Resin dispersion, coating material, can lid, and can body

Abstract

Provided are: a resin dispersion which has excellent stability, and is capable of forming a coating film excellent in terms of processability, retort resistance and openability and suitable as a coating film for a can body, a can lid or the like, wherein a polyester resin which does not have any structural unit derived from bisphenol A, bisphenol F or bisphenol S and has neither a sulfo group nor a salt thereof is used; a coating material; and a can lid and a can body both using the coating material. A resin dispersion according to the present disclosure comprises a polyester resin (A) having an acid value of 16 mg KOH / g or less and a number average molecular weight of 8,000 or more, a phenolic resin (B) having a weight average molecular weight of 500 to 2,700 and having a specific structure, a neutralizing agent, an organic solvent, and water, wherein the organic solvent is contained in an amount of 30 to 130 parts by mass per 100 parts by mass of the total amount of the resin (A) and the resin (B).

Description

Resin dispersions, paints, can ends and can bodies

[0001] The present disclosure relates to a resin dispersion, a paint containing the resin dispersion, a can lid formed using the paint, and a can body formed using the paint.

[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 paint 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) or the like as 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 or the like as raw materials have been proposed as paints for coating can lids and can bodies.

[0003] Patent Document 1 describes a method for producing a cellulose acetate having an acid value of 150 eq / 10 ６ Patent Document 2 discloses the use of a polyester resin (A) having an acid value of 2 to 50 mgKOH / g and a polyester resin (B) having an acid value of 0 to 50 mgKOH / g. Patent Document 3 discloses the use of a polyester resin (A) and a polyester resin (B) having an acid value difference of 5 mgKOH / g or more.

[0004] JP 2004-292665 A JP 2013-249376 A JP 2019-163454 A

[0005] Because can bodies and can lids are manufactured through severe processes (e.g., necking, beading, scoring, riveting, etc.), the coating film coating the metal substrate is also required to have high process resistance. Furthermore, depending on the type of contents, after filling the can with the contents, a high-temperature retort treatment may be performed to sterilize the contents. Therefore, the coating film coating the metal substrate is required to have excellent retort resistance. Furthermore, various properties are required of the coating film coating the metal substrate, such as corrosion resistance (acid resistance and alkali resistance) to prevent corrosion of the metal substrate by the contents after filling, and excellent hygiene with no leaching of paint components. In addition, in the case of can lids, excellent opening properties are also required.

[0006] However, conventional paints, even when they have excellent retort resistance, have problems with their stability as water-based paints. Furthermore, even when excellent stability as water-based paints is achieved by using resins containing sulfo groups or their salts or high-acid-value polyesters, the retort resistance and processability of the coating film are often insufficient, and improvements that can achieve both of these properties are desired. In particular, can lids require extremely high processability, so the coating film must have "flexibility" and "toughness." However, from the perspective of opening, "hardness" and "sharpness," which are the opposite of "flexibility" and "toughness," are also required. The market is demanding 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 a can lid and can body that use the paint.

[0008] The present inventors have conducted extensive research and found that the problems of the present disclosure can be solved in the following aspects, leading to the completion of the present disclosure. [1]: A resin dispersion containing a polyester resin (A), a phenolic resin (B), a neutralizing agent, an organic solvent, and water, wherein the polyester resin (A) has an acid value of 16 mgKOH / g or less and a number-average molecular weight of 8,000 or more, and the phenolic resin (B) has a weight-average molecular weight of 500 to 2,700, and contains 50 mol % or more of meta-cresol-derived structural units out of a total of 100 mol % of structural units derived from phenolic compounds, and contains 0.01 to 0.2 methylol groups, 0.8 to 1.3 butoxymethyl groups, and a total of 0.15 to 0.5 methylene bonds and dimethylene ether bonds per aromatic ring in the phenolic resin (B), and the resin dispersion contains 30 to 130 parts by mass of the organic solvent per 100 parts by mass of the polyester resin (A) and the phenolic resin (B). [2]: The resin dispersion according to [1], wherein the mass ratio of the polyester resin (A) to the phenolic resin (B) is polyester resin (A) / phenolic resin (B) = 95 / 5 to 70 / 30. [3]: The resin dispersion according to [1] or [2], wherein the phenolic resin (B) has structural units derived from para-cresol in a proportion of 50 mol % or less relative to a total of 100 mol % of structural units derived from phenolic compounds.[4]: The resin dispersion according to any one of [1] to [3], wherein the polyester resin (A) has structural units derived from one or more polycarboxylic acid components selected from the group consisting of terephthalic acid, isophthalic acid, sebacic acid, and trimellitic acid (anhydride), and structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, ethylene glycol, 1,4-butanediol, and trimethylolpropane, and wherein, out of 100 mol% of the structural units derived from the polyhydric alcohol components of the polyester resin (A), 20 to 99.9 mol% of structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol and 0.1 to 80 mol% of structural units derived from one or more polyhydric alcohol components selected from the group consisting of ethylene glycol, 1,4-butanediol, and trimethylolpropane. [5]: The resin dispersion according to any one of [1] to [4], wherein the water accounts for 40 to 90% by mass of a total of 100% by mass of the water and the organic solvent. [6]: A coating material comprising the resin dispersion according to any one of [1] to [5]. [7]: A can lid obtained by coating a metal substrate with the coating material according to [6]. [8]: A can body obtained by coating a metal substrate with the coating material according to [6].

[0009] According to the present disclosure, it is possible to provide an excellent effect of providing a resin dispersion and paint that are excellent in stability and that can form a coating film that is suitable for coating can bodies, can lids, etc. and has excellent processability, retort resistance, corrosion 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 that use the paint.

[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. 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 phenolic resin (B), 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 hydroxyl 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 resin dispersion of the present disclosure may use polyester resins other than those described above, as long as they do not deviate from the spirit of the present disclosure.

[0013] It is important that the polyester resin (A) has an acid value of 16 mgKOH / g or less, preferably 1 to 11 mgKOH / g, more preferably 1 to 8 mgKOH / g, and even more preferably 3 to 8 mgKOH / g. The higher the acid value of the polyester resin (A), the more hydrophilic it becomes, and therefore the water resistance of the coating film becomes poor. By using a polyester resin (A) having an acid value of 16 mgKOH / g or less and a phenolic resin (B) described below, it is possible to achieve both processability, retort resistance, openability, and corrosion resistance.

[0014] The number average molecular weight (hereinafter also referred to as Mn) of the polyester resin (A) is set to be 8,000 or more. There is no upper limit to the Mn, but it is preferably 100,000 or less, and more preferably in the range of 9,000 to 50,000. 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.

