Metal paste

Abstract

The present invention relates to a metal paste for forming metal wiring, which is formed by kneading a solid component composed of silver particles in a solvent. The solid component of the metal paste has a predetermined particle size distribution and average particle size and is composed of silver particles with an amine compound as a protective agent. The solvent is a mixed solvent formed by mixing two organic solvents, solvent A and solvent B. Solvent A is dihydroterpineol or terpineol, and solvent B is at least one organic solvent having a boiling point of 240°C or higher. Furthermore, the Hansen solubility parameter distance Ra of the mixed solvent relative to dihydroterpineol is 3.0 MPa. 1 / 2 The metal paste further comprises high molecular weight ethyl cellulose as a first additive and polyvinyl acetal resin as a second additive. The metal paste of the present invention can form metal wiring having excellent printability, continuous printability, and good adhesion.

Description

Technical Field

[0001] The present invention relates to a metal paste comprising silver particles dispersed in a solvent. Specifically, the present invention relates to a metal paste comprising silver particles having a predetermined average particle size and particle size distribution as a solid component, exhibiting excellent low-temperature sintering properties, and exhibiting excellent printability, enabling the formation of metal wiring in a designed pattern and line width. Furthermore, the present invention relates to a metal paste exhibiting excellent continuous printability and capable of forming wiring with excellent adhesion to a substrate. Background Art

[0002] In the formation of metal wiring for LED components and power semiconductor components for display light sources such as PCs, smartphones, and tablet terminals, the use of metal paste (metal ink), which is formed by dispersing metal particles in a solvent, has been expanding in recent years. Metal paste can be easily applied to efficient pattern forming technologies such as screen printing, and can cope with the formation of fine wiring patterns. For these reasons, it is expected that the wiring formation process using metal paste printing will replace the photoresist method, plating method, etc. that have been the mainstream so far.

[0003] As a metal paste suitable for such wiring formation purposes, the applicant of the present application has disclosed a metal paste containing silver nanoparticles of a prescribed composition (Patent Document 1). If the metal particles are nano-scale microparticles of less than tens of nm, the melting point will show a significant decrease compared to the bulk material. The metal paste of the applicant of the present application uses silver nanoparticles whose average particle size and particle size distribution are controlled by utilizing this phenomenon as a metal component, and can form wiring at low temperatures. In addition, the previous metal paste contains high molecular weight ethyl cellulose as an additive. The metal paste is required to have printability that allows the metal particles to be transferred to the substrate in a manner faithful to the designed fine wiring pattern shape. In this regard, the metal paste formed by simply dispersing metal nanoparticles in a solvent lacks printability and sometimes forms wiring including bleeding and disconnection. The metal paste of the applicant of the present application mentioned above optimizes the rheological properties of the metal paste by adding high molecular weight ethyl cellulose, thereby achieving improved printability. Moreover, through these compositions, the metal paste of the applicant of the present application can fully cope with the wiring formation process for the above-mentioned various purposes.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6491753 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, in the wiring patterns of electronic devices such as LED elements, there is a demand for further narrowing of the wiring width and increasing complexity of the shape. Specifically, the wiring width, which has been set to more than 100 μm so far, is required to be less than 100 μm, and even around 50 μm may be achievable in the future.

[0009] Regarding the metal paste's ability to cope with such narrowed and complex wiring patterns, the metal paste of the applicant of the present application can also cope to some extent, but it is difficult to say that it is sufficient. For example, from the perspective of the narrowing of the wiring width, it has been confirmed that even the metal paste of the applicant of the present application sometimes forms wiring that is slightly wider than the design value. In this application, the ability to form wiring with the designed line width is defined as printability. Regarding subsequent metal pastes, metal pastes with excellent printability are required, and it has been confirmed that the metal paste of the applicant of the present application also has room for improvement.

[0010] While it is possible to address the narrowing and complexity of wiring patterns through improvements in printing technology, such as improvements in printing machines, improvements in metal pastes containing metal particles, which are precursors to wiring, are essential.

[0011] While improving the printability of metal pastes is crucial, changes to the metal paste's composition must be made without compromising the required properties. Specifically, the low-temperature sinterability and printability of the metal pastes described above by the applicants of this application are essential. When improving metal pastes, these fundamental required properties must be maintained.

[0012] Furthermore, in the manufacturing process of wiring substrates for mass-produced electrical / electronic devices, it is necessary to continuously and stably form the same wiring pattern. Furthermore, the temporarily formed wiring pattern must maintain a state of good adhesion to the substrate. Since it is expected that the narrowing of the wiring pattern will affect continuous printing and adhesion to the substrate, it is also necessary to consider the balance between these when improving printability.

[0013] The present invention has been completed based on the above background. The present invention provides a metal paste for forming wiring that contains metal particles composed of silver particles as a solid component. The paste is capable of forming wiring with a designed line width and pattern, while minimizing the wiring width. Furthermore, the present invention provides a metal paste that exhibits excellent printability, ensures continuous printability, and maintains good adhesion of the wiring.

[0014] Methods used to solve problems

[0015] The printing depictability of the metal paste as the subject of the present invention is evaluated by the deviation width of the wiring formed relative to the size of the design width. The inventor, while evaluating the printing depictability of the metal paste of the applicant of the above-mentioned application, carried out preliminary tests on the main reason that its printing depictability reduces. As a result, it was found that the printing depictability of the metal paste is greatly affected by the solvent. Moreover, the inventor set out from the research on the solvent that can improve the printing depictability, and found that it is effective to use dihydroterpineol (menthol) or terpineol as solvent. Particularly dihydroterpineol can be said to be the best solvent, thus confirmed that the printing depictability can be made good. About the content of the preliminary test carried out by the inventor, it will be described later, but in the wiring pattern formation of the metal paste using dihydroterpineol as solvent, it was confirmed that the deviation width becomes minimal relative to the design width.

[0016] However, while improvements in printability were observed in metal pastes using dihydroterpineol and other solvents, these effects were short-lived, and repeated printing resulted in blurred wiring patterns, leading to the conclusion that continuous printability was insufficient. Furthermore, no improvement in wiring adhesion was observed with any solvent, including dihydroterpineol.

[0017] Therefore, the present inventors have considered that the problems of printability and continuous printing properties can be solved by a solvent, but on the other hand, other means should be applied to improve adhesion.

[0018] (I) Improvement of printing properties and continuous printing properties using solvents

[0019] As mentioned above, dihydroterpineol is the best solvent that can be said to be in printing depiction property, but continuous printability is poor.Dihydroterpineol makes the deviation width extremely small and the reason that improves depictability is still unclear.As the hypothesis of the inventor, think that dihydroterpineol etc. become the buffer agent, the protective agent of silver particles (and protective agent thereof), suppress excessive expansion when printing by the interaction of solvent and silver particles, but be uncertain.On the other hand, as one of main causes that dihydroterpineol makes continuous printability reduce, it is inferred that it is the volatilization of the solvent in printing.If it is assumed that the reduction of continuous printability is the volatilization of solvent, then think that by mixing boiling point than their high solvent in dihydroterpineol etc., the boiling point of solvent whole body is risen, can realize the improvement of continuous printability.

