Can paints, coated plates, and coated cans

Abstract

To provide a coating material suitable for food and drink cans, capable of forming a coating film having good abrasion resistance, processing adhesion and hardening property. [Solution] A can coating that satisfies (i) and (ii) in the following nano-scratch test. <Nano scratch test> The can paint was applied to the body of an aluminum can, baked at 180°C for 52 seconds and 200°C for 2 minutes, and the coating surface of the resulting sample was measured at 23°C using a nanoindenter. (i) the average coefficient of friction is 2 or less, and (ii) the maximum scratch size is 120 nm or less.

Description

[Technical Field]

[0001] The present invention relates to a can coating material that can be used to form a coating film on a coated can or the like. [Background technology]

[0002] On the outer surfaces of beverage cans for storing alcoholic beverages such as soft drinks, coffee, or beer, and food cans for storing fish and meat (hereinafter, both of these cans are collectively referred to as food and beverage cans), a coating film is formed using paint to protect the surface and enhance its appearance. In addition, the coating film is required to be resistant to scratches and abrasion during transportation and during movement on the manufacturing line of food and beverage cans. In addition, the speed at which cans are transported during the can-making and filling processes is becoming increasingly faster, creating a demand for paints that are scratch-resistant, abrasion-resistant, and hard, and can form coatings that can withstand high-speed transport.

[0003] Patent Document 1 (JP 2023-075011 A) discloses an aqueous coating composition for cans that contains an acrylic-modified epoxy resin, at least one wax selected from three types of wax with different melting points, a polyolefin aqueous dispersion, and a phenolic resin, and that has excellent lubricity, abrasion resistance, and processability.

[0004] However, in the coating composition described in Patent Document 1, when a large amount of wax or polyolefin aqueous dispersion is blended to improve lubricity and abrasion resistance, the smoothness of the coating surface deteriorates, resulting in a decrease in scratch resistance, making it difficult to achieve high levels of lubricity, abrasion resistance, and scratch resistance.Furthermore, there is no mention of hardness. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-075011 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coating material suitable for food and beverage cans, which is capable of forming a coating film having good abrasion resistance, processing adhesion, and curing properties. [Means for solving the problem]

[0007] [1] A can coating that satisfies (i) and (ii) in the nano-scratch test below. <Nano scratch test> [1] The coating material was applied to the body of an aluminum can and baked at 180°C for 52 seconds and 200°C for 2 minutes. The coating surface of the sample was measured at 23°C using a nanoindenter. (i) the average coefficient of friction is 2 or less, and (ii) the maximum scratch depth is 120 nm or less. [2] A can coating according to [1], which satisfies (iii) in the following indentation test. <Indentation test> The can paint was applied to the body of an aluminum can, baked at 180°C for 52 seconds and 200°C for 2 minutes, and the coating surface of the resulting sample was measured at 23°C using a nanoindenter. (iii) The film hardness is 0.35 GPa or less. [3] The can paint according to [1], wherein the can paint contains an acrylic resin, a polyester resin, and an amino resin, and the amino resin is contained in an amount of 25 to 185 parts by mass per 100 parts by mass of the total of the acrylic resin and the polyester resin. [4] The amino resin includes a melamine resin and a benzoguanamine resin, or includes only a melamine resin; The can coating material according to [3], wherein the mass ratio of the melamine resin to the benzoguanamine resin is melamine resin / benzoguanamine resin=30 / 70 to 100 / 0. [5] The can paint according to [1], wherein the content of the fluorine atom-containing compound in the can paint is 2 parts by mass or less per 100 parts by mass of the total of the resin components of the can paint. [6] A coated plate comprising a metal plate and a coating film that is a cured product of the can coating material according to any one of [1] to [5]. [7] A coated can comprising a metal plate and a coating film that is a cured product of the can coating material according to any one of [1] to [5]. [Effects of the Invention]

[0008] According to the present invention having the above-mentioned configuration, it is possible to provide a coating material suitable for food and beverage cans, which is capable of forming a coating film having good abrasion resistance, processing adhesion, and curing properties. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail the embodiments of the present invention.

[0010] <Can paint> The can coating material of the present invention is used to coat can surfaces (exterior and interior surfaces), and is particularly suitable as a can exterior coating material for protecting the exterior surfaces of food and beverage cans and improving their appearance.

[0011] <Method for forming coating film for evaluation> In the present invention, the coating film for evaluating various physical properties is obtained by applying the paint to an aluminum substrate, baking at 180°C for 52 seconds, and then baking and curing at 200°C for 2 minutes.

[0012] <Nano scratch test> The nano-scratch test in the present invention is carried out using a micro-area mechanical property evaluation device (nanoindenter), which makes it possible to measure the average coefficient of friction of the coating film and the depth of scratch marks on the coating film.

