Paint composition, painted metal sheet, and a pressing can and its manufacturing method.

Abstract

To provide a coating composition which enables making of a coated metal plate and a drawn and ironed can having canning workability, adhesion to a base material, and resistance to flavor sorption property.SOLUTION: A coating composition contains: a polyester resin blended body containing a polyester resin (A) having a glass transition temperature of higher than 40°C and an acid value of less than 10 mgKOH / g, and a polyester resin (B) having a glass transition temperature of higher than 40°C and an acid value of equal to or more than 10 mgKOH / g and less than 50 mgKOH / g, as main agent resins; and a curing agent (C).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a paint composition and a painted metal sheet coated therewith. Furthermore, it relates to a drawing can using the painted metal sheet and a method for manufacturing the same. [Background technology]

[0002] A known manufacturing method for seamless cans, widely used for beverages and the like, is called drawing and ironing. This method involves punching out a circular shape from a metal sheet, such as an aluminum or steel sheet, drawing it to form a cylindrical cup consisting of a body without side seams and a bottom seamlessly connected to the body, and then applying ironing to thin the body. Seamless cans produced by this method are called drawing and ironing cans.

[0003] One known method for manufacturing these pressed metal cans involves using a laminated metal plate pre-coated with a thermoplastic resin film such as polyethylene terephthalate. This method allows for pressing and ironing under dry conditions without the use of liquid coolant (water-based lubricant) because the thermoplastic resin film provides lubrication. This has the advantage of reducing environmental impact compared to conventional pressing and ironing methods using liquid coolant. However, the thermoplastic resin film used in this method has a certain thickness due to the film formation process, which can sometimes pose economic problems.

[0004] In contrast to the above method, a method for manufacturing drawn metal cans by drawing and ironing painted metal sheets has been proposed (Patent Document 1). According to this method, when drawing and ironing is performed on a metal sheet with a painted film (coating film) formed on it, the coating film has a lubricating function, making it possible to perform the drawing and ironing under dry conditions. Furthermore, by making the coating film thin, it is also economically superior. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3872998 [Patent Document 2] Patent No. 4091266 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0006] However, in the manufacturing method of cans using painted metal sheets as described above, no method has yet been proposed that fully satisfies the requirements in terms of can-making processability of the coating, adhesion to the substrate, and resistance to flavor adsorption of the contents.

[0007] In other words, in the drawing and ironing process, it is required that no defects occur in the coating during the can manufacturing process (can manufacturing processability), and that the coating does not peel off from the substrate (substrate adhesion). Furthermore, when contents are filled into containers manufactured by the aforementioned squeezing and drawing process, if flavor components (aroma components) such as limonene contained in the contents are adsorbed onto the coating, the flavor of the contents will change. Therefore, the coating on the inside of the can must not allow such adsorption (flavor adsorption resistance).

[0008] The inventors diligently studied to solve the above problems. As a result, they found that by using a paint composition containing a polyester resin and a curing agent, mixing polyester resins with different acid values, and setting the glass transition temperature of each resin above a predetermined temperature, the above problems can be solved at a high level. Furthermore, they found that in addition to the above problems, the requirements for the elongation and heat resistance of the coating film, which are necessary when used on the inner and outer surfaces of a drawing can, can also be met, leading to the present invention. [Means for solving the problem]

[0009] To achieve the above objective, the paint composition in one embodiment of the present invention is characterized by containing (1) a polyester resin blend as the main resin, comprising a polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mg KOH / g, and a polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g, and a curing agent (C). Furthermore, in (1) above, it is preferable that (2) the average acid value of the polyester resin blend is greater than 2.0 mg KOH / g and less than 16.0 mg KOH / g. Furthermore, in (1) or (2) above, it is preferable that (3) the glass transition temperature of the polyester resin blend is 50 to 120°C. Furthermore, in any of (1) to (3) above, (4) it is preferable that the blending ratio of polyester resin (A) / polyester resin (B) in the polyester resin blend is 30 / 70 to 99 / 1 in terms of solid content by mass. In any of the above (1) to (4), (5) it is preferable that the curing agent (C) is a resol-type phenolic resin. In any of the above (1) to (5), it is preferable that the content of curing agent (C) is 5.5 parts by mass or more per 100 parts by mass of the main resin (polyester resin blend). In any of the above (1) to (6), it is preferable that (7) the number average molecular weight of the polyester resin (A) is 13,000 or more and the number average molecular weight of the polyester resin (B) is less than 13,000. In any of the above (1) to (7), (8) it is preferable that the paint composition is a solvent-type paint composition. Furthermore, in order to achieve the above objective, the painted metal plate in one embodiment of the present invention is characterized in that (9) a coating film formed on at least one side of the metal plate is made from the paint composition described in any of (1) to (8) above. Furthermore, in order to achieve the above objective, the drawn can in one embodiment of the present invention is obtained by drawing the painted metal sheet described in (9) above. In the above (10), it is preferable that the thickness of the coating film at the central portion of the can body side wall on the inner surface and / or outer surface (11) is 20 to 75% of the thickness of the coating film at the can bottom. In order to achieve the above object, a method for producing a drawn and ironed can according to an embodiment of the present invention is characterized by comprising producing the coated metal sheet according to (9) above by drawing and ironing at an ironing ratio of 25 to 80%.

Effects of the Invention

[0010] According to the coating composition of the present invention, it is possible to provide a coated metal sheet for drawn and ironed cans that combines all of can processing properties, substrate adhesion, and flavor sorption resistance.

