JP3546120B2

JP3546120B2 - 2-layer composite resin coating pre-coated metal sheet with excellent draw formability

Info

Publication number: JP3546120B2
Application number: JP03430797A
Authority: JP
Inventors: 浩平植田; 良二西岡
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1997-02-04
Filing date: 1997-02-04
Publication date: 2004-07-21
Anticipated expiration: 2017-02-04
Also published as: JPH10217393A

Description

【０００１】
【発明の属する技術分野】
本発明は、家電製品、家具、建材及び自動車部品などの外板に用いられる絞り成形性に優れた２層複合樹脂塗膜プレコート金属板に関する。
【０００２】
【従来の技術】
家電製品、家具、建材及び自動車部品などの外板用途に対して、プレコート金属板は、従来、加工を行わない平板部や曲げ加工等の単純な加工部にのみ適応し、絞り成形部には冷延鋼板及びめっき鋼板等の金属板を成形加工後に塗装するポストコート方式を採用していた。しかし、近年になり、プレコート金属板の普及率の増加に伴い、絞り加工部へもプレコート金属板が採用されつつある。
【０００３】
絞り加工部へプレコート金属板を採用する際には、従来は塗膜の引張試験による伸び率の高い塗膜やＴ折り曲げ試験結果の良い塗膜を選択し、円筒絞りや角筒絞り試験を実施して評価結果の良いものを絞り加工部に採用してきた。
【０００４】
【発明が解決しようとする課題】
絞り加工は、金属板に引張と圧縮の歪みが発生する変形様式であり、曲げ加工性が良く、単に伸びるだけの塗膜からなるプレコート金属板は、絞り加工に十分に適応できず、加工後に塗膜が剥離してしまう場合が多い。
【０００５】
そこで、本発明の目的は、絞り加工部に採用した場合に塗膜剥離や塗膜割れ等が発生せず、外観良好な絞り成形性に優れたプレコート金属板を提供することである。
【０００６】
【課題を解決するための手段】
本発明は、金属板に、下記 (a) の条件を満たす機械特性を有する樹脂塗膜と下記 (b) の条件を満たす機械特性を有する樹脂塗膜とを積層し、積層した樹脂塗膜が積層した状態での引張試験値として100MPa以上の引張弾性率を有し、かつ降伏点を有し、破断伸び率が10% 以上であることを特徴とする絞り成形性に優れた2層複合樹脂塗膜プレコート金属板である。
(a) 単層で、引張試験値として 5 〜 800MPa の引張弾性率を有し、破断強度が 50MPa 以下、破断伸び率が 30% 以上である樹脂塗膜。
(b) 単層で、引張試験値として 300 〜 3000MPa の引張弾性率を有し、破断強度が 10MPa 以上である樹脂塗膜。
【０００７】
本発明は、特定の異なる機械特性を有する樹脂塗膜を２層に積層し、２層複合塗膜にすると、絞り成形に適した最適機械特性値に制御でき、絞り成形性が良くなるという知見に基いている。
【０００８】
【発明の実施の形態】
本発明が対象とする金属板は、冷延鋼板や亜鉛めっき鋼板等の表面処理鋼板やその他の金属薄板で、特に制約するものではない。必要があれば、金属板上にクロメート処理等の化成処理を施してプレコート金属板用に供することも可能である。
【０００９】
本発明のプレコート金属板は、絞り成形性を良好とするために、金属板上に異なる機械特性を有する樹脂塗膜を積層した。樹脂塗膜は、２層積層した状態での引張試験値として１００ＭＰａ以上の引張弾性率を有し、かつ降伏点を有し、破断伸び率が１０％以上である。引張弾性率が１００ＭＰａ未満では塗膜中の弾性的性質が強いため、絞り成形後、塗膜に元の形状に戻ろうとする力が作用して、塗膜が剥離してしまう。降伏点がなく、伸び率が１０％未満では成形時に塗膜が割れてしまうため、絞り成形には適さない。
【００１０】
また、２層積層した状態で前述の特性を有するためには、単層で、引張試験値として５〜８００ＭＰａの引張弾性率を有し、破断強度が５０ＭＰａ以下、破断伸び率が３０％以上である樹脂塗膜と、単層で、引張試験値として３００〜３０００ＭＰａの引張弾性率を有し、破断強度が１０ＭＰａ以上である樹脂塗膜とを積層することが好ましい。この条件を満たさない塗膜を組み合わせると、２層積層した複合塗膜が降伏点を有しないため、絞り成形には適さない。
【００１１】
以上のように機械特性の異なる樹脂塗膜を２層積層することによって、２層複合塗膜としての機械特性を最適値に制御することができ、また、上記のように樹脂塗膜の機械特性を特定することにより、より良い絞り成形性を得ることができる。
【００１２】
絞り成形では鋼板等の金属薄板に引張と圧縮の力が作用し、金属薄板上の樹脂塗膜にも同様の力が作用する。金属は塑性体であり、変形後も永久歪みにより変形した形状を保つのに対し、樹脂塗膜は弾性体であるため、弾性的性質の高い樹脂塗膜では変形後に元の形状に戻ろうとする力が樹脂塗膜内に発生する。金属薄板に樹脂塗膜を被覆したプレコート金属板は、このように絞り成形による変形後、被覆した樹脂塗膜のみに元の形状に戻ろうとする力が働くため、特に圧縮の力が作用する部位において塗膜が剥離する。本発明は、樹脂塗膜の機械特性値を上記条件に設定することで、樹脂塗膜の弾性的性質を少なくし、変形後も変形した状態を保ち、より良い絞り成形性を得ることができる。
【００１３】
塗膜として用いる樹脂の種類は特に制約するものではないが、ポリエステル樹脂、アクリル樹脂、エポキシ樹脂等を通常用いて良い。
【００１４】
上記樹脂を用いて、上記条件の機械特性を付与するには、樹脂塗膜のＴｇを上げる、樹脂に硬化剤を添加する、塗膜の焼き付け温度を高くすることで塗膜の架橋密度を上げる等の手段があり、これらを適宜選定することによって目的とする機械特性が得られる。
【００１５】
【実施例】
単層塗膜の機械特性値を測定するために、まず塗膜として高分子ポリエステル系樹脂をベースとした塗料をテフロンシート上にバーコーターで塗装し、焼き付け後、テフロンシートより塗膜を剥離して塗膜のフリーフィルムを作成し、このフリーフィルムから図１に示す形状の試験片を作成し、引張試験を実施した。更に２層塗膜の機械特性値を測定するために、まず１層目の塗膜をテフロンシート上にバーコーターで塗装し、焼き付け後更に２層目の塗膜をバーコーターで塗装し、焼き付け後、テフロンシートより２層塗膜を剥離し、図１に示す形状の試験片を作成し、引張試験を実施した。単層塗膜フリーフィルムの膜厚は１５μｍ、２層塗膜フリーフィルムの膜厚は下層５μｍ＋上層１５μｍの計２０μｍとした。
【００１６】
引張試験はオリエンテック社製「テンシロンＣＴ−１０Ｔ」を用いて室温で引張スピード５ｍｍ／ｍｉｎで行い、塗膜の応力−伸び率線図より機械特性値を得た。
【００１７】
表１に各種塗膜の単層と２層での機械特性値を、図２〜７にこれらの応力−伸び率線図を示す。表１、図２〜７から明らかなように、機械特性の異なる２種の単層塗膜を積層すると単層状態とは異なった機械特性が得られる。
【００１８】
【表１】

