TW201829664A - Silver paste for resin substrate - Google Patents

Abstract

Provided is a silver paste for a resin substrate with which a conductive film having a lower resistance in comparison to prior art can be formed, at a low temperature and with good adhesion, on a resin substrate having low thermal resistance. This silver paste for a resin substrate includes a silver powder (A), a binder (B), and a solvent (C) capable of dissolving the binder. The silver powder (A) has an average particle diameter of 40 nm to 100 nm. The binder (B) includes a thermoplastic polyester urethane resin (B1) and a thermoplastic polyester resin (B2), both of which have a glass transition point of 60 DEG C to 90 DEG C. Moreover, the total ratio of the thermoplastic polyester urethane resin (B1) and the thermoplastic polyester resin (B2) included is 3 to 6 parts by mass relative to 100 parts by mass of the silver powder (A).

Description

Silver paste for resin substrate

The present invention relates to a silver paste which can form a conductive film on a substrate having low heat resistance such as a resin. The present application claims priority based on Japanese Patent Application No. 2016-182292, filed on Sep. The entire contents of this application are incorporated herein by reference.

The circuit board on which the electronic component is mounted is reduced in size, thickness, weight, and functionality, and the conductive film is printed on the polymer substrate instead of the inorganic substrate. Since the heat resistance of the polymer substrate is inferior to that of the inorganic substrate, it is required to form a film at a low temperature (for example, 400 ° C or lower) with respect to the conductive paste for forming a conductive film. In Patent Document 1 to Patent Document 2, for example, a silver powder excellent in low-temperature sinterability for forming a film at a low temperature and a silver paste containing the silver powder are used. Further, Patent Document 3 discloses a silver paste containing a silver powder and a thermoplastic resin which is cured at a low temperature. [Prior Art Document] [Patent Literature]

[Patent Document 1] International Publication No. 2014/084275 [Patent Document 2] Japanese Patent Application Publication No. 2013-36057 (Patent Document 3) International Publication No. 2013/081664

[Problems to be Solved by the Invention] In recent years, a resin sheet represented by a silver paste is printed by using a thin and flexible resin sheet as a substrate, thereby producing a large amount of high-yield and low-cost. Production of flexible printed circuits (FPC). Regarding the wiring printed on such a substrate, since the conductor film itself is required to have flexibility, a silver paste containing a resin (organic binder) as a binder has been used. Further, the printed wiring can be formed at a lower temperature (for example, 140 ° C or lower) than the heat resistance of the resin sheet used as the substrate, and further, the adhesion to the flexible resin sheet is required. good. Moreover, in addition, the printed conductive film is potentially required to have a further lower resistance.

The present invention has been made in view of the above, and it is an object of the invention to provide a silver paste for a resin substrate which can form a conductive film having a lower electric resistance at a lower temperature than a resin substrate having a low heat resistance. [Means for solving the problem]

In the prior silver paste, an insulating thermosetting resin is used as a binder of silver particles. However, the thermosetting resin has a relatively high flexibility after curing, and has a limit in forming a conductive film having a low flexibility in a resin sheet having high flexibility. Therefore, the inventors of the present invention have conducted intensive studies, and as a result, it has been found that a conductive film having a low electrical resistance and excellent adhesion can be formed by using a specific type of thermoplastic resin as a binder of a silver paste by doping, thereby completing the present invention. In other words, in order to solve the problem, the silver paste for a resin substrate (hereinafter, simply referred to as "silver paste" or "paste") is used to form a conductive film on a resin substrate such as a polymer film. Silver paste. The silver paste for a resin substrate includes (A) a silver powder, (B) a binder, and (C) a solvent that dissolves the binder. Further, the binder is characterized by comprising (B1) a thermoplastic polyester urethane resin having a glass transition point of 60 ° C or more and 90 ° C or less and (B2) a thermoplastic polyester resin. In addition, (B1) a thermoplastic polyester urethane resin and (B2) a thermoplastic polyester resin are contained in a ratio of 3 parts by mass or more and 6 parts by mass or less based on 100 parts by mass of the (A) silver powder.

By using such a silver paste for a resin substrate, it is possible to form a conductive film having a low electrical resistance (for example, a sheet resistance of 12 mΩ/□ or less) at a low temperature of 140 ° C or lower with respect to the resin substrate. . Thereby, a printed wiring having low electric resistance and good adhesion can be formed on the flexible substrate.

Further, the glass transition point of the thermoplastic polyester resin can be measured in accordance with the method for measuring the glass transition point specified in Japanese Industrial Standards (JIS) K7121:1987 "Method for Measuring Transfer Temperature of Plastics". Regarding the glass transition point of the thermoplastic polyester resin, specifically, for example, a differential thermal analysis (DTA) device or a differential scanning calorimetry (DSC) device is used to measure the sample at a certain speed. Heating with the standard substance, the difference in heat capacity between the sample and the standard substance is measured based on the change in the heat capacity in the sample, whereby the glass transition point of the sample can be grasped. When heating is performed, for example, it is preferably heated to a temperature at least about 30 ° C higher than the end of the glass transition of the sample, and after maintaining the temperature for about 10 minutes, quenching to a temperature lower by about 50 ° C than the glass transition point. . Further, when a commercially available thermoplastic polyester resin is used, the glass transition point described in the information sheet of the product or the like can be used.

In a preferred aspect of the silver paste for a resin substrate disclosed herein, the ratio of (B1) the thermoplastic polyester urethane resin and (B2) the thermoplastic polyester resin is (B1): The mass ratio of B2) is from 85:15 to 20:80. With such a configuration, for example, even when the heat treatment temperature after printing varies, it is possible to obtain a conductive film in which variations in resistance characteristics are suppressed. In addition, it is possible to provide a high-quality silver paste that combines durability and printability.

In a preferred aspect of the silver paste for a resin substrate disclosed herein, the average particle diameter of the (A) silver powder is 40 nm or more and 100 nm or less. Thereby, the sintering of the silver powder can be preferably promoted, so that a conductive film having a lower sheet resistance can be formed. Further, for example, a fine line conductive film can be formed with a high aspect ratio.

In addition, the average particle diameter of the silver powder means the cumulative 50% particle diameter in the particle size distribution based on the number basis measured by the electron microscope observation. Specifically, for example, a silver powder can be observed at an appropriate magnification (for example, 50,000 times) using a scanning electron microscope (SEM) or the like, and based on 100 or more (for example, 100 to 1000). The circle obtained by the silver particles has a diameter which is equivalent to a particle size distribution.

In a preferred aspect of the silver paste for a resin substrate disclosed herein, a protective agent containing an organic amine having 5 or less carbon atoms is attached to the surface of the (A) silver powder. Thereby, the dispersion stability of the silver powder in the paste is improved, and the silver particles are placed at a preferred position while being paste-coated on the substrate and baked in a paste-preserved state, whereby a dense and homogeneous conductive film can be formed. .

In a preferred aspect of the silver paste for a resin substrate disclosed herein, the solvent (C) is propylene glycol monophenyl ether. Thereby, a high-high (B1) thermoplastic polyester urethane resin can be preferably dissolved, and a paste excellent in printability can be realized.

In other aspects, the techniques disclosed herein provide an electronic component. The electronic component includes a resin substrate and a conductive film provided on the resin substrate. Further, the conductive film is a cured product of the silver paste for a resin substrate described in any of the above. In other words, the electronic component can be provided, for example, in the form of a conductive film having low electrical resistance and excellent adhesion on a flexible resin substrate.

In a preferred aspect of the electronic component disclosed herein, the conductive film has an arithmetic mean roughness of 0.3 or less. The conductive film has a tendency to cause an increase in electric resistance, for example, as the surface roughness is rougher. The smaller the cross-sectional dimension of the conductor film (for example, a thin line), the more remarkable the tendency. However, the conductive film provided herein can be realized in the form of an excellent surface smoothness. As a result, the sheet resistance of the conductive film can be reduced to, for example, 12 mΩ/□ or less in terms of the thickness of the conductive film in terms of 10 μm. Thereby, a conductive film having a further lower electric resistance can be realized.

Further, in other aspects, the techniques disclosed herein provide a method of fabricating an electronic component. The manufacturing method includes preparing a resin substrate, preparing the silver paste for any of the resin substrates, supplying the resin substrate with a silver paste to the resin substrate, and supplying the silver paste for the resin substrate The flexible film substrate is dried; and the dried resin substrate to which the silver paste for a resin substrate is supplied is subjected to heat treatment to form a conductive film. Further, the temperature for performing the drying is lower than the temperature of the glass transition point of the thermoplastic polyester resin contained in the silver paste for a resin substrate, the temperature of the heat treatment being higher than the glass The transfer point is 20 ° C above the temperature. By using the silver paste for a resin substrate disclosed herein, an electronic component having a conductive film having excellent adhesion and conductivity on a flexible substrate can be preferably produced.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Furthermore, matters other than those specifically mentioned in the present specification (for example, the composition of a silver paste for a resin substrate or a property thereof) are required in the practice of the present invention (for example, to apply the paste to The detailed method of the substrate, the configuration of the electronic component, and the like can be implemented based on the technical contents indicated by the present specification and the usual technical common sense of practitioners in the field. In the present specification, the expression "A to B" indicating the numerical range means A or more and B or less.

