TWI642067B - Aggregate of flaky silver particles and paste containing aggregates of the silver particles - Google Patents

Abstract

An object of the present invention is to provide an aggregate of small flaky silver particles having high light reflectance, and when the aggregate of the flaky silver particles is dispersed in a resin, it can be uniformly dispersed and can be manufactured to have high A paste having high reflectance, high gloss, and excellent electrical conductivity, and capable of producing a paste which is less prone to segregation and has high work efficiency.

The solution of the present invention is an aggregate of the flaky silver particles, which has a specific surface area value of 0.5 or more and less than 1.5 m ² /g by a BET method, and a 50% particle diameter obtained by a laser diffraction method is 1 ~4 μm, and the ratio of the 75% particle diameter to the 25% particle diameter is 1.8 or less.

Description

Aggregate of flaky silver particles and paste containing aggregates of the silver particles

Field of invention

The present invention relates to an aggregate of small flaky silver particles having high light reflectance (hereinafter, an aggregate of silver particles is also referred to as silver powder), and in the case where the silver powder is dispersed in a resin, the silver powder is uniformly dispersed. A paste having a high reflectance, a high gloss, and excellent conductivity can be produced, and since the sedimentation rate of the silver powder is low, segregation can be suppressed, so that a paste having uniform viscosity and high work efficiency can be produced.

Background of the invention

At present, a light-emitting diode (hereinafter referred to as an LED) is used for many purposes such as a liquid crystal display, a signal, an illumination lamp, and various display devices. In addition, since LEDs are energy-saving and low-cost, and have a negative impact on the global environment, it is expected that the use of LEDs will be extended to novel fields such as headlights of automobiles.

In general, in a liquid crystal display or the like, an LED chip is fixed using a conductive adhesive, and a reflective film for efficiently emitting light to the LED wafer to the outside is provided. However, in order to emit light more efficiently, it is preferable that the adhesive for fixing the wafer is also highly reflective.

The reflectivity of the binder is greatly affected by the nature of the powder dispersed as a conductive filler into the binder.

In the adhesive for fixing the LED wafer, silver powder is generally used as the conductive filler, so that when the reflectance of the dispersed silver powder is high, the reflectance of the binder is also high.

Regarding the reflectance of silver powder, the aggregate of flaky silver particles is more spherical than the spherical particles. The aggregate of the particles is high, and the aggregate of the silver particles having a large particle diameter is higher than the aggregate of the silver particles having a small particle diameter.

However, when the small flake-shaped silver powder having a large particle diameter is dispersed in the resin as a raw material of the binder in order to increase the reflectance, segregation is likely to occur because the silver powder is liable to settle.

When segregation occurs, there is a problem in that the viscosity of the portion having a high silver concentration is lowered, so that the viscosity of the paste is not uniform, and when the nozzle is applied, the ejection amount is not uniform, and the nozzle is easily clogged, resulting in a decrease in work efficiency.

Further, there is a problem that in the nozzle of the small diameter for fine coating, the nozzle is clogged and cannot be used.

Although the flaky silver powder having fine particles having a small particle diameter is less likely to be segregated, the reflectance is originally low, and the reflectance is lower due to the disordered reflection of light, so that a desired reflectance cannot be obtained.

Therefore, it has been desired to develop a silver powder which can produce a binder which has sufficient reflectance and conductivity, is suitable for use in fixing of an LED wafer, is less prone to segregation, and has high work efficiency.

Prior art literature Patent literature

Patent Document 1: Japanese Special Open 2005-15647

Patent Document 1 discloses a coating material comprising plate-like metal fine particles having a thickness of 50 nm or less and a long diameter of 5 μm or less.

However, the metal powder contained in the coating material disclosed in Patent Document 1 has a problem in that since the metal powder is a very thin plate-like metal fine particle, the reflectance of the metal fine particle is originally low, and the reflection is caused by the disordered reflection of light. The rate is lower, so that the metal microparticles are heat-sealed by heating to form a metal thin film to obtain high reflectance.

The inventors of the present invention have solved a number of trials and experiments repeatedly by solving the above problems, and have found that an important knowledge is that the specific surface area value obtained by the BET method is 0.5 or more and less than 1.5 m ² /g. An aggregate of flaky silver particles having a 50% particle diameter of 1 to 4 μm and a ratio of 75% particle diameter to 25% particle diameter of 1.8 or less obtained by a laser diffraction method, even if the 50% particle diameter is small, Since the content of the fine particles is also low, it is possible to suppress the irregular reflection and obtain a high reflectance. Therefore, when the resin contains the aggregate, a paste having a high reflectance and excellent conductivity can be obtained, and because the paste is in the paste. Since the silver powder is not easily settled and segregation is less likely to occur, it is possible to manufacture an adhesive having high work efficiency, thereby solving the above technical problems.

