JP6594156B2 - Heat-curing conductive paste - Google Patents

Description

  The present invention relates to a thermosetting conductive paste.

  In recent years, various electric / electronic devices have been improved in performance, such as downsizing, higher density, and higher operation speed. Along with this, electronic parts for electric and electronic devices are required to have finer and finer electrodes. However, in a printing method that has been widely used at the time of electrode formation, a thin line-like electrode, for example, an electrode having a line width and a space (line and space: L / S) of 80 μm / 80 μm or less, and further 50 μm / 50 μm or less is used. It is difficult to form with high accuracy.

  Then, utilization of the laser etching method using a laser beam is examined. In this method, first, a conductive paste is prepared as in the prior art. Next, the prepared conductive paste is printed on a desired substrate to form a conductive film (conductive film). Then, the other part is irradiated with laser light, leaving the formed conductive film in a desired thin line shape. The conductive film is thermally decomposed and removed at the portion irradiated with the laser light, and an electrode is formed from the conductive film at the portion not irradiated with the laser light.

Patent Documents 1 to 4 disclose a conductive paste for laser etching that can be used for such applications. For example, Patent Document 1 discloses a conductive paste containing a binder resin made of a thermoplastic resin, a conductive powder, and an organic solvent. In paragraphs 0025 and 0026 of Patent Document 1, the conductive powder has a spherical shape, agglomerated shape (a shape in which spherical primary particles are aggregated three-dimensionally), or a scaly shape with a center diameter ( It is described that it is preferable to use one having a D ₅₀ ) of 4 μm or less.

International Publication No. 2014/013899 JP 2014-225709 A JP 2014-29992 A JP 2014-107533 A

As described in Patent Document 1 and the like, it is common to use a thermoplastic resin as an adhesive component in a conductive paste for laser etching. This has the purpose of facilitating thermal decomposition / removal by laser light by increasing the thermal decomposability of the binder resin. However, if the heat of the laser is transmitted to the resin remaining as an electrode, the resin may be deteriorated or the conductive film may be scraped more than necessary. In addition, electrodes made of thermoplastic resin tend to have lower heat resistance, chemical resistance, and film hardness (mechanical strength) due to the high thermal decomposability of the binder resin. May be unreliable.
Therefore, the present inventors tried to form a conductive film using a thermosetting resin. However, considering electrode formation using a thermosetting resin in particular, it has been difficult to form an electrode with high electrical conductivity by laser etching.

This will be described in detail with reference to FIGS.
FIG. 2 is an explanatory diagram of a conductive film using aggregated conductive powder (hereinafter also referred to as “aggregated conductive powder”). As shown in FIG. 2, in the conductive film 20 using the aggregated conductive powder, the aggregated particles 13 constituting the aggregated conductive powder are densely packed. Thereby, the stacking property in the conductive film 20 is improved as compared with the case of using non-aggregated (for example, spherical) conductive powder. Further, the number of contacts in the aggregated particles 13 or between the aggregated particles 13 increases. This is advantageous from the viewpoint of reducing resistance.

  However, the agglomerated particles 13 are generally unfamiliar with the binder resin. For this reason, the aggregated particles 13 and the binder resin are difficult to mix in the conductive paste, and the conductive film 20 may become inhomogeneous. That is, in the conductive film 20, there may be a portion where the aggregated particles 13 are locally unevenly distributed and a resin pool 16 where the binder resin is locally unevenly distributed. Furthermore, as described above, thermosetting resins are characterized by low thermal decomposability. Therefore, when a thermosetting resin is used as the binder resin, even if the laser irradiation part 18 is irradiated with laser light, the part of the resin reservoir 16 is not easily decomposed and removed, and the yield deteriorates or the part is “ It may remain as a “residue”. As a result, in the electrode 22 after laser etching, the width is locally increased or a protrusion-like portion is generated, and the processing accuracy is reduced, or the adjacent electrodes 22 are brought into contact with each other and slightly short-circuited. Sometimes. Such an event becomes more serious as the electrode becomes thinner.

  FIG. 3 is an explanatory diagram of a conductive film using non-aggregated conductive powder (hereinafter also referred to as “non-aggregated conductive powder”). The non-aggregated particles 14 constituting the non-aggregated conductive powder are more familiar with the binder resin 17 than the aggregated particles. For this reason, as shown in FIG. 3, in the conductive film 30 using the non-aggregated conductive powder, the binder resin 17 is loosened, and the occurrence of the resin pool is suppressed. That is, the homogeneity is higher than in the case of using the aggregated conductive powder. Therefore, even when a thermosetting resin is used as the binder resin, the laser irradiated portion 18 can be easily decomposed and removed. This is advantageous from the viewpoint of improving the accuracy of laser processing.

  However, when the non-aggregated particles 14 and the binder resin are uniformly dispersed in the conductive film 30, the periphery of each non-aggregated particle 14 is covered with the binder resin. As a result, in the electrode 32, the distance between the non-aggregated particles 14 is long, and the direct contact between the non-aggregated particles 14 is hindered by the binder resin, so that the resistance tends to increase.

  This invention is made | formed in view of this point, The objective is to provide the electrically conductive paste which is excellent in laser processing suitability and can form an electrode with high electrical conductivity.

The inventors of the present invention have intensively studied and conceived of mixing predetermined two kinds of conductive powders as conductive powders. And after further earnest study, the present invention was completed.
According to the present invention, a thermosetting conductive paste is provided. This heat curable conductive paste includes a conductive powder, a thermosetting resin, and a curing agent. The ratio of the conductive powder has a mean particle size based on the number based on electron microscopy (SEM-D _50), and the average particle diameter on a volume basis, based on the laser diffraction scattering particle size distribution measuring method (L-D _{50) (L-D 50 / SEM-} D 50) cohesion which is expressed by and a cohesive conductive powder and the non-agglomerated conductive powder mutually different. The degree of aggregation of the non-aggregated conductive powder is 1.5 or less. The aggregation degree of the aggregated conductive powder is more than 1.5 and 3 or less. The LD ₅₀ of the aggregated conductive powder does not exceed the LD ₅₀ of the non-aggregated conductive powder.

