TW201402252A - Silver microparticles, method for producing same, and electronic device, conductive film, and conductive paste containing said silver microparticles - Google Patents

Abstract

The present invention pertains to: silver microparticles having superior heat shrinkability and low-temperature sinterability, superior filling properties in a circuit pattern or electrode formed on a substrate, and an average particle size of 30-100 nm; a method for producing the silver microparticles; and an electronic device, conductive film, and conductive paste containing the silver microparticles. In the method for producing silver microparticles by preparing an aqueous solution (solution A) using silver nitrate and a high-molecular-weight protecting agent, preparing an aqueous solution (solution B) separately from solution A and resulting from dissolving a reducing agent and a low-molecular-weight protecting agent, dripping solution B into solution A, and isolating, cleaning, and drying silver microparticles obtained by reductive precipitation, regardless of the fact that the temperature of the mixed solution when dripping solution B into solution A is controlled to no greater than 40 DEG C and the silver microparticles obtained by means of vacuum freeze-drying in the drying step are microparticles having an average particle size of 30-100 nm, the silver microparticles have a high tapped density of at least 3.0 g/cm3, and so have superior filling properties in a circuit pattern or electrode formed on a substrate.

Description

Silver microparticles and manufacturing method thereof, and conductive paste, conductive film and electronic device containing the same

The present invention relates to a silver fine particle having an average particle diameter of 30 to 100 nm which is excellent in heat shrinkability and low-temperature sinterability, and which is excellent in filling property in an electrode or a circuit pattern formed on a substrate, a method for producing the same, and a conductive film containing the silver fine particles. Paste, conductive film and electronic device.

The electrode or circuit pattern of the electronic device is formed by printing an electrode or a circuit pattern on a substrate using a conductive paste containing metal particles, and then firing the metal particles contained in the conductive paste by heating, but In recent years, the heating and firing temperature tends to decrease.

For example, the mounting substrate of an electronic device can be generally heated to about 300 ° C, and a flexible substrate made of polyimide is used for excellent heat resistance. However, since it is expensive, PET (polyphenylene terephthalate) has been recently reviewed. A polyethylene dicarboxylate substrate or a PEN (polyethylene naphthalate) substrate is used as an alternative material. However, the PET substrate or the PEN substrate has lower heat resistance than the flexible substrate made of polyimide. In particular, the PET film substrate used in the film wiring board must be heated and fired at 150 ° C or lower.

Also, if it can be heated at a temperature lower than 200 ° C In addition, it is also possible to form an electrode or a circuit pattern on a substrate such as polycarbonate or paper, and it is expected to expand the use of various electrode materials and the like.

As a raw material of such a low-temperature fired conductive paste Metal particles, nano-sized silver particles are expected. The reason for this is that when the size of the metal particles becomes nanometer, the surface activity becomes high, and the melting point is lower than that of the metal block, so that sintering can be performed at a low temperature. Moreover, compared with other conductive particles such as copper, the silver fine particles are expensive, and even if they are easily caused to migrate in the metal particles, they are less susceptible to oxidation than copper having the same specific resistance. Easy to operate.

Moreover, the nano-sized silver particles can be sintered at a low temperature, the same When heat resistance is maintained at the time of one sintering, it is expected to be a substitute for lead-free solder by utilizing properties not found in conventional solders.

On the other hand, silver particles generally have a larger particle size. In the case of a small tap, the smaller the degree of tightness is, the fine wiring formed of the conductive paste containing the silver fine particles is less likely to increase the filling ratio of the silver fine particles, which is disadvantageous for the decrease in the resistance value.

In addition, the silver particles with low crystallinity of the particles will be heated. In the case of an electronic component, for example, in the case of an electronic component, the fine wiring formed of the conductive paste containing the silver fine particles is peeled off from the substrate, and the wiring becomes thin and becomes high resistance. The problem. Further, in powder metallurgy, problems such as deterioration in dimensional accuracy of the sintered body occur.

Heretofore, metal colloidal particles having a particle size distribution including metal nanoparticles and a dispersing agent have been proposed as metal colloidal particles containing metal nanoparticles which can form a hard film excellent in low-temperature sinterability (Patent Document 1). Further, silver fine particles bonded to a linear fatty acid having 6 or less carbon atoms as a protective agent have been proposed as fine silver particles which are also stably present in a polar solvent containing water (Patent Document 2). Further, as a silver powder having high dispersibility and having solder wettability and solder resistance, it is known that crystal particles having a minimum crystal grain size of at least 0.3 μm or more and a knocking degree of 4 g/cm ³ or more are known. A silver powder formed by a plurality of crystalline silver fine particles (Patent Document 3).

