JP7728664B2 - Low temperature baking compatible resist ink - Google Patents

Description

The present invention relates to a resist ink that can be baked at low temperatures and is used when creating circuit boards with circuit patterns from metal foil.

In recent years, the "RFID (Radio Frequency Identifier) system," which exchanges information via short-range wireless communication using electromagnetic fields and radio waves, has become increasingly popular as a logistics management system in countries around the world, replacing IC tags with embedded ID information for the purposes of product information management and theft prevention.
In Japan, demand for RF tags is expanding year by year, as they are used in transportation IC cards, and RF tags with registered electronic information are attached to products and food, and the contents are read by a dedicated reader and used for product management. These methods use dedicated IC tags, and resist ink is used in the production of these IC tags.
IC tags are generally made by masking a metal foil with a coil-shaped resist ink to form a circuit pattern, then curing the printed area with UV light or heat as needed, and then immersing the foil in an acidic etching solution to etch away any unnecessary circuit pattern parts, creating a coil and creating the required circuit pattern (see, for example, Patent Document 1: JP 2015-65384).

Furthermore, there may be cases where a step of immersing the resist ink coating in an alkaline etching solution is required to peel off the resist ink coating that has completed its role as a resist.
Furthermore, in the case of a type in which a printed film that acts as a resist during etching is thermally cured, baking is typically required in an oven at 130°C to 150°C, and therefore lowering the baking temperature is desirable from the perspective of energy conservation and cost reduction. Meanwhile, resist inks that can be baked at low temperatures have been disclosed that can provide both adhesion to the metal foil that forms the circuit and acid etching resistance even when the oven temperature is low (for example, Patent Document 1: WO2017/073309A1).
Lowering the baking temperature tends to decrease the adhesion between the metal foil of the substrate and the printed film, which tends to cause problems such as a decrease in acid etching resistance during the acid etching process, and furthermore, in the process of peeling the resist ink film with an alkaline solution, it is desirable for the resist ink to also be alkali-soluble.Even under low-temperature conditions of oven temperatures of 90 to 120°C, it is desirable for a resist ink that can be baked at low temperatures to have both adhesion to the metal foil, acid etching resistance, and alkali solubility, and the above-mentioned conventional techniques are by no means sufficient to achieve both adhesion and the scratch resistance, acid etching resistance, and alkali solubility that are indicators of the strength of the resist film.

JP 2015-65384 A WO2017/073309A1 publication

The objective of the present invention is to provide a resist ink that can be baked at low temperatures and that has adhesion to the metal foil that forms the circuit, scratch resistance, acid etching resistance, and alkali solubility, even when the oven temperature is low.

As a result of extensive research into solving the above-mentioned problems, the inventors discovered that a resist ink compatible with low-temperature baking containing a specific acrylic resin, a specific amount of color pigment, and polyester polycarboxylic acid as essential components is effective in solving the problems.

That is, the present invention provides a resist ink suitable for low-temperature baking, which contains an acrylic resin, a color pigment, and a polyester polycarboxylic acid, wherein the acrylic resin has a weight-average molecular weight of 1,500 to 50,000, a glass transition temperature of 60 to 90°C, and an acid value of 70 to 250 mgKOH/g, and the color pigment accounts for 3 to 15% by mass of the total solids content of the ink.

The present invention also provides a resist ink suitable for low-temperature baking, in which the mass ratio of the color pigment to the polyester polycarboxylic acid is in the range of 1:20 to 1:2.

The present invention also provides a resist ink suitable for low-temperature baking, in which the acid value of the polyester polycarboxylic acid is in the range of 1 to 150 mgKOH/g.

The present invention also provides a resist ink suitable for low-temperature baking, in which the color pigment is titanium oxide.

The present invention also provides a method for producing a resist printed matter, which comprises, in this order: a step of printing a metal foil with resist ink; a step of heating and curing the resist ink film formed by printing at 80°C or higher; a step of etching the cured resist ink film from above with an acidic etching solution; and a step of peeling off the resist ink film with an alkaline solution,
The method for producing a resist print is characterized in that the resist ink is a low-temperature baking-compatible resist ink, and the amount of ink printed on the metal foil is approximately 0.5 to 3 g/ ^m2 .