Brief Description of Drawings

[0011] [Figure 1] It is an explanatory diagram for 180° peel strength measurement. [Figure 2] It is an explanatory diagram for 180° peel strength measurement. [Figure 3] It is an explanatory diagram for 180° peel strength measurement.

Mode for Carrying Out the Invention

[0012] <Coating Composition> Hereinafter, the coating composition of the present invention will be described with reference to embodiments, but the present invention is not limited to the following embodiments. The coating composition of the present embodiment is characterized by containing a base resin and a curing agent. Specifically, a polyester resin is used as the base resin, and the base resin is crosslinked by the curing agent, thereby forming a coating film having heat resistance.

[0013] In the present embodiment, the base resin is a polyester resin blend containing a polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mgKOH / g, and a polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mgKOH / g or more and less than 50 mgKOH / g. This is for the following reasons.

[0014] First, regarding the problems in this invention, in order to achieve both processability and adhesion to the substrate, it is necessary to set the acid value (quantity of carboxyl groups) of the polyester resin to a predetermined value. That is, if the acid value of the resin is high, the crosslinking density increases, which reduces processability. On the other hand, if the acid value of the resin is low, while processability improves, the acid-base interaction between the substrate (e.g., aluminum) surface and the carboxyl groups in the resin decreases, which reduces the adhesion between the coating film and the substrate.

[0015] The inventors, through trial and error in order to form a coating film that balances processability and substrate adhesion, arrived at the above-mentioned method of blending polyester resins with different acid values ​​to form the main resin. In other words, by blending a polyester resin (A) with a relatively low acid value and a polyester resin (B) with a relatively high acid value to form the main resin, the resulting coating film can possess both the excellent processability derived from polyester resin (A) and the excellent substrate adhesion derived from polyester resin (B). As a result, it is presumed that it is possible to achieve both processability and substrate adhesion, which is difficult to achieve with a coating film made from a single main resin.

[0016] In order to efficiently achieve the above effects, it is preferable to use a polyester resin (A) having an acid value of less than 10 mg KOH / g, preferably 0.5 to 6 mg KOH / g, more preferably 1 to 4 mg KOH / g, and a polyester resin (B) having an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g, preferably 11 mg KOH / g to 40 mg KOH / g, more preferably 12 mg KOH / g to 25 mg KOH / g.

[0017] Next, regarding the issue of flavor sorption resistance, which is one of the problems in this invention, the inventors conducted repeated experiments and found that there is a correlation between the glass transition temperature of the resin and flavor sorption resistance. Specifically, they found that when the glass transition temperatures of polyester resin (A) and polyester resin (B) used as the main resin are above a predetermined temperature, the adsorption rate of aroma components contained in the contents can be reduced.

[0018] The reason why there is a correlation between the glass transition temperature and flavor sorption resistance is presumed to be as follows: When polyester resin (A) and / or polyester resin (B) are used, the mobility of the resin increases, making it easier for flavor components to diffuse into the coating film. As a result, it is thought that more flavor components are sorbed into the coating film.

[0019] Therefore, the inventors considered that it is possible to improve flavor sorption resistance by controlling the glass transition temperature, and decided to control the glass transition temperature of the polyester resin in this embodiment.

[0020] Based on the above, in this embodiment, in order to achieve a high level of balance between can-making processability, substrate adhesion, and flavor sorption resistance, the polyester resin blend is characterized by comprising a polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mg KOH / g, and a polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g.

[0021] The main resin blend in this embodiment is the average acid value (AV), which is the sum of the values ​​obtained by multiplying the acid value and mass fraction of each polyester resin. mixThe range of the average acid value of the blend is preferably greater than 2.0 mg KOH / g and less than 16.0 mg KOH / g, preferably 2.0 to 12.0 mg KOH / g, and more preferably 2.5 to 8.0 mg KOH / g. If the average acid value of the blend is 2.0 mg KOH / g or less, it is undesirable because the adhesion of the coating film to the substrate may not be ensured when manufacturing a pressed can. On the other hand, if the average acid value of the blend is 16.0 mg KOH / g or more, it is undesirable because the processability of the coating film for can manufacturing may be insufficient.

[0022] The glass transition temperature (Tg) of the polyester resin blend, which is the main resin of this embodiment. mix The glass transition temperature of the blend is preferably in the range of 50°C or higher, more preferably 60°C or higher, more preferably 60 to 120°C, even more preferably 65 to 100°C, and particularly preferably 65 to 90°C. If the glass transition temperature of the blend is lower than the above range, it is undesirable because flavor components (aroma components) such as limonene contained in the contents are more likely to adhere to the coating film after the can manufacturing process. On the other hand, if the glass transition temperature of the blend exceeds 120°C, it is undesirable because the can manufacturing processability is insufficient and coating defects occur during can manufacturing.

[0023] The glass transition temperatures of polyester resin (A) and polyester resin (B) may be different or the same, as long as both are above 40°C, as described above. The glass transition temperature of the blend is calculated using the following formula (1). 1 / Tg mix =(W1 / Tg1)+(W2 / Tg2)+…+(Wm / Tgm) ...(1) W1 + W2 + ... + Wm = 1 In the formula, Tg mixTg1, Tg2, ..., Tgm represent the glass transition temperature (K) of the polyester resin blend, while Tg1, Tg2, ..., Tgm represent the glass transition temperature (K) of each individual polyester resin used (polyester resin 1, polyester resin 2, ..., polyester resin m). Furthermore, W1, W2, ..., Wm represent the mass fraction of each polyester resin (polyester resin 1, polyester resin 2, ..., polyester resin m).

