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TW-I916315-B - COATED METAL SHEET AND DRAWN-IRONED CAN

Abstract

The present invention provides a coated metal sheet having a coating on at least one surface thereof. The coating contains a polyester resin as a main component and a β-hydroxyalkylamide compound as a curing agent. Since the coating has elongation percentage of 200% or more under a test condition of 90°C, the coated metal sheet has excellent workability in can production to prevent exposure of metal even when it is subjected to severe working such as drawing and ironing, and has also excellent productivity. The present invention provides also a drawn-ironed can formed of the coated metal sheet.

Inventors

  • KASHIWAKURA, Takuya
  • YAMAMOTO, HIROMI
  • SAKURAGI, Arata
  • ZHANG, NAN

Assignees

  • 日商東洋製罐集團控股股份有限公司

Dates

Publication Date
20260301
Application Date
20191113
Priority Date
20181113

Claims (12)

  1. A coated metal sheet, having at least one side a coating film formed of an aqueous coating composition, characterized in that: the coating film is composed of a polyester resin as the main component and a β-hydroxyalkylamide compound as a hardener; the polyester resin is a blend of two polyester resins with different Tg, i.e., a mixed polyester resin; the average acid value of the mixed polyester resin is 10 mg KOH/g or more and less than 30 mg KOH/g; and the difference in acid values of the polyester resins constituting the mixed polyester resin is 5–30 mg KOH/g; the elongation of the coating film at a test condition of 90°C is 200% or more; the elongation is measured using the following method: Cut the coated metal sheet into pieces 5mm wide and 30mm long, and immerse them in a diluted hydrochloric acid solution to dissolve the metal sheet. Remove the thin-film coating monomer, wash it thoroughly with distilled water, and dry it to obtain a 5mm wide and 30mm long sample for testing. Use the top and bottom 5mm as clamping parts and clamp it in a tensile testing machine, making the distance between the clamps (the original length of the sample) 20mm. Perform a tensile test under the following conditions: Ambient temperature: 90℃; Tensile speed: 500mm/min. Measure the elongation of the coating until fracture under the test conditions of 90℃, replacing the movement of the cross joint of the testing machine until fracture. Calculate the elongation using the following formula. Elongation (%) = 100 × (ΔL/ L0 ) L0 : Original length of the sample (mm) ΔL: Elongation of the sample up to the point of breakage (mm).
  2. For example, in the coated metal plate of claim 1, the MEK extraction rate of the coating is 50% or less; the MEK extraction rate is measured using the following method: Test pieces measuring 5cm x 5cm were cut from the self-coated metal plate. When the coated metal plate was coated on both sides, the coating on the non-test side was removed. After measuring the mass of the test piece (W1), 200ml of MEK (methyl ethyl ketone) was used to immerse the test piece in boiling MEK (reflux at 80°C) for 1 hour. MEK extraction was performed at boiling point for 1 hour. After extraction, the test piece was washed with MEK and dried at 120°C for 1 hour. The mass of the extracted test piece was measured (W2). Further decomposition using concentrated sulfuric acid was used to peel, remove, wash, and dry the sample. The mass of the test piece was measured (W3). The MEK extraction rate of the coated metal plate was calculated using the following formula. MEK extraction rate (%) = 100 × (W1 - W2) / (W1 - W3).
  3. For example, the coated metal plate of request item 1 or 2, wherein the MEK extraction rate of the coating is 14-50%.
  4. For the coated metal plate requested in item 1 or 2, the glass transition temperature of the coating is in the range of 20–120°C. This glass transition temperature is measured using the following method: The coated metal plate is immersed in a diluted hydrochloric acid solution to dissolve it, thereby removing a thin film of coating. This film is then thoroughly washed with distilled water and dried to prepare a sample for testing. The glass transition temperature of the obtained coating is measured using a differential scanning calorimeter (DSC) under the following conditions: Sample size: 5 mg; Heating rate: 10°C/min; Temperature range: -80–200°C (heating, cooling, heating); Environmental conditions: nitrogen flow. Furthermore, in the 2nd-run (heating), the temperature at which the tangent line drawn from the straight line obtained by extending the baseline from the low-temperature side to the high-temperature side intersects the curve whose slope is the maximum in the phased change part of the glass transition is defined as the glass transition temperature of the coating (coating Tg).
  5. The coated metal sheet of claim 1 or 2 contains 2 to 10 parts by weight of the β-hydroxylamine compound relative to 100 parts by weight of the polyester resin.
  6. For example, in the coated metal sheet of request item 1 or 2, the polyester resin is an unmodified acrylic polyester resin or an acrylic-modified polyester resin with an acrylic resin content of less than 10% by mass.
