Water-based paint composition, painting method, painted film, painted article, and method for forming painted film

Abstract

The present invention relates to an aqueous coating composition containing a water dispersion of a crystalline acrylic-modified polyester resin (A) having a melting point of 125°C or higher.

Description

Technical Field

[0001] This invention relates to water-based coating compositions, coating methods, coating films, coated articles, and methods for forming coating films. Background Technology

[0002] As coatings for tank bodies, from the viewpoint of coating performance such as corrosion resistance, various coating compositions such as epoxy resins, polyvinyl chloride resins, and polyester resins have been used.

[0003] Coating compositions that use epoxy resins, which are made from raw materials containing bisphenol A (BPA) and the like, as the base resin are generally widely used.

[0004] From an environmental perspective, it is desirable to use coating compositions for tanks that do not contain bisphenol A (BPA) (including raw materials that may contain residual levels of BPA).

[0005] Therefore, as a waterborne coating composition with low BPA leaching, Patent Document 1 discloses a waterborne resin composition, which is obtained by neutralizing "an acrylic-modified epoxy resin obtained by partially esterifying an aromatic epoxy resin (A), an aromatic epoxy resin with modified ends (B), and an acrylic resin (C) containing carboxyl groups in an organic solvent" with an alkali and dispersing it in an aqueous medium. The acrylic resin (C) containing carboxyl groups in this waterborne resin composition is an acrylic resin (D) containing carboxyl groups with a Tg of 100°C or higher, or an acrylic resin (E) containing carboxyl groups with a Tg of less than 100°C, or a mixture thereof.

[0006] Furthermore, Patent Document 2 discloses a water-based coating composition that is safe for human use. This water-based coating composition is formed by grafting and polymerizing "an acrylic-modified polyester resin (C) containing a polymeric unsaturated monomer component (B) having a number average molecular weight of 2,000 to 50,000 with olefinic double bonds at the resin end" onto a polyester resin (A) stably dispersed in an aqueous medium, and "a β-hydroxyalkylamide crosslinking agent (D) having a specific structural formula".

[0007] In addition, Patent Document 3 discloses a water-based coating composition for coating a can body, which comprises core-shell type acrylic resin particles (A) consisting of a shell and a cross-linked core, and a methyl phenolic resin (C1) and / or an amino resin (C2), and does not contain resins manufactured using BPA or raw materials containing BPA.

[0008] Existing technical documents

[0009] [Patent Literature]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2004-331694

[0011] [Patent Document 2] Japanese Patent Application Publication No. 2003-026992

[0012] [Patent Document 3] Japanese Patent Application Publication No. 2016-113561

[0013] The problem that the invention aims to solve

[0014] In response, in recent years, laws and regulations have been continuously enacted to expand and tighten the scope of regulated substances, especially in Europe and the United States. Specifically, not only BPA, but also styrene, formaldehyde, isocyanates, and other substances can be considered as regulated substances.

[0015] In view of the above, the waterborne coating composition in Patent Document 1, because its base resin skeleton is an aromatic epoxy resin containing BPA, raises concerns about its potential harm to the environment and human health. Furthermore, the waterborne coating composition in Patent Document 3, because it contains phenolic resin or styrene, cannot be used under the expanded legal regulations governing the aforementioned controlled substances.

[0016] The current situation is that with the increase in regulated substances, the freedom to choose raw materials that can be used in coating compositions is becoming increasingly limited.

[0017] Of these, the waterborne coating composition in Patent Document 2 is safe for human use. However, since the aforementioned waterborne coating composition contains a considerable amount of β-hydroxyalkylamide crosslinking agent, it is difficult to achieve both good coating properties and water resistance. Furthermore, better corrosion resistance is desired.

[0018] Therefore, the problem to be solved by the present invention is to provide a waterborne coating composition with excellent coating properties such as corrosion resistance, processability and boiling resistance without using raw materials containing legally regulated substances such as bisphenol A.

[0019] In addition, the subject also includes providing a coating method, coating film, coated article, and coating film formation method using the above-mentioned water-based coating composition.

[0020] Methods for solving problems

[0021] In order to solve the aforementioned problems, the inventors conducted intensive research on developing waterborne coating compositions free from BPA and legally regulated substances such as phenolic resins and crosslinking agents such as polyisocyanate compounds. Focusing on crystallization, they considered crystallized polyester resins. It was understood that good processability could be achieved by using crystallized polyester resins. Furthermore, further research revealed that crystalline acrylic-modified polyester resins showed promise from the viewpoint of water dispersibility in the coating state. It was discovered that this also allowed for further improvement in corrosion resistance and boiling resistance, thus solving the aforementioned problems and completing the present invention.

[0022] In other words, the key points of this invention are as follows.

[0023] [1]. A water-based coating composition comprising an aqueous dispersion of a crystalline acrylic-modified polyester resin (A),

[0024] The crystalline acrylic modified polyester resin (A) has a melting point of 125°C or higher.

[0025] [2]. The heat of fusion of the water-based coating composition as described in [1] above, obtained by heating and crystallizing it, is 1.0~17 J / g.

[0026] [3]. The water-based coating composition described in [1] or [2] above, when heated to crystallize, produces a coating film with a storage modulus of 3.2 × 10⁻⁶ at 50°C. 7 ~2.4×10 8 Pa.

[0027] [4]. The waterborne coating composition as described in any of [1] to [3] above, wherein the ratio of the crystalline acrylic modified polyester resin (A) expressed by (a1) / (a2) is in the range of 60 / 40 to 90 / 10, wherein (a1) / (a2) is the mass solids ratio of the polyester resin component (a1) to the acrylic resin component (a2).

[0028] [5]. The waterborne coating composition as described in any of [1] to [4] above, wherein the crystalline acrylic modified polyester resin (A) has an acid value of 180 to 400 mg KOH / g and a glass transition temperature of 20 to 160 °C.

[0029] [6]. The aqueous coating composition as described in any of [1] to [5] above, wherein the aqueous dispersion of the crystalline acrylic-modified polyester resin (A) contains an organic solvent (a3), and

[0030] The content of the organic solvent (a3) ​​is 50 parts by mass or more relative to the total solid content of the crystalline acrylic modified polyester resin (A) of 100 parts by mass.

[0031] [7]. The waterborne coating composition as described in any of [1] to [6] above further contains a β-hydroxyalkylamide compound (B).

[0032] [8]. A water-based coating composition as described in any of [1] to [7] above, used in a can.

[0033] [9]. A coating method comprising coating an object with the waterborne coating composition described in any one of [1] to [8] above.

[0034]

[10] . A coating film is formed by applying the aqueous coating composition described in any one of [1] to [8] above onto a substrate and crystallizing it.

[0035]

[11] . A coated article comprising a substrate and a coating film formed on the substrate.

[0036] The coating film is formed by applying any of the above-described water-based coating compositions [1] to [8] and crystallizing them.

[0037]

[12] . A method for forming a coating film, comprising, in sequence:

[0038] Apply the water-based coating composition described in any one of [1] to [8] above to the object to be coated.

[0039] To cause the water dispersion in the water-based coating composition to evaporate, and

[0040] Dry at 70~140℃ for 10~60 minutes.

[0041]

[13] . A coating film obtained by sequentially performing the following steps:

[0042] Apply the water-based coating composition described in any one of [1] to [8] above to the object to be coated.

[0043] To cause the water dispersion in the water-based coating composition to evaporate, and

[0044] Dry at 70~140℃ for 10~60 minutes.

[0045]

[14] . A coated article comprising a substrate and a coating film formed on the substrate.

[0046] The coating is obtained through the following processes in sequence:

[0047] The water-based coating composition described in any one of [1] to [8] above is applied.

[0048] To cause the water dispersion in the water-based coating composition to evaporate, and

[0049] Dry at 70~140℃ for 10~60 minutes.

[0050] Invention Effects

[0051] The water-based coating composition of this embodiment, without using raw materials containing legally regulated substances, can produce a coating film with excellent properties such as corrosion resistance, processability, and resistance to boiling. Therefore, the above-described water-based coating composition is particularly suitable for tank applications.

[0052] In addition, an excellent coating method, coating film, coated article, and coating film formation method using the above-described water-based coating composition are also provided. Detailed Implementation

[0053] The present invention will be described in detail below, but the present invention is not limited to the following embodiments. Any changes may be made to implement the invention without departing from the spirit of the invention.

[0054] In this specification, the symbol "~" indicating a numerical range is used to indicate that the values ​​before and after it are included in the lower and upper limits. Furthermore, in this specification, parts by mass and parts by weight, and mass% and weight% are synonymous.

[0055] Waterborne Coating Compositions

[0056] The aqueous coating composition of this embodiment contains an aqueous dispersion of a crystalline acrylic modified polyester resin (A), and the melting point of the crystalline acrylic modified polyester resin (A) is 125°C or higher.