[0024] Known methods can be applied to measure the glass transition temperature; for example, it can be done using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0025] In the polyester resin blend of this embodiment, which is the main resin, the desired blending ratio of polyester resin (A) / polyester resin (B) is 30 / 70 to 99 / 1 in terms of solid content by mass, preferably 40 / 60 to 98 / 2, more preferably 50 / 50 to 98 / 2, even more preferably 70 / 30 to 97 / 3, and particularly preferably 80 / 20 to 95 / 5.

[0026] In this embodiment, the polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mg KOH / g, and the polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g, can be selected from known polyester resins commonly used in paint compositions.

[0027] The polycarboxylic acid components constituting polyester resin (A) and polyester resin (B) are not particularly limited as monomers commonly used in the polymerization of polyester resins. Examples include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedionic acid, and dimer acid; unsaturated dicarboxylic acids such as (anhydride) maleic acid, fumaric acid, and terpene-maleic acid adducts; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, and 1,2-cyclohexenedicarboxylic acid; and polycarboxylic acids with a valency of 3 or higher, such as (anhydride) trimellitic acid, (anhydride) pyromellitic acid, and methylcyclohexentricarboxylic acid. One or more of these can be selected and used. Among the polycarboxylic acid components mentioned above, terephthalic acid, isophthalic acid, adipic acid, sebacic acid, and 1,4-cyclohexanedicarboxylic acid can be suitably used as components constituting polyester resins.

[0028] In this embodiment, from the viewpoint of flavor sorption resistance, corrosion resistance, and retort resistance, it is preferable that the proportion of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid in the polycarboxylic acid components constituting polyester resin (A) and / or polyester resin (B) is 80 mol% or more, more preferably 80 to 100 mol%, and particularly preferably 90 to 100%. Furthermore, linear aliphatic dicarboxylic acids with more than 6 carbon atoms, such as adipic acid, azelaic acid, sebacic acid, and dodecanedionic acid, may be included in an amount equal to the remainder of the aromatic dicarboxylic acids, i.e., 20 mol% or less. However, linear aliphatic dicarboxylic acids with more than 6 carbon atoms tend to have a high affinity for hydrophobic flavor components such as limonene and are prone to sorption. Therefore, when a coating film is formed using polyester resin (A) and / or polyester resin (B) that contain a large amount of linear aliphatic dicarboxylic acids with more than 6 carbon atoms as the polycarboxylic acid components constituting the polyester resin, the flavor sorption properties of the coating film will be poor. Therefore, it is desirable that the proportion of linear aliphatic dicarboxylic acids with more than 6 carbon atoms in the polycarboxylic acid components constituting the polyester resin be less than 20 mol%, preferably less than 10 mol%, more preferably less than 7 mol%, and even more preferably less than 5 mol%. In polyester resin blends, it is desirable that the proportion of linear aliphatic dicarboxylic acids with more than 6 carbon atoms in the total of all polycarboxylic acid components constituting the polyester resin blend be less than 20 mol%, preferably less than 10 mol%, more preferably less than 7 mol%, and even more preferably less than 5 mol%.

[0029] The polyhydric alcohol components constituting polyester resin (A) and polyester resin (B) are not particularly limited and include ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, and 4-methyl-1,7-heptanediol. One or more of the following polyhydric alcohol components can be used: aliphatic glycols such as 4-methyl-1,8-octanediol, 4-propyl-1,8-octanediol, and 1,9-nonanediol; ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; alicyclic polyalcohols such as 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, tricyclodecane glycols, and hydrolyzed bisphenols; and trivalent or higher polyalcohols such as trimethylolpropane, trimethylolethane, and pentaerythritol. In this embodiment, among the above polyhydric alcohol components, ethylene glycol, propylene glycol, neopentyl glycol, diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol can be suitably used as components constituting the polyester resin.

[0030] Furthermore, in this embodiment, from the viewpoint of flavor sorption resistance, it is desirable that the proportion of at least one selected from ethylene glycol, propylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, and 1,4-cyclohexanedimethanol in the polyhydric alcohol component constituting polyester resin (A) and / or (B) be 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more.

[0031] In the main resin of this embodiment, it is preferable from the viewpoint of can manufacturing processability that the number average molecular weight of the polyester resin (A) is 13,000 or more, and the number average molecular weight of the polyester resin (B) is less than 13,000.

[0032] Furthermore, as the polyester resin, amorphous polyester resin is preferable from the viewpoint of can-making processability, dent resistance, and paint-forming properties. Here, amorphous means that it does not show a clear melting point for crystalline components when measured by a scanning calorimeter. In the case of amorphous polyester resin, compared to crystalline polyester resin, it has superior solubility in solvents, is easy to form into paint, and can form a coating film with excellent can-making processability and dent resistance.

[0033] The hydroxyl value of the polyester resin is not limited to this, but is preferably 20 mg KOH / g or less, more preferably 10 mg KOH / g or less.

[0034] <Hardening agent> Next, the curing agent used in the paint composition of this embodiment will be described. As the curing agent (C) used in this embodiment, a resol-type phenolic resin and / or an amino resin can be suitably used from the viewpoint of hygiene and curability.