  According to the above configuration, it is possible to realize an electrode having high electrical conductivity while maintaining good laser processability despite using a thermosetting resin. That is, it is possible to stably realize a desired thin line shape by reducing uncut residue during laser processing. Further, for example, a low resistance electrode having a volume resistivity (heat curing condition of 130 ° C., 30 minutes) of 130 μΩ · cm or less can be realized. Furthermore, according to the said structure, the essential property of a thermosetting resin is exhibited and the electrode excellent in heat resistance and durability compared with the case where a thermoplastic resin is used can be obtained.

In this specification, “LD ₅₀ ” means a particle diameter D ₅₀ value corresponding to a cumulative 50% from the smaller particle diameter in the volume-based particle size distribution based on the laser diffraction / scattering particle size distribution measurement method ( Median diameter). The laser diffraction / scattering particle size distribution measurement is performed using ultrasonic waves after appropriately diluting with isopropyl alcohol as a dispersion medium so that the sample concentration falls within a predetermined concentration range set based on the apparatus. And distributed processing.
In the present specification, “SEM-D ₅₀ ” refers to a particle diameter D ₅₀ value (median diameter) corresponding to a cumulative 50% from the smallest particle diameter in a number-based particle size distribution based on electron microscope observation. .
The “aggregation degree” is 1 when the L-D ₅₀ is equal to the SEM-D ₅₀ , that is, when the aggregation is not at all, and indicates that the larger the value is, the more intense the aggregation is.

In a preferred embodiment disclosed herein, the LD _{50 of the} non-aggregated conductive powder is 5 μm or less. By making the particles (secondary particles) that make up the conductive powder below the specified value, the laser irradiation site (site that is thermally decomposed and removed by laser) and the area that remains as an electrode during laser processing The conductive powder present in can be reduced. As a result, laser processability can be improved. Therefore, a thin wire electrode can be formed more stably.

In a preferred embodiment disclosed herein, the SEM-D ₅₀ of the non-aggregated conductive powder is 1.1 μm or more and 3 μm or less. Further, the SEM-D ₅₀ of the aggregated conductive powder is not less than 0.1 μm and not more than 1 μm. Thereby, the range of the aggregation degree can be better realized while maintaining the LD ₅₀ . Moreover, the handleability of electroconductive powder and adhesiveness with a base material can be improved.

In a preferred embodiment disclosed herein, the LD ₅₀ of the non-aggregated conductive powder is 1.5 times or more of the LD ₅₀ of the aggregated conductive powder. Thereby, the gap between the non-aggregated conductive powders is better filled with the aggregated conductive powder, and the stacking property is improved. As a result, an electrode with higher density and lower resistance can be realized.

  In a preferred embodiment disclosed herein, the mixing ratio of the non-aggregated conductive powder and the aggregated conductive powder is 30:70 to 95: 5. As a result, it is possible to balance good laser processability and low electrode resistance at a high level.

In a preferred embodiment disclosed herein, the non-aggregated conductive powder is composed of spherical particles having an aspect ratio of 2 or less. Thereby, for example, laser workability is further improved as compared with the case of using non-aggregated conductive powder having an average aspect ratio of 2 or more. For this reason, the effect of the present invention can be achieved at a higher level.
In the present specification, the “aspect ratio” means the average of the major axis / minor axis ratio of conductive particles (non-aggregated particles). For example, the conductive particles are observed using an electron microscope. Then, a minimum rectangle circumscribing the particle image can be drawn, and the ratio (A / B) of the long side length A to the short side length (eg, thickness) B of the rectangle can be calculated as the aspect ratio.

  In a preferred embodiment disclosed herein, the conductive powder is silver powder and / or silver-coated copper powder. Thereby, an electrode with further excellent electrical conductivity can be realized.

In a preferred embodiment disclosed herein, the number average molecular weight of the thermosetting resin is 10,000 or less. Thereby, an electrode with further excellent electrical conductivity can be realized.
In the present specification, the “number average molecular weight” means an average molecular weight measured by gel chromatography (Gel Permeation Chromatography: GPC) and converted using a standard polystyrene calibration curve.

  In a preferred embodiment disclosed herein, when the conductive powder is 100 parts by weight, the total of the thermosetting resin and the curing agent is 30 parts by weight or less. As a result, the conductive film is easily thermally decomposed and removed by laser light, and laser processability can be improved. In addition, an electrode with further excellent electrical conductivity can be realized.

It is explanatory drawing of the electrically conductive film which concerns on one Embodiment of this invention. It is explanatory drawing of the electrically conductive film using the aggregation electroconductive powder. It is explanatory drawing of the electrically conductive film using non-aggregated conductive powder. It is a laser microscope image of an electrode, (a) is Example 4, (b) is Reference Example 1, (c) is an image concerning Reference Example 2.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification (for example, composition of heat-curable conductive paste) and matters necessary for carrying out the present invention (for example, a method for preparing heat-curable conductive paste) And a method for forming an electrode (conductive film) and the like can be understood as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Heat-curing type conductive paste>
The thermosetting conductive paste disclosed herein (hereinafter sometimes simply referred to as “paste”) includes (A) conductive powder, (B) thermosetting resin, and (C ) Hardener. The above (A) is characterized by containing at least two predetermined types of powders. Therefore, the other is not particularly limited, and can be arbitrarily determined in light of various criteria. For example, components other than the above (A) to (C) can be blended, or the composition ratio of these components can be appropriately changed. Hereinafter, the components of the paste will be described.

