JP2004106246A

JP2004106246A - Resin coated steel sheet for drawn-ironed can and can body

Info

Publication number: JP2004106246A
Application number: JP2002269331A
Authority: JP
Inventors: Hiroshi Nishida; 西田　浩; Masayoshi Suehiro; 末廣　正芳; Tooru Chijiki; 千々木　亨; Keiichiro Torisu; 鳥巣　慶一郎; Takeharu Kataoka; 片岡　毅晴; Suehito Kusuda; 楠田　季仁
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-09-17
Filing date: 2002-09-17
Publication date: 2004-04-08
Anticipated expiration: 2022-09-17
Also published as: JP4102146B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin coated steel sheet for a drawn-ironed can excellent in processability and processing corrosion resistance. <P>SOLUTION: In the resin coated steel sheet for the drawn-ironed can, a thermosetting resin film with a thickness of 1-20 μm is applied to the surface corresponding to the outer surface side of the can of a steel sheet and contains a metal filler in an amount of 5 mass % or more in a coating dry mass ratio. The penetration depth by thermomechanical analysis of the thermosetting resin film is not more than 3.5 μm and the mass change thereof due to a thermal balance is not more than 10%. The surface corresponding to the inner surface side of the can is coated with a polyester resin having orientation crystallizability. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、絞りしごき加工缶用樹脂被覆鋼板に関するものであり、さらに詳しくは少なくとも缶外面相当面が熱硬化性樹脂である絞りしごき加工缶用樹脂被覆鋼板に関する。
【０００２】
【従来の技術】
従来から、食缶あるいは飲料缶には、缶胴、缶蓋、底蓋の三つの部分からなる３ピース缶と缶胴と底蓋が一体となった缶体、缶蓋の二つの部分からなる２ピース缶が用いられている。この３ピース缶の缶胴には一回あるいは数回の塗装を施したぶりき、電解クロム酸処理鋼板（一般にティンフリースチールと呼ばれ、以下、ＴＦＳと略す）が使用され、接合にははんだ付け、ナイロンによる接着、あるいは抵抗溶接をする方法が使用されている。このように塗装を施すことは、焼付工程が煩雑であるばかりでなく、焼付けのため長時間の加熱が必要である。また、焼付工程で塗料中の多量の溶剤成分が排出されるため、公害面から排出溶剤を特別な焼却炉に導き焼却しなければならないという欠点をもっていた。
【０００３】