The present invention makes it possible to obtain a resist ink that can be baked at low temperatures and that combines adhesion to the metal foil that forms the circuit, scratch resistance, acid etching resistance, and alkali solubility, even at low oven temperatures.

The present invention will now be described in detail. Note that in the following description, all references to "ink" refer to "resist ink." Furthermore, all references to "parts" refer to "parts by mass," and all references to "%" refer to "% by mass."

The low-temperature bakeable resist ink of the present invention is a resist ink containing an acrylic resin, a color pigment, and a polyester polycarboxylic acid, wherein the acrylic resin has a weight-average molecular weight of 1,500 to 50,000, a glass transition temperature of 60 to 90°C, and an acid value of 70 to 250 mgKOH/g, and the color pigment accounts for 3 to 10 mass% of the total solid content of the ink.
The temperature range for the "low temperature baking" is 90 to 120°C, compared to the general baking oven temperature of 130 to 150°C.

Specifically, the resist ink of the present invention is made by dissolving a binder resin containing the acrylic resin in various organic solvents such as ethyl acetate, methyl ethyl ketone, and toluene. A color pigment is kneaded with the binder resin and the various organic solvents to produce an ink. A color pigment and various additives are added to the ink and further stirred to obtain a well-dispersed resist ink.

(acrylic resin)
The acrylic resin used in the present invention must have a weight average molecular weight of 1,500 to 50,000, a glass transition temperature of 60 to 90° C., and an acid value of 70 to 250 mgKOH/g.
If the weight-average molecular weight is 1500 or more, the adhesiveness and acid resistance tend to be maintained while maintaining alkali solubility.If the weight-average molecular weight is 50000 or less, the acid resistance can be maintained while maintaining alkali solubility, and the viscosity adjustment and dispersibility as a resist ink tend to be favorably maintained.
Furthermore, if the glass transition temperature is 60° C. or higher, adhesion, scratch resistance, and acid resistance tend to be maintained while maintaining alkali solubility. If the glass transition temperature is 250° C. or lower, cracking of the cured coating of the resist ink tends to be suppressed.
Furthermore, if the acid value is 70 mgKOH/g or more, the adhesiveness and, in particular, the acid resistance under low-temperature baking conditions such as 90°C tend to be maintained while maintaining alkali solubility.
If the acid value is 250 mgKOH/g or less, the adhesiveness and acid resistance tend to be maintained while maintaining alkali solubility.

Furthermore, the total amount of the acrylic resins is in the range of 60 to 95% by mass, more preferably 70 to 90% by mass, and even more preferably 80 to 90% by mass of the total ink solids.

The acrylic resin is not particularly limited as long as it is a copolymer of polymerizable monomers whose main component is a (meth)acrylic acid ester. Examples of polymerizable monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, iso-nonyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and phenoxyethyl (meth)acrylate. The polymerization method is also not particularly limited, and resins obtained by known methods such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization can be used.

(Polyester polycarboxylic acid)
The resist ink for low temperature baking of the present invention must contain a polyester polycarboxylic acid.
The polyester polycarboxylic acid can be obtained, for example, by reacting a polybasic acid with a polyhydric alcohol.
Examples of polybasic acids include oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, other aliphatic dicarboxylic acids (having 11 to 13 carbon atoms), hydrogenated dimer acid, maleic acid, fumaric acid, itaconic acid, orthophthalic acid, isophthalic acid, terephthalic acid, toluenedicarboxylic acid, dimer acid, and HET acid, and other dicarboxylic acids, and alkyl esters of these dicarboxylic acids.

Furthermore, the polybasic acids include acid anhydrides derived from the above-exemplified carboxylic acids, such as oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, 2-alkyl (having 12 to 18 carbon atoms) succinic anhydride, tetrahydrophthalic anhydride, and trimellitic anhydride.
Furthermore, the polybasic acids include acid halides derived from the above-exemplified carboxylic acids, such as oxalic acid dichloride, adipic acid dichloride, and sebacic acid dichloride.

These polybasic acids can be used alone or in combination of two or more. Preferred are dicarboxylic acids and alkyl esters thereof.
Examples of polyhydric alcohols include diols having two hydroxyl groups and polyols having three or more hydroxyl groups.
Examples of diols include aliphatic diols such as C2-22 alkanediols such as ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,5-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dimethylolheptane, 2-ethyl-2-butyl-1,3-propanediol, 1,12-dodecanediol, and 1,18-octadecanediol; and alkenediols such as 2-butene-1,4-diol and 2,6-dimethyl-1-octene-3,8-diol.

