WO2016114189A1

WO2016114189A1 - Silver-coated resin particles, method for manufacturing same, and electroconductive paste using same

Info

Publication number: WO2016114189A1
Application number: PCT/JP2016/050217
Authority: WO
Inventors: 謙介影山; 博一塚田
Original assignee: 三菱マテリアル電子化成株式会社
Priority date: 2015-01-13
Filing date: 2016-01-06
Publication date: 2016-07-21

Abstract

Silver-coated resin particles, provided with resin core particles having heat resistance and a silver coating layer formed on the surface of the resin core particles, the resin core particles being resin particles having an average grain diameter of 0.1-10 μm, wherein the amount of silver contained in the silver coating layer is 60-90 parts by mass in relation to 100 parts by mass of the silver-coated resin particles, and the exothermic peak temperature obtained by differential thermal analysis of the silver-coated resin particles is at least 265°C.

Description

Silver-coated resin particles, production method thereof, and conductive paste using the same

The present invention relates to silver-coated resin particles suitable as a conductive filler contained in a conductive paste and a method for producing the same. More specifically, the conductivity and smoothness of the conductive film after coating and curing are excellent, and even if the conductive film is used in an environment where the temperature change is severe, cracking of the ceramic body is caused by high stress relaxation. The present invention relates to a silver-coated resin particle used for a conductive paste that prevents and does not cause cracks in a conductive film, and the conductive paste. This application claims priority based on Japanese Patent Application No. 2015-3827 filed in Japan on January 13, 2015 and Japanese Patent Application No. 2015-155600 filed in Japan on August 6, 2015. The entire contents of Japanese Patent Application Nos. 2015-3827 and 2015-155600 are incorporated herein by reference.

Known chip-type electronic components include a chip inductor, a chip resistor, a chip-type multilayer ceramic capacitor, a chip-type multilayer ceramic capacitor, and a chip thermistor. These chip-type electronic components are provided on both end surfaces of the chip-shaped element body so as to be electrically connected to the chip-shaped element body made of a ceramic sintered body, an internal electrode provided therein, and the internal electrode. It is mainly composed of external electrodes, and is mounted by soldering the external electrodes to a substrate.

In such a chip-type electronic component, the external electrode is used to connect the chip-type electronic component and an electric circuit on the substrate. The quality of the product depends on the electrical characteristics, reliability, mechanical characteristics, etc. of the product. Has a major impact on

Conventionally, external electrodes of chip-type electronic components have been prepared by kneading a mixture of noble metal powders such as Ag, Pd, and Pt and an inorganic binder into an inorganic vehicle, and applying the resulting conductive paste to both end surfaces of the chip-shaped element body. After coating, it is formed by firing at a temperature of about 500 to 800 ° C. (referred to as “sintered electrode”).

However, in the case of a conventional external electrode composed only of a sintered type external electrode, 1) a nickel plating film for preventing a crack (solubilization of the external electrode into the solder) at the time of soldering on the external electrode surface Furthermore, due to the formation of a tin or tin / palladium plating electrode layer to suppress a decrease in solderability due to oxidation of the plating film, the firing conditions at the time of external electrode formation formed a plating film The electrical characteristics of the chip-type electronic component obtained later will be affected, and as a result, it is difficult to obtain a highly reliable chip-type electronic component. 2) Since the external electrode is formed with a metal sintered structure with high hardness, it is used There is a problem that cracks may occur in the ceramic sintered body constituting the chip-like element body at the time temperature cycle.

Therefore, in such a chip-type electronic component, by applying and curing a resin composition in which a conductive filler typified by silver powder is dispersed in a binder resin typified by epoxy resin on the end face of the chip-shaped element body. It has been proposed to form a resin electrode layer, which is a conductive film, as a component of the external terminal electrode. This resin electrode layer is used for the purpose of alleviating thermal expansion of the external terminal electrode when thermal stress acts on the external terminal electrode and preventing cracks (see, for example, Patent Documents 1 to 3).

As another chip-type electronic component, a multilayer ceramic capacitor using a conductive resin composition containing a silicone resin made of polydimethylsiloxane (PDMS) and conductive metal particles (conductive filler) is disclosed (for example, , See Patent Document 4). This multilayer ceramic capacitor has a conductive resin layer, which is a conductive film made of the above conductive composition, between an external electrode formed on the end face of the ceramic body and the outermost plating layer. The conductive metal particles are composed of copper, silver, or copper whose surface is coated with silver. This multilayer ceramic capacitor is excellent in moisture resistance due to the conductive resin layer, and can improve the bending strength of the external electrode in the multilayer ceramic capacitor. Further, since the conductive resin layer is a silicone resin whose binder component is PDMS, the thermal expansion relaxation property when the thermal stress is applied to the external terminal electrode on the end face of the ceramic body is high.

On the other hand, metal-coated resin particles obtained by conducting conductive metal plating on the surface of spherical resin particles are disclosed as an alternative material for the conductive filler made of the metal powder or metal particles (see, for example, Patent Document 5). In Patent Document 5, acrylic resin or styrene resin is used for the resin core particles. The metal-coated resin particles are characterized by flexibility and low specific gravity because the core is made of resin instead of the conventional conductive metal powder made of silver powder.

JP-A-10-284343 (Claims 1, 2 and paragraphs [0002] and [0026]) WO2003 / 075295 (claims, page 13) WO2011 / 096288 (paragraphs [0002], [0003], [0024]) JP 2014-135463 A (claims, paragraph [0024]) WO2012 / 023566 (Claims)

In recent years, the chip-type electronic components mounted around the engine room of an automobile are resistant to thermal durability, that is, heat resistance, and even strong vibration and impact in an environment where temperature change is more significant than before. Therefore, not only the reliability of the component itself but also the bonding reliability when mounted as a unit has been strongly demanded. For this reason, when the chip-type electronic component shown in Patent Documents 2 and 3 is used in an environment where the temperature change is severe, thermal expansion is caused in the resin electrode layer (conductive film) which is one component of the external terminal electrode. There is not enough relaxation for vibration and impact, thermal expansion relaxation and anti-vibration and shock relaxation are insufficient, and cracks may occur in the ceramic body, or cracks may occur in the resin electrode layer (conductive film) itself. There is. The reason is that when thermal stress acts on the external terminal electrode, the difference between the thermal expansion coefficient of the conductive filler made of metal powder or metal particles contained in the resin electrode layer (conductive film) and the thermal expansion coefficient of the binder resin is In order to keep the electrical conductivity of the conductive resin high, the amount of the resin that contributes to stress relaxation is small due to the increase in the amount of conductive filler added.

