JP4919595B2 - Silver fine particle colloidal dispersion, silver film-forming coating liquid and method for producing the same, and silver film - Google Patents

Description

  The present invention relates to a silver fine particle colloid dispersion used for the production of a silver film forming coating solution for forming a silver conductive film on a substrate, particularly a silver fine particle colloid dispersion having a large particle size, and the silver fine particle colloid. The present invention relates to a silver film-forming coating liquid produced using a dispersion, a method for producing the same, and a silver film obtained using the silver film-forming coating liquid.

  Conventionally, a colloidal dispersion liquid in which noble metal fine particles containing silver are dispersed in a solvent is used as a coating liquid for forming a transparent conductive layer used for preventing leakage electromagnetic waves in computer displays (Japanese Patent Laid-Open Nos. 11-329071 and 2000-268639). ), An antibacterial coating-forming coating solution (Japanese Patent Laid-Open No. 4-321628), and the like. For example, in the former application, a transparent conductive film forming coating solution is applied to the front glass (front plate) of a cathode ray tube (CRT) by a spin coat method or the like, dried and then baked at a temperature of about 200 ° C. Forming a layer.

  Also proposed is a method in which a silver conductive layer is obtained by printing a high-concentration silver fine particle colloidal dispersion (paste) using screen printing or the like and firing at a temperature of about 200 ° C. (Japanese Patent Laid-Open No. 2002-334618). Issue gazette). However, the silver fine particle colloidal dispersion used in this application was manufactured using a gas evaporation method in which silver was evaporated and condensed in a gas under reduced pressure and recovered in a solvent containing a dispersant. Further, the productivity was poor, and therefore the resulting silver fine particle colloidal dispersion was very expensive. In addition, in the case of this silver fine particle colloid dispersion liquid, in order to enhance the dispersion stability, a dispersing agent that strongly binds to the surface of the silver fine particles is included, so that it is heated at about 200 ° C. after coating (printing) and drying. It was necessary to perform treatment to decompose and remove the dispersant, which was not preferable.

  On the other hand, the Carey-Lea method [Am. J. Sci., 37, 38, 47 (1889)] is a method for more easily producing a silver fine particle colloidal dispersion containing no dispersant. In the Carey-Lea method, an aqueous solution of iron nitrate (II) and an aqueous solution of sodium citrate are mixed and reacted with an aqueous solution of silver nitrate, and the resulting silver fine particle aggregate is filtered and washed, and then pure water is added to the cake. Is added to obtain a silver fine particle colloid dispersion (Ag: 0.1 to 10% by weight) having a relatively high concentration. The present inventors have already proposed in PCT / JP2004 / 006053 one method for obtaining a coating solution for forming a silver film using this silver fine particle colloidal dispersion.

  Silver fine particles obtained by the Carey-Lea method are fine nanocolloid particles having a particle diameter of 2 to 15 nm. In addition, in the actual production process, in the case of the batch type that is generally performed, when the other raw material aqueous solution is added all at once to a container containing one raw material aqueous solution, the mixed state of the liquid tends to be uneven, and the generated silver fine particles Since it is difficult to control the particle size, coarse particles are likely to be generated in part. For example, coarse particles having a particle size of about 30 nm may be mixed with normal silver fine particles having a particle size of about 5 to 15 nm, particularly when the amount of treatment liquid is large.

  Therefore, in order to achieve uniform mixing and reaction of raw material aqueous solutions in the manufacturing process and to efficiently obtain a colloidal dispersion of silver fine particles with a narrow particle size distribution, recently, the mixing and reaction state of the aqueous raw material solution using a static mixer etc. A method of continuously generating silver fine particles while maintaining a constant value (Japanese Patent Laid-Open No. 2004-18891) and a method of discharging raw material aqueous solutions from separate nozzles and mixing them (Japanese Patent Laid-Open No. 2004-68072) are also proposed. Has been.

  According to these methods, it is possible to obtain a colloidal dispersion of silver fine particles having a narrow particle size distribution, for example, in the range of 2 to 7 nm for a small particle size or in the range of 10 to 15 nm for a large particle size. is there. However, in the conventional methods using the Carey-Lea method, even if the reaction conditions were changed, it was not possible to obtain a silver fine particle colloidal dispersion containing uniform silver fine particles having an average particle size exceeding 20 nm. .

