JP2011057859A - Low temperature-curable electroconductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroconductive paste thermally curable at ≤150°C, capable of forming an electroconductive film exhibiting excellent adhesiveness, for example, to the surface of a PET film or a polyimide film, and having flexibility and toughness, and suitable for the formation of a wiring layer of a flexible printed board. <P>SOLUTION: The electroconductive paste is obtained by selecting an acrylic resin having 284-946 epoxy equivalent, 58-155 hydroxy value, 30,000-170,000 molecular weight, and 10-55°C glass transition temperature as a resin component, and compounding 3-8 pts.mass of the acrylic resin, 0.1-1.5 pts.mass of a silane coupling agent and 8-25 pts.mass of an organic solvent having ≥150°C and ≤266°C boiling point under the normal pressure with 100 pts.mass of metallic silver powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a conductive paste that can be cured by heat treatment at 150 ° C. or lower. In particular, the present invention relates to a low-temperature curable conductive paste that can be used for forming a conductive film having good adhesion to the surface of a PET film or polyimide film, which is used as a base material for a flexible printed circuit board.

  The conductive paste is widely used for forming a conductive film for wiring on a printed wiring board. Specifically, a conductive paste coating film is formed on a substrate of a printed circuit board in accordance with the wiring pattern, and a conductive film for wiring is formed by heat treatment.

  For example, in the case of a rigid substrate using a ceramic material as a base material of a printed board, various coupling agents are used to improve the adhesion between the ceramic material and the resin component blended in the conductive paste. . For example, by using a silane coupling agent, various reactive functional groups derived from the silane coupling agent are introduced on the surface of the ceramic material. The reactive functional group contained in the resin component is reacted with the reactive functional group to generate a covalent bond, so that the resin component is covalently bonded to the surface of the ceramic material. Various reactive functional groups derived from the silane coupling agent are also introduced into the surfaces of conductive fillers, for example, various metal filler particles, which are blended in the conductive paste. As a result, the resin component is also covalently bonded to the surface of the conductive filler, for example, various metal filler particles.

  That is, by applying a heat treatment to the coating film of the conductive paste on the surface of the ceramic material, the blended resin component is covalently bonded to the surface of the ceramic material and various metal filler particles. As a result, physical contact between various metal filler particles is achieved by the adhesive force of the cured resin as the resin component to be blended is thermally cured, and a conductor film is formed. At the same time, the formed conductor film is in close contact with the surface of the ceramic material due to the adhesion of the cured resin that is covalently bonded to the surface of the ceramic material.

  The ceramic material used for the base material of the rigid substrate is usually excellent in heat resistance, and can be heat-treated at a temperature of 250 ° C. or higher, for example. Therefore, a thermosetting resin material that can be thermoset by heat treatment at 200 ° C. or higher is used as a resin component blended in the conductive paste to be used. Specifically, when applied to a printed wiring board having a ceramic material as a base material, a thermosetting epoxy resin having a thermosetting temperature of 200 ° C. or higher is widely used as a resin component to be blended in the conductive paste. A thermosetting epoxy resin having a thermosetting temperature of 200 ° C. or higher is not reactive under normal storage conditions, for example, a temperature of 50 ° C. or lower, and the viscosity increases due to the reaction between the blended resin components. Is almost nothing.

  A rigid substrate, for example, a printed wiring board having a ceramic material as a base material, does not inherently cause bending deformation. Therefore, the conductor film formed on the surface of the printed wiring board does not have to be flexible enough to bend and deform following the deformation of the printed wiring board. A cured product of a thermosetting epoxy resin is poor in flexibility but does not require bending deformation. For example, when applied to a printed wiring board based on a ceramic material, lack of flexibility is a problem. Must not.

  On the other hand, a flexible printed circuit board that uses an insulating resin material that has excellent flexibility and can be repeatedly bent and deformed as a base material that constitutes a printed wiring board. A material capable of bending deformation is used. At present, a copper plating foil film that can be repeatedly bent and deformed and exhibits excellent electrical conductivity without causing internal breakage due to the bending deformation is used. The base material (base film) of the flexible printed board is a film-like insulating resin material having a thickness of 50 μm or less, and an adhesive layer is formed on the surface, and then a copper plating foil film layer is formed. Further, the copper plating foil film layer is covered with an insulating resin film for the purpose of preventing peeling of the copper plating foil film layer and protecting the surface. That is, substantially the entire surface of the flexible printed circuit board is covered with the insulating resin film except for the terminal portion provided on the printed circuit board and the part where various electronic components are soldered and fixed on the printed circuit board. Adhesion between the insulating resin film for coating and the copper plating foil film layer is also achieved by providing an adhesive layer. In other words, the adhesive fixing is performed using two adhesive layers so that the copper plating foil film layer is sandwiched between the insulating resin material film of the base material (base film) and the insulating resin film for covering. Yes.

  Similar to the formation of the wiring layer of the rigid substrate, it has been studied to use a conductive paste for forming the wiring layer of the flexible printed circuit board in place of the copper plating foil film layer. In that case, the conductor film produced using the conductive paste is required to exhibit high adhesion to the base material (base film) surface of the flexible printed circuit board. Further, like the copper plating foil film, the conductor film itself can be repeatedly bent and deformed, and it is also required that the internal deformation does not occur due to the bending deformation.

  That is, the resin material constituting the conductive film formed by using the conductive paste has flexibility that allows repeated bending deformation, and toughness that does not cause internal breakage due to bending deformation. It is necessary to be. In addition, it is required to be a resin material having high adhesion to the surface of the substrate (base film).

  The softening point (Vicat B) of PET (Polyethylene terephthalate) film, which is widely used as a base material (base film) for flexible printed circuit boards, is about 160 ° C, or the softening point of polyimide film (Polyimide terephthalate) Vicat B) is around 220 ° C. Therefore, when a conductive film is formed on the surface of a PET film or polyimide film using a conductive paste, the contained thermosetting resin material is heated at a heating temperature significantly lower than the softening point. It must be curable.

  That is, when producing a conductor film from a conductive paste, heat is applied at a heating temperature significantly lower than the softening point of various film-like insulating resin materials used as a base material (base film) of a flexible printed circuit board. A curable conductive paste is desired. Furthermore, the produced conductor film exhibits excellent adhesion to the surface of various film-like insulating resin materials, and can be repeatedly bent and deformed, and the internal deformation may be caused by bending deformation. It is desired to have no toughness.

  The present invention solves the above problems. The object of the present invention is to be thermosetable at a heating temperature significantly lower than the softening point of various film-like insulating resin materials used as a base material (base film) of a flexible printed circuit board, and produced. The conductor film has excellent adhesion to the surface of various film-like insulating resin materials, has flexibility that allows repeated bending deformation, and toughness that does not cause internal breakage due to bending deformation. It is an object of the present invention to provide a novel conductive paste that satisfies the requirement of being prepared. In particular, the object of the present invention is to thermally cure at a heating temperature of 150 ° C. or lower, which is significantly lower than the softening point of a PET film or a polyimide film that is widely used as a base material (base film) of a flexible printed circuit board. It is possible, and the produced conductor film exhibits excellent adhesion to the surface of the PET film or polyimide film, and can be repeatedly bent and deformed, and does not cause internal breakage due to bending deformation. It is an object of the present invention to provide a novel conductive paste that satisfies the requirement of having toughness and a method for producing the same.

  In order to solve the above-described problems, the present inventors have searched for a resin component that can be used for producing a conductive paste that can be thermoset at a heating temperature of 150 ° C. or lower.

  At this time, this resin component does not show reactivity under normal storage conditions, for example, at a temperature of 30 ° C. or lower, and a significant increase in viscosity occurs due to a reaction between the resin components blended in the conductive paste. We searched for things that satisfy the condition of not.

  First, when a conductive film is formed using a conductive paste, the formed conductive film exhibits conductivity when a conductive filler is in close contact therewith. Therefore, in order to make the conductivity of the conductor film comparable to that of the copper plated foil film layer, the conductivity of the conductive material (metal) itself constituting the conductive filler is superior to that of copper. I thought it was necessary. Therefore, metallic silver powder was adopted as a conductive filler component blended in the conductive paste.

  In order to bring the metallic silver powder into close contact, it was thought that when the binder resin was cured, it was necessary to exhibit high adhesion even to the surface of the metallic silver powder. Therefore, a silane coupling agent was used as a means for improving the adhesion to the surface of the metal silver powder in the conductive paste. On the other hand, it is desirable that the silane coupling agent reacts with a functional group introduced on the surface of the metal silver powder and the binder resin is bonded covalently. That is, the resin component desirably contains a functional group having reactivity with respect to the functional group derived from the silane coupling agent.

  At the same time, in order to show excellent adhesion to the surface of the PET film or the polyimide film, a functional group is previously provided on the surface of these films, reacts with the functional group, and the binder resin is covalently bonded. Desirably, the form is combined. That is, it is desirable that the resin component contains a functional group having reactivity with a functional group provided in advance on the film surface.

  Furthermore, the resin component itself needs to cause curing when subjected to heat treatment, and it is necessary that a crosslink be formed between the resin components via a covalent bond. That is, it is desirable that the resin component has at least two functional groups that can be used to form a crosslink through a covalent bond.