Examples of diols include alicyclic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A or its C2-4 alkylene oxide adduct.
Examples of diols include aromatic diols such as resorcinol, xylylene glycol, bishydroxyethoxybenzene, bishydroxyethylene terephthalate, bisphenol A, bisphenol S, bisphenol F, and C2-4 alkylene oxide adducts of these bisphenols.

Further, examples of the diol include polyether diols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polyethylene polypropylene block glycol, and polytetramethylene ether glycol.
Examples of polyols having three or more hydroxyl groups include triols such as glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-(hydroxymethyl)pentane, 2,2-bis(hydroxymethyl)-3-butanol, and other aliphatic triols (having 8 to 24 carbon atoms); and polyols having four or more hydroxyl groups such as tetramethylolmethane, pentaerythritol, dipentaerythritol, D-sorbitol, xylitol, D-mannitol, and D-mannite.

Among the polyester polycarboxylic acids used in the present invention, those that are the reaction product of adipic acid, a polybasic acid, and trimethylolpropane, a polyol having three or more hydroxyl groups, are more preferred.

These polyhydric alcohols can be used alone or in combination of two or more. Diols are preferred.
The polyester polycarboxylic acid can be obtained by blending a polybasic acid and a polyhydric alcohol in a ratio such that the acid groups of the polybasic acid (carboxyl groups, carboxylic acid esters, acid anhydride groups, acid halides) are in excess of the hydroxyl groups of the polyhydric alcohol (COOH/OH ratio exceeding 1.0, preferably 1.01 to 2.10), and then subjecting them to an esterification reaction.

The esterification reaction may be, for example, a condensation reaction or a transesterification reaction, and may be carried out under known conditions, such as atmospheric pressure, an inert gas atmosphere, a reaction temperature of 100 to 250°C, and a reaction time of 1 to 50 hours. If necessary, a catalyst (such as an organotin catalyst, organotitanium catalyst, amine catalyst, or alkali metal salt or alkaline earth metal salt described below) or a solvent may be used.

The polyester polycarboxylic acid obtained in this manner has a number average molecular weight of 200 to 20,000, preferably 500 to 10,000. It also has an acid value of 1 to 150 mgKOH/g, more preferably 5 to 100 mgKOH/g, and even more preferably 10 to 50 mgKOH/g.

Furthermore, the mass ratio of the color pigment to the polyester polycarboxylic acid is preferably in the range of 1:20 to 1:2, and more preferably 1:10 to 1:5.

(Coloring pigments)
Color pigments used in the low-temperature bakeable resist ink of the present invention include inorganic pigments and organic pigments used in general inks, paints, recording agents, etc. Examples of organic pigments include soluble azo pigments, insoluble azo pigments, azo pigments, phthalocyanine pigments, halogenated phthalocyanine pigments, anthraquinone pigments, anthanthrone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, perylene pigments, perinone pigments, quinacridone pigments, thioindigo pigments, dioxazine pigments, isoindolinone pigments, quinophthalone pigments, azomethine azo pigments, flavanthrone pigments, diketopyrrolopyrrole pigments, isoindoline pigments, indanthrone pigments, and carbon black pigments. Other examples include carmine 6B, lake red C, permanent red 2B, disazo yellow, pyrazolone orange, carmine FB, cromophtal yellow, cromophtal red, phthalocyanine blue, phthalocyanine green, dioxazine violet, quinacridone magenta, quinacridone red, indanthrone blue, pyrimidine yellow, thioindigo bordeaux, thioindigo magenta, perylene red, perinone orange, isoindolinone yellow, aniline black, diketopyrrolopyrrole red, and daylight fluorescent pigments. Both non-acid-treated and acid-treated pigments can be used. Specific examples of preferred organic pigments are listed below.

Examples of black pigments include C.I. Pigment Black 1, C.I. Pigment Black 6, C.I. Pigment Black 7, C.I. Pigment Black 9, and C.I. Pigment Black 20.

