Copper film-forming ink, inkjet ink, printed matter, and copper circuit formation method

Abstract

The purpose of this invention is to provide a copper film-forming ink according to which high printability and high printing stability can be achieved. Specifically, disclosed is a copper film-forming ink, which contains a copper complex composed of copper formate and a five-membered or six-membered nitrogen-containing heterocyclic compound having one alkyl substituent composed of 2-5 carbon atoms or two or more alkyl substituents composed of 1-5 carbon atoms and having 1-3 nitrogen atoms, and a monovalent alcohol having 2-6 carbon atoms and optionally having an ether bond.

Description

Copper film-forming ink, inkjet ink, printed matter, and copper circuit forming method

[0001] The present invention relates to a copper film-forming ink, an inkjet ink, a printed matter, and a copper circuit forming method.

[0002] Copper has the second highest conductivity among all metals and is inexpensive, so it is widely used as a wiring material. As a method for forming wiring, a method of forming a copper layer on a substrate and removing unnecessary portions by etching (subtractive process) is generally used.

[0003] In the subtractive process, for example, after forming a copper layer on the substrate surface by plating, vapor deposition, or attaching a copper foil, an etching resist is applied, and after dissolving the unnecessary copper, the etching resist is peeled off to form wiring. Therefore, the subtractive process has problems such as a large number of process steps, the need to treat etching waste liquid, high costs, and a large environmental load.

[0004] On the other hand, an additive process (semi-additive process or full-additive process) for forming a circuit by applying copper plating to necessary portions is also known. In the additive process, cost reduction and reduction of environmental load can be achieved by shortening the manufacturing process and reducing waste liquid when manufacturing a wiring board for forming a circuit. In the additive process, it is necessary to provide a seed layer on the substrate surface or perform surface treatment such as catalyzation in order to apply copper plating.

[0005] Patent Document 1 describes, as examples, a copper film-forming material composed of a copper complex composed of a 5- or 6-membered nitrogen-containing heterocyclic compound having 1 to 3 nitrogen atoms and copper formate, and a copper film-forming material containing the copper complex and diethylene glycol as a solvent.

[0006] Patent Document 2 describes, as examples, a copper film-forming material containing a copper complex composed of a 5- or 6-membered nitrogen-containing heterocyclic compound having 1 to 3 nitrogen atoms and copper formate and ethylene glycol or terpineol as a solvent.

[0007] In the additive process, from the perspective of further reducing environmental impact and costs, when providing a seed layer or performing surface treatment such as catalysis, it is required to apply an inkjet method that can depict fine circuit patterns with almost no loss of material (ink) and without requiring plate manufacturing. Further, as the target substrate, it is required to use inexpensive materials such as PET film or paper (cellulose).

[0008] International Publication No. 2014 / 010328, Japanese Patent Application Laid-Open No. 2015-129318

[0009] The inventors of the present invention have found that when using the conventional copper film-forming material as described above as an ink for forming a copper film, there is room for improvement in the printability of the ink for forming a copper film on a substrate and the stability of printing.

[0010] One aspect of the present invention aims to realize an ink for forming a copper film with high printability and printing stability.

[0011] In order to solve the above problems, an ink for forming a copper film according to one aspect of the present invention comprises a copper complex composed of a 5- or 6-membered nitrogen-containing heterocyclic compound having one alkyl substituent consisting of 2 to 5 carbon atoms or two or more alkyl substituents consisting of 1 to 5 carbon atoms and having 1 to 3 nitrogen atoms, and copper formate, and contains a monohydric alcohol having 2 to 6 carbon atoms which may have an ether bond.

[0012] According to one aspect of the present invention, an ink for forming a copper film with high printability and printing stability can be realized.

[0013] One embodiment of the present invention will be described below. However, the present invention is not limited to the respective configurations described below. The present invention can be variously modified within the scope shown in the claims. The technical scope of the present invention also extends to embodiments or examples obtained by appropriately combining a plurality of technical means disclosed in this specification. At this time, the plurality of technical means may be disclosed over a plurality of embodiments or examples.

[0014] Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B".

[0015] [1. Ink for Copper Film Forming] An ink for copper film forming according to one aspect of the present invention contains a copper complex and an alcohol. The copper complex consists of a five-membered or six-membered nitrogen-containing heterocyclic compound having one alkyl substituent consisting of two to five carbon atoms, or two or more alkyl substituents consisting of one to five carbon atoms, and having one to three nitrogen atoms, and copper formate. The alcohol is a monohydric alcohol having two to six carbon atoms, which may have an ether bond.

[0016] In this specification, the copper film-forming ink according to one aspect of the present invention may be referred to as "the ink," the above-mentioned copper complex as "the copper complex," the above-mentioned nitrogen-containing heterocyclic compound as "the nitrogen-containing heterocyclic compound," and the above-mentioned alcohol as "the alcohol."

[0017] [1-1. Copper Complex] This ink contains this copper complex capable of forming a copper film. The copper film constitutes, for example, a copper circuit pattern formed by this ink. A "copper circuit pattern" may be a pattern in which copper films are continuously formed and which functions electrically as a copper circuit, but the concept also includes copper films formed on a substrate as part of a copper circuit. As described above, this copper complex consists of this nitrogen-containing heterocyclic compound and copper formate.

[0018] This nitrogen-containing heterocyclic compound has one alkyl substituent consisting of 2 to 5 carbon atoms, or two or more alkyl substituents consisting of 1 to 5 carbon atoms, and has a 5-membered or 6-membered heterocyclic skeleton having 1 to 3 nitrogen atoms. This nitrogen-containing heterocyclic compound may have one or two ring structures, and elements other than carbon atoms in this nitrogen-containing heterocyclic compound may not be bonded to hydrogen atoms. Such a nitrogen-containing heterocyclic compound can coordinate to a copper ion by a lone pair of electrons on the nitrogen.