  As described above, the conventional method using the Carey-Lea method cannot obtain a silver fine particle colloidal dispersion containing uniform silver fine particles having an average particle diameter exceeding 20 nm. Similarly, in the above-described coating solution for forming a silver film obtained from No. 1, a liquid containing uniform silver fine particles having an average particle diameter exceeding 20 nm was not obtained.

  Recently, when a silver conductive film is formed, it is desired to increase the film thickness to reduce the resistance. However, when the conventional coating liquid for forming a silver film composed of silver fine particles having a small average particle diameter is used, when the film thickness is increased to, for example, several μm, cracks occur during film firing, There was a problem that the electrical conductivity and adhesion of the material deteriorated significantly.

  In order to overcome this problem, it is necessary to suppress shrinkage during film firing. Specifically, it is necessary to make the average particle size of silver fine particles at least about 20 nm or more. However, with the conventional Carey-Lea method, it was difficult to obtain a silver fine particle colloidal dispersion having an average particle size exceeding 20 nm as described above. Therefore, it is also difficult to obtain a coating solution for forming a silver film, in which silver fine particles having an average particle diameter exceeding 20 nm are dispersed, at a low cost and with a simple method.

Japanese Patent Laid-Open No. 11-329071 JP 2000-268639 A Japanese Patent Laid-Open No. 4-321628 JP 2002-334618 A JP 2004-18891 A JP 2004-68072 A Am. J. Sci., 37 (1889) Am. J. Sci., 38 (1889) Am. J. Sci., 47 (1889)

  The present invention has been made in view of such conventional circumstances, and has an average particle size larger than that of the conventional silver fine particle colloid dispersion by the Carey-Lea method, is extremely inexpensive, and has excellent dispersion stability. Provided are a silver fine particle colloid dispersion, a silver film-forming coating solution produced using the silver fine particle colloid dispersion, a method for producing the same, and a silver film formed using the silver film-forming coating solution. For the purpose.

In order to achieve the above object, a method for producing a colloidal dispersion of silver fine particles provided by the present invention, wherein the invention according to claim 1 includes a silver nitrate aqueous solution in a mixed solution of an iron (II) sulfate aqueous solution and a sodium citrate aqueous solution. To produce aggregates of silver fine particles having a particle diameter of 2 to 15 nm protected with citrate ions in a reaction solution containing iron ions and sodium ions, and the resulting citrate ions protect the aggregates. the reaction was left at a temperature still 40 to 100 ° C. in a state where silver particles are aggregated with containing aggregates of fine silver particles having an average particle diameter grain growth granulated with 20~200nm and citrate ion A ripening step for obtaining an aggregate of protected silver fine particles, a filtration step for obtaining a cake of silver fine particle agglomerates by filtering the silver fine particle agglomerates and growing into granules and protected with citrate ions, Ke Characterized in that it comprises a dispersion step of obtaining a colloidal dispersion of fine silver particles protected with grain growth and citrate ions granulated by adding pure water to key.

A method for producing a coating solution for forming a silver film provided by the present invention, wherein the invention according to claim 2 is a colloid of silver fine particles formed by the reaction step, the aging step, the filtration step and the dispersion step according to claim 1. A concentration and washing step for producing a dispersion liquid, concentrating and washing the obtained colloidal dispersion of silver fine particles to obtain a silver fine particle colloid concentrated washing dispersion liquid, and a solvent for adding an organic solvent to the silver fine particle colloid concentrated washing dispersion liquid And a blending step.

A method for producing a coating solution for forming a silver film provided by the present invention, wherein the invention according to claim 3 is the method for producing a coating solution for forming a silver film according to claim 2 , wherein the organic solvent is at least dimethyl sulfoxide. It is characterized by including. The invention according to claim 4 is the method for producing a coating solution for forming a silver film according to claim 2 or 3 above, wherein the electricity of the solvent part is obtained by removing silver fine particles from the silver fine particle colloid concentrated washing dispersion liquid in the concentration and washing step. The conductivity is 500 μS / cm or less.

Further, the present invention provides a method for producing a coating solution for forming a silver film, wherein the invention according to claim 5 is the method for producing a coating solution for forming a silver film according to any one of claims 2 to 4 , The silver fine particle concentration in the coating solution for forming a silver film is 10 to 70% by weight . The invention according to claim 6 is the method for producing a coating solution for forming a silver film according to any one of claims 2 to 5 , wherein the average particle size of silver fine particles in the coating solution for forming a silver film is 20 to 20%. It is characterized by 200 nm .