Also in the conductive resin layer (conductive film) shown in Patent Document 4, since the conductive filler is metal particles, the difference is still large, and the thermal expansion relaxation property of the conductive resin layer (conductive film) is sufficient. Otherwise, there is a risk of cracking of the ceramic body or cracking of the resin conductive layer.

On the other hand, the metal-coated resin particles shown in Patent Document 5 have low heat resistance of the resin core particles themselves such as acrylic resin and styrene resin, and are conductive including the metal-coated resin particles (conductive filler) and the binder resin. When a resin electrode layer is formed with a paste, this resin electrode layer has high thermal expansion relaxation properties, but when the external terminal electrode is soldered to the substrate, the resin core particles cannot withstand high temperatures and are thermally decomposed to form an electrode structure. There was a problem that was easily destroyed. Accordingly, the present inventors have found that a silver-coated resin particle powder that can withstand high temperatures can be obtained by substituting the resin core particles with a silicone resin, a fluororesin, or the like that has higher heat resistance than the above resin. On the other hand, some of these heat resistant resins have water repellency, and it is difficult to form a tin adsorption layer using electroless plating performed in an aqueous medium shown in Patent Document 5, and the silver coating layer has high adhesion. In some cases, it is difficult to form uniformly on the surface of the resin core particles, and it has been simultaneously demanded to solve this problem.

An object of the present invention is to provide silver-coated resin particles in which a silver coating layer is uniformly formed with high adhesion on the surface of resin core particles having heat resistance, and a method for producing the same. Another object of the present invention is to provide a conductive paste that is excellent in conductivity and smoothness of a conductive film after coating and curing, and does not crack in a conductive film even when the conductive film is used in an environment where temperature change is severe. Is to provide.

The present inventors adopted a heat-resistant resin as the resin core particles, and reached the silver-coated resin particles having heat resistance according to the first invention. In addition, the method for producing silver-coated resin particles according to the second aspect of the present invention is characterized by modifying the surface of a heat-resistant resin that has water repellency and is difficult to obtain a silver-coated film in a normal process, and applying a hydrophilic treatment. Reached.

The first aspect of the present invention is silver-coated resin particles comprising resin core particles having heat resistance and a silver coating layer formed on the surface of the resin core particles. The resin core particles are resin particles having an average particle size of 0.1 to 10 μm, and the amount of silver contained in the silver coating layer is 60 to 90 parts by mass with respect to 100 parts by mass of the silver coated resin particles, And the exothermic peak temperature when silver-coated resin particles are subjected to differential thermal analysis is 265 ° C. or higher.

A second aspect of the present invention is the invention based on the first aspect, wherein the resin core particles having heat resistance are silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber or silicone shell Acrylic core resin particles.

A third aspect of the present invention is the invention based on the first or second aspect, wherein the silver-coated resin particles are obtained by heating the silver-coated resin particles to 300 ° C. in thermogravimetry. The weight reduction rate of the particles is 10% or less.

According to a fourth aspect of the present invention, there is provided a step of modifying the surface of the resin particles by subjecting the resin core particles having heat resistance to plasma treatment, ozone treatment, acid treatment, alkali treatment or silane treatment; Forming a tin adsorbing layer on the surface of the resin particle by adding resin core particles made of the modified resin particles to an aqueous solution of a tin compound kept at 25 to 45 ° C., and forming on the surface of the resin core particle An electroless silver plating solution containing no reducing agent is brought into contact with the formed tin adsorption layer, and resin core particles are formed by a substitution reaction between the tin adsorption layer formed on the surface of the resin core particles and silver in the electroless plating solution. A silver-coated resin comprising: forming a silver-substituted layer on the surface of the resin; and adding a reducing agent to the electroless silver plating solution to form a silver-coated layer on the surface of the silver-substituted layer of the resin core particles. A method for producing particles.

A fifth aspect of the present invention is the invention based on the fourth aspect, wherein the resin core particles having heat resistance are silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber or silicone shell This is a method for producing silver-coated resin particles that are particles of an acrylic core resin.

A sixth aspect of the present invention is a conductive property comprising silver-coated resin particles based on any one of the first to third aspects, and one or more binder resins of epoxy resin, phenol resin, or silicone resin. It is a paste.

A seventh aspect of the present invention is a silver-coated resin particle based on any one of the first to third aspects, a silver particle, and one or more binder resins of an epoxy resin, a phenol resin, or a silicone resin, and This is a conductive paste made of

According to an eighth aspect of the present invention, there are provided silver-coated resin particles based on any one of the first to third aspects, flat silver-coated inorganic particles coated with flat inorganic core particles, epoxy resin, phenol It is a conductive paste made of one or more binder resins of resin or silicone resin.

９A ninth aspect of the present invention is a method for forming a thermosetting conductive film by applying a conductive paste based on any one of the sixth to eighth aspects to a substrate and curing it.

Since the silver-coated resin particles according to the first aspect of the present invention use heat-resistant resin core particles, the peak temperature of heat generation when the silver-coated resin particles are subjected to differential thermal analysis is as high as 265 ° C. or higher. In addition, the resin core particles are not thermally decomposed even in a temperature environment at the time of soldering such as reflow soldering, and are excellent in heat resistance.

The resin core particles having heat resistance according to the second and fifth aspects of the present invention are particles of silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber or silicone shell-acrylic core resin. These resin core particles can be easily obtained.

Since the silver-coated resin particles according to the third aspect of the present invention further have a weight reduction rate of 10% or less when the silver-coated resin particles are heated to 300 ° C. in thermogravimetry, Excellent heat resistance.

In the method for producing silver-coated resin particles according to the fourth aspect of the present invention, the resin core particles having heat resistance are subjected to plasma treatment, ozone treatment, acid treatment, alkali treatment or silane treatment, and the resin surface particles serving as the core By modifying the surface, the surface of the resin core particles is hydrophilized. For this reason, a tin adsorption layer is uniformly formed on the surface of the resin core particles in an aqueous medium, and a silver coating layer is uniformly and uniformly formed on the surface of the resin core particles by subsequent electroless silver plating.

The conductive paste based on the sixth aspect of the present invention is excellent in heat resistance because it contains the silver-coated resin particles as the conductive filler and the epoxy resin, phenol resin or silicone resin as the binder resin.

The conductive paste according to the seventh aspect of the present invention contains silver particles in addition to the silver-coated resin particles as a conductive filler, and includes an epoxy resin, a phenol resin, or a silicone resin as the conductive filler and a binder resin. In addition to heat resistance, the conductive film after coating and curing is further excellent in conductivity.