  7. For example, the coated metal sheet of request item 1 or 2, wherein the thickness of the coating film is less than 30 μm.
  8. A deep-drawn can is made of a coated metal sheet as described in any of requests 1 to 7.
  9. For example, the deep-drawing can described in claim 8, wherein the coating on the inner and/or outer surfaces of the can bottom contains polyester resin as the main component and β-hydroxylamine compound as a hardener, and the elongation at 90°C is greater than 200%, and the MEK extraction rate is less than 50%; the elongation is measured using the following method: A 5mm wide and 30mm long sample was cut from the bottom of the can and immersed in a diluted hydrochloric acid solution to dissolve the metal plate. The thin film-like coating monomer was removed, thoroughly washed with distilled water, and dried to obtain a 5mm wide and 30mm long sample for testing. The top and bottom 5mm were used as clamping parts and clamped in a tensile testing machine, with the distance between the clamps (the original length of the sample) being 20mm. The tensile test was conducted under the following conditions: Ambient temperature: 90℃; Tensile speed: 500mm/min. The elongation of the coating until fracture was measured under the test conditions of 90℃, using the movement of the cross joint of the testing machine until fracture as the elongation was obtained. The elongation rate was calculated using the following formula. Elongation (%) = 100 × (ΔL/ L0 ) L0 : Original length of the sample (mm) ΔL: Elongation of the sample up to breakage (mm); The MEK extraction rate was determined using the following method: Cut a 5cm x 5cm test piece from the bottom of the tank. When forming a coated test piece on both sides, remove the coating from the non-test side and measure the mass of the test piece (W1). Use 200ml of MEK (methyl ethyl ketone) to immerse the test piece in boiling MEK (reflux at 80℃) for 1 hour. Perform MEK extraction at boiling point for 1 hour. After extraction, wash the test piece with MEK and dry it at 120℃ for 1 hour. Measure the mass of the extracted test piece (W2). Further use concentrated sulfuric acid for decomposition, peeling, removal, washing, and drying, measure the mass of the test piece (W3), and calculate the MEK extraction rate of the deep-press tank using the following formula. MEK extraction rate (%) = 100 × (W1 - W2) / (W1 - W3).
  10. A method for manufacturing a coated metal plate, comprising a method for manufacturing a coated metal plate as described in any one of claims 1 to 7, characterized in that: after applying an aqueous coating composition containing polyester resin as the main component and β-hydroxylamine compound as a hardener to at least one side of the metal plate, the coating is heated at a temperature above 200°C and below 320°C for 5 to 60 seconds, thereby forming a coating film with a MEK extraction rate of 14 to 50% as measured by the following determination method; Test pieces measuring 5cm x 5cm were cut from the self-coated metal plate. When the coated metal plate was coated on both sides, the coating on the non-test side was removed. After measuring the mass of the test piece (W1), 200ml of MEK (methyl ethyl ketone) was used to immerse the test piece in boiling MEK (reflux at 80°C) for 1 hour. MEK extraction was performed at boiling point for 1 hour. After extraction, the test piece was washed with MEK and dried at 120°C for 1 hour. The mass of the extracted test piece was measured (W2). Further decomposition using concentrated sulfuric acid was used to peel, remove, wash, and dry the sample. The mass of the test piece was measured (W3). The MEK extraction rate of the coated metal plate was calculated using the following formula. MEK extraction rate (%) = 100 × (W1 - W2) / (W1 - W3).
  11. A method for manufacturing a deep-drawing can, characterized in that: after deep-drawing a coated metal sheet as described in any of claims 1 to 7, a heating step is applied to the obtained deep-drawing can, thereby reducing the MEK extraction rate of the coating to less than 14%; the MEK extraction rate is measured using the following method: Cut a 5cm x 5cm test piece from the bottom of the tank. When forming a coated test piece on both sides, remove the coating from the non-test side and measure the mass of the test piece (W1). Use 200ml of MEK (methyl ethyl ketone) to immerse the test piece in boiling MEK (reflux at 80℃) for 1 hour. Perform MEK extraction at boiling point for 1 hour. After extraction, wash the test piece with MEK and dry it at 120℃ for 1 hour. Measure the mass of the extracted test piece (W2). Further use concentrated sulfuric acid for decomposition, peeling, removal, washing, and drying, measure the mass of the test piece (W3), and calculate the MEK extraction rate of the deep-press tank using the following formula. MEK extraction rate (%) = 100 × (W1 - W2) / (W1 - W3).
  12. For example, in the method of manufacturing a deep-drawing can as described in claim 11, the heating condition in the heating step is carried out at 150-250°C for 20-180 seconds.

