JP2019167421A - Metallic ink - Google Patents

Abstract

To provide metallic ink containing copper, capable of forming a low-resistance metal film.SOLUTION: Metallic ink contains metal colloid, polyether polyol having at least one branched chain, and a dispersant. At least one branched chain has at least one hydroxy group. A metal contained in the metal colloid contains copper.SELECTED DRAWING: None

Description

  The present invention relates to a metal ink containing a metal colloid containing copper.

  Conventionally, when forming a circuit pattern on a circuit board or forming a conductive layer of an electrode, a conductive paste containing metal particles has been used. A conductive pattern (circuit pattern, conductive layer, etc.) is formed by applying the conductive paste on the substrate by screen printing or the like. The applied coating film may be baked. From the viewpoint of obtaining a low resistance conductive pattern by low-temperature firing, silver particles are generally used as the metal particles.

  Attempts have also been made to use copper particles that are more cost effective than silver particles. However, since an oxide film is easily formed on the surface of copper particles, in order to ensure the conductivity of the conductive pattern (specifically, the metal film) to some extent, it is under a reducing atmosphere or an inert gas atmosphere or at a high temperature. Need to be fired.

  In Patent Document 1, a metal pattern is obtained by heat-treating a coating film obtained by repeatedly applying an ink containing copper nanoparticles having a particle size of 10 to 100 nm and an ink containing propionaldehyde at 350 ° C. in a nitrogen gas atmosphere. Is forming. It is described that cupric oxide is reduced by heat treatment.

  Patent Document 2 proposes forming a conductive material by sintering a copper fine particle dispersion containing copper fine particles having an average particle diameter of 1 to 150 nm and a polyol solvent. As the copper fine particle dispersion of Patent Document 2, one having a peak half-value width in the range of 5 to 75 ° C. in the temperature-reduction reduction spectrum measurement when heated at a temperature increase rate of 10 ° C./min is used.

Japanese Patent Application Laid-Open No. 2004-164876 JP 2014-028994 A

  Copper particles are easily oxidized and have low sinterability. Therefore, it is difficult to obtain a low resistance metal film using a metal ink containing copper.

One aspect of the present invention includes a metal colloid, a polyether polyol having at least one branched chain, and a dispersion medium.
The at least one branched chain has at least one hydroxy group;
The metal contained in the metal colloid relates to a metal ink containing copper.

  According to the above aspect of the present invention, a metal ink containing copper capable of forming a low-resistance metal film can be provided.

  In the metal colloid containing metal particles containing copper, an oxide film is easily formed on the metal particles in the process of preparing the metal colloid and the process of forming the metal film using the metal ink containing the metal colloid. In order to form a metal film using such a metal ink, it is necessary to sinter the metal particles while reducing the oxide film. Therefore, it is necessary to fire the metal ink coating film in a reducing atmosphere or an inert gas atmosphere or at a high temperature. However, even if firing is performed under such severe conditions, it is difficult to reduce the resistance of the metal film. For this reason, silver particles that can be fired at low temperatures in the atmosphere and that are easy to obtain a low-resistance metal film are generally used for the metal ink.

[Metal ink]
The metal ink according to one aspect of the present invention includes a metal colloid, a polyether polyol having at least one branched chain, and a dispersion medium. At least one branched chain has at least one hydroxy group. The metal contained in the metal colloid contains copper. By using such a polyether polyol (hereinafter sometimes referred to as a branched polyether polyol), even if an oxide film of metal particles containing copper is formed, it can be effectively reduced and oxidized. The formation of the coating itself can be reduced or suppressed. Thereby, the sinterability of the metal colloid containing copper (more specifically, the metal particle containing copper contained in the metal colloid) can be improved. Therefore, a low-resistance metal film can be obtained in spite of using a metal colloid containing copper.

In the above aspect of the present invention, details of the reason why the sinterability of the metal particles containing copper is improved are not clear, but are presumed to be as follows.
First, by using a branched polyether polyol, the viscosity of the metal ink can be kept relatively low, so that the branched polyether polyol can easily approach the metal particles. The branched polyether polyol is easily coordinated (or interacts) with metal particles containing copper by the action of a flexible polyether chain and a plurality of hydroxy groups including a branched hydroxy group. Therefore, the reducing action of the branched polyether polyol is effectively exerted on the metal particles. This facilitates reduction of the oxide film and reduces or suppresses the formation of the oxide film itself. Thus, it is thought that the sinterability of the metal particle containing copper increases.