[0057] The waterborne coating composition of this embodiment can achieve good processability because the acrylic modified polyester resin has sufficient crystallinity. Furthermore, since the crystalline acrylic modified polyester resin with a melting point of 125°C or higher is used as the base resin composition, it can also achieve coating performance with so-called good corrosion resistance or excellent boiling resistance.

[0058] Specifically, because the polyester resin is modified with acrylic acid, it exhibits excellent water dispersibility, and the resulting waterborne coating composition also demonstrates excellent stability. Furthermore, although details will be discussed later, it also contains β-hydroxyalkylamide compounds as crosslinking agents, which further enhances corrosion resistance.

[0059] Therefore, the water-based coating composition of this embodiment does not contain raw materials that are "substances that are widely regulated by law, such as bisphenol A," yet it yields a coating film with excellent corrosion resistance, processability, and boiling resistance, and also exhibits excellent stability as a water-based coating composition. Therefore, it is particularly suitable for tank applications.

[0060] The water-based coating composition of this embodiment will now be described in detail.

[0061] <Crystall Acrylic Modified Polyester Resin (A)>

[0062] The aqueous dispersion of the crystalline acrylic modified polyester resin (A) in this embodiment is a dispersion in which the crystalline acrylic modified polyester resin (A) exists in a medium in which water is the main component.

[0063] Here, in this specification, the main component refers to the component that has the highest content among the components constituting the medium. That is, the above-mentioned medium is a medium in which water has the highest content among its components. In addition, the above-mentioned medium with water as the main component is sometimes referred to as an "aqueous medium".

[0064] In this specification, acrylic modified polyester resin is described as "crystalline," meaning that in the differential calorimetry curve measured by differential scanning calorimetry (DSC), the endothermic change is not stepwise, but rather has a distinct endothermic peak.

[0065] In this specification, "obvious endothermic peak" specifically refers to a peak value with a half-width of less than 35°C when measured by DSC at a heating rate of 20°C / min.

[0066] The crystalline acrylic-modified polyester resin (A) of this embodiment has a melting point of 125°C or higher, preferably 125 to 180°C. From the viewpoint of obtaining good resistance to boiling, a melting point of 125°C or higher is acceptable, but 130°C or higher, or 140°C or higher is also acceptable. Furthermore, while there is no particular limitation on the upper limit, from the viewpoint of obtaining an aqueous dispersion with high dispersibility, a melting point of 180°C or lower is preferred, more preferably 170°C or lower, and even more preferably 160°C or lower.

[0067] In this specification, the melting point of the crystalline acrylic modified polyester resin (A) is the value determined using a differential scanning calorimeter (Hitachi High-Tech, DSC600) and by the following steps.

[0068] The sample is prepared according to the following steps.

[0069] First, an aqueous dispersion of crystalline acrylic-modified polyester resin (A) was coated onto the substrate, and after the solvent evaporated, it was dried at 110°C for 30 minutes. Then, a 4.5 mm diameter sample was cut from each substrate, placed in a 5.2 mm diameter aluminum crucible, and then covered with a 5.0 mm diameter lid and sealed with rolled edges. This sample was used for testing.

[0070] Using a differential scanning calorimeter (Hitachi High-Tech, DSC600), the DSC curve of the sample was measured as the temperature increased from -30°C to 200°C at a rate of 20°C / min. The peak with a significant endothermic peak after the glass transition temperature was taken as the melting point.

[0071] The crystalline acrylic-modified polyester resin (A) of this embodiment can be obtained by modifying acrylic acid into crystalline polyester resin, and the acrylic acid also has crystallinity after modification.

[0072] The crystalline acrylic modified polyester resin (A) of this embodiment is obtained by graft polymerization of a polymeric unsaturated monomer component containing a carboxyl-containing polymeric unsaturated monomer, for example, a crystalline polyester resin containing olefinic double bonds.

[0073] The aforementioned crystalline polyester resins containing olefinic double bonds are mainly esters of polyacid and polyol components.

[0074] The polyacid compounds mentioned above are compounds containing two or more carboxyl groups in one molecule, and also include alkyl esters, acid anhydrides and acyl chlorides of polycarboxylic acid compounds.

[0075] Furthermore, the polyol compounds mentioned above refer to compounds having two or more hydroxyl groups in one molecule.

[0076] Examples of the aforementioned polycarboxylic acid compounds include, for example, divalent aliphatic carboxylic acids such as oxalic acid, succinic acid, malonic acid, adipic acid, β-methyl adipic acid, pimelic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, maleic acid, fumaric acid, citrate, diethanolic acid, cyclohexane-3,5-diene-1,2-dicarboxylic acid, malic acid, citric acid, hexahydroterephthalic acid, tartaric acid, and mucinic acid; phthalic acid, isophthalic acid, and terephthalic acid. Aromatic carboxylic acids with a valence of divalent, such as formic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, terephthalic acid, isophthalic acid, terephthalic acid, phthalic acid, biphenyl-p,p'-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, and dodecenylsuccinic acid; and aromatic carboxylic acids with a valence of trivalent or higher, such as trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid.

[0077] From the viewpoint of improving the crystallinity of crystalline polyester resins, it is preferable that the polycarboxylic acid compound contains a divalent aliphatic carboxylic acid. Furthermore, the polycarboxylic acid compound may be used alone or in combination with two or more compounds.

[0078] Examples of the aforementioned polyol compounds include divalent straight-chain aliphatic alcohols such as ethylene glycol, propylene glycol (also known as propanediol), butanediol, diethylene glycol, hexanediol, octanediol, decanediol, and dodecanediol; divalent alicyclic alcohols such as cyclohexanediol; divalent aromatic alcohols; trivalent or higher aliphatic alcohols such as glycerol and pentaerythritol; and alcohols with a guanidine skeleton such as hexamethylolmelamine, tetramethylolbenzoguanamine, and tetraethanolylbenzoguanamine.

[0079] From the viewpoint of improving the crystallinity of crystalline polyester resins, the polyol compound preferably contains a divalent aliphatic alcohol, more preferably a divalent linear aliphatic alcohol. Furthermore, the polyol compound may be used alone or in combination with two or more compounds.

[0080] The esterification reaction between polyacid components and polyol components can be carried out by known methods.

[0081] In addition, esterification can also be carried out by replacing the polybasic acid with a lower alkyl ester of the polybasic acid (such as methyl ester, ethyl ester, etc.) through transesterification. The transesterification reaction of the two components can be carried out using known methods.

[0082] As a method for introducing hydroxyl groups into crystalline polyester resin, firstly, a crystalline polyester resin containing hydroxyl groups is synthesized, and then the obtained crystalline polyester resin containing said hydroxyl groups is reacted with acid anhydride to half-esterify it, thereby forming a crystalline polyester resin containing carboxyl and hydroxyl groups.

[0083] In addition, a crystalline polyester resin containing carboxyl groups can be synthesized first, and then the above-mentioned alcohol components can be added to produce a crystalline polyester resin containing hydroxyl groups.

[0084] As a method for introducing carboxyl groups into crystalline polyester resin, one approach is to first synthesize a crystalline polyester resin containing hydroxyl groups, and then react a polybasic acid with the hydroxyl groups in the resulting crystalline polyester resin to introduce carboxyl groups into the resin, thereby producing a crystalline polyester resin containing carboxyl groups.

[0085] Examples of the aforementioned polybasic acids include maleic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, and tetrahydrophthalic anhydride.

[0086] One method for synthesizing crystalline polyester resins containing olefinic double bonds is to synthesize them by using unsaturated polyacids with olefinic double bonds as raw materials.

[0087] Examples of unsaturated polybasic acids include fumaric acid, maleic acid, itaconic acid, citraconic acid, their lower alkyl esters, and their anhydrides.

[0088] Although it is fine to introduce polybasic acids with olefinic double bonds from the very beginning of the reaction, the branching caused by the grafting polymerization of acrylic acid monomers at the beginning can lead to easy gelation and a tendency to deteriorate stability.

[0089] Therefore, from the viewpoint of manufacturing stability, a method in which a compound containing olefinic double bonds is reacted with the hydroxyl or carboxyl groups of the saturated crystalline polyester resin after the synthesis of a saturated crystalline polyester resin that does not contain olefinic double bonds is preferred. However, this does not preclude the introduction of the aforementioned polybasic acid in the initial form of the reaction.

[0090] As a method of synthesizing a saturated crystalline polyester resin that does not contain olefinic double bonds by reacting a compound containing olefinic double bonds with the saturated crystalline polyester resin, examples include the following methods 1 and 2.

[0091] Method 1. After synthesizing a saturated crystalline polyester resin that does not contain olefinic double bonds, an anhydride of a polybasic acid containing olefinic double bonds is added, preferably at 100~160°C, to add it to the hydroxyl group in the saturated crystalline polyester resin, thereby introducing olefinic double bonds into the end portion of the saturated crystalline polyester resin.