[0020] However, it is predicted that when other solvents are mixed with dihydroterpineol, the drawing properties based on dihydroterpineol will decrease. In preliminary experiments by the present inventors, when solvents other than dihydroterpineol are used, there is a tendency for the deviation width to increase overall. Therefore, it is not preferred to use a mixed solvent that is only used to adjust the boiling point. Therefore, the present inventors believe that if the main reason for improving the printing drawing properties is the interaction between the solvent and the silver particles, then a solvent that can exert similar interactions as dihydroterpineol should be formed.

[0021] Here, as a direction for forming a solvent with properties close to those of dihydroterpineol, the inventors conducted research based on Hansen Solubility Parameters. Hansen Solubility Parameters (hereinafter sometimes referred to as HSP) are one of the methods for specifying the solubility parameters of a solvent (solvent). HSP is a vector that is expressed in three-dimensional space by dividing the so-called Hildebrand Solubility Parameter (SP value) into three components: dispersion term (δd), polar term (δp), and hydrogen bonding term (δh). HSP is usually introduced to estimate the affinity between a solvent and a solute, and is used to estimate the extent to which a certain solvent can dissolve a certain solute. In this regard, in the metal paste that is the object of the present invention, the metal particles (silver nanoparticles) are in a state of dispersion in the solvent and will not dissolve in the solvent. However, regarding the behavior generated between the solvent and the metal particles, it is believed that solvents with similar HSPs show similar behavior to each other. In particular, it was found that the metal particles of the applicant of this application were previously protected by a specified organic compound (amine compound). Therefore, HSP is useful for examining the behavior between the solvent as an organic compound and the metal particles.

[0022] Furthermore, based on studies based on HSP, the present inventors have found that a mixed solvent having a boiling point above a predetermined temperature and having an HSP distance Ra relative to dihydroterpineol below a predetermined value by mixing has excellent printability and continuous printing properties.

[0023] (II) Improvement of wiring adhesion

[0024] As mentioned above, printability and continuous printability can be improved by applying an appropriate mixed solvent. On the other hand, with regard to adhesion, improvement by solvents cannot be expected. Therefore, as a means of improving the adhesion of metal paste, the present inventors applied a new additive to the prior art. In this regard, in the previous metal paste of the applicant of the present application, high molecular weight ethyl cellulose was added as an additive for improving printability. In addition, in order to further improve the thixotropy of the metal paste, low molecular weight ethyl cellulose (number average molecular weight 10,000 to 25,000) was optionally added. The present inventors conducted research based on this prior art and found that the use of high molecular weight ethyl cellulose is necessary due to basic printability, but by applying polyvinyl acetal resin as a new additive instead of low molecular weight ethyl cellulose, an improvement in adhesion can be observed.

[0025] Through the above-described methods, the inventors discovered solutions for improving printability and continuous printing properties and improving wiring adhesion, respectively, and thus conceived the present invention. Specifically, the present invention is a metal paste formed by kneading a solid component composed of silver particles bonded with a protective agent in a solvent, wherein the solid component is composed of silver particles containing, by number of particles, at least 30% of silver particles having a particle size of 100 to 200 nm, and the average particle size of the silver particles as a whole is 60 to 800 nm. The protective agent bonded to the silver particles is at least one amine compound having 4 to 8 carbon atoms. The solvent is a mixed solvent formed by mixing at least two organic solvents selected from solvent A and solvent B, wherein solvent A is at least one of dihydroterpineol and terpineol, and solvent B is at least one organic solvent having a boiling point of 240°C or higher. The mixed solvent has a Hansen solubility parameter distance Ra relative to dihydroterpineol of 3.0 MPa. 1 / 2 Hereinafter, high molecular weight ethyl cellulose having a number average molecular weight of 40000 to 90000 is contained as a first additive, and polyvinyl acetal resin is contained as a second additive. Hereinafter, the metal paste of the present invention and a method for forming a metal wiring pattern using the same are described.

[0026] (A) Metal paste of the present invention

[0027] As described above, the metal paste of the present invention includes as essential components (1) a solid component composed of silver particles, (2) a solvent obtained by mixing solvent A and solvent B, and (3) first and second additives. These components of the metal paste of the present application will be described below.

[0028] (1) Silver particles

[0029] The metal paste of the present invention contains a solid component composed of silver particles, which serve as a precursor for metal wiring. Silver particles are used because silver is a metal with low resistivity, and its sintered form effectively functions as a conductive film. Silver also has the advantage of excellent thermal conductivity, making metal pastes based on silver effective as bonding materials and thermal conductive materials for the manufacture of high-current, high-temperature semiconductor devices, such as power devices.

[0030] In the metal paste of the present invention, the number of silver particles with a particle size of 100 to 200 nm needs to be 30% or more based on the number of all silver particles. The metal paste for forming a wiring pattern requires low-temperature sintering properties that allow the metal particles to be sintered at low temperatures. In the present invention, the meaning of low-temperature sintering is intended to be sintering at 150°C or below. Moreover, in the present invention, silver particles with fine to medium particle sizes as described above contribute to low-temperature sintering. When the number ratio of silver particles with a particle size of 100 to 200 nm is less than 30%, sintering at low temperatures does not occur at all or is insufficient. Regarding the upper limit of the number ratio of silver particles with a particle size of 100 to 200 nm, the effect of the present invention is achieved even if it is 100%.

[0031] In the metal paste of the present invention, it is preferred that all silver particles contained in the paste have a particle size of 100-200 nm, i.e., a proportion of 100%, but this is not required. If the silver particles have a particle size of 100-200 nm or more, and more preferably, 50% or more, particles outside this particle size range may be present. For example, even a metal paste containing a mixture of silver particles with a particle size of 100-200 nm and fine silver particles with a particle size of 20-30 nm can be sintered at low temperatures below 150°C, and the resistance of the sintered body is low, as long as the proportion of silver particles with a particle size of 100-200 nm is at least 30%. Alternatively, a metal paste containing silver particles with a particle size of 100-200 nm and coarse silver particles with a particle size greater than 500 nm may be mixed. Generally, coarse silver particles greater than 500 nm (0.5 μm) will not sinter below 200°C. However, when silver particles having a particle size of 100 to 200 nm used in the present invention exist at a certain ratio or more, the entire silver particles including such coarse particles are sintered at a low temperature.

[0032] In the present invention, silver particles with a particle size of 100 to 200 nm may be mixed with finer or coarser silver particles. However, in the present invention, the average particle size (number average) of all silver particles is required to be 60 to 800 nm. If the average particle size is less than 60 nm, cracks are likely to form when the particles are sintered, resulting in decreased adhesion and increased resistance. If the average particle size is greater than 800 nm, sintering becomes difficult and the sintered body is prone to cracking.