[Silver paste for resin substrate] The silver paste for a resin substrate disclosed herein can be formed into a cured product by heat treatment at a low temperature (for example, 140 ° C or lower), and the cured product thereof exhibits electrical conductivity (electrical conductivity). Conductive film. Furthermore, the silver paste may be dried by heat treatment. Here, the conductive film itself has flexibility and adhesion to the resin substrate, and can be realized, for example, in a form that exhibits good substrate followability with respect to the flexible resin substrate. Such a silver paste for a resin substrate includes (A) a silver powder, (B) a binder, and (C) a solvent which dissolves the binder as a main constituent component. Hereinafter, each constituent component of the silver paste for a resin substrate disclosed herein will be described.

(A) Silver powder The silver powder is a material for forming a film body (conductive film) having high electrical conductivity (hereinafter, simply referred to as "conductivity") such as an electrode, a lead wire, or an electrically conductive film in an electronic component or the like. Silver (Ag) is not as expensive as gold (Au), is difficult to oxidize, and is excellent in electrical conductivity, and therefore is preferable as a conductor material. The silver powder is not particularly limited as long as it is a powder containing silver as a main component (a collection of particles), and a silver powder having desired conductivity or other physical properties can be used. Here, the main component means the largest component among the components constituting the silver powder. Examples of the silver particles constituting the silver powder include particles containing silver and a silver alloy, and a mixture or a composite thereof. Examples of the silver alloy include a silver-palladium (Ag-Pd) alloy, a silver-platinum (Ag-Pt) alloy, and a silver-copper (Ag-Cu) alloy. For example, a core including a metal such as copper or a silver alloy other than silver, and a shell covering the core may contain silver core-shell particles or the like.

The higher the purity (silver (Ag) content) of the silver powder tends to be, the higher the conductivity is. Therefore, it is preferred to use a high purity. The purity of the silver powder is preferably 95% or more, more preferably 97% or more, and particularly preferably 99% or more. For example, by using a silver powder having a purity of about 99.5% or more (for example, about 99.8% or more), a conductive film having an extremely low electric resistance can be formed, which is more preferable.

Although not particularly limited, in the technique disclosed herein, in order to preferably achieve sintering using a relatively low temperature (for example, 140 ° C or lower, typically about 110 ° C to 135 ° C), as a silver powder. Preferably, those having an average particle diameter of 40 nm or more and 100 nm or less are used. In general, particles having a smaller particle diameter (for example, fine particles of several nm to several tens of nm) have higher sinterability at a low temperature, and therefore, it is preferable to reduce the amount of the binder used. However, a sintered body of silver particles having a small amount of binder forms a dense sintered body, and the bulk characteristics appear strong, and cracking may occur when the conductive film is bent. That is, it is difficult to exhibit flexibility (softness). Further, when the average particle diameter is less than 40 nm, the silver particles are at a lower temperature than the heat treatment (for example, a lower temperature environment such as when the silver paste is supplied to the substrate or during drying; for example, about 20 ° C to 100 ° C) It is also easy to cause sintering (including self-sintering), and it is not preferable to perform stable film formation. From this point of view, the average particle diameter of the silver powder is preferably 40 nm or more (over 40 nm), more preferably 45 nm or more, and particularly preferably 50 nm or more.

On the other hand, when the average particle diameter of the silver particles is too large, sintering at a low temperature is difficult, and it is difficult to obtain a conductive film having good conductivity. Further, even if sintering at a low temperature can be performed, the minimum thickness of the conductive film which is low in electric resistance and stably formed can be increased, and as a result, it is difficult to exhibit sufficient flexibility due to the thickness of the conductive film. From this point of view, the average particle diameter of the silver powder is preferably 100 nm or less (less than 100 nm), more preferably 95 nm or less, and particularly preferably 90 nm or less. For example, it is preferably 55 nm or more and 85 nm or less.

Further, from the viewpoint of quality stability, the silver powder preferably contains particles having an excessively small particle diameter or particles having an excessively large particle diameter. For example, in the particle size distribution based on the number of silver powders, the minimum value (Dmin) of the particle diameter is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more. In other words, it is preferred that substantially no ultrafine particles of less than 10 nm, preferably less than 20 nm, for example less than 30 nm are contained. Further, for example, in the particle size distribution of the number-based basis, the maximum value (Dmax) of the particle diameter is preferably 300 nm or less, more preferably 250 nm or less, and particularly preferably 200 nm or less. In other words, it is preferred that substantially no coarse particles of more than 300 nm, preferably more than 250 nm, for example more than 200 nm are contained.

The silver powder disclosed herein preferably has a modest spread in the particle size distribution. For example, specifically, the value (D90-D10) obtained by subtracting the cumulative 10% particle diameter (D10) from the cumulative 90% particle diameter (D90) in the particle size distribution of the number-based basis is preferably 70 nm or more, typically It is 75 nm or more, and preferably about 220 nm or less, for example, 210 nm or less. By having a moderate expansion in the particle size distribution as described above, when the silver powder is sintered, the silver particles having a relatively small particle diameter can be disposed and sintered in such a manner as to fill a gap of the silver particles having a relatively large particle diameter. . As a result, the silver powder can be sintered in a state of being filled at a higher density, and a conductive film excellent in conductivity can be realized.

Further, between the cumulative 90% particle diameter (D90) and the cumulative 10% particle diameter (D10), it is preferable that the ratio (D10/D90) is about 0.3 or more, and for example, more preferably 0.33 or more. Further, the ratio (D10/D90) is preferably 0.6 or less, more preferably 0.55 or less.

The shape of the silver particles constituting the above silver powder is not particularly limited. For example, it may be spherical, elliptical, broken, scaly, flat, fibrous, or the like. In terms of forming a thin line (for example, a line width of 50 μm or less) and a high aspect ratio (for example, a thickness of 2 μm or more) and a film having a low electric resistance by printing, the shape of the silver particles is preferably spherical or Close to the sphere. As an index indicating the sphericity of the silver particles, an aspect ratio when the shape of the silver particles is evaluated in two dimensions can be cited. In the aspect ratio, for example, it is possible to observe 100 or more (for example, 100 to 1000) silver particles by an electron microscope or the like, and to draw a rectangle in which the outer shape of the silver particles is circumscribed in the observation image. The ratio of the length of the side to the length of the short side (long diameter / short diameter) is calculated. Here, the arithmetic mean of the aspect ratios associated with the respective silver particles is used as the aspect ratio of the silver powder. Further, the closer the aspect ratio is to 1, the more excellent the isotropy, and the closer the shape of the silver particles in three dimensions is to the spherical shape. On the other hand, the larger the aspect ratio, the higher the anisotropy, and the shape of the silver particles is closer to a shape such as a non-spherical shape such as a flat plate shape or a fibrous shape. Here, silver particles having an aspect ratio of 1.5 or less are referred to as "spherical particles", and silver particles having an aspect ratio of less than 1.5 are referred to as "non-spherical particles".

Additionally, the silver powders disclosed herein may also comprise spherical silver particles and non-spherical silver particles. In a mixture of spherical silver particles and non-spherical silver particles, for example, spherical particles enter a gap in which non-spherical particles are arranged or non-spherical particles enter a gap in which spherical particles are arranged, thereby obtaining overall filling property. High sintered body. Thereby, the contact area of the silver particles increases, and a conductor film excellent in conductivity can be formed. Further, in the silver powder disclosed herein, the proportion of the spherical silver particles having an aspect ratio of 1.5 or less is preferably 60% by number or more of the entire silver powder. In other words, the non-spherical silver particles having an aspect ratio of less than 1.5 are preferably 40% or less of the silver particles constituting the silver powder. The spherical silver particles are more preferably 70% by number or more of the entire silver powder, and particularly preferably 80% by number or more, and may be, for example, 85 % by number or more or 90 % by number or more. When the silver powder contains particles having such a shape, the stability, surface smoothness, homogeneity, filling property, and the like of the silver particles which are supplied to the substrate from the silver paste to the heat treatment are effectively improved. Thereby, the filling property of the silver particles or the surface smoothness of the formed conductive film is improved, and a conductive film having higher conductivity can be obtained.

Further, as described above, the silver particles disclosed herein have an average particle diameter of the nanometer order and are relatively fine. Therefore, since the silver powder of this size is generally easy to aggregate, it is possible to provide a protective agent for suppressing aggregation on the surface of the silver particles. Typically, the surface of the silver powder (silver particles) is coated with a protective agent. Thereby, the surface stability of the silver particles can be maintained, and aggregation of the silver particles can be effectively suppressed. As a result, in the silver paste disclosed herein, the aggregation of the silver particles in the solvent is suppressed, and the dispersion is good for a long period of time and is stably stored. Further, for example, when the silver paste is supplied to the substrate by various printing methods, the fluidity of the silver particles is also improved, and the printability can be improved. Further, it is possible to homogenize a coating film in which unevenness is suppressed.

The type of the surface protective agent is not particularly limited, and the protective agent is preferably self-sliding from the viewpoint of heat treatment (calcination) at a low temperature and for a short period of time from the surface of the silver particles. The surface of the particle is detached. The protective agent is preferably, for example, a sublimation point or a boiling point at atmospheric pressure, a low decomposition temperature, and a relatively weak bond (for example, coordination bonding) with silver.

