a chromium hydrate oxide layer thereabove is formed. When the chromium deposition amount of the metal chromium layer is less than 5 mg / m ² , the effect of suppressing the oxidation of the granular tin portion and the effect of improving the adhesion between the metal hydrated chromium oxide layer and metal tin cannot be sufficiently obtained. Good laminate adhesion cannot be obtained. Therefore, the amount of chromium deposited on the metallic chromium layer is set to 5 mg / m ² or more. Further, in order to secure sufficient laminate adhesion in neck-in processing where the processing rate exceeds 15%,
The amount of chromium deposited on the metallic chromium layer is preferably 10 mg / m ² or more. The upper limit of the amount of chromium deposited on the metal chromium layer is the upper limit of the amount of chromium deposited on the chemical conversion treatment layer (calculated as metallic chromium) and the lower limit of the amount of chromium deposited on the chromium hydrate oxide layer (calculated on metallic chromium). From substantially 25 mg /
It becomes m ² .

If the amount of chromium deposited on the hydrated chromium oxide layer is less than 5 mg / m ^{2 in} terms of metallic chromium, sufficient corrosion resistance cannot be obtained, while if it is 15 mg / m ² or more, high-speed weldability deteriorates. Thus the chromium coating weight of hydrated chromium oxide layer is set to 5 mg / m ² or more 15 mg / m of less than ² reckoned as metal chromium. When the total amount of chromium deposited on the metal chromium layer and the chromium hydrated oxide layer is less than 10 mg / m ^{2 in} terms of metal chromium, sufficient corrosion resistance cannot be obtained, while on the other hand, 30 mg / m ²
If it exceeds, the high-speed weldability deteriorates. Therefore, the total amount of chromium deposited on the metallic chromium layer and the chromium hydrate oxide layer is 10 to 30 mg / m ^{2 in} terms of metallic chromium.

The laminate film layer is usually formed on the chemical conversion treatment layer except for the portion which becomes the weld seam portion of the can body blank. As the film constituting the laminate film layer, a film containing PET as a main component is preferable, and among them, a biaxially stretched PET film is excellent in shape stability, and when combined with the plating film structure of the present invention, it forms granular tin. Excellent adhesion of laminate due to the anchor effect, ie 15% in neck-in processing
It is preferable because excellent laminate adhesion that can withstand the heavy processing with the above processing rate is obtained.

When laminating a biaxially stretched PET film, the PET film is laminated via an adhesive layer, or a PET film having at least 10 to 25 mol% of isophthalic acid copolymerized on the surface to be adhered to a steel plate is laminated. It is preferable to perform heat fusion. In the former case, the laminate film layer has a structure having an adhesive layer and a PET film layer from the lower layer side. In the case of the latter, PET in which isophthalic acid is copolymerized on at least the surface to be bonded to the steel plate is used.
The film has a structure in which one or more layers are heat-sealed on the chemical conversion treatment layer. Usually, printing is performed on one side of the PET film.

As the adhesive constituting the adhesive layer, an adhesive having an adhesive temperature of 200 ° C. or higher at which alloying of the tin layer proceeds and less than 232 ° C. which is the melting point of tin, for example, a curing temperature is It is preferable to use a thermosetting epoxy resin adhesive in the range. Curing temperature is 200 ~ 232 ℃
Outside the range, appropriate alloying of the tin layer (alloying to the extent that metallic tin remains on the upper layer side of the granular tin portion) cannot be achieved. Also, when the PET film is heat-sealed, 20
It is preferable to perform heat fusion treatment in the range of 0 to 232 ° C. Further, a pigment such as a white pigment can be added to the PET film and / or the adhesive in order to obtain a good color tone. However, the addition of an excessive pigment exceeding 50 wt% impairs the laminate adhesion and is not preferable.