[0019] It has long been known that when copper formate is heated under a nitrogen atmosphere, a reduction reaction of copper ions by formate ions occurs, resulting in the deposition of copper. It is also well known that coordinating amines to copper formate lowers the temperature of the reduction reaction. Since reduction reactions generally proceed more readily at higher pH levels, it can be inferred that the basicity of amines contributes to the lowering of the temperature of the reduction reaction.

[0020] However, when primary or secondary amines are used, these amines bind to the precipitated copper, allowing the reduction reaction to proceed at relatively low temperatures, but residues tend to remain, making it difficult to obtain good conductivity. Furthermore, while the residue problem is solved when tertiary amines are used, the steric hindrance caused by substituents is significant, preventing stable coordination to copper and thus failing to achieve sufficient low-temperature reduction. Attempts have also been made to introduce highly polar substituents such as hydroxyl groups into tertiary amines to achieve stable coordination to copper through chelating. However, these attempts have problems such as reduced volatility requiring high-temperature heating, or the reduction reaction proceeding even at room temperature due to the strong basicity of the tertiary amine. Attempts have also been made to lower the temperature of the reduction reaction by using certain metal catalysts, but sufficient effects have not been achieved.

[0021] When this nitrogen-containing heterocyclic compound is used, it has moderate basicity and low steric hindrance, allowing for stable coordination to copper and the formation of a relatively stable copper formate complex at room temperature. After copper deposition, this nitrogen-containing heterocyclic compound volatilizes relatively quickly without bonding to copper, resulting in the deposition of copper with little residue and excellent conductivity. In particular, by introducing one alkyl substituent consisting of 2 to 5 carbon atoms, or two or more alkyl substituents consisting of 1 to 5 carbon atoms, moderate volatility is imparted, allowing the copper deposition process to proceed in a fluid state, resulting in a highly uniform copper film. Furthermore, moderate polarity is imparted, allowing the affinity to hydrophilic surfaces to be maintained even in a fluid state, resulting in good adhesion to hydrophilic substrate surfaces.

[0022] This nitrogen-containing heterocyclic compound has one alkyl substituent consisting of 2 to 5 carbon atoms, or two or more alkyl substituents consisting of 1 to 5 carbon atoms. If this nitrogen-containing heterocyclic compound has only one alkyl substituent (methyl group) consisting of 1 carbon atom as the alkyl substituent, the mixture of copper formate and the nitrogen-containing heterocyclic compound separates from this alcohol, making it difficult to prepare the copper film-forming ink. If this nitrogen-containing heterocyclic compound has one alkyl substituent consisting of 2 to 5 carbon atoms, or two or more alkyl substituents consisting of 1 to 5 carbon atoms, the separation of the mixture of copper formate and the nitrogen-containing heterocyclic compound from this alcohol can be reduced. Furthermore, if the number of carbon atoms in the alkyl substituent exceeds 5, the copper film-forming ink becomes less volatile when heated by firing or other means, making it difficult to complete heating in the applicable low-temperature range even when the substrate is a resin.

[0023] Examples of alkyl substituents consisting of 2 to 5 carbon atoms include ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, and neopentyl group. When the nitrogen-containing heterocyclic compound has two or more of these alkyl substituents, they may be the same alkyl substituent or they may be different alkyl substituents.

[0024] The nitrogen-containing heterocyclic compound preferably has one or more alkyl substituents consisting of 2 to 5 carbon atoms. Furthermore, the nitrogen-containing heterocyclic compound may further contain substituents other than alkyl substituents consisting of 1 to 5 carbon atoms. Such substituents may be, for example, at least one selected from the group consisting of alkenyl groups, alkynyl groups, alkoxyl groups, and alkoxyalkyl groups.

[0025] Examples of nitrogen-containing heterocyclic compounds include imidazole compounds, triazole compounds, pyridine compounds, and pyrazole compounds.

[0026] (Imidazole Compound) As this nitrogen-containing heterocyclic compound, an imidazole compound represented by the following formula (I) can be mentioned.

[0027]

[0028] (In formula (I), R １ represents a linear, branched or cyclic hydrocarbon group having 1 to 5 carbon atoms, or a linear, branched or cyclic substituent comprising a hydrocarbon having 1 to 5 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or combines with adjacent R ２ or R ４ to form a heterocycle. R ２ to R ４ each independently represents a hydrogen atom, a linear, branched or cyclic hydrocarbon group having 1 to 4 carbon atoms, or a linear, branched or cyclic substituent comprising a hydrocarbon having 1 to 4 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or combines with adjacent R １ , R ３ or R ４ to form a ring or a heterocycle. However, at least one of R １ to R ４ is an alkyl substituent having 2 to 5 carbon atoms that does not form a heterocycle, or two or more of R １ to R ４ are methyl groups.)

[0029] Examples of R １ include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a vinyl group, etc. From the viewpoints of volatility and polarity, it is preferable that at least one of R １ to R ４ is an alkyl substituent having 2 to 5 carbon atoms that does not form a heterocycle, and among them, it is more preferable that R １ is an alkyl substituent having 2 to 5 carbon atoms.

[0030] The imidazole compounds represented by formula (I) include, specifically, 1-ethylimidazole, 1-propylimidazole, 1-isopropylimidazole, 1-butylimidazole, 1-isobutylimidazole, 1-sec-butylimidazole, 1-tert-butylimidazole, 1-pentylimidazole, 1-isopentylimidazole, 1-(2-methylbutyl)imidazole, 1-(1-methylbutyl)imidazole, 1-(1-ethylpropyl)imidazole, 1-tert-pentylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole, 1,2,4-trimethylimidazole, 1,4,5-trimethylimidazole, 1,2,4,5-tetramethylimidazole, 1-ethyl-2-methylimidazole, Examples include 2-ethyl-1-methylimidazole, 2-methyl-1-propylimidazole, 2-methyl-1-isopropylimidazole, 1-butyl-2-methylimidazole, 1-isobutyl-2-methylimidazole, 1-sec-butyl-2-methylimidazole, and 1-tert-butyl-2-methylimidazole.