[0015] The polyester resin (A) preferably has at least one of the following structures: (i) an alkyl group in the side chain; and (ii) an alicyclic structure in the main chain. This improves the solubility in the organic solvent described below. It is believed that the improved solubility causes the polyester resin (A) to swell when water is added, and the alkyl group in the side chain and / or the alicyclic structure in the main chain of the polyester resin (A) become compatible with the phenolic resin (B), thereby enabling the polyester resin (A) to be effectively made water-soluble. It is more preferable that the polyester resin (A) have both of the above structures (i) and (ii).

[0016] Examples of polycarboxylic acids used as monomers for forming the polyester resin (A) include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, and 1,4-cyclohexanedicarboxylic acid. Other aromatic dibasic acids, aliphatic dibasic acids, alicyclic dibasic acids, α,β-unsaturated dicarboxylic acids, and their anhydrides and alkyl esters can also be used as the polycarboxylic acids. Examples of aromatic dibasic acids include orthophthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid. Examples of aliphatic dibasic acids include succinic acid, azelaic acid, dodecanedioic acid, and dimer acid. Examples of alicyclic dibasic acids include 1,3-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid. Examples of α,β-unsaturated dicarboxylic acids include fumaric acid, maleic acid, itaconic acid, and citraconic acid.

[0017] The polyester resin (A) may have a branched structure. To introduce the branched structure, a trifunctional or higher functional acid may be used in addition to a dibasic acid. Specific examples include trimellitic acid (anhydride) (trimellitic acid and trimellitic acid anhydride are collectively referred to as "trimellitic acid (anhydride)." Hereinafter, "anhydride" will be used.), pyromellitic acid (anhydride), and ethylene glycol bistrimellitate dianhydride.

[0018] Among the polycarboxylic acids, terephthalic acid, isophthalic acid, sebacic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, and trimellitic acid (anhydride) are preferred. The polyester resin (A) preferably has structural units derived from one or more polycarboxylic acid components selected from the group consisting of terephthalic acid, isophthalic acid, sebacic acid, and trimellitic acid (anhydride). Of 100 mol% of the structural units derived from polycarboxylic acids in the polyester resin (A), it is preferred that the structural units derived from terephthalic acid account for 5 to 100 mol%, and that the structural units derived from one or more polycarboxylic acids selected from the group consisting of isophthalic acid, sebacic acid, and trimellitic acid (anhydride) account for 0 to 95 mol% in total. Furthermore, it is preferred that the structural units derived from isophthalic acid account for 0 to 90 mol%, the structural units derived from sebacic acid account for 0 to 45 mol%, and the structural units derived from trimellitic acid (anhydride) account for 0 to 5 mol%.

[0019] The polyester resin (A) may use a polycarboxylic acid other than the above-mentioned polycarboxylic acid or a monofunctional carboxylic acid. In 100 mol% of the structural units derived from the polycarboxylic acid component of the polyester resin (A), the structural units derived from the polycarboxylic acid of the polyester resin (A) other than the above-mentioned polycarboxylic acid are preferably 2 mol% or less in total. In addition, in 100 mol% of the structural units derived from the carboxylic acid component of the polyester resin (A), the structural units derived from the monofunctional carboxylic acid are preferably 2 mol% or less.

[0020] Examples of polyhydric alcohols used as monomers for forming polyester resin (A) include aliphatic diols having 2 to 10 carbon atoms, alicyclic diols having 6 to 12 carbon atoms, and diols containing an ether bond. 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, 2-methyl-1,3-propanediol, and 2-ethyl-2-butyl-1,3-propanediol. Examples of alicyclic diols having 6 to 12 carbon atoms include 1,6-cyclohexanedimethanol and 1,4-cyclohexanedimethanol. Examples of diols having an ether bond include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0021] Of the polyhydric alcohols, the diol is preferably ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, 1,6-cyclohexanedimethanol, or diethylene glycol, and among these, ethylene glycol, 1,2-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, or 1,4-cyclohexanedimethanol is more preferred.

[0022] In order to introduce a branched structure into the polyester resin (A), a monomer having a tri- or higher functional hydroxyl group may be used in addition to the diols described above. Specific examples include trimethylolpropane, glycerin, trimethylolethane, mannitol, sorbitol, pentaerythritol, and α-methylglucoside.

[0023] The polyester resin (A) has structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, ethylene glycol, 1,4-butanediol, and trimethylolpropane, and preferably contains, out of 100 mol % of structural units derived from polyhydric alcohol components of the polyester resin (A), 20 to 99.9 mol % of structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol and 0.1 to 80 mol % of structural units derived from one or more polyhydric alcohol components selected from the group consisting of ethylene glycol, 1,4-butanediol, and trimethylolpropane. When forming the polyester resin (A), "other" polyhydric alcohols may be used in addition to the polyhydric alcohols selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, and trimethylolpropane. However, the total amount of structural units derived from the "other" polyhydric alcohols is preferably 2 mol% or less based on 100 mol% of the structural units derived from the polyhydric alcohol component in the polyester resin (A). Furthermore, if necessary, a small amount of a monofunctional alcohol may be used. For example, the structural units derived from the monofunctional alcohol are preferably 2 mol% or less based on 100 mol% of the structural units derived from the alcohol component.

[0024] The polyester resin (A) may be a commercially available product. Suitable examples include Vylon GK-880 (acid value: 1 mg KOH / g, Mn: 18,000), Vylon GK-640 (acid value: 3 mg KOH / g, Mn: 18,000), Vylon GK-330 (acid value: 1 mg KOH / g, Mn: 17,000), and Vylon GK-360 (acid value: 5 mg KOH / g, Mn: 16,000), manufactured by Toyobo Co., Ltd., DYNAPOL L490 (acid value: 3 mg KOH / g, Mn: 15,000) manufactured by Evonik, and UE-9800 (acid value: 3 mg KOH / g, Mn: 13,000) manufactured by Unitika Ltd.

[0025] <Phenol Resin (B)> Examples of the phenol resin (B) include resins synthesized by an addition condensation reaction between a phenol compound and an aldehyde such as formaldehyde. The phenol resin (B) can be synthesized by a known method.

[0026] Examples of the phenolic resin (B) include resol-type phenolic resins and novolac-type phenolic resins. Resol-type phenolic resins are phenolic resins obtained using an alkaline catalyst, and novolac-type phenolic resins are phenolic resins obtained using an acidic catalyst. Other examples include resol-type novolac-type phenolic resins obtained by further reacting novolac-type phenolic resins with an alkaline catalyst, and novolac-type resol-type phenolic resins obtained by further reacting resol-type phenolic resins with an acidic catalyst. Among these, resol-type phenolic resins are preferred as the phenolic resin (B) from the viewpoints of self-crosslinking or as a curing agent that reacts with the polyester resin (A), as well as the dispersibility of the polyester resin (A).

