Dispersant for conductive paste and conductive paste

Abstract

The present invention provides a dispersant for a conductive paste containing a component (A) represented by formula (1) and a component (B) represented by formula (2), wherein the content of the component (A) is 93-99.9 mass% and the content of the component (B) is 0.1-7 mass% with respect to the entire dispersant.　Formula (1): R1CO-NH-(R2)-OH (in formula (1), R1CO represents an aliphatic acyl group that has 6-22 carbon atoms and may have a hydroxy group, and R2 represents an alkylene group having at least 2 and no more than 3 carbon atoms).　Formula (2): R3CO-OH (in formula (2), R3CO represents an aliphatic acyl group having 6-22 carbon atoms).

Description

Dispersants for conductive pastes and conductive pastes

[0001] The present invention relates to a dispersant for a conductive paste and a conductive paste.

[0002] In recent years, the development of thinner and more miniaturized electronic circuits and electronic substrates has progressed in line with the trend toward smaller and lighter electronic devices. To meet this demand for thinner and more miniaturized electronic devices, printed electronics has been put to practical use. A widely used method for forming circuit wiring involves drawing a pattern on a conductive paste containing a binder resin and metals or other additives by screen printing or other methods, followed by curing the pattern by applying light or heat.

[0003] For the conductive pastes used in these methods, it is important to control the viscosity characteristics to enable continuous and stable circuit formation. Furthermore, in order to accommodate the recent trend of fine pattern drawing, importance is placed on the reduction of bleeding and rubbing to enable fine pattern formation, as well as on the adhesion to the substrate to be printed and the effect on the substrate during the printing process.

[0004] To address the above-mentioned issues, various methods have been proposed to improve the performance of conductive pastes. Ethyl cellulose is typically used as a binder resin, but it is known that the coating film obtained using ethyl cellulose has low strength, is subject to damage upon impact, and peels off from the substrate. To address this issue, proposals have been made to improve the strength and adhesion of the resulting coating film by using polyvinyl butyral resin, poly(meth)acrylic ester resin, or the like as a binder resin.

[0005] For example, Patent Document 1 proposes a conductive paste containing a polyvinyl acetal resin to achieve both excellent printability and surface smoothness. However, because this paste contains a polyvinyl acetal resin, it may become stringy, which may deteriorate the printability.

[0006] Furthermore, Patent Document 2 proposes a conductive paste that uses a butyral resin and ethyl cellulose as a binder resin in combination with a low-polarity organic solvent as a method for preventing short-circuit defects in multilayer ceramic electronic components and improving the printability of the paste. However, when using such a low-polarity organic solvent, there is a concern that the difference in polarity between the binder resin and the organic solvent may result in poor solubility of the binder resin in the organic solvent, which may deteriorate the dispersibility of the inorganic powder and reduce the printability of the paste. Therefore, dispersants for conductive pastes are required to have excellent solubility in various organic solvents.

[0007] In the proposals of Patent Documents 1 and 2, the desired paste properties can be achieved by changing the combination of binder resins, etc., but optimizing the combination requires extensive consideration. Therefore, there is a need for a dispersant that can achieve good paste properties simply by adding it to the paste.

[0008] JP 2021-80469 A JP 2005-243561 A

[0009] The present invention has been made in consideration of the above-described circumstances, and the problem to be solved by the present invention is to provide a dispersant that has excellent solubility in organic solvents used in conductive pastes, and that can improve the thixotropy of the conductive paste and the adhesion of the coating film (e.g., circuit wiring) obtained from the conductive paste.

