JP6457298B2 - Conductive substrate, method for producing the same, and precursor - Google Patents

Description

  The present invention relates to a conductive base material in which a conductive film formed of silver is laminated on a polycarbonate substrate, a method for producing the same, and a precursor thereof.

  Silver has the lowest electrical resistivity at room temperature among metals and has high conductivity, so that it is widely used as a conductive film for a conductive substrate. For example, as a conductive substrate such as a printed wiring board, a conductive substrate obtained by sintering a conductive film formed of silver on a heat-resistant substrate such as a glass substrate has been widespread. On the other hand, in recent years, the use of polycarbonate, which is inexpensive and excellent in transparency and impact resistance, has been studied as a flexible substrate of a conductive base material. However, unlike inorganic materials such as glass and ceramics, polycarbonate is a resin with low heat resistance, and it is difficult to raise the sintering temperature of the conductive film. Therefore, it is difficult to form a conductive film having good adhesion to the polycarbonate substrate and having a low resistance.

  As a method for forming a conductive film having high adhesion and conductivity on a resin substrate, Japanese Patent Application Laid-Open No. 2010-80442 (Patent Document 1) discloses a method of forming silver nanoparticles on a base material formed of an organic material. And a dispersion liquid containing silver colloid particles composed of a protective colloid covering the silver nanoparticles, wherein the protective colloid is composed of an organic compound having a carboxyl group and a polymer dispersant. A method of manufacturing a conductive substrate by coating a dispersion and then heat-treating the obtained precursor to form a metal film is disclosed. In this document, an organic material containing polycarbonate is exemplified as the organic material, and among these organic materials, heat-resistant materials such as aromatic polyester resins, polyimide resins, polysulfone resins, liquid crystal polymers, and fluororesins are used. High materials are described as preferred. Further, it is described that the base material may be subjected to easy adhesion treatment. In the examples, polyethylene terephthalate having a polyester easy-adhesion layer formed on the surface is used. In addition, this document exemplifies a solvent containing diethylene glycol and cellosolves as a solvent contained in the dispersion, and among these solvents, water and water-soluble solvents (alcohols such as aliphatic polyhydric alcohols) are preferable. In the examples, ethylene glycol is used.

  However, in this method, since the adhesion of the conductive film is low, it is necessary to form an easy-adhesion layer on the base material, and productivity is lowered.

  JP 2012-18783 A (Patent Document 2) discloses silver particles having an average particle diameter of 0.5 μm or more and an average primary particle diameter of 10 as a conductive paste capable of forming conductive film wiring even when heated at a low temperature. An electrically conductive paste containing a metal component composed of silver fine particles of ˜200 nm, a binder resin such as a phenol resin or an epoxy resin, a curing agent, and a solvent is disclosed. In this document, it is preferable to use an organic solvent such as ester, ether, ketone, ether ester, alcohol, hydrocarbon, or amine as the solvent, and has a high boiling point with low volatility during printing. It is described that diols such as terpineol, butyl carbitol acetate, and octanediol are more preferable as the solvent. In the example of this document, a conductive paste containing terpineol as a solvent is drawn on a glass substrate and then heated at 200 ° C.

  However, since this conductive paste contains a binder resin, the resin component impedes contact between metal fillers that are conductive components, and the resistance increases.

JP 2010-80442 (Claim 8, paragraphs [0021] to [0023] [0083] [0084] [0087], Example) JP 2012-18783 A (claim 1, paragraph [0025], example)

  Accordingly, an object of the present invention is to provide a conductive substrate (metal composite film) on which a conductive film having high adhesion to a polycarbonate substrate and having a low resistance is formed, a method for producing the same, and a precursor thereof. .

  Another object of the present invention is to provide a method for producing the conductive substrate by a simple method without using an easy adhesion layer and a resin binder.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have combined a specific silver colloidal particle with a dispersion medium having a hydroxyl group and an ether bond as a surface modifying agent for the substrate, thereby producing a polycarbonate substrate. It was found that a conductive film having high adhesion and low resistance can be formed, and the present invention was completed.

