Polyester resin dispersions, coatings, can ends, and can bodies

Abstract

To provide a resin dispersion excellent in stability and capable of forming a coating film excellent in processability, retort resistance and openability, which is suitable as a coating film for a can body, a can lid and the like, using a polyester resin having no structural unit derived from bisphenol A, bisphenol F and bisphenol S and having no sulfo group and salt thereof, a coating material, and a can lid and a can body using the coating material.SOLUTION: (A) having an acid number of 2mgKOH / g or more and 8mgKOH / g or less, a number-average molecular weight of 10,000 or more, and a specific structure, 30 to 130 parts by mass of organic solvents including glycol ether-based organic solvents and cycloaliphatic ketone-based organic solvents with respect to 100 parts by mass of the polyester (A), a neutralizing agent, and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a polyester resin dispersion, a coating material using the polyester resin dispersion, a can lid using the coating material, and a can body using the coating material. [Background technology]

[0002] Epoxy resin-based paints, such as epoxy resin-phenolic resin-based paints, epoxy resin-amino resin-based paints, and epoxy resin-acrylic resin-based paints, are widely used as coating compositions for metal containers such as beverage cans (hereinafter sometimes referred to as can bodies) and metal lids (hereinafter sometimes referred to as can lids or lids). However, because many epoxy resin-based paints are manufactured using bisphenol A (hereinafter sometimes referred to as BPA) and other raw materials, there is a growing demand for paints that do not contain bisphenol A. Against this background, polyester-based water-based paints that do not use bisphenol A and other raw materials, and polyester-based water-based paints that use raw materials with a structure derived from sulfonic acid or sulfonate salts, have been proposed as paints for coating can lids and can bodies.

[0003] Patent Document 1 discloses a method for producing an aqueous dispersion of a polyester resin having an acid value of 0.5 to 10 KOH mg / g, which is composed of a specific polycarboxylic acid component containing a specific amount of aromatic dicarboxylic acid in which a group represented by the general formula -SO3M is bonded to the aromatic nucleus, and a polyol component. Patent Document 2 discloses a polyester resin water dispersion made from a copolymerized polyester resin produced using a specific polymerization catalyst and having a resin acid value of 3 to 110 mgKOH / g. In Patent Documents 3 and 4, the resin acid value is 150 eq / 10 6 g~800eq / 10 6 The use of a polyester resin having a molecular weight of 5,000 to 100,000 is disclosed. Patent Document 5 discloses a water-based paint for metal packaging, which contains an aromatic polyester resin having an acid value (AV) of 10 to 30 mgKOH / g and a number average molecular weight (Mn) of 3,000 to 10,000. Patent Document 6 discloses an aqueous coating agent containing a polyester resin (A) that contains 20 mol % or more of a linear glycol having no side chain as a polyhydric alcohol component and has an acid value of 5 to 40 mgKOH / g. Patent Document 7 discloses the use of a polyester resin containing an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid having 6 to 14 carbon atoms in a molar ratio of 95:5 to 80:20 and having an acid value of 10 to 40 mgKOH / g. Patent Document 8 discloses the use of a polyester resin having an acid value of 5 mgKOH / g or more and less than 30 mgKOH / g. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-245769 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-007719 [Patent Document 3] Special Publication No. 2003-089746 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-143891 [Patent Document 5] Japanese Patent Application Laid-Open No. 2003-321646 [Patent Document 6] Japanese Patent Application Laid-Open No. 2014-234450 [Patent Document 7] WO2016 / 056509 [Patent Document 8] Japanese Patent Application Publication No. 2019-155352 Summary of the Invention [Problem to be solved by the invention]

[0005] Since can bodies and can ends are manufactured through severe processing (for example, necking, beading, scoring, riveting, etc.), the coating film that coats the metal substrate also requires high processing resistance. Depending on the type of contents, after filling the can, the contents may be subjected to high-temperature retort treatment for the purpose of sterilization, and therefore the coating film covering the metal substrate is required to have excellent retort resistance. After the contents are filled, the coating film that covers the metal substrate must have various properties, such as corrosion resistance (acid resistance, alkali resistance) to prevent corrosion of the metal substrate due to the contents, no elution of paint components, and excellent hygiene. Furthermore, in the case of can lids, excellent opening properties are required.

[0006] However, while conventional paints have excellent retort resistance, they often lack stability as water-based paints. Furthermore, even when excellent stability is achieved as a water-based paint using resins with sulfo groups and their salts or high-acidity polyesters, the resulting coatings often lack sufficient retort resistance and processability. Improvements that can achieve both of these properties are desired. In particular, can lids require extremely high processability, so the coating must have flexibility and stiffness. However, for ease of opening, the coating must also have the opposing properties of hardness and sharpness. The market demands paints that can achieve both of these properties.

[0007] An object of the present disclosure is to provide a resin dispersion and paint that are excellent in stability and that can form coating films suitable for coating can bodies, can lids, etc., that have excellent processability, retort resistance, and openability, using a polyester resin that does not have any structural units derived from bisphenol A, bisphenol F, or bisphenol S and that does not have any sulfo group or salt thereof, and also to provide can lids and can bodies using the paint. [Means for solving the problem]

[0008] [1]: A polyester resin dispersion containing a polyester resin (A), a neutralizing agent, an organic solvent, and water, The polyester resin (A) has an acid value of 2 mgKOH / g or more and 8 mgKOH / g or less, a number average molecular weight of 10,000 or more, and is a polyester resin that does not contain any structural units derived from bisphenol A, bisphenol F, or bisphenol S, and further does not contain any sulfo group or salt thereof; the polyester resin (A) contains structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol, which are polyhydric alcohol components, and the total amount of structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol is 95 to 100 mol % out of 100 mol % of the structural units derived from the polyhydric alcohol components of the polyester resin (A); The polyester resin (A) contains 95 to 100 mol % of structural units derived from an aromatic polycarboxylic acid component, based on 100 mol % of structural units derived from a polycarboxylic acid component of the polyester resin (A), The organic solvent is contained in an amount of 30 to 130 parts by mass relative to 100 parts by mass of the polyester resin (A), The polyester resin dispersion contains an organic solvent including a glycol ether-based organic solvent and an alicyclic ketone-based organic solvent. [2]: The polyester resin dispersion according to [1], wherein the alicyclic ketone organic solvent is a cycloalkane ketone organic solvent or a cycloalkene ketone organic solvent. [3]: The polyester resin dispersion according to [2], wherein the cycloalkane ketone organic solvent is selected from the group consisting of cyclohexanone, cyclopentanone, and cyclobutanone, and the cycloalkene ketone organic solvent is selected from the group consisting of isophorone and 2-cyclohexene-1-one. [4]: The polyester resin dispersion according to [1] or [2], wherein the organic solvent contains 15% by mass or more of a glycol ether-based organic solvent relative to 100% by mass of the organic solvent. [5]: The polyester resin dispersion according to [1] or [2], wherein the water is contained in an amount of 40 to 90 mass % relative to 100 mass % in total of the water and the organic solvent. [6]: The polyester resin dispersion according to [4], wherein 100% by mass of the organic solvent contains 15 to 90% by mass of a glycol ether-based organic solvent. [7]: The polyester resin dispersion according to [1] or [2], wherein the glycol ether organic solvent is selected from the group consisting of ethylene glycol monobutyl ether and diethylene glycol monobutyl ether. [8]: The polyester resin dispersion according to [1] or [2], wherein the polyester resin (A) contains 47 to 82 mol % of structural units derived from 2-methyl-1,3-propanediol and 17 to 50 mol % of structural units derived from 1,4-cyclohexanedimethanol, relative to 100 mol % of structural units derived from the polyhydric alcohol component of the polyester resin (A). [9]: The polyester resin dispersion according to [8], wherein the polyester resin (A) further contains structural units derived from trimethylolpropane, which is a polyhydric alcohol component, and the structural units derived from trimethylolpropane account for 0.1 to 3 mol % of 100 mol % of the structural units derived from the polyhydric alcohol component of the polyester resin (A).