<(A) Conductive powder (mixed powder)>
The conductive powder contained in the paste is a component for imparting electrical conductivity to the electrode.
The conductive powder disclosed here comprises two types of components having different aggregation degrees (LD ₅₀ / SEM-D ₅₀ ) as main components, that is, a non-aggregated conductive powder and an aggregated conductive powder. Contains. The two types of powders can cause the above-mentioned problems when used alone, but by mixing these, the low resistance electrode can be maintained while maintaining good laser processability. Can be realized.

  FIG. 1 is an explanatory diagram of a conductive film according to an embodiment of the present invention. That is, as shown in FIG. 1, the conductive powder includes the aggregated particles 13, so that the stacking property in the conductive film 10 is improved and the contact points between the conductive particles are increased. As a result, the resistance of the conductive film 10 is reduced as compared with the case where the non-aggregated conductive powder is used alone. Further, since the conductive powder includes the non-aggregated particles 14, the binder resin 15 is suitably loosened, and the occurrence of “resin pool” unevenly distributed in the conductive film 10 is suppressed. As a result, the laser processability of the conductive film 10 can be improved and the electrode 12 with high laser processing accuracy can be obtained as compared with the case where the aggregated conductive powder is used alone.

<(A1) Non-aggregated conductive powder>
The non-aggregated conductive powder has an aggregation degree of 1 or more and 1.5 or less. That is, most of the non-aggregated particles (for example, 50% by number or more) constituting the non-aggregated conductive powder are stably present in a single particle state without agglomeration. The degree of aggregation of the non-aggregated conductive powder is, for example, 1.1 or more and can be 1.3 or less, for example.

  The non-aggregated particles constituting the non-aggregated conductive powder are not particularly limited, and various conductive materials having desired conductivity and other physical properties, such as metals and alloys, may be appropriately used depending on applications. it can. As a preferable example, gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os), Examples thereof include metals such as nickel (Ni) and aluminum (Al), and coating mixtures and alloys thereof. Among them, simple metals such as silver (Ag), platinum (Pt), palladium (Pd), and mixtures thereof (for example, silver-coated copper, silver-coated nickel, etc.) and alloys thereof (for example, silver-palladium) (Ag—Pd), silver-platinum (Ag—Pt), silver-copper (Ag—Cu), etc.) are preferred. In particular, silver, a silver coated product, and an alloy containing silver are preferable because of relatively low cost and excellent electrical conductivity.

The SEM-D ₅₀ (number-based average particle diameter based on electron microscope observation) of the non-aggregated particles is not particularly limited as long as it satisfies the above range of the aggregation degree. Usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1.1 μm or more, for example 1.4 μm or more, and generally 5 μm or less, preferably 4 μm or less, more preferably 3 μm or less, for example 2.8 μm. It may be the following. Thereby, the range of the said aggregation degree can be implement | achieved better.

The shape of the non-aggregated particles is not particularly limited, and various shapes such as a spherical shape, a scale shape (flake shape), and a needle shape can be considered. Of these, a true spherical shape or a spherical shape is preferable. Thereby, the viscosity of a paste can be maintained low and handling property, storage stability, and workability | operativity at the time of printing can be improved. Therefore, the conductive film can be stably formed.
In the present specification, the term “spherical” is a term including a spherical shape, a rugby ball shape, a polygonal shape, and the like. For example, the average aspect ratio (major axis / minor axis ratio) is 2 or less, typically 1.5 or less, for example, about 1.1 to 1.4.

In a preferred embodiment, the non-agglomerated conductive powder does not comprise conductive particles having an aspect ratio of greater than 10, typically greater than 5, such as greater than 3, especially greater than 2. That is, the non-aggregated conductive powder preferably does not contain scale-like particles. In particular, the non-aggregated conductive powder is preferably composed of spherical particles having an aspect ratio of 2 or less. Thereby, the laser processability is remarkably improved, and the fine wire electrode can be better formed with a predetermined processing line width.
That is, the non-aggregated particles having a large aspect ratio generally have a large area in the plan view of one particle. For this reason, at the time of laser etching, one particle may exist in a state straddling the part irradiated with laser (part removed by laser processing) and the part left as an electrode. When laser light is irradiated in this state, a portion that should be left as an electrode is scraped more than necessary, and the width of the electrode may be narrower than the default. By not including scale-like particles, the laser processing accuracy can be improved. Furthermore, when the paste is printed on the substrate, the detachability from the plate making (disengagement from the mesh) becomes good, so that the printing accuracy can be improved.

The L-D ₅₀ (volume-based average particle diameter based on the laser diffraction / scattering particle size distribution measurement method) of the non-aggregated conductive powder is not particularly limited as long as it satisfies the above range of aggregation degree. Usually, it is 0.5 μm or more, preferably 1 μm or more, for example, 2 μm or more, and is generally 7 μm or less, preferably 5 μm or less, more preferably 4 μm or less, for example 3.6 μm or less.
When the LD ₅₀ is equal to or greater than a predetermined value, the internal resistance is reduced, and an electrode having excellent electrical conductivity can be realized better. In addition, the viscosity of the paste can be kept low, and handling and printing workability can be improved. When LD ₅₀ is less than or equal to a predetermined value, a thin-film or thin-line electrode can be formed more stably. For example, it is possible to effectively reduce the number of particles that are in a state straddling a portion to be removed during laser etching and a portion to be left as an electrode. As a result, the suitability for laser processing is dramatically improved, and a thin wire electrode can be formed better with a stable processing line width.