  On the other hand, as a result of the cross-linking formed between the resin components through a covalent bond between the resin components, the cured resin has a flexibility that allows repeated bending deformation and the bending deformation. It is necessary to have toughness that does not cause breakage. That is, the thermosetting product of the resin component needs to be elastically deformable and at the same time be difficult to break due to tension.

  Moreover, it is also necessary that the uncured resin component can be uniformly dissolved in the dispersion solvent for the metallic silver powder used for the preparation of the conductive paste. That is, the uncured resin component needs to be soluble in the dispersion solvent.

  The present inventors have found that an acrylic resin into which two types of functional groups of an epoxy group and a hydroxyl group are introduced is suitable as a resin component that satisfies all the above requirements. At that time, the average molecular weight of the acrylic resin is 300,000 or less in order to satisfy the condition that it is soluble in the dispersion solvent, and the average molecular weight is 3 to exhibit sufficient toughness when crosslinked. We also found that it is desirable to be over 10,000. On the other hand, the abundance ratio of the two types of functional groups introduced epoxy group and hydroxyl group is within the range of 284 to 946 epoxy equivalent for the epoxy group, and within the range of 58 to 155 for the hydroxyl group. It has also been found that it is preferable.

  That is, when the existing ratio of the two types of functional groups of the introduced epoxy group and hydroxyl group is selected within the above range, the density of crosslinking via the covalent bond between the resin components in the thermosetting product of the resin component Verifies that the required characteristics, ie, elastic deformation is possible, and at the same time, it is within an appropriate range for achieving toughness that is less likely to break due to tension.

  It was also confirmed that two types of functional groups, an epoxy group and an epoxy group introduced into the acrylic resin, for example, an epoxy group have reactivity with a functional group provided in advance on the film surface. Moreover, two types of functional groups of an epoxy group and a hydroxyl group, for example, an epoxy group have reactivity with a functional group introduced by a silane coupling agent.

  Moreover, if the existing ratio of the two types of functional groups of the introduced epoxy group and hydroxyl group is in the above range, it is dissolved in a dispersion solvent at normal storage conditions, for example, at a temperature of 30 ° C. or lower. It was also confirmed that there was no crosslink formation between the acrylic resins, and the fluidity was not significantly reduced (viscosity was significantly increased).

  On the other hand, it was also verified that the glass transition point of the acrylic resin itself can be selected in the range of 10 to 55 ° C. by adjusting the average molecular weight. The cross-linking by the two functional groups, epoxy group and hydroxyl group, is usually progressed by heating to 120 ° C. or higher, and the desired thermoset under heating conditions of 150 ° C. or lower at the highest. It was also verified that the formation of

  That is, metal silver powder is used as the conductive filer component, and the epoxy equivalent of 284 to 946 and the hydroxyl value of 58 to 155 are used as the thermosetting resin component, the molecular weight is 30,000 to 170,000, and the glass transition point is 10 to 55. Select an acrylic resin in the range of ° C., add a suitable amount of a silane coupling agent, and become a reaction solvent that causes the reaction between the above functional groups during the thermosetting treatment, and a solvent that dissolves the acrylic resin As described above, it was found that a conductive paste capable of achieving the object of the present invention can be prepared by selecting a high boiling point solvent having a boiling point of 150 ° C. or higher and 266 ° C. or lower at normal pressure. The composition of the conductive paste is 3 to 8 parts by mass of the acrylic resin, 0.1 to 1.5 parts by mass of the silane coupling agent, and 8 to 25 parts by mass of the high boiling point solvent per 100 parts by mass of the metallic silver powder. It was also confirmed that by selecting the range, it was possible to adjust the viscosity to be suitable for forming a coating film having a wiring layer pattern shape.

  Based on the above series of findings, the present inventors have completed the present invention.

That is, the conductive paste according to the present invention is
A conductive paste that can be cured at low temperature,
As the resin component, an acrylic resin having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000 and a glass transition point of 10 to 55 ° C. is selected.
In the conductive paste,
Per 100 parts by mass of metallic silver powder,
3 to 8 parts by mass of the acrylic resin,
0.1 to 1.5 parts by mass of a silane coupling agent,
8 to 25 parts by mass of an organic solvent having a boiling point of 150 ° C. or higher and 266 ° C. or lower at normal pressure,
It is the electrically conductive paste characterized by each being contained.

that time,
It is preferable that the organic solvent does not contain a functional group having high reactivity with respect to an epoxy group and a hydroxyl group.

Contained in the conductive paste,
The ratio of the total volume of the metal silver powder and the total volume of the acrylic resin: [metal silver powder volume: acrylic resin volume] is preferably selected in the range of 100: 27 to 100: 73.

Contained in the conductive paste,
The content ratio of the organic solvent is preferably selected in the range of 40% by volume to 70% by volume of the conductive paste.

  The viscosity of the conductive paste is preferably selected in the range of 5 Pa · s to 70 Pa · s.

On the other hand, in the conductive paste according to the present invention,
The metallic silver powder is a spherical metallic silver powder having an average particle size of 7 μm or less and 0.3 μm or more;
The metallic silver powder is a flaky metallic silver powder having an average particle size of 10 μm or less, 1.0 μm or more;
The metallic silver powder is
A mixture of flaky metallic silver powder having an average particle size of 10 μm or less and 0.3 μm or more, and a spherical metal silver powder having an average particle size of 7 μm or less and 1.0 μm or more,
The mixing ratio (mass ratio) of the flaky metallic silver powder and the spherical metallic silver powder is the total mass of the flaky metallic silver powder: the total mass of the spherical metallic silver powder is selected in the range of 9: 1 to 2: 8 Three forms can be selected.

  In addition, the functional group introduced by the silane coupling agent preferably has reactivity with an epoxy group or a hydroxyl group.

  For example, the functional group introduced by the silane coupling agent is preferably an epoxy group.

Further, in the conductive paste, a dispersant for the metallic silver powder is further added.
The form added in the range of 0.1 to 1.5 parts by mass per 100 parts by mass of the metallic silver powder can also be selected.

In the conductive paste according to the present invention,
The ratio of the epoxy groups and hydroxyl groups present in the acrylic resin is preferably selected so that an average of 0.3 to 2.6 hydroxyl groups per epoxy group is present. .

  It is desirable that the acrylic resin has a molecular weight of 50,000 to 130,000 and a glass transition point of 20 to 50 ° C.

  In particular, it is desirable that the acrylic resin is capable of producing a thermosetting product of the acrylic resin by selecting a heating temperature in a range of 100 ° C. to 150 ° C. and heating for 30 minutes or more.

  The conductive paste according to the present invention has, as a resin component, an acrylic resin having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000, and a glass transition point of 10 to 55 ° C. As a base material (base film) of a flexible printed circuit board, it is cured by a heat treatment significantly lower than the softening point of a PET film or a polyimide film that is widely used, for example, 150 ° C. or less. It is a possible conductive paste. In addition, the conductor film produced by thermosetting the conductive paste according to the present invention exhibits excellent adhesion to the surface of the PET film or polyimide film, and is flexible and capable of repeated bending deformation. It has toughness that does not cause internal breakage due to deformation. Furthermore, the conductive paste according to the present invention does not increase in viscosity due to cross-linking between the acrylic resins during storage at room temperature, and is excellent in storage stability at room temperature.

  Below, the electrically conductive paste concerning this invention and its manufacturing method are demonstrated in detail.

  First, in the conductive paste of the present invention, metallic silver powder is selected as the conductive filler. The shape of the metallic silver powder used can be selected from either a spherical metallic silver powder or a scaly metallic silver powder.

  The size (average particle diameter d) of the metallic silver powder used is selected in consideration of the average film thickness W of the conductive film to be produced. Actually, the microscopic structure of the produced conductive film is a structure in which a resin component is filled in the gap with respect to the electric conduction path composed of a laminated structure of metallic silver powder, and the metallic silver powder is bonded and fixed together. ing. Therefore, the average film thickness W of the produced conductive film is determined by the average thickness of the laminated structure of the metal silver powder as the skeleton. On the other hand, on the surface of the laminated structure of the metallic silver powder, there are microscopic irregularities of about 1/4 to 1/3 of the size (average particle diameter d) of the metallic silver powder constituting the surface.

  As a result, the microscopic variation ΔW in the thickness of the conductive film to be produced is about ¼ to ３ of the size (average particle diameter d) of the metal silver powder to be used. In order to make the microscopic variation ΔW of the film thickness of the conductive film to be produced at least 1/10 or less of the average film thickness W, preferably 1/20 or less, the size of the metal silver powder to be used ( It is desirable that 1/4 of the average particle diameter d) is 1/10 or less, preferably 1/20 or less, of the average film thickness W of the conductive film to be produced. Accordingly, the size (average particle diameter d) of the metallic silver powder to be used is at least d ≦ (2/5) W, preferably d ≦ (1/5) W.

  The film thickness of the wiring layer used in the flexible printed board is usually selected in the range of 50 μm or less. When used for the production of a wiring layer used in a flexible printed circuit board, the average film thickness W of the produced conductive film is W ≦ 50 μm, and accordingly, the size of the metal silver powder used (average particle diameter d) ) At least d ≦ 20 μm, preferably d ≦ 10 μm.