[10] : The structural units derived from the polycarboxylic acid component of the polyester resin (A) are composed only of structural units derived from an aromatic polycarboxylic acid component, the structural units derived from the aromatic polycarboxylic acid component include structural units derived from terephthalic acid and structural units derived from isophthalic acid, The polyester resin dispersion according to [1] or [2], wherein the structural units derived from terephthalic acid and the structural units derived from isophthalic acid account for 95 to 100 mol % in total, out of 100 mol % of the structural units derived from the aromatic polycarboxylic acid component.

[11] : The polyester resin dispersion according to

[10] , wherein, based on 100 mol% of the structural units derived from the aromatic polycarboxylic acid component, the structural units are 8 to 30 mol% of structural units derived from terephthalic acid and 68 to 90 mol% of structural units derived from isophthalic acid.

[12] : The polyester resin dispersion according to

[11] , wherein the polyester resin (A) further contains structural units derived from trimellitic acid (anhydride), which is a polycarboxylic acid component, and the structural units derived from trimellitic acid (anhydride) account for 0.1 to 2 mol % of the structural units derived from the aromatic polycarboxylic acid component of the polyester resin (A) in 100 mol %.

[13] : A coating material comprising the polyester resin dispersion according to [1] or [2] and a curing agent.

[14] : The paint according to

[13] , wherein the glycol ether organic solvent is contained in an amount of 15 to 90 mass % relative to 100 mass % of the organic solvent.

[15] : The paint according to

[14] , further comprising water, wherein the water accounts for 40 to 90 mass % of 100 mass % of the total of the water and the organic solvent.

[16] : A can lid formed by coating a metal with the paint according to

[13] .

[17] : A can body made by coating a metal with the paint according to

[13] . [Effects of the Invention]

[0009] The present disclosure has the excellent effect of providing a dispersion and coating material that are excellent in stability and that can form coating films suitable for coating can bodies, can lids, and the like, and that have excellent processability, retort resistance, and openability, using a polyester resin that does not have any structural units derived from bisphenol A, bisphenol F, or bisphenol S and does not have any sulfo group or salt thereof, as well as a can lid and can body using the coating material. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure will be described in detail below. Other embodiments are also included within the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits. Unless otherwise noted, the various components in this specification may be used independently, either singly or in combination of two or more types. The numerical values ​​described in this specification refer to values ​​obtained by the methods described in the Examples below, etc.

[0011] The resin dispersion of the present disclosure contains a polyester resin (A), a neutralizing agent, an organic solvent, and water. Each component will be described below.

[0012] <Polyester resin (A)> The polyester resin (A) is a polymerization product of a polycarboxylic acid or its ester-forming derivative with a polyhydric alcohol, and does not contain any structural units derived from bisphenol A, bisphenol F, or bisphenol S. The polyester resin (A) also does not contain any sulfo group or salt thereof. The polyester resin (A) can be obtained, for example, by dehydration condensation of a carboxy group of a polycarboxylic acid with a hydroxy group of a polyhydric alcohol. Alternatively, the polyester resin (A) can be obtained by dealcoholization of an ester of a polycarboxylic acid with a lower alcohol such as methanol or ethanol with a polyhydric alcohol. The aqueous dispersion of the present disclosure may contain polyester resins other than those described above, as long as they do not deviate from the spirit and scope of the present disclosure.

[0013] It is important that the polyester resin (A) has an acid value of 2 mgKOH / g or more and 8 mgKOH / g or less, preferably 4 to 6 mgKOH / g. By using such a polyester resin, it is possible to achieve excellent retort resistance, openability, and corrosion resistance.

[0014] The number average molecular weight (hereinafter also referred to as Mn) of the polyester resin (A) is preferably 10,000 or more and 100,000 or less, more preferably 10,000 to 50,000, and even more preferably 10,000 to 25,000. When the number average molecular weight is within this range, the processability and alkali resistance are further improved, and the solubility of the polyester resin (A) in solvents can be further improved. Furthermore, the polyester resin (A) does not have any structural units derived from bisphenol A, bisphenol F, or bisphenol S.

[0015] Aromatic polycarboxylic acids are preferably used as the polycarboxylic acid component used as a monomer for forming the polyester resin (A). Among the aromatic polycarboxylic acids, aromatic dibasic acids include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid. The polyester resin (A) may have a branched structure. Therefore, in addition to a dibasic acid, a trifunctional or higher functional acid may be used. Examples include trimellitic acid (anhydride) (trimellitic acid and trimellitic acid anhydride are collectively referred to as "trimellitic acid (anhydride)." The term "anhydride" will be used hereinafter.), pyromellitic acid (anhydride), and ethylene glycol bistrimellitate dianhydride.

[0016] As the polycarboxylic acid component, in addition to the above-mentioned aromatic polycarboxylic acids, aliphatic dibasic acids, alicyclic dibasic acids, α,β-unsaturated dicarboxylic acids, acid anhydrides thereof, and alkyl esters thereof can be used. Examples of the aliphatic dibasic acid include sebacic acid, adipic acid, succinic acid (anhydride), azelaic acid, dodecanedioic acid, and dimer acid. Examples of alicyclic dibasic acids include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid (anhydride). Examples of the α,β-unsaturated dicarboxylic acid include fumaric acid, maleic acid (anhydride), itaconic acid, and citraconic acid.

[0017] It is important that the polyester resin (A) contains 95 to 100 mol % of structural units derived from aromatic polycarboxylic acid components out of 100 mol % of structural units derived from the polycarboxylic acid components of the polyester resin (A), and that the structural units derived from the polycarboxylic acid components are exclusively structural units derived from aromatic polycarboxylic acid components. Preferred aromatic polycarboxylic acid components are terephthalic acid, isophthalic acid, and trimellitic acid (anhydride). By using trimellitic acid (anhydride) as a terminal modifier, carboxy groups can be introduced into the terminals of the resin.

[0018] It is important that the structural units derived from terephthalic acid and the structural units derived from isophthalic acid account for 95 to 100 mol % in total of 100 mol % of the structural units derived from the aromatic polycarboxylic acid component. Furthermore, in a specific preferred embodiment, the structural units derived from terephthalic acid account for 8 to 30 mol % and the structural units derived from isophthalic acid account for 68 to 90 mol %, and it is also preferred that the structural units derived from trimellitic acid (anhydride) account for 0.1 to 2 mol %.