[0013] <Average friction coefficient of coating film> The friction coefficient measured by the nano scratch test is the value obtained by dividing the horizontal load applied to the indenter of the nanoindenter by the vertical load at that time, and in this invention is the value measured using a Hysitron TI Premier (manufactured by Bruker). The average coefficient of friction of the coating film was calculated as follows. A conical indenter with a conical shape was used as the indenter of the nanoindenter. The conical indenter was brought into contact with the measurement sample, and at 23°C, the indenter was moved horizontally at 0.4 μm / s for 6 μm while simultaneously applying a maximum load of 100 μN in the vertical direction at a loading rate of 6.7 μN / s. The average coefficient of friction was obtained by averaging the values ​​of the coefficient of friction over a horizontal movement distance of 1 μm to 5 μm. In the present invention, a conical indenter having a tip with a radius of curvature of 1 μm or less is used.

[0014] The coating surface of a coating film formed from the can coating material of the present invention has an average coefficient of friction of 2 or less as measured by the nanoindentation method. There is no particular lower limit to the average coefficient of friction, but it is preferably 0.2 or more, for example. If the average coefficient of friction of the coating film measured by the nanoindentation method is 2 or less, friction during scratching is reduced, and the abrasion resistance of the coating film is improved. If the abrasion resistance is poor, the coating film is more susceptible to damage.

[0015] <Maximum scratch depth on coating> The maximum scratch depth measured by the nanoscratch method is a value that represents the horizontal durability of a coating film, measured using a nanoindenter, and in the present invention, is measured using the same device as that used to measure the average coefficient of friction of the coating film. The deeper the scratch, the lower the durability to horizontal stimuli and the more susceptible the coating film is to scratches. The scratch depth of the coating film was measured by moving a conical indenter horizontally on the measurement sample under the indentation conditions described below, and then tracing the depth at the same point on the coating film with a weak load that did not cause deformation, and the maximum value was taken as the maximum scratch depth (nm). The indentation conditions were as follows: the indenter was moved horizontally at 0.4 μm / s for 6 μm, and a maximum load of 100 μN was applied vertically at a loading rate of 6.7 μN / s.

[0016] The coating film surface formed from the can coating material of the present invention has a maximum scratch depth of 120 nm or less, preferably 90 nm or less, as measured by the nanoindentation method. By keeping the maximum scratch depth of the coating film to 120 nm or less, deformation due to horizontal load when scratched is suppressed, and the abrasion resistance of the coating film is improved.

[0017] The average coefficient of friction and maximum scratch depth of the coating film surface formed from the can coating of the present invention can be adjusted mainly by the composition and type of the curing agent component constituting the can coating. Specifically, by keeping the content of the curing agent component within an appropriate range, the scratch resistance of the coating film is improved, and the average coefficient of friction and maximum scratch depth of the coating film surface are reduced. On the other hand, if the curing agent component is insufficient, curing is insufficient, resulting in the formation of a coating film, and the average coefficient of friction and maximum scratch depth of the coating film surface are increased. If the curing agent component is too much, the coating film becomes brittle and easily damaged, and the maximum scratch depth is increased. Furthermore, when an amino resin is used as the curing agent component, adding a melamine resin with many reactive sites tends to achieve an appropriate crosslink density, and the average coefficient of friction and maximum scratch depth of the coating film surface are reduced. On the other hand, adding a benzoguanamine resin with a rigid structure tends to increase the average coefficient of friction and maximum scratch depth of the coating film surface.

[0018] <Indentation test> The indentation test of the present invention is performed using a micro-area mechanical property evaluation device (nanoindenter). This test allows the hardness of the coating surface to be measured by the nanoindentation method.

[0019] <Coating film hardness> Hardness measured by the nanoindentation method is the indentation hardness value measured using a micro-area mechanical property evaluation device (nanoindenter), and in the present invention, it is measured using the same device as that used to measure the average coefficient of friction of the coating surface. The nanoindenter indents only the very surface layer of the coating film, making it possible to measure the mechanical properties of only the thin coating film without being affected by the substrate. With other measurement methods, the indentation load and displacement are too large, making it susceptible to the influence of the substrate and making it difficult to measure only the thin layer. In the present invention, it is possible to evaluate the hardness of only the coating film. The indentation hardness (H) of the coating film is measured as follows, and is calculated by the following (Equation 1). H=Fmax / Ac (Equation 1) A triangular pyramidal Berkovich indenter is used as the nanoindenter's indenter. The Berkovich indenter is pressed into the measurement sample under the indentation conditions described below, and the indentation depth h (nm) is continuously measured against the indentation load F (μN) to create a load-displacement curve. The maximum indentation load Fmax (μN) is then determined from the created load-displacement curve. The indentation hardness (H) is then calculated by dividing the maximum indentation load Fmax (μN) by the contact projected area Ac (μ) between the indenter and the sample at that time. Here, Ac is the contact projected area corrected for the indenter tip curvature using a standard sample of fused silica according to the instrument's standard method. The contact projected area Ac is calculated from the indentation depth h (nm), and Ac = 24.56h 2 (nm 2 )

[0020] The indentation conditions were as follows: at 23°C, the indenter was first pressed to a depth of 200 nm over 5 seconds (i.e., the indentation speed was 40 nm / s), then held at the 200 nm depth for 2 seconds, and finally unloaded to 0 nm over 5 seconds. The maximum indentation load Fmax used in calculating hardness is the load value after holding for 2 seconds. The coating film of the present invention preferably has a hardness of 0.35 GPa or less, more preferably 0.20 GPa or more and 0.30 GPa or less, as measured by the nanoindentation method. If the hardness of the coating film measured by the nanoindentation method is within this range, the desired hardness of the coating film and performance such as processing adhesion and curability can be effectively optimized. The hardness of the coating surface of the coating film formed from the can coating material of the present invention can be adjusted by the type and composition of the resin components and curing agent components that make up the can coating material. Specifically, the use of a large amount of curing agent tends to result in a large indentation hardness. On the other hand, the opposite tendency occurs when the amount of curing agent is reduced or a resin with a low glass transition temperature is used.

