JP7514780B2 - Metal substrate for printing, its manufacturing method, and coated metal material - Google Patents

Description

The present invention relates to a metal substrate for printing, a method for producing the same, and a coated metal material.

In recent years, there has been a demand for highly decorative coated metal materials, and there is a demand for forming coating films of various colors on metal sheets and applying fine patterns to the surface of metal sheets. Therefore, the application of active energy ray-curable compositions to metal sheets has been considered.

Active energy ray curable compositions are cured by irradiation with active energy rays. Therefore, images can be formed on substrates that do not absorb solvents. However, active energy ray curable compositions shrink relatively greatly when cured. Therefore, when active energy ray curable compositions are used for image formation, there is a problem that the ink layer, which is the cured product, is easily peeled off from various substrates.

In response to these problems, several methods have been proposed to improve the adhesion of the ink layer to the substrate. For example, Patent Document 1 describes a method in which an active energy ray-curable composition is applied to a substrate, which is then irradiated with active energy rays, and then heated with a heater. It is believed that this method improves the curability of the ink layer, thereby improving the adhesion between the ink layer and the substrate. Patent Document 2 describes a method in which an active energy ray-curable composition is applied to a preheated substrate. It is believed that this method allows the active energy ray-curable composition to be sufficiently wetted and spread over the substrate, improving the adhesion between the ink layer and the substrate.

Furthermore, Patent Documents 3 and 4 describe a method in which the resin film is subjected to a corona discharge treatment before applying an active energy ray-curable composition onto the resin film to increase the adhesion between the resin film and the ink layer.

JP 2001-009367 A JP 2008-087242 A International Publication No. 2018/163941 Japanese Patent Application Laid-Open No. 9-300477

However, when applying an active energy ray-curable composition to a metal plate, it was difficult to sufficiently increase the adhesion between the metal plate and the ink layer, regardless of which of the methods described in Patent Documents 1 to 4 was used. In particular, when the applied thickness of the active energy ray-curable composition was increased, the amount of cure shrinkage that occurred during curing increased, making the ink layer more susceptible to peeling.

The present invention aims to provide a metal substrate for printing that has a printable layer that is capable of firmly adhering to a cured product of an actinic energy ray-curable composition and has excellent processability and scratch resistance, a method for producing the same, and a coated metal material.

The present invention provides the following metal substrate for printing.
A metal substrate for printing comprising: a metal plate; and a printable layer disposed on the metal plate, the printable layer comprising a cured product of a paint containing a polyester resin and a melamine resin, the number average molecular weight of the polyester resin being 12,000 to 30,000; when a composition of a region from the surface of the printable layer to a depth of 10 nm is analyzed in the depth direction by X-ray photoelectron spectroscopy using an AlKα ray as an X-ray source, the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms is 5 to 30 atom %.

The present invention provides the following coated metal material.
A coated metal material comprising: the metal substrate to be printed; and an ink layer disposed on the printable layer of the metal substrate to be printed, the ink layer being a cured product of an active energy ray-curable composition.

The present invention provides the following method for producing a metal substrate for printing.
The method for producing the above-mentioned metal substrate for printing includes a step of applying a coating material containing a polyester resin having a number average molecular weight of 12,000 to 30,000 and a melamine resin onto a metal plate, and curing the coating material to form a printable layer.

According to the printing metal substrate of the present invention, when an ink layer is formed using an active energy ray-curable composition, the ink layer is unlikely to peel off. In addition, the printing layer of the printing metal substrate has good processability and scratch resistance. Therefore, it is possible to form various coated metal materials with high design appeal.

FIG. 1 is a graph showing the relationship between the ratio of each element to the total of N atoms, C atoms, and O atoms and the depth from the surface when the composition of the printing layer of the printing metal substrate of Example 8 was analyzed in the depth direction by X-ray photoelectron spectroscopy. FIG. 2 is a graph showing the relationship between the ratio of each element to the total of N atoms, C atoms, and O atoms and the depth from the surface when the composition of the printing layer of the printing metal substrate of Example 5 was analyzed in the depth direction by X-ray photoelectron spectroscopy. FIG. 3 is a graph showing the relationship between the ratio of each element to the total of N atoms, C atoms, and O atoms and the depth from the surface when the composition of the printing layer of the printing metal substrate of Example 2 was analyzed in the depth direction by X-ray photoelectron spectroscopy. FIG. 4 is a graph showing the relationship between the ratio of each element to the total of N atoms, C atoms, and O atoms and the depth from the surface when the composition of the printing layer of the printing metal substrate of Comparative Example 8 was analyzed in the depth direction by X-ray photoelectron spectroscopy. FIG. 5 is a graph showing the relationship between the ratio of each element to the total of N atoms, C atoms, and O atoms and the depth from the surface when the composition of the printing layer of the printing metal substrate of Comparative Example 2 was analyzed in the depth direction by X-ray photoelectron spectroscopy.

1. Metal Substrate for Printing The metal substrate for printing of the present invention has at least a metal plate and a printable layer disposed on the metal plate, and may further include other layers as necessary. The metal substrate for printing is used as a substrate for forming an ink layer by applying, for example, an active energy ray-curable composition described below. The substrate for printing may be a precoated metal plate or a postcoated metal plate.

As mentioned above, coating an active energy ray-curable composition on a metal plate has been considered in the past, but it is difficult to improve the adhesion of the ink layer, which is the cured product of the active energy ray-curable composition, and peeling is particularly likely to occur at the interface when the ink layer becomes thick. This is thought to be because the active energy ray-curable composition shrinks significantly when cured, causing residual stress in the ink layer after curing or stress at the interface between the metal plate and the ink layer during curing, which causes the ink layer to peel off.

In contrast, the printing metal substrate of the present invention has a printing layer on a metal plate. The printing layer contains a cured product of a coating containing a polyester resin and a melamine resin having a number average molecular weight of 12,000 to 30,000. In addition, when the composition is analyzed in the depth direction from the surface to a depth of 10 nm by X-ray photoelectron spectroscopy (hereinafter also referred to as the "XPS method"), the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms is 5 to 30 atom%. According to the inventors' intensive research, it has become clear that the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms in the region from the surface of the printing layer to a depth of 10 nm is closely related to the peeling of the ink layer, and by setting the maximum value to 5 to 30 atom%, the adhesion with the ink layer is increased. In addition, by setting the maximum value in the above-mentioned range, the workability and scratch resistance of the printing metal substrate are also improved. The reasons for this are considered to be as follows.

The N atoms observed when the printed layer is analyzed by XPS are mainly N atoms derived from the melamine resin, and the above-mentioned maximum value is an index showing the degree of concentration of the melamine resin on the surface. A printed layer with a large maximum value of N atoms has a high crosslink density of the polyester resin near the surface of the printed layer, and the surface of the printed layer is said to be high in hardness. Having such a printed layer improves the scratch resistance of the metal substrate to be printed, but a printed layer with high hardness is likely to have low adhesion to the above-mentioned ink layer and is also likely to have poor processability.

On the other hand, a printable layer with a small maximum value of N atoms has a low crosslink density of the polyester resin near the surface of the printable layer, and the surface is soft. Such a printable layer tends to improve adhesion between the ink layer and the printable layer, and improves processability, but reduces the scratch resistance of the metal substrate to be printed, making it difficult to use for various applications.

In contrast, when the maximum value of the above-mentioned N atoms is set to 5 atom% or more and 30 atom% or less, the crosslink density of the polyester resin becomes appropriate, and even if the active energy ray curable composition shrinks when cured, the stress can be alleviated by the printable layer. In other words, residual stress is unlikely to occur in the ink layer. In addition, the printable layer can follow and deform in accordance with the cure shrinkage of the active energy ray curable composition. Therefore, stress is unlikely to act between the printable layer and the ink layer, and the adhesion between them can be improved. In addition, because the crosslink density of the polyester resin is in an appropriate range, the processability and scratch resistance of the printable layer are also good.