  The laminated structure of the metallic silver powder formed is different when the metallic silver powder used is a spherical metallic silver powder or a scale-like metallic silver powder. When spherical metal silver powder is used, there is no substantial difference in the laminated structure of the metal silver powder formed between the film thickness direction and the in-plane direction. On the other hand, when scale-like metallic silver powder is used, the laminated structure of the metallic silver powder to be formed has a high tendency to take an arrangement in which the scales are arranged flat in the film thickness direction.

  In consideration of the above difference, when spherical metal silver powder is used, the size (average particle diameter d) of the metal silver powder is preferably selected to be d ≦ 10 μm, more preferably d ≦ 7 μm. On the other hand, when using scale-like metallic silver powder, the size of metallic silver powder (average) is used when spherical metallic silver powder is used even if the size of metallic silver powder (average particle diameter d) is selected as d ≦ 10 μm. The microscopic variation ΔW of the thickness of the conductive film to be produced is the same as when the particle size d) is selected as d ≦ 7 μm. In other words, when using scale-like metallic silver powder, it is desirable to select the size (average particle diameter d) of the metallic silver powder as d ≦ 10 μm.

  On the other hand, in the electric conduction path constituted by the laminated structure of the metal silver powder to be formed, a substantial part of the resistance component is the contact resistance at the contact portion between the metal silver powder. The sum of the contact resistance at the contact sites between the metal silver powders is the result that the size of the metal silver powder to be used (average particle size d) decreases, the number of contact sites increases, and the contact area of the contact sites also decreases. To increase. Therefore, in order to suppress an increase in the resistance value of the entire electric conduction path constituted by the laminated structure of the formed metal silver powder, the size (average particle diameter d) of the metal silver powder to be used is at least d ≧ 0.3 μm. Preferably, it is desirable to select in the range of d ≧ 0.5 μm.

  Considering the above two requirements, when spherical metal silver powder is used, the size (average particle diameter d) of the metal silver powder is 0.3 μm ≦ d ≦ 10 μm, more preferably 0.5 μm ≦ d ≦ 7 μm. It is desirable to select the range. When scale-like metallic silver powder is used, the size (average particle diameter d) of the metallic silver powder is preferably selected in the range of 0.3 μm ≦ d ≦ 10 μm, more preferably 0.5 μm ≦ d ≦ 10 μm.

  Furthermore, when the film thickness of the wiring layer used in the flexible printed circuit board is normally selected within a range of 30 μm or less, the size (average particle diameter d) of the metal silver powder to be used is selected as follows. It is preferable.

  When spherical metal silver powder is used, the size (average particle diameter d) of the metal silver powder is preferably selected in the range of 0.3 μm ≦ d ≦ 5 μm, more preferably 0.5 μm ≦ d ≦ 4 μm. When scale-like metallic silver powder is used, the size (average particle diameter d) of the metallic silver powder is preferably selected in the range of 0.3 μm ≦ d ≦ 5 μm, more preferably 0.5 μm ≦ d ≦ 5 μm.

  On the other hand, the microscopic structure of the produced conductive film has a structure in which a resin component is filled in the gap with respect to an electric conduction path composed of a laminated structure of metal silver powder, and the metal silver powder is bonded and fixed to each other. . Therefore, the volume of the resin component is obtained by subtracting the sum of the volumes of the metallic silver powder constituting the laminated structure of the metallic silver powder from the entire volume of the conductive film to be produced.

Generally, the higher the ratio of the total volume of metallic silver powder constituting the laminated structure of metallic silver powder in the entire volume of the produced conductive film, the higher the overall conductivity of the produced conductive film. Become. The metallic silver powder to be used is, for example, a mixture of a flaky metallic silver powder having an average particle diameter of 10 μm or less and 1.0 μm or more and a spherical metallic silver powder having an average particle diameter of 7 μm or less and 0.3 μm or more,
The mixing ratio (mass ratio) of the flaky metallic silver powder and the spherical metallic silver powder is selected by selecting the total mass of the flaky metallic silver powder: the total mass of the spherical metallic silver powder within the range of 9: 1 to 2: 8. The ratio of the sum total of the volume of the metal silver powder which comprises the laminated structure of silver powder may become high. It is also possible to select the form.

When the flaky metallic silver powder and the spherical metallic silver powder are used in combination, the ratio of the average particle diameter d _flake of the flaky metallic silver powder to the d _ball of the spherical metallic silver powder; d _flake : d _ball is 10.0: 7 It is desirable to select in the range of 0.0 to 1.0: 0.3, preferably in the range of 5.0: 3.0 to 1.0: 0.5. When the ratio is selected, for example, the spherical metallic silver powder enters the gap between the flaky metallic silver powders, and the conductive path of the entire metallic silver powder is increased, so that the electrical conductivity can be improved.

  In the electrically conductive paste of this invention, the said acrylic resin is mix | blended in the range of 3-8 mass parts per 100 mass parts of metal silver powder, More preferably, it is the range of 5-7 mass parts. In that case, the produced conductive film contains the thermosetting product of the acrylic resin in a range of about 3 to 8 parts by mass, more preferably in a range of about 5 to 7 parts by mass per 100 parts by mass of the metal silver powder. It becomes a state.

The density ρ _Ag of silver is 10.49 g / cm ³ (20 ° C.), while the average density ρ _resin of the acrylic _resin is in the range of 1.10 g / cm ^{3 to} 1.18 g / cm ³ . Therefore, in a state where the thermosetting product of the acrylic resin is included in a range of about 3 to 8 parts by mass per 100 parts by mass of the metal silver powder, the volume ratio is [100 / 10.49]: [3 / ρ _resin ( For example, the range is [rho _resin = 1.15)] to [100 / 10.49]: [8 / [rho] _resin (for example, [rho] _resin = 1.15)]. In a state where the thermosetting product of the acrylic resin is included in a range of about 5 to 7 parts by mass per 100 parts by mass of the metallic silver powder, the volume ratio is [100 / 10.49]: [5 / ρ _resin (for example, ρ _resin = 1.15)] to [100 / 10.49]: [7 / ρ _resin (for example, ρ _resin = 1.15)].

  The volume of the thermosetting product of the acrylic resin is obtained by subtracting the total volume of the metal silver powder constituting the laminated structure of the metal silver powder from the total volume of the conductive film to be produced. Therefore, the ratio of the total volume of the metal silver powder and the total volume of the acrylic resin contained in the conductive paste of the present invention: [metal silver powder volume: acrylic resin volume] is at least 100: 27-100. : 73, more preferably 100: 45 to 100: 64.

  When an electric conduction path consisting of a laminated structure of metallic silver powder is filled with an acrylic resin thermosetting material in the gap and a structure for bonding and fixing the metallic silver powder together is formed, the thermosetting material of the acrylic resin is a metal It is preferable to show high adhesiveness on the surface of the silver powder. The conductive paste of the present invention achieves high adhesion to the thermosetting product of the acrylic resin and the surface of the metallic silver powder using a silane coupling agent. That is, by using a silane coupling agent, a reactive functional group is introduced on the surface of the metallic silver powder, and covalently bonded to the surface of the metallic silver powder through a reaction with the functional group present in the acrylic resin. Acrylic resin adhesion is achieved.

  The addition amount of the silane coupling agent is selected depending on the content of the metallic silver powder. Specifically, it is preferable to select the addition amount of the silane coupling agent in consideration of the total area of the surface of the contained metal silver powder. In the conductive paste of the present invention, the addition amount of the silane coupling agent is in the range of 0.1 to 1.5 parts by mass, more preferably in the range of 0.3 to 1.0 parts by mass per 100 parts by mass of the metallic silver powder. It is desirable to choose.

  The functional group introduced by the silane coupling agent preferably has reactivity with an epoxy group or a hydroxyl group. For example, the functional group introduced by the silane coupling agent is preferably an epoxy group.

  The silane coupling agent can be in a form that is uniformly dissolved in an organic solvent. In that case, the ratio (mass ratio) of the content of the silane coupling agent and the organic solvent; [silane coupling agent content]: [organic solvent content] is preferably in the range of 1: 5 to 1: 250. Is preferably selected in the range of 1: 8 to 1:85, for example, in the range of 1:10 to 1:70.

  The conductive paste of the present invention is a paste having a desired viscosity by uniformly dispersing metallic silver powder in a liquid phase in which the above-mentioned acrylic resin and silane coupling agent are dissolved. In order to form a liquid phase in which the acrylic resin and the silane coupling agent are dissolved, an organic solvent that dissolves the acrylic resin and the silane coupling agent is blended. The content of the organic solvent is also selected depending on the content of the metal silver powder. Specifically, since the content of the acrylic resin and the silane coupling agent is selected depending on the content of the metallic silver powder, the organic solvent used for dissolving the acrylic resin and the silane coupling agent is selected. The content is also selected depending on the content of the metallic silver powder.

  In the conductive paste of the present invention, the content of the organic solvent is selected in the range of 8 to 25 parts by mass, and more preferably in the range of 10 to 15 parts by mass per 100 parts by mass of the metal silver powder.