Therefore, in the technique disclosed herein, the protective agent is preferably an organic amine having a carbon number of 5 or less. Specific examples of the organic amine having 5 or less carbon atoms include methylamine, ethylamine, n-propylamine, isopropylamine, butylamine, pentylamine, and 2-methoxyethylamine. a primary aliphatic amine such as 2-ethoxyethylamine, 3-methoxypropylamine or 3-ethoxypropylamine; dimethylamine, diethylamine, methylbutylamine, ethyl a secondary aliphatic amine such as propylamine or ethylisopropylamine; a tertiary aliphatic amine such as trimethylamine, dimethylethylamine or diethylmethylamine. The carbon number of the organic amine is preferably 3 or more, more preferably 4 or more. Further, the organic amine may contain an alkoxy group such as a methoxy group or an ethoxy group in the structure. These organic amines may be used singly or in combination of two or more. Thereby, the dispersion stability can be further preferably achieved.

Further, although it is described later, when the dried silver paste (coating film) supplied to the substrate is subjected to heat treatment (baking) for a short period of time at a low temperature, it is important to exhibit high conductivity in the conductive film after firing. The residual amount of the protective agent and the amount of thermal shrinkage of the silver particles are suppressed to be small. Further, in order to suppress the residual of the protective agent or the heat shrinkage of the silver particles, it is effective to reduce the proportion of the protective agent in the silver powder as much as possible. In the technique disclosed herein, by setting the average particle diameter of the silver particles within the above range, a significantly lower content ratio of the protective agent is achieved as compared with the prior art. Specifically, when the silver powder (silver particle portion) is 100 parts by mass, the ratio of the protective agent can be 1.2 parts by mass or less. In other words, 98.8 parts by mass or more of the silver powder can be composed of silver particles. The proportion of the protective agent is preferably 1.1 parts by mass or less, and may be, for example, 1 part by mass or less. Thereby, even if calcination is performed for a short time at a low temperature, the residual of a protective agent and the thermal contraction of a silver particle can be effectively suppressed, and the coating film which is excellent in electroconductivity can be formed.

Further, the silver paste disclosed herein preferably contains substantially no components (corrosive components) which can generate an etching gas when calcined. In other words, it is preferable that the corrosion component due to, for example, the production step of the silver powder or the manufacturing equipment or the like is inevitably mixed, but it is preferable not to include such a corrosion component. Examples of such a corrosion component include a halogen component such as fluorine (F) or chlorine (Cl), and a sulfur (S) component. These components are preferably not contained in the silver powder itself, and are preferably not contained in the protective agent. Since the silver paste does not substantially contain such a corrosive component, it is possible to suppress corrosion deterioration of a semiconductor manufacturing apparatus, or contamination of a semiconductor element into a semiconductor element, and deterioration of an electrode or a substrate of a semiconductor element. Further, it is preferable to further contain a component which can adversely affect the human body or the environment, such as a lead (Pb) component or an arsenic (As) component. For example, when the silver powder is 100 parts by mass, the corrosion components such as fluorine (F), chlorine (Cl), sulfur (S), lead (Pb), and arsenic (As) are preferably suppressed to 0.1 mass. Parts (1000 ppm) or less. When the amount of the silver powder is 100 parts by mass, the corrosion components are preferably suppressed to 0.1 part by mass or less (1000 ppm) or less in total.

(B) Adhesive The binder functions as a binder in the silver paste disclosed herein. Typically, the binder facilitates bonding of the sintered silver powder to the substrate. Moreover, the binder contains a thermoplastic resin. Due to the inclusion of the thermoplastic resin, in the silver paste disclosed herein, the binder is softened by heating, and the binder is hardened by the subsequent exothermic (cooling), thereby bonding the silver particles or the subsequent adhesion of the silver particles to the substrate. Support. Further, in the binder resin, those having thermosetting properties and thermoplastics are present, and in the prior silver paste, a thermosetting resin (for example, a thermosetting polyester resin) or the like is used as a binder. In contrast, in the technique disclosed herein, the adhesive function is achieved by the reversible plasticizing property brought about by the heating of the thermoplastic binder resin as described above.

Further, in addition, in the technique disclosed herein, as such a thermoplastic binder resin, two resins of (B1) a thermoplastic polyester urethane resin and (B2) a thermoplastic polyester resin are used in combination. In general, when two kinds of resins are doped, the characteristics of the resin after the pre-doping are in the middle of the characteristics of the resin before doping, and the characteristics of the resin before the mixing are substantially linear according to the mixing ratio. Regarding (B1) thermoplastic polyester urethane resin and (B2) thermoplastic polyester resin, several characteristics are also in the middle of the characteristics of the resin before doping. However, for example, regarding the most important resistance characteristics in the conductive film, the resistance value of the resin after doping can be reduced as compared with the resistance value of the resin before doping. Hereinafter, the binder resin which can be used in the technology disclosed herein will be described.

As described above, the state of the binder resin is softened by heat treatment and hardened by subsequent cooling. Here, (1) the thermoplastic binder resin is softened before the sintering of the silver powder, and is hardened after sintering, and is preferable from the viewpoint of improving the adhesion to the substrate. In other words, as the thermoplastic binder resin, a relatively low and appropriate glass transition point (Tg) corresponding to the heat treatment temperature for sintering the silver powder can be preferably used. The details are not clear, but it is considered that, in the heat treatment, most of the binder resin softens to reach the interface between the silver powder and the substrate, and does not hinder the sintering of the silver powder, preferably contributing to the silver powder and Bonding of the substrate.

Further, (2) the thermoplastic binder resin is inferior in this respect by a large volume change by heat treatment or temperature change similarly to the silver powder. Further, since the thermoplastic binder resin is in a cured state at normal temperature, it is preferably soluble in a solvent to be described later. As a thermoplastic binder resin, those which satisfy such requirements are preferably used, and amorphous (non-crystalline) can be preferably used. The amorphous resin is understood to be a resin having a structure in which a regular arrangement is not observed in a molecular chain and a molecular chain is randomly mixed in a hardened state. The amorphous thermoplastic binder resin is, for example, soluble in a solvent and has a glass transition point, and can be grasped in the form of a compound which does not have a clear crystalline melting point.

The glass transition point of the thermoplastic binder resin also depends on the heat resistant temperature of the material constituting the substrate, and therefore cannot be generalized, but is preferably, for example, a heat treatment temperature (for example, 140 ° C or less, typically 110) for sintering the silver powder. A sufficiently low temperature from °C to 135 °C. As a preferable example, for example, a temperature lower than the heat treatment temperature by 20 ° C or more (for example, about 20 ° C to 50 ° C) is preferable. From the above viewpoints, the glass transition point is preferably 90 ° C or lower, more preferably 85 ° C or lower, and particularly preferably 80 ° C or lower. On the other hand, the glass transition point of the thermoplastic binder resin is preferably higher than the temperature at which the solvent in the silver paste is substantially volatilized, for example, the drying temperature of the silver paste. For example, it is preferably about 20 ° C higher than the drier temperature. From the above viewpoint, the glass transition point is preferably 60 ° C or more (over 60 ° C), more preferably 63 ° C or more, and particularly preferably 65 ° C or more. Such glass transition points are of a relatively high class among the commonly used thermoplastic binder resins. For example, a binder for a resin substrate such as polyethylene terephthalate (PET) can be said to have an extremely high temperature.

(B1) Thermoplastic polyester urethane resin As the first thermoplastic adhesive resin, a thermoplastic polyester urethane (PEsUR) resin can be used. The thermoplastic polyester urethane resin has a coating stabilizing function which is not applied during the application of the silver paste disclosed herein to the substrate by printing until the silver paste is dried. The object sags to maintain its shape or volume. By the presence of the thermoplastic polyester urethane resin, the silver paste can maintain a shape at the time of printing to form a conductive film having a low electrical resistance. Thereby, a silver paste having good printability can be provided. Further, the thermoplastic polyester urethane resin imparts durability to the conductor film after curing. Thereby, for example, a conductive film excellent in resistance to temperature change from high temperature such as -20 ° C to 85 ° C or the like (heat cycle resistance) or resistance to high temperature and high humidity environment (high temperature and high humidity resistance) can be obtained. .

As the thermoplastic polyester urethane resin, for example, a polyester-based structure may be contained in the form of a main monomer (also referred to as a basic skeleton) as a repeating unit constituting the resin, and may be further contained in the form of a sub-monomer. The main monomer has a polymer of a copolymerizable urethane-based monomer raw material. Also known as urethane modified copolyester. Here, the term "main monomer" means the largest component of the monomer composition in the monomer raw material (typically, a component exceeding 50% by weight). The term "submonomer" means a component composed of a second most monomer after the monomer composition constituting the main monomer in the monomer raw material. The thermoplastic polyester urethane resin disclosed herein may be a polymer comprising a primary monomer and a secondary monomer, or a polymer comprising other monomer components.

