HK1169967B - Low-temperature sinterable silver nanoparticle composition and electronic component formed using that composition - Google Patents

Description

Low-temperature sinterable silver nanoparticle composition and electronic article formed using same

Technical Field

The present invention relates to a composition of silver nanoparticles which has excellent adhesion to a substrate and can form a metal film or a conductive circuit at a low temperature in a short time.

Background

As a main wiring method for a printed circuit board which is commonly used for electric products, there is a method of etching a metal foil such as aluminum or copper. According to this conventional method, since a large amount of loss of the raw material occurs in the portion to be removed by etching, it is not preferable from the viewpoint of effective utilization of the raw material.

In addition, this method generates waste liquid and the like due to etching, and thus the load on the environment is not small. In recent years, it has been actively studied to form wiring by other techniques from the viewpoint of resource saving and environmental countermeasure strategies.

Among these new wiring forming techniques, the use of the existing printing techniques and the "printed electronics" for forming the wiring and the conductive film are expected to allow a desired product to be easily obtained in a large amount, and therefore, the present invention is particularly drawing attention.

The printed CPU, the printed illumination, the printed label, the full-print display, the sensor, the printed wiring board, the organic solar cell, the electronic book, the nanoimprint LED, the liquid crystal PDP panel, the printed memory, and the RF-ID have been studied as applications of the printed electronics, and the application range thereof is very wide.

The success of such printed electronics is greatly affected by the metal component exhibiting conductivity. Therefore, in order to further promote printed electronics, studies on metal nanoparticles having a particle diameter of the order of nanometers have been widely conducted from the viewpoint of metal particles as conductive particles, particularly in the field of fine wiring expected to be large for printing methods and low-temperature sinterability (for example, see patent documents 1 and 2).

It is known that metals have properties largely different from physical properties in a bulk state when they have a size of nanometer order. The activity of the nano-scale particles is very high, and thus the particles in this state become unstable. Therefore, the nanoparticles are usually provided in a state where a coating layer mainly composed of an organic material such as a surfactant is formed on the surface, and are provided as a composition in a manner such that the metal particles coated with the surfactant are dispersed mainly in an organic solvent.

As described above, the metal particles are coated with an organic substance such as a surfactant on the surface thereof to prevent sintering or aggregation between the particles. By using a long-chain surfactant, sintering or aggregation between particles can be avoided, independence of particles in a liquid can be ensured, and stability can be maintained. However, even if the metal is made to be nano-scale, if the surfactant constituting the outer periphery is made of a high molecular weight compound, it is necessary to perform a long-term treatment at a high temperature for removing or decomposing the surfactant on the particle surface for about 30 minutes to 1 hour in the case of forming a metal film. In this case, it is difficult to use an inexpensive wiring board having poor heat resistance, and therefore, there is a high possibility that the use of metal nanoparticles is less likely. Further, it is also not suitable from the viewpoint of energy saving.

The metal nanoparticles are polydispersed in an organic solvent such as decane or terpineol. When the organic solvent is discarded, it may cause environmental pollution if careless. Further, since the evaporated organic component is easily diffused, a local exhaust device or the like is required when a large amount of processing is performed. Of course, there are times when damage to the body may occur. Therefore, it is desirable to use a dispersion medium containing no organic solvent as a main component, from both environmental and operational viewpoints.

In addition, when the metal species of the metal nanoparticles is used as a conductive material, silver is most suitable in terms of low metal-specific resistance, high oxidation resistance, easy sintering at a low melting point, and raw gold price.

Based on the above facts, the inventors of the present application developed a technique of metal nanoparticles having low-temperature sinterability and capable of forming a metal film in a short time, and disclosed the contents thereof in the previous application (refer to patent document 3).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2005-200604

Patent document 2: japanese patent laid-open No. 2005-310703

Patent document 3: international patent publication No. WO2008/048316

Disclosure of Invention

Problems to be solved by the invention

The present inventors have shown that a conductive film having low resistance and good film adhesion can be obtained even by a short-time treatment at low temperature using the silver nanoparticle composition disclosed in patent document 3. Specifically, the composition was applied to a substrate using a simple printer in a laboratory, and heat treatment was performed at 140 ℃ or more and 30 seconds or more using a dryer or the like, whereby good conductivity was shown.

However, Roll-to-Roll (Roll-to-Roll) continuous printing, which is generally used in the industry, is used, and an inexpensive and low heat-resistant substrate such as a PET film or paper is used. When printing and heat treatment are performed, the printing speed is required to be 30 m/min or more. In such high-speed processing, it is assumed that even if the inside of the heat treatment furnace attached to the printer is set at 140 ℃, the substrate itself is sent out from the heat treatment furnace before being heated to that temperature. Further, if the set temperature is set to a high temperature, there is a problem that the base material is deformed or scorched by heat before the silver nanoparticle composition is fired. As a result, the sintering is not sufficiently performed in the heat treatment step, and good conductivity cannot be obtained.

Therefore, it is required to develop a composition which can obtain a good electric resistance even when the treatment is performed at a low temperature in a short time. In view of the above problems, an object of the present invention is to provide a silver nanoparticle composition that can obtain good electrical resistance and good adhesion even at a lower temperature in a shorter time.

Further, another object of the present invention is to provide a silver thin film, a wiring formed using the above silver nanoparticle composition, and an RF-ID antenna, an RF-ID antenna insert, an EMI shield, and an electronic circuit using the same.

Means for solving the problems

The above problem can be solved by the following configuration. The present invention uses a silver nanoparticle composition characterized in that the main component of the solvent is water, the pH of the composition is in the range of 5.3 to 8.0, the silver nanoparticles contained in the composition are protected by an organic acid or a derivative thereof, and the content of the organic acid or the derivative thereof is in the range of 2 to 20 mass% relative to silver.

Next, the features of the present invention will be described. The invention of claim 2 is the silver nanoparticle composition of claim 1, wherein the content of the silver nanoparticles is in the range of 15 to 75 mass% with respect to the total amount of the composition.

The present invention is the silver nanoparticle composition according to the invention 1 or 2, wherein the ammonia component is present in an amount of more than 0.1% by mass based on the composition.

The present invention 4 is the silver nanoparticle composition according to any one of the inventions 1 to 3, wherein the nitric acid component is present in the composition in an amount of more than 0.1% by mass based on the composition.

The 5 th invention is the silver nanoparticle composition according to any one of the 1 st to 4 th inventions, wherein the primary particle diameter of the silver nanoparticles is 100nm or less as measured by a transmission electron microscope.

The 6 th invention is the silver nanoparticle composition according to any one of the 1 st to 5 th inventions, which is characterized by containing a polymer obtained by polymerizing a monomer having a vinyl group.

The 7 th invention is the silver nanoparticle composition according to any one of the 1 st to 6 th inventions, wherein the organic acid or the derivative thereof is a carboxylic acid having 5 to 8 carbon atoms or a derivative thereof.

The present invention is the silver nanoparticle composition according to any one of the invention 1 to 7, wherein the organic acid or the derivative thereof is heptanoic acid or the derivative thereof.

The 9 th invention is the silver nanoparticle composition according to any one of the 6 th to 8 th inventions, wherein the polymer obtained by polymerizing the vinyl group-containing monomer contains at least one of a vinyl chloride homopolymer, a vinyl chloride copolymer, a vinyl acetate homopolymer, and a vinyl acetate copolymer.

The 10 th aspect of the present invention is the silver nanoparticle composition according to any one of the 1 st to 9 th aspects of the present invention, which contains a polymer characterized by having a glass transition temperature (Tg) of 0 ℃ to 100 ℃.

The 11 th aspect of the present invention is the silver nanoparticle composition according to any one of the 1 st to 10 th aspects of the present invention, which is characterized by containing a water-dispersible polymer having at least one or more groups selected from an OH group, a polyoxyethylene glycol group, and a polyethylene glycol group.

The 12 th invention is the silver nanoparticle composition according to the 11 th invention, which is characterized by containing a polymer having a urethane bond.

The 13 th invention is the silver nanoparticle composition according to any one of the 1 st to 12 th inventions, wherein the surface resistivity of the silver thin film after the silver nanoparticle composition according to any one of the 1 st to 11 th inventions is applied to a substrate and heat-treated at 60 ℃ for 15 seconds in the atmosphere is 100 Ω/□ or less.