1 and 2 schematically show the film structure of a laminated steel sheet for welding cans of the present invention, where 1 is a steel sheet,
In the granular tin portion, 2 is metallic tin on the upper layer side, 3 is also a tin-iron alloy on the lower layer side, 4 is a metallic chromium layer forming the chemical conversion treatment layer, and 5 is also a hydrated chromium oxide layer. Also, FIG.
2 is a film layer constituting the laminated film layer, 7 is an adhesive layer, and in FIG. 2, 8 is a laminated film layer formed by heat-sealing the film. Further, FIG. 3 is a cross section of the granular tin layer of the laminated steel sheet for a welding can of the present invention (cross section with the laminate film removed).
3 is an electron micrograph magnified image of FIG. As shown in these drawings and photographs, the laminated steel sheet for welded cans of the present invention has a film structure in which granular tin portions are dispersed (discretely) distributed on the steel sheet surface, and the granular tin portions are treated with molten tin. Since most of the granular tin portions are formed without being applied, they have a shape in which the upper surface is relatively flat and the peripheral edge is relatively steep.

The laminated steel sheet of the present invention is, for example, phenol sulfonic acid: 10 to 40 g / l (sulfuric acid conversion), divalent tin ion concentration is 15 to 40 g / l, and the balance is water and inevitable impurities. 10 to 50
It can be obtained by performing tin electroplating by cathodic electrolysis treatment at an A / dm ² current density, and then sequentially performing chemical conversion treatment and lamination without performing molten tin treatment. Chemical treatment, for example, the bath composition CrO _3: from 15 to 4
0 g / l, H ₂ SO ₄ : 0.01 to 0.5 g / l, current density 20 to 40 A / dm ^2, and the electrolysis time and electrolysis pattern are adjusted according to the amount of chromate deposition.

[0033]

EXAMPLE A cold rolled steel sheet was electrolytically degreased, washed with water, electrolytically pickled, washed with water, and then electrotin-plated under any of the conditions [1] to [5] shown in (A) below, followed by (B) below. After the chemical conversion treatment was performed under the conditions shown in (1), ordinary oil was applied and the test was performed. The pretreatment of tin plating was performed according to the treatment conditions of an ordinary tin plating line for steel sheets for cans, and the tin plating baths were all set at a flow rate of 2 m / sec and a bath temperature of 45 ° C.

(A) Electrotin plating conditions Conditions [1] ・ Plating bath composition; phenolsulfonic acid: 15 g / l
(Sulfuric acid conversion) Divalent tin ion concentration: 30 g / l Current density: 15-30 A / dm ² Electrolysis time was adjusted according to the deposition form of tin plating. Condition [2] Plating bath composition: methanesulfonic acid: 30 g / l (sulfuric acid equivalent), divalent tin ion concentration: 200 g / l · Current density: 30~60A / dm ² · electrolysis time to adhere the form of tinned Adjusted accordingly.

Condition [3] -Plating bath composition; phenolsulfonic acid: 30 g / l
(Sulfuric acid conversion) Divalent tin ion concentration: 35 g / l, ethoxylated naphthol sulfonic acid: 5 g / l Current density: 15-30 A / dm ² Electrolysis time was adjusted according to the amount of plating deposit. -The tin plating layer was prepared so that the metal tin was uniform. Condition [4] -An inert treatment such as Ni plating was performed before tin plating.・ Plating bath composition; phenol sulfonic acid: 30 g / l
(Sulfuric acid conversion) Divalent tin ion concentration: 35 g / l, ethoxylated naphthol sulfonic acid: 5 g / l Current density: 15-30 A / dm ² Electrolysis time was adjusted according to the amount of plating deposit. A molten tin treatment was performed after electrolysis to prepare a tin-plated layer so that a plated surface in which an island-shaped tin layer and a tin-iron alloy layer were mixed was formed.