また、２ピース缶には絞り缶、絞り再絞り缶（Ｄｒａｗｎ　ａｎｄ　Ｒｅｄｒａｗｎ　ｃａｎ、ＤＲＤ缶）、絞りしごき缶（Ｄｒａｗｎ　ａｎｄ　Ｉｒｏｎｅｄ　Ｃａｎ、ＤＩ缶）があるが、絞り缶、ＤＲＤ缶のような比較的絞り比の小さい缶には上記の３ピース缶用の材料と同様に塗装を施したぶりき、またはＴＦＳが使用されている。そのため上記同様に工程面および環境汚染の面から問題がある。また、絞り缶、ＤＩ缶にはぶりきおよびアルミニウムが使用されているが、ＤＩ缶の製造には成形時に潤滑油を用い、成形加工後、この潤滑油を洗浄で除去し、乾燥後、缶の内外面に塗装が施される。このＤＩ缶の製造工程は公害面から潤滑油の処理、塗料焼き付け時における塗料中から揮散される溶剤成分の処理などに問題がある。
【０００４】
特許文献１には、電解クロム処理鋼板の両面に熱可塑性樹脂を被覆した高温揮発性潤滑性物質を塗布してなる乾式絞りしごき加工缶用樹脂被覆鋼板が提案されているが、目的とする缶壁の厚さが元板厚の７０〜４０％と厚い水準でありながら、実際には缶体外面の印刷鮮映性が不十分であり、成型後に白色塗装を行う必要があり、コスト上問題である。
【０００５】
【引用文献】
（ａ）特許文献１（特開平７−２５８７９４号公報）
【０００６】
【発明が解決しようとする課題】
加工度が大きくなるにしたがい、皮膜の隠蔽率が低下することになり、母材が鋼板であると印刷鮮映性が低下することから、外面塗装を省略してなおかつ印刷鮮映性に優れた缶体を提供することが本発明の課題とする点である。
【０００７】
【課題を解決するための手段】
本発明者らは上記の課題を解決するために、種々の検討を行い本発明に至ったものであり、その要旨とするところは、
（１）鋼板の缶外面側相当面が厚さ１〜２０μｍ熱硬化性樹脂皮膜で被覆され、塗装質量乾燥比で５ｍａｓｓ％以上の金属フィラーを含有し、該熱硬化性樹脂皮膜の熱機械分析による没入深さが３．５μｍ以下であり、かつ熱天秤での質量変化が１０％以下であり、缶内面側相当面が配向結晶性を有するポリエステル樹脂で被覆された絞りしごき加工缶用樹脂被覆鋼板。
【０００８】
（２）熱硬化性樹脂皮膜が１．０〜２０．０ｍａｓｓ％のインナーワックスを含有する前記（１）に記載された乾式絞りしごき加工缶用樹脂被覆鋼板。
（３）缶内面相当面がポリエステル樹脂で被覆され、鋼板と相接しているポリエステル樹脂層の面配向係数をｎ１とし、最表層のポリエステル樹脂層の面配向係数をｎ２とした時、ｎ１が０以上で、０．１０以下、ｎ２が０．０１以上で、０．１５以下で、かつｎ２≧ｎ１あることを特徴とする前記（１）〜（２）に記載の絞りしごき加工缶用樹脂被覆鋼板。
【０００９】
（４）缶内面相当面に被覆されたポリエステル樹脂の複屈折法配向度（Δｎ）が０．０４以上であることを特徴とする前記（１）〜（３）に記載の絞りしごき加工缶用樹脂被覆鋼板。
但し、Δｎ＝ｎ３−ｎ４
ｎ３：フィルムの表面内の最大配向の屈折率であり、ｎ４はフィルム厚み方向の屈折率。
（５）前記（１）〜（４）の鋼板を成形して製造された缶体である。
【００１０】
以下、本発明の内容について詳細に説明する。まず、本発明の樹脂被覆鋼板は缶外面相当側に金属フィラー５％以上を含有する厚さ１〜２０μｍ熱硬化性樹脂皮膜を有する。これは、成型缶の印刷鮮映性を確保するためである。鉄はアルミに比較して分光反射率が低いためにその外観は暗く、その上の印刷の鮮映性は劣るものである。そのため、缶外面相当側に熱可塑性樹脂フィルムを積層した熱可塑性樹脂膜とした場合には、熱可塑性樹脂フィルム中に主に白色顔料を加えて、印刷の鮮映性を補ってきた。しかしながら、しごき成型の加工度が大きくなると、しごき加工後の単位面積当たりの顔料量が少なくなるため、印刷の鮮映性の悪さを補いきれなくなる。
【００１１】
熱可塑性樹脂フィルムの生産性から含有可能な白色顔料或いは有色顔料の量が大きく制限されるため、フィルム中の顔料含有率を高くすることも限界があり、フィルム厚みを厚くすることもコストの点から有利ではない。このことから、発明者らは熱硬化性樹脂皮膜に注目し、その厚みを１〜２０μｍとし、金属フィラーを５％以上含有させることで成型缶の印刷鮮映性を確保できることを見い出したものである。熱硬化性樹脂皮膜厚みが１μｍ未満では皮膜が薄すぎてしごき成型後の印刷鮮映性の確保が不十分となるためであり、また、皮膜が２０μｍ超では成形性が低下するとともに、コストの点から有利ではない。好ましくは２〜８μｍである。また、皮膜中の金属フィラーはしごき成型後の印刷鮮映性を確保のために５ｍａｓｓ％以上が必要であり、その加工性を考慮するとその上限は７０％以下が望ましい。