The 14 th invention is a silver thin film and a silver wire formed using the silver nanoparticle composition according to any one of the 1 st to 13 th inventions.

The 15 th invention is a method for forming a silver wire by coating a silver nanoparticle composition according to any one of the 1 st to 13 th inventions on a base material by firing using an RF-ID antenna, wherein the wire forms an antenna portion of the RF-ID.

The 16 th invention is an RF-ID insert using the antenna of the 15 th invention.

The 17 th invention is to silverize a wiring formed by the silver nanoparticle composition described in any one of the 1 st to 13 th inventions by firing using an EMI shield to form a silver wiring, the wiring forming a gate portion of the EMI shield.

The 18 th invention is an electronic circuit using a silver wiring formed by firing a wiring formed by silvering by a printing method using the silver nanoparticle composition according to any one of the 1 st to 13 th inventions.

ADVANTAGEOUS EFFECTS OF INVENTION

The invention provides a silver nanoparticle composition which has excellent low-temperature short-time sintering property and excellent adhesion with a substrate at a level required by industry and can be used for preparing a low-resistance silver conductive film and wiring, and an article using the silver nanoparticle composition.

Brief description of the drawings

Fig. 1 is a diagram illustrating criteria for evaluating adhesion.

Fig. 2 is a diagram illustrating an outline of an antenna of an RF-ID.

Fig. 3 is a view showing a cross section of the RF-ID insert.

Fig. 4 is a diagram illustrating an EMI shield.

Fig. 5 is a diagram showing a configuration of a simple coating device.

Modes for carrying out the invention

< silver nanoparticle composition >

< solvent >

The solvent of the silver nanoparticle composition of the present invention (hereinafter also simply referred to as "composition") is mainly water. The term "mainly" as used herein means that the proportion of water in the medium of the composition is 50% by mass or more. In such a composition, a co-solvent may be added in an amount of 50% by mass or less in total.

< second solvent >

The secondary solvent may be one of polar solvents represented by derivatives thereof such as alcohols, polyhydric alcohols, ethers, and the like, or a combination of a plurality of these solvents. The solubility of the additive can be adjusted to improve the wettability with the substrate.

< about pH >

The pH of the composition is preferably 5.3 to 8.0. The composition of the invention is formed by the main solvent water, organic acid and silver nano particles into an emulsion structure. These organic acids and their derivatives are inherently low in solubility in water itself. However, these organic acids are characterized in that the solubility thereof is increased at the same time as the pH of the solvent is increased. At a pH of 5.2 or less, the organic acid and the derivative thereof are hardly dissolved in the solvent, and thus the particles are aggregated with each other by an excessive amount of the organic acid and the derivative thereof. Therefore, the particles are aggregated or the viscosity of the composition is significantly increased, and thus the composition is not suitable for use as a coating material. When the pH is 8.1 or more, the solubility of the organic acid or the derivative thereof in water as a solvent is too high, and thus the amount of the organic acid or the derivative thereof in the periphery of the particles is not sufficient for dispersing the particles. Therefore, aggregation or bonding between particles is caused, and thus it is not suitable for use as a coating material.

< concerning silver nanoparticles >

The silver nanoparticles of the present invention can be produced by a wet method as long as they are produced by the method, and the kind of the production method is not particularly limited.

The diameter of the silver nanoparticles is 100nm or less, preferably 50nm or less, as measured by a Transmission Electron Microscope (TEM). Particles having a particle size larger than this range are not preferable because it is difficult to obtain low-temperature sinterability desired as silver nanoparticles. In the present specification, the term "diameter of silver nanoparticles" refers to "average primary particle diameter of silver nanoparticles", and the detailed measurement method is described below.

The silver concentration in the composition may be in the range of 15 to 75 mass%, preferably 30 to 75 mass%, more preferably 40 to 75 mass%. From the viewpoint of low-temperature firing and short-time firing, a high silver concentration with a small solvent is preferable, but since the viscosity of the high silver concentration is high, the silver concentration may be used within an appropriate range depending on the printing method. In the case of a spray printing method or the like, printing cannot be performed unless the concentration is low, and therefore, in this case, the low concentration is more advantageous, and therefore, there is a possibility that the silver concentration may be reduced.

< organic acid >

The surface of the silver nanoparticles in the composition of the present invention is coated with an organic acid having 5 to 8 carbon atoms or a derivative thereof. The organic acid or its derivative exerts effects of preventing sintering and aggregation between particles and maintaining an appropriate distance between particles, that is, exerts an effect as a protective agent. If the carbon number is more than 8, the boiling point of the organic acid or its derivative approaches the heat resistant temperature of the low heat resistant substrate or greatly exceeds the temperature, and thus, the thermal energy and time for dissociating it from the silver nanoparticles are very consumed, and thus it is not suitable for use in applications requiring low temperature and short time sinterability. However, in order to stabilize the dispersion of the particles in a solution and to suppress aggregation of the particles in a room temperature range during storage, an appropriate intermolecular distance and thermal stability of the organic acid or its derivative are required, and therefore the carbon number of the organic acid or its derivative is preferably 5 or more and 8 or less, and more preferably a carboxylic acid. Heptanoic acid is most preferred.

The content of the organic acid or the derivative thereof is preferably in the range of 2 to 20 mass% with respect to silver. When the content of the organic acid or the derivative thereof is less than 2% by mass, the effect as a protective agent is remarkably reduced, aggregates are generated, and as a result, deterioration of low-temperature sinterability and deterioration of density of the conductive film occur, which is not preferable. Further, when they are more than 20% by mass, low temperature and short time sintering thereof are inhibited, and therefore, they are not preferable. This is because these organic substances and derivatives thereof have a higher boiling point than water, which is the main solvent.

< nitric acid content >

The nitric acid component in the composition plays a role of promoting decomposition of the surfactant, the dispersant, and other additive resins when the composition is heated in a drying and firing step or the like after being applied to a substrate. Therefore, if the nitric acid component concentration is too low, the low-temperature sinterability deteriorates, and it becomes difficult to form a film having good conductivity on a low heat-resistant substrate such as a PET substrate.

When nitrate is used as the silver salt to be the raw material, the nitrate supplies the nitric acid component. When other silver salts are used, they may be supplied as nitric acid or other nitrates after the synthesis of the particles.

The nitrate ion concentration in the composition obtained as described above is more than 0.1% by mass, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more.

< composition of Ammonia >

The ammonia content in the composition is more than 0.1% by mass, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. If the amount is outside this range, the secondary aggregation diameter of the silver nanoparticle ink becomes large, the ink is rapidly sedimented, the coating film itself has irregularities, and the conductivity of the film after firing is also deteriorated, which is not preferable. The ammonia component is derived from an alkali and a reducing agent in the synthesis of the silver nanoparticles, and ammonia added in the adjustment of pH after the reaction.

The nitric acid and ammonia components of the composition can be controlled by adding ammonia and nitric acid to achieve the above pH range. However, if the nitric acid and ammonia components are equal to or higher than a certain value, the ionic strength becomes too high, and it is confirmed that silver ions are strongly aggregated. For the above reasons, the nitric acid component is 5% by mass or less, preferably 3% by mass or less; the ammonia content is 2% by mass or less, preferably 1.5% by mass or less.

< materials for improving adhesion >

In addition, in order to further enhance the adhesion between the conductive film and the substrate, the composition of the present invention preferably contains a polymer obtained by polymerizing a monomer having a vinyl group. The polymer to be added may be a water-soluble polymer which can be directly dissolved in a solvent, or may be a system (emulsion) in which fine particles of a resin are stably dispersed in an aqueous solvent, that is, latex, and the like, and the form is not limited. Any dispersion in a solvent can be suitably used. These polymers are also known as water dispersible polymers.

Whether or not the water-dispersible polymer is a polymer obtained by polymerizing a monomer having a vinyl group can be determined by FT-IR analysis, FT-Raman analysis, or thermal decomposition type GCMS.

The polymer obtained by polymerizing a monomer having a vinyl group is preferably any of a vinyl chloride homopolymer, a vinyl chloride copolymer, a vinyl acetate homopolymer and a vinyl acetate copolymer, and 1 or 2 or more of them are preferably used in the composition. These polymers have high adhesion to silver and are suitable for improving adhesion to a substrate. Further, these polymers are chemically stable, and therefore, the characteristics of the composition during use and storage are also stable.