As described below, the present invention can solve the above technical problems.

The present invention is an aggregate of flaky silver particles having a specific surface area value of 0.5 or more and less than 1.5 m ² /g by a BET method, and a 50% particle diameter obtained by a laser diffraction method of 1 to 4 μm, and The ratio of the 75% particle diameter to the 25% particle diameter is 1.8 or less (Item 1).

Further, the present invention is an aggregate of flaky silver particles according to item 1 in which the reflectance of light of 400 to 800 nm is 40% or more (term 2).

Further, the present invention is a paste (Item 3) comprising the aggregate of the flaky silver particles according to Item 1 or 2.

Further, the present invention is the paste (Item 4) of Item 3 in which the content of the aggregate of the flaky silver particles is 50 to 90% by weight.

Further, the present invention is a paste (Item 5) described in the item 3 or 4 having a specific resistance value of 10 ^-4 Ωcm or less.

Further, the present invention is a paste (Item 6) according to any one of Items 3 to 5, wherein the silver sedimentation rate is 0.5% or less.

Further, the present invention is the paste (Item 7) according to any one of Items 3 to 6, wherein the paste is a binder for a light-emitting diode (LED) wafer.

Further, the present invention is a method for producing an aggregate of flaky silver particles according to Item 1 or 2 (Item 8).

The method of producing a paste according to any one of items 3 to 7 (Item 9).

In the silver powder of the present invention, the 50% particle diameter obtained by the laser diffraction method is small, but the particle size distribution is narrow, the ratio of fine particles is small, the irregular reflection of light of the fine particles is small, and the reflectance is high.

In particular, the silver powder of the present invention can obtain a reflectance of 40% or more in light of 400 to 800 nm.

Further, in the paste prepared by dispersing the silver powder of the present invention in a resin, the silver powder is uniformly dispersed in the resin, and the reflectance and gloss are high.

Further, since the silver powder is less likely to settle and segregation is less likely to occur, a paste having a uniform viscosity can be produced, and since the ejection failure is less likely to occur, a paste having high work efficiency can be produced.

Since the silver powder of the present invention is an aggregate of flaky silver particles, the silver particles are in contact with each other in a large area in the paste prepared by dispersing into the resin, and therefore the paste has excellent conductivity.

The paste containing the silver powder of the present invention can produce a paste having a specific resistance value of 1 × 10 ^-4 Ωcm or less.

Further, since the paste of the present invention has high reflectance and gloss and high conductivity, it is suitable as a binder for fixing an LED chip.

Further, in the paste of the present invention, since the ratio of the silver particles having a uniform viscosity and a large particle diameter is small, the nozzle is less likely to be clogged, and the ejection failure is less likely to occur, which is a paste having high work efficiency.

Further, the paste of the present invention can be used for fine coated small diameter nozzles.

1 is a graph comparing the reflectance of silver powder of the embodiment of the present invention with the reflectance of silver powder of a comparative example; and FIG. 2 is a comparison of reflectance and inclusion of a paste containing silver powder of an embodiment of the present invention. A graph of the reflectance of the paste of the silver powder of the example; FIG. 3 is a photograph of 5000 times of the scanning electron microscope SEM (JSM-6010LA manufactured by JEOL Ltd.) of the silver powder of the present invention.

detailed description

The specific surface area obtained by the BET method of the silver powder of the present invention is 0.5 or more and less than 1.5 m ² /g, preferably 0.8 to 1.2 m ² /g. When the specific surface area is less than 0.5 m ² /g, the particles having a large particle diameter increase, the sedimentation rate increases, and the segregation becomes large. When the specific surface area is 1.5 m ² /g or more, the fine particles increase and the reflectance decreases. Therefore, both cases are not satisfactory.

The thickness of the silver particles of the present invention is preferably from 180 to 220 nm, and the aspect ratio (long diameter/thickness) is preferably from 7 to 13.

Further, when the silver particles having a specific surface area of 0.5 or more and less than 1.5 m ² /g have a thickness calculated as a disk-shaped uniform particle mode, the thickness is 140 or more and is thinner than 620 nm.

In the silver powder of the present invention, the 50% particle diameter obtained by the laser diffraction method is 1 to 4 μm, and the ratio of the 75% particle diameter to the 25% particle diameter is 1.8 or less.

In the case where the 50% particle diameter is less than 1 μm, the fine particles are increased and the reflectance is decreased; in the case where the 50% particle diameter is more than 4 μm, the weight of each particle is increased, and when the silver powder is made into a paste, the sedimentation rate is obtained. Ascending, the segregation becomes large, the viscosity is uneven, the nozzle is easily clogged, and the ejection is poor, so both cases are unsatisfactory.