【００１２】
また、熱硬化性樹脂皮膜は熱機械分析による没入深さが３．５μｍ以下であり、かつ熱天秤での質量変化が１０％以下であることが重要である。ここでいう熱機械分析による没入深さとは、分析に影響の出ないようにカッター等で熱可塑性樹脂皮膜を除去した鋼板を試料として、熱硬化性樹脂皮膜側から直径１ｍｍの先端の平坦な石英プローブに１ｇの荷重をかけて毎分１０℃の昇温速度で室温から１７０℃まで測定した時の１７０℃の没入深さをいう。没入深さが３．５μｍ超ではしごき成型性が不良になる場合がある。
【００１３】
また、ここでいう熱天秤での質量変化とは、樹脂被覆鋼板から熱硬化性樹脂皮膜をカッター等で採取しこれを試料として、窒素雰囲気で１０℃の昇温速度で室温から２７０℃まで測定した時室温と２７０℃と差から求められる。質量変化が１０％超では、しごき成型性が不良になる。望ましくは質量変化が５％以下である。なお、金属フィラーは印刷鮮映性を確保の上から分光反射率の大きいアルミあるいはアルミ合金が好ましく、その形態は加工性確保の点から鱗片状のものが好ましい。さらにその粒子径は平均粒子径として５〜２０μｍが望ましい。また、皮膜中に１．０〜２０．０ｍａｓｓ％のインナーワックスを含有することが成型性確保上から望ましい。また、本発明では缶内面側相当面が配向結晶性ポリエステル樹脂で被覆されていることが重要である。ポリエステル樹脂はそのコストおよび内容物の風味を変え難いといった点で優れ、かつ、配向結晶性ポリエステル樹脂は耐衝撃性に優れる。
【００１４】
また、本発明において使用されるポリエステル樹脂フィルムの厚さは特に限定するものではないが、５〜４０μｍが好ましい。厚さが５μｍ未満になると、ラミネート作業性が著しく低下するとともに、十分な加工耐食性が得られにくい。また、厚さが４０μｍ超になると、製缶用材料に広く使用されているエポキシ系樹脂塗料などと比較し経済的でない。缶内面相当面がポリエステル樹脂の鋼板と相接しているポリエステル樹脂層の面配向係数をｎ１とし、最表層のポリエステル樹脂層の面配向係数をｎ２とした時、ｎ１が０以上で、０．１０以下、ｎ２が０．０１以上で、０．１５以下で、かつｎ２≧ｎ１であることが、内面皮膜の密着性、加工性および耐デント性の点から望ましい。
【００１５】
ポリエステル樹脂被覆鋼板の鋼板と相接しているポリエステル樹脂層および最表層のポリエステル樹脂層の面配向係数は次に示す方法で求められる。すなわち、得られたポリエステル樹脂被覆鋼板を塩酸に浸漬し、金属板表面を化学的に溶解させ、ポリエステル樹脂フィルムのみを剥離し、そのフィルムの表面側および金属との接触面側のそれぞれの縦方向、横方向および厚さ方向の屈折率をアッベの屈折率計で測定し、次式から求める。
【００１６】
面配向係数−（Ａ＋Ｂ）／２−Ｃ
Ａ：縦方向のポリエステル樹脂層の屈折率
Ｂ：横方向のポリエステル樹脂層の屈折率
Ｃ：厚さ方向のポリエステル樹脂層の屈折率
さらに、缶内面相当面に被覆されたポリエステル樹脂の複屈折法配向度（Δｎ）が０．０４以上であることが耐デント性の点から望ましい。
但し、Δｎ＝ｎ３−ｎ４
ｎ３はフィルムの表面内の最大配向の屈折率であり、ｎ４はフィルムの厚み方向の屈折率である。
本発明の樹脂が被覆される鋼板は、表面処理の無い鋼板および電解クロム酸処理、あるいは、Ｎｉ、Ｓｎの単独あるいは両方のメッキ鋼板あるいはその後電解クロム酸処理した鋼板等の公知の鋼板を用いることができる。
【００１７】
【実施例】
表２に示す樹脂を付与した鋼板を（缶内面側の樹脂は表１に示す）缶成型、外面印刷を行い、ＤＩ成形性、印刷鮮映性および耐デント性を評価した。
なお、耐デント性の評価は、内容物（コカコーラ、ウーロン茶、オレンジジュース）を充填し、８０ｃｍの高さから型鋼の凸状部に缶を落下させ、意図的に缶の底部及び胴部に凹みを入れ、３ヶ月間、３０℃で貯蔵した後、缶内面凹み部の腐蝕状況を観察した。その結果を表２に示す。
【００１８】
【表１】

