阅读说明：本技术 丙烯酸树脂及其制造方法、以及金属微粒子分散体 (Acrylic resin, process for producing the same, and metal microparticle dispersion ) 是由 渡部功治 山口善之 于 2019-02-21 设计创作，主要内容包括：一种丙烯酸树脂以及含有该丙烯酸树脂的金属微粒子分散体,该丙烯酸树脂含有具有聚亚烷基二醇部位的(甲基)丙烯酸酯单体A的单元,且在至少一个末端具有羧酸基及/或羧酸盐基。(An acrylic resin containing a unit of a (meth) acrylate monomer A having a polyalkylene glycol moiety and having a carboxylic acid group and/or a carboxylate group at least one terminal, and a metal microparticle dispersion containing the acrylic resin.)

1. An acrylic resin comprising a unit of a (meth) acrylate monomer A having a polyalkylene glycol moiety, and having a functional group selected from the group consisting of a carboxylic acid group and a carboxylic acid salt group at least one terminal.

2. The acrylic resin according to claim 1, wherein the number of repeating alkylene glycol units in the polyalkylene glycol moiety is 4 to 120.

3. The acrylic resin according to claim 1 or 2, wherein the polyalkylene glycol moiety contains a polyethylene glycol moiety.

4. The acrylic resin according to any one of claims 1 to 3, wherein the acrylic resin further contains a unit of a (meth) acrylate monomer B having a hydrophobic group.

5. The acrylic resin of claim 4 wherein the hydrophobic group is an alkyl group.

6. The acrylic resin according to claim 4 or 5, wherein the content of the unit of the (meth) acrylate monomer A in the acrylic resin is 10 to 50% by mass.

7. The acrylic resin according to any one of claims 1 to 6, wherein the weight average molecular weight of the acrylic resin is 5,000 to 100,000.

8. The acrylic resin according to any one of claims 1 to 7, wherein the acrylic resin further contains a unit of monomer C having a heterocyclic ring.

9. The acrylic resin according to claim 8, wherein the monomer C contains at least a unit of a (meth) acrylate monomer having an oxygen-containing ring.

10. A metal fine particle dispersion comprising the acrylic resin according to any one of claims 1 to 9, metal fine particles, and a dispersion medium.

11. The metal microparticle dispersion according to claim 10, wherein the metal comprises at least 1 selected from silver and copper.

12. A method for producing an acrylic resin, comprising the steps of:

preparing a polymerization liquid containing a (meth) acrylate monomer a having a polyalkylene glycol moiety, a polymerization initiator, and a chain transfer agent, at least one of the chain transfer agent and the polymerization initiator having at least one functional group selected from the group consisting of a carboxylic acid group and a carboxylic acid salt group; and

and a step of polymerizing the (meth) acrylate monomer a in the polymerization solution to synthesize an acrylic resin containing a unit of the (meth) acrylate monomer a and having the functional group at least one end.

13. The method for producing an acrylic resin according to claim 12, wherein the chain transfer agent contains 3-mercaptopropionic acid.

14. The method for producing an acrylic resin according to claim 12 or 13, wherein the polymerization initiator contains disuccinic acid peroxide.

Technical Field

The present invention relates to an acrylic resin used as a dispersant for a metal fine particle dispersion, a method for producing the same, and a metal fine particle dispersion.

Background

In order to form a fine electrode, a circuit, or the like of an electronic component, it has been proposed to use a metal fine particle dispersion in which metal fine particles (metal nanoparticles) having a particle diameter of about several nm to several tens nm are dispersed in a dispersion medium. The metal microparticle dispersion is also referred to as a metal ink, a metal paste, or the like. The metal paste is a conductive paste containing a binder resin. After the metal fine particle dispersion is coated on a substrate, the metal fine particles are sintered to each other or the binder resin is cured by applying energy such as heat or light to form a conductive film.

Fine metal particles having high activity are easily sintered even at low temperatures, and are unstable as particles. Therefore, various methods have been studied to prevent sintering and aggregation of metal fine particles to improve storage stability.

For example, as the binder resin, a method of using an acrylic resin having a specific structure is studied. Patent document 1 proposes a method of using a (meth) acrylic resin having a glass transition temperature of 50 ℃ or lower, which is obtained by polymerizing a monomer mixture containing a polyoxyethylene (meth) acrylate monomer. Patent document 2 proposes a binder resin for conductive paste, which is composed of a polymer having a main chain composed of a segment derived from a (meth) acrylate monomer and a phosphoric acid-based component at the ω -position.

Disclosure of Invention

Problems to be solved by the invention

As the substrate to which the metal fine particle dispersion is applied, resins (polyimide, polyethylene terephthalate, polyethylene naphthalate, and the like) are used in addition to glass and ceramics. When such a resin is used as a substrate, it is necessary to set the firing temperature to a low temperature of about 100 to 200 ℃.