[0010] [1] A dispersant for a conductive paste, comprising a component (A) represented by the following formula (1) and a component (B) represented by the following formula (2), wherein the content of the component (A) is 93% by mass or more and 99.9% by mass or less, and the content of the component (B) is 0.1% by mass or more and 7% by mass or less, based on the total amount of the dispersant. １ CO-NH-(R ２ )-OH... (1) (In formula (1), R １ CO represents an aliphatic acyl group having 6 to 22 carbon atoms which may have a hydroxy group, and R ２ represents an alkylene group having 2 to 3 carbon atoms.３ CO-OH... (2) (In formula (2), R ３ CO represents an aliphatic acyl group having 6 to 22 carbon atoms.) [2] R １ The dispersant according to [1], wherein CO is an aliphatic acyl group having 6 to 22 carbon atoms and a hydroxyl group. [3] A conductive paste containing the dispersant according to [1] or [2], a binder resin, an organic solvent, and metal particles. [4] The conductive paste according to [3], wherein, relative to 100 parts by mass of the metal particles, the content of the dispersant is 0.5 to 10 parts by mass, the content of the binder resin is 0.5 to 30 parts by mass, and the content of the organic solvent is 1 to 200 parts by mass. [5] The conductive paste according to [3] or [4], wherein the metal of the metal particles is at least one selected from the group consisting of nickel, copper, and silver.

[0011] The dispersant for conductive paste of the present invention has excellent solubility in organic solvents used in conductive pastes, and can improve the thixotropy of the conductive paste and the adhesion of the coating film obtained therefrom.

[0012] Hereinafter, embodiments of the dispersant for conductive paste of the present invention will be described in order. Note that the descriptions in this specification can be combined with each other unless it is clear that they cannot be combined. Furthermore, hereinafter, "dispersant for conductive paste" may be abbreviated as "dispersant," and "conductive paste" may be abbreviated as "paste."

[0013] <Dispersant> The dispersant of the present invention contains a component (A) represented by the following formula (1) and a component (B) represented by the following formula (2): R １ CO-NH-(R ２ )-OH... (1) (In formula (1), R １ CO represents an aliphatic acyl group having 6 to 22 carbon atoms which may have a hydroxy group, and R ２ represents an alkylene group having 2 to 3 carbon atoms. ３ CO-OH... (2) (In formula (2), R ３CO represents an aliphatic acyl group having 6 to 22 carbon atoms.) Component (A) and component (B) will be described below in order.

[0014] [Component (A)] Component (A) may be used alone or in combination of two or more. Examples of a mixture of two or more components (A) include R １ The CO may be a mixture of components (A) different in content.

[0015] R in formula (1) １ CO is an aliphatic acyl group having 6 to 22 carbon atoms which may have a hydroxyl group. Here, the "aliphatic acyl group which may have a hydroxyl group" refers to a hydrocarbon group contained therein (R １ ) means an acyl group which is an aliphatic hydrocarbon group which may have a hydroxy group. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. １ The number of carbon atoms in CO is preferably 10 or more and 20 or less. When the fatty acid acyl group has a hydroxy group, the bonding position of the hydroxy group is not particularly limited.

[0016] Examples of the aliphatic acyl group having 6 to 22 carbon atoms and optionally having a hydroxy group include a caproyl group, a 2-hydroxycaproyl group, a 3-hydroxycaproyl group, a 6-hydroxycaproyl group, a capryloyl group, a 2-hydroxycapryloyl group, a 3-hydroxycapryloyl group, an 8-hydroxycapryloyl group, a caprinoyl group, a 2-hydroxycaprinoyl group, a 3-hydroxycaprinoyl group, a 10-hydroxycaprinoyl group, a lauroyl group, a 2-hydroxylauroyl group, a 6-hydroxylauroyl group, a 12-hydroxylauroyl group, a myristoyl group, a 3-hydroxymyristoyl group, a palmitoyl group, a 2-hydroxypalmitoyl group, a 3-hydroxypalmitoyl group, a 16-hydroxypalmitoyl group, a stearoyl group, a 12-hydroxystearoyl group, and a ricinoleoyl group.

[0017] In one embodiment of the present invention, R １CO is preferably an aliphatic acyl group having a hydroxy group and having 6 to 22 carbon atoms, more preferably a 3-hydroxycaprinoyl group, a 6-hydroxylauroyl group, a 3-hydroxymyristoyl group, a 3-hydroxypalmitoyl group, a 12-hydroxystearoyl group, or a ricinoleoyl group, even more preferably a 12-hydroxystearoyl group or a ricinoleoyl group, and particularly preferably a 12-hydroxystearoyl group.

