WO2014104053A1 - Conductive paste for screen printing, method for producing wiring line, and method for producing electrode - Google Patents

Abstract

A conductive paste for screen printing according to one embodiment of the present invention contains a conductive metal powder, a binder resin and a solvent. The binder resin contains (A) a high molecular weight component that has a weight average molecular weight of from 40,000 to 100,000 (inclusive) and (B) a low molecular weight component that has a weight average molecular weight of from 5,000 to 10,000 (inclusive). The weight fraction of the low molecular weight component (B) relative to the total weight of the high molecular weight component (A) and the low molecular weight component (B), namely [100 × (B)/{(A) + (B)}] is from 5% to 70% (inclusive).

Description

Conductive paste for screen printing, wiring manufacturing method and electrode manufacturing method

The present invention relates to a conductive paste for screen printing, a wiring manufacturing method, and an electrode manufacturing method.

The screen printing method is widely adopted as a method for manufacturing electronic parts such as wiring and electrodes at a low cost. In a printing method such as gravure printing, the limit is to form a conductive circuit having a thickness of about 1 to 2 μm. On the other hand, a screen printing method is a suitable method for securing a thickness of several μm or more. .

The conductive paste used here is generally called a resin-cured or polymer-type conductive paste, and refers to a dispersion of conductive particles in an organic binder resin. Since it is in the form of a paste, it can be expected to reduce the size and weight of electronic components, improve productivity, and reduce costs. Moreover, a conductive circuit can be easily formed by printing or coating on a base material and drying. Furthermore, this drying and curing process can be performed at a low temperature without applying a high temperature to the substrate or the electronic component (see Patent Document 1).

In recent years, touch panels have been rapidly spreading as represented by smartphones and tablet terminals as intuitive and user-friendly input devices. In such touch panels for mobile terminals, which have advanced functions and high image quality, it is necessary to detect the contact position with a finger or a touch pen with high accuracy, and therefore the wiring and electrodes formed around the touch panel are miniaturized. Required. Recently, the line width of circuit wiring itself and the width between wiring lines are required to be 50 μm or less.

Various improvements in the physical properties of the conductive paste have been proposed to enable high-definition screen printing. Many of them are intended to increase the paste viscosity or to impart thixotropic properties.

For example, the viscosity of a conductive paste generally used in a screen printing method is from about several Pa · s to about 100 Pa · s at the most. Patent Document 2 discloses a conductive paste having a viscosity of 30.0 Pa · s or less at a shear rate of 500 s ⁻¹ .

On the other hand, in order to perform high-accuracy screen printing, a low viscosity is applied when an external force is applied by a squeegee or the like, but a high viscosity is maintained when no external force is applied. The paste was considered necessary.

考 え る Considering the behavior of the screen printing paste during printing, the paste moves on the screen mask plate while rotating by a squeegee called rolling. When an opening having a predetermined pattern provided on the screen is filled, the film is supplied onto the substrate through the opening to complete the transfer to the substrate. In the past, in order to be a paste capable of forming a high-definition printed pattern, it exhibits a lower viscosity when rolling and filling into openings, and the viscosity increases rapidly when transferred to the substrate. It has been considered necessary to maintain the printed shape on the substrate.

In Patent Document 3, the viscosity measured at 25 ° C. is 10 Pa · s to 200 Pa · s at 5 rpm, and the ratio (TI value) between 2 rpm and 20 rpm is 4.0 to 10.0. A paste is disclosed. Patent Document 4 discloses a thixotropic index (when a viscosity value at a shear rate of 0.6 / sec at 23 ° C. is a viscosity value A and a viscosity value at a shear rate of 6 / sec is a viscosity value B). A conductive paste having a viscosity value A / viscosity value B) of 1.2 to 2.5 and a viscosity value B of 30 Pa · s to 75 Pa · s is disclosed. However, even when a conductive paste imparted with only thixotropy is used, the print transfer amount of the paste cannot be sufficiently controlled, and it is difficult to print a high-definition pattern.

Japanese Patent Application Laid-Open No. 06-68924 JP2012-094772A JP 2010-47716 A JP 2012-17411 A

However, in the case of high-definition wiring patterns, for example, if a resin-cured conductive paste is used, even if an attempt is made to form a high-definition pattern in which the line width of the circuit wiring itself or the width between the wirings is 100 μm or less, The line width of the wiring obtained by printing is often larger than the target line width. Therefore, the use of a resin-curing type conductive paste leads to non-uniform shapes and unclear boundaries due to electrical short-circuiting and bleeding of the edge portion of the wiring, so that a favorable conductive circuit cannot be formed. Problems can become apparent.

The above-mentioned problems are mainly due to the fact that the amount of paste transferred onto the substrate greatly depends on the amount of passage from the screen opening during conductive paste printing. For this reason, if the amount of passage increases at the time of printing the conductive paste, the thin line portion is likely to bleed or become thick. At this time, the amount of passage increases as the fluidity of the paste increases. In addition, the conductive paste generally contains a large amount of conductive particles having a high specific gravity. For this reason, the final application area is printed because it flows out of the printing area due to the weight of the conductive paste itself, etc., until it is dried, solidified or cured after being transferred onto the substrate by printing. It is easy to spread over a predetermined area.

Furthermore, in order to print a high-definition circuit pattern, it is necessary to use a fine screen mesh. In order to use a fine screen mesh, it is necessary to use a conductive metal powder having a particle size as small as possible. However, the conductive metal powder having a small particle size is more likely to flow on the movement of the solvent and binder resin contained in the conductive paste being dried and solidified after printing, as compared with a powder having a large particle size. As a result, the final application region is more likely to protrude beyond the printing region, and the “widthening” phenomenon of the line width is more likely to occur. In addition, when the conductive metal powder size is reduced below a certain level, in the case of a resin-cured conductive paste, the conductivity tends to decrease due to insufficient contact between particles. For this reason, a device for increasing the conductivity (increase in the content of conductive powder, combined use of amorphous particles, addition of carbon powder, etc.) is required separately. However, the increase in the content of the conductive metal powder and the inclusion of irregular shaped particles are likely to cause an increase in the viscosity and thixotropy of the paste. Become. Furthermore, when the particle size of each powder or each particle described above becomes small, the surface area per volume of the fine powder increases as the surface energy increases due to the curvature effect. As a result, secondary agglomeration of each of the above-mentioned powders is likely to occur, and there is a problem that defects in the aging stability of the paste such as increase in viscosity during storage tend to occur.

By the way, in order to suppress the passing amount of the paste, it is generally considered that it is better to increase the paste viscosity. Therefore, in order to increase the viscosity of the paste, conventionally, there have been methods such as increasing the solid content contained in the paste, increasing the content of the conductive metal powder, or using a resin having a high molecular weight as the resin as the binder component. Has been adopted.