However, the higher the dispersibility and storage stability of the metal fine particles, the more difficult the metal fine particles are sintered at a low temperature.

Means for solving the problems

One aspect of the present invention relates to an acrylic resin containing a unit of a (meth) acrylate monomer a having a polyalkylene glycol moiety and having a functional group selected from the group consisting of a carboxylic acid group and a carboxylate group at least one terminal.

Another aspect of the present invention relates to a metal fine particle dispersion containing the above-described acrylic resin, metal fine particles, and a dispersion medium.

Still another aspect of the present invention relates to a method for producing an acrylic resin, comprising the steps of: preparing a polymerization liquid containing a (meth) acrylate monomer a having a polyalkylene glycol moiety, a polymerization initiator, and a chain transfer agent, at least one of the chain transfer agent and the polymerization initiator having at least one functional group selected from the group consisting of a carboxylic acid group and a carboxylic acid salt group; and a step of polymerizing the (meth) acrylate monomer a in the polymerization solution to synthesize an acrylic resin that contains a unit of the (meth) acrylate monomer a and has the functional group at least one end.

Effects of the invention

By using the acrylic resin of the present invention, a metal fine particle dispersion in which the dispersibility and storage stability of metal fine particles are improved and the metal fine particles can be fired even at low temperatures can be obtained.

The novel features of the present invention are set forth in the appended claims, but both the structure and the content of the present invention can be better understood together with other objects and features of the present invention by referring to the following detailed description taken in conjunction with the accompanying drawings.

Detailed Description

The acrylic resin according to an embodiment of the present invention contains a unit a of a (meth) acrylate monomer having a polyalkylene glycol moiety, and has a functional group selected from the group consisting of a carboxylic acid group and a carboxylate group at least one terminal.

In the present specification, the acrylic resin is used to include a methacrylic resin. In addition, acrylates and methacrylates are sometimes collectively referred to as (meth) acrylates.

By having not only a polyalkylene glycol moiety but also a carboxylic acid group and/or a carboxylic acid salt group at least one terminal of the main chain, the acrylic resin can exhibit excellent performance as a dispersant for a metal fine particle dispersion for forming an electrode, a circuit, or the like. It is considered that the carboxylic acid group and/or the carboxylate group at the end of the main chain has a moderate interaction with the metal fine particles.

The acrylic resin containing a unit of a (meth) acrylate monomer B having a hydrophobic group in addition to a unit of a (meth) acrylate monomer a functions as a dispersant having a particularly excellent balance between hydrophilicity and hydrophobicity. It is considered that the polyalkylene glycol moiety having hydrophilicity interacts with the surface of the metal fine particle. On the other hand, the hydrophobic portion is located outside the polyalkylene glycol portion in view of the metal fine particles, whereby the distance between the metal fine particles can be maintained. As a result, the dispersibility and storage stability of the metal fine particles can be improved.

It is considered that if the carboxylic acid group and/or the carboxylic acid salt group is present at least at one end of the main chain of the acrylic resin, steric hindrance becomes smaller than in the case where the carboxylic acid group and/or the carboxylic acid salt group is not present at the end of the main chain. From this, it is considered that the interaction between the carboxylic acid group and/or the carboxylate group and the metal fine particle tends to be strong. Therefore, it is considered that high dispersibility and storage stability of the metal fine particles can be obtained by a balance between hydrophilicity and hydrophobicity of the acrylic resin and a synergistic effect with the carboxylic acid group and/or the carboxylic acid salt group present at the terminal of the main chain. Further, it is considered that the metal fine particles strongly interact only with the ends of the main chain of the acrylic resin, and the acrylic resin is likely to be detached from the metal fine particles, and is likely to be fired even at low temperature.

The acrylic resin according to the embodiment of the present invention, a method for producing the same, and a metal fine particle dispersion using the acrylic resin will be described in more detail below.

[ acrylic resin ]

The acrylic resin contains a unit derived from a (meth) acrylate monomer a having a polyalkylene glycol moiety (hereinafter, also referred to as a monomer a). The monomer A is a raw material monomer of acrylic resin. Examples of the monomer a include mono (meth) acrylates having a polyalkylene glycol moiety. Examples of the polyalkylene glycol corresponding to the polyalkylene glycol site include polyethylene glycol, polypropylene glycol, and a copolymer of ethylene glycol and propylene glycol. The monomer A may be used alone or in combination of two or more. In addition, one monomer A may have two or more polyalkylene glycol sites.

