Water-based paint composition for cans

Abstract

To provide an aqueous coating composition for cans that excels in lubricity and wear resistance and also excels in processability.SOLUTION: A aqueous coating composition for cans contains an acryl modified epoxy resin (A), at least one wax selected from a group consisting of three waxes with different melting points (B), a polyolefin aqueous dispersion with an average particle size of 0.1-5 μm and a polyolefin penetration of 8 or less (C), and a phenolic resin (D) in a specific compositional ratio.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous coating composition for cans, which is excellent in lubricity, wear resistance, and processability.

Background Art

[0002] For metal cans, metal substrates such as aluminum, tin-free steel, and iron are used. A coating film is formed on the outer surfaces of cans, can lids, and tabs obtained by processing these metal substrates for the purposes of formability, design, and protection of the metal surface. In particular, since the coating film on the can lid is required to have resistance to severe processing during forming, an inner wax type coating for cans containing wax in the paint has been developed for the purpose of imparting lubricity.

[0003] For example, Patent Document 1 discloses an aqueous coating composition for the outer surface of a can lid, which contains a pigment, a pigment dispersion resin, and a binder resin, and the pigment dispersion resin is an acrylic copolymer having methacrylic acid, styrene, and ethyl acrylate as constituent components.

[0004] Further, Patent Document 2 discloses an aqueous coating composition for the outer surface of a can, which contains a water-soluble acrylic resin (A) containing an animal wax (a) having a melting point of 40 to 70°C, an aqueous wax dispersion (B) containing an animal wax (a), a water-soluble polyester resin (C), and an amino resin (D).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the paint compositions described in Patent Documents 1 and 2, if a large amount of wax is added to improve the lubricity of the paint film, the paint film becomes plasticized and its abrasion resistance decreases. Therefore, it is difficult to achieve a high level of both lubricity and abrasion resistance, and in some cases, the processability is insufficient.

[0007] The problem that this invention aims to solve is to provide an aqueous coating composition for cans that has excellent lubricity and abrasion resistance, as well as excellent processability. [Means for solving the problem]

[0008] As a result of diligent research, the inventors of the present invention have found that the above problems can be solved by a coating composition containing an acrylic-modified epoxy resin, a wax, a polyolefin aqueous dispersion, and a phenolic resin, and have completed the present invention.

[0009] In other words, the present invention is 1. A paint composition containing an acrylic-modified epoxy resin (A), a wax (B), a polyolefin aqueous dispersion (C), and a phenolic resin (D), The wax (B) contains at least one type of wax selected from the group consisting of waxes with a melting point of less than 50°C (b1), waxes with a melting point of 50°C or higher and less than 100°C (b2), and waxes with a melting point of 100 to 160°C and an average particle size of 1 to 15 μm (b3). The average particle size of the polyolefin aqueous dispersion (C) is 0.1 to 5 μm, and the penetration degree of the polyolefin is 8 or less. A water-based paint composition for cans, characterized in that, based on the total solid content of acrylic-modified epoxy resin (A), the total solid content of wax (B) is 0.3 to 10% by mass, the total solid content of polyolefin aqueous dispersion (C) is 1 to 10% by mass, and the total solid content of phenolic resin (D) is 0.5 to 20% by mass. 2. The water-based paint composition for cans according to item 1 above, wherein the wax (b1) is at least one selected from the group consisting of lanolin wax, palm oil, and glycerin triester. 3. The water-based paint composition for cans according to item 1 or 2 above, wherein the wax (b2) is at least one selected from the group consisting of microcrystalline wax and carnauba wax. 4. The water-based paint composition for cans according to any one of the above items 1 to 3, wherein the wax (b3) is at least one selected from the group consisting of polyethylene wax and polypropylene wax. 5. The aqueous paint composition for cans according to any one of items 1 to 4 above, wherein the solid content of wax (b1), wax (b2), and wax (b3) is 0.1 to 5% by mass of wax (b1), 0.1 to 5% by mass of wax (b2), and 0.1 to 5% by mass of wax (b3), based on the total solid content of the acrylic modified epoxy resin (A). 6. A water-based paint composition for cans according to any one of claims 1 to 5, which is for use as a can lid. 7. Can lid having a coating of the aqueous paint composition for cans according to any one of claims 1 to 6. Regarding, [Effects of the Invention]

[0010] The aqueous coating composition for cans of the present invention can produce a coating film that is excellent in lubricity and abrasion resistance, as well as in processability. [Modes for carrying out the invention]

[0011] The present invention relates to an aqueous coating composition for cans (hereinafter sometimes referred to as the "inventive composition") characterized by containing an acrylic-modified epoxy resin (A), a wax (B), a polyolefin aqueous dispersion (C), and a phenolic resin (D). A detailed description follows below.

[0012] <Water-based paint composition for cans> <Acrylic-modified epoxy resin (A)> The acrylic-modified epoxy resin (A) may be, for example, either resin (1) or resin (2) described below.

[0013] Resin (1): A resin obtained by subjecting bisphenol-type epoxy resin (a1) (hereinafter sometimes abbreviated as "epoxy resin (a1)") and carboxyl group-containing acrylic resin (a2) (hereinafter sometimes abbreviated as "acrylic resin (a2)") to an ester addition reaction.

[0014] Resin (1) can be easily obtained by subjecting epoxy resin (a1) and acrylic resin (a2) to an ester addition reaction by heating them, for example, in an organic solvent in the presence of an esterification catalyst.

[0015] Resin (2): A resin obtained by subjecting a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer to graft polymerization on epoxy resin (a1).

