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

Abstract

The present invention relates to a draw-and-iron thin can having a draw-and-iron thin can having an inner surface coating film on at least the inner surface side of the can, the inner surface coating film containing a polyester resin and a curing agent, the stress relaxation rate of the inner surface coating film in the bottom of the can after 10 minutes at 1% elongation under test conditions of 100°C being 50% or more, whereby metal exposure caused by severe processing such as draw processing, iron processing, etc. and peeling of the coating film caused by heat treatment after molding are effectively prevented.

Description

TECHNICAL FIELD

[0001] The present application relates to a draw-and-wall-ironed can formed of a coated metal sheet and a coated metal sheet for a draw-and-wall-ironed can, and more particularly to a draw-and-wall-ironed can in which metal exposure caused by severe processing such as drawing processing, wall-ironing processing, and the like, and peeling of a coating film caused by heat treatment after forming are effectively prevented, and a coated metal sheet for a draw-and-wall-ironed can which can be used to form such a draw-and-wall-ironed can with good productivity. BACKGROUND

[0002] An organic resin-coated metal sheet in which a metal sheet such as aluminum is coated with a thermoplastic resin film has long been known as a can material, and it is also known that the organic resin-coated metal sheet is subjected to drawing processing or draw-and-wall-ironing processing, or the like, to be formed into a seamless can for filling beverages or the like, or a can end such as a pop-top end. For example, an organic resin-coated metal sheet having a thermoplastic resin film formed of a crystalline polyester resin in which an ethylene terephthalate unit is the main component as an organic resin coating layer is used as a can-making material for a seamless can (draw-and-wall-ironed can) formed by draw-and-wall-ironing processing (Patent Document 1 and the like). Such an organic resin-coated metal sheet can be subjected to stretch-and-wall-ironing forming under dry conditions without using a coolant (cooling / lubricating agent), and thus has an advantage in terms of the environment compared to the case where a conventional metal sheet is subjected to stretch-and-wall-ironing forming using a coolant.

[0003] Such an organic resin-coated metal sheet can be manufactured by a film lamination method such as a method in which a film of a thermoplastic polyester resin or the like is previously formed and is adhered to a metal sheet by heat bonding, an extrusion lamination method in which a molten film of an extruded thermoplastic polyester resin or the like is adhered to a metal sheet.

[0004] However, in the film lamination method, it is difficult to control the film thickness to be thin, and thus the film thickness tends to be thick, which sometimes becomes a problem in terms of economy.

[0005] Instead of an organic resin-coated metal sheet obtained by such a film lamination method, it has also been proposed to manufacture a draw-and-wall-ironed can under dry conditions using a coated metal sheet in which a coating film is formed on a metal sheet by a coating method in which a film can be formed in a thin film.

[0006] For example, in Patent Document 2 described below, a coated metal sheet for a draw-and-wall-ironed can is proposed, which is a two-sided coated metal sheet, and the dry coating amount of a skin film of the coated metal sheet after processing, which becomes the inner surface side of a can, is 90 mg / 100 cm 2 ~ 400 mg / 100 cm 2, the glass transition temperature is 50°C to 120°C, and the pencil hardness is H or more under test conditions at 60°C, and the elongation is 200% to 600% and the dynamic friction coefficient is 0.03 to 0.25, and the dry coating amount of the film after processing on the outer surface side of the can is 15 mg / 100 cm 2 ~ 150 mg / 100 cm 2 , the glass transition temperature is 50°C to 120°C, and the pencil hardness is H or more under test conditions at 60°C.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-353812

[0010] Patent Document 2: Japanese Patent No. 3872998 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] In a draw-and-iron can which is formed from a coated metal sheet under dry conditions, the adhesion between the coating film and the metal substrate (hereinafter, sometimes referred to as "coating film adhesion") is sometimes remarkably reduced due to residual stress in the coating film resulting from severe draw-and-iron processing after the can body is formed. This residual stress can be removed by applying heat treatment to the can body under prescribed conditions, but in the case where such heat treatment is applied, the residual stress in the coating film resulting from severe processing is suddenly relaxed, shrinkage force acts on the interface between the coating film and the metal substrate, and particularly at portions where the processing of the can main body portion is strictly thinned, the coating film is peeled from the metal substrate, thereby causing metal exposure, and sometimes the coating film coverage is reduced.

[0013] However, the above-described Patent Document 2 proposes a coated metal sheet and a draw-and-iron can formed from the same, in which a coating film which exhibits hardness, elongation, etc. even when heat generation of approximately 60°C resulting from continuous draw-and-iron processing occurs is formed on the side of the inner surface of the can, and thus the coated metal sheet can withstand draw-and-iron processing, but there is no insight into the removal of residual stress resulting from heat treatment after forming processing of a draw-and-iron can using the coated metal sheet, and there is no insight into peeling of the coating film resulting from the heat treatment, and the problems described above are not solved.

[0014] Therefore, the object of the present application is to provide a draw-and-iron can which has excellent coating film peeling resistance in which peeling of the coating film does not occur due to heat treatment after forming, which suppresses metal exposure, which has high coating film coverage after heat treatment, and which has excellent corrosion resistance.

[0015] Further, another object of the present application is to provide a coated metal sheet for drawing-reducing cans having a coating film which does not cause the problems described above.

[0016] Technical Solution

[0017] According to the present application, there is provided a drawing-reducing can characterized by having an inner surface coating film on at least the inner surface side of the can, the inner surface coating film containing a polyester resin and a curing agent, the stress relaxation rate of the inner surface coating film in the bottom portion of the can after 10 minutes at 1% elongation under test conditions of 100°C being 50% or more.

[0018] In the drawing-reducing can of the present application, the following is preferable.

[0019] 1. The curing agent contained in the inner surface coating film is a resol-type phenol resin and / or an amino resin.

[0020] 2. The curing agent contained in the inner surface coating film is a meta-cresol-based resol-type phenol resin.

[0021] 3. The inner surface coating film further contains an acid catalyst.

[0022] 4. The content of the acid catalyst in the inner surface coating film is less than 0.5 parts by mass with respect to 100 parts by mass of the polyester resin.

[0023] 5. The polyester resin contained in the inner surface coating film contains a total of 20 mol% or more of one or two or more selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol, when the total amount of the polyol component constituting the polyester resin is taken as 100 mol%.

[0024] 6. The outer surface of the can further has an outer surface coating film, the outer surface coating film containing a polyester resin and a curing agent, the stress relaxation rate of the outer surface coating film in the bottom portion of the can being higher than 40%.

[0025] 7. The thickness of the central portion of the can body is 20% to 75% of the thickness of the central portion of the bottom of the can.

[0026] 8. The thickness of the inner surface coating film in the central portion of the can body is 20% to 75% of the thickness of the inner surface coating film in the central portion of the bottom of the can.

[0027] 9. The thickness ratio of the inner surface coating film to the metal substrate (thickness of the inner surface coating film / thickness of the metal substrate) is almost the same in the bottom portion and the body portion of the can.

[0028] 10. The heat shrinkage of the inner surface coating film in the central portion of the can body, represented by the following formula, is 30% or less,

[0029] Thermal shrinkage (%) = (ΔL1 / L0) x 100

[0030] L0: initial length in the height direction of the coating film from the central portion of the can body;

[0031] ΔL1: maximum shrinkage length in the height direction of the coating film of the portion corresponding to L0 when a load of 5.20 x 10 5 N / m 2 is applied per unit area while being warmed at a rate of 5°C / min from 30°C to 200°C.

[0032] 11. The coverage of the inner surface coating film is less than 200 mA in terms of ERV.

[0033] Further, according to the present application, there is provided a coated metal sheet for a draw-reduced can, characterized in that both surfaces have a coating film, the inner surface coating film of the surface which becomes the inner surface side of the can after draw-reducing processing contains a polyester resin and, as a curing agent, a resol-type phenol resin and / or an amino resin, the outer surface coating film of the surface which becomes the outer surface side of the can after draw-reducing processing contains a polyester resin and, as a curing agent, an amino resin, the stress relaxation rate of the inner surface coating film after 10 minutes at 1% elongation under test conditions of 100°C is 50% or more, and the stress relaxation rate of the outer surface coating film after 10 minutes at 1% elongation under test conditions of 100°C is higher than 40%.

[0034] In the coated metal sheet for a draw-reduced can of the present application, it is preferable that the polyester resin contained in the inner surface coating film contains, in total, 20 mol% or more of one or two or more selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol, when the total amount of the polyol component constituting the polyester resin is taken as 100 mol%.

[0035] According to the present application, there is also provided a draw-reduced can, characterized by being formed from the above-mentioned coated metal sheet for a draw-reduced can.

[0036] In the above-mentioned draw-reduced can of the present application, the following is preferable.

[0037] 1. The thickness of the central portion of the can body is 20% to 75% of the thickness of the central portion of the can bottom;

[0038] 2. The thickness of the inner surface coating film in the central portion of the can body is 20% to 75% of the thickness of the inner surface coating film in the central portion of the can bottom;

[0039] 3. The coverage of the inner surface coating film is less than 200 mA in terms of ERV.

[0040] Effects of the Invention

[0041] The present inventors, in view of the above background, conducted intensive studies on the peeling of the coating film caused by heat treatment of a draw-and-wall-ironing can formed of a coated metal sheet, and as a result, found that the ease of occurrence of peeling of the coating film at the time of heat treatment is correlated with the behavior of stress relaxation (stress relaxation rate) when the coating film is elongated under prescribed conditions, and found a range of stress relaxation rates at which peeling of the coating film does not occur and a coating film that can exhibit such a stress relaxation rate.

[0042] That is, in the draw-and-wall-ironing can of the present application, peeling of the coating film at the time of heat treatment is suppressed, and therefore even when the coverage of the inner surface coating film expressed in terms of ERV is less than 200 mA after heat treatment is performed after the draw-and-wall-ironing can is formed, metal exposure is effectively prevented, and excellent corrosion resistance is exhibited.

[0043] Further, the coated metal sheet from which such a draw-and-wall-ironing can is formed has excellent elongation and processability of the coating film, and can effectively prevent the occurrence of breakage at the can body portion (sometimes referred to as body breakage) and metal exposure even in the case of severe processing such as draw processing and wall-ironing processing under drying conditions, and therefore has high coating film coverage after draw-and-wall-ironing processing and excellent can-making processability. That is, in the present application, by using a specific combination of a polyester resin and a curing agent as the polyester resin and the curing agent that constitute the coating film, the degree of curing, the crosslinking density, and the like of the coating film are controlled, excellent can-making processability is exhibited, and by controlling the stress relaxation rate and reducing residual stress resulting from can-making processing, peeling of the coating film at the time of heat treatment performed after the can body is formed is effectively suppressed, and a draw-and-wall-ironing can having high coating film coverage and excellent corrosion resistance can be provided. DETAILED DESCRIPTION

[0044] (coated metal sheet)

[0045] The coated metal sheet used for the formation of the draw-and-wall-ironing can of the present application, as described above, is a coated metal sheet in which the face on the inner surface side of the can after draw-and-wall-ironing processing has an inner surface coating film, the inner surface coating film contains a polyester resin and a curing agent, and the important feature is that the stress relaxation rate after 10 minutes at 1% elongation under test conditions of 100°C is 50% or more.

[0046] The above stress relaxation rate in the present application is explicitly known from the measurement method described later, and the stress relaxation rate is calculated from the following equation (1) based on the time change in stress measured while maintaining a 1% elongation rate strain applied to the coating film under test conditions of 100°C using a thermal mechanical analysis device or the like.

[0047] Stress relaxation rate (%) = (δ1- δ2) / δ1 x 100... (1)

[0048] In the formula, δl is the stress at 1% elongation of the separated inner surface coating film, and δ2 is the stress after 10 minutes.

[0049] In the case where a draw-reduced can is formed at high speed using a coated metal sheet under dry conditions, the coated metal sheet is subjected to severe processing / deformation while the temperature thereof is rising due to heat generated by the processing. At this time, the coating film formed on the coated metal sheet is subjected to a large deformation due to the can-making processing, and thus residual stress is generated in the coating film after the processing. In particular, in the case where the main agent resin such as a polyester resin constituting the coating film is highly cross-linked by a curing agent, it is difficult to relax the stress generated by the processing, and the residual stress tends to be large. It is considered that, if the residual stress of the coating film is kept large, and heat treatment is performed on the formed can body to heat it to a temperature above the glass transition temperature of the polyester resin, a shrinkage force acts on the interface between the coating film and the base, and thus the coating film is peeled off, and the metal is exposed.

[0050] The above-mentioned large stress relaxation rate in the coating film of the coated metal sheet means that, in the case where the coated metal sheet is formed at high speed, and the coating film is processed while being brought to a high temperature state by heat generated by the processing, the stress generated by the processing is relaxed immediately, that is, the residual stress of the coating film after the processing is small. Thus, the shrinkage force generated at the interface between the coating film and the metal base with the relaxation of the residual stress can be made small, and as a result, the generation of the peeling of the coating film can be prevented. This is also clear from the results of the examples described later, and in the case where the stress relaxation rate of the inner surface coating film is less than 50%, it is difficult to suppress the generation of the peeling of the coating film by heat treatment.