  Specifically, the metal ink according to the above aspect is a fired metal ink. Firing type metal ink is used to form a metal film by firing a coating film of metal ink.

Hereinafter, the configuration of the metal ink will be described more specifically.
(Metal colloid)
The metal colloid contains a metal, and the metal contains copper. The metal is usually contained as particles. The metal colloid may include metal particles and a dispersant coordinated to the metal particles.

(Metal (or metal particles))
The metal should just contain copper. The metal is, for example, at least one selected from the group consisting of simple copper and copper alloys. As a metal containing copper constituting the metal particles (hereinafter sometimes referred to as copper material), in addition to copper alone, a copper alloy, for example, a Cu—Ag alloy, a Cu—Sn alloy, a Cu—Cr alloy, and the like. An alloy, a Cu-Zr alloy, etc. are mentioned. In addition, a copper alloy says the thing with most copper being the metal which comprises an alloy. The copper content in the copper alloy is, for example, 90% by mass or more, preferably 95% by mass or more, and more preferably 98% by mass or more.

  The metal colloid may include a plurality of types of metal particles composed of different copper materials. In addition, the metal colloid may include metal particles containing copper and other metal particles (for example, silver particles, silver alloy particles, etc.). For example, the metal colloid may include copper particles composed of simple copper and copper alloy particles composed of a copper alloy. Moreover, the metal colloid may include, for example, first copper alloy particles made of a Cu—Ag alloy and second copper alloy particles made of a Cu—Sn alloy. In these cases, it is preferable that the total content of copper element in the total amount of metal particles contained in the metal colloid is, for example, 90% by mass or more, 95% by mass or more, or 98% by mass or more.

  The average particle diameter of the metal particles is, for example, 1000 nm or less. When metal particles having an average particle diameter of less than 1000 nm are used, the sinterability of the metal particles can be easily improved. Metal particles having an average particle diameter of less than 1000 nm are also referred to as metal nanoparticles. The average particle diameter of the metal particles is preferably, for example, 5 nm or more and less than 1000 nm, and may be 5 nm or more and 700 nm or less. The average particle diameter of the metal particles may be 100 nm or more and 700 nm or less. When metal particles having such an average particle diameter are used, higher sinterability can be ensured. When metal particles having a small average particle diameter (for example, less than 200 nm) are used, the metal particles can be sintered at a relatively low temperature due to the nanoparticle effect. However, according to the above aspect of the present invention, the reducing action of the branched polyether polyol can be effectively exhibited. Therefore, even if the average particle diameter of the metal particles is 200 nm or more (particularly 300 nm or more), high sinterability can be ensured. From such a viewpoint, the average particle diameter of the metal particles may be 300 nm or more and 700 nm or less.

  In addition, in this specification, an average particle diameter is a particle size (D50) in 50% of cumulative volume of 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 average particle diameter of the metal particles is the same as the area surrounded by the outer edges of a plurality of (for example, 10) arbitrarily selected metal particles in a scanning electron microscope (SEM) photograph of the coating film of the metal ink. You may calculate by calculating | requiring and averaging the diameter of the circle which has.

  The shape of the metal particles is not particularly limited, and may be any shape such as a spherical shape, an elliptical spherical shape, a polygonal column shape, a polygonal pyramid shape, a flat shape (flaky shape, scale shape, flake shape, etc.), or a similar shape thereof. May be. From the viewpoint of easily increasing the contact between the metal particles, a spherical shape, an elliptical spherical shape, a flat shape, or a shape similar to these may be used.

  As a metal particle, a commercially available thing may be used and what was formed by evaporating the metal material used as a raw material may be used. Moreover, you may use the metal particle produced using the chemical reaction in a liquid phase or a gaseous phase.

(Dispersant)
By using the dispersant, aggregation of metal particles in the metal ink is suppressed, and the metal colloid can be stabilized in the metal ink. The dispersant may be added when the metal ink is prepared and coordinated with the metal particles, but it is preferable to coordinate with the metal particles prior to preparation of the metal ink. The dispersant may be mixed with the metal particles and coordinated to the metal particles by heating if necessary, or may be coordinated to the metal particles by using a dispersant in the process of producing the metal particles.