[0021] <Composition of can paint> The composition of the can coating material of the present invention will be described below: The composition of the coating material includes an acrylic resin, a polyester resin, an amino resin, an organic solvent, water, a lubricity-imparting agent, and the like.

[0022] <Acrylic resin> The acrylic resin in the present invention is a polymer of an ethylenically unsaturated monomer (hereinafter also simply referred to as a monomer) that essentially contains a compound having a (meth)acryloyl group (an acryloyl group and a methacryloyl group are collectively referred to as a (meth)acryloyl group; the same applies hereinafter).

[0023] In the present invention, (meth)acrylamides, alkyl (meth)acrylates, vinyl monomers, monomers having a hydroxy group, monomers having a carboxy group, and the like are used as monomers. Examples of (meth)acrylamides include N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, Nn-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, Nn-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N-pentyloxymethyl(meth)acrylamide, N-hexyloxymethyl(meth)acrylamide, N-heptyloxymethyl(meth)acrylamide, N-octyloxymethyl(meth)acrylamide, N-2-ethylhexyloxymethyl(meth)acrylamide, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, isobutyl(meth)acrylamide, t-butyl(meth)acrylamide, t-octyl(meth)acrylamide, and diacetone(meth)acrylamide.

[0024] Among these, from the viewpoint of the scratch resistance of the coating film, it is preferable to use N-alkoxymethyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, Nn-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, Nn-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N-pentyloxymethyl(meth)acrylamide, N-hexyloxymethyl(meth)acrylamide, N-heptyloxymethyl(meth)acrylamide, N-octyloxymethyl(meth)acrylamide, or N-2-ethylhexyloxymethyl(meth)acrylamide. N-Alkoxymethyl(meth)acrylamide is a crosslinkable monomer that easily crosslinks with other resins under heat or acidic conditions, further improving the scratch resistance and processing adhesion of the coating film.

[0025] Alkyl (meth)acrylates are primarily used to adjust the glass transition temperature (also referred to as Tg) of acrylic resins. The alkyl group in the alkyl (meth)acrylate of the present invention may be substituted with a substituent other than a substituent containing a hydroxy group or a carboxy group. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, Examples of the acrylate include methyl (meth)acrylate, ...

[0026] Examples of vinyl monomers include styrene, p-methylstyrene, α-methylstyrene, Examples of the vinyl alcohol include vinyl toluene, vinyl acetate, and vinyl propionate. The monomer having a hydroxyl group imparts a hydroxyl group to the acrylic resin, and reacts with the curing agent to increase the crosslink density of the coating film, thereby improving the processing adhesion and scratch resistance of the resulting coating film. Examples of hydroxy group-containing monomers include hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0027] The monomer having a carboxy group imparts an appropriate degree of hydrophilicity to the acrylic resin, and by neutralizing it with a basic compound, the acrylic resin can be made into an aqueous solution or dispersion. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, etc. Among these, (meth)acrylic acid is preferred from the viewpoint of copolymerizability with other monomers. All of the usable monomers may be used alone or in combination of two or more.

[0028] Acrylic resins can be synthesized by methods such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Among these, solution polymerization is preferred because it is easy to control the reaction. Furthermore, radical polymerization initiators commonly used in the synthesis of acrylic resins can be used to synthesize acrylic resins. Examples of the radical polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]. Examples of peroxide compounds include benzoyl peroxide, t-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, t-butylperoxy-2-ethylhexanoate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl)peroxide, dipropionyl peroxide, and diacetyl peroxide. The radical polymerization initiator is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the total of the monomers.

[0029] The weight-average molecular weight of the acrylic resin is preferably 1,000 to 100,000. By making it 1,000 or more, the hardness of the coating film that is formed is improved, and by making it 100,000 or less, the paint stability when made water-based is easily ensured. The glass transition temperature (Tg) of the acrylic resin is preferably 0 to 60° C. By setting it to 0° C. or higher, the hardness of the coating film that is formed is improved, and by setting it to 60° C. or lower, it is easy to ensure adhesion during processing. The glass transition temperature (Tg) of the acrylic resin in the present invention is a calculated value calculated from the Tg of the homopolymer of each monomer and the blending ratio of each monomer. In the present invention, the value obtained using the FOX formula is used. The Tg of the homopolymer of the monomer is the value described in the Polymer Handbook (published in 1975, second edition).