[0016] Resin (2) can be obtained, for example, by subjecting a polymerizable unsaturated monomer component to graft polymerization on epoxy resin (a1) in an organic solvent in the presence of a radical generator such as benzoyl peroxide.

[0017] Examples of the epoxy resin (a1) used in the above resin (1) and resin (2) include resins obtained by polycondensing epichlorohydrin and bisphenol to a high molecular weight in the presence of a catalyst such as an alkali catalyst as an optional choice, resins obtained by condensing epichlorohydrin and bisphenol in the presence of a catalyst such as an alkali catalyst as an optional choice to form a low molecular weight epoxy resin and subjecting this low molecular weight epoxy resin and bisphenol to a polyaddition reaction, and epoxy ester resins obtained by reacting a dibasic acid with the obtained resins or the above low molecular weight epoxy resin, and any of them may be used.

[0018] Examples of the above bisphenol include bis(4-hydroxyphenyl)methane [bisphenol F], 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane [bisphenol A], 2,2-bis(4-hydroxyphenyl Examples of the bisphenols include butanebisphenol B, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butylphenyl)-2,2-propane, p-(4-hydroxyphenyl)phenol, oxybis(4-hydroxyphenyl), sulfonylbis(4-hydroxyphenyl), 4,4'-dihydroxybenzophenone, bis(2-hydroxynaphthyl)methane, etc. Among them, bisphenol A and bisphenol F can be preferably used. These bisphenols can be used alone or in combination of two or more.

[0019] Examples of the dibasic acid used for producing the epoxy ester resin include the following formula (1) HOOC-(CH2) n -COOH ··· Formula (1) (In the formula, n is an integer of 1 to 12), and compounds represented by this can be preferably used. Specifically, succinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexahydrophthalic acid, etc. can be exemplified.

[0020] Examples of commercially available products of the epoxy resin (a1) include, for example, jER828 (epoxy equivalent about 190), jER1007 (epoxy equivalent about 1,700), jER1009 (epoxy equivalent about 3,500), jER1010 (epoxy equivalent about 4,500) manufactured by Mitsubishi Chemical Corporation; Araldite AER6099 (epoxy equivalent about 3,500) manufactured by Asahi Kasei Corporation; and Epomic R-309 (epoxy equivalent about 3,500) manufactured by Mitsui Chemicals, Inc., etc.

[0021] As the epoxy resin (a1), among them, bisphenol type epoxy resins having a number average molecular weight of 2,000 to 35,000, preferably 4,000 to 30,000, and an epoxy equivalent of 1,000 to 12,000, preferably 3,000 to 10,000, can be preferably used from the viewpoint of the corrosion resistance of the obtained coating film.

[0022] In this specification, the number-average molecular weight is the value obtained by converting the number-average molecular weight measured using gel permeation chromatography (GPC) to the molecular weight of standard polystyrene.

[0023] Specifically, the measurement can be performed using the "HLC8120GPC" (product name, manufactured by Tosoh Corporation) as the gel permeation chromatograph, and four columns: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (product names, all manufactured by Tosoh Corporation) as the columns, under the conditions of tetrahydrofuran as the mobile phase, a measurement temperature of 40°C, a flow rate of 1 mL / min, and a radioisotope detector.

[0024] In the resin (1) mentioned above, during the esterification reaction, the carboxyl groups in the acrylic resin (a2) undergo an esterification reaction with the epoxy groups in the epoxy resin (a1). Therefore, epoxy groups are necessary in the epoxy resin (a1), and it is preferable that the number of epoxy groups per molecule of epoxy resin is in the range of 0.5 to 2 on average, and particularly in the range of 0.5 to 1.6.

[0025] On the other hand, in resin (2), the graft reaction occurs by hydrogen abstraction of the epoxy resin main chain, and the graft polymerization reaction proceeds, so epoxy groups do not substantially need to be present in epoxy resin (a1).

[0026] The acrylic resin (a2) used in the resin (1) is a copolymer resin having a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers as monomer components.

[0027] Examples of the carboxyl group-containing polymerizable unsaturated monomers mentioned above include (meth)acrylic acid, maleic acid, crotonic acid, itaconic acid, and fumaric acid, which can be used individually or in combination of two or more.

[0028] Other polymerizable unsaturated monomers can be selected and used as appropriate, depending on the required performance, as long as they are monomers copolymerizable with the above-mentioned carboxyl group-containing polymerizable unsaturated monomers.

[0029] Specifically, for example, aromatic vinyl monomers such as styrene, vinyltoluene, 2-methylstyrene, t-butylstyrene, and chlorostyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-,i- or t-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-,i- or t-butyl methacrylate, and hexyl methacrylate. Examples include alkyl esters or cycloalkyl esters of acrylic acid or methacrylic acid having 1 to 18 carbon atoms, such as 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate; hydroxyalkyl esters of acrylic acid or methacrylic acid having 2 to 8 carbon atoms, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and hydroxybutyl methacrylate; and N-substituted acrylamide or N-substituted methacrylamide monomers such as N-methylolacrylamide, N-butoxymethylacrylamide, N-methoxymethylacrylamide, N-methylolmethacrylamide, and N-butoxymethylmethacrylamide. The above other polymerizable unsaturated monomers can be used individually or in combination of two or more.

[0030] Among the other polymerizable unsaturated monomers mentioned above, a mixture of styrene and ethyl acrylate is particularly preferred, and the styrene / ethyl acrylate compositional mass ratio is preferably in the range of 99.9 / 0.1 to 20 / 80, and particularly preferably in the range of 99 / 1 to 40 / 60.