[0027] Examples of the alkali catalyst include alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, amines such as triethylamine, trimethylamine, and ethanolamine, and ammonia, etc. Alkali metal hydroxides or alkaline earth metal hydroxides are preferred, sodium hydroxide, lithium hydroxide, and magnesium hydroxide are more preferred, and sodium hydroxide is most preferred.

[0028] Examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, oxalic acid, succinic acid, maleic acid, fumaric acid, and p-toluenesulfonic acid.

[0029] In phenolic compounds, the ortho and para positions of the phenolic hydroxyl group are reactive sites. That is, aldehydes can be added to the carbon atoms at the ortho and para positions. Therefore, a bifunctional phenol refers to a phenol having a substituent such as an alkyl group or a phenyl group at either the ortho or para position. Such a bifunctional phenol has two reactive sites per molecule. Furthermore, a trifunctional phenol refers to a phenol having no substituents at the ortho and para positions. Such a trifunctional phenol has three reactive sites per molecule.

[0030] Specific examples of difunctional phenols include o-cresol, p-cresol, p-phenylphenol, p-nonylphenol, 2,3-xylenol, and 2,5-xylenol. Specific examples of trifunctional phenols include phenol (carbolic acid), m-cresol, 3,5-xylenol, and resorcinol. Note that "o-" is an alternative notation for "ortho," "p-" is an alternative notation for "para," and "m-" is an alternative notation for "meta."

[0031] It is important that the phenolic resin (B) contains at least 50 mol% of structural units derived from meta-cresol (m-cresol) out of a total of 100 mol% of structural units derived from phenolic compounds. It is also preferable that the phenolic resin (B) contains structural units derived from para-cresol (p-cresol). In other words, it is desirable to use both m-cresol and p-cresol as the phenolic compound. Phenolic resin (B) obtained using m-cresol has high reactivity with polyester resin (A), and its use can achieve high processability, retort resistance, and openability. On the other hand, phenolic resin (B) obtained using p-cresol has poor reactivity but imparts good dispersibility to polyester resin (A). This is thought to be because p-cresol only reacts at the ortho position, resulting in a two-dimensional molecular structure that acts as a dispersant for polyester resin (A).

[0032] The phenolic resin (B) preferably contains 10 to 50 mol %, and more preferably 20 to 40 mol %, of structural units derived from p-cresol, based on a total of 100 mol % of structural units derived from phenolic compounds. By containing 10 to 50 mol % of structural units derived from p-cresol, the dispersibility of the polyester resin (A) is improved, and structural units derived from m-cresol, which have high reactivity with the polyester resin (A), can be used in combination with the phenolic resin (B).

[0033] As the phenolic compound for obtaining the phenolic resin (B), a phenolic compound other than m-cresol and p-cresol may be used. Of the total 100 mol% of structural units derived from phenolic compounds in the phenolic resin (B), the total of structural units derived from phenolic compounds other than m-cresol and p-cresol is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less. Among phenolic compounds other than m-cresol and p-cresol, o-cresol is preferred from the viewpoint of compatibility with the polyester resin (A).

[0034] For example, a resol-type phenolic resin can be obtained by reacting the above-mentioned phenolic compound with an aldehyde in the presence of an alkali catalyst. The resol-type phenolic resin obtained by this method has alkylol groups at at least some of the ortho- and para-positions, and further has a structure in which the aromatic rings of the phenolic compound are bonded to each other via alkylene groups or dialkylene ether groups.

[0035] Examples of the alkylol group in the resol-type phenolic resin include alkylol groups having 1 to 5 carbon atoms, with methylol, ethylol, and propylene groups being preferred, and methylol groups being more preferred. Furthermore, examples of the alkylene group connecting the aromatic rings of the phenolic compound include alkylene groups having 1 to 5 carbon atoms, with methylene, ethylene, and propylene groups being preferred, and methylene groups being more preferred. The number of carbon atoms in the alkylol and alkylene groups is the same as the number of carbon atoms in the aldehyde used as the raw material. The same applies to the alkylene portion of the dialkylene ether group connecting the aromatic rings of the phenolic compound. In this embodiment, formaldehyde is preferably used as the aldehyde.

[0036] From the viewpoint of curability and dispersibility, it is important that the weight average molecular weight of the phenolic resin (B) is 500 to 2,700, and preferably 600 to 2,500.

[0037] Furthermore, it is desirable that at least a portion of the alkylol groups of the phenolic resin (B) be etherified with an alcohol having 1 to 12 carbon atoms, and more preferably butyl-etherified. If the number of carbon atoms in the ether moiety is too large, compatibility with water will be reduced, and if the number is too small, compatibility with the polyester resin (A) will be reduced. Butyl-etherification improves compatibility with the polyester resin (A), promotes the crosslinking reaction, and further improves dispersibility.

[0038] It is important that the number of methylol groups per aromatic ring in the phenolic resin (B) is 0.01 to 0.2 and the number of butoxymethyl groups is 0.8 to 1.3.

[0039] Phenolic resin (B) contains methylene bonds and dimethylene ether bonds. Methylene bonds and dimethylene ether bonds are crosslinking components of phenolic resins, and the more these bonds there are, the higher the molecular weight or the more three-dimensional crosslinking is thought to occur. Two-dimensional crosslinking is preferred for phenolic resin (B) to ensure dispersibility. Therefore, it is important that each aromatic ring in phenolic resin (B) contains a total of 0.15 to 0.5 methylene bonds and dimethylene ether bonds.

[0040] <Resin Dispersion> The resin dispersion of the present disclosure will be described. The resin dispersion contains a polyester resin (A), a phenolic resin (B), a neutralizing agent, an organic solvent, and water. The resin dispersion can be obtained, for example, as follows. The polyester resin (A) is dissolved in an organic solvent, cooled as necessary, and then the phenolic resin (B) and the neutralizing agent are added. Water is then added to form a mixture of water and the organic solvent into a liquid dispersion medium, and the polyester resin (A) and the phenolic resin (B) are dispersed in particulate form in the liquid dispersion medium. Alternatively, the polyester resin (A) is dissolved in an organic solvent, a neutralizing agent is added, and water is then added to form a mixture of water and the organic solvent into a liquid dispersion medium, and the polyester resin (A) is dispersed in particulate form in the liquid dispersion medium. The phenolic resin (B) is then added to obtain a resin dispersion. Alternatively, the polyester resin (A) and the phenolic resin (B) may be kneaded, and then an organic solvent is added to dissolve the mixture, and then a neutralizing agent and water are added to obtain a resin dispersion. Among these, it is preferred to dissolve the polyester resin (A) in an organic solvent, cool it if necessary, add the phenolic resin (B) and a neutralizing agent, and then add water to form a liquid dispersion medium using a mixture of water and the organic solvent, and then disperse the polyester resin (A) and the phenolic resin (B) in the form of particles in the liquid dispersion medium.

[0041] The dispersed particles in the resin 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 resin 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.