[0092] Method 2. After synthesizing a saturated crystalline polyester resin that does not contain olefinic double bonds, a compound having olefinic double bonds and epoxy groups is added, preferably at 100~160°C, to add the compound to the carboxyl group of the saturated crystalline polyester resin, thereby introducing olefinic double bonds into the end portion of the saturated crystalline polyester resin.

[0093] In method 2 above, compounds having olefinic double bonds and epoxy groups can be listed as glycidyl acrylate (meth)acrylate, allyl glycidyl ether, β-methyl glycidyl acrylate (meth)acrylate, 3,4-epoxycyclohexyl methyl acrylate (meth)acrylate, etc.

[0094] Furthermore, the term "(meth)acrylate" in this specification refers to "at least one of acrylate and methacrylate". Additionally, the term "(meth)acrylamide" refers to "at least one of acrylamide and methacrylamide".

[0095] In this embodiment, from the viewpoint of shortening the reaction time, method 2 is preferred among methods 1 and 2 described above.

[0096] In the above, from the viewpoint of the manufacturability and retortability of the aqueous dispersion, it is desirable for the melting point temperature of the saturated crystalline polyester resin to be 125~170℃, and especially desirable to be in the range of 125~160℃.

[0097] Furthermore, from the viewpoint of manufacturability and corrosion resistance of the aqueous dispersion, the glass transition temperature of the above-mentioned saturated crystalline polyester resin is preferably in the range of 20~55°C, especially 30~55°C.

[0098] Furthermore, from the viewpoint of manufacturability and corrosion resistance of aqueous dispersions, the number average molecular weight of the aforementioned saturated crystalline polyester resin is preferably in the range of 10,000 to 35,000, and especially in the range of 14,000 to 30,000.

[0099] Furthermore, from the viewpoints of manufacturability and corrosion resistance of aqueous dispersions, the acid value of the aforementioned saturated crystalline polyester resin is preferably in the range of 0 to 15 mg KOH / g, and especially in the range of 5.0 to 10 mg KOH / g.

[0100] In this embodiment, the saturated crystalline polyester resin is more preferably such that two or more of the following are within the range of the above-mentioned range: melting point temperature, glass transition temperature, number-average molecular weight, and acid value; more preferably, three or more of the following are within the above-mentioned range; and even more preferably, all four of the following are within the above-mentioned range.

[0101] As a polymerizable unsaturated monomer used in the synthesis of crystalline acrylic modified polyester resin, a polymerizable unsaturated monomer containing a carboxyl group, such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, etc., can be used as an essential component. Other polymerizable unsaturated monomers may be used if necessary.

[0102] Other polymerizable unsaturated monomer components include, for example, alkyl esters of acrylic acid or methacrylic acid having 1 to 18 carbon atoms, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, benzyl methacrylate, stearyl methacrylate, cetyl methacrylate, etc.; cyclohexyl methacrylate, isobornyl methacrylate; aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, etc.; hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxypentyl methacrylate, etc. Hydroxyalkyl methacrylates such as hydroxyhexyl methacrylate, and hydroxyl-containing polymerizable unsaturated monomers such as caprolactone-modified alkyl methacrylates formed by reacting 1 to 5 moles of ε-caprolactone with 1 mole of said hydroxyalkyl methacrylate via a ring-opening addition reaction; acrylamide monomers such as (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, N-n-propoxymethyl (meth)acrylamide, N-isopropoxymethyl (meth)acrylamide, N-n-butoxymethyl (meth)acrylamide, N-sec-butoxymethyl (meth)acrylamide, N-tert-butoxymethyl (meth)acrylamide, etc.; acrylonitrile, methacrylonitrile, vinyl acetate, ethylene, butadiene, etc.

[0103] In light of the above, considering potential future legal regulations or the impact on the environment and human health, it is preferable not to use styrene or α-methylstyrene.

[0104] Although polymerizable unsaturated monomers can be used alone or in combination of two or more, since the resulting crystalline acrylic modified polyester resin is water-based through the introduction of carboxyl groups, it is preferable to adjust the amount of polymerizable unsaturated monomers containing carboxyl groups so that the acid value of the crystalline acrylic modified polyester resin is in the range of 15~100 mgKOH / g, especially 30~80 mgKOH / g.

[0105] As a method for synthesizing crystalline acrylic-modified polyester resin by polymerizing a crystalline polyester resin containing olefinic double bonds with a polymerizable unsaturated monomer, free radical polymerization in an organic solvent can be utilized. For example, the method can involve using the aforementioned crystalline polyester resin containing olefinic double bonds with a polymerizable unsaturated monomer and a free radical polymerization initiator, and further, if necessary, adding a chain transfer agent, followed by heating. Examples of heating temperatures include 90 to 120°C. Furthermore, examples of heating times include 1 to 5 hours.

[0106] As the polymerization initiator mentioned above, polymerization initiators such as organic peroxide-based and azo-based initiators can be used.

[0107] Examples of organic peroxide-based polymerization initiators include benzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, di-tert-butylperoxide, tert-butylperoxybenzoate, and tert-pentylperoxy-2-ethylhexanoate.

[0108] Examples of azo polymerization initiators include azobisisobutyronitrile (AIO) and azobisdimethylvalerate (ADM).

[0109] Examples of chain transfer agents include α-methylstyrene dimers and thiols.

[0110] The mass solids ratio of the crystalline polyester resin to the polymerizable unsaturated monomer, that is, the mass solids ratio of the polyester resin component (a1) to the acrylic resin component (a2) in the crystalline acrylic modified polyester resin (A) of this embodiment, expressed as (a1) / (a2), is preferably in the range of 60 / 40 to 90 / 10, more preferably in the range of 60 / 40 to 85 / 15 or 65 / 35 to 90 / 10, and even more preferably in the range of 65 / 35 to 85 / 15.

[0111] Here, the proportion of the polyester resin component (a1) relative to the total of the polyester resin component (a1) and the acrylic resin component (a2) is preferably 60% by mass or more, more preferably 65% ​​by mass or more, from the viewpoint of obtaining good corrosion resistance or boiling resistance. Furthermore, from the viewpoint of processability, the above proportion is preferably 90% by mass or less, more preferably 85% by mass or less.

[0112] Furthermore, from the viewpoint of dispersibility and corrosion resistance, the acrylic resin component (a2) of the crystalline acrylic modified polyester resin (A) preferably satisfies at least one of high acid value and high glass transition temperature (Tg), and more preferably satisfies both high acid value and high Tg.

[0113] The acid value of the above-mentioned acrylic resin component (a2) is preferably 180~400 mgKOH / g, and the glass transition temperature is preferably 20~160℃. More preferably, both the acid value and the glass transition temperature are 180~400 mgKOH / g and 20~160℃.

[0114] Here, the acid value is preferably 180 mg KOH / g or higher, more preferably 200 mg KOH / g or higher. Furthermore, the acid value is preferably 400 mg KOH / g or lower, more preferably 350 mg KOH / g or lower.

[0115] Furthermore, the glass transition temperature is preferably 20°C or higher, more preferably 40°C or higher. Additionally, the glass transition temperature is preferably 160°C or lower, more preferably 150°C or lower.

[0116] The crystalline acrylic modified polyester resin (A) of this embodiment preferably has an acid value of 30~120 mgKOH / g and a glass transition temperature of 20~80℃, more preferably having an acid value of 30~120 mgKOH / g and a glass transition temperature of 20~80℃.

[0117] The acid value of the crystalline acrylic modified polyester resin (A) in this embodiment is preferably 30 mg KOH / g or more, and more preferably 120 mg KOH / g or less, and even more preferably 80 mg KOH / g or less.

[0118] Furthermore, the glass transition temperature of the crystalline acrylic modified polyester resin (A) in this embodiment is preferably 20°C or higher, more preferably 30°C or higher, and preferably 80°C or lower, more preferably 70°C or lower.

[0119] <Aqueous Dispersion>

[0120] The aqueous coating composition of this embodiment comprises an aqueous dispersion of the above-mentioned crystalline acrylic modified polyester resin (A). The above-mentioned aqueous dispersion is obtained by neutralizing and dispersing the synthesized crystalline acrylic modified polyester resin (A) with water.

[0121] Amines or ammonia are preferred as neutralizing agents used in neutralization.

[0122] Examples of the aforementioned amines include triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, and morpholine. Among these, triethylamine and dimethylethanolamine are particularly preferred.

[0123] While the degree of neutralization of the crystalline acrylic-modified polyester resin (A) is not particularly limited, from the viewpoint of manufacturing aqueous dispersions, a degree of neutralization in the range of, for example, 0.3 to 1.0 equivalents relative to the carboxyl groups in the crystalline acrylic-modified polyester resin (A) is preferred, especially in the range of 0.5 to 1.0 equivalents. Furthermore, the above amount is sometimes referred to as the neutralization equivalent.