It is difficult to satisfy such a concentration of N atoms in a coating film obtained from a paint containing a conventional polyester resin and a melamine resin. For example, methylated melamine resin, butylated melamine resin, etc. are conventionally known as melamine resins, but methylated melamine resins are difficult to concentrate on the surface, and when used in a general blending amount, the maximum value of the above-mentioned N atoms is likely to be less than 5 atom%. On the other hand, butylated melamine resins tend to concentrate on the surface, and when used in a general blending amount, the maximum value of the above-mentioned N atoms is likely to exceed 30 atom%. Therefore, in the present application, the amount of melamine resin is adjusted or multiple melamine resins are combined to adjust the maximum value of the above-mentioned N atoms to be within the desired range. The metal substrate for printing of the present invention will be described in detail below.

Metal Plate The metal plate may have any shape as long as it has a structure capable of forming a printing layer described later. For example, it may be flat or may have a three-dimensional structure. The metal plate may also be strip-shaped. The thickness of the metal plate is not particularly limited and is appropriately selected depending on the application of the coated metal material.

The material of the metal sheet is not particularly limited, and includes plated steel sheets such as hot-dip Zn-plated steel sheets, hot-dip Zn-55% Al alloy-plated steel sheets, hot-dip Zn-Al-Mg alloy-plated steel sheets, hot-dip Al-plated steel sheets, electrolytic Zn-plated steel sheets, and electrolytic Cu-plated steel sheets; steel sheets such as ordinary steel sheets and stainless steel sheets; aluminum sheets; copper sheets, and the like. The metal sheet may have a chemical conversion coating or an undercoat coating formed on its surface, as long as the effect of the present invention is not impaired. Furthermore, the metal sheet may be subjected to uneven processing such as embossing or drawing, as long as the effect of the present invention is not impaired.

The type of chemical conversion treatment used to form the chemical conversion coating is not particularly limited. Examples of chemical conversion treatments include chromate treatment, chromium-free treatment, phosphate treatment, etc. The amount of the chemical conversion coating applied is not particularly limited as long as it is within a range that is effective in improving corrosion resistance.

Furthermore, the undercoat coating is a layer that is formed directly on the metal plate or on the above-mentioned chemical conversion coating, and improves the adhesion of the printed layer and the corrosion resistance of the metal plate.

The undercoat coating film is formed, for example, by applying a resin-containing undercoat paint to the surface of a metal plate or a chemical conversion coating film and then drying (or curing). There are no particular limitations on the type of resin contained in the undercoat paint. Examples of resins include polyester, epoxy resin, acrylic resin, etc. Epoxy resin is particularly preferred because it has high polarity and good adhesion to the metal plate. The thickness of the undercoat coating film is selected appropriately according to the final application and type of painted metal material, and is, for example, about 5 μm.

Printable layer The printable layer is a layer including a cured product of a paint including a polyester resin and a melamine resin having a number average molecular weight of 12,000 to 30,000. The printable layer is formed by applying a printable layer-forming paint including a polyester resin and a melamine resin having a number average molecular weight of 12,000 to 30,000 onto the above-mentioned metal plate, and then curing the paint.

The layer made of the cured product of the coating material for forming the printable layer may be used as the printable layer as is, but it is more preferable to use the layer that has been further subjected to frame treatment or corona discharge treatment as the printable layer. By performing frame treatment or corona discharge treatment, the adhesion of the ink layer described below to the printable layer is significantly improved, so that even if a thick ink layer is formed, it is less likely to peel off. Among these, printable layers that have been subjected to frame treatment are particularly preferable from the viewpoint of adhesion of the ink layer, etc.

There are no particular limitations on the method for applying the paint for forming the printable layer onto the metal plate, and the method is appropriately selected according to the shape of the metal plate, the pattern of the printable layer to be formed, the area of the printable layer to be formed, etc. Examples of application methods include inkjet printing, gravure printing, offset printing, screen printing, roll coating, bar coating, spin coating, air spraying, airless spraying, immersion and pulling, etc. Two or more of these methods may be combined when applying the paint for forming the printable layer.

The coating material for forming the printable layer may contain a polyester resin having a number average molecular weight of 12,000 to 30,000 and a melamine resin. The polyester resin and the melamine resin are appropriately combined so that when the cured product (printable layer) of the coating material for forming the printable layer is measured by the XPS method, the amount of N atoms is 5 to 30 atom% relative to the amount of N atoms, C atoms, and O atoms in a region 10 nm from the surface. For example, the degree of concentration of the melamine resin on the coating surface side varies depending on the number average molecular weight of the polyester resin. When the number average molecular weight of the polyester resin is large, the melamine resin is less likely to concentrate on the coating surface. Therefore, it is preferable to increase the amount of butylated melamine resin, which is easily concentrated on the surface. On the other hand, when the number average molecular weight of the polyester resin is small, the butylated melamine resin is easily concentrated on the coating surface, so the amount of butylated melamine resin is reduced and the amount of melamine resin other than butylated melamine resin is increased, so that the amount of the above-mentioned N atoms is adjusted to be within the desired range. In addition, the coating material for forming the printable layer may contain other components such as catalysts, amines, extender pigments, and coloring pigments as necessary.

Polyester resins are any resin that has multiple ester structures in its molecular chain, and are usually prepared by polymerizing polycarboxylic acids and polyhydric alcohols.

Examples of polycarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, and their anhydrides; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid, and their anhydrides; lactones such as γ-butyrolactone and ε-caprolactone; and trivalent or higher polyvalent carboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid. The polyester resin may contain only one type of carboxylic acid structural unit derived from the above polycarboxylic acids, or may contain two or more types.

In the polyester resin, the ratio of the amount of structural units derived from trivalent or higher polycarboxylic acids to the total amount of alcohol structural units derived from polyhydric alcohols and carboxylic acid structural units derived from polycarboxylic acids is preferably 20 mol% or less, and more preferably 10 mol% or less, so as to prevent the crosslinking density of the coating film from becoming excessively high.

On the other hand, examples of polyhydric alcohols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, glycols such as ethyl-1,3-propanediol, diethylene glycol, triethylene glycol, 1,2-dodecanediol, 1,2-octadecanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adducts, and bisphenol S alkylene oxide adducts; and trihydric or higher polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol. The polyester resin may contain only one type of alcohol structural unit derived from the above polyhydric alcohols, or may contain two or more types.

The number average molecular weight of the polyester resin may be 12,000 to 30,000, preferably 12,000 to 25,000, and more preferably 14,000 to 23,000. The number average molecular weight of the polyester resin is a styrene-equivalent value determined by gel permeation chromatography (GPC). If the number average molecular weight of the polyester resin is excessively small, the strength of the printed layer is low and the hardness of the printed layer is likely to be low. In contrast, if the number average molecular weight of the polyester resin is 12,000 or more, a printed layer having sufficient strength (scratch resistance) can be obtained. On the other hand, if the number average molecular weight is 30,000 or less, the viscosity of the paint containing the polyester resin does not increase excessively, making it easier to form a coating film using a paint for forming a printed layer containing the polyester resin. Furthermore, the processability of the printed layer is also improved.

