JP4597582B2 - Nickel compound-containing solution, method for producing the same, and method for forming a nickel metal thin film using the same - Google Patents

Description

The present invention relates to a nickel compound-containing solution (paste) for forming a nickel metal thin film layer on a substrate using a screen printing method. Especially, it is related with the nickel compound containing solution (paste) for forming the internal electrode of a multilayer ceramic capacitor (MLCC). In particular, the present invention relates to a solution-type nickel compound-containing paste that is advantageous for densification and thinning of a nickel metal film and can improve productivity.

In recent years, with the trend toward miniaturization of portable terminals and AV devices, electronic components have become lighter, thinner and smaller, and capacitors have become smaller and larger in capacity. Among them, the increase in the size and capacity of MLCCs is an indispensable issue for high-density mounting, and has been actively studied.
The MLCC has a structure in which a number of ceramic dielectric layers and metal internal electrode layers are alternately laminated. For the internal electrode layer, a so-called nickel paste in which nickel metal fine particles are dispersed in an organic solvent containing an organic binder is used. For the dielectric layer, a green sheet in which ceramics such as barium titanate is solidified with an organic binder is used. It is used. A fine pattern of nickel paste is printed on a green sheet by a screen printing method, a large number of these are stacked, thermocompression bonded, and fired, whereby a dielectric layer and an internal electrode layer are formed simultaneously. In order to increase the size and capacity of the MLCC, it is required to reduce the thickness of both the internal electrode layer and the dielectric layer.

The above nickel paste is prepared by mixing nickel metal powder in an organic vehicle prepared by dissolving an organic binder in an organic solvent, kneading and dispersing with a three-roll mill or the like, and diluting organic solvent as necessary for viscosity adjustment It is manufactured by adding. Terpineol is mainly used as the organic solvent, and methyl ethyl ketone, butyl carbitol acetate or the like may be used in combination. Cellulosic resins such as ethyl cellulose or nitrocellulose, or acrylic resins such as methyl methacrylate are used as the organic binder. . An aromatic hydrocarbon such as triethylbenzene is used as the diluting organic solvent.
The nickel paste is used after the viscosity by a rotational viscometer is adjusted to several to several tens Pa · s in order to impart printing suitability by the screen printing method.

As described above, in order to increase the size and capacity of the MLCC, it is necessary to reduce the thickness of the internal electrode layer. However, since the number of particles in the film thickness direction decreases as the film thickness is reduced, pinholes and cracks are likely to occur, and it becomes difficult to form a dense film. For this reason, conventionally, nickel metal particles have been reduced in particle size. Recently, particles having a particle size of 100 to 200 nm or several tens of nm have been used. However, due to an increase in specific surface area due to a reduction in particle size, due to an increase in paste viscosity due to poor dispersibility of nickel metal particles, the occurrence of pinholes and cracks is still one of the greatest factors that hinder thinning. The current situation is that the film thickness is not fully reduced. This is essentially due to the use of metal particles as a nickel source.

In order to solve this problem, attempts have been reported to use a solution-type paste in which a nickel compound is dissolved. For example, it is shown that a conductive film made of nickel fine particles can be obtained by dissolving nickel acetate in an organic solvent such as tetraethylene glycol to form a paste, forming a coating film by screen printing, and firing (non-patent document). Reference 1). However, in reality, the solubility of nickel acetate in organic solvents such as tetraethylene glycol is not sufficient, and the paste lacks stability over time, and this type of solvent has a higher surface tension than terpineol etc. There is a problem that the reproducibility of the pattern image is inferior at the time of printing.

On the other hand, a method using a nickel metal film forming solution comprising an alcohol solution containing a reducing chelate ligand having a hydrazone unit and nickel ions is disclosed (see Patent Document 1). According to this method, an acetol hydrazone derived from acetol and hydrazine is reacted with nickel acetate to prepare a solution of a nickel compound in which acetol hydrazone is coordinated to nickel in a solvent such as isopropyl alcohol. This solution is applied on a substrate by a dip coating method or a spin coating method and baked to obtain a nickel metal thin film. A nickel thin metal film is formed by the reducing power of the ligand, and a highly dense film can be obtained.