[0018] In another embodiment of the present invention, R １ CO is preferably a lauroyl group, a 12-hydroxystearoyl group, or a ricinoleoyl group, more preferably a lauroyl group or a 12-hydroxystearoyl group, and even more preferably a 12-hydroxystearoyl group.

[0019] R in formula (1) ２ represents an alkylene group having 2 to 3 carbon atoms, i.e., an ethylene group (—CH ２ CH ２ -), propylene group (-CH ２ CH (CH ３ ) - or -CH(CH ３ ) CH ２ -), or a trimethylene group (-(CH ２ ) ３ -). R ２ is preferably an ethylene group or a propylene group, more preferably an ethylene group.

[0020] From the viewpoint of the thixotropy of the paste and the adhesion of the coating film obtained from the paste, the content of component (A) relative to the entire dispersant of the present invention must be 93% by mass or more and 99.9% by mass or less, and this content is preferably 96% by mass or more and 99.5% by mass or less, and more preferably 97% by mass or more and 99% by mass or less.

[0021] The component (A) may be a commercially available product or may be produced by a known method. For example, a carboxylic acid (R １ CO—OH) or its derivatives and amines having a hydroxy group (NH ２ - (R ２Component (A) can be produced by reacting (A) with (A)--OH).

[0022] [Component (B)] Component (B) may be used alone or in combination of two or more. ３ CO is an aliphatic acyl group having 6 to 22 carbon atoms. Here, the "aliphatic acyl group" without the restriction that "may have a hydroxy group" refers to the hydrocarbon group contained therein (R ３ ) means an acyl group, which is an aliphatic hydrocarbon group having no hydroxy group.

[0023] Examples of the aliphatic acyl group having 6 to 22 carbon atoms include a caproyl group, a capryloyl group, a caprinoyl group, a lauroyl group, a myristoyl group, a palmitoyl group, a stearoyl group, an arachidoyl group, a behenoyl group, a 2-ethylhexanoyl group, an isopalmitoyl group, an isostearoyl group, a palmitoleoyl group, an oleoyl group, an elaidoyl group, a linoleoyl group, and a linolenoyl group.

[0024] R ３ CO is preferably an alkanoyl group having 6 to 22 carbon atoms, more preferably an alkanoyl group having 12 to 18 carbon atoms, even more preferably a lauroyl group or a stearoyl group, and particularly preferably a stearoyl group.

[0025] Examples of component (B) include linear saturated fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid; branched saturated fatty acids such as 2-ethylhexanoic acid, isopalmitic acid, and isostearic acid; and unsaturated fatty acids such as palmitoleic acid, oleic acid, elaidic acid, linoleic acid, and linolenic acid.

[0026] As described above, two or more types of component (B) can be used, and therefore, a mixture of fatty acids derived from animal and vegetable fats and oils, such as coconut oil fatty acid, palm kernel oil fatty acid, beef tallow fatty acid, and hardened beef tallow fatty acid, can also be used as component (B).

[0027] Component (B) is preferably lauric acid and / or stearic acid, more preferably lauric acid or stearic acid, and even more preferably stearic acid.

[0028] From the viewpoint of the thixotropy of the paste and the adhesion of the coating film obtained from the paste, the content of component (B) relative to the entire dispersant of the present invention must be 0.1% by mass or more and 7% by mass or less, and this content is preferably 0.5% by mass or more and 4% by mass or less, and more preferably 1% by mass or more and 3% by mass or less.

[0029] A variety of fatty acids are commercially available, and therefore, a commercially available product can be used as the fatty acid component (B).

[0030] <Paste> The paste of the present invention contains the dispersant of the present invention, a binder resin, an organic solvent, and metal particles. Each of these components may be used alone or in combination of two or more.

[0031] The content of the dispersant of the present invention in the paste of the present invention is preferably 0.5 parts by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 8 parts by mass or less, and even more preferably 1.5 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the metal particles, from the viewpoints of the thixotropy of the paste and the adhesion of the coating film obtained from the paste.