[0051] The coated metal sheet used in the present application for the formation of the draw-reduced can is as described above, and is a coated metal sheet having at least an inner surface coating film on the surface on the side of the inner surface of the can after the draw-reduction processing, the inner surface coating film being formed of a polyester resin and a curing agent. Desirably, the above-mentioned stress relaxation rate of the inner surface coating film is 50% or more, preferably in the range of 50% to 95%, more preferably in the range of 54% to 90%, further preferably in the range of 54% to 85%, particularly preferably in the range of 54% to 80%, and most preferably in the range of 60% to 80%.

[0052] Further, the surface on the side of the outer surface of the can after the draw-reduction processing has an outer surface coating film, and the outer surface coating film is also formed of a polyester resin and a curing agent. Desirably, the above-mentioned stress relaxation rate of the outer surface coating film is more than 40%, preferably in the range of 45% to 95%, more preferably in the range of 50% to 90%, further preferably in the range of 54% to 85%, particularly preferably in the range of 54% to 80%, and most preferably in the range of 60% to 80%.

[0053] By using the coated metal sheet having at least an inner surface coating film on the surface on the side of the inner surface of the can as described above for the formation of the draw-reduced can, the entire portion from the bottom on the side of the inner surface of the can to the main body portion can be covered by the continuous inner surface coating film.

[0054] Further, in the case of using a two-sided coated metal sheet in which the surface that becomes the outer surface of the can after the draw-and-iron processing also has an outer surface coating film, the entire portion from the bottom on the can outer surface side to the main body portion can be covered by the continuous outer surface coating film. The outer surface coating film in the coated metal sheet of the present application is also excellent in cooking resistance, and thus a draw-and-iron can having an excellent cooking resistance of the can outer surface can be obtained. The bottom of a general seamless can is often composed of a lower bottom portion located in the central portion, a ground portion (rim) descending from the edge of the lower bottom portion, and a chime portion extending obliquely outward and upward from the ground portion and connected to the lower end of the main body portion, and the bottom of a general draw-and-iron can is often composed of a lower bottom portion located in the central portion, a ground portion (rim) descending from the edge of the lower bottom portion, and a chime portion extending obliquely outward and upward from the ground portion and connected to the lower end of the main body portion. In the conventional draw-and-iron can formed using a non-coated metal sheet with a coolant, it is necessary to coat the ground portion on the outer surface side with a paint for improving the conveyability of the can body immediately after the can body is formed, and further, in the case where the chime portion and the lower bottom portion are also coated in consideration of cooking resistance and the like, after the inner surface coating and the printing coating of the outer surface main body portion are performed, it is necessary to coat the chime portion and the lower bottom portion on the outer surface side with different paint compositions by different coating methods / devices, respectively, and thus the number of steps is large, and sometimes the productivity and the economy become problems. On the other hand, as described in the present application, in the case of forming a draw-and-iron can using a coated metal sheet in which the surface that becomes the outer surface of the can has an outer surface coating film, the entire portion from the bottom on the can outer surface side to the main body portion can be continuously covered by the same outer surface coating film, and thus it is not necessary to coat the chime portion, the ground portion, and the lower bottom portion that constitute the can bottom portion with different paint compositions by different coating methods / devices, respectively, and thus the productivity and the economy are excellent.

[0055] In the coated metal sheet of the present application, it is preferable that the glass transition temperature (Tg) of the above-mentioned inner surface coating film be 30°C or higher, preferably higher than 40°C, more preferably higher than 50°C and 120°C or lower, further preferably 60°C to 110°C, particularly preferably higher than 65°C and 100°C or lower, and most preferably 68°C to 90°C. In the case where the Tg is lower than the above-mentioned range, when the can body after the formation is filled with a content, it becomes easy to adsorb flavor (aroma) components of the content, and there is a possibility that the flavor adsorption resistance becomes poor, and there is a possibility that the barrier property of the coating film is reduced and the corrosion resistance is poor. On the other hand, in the case where the Tg exceeds 120°C, the can-making processability of the coating film is reduced, there is a possibility that the metal is exposed due to the formation, the covering property of the inner surface coating film is reduced, and the corrosion resistance is poor.

[0056] Further, it is preferable that the Tg of the outer surface coating film described above be 30°C or higher, preferably higher than 40°C, more preferably higher than 50°C and 120°C or lower, further preferably 60°C to 110°C, particularly preferably higher than 65°C and 100°C or lower, and most preferably 68°C to 90°C. In the case where the Tg is lower than the range described above, the hardness of the coating film becomes low, and thus there is a possibility that the outer surface will be damaged, etc. On the other hand, in the case where the Tg exceeds 120°C, the can processing property of the coating film becomes poor, and there is a possibility that the metal will be exposed due to the forming, and the coating property of the outer surface becomes poor.

[0057] Further, the film thickness of the inner surface coating film described above is preferably 0.2 μm to 20 μm, preferably 1 μm to 12 μm, and more preferably greater than 2 μm and 12 μm or lower, in terms of dry film thickness. Further, as the dry coating film weight, it is preferable that it be 3 mg / dm 2 to 300 mg / dm 2 , preferably 15 mg / dm 2 to 150 mg / dm 2 , and more preferably greater than 25 mg / dm 2 and 150 mg / dm 2 or lower. In the case of a film thinner than the range described above, the metal is easily exposed during the forming, and the coating property of the inner surface coating film becomes poor. On the other hand, in the case of a film thicker than the range described above, the internal stress generated during the processing becomes large, and thus the coating film is easily peeled off during the heat treatment after the stretch-reducing forming, and it becomes necessary to have a thicker film, and thus the economy becomes poor.

[0058] Further, in the case where the content filled in the stretch-reducing can is an acidic beverage having a strong corrosive property, in order to ensure the corrosion resistance, it is necessary to have a film thickness that is relatively thick, and it is preferable that it be greater than 6 μm and 12 μm or lower, and preferably 6.5 μm to 10 μm. Further, as the dry coating film weight, it is preferable that it be greater than 85 mg / dm 2 and 150 mg / dm 2 , and preferably 90 mg / dm 2 to 140 mg / dm 2 . In the case of a film thinner than the range described above, the corrosion resistance is poor, and in the case where it exceeds the range described above, the coating film is easily peeled off during the heat treatment after the stretch-reducing forming.

[0059] On the other hand, in the case where the content filled in the stretch-reducing can is a low-acidic beverage having a weak corrosive property, etc., even a thin film can ensure the corrosion resistance, and thus it is preferable that it be 1 μm or higher and less than 6.5 μm, and preferably greater than 2 μm and less than 6.5 μm, and more preferably 2.5 μm to 6 μm. Further, as the dry coating film weight, it is preferable that it be 15 mg / dm2 more than 25 mg / dm2and less than 90 mg / dm2 2 more than 25 mg / dm2and less than 90 mg / dm2 2 more than 25 mg / dm2and less than 90 mg / dm2 2 more than 25 mg / dm2and less than 90 mg / dm2 2 more than 25 mg / dm2and less than 90 mg / dm2 2 more than 25 mg / dm2and less than 90 mg / dm2 In the case of a film thinner than the above range, corrosion resistance is poor, and in the case of a film thicker than the above range, a film thicker than necessary is required, and economy is poor.

[0060] Further, it is preferable that the film thickness of the outer surface coating film be in the range of 0.2 μm to 20 μm, preferably 1 μm to 12 μm, more preferably more than 2 μm and 10 μm or less, further preferably more than 2 μm and 6.5 μm or less, in terms of dry film thickness. Further, as the dry coating film weight, it is preferable that it be in the range of 3 to 300 mg / dm2 2 , preferably 15 to 150 mg / dm2 2 , preferably 15 to 150 mg / dm2 2 , preferably 15 to 150 mg / dm2 2 , preferably 15 to 150 mg / dm2 2 , preferably 15 to 150 mg / dm2 2 , preferably 15 to 150 mg / dm2 In the case of a film thinner than the above range, metal exposure is likely to occur during forming, and the coating film covering property of the outer surface is poor. On the other hand, in the case of a film thicker than the above range, internal stress generated during processing becomes large, and thus coating film peeling is likely to occur during heat treatment after stretch-reducing forming.

[0061] Note that, regarding the film thickness of the inner surface coating film and the outer surface coating film of the coated metal sheet, the film thickness of the inner surface coating film, which requires a higher covering property, is thicker than that of the outer surface coating film.

[0062] The coated metal sheet, the inner surface coating film and the outer surface coating film of the deep-drawn reduced can of the present application are composed of a polyester resin and a curing agent as main agents.

[0063] In the inner surface coating film, the content of the polyester resin, preferably the non-crystalline polyester resin described later, is preferably higher than 50 mass%, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more.

[0064] In the outer surface coating film as well, the content of the polyester resin, preferably the non-crystalline polyester resin, is preferably higher than 50 mass%, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more.

[0065] (Polyester Resin)

[0066] In the deep-drawn and reduced can and the coated metal sheet of the present application, a polyester resin is used as a main agent (main component) constituting the inner surface coating film and the outer surface coating film, and the main agent refers to a substance having the largest content (mass ratio) among resin components constituting the coating film. In the present application, the mass ratio of the polyester resin in the resin components constituting the inner surface coating film and the outer surface coating film is preferably higher than 50 mass%, more preferably 60 mass% or more, further preferably 70 mass% or more, and particularly preferably 80 mass% or more.

[0067] As the polyol component constituting the polyester resin used, it is preferable to contain a polyol component having a molecular structure of a small volume and a steric hindrance that does not easily generate a high molecular chain in an amount of 20 mol% or more, when the total amount of the polyol component constituting the polyester resin is 100 mol%. As such a polyol component, not limited to these, ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, diethylene glycol, and the like can be exemplified, and it is preferable to contain at least one or two or more selected from these in a total amount of 20 mol% or more. It is considered that, when the coated metal sheet is formed into a deep-drawn and reduced can, stress relaxation due to rotation of a high molecular chain is easily generated, and as a result, it is presumed to be associated with reduction of residual stress of the coating film after forming, and suppression of coating film peeling during heat treatment. Note that, as a polyol having a large volume, not limited to these, alicyclic polyols such as 1,4-cyclohexane dimethanol, neopentyl glycol, and the like can be exemplified, and it is presumed that such a polyol is relatively less likely to generate stress relaxation due to rotation of a molecular chain due to steric hindrance.

[0068] It is preferable that the glass transition temperature (Tg) of the polyester resin is 30°C or higher, preferably higher than 40°C, more preferably higher than 50°C and 120°C or lower, further preferably 60°C to 110°C, particularly preferably higher than 65°C and 100°C or lower, and most preferably 68°C to 90°C. If the Tg becomes lower than the above range, when the container manufactured by the deep-drawing and reducing processing as described above is filled with a content, the flavor component (aroma component) contained in the content is easily diffused into the inside of the coating film due to the increase in the mobility of the resin, and thus the adsorption amount of the flavor component also increases, and there is a possibility that the flavor adsorption resistance is deteriorated, and there is a possibility that the heat resistance, corrosion resistance, and boiling resistance are also deteriorated. On the other hand, in the case where the Tg exceeds 120°C, the processability and elongation of the coating film are reduced, and thus there is a possibility that the can manufacturing processability is deteriorated, and the metal is exposed due to forming, and as a result, there is a possibility that the coating property of the coating film after forming is deteriorated, and the stress relaxation rate is reduced, and the coating film peeling resistance is deteriorated.

[0069] In the present application, two or more kinds of polyester resins having different Tg can also be mixed and used. By mixing polyester resins having different Tg, a coating film having excellent impact resistance, which is not easily damaged by external impact, can sometimes be formed compared to the case where only one kind of polyester resin is used.

[0070] In this case, the Tg of the polyester resin mixture calculated from the following formula (2) mix In the above Tg range.

[0071] 1 / Tg mix = (W1 / Tg1) + (W2 / Tg2) +... + (Wm / Tgm)... (2)

[0072] W1 + W2 +... + Wm = 1

[0073] In the formula, Tg mix represents the glass transition temperature (K) of the polyester resin mixture, Tg1, Tg2,..., Tgm represent the glass transition temperature (K) of the monomers of each polyester resin (polyester resin 1, polyester resin 2,..., polyester resin m) used. In addition, W1, W2,..., Wm represent the mass fraction of each polyester resin (polyester resin 1, polyester resin 2,..., polyester resin m).

[0074] As the polycarboxylic acid component constituting the polyester resin, for example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalene dicarboxylic acid, aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, unsaturated dicarboxylic acids such as maleic acid (anhydride), fumaric acid, terpene-maleic acid adduct, alicyclic dicarboxylic acids such as 1,4-cyclohexane dicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexene dicarboxylic acid, and three or more polycarboxylic acids such as trimellitic acid (anhydride), pyromellitic acid (anhydride), methylcyclohexene tricarboxylic acid can be used, and one or two or more kinds thereof can be selected for use. Of the above polycarboxylic acids, one or more kinds selected from the group consisting of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, trimellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, dimer acid, and 1,4-cyclohexane dicarboxylic acid are preferably used.