[0033] In the paste of the present invention, silver particles are dispersed in a solvent while protected by a protective agent. The protective agent is a compound that bonds to a portion or the entire surface of the metal particles suspended in the solvent, inhibiting aggregation of the metal particles. This protective agent is associated with the sintering properties of silver particles with a particle size of 100 to 200 nm.

[0034] In the present invention, the protective agent bonded to the silver particles is an amine compound having 4 to 8 carbon atoms. The protective agent used in the present invention is limited to an amine compound because, when a protective agent other than an amine is used, sintering of the silver particles at low temperatures is difficult to occur. Furthermore, the amine compound used as the protective agent is limited to 4 to 8 carbon atoms because, depending on the particle size of the silver particles, the carbon number of the amine affects the stability and sintering characteristics of the silver particles. Amines with fewer than 4 carbon atoms have difficulty stably maintaining silver particles with a particle size of 100 nm or greater, making it difficult to form a uniform sintered body. On the other hand, amines with more than 8 carbon atoms tend to excessively increase the stability of the silver particles, leading to higher sintering temperatures. Therefore, the protective agent used in the present invention is limited to an amine compound having 4 to 8 carbon atoms.

[0035] Furthermore, the amine compound is preferably one with a boiling point of 220° C. or lower. Silver particles bound with an amine compound having a boiling point higher than 220° C. will have difficulty separating the amine compound during sintering, hindering sintering, even if the particle size is within an appropriate range.

[0036] Regarding the number of amino groups in the amine compound used as a protective agent, (mono)amines having one amino group and diamines having two amino groups can be used. Furthermore, the number of hydrocarbon groups bonded to the amino groups is preferably one or two, that is, primary amines (RNH2) or secondary amines (R2NH) are preferred. Furthermore, when using a diamine as a protective agent, it is preferred that at least one of the amino groups is a primary or secondary amine. The hydrocarbon group bonded to the amino group may be a linear or branched hydrocarbon or a cyclic hydrocarbon group. Furthermore, it may contain oxygen in part.

[0037] Preferred specific examples of the protective agent used in the present invention include butylamine, isobutylamine, 1,4-diaminobutane, 3-methoxypropylamine, pentylamine, neopentylamine, 2-methylbutylamine, 2,2-dimethylpropylamine, 3-ethoxypropylamine, N,N-dimethyl-1,3-propylenediamine, hexylamine, 3-isopropoxypropylamine, heptylamine, benzylamine, N,N-diethyl-1,3-diaminopropane, octylamine, and 2-ethylhexylamine, each having 4 or more carbon atoms. The protective agent may contain only one amine compound or multiple amine compounds. When multiple amine compounds are used as the protective agent, they may all be amine compounds having 4 or more and 8 or less carbon atoms.

[0038] Regarding the amount of protective agent (amine compound) in the paste of the present invention, the balance between the nitrogen concentration and the silver concentration in the paste is important. Specifically, the ratio of nitrogen concentration (mass %) to silver particle concentration (mass %) (N (mass %) / Ag (mass %)) is preferably 0.0001 to 0.015. If it is less than 0.0001, the protective effect on the silver particles is insufficient, while if it is greater than 0.015, the sintered body may crack. It should be noted that the nitrogen concentration in the metal paste can be measured by elemental analysis of the paste (such as CHN analysis), and the silver particle concentration can be easily determined from the mass of silver particles and the amount of solvent used in paste production.

[0039] (2) Solvent (mixed solvent)

[0040] As described above, the metal paste of the present invention uses a mixed solvent of solvent A and solvent B as a solvent for dispersing silver particles to improve drawing properties and continuous printing properties. Furthermore, the mixed solvent is optimized for the HSP distance Ra based on dihydroterpineol.

[0041] (2-1) Solvent A

[0042] The essential solvent as solvent A is at least one of dihydroterpineol and terpineol. As described above, dihydroterpineol itself is a solvent with good drawing properties relative to the silver particles used in the metal paste of the present invention. Furthermore, although terpineol is not as good as dihydroterpineol, it has good drawing properties. Therefore, these are essential as solvent A of the present invention.

[0043] It should be noted that dihydroterpineol (menthol) has the structural isomer of α, β, and terpineol has the structural isomer of α, β, γ, which can be any structure or the material formed by structural isomer mixing. In addition, solvent A can be dihydroterpineol, terpineol independently, or they can be mixed. But, when solvent A is terpineol or the mixing of dihydroterpineol and terpineol, it is necessary to make the HSP distance Ra of dihydroterpineol below 3.0 in the mixed solvent with solvent B. It should be noted that the HSP distance Ra of terpineol relative to dihydroterpineol is 1.2MPa. 1 / 2 .

[0044] (2-2) Solvent B

[0045] The purpose of mixing solvent B with solvent A, which is composed of dihydroterpineol and the like, is to improve continuous printing properties while maintaining drawing properties. As a prerequisite, solvent B must be an organic solvent with a boiling point of 240°C or higher. This boiling point is higher than that of dihydroterpineol (boiling point 210°C) and terpineol (boiling point 219°C). The high-boiling-point solvent B suppresses the volatilization of dihydroterpineol and the like, maintaining drawing properties, and also prevents changes in the solvent's state.

[0046] (i) Solvent B based on the Ra and chemical structure of HSP

[0047] According to the research of the present inventors, a preferred organic solvent as solvent B is an organic solvent having an HSP distance Ra of 3.0 MPa relative to dihydroterpineol. 1 / 2 The following organic solvents contain two or more ester groups in their structure.

[0048] As a specific selection criterion for solvent B, the HSP distance Ra between the organic solvent and dihydroterpineol should be given priority. This is because dihydroterpineol is a solvent constituting solvent A and serves as a criterion for the HSP distance Ra of the mixed solvent (3.0 MPa 1 / 2 Furthermore, the solvent B of the present invention preferably has an HSP distance Ra of 3.0 MPa relative to dihydroterpineol. 1 / 2 the following.

[0049] Here, we will explain the HSP distance Ra. HSP is a parameter defined by three components for various organic solvents: the dispersion term δd, the polar term δp, and the hydrogen bonding term δh. Organic solvents have unique HSPs depending on their structure. The HSP distance Ra, based on dihydroterpineol, can be calculated using the following formula.