The amount of the polymer obtained by polymerizing the monomer having a vinyl group is 0.5 to 10% by mass, preferably 1 to 8% by mass, and more preferably 1 to 7% by mass, based on the total composition. If the amount is less than 0.5% by mass, the adhesion is not sufficient, while if it is more than 10% by mass, the conductivity at the time of film formation is adversely affected, which is not preferable.

< thickening agent (thickening Material) >

Further, a resin (hereinafter, the term "tackifier" is used synonymously with the term "thickener") may be added for the purpose of appropriate viscosity adjustment. The resin to be added is preferably a water-dispersible polymer which can be stably dispersed in water as a main solvent, and the polymer may have at least one group selected from an OH group, a polyoxyethylene glycol group and a polyethylene glycol group.

These water-dispersible polymers can also be the same as the previous polymers with vinyl groups. In this case, the polymer may have at least one or more of an OH group, a polyoxyethylene glycol group, and a polyethylene glycol group in addition to the vinyl group. In addition, it may be added as another polymer other than the vinyl group polymer. Further, polymers each having an OH group, a polyoxyethylene glycol group or a polyethylene glycol group may be added. By having these groups, the composition of the present invention has good dispersibility in a solvent, and exhibits a function as a thickener.

Whether or not the water-dispersible polymer contains an OH group, a polyoxyethylene glycol group or a polyethylene glycol group can be determined by FT-IR analysis, FT-Raman analysis or thermal decomposition type GCMS.

The polymer having at least one of an OH group, a polyoxyethylene glycol group and a polyethylene glycol group is preferably a polymer further having a urethane bond. The polymer having a urethane bond also has chemical stability, and therefore, a thickening effect stable for a long period of time is obtained in the solvent of the composition of the present invention.

Whether or not the water-dispersible polymer contains a urethane bond can be determined by FT-IR analysis, FT-Raman analysis, or thermal decomposition type GCMS.

In this case, the amount of the water-dispersible polymer added is more than 0% by mass and less than 10% by mass, preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, based on the total composition. The amount added is preferably an amount to achieve a minimum rheological property suitable for printing. The rheological properties suitable for printing vary greatly depending on the printing method (flexographic printing, gravure printing, screen printing), the printing conditions (printing speed, substrate), and the like, and therefore, it is necessary to adjust the rheological properties appropriately in accordance therewith. The excessive addition of the silver nanoparticles is not preferable because it inhibits sintering between particles, and also, it enters gaps between particles to increase the resistance of the existing portions, thereby lowering the conductivity.

<T for the contained polymers_g>

As mentioned above, the composition may, depending on its use, contain a polymer, preferably having a high T_g(glass transition temperature). In general, it is known to use T in the field of adhesives_gSince a low polymer exhibits adhesion at a relatively low temperature, T is preferably used for the purpose of securing adhesion_gLow polymer content.

However, the inventors of the present application have foundNow, T is added to the composition using silver nanoparticles_gIn the case of a low polymer, the polymer adheres to the surface of the silver nanoparticles before the silver nanoparticles are sintered to each other, and this action results in inhibition of sintering, and low resistance characteristics cannot be obtained although adhesion is obtained.

According to the above facts, T of the added polymer_gPreferably in the range of 0 ℃ to 100 ℃. When the temperature is lower than 0 ℃, sintering of the silver nanoparticles is inhibited, and low resistance cannot be obtained, which is not preferable. In addition, when the temperature exceeds 100 ℃, sintering between particles proceeds, but adhesion between resins is insufficient at low temperature and short time sintering, and thus good adhesion to a base material cannot be secured.

For polymers added to improve adhesion to the substrate, at T_gWhen the above is used, the polymer has strong adhesion to silver ions, and T is used_gPolymers within the above range are particularly important. The polymer having a function of controlling the viscosity of the composition by dispersing in a solvent of the composition as a thickener and having weak adhesion to the surface of the silver nanoparticles may not be limited to the high T_gRanges may be added to the composition.

T of Polymer_gThe measurement can be carried out by DSC (differential scanning calorimetry), DTA (differential thermal analysis), or TMA (thermomechanical measurement). Furthermore, T of the homopolymer_gDescribed in various documents (e.g., Polymer handbook, etc.), T of the copolymer_gT also from various homopolymers_gn(K) And mass fraction of monomer (W)_n) The following equation (1) is used to obtain the target compound.

(1/T_g)＝(W₁/T_g1)+(W₂/T_g2)+·····+(W_n/T_gn)····················(1)

Here, W_nIs the mass fraction of each monomer, T_gnT being a homopolymer of each monomer_g(K)。

< resistance value >

The silver nanoparticle composition of the present invention is characterized in that the surface resistivity of a silver thin film obtained by applying the silver nanoparticle composition to a substrate and then heat-treating the silver thin film at 60 ℃ for 15 seconds in the atmosphere is 100 Ω/□ or less.

It is highly desirable to use a PET substrate having high versatility and a paper having a lower price as a substrate. In the case of a PET substrate, shrinkage becomes large when heat treatment is carried out at 140 ℃ and there is a problem in dimensional stability. Further, in the case of a paper substrate, the heat resistance is low, and it is known that when the heat treatment is performed, the strength is extremely lost when the moisture in the substrate is reduced, and it is required to obtain the conductivity at a low temperature in a short time.

In order to accomplish this, it is desirable to obtain a good conductive film under the conditions of 120 ℃ or lower and 30 seconds or lower, preferably 100 ℃ or lower and 30 seconds or lower. Conventionally, a resin-cured silver paste exhibiting conductivity in a temperature range of about 150 to 200 ℃ is known. The silver nanoparticle composition of the present invention was confirmed to exhibit a good resistance value with a surface resistivity of 100 Ω/□ or less under the condition of heat treatment at 60 ℃ for 15 seconds. This fact shows excellent low-temperature and short-time sinterability of a conductive film which can be formed on a substrate having extremely low heat resistance such as thermal paper.

Therefore, by coating or pattern-printing the silver nanoparticle composition of the present invention on a substrate and sintering the composition at a low temperature for a short time, a silver film or wiring having high conductivity can be formed.

Further, such a conductive printed matter can be used not only for wiring but also for an antenna for RF-ID (Radio-frequency identification) or an RF-ID interposer using the same. Fig. 2 illustrates an RF-ID antenna 1 formed of a conductive pattern using the silver nanoparticle composition of the present invention. It is an RF-ID antenna with a total length (2) of 32mm, a total width (3) of 18.5mm and a line width 4 of 0.7 mm. The substrate was made of PET having a thickness of 60 μm and was made using the silver nanoparticle composition of the present invention under firing conditions of 80 ℃ for 30 seconds. The linear resistance was 35 Ω.

An RF-ID interposer may be fabricated by bonding the RF-ID antenna to the IC with bumps. Fig. 3 shows a perspective view (fig. 3(a)) and a side view (fig. 3(b)) of an IC7 mounted on an RF-ID antenna 1 formed on a substrate 5. The IC7 is connected to the RF-ID antenna 1 by bumps 8.

In addition, the silver nanoparticle composition of the present invention can also be used for an EMI Shield (electromagnetic interference Shield). A simplified diagram of the EMI shield 10 of the present invention is shown in fig. 4. The frame 11 is an aluminum chassis, and the base material 12 laid in the center of the frame 11 is a transparent sheet (polycarbonate). On the substrate, a conductive pattern 13 having a width of 35 μm in a lattice shape was formed, and the pattern was formed from the silver nanoparticle composition of the present invention. The EMI shield had a total light transmission of 72% and a surface resistance of 1.0 Ω/□.

< production of silver nanoparticles >

The method for producing silver nanoparticles of the present invention will be described. The method for producing silver nanoparticles of the present invention is characterized by conducting the production of the composition without the steps usually required, such as filtration and drying. By obtaining the composition without the filtration and drying steps, a silver nanoparticle composition having excellent dispersibility and low-temperature sinterability can be obtained. Further, since these steps are eliminated, simplification of manufacturing equipment can be achieved.

< preparation of raw Material solution >

The silver nanoparticles of the present invention are obtained by preparing three solutions in advance and mixing them in sequence. First, each solution will be described in turn.

(solution A)

For the ion-exchanged water, ammonia water and an organic acid are dissolved.