Density [rho _Ag of silver is ^{10.49g / cm 3 (20 ℃)} , whereas, the density [rho _Solvent organic solvent, generally in a range of 0.89g / cm ³ ~1.08g / cm ³ Yes. Therefore, in the state which contains the said organic solvent in the range of 8-25 mass parts per 100 mass parts of metal silver powder, the volume ratio is [100 / 10.49]: [8 / (rho) _solvent ]-[100/10]. .49]: [25 / ρ _solvent ]. In the state which contains the said organic solvent in the range of about 10-15 mass parts per 100 mass parts of metal silver powder, the volume ratio is [100 / 10.49]: [10 / (rho) _solvent ]-[100/10. 49]: [15 / ρ _solvent ].

  The organic solvent to be used must have a function as a reaction solvent in the process of forming a thermoset of acrylic resin and in the process of allowing the silane coupling agent to act on the surface of the metallic silver powder. Therefore, it is necessary not to cause the organic solvent to completely evaporate until it is heated to the heat treatment temperature at which the above process is performed, and an organic solvent having a boiling point of 150 ° C. to 266 ° C. at normal pressure is used. is doing. More preferably, it is desirable to use an organic solvent having a boiling point of 180 ° C. or higher and 230 ° C. or lower at normal pressure.

  That is, the acrylic resin can be in a form that is uniformly dissolved in the organic solvent. In that case, the ratio (mass ratio) of the acrylic resin and organic solvent content; [acrylic resin content]: [organic solvent content] is in the range of 1: 1 to 1: 8.5, preferably It is desirable to select a range of 1: 1.1 to 1: 5, for example, a range of 1: 1.5 to 1: 4.

  In addition, the organic solvent to be used must not contain any functional groups that are highly reactive with respect to epoxy groups and hydroxyl groups, which are reactive functional groups present in the acrylic resin. preferable. For example, n-butyl carbitol (diethylene glycol monobutyl ether; boiling point: 226 ° C.), dipropylene glycol monomethyl ether (boiling point: 189 ° C.) and the like can be suitably used as the organic solvent. As the organic solvent, generally, diethylene glycol monoalkyl ether or dipropylene glycol monoalkyl ether having a boiling point in the range of 150 ° C. or higher and 266 ° C. or lower can be suitably used. Furthermore, as an organic solvent, in addition to the glycol monoalkyl ether type solvent, an acetic acid ester of the glycol monoalkyl ether, that is, a glycol monoalkyl ether monoacetate has a boiling point in the range of 150 ° C. or higher and 266 ° C. or lower. Can be used.

  This organic solvent also has a function of a diluting solvent for adjusting the viscosity of the produced conductive paste. Therefore, the content of the organic solvent is selected to be a suitable content within the content range described above for adjusting to a desired viscosity. The content ratio of the organic solvent contained in the conductive paste is selected in the range of 40% by volume to 70% by volume of the conductive paste, more preferably in the range of 40% by volume to 60% by volume. It is preferable.

  On the other hand, when the conductive paste of the present invention forms a coating film in accordance with the shape of the wiring pattern, for example, a screen printing method is applied. When applying the screen printing method, the viscosity of the conductive paste is preferably selected in the range of 5 Pa · s to 70 Pa · s, more preferably in the range of 20 Pa · s to 70 Pa · s. Furthermore, the viscosity of the conductive paste is more preferably selected in the range of 30 Pa · s to 60 Pa · s.

  Furthermore, in the conductive paste of the present invention, it is necessary to achieve a state in which the metal silver powder is uniformly dispersed in the conductive paste. Depending on the type of organic solvent constituting the liquid phase and the content thereof, for the purpose of improving the dispersibility of the metallic silver powder, the dispersant for the metallic silver powder is 0.1 to 1.5 parts by mass per 100 parts by mass of the metallic silver powder. The form added in the range of mass parts, more preferably in the range of 0.3 mass parts to 1.0 mass parts can also be selected. At that time, as a dispersing agent for metallic silver powder, a chelating agent type dispersing agent such as BYK-W980 (main component: unsaturated fatty acid polyamine amide and acidic ester, acid value: 40, amine value: 30) manufactured by Big Chemie Japan It is desirable to use it.

  In the conductive paste according to the present invention, the thermosetting product of the acrylic resin is formed between the epoxy groups present in the acrylic resin and the hydroxyl groups, and between the acrylic resin chains, a cross-linking bond is formed. It progresses by being done.

  Therefore, an acrylic resin having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000, and a glass transition point of 10 to 55 ° C. is selected as the acrylic resin to be used. ing.

  In that case, the ratio of the epoxy group and hydroxyl group present in the acrylic resin is a ratio of 0.3 to 2.6 hydroxyl groups on average per one epoxy group, more preferably, It is desirable that the ratio is selected so that an average of 0.7 to 1.5 hydroxyl groups are present.

  The epoxy equivalent of the acrylic resin is preferably selected at least in the range of 284 to 946, more preferably in the range of 284 to 470. That is, it is preferable to select a ratio in which one epoxy group is present per 2 to 8 units, more preferably 2 to 4 units constituting the acrylic resin. At the same time, the hydroxyl value of the acrylic resin is preferably selected in the range of 58 to 155, more preferably in the range of 75 to 120. In terms of the hydroxyl equivalent of the acrylic resin, the hydroxyl equivalent is in the range of 1000 × (56.11 / 58) to 1000 × (56.11 / 155), that is, in the range of 967 to 360, more preferably 1000 × (56.11 / 75 ) To 1000 × (56.11 / 120), that is, a range of 748 to 469 is desirable. That is, it is preferable to select a ratio in which one hydroxyl group is present per 9 to 3 units, more preferably 7 to 4 units constituting the acrylic resin.

  When the epoxy equivalent of the acrylic resin is 946 and the hydroxyl value of the acrylic resin is 155 (that is, the hydroxyl equivalent is equivalent to 362), an average of 2.6 hydroxyl groups exist per one epoxy group. When the epoxy equivalent of the acrylic resin is 284 and the hydroxyl value of the acrylic resin is 58 (that is, the hydroxyl equivalent is equivalent to 967), an average of 0.3 hydroxyl groups per epoxy group This is the proportion of groups present. When the epoxy equivalent of the acrylic resin is 284 and the hydroxyl value of the acrylic resin is 155 (that is, the hydroxyl equivalent is equivalent to 362), there are an average of 0.8 hydroxyl groups per epoxy group. In the case where the epoxy equivalent of the acrylic resin is 946 and the hydroxyl value of the acrylic resin is 58 (that is, the hydroxyl equivalent is equivalent to 967), one hydroxyl group is averaged per one epoxy group. It is the ratio that exists.

  When the epoxy equivalent of the acrylic resin is 470 and the hydroxyl value of the acrylic resin is 120 (that is, the hydroxyl equivalent is equivalent to 469), an average of one hydroxyl group exists per one epoxy group. When the epoxy equivalent of the acrylic resin is 284 and the hydroxyl value of the acrylic resin is 75 (that is, the hydroxyl equivalent is equivalent to 748), an average of 0.4 hydroxyl groups per epoxy group It is the ratio that exists. When the epoxy equivalent of the acrylic resin is 470 and the hydroxyl value of the acrylic resin is 75 (that is, the hydroxyl equivalent is equivalent to 748), there is an average of 0.6 hydroxyl groups per epoxy group. In the case where the epoxy equivalent of the acrylic resin is 284 and the hydroxyl value of the acrylic resin is 120 (that is, the hydroxyl equivalent is equivalent to 467), an average of 0.6 hydroxyl groups per epoxy group This is the proportion of groups present.

  The acrylic resin has a molecular weight of 30,000 to 170,000 and a glass transition point in the range of 10 to 55 ° C., more preferably a molecular weight of 50,000 to 130,000 and a glass transition point of 20 to 50 ° C. It is desirable that

  In particular, it is desirable that the acrylic resin is capable of producing a thermosetting product of the acrylic resin by selecting a heating temperature in a range of 100 ° C. to 150 ° C. and heating for 30 minutes or more.

  The epoxy group and hydroxyl group present in the acrylic resin used in the conductive paste according to the present invention function as a reactive functional group.

  By utilizing this feature, the surface of a PET film or polyimide film that is widely used as the base material (base film) of a flexible printed circuit board is subjected to an easy-adhesive surface treatment to generate reactive functional groups. In this case, a covalent bond can be formed between the reactive functional group on the surface and the reactive functional group present in the acrylic resin, and the acrylic resin can be adhered. That is, in the course of the thermosetting treatment of the acrylic resin, the reactive functional group present in the surface of the PET film or polyimide film subjected to the easy-adhesive surface treatment and the reactive functional group present in the acrylic resin. A covalent bond can be formed with the group, and the thermosetting product of the acrylic resin can be adhered.

  Further, even when the easy-adhesive surface treatment is not performed, if a hydroxyl group acts on the ester bond on the surface of the PET film in the course of the heat treatment, the ester exchange reaction proceeds, and the hydroxyl group is formed on the surface of the PET film. When a hydroxyl group acts on the imide bond on the surface of the polyimide film to be generated, the exchange reaction proceeds and an amino group is generated on the surface of the polyimide film. Utilizing the reactive functional groups generated during the heat treatment, a covalent bond is formed between the reactive functional groups present in the acrylic resin, and the thermosetting product of the acrylic resin is in close contact with the reactive functional group. Can be made.