[0050] [Mathematical formula 1]

[0051] Ra=((4×(δd D -δd B ) 2 +(δp D -δp B ) 2 +(δh D -δh B ) 2 ) 1 / 2

[0052] δd D ,δp D ,δh D :δd,δp,δh of dihydroterpineol (16.7,3.5,6.7)

[0053] δd B ,δp B ,δhB : δd, δp, δh of solvent B

[0054] Moreover, the preferred solvent B in the present invention is one having an HSP distance Ra of 3.0 MPa with dihydroterpineol. 1 / 2 The following solvents. This is because if Ra is greater than 3.0MPa 1 / 2 When a solvent of the type B is mixed as solvent B, the distance Ra between the HSP of the mixed solvent and dihydroterpineol tends to increase. As a result, the drawing properties of the metal paste are reduced, and it may be difficult to form wiring with the designed line width and pattern. The Ra of solvent B is preferably 2.0 MPa. 1 / 2 It should be noted that the lower limit of Ra is preferably 1.0 MPa. 1 / 2 above.

[0055] In addition, the solvent B preferably has a Hildebrand solubility parameter, i.e., a SP value, of 8.5 (cal / cm3). 1 / 2 Above and 9.5 (cal / cm3) 1 / 2 The following organic solvents. The HSP represented by the dispersion term δd, polar term δp, and hydrogen bonding term δh is a vector related to the solubility parameter of the solvent. The Hildebrand solubility parameter (SP) value corresponds to the length of this vector. The SP value of solvent B can be calculated using the following formula.

[0056] [Mathematical formula 2]

[0057] SP=(δd B 2 +δp B 2 +δh B 2 ) 1 / 2

[0058] δd B ,δp B ,δh B : δd, δp, δh of solvent B

[0059] For the above HSP distance Ra is 3.0 MPa 1 / 2 The following solvent B is considered to have a preferred SP value within the approximate range. In addition, considering the SP value of dihydroterpineol (8.94 (cal / cm3) used as a basis for calculating the HSP distance Ra of solvent B in the present invention, 1 / 2 ), it is considered that the SP value of solvent B is preferably within a certain range relative to the SP value of dihydroterpineol. Based on these reasons, the SP value of solvent B of the present invention is preferably within the above range.

[0060] Furthermore, the numerical ranges of the dispersion term δd, polar term δp, and hydrogen bonding term δh of the HSP of the solvent B in the present invention are preferably 15≤δd≤17, 2≤δp≤7, and 2≤δh≤10.

[0061] It should be noted that the numerical values ​​and calculation methods of the components of the dispersion term δd, polar term δp, and hydrogen bonding term δh used in calculations related to HSP are described, for example, in "INDUSTRIAL SOLVENT SHANDBOOK" (pp. 35-68, Marcel Dekker, Inc., published in 1996), "HANSEN SOLUBILITY PARAMETERS: A USER'S SHANDBOOK" (pp. 1-41, CRC Press, 1999), and "DIRECTORY OF SOLVENTS" (pp. 22-29, Blackie Academic & Professional, published in 1996). In addition, as a simpler research method, the values ​​in the database included in the calculation software "Hansen Solubility Parameters in Practice (HSPiP) Version 4.1.03" (Steven Abbott, Charles M. Hansen, Hiroshi Yamamoto) can be used. In addition, calculations can be performed based on the chemical structural formula of the solvent using the above calculation software.

[0062] Moreover, in addition to the selection criteria based on the HSP distance Ra mentioned above, solvent B is also selected from the perspective of chemical structure. That is, the preferred solvent B in the present invention is an organic solvent having at least two ester groups in its structure. The conditions related to the number of ester groups are based on the experimental results of the inventors. As for the reason for preferring organic solvents having ester groups, the inventors have considered that it is because they can impart appropriate polarity to the solvent molecules, which is effective for particle dispersion. On the other hand, solvent molecules having amino, alcohol, or carboxyl groups as polar groups act as surfactants and are adsorbed on the particle surface and printed substrate, which may change the original properties of the particles and substrate surface. In such a case, the wettability of the paste to the substrate becomes too good, which may result in the printed line width of the wiring significantly exceeding the designed line width. Therefore, it is speculated that as the polarity imparting group of the solvent molecule, an ester group that is not easily adsorbed is suitable. Moreover, the ester group is preferably more than 2. It should be noted that as the upper limit of the number of ester groups, an organic solvent with 5 or less is preferred.

[0063] Specific examples of the solvent B selected based on the above-mentioned Hansen solubility parameters and chemical structural factors include the following organic solvents.

[0064] [Chemical Formula 1]

[0065]

[0066] (ii) Other high boiling point solvents that can be used as solvent B

[0067] Regarding solvent B, even if the HSP distance Ra with dihydroterpineol is greater than 3.0 MPa 1 / 2 This is because the requirement of the present invention is that the Ra of the mixed solvent is 3.0 MPa. 1 / 2 The following conditions are met, therefore, the HSP distance Ra with dihydroterpineol is greater than 3.0 MPa 1 / 2 The organic solvent can also satisfy the criteria for a mixed solvent for a metal paste depending on the mixing ratio with dihydroterpineol.

[0068] Specific examples of the organic solvent in this case include texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate: known as the product name of Rixiang NG-120), butyl glycol acetate, etc. It should be noted that the HSP distance Ra with dihydroterpineol is greater than 3.0 MPa. 1 / 2 The upper limit of Ra of other high boiling point solvents that can become solvent B is preferably 5.5 MPa. 1 / 2 until.

[0069] (2-2) HSP distance Ra between mixed solvent and dihydroterpineol

[0070] The HSP distance Ra between the mixed solvent, which is the solvent of the metal paste of the present invention, and dihydroterpineol is set to 3.0 MPa. 1 / 2 The HSP distance Ra can be used to calculate the HSP of the mixed solvent (δd m ,δp m ,δh m ), according to the HSP of dihydroterpineol (δd D ,δp D ,δh D ) is calculated by the following formula 3. In addition, the HSP (δd m ,δp m ,δh m ) can be measured by the HSP of solvent A (δd A ,δp A ,δh A ) and HSP of solvent B (δd B ,δp B ,δh B ), and the mixing ratio of solvent A and solvent B (volume ratio: a, b (a+b=1)) are calculated by the following formula 4.

[0071] [Mathematical formula 3]

[0072] Ra=((4×(δd D -δd m ) 2 +(δp D -δp m ) 2 +(δh D -δh m ) 2 ) 1 / 2

[0073] δd D ,δp D ,δh D :δd,δp,δh of dihydroterpineol (16.7,3.5,6.7)

[0074] δd m ,δp m ,δh m :δd,δp,δh of mixed solvent

[0075] [Formula 4]

[0076] [δd m ,δp m ,δh m ]=[(a×δd A +b×δd B ),(a×δp A +b×δp B ),(a×δh A +b×δh B )]

[0077] δd m ,δp m ,δh m :δd,δp,δh of mixed solvent

[0078] δd A ,δp A ,δh A : δd, δp, δh of solvent A

[0079] δd B ,δp B ,δh B : δd, δp, δh of solvent B

[0080] a: Mixing ratio of solvent A, b: Mixing ratio of solvent B

[0081] It should be noted that when solvent A and / or solvent B is a mixed solvent (for example, when solvent A is a mixed solvent of dihydroterpineol and terpineol, etc.), the HSP of solvents A and B can be calculated using the same calculation method as in the above formula 4, and then the parameters of the mixed solvent can be calculated.