The mono (meth) acrylate having a polyalkylene glycol moiety is not particularly limited, and examples thereof include a monomer in which a hydroxyl group at one terminal of a polyalkylene glycol is substituted with a (meth) acryloyloxy group, a monomer in which a hydroxyl group at one terminal of a polyalkylene glycol is substituted with a (meth) acryloyloxy group and a hydroxyl group at the other terminal is substituted with — OR (R is a hydrocarbon group which may have a substituent, OR the like). Examples of R include an alkyl group (C)_1-26Alkyl or C_1-20Alkyl, etc.), alicyclic hydrocarbon group (cycloalkyl, etc.) and aryl group (C)_6-14Aryl, etc.), and the like. Examples of the substituent group of R include a hydroxyl group, an alkoxy group, and/or an ester group.

The mono (meth) acrylate having a polyalkylene glycol moiety is not particularly limited, and examples thereof include methoxy polyethylene glycol mono (meth) acrylate, octyloxy polyethylene glycol-polypropylene glycol mono (meth) acrylate, lauryloxy polyethylene glycol mono (meth) acrylate, stearyloxy polyethylene glycol-polypropylene glycol mono (meth) acrylate, allyloxy polyethylene glycol-polypropylene glycol mono (meth) acrylate, and hydroxyl-terminated polyethylene glycol mono (meth) acrylate. Further, "polyethylene-polypropylene glycol" refers to a block copolymerization site of ethylene glycol and propylene glycol.

In addition, a lighter 130MA or a lighter 041MA (both of Kyoeis chemical Co., Ltd.) may be used; NK ester M-90G, NK ester M-230G (all of the new Zhongcun chemical industry Co., Ltd.); (meth) acrylates commercially available under the trade names BLEMMERPME, BLEMMER AME, BLEMMER 50POEP-800B, BLEMMER 50AOEP-800B, BLEMMER ALE, BLEMMERPSE, BLEMMER ASEP, BLEMMER PKEP, BLEMMER AKEP, BLEMMER PME, BLEMMERER AME, BLEMMERPE-350 (both manufactured by Nissan oil Co., Ltd.).

When the acrylic resin is used as a dispersant for the metal fine particle dispersion, the acrylic resin preferably contains at least a unit of a (meth) acrylate monomer containing a polyethylene glycol unit. In the unit of the monomer a contained in the acrylic resin, the polyalkylene glycol moiety preferably contains at least a polyethylene glycol moiety. The polymerization of the monomer a having a polyethylene glycol site is easily and stably carried out, and a hydrophilic site desired as a dispersant for metal fine particles can be easily imparted to the obtained acrylic resin. Therefore, when the obtained acrylic resin is used as a dispersant for the metal fine particle dispersion, the dispersibility and storage stability of the metal fine particles can be improved.

The number of repeating alkylene glycol units (or oxyalkylene units) in the polyalkylene glycol moiety is preferably 4 to 120, more preferably 9 to 90. Such a monomer a having a polyalkylene glycol moiety is easily and stably polymerized, and a hydrophilic moiety desired as a dispersant for metal fine particles can be easily provided to the obtained acrylic resin. Therefore, the dispersibility and storage stability of the metal fine particles can be improved. When two or more kinds of polyalkylene glycol sites are present in one monomer A (for example, when the monomer A contains different block copolymerization sites of alkylene glycol), the total number of repeating alkylene glycol units is preferably within the above range.

The acrylic resin preferably has a unit derived from a (meth) acrylate monomer B having a hydrophobic group (hereinafter, also referred to as a monomer B in some cases), in addition to a unit derived from the monomer a. The monomer B is a raw material monomer of acrylic resin. The acrylic resin can be provided with a hydrophobic portion preferable as a dispersant for the metal fine particles by a unit derived from the monomer B. Examples of the hydrophobic group include a hydrocarbon group (an aliphatic, alicyclic or aromatic hydrocarbon group, etc.). Examples of the aliphatic hydrocarbon group include an alkyl group. As alkyl, there may be mentionedGive an example of C_1-26Alkyl, which may also be C_1-20An alkyl group. Specific examples of the alkyl group include methyl, ethyl, propyl, butyl, hexyl, decyl, and octadecyl. Examples of the alicyclic hydrocarbon group include cycloalkyl (C)_4-10Cycloalkyl or C_5-8Cycloalkyl (e.g., cyclopentyl, cyclohexyl, etc.), crosslinked cyclic hydrocarbon group (C)_6-20Crosslinked cyclic hydrocarbon groups (e.g., bornyl, isobornyl, etc.) and the like. As the aromatic hydrocarbon group, there may be mentioned an aryl group (C)_6-20Aryl or C_6-14Aryl, etc.). Specific examples of the aryl group include phenyl, tolyl, naphthyl and the like. The aliphatic hydrocarbon group (e.g., alkyl group) may have an alicyclic hydrocarbon group and/or an aromatic hydrocarbon group as a substituent. The alicyclic hydrocarbon group and the aromatic hydrocarbon group may each have an aliphatic hydrocarbon group as a substituent. The hydrocarbon group as the substituent may be selected from the hydrocarbon groups exemplified above, and examples thereof include C_1-4Alkyl radical, C_5-8Cycloalkyl radical, C_6-10Aryl, and the like.