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1]: Special Opening 2010-229544

[Patent Document 2]: JP-A-2009-120949

[Patent Document 3]: JP-A-2011-1581

In the above-mentioned Patent Document 1, metal colloidal particles having a particle size distribution of the metal nanoparticle and the dispersing agent are disclosed, but the manufacturing method described in Patent Document 1 is not considered for the temperature control in the mixing of the silver nitrate solution and the reducing agent solution. Further, for the drying step, only the silver colloidal particle agglomerates were recovered by a pressure filter. Therefore, as shown in the comparative example described later, the silver colloidal particles obtained by the production method described in Patent Document 1 have a knocking degree of 3 g/cm ³ or less, and it is difficult to increase the silver by the fine wiring formed of the conductive paste containing the silver colloidal particles. The filling rate of the microparticles is not conducive to the reduction of the resistance value. Further, since the amount of the organic substance remaining on the surface of the silver fine particles is 2.5% by weight or more, it is difficult to be said to be excellent in low-temperature sintering property.

Further, in Patent Document 2, silver particles bonded to a linear fatty acid having 6 or less carbon atoms as a protective agent are disclosed, but as shown in a comparative example described later, the obtained silver fine particles have a knocking degree of 3 g/cm ³ or less, and Since the BET specific surface area value is also 7 m ² /g or more, it is difficult to increase the filling ratio of the silver fine particles by the fine wiring formed of the conductive paste containing the silver fine particles, which is disadvantageous in reducing the resistance value.

Patent Document 3 discloses a silver powder composed of polycrystalline silver particles containing at least one crystal grain having a minimum crystal grain size of 0.3 μm or more and a knock density of 4 g/cm ³ or more, but the minimum particle diameter is 0.21 μm. As described above, since the particle size is large, it is disadvantageous for the miniaturization of the fine electrode or circuit pattern printing formed on the substrate in recent years. Further, since the particle size is large, it is difficult to be said to be excellent in low-temperature sinterability.

Therefore, the technical problem of the present invention is to provide a fine particle having an average particle diameter (D _SEM ) of 30 to 100 nm and a high knocking degree of 3.0 g/cm ³ or more, and excellent heat shrinkability and low-temperature sinterability, and at the same time Silver fine particles excellent in filling property in an electrode or a circuit pattern formed on a substrate and a method for producing the same.

The above technical problems can be achieved by the present invention as follows.

That is, the present invention is a silver fine particle characterized by an average particle diameter (D _SEM ) of 30 to 100 nm and a tap density of 3.0 g/cm ³ or more (Invention 1).

Further, the present invention is the silver fine particles of claim 1, which has a BET specific surface area of 7.0 m ² /g or less (Invention 2).

Further, the present invention is the silver fine particles according to claim 1 or 2, which has a crystal grain size (D _x ) of 30 nm or more (Invention 3).

Further, the present invention is the silver according to any one of claims 1 to 3 The microparticles, wherein the residual amount of the organic substance on the surface of the silver fine particles is 0.5 to 2.0% by weight (Invention 4).

Furthermore, the present invention is the silver according to any one of claims 1 to 4. The fine particles have a heat shrinkage ratio at 240 ° C of 2.0% or more (Invention 5).

Moreover, the present invention is a conductive paste comprising, for example, The silver fine particles of any one of items 1 to 5 (Invention 6).

Moreover, the present invention is a conductive film which is used as such The conductive paste of Item 6 is formed (Invention 7).

In addition, the present invention is an electronic device having a request The conductive film of claim 7 (Invention 8).

Moreover, the present invention is a method of manufacturing silver microparticles, The method is characterized in that an aqueous solution (solution A) is prepared by using silver nitrate and a macromolecular protective agent, and the aqueous solution (solution B) is prepared by dissolving the reducing agent and the low molecular protection agent together with the liquid A, and the B liquid is added to the liquid A described above. In the method for producing silver fine particles obtained by separating, washing and drying the silver fine particles obtained by the precipitation, the mixed solution of the B liquid droplets added to the liquid A The temperature was controlled to be 40 ° C or lower while the drying step was carried out by vacuum freeze drying (Invention 9).

Further, the present invention is the manufacture of silver fine particles as claimed in claim 9. The method wherein the moisture content of the hydrate before vacuum freeze-drying is 30% or more (Invention 10).

Further, the present invention is a silver microparticle according to claim 9 or 10. The production method, wherein the silver fine particles obtained are the silver fine particles according to any one of claims 1 to 5 (Invention 11).

In general, the smaller the particle size of the silver fine particles, the smaller the tapping degree tends to be. However, in the method for producing the silver fine particles of the present invention, although the silver fine particles are fine particles having an average particle diameter (D _SEM ) of 30 to 100 nm, However, since silver fine particles having a high knocking degree of 3.0 g/cm ³ or more are obtained, it is suitable as a method for producing silver fine particles excellent in low-temperature sinterability and filling property in an electrode or a circuit pattern.

Further, in the silver fine particles of the present invention, although the obtained silver fine particles are fine particles having an average particle diameter (D _SEM ) of 30 to 100 nm, they have a high knocking degree of 3.0 g/cm ³ or more, and are suitable for the silver fine particles. It is a raw material of a conductive paste or the like which is excellent in filling property in an electrode or a circuit pattern formed on a substrate.

The structure of the present invention will be described in more detail below.

First, the silver fine particles of the present invention will be described.

The silver fine particles of the present invention are characterized by an average particle diameter (D _SEM ) of 30 to 100 nm and a knocking degree of 3.0 g/cm ³ or more.