[0042] The resin dispersion uses a combination of polyester resin (A) and phenolic resin (B), which is thought to preferentially crosslink intra-particles and preferentially fuse particles together, making it possible to form a coating film that has flexibility and stiffness, which are usually difficult to achieve, while also achieving the opposing properties of hardness and sharpness.

[0043] The mass ratio of the polyester resin (A) to the phenolic resin (B), polyester resin (A) / phenolic resin (B), is preferably from 95 / 5 to 70 / 30, and more preferably from 90 / 10 to 80 / 20.

[0044] <Organic Solvent> The resin 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. This does not include the phenolic resin (B) contained in the "phenolic resin solution" or the liquid components of the "neutralizing agent" described below. Liquid additives such as Surfynol 420 used in the examples described below are also not included in the organic solvent. Note that liquids used to dissolve and / or disperse solid neutralizing agents are organic solvents. It is important that the resin dispersion contains 30 to 130 parts by mass of organic solvent per 100 parts by mass of the polyester resin (A) and phenolic resin (B) combined, with 35 to 120 parts by mass being preferred, and 40 to 100 parts by mass being more preferred. If the amount of organic solvent is too small, the polyester resin will not swell, making it impossible to obtain a stable dispersion. If the amount of organic solvent is too large, the polyester resin will dissolve in the organic solvent even when water is added, making it impossible to form dispersed particles.

[0045] The organic solvent is not particularly limited, and examples thereof include ketone-based solvents, glycol ether-based solvents, alcohol-based solvents, glycol solvents, acetate-based solvents, etc. Specific examples of ketone-based solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, diacetone alcohol, and isophorone. Specific examples of glycol ether-based 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, diethylene glycol di(iso)butyl ether, diethylene glycol monohexyl ether, 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, dipropylene glycol di(iso)butyl ether; 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, 1,2-propanediol, dipropylene glycol, 1,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, such as ethyl acetate, butyl acetate, dibasic acid esters, toluene, xylene, aromatic hydrocarbon compounds, aliphatic hydrocarbons, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylformamide, and solvent naphtha, may also be used as appropriate. Furthermore, organic solvents may be used when preparing the coating material, if necessary.

[0046] The organic solvent preferably contains a ketone solvent or a glycol ether solvent. It is more preferable that the organic solvent selected from the group consisting of ketones and glycol ethers account for 60 to 100% by mass in total, based on 100% by mass of the organic solvent. It is even more preferable that the organic solvent contains both ketone and glycol ether organic solvents. It is preferable that the organic solvent contains 10 to 60% by mass of the ketone organic solvent, based on 100% by mass of the organic solvent. As the ketone organic solvent, cyclohexanone and methyl ethyl ketone are preferred, and cyclohexanone is more preferred. As the glycol ether organic solvent, ethylene glycol monobutyl ether and diethylene glycol monobutyl ether are preferred, and diethylene glycol monobutyl ether is more preferred.

[0047] <Water> The resin dispersion contains water to make it aqueous. The amount of water is preferably 40 to 90% by mass, with the total of the organic solvent and water being 100% by mass. If the water content is too low, the polyester resin dissolves in the organic solvent, making it difficult to form dispersed particles. On the other hand, if the water content is too high, there will not be enough organic solvent to swell the polyester resin, making it difficult to form particles.

[0048] <Neutralizing Agent> The neutralizing agent is primarily used to neutralize the carboxyl groups in the polyester resin (A) and impart water affinity to the polyester resin (A). However, some of the neutralizing agent also forms bonds with the hydroxyl groups in the phenolic resin (B), imparting ionicity as well as water affinity, and is thought to enhance dispersibility in the polyester resin (A). Examples of neutralizing agents include dimethylaminoethanol, triethanolamine, ammonia, aminoethanol, sodium hydroxide, and sodium carbonate. Among these, dimethylaminoethanol, triethanolamine, ammonia, and aminoethanol are preferred. 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). Note that among neutralizing agents, dimethylaminoethanol and the like are not considered organic solvents in this specification.

[0049] <Paint> The present resin dispersion is suitable for use in a paint. In the paint of the present disclosure (hereinafter also referred to as the present paint), the phenolic resin (B) functions as a curing agent. The present paint preferably contains 30 to 120 parts by mass of an organic solvent per 100 parts by mass of the polyester resin (A) and the phenolic resin (B), and the organic solvent preferably contains a glycol ether-based organic solvent and a ketone-based organic solvent. Furthermore, the present paint preferably contains 40 to 90% by mass of water relative to a total of 100% by mass of water and the organic solvent. The present paint is preferably used to coat beverage cans and the like.

[0050] <Curing Agent> The resin dispersion of the present disclosure can be used alone as a coating material, but may contain various additives as needed, or a curing agent other than the phenolic resin (B) within a range that does not impair the effects of the present disclosure.

[0051] Examples of the curing agent include a phenolic resin (Y) other than the phenolic resin (B), an amino resin, a component having an isocyanate group or a derivative thereof, a component having an acid anhydride group, a metal alkoxide compound, a metal chelate compound, and tris(alkoxycarbonylamino)triazine. Among these, the phenolic resin (Y) and the amino resin are preferred. The phenolic resin (Y) and the amino resin can undergo self-crosslinking reactions and can also react with the hydroxyl groups of the polyester resin. 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.

[0052] Examples of the phenolic resin (Y) include resins synthesized by an addition condensation reaction between a phenolic compound and an aldehyde such as formaldehyde. The phenolic resin (Y) can be synthesized by a known method. Examples of the phenolic compound 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.

[0053] The phenolic resin (Y) may be a commercially available product. Suitable examples include Phenodur PR285, PR516, PR517, PR519, PR520, PR521, PR827, PR566, PR612, and VPR1785 manufactured by Allnex Corporation; Sumilite Resin PR-55819 manufactured by Sumitomo Bakelite Co., Ltd.; and Shounol BKM-2620, CKM-908, CKS-380A, and CKM-1634 manufactured by Aica Kogyo Co., Ltd.

[0054] 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 may be used alone or in combination of two or more.

[0055] Commercially available amino resins may be used. Suitable examples include Cymel 301, 303LF, 304, 323, 325, 328, 370, 659, and 1123 manufactured by Allnex Corporation; Luwipal 014, 015, 018, 066, 070, 052, and B017 manufactured by BASF; and Amidya P-138, P-196-M, TD-126, ED-126-60S, and 15-159 manufactured by DIC Corporation.

[0056] The phenol resin (Y) and amino resin 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.

[0057] <Acid Catalyst> It is preferable to incorporate a conventionally known curing catalyst into the present coating material in order to promote the crosslinking reaction between the polyester resin (A) and the phenolic resin (B). 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 neutralized products of these acid catalysts. One or more curing catalysts can be used in combination. Of the above acid catalysts, dodecylbenzenesulfonic acid and its neutralized products are preferred as the curing catalyst.