[0031] In the acrylic resin (a2), the type and composition ratio of monomers are not particularly limited, but it is generally preferable that the carboxyl group-containing polymerizable unsaturated monomers make up 15 to 80% by mass, particularly 20 to 60% by mass, and the other polymerizable unsaturated monomers make up 85 to 20% by mass, particularly 80 to 40% by mass.

[0032] The synthesis of acrylic resin (a2) can be easily carried out, for example, by polymerizing the above-mentioned monomer mixture in an organic solvent in the presence of a polymerization initiator. The acrylic resin (a2) preferably has a resin acid value in the range of 100 to 400 mg KOH / g and a number-average molecular weight in the range of 5,000 to 100,000.

[0033] The above reaction can be carried out by known methods, for example, by mixing an esterification catalyst into a homogeneous organic solvent solution of epoxy resin (a1) and acrylic resin (a2), and reacting at a reaction temperature of typically 60 to 130°C for about 1 to 6 hours until substantially all of the epoxy groups are consumed. Examples of the esterification catalyst include tertiary amines such as triethylamine and dimethylethanolamine, and quaternary salt compounds such as triphenylphosphine, among which tertiary amines can be preferably used.

[0034] The solid content concentration in the reaction system between epoxy resin (a1) and acrylic resin (a2) is not particularly limited, as long as the viscosity of the reaction system is within a range that does not hinder the reaction. Furthermore, when an esterification catalyst is used during the esterification reaction, it is generally preferable to use it in the range of 0.1 to 1 equivalent per equivalent of epoxy groups in epoxy resin (a1).

[0035] When the acrylic-modified epoxy resin is the resin (2), the polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer to be graft polymerized onto the epoxy resin (a1) can include the carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers that are monomer components used in the production of the carboxyl group-containing acrylic resin (a2) in the resin (1).

[0036] The graft polymerization reaction in the resin (2) described above can be carried out by known methods, for example, by gradually adding a homogeneous mixed solution of a radical generator and a polymerizable unsaturated monomer component to an organic solvent solution of epoxy resin (a1) heated to 80-150°C, and maintaining the temperature at the same temperature for about 1-10 hours. Examples of the radical generator include azobisisobutyronitrile, benzoyl peroxide, t-butyl perbenzoyl octanoate, and t-butyl peroxy-2-ethylhexanoate.

[0037] As for the organic solvent, any known organic solvent can be used as long as it dissolves the epoxy resin (a1) and the acrylic resin (a2) or a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer, and does not hinder emulsion formation when neutralizing and aqueousizing the acrylic-modified epoxy resin (A), which is the reaction product of these solvents.

[0038] Specific examples of the above organic solvents include, for example, isopropanol, butyl alcohol, 2-hydroxy-4-methylpentane, 2-ethylhexyl alcohol, cyclohexanol, ethylene glycol, diethylene glycol, 1,3-butylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol monomethyl ether.

[0039] The acrylic-modified epoxy resin, which is resin (1) or resin (2) above, preferably has a carboxyl group and a resin acid value in the range of 10 to 160 mgKOH / g, particularly 20 to 100 mgKOH / g, from the viewpoint of dispersibility, coating film performance, etc.

[0040] Acrylic-modified epoxy resins can be dispersed in an aqueous medium by neutralizing at least some of the carboxyl groups in the resin with a basic compound.

[0041] Suitable basic compounds include amines, ammonia, and the like. Specifically, examples of amines include alkylamines such as trimethylamine, triethylamine, and tributylamine; alkanolamines such as dimethylethanolamine, diethanolamine, and aminomethylpropanol; and cyclic amines such as morpholine. The degree of neutralization of the acrylic-modified epoxy resin is not particularly limited, but is preferably in the range of 0.1 to 2.0 equivalents relative to the carboxyl groups in the resin.

[0042] The aqueous medium may be water alone, or it may be a mixture of water and an organic solvent. Known organic solvents can be used, and those listed as organic solvents usable in the production of the acrylic-modified epoxy resin are preferably used. The amount of organic solvent in the composition of the present invention is preferably 20% by mass or less, and particularly 10% by mass or less, relative to the total resin solid content of the composition of the present invention, from the viewpoint of environmental protection and other factors.

[0043] The dispersion of acrylic-modified epoxy resin in an aqueous medium can be carried out by conventional methods. Examples include gradually adding the acrylic-modified epoxy resin to an aqueous medium containing a basic compound as a neutralizing agent while stirring; neutralizing the acrylic-modified epoxy resin with a basic compound, and then adding the aqueous medium to the neutralized product while stirring; or adding the neutralized product to the aqueous medium.

[0044] <Wax (B)> Specifically, wax (B) can include natural waxes or synthetic waxes, glycerides and waxes, as well as oxides and acid-modified products thereof, and can be used individually or in combination of two or more types.

[0045] Examples of natural waxes include hydrogenated hardened oils obtained by hydrogenating beef or pork fat, beeswax, lanolin wax, whale wax, hydrogenated whale wax, carnauba wax, candelilla wax, rice wax, wood wax, jojoba wax, shellac, and other animal and plant waxes, as well as mineral waxes such as paraffin wax, microcrystalline wax, montan wax, and sericin wax.

[0046] Examples of synthetic waxes include polyethylene wax, polypropylene wax, polytetrafluoroethylene wax, and silicone wax.