  As the dispersant, for example, an organic compound having a polar functional group coordinated to the metal particles and an organic group having a low affinity for the metal particles (for example, a hydrophobic organic group) is used. Examples of polar functional groups include oxygen-containing groups such as amino groups, mercapto groups, hydroxy groups (including phenolic hydroxy groups), carbonyl groups, ester groups, and carboxy groups. The dispersant may contain one type of polar functional group, or may contain two or more types.

From the viewpoint of obtaining high room temperature stability, an organic amine that is a compound containing an amino group may be used. The organic amine may be any of primary amine, secondary amine, and tertiary amine, and may be any of cyclic amine and chain amine. From the viewpoint of easy coordination to metal particles, primary amines (in particular, primary chain amines) are preferable. As the organic amine, for example, alkylamines such as n-butylamine, pentylamine, hexylamine, octylamine, decylamine, dodecylamine and myristylamine are preferable. From the viewpoint of high dispersion stability of the metal particles and easy removal in the process of producing the metal film, a C _6-14 alkylamine or a C _8-12 alkylamine may be used. Further, from the viewpoint of high reactivity and easy formation of a metal film under mild conditions, C _4-10 alkylamine or C _6-10 alkylamine may be used.

  The amount of the dispersant (preferably the dispersant coordinated to the metal particles) contained in the metal ink is, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the metal particles. It may be 5 parts by mass or more and 5 parts by mass or less. When the amount of the dispersant is within such a range, the metal particles are easily stabilized in the metal ink, and the dispersant can be easily removed.

(Branched polyether polyol)
The branched polyether polyol has a main chain and a branched chain branched from the main chain. The branched polyether polyol has at least one branched chain. When there is one branched chain, the branched chain has at least one hydroxy group. When there are two or more branched chains, at least one branched chain has at least one hydroxy group.
In addition, a branched chain says what contains at least 1 carbon atom.

  The branched polyether polyol contains a polyether chain. The polyether chain may be included in either the main chain or the branched chain, but is preferably included in at least the main chain, and may be included in both the main chain and the branched chain. Since the branched polyether polyol has a high flexibility by including a polyether chain, it is considered that a high coordination property to the metal particles can be easily secured.

The polyether chain preferably contains a polyoxyalkylene unit. Examples of the polyoxyalkylene unit include poly (oxy C _2-4 alkylene) units such as a polyoxyethylene unit, a polyoxypropylene unit, a polyoxytrimethylene unit, and a polyoxytetramethylene unit. The branched polyether polyol may contain one or more of these polyoxyalkylene units. From the viewpoint of easily ensuring high flexibility, the branched polyether polyol may contain at least a polyoxyethylene unit, a polyoxytrimethylene unit, and / or a polyoxytetramethylene unit. The branched polyether polyol particularly preferably contains at least a polyoxyethylene unit.

  The branched polyether polyol contains a plurality of hydroxy groups. At least one branched chain has at least one hydroxy group. The presence of these hydroxy groups is thought to increase the coordination properties of the branched polyether polyol with respect to the metal particles. As long as at least one branched chain has at least one hydroxy group, the position of the other hydroxy group is not particularly limited, and may be bonded to the main chain or may be bonded to the branched chain.

  Of all the hydroxy groups contained in the branched polyether polyol, at least one hydroxy group is preferably located at the end of at least one chain selected from the group consisting of the main chain and the branched chain of the branched polyether polyol. . Such a hydroxy group located at the end of the chain is called a terminal hydroxy group. When the branched polyether polyol has a terminal hydroxy group, it is considered that the coordination property to the metal particles is further enhanced. Of the hydroxy groups contained in the branched polyether polyol, some may be terminal hydroxy groups, and all may be terminal hydroxy groups.

