Drawn/ironed can and coated metal sheet for drawn/ironed cans

Patent metadata

Field	Value
Publication number	US-12528619-B2
Application number	US-202117924777-A
Country	US
Kind code	B2
Filing date	May 10, 2021
Priority date	May 12, 2020
Publication date	Jan 20, 2026
Grant date	Jan 20, 2026

Abstract

The disclosure relates to a drawn/ironed can having at least an inner surface coating film on a can inner surface side, the inner surface coating film containing a polyester resin and a curing agent, and a stress relaxation ratio of the inner surface coating film after 10 minutes at 1% elongation in a can bottom portion is 50% or higher under a test condition of 100° C., whereby metal exposure due to severe processing such as drawing or ironing and coating film peeling due to heat treatment after molding are effectively prevented.

First claim

The invention claimed is:

1 . A drawn/ironed can comprising at least an inner surface coating film on a can inner surface side, the inner surface coating film comprising a polyester resin and a curing agent, wherein a stress relaxation ratio of the inner surface coating film after 10 minutes at 1% elongation in a can bottom portion is 50% or higher;
wherein, when a total amount of polyhydric alcohol components constituting the polyester resin is 100 mol %, the polyester resin contained in the inner surface coating film comprises one, or two or more selected from ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol in an amount of 20 mol % or greater in total, wherein the stress relaxation ratio is measured as follows:
a sample for measurement is prepared by removing the inner surface coating film from the can bottom portion and then cutting the inner surface coating film into 40 mm long with 4 mm wide to obtain the sample,
using a thermomechanical analyzer for the sample, after the sample was chucked with no deflection in the thermomechanical analyzer, an inter-chuck distance corresponding to the initial length of the sample was set to 10 mm; then, a measurement atmosphere temperature was raised, and 10 minutes after 100° C. was reached, the sample was elongated by 1% of the initial length of the sample at a tensile rate of 1 mm/min, and held in the state for 10 minutes; and then the stress relaxation ratio was calculated from a stress (Δ1) at 1% elongation and a stress (Δ2) after the 10-minute holding by the following formula (1) under the following Measurement conditions:
Instrument: thermomechanical analyzer TMA/SS6100, available from Seiko Instruments Inc.
Measurement atmosphere temperature: 100° C.
Inter-chuck distance: 10 mm
Tensile rate: 1 mm/min
Elongation rate (tensile elongation strain): 1%
Stress relaxation ratio (%)=(Δ1−Δ2)/Δ1×100  (1),

wherein, in formula (1), Δ1 is a stress at 1% elongation, and →2 is a stress after 10-minute holding, and a numerical value of each of Δ1 and Δ2 is a correction value obtained by subtracting a numerical value of a stress immediately before 1% elongation after reaching 100° C. from an actual measurement value.

2 . The drawn/ironed can according to claim 1 , further comprising an outer surface coating film on a can outer surface side, the outer surface coating film comprising a polyester resin and a curing agent, wherein a stress relaxation ratio of the outer surface coating film after 10 minutes at 1% elongation in a can bottom portion is higher than 40% under a test condition of 100° C.

3 . The drawn/ironed can according to claim 1 , wherein a thickness of a central portion of a can trunk is 20 to 75% of a thickness of a central portion of a can bottom.

4 . The drawn/ironed can according to claim 1 , wherein a thickness of the inner surface coating film in the central portion of the can trunk is 20 to 75% of a thickness of the inner surface coating film in the central portion of the can bottom.

5 . The drawn/ironed can according to claim 1 , wherein a thickness ratio of the inner surface coating film to a metal substrate (thickness of the inner surface coating film/thickness of the metal substrate) is substantially identical in a can bottom portion and a can trunk portion.

6 . The drawn/ironed can according to claim 1 , wherein a heat shrinkage rate of the inner surface coating film in the central portion of the can trunk represented by the following formula is 30% or less:
Heat shrinkage rate (%)=(Δ L 1 /L 0 )×100
L 0 : initial length of the coating film isolated from the central portion of the can trunk in a height direction ΔL 1 : maximum shrinkage length in the height direction of a portion corresponding to L 0 when temperature is raised from 30° C. to 200° C. at a temperature raising rate of 5° C./min while applying a load of 5.20×10 5 N/m 2 per unit area.