[0047] As for wax (B), lanolin wax, olive oil, palm oil, linseed oil, microcrystalline wax, polyethylene wax, etc., can be suitably used from the viewpoint of lubricity and wear resistance.

[0048] Commercially available waxes (B) include refined lanolin (lanolin wax, trade name, manufactured by CRODA), CERACOL 609N (lanolin wax, trade name, manufactured by BYK), Lanolin R (lanolin wax, trade name, manufactured by Nippon Seika Co., Ltd.), Outer Lo-1 (olive oil, trade name, manufactured by Riken Vitamin Co., Ltd.), refined palm oil (palm oil, trade name, manufactured by Nisshin Oil Co., Ltd.), HI-DISPER 1260 (microcrystalline wax, trade name, manufactured by Gifu Cerator Manufacturing Co., Ltd.), Topco S923 (microcrystalline wax, trade name, manufactured by Toyo Petrolite Co., Ltd.), CERAFLOUR 991 (BYK, trade name, polyethylene wax, average particle size 5 μm, melting point 115℃), HIGH Examples include FLAT2352 (manufactured by Gifu Cerac Manufacturing Co., Ltd., product name, polyethylene oxide wax, average particle size 5 μm, melting point 138°C) and Lanco1370LF (manufactured by Lubrizol Japan, product name, polypropylene wax, average particle size 9 μm, melting point 150°C).

[0049] The amount of wax (B) varies depending on the type of wax used, but from the viewpoint of lubricity and wear resistance, it is preferable that it be in the range of 0.3 to 10% by mass, preferably 0.3 to 6% by mass, and more preferably 0.5 to 1.5% by mass, based on the total solid content of the acrylic-modified epoxy resin (A) (with the total solid content of the acrylic-modified epoxy resin (A) being 100% by mass).

[0050] The composition of the present invention uses at least one type of wax selected from the group consisting of waxes (B) above, a wax with a melting point of less than 50°C (b1), a wax with a melting point of 50°C or higher and less than 100°C (b2), and a wax with a melting point of 100°C to 160°C and an average particle size of 1 to 15 μm (b3).

[0051] By using at least one type of wax selected from the group consisting of the three types described above, the surface roughness of the coating can be adjusted, and a can body can be provided that exhibits reduced dynamic friction coefficient, excellent lubricity, wear resistance, and processability, as well as excellent lid manufacturing properties.

[0052] Wax (b1) The wax (b1) is not particularly limited as long as it has a melting point of less than 50°C. Lanolin wax, olive oil, palm oil, linseed oil, glycerin triester, etc., can be suitably used in terms of reducing the coefficient of dynamic friction, improving lubricity, wear resistance, and processability.

[0053] Examples of commercially available waxes (b1) include refined lanolin (lanolin wax, trade name, manufactured by CRODA), Outer Lo-1 (olive oil, trade name, manufactured by Riken Vitamin Co., Ltd.), and refined palm oil (palm oil, trade name, manufactured by Nisshin Oil Co., Ltd.).

[0054] Wax (b2) The wax (b2) is not particularly limited as long as it has a melting point of 50°C or higher and less than 100°C, preferably 60°C to 90°C. Microcrystalline wax and carnauba wax can be suitably used in terms of reducing the coefficient of dynamic friction, lubricity, wear resistance, and processability.

[0055] Examples of commercially available waxes (b2) include HI-DISPER 1260 (microcrystalline wax, trade name, manufactured by Gifu Cerate Manufacturing Co., Ltd.), Topco S923 (microcrystalline wax, trade name, manufactured by Toyo Petrolite Co., Ltd.), HD-3028 (manufactured by Gifu Cerate Manufacturing Co., Ltd., carnauba wax, melting point 82℃), and Hi-Mic-1070 (manufactured by Nippon Seiro Co., Ltd., microcrystalline wax, melting point 80℃).

[0056] Wax (b3) The wax (b3) is not particularly limited as long as it has an average particle size of 1 to 15 μm, preferably 2 to 11 μm, and a melting point of 100°C to 160°C, preferably 120°C to 155°C. Polyethylene wax and polypropylene wax can be suitably used in terms of reducing the coefficient of dynamic friction, lubricity, wear resistance, and processability.

[0057] Examples of commercially available waxes (b3) include CERAFLOUR 991 (manufactured by BYK, trade name, polyethylene wax, average particle size 5 μm, melting point 115°C), HIGH FLAT 2352 (manufactured by Gifu Ceraduc Manufacturing Co., Ltd., trade name, oxidized polyethylene wax, average particle size 5 μm, melting point 138°C), and Lanco 1370LF (manufactured by Lubrizol Japan, trade name, polypropylene wax, average particle size 9 μm, melting point 150°C).

[0058] In this invention, the melting point of wax (B) is the endothermic peak temperature measured by differential scanning calorimeter (DSC) at a heating rate of 10°C / min. If the wax has multiple endothermic peaks, the melting point is defined as the maximum endothermic peak. The average particle size of the wax was measured by volume-average diameter using the laser diffraction-scattering method with a Microtrac UPA (particle size analyzer manufactured by Nikkiso Co., Ltd.).