  In a preferred embodiment, the non-aggregated particles are provided with a coating containing a fatty acid on the surface. According to the said structure, the hydroxyl group (hydroxyl group) on the surface of a non-aggregated particle increases, and hydrophilicity is improved. Since thermosetting resins are typically hydrophobic, this reduces the wettability of the non-aggregated particles and the thermosetting resin. As a result, the thermosetting resin is less likely to cling to the non-aggregated particles, and the non-aggregated particles or the non-aggregated particles and the aggregated particles easily form a contact. Therefore, it is possible to form an electrode with further excellent electrical conductivity. Typical examples of fatty acids include saturated higher fatty acids and unsaturated fatty acids having 10 or more carbon atoms. From the viewpoint of exhibiting the above effect at a high level, polyunsaturated fatty acids such as alkyl succinic acid and alkenyl succinic acid are preferable.

<(A2) Aggregated conductive powder>
The agglomerated conductive powder has a degree of aggregation of more than 1.5 and 3 or less. That is, the aggregated particles constituting the aggregated conductive powder are configured by aggregating about 1.5 to 3 fine particles on average. By satisfying such a degree of aggregation, excellent laser processability can be realized while being an aggregated conductive powder. The aggregation degree of the aggregated conductive powder is, for example, 1.6 or more, and can be approximately 2.5 or less, for example, 2.1 or less.

  The agglomerated particles constituting the agglomerated conductive powder are not particularly limited, and various metals, mixtures, alloys, and the like having desired conductivity and other physical properties can be appropriately used depending on the application. As a suitable example, the above-mentioned thing in (A1) is mentioned. Note that the non-aggregated particles constituting the non-aggregated conductive powder and the aggregated particles constituting the aggregated conductive powder may use the same type of conductive material or different conductive materials. .

The SEM-D ₅₀ (number-based average particle diameter based on observation with an electron microscope) of the fine particles (primary particles) constituting the aggregated particles is not particularly limited as long as the range of the aggregation degree is satisfied. Usually, it is smaller than the SEM-D ₅₀ of the non-aggregated particles of (A1), and is typically 1/2 or less, for example, about 1/10 to 1/2 of the non-aggregated particles. Specifically, it is generally 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, for example 0.2 μm or more, and is generally 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, For example, it may be 0.7 μm or less. Thereby, the range of the said aggregation degree can be implement | achieved better. Further, by the SEM-D ₅₀ equal to or higher than a predetermined value, it is possible to improve the handling properties of the conductive powder.

The LD ₅₀ (volume average particle diameter based on the laser diffraction / scattering particle size distribution measurement method) of the aggregated conductive powder does not exceed the LD ₅₀ of the above (A1). That, (A2) _{L-D 50} of the aggregate conductive powder is equal to or _{L-D 50} of the (A1) non-agglomerated conductive powder is smaller than that. Specifically, it is about 0.1 μm or more, preferably 0.5 μm or more, for example 1 μm or more, and is about 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less, for example 1.2 μm or less. When the LD ₅₀ satisfies the predetermined range, it is possible to balance good laser processability and low resistance of the electrode at a high level.

In a preferred embodiment, (A1) the non-aggregated conductive powder has an LD ₅₀ that is more than 1 times the LD ₅₀ of (A2) the aggregated conductive powder, and is approximately 1.5 times or more, for example, 2 times or more. It is. Thereby, the clearance gap between the non-aggregated particles constituting the non-aggregated conductive powder is better filled with the aggregated particles constituting the aggregated conductive powder, and the stacking property is improved. As a result, a high-density, low-resistance electrode can be realized better.

In a preferred embodiment, (A) the conductive powder is, by mass ratio, the following components:
(A1) Non-aggregated conductive powder 20 to 97% by mass (preferably 30 to 95% by mass);
(A2) Aggregated conductive powder 3 to 80% by mass (preferably 5 to 70% by mass);
including. When the conductive powder contains (A1) and (A2) at the above mass ratio, the effect of using two kinds of powders together is exhibited at a very high level. In particular, in forming the thin wire electrode, from the viewpoint of further improving the laser workability, (A1) may occupy 50% by mass or more of the entire conductive powder. Alternatively, from the viewpoint of low resistance, (A2) may occupy 50% by mass or more of the entire conductive powder.

  The proportion of the (A) conductive powder in the total mass (that is, (A) + (B) + (C)) of the essential constituents of the paste is not particularly limited, but is usually 50% by mass or more, typically 60%. It is good in it being -98 mass%, for example, 70-95 mass%. By satisfying the above range, it is possible to form an electrode having high electrical conductivity while maintaining excellent workability and paste handling.

<(B) Thermosetting resin>
The thermosetting resin contained in the paste is a component for imparting adhesion and durability to the electrode. When the thermosetting resin is heated by adding a curing agent, a network-like crosslinked structure is formed and cured. Once cured, it is difficult to dissolve in a solvent, and plasticity does not appear even when heated (does not deform). Therefore, when a thermosetting resin is used, it is less likely to be deteriorated by laser etching than when a thermoplastic resin is used, and the heat resistance, chemical resistance, mechanical strength, and durability are improved. An excellent electrode can be suitably realized.

  It does not specifically limit as a thermosetting resin, According to a use etc., what is conventionally known can be used suitably. Preferable examples include phenol resins such as epoxy resins, novolak resins, resol resins, alkylphenol resins, urea resins, melamine resins, alkyd resins, silicone resins, urethane resins, and the like. These thermosetting resins may be used alone or in combination of two or more. Of these, epoxy resins and phenol resins are preferred from the viewpoint of laser processability (thermal decomposability) and adhesiveness.