  According to the present invention, by a simple method using the Carey-Lea method, the average particle size of silver fine particles is as large as 20 to 200 nm and the particle size distribution is small compared with conventional silver fine particle colloidal dispersions. A silver fine particle colloid dispersion having excellent properties and a silver film forming coating solution produced using the silver fine particle colloid dispersion can be provided at low cost.

  In addition, since the silver fine particles in the silver film forming coating liquid of the present invention have a large average particle diameter of 20 to 200 nm, the film that can be formed by a coating method using the silver film forming coating liquid. Since the thickness range is widened and the film resistance value and the like can be controlled by the film thickness, the firing temperature, and the like, the silver conductive film can be used in a wide range of applications. For example, the silver conductive film obtained by applying and printing using bar coating, screen printing, etc., and firing can suppress the shrinkage during film firing and prevent the occurrence of cracks. Can be achieved.

  In the method of the present invention, first, in the reaction step, aggregates of silver fine particles having a small particle diameter are compared using a well-known Carey-Lea method [Am. J. Sci., 37, 38, 47 (1889)]. A reaction solution containing a high concentration is obtained. That is, a silver nitrate aqueous solution is mixed with a mixed solution of an iron (II) sulfate aqueous solution and a sodium citrate aqueous solution to form silver fine particles. The formation reaction of the silver fine particles is represented by the following chemical formula 1.

[Chemical 1]
Ag ⁺ + Fe ²⁺ → Ag + Fe ³⁺

  A series of reactions including the above chemical formula 1 occurs within 1 to 2 seconds after mixing the raw material aqueous solutions. In addition, the produced silver fine particles are protected by the coexisting citrate ions, and at the same time, rapidly aggregate due to high concentrations of iron ions, sodium ions, etc., so the aggregates of silver fine particles protected with citrate ions It is formed. In addition, the particle size of the silver fine particles produced | generated at this time is about 2-15 nm usual.

  In addition, as a method of mixing a silver nitrate aqueous solution into a mixed solution of an iron (II) sulfate aqueous solution and a sodium citrate aqueous solution, a batch method or a continuous method may be used. For example, using a static mixer (mixing device having no mechanically movable part) or the like, it is possible to continuously generate silver fine particles while keeping the mixing / reaction state constant.

  Next, in the ripening step, the reaction solution containing the silver fine particle aggregate obtained in the reaction step is allowed to stand. By this standing and aging, aggregates of silver fine particles grown in a granular form are obtained, and the average particle diameter of the silver fine particles when finally obtained as a silver fine particle colloidal dispersion can be set to 20 nm or more. An average particle diameter exceeding 200 nm is not preferable because silver fine particles cause sedimentation. In this ripening step, it is preferable to leave the reaction solution as it is, but for example, the reaction solution produced continuously may be left in the container.

  As the leaving condition of the reaction solution containing the silver fine particle aggregate, that is, the aging (grain growth) condition of the silver fine particles, the leaving temperature is preferably 0 to 100 ° C, and more preferably 40 to 100 ° C. The standing time depends on the standing temperature, and ranges from several minutes to several months, preferably several tens of minutes to several days. The final average particle diameter of the silver fine particles is determined by setting the standing temperature and the standing time. The higher the standing temperature or the longer the standing time, the larger the average particle diameter of the silver fine particles. In particular, when the standing temperature is set to 40 to 100 ° C., silver fine particles having an average particle diameter of more than 30 nm can be obtained in a standing time within 24 hours, which is particularly preferable in terms of production efficiency. The particle size of the silver fine particles can also be controlled by changing the amount of ions in the reaction solution by removing the supernatant or adding citrate.

  The reason why silver fine particles grow by leaving the reaction solution containing the above-mentioned silver fine particle aggregates is not clear, but it seems that excessive ions such as citric acid coexist in the reaction solution. For example, a silver fine particle colloidal dispersion obtained by filtering the above reaction solution before ripening to obtain a silver fine particle aggregate cake and then re-dispersing the silver fine particles in pure water by adding pure water is allowed to stand and ripen. Even if it carries out, the silver fine particle which carried out the grain growth uniformly cannot be obtained. In this case, when specific silver fine particles begin to grow, only the silver fine particles grow, and other silver fine particles gradually decrease (Ostwald growth). When mixed with silver fine particles, coarse silver fine particles having a hexagonal or triangular plate shape are generated, and silver fine particles cannot be grown uniformly.