[0031] The nitrogen-containing heterocyclic compound is preferably one or more selected from the group consisting of 1-ethylimidazole, 1,2-dimethylimidazole, 1-propylimidazole, 1-butylimidazole, and 1-pentylimidazole.

[0032] In one embodiment of the present invention, in addition to using one appropriate imidazole compound represented by formula (I), it is also possible to use a combination of different imidazole compounds.

[0033] (Triazole compounds) Examples of nitrogen-containing heterocyclic compounds include triazole compounds represented by the following formula (IIa) or formula (IIb).

[0034]

[0035] (In equations (IIa) and (IIb), R ５ and R ８Each of these independently represents a linear, branched, or cyclic hydrocarbon group having 1 to 5 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 5 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or adjacent R ７ or R １０ It combines with R to form a heterocycle. ６ and R ７ Each of these independently represents a hydrogen atom, a linear, branched, or cyclic hydrocarbon group having 1 to 4 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 4 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or R ５ , R ６ or R ７ It combines with to form a ring or a heteroring. ９ R represents a hydrogen atom, a linear, branched, or cyclic hydrocarbon group having 1 to 4 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 4 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom. １０ R represents a hydrogen atom, a linear, branched, or cyclic hydrocarbon group having 1 to 4 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 4 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or adjacent R ８ It combines with R to form a heterocycle. ５ ~R ７ At least one of them is a C2-C5 alkyl substituent that does not form a ring or heterocycle, or R ５ ~R ７ Two or more of them are methyl groups. Also, R ８ ~R １０ At least one of them is a C2-C5 alkyl substituent that does not form a ring or heterocycle, or R ８ ~R １０ (Two or more of them are methyl groups.)

[0036] R ５ and R ８ Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, and vinyl group. From the viewpoint of volatility and polarity, R ５~R ７ and R ８ ~R １０ Preferably, at least one of each of these is a C2-C5 alkyl substituent that does not form a ring or heterocycle, and among them R ５ and R ８ It is more preferable that the substituent has 2 to 5 carbon atoms.

[0037] Specific examples of triazole compounds represented by formula (IIa) or formula (IIb) include 1-ethyl-1,2,4-triazole, 1-propyl-1,2,4-triazole, 1-isopropyl-1,2,4-triazole, 1-butyl-1,2,4-triazole, 1-ethyl-1,2,3-triazole, 1-propyl-1,2,3-triazole, 1-isopropyl-1,2,3-triazole, and 1-butyl-1,2,3-triazole.

[0038] In one embodiment of the present invention, in addition to using one appropriate triazole compound represented by formula (IIa) or formula (IIb), it is also possible to use a combination of different triazole compounds.

[0039] (Pyridine compounds) Examples of nitrogen-containing heterocyclic compounds include pyridine compounds represented by the following formula (III).

[0040]

[0041] (In formula (III), R １１ ~R １５ Each of these independently represents a hydrogen atom, a linear, branched, or cyclic hydrocarbon group having 1 to 5 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 5 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or adjacent R １１ , R １２ , R １３ , R １４ or R １５ It combines with R to form a ring or heteroring. １１ ~R １５ At least one of them is a C2-C5 alkyl substituent that does not form a ring or heterocycle, or R１１ ~R １５ (Two or more of them are methyl groups.)

[0042] R １１ ~R １５ Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, vinyl group, methoxy group, and ethoxy group. From the viewpoint of volatility and polarity, R １１ ~R １５ At least one of them is preferably a C2-C5 alkyl substituent that does not form a ring or heterocycle, and among them R １３ It is more preferable that the substituent has 2 to 5 carbon atoms.

[0043] Specific examples of pyridine compounds represented by formula (III) include 4-ethylpyridine, 4-propylpyridine, 4-butylpyridine, and 4-pentylpyridine.

[0044] In one embodiment of the present invention, in addition to using one appropriate pyridine compound represented by formula (III), it is also possible to use a combination of different pyridine compounds.

[0045] (Pyrazole compounds) Examples of nitrogen-containing heterocyclic compounds include pyrazole compounds represented by the following formula (IV).

[0046]

[0047] (In formula (IV), R １６ This represents a linear, branched, or cyclic hydrocarbon group having 1 to 5 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 5 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or adjacent R １９ It combines with R to form a heterocycle. １７ ~R １９ Each of these independently represents a hydrogen atom, a linear, branched, or cyclic hydrocarbon group having 1 to 4 carbon atoms, or a linear, branched, or cyclic substituent comprising a hydrocarbon having 1 to 4 carbon atoms and an element other than a carbon atom not bonded to a hydrogen atom, or adjacent R １６, R １７ , R １８ or R １９ It combines with R to form a ring or heteroring. １６ ~R １９ At least one of them is a C2-C5 alkyl substituent that does not form a ring or heterocycle, or R １６ ~R １９ (Two or more of them are methyl groups.)

[0048] R １６ Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, and vinyl group. From the viewpoint of volatility and polarity, R １６ ~R １９ At least one of them is preferably a C2-C5 alkyl substituent that does not form a ring or heterocycle, and among them R １６ It is more preferable that the substituent has 2 to 5 carbon atoms.

[0049] Specific examples of pyrazole compounds represented by formula (IV) include 1-ethylpyrazole, 1-propylpyrazole, 1-isopropylpyrazole, 1-butylpyrazole, and 1-pentylpyrazole.

[0050] In one embodiment of the present invention, in addition to using one appropriate pyrazole compound represented by formula (IV), it is also possible to use a combination of different pyrazole compounds.