The average particle diameter (D _SEM ) of the silver fine particles of the present invention is 30 to 100 nm, preferably 35 to 95 nm, more preferably 40 to 90 nm. By setting the average particle diameter (D _SEM ) within the above range, it is easy to refine the electronic device obtained by the above. When the average particle diameter (D _SEM ) is less than 30 nm, the surface activity of the silver fine particles is high, and it is not preferable to adhere a large amount of organic substances in order to maintain the fine particle diameter stably.

The knocking degree of the silver fine particles of the present invention is 3.0 g/cm ³ or more, preferably 3.5 g/cm ³ or more, more preferably 4.0 g/cm ³ or more. When the knocking degree is less than 3.0 g/cm ³ , it is difficult to increase the filling ratio of the silver fine particles by the fine wiring formed of the conductive paste containing the silver fine particles, which is disadvantageous in reducing the resistance value. The upper limit of the knocking degree of the silver fine particles is about 6.0 g/cm ³ , more preferably about 5.5 g/cm ³ .

The silver particles of the present invention is preferably a value of BET specific surface area 7m ² / g or less, more preferably 6m ² / g or less. When the BET specific surface area value exceeds 7 m ² /g, the viscosity of the conductive paste obtained by using it becomes high, which is not preferable. The silver particles BET specific surface area value below the limit value is about 1.5m ² / g, more preferably about 2.0m ² / g.

The crystal grain size (D _x ) of the silver fine particles of the present invention is preferably 30 nm or more, more preferably 35 to 95 nm, and still more preferably 40 to 90 nm. When the grain size (D _x ) is less than 30 nm, the silver particles become unstable, and partial sintering will start to occur even at normal temperature. Melting is not good.

The degree of crystallization of the silver fine particles of the present invention [ratio of the average particle diameter (D _SEM ) to the crystal grain size (D _x ) (D _SEM /D _x )] is preferably 2.7 or less, more preferably 2.5 or less, and further Good for 2.3 or less. The closer the degree of crystallization is to 1, the more it appears as a single crystal. When the degree of crystallization exceeds 2.7, the thermal shrinkage rate of the silver fine particles is increased. Therefore, the fine wiring formed of the conductive paste obtained by using the conductive paste is peeled off from the substrate, and the wiring becomes fine and becomes a problem of high electrical resistance.

The residual amount of organic substances on the surface of the silver microparticles of the invention is better It is 0.5 to 2.0% by weight, more preferably 0.6 to 1.9% by weight, still more preferably 0.7 to 1.8% by weight. When the residual amount of the organic substance on the surface of the silver fine particles exceeds 2.0% by weight, the amount of organic substances present on the surface of the silver fine particles is excessive, and the low-temperature sinterability is impaired. On the other hand, when it is less than 0.5% by weight, the wettability to the solvent and the resin is lowered, so that the uniform dispersibility of the conductive paste obtained by using it is impaired.

The heat shrinkage rate of the silver microparticles of the invention is 240 ° C The shrinkage ratio is preferably 2.0% or more, more preferably 2.1% or more. Generally, a silver coating film formed of a conductive paste containing silver fine particles generates a narrow gap between the silver fine particles, and a silver film having a lower resistance can be obtained by eliminating the gap, but the silver fine particle of the present invention Since the heat shrinkage rate at 240 ° C is as high as 2.0% or more, the gap between the silver fine particles of the coating film formed using the conductive paste obtained therefrom is easily buried, so that the electric resistance value can be further reduced.

The particle shape of the silver microparticles of the present invention is preferably spherical or granular.

Next, the method for producing silver microparticles of the present invention is added To describe.

The silver microparticles of the present invention can be used by using silver nitrate and high The aqueous solution (solution A) is prepared by a molecular protection agent, and the aqueous solution (solution B) is prepared by dissolving the reducing agent and the low molecular protection agent together with the liquid A, and the B liquid droplet is added to the liquid A to cause precipitation reduction. Silver particles are separated. Wash. In the method for producing dry silver fine particles, the temperature of the mixed solution in which the B liquid droplet is added to the liquid A is controlled to 40 ° C or lower, and the drying step is carried out by vacuum freeze drying.

First, use silver nitrate and a polymer protective agent to prepare water-soluble Liquid (liquid A). The polymer protective agent in the present invention is preferably water-soluble or water-soluble. Further, it is preferred to have an acid value, and it is preferred to use an acid value of 1 mgKOH/g or more, more preferably 10 mgKOH/g or more. The upper limit of the acid value can be used without particular limitation. However, when the acid value is 0 mgKOH/g, silver particles having a large particle size are formed, so that it is difficult to obtain fine silver fine particles of 100 nm or less. Further, the amine value is preferably 0 mgKOH/g. When a polymer protective agent having an amine value is used, a silver amine complex is formed when mixed with silver nitrate, and it takes a very long time to complete the reduction reaction or the reduction reaction, and thus the silver fine particles obtained are poorly distributed, which is not preferable. . Further, the polymer protective agent may be used singly or in combination of two or more.

The number average molecular weight of the polymer protective agent is preferably 1,000. Preferably, it is 1,000 to 150,000, and more preferably 5,000 to 100,000.