The monomer B is preferably an alkyl (meth) acrylate, a (meth) acrylate having an aliphatic hydrocarbon group, an aryl (meth) acrylate, or the like. These monomers may also have a substituent. Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octadecyl (meth) acrylate, and benzyl (meth) acrylate. Examples of the (meth) acrylate having an aliphatic hydrocarbon group include a cycloalkyl (meth) acrylate (e.g., cyclohexyl (meth) acrylate), and a (meth) acrylate having a crosslinked cyclic hydrocarbon group (e.g., isobornyl (meth) acrylate). Examples of the aryl (meth) acrylate include phenyl (meth) acrylate, tolyl (meth) acrylate, and the like. However, the monomer B is not limited to these. The monomer B may be used alone or in combination of two or more.

Among these monomers B, alkyl (meth) acrylates in which the hydrophobic group is an alkyl group are preferably used. When the hydrophobic group is an alkyl group, the resulting acrylic resin exhibits more desirable hydrophobicity as a dispersant for metal fine particles. Therefore, the dispersibility and storage stability of the metal fine particles can be improved. Further, the acrylic resin obtained is more likely to be detached from the metal fine particles, and is more likely to be fired at a low temperature.

The acrylic resin may have a unit derived from the monomer C different from the unit derived from the monomer a and the unit derived from the monomer B. The monomer C is selected from monomers a and B which have less influence on hydrophilicity and hydrophobicity obtained from the monomers a and B and performance (for example, thermal decomposition property) of the acrylic resin as a dispersant. The monomer C is not particularly limited to acrylic monomers as long as it is polymerizable with the monomer a and/or the monomer B, but acrylic monomers ((meth) acrylate and the like) are preferable from the viewpoint of easy polymerization with the monomer a and/or the monomer B. Examples of the monomer C include glycidyl methacrylate, glycerol monomethacrylate, N, N, N-trimethyl-N- (2-hydroxy-3-methacryloyloxypropyl) -ammonium chloride, and urethane acrylate.

As the monomer C, a monomer having a heterocyclic ring may also be used. When the acrylic resin has a unit derived from a monomer having a heterocycle, high adhesion to a substrate can be ensured. Examples of the hetero atom of the heterocyclic ring include an oxygen atom, a nitrogen atom and a sulfur atom. The heterocyclic ring may have one kind of hetero atom, or may have two or more kinds of hetero atoms. The number of hetero atoms contained in the heterocycle is not particularly limited, and may be 1 or 2 or more. The number of hetero atoms contained in the heterocycle may be, for example, 4 or less or 3 or less. These lower limit values and upper limit values may be arbitrarily combined. The heterocyclic ring may be either saturated or unsaturated. The heterocycle may have, for example, 3 or more, 4 or more, or 5 or more rings. The heterocycle may be, for example, 3-membered ring or more and 8-membered ring or less (or 6-membered ring or less), 4-membered ring or more and 8-membered ring or less (or 6-membered ring or less), or 5-membered ring or more and 8-membered ring or less (or 6-membered ring or less).

Examples of the monomer C having a heterocyclic ring include (meth) acrylates having a heterocyclic ring. Examples of the monomer C having a heterocyclic ring include a hydroxyl compound having a heterocyclic ring (havingHeterocyclic alkyl alcohols, etc.) and the like. Examples of the heterocyclic ring include an oxygen-containing ring (tetrahydrofuran, dioxolane, furan, tetrahydropyran, dioxane, etc.), a nitrogen-containing ring (pyrrolidine, pyrrole, imidazoline, pyrimidine, etc.), a sulfur-containing ring (tetrahydrothiophene, thiophene, etc.), a heterocyclic ring having two or more kinds of hetero atoms (e.g., oxazole, thiazole, morpholine, etc.), and the like. Examples of the alkyl alcohol include C_1-10Alkyl alcohol (C)_1-6Alkyl alcohol or C_1-4Alkyl alcohols, etc.), and the like. Examples of the alkyl alcohol include methanol, ethanol, propanol, 2-propanol, butanol, and hexanol. Among them, a (meth) acrylate having an oxygen-containing ring (e.g., furfuryl (meth) acrylate) is preferable because it is easy to obtain and to ensure high adhesion to a substrate.

In the acrylic resin containing units of the monomer a, the monomer B, and if necessary, another monomer C, the content of the unit of the monomer a is preferably 10 to 50% by mass, and more preferably 15 to 30% by mass. At this time, the acrylic resin exhibits more appropriate hydrophilicity as a dispersant for the metal fine particle dispersion. Further, in the synthesis of the acrylic resin, the hydrophilicity does not become too high, and the polymerization of the monomer can be stably performed. The content of the unit of the monomer a corresponds to a mass ratio of the monomer a to the total amount of the raw material monomers of the acrylic resin.