[0035] In this embodiment, the resol-type phenol resin is obtained by reacting a phenol monomer with formaldehyde in the presence of an alkaline catalyst. Examples of phenol monomers include o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, phenol, m-cresol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol. These can be used individually or in mixtures of two or more, and among them, m-cresol is preferred as the phenol monomer from the viewpoint of curability. Furthermore, a product in which some or all of the methylol groups are alkyl etherified (alkoxymethylated) with C1-C12 alcohols can also be used. In this embodiment, from the viewpoint of reactivity and compatibility with the main resin, a product in which some or all of the methylol groups are alkyl etherified with C1-C12 alcohols can be suitably used, and in particular, a product in which the methylol groups of a resol-type phenolic resin derived from m-cresol (m-cresol-based resol-type phenolic resin) are alkyl etherified with n-butanol is preferred.

[0036] In this embodiment, examples of amino resins include methylolated amino resins obtained by the reaction of amino components such as melamine, urea, benzoguanamine, acetoganaamine, steroguanamine, spiloganamine, and dicyandiamide with aldehyde components such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. The above amino resins also include those obtained by alkyl etherifying the methylol group of the methylolated amino resin with an alcohol having 1 to 6 carbon atoms. These can be used individually or in combination of two or more. From a hygienic standpoint, methylolated amino resins using melamine (melamine resins) and methylolated amino resins using benzoguanamine (benzoguanamine resins) are particularly preferred. As the benzoguanamine resin, benzoguanamine resins in which some or all of the methylol groups of the benzoguanamine resin are alkyl etherified with alcohols such as methanol, ethanol, n-butanol, and i-butanol are preferred, particularly methyl etherified benzoguanamine resins etherified with methyl alcohol, butyl etherified benzoguanamine resins etherified with butyl alcohol, or mixed etherified benzoguanamine resins of methyl ether and butyl ether etherified with both methyl alcohol and butyl alcohol are preferred. As the butyl alcohol, isobutyl alcohol and n-butyl alcohol are preferred. As for the melamine resin, a melamine resin in which some or all of the methylol groups of the melamine resin are alkyl etherified with an alcohol such as methanol, ethanol, n-butanol, or i-butanol is preferred, particularly a methyl etherified melamine resin etherified with methyl alcohol, a butyl etherified melamine resin etherified with butyl alcohol, or a mixed etherified melamine resin of methyl ether and butyl ether etherified with both methyl alcohol and butyl alcohol is preferred.

[0037] Furthermore, among the above, it is preferable that the curing agent (C) used in the paint composition of this embodiment be a resol-type phenolic resin, from the viewpoint of the processability of the paint film for fabrication and heat resistance.

[0038] In this embodiment, the curing agent content is 5.5 parts by mass or more, preferably 6 to 40 parts by mass, more preferably 7 to 30 parts by mass, and even more preferably 8 to 20 parts by mass, per 100 parts by mass of the polyester resin blend, which is the main resin. If the curing agent content is less than the above range, the curing will be insufficient, and when a pressed can is formed, the heat resistance, retort resistance, content resistance, corrosion resistance, etc. of the coating film may be insufficient, which is undesirable. If the curing agent content exceeds 40 parts by mass, excessive curing may occur, which may lead to a decrease in the can-making processability and impact resistance of the coating film.

[0039] <Curing catalyst> The coating composition of this embodiment preferably contains a conventionally known curing catalyst to promote the crosslinking reaction between the main resin and the curing agent. As the curing catalyst, any known curing catalyst used in coating compositions can be used. Specifically, examples include acid catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphor sulfonic acid, phosphoric acid, alkyl phosphoric acid, and amine neutralized products of these acid catalysts. One or more of these can be used in combination. Among the above acid catalysts, dodecylbenzenesulfonic acid and its neutralized product are preferred as curing catalysts.

[0040] The content of the curing catalyst is preferably in the range of 0.01 to 5.0 parts by mass, preferably 0.02 to 1.0 parts by mass, more preferably 0.03 to 0.5 parts by mass, even more preferably 0.03 parts by mass or more and less than 0.3 parts by mass, and particularly preferably 0.03 to 0.2 parts by mass, per 100 parts by mass of solids of polyester resin. Furthermore, when an amine neutralized product of the above acid catalyst (for example, an amine neutralized product of dodecylbenzenesulfonic acid) is used as the curing catalyst, it is sufficient if the content of the acid catalyst excluding the amine is within the above range. If the amount of curing catalyst added is less than the above range, the curing reaction acceleration effect obtained by adding the curing catalyst cannot be fully obtained. On the other hand, if the amount of curing catalyst added is more than the above range, no further effect can be expected, and the water resistance of the coating film may deteriorate.

[0041] <Paint composition> The paint composition of this embodiment contains at least the above-mentioned specific polyester resin as a main agent (main component), a resol-type phenolic resin and / or amino resin as a curing agent, a solvent, and, if necessary, an acid catalyst. In the paint composition of this embodiment, the main agent (main component) is defined as the component with the highest content (mass percentage) among the solid components (non-volatile components excluding volatile substances such as water and solvents) that form the paint film in the paint composition. Examples of the paint composition in this embodiment include solvent-based paint compositions and water-based paint compositions, but in this embodiment, solvent-based paint compositions are preferred from the viewpoint of paintability and other factors.

[0042] <Solvent> When the paint composition of this embodiment is a solvent-type paint composition, it contains the polyester resin, curing agent, and organic solvent described above. In this embodiment, a solvent-type paint composition is defined as a paint composition in which the main resin, curing agent, etc. are dissolved in a known organic solvent and formed into a paint, and in which the mass proportion of the organic solvent in the paint composition is 40% by mass or more. As the aforementioned organic solvent, one or more are selected and used from 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 monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, solvent naphtha, etc., taking into consideration solubility, evaporation rate, etc.