Examples of indigo pigments include C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 15:5, C.I. Pigment Blue 15:6, C.I. Pigment Blue 16, C.I. Pigment Blue 17:1, C.I. Pigment Blue 22, C.I. Pigment Blue 24:1, C.I. Pigment Blue 25, C.I. Pigment Blue 26, C.I. Pigment Blue 60, C.I. Pigment Blue 61, C.I. Pigment Blue 62, C.I. Examples of pigments include C.I. Pigment Blue 63, C.I. Pigment Blue 64, C.I. Pigment Blue 75, C.I. Pigment Blue 79, and C.I. Pigment Blue 80.

Examples of green pigments include C.I. Pigment Green 1, C.I. Pigment Green 4, C.I. Pigment Green 7, C.I. Pigment Green 8, C.I. Pigment Green 10, and C.I. Pigment Green 36.

Examples of red pigments include C.I. Pigment Red 1, C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 4, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Red 8, C.I. Pigment Red 9, C.I. Pigment Red 10, C.I. Pigment Red 11, C.I. Pigment Red 12, C.I. Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 17, C.I. Pigment Red 18, C.I. Pigment Red 19, C.I. Pigment Red 20, C.I. Pigment Red 21, C.I. Pigment Red 22, C.I. Pigment Red 23, C.I. Pigment Red 31, C.I. Pigment Red 32, C.I. Pigment Red 38, C.I. Pigment Red 41, C.I. Pigment Red 43, C.I. Pigment Red 46, C.I. Pigment Red 48, C.I. Pigment Red 48:1, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red 48:4, C.I. Pigment Red 48:5, C.I. Pigment Red 48:6, C.I. Pigment Red 49, C.I. Pigment Red 49:1, C.I. C.I. Pigment Red 49:2, C.I. Pigment Red 49:3, C.I. Pigment Red 52, C.I. Pigment Red 52:1, C.I. Pigment Red 52:2, C.I. Pigment Red 53, C.I. Pigment Red 53:1, C.I. Pigment Red 53:2, C.I. Pigment Red 53:3, C.I. Pigment Red 54, C.I. Pigment Red 57, C.I. Pigment Red 57:1, C.I. Pigment Red 58, C.I. Pigment Red 58:1, C.I. Pigment Red 58:2, C.I. Pigment Red 58:3, C.I. Pigment Red 58:4, C. C.I. Pigment Red 60:1, C.I. Pigment Red 63, C.I. Pigment Red 63:1, C.I. Pigment Red 63:2, C.I. Pigment Red 63:3, C.I. Pigment Red 64:1, C.I. Pigment Red 68, C.I. Pigment Red 68, C.I. Pigment Red 81:1, C.I. Pigment Red 83, C.I. Pigment Red 88, C.I. Pigment Red 89, C.I. Pigment Red 95, C.I. Pigment Red 112, C.I. Pigment Red 114, C.I. Pigment Red 119, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 136, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 147, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I. Pigment Red 164, C.I. Pigment Red 166, C.I. Pigment Red 168, C.I. Pigment Red 169, C.I. Pigment Red 170, C.I. Pigment Red 171, C.I. Pigment Red 172, C.I. Pigment Red 175, C.I. Pigment Red 176, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 179, C.I. Pigment Red 180, C.I. Pigment Red 181, C.I. Pigment Red 182, C.I. Pigment Red 183, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 187, C.I. Pigment Red 188, C.I. Pigment Red 190, C.I. Pigment Red 192, C.I. Pigment Red 193, C.I. Pigment Red 194, C.I. Pigment Red 200, C.I. Pigment Red 202, C.I. Pigment Red 206, C.I. Pigment Red 207, C.I. Pigment Red 208, C.I. Pigment Red 209, C.I. Pigment Red 210, C.I. Pigment Red 211, C.I. Pigment Red 213, C.I. Pigment Red 214, C.I. Pigment Red 216, C.I. Pigment Red 215, C.I. Pigment Red 216, C.I. Pigment Red 220, C.I. Pigment Red 221, C.I. Pigment Red 223, C.I. Pigment Red 224, C.I. Pigment Red 226, C.I. Pigment Red 237, C.I. Pigment Red 238, C.I. Pigment Red 239, C.I. Pigment Red 240, C.I. Pigment Red 242, C.I. Pigment Red 245, C.I. Pigment Red 247, C.I. Pigment Red 248, C.I. Pigment Red 251, C.I. Pigment Red 253, C.I. Pigment Red 254, C.I. Pigment Red 255, C.I. Pigment Red 256, C.I. Pigment Red 257, C.I. Pigment Red 258, C.I. Pigment Red 260, C.I. Pigment Red 262, C.I. Pigment Red 263, C.I. Pigment Red 264, C.I. Examples of pigments include C.I. Pigment Red 266, C.I. Pigment Red 268, C.I. Pigment Red 269, C.I. Pigment Red 270, C.I. Pigment Red 271, C.I. Pigment Red 272, and C.I. Pigment Red 279.