[0019] Of 100 mol% of structural units derived from the polycarboxylic acid component of the polyester resin (A), the total of structural units derived from polycarboxylic acid components other than the above-mentioned polycarboxylic acid components is preferably 2 mol% or less.Of 100 mol% of structural units derived from the carboxylic acid component of the polyester resin (A), the total of structural units derived from monofunctional carboxylic acid components is preferably 2 mol% or less.

[0020] The polyester resin (A) contains structural units derived from the polyhydric alcohol components 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol. Of 100 mol% of the structural units derived from the polyhydric alcohol components, the total of the structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol is 95 to 100 mol%. The polyester resin (A) preferably contains 47 to 82 mol% of structural units derived from 2-methyl-1,3-propanediol and 17 to 50 mol% of structural units derived from 1,4-cyclohexanedimethanol, and more preferably contains 55 to 73 mol% of structural units derived from 2-methyl-1,3-propanediol and 25 to 43 mol% of structural units derived from 1,4-cyclohexanedimethanol.

[0021] Although the polyester resin (A) may contain structural units derived from other polyhydric alcohol components, by setting the proportions of structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol within the above ranges, the solubility in organic solvents described below is improved. It is believed that the improved solubility causes the polyester resin to swell when water is added, and the alkyl groups in the side chains derived from 2-methyl-1,3-propanediol and the alicyclic structure in the main chain derived from 1,4-cyclohexanedimethanol become steric hindrances, effectively making it water-soluble.

[0022] In addition to the two types of monomers mentioned above, for example, an aliphatic diol having 2 to 10 carbon atoms, an alicyclic diol having 6 to 12 carbon atoms, and a diol containing an ether bond can be used as the polyhydric alcohol component. Examples of aliphatic diols having 2 to 10 carbon atoms include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, and 2-ethyl-2-butyl-1,3-propanediol. Examples of the alicyclic diol having 6 to 12 carbon atoms include 1,2-cyclohexanedimethanol, 1,4-cyclohexanediol, and 1,2-cyclohexanediol. Examples of diols containing an ether bond include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0023] The polyester resin (A) may have a branched structure. To this end, a trifunctional or higher alcohol may be used in addition to the two monomers described above. Specific examples include trimethylolpropane, glycerin, trimethylolethane, mannitol, sorbitol, pentaerythritol, and α-methylglucoside, with trimethylolpropane being preferred. Of the 100 mol% of structural units derived from the polyhydric alcohol component of the polyester resin (A), the structural units derived from trimethylolpropane preferably account for 0.1 to 3 mol%, more preferably 0.5 to 2 mol%.

[0024] Furthermore, if necessary, a small amount of a monofunctional alcohol may be used. For example, the structural units derived from the monofunctional alcohol preferably account for 2 mol % or less of 100 mol % of the structural units derived from the alcohol component.

[0025] As the polyester resin (A), commercially available products may be used, for example, Vylon GK-360 (acid value: 5 mg KOH / g, Mn: 16,000) manufactured by Toyobo Co., Ltd.

[0026] <Polyester resin dispersion> The polyester resin dispersion of the present disclosure (hereinafter also referred to as the present dispersion) will be described. The present dispersion contains a polyester resin (A), a neutralizing agent, an organic solvent, and water. The present dispersion can be obtained, for example, as follows. The polyester resin (A) can be obtained by dissolving the polyester resin (A) in an organic solvent, adding a neutralizing agent, and then adding water to form a liquid dispersion medium made of a mixture of water and the organic solvent, and dispersing the polyester resin (A) in particulate form in the liquid dispersion medium. Alternatively, the polyester resin (A) may be melted, and then an organic solvent is added to dissolve it, followed by adding a neutralizing agent and water to make it aqueous.

[0027] The dispersed particles in the present dispersion preferably have an average particle diameter D50 of 0.1 to 5 μm, more preferably 0.15 to 1 μm, and even more preferably 0.15 to 0.4 μm. A smaller dispersed particle diameter improves the stability of the dispersion and the coating material. A larger dispersed particle diameter reduces the affinity between particles when forming a coating film, improving the openability of a coating film formed using a coating material according to the present disclosure, as described below, for example, a coating film covering a metal can lid or can body.

[0028] <Organic solvents> The present dispersion contains an organic solvent. An organic solvent is an organic compound used to dissolve and / or disperse substances and is liquid at 25°C and 1 atmosphere. Liquid components of the "neutralizing agent" described below are not included in the organic solvent. Liquid additives such as Surfynol 420 used in the examples described below are also not included in the organic solvent. Liquids used to dissolve and / or disperse solid neutralizing agents are organic solvents. It is important that the present dispersion contains 30 to 130 parts by mass of organic solvent per 100 parts by mass of polyester resin (A), with 40 to 100 parts by mass being preferred. If the organic solvent content is too low, the polyester resin will not swell, making it impossible to obtain a stable dispersion. If the organic solvent content is too high, the polyester resin will dissolve in the organic solvent even when water is added, making it impossible to form dispersed particles.

[0029] As the organic solvent, it is important to use a glycol ether organic solvent and an alicyclic ketone organic solvent. Polyester resins with a structure derived from 1,4-cyclohexanedimethanol have a high affinity for alicyclic ketone organic solvents, which not only allows them to effectively swell, but also makes the swollen polyester more compatible with water due to the slight solubility of the alicyclic ketone solvents in water, which is thought to make it possible to disperse low-acid-value polyesters, which are normally difficult to achieve. By combining this with a glycol ether organic solvent, which is compatible with both water and organic solvents, the affinity for water is further improved, allowing for the production of stable polyester resin dispersions even at low acid values. The glycol ether organic solvent preferably accounts for 15% by mass or more and 90% by mass or less, and more preferably 20% by mass or more and 70% by mass or less, of 100% by mass of the organic solvent.

[0030] Examples of the alicyclic ketone organic solvent include a cycloalkane ketone organic solvent and a cycloalkene ketone organic solvent. Examples of cycloalkane ketone organic solvents include cyclohexanone, cyclopentanone, and cyclobutanone. Examples of cycloalkene ketone organic solvents include isophorone and 2-cyclohexene-1-one. As the cycloalkane ketone organic solvent, cyclohexanone is preferred. As the cycloalkene ketone organic solvent, isophorone is preferred.

[0031] Specific examples of glycol ether organic solvents include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol mono(iso)propyl ether, ethylene glycol di(iso)propyl ether, ethylene glycol mono(iso)butyl ether, ethylene glycol di(iso)butyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, 1,3-butylene glycol-3-monomethyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol mono(iso)propyl ether, diethylene glycol di(iso)propyl ether, diethylene glycol mono(iso)butyl ether, and diethylene glycol di(iso)butyl ether. Examples of the ethylene glycol monohexyl ether include diethylene glycol dihexyl ether, triethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono(iso)propyl ether, propylene glycol mono(iso)butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di(iso)propyl ether, propylene glycol di(iso)butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono(iso)propyl ether, dipropylene glycol mono(iso)butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, diethylene glycol di(iso)propyl ether, and dipropylene glycol di(iso)butyl ether. Of these, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether are preferred.