However, if the paste viscosity is simply increased, bleeding is less likely to occur, but the paste cannot be sufficiently dropped onto the screen plate even when pressed with a squeegee or the like. As a result, it becomes difficult to sufficiently pass through the opening of the screen plate, so that the circuit and the electrodes are chipped or faded, the wiring height is reduced and the wiring shape is uneven, resulting in a decrease in conductivity (circuit resistance). Rise) and disconnection failure may occur. Moreover, when the viscosity of the paste is high, there are problems that the paste does not spread uniformly on the printing mask plate, the paste adheres to the squeegee during printing, or does not roll uniformly. In addition, when continuous printing is performed, problems in printing work such as a change in printability with time may occur. Further, the bleeding at the time of transfer cannot be suppressed only by reducing the viscosity at a high shear rate.

Furthermore, in the so-called high-speed printing process of about 100 mm / sec requested from the industry in recent years, when the shear rate is increased, the viscosity is naturally reduced, and thus the occurrence rate of “bleeding” phenomenon is increased. Accordingly, the present inventors believe that high-definition printability cannot be realized only by controlling the viscosity of the entire paste as in the conventional method, and a multifaceted approach is necessary. Furthermore, when the paste viscosity is increased by using the above-described conventional method, there may be a problem that the adhesion with the substrate is lowered. Since a resin film is used as a base material in the touch panel, a problem of adhesion is particularly likely to occur when the base material is repeatedly deformed during operation.

Generally, a conductive paste containing an organic binder has a property (viscoelasticity) that has an elastic property (elastic deformation) simultaneously with flow (viscous flow). For this reason, it is difficult to evaluate the fluidity of the paste as a dispersion and the resulting printability by simply measuring the viscosity (steady viscosity) measured in a steady flow. Simply grasping and controlling the steady viscosity and thixotropy is not sufficient.

The above-mentioned problems are particularly noticeable when a high-definition pattern in which the line width of the circuit wiring itself and the width between the wirings are 100 μm or less is formed. Accordingly, development of a resin-cured conductive paste used for screen printing corresponding to wiring widths and wiring intervals such as 50 μm and 30 μm, which has been further improved in definition, is still halfway.

The present invention has been made in view of the above-mentioned problems, and can greatly contribute to the realization of, for example, a conductive paste used for forming fine wiring of 50 μm or less used for portable devices such as a touch panel and electrodes. .

The present inventors pay attention to the fact that the conductive paste is a dispersion system, and based on a concept different from the invention described in each of the above-mentioned prior art documents, while trying a multifaceted design based on viscous flow We conducted intensive analysis and examination. Until now, both the viscous flow and elastic deformation of the paste, more specifically, both the storage elastic modulus (elastic component) and the loss elastic modulus (viscous component) of the paste, There has been no analysis of independent control through optimization. As a result of repeated trial and error by the present inventors, as an example of its realization, a binder resin is formed by mixing a high molecular weight component and a low molecular weight component in a certain range of weight ratio. It has been found that such an appropriate relationship can be realized. The present invention was created from such a viewpoint.

That is, one conductive paste of the present invention is a conductive paste containing a conductive metal powder, a binder resin, and a solvent, and the binder resin has a high molecular weight component having a weight average molecular weight of 40,000 to 100,000. (A) and a low molecular weight component (B) having a weight average molecular weight of 5,000 or more and 10,000 or less, and the low molecular weight component (B) relative to the total amount of the high molecular weight component (A) and the low molecular weight component (B). ) Weight fraction [100 × (B) / {(A) + (B)}] satisfies 5% to 70%.

This conductive paste is excellent in printing workability and continuous printability, enables formation of a circuit pattern having a wiring width of, for example, 50 μm or less at high speed, and has good conductivity and adhesion to a substrate such as a PET film. Excellent in properties. As a result, high definition and printing workability are compatible, and further, performance required as a conductive coating film can be achieved.

Another conductive paste of the present invention is a conductive paste containing a conductive metal powder, a binder resin, and a solvent, and the viscosity of the conductive paste at 50 rpm at 25 ° C. by a rotational viscosity measurement method. 160 Pa · s to 300 Pa · s, and the loss elastic modulus at a strain amount of 0.1% is 7000 Pa to 30000 Pa.

This conductive paste is excellent in printing workability and continuous printability, enables formation of a circuit pattern having a wiring width of, for example, 50 μm or less at high speed, and has good conductivity and a substrate such as a PET film. Excellent adhesion. As a result, high definition and printing workability are compatible, and further, performance required as a conductive coating film can be achieved.

According to the present invention, high-definition and printing workability in the screen printing method are compatible, and further, performance required as a conductive coating film can be achieved. Therefore, it is possible to realize a conductive paste suitable for use in the formation of wiring and electrodes for touch panels used particularly for smartphones and tablet terminals.

Embodiments of the present invention will be described in detail below.

<First Embodiment>
The conductive paste of this embodiment is a conductive paste containing a conductive metal powder, a binder resin, and a solvent. The conductive paste as a typical example has a viscosity at 25 ° C. and 50 rpm by a rotational viscosity measurement method of 160 Pa · s to 300 Pa · s, and a loss elastic modulus at a strain amount of 0.1% is 7000 Pa to 30000 Pa. It is.

In addition, a process of applying the above-described conductive paste on a substrate typically by a screen printing method will be described below.

(Steady viscosity)
The conductive paste of the present embodiment is specified by paste viscosity at 25 ° C. and 50 rpm (hereinafter also simply referred to as “steady viscosity”) by a rotational viscosity measurement method.

A conductive paste for screen printing (hereinafter, also simply referred to as “conductive paste” or “paste”) moves on the screen mask plate while being rotated by a squeegee called rolling. The 25 ° C. and 50 rpm measured by the rotational viscosity measurement method in the present embodiment corresponds to a state where the paste is rolling in a generally performed screen printing method. This conductive paste can be screen-printed by satisfying the viscosity under the above-mentioned conditions in the range of 160 Pa · s to 300 Pa · s, more preferably 180 Pa · s to 280 Pa · s, For example, high-definition printability of 50 μm or less is possible.

If the paste viscosity is smaller than 160 Pa · s, the paste fluidity becomes too high, so that an excess paste is supplied to the opening of the mask plate provided in the screen mesh, so that the print transfer The applied paste shape tends to be non-uniform. On the other hand, if the paste viscosity exceeds 300 Pa · s, the fluidity becomes insufficient and sufficient paste is not supplied to the opening of the mask plate, so that the printed and transferred conductive paste is likely to be chipped or disconnected. .

(Loss elastic modulus)
The conductive paste of this embodiment further has a loss elastic characteristic in a specific range at a strain amount of 0.1%.

Specifically, the loss elastic modulus at a strain amount of 0.1% is preferably 7000 Pa or more and 30000 Pa or less, and more preferably 7000 Pa or more and 28500 Pa or less. The distortion amount of 0.1% corresponds to the physical properties of the paste in a static state at the start of fluidization of the paste by squeezing in the screen printing method or on the substrate through the opening. The loss elastic modulus characterizes the mechanical characteristics of the viscous component in the paste. Note that, by setting the loss elastic modulus within the above-described range at a strain amount of 0.1%, it is possible to achieve both high-definition printing and improved printing workability.