[0124] In the aqueous dispersion of this embodiment, the aqueous medium in which the crystalline acrylic-modified polyester resin (A) is dispersed needs to dissolve the crystalline acrylic-modified polyester resin (A) during the synthesis process. Therefore, the aqueous dispersion of this embodiment preferably contains, in addition to the crystalline acrylic-modified polyester resin (A) and water, an organic solvent (a3). That is, the aqueous medium of this embodiment is preferably a mixture of water and organic solvent (a3).

[0125] As for the aforementioned organic solvent (a3), any organic solvent that does not impede the stability of the crystalline acrylic-modified polyester resin (A) in an aqueous medium may be used.

[0126] As the organic solvent (a3) ​​mentioned above, alcohol-based solvents, cellosol solvents, aprotic polar solvents, amide-based solvents, carbitol-based solvents, etc. are preferred.

[0127] Specific examples of the aforementioned organic solvents (a3) ​​include alcohol solvents such as n-butanol, cellosol solvents such as ethylene glycol monobutyl ether (butyl cellosol), ethylene glycol monoisopropyl ether, ethylene glycol monomethyl ether, and propylene glycol monomethyl ether, aprotic polar solvents such as N-methyl-2-pyrrolidone, amide solvents such as 3-butoxy-N,N-dimethylpropaneamide and 3-methoxy-N,N-dimethylpropaneamide, carbitol solvents such as diethylene glycol monoethyl ether, and other amphiphilic solvents.

[0128] Furthermore, as an organic solvent (a3), inert organic solvents that are not miscible with water, other than those mentioned above, can be used in a range that does not impede the stability of the crystalline acrylic-modified polyester resin (A) in an aqueous medium.

[0129] Specifically, examples of such organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, and ketone solvents such as methyl ethyl ketone and cyclohexanone.

[0130] From the perspective of the solubility and dispersibility of crystalline polyesters, N-methyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropaneamide, cyclohexanone, and ethylene glycol monobutyl ether (butyl solvent) are preferred organic solvents.

[0131] In the waterborne coating composition of this embodiment, the content of organic solvent (a3) ​​relative to 100 parts by mass of the total solid content of the crystalline acrylic modified polyester resin (A) is preferably, for example, 50 parts by mass or more, more preferably 50 to 200 parts by mass. Here, from the viewpoint of the solubility and dispersibility of the crystalline polyester, the content of the above-mentioned organic solvent (a3) ​​is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 100 parts by mass or more. Furthermore, from the viewpoint of the storage stability of the resulting waterborne coating composition, the above-mentioned content is preferably 200 parts by mass or less.

[0132] Furthermore, when the aqueous dispersion of this embodiment contains two or more organic solvents (a3), it is preferable that their total content is within the range described above.

[0133] To obtain the aqueous dispersion of this embodiment, the crystalline acrylic-modified polyester resin (A) can be neutralized and dispersed in an aqueous medium using conventional methods. Examples include slowly adding the crystalline acrylic-modified polyester resin (A) to an aqueous medium containing a neutralizing agent while stirring, neutralizing the crystalline acrylic-modified polyester resin (A) with a neutralizing agent, and then adding the neutralized product to an aqueous medium while stirring, or adding the neutralized product to an aqueous medium.

[0134] When an aqueous dispersion contains an organic solvent (a3), from the viewpoint of reducing the amount of organic solvent (a3), a dispersion method by pressure emulsification can also be used.

[0135] Pressurized emulsification is a method in which the aqueous and oil phase components are pre-emulsified, if necessary, by using a homogenizer, and then, under pressure, the emulsion with fine emulsion particles is obtained by using the high shear force of a high-pressure homogenizer such as a Manton Gaulin high-pressure homogenizer, a Freund's crusher, or a high-pressure microfluidizer.

[0136] When obtaining an aqueous dispersion of crystalline acrylic-modified polyester resin (A) by pressure emulsification, it is preferable to prepare the aqueous dispersion by adding a mixture of water, an organic solvent, and a neutralizing agent, and then stirring the mixture under pressure. The pressure applied during this process is preferably 0.40 MPa or higher, more preferably 0.45 MPa or higher, and even more preferably 0.50 MPa or higher. While there is no particular limitation on the upper limit of the pressure, it can be, for example, 0.9 MPa or lower.

[0137] Water dispersion under pressure can be performed by adding the above mixture dropwise if necessary. The preferred temperature conditions are, for example, 110-150°C. Here, the preferred temperature conditions are 110°C or higher, more preferably 125°C or higher, even more preferably 135°C or higher, and further preferably 150°C or lower.

[0138] The dispersion time described above is preferably, for example, 20 to 60 minutes. Here, the dispersion time is preferably 20 minutes or more, more preferably 30 minutes or more, and further preferably 60 minutes or less, more preferably 50 minutes or less.

[0139] The stirring speed described above is preferably, for example, 3000 to 6000 rpm. Here, the stirring speed is preferably 3000 rpm or more, more preferably 4000 rpm or more, and further preferably 6000 rpm or less, more preferably 5000 rpm or less.

[0140] In addition, water dispersion under pressure can be carried out by adding the above mixture dropwise if necessary, and more preferably by stirring at 3000 to 6000 rpm for 20 to 150°C for 20 to 60 minutes.

[0141] The average particle size of the main peak in the aqueous dispersion of the crystalline acrylic modified polyester resin (A) of this embodiment is preferably, for example, 100 to 400 nm. Here, from the viewpoint of the storage properties of the coating, the above-mentioned average particle size is preferably 100 nm or more, more preferably 150 nm or more, and further preferably 400 nm or less, more preferably 300 nm or less, and even more preferably 250 nm or less.

[0142] The average particle size of the aforementioned main peak is the average particle size based on the number of particles measured by a particle size measuring device, such as the particle size distribution meter ELSZ-2000 (manufactured by Otsuka Electronics Co., Ltd.).

[0143] <β-hydroxyalkylamide compound (B)>

[0144] In today's world, with an increasing number of compounds becoming unusable due to legal restrictions, the water-based coating composition of this embodiment allows the use of harmless compounds. For example, from the viewpoint of food contact applications, the water-based coating composition of this embodiment may contain a β-hydroxyalkylamide compound (B) if necessary to improve corrosion resistance.

[0145] The β-hydroxyalkylamide compound (B) of this embodiment is a compound having an amide group (-CONR-, R represents a hydrogen atom or a hydrocarbon group) and a hydroxyl group (-OH), with the hydroxyl group present at the β-position and having an alkyl chain. The above-mentioned β-hydroxyalkylamide compound (B) is a compound having a functional group that can react with the carboxyl group contained in the crystalline acrylic modified polyester resin (A), and examples of compounds represented by the following general formula (1) are provided.

[0146]

[0147] (In equation (1), R) 1 R represents a hydrogen atom, methyl, or ethyl group. 2 Indicates an alkyl group with 1 to 5 carbon atoms or HOCH(R) 1 CH2-, where A represents a divalent hydrocarbon group, and multiple R groups exist. 1 R 2 They can be the same or different.

[0148] Examples of the aforementioned β-hydroxyalkylamide compounds (B) include Primid (registered trademark) XL-522, Primid (registered trademark) SF-4510, Primid (registered trademark) QM-1260 (all manufactured by EMS-GRILTECH), N,N,N',N'-tetra(2-hydroxyethyl)hexamethylenediamide, etc.

[0149] When the waterborne coating composition of this embodiment further contains a β-hydroxyalkylamide compound (B), its blending amount (content) is preferably 0.1 to 6 parts by mass relative to 100 parts by mass of the total solid content of the crystalline acrylic modified polyester resin (A). Here, from the viewpoint of corrosion resistance, the above-mentioned blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and further preferably 6 parts by mass or less, more preferably 5 parts by mass or less.

[0150] <Other arbitrary ingredients>

[0151] The aqueous coating composition of this embodiment may further contain, if necessary, conventionally known raw materials such as defoamers, surfactants, lubricants, waxes, viscosity modifiers, nucleating agents, and pigments. Furthermore, these raw materials may be used in combination as appropriate.

[0152] Examples of defoamers include acrylic, vinyl ether, and dimethylpolysiloxane compounds, and two or more of them may be used together.

[0153] Examples of nucleating agents include inorganic and organic types.

[0154] As nucleating agents for the aforementioned inorganic systems, talc, calcium carbonate, mica, boron nitride, synthetic silica, silicates, silicon dioxide, kaolin, carbon black, zinc oxide, montmorillonite, clay minerals, basic magnesium carbonate, quartz powder, glass fiber, glass powder, diatomaceous earth, dolomite powder, titanium dioxide, zinc oxide, antimony oxide, barium sulfate, calcium sulfate, aluminum oxide, calcium silicate, boron nitride, etc., can be used. One or more of these can be used together.

[0155] From the viewpoint of coating transparency, talc and silica are preferred.

[0156] Examples of nucleating agents for the above-mentioned organic systems include (1) to (10) below. One type may be used, or two or more types may be used together.