  For example, a covalent bond can be formed by a reaction between a hydroxyl group generated on the surface of the PET film and an epoxy group present in the acrylic resin, and the thermosetting product of the acrylic resin can be brought into close contact. For example, a covalent bond can be formed by a reaction between an amino group generated on the surface of a polyimide film and an epoxy group present in the acrylic resin, and the thermosetting product of the acrylic resin can be brought into close contact.

  Moreover, the thermosetting of the acrylic resin is due to the formation of crosslinks between the polymer chains by the reaction between the epoxy group and the hydroxyl group present in the acrylic resin. Furthermore, the silane coupling agent forms a covalent bond by a reaction between a functional group introduced on the surface of the metal silver powder, for example, an epoxy group and a hydroxyl group present in the acrylic resin, and the acrylic resin is thermally cured. An object can be brought into close contact with the metal silver powder.

In the organic solvent, when a cross-link is formed between the polymer chains by the reaction between the epoxy group and the hydroxyl group present in the acrylic resin, the acrylic resin partially cross-linked between the polymer chains is formed. The fluidity of the containing liquid phase is reduced. Furthermore, the reaction rate of the cross-linking formation between the polymer chains depends on the concentration of the acrylic resin contained in the organic solvent. That is, the concentration of the acrylic resin contained in the organic solvent increases, and the reaction rate increases in proportion to the [acrylic resin concentration] ² . The reaction rate of cross-linking formation between polymer chains also depends on the content ratio of epoxy groups and hydroxyl groups present in the acrylic resin, that is, epoxy equivalent and hydroxyl equivalent. That is, the reaction rate of cross-linking formation between polymer chains accompanying the reaction of an epoxy group and a hydroxyl group is generally inversely proportional to the product of epoxy equivalent and hydroxyl equivalent: [epoxy equivalent] · [hydroxyl equivalent].

  In the conductive paste according to the present invention, the concentration of the acrylic resin contained in the organic solvent and the content ratio of the epoxy group and the hydroxyl group present in the acrylic resin, that is, the epoxy equivalent and the hydroxyl equivalent are selected within the above range. By doing so, it is possible to avoid a decrease in fluidity, that is, an increase in liquid viscosity associated with the formation of crosslinks between the polymer chains of the acrylic resin contained during storage at room temperature.

  In the conductive paste according to the present invention, an epoxy group and a hydroxyl group present in an acrylic resin used as a resin component function as a reactive functional group. The film can be thermally cured at a heating temperature of 150 ° C. or lower, which is significantly lower than the softening point of a commonly used PET film or polyimide film. In addition, the produced conductor film exhibits excellent adhesion to the surface of the PET film or polyimide film. Moreover, the thermosetting material of an acrylic resin is provided with flexibility that allows repeated bending deformation and toughness that does not cause internal breakage due to bending deformation. Therefore, the conductor film produced using the thermosetting product of the acrylic resin as a resin component exhibits excellent adhesion to the surface of the PET film or polyimide film, and can be flexibly bent repeatedly. Satisfies the requirement that the deformation has toughness that does not cause internal breakage.

  Below, the acrylic resin used in the conductive paste according to the present invention, that is, having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000, and a glass transition point of 10 to 10. An example of a method for preparing an acrylic resin in the range of 55 ° C. will be briefly described.

For example, when an epoxy group existing in an acrylic resin and a hydroxyl group are introduced, methyl methacrylate (CH ₂ = C (CH ₃ )) is used as the (meth) acrylic acid monomer constituting the acrylic resin. -COO-CH _3; molecular weight: 100.1), glycidyl methacrylate _{(CH 2 = C (CH 3} ) -COO-CH 2 -CH (O) CH 2; molecular weight: 142.2), 2-hydroxypropyl methacrylate _{(CH 2 = C (CH 3} ) -COOH-CH 2 CH (OH) CH 3; molecular weight: 145.2), acrylate n- butyl _{(CH 2 = CH-COOH-} C 4 H 9; molecular weight: 129. 2) is used together. An epoxy group derived from the glycidyl group of glycidyl methacrylate and a hydroxyl group derived from the 2-hydroxypropyl group of 2-hydroxypropyl methacrylate are introduced.

  On the other hand, it becomes possible to adjust the glass transition point of the acrylic copolymer to be formed by adjusting the content ratio of methyl methacrylate and n-butyl acrylate.

The average molecular weight of the acrylic copolymer formed is the amount of (meth) acrylic acid monomer present in the reaction system and the radical polymerization initiator used as a polymerization reaction initiator, for example, 1,1, 3,3-tetramethylbutyl peroxy-2-ethylhexanoate _{(C 4 H 9 -CH (C} 2 H 5) COO-OC (CH 3) 2-CH 2 -C (CH 3) 3; molecular weight: 272. Depends on the amount ratio of 4). By adjusting the average number of (meth) acrylic acid monomer molecules per molecule of the radical polymerization initiator, the average molecular weight of the acrylic copolymer formed can be adjusted.

In addition to the (meth) acrylic acid monomer, a small amount of a monomer having significantly different reactivity, for example, styrene (C ₆ H ₅ —CH═CH ₂ ; molecular weight: 104.2) is added. Thus, the distribution of the average molecular weight of the acrylic copolymer to be formed can be adjusted by adjusting the progress speed of the polymerization.

  Since the actual polymerization reaction speed depends on the concentration of the (meth) acrylic acid monomer present in the reaction solution and the concentration of the radical polymerization initiator, these concentrations are substantially constant during the reaction. Adjust so that For example, a raw material monomer mixed solution in which a plurality of types of (meth) acrylic acid monomers to be used are uniformly mixed is prepared in advance. On the other hand, the radical polymerization initiator is dissolved in a reaction solvent and diluted in advance to prepare a polymerization initiator mixed solution.

  On the other hand, a large amount of the reaction solvent is previously heated to the reaction temperature, and the raw material monomer mixed solution and the polymerization initiator mixed solution are individually dropped into the reaction solvent at a constant dropping rate, and are stirred and mixed. Thus, the polymerization reaction can be carried out while maintaining the concentration of the (meth) acrylic acid monomer and the concentration of the radical polymerization initiator in the reaction system substantially constant.

  When the dropping of the raw material monomer mixed solution and the polymerization initiator mixed solution is completed, a slight amount of unreacted raw material monomer remains in the reaction system. Thereafter, by maintaining the temperature of the reaction system, the polymer chain that has already been extended is allowed to further react with the unreacted raw material monomer. The polymerization reaction is completed when it is completely consumed.

  Since the radical polymerization reaction is initiated by the generation of radical species derived from the radical polymerization initiator, the reaction temperature is selected within a temperature range in which the radical species can be generated. To avoid evaporation of the reaction solvent during heating to the selected reaction temperature, causing an increase in the concentration of (meth) acrylic acid monomer and radical polymerization initiator in the reaction system. A reflux condenser is added to the reaction vessel. On the other hand, when the reaction solvent reaches a boiling state, the temperature of the reaction solution does not become higher than the boiling point of the reaction solvent due to the heat of vaporization. Considering this point, the boiling point of the reaction solvent needs to be higher than the target reaction temperature.

  In addition, in the state heated to the reaction temperature, the reaction solvent needs to uniformly dissolve the (meth) acrylic acid monomer, the radical polymerization initiator, and the produced acrylic copolymer. Usually, when heated to the reaction temperature, the (meth) acrylic acid monomer is liquid, and the radical polymerization initiator is also liquid. When the raw material monomer mixed solution is dropped into the reaction solution, it is necessary to quickly dissolve in the reaction solution to make the concentration uniform. Considering this point, it is preferable to use an organic solvent excellent in solubility of the (meth) acrylic acid monomer, the radical polymerization initiator, and the produced acrylic copolymer as the reaction solvent.

  When synthesizing an acrylic copolymer having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000 and a glass transition point of 10 to 55 ° C., the reaction temperature is It is preferable to select in the range of 70 to 100 ° C.

  The average composition of the acrylic copolymer produced by the above method is substantially equal to the content ratio of the plural (meth) acrylic monomers contained in the raw material monomer mixture. Yes. Further, the average number of units of the monomers constituting the acrylic copolymer to be formed should be less than the average number of (meth) acrylic acid monomer molecules used per one radical polymerization initiator molecule. There is no.

  After completing the “aging” process, the reaction solution is cooled.

  The “glass transition point” of the acrylic copolymer is generally measured using an acrylic copolymer that does not contain a solvent component.

  After completion of the above reaction, thin film drying or the like can be used as a means for obtaining an acrylic copolymer that does not contain a solvent component.

  Hereinafter, the present invention will be described more specifically by showing specific examples. Although these specific examples are examples of the best embodiments according to the present invention, the present invention is not limited to the forms shown in these specific examples.

  First, Reference Example 1 shows a production process of an acrylic copolymer (1) used for preparing conductive pastes of Examples 1 and 2 described later.

(Reference Example 1) Production method of acrylic copolymer (1) Epoxy equivalent of 284 to 946, hydroxyl value of 58 to 155, molecular weight of 30,000 to 250,000, glass transition point of 10 to 55 ° C As an example of the manufacturing method of the acrylic resin of a range, an example of the manufacturing process of an acrylic copolymer (1) is described below.