[0032] In the present invention, in addition to glycol ether organic solvents and alicyclic ketone organic solvents, other ketone solvents, alcohol solvents, glycol solvents, acetate solvents, etc. can also be used. Specifically, for example, Other ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, diacetone alcohol, etc. Specific examples of alcohol-based solvents include ethanol, n-propanol, isopropanol, n-butyl alcohol, isobutyl alcohol, n-amyl alcohol, amyl alcohol, methyl amyl alcohol, octanol, and 2-ethylhexanol. Specific examples of glycol-based solvents include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, and 1,3-butylene glycol. Specific examples of acetate solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methoxybutyl acetate, ethylene glycol monobutyl ether acetate, and 3-methyl-3-methoxybutyl acetate. Other organic solvents may also be used as appropriate, such as ethyl acetate, butyl acetate, dibasic acid esters, toluene, xylene, aromatic hydrocarbon compounds, aliphatic hydrocarbons, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, solvent naphtha, etc. Furthermore, organic solvents may be used when producing a coating material, if necessary.

[0033] The dispersion contains water to make it aqueous, and the amount of water is preferably 40 to 90% by mass relative to 100% by mass of the total of the organic solvent and the water.

[0034] <Neutralizer> The neutralizing agent refers to a compound used for neutralization, and is used to neutralize the carboxyl groups of the polyester resin (A). Examples of the neutralizing agent include dimethylaminoethanol, triethanolamine, ammonia, aminoethanol, sodium hydroxide, and sodium carbonate. Among these, dimethylaminoethanol, triethanolamine, ammonia, and aminoethanol are preferred. Note that among the neutralizing agents, dimethylaminoethanol and the like are not considered organic solvents in this specification. The amount of the neutralizing agent is preferably 0.3 to 5 molar equivalents, more preferably 0.5 to 3 molar equivalents, relative to the carboxyl groups in the polyester resin (A).

[0035] <Paint> The present dispersion is suitable for use in paints. The paint of the present disclosure (hereinafter also referred to as the present paint) preferably contains a curing agent when made into a paint. The present paint contains 30 to 120 parts by mass of an organic solvent per 100 parts by mass of polyester resin (A), and the organic solvent preferably contains a glycol ether-based organic solvent and an alicyclic ketone-based organic solvent. The glycol ether-based organic solvent preferably accounts for 15 to 90% by mass, more preferably 20 to 70% by mass, of 100% by mass of the organic solvent. The present paint is preferably used to coat beverage cans and the like.

[0036] <Curing agent> The curing agent in the coating composition of the present disclosure is blended to cause a crosslinking reaction with the polyester resin (A) to cure the composition.

[0037] Examples of the curing agent include phenolic resins, amino resins, components having an isocyanate group or derivatives thereof, components having an acid anhydride group, metal alkoxide compounds, metal chelate compounds, and tris(alkoxycarbonylamino)triazines. Among these, phenolic resins and amino resins are preferred. Phenolic resins and amino resins can undergo self-crosslinking reactions and can also react with hydroxyl groups in polyester resins. The curing agent may be used alone, or two or more of the same type may be used in combination, or two or more of different types may be used in combination.

[0038] The phenolic resin may be a resin synthesized by an addition-condensation reaction between a phenolic compound and an aldehyde such as formaldehyde, etc. The phenolic resin can be synthesized by a known method. Examples of the phenolic compounds include phenol, o-cresol, p-cresol, m-cresol, p-tert-butylphenol, p-phenylphenol, p-nonylphenol, 2,3-xylenol, 2,5-xylenol, 3,5-xylenol, catechol, resorcinol, and hydroquinone. Among these, phenol, o-cresol, p-cresol, m-cresol, and p-tert-butylphenol are preferred. The phenolic compounds may be used alone or in combination of two or more. Note that "o-" is an alternative notation for "ortho," "p-" is an alternative notation for "para," and "m-" is an alternative notation for "meta."

[0039] Commercially available phenolic resins may be used, and suitable examples include Phenodur PR285, PR516, PR517, PR519, PR520, PR521, PR827, PR566, PR612, and VPR1785 manufactured by Allnex Corporation, Sumilite Resin PR-55317 and PR-55819 manufactured by Sumitomo Bakelite Co., Ltd., and Shounol CKS-3898, BKM-2620, CKM-908, CKS-380A, and CKM-1634 manufactured by Aica Kogyo Co., Ltd.

[0040] From the viewpoint of the can-forming processability and heat resistance of the coating film, the curing agent is preferably a resol-type phenolic resin. Among them, a phenolic resin obtained by reacting m-cresol with an aldehyde is more preferable. This phenolic resin has high reactivity with polyester resin and excellent curing properties, so that a coating film having excellent retort resistance and alkali resistance and having less deterioration in processability can be obtained. Commercially available meta-cresol phenolic resins include, for example, Shownol CKS-3898 and Sumilite Resin PR-55317 manufactured by Aica Kogyo Co., Ltd.

[0041] Examples of the amino resin include those obtained by addition reaction of formaldehyde with an amino compound such as urea, melamine, or benzoguanamine. The amino compounds can be used alone or in combination of two or more.

[0042] Commercially available amino resins may be used. Suitable examples include Cymel 301, 303LF, 304, 323, 325, 328, 370, 659, and 1123 manufactured by Allnex; Luwipal 014, 015, 018, 066, 070, 052, and B017 manufactured by BASF; and Amidia P-138, P-196-M, TD-126, ED-126-60S, and 15-159 manufactured by DIC.

[0043] The above phenol resins and amino resins may also be suitably used in which a part or all of the methylol groups formed by addition of formaldehyde are etherified with alcohols having 1 to 12 carbon atoms.

[0044] With this paint, the combination of polyester resin (A) and a curing agent is thought to prioritize cross-linking within the particles, while fusion between particles takes precedence. This is thought to make it possible to create a coating film that has the normally difficult qualities of flexibility and stiffness, while also achieving the opposing qualities of hardness and sharpness.

[0045] In the present coating material, the curing agent is preferably used in an amount of 5 to 100 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the polyester resin (A). By setting the mass ratio of the two within this range, processability, retort resistance, etc. are further improved.

[0046] <Acid catalyst> It is preferable to incorporate a conventionally known curing catalyst into this coating material in order to promote the crosslinking reaction between the polyester resin and the curing agent. Any known curing catalyst used in coating compositions can be used as the curing catalyst. Suitable examples include acid catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphorsulfonic acid, phosphoric acid, and alkylphosphoric acid, as well as amine neutralization products of these acid catalysts. One or more curing catalysts can be used in combination. Among the above acid catalysts, dodecylbenzenesulfonic acid and its neutralization products are preferred as the curing catalyst.

[0047] The content of the curing catalyst is 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 to 0.3 parts by mass, and particularly preferably 0.03 to 0.2 parts by mass, based on 100 parts by mass of the solid content of the polyester resin (A). When an amine-neutralized product of the acid catalyst (e.g., an amine-neutralized product of dodecylbenzenesulfonic acid) is used as the curing catalyst, the content of the acid catalyst excluding the amine should be within the above range. If the amount of the curing catalyst is less than the above range, the curing reaction acceleration effect obtained by adding the curing catalyst cannot be fully achieved. On the other hand, if the amount of the curing catalyst is more than the above range, further effects cannot be expected, and the water resistance of the coating film may be deteriorated.