【００１９】
次に、板厚０．６ｍｍの冷延鋼板上にクロメート処理を施し、その上に高分子ポリエステル系樹脂をベースとした異なる機械特性値を持つ塗膜を下層、上層の２層積層し、プレコート鋼板を作成した。その後に角筒絞り成形試験を行い、コーナー絞り部の塗膜の破壊形態を観察した。各塗膜の膜厚は下層が５μｍ、上層が１５μｍとした。
【００２０】
角筒絞り成形は、ポンチサイズ：７０ｍｍ角、ポンチ肩Ｒ：２ｍｍ、ポンチコーナー：１０ｍｍの金型を使い、ブランクサイズ：１４０ｍｍ角、ＢＨＦ：５ｔ、成形高さ：３０ｍｍで実施し、成形品のコーナー絞り部の外観観察を行い、表２の基準で判定した。
【００２１】
【表２】
◎：塗膜剥離、塗膜割れが認められない
○：塗膜剥離、塗膜割れが少し認められるが問題ないレベル
△：塗膜剥離、塗膜割れが共に認められる
×：塗膜剥離、塗膜割れが共に大いに認められる
【００２２】
また、各塗膜の機械特性値は、前述と同様に単層、２層の各塗膜のフリーフィルムから図１に示す形状の試験片を作成し、同様の条件で引張試験を実施し、応力−伸び率線図より得た。
【００２３】
表３に２層複合塗膜プレコート金属板の絞り成形評価結果を示す。表３から明らかなように、異なる機械特性を有する樹脂を２層積層した状態で引張試験したときに１００ＭＰａ以上の引張弾性率を有し、かつ降伏点を有し、破断伸び率が１０％以上であるプレコート金属板が絞り成形性に優れ、塗膜剥離、塗膜割れがなく外観が良かった。また、２層積層した状態で前述の機械特性を有するものは、各単層で、引張試験値として５〜８００ＭＰａの引張弾性率を有し、破断強度が５０ＭＰａ以下、破断伸び率が３０％以上である樹脂塗膜と、引張試験値として３００〜３０００ＭＰａの引張弾性率を有し、破断強度が１０ＭＰａ以上である樹脂塗膜とを積層したものが多かった。
【００２４】
【表３】