The hydroxyl value of the polyester resin is preferably 3 to 40 mgKOH/g, more preferably 5 to 20 mgKOH/g. The hydroxyl value is determined by potentiometric titration as specified in JIS K0070 using a 0.5 mol/L KOH alcohol solution. When the hydroxyl value of the polyester resin is within this range, the OH groups on the metal plate surface and the OH groups in the polyester resin (printable layer) tend to form hydrogen bonds, etc., and the adhesion between the metal plate and the printable layer is improved. Similarly, the OH groups in the polyester resin (printable layer) tend to form hydrogen bonds with hydrophilic groups in the ink layer, further improving the adhesion between them.

The glass transition temperature of the polyester resin is preferably -10 to 80°C, and more preferably 0 to 50°C. When the glass transition temperature of the polyester resin is in the above range, the resulting printable layer has good processability.

On the other hand, the melamine resin contained in the coating material for forming the printable layer is a thermosetting resin obtained by reacting melamine with aldehyde. The melamine resin is appropriately selected so as to realize the above-mentioned maximum value of N atoms when the printable layer is analyzed by the XPS method. The melamine resin has three reactive functional groups -NX ¹ X ² per one molecule of triazine nucleus. X ¹ and X ² usually represent CH ₂ OR (R is an alkyl group), CH ₂ OH, or a hydrogen atom. However, they are not limited to this structure.

Specific examples of melamine resins include four types: a fully alkyl melamine resin in which all three reactive functional groups are composed of -N-(CH ₂ OR) ₂ ; a methylol group type melamine resin in which at least one reactive functional group is -N-(CH ₂ OR)(CH ₂ OH); an imino group type melamine resin in which at least one reactive functional group is -N-(CH ₂ OR)(H); and a methylol/imino group type melamine resin containing -N-(CH ₂ OR)(CH ₂ OH) and -N-(CH ₂ OR)(H) as reactive functional groups, or containing -N-(CH ₂ OH)(H). The melamine resin may be a melamine polymer in which reactive functional groups are condensed together. The coating material for forming the printable layer may contain only one type of melamine resin, or may contain two or more types.

The R of the reactive group of the melamine resin, i.e., the alkyl group, is preferably an alkyl group having 1 to 4 carbon atoms, and the alkyl group may be linear or branched. Among these, a methyl group or a butyl group is particularly preferred.

The melamine resin may be a commercially available resin. Examples of commercially available melamine resins include fully alkylated methyl/butyl mixed etherified melamine resins such as Cymel 232, Cymel 232S, Cymel 235, Cymel 236, Cymel 238, Cymel 266, Cymel 267, and Cymel 285 manufactured by Allnex Japan Co., Ltd.; methylol group type methyl/butyl mixed etherified melamine resins such as Cymel 272 manufactured by Allnex Japan Co., Ltd.; imino group type methyl/butyl mixed etherified melamine resins such as Cymel 202, Cymel 207, Cymel 212, Cymel 253, and Cymel 254 manufactured by Allnex Japan Co., Ltd.; Cymel 300 and Cymel 301 manufactured by Allnex Japan Co., Ltd. , Cymel 303, Cymel 350 and other fully alkylated methylated melamine resins (sometimes referred to as "fully alkylated methyl etherified melamine resins"); imino group type methylated melamine resins such as Cymel 325, Cymel 327, Cymel 703, Cymel 712, Cymel 253, Cymel 212, Cymel 1128 from Allnex Japan; methylol group type methylated melamine resins such as Cymel 370 from Allnex Japan; butylated melamine resins (sometimes referred to as "butyl etherified melamine resins") such as U-BAN 20SE60 from Mitsui Chemicals and Super Beckamin J830 from DIC.

In this specification, "methylated melamine resin" refers to fully alkylated methyl etherified melamine resin, imino group type methyl etherified melamine resin, methylol group type methyl etherified melamine resin, or a mixed resin of these. "Butylated melamine resin" refers to fully alkylated butyl etherified melamine, butyl etherified melamine resin whose main structure is imino group type butyl etherified melamine, or a mixed resin of these. Melamine resins that have both methyl groups and butyl groups, such as fully alkylated methyl/butyl mixed etherified melamine resin, methylol group type methyl/butyl mixed etherified melamine resin, and imino group type methyl/butyl mixed etherified melamine resin, are also referred to as "methyl/butyl mixed melamine resin".

The melamine resin may contain only one type of melamine resin selected from the above, but from the viewpoint of being able to realize the above-mentioned amount of N atoms when the printed layer is analyzed by the XPS method, it is preferable to contain two or more types of melamine resin, and it is more preferable to be a mixture of butylated melamine resin and other melamine resin, i.e., methylated melamine resin or methyl/butyl mixed melamine resin. Also, it is particularly preferable to be a mixture of butylated melamine resin and methylated melamine resin. In this case, the mass ratio of butylated melamine resin to methylated melamine resin is preferably 1:1 to 1:8, and more preferably 2:3 to 1:6. The melamine resin may contain three or more types of melamine resin.

The ratio (mass ratio) of polyester resin and melamine resin contained in the paint for forming the printable layer is preferably 90:10 to 60:40, and more preferably about 85:15 to 70:30. When the mass ratio of polyester resin and melamine resin is within this range, a printable layer with excellent weather resistance and impact resistance is obtained.

The total amount of polyester resin and melamine resin per 100 parts by mass of solids in the paint for forming the printable layer is preferably 30 to 80 parts by mass, more preferably 50 to 70 parts by mass. When the total amount of polyester resin and melamine resin is within this range, the strength of the printable layer obtained from the paint for forming the printable layer is likely to be sufficiently high. Furthermore, the adhesion between the printable layer and the ink layer is likely to be good.

The coating material for forming the printable layer may further contain a catalyst. Examples of catalysts include dodecylbenzenesulfonic acid, paratoluenesulfonic acid, benzenesulfonic acid, etc. The amount of catalyst used is preferably 0.1 to 8 mass% based on the total solid content of the coating material for forming the printable layer.

The coating material for forming the printable layer may further contain an amine. The amine is a compound for neutralizing the catalyst, and examples thereof include triethylamine, dimethylethanolamine, dimethylaminoethanol, monoethanolamine, isopropanolamine, and the like. The amount of amine used is not particularly limited, but is preferably 50 mol% or more of the acid (catalyst) equivalent.

The coating material for forming the printable layer may further contain extender pigments (including beads) and color pigments. Examples of extender pigments include silica, calcium carbonate, barium sulfate, aluminum hydroxide, talc, mica, resin beads, glass beads, etc. Examples of resin beads include acrylic resin beads, polyacrylonitrile beads, polyethylene beads, polypropylene beads, polyester beads, urethane resin beads, epoxy resin beads, etc.

These resin beads may be manufactured using known methods, or commercially available products may be used. Examples of commercially available acrylic resin beads include "Tuftic AR650S (average particle size 18 μm)", "Tuftic AR650M (average particle size 30 μm)", "Tuftic AR650MX (average particle size 40 μm)", "Tuftic AR650MZ (average particle size 60 μm)", "Tuftic AR650ML (average particle size 80 μm)", "Tuftic AR650L (average particle size 100 μm)" and "Tuftic AR650LL (average particle size 150 μm)" from Toyobo Co., Ltd. Examples of commercially available polyacrylonitrile beads include Toyobo Co., Ltd.'s "Tuftic A-20 (average particle size 24 μm)," "Tuftic YK-30 (average particle size 33 μm)," "Tuftic YK-50 (average particle size 50 μm)," and "Tuftic YK-80 (average particle size 80 μm)." The coating material for forming the printable layer may contain only one of these, or may contain two or more of them.

On the other hand, examples of color pigments include carbon black, titanium oxide, iron oxide, yellow iron oxide, phthalocyanine blue, cobalt blue, etc. The amount of pigment is appropriately selected depending on the type of pigment, particle size, etc. The paint for forming the printable layer may contain only one of these, or may contain two or more types.