Further, when the ratio of the 75% particle diameter to the 25% particle diameter exceeds 1.8, the ratio of the fine particles and the silver particles having a large particle diameter increases, which is unsatisfactory.

The silver powder of the present invention can be produced by a method described in JP-A-2003-55701, in which a granular silver powder having an average particle diameter of 0.5 to 3 μm is added to a ball mill equipped with a stirring blade to rotate the stirring blade. The granular silver powder is thinned.

The magnitude of the centrifugal force generated in the contents of the agitating ball milled container is not particularly limited, and the stirring blade is rotated as long as it is produced in the contents of the container. The centrifugal force of 5~300G can be used.

Alternatively, a well-known metal pellet can be placed in the agitating ball mill.

The granular silver powder of the raw material is not particularly limited, and a granular silver powder obtained by a conventionally known atomization method, electrolytic method, chemical reduction method or the like can be used.

In order to adjust the particle size and the like, various solvents or various treatment agents may be added to the agitating ball mill while stirring.

The solvent to be added is not particularly limited and may be, for example, water, methanol, ethanol, propanol, butanol, pentanol, dimethyl ketone, 3-pentanone, diethyl ether, dimethyl ether, diphenyl ether, toluene and Toluene. These solvents may be used singly or in combination as appropriate.

The treatment agent to be added is not particularly limited, and may be, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, fatty acid polyoxyethylene ester, polyoxyethylene sorbitan fatty acid ester, sorbitan A nonionic surfactant such as a fatty acid ester.

These surfactants may be used singly or in combination of two or more.

Further, as the treating agent, a fatty acid such as oleic acid, octadecanoic acid or myristic acid can also be used. These fatty acids may be used singly or in combination of two or more.

In the case of using a treating agent, it is preferred to add a treating agent to the stirring ball mill so that the total amount of the treating agent per surface area of 1 m ² of the obtained flaky silver powder is 0.001 to 0.05 g.

The resin which disperses the silver powder of the present invention is not particularly limited as long as it is a resin capable of emitting reflected light of the silver powder, and is preferably a transparent resin.

The resin containing the silver powder of the present invention may be, for example, an anthrone resin, an epoxy resin, an acrylic resin, a polyester resin, a melamine resin or the like.

The content of the silver powder in the paste of the present invention is not particularly limited, but is preferably from 50 to 90% by weight, more preferably from 70 to 85% by weight.

When the content of the silver powder is 50% by weight or less, sufficient reflectance and conductivity cannot be ensured, and when the content of the silver powder is 90% or more, the reflectance and the conductivity are not expected to be increased, and the nozzle is easily clogged. The situation is not satisfactory.

Example

Embodiments of the invention are shown below, but the invention is not limited thereto.

<Example 1>

To a medium agitating wet pulverizing disperser having a cylindrical container having a diameter of 107 mm × a height of 320 mm, zirconia beads having a diameter of 0.05 mm were appropriately added, and the speed of the stirring rotor was set to 7 m/s, and the mixture was circulated for 1.5 hours. A slurry of 700 g of spherical silver powder having an average particle diameter of 1.5 μm and 6 L of ethanol was used.

Then, the contents of the cylindrical container were filtered, ethanol was removed from the filtrate, and dried to obtain flaky silver powder.

<Example 2>

A flaky silver powder was obtained by the same method as in Example 1 except that spherical silver powder having an average particle diameter of 2.5 μm was used.

The SEM photograph of the scanning electron microscope shown in Fig. 3 is a photograph in which the flaky silver powder of Example 2 was enlarged to 5000 times.

<Comparative Examples 1 to 7>

A ball mill having a cylindrical container having a diameter of 150 mm and a height of 190 mm is appropriately added with 700 g of granular silver powder having an average particle diameter of 0.1 to 3 μm obtained by a chemical reduction method, 1 L of ethanol, and a well-known metal ball having a diameter of 1 to 2 mm. Set the rotation speed of the container to 40~80rpm, run for 5~20 hours, and then stop the rotation. Then, the contents of the cylindrical container were filtered, ethanol was removed from the filtrate, and dried to obtain flaky silver powders of Comparative Examples 1 to 7.

<Comparative Example 8>

The spherical silver powder having an average particle diameter of 1.5 μm obtained by the atomization method was measured in a state of not being thinned.

Each of the silver powders of the examples and the comparative examples was evaluated by the following method.

(BET specific surface area value)

The specific surface area value of each silver powder was measured by the BET method using a flow type specific surface area automatic measuring instrument FlowSorb II 2100 (manufactured by Shimadzu Corporation, Japan).