【００２５】
【発明の効果】
本発明のプレコート金属板は、金属板に２種類の異なる機械特性を有する樹脂塗膜を積層することで、絞り成形加工を行っても塗膜剥離や塗膜割れが発生しない。これにより、深絞り加工など厳しい成形加工部にもプレコート金属板を使用することが可能となり、プレコート金属板の用途が広まる。また、現在プレコート金属板を折り曲げ加工で使用している製品についても、絞り成形で製造することが可能となり、製品のデザイン面でも自由度が増し、加工形状に広がりができる。
【図面の簡単な説明】
【図１】塗膜フリーフィルムの引張試験片を示す図である。
【図２】単層塗膜と２層塗膜の応力−伸び率線図である。
【図３】単層塗膜と２層塗膜の応力−伸び率線図である。
【図４】単層塗膜と２層塗膜の応力−伸び率線図である。
【図５】単層塗膜と２層塗膜の応力−伸び率線図である。
【図６】単層塗膜と２層塗膜の応力−伸び率線図である。
【図７】単層塗膜と２層塗膜の応力−伸び率線図である。
【符号の説明】
Ａ全長１７５ｍｍ
Ｂ両端の幅２０ｍｍ
Ｃ平行部分の長さ６０ｍｍ
Ｄ平行部分の幅１０ｍｍ
Ｅ肩の丸みの半径６０ｍｍ
Ｆ厚さ５〜２０μｍ
Ｇ標線間距離５０ｍｍ
Ｈつかみ具間距離１１５ｍｍ[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a two-layer composite resin coating precoated metal sheet excellent in drawability used for an outer panel of home electric appliances, furniture, building materials, automobile parts, and the like.
[0002]
[Prior art]
For outer panel applications such as home appliances, furniture, building materials and automotive parts, pre-coated metal sheets are conventionally applied only to flat parts that are not processed or simple processed parts such as bending, and draw-formed parts are A post-coat method was adopted in which a metal plate such as a cold-rolled steel plate or a plated steel plate was painted after forming. However, in recent years, with the increase in the prevalence of the precoated metal sheet, the precoated metal sheet is also being used for the drawn portion.
[0003]
Conventionally, when using a pre-coated metal sheet for the drawn part, a film with a high elongation or a film with a good T-bend test result is selected by a tensile test of the film, and a cylindrical or square tube drawing test is performed. Those with good evaluation results have been adopted for the drawing section.
[0004]
[Problems to be solved by the invention]
Drawing is a deformation mode in which tensile and compression strains are generated in the metal plate, and has good bending workability, and a precoated metal plate consisting of a coating that simply stretches cannot be adequately applied to drawing, and after processing. In many cases, the coating film is peeled off.
[0005]
Accordingly, an object of the present invention is to provide a precoated metal sheet which does not cause peeling of a coating film or cracking of a coating film when employed in a drawn portion and has excellent appearance and excellent drawability.
[0006]
[Means for Solving the Problems]
The present invention relates to a metal plate, is satisfying mechanical properties by laminating a resin film having a satisfying mechanical properties of the resin film and (b) below having the laminated resin film of the following (a) A two-layer composite resin with excellent draw moldability, having a tensile modulus of 100 MPa or more as a tensile test value in a laminated state, having a yield point, and having an elongation at break of 10% or more. Prepainted metal plate.
(a) A single-layer resin coating film having a tensile modulus of 5 to 800 MPa as a tensile test value , a breaking strength of 50 MPa or less , and a breaking elongation of 30% or more.
(b) A single-layer resin coating film having a tensile modulus of 300 to 3000 MPa as a tensile test value and a breaking strength of 10 MPa or more.
[0007]
The present invention is based on the finding that when two layers of resin coatings having specific different mechanical properties are laminated to form a two-layer composite coating, the optimum mechanical property values suitable for drawing can be controlled, and the drawability can be improved. It is based on
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The metal sheet targeted by the present invention is a surface-treated steel sheet such as a cold-rolled steel sheet or a galvanized steel sheet or other thin metal sheet, and is not particularly limited. If necessary, it is also possible to subject the metal plate to a chemical conversion treatment such as a chromate treatment and use it for a precoated metal plate.
[0009]
In the precoated metal sheet of the present invention, a resin coating film having different mechanical properties was laminated on the metal sheet in order to improve draw formability. The resin coating film has a tensile modulus of 100 MPa or more as a tensile test value in a state where two layers are laminated, has a yield point, and has an elongation at break of 10% or more. If the tensile modulus is less than 100 MPa, the elastic properties in the coating film are strong, so that after drawing, a force is applied to the coating film to return to the original shape, and the coating film peels off. If there is no yield point and the elongation is less than 10%, the coating film breaks during molding, and is not suitable for drawing.
[0010]
Further, in order to have the above-mentioned properties in a state where two layers are laminated, a single layer has a tensile modulus of 5 to 800 MPa as a tensile test value, a breaking strength of 50 MPa or less, and a breaking elongation of 30% or more. It is preferable to laminate a certain resin coating film and a single-layer resin coating film having a tensile modulus of 300 to 3000 MPa as a tensile test value and a breaking strength of 10 MPa or more. If a coating film that does not satisfy this condition is combined, the composite coating film formed by laminating two layers does not have a yield point, and is not suitable for drawing.
[0011]
By laminating two resin coatings having different mechanical properties as described above, the mechanical properties of the two-layer composite coating can be controlled to an optimum value. By specifying, it is possible to obtain better draw formability.
[0012]
In drawing, tensile and compressive forces act on a thin metal plate such as a steel plate, and similar forces act on a resin coating on the thin metal plate. Metal is a plastic body and retains its shape after deformation due to permanent deformation, whereas resin coatings are elastic, so resin coatings with high elastic properties tend to return to their original shape after deformation Force is generated in the resin coating. In a pre-coated metal sheet in which a thin metal sheet is coated with a resin coating, after the deformation by drawing, a force is applied to only the coated resin coating to return to the original shape. In, the coating film is peeled off. In the present invention, by setting the mechanical property value of the resin coating film to the above condition, the elastic properties of the resin coating film are reduced, the deformed state is maintained even after the deformation, and better drawability can be obtained. .
[0013]
The type of resin used as the coating film is not particularly limited, but polyester resin, acrylic resin, epoxy resin, or the like may be usually used.
[0014]
To give the mechanical properties under the above conditions using the above resin, raise the Tg of the resin coating, add a curing agent to the resin, and increase the baking temperature of the coating to increase the crosslink density of the coating. The desired mechanical characteristics can be obtained by appropriately selecting these.
[0015]
【Example】
To measure the mechanical properties of a single-layer coating, first apply a coating based on a high-molecular polyester resin as a coating on a Teflon sheet with a bar coater, and after baking, peel off the coating from the Teflon sheet. Thus, a free film of a coating film was prepared, a test piece having the shape shown in FIG. 1 was prepared from the free film, and a tensile test was performed. Further, in order to measure the mechanical properties of the two-layer coating, first coat the first-layer coating on a Teflon sheet with a bar coater, and after baking, apply the second-layer coating with a bar coater and bake. Thereafter, the two-layer coating film was peeled off from the Teflon sheet, a test piece having the shape shown in FIG. 1 was prepared, and a tensile test was performed. The film thickness of the single-layer coating free film was 15 μm, and the film thickness of the two-layer coating free film was 5 μm for the lower layer and 15 μm for the upper layer, for a total of 20 μm.
[0016]
The tensile test was performed at room temperature at a tensile speed of 5 mm / min using "Tensilon CT-10T" manufactured by Orientec, and mechanical properties were obtained from a stress-elongation diagram of the coating film.
[0017]
Table 1 shows the mechanical property values of the single layer and the two layers of the various coating films, and FIGS. 2 to 7 show the stress-elongation diagrams thereof. As is clear from Table 1 and FIGS. 2 to 7, when two kinds of single-layer coating films having different mechanical properties are laminated, mechanical properties different from the single-layer state can be obtained.
[0018]
[Table 1]