However, the alcohol used in this method is highly volatile and has a relatively high surface tension like isopropyl alcohol, and the viscosity of the solution is also low. This is difficult and results in poor productivity. In order to apply the screen printing method, terpineol having a low volatility as a solvent and a surface tension suitable for screen printing is required. In addition, the viscosity of the solution is desirably in the above-described range. However, the nickel compounds described in this method have low compatibility with such solvents, or are unstable in these solvents, so that problems such as precipitation of nickel compounds occur. Further, due to this, there arises a problem that it is difficult to control the viscosity of the solution.

JP 2001-192843 A Niigata Industrial Research Institute Industrial Technology Research Report 2003, 42-46

An object of the present invention is to develop a solution-type nickel paste that contains a nickel compound having a reducing ligand and uses a solvent that is suitable for the screen printing method. Specifically, the solubility is high in solvents such as terpineol, a stable nickel compound is used in these solvents, and the viscosity of the solution-type nickel paste is suitable for screen printing. The goal was to be able to control it.

The present invention has been made to solve the above-mentioned problems in the prior art. First, an α-hydroxyketone is reacted with an N-1 substituted or N, N-2 substituted hydrazine. A hydrazone obtained by reacting a nickel salt of an organic acid with terpineol as a solvent, and the N-1 substituted hydrazine is hydroxyethylhydrazine, and the N, N -2 substituted hydrazines relate to a nickel compound-containing solution which is dimethylhydrazine .
Second, it relates to a nickel compound-containing solution in which nickel acetate or nickel formate is used as the organic acid nickel salt.
Thirdly, the present invention relates to a nickel compound-containing solution further containing a cellulose or acrylic resin.
Furthermore, fourthly, the present invention relates to a method for forming a nickel metal thin film, which comprises applying a heat treatment after applying these nickel compound-containing solutions onto a substrate by a screen printing method.

Hereinafter, the present invention will be described in detail.
Hydrazones composed of α-hydroxyketones and unsubstituted hydrazine are reducible and have a strong effect of promoting dissolution of organic acid nickel salts in isopropyl alcohol and the like, but terpineol with low polarity does not have a dissolution effect. The present inventors use organic acid nickel by using hydrazone obtained by reacting N-1 substituted or N, N-2 substituted hydrazine instead of unsubstituted hydrazine and reacting this with α-hydroxyketone. It was found that the salt dissolves stably in terpineol. The present invention has been made because this finding is decisive for solving the above-mentioned problems.

Examples of the α-hydroxy ketones in the present invention include acetol, acetoin, dihydroxyacetone and the like.
The N-1 substituted or N, N-2 substituted hydrazines to be reacted with these are those in which one or two hydrogen atoms of one amino group of hydrazine are substituted. As the substituent, an alkyl group is preferable. The alkyl group may have a hydroxyl group, and examples of such an alkyl group include a methyl group, an ethyl group, a hydroxyethyl group, and a propyl group. In the case of N, N-2 substituents, the two substituents may be the same or different. Specifically, N-1, N-substituted hydrazine such as monomethyl hydrazine and hydroxyethyl hydrazine, N, N-2 substituted hydrazine such as dimethyl hydrazine and the like can be mentioned.

The α-hydroxy ketones and N-1 substituted or N, N-2 substituted hydrazines react at room temperature to form hydrazone. It is considered that the unshared electron pair of these hydroxyl groups and amino groups is coordinated to nickel ions in a chelate form and exhibits an effect of promoting dissolution in terpineol.

As a nickel salt of an organic acid, a carboxylate of Ni (II) can be used. Examples thereof include nickel formate and nickel acetate. These may or may not have crystallization water. Specific examples include nickel acetate tetrahydrate and nickel formate dihydrate.

The nickel compound-containing solution of the present invention reacts these α-hydroxy ketones with hydrazones composed of N-1 substituted or N, N-2 substituted hydrazines and a nickel salt of an organic acid in a suitable solvent, It can be obtained by replacing the solvent with terpineol. The solvent used in the reaction is particularly limited as long as it dissolves hydrazones composed of α-hydroxy ketones and N-1 substituted or N, N-2 substituted hydrazines and the reaction product nickel compound. It is not a thing. For example, low molecular weight solvents such as methanol, ethanol, propyl alcohol, and isopropyl alcohol can be used. The reaction may be performed at the boiling point of the reaction solvent, and the end point may be where the unreacted organic acid nickel salt disappears or no longer decreases. The reaction can be carried out without solvent, and terpineol can be used as a reaction solvent from the beginning, and solvent replacement can be omitted. However, in this case, if a nickel salt of organic acid having crystal water is used, the crystal water is separated into the system as the reaction proceeds, and therefore dehydration is necessary. Moreover, when the unreacted organic acid nickel salt remains, it may be removed by filtration or centrifugation.