In addition, the above polymer protective agent can be used in combination with acrylic acid General commercial products such as polymers or polyoxyalkylene-based resins, specifically listed as DISPERBYK-190, DISPERBYK-194, DISPERBYK-2015, DISPERBYK-2090, DISPERBYK-2091, DISPERBYK-2095 (manufactured by BYK Co., Ltd., Japan); AKM-0531, HKM-50A, AKM-1511-60, AFB-1521 (manufactured by Nippon Oil Co., Ltd.), and the like. These polymer protective agents can be used singly or in combination of two or more.

The amount of the polymeric protective agent added is relatively good relative to the silver fine particles. It is 1 to 10% by weight, more preferably 1.5 to 8% by weight. When the amount of the polymer protective agent added is less than 1% by weight, the particle size of the obtained silver fine particles becomes large, which is not preferable. When the amount is more than 10% by weight, the residual amount of the organic substance on the surface of the obtained silver fine particles exceeds 2.0% by weight, so that the low-temperature sinterability is impaired.

The reducing agent in the present invention can be used in water solubility or water solubility. However, hydrazine, borohydride alkali salt, lithium aluminum hydride, ascorbic acid, erythorbic acid and the like are not preferable because the reducing power is too strong. In terms of reducing power, an amine alcohol can be preferably used in the present invention, more preferably N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-diethylisopropyl An amine-based alcohol having a tertiary amine such as an alcoholamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-n-butyldiethanolamine or N-t-butyldiethanolamine.

The amount of reducing agent added is better than that of silver nitrate. The original agent is 2.0 to 5.0 moles, more preferably 2.2 to 4.0 moles. When the amount of the reducing agent added is less than 2.0 mol per mol of silver nitrate, the reduction reaction is not sufficiently performed, which is not preferable.

Next, in addition to the aforementioned liquid A, the reducing agent and the low molecule are additionally protected. The protective agent is dissolved to prepare an aqueous solution (solution B). Low molecular protection when a low molecular weight protective agent is added to an aqueous solution containing silver nitrate (solution A) to prepare an aqueous solution The protective agent reacts with silver nitrate to form silver carboxylate to lower the yield of the silver fine particles, and at the same time, the silver fine particles obtained by this are poor in distribution.

The low molecular protection agent of the present invention can use a carboxyl group having 3 to 7 carbon atoms. acid. Preferred are propionic acid, caproic acid and heptanoic acid, more preferably caproic acid and heptanoic acid. The longer the carbon chain of the low molecular protection agent, the easier it is to obtain silver fine particles with a higher degree of knock. The low molecular weight protective agent may be used singly or in combination of two or more.

The amount of low molecular protection agent added is 1 mol relative to silver nitrate Preferably, the low molecular protection agent is 0.05 to 0.4 moles, more preferably 0.1 to 0.35 moles. When the amount of the low molecular weight protecting agent added is more than 0.4 mol with respect to 1 mol of silver nitrate, the silver fine particles formed tend to aggregate with each other, which is not preferable.

An aqueous solution in which a reducing agent and a low molecular protective agent are dissolved (B The liquid is added dropwise to an aqueous solution (liquid A) prepared by using silver nitrate and a macromolecular protective agent to carry out a mixing reaction. The temperature at the time of the mixing reaction rises to 50 ° C or more although the temperature control is normally carried out, but in the present invention, it is preferably controlled in the range of 25 to 40 ° C, more preferably in the range of 30 to 35 ° C. When the temperature at the time of the mixing reaction exceeds 40 ° C, the distribution of the generated silver fine particles tends to be uneven and is not preferable.

After adding the above liquid B, the reaction solution is heated to At 60 to 80 ° C, stirring is carried out to complete the reduction reaction. The heating temperature of the reaction solution is preferably from 65 to 75 °C. When the heating temperature of the reaction solution is less than 60 ° C, it takes a very long time until the reduction reaction is completed, which is industrially disadvantageous. Further, when the heating temperature exceeds 80 ° C, the silver fine particles formed tend to aggregate with each other, which is not preferable. The reduction reaction is used as an end point when the pH of the reaction solution becomes constant. The reduction reaction is preferably carried out as slowly as possible, in this respect, Low molecular weight protectants are preferably used as long as possible with long chain fatty acids.

The reaction solution after the reduction reaction is repeatedly subjected to decantation and water After washing until the conductivity of the supernatant liquid becomes 50 μS/cm or less, the hydrate containing the obtained silver fine particles is vacuum-dried, and then the silver fine particles of the present invention are obtained by pulverization by a usual method. When vacuum freeze-drying is not performed, when it is dried by a usual dryer, the silver fine particles become a large block and cannot be taken out, and the subsequent pulverization treatment becomes extremely complicated, and at the same time, it is necessary to apply a necessary shear force to the silver fine particles. Therefore, the obtained particles are coarsened and the knocking degree is lowered, so that the silver fine particle powder of the object of the present invention cannot be obtained.