【００１９】
【表２】

【００２０】
【発明の効果】
以上説明したように、本発明の絞りしごき加工缶用樹脂被覆鋼板は加工性および加工耐食性に優れた材料であり、絞りしごき加工用に用いられるだけでなく、絞り缶、缶蓋、イージーオープン可能な缶蓋、王冠、キャップ類など容器用材料としても、広く適用できる。その工業的意義は極めて大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a resin-coated steel sheet for drawn and ironed cans, and more particularly to a resin-coated steel sheet for drawn and ironed cans in which at least a surface corresponding to the outer surface of the can is a thermosetting resin.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a food or beverage can has a three-piece can consisting of a can body, a can lid, and a bottom lid, and a can body in which the can body and the bottom lid are integrated, and two parts of a can lid. Two-piece cans are used. The can body of this three-piece can is made of tinplate that has been painted once or several times, and is made of electrolytic chromic acid-treated steel sheet (generally called tin-free steel, hereinafter abbreviated as TFS). Attachment, adhesion by nylon, or resistance welding is used. Applying the coating in this manner not only complicates the baking process, but also requires long-time heating for baking. Further, since a large amount of solvent components in the paint are discharged in the baking step, there is a drawback that the discharged solvent has to be led to a special incinerator for incineration in view of pollution.
[0003]
There are two-piece cans such as drawn cans, drawn and drawn cans (DRD cans), and drawn and ironed cans (Drawn and Ironed Cans, DI cans). Tin cans with a small drawing ratio use tinplate or TFS that has been coated in the same manner as the above-mentioned three-piece can material. Therefore, there is a problem in terms of process and environmental pollution as in the above. In addition, tin and aluminum are used for drawn cans and DI cans, but lubricating oil is used in the production of DI cans during molding, and after molding, the lubricating oil is removed by washing. The inside and outside surfaces of the are painted. The manufacturing process of this DI can has problems in treating lubricating oil and treating solvent components volatilized from the paint at the time of baking the paint in terms of pollution.
[0004]
Patent Document 1 proposes a resin-coated steel sheet for dry drawing and ironing cans in which a high-temperature volatile lubricating substance coated with a thermoplastic resin is applied to both sides of an electrolytic chromium-treated steel sheet. Despite the fact that the wall thickness is as high as 70 to 40% of the original plate thickness, the print sharpness of the outer surface of the can body is actually insufficient, and it is necessary to perform white painting after molding, which is a cost problem. It is.
[0005]
[References]
(A) Patent Document 1 (Japanese Patent Application Laid-Open No. 7-258794)
[0006]
[Problems to be solved by the invention]
As the degree of processing increases, the concealment rate of the film decreases, and if the base material is a steel plate, the print sharpness is reduced, so the outer surface coating is omitted and the print sharpness is excellent. It is an object of the present invention to provide a can body.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted various studies and arrived at the present invention.
(1) A surface corresponding to the outer surface of a can of a steel sheet is coated with a thermosetting resin film having a thickness of 1 to 20 μm, contains a metal filler in a coating mass dry ratio of 5 mass% or more, and is thermomechanical analysis of the thermosetting resin film. For squeezing and ironing cans whose immersion depth is 3.5 μm or less and whose mass change by a thermobalance is 10% or less, and whose inner surface side is coated with a polyester resin having oriented crystallinity. Coated steel sheet.
[0008]
(2) The resin-coated steel sheet for dry drawing and ironing can as described in (1) above, wherein the thermosetting resin film contains 1.0 to 20.0 mass% of inner wax.
(3) When the inner surface of the can is covered with a polyester resin and the plane orientation coefficient of the polyester resin layer in contact with the steel sheet is n1, and the plane orientation coefficient of the outermost polyester resin layer is n2, n1 is The resin for a drawn and ironed can according to any one of (1) to (2), wherein 0 to 0.10, n2 is 0.01 to 0.15, and n2 ≧ n1. Coated steel sheet.
[0009]
(4) The drawn and ironed can according to (1) to (3), wherein the polyester resin coated on the inner surface corresponding to the inner surface of the can has an orientation degree (Δn) of 0.04 or more in a birefringence method. Resin coated steel sheet.
Where Δn = n3-n4
n3 is the refractive index of the maximum orientation in the film surface, and n4 is the refractive index in the film thickness direction.
(5) A can body manufactured by forming the steel sheet of (1) to (4).
[0010]
Hereinafter, the contents of the present invention will be described in detail. First, the resin-coated steel sheet of the present invention has a thermosetting resin film having a thickness of 1 to 20 μm containing 5% or more of a metal filler on the side corresponding to the outer surface of the can. This is to ensure print sharpness of the molded can. Iron has a low spectral reflectance as compared with aluminum, so its appearance is dark, and the clarity of printing on it is poor. Therefore, when a thermoplastic resin film is formed by laminating a thermoplastic resin film on the side corresponding to the outer surface of a can, a white pigment is mainly added to the thermoplastic resin film to supplement the sharpness of printing. However, when the workability of the ironing becomes large, the amount of pigment per unit area after the ironing becomes small, so that it is not possible to compensate for the poor clarity of printing.
[0011]