Moreover, it is preferable that at least one hydroxy group among all the hydroxy groups contained in the branched polyether polyol is located at the end of the polyether chain. In this case, it is considered that the coordination property to the metal particles can be more easily enhanced by the effect of the chain length of the polyether chain and the effect of flexibility. Some hydroxy groups may be located at the end of the polyether chain, and all hydroxy groups may be located at the end of the polyether chain. From the viewpoint that high coordination properties due to the branched structure are likely to be obtained, it is preferable that at least one of the ends of the main chain and at least one of the ends of the branched chain each have a hydroxy group. The hydroxy group located at the end of the polyether chain may be directly bonded to the end of the polyether chain, or may be bonded indirectly. In the latter case, the hydroxy group may be bonded to the end of the polyether chain via a linking group such as an alkylene group (for example, a C _1-4 alkylene group). Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, and a trimethylene group. The linking group is bonded to the oxygen atom at the end of the polyether chain. The alkylene group and the linking group of the polyether chain bonded to the terminal oxygen atom are different. For example, when the polyether chain is a polyoxyethylene unit, the linking group is an alkylene group other than an ethylene group.

  If the coordination property (or interaction) of the branched polyether polyol to the metal particles is increased, it is considered that the reducing action of the branched polyether polyol is easily exerted on the metal particles.

  The number of branched chains in one molecule of the branched polyether polyol may be one or more, and may be two or more. The number of branched chains is, for example, 6 or less, and may be 4 or less. When the branched chain is in such a range, it is considered that the viscosity of the metal ink can be easily reduced and a high coordination property to the metal particles can be easily secured. These lower limit values and upper limit values can be arbitrarily combined.

The weight average molecular weight (Mw) of the branched polyether polyol is, for example, 100 or more, 200 or more, or 250 or more. When Mw is in such a range, the ratio of the polyether chain in the molecule can be easily increased, so that high flexibility is easily obtained and the coordination property to the metal particles can be improved. From the viewpoint of easily ensuring high coordination properties, the Mw of the branched polyether polyol is, for example, 3000 or less and may be 2500 or less. These lower limit values and upper limit values can be arbitrarily combined.
In addition, Mw is the weight average molecular weight of polystyrene conversion measured by gel permeation chromatography (GPC).

  The amount of the branched polyether polyol with respect to 100 parts by mass of the metal colloid is not particularly limited, but a sufficiently high sinterability can be secured even at 15 parts by mass or less, and a low-resistance metal film can be obtained. Even when a branched polyether polyol exceeding 15 parts by mass is used, the sinterability is not so different from the case of 15 parts by mass or less. The amount of the branched polyether polyol with respect to 100 parts by mass of the metal colloid may be 12 parts by mass or less, or 10 parts by mass or less. Even if the amount of the branched polyether polyol relative to 100 parts by mass of the metal colloid is as small as 5 parts by mass or less, or 3 parts by mass or less, the effect of improving the sinterability can be sufficiently ensured.

(Dispersion medium)
Examples of the dispersion medium include alcohol, ether, ester, ketone, and hydrocarbon. You may use a dispersion medium individually by 1 type or in combination of 2 or more types.
As alcohol, what does not contain a polyether chain | strand is mentioned, for example, Monohydric alcohol (For example, alkyl alcohol etc.) may be sufficient. Examples of the alkyl alcohol include C _1-12 alkyl alcohols such as methanol, ethanol, butanol, hexanol, octanol, and decanol. C _4-12 alkyl alcohol or C _6-10 alkyl alcohol may be used.

  The ether is different from the branched polyether polyol, and examples thereof include those not containing a polyether chain and / or a hydroxy group. Examples of ethers include aliphatic ethers such as diethyl ether and cyclic ethers such as tetrahydrofuran.

Examples of the ester include aliphatic esters such as alkyl esters of C _1-4 carboxylic acids such as ethyl acetate, butyl acetate, and ethyl butyrate (eg, C _1-4 alkyl esters or C _1-2 alkyl esters). It is done. The ester may have no hydroxy group.

Examples of the ketone include aliphatic ketones such as acetone and ethyl methyl ketone (aliphatic ketones having 3 to 6 carbon atoms), alicyclic ketones such as cyclohexanone (C _5-6 cycloalkanone, etc.), and the like. .

Examples of the hydrocarbon include C _6-10 alkane such as hexane, C _5-8 cycloalkane such as cyclohexane, benzene, toluene and the like.

These dispersion media have an appropriate affinity for the branched polyether polyol, and can suppress the coordination property to the metal particles while dissolving the branched polyether polyol. Therefore, by using these dispersion media, it becomes easier to ensure high coordination with the metal particles. When an amine having a small number of carbon atoms such as C _6-10 alkylamine is used as a dispersant, a free amine is easily generated. Since free amines may react with esters and ketones, it is preferable to use a dispersion medium other than esters and ketones.