[0019]
Next, a cold-rolled steel sheet having a thickness of 0.6 mm is subjected to a chromate treatment, and a lower layer and an upper layer of a coating film having different mechanical property values based on a high-molecular polyester resin are laminated on the cold-rolled steel sheet. A steel plate was created. Thereafter, a square tube drawing test was performed to observe the destruction form of the coating film at the corner drawn portion. The thickness of each coating film was 5 μm for the lower layer and 15 μm for the upper layer.
[0020]
The square tube drawing is performed using a mold having a punch size: 70 mm square, a punch shoulder R: 2 mm, a punch corner: 10 mm, a blank size: 140 mm square, BHF: 5 t, a molding height: 30 mm. The appearance of the corner drawing portion was observed, and the evaluation was made based on the criteria in Table 2.
[0021]
[Table 2]
◎: No peeling of the coating film and no cracking of the coating film are observed. ○: A little peeling of the coating film and cracking of the coating film are recognized, but there is no problem. Δ: Both the peeling of the coating film and the cracking of the coating film are recognized. Both film cracks are greatly recognized.
In addition, the mechanical property value of each coating film was prepared in the same manner as described above, by preparing a test piece having the shape shown in FIG. It was obtained from a stress-elongation diagram.
[0023]
Table 3 shows the results of draw forming evaluation of the two-layer composite coating precoated metal sheet. As is evident from Table 3, when a tensile test is performed in a state where two layers of resins having different mechanical properties are laminated, the resin has a tensile modulus of 100 MPa or more, has a yield point, and has an elongation at break of 10% or more. The precoated metal sheet was excellent in draw formability, and had good appearance without peeling of the coating film and cracking of the coating film. Further, those having the above-mentioned mechanical properties in a state where two layers are laminated, each of the single layers has a tensile elasticity of 5 to 800 MPa as a tensile test value, a breaking strength of 50 MPa or less, and a breaking elongation of 30% or more. And a resin coating film having a tensile modulus of 300 to 3000 MPa as a tensile test value and a breaking strength of 10 MPa or more was laminated in many cases.
[0024]
[Table 3]