[0051] (Other) Examples of nitrogen-containing heterocyclic compounds include pyridazines, pyrimidines, and pyrazines having two nitrogen atoms, and triazines having three nitrogen atoms, in which one alkyl substituent consisting of two to five carbon atoms, or two or more alkyl substituents consisting of one to five carbon atoms are substituted.

[0052] This nitrogen-containing heterocyclic compound may be used as a single compound or in combination of two or more compounds.

[0053] (Copper Forate) Suitable copper forate includes anhydrous copper(II) forate, copper(II) forate dihydrate, or copper(II) forate tetrahydrate. Alternatively, one or more copper compounds such as copper(II) oxide, copper(I) oxide, basic copper(II) carbonate, copper(II) acetate, or copper(II) oxalate may be mixed with formic acid to produce copper forate in situ.

[0054] The molar ratio of copper formate to nitrogen-containing heterocyclic compounds in this ink is typically 1:1 to 1:5. From the viewpoint of the conductivity of the formed copper film, a ratio of 1:1.2 to 1:4 is preferred, 1:1.5 to 1:3 is more preferred, 1:1.6 to 1:2.5 is even more preferred, and 1:1.8 to 1:2.2 is particularly preferred.

[0055] [1-2. Monohydric Alcohols] This ink contains a monohydric alcohol with 2 to 6 carbon atoms, which may have ether bonds, as a solvent. If a dihydric or higher alcohol is used as the solvent, it becomes difficult to adjust the viscosity of this ink to a viscosity range suitable for use in inkjet printing, for example. Also, if the monohydric alcohol contains fewer than 2 carbon atoms, the volatility of this ink is too high, which may cause nozzle clogging when used in inkjet printing, resulting in problems with ink discharge. Furthermore, if the monohydric alcohol contains more than 6 carbon atoms, the copper film-forming ink becomes difficult to volatilize during firing, making it difficult to complete firing in a low-temperature range that is applicable even when the substrate is a resin.

[0056] By using a monohydric alcohol having 2 to 6 carbon atoms, which may have an ether bond, as the alcohol, it is possible to obtain an ink that has a viscosity suitable for use in inkjet printing and also has appropriate volatility.

[0057] Examples of this alcohol include ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, cyclopentanol, cyclohexanol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol.

[0058] The alcohol is preferably one or more selected from the group consisting of ethanol, 1-butanol, 1-hexanol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol.

[0059] This alcohol may be used individually or in combination of two or more types.

[0060] The alcohol used is not particularly limited as long as it can make the ink into a solution or dispersion, and one or more types may be used in combination. The amount of alcohol contained in the ink can be a general amount, and an appropriate amount should be determined considering the viscosity and applicability of the resulting ink.

[0061] This ink, by containing this alcohol as a solvent for the nitrogen-containing heterocyclic compound, obtains a viscosity suitable for use in applications such as inkjet printing. The viscosity of this ink at 25°C is preferably, for example, 4 to 14 mPa·s. With such a viscosity, this ink can be suitably used as an inkjet ink for inkjet printing.

[0062] The viscosity of this ink is obtained by measuring it at 25°C using a dynamic viscoelasticity measuring device.

[0063] The solvent of this ink may contain components other than the alcohol. These other components include components that are unintentionally mixed in, such as water contained in the form of hydrated water (crystal water), hydrolysates of alkoxy groups, and other impurities. The solvent of this ink preferably contains 90 parts by mass or more, more preferably 95 parts by mass or more, more preferably 98 parts by mass or more, and more preferably 99 parts by mass or more, of the alcohol per 100 parts by mass of the solvent.

[0064] [1-3. Other Components] In this ink, in order to increase the thickness of the copper coating, fillers such as particles or powders made of copper or other metals, resin or ceramic, may be included to the extent that they do not impair the effects of the present invention.

[0065] Furthermore, in order to shorten the time required for the formation of the copper film in this ink, an alkalizing agent or a metal catalyst may be included, to the extent that it does not impair the effects of the present invention. Examples of alkalizing agents include caustic soda, caustic potassium, ammonia, primary amines, secondary amines, and tertiary amines. Examples of metal catalysts include silver, platinum, rhodium, and palladium.

[0066] Furthermore, this ink may contain additives such as stabilizers, dispersants, viscosity modifiers, surfactants, or pH adjusters, to the extent that they do not impair the effects of the present invention.

[0067] Examples of pH adjusters include acids or their salts. For example, the pH adjuster may be one or more selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, and propionic acid, as well as hydrochloride salts, sulfates, phosphates, formates, and acetates. One of these acids and their salts may be used alone as the pH adjuster, or two or more may be used in combination. These also contribute to the stabilization of the ink.

[0068] The amount of additives in this ink can be appropriately set within a range that allows the effects of the present invention to be exhibited. The amount of additives is usually 0 to 50% by mass, preferably 0.1 to 30% by mass, and more preferably 0.5 to 20% by mass, when the total mass of this ink is 100% by mass.

[0069] [1-4. Method for manufacturing copper film-forming ink] This ink can be easily prepared by mixing the nitrogen-containing heterocyclic compound, copper formate, and this alcohol as raw materials, and grinding and kneading as necessary, without requiring any special synthesis operations.

[0070] The copper complex may be included in the ink as part of the composition, or it may be prepared separately and mixed with other components of the ink, such as the alcohol. Alternatively, the raw materials constituting the copper complex may be directly mixed with other components of the ink, such as the alcohol, to form the ink.

[0071] When preparing this copper complex separately, for example, copper formate is dissolved or dispersed in an appropriate amount of solvent, and the nitrogen-containing heterocyclic compound is added and stirred. The solvent is then removed by vacuum distillation to obtain the complex. Water, methanol, or ethanol are preferred as the solvent used in preparing this copper complex.