  The raw material monomer of the acrylic copolymer (1) is uniformly mixed in advance to obtain a raw material monomer mixed solution.

Specifically, as a (meth) acrylic acid monomer, methacrylic acid methyl (CH ₂ = C (CH ₃ ) -COO-CH ₃ ; molecular weight: 100.1) 430 g, acrylic acid n-butyl (CH ₂ = CH -COOH-C ₄ H ₉ ; molecular weight: 129.2) 165 g, 2-hydroxypropyl methacrylate (CH ₂ = C (CH ₃ ) -COOH-CH ₂ CH (OH) CH ₃ ; molecular weight: 145.2) 450 g, glycidyl methacrylate ( CH ₂ = C (CH ₃ ) —COO—CH ₂ —CH (O) CH ₂ ; molecular weight: 142.2) 450 g, and further styrene (C ₆ H ₅ —CH═CH ₂ ; molecular weight: 104.2) 5 g are mixed. To prepare a raw material monomer mixture.

  The total of the raw material monomers is 1500 g. Moreover, the composition ratio of the raw material monomer shown by molar amount is as follows: methyl methacrylate: 4.3 mol, n-butyl acrylate: 1.3 mol, 2-hydroxypropyl methacrylate: 3.1 mol, glycidyl methacrylate: 3. 2 mol, and further styrene: 0.05 mol.

On the other hand, a radical polymerization initiator, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate _{(C 4 H 9 -CH (C} 2 H 5) COO-OC (CH 3) 2-CH _2- C (CH ₃ ) ₃ ; molecular weight: 272.4) 28 g is uniformly mixed with 1250 g of dipropylene glycol monomethyl ether (boiling point: 189 ° C.) of the solvent to prepare a polymerization initiator mixed solution. The polymerization initiator mixed solution contains 0.1 mol of the radical polymerization initiator.

  Accordingly, the total amount of raw material monomers per molecule of the radical polymerization initiator is 119.5 molecules.

  Into a 5-liter four-necked flask equipped with a reflux condenser and a stirrer is charged 2250 g of dipropylene glycol monomethyl ether and nitrogen blowing is started.

  Then, the dipropylene glycol monomethyl ether is heated to 85 ° C. while stirring.

  Thereafter, the raw material monomer mixed solution and the polymerization initiator mixed solution are continuously dropped at a constant dropping rate from separate dropping nozzles attached to the four-necked flask. By setting the dropping rate of the raw material monomer mixed solution to 6.9 ml / min and the dropping rate of the polymerization initiator mixed solution to 5.5 ml / min, the whole amount is dropped over 4 hours.

  As a result, a total of 1500 g of raw material monomers, 28 g of the radical polymerization initiator, and a total of 3500 g of dipropylene glycol monomethyl ether as a solvent are charged into a 5-liter four-necked flask.

  After completion of the dropping, the liquid temperature is kept at 85 ° C., and the polymerization reaction liquid is aged for 6 hours as it is to complete the polymerization reaction. An acrylic resin solution in which the resulting acrylic copolymer (1) is dissolved in dipropylene glycol monomethyl ether as a solvent is obtained.

  In the obtained acrylic resin solution, the concentration (solid content concentration) of the acrylic copolymer (1) was 30.0%. Moreover, the weight average molecular weight (Mw) of the acrylic copolymer (1) was 120,000 in terms of polystyrene-converted mass average molecular weight.

  That is, the average composition of the acrylic copolymer (1) was as follows: the content ratio of each monomer: methyl methacrylate: 36.0 units, n-butyl acrylate: 10.9 units, 2-hydroxypropyl methacrylate: 25 9 units, glycidyl methacrylate: 26.8 units, and styrene: 0.4 units.

  As a result, the content ratio of the epoxy group derived from the glycidyl group of glycidyl methacrylate in the acrylic copolymer (1) corresponds to an epoxy equivalent of 473. Further, the content ratio of hydroxyl group (—OH) by 2-hydroxypropyl group of 2-hydroxypropyl methacrylate corresponds to a hydroxyl value of 117. In terms of hydroxyl equivalent, it corresponds to 479.

  Therefore, the content ratio of the epoxy group and the hydroxyl group (—OH) contained in the acrylic copolymer (1) is an average of about one hydroxyl group (—OH) per one epoxy group. It corresponds to the ratio.

  The glass transition point of the acrylic copolymer (1) was 37 ° C.

  First, Reference Example 2 shows a production process of an acrylic copolymer (2) used for preparing the paste of Comparative Example 1 described later.

Reference Example 2 Production Method of Acrylic Copolymer (2) Epoxy equivalent is 0, has a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000, and a glass transition point of 10 to 55 ° C. As an example of the production method of the acrylic resin, an example of the production process of the acrylic copolymer (2) will be described below.

  The raw material monomer of the acrylic copolymer (2) is uniformly mixed in advance to obtain a raw material monomer mixed solution.

  Specifically, as the (meth) acrylic acid monomer, 757 g of methyl methacrylate, 288 g of n-butyl acrylate, 450 g of 2-hydroxypropyl methacrylate, 0 g of glycidyl methacrylate, and 5 g of styrene were mixed, A raw material monomer mixture is prepared.

  The total of the raw material monomers is 1500 g. Moreover, the composition ratio of the raw material monomer shown by molar amount is methyl methacrylate: 7.6 mol, acrylate n-butyl: 2.2 mol, 2-hydroxypropyl methacrylate: 3.1 mol, glycidyl methacrylate: 0 mol Furthermore, styrene: 0.05 mol.

  On the other hand, 28 g of 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, which is a radical polymerization initiator, is uniformly mixed with 1250 g of dipropylene glycol monomethyl ether as a solvent to obtain a polymerization initiator. Prepare a mixture. The polymerization initiator mixed solution contains 0.1 mol of the radical polymerization initiator.

  Therefore, the total amount of raw material monomers per molecule of the radical polymerization initiator is 129.5 molecules.

  Into a 5-liter four-necked flask equipped with a reflux condenser and a stirrer is charged 2250 g of dipropylene glycol monomethyl ether and nitrogen blowing is started.

  Then, the dipropylene glycol monomethyl ether is heated to 85 ° C. while stirring.

  Thereafter, the raw material monomer mixed solution and the polymerization initiator mixed solution are continuously dropped at a constant dropping rate from separate dropping nozzles attached to the four-necked flask. By setting the dropping rate of the raw material monomer mixed solution to 6.9 ml / min and the dropping rate of the polymerization initiator mixed solution to 5.5 ml / min, the whole amount is dropped over 4 hours.

  As a result, a total of 1500 g of raw material monomers, 28 g of the radical polymerization initiator, and a total of 3500 g of dipropylene glycol monomethyl ether as a solvent are charged into a 5 liter four-necked flask.

  After completion of the dropping, the liquid temperature is kept at 85 ° C., and the polymerization reaction liquid is aged for 6 hours as it is to complete the polymerization reaction. An acrylic resin solution in which the resulting acrylic copolymer (2) is dissolved in dipropylene glycol monomethyl ether as a solvent is obtained.

  In the obtained acrylic resin solution, the concentration (solid content concentration) of the acrylic copolymer (2) was 30.0%. Moreover, the weight average molecular weight (Mw) of the acrylic copolymer (2) was 130,000 in terms of polystyrene equivalent.

  That is, the average composition of the acrylic copolymer (1) is as follows: the content ratio of each monomer: methyl methacrylate: 58.6 units, n-butyl acrylate: 17.0 units, 2-hydroxypropyl methacrylate: 23 .9 units, glycidyl methacrylate: 0 units, and styrene: 0.05 units.

  As a result, the epoxy group content ratio in the acrylic copolymer (2) is 0 epoxy equivalent. Further, the content ratio of hydroxyl group (—OH) by 2-hydroxypropyl group of 2-hydroxypropyl methacrylate corresponds to a hydroxyl value of 117.

  The glass transition point of the acrylic copolymer (2) was 37 ° C.

Example 1
In Example 1, an acrylic copolymer (1) having an epoxy equivalent of 473, a hydroxyl value of 117, a glass transition point of 37 ° C., and a molecular weight of 120,000 as described in Reference Example 1 is used as the acrylic resin component. In use, a conductive paste is prepared according to the following procedure.

  The acrylic copolymer (1) is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and the acrylic resin component (solid content) content is 30% by mass in the form of an acrylic resin solution. As a raw material.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer (1) is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of flaky silver powder having an average particle diameter of 3 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 3 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste is 10 parts by mass of the acrylic resin (acrylic copolymer (1)) and 1 part by mass of the silane coupling agent per 189 parts by mass of the flaky silver powder having an average particle size of 3 μm. In total, 26 parts by mass of n-butyl carbitol as a solvent is contained. Therefore, the volume ratio of the scaly silver powder and the acrylic resin (acrylic copolymer (1)) in the prepared paste; [metal silver powder volume: acrylic resin volume] corresponds to 100: 47. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 50% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  As the base film, PET film is Tetoron SL manufactured by Teijin DuPont Films (without easy-adhesive surface treatment), Tetron HLEW manufactured by Teijin DuPont Films (with easy-adhesive surface treatment), Lumirror U-98 manufactured by Toray Industries, Inc. Three types of adhesive surface treatment are used. The polyimide film uses Kapton 500H (no easy-adhesive surface treatment) manufactured by Toray DuPont.