If the loss elastic modulus is less than 7000 Pa, bleeding tends to occur after print transfer. On the other hand, if the loss elastic modulus is larger than 30000 Pa, there may be a problem in printing workability that it is difficult to roll by squeezing. Furthermore, in the case of such a loss elastic modulus, it is difficult to spread (spread) the paste on the mask plate with a spatula or the like in the first place, and the amount of paste applied to the mask plate may be uneven. As a result, when printing with a particularly large mask plate, there may be a problem that local printing amount non-uniformity occurs.

(Storage modulus and yield stress)
It is a further preferable aspect of the conductive paste of the present embodiment that the storage elastic modulus and / or the yield stress at a strain amount of 0.1% are within an appropriate range.

In the conductive paste of the present embodiment, the storage elastic modulus at a strain amount of 0.1% is preferably in the range of 10000 Pa to 80000 Pa, and more preferably 15000 Pa to 50000 Pa. The storage elastic modulus characterizes the elastic component in the paste, and screen printing is possible by setting the storage elastic modulus at a strain amount of 0.1% within the above range. In addition, high-definition printing can be realized by satisfying such a range. If the storage elastic modulus is smaller than 10000 Pa, it becomes difficult to maintain the shape after print transfer. On the other hand, if it exceeds 80000 Pa, the paste is difficult to fluidize, that is, it does not roll due to squeezing, or it tends to adhere to the squeegee.

In the conductive paste of this embodiment, the yield stress is typically preferably in the range of 10 Pa to 45 Pa, and more preferably in the range of 15 Pa to 36 Pa.

Yield stress represents the difficulty of deformation and fluidization of the paste at the start of squeezing in the screen printing method, and the difficulty of deformation of the transferred shape due to its own weight in the stationary state after print transfer. If the yield stress of the paste satisfies the above range, high-definition printability and printing workability can be achieved at a higher level. Note that if the yield stress is less than 10 Pa, the paste is easily deformed, and thus deforms after printing and deteriorates the high definition of printing. On the other hand, if the yield stress is greater than 45 Pa, the paste is difficult to deform, causing a problem that it does not deform at the start of squeezing and does not roll or adheres to the squeegee.

These viscoelastic properties can be evaluated by measuring the shear stress dependence of the dynamic viscoelastic properties using a general viscoelasticity measuring device (rheometer). In addition, although the above-mentioned storage elastic modulus and yield stress are a preferable aspect even if only one is stored in the above-mentioned range, the above-mentioned storage elastic modulus and yield stress are within the above-mentioned range. It is a more preferable aspect that both are contained.

The conductive paste of the present embodiment has the above characteristics. Preferred components and compositions for imparting these characteristics will be further described below.

(Binder resin)
The binder resin of the present embodiment, which is a binder component, forms a paste-like substance form called a dispersion system together with the conductive powder, and realizes workability and printability suitable for the screen printing method in combination with the conductive powder. To do.

The type of binder resin used in this embodiment is not particularly limited. On the other hand, the present inventors employ the binder resin that combines a resin having a high weight average molecular weight (resin having a high molecular weight component) and a resin having a low weight average molecular weight (resin having a low molecular weight component). Has been found to be more accurate.

Specifically, the low molecular weight component resin is blended in the binder resin component (that is, in the total amount of the high molecular weight component resin and the low molecular weight component resin) at a ratio of 5 wt% to 70 wt%. This facilitates the development of the paste on the mask plate in the screen printing method and facilitates the wrapping of the paste into the non-opening portion of the circuit pattern. From the above viewpoint, it is more preferably 8 wt% or more and 70 wt% or less. In other words, the weight fraction [100 × (B) / {(A) + (B)}] of the low molecular weight component to the total amount of the high molecular weight component and the low molecular weight component is 5% or more and 70%. Below, more preferably 8% or more and 70% or less is satisfied.

The above action lowers the elastic modulus of the viscous component as the conductive paste, and the paste has flexibility as the paste, while the steady viscosity of the conductive paste is extremely high compared to the conventional one. This is considered to be because Moreover, by mix | blending in the above-mentioned ratio, the problem that a paste does not roll at the time of printing or it adheres to a squeegee can be avoided. Furthermore, the high viscosity of the paste as a whole is maintained at this time, thereby preventing an increase in wiring width and deterioration of high definition due to bleeding in the paste after printing.

As described above, by combining a resin with a high weight average molecular weight (resin with a high molecular weight component) and a resin with a low weight average molecular weight (resin with a low molecular weight component), even a paste with a high viscosity is caused by a flexible viscous component. Excellent printing workability and high definition can be realized. That is, as an example of the realization, the present inventors have found that a high molecular weight component and a low molecular weight component are mixed at a weight ratio within the above range, for example, a wiring having a thickness of 50 μm or less, even at high speed processing. It has been found that it is possible to form a circuit pattern with a width, and that it leads to good conductivity and excellent adhesion to a substrate such as a PET film.

From the viewpoints described above, as the resin of the high molecular weight component (also referred to as “high molecular weight component (A)”) of the present embodiment, for example, a phenoxy resin having a weight average molecular weight of 40,000 to 100,000 (hereinafter “phenoxy”). Resin (A) ") is preferably employed. In addition, it is more preferable from the above viewpoints that a phenoxy resin (A) of 50,000 or more and 80,000 or less is employed. The phenoxy resin is typically bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethyl bisphenol A, tetramethyl bisphenol F, tetramethyl bisphenol AD, tetramethyl bisphenol S, tetrabromobisphenol A, tetrachlorobisphenol A. It can be obtained by using bisphenols such as tetrafluorobisphenol A and epichlorohydrin.

(Urethane resin)
Moreover, as a high molecular weight component (A) of this embodiment, a urethane resin, a urethane modified polyester resin, and a urethane modified epoxy resin can be employ | adopted, for example. It is preferable to employ these urethane-based high molecular weight components (A) because excellent adhesion can be exhibited or maintained even when an external force or deformation is applied such that the film substrate is bent. It is one mode.

Here, the example of the above-mentioned polyurethane resin is a poly (urea) urethane resin using a polymer polyol and a polyisocyanate and, if necessary, an amine as a raw material.
Examples of the polymer polyol include polyester polyol (hydroxyl-terminated polyester resin), polycarbonate polyol, polyether polyol, polyoxyalkylene polyol, and the like.
In addition, the raw material of this polyester polyol is the same as that of the polyester resin mentioned later.
Examples of the polyisocyanate include butane-1,4-diisocyanate, 1,6-hexamethylene diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, Cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane, 1,5-naphthylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4, 4'-diphenyldimethylmethane diisocyanate, tolylene diisocyanate and the like.
Examples of the amine include diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4′-diamine, n-butylamine, mono-n-butylamine, diethanolamine, monoethanolamine, etc. Alkanolamines such as monoamine, monoethanolamine and diethanolamine.
In addition, the polyurethane resin employs an isocyanate group-terminated urethane prepolymer obtained by reacting the aforementioned polymer polyol and the aforementioned polyisocyanate with chain extension and / or chain termination with the aforementioned amine. obtain.
The weight average molecular weight of the polyurethane resin is not particularly limited. However, in consideration of the adhesion at the time of bending between the paste according to this embodiment and the substrate, the representative weight average molecular weight is 30,000 to 100,000, preferably 40,000 to 80,000.