[0082] The smaller the HSP distance Ra value of the mixed solvent and dihydroterpineol, the better the printing and drawing properties of the metal paste, and the smaller the deviation width from the design width of the wiring. Therefore, the HSP distance Ra of the mixed solvent is more preferably 2.5 MPa. 1 / 2 Below. Including HSP distance Ra is 2.5MPa 1 / 2 The following mixed solvent metal paste has high printability regardless of the substrate material. As described later, as a substrate material, in addition to glass, there are resins such as PET and PEI, but glass substrates have a tendency to be difficult to ensure printability. By making the mixed solvent Ra 2.5MPa 1 / 2 Hereinafter, high printing properties can be ensured even for glass substrates. Moreover, the value of the HSP distance Ra of the mixed solvent is particularly preferably 1.0 MPa. 1 / 2 As a result, it is possible to achieve extremely high printing properties on all substrates. However, the material of the substrate to which the present invention can be applied should not be limited. In this regard, if the HSP distance Ra of the mixed solvent is 3.0 MPa 1 / 2 The following can demonstrate high printing and drawing properties on the resin substrate.

[0083] The mixing ratio of solvent A to solvent B is generally adjusted so that the HSP Ra of the resulting mixed solvent is within a reference value. As a standard, this mixing ratio is preferably set at a volume ratio of solvent A:solvent B = 0.08:0.92 to 0.52:0.48. Furthermore, when setting the mixing ratio by mass, solvent B is preferably mixed so that it comprises 10% to 50% by mass of the total mixed solvent.

[0084] (2-4) Mixing ratio of solid component and solvent (mixed solvent)

[0085] The metal paste of the present invention preferably has a solvent content of 5% to 60% by mass. If the content is less than 5%, the paste viscosity becomes too high. If the content is greater than 60%, it becomes difficult to obtain a sintered body of the required thickness. The solvent content is more preferably 25% to 40% by mass.

[0086] (3) Additives

[0087] (3-1) First additive

[0088] The metal paste of the present invention must contain high-molecular-weight ethyl cellulose as a first additive. High-molecular-weight ethyl cellulose, as an essential additive, optimizes the metal paste's rheological properties, such as viscosity and thixotropy, thereby improving fundamental printability. High-molecular-weight ethyl cellulose has a number-average molecular weight of 40,000 to 90,000, preferably 55,000 to 85,000. By using such high-molecular-weight ethyl cellulose, when forming a wiring pattern using the metal paste, silver particles can be transferred to a substrate for printing without causing paste adhesion to a squeegee or transfer defects.

[0089] The molecular weight of the ethyl cellulose is set to the above-mentioned high molecular weight in order to make the wiring resistance value of the silver particles after sintering appropriate. According to the research of the present inventors, when the number average molecular weight of the ethyl cellulose is too small, the resistance value after sintering sometimes becomes high. In addition, when the number average molecular weight of the high molecular weight ethyl cellulose is too high, it is difficult to obtain the effect of improving printability. Therefore, in addition to obtaining basic printability, the above-mentioned high molecular weight ethyl cellulose is also used in consideration of the resistance value of the sintered body.

[0090] The amount of high-molecular-weight ethyl cellulose added to the metal paste is preferably from 1.0% to 3.0% by mass relative to the total mass of the metal paste. If the amount is less than 1.0% by mass, the aforementioned effect of improving printability is difficult to achieve. If the amount is greater than 3.0% by mass, the resistance of the sintered body increases, potentially impairing its function as wiring or electrode.

[0091] (3-2) Second additive

[0092] The metal paste of the present invention also contains a polyvinyl acetal resin as a second additive. The second additive helps improve the adhesion between the metal film formed by sintering the silver particles and the substrate. The polyvinyl acetal resin used as the second additive is a resin having an acetal group, an acetyl group, and a hydroxyl group, as shown in the following formula 2.

[0093] [Chemical Formula 2]

[0094]

[0095] The polyacetal resins preferred as the second additive in the present invention are polyvinyl acetal (R=CH3) and polyvinyl butyral (R=C3H7). Furthermore, the polyacetal resin preferably has a hydroxyl content of 20 mol% to 40 mol% and an acetalization degree of 60 mol% to 75 mol%. Furthermore, the calculated molecular weight is preferably 1.0×10 4 Above and 13×10 4 the following.

[0096] In addition, the content of the polyacetal resin is preferably set to 10% by mass or more and 70% by mass or less relative to the content of the high molecular weight cellulose. This is because, when it is less than 10% by mass, it is difficult to obtain an effect of improving adhesion, and when it is greater than 70% by mass, it is impossible to obtain the viscoelastic properties required for metal pastes used in printing methods such as screen printing. The content of the polyacetal resin is more preferably set to 10% by mass or more and 50% by mass or less relative to the content of the high molecular weight cellulose.

[0097] (3-3) Other additives (optional additives)

[0098] The metal paste of the present invention must contain high molecular weight ethyl cellulose and polyacetal resin as additives, but additives other than these may be added as needed. As an optional additive, a binder composed of a polymer resin may be used. Examples of such polymer resins include polyester resins, polystyrene resins, polyethylene resins, acrylic resins, phenolic resins, polycarbonate resins, polyurethane resins, and epoxy resins. By adding such a binder to the metal paste of the present invention, it is possible to improve the adhesion to liquid crystal polymers. The binder is preferably contained in an amount of 0.8 to 2.5% by mass relative to the metal paste of the present invention, and particularly preferably 1.0 to 1.5%. However, the metal paste of the present invention has good adhesion to a variety of substrates, so the addition of a binder is not necessary. In addition, the present invention is a metal paste for forming thin film wiring and therefore does not contain glass frit, which has been used in certain thick film pastes in the past. In addition, the metal film that becomes the wiring is formed by the sintering action of silver nanoparticles and is thereby fixed to the substrate, so the metal paste does not contain an adhesive component.

[0099] (II) Method for producing the metal paste of the present invention

[0100] The metal paste of the present invention is produced by kneading a solid component containing 30% or more of the silver particles having a particle size of 100 to 200 nm and a first (and second) additive in a solvent.

[0101] In the present invention, a solid component composed of silver particles containing more than 30% silver particles with a particle size of 100 to 200 nm is used. Therefore, in the production of silver particles, the particle size and particle size distribution are controlled. The prior art (Patent Document 1) describes in detail the method for producing silver particles. A preferred method for producing silver particles is a thermal decomposition method using a silver complex as a precursor. The thermal decomposition method uses a thermally decomposable silver compound such as silver oxalate (Ag2C2O4) and silver carbonate (Ag2CO3) as a starting material, adds an amine compound as a protective agent to the compound to form a silver-amine complex that serves as a precursor of the silver particles, and heats the resulting silver particles.