[0032] [Binder Resin] The binder resin is not particularly limited, and known resins used in pastes can be used. For example, thermoplastic resins, photocurable resins, and thermosetting resins can be used. Examples of thermoplastic resins include cellulose-based resins such as methyl cellulose, ethyl cellulose, and hydroxyethyl cellulose. Examples of photocurable resins include poly(meth)acrylic acid-based resins, polyvinyl ether resins, urethane acrylate resins, epoxy acrylate resins, polyester acrylate resins, alicyclic epoxy resins, and glycidyl epoxy resins. Examples of thermosetting resins include polyurethane resins, epoxy resins, unsaturated polyester resins, furan resins, silicon resins, alkyd resins, amino resins, urea resins, and phenolic resins.

[0033] The binder resin is preferably a thermoplastic resin, more preferably ethyl cellulose.

[0034] As described above, a paste containing a polyvinyl acetal resin may have poor printability due to stringiness, and therefore the paste of the present invention preferably does not contain a polyvinyl acetal resin.

[0035] The content of the binder resin in the paste of the present invention is preferably 0.5 parts by mass or more and 30 parts by mass or less, more preferably 1 part by mass or more and 25 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the metal particles, from the viewpoints of the thixotropy of the paste and the adhesion of the coating film obtained from the paste.

[0036] [Organic Solvent] Examples of organic solvents (dispersion media for metal particles) include aromatic hydrocarbon solvents such as toluene and xylene, hydrocarbon solvents such as cyclohexane, ketone solvents such as acetone and methyl ethyl ketone, ester solvents such as ethyl acetate and n-propyl acetate, glycol ether solvents such as ethylene glycol monoethyl ether and ethylene glycol monoisopropyl ether, glycol ether ester solvents such as ethylene glycol monoethyl ether acetate and ethylene glycol monoisopropyl ether acetate, terpene solvents such as terpineol and dihydroterpineol, and alcohol solvents such as methanol, ethanol, and n-propanol. Among these, terpene solvents are more preferred, and dihydroterpineol is even more preferred.

[0037] From the viewpoint of the thixotropy of the paste and the adhesion of the coating film obtained from the paste, the content of the organic solvent in the paste of the present invention is preferably 1 part by mass or more and 200 parts by mass or less, more preferably 5 parts by mass or more and 180 parts by mass or less, and even more preferably 10 parts by mass or more and 150 parts by mass or less, per 100 parts by mass of the metal particles.

[0038] [Metal Particles] Examples of the metal of the metal particles include nickel, cobalt, palladium, copper, silver, gold, platinum, etc. From the viewpoint of the conductivity of the coating film obtained from the paste, the metal is preferably at least one selected from the group consisting of nickel, copper, and silver, and more preferably nickel.

[0039] From the viewpoints of the printability of the paste and the electrical properties of the coating film obtained from the paste, the number-average particle diameter of the metal particles in the paste is preferably 0.01 to 10 μm, more preferably 0.01 to 5 μm, and even more preferably 0.01 to 1 μm. The number-average particle diameter can be measured by dynamic light scattering in accordance with the particle size analysis - dynamic light scattering method described in JIS Z8828.

[0040] [Other Components] The paste of the present invention may contain other components different from the dispersant of the present invention, the binder resin, the organic solvent, and the metal particles described above. The other components may be used alone or in combination of two or more.

[0041] Examples of other components include inorganic fillers other than metal particles (hereinafter sometimes abbreviated as "other inorganic fillers"). Examples of other inorganic fillers include oxides such as zirconium oxide, magnesium oxide, aluminum oxide, iron oxide, zinc oxide, indium tin oxide, and titanium oxide, and titanate compounds such as barium titanate, calcium titanate, and strontium titanate. From the viewpoints of heat resistance and thermal conductivity, the other inorganic filler is preferably aluminum oxide and / or barium titanate, and more preferably barium titanate.

[0042] From the viewpoints of printability of the paste and electrical properties of a coating film obtained from the paste, the number average particle diameter of the other inorganic filler is preferably 0.01 to 10 μm, more preferably 0.01 to 5 μm, and even more preferably 0.01 to 1 μm. The number average particle diameter can be measured by dynamic light scattering in accordance with particle size analysis—dynamic light scattering method described in JIS Z8828.