[0025]
【The invention's effect】
In the precoated metal sheet of the present invention, by laminating two types of resin coating films having different mechanical properties on the metal sheet, peeling of the coating film and cracking of the coating film do not occur even when drawing is performed. This makes it possible to use the precoated metal sheet even in a severely formed portion such as a deep drawing process, and the use of the precoated metal sheet is widened. In addition, it is possible to manufacture a product in which a precoated metal plate is currently used by bending, by drawing, thereby increasing the degree of freedom in the design of the product and expanding the processed shape.
[Brief description of the drawings]
FIG. 1 is a view showing a tensile test piece of a paint-free film.
FIG. 2 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
FIG. 3 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
FIG. 4 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
FIG. 5 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
FIG. 6 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
FIG. 7 is a stress-elongation diagram of a single-layer coating film and a two-layer coating film.
[Explanation of symbols]
A total length 175mm
B Both ends width 20mm
C Length of parallel part 60mm
D Width of parallel part 10mm
E radius of shoulder roundness 60mm
F thickness 5-20μm
G Distance between marked lines 50mm
H Distance between gripping tools 115mm

Claims

A metal plate, in a state in which by laminating a resin film having a satisfying mechanical properties the following (a) a resin coating film and the below having satisfying mechanical properties (b), laminated resin film are laminated A two-layer composite resin coating precoated metal excellent in draw formability, having a tensile modulus of 100 MPa or more as a tensile test value, having a yield point, and having an elongation at break of 10% or more. Board.
(a) A single-layer resin coating film having a tensile modulus of 5 to 800 MPa as a tensile test value , a breaking strength of 50 MPa or less , and a breaking elongation of 30% or more.
(b) A single-layer resin coating film having a tensile modulus of 300 to 3000 MPa as a tensile test value and a breaking strength of 10 MPa or more.