Further, from the viewpoints described above, as the resin of the low molecular weight component (also referred to as “low molecular weight component (B)”) of the present embodiment, a phenoxy resin (hereinafter referred to as “phenoxy resin”) having a weight average molecular weight of 5000 to 10,000. B) ") is preferably employed. In addition, it is more preferable from the above viewpoints that a phenoxy resin (B) of 6000 or more and 8000 or less is employed. Therefore, the combination of the above-described high molecular weight component (A) and low molecular weight component (B) is a suitable example as a binder resin, and thus a conductive paste.

In addition, if the weight average molecular weight is less than 5000, the fluidity of the binder is increased, and bleeding tends to occur and the line width tends to increase. On the other hand, if the weight average molecular weight is greater than 10,000, the viscosity of the binder resin is increased, the flexibility of the paste is lost, and printing workability may be hindered such as difficulty in rolling during printing.

(Polyester resin)
Further, all or part of the phenoxy resin (B), which is the resin of the low molecular weight component (B), has a weight average molecular weight of 5000 to 10,000 and an acid value in the range of 10 to 50 (hereinafter referred to as “ It is also possible to replace it with “polyester resin (C)”. In the present embodiment, by combining a part or all of the above phenoxy resin (B) and the polyester resin (C), in a conductive paste used for wiring or electrodes, It is possible to obtain a wiring and / or electrode that is further excellent in film-forming properties, and that is more excellent in adhesion to a substrate, mechanical strength, and conductivity after drying / solidification / curing when formed on a resin film substrate. .

Examples of polyester resins are those obtained by reacting an acid component and a glycol component.
Examples of acid components are
Aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid; or
Aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid; or
Alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic anhydride, 1,1′-bicyclohexane-4,4′-dicarboxylic acid, 2,6-decalin dicarboxylic acid; or
And trivalent or higher polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride.
Examples of glycol components are:
Ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, neopentyl glycol, 1,4 -Aliphatic diols such as butanediol, 1,5-pentanediol, 1,6-hexanediol, dipropylene glycol; or
Alicyclic diols such as 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F; or
Trivalent or higher polyols such as glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, dipentaerythritol, sorbitol, mannitol.
In addition, although the physical property of this polyester resin is not specifically limited, A typical acid value is 10-50.

In particular, by keeping the acid value within the range of 10 or more and 50 or less, the compatibility between the above-mentioned polyester resin and the solvent is improved and appropriate flexibility is imparted to the paste. Printing workability is provided. Furthermore, it is more preferable to set the acid value to 10 or more and 50 or less from the viewpoint of obtaining sufficient adhesion to a substrate such as a resin film. If the acid value is less than 10, the adhesion to the substrate is not sufficient. On the other hand, if the acid value is higher than 50, a reaction product is generated on the surface of the conductive metal powder, and the viscosity of the paste rises during storage, which causes a problem in the temporal stability of the paste. Since the kind of polyester resin (C) used for this embodiment will not be restrict | limited especially if the said molecular weight and an acid value are satisfy | filled, what is generally known can be used.

(Polyvinyl acetal resin)
A polyvinyl acetal resin is obtained by acetalizing a polyvinyl alcohol and an aldehyde. Examples of the polyvinyl acetal resin include a polyvinyl formal resin, a polyvinyl acetoacetal resin, a polyvinyl alkyl acetal resin, a polyvinyl propional resin, a polyvinyl butyral resin, and a polyvinyl hexyl resin.

(Modified epoxy resin)
Examples of modified epoxy resins include those obtained by modifying various known epoxy resins (including the phenoxy resin) with an amine compound (amine-modified epoxy resin), and further modifying the amine-modified epoxy resin with an isocyanate compound (amine / urethane). Modified epoxy resin).
Examples of the epoxy resin include a bisphenol type epoxy resin produced by glycidylating various bisphenols, a hydrogenated product of the bisphenol type epoxy resin, a phenol novolac resin, a novolac type obtained by reacting a cresol novolac resin with a haloepoxide. Examples thereof include epoxy resins and biphenyl type epoxy resins.
Examples of the bisphenols include those described above.
Examples of the amines include aromatic amines such as toluidines, xylidines, cumidine (isopropylaniline), hexylanilines, nonylanilines, dodecylanilines; or
Cycloaliphatic amines such as cyclopentylamines, cyclohexylamines, norbornylamines; or
Methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, dodecylamine, stearylamine, icosylamine, 2-ethylhexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, diheptylamine, etc. Or alkanolamines such as diethanolamine, diisopropanolamine, di-2-hydroxybutylamine, N-methylethanolamine, N-ethylethanolamine, N-benzylethanolamine, and the like.
Examples of the polyisocyanate include those described above.

(Conductive particles)
The conductive paste exhibiting the steady viscosity and viscoelastic behavior as described above can be obtained by containing a specific conductive metal powder or a specific binder resin.

The conductive metal powder is a component that is formed by the conductive paste of the present embodiment, for example, imparts conductivity to wirings and electrodes that form a circuit.

The powder is usually mixed with primary particles and secondary particles. In the conductive metal powder in the present embodiment, it is preferable that the average particle size of primary particles is 0.1 μm or more and 2 μm or less, and the maximum particle size of secondary particles is 10 μm or less. In the screen printing method, the conductive paste is printed on the substrate through an opening provided in the screen mask plate.

In a general screen printing method using a mesh mask, the square opening formed by the stainless steel wire forming the mesh has an area ratio of 35% to 50% in order to maintain the mask strength. For example, when forming a wiring or electrode having a width of 50 μm, the maximum length of the opening is at most about 25 μm. By using a conductive metal powder with a particle size in the above-mentioned range, not only does the conductive metal powder pass smoothly through the mesh opening even when the conductive metal powder is a rigid body such as a metal, it also causes clogging during printing operations. Can not be. In addition, by using a particle size in the above-mentioned range, it is possible to prevent a decrease in steady-state viscosity and a decrease in thixotropy due to the use of extremely sized fine particles such as so-called nanoparticles having a particle size of several nanometers to several tens of nanometers. The stationary viscosity and storage elastic modulus can be expressed.