  Aggregates of silver fine particles that have grown in the ripening step are filtered in a subsequent filtration step to obtain a cake of silver fine particle aggregates. Conventional methods such as membrane filter filtration, centrifugation, and filter press can be used for filtration of the silver fine particle aggregates. In this filtration step, it is also possible to wash the cake with a small amount of pure water that does not wash out silver particles.

  Thereafter, in the dispersing step, pure water is added to the silver fine particle aggregate cake to obtain a silver fine particle colloidal dispersion. When pure water is added to the silver fine particle agglomerated cake, the concentration of iron ions and sodium in the liquid is greatly reduced, eliminating the cause of aggregation, and silver fine particles protected with citrate ions are redispersed in the liquid. Thus, a colloidal dispersion of silver fine particles is obtained. Such a colloid production method is generally called a washing-out method.

  The silver fine particle colloidal dispersion obtained by the production method of the present invention described above has a larger average particle size of silver fine particles than the conventional one, preferably 20 to 200 nm, more preferably more than 30 nm and 200 nm or less. In addition, it can be produced at a low cost by a simple method, has few impurities such as a dispersant, and is excellent in dispersion stability. The particle size in the present invention is the particle size of silver fine particles observed with a transmission electron microscope (TEM).

  Next, a method for producing the silver film-forming coating solution of the present invention using the above-mentioned silver fine particle colloidal dispersion will be described. First, the silver fine particle colloid dispersion liquid (silver fine particle concentration: 0.1 to 10% by weight) is concentrated and washed in the concentration / washing step so that silver fine particles are dispersed in a high concentration in a solvent of water. A colloid concentrated washing dispersion is obtained. The concentration treatment of the silver fine particle colloidal dispersion can be performed by a common method such as a vacuum evaporator or ultrafiltration. The washing treatment can be performed using methods such as dialysis, electrodialysis, ion exchange, and ultrafiltration. Among them, the ultrafiltration method can perform concentration treatment and washing treatment at the same time. Is the preferred method.

  In the resulting silver fine particle colloid concentrated cleaning dispersion, the electrolyte concentration in the solvent is reduced by the cleaning treatment, so that the dispersion stability of the silver fine particles is improved. This improvement in dispersion stability is because colloids generally aggregate in the electrolyte when the electrolyte concentration is high, but aggregation is hindered when the electrolyte concentration is low. In order to increase the dispersion stability of the silver fine particles to a practical level, the electric conductivity of the solvent portion from which the silver fine particles are removed from the silver fine particle colloid concentrated washing dispersion liquid in the concentration and washing step is preferably 500 μS (Siemens) / cm or less, preferably It is preferable to reduce the electrolyte concentration until it becomes 200 μS / cm or less.

  The silver fine particle colloid concentrated cleaning dispersion liquid can be printed and applied as it is, but since the solvent is aqueous, depending on the type of base material such as plastic, coating defects such as repelling may occur in the film forming process. is there. Therefore, in the next solvent blending step, an organic solvent is added to the silver fine particle colloid concentrated cleaning dispersion liquid to obtain the coating solution for forming a silver film of the present invention. The applicability of this silver film forming coating solution is greatly improved by the addition of an organic solvent.

  Incidentally, the dispersion stability of the silver fine particles is improved by the decrease in the electrolyte concentration as well in the silver film-forming coating solution containing an organic solvent. Therefore, in the solvent blending step of adding an organic solvent to the silver fine particle colloid concentrated cleaning dispersion liquid to obtain a silver fine particle colloid dispersion concentrated liquid, for example, a washing step such as adding an ion exchange resin is added to lower the electrolyte concentration. It can also be made.

  As the organic solvent, an organic solvent containing at least dimethyl sulfoxide is preferably used. This is because dimethyl sulfoxide (DMSO) acts on the silver fine particles and has an effect of improving the stability of the silver fine particles in the coating solution for forming a silver film. The blending amount of dimethyl sulfoxide is preferably in the range of 0.5 to 300 parts by weight and more preferably in the range of 2 to 50 parts by weight with respect to 100 parts by weight of the silver fine particles. When the amount of the dimethyl sulfoxide is less than 0.5 parts by weight, the effect of adding dimethyl sulfoxide is not observed, and when the amount exceeds 300 parts by weight, no further improvement in the stability of the silver fine particles is observed. It only increases the drying time after application.