[0030] <Polyester resin> The polyester resin of the present invention can be synthesized by a polycondensation reaction (esterification reaction) between a polycarboxylic acid (including an anhydride thereof) and a polyol. The polycarboxylic acid is a divalent or higher carboxylic acid, and examples thereof include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trifunctional or higher polycarboxylic acids. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, and biphenyldicarboxylic acid. Examples of the aliphatic dicarboxylic acid include succinic acid (anhydride), fumaric acid, maleic acid (anhydride), adipic acid, sebacic acid, azelaic acid, himic acid, dodecanedioic acid, and dimer acid. Examples of the alicyclic dicarboxylic acid include 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and anhydrides thereof. Examples of tri- or higher functional polycarboxylic acids include pyromellitic acid (anhydride), trimellitic acid (anhydride), and ethylene glycol bistrimellitate dianhydride. The polycarboxylic acids can be used singly or in combination of two or more. In the present invention, monocarboxylic acids such as benzoic acid, para-t-butylbenzoic acid, 12-hydroxystearic acid, myristic acid, and crotonic acid can also be used as the carboxylic acid component for the purpose of adjusting the molecular weight of the polyester resin.

[0031] The polyol is a dihydric alcohol or a polyhydric alcohol having three or more functional groups. Dihydric alcohols include, for example, aliphatic diols such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 3-methyl-1,5-pentanediol, 2-methylidene-1,4-butanediol, 2-methylidene-1,5-pentanediol, and 2-methylidene-1,6-hexanediol; Alicyclic diols such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-hydroxycyclohexyl-methanol, 3-hydroxycyclohexyl-methanol, 4-hydroxycyclohexyl-methanol, hydrogenated bisphenol A, hydrogenated bisphenol AP, hydrogenated bisphenol F, hydrogenated bisphenol S, and hydrogenated biphenol; aromatic diols such as propylene oxide adducts of bisphenol A (2 to 8 moles added), propylene oxide adducts of bisphenol F (2 to 8 moles added), and adducts of ethylene oxide with bisphenol A or bisphenol F; etc. Examples of tri- or higher functional polyhydric alcohols include trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, dipentaerythritol, mannitol, sorbitol, and α-methyl glucoside. The polyols can be used alone or in combination of two or more.

[0032] The weight-average molecular weight of the polyester resin is preferably 1,000 to 50,000. By making it 1,000 or more, the processing adhesion of the coating film that is formed is improved, and by making it 50,000 or less, it is easy to adjust the viscosity to an appropriate level when it is made into a water-based coating material. The acid value is preferably 10 to 50 mgKOH / g, as this range makes it easier to ensure paint stability when made water-based.

[0033] Polyester resins can be synthesized by polycondensation (esterification) of polycarboxylic acid and polyol, either under normal pressure or reduced pressure. The molecular weight of the reaction product is adjusted by adjusting the charging ratio of acid groups derived from polycarboxylic acid to hydroxyl groups derived from polyol (excess ratio: equivalent ratio of hydroxyl groups to acid groups). During the polycondensation reaction (esterification reaction) of polycarboxylic acid and polyol, an antioxidant may be used to ensure polymerization stability, such as a phenol-based antioxidant (including a hindered phenol-based antioxidant), etc. The antioxidant is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the total of polycarboxylic acid and polyol. For the purpose of adjusting the acid value, a trivalent or higher polycarboxylic acid may be newly added during the synthesis reaction, and the reaction may be allowed to proceed until the required acid value is reached.

[0034] The polyester resin is preferably used in a mass ratio to the acrylic resin of acrylic resin / polyester resin = 10 / 90 to 90 / 10, more preferably acrylic resin / polyester resin = 30 / 70 to 70 / 30. If the mass ratio of the polyester resin is 10 or more, the processability and processing adhesion of the resulting coating film tend to be improved. Furthermore, if the mass ratio of the polyester resin is 90 or less, the hardness of the resulting coating film tends to be improved.

[0035] <Amino resin> The amino resin in this invention is a resin obtained by adding an aldehyde compound to some or all of the amino groups of an amino component to generate N-methylol groups, and then etherifying some or all of the resulting N-methylol groups by dehydrating them with an alcohol to generate N-alkoxymethyl groups. Because it can react with the above-mentioned acrylic resin and polyester resin, it acts as a curing agent. Examples of amino resins include urea resins, melamine resins, benzoguanamine (also known as 2,4-diamino-6-phenyl-1,3,5-triazine) resins, acetoguanamine resins, steroguanamine resins, spiroguanamine resins, and dicyandiamide resins. Melamine-benzoguanamine co-condensation resins, which are obtained from the reaction product of melamine and benzoguanamine, are also included. Examples of the aldehyde compound include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. The alcohol used for etherifying the N-methylol group is preferably, for example, a monoalcohol having 1 to 6 carbon atoms, more preferably methyl alcohol, ethyl alcohol, isobutyl alcohol, or n-butyl alcohol. The alcohol can be used alone or in combination of two or more kinds. From the viewpoint of the hardness and processability of the resulting coating film, it is preferable to use melamine resin, melamine-benzoguanamine co-condensation resin, or benzoguanamine resin as the amino resin, and in particular, from the viewpoint of abrasion resistance, it is more preferable to use melamine resin.