Since the amount of white pigments or colored pigments that can be contained is greatly limited due to the productivity of the thermoplastic resin film, there is a limit to increasing the pigment content in the film, and increasing the film thickness and the cost point. Not advantageous from. From this, the inventors paid attention to the thermosetting resin film, and found that by setting the thickness thereof to 1 to 20 μm and containing a metal filler of 5% or more, the printing clearness of the molded can can be ensured. is there. If the thickness of the thermosetting resin film is less than 1 μm, the film is too thin to ensure sufficient print clarity after ironing, and if the thickness exceeds 20 μm, the moldability decreases and the cost is reduced. Not advantageous in point. Preferably it is 2 to 8 μm. In addition, the metal filler in the film needs to be 5 mass% or more in order to ensure print sharpness after ironing, and the upper limit is desirably 70% or less in consideration of workability.
[0012]
It is important that the thermosetting resin film has an immersion depth of 3.5 μm or less by thermomechanical analysis and a mass change of 10% or less with a thermobalance. The immersion depth by thermomechanical analysis here is a flat steel tip with a diameter of 1 mm from the thermosetting resin film side, using a steel sheet from which the thermoplastic resin film has been removed with a cutter or the like so as not to affect the analysis. It refers to the immersion depth of 170 ° C. when measured from room temperature to 170 ° C. at a rate of 10 ° C./minute with a load of 1 g applied to the quartz probe. If the immersion depth is more than 3.5 μm, the ironing formability may be poor.
[0013]
The term "mass change with a thermobalance" as used herein means that a thermosetting resin film is sampled from a resin-coated steel sheet with a cutter or the like, and is measured from room temperature to 270 ° C at a temperature rising rate of 10 ° C in a nitrogen atmosphere. It is determined from the difference between room temperature and 270 ° C. If the mass change exceeds 10%, the ironing formability becomes poor. Desirably, the mass change is 5% or less. The metal filler is preferably aluminum or an aluminum alloy having a large spectral reflectance from the viewpoint of ensuring print sharpness, and the form thereof is preferably a scaly shape from the viewpoint of ensuring workability. Further, the particle diameter is desirably 5 to 20 μm as an average particle diameter. Further, it is desirable from the viewpoint of ensuring moldability that the coating contains 1.0 to 20.0 mass% of the inner wax. In the present invention, it is important that the surface corresponding to the inner surface of the can is coated with the oriented crystalline polyester resin. Polyester resin is excellent in that it is difficult to change the cost and flavor of the contents, and oriented crystalline polyester resin is excellent in impact resistance.
[0014]
The thickness of the polyester resin film used in the present invention is not particularly limited, but is preferably 5 to 40 μm. When the thickness is less than 5 μm, the laminating workability is remarkably reduced, and sufficient working corrosion resistance is hardly obtained. On the other hand, when the thickness exceeds 40 μm, it is not economical as compared with an epoxy resin paint widely used as a material for cans. When the plane orientation coefficient of the polyester resin layer in which the inner surface corresponding to the can is in contact with the steel sheet of the polyester resin is n1, and the plane orientation coefficient of the outermost polyester resin layer is n2, n1 is 0 or more. It is desirable that n is 10 or less, n2 is 0.01 or more, 0.15 or less, and n2 ≧ n1 from the viewpoint of the adhesion of the inner surface film, the workability, and the dent resistance.
[0015]
The plane orientation coefficient of the polyester resin layer in contact with the steel sheet of the polyester resin-coated steel sheet and the outermost polyester resin layer can be determined by the following method. That is, the obtained polyester resin-coated steel sheet is immersed in hydrochloric acid, the metal plate surface is chemically dissolved, only the polyester resin film is peeled off, and the respective longitudinal directions of the film surface side and the metal contact surface side are separated. , And the refractive index in the lateral direction and the thickness direction are measured with an Abbe refractometer, and are obtained from the following equations.
[0016]
Plane orientation coefficient-(A + B) / 2-C
A: Refractive index of the polyester resin layer in the vertical direction B: Refractive index of the polyester resin layer in the horizontal direction C: Refractive index of the polyester resin layer in the thickness direction Further, the birefringence method of the polyester resin coated on the inner surface of the can. It is desirable that the degree of orientation (Δn) is 0.04 or more from the viewpoint of dent resistance.
Where Δn = n3-n4
n3 is the refractive index of the maximum orientation in the surface of the film, and n4 is the refractive index in the thickness direction of the film.
As the steel sheet coated with the resin of the present invention, a known steel sheet such as a steel sheet having no surface treatment and electrolytic chromic acid treatment, or a plated steel sheet of Ni or Sn alone or both, or a steel sheet subsequently subjected to electrolytic chromic acid treatment is used. Can be.
[0017]
【Example】
The steel sheet provided with the resin shown in Table 2 was subjected to can molding (the resin on the inner surface side of the can is shown in Table 1) and outer surface printing, and DI moldability, print sharpness, and dent resistance were evaluated.
The dent resistance was evaluated by filling the contents (Coca-Cola, oolong tea, orange juice), dropping the can from a height of 80 cm onto the convex part of the mold steel, and intentionally recessing the bottom and body of the can. After storing at 30 ° C. for 3 months, the state of corrosion of the concave portion on the inner surface of the can was observed. Table 2 shows the results.
[0018]
[Table 1]