  An organic solvent other than dimethyl sulfoxide can be appropriately selected in consideration of compatibility with the above-described silver fine particle colloid concentrated cleaning dispersion, solubility in a substrate, film forming conditions, and the like. For example, alcohol solvents such as methanol (MA), ethanol (EA), 1-propanol (NPA), isopropanol (IPA), butanol, pentanol, benzyl alcohol, diacetone alcohol (DAA), acetone, methyl ethyl ketone (MEK) Ketone solvents such as methyl propyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, isophorone, ethylene glycol monomethyl ether (MCS), ethylene glycol monoethyl ether (ECS), ethylene glycol isopropyl ether (IPC), propylene glycol methyl ether (PGM), propylene glycol ethyl ether (PE), propylene glycol methyl ether acetate (PGM-AC), propylene glycol ether Ether ether (PE-AC), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene Glycol derivatives such as glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, formamide (FA), N-methylformamide, dimethylformamide (DMF), dimethylacetamide N- methyl-2-pyrrolidone (NMP), ethylene glycol, diethylene glycol, toluene, xylene, tetrahydrofuran (THF), chloroform, mesitylene, but as benzene derivatives such as dodecyl benzene, but is not limited thereto.

  The silver film forming coating solution obtained by the concentration / washing step and the solvent blending step preferably has a concentration of silver fine particles in the range of 10 to 70% by weight, and more preferably in the range of 15 to 60% by weight. If the concentration of silver fine particles is less than 10% by weight, it is difficult to obtain a film having a sufficient thickness by one printing, but if it is 10% by weight or more, a film having a sufficient thickness can be formed. By setting the content to 15% by weight or more, an excellent low-resistance silver conductive film can be stably formed by a printing method. Conversely, if the concentration of the silver fine particles exceeds 70% by weight, the dispersion stability of the silver fine particles in the coating solution for forming a silver film deteriorates and is likely to aggregate, which is not preferable.

  The coating solution for forming a silver film of the present invention thus obtained contains silver fine particles having an average particle diameter of 20 nm or more dispersed in water and an organic solvent, and the silver fine particles are contained at a high concentration that can be applied to a printing method. Therefore, the impurity content is low and the dispersion stability is excellent. In addition, this silver film-forming coating solution is not only excellent in dispersion stability, but even when the film thickness is increased, shrinkage during film baking is suppressed, and the occurrence of cracks can be prevented. Therefore, for example, a silver film having a thickness of several μm and excellent conductivity can be formed.

  The average particle diameter of the silver fine particles in the coating solution for forming a silver film is preferably in the range of 20 to 200 nm, more preferably more than 30 nm and 200 nm or less. If the average particle diameter of the silver fine particles in the coating solution for forming a silver film is less than 20 nm, the occurrence of cracks cannot be suppressed with a silver film having a thickness of several μm or more. On the other hand, when the average particle diameter exceeds 200 nm, the silver fine particles are likely to settle in the silver film forming coating solution, and further, the silver fine particles are baked in the heat treatment after printing and drying the silver film forming coating solution. Since it becomes difficult to proceed, it is difficult to obtain a conductive film having a low resistance. Moreover, the silver fine particles in the coating solution for forming a silver film are excellent in uniformity. For example, it is preferable that silver fine particles having an average particle diameter of ± 20 nm occupy 90% or more of the whole.

  The silver film can be easily formed by a coating method using the silver film forming coating solution. That is, after coating the coating solution for forming a silver film on the substrate, it is usually heat-treated at a temperature of several hundreds of degrees Celsius of 60 to 250 ° C. or more to dry the coating solution and sinter the silver fine particles. Thus, a silver film can be formed. The coating liquid for forming a silver film of the present invention can obtain a silver conductive film having a low resistance even by a heat treatment at about 60 ° C. unless an additive component such as a binder is added. Since it may be determined in consideration of the heat resistance, there is no particular limitation.

  What is necessary is just to select the base material which apply | coats the coating liquid for silver film formation suitably according to a use. For example, a film or plate made of plastic such as acrylic (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyimide (PI), or glass plate Can be used. Examples of methods for printing and applying the silver film forming coating solution on the substrate include screen printing, gravure printing, ink jet printing, wire bar coating method, doctor blade coating method, roll coating method, spin coating method, etc. The various methods are applicable.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples. Further, “%” in the text indicates “% by weight”, and “part” indicates “part by weight”.