[0102] Then, during the heating step of the reaction system containing the silver-amine complex, the amount of water in the reaction system is specified. Specifically, the amount is set to 5 to 100 parts by mass relative to 100 parts by mass of the raw silver compound. It is believed that this water acts as a buffer to ensure uniform heating during the decomposition step of the silver-amine complex. Furthermore, this buffering effect mitigates temperature differences within the reaction system during heating, while also promoting uniform nucleation and growth of the silver particles.

[0103] Furthermore, during the heating step of the silver-amine complex, a homogenizing agent, which is an organic compound having an amide backbone, is preferably added to adjust the particle size distribution. Examples of homogenizing agents include urea and urea derivatives, N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dimethylacetamide, N,N-dimethylpropionamide, and N,N-diethylacetamide.

[0104] The heating temperature (decomposition temperature) of the reaction system containing the silver-amine complex is preferably set to 90 to 130°C. In addition, the heating rate in the heating process is preferably adjusted within the range of 2.5 to 50°C / minute until the above-mentioned decomposition temperature is reached. Moreover, silver particles with an appropriate particle size distribution are precipitated through the heating process. The precipitated silver particles are recovered through solid-liquid separation and appropriately cleaned to become the solid component of the metal paste. It should be noted that, as a cleaning solvent, alcohols such as methanol, ethanol, and propanol are preferred. As mentioned above, dihydroterpineol is also used.

[0105] The recovered silver particles are mixed as a solid component with a solvent to prepare a metal paste. As for the solvent, the above-mentioned mixed solvent is used. The mixed solvent can be prepared by pre-mixing solvent A and solvent B, to which the solid component and the first and second additives are added simultaneously or sequentially. Alternatively, the silver particles can be pre-mixed with either solvent A or solvent B, and the mixture can be mixed with the other solvent. Similarly, the first and second additives can be added by pre-dissolving the additives in either solvent A or B. Furthermore, the additives can be pre-added to the reaction system containing the silver-amine complex formed during the production process of the silver particles.

[0106] (III) Method for forming a wiring pattern using the metal paste of the present invention

[0107] In the method for forming a wiring pattern using the metal paste of the present invention, the metal paste described above is applied to a substrate, and then a heat treatment is performed to sinter the silver particles.

[0108] The material, shape, and size of the substrate are not particularly limited. Examples of substrate materials include resin substrates such as glass and PET, as well as metal substrates and ceramic substrates. In the present invention, the addition of the second additive (polyvinyl acetal resin) makes it effective even for substrates such as glass that have a poor affinity for metals (silver).

[0109] The method for applying the metal paste is not particularly limited. In recent years, screen printing has been used to form fine wiring patterns. However, the method is not limited thereto and a dropwise application method using a coating member such as dipping, spin coating, a roll coater, or a scraper / blade may also be used.

[0110] After the metal paste is applied to the substrate in the target wiring pattern, it is sintered to form a metal film. The sintering treatment is carried out to sinter the silver particles and remove the protective agent components that may remain in the metal film. The sintering treatment is preferably carried out at a temperature of 40°C or above and 250°C. When the temperature is lower than 40°C, the detachment and volatilization of the protective agent takes a long time, so it is not preferred. In addition, when the temperature exceeds 250°C, deformation sometimes occurs depending on the material of the substrate. The metal paste of the present invention has excellent low-temperature sintering properties, so the upper limit of the sintering temperature can also be set to below 150°C. The sintering time is preferably 10 minutes or more and 120 minutes or less. It should be noted that the sintering process can be carried out in an atmospheric atmosphere or in a vacuum atmosphere.

[0111] By the firing process, the silver particles in the metal paste are bonded and sintered, thereby forming a metal wiring composed of a metal film having a desired pattern.

[0112] Effects of the Invention

[0113] The metal paste of the present invention achieves improved printability and continuous printing properties by imposing specific restrictions on the silver particle-dispersed solvent as a mixed solvent. The metal paste of the present invention enables the formation of wiring patterns that conform to the designed size and shape, enabling the production of increasingly narrow and complex wiring patterns. Furthermore, the metal paste of the present invention can be fired at low temperatures, enabling the formation of wiring patterns without damaging or degrading the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0114] Figure 1 The diagram shows the appearance of a wiring pattern used to evaluate the printability and continuous printability of a metal paste.

[0115] Figure 2 These are photographs showing the appearance of wiring printed using a metal paste using butyl glycol acetate and dihydroterpineol as solvents in a preliminary test.

[0116] Figure 3This is a photograph showing the appearance of wiring (solvent: dihydroterpineol) in which printing blurring occurred in the continuous printability evaluation test of the first embodiment. DETAILED DESCRIPTION

[0117] First embodiment :The following describes a preferred embodiment of the present invention. In this embodiment, first, as a preliminary study, various solvents (single solvent) are used to prepare metal pastes having the same composition as in the prior art, and their printability is confirmed. This preliminary study is used to confirm the deviation width of the formed wiring width from the designed width and to infer the main cause. Then, in this embodiment, while referring to the results of the above-mentioned preliminary study, a plurality of solvents are selected based on the Hansen solubility parameters to produce metal pastes, and their printability and continuous printability are evaluated.

[0118] Manufacturing of metal paste

[0119] First, silver particles having the particle size distribution of the present invention were produced by thermal decomposition. 102.2 g of silver carbonate (silver content 80.0 g) was added to 37.3 g of water (36.4% by weight relative to 100 parts by mass of silver carbonate) until wet, and the resulting mixture was used as a silver compound raw material. Then, 3-methoxypropylamine, an amine compound, was added to the silver compound in an amount six times the molar ratio relative to the mass of silver as a protective agent to produce a silver-amine complex.

[0120] To the silver-amine complex, a homogenizing agent (DMF) is further added while adjusting the water content. For the reaction system, the decomposition temperature is set to 130°C, and heating is started from room temperature (heating rate 10°C / min), and the silver-amine complex is decomposed at 130°C to precipitate silver particles. During heating, heating is continued until the generation of carbon dioxide stops. In this heating step, a liquid in which silver particles are suspended is obtained. Methanol is added to the reaction liquid for washing, centrifugation, and recovery of silver particles. The silver particles have an average particle size of 100 nm and contain more than 80% of silver particles of 100 to 200 nm based on the number of particles.