Further, those having an irregular shape in the primary particle shape exceed 60% by weight fraction in the conductive metal powder, or those having a spherical shape in the primary particle have a weight fraction in the conductive metal powder of 50% or less. It is preferable that By using a certain amount of irregularly shaped particles, the contact probability and the contact area between the conductive particles during drying / solidification / curing can be increased, and sufficiently high conductivity can be obtained as a wiring or an electrode. Further, by including an appropriate amount of spherical particles, it is possible to prevent an increase in steady viscosity and storage elastic modulus while having a high conductive solid content. In addition, since the surface area per volume is smaller than that of the irregular shape, the increase in loss elastic modulus is suppressed, and good printing workability is achieved in the spreadability of the paste on the mask plate and the rolling property during printing. Obtainable.

The primary particles in the present invention are those that are recognized as a single particle under SEM observation (observation magnifications from 1000 to 10,000 times), and the secondary particles are a plurality of particles under the same conditions. It means what is recognized as agglomerated. An indefinite shape is clearly recognized as a polygonal shape under the same observation conditions as described above. Further, the average particle size of the primary particle size is a value obtained by obtaining a circle-converted diameter by image analysis of an SEM image obtained under the same observation conditions as described above. The maximum particle diameter of the secondary particles means the maximum length of aggregates (secondary particles) obtained by observing at least 10 visual fields under the same observation conditions as described above. In addition, each particle size can be determined by using, for example, a laser diffraction / scattering particle size distribution measuring apparatus (for example, Microtrack FRA 9220 manufactured by Leeds & Northrup).

Examples of the conductive metal powder that can be used in the present embodiment include gold, silver, copper, silver-plated copper powder, silver-copper composite powder, silver-copper alloy, amorphous copper, nickel, chromium, palladium, rhodium, Metal powders such as ruthenium, indium, silicon, aluminum, tungsten, morphbutene and platinum, inorganic powders coated with these metals, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide and ruthenium oxide Etc. These conductive particles may be used alone or in combination of two or more selected from the above group. Among these conductive particles, they are highly conductive and have little increase in resistivity due to surface oxidation, so silver, copper coated with silver on the surface, and copper alloys coated with silver on the surface (zinc It is preferable to employ at least one selected from the group consisting of (and / or nickel).

(Thixotropic agent)
A thixotropic agent can be added to the conductive paste of this embodiment in order to impart thixotropic properties suitable for the screen printing method. The type of thixotropic agent is not particularly limited. For example, metal oxides such as alumina and titania, inorganic fine powders such as glass and carbon (including carbon black and graphite), and organic materials such as amide and polyethylene can be employed as the thixotropic agent. In order not to increase the storage elastic modulus and viscosity, the amount of thixotropic agent added is 1% or more and 5% or less, more preferably 1.2% or more and 4.5% or less in terms of weight fraction with respect to the total amount of paste. It is. Moreover, when a thixotropic agent shows insulation, it is preferable to set it as the said addition amount range also from a viewpoint of preventing electroconductivity. From the same viewpoint, it is desirable that the addition amount of the thixotropic agent is 1% or more and 6% or less by weight with respect to the conductive powder. In addition, when an inorganic powder thixotropic agent is used, the particle size is preferably set to 1 μm or less in order not to impede physical properties such as screen printing property, conductivity, and adhesion to a substrate.

(Curing agent)
A curing agent can be added to the conductive paste of the present embodiment from the viewpoint of promoting the curing of the binder resin and suppressing the increase in the resistance value between terminals before and after exposure to high temperature and high humidity due to the curing. Examples of curing agents that can be added are isocyanate compounds, amine compounds, acid anhydride compounds, and the like. Examples of isocyanate compounds that can be used as curing agents include polyisocyanates (unblocked isocyanates) used as raw materials for the above-mentioned polyurethane resins, blocked isocyanates produced by sealing them with various sealants, and the polyisocyanates Dimer to trimer of the above.

Examples of amine compounds among the above curing agents include aliphatic amines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenediamine, diethylaminopropylamine, N-aminoethylpiperazine, mensendiamine, isophoronediamine, hydrogenated and alicyclic amines such as m-xylenediamine, aromatic amines such as m-xylylenediamine, m-phenylenediamine, diaminodiphenylmethane, and diaminodiphenylsorbone. In addition, amine adducts, ketimines modified with these amines, polyamide resins having a reactive primary amine and secondary amine in the molecule, produced by condensation of dimer acid and polyamine, and the like can also be employed.

Examples of the acid anhydride compound among the above-mentioned curing agents include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bistrimellitate, glycerol tris trimellitate, maleic anhydride, Tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride Succinic anhydride, methylcyclohexene dicarboxylic acid anhydride, alkylstyrene-maleic anhydride copolymer, chlorendic acid anhydride, polyazeline acid anhydride, methyl nadic acid anhydride, and the like.

(solvent)
The solvent used for the conductive paste of the present embodiment is not particularly limited. It can select suitably according to types, such as the solubility of the resin to be used, and the printing method. Examples of the solvent of this embodiment include one or two types of ester solvents, ketone solvents, glycol ether solvents, aliphatic solvents, alicyclic solvents, aromatic solvents, alcohol solvents, water, and the like. It is a mixture of the above.

Examples of ester solvents include ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, dimethyl carbonate, and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone benzene, diisobutyl ketone, diacetone alcohol, isophorone, and cyclohexanenone. Examples of glycol ether solvents include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, etc., acetates of these monoethers, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene Glycol monomethyl ether, propylene glycol monoethyl ether, and the like, and acetates of these monoethers.

On the other hand, examples of the aliphatic solvent include n-heptane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane and the like. Examples of alicyclic solvents are methylcyclohexane, ethylcyclohexane, cyclohexane and the like. Examples of the aromatic solvent are toluene, xylene, tetralin and the like. Examples of alcohol solvents (excluding the above-mentioned glycol ether solvents) are ethanol, propanol, butanol and the like.

(Other additives)
The conductive paste of the present embodiment includes a dispersant, a surface treatment agent, a friction improver, an infrared absorbent, an ultraviolet absorbent, an aromatic, an antioxidant, an organic pigment, an inorganic pigment, and an antifoaming agent as necessary. , Silane coupling agents, titanate coupling agents, plasticizers, flame retardants, humectants, ion scavengers, and the like.

(Method of mixing components)
The conductive paste of the present embodiment is prepared by blending a conductive metal powder, a binder resin, a solvent, and the above-mentioned thixotropic agent in a predetermined ratio as necessary, and mixing with a known kneader or disper. Obtained by. In addition, an electrically conductive paste can also be obtained by mixing and dispersing with a three roll etc. as needed.
In addition, the usage-amount of the above-mentioned electroconductive metal powder, binder resin, a solvent, and a thixotropic agent is not specifically limited. However, in order to make it easy to set the viscosity, loss elastic modulus, and storage elastic modulus of the conductive paste of the present embodiment within the above-described ranges, typical numerical ranges are set as follows.
Conductive metal powder: 65 wt% or more and 85 wt% or less Binder resin: 4 wt% or more and 8 wt% or less Solvent: 10 wt% or more and 30 wt% or less Thixo agent: 1 wt% or more and 6 wt% or less

(Paste printing method)
By using the conductive paste of this embodiment and printing on a substrate by various printing methods, high-definition wiring and electrodes can be formed. The shape of the formed wiring or electrode is not particularly limited because it can appropriately correspond to various wiring patterns, electrode patterns, and the like.