The coating material for forming the printable layer may further contain a solvent as necessary. The solvent is not particularly limited as long as it can sufficiently dissolve the polyester resin or melamine resin and uniformly disperse the extender pigment or color pigment. Examples of the solvent include hydrocarbon solvents such as toluene, xylene, Solvesso (registered trademark) 100 (trade name, Exxon Mobil Corporation), Solvesso (registered trademark) 150 (trade name, Exxon Mobil Corporation), and Solvesso (registered trademark) 200 (trade name, Exxon Mobil Corporation); ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester solvents such as ethyl acetate, butyl acetate, and ethylene glycol monoethyl ether acetate; alcohol solvents such as methanol, isopropyl alcohol, and n-butyl alcohol; ether alcohol solvents such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether; n-methylpyrrolidone; and ethyl-3-ethoxy-propionate. The coating material for forming the printable layer may contain only one of these, or may contain two or more of these. Among these, from the viewpoint of compatibility with polyester resins and melamine resins, xylene, Solvesso (registered trademark) 100, Solvesso (registered trademark) 150, cyclohexanone, and n-butyl alcohol are preferred.

There are no particular limitations on the method for preparing the coating material for forming the printable layer, and the polyester resin, melamine resin, and other components, if necessary, may be mixed by a known method.

Then, after the paint for forming the printable layer is applied onto the metal plate, the paint for forming the printable layer is heated (hereinafter also referred to as "baking") to harden it. There are no particular restrictions on the baking method, but it is preferable to heat the metal plate so that the plate temperature reaches a range of 150 to 250°C.

In addition, if the printable layer is to be frame-treated after the paint for forming the printable layer is baked, the metal plate on which the printable layer is formed is placed on a conveyor such as a belt conveyor. Then, while moving in a certain direction, a flame is emitted onto the printable layer using a flame treatment burner.

Here, the frame treatment amount is preferably 100 to 600 kJ/ ^m2 . In this specification, the "frame treatment amount" refers to the amount of heat per unit area of the metal substrate calculated based on the supply amount of combustion gas such as LPG. The frame treatment amount can be adjusted by the distance between the burner head of the frame treatment burner and the surface of the printed layer, the conveying speed of the printed layer, etc. If the frame treatment amount is 100 kJ/ ^m2 or more, the entire surface of the printed layer is more likely to be treated uniformly. On the other hand, if the frame treatment amount is 600 kJ/ ^m2 or less, the printed layer is less likely to yellow, etc.

Prior to the above frame treatment, a preheating treatment may be performed to heat the surface of the printed layer to 40°C or higher. When a flame is applied to a printed layer formed on the surface of a metal substrate with high thermal conductivity (e.g., a metal substrate with thermal conductivity of 10 W/mK or more), the water vapor generated by the combustion of combustible gas is cooled and turns to water, which temporarily accumulates on the surface of the printed layer. This water may then absorb the energy during frame treatment and turn to water vapor, which may impede the frame treatment. In response to this, the generation of water during flame treatment can be suppressed by preheating the surface of the printed layer.

The means for preheating the printed layer is not particularly limited and is appropriately selected according to the shape of the metal plate, etc. For example, a heating device generally called a drying oven can be used. For example, a batch-type drying oven (also called a "safe oven") can be used, and specific examples include a low-temperature incubator manufactured by Isuzu Manufacturing Co., Ltd. (model Mini Catalina MRLV-11), an automatic discharge type dryer manufactured by Tojo Thermal Engineering Co., Ltd. (model ATO-101), and a simplified explosion-proof dryer manufactured by Tojo Thermal Engineering Co., Ltd. (model TNAT-1000).

On the other hand, when the printing layer is subjected to a corona discharge treatment, the metal plate on which the printing layer is formed is placed between an insulated electrode and a grounded counter electrode dielectric roll. Then, a high frequency of 1 to 600 KHz and a high voltage of 5 to 30 KV are applied between them to generate a corona discharge. Corona discharge treatment devices include spark gap type, vacuum tube type, solid state type, etc., and any of them can be used. The corona discharge treatment conditions are preferably 200 W/m ² /min or more, and more preferably 200 to 800 W/m ² /min. If it is less than 200 W/m ² /min, the amount of corona discharge treatment may be insufficient, and if it exceeds 800 W/m ² /min, the treatment becomes excessive, which is not economically preferable.

Here, the thickness of the printable layer is not particularly limited, but is preferably 10 to 40 μm, and more preferably 12 to 25 μm. When the thickness of the printable layer is 10 μm or more, the durability of the printable layer is likely to be good. In addition, the printable layer is likely to be flexible, and the adhesion of the ink layer described below is likely to be improved. On the other hand, when the thickness is 40 μm or less, popping is unlikely to occur during the above-mentioned heating, and the surface condition is likely to be good. Furthermore, when the surface condition of the printable layer is good, the active energy ray-curable composition described below is likely to wet and spread uniformly, and the adhesion between the ink layer obtained from this and the printable layer is likely to be improved.

As described above, when the composition is analyzed in the depth direction by XPS using AlKα radiation as the X-ray source for the region from the surface of the printed layer to a depth of 10 nm, the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms may be 5 to 30 atom%, more preferably 12 to 28 atom%, and even more preferably 15 to 25 atom%. The concentration of each atom from the surface of the printed layer to a depth of 10 nm is measured by an XPS analyzer under the following conditions while etching the printed layer from the surface to a depth of 10 nm.
(Measurement condition)
Measurement equipment: ULVAC-PHI Versaprobe II scanning X-ray photoelectron spectrometer X-ray source: AlKα (monochrome: 50 W, 15 kV) 1486.6 eV
Analysis area: 1.0 x 1.0 ^mm2
Pass Energy: 5.85 eV (C1s, O1s), 187.85 eV (N1s)
Charge neutralization (electron neutralization + ion gun)
Analysis chamber vacuum level: 1.0×10 ⁻⁷ Pa
(Etching conditions)
Etching conditions: Ar-gas cluster ion beam Acceleration voltage: 5 kV
Etching rate: Approximately 1 nm/min (polymethyl methacrylate resin (PMMA) equivalent)

Here, in order to allow the active energy ray-curable ink described below to sufficiently wet and spread over the surface of the printable layer, it is preferable that the surface of the printable layer is made uniformly hydrophilic. Whether the surface of the printable layer is made uniformly hydrophilic or not can be evaluated by the methylene iodide sliding angle described below. For example, when the methylene iodide sliding angle of the printable layer is 10° or more and 40° or less, it can be said that the surface is made uniformly hydrophilic. It is more preferable that the methylene iodide sliding angle is 35° or less.

The methylene iodide sliding angle is likely to fall within the above range when the hydrophilicity of the printed layer surface is sufficiently high or when the surface roughness of the printed layer is high. However, when the hydrophilicity of the printed layer is non-uniform, the methylene iodide sliding angle will be higher than 40°. For example, when the surface is treated by corona treatment, the methylene iodide sliding angle is likely to exceed 40°. In contrast, when frame treatment is performed, the surface is uniformly hydrophilized and the methylene iodide sliding angle is 40° or less.