The conductive paste according to the eighth aspect of the present invention includes flat silver-coated inorganic particles as the conductive filler in addition to the silver-coated resin particles, and the conductive filler and binder resin are epoxy resin, phenol resin, or silicone. Since the resin is contained, in addition to heat resistance, the conductive film after coating and curing is further excellent in conductivity.

Since the thermosetting conductive film formed based on the ninth aspect of the present invention has flexibility not only in the binder resin part constituting the film but also in the silver-coated resin particles as the conductive filler, This thermal stress is relieved by thermal expansion when. For this reason, it is excellent in thermal stress relaxation property, and even if this conductive film is used in an environment where the temperature change is severe, the conductive film does not crack.

Next, a mode for carrying out the present invention will be described.

[Silver-coated resin particles]
The silver-coated resin particles of this embodiment include resin core particles having heat resistance and a silver coating layer formed on the surface of the resin core particles. Examples of the resin core particles having heat resistance include silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber, or silicone shell-acrylic core resin particles. The average particle diameter of the resin core particles is in the range of 0.1 to 10 μm. Further, the amount of silver contained in the silver coating layer is 60 to 90 parts by mass with respect to 100 parts by mass of the silver-coated resin particles, and the exothermic peak temperature when the differential thermal analysis of the silver-coated resin particles is 265 ° C. or more, Preferably it is 310 degreeC or more. The upper limit is 700 ° C. The thickness of the silver coating layer is preferably 0.1 to 0.3 μm.

The silver coating amount (content) is determined by the average particle size of the resin and the required conductivity. When the amount of silver contained in the silver coating layer is less than 60 parts by mass of the lower limit, and when the thickness of the silver coating layer is less than 0.1 μm, when the silver-coated resin particles are dispersed as the conductive filler, The contact is difficult to take and sufficient conductivity cannot be imparted. On the other hand, if the silver content exceeds 90 parts by mass, and if the thickness of the silver coating layer exceeds 0.3 μm, the specific gravity of the silver-coated resin particles increases, the cost increases, and the conductivity is saturated. . The silver content is preferably 70 to 80 parts by mass. The amount of silver contained in the silver coating layer is the same regardless of whether only silver-coated resin particles are used as conductive fillers or when silver particles are used as conductive fillers in addition to the silver-coated resin particles described later. The silver coating amount is obtained, for example, by ICP emission spectroscopic measurement after acid-decomposing silver-coated resin particles.

[Resin core particles]
The resin core particles of the present embodiment are silicone resin particles, silicone rubber particles, polyimide resin particles, aramid resin particles, fluororesin particles, fluororubber particles, or silicone shell-acrylic core resin particles. The resin core particles have an exothermic peak temperature of 265 ° C. or higher when subjected to differential thermal analysis, and a weight reduction rate of the silver-coated resin particles of 10% or less when heated to 300 ° C. in thermogravimetry. Excellent. When the exothermic peak temperature is less than 265 ° C., a conductive film is formed with a conductive paste containing the silver-coated resin particles as a conductive filler, and when the conductive film is soldered, the resin core particles are thermally decomposed and are excellent. A conductive film cannot be formed. Further, when the weight reduction rate of the silver-coated resin particles exceeds 10% when the silver-coated resin particles are heated to 300 ° C. in thermogravimetry, the conductive film is made of a conductive paste containing the silver-coated resin particles as a conductive filler. When the conductive film is soldered and the conductive film is soldered, the resin core particles are thermally decomposed and a good conductive film cannot be formed.

Examples of such heat-resistant resin particles include silicone-based particles such as polysilsesquioxane resin (PSQ resin) particles and polymethylsilsesquioxane resin particles. Silicone rubber particles and silicone shell-acrylic core resin particles can also be used. Silicone shell-acrylic core resin particles are made by coating acrylic resin particles with a silicone resin film, and further coated with an inorganic substance such as titanium oxide or alumina, and the surface is made of an inorganic substance such as silicone or titanium oxide or alumina. Some have protrusions. Polyimide resin particles include polyamideimide (PAI) resin particles, and aramid resin particles include polymetaphenylene isophthalamide (MPIA) resin particles, polyparaphenylene terephthalamide (PPTA) resin particles, and the like. Polytetrafluoroethylene (PTFE) resin particles, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV) resin particles, polyvinylidene fluoride (PVDF) resin particles, polychlorotrifluoroethylene (PCTFE) Resin particles, chlorotrifluoroethylene-ethylene (ECTFE) resin particles, tetrafluoroethylene-ethylene (ETFE) resin particles, tetrafluoroethylene-hexafluoropropylene (FEP) resin particles Tetrafluoroethylene - perfluoroalkyl vinyl ether (PFA) resin particles, and the like. Moreover, a fluororubber particle is also mentioned. Other heat-resistant resins constituting the resin particles include sulfone resins such as polyphenylene sulfide (PPS) resin and polyethersulfone (PES) resin, cured epoxy (EP) resin powder, polyether ether ketone (PEEK). ), Polyphenylene ether (PPE), and the like, and these resins can also be used.

The resin core particles are resin particles having an average particle size of 0.1 to 10 μm. The resin core particles are preferably single particles without aggregation. The average particle size is more preferably in the range of 0.1 to 5 μm. The reason why the average particle diameter of the resin core particles is within the above range is that if the lower limit value is less than 0.1 μm, the resin core particles are likely to aggregate, and the surface area of the resin core particles is increased, which is necessary for the conductive filler. This is because it is necessary to increase the amount of silver for obtaining a good silver coating, and it is difficult to form a good silver coating layer. Furthermore, it is difficult to obtain resin core particles of less than 0.1 μm. On the other hand, if the average particle diameter of the resin core particles exceeds 10 μm, the surface smoothness of the resin electrode film decreases, the contact ratio of the conductive particles decreases, and the resistance value increases. In the present specification, the average particle diameter of the resin core particles is a magnification of 5000 using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model name: SU-1500) and software (product name: PC SEM). The diameter of 300 silver-coated resins is measured twice, and the calculated average value is used. The values other than the true sphere mean the average of the long sides. The resin core particle may be a spherical particle, or may have a different shape such as a flat shape, a plate shape, or a needle shape instead of a spherical shape.

The coefficient of variation of the particle diameter of the resin core particle particles is 10.0% or less, and it is preferable that the particle diameters are uniform. This is because if the coefficient of variation exceeds 10.0% and the particle diameter is not uniform, the reproducibility of imparting conductivity when used as a conductive filler is impaired. The coefficient of variation (CV value, unit:%) is determined from the particle size of the 300 resins by the formula: [(standard deviation / average particle size) × 100].

[Method for surface modification of resin core particles]
Surface modification of resin particles of silicone, polyimide, aramid, fluorine, silicone shell-acrylic core is performed by plasma treatment, ozone treatment, acid treatment, alkali treatment or silane treatment. Two or more of these processes may be combined. These surface modifications make the resin particles hydrophilic.