  That is, the precursor of the conductive substrate of the present invention is a precursor of a conductive substrate including a polycarbonate substrate and a coating film laminated on the substrate, and the coating film contains silver nano-particles. Dispersion medium comprising silver colloid particles containing particles and protective colloid and a surface modifier, wherein the silver nanoparticles have a maximum primary particle size of 200 nm or less, and the surface modifier has a hydroxyl group and an ether bond It is. The surface modifier may be an aliphatic hydrocarbon having a hydroxyl group and an ether bond in the molecule, and the boiling point may be about 100 to 300 ° C. The mass ratio of the silver colloid particles and the surface modifier may be the former / the latter = about 40/60 to 95/5. The coating film may not contain a resin component. In the precursor of the present invention, an easy adhesion layer may not be interposed between the substrate and the coating film.

  The manufacturing method of the electroconductive base material including the baking process which bakes the said precursor and forms an electrically conductive film on a base material is also contained in this invention. In the firing step, the firing temperature may be about 80 to 150 ° C. Before the firing step, a drying step of pre-drying the precursor at less than 80 ° C. may be included.

  The conductive substrate obtained by the above method is also included in the present invention. The conductive substrate may have a specific resistance of the conductive film of 10 μΩ · cm or less.

  In the present invention, a specific silver colloid particle and a dispersion medium having a hydroxyl group and an ether bond as a surface modifier are combined, so that a polycarbonate substrate can be obtained by a simple method without using an easy adhesion layer and a resin binder. In contrast, a conductive film having high adhesion and low resistance can be formed.

  The precursor of the conductive substrate of the present invention is a laminate comprising a polycarbonate substrate and a coating film (conductive paste) laminated on the substrate. In the present invention, since a silver nanoparticle paste is used, which includes a dispersion medium that functions as a surface modifier of the base material (substrate), low-temperature sintering is possible, and in addition, a conductive film is formed by the surface modifier. And the adhesion between the polycarbonate substrate and the substrate are improved. In particular, when a silver nanoparticle paste is prepared without blending a resin component, the proportion of components other than silver (such as a resin component that hinders conductivity) is reduced in the conductive film, and high conductivity can be realized. In addition, it is possible to omit the process of forming an easy-adhesion layer on the substrate itself and the process of overcoating the conductive film, which makes it extremely easy to manufacture.

[Polycarbonate substrate]
The polycarbonate constituting the polycarbonate substrate (substrate) can be a conventional polycarbonate and may be either an aliphatic polycarbonate or an aromatic polycarbonate, but it is inexpensive and has excellent transparency and mechanical properties. Polycarbonates based on bis (hydroxyphenyl) C _1-6 alkanes such as bisphenol A type polycarbonates are particularly preferred.

The viscosity average molecular weight of the polycarbonate is, for example, about 1,000 to 100,000, preferably about 3,000 to 50,000, and more preferably about 6,000 to 30,000. The viscosity average molecular weight is obtained by dissolving polycarbonate in methylene chloride (concentration 6.0 g / L), measuring the specific viscosity (η _sp ) at 20 ° C. using an Ubbelohde viscosity tube, and calculating the viscosity average molecular weight (Mv) by the following formula: Can be calculated.

η _sp /C=[η](1+0.28η _sp)
[η] = 1.23 × 10 ⁻⁴ Mv ^0.83
([Η] is the intrinsic viscosity and C is the polymer concentration).

  The polycarbonate substrate is usually plate-shaped, and examples of commercially available polycarbonate substrates include Iupilon sheet (manufactured by Mitsubishi Gas Chemical Co., Ltd.), Panlite sheet (manufactured by Teijin Chemicals Ltd.), Carbograss (Asahi Glass). (Manufactured by Co., Ltd.), Lexan sheet (manufactured by Asahi Glass Co., Ltd.), Takiron polycarbonate plate (manufactured by Takiron Co., Ltd.), and the like.

  The polycarbonate substrate may have an easy-adhesion layer, but from the viewpoint of the productivity of the conductive substrate, a substrate that does not have an easy-adhesion layer (a substrate that has not been subjected to an easy-adhesion treatment) is preferred. .

  What is necessary is just to select suitably the thickness (average thickness) of a polycarbonate base material (board | substrate) according to a use, for example, 0.001-10 mm, Preferably it is 0.01-5 mm, More preferably, it is 0.05-3 mm (especially). 0.1 to 1 mm).