The content of the unit of the monomer B is preferably 50 to 90% by mass, more preferably 70 to 85% by mass. At this time, the acrylic resin exhibits more appropriate hydrophobicity as a dispersant for the metal fine particle dispersion. The content of the unit of the monomer B corresponds to a mass ratio of the monomer B to the total amount of the raw material monomers of the acrylic resin.

The unit content of the monomer C is, for example, 30% by mass or less, preferably 10% by mass or less. The content of the unit of the monomer C is preferably 1% by mass or more from the viewpoint of easily ensuring high adhesion. The content of the unit of the monomer C corresponds to a mass ratio of the monomer C to the total amount of the raw material monomers of the acrylic resin.

The acrylic resin has a functional group selected from the group consisting of a carboxylic acid group and a carboxylic acid salt group at least one end of the main chain. The number of the carboxylic acid groups and/or carboxylic acid salt groups is not particularly limited, but the acrylic resin preferably has a carboxylic acid group and/or a carboxylic acid salt group at one end of the main chain. In this case, in the metal fine particle dispersion, the hydrophobic portion of the acrylic resin is more likely to spread spatially, and the distance between the metal fine particles is likely to be appropriately maintained. The acrylic resin may have the functional group in the side chain, but from the viewpoint of easily maintaining an appropriate distance between the metal fine particles, the number of functional groups is preferably small, and the functional group is not preferably present in the side chain.

Examples of the carboxylate group include an ammonium salt and a metal salt. Examples of the metal salt include alkali metal salts (e.g., sodium salts and potassium salts) and alkaline earth metal salts (e.g., calcium salts).

The introduction of a carboxylic acid group and/or a carboxylic acid salt group into at least one terminal of the main chain of the acrylic resin can be confirmed, for example, by measuring the acid value or amine value of the acrylic resin by the following method. When a carboxylic acid group and/or a carboxylic acid salt group is introduced into at least one end of the main chain of the acrylic resin, the acid value or amine value is, for example, 3mg/g to 15 mg/g.

(acid value)

1g of an acrylic resin as a sample was dissolved in 100g of isopropyl alcohol. The acid value of the acrylic resin was determined by performing neutralization titration with a 0.1N aqueous solution of potassium hydroxide using phenolphthalein as an indicator to the obtained solution, and measuring the amount (mg) of potassium hydroxide required to neutralize 1g of the acrylic resin.

(amine number)

1g of an acrylic resin as a sample was dissolved in 100g of isopropyl alcohol. The amine value of the acrylic resin was determined by performing neutralization titration with a 0.1N aqueous hydrochloric acid solution using methyl orange as an indicator and measuring the amount (mg) of potassium hydroxide equivalent to 1g of acid required for neutralizing the acrylic resin.

The weight average molecular weight of the acrylic resin is preferably 5,000 to 10 ten thousand, more preferably 1 ten thousand to 5 ten thousand. This is because the viscosity of the acrylic resin-containing metal fine particle dispersion does not become too high, and the dispersibility and storage stability of the metal fine particles can be improved. Further, since the metal fine particles are easily decomposed at low temperature, the metal fine particles are easily fired at low temperature. The weight average molecular weight can be determined, for example, by Gel Permeation Chromatography (GPC) and converted to polystyrene.

[ method for producing acrylic resin ]

The method for producing an acrylic resin according to the present embodiment includes, for example, the steps of: preparing a polymerization liquid containing a (meth) acrylate monomer A having a polyalkylene glycol moiety, a polymerization initiator, and a chain transfer agent, at least one of the chain transfer agent and the polymerization initiator having at least one carboxylic acid group and/or carboxylic acid salt group; and a step of polymerizing the monomer A in a polymerization solution to synthesize an acrylic resin containing a unit of the monomer A and having a carboxylic acid group and/or a carboxylate group at least one end.

The polymerization liquid contains the monomer A, and if necessary, the monomer B, and may contain another monomer C.

The content of the monomer a and the content of the monomer B in the entire monomer may be selected according to the desired structure of the acrylic resin.

The content of the whole monomer (monomer concentration) in the polymerization liquid is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass. This is because the polymerization reaction of the monomer is easily performed.

The method of introducing a carboxylic acid group and/or a carboxylic acid salt group into at least one end of the main chain is not particularly limited, and examples thereof include a method of using a polymerization initiator having at least one carboxylic acid group and/or carboxylic acid salt group, a chain transfer agent having at least one carboxylic acid group and/or carboxylic acid salt group, and the like, when synthesizing an acrylic resin. Any of the above-mentioned polymerization initiators and chain transfer agents may be used, and a polymerization initiator and a chain transfer agent may be used in combination. In addition, a carboxylic acid group and/or a carboxylate group may be introduced only at one end of the main chain of the acrylic resin, or may be introduced at both ends of the main chain.