The main monomer may be any polyester structure obtained by polycondensation of a polycarboxylic acid and a polyhydric alcohol. The monomer component corresponding to the polycarboxylic acid constituting the polyester structure is not particularly limited. The polycarboxylic acid may be an acyclic polycarboxylic acid or a saturated or unsaturated alicyclic polycarboxylic acid. For example, aliphatic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, glutamic acid, sebacic acid, dodecanedioic acid, tridecanedioic acid, and dimer acid may be mentioned. Dibasic acid; alicyclic dicarboxylic acid such as furan dicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid; phthalic acid, isophthalic acid, terephthalic acid, A dibasic acid such as an aromatic dibasic acid such as naphthalened dicarboxylic acid is preferred. Among them, an aromatic dibasic acid is preferred. Further, the monomer component corresponding to the polyol constituting the polyester structure is also not particularly limited. Examples of the polyhydric alcohol include an aliphatic polyhydric alcohol, an alicyclic polyhydric alcohol, and an aromatic polyhydric alcohol. From the viewpoint of obtaining high adhesion, an aliphatic diol or an alicyclic diol is preferred. Specific examples of the monomer component corresponding to the polyol include ethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, and 1,3-butylene glycol. A glycol such as 1,4-cyclohexanedimethanol. These may be those having an alicyclic skeleton in the side chain, or those having no alicyclic skeleton in the side chain.

The main monomer may be, for example, an ester of a polycarboxylic acid typified by the above-exemplified dibasic acid and a polyhydric alcohol represented by a glycol. Further, as another example, the main monomer may be a polycondensation reaction product of terephthalic acid and ethylene glycol (PET main monomer), a polycondensation reaction of terephthalic acid and butylene glycol (polybutylene terephthalate). Polybutylene terephthalate (PBT) main monomer), polycondensation reaction of naphthalene dicarboxylic acid and ethylene glycol (polyethylene naphthalate (PEN) main monomer), naphthalene dicarboxylic acid A polycondensation reactant (polybutylene naphthalate (PBN) main monomer) with butylene glycol. These main monomers may be contained alone or in combination of two or more.

The sub-monomer may be a monomer component constituting a polyester-based structure which is formed by an addition polymerization reaction of a compound having an isocyanate group and a hydroxyl group. In other words, it may be a component having one or two or more urethane bonds in its structure. Examples of such a secondary monomer include isophorone diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, m-xylene diisocyanate, p-phenylene diisocyanate, and isophthalic acid. Isocyanate, 1,5-naphthalene diisocyanate, 2,6-naphthalene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenyl Methane diisocyanate, 3,3'-dimethoxy-4,4'-extended biphenyl diisocyanate, 3,3'-dimethyl-4,4'-extended biphenyl diisocyanate, 4,4'- Diphenyl diisocyanate, 4,4'-diisocyanate diphenyl ether, and the like. These sub monomers may be contained alone or in combination of two or more.

Further, the thermoplastic polyester urethane resin preferably has moderate flexibility after curing. Therefore, a component such as a crosslinking agent or a crosslinking assistant may be contained for the purpose of improving flexibility, adhesion, and the like after curing. Examples of such a crosslinking agent and a crosslinking auxiliary agent include an isocyanate compound, a polyfunctional melamine compound, a polyfunctional epoxy compound, and a polyhydroxy compound. Specific examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, aromatic aliphatic polyisocyanates, and polyhydroxy compounds. The crosslinking agent and the crosslinking assistant may be used alone or in combination of two or more.

When the thermoplastic polyester urethane resin is used, the weight average molecular weight (Mw) is not particularly limited, and if the weight average molecular weight is less than 2,000, it is difficult to develop the adhesion and/or adhesion required as a binder. Sexual situation, so it is not good. From the above viewpoints, the weight average molecular weight is preferably 2,000 or more, more preferably 5,000 or more, still more preferably 10,000 or more. On the other hand, when the weight average molecular weight of the thermoplastic polyester urethane resin exceeds 100,000, there is a problem that solubility in a solvent is extremely lowered and printability is deteriorated. From the above viewpoints, the weight average molecular weight is preferably 100,000 or less, more preferably 50,000 or less, and may be 10,000 or more and 30,000 or less. Such a weight average molecular weight is a relatively high class among the amorphous thermoplastic polyester urethane resins which are usually used.

Further, as for the thermoplastic polyester urethane resin having the above characteristics, as long as it is a person who has been exposed to the disclosure of the present specification, for example, the main monomer and the sub-monomer can be adjusted depending on the resin substrate to be used. The combination or blending amount, glass transition point, molecular weight, etc. are suitably designed and blended. Further, such a thermoplastic polyester resin can also be obtained by using a commercially available product. Examples of the commercially available product include, for example, Fonta (registered trademark) manufactured by Hitachi Chemical Co., Ltd., and 8UA (registered trademark) of Daewoo Fine Chemical Co., Ltd., and the like.

(B2) Thermoplastic Polyester Resin As the second thermoplastic adhesive resin, a thermoplastic polyester (PEs) resin can be used. The thermoplastic polyester resin imparts adhesion to the resin substrate to the silver paste, and exhibits excellent adhesion between the formed conductive film and the resin substrate. Typically, it facilitates the bonding of the sintered silver powder to the substrate. Further, when only the thermoplastic polyester urethane resin is used as the binder, the binder is too hard to prepare a silver paste suitable for printing properties, and as a result, the surface of the printed matter is roughened on the surface of the conductive film. Forming irregularities. In addition, when a powder having a relatively small particle diameter is used as the silver powder, the viscosity of the paste rises and remains remarkably in a printing machine (for example, a mesh), and thus the printability is deteriorated. Therefore, by the presence of the thermoplastic binder resin, the meshability of the silver paste at the time of printing can be improved, and the disadvantage of the thermoplastic polyester urethane resin can be compensated for. Thereby, a conductive film having a smooth surface and a lower electric resistance can be formed. Further, for example, since the thin plate is highly permeable and has the shape retainability of the printed body, it is possible to print a conductive film having a high aspect ratio although it is a thin line in one printing.

As such a thermoplastic polyester resin, a polyester-based structure obtained by polycondensing a polycarboxylic acid and a polyol in the form of a main component or a main monomer can be used as various compounds constituting a repeating unit of the resin. In addition, the "main component" means the monomer component corresponding to the repeating unit containing the most on the mass basis among the repeating unit which comprises the main skeleton of a thermoplastic polyester resin. The main component preferably contains more than 50% by mass of a monomer component in the thermoplastic polyester resin.

The monomer component corresponding to the polycarboxylic acid constituting the polyester structure is not particularly limited. The polycarboxylic acid may be an acyclic polycarboxylic acid or a saturated or unsaturated alicyclic polycarboxylic acid. For example, aliphatic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, glutamic acid, sebacic acid, dodecanedioic acid, tridecanedioic acid, and dimer acid may be mentioned. Dibasic acid; alicyclic dicarboxylic acid such as furan dicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid; phthalic acid, isophthalic acid, terephthalic acid, A dibasic acid such as an aromatic dibasic acid such as naphthalened dicarboxylic acid is preferred. Among them, a saturated aliphatic dibasic acid or an alicyclic dicarboxylic acid is preferred. Further, the monomer component corresponding to the polyol constituting the polyester structure is also not particularly limited. Examples of the polyhydric alcohol include an aliphatic polyhydric alcohol, an alicyclic polyhydric alcohol, and an aromatic polyhydric alcohol. From the viewpoint of obtaining high adhesion, an aliphatic diol or an alicyclic diol is preferred. Specific examples of the monomer component corresponding to the polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-. A glycol such as cyclohexane dimethanol. These may be those having an alicyclic skeleton in the side chain, or those having no alicyclic skeleton in the side chain.

Further, the thermoplastic polyester resin may be, for example, a polymer of a monomer raw material containing a polyester-based structure as a main monomer and further containing a sub-monomer having copolymerizability with the main monomer. Here, the term "main monomer" means a component which accounts for 50% by weight of the monomer composition in the monomer raw material. The main monomer may be, for example, an ester of a polycarboxylic acid typified by the above-exemplified dibasic acid and a polyhydric alcohol represented by a glycol. Further, as another example, the main monomer may be a polycondensation reaction product of PET and ethylene glycol (PET main monomer), a polycondensation reaction product of terephthalic acid and butylene glycol (PBT main monomer). a polycondensation reaction product of a naphthalene dicarboxylic acid and ethylene glycol (a PEN main monomer), a polycondensation reaction product of a naphthalene dicarboxylic acid and a butanediol (a PBN main monomer). These main monomers may be contained alone or in combination of two or more.

As the secondary monomer, a component which can introduce a crosslinking point to a polyester structure or an adhesive force which can improve a polyester structure is preferable. Examples of the secondary monomer include a carboxyl group-containing monomer typified by a monocarboxylic acid, a dicarboxylic acid, an acid anhydride thereof, and the like; a hydroxyalkyl (meth)acrylate compound, an alcohol compound, an ether compound, and a poly A hydroxyl group-containing monomer represented by an ether compound or the like; a mercapto group-containing monomer typified by (meth) acrylamide or the like; and an isocyanate group-containing single typified by (meth) acryl decyl isocyanate A phenyl group-containing monomer represented by a styrene compound, a phenyl ether compound or the like. These sub monomers may be contained alone or in combination of two or more.