The reason why the methylene iodide sliding angle becomes larger than 40° when the hydrophilicity of the surface of the printed layer becomes non-uniform due to corona discharge treatment, etc., is considered as follows. It is assumed that there are two types of coating films with the same number of hydrophilic and hydrophobic groups on the surface, one of which has no bias in the distribution of hydrophilic and hydrophobic groups, and the other has a bias in the distribution of hydrophilic and hydrophobic groups. In this case, the static contact angles of both are not easily affected by the distribution of hydrophilic and hydrophobic groups and are approximately the same. In contrast, the dynamic contact angles of both (methylene iodide sliding angles) are affected by the distribution of hydrophilic and hydrophobic groups and are different values. When measuring the methylene iodide sliding angle, if the distribution of hydrophilic and hydrophobic groups is non-uniform, methylene iodide droplets are adsorbed to areas with a high density of hydrophilic groups. In other words, if there is an uneven distribution of hydrophilic and hydrophobic groups, the methylene iodide droplets will be less likely to move than if there was no uneven distribution, and the sliding angle will be larger. Therefore, if a large number of hydrophilic groups are introduced onto the surface of the printing layer, as in the case of corona discharge treatment, but there is unevenness in their distribution, the methylene iodide sliding angle will be a high value exceeding 40°.

The methylene iodide sliding angle is measured as follows. First, 2 μl of methylene iodide is dropped onto the printing layer. Then, using a contact angle measuring device, the inclination angle of the printing layer (the angle between the plane perpendicular to gravity and the printing layer) is increased at a speed of 2 degrees/second. At this time, the methylene iodide droplet is observed using a camera attached to the contact angle measuring device. The inclination angle at the moment when the methylene iodide droplet slides down is identified, and the average value of five measurements is taken as the methylene iodide sliding angle of the printing layer. The moment when the methylene iodide droplet slides down is the moment when both the end point of the methylene iodide (droplet) in the downward direction of gravity and the end point in the upward direction of gravity start to move.

2. Coated Metal Material The coated metal material has the above-mentioned metal substrate for printing, and an ink layer that is a cured product of an active energy ray curable composition (hereinafter also referred to as "curable composition") that is disposed on the printable layer of the metal substrate for printing. The ink layer may be disposed in the entire area where the printable layer is formed, or may be disposed only in a part of the area where the printable layer is formed.

The ink layer may be a cured product of only one type (e.g., one color) of curable composition, or may be a cured product of two or more types (e.g., two or more colors) of curable compositions. The composition of the curable composition will be described later. The type of curable composition, the arrangement area, the arrangement pattern, etc. are appropriately selected according to the application of the coated metal material. Examples of active energy rays in this specification include electron beams, ultraviolet rays, α rays, γ rays, X-rays, etc.

The method of applying the curable composition is not particularly limited and may be appropriately selected from known methods. Examples of methods of applying the curable composition include inkjet printing, gravure printing, offset printing, screen printing, roll coating, bar coating, and the like. Among these, the inkjet method is preferred from the viewpoint of easily forming multicolored patterns or complex patterns in a short time. These methods may be combined when applying the curable composition.

Furthermore, the amount of the curable composition applied is not particularly limited, and it is preferable to apply the composition so that the thickness after curing is about 5 to 150 μm, and more preferably about 10 to 100 μm. The above thickness may be achieved by applying the curable composition multiple times to the same location. As described above, generally, the more the amount of the curable composition applied, the greater the cure shrinkage during curing, and the more likely the resulting ink layer is to peel off. However, the above-mentioned metal substrate for printing (especially when it has a printable layer that has been frame-treated) has high adhesion between the printable layer and the ink layer formed, and peeling is unlikely to occur even when an ink layer having a thickness of, for example, 40 μm or more is formed.

The curable composition may be applied so that the thickness of the cured ink layer changes continuously or intermittently. When a printable layer of a different thickness is formed on a general printable layer, adhesion changes between the thick and thin ink layer, and peeling may occur from the areas with low adhesion. In contrast, in the above-mentioned metal substrate for printing (particularly when the printable layer has been subjected to frame treatment), the ink layer and the printable layer have high adhesion both when the ink layer is thin and when the ink layer is thick. Therefore, peeling is unlikely to occur even when an ink layer with a variable thickness is formed.

After the curable composition is applied, the coating is irradiated with active energy rays to cure it. The active energy can be any of electron beams, ultraviolet rays, α rays, γ rays, and X-rays. Among these, electron beams or ultraviolet rays are preferred from the viewpoints of energy efficiency and the absence of the need for large-scale equipment, and ultraviolet rays are particularly preferred.

The amount of active energy rays to be irradiated is appropriately selected depending on the type and amount of the photopolymerization initiator and photoacid generator in the curable composition described below. The dominant wavelength of the active energy rays to be irradiated is also appropriately selected depending on the type of photopolymerization initiator and photoacid generator, and can be, for example, a wavelength of 360 to 425 nm.

When multiple types of curable compositions are applied, active energy rays may be irradiated after each type of curable composition is applied, or active energy rays may be irradiated after multiple types of curable compositions are applied.

The curable composition to be applied onto the print layer may be a known composition that has been used for printing on metal plates. The curable composition includes a radical polymerization composition and a cationic polymerization composition, and either of them can be used in the present invention.

The radical polymerization type composition may be, for example, a composition containing a photopolymerizable compound, a photopolymerization initiator, and a colorant. The photopolymerizable compound may be a compound having at least one photopolymerizable group that exhibits reactivity when irradiated with active energy rays. Examples of the photopolymerizable compound include known (meth)acrylic monomers or (meth)acrylic oligomers having 1 to 6 (meth)acryloyloxy groups. In this specification, the term "(meth)acryloyl" refers to either or both of methacryloyl and acryloyl, and the term "(meth)acrylic" refers to either or both of methacryl and acrylic. The radical polymerization type composition may contain only one type of photopolymerizable compound, or may contain two or more types.

The radical polymerization type composition preferably contains 50 to 90% by mass of the above-mentioned photopolymerizable compound in the solid content. When the amount of the photopolymerizable compound in the radical polymerization type composition is within this range, the radical polymerization type composition tends to sufficiently wet and spread on the above-mentioned print layer, and the ink layer tends to adhere to the print layer.

On the other hand, the photopolymerization initiator may be any compound capable of generating radicals when irradiated with active energy rays, and is preferably a compound having an absorption wavelength corresponding to the wavelength of the active energy rays. Examples of photopolymerization initiators include benzophenone-based compounds, acetophenone-based compounds, thioxanthone-based compounds, and phosphine oxide-based compounds. In particular, phosphine oxide-based compounds have an absorption wavelength of 370 nm or more, and therefore are preferably added to promote deep curing of the ink layer. The radical polymerization composition may contain only one type of photopolymerization initiator, or may contain two or more types.

The radical polymerization type composition preferably contains the above-mentioned photopolymerization initiator in an amount of 1 to 25% by mass based on the solid content. When the amount of the photopolymerization initiator in the radical polymerization type composition is within this range, it becomes possible to cure the above-mentioned photopolymerizable compound.

The type of colorant is not particularly limited, and known pigments or dyes can be used. The radical polymerization type composition preferably contains 0.1 to 10% by mass of the colorant in the solid content. The radical polymerization type composition may contain only one type of colorant, or may contain two or more types.

On the other hand, the cationic polymerization type composition can be a composition containing a photopolymerizable compound, a photoacid generator, and a colorant.

The photopolymerizable compound may be any compound having at least one photopolymerizable group that exhibits reactivity when irradiated with active energy rays. Examples of photopolymerizable compounds include epoxy compounds having an oxirane group. Examples of epoxy compounds include aromatic epoxides, alicyclic epoxides, and aliphatic epoxides.

The photopolymerizable compound may be an epoxidized fatty acid ester or an epoxidized fatty acid glyceride in which an epoxy group has been introduced into a fatty acid ester or a fatty acid glyceride. Furthermore, the photopolymerizable compound may be a compound containing an oxetane ring or a vinyl ether compound. The cationic polymerization type composition may contain only one type of photopolymerizable compound, or may contain two or more types.