The acrylic resin is synthesized by polymerizing the monomer a, the monomer B, and, if necessary, another monomer C by a known polymerization method such as radical polymerization or cationic polymerization. Polymerization is initiated using a polymerization initiator that generates radicals or ions by thermal or photolysis. Therefore, in synthesizing an acrylic resin, a polymerization initiator that generates radicals or ions by thermal or photolysis is used.

The polymerization initiator having at least one carboxylic acid group and/or carboxylic acid salt group is not particularly limited, and examples thereof include disuccinic acid peroxide, 4' -azobis (4-cyanovaleric acid), and salts thereof (ammonium salt, sodium salt, potassium salt, calcium salt, and the like). Further, an initiator commercially available under the trade name PEROYL SA (manufactured by NOF corporation) or V-501 (manufactured by Wako pure chemical industries, Ltd.) may be used. These polymerization initiators may be used alone or in combination of two or more. Among them, disuccinic acid peroxide is preferable in that the initiator efficiency is high.

The chain transfer agent having at least one carboxylic acid group and/or one carboxylic acid salt group is not particularly limited, and examples thereof include a mercaptocarboxylic acid (e.g., 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoacetic acid, mercaptosuccinic acid, etc.) and salts thereof (e.g., ammonium salt, sodium salt, potassium salt, calcium salt, etc.). These chain transfer agents may be used alone or in combination of two or more. Among them, 3-mercaptopropionic acid is preferable in that the weight average molecular weight of the acrylic resin can be easily adjusted.

As the polymerization initiator and the chain transfer agent contained in the polymerization liquid, in addition to the polymerization initiator or the chain transfer agent having a carboxylic acid group and/or a carboxylic acid salt group, a polymerization initiator and a chain transfer agent having no carboxylic acid group and/or carboxylic acid salt group may be used. As such a polymerization initiator and a chain transfer agent, for example, a known polymerization initiator and a known chain transfer agent can be used.

The polymerization initiator having no carboxylic acid group and/or carboxylic acid salt group is not particularly limited, and a polymerization initiator generally used in polymerization of a (meth) acrylate monomer can be used. Examples thereof include azo polymerization initiators (azobisisobutyronitrile (AIBN), etc.), organic peroxide polymerization initiators (peroxyketal, hydroperoxide, dialkyl peroxide, peroxydicarbonate, diacyl peroxide, peroxyester, etc.), etc. These may be used alone or in combination of two or more.

The content of the polymerization initiator contained in the polymerization liquid is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 3 parts by mass, per 100 parts by mass of the total amount of the monomers. This increases the polymerization rate, and prevents an excessive amount of unreacted initiator from remaining after the polymerization.

The chain transfer agent having no carboxylic acid group and/or carboxylic acid salt group is not particularly limited, and examples thereof include thiol compounds. Examples of such a chain transfer agent include alkyl mercaptans (e.g., n-butyl mercaptan, tert-butyl mercaptan, n-octyl mercaptan, tert-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, etc.), esters of mercaptocarboxylic acids (e.g., alkyl mercaptopropionates (e.g., 2-ethylhexyl 3-mercaptopropionate, n-octyl 3-mercaptopropionate, methoxybutyl 3-mercaptopropionate, stearyl 3-mercaptopropionate, etc.), and the like). These may be used alone or in combination of two or more.

The content of the chain transfer agent contained in the polymerization liquid is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the total amount of the monomers. Thereby, an acrylic resin having a desired weight average molecular weight is easily synthesized.

The polymerization solution may contain, for example, a solvent as needed, in addition to the monomer, the polymerization initiator, and the chain transfer agent. The kind of the solvent may be appropriately selected from known solvents according to the monomer and the like. For example, esters (ethyl acetate, butyl acetate, etc.), hydrocarbons (toluene, etc.), ethers (methyl cellosolve, dioxane, butyl carbitol, etc.), ketones (methyl ethyl ketone, methyl isobutyl ketone, etc.), terpenes (terpineol (dihydroterpineol, terpineol, etc.), esters of terpineol (dihydroterpineol acetate, etc.), etc. can be used. One solvent may be used alone, or two or more solvents may be used in combination.

In preparing the polymerization solution, the monomer, the polymerization initiator, the chain transfer agent, the solvent and the like may be mixed at the same time, may be added sequentially, or may be added after mixing a part of the components. For example, a polymerization solution containing a monomer, a polymerization initiator, a chain transfer agent, and a solvent may be mixed at room temperature, heated, and then added with the polymerization initiator.