[0059] If wax (B) contains wax (b1), it is desirable that the solid content of wax (b1) in wax (B) be in the range of 0.1 to 5% by mass, preferably 0.2 to 2% by mass, and more preferably 0.2 to 1.0% by mass, based on the total solid content of acrylic-modified epoxy resin (A), from the viewpoint of reducing the coefficient of dynamic friction, lubricity, wear resistance, and processability. If wax (B) contains wax (b2), it is desirable that the solid content of wax (b2) in wax (B) be in the range of 0.1 to 5% by mass, preferably 0.2 to 2% by mass, and more preferably 0.2 to 1.0% by mass, based on the total solid content of acrylic-modified epoxy resin (A), from the viewpoint of reducing the coefficient of dynamic friction, lubricity, wear resistance, and processability. When wax (B) contains wax (b3), the amount of solids in wax (B) is preferably in the range of 0.1 to 5% by mass, more preferably 0.2 to 2% by mass, and more preferably 0.2 to 1.0% by mass, based on the total amount of solids in the acrylic-modified epoxy resin (A), which is desirable from the viewpoint of reducing the coefficient of dynamic friction, lubricity, wear resistance, and processability. Furthermore, the sum of the solids of wax (b1), wax (b2), and wax (b3), based on the total amount of solids in wax (B) (100% by mass), is, for example, 85% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0060] <Polyolefin aqueous dispersion (C)> Polyolefin aqueous dispersion (C) can be any product that has been processed to be dispersible in aqueous compositions such as aqueous paints, aqueous dispersions, or aqueous emulsions. This can include products produced by emulsion polymerization, or those in which polyolefins are mechanically dispersed in an aqueous medium. It can be used alone or in combination of two or more types.

[0061] In the composition of the present invention, from the viewpoint of minimizing the use of emulsifiers and ensuring water resistance, a material in which polyolefins are mechanically dispersed in an aqueous medium can be suitably used.

[0062] The polyolefin in the polyolefin aqueous dispersion (C) preferably has an average particle size of 0.1 to 5 μm, particularly 0.2 to 4.0 μm, and even more preferably 0.3 to 3.0 μm, from the viewpoint of the lubricity, abrasion resistance, and processability of the resulting coating film.

[0063] In the composition of the present invention, the average particle size of the polyolefin aqueous dispersion (C) is a value measured by the microtrac method.

[0064] In the composition of the present invention, the polyolefin of the polyolefin aqueous dispersion (C) is preferably puncture-free, more preferably 4 or less, and more preferably 1 or less, from the viewpoint of processability and abrasion resistance.

[0065] The penetration degree of the polyolefin constituting the polyolefin aqueous dispersion (C) is standardized in JIS K2207. This standard is determined by vertically inserting a needle of a specified weight into the polyolefin at a temperature of 25°C, a load of 100g, and a penetration time of 5 seconds, and the length of penetration is expressed as the penetration degree, with 0.1mm representing a penetration degree of 1. Therefore, the smaller the penetration degree, the harder the polyolefin, and the larger the penetration degree, the softer the polyolefin. The present invention uses a polyolefin aqueous dispersion obtained using a polyolefin having a penetration degree within the above range.

[0066] Examples of polyolefin types include low-density polyolefins, low-molecular-weight polyolefins, ethylene-methacrylic acid copolymers, and ionomers such as metal salts of ethylene-methacrylic acid copolymers.

[0067] Of the above, low molecular weight polyolefins, particularly low molecular weight polyethylene, can be suitably used from the viewpoint of water dispersibility.

[0068] Commercially available polyolefin aqueous dispersions (C) can also be used. Specific examples of commercially available products include Arrowbase from Unitika Corporation, Chemipearl from Mitsui Chemicals, Inc., and AB-50 from Gifu Ceraduc Manufacturing Co., Ltd.

[0069] The amount of polyolefin aqueous dispersion (C) can be adjusted according to the desired degree of lubricity, abrasion resistance, and processability, and it is also possible to use two or more types in combination. From the viewpoint of lubricity, abrasion resistance, and processability, it is preferable that the total solid content of the polyolefin is in the range of 1.0 to 10.0% by mass, particularly 2.0 to 8.0% by mass, and even more particularly 3.0 to 7.0% by mass, relative to the total solid content of the acrylic-modified epoxy resin (A).

[0070] Phenolic resin (D) Examples of phenolic resins (D) include resol-type phenolic resins obtained by introducing methylol groups through a condensation reaction between phenol compounds, phenols such as bisphenol A (d1), and aldehydes such as formaldehyde (d2) in the presence of a reaction catalyst.

[0071] The above-mentioned phenols (d1) can be any one or more of the following phenol compounds: difunctional phenol compounds such as o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol; trifunctional phenol compounds such as carbolic acid, m-cresol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol; or tetrafunctional phenol compounds such as bisphenol A and bisphenol F.

[0072] Examples of the above-mentioned aldehydes (d2) include formaldehyde, paraformaldehyde, or trioxane, and they can be used individually or in combination of two or more.

[0073] The methylol group of the methylolated phenol resin can optionally be further alkyl etherified. Suitable alcohols for alkyl etherification include monohydric alcohols with 1 to 6 carbon atoms, particularly 1 to 4 carbon atoms. Examples of suitable monohydric alcohols include methanol, ethanol, n-propanol, n-butanol, and isobutanol.

[0074] From the viewpoint of reactivity, the phenolic resin (D) preferably has a number-average molecular weight in the range of 200 to 2,000, particularly 300 to 1,200, and an average number of methylol groups per benzene ring of 0.3 to 3.0, particularly 0.5 to 3.0.

[0075] From the viewpoint of processability, the amount of phenolic resin (D) is preferably in the range of 0.5 to 20% by mass, particularly 1 to 15% by mass, and even more preferably 2 to 10% by mass, relative to the total solid content of acrylic-modified epoxy resin (A).