Further, the thermoplastic polyester resin preferably has moderate flexibility after curing. Therefore, a component such as a crosslinking agent or a crosslinking assistant may be contained for the purpose of improving flexibility, adhesion, and the like after curing. Examples of such a crosslinking agent and a crosslinking auxiliary agent include an isocyanate compound, a polyfunctional melamine compound, a polyfunctional epoxy compound, and a polyhydroxy compound. Specific examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, aromatic aliphatic polyisocyanates, and polyhydroxy compounds. The crosslinking agent and the crosslinking assistant may be used alone or in combination of two or more.

Further, in order to improve the chemical stability and photochemical stability of the conductive film, the secondary monomer or the crosslinking agent and the crosslinking assistant are preferably those which do not introduce an unsaturated group into the thermoplastic polyester resin. That is, the thermoplastic polyester resin is preferably a saturated copolymerized polyester. Therefore, it is preferable to improve the adhesiveness of the PET film substrate which is common to the flexible film substrate.

When the thermoplastic polyester resin is used, the number average molecular weight (Mn) is not particularly limited, and if the number average molecular weight is less than 2,000, it is difficult to exhibit the adhesion and/or adhesion required as a binder. Poor. From the above viewpoints, the number average molecular weight is preferably 2,000 or more, more preferably 5,000 or more, still more preferably 10,000 or more. On the other hand, when the number average molecular weight of the thermoplastic polyester resin exceeds 100,000, there is a problem that the solubility in a solvent is extremely lowered to cause deterioration in printability. From the above viewpoints, the number average molecular weight is preferably 100,000 or less, more preferably 50,000 or less, and may be 10,000 or more and 30,000 or less. Such a number average molecular weight is a relatively high class among the amorphous thermoplastic polyester resins generally used.

Further, regarding the properties such as flexibility, adhesion, and solvent solubility in the thermoplastic polyester resin, as long as it is a person who is exposed to the disclosure of the present specification, the main monomer can be adjusted depending on the film substrate to be used. The combination of the sub-monomers or the blending amount thereof, the glass transition point, the molecular weight, and the like are suitably designed and blended. Further, such a thermoplastic polyester resin can also be obtained by using a commercially available product. Examples of the commercially available product include Elitel (registered trademark) UE3200, UE9200, UE3201, UE3203, UE3600, UE9600, and UE3660 manufactured by Unitika. UE3690, Polyester (registered trademark) TP236, TP220, TP235, manufactured by Japan Synthetic Chemical Industry Co., Ltd., Dynapol, manufactured by Evonik Industries AG Trademarks) L205, L206, L208, L952, L907, VITEL (registered trademark) 2100, 2200, etc. manufactured by Bostik Corporation.

With respect to the above (B1) thermoplastic polyester urethane resin and (B2) thermoplastic polyester resin, for example, it is preferable to form a conductive film having a low electric resistance by printing at a low temperature. Provisioning. Regarding the (B1) thermoplastic polyester urethane resin and the (B2) thermoplastic polyester resin, the resistance of the conductive film can be reduced even if it is used in a small amount by using either of them in combination. However, for example, in order to reduce electrical resistance by making the surface of the formed conductive film smoother, (B1) thermoplastic polyester urethane resin to (B1) thermoplastic polyester urethane resin and (B2) The proportion of the total of the thermoplastic polyester resin is preferably 90% by mass or less, more preferably 85% by mass or less, and particularly preferably 80% by mass or less. Further, in order to prevent the sag of the printed paste-coated body from being favored, maintain the cross-sectional shape and the like, and reduce the electric resistance, (B1) a thermoplastic polyester urethane resin to (B1) a thermoplastic polyester urethane resin and The proportion of the total of the thermoplastic polyester resin (B2) is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 30% by mass or more. Further, in order to suppress the sheet resistance to be as low as, for example, 12 mΩ/□ or less, the (B1) thermoplasticity can be preferably adjusted in the range of 85:15 to 20:80 by mass ratio of (B1):(B2). Formulation of polyester urethane resin with (B2) thermoplastic polyester resin.

Further, in order to impart sufficient flexibility and adhesion to the conductive film of the sintered body containing the silver powder, the binder resin preferably has a first binder and a second binder with respect to 100 parts by mass of the silver powder. The total amount of the agents is included in a ratio of 3 parts by mass or more. The binder resin is more preferably 3.2 parts by mass or more, particularly preferably 3.5 parts by mass or more. On the other hand, since the binder resin exhibits insulation, it is preferred that the content in the silver paste be suppressed as little as possible. In view of the above, the total amount of the first binder and the second binder is preferably 6 parts by mass or less, more preferably 5.5 parts by mass or less, based on 100 parts by mass of the silver powder. It is preferably 5 parts by mass or less.

(C) Solvent As the solvent, various solvents which can dissolve the (B) binder can be used. Further, it also has a function of dispersing the silver powder which is a solid component of the silver paste. The solvent is not particularly limited. For example, the silver paste in which the (A) silver powder and the (B) binder resin are used in combination can be preferably calcined, and a conductive film having excellent conductivity can be produced. From the viewpoint, a solvent having a boiling point of 180 ° C or more and 250 ° C or less is preferred. Further, it is preferred to include a phenyl group in the molecular structure.

The solvent is a high-boiling solvent having a boiling point of 180 ° C or higher. For example, when the silver paste is continuously supplied to an arbitrary substrate by a printing method, the solvent is volatilized and the properties of the silver paste are changed. The volatilization of the solvent before the supply of the silver paste to the substrate increases the viscosity of the silver paste, makes the printing conditions unstable, or increases the content of the silver powder in the silver paste, thereby deviating from the film thickness of the formed conductive film. Poor. Further, by the boiling point of the solvent being 250 ° C or lower, the solvent can be rapidly volatilized in a short time at a temperature sufficiently lower than the heat treatment temperature for sintering the silver powder. Further, when the boiling point of the solvent exceeds 250 ° C, the solvent component often remains on the coating film obtained by drying the silver paste, and it is difficult to perform film formation, which is not preferable.

Further, since the solvent contains a phenyl group in the molecular structure, the solubility of the thermoplastic polyester urethane resin or the thermoplastic polyester resin is improved, and it is easy to adjust the paste property suitable for printing, which is preferable. That is, since the solvent contains a phenyl group, the affinity with respect to the non-aqueous thermoplastic polyester resin is improved, thermodynamically stable, and it is difficult to be subjected to oxidation x reduction. Further, by exhibiting the presence of a rigid benzene ring, it is possible to stably and preferably impart a moderate viscosity to the silver paste. As a result, when the silver paste is supplied to the substrate, a silver paste having high workability or printing stability can be prepared. Further, a homogeneous coating film (including a conductive film) can be stably formed. The number of phenyl groups in the molecular structure may be one.

As described above, by adjusting the silver paste with a suitable solvent, the properties of the silver paste can be stably maintained and the silver paste can be supplied to the substrate by a printing method. In the future manufacture of electronic components, for example, when a roll-to-roll process is fully utilized, this situation can be an extremely advantageous characteristic. Furthermore, although the boiling point and the volatility of the solvent are not strictly identical, considering the use of the silver paste disclosed herein and the characteristics of the solvent used, even if the volatility is grasped based on the boiling point of the solvent, it can be said that It is unimpeded.

As such a solvent, it may be associated with a specific composition of a thermoplastic polyester urethane resin or a thermoplastic polyester resin, and thus it is not possible to generalize, but it is preferred to use an alkylene monophenyl ether, among which It is preferred to use propylene glycol monophenyl ether.

The ratio of the solvent (C) in the silver paste is not particularly limited as long as it is an amount capable of dissolving the thermoplastic polyester resin. For example, it can be suitably adjusted according to a supply method, and workability and supply property at the time of supplying a silver paste to a base material are favorable. For example, when the silver paste is supplied to the substrate by a printing method, the ratio of the silver powder may be about 50% by mass or more, preferably 60% by mass or more, for example, 70% by mass, as an approximate standard. %the above. In addition, the ratio of the silver powder is 90% by mass or less, preferably 85% by mass or less, and is, for example, 80% by mass or less. In addition, the ratio of the solvent may be about 10% by mass or more, preferably 15% by mass or more, and for example, 20% by mass or more. In addition, the ratio of the solvent may be 50% by mass or less, preferably 40% by mass or less, and may be, for example, 30% by mass or less. By increasing the proportion of the silver powder as described above, the denseness of the conductive film can be improved. As a result, even if it is baked at a low temperature for a short time, a conductive film excellent in electrical conductivity can be stably formed. Further, when a relatively thin conductive film (for example, having a thickness of 3 μm or less) is formed, a conductive film having no unevenness and uniformity can be formed.

(D) Other components The silver paste disclosed herein does not need to contain components other than the (A) silver powder, (B) binder, and (C) solvent. However, various components may be contained in addition to the (A) silver powder, (B) binder, and (C) solvent, without departing from the object of the present application. As such a component, an additive added for the purpose of improving the properties of the silver paste for a resin substrate or an additive added for the purpose of improving the properties of the conductive film as a cured product can be considered. As an example, a surfactant, a dispersing agent, a filler (organic filler, inorganic filler), a viscosity modifier, an antifoamer, a plasticizer, a stabilizer, an antioxidant, a preservative, etc. are mentioned. Silver paste for resin substrate These additives (compounds) may be contained alone or in combination of two or more. However, it is less preferable to contain a component which inhibits the adhesion of (A) silver powder and (B) the adhesive property of the binder or an additive which inhibits the above-mentioned amount. From this point of view, for example, a protective agent or an inorganic filler containing an inappropriate silver powder is preferred. In addition, when the additive is contained, the total content of the components is preferably about 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 1% by mass or less based on the entire silver paste.