Examples of purple pigments include C.I. Pigment Violet 1, C.I. Pigment Violet 2, C.I. Pigment Violet 3, C.I. Pigment Violet 3:1, C.I. Pigment Violet 3:3, C.I. Pigment Violet 5:1, C.I. Pigment Violet 13, C.I. Pigment Violet 19 (γ-type, β-type), C.I. Pigment Violet 23, C.I. Pigment Violet 25, C.I. Pigment Violet 27, C.I. Pigment Violet 29, C.I. Pigment Violet 31, C.I. Pigment Violet 32, C.I. Pigment Violet 36, C.I. Pigment Violet 37, C.I. Examples include C.I. Pigment Violet 38, C.I. Pigment Violet 42, and C.I. Pigment Violet 50.

Examples of yellow pigments include C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, Pigment Yellow 17, C.I. Pigment Yellow 24, C.I. Pigment Yellow 42, C.I. Pigment Yellow 55, C.I. Pigment Yellow 62, C.I. Pigment Yellow 65, C.I. Pigment Yellow 74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 86, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 117, C.I. Pigment Yellow 120, Pigment Yellow 125, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 137, C.I. Pigment Yellow 138, C.I. Pigment Yellow 139, C.I. Pigment Yellow 147, C.I. Pigment Yellow 148, C.I. Pigment Yellow 150, C.I. Pigment Yellow 151, C.I. Pigment Yellow 153, C.I. Pigment Yellow 154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 166, C.I. Pigment Yellow 168, C.I. Examples of suitable pigments include C.I. Pigment Yellow 174, C.I. Pigment Yellow 180, C.I. Pigment Yellow 185, and C.I. Pigment Yellow 213.

Examples of orange pigments include C.I. Pigment Orange 5, C.I. Pigment Orange 13, C.I. Pigment Orange 16, C.I. Pigment Orange 34, C.I. Pigment Orange 36, C.I. Pigment Orange 37, C.I. Pigment Orange 38, C.I. Pigment Orange 43, C.I. Pigment Orange 51, C.I. Pigment Orange 55, C.I. Pigment Orange 59, C.I. Pigment Orange 61, C.I. Pigment Orange 64, C.I. Pigment Orange 71, and C.I. Pigment Orange 74.

Examples of brown pigments include C.I. Pigment Brown 23, C.I. Pigment Brown 25, and C.I. Pigment Brown 26.

Among these, preferred pigments include C.I. Pigment Black 7 as a black pigment,
Indigo pigments include C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 15:6,
C.I. Pigment Green 7 as a green pigment,
Red pigments include C.I. Pigment Red 57:1, C.I. Pigment Red 48:1, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red 146, C.I. Pigment Red 242, C.I. Pigment Red 185, C.I. Pigment Red 122, C.I. Pigment Red 178, C.I. Pigment Red 149, C.I. Pigment Red 144, C.I. Pigment Red 166,
As purple pigments, C.I. Pigment Violet 23, C.I. Pigment Violet 37,
Yellow pigments include C.I. Pigment Yellow 83, C.I. Pigment Yellow 14, C.I. Pigment Yellow 180, C.I. Pigment Yellow 139,
Orange pigments include C.I. Pigment Orange 38, C.I. Pigment Orange 13, C.I. Pigment Orange 34, and C.I. Pigment Orange 64.
It is preferable to use at least one or two or more selected from this group.

Inorganic pigments include white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, lithopone, antimony white, and gypsum. Among inorganic pigments, titanium oxide is particularly preferred. Titanium oxide exhibits a white color and is preferred in terms of coloring power, hiding power, chemical resistance, and weather resistance. In particular, titanium oxide that has been treated with silica and/or alumina is preferred because it provides good dispersibility.