[0076] <Water-based paint composition for cans> The aqueous paint composition for cans of the present invention is an aqueous paint composition in which an acrylic-modified epoxy resin (A) is neutralized and dispersed in an aqueous medium, and the composition contains wax (B), polyolefin aqueous dispersion (C), and phenol resin (D) as essential components, and may optionally contain other additives, such as surfactants, defoamers, pigments, fragrances, etc.

[0077] Of the above, surfactants can be suitably used from the viewpoint of the dispersion stability of polyolefin (component C) and the stability of the appearance of the coating film when pigment is included.

[0078] As surfactants, for example, alkylbenzenesulfonic acid (and amine neutralized products) can be used particularly suitably.

[0079] The solid content concentration of the composition of the present invention is not particularly limited, but from the viewpoint of paint stability, it is preferably in the range of 20 to 45% by mass, more preferably 22 to 40% by mass.

[0080] The compositions of the present invention can be applied to various substrates, including metals such as tinplate, aluminum, tin-free steel, iron, zinc, copper, galvanized steel sheets, and alloy-plated steel sheets; chemically treated metal sheets obtained by surface treatment such as phosphate treatment or chromate treatment on these metals; metal sheets coated with primers such as epoxy resin or vinyl resin; and substrates obtained by processing these metal sheets into cans or the like.

[0081] The composition of the present invention can be used particularly suitably for the inner and outer surfaces of cans, especially for can lids where strict lid-making properties are required.

[0082] The composition of the present invention can be coated by known methods, such as roll coating or spray coating, to a dry film thickness of 1 to 20 μm, preferably 2 to 10 μm, and then heated and dried by maintaining a temperature of 120 to 300°C, preferably 200 to 280°C, for about 10 seconds to 30 minutes, preferably about 15 seconds to 15 minutes. [Examples]

[0083] The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited in any way by the following examples. In the following, "parts" and "%" are all based on mass.

[0084] Manufacturing of acrylic-modified epoxy resin (A) Manufacturing Example 1: Manufacturing of Epoxy Resin Solution No. 1 A four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet was charged with 558 parts of jER828 (Note 1), 329 parts of bisphenol A, and 0.6 parts of tetrabutylammonium bromide, and the reaction was carried out at 160°C under a nitrogen stream. The reaction was monitored by epoxy equivalents, and after approximately 5 hours of reaction, epoxy resin solution No. 1 was obtained. The obtained epoxy resin No. 1 had a number-average molecular weight of approximately 8,000. (Note 1) jER828: Manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent weight approximately 190, number average molecular weight approximately 380 Manufacturing Example 2: Manufacturing of Epoxy Resin No. 2 Solution 550 parts of jER828 (Note 1) and 450 parts of bisphenol A were placed in a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, and the mixture was heated under a nitrogen stream while stirring. When the bisphenol A dissolved and the mixture became clear (around 100°C), 5.0 parts of tri-n-butylamine were added, and the reaction was carried out at 160°C under a nitrogen stream.

[0085] The reaction was monitored using epoxy equivalents, and after approximately 4 hours of reaction, epoxy resin solution No. 2 was obtained. The obtained epoxy resin No. 2 had a number-average molecular weight of approximately 4,500.

[0086] Manufacturing Example 3: Manufacturing of Acrylic Resin Solution In a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, 882 parts of n-butanol were charged. A mixture of "180 parts methacrylic acid, 240 parts styrene, 180 parts ethyl acrylate, and 18 parts t-butyl peroxy-2-ethylhexanoate" was heated to 100°C under a nitrogen stream. The mixture was then added dropwise from a dropping funnel over approximately 3 hours. After addition, stirring was continued at the same temperature for another 2 hours, and then the mixture was cooled to obtain an acrylic resin solution with a solid content of 40%. The obtained acrylic resin had a number-average molecular weight of approximately 19,000 and an acid value of 196 mgKOH / g.

[0087] Manufacturing Example 4: Production of Acrylic Modified Epoxy Resin No. 1 Aqueous Dispersion In a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, 80 parts (solids) of epoxy resin solution No. 1 obtained in Production Example 1, 20 parts (solids) of acrylic resin solution obtained in Production Example 3, and 33 parts of diethylene glycol monobutyl ether were added and heated to 100°C to dissolve. Then, 2 parts of N,N-dimethylaminoethanol were added and the reaction was carried out for approximately 2 hours, after which 3 parts of N,N-dimethylaminoethanol were added and the reaction was continued for 20 minutes. Subsequently, 165 parts of deionized water were added dropwise over 1 hour to obtain an aqueous dispersion of acrylic-modified epoxy resin No. 1 with an acid value of 34 mg KOH / g and a solids content of 30%.

[0088] Manufacturing Example 5: Production of Acrylic Modified Epoxy Resin No. 2 Aqueous Dispersion In a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, 25 parts ethylene glycol monobutyl ether and 80 parts (solid content) of epoxy resin No. 2 solution obtained in Production Example 2 were added, and the mixture was heated to 120°C under a nitrogen stream while stirring.

[0089] After the epoxy resin No. 2 solution was completely dissolved, a mixed solution of "4 parts styrene, 4 parts methyl methacrylate, 6 parts n-butyl acrylate, 6 parts methacrylic acid, and 1 part benzoyl peroxide" was added dropwise over 1 hour at 120°C. After the dropwise addition was complete, the mixture was held at 120°C for 1 hour. Then, it was cooled to 90°C, 6.2 parts dimethylethanolamine was added, and the mixture was stirred for 15 minutes. Furthermore, while stirring, 201 parts deionized water was added dropwise over 1 hour to obtain an acrylic-modified epoxy resin No. 2 aqueous dispersion with an acid value of 44 mg KOH / g and a solid content of 30%.