[0036] The amino resin preferably has a mass ratio of melamine resin to benzoguanamine resin of melamine resin / benzoguanamine resin = 30 / 70 to 100 / 0, more preferably 50 / 50 to 100 / 0. When the mass ratio of melamine resin is 30 or more, sufficient crosslink density is obtained, improving the curability and hardness of the resulting coating film, and the proportion of benzoguanamine resin, which has low solubility in water, is reduced, making it easier to ensure paint stability when made water-based. The amino resins can be used alone or in combination of two or more.

[0037] Commercially available amino resins may be used, including, for example, Cymel 232, 303LF, 325N, 370N, 659E, 1123, and Mycoat 106, 137, 159, 212, and 779 manufactured by Allnex; Luwipal 014, 015, 018, 066, 070, 052, and B017 manufactured by BASF; and Amidia L-105-60, Amidia L-109-65, Amidia L-110-60, Amidia TD-126, and Amidia 15-594 manufactured by DIC Corporation.

[0038] In the present invention, the amino resin is preferably used in an amount of 25 to 185 parts by mass, more preferably 40 to 100 parts by mass, per 100 parts by mass of the total of the acrylic resin and polyester resin. An amount of 25 parts by mass or more improves the crosslink density, and the curability and abrasion resistance of the resulting coating film. Furthermore, an amount of 185 parts by mass or less makes it easier to obtain an appropriate crosslink density, and improves the processing adhesion of the coating film.

[0039] <Other resins> The can coating material of the present invention may contain other resins, such as polyether polyol resins, polyester polyol resins, and modified epoxy resins in which the glycidyl groups of epoxy resins are addition-modified with amines, phosphoric acid, or the like.

[0040] <Basic compounds> The can paint of the present invention is preferably in the form of a water-based paint, that is, a water-soluble paint or a water-dispersible paint. In the present invention, the carboxyl groups in the acrylic resin and polyester resin can be neutralized to make the resin water-soluble or water-dispersible. For neutralization, it is preferable to use a basic compound such as an amine compound, ammonia, or an alkali metal hydroxide. Examples of the amine compound include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N,N-dimethyl-ethanolamine, N,N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine. Examples of the alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The basic compounds can be used singly or in combination of two or more.

[0041] <Water> For the purpose of protecting the environment and ensuring a safe working environment, the can paint of the present invention preferably contains 10 to 45 mass % of water, more preferably 20 to 35 mass %, based on 100 mass % of the can paint. If the water content is 10 to 45 mass %, the paint stability can be ensured when it is made water-based, and the amount of organic solvents discharged during the paint baking process can be reduced.

[0042] <Organic solvents> The water-based can paint may contain 5 to 40 mass % of an organic solvent for the purpose of improving the coatability and storage stability. The organic solvent is preferably a hydrophilic organic solvent. Examples of the hydrophilic organic solvent include alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, iso-butanol, t-butanol, and diacetone alcohol; Examples of glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether. The organic solvents can be used alone or in combination of two or more kinds.

[0043] <Curing catalyst> The can coating composition of the present invention may contain a curing catalyst, preferably an acid catalyst, as needed, which allows the curing rate to be appropriately adjusted. Examples of the curing catalyst include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, phosphoric acid, and block products thereof. The curing catalyst can be blended in an amount of 0.001 to 1 part by mass per 100 parts by mass of the total resin content of the can coating (including the amino resin used as a curing agent).

[0044] <Lubricity imparting agent> The can coating material of the present invention may contain a lubricity-imparting agent as needed. The lubricity-imparting agent improves the sliding properties of the coating film, and can, for example, prevent the coating film from being scratched when coated cans come into contact with each other. The lubricity imparting agent is preferably, for example, a wax or a silicone-based lubricity imparting agent. The wax may be a natural wax or a synthetic wax. Natural waxes include, for example, animal waxes such as lanolin, beeswax, and whale wax; Vegetable waxes such as carnauba wax, candelilla wax, and rice wax; Examples of the wax include mineral waxes such as paraffin wax, microcrystalline wax, and montan wax. Examples of synthetic waxes include polyolefin waxes, fluorine waxes, and fatty acid ester waxes. Examples of silicone-based lubricity-imparting agents include dimethylpolysiloxane and modified products thereof. The lubricity imparting agents can be used alone or in combination of two or more. The lubricity imparting agent can be contained in an amount of 0.001 to 10 parts by mass relative to 100 parts by mass in total of the resin components of the can coating (including the amino resin used as a curing agent, etc.).