In the above reaction, the hydrazone composed of α-hydroxy ketones and N-1 substituted or N, N-2 substituted hydrazines should be used in an amount of 1 to 2 times the molar amount of nickel ions, and more preferably 2 times. A molar amount is preferred. When the amount is too small, the yield of the above reaction is lowered, and the effect of promoting dissolution of the obtained nickel compound in terpineol is also lowered. On the other hand, when it is excessive, the dissolution promoting effect reaches its peak.

The nickel compound-containing solution of the present invention uses terpineol as a solvent, but methyl ethyl ketone, butyl carbitol acetate or the like may be used in combination with terpineol.

The nickel compound-containing solution of the present invention may contain a cellulose-based or acrylic-based resin as necessary. This utilizes the adjustment of the viscosity of the nickel compound-containing solution or the function as a binder, and those used in conventional nickel pastes can be used without any particular limitation. Specifically, ethyl cellulose or nitrocellulose can be used as the cellulose resin, and methyl methacrylate or the like can be used as the acrylic resin. The content of these resins in the nickel compound-containing solution may be up to about 5% by weight. A terpineol solution of these resins is prepared in advance, and the above-described terpineol solution of the nickel compound may be mixed therewith. Alternatively, when replacing the reaction solvent, a terpineol solution of these resins may be used instead of terpineol.

Moreover, a dilution solvent can be added to the nickel compound-containing solution of the present invention as necessary. As a dilution solvent, what was used with the conventional nickel paste can be used without a restriction | limiting in particular, Specifically, aromatic hydrocarbons, such as a triethylbenzene, etc. are mentioned.
In the present invention, the viscosity of the nickel compound-containing solution is suitable for screen printing by using a binder resin and a diluting solvent as necessary, or simply adjusting the content of terpineol, as appropriate. It can be controlled within a range of 10 Pa · s.

The method for forming a nickel metal thin film of the present invention comprises applying the above-described nickel compound-containing solution onto a substrate by a screen printing method followed by heat treatment.

In the present invention, a nickel compound-containing solution in which a nickel compound is dissolved in terpineol suitable for screen printing can be obtained. This nickel compound-containing solution or a solution whose viscosity has been adjusted by adding a binder resin to this solution has suitability for screen printing, and can be applied to a substrate and baked to form a nickel metal thin film. it can.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these without departing from the spirit and scope of application. In the following description, “parts” represents parts by weight, and “%” represents% by weight.
<Viscosity>
The viscosity was measured using a TV-20 type rotational viscometer manufactured by Toki Sangyo Co., Ltd. The L type was used in the low viscosity region, and the H type was used in the high viscosity region.

Example 1
222 parts of acetol was dissolved in 700 parts of isopropyl alcohol, and 228 parts of hydroxyethylhydrazine was added dropwise during stirring. After dropping, the mixture was stirred at room temperature for 3 hours or more to obtain hydrazone. This was added to 373 parts of nickel acetate tetrahydrate and refluxed for 1 hour to obtain an isopropyl alcohol solution of a nickel compound. 271 parts of terpineol was added to the resulting solution, and isopropyl alcohol was removed by distillation under reduced pressure to obtain a terpineol solution containing 8% nickel. At this time, the solution was brown and the viscosity was 15.1 Pa · s (H type / 20 rpm). 300 parts of the obtained terpineol solution of nickel compound and 132 parts of 10% terpineol solution of ethyl cellulose were mixed by three rolls to obtain a nickel paste containing 5.6% nickel and 3.1% ethyl cellulose. . The viscosity of the nickel paste at this time was 30 Pa · s (H type / 10 rpm). Using this, screen printing (200 mesh) was performed on a heat-resistant glass plate of 2 cm × 7 cm (Corning # 1737). The film was dried at 110 ° C. for 30 minutes, and further heat treated at 500 ° C. to obtain a thin film. It was confirmed by X-ray diffraction that this thin film was formed of nickel metal.