Plasma treatment is performed by irradiating the resin particles with plasma. Examples of the plasma include air plasma, oxygen plasma, nitrogen plasma, argon plasma, helium plasma, water vapor plasma, ammonia plasma, and the like. The plasma treatment is performed at any suitable temperature, for example from room temperature to a high temperature such as the temperature used in the heating operation, including about 100 ° C., including room temperature to 60 ° C. In particular, room temperature is included. The plasma treatment is performed over a period of about 1 second to about 30 minutes.

The plasma treatment is performed using a plasma generator at a frequency of about 24 kHz to about 13.56 MHz and a power of about 100 W to about 50 kW. The plasma generator is preferably a high frequency emission plasma, and the ion energy is preferably less than about 12.0 eV.

For the ozone treatment, a method of immersing the resin particles in a solution in which ozone gas is dissolved, a method of bringing the resin particles into contact with ozone gas, or other known methods can be used. For example, in the method of immersing the resin particles in an ozone solution, the ozone solution can be prepared by dissolving ozone gas in a polar solvent. When ozone is dissolved in a polar solvent, the activity of ozone increases and the treatment time of the hydrophilization process can be shortened. As the polar solvent, water is particularly preferable, but if necessary, a water-soluble solvent such as alcohols, amides, and ketones can be mixed with water and used.

The concentration of ozone in the ozone solution is preferably 1 to 300 mg / L, more preferably 10 to 200 mg / L, and still more preferably 20 to 100 mg / L. The ozone treatment time (immersion time of the resin particles in the ozone solution) is preferably 1 to 100 minutes. If the treatment temperature with the ozone solution is increased, the reaction rate increases, but the solubility of ozone decreases at atmospheric pressure, so a pressurizing device is required. Accordingly, the treatment temperature can be appropriately set in consideration of these relationships, but it is easy to set the temperature in the range of about 10 to 50 ° C., for example, and it is particularly preferable to be about room temperature. The pressure condition during the ozone treatment is set to maintain the ozone gas at a predetermined concentration, and is usually set from the pressurization condition and the normal pressure condition according to the set ozone concentration and the treatment temperature.

When ozone treatment is performed, decomposition of dissolved ozone, such as ultraviolet irradiation or ultrasonic irradiation with the resin particles immersed in an ozone solution, or addition of alkaline water to an ozone solution in which substrate particles are immersed It is preferable to use a means for promoting the above. By using these means in combination, decomposition of dissolved ozone is promoted, and it becomes easy to generate hydroxy radicals that are considered to have high oxidizing power by decomposition of ozone, so that the effect of hydrophilization can be further enhanced. This is probably because As a result, the generation of hydrophilic groups (OH group, CHO group, COOH, etc.) on the surface of the resin particles can be further promoted.

In the acid treatment, the resin particles are immersed or stirred in an aqueous solution of chromic acid-sulfuric acid, permanganic acid-sulfuric acid, nitric acid-sulfuric acid having a concentration of 0.1 to 15% by mass, and held at 30 to 50 ° C. for 10 to 300 minutes. Is done.

The alkali treatment is performed by immersing or stirring the resin particles in an aqueous solution of caustic soda, potassium hydroxide or the like having a concentration of 0.5 to 15% by mass and holding at 30 to 50 ° C. for 10 to 300 minutes. Moreover, it is also possible to use alkaline electrolyzed water obtained by adding an electrolyte such as sodium chloride and performing electrolysis or using it together.

The silane treatment is performed by subjecting the resin particles to a dry treatment or a wet treatment with a silane-based material such as a silane coupling agent or a silane compound. The silane coupling agent is not particularly limited. For example, polyether type silane, 3-glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane. , 3-isocyanatopropyltrimethoxysilane, imidazolesilane and the like. Examples of the silane compound include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetra-nbutoxysilane. It is more effective to perform silane treatment after plasma treatment.

[Method for producing silver-coated resin particles]
The silver-coated resin particles of this embodiment are produced by the following method. First, the resin core particles made of the surface-modified resin particles are added to an aqueous solution of a tin compound kept at 25 to 45 ° C. to form a tin adsorption layer on the surface of the resin core particles. Next, an electroless silver plating solution containing no reducing agent is brought into contact with the tin adsorption layer formed on the surface of the resin core particles, so that the tin adsorption layer formed on the surface of the resin core particles and the silver in the electroless plating solution A silver substitution layer is formed on the surface of the resin core particles by a substitution reaction with Next, a reducing agent is added to the electroless silver plating solution to form a silver coating layer on the surface of the silver replacement layer of the resin core particles.

[Method of forming silver coating layer by electroless silver plating]
A silver coating layer is provided on the surface of the resin core particles. Generally, when electroless plating is performed on the surface of a nonconductor such as an organic material or an inorganic material, it is necessary to perform a catalyst treatment on the surface of the nonconductor in advance. In the present embodiment, a treatment for providing a tin adsorption layer on the surface of the resin core particles is performed as a catalyst treatment, and then an electroless silver plating treatment is performed to form a silver coating layer. Specifically, the silver coating layer of this embodiment is manufactured by the following method. First, the resin core particles are added to an aqueous solution of a tin compound kept at 25 to 45 ° C. to form a tin adsorption layer on the surface of the resin core particles. Next, an electroless silver plating solution not included in the tin adsorption layer is brought into contact with the surface of the resin core particles by a substitution reaction between the tin adsorption layer formed on the surface of the resin core particles and silver in the electroless plating solution. A substitution layer is formed. Next, a reducing agent is added to the electroless silver plating solution to form a silver coating layer on the surface of the silver replacement layer of the resin core particles.

In order to form the tin adsorption layer, resin core particles are added to an aqueous solution of a tin compound and stirred, and then the resin core particles are separated by filtration or centrifuged and washed with water. The stirring time is appropriately determined depending on the temperature of the following tin compound aqueous solution and the content of the tin compound, and is preferably 0.5 to 24 hours. The temperature of the aqueous solution of the tin compound is 25 to 45 ° C, preferably 25 to 35 ° C, and more preferably 27 to 35 ° C. If the temperature of the aqueous solution of the tin compound is less than 25 ° C., the temperature is too low and the activity of the aqueous solution becomes low, and the tin compound does not sufficiently adhere to the resin core particles. On the other hand, when the temperature of the aqueous solution of the tin compound exceeds 45 ° C., the tin compound is oxidized, so that the aqueous solution becomes unstable and the tin compound does not sufficiently adhere to the resin core particles. When this treatment is carried out in an aqueous solution at 25 to 45 ° C., divalent ions of tin adhere to the surface of the resin core particles, and a tin adsorption layer is formed.