[0072] In this ink, the ratio of this nitrogen-containing heterocyclic compound to copper formate should be at least 1 mole of this nitrogen-containing heterocyclic compound per 1 mole of copper formate, preferably at least 2 moles.

[0073] In addition to the methods described above for mixing the nitrogen-containing heterocyclic compound with copper formate, the nitrogen-containing heterocyclic compound may also be added to a slurry in which copper formate is dispersed in the alcohol, or copper formate may be added to the alcohol in which the nitrogen-containing heterocyclic compound is dissolved.

[0074] [1-5. Applications of the Copper Film Forming Ink] This ink can be used in various methods for forming a copper film. For example, this ink is preferably used as an inkjet ink for printing with an inkjet device.

[0075] Conventionally, when attempting to print ink onto substrates such as PET film or paper using inkjet printing, problems sometimes arose with ink ejection from the inkjet nozzle due to excessively high ink viscosity or high ink volatility. Excessively high ink viscosity can cause the inkjet nozzle to clog. Similarly, excessively high ink volatility can lead to high viscosity at the nozzle opening, also causing nozzle clogging.

[0076] This ink is easily adjusted to a viscosity suitable for inkjet printing, resulting in good ejection from inkjet nozzles. Therefore, this ink can be suitably used as an inkjet ink.

[0077] Furthermore, this ink may be used in printing methods other than inkjet printing. Examples of such printing methods include screen printing, gravure printing, offset printing, and flexographic printing.

[0078] Furthermore, a printed material obtained by such a printing method, which includes a copper circuit pattern formed with the ink, is also included in one aspect of the present invention. Such a printed material is obtained by a copper circuit formation method described later.

[0079] Furthermore, this ink may be applied using methods other than printing to form a copper film. Examples of such application methods include spin coating, dip coating, spray coating, mist coating, flow coating, curtain coating, roll coating, knife coating, blade coating, air doctor coating, bar coating, and brush coating.

[0080] When forming copper circuit patterns using these coating methods, a pattern mask with the circuit pattern formed on it may be placed in contact with the substrate (substrate), and the ink may be applied from above using a spin coating method or a dip method, etc.

[0081] Examples of substrates include resin substrates, fiber substrates, glass substrates, silicon substrates, metal substrates, rubber (elastomer) substrates, and ceramic substrates.

[0082] Examples of resin types for resin substrates include thermosetting resins such as polyimide resin, epoxy resin, bismaleimide-triazine resin, and modified polyphenylene ether resin, as well as thermoplastic resins such as ABS resin, polyamide resin, polyethylene resin, polypropylene resin, polycarbonate resin, polyethylene terephthalate (PET) resin, polyvinyl chloride resin, fluororesin, and liquid crystal polymer.

[0083] Examples of fibrous base materials include pulp and plant fibers such as cellulose. Paper is preferred as the fibrous base material.

[0084] Among these substrates, if the substrate material is an inorganic oxide that has poor adhesion to the copper coating, such as a glass substrate or a ceramic substrate, it is preferable to provide a primer resin layer (hereinafter also referred to as the "resin layer") on these substrates.

[0085] From the viewpoint of enhancing the effects of the present invention, the primer resin layer is preferably a resin layer having hydrophilic residues.

[0086] The primer resin layer provided on the substrate is preferably one that has high adhesion to the substrate, especially an inorganic oxide substrate, and may be a thermoplastic resin, a thermosetting resin, or a photosensitive resin. Specifically, acrylic resins, (meth)acrylic resins, chloroprene rubber resins, polyimide resins, silicone rubber resins, nitrocellulose resins, urethane resins, melamine resins, polypropylene resins, epoxy resins, phenolic resins, polyethylene resins, polyurethane resins, polyester resins, polyvinyl chloride resins, polyvinyl alcohol resins, polyester urethane resins, polyamide resins, polyamide-imide resins, polybutyl acetate resins, polyvinyl acetal resins, polyvinyl butyral resins, polyvinyl ether resins, and polymethyl methacrylate resins. Examples include resins, polycarbonate resins, ionomer resins, polyvinyl acetate resins, urea resins, alkyd resins, silicone resins, cellulose derivatives, hydroxyl-functional acrylic resins, carboxyl-functional acrylic resins, ethylene-isobutyl acrylate copolymer resins, amide-functional copolymer resins, unsaturated polyester resins, (meth)acrylic acid ester-olefin copolymer resins, vinyl chloride-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymer resins (EVA resins), olefin-α-olefin copolymer resins, thermoplastic elastomers such as SBS, SIS, SEBS, and SEPS.

[0087] The thickness of the primer resin layer is, for example, 0.1 μm to 50 μm, preferably 1 μm to 10 μm.

[0088] This ink is suitable for forming copper circuits on circuit boards, but it may also be used to form a copper coating on any other article where a copper coating is desired. Examples of such articles include, in addition to circuit boards, resins, rubber (elastomers), glass, ceramics, films, plates, powders, particles, fibers such as cloth and nonwoven fabrics, paper, leather, models, and works of art.

[0089] Examples of resins used in articles include polyimide resin, polyethylene terephthalate (PET) resin, polyolefin resin (including polyethylene resin and polypropylene resin), polyetheretherketone (PEEK) resin, polyphenylene ether (PPE) resin, polyphenylene sulfide (PPS) resin, polyethersulfone (PES) resin, LCP resin (liquid crystal polymer), epoxy resin, polyacetal resin, polyamide resin, polycarbonate resin, and polyetherimide resin.

[0090] Furthermore, when manufacturing wiring boards with circuits formed by a semi-additive or fully additive process, the copper film of the copper circuit pattern formed with this ink can be used as a seed layer. This allows for a reduction in the manufacturing process and costs.