[0075] In the present application, from the viewpoints of the hardness, heat resistance, flavor adsorption resistance, boiling resistance, and the like of the obtained coating film, it is preferable that, when the total amount of the polybasic acid component constituting the polyester resin is taken as 100 mol%, at least one or two or more selected from terephthalic acid, phthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid as the aromatic dicarboxylic acid is contained in a total amount of 60 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and further preferably 90 mol% or more. In addition, among the above-mentioned aromatic dicarboxylic acids, terephthalic acid and isophthalic acid are particularly preferable, and it is preferable that, when the total amount of the polybasic acid component constituting the polyester resin is taken as 100 mol%, the total content of terephthalic acid and isophthalic acid is preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and particularly preferably 90 mol% or more.

[0076] As the polyhydric alcohol component constituting the polyester resin, it is preferable that, when the total amount of the polyhydric alcohol component constituting the polyester resin is taken as 100 mol%, at least one or two or more selected from ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol is contained in a total amount of 20 mol% or more, preferably 30 mol% or more, more preferably 40 mol% or more, further preferably 50 mol% or more, particularly preferably 60 mol% or more, and most preferably 70 mol% or more.

[0077] As the remaining component of the polyhydric alcohol component, one or two or more of the following can be used in combination: 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 2,4-dimethyl-1,5-pentanediol, 1-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, 4-propyl-1,8-octanediol, 1,9-nonanediol, and the like aliphatic glycols; diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like ether alcohols; 1,4-cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,2-cyclohexane dimethanol, tricyclodecane glycols, hydrogenated bisphenols, and the like alicyclic polyols; trimethylolpropane, trimethylolethane, pentaerythritol, and the like polyols of three or more valences, and the like.

[0078] The polyester resin can be produced by a publicly known method of polycondensing one or more of the above-described polybasic acid component and one or more of the polyhydric alcohol component, and, after the polycondensation, a method of depolymerizing the polybasic acid component such as terephthalic acid, isophthalic acid, trimellitic anhydride, trimellitic acid, pyromellitic acid, etc., and, further, ring-opening addition of an anhydride such as phthalic anhydride, maleic anhydride, trimellitic anhydride, ethylene glycol bistrimellitate dianhydride, etc.

[0079] From the viewpoints of curability and resistance to cooking whitening, adhesion to a metal base, etc., it is desirable that the acid value of the polyester resin be in the range of 0.1 mgKOH / g to 40 mgKOH / g, preferably in the range of 0.5 mgKOH / g to 25 mgKOH / g, more preferably in the range of 1 mgKOH / g to 10 mgKOH / g, further preferably higher than 2 mgKOH / g and 10 mgKOH / g or lower, particularly preferably in the range of 2.5 mgKOH / g to 8 mgKOH / g, and most preferably in the range of 3 mgKOH / g to 7 mgKOH / g. In the case where the acid value is lower than the above range, there is a possibility that the adhesion of the metal base to the coating film is reduced. On the other hand, in the case where the acid value is higher than the above range, the coating film becomes easy to absorb water as compared with the case where the acid value is in the above range, there is a possibility that the resistance to cooking is reduced, and there is a possibility that the reaction points with the curing agent are increased, the crosslinking density of the coating film is thereby increased, the canning workability and the coating film peeling resistance are reduced, the metal is thereby exposed, and the covering property of the coating film is reduced.

[0080] Note that, in the case where the polyester resin is a mixture of two or more kinds of polyester resins, the sum of the values obtained by multiplying the acid value of each of the polyester resins by the mass fraction is used as the average acid value (AV mix ) of the mixture, and the average acid value thereof is only required to be in the above acid value range.

[0081] The hydroxyl value of the polyester resin is not limited thereto, and it is preferable that it be 20 mgKOH / g or lower, and more preferable that it be 10 mgKOH / g or lower.

[0082] The number average molecular weight (Mn) of the polyester resin is not limited thereto, and, from the viewpoint of the canning workability, it is preferable that it be in the range of 1000 to 100000, more preferable that it be in the range of 3000 to 50000, and further preferable that it be in the range of 5000 to 20000. If the number average molecular weight of the polyester resin is less than the above range, the coating film becomes brittle, and sometimes the canning workability is poor, and if the number average molecular weight of the polyester resin is greater than the above range, there is a possibility that the paint stability is reduced.

[0083] Further, as the polyester resin, from the viewpoints of can-making workability, dent resistance, and paintability, a non-crystalline polyester resin is preferred. Here, the non-crystalline means that no clear melting point of the crystal component is shown in the measurement using a differential scanning calorimeter (DSC). In the case of the non-crystalline polyester resin, compared with the crystalline polyester resin, the solubility in a solvent is excellent, the paintability is easy, and a film having excellent workability and dent resistance can be formed.

[0084] As for the hydroxyl value of the polyester resin, it is not limited thereto, and it is preferably 20 mgKOH / g or less, and more preferably 10 mgKOH / g or less.

[0085] (Curing agent)

[0086] As the curing agent used in the present application, a substance which reacts with the functional group of the polyester resin, such as a carboxyl group, a hydroxyl group, to form a crosslinked structure can be used.

[0087] As such a curing agent, isocyanate compounds, resols, amino resins, compounds containing an epoxy group, compounds containing an oxazoline group, compounds containing a carbodiimide group, β-hydroxyalkylamide compounds, and the like can be exemplified. In particular, from the viewpoints of curability, hygiene, and the like, resols and amino resins are preferred.

[0088] In the coated metal plate and the draw-and-reduce can of the present application, in the paint composition for forming an inner surface coating film (hereinafter, sometimes referred to as "inner surface paint composition"), a resol, an amino resin, and in particular, from the viewpoint of can-making workability, a resol can be preferably used. In the paint composition for forming an outer surface coating film (hereinafter, sometimes referred to as "outer surface paint composition"), an amino resin which can form a coating film which is not colored or transparent due to the curing agent can be preferably used. On the other hand, the coating film formed by the above-described resol is yellow, and thus attention is required in the case of the paint composition for forming an outer surface coating film.

[0089] (Resol)

[0090] As the resol, a resol obtained by reacting a phenolic compound, such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-dimethylphenol, 2,5-dimethylphenol, phenol, m-cresol, m-ethylphenol, 3,5-dimethylphenol, m-methoxyphenol, or the like, with formaldehyde in the presence of an alkali catalyst, using one kind or two or more kinds in combination, can be used.

[0091] From the viewpoint of curability, among the above-mentioned phenol compounds, a resol-type phenol resin in which more than 50% by mass, preferably 60% by mass or more, further preferably 80% by mass or more, of a phenol compound that becomes trifunctional by reaction with formaldehyde is used as a starting material is preferred. As the phenol compound that becomes trifunctional by reaction with formalin, phenol, m-cresol, m-ethylphenol, 3,5-dimethylphenol, m-methoxyphenol can be cited, and one or two or more of these can be used. If the amount of these trifunctional phenol compounds is 50% by mass or less, sufficient curability cannot be obtained, and there is a possibility that the degree of cure of the coating film will decrease. Among these trifunctional phenol compounds, m-cresol is more preferred from the viewpoint of curability, and a resol-type phenol resin in which more than 50% by mass of m-cresol is used as a starting material (hereinafter sometimes referred to as "m-cresol-based resol-type phenol resin") is particularly preferred. This is ideal from the viewpoint of being able to obtain sufficient curability of the coating film, heat resistance, corrosion resistance, boiling resistance, and the like of the coating film. As the m-cresol-based resol-type phenol resin, it is preferred that more than 50% by mass, preferably 60% by mass or more, further preferably 80% by mass or more, of m-cresol be used as a starting material.

[0092] In addition to the above-mentioned trifunctional phenol compounds, it is preferred that the amount of a phenol compound that becomes difunctional by reaction with formaldehyde be less than 50% by mass, preferably less than 40% by mass, more preferably less than 20% by mass, when used as a starting material. If it is 50% by mass or more, there is a possibility that the curability will decrease. As the phenol compound that becomes difunctional, o-cresol, p-cresol, p-t-butylphenol, p-ethylphenol, 2,3-dimethylphenol, 2,5-dimethylphenol, and the like are present.

[0093] Further, as the resol-type phenol resin used in the present application, from the viewpoints of compatibility with the polyester resin and curability, a substance in which a part or all of the methylol groups contained are alkyl-etherified (alkoxymethylated) by an alcohol having 1 to 12 carbon atoms can be preferably used. As the proportion of the methylol groups that are alkyl-etherified, 50% or more, more preferably 60% or more, further preferably 80% or more is preferred. If the proportion of the methylol groups that are alkyl-etherified is less than 50%, the compatibility with the polyester resin decreases, the coating film becomes cloudy, or sufficient curability cannot be obtained. As the alcohol used in the alkyl-etherification, a monovalent alcohol having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms is used, and as the preferred monovalent alcohol, methanol, ethanol, n-propanol, n-butanol, isobutanol, and the like can be cited, with n-butanol being more preferred.

[0094] Further, the number of alkyl-etherified hydroxymethyl groups (alkoxymethyl groups) is preferably 0.3 or more, and preferably 0.5 to 3, on average per nucleus of the phenol nucleus. If less than 0.3, the curability with a polyester resin becomes poor. Further, the number average molecular weight (Mn) of the above-described resol-type phenol-formaldehyde resin is preferably in the range of 500 to 3000, and preferably in the range of 800 to 2500. If less than the above range, there is a tendency that the crosslinking density of the formed coating film becomes high, and thus there is a possibility that stress relaxation becomes difficult at the time of molding, and the coating film peeling resistance becomes poor. On the other hand, if more than the above range, the curability becomes poor, and as a result, there is a possibility that the heat resistance, corrosion resistance, boiling resistance, and the like of the coating film become poor.

[0095] (Amino Resin)

[0096] As the amino resin, for example, a hydroxymethylated amino resin obtained by the reaction of an amino component such as melamine, urea, benzoguanamine, methylguanamine, steroidal guanamine, spiroguanamine, dicyandiamide, and an aldehyde component such as formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde can be exemplified. A substance in which a part or all of the hydroxymethyl groups of the hydroxymethylated amino resin are alkyl-etherified with an alcohol having 1 to 6 carbon atoms is also included in the above-described amino resin. They can be used alone or in combination of two or more. As the amino resin, from the viewpoints of hygiene, can processing, curability, and the like, a hydroxymethylated amino resin using benzoguanamine (benzoguanamine resin), a hydroxymethylated amino resin using melamine (melamine resin) are preferably used.

[0097] As the benzoguanamine resin, a benzoguanamine resin in which a part or all of the hydroxymethyl groups of a hydroxymethylated benzoguanamine resin are alkyl-etherified with an alcohol such as methanol, ethanol, n-butanol, isobutanol, for example, a methyl-etherified benzoguanamine resin, an ethyl-etherified benzoguanamine resin, a butyl-etherified benzoguanamine resin, or a mixed etherified benzoguanamine resin of methyl ether and butyl ether, a mixed etherified benzoguanamine resin of methyl ether and ethyl ether, a mixed etherified benzoguanamine resin of ethyl ether and butyl ether is preferable. Among them, a methyl-etherified benzoguanamine resin is more preferable, and a methyl-etherified benzoguanamine resin of a partial ether type containing an imino group / hydroxymethyl group is particularly preferable.

[0098] As the melamine resin, a melamine resin in which a part or all of the hydroxymethyl groups of a hydroxymethylated melamine resin are alkyl-etherified with an alcohol such as methanol, ethanol, n-butanol, isobutanol, for example, a methyl-etherified melamine resin, an ethyl-etherified melamine resin, a butyl-etherified melamine resin, or a mixed etherified melamine resin of methyl ether and butyl ether, a mixed etherified melamine resin of methyl ether and ethyl ether, a mixed etherified melamine resin of ethyl ether and butyl ether is preferable. Among them, a methyl-etherified melamine resin is more preferable, and a methyl-etherified melamine resin of a total ether type is particularly preferable.

[0099] As the functional groups possessed by the above-mentioned melamine resin and benzoguanamine resin, imino group (>NH), N-hydroxymethyl group (>NCH2OH), and N-alkoxymethyl group (>NCH2OR; R is an alkyl group) can be exemplified, which function as reaction points in cross-linking reaction with carboxyl group (-COOH) or hydroxyl group (-OH) contained in the polyester resin as the main agent, or self-condensation reaction of the amino resins with each other (note that imino group only contributes to the self-condensation reaction). Note that as to the number of the above-mentioned reaction points (functional groups), if the monomers of the melamine resin and the benzoguanamine resin are compared, the melamine resin is more in the molecular structure. Due to this, the melamine resin is excellent in curability, on the other hand, the cross-linking density of the formed coating film tends to be high, and depending on the blending amount, the stress relaxation rate tends to be low, and there is a possibility that coating film peeling occurs at the time of heat treatment. On the other hand, the benzoguanamine resin, although it is inferior in curability to the melamine resin, the cross-linking density of the formed coating film does not tend to be high, and from the viewpoint of the coating film peeling resistance, it can be said that it is more preferable than the melamine resin. Therefore, in order to obtain a balance between the curability and the coating film peeling resistance, the melamine resin and the benzoguanamine resin can be used in combination, and a mixed amino resin in which they are mixed at a prescribed ratio can be used. In this case, it is desirable that the blending amount ratio (mass ratio) of the melamine resin and the benzoguanamine resin is set to 95:5 to 5:95, it is preferable that it is set to 90:10 to 10:90, it is more preferable that it is set to 80:20 to 15:85, and it is further preferable that it is set to 70:30 to 25:75.