  The dispersion medium needs to be volatile because it is removed in the process from the formation of the coating film to the formation of the metal film, but it is liquid at room temperature in consideration of storage of the metal ink. It is desirable. From such a viewpoint, the boiling point of the dispersion medium may be 40 ° C. or more and 250 ° C. or less, or 100 ° C. or more and 200 ° C. or less.

(Other)
The metal ink may contain a known additive as required. The amount of the additive in the metal ink is, for example, 10 parts by mass or less or 5 parts by mass or less with respect to 100 parts by mass of the metal colloid.

  The metal ink can contain a polyol compound other than the branched polyether polyol. Examples of such a polyol compound include a polyol not containing a polyether chain, a linear polyol containing a polyoxyalkylene unit, and a polyol having no hydroxy group in a branched chain. The metal ink may contain one or more of these polyol compounds.

  Examples of the polyol not containing a polyether chain include aliphatic polyols and polyester polyols. Examples of the aliphatic polyol include alkylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sugar alcohol. Examples of the alkylene glycol include ethylene glycol and propylene glycol.

  Examples of the linear polyol containing a polyoxyalkylene unit and the polyol having no hydroxy group in the branched chain include diethylene glycol, triethylene glycol, polyethylene glycol (PEG), polypropylene glycol, polytrimethylene glycol, and polytetramethylene. And polyalkylene glycols such as glycol (PTMG). The polyol compound may be a copolymer containing a polyoxyalkylene unit. Examples of the copolymer include an ethylene glycol-propylene glycol copolymer, a tetramethylene glycol-ethylene glycol copolymer, and a tetramethylene glycol-propylene glycol copolymer.

  However, the amount of such a polyol compound is preferably 5 parts by mass or less, more preferably 1 part by mass or less, and 0.1 parts by mass or less with respect to 100 parts by mass of the metal colloid. Also good. Further, the metal ink may not contain such a polyol compound. The polyol compound has a high affinity with the branched polyether polyol. Therefore, when the amount of the polyol compound is in the above range or when the polyol compound is not included, it becomes easier to ensure the coordination property of the branched polyether polyol to the metal particles.

  The viscosity of the metal ink at room temperature (25 ° C.) is, for example, 500 mPa · s or less, and may be 100 mPa · s or less. The viscosity of the metal ink can be measured using, for example, a cone plate type E viscometer.

  The metal ink can be obtained by mixing constituent components. More specifically, a metal ink can be prepared by mixing metal particles, a branched polyether polyol, a dispersion medium, and a dispersant as required. In order to disperse the constituents more uniformly, a known stirrer, mixer or the like may be used.

  The mixing order of the constituent components is not particularly limited. For example, some components may be mixed in advance, and the remaining components may be added and further mixed. Each component may be added at once, or may be added in multiple portions. Since the metal particles are solid, it is preferable to disperse them in a dispersion medium in advance. For example, a metal ink may be prepared by preparing a metal colloid by coordinating a dispersant to metal particles and dispersing the metal colloid in a dispersion medium.

[Method for producing metal film]
The above metal ink is suitable for forming a low resistance metal film by firing.
The metal film can be produced, for example, by a production method including a step of forming the coating film by applying the metal ink to a substrate and a step of baking the coating film to form the metal film. Since the metal ink contains the branched polyether polyol, it is considered that the reducing action is exerted in a state where the metal ink is coordinated (or interacts) with the metal particles containing copper in the metal colloid. The branched polyether polyol used in the reduction reaction is oxidatively decomposed and removed in the firing step.

In the coating film forming step, metal ink is applied to the surface of the substrate. Application of the metal ink is not particularly limited, and can be performed by a known application method such as spin coating, spray coating, blade coating, screen printing, and ink jet.
The material of the substrate is not particularly limited, and examples thereof include glass, silicon, polyimide resin, aromatic polyester resin (polyethylene terephthalate, etc.), polycarbonate resin, and / or polystyrene resin.