(solution B)

The reducing agent for reducing silver ions is diluted with ion-exchanged water, or the reducing agent which is solid at room temperature is dissolved. The reducing agent is sufficient as long as it has a reducing ability to reduce silver ions in the aqueous solution. As the reducing agent, any one of hydrazine, hydrazine hydrate, sodium borohydride, lithium borohydride, ascorbic acid, primary amine, secondary amine, tertiary amine, and lithium aluminum hydride, or a plurality of these may be appropriately selected.

(solution C)

For the ion exchange water, the water-soluble silver salt of the silver species as described above is dissolved.

When the silver salt is silver, for example, silver nitrate or the like can be used. Further, it may be selected from acetate, carbonate, sulfate, chloride, hydrate, and the like. In this case, when the selected salt is hardly dissolved in water at normal temperature, the solution may be heated or a dissolution assistant may be added within a range not affecting the reaction.

< reaction step >

A predetermined amount of ion-exchanged water was previously added to the reaction vessel, and the solution A was added thereto at a predetermined temperature, followed by sequentially adding the solution B and the solution C to the reaction vessel to carry out the reaction.

In this case, the solution C is prepared so that the silver concentration in the reaction vessel is 0.3 to 0.9 mol/liter, preferably 0.4 to 0.7 mol/liter. When the silver concentration is lower than the above concentration, the amount of silver nanoparticles obtained after the reaction is small, and the productivity is not preferable, and when the silver concentration is higher than the above concentration, the reaction proceeds extremely rapidly, and is difficult to control, and the reaction becomes non-uniform, which is not preferable.

The reaction temperature (temperature of the reaction solution) at this time is set to a temperature of from room temperature to 70 ℃.

< separation step >

The obtained reaction solution was naturally settled to separate the supernatant from the reaction product. In this case, the liquid is preferably left to stand for at least half a day, and preferably left to stand by natural sedimentation until the upper half of the volume of the liquid becomes a supernatant. The product obtained was separated from the supernatant by decantation to obtain a concentrate of silver nanoparticles. In addition, a centrifugal separator may be used to shorten the time.

The composition of the present invention is characterized in that the concentrate obtained is directly combined without washing. If washing is performed, significant aggregation occurs between particles, which is not preferable. The silver particles and powders reported so far are washed with an appropriate solvent after the synthesis of the particles, but the concentrate of the present invention does not require washing and can be directly combined into a composition, so that the process can be shortened and the effect of high productivity can be obtained.

< pH adjustment step >

In addition, the composition of the present invention is characterized in that the pH is once controlled to pH5.3 to 8.0 after the synthesis of the particles and before the concentrate is obtained. In the synthesis of silver nanoparticles, since the reaction is carried out under conditions of increased liquid temperature and strong agitation, it is necessary to use an excessive amount of an organic acid or a derivative thereof as a surfactant in order to suppress aggregation and binding during the synthesis of the particles. The excessive organic acid and its derivative have low solubility in water as a main solvent, and therefore contain an excessive portion and are disposed around almost all the particles. Therefore, these excessive organic acids reduce the dispersibility of the silver particles, and also prevent sintering between the silver particles due to their high boiling points.

However, the organic acid and the derivative thereof are characterized in that the pH of the solvent is increased and the solubility thereof in the solvent (water) is also increased. Then, the present inventors have found that when a concentrate is obtained at room temperature, an excessive amount of organic acid or a derivative thereof disposed around particles is dissociated from the surroundings of the particles by setting the pH to a pH in the range of 5.3 to 8.0, and have thought to utilize the organic acid or the derivative. In other words, by operating the pH, these excess organic acids and derivatives thereof are intentionally dissociated from the periphery of the silver particles and dissolved in the solvent, and the portion that is not completely dissolved in the solvent is separated as an emulsion of the water-organic acids and derivatives thereof in the upper part of the composition.

The pH adjustment step may be performed simultaneously with the separation step or prior to the separation step. That is, the supernatant liquid may be left to stand to separate the silver nanoparticles from the supernatant liquid, and the pH adjustment step may be performed after removing the supernatant liquid to dissociate the excessive organic acid from the surface of the silver particles, or the pH adjustment may be performed in advance at the time of the separation step or before the separation step is performed by standing to remove the solvent and the excessive organic acid dissociated from the periphery of the silver particles as the supernatant liquid. Thus, after the excess organic acid is dissociated from around the silver particles, a concentrate concentrated to a target silver concentration is obtained. Then, it was found that a composition having excellent dispersibility and excellent low-temperature short-time sinterability was formed when the composition was prepared using the concentrate.

Further, the pH adjustment step may be performed a plurality of times in combination with the separation step. That is, the separation step is performed a plurality of times, for example, by performing the separation step for a predetermined time, performing the pH adjustment step when the concentration is performed to a certain extent, and then performing the separation step by standing. In this case, the separation step after pH adjustment has a meaning of precipitating the silver nanoparticles and promoting the dissociation of the organic acid from the periphery of the silver particles, and the separation step may include such a meaning.

The following findings were obtained for the pH range. When the pH is 5.2 or less, the solubility of the organic acid and the derivative thereof in water is low, and thus the removal efficiency of the excessive organic acid and the derivative thereof is low. Further, when the pH is 8.1 or more, the solubility of the organic acid and the derivative thereof in water is too high, and the organic acid and the derivative thereof in an amount sufficient for dispersing the particles with each other become insufficient around the particles, and aggregation or bonding between the particles is caused, and thus it is not suitable for use as a coating material.

< dispersing step >

In the separation step, nitric acid having the effect of the sintering accelerator is added to the concentrate in which the concentration of the silver nanoparticles is increased to an appropriate level in a preferred range. In addition, ammonia and nitric acid are then added to achieve a combinationProper pH value, proper ammonia concentration and proper nitric acid concentration. Then, fine adjustment is performed by adding the supernatant in order to bring the concentration to the final target silver concentration. Then, a high T for improving the adhesion to the above-mentioned base material to be targeted is added_gA resin polymer and a water-dispersible polymer for adjusting viscosity (thickener) to obtain a silver nanoparticle composition.

The adjusted composition is coated onto a substrate using a printing process. The printing method may be selected according to the application purpose of flexographic printing, gravure printing, screen printing, offset printing, dispenser, spray coating, etc.

< evaluation of average particle diameter of Primary particles >

In the present specification, the diameter of the silver nanoparticles refers to the average value of the primary particle diameters obtained from TEM images, that is, the average primary particle diameter, and is measured by the following method. 2 parts by mass of the silver nanoparticle composition was added to a mixed solution of 96 parts by mass of cyclohexane and 2 parts by mass of oleic acid, and dispersed by ultrasonic waves. The dispersion solution was dropped on a Cu micro grid with a supporting film, and dried to prepare a TEM sample. The resulting micro-grid was observed for particles in a bright field at an acceleration voltage of 100kV using a transmission electron microscope (JEM-100 CX Mark-ii manufactured by japan electron corporation), and the observed image was photographed at a magnification of 300000 times.

Image analysis software (a image く (registered trademark) manufactured by asahi chemical engineering co., ltd., asahi chemical エンジニアリング, inc.) was used to calculate the average particle diameter of the primary particles. This image analysis software recognizes each particle according to the lightness of color, performs circular particle analysis on a 300000-fold TEM image under the conditions of "brightness of the particle" being "dark", "presence of noise removal filter", "circle threshold" being "20", and "degree of overlap" being "50", measures primary particles for 200 or more particles, and obtains the number average diameter thereof as the average primary particle diameter. In addition, when there are a large number of coagulated particles and abnormal particles in the TEM image, it is determined that the measurement cannot be performed.

< measurement of Ammonia concentration and nitric acid concentration >

The ammonia concentration and the nitric acid concentration of the composition were measured by placing the composition on a membrane filter and an ultracentrifuge to perform solid-liquid separation of the composition, and then measuring the concentration of the liquid by an ion chromatograph.

< measurement of organic acid >

For the quantitative determination of the organic acid in the composition, after adding an excessive amount of nitric acid to the composition, heating was performed to completely dissolve the metal component, n-hexane extraction was performed 4 times, and then the organic acid was quantitatively determined by GCMS.

The rheology of the composition was evaluated using a Haake (HAAKE) rheometer, trade name RheoStress600, cone C35/2. Specifically, the shear rate was measured for 10s^-1And 1000s^-1Viscosity of (2). Thixotropy, which indicates a property of increasing fluidity when stirred and returning to its original state when left standing, was defined as 10 seconds^-1Viscosity of (2)/1000 s^-1The viscosity of (3) was evaluated.