  The number average molecular weight of the thermosetting resin is not particularly limited, but is generally about 10,000 or less, preferably 9000 or less, typically 100 to 9000, more preferably 5000 or less, for example, about 200 to 5000. When the number average molecular weight is not more than a predetermined value, when the paste is printed on the substrate, the detachability (release property) from the plate making becomes good, and problems such as stringing can be suppressed. Therefore, printing accuracy can be improved. Further, among thermosetting resins, those having a smaller number average molecular weight tend to have higher thermal decomposability, so that the ease of processing by laser etching can be improved. Furthermore, when the number average molecular weight is a predetermined value or more, the adhesion between the substrate and the electrode is increased, and the shape integrity as an electronic member can be improved.

  In a preferred embodiment, the thermosetting resin includes an epoxy resin. In the present specification, “epoxy resin” refers to all compounds having one or more epoxy groups in the molecule, which are ethers of three-membered rings. Epoxy resins are excellent in adhesiveness, heat resistance, chemical resistance, and mechanical durability among thermosetting resins. Therefore, by including an epoxy resin, it is possible to realize an electrode wiring having further excellent durability characteristics and reliability.

The epoxy equivalent of the epoxy resin is not particularly limited, but is preferably about 100 to 3000 g / eq for the purpose of exhibiting the above-described characteristics (particularly adhesiveness) at a high level.
In this specification, “epoxy equivalent” means a value measured according to JIS K7236 (2009).

  Especially, it is preferable that thermosetting resin contains the glycidyl ether type epoxy resin which contains a glycidyl ether group in a molecule | numerator, and / or a glycidyl ester group in a molecule | numerator. Thereby, the effect of this invention can be exhibited at a higher level.

  When using an epoxy resin, a monofunctional epoxy resin (monofunctional epoxy resin) having one epoxy group in the molecule is preferable from the viewpoint of obtaining a thin film electrode (for example, a thickness of 10 μm or less) suitable for laser etching. is there. The monofunctional epoxy resin is effective in giving the paste sufficient fluidity because of its low viscosity among epoxy resins. Thereby, workability | operativity at the time of paste coating (printing) can be improved, and a thin film-like electrically conductive film can be formed accurately. Moreover, the flexibility of the thermosetting resin is increased by using the monofunctional epoxy resin, and the thermosetting resin easily flows during the heat curing of the paste. As a result, the thermosetting resin is extruded from between the conductive particles, and the number of contacts between the conductive particles tends to increase. Therefore, the resistance of the electrode can be further reduced.

  Examples of monofunctional epoxy resins include glycidyl ether-based epoxy resins such as alkyl glycidyl ether, alkylphenyl glycidyl ether, alkenyl glycidyl ether, alkynyl glycidyl ether, and phenyl glycidyl ether; alkyl glycidyl esters, alkenyl glycidyl esters, phenyl glycidyl esters, and the like. Glycidyl ester epoxy resin; and the like. These resins may be used alone or in a suitable combination of two or more.

  Alternatively, an acrylic glycidyl ester copolymer is suitable from the viewpoint of obtaining an electrode having high adhesion and surface smoothness. Since the acrylic glycidyl ester copolymer has an acryloyl group, it is effective for strongly adhering various substrates and electrodes. The acrylic glycidyl ester copolymer can also function as a surface conditioner (leveling agent). That is, it can function to float on the surface of the conductive film before the resin is completely cured, and to homogenize the surface tension. Thereby, the smoothness of the electrode surface can be improved.

  Examples of the acrylic glycidyl ester copolymer include a homopolymer of an epoxy group-containing polymerizable monomer containing an epoxy group, a copolymer of the epoxy group-containing polymerizable monomer and another polymerizable monomer, and the like. Examples of the epoxy group-containing polymerizable monomer include glycidyl (meth) acrylate, glycidyl methacrylate (GMA), α-methyl glycidyl methacrylate, vinyl glycidyl ether, and allyl glycidyl ether. Examples of the other polymerizable monomers include acrylic acid and acrylic acid esters such as methyl (meth) acrylate, and methacrylic acid esters such as methacrylic acid and methyl methacrylate (MMA). The mixing ratio of the epoxy group-containing polymerizable monomer and the other polymerizable monomer is not particularly limited, but as a rough guide, in a preferred example, about 3: 1 to 1: 3, for example, about 2: 1 to 1: 2. It is good to be.

  The content of the thermosetting resin is not particularly limited, but from the viewpoint of improving the adhesion with the base material and the integrity of the electrode, typically 5 parts by mass or more when the conductive powder is 100 parts by mass. The amount is preferably 10 parts by mass or more, for example, 15 parts by mass or more. Further, from the viewpoint of low resistance, it is generally 30 parts by mass or less, preferably 25 parts by mass or less, for example, 20 parts by mass or less. Thereby, the electrode which was further excellent in adhesiveness with a board | substrate, durability, and electrical conductivity can be obtained.

  The proportion of (B) thermosetting resin (mixture) in the total mass (that is, (A) + (B) + (C)) of the essential constituents of the paste is not particularly limited, but is typically 5% by mass. Above, preferably 7% by mass or more, for example 10% by mass or more, and generally 25% by mass or less, preferably 20% by mass or less, for example 15% by mass or less. By satisfying the above range, the effect of the present invention can be achieved at a higher level.

<(C) Curing agent>
The curing agent contained in the paste is a component for forming a three-dimensional crosslinked structure between the molecules of the thermosetting resin and curing it. It does not specifically limit as a hardening | curing agent, According to the kind etc. of thermosetting resin, it can use suitably. For example, when an epoxy resin is used as the thermosetting resin, a compound that can react with an epoxy group to form a crosslinked structure may be used. Preferable examples of the curing agent include amine-based curing agents, imidazole-based curing agents, phenol-based curing agents, amide-based curing agents, organic phosphines, and derivatives thereof. From the viewpoint of high durability, for example, heat resistance, mechanical strength, chemical resistance (particularly alkali resistance) and the like, an amine-based curing agent is preferable. These compounds may be used individually by 1 type, and may use 2 or more types together.