Examples of the tin compound include stannous chloride, stannous fluoride, stannous bromide, stannous iodide, and the like. When stannous chloride is used, the content of stannous chloride in the tin compound aqueous solution is preferably 30 to 100 g / dm ³ . If the content of stannous chloride is 30 g / dm ³ or more, a uniform tin adsorption layer can be formed. If the stannous chloride content is 100 g / dm ³ or less, the amount of inevitable impurities in stannous chloride is suppressed. Note that stannous chloride can be contained in an aqueous solution of a tin compound until saturation.

The aqueous solution of the tin compound preferably contains hydrochloric acid: 0.5 to 2 cm ³ with respect to 1 g of stannous chloride. When the amount of hydrochloric acid is 0.5 cm ³ or more, the solubility of stannous chloride can be improved and the hydrolysis of tin can be suppressed. When the amount of hydrochloric acid is 2 cm ³ or less, the pH of the aqueous solution of the tin compound does not become too low, so that tin can be efficiently adsorbed on the resin core particles.

After forming a tin adsorption layer on the surface of the resin core particle, an electroless plating solution not containing a reducing agent is brought into contact with the tin adsorption layer, and a silver substitution layer is formed on the surface of the resin core particle by a substitution reaction of tin and silver. Then, a reducing agent is added to the electroless silver plating solution to perform electroless plating, thereby forming a silver coating layer on the surface of the resin core particles to produce silver coated resin particles. As the electroless silver plating method, (1) a method in which resin core particles having a silver substitution layer formed on the surface are immersed in an aqueous solution containing a complexing agent, a reducing agent, etc., and an aqueous silver salt solution is dropped, (2) A method of immersing resin core particles having a silver-substituted layer on the surface thereof in an aqueous solution containing a silver salt and a complexing agent, and dropping a reducing agent aqueous solution, (3) including a silver salt, a complexing agent, a reducing agent, etc. A method in which resin core particles having a silver substitution layer formed on the surface is immersed in an aqueous solution and a caustic aqueous solution is dropped.

As the silver salt, silver nitrate or silver nitrate dissolved in nitric acid can be used. Complexing agents include ammonia, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid tetrasodium, nitrotriacetic acid, triethylenetetraamminehexaacetic acid, sodium thiosulfate, succinate, succinimide, citrate or iodide salts, etc. Can be used. As the reducing agent, formalin, glucose, imidazole, Rochelle salt (sodium potassium tartrate), hydrazine and its derivatives, hydroquinone, L-ascorbic acid or formic acid can be used. As the reducing agent, formaldehyde is preferable because of its strong reducing power, a mixture of two or more reducing agents containing at least formaldehyde is more preferable, and a mixture of reducing agent containing formaldehyde and glucose is most preferable.

In the previous step of the electroless silver plating process, tin in the tin adsorption layer elutes by releasing electrons by coming into contact with silver ions in the solution, while silver ions receive electrons from tin and are resin as metals. Substitutional deposition is performed on the core particles where the tin is adsorbed. Thereafter, when all the tin is dissolved in the aqueous solution, the substitution reaction of tin and silver is completed. Subsequently, a reducing agent is added to the electroless plating solution, and a silver coating layer is formed on the surface of the resin core particles by a reduction reaction with the reducing agent, thereby producing silver-coated resin particles.

[Conductive paste]
The conductive paste is an organic vehicle including the silver-coated resin particles as a conductive filler, an epoxy resin, a phenol resin or a silicone resin as a binder resin, a curing agent, and a solvent. The conductive paste can use, as the conductive filler, silver particles having an average particle diameter of 5 μm or less, or flat silver-coated inorganic particles having an average particle diameter of 10 μm or less, together with the silver-coated resin particles. The flat silver-coated inorganic particles are formed by covering flat inorganic core particles with silver. Examples of the flat inorganic particles include graphite, talc, and mica. Other than graphite, talc, and mica, flat inorganic particles having heat resistance of 300 ° C. or higher can be used as core particles.

[Ratio of silver-coated resin particles in the conductive paste]
When the conductive filler to be included in the conductive paste is only silver-coated resin particles, the ratio of the silver-coated resin particles is preferably 70 to 90% by mass in 100% by mass of the paste, 75 It is more preferable to set the ratio to ˜85% by mass. If it is less than 70% by mass, the resistance value of the electrode or wiring formed by applying and curing the conductive paste increases, and it becomes difficult to form an electrode or wiring having excellent conductivity. On the other hand, when it exceeds 90% by mass, there is a tendency that a paste having good fluidity cannot be obtained, and thus it becomes difficult to form good electrodes and the like in terms of printability.

[Ratio of silver-coated resin particles and silver particles or flat silver-coated inorganic particles in the conductive paste]
When the conductive filler to be included in the conductive paste is silver-coated resin particles and silver particles or flat silver-coated inorganic particles, the ratio of the silver-coated resin particles and silver particles or flat silver-coated inorganic particles is the paste In 100% by mass, it is preferable that 50% by mass or more and less than 100% by mass of silver-coated resin particles, and more than 0% by mass and less than 50% by mass of silver particles or flat silver-coated inorganic particles. Further, in 100% by mass of the paste, the proportion of the conductive filler in which the silver-coated resin particles and the silver particles or the flat silver-coated inorganic particles are combined is preferably 70 to 90% by mass, preferably 75 to 85% by mass. It is more preferable to use a ratio. The silver particles may be spherical, but a flat shape is preferable because the number of contact points between the fillers increases and the conductivity becomes higher. The average particle size of the silver particles is 5 μm or less, and the average particle size of the flat silver-coated inorganic particles is 10 μm or less, so that the conductivity after applying and curing the conductive paste is kept smooth. In addition, it is preferable. The flat shape refers to a shape having an aspect ratio (long side / short side) of 2.0 or more. The silver particles preferably have an aspect ratio of 1.5 to 10.0. The flat silver-coated inorganic particles preferably have an aspect ratio of 10.0 to 30.0. The average particle diameter of the silver particles or the flat silver-coated inorganic particles is determined in the same manner as the average particle diameter of the resin core particles described above. When silver particles or flat silver-coated inorganic particles are included as the conductive filler, higher conductivity than that of the silver-coated resin particles alone can be obtained.