[Coating film (conductive paste)]
The coating film is a paste containing silver as a conductive material (conductive paste) and includes silver colloid particles and a surface modifier.

(Silver colloidal particles)
Silver colloidal particles include silver nanoparticles and protective colloids. The protective colloid affects the dispersibility of the silver nanoparticles in the paste, and the presence form (bonding state or form with the silver nanoparticles) in the paste is not particularly limited, but the surface of the silver nanoparticles is coated. May be.

(1) Silver nanoparticles Silver nanoparticles are nanometer-sized. The number average particle size (number average primary particle size) of the silver nanoparticles is 50 nm or less (for example, 1 to 50 nm), preferably 1.5 to 45 nm, more preferably 2 to 40 nm, especially about 5 to 40 nm. It may be about 10 to 40 nm (for example, about 20 to 35 nm).

  Further, the silver nanoparticles have the above average particle diameter and a wide particle size distribution in a range of 200 nm or less, but may contain almost no coarse particles exceeding 200 nm. Therefore, the maximum primary particle size of the metal nanoparticles is, for example, 200 nm or less, preferably 150 nm or less, and more preferably 100 nm or less.

  The silver nanoparticles as a whole have such a small average particle diameter of several tens of nanometers, and a characteristic that a certain amount of particles having a relatively large particle diameter of 100 to 200 nm is contained. That is, silver nanoparticles exhibit a wide particle size distribution in a range of 200 nm or less. Specifically, the volume ratio of silver nanoparticles (small particle group) having a particle diameter of less than 100 nm and silver nanoparticles (large particle group) having a particle diameter of 100 to 200 nm is small particle group / large particle group = It is about 90/10 to 30/70, preferably 70/30 to 30/70, more preferably about 60/40 to 35/65 (particularly 50/50 to 40/60). It is presumed that when the particles of 100 nm or more occupy a certain volume, the small particles are filled in the gaps between the large particles, and the characteristics of the sintered film by firing are improved.

  Further, the particle size distribution in the present invention may be a distribution close to a normal distribution with little bias, but may also be a biased distribution, for example, one or more in each of the small particle group and the large particle group. May have a peak (local maximum). In particular, the small particle group preferably has a relatively uniform distribution, and the large particle group preferably has a distribution in which the proportion of relatively large particles of 150 to 200 nm is large. For example, the volume ratio of 150 to 200 nm particles may be, for example, 10 to 60% by volume, preferably 20 to 55% by volume, and more preferably 30 to 50% by volume with respect to all particles. It is presumed that the filling efficiency is improved by uniformly presenting particles smaller than 100 nm with respect to such particles larger than 150 nm. Furthermore, the number average particle diameter of the small particle group is, for example, 5 to 50 nm, preferably 10 to 40 nm, more preferably about 15 to 35 nm, and the number average particle diameter of the large particle group is, for example, 120 to 195 nm, Preferably, it may be about 150 to 190 nm, more preferably about 160 to 190 nm.

  The silver nanoparticles having such a distribution can form a dense film even when fired at a low temperature, and can form a film having high conductivity and high hardness. In addition, when large particles increase, the surface area of the particles decreases, and the amount of dispersant adsorbed on the surface decreases, making it easier to remove organic matter derived from protective colloids from the film when firing, resulting in a thick film In addition, a low-resistance conductor can be obtained.

(2) Protective colloid The protective colloid is composed of an organic compound having a carboxyl group and a polymer dispersant.

Examples of the organic compound having a carboxyl group include the organic compounds described in JP 2010-80442 A (Patent Document 1). Among them, saturated aliphatic carboxylic acids (for example, C _1-24 alkanoic acids such as formic acid, acetic acid, propionic acid, stearic acid, alicyclic hydroxycarboxylic acids (or hydroxycarboxylic acids having an alicyclic skeleton such as chol C _6-34 alicyclic hydroxycarboxylic acids such as acids, preferably C _10-34 alicyclic hydroxycarboxylic acids, more preferably C _16-30 alicyclic hydroxycarboxylic acids). C _1-10 alkanoic acids (alkane carboxylic acids) such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid and the like have high affinity with the surface and are excellent in moderate dispersibility (cohesiveness) and sinterability. preferably, _{C 1-6} alkanoic acid (preferably _{C 1-4} alkanoic acid such as acetic acid or propionic acid, more preferably _{C 2-3} alkanoic acid, especially acetic acid Are more preferred. Particularly, the use of C _1-4 alkanoic acid such as acetic acid, or the metal colloid particles are appropriately dispersed, and aggregation, generation of cracks and voids at the time of combustion is suppressed, a dense and hard A fired film can be formed.