[0045] Conventional can coatings often contain fluorine wax, which provides excellent scratch resistance, abrasion resistance, and slip resistance. However, the organic fluorine compounds contained in fluorine waxes are subject to certain restrictions in Europe due to concerns about their persistence and bioaccumulation. Therefore, for environmental protection purposes, the can coating of the present invention preferably does not contain fluorine atom-containing compounds such as fluorine waxes. The can coating of the present invention can form a coating film with excellent scratch resistance and slip resistance even without fluorine atom-containing compounds such as fluorine waxes. The can coating of the present invention may also contain fluorine atom-containing compounds such as fluorine waxes. If a fluorine atom-containing compound is contained, the amount is preferably 2 parts by mass or less, and more preferably 1.5 parts by mass or less, per 100 parts by mass of the total resin content of the can coating (including the amino resin used as a curing agent). By limiting the amount to 2 parts by mass or less, precipitation of fluorine atom-containing compounds with a high specific gravity, such as polytetrafluoroethylene wax, is suppressed, improving the redispersibility of the wax when using the can coating after static storage, and resulting in a coating film with a good surface with fewer aggregates.

[0046] <Curing aid> The can coating material of the present invention may contain a curing aid. Examples of the curing aid include polyisocyanates. Examples of the polyisocyanates include blocked isocyanates in which active methylene, MEK oxime, ε-caprolactam, or the like is used as a blocking agent.

[0047] <Preparation of can paint> The can coating of the present invention can be prepared by stirring and mixing the materials that constitute it. The can coating material of the present invention is preferably used as a colored coating material containing a colorant such as a pigment or a dye, a clear coating material containing no colorant, or a topcoat coating material for protecting a colored coating film formed by applying a colored coating material. Examples of the pigment include chromatic pigments (for example, quinacridone) and achromatic pigments (for example, titanium oxide, aluminum pigments). The colored coating material is preferably prepared by blending a colorant and, if necessary, a dispersant, and using a dispersing machine such as a sand mill or a disperser.

[0048] <Painted board> The coated plate of the present invention comprises a metal plate and a coating film that is a cured product of the can coating material of the present invention. The coated plate can be obtained by applying the can coating material to a metal plate and drying and curing it. Suitable materials for the metal plate include electroplated tin steel plate, aluminum steel plate, stainless steel plate, and laminated steel plate obtained by laminating these with a polyester film (e.g., polyethylene terephthalate film, polybutylene terephthalate film, etc.). The metal plate is not limited to a flat plate, but may be a three-dimensional object such as a can body. By applying the can coating material of the present invention to a can body, a coated can can be obtained. Examples of coating methods for can paints include roll coating, spraying, and brush application. Drying and curing conditions are usually 140 to 240°C for about 5 seconds to 10 minutes, and the mass thickness of the cured coating film is 10 mg / dm 2 ~150mg / dm 2 That's about it.

[0049] <Coated can> The coated can of the present invention comprises a can body and a coating film which is a cured product of the can coating material of the present invention. The can body is preferably made of the above-mentioned metal plate. Examples of the can body of the covered can include a two-piece can made up of one lid and one can body member, and a three-piece can made up of two upper and lower lid members and one can body member. The can body member of the two-piece can is cylindrical with a bottom. Further, examples of the coated can include so-called bottle cans that have a cap that can be opened and closed, and a bottle portion. The bottle can has a screw-type drinking spout onto which the cap can be attached. The coating film can be formed on the can body at any stage of the process, such as when the metal plate is in the flat state or when the plate has been formed into, for example, a cup shape. The coated can of the present invention can be used as, for example, food and beverage cans, industrial cans such as 18L cans, art cans, etc., and is preferably used as a food and beverage can. The can coating material of the present invention is preferably used as an inner or outer coating material for coated cans, and more preferably as an outer coating material. However, it goes without saying that the can coating material of the present invention can also be used for coating film formation applications other than coated cans. [Example]

[0050] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0051] [Manufacturing Example 1] <Synthesis of acrylic resin (A-1)> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 100 parts of ethylene glycol monobutyl ether. While introducing nitrogen gas, heating was initiated with stirring. At an internal temperature of 120°C, a mixture consisting of 15 parts of N-butoxymethylacrylamide, 35 parts of methyl methacrylate, 25 parts of lauryl methacrylate, 15 parts of styrene, 5 parts of 2-hydroxyethyl methacrylate, 5 parts of acrylic acid, and 5 parts of benzoyl peroxide was added dropwise from the dropping tank over a 2-hour period. The internal temperature was then maintained at 120°C, and the reaction was allowed to proceed for 30 minutes. Next, 0.2 parts of benzoyl peroxide was added, and the reaction was allowed to proceed for 30 minutes. Another 0.2 parts of benzoyl peroxide was added, and the reaction was allowed to proceed for 30 minutes, completing the reaction. The ethylene glycol monobutyl ether was then distilled off under reduced pressure at 110°C until the nonvolatile content of the reaction system reached 65%. Then, 6.2 parts of N,N-dimethylethanolamine and an appropriate amount of ion-exchanged water were added to obtain a solution of acrylic resin (A-1) with a non-volatile content of 50%. The Tg of the acrylic resin (A-1) was 35°C and the weight-average molecular weight was 15,000.