[0157] (1) Organic carboxylic acids: Octyl acid, octanoic acid, methyl benzoic acid, heptanoic acid, nonanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, wax acid, lignite acid, beeswax acid, benzoic acid, p-tert-butylbenzoic acid, terephthalic acid, monomethyl terephthalate, isophthalic acid, monomethyl isophthalate, rosin acid, 12-hydroxystearic acid, cholic acid, etc.

[0158] (2) Alkali metal salts and alkaline earth metal salts of organic carboxylic acids: Alkali metal salts and alkaline earth metal salts of organic carboxylic acids as described in (1) above.

[0159] (3) High molecular weight organic compounds containing carboxyl groups: Carboxyl-containing polyethylene obtained by oxidation of polyethylene, carboxyl-containing polypropylene obtained by oxidation of polypropylene, copolymers of olefins such as ethylene, propylene, and butene-1 with acrylic acid or methacrylic acid, copolymers of styrene with acrylic acid or methacrylic acid, copolymers of olefins with maleic anhydride, and metal salts of copolymers of styrene with maleic anhydride, etc.

[0160] (4) Aliphatic carboxylic amides: oleamide, stearamide, erucamide, behenamide, N-oleopalmitamide, N-stearylerucamide, N,N'-ethylenebis(stearamide), N,N'-methylenebis(stearamide), hydroxymethylstearamide, ethylenedioleamide, ethylenedibenzeneamide, ethylenedisteacidamide, ethylenedilaurate, hexamethylenedioleamide, hexamethylenedisteacidamide, butylenebissteacidamide, N,N'-dioleodicaprylate, N,N'-dioleodihexadiamide, N,N'-distearate hexamethylenedicaprylate, N,N'-distearate sebacamide, isophthalimide bisstearamide Amides, N,N'-distearate isophthalamide, N,N'-distearate terephthalamide, N-oleyl oleamide, N-stearyl oleic acid amide, N-stearyl erucamide, N-oleyl stearamide, N-stearyl stearamide, N-butyl-N'-stearyl urea, N-propyl-N'-stearyl urea, N-allyl-N'-stearyl urea, N-phenyl-N'-stearyl urea, N-stearyl-N'-stearyl urea, dimethylol oleamide, dimethyl lauramide, dimethyl stearamide, N,N'-cyclohexanebis(stearamide), N-lauroyl-L-glutamic acid-α,γ-n-butyramide, etc.

[0161] (5) High molecular weight organic compounds: polymers of 3-branched α-olefins with 5 or more carbon atoms, such as 3,3-dimethyl-1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methyl-1-hexene, and 3,5,5-trimethyl-1-hexene, and vinylcyclopentane, vinylcyclohexane, vinylnorbornene, etc.; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; polyglycolic acid; cellulose; cellulose esters; cellulose ethers; polyesters; polycarbonates, etc.

[0162] (6) Organic compounds of phosphoric acid or phosphorous acid and their metal salts: diphenyl phosphate, diphenyl phosphite, sodium bis(4-tert-butylphenyl) phosphate, sodium methylene(2,4-tert-butylphenyl) phosphate, etc.

[0163] (7) Sorbitol derivatives such as bis(p-methylbenzyl)sorbitol and bis(p-ethylbenzyl)sorbitol.

[0164] (8) Cholesterol derivatives such as cholesterol stearate and cholesterol oxystearamide,

[0165] (9) Thioacetic anhydride, p-toluenesulfonic acid, lauryl sulfate, p-toluenesulfonamide and their metal salts, etc.

[0166] (10) Phenylophosphonic acid and its metal salts, etc.

[0167] Among them, a nucleating agent composed of neutral substances that does not promote the hydrolysis of polyester is preferred because it can inhibit the hydrolysis of crystalline acrylic modified polyester resin (A) and thus inhibit the decrease in molecular weight.

[0168] Furthermore, from the viewpoint of suppressing the reduction in molecular weight caused by the transesterification reaction of the aforementioned crystalline acrylic modified polyester resin (A), ester or amide compounds as derivatives of carboxyl groups are more preferred than nucleating agents with carboxyl groups, and similarly, ester or ether compounds as derivatives of hydroxyl groups are more preferred than nucleating agents with hydroxyl groups.

[0169] As the above-mentioned nucleating agents, inorganic nucleating agents and organic nucleating agents can be used together, or multiple types can be combined for use.

[0170] The content of the aforementioned nucleating agent is preferably 0.1 to 20 parts by mass relative to 100 parts by mass of the total solid content of the crystalline acrylic-modified polyester resin (A). Here, the aforementioned content is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and further preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 2 parts by mass or less. Furthermore, when two or more nucleating agents are contained, their combined content is preferably within the aforementioned range.

[0171] <Physical properties, characteristics>

[0172] The aqueous coating composition of this embodiment, as described above, is a dispersion in which crystalline acrylic-modified polyester resin (A) is dispersed in a medium in which water is the main component. Therefore, the solid content concentration of the above-described aqueous coating composition is preferably 10 to 50% by mass. Here, from the viewpoint of coating workability and storage stability, the above-described solid content concentration is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 50% by mass or less, more preferably 40% by mass or less.

[0173] The water-based coating composition of this embodiment can be heated to crystallize and solidify, thus obtaining a coating film. The heat of fusion of the coating film is preferably 1.0 to 17 J / g. Here, from the viewpoint of corrosion resistance, boiling resistance and processability, the heat of fusion is preferably 1.0 J / g or more, more preferably 3.0 J / g or more, and further preferably 17 J / g or less, more preferably 10 J / g or less.

[0174] Furthermore, the heat of fusion of the coating in this specification is a measured value relative to the coating formed in the following manner, as determined below.

[0175] The sample is prepared using the following steps.

[0176] A coating film is formed by applying an aqueous coating composition containing crystalline acrylic modified polyester resin (A) to a substrate, allowing the solvent to evaporate, and then drying it at 110°C for 30 minutes.

[0177] Then, the coating and substrate are cut to a diameter of 4.5 mm and placed in an aluminum pot with a diameter of 5.2 mm. A lid with a diameter of 5.0 mm is then rolled and sealed on top, and this is used as a test sample.

[0178] The sample obtained through the above steps was measured using a differential scanning calorimeter (Hitachi High-Tech, DSC600) at a rate of 20°C / minute, from -30°C to 200°C, to obtain its DSC curve. Based on the peak area (ΔHcJ / g) of the significant exothermic peak appearing after the glass transition temperature in the obtained DSC curve, and the peak area (ΔHmJ / g) of the significant endothermic peak appearing after the glass transition temperature, the heat of fusion of the coating was calculated using the following formula.

[0179] Formula: (-ΔHm-ΔHc) / weight fraction of the sample occupied by the coating

[0180] The water-based coating composition of this embodiment is cured by heating to crystallize it, thereby obtaining a coating film. The storage modulus of the coating film at 50°C is preferably 3.2 × 10⁻⁶. 7 ~2.4×10 8 Pa. Here, from the viewpoint of corrosion resistance, processability, and resistance to boiling, the above-mentioned storage modulus is preferably 3.2 × 10⁻⁶. 7 Pa or higher, more preferably 1.0 × 10 Pa 8 Pa or higher, and preferably 2.4 × 10 Pa. 8 Pa or less, more preferably 2.0 × 10 Pa. 8 Below Pa.

[0181] Furthermore, the storage modulus of the coating in this specification is a measured value relative to the coating formed in the manner described below.

[0182] The sample is prepared using the following steps.

[0183] A coating film is formed by applying an aqueous coating composition containing crystalline acrylic modified polyester resin (A) to a substrate, allowing the solvent to evaporate, and then drying it at 110°C for 30 minutes.

[0184] Then, the coating is peeled off from the substrate and compressed to form a test sample with a diameter of 12 mm and a thickness of 0.5~0.8 mm.

[0185] The test sample obtained by the above steps is placed on a 10 mm parallel plate of a rheometer (TA Instruments, ARES-G2), fully melted at 200°C, and then crystallized at 110°C for 30 minutes to form a coating film.

[0186] Then, after rapid cooling to -100°C, the temperature was increased to 200°C at a rate of 20°C / minute, while the dynamic viscoelasticity was measured at a measurement frequency of 1 Hz.

[0187] <Uses>

[0188] The water-based coating composition of this embodiment is applicable to various substrates. Examples of such substrates include untreated or surface-treated metal plates such as aluminum plates, steel plates, and tin-plated steel plates, metal plates coated with epoxy, vinyl, or other primers, and cans made from these metal plates.

[0189] The water-based coating composition of this embodiment is particularly preferred for use in tanks due to its excellent corrosion resistance, processability, and boiling resistance.

[0190] While there is no particular limitation on the shape of the can for coating the above-mentioned water-based paint composition, examples include two cans consisting of a lid and a bottom and an integral can body, or three cans or bottles consisting of a lid, a bottom and a can body.