[0043] <Additives> The paint composition of this embodiment may further contain known additives, to the extent that they do not impair the objectives of the present invention. For example, it may contain lubricants, pigments, leveling agents, defoaming agents, and the like. The lubricants that can be added to the paint composition are not particularly limited, but examples include fatty acid ester waxes, which are esters of polyol compounds and fatty acids; silicone waxes; fluorine waxes such as polytetrafluoroethylene; polyolefin waxes such as polyethylene; paraffin wax; lanolin; montan wax; microcrystalline wax; carnauba wax; and silicone compounds and petrolatum. These lubricants can be used individually or in mixtures of two or more.

[0044] <Painted metal sheet> Next, the painted metal sheet of this embodiment will be described. The painted metal sheet of this embodiment preferably has a coating on at least one side of the metal sheet, preferably the side that will become the inner surface of the can, and more preferably has a coating on both sides of the metal sheet. The coating can be formed by applying the above-mentioned paint composition to the metal sheet and then baking it by heating or the like, and preferably the coating is formed on the metal surface of the metal sheet (the coating is formed so as to be in direct contact with the metal sheet). The painted metal sheet of this embodiment is a metal sheet suitable for a can made by drawing and ironing.

[0045] Suitable metal sheets for use in the painted metal sheet of this embodiment include, for example, hot-rolled steel sheets, cold-rolled steel sheets, hot-dip galvanized steel sheets, electro-galvanized steel sheets, alloy-plated steel sheets, aluminum-zinc alloy-plated steel sheets, aluminum sheets, aluminum alloy sheets, tin-plated steel sheets, stainless steel sheets, copper sheets, copper-plated steel sheets, tin-free steel, nickel-plated steel sheets, ultra-thin tin-plated steel sheets, and chromium-treated steel sheets. If necessary, these may be used after undergoing various surface treatments such as chromate phosphate treatment or zirconium phosphate treatment.

[0046] Regarding the painted metal sheet of this embodiment, the above-mentioned paint composition can be applied to the metal sheet by known painting methods such as roll coater painting or spray painting. After painting, the paint film can be obtained by baking it using a heating means such as a coil oven.

[0047] The baking conditions for the paint composition are appropriately adjusted depending on the type of polyester resin, curing agent, metal substrate, and coating amount. However, in order to obtain sufficient curability, the above-mentioned paint composition is heated and cured at a baking temperature of 150°C to 350°C, preferably higher than 200°C and 320°C or lower, for 5 seconds or more, preferably 5 seconds to 30 minutes, and particularly preferably 5 seconds to 180 seconds.

[0048] The weight of the coating film is not particularly limited, but the weight of the coating film after drying and baking is 300 mg / dm².2 Hereinafter, it is preferably 20 mg / dm 2 to 200 mg / dm 2 , more preferably 30 mg / dm 2 to 150 mg / dm 2 , still more preferably 40 mg / dm 2 to 140 mg / dm 2 is preferably within the above range. The coating weight is appropriately determined depending on the application of the coated metal sheet. The baking conditions for the coating film are appropriately adjusted depending on the solvent used, the type and thickness of the metal material to be coated, the coating speed, and other factors.

[0049] <Drawn and ironed can> The drawn and ironed can of the present embodiment can be obtained by a conventionally known drawing and ironing method using the above-described coating composition and / or coated metal sheet. Since the coated metal sheet of the present embodiment is excellent in moldability and lubricity, it can form a drawn and ironed can not only when a liquid coolant is used, but also when molding is performed under dry conditions without using a liquid coolant.

[0050] Specifically, the drawn and ironed can of the present embodiment can be molded by the following production method. First, prior to drawing and ironing molding, it is preferable to apply a wax-based lubricant, for example, paraffin wax, white petrolatum, palm oil, various natural waxes, polyethylene wax, etc., to the surface of the coated metal sheet, which enables efficient drawing and ironing processing under dry conditions. A blank is punched from the coated metal sheet coated with the wax-based lubricant by a cupping press, and a drawn cup is molded by a drawing method. In the present embodiment, it is desirable that the drawing ratio RD defined by the following formula (2) is in the range of 1.1 to 2.6, particularly 1.4 to 2.6 in total (up to the drawn and ironed can). If the drawing ratio is larger than the above range, drawing wrinkles become large, which may cause cracks in the coating film and lead to exposure of the metal. RD=D / d···(2) In the formula, D represents the blank diameter, and d represents the can body diameter.

[0051] Next, the squeegee cup is subjected to a re-squeegeeing process in one or several stages.

[0052] In this embodiment, it is desirable that the ironing ratio R, represented by the following formula (3), be in the range of 25 to 80%, particularly 40 to 80%, and more preferably 50 to 70%. If the ironing ratio is lower than the above range, the side wall of the can shell cannot be sufficiently thinned, which is not economically satisfactory. On the other hand, if the ironing ratio is higher than the above range, there is a risk of metal exposure. R(%) = (tb-tw) / tb × 100 ... (3) In the formula, tb represents the thickness of the original painted metal sheet, and tw represents the thickness of the center of the side wall of the can body of the drawn and ironed can.

[0053] Furthermore, in the drawing can of this embodiment, it is preferable that the thickness of the central part of the can body side wall (the thinnest part of the can body side wall) is 20 to 75%, preferably 20 to 60%, and more preferably 30 to 50%, of the thickness of the can bottom (central part).