Vacuum freeze-drying is to place the hydrate containing silver particles After the dryer, the pressure was reduced until the product temperature became -40 to -10 ° C, and then the temperature was raised to about 40 ° C and maintained for 2 hours or more.

a hydrate containing silver particles when vacuum freeze-dried The water content is preferably 30% or more, more preferably 35 to 80%, and even more preferably 40 to 70%. When the water content is less than 30%, even if vacuum freeze-drying is carried out, as in the case of using a normal dryer as described above, the silver fine particles become a large block and cannot be taken out, and the obtained particles are coarsened, and the knocking degree is lowered, so that the present invention cannot be obtained. Silver microparticle powder for the purpose.

The present invention can be produced by the above method for producing silver fine particles Silver microparticles as described in 1~5. In other words, as a preferred method for producing the silver fine particles described in the first to fifth aspects of the invention, the above-described production methods (inventions 9 and 10) are exemplified.

Next, the conductive paste containing the silver fine particles of the present invention It is described.

The conductive paste of the present invention may be a calcined paste and polymerized Any form of the paste of the type is composed of the silver fine particles and the glass frit of the present invention in the case of firing the paste, and other components such as a binder resin and a solvent may be blended as needed. Further, in the case of the polymer type paste, it is composed of the silver fine particles and the solvent of the present invention, and other components such as a binder resin, a curing agent, a dispersing agent, and a rheology adjusting agent may be blended as needed.

As for the binder resin, a person skilled in the art can be used. For example, a cellulose resin such as ethyl cellulose or nitrocellulose, a polyester resin, a urethane-modified polyester resin, an epoxy-modified polyester resin, an acrylic modified polyester, or the like. Various modified polyester resin, polyurethane resin, vinyl chloride. Vinyl acetate copolymer, acrylic resin, epoxy resin, phenol resin, alkyd resin, butyral resin, polyvinyl alcohol, polyimide, polyamidimide, and the like. These binder resins may be used alone or in combination of two or more.

As the solvent can be used, it is exemplified in the art. Such as tetradecane, toluene, xylene, ethylbenzene, diethylbenzene, cumene, pentylbenzene, p-isopropyl cymene, tetrahydronaphthalene and petroleum-based aromatic hydrocarbon mixtures, etc. Hydrocarbon solvent; ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-telebutyl ether, diethylene glycol An ether such as alcohol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether or tripropylene glycol monomethyl ether, or a glycol ether solvent; ethylene glycol single Methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate a glycol ester solvent such as an ester; a ketone solvent such as methyl isobutyl ketone or cyclohexanone; terpineol, linalool, geraniol, citronellol Or a terpene alcohol; an alcohol solvent such as n-butanol, a second butanol or a third butanol; a glycol solvent such as ethylene glycol or diethylene glycol; and γ-butyrolactone; And water, etc. The solvent may be used singly or in combination of two or more.

The content of silver microparticles in the conductive paste is based on the use However, it is preferably as close as possible to 100% by weight as much as possible, for example, in the case of wiring formation.

The conductive paste of the present invention can be used by using a crushing machine or a can Grinding machine, three-axis roller grinder, rotary mixer, two-axis kneading machine and other mixing machines, dispersing machines, so that the components are mixed. Obtained by dispersion.

The conductive paste of the invention can be used for screen printing and spraying Various coating methods such as ink method, gravure printing, transfer printing, roll coating, flow coating, spray coating, spin coating, dipping, blade coating, and plating.

In addition, the conductive paste of the present invention can be used as an FPD (Flat panel display), electrode formation of a solar cell, an organic EL, or the like, or wiring of an LSI substrate, and a wiring forming material such as a fine groove, a through hole, or a buried hole of a contact hole can be used. Moreover, it can be suitably used for high-temperature baking applications for forming an internal electrode of a laminated ceramic capacitor or a laminated inductor, and of course, it can be suitably used as a flexible substrate or an IC card because it can be fired at a low temperature. And wiring forming materials and electrode forming materials on other substrates. Moreover, it can also be used as a conductive film for an electromagnetic wave shielding film. Or infrared reflection shielding. It is also possible to use a bonding material for component mounting in electronic mounting.

<effect>

The present invention is directed to the fact that the silver fine particles of the present invention have excellent heat shrinkability and are excellent in filling property in an electrode or a circuit pattern formed on a substrate.

The reason why the silver fine particles of the present invention are excellent in the filling property in the electrode or the circuit pattern formed on the substrate is considered to be because the obtained silver fine particles are microparticles having an average particle diameter (D _SEM ) of 30 to 100 nm. By having a high knockness of 3.0 g/cm ³ or more. That is, it is difficult to increase the filling ratio of the silver fine particles by the fine wiring formed of the conductive paste containing the silver fine particles having a low knocking degree, which is disadvantageous for the reduction of the electric resistance value, but the silver fine particles generally have a smaller particle size and a tighter degree of tightening. Small tendency, it is difficult to meet the characteristics of both particle size and knock tightness. However, since the silver fine particles of the present invention are fine particles having an average particle diameter (D _SEM ) of 30 to 100 nm and have a high knocking degree of 3.0 g/cm ³ or more, it is considered that an electrode or a circuit pattern formed on a substrate can be obtained. Excellent filling in the middle.

[Examples]

The invention is specifically illustrated by the following examples of the invention, but the invention is not limited to the examples below.