The base material having the coating film obtained in the coating film forming step may be dried as necessary prior to the firing step. The drying conditions can be appropriately determined according to the constituent components of the metal ink. In the drying step, it is preferable to remove the dispersion medium.
The drying temperature is not particularly limited, and may be performed at a temperature at which the dispersion medium can be removed. The drying temperature is desirably lower than the firing temperature described later.

  In the firing step, the base material having the coating film obtained in the coating film forming step is fired. In general, metal particles containing copper are easily formed with an oxide film in the firing step. However, since the branched polyether polyol is contained in the metal ink, the action of the branched polyether polyol suppresses the formation of an oxide film in the firing step and can reduce the formed oxide film. It is done. Therefore, by firing, the metal particles are easily fused together, and the resistance of the resulting metal film can be greatly reduced.

Firing may be performed at, for example, 100 to 350 ° C or 150 to 350 ° C.
Firing can be performed in an inert gas atmosphere. Firing may be performed in the presence of a strong reducing agent such as hydrogen gas (specifically, in an atmosphere or under circulation). However, since a branched polyether polyol is used, a strong reducing agent such as hydrogen gas is used. Even if it is not used, a low-resistance metal film containing copper can be formed.
The firing time is not particularly limited, but may be, for example, 5 to 120 minutes.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Examples 1-10 and Comparative Examples 1-10
(1) Preparation of copper colloid 20 g of copper sulfate, 100 g of isobutanol, and 100 g of a dispersant (dodecylamine) were mixed. The mixture was heated until its temperature was 100 ° C. and then refluxed for 5 hours. The solid content in the obtained mixture was collected by sedimentation by centrifugation. The collected solid content was washed with methanol three times and then centrifuged to collect a copper colloid containing copper particles coordinated with dodecylamine. The mass ratio of the copper particles and dodecylamine coordinated to the copper particles was 100: 3. In Examples 6 to 10 and Comparative Example 8, the amounts of isobutanol and dodecylamine were 20 g, respectively.

(2) Preparation of Metal Ink A dispersion was prepared by dispersing the copper colloid recovered in (1) and the additive shown in Table 1 in 1-octanol using an ultrasonic disperser. The blending amount of each component was adjusted so that the content of the copper colloid in the dispersion was 40% by mass and the amount of the additive relative to 100 parts by mass of the solid content of the copper colloid was the value shown in Table 1. The dispersion was filtered using a membrane filter having a pore size of 1 μm, and the filtrate was recovered as metal ink.

  Metal ink was applied to the substrate by spin coating, and an SEM photograph of copper particles was taken. In this captured image, the average particle diameter of the copper particles was calculated by the method described above. The average particle diameter is shown in Table 1.

In addition, the additive used was as follows.
(A1) Polyol 3165 (manufactured by Perstorp, branched polyether polyol, number of branched chains 1, number of terminal hydroxy groups 3, Mw 1000)
(A2) Polyol 3610 (manufactured by Perstorp, branched polyether polyol, 1 branched chain, 3 terminal hydroxy groups, Mw280)
(A3) Polyol 4290 (manufactured by Perstorp, branched polyether polyol, number of branched chains 2, number of terminal hydroxy groups 4, Mw 800)
(A4) Polyol 4525 (manufactured by Perstorp, branched polyether polyol, number of branched chains 2, number of terminal hydroxy groups, Mw 430)
(A5) PEG300 (polyethylene glycol, 0 branched chains, 2 terminal hydroxy groups, Mw300)
(A6) PEG1000 (polyethylene glycol, 0 branched chains, 2 terminal hydroxy groups, Mw1000)
(A7) PEG2000 (polyethylene glycol, 0 branched chains, 2 terminal hydroxy groups, Mw2000)
(A8) PTMG1000 (polytetramethylene glycol, 0 branched chains, 2 terminal hydroxy groups, Mw1000)
(A9) PTMG1500 (polytetramethylene glycol, 0 branched chains, 2 terminal hydroxy groups, Mw1500)
(A10) Capa3091 (manufactured by Perstorp, polyester triol, number of branched chains 1, number of terminal hydroxy groups 3, Mw900)
(A11) EG (ethylene glycol, 0 branched chains, 2 terminal hydroxy groups, molecular weight 62.07)
(A12) GR (glycerin, number of branched chains 0, number of hydroxy groups 3, number of terminal hydroxy groups, molecular weight 92.09)

(3) Evaluation The following evaluation was performed using the metal ink obtained above.
(A) Dispersion stability After the metal ink was stored at 25 ° C. for 1 month, the presence or absence of precipitation was visually observed and evaluated according to the following criteria.
○: Precipitation is not confirmed.
X: Precipitation is confirmed.