(Example 2)
264 parts of acetoin was dissolved in 700 parts of isopropyl alcohol, and 228 parts of hydroxyethylhydrazine was added dropwise during stirring. After dropping, the mixture was stirred at room temperature for 3 hours or more to obtain hydrazone. This was added to 373 parts of nickel acetate tetrahydrate and refluxed for 1 hour to obtain an isopropyl alcohol solution of a nickel compound. 895 parts of terpineol was added to the obtained solution, and isopropyl alcohol was removed by distillation under reduced pressure to obtain a terpineol solution containing 5% of nickel. At this time, the solution was yellowish brown and the viscosity was 1.1 Pa · s (H type / 100 rpm). 100 parts of the obtained terpineol solution of nickel compound and 44 parts of 10% terpineol solution of ethyl cellulose were mixed by three rolls to obtain a nickel paste containing 3.5% nickel and 3.1% ethyl cellulose. . The viscosity of the nickel paste at this time was 8.1 Pa · s (H type / 50 rpm). Using this, screen printing (200 mesh) was performed on a heat-resistant glass plate of 2 cm × 7 cm (Corning # 1737). The film was dried at 110 ° C. for 30 minutes, and further heat treated at 500 ° C. to obtain a thin film. It was confirmed by X-ray diffraction that this thin film was formed of nickel metal.

(Example 3)
74 parts of acetol was dissolved in 300 parts of isopropyl alcohol, and 60 parts of dimethylhydrazine was added dropwise while stirring. After dropping, the mixture was stirred at room temperature for 3 hours or more to obtain hydrazone. This was added to 124 parts of nickel acetate tetrahydrate and refluxed for 1 hour to obtain an isopropyl alcohol solution of a nickel compound. 322 parts of terpineol was added to the resulting solution, and isopropyl alcohol was removed by distillation under reduced pressure to obtain a terpineol solution containing 5% nickel. At this time, the solution was yellowish brown and the viscosity was 137 mPa · s (L-type / 20 rpm). 100 parts of the obtained terpineol solution of nickel compound and 50 parts of 10% terpineol solution of ethyl cellulose were mixed by three rolls to obtain a nickel paste containing 3.3% nickel and 3.3% ethyl cellulose. . The viscosity of the nickel paste at this time was 3.9 Pa · s (H type / 100 rpm). Using this, screen printing (200 mesh) was performed on a heat-resistant glass plate of 2 cm × 7 cm (Corning # 1737). The film was dried at 110 ° C. for 30 minutes, and further heat treated at 500 ° C. to obtain a thin film. It was confirmed by X-ray diffraction that this thin film was formed of nickel metal.

(Comparative Example 1)
444 parts of acetol was dissolved in 1500 parts of isopropyl alcohol, and 300 parts of hydrazine monohydrate was added dropwise during stirring. After dropping, the mixture was stirred at room temperature for 3 hours or more to obtain hydrazone. This was added to 747 parts of nickel acetate tetrahydrate and refluxed for 1 hour to obtain an isopropyl alcohol solution of the nickel compound. 382 parts of terpineol was added to the obtained solution, and isopropyl alcohol was removed by distillation under reduced pressure, but a precipitate was observed.

In the present invention, a nickel compound-containing solution in which a nickel compound is dissolved in terpineol suitable for screen printing can be obtained. This nickel compound-containing solution or a solution whose viscosity is adjusted by adding a binder resin to this solution has suitability for screen printing, and can be applied to a substrate and baked to form a nickel metal thin film. it can.

Claims (4)

It contains a hydrazone obtained by reacting an α-hydroxyketone with N-1 substituted or N, N-2 substituted hydrazine and a nickel compound obtained by reacting a nickel salt of an organic acid with terpineol. A nickel compound-containing solution as a solvent , wherein the N-1 substituted hydrazine is hydroxyethyl hydrazine, and the N, N-2 substituted hydrazine is dimethylhydrazine . The nickel compound-containing solution according to claim 1, wherein nickel acetate or nickel formate is used as the nickel salt of the organic acid. The nickel compound-containing solution according to claim 1 or 2, further comprising a cellulose-based or acrylic-based resin. A method for forming a nickel metal thin film, comprising applying the nickel compound-containing solution according to any one of claims 1 to 3 onto a substrate by a screen printing method and then performing a heat treatment.