[0100] It is desirable that the curing agent is blended in the range of 1 to 40 parts by mass, preferably 1 to 30 parts by mass, and more preferably 2 to 20 parts by mass, with respect to 100 parts by mass of the polyester resin.

[0101] In the case of using a resol-type phenol resin as the curing agent, it is preferable to blend in a range of 2 to 40 parts by mass, preferably 3 to 30 parts by mass, more preferably 3 to 25 parts by mass, further preferably 3 to 20 parts by mass, particularly preferably 4 to 15 parts by mass, relative to 100 parts by mass of the polyester resin as the main agent (solid content). In the case of using a melamine resin as the curing agent, it is preferable to blend in an amount of 1 to 15 parts by mass, preferably 1 part by mass or more and less than 10 parts by mass, more preferably 2 to 5.5 parts by mass, particularly preferably 2 to 5 parts by mass, relative to 100 parts by mass of the polyester resin. In the case of using a benzoguanamine resin as the curing agent, it is preferable to blend in 4 to 40 parts by mass, preferably 5 to 30 parts by mass, more preferably 6 to 28 parts by mass, further preferably 8 to 25 parts by mass, particularly preferably 10 to 24 parts by mass, relative to 100 parts by mass of the polyester resin. In the case of using a mixed amino resin of the above-described melamine resin and benzoguanamine resin as the curing agent, it is preferable to blend in 2 to 25 parts by mass, preferably 2 to 20 parts by mass, 2.5 to 15 parts by mass, 3 parts by mass or more and less than 10 parts by mass, relative to 100 parts by mass of the polyester resin.

[0102] In the case where the amount of the curing agent is less than the above-described range, sufficient curability cannot be obtained, and there is a tendency for the degree of curing of the coating film to be low and the heat resistance to be reduced. Therefore, in the case of forming a draw-reduced thin can at high speed, the temperature rise becomes more significant, and thus there is a possibility that the coating film can easily adhere to the mold during forming. In particular, on the inner surface side of the can, at the time point at which the can body is extracted from the forming punch after draw-reduced forming, the can body adheres to the forming punch, and a phenomenon in which the forming punch and the can body are not easily separated (stripping property is poor) occurs, and thus the can body is bent, or the main body is broken, and the like, and there is a possibility that the productivity is reduced. In the case of the outer surface side of the can, there is a possibility that a coating film abrasion or the like occurs, and the like.

[0103] On the other hand, in the case where the amount of the curing agent is more than the above-described range, depending on the kind of the curing agent used, there is a possibility that the can-making workability of the coating film is reduced, and metal exposure occurs during draw-reduced working, and the crosslinking density of the coating film is high, and thus stress relaxation during forming becomes difficult, and it is difficult to adjust the stress relaxation rate of the inner surface coating film to 50% or more, and as a result, there is a possibility that the covering property of the coating film is reduced.

[0104] In the inner surface coating composition and the outer surface coating composition used in the present application, a curing catalyst is preferably blended for the purpose of promoting the crosslinking reaction of the polyester resin and the curing agent.

[0105] As the curing catalyst, a conventionally known curing catalyst such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalene disulfonic acid, phosphoric acid, alkylphosphoric acid, or an amine neutralized product thereof, or the like organic sulfonic acid-based and phosphoric acid-based acid catalyst can be used. Among the above-mentioned curing catalysts, an organic sulfonic acid-based acid catalyst is preferably used, and dodecylbenzenesulfonic acid, an amine neutralized product thereof is particularly preferred.

[0106] It is desirable that the content of the curing catalyst be in the range of 0.01 to 3 parts by mass, preferably 0.02 to 1.0 parts by mass, more preferably 0.02 parts by mass or more and less than 0.5 parts by mass, further preferably 0.03 parts by mass or more and less than 0.3 parts by mass, particularly preferably 0.04 parts by mass or more and less than 0.2 parts by mass, relative to 100 parts by mass of the polyester resin, in terms of solid content. In addition, in the case where an amine neutralized product of the above-mentioned acid catalyst (for example, an amine neutralized product of dodecylbenzenesulfonic acid) is used as the curing catalyst, it is only necessary that the content of the acid catalyst other than the amine be within the above-mentioned range. In the case where the content of the curing catalyst is less than the above-mentioned range, there is a possibility that the effect of promoting the curing reaction cannot be sufficiently obtained, on the other hand, in the case where the content of the curing catalyst is more than the above-mentioned range, no further effect can be expected, and in addition, the water resistance of the coating film is reduced, and as a result, there is a possibility that the corrosion resistance, the retort resistance, and the like are deteriorated. In addition, the acid catalyst is localized on the surface of the metal substrate by acid-base interaction, and thus there is a possibility that the adhesion between the coating film and the metal substrate is reduced, and there is a possibility that peeling of the coating film and the like occurs at the time of can forming.

[0107] (coating composition)

[0108] The coating composition for forming the coating film of the coated metal sheet of the present application contains at least the above-mentioned polyester resin and the above-mentioned curing agent as the main agent, and further preferably contains the above-mentioned curing catalyst (acid catalyst). Note that, in the present application, the component having the largest content (mass ratio) among the solid components (non-volatile components excluding the volatilized substances such as water and solvent) of the coating film in the coating composition is defined as the main agent (main component). In addition, in the coating composition used in the present application, the content of the above-mentioned polyester resin, preferably the non-crystalline polyester resin, as the main agent is preferably higher than 50% by mass, more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, among all the resin components contained in the coating composition.

[0109] In the present application, as the form of the coating composition which can be used for forming the coating film, a solvent type coating composition and an aqueous coating composition can be exemplified. In the present application, from the viewpoint of coatability and the like, a solvent type coating composition is preferably used.

[0110] When the coating composition is a solvent-based coating composition, it contains the aforementioned polyester resin, curing agent, and an organic solvent as a solvent. It should be noted that, in this embodiment, a solvent-based coating composition refers to a coating composition formed by dissolving the main resin, curing agent, etc., in a known organic solvent, and wherein the organic solvent in the coating composition accounts for 40% or more by mass.

[0111] As the organic solvent, factors such as solubility and evaporation rate can be considered, and one or more of the following substances can be selected for use: toluene, xylene, aromatic hydrocarbon compounds, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monoethyl ether, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, solvent naphtha, etc.

[0112] In the case of a water-based coating composition, an aqueous medium is contained as a solvent along with conventionally known water-dispersible or water-soluble polyester resin and curing agent.

[0113] As an aqueous medium, water, or a substance mixed with water and an organic solvent such as an alcohol, polyol, or its derivatives, can be used as the aqueous medium, similar to known aqueous coating compositions. When using an organic solvent, it is preferable to include it in an amount of 1 to 45% by mass relative to the total aqueous medium in the aqueous coating composition, and particularly preferably in an amount of 5 to 30% by mass. Including the solvent within the above range improves film-forming performance.

[0114] As such organic solvents, amphiphilic organic solvents are preferred, such as: methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, ethylene glycol, methyl ethyl ketone, butyl cellosolve, carbitol, butyl carbitol, propylene glycol monopropyl ether, propylene glycol ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, 3-methyl-3-methoxybutanol, etc.

[0115] Lubricant

[0116] The coating composition may contain a lubricant as needed. Preferably, 0.1 to 10 parts by weight of lubricant are added relative to 100 parts by weight of polyester resin.

[0117] By adding lubricant, scratches on the coating during molding can be suppressed, and the sliding properties of the coating can be improved.

[0118] As the lubricant which can be added to the coating composition, for example, fatty acid ester wax which is an esterification product of a polyhydric alcohol compound and a fatty acid, silicon-based wax, fluorine-based wax such as polytetrafluoroethylene, polyolefin wax such as polyethylene, paraffin wax, lanolin, montan wax, microcrystalline wax, carnauba wax, and silicon-based compounds, vaseline, and the like can be exemplified. These lubricants can be used singly, or two or more kinds can be used in mixture.

[0119] <Other>

[0120] In the coating composition, in addition to the above-mentioned components, a leveling agent, a pigment, a defoaming agent, a colorant, and the like which have been conventionally incorporated in the coating composition can be added in accordance with a conventionally known prescription.

[0121] Further, other resin components can be contained together with the polyester resin within a range not impairing the object of the present application, for example, polyvinyl acetate, ethylene / vinyl acetate copolymer, polyolefin-based resin, epoxy resin, polyurethane resin, acrylic resin, polyvinyl chloride-based resin, polyvinyl chloride-vinyl acetate copolymer resin, polyvinyl alcohol, ethylene / vinyl alcohol copolymer, polyvinyl pyrrolidone, polyvinyl ethyl ether, polyacrylamide, acrylamide-based compound, polyethylene imine, starch, gum arabic, and methyl cellulose, and the like can be contained.

[0122] In the coating composition, it is preferable that the polyester resin is contained in an amount of 5 to 55 mass% in terms of solid content. In a case where the resin solid content is less than the above-mentioned range, a proper coating film amount cannot be ensured, and the covering property of the coating film becomes poor. On the other hand, in a case where the resin solid content is more than the above-mentioned range, sometimes the workability and the applicability are poor.

[0123] (Method for manufacturing coated metal sheet)

[0124] In the present application as described above, the inner surface coating composition containing the polyester resin and the curing agent as the main agent, preferably the amino resin, is applied to at least the surface of the metal sheet which becomes the inner surface. It is preferable that the outer surface coating composition containing the above-mentioned main agent, i.e., the polyester resin and the curing agent, preferably the amino resin, is further applied to the surface of the metal sheet which becomes the outer surface.

[0125] The sintering conditions of the coating composition can be appropriately adjusted depending on the kind of polyester resin, curing agent, metal base, coating amount, and the like. In the case of the coating composition described above, in order to obtain sufficient curing degree, it is preferable to heat and cure at a sintering temperature of 150°C to 350°C, preferably higher than 200°C and lower than 320°C, for 5 seconds or more, preferably 5 seconds to 30 minutes, particularly preferably 5 seconds to 180 seconds. In the case where the sintering temperature is lower than the above range, there is a possibility that sufficient curing degree cannot be obtained. On the other hand, in the case where the sintering temperature is higher than the above range, there is a possibility that the polyester resin is thermally decomposed by excessive heating. In the case where the sintering time is shorter than the above range, there is a possibility that sufficient curing degree cannot be obtained, and in the case where the sintering time is longer than the above range, economy and productivity are poor.

[0126] Further, in the inner surface coating film and / or the outer surface coating film after sintering, it is preferable that the MEK extraction rate (MEK boiling point, 1 hour), which is an index of the curing degree, is in the range of 50% or less, preferably 1% to 40%, more preferably 2% to 30%, further preferably 3% to 25%, particularly preferably 3% to 20%. By the MEK extraction rate being in the above range, the curing degree of the coating film is controlled, which is preferable from the viewpoint of heat resistance, corrosion resistance, boiling resistance, and coating film peeling resistance (stress relaxation rate) of the coating film.

[0127] In the case where the MEK extraction rate is higher than the above range, there is a tendency that the curing degree of the coating film becomes low and the heat resistance decreases, and thus in the case of forming a draw-reduced can at high speed, temperature rise becomes more remarkable, and thus the coating film is sometimes easily adhered to a mold at the time of forming. In particular, on the can inner surface side, at the time point when the can body is extracted from the forming punch after the stretch-reduced forming, the can body is adhered to the forming punch, and thus a phenomenon that the forming punch and the can body are not easily separated (poor demolding property) occurs, and thus the can body is bent, or the main body is broken, and the like, and there is a possibility that productivity decreases. On the can outer surface side, there is a possibility that an outer surface defect such as coating film abrasion occurs, and there is a possibility that boiling resistance whitening property becomes poor.

[0128] On the other hand, in the case where the MEK extraction rate is lower than 1%, it is difficult to set the stress relaxation rate described above to the above range, and there is a possibility that the coating film is peeled.

[0129] It can be manufactured by coating at least the face of the metal sheet which becomes the can inner surface side, preferably both faces, by a publicly known coating method such as roll coater coating, spray coating, dip coating, and the like as a coating method, and then sintering by a heating unit such as a coil oven.