[0121] The silver particles obtained above are added to the solvent as a solid component, and a high molecular weight ethyl cellulose (ETHOCEL (registered trademark) STD100 (number average molecular weight 63420) manufactured by Dow Chemical Company) is further added as a first additive for mixing to make a metal paste. The content of the silver particles as a solid component is 70% by mass, and the content of ethyl cellulose (STD100) is 1.7% by mass relative to the entire metal paste. In this preliminary test, dodecyl alcohol ester (trade name: Rixiang NG-120), butyl glycol acetate, dihydroterpineol, and terpineol are used as solvents to manufacture four kinds of metal pastes with the same ratio. The solvents are all commercially available solvents. Commercially available dihydroterpineol and terpineol are presumed to be a mixture of structural isomers, but their ratio is not yet clear. In the present embodiment, as each parameter (δd, δp, δh) of the HSP of dihydroterpineol and terpineol, the value of the α-type compound is used to calculate the distance Ra, etc. The metal paste here consists of 70% solids (silver particles), 2% high molecular weight ethyl cellulose, and the remainder being solvent. It should be noted that in this preliminary experiment, no polyvinyl acetal resin was added in order to focus on the relationship between solvent and printability.

[0122] Confirmation of printing properties of conventional technology (preliminary test)

[0123] The metal paste was applied to a linear wiring pattern by screen printing. The metal paste was printed onto a glass substrate from a screen mask. Printing was performed using a screen printing device (LS-150 manufactured by Newland Precision Industry Co., Ltd.) with Figure 1 The screen mask with the pattern shown (design width of the straight line pattern is 50μm, 100μm, 200μm) was printed on the glass substrate at a printing speed of 50mm / second. Then, it was fired at 150℃ for 30 minutes to form a straight metal wiring. Then, the line width of the three types of wiring formed was measured and the average value was obtained to calculate the deviation width. The results of this preliminary test are shown in Table 1. In addition, Figure 2 A photograph showing the appearance of wiring formed using a metal paste containing butyl glycol acetate and dihydroterpineol as a solvent.

[0124] [Table 1]

[0125]

[0126] The results of these preliminary tests confirmed that, for metal pastes using the same solvent, the deviation width maintained a substantially constant value, regardless of the design width. While the deviation width varied depending on the solvent, the aforementioned tendency to maintain a constant value was consistent. Based on these results, the present inventors believe that solvent behavior is closely related to printability.

[0127] In addition, according to the preliminary test, it was confirmed that dihydroterpineol is the best solvent from the viewpoint of printing depictability. In addition, terpineol can be said to be a preferred solvent in terms of printing depictability after dihydroterpineol. Moreover, in the embodiment of the present application, as the pass or fail benchmark of printing depictability, it does not depend on the design width, and the deviation width is judged to be good (qualified=0) for being less than 20 μm for depictability. The benchmark for the pass or fail judgment is set to less than 20 μm based on the following investigation: with reference to terpineol, which is a well-known solvent and has a relatively good deviation width (on average about 12 to 13 μm) in the preliminary test; and considering the formation of wiring with a width less than 50 μm that may be required in the future, the deviation width needs to be less than half of its line width.

[0128] Preparation and Evaluation of Metal Paste of the Present Embodiment Using a Mixed Solvent

[0129] Based on the results of the preliminary tests, the present inventors prepared a metal paste using a mixed solvent of dihydroterpineol (Solvent A) and Solvent B as a solvent, and conducted evaluation.

[0130] Selection of solvent B

[0131] In this embodiment, the organic solvents listed in Table 2 are used as solvent B constituting a mixed solvent with solvent A. Table 2 shows the boiling point of the solvent, the components of the Hansen solubility parameter (dispersion term δd, polar term δp, hydrogen bonding term δh), the HSP distance Ra relative to dihydroterpineol, and the SP value of the HSP.

[0132]

[0133] The metal paste production process of this embodiment uses the same silver particles as in the preliminary experiment. After mixing the silver particles with solvent A, solvent B is added to the mixture to prepare the metal paste. Ethyl cellulose, the same substance as described above, was added as the first additive in the same amount. As the second additive, polyvinyl butyral resin (S-LEC BH-S, manufactured by Sekisui Chemical Co., Ltd.) was added at 33% by mass relative to the ethyl cellulose. These additives were added after mixing the silver particles with the respective solvents. The mixing ratio of solvent A to solvent B was set to 6:1 by mass (see Table 3 below for the mixing ratio by volume).

[0134] After preparing metal pastes using various solvents B, each metal paste was screen printed to evaluate the printability and continuous printing properties. In the printability evaluation test, the same printer as in the preliminary test was used. Figure 1The pattern was printed at a printing speed of 50 mm / s. After the metal paste was printed and applied, it was sintered at 150°C for 30 minutes to form metal wiring. To evaluate the printing traceability, the deviation width of all metal wirings (3 lines of 3 different widths) formed after the above printing process was measured. If the average deviation width was less than 20 μm relative to the design width, the traceability was determined to be "good (○)". On the other hand, if the average deviation width was greater than 20 μm, the traceability was determined to be "poor (×)".

[0135] In addition, in the evaluation test of continuous printability, a screen mask with 200 slits (wiring spacing 0.3 mm) with a line width of 20 μm (length 100 mm) was used as a wiring pattern. Then, 100 continuous printings were performed using each metal paste. The printing machine was the same as that of the preliminary test. Then, in the evaluation of continuous printability, the wiring of the 3rd, 20th, 40th, 60th, and 100th times was observed using an optical microscope image during the above-mentioned continuous printing process. In the observation after each printing, 3 wirings were randomly selected from the 200 printed wirings, and the full length was observed to confirm whether there were any broken wires. Then, if there were two or more broken wires in any of the selected wirings, it was judged that printing blurring had occurred. Then, the metal paste that did not produce printing blurring even in the 100th printing was evaluated as "good (○)" for continuous printability, and the metal paste that produced printing blurring before the 100th time was evaluated as "poor (×)" for continuous printability. Table 3 shows the results of the printing drawing properties and continuous printing properties obtained through the printing test.

[0136]

[0137] From Table 3, it was confirmed that the HSP distance Ra of the mixed solvent used in this embodiment with respect to dihydroterpineol was 1.0 MPa. 1 / 2 The metal pastes obtained in this manner exhibited extremely good printability (P-1 to P-7). Furthermore, the metal paste using a single solvent of dihydroterpineol (P-8) exhibited the best printability. However, the metal paste using a single solvent of dihydroterpineol exhibited poor continuous printability. Figure 3 The figure shows a photograph of blurred printing observed in wiring using paste P-8 (a single solvent containing dihydroterpineol). In a metal paste using only dihydroterpineol as a solvent, wiring breakage began to occur in multiple locations by the third print run, and by the 100th print run, islands of metal were scattered, resulting in blurred wiring. It should be noted that while lauryl alcohol ester (P-9), a conventional solvent for metal pastes, exhibited good continuous printing properties, its printability significantly deteriorated. This is consistent with the results of the preliminary tests described above.

[0138] Next, each metal paste was subjected to an evaluation test for adhesion to wiring. Adhesion was evaluated for Paste P-2 (Solvent B: tributyrin), Paste P-3 (Solvent B: triethyl acetyl citrate), and Paste P-8 (a single solvent containing dihydroterpineol), which are portions of the aforementioned metal pastes. For these three metal pastes, a metal paste without the addition of the polyacetal resin as a second additive was prepared for comparison.