Further, the conductive paste of the present embodiment can be suitably applied particularly to the screen printing method, but may be applied to various conventionally known printing methods. In the screen printing method, a screen with a fine mesh of 500 mesh or more is particularly preferable in order to cope with the high definition of the wiring width of 50 μm or less and the distance between the wiring and the electrode. It is preferable to use one having a diameter of 20 μm or less. Arbitrary wirings and electrode patterns are formed on the screen mask plate with an emulsion or the like. In addition, the conductive paste is printed on the substrate through a screen mask opening formed by an opening such as an emulsion and a mesh opening. The area of the screen mask opening is preferably at least 30% with respect to the area of the opening of the transfer pattern formed by an emulsion or the like.

The typical screen plate type of this embodiment is a polyester screen, a combination screen, a metal screen, a nylon screen, or the like. In particular, when printing the conductive paste of the present embodiment, which has a relatively higher viscosity than before, it is preferable to use a high-tensile stainless steel wire. The squeegee used for screen printing may be round, rectangular or square, and an abrasive squeegee can also be used to reduce the attack angle (the angle between the printing plate and the squeegee). . Conventionally known conditions can be appropriately adopted as other printing conditions.

(Drying / solidification / curing method after printing)
The conductive paste according to this embodiment is printed and transferred onto a substrate such as a substrate as described above, and then heated and dried and solidified, and is cured by a reaction between a curing agent and a binder resin. For sufficient volatilization of the solvent and reaction between the curing agent and the binder resin, the heating temperature is preferably 100 ° C. or higher and 150 ° C. or lower, and the heating time is preferably 5 minutes or longer and 120 minutes or shorter, for example.

(Base film)
The kind of the substrate on which the conductive paste of this embodiment is printed is not particularly limited, and a known material can be used. For example, typical resin film substrates are polyimide films, polyparaphenylene terephthalamide films, polyether nitrile films, polyether sulfone films, polyethylene terephthalate films, polyethylene naphthalate films, polyvinyl chloride films, and the like. Typical substrate films are so-called ITO films formed by sputtering, wet coating, etc. on polymer films such as polyethylene terephthalate, polyethylene naphthalate polyester film, polycarbonate, polyethersulfone, acrylic resin, etc. ITO glass having an ITO layer formed on glass. Moreover, a ceramic, a glass base material, etc. can be used as a base material with which the conductive paste of this embodiment is printed.

In particular, in the touch panel, an ITO film in which an ITO layer is formed on a polyester film or an ITO glass in which an ITO layer is formed on glass is often used. Further, if necessary, an anchor coat layer may be provided on the substrate, and a conductive paste may be printed on the anchor coat layer. An anchor coat layer will not be specifically limited if the adhesiveness with a base material and also the adhesiveness of an electroconductive paste are favorable. Moreover, organic fillers, such as resin beads, and inorganic fillers, such as a metal oxide, can also be added as needed. The method for providing the anchor coat layer is not particularly limited. For example, the anchor coat layer can be obtained by coating, drying and curing using a conventionally known coating method.

(Preferred example of application)
The conductive paste according to the present embodiment can be used for forming wiring and electrodes in a touch panel used for a smartphone, a tablet terminal, or the like. However, the application is not particularly limited because it can be widely used in various industries.

[Example]
Hereinafter, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the following examples are only for exemplification of the present embodiment, and do not limit the present embodiment. In the examples, “parts” and “%” mean parts by weight and% by weight, respectively.

Each component was blended at a blending ratio shown in Table 1, and kneaded with a three-roll mill to obtain a conductive paste.

The abbreviations and symbols in Table 1 are as follows.
-Phenoxy resin 1: manufactured by Mitsubishi Chemical, 1256, weight average molecular weight 56000
-Phenoxy resin 2: manufactured by Nippon Steel & Sumitomo Chemical, YP-50, weight average molecular weight 70000
-Modified epoxy resin: Arakawa Chemicals, KA1433J, weight average molecular weight 90000
Polyvinyl acetal resin a: manufactured by Sekisui Chemical Co., Ltd., ESREC BM-5, weight average molecular weight 53000
Urethane modified polyester resin: manufactured by Toyobo, Byron UR-3200, weight average molecular weight 40000
Urethane resin: manufactured by Asahi Glass, Preminol-4019, Sumika Bayer Urethane Sumidur 44S, and solvent (carbitol acetate type) mixed and heated, weight average molecular weight 56000
Phenoxy resin 3: manufactured by Mitsubishi Chemical Corporation, 4010P, weight average molecular weight 6000
-Polyester resin A: manufactured by Unitika, XA0847, weight average molecular weight 8000, acid value 10 mgKOH / g
Polyester resin B: manufactured by Unitika, XA0653, weight average molecular weight 5000, acid value 20 mgKOH / g
Polyester resin C: manufactured by Toyobo, Byron 200, weight average molecular weight 17000, acid value <2 mg KOH / g
Phenoxy resin 4: manufactured by Mitsubishi Chemical, YX6954, weight average molecular weight 38000
Polyvinyl acetal resin b: manufactured by Sekisui Chemical Co., Ltd., ESREC KS-5, weight average molecular weight 130000
AgC-251 (irregular shape, silver powder): manufactured by Fukuda Metal Foil Powder Industry, AgC-251 (irregular shape, silver powder), average primary particle size 1.5 μm, maximum primary particle size 6 μm
AG-2-1C (spherical, silver powder): manufactured by DOWA Electronics, AG-2-1C (spherical, silver powder), average primary particle size 0.8 μm, maximum primary particle size 3 μm
AgC-201Z (flaky silver powder): manufactured by Fukuda Metal Foil Powder Industry, AgC-201Z (flaky silver powder), average primary particle size 4 μm, maximum primary particle size 10 μm
AO-SCX-1 (spherical, silver-coated powder): manufactured by DOWA Electronics, AO-SCX-1 (spherical silver-coated copper-zinc powder), average primary particle size 2 μm, maximum primary particle size 8 μm
AO-SCX-3 (spherical, silver coated powder): manufactured by DOWA Electronics, AO-SCX-3 (spherical, silver coated copper zinc nickel powder), average primary particle size 2 μm, maximum primary particle size 9 μm
AgC-B (indefinite shape, silver powder): manufactured by Fukuda Metal Foil Powder Industry, AgC-B (indefinite shape, silver powder), average primary particle size 5 μm, maximum primary particle size 20 μm
・ Curing agent: Blocked isocyanate (manufactured by Asahi Kasei Chemicals, Duranate SBN-70D)
・ Surface treatment agent: Titanate coupling agent (manufactured by Ajinomoto Fine-Techno, Plenact KR-TTS)
・ Thixotropic agent 1: metal oxide (manufactured by Nippon Aerosil Co., Ltd., AEROSIL, R202)
・ Thixotropic agent 2: inorganic fine powder (made by Lion, carbon ECP600JD)

The various characteristics of each conductive paste obtained by the above treatment were evaluated. The evaluation results are shown in Table 2. A specific evaluation method is as follows.