[0058] The content of the curing catalyst is 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, and even more preferably 0.03 to 0.3 parts by mass, based on 100 parts by mass of the combined solids of the polyester resin (A) and the phenolic resin (B). Furthermore, 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 is sufficient as long as it is within the above range. If the amount of 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 curing catalyst is greater than the above range, further effects cannot be expected, and the water resistance of the coating film may be deteriorated.

[0059] <Additives> The coating material of the present disclosure is preferably used to coat beverage cans, etc., and additives such as lubricants such as waxes and leveling agents can be blended as needed to prevent scratches on the coating film during the can manufacturing process. Examples of waxes include animal and vegetable waxes such as carnauba wax, lanolin wax, palm oil, candelilla wax, and rice wax; petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum; and synthetic waxes such as polyolefin wax and Teflon (registered trademark) wax.

[0060] <Application fields of the present paint> The present paint is preferably used to coat storage containers such as cans for storing beverages, food, etc., and can be used on both the interior and exterior surfaces. Because the present paint exhibits high levels of processability and corrosion resistance when used in the above applications, it is particularly suitable for coating the interior surfaces of cans, and is particularly suitable for use on the interior surfaces of beverage cans and food cans (meaning cans for storing food).

[0061] <Can Components and Cans> Cans for storing beverages, food, etc. come in a variety of shapes, but are typically formed by combining at least two can components. They can be broadly classified into two-piece cans (in a broad sense), consisting of a bottomed cylindrical member in which the can body and bottom are integrated, and a lid member, and three-piece cans, consisting 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 cans, which are equipped with a recapable lid member and a bottle member. The drinking spout of the bottle member of a bottle 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).

[0062] The can body of a two-piece can is produced, for example, by punching out a metal substrate into a flat circular plate for each can, forming the member into a predetermined bottomed cup shape, and then spray-painting the coating composition onto the inner surface of the can and curing it to form a coating film on the inner surface. After forming the coating film on the inner surface, the open end is subjected to processes such as necking, beading, and scoring. In the case of a bottomed cup-shaped member for a two-piece can, the coating is preferably cured at a temperature of 150 to 300°C for 10 seconds to 10 minutes, more preferably 30 seconds to 5 minutes, at a temperature of 150 to 300°C, and baked for 10 seconds to 10 minutes. The thickness (coating amount) 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.

[0063] Can lids (excluding bottle can lids) are obtained, for example, by applying a paint to a metal substrate, curing the paint, forming a coating, punching out a circular flat 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 (clearness). Poor opening results in peeled paint residues around the opening. For can lids, the curing conditions are preferably a temperature of 150 to 350°C, baked for 10 seconds to 30 minutes, more preferably 10 seconds to 15 minutes. For can lids, the thickness (coating amount) of the coating after drying is typically 10 to 200 mg / dm². 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 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.

[0064] 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.

[0065] Cans having the can lid or can body of the present disclosure as constituent members are preferably used to store beverages such as drinking water, soft drinks, coffee, tea, beer, chuhai (shochu with carbonated water added), sake, whiskey, and water-based cocktails, as well as foods such as fish, meat, vegetables, fruit, oil, and sauces.

[0066] One embodiment of the beverage can of the present disclosure includes a can lid and a can body member coated with the paint of the present disclosure, and another embodiment of the beverage can of the present disclosure includes a can body member coated with the paint of the present disclosure.

[0067] The present disclosure 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.

[0068] (Number average molecular weight, weight average molecular weight) Mn (number average molecular weight) and Mw (weight average molecular weight) were measured using a high-speed GPC apparatus 8020 series (tetrahydrofuran solvent, column temperature 40°C, polystyrene standard) manufactured by Tosoh Corporation. Specifically, four columns manufactured by Tosoh Corporation, G1000HXL, G2000HXL, G3000HXL, and G4000HXL, were connected in series and measured at a flow rate of 1.0 mL / min.

[0069] (Acid Value) 0.2 g of polyester resin was precisely weighed into a stoppered Erlenmeyer flask and dissolved in 20 mL of THF (tetrahydrofuran). 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 (mg KOH / g) = (a × F × 56.1 × 0.1) / S, where S is the amount of polyester resin collected × (solid content of acrylic copolymer solution / 100) (g), a is the titration amount (mL) of the 0.1 mol / L alcoholic potassium hydroxide solution, and F is the titer of the 0.1 mol / L alcoholic potassium hydroxide solution.

[0070] (Polyester Resin Composition) １ H-NMR analysis (BRUKER ULTRA SHIELD TM 400 PLUS). １ Resins 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, and then quantitative analysis was performed by gas chromatography.

[0071] (Phenol Resin Composition) １３ The values ​​were determined by C-NMR analysis (JNM-ECX400 manufactured by JEOL Ltd.). The phenolic resin was coated on a glass plate as a thin film, vacuum dried at 40°C for 12 hours, then dissolved in deuterated chloroform and measured with a pulse interval of 25 seconds and an accumulation count of 7,000. For the analysis, the center of the deuterated chloroform triplet was set to 77.0 ppm. The integral value from 150 to 160 ppm was set to 1, and the structural unit derived from the phenolic compound was taken as follows: Butoxymethyl group: 29.5 to 32.5 ppm Methylol group: 61.5 to 64.5 ppm Methylene bond: 34.0 to 38.0 ppm Dimethylene ether bond: 65.0 to 67.0 ppm (since there are two carbon atoms, the value divided by 2 is the bond number).

[0072] <Production Example of Polyester Resin>

[0073] [Production Example A-1] A polymerization reactor was charged with 93.1 parts of terephthalic acid (19.8 mol% of 100 mol% polycarboxylic acid components), 372.5 parts of isophthalic acid (79.2 mol% of 100 mol% polycarboxylic acid components), 189.3 parts of 2-methyl-1,3-propanediol (67.6 mol% of 100 mol% polyhydric alcohol components), 141.9 parts of 1,4-cyclohexanedimethanol (31.5 mol% of 100 mol% polyhydric alcohol components), 3.76 parts of trimethylolpropane (0.9 mol% of 100 mol% polyhydric alcohol components), and 0.05 parts of titanium butoxide. The temperature was gradually increased to 250°C under a nitrogen atmosphere, and an esterification reaction was carried out over 6 hours. Next, the mixture 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 that condition for 2 hours. The resin was then cooled to 200°C under a nitrogen stream, and 5.35 parts of trimellitic anhydride (1.0 mol% of 100 mol% of the polycarboxylic acid component) was added thereto and reacted for 2 hours to obtain Polyester Resin A-1. The analytical results of the obtained Polyester Resin A-1 are shown in Table 1.