< production of conductive film >

The silver nanoparticle composition was coated onto the substrate using a Flexo Proof (フレキソプル - フ, manufacturer: RK printing Instrument (RK Print coaters), model: ESI12, Anilox; 200 lines).

The setting of the Flexo Proof is performed by pressure adjustment of the Anilox roll (Anilox roll) and the rubber blanket. The pressure adjustment is performed by pressing 0.05 to 0.10mm from the position where the mesh is just in contact with the rubber plate by using the handles for adjustment at both ends. Then, about 1ml of the composition was dropped onto the web, and the resultant was coated for about 1 second.

Immediately after the coating, firing was performed for a predetermined time using a hot plate set at a predetermined temperature. In addition, in the firing, in order to maintain good contact between the substrate and the hot plate, first, an unprinted substrate portion was pressed against the hot plate, the firing was continued until the composition was no longer transferred to BEMCOT (ベンコツト), and then the entire substrate was fired so as to be pressed against the hot plate using BEMCOT.

In addition, a conceptual diagram of the Flexo Proof is shown in fig. 5. Fig. 5(a) is a perspective view showing a state at the time of coating, and fig. 5(b) is a side view at that time. The Flexo Proof 20 is such that an anilox roller 22 is disposed above a cylindrical rubber plate 21, and a doctor blade 23 is attached to the anilox roller 22. The distance between the rubber plate 21 and the anilox roller 22 and the distance between the doctor blade 23 and the anilox roller 22 can be adjusted as described above. The coating material 24 is dropped between the doctor blade 23 and the anilox roller 22. The rubber sheet 21 is pressed against the base material 28, and thus the whole is pulled in the direction of the arrow, and the rubber sheet 21 is rotated while the anilox roller 22 is rotated in the reverse direction.

The coating material 24 is attached to the surface of the anilox roller 22 at a certain thickness from between the rotating anilox roller 22 and the doctor blade 23, and the coating material 24 is transferred to the blanket plate 21 through the contact surface with the blanket plate 21. The coating material 23 transferred to the rubber plate 21 is carried to the base material 28 by the rotation of the rubber plate 21, and is transferred to the base material 28, thereby obtaining a coating film 25. The Flexo Proof 20 applies the coating 24, operating as above. Therefore, even if the coating apparatus of the above-described type is not provided, the apparatus can be used for producing a conductive film for measuring resistance as long as the apparatus has the configuration of fig. 5.

< surface resistivity >

After the coating, heat treatment is performed at a predetermined temperature and for a predetermined time. The silver nanoparticles are sintered and integrated with each other by the heat treatment, thereby exhibiting conductivity. The conductivity was evaluated by Surface Resistivity (Surface Resistivity, unit: Ω/□, Ω/sq., read in ohm/square, and resistance per unit area, also referred to as sheet resistance or simply Surface resistance, used in the fields of coating films, etc.) by the four-terminal method.

< volume resistivity >

The relationship between volume resistivity and surface resistivity is: volume resistivity is surface resistivity x specimen thickness. The volume resistivity was calculated from the surface resistivity and the thickness of the sample obtained by a laser microscope. Further, in this embodiment, mirror coated paper (ミラコ - ト manufactured by prince paper company) is basically used as the base material, but when paper is used as the base material, the penetration of the composition into the base material and the difference in surface roughness make the measurement of the sample thickness by the laser microscope difficult. Therefore, in the calculation of the volume resistivity, a PET (polyethylene terephthalate) film (Melinex (registered trademark) 545, manufactured by monarch film corporation, du pont, ltd. (デユポンテイジンフイルム)) was used as a base material. In the examples of the present specification, a PET substrate is used for measuring the volume resistivity from the viewpoint of measuring the film thickness, but if the film thickness can be appropriately measured by a film thickness measuring method using fluorescent X-rays or the like, the base material is not particularly limited to PET, and any base material can be used.

< evaluation of adhesion >

Adhesion between the silver film and the substrate after the coating on the substrate and the firing is performed by a cross cut method. The adhesive tape was a repair tape (manufactured by 3M). The cross-cut method is carried out in accordance with JIS56000-5-6, but when the substrate is paper, the tape is peeled off in several seconds so as not to damage the substrate itself. The judgment was made by visual observation. The judgment criteria are shown in FIG. 1. The evaluation is a 6-grade evaluation of 0 to 5, and 0 is no peeling from the substrate at all. And 5 represents a state of almost complete peeling.

< measurement of pH >

For the measurement of pH, a portable pH/Do meter D-55 manufactured by horiba division (horiba, Ltd.) based on JIS Z8802 (1984's) pH measurement method or an equivalent thereof was used. The pH electrode was manufactured by the same company as 9611-10D. Before the measurement, two-point calibration was carried out using standard solutions of pH6.86 and pH 4.01. When the pH was measured, the mixture was stirred sufficiently for 30 minutes and then left to stand for about 30 seconds to 1 minute, and then the test tip (pH electrode) was immersed in the solution to read the measurement value.

Examples

< examples 1 to 8, comparative examples 1 to 4> Effect on pH

< example 1>

< preparation of raw Material solution >

As the raw material liquid A, 0.31kg of 28 mass% aqueous ammonia and 0.36kg of heptanoic acid were mixed in 1.2kg of ion-exchanged water.

As a raw material liquid B, 0.39kg of 85 mass% aqueous hydrazine was diluted with 1.0kg of ion-exchanged water.

As the raw material liquid C, a solution was prepared in which 1.4kg of silver nitrate crystals was dissolved in 1.2kg of heated ion-exchanged water.

< Synthesis reaction of silver nanoparticle >

In order to suppress the volatilization of the contents during the reaction, 11kg of ion-exchanged water was added to the reaction vessel equipped with a reflux condenser, and the mixture was heated while stirring. When the liquid temperature is within the range of 30 to 50 ℃, the raw material liquid A, B, C is added in order while stirring to start the reaction.

< concentrates >

In the reaction process, the reaction tank is cooled and controlled so that the temperature cannot reach more than 60 ℃. The cooling is performed by providing a cooling pipe for cooling the inside of the reaction tank to the reaction tank itself. Even if the cooling of the reaction vessel is stopped, the reaction is terminated at this point without increasing the temperature due to the reaction heat. The reaction solution was then transferred to another container and left to stand for 24 hours, whereby concentration of the reaction product was performed.

After standing for 24 hours, the supernatant was removed, and the resulting concentrate was poured into a bottle with a cap having high airtightness so that the components in storage were not volatilized, and left to stand in the shade for 3 months for further concentration. The supernatant is then suitably removed to give a further concentrated reaction. The above-mentioned 24-hour standing and 3-month standing were both separation steps.

< pH adjustment >

To accelerate the dissociation of the excess heptanoic acid disposed around the particles, the concentrate was adjusted to ph7.3 by adding ammonia water to the concentrate. Immediately after the adjustment, the solution was left for 3 to 4 days to accelerate the dissociation of the excessive heptanoic acid. The supernatant obtained by standing for 3 and 4 days was also observed to be removed when the water-organic acid and its derivative emulsion in the upper part thereof was separated, to obtain a final concentrate having the silver concentration necessary for preparing the composition. In addition, the supernatant obtained by separation at this time was used for the silver concentration adjustment of the composition. This is because the pH of the composition does not change even when the composition is used for adjusting the silver concentration, and therefore, the silver nanoparticles do not change due to aggregation or the like.

< physicochemical compositions >

To improve adhesion to the substrate, a high T is added to the pH-adjusted concentrate_gT of Polymer_gIs a latex of a vinyl chloride copolymer at 73 ℃. In addition, a polyurethane thickener was added for viscosity adjustment, propylene glycol was added as a wetting agent, and the supernatant obtained after pH adjustment was added for silver concentration adjustment, followed by stirring, thereby obtaining a silver concentration of 60 mass% and a vinyl chloride copolymer latex of 3 mass% (T:)_g73 c), 2% by mass of a polyurethane thickener and 2.5% by mass of propylene glycol. The pH of the composition was the same as the pH of the pH adjusted concentrate, i.e., pH 7.3. In addition, the amount of heptanoic acid in the concentrate and the amount of heptanoic acid in the supernatant were examined in advance, and the amount of heptanoic acid in the composition was adjusted according to the amounts. Their properties are shown in table 1.