The polymerization is initiated by a polymerization initiator. An acrylic resin containing a unit of the monomer a is synthesized by polymerizing at least the monomer a in a polymerization liquid and stopping the polymerization reaction of the main chain with a chain transfer agent. In this case, at least one of the chain transfer agent and the polymerization initiator has a carboxylic acid group and/or a carboxylic acid salt group, and thus the carboxylic acid group and/or the carboxylic acid salt group is introduced into at least one end of the main chain of the acrylic resin.

The method for preparing the polymerization liquid and the method for polymerizing the polymerization liquid are not particularly limited. For example, a polymerization solution can be prepared by adding a predetermined amount of a monomer, a chain transfer agent, a solvent, and the like to a separable flask equipped with a stirrer, a cooler, a thermometer, a hot water bath, and a nitrogen gas inlet and stirring the mixture.

After removing dissolved oxygen in the polymerization liquid by bubbling the polymerization liquid with nitrogen gas, the separable flask system was purged with nitrogen gas and heated to a predetermined temperature with stirring. Subsequently, a solution obtained by diluting the polymerization initiator with a solvent is added to the polymerization solution to initiate polymerization. After a predetermined time has elapsed from initiation of polymerization, the reaction solution is cooled to room temperature to complete the polymerization, and the solvent is dried and removed to obtain an acrylic resin.

The polymerization temperature may be suitably determined depending on the kind of the monomer, and may be, for example, 60 ℃ to 100 ℃. The polymerization time may be appropriately determined depending on the kind of the monomer, the polymerization temperature, and the like, and is, for example, 2 to 24 hours.

[ Dispersion of Fine Metal particles ]

The acrylic resin of the present embodiment can be suitably used as a dispersant for the metal fine particle dispersion. The metal microparticle dispersion includes metal microparticles, a dispersant, and a dispersion medium.

The metal fine particle dispersion of the present embodiment uses, as a dispersant, an acrylic resin having not only a polyalkylene glycol moiety but also a carboxylic acid group and/or a carboxylic acid salt group at least one terminal of the main chain, and therefore has high dispersibility and storage stability of the metal fine particles. Further, when the metal fine particle dispersion is fired, the dispersant is easily detached from the metal fine particles, and the firing is easily performed even at low temperature. Therefore, the metal microparticle dispersion of the present embodiment can be suitably used as a metal ink and a metal paste used for forming a fine electrode, a circuit, or the like of an electronic component.

Generally, the amount of the dispersion medium contained in the metal ion and the amount of the dispersion medium contained in the metal paste are different. A metal ink is called a metal ink when the amount of the dispersion medium added is large and the viscosity is low. The metal paste is also referred to as a metal paste when the amount of the dispersion medium to be blended is small and the viscosity is high. Therefore, the metal microparticle dispersion may be a metal ink or a metal paste depending on the application.

As the metal material forming the metal fine particles, a simple metal, an alloy, or the like can be used. The metal element contained in the simple metal or the alloy includes typical metal elements, transition metal elements, and the like. Typical examples of the metal element include zinc (Zn), aluminum (Al), gallium (Ga), indium (In), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), and the like. Examples of the transition metal element include titanium (Ti), zirconium (Zr), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), silver (Ag), copper (Cu), and gold (Au). The alloy preferably contains two or more of these metal elements. Particularly, at least 1 kind selected from silver and copper is preferably contained, and as the metal material, a simple substance of Ag, an Ag alloy, a simple substance of Cu, a Cu alloy, or the like is preferable. Further, the metal fine particles may include 2 or more kinds of metal fine particles having different materials.

The average particle diameter of the metal fine particles is preferably 5nm to 500nm, more preferably 5nm to 100 nm. By using metal fine particles having such an average particle diameter, sintering at a low temperature is facilitated, and the conductivity of the conductive film to be formed is also increased.

The average particle diameter is a particle diameter (D50) of 50% of the cumulative volume of the volume particle size distribution. The average particle diameter (D50) can be measured by a laser diffraction scattering method using a laser diffraction particle size distribution measuring apparatus.

The shape of the metal fine particles is not particularly limited, and may be any of spherical, ellipsoidal, polygonal columnar, polygonal pyramidal, flat (flake, scale, flake, etc.), and the like. From the viewpoint of facilitating the improvement of the contact between the metal fine particles, a spherical shape, an elliptical shape, a flat shape, or the like is preferable.

As the metal fine particles, commercially available ones can be used, and metal fine particles formed by evaporating a metal material can also be used. In addition, metal fine particles produced by a chemical reaction in a liquid phase or a gas phase may be used.

The metal fine particles contained in the metal fine particle dispersion are preferably 10 to 80% by mass, and more preferably 20 to 70% by mass, from the viewpoint of improving dispersibility.

The content of the acrylic resin (dispersant) contained in the metal fine particle dispersion is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the metal fine particles (or a colloid of the metal fine particles described later). When the content of the acrylic resin is within the above range, the dispersibility and storage stability of the metal fine particles are high, and the acrylic resin is likely to be decomposed during firing.