[Example 1]
To a mixture of 208 g of an aqueous solution of 23.1% iron sulfate (FeSO ₄ · 7H ₂ O) and 256 g of an aqueous solution of 37.5% sodium citrate (C ₃ H ₄ (OH) (COONa) ₃ · 2H ₂ O), 9. 176 g of 1% silver nitrate (AgNO ₃ ) aqueous solution was mixed and reacted to obtain a reaction solution containing silver fine particle aggregates. The liquid temperature of the iron sulfate aqueous solution and sodium citrate aqueous solution and the silver nitrate aqueous solution were set to 20 ° C. and 10 ° C., respectively.

  The obtained reaction solution was left in a container and left in a refrigerator at 5 ° C. for 6 months. Silver fine particle aggregates were filtered from the reaction solution that had undergone the ripening step with a centrifugal separator to obtain a cake of silver fine particle aggregates. Pure water was added to the cake and washed out to obtain 1050 g of a silver fine particle colloid dispersion (Ag: 0.94%).

  The silver fine particles in the obtained silver fine particle colloidal dispersion had an average particle size of 60 nm and a uniform particle size distribution in which the granular silver fine particles having a particle size of 40 to 80 nm account for 90% or more of the total. . The particle size of the silver fine particles was measured by observing the silver fine particle colloid dispersion with a transmission electron microscope (TEM).

[Example 2]
In the same manner as in Example 1, a reaction solution containing silver fine particle aggregates was obtained. The obtained reaction liquid was left in a container in a 65 ° C. incubator for 16 hours. The silver fine particle aggregate is filtered from the reaction solution that has undergone the ripening step with a centrifuge, and the resulting silver fine particle aggregate cake is washed out by adding pure water to a silver fine particle colloidal dispersion (Ag: 0.96). %) 1050 g was obtained.

  The silver fine particles in the obtained silver fine particle colloidal dispersion had an average particle size of 50 nm, and a uniform particle size distribution in which granular silver fine particles having a particle size of 35 to 65 nm accounted for 90% or more of the total. .

[Example 3]
By concentrating and washing the silver fine particle colloid dispersion (Ag: 0.96%) obtained in Example 2 above by ultrafiltration, the silver fine particle colloid concentrated washing dispersion (Ag: 65%, balance: water) ) The electric conductivity of water as a solvent in the silver fine particle colloid concentrated cleaning dispersion was 200 μS / cm as a value obtained by measuring the filtrate of ultrafiltration.

Dimethyl sulfoxide (DMSO), 1-butanol (NBA), diacetone alcohol (DAA), and ethanol (EA) are added as an organic solvent to the silver fine particle colloid concentrated cleaning dispersion, and a silver film forming coating solution (Ag: 40%, DMSO: 2.5%, H ₂ O: 21.5%, EA: 21.0%, NBA: 5%, DAA: 10%). The silver fine particles in the obtained coating solution for forming a silver film have an average particle size of 50 nm and a uniform particle size distribution in which the granular silver fine particles having a particle size of 35 to 65 nm account for 90% or more of the whole. It was. The viscosity of the silver film forming coating solution was 5 mPa · s.

  Next, the above-mentioned coating solution for forming a silver film is applied to a PET film (Teijin Limited, Tetron HLEW, thickness: 100 μm, primer-treated product) as a base material with a wire bar having a wire diameter of 1.0 mm. After that, a silver conductive film was obtained by performing a heat treatment at 70 ° C. for 3 minutes to 130 ° C. for 60 minutes in the air.

The obtained silver conductive film had a film thickness of 3.0 μm and a surface resistance value of 0.08 Ω / □ (24.0 μΩ · cm in terms of a specific resistance value). In addition, as a result of observation with a scanning electron microscope, it was confirmed that no cracks occurred in the silver conductive film. The adhesion between the silver conductive film and the substrate film is determined by the cross-cut cello tape peel test method (JIS
K 5400), it was 100/100 (no peeling) and was good.

  The viscosity of the silver fine particle colloid dispersion concentrate was measured using a vibration viscometer VM-100-L manufactured by Yamaichi Electronics Co., Ltd. The surface resistance of the silver conductive film was measured using a surface resistance meter Loresta AP (MCP-T400) manufactured by Mitsubishi Chemical Corporation. The film thickness of the silver conductive film was measured by transmission electron microscope (TEM) observation of the film cross section.

[Example 4]
In the same manner as in Example 3 except that the silver film-forming coating solution of Example 3 was applied to the substrate in the same manner and then heat-treated at 80 ° C. for 180 minutes in the air. A film was formed. The film thickness of this silver conductive film was 3.0 μm, and the surface resistance value was 0.09 Ω / □ (27 μΩ · cm in terms of specific resistance value).