[0091] As described above, this ink is suitable for inkjet printing, which produces almost no material loss and can depict fine copper circuit patterns without the need for plate manufacturing. Furthermore, the copper circuit patterns formed with this ink are also suitable for additive processes, which are effective in reducing environmental impact. Thus, one aspect of the present invention contributes, for example, to achieving Sustainable Development Goal 12, "Ensure sustainable consumption and production patterns," as advocated by the United Nations.

[0092] [2. Copper Circuit Formation Method] [2-1. Printing Process] A copper circuit formation method according to one aspect of the present invention includes a step of printing the ink onto a substrate. In this specification, the copper circuit formation method according to one aspect of the present invention may be referred to as "this formation method" below.

[0093] Regarding the substrate, the examples of substrates used in the printed materials described above can be applied. Furthermore, the methods used in the manufacture of the printed materials described above can also be applied to the method of printing this ink onto the substrate. As described above, this ink is suitably usable as an inkjet ink. Therefore, in this formation method, the inkjet printing method can be suitably used as the method for printing this ink onto the substrate.

[0094] After printing the ink onto the substrate, it is preferable to subject the printed material containing the ink to a drying process, for example, at a temperature of 30 to 70°C for 1 to 10 minutes.

[0095] [2-2. Heating step] This formation method may further include a step of heating the copper film forming ink printed on the substrate.

[0096] The atmosphere during heating is preferably a non-oxidizing atmosphere, such as a reducing gas, an inert gas, or a degassed atmosphere. Examples of reducing gas atmospheres include hydrogen and formic acid, while examples of inert gas atmospheres include helium, nitrogen, argon, and carbon dioxide. Of these, from the viewpoint of safety and cost, it is preferable to perform heating under an inert gas atmosphere.

[0097] The heating method is not particularly limited, but examples include firing or light irradiation. Firing methods include applying warm air or hot air to the printed surface, and light irradiation methods include irradiating with ultraviolet light, infrared light, or visible light for a long period of time or instantaneously. Separately from these, other methods include contacting the substrate with a heated medium, exposing it to a heated gas atmosphere, and exposing it to solvent vapor.

[0098] The heating temperature should be above the temperature at which the copper complex can decompose under the treatment atmosphere. The preferred heating temperature can be set appropriately depending on the type of copper complex, the type of alcohol, or the atmosphere during heating. If the heating temperature is too high, the substrate may deteriorate if its heat resistance is low, or energy may be wasted. Therefore, a temperature of 150°C or lower is preferred, and 130°C or lower is more preferred. Furthermore, the lower limit is preferably above the temperature at which the copper complex of the present invention can decompose, and 100°C or higher is more preferred.

[0099] When forming a copper circuit by heating ink printed on a resin substrate such as PET film, heating in a low-temperature range of about 130°C, which is applicable to the resin substrate, is required. However, with conventional copper film-forming inks, the volatilization of components other than copper may not proceed sufficiently in such low-temperature ranges, which can cause problems with copper circuit formation. This ink exhibits sufficient volatility even in low-temperature ranges of about 130°C, thus demonstrating good copper circuit formation properties.

[0100] Similarly, the heating time should be set appropriately depending on the type of copper complex, the type of alcohol, or the atmosphere during heating.

[0101] Furthermore, in order to increase the thickness of the copper coating in the copper circuit pattern, the printing and heating of this ink may be repeated multiple times.

[0102] [2-3. Copper Plating Process] This formation method may further include a step of copper plating on the copper circuit pattern formed by heating. That is, when manufacturing a wiring board in which circuits are formed by a semi-additive process or a fully additive process, the copper circuit pattern formed by the printing and heating processes described above can be used as a seed layer for copper plating.

[0103] The method for copper plating is not particularly limited, but examples include wet plating, dry plating, and hot-dip plating. Among these, the wet plating method is preferred because it allows for easy application of copper plating to the formed copper circuit pattern. Copper plating by the wet plating method may be electroless copper plating or electrolytic copper plating.

[0104] Conventional known methods can be used for copper plating. For example, when performing electroless copper plating, the copper circuit pattern on the substrate may be pickled with an aqueous formic acid solution and rinsed with water, and then treated with an electroless copper plating solution. After that, it may be carried out by rinsing with water and drying.

[0105] [2-4. Surface Modification Step for Substrate] The circuit formation method may include steps other than the printing step, heating step, and copper plating step described above. For example, the formation method may further include a step of providing a primer resin layer on the substrate before the step of printing the ink onto the substrate. Such a step is effective in improving the affinity between the ink and the substrate surface when the material of the substrate is an inorganic oxide that has poor adhesion to the copper film, such as a glass substrate or a ceramic substrate. The types of primer resin layers can be the examples given in the description of the substrate used in the printed material described above.

[0106] A resin layer having hydrophilic residues can be provided mainly by the following two means: (1) a method of coating a substrate with a resin having hydrophilic residues; (2) a method of providing a resin layer on a substrate and then subjecting the resin layer to UV irradiation, plasma irradiation, corona discharge treatment, etc., to generate hydrophilic residues on the surface of the resin layer.

[0107] In the method described in (1) above, examples of resins having hydrophilic residues include resins having hydroxyl groups or carboxyl groups, specifically, phenolic resins, polyvinyl alcohol resins, cellulose resins, and polymers or copolymers of (meth)acrylic acid. Among these, phenolic resins are preferred because they have hydroxyl groups in their skeleton, are readily available, and can easily form coating films. One type of resin having hydrophilic residues may be used alone, or two or more types may be used in mixture form.

[0108] Resin compositions containing such resins can be provided either as is or by dissolving them in various solvents and applying them to a substrate.

[0109] Coating methods for providing a resin layer include spin coating, dip coating, spray coating, mist coating, flow coating, curtain coating, roll coating, knife coating, blade coating, air doctor coating, bar coating, screen printing, gravure printing, offset printing, flexographic printing, and brush coating.