[0074] [Production Examples A-3] to [Production Examples A-31], [Production Examples A-101], [Production Example A-102] Polyester resins A-3 to A-31 and A-101 to A-102 were obtained in the same manner as in Production Example A-1, except that the types and amounts of the polycarboxylic acid component and polyhydric alcohol component were changed, and analyzed in the same manner. Note that in the examples and comparative examples in which trimellitic acid (TMA) was not added, the step corresponding to "cooling the resin to 200°C under a nitrogen stream, adding 5.35 parts of trimellitic anhydride (1.0 mol% of 100 mol% of the polycarboxylic acid component), and allowing to react for 2 hours" described in Production Example A-1 was not performed.

[0075]

[0076] The abbreviations in Table 1 are as follows: TPA: terephthalic acid IPA: isophthalic acid SEA: sebacic acid TMA: trimellitic acid EG: ethylene glycol PG: 1,2-propanediol MPO: 2-methyl-1,3-propanediol CHDM: 1,4-cyclohexanedimethanol 1,4-BD: 1,4-butanediol TMP: trimethylolpropane

[0077] <Production example of phenolic resin>

[0078] [Production Example B-1] A four-neck flask was charged with 75.6 g (0.7 mol) of m-cresol, 32.4 g (0.3 mol) of p-cresol, 324.3 g of 37% formalin (4.0 mol as formaldehyde), and 16.0 g of 25% sodium hydroxide (0.1 mol as sodium hydroxide). The mixture was reacted at 40°C for 8 hours, followed by 3 hours at 70°C. After completion of the reaction, 18.2 g of 20% aqueous hydrochloric acid was slowly added while cooling to neutralize the mixture. The separated and precipitated resin was washed with water four times. Water was then removed by dehydration under reduced pressure. This water washing and dehydration under reduced pressure procedure was repeated three times for purification, and the resulting resin was dehydrated under reduced pressure until the water content was 1% or less. 400 parts of n-butanol was added to 100 parts of the resin after the dehydration treatment was completed. The internal temperature was raised until reflux began at normal pressure, and the alkoxylation reaction was carried out at 115-123°C for 10 hours. During this time, the reaction was continued while constantly removing water generated during the reaction to complete the reaction, and then excess unreacted n-butanol was removed under reduced pressure to adjust the solid content to 50% by mass, thereby obtaining phenolic resin solution B-1. The analytical results of the obtained phenolic resin are shown in Table 2.

[0079] [Production Example B-2] 100 parts of butyl cellosolve was added to 100 parts of phenolic resin solution 1, and the mixture was heated at 115 to 123°C. After removing n-butanol, butyl cellosolve was added so that the solid concentration became 50%, thereby obtaining phenolic resin solution B-2.

[0080] [Production Examples B-3 to B-8] [Production Examples B-1001 to B-1007] Phenol resin solutions B-3 to B-8 and B-1001 to B-1007 were obtained in the same manner as in Production Example 1, except that the types and quantitative ratios of the monomer components were changed as shown in Table 2, and the amounts of 37% formalin and n-butanol, as well as the reaction temperature and reaction time were changed as appropriate.

[0081]

[0082] Example 1 149 parts of polyester resin A-1 and 82 parts of diethylene glycol monobutyl ether were placed in a reaction vessel 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 80°C with stirring. Thereafter, 52.5 parts of phenolic resin solution B-1 and 1.18 parts of dimethylaminoethanol were added, and 215.3 parts of ion-exchanged water was added dropwise over 30 minutes while maintaining the temperature at 80°C to obtain resin dispersion 1, whose stability was evaluated and whose average particle size was measured.

[0083] The abbreviations in Tables 3 to 7 are as follows: S1: Diethylene glycol monobutyl ether S2: Butyl cellosolve S3: Cyclohexanone S4: Methyl ethyl ketone S5: Isopropanol

[0084] <Dispersion Stability> Resin dispersion 1 placed in a container with a lid was placed in a thermostatic chamber at 25°C, and the state was checked every week and evaluated according to the following evaluation criteria: 5: No separation even after 6 months or more (very good) 4: Separation occurred in 3 months or more but less than 6 months (good) 3: Separation occurred in 1 month or more but less than 3 months (sufficient for practical use) 2: Separation occurred in 1 week or more but less than 1 month (sufficient for practical use depending on the conditions) 1: Separation occurred in less than 1 week (not suitable for practical use) Note that if separation occurred in less than 1 week, the dispersion was not evaluated as a coating material, as described below.

[0085] <Average particle size> The average particle size referred to 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 placed in the device, and Resin Dispersion 1 was added so that the TR was 0.95 to 0.8, and 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 cumulative number of measurements was 2. Note that dispersions in which sedimentation occurred immediately after preparation were marked "unmeasurable."

[0086] [Examples 2 to 67] [Comparative Examples 1001 to 1016] Resin dispersions 2 to 67 and 1001 to 1016 were obtained according to the formulations shown in Tables 3 to 7 and in accordance with Example 1, and were evaluated in the same manner. For convenience, Example 1 is shown as Example 45 in Table 5 and Example 56 in Table 6, and Example 32 is shown as Example 39 in Table 5.

[0087] [Example 68] 12.35 parts of phenolic resin solution B-1 was added to 100 parts of resin dispersion 1014 while stirring to obtain resin dispersion 68, whose stability was evaluated and whose average particle size was measured. The stability was "4" and the average particle size was "0.25 μm."

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] The abbreviations in Tables 3 to 7 are as follows: DMAE: dimethylaminoethanol TEA: triethanolamine

[0094] In Comparative Examples 1001 to 1003, which contained polyester resin (A) but did not contain phenolic resin (B), the stability of the dispersion was not practical, whereas the resin dispersions of Examples 1 to 67 according to the present disclosure were confirmed to exhibit excellent stability.

[0095] On the other hand, in Comparative Examples 1006 to 1011, which did not use the phenolic resin (B) specified in the present disclosure, the stability of the resin dispersion was confirmed to be unpractical. Furthermore, when the amount of organic solvent exceeded 130 parts by mass per 100 parts by mass of the total of polyester resin (A) and phenolic resin (B), the stability of the resin dispersion was confirmed to be poor, as shown in Comparative Example 1005. Furthermore, when the amount of the organic solvent was less than 30 parts by mass, the stability of the resin dispersion was confirmed to be poor, as shown in Comparative Example 1004.

[0096] Furthermore, considering that resin dispersion 68 (Example 68), which was prepared by preparing resin dispersion 1014 that did not contain phenolic resin (B) and then adding phenolic resin (B), had improved stability and a smaller average particle diameter than resin dispersion 1014, it is believed that adding phenolic resin (B) after preparing a polyester resin dispersion also has the effect of improving the stability of the dispersion.