(B) Chemical conversion treatment conditions-Bath temperature: 45 ° C-Bath composition: CrO ₃ : 20 g / l, H ₂ SO ₄ : 0.20
g / l Current density: 10 to 30 A / dm ² , electrolysis time was adjusted according to the amount of chromate deposition.

After cutting the produced surface-treated steel sheet, it was slit into a predetermined shape to prepare a can body blank, which was laminated or coated under the conditions [1] to [4] shown in (C) below. After that, predetermined blanking is performed, high-speed welding,
Welding repair, neck-in processing, and flange processing were performed. (C) Organic coating (lamination or coating) conditions Condition [1] 2 to 4 on one side of a biaxially stretched PET film having a thickness of 12 μm
Apply a thermosetting epoxy resin adhesive of g / m ² ,
It was heated and dried at a temperature of 140 ° C. or lower. The film 2
The surface-treated steel sheet preheated to 10 ° C. was bonded to the surface-treated steel sheet via an adhesive layer and thermocompression-bonded through a pressure roll. At that time, a laminate avoiding portion was provided at a portion corresponding to the welded joint portion of the can body blank.

Condition [2] Isophthalic acid was applied to the surface to be adhered to the steel plate with a thickness of 25 μm in an amount of 1
Biaxially stretched PET film copolymerized with 0 to 25 mol% (the surface to be adhered to the steel plate is composed of PET film with 10 to 25 mol% of isophthalic acid copolymerized 2
Layer film) was laminated on a surface-treated steel sheet preheated to 230 ° C., thermocompression-bonded through a pressure roll, and water-cooled.
At that time, a laminate avoiding portion was provided at a portion corresponding to the welded joint portion of the can body blank. Condition [3] Isophthalic acid is applied to the surface of 25 μm thick that is bonded to the steel plate.
The biaxially stretched PET film copolymerized by mol% is
It was attached to a surface-treated steel sheet preheated to 0 ° C., thermocompression-bonded through a pressure roll, and water-cooled. At that time, a laminate avoiding portion was provided at a portion corresponding to the welded joint portion of the can body blank. Condition [4] Epoxyphenol-based paint used for normal can coating was applied to the surface-treated steel sheet and baked at 208 ° C for 10 minutes to form a coating film with a thickness of 5 µm after baking. .

The high-speed welding was carried out using a wire seam welding machine FBB5600 manufactured by Sudronic Co., Ltd., at a wire feeding speed of 80 m / min. The following properties were evaluated for the obtained test materials. The results are shown in Tables 1 to 9 together with the coating composition of each steel sheet. (1) High-speed welding property Welding is performed by changing the setting value of welding current, and the appropriate current between the minimum current setting value that provides sufficient welding strength and the maximum current value at which welding defects such as scattering and perforation begin to stand out. The setting range was examined, and the practicality and availability of operation were evaluated. The evaluation criteria are as follows. ○: Practical (pass) △: Proper current setting range is too small to be practical (fail) ×: Proper current setting range does not exist (fail)

(2) Lamination Adhesion and Paint Adhesion The processed part subjected to the neck-in process is subjected to retort treatment in 1.5% saline solution at 130 ° C. for 30 minutes, and the film of the processed part after retort is applied. Alternatively, the presence or absence of peeling of the coating film was observed. The evaluation criteria are as follows. ◯: No peeling (pass) X: Peeling (fail) (3) Tin peeling resistance After 100 cans were continuously made using a welding machine, the presence of metal powder on the Z bar and the metal powder The presence or absence of adhesion was evaluated. The evaluation criteria are as follows. ◯: Metal powder adhered to both Z bar and can was slight (pass) X: Metal powder adhered to can (fail)