  Examples of the polymer dispersant include amphiphilic polymer dispersants (or oligomer type dispersants) described in Patent Document 1. Among them, poly (meth) acrylic acid [or polyacrylic acid-based resins such as poly (meth) acrylic acid, (meth) acrylic acid and copolymerizable monomers may be used as polymer dispersants having acid groups such as carboxyl groups. Polymers based on (meth) acrylic acid such as copolymers with monomers (for example, (meth) acrylate, maleic anhydride, etc.), salts thereof (for example, alkali metal salts such as sodium polyacrylate, etc.) Etc.], Dispersic 190, Dispersic 194 [manufactured by Big Chemie Japan Co., Ltd.], polymer dispersants having basic groups such as amino groups, polyalkyleneimines (polyethyleneimine, etc.), polyvinylpyrrolidone, polyallylamine , Polyether polyamines (polyoxyethylene polyamine, etc.) are widely used. Polymer dispersing agent having a Bokishiru group.

  In the polymer dispersant having an acid group (particularly a carboxyl group), the acid value is, for example, 1 mgKOH / g or more (for example, about 2 to 1500 mgKOH / g), preferably 3 mgKOH / g or more (for example, 4 to 1200 mgKOH / g). About 5 mg KOH / g (for example, about 8 to 1000 mg KOH / g), particularly 10 mg KOH / g or more (for example, about 12 to 900 mg KOH / g). In particular, when the polymer dispersant having an acid group (particularly a carboxyl group) is a compound having a hydrophilic unit and a hydrophobic unit, the acid value is, for example, 1 mgKOH / g or more (for example, 2 to 100 mgKOH / g). Degree), preferably 3 mgKOH / g or more (for example, about 4 to 90 mgKOH / g), more preferably 5 mgKOH / g or more (for example, about 6 to 80 mgKOH / g), particularly 7 mgKOH / g or more (for example, 8 to 70 mgKOH / g). g), or about 3 to 50 mgKOH / g (for example, about 5 to 30 mgKOH / g). In the polymer dispersant having an acid group, the amine value may be 0 (or almost 0).

  The number average molecular weight of the polymer dispersant can be selected from a range of about 1,000 to 1,000,000 (for example, 1200 to 900,000) in terms of polystyrene when measured by gel permeation chromatography (GPC), for example, 1500 to 800,000, preferably May be from 2,000 to 700,000, more preferably from 3,000 to 500,000 (for example, from 5,000 to 300,000), particularly from about 7,000 to 200,000.

  In the silver colloidal particles, the ratio of the protective colloid (the total amount of the organic compound having a carboxyl group and the polymer dispersant) is, for example, 0.1 to 100 parts by mass (for example, 0.1% by mass) with respect to 100 parts by mass of the silver nanoparticles. 5 to 80 parts by mass), preferably 1 to 50 parts by mass, more preferably about 2 to 40 parts by mass (particularly 3 to 30 parts by mass).

  In the silver colloid particles, the proportion of the organic compound having a carboxyl group is, for example, 0.05 to 50 parts by mass, preferably 0.1 to 40 parts by mass, more preferably 100 parts by mass of the silver nanoparticles. About 0.3-30 mass parts may be sufficient.

  In the silver colloidal particles, the ratio of the polymer dispersant is, for example, 0.01 to 50 parts by mass, preferably 0.05 to 30 parts by mass, and more preferably 0.00 to 100 parts by mass of the silver nanoparticles. About 1-20 mass parts may be sufficient.