[0097] <Liding paint> [Example 101] As shown in Table 8, 1,000 parts by mass of resin dispersion 1 (containing 298 parts by mass of polyester resin and 52.5 parts by mass of phenolic resin) obtained in Example 1 was placed in a container, and while stirring, 1.00 part by mass of Surfynol 420 (acetylene glycol-based nonionic surfactant, manufactured by Nissin Chemical Industry Co., Ltd.) as an additive and 2.10 parts by mass of Nacure 5925 (dodecylbenzenesulfonic acid-based acid catalyst, active ingredient 25%, isopropanol solution) as a catalyst were added to obtain paint 101. Various evaluations were carried out using the methods described below.

[0098] [Examples 102 to 162] Paints 102 to 162 were obtained and evaluated in the same manner as in Example 101 according to the formulations shown in Tables 8 to 12. For convenience, Example 101 is listed as Examples 139 and 145 in Table 10.

[0099] Comparative Examples 2001 to 2005 As shown in Table 10, Resin Dispersions 1012 to 1016 were used instead of Resin Dispersion 1, and paints 2001 to 2005 were obtained in the same manner as in Example 101, and evaluated in the same manner.

[0100] [Comparative Example 2006] 193.4 parts of polyester resin A-1, 145 parts of Flexisolv DBE esters (manufactured by Invista) as an organic solvent, and 145 parts of xylene were placed in a container and heated. Once the temperature reached 120 ° C, stirring was performed. After 2 hours, it was confirmed that the resin had dissolved, and the mixture was cooled to room temperature. Then, while stirring, 68.2 parts of phenolic resin solution 1, 153.4 parts of Flexisolv DBE esters (manufactured by Invista), 191.1 parts of xylene, 52 parts of butyl cellosolve, and 76.8 parts of cyclohexanone were added and mixed, and 1.6 parts of Nacure 5925 was added as a catalyst to obtain water-free paint 2006.

[0101] <Evaluation of paint properties> The paints obtained were used to evaluate the following physical properties. [Paint stability] As in the evaluation of the stability of the resin dispersion, each paint obtained was placed in a thermostatic chamber at 30°C, and the condition was checked every week and evaluated according to the following criteria: 5: No separation even after 6 months or more (very good) 4: Separation after 3 months or more but less than 6 months (good) 3: Separation after 1 month or more but less than 3 months (sufficient for practical use) 2: Separation after 1 week or more but less than 1 month (sufficient for practical use depending on the conditions) 1: Separation after less than 1 week (not practical use)

[0102] <Average Particle Diameter> The average particle diameter was measured in the same manner as in the measurement of the average particle diameter of the resin dispersion.

[0103] [Preparation of Lid Test Panels] Each paint was applied to an aluminum plate having a thickness of 0.26 mm so that the dry mass was 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 equipped with a coating. The resulting test panels for lids were evaluated as follows.

[0104] <Adhesion Strength Evaluation> The test panel was cut into a length of 100 mm and a width of 5 mm to prepare a test plate for measuring adhesion strength. Except for a section 25 mm from the tip of the long piece of the test plate for measuring adhesion strength, two test plates were stacked with the coated surfaces facing inward, nylon tape was sandwiched between them, and heat fusion was performed at 200°C for 30 seconds using the nylon tape as a hot melt adhesive. After spreading out the unbonded portion, a tensile tester (Tensilon) was used to measure the T-peel strength between the cured coating film and the aluminum plate at a pulling rate of 200 mm / min, and the results were evaluated according to the following criteria: 5: T-peel strength of 3 kgf or more (very good); 4: T-peel strength of less than 3 kgf, 2 kgf or more (good); 3: T-peel strength of less than 2 kgf, 1 kgf or more (practical); 2: T-peel strength of less than 1 kgf, 0.4 kgf or more (practical depending on conditions); 1: Less than 0.4 kgf (not practical).

[0105] <Bending Workability Test> <<Initial>> The test panel was cut into a size of 30 mm wide and 50 mm long to prepare a test plate for evaluating bending workability. 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. Next, the test plate was 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 folded portion of the test specimen to completely bend it. Next, the aluminum plates were removed, and the folded portion of the test specimen was immersed in 1% saline solution. Next, a current of 6.0 V was applied between the metal portion of the flat portion of the test specimen that was not immersed in the saline solution and the saline solution for 6 seconds, and the current value was measured. If the coating film has poor workability, the coating film at the folded section will crack, exposing the underlying metal plate and increasing the conductivity, resulting in a higher current value. Evaluation was based on the following criteria: 5: Less than 5 mA (very good) 4: 5 mA or more but less than 10 mA (good) 3: 10 mA or more but less than 20 mA (practical) 2: 20 mA or more but less than 50 mA (practical depending on conditions) 1: 50 mA or more (not practical)

[0106] <<After Aging>> A new test plate for evaluating bending processability was prepared, and left to stand in a thermostatic bath at 37°C for 60 days. After this, the temperature was returned to room temperature (25°C). The test plate was then bent at room temperature in the same manner as in the above-mentioned bending processability test, and the current value was measured. Next, the current value after standing in the thermostatic bath at 37°C for 60 days minus the initial current value was calculated, and the value was evaluated according to the following evaluation criteria: 5: Less than 1 mA (very good) 4: 1 mA or more and less than 5 mA (good) 3: 5 mA or more and less than 10 mA (practical) 2: 10 mA or more and less than 15 mA (practical depending on conditions) 1: 15 mA or more (not practical)

[0107] <Openability Test> <<Before Retort Treatment>> A test panel was cut into a size of 50 mm length x 50 mm width, and a press was used to form irregularities on the coated 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 uncoated side of the test panel along the shape of the opening, and the resulting opening was magnified and visually evaluated using a microscope. Poor openability means that the coating film is more likely to remain around the periphery of the opening, resulting in a large protrusion width into the opening. Good openability refers to a state in which the coating film does not protrude into the opening at all, or if it does protrude, the protrusion width 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 film was less than 100 μm (very good); 4: The maximum width of the protruding coating film was 100 μm or more but less than 200 μm (good). 3: The maximum width of the protruding coating film is 200 μm or more and less than 500 μm (practical use is possible). 2: The maximum width of the protruding coating film is 500 μm or more and less than 800 μm (practical use is possible depending on the conditions). 1: The maximum width of the protruding coating film is 800 μm or more (practical use is not possible).

[0108] <<After Retort Treatment>> 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.

[0109] <Retort durability test> Test panels were immersed in water, an aqueous solution containing 2% by mass of citric acid with a pH of about 2, and an aqueous solution adjusted to pH 12 with sodium hydroxide, and retorted in a retort oven at 125°C for 30 minutes, and the appearance of the coating film was visually evaluated according to the following criteria: 5: No change at all (very good). 4: Some change, but almost no whitening (good). 3: Very slight whitening (sufficient for practical use). 2: Slight whitening (sufficient for practical use depending on conditions). 1: Significant whitening (not suitable for practical use).