(4) Corrosion resistance After the repair or coating is applied to the non-lamination part or the non-painting part of the surface-treated steel sheet after laminating or painting and before welding, a scratch reaching the base is made with a cutter, and 38 ° C., 3.5% salt After soaking in water and washing with water, the relative humidity at 90
% Exposure for 1 week, and the rust generation state was evaluated. The evaluation criteria are as follows. ◯: No rust generation (pass) X: Rust generation (fail) (5) Color tone Compared to the lightness (L value) of the surface of the steel sheet where a film with a white pigment of 20 μm thickness was laminated on the existing thin plating. Then, it was evaluated whether or not the decrease in L value after lamination or coating was within 20%. The evaluation criteria are as follows. ◯: less than 20% (pass) x: 20% or more (fail)

In the present example, the thickness of the granular tin portion was measured by observing the cross section of the coating with a transmission electron microscope. At this time, the Dupont-
Using a Sorvall MT6000 type ultramicrotome, the resin-embedded sample material was ultrathin sliced in the cross-sectional direction of the sample material with a diamond knife manufactured by Diatome, which was fixed to the same device, to obtain an observation sample. A 200CX manufactured by JEOL Ltd. was used as a transmission electron microscope for observing the cross section of the sample, and the acceleration voltage at the time of observation was 200 kV. Electron diffraction was used to discriminate between the metallic tin on the upper layer side of the granular tin portion and the tin-iron alloy on the lower layer side. Also,
The area of the granular tin portion, the coverage area ratio of the granular tin portion, and the area ratio of the steel sheet surface not coated with the granular tin portion were measured by observation with a scanning electron microscope. As the scanning electron microscope for observation, JSM-840F manufactured by JEOL Ltd. was used, and the acceleration voltage during observation was set to 15 kV.

In Tables 1 to 9, Comparative Examples 1 to 12 are out of the scope of the present invention for any of the conditions relating to the granular tin portion or the chemical conversion treatment layer, and therefore high speed weldability, laminate adhesion, tin peeling resistance, Poor properties in either corrosion resistance or color. In Comparative Example 14, the granular tin portion was formed without the molten tin treatment, but the tin layer had a uniform thickness, and thus the laminate adhesion was poor. Further, in Comparative Example 15, since the granular tin layer was formed by the molten tin treatment, the laminate adhesion was poor.
Comparative Examples 16 to 19 are existing typical welded can laminated steel sheets having an island-shaped (or discontinuous) metal tin layer. Among these Comparative Examples, Comparative Example 18 and Comparative Example 19 have the same constitution of the tin layer and the chemical conversion treatment layer, and the former is P
The ET film is laminated, and the latter is formed with a coating film using an epoxyphenol-based paint that has been conventionally used. By comparing the two, it is understood that the laminate and the coating film behave differently in terms of adhesion.

As shown in Examples 5 to 7 of the present invention, when the laminate film is a copolymerized PET film, good laminate adhesion is exhibited even by adhesion by heat fusion. On the other hand, as shown in Examples 1 to 4, when laminating homo-PET or a PET film having a low degree of polymerization, it is necessary to bond them with an adhesive. Further, as shown in Comparative Example 13, even when it has a granular tin portion and a chemical conversion treatment layer that satisfy the conditions of the present invention, PE that is laminated by thermal fusion bonding
If the T film is a film having a low degree of polymerization, sufficient laminate adhesion cannot be obtained. In addition, Comparative Example 16 and Comparative Example 1
In the case of the conventional laminated steel sheet shown in Fig. 7, when the copolymerized PET film is heat-sealed or adhered through an adhesive, good laminate adhesion is obtained when the processing rate of neck-in processing is about 6%. However, sufficient laminate adhesion cannot be obtained by the severe neck-in processing such that the processing rate exceeds 15%.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

[0051]

[Table 7]

[0052]

[Table 8]

[0053]

[Table 9]

[0054]

EFFECTS OF THE INVENTION According to the laminated steel sheet for a welding can of the present invention described above, excellent high-speed weldability can be obtained regardless of the sheet thickness of the steel sheet, and neck-in processing with a processing rate of 15% or more is achieved. In addition, it has sufficient laminate adhesion to endure, good corrosion resistance, tin releasability and color tone, and can be manufactured at low cost without any special process.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an example of a coating film cross section of a laminated steel sheet for welding cans of the present invention.