[0090] Manufacturing of phenolic resin (D) Manufacturing Example 6: Production of Phenolic Resin No. 1 Solution In a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, 188 parts of phenol and 324 parts of 37% formaldehyde aqueous solution were charged and heated to 50°C to uniformly dissolve the contents. Next, zinc acetate was added and mixed to adjust the pH of the system to 5.0, and the reaction was carried out at 90°C for 5 hours. Then, the mixture was cooled to 50°C, and a 32% calcium hydroxide aqueous dispersion was slowly added to adjust the pH to 8.5, and the reaction was carried out at 50°C for 4 hours.

[0091] After the reaction was complete, the pH was adjusted to 4.5 with 20% hydrochloric acid, and then the resin was extracted with a mixed solvent of xylene / n-butanol / cyclohexane = 1 / 2 / 1 (mass ratio) to remove the catalyst and neutralization salt. Subsequently, azeotropic dehydration was performed under reduced pressure to obtain phenol resin solution No. 1 with a solid content of 50%. The resin solid content of phenol resin solution No. 1 had a number-average molecular weight of 350 and an average number of methylol groups per benzene ring of 1.3.

[0092] Manufacturing Example 7: Production of Phenolic Resin No. 2 Solution In a four-necked glass flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen inlet, 108 parts of m-cresol, 216 parts of 37% formaldehyde aqueous solution, and 160 parts of 25% sodium hydroxide aqueous solution were charged. The mixture was reacted at 50°C under a nitrogen stream, then the temperature was raised to 100°C and the reaction was continued for another hour. After neutralization with hydrochloric acid, the resin was extracted with a xylene / n-butanol = 1 / 1 (mass ratio) mixed solvent to remove the catalyst and neutralized salt. Then, azeotropic dehydration was performed under reduced pressure to obtain a phenol resin No. 2 solution with a solid content of 50%. The resin solid content of the phenol resin No. 2 solution had a number-average molecular weight of 350 and an average number of methylol groups per benzene ring of 0.7.

[0093] Manufacturing of water-based paint compositions for cans Example 1 In a container, 100 parts (solids) of the acrylic-modified epoxy resin No. 1 aqueous dispersion obtained in Production Example 4, 0.3 parts of refined palm oil (Note 2), 1 part of AB-50 (Note 9), and 3 parts (solids) of the phenol resin No. 1 solution obtained in Production Example 6 were uniformly mixed and adjusted with deionized water to obtain a water-based paint composition No. 1 for cans with a solids content of 30% by mass.

[0094] Examples 2-84 and Comparative Examples 1-65 Water-based paint compositions for cans No. 2 to No. 149 were obtained in the same manner as in Example 1, except for the formulations shown in Table 1. The results of tests conducted according to the following test methods are also shown. The composition ratios in Table 1 are solid content mass ratios.

[0095] Note that water-based paint compositions No. 85 to 149 for cans are for comparative examples only.

[0096] Furthermore, the notes in the table are as follows: (Note 2) Refined palm oil: Manufactured by Nisshin Oil Co., Ltd., palm oil, melting point 39℃ (Note 3) Refined lanolin: Manufactured by CRODA, lanolin wax, melting point 39°C (Note 4) HD-3028: Manufactured by Gifu Ceratex Manufacturing Co., Ltd., carnauba wax, melting point 82℃ (Note 5) Hi-Mic-1070: Manufactured by Nippon Seiro Co., Ltd., microcrystalline wax, melting point 80℃ (Note 6) Lanco1370LF: Manufactured by Lubrizol Japan, polypropylene wax, melting point 150℃, average particle size 9μm (Note 7) CERAFLOUR 991: Manufactured by BYK, polyethylene wax, melting point 115℃, average particle size 5μm (Note 8) CERAFLOUR 913: Manufactured by BYK, trade name, polypropylene wax, melting point 160℃, average particle size 18μm (Note 9) AB-50: Manufactured by Gifu Cerac Manufacturing Co., Ltd., average particle size 1 μm, penetration degree 1-2 (Note 10) A-375: Manufactured by Gifu Cerac Manufacturing Co., Ltd., average particle size 2 μm, penetration degree 1-2 (Note 11) A-110: Manufactured by Gifu Ceratex Manufacturing Co., Ltd., average particle size 5 μm, penetration degree less than 1. (Note 12) Chemipearl W300: Manufactured by Mitsui Chemicals, Inc., average particle size 3 μm, penetration degree less than 1. (Note 13) Chemipearl W500: Manufactured by Mitsui Chemicals, Inc., average particle size 2.5 μm, penetration degree 10 (Note 14) Chemipearl F640: Manufactured by Mitsui Chemicals, Inc., average particle size 1 μm, penetration degree 10 Note that (Notes 9) to (Note 14) are polyolefin dispersions. (Note 15) Naicure 5225: Manufactured by King Industries, USA, trade name, amine neutralization solution of dodecylbenzenesulfonic acid (Note 16) Naicure 2500: Manufactured by King Industries, USA, trade name, amine neutralization solution of p-toluenesulfonic acid [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8] [Table 9] Preparation of test boards On an aluminum plate with a thickness of 0.26 mm, each of the water-based paint compositions No. 1 to 149 for cans obtained in the above examples and comparative examples was measured, and the dry film weight was 40 mg / 100 cm². 2 The material was coated using a bar coater, and then baked in a drying oven for 17 seconds under conditions of an ambient temperature of 315°C and an airflow of 30 m / min, so that the maximum temperature the material could reach was 270°C, to obtain the corresponding test plates.