[0054] The resulting drawn can is subjected to doming of the bottom and trimming of the opening edge according to conventional methods. Then, if desired, it is subjected to one or more stages of neck-in processing and flange processing to create a can for seam sealing. Alternatively, after forming the drawn can, the top can be deformed into a bottle shape, or the bottom can be cut off and another can end attached to create a bottle shape. [Examples]

[0055] The present invention will be described in more detail below using examples, but it is not limited to the following examples. In the examples and comparative examples, "parts" refers to parts by mass.

[0056] (Example 1) [Preparation of interior coating compositions] Polyester resin (A) was polyester resin (A)-(a) (amorphous polyester resin, acid value: 2 mg KOH / g, Tg: 80℃, Mn=18,000, monomer composition: terephthalic acid component / isophthalic acid component / ethylene glycol component / propylene glycol component = 38 / 12 / 17 / 33 mol%), polyester resin (B) was polyester resin (B)-(a) (amorphous polyester resin, acid value: 22 mg KOH / g, Tg: 82℃, Mn=6,000, monomer composition: terephthalic acid component / trimellitic acid component / ethylene glycol component / propylene glycol component = 49 / 1 / 12 / 38 mol%), m-cresol-type resol phenolic resin with methylol groups alkyl etherified with n-butanol (percentage of etherified methylol groups: 90 mol%, Mn=1,600) as the curing agent, and dodecylbenzenesulfonic acid (amine neutralized product) was used as the curing catalyst.

[0057] Polyester resin (A)-(a) and polyester resin (B)-(a) were dissolved in a mixed solvent of methyl ethyl ketone / solvent naphtha = 50 / 50 (mass ratio) to obtain solutions of polyester resin (A)-(a) and polyester resin (B)-(a) with a solid content of 30% by mass. An n-butanol solution of resol-type phenolic resin (50% by mass solid content) was diluted with methyl ethyl ketone to obtain a resol-type phenolic resin solution with a solid content of 30% by mass. Dodecylbenzenesulfonic acid was amine-neutralized with 2-dimethylaminoethanol, and then dissolved in isopropanol to obtain an acid catalyst solution of dodecylbenzenesulfonic acid with a solid content of 30% by mass.

[0058] Next, a paint composition (solid content concentration: approximately 30% by mass, solid content ratio: polyester resin (A)-(a) / polyester resin (B)-(a) / curing agent / acid catalyst (dodecylbenzenesulfonic acid) = 90 / 10 / 10 / 0.2) was prepared using 300 parts of polyester resin (A)-(a) solution (90 parts solid content), 33 parts of polyester resin (B)-(a) solution (10 parts solid content), 33 parts of resol-type phenolic resin solution (10 parts solid content), and 0.66 parts of acid catalyst solution (0.20 parts solid content).

[0059] [Preparation of exterior coating compositions] Polyester resin (A)-(a) was used as polyester resin (A), polyester resin (B)-(a) was used as polyester resin (B), amino resin (methyl etherified melamine resin) was used as the curing agent, and dodecylbenzenesulfonic acid (amine neutralized product) was used as the curing catalyst.

[0060] Similar to the preparation of the interior coating composition described above, a 30% by mass solution of polyester resin (A)-(a) and polyester resin (B)-(a), and an acid catalyst solution of dodecylbenzenesulfonic acid were obtained. Methyl etherified melamine resin (100% by mass solids) was diluted with methyl ethyl ketone to obtain a 30% by mass solution of methyl etherified melamine resin. Next, a coating composition [solids concentration: approximately 30% by mass, solids ratio: polyester (A)-(a) / polyester resin (B)-(a) / curing agent / acid catalyst (dodecylbenzenesulfonic acid) = 90 / 10 / 6 / 0.2] was prepared using 300 parts (90 parts solids) of polyester resin (A)-(a) solution, 33 parts (10 parts solids) of polyester resin (B)-(a) solution, 20 parts (6 parts solids) of methyl etherified melamine resin solution, and 0.66 parts (0.20 parts solids) of acid catalyst solution.

[0061] The following measurement parameters for polyester resin were measured according to the following method. (1) Measurement of the number-average molecular weight of polyester resin The measurements were performed using gel permeation chromatography (GPC) with a calibration curve for standard polystyrene.

[0062] (2) Measurement of glass transition temperature Measurements were taken using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0063] (3) Measurement of acid value According to the neutralization titration method specified in JIS 0070, 4 g of polyester resin was dissolved in 20 mL of chloroform and titrated with a 0.1 N KOH ethanol solution to determine the resin acid value (mg KOH / g). Phenolphthalein was used as the indicator.

[0064] (4) Measurement of monomer composition Dissolve 30 mg of polyester resin solid in 0.6 mL of deuterated chloroform. 1 1H-NMR measurements were performed, and the monomer composition ratio was determined from the peak intensity. Trace amounts of components (less than 1 mol% of the total monomer components) were excluded before determining the final composition ratio.

[0065] (5) Creation of painted metal sheets As a metal sheet, we used a chromate phosphate surface-treated aluminum sheet (3104 alloy, sheet thickness: 0.27 mm, chromium weight in surface treatment film: 20 mg / m²). 2 Using this method, first, the outer surface that will be formed after molding is coated with a coating weight of 40 mg / dm² after drying and baking. 2 The exterior coating composition was applied using a bar coater and dried at 120°C for 60 seconds. Then, the opposite side, which would become the interior side, was coated with a coating weight of 90 mg / dm² after drying and baking. 2 The coating was created by applying an interior coating composition using a bar coater and baking it at 250°C (oven temperature) for 30 seconds.