The average particle diameter of the silver microparticles was photographed using a scanning electron microscope photograph "S-4800" (manufactured by HITACHI), and the particle diameter of 100 or more particles was measured using the photograph, and the average value was calculated as an average particle diameter (D). _SEM ).

The specific surface area of silver particles is "Monosorb MS- 11 (manufactured by Quantachrome Co., Ltd.), expressed by the value measured by the BET method.

The knocking degree of silver particles (ρt) is measured by oscillating specific gravity The device was placed in a 25 ml tight-fitting container, filled into a full cup of the container, and tapped for 600 times with a tapping length of 25 mm.

The residual amount of organic matter of silver particles is a thermal analysis device (EXSTAR 6000 TG/DTA6300 manufactured by Seiko Instruments Inc.) was heated from room temperature (30 ° C) to 550 ° C at 10 ° C/min under conditions of flowing dry air at 300 ml/min, and started from heating (30 ° C). The amount of the sample is subtracted until the end of the amount of reduction (the amount of the sample at the time when the silver fine particles start to oxidize (although depending on the sample, but 250 to 300 ° C) is expressed.

The grain size (D _X ) of the silver fine particles was obtained by using an X-ray diffraction device "RINT 2500" (manufactured by RIGAKU Co., Ltd.), and the surface index (1, 1, 1) was obtained by using the Kα line of Cu as a line source. The half value of the peak is wide, and the grain size is calculated by Scherrer's formula.

The degree of crystallinity of the silver fine particles is expressed by the ratio of the average particle diameter (D _SEM ) to the crystal grain size (D _X ) (D _SEM /D _X ).

Thermal shrinkage of silver particles using a thermomechanical analyzer "Thermo Plus2 TMA8310" (made by RIGAKU Co., Ltd.) Manufactured into a granular silver microparticle sample prepared by applying a temperature of 5 ° C / min from 30 to 300 ° C to form a particle having a height of 5 mm into a mold having a diameter of 4 mm and applying a load of 1,225.8 N to the silver microparticles. The length of the sample was measured, and the value was calculated according to the following number 1.

<number 1>

Thermal shrinkage at 240 ° C (%) = {(sample length of sample at 30 ° C - length of sample at 240 ° C) / sample length of 30 ° C} × 100

The specific resistance of the conductive coating film was applied to a polyimide film by applying a conductive paste to be described later, and after pre-drying at 120 ° C, it was heat-cured at 150 ° C for 10 minutes, and then immersed in 1 mol of HCl. The conductive film obtained by heating and drying at 150 ° C for 1 minute in an aqueous solution for 20 seconds was measured by a 4-terminal resistance measuring device "ROLESTA GP/MCP-T600" (manufactured by Mitsubishi Chemical Corporation). The sheet resistance and the film thickness were calculated as specific resistance.

<Example 1A-1: Production of Silver Fine Particles>

In a 60 L container, 2.8 kg of silver nitrate and 25.2 L of water and a polymer protective agent "DISPERBYK-190" (trade name: manufactured by Japan BYK Co., Ltd.) (acid value: 10 mgKOH/kg, amine price: 0 mgKOH/kg), 89 g, were mixed. . Stir the preparation of solution A. In addition, 4.41 kg of N,N-dimethylethanolamine and 214.5 g of heptanoic acid as a low molecular protection agent were added to a 50 L vessel for mixing. After stirring, add 18.8L of water for mixing. Stir and prepare solution B.

Next, the temperature of the mixed solution was controlled at 32 ° C while On the lower side, B liquid was added to the A liquid, and the temperature was raised to 70 ° C, and the mixture was stirred for 3 hours, and allowed to stand for 30 minutes to precipitate a solid component. After removing the supernatant, wash it with pure water and repeat the decantation. Wash until the conductivity of the supernatant is 50 μS/cm or less.

The hydrate containing the silver-containing microparticles is placed in a vacuum freeze-dried In the dryer, the degree of vacuum is about 10 Pa and the temperature is -30 ° C to self-freeze. Subsequently, the temperature was raised to 40 ° C in a state where the degree of vacuum was maintained at 10 Pa (the product temperature was about 30 ° C), and after maintaining this state for 2 hours, the silver fine particles of Example 1-1 were obtained by pulverization.

The particle shape of the obtained silver fine particles was granular, the average particle diameter (D _SEM ) was 75 nm, the crystal grain size (D _x ) was 45.2 nm, the degree of crystallinity (D _SEM /D _x ) was 1.7, and the knocking degree (ρt) was obtained. The content was 4.55 g/cm ³ , the BET specific surface area was 3.1 m ² /g, the residual amount of organic matter was 1.36 wt%, and the heat shrinkage ratio was 2.58%.

<Example 2A-1: Production of Conductive Paste>

To 100 parts by weight of the silver fine particles of Example 1A-1, 11.0 parts by weight of a polyester resin and 1.4 parts by weight of a curing agent were added, and diethylene glycol monoethyl ether was added so that the content of silver fine particles in the conductive paste became 70% by weight. , use rotation. The remixing machine "AWATORY ritaro ARE-310" (manufactured by THINKY Co., Ltd., registered trademark) was premixed and then uniformly kneaded using a triaxial roller. Dispersion treatment to obtain a conductive paste.