[Binder resin in conductive paste]
The epoxy resin as the binder resin to be included in the conductive paste is, for example, a resin that shows a solid state at room temperature and has a property that the melt viscosity of the resin at 150 ° C. is 0.5 Pa · s or less. For example, biphenyl type, biphenyl mixed type, naphthalene type, cresol novolac type, and dicyclopentadiene type epoxy resin can be used. Examples of the biphenyl type and biphenyl mixed type include NC3100, NC3000, NC3000L, CER-1020, CER-3000L manufactured by Nippon Kayaku Co., Ltd., YX4000, YX4000H, YL6121H manufactured by Mitsubishi Chemical Corporation. In addition, for the cresol novolac type, N-665-EXP-S manufactured by DIC, etc. can be mentioned. Moreover, as for the naphthalene type, HP4032 manufactured by DIC, or the like can be given. Furthermore, in dicyclopentadiene type, HP7200L, HP7200, etc. made from DIC are mentioned. Two or more of these epoxy resins may be used in combination. The value of the melt viscosity shown here is a value measured using a cone and plate type ICI viscometer (manufactured by Research Equipment London).

The phenol resin as the binder resin to be included in the conductive paste may be of any structure as long as the thermosetting phenol resin is a thermosetting type, but the molar ratio of formaldehyde / phenol is in the range of 1-2. Preferably there is. The thermosetting phenol resin preferably has a weight average molecular weight of 300 to 5,000, more preferably 1,000 to 4,000. If it is less than 300, the amount of water vapor generated during heat curing is large, and voids are easily formed in the film, and it is difficult to obtain sufficient film strength. If it is greater than 5000, the solubility is insufficient and it becomes difficult to form a paste. A part of the thermosetting phenol component used in the present invention may be replaced with another compound having a phenolic hydroxyl group. Examples of the resin having a phenolic hydroxyl group include a mixture with p-cresol or o-cresol, an alkylphenol resol type resin using x-cresol or 3,5-dimethylphenol, a xylene resin-modified resin resin, a rosin-modified phenol resin, etc. Is mentioned. The weight average molecular weight is obtained by converting a value measured by gel permeation chromatography (GPC) into styrene.

Generally used silicone resin can be used as the binder resin included in the conductive paste. For example, straight silicone resins such as methyl and methylphenyl, modified silicone resins modified with epoxy resins, alkyd resins, polyesters, acrylic resins, etc., can be used alone or in combination. it can.

The above-mentioned epoxy resin, phenol resin, or silicone resin can suppress deterioration of quality due to aging of the conductive paste, and at the same time has a rigid skeleton in the main chain, and the cured product has excellent heat resistance and moisture resistance. The durability of the electrode to be formed can be improved. One or more binder resins of epoxy resin, phenol resin or silicone resin have a mass ratio of 10 to 40:60 to 90, preferably 20 to 30:70 to 80 (binder resin: conductive). Contained in the conductive paste in such a ratio that it becomes a conductive filler). When the ratio of the binder resin is less than the lower limit, problems such as poor adhesion occur. Exceeding the upper limit causes problems such as a decrease in conductivity.

[Curing agent in conductive paste]
As the curing agent, commonly used imidazoles, tertiary amines, Lewis acids containing boron fluoride, or compounds thereof are suitable. Examples of imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4 -Methyl-5-hydroxymethylimidazole, 2-phenylimidazole isocyanuric acid adduct and the like. Tertiary amines include piperidine, benzyldiamine, diethylaminopropylamine, isophoronediamine, diaminodiphenylmethane, and the like. The Lewis acid containing boron fluoride includes an amine complex of boron fluoride such as boron fluoride monoethylamine. Further, a curing agent having a high potential such as DICY (dicyandiamide) may be used, and the curing agent may be used in combination as the accelerator. Of these, imidazoles such as 2-ethyl-4-methylimidazole and 2-phenyl-4,5-dihydroxymethylimidazole are particularly preferred for the purpose of improving adhesion.

[Solvent in conductive paste]
Solvents include dioxane, hexane, toluene, methyl cellosolve, cyclohexane, diethylene glycol dimethyl ether, dimethylformamide, N-methylpyrrolidone, diacetone alcohol, dimethylacetamide, γ-butyrolactone, butyl carbitol, butyl carbitol acetate, ethyl carbitol, Examples thereof include ethyl carbitol acetate, butyl cellosolve, butyl cellosolve acetate, ethyl cellosolve, and α-terpineol. Of these, ethyl carbitol acetate, butyl carbitol acetate, and α-terpineol are particularly preferred.

[Method for preparing conductive paste]
The conductive paste is prepared by first mixing the binder resin with the solvent under a temperature of preferably 50 to 70 ° C., more preferably 60 ° C. At this time, the ratio of the binder resin is preferably 5 to 50 parts by mass, more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the solvent. Next, an appropriate amount of the curing agent is mixed, the conductive filler is further added, and, for example, a kneader such as a three-roll mill or a reiki machine is preferably kneaded for 0.1 to 1 hour to form a paste. Thus, a conductive paste is prepared. At this time, in order to give the prepared conductive paste an appropriate viscosity and necessary fluidity, and for the reasons described above, the conductive filler in the conductive paste is 70 to 90% by mass as described above. To mix. Moreover, the usage-amount of binder resin is adjusted so that mass ratio with an electroconductive filler may become the above-mentioned ratio from the reason mentioned above. As a result, the viscosity is preferably adjusted to 10 to 300 Pa · s. By adjusting the viscosity within this range, the printability of the conductive paste is improved and the printed pattern shape after printing is also kept good.

The conductive paste thus prepared is applied to, for example, the end face of the chip-shaped element body of a chip-type electronic component, and is a resin electrode that is one component of the external terminal electrode by drying, baking, or the like at a predetermined temperature. Formed as a layer. Firing is performed, for example, by using an apparatus such as a hot-air circulating furnace, and preferably holding at a temperature of 150 to 250 ° C. for 0.5 to 1 hour. The silver-coated resin particles of the present invention are heat-treated in the atmosphere at a temperature of 250 ° C. or higher and lower than the melting temperature of the resin core particles, whereby the silver in the coating layer is melt-sintered. If the silver-coated resin particles having a coating layer in which silver is melt-sintered are used to form the resin electrode layer, a conductive path in the resin electrode can be easily obtained, and a higher conductive resin electrode layer can be obtained. can get.

Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, the surface of the resin core particles was modified by irradiating the silicone resin particles (PSQ resin particles) of the resin core particles having an average particle diameter of 2 μm and a coefficient of variation of the particle diameter of 5% with oxygen plasma. . Specifically, the resin particles were plasma-treated for 30 minutes at a temperature of 50 ° C. with a power of 300 W at a frequency of 13.56 MHz with a plasma generator (manufactured by Plasma Ion Assist).