The silver paste for a resin substrate can be prepared by blending the constituent components in a predetermined ratio, and uniformly mixing and kneading. When mixing is carried out, each constituent material may be mixed at the same time. For example, (B) a binder resin may be mixed with (C) a solvent to prepare a vehicle, and then (A) silver powder may be mixed into the carrier. Further, here, in the technique disclosed herein, two resin components of (B1) a thermoplastic polyester urethane resin and (B2) a thermoplastic polyester resin are used as a binder component. It is preferred that the two binders are uniformly and preferably dissolved and the paste properties at the time of fine line printing are preferably prepared. Here, for example, when (B1) a thermoplastic polyester urethane resin or a (B2) thermoplastic polyester resin is prepared in a liquid form dissolved in a solvent, it is preferred to use the paste as the solvent. (C) Solvent. When the (B1) thermoplastic polyester urethane resin or the (B2) thermoplastic polyester resin is dissolved in another solvent, it is preferred to use the appropriate (C) solvent after removing the other solvent. Further, when other additives are added, the timing of addition thereof is not particularly limited. When mixing these raw materials, for example, a three-roll mill can be used.

The silver paste for a resin substrate prepared as described above can be cured, for example, at a temperature lower than the previous temperature (typically 140 ° C or lower, for example, 110 ° C to 135 ° C). In addition, the resin substrate silver paste is applied to an arbitrary substrate with a desired fine line and a high aspect ratio pattern, and then cured, whereby a conductive film (cured material) having a desired fine line form can be formed on the substrate.

[Conductive Film] Further, since the conductive film uses the binder resin as a binder, the conductive film itself has better substrate followability. Further, since two resins (B1) thermoplastic polyester urethane resin and (B2) thermoplastic polyester resin are used in combination as a binder, a conductive film having low electrical resistance and high adhesion can be obtained. Further, the silver paste disclosed herein is provided in the form of a plate passability at the time of printing or a shape maintainability of the printed body. Therefore, the conductor film may be particularly formed with a fine line and a high aspect ratio. Therefore, the line width of the conductive film formed of the silver paste is not particularly limited, and may be, for example, 50 μm or less (less than 50 μm), 45 μm or less, and for example, 30 μm or less. Further, the average thickness of the conductive film is not limited, and for example, the thickness can be 2 μm or more, for example, preferably 2.5 μm or more, particularly preferably 3 μm or more, and for example, 3.5 μm or more. Thereby, a conductive film having a fine line and a high aspect ratio can be formed. Since the conductive film uses a highly flexible adhesive, excellent adhesion to the substrate and substrate followability can be maintained.

In addition, in order to further improve the conductivity of the conductive film, it is preferred to set the surface roughness (arithmetic mean roughness) of the conductive film to 0.3 (μm) or less. Thereby, an increase in electric resistance caused by the unevenness of the surface of the conductive film can be suppressed. Further, the arithmetic mean roughness is preferably 0.2 or less, and particularly preferably 0.1 or less. The conductivity of such a conductive film depends on the shape or thickness of the conductive film, and therefore cannot be generalized. For example, the thickness of the conductive film which is hardened by heat treatment at 110 ° C to 135 ° C can be converted into a sheet resistance of 12 mΩ at 10 μm. /□ The form of the following is obtained. The sheet resistance can be, for example, 11 mΩ/□ or less, preferably 10 mΩ/□ or less, particularly preferably 8 mΩ/□ or less, and for example, 7 mΩ/□ or less.

[Substrate] The substrate to which the silver paste for a resin substrate disclosed in the present invention is applied is not particularly limited as long as it is a substrate containing a resin. For example, it may be a flexible film substrate (hereinafter sometimes simply referred to as a "flexible substrate") containing various resins. As the flexible substrate, a polyester resin such as polyethylene terephthalate (PET), a polyolefin resin such as polypropylene or an ethylene-propylene copolymer, and a polyamide resin are generally used. A polymer film of a thermoplastic resin such as vinyl chloride. The silver paste disclosed herein uses a binder mainly composed of a polyester resin, so that adhesion to a PET resin substrate can be particularly excellent. These substrates may have a form of either a single layer or a plurality of layers. In the case of a plurality of layers, a film substrate having a different raw material can be bonded, and a film substrate of a raw material of a contract can be attached. The flexible substrate may also constitute a flexible portion in a rigid flexible substrate including a rigid portion such as a mounting component and a flexible portion that performs buckling.

In addition, "flexibility" means that it is soft and can be flexed or bent. Generally, it means that the force can be flexed or bent at a relatively low temperature at normal temperature without causing damage to the object itself. The flexible substrate is a term used for a rigid substrate that does not have a temperature change or a coating layer and does not flex. The amount of deflection of the flexible substrate (the amount of flexibility that can be flexed) is not particularly limited. However, if necessary, the substrate can be grasped as a substrate having a deflection metric of 0.001 or more with respect to the substrate size at a normal temperature, for example, when a load is applied to the tip end of the cantilever-shaped substrate (typically It is a deformation of 0.1 or more, for example, 1 or more.

Further, since the flexible substrate is lightweight and buckbable, it can be used, for example, as a flexible printed circuit (FPC) or the like. Further, since the flexible substrate can be repeatedly bent or deformed, it is preferable to have a predetermined rigidity (strength). From the viewpoint of the above, as the flexible substrate, a polyester film can be preferably used, and among them, a PET film substrate can be particularly preferably used. The PET film substrate is mostly used as a touch panel raw material or a flexible cable substrate, and is also preferable in this respect. Therefore, a method of forming a conductive film with a silver paste for a resin substrate disclosed in the present invention and preferably manufacturing an electronic component will be described below, for example, on a PET film substrate.

[Manufacturing Method of Electronic Component] The method of manufacturing an electronic component disclosed herein essentially includes the following steps (1) to (5). (1) Prepare a PET film substrate. (2) Prepare the silver paste disclosed herein. (3) The silver paste is supplied onto the PET film substrate. (4) The PET film substrate to which the silver paste is supplied is dried. (5) The dried PET film substrate to which the silver paste is supplied is subjected to heat treatment to form a conductive film.

Further, the steps (1) and (2) can be understood by the description of the silver paste and the substrate, and thus the description thereof will be omitted here. In the step (3), the silver paste disclosed herein is supplied onto the prepared PET film substrate. The method of supplying the silver paste is not particularly limited. For example, various printing methods such as inkjet printing, gravure printing, screen printing, flexographic printing, lithography, spin coating, and jet sol printing can be employed. The printing may be carried out in a stage (intermittent) manner or in a continuous manner such as a roll-to-roller. The silver paste can be prepared into a trait suitable for various printing methods. The silver paste disclosed herein can be preferably used, for example, for the purpose of forming a conductive film of any pattern across a relatively wide area on a PET film substrate by screen printing.

The printed pattern is not particularly limited. The pattern can be fully applied, and a predetermined wiring pattern can also be formed. Further, as described above, in order to finish the calcined conductive film to a low electric resistance by a thin wire, it is preferred that the conductive film obtained after the heat treatment has a line width of 50 μm or less (for example, less than 50 μm). The amount of silver paste supplied is controlled such that the thickness is 2 μm or more (for example, more than 2 μm). Further, the thickness of the conductive film can be obtained in the form of an arithmetic mean value (i.e., average thickness) when a dimension in a direction perpendicular to the substrate surface of 10 points or more is measured.

Next, in the steps (4) and (5), the silver paste supplied to the PET film substrate is subjected to "drying" and "heat treatment", respectively. A conductive film is formed by the drying and heat treatment. When a conductive film is formed, the solvent is volatilized with respect to each component contained in the silver paste, the resin is softened and then hardened, and the silver powder is sintered. A conductive film can be formed by the sintered silver powder and the hardened resin.

Here, it is unsatisfactory to simultaneously volatilize the solvent, soften and harden the binder resin, and sinter the silver powder. In other words, the solvent is completely volatilized, and the silver powder is sintered in a state in which only the solid content of the silver paste is densely deposited on the substrate, whereby the silver particles are bonded to each other at a larger contact point, whereby a conductive film having a low electric resistance can be obtained. Preferably. Further, the solvent is completely volatilized, and the resin is softened and hardened in a state in which only the solid component of the silver paste remains on the substrate, whereby a suitable binder function can be exhibited with a smaller amount of resin, which is preferable. Further, the resin is preferably cured after the silver powder is completely sintered, whereby the inhibition of the sintering of the silver powder can be suppressed and the sintered silver can be bonded to the substrate.

In addition, the "drying" in the step (4) is a step mainly performed for the purpose of volatilizing the solvent contained in the silver paste and leaving only the solid content of the silver paste on the substrate. Further, the "heat treatment" in the step (5) is a step mainly performed for the purpose of sintering the silver powder on the substrate. Further, in the middle of the step (5) after the step (4), the resin is softened, and the resin is cured in the middle of cooling by the heating of the step (5). Thus, when manufacturing the electronic components disclosed herein, it is important to appropriately control the drying in the step (4) and the temperature in the heat treatment in the step (5) in accordance with the silver paste.