[0130] As the metal plate to be used as a metal base of a coated metal plate, not limited to this, for example, hot-rolled steel sheet, cold-rolled steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, alloy plated steel sheet, aluminum-zinc alloy plated steel sheet, aluminum sheet, tin-plated steel sheet, stainless steel sheet, copper sheet, copper-plated steel sheet, tin-free steel sheet, nickel-plated steel sheet, ultra-thin tin-plated steel sheet, chromium-treated steel sheet, and the like can be listed, and a metal plate subjected to various surface treatments such as chromate-phosphate treatment, zirconium-based chemical conversion treatment, coating-type treatment combining a water-soluble resin such as polyacrylic acid and a zirconium salt such as zirconium ammonium carbonate, and the like can be used as needed.

[0131] In the present application, among the above metal plates, an aluminum sheet is preferable, and as the aluminum sheet, in addition to a pure aluminum sheet, an aluminum alloy sheet can be preferably used, and specifically, an aluminum alloy sheet of the 3000 series, 5000 series, 6000 series in "JIS H 4000" is preferable, and from the viewpoint of strength and the like, an aluminum alloy sheet is preferable. As the aluminum alloy sheet, in addition to a surface-treated aluminum alloy sheet subjected to the above various surface treatments, a coating film formed from the above coating composition has excellent adhesion to a metal base, and thus an untreated aluminum alloy sheet not subjected to surface treatment can be preferably used.

[0132] From the viewpoint of can body strength and moldability, the thickness of the metal plate is preferably in the range of 0.1 mm to 1.00 mm, more preferably 0.15 mm to 0.40 mm, even more preferably 0.15 mm to 0.30 mm, and further preferably 0.20 mm to 0.28 mm.

[0133] In the coated metal plate of the present application, a coating film formed from another coating composition can be formed on the above inner surface coating film formed on the side of the inner surface of the can after the drawing and ironing process and / or the above outer surface coating film formed on the side of the outer surface of the can after the drawing and ironing process as needed.

[0134] Further, in the coated metal plate of the present application, the inner surface coating film and the outer surface coating film formed from the above coating composition have excellent adhesion to a metal base, and thus it is preferable to form in a manner that the inner surface coating film and / or the outer surface coating film directly contact the above metal plate as a metal base.

[0135] (Drawing and ironing can)

[0136] An important feature of the drawing and ironing can of the present application is that it is a drawing and ironing can formed by drawing and ironing the above coated metal plate, and at least the drawing and ironing can on the side of the inner surface of the can has an inner surface coating film containing a polyester resin and a curing agent, and the stress relaxation rate after 10 minutes at 1% elongation under test conditions of 100°C in the inner surface coating film in the bottom portion of the can is 50% or more.

[0137] It is desirable that the stress relaxation rate of the inner surface coating film be 50% or more, preferably in the range of 50% to 95%, more preferably in the range of 54% to 90%, further preferably in the range of 54% to 85%, particularly preferably in the range of 54% to 80%, and most preferably in the range of 60% to 80%.

[0138] Further, it is preferable that the draw-and-reduce can also have an outer surface coating film on the outer surface side of the can, the outer surface coating film containing a polyester resin and a curing agent, the stress relaxation rate of the outer surface coating film in the can bottom after 10 minutes at 1% elongation under test conditions of 100°C be higher than 40%.

[0139] It is desirable that the stress relaxation rate of the outer surface coating film be more than 40%, preferably in the range of 45% to 95%, more preferably in the range of 50% to 90%, further preferably in the range of 54% to 85%, particularly preferably in the range of 54% to 80%, and most preferably in the range of 60% to 80%.

[0140] Further, the draw-and-reduce can preferably have at least the can bottom and the can main body portion on the inner surface side thereof continuously coated with the inner surface coating film, and further preferably the can bottom and the can main body portion on the outer surface side thereof continuously coated with the outer surface coating film.

[0141] Note that the stress relaxation rate is measured using the coating film of the can bottom of the draw-and-reduce can because the can bottom is processed to a very small degree compared to the can main body portion, and thus has similar characteristics to the coating film of the coated metal sheet before forming.

[0142] (Method for manufacturing draw-and-reduce can)

[0143] The draw-and-reduce can of the present application can be manufactured by a conventionally known forming method using the above-described coated metal sheet. The coated metal sheet of the present application has excellent elongation, processability, and adhesion, and thus can form a draw-and-reduce can without causing breakage of the main body or peeling of the coating film at the can mouth end even when subjected to severe draw-and-reduce processing. Note that the coated metal sheet of the present application is a metal sheet having excellent formability and lubricity, and thus can form a draw-and-reduce can even when forming is performed under dry conditions without using a coolant, not to mention when a coolant is used.

[0144] Before the stretch thinning forming, the surface of the coated metal sheet is preferably coated with a wax-based lubricant, such as a paraffin-based wax, white vaseline, palm oil, various natural waxes, polyethylene wax, or the like, whereby the drawing thinning processing can be efficiently performed under dry conditions. The coated metal sheet coated with the wax-based lubricant is passed through a drawing / pressing punch blank, and a drawing cup is formed by a drawing processing method. In the present application, it is desirable that the draw ratio RD defined by the following equation (3) is in the range of 1.1 to 2.6 in total (up to the drawing thinning can), and particularly in the range of 1.4 to 2.6. If the draw ratio is greater than the above range, the drawing wrinkle becomes large, and there is a possibility that the coating film is cracked and the metal is exposed.

[0145] RD = D / d... (3)

[0146] In the equation, D represents the blank diameter, and d represents the can main body diameter.

[0147] Next, the drawing cup is subjected to a redraw-drawing thinning processing (drawing thinning processing) in one stage or multiple stages, and the thinning of the can main body portion is performed.

[0148] In the present application, it is desirable that the thinning ratio R represented by the following equation (4) is in the range of 25% to 80%, preferably in the range of 40% to 80%, more preferably in the range of 50% to 80%, further preferably in the range of 55% to 75%, particularly preferably in the range of 55% to 70%, and most preferably in the range of higher than 60% and 70% or less. If the thinning ratio is lower than the above range, the thinning is not sufficiently performed, and it is not sufficient in terms of economy, on the other hand, in the case where the thinning ratio is higher than the above range, there is a possibility that the metal is exposed.

[0149] R (%) = (tp - tw) / tp x 100... (4)

[0150] In the equation, tp represents the thickness of the original coated metal sheet, and tw represents the thickness of the central portion of the can main body side wall of the drawing thinning can.

[0151] Further, in the deep-drawn reduced thickness can of the present application, it is preferable that the thickness of the central portion of the can body (the central portion in the height direction, the portion of which is thinnest) is 20 to 75% of the thickness of the central portion of the can bottom, preferably 20 to 60%, more preferably 20 to 50%, further preferably 25 to 45%, particularly preferably 30 to 45%, and most preferably 30% or more and less than 40%. It is preferable that the thickness of the metal base of the deep-drawn reduced thickness can is also the same, that is, the thickness of the metal base of the central portion of the can body is 20 to 75% of the thickness of the metal base of the central portion of the can bottom, preferably 20 to 60%, more preferably 20 to 50%, further preferably 25 to 45%, particularly preferably 30 to 45%, and most preferably 30% or more and less than 40%. Further, in the case where the deep-drawn reduced thickness can is formed by deep-drawing and reducing the thickness of a coated metal sheet, the thickness of the coating film on the can body portion is reduced by the processing in the same manner as the metal base. Therefore, it is preferable that the thickness of the coating film of the central portion of the can body is 20 to 75% of the thickness of the coating film of the central portion of the can bottom, which is hardly thinned at the time of can-making, preferably 20 to 60%, more preferably 20 to 50%, further preferably 25 to 45%, particularly preferably 30 to 45%, and most preferably 30% or more and less than 40%.

[0152] As the thickness of the metal base of the central portion of the can bottom, it is preferable that it is 0.10 to 0.50 mm, preferably 0.15 to 0.40 mm, more preferably 0.15 to 0.30 mm, and further preferably 0.20 to 0.28 mm.

[0153] Further, it is preferable that the film thickness of the above-mentioned inner surface coating film of the central portion of the can bottom is 0.2 to 20 μm, preferably 1 to 12 μm, and more preferably 2 μm or more and 12 μm or less, in terms of dry film thickness. Further, as the dry coating film weight, it is preferable that it is 3 to 300 mg / dm 2 , preferably 15 to 150 mg / dm 2 , and more preferably 25 mg / dm 2 or more and 150 mg / dm 2 or less. Furthermore, in the case where the content filled in the deep-drawn reduced thickness can is a strongly corrosive acidic beverage, it is preferable that the film thickness is 6 μm or more and 12 μm or less, and preferably 6.5 to 10 μm. Further, as the dry coating film weight, it is preferable that it is 85 mg / dm 2 or more and 150 mg / dm 2 or less, and preferably 90 to 140 mg / dm 2μm or more and less than 6.5 μm, preferably more than 2 μm and less than 6.5 μm, more preferably in the range of 2.5 μm to 6 μm. Further, as the dry coating film weight, it is preferable that it be in the range of 15 mg / dm 2 2 μm or more and less than 90 mg / dm 2 , preferably more than 25 mg / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 , more preferably in the range of 30 mg / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 85 mg / dm

[0154] Further, it is preferable that the film thickness of the above-mentioned outer surface coating film of the central portion of the can bottom be in the range of 0.2 μm to 20 μm, preferably 1 μm to 10 μm, more preferably more than 2 μm and 10 μm or less, further preferably more than 2 μm and 6.5 μm or less, in terms of dry film thickness. Further, as the dry coating film weight, it is preferable that it be in the range of 3 mg / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 15 g / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 25 g / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 , more preferably in the range of 30 mg / dm 2 2 μm or less, further preferably more than 2 μm and 6.5 μm or less. 2 85 mg / dm

[0155] Further, as described above, in the case where the draw-and-wall-ironed can is formed by draw-and-wall-ironing a coated metal sheet having an inner surface coating film, the thickness of the inner surface coating film at the can body portion is thinned by the processing as well as the metal base at the can body portion. Therefore, in the draw-and-wall-ironed can of the present application, the thickness ratio of the inner surface coating film to the metal base at the can body portion and the thickness ratio of the inner surface coating film to the metal base in the can bottom portion are almost the same. That is, in the draw-and-wall-ironed can of the present application, it is characterized in that the thickness ratio of the inner surface coating film to the metal base (= thickness of the inner surface coating film / thickness of the metal base) is substantially almost the same at the can bottom portion and the can body portion. Note that "almost the same" here means that it also includes manufacturing errors within its range, for example, it means that the (thickness of the inner surface coating film / thickness of the metal base) at the can body portion is in the range of 0.9 to 1.1 times the (thickness of the inner surface coating film / thickness of the metal base) at the can bottom portion. Note that the same applies to the outer surface coating film as well.

[0156] Note that the processing speed (moving speed of the punch) of the one-stage or multi-stage thinning processing is desirably 1500 mm / sec or more, preferably 3000 mm / sec or more, more preferably 4000 mm / sec or more, further preferably 5000 mm / sec or more, and particularly preferably 6000 mm / sec or more. By setting the processing speed of the thinning processing to be the above speed or more, the processing heat generation becomes large, and the coating film becomes in a high temperature state, whereby the processability (elongation) of the coating film is improved. As a result, the metal exposure at the time of forming can be suppressed, and the coatability of the inner surface coating film and the outer surface coating film after forming is further improved. Furthermore, by forming at a high temperature, stress relaxation is easy in the forming processing, and thus the residual stress of the coating film after forming can be reduced, and this is also preferable in terms of suppressing peeling of the coating film at the time of heat treatment.

[0157] After the drawing and thinning processing, the bottom is formed in a bulged shape, and the opening end edge is subjected to trimming processing, according to a usual method, as desired.

[0158] According to the present application, after the drawing and thinning processing of the coated metal sheet, a heat treatment step is performed on the obtained drawing and thinning can. As described above, in the coated metal sheet and the drawing and thinning can of the present application, the stress relaxation rate of the coating film is 50% or more on the inner surface of the can, and more than 40% on the outer surface of the can, and thus peeling of the coating film is effectively prevented even in the case where heating is performed in the heat treatment step.

[0159] By performing at least one stage of heat treatment on the drawing and thinning can after forming, the residual stress of the coating film due to processing can be removed. By removing the residual stress of the coating film, the adhesion between the coating film and the metal substrate after processing (coating film adhesion) can be improved. As a result, the corrosion resistance of the coating film is significantly improved, and for example, when a drawing and thinning can is filled with a highly corrosive content, the occurrence of corrosion under the coating film can be suppressed. The temperature of the heat treatment needs to be a temperature higher than the glass transition temperature of the coating film, and is preferably in the range of 100°C to 300°C, and more preferably in the range of 150°C to 250°C. The time of the heat treatment is not particularly limited, and is preferably 0.1 seconds to 600 seconds, more preferably 1 second to 300 seconds, and further preferably 20 seconds to 180 seconds.