Next, 20 g of stannous chloride and 15 cm ³ of hydrochloric acid having a concentration of 35% were diluted to 1 dm ³ with water using a 1 dm ³ volumetric flask and kept at 30 ° C. The plasma-treated silicone resin particles were added to this aqueous solution and stirred for 1 hour, and then the silicone resin particles were filtered and washed with water.

Next, a silver substitution layer was formed by electroless plating on the surface of the silicone resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 16 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated silicone resin particles in this aqueous solution.

Next, 63 g of silver nitrate, 25% aqueous ammonia, and 320 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 920 cm ³ of formalin (formaldehyde concentration: 37%) is added as a reducing agent to the slurry after the dropwise addition of the silver nitrate-containing aqueous solution, and then the pH is adjusted to 12 by dropwise addition of an aqueous sodium hydroxide solution and maintained at a temperature of 25 ° C. While stirring, silver was deposited on the surface of the resin particles to form a silver coating layer. Thereafter, washing and filtration were performed, and finally, drying was performed at a temperature of 60 ° C. using a vacuum dryer to obtain silver-coated resin particles in which the amount of silver was 80% by mass with respect to 100% by mass of the silver-coated resin particles. .

Subsequently, a conductive paste was prepared using the silver-coated resin particles as a conductive filler at a predetermined ratio. Specifically, first, in addition to the conductive filler, a biphenyl type epoxy resin composition having a melt viscosity of 0.01 Pa · s at 150 ° C. as a binder resin constituting an organic vehicle and showing a solid state at room temperature (Nippon Kayaku Co., Ltd., product name: NC3100), 2-ethyl-4-methylimidazole as an imidazole curing agent as a curing agent, and butyl carbitol acetate as a solvent were prepared.

Next, 30 parts by mass of a binder resin was mixed with 100 parts by mass of the prepared solvent under the condition of a temperature of 60 ° C. Further, an appropriate amount of a curing agent was added to this mixture. The mixture after the addition of the curing agent has a mass ratio of the conductive filler to the binder resin of 80:20 (conductivity) so that the proportion of non-volatile components contained in the prepared paste is 60% by mass. The conductive paste was prepared by adding the conductive filler so as to be a filler: binder resin), kneading with a three-roll mill, and forming a paste.

<Example 2>
First, the resin core particle silicone resin particles (PSQ resin particles) having an average particle diameter of 3 μm and a particle diameter variation coefficient of 5% were subjected to acid treatment to modify the surface of the resin core particles. Specifically, the mixture was stirred in a 2 mass% chromic acid-sulfuric acid solution at 50 ° C. for 60 minutes, and then the slurry was separated by filtration to obtain a washing cake. The washed cake was dried to obtain hydrophilic resin particles.

Next, the acid-treated silicone resin particles were pretreated in the same manner as in Example 1. Next, a silver substitution layer was formed by electroless plating on the surface of the silicone resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 364 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated silicone resin particles in this aqueous solution.

Next, 37 g of silver nitrate, 25% aqueous ammonia, and 280 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Thereafter, silver was deposited on the surface of the resin particles in the same manner as in Example 1 to form a silver coating layer. Then, washing | cleaning and filtration were performed, and it was made to dry at the temperature of 60 degreeC finally using the vacuum dryer, and obtained the silver coating resin particle whose quantity of silver is 70 mass% with respect to 100 mass% of silver coating resin particles. .

Subsequently, a conductive paste was prepared using the silver-coated resin particles as a conductive filler at a predetermined ratio. Specifically, in addition to the conductive filler, the same binder resin as in Example 1, the same curing agent as in Example 1, and the same solvent as in Example 1 were prepared.

Next, 30 parts by mass of a binder resin was mixed with 100 parts by mass of the prepared solvent under the condition of a temperature of 60 ° C. Further, an appropriate amount of a curing agent was added to this mixture. The mixture after the addition of the curing agent has a mass ratio of the conductive filler to the binder resin of 80:20 (conductivity) so that the ratio of the nonvolatile content contained in the prepared paste is 70% by mass. The conductive paste was prepared by adding the conductive filler so as to be a filler: binder resin), kneading with a three-roll mill, and forming a paste.

<Example 3>
First, silicone resin particles (PSQ resin particles) of resin core particles having an average particle diameter of 10 μm and a particle diameter variation coefficient of 5% were subjected to silane treatment to modify the surface of the resin core particles. Specifically, a silicone resin is put in a kneader, and a silane coupling agent (structural formula (MeO) ₃ SiC ₃ H ₆ (OC ₂ H ₄ ) _n OMe) mixed solution dissolved in ethanol is stirred in the kneader. Slowly charged and stirred for 10 minutes. The obtained powder was dried.

Next, in the same manner as in Example 1, the silane-treated silicone resin particles were pretreated. Next, a silver substitution layer was formed by electroless plating on the surface of the silicone resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 312 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated silicone resin particles in this aqueous solution.

Next, 24 g of silver nitrate, 25% aqueous ammonia, and 240 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 144 cm ³ of formalin (formaldehyde concentration: 37% by mass) as a reducing agent was added to the slurry after dropping the aqueous solution containing silver nitrate, and then the pH was adjusted to 12 by adding aqueous sodium hydroxide solution to a temperature of 25 ° C. By stirring while being held, silver was deposited on the surface of the resin particles to form a silver coating layer. Then, washing | cleaning and filtration were performed, and it was made to dry at the temperature of 60 degreeC finally using a vacuum dryer, and obtained the silver coating resin particle whose quantity of silver is 60 mass% with respect to 100 mass% of silver coating resin particles. .

Next, 30 parts by mass of a binder resin was mixed with 100 parts by mass of the prepared solvent under the condition of a temperature of 60 ° C. Further, an appropriate amount of a curing agent was added to this mixture. Then, in the mixture after the addition of the curing agent, the mass ratio of the conductive filler and the binder resin is 85:15 (conductivity so that the ratio of the nonvolatile content contained in the prepared paste is 70% by mass. The conductive paste was prepared by adding the conductive filler so as to be a filler: binder resin), kneading with a three-roll mill, and forming a paste.

<Example 4>
First, silicone shell-acrylic core resin particles, which are resin core particles having an average particle diameter of 3 μm and a coefficient of variation of the particle diameter of 5%, were prepared. The silicone shell-acrylic core resin particles are obtained by adding organotrialkoxysilane to a system in which acrylic particles are dispersed in water and ethanol solution with stirring to obtain a hydrolyzate of organotrialkoxysilane. It was obtained by adding an alkaline substance or an aqueous solution thereof, dehydrating and condensing the organotrialkoxysilane hydrolyzate, and precipitating it as polyorganosilsesquioxane on the surface of the acrylic particles. The obtained resin core particles were subjected to ozone treatment with an ozone generator (model ozone super ace, manufactured by Japan Ozone Generator Co., Ltd.) at a gas concentration of 2 vol% for 30 minutes to modify the surface.