< examples 2 to 7 and comparative examples 1 and 2>

Compositions of examples 2 to 7 and comparative examples 1 and 2 were obtained in the same manner as in example 1, except that either ammonia water or nitric acid was added in the pH adjustment step to adjust the pH to the pH of examples 2 to 7 and comparative examples 1 and 2 shown in table 1. Their properties are shown in table 1. In addition, since the supernatant obtained in the separation step performed after the pH adjustment was used in order to adjust the silver concentration of the composition to the same level as in example 1, the pH of the composition was the same as the pH after the pH adjustment.

< comparative examples 3 and 4>

Comparative example 3 and comparative example 1 were produced in the same manner, and comparative example 4 and comparative example 2 were produced in the same manner, except that the silver concentration was adjusted to 40 mass% based on the total composition, to obtain compositions of comparative examples 3 and 4. The composition of comparative example 3 had a pH of 5.2 and the composition of comparative example 4 had a pH of 8.1. Their properties are shown in table 1.

< example 8 and comparative example 5>

The composition described in example 2 was stirred by a stirrer at 300 rpm. It was confirmed that the stirring was continued, and the ammonia component in the solution was volatilized, and thus the pH was gradually decreased as the stirring time was increased. By this stirring operation, samples of example 8 at pH5.3 and comparative example 5 at pH5.2 were obtained. That is, the pH at the time of concentration in example 8 and comparative example 5 was the same as that in example 2 and was 6.8, but the final pH was different between the two samples. Their properties are shown in table 1.

[ Table 1]

The compositions shown in examples 1 to 8 and comparative examples 1 to 5 thus obtained were coated on mirror coated paper (manufactured by Wang paper Co., Ltd.) using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 1.

As a result of comparison between examples 1 to 8 and comparative examples 1 to 5, it was observed that the pH of the ink (composition) greatly affects the rheology of the ink, and that the ink composition has a low shear rate (10 s) particularly at a pH of not more than 5.2 and not less than 8.1^-1) The viscosity of (3) is greatly increased.

In examples 1 to 8, it was confirmed that the coating on the substrate was good, and that good conductivity and adhesion to the substrate were reliably obtained even after the heat treatment.

In comparative example 1, since there was no fluidity, the viscosity could not be measured. In addition, it cannot be applied to a substrate. Comparative examples 2 and 5 were applied to a substrate, but the substrate had a large number of irregularities and no conductivity was obtained. Further, the adhesion was also confirmed to be insufficient.

Comparative examples 1 and 2 were prepared as comparative examples 3 and 4 by lowering the silver concentration to 40 mass% because the viscosity was too high. Although they can be applied to a substrate, they cannot obtain conductivity under the condition of heat treatment at 60 ℃ for 15 seconds.

In comparative examples 3 and 4, no conductivity was exhibited when the heat treatment conditions were 60 ℃ for 15 seconds, but a conductive film was obtained when the heat treatment conditions were 140 ℃ for 30 seconds. Specifically, the surface resistivity was 5.8. omega./□ in comparative example 3 and 4.4. omega./□ in comparative example 4. Further, it was also confirmed that the film adhesion was insufficient.

From the above results, it was confirmed that a composition having a pH of 5.3 to 8.0 was obtained and that a composition having excellent low-temperature sinterability was obtained. In addition, in the case of a composition having a pH outside the range of the present invention (5.3 to 8.0), when the composition is observed after being left to stand for 24 hours after the preparation thereof, the presence of a precipitate and a supernatant due to aggregation is observed, but the case is not observed in the case of a composition having a pH within the range.

< volume resistivity >

< example 1>

The composition shown in example 1 was coated on a PET (polyethylene terephthalate) film (Melinex (registered trademark) 545, manufactured by Dupont Techni film Co., Ltd.) using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200).

The obtained coating film had a thickness of 1.3 μm and a volume resistivity of 2X 10 when it was baked at 120 ℃ for 30 seconds^-5Omega cm. Further, when another coating film was fired at 100 ℃ for 30 seconds, the thickness of the fired film was 1.1 μm, and the volume resistivity was 2X 10^-5Omega cm. It was confirmed that a film having a volume resistivity equal to or lower than that of a conventional resin-curable silver paste was obtained under heat treatment conditions at a low temperature for a very short time.

< examples 9 to 12, comparative examples 5 and 6> Effect on the amount of heptanoic acid

< example 9>

< pH adjustment >

Until the concentrate, example 1 was repeated. In order to accelerate the dissociation of the excessive heptanoic acid disposed around the particles, the ph of the concentrate was adjusted to about 6.0 by adding ammonia water to the concentrate. Immediately after the adjustment, the solution was left for 3 to 4 days to accelerate the dissociation of the excessive heptanoic acid. The supernatant obtained by standing for 3 and 4 days was also observed to be removed when the water-organic acid and its derivative emulsion in the upper part thereof was separated, to obtain a final concentrate having the silver concentration necessary for preparing the composition. In addition, the supernatant obtained by separation at this time was used for the silver concentration adjustment of the composition.

< physicochemical compositions >

In order to improve the adhesion to the substrate, a high T is added to the concentrate whose pH is adjusted to about 6.0_gT of Polymer_gIs a latex of a vinyl chloride copolymer at 40 ℃. In addition, a polyurethane thickener is added for viscosity adjustment, propylene glycol is added as a wetting agent, and a supernatant obtained after pH adjustment is added for silver concentration adjustment, and stirring is performed, thereby obtaining silver relative to the total amount of the composition60% by mass of the concentration and 3% by mass of a vinyl chloride copolymer latex (T)_g40 c), a polyurethane thickener 2 mass%, propylene glycol 2.5 mass%, and a heptanoic acid concentration 4 mass% (the ratio to silver in table 2 is expressed as "6 mass%") of the composition of example 9. The pH of the composition was 5.9. The properties are shown in Table 2.

< example 10>

The composition of example 10 was obtained in the same manner as in example 9, except that the amount of heptanoic acid used in the raw material preparation step was 2 times that used, that is, 0.72 kg. The pH of the composition was 6.0. The properties are shown in Table 2.

< example 11>

< physicochemical compositions >

The same operation as in example 9 was performed until the composition was formed. In order to improve the adhesion to the substrate, a high T is added to the concentrate whose pH is adjusted to about 6.0_gT of Polymer_gIs a latex of a vinyl chloride copolymer at 40 ℃. In addition, a polyurethane thickener was further added for viscosity adjustment, propylene glycol as a wetting agent, and heptanoic acid so that the heptanoic acid concentration in the composition was 10 mass% (expressed as "14 mass%" in a ratio to silver in table 2).

The supernatant obtained after the pH adjustment was added for silver concentration adjustment, and after stirring, the pH was adjusted to about 6.0 again with ammonia because the pH was lowered by adding heptanoic acid, thereby obtaining a silver concentration of 60 mass% and a vinyl chloride copolymer latex of 3 mass% (T)_g40 c), 2% by mass of a polyurethane thickener, 2.5% by mass of propylene glycol, and 14% by mass of heptanoic acid with respect to silver of the composition of example 11. The pH of the composition was 6.1. The properties are shown in Table 2.

< example 12>

< physicochemical compositions >

The composition of example 12 was obtained by the same preparation method as that of example 11, except that the amount of heptanoic acid was added so that the heptanoic acid concentration became 20 mass% with respect to silver in the step of forming a composition. The properties are shown in Table 2.

< comparative example 6>

The synthesis and concentration of the particles were carried out under the conditions described in example 1, except that 1/2 times, that is, 0.18kg of heptanoic acid was used in the step of preparing the raw material.

< pH adjustment >

In order to accelerate the dissociation of the excessive heptanoic acid disposed around the particles, the ph of the concentrate was adjusted to about 6.0 by adding ammonia water to the concentrate as in example 9. Immediately after the adjustment, the solution was left for 3 to 4 days to accelerate the dissociation of the excessive heptanoic acid. The supernatant obtained by standing for 3 and 4 days was also observed to be removed when the water-organic acid and its derivative emulsion in the upper part thereof was separated, to obtain a final concentrate having the silver concentration necessary for preparing the composition. In addition, the supernatant obtained by separation at this time was used for the silver concentration adjustment of the composition.