The conductive paste obtained above was applied to a film thickness of 50 μm. On the polyimine film, after pre-drying at 120 ° C, heat-hardening at 150 ° C for 10 minutes, immersed in 1 mol of HCl aqueous solution for 20 seconds, washed with water, and then dried at 150 ° C for 1 minute, to obtain electricity. Sex film.

The specific resistance of the obtained conductive coating film is 7.3 μΩ. Cm.

Examples 1A-2 to 1A-3 and Comparative Example 1A-1:

Silver fine particles are obtained by changing various generation conditions of silver fine particles.

The manufacturing conditions at this time are shown in Table 1, and the properties of the obtained silver fine particles are shown in Table 2.

Comparative Example 1A-2: JP-A-2010-229544 (additional test of Example 1)

66.8 g of silver nitrate, 10 g of acetic acid having a carboxyl group as an agglomeration aid, and 2.0 g of a polymer dispersant "DISPERBYK-190" (trade name: manufactured by Japan BYK Co., Ltd.) as a polymer dispersant were put into ion exchange. In 100 g of water, stir vigorously. After 100 g of N,N-dimethylethanolamine was slowly added thereto, the reaction solution was heated to 60 °C. The mixture was heated and stirred for 2 hours in a water bath set at 70 ° C without lowering the liquid temperature to 50 ° C. After 1 hour, silver colloidal particle agglomerates were obtained as a gray precipitate.

Next, the supernatant solution on which the silver colloidal particle agglomerates were precipitated was removed, and diluted with ion-exchanged water. After standing, the supernatant was removed and further diluted with methanol. After standing again, the supernatant was removed and diluted with methanol. Subsequently, silver colloidal particle agglomerates were collected by a pressure filter equipped with a membrane filter (manufactured by ADVENTECH Co., Ltd., pore size: 0.5 μm). The properties of the obtained silver colloidal particle agglomerates are shown in Table 2.

Comparative Example 1A-3: JP-A-2009-120949 (additional test of Example 1)

273 g of water was fed into a reaction tank of a 1 L beaker, and nitrogen gas was flowed through the lower portion of the reaction vessel at a flow rate of 500 mL/min for 600 seconds to remove residual oxygen, and then nitrogen gas was supplied from the upper portion of the reaction vessel at a flow rate of 500 mL/min to cause a reaction. The tank becomes a nitrogen atmosphere. The rotation speed of the stirring bar was adjusted to 280 to 320 rpm, and the temperature was adjusted so that the temperature of the solution in the reaction tank became 60 °C.

7.5 g of ammonia water (30% by mass in terms of ammonia) was placed in the reaction vessel, and the mixture was stirred for 1 minute to make the liquid uniform. Then, 7.5 g of hexanoic acid (corresponding to 2.01 mol of silver) as a protective agent was added, and the mixture was stirred. Minutes to dissolve the protective agent. Subsequently, 20.9 g of a 50% by weight aqueous solution of hydrazine hydrate as a reducing agent was added.

In a separate container, 36 g of silver nitrate crystals were dissolved in 175 g of water to prepare an aqueous solution of silver nitrate, which was used as a raw material liquid. Further, the aqueous silver nitrate solution was adjusted to a temperature of 60 ° C in the same manner as the solution in the reaction tank.

Subsequently, the raw material liquid is added to the reducing liquid in a single addition to carry out a reduction reaction. Stirring was continued, and the mixture was directly cooked for 10 minutes in this state. Then, stop stirring and filter. The water washing step and the drying step obtain a block of tiny silver particles. The characteristics of the obtained minute silver particle pieces are shown in Table 2.

<Manufacture of Conductive Coatings> Examples 2A-2 to 2A-3 and Comparative Examples 2A-1 to 2A-3:

In addition to the type of the silver fine particles, the conductive paint and the conductive film were produced in accordance with the method for producing a conductive paint of the above Example 2A-1.

The production conditions at this time and the properties of the obtained conductive coating film are shown in Table 3.

<Example 1B-1: Production of Silver Microparticles>

In a 60 L container, 2.8 kg of silver nitrate and 25.2 L of water and a polymer protective agent "DISPERBYK-190" (trade name: manufactured by Japan BYK Co., Ltd.) (acid value: 10 mgKOH/kg, amine price: 0 mgKOH/kg) 92 g were added and mixed. . Stir the preparation of solution A. In addition, 4.41 kg of N,N-dimethylethanolamine and 214.5 g of heptanoic acid as a low molecular protection agent were added to a 50 L vessel for mixing. After stirring, add 18.8L of water for mixing. stir Mix and modulate liquid B.

Next, while controlling the temperature of the mixed solution to be below 35 ° C B liquid was added to the A liquid, and the temperature was raised to 70 ° C, and the mixture was stirred for 3 hours, and allowed to stand for 30 minutes to precipitate a solid component. After removing the supernatant, wash it with pure water and repeat the decantation. Wash until the conductivity of the supernatant is 50 μS/cm or less.