[0160] In the case where the residual stress of the coating film of the draw-ironing can is not removed by heat treatment, when the coating film of the large-processed can body central portion (central portion in the height direction) is separated from the metal base and heated, the dimension greatly changes in the direction in which the residual stress is released (mainly the height direction of the can), and therefore, by measuring the dimensional change amount (thermal shrinkage) of the separated coating film due to heating, it is possible to use it as a reference value for whether the residual stress is removed by heat treatment. It is desirable that the thermal shrinkage (under load) represented by the following formula (5) in the above-mentioned inner surface coating film of the can body central portion separated from the draw-ironing can be 30% or less, preferably 20% or less, more preferably 15% or less, and further preferably 10% or less. Furthermore, it is desirable that the thermal shrinkage (without load) represented by the following formula (6) be 50% or less, preferably 45% or less, more preferably 40% or less, and further preferably 35% or less. In the case where the thermal shrinkage is within the above-mentioned range, the coating film adhesion is improved, and excellent corrosion resistance is exhibited. In the case where the thermal shrinkage is larger than the above-mentioned range, the residual stress is not sufficiently removed, and the coating film adhesion is insufficient, and therefore, there is a possibility that the corrosion resistance is reduced, and there is a possibility that the coating film is peeled off when the can is dented by an impact or the like. Furthermore, in the case where the above-mentioned outer surface coating film is provided on the outer surface side of the can, it is desirable that the thermal shrinkage be within the above-mentioned range even in the outer surface coating film of the can body central portion.

[0161] Note that the dimensional change amount (shrinkage amount) due to heating of the separated coating film can be measured by a thermal mechanical analysis device (TMA) or the like.

[0162] Thermal shrinkage (under load) = (ΔL1 / L0) x 100 (%) (5)

[0163] In the formula, L0 is the initial length in the height direction of the coating film separated from the can body central portion (measuring portion), ΔL1 is the maximum shrinkage amount in the height direction of the coating film of the portion corresponding to L0 when the load of 5.20 x 10 5 N / m 2 is applied while being heated at a temperature increase rate of 5°C / min from 30°C to 200°C.

[0164] Thermal shrinkage (without load) = (ΔL2 / L0) x 100 (%) (6)

[0165] In the formula, L0 is the initial length in the height direction of the coating film separated from the can body central portion, ΔL2 is the maximum shrinkage amount in the height direction of the coating film of the portion corresponding to L0 when heated at a temperature increase rate of 5°C / min from 30°C to 200°C in a state without load (maximum value of the shrinkage length).

[0166] After the heat treatment, a printing layer is formed on the can body portion by a printing / sintering process, and a finishing varnish layer for protecting the printing layer is formed on the printing layer, as needed, after quenching or after cooling, by a method known in the art. As desired, one-stage or multi-stage necking processing is performed, flange processing is performed, and a can for a curl seal is manufactured. In addition, after the drawing and ironing can is formed, the upper portion thereof can be deformed to form a bottle shape, or the bottom portion can be cut off and another can end can be fitted to form a bottle shape.

[0167] The capacity of the drawing and ironing can according to the present application is preferably 150 mL or more, more preferably 150 mL to 2200 mL, further more preferably 180 mL to 1200 mL, and even more preferably 300 mL to 700 mL.

[0168] The coated metal sheet according to the present application has excellent can-making processability, and thus can withstand severe processing such as the manufacture of a drawing and ironing can. In addition, even in heat treatment after forming, peeling of the coating film does not occur, and thus by adjusting the ironing processing speed and the like, a drawing and ironing can having an inner surface coating film with a coverage of less than 200 mA in terms of ERV (Enamel Rater Value) and excellent coating film coverage can be obtained. Here, the coverage of the inner surface coating film in terms of ERV is set to a value obtained by filling the drawing and ironing can with a 1 mass% saline solution as an electrolyte to the vicinity of the can opening, measuring the ERV by an enamel rater, and setting the value to a value obtained by forming a metal exposed portion on the outer surface side of the can bottom, connecting a positive electrode, and on the other hand, immersing a negative electrode in the saline solution filled in the can, and measuring the current value after applying a direct current voltage of 6.3 V at room temperature (about 23°C) for 4 seconds. In such a measurement, the more the current flows, the more the inner surface coating film as an insulator has a defect, and the larger the area of the metal exposed on the inner surface of the can.

[0169] It is desirable that the coverage of the inner surface coating film in terms of ERV be less than 200 mA, preferably less than 100 mA, and more preferably less than 50 mA. In the case where the ERV per unit area (cm 2 ) is expressed, it is desirable that the ERV be less than 0.70 mA / cm 2 , preferably less than 0.35 mA / cm 2 , and more preferably less than 0.18 mA / cm 2 . Here, the ERV per unit area means a value obtained by dividing the ERV of the drawing and ironing can measured by the above-described method by the evaluation area (the area of the inner surface of the can body portion and the can bottom portion which contacts the above-described saline solution).

[0170] Note that, as for the inner surface side of the draw-and-iron can, the inner surface can be further sprayed with a coating material, etc. after forming, as needed, to form another coating film on the inner surface coating film, but as described above, the inner surface coating film has a high coverage after forming, and thus spraying is not needed, and from the economic aspect, it is preferable that spraying not be performed.

[0171] Further, as for the outer surface side of the can, as for the bottom portion on which the print layer is not formed at least substantially, the outer surface coating film can be located in the surface layer, but for the purpose of improving the conveyability of the can body, etc., a coating film formed from another coating material composition can be further formed on the outer surface coating film of the surface layer formed on the outer surface side of the bottom portion.

[0172] The coated metal sheet of the present application can be preferably applied to uses other than the draw-and-iron can, such as a draw can (DR can), a deep draw can (DRD can), a DTR can, a stretch draw-iron processing can, or a can lid, etc. obtained by the method known in the art. The can lid can have a shape known in the art such as a pop-top lid provided with a score for forming an opening for ejection of contents and a pull-tab for opening, and can be any one of a full-open type or a stay-on-tab type.

[0173] Examples

[0174] The present application is specifically described below by citing examples, comparative examples, and reference examples. Note that the unit of parts is the mass parts.

[0175] Various measurement items of the polyester resins A to D were performed according to the following methods. Note that the polyester resins A to D are all non-crystalline polyester resins.

[0176] (Measurement of Number Average Molecular Weight)

[0177] The measurement was performed by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene.

[0178] (Measurement of Glass Transition Temperature)

[0179] The measurement was performed using a differential scanning calorimeter (DSC) at a temperature increase rate of 10°C / min.

[0180] (Measurement of Acid Value)

[0181] The acid value (mgKOH / g) of the resin was calculated by dissolving 1 g of the solid matter of the polyester resin in 10 ml of chloroform and titrating with a 0.1 N KOH ethanol solution. Phenothalin was used as the indicator.

[0182] (Measurement of Monomer Composition)

[0183] The monomer composition ratio was determined from the peak intensity based on the 1H-NMR spectrum of the polyester resin A (30 mg of solid matter) dissolved in chloroform (0.6 mL). Note that the composition ratio was determined excluding a trace amount of components (less than 1 mol% relative to the total monomer components).

[0184] (Example 1)

[0185] [Preparation of the coating composition for the inner surface]

[0186] As the polyester resin, polyester resin A (acid value: 2 mgKOH / g, Tg: 75°C, Mn = 18000, monomer composition: terephthalic acid component / isophthalic acid component / ethylene glycol component / propylene glycol component = 38 / 12 / 17 / 33 mol%) was used, as the curing agent, a resol-type phenol resin was used, and as the curing catalyst (acid catalyst), dodecylbenzenesulfonic acid was used. Note that as the resol-type phenol resin, a m-cresol-based resol-type phenol resin (proportion of alkyl-etherified hydroxymethyl: 90 mol%, Mn = 1200) obtained by alkyl-etherification of hydroxymethyl with n-butanol was used, and as the acid catalyst, "Dodecylbenzenesulfonic acid (soft type) (mixture)" manufactured by Tokyo Chemical Industry Co., Ltd. was used.

[0187] The polyester resin A was dissolved in a mixed solvent of methyl ethyl ketone / solvent naphtha = 50 / 50 (mass ratio) to obtain a polyester resin A solution having a solid content of 30 mass%. A n-butanol solution of the resol-type phenol resin (solid content: 50 mass%) was diluted with methyl ethyl ketone to obtain a resol-type phenol resin solution having a solid content of 30 mass%. The dodecylbenzenesulfonic acid, which had been amine-neutralized with 2-dimethylaminoethanol, was dissolved in isopropyl alcohol to obtain a dodecylbenzenesulfonic acid solution having a solid content of 30 mass%.

[0188] Next, the polyester resin A solution (333 parts (100 parts of solid content)), the resol-type phenol resin solution (33.3 parts (10 parts of solid content)), and the acid catalyst solution (0.33 parts (0.10 parts of solid content)) were added to a glass container, and stirred for 10 minutes to prepare a solvent-type coating composition [solid content concentration: about 30 mass%, solid content blending ratio: polyester resin A / resol-type phenol resin / acid catalyst = 100 / 10 / 0.1 (mass ratio)].

[0189] [Preparation of the coating composition for the outer surface]

[0190] As the polyester resin, polyester resin A was used, as the curing agent, melamine resin (methyl etherified melamine resin, full ether type, weight average degree of polymerization 1.3) and benzoguanamine resin (methyl etherified benzoguanamine resin, imino / hydroxymethyl-containing partial ether type, weight average degree of polymerization 1.5) were used, and as the curing catalyst (acid catalyst), dodecylbenzenesulfonic acid was used.

[0191] Polyester resin A was dissolved in a mixed solvent of methyl ethyl ketone / solvent naphtha = 50 / 50 (mass ratio) to obtain a polyester resin A solution having a solid content of 30 mass%. Melamine resin and benzoguanamine resin were dissolved in methyl ethyl ketone to obtain a melamine resin solution and a benzoguanamine resin solution each having a solid content of 30 mass%. Dodecylbenzenesulfonic acid was amine-neutralized with 2-dimethylaminoethanol and then dissolved in isopropyl alcohol to obtain a dodecylbenzenesulfonic acid solution having a solid content of 30 mass%.

[0192] Next, to a glass container, polyester resin A solution 333 parts (100 parts of solid content), melamine resin B solution 10 parts (3 parts of solid content), benzoguanamine resin solution 10 parts (3 parts of solid content), and acid catalyst solution 0.33 parts (0.10 parts of solid content) were added, and stirring was performed for 10 minutes to prepare a solvent-type coating composition [solid content concentration: about 30 mass%, solid content blending ratio: polyester resin A / melamine resin / benzoguanamine resin / acid catalyst (dodecylbenzenesulfonic acid) = 100 / 3 / 3 / 0.1 (mass ratio)].

[0193] [Production of coated metal sheet]

[0194] As the metal sheet, a chromate phosphate system surface-treated aluminum sheet (3104 alloy, sheet thickness: 0.27 mm, chromium weight in surface treatment film: 20 mg / m 2 ) was used. First, the surface on the outer surface side after molding was coated with the above-mentioned outer surface coating composition in such a manner that the dry coating film weight after sintering became 40 mg / dm 2 (approximately 3 μm) using a bar coater, and drying was performed at 120°C for 60 seconds. Subsequently, the surface on the inner surface side on the opposite side was coated with the above-mentioned inner surface coating composition in such a manner that the dry coating film weight after sintering became 88 mg / dm 2 (approximately 6.4 μm) using a bar coater, and after drying was performed at 120°C for 60 seconds, sintering was performed at 250°C (furnace temperature inside the oven) for 30 seconds, whereby a

[0195] [Production of draw-reduced can]

[0196] After coating both sides of the metal sheet produced by the above method with paraffin wax, it was stamped into a circle with a diameter of 142mm to produce a shallow deep-drawn cup. Next, using a punch with an outer diameter of Φ66mm, the shallow deep-drawn cup under dry conditions underwent further deep drawing, thinning (three stages), and bulging. Afterwards, it was heat-treated in an oven at 201℃ for 75 seconds to obtain a deep-drawn and thinned can [can diameter: 66mm, height: approximately 130mm, capacity: approximately 370ml, total deep drawing ratio: 2.15, thinning rate: 61%, thickness of the central part of the can body / thickness of the central part of the can bottom × 100 = approximately 40%, thickness of the metal substrate in the central part of the can body / thickness of the metal substrate in the central part of the can bottom × 100 = approximately 40%, coating thickness of the inner surface of the central part of the can body / coating thickness of the inner surface of the central part of the can bottom × 100 = approximately 39%, coating weight (film thickness) of the inner surface of the central part of the can bottom: 86mg / dm³]. 2 (Approximately 6.2 μm), the coating thickness on the inner surface of the central part of the can bottom / the thickness of the metal substrate in the central part of the can bottom = approximately 0.024, and the coating thickness on the inner surface of the central part of the can body / the thickness of the metal substrate in the central part of the can body = approximately 0.023. It should be noted that the average processing speed during the thinning process (the average moving speed of the punch during the thinning process) is set to 5500 mm / sec.