[0110] After applying the resin composition to the substrate, it is cured by drying or heating to form a resin layer.

[0111] In the method described in (2) above, the resin layer may also be applied to the substrate either as is or dissolved in various solvents, similar to the method described in (1), and the coating process is the same.

[0112] Then, after providing a resin layer on the substrate, the resin layer is subjected to energy ray irradiation such as UV irradiation, plasma irradiation, or corona discharge treatment to generate hydrophilic residues on the surface of the resin layer. Such hydrophilic residue generation treatments are well known, and the irradiation conditions can be appropriately determined depending on the material of the substrate and the resin layer.

[0113] [3. Summary] The copper film-forming ink according to Embodiment 1 of the present invention contains a copper complex comprising a 5-membered or 6-membered nitrogen-containing heterocyclic compound having one alkyl substituent consisting of 2 to 5 carbon atoms, or two or more alkyl substituents consisting of 1 to 5 carbon atoms, and having 1 to 3 nitrogen atoms, and copper formate, and a monohydric alcohol having 2 to 6 carbon atoms which may have an ether bond.

[0114] In the copper film-forming ink according to embodiment 2 of the present invention, in embodiment 1, the nitrogen-containing heterocyclic compound may be one or more selected from the group consisting of 1-ethylimidazole, 1,2-dimethylimidazole, 1-propylimidazole, 1-butylimidazole, and 1-pentylimidazole.

[0115] In the copper film-forming ink according to embodiment 3 of the present invention, in embodiment 1 or 2, the monohydric alcohol may be one or more selected from the group consisting of ethanol, 1-butanol, 1-hexanol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol.

[0116] In any of the embodiments 1 to 3, the copper film forming ink according to embodiment 4 of the present invention may have a viscosity of 4 to 14 mPa·s at 25°C.

[0117] The inkjet ink according to embodiment 5 of the present invention includes any of the copper film forming inks of embodiments 1 to 4.

[0118] A printed material according to embodiment 6 of the present invention includes a copper circuit pattern formed with a copper film forming ink according to any of embodiments 1 to 4.

[0119] A copper circuit formation method according to embodiment 7 of the present invention includes the step of printing a copper film forming ink according to any of embodiments 1 to 4 onto a substrate.

[0120] The copper circuit formation method according to embodiment 8 of the present invention may further include the step of heating the printed copper film forming ink in embodiment 7.

[0121] The copper circuit formation method according to embodiment 9 of the present invention may further include a step of copper plating the copper circuit pattern formed by heating in embodiment 8.

[0122] In the copper circuit formation method according to embodiment 10 of the present invention, the copper plating may be electroless copper plating in embodiment 9.

[0123] One aspect of the present invention will be specifically described below with reference to examples and comparative examples.

[0124] [Raw Materials] The following raw materials were used to prepare the inkjet inks according to the examples or comparative examples.

[0125] (Copper Forate) ・Copper(II) Forate Tetrahydrate: "Copper Forate Hydrate" manufactured by Terada Yakusen Kogyo Co., Ltd.

[0126] (Nitrogen-containing heterocyclic compounds) ・1-Methylimidazole: "1-Methylimidazole" manufactured by Tokyo Chemical Industry Co., Ltd. ・1-Ethylimidazole: "1-Ethylimidazole" manufactured by Tokyo Chemical Industry Co., Ltd. ・1-Propylimidazole: "1-Propylimidazole" manufactured by Tokyo Chemical Industry Co., Ltd. ・1-Butylimidazole: "1-Butylimidazole" manufactured by Tokyo Chemical Industry Co., Ltd. ・1-Pentylimidazole: "1-Pentylimidazole" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・1-Hexylimidazole: "1-Hexylimidazole" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0127] (Solvents) ・Methanol: Methanol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Ethanol: Ethanol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Butanol: Butanol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Hexanol: Hexanol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Terpineol: α-Terpineol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・2-(2-Ethylhexyloxy)ethanol: 2-(2-Ethylhexyloxy)ethanol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Ethylene glycol: Ethylene glycol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Diethylene glycol: Diethylene glycol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Propylene glycol monomethyl ether: Propylene glycol monomethyl ether manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0128] (Additives) ・Acetic acid: "Acetic acid" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Formic acid: "Formic acid" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. ・Sulfuric acid: "Sulfuric acid" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0129] [Preparation and Evaluation of Inkjet Ink] (Example 1) The copper film-forming ink of Example 1 was prepared by grinding and kneading the amounts of copper(II) formate tetrahydrate and 1-ethylimidazole listed in Table 1 below in a mortar for 10 minutes, and then adding ethanol as a solvent and mixing until the viscosity was 4 to 14 mPa·s. The viscosity of the copper film-forming ink was measured at 25°C using a dynamic viscoelasticity measuring device (Rheosol-G5000; manufactured by UBM) with an E-type viscometer (cone plate type) attachment.

[0130] (Examples 2-22, Comparative Examples 1-9) Copper film-forming inks for Examples 2-22 and Comparative Examples 1-9 were prepared in the same manner as in Example 1, except that the amounts of copper formate, nitrogen-containing heterocyclic compound, solvent, and additives listed in Table 1 below were used. Ink with a viscosity of 4-14 mPa·s and uniformity was prepared was evaluated as "best," and ink that could not be prepared with a viscosity of 4-14 mPa·s or that could not be prepared as uniform ink was evaluated as "unacceptable." The results are shown in Table 2 below.

[0131] In Comparative Examples 1 to 4, the viscosity of the ink remained higher than 14 mPa·s regardless of how the solvent content was adjusted, making it impossible to prepare ink with the desired viscosity. Furthermore, in Comparative Example 5, the mixture of copper formate and nitrogen-containing heterocyclic compound (copper complex) separated from the solvent, making it impossible to prepare a uniform ink.