The cationic polymerization composition preferably contains 60 to 95% by mass of the photopolymerizable compound in the solid content. When the amount of the photopolymerizable compound in the cationic polymerization composition is within this range, the cationic polymerization composition easily wets and spreads sufficiently on the above-mentioned printable layer, and the ink layer easily adheres to the printable layer.

The photoacid generator includes, for example, salts of aromatic onium compounds; sulfonates that generate sulfonic acid; halides that generate hydrogen halides; and the like. The cationic polymerization composition preferably contains 3 to 20 mass % of the photoacid generator in the solid content. When the amount of the photoacid generator in the cationic polymerization composition is within this range, it becomes possible to sufficiently cure the photopolymerizable compound.

The colorant contained in the cationic polymerization composition is the same as the colorant contained in the radical polymerization composition.

The curable composition may contain other components as necessary. Examples of other components include polymerization inhibitors, antioxidants, silane coupling agents, plasticizers, rust inhibitors, solvents, non-reactive polymers, fillers, pH adjusters, defoamers, charge control agents, stress relaxation agents, surface conditioners, etc.

- Uses of the painted metal material The uses of the above-mentioned painted metal material are not particularly limited, and it can be used for a wide variety of components and applications that use a metal substrate. Examples of applications include home appliances such as refrigerator outer panels, microwave oven outer panels, personal computer housings, and air conditioner housings; interior decorative building materials such as partitions, doors, ceiling materials, floor materials, elevator doors, and elevator interior panels; various residential equipment such as range hoods and bathroom interior components; furniture such as desks, chairs, lockers, and shelves; and vehicle components such as passenger car interiors and railway car interiors. However, the uses of the painted metal material are not limited to these.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

1. Preparation of metal plate A hot-dip Zn-plated steel plate with a plate thickness of 0.3 mm and an A4 size with a plating weight of 45 g/ ^m2 per side was used. After alkaline degreasing of the plated steel plate, a paint-type chromate (NRC300NS: manufactured by Nippon Paint Industrial Coatings Co., Ltd.) was applied to the plate so that the Cr was 50 mg/ ^m2 , and a primer composition (FL641EU primer, manufactured by Nippon Paint Industrial Coatings Co., Ltd.) was applied to the plate so that the dry film thickness was 5 μm using a roll coater. After that, the plate was baked so that the maximum plate temperature reached was 215° C. to obtain a metal plate.

2. Preparation of paint for forming printable layer The polyester resin and melamine resin shown below were mixed in the mass ratio shown in Table 1. Furthermore, the catalyst and color pigment shown below were also mixed to prepare a paint for forming a printable layer.

(1) Polyester resin The following four types of polyester resin were used. The polyester resin was dissolved in a solvent and mixed with other components. The solvent was one of n-methylpyrrolidone, cyclohexanone, an aromatic solvent (Solvesso (registered trademark) 150, surface tension 30 mN/m), and ethyl-3-ethoxy-propionate (surface tension 25 mN/m), or a mixture of multiple solvents.

Polyester resin A (prepared by the following method, number average molecular weight: 10,000)
Polyester resin B (manufactured by Toyobo Co., Ltd., Vylon (registered trademark) GK140, Tg: 20°C, number average molecular weight: 14,000, amorphous)
Polyester resin C (manufactured by Toyobo Co., Ltd., Vylon (registered trademark) 630, Tg: 7°C, number average molecular weight: 23,000, amorphous)
Polyester resin D (prepared by the following method, number average molecular weight: 31,000)

(Method of preparing polyester resins A and D)
Dimethyl terephthalic acid, dimethyl isophthalic acid, trimellitic anhydride, ethylene glycol, neopentyl glycol, 1,6-hexanediol, and 2-methyl-1,3-propanediol were charged in appropriate amounts into a reaction vessel equipped with a stirrer, a condenser, and a thermometer, and an ester exchange reaction was carried out over 4 hours at 160°C to 240°C. Then, the reaction vessel was cooled to 200°C, adipic acid was charged, and the reaction vessel was gradually heated to 240°C to carry out an esterification reaction. The pressure in the system was gradually reduced to 5 mmHg over 50 minutes, and a polycondensation reaction was carried out at 260°C for 60 minutes under a vacuum of 0.3 mmHg or less. Polyester resins A and D were obtained by changing the composition ratio during polymerization.

(2) Melamine resin The following two types of melamine resin were used: Methylated melamine (Allnex Japan, Cymel 303, fully alkylated methylated melamine resin)
-Butylated melamine (DIC Corporation, Super Beckamin (registered trademark) J830, butylated melamine resin)

(3) Catalyst The catalyst used was dodecylbenzenesulfonic acid. More specifically, dodecylbenzenesulfonic acid was neutralized with triethylamine so that the amine equivalent was 1.25 times the acid equivalent, and the neutralized catalyst was added in an amount of 1 mass % based on the resin solid content of the coating material for forming the printable layer.

(4) Coloring Pigment Titanium oxide (Taipaque (registered trademark) CR-95, manufactured by Ishihara Sangyo Kaisha, Ltd.) was used as the coloring pigment. The amount of the pigment added was 50% by mass based on the total amount of the amorphous polyester resin and the melamine resin.

3. Formation of the printable layer On one side of the metal plate having the above-mentioned primer layer, the paints P1 to P16 for forming the printable layer were each applied with a roll coater so that the dry film thickness was 18 μm. Then, the plate was baked for 60 seconds so that the maximum plate temperature reached was 225° C., and a printable layer was formed on the metal plate.

4. Frame treatment and corona discharge treatment 4-1. Frame treatment The metal substrate for printing on which the above-mentioned printed layer was formed was placed on a conveyor, and the printed layer was subjected to frame treatment. The burner for frame treatment was F-3000 manufactured by Flynn Burner (USA). In addition, a mixed gas (LP gas: clean dry air (volume ratio) = 1:25) in which LP gas (combustion gas) and clean dry air were mixed with a gas mixer was used as the combustible gas. In addition, the flow rate of each gas was adjusted so that LP gas (combustion gas) was 1.67 L/min and clean dry air was 41.7 L/min per 1 ^cm2 of the burner's flame port. The length of the flame port of the burner head in the conveying direction of the printed layer was 4 mm. On the other hand, the length of the flame port of the burner head in the conveying direction and perpendicular to the conveying direction was 450 mm. In addition, the distance between the burner head flame and the surface of the printing layer was set to 50 mm according to the desired flame treatment amount. Furthermore, the conveying speed of the printing layer was set to 30 m/min, so that the flame treatment amount was adjusted to 212 kJ/ ^m2 .

4-2. Corona Discharge Treatment The printing layer of the metal substrate for printing on which the printing layer was formed was subjected to a corona discharge treatment using a corona discharge treatment device manufactured by Kasuga Electric Co., Ltd.
(specification)
・Ceramic electrode ・Electrode length 430mm
Output: 310W
The number of corona discharge treatments for each printing layer was one. The amount of corona discharge treatment was adjusted by the treatment speed. Specifically, the treatment was performed at 2.8 m/min, and the amount of corona discharge treatment was 250 W/m ² /min.

5. Preparation of active energy ray curable composition An active energy ray curable composition (the following radical polymerization type composition or cationic polymerization type composition) prepared as described below was applied to the printable layer that had been subjected to the above-mentioned frame treatment or corona discharge treatment and to an untreated printable layer under the conditions described below.