The drying of the step (4) may be natural drying, or may be carried out by air drying, heat drying, vacuum drying, freeze drying or the like. In terms of being easily dried in a shorter period of time, it is preferably heated and dried. The heating method in the heating and drying is not particularly limited, and drying can be carried out by using various known dryers.

This drying step is carried out at a temperature lower than the glass transition point (Tg) of the thermoplastic binder resin used in the silver paste. From the viewpoint of shortening the drying time, for example, the drying step is preferably carried out by heating to a temperature lower by about 20 to 30 ° C than the glass transition point. The drying temperature is a temperature lower than the glass transition point, and is preferably set to, for example, a range of about 60 ° C ± 10 ° C.

The heat treatment of the step (5) is carried out at a temperature at which the sintering of the silver powder can be achieved and at a temperature higher than the glass transition point of the thermoplastic binder resin. In the technique disclosed herein, the formation of the conductive film is performed by performing heat treatment at a lower temperature, so that heat treatment can be performed in a temperature range of 140 ° C or lower. Further, in the technique disclosed herein, as the thermoplastic binder resin, a glass transition point of 60 ° C or more and 90 ° C or less is used, so the heat treatment temperature can be set according to the glass transition point of the thermoplastic binder resin contained in the silver paste. . Further, the heat treatment temperature is preferably carried out based on the glass transition point of the thermoplastic binder resin used in the silver paste at a temperature of (glass transition point + 20) ° C or higher. For example, the heat treatment temperature is preferably from about 100 ° C to 135 ° C, more preferably from 100 ° C to 130 ° C, particularly preferably from 100 ° C to 120 ° C. This heat treatment can be carried out using various known heating devices, drying devices, and the like.

By this heat treatment, the silver powder which is a solid component of the silver paste is sintered, and the silver particles form a good electrical contact with each other. In addition, by the cooling after the heat treatment, the thermoplastic binder resin is cured to support the bonding of the sintered bodies of the silver powder, and the soft and firm adhesion of the sintered body and the PET film substrate is achieved. Thereby, a conductive film having a low electric resistance can be easily formed at a low temperature in the form of a conductive film having good adhesion to the resin substrate having flexibility. Since the conductive film is formed by a printing technique, it can be realized in any pattern to have a uniform film thickness. For example, a thin line can also be realized as the aspect ratio is higher.

Therefore, the resin substrate on which the conductive film is formed can maintain excellent adhesion between the substrate and the conductive film after being deformed. In addition, the conductive film can maintain conductivity after being deformed. Specifically, even when the substrate is deflected with a little force, peeling or cracking of the conductive film is highly suppressed. Therefore, according to the technology disclosed herein, for example, an electric circuit or the like disposed with respect to a transparent film substrate such as a touch panel or a display can be preferably formed. The substrate with a fine-line conductive film can be preferably used, for example, as an electronic component used in various fields such as an electric machine, a semiconductor device, a solar cell, a display, a sensor, and a biomedical device.

In the following, several embodiments related to the present invention are described, but the present invention is not intended to be limited to the embodiments shown.

[Preparation of Silver Powder] Silver powder was prepared in the following order. Specifically, at room temperature (25 ° C), butylamine as a surface modifier and a butanol as a solvent and particle size control agent are mixed at a predetermined molar ratio, and after adding silver oxalate, the mixture is heated while stirring. About 100 ° C, thereby obtaining a silver powder which stabilizes the surface with butylamine. The average particle diameter of the silver powder is controlled by adjusting the addition amount of the particle size controlling agent (the molar ratio of butylamine to the particle size controlling agent) and further classifying. The silver powder obtained by SEM observation had an average particle diameter of 70 nm. Further, it was confirmed that the shape of the silver powder was substantially spherical, and the spherical silver particles having an aspect ratio of less than 1.5 were 10% or less.

[Preparation of Carrier] Next, the carrier in which the silver powder was dispersed was adjusted. Specifically, as the binder, two kinds of non-crystalline thermoplastic polyester urethane resins having a softening point (Ts) and a number average molecular weight (Mn) as shown below are prepared and two kinds of non-crystalline ones are prepared. Thermoplastic polyester resin was used in the formulations and combinations shown in Tables 1 and 2 below. In addition, the amorphous polyester urethane resin is obtained by dissolving in a mixed solvent of methyl ethyl ketone and toluene. Therefore, the resin solution was evaporated to dryness, and only the amorphous polyester urethane resin was taken out and then formulated.

B1. Thermoplastic polyester urethane resin (1) Ts: 65 ° C, Mn: 40 × 10 ³ (2) Ts: 68 ° C, Mn: 20 × 10 ³ B2. Thermoplastic polyester resin (1) Ts: 67 ° C, Mn: 23 × 10 ³ (2) Ts: 84 ° C, Mn: 18 × 10 ³

Further, as a solvent, (C1) propylene glycol monophenyl ether having a boiling point of 243 ° C and (C2) ethylene glycol monophenyl ether having a boiling point of 245 ° C were prepared. Then, the resin and the solvent to be prepared are placed in a glass bottle, stirred, and then heated in a steam oven at about 100 ° C for about 10 to 20 hours to dissolve the resin. Furthermore, it is necessary to carry out hand stirring during heating. Thus, the carriers of Examples 1 to 12 were obtained.

[Preparation of Silver Paste] The prepared silver powder and the carrier were blended at a mass ratio of 74:26, and mixed and kneaded by a three-roll mill to prepare silver pastes of Examples 1 to 12. Further, the silver paste was adjusted so as to have a viscosity at 25 ° C to 20 rpm of 50 Pa × s to 150 Pa × s by adding a solvent.

[Formation of Conductive Film] The silver pastes of Examples 1 to 12 prepared as described above were applied to the surface of a film substrate (thickness: 100 μm) made of PET resin by a screen printing method. In screen printing, a #500 stainless steel mesh is used. The printed pattern is a rectangular full-coating pattern in which 3 cm × 1.5 cm is arranged and arranged, and a pattern for sheet resistance measurement to be described later. In addition, the sheet resistance measurement pattern is a linear pattern adjusted so that the total length is 10 cm or more and the width is 0.5 mm after the calcination. The substrate after the printing paste was dried by a dryer at 60 ° C for 10 minutes, and then heat-treated for 20 minutes to form the conductive films of Examples 1 to 12. In addition, the temperature of the heat treatment is set to three different types of 110 ° C, 120 ° C, and 130 ° C unless otherwise specified, thereby producing conductive films having different calcination temperatures. The film thickness of the obtained conductive film was measured and shown in the column of "calcination thickness" in Table 1 below. Further, regarding the obtained conductive film, each of the properties of sheet resistance, adhesion, durability, arithmetic mean roughness, and fine line printability was evaluated by the following method, and the results are shown in Tables 1 and 2 below. In the column.

[Sheet resistance] The sheet resistance of the linear sheet resistance measuring film formed as described above was measured. Specifically, the resistance value of the conductive film was measured by a two-terminal method under the conditions of a terminal interval (conductor length) of 100 mm and a line width (conductor width) of 500 μm using a digital multimeter. Then, based on the resistance value, the sheet resistance value is calculated based on the following equation. In addition, the sheet resistance value was converted into a value obtained by setting the converted thickness to 10 μm and the thickness of the conductive film to 10 μm. The results are shown in the columns of Tables 1 and 2. Further, the relationship between the sheet resistance of the conductive film of Examples 1 to 9 and the formulation of the binder is shown in Fig. 1 . Sheet resistance value (mΩ/□)=resistance value (Ω)×{conductor width (mm)/conductor length (mm)}×{conductor thickness (μm)/converted thickness (μm)}

[Adhesiveness] With respect to the conductive film formed as described above, the adhesion of the conductive film to the substrate was evaluated by performing an adhesion test using a double-sided tape. Specifically, first, a double-sided tape (manufactured by Nichiban Co., Ltd.), Nicetack (usually NW-10, width 1 cm × length 1.5 cm) was attached to the test stand. Then, the conductive film portion formed on the PET substrate is attached to the adhesive surface on the upper side of the double-sided tape attached to the stage, and is pressed by the finger from the back surface of the PET substrate to be sufficiently adhered. Further, the end portion of the PET substrate held by the finger is oriented in the direction along the longitudinal direction of the double-sided tape and from the initial attachment position of the PET substrate to the direction of 120° to 150° (that is, the angle formed with the PET substrate becomes The film substrate is stretched from the double-sided tape by stretching from 60° to 30° obliquely upward and rearward. When the conductive film of the film substrate after the peeling was observed, the peeling was not observed as "○" in the portion next to the double-sided tape, and "X" was observed in the peeling. The results are shown in the columns of Tables 1 and 2.

[Durability] With respect to the durability of the conductor film obtained by heat treatment at 120 ° C, heat cycle resistance and high temperature and high humidity resistance were evaluated. Regarding the heat cycle resistance, the conductor film and the substrate were held at a temperature of -20 ° C for 30 minutes, and then held at 85 ° C for 30 minutes, and the cycle was repeated for 500 cycles, and the adhesion was evaluated. With respect to high temperature and high humidity resistance, the adhesion was evaluated after the conductor film and the substrate were kept in an environment of a temperature of 60 ° C and a humidity of 90% for 500 hours. As a result of the above, the conductive film of the film substrate after the peeling was observed, and the peeling was not indicated as "○" in the portion following the double-sided tape, and the peeling was observed as "x". The results are shown in the column of Table 1.