As a result of observation with a scanning electron microscope (TEM), it was confirmed that no cracks occurred in the silver conductive film. In addition, the adhesion between the silver conductive film and the substrate film is determined by the cross-cut cello tape peeling test method (JIS
K 5400), it was 100/100 (no peeling) and was good.

[Example 5]
Using the silver film-forming coating solution of Example 3 above, a polyimide film (Ube Industries, Ltd., Upilex S, thickness: 50 μm) was coated with a wire bar with a wire diameter of 1.0 mm, A silver conductive film was formed in the same manner as in Example 3 except that heat treatment was performed at 70 ° C. for 3 minutes to −220 ° C. for 60 minutes in the air.

This silver conductive film had a film thickness of 3.2 μm and a surface resistance value of 0.04 Ω / □ (12.8 μΩ · cm when converted to a specific resistance value). As a result of TEM observation, it was confirmed that no cracks occurred in the silver conductive film. In addition, the adhesion between the silver conductive film and the substrate film is determined by the cross-cut cello tape peeling test method (JIS
K 5400), it was 100/100 (no peeling) and was good.

[Example 6]
Using the coating solution for forming a silver film of Example 3 above, coated with a wire bar with a wire diameter of 1.0 mm on the glossy surface of a polyimide film (manufactured by Toray DuPont, Kapton H, thickness: 25 μm), A silver conductive film was formed in the same manner as in Example 3 except that heat treatment was performed at 70 ° C. for 3 minutes to −220 ° C. for 60 minutes in the air.

This silver conductive film had a film thickness of 3.1 μm and a surface resistance value of 0.04 Ω / □ (12.4 μΩ · cm when converted to a specific resistance value). As a result of TEM observation, it was confirmed that no cracks occurred in the silver conductive film. In addition, the adhesion between the silver conductive film and the substrate film is determined by the cross-cut cello tape peeling test method (JIS
K 5400), it was 100/100 (no peeling) and was good.

[Comparative Example 1]
To a mixture of 208 g of an aqueous solution of 23.1% iron sulfate (FeSO ₄ · 7H ₂ O) and 256 g of an aqueous solution of 37.5% sodium citrate (C ₃ H ₄ (OH) (COONa) ₃ · 2H ₂ O), 9. 176 g of 1% silver nitrate (AgNO ₃ ) aqueous solution was mixed and reacted to obtain a reaction solution containing silver fine particle aggregates. The liquid temperature of the iron sulfate aqueous solution and sodium citrate aqueous solution and the silver nitrate aqueous solution were set to 20 ° C. and 10 ° C., respectively.

  The resulting reaction solution was filtered through a centrifuge to obtain a cake of silver fine particle aggregates without going through an aging step by standing. Thereafter, pure water was added to the cake for washing, and 1050 g of a silver fine particle colloid dispersion (Ag: 0.75%) was obtained. The silver fine particles in this silver fine particle colloidal dispersion consisted of granular silver fine particles having a particle diameter of 2 to 10 nm, and the average particle diameter was 7 nm.

[Comparative Example 2]
The silver fine particle colloidal dispersion obtained in Comparative Example 1 was placed in an incubator at 25 ° C. and left for 2 months. Thereafter, when the colloidal dispersion of silver fine particles was observed with a transmission electron microscope, triangular or hexagonal plate-like coarse silver fine particles having a particle diameter of 20 to 150 nm were produced by being mixed with granular silver fine particles having a particle diameter of about 2 to 10 nm.

[Comparative Example 3]
By concentrating and washing the silver fine particle colloid dispersion liquid (Ag: 0.75%) obtained in Comparative Example 1 above by ultrafiltration, the silver fine particle colloid concentrated washing dispersion liquid (Ag: 40%, balance: water) Got. The electric conductivity of water as a solvent in the silver fine particle colloid concentrated cleaning dispersion was 190 μS / cm as a value obtained by measuring the filtrate of ultrafiltration.

To the silver fine particle colloid concentrated washing dispersion liquid, dimethyl sulfoxide (DMSO), 1-butanol (NBA), diacetone alcohol (DAA), and ethanol (EA) are added, and a silver film forming coating liquid (Ag: 10%, DMSO: 2.5%, H ₂ O: 15%, EA: 48.5%, NBA: 8%, DAA: 16%). The silver fine particles in the obtained coating solution for forming a silver film were composed of granular silver fine particles having a particle diameter of 2 to 10 nm, and the average particle diameter was 7 nm. Moreover, the viscosity of the coating solution for forming a silver film was 4 mPa · s.