[0191] The water-based coating composition of this embodiment can be applied to the aforementioned parts of the can.

[0192] The coating film obtained by applying the water-based coating composition of this embodiment is more preferably used for can applications, especially for beverage cans and the like, and even more preferably for coating the inner surface of the can.

[0193] In addition to the above, the water-based coating composition of this embodiment can also preferably be used for repair coating of seam parts inside the can, coating of the outer surface of the can lid or pull ring part, etc.

[0194] Coating Methods, Coating Films, Coating Formation Methods, Coated Items

[0195] The coating method of this embodiment includes the step of applying the water-based coating composition described in the above-described "Water-based Coating Composition" to a substrate. Here, the preferred form of the water-based coating composition is the same as the preferred form described in the above-described "Water-based Coating Composition".

[0196] The coating film of this embodiment is a film formed by coating an object with the water-based coating composition described in the above-mentioned "Water-based Coating Composition" and then crystallizing it. Here, the preferred form of the water-based coating composition is the same as the preferred form described in the above-mentioned "Water-based Coating Composition".

[0197] The coating film formation method of this embodiment involves applying the aqueous coating composition described in the above-mentioned "Aqueous Coating Composition" onto a substrate, allowing the aqueous dispersion of the aqueous coating composition to evaporate and then crystallize, thereby forming a coating film. Here, the preferred form of the aqueous coating composition is the same as the preferred form described in the above-mentioned "Aqueous Coating Composition".

[0198] The coated article of this embodiment includes a substrate and a coating film formed on the substrate. The coating film is a crystallized film formed by applying the water-based coating composition described in the above-described "Water-based Coating Composition". Here, the preferred form of the water-based coating composition is the same as the preferred form described in the above-described "Water-based Coating Composition".

[0199] As a method for applying the water-based coating composition of this embodiment to a substrate, various known methods can be used. For example, spraying, roller coating, dip coating, or electrophoretic coating can be applied. Among these, spraying and roller coating are preferred.

[0200] The coating amount of the water-based coating composition on the substrate can be appropriately selected according to the application, but in terms of the dry film thickness, it can be, for example, 1 to 30 μm. The aforementioned dry film thickness can be 1 μm or more, or 2 μm or more, or it can be 30 μm or less, or 20 μm or less.

[0201] The application viscosity of the water-based coating composition, when applied to the substrate, is preferably adjusted to within 15 to 30 seconds using a No. 4 Ford cup (according to ISO 2431 standard) at a liquid temperature of 23°C. This is preferred from the viewpoint of coating workability.

[0202] The water-based coating composition of this embodiment is mainly a coating composition that can form a coating film through crystallization. Therefore, it is preferable to apply the water-based coating composition of this embodiment to the substrate, and allow the water dispersion in the water-based coating composition, especially the solvent in the water dispersion that is a volatile component, to evaporate, and then dry it to crystallize and form a coating film.

[0203] The preferred drying temperature is 70~140℃, and the preferred drying time is 10~60 minutes.

[0204] From the viewpoints of corrosion resistance, resistance to boiling and productivity, the above-mentioned temperature is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. In addition, it is preferably 140°C or lower.

[0205] Furthermore, from the viewpoints of corrosion resistance, boiling resistance and productivity, the above-mentioned time is preferably 10 minutes or more, more preferably 15 minutes or more, and even more preferably 30 minutes or more, and preferably 60 minutes or less.

[0206] That is, one form of the coating film in this embodiment is obtained by applying the above-mentioned water-based coating composition to the object to be coated, and then drying the water dispersion (solvent) in the water-based coating composition at a temperature preferably 70 to 140°C for 10 to 60 minutes.

[0207] Furthermore, one embodiment of the coating film forming method includes, in sequence, a step of applying the above-mentioned water-based coating composition to a substrate, a step of evaporating the water dispersion (solvent) in the water-based coating composition, and a step of drying under conditions preferably 70 to 140°C for 10 to 60 minutes.

[0208] Furthermore, one form of the coated article in this embodiment includes a substrate and a coating film formed on the substrate. The coating film is obtained by applying the above-mentioned water-based paint composition to the substrate, allowing the water dispersion (solvent) in the water-based paint composition to evaporate, and then drying it under conditions preferably 70 to 140°C for 10 to 60 minutes.

[0209] When applying a water-based coating composition to a substrate and heating is performed while the solvent evaporates, if the heating temperature is higher than the drying temperature, it is preferable to immediately cool the coating film to the respective drying temperature and then dry it after the solvent has evaporated. However, even if it is not possible to dry the coating film immediately after the solvent has evaporated, the same coating film can be obtained by rapidly cooling the coating film to below room temperature, even if drying is not performed immediately.

[0210] The coating film obtained above can be subjected to differential scanning calorimetry. By confirming the presence of a significant exothermic peak after the glass transition temperature, it can be confirmed that there is a crystallized portion. Specifically, the apex of the aforementioned significant exothermic peak is the melting point. If its temperature is above 125°C, it can be considered as the water-based coating composition described in the aforementioned "Water-based Coating Compositions", which can also be considered as a coating film obtained from an water-based coating composition containing an aqueous dispersion of a crystalline acrylic-modified polyester resin (A) with a melting point above 125°C.

[0211] [Example]

[0212] The present invention will be described in more detail below through examples. Here, "parts" and "%" mean "parts by mass" and "% by mass," respectively. Furthermore, in the following synthesis examples, manufacturing examples, examples, and comparative examples, the parts by mass of raw materials refer to the parts by mass of the solid components of the raw materials (or, where they are described as active ingredients).

[0213] Synthesis of Crystalline Polyester Resins

[0214] <Synthesis example 1>

[0215] 415 parts by mass of terephthalic acid, 125 parts by mass of isophthalic acid, 203 parts by mass of dimethyl 2,6-naphthalenedicarboxylic acid, 16 parts by mass of trimellitic anhydride, 713 parts by mass of 1,4-butanediol, 60 parts by mass of 1,4-cyclohexanediethanol, and 0.4 parts by mass of tetrabutyl titanate as a catalyst were added to a 3L four-necked flask. The esterification and transesterification reactions were carried out over 3 hours while the temperature was slowly increased to 240°C.

[0216] After the reaction was completed, the pressure in the system was slowly reduced for 1 hour until it reached 10 mmHg. Then, depressurized polymerization was carried out, and the temperature was raised to 240°C. Finally, the late-stage polymerization was carried out for 120 minutes under a vacuum of less than 1 mmHg.

[0217] After the polycondensation reaction is completed, the mixture is cooled to 220°C under nitrogen atmosphere. Then, a specified amount of trimellitic anhydride is added, and the mixture is stirred continuously at 220°C under nitrogen atmosphere for 30 minutes.

[0218] After the reaction was complete, the reactants were transferred to a reactor equipped with a stirrer, reflux cooler, and thermometer. 30.0 parts of N-methyl-2-pyrrolidone and 29.0 parts of cyclohexanone were added per 100.0 parts of the reactants, and the mixture was heated to 140°C. Then, stirring was initiated to allow the reactants to completely dissolve.

[0219] Next, by adding 0.9 parts of glycidyl methacrylate, 0.1 parts of tetrabutylammonium bromide and 2.0 parts of cyclohexanone, and reacting at 140°C for 1 hour, a solution of crystalline polyester resin 1 was obtained.

[0220] The resulting crystalline polyester resin 1 has a number average molecular weight of 14400, a glass transition temperature (Tg) of 36℃, a melting point (Tm) of 147℃, an acid value of 6.6 mgKOH / g, and a hydroxyl value of 3.6 mgKOH / g.

[0221] <Synthetic Examples 2, 4, 5, 6, 7, 10, 15 and 16>

[0222] Except for changing the type and ratio of monomers in Synthesis Example 1, the other synthesis reactions were carried out in the same manner as in Synthesis Example 1, and solutions of each of the crystalline polyester resins 2, 4, 5, 6, 7, 10, 15 and 16 with the values ​​recorded in Table 1 were obtained.

[0223] Furthermore, although Table 1 lists crystalline polyester resin 16, this is a non-crystalline polyester resin produced by adding glycidyl methacrylate to GK-622 (a non-crystalline polyester resin manufactured by Toyobo Co., Ltd.). It is not crystalline, but for convenience, it is listed as crystalline polyester resin.

[0224]

[0225] <Synthesis Example 12>

[0226] 557 parts by mass of terephthalic acid, 141 parts by mass of isophthalic acid, 8 parts by mass of trimellitic anhydride, 130 parts by mass of 1,2-propanediol, 500 parts by mass of 1,4-butanediol, 184 parts by mass of 1,4-cyclohexanediol, and 0.4 parts by mass of tetrabutyl titanate as a catalyst were added to a 3L four-necked flask. The esterification reaction was carried out over 3 hours while the temperature was slowly increased to 240°C.