  The ratio of the organic compound having a carboxyl group to the polymer dispersant (solid content when a solvent or the like is included) can be selected from the range of the former / the latter (mass ratio) = 99/1 to 1/99. / 3 to 1/99, preferably 95/5 to 2/98, more preferably about 92/8 to 3/97.

  In addition, the silver colloid particle should just contain the said protective colloid at least as a protective colloid, and may contain the other protective colloid. Examples of other protective colloids include organic compounds described in Patent Document 1. The proportion of the protective colloid may be, for example, 0.1 to 100 parts by mass, preferably 0.5 to 50 parts by mass, and more preferably about 1 to 30 parts by mass with respect to 100 parts by mass of the protective colloid. .

  The ratio of the protective colloid in the silver colloid particles can be measured by a conventional method, for example, thermal analysis (for example, thermal mass / differential thermal simultaneous analysis).

  The method for producing silver colloid particles is not particularly limited, and can be prepared by a conventional method, for example, by reducing a silver compound corresponding to silver nanoparticles in a solvent in the presence of a protective colloid and a reducing agent. Specific examples of the manufacturing method include the methods described in Patent Document 1 and Japanese Patent Application Laid-Open No. 2010-229544.

(Surface modifier)
The surface modifier (base surface modifier) is a compound having a hydroxyl group and an ether bond, and has a function of roughening the surface of the polycarbonate substrate to improve the adhesion of the conductive film to the substrate. Also, it has a function as a dispersion medium (solvent).

  In the surface modifier, the number of hydroxyl groups in the molecule may be 1 or more, for example, 1 to 10, preferably 1 to 5, more preferably 1 to 3 (particularly 1 to 2). The number of ether bonds in the molecule may be one or more, for example, 1 to 10, preferably 1 to 5, and more preferably 1 to 3 (particularly 1 to 2).

  The surface modifier only needs to have a hydroxyl group and an ether bond in the molecule within the above range, but is usually a hydrocarbon (ether alcohol) having a hydroxyl group and an ether bond in the molecule. The ether alcohol may be a hydrocarbon having a hydroxyl group and an unsaturated ether bond, but is preferably a hydrocarbon having a hydroxyl group and a saturated ether bond from the viewpoint of handleability.

Examples of ether alcohols (boiling point in parentheses) include polyalkylene glycols [eg, diethylene glycol (245 ° C.), triethylene glycol (179 ° C.), tetraethylene glycol (327.3 ° C.), polyethylene glycol, etc.], cellosolve [For example, methyl cellosolve (also known as ethylene glycol monomethyl ether) (124.5 ° C), ethyl cellosolve (ethylene glycol monoethyl ether) (135.1 ° C), ethylene glycol monobutyl ether (171.2 ° C), ethylene glycol C _1-4 alkyl cellosolve such as mono-t-butyl ether (also known as 2-t-butoxyethanol) (152 ° C.); propylene glycol monomethyl ether, propylene glycol monoethyl ether, pro Propylene glycol mono C _1-4 alkyl ether such as pyrene glycol monobutyl ether], carbitols [eg, methyl carbitol (also known as diethylene glycol monomethyl ether) (194 ° C.), ethyl carbitol (200 ° C.), butyl carbitol (Alternative name: 2- (2-butoxyethoxy) ethanol) (230.4 ° C.) and other C _1-4 alkyl carbitols; Dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether propylene glycol mono C _1-4 alkyl ether, etc.], triethylene glycol monoalkyl ethers [e.g., triethylene glycol monomethyl ether (249 ° C.), triethylene glycol And triethylene glycol mono C _1-4 alkyl ethers, such as mono butyl ether (271 ° C.)], a cyclic ether alcohols (e.g., hydroxy tetrahydrofuran, hydroxy dioxane) and the like. These ether alcohols can be used alone or in combination of two or more.

Among these ether alcohols, aliphatic hydrocarbons having a hydroxyl group and an ether bond in the molecule, for example, poly C _2-4 alkylene glycol such as diethylene glycol, C _1-4 alkyl cellosolv such as butyl cellosolv, butyl carbitol, etc. C _1-4 alkyl carbitol and the like are preferable. The total carbon number of these aliphatic hydrocarbons should just be 3 or more, for example, 3-12, Preferably it is 4-10, More preferably, it is about 4-8.