[0052] The weight-average molecular weight was measured using a Tosoh Corporation 8020 Series GPC apparatus (THF (tetrahydrofuran) solvent, column temperature 40°C, polystyrene standard). Four columns, G1000HXL, G2000HXL, G3000HXL, and G4000HXL, manufactured by Tosoh Corporation, connected in series were used, and measurements were performed at a flow rate of 1.0 ml / min.

[0053] [Manufacturing Examples 2 to 4] <Synthesis of acrylic resins (A-2) to (A-4)> Solutions of acrylic resins (A-2) to (A-4) were obtained in the same manner as in Production Example 1, except that the types and amounts (parts) of each component were changed as shown in Table 1.

[0054] [Manufacturing Example 5] <Synthesis of Polyester Resin (B-1)> A reaction vessel equipped with a thermometer, a stirrer, a nitrogen gas inlet, a fractionating apparatus, and a cooling tube was charged with 22 parts of 1,4-butanediol, 10 parts of diethylene glycol, 11.3 parts of trimethylolpropane, 29.8 parts of isophthalic acid, 16.4 parts of hexahydrophthalic anhydride, and 10.5 parts of adipic acid, and the mixture was stirred and esterified at 220 ° C. under nitrogen gas inlet. The reaction was terminated and cooled when the acid value reached 30 mg KOH / g. When the internal temperature reached 100 ° C., 25 parts of ethylene glycol monobutyl ether was added to obtain a solution of polyester resin (B-1) with a weight average molecular weight of 3,000 and a nonvolatile content of 65%.

[0055] The acid value was measured by the following method. 0.2 g of resin calculated as nonvolatile matter was dissolved in 20 ml of THF (tetrahydrofuran), titrated with a 0.1 N KOH ethanol solution, and the acid value was calculated by the following (Equation 2). Acid value (mgKOH / g)=5.611×A×F / 0.2 (Formula 2) A: Titration volume of KOH ethanol solution (ml) F: Potency of 0.1N KOH ethanol solution

[0056] [Manufacturing Example 6] <Synthesis of amino resin (C-1)> A reaction vessel equipped with a thermometer, stirrer, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 187 parts of benzoguanamine, 187.5 parts of 80% paraformaldehyde, and 518 parts of n-butanol. The mixture was adjusted to pH 9.0 with 25% aqueous sodium hydroxide, then heated to 100°C and reacted for 3 hours. Subsequently, 60% aqueous nitric acid was added until the reaction solution reached pH 4, and the reaction was continued for another 3 hours while refluxing and dehydrating. After the reaction was complete, the mixture was neutralized with 25% aqueous sodium hydroxide, and the n-butanol and water were removed under reduced pressure. Ethylene glycol monobutyl ether was added to the product to obtain a solution of amino resin (C-1) with a nonvolatile concentration of 80%.

[0057] [Example 1] The acrylic resin (A-1) obtained in Production Example 1 was mixed with 22 parts in terms of nonvolatile matter, and the acrylic resin (A-2) obtained in Production Example 5 was mixed with 22 parts in terms of nonvolatile matter. 42 parts of ester resin (B-1) in terms of non-volatile content, Cymel 303L as amino resin 36 parts of F (Allnex, methylated melamine amino resin) and p-toluidine as an acid catalyst. 0.2 parts of benzene sulfonic acid, BYK302 (Bitcoin) as a silicone leveling agent 0.5 parts of "CERACOL604" (manufactured by BYK) as a wax Carnauba wax), CERAFLOUR1050 (Byk-Chemie, Polyester 0.6 parts of polyethylene wax) were mixed. Add an appropriate amount of ion-exchanged water and ethylene glycol monobutyl ether to make the solution 30%. After mixing, a water-based can paint was obtained. [Example 2] to [Example 16] In Example 1, the types and amounts (parts) of each component were changed as shown in Tables 2 and 3. A can paint was obtained in the same manner as in Example 1 except for the above. However, Examples 2 and 15 are reference examples.

[0058] In Tables 2 and 3, the amounts of acrylic resins (A-1) to (A-4), polyester resin (B-1), amino resins "Cymel 303LF", "Cymel 232", "Mycoat 106", and amino resin (C-1) are calculated as non-volatile contents. The materials used in Tables 1, 2, and 3 are listed below. Cymel 232: Methylbutylated melamine amino resin manufactured by Allnex (non-volatile content: 97%) Cymel 303LF: Methylated melamine amino resin manufactured by Allnex (non-volatile content: 98%) Mycoat 106: Methylated benzoguanamine amino resin manufactured by Allnex (non-volatile content: 77%) BYK302: Polyether-modified polydimethylsiloxane leveling agent manufactured by BYK-Chemie CERACOL604: BYK carnauba wax (non-volatile content 20%) CERAFLOUR1050: BYK polyethylene wax CERAFLOUR981: Polytetrafluoroethylene wax manufactured by BYK N-BMA: Nn-butoxymethylacrylamide (Tg of homopolymer: 50°C) MMA: Methyl methacrylate (Tg of homopolymer: 105°C) nBA: n-butyl acrylate (Tg of homopolymer: -48°C) LMA: Lauryl methacrylate (Tg of homopolymer: -65°C) St: styrene (Tg of homopolymer: 100°C) 2-HEMA: 2-hydroxyethyl methacrylate (Tg of homopolymer: 55°C) AA: acrylic acid (Tg of homopolymer: 57°C) p-TSA: paratoluene sulfonic acid

[0059] [Comparative Example 1] to [Comparative Example 5] A can coating material was obtained in the same manner as in Example 1, except that the type and amount (parts) of each component in Example 1 were changed as shown in Table 3.