In the titanium oxide surface-treated with silica and alumina, known rutile and anatase titanium dioxides can be used as the titanium oxide, and rutile titanium dioxide is more preferred.
The average particle size of the titanium oxide is preferably 100 to 500 nm, and more preferably 150 to 400 nm. If the average particle size is 100 nm or less, dispersion stability is more easily achieved, but the whiteness decreases, making color control difficult for color IC chips. On the other hand, if the average particle size is 500 nm or more, the smoothness and apparent gloss of the ink coating tend to decrease. For practical purposes, a particle size of 200 to 300 nm is even more preferable.
The average particle size of titanium oxide as the raw material was determined by measuring the particle size of 20 particles using an electron microscope photograph and averaging the measured particle size.

In titanium oxide surface-treated with silica and alumina, silica is generally used to adjust the acid-base state of the titanium oxide surface and to impart durability to the resulting ink or paint film, while alumina is used to improve the wetting of titanium oxide during dispersion. Surface treatment methods for titanium oxide include aqueous treatment and gas-phase treatment. From the perspective of dispersion stability, the ratio of the amount of silica to alumina treated is preferably 35% by mass or more and 80% by mass or less. The amount of the inorganic substance relative to titanium oxide is not necessarily limited, but is generally 30 parts or less per 100 parts of titanium oxide.

Titanium oxide surface-treated with silica and alumina may be commercially available, and is sold by titanium oxide manufacturers such as Ishihara Sangyo Kaisha, Ltd. and Teika Corporation. For example, varieties with a higher silica treatment amount than the alumina treatment amount, and varieties with a higher alumina treatment amount than the silica treatment amount, are commercially available, and titanium oxide with an alumina treatment amount within the above ratio range can also be obtained.

Non-white inorganic pigments include, for example, aluminum particles, mica, bronze powder, chrome vermilion, yellow lead, cadmium yellow, cadmium red, ultramarine, Prussian blue, red iron oxide, yellow iron oxide, iron black, and zircon. Aluminum is available in powder or paste form, but it is preferable to use it in paste form for ease of handling and safety reasons. Whether leafing or non-leafing aluminum is used can be selected appropriately based on brightness and density.

The color pigment used in the low-temperature bakeable resist ink of the present invention, whether the pigment is organic or inorganic, preferably accounts for 5% by mass or more of the total resist ink in order to maintain sufficient etching resistance when the resist film is formed, and 30% by mass or less in order to achieve appropriate ink viscosity and work efficiency during ink production and printing, and preferably accounts for 3 to 15% by mass of the total solids content of the resist ink.

There are no particular restrictions on the solvents that can be used in the low-temperature bakeable resist ink of the present invention, but examples include various organic solvents such as aromatic hydrocarbons such as toluene, xylene, Solvesso #100, Solvesso #150, etc., aliphatic hydrocarbons such as hexane, heptane, octane, decane, etc., and esters such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, ethyl formate, and butyl propionate. Examples of water-miscible organic solvents include alcohols such as methanol, ethanol, isopropyl alcohol, and n-butanol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; and glycol ethers such as ethylene glycol (mono- and di-)methyl ether, ethylene glycol (mono- and di-)ethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol (mono- and di-)methyl ether, diethylene glycol (mono- and di-)ethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol (mono- and di-)methyl ether, propylene glycol (mono- and di-)methyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol (mono- and di-)methyl ether. Among these, a mixture of toluene, isopropyl alcohol, and methyl ethyl ketone is more preferred from the viewpoint of solubility in polyester resins.

The present invention may also contain extender pigments, pigment dispersants, leveling agents, defoamers, waxes, plasticizers, infrared absorbers, ultraviolet absorbers, fragrances, flame retardants, etc., as needed.

The particle size distribution of the color pigment can be adjusted by appropriately adjusting the size of the grinding media in the disperser, the filling rate of the grinding media, the dispersion processing time, the discharge speed of the pigment dispersion, the viscosity of the pigment dispersion, etc. Commonly used dispersers, such as roller mills, ball mills, pebble mills, attritors, and sand mills, can be used. If the ink contains air bubbles or unexpectedly large particles, these can degrade the quality of the printed product, so it is preferable to remove them by filtration or other means. Conventional filters can be used.