  The volume resistivity is calculated from the line resistance and the average film thickness.

  Adhesion is evaluated by performing a peel test using a commercially available Nichiban cello tape.

  The pencil hardness is evaluated according to JIS K5600.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 17 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 49. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

The viscosity change rate is calculated from the following formula by measuring the viscosity immediately after production and the viscosity after storage for 24 hours in a thermostatic bath at 23 ° C. for the prepared paste.
Viscosity change rate (%) = (viscosity after 24 hours storage / viscosity immediately after production) × 100
The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was 40 Pa · s, while the viscosity after being stored in a thermostat at 23 ° C. for 24 hours was 40 Pa · s.

(Example 2)
Also in Example 2, an acrylic copolymer (1) having an epoxy equivalent of 473, a hydroxyl value of 117, a glass transition point of 37 ° C., and a molecular weight of 120,000 as described in Reference Example 1 was used as the acrylic resin component. In use, a conductive paste is prepared according to the following procedure.

  The acrylic copolymer (1) is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and the acrylic resin component (solid content) content is 30% by mass in the form of an acrylic resin solution. As a raw material.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer (1) is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 2 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The viscosity-adjusted paste has a composition of 10 parts by mass of the acrylic resin (acrylic copolymer (1)) and 1 part by mass of the silane coupling agent per 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm. In total, 25 parts by mass of n-butyl carbitol as a solvent is contained. Therefore, the volume ratio of the spherical silver powder and the acrylic resin (acrylic copolymer (1)) in the prepared paste; [metal silver powder volume: acrylic resin volume] corresponds to 100: 48. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 47% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 41 Pa · s.

(Example 3)
In Example 3, an acrylic copolymer having an epoxy equivalent of 946, a hydroxyl value of 58, a glass transition point of 12 ° C., and a molecular weight of 150,000, synthesized according to the method described in Reference Example 1 as an acrylic resin component. Is used to prepare a conductive paste according to the following procedure.

  The acrylic copolymer is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and is used as a raw material in the form of an acrylic resin solution having a content of acrylic resin component (solid content) of 30% by mass. It is used as. A hydroxyl value of 58 corresponds to a hydroxyl equivalent weight of 967. Therefore, about one hydroxyl group exists per one epoxy group in the acrylic copolymer.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer is added, 1 part by mass of a silane coupling agent, and 1 part by mass of a BYK-W980 dispersant manufactured by Big Chemie Japan. Added. After the addition of the silane coupling agent and the dispersant, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 1 part by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 38 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste was 10 parts by mass of the acrylic resin (acrylic copolymer), 1 part by mass of the silane coupling agent, and a dispersant per 189 parts by mass of spherical silver powder having an average particle size of 1 μm. However, 1 part by mass and a total of 24 parts by mass of the solvent n-butyl carbitol are contained. Therefore, the volume ratio of the spherical silver powder and the acrylic resin (acrylic copolymer (1)) in the prepared paste; [metal silver powder volume: acrylic resin volume] corresponds to 100: 48. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 47% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 38 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 38 Pa · s.

Example 4
In Example 4, an acrylic copolymer having an epoxy equivalent of 284, a hydroxyl value of 155, a glass transition point of 49 ° C., and a molecular weight of 50,000 was synthesized as an acrylic resin component according to the method described in Reference Example 1 above. Is used to prepare a conductive paste according to the following procedure.

  The acrylic copolymer is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and is used as a raw material in the form of an acrylic resin solution having a content of acrylic resin component (solid content) of 30% by mass. It is used as. The hydroxyl value 155 corresponds to a hydroxyl equivalent 362. Accordingly, there are about 0.8 hydroxyl groups per epoxy group in the acrylic copolymer.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Further, 4 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 43 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste was 10 parts by mass of the acrylic resin (acrylic copolymer), 1 part by mass of the silane coupling agent, and a dispersant per 189 parts by mass of spherical silver powder having an average particle size of 1 μm. However, 1 part by mass and 27 parts by mass in total of n-butyl carbitol as a solvent are contained. Therefore, the volume ratio of the spherical silver powder and the acrylic resin (acrylic copolymer); [metal silver powder volume: acrylic resin volume] in the prepared paste corresponds to 100: 47. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 51% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 43 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 44 Pa · s.

(Example 5)
In Example 5, an acrylic copolymer having an epoxy equivalent of 284, a hydroxyl value of 155, a glass transition point of 22 ° C., and a molecular weight of 70,000, synthesized according to the method described in Reference Example 1 as an acrylic resin component. Is used to prepare a conductive paste according to the following procedure.

  The acrylic copolymer is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and is used as a raw material in the form of an acrylic resin solution having a content of acrylic resin component (solid content) of 30% by mass. It is used as. The hydroxyl value 155 corresponds to a hydroxyl equivalent 362. Accordingly, there are about 0.8 hydroxyl groups per epoxy group in the acrylic copolymer.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Further, 5 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste was 10 parts by mass of the acrylic resin (acrylic copolymer), 1 part by mass of the silane coupling agent, and a dispersant per 189 parts by mass of spherical silver powder having an average particle size of 1 μm. However, 1 part by mass and a total of 28 parts by mass of the solvent n-butyl carbitol are contained. Therefore, the volume ratio of the spherical silver powder and the acrylic resin (acrylic copolymer); [metal silver powder volume: acrylic resin volume] in the prepared paste corresponds to 100: 48. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 52% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 42 Pa · s.

(Example 6)
In Example 4, an acrylic copolymer having an epoxy equivalent of 284, a hydroxyl value of 58, a glass transition point of 47 ° C., and a molecular weight of 80,000, synthesized according to the method described in Reference Example 1 as an acrylic resin component. Is used to prepare a conductive paste according to the following procedure.

  The acrylic copolymer is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and is used as a raw material in the form of an acrylic resin solution having a content of acrylic resin component (solid content) of 30% by mass. It is used as. A hydroxyl value of 58 corresponds to a hydroxyl equivalent weight of 967. Accordingly, there are about 0.3 hydroxyl groups per epoxy group in the acrylic copolymer.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of spherical silver powder having an average particle diameter of 1 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 3 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste was 10 parts by mass of the acrylic resin (acrylic copolymer), 1 part by mass of the silane coupling agent, and a dispersant per 189 parts by mass of spherical silver powder having an average particle size of 1 μm. However, 1 part by mass and a total of 26 parts by mass of n-butyl carbitol as a solvent are contained. Therefore, the volume ratio of the spherical silver powder and the acrylic resin (acrylic copolymer (1)) in the prepared paste; [metal silver powder volume: acrylic resin volume] corresponds to 100: 48. The volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 50% by volume. In addition, an epoxy group is introduced as a reactive functional group by the silane coupling agent.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 42 Pa · s.

(Comparative Example 1)
In Comparative Example 1, an acrylic copolymer (2) having an epoxy equivalent of 0, a hydroxyl value of 117, a glass transition point of 37 ° C., and a molecular weight of 130,000 described in Reference Example 2 was used as the acrylic resin component. In use, the paste is prepared according to the following procedure.

  The acrylic copolymer (2) is dissolved in a solvent n-butyl carbitol (boiling point: 226 ° C.), and the content of the acrylic resin component (solid content) is 30% by mass in the form of an acrylic resin solution. As a raw material. In the acrylic copolymer (2), there is no epoxy group capable of reacting with a hydroxyl group, so that crosslinking between polymer chains cannot be formed. Further, for example, a covalent bond is formed by a reaction between a hydroxyl group generated on the surface of the PET film and an epoxy group, and the thermosetting product of the acrylic resin cannot be adhered. For example, a covalent bond can be formed by the reaction between an amino group generated on the surface of a polyimide film and an epoxy group, and a thermosetting product of an acrylic resin cannot be adhered.

  In a reaction vessel, 33 parts by mass of an n-butyl carbitol solution (solid content 30%) of the acrylic copolymer (2) is added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 189 parts by mass of flaky silver powder having an average particle diameter of 3 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 2 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste is 10 parts by mass of the acrylic resin (acrylic copolymer (2)) and 1 part by mass of the silane coupling agent per 189 parts by mass of the flaky silver powder having an average particle size of 3 μm. In total, 25 parts by mass of n-butyl carbitol as a solvent is contained. Therefore, the volume ratio of the scaly silver powder and the acrylic resin (acrylic copolymer (2)) in the prepared paste; [metal silver powder volume: acrylic resin volume] corresponds to 100: 48. Moreover, the volume ratio of n-butyl carbitol as a solvent contained in the prepared paste corresponds to 49% by volume.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 18 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 51. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 40 Pa · s.

(Comparative Example 2)
In Comparative Example 2, a paste was prepared according to the following procedure using a bisphenol A type epoxy resin (jER Epicoat 828EL) having an epoxy equivalent of 180 as a resin component. In addition, the hardening agent component with respect to the said epoxy resin is not mix | blended in the prepared paste. Therefore, the epoxy resin cannot be thermally cured by a curing agent.