[0227] After the esterification reaction is completed, the pressure in the system is slowly reduced to 10 mmHg over 1 hour, and then reduced pressure polymerization is carried out. The temperature is then raised to 240°C, and then a later-stage polymerization is carried out under a vacuum of less than 1 mmHg for 120 minutes.

[0228] After the polycondensation reaction is completed, the mixture is cooled to 220°C under nitrogen atmosphere. Then, a specified amount of trimellitic anhydride is added, and the mixture is stirred continuously at 220°C under nitrogen atmosphere for 30 minutes.

[0229] After the reaction was complete, the reactants were transferred to a reactor equipped with a stirrer, reflux cooler, and thermometer. 30.0 parts of N-methyl-2-pyrrolidone and 29.0 parts of cyclohexanone were added per 100.0 parts of the reactants, and the mixture was heated to 140°C. Then, stirring was initiated to allow the reactants to completely dissolve.

[0230] Next, by adding 0.75 parts of glycidyl methacrylate, 0.1 parts of tetrabutylammonium bromide and 2.0 parts of cyclohexanone, and reacting at 140°C for 1 hour, a solution of crystalline polyester resin 12 was obtained.

[0231] The resulting crystalline polyester resin 12 has a number average molecular weight of 25,400, a glass transition temperature (Tg) of 35℃, a melting point (Tm) of 104℃, an acid value of 0.0 mg KOH / g, and a hydroxyl value of 3.0 mg KOH / g.

[0232] <Synthesis Examples 3, 8, 9, 11, 13, 14>

[0233] Except for changing the type and ratio of monomers in Synthesis Example 12, the other synthesis reactions were carried out in the same manner as in Synthesis Example 12 to obtain solutions of each of the crystalline polyester resins 3, 8, 9, 11, 13 and 14 with the characteristic values ​​recorded in Table 2.

[0234]

[0235] Furthermore, in the above-mentioned crystalline polyester resins 12 to 16 are polyester resins used in the manufacture of crystalline acrylic modified polyester resins for comparative examples, and do not meet the requirement of a melting point of 125°C or higher.

[0236] Preparation of Aqueous Dispersions of Crystalline Acrylic Modified Polyester Resin (A)

[0237] <Manufacturing Example 1>

[0238] In a reactor equipped with a stirrer, reflux cooler, and thermometer, 128.5 parts (80 parts solids) of the solution of crystalline polyester resin 1 obtained in Synthesis Example 1 were added, and the mixture was heated to 140°C while stirring. Next, 95.2 parts of N-methyl-2-pyrrolidone were added, and the mixture was cooled to 120°C. Next, 4.7 parts of methyl methacrylate, 7.8 parts of n-butyl acrylate, 7.5 parts of acrylic acid, and 0.1 parts of PERBUTYL (registered trademark) O (polymerization initiator, manufactured by Nippon Oil Co., Ltd.) were added, and polymerization was carried out for 30 minutes. Then, to allow unreacted monomers to react, 0.09 parts of PERBUTYL (registered trademark) O were further added, and polymerization was carried out for 1 hour.

[0239] Next, in order to disperse the water, the reactants were cooled to 95°C, and 7.6 parts of dimethylaminoethanol (neutralization equivalent 0.82) and 15.1 parts of butyl cellosolve were added, and the mixture was stirred thoroughly until homogeneous.

[0240] Finally, while maintaining the temperature of the reactants at 95°C, 233.9 parts of deionized water were added dropwise over 90 minutes with stirring to obtain an aqueous dispersion of crystalline acrylic modified polyester resin 1 with a solid component concentration of 20% by mass, an acid value (AV) of 59 mg KOH / g, a melting point (Tm) of 145°C, and a glass transition temperature (Tg) of 39°C.

[0241] The mass solids ratio of polyester resin component (a1) to acrylic resin component (a2), expressed as (a1) / (a2), is 80 / 20, and the average particle size of the main peak is 230 nm.

[0242] <Manufacturing Examples 2-40 and 42-53>

[0243] Except for changing the solution, monomer type, and ratio of the crystalline polyester resin in Manufacturing Example 1, the synthesis reaction was carried out in the same manner as in Manufacturing Example 1, yielding crystalline acrylic modified polyester resins 2-40 and 42-53 with the characteristic values ​​recorded in Tables 3-9. Furthermore, the blank columns in Tables 3-9 indicate no addition.

[0244] Furthermore, although crystalline acrylic modified polyester resin 53 is described, as mentioned above, since non-crystalline polyester resin 16 is used, the acrylic modified polyester resin is also non-crystalline. Although it is not crystalline, it is described as crystalline acrylic modified polyester resin for convenience.

[0245] <Manufacturing Example 41>

[0246] In a reactor equipped with a mixer, reflux cooler, and thermometer, 128.5 parts (80 parts solids) of the solution of crystalline polyester resin 1 obtained in Synthesis Example 1 were added, and the mixture was heated to 140°C while stirring. Next, 35.7 parts of N-methyl-2-pyrrolidone were added, and the mixture was cooled to 120°C. Next, 10.1 parts of methyl methacrylate, 2.4 parts of n-butyl acrylate, 7.5 parts of acrylic acid, and 0.10 parts of PERBUTYL (registered trademark) O (manufactured by Nippon Oil Co., Ltd.) were added, and polymerization was carried out for 30 minutes. Then, to allow unreacted monomers to react, 0.09 parts of PERBUTYL (registered trademark) O were further added, and polymerization was carried out for 1 hour.

[0247] Next, in order to disperse the water, the reactants were cooled to 95°C, and 7.6 parts of dimethylaminoethanol (neutralization equivalent 0.82) and 15.1 parts of butyl cellosolve were added, and the mixture was stirred thoroughly until homogeneous.

[0248] Then, the mixture was transferred to a pressurized intermittent disperser, and under a pressure of 0.5 MPa, 293.4 parts of deionized water were added dropwise over 30 minutes while maintaining the tank temperature at 140°C. At this point, the mixture was stirred at 4500 rpm using a homogenizer to obtain an aqueous dispersion of crystalline acrylic-modified polyester resin 41 with a solid content of 20% by mass, an acid value (AV) of 59 mg KOH / g, a melting point (Tm) of 145°C, and a glass transition temperature (Tg) of 44°C.

[0249] The mass solids ratio of polyester resin component (a1) to acrylic resin component (a2), expressed as (a1) / (a2), is 80 / 20, and the average particle size of the main peak is 205 nm.

[0250] Furthermore, by performing pressurized emulsification, compared with crystalline acrylic modified polyester resin 23, the amount of solvent can be reduced by 30 parts by mass relative to 100 parts by mass of resin solids.

[0251] Furthermore, in Tables 3-9, the amount of crystalline polyester resin is the amount of solid component. Additionally, the amount of solvent is the part (amount) relative to 100 parts by mass of the solid component of the crystalline acrylic-modified polyester resin. Furthermore, the value of dimethylethanolamine (neutralizing agent) is the neutralization equivalent relative to the crystalline acrylic-modified polyester resin.

[0252] Furthermore, the crystalline acrylic modified polyester resins 42 to 53 are comparative examples of crystalline acrylic modified polyester resins that do not meet the requirement of a melting point of 125°C or higher. In addition, although the table lists crystalline acrylic modified polyester resin 53, it is actually a non-crystalline acrylic modified polyester resin, but it is listed as crystalline acrylic modified polyester resin for convenience.

[0253] The manufacturability of aqueous dispersions of each of the crystalline acrylic modified polyester resins 1 to 53 was evaluated using the following criteria, and the results of the evaluation are shown in Tables 3 to 9.

[0254] [Manufacturing]

[0255] ◎: No problem, it can be dispersed in water.

[0256] 〇: Although it can be dispersed in water, there is some floating paint.

[0257] △: Poor water dispersion, resulting in particles.

[0258] ×: Cannot be dispersed in water.

[0259] If the above is marked with ◎ or ○, then it is considered acceptable.

[0260] Furthermore, neither of the crystalline acrylic modified polyester resins 47 nor 48 can be dispersed in water. Since the acid value, melting point, and average particle size of the main peak were not evaluated, they are recorded as "-" in Tables 8 and 9.

[0261]

[0262]

[0263]

[0264]

[0265] Manufacturing of Waterborne Coating Compositions

[0266] <Example 1>

[0267] In a mixing vessel, 100 parts by weight of the aqueous dispersion of the crystalline acrylic-modified polyester resin 1 obtained in Manufacturing Example 1 (solid component) were placed. While stirring, 2 parts by weight of an aqueous solution of Primid (registered trademark) QM-1260 (N,N,N',N'-tetratetra(2-hydroxypropyl)butadiamide, β-hydroxyalkylamide compound) was added as a solid component. Then, while continuing stirring, 1 part by weight of DOWSIL (registered trademark) 71 Additive (defoamer, silicone, Dow & Toray Industries, Inc.), 1.5 parts by weight of HD-3028 (wax, manufactured by Gifu Ceramic Manufacturing Co., Ltd.), and 6 parts by weight of isopropanol were added. Next, 31.5 parts by weight of deionized water were added, and the mixture was stirred thoroughly until homogeneous to prepare an aqueous coating composition 1 with a solid component concentration of 22% by weight.