The content ratio of the curing agent is not particularly limited, but is typically 0.1 parts by mass or more, preferably 0.5 parts by mass or more, for example, 1 part by mass or more when the conductive powder is 100 parts by mass. In general, it is 7 parts by mass or less, preferably 5 parts by mass or less, for example, 3 parts by mass or less. Thereby, it is possible to prevent the curing failure from occurring and allow the curing reaction to proceed smoothly. Moreover, it can suppress that unreacted hardening | curing agent remains in an electrode, and can suppress resistance lower.
Further, from the viewpoint of low resistance, when the conductive powder is 100 parts by mass, the total of the thermosetting resin and the curing agent ((B) + (C)) is approximately 35 parts by mass or less, preferably 30 It is good if it is not more than part by mass, more preferably not more than 20 parts by mass, especially not more than 15 parts by mass.

  The proportion of the curing agent in the total mass (that is, (A) + (B) + (C)) of the essential constituents of the paste is not particularly limited, but is typically 0.1% by mass or more, preferably 0.8. It is 5 mass% or more, for example, 1 mass% or more, and is generally 7 mass% or less, preferably 5 mass% or less, for example, 3 mass% or less. By satisfying the above range, an electrode with reduced resistance can be stably formed.

<(D) Other ingredients>
The paste disclosed here typically contains an organic dispersion medium (typically an organic solvent) in which the components (A) to (C) are dispersed. Thereby, the viscosity and thixotropy of a paste can be adjusted and workability | operativity and applicability | paintability (printability) can be improved.
The organic dispersion medium is not particularly limited, and examples thereof include organic solvents such as glycol solvents, glycol ether solvents, glycol ester solvents, ether solvents, ester solvents, alcohol solvents, and hydrocarbon solvents. . When an epoxy resin is used as the (B), a glycol ester solvent is preferable from the viewpoint of viscosity adjustment and printability improvement.

  The content of the organic dispersion medium is not particularly limited, but when the conductive powder is 100 parts by mass, it is generally 100 parts by mass or less, and from the viewpoint of reducing environmental burden, it is preferable to keep it as small as possible. Specifically, it is 50 parts by mass or less, preferably 30 parts by mass or less, for example, 10 parts by mass or less.

  The paste disclosed here may further contain various additive components as necessary. Examples of such additive components include reaction accelerators (promoters), laser light absorbers, dispersants, thickeners, surfactants, antifoaming agents, plasticizers, stabilizers, antioxidants, pigments, and the like. Can be mentioned. As these additive components, those known to be usable for general conductive pastes can be appropriately used.

  Examples of the reaction accelerator (promoter) include alkoxides containing metal elements such as zirconium (Zr), titanium (Ti), aluminum (Al), tin (Sn), chelate (complex), and acylate. These compounds may be used individually by 1 type, and may use 2 or more types together. Of these, an organozirconium compound is preferable. As the laser light absorber, any material having an absorption band strong against the wavelength of the laser light to be used may be used. For example, when an IR fiber laser (fundamental wavelength: 1064 nm) is used, a material having an absorption wavelength in the vicinity of 1060 nm is preferable. An example is carbon powder such as carbon black. Examples of the dispersant include a polyether type polymer dispersant.

  The content ratio of the additive component is not particularly limited, but from the viewpoint of improving conductivity, when the conductive powder is 100 parts by mass, for example, 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 3 parts by mass. Or less.

<Preparation of paste>
Such a paste can be prepared by weighing the above-described materials so as to have a predetermined content (mass ratio) and stirring and mixing them uniformly. Stirring and mixing of materials can be performed using various conventionally known stirring and mixing devices such as a roll mill, a magnetic stirrer, a planetary mixer, a disper, and the like.
The suitable viscosity of the paste is not particularly limited because it varies depending on the formation thickness of the conductive film. For example, when forming a thin film electrode (for example, a thickness of 10 μm or less) suitable for laser etching, it is rotated by a Brookfield viscometer using a SC-4-14 spindle at a temperature of 25 ° C. It is good to prepare so that the viscosity measured on condition of speed 100rpm may become about 10-100 Pa * s, for example, 20-50 Pa * s in general. Thereby, a thin film-like conductive film can be stably formed.

<How to use the paste>
In one example of using the paste, first, a substrate is prepared. As the substrate, for example, a plastic substrate, an amorphous silicon substrate, a glass substrate, or the like can be considered. In particular, a substrate made of a material having low heat resistance can be preferably used.
Next, the prepared paste is applied onto the substrate so as to have a desired thickness (for example, 1 to 50 μm, preferably 10 μm or less, for example 1 to 10 μm, more preferably 7 μm or less). The application (coating) of the paste can be performed using, for example, screen printing, bar coater, slit coater, gravure coater, dip coater, spray coater or the like.
Next, the paste applied on the substrate is heated and dried. From the viewpoint of suppressing damage to the substrate and improving productivity, it is preferable to set the heating and drying temperature sufficiently lower than the heat resistant temperature of the flexible substrate, and when using a substrate with low heat resistance, It is good to set it as 200 degrees C or less, Preferably it is 180 degrees C or less, More preferably, it is 100-150 degreeC, Especially 100-130 degreeC is good. The heat drying time is typically about 1 to 60 minutes, for example, 10 to 30 minutes, considering productivity and the like. By heat drying, the thermosetting resin in the paste is cured, and a film-like conductive film is formed on the substrate.

Next, in the case of forming a thin line electrode, the conductive film is preferably subjected to laser etching. In other words, it is preferable to leave the conductive film in a desired thin line shape and irradiate other portions with laser light. The type of laser is not particularly limited, and those known to be usable for this type of application can be used as appropriate. As a suitable example, an IR laser, a fiber laser, a CO ₂ laser, an excimer laser, a YAG laser, a semiconductor laser, and the like can be given.