(Steady viscosity measurement)
In this example, the paste viscosity at each rotational speed of 1, 10, 50, and 100 rpm at 25 ° C. was measured with a Brookfield viscometer (model, HBT).
(Dynamic viscoelasticity measurement)
In this example, dynamic viscoelasticity measurement at 25 ° C. was performed with a Haake viscoelasticity measuring device (model, MARS). The specific measurement method is as described in (1) to (3) below.
(1) First, using a parallel plate made of titanium having a diameter of 35 mm, a conductive paste (sample) is sandwiched so that the gap is 0.3 mm.
(2) Next, a shear strain of 0.01 to 100% is applied to the sample at a frequency of 1 Hz while sweeping.
(3) The yield stress is measured from the linear deformation region of the dynamic storage elastic modulus and dynamic loss elastic modulus when the shear stress of (2) is applied, and the storage elastic modulus.

Printing of each conductive paste shown in each example and comparative example was performed using a high-precision screen printing apparatus (manufactured by Mino Group, model, access ASII-S5565). More specifically, using a screen mask plate (manufactured by Murakami Co., Ltd.) having a number of fine wiring patterns of 50 μm, 30 μm and 25 μm line and space shapes, on a polyethylene terephthalate film substrate (manufactured by Toray Industries, Inc., model, 100 sheets were continuously printed in a 500 × 500 mm area of Lumirror T60, 125 μm thick). Then, it was dried at 130 ° C. for 30 minutes. The conditions for screen printing are as follows.

(Printing conditions)
・ Screen: Stainless steel mask 640 mesh ・ Screen frame: 950 × 950 mm
・ Wire diameter: φ15mm
・ Emulsion: IC-10000
・ Thickness: 21μm
・ Total thickness: 33μm Tolerance ± 2μm
・ Squeegee: Urethane polishing squeegee ・ Squeegee angle: 75 °
・ Ski Dia Attack Angle: 50 °
・ Squeegee hardness: 80 degrees ・ Squeegee speed: 50 to 100 mm / second ・ Squeegee push-in amount: 2.0 mm
・ Clearance: 3.0mm

Various performances of the conductive paste wiring pattern coating obtained by the above process were evaluated. The evaluation results are shown in Table 3. A specific evaluation method is described below.

(Printability evaluation)
The shape of the wiring part printed on the screen (linearity and bleeding of the wiring) is observed using a three-dimensional laser microscope (VK-X200 manufactured by Keyence Corporation), and the fine line after printing using the attached image analyzer I read the width. Specifically, with respect to the fifth printed matter, an arbitrary value of line width and space width was determined by selecting five arbitrary line and space sets and measuring 200 locations per set. .

(High-definition printability)
Appearance shape, average line width, and average line height were evaluated.
[Appearance shape]
The evaluation criteria (◯, Δ, ×) of the external shape in the fine wiring portion of the line (wiring) portion are as follows.
○: The fine wiring portion was free from variation in thickness due to meandering, bleeding, wrinkling, and chipping, and the boundary line of the fine wiring portion was clear and good.
Δ: Some variation in thickness due to meandering was observed in the fine wiring part, but no bleeding, wrinkling or chipping occurred, and there was no problem in practical use.
X: The fine wiring portion had a variation in thickness due to meandering, bleeding, wrinkling and chipping, and the boundary line was unclear.
[Line width]
The evaluation criteria (◯, Δ, ×) of the high definition of the printed line and space are as follows.
A: The difference in the line width of the printed conductive paste with respect to the line pattern width of the screen mask plate was good within 10%.
Δ: The difference in the line width of the printed conductive paste with respect to the line pattern width of the screen mask plate is more than 10% and within 20%, which is practically satisfactory.
X: The difference in the line width of the printed conductive paste exceeded 20% with respect to the line pattern width of the screen mask plate, which was a practically problematic level.
[Line height]
The evaluation criteria (◯, Δ, ×) of the print transferability of the printed line and space are as follows.
A: The average line height of the printed conductive paste was 5 μm or more, which was good.
Δ: The average line height of the printed conductive paste was 3 μm or more and less than 5 μm, and there was no practical problem.
X: The average line height of the printed conductive paste was less than 3 μm, which was a practically problematic level.

(Basic performance evaluation)
Furthermore, the conductivity and adhesiveness which become the basic performance were evaluated about the coated object of the electrically conductive paste of this embodiment. The evaluation results are shown in Table 3. The specific evaluation method is as follows.
(Printability)
The spreadability of the paste on the screen mask plate, the rolling property during printing, and the squeegee adhesion during printing were evaluated by appearance observation. Evaluation criteria (◯, ×) are as follows.
[Paste expandability]
◯: When the paste was spread on the mask plate, it was faint, and the paste amount was hardly generated, and the spreadability was good.
X: When paste was spread on the mask plate, it was faint, and the paste amount was likely to be non-uniform, resulting in a practical problem.
[Rolling property during printing]
○: The paste did not roll during printing, or a difficult situation did not occur and was good.
X: The paste was difficult to roll during printing, and it was a level causing a problem in practical use.
[Squeegee adhesion during printing]
○: No squeegee adhesion of paste occurred during printing.
X: Squeegee adhesion of the paste is likely to occur at the time of printing, which is a level that causes a practical problem.

(Conductivity measurement)
A pattern of 0.5 cm × 10 cm is formed on a glass substrate, and after heat treatment at 130 ° C. for 30 minutes, the resistance value is measured by a four-probe method, and the specific resistance is based on the sheet resistance and film thickness. The value was calculated to determine the conductivity. Evaluation criteria (◯, Δ, ×) are as follows.
○: The specific resistance value was less than 5.0 × 10 ⁻⁵ Ωcm, which was favorable.
Δ: Specific resistance value is 5.0 × 10 ⁻⁵ Ωcm or less and less than 1.0 × 10 ⁻⁴ Ωcm, which is a practically acceptable level.
X: The specific resistance value was 1.0 × 10 ⁻⁴ Ωcm or more, which was a practically problematic level.
(Adhesion evaluation)
Screen printing of polyethylene terephthalate film (manufactured by Toray Industries, Inc., model, Lumirror T60, 125 μm thickness) with each conductive paste shown in each example and comparative example so that the film thickness after drying is about 5 μm to 10 μm. did. Then, it is dried at 150 ° C. for 30 minutes, and a cross-cut cello tape (registered trademark) peel test based on a test method related to JIS (Japanese Industrial Standards), K5600-5-6 (Coating adhesion (cross-cut method)) The adhesion was evaluated. The evaluation criteria (◎, ○, Δ, ×) are as follows.
In addition, the test piece which was ○ in the above adhesion evaluation was further bent 180 ° three times in a state where it was wound around a cylindrical mandrel having a diameter of 20 mm in accordance with JIS (Japanese Industrial Standard), K5600-5-1. Thereafter, the occurrence of cracks was visually confirmed to evaluate whether or not there was a change in conductivity. In this test, no peeling occurred and no change in conductivity was evaluated as “◎”.
○: Good adhesion without peeling.
Δ: Slightly peeled off, adhesion slightly poor.
X: There is peeling across the entire surface and poor adhesion.
(Double-circle): After a bending test, there is no peeling visually and there is no change in electroconductivity.