The metal foil to be printed with the low-temperature bakeable resist ink of the present invention can be either pre-laminated to a plastic film such as a polyester resin film, or laminated to various resin films after printing, etching, and circuit formation. In either case, the adhesive surface for the resist ink is the metal foil. The thickness of the metal foil and the thickness of the laminated plastic film vary from a few microns to several tens of microns depending on the application.

The present invention will be explained in more detail with reference to the following examples. Hereinafter, "parts" and "%" are all based on mass.
In the present invention, the weight average molecular weight (polystyrene equivalent) Mw was measured by GPC (gel permeation chromatography) using an HLC8220 system manufactured by Tosoh Corporation under the following conditions.
Separation columns: Four TSKgel GMHHR-N columns manufactured by Tosoh Corporation were used. Column temperature: 40°C. Mobile phase: tetrahydrofuran manufactured by Wako Pure Chemical Industries, Ltd. Flow rate: 1.0 ml/min. Sample concentration: 1.0 wt%. Sample injection volume: 100 microliters. Detector: differential refractometer.
The glass transition temperature (Tg) was measured using a differential scanning calorimeter ("DSC Q100" manufactured by TA Instruments Co., Ltd.) by scanning in a nitrogen atmosphere using a cooling device in a temperature range of -80 to 450°C with a temperature increase rate of 10°C/min.
The acid values of the acrylic resin and polyester polycarboxylic acid represent the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of the solid content, and were calculated by potentiometric titration using a potassium hydroxide-ethanol solution in accordance with JIS K2501.

[Example 1]
A white resist ink was prepared by mixing and stirring a total of 100 parts of a commercially available acrylic resin (A) having a weight average molecular weight of 36,000, a glass transition temperature of 80°C, and an acid value of 102 mgKOH/g, 60 parts of rutile-type titanium dioxide prepared by a sulfuric acid process (average particle size 0.27 μm, oil absorption 23), 0.4 parts of polyester polycarboxylic acid, 11 parts of toluene, 12.5 parts of methyl ethyl ketone, 9 parts of isopropyl alcohol, and 0.1 part of a fluorine-modified silicone antifoaming agent.
The above-mentioned toluene/methyl ethyl ketone/isopropyl alcohol (a mixed liquid with a mass ratio of 50/30/20) was further added to the obtained resist ink, and the viscosity was adjusted to 18 seconds (25°C) using a Zahn cup # ^{3 (manufactured by Rigo Co., Ltd.). Two solid prints were then made on a metal foil (size: 20 cm length x 10 cm width) using a gravure proofing machine equipped with a heliodirect engraving gravure intaglio plate (225 lines/inch) so that the coating amount was 2.7 g/m2} .

[Examples 2 to 20]
Resist inks were prepared for Examples 2 to 20 and Comparative Examples 1 to 9 using the compositions shown in Tables 1 to 6, and the viscosities were adjusted in the same manner as in Example 1. Then, solid printing was carried out on metal foil in the same manner.
In Examples 6 to 10, 60 parts of a commercially available acrylic resin (B) having a weight average molecular weight of 12,500, a glass transition temperature of 73°C, and an acid value of 213 mgKOH/g was added in place of the acrylic resin (A).
In Examples 11 to 15, 60 parts of a commercially available acrylic resin (C) having a weight average molecular weight of 8,500, a glass transition temperature of 65°C, and an acid value of 105 mgKOH/g was added in place of the acrylic resin (A).
In Examples 16 to 20, 7 parts of a blue pigment (phthalocyanine pigment blue 15:4) was added instead of titanium oxide to prepare blue resist inks.

[Comparative Examples 1 to 9]
In Comparative Example 1, no polyester polycarboxylic acid was added.
In Comparative Examples 2 to 5, 60 parts of a commercially available acrylic resin (D) having a weight average molecular weight of 8,100, a glass transition temperature of 50° C., and an acid value of 53 mgKOH/g was added in place of the acrylic resin (A).
In Comparative Examples 6 to 9, 60 parts of a commercially available acrylic resin (D) having a weight average molecular weight of 1,700, a glass transition temperature of 56°C, and an acid value of 238 mgKOH/g was added in place of the acrylic resin (A).