[0019]
[Table 2]

[0020]
【The invention's effect】
As described above, the resin-coated steel sheet for drawn and ironed cans of the present invention is a material having excellent workability and corrosion resistance, and can be used not only for drawing and ironing, but also for drawing cans, can lids, and easy-opening. It can be widely applied as materials for containers such as cans, crowns and caps. Its industrial significance is extremely large.

Claims

A surface corresponding to the outer surface of the can of the steel sheet is coated with a thermosetting resin film having a thickness of 1 to 20 μm and contains a metal filler in a coating dry mass ratio of 5 mass% or more, and the thermosetting resin film is immersed by thermomechanical analysis. A resin-coated steel sheet for drawn and ironed cans having a depth of 3.5 μm or less, a mass change by a thermobalance of 10% or less, and a surface corresponding to the inner surface of the can coated with a polyester resin having oriented crystallinity.

The resin-coated steel sheet for dry drawing and ironing can according to claim 1, wherein the thermosetting resin film contains 1.0 to 20.0 mass% of inner wax.

The inner surface of the can is covered with a polyester resin, and the plane orientation coefficient of the polyester resin layer in contact with the steel sheet is defined as n1, and the plane orientation coefficient of the outermost polyester resin layer is defined as n2. 3. The resin-coated steel sheet for drawn and ironed cans according to claim 1, wherein n2 is 0.01 or more, 0.15 or less, and n2 ≧ n1.

4. The resin-coated steel sheet for drawn and ironed cans according to claim 1, wherein the polyester resin coated on the inner surface corresponding to the inner surface of the can has a birefringence orientation degree (Δn) of 0.04 or more. 5.
Where Δn = n3-n4
n3: refractive index of the maximum orientation in the surface of the film, n4: refractive index in the thickness direction of the film

A can body produced by molding the steel sheet according to claim 1.