  The boiling point of the surface modifier (in the case of a mixture, the boiling point of each dispersion medium) is, for example, about 100 to 300 ° C, preferably about 140 to 250 ° C, and more preferably about 200 to 250 ° C. If the boiling point is too low, there is a risk that the conductive paste will be volatilized during the operation and the conductive paste will solidify. If it is too high, removal by drying and baking may be difficult.

  The mass ratio between the silver colloid particles and the surface modifier is, for example, the former / the latter = 40/60 to 95/5, preferably 50/50 to 94/6, more preferably 70/30 to 93/7 (particularly 80/20 to 90/10). If the ratio of the surface modifier is too small, the adhesion of the conductive film may be reduced, and if it is too large, the conductive film is likely to crack.

(Other ingredients)
The conductive paste may contain a conductive material (conductive filler) other than silver nanoparticles. As the conductive filler, a conventional conductive filler can be used. For example, metal particles (silver particles (silver powder) or silver flakes having a primary particle size of more than 200 nm, copper nanoparticles, silver-coated copper powder, gold nanoparticles, gold powder, etc.) ), Carbon materials (carbon black, graphite, etc.) can be used.

  Depending on the application, the conductive paste may further contain conventional additives such as colorants (dyeing pigments, etc.), hue improvers, dye fixing agents, gloss imparting agents, metal corrosion inhibitors, stabilizers (antioxidants, UV absorbers, etc.), surfactants or dispersants (anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc.), dispersion stabilizers, thickeners or viscosity modifiers , Moisturizers, thixotropic agents, leveling agents, antifoaming agents, bactericides, fillers, and the like. These additives can be used alone or in combination of two or more.

  In order to improve the adhesion, the conductive paste may contain a resin component such as a binder resin. However, in the present invention, the coating film containing silver colloid particles and the surface modifier is an adhesion of the conductive film. Therefore, even when the binder resin is not included, a tightly adhered conductive film can be formed. Therefore, it is preferable that a resin component such as a binder resin is not substantially contained from the viewpoint that the conductivity can be improved.

  The conductive paste is not particularly limited as long as the paste having the above configuration can be obtained. Usually, the silver colloidal particles can be obtained by dispersing the silver colloid particles in the surface modifier (dispersion medium) by a conventional method. .

  Although an easy adhesion layer may be formed between the polycarbonate substrate and the coating film, as described above, in the present invention, a strong conductive film can be formed without interposing the easy adhesion layer. Therefore, from the viewpoint of productivity, a laminate having no easy-adhesion layer interposed is preferable.

[Precursor of conductive substrate and method for producing conductive substrate]
The precursor (laminated body) of the conductive base material of the present invention can be produced by forming a coating film on the polycarbonate base material using the conductive paste.

  Methods for forming a coating film using a conductive paste include conventional coating methods such as flow coating method, dispenser coating method, spin coating method, spray coating method, screen printing method, flexographic printing method, casting method, bar A coating method, a curtain coating method, a roll coating method, a gravure coating method, a dipping method, a slit method, a photolithography method, an ink jet method and the like can be used. In the coating method, a pattern may be formed (drawn) with a coating film, and a sintered pattern (sintered film, metal film, sintered body layer, conductor layer) is formed by firing the formed pattern (drawn pattern). ) Can be formed. The drawing method (or printing method) for drawing the pattern (coating layer) is not particularly limited as long as it is a pattern forming printing method. For example, a screen printing method, an ink jet printing method, an intaglio printing method (for example, Gravure printing method), offset printing method, intaglio offset printing method, flexographic printing method and the like.

  The obtained laminate is a precursor of a conductive substrate, and is subjected to a firing step in which the coating film is heated (or baked or heat-treated) at a predetermined temperature. In addition, you may use for a preliminary | backup drying process before a baking process as needed.

  In the preliminary drying step, natural drying may be performed, but heating and drying may be performed. In the preliminary drying step, the film is dried at a temperature corresponding to the type of the solvent, and is dried at, for example, less than 80 ° C. (eg, 10 ° C. or more and less than 80 ° C.), preferably 20 to 60 ° C., more preferably 30 to 50 ° C. Also good. Preliminary drying may be performed as long as the surface of the coating film is dried, and the drying method and time are not particularly limited. May be. By this preliminary drying, cracking of the conductive film after the baking treatment can be suppressed.