In a preferred embodiment, the laser type is selected so that the absorption wavelength region of the substrate does not match the fundamental wavelength of the laser beam. As a result, damage to the substrate can be minimized.
More preferably, the laser type is selected so that the wavelength of the laser light matches the absorption wavelength region of the component constituting the conductive film. As a result, the conductive film has an absorption band at the wavelength of the laser beam, and workability and productivity during laser etching can be improved. For example, the absorption wavelength region of the cured film constituting the conductive film (specifically, a cured product obtained by curing a thermosetting resin with a curing agent) is approximately 9000 to 10000 cm ⁻¹ (for example, 9300 to 9900 cm ⁻¹ ). When it is within the range, an IR laser (fundamental wavelength: 1064 nm) can be preferably used.

  The irradiation condition of the laser beam is not particularly limited. For example, the laser output may vary depending on the thickness of the conductive film. In a preferred embodiment, the power is generally set to 0.5 to 100 W from the viewpoint of appropriately removing unnecessary portions of the conductive film while avoiding damage to the substrate. For example, when an electrically conductive film having a thickness of about 1 to 10 μm is processed using an IR laser, the laser output is preferably about 1 to 10 W. The laser scanning speed is preferably about 1000 to 10000 mm / s, for example 1500 to 5000 mm / s, from the viewpoint of appropriately removing unnecessary portions of the conductive film while maintaining high productivity.

The light energy of the laser is converted into thermal energy and reaches the conductive film. As a result, the conductive film is thermally decomposed, melted and removed at the laser light irradiation site. And only the part which was not irradiated with a laser beam remains, and the electrode of a desired shape is shape | molded.
As described above, an electrode (wiring) can be formed on a substrate using a paste.

<Use of paste>
Since the paste disclosed here is excellent in laser processability, it can be preferably used to form a thin wire electrode having L / S = 80 μm / 80 μm or less, for example, L / S = 50 μm / 50 μm or less. For this reason, it can be preferably used in applications where miniaturization, weight reduction, thinning, high functionality, etc. proceed.
Moreover, the paste disclosed here can form a low-resistance electrode by low-temperature and short-time thermosetting. For example, it is possible to realize an electrode having a volume resistivity of 130 μΩcm or less, preferably 120 μΩcm or less, more preferably 100 μΩcm or less, further preferably 70 μΩcm or less, particularly 50 μΩcm or less when the heat curing conditions are 130 ° C. and 30 minutes. it can. Therefore, it can be particularly preferably used in an application where a highly conductive electrode is formed on a substrate having low heat resistance, whose performance deteriorates when exposed to a high temperature.

  One typical use of the paste disclosed herein is to form electrodes for various electronic components, and to form conductive circuits such as touch panels, liquid crystal displays, and electronic paper having a substrate with low heat resistance. Examples of the substrate having low heat resistance include plastic substrates made of resins such as polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), and polyamide, and ITO films (Indium Tin Oxide: Examples thereof include a glass substrate with an indium tin oxide film).

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

  First, the following materials to be constituent components of the thermosetting conductive paste were prepared.

≪Conductive powder≫

≪Thermosetting resin≫

≪Dispersion medium (organic solvent) ≫
・ Glycol-based << curing agent >>
・ Curing agent 1: Imidazole-based curing agent (Ajinomoto Fine Techno Co., Ltd.)
Curing agent 2: Tertiary amine curing agent (manufactured by Ajinomoto Fine Techno Co., Ltd.)
≪Reaction accelerator (cocatalyst) ≫
・ Zirconium chelate (Matsumoto Fine Chemical Co., Ltd.)
≪Laser light absorber≫
・ Carbon black (manufactured by Lion Corporation, Ketjen Black EC 600JD)
≪Dispersant≫
・ Dispersant 1: Polyether acid dispersant (manufactured by Enomoto Kasei Co., Ltd.)
-Dispersant 2: Polyether phosphate ester dispersant (manufactured by Enomoto Kasei Co., Ltd.)

[Formation of conductive film]
The prepared materials were weighed and mixed so as to have the mass ratios shown in Tables 4 and 5 to prepare a thermosetting conductive paste.
The prepared paste is applied in a square shape of □ 2 cm × 2 cm on the following four types of substrates by the screen printing method, followed by heat drying at 130 ° C. for 30 minutes or 200 ° C. for 30 minutes. It was. Thereby, the electrically conductive film (cured film) was formed.
≪Base material≫
・ PET film with ITO film (Nitto Denko Corporation)
・ PET film (Toray Industries, Inc., annealed)
・ PC film (Asahi Glass Co., Ltd.)
・ Glass substrate (Nippon Electric Glass Co., Ltd.)

[Adhesion evaluation]
With respect to the conductive film formed under the above-mentioned heating and drying conditions at 130 ° C. for 30 minutes, adhesion evaluation (cross-cut method—100 grid cross-cut test) was performed according to JIS K5400 (1990). The results are shown in the column of “Adhesiveness” in Tables 4 and 5, respectively. In this column, “◯” indicates that there was no peeling (0/100), “△” indicates that the peeling was 1 to 5 squares, and “×” indicates that the peeling was more than 5 squares. , Respectively.

(Measurement of volume resistivity)
About the formed electrically conductive film, the volume resistivity was measured by the 4 terminal method using the resistivity meter (The Mitsubishi Chemical Analytech Co., Ltd. make, type | model: Loresta GP MCP-T610). The results are shown in the “volume resistivity” column of Tables 4 and 5, respectively.