(particle size)

The laser diffraction type particle size distribution measuring instrument SALD-3100 (manufactured by Shimadzu Corporation, Japan) was used to measure the particle diameters of 25%, 50%, and 75% of each silver powder.

(reflectance: silver powder)

The reflectance of each silver powder was measured using a spectrophotometer SE6000 (manufactured by Nippon Denshoku Industries Co., Ltd.) at a measurement wavelength of 550 nm.

In addition, the reflectance of 380 to 780 nm of each silver powder was measured using a spectrophotometer SE6000 (Fig. 1).

(electrical conductivity)

A paste prepared by disposing each silver powder in an amount of 87% by weight to an epoxy resin was applied onto a glass substrate, and then treated at a temperature of 200 ° C for 30 minutes to obtain a coating film according to the resistance value of the coating film ( The specific resistance value (ρ) is calculated from R) and the cross-sectional area (S).

ρ=R. S/L

(R: resistance value (Ω), S: cross-sectional area (cm ² ), L: pole spacing (cm))

(silver settlement rate)

The same paste as that used for the conductivity evaluation was injected into a 10 cc syringe, and placed in a vertical state for three days under an atmosphere of 25 ° C, and then the difference in silver content between the uppermost 1 cc and the lowermost 1 cc was measured. The paste was treated at a temperature of 800 ° C for 60 minutes, and the silver content was calculated from the ignition loss.

(reflectance: paste)

A paste prepared by disposing each of the silver powders of Example 1, Comparative Examples 1, 7, and 8 to an epoxy resin at a ratio of 87% by weight was applied to the paper by a bar coater, and then treated at a temperature of 200 ° C. A coating film was obtained in a minute, and the reflectance of the coating film was measured using a spectrophotometer SE6000 (manufactured by Nippon Denshoku Industries Co., Ltd.) at a measurement wavelength of 550 nm.

Further, the reflectance of 380 to 780 nm of the paste containing each of the silver powders was measured using a spectrophotometer SE6000 (Fig. 2).

(Gloss)

A paste prepared by disposing each of the silver powders of Example 1, Comparative Examples 1, 7, and 8 at a ratio of 87% by weight to an epoxy resin using a bar coater, and then applying the temperature at 200 ° C The film was treated for 30 minutes to obtain a coating film, and the glossiness of the coating film at a reflection angle of 60 degrees was measured using a gloss meter GM-268Plus (manufactured by Konica Minolta Co., Ltd., Japan).

Table 1 shows each evaluation value of the examples and comparative examples.

Figure 1 shows the reflectance of 380 to 780 nm for each silver powder.

In addition, FIG. 2 shows the reflectance of 380 to 780 nm of the paste containing each of the silver powders of Example 1, Comparative Examples 1, 7, and 8.

As is clear from Table 1 and Fig. 1, in the silver powder of the present invention, although the 50% particle diameter obtained by the laser diffraction method is small, it is 1 to 4 μm, but the reflectance is high.

As is apparent from Table 1 and FIG. 2, in the paste containing the silver powder of the present invention, the reflectance and the gloss are high, the silver sedimentation rate is low, and the conductivity is excellent.

Further, it was also found that the paste of the present invention has a higher glossiness than the paste of the comparative example and can be visually recognized.

Industrial availability

In the silver powder of the present invention, although the 50% particle diameter obtained by the laser diffraction method is small, the particle size distribution is narrow, the reflectance is high, and in the paste containing the silver powder of the present invention, the chaotic reflection is small and the reflectance is high. The gloss is high, the conductivity is excellent, the segregation is small, the viscosity is uniform, and the work efficiency is high, so the paste is suitable for use as an adhesive for an LED wafer.

Therefore, the present invention is an industrially usable invention.

Claims (7)

An aggregate of small flaky silver particles having a specific surface area value of 0.5 or more and less than 1.5 m ² /g by a BET method, and a 50% particle diameter of 1 to 4 μm by a laser diffraction method, and 75% of particles The ratio of the diameter to the 25% particle diameter is 1.8 or less. The aggregate of the flaky silver particles according to claim 1 has a reflectance of 40% or more of light of 400 to 800 nm. A paste comprising the aggregate of flaky silver particles as claimed in claim 1 or 2. The paste according to claim 3, wherein the aggregate of the flaky silver particles is contained in an amount of 50 to 90% by weight. The paste according to claim 3 or 4 has a silver sedimentation rate of 0.5% or less. The paste according to claim 3 or 4, wherein the paste is a binder for a light-emitting diode (LED) wafer. The paste according to claim 5, wherein the paste is a binder for a light-emitting diode (LED) wafer.