[0048] <Additives> The coating material of the present disclosure is preferably used to coat beverage cans and the like, and additives such as lubricants such as wax and leveling agents can be blended as needed to prevent scratches on the coating film during the can manufacturing process. Waxes include animal and plant waxes such as carnauba wax, lanolin wax, palm oil, candelilla wax, and rice wax; Petroleum-based waxes such as paraffin wax, microcrystalline wax, and petrolatum; Examples include synthetic waxes such as polyolefin wax and Teflon (registered trademark) wax.

[0049] <Applications of this paint> This paint is preferably used to coat storage containers such as cans for storing beverages, food, etc., and can be used on both the inside and outside of these containers. Because this paint exhibits high levels of processability and corrosion resistance when used for the above purposes, it is particularly suited to coating the inside surfaces of cans, and is particularly suited to use on the inside surfaces of beverage cans and food cans (meaning cans for storing food).

[0050] <Can materials and cans> Cans for storing beverages, food, etc. come in a variety of shapes, but are formed by combining at least two can components. They can be broadly classified into two-piece cans (in a broad sense), which consist of a cylindrical, bottomed member in which the can body and bottom are integrated, and a lid member, and three-piece cans, which consist of a cylindrical can body and lid and bottom members located above and below the can body. Two-piece cans (in a broad sense) also include so-called bottle-shaped cans, which are equipped with a recapable lid member and a bottle member. The drinking spout of the bottle member of a bottle-shaped can is provided with a screw that can be opened and closed using the lid member. The coating material of the present disclosure is suitable for coating can bodies (particularly can bodies of two-piece cans (including bottle cans)) and can lids (excluding bottle can lids).

[0051] The can body of a two-piece can is obtained, for example, by punching out a metal substrate into a flat circular plate for each can, molding the member into a predetermined cup shape with a bottom, spraying a coating composition onto the inner surface of the can, and curing the coating to form an inner coating film. After forming the inner coating film, the can is obtained through processes such as necking, beading, and scoring at the open end. In the case of a bottomed cup-shaped member for a two-piece can, the curing conditions for the coating material are preferably baking at a temperature of 150 to 300°C for 10 seconds to 10 minutes, more preferably 30 seconds to 5 minutes. The thickness (amount of coating) of the coating film after drying on the bottomed cup-shaped member for a can is usually 5 to 150 mg / dm 2 The preferred range is 10 to 100 mg / dm 2 is more preferred.

[0052] Can lids (excluding bottle can lids) are obtained, for example, by applying paint to a metal substrate, curing the paint, forming a coating, punching out a flat circular plate for each can, and then forming the opening. Because can lids have complex, highly irregular shapes, their coatings require higher processability than coatings for other components. On the other hand, when opening a can lid, the coating around the opening of the lid must conform to the metal substrate of the lid, ensuring good opening properties (clearness). In cases of poor opening properties, peeling residue of the coating is observed around the opening. In the case of can lids, the curing conditions for the coating are preferably baking at a temperature of 150 to 350°C for 10 seconds to 30 minutes, more preferably 10 seconds to 15 minutes. In the case of can lids, the thickness of the coating film after drying (coating amount) is usually 10 to 200 mg / dm 2 The preferred range is 20 to 180 mg / dm 2 When a rolled long can substrate is used, the curing conditions for the coating material are preferably a temperature of 200 to 350°C and baking for 10 seconds to 3 minutes, more preferably 10 seconds to 1 minute. The thickness of the coating film after drying (coating amount) is usually 10 to 200 mg / dm 2 The preferred range is 20 to 180 mg / dm 2 is more preferred.

[0053] Examples of metal substrates for cans include aluminum, tin-plated steel sheets, chromium-treated steel sheets, and nickel-treated steel sheets, which may further be subjected to surface treatments such as zirconium treatment and phosphate treatment.

[0054] Cans having the can lid or can body of the present invention as constituent members are preferably used to store beverages such as drinking water, soft drinks, coffee, tea, beer, chuhai, sake, whiskey, and water-based cocktails, as well as foods such as fish, meat, vegetables, fruit, oil, and sauces.

[0055] One embodiment of the beverage can of the present invention comprises a can lid and a can body member coated with the paint of the present invention. Another embodiment of the beverage can of the present invention has a can body member coated with the paint of the present invention. [Example]

[0056] The present invention will be described in more detail below with reference to examples. In the examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." Furthermore, "Mn" means number average molecular weight, and "Mw" means weight average molecular weight.

[0057] (number average molecular weight) Mn and Mw were measured using a Tosoh Corporation high-speed GPC system 8020 series (tetrahydrofuran solvent, column temperature 40°C, polystyrene standard). Specifically, four Tosoh Corporation columns, G1000HXL, G2000HXL, G3000HXL, and G4000HXL, were connected in series and measurements were performed at a flow rate of 1.0 mL / min.

[0058] (acid number) 0.2 g of polyester resin was precisely weighed and placed in a stoppered Erlenmeyer flask, and 20 mL of THF (tetrahydrofuran) was added to dissolve it. Phenolphthalein test solution was added as an indicator and the mixture was left to stand for 30 seconds. The solution was then titrated with 0.1 mol / L alcoholic potassium hydroxide solution until it turned a pale pink color. The acid value was calculated using the following formula. The acid value was the value for the polyester resin in its dry state. Acid value (mgKOH / g)=(a×F×56.1×0.1) / S S: Amount of polyester resin collected × (solid content of acrylic copolymer solution / 100) (g) a: Titration volume (mL) of 0.1 mol / L alcoholic potassium hydroxide solution F: Potency of 0.1 mol / L alcoholic potassium hydroxide solution

[0059] (Polyester Resin Composition) 1 H-NMR analysis (BRUKER ULTRA SHIELD TM 400 PLUS). 1Resins containing constituent monomers for which no assignable or quantifiable peaks were observed in the H-NMR spectrum were subjected to methanol decomposition in a sealed tube at 230°C for 3 hours, followed by gas chromatographic analysis for quantitative analysis.

[0060] [Manufacturing example A-1] A polymerization reactor was charged with 93.1 parts of terephthalic acid, 372.5 parts of isophthalic acid, 189.3 parts of 2-methyl-1,3-propanediol, 141.9 parts of 1,4-cyclohexanedimethanol, 3.76 parts of trimethylolpropane, and 0.05 parts of titanium butoxide, and the temperature was gradually increased to 250°C under a nitrogen atmosphere, and an esterification reaction was carried out over 6 hours. Next, the temperature was cooled to 230°C under a nitrogen stream, and the pressure was reduced to 5 mmHg or less over 30 minutes, and the polymerization reaction was carried out under this condition for 2 hours. The resin was then cooled to 200°C under a nitrogen stream, and 5.35 parts of trimellitic anhydride was added thereto and reacted for 2 hours. The resin was removed from the reactor to obtain Polyester Resin A-1. The analytical results of the obtained Polyester Resin A-1 are shown in Table 1.

[0061] [Manufacturing example A-2] ~ [Manufacturing example A-8], [Manufacturing example B-1] ~ [Manufacturing example B-6] A polyester resin using trimellitic anhydride was obtained in the same manner as in Production Example A-1, except that the types and amounts of the polycarboxylic acid component and the polyhydric alcohol component were changed, and was analyzed in the same manner.