  Next, in the same manner as in Example 3 above, the silver film forming coating solution was applied onto a PET film (thickness: 100 μm, primer-treated product) with a wire bar having a wire diameter of 1.0 mm, and then into the atmosphere. A silver conductive film was formed by performing a heat treatment at 70 ° C. × 3 minutes to −130 ° C. × 60 minutes.

This silver conductive film had a thickness of 0.8 μm, but it was visually observed that cracks occurred on the entire surface of the silver conductive film, and the surface resistance value was 1 × 10 ⁶ Ω / □ or more. Met. In addition, the adhesion between the silver conductive film and the substrate film is determined by the cross-cut cello tape peeling test method (JIS
K 5400), it was 0/100 and all peeled off.

  From the results of Examples 1 and 2 and Comparative Example 1, in Comparative Example 1 by the conventional method using the Carey-Lea method, the average particle diameter of the silver fine particles is 7 nm, whereas in each Example of the method of the present invention, It can be seen that a silver fine particle colloidal dispersion in which granular silver fine particles having an average particle diameter exceeding 30 nm are dispersed can be obtained very easily. Further, in Comparative Example 2, the reaction solution was not allowed to stand and ripen, but was left to stand and ripened as a colloidal dispersion. Coarse silver particles having a triangular or hexagonal plate shape are generated.

  Further, from the results of Examples 3 to 6 and Comparative Example 3 above, in the silver conductive film of Comparative Example 3 using the silver film forming coating solution composed of silver fine particles having an average particle diameter of 7 nm according to the conventional method, the film thickness Even though the thickness of the film was as small as 0.8 μm, cracks were generated on the entire surface of the film, whereas in each example according to the present invention, a coating solution for forming a silver film in which granular silver fine particles having an average particle diameter exceeding 30 nm were dispersed was used. Therefore, it can be seen that even when the film thickness is as thick as 3.0 to 3.2 μm, no crack occurs in the film, and a silver conductive film having excellent conductivity can be obtained.

Further, from the results of Example 4 above, in the case of the coating solution for forming a silver film of the present invention, even when the heat treatment temperature after coating is as low as 80 ° C., the surface resistance is 0.09Ω / □. It can be seen that a silver conductive film is obtained.

Claims (6)

A mixture of an aqueous iron (II) sulfate solution and an aqueous sodium citrate solution is reacted with an aqueous silver nitrate solution, and an aggregate of silver fine particles having a particle diameter of 2 to 15 nm protected with citrate ions is reacted with iron ions and sodium ions. a reaction step of producing during the silver particles the reaction solution containing aggregates of fine silver particles protected with the resulting citrate ion is allowed to stand at a temperature of still 40 to 100 ° C. in an aggregated state, the average a ripening step of particle size obtained aggregates of fine silver particles protected with grain growth and citrate ions granulated with 20 to 200 nm, and grain growth granulated filtration aggregates of silver particles and citrate ions provided in a filtration step to obtain a cake of protected agglomerate of fine silver particles and a dispersion step of obtaining a colloidal dispersion of a protective silver particles with a grain growth and citrate ions granulated by adding pure water to the cake Method for producing a fine silver particle colloidal dispersion, characterized in that. A colloidal dispersion of silver fine particles is produced by the reaction step, the ripening step, the filtration step and the dispersion step according to claim 1, and the resulting silver fine particle colloidal dispersion is concentrated and washed to obtain a silver fine particle colloid concentrated washing dispersion. And a solvent blending step of adding an organic solvent to the silver fine particle colloid concentrated cleaning dispersion . The method for producing a coating solution for forming a silver film according to claim 2, wherein the organic solvent contains at least dimethyl sulfoxide . 4. The silver film formation according to claim 2, wherein in the concentration and washing step, the electric conductivity of the solvent part from which the silver fine particles are removed from the silver fine particle colloid concentrated washing dispersion liquid is 500 μS / cm or less. 5. Method for producing a coating liquid for use . The method for producing a coating solution for forming a silver film according to any one of claims 2 to 4, wherein the concentration of silver fine particles in the coating solution for forming a silver film is 10 to 70% by weight . The method for producing a coating liquid for forming a silver film according to any one of claims 2 to 5, wherein an average particle diameter of silver fine particles in the coating liquid for forming a silver film is 20 to 200 nm .