[0097] Each test plate obtained was tested and evaluated against the following evaluation criteria. The evaluation results are shown in Table 1.

[0098] Coating Appearance: The appearance of each test panel was evaluated visually. The appearance was evaluated according to the following criteria regarding the smoothness, blemishes, and repellency of the coating surface: ◎: The painted surface is smooth and free from any blemishes or streaks larger than 1 mm in diameter. ○: Very few blemishes and / or imperfections larger than 1 mm in diameter, and very few yuzu peel-like spots may be observed. △: Objects with a diameter of 1 mm or more and / or defects are observed. ×: Significantly noticeable defects and / or imperfections larger than 1 mm in diameter are observed. Processability: After cutting the test plate 5 cm in the rolling direction and 4 cm in the vertical direction, the lower part was folded in half parallel to the shorter side. Two 0.26 mm thick aluminum plates were placed between the folded parts of the test piece in a room at 20°C, and the piece was set in a special seam-folding DuPont impact tester. A 1 kg iron weight with a flat contact surface was dropped from a height of 50 cm to impact the folded parts. After that, a voltage of 6.5 V was applied to the folded tip for 6 seconds, and the current value (mA) across a 20 mm width at the folded tip was measured and evaluated according to the following criteria: ◎ indicates less than 10mA ○ indicates a current of 10mA or more, and less than 20mA. △ indicates a current of 20mA or more, and less than 40mA. × indicates a current of 40mA or more. Dynamic friction coefficient: A 1kg mass supported by three steel balls was placed on a test plate adjusted to a size of 15cm x 30cm and pulled at a speed of 150cm / min to determine the dynamic friction coefficient (μ value). A smaller dynamic friction coefficient (μ value) indicates better lubricity. ◎ indicates a μ value of less than 0.06. ○ indicates a μ value of 0.06 or higher and less than 0.1. △ indicates that the μ value is 0.1 or greater, and less than 0.15. × indicates a μ value of 0.15 or higher. Scratch resistance: A test plate adjusted to a size of 10cm x 20cm was tested using a tribogear (manufactured by Shinto Kagaku Co., Ltd., product name HEIDON-22H, test needle 150μm, scratching speed 60mm / min). The scratch resistance was evaluated by the load at which the test needle reached the aluminum plate. ◎ indicates that the load at which the test needle reached the aluminum plate was 300g or more. ○ indicates that the load at which the test needle reached the aluminum plate was 200g or more, and less than 300g. △ indicates that the load at which the test needle reached the aluminum plate was 150g or more, but less than 200g. × indicates that the load at which the test needle reached the aluminum plate was less than 150g. Abrasion resistance: A friction test was performed on a test plate adjusted to a size of 1.5 cm x 16 cm using a Bowden abrasion tester (manufactured by Shinko Seiki Co., Ltd., Soda type adhesive sliding tester, friction part ball indenter 3 / 16 inch steel ball, load 4 kgf, friction speed 7 reciprocations / min). The number of friction cycles until scratches appeared on the coating was measured and evaluated according to the following criteria. ◎ indicates that the coating shows no scratches after 50 friction cycles. ○ indicates that scratches occur on the coating after 30 or more friction cycles, but no more than 49. △ indicates that scratches occur on the coating after 10 or more friction cycles, but 29 or fewer. × indicates that scratches occurred on the coating after 9 or fewer friction cycles. [Industrial applicability]

[0099] This invention provides a can body having a coating that exhibits excellent lubricity, wear resistance, and processability.

Claims

1. A paint composition containing an acrylic-modified epoxy resin (A), a wax (B), a polyolefin aqueous dispersion (C), and a phenolic resin (D), The wax (B) contains at least one type of wax selected from the group consisting of waxes with a melting point of less than 50°C (b1), waxes with a melting point of 50°C or higher and less than 100°C (b2), and waxes with a melting point of 100 to 160°C and an average particle size of 1 to 15 μm (b3). The average particle size of the polyolefin aqueous dispersion (C) is 0.1 to 5 μm, and the penetration degree of the polyolefin is 8 or less. An aqueous paint composition for cans, characterized in that, based on the total solid content of the acrylic-modified epoxy resin (A), the total solid content of the wax (B) is 0.3 to 10% by mass, the total solid content of the polyolefin aqueous dispersion (C) is 1 to 10% by mass, and the total solid content of the phenolic resin (D) is 0.5 to 20% by mass.

2. The aqueous paint composition for cans according to claim 1, wherein the wax (b1) is at least one selected from the group consisting of lanolin wax, palm oil, and glycerin triester.

3. The aqueous paint composition for cans according to claim 1 or 2, wherein the wax (b2) is at least one selected from the group consisting of microcrystalline wax and carnauba wax.

4. The aqueous paint composition for cans according to claim 1 or 2, wherein the wax (b3) is at least one selected from the group consisting of polyethylene wax and polypropylene wax.

5. The aqueous paint composition for cans according to claim 1 or 2, wherein the solid content of wax (b1), wax (b2), and wax (b3) is 0.1 to 5% by mass of wax (b1), 0.1 to 5% by mass of wax (b2), and 0.1 to 5% by mass of wax (b3), based on the total solid content of the acrylic-modified epoxy resin (A).

6. The aqueous paint composition for cans according to claim 1 or 2, which is for use as a can lid.

7. A can lid having a coating film of the aqueous paint composition for cans according to claim 1 or 2.

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