[0043] When another inorganic filler is used, the content thereof in the paste of the present invention is preferably 1 part by mass or more and 100 parts by mass or less, more preferably 5 parts by mass or more and 90 parts by mass or less, and even more preferably 10 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of metal particles, from the viewpoints of the thixotropy of the paste and the adhesion of the coating film obtained from the paste.

[0044] Next, the present invention will be described in more detail with reference to examples and comparative examples.

[0045] (Component (A) and Component (B)) R of component (A) used in the following examples and comparative examples １ CO and R ２ and R of component (B). ３ CO is as shown in Tables 1 and 2 below. ３CO is an "aliphatic acyl group having a hydroxy group" and R in formula (2) ３ Since it is not CO (that is, an "aliphatic acyl group" having no hydroxy group), component (B-3) is not component (B) in the dispersant of the present invention.

[0046]

[0047]

[0048] Component (A-1) is a reaction product of 12-hydroxystearic acid and monoethanolamine. Component (A-2) is a reaction product of ricinoleic acid and monoethanolamine. Component (A-3) is a reaction product of lauric acid and isopropanolamine.

[0049] Component (B-1) is stearic acid, component (B-2) is lauric acid, and component (B-3) is 12-hydroxystearic acid.

[0050] (Dispersant) In Examples 1 to 5, dispersants were prepared by mixing any one of components (A-1) to (A-3) with component (B-1) or (B-2) in the amounts shown in Table 3 below. In Comparative Example 1, component (A-1) was used as the dispersant. In Comparative Example 2, components (A-1) and (B-1) were mixed in the amounts shown in Table 3 below to prepare a dispersant. However, in Comparative Example 2, component (B-1) was used in excess. In Comparative Example 3, components (B-1) and (B-3) were mixed in the amounts shown in Table 3 below to prepare a dispersant. In Comparative Example 4, xanthan gum was used as the dispersant.

[0051] (Solubility of Dispersant) The solubility of the obtained dispersant was evaluated as follows. Specifically, 2.5 g of dispersant was weighed into a 100 mL screw tube, and then diluted 20 times with 47.5 g of organic solvent. The mixture was stirred at 60°C for 10 minutes using a stirrer tip. After stirring, the mixture was cooled to room temperature and the appearance of the mixture was visually evaluated, and the solubility of the dispersant was evaluated according to the following criteria. Ethanol, toluene, terpineol, dihydroterpineol, or methyl ethyl ketone was used as the organic solvent. The results are shown in Table 3 below. <Criteria> ○: The mixture of dispersant and organic solvent is a uniform, transparent solution. ×: The appearance of the mixture of dispersant and organic solvent is non-uniform, cloudy, or separated.

[0052] (Paste) Using the obtained dispersant, Ni paste was prepared. Specifically, in a 50 mL screw tube, Ni powder (product name: NFP201S, manufactured by JFE Mineral Co., Ltd., number average particle size: 0.2 μm) 11.5 g, barium titanate (product name: BT-01, manufactured by Sakai Chemical Industry Co., Ltd., number average particle size: 0.5 μm) 2.3 g, dihydroterpineol 1.3 g, ethyl cellulose (product name: ETHOCEL STD4, manufactured by The Dow Chemical Company) 1.2 g and dispersant 0.2 g were weighed, and a slurry Ni paste was obtained using a three-roll mill.