7 . The drawn/ironed can according to claim 1 , wherein a covering degree of the inner surface coating film is less than 200 mA in terms of ERV,
wherein the covering degree in terms of ERV is measured as follows:
a metal exposed portion is formed on an outer surface side of the can bottom of the drawn/ironed can, the can body is connected to an anode electrode of an enamel rater, while 360 mL of 1% salt solution is poured into the can and the cathode electrode of the enamel rater is immersed in the salt solution filled in the can, whereby a current value (ERV) after applying a voltage of 6.3 V for 4 seconds at room temperature is measured.

8 . The drawn/ironed can according to claim 1 , wherein a MEK extraction rate of the inner surface coating film is in a range of from 2 to 30%.

9 . The drawn/ironed can according to claim 1 , wherein the curing agent contained in the inner surface coating film comprises a resol phenolic resin and/or an amino resin.

10 . The drawn/ironed can according to claim 9 , wherein the resol phenolic resin comprises an m-cresol-based resol-type phenolic resin.

11 . The drawn/ironed can according to claim 1 , wherein the inner surface coating film further comprises an acid catalyst.

12 . The drawn/ironed can according to claim 11 , wherein a content of the acid catalyst in the inner surface coating film is less than 0.5 parts by mass per 100 parts by mass of the polyester resin.

13 . A coated metal sheet for a drawn/ironed can comprising a coating film on both surfaces, wherein an inner surface coating film of a surface to be on a can inner surface side after drawing and ironing contains a polyester resin and a resol phenolic resin and/or an amino resin as a curing agent, an outer surface coating film of a surface to be on a can outer surface side after drawing and ironing contains a polyester resin and an amino resin as the curing agent, and wherein a stress relaxation ratio of the inner surface coating film after 10 minutes at 1% elongation is 50% or higher, and a stress relaxation ratio of the outer surface coating film after 10 minutes at 1% elongation is higher than 40% under a test condition of 100° C.;
wherein when a total amount of polyhydric alcohol components constituting the polyester resin is 100 mol %, the polyester resin contained in the inner surface coating film contains one, or two or more selected from ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol in an amount of 20 mol % or greater in total,
wherein the stress relaxation ratio is measured as follows:
a sample for measurement is prepared by removing the inner surface coating film from the can bottom portion and then cutting the inner surface coating film into 40 mm long with 4 mm wide to obtain the sample,
using a thermomechanical analyzer for the sample, after the sample was chucked with no deflection in the thermomechanical analyzer, an inter-chuck distance corresponding to the initial length of the sample was set to 10 mm; then, a measurement atmosphere temperature was raised, and 10 minutes after 100° C. was reached, the sample was elongated by 1% of the initial length of the sample at a tensile rate of 1 mm/min, and held in the state for 10 minutes; and then the stress relaxation ratio was calculated from a stress (Δ1) at 1% elongation and a stress (Δ2) after the 10-minute holding by the following formula (1) under the following Measurement conditions:
Instrument: thermomechanical analyzer TMA/SS6100, available from Seiko Instruments Inc.
Measurement atmosphere temperature: 100° C.
Inter-chuck distance: 10 mm
Tensile rate: 1 mm/min
Elongation rate (tensile elongation strain): 1%
Stress relaxa

Assignees

• Toyo Seikan Group Holdings Ltd

Inventors

• Yamamoto Hiromi
• Kashiwakura Takuya
• Sakuragi Arata
• Zhang Nan

Classifications

• B65D25/34

  Coverings or external coatings (of containers made by folding or erecting blanks made of paper B65D5/62; covering or external coating for bottles or jars not otherwise provided for B65D23/08; wrappers B65D65/00) · CPC title

• B65D1/165 Primary

  Cylindrical cans · CPC title

• B21D51/26

  cans or tins; Closing same in a permanent manner (making outlet arrangements B21D51/38; welding or soldering B23K) · CPC title

• B21D22/28

  of cylindrical articles using consecutive dies · CPC title

• C08G63/183

  Terephthalic acids · CPC title