Description

Coated metal sheets and deep-drawing cans This invention relates to a coated metal sheet and a deep-drawn can made from the coated metal sheet. More specifically, it relates to a coated metal sheet and a deep-drawn can that have excellent can-making processability, effectively preventing metal exposure even when subjected to harsh processing such as drawing and ironing, and excellent coating peel resistance, preventing coating peeling during heat treatment after forming. Coated organic resin metal sheets, made by coating metal sheets such as aluminum with thermoplastic resin films, have been known as can materials in the past. It is also known that these coated organic resin metal sheets are subjected to drawing or drawing-shrinking processes to produce seamless cans for filling beverages, etc., or are pressed to produce easy-open can lids. For example, a coated organic resin metal sheet having a thermoplastic resin film as the organic resin coating layer, wherein the thermoplastic resin film is composed of polyester resin mainly composed of polyethylene terephthalate units, is used as a can-making material for seamless cans formed by deep drawing (Patent 1, etc.). Such resin-coated metal sheets can be deep-drawn under dry conditions without the use of liquid coolant. Therefore, compared to deep-drawing metal sheets coated with unrefined organic resin using a large amount of liquid coolant, this method can significantly reduce environmental impact. Such resin-coated metal sheets can be manufactured using film lamination methods, such as thermally bonding a pre-formed film of thermoplastic polyester resin to a metal sheet, or extrusion lamination bonding a molten film of extruded thermoplastic polyester resin to a metal sheet. However, in film lamination methods, the difficulty in film fabrication and the tendency for the film thickness to become excessive can lead to economic problems. Instead of using such a thin-film lamination method to produce coated organic resin metal sheets, it has been proposed to manufacture deep-drawing cans by forming a coating film on the metal sheet using a film-forming coating method. For example, in Patent Document 2 below, a coated metal sheet for deep-drawing cans is proposed. This sheet is a double-sided coated metal sheet. After processing, the dry coating amount of the film on the inner surface of the can is 90-400 mg/100 cm² , the glass transition temperature is 50-120°C, and under test conditions at 60°C, the pencil hardness is H or higher, the elongation is 200-600%, and the coefficient of sliding friction is 0.03-0.25. The dry coating amount of the film on the outer surface of the can is 15-150 mg/100 cm² , the glass transition temperature is 50-120°C, and under test conditions at 60°C, the pencil hardness is H or higher. [Previous Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2001-246695 [Patent Document 2] Japanese Patent No. 3872998 [The problem the invention aims to solve] However, in the aforementioned patent 2, a coating composition containing polyester resin and soluble phenolic resin is used as the coating composition for the inner surface of the can, and a coating composition containing polyester resin, amine resin and/or soluble phenolic resin is used as the coating composition for the outer surface of the can. The coating film formed by such a coating composition has hard and brittle microdomains formed in the coating film due to the formation of autocondensates from phenolic resin or amine resin. Such microdomains may lead to a reduction in the processability of the coating film, which becomes a problem from the perspective of can manufacturing processability. Furthermore, when using soluble phenolic resins, the resulting coating has a characteristic yellow tint, which can sometimes cause color problems when used on exterior surfaces. On the other hand, in deep-drawn cans formed from coated metal sheets, after the can body is formed, during heat treatment to remove residual deformation of the coating caused by processing, or to dry and harden inks and varnishes applied to the can's exterior surface, the internal stress (residual stress) of the coating caused by harsh processing is relieved. This is especially true in areas where the can body sidewalls have been severely processed and thinned, where the coating may peel off from the metal substrate. Therefore, the purpose of this invention is to provide: a coated metal sheet that does not suffer from the aforementioned problems, possesses excellent can-making processability suitable for harsh processes such as deep drawing under dry conditions, exhibits excellent coating peel resistance even when heat treatment is applied after can forming, and has excellent manufacturability, as well as a deep-drawn can made from the coated metal sheet. [Means of Solving the Problem] According to the present invention, a coated metal sheet is provided, having a coati