< physicochemical compositions >

The additive was added and stirred in the same manner as in example 9, whereby the composition of comparative example 6 having a heptanoic acid concentration of 1 mass% with respect to silver was obtained. The properties are shown in Table 2.

< comparative example 7>

A composition of comparative example 7 was obtained by the same preparation method as in example 11, except that the amount of heptanoic acid was added so that the heptanoic acid concentration became 25 mass% with respect to silver in the step of forming a composition. The properties are shown in Table 2.

[ Table 2]

The compositions shown in examples 9 to 12 and comparative examples 6 and 7 thus obtained were coated on mirror coated paper (manufactured by Wang paper Co., Ltd.) by using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 2.

It is understood from comparison between examples 9 to 12 and comparative examples 6 and 7 that the heptanoic acid concentration in the composition has a large influence on the resistance value of the conductive film. In examples 9 to 12 in which the heptanoic acid concentration in the composition was in the range of 2 to 20 mass% relative to silver, conductive films having good conductivity and adhesion were obtained.

On the other hand, in the case of comparative example 6 in which the heptanoic acid concentration in the composition was 1 mass% with respect to silver, the aggregation of the particles was extremely intense, and the composition was produced but could not be applied to a substrate. From this, it is presumed that the amount of heptanoic acid protecting the silver nanoparticles is small, and therefore, the dispersed state cannot be maintained, and extremely sharp aggregation occurs.

In addition, in the composition of the heptanoic acid concentration relative to silver more than 20 mass% of the case of comparative example 7, although can produce composition, also can be coated, but after heat treatment of the film does not get resistance value, and the adhesion is extremely poor.

The reason for this is considered to be that since the boiling point of heptanoic acid is a temperature as high as 223 ℃, if present in excess, sintering of silver nanoparticle synthesis at the time of heat treatment is significantly hindered.

In order to accelerate the dissociation of the excessive heptanoic acid disposed around the particles, the ph of the concentrate was adjusted to about 6.0 by adding ammonia water to the above concentrate, and in examples 11 and 12 and comparative example 7, the change in low-temperature sinterability caused by the addition of heptanoic acid to the composition was examined. In examples 11 and 12, even when heptanoic acid was added, a significant increase in viscosity was not observed as in comparative example 1, and a significant deterioration in low-temperature sinterability was not observed. This fact, i.e., the increase in viscosity and the deterioration in low-temperature sinterability, leads to the following conclusion: the solubility of heptanoic acid in a solvent is low, and the excessive amount of heptanoic acid disposed around the particles has a great adverse effect.

When the heptanoic acid is soluble in the solvent and the amount of heptanoic acid around the particles is appropriate, even if a certain amount of heptanoic acid is soluble in the solvent, it is assumed that the characteristics are not adversely affected. Further, since the heptanoic acid molecules disposed around the particles reversibly repeat desorption/adsorption from the particles, it is assumed that a certain amount of heptanoic acid is present in the solvent, and is preferable from the viewpoint of storage stability and the like.

As described above, the heptanoic acid concentration is preferably 2 mass% or more and 20 mass% or less with respect to silver. More preferably, the content is 4 to 15 mass%.

< examples 13 to 15 and comparative example 8> influence on Ammonia concentration and nitric acid concentration in composition

< example 13>

< pH adjustment >

Until the concentrate, example 1 was repeated. The pH of the concentrate was adjusted to about pH7.0 by adding ammonia water and nitric acid to the concentrate obtained by standing for 3 months. Immediately after the adjustment, the solution was left for 3 to 4 days to accelerate the dissociation of the excessive heptanoic acid. The supernatant obtained by standing for 3 to 4 days was also observed to be removed when the separation of the water-organic acid and its derivative emulsion was observed in the upper part thereof, to obtain the final concentrate. In addition, the supernatant obtained by separation at this time was used for the silver concentration adjustment of the composition.

< physicochemical compositions >

To improve the adhesion to the substrate, a high T is added to the concentrate whose pH is adjusted to about 7_gT of Polymer_gIs a latex of a vinyl chloride copolymer at 7 ℃. In addition, a polyurethane thickener was added for viscosity adjustment, propylene glycol was added as a wetting agent, and the supernatant obtained after pH adjustment was added for silver concentration adjustment, followed by stirring, thereby obtaining a silver concentration of 60 mass% and a vinyl chloride copolymer latex of 3 mass%(T_gNo. 7 ℃), 2% by mass of a polyurethane thickener, 2.5% by mass of propylene glycol, and the composition had an ammonia concentration of 0.4% by mass and a nitric acid content of 1.0% by mass. The pH of the composition was 7.0. The properties are shown in Table 3.

< example 14>

The composition of example 14 having an ammonia concentration of 0.9 mass% and a nitric acid component of 2.7 mass% was obtained in the same manner as the preparation method of example 13 except that, in the pH adjustment, after adding a little more nitric acid than usual, ammonia was added so that the pH was about 7.0 in the same manner as in example 13 to adjust the pH. The pH of the composition was 7.3. The properties are shown in Table 3.

< example 15>

In the same manner as in the preparation method of example 13 except that the silver concentration was not adjusted by using the supernatant liquid obtained in the concentration step but was adjusted by using pure water in the formation of the composition, the composition of example 15 having an ammonia concentration of 0.2 mass% and a nitric acid content of 0.6 mass% was obtained. The pH of the composition was 7.2. The properties are shown in Table 3.

< comparative example 8>

Until the concentrate, example 1 was repeated. The concentrate obtained by standing for 3 months was filtered and washed to obtain a concentrated product. The concentrate is added as a high T for improving the adhesion to the substrate_gT of Polymer_gIs a latex of a vinyl chloride copolymer at 7 ℃. In addition, polyurethane thickeners are added for viscosity control, and propylene glycol is added as a wetting agent. Pure water was also added for silver concentration adjustment and stirring was performed, thereby obtaining a composition of comparative example 8. The ammonia concentration in the composition was 0.1 mass% or less, and the nitric acid content was 0.1 mass%. The pH of the composition was 7.0. The properties are shown in Table 3.

[ Table 3]

The compositions shown in examples 13 to 15 and comparative example 8 thus obtained were coated on mirror coated paper (manufactured by Wang paper Co., Ltd.) using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 3.

It is understood from comparison between examples 13 to 15 and comparative example 8 that the ammonia concentration and the heptanoic acid concentration in the composition have a large influence on the resistance value and the secondary aggregate particle diameter of the conductive film. If the ammonia concentration in the composition is 0.1 mass% and the nitric acid concentration is 0.1 mass% or less, the particles are strongly aggregated, and even if the composition is applied, the quality is poor and many pores are formed, and a uniform coating film cannot be obtained. Therefore, even when fired, the resistance value and the good adhesion were not obtained.

<Examples 16 to 19 and comparative example 9>Glass transition temperature (T)_g) Is different from

< pH adjustment >

Until the concentrate, example 1 was repeated. The pH was adjusted to about pH7.0 by adding ammonia water to the concentrate obtained by standing, and the concentrate was further left standing for 3 to 4 days immediately after the adjustment to accelerate the dissociation of the excessive heptanoic acid. The supernatant obtained by standing for 3 to 4 days was also observed to be removed when the separation of the water-organic acid and its derivative emulsion was observed in the upper part thereof, to obtain the final concentrate. In addition, the supernatant obtained by separation at this time was used for the silver concentration adjustment of the composition.

< physicochemical compositions >

In order to improve the adhesion to the substrate, a high T is added to the concentrate whose pH is adjusted to about 7.0_gGlass transition temperature (T) of the Polymer_g) Different vinyl chloride copolymer latexes. In addition, other polyurethane thickeners are added for viscosity adjustmentAdding propylene glycol as a wetting agent and adding a supernatant obtained after pH adjustment for silver concentration adjustment, and stirring to obtain a silver-containing silver paste composed of 60 mass% of silver, 3 mass% of vinyl chloride copolymer latex, 2 mass% of polyurethane thickener, and 2.5 mass% of propylene glycol, and having a pH of about T_gThe compositions of examples 16 to 19 and comparative example 9 were composed of different vinyl chloride copolymers. Their properties are shown in Table 4.

[ Table 4]

The compositions shown in examples 16 to 19 and comparative example 9 thus obtained were coated on mirror coated paper (manufactured by Wang paper Co., Ltd.) by using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 4.