1) Adhesion Metal foils on which resist ink was solid printed were oven-heated at 90°C and 120°C for 6 minutes (using an environmental tester, HSPEC HT310, manufactured by Kusumoto Chemicals), left at room temperature (25°C) for 2 hours, and then baked at 90°C and 120°C. Cellophane tape (manufactured by Nichiban) was applied to the printed surface, and the tape was quickly peeled off, and the appearance of the resist printing film was visually evaluated. The evaluation criteria were as follows:
⊚: The resist film was not peeled off at all.
◯: 70% to 90% of the resist film remained on the metal foil.
Δ: 50% or more but less than 70% of the resist film remained on the metal foil.
x: 50% or less of the resist film remained on the metal foil.

2) Scratch Resistance Metal foils on which resist ink was solid printed were oven heated at 90°C and 120°C for 6 minutes (using an environmental tester, HSPEC HT310, manufactured by Kusumoto Chemicals), left at room temperature (25°C) for 2 hours, and then baked at 90°C and 120°C. After rubbing the foil with a fingernail 10 times, the appearance of the resist printing film was visually evaluated. The evaluation criteria were as follows:
⊚: The resist film was not peeled off at all.
◯: 70% to 90% of the resist film remained on the metal foil.
Δ: 50% or more but less than 70% of the resist film remained on the metal foil.
x: 50% or less of the resist film remained on the metal foil.

3) Acid Etching Resistance A 9% hydrochloric acid solution was stored in an acid-resistant tray at a liquid temperature of 25°C, and the resist ink was solid printed therein. The metal foils that had been baked at 90°C and 120°C were then immersed in the solution for 1 hour, then removed and washed with water, and the appearance of the resist printing film was visually evaluated according to the following four-level evaluation criteria.
⊚: The resist film was not peeled off at all.
◯: 70% to 90% of the resist film remained on the metal foil.
Δ: 50% or more but less than 70% of the resist film remained on the metal foil.
x: 50% or less of the resist film remained on the metal foil.

4) Alkali solubility A 1% sodium hydroxide solution was prepared at 25°C, and the resist ink was solid printed in it. The metal foils that had been baked at 90°C and 120°C were then immersed in the solution for 5 minutes, and then removed and washed with water. The peeling state of the resist printing film was visually evaluated according to the following four-level evaluation criteria.
⊚: The resist film was completely peeled off.
◯: 70% to 90% of the resist film was peeled off.
Δ: 50% to 70% of the resist film was peeled off.
x: 50% or less of the resist film was peeled off.

The evaluation results are shown in Tables 1 to 6.

The resist ink shown in the examples exhibits excellent adhesion to the metal foil that forms the circuit, scratch resistance, acid etching resistance, and alkali solubility, even at low oven temperatures of 90 to 120°C.

Claims (5)

A resist ink containing an acrylic resin, a color pigment, and a polyester polycarboxylic acid, wherein the acrylic resin has a weight average molecular weight of 1,500 to 50,000, a glass transition temperature of 60 to 90°C, and an acid value of 70 to 250 mgKOH/g, and the color pigment accounts for 3 to 15% by mass of the total solid content of the ink;
The resist ink for low-temperature baking is characterized in that the polyester polycarboxylic acid is a reaction product of adipic acid and trimethylolpropane, which is a polyol having three or more hydroxyl groups. The low-temperature bakeable resist ink according to claim 1, wherein the mass ratio of the color pigment to the polyester polycarboxylic acid is in the range of 1:20 to 1:2. The low-temperature bakeable resist ink according to claim 1 or 2, wherein the acid value of the polyester polycarboxylic acid is in the range of 1 to 150 mg KOH/g. The low-temperature bakeable resist ink according to any one of claims 1 to 3, wherein the color pigment is titanium oxide. A method for producing a resist printed product, comprising the steps of: printing a resist ink on a metal foil; heating and curing the resist ink film formed by printing at 80°C or higher; etching the cured resist ink film from above with an acidic etching solution; and peeling off the resist ink film with an alkaline solution, in this order;
A method for producing a resist print, characterized in that the resist ink is a low-temperature bakeable resist ink according to any one of claims 1 to 4, and the amount of ink printed on the metal foil is 0.5 to 3 g/ ^m2 .