  In the present invention, even at a relatively low temperature, the surface of the polycarbonate substrate is roughened by the surface modifier, and the silver nanoparticles are fused to form a continuous film. Even a substrate made of polycarbonate can be fired. A calcination temperature is about 80-150 degreeC, for example, Preferably it is 90-140 degreeC, More preferably, it is about 100-130 degreeC (especially 110-120 degreeC) grade. As the firing temperature is higher, the sintering of the silver nanoparticles proceeds and the conductivity is improved. However, if the firing temperature is too high, the polycarbonate substrate may be deteriorated or deformed. The firing time (heating time) may be, for example, 30 minutes or more, preferably 30 minutes to 3 hours, more preferably 45 minutes to 2 hours (for example, about 1 hour).

  The firing may be performed in air or in an atmosphere of an inert gas (for example, nitrogen gas, argon gas, helium gas, etc.).

  The thickness of the obtained fired film or conductive film (coating after sintering, sintered pattern) can be appropriately selected from the range of about 0.01 to 10000 μm depending on the application, for example, 0.1 to 50 μm, preferably May be about 0.3 to 30 μm, more preferably about 0.5 to 10 μm.

  The obtained conductive film may have high conductivity and a specific resistance of 100 μΩ · cm or less, for example, 50 μΩ · cm or less (for example, 0.1 to 50 μΩ · cm), preferably 30 μΩ · cm or less ( For example, it may be about 0.5 to 30 μΩ · cm, more preferably about 20 μΩ · cm or less (for example, 1 to 20 μΩ · cm). In particular, when no binder resin is used, the conductivity can be improved, and the specific resistance is, for example, 15 μΩ · cm or less (for example, 1 to 15 μΩ · cm), preferably 10 μΩ · cm or less (for example, 5 to 10 μΩ · cm). ).

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, the measurement methods for the physical properties of the conductive film and the materials used in the examples are shown below.

[Break of conductive film]
The crack of the conductive film was evaluated by visually observing the presence or absence of the crack.

[Specific resistance of conductive film]
The specific resistance was calculated from the surface resistance and film thickness obtained by the four probe method. About the electrically conductive film obtained by the Example and the comparative example, 10 samples were measured, respectively, and the average value was calculated | required.

[Adhesiveness of conductive film]
The adhesion of the conductive film was classified and evaluated according to the following criteria described in the crosscut method according to the test method described in JIS K5600-5-6 crosscut method.

Category 0: The edges of the cut are completely smooth and there is no peeling to the eyes of any grid. Category 1: Small peeling of the coating film at the intersection of the cuts. It is clearly not more than 5% that is affected by the crosscut part. Category 2: The coating is peeled along the edge of the cut and / or at the intersection. The cross-cut part is clearly affected more than 5% but not more than 15%. Classification 3: The coating is partially or totally peeled along the edge of the cut, and / Or various parts of the eye are partially or totally peeled off. The cross-cut part is clearly affected by more than 15% but not more than 35%. Category 4: The coating is partially or totally peeled along the edge of the cut, And / or some of the eyes are partially or completely peeled off. The cross-cut part is clearly not affected by more than 35%. Category 5: Either the degree of peeling that cannot be classified even in Category 4.

[Example 1]
(Synthesis of silver colloidal particle aggregates)
66.8 g of silver nitrate, 10 g of acetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as an agglomeration aid (B1) having a carboxyl group, and a polymer dispersant having a carboxyl group as a polymer dispersant (manufactured by Big Chemie Japan Ltd.) , "Dispervic 190", an amphiphilic dispersant having a polyethylene oxide chain which is a hydrophilic unit and an alkyl group which is a hydrophobic unit, solvent: water, nonvolatile component 40%, acid value 10 mgKOH / g, amine value 0 ) 2.0 g was put into 100 g of ion-exchanged water and stirred vigorously. When 100 g of 2-dimethylaminoethanol (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added thereto, the reaction solution rose to 60 ° C. When the liquid temperature dropped to 50 ° C., the mixture was heated and stirred in a water bath set at 70 ° C. for 2 hours. After 1 hour, silver colloidal particle aggregates were obtained as gray precipitates. The supernatant of the reaction solution in which the silver colloid aggregates were precipitated was removed and diluted with ion-exchanged water. After standing, the supernatant was removed and further diluted with methanol. After standing again, the supernatant was removed and diluted with methanol. Thereafter, the silver colloidal particle aggregates were collected with a pressure filter equipped with a membrane filter (manufactured by Advantech, pore size 0.5 μm).