[0062] [Table 1]

[0063] The abbreviations in Table 1 are as follows: TPA: Terephthalic acid IPA: Isophthalic acid TMA: Trimellitic acid MPO: 2-methyl-1,3-propanediol CHDM: 1,4-cyclohexanedimethanol EG: Ethylene glycol NPG: Neopentyl glycol 1,4-BD: 1,4-butanediol TMP: Trimethylolpropane

[0064] [Example 1] 400 parts of polyester resin A-1, 154 parts of cyclohexanone, and 66 parts of diethylene glycol monobutyl ether were placed in a container and heated. When the temperature reached 120°C, stirring was carried out. After 3 hours, it was confirmed that the resin had dissolved, and the mixture was cooled to 65°C with stirring. 3.77 parts of dimethylaminoethanol was added, and then 376.2 parts of ion-exchanged water was added dropwise over 60 minutes while maintaining the temperature at 65°C to obtain polyester resin dispersion 1. The stability of the dispersion was evaluated, and the average particle size was measured.

[0065] <Dispersion stability> The polyester resin dispersion 1 contained in a container with a lid was placed in a thermostatic chamber at 25°C, and the state was checked every week. Evaluation was made according to the following evaluation criteria. 5: No separation even after 6 months or more (very good) 4: Separation between 3 and 6 months (good) 3: Separation within 1 month to 3 months (practical) 2: Separation takes between one week and one month (practical depending on conditions) 1: Separation in less than a week (not practical) If the coating separated within one week, it was not evaluated as a coating material, as described below.

[0066] <Average particle size> The average particle size here refers to the particle size (D50) at which the cumulative frequency is 50% in volume terms. The average particle size is the D50 value measured using a dynamic light scattering distribution measurement device (Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd.). Water was poured into the device, and polyester resin dispersion 1 was added so that the TR was 0.95 to 0.8, and the measurement was performed. The measurement conditions were particle conditions: transmittance: transparent, refractive index: 1.52, shape: aspherical, and solvent conditions: refractive index: 1.333. The measurement time was 20 seconds, and the number of measurements was 2. Note that if sedimentation occurred immediately after dispersion preparation, it was marked as "unmeasurable."

[0067] [Examples 2 to 8] [Comparative Examples 1001 to 1006] As shown in Table 2, 400 parts of polyester resins A-2 to A-8 and B-1 to B-6 were used instead of 400 parts of polyester resin A-1, and polyester resin dispersions 2 to 8 and 1001 to 1006 were obtained in the same manner as in Example 1 and evaluated in the same manner.

[0068] [Examples 9 to 25] [Comparative Examples 1007 to 1009] The number of parts of polyester resin A-1, the type and number of parts of organic solvent, and the number of parts of water were changed as shown in Table 3, and polyester resin dispersions 9 to 25 and 1007 to 1009 were obtained and evaluated in the same manner as in Example 1. In Table 3, Example 1 is shown as Example 10 for convenience.

[0069] [Examples 26 to 32] Polyester resin dispersions 26 to 32 were obtained in the same manner as in Example 1, except that polyester resin A-1 was used and the neutralizer was changed as shown in Table 4, and were similarly evaluated.

[0070] [Table 2]

[0071] [Table 3]

[0072] [Table 4]

[0073] The abbreviations in Tables 2 to 4 are as follows: DMAE: Dimethylaminoethanol TEA: Triethanolamine

[0074] <Lid paint> [Example 101] As shown in Table 5, 1000 parts by weight of the polyester resin dispersion 1 (containing 400 parts by weight of polyester resin) obtained in Example 1 was placed in a container and stirred. 138 parts by weight of CKS-3898 (metacresol-based phenolic resin, butyl cellosolve solution with a nonvolatile content of 50%, manufactured by Aica Kogyo Co., Ltd.) phenolic resin as a curing agent, 1.34 parts by weight of Surfynol 420 (acetylene glycol-based nonionic surfactant, manufactured by Nissin Chemical Industry Co., Ltd.) as an additive, 0.94 parts by weight of BYK333 (silicon-based leveling agent, manufactured by BYK), 2.82 parts by weight of Nacure 5925 (dodecylbenzenesulfonic acid-based acid catalyst, active ingredient 25%, isopropanol solution) as a catalyst, and 201.02 parts by weight of water were added to obtain paint 101. Various evaluations were performed using the methods described below.

[0075] [Examples 102 to 137] [Comparative Examples 2001 and 2002] According to the formulations shown in Tables 5 to 8, paints 102 to 137, 2001, and 2002 were obtained and evaluated in the same manner as in Example 101. For convenience, Example 101 is shown as Example 110 in Table 6 and as Example 132 in Table 8.

[0076] [Comparative Example 2003] 193.4 parts of polyester resin A-1, 145 parts of Flexisolv DBE esters (Invista) as an organic solvent, and 145 parts of xylene were added and heated. Once the temperature reached 120°C, stirring was continued. After 2 hours, the resin was confirmed to be dissolved and the mixture was cooled to room temperature. Subsequently, 68.2 parts of CKS-3898 as a phenolic resin, 153.4 parts of Flexisolv DBE esters (Invista), 191.1 parts of xylene, 52 parts of n-butanol, and 76.8 parts of cyclohexanone were mixed with stirring, and 1.6 parts of Nacure 5925 as a catalyst was added to obtain water-free paint 2003.

[0077] <Evaluation of paint properties> The resulting paint was used to evaluate the following physical properties. [Paint stability] As in the case of evaluating the stability of the polyester resin dispersion, each of the resulting paints was placed in a thermostatic chamber at 30°C, and the state was checked every week and evaluated according to the following criteria. 5: No separation even after 6 months or more (very good) 4: Separation between 3 and 6 months (good) 3: Separation within 1 month to 3 months (practical) 2: Separation takes between one week and one month (practical depending on conditions) 1: Separation in less than a week (not practical)

[0078] <Average particle size> The average particle size was measured in the same manner as in the measurement of the average particle size of the polyester resin dispersion.

[0079] [Preparation of lid test panel] Each paint was applied to an aluminum plate with a thickness of 0.26 mm, with a dry mass of 110 mg / dm 2 The coated panels were then dried and cured by passing them through a double conveyor oven in 24 seconds, with the first zone having a temperature of 286°C and the second zone having a temperature of 326°C, to prepare test panels for lids with a coating. The resulting test panels for lids were evaluated as follows.