[0132]

[0133]

[0134] [Evaluation of Printability on Substrate] Using the copper film-forming inks of Examples 1 to 22 and Comparative Examples 6 to 9, a copper film pattern with a width of 10 mm x 40 mm was applied to a commercially available PET film (Cosmoshine [Registered Trademark in Japan] A4360; manufactured by Toyobo Co., Ltd.). The printability and printing stability of the copper film-forming ink on the substrate were evaluated by measuring the change in the application width over time (after 5 minutes and 10 minutes).

[0135] Specifically, a masking tape with a thickness of 80 μm was applied to a PET film, covering the outer perimeter of a rectangular pattern-forming area measuring 10 mm wide x 40 mm wide. Ink was then dropped onto the pattern-forming area. Subsequently, ink was applied by sliding a stainless steel rod over the masking tape, and the masking tape was peeled off to form the pattern. The minimum value of the applied line width after 10 minutes relative to the applied line width (10 mm) immediately after application was evaluated as follows: "Best" if the minimum value was between 95% and 100%, "Good" if it was between 90% and 95%, "Acceptable" if it was between 80% and 90%, and "Unacceptable" if it was below 80%. The results are shown in Table 2 above.

[0136] In Comparative Example 9, the copper film-forming ink was repelled by the PET film, making it impossible to form a rectangular pattern, resulting in problems with printability and print stability on the substrate.

[0137] [Inkjet Evaluation (Ejection Performance, Copper Circuit Formation)] Using the copper film-forming inks of Examples 1 to 22 and Comparative Examples 6 to 9, 300 μm wide line patterns were drawn using an inkjet device (DMP-2850; Fujifilm Corporation). Three types of commercially available PET films (Cosmoshine [Registered Trademark in Japan] A4360; Toyobo Co., Ltd.; SHINPEX [Registered Trademark in Japan]; Shinko Synthetic Fiber Co., Ltd.; Lumirror [Registered Trademark in Japan] E22; Toray Industries, Inc.) were subjected to copper film-forming ink ejection from the inkjet nozzle to draw 300 μm wide line patterns on the PET films. After drying the line patterns on the PET films on the inkjet device stage heated to 60°C, the films were heated and baked in an oven at 130°C under a nitrogen atmosphere for 10 minutes to form metallic copper line patterns on the PET films.

[0138] Regarding ejection performance, those in which the copper film-forming ink was ejected from the inkjet nozzle without problems were rated as "best," and those with ejection problems were rated as "unacceptable." The results are shown in Table 2 above.

[0139] In Comparative Examples 7 and 9, the copper film-forming inks were excessively volatile, leading to an increase in viscosity and nozzle clogging. As a result, line patterns could not be formed, and the ejection performance was deemed problematic. In Examples 1 to 22 and Comparative Examples 6 and 8, the copper film-forming inks were ejected without problems, and line patterns could be drawn on the PET film.

[0140] Regarding the formation of copper circuits, those in which a line pattern of metallic copper was formed on the PET film after firing were evaluated as "best," and those in which no line pattern was formed were evaluated as "unacceptable." The results are shown in Table 2 above. In Comparative Examples 6 and 8, the copper film forming inks did not dry completely within the firing time, and a line pattern of metallic copper could not be formed. In Examples 1 to 22, the copper film forming inks were able to form a line pattern of metallic copper after firing, regardless of the type of PET film.

[0141] [Electroless Copper Plating Treatment] Line patterns made of metallic copper prepared in Examples 11 and 14 were subjected to electroless copper plating treatment. OPC Copper HFS (manufactured by Okuno Pharmaceutical Co., Ltd.) was used as the electroless copper plating solution. The electroless copper plating treatment was carried out by performing the following steps on the line patterns on the PET film: pickling with a 10% formic acid aqueous solution, rinsing with water, electroless copper plating treatment (60 minutes / 40°C), rinsing with water, and drying (100°C / 1 minute). In all examples, copper plating could be applied without any problems.

[0142] As described above, according to one aspect of the present invention, it has been shown that a copper film forming ink capable of forming circuit patterns on various resin substrates can be provided.

[0143] A copper film-forming ink according to one aspect of the present invention is useful as a material for forming various circuits and electrodes used in electronic devices and the like.

Claims

1. A copper film-forming ink comprising a copper complex comprising a five-membered or six-membered nitrogen-containing heterocyclic compound having one alkyl substituent consisting of two to five carbon atoms, or two or more alkyl substituents consisting of one to five carbon atoms and having one to three nitrogen atoms, and copper formate, and a monohydric alcohol having two to six carbon atoms which may have an ether bond.

2. The copper film-forming ink according to claim 1, wherein the nitrogen-containing heterocyclic compound is one or more selected from the group consisting of 1-ethylimidazole, 1,2-dimethylimidazole, 1-propylimidazole, 1-butylimidazole, and 1-pentylimidazole.

3. The copper film-forming ink according to claim 1, wherein the monohydric alcohol is one or more selected from the group consisting of ethanol, 1-butanol, 1-hexanol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol.

4. The copper film forming ink according to claim 1, wherein the viscosity at 25°C is 4 to 14 mPa·s.

5. An inkjet ink comprising the copper film-forming ink according to any one of claims 1 to 4.

6. A printed article comprising a copper circuit pattern formed with the copper film-forming ink described in any one of claims 1 to 4.

7. A method for forming a copper circuit, comprising the step of printing a copper film-forming ink according to any one of claims 1 to 4 onto a substrate.

8. The method for forming a copper circuit according to claim 7, further comprising the step of heating the printed copper film forming ink.

9. The copper circuit formation method according to claim 8, further comprising the step of copper plating the copper circuit pattern formed by the heating.

10. The method for forming a copper circuit according to claim 9, wherein the copper plating is electroless copper plating.

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