[0066] The painted metal sheets were evaluated according to the following method. (6) Evaluation of substrate adhesion (180° peel test) From the painted metal plate prepared as described above, a strip-shaped test piece 1 with a height of 50 mm and a width of 30 mm was cut out, as shown in Figure 1(a), with the rolling (rolling direction) of the metal substrate being the longer side. Using a utility knife, two scratches 2 were made 7.5 mm from both ends of the evaluation surface, perpendicular to the tip of the strip and reaching the base material of the metal substrate m. The width between the two scratches 2 is 15 mm. Next, on the back side of the evaluation surface, a scratch 3 was made 15 mm from the tip of the longer side of the strip, parallel to the width direction (Figure 1(b)). Then, using metal scissors or the like, a cut 6 was made from the bottom 5 of the test piece towards the top 4 of the test piece, following the scratch 2 until it reached the scratch 3 (Figure 2). The end 1a of the test piece between the cuts 6 was bent so that the coating 8 on the evaluation surface was on the inside, starting from the scratch 3, leaving the ends 1b on both sides of the cut 6 intact, and the substrate m was cut in the width direction only between the two scratches 2 along the scratch 3. At this time, in the peel strength evaluation section 7, the coating 8 on the evaluation surface remains connected to each of the cut and separated metal plates without being cut (Figure 3(b)). On the other hand, the coating 9 on the back side is cut along the scratch 3. A 180° peel test was performed using a peel tester at 23°C and a tensile speed of 5 mm / min to measure the peel strength (180° peel strength).

[0067] In the 180° peel test, when the coating film in the measurement area peeled off uniformly, the peel strength was measured by reading the average value of the area where the strength stabilized, 5 to 10 mm from the start of measurement (1 to 2 minutes from the start of measurement).

[0068] Furthermore, the evaluation section 7, where the coating 8 was forcibly peeled off from the substrate m, was visually observed. If the coating 8 in the evaluation section 7 was completely peeled off from the substrate and no coating 8 remained on the substrate m after peeling, it was evaluated that the coating had undergone interfacial delamination. If the coating 8 fractured before peeling off from the substrate m, it was evaluated that the coating had undergone cohesive failure. The evaluation results ◎: Interfacial delamination with a peel strength of 5.0 N / 15 mm or higher, or cohesive failure. ○: In interfacial delamination, the delamination strength is less than 5.0 N / 15 mm, and 1.0 N / 15 mm or more. ×: Delamination strength less than 1.0 N / 15 mm in interfacial delamination. As shown.

[0069] (7) Evaluation of curability (MEK extraction test) A painted metal plate was prepared by forming a coating only on the inner surface using the same method as described above. A 5.0 cm × 5.0 cm test piece was cut from the obtained painted metal plate, and after measuring the mass of the test piece (W1), the test piece was immersed in 200 mL of MEK (methyl ethyl ketone) in boiling MEK (80°C reflux) for 1 hour, and MEK extraction was performed at the boiling point for 1 hour. After extraction, the test piece was washed with MEK and dried at 120°C for 1 minute, and the mass of the extracted test piece (W2) was measured. Furthermore, the coating was removed by decomposition with concentrated sulfuric acid, and the mass of the test piece (W3) was measured. The MEK extraction rate, which indicates the degree of hardening of the coating on the painted metal plate, can be calculated using the following formula (5). MEK extraction rate %=100×(W1-W2) / (W1-W3)...(5) The evaluation results ◎: Less than 10% ○: 10% or more but less than 20% △: 20% or more but less than 30% ×: 30% or more As shown.

[0070] (8) Making a squeezing can After applying paraffin wax to both sides of the painted metal sheet created using the method described above, it was punched out into a circle with a diameter of 142 mm, and then drawn to create a shallow-drawn cup. Next, this shallow-drawn cup was subjected to redrawing, ironing (3 stages), and doming under dry conditions to obtain a drawn and ironed can (can diameter: approximately 66 mm, height: approximately 130 mm, total drawing ratio: 2.15, ironing rate: 64%, thickness of the center of the can body side wall: 38.5% of the thickness of the center of the can bottom).

[0071] (9) Evaluation of can fabrication feasibility (can body ERV test) A metal exposure was formed on the outer surface of the bottom of the squeezed can prepared using the method described above. The can body was connected to the anode of an enamelizer, and 360 mL of 1% saline solution was poured into the can. The cathode of the enamelizer was immersed in the saline solution filling the can, and the current value (ERV) was measured after applying a voltage of 6.30 V for 4 seconds at room temperature. In such measurements, a higher current flow indicates the presence of defects in the insulating coating layer and the exposure of the metal on the inner surface of the can. The evaluation results are, ◎: Current value less than 50mA ○: Current value 50mA or more and less than 100mA △: Current value 100mA or more and less than 300mA ×: Current value 300mA or more As shown.

[0072] (10) Evaluation of adhesion to the workpiece The open end of the cans produced using the above method was observed, and the degree of paint peeling near the open end was visually assessed to evaluate the adhesion during can manufacturing (processing adhesion). The evaluation results ○: No peeling of the coating was observed near the open end. ×: Peeling of the coating was observed near the open end.