FIG. 2 is an explanatory view schematically showing another example of the coating film cross section of the laminated steel sheet for welding cans of the present invention.

FIG. 3 is an electron microscope enlarged photograph showing a cross section of the grain structure of the granular tin portion of the laminated steel sheet for a welding can of the present invention.

[Explanation of symbols]

1 ... Steel plate, 2 ... Metal tin that constitutes the upper layer side of the granular tin portion, 3
... tin-iron alloy constituting the lower layer side of the granular tin portion, 4 ... metal chromium layer, 5 ... chromium hydrate oxide layer, 6 ... film layer, 7
... Adhesive layer, 8 ... Laminate film layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Okude 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) In-house Hisato Noro 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Tube Co., Ltd.

Claims (6)

[Claims] 1. A steel sheet has a granular tin portion formed on at least one surface thereof without being subjected to a tin treatment and dispersedly formed on the steel sheet surface, and covers the upper portion of the granular tin portion and the granular tin portion. A laminated film having a chemical conversion treatment layer composed of a metal chromium layer and a chromium hydrate oxide layer thereabove on the surface of the steel sheet that is not formed, and further covering at least a part of the conversion treatment layer on the chemical conversion treatment layer. A laminated steel sheet having a layer, wherein the granular tin portion is composed of a tin-iron alloy on the lower layer side and metallic tin on the upper layer side, and 90% or more of each of the granular tin portions has a maximum granular tin portion. The thickness of the thick portion is 0.8 μm or less, and the maximum thickness of the metal tin constituting the upper layer side is 0.
2 to 0.7 μm, the 50% separated average particle size of the granular tin portion satisfying the thickness of these maximum thickness portions is 0.3 μm or more and less than 1.5 μm, and satisfies the thickness of the maximum thickness portion. The area ratio of the steel sheet surface covered by the granular tin portion is 10% or more, the area ratio of the steel sheet surface not covered by the granular tin portion is 60% or more, and the chemical conversion treatment layer is formed of the metallic chromium layer. Chromium adhesion amount of 5 mg / m ² or more, chromium adhesion amount of the hydrated chromium oxide layer is 5 mg / m in terms of metallic chromium.
² or more and less than 15 mg / m ² , and the total amount of chromium deposited on the metallic chromium layer and the hydrated chromium oxide layer is 10 in terms of metallic chromium.
A laminated steel sheet for welding cans, which has an excellent corrosion resistance, weldability and laminate adhesion of 30 mg / m ² . 2. A laminated steel sheet for a welding can having excellent corrosion resistance, weldability and laminate adhesion according to claim 1, wherein the thickness of the tin-iron alloy constituting the lower layer side of the granular tin portion is 0.01 μm or more. . 3. The amount of chromium deposited on the metallic chromium layer is 10 mg.
/ M ² or more, the corrosion resistance according to claim 1 or 2,
Laminated steel sheet for welding cans with excellent weldability and laminate adhesion. 4. A welded can having excellent corrosion resistance, weldability and laminate adhesion according to claim 1, 2 or 3, wherein the laminate film layer has an adhesive layer and a biaxially oriented polyethylene terephthalate film layer from the lower side. Laminated steel sheet. 5. The laminated steel sheet for a welding can having excellent corrosion resistance, weldability and laminate adhesion according to claim 4, wherein the adhesive constituting the adhesive layer is a thermosetting epoxy resin adhesive. 6. The corrosion resistance according to claim 1, 2 or 3, wherein the laminate film layer is composed of at least one biaxially stretched polyethylene terephthalate film obtained by copolymerizing isophthalic acid on at least a surface to be adhered to a steel plate. Laminated steel sheet for welding cans with excellent weldability and laminate adhesion.