(Analysis of silver colloidal particle aggregates)
When the number average particle diameter of the obtained silver nanoparticles was calculated by the method described in Example 1 of JP 2010-229544 A, it was 33 nm, and particles less than 100 nm were 65.3 in the total volume of the particles. Volume%, particles of 100-200 nm were 34.7% by volume.

(Sintering of silver colloidal particle aggregates)
To the silver colloidal particle aggregate obtained by synthesis, 10 g of 2- (2-butoxyethoxy) ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) as a dispersion medium (surface modifier) is added and stirred. A silver nanoparticle paste dispersed in (2-butoxyethoxy) ethanol was prepared. This paste was spin-coated on a polycarbonate sheet (Takiron Co., Ltd., size 2 cm × 2 cm × thickness 0.5 mm) at 7000 rpm for 10 seconds, pre-dried on a hot plate at 40 ° C., and then baked at 120 ° C. for 60 minutes. Thus, a conductive substrate having a conductive film with a thickness of 7 μm was obtained.

[Example 2]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to diethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.).

[Comparative Example 1]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to 2- (2-butoxyethoxy) ethyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.). .

[Comparative Example 2]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to 1-decanol (manufactured by Wako Pure Chemical Industries, Ltd.).

[Comparative Example 3]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to 1,5-pentanediol (manufactured by Wako Pure Chemical Industries, Ltd.).

[Comparative Example 4]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to N-methylpyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.).

[Comparative Example 5]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to ethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.).

[Comparative Example 6]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to p-isopropylbenzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd.).

[Comparative Example 7]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to N, N-dimethylpropylamide (manufactured by Tokyo Chemical Industry Co., Ltd.).

[Comparative Example 8]
A conductive substrate was obtained in the same manner as in Example 1 except that 2- (2-butoxyethoxy) ethanol was changed to isophorone (manufactured by Tokyo Chemical Industry Co., Ltd.).

  Table 1 shows the evaluation results of the conductive substrates obtained in Examples and Comparative Examples.

  The conductive base materials obtained in the examples had high conductivity, were not cracked, and had high adhesion. On the other hand, cracks occurred in the conductive substrates obtained in Comparative Examples 1, 2, 4, and 7. Moreover, in the electroconductive base materials of Comparative Examples 3, 5, 6 and 8, although no crack was generated, the adhesion was low.

  The conductive substrate of the present invention and its precursor are various conductors such as liquid crystal display (LCD), organic electroluminescence display (ELD), fluorescent display tube (VFD), plasma display panel (PDP) display, etc. It can be used as an electrode for a device, a touch panel display device, an RFID tag, an electromagnetic wave shield, a conductive film used for home or a learning wiring kit, a conductive bonding agent, and the like.

Claims (4)

A conductive base material precursor comprising a polycarbonate base material and a coating film laminated on the base material, wherein the coating film comprises silver colloidal particles containing silver nanoparticles and protective colloid and a dispersion medium. The silver nanoparticles have a maximum primary particle size of 200 nm or less, the protective colloid contains a polymer dispersant, and the surface modifier has a boiling point of 140 to 250 ° C. and and a hydroxyl group and a precursor of the electroconductive substrate ing from a compound having an ether bond.   The precursor according to claim 1, wherein the surface modifier is an aliphatic hydrocarbon having a hydroxyl group and an ether bond in the molecule. The precursor according to claim 1 or 2 , wherein the mass ratio of the silver colloid particles and the surface modifier is the former / the latter = 40/60 to 95/5. The precursor according to any one of claims 1 to 3 , wherein the coating film does not contain a resin component.