[0197] (Examples 2 and 3)

[0198] As shown in Table 1, coating compositions for inner surfaces were prepared by changing the type of polyester resin and the solid component ratio. Using this composition, a coated metal sheet was fabricated in the same manner as in Example 1, and a deep-drawn, thin-film can was produced. It should be noted that, in addition to the polyester resins described above, polyester resin B (acid value: 2 mg KOH / g, Tg: 85°C, Mn = 18000, monomer composition: terephthalic acid / ethylene glycol / propylene glycol = 50 / 14 / 36 mol%) and polyester resin C (acid value: 5 mg KOH / g, Tg: 55°C, Mn = 16000, monomer composition: terephthalic acid / isophthalic acid / 1,4-cyclohexanediol / 2-methyl-1,3-propanediol = 10 / 40 / 21 / 29 mol%) were also used.

[0199] (Example 4)

[0200] As shown in Table 1, the polyester resin used is a resin prepared by mixing polyester resin A and polyester resin D (acid value: 22 mg KOH / g, Tg: 82 °C, Mn = 6000, monomer composition: terephthalic acid / trimethicone / ethylene glycol / propylene glycol = 49 / 1 / 12 / 38 mol%) in a mass ratio of 90:10 (Tg... mix 76℃, AVmix : 4 mgKOH / g), an inner surface coating composition was prepared. As a curing agent, a benzoguanamine resin (methyl etherified benzoguanamine resin, partially etherified type containing imino / hydroxymethyl, weight average degree of polymerization 1.5) was used, and an outer surface coating composition was prepared by changing the solid content blending ratio, and a coated metal sheet was produced in the same manner as in Example 1 using the composition, and a draw-reduced can was produced.

[0201] (Example 5)

[0202] As a polyester resin, a resin obtained by mixing polyester resin A and polyester resin D at a mass ratio of 90:10 was used, and as a curing agent, the above-described benzoguanamine resin (methyl etherified benzoguanamine resin, partially etherified type containing imino / hydroxymethyl, weight average degree of polymerization 1.5) was used, and an inner surface coating composition was prepared by changing the solid content blending ratio, and a coated metal sheet was produced in the same manner as in Example 1, and a draw-reduced can was produced.

[0203] (Example 6)

[0204] In the production of the draw-reduced can, the average processing speed at the time of the reduction processing (average moving speed of the punch at the time of the reduction processing) was set to 1000 mm / sec, and a coated metal sheet was produced in the same manner as in Example 1, and a draw-reduced can was produced.

[0205] (Comparative Examples 1, 2)

[0206] As shown in Table 1, the type of the polyester resin and the solid content blending ratio were changed, and an inner surface coating composition and an outer surface coating composition were prepared, and a coated metal sheet was produced in the same manner as in Example 1, and a draw-reduced can was produced.

[0207] (Reference Example 1)

[0208] As shown in Table 1, the type of the polyester resin and the solid content blending ratio were changed, and an inner surface coating composition was prepared, and a coated metal sheet was produced in the same manner as in Example 1.

[0209] The properties of the coating film obtained using the inner surface coating composition and the outer surface coating composition used in each of the examples, the comparative examples, and the reference example were tested in accordance with the following test methods.

[0210] [Stress relaxation rate of coating film]

[0211] The coating film samples for measurement were produced using the inner surface coating composition and the outer surface coating composition used in each of the examples, the comparative examples, and the reference examples, as described below. The non-glossy side of an aluminum foil ("nippaku foil" manufactured by Mitsubishi Aluminum Co., Ltd., thickness 12 μm) was coated using a bar coater in the same manner as the coating conditions (coating type, dry coating film weight, drying / sintering conditions) of the inner surface coating film of the coated metal sheets of each of the examples, the comparative examples, and the reference examples, and a coating film was formed on the aluminum foil after drying at 120°C for 60 seconds and sintering at 250°C for 30 seconds. After cooling to room temperature, the aluminum foil on which the coating film was formed was cut to a width of 50 mm and a length of 40 mm, and immersed in a diluted hydrochloric acid aqueous solution to dissolve the aluminum foil. Next, the film-like coating film was taken out, washed thoroughly with distilled water, and dried, and the obtained film-like coating film was cut to a width of 4 mm and a length of 40 mm, thereby obtaining a sample for measurement.

[0212] The stress relaxation rate of the obtained sample for measurement was measured using a thermal mechanical analysis device (TMA). First, the sample was clamped in the thermal mechanical analysis device without deflection, and the stress relaxation rate of the obtained sample for measurement was measured using the thermal mechanical analysis device (TMA). First, the sample was clamped in the thermal mechanical analysis device without deflection, and the distance between the clamps (corresponding to the initial length of the sample) was set to 10 mm. Next, the measurement environment was warmed up, and after reaching 100°C, the sample was elongated by 1% of the initial length of the sample at a stretching speed of 1 mm / min after 10 minutes, and maintained in this state for 10 minutes. The stress relaxation rate was calculated from the stress at 1% elongation (δ1) and the stress after 10 minutes (δ2) using the following equation (1). The measurement conditions are described below.

[0213] Apparatus: TMA / SS6100 manufactured by Seiko Instruments Inc.

[0214] Measurement atmosphere temperature: 100°C.

[0215] Distance between clamps: 10 mm.

[0216] Stretching speed: 1 mm / min.

[0217] Elongation (tensile elongation strain): 1%.

[0218] Stress relaxation rate (%) = (δ1-δ2) / δ1 x 100... (1)

[0219] In the equation, δ1 is the stress at 1% elongation, and δ2 is the stress after 10 minutes. Note that the values of δ1 and δ2 are corrected values obtained by subtracting the value of the stress immediately before 1% elongation after warming up to 100°C from the actual measured values.

[0220] Note that, in the case where the sample for measurement is obtained from a coated metal sheet having a coating film formed on both surfaces, the coated metal sheet can be cut, immersed in boiling hydrogen peroxide for several minutes, washed thoroughly with distilled water, and then the film-like coating film can be peeled off from the metal substrate and dried. The obtained film can be cut to a width of 4 mm and a length of 40 mm to obtain the sample for measurement.

[0221] [Stress relaxation rate of coating film on inner surface of bottom of can]

[0222] The stress relaxation rate of the coating film on the inner surface of the bottom of the deep-drawn and reduced can of Example 4 and Comparative Example 1, which had been subjected to heat treatment at 201°C for 75 seconds, was measured by forming the deep-drawn and reduced can as described in the above "Production of deep-drawn and reduced can" item. The production method of the sample for measurement is as follows.

[0223] The bottom portion of the deep-drawn and reduced can after heat treatment was cut out from the bottom of the deep-drawn and reduced can in such a manner that the center portion of the bottom was taken as the center and the size in the 0° direction with respect to the rolling direction of the metal substrate was 35 mm and the size in the 90° direction was 30 mm. The cut-out sample was immersed in boiling hydrogen peroxide for 2 to 3 minutes, washed thoroughly with distilled water, and then the film-like coating film on the inner surface side of the can was peeled off from the metal substrate and dried. The obtained film-like coating film was cut to a width of 4 mm and a length of 35 mm to obtain the sample for measurement.

[0224] The measurement of the stress relaxation rate was performed in the same manner as described in the above "Stress relaxation rate of coating film" item. The results are shown below.

[0225] The stress relaxation rate of the coating film on the inner surface of the bottom of the deep-drawn and reduced can of Example 4: 67%.

[0226] The stress relaxation rate of the coating film on the inner surface of the bottom of the deep-drawn and reduced can of Comparative Example 1: 45%.

[0227] [Glass transition temperature of coating film (coating film Tg)]

[0228] The coating film samples for measurement were produced using the inner surface coating composition and the outer surface coating composition used in each of the examples, the comparative examples, and the reference examples, as described below. In the same manner as the coating conditions (coating type, dry coating film weight, drying / sintering conditions) of the inner surface or the outer surface coating film in the coated metal sheet of each of the examples, the comparative examples, and the reference examples, the non-glossy side of an aluminum foil ("nippaku foil" manufactured by Mitsubishi Aluminum Co., Ltd., thickness 12 μm) was coated using a bar coater, and after drying at 120°C for 60 seconds and sintering at 250°C for 30 seconds, a coating film was formed on the aluminum foil. After cooling to room temperature, the aluminum foil on which the coating film was formed was immersed in a diluted hydrochloric acid aqueous solution, and the aluminum foil was dissolved. Subsequently, the film-like coating film was taken out, washed thoroughly with distilled water, and dried to obtain a sample for measurement. The glass transition temperature of the coating film obtained was measured using a differential scanning calorimeter (DSC) under the following conditions. Note that in the 2nd-run (temperature increase), the extrapolated glass transition start temperature was set as the glass transition temperature of the coating film (coating film Tg), and the temperature at the intersection of the tangent line drawn from the point at which the gradient of the curve in the stage-like change portion of the glass transition was the largest and the straight line in which the baseline on the low temperature side was extended to the high temperature side.

[0229] Apparatus: DSC6220 manufactured by Seiko Instruments Inc.

[0230] Sample amount: 5 mg

[0231] Temperature increase rate: 10°C / min

[0232] Temperature range: -80°C to 200°C (temperature increase, cooling, temperature increase)

[0233] Ambient conditions: under nitrogen flow

[0234] Note that in the case where the sample for measurement is obtained from a coated metal sheet on both sides of which a coating film is formed and a drawn and thinned can, the coating film on one side which is not measured can be removed by sanding or the like so that the metal surface is exposed, and the coated metal sheet is cut out, and the metal substrate (metal sheet) is dissolved by immersion in a diluted hydrochloric acid aqueous solution or the like, and the film-like coating film is taken out, washed thoroughly with distilled water, and dried to obtain a sample for measurement.

[0235] [MEK extraction rate]

[0236] The coating film samples for evaluation were produced using the inner surface coating composition and the outer surface coating composition used in each of the examples, the comparative examples, and the reference examples, as described below. The coating film samples were produced by coating each of the phosphoric chromate-based surface-treated aluminum sheets (3104 alloy, sheet thickness: 0.27 mm, chromium weight in surface treatment film: 20 mg / m2) using a bar coater in the same manner as the coating conditions (coating type, dry coating film weight, drying / sintering conditions) for the inner surface or the outer surface coating film of the coated metal sheets of each of the examples, the comparative examples, and the reference examples, and then drying at 120°C for 60 seconds and sintering at 250°C for 30 seconds to produce the coated metal sheets. Test pieces of 5 cm x 5 cm were cut from the coated metal sheets, and after measuring the mass of the test pieces (W1), the test pieces were immersed in boiling MEK (refluxing at 80°C) for 1 hour using 200 ml of MEK (methyl ethyl ketone), and MEK extraction was performed at the boiling point for 1 hour. After cleaning the test pieces after extraction with MEK, drying was performed at 120°C for 1 hour, and the mass of the test pieces after extraction (W2) was measured. Furthermore, the coating film was peeled off and removed by the decomposition method using concentrated sulfuric acid, and the test pieces were cleaned and dried, and the mass of the test pieces (W3) was measured. The MEK extraction rate (%) of the coating film of the coated metal sheet was calculated from the following equation (7). The results are shown in Table 1. 2 MEK extraction rate (%) = 100 x (W1-W2) / (W1-W3) (7)

[0237] MEK extraction rate (%) = 100 x (W1-W2) / (W1-W3) (7)

[0238] Note that, in the case where the test pieces were obtained from the coated metal sheets having coating films formed on both surfaces and the drawn and reduced cans, the MEK extraction rate of the coating film of the coated metal sheet was measured by the above-described method after removing the coating film on one side which was not measured by sanding or the like.

[0239] The drawn and reduced cans and the coated metal sheets obtained in each of the examples, the comparative examples, and the reference examples were evaluated according to the following test methods.

[0240] [Inner surface coating film covering property evaluation (ERV evaluation)]

[0241] The inner surface coating film covering property evaluation was performed on the drawn and reduced cans (indicated as "no heat treatment" in the table) that were subjected to the drawn and reduced processing and the bulging processing up to that point, and the drawn and reduced cans (indicated as "heat treatment" in the table) that were subjected to heat treatment at 201°C for 75 seconds using an oven after that, as described in the above "production of drawn and reduced cans" item, as follows.

[0242] A metal exposed portion was formed on the outer surface side of the bottom of the deep-drawn and reduced can, and the anode of an enamel rater was connected to the can body. On the other hand, 360 mL of 1% salt water was injected into the can, and the cathode of the enamel rater was immersed in the salt water filled in the can, and the current value (ERV) after 4 seconds of voltage application at room temperature of 6.3 V was measured.

[0243] The evaluation criteria were as follows.

[0244] ◎: The current value was less than 50 mA (less than 0.18 mA / cm 2 ) per unit area.

[0245] O: The current value was 50 mA or more and less than 200 mA (0.18 mA / cm 2 or more and less than 0.70 mA / cm 2 ) per unit area.

[0246] Δ: The current value was 200 mA or more and less than 700 mA (0.70 mA / cm 2 or more and less than 2.50 mA / cm 2 ) per unit area.

[0247] X: The current value was 700 mA or more (2.50 mA / cm 2 or more) per unit area.