Examples of the dispersion medium of the metal fine particle dispersion include liquid dispersion media, and examples thereof include alcohols, ethers, esters, ketones, and hydrocarbons. Terpenes may also be contained as the dispersion medium. One kind of the dispersion medium may be used alone, or two or more kinds may be used in combination.

Examples of the alcohol include methanol, ethanol, and cyclohexanol. Examples of the ether include aliphatic ethers (chain ethers, such as diethyl ether, butyl carbitol and methyl cellosolve), cyclic ethers (tetrahydrofuran) and the like. Examples of the ester include aliphatic esters (e.g., ethyl acetate, butyl acetate, and ethyl butyrate). Examples of the ketone include aliphatic ketones (chain ketones, such as acetone, ethyl methyl ketone, and methyl isobutyl ketone), and alicyclic ketones (cyclohexanone) and the like. Examples of the hydrocarbon include aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (benzene, toluene, etc.), and the like. Examples of terpenes include terpineol (dihydroterpineol, terpineol, etc.), an ester of terpineol (dihydroterpineol acetate, etc.), and the like.

The metal fine particle dispersion may contain a stabilizer in addition to the metal fine particles, the dispersant, and the dispersion medium. By using the stabilizer, the metal fine particles can be stabilized by keeping a suitable distance without being aggregated in the metal fine particle dispersion.

The stabilizer may be added when preparing the metal fine particle dispersion, but is preferably used in a state of being coordinated to the metal fine particles (metal colloid). The stabilizer may be mixed with the metal fine particles and coordinated to the metal fine particles by heating as necessary, or may be coordinated to the metal fine particles by using the stabilizer in the production process of the metal fine particles.

As the stabilizer, for example, an organic compound having a polar functional group capable of coordinating to the metal fine particles and a hydrophobic organic group can be used. Examples of the polar functional group include an amino group, a mercapto group, an oxygen-containing group (a hydroxyl group (including a phenolic hydroxyl group), a carbonyl group, an ester group, and a carboxyl group). The stabilizer may contain one kind of polar functional group or two or more kinds thereof.

Among them, from the viewpoint of stability at room temperature, organic amines as amino group-containing compounds are preferably used. The organic amine may be any of primary amine, secondary amine, and tertiary amine, or may be any of cyclic amine and chain amine. Primary amines (especially chain primary amines) are preferable from the viewpoint of being easily coordinated to the metal fine particles. As the organic amine, for example, alkylamine (hexylamine, octylamine, decylamine, dodecylamine, tetradecylamine, and the like) is preferable. From the viewpoint of high dispersion stability of the metal fine particles and easy removal during firing, C is preferable_6-14Alkylamines or C_8-12An alkyl amine.

Amines having a small carbon number may have a low storage stability due to high reactivity. However, when the acrylic resin of the present invention is used as a dispersant, high storage stability can be ensured even when such an amine having a small carbon number is used.

Since the stabilizer is preferably removed at an appropriate stage in the firing process, a low molecular weight compound (for example, a compound having a molecular weight of 500 or less) is preferable.

The amount of the stabilizer (preferably, a stabilizer coordinated to the metal fine particles) contained in the metal fine particle dispersion is, for example, 0.1 to 5 parts by mass, and more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the metal fine particles. When the amount of the stabilizer is within the above range, the metal fine particles are easily stabilized in the metal fine particle dispersion, and are also easily removed during firing.

The metal microparticle dispersion may contain a known additive (e.g., a leveling agent, an adhesion-imparting agent, etc.) as needed.

The metal fine particle dispersion of the present invention has high dispersibility and storage stability of the metal fine particles. For example, no precipitation was observed even after the prepared metal microparticle dispersion was stored at 25 ℃ for 1 month.

The metal fine particle dispersion of the present invention can sufficiently perform firing of the metal fine particles even at a low temperature of about 100 to 200 ℃. Therefore, as a substrate to which the metal fine particle dispersion is applied, a resin substrate (for example, a substrate formed of a resin such as polyimide, polyethylene terephthalate, or polyethylene naphthalate) can be used.

Sufficient firing even at low temperatures can be confirmed, for example, by firing a metal fine particle dispersion by the following method and measuring the volume resistivity. When the volume resistivity showed a low value of 20 μ Ω · cm or less, it was evaluated that the firing was sufficiently performed.

(firing)

The metal fine particle dispersion was applied to a glass substrate by a bar coater, and heated and fired at 120 ℃ for 30 minutes by a blast dryer.

(volume resistivity)

The volume resistivity was measured by measuring the surface resistivity by a 4-probe method using a low resistivity meter and converting the surface resistivity into a film thickness measured by a contact film thickness meter.