[0080] <Adhesion strength evaluation> The test panel was cut into a length of 100 mm and a width of 5 mm to serve as a test plate for measuring adhesion. A 25 mm section was removed from the tip of the long piece of the test plate for measuring adhesion, and two test plates were stacked with the coated surfaces facing inward. Nylon tape was sandwiched between the test plates, and the nylon tape was used as a hot-melt adhesive to perform heat fusion at 200°C for 30 seconds. After spreading out the unbonded portion, the T-peel strength between the cured coating and the aluminum plate was measured using a tensile tester (Tensilon) at a pulling rate of 200 mm / min, and rated according to the following criteria. 5: T-peel strength is 3kgf or more (very good) 4: T-peel strength is less than 3 kgf, 2 kgf or more (good) 3: T-peel strength is less than 2kgf, 1kgf or more (practical) 2: T-peel strength is less than 1 kgf, 0.4 kgf or more (practical depending on conditions) 1: Less than 0.4 kgf (not practical)

[0081] <Bending workability test> <<Initial>> The test panel was cut into a size of 30 mm wide x 50 mm long to prepare a test plate for evaluating bending processability. Next, at room temperature (25°C), a 3 mm diameter round bar was attached to the test plate at a position 30 mm long with the coating facing outward. The test plate was then folded in half along the round bar to prepare a test specimen. Two 0.26 mm thick aluminum plates were sandwiched between the folded test specimens, and a 1 kg rectangular weight measuring 15 cm wide x 5 cm high x 5 cm deep was dropped from a height of 40 cm onto the bent portion of the test specimen to completely fold it. The aluminum plate was then removed, and the folded portion of the test piece was immersed in 1% saline solution. A current of 6.0 V was then applied for 6 seconds between the metal part of the flat portion of the test piece that was not immersed in the saline solution and the saline solution, and the current value was measured. If the coating film has poor workability, the coating film at the bent portion will crack, exposing the underlying metal plate and increasing the conductivity, resulting in a high current value. Evaluation was made according to the following evaluation criteria. 5: Less than 5mA (very good) 4: 5mA or more and less than 10mA (good) 3: 10mA or more but less than 20mA (practical) 2: 20mA or more but less than 50mA (practical depending on conditions) 1: 50mA or more (not practical)

[0082] <<After time has passed>> A new test plate for evaluating bending processability was prepared, and left to stand in a thermostatic chamber at 37°C for 60 days, then returned to room temperature (25°C), and bent at room temperature in the same manner as in the bending processability test described above, and the current value was measured. Next, the current value after standing in the thermostatic chamber at 37°C for 60 days was subtracted from the initial current value to determine the current value, and the value was evaluated according to the following criteria. 5: Less than 1mA (very good) 4: 1mA or more and less than 5mA (good) 3: 5mA or more but less than 10mA (practical) 2: 10mA or more but less than 15mA (practical depending on conditions) 1: 15mA or more (not practical)

[0083] <Opening test> <<Before retort processing>> The test panel was cut into a size of 50 mm x 50 mm, and a press was used to create an irregularity on the painted surface of the test panel in the shape of a typical stay-on tab opening on a beverage can to prepare an evaluation sample. Next, an aluminum plate was peeled off from the unpainted side of the test panel along the shape of the opening, and the resulting opening was magnified under a microscope and visually evaluated. Poor openability means that the coating film tends to remain around the opening, resulting in a large protrusion into the opening. Good openability means that the coating film does not protrude into the opening at all, or if it does protrude, the protrusion is very small. Specifically, the width of the protruding coating film was measured and evaluated according to the following criteria. 5: The maximum width of the protruding coating is less than 100 μm (very good) 4: The maximum width of the protruding coating is 100 μm or more and less than 200 μm (good) 3: The maximum width of the protruding coating is 200 μm or more and less than 500 μm (practical use possible) 2: The maximum width of the protruding coating is 500 μm or more and less than 800 μm (practical depending on the conditions) 1: The maximum width of the protruding coating is 800 μm or more (not practical)

[0084] <<After retort processing>> A newly prepared evaluation sample was immersed in water and retorted in a retort oven at 125°C for 30 minutes, and then tested and evaluated in the same manner as in the above-mentioned openability test.

[0085] <Retort resistance test> The test panels were immersed in water, an aqueous solution containing 2% by mass of citric acid at a pH of approximately 2, and an aqueous solution adjusted to pH 12 using sodium hydroxide, and then retorted in a retort oven at 125°C for 30 minutes.The appearance of the coating was then visually evaluated according to the following criteria. 5: No change at all (very good) 4: There is some change, but almost no whitening (good) 3: Very slight whitening (usable) 2: Light whitening (practical depending on conditions) 1: Significant whitening (not practical)

[0086] <Acetic acid resistance> A test panel measuring 60 x 40 mm was prepared. It was immersed in a 4% acetic acid solution and sealed. After 10 days at 50°C, the state of the coating was observed. Evaluation was made according to the following criteria. 5: No change at all (very good) 4: Slight blistering (good) 3: Small blisters are visible on the entire surface (usable) 2: Large blister present (may be usable depending on conditions) 1: The entire coating has peeled off (not practical)

[0087] <Overall rating> The average value of each evaluation result was calculated by rounding up or down, and the result was evaluated on a five-point scale: 5 (best), 4 (excellent), 3 (good), 2 (acceptable), and 1 (unacceptable). However, if there was even one evaluation of 1 (unsuitable for practical use) in each evaluation, it was marked as 1 (unacceptable).

[0088] [Table 5]

[0089] [Table 6]

[0090] [Table 7]

[0091] [Table 8]

[0092] The abbreviations in Tables 5 to 8 are as follows: CKS-3898: Meta-cresol phenolic resin, butyl cellosolve solution with 50% non-volatile content, manufactured by AICA Kogyo Co., Ltd. PR-55317: Meta-cresol phenolic resin, 50% non-volatile content in n-butanol solution, manufactured by Sumitomo Bakelite Co., Ltd. Luwipal B017: Benzoguanamine amino resin, 80% non-volatile content in n-butanol Surfynol 420: Acetylene glycol-based nonionic surfactant, manufactured by Nissin Chemical Industry Co., Ltd. BYK333: Silicone leveling agent, manufactured by BYK Nacure 5925: Dodecylbenzenesulfonic acid catalyst, 25% active ingredient, isopropyl alcohol solution

[0093] As shown in Tables 5 to 8, Examples 101 to 137, which used the resin dispersion according to the present disclosure, exhibited good performance, particularly in terms of opening properties, demonstrating a significant effect compared to the comparative examples. The polyester resin in the present invention is not dissolved uniformly in the coating material, but is dispersed as particles combined with the curing agent. These particles are cured and fused together during the heating and drying process when forming a cured coating film, but rather than each particle being completely melted and homogenized, the cured coating film is in a state in which fused interfaces between particles remain, which is presumably why a cured coating film with excellent openness can be formed. The use of low-polarity resins is believed to be advantageous for performance involving water. However, low-polarity resins have poor adhesion to substrates such as metals, and when the coating film is subjected to stress such as bending, microvoids tend to form between the substrate and the resin. By water-dispersing polyester resin (A) with a glycol ether-based organic solvent and an alicyclic ketone-based organic solvent, low-polarity polyester resins that are normally not suitable for use as aqueous dispersions can be used as aqueous dispersions, and we believe that this allows for high water resistance, adhesion, and bending processability. Furthermore, by forming particles in water, the hydrophilic groups derived from polyester resin (A) are believed to face outward. This is believed to result in improved adhesion to substrates and bending processability.

[0094] <Evaluation of paints on the inside of can bodies> [Example 201] 1,000 parts by mass of the polyester resin dispersion 1 (containing 400 parts by mass of polyester resin) obtained in Example 1 was placed in a container, and while stirring, 96 parts by mass of CKS-3898, a meta-cresol phenolic resin, 1.34 parts by mass of Surfynol 420, 0.94 parts by mass of BYK333, 0.94 parts by mass of Nacure 5925, and 201.02 parts by mass of water were added to obtain paint 201, which was then subjected to various evaluations using the methods described below.