[0139] In the evaluation test of adhesion, the same wiring pattern was printed (once) using the same screen printer as described above. The firing treatment after printing was carried out at firing temperatures of 60°C, 80°C, and 100°C for three patterns, and the adhesion of the metal wiring manufactured at each firing temperature was evaluated. For the metal paste without polyacetal resin as a comparative example, the firing temperature was only 100°C. Then, the evaluation of the adhesion of the wiring after printing was evaluated by a peeling test. In the peeling test, an adhesive tape (ASTM D3359 Cross Hatch Adhesion Test Tape) was pasted on the area where the wiring was formed on the substrate and then peeled off all at once. After the adhesive tape was peeled off, the situation where all the wiring did not peel off was judged as "good (0)" adhesion. In addition, even if one line peeled off, it was set as "poor (×)" adhesion. The evaluation results of the adhesion of the wiring are shown in Table 4.

[0140] [Table 4]

[0141]

[0142] Table 4 confirms that the addition of polyvinyl acetal resin as a second additive to the metal paste significantly improves the adhesion of the metal wiring. Furthermore, it can be seen that the adhesion of the metal wiring is good even at a relatively low firing temperature (60°C). The peel test of this embodiment is a test method that forcibly peels the metal film, resulting in a relatively strict assessment of adhesion, confirming that the polyacetal resin as a second additive can ensure the adhesion of the wiring even under these strict conditions.

[0143] Second embodiment In this embodiment, an organic solvent having a large HSP distance Ra relative to dihydroterpineol (Ra: greater than 3.0 MPa) is used to produce 1 / 2 ) as a metal paste of a mixed solvent of solvent B and evaluated. In addition, for the solvent B (Ra: 3.0 MPa) evaluated in the first embodiment 1 / 2 The organic solvents used in this embodiment are shown in Table 5.

[0144] [Table 5]

[0145]

[0146] *: Ra is the HSP distance relative to dihydroterpineol.

[0147] In this embodiment, the metal paste was also produced using the same process and configuration as in the first embodiment. Then, printing tests (evaluation of printability and continuous printability) and adhesion evaluation (peel test) were performed in the same manner as in the first embodiment. In this embodiment, in addition to the same glass substrates as in the first embodiment, PET substrates and PEI substrates were used as substrates, and the printability, etc. of each substrate material was evaluated (only adhesion was evaluated for the glass substrate). The dimensions and print patterns of each substrate were the same as in the first embodiment. The test results of each metal paste in this embodiment are shown in Table 6.

[0148]

[0149] The results of the preliminary test confirmed that lauryl alcohol ester is a solvent with poor printability as a single solvent. In addition, the same is true for Japanese MARS, whose HSP Ra is close to it. However, it is confirmed that these solvents can also become suitable mixed solvents by mixing with dihydroterpineol (solvent A) as solvent B. Regarding the HSP Ra of the mixed solvent adjusted by the mixing ratio of solvent B, it is known that if it is greater than 3.0 MPa 1 / 2 , then for any substrate material, the printing drawing properties are reduced. Regarding the Ra of the mixed solvent, if it is 2.5MPa 1 / 2 Below, it is effective for both glass substrates and resin substrates, but even at 3.0 MPa 1 / 2 The following also shows good drawing properties on resin substrates. Furthermore, from the perspective of HSP Ra, even if the mixing ratio of tributyrin and acetyl triethyl citrate, which are preferred solvents B, increases, the Ra of the mixed solvent does not increase significantly, showing excellent printing drawing properties and continuous printing properties. It should be noted that the addition of polyacetal resin also improves the adhesion of the wiring.

[0150] Industrial applicability

[0151] As described above, the silver paste of the present invention exhibits excellent drawing and continuous printing properties. The present invention also enables the accurate formation of wiring patterns with line widths of 100 μm or less. The present invention is suitable for forming electrodes and wiring for electrical and electronic devices such as LED elements and power semiconductor elements.

Claims

1. A metal paste comprising a solid component composed of silver particles bonded with a protective agent and kneaded in a solvent, characterized in that: The solid component is composed of silver particles containing 30% or more of silver particles having a particle size of 100 to 200 nm based on the number of particles, and the average particle size of the silver particles as a whole is 60 to 800 nm. The protective agent bonded to the silver particles is at least one of amine compounds having 4 or more and 8 or less carbon atoms. The solvent is a mixed solvent formed by mixing at least two organic solvents of solvent A and solvent B. The solvent A is at least one of dihydroterpineol or terpineol, The solvent B is at least one organic solvent having a boiling point of 240°C or above, The Hansen solubility parameter distance Ra of the mixed solvent relative to dihydroterpineol is 3.0 MPa 1 / 2 the following, Furthermore, the invention contains high molecular weight ethyl cellulose having a number average molecular weight of 40,000 to 90,000 as a first additive, and contains polyvinyl acetal resin as a second additive.

2. The metal paste according to claim 1, wherein The Hansen solubility parameter distance Ra of the mixed solvent relative to dihydroterpineol is 2.5 MPa 1 / 2 the following.

3. The metal paste according to claim 1 or claim 2, wherein Solvent B has a Hansen solubility parameter Ra of 3.0 MPa relative to dihydroterpineol. 1 / 2 The following organic solvents contain two or more ester groups in their structure.

4. The metal paste according to claim 3, wherein The Hildebrand solubility parameter SP value of solvent B is 8.5 (cal / cm 3 ) 1 / 2 Above and 9.5 (cal / cm 3 ) 1 / 2 the following.

5. The metal paste according to claim 3 or claim 4, wherein The Hansen solubility parameter distance Ra of the mixed solvent relative to dihydroterpineol is 1.0 MPa 1 / 2 the following.

6. The metal paste according to claim 1 or claim 2, wherein The Hansen solubility parameter distance Ra of solvent B relative to dihydroterpineol is greater than 3.0 MPa 1 / 2 .

7. The metal paste according to claim 6, wherein The solvent B is at least one of lauryl alcohol ester and butyl glycol acetate.

8. The metal paste according to any one of claims 1 to 7, wherein The content of the high-molecular ethyl cellulose as the first additive is 1.0% by mass or more and 3.0% by mass or less relative to the entire metal paste.

9. The metal paste according to any one of claims 1 to 8, wherein The content of the second additive is 10% by mass or more and 70% by mass or less relative to the content of the first additive.

10. The metal paste according to any one of claims 1 to 9, wherein Amine compounds used as protective agents include butylamine, 1,4-diaminobutane, 3-methoxypropylamine, pentylamine, 2,2-dimethylpropylamine, 3-ethoxypropylamine, N,N-dimethyl-1,3-diaminopropane, 3-ethoxypropylamine, hexylamine, heptylamine, N,N-diethyl-1,3-diaminopropane, benzylamine, isobutylamine, and 3-isopropoxypropylamine.

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