Further, Examples 1, 4, 9, 11, 13, and 14 and Comparative Examples 1, 3, 6, and 7 were evaluated for continuous printability and high-speed printability. The evaluation results are shown in Table 4. The specific evaluation method is as follows.
(Continuous printability)
Change rate of line width ((average line width of 100th sheet−average line width of 5th sheet) ÷ average line width of 5th sheet) and change rate of line height ((average line height of 100th sheet− The average line height of the fifth sheet) / average line height of the fifth sheet) was determined. Evaluation criteria (◯, Δ, ×) are as follows.
○: The rate of change was within 10%, which was good.
(Triangle | delta): The change rate exceeded 10% and was 20% or less, and it was the level which is practically satisfactory.
X: The rate of change exceeded 20%, and it was at a level causing practical problems.

(High-speed printability)
Change rate of line width of 100 mm / second with respect to squeegee speed of 50 mm / second ((average line width at 100 mm / second−average line width of 50 mm / second) ÷ 50 mm in the fifth printed matter with a line and space of 30 μm Average line width of / second) and the rate of change of the line height ((average line height at 100 mm / second−average line height of 50 mm / second) ÷ average line height of 50 mm / second), respectively. Evaluation criteria (◯, Δ, ×) are as follows.
○: The rate of change was within 10%, which was good.
(Triangle | delta): The change rate exceeded 10% and was 20% or less, and it was the level which is practically satisfactory.
X: The rate of change exceeded 20%, and it was at a level causing practical problems.

The disclosure of each of the above-described embodiments is described for explaining the embodiments, and is not described for limiting the present invention. In addition, modifications that exist within the scope of the present invention including other combinations of the above-described embodiments and examples are also included in the scope of the claims.

The conductive paste of the present invention can be widely used in various industries. Particularly preferably, the conductive paste is used for the formation of wiring and electrodes for touch panels used in smartphones and tablet terminals, but the use is not particularly limited.

Claims (20)

1. A conductive paste containing a conductive metal powder, a binder resin, and a solvent,
   The binder resin is
   A high molecular weight component (A) having a weight average molecular weight of 40,000 to 100,000, and a low molecular weight component (B) having a weight average molecular weight of 5,000 to 10,000, and the high molecular weight component (A) and the low molecular weight component ( The weight fraction [100 × (B) / {(A) + (B)}] of the low molecular weight component (B) with respect to the total amount of B) satisfies 5% to 70%,
   Conductive paste for screen printing.
2. The viscosity of the conductive paste at 25 ° C. and 50 rpm by a rotational viscosity measurement method is 160 Pa · s to 300 Pa · s, and the loss elastic modulus at a strain amount of 0.1% is 7000 Pa to 30000 Pa.
   The conductive paste for screen printing according to claim 1.
3. The storage elastic modulus at a strain amount of 0.1% is 10,000 Pa or more and 80,000 Pa or less.
   The conductive paste for screen printing according to claim 1 or 2.
4. Yield stress is 10 Pa or more and 45 Pa or less,
   The conductive paste for screen printing according to any one of claims 1 to 3.
5. The binder resin further includes a polyester resin (C) having an acid value of 10 or more and 50 or less,
   The conductive paste for screen printing according to any one of claims 1 to 4.
6. The average particle size of primary particles contained in the conductive metal powder is 0.1 μm or more and 2 μm or less,
   With respect to the conductive metal powder, the weight fraction of the primary particles exhibiting an indefinite shape exceeds 60%, and
   The maximum particle size of the secondary particles contained in the conductive metal powder is 10 μm or less,
   The conductive paste for screen printing according to any one of claims 1 to 5.
7. The average particle size of primary particles contained in the conductive metal powder is 0.1 μm or more and 2 μm or less,
   The weight fraction of the primary particles that are spherical with respect to the conductive metal powder is 50% or less, and the maximum particle size of the secondary particles contained in the conductive metal powder is 10 μm or less.
   The conductive paste for screen printing according to any one of claims 1 to 5.
8. In addition, it contains a thixotropic agent,
   The weight fraction of the thixotropic agent is 1% or more and 5% or less with respect to the entire conductive paste.
   The conductive paste for screen printing according to any one of claims 1 to 7.
9. The conductive metal powder is at least one selected from the group consisting of silver, copper coated with silver, and a copper alloy coated with silver.
   The conductive paste for screen printing according to any one of claims 1 to 8.
10. The conductive paste is for touch panel wiring or electrodes,
    The conductive paste for screen printing according to any one of claims 1 to 9.
11. A step of applying the conductive paste according to any one of claims 1 to 10 on a substrate by a screen printing method,
    Wiring manufacturing method.
12. A step of applying the conductive paste according to any one of claims 1 to 10 on a substrate by a screen printing method,
    Electrode manufacturing method.
13. The screen mesh is formed of a high-tensile stainless steel wire of 500 mesh or more,
    The manufacturing method of the wiring of Claim 11 or Claim 12.
14. A conductive paste containing a conductive metal powder, a binder resin, and a solvent,
    The viscosity of the conductive paste at 25 ° C. and 50 rpm by a rotational viscosity measurement method is 160 Pa · s to 300 Pa · s, and the loss elastic modulus at a strain amount of 0.1% is 7000 Pa to 30000 Pa.
    Conductive paste for screen printing.
15. The binder resin is
    A high molecular weight component (A) having a weight average molecular weight of 40,000 to 100,000, and a low molecular weight component (B) having a weight average molecular weight of 5,000 to 10,000, and the high molecular weight component (A) and the low molecular weight component ( The weight fraction [100 × (B) / {(A) + (B)}] of the low molecular weight component (B) with respect to the total amount of B) satisfies 5% to 70%,
    The conductive paste for screen printing according to claim 14.
16. The storage elastic modulus at a strain of 0.1% is 10,000 or more and 80,000 Pa or less.
    The conductive paste for screen printing according to claim 14 or claim 15.
17. Yield stress is 10 Pa or more and 45 Pa or less,
    The conductive paste for screen printing according to any one of claims 14 to 16.
18. A step of applying the conductive paste according to any one of claims 14 to 17 on a substrate by a screen printing method,
    Wiring manufacturing method.
19. A step of applying the conductive paste according to any one of claims 14 to 17 on a substrate by a screen printing method,
    Electrode manufacturing method.
20. The screen mesh is formed of a high-tensile stainless steel wire of 500 mesh or more,
    20. A method for manufacturing a wiring according to claim 18 or claim 19.