[Arithmetic Mean Roughness] The arithmetic mean roughness was calculated by investigating the surface roughness (surface property) of the conductive film obtained by heat treatment at 120 ° C. Specifically, a high-precision surface roughness × contour shape integrated measuring machine (Tokyo Precision Co., Ltd., Surfcom) was used, and electric conduction was obtained according to Japanese Industrial Standards (JIS) B0601:2013. The cross-sectional curve in the longitudinal direction of the film was calculated from the roughness curve at a cutoff value of 0.8 mm to calculate the arithmetic mean roughness (μm). Furthermore, the scanning distance of the surface properties was set to 6 mm. The results obtained are shown in the columns of Tables 1 and 2. Further, the relationship between the arithmetic mean roughness of the conductive films of Examples 1 to 9 and the formulation of the adhesive is shown in Fig. 1 .

[Thin Line Printability] In order to evaluate the fine line printability, the silver paste was screen-printed on a PET substrate in a fine-line stripe pattern using a 500-grid screen plate. The thin line stripe pattern is a pattern in which the line and space (line width and gap) are both 50 μm and the number of lines is 20. The substrate on which the silver paste was printed as described above was placed in a dryer having a temperature of 60° C. and dried for 10 minutes, and then heat-treated for 20 minutes in a dryer at 120° C. to obtain a conductive film. Then, for the 20 linear conductor films, the thickness of the central portion was measured, and the difference between the maximum value and the minimum value of the thicknesses of the 18 linear conductive films excluding the thickest thickness and the thinnest thickness was determined. (That is, the difference D between the thickness of the second thickness of the 20 and the thickness of the second thin is obtained). Further, the difference D was evaluated based on the following indexes, and the results are shown in Table 1. D<1.5 μm: A 1.5 μm≦D<2.0 μm: B 2.0 μm≦D<2.5 μm: C 2.5 μm≦D<3.0 μm: D 3.0 μm≦D:E

[Table 1] Table 1

[Table 2] Table 2

(Evaluation) The (B1) polyester urethane resin was slightly hard compared to the (B2) polyester urethane resin and the (B2) polyester resin. Therefore, when only the polyester urethane resin (Example 1) or only the polyester resin (Example 9) is used as the binder of the silver paste, as shown in Table 1, it is known that the silver paste is used. The surface roughness (arithmetic average roughness) of the obtained conductive film, the conductive film of Example 1 was rougher than that of the conductive film of Example 9. Moreover, as shown in FIG. 2, it is known that the surface roughness of the conductive film formed using the paste containing both the (B1) polyester urethane resin and the (B2) polyester resin is probably polyesteramine. The higher the proportion of the urethane resin, the more rough it tends.

Further, as shown in Fig. 1, when only a polyester urethane resin (Example 1) or a polyester resin (Example 9) is used as a binder for a silver paste, only a polyester urethane resin is used. The conductive film of Example 1 had a high sheet resistance. However, as shown in Examples 2 to 8, it was confirmed that a sheet of a conductive film obtained from a silver paste was used by using (B1) a polyester urethane resin and a (B2) polyester resin as a binder in combination. The resistance becomes lower. When both are used in combination, it is considered that the sheet resistance is the lowest (B1) polyester urethane resin compounding ratio is about 50% by mass to 60% by mass, so that it is known that not only the two are mixed but also increased (B1) The formulation of the polyester urethane resin can also obtain a conductor film having a low electrical resistance, which is preferable in this respect. For example, it is known that in order to obtain a conductor film having a sheet resistance of about 10 mΩ/□ or less (for example, 12 mΩ/□ or less), it is only necessary to use (B1) polyester urethane resin relative to (B1) polyester amine group. The ratio of the total of the formate resin to the (B2) polyester resin may be 20% by mass to 85% by mass.

Further, it was confirmed that by using the (B1) polyester urethane resin and the (B2) polyester resin in combination, variation in sheet resistance of the conductor film caused by the firing temperature can be suppressed. For example, it is known that in order to suppress the difference between the conductive film heat-treated at 110 ° C and the conductive film heat-treated at 130 ° C to 4 mΩ/□ or less, it is only necessary to use (B1) polyester urethane. The ratio of the total of the resin (B1) polyester urethane resin to the (B2) polyester resin is about 10% by mass to 95% by mass, and is preferably set to 3 mΩ/□ or less. It is about 20% by mass to 85% by mass.

Further, regarding the adhesion of the conductive film to the PET substrate, all of the conductive films of the heat treatment temperatures of Examples 1 to 9 having a heat treatment temperature of 110 ° C to 130 ° C obtained good results. On the other hand, it was found that the durability of the conductive film of Example 9 using only the (B2) polyester resin was confirmed to be high in the durability of the conductor film of Examples 1 to 8 with respect to the heat cycle or the high temperature and high humidity environment. low. On the other hand, it was found that the fineness of the fine line printability was observed, and the silver paste of Examples 2 to 9 could print a fine line having a line width of 30 μm to 50 μm or more, but the silver of Example 1 The fine line of the paste is low in printability. The reason for this is considered to be that the printability (mesh passability) of screen printing is lowered by using only a relatively hard (B1) polyester urethane resin as a binder. Therefore, it has been found that a polyester urethane resin and a polyester resin can be used in combination as a binder in order to obtain a silver paste having both printability and durability.

Further, as shown in Table 2, Example 10 was used instead of (1) a polyester urethane resin having a glass transition temperature of 83 ° C instead of (4) a polyester amine group having a glass transition temperature of 68 ° C. An example of an acid ester resin. Example 11 is an example in which (2) a polyester resin having a glass transition temperature of 67 ° C and (2) a glass transition temperature of 84 ° C was used instead of (1) a polyester resin having a glass transition temperature of 67 ° C. As described above, it is known that a conductive film having low electrical resistance and good adhesion can be formed in the same manner as in Example 4, even if the type of the resin is changed.

On the other hand, as shown in Example 12, when (C2) ethylene glycol monophenyl ether was used as a solvent instead of (C1) propylene glycol monophenyl ether, the (B1) polyester urethane resin could not be made uniform. As a result, the surface of the obtained conductive film became rough, and the sheet resistance was the highest through all the examples. The reason for this is considered to be that the combination of the increase in electrical resistance caused by the surface roughness of the conductive film and the silver powder caused by the binder is not well performed. As the solvent, a solvent having a high solubility of the binder is preferably selected.

The specific examples of the present invention have been described in detail above, but these are merely examples and are not intended to limit the scope of the claims. The technology described in the patent application scope includes various modifications and changes to the specific examples described above.

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Fig. 1 is a graph showing the relationship between the sheet resistance of the conductive film of Examples 1 to 9 and the formulation of the binder. 2 is a graph showing the relationship between the arithmetic mean roughness of the conductive films of Examples 1 to 9 and the formulation of the binder.

Claims (9)

A silver paste for a resin substrate, which is a silver paste for forming a conductive film on a resin substrate, the silver paste for a resin substrate comprising: (A) silver powder, (B) a binder, and (C) The solvent in which the binder is dissolved, (B) the binder comprises (B1) thermoplastic polyester urethane resin having a glass transition point of 60 ° C or more and 90 ° C or less, and (B2) thermoplastic polyester resin, (B1) the thermoplastic polyester urethane resin and (B2) the thermoplastic polyester resin in a ratio of 3 parts by mass or more and 6 parts by mass or less in total of 100 parts by mass of the silver powder (A) . The silver paste for a resin substrate according to claim 1, wherein the ratio of (B1) the thermoplastic polyester urethane resin and (B2) the thermoplastic polyester resin is (B1): (B2) The mass ratio is 85:15 to 20:80. The silver paste for a resin substrate according to the above aspect of the invention, wherein the silver powder of (A) has an average particle diameter of 40 nm or more and 100 nm or less. The silver paste for a resin substrate according to any one of the above-mentioned claims, wherein a protective agent containing an organic amine having 5 or less carbon atoms is adhered to the surface of the silver powder of (A). The silver paste for a resin substrate according to any one of the items 1 to 3, wherein the solvent (C) is propylene glycol monophenyl ether. An electronic component, comprising: a resin substrate; and a conductive film provided on the resin substrate, wherein the conductive film is silver for a resin substrate according to any one of claims 1 to 5 Hardened paste. The electronic component according to claim 6, wherein the conductive film has an arithmetic mean roughness of 0.3 or less. The electronic component according to claim 6 or 7, wherein the conductive film has a sheet resistance of 12 mΩ/□ or less. A method for producing an electronic component, comprising: preparing a resin substrate; preparing a silver paste for a resin substrate according to any one of claims 1 to 5; and supplying the resin substrate with a silver paste On the flexible film substrate; drying the flexible film substrate on which the silver paste for the resin substrate is supplied; and the flexibility of supplying the silver paste for the resin substrate to the dried The film substrate is subjected to heat treatment to form a conductive film, and the temperature for performing the drying is lower than a temperature at a glass transition point of the binder contained in the silver paste for a resin substrate, and the temperature of the heat treatment is higher. The glass transition point is higher than 20 ° C.