(B) Volume resistance of metal film Metal ink was applied onto a glass substrate with a bar coater. The board | substrate with which the coating film was formed was baked by heating at 300 degreeC for 10 minute (s) in nitrogen atmosphere with the electric tubular furnace, and the board | substrate which has a metal film was produced. Then, the initial surface resistivity of the metal film was measured by a four-terminal method using a resistivity meter (Loresta GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
Separately, the film thickness (cm) of the metal film was measured using a commercially available contact film thickness meter. The volume resistivity (μΩ · cm) was determined from the initial sheet resistivity and the measured film thickness (cm).

The evaluation results are shown in Table 1 together with the compositions of the metal inks of Examples 1 to 10 and Comparative Examples 1 to 10. The volume resistivity exceeding 1 × 10 ⁷ μΩ · cm was indicated by OV. The measurement limit is 1 × 10 ⁹ μΩ · cm.

As shown in Table 1, in the comparative example, the volume resistivity of the metal film was an extremely high value exceeding 1 × 10 ³ μΩ · cm. On the other hand, in the examples, the volume resistivity of the metal film was 290 μΩ · cm or less, which was much lower than that of the comparative example. Thus, although the metal ink using the branched polyether polyol contains copper particles, the sinterability of the copper particles is improved, and a low-resistance metal film is obtained. Moreover, both the metal inks of Examples and Comparative Examples had high dispersion stability.

  The volume resistivity value is almost the same between the case where the amount of the branched polyether polyol is 10 parts by mass and the case where it is 2 parts by mass with respect to 100 parts by mass of the metal colloid. That is, it can be said that the reducing action of the branched polyether polyol is effectively exhibited only by using a small amount of the branched polyether polyol. Therefore, it is considered that the branched polyether polyol efficiently reduces the copper particles in a state where they are located in the vicinity of the copper particles and interact with each other (perhaps in a state where they are coordinated to the copper particles). In a comparative example using an additive having no linear polyol or polyether chain, a low-resistance metal film cannot be obtained. From this, compared with the additive of a comparative example, it is thought that the branched polyether polyol is in the state which is easy to act with respect to a metal particle, and it is estimated that the coordinating property is high.

  In general, the smaller the average particle diameter of the metal particles, the better the sinterability due to the nanoparticle effect. However, since the metal particles can be effectively reduced by using the branched polyether polyol, high sinterability is obtained even when the average particle diameter is as large as 500 nm, and a low-resistance metal film is formed. be able to.

  The metal ink according to the above aspect of the present invention can form a low-resistance metal film despite containing copper. Therefore, the metal ink is useful for various applications in which a low-resistance metal film is used, for example, for forming a circuit pattern such as a wiring board.

Claims (8)

A metal colloid, a polyether polyol having at least one branched chain, and a dispersion medium,
The at least one branched chain has at least one hydroxy group;
The metal contained in the metal colloid is a metal ink containing copper.   The metal ink according to claim 1, wherein the metal is at least one selected from the group consisting of a simple copper and a copper alloy.   The at least one hydroxy group among all the hydroxy groups contained in the polyether polyol is located at the end of at least one chain selected from the group consisting of the main chain of the polyether polyol and the branched chain. Item 3. The metal ink according to Item 1 or 2.   The metal ink according to claim 3, wherein at least one hydroxy group among all hydroxy groups contained in the polyether polyol is located at an end of the polyether chain.   The metal ink according to any one of claims 1 to 4, wherein the number of the branched chain in one molecule of the polyether polyol is 1 or more and 4 or less.   The metal ink according to claim 1, wherein the polyether polyol has a weight average molecular weight of 200 or more.   The amount of the said polyether polyol with respect to 100 mass parts of said metal colloids is a metal ink of any one of Claims 1-6 which is 15 mass parts or less. The metal colloid includes metal nanoparticles and a dispersant coordinated to the metal nanoparticles,
The metal ink according to any one of claims 1 to 7, wherein an average particle diameter of the metal nanoparticles is 100 nm or more and 700 nm or less.