[Evaluation of laser processability]
About the electrically conductive film formed on the glass substrate on the said 130 degreeC and 30-minute heat-drying conditions, the laser was irradiated on the following conditions, and formation of a thin wire-shaped electrode was tried.
≪Laser processing conditions≫
・ Laser type: IR fiber laser (fundamental wavelength: 1064 nm)
・ Laser output: 7W
・ Scanning speed: 2500mm / s
・ Frequency: 300khz
・ Number of scans: 3 times

The thin wire electrode formed by laser processing was observed with a laser microscope (magnification 10 ×, 3 fields of view) to confirm whether or not a desired thin wire was formed. The results are shown in the column of “Laser workability” in Tables 4 and 5. In this column,
・ "◎" means that the fine lines are smooth with no irregularities, and the fine lines are not connected.
・ "○" means that there are almost no protruding protrusions on the thin lines, and the thin lines are not connected.
・ "△" indicates that protruding lines are recognized on the thin lines, but the thin lines are not connected.
・ "X" means that the protrusions on the thin lines are recognized and the thin lines are connected.
Represents each.
As an example, the observation image according to Example 4 is shown in FIG. 4A, and the observation images according to Reference Examples 1 and 2 are shown in FIGS. 4B and 4C.

As shown in Tables 4 and 5, Examples 1 to 23 include two types of conductive powders (that is, non-aggregated conductive powder having an aggregation degree of 1.5 or less and aggregated conductivity having an aggregation degree of 1.5 to 3). This is a test example in which the LD ₅₀ of the aggregated conductive powder is not higher than the LD ₅₀ of the non-aggregated conductive powder. These had good adhesion to the base material, had higher laser processability than Reference Examples 1 and 3-7, and further had a low volume resistivity compared to Reference Example 2. From these results, it is confirmed that using two types of powders with different cohesion levels can balance laser workability and low resistance (good electrical conductivity) at a high level compared to using them individually. It was done.

  Next, when Examples 1 to 8 having different mixing ratios of the non-aggregated conductive powder and the aggregated conductive powder were compared, Examples 2 to 8 were more excellent in laser processability. From this, it was found that from the viewpoint of improving the laser processing suitability, it is preferable that the non-aggregated conductive powder accounts for 30% by mass or more of the entire conductive powder. Moreover, it turned out that it is preferable that the aggregated electroconductive powder occupies 5 mass% or more of the whole electroconductive powder from a viewpoint of low resistance. Thereby, volume resistivity (130 degreeC * 30 minutes) was able to be suppressed to 100 microhm * cm or less.

  In addition, in Example 22 in which the binder content was 5 parts by mass, the adhesiveness was slightly low. From this, it was found that the content of the binder should be more than 5 parts by mass in applications where high adhesiveness is required. Further, in Example 23 in which the binder content was 30 parts by mass, the volume resistivity (130 ° C., 30 minutes) was slightly high. From this, it was found that when performing low temperature drying at about 130 ° C., the binder content should be less than 30 parts by mass. Further, in Reference Example 8 using a binder having a number average molecular weight of 50,000, not only laser processability but also electrical conductivity was greatly reduced. From this, it was found that the number average molecular weight of the binder is smaller than 50,000, for example, 10,000 or less.

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

DESCRIPTION OF SYMBOLS 10 Conductive film 12 Electrode 13 Aggregated particle 14 Non-aggregated particle 16 Resin pool 18 Laser irradiation site

Claims (10)

Including a conductive powder, a thermosetting resin, and a curing agent,
Wherein the conductive powder, the ratio of the average particle diameter based on a volume average particle diameter based on the number based on electron microscopy (SEM-D ₅₀₎ based on the laser diffraction scattering particle size distribution measuring method (L-D ₅₀₎ ( L-D ₅₀ / SEM-D ₅₀ ), the non-aggregated conductive powder and the aggregated conductive powder having different degrees of aggregation,
The non-aggregated conductive powder is
The average aspect ratio (major axis / minor axis ratio) is 2 or less,
The L-D ₅₀ is 0.5 μm or more and 7 μm or less,
The degree of aggregation is 1.5 or less,
The agglomerated conductive powder is:
The L-D ₅₀ is 0.1 μm or more and 5 μm or less,
The degree of aggregation is more than 1.5 and 3 or less, and
The thermosetting conductive paste, wherein the LD ₅₀ of the aggregated conductive powder does not exceed the LD ₅₀ of the non-aggregated conductive powder. The LD ₅₀ of the non-aggregated conductive powder is 5 μm or less.
The thermosetting conductive paste according to claim 1. The SEM-D ₅₀ of the non-aggregated conductive powder is 1.1 μm or more and 3 μm or less,
The SEM-D ₅₀ of the aggregated conductive powder is 0.1 μm or more and 1 μm or less,
The heat-curable conductive paste according to claim 1 or 2. The LD ₅₀ of the non-aggregated conductive powder is 1.5 times or more of the LD ₅₀ of the aggregated conductive powder.
The thermosetting conductive paste according to any one of claims 1 to 3. The mixing ratio of the non-aggregated conductive powder and the aggregated conductive powder is 30:70 to 95: 5.
The thermosetting conductive paste according to any one of claims 1 to 4. The non-aggregated conductive powder is composed of spherical particles having an aspect ratio of 2 or less.
The thermosetting conductive paste according to any one of claims 1 to 5. The conductive powder is silver powder and / or silver-coated copper powder,
The thermosetting conductive paste according to any one of claims 1 to 6. The number average molecular weight of the thermosetting resin is 10,000 or less,
The thermosetting conductive paste according to any one of claims 1 to 7. When the conductive powder is 100 parts by weight, the total of the thermosetting resin and the curing agent is 30 parts by weight or less.
The thermosetting conductive paste according to any one of claims 1 to 8. Used for laser etching,
The thermosetting conductive paste according to any one of claims 1 to 9.