[0053] (Thixotropy of Paste) Viscosity measurements were performed using the above-mentioned Ni paste to evaluate the thixotropy. Using a dynamic viscoelasticity measuring device (product name: MCR 302, manufactured by Anton-Paar), the viscosity of the Ni paste was measured at a temperature of 20°C and a rotation speed of 10 rpm or 100 rpm (hereinafter, the viscosities measured at a rotation speed of 10 rpm or 100 rpm will be referred to as the "10 rpm viscosity" or "100 rpm viscosity," respectively). The viscosity ratio was calculated using the following formula: Viscosity ratio = 10 rpm viscosity (Pa·s) / 100 rpm viscosity (Pa·s), and the thixotropy was evaluated according to the following criteria. The results are shown in Table 3 below. <Criteria> ◎: Viscosity ratio is 1.8 or more ○: Viscosity ratio is 1.6 or more but less than 1.8 ×: Viscosity ratio is less than 1.6

[0054] (Adhesion of Coating Film) The adhesion of the coating film was evaluated by a cross-cut peel test in accordance with the cross-cut method of JIS-K5600-5-6. Specifically, the above-mentioned Ni paste was uniformly applied to a copper plate using a bar coater to a film thickness of approximately 1 μm, and then heated on a hot plate heated to 150°C to form a coating film. Then, using a cutter knife, 11 vertical and 11 horizontal cuts were made in the coating film at 1 mm intervals in a checkerboard pattern, penetrating all the way to the copper plate, resulting in a total of 100 square grids. Sekisui Chemical Co., Ltd.'s adhesive tape No. 252 was applied thereon and pressed evenly with a spatula. The adhesive tape was then peeled off in a 180° direction, and the number of remaining grids of the coating film was measured and evaluated according to the following criteria. The results are shown in Table 3 below. <Criteria> ⊚: Number of remaining grids: 99 or more ◯: Number of remaining grids: 90 to 98 ×: Number of remaining grids: 89 or less

[0055]

[0056] (Evaluation Results) It was confirmed that the dispersants of Examples 1 to 5 have excellent solubility in various organic solvents, and that adding these to a conductive paste can improve the thixotropy of the conductive paste and the adhesion of a coating film (e.g., circuit wiring) obtained therefrom.

[0057] Compared to the dispersants of Examples 1 to 5, the dispersants of Comparative Examples 1 to 4 did not exhibit sufficient performance. The dispersant of Comparative Example 1 did not contain component (B), and therefore did not have good solubility in ethanol or methyl ethyl ketone. The dispersant of Comparative Example 2 had contents of components (A) and (B) outside the range of the present invention, and therefore did not have good solubility in ethanol or good coating film adhesion. The dispersant of Comparative Example 3 did not contain component (A), and therefore did not have good paste thixotropy or coating film adhesion. The dispersant of Comparative Example 4, which was xanthan gum, did not have good solubility in terpineol, dihydroterpineol, or toluene, and did not have good coating film adhesion.

[0058] A paste containing the dispersant of the present invention can form a coating film (e.g., circuit wiring) that is excellent in thixotropy and adhesion, and is therefore useful for forming circuit wiring and the like.

[0059] This application is based on Japanese Patent Application No. 2023-147200, the contents of which are incorporated in their entirety herein.

Claims

1. A dispersant for a conductive paste, comprising a component (A) represented by the following formula (1) and a component (B) represented by the following formula (2), wherein the content of the component (A) is 93% by mass or more and 99.9% by mass or less, and the content of the component (B) is 0.1% by mass or more and 7% by mass or less, based on the total content of the dispersant. １ CO-NH-(R ２ )-OH... (1) (In formula (1), R １ CO represents an aliphatic acyl group having 6 to 22 carbon atoms which may have a hydroxyl group; and R ２ represents an alkylene group having 2 to 3 carbon atoms. ３ CO-OH... (2) (In formula (2), R ３ CO represents an aliphatic acyl group having 6 to 22 carbon atoms.

2. R １ 2. The dispersant according to claim 1, wherein CO is an aliphatic acyl group having 6 to 22 carbon atoms and a hydroxyl group.

3. A conductive paste comprising the dispersant according to claim 1 or 2, a binder resin, an organic solvent, and metal particles.

4. A conductive paste as described in claim 3, wherein the content of the dispersant is 0.5 parts by mass or more and 10 parts by mass or less, the content of the binder resin is 0.5 parts by mass or more and 30 parts by mass or less, and the content of the organic solvent is 1 part by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the metal particles.

5. The conductive paste according to claim 3, wherein the metal of said metal particles is at least one selected from the group consisting of nickel, copper and silver.

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