5-1. Preparation of Radical Polymerization Type Black Composition Composition The following components were mixed to prepare a radical polymerization type black composition.
Pigment dispersion (pigment: 10% by mass) 10 parts by mass Photopolymerizable compound A 25 parts by mass Photopolymerizable compound B 57 parts by mass Photopolymerization initiator a 5 parts by mass Photopolymerization initiator b 3 parts by mass

Materials The following compounds were used as materials for the radical polymerization type black composition.
Pigment dispersion: a mixture of carbon black (NIPex 35, manufactured by Degussa Japan) and a dispersion medium (SR9003, PO-modified neopentyl glycol diacrylate, manufactured by Sartomer Japan) Photopolymerizable compound A: CN985B88 (a mixture of 88% by mass of bifunctional aliphatic urethane acrylate and 12% by mass of 1,6-hexanediol diacrylate), manufactured by Sartomer Japan
Photopolymerizable compound B: 1,6-hexanediol diacrylate Photopolymerization initiator a: Irgacure 184 (hydroxyketones) manufactured by Ciba Japan Co., Ltd.
Photopolymerization initiator b: Irgacure 819 (acylphosphine oxides) manufactured by Ciba Japan Co., Ltd.

5-2. Preparation of Cationic Polymerization Type Black Composition The cationic polymerization type black composition was prepared by first preparing a pigment dispersion and then mixing the pigment dispersion with other components.

Preparation of pigment dispersion 9 parts by mass of a polymer dispersant (PB821, manufactured by Ajinomoto Fine-Techno Co., Ltd.), 71 parts by mass of an oxetane compound (OXT211, manufactured by Toa Gosei Co., Ltd.), and 20 parts by mass of a black pigment (Pigment Black 7) were mixed. The mixture was then placed in a glass bottle together with 200 g of zirconia beads having a diameter of 1 mm, sealed, and dispersed for 4 hours using a paint shaker. The zirconia beads were then removed to obtain a pigment dispersion.

Composition The following components were mixed to prepare a cationic polymerization type black composition.
Pigment dispersion 14 parts by weight Photopolymerizable compound C 4 parts by weight Photopolymerizable compound D 34 parts by weight Photopolymerizable compound E 24 parts by weight Photopolymerizable compound F 8.9 parts by weight Basic compound 0.05 parts by weight Surfactant a 0.025 parts by weight Surfactant b 0.025 parts by weight Compatibilizer 10 parts by weight Photoacid generator 5 parts by weight

Materials The following compounds were used as materials for the cationic polymerization type black composition.
Photopolymerizable compound C: Epoxidized linseed oil (ATOFINA, Vikoflex 9040)
Photopolymerizable compound D: a compound represented by the following formula:
Photopolymerizable compound E: Oxetane compound (manufactured by Toagosei Co., Ltd., OXT-221)
Photopolymerizable compound F: Oxetane compound (manufactured by Toagosei Co., Ltd., OXT-211)
Basic curing composition: N-ethyldiethanolamine Surfactant a: Megafac F178k (perfluoroalkyl group-containing acrylic oligomer), manufactured by DIC Corporation
Surfactant b: Megafac F1405 (perfluoroalkyl group-containing ethylene oxide adduct), manufactured by DIC Corporation
Compatibilizer: Hisorb BDB (glycol ether), manufactured by Toho Chemical Industry Co., Ltd.
Photoacid generator: UV16992, manufactured by The Dow Chemical Company

5-3. Printing Conditions for Active Energy Ray-Curable Composition The printing conditions for the above-mentioned radical polymerization type black composition and cationic polymerization type black composition are as follows.

(Inkjet printing conditions for radically polymerizable composition)
(a) Nozzle diameter: 35 μm
(b) Applied voltage: 11.5 V
(c) Pulse width: 10.0 μs
(d) Drive frequency: 3,483 Hz
(e) Resolution: 360 dpi
(f) Droplet volume: 42 pl
(g) Head heating temperature: 45° C.
(h) Coating amount: 8.4 g / ^m2
(i) Distance between head and recording surface: 5.0 mm
(j) Initial velocity of droplet: 5.9 m/sec

(Inkjet printing conditions for cationic polymerization composition)
(a) Nozzle diameter: 35 μm
(b) Applied voltage: 13.2 V
(c) Pulse width: 10.0 μs
(d) Drive frequency: 3,483 Hz
(e) Resolution: 360 dpi
(f) Droplet volume: 42 pl
(g) Head heating temperature: 45° C.
(h) Coating amount: 8.4 g / ^m2
(i) Distance between head and recording surface: 5.0 mm
(j) Initial velocity of droplet: 6.1 m/sec

6. Evaluation For each printed layer, the following analysis by XPS method, measurement of methylene iodide sliding angle, pencil hardness (untreated only), coating processability test (untreated only), solvent rubbing test (untreated only), and wet spread evaluation (dot diameter evaluation) were performed. Furthermore, the adhesion of the ink layer was evaluated for the coated metal material after the active energy ray curable composition was applied to form an ink layer. The results are shown in Tables 2, 3, and 4.

6-1. Analysis by XPS method (determining the amount of N atoms, C atoms, and O atoms in the printed layer)
The concentrations of N atoms, C atoms, and O atoms in the depth direction (the total amount of N atoms, C atoms, and O atoms is 100 atom%) were measured under the following conditions while etching from the surface of the printing layer to a depth of 10 nm using an XPS analyzer. The maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms was then identified. The relationship between the concentration of each atom and the depth when the printing layer of Example 8, Example 5, Example 2, Comparative Example 8, and Comparative Example 2 were analyzed by the XPS method is shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4, and FIG. 5, respectively.
(Measurement condition)
Measurement equipment: ULVAC-PHI Versaprobe II scanning X-ray photoelectron spectrometer X-ray source: AlKα (monochrome: 50 W, 15 kV) 1486.6 eV
Analysis area: 1.0 x 1.0 ^mm2
Pass Energy: 5.85 eV (C1s, O1s), 187.85 eV (N1s)
Charge neutralization (electron neutralization + ion gun)
Analysis chamber vacuum level: 1.0×10 ⁻⁷ Pa
(Etching conditions)
Etching conditions: Ar-gas cluster ion beam Acceleration voltage: 5 kV
Etching rate: Approximately 1 nm/min (polymethyl methacrylate resin (PMMA) equivalent)

6-2. Measurement of methylene iodide sliding angle 2 μl of methylene iodide was dropped onto the printing layer held horizontally. Then, using a contact angle measuring device (DM901 manufactured by Kyowa Interface Science Co., Ltd.), the inclination angle of the printing layer (the angle between the horizontal plane and the printing layer) was increased at a speed of 2 degrees/second. Then, the methylene iodide droplet was observed with a camera attached to the contact angle measuring device. The inclination angle of the printing layer at the moment when the methylene iodide droplet fell was specified, and the average value of five times was taken as the methylene iodide sliding angle of the printing layer. The moment when the methylene iodide droplet fell was taken as the moment when both the end point of the methylene iodide droplet in the downward direction of gravity and the end point in the upward direction of gravity began to move.

Pencil hardness The pencil hardness of the printable layer was measured according to the measurement method specified in JIS K5600-5-4.
◎: H or above ○: HB-F
×: B or below

6-4. Coating workability test The prepared coated steel sheet for printing was bent 180° (close bending) according to the bending test of JIS G3322, and the state of the coating at the bent part was visually observed to check for the presence or absence of coating cracks. When bending 180°, the printed surface of the coated steel sheet for printing was bent to the outside of the bend, and close bending was performed (generally known as 0T bending). In addition, when observing the bent part, the observation was made with a 10x magnifying glass, and a processed part adhesion test was also performed in which tape was applied to the processed part and peeled off. Then, the adhesion after peeling off the tape was visually observed. The evaluation was based on the following criteria, and an evaluation of △ or higher was considered to be acceptable.
◎: No peeling, no cracks (cracks in the coating) ○: No peeling, cracks (cracks in the coating) △: Very slight peeling ×: Slight peeling ××: Peeling

6-5. Solvent rubbing test A load of 1 kg was pressed against the surface of the print layer through gauze soaked in xylol, and the surface was rubbed back and forth 100 times. The appearance of the print layer was then observed and evaluated as follows. The length of the xylol-soaked gauze rubbed against the surface of the print layer was 70 mm in one direction. Only ○ was considered to be pass.
◯: The printed layer was not mechanically worn away or peeled off by solvents, and maintained a good appearance. △: The printed layer was mechanically worn away or peeled off by solvents, exposing the primer layer. ×: All layers, including the primer layer, were mechanically worn away, or the printed layer was peeled off by solvents, exposing the original metal plate.