The obtained hydrate containing 55% of the water content of the silver microparticles is placed Into the vacuum freeze dryer, the vacuum is about 10Pa, and the product temperature is -30 °C to freeze itself. Subsequently, the temperature was raised to 40 ° C while maintaining the degree of vacuum at 10 Pa (the product temperature was about 30 ° C), and after maintaining this state for 2 hours, the silver fine particles of Example 1B-1 were obtained by pulverization.

The obtained silver fine particles have a granular shape, an average particle diameter (D _SEM ) of 72 nm, a crystal grain size (D _x ) of 41.8 nm, a crystallinity (D _SEM /D _x ) of 1.7, and a knocking degree (ρt). The content was 4.59 g/cm ³ , the BET specific surface area was 3.5 m ² /g, the residual amount of organic matter was 1.37 wt%, and the heat shrinkage ratio was 2.63%.

<Example 2B-1: Production of Conductive Paste>

To 100 parts by weight of the silver fine particles of Example 1B-1, 11.0 parts by weight of a polyester resin and 1.4 parts by weight of a curing agent were added, and diethylene glycol monoethyl ether was added to make the content of silver fine particles in the conductive paste 70% by weight. Use rotation. The remixing machine "AWATORY ritaro ARE-310" (manufactured by THINKY Co., Ltd., registered trademark) was premixed and then uniformly kneaded using a triaxial roller. Dispersion treatment to obtain a conductive paste.

The conductive paste obtained above was applied to a film thickness of 50 μm. On the polyimide film, after pre-drying at 120 ° C, heat-hardening at 150 ° C for 10 minutes, immersed in a 1 molar aqueous solution of HCl for 20 seconds, washed with water, and then dried by heating at 150 ° C for 1 minute to obtain electricity. Sex film.

The specific resistance of the obtained conductive coating film is 7.5 μΩ. Cm.

Examples 1B-2 to 1B-3 and comparative particles 1B-1 to 1B-2:

Silver fine particles are obtained by changing various generation conditions of silver fine particles.

The manufacturing conditions at this time are shown in Table 4, and the characteristics of the obtained silver fine particles are shown in Table 5.

Comparative Example 1B-3:

The same as Comparative Example 1A-2 described above. The properties of the aggregates of the obtained silver colloidal particles are shown in Table 5.

Comparative Example 1B-4:

The same as Comparative Example 1A-3 described above. The characteristics of the obtained minute silver particle block are shown in Table 5.

<Manufacture of Conductive Coatings> Examples 2B-2 to 2B-3 and Comparative Examples 2B-1 to 2B-4:

In addition to the type of the silver fine particles, the conductive paint and the conductive film were produced in accordance with the method for producing a conductive paint of the above Example 2B-1.

The production conditions at this time and the properties of the obtained conductive coating film are shown in Table 6.

[Industrial Applicability]

In general, the smaller the size of the silver fine particles, the smaller the knocking degree tends to be. However, the silver fine particles obtained by the method of the present invention have the above-mentioned average particle diameter (D _SEM ) of 30 to 100 nm. Since 3.0 g/cm ³ or more has a high degree of tightness, it is suitable as a method for producing silver fine particles excellent in low-temperature sinterability and filling property in an electrode or a circuit pattern.

Further, in the above-described production method, the silver fine particles of the present invention are preferably formed on a substrate, although they have fine particles having an average particle diameter (D _SEM ) of 30 to 100 nm and have a high knocking degree of 3.0 g/cm ³ or more. A raw material such as a conductive paste excellent in filling property in an electrode or a circuit pattern.

Claims (11)

A silver fine particle having an average particle diameter (D _SEM ) of 30 to 100 nm and a tap density of 3.0 g/cm ³ or more. The silver fine particles of claim 1 have a BET specific surface area of 7.0 m ² /g or less. The silver fine particles of claim 1 or 2 have a crystal grain size (D _x ) of 30 nm or more. The silver fine particles according to any one of claims 1 to 3, wherein the residual amount of the organic substance on the surface of the silver fine particles is 0.5 to 2.0% by weight. The silver fine particles according to any one of claims 1 to 4, which have a heat shrinkage ratio at 240 ° C of 2.0% or more. A conductive paste comprising the silver fine particles according to any one of claims 1 to 5. A conductive film formed using the conductive paste of claim 6. An electronic device having the conductive film of claim 7. A method for producing silver microparticles, which comprises preparing an aqueous solution (liquid A) using silver nitrate and a macromolecular protective agent, and dissolving the reducing agent and the low molecular protective agent in the liquid A to prepare an aqueous solution (solution B). a method in which B droplets are added to the liquid A to separate, wash, and dry the silver fine particles obtained by the reduction and precipitation, and the temperature of the mixed solution when the B liquid droplets are added to the liquid A is controlled at 40. Below °C, the drying step is carried out by vacuum freeze drying. The method for producing silver particles according to claim 9, wherein the vacuum is cold The moisture content of the hydrate before lyophilization is 30% or more. The method of producing silver microparticles according to claim 9 or 10, wherein the silver microparticles obtained are silver microparticles according to any one of claims 1 to 5.