[0095] <Evaluation of paint properties> [Paint stability] The same tests were carried out as for the lid coating, and the evaluation was carried out according to the same criteria.

[0096] [Preparation of test panels for can body inner surface] The obtained paint 201 was applied to an aluminum plate having a thickness of 0.26 mm so that the dry mass of the coating film was 45 mg / dm 2 The coating was applied using a bar coater so that the coating was as follows: and the coating was baked in a gas oven at an atmospheric temperature of 200°C for 2 minutes to prepare a test panel for the inner surface of a can body. The obtained test panels for can body inner surfaces were evaluated in the same manner as the test panels for lids, including adhesive strength, bending processability (initial and after standing at 37°C for 60 days), and retort resistance (water, acidic citric acid (pH 2), and alkaline NaOH (pH 12)). Furthermore, the acetic acid resistance before and after denting was evaluated as described below. The results are shown in Table 9.

[0097] <Acetic acid resistance> <<Before dent processing (untreated)>> As in the case of the lid test panel, the can body inner surface test panel was immersed in a 4% acetic acid solution and sealed. After 10 days at 50°C, the state of the coating film was observed and evaluated according to the following evaluation criteria. <<After dent processing>> A test panel for the inner surface of a can body was cut to 5 cm x 5 cm and processed in a DuPont testing machine under conditions of 1 / 4 inch, a load of 300 g, and a height of 25 cm so that the painted surface was convex. The panel was then immersed in a 4% acetic acid solution and sealed. After 10 days at 37°C, the condition of the coating film in the processed area was observed. Evaluation was based on the following criteria. 5: No change at all (very good) 4: Slight blistering (good) 3: Small blisters are visible on the entire surface (usable) 2: Large blister present (may be usable depending on conditions) 1: The entire coating has peeled off (not practical)

[0098] [Examples 202 to 208] [Comparative Example 3001] As shown in Table 9, paints 202 to 208 and 3001 were obtained in the same manner as in Example 201, except that the type of polyester resin dispersion was changed, and were evaluated in the same manner.

[0099] [Comparative Example 3002] As shown in Table 9, evaluation was carried out in the same manner as in Example 201, except that paint 2003, which does not contain water, was used instead of paint 201.

[0100] [Table 9] [Industrial Applicability]

[0101] This paint is suitable for use in coating containers such as cans for storing beverages, food, etc. It is particularly suitable for coating the inner surface of the can body and the can lid. It is also suitable for coating the outer surface. It can also be used in containers for purposes other than food, such as engine oil. It can also be used to coat materials other than metals, such as plastics.

Claims

1. A polyester resin dispersion comprising a polyester resin (A), a neutralizing agent, an organic solvent, and water, The polyester resin (A) has an acid value of 2 mgKOH / g or more and 8 mgKOH / g or less, a number average molecular weight of 10,000 or more, and is a polyester resin that does not contain any structural units derived from bisphenol A, bisphenol F, or bisphenol S, and further does not contain any sulfo group or salt thereof, the polyester resin (A) contains structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol, which are polyhydric alcohol components, and the total amount of structural units derived from 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol is 95 to 100 mol % relative to 100 mol % of the structural units derived from the polyhydric alcohol components of the polyester resin (A); The polyester resin (A) contains 95 to 100 mol % of structural units derived from an aromatic polycarboxylic acid component, based on 100 mol % of structural units derived from a polycarboxylic acid component of the polyester resin (A); The polyester resin (A) contains 47 to 82 mol % of structural units derived from 2-methyl-1,3-propanediol and 17 to 50 mol % of structural units derived from 1,4-cyclohexanedimethanol, based on 100 mol % of structural units derived from a polyhydric alcohol component of the polyester resin (A); The organic solvent is contained in an amount of 30 to 130 parts by mass per 100 parts by mass of the polyester resin (A), The polyester resin dispersion contains an organic solvent including a glycol ether-based organic solvent and an alicyclic ketone-based organic solvent.

2. The polyester resin dispersion according to claim 1 , wherein the alicyclic ketone organic solvent is a cycloalkane ketone organic solvent or a cycloalkene ketone organic solvent.

3. 3. The polyester resin dispersion according to claim 2, wherein the cycloalkane ketone organic solvent is selected from the group consisting of cyclohexanone, cyclopentanone, and cyclobutanone, and the cycloalkene ketone organic solvent is selected from the group consisting of isophorone and 2-cyclohexene-1-one.

4. The polyester resin dispersion according to claim 1 or 2, wherein the organic solvent contains 15% by mass or more of a glycol ether-based organic solvent relative to 100% by mass of the organic solvent.

5. 3. The polyester resin dispersion according to claim 1, wherein the water content is 40 to 90% by mass, based on a total of 100% by mass of the water and the organic solvent.

6. The polyester resin dispersion according to claim 4, wherein the organic solvent contains 15 to 90% by mass of a glycol ether-based organic solvent relative to 100% by mass of the organic solvent.

7. 3. The polyester resin dispersion according to claim 1, wherein the glycol ether organic solvent is selected from the group consisting of ethylene glycol monobutyl ether and diethylene glycol monobutyl ether.

8. 2. The polyester resin dispersion according to claim 1, wherein the polyester resin (A) further contains structural units derived from trimethylolpropane, which is a polyhydric alcohol component, and the structural units derived from trimethylolpropane account for 0.1 to 3 mol % of 100 mol % of the structural units derived from the polyhydric alcohol component of the polyester resin (A).

9. the structural units derived from the polycarboxylic acid component of the polyester resin (A) are composed solely of structural units derived from an aromatic polycarboxylic acid component, the structural units derived from the aromatic polycarboxylic acid component include structural units derived from terephthalic acid and structural units derived from isophthalic acid, 3. The polyester resin dispersion according to claim 1, wherein the structural units derived from terephthalic acid and the structural units derived from isophthalic acid account for 95 to 100 mol% in total of 100 mol% of the structural units derived from the aromatic polycarboxylic acid component.

10. 10. The polyester resin dispersion according to claim 9, wherein, based on 100 mol% of the structural units derived from the aromatic polycarboxylic acid component, the structural units derived from terephthalic acid are 8 to 30 mol% and the structural units derived from isophthalic acid are 68 to 90 mol%.

11. The polyester resin dispersion according to claim 10, wherein the polyester resin (A) further contains structural units derived from trimellitic acid (anhydride), which is a polycarboxylic acid component, and the structural units derived from trimellitic acid (anhydride) account for 0.1 to 2 mol % of 100 mol % of the structural units derived from the aromatic polycarboxylic acid component of the polyester resin (A).

12. A coating material comprising the polyester resin dispersion according to claim 1 or 2 and a curing agent.

13. The paint according to claim 12, wherein the glycol ether organic solvent accounts for 15 to 90% by mass of 100% by mass of the organic solvent.

14. The paint described in claim 13, wherein the water accounts for 40 to 90 mass % of a total of 100 mass % of the water and the organic solvent.

15. A can lid obtained by coating a metal with the paint according to claim 12.

16. A can body formed by coating a metal with the coating material according to claim 12.

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