As is clear from the comparison between examples 16 to 19 and comparative example 9, T of the vinyl chloride copolymer latex added for improving the adhesion to the substrate_gThe resistance value and adhesion of the conductive film are greatly affected. Confirm if T_gBelow 0c, the resistance increases sharply. The reason for this is considered to be if T_gIf the amount is too low, the polymer tends to adhere to the surface of the silver nanoparticles during storage of the composition or during printing, and therefore sintering inhibition occurs during heat treatment.

< examples 20 to 26 and comparative examples 10 and 11> others (different polymers, silver concentration)

< example 20>

Except for the addition of T_gThe same procedure for the preparation of example 16 was repeated except that the temperature was changed to 75 ℃ to obtain the composition of example 20. The properties are shown in Table 5.

< example 21>

Except for the addition of T_gThe same procedure for the preparation of example 16 was repeated except that the latex was a homopolymer of vinyl chloride at 70 ℃ to obtain the composition of example 21. The properties are shown in Table 5.

< example 22>

Except for the addition of T_gThe same procedure for the preparation of example 16 was repeated except that the temperature of the vinyl acetate copolymer latex was changed to 53 ℃ to obtain the composition of example 22. The properties are shown in Table 5.

< example 23>

Except for the addition of T_gThe same procedure for the preparation of example 16 was repeated except that the latex was a homopolymer of vinyl acetate at 65 ℃ to obtain a composition of example 23. The properties are shown in Table 5.

< example 24>

The same procedure for the preparation of example 22 was repeated except that the silver concentration was 70% by mass, to obtain a composition of example 24. The properties are shown in Table 5.

< example 25>

The same procedure for the preparation of example 22 was repeated except that the silver concentration was changed to 40% by mass, to obtain a composition of example 25. The properties are shown in Table 5.

< example 26>

The same procedure for the preparation of example 22 was repeated except that the silver concentration was 30% by mass, to obtain a composition of example 26. The properties are shown in Table 5.

< comparative example 10>

A composition of comparative example 10 was obtained in the same manner as in the preparation method of example 22 except that the silver concentration was 80 mass%. The properties are shown in Table 5.

< comparative example 11>

The same procedure for the preparation of example 22 was repeated except that the silver concentration was 10% by mass, to obtain a composition of comparative example 11. The properties are shown in Table 5.

[ Table 5]

The compositions shown in examples 20 to 26 and comparative examples 10 and 11 thus obtained were coated on mirror coated paper (manufactured by Wang paper Co., Ltd.) using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; line 200). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 5.

From the results of examples 20 to 23, it was confirmed that the same characteristics were obtained even when the types of the polymers were different. It is understood from comparison of examples 23 to 26 with comparative examples 10 and 11 that the silver concentration has a large influence on the resistance value of the conductive film.

The composition having a silver concentration of 80% by mass had no fluidity and could not be applied. In addition, it is considered that the composition having a silver concentration of 10 mass% may have an excessive solvent component, and therefore, sintering may not be sufficiently performed under the heat treatment condition of 60 ℃ for 15 seconds, and the resistance value may not be obtained. Further, the adhesion is not sufficient. Examples 25 and 26 can obtain conductivity. The reason why conductivity was obtained in examples 25 and 26 is not clear even when the silver concentration was 40 mass% in comparative examples 3 and 4 in which the pH was not within the appropriate range, but it is considered to be related to the difference in leveling property due to the difference in emulsion structure of the composition.

< examples 27 to 34> other

< example 27>

Except for the addition of T_gThe same procedure used in example 1 was repeated except that the temperature was changed to 7 ℃ to obtain a vinyl chloride copolymer latex, thereby obtaining a composition of example 27. The properties are shown in Table 6.

< examples 28 to 34>

Compositions of examples 28 to 34 were obtained in the same manner as in example 27 except that the amounts of the latex, the thickener and the propylene glycol as additives were the compositions shown in Table 6. The properties are shown in Table 6.

[ Table 6]

The compositions shown in examples 27 to 34 thus obtained were coated on mirror coated paper (manufactured by Wanzi paper Co., Ltd.) using Flexo Proof (manufacturer: RK printing apparatus, model: ESI12, texture; 200 lines). The obtained coating film was subjected to a heat treatment at 60 ℃ for 15 seconds to form a fired film. The surface resistivity and the adhesion obtained are shown in table 6.

From the results of examples 27 to 34, it was confirmed that there were printed matters having good conductivity and adhesion even if the amount and the ratio of the additive were changed.

Possibility of industrial utilization

The silver nanoparticle composition of the present invention is considered to be suitable for use in printed electronics, and can be used for products currently under investigation such as printed CPUs, printed illuminations, printed labels, full-print displays, sensors, printed wiring boards, organic solar cells, electronic books, nanoimprint LEDs, liquid crystal-PDP panels, printed memories, and RF-IDs.

Description of the symbols

1 RF-ID antenna

2 total length

3 total width

4 line width

5 base plate

7 IC

8 salient points

10 EMI shield

11 frame

12 base material

13 conductive pattern

20 Flexo Proof (フレキソプル - フ)

21 rubber plate

22 anilox ink transfer roller

23 scraper

24 coating

25 coating film

28 base material

Claims (16)

1. A silver nanoparticle composition characterized in that the main component of a solvent is water, the pH of the composition is in the range of 5.3 to 8.0, silver nanoparticles contained in the composition are protected by an organic acid or a derivative thereof, and the content of the organic acid or the derivative thereof is in the range of 2 to 20 mass% relative to silver;

the amount of the ammonia component in the composition is 0.1-2% by mass relative to the total amount of the composition;

the amount of the nitric acid component in the composition is 0.1-5% by mass relative to the total amount of the composition;

comprises a polymer obtained by polymerizing a monomer having a vinyl group;

the polymer obtained by polymerizing a vinyl group-containing monomer contains at least one of a vinyl chloride homopolymer, a vinyl chloride copolymer, a vinyl acetate homopolymer, and a vinyl acetate copolymer.

2. The silver nanoparticle composition according to claim 1, wherein the content of the silver nanoparticles is in the range of 15 to 75 mass% with respect to the total amount of the composition.

3. The silver nanoparticle composition according to claim 1 or 2, wherein the ammonia component is present in the composition in an amount of 0.2 to 0.9 mass% based on the total amount of the composition.

4. The silver nanoparticle composition according to claim 1 or 2, wherein the nitric acid component is present in the composition in an amount of 0.6 to 2.7% by mass based on the total amount of the composition.

5. The silver nanoparticle composition according to claim 1 or 2, wherein the silver nanoparticles have an average primary particle diameter of 100nm or less as measured by a transmission electron microscope.

6. The silver nanoparticle composition according to claim 1 or 2, wherein the organic acid or the derivative thereof is a carboxylic acid having 5 to 8 carbon atoms or a derivative thereof.

7. A silver nanoparticle composition according to claim 1 or 2, wherein the organic acid or derivative thereof is heptanoic acid or a derivative thereof.

8. The silver nanoparticle composition of claim 1 or 2, comprising a polymer characterized by a glass transition temperature Tg of from 0 ℃ to 100 ℃.

9. The silver nanoparticle composition according to claim 1 or 2, which comprises a water-dispersible polymer having at least one group selected from an OH group, a polyoxyethylene glycol group and a polyethylene glycol group.

10. The silver nanoparticle composition of claim 9, comprising a polymer having urethane linkages.

11. The silver nanoparticle composition according to claim 1 or 2, wherein the silver nanoparticle composition according to any one of claims 1 to 9 is applied to a substrate, and then the silver thin film is heat-treated at 60 ℃ for 15 seconds in the atmosphere, whereby the surface resistivity of the silver thin film is 100 Ω/□ or less.

12. A silver thin film and a wiring formed by using the silver nanoparticle composition according to any one of claims 1 to 11.

13. An RF-ID antenna, wherein a wiring formed by applying the silver nanoparticle composition according to any one of claims 1 to 11 to a substrate is converted into silver by firing to form a silver wiring, and the wiring forms an antenna portion of the RF-ID antenna.

14. An RF-ID insert using the antenna of claim 13.

15. An EMI shield characterized in that a wiring formed of the silver nanoparticle composition of any one of claims 1 to 11 is silvered by firing to form a silver wiring, the wiring forming a gate portion of the EMI shield.

16. An electronic circuit having silver wiring formed by firing a wiring formed by silvering by a printing method using the silver nanoparticle composition according to any one of claims 1 to 11.