[0073] (11) Evaluation of flavor sorbation tolerance (flavor sorbation test) A test piece measuring 2.5 cm x 5.0 cm was cut from the squeezing can prepared using the method described above, centered at a height of 8.0 cm from the bottom of the can. The coating on the outer surface was sanded with sandpaper, and the can was washed and dried. A 5% ethanol aqueous solution containing 2 ppm limonene was prepared as a model flavor test solution. The model flavor test solution was placed in a glass bottle with a gasket (Durand bottle), the test piece was immersed in it, the bottle was sealed, and stored at 30°C for two weeks. The test piece was removed from the glass bottle, washed with water, the water droplets were removed, and it was immersed in 50 mL of diethyl ether, sealed, and stored at room temperature overnight. The extract was concentrated using a concentrator, and GC-MS analysis (gas chromatography-mass spectrometry) was performed. From the limonene-derived component peak obtained from the GC-MS analysis, the amount of sorbed was determined using a calibration curve, and the ratio of limonene to the amount charged was calculated as the limonene sorbent rate (%) using the following formula (6). Limonene sorbing rate (%) = Amount of limonene sorbed / Amount of limonene used × 100 ... (6) The evaluation results ○: Limonene sorbation rate is less than 2% ×: Limonene sorbent rate is 2% or higher As shown.

[0074] (Examples 2-13, Comparative Examples 1-5) Except for preparing interior coating compositions by changing the type of polyester resin, the type of curing agent, and the solid content ratio as shown in Table 1, the procedure was the same as in Example 1 and evaluated. The results are shown in Table 1. In addition to the polyester resin mentioned above, polyester resin (A) was also used for polyester resin (A) and polyester resin (A)-(b) (amorphous polyester resin, acid value: 2 mg KOH / g, Tg: 84℃, Mn=18,000, monomer composition: terephthalic acid component / ethylene glycol component / propylene glycol component = 50 / 14 / 36 mol%), polyester resin (A)-(c) (amorphous polyester resin, acid value: 2 mg KOH / g, Tg: 65℃, Mn=20,000, Monomer composition: Terephthalic acid component / Isophthalic acid component / Ethylene glycol component / Neopentyl glycol component / Diethylene glycol component = 25 / 25 / 22 / 27 / 1 mol%), Polyester resin (A)-(d) (Amorphous polyester resin, Acid value: 3 mg KOH / g, Tg: 40℃, Mn = 15,000, Monomer composition: Terephthalic acid component / Isophthalic acid component / Sebacic acid component / Ethylene glycol component / Propylene glycol component / Neopentyl glycol component The kohl component / 1,4-butanediol component = 25 / 20 / 5 / 16 / 14 / 3 / 17 mol%, and the polyester resin (B) is polyester resin (B)-(b) (amorphous polyester resin, acid value: 14 mg KOH / g, Tg: 55℃, Mn=12,000), polyester resin (B)-(c) (amorphous polyester resin, acid value: 36 mg KOH / g, Tg: 80℃, Mn=5,000), polyester resin (B)-(d) (amorphous polyester resin Polyester resin (B)-(e) (amorphous polyester resin, acid value: 12 mg KOH / g, Tg: 16°C, Mn=11,000), and polyester resin (B)-(f) (acid value: 11 mg KOH / g, Tg: -25°C, Mn=17,000, monomer composition: terephthalic acid component / isophthalic acid component / sebacic acid component / 1,4-butanediol component = 14 / 17 / 19 / 50 mol%) were used. In addition to the resol-type phenolic resin mentioned above, an amino resin (methyl ether-modified benzoguanamine resin) was used as a curing agent.

[0075] [Table 1]

[0076] It is clear that the painted metal sheet using the paint composition of the present invention and the pressed can using the same possess all of the following qualities: can-making processability, adhesion to the substrate, and resistance to flavor adsorption. [Industrial applicability]

[0077] This invention can be suitably used in the field of metal processing, which requires environmental considerations while maintaining high machinability. [Explanation of Symbols]

[0078] 1 Test specimen 1a end 1b end 2. Wounds 3. Wounds 4. Top of the test specimen 5. Lower part of the test specimen 6 slices 7. Evaluation Department 8. Coating film (evaluation surface) 9. Coating film

Claims

1. A pressed and pressed can obtained by pressing and pressing a painted metal sheet, The aforementioned painted metal plate has a coating film formed from a solvent-based paint composition on at least one side of the metal plate. The aforementioned solvent-type paint composition is The main component resin is a polyester resin blend containing a polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mg KOH / g, and a polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g, and a curing agent (C). The average acid value of the polyester resin blend is greater than 2.0 mg KOH / g and 8.0 mg KOH / g or less. The curing agent (C) is a resol-type phenolic resin and / or an amino resin. Characterized by, Squeezing and squeezing can.

2. The can-to-can according to claim 1, wherein the thickness of the coating film in the central part of the inner and / or outer side wall of the can body is 20 to 75% of the thickness of the coating film in the bottom of the can.

3. A method for manufacturing a pressed and ironed can obtained by pressing and ironing a painted metal sheet, The aforementioned painted metal plate has a coating film formed from a solvent-based paint composition on at least one side of the metal plate. The aforementioned solvent-type paint composition is The main component resin is a polyester resin blend containing a polyester resin (A) having a glass transition temperature higher than 40°C and an acid value of less than 10 mg KOH / g, and a polyester resin (B) having a glass transition temperature higher than 40°C and an acid value of 10 mg KOH / g or more and less than 50 mg KOH / g, and a curing agent (C). The average acid value of the polyester resin blend is greater than 2.0 mg KOH / g and 8.0 mg KOH / g or less. The curing agent (C) is a resol-type phenolic resin and / or an amino resin. A method for manufacturing a drawn and ironed can, characterized by manufacturing the aforementioned painted metal sheet by drawing and ironing it at an ironing rate of 25 to 80%.

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