6-6. Evaluation of Wetting and Spreading Properties of Active Energy Ray-Curable Compositions (Dot Diameter Evaluation)
On the above-mentioned printed layer, the active energy ray curable composition (radical polymerization type black composition and cationic polymerization type black composition) was applied in the form of dots. Specifically, dots were printed using an inkjet printer (Patterning Jet, manufactured by Tritec Co., Ltd.) so that the volume of each droplet was 42 pl. The distance between the dots was set to 500 μm so that the dots would not overlap each other. Then, the diameter of each dot was measured using a scanning confocal laser microscope LEXT OLS3000 manufactured by Olympus Co., Ltd. More specifically, the dot diameters of eight dots were measured by enlarging the area to a range where only one dot was visible (200 times), and the average value was evaluated as the dot diameter. When the spread of the dots was close to an ellipse, the average value of the major axis and minor axis was taken as the dot diameter and evaluated as follows. Note that when the dot diameter is less than 100 μm, the active energy ray curable composition is difficult to wet and spread, and even if 100% printing is performed, the surface of the printed layer cannot be completely covered with the active energy ray curable composition. Therefore, the smaller the dot diameter, the lower the evaluation. However, if it is rated △ or higher, there is no problem in practical use.
◎: Dot diameter 130 μm or more ○: Dot diameter 100 μm or more and less than 130 μm △: Dot diameter 80 μm or more and less than 100 μm ×: Dot diameter less than 80 μm

6-7. Evaluation of adhesion of ink layer An active energy ray curable composition was printed on the above-mentioned printing layer at 100 to 1000% (ink coating amount: 8.4 to 84.0 g/m ² ) under the above-mentioned conditions so as to obtain a resolution of 360 dpi. Then, ultraviolet rays were irradiated using a high pressure mercury lamp (H bulb, manufactured by Fusion UV Systems Japan) with a lamp output of 200 W/cm and an accumulated light amount of 600 mJ/cm ² (measured using an ultraviolet light meter UV-351-25, manufactured by Oak Manufacturing Co., Ltd.) to form an ink layer. A cross-cut test in accordance with JIS K5600-5-6 G 330 was carried out on the obtained coated metal material. Specifically, a cross-cut cut was made on the surface of the ink layer so that 25 squares were formed at 2 mm intervals. Then, an adhesive tape was attached to the corresponding part and peeled off. After peeling off the adhesive tape, the remaining rate of the ink layer was observed. The evaluation was performed according to the following criteria, with a grade of △ or better being considered a pass.
○: The peeled area of the ink layer is 0%.
△: The peeled area of the ink layer is more than 0% and not more than 20%. ×: The peeled area of the ink layer is more than 20%.

6-8. Adhesion test An active energy ray curable composition was printed on the above-mentioned print layer at 100% (ink coating amount: 8.4 g/m ² ) under the above-mentioned conditions so as to obtain a resolution of 360 dpi, and cured by irradiation with ultraviolet light in the same manner as above to form an ink layer. The obtained coated metal material was subjected to a 4T bending test in accordance with the bending test of JIS G3322. Then, an adhesive tape was applied to the surface of the ink layer at the bent portion and peeled off. The appearance of the coated metal material was observed before and after the adhesive tape was applied and was evaluated as follows. Coated metal materials printed at 500% and 1000% were also evaluated in the same manner. Evaluations of △ or higher were considered to be pass.
○: No peeling of the ink layer or printed layer △: Spot-like peeling of 1 mm or less occurred in the ink layer or printed layer ×: Peeling occurred in the ink layer or printed layer

As shown in Figures 1 to 5 and Tables 2 to 4, when the composition was analyzed in the depth direction of the printed layer using the XPS method, it became clear that the ratio of N atoms changes significantly in the region from the surface to a depth of 10 nm depending on the amount, type, and combination of melamine resin.

In addition, when the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms in the region from the surface of the printable layer to a depth of 10 nm was 5 to 30 atom%, the pencil hardness, coating processability test, and rubbing test were all good. Furthermore, when an ink layer was formed on the printable layer, the adhesion was also good; for example, even when the ink layer was a thick film with a coating amount of 1000%, good adhesion was obtained (Examples 1 to 18).

In addition, when comparing the untreated printable layer (Examples 1, 4, 7, 10, 13, and 16), the frame-treated printable layer (Examples 2, 5, 8, 11, 14, and 17), and the corona discharge-treated printable layer (Examples 3, 6, 9, 12, 15, and 18), the frame-treated printable layer had the best dot diameter evaluation results and also had good adhesion to all of the polymerizable inks.

In contrast, when the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms exceeds 30 atom%, the pencil hardness evaluation results are good, but the adhesion of the ink layer is low, and furthermore, the results of the coating processability test and the rubbing test are poor (Comparative Examples 1 to 18). It is believed that when the maximum value of N atoms is large, the printed layer becomes hard, and the adhesion of the ink layer decreases.

On the other hand, when the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms was less than 5 atom%, the pencil hardness was low and the results of the rubbing test were also poor (Comparative Examples 19 to 24).

In addition, when the number average molecular weight of the polyester resin was less than 12,000, sufficient processability was not obtained (Comparative Examples 25 to 27). On the other hand, when the number average molecular weight of the polyester resin exceeded 30,000, sufficient coating hardness was not obtained (Comparative Examples 28 to 30).

According to the printing metal substrate of the present invention, when an ink layer is formed using an active energy ray-curable composition, the ink layer is unlikely to peel off. In addition, the printing layer of the printing metal substrate has good processability and scratch resistance. Therefore, it is possible to form various coated metal materials with high design appeal.

Claims (6)

A metal plate;
A printable layer including a cured product of a coating material including a polyester resin having a number average molecular weight of 12,000 to 30,000 and a melamine resin, which is disposed on the metal plate;
having
When a composition is analyzed in a depth direction by X-ray photoelectron spectroscopy using AlKα radiation as an X-ray source in a region from the surface of the printing layer to a depth of 10 nm, the maximum value of N atoms relative to the total amount of N atoms, C atoms, and O atoms is 5 to 30 atom %.
A metal substrate for printing on which an active energy ray-curable composition is applied . The metal substrate for printing according to claim 1, wherein the melamine resin is a mixture of at least a butylated melamine resin and a melamine resin other than the butylated melamine resin. The methylene iodide sliding angle on the surface of the printing layer is 10° or more and 40° or less.
The metal substrate for printing according to claim 1 or 2. The metal substrate for printing according to any one of claims 1 to 3,
an ink layer, which is a cured product of an active energy ray-curable composition, disposed on the printable layer of the metal substrate;
having
Painted metal material. A method for producing a metal substrate for printing according to any one of claims 1 to 3,
The method includes a step of applying a coating material containing a polyester resin having a number average molecular weight of 12,000 to 30,000 and a melamine resin onto a metal plate and curing the coating material to form a printable layer.
A method for producing a metal substrate for printing on which an active energy ray-curable composition is applied . The printing layer may further include a step of subjecting the printing layer to a frame treatment or a corona discharge treatment.
The method for producing the metal substrate for printing according to claim 5 .