[0268] <Examples 2-43 and Comparative Examples 1-10>

[0269] Except that in Example 1 above, the aqueous dispersions of the crystalline acrylic-modified polyester resins 2-53 obtained in Manufacturing Examples 2-53 were used, and the compositions shown in Tables 10-15 were employed, all other procedures were carried out in the same manner as in Example 1 to manufacture each waterborne coating composition 2-53. Waterborne coating compositions 44-53 were used as comparative examples.

[0270] The blending amounts in Tables 10-15 are the solid content amounts excluding isopropanol.

[0271] Furthermore, in Tables 10-15, SCT-275 is a thickener for polyether polyurethane systems manufactured by Dow Chemical Company, and sodium octanoate is a nucleating agent. Additionally, empty columns in the tables indicate that no additives were used.

[0272] "evaluate"

[0273] <Preparation of Experimental Coated Panels>

[0274] Regarding the water-based coating compositions 1-53 obtained in the above examples and comparative examples, rod coating was performed on a #5052 aluminum plate with a thickness of 0.26 mm to achieve a cured coating film thickness of 5 μm. The plate was heated in a dryer at 200°C for 1 minute. The plate was then immediately removed from the dryer and cooled to below 25°C within 15 seconds. The plate was then placed back into the dryer and heated at 110°C for 30 minutes. This reheating process at 110°C for 30 minutes is a drying process. After drying, the plate was immediately removed from the dryer and cooled to below 25°C within 15 seconds to obtain the test coated plates.

[0275] For each waterborne coating composition and the resulting coated panels, tests were conducted according to the following test methods. The test results are shown in Tables 10-15.

[0276] Furthermore, a tin-plated steel plate was separately prepared as a sample for determining the storage modulus of the coating. This tin-plated steel plate was obtained in the same manner as the coating plate used for the above-mentioned test, except that it replaced the #5052 aluminum plate with tin-plated steel.

[0277] The test specimens for measuring the heat of fusion of the coating were obtained in the same manner as those obtained using #5052 aluminum plates, but the temperature and time of the drying process were changed to the conditions recorded in Table 16, namely "Drying Temperature °C" and "Drying Time Minutes".

[0278] [Machinability: T-bend bending machinability]

[0279] A 5cm section of the coated test sheet was cut along the rolling direction and a 4cm section was cut perpendicularly. The bottom section was then folded in half parallel to the short side. In a 20°C room, three 0.26mm thick aluminum plates were sandwiched between the bent portions of the test sheet and placed in a special-joint folding type DuPont impact testing machine (DuPont bending impact testing machine).

[0280] A 1kg iron weight with a flat contact surface is dropped from a height of 50cm onto the bent portion of the test piece. A voltage of 6.5V is then applied to the top of the bend for 6 seconds. The current (mA) at a 20mm width at the top of the bend is then measured and evaluated according to the following criteria.

[0281] ◎: Less than 10mA

[0282] ○: 10mA or higher but less than 40mA

[0283] △: Above 40mA and below 80mA

[0284] ×: 80mA or more

[0285] In the above, if it is ◎ or ○, it is considered qualified.

[0286] [Resistance to boiling]

[0287] The test coated panels were immersed in water and treated at 125°C for 30 minutes. The whitening status of the coating was then visually observed and evaluated according to the following criteria.

[0288] ◎: No albinism was observed at all

[0289] ○: Only slight partial albinism was observed.

[0290] △: A considerable degree of albinism was observed.

[0291] ×: Significant whitening was observed.

[0292] In the above, if it is ◎ or ○, it is acceptable. Furthermore, the above "○" indicating only slight partial whitening means that the whitened area is less than 2% of the coating area.

[0293] [Corrosion Resistance]

[0294] The test coated panels were immersed in a mixed aqueous solution containing 3% citric acid and 3% sodium chloride, stored at 40°C for 2 weeks, and the coating condition was visually observed and evaluated according to the following criteria.

[0295] ◎: No signs of "loss of luster" or "corrosion" were observed.

[0296] ○: Although it has lost its luster, no corrosion was observed.

[0297] △: Observe slight corrosion

[0298] ×: Significant corrosion was observed.

[0299] In the above, if it is ◎ or ○, it is considered qualified.

[0300] <Coating Stability>

[0301] Each water-based coating composition was left to stand at room temperature for one week, and its appearance after standing was visually assessed.

[0302] ◎: No precipitation observed

[0303] ○: Slight sedimentation was observed.

[0304] △: Although a considerable amount of sediment was observed, it could be dispersed by stirring.

[0305] ×: A considerable amount of precipitate was observed, which could not be dispersed by stirring.

[0306] Of the above, ◎ or ○ are preferred.

[0307]

[0308]

[0309] <Examples 44-52>

[0310] A coating film is formed using the coating composition 4 obtained in Example 4.

[0311] Specifically, except that the drying temperature and time conditions of the method described in "Preparation of Test Coated Panels" were changed to those described in Table 15, the process was the same as described in "Preparation of Test Coated Panels" to form a coating film on an aluminum substrate. The storage modulus and heat of fusion of the resulting coating film were measured in the same manner as in Example 1. Furthermore, even for the aluminum plate on which the coating film was formed, evaluation tests for processability, resistance to boiling, corrosion resistance, and coating stability were performed in the same manner as in Example 1. Here, the evaluation criteria in each evaluation test were the same as in Example 1.

[0312]

[0313] Although the present invention has been described in detail and with reference to specific embodiments, those skilled in the art will understand that various changes or modifications can be made to the present invention without departing from its spirit and scope. This application is based on Japanese Patent Application No. 2024-65076, filed April 15, 2024, the contents of which are incorporated herein by reference.

[0314] Industry availability

[0315] The water-based coating composition according to this embodiment, especially for tank applications, provides a coating film with excellent corrosion resistance, boiling resistance, and processability. Furthermore, the water-based coating composition of this embodiment does not contain raw materials that are "substances widely regulated by law, such as bisphenol A," and exhibits excellent stability.

Claims

1. A water-based coating composition comprising an aqueous dispersion of a crystalline acrylic-modified polyester resin (A), The crystalline acrylic modified polyester resin (A) has a melting point of 125°C or higher.

2. The water-based coating composition according to claim 1, wherein the heat of fusion of the coating film obtained by heating and crystallizing it is 1.0~17 J / g.

3. The water-based coating composition as described in claim 1 or 2, wherein the coating film obtained by heating and crystallizing has a storage modulus of 3.2 × 10⁻⁶ at 50°C. 7 ~2.4×10 8 Pa.

4. The waterborne coating composition according to claim 1 or 2, wherein the ratio of the crystalline acrylic modified polyester resin (A) expressed by (a1) / (a2) is in the range of 60 / 40 to 90 / 10, wherein (a1) / (a2) is the mass solids ratio of the polyester resin component (a1) to the acrylic resin component (a2).

5. The waterborne coating composition according to claim 1 or 2, wherein in the crystalline acrylic modified polyester resin (A), the acid value of the acrylic resin component (a2) is 180~400 mgKOH / g, and the glass transition temperature is 20~160℃.

6. The waterborne coating composition of claim 1 or 2, wherein the aqueous dispersion of the crystalline acrylic-modified polyester resin (A) contains an organic solvent (a3), and The content of the organic solvent (a3) ​​is 50 parts by mass or more relative to the total solid content of the crystalline acrylic modified polyester resin (A) of 100 parts by mass.

7. The waterborne coating composition according to claim 1 or 2, further comprising a β-hydroxyalkylamide compound (B).

8. The water-based coating composition as described in claim 1 or 2, for use in a can.

9. A coating method comprising applying the water-based coating composition of claim 1 or 2 onto a workpiece.

10. A coating film formed by applying the water-based coating composition of claim 1 or 2 onto a substrate and crystallizing it.

11. A coated article comprising a substrate and a coating film formed on the substrate. The coating film is formed by applying the water-based coating composition of claim 1 or 2 and crystallizing it.

12. A method for forming a coating film, comprising, in sequence: Apply the water-based coating composition of claim 1 or 2 to the object to be coated. To cause the water dispersion in the water-based coating composition to evaporate, and Dry at 70~140℃ for 10~60 minutes.

13. A coating film obtained by sequentially performing the following steps: Apply the water-based coating composition of claim 1 or 2 to the object to be coated. To cause the water dispersion in the water-based coating composition to evaporate, and Dry at 70~140℃ for 10~60 minutes.

14. A coated article comprising a workpiece and a coating film formed on the workpiece. The coating is obtained by sequentially performing the following processes: Apply the water-based coating composition according to claim 1 or 2. To cause the water dispersion in the water-based coating composition to evaporate, and Dry at 70~140℃ for 10~60 minutes.

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