[0248] [Coating film peeling resistance evaluation]

[0249] For the coating film peeling resistance evaluation, the deep-drawn and reduced can after heat treatment at 201°C for 75 seconds was observed for peeling of the inner and outer surface coating films of the can body.

[0250] The evaluation criteria were as follows.

[0251] O: No peeling of the coating film was confirmed.

[0252] Δ: Peeling of the coating film was confirmed in a very small area of the portion where the processing of the can body side wall was strictly reduced in thickness.

[0253] X: Peeling of the coating film was confirmed in a large area of the portion where the processing of the can body side wall was strictly reduced in thickness.

[0254] [Substrate adhesion evaluation]

[0255] A test piece in a long strip shape having a height of 50 mm and a width of 15 mm was cut out from the coated metal sheet produced as described above. A scratch reaching the metal substrate was applied to the face of the coated metal sheet which became the side of the outer surface of the can at a position 35 mm from the top end of the long strip shape. By repeatedly bending from the scratch applied in advance as a starting point, a portion in which only the metal substrate was cut and only the inner surface coating film remained was produced, and then the portion was bent so that the portion became the inner side. A 180° peel test was performed at 23°C at a tensile speed of 5 mm / min using a tensile testing machine ("Autograph AG-IS" manufactured by Shimadzu Corporation) to measure the peel strength (180° peel strength).

[0256] The evaluation section in which the inner surface coating film was peeled from the metal substrate was observed visually. When the inner surface coating film of the evaluation section was peeled off from the metal substrate in its entirety, the coating film was evaluated as having interfacial peeling, and the adhesion between the coating film and the metal substrate was strong. When the inner surface coating film was broken before the coating film was peeled from the metal substrate, the coating film was evaluated as having cohesive failure.

[0257] The evaluation criteria were as follows.

[0258] ◎: interfacial peeling and a peel strength of 2.0 N / 15 mm or more, or cohesive failure.

[0259] O: interfacial peeling and a peel strength of less than 2.0 N / 15 mm and 1.0 N / 15 mm or more.

[0260] Δ: interfacial peeling and a peel strength of less than 1.0 N / 15 mm.

[0261] (Thermal shrinkage ratio evaluation)

[0262] The inner surface coating film of the central portion of the can body of the draw-reduced and ironed can (without heat treatment) of Example 4, which was produced up to the draw-reduction and ironing processes and the bulging process as described in the item "Production of draw-reduced and ironed cans" above, and the inner surface coating film of the central portion of the can body of the draw-reduced and ironed can (with heat treatment) of Example 4, which was subjected to heat treatment at 201°C for 75 seconds in an oven after the draw-reduction and ironing processes and the bulging process, were evaluated as follows.

[0263] A sample having a can body circumferential direction of 10 mm and a can height direction of 20 mm was cut out from the draw-reduced and ironed can described above, with the central portion of the can body (the thinnest portion) in the 0° direction with respect to the metal substrate as the center. The coating film on the side of the outer surface of the can was removed by sanding to expose the metal surface, and then the metal substrate was dissolved by immersion in a diluted hydrochloric acid aqueous solution. Next, the film-like coating film on the side of the inner surface of the can was taken out, washed thoroughly with distilled water, and dried. The obtained film-like coating film was cut out to have a width of 4 mm (can body circumferential direction) and a length of 20 mm (can height direction), and thus a sample for measurement was obtained.

[0264] The sample for measurement was clamped in a thermal mechanical analysis device, and the distance between the clamps (corresponding to the initial length of the measurement portion in the height direction of the coated film) was set to 5 mm. The displacement amount of the measurement sample was measured under the following conditions, and the thermal shrinkage in the height direction of the can was evaluated under a load and under no load.

[0265] Device: TMA / SS6100 manufactured by Seiko Instruments Inc.

[0266] Temperature increase rate: 5°C / min.

[0267] Temperature range: 30°C to 200°C.

[0268] Measurement mode: Tensile mode.

[0269] Measurement load: 5 mN (5.20 x 10 5 N / m 2 ) or no load.

[0270] Distance between clamps: 5 mm

[0271] The distance between the clamps before measurement (corresponding to the initial length of the measurement portion of the coated film) was set to L0, the maximum value of the shrinkage amount in the height direction of the portion corresponding to L0 when the temperature was increased from 30°C to 200°C at a temperature increase rate of 5°C / min while applying a load of 5.20 x 10 5 N / m 2 per unit area was set to ΔL1, and the value calculated from the numerical formula represented by the following formula (5) was taken as the thermal shrinkage (under a load). Note that, in terms of the displacement amount, shrinkage was taken as a positive value, and expansion or elongation was taken as a negative value. The results are shown below.

[0272] Thermal shrinkage (under a load) = (ΔL1 / L0) x 100 (%) (5)

[0273] Thermal shrinkage (under a load) of the inner surface coated film of the drawn and reduced can (without heat treatment) of Example 4: 68%.

[0274] Thermal shrinkage (under a load) of the inner surface coated film of the drawn and reduced can (with heat treatment) of Example 4: 8%.

[0275] Further, the distance between the jaws before measurement (corresponding to the initial length of the measurement part of the coated film) was set to L0, the maximum value of the shrinkage amount in the height direction of the portion corresponding to L0 when the temperature was increased at a rate of 5°C / min from 30°C to 200°C in the unloaded state was set to ΔL2, and the value calculated from the numerical formula represented by the following formula (6) was used as the heat shrinkage rate (unloaded). Note that, in terms of displacement amount, shrinkage was set to a positive value, and expansion or elongation was set to a negative value. The results are shown below.

[0276] Heat shrinkage rate (unloaded) = (ΔL2 / L0) x 100 (%) (6)

[0277] Heat shrinkage rate (unloaded) of the inner surface coated film of the draw-reduced can (without heat treatment) of Example 4: 69%.

[0278] Heat shrinkage rate (unloaded) of the inner surface coated film of the draw-reduced can (with heat treatment) of Example 4: 30%.

[0279] (Evaluation of Corrosion Resistance)

[0280] The evaluation of corrosion resistance was performed on the inner surface coated film of the central part of the can body of the draw-reduced can (without heat treatment) of Example 4, which was produced up to the draw-reduced processing and the bulging processing as described in the above "Production of Draw-Reduced Can" item, and the draw-reduced can (with heat treatment) of Example 4, which was subjected to heat treatment at 201°C for 75 seconds using an oven thereafter, as follows.

[0281] A test piece having a can body circumferential direction of 40 mm and a can height direction of 40 mm was cut out from the draw-reduced can described above, with the central part of the can body (the thinnest part) as the center. A cross-shaped cut reaching the substrate having a length of 4 cm was applied to the test piece using a cutter, and the test piece was immersed in an acidic model solution containing salt, and was left for 2 weeks at 37°C, and the corrosion state was evaluated. Note that the model solution used for the test was a solution in which salt was set to 0.2%, and citric acid was added to adjust the pH to 2.5. In terms of evaluation criteria, samples in which the maximum width of the corrosion under the coated film was 1.5 mm or more on each side were set to x, samples in which the maximum width was 0.5 mm or more but less than 1.5 mm were set to o, and samples in which the maximum width was less than 0.5 mm were set to. The results are shown below.

[0282] Corrosion state of the draw-reduced can (without heat treatment) of Example 4: x.

[0283] Corrosion state of the draw-reduced can (with heat treatment) of Example 4:.

[0284] The blending composition of the inner surface coating composition and the outer surface composition, the coating film properties of the inner surface coating film and the outer surface coating film (coating film Tg, MEK extraction rate, stress relaxation rate), and the evaluation results of each of the examples, the comparative examples, and the reference examples are shown in Table 1.

[0285]

[0286] Industrial availability

[0287] The drawing-reduced thin can of the present application has no coating film peeling at the time of heat treatment, effectively prevents the exposure of metal, has excellent corrosion resistance, and can be preferably used for beverage containers and the like. Furthermore, the drawing-reduced thin can coating metal sheet of the present application has excellent can-making workability and productivity, has excellent coating film peeling resistance that does not cause coating film peeling even at the time of heat treatment after forming, and thus can be preferably used for the manufacture of drawing-reduced thin cans.

Claims

1. A deep-drawn and thinned can, characterized in that, At least the inner surface of the can has an inner surface coating. The inner surface coating contains polyester resin and a curing agent. Under test conditions of 100°C, the stress relief rate of the inner surface coating at the bottom of the tank after 10 minutes at 1% elongation is greater than 50%. The coverage of the inner surface coating is less than 200 mA when converted to ERV. The stress relief rate is calculated by applying a 1% elongation strain to the coating film under test conditions of 100°C using a thermomechanical analysis device, and measuring the stress change over time while maintaining this strain. The result is calculated according to the following formula (1). Stress mitigation rate = (δ1-δ2) / δ1×100……(1), unit %, In the formula, δ1 is the stress required to elongate the inner surface coating by 1% after separation, and δ2 is the stress after 10 minutes.

2. The deep-drawn thinning can according to claim 1, wherein, The curing agent contained in the inner surface coating is a methyl phenolic resin and / or an amino resin.

3. The deep-drawn thinning can according to claim 2, wherein, The first-stage phenolic resin is a m-cresol-based first-stage phenolic resin.

4. The deep-drawn thinning can according to any one of claims 1 to 3, wherein, The inner surface coating also contains an acid catalyst.

5. The deep-drawn thinning can according to claim 4, wherein, The content of the acid catalyst in the inner surface coating is less than 0.5 parts by mass relative to 100 parts by mass of polyester resin.

6. The deep-drawn thinning can according to any one of claims 1 to 3, wherein, The inner surface coating contains a polyester resin that, when the total amount of the polyol components constituting the polyester resin is set to 100 mol%, contains a total of more than 20 mol% of one or more of ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol.

7. The deep-drawn thinning can according to any one of claims 1 to 3, wherein, The outer surface of the can also have an outer surface coating containing polyester resin and a curing agent. The outer surface coating at the bottom of the can has a stress relief rate of more than 40% after 10 minutes at 1% elongation under test conditions of 100°C.

8. The drawn thinning can according to any one of claims 1 to 3, wherein, The thickness of the central part of the tank body is 20% to 75% of the thickness of the central part of the tank bottom.

9. The deep-drawn thinning can according to any one of claims 1 to 3, wherein, The thickness of the inner surface coating in the central part of the can body is 20% to 75% of the thickness of the inner surface coating in the central part of the bottom of the can.

10. The drawn thinning can according to any one of claims 1 to 3, wherein, The thickness ratio of the inner surface coating to the metal substrate, i.e., the thickness of the inner surface coating / the thickness of the metal substrate, is almost the same at the bottom of the can and the main body of the can.

11. The drawn thinning can according to any one of claims 1 to 3, wherein, The thermal shrinkage rate of the coating on the inner surface of the central part of the can body, expressed by the following formula, is 30% or less. Thermal shrinkage rate = (ΔL1 / L0) × 100, in % L0: The initial length of the coating in the height direction, separated from the center of the can body; ΔL1: Apply 5.20 × 10 to each unit area on one side. 5 N / m 2 The maximum shrinkage length in the height direction of the coating film corresponding to the portion L0 when the load side is heated from 30℃ to 200℃ at a heating rate of 5℃ / min.

12. A deep-drawn and thinned can, characterized in that, Formed from a deep-drawn, thinned, coated metal sheet for cans, with a coating on both sides. The deep-drawn and thinned coated metal sheet for the can has an inner surface coating containing polyester resin and a first-order phenolic resin and / or amino resin as a curing agent, which forms the inner surface of the can after deep drawing and thinning. The outer surface coating containing polyester resin and an amino resin as a curing agent also forms the outer surface coating. The inner surface coating exhibits a stress relief rate of over 50% after 10 minutes of 1% elongation under test conditions at 100°C, and the outer surface coating exhibits a stress relief rate of over 40% after 10 minutes of 1% elongation under test conditions at 100°C. The coverage of the inner surface coating is less than 200 mA when converted to ERV. The stress relief rate is calculated by applying a 1% elongation strain to the coating film under test conditions of 100°C using a thermomechanical analysis device, etc., and measuring the stress change over time while maintaining this strain. The result is calculated according to the following formula (1). Stress mitigation rate = (δ1-δ2) / δ1×100……(1), unit %, In the formula, δ1 is the stress required to elongate the inner surface coating by 1% after separation, and δ2 is the stress after 10 minutes.

13. The deep-drawn thinning can according to claim 12, wherein, The inner surface coating contains a polyester resin that, when the total amount of the polyol components constituting the polyester resin is set to 100 mol%, contains a total of more than 20 mol% of one or more of ethylene glycol, propylene glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, and diethylene glycol.

14. The deep-drawn thinning can according to claim 12, wherein, The thickness of the central part of the tank body is 20% to 75% of the thickness of the central part of the tank bottom.

15. The deep-drawn thinning can according to any one of claims 12 to 14, wherein, The thickness of the inner surface coating in the central part of the can body is 20% to 75% of the thickness of the inner surface coating in the central part of the bottom of the can.

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