  In a reaction vessel, 12 parts by mass of bisphenol A type epoxy resin having an epoxy equivalent of 180 (Epicoat 828EL manufactured by jER) and 14 parts by mass of n-butyl carbitol are added, and 1 part by mass of a silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 215 parts by mass of flaky silver powder having an average particle diameter of 3 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 3 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the paste whose viscosity was adjusted was 12 parts by mass of the bisphenol A type epoxy resin, 1 part by mass of the silane coupling agent, and n-butylcarbyl solvent as the solvent per 215 parts by mass of the flaky silver powder having an average particle size of 3 μm. A total of 17 parts by mass of Toll is contained. Therefore, the volume ratio of the flaky silver powder and the bisphenol A type epoxy resin in the prepared paste; [metal silver powder volume: epoxy resin volume] corresponds to 100: 57. Moreover, the volume ratio of the solvent n-butyl carbitol contained in the prepared paste corresponds to 38% by volume.

  The prepared paste was subjected to a pattern drawing of 10 mm × 50 mm by screen printing on various films and subjected to a heat treatment at 120 ° C. × 15 min. After cooling, the average film thickness of the film is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the film after the heat treatment was 23 μm. The ratio of the average film thickness of the film after the heat treatment to the average film thickness of the coating film is 100: 64. Therefore, it is judged that the solvent n-butyl carbitol substantially does not remain in the film after the heat treatment.

  The pencil hardness of the film after heat treatment was <5B and was not substantially cured. Further, the film after the heat treatment did not show conductivity.

  Therefore, it was impossible to evaluate volume resistivity and adhesion.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 40 Pa · s.

(Comparative Example 3)
In Comparative Example 3, a bisphenol A type epoxy resin having an epoxy equivalent weight of 180 (jER Epicoat 828EL) is used as a resin component, and an amine type latent curing agent (Ajinomoto Fine Techno Amicure PN-23) is used as its curing agent component. Thus, a conductive paste is prepared according to the following procedure. The ratio of the amino group of the amine-type latent curing agent to the epoxy group of the epoxy resin in the prepared paste is such that one or less amino group is blended per one epoxy group. It has become.

  In a reaction vessel, 10 parts by mass of a bisphenol A type epoxy resin having an epoxy equivalent of 180 (Epicoat 828EL manufactured by jER), 2 parts by mass of an amine-type latent curing agent (Amicure PN-23 manufactured by Ajinomoto Fine-Techno), 14 parts by mass of n-butylcarbitol 1 part by mass of the silane coupling agent is added. After the addition of the silane coupling agent, the mixture is sufficiently stirred and mixed to prepare a uniform liquid resin. As the silane coupling agent, KBM403 (manufactured by Shin-Etsu Chemical Co., Ltd.), which is an epoxy silane coupling agent, is used.

  Next, 215 parts by mass of flaky silver powder having an average particle diameter of 3 μm is added to the uniform liquid resin. Thereafter, the mixture is sufficiently stirred and mixed to prepare a uniform paste.

  Furthermore, 3 parts by mass of n-butyl carbitol is added as a diluent solvent, and the viscosity of the paste is adjusted to about 40 Pa · s by sufficiently stirring and mixing.

  The composition of the viscosity-adjusted paste was 10 parts by mass of the bisphenol A type epoxy resin per 215 parts by mass of the flaky silver powder having an average particle size of 3 μm. However, 2 parts by mass, 1 part by mass of the silane coupling agent, and 17 parts by mass in total of n-butyl carbitol as a solvent are contained. Therefore, the volume ratio of the flaky silver powder and (the bisphenol A type epoxy resin + amine type latent curing agent) in the prepared paste; [metal silver powder volume: (epoxy resin + curing agent) volume] is 100: 57. It corresponds to. The volume ratio of n-butyl carbitol as a solvent contained in the prepared paste corresponds to 36% by volume.

  The prepared paste carries out pattern drawing of 10 mm x 50 mm by screen printing on various films, and is hardened at 120 degreeC x 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 23 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 64. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  The viscosity of the paste is measured at 25 ° C. using a spiral viscometer (Malcom).

  The viscosity immediately after the production was about 40 Pa · s, while the viscosity after being stored in a thermostatic bath at 23 ° C. for 24 hours was 84 Pa · s.

(Comparative Example 4)
In Comparative Example 4, the conductive paste described in Comparative Example 3 is used, and the heat treatment conditions are changed to produce a cured product.

  The paste prepared in Comparative Example 3 draws a pattern of 10 mm × 50 mm by screen printing on various films and is cured at 150 ° C. × 15 min. After cooling, the average film thickness of the produced cured product is measured.

  The average film thickness of the coating film of the prepared paste was selected to be 35 μm. The average film thickness of the produced cured product was 23 μm. The ratio of the average film thickness of the produced cured product to the average film thickness of the coating film is 100: 64. Therefore, it is judged that the solvent n-butyl carbitol does not substantially remain in the produced cured product.

  As the base film, four types of films described in Example 1 are used.

  The volume resistivity, adhesion, pencil hardness, and viscosity change rate were evaluated by the evaluation method described in Example 1.

  Table 1 summarizes the evaluation results of the viscosity change rate for the pastes prepared in Examples 1 to 6 and the pastes prepared in Comparative Examples 1 to 3.

  Further, in Examples 1 to 6 and Comparative Examples 1 to 4, a cured film was prepared using each paste, and the results of evaluating the volume resistivity, adhesion, and pencil hardness were In addition, it is shown in Table 1.

  The electrically conductive paste concerning this invention can be utilized for preparation of the conductor film which can be utilized for formation of the wiring layer of a flexible printed circuit board. In particular, as a base material (base film) of a flexible printed circuit board, it exhibits excellent adhesion to the surface of a widely used PET film or polyimide film, and can be repeatedly bent and deformed, and by bending deformation, The conductive film having toughness that does not cause internal breakage can be used for the purpose of producing with good reproducibility by thermosetting at a heating temperature of 150 ° C. or less.

Claims (14)

A conductive paste that can be cured at low temperature,
As the resin component, an acrylic resin having an epoxy equivalent of 284 to 946, a hydroxyl value of 58 to 155, a molecular weight of 30,000 to 170,000 and a glass transition point of 10 to 55 ° C. is selected.
In the conductive paste,
Per 100 parts by mass of metallic silver powder,
3 to 8 parts by mass of the acrylic resin,
0.1 to 1.5 parts by mass of a silane coupling agent,
8 to 25 parts by mass of an organic solvent having a boiling point of 150 ° C. or higher and 266 ° C. or lower at normal pressure,
A conductive paste characterized by being contained in each. The conductive paste according to claim 1, wherein the organic solvent does not contain a functional group having high reactivity with respect to an epoxy group and a hydroxyl group. Contained in the conductive paste,
The ratio of the total volume of the metallic silver powder and the total volume of the acrylic resin: [metallic silver powder volume: acrylic resin volume] is selected in the range of 100: 27 to 100: 73. The conductive paste according to 1 or 2. Contained in the conductive paste,
The content rate of the said organic solvent is selected in the range of 40 volume%-70 volume% of this electrically conductive paste, The electrically conductive paste as described in any one of Claims 1-3 characterized by the above-mentioned. The conductive paste according to any one of claims 1 to 4, wherein the viscosity of the conductive paste is selected in a range of 5 Pa · s to 70 Pa · s. 6. The conductive paste according to claim 1, wherein the metallic silver powder is a spherical metallic silver powder having an average particle diameter of 7 μm or less and 0.3 μm or more. The conductive paste according to any one of claims 1 to 5, wherein the metallic silver powder is a flaky metallic silver powder having an average particle size of 10 µm or less and 1.0 µm or more. The metallic silver powder is
A mixture of flaky metallic silver powder having an average particle size of 10 μm or less and 1.0 μm or more, and a spherical metal silver powder having an average particle size of 7 μm or less and 0.3 μm or more,
The mixing ratio (mass ratio) of the flaky metallic silver powder and the spherical metallic silver powder is such that the total mass of the flaky metallic silver powder: the total mass of the spherical metallic silver powder is selected in the range of 9: 1 to 2: 8. The electrically conductive paste as described in any one of Claims 1-5 characterized by the above-mentioned. The conductive paste according to any one of claims 1 to 8, wherein the functional group introduced by the silane coupling agent has reactivity with an epoxy group or a hydroxyl group. The conductive paste according to claim 1, wherein the functional group introduced by the silane coupling agent is an epoxy group. In the conductive paste, a dispersant for the metallic silver powder is further added.
The conductive paste according to any one of claims 1 to 10, wherein the conductive paste is added in a range of 0.1 to 1.5 parts by mass per 100 parts by mass of metallic silver powder. The ratio of epoxy groups and hydroxyl groups present in the acrylic resin is selected such that an average of 0.3 to 2.6 hydroxyl groups are present per epoxy group. The conductive paste according to any one of claims 1 to 11. The conductive paste according to any one of claims 1 to 12, wherein the acrylic resin has a molecular weight of 50,000 to 130,000 and a glass transition point of 20 to 50 ° C. . The said acrylic resin can produce the thermosetting material of this acrylic resin by selecting heating temperature in the range of 100 to 150 degreeC, and heating for 30 minutes or more. The electrically conductive paste as described in any one of these.