[0110] <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 condition of the coating film was observed. Evaluation was based on the following evaluation criteria: 5: No change at all (very good). 4: Some blisters (good). 3: Small blisters observed over the entire surface (suitable for practical use). 2: Large blisters (suitable for practical use depending on conditions). 1: Peeling of the entire coating film (unsuitable for practical use).

[0111] <Overall evaluation> The average value of each evaluation result was calculated by rounding off the results and evaluated on a 5-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 recorded as 1 (unacceptable).

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] The abbreviations in Tables 8 to 12 are as follows: Surfynol 420: acetylene glycol-based nonionic surfactant, manufactured by Nissin Chemical Industry Co., Ltd. Nacure 5925: dodecylbenzenesulfonic acid-based acid catalyst, active ingredient 25%, isopropyl alcohol solution

[0118] As shown in Tables 8 to 12, Examples 101 to 163, which used resin dispersions according to the present disclosure, demonstrated excellent performance. In particular, the effects on openability were significantly greater than those of the comparative examples. The polyester resin (A) in the present disclosure is not uniformly dissolved in the paint, but is dispersed as particles. The polyester resin (A) particles fuse together during drying during coating film formation, and then react with the curing agent to form a cured coating film. It is presumed that the remnants of the interface between the original polyester resin (A) and phenolic resin (B) particles allowed the formation of a cured coating film with excellent openability. The use of a low-polarity resin is considered 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 loads such as bending, slight gaps tend to form between the substrate and the resin. The use of a phenolic resin (B), which functions as both a curing agent and a dispersant, allows low-polarity polyester resins, which are normally not usable as aqueous dispersions, to be used as aqueous dispersions, while achieving high water resistance, adhesion, and bending processability. It is also believed that the phenolic resin (B) surrounds the polyester resin (A), and the functional groups derived from the phenolic resin (B) face outward from the particles, which is believed to result in improved adhesion to the substrate and improved bending processability.

[0119] <Evaluation of can body inner surface coating material> [Example 201] 1,000 parts by mass of resin dispersion 60 obtained in Example 60 was placed in a container, and 750 parts by mass of water, 1.0 part by mass of Surfynol 420, and 2.1 parts by mass of Nacure 5925 were added with stirring to obtain coating material 201, which was then subjected to various evaluations using the methods described below.

[0120] <Evaluation of Paint Properties> [Paint Stability] The same tests as for the lid paint were carried out and evaluated according to the same criteria.

[0121] [Preparation of test panel 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 ２The coating was applied using a bar coater so that the coating would become a uniform layer, and baked in a gas oven at an ambient temperature of 200°C for 2 minutes to prepare test panels for the inner surface of can bodies. The resulting test panels for the inner surface of can bodies were evaluated in the same manner as the test panels for lids, for adhesion strength, bending processability (initial, 37°C, after standing for 60 days), and retort resistance (water, acidic citric acid (pH 2), alkaline NaOH (pH 12)), and further for acetic acid resistance before and after denting as described below. The results are shown in Table 13.

[0122] <Acetic Acid Resistance> <<Before Dent Processing (Untreated)>> As with the end test panels, the can body inner surface test panels were immersed in a 4% acetic acid solution and sealed. After 10 days at 50°C, the condition of the coating film was observed. Evaluation was based on the following evaluation criteria. <<After Dent Processing>> The can body inner surface test panels were cut into 5 cm x 5 cm pieces and processed using a DuPont testing machine under conditions of ¼ inch, a load of 300 g, and a height of 25 cm so that the coated surface was convex. The pieces were 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 evaluation criteria. 5: No change at all (very good). 4: Some blisters (good). 3: Small blisters visible all over (suitable for use). 2: Large blisters present (suitable for use depending on conditions). 1: Coating peeled off completely (unsuitable for use).

[0123] Examples 202 to 208 Comparative Examples 3001 to 3003 As shown in Table 13, paints 202 to 208 and 3001 to 3003 were obtained in the same manner as in Example 201, except that the type of resin dispersion was changed, and were evaluated in the same manner.

[0124] Comparative Example 3003 As shown in Table 13, evaluation was carried out in the same manner as in Example 201, except that paint 2005, which does not contain water, was used instead of paint 201.

[0125]

[0126] As shown in Table 13, Examples 201 to 208, which used resin dispersions according to the present disclosure, showed good performance.

[0127] 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.

[0128] This application claims priority based on Japanese Patent Application No. 2024-098044, filed on June 18, 2024, the disclosure of which is incorporated herein in its entirety by reference.

Claims

1. A resin dispersion containing a polyester resin (A), a phenolic resin (B), a neutralizing agent, an organic solvent, and water, wherein the polyester resin (A) has an acid value of 16 mgKOH / g or less and a number-average molecular weight of 8,000 or more, and the phenolic resin (B) has a weight-average molecular weight of 500 to 2,700, and contains 50 mol % or more of meta-cresol-derived structural units out of a total of 100 mol % of structural units derived from phenolic compounds, and contains 0.01 to 0.2 methylol groups, 0.8 to 1.3 butoxymethyl groups, and a total of 0.15 to 0.5 methylene bonds and dimethylene ether bonds per aromatic ring in the phenolic resin (B), and the resin dispersion contains 30 to 130 parts by mass of the organic solvent per 100 parts by mass of the polyester resin (A) and the phenolic resin (B).

2. The resin dispersion according to claim 1, wherein the mass ratio of the polyester resin (A) to the phenolic resin (B) is polyester resin (A) / phenolic resin (B) = 95 / 5 to 70 / 30.

3. The resin dispersion according to claim 1, wherein the phenolic resin (B) contains structural units derived from para-cresol in a proportion of 50 mol % or less out of a total of 100 mol % of structural units derived from phenolic compounds.

4. The resin dispersion according to claim 1, wherein the polyester resin (A) has structural units derived from one or more polycarboxylic acid components selected from the group consisting of terephthalic acid, isophthalic acid, sebacic acid, and trimellitic acid (anhydride), as well as structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, ethylene glycol, 1,4-butanediol, and trimethylolpropane, and wherein, out of 100 mol % of the structural units derived from the polyhydric alcohol components of the polyester resin (A), 20 to 99.9 mol % of structural units derived from one or more polyhydric alcohol components selected from the group consisting of 1,2-propanediol, 1,4-cyclohexanedimethanol, and 2-methyl-1,3-propanediol and 0.1 to 80 mol % of structural units derived from one or more polyhydric alcohol components selected from the group consisting of ethylene glycol, 1,4-butanediol, and trimethylolpropane.

5. The resin dispersion according to claim 1, wherein the water accounts for 40 to 90% by mass of the total of the water and the organic solvent, 100% by mass.

6. A paint containing the resin dispersion according to any one of claims 1 to 5.

7. A can lid having a metal substrate coated with the paint according to claim 6.

8. A can body having a metal substrate coated with the paint according to claim 6.

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