[0060] <Evaluation of coating properties> Using the can paint obtained in each example, coated plates were prepared in the following manner and evaluated. The aluminum can body (a cylindrical member with a bottom and body integrated into one) for a two-piece can was coated with a roll coater to a mass thickness of 50 mg / dm2 after drying. 2 The can body was then baked in a gas oven at 180°C for 52 seconds, and then baked for another 2 minutes at 200°C for hardening. The can body was then cut open, and the can body portion on which the coating film was provided was flattened to prepare a coated plate for evaluation. The resulting coated plates were evaluated as follows, and the results are shown in Tables 2 and 3.

[0061] <Average friction coefficient, maximum scratch depth, and hardness of coating film> The average coefficient of friction, maximum scratch depth, and hardness of the coating film were measured on the coating film surface using a Hysitron TI Premier (manufactured by Bruker) according to the conditions described in [Mode for Carrying Out the Invention].

[0062] <Wear resistance test> The resulting coating film on the coated plate was subjected to an abrasion wear test using a Model 7 RCA Abrasion Wear Tester manufactured by Norman Tools, and the number of abrasion cycles required until the base material began to become visible was recorded and evaluated. The evaluation criteria were as follows: ◎: 25 times or more. Good. ○: 10 times or more and 24 times or less. No practical problems. ×: 9 times or less. Not practical.

[0063] <Processing adhesion> The resulting coated panels were subjected to an impact processing test using a DuPont impact tester, with the coating facing the convex side. After the test, commercially available cellophane tape was applied to the coating in the processed area, and after strong peeling, the peeling state of the coating surface was evaluated visually. The impact processing was performed by dropping a 300g weight from a height of 50cm using a 3 / 8 inch diameter impact core. The evaluation criteria were as follows: ◎: No peeling at the processed area. Good. ○: Peeling occurred in the processed area of ​​less than 5%. No practical problems. ×: Peeling of 5% or more of the processed area occurred. Unsuitable for practical use. <Curability> The coating film of the resulting coated plate was rubbed back and forth with a 2-pound hammer wrapped in gauze soaked in methyl ethyl ketone, and the number of rubs until the coating film dissolved or peeled off was measured. The evaluation criteria were as follows: ◎: More than 200 times. Good. ○: 100 times or more and 199 times or less. No practical problems. ×: 99 times or less. Not practical. <Wax redispersibility> The can paint obtained above was stored at 25°C for 30 days, and then stirred to prepare a coated plate. The state of the coating film was evaluated visually. The evaluation criteria were as follows: ⊚: No agglomerates are observed in the coating film. Good. ◯: A small amount of aggregates was observed on the coating film. No practical problems. ×: Numerous aggregates were observed on the coating film. Not suitable for practical use.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] As shown in Tables 2 and 3, the can paints of Examples 1 to 16 were good in all physical properties, whereas the can paints of Comparative Examples 1 to 5 were poor in some of the physical properties, and no paints were good in all properties.

Claims

1. A can coating that satisfies (i) and (ii) in the nano-scratch test described below, and satisfies (iii) in the indentation test described below. <Nano scratch test> The can paint was applied to the body of an aluminum can, and the can was baked at 180°C for 52 seconds and 200°C for 2 minutes. The coating surface of the sample was measured at 23°C using a nanoindenter. (i) the average coefficient of friction is 2 or less, and (ii) the maximum scratch depth is 120 nm or less. <Indentation test> The can paint was applied to the body of an aluminum can, and the can was baked at 180°C for 52 seconds and 200°C for 2 minutes. The coating surface of the sample was measured at 23°C using a nanoindenter. (iii) The film hardness is 0.20 GPa or more and 0.35 GPa or less.

2. 2. The can paint according to claim 1, wherein the can paint contains an acrylic resin, a polyester resin, and an amino resin, and the amino resin is contained in an amount of 25 to 185 parts by mass per 100 parts by mass of the acrylic resin and the polyester resin combined.

3. the amino resin comprises a melamine resin and a benzoguanamine resin, or comprises only a melamine resin; 3. The can coating according to claim 2, wherein a mass ratio of the melamine resin to the benzoguanamine resin is melamine resin / benzoguanamine resin=30 / 70 to 100 / 0.

4. 2. The can paint according to claim 1, wherein the content of the fluorine atom-containing compound in the can paint is 2 parts by mass or less per 100 parts by mass of the total of the resin components of the can paint.

5. A coated plate comprising a metal plate and a coating film which is a cured product of the can coating material according to any one of claims 1 to 4.

6. A coated can comprising a metal plate and a coating film which is a cured product of the can coating material according to any one of claims 1 to 4.

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