Then, in the same manner as in Example 1, the ozone-treated silicone shell-acrylic core resin particles were pretreated. Next, a silver substitution layer was formed by electroless plating on the surface of the silicone shell-acrylic core resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 364 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated silicone shell-acrylic core resin particles in this aqueous solution.

Next, 37 g of silver nitrate, 25% aqueous ammonia, and 280 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 168 cm ³ of formalin (formaldehyde concentration: 37% by mass) is added as a reducing agent to the slurry after the dropwise addition of the silver nitrate-containing aqueous solution, and then the pH is adjusted to 12 by adding a sodium hydroxide aqueous solution to a temperature of 25 ° C. By stirring while being held, silver was deposited on the surface of the resin particles to form a silver coating layer. Then, washing | cleaning and filtration were performed, and it was made to dry at the temperature of 60 degreeC finally using the vacuum dryer, and obtained the silver coating resin particle whose quantity of silver is 70 mass% with respect to 100 mass% of silver coating resin particles. .

<Example 5>
First, the resin core particle polytetrafluoroethylene resin particle (PTFE resin particle) having an average particle diameter of 2 μm and a particle diameter variation coefficient of 10% is subjected to plasma treatment and silane treatment, and the resin core particle The surface was modified. Specifically, polytetrafluoroethylene resin particles plasma-treated in the same manner as in Example 1 were used as a polyether type silane coupling agent (structural formula (MeO) ₃ SiC ₃ H ₆ (OC ₂ H ₄ ) _n OMe) 2 mass It added in ethanol of% concentration, and stirred for 30 minutes at room temperature. Thereafter, the slurry was filtered, washed with water, and dried to obtain hydrophilic fluororesin resin particles.

Next, pretreatment of polytetrafluoroethylene (PTFE) resin particles subjected to the above plasma treatment and silane treatment was performed in the same manner as in Example 1. Next, a silver substitution layer was formed by electroless plating on the surface of the polytetrafluoroethylene resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 416 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated polytetrafluoroethylene resin particles in this aqueous solution.

Next, 63 g of silver nitrate, 25% aqueous ammonia, and 320 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 192 cm ³ of formalin (formaldehyde concentration: 37% by mass) as a reducing agent was added to the slurry after the dropwise addition of the silver nitrate-containing aqueous solution, and then the pH was adjusted to 12 by adding a sodium hydroxide aqueous solution to a temperature of 25 ° C. By stirring while being held, silver was deposited on the surface of the resin particles to form a silver coating layer. Thereafter, washing and filtration were performed, and finally, drying was performed at a temperature of 60 ° C. using a vacuum dryer to obtain silver-coated resin particles in which the amount of silver was 80% by mass with respect to 100% by mass of the silver-coated resin particles. .

Next, 30 parts by mass of a binder resin was mixed with 100 parts by mass of the prepared solvent under the condition of a temperature of 60 ° C. Further, an appropriate amount of a curing agent was added to this mixture. The mixture after the addition of the curing agent has a mass ratio of the conductive filler to the binder resin of 85:15 (conductivity) so that the non-volatile content in the prepared paste is 60% by mass. The conductive paste was prepared by adding the conductive filler so as to be a filler: binder resin), kneading with a three-roll mill, and forming a paste.

<Example 6>
First, polytetrafluoroethylene resin particles (PTFE resin particles) of resin core particles having an average particle diameter of 5 μm and a particle diameter variation coefficient of 7% were used in the same manner as in Example 1. Oxygen plasma was irradiated to modify the surface of the resin core particles.

Next, pretreatment of the plasma-treated polytetrafluoroethylene resin particles was performed in the same manner as in Example 1. Next, a silver coating layer was formed by electroless plating on the surface of the polytetrafluoroethylene resin particles having the tin adsorption layer formed on the surface by the pretreatment. Specifically, first, 328 g of sodium ethylenediaminetetraacetate as a complexing agent, 76.0 g of sodium hydroxide as a pH adjusting agent, and 151 cm ³ of formalin (formaldehyde concentration 37% by mass) as a reducing agent are added to 2 dm ³ of water. By dissolving these, an aqueous solution containing a complexing agent and a reducing agent was prepared. Next, a slurry was prepared by immersing the pretreated polytetrafluoroethylene resin particles in this aqueous solution.

Then, silver nitrate 27 g, 25% ammonia water 63cm ^3, water 252Cm ³ mixture of silver nitrate-containing aqueous solution to prepare, with stirring the slurry, was added dropwise the silver nitrate-containing aqueous solution. Furthermore, by adding sodium hydroxide aqueous solution to the slurry after dropping the silver nitrate-containing aqueous solution to adjust the pH to 12 and stirring while maintaining the temperature at 25 ° C., silver is deposited on the surface of the resin particles to cover the silver A layer was formed. Thereafter, washing and filtration were performed, and finally, drying was performed at a temperature of 60 ° C. using a vacuum dryer to obtain silver-coated resin particles in which the amount of silver was 63% by mass with respect to 100% by mass of the silver-coated resin particles. .

<Example 7>
First, the resin core particle polyimide resin particles (PAI resin particles) having an average particle diameter of 3 μm and a coefficient of variation in particle diameter of 10% were subjected to alkali treatment to modify the surface of the resin core particles. Specifically, the mixture was stirred for 300 minutes in a 5 mass% caustic soda solution at 50 ° C, and then the slurry was separated by filtration to obtain a washing cake. The washed cake was dried to obtain hydrophilic polyimide resin particles.

Next, in the same manner as in Example 1, pretreatment of the alkali-treated polyimide resin particles was performed. Next, a silver coating layer was formed by electroless plating on the surface of the polyimide resin particles having a tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 333 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing 10 g of the pretreated polyimide resin particles in this aqueous solution.

Next, 28 g of silver nitrate, 25% aqueous ammonia, and 284 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 154 cm ³ of formalin (formaldehyde concentration: 37% by mass) as a reducing agent was added to the slurry after the dropwise addition of the silver nitrate-containing aqueous solution, and then the pH was adjusted to 12 by adding an aqueous sodium hydroxide solution to a temperature of 25 ° C. By stirring while being held, silver was deposited on the surface of the resin particles to form a silver coating layer. Thereafter, washing and filtration were performed, and finally, drying was performed at a temperature of 60 ° C. using a vacuum dryer to obtain silver-coated resin particles having a silver amount of 64% by mass with respect to 100% by mass of the silver-coated resin particles. .

<Example 8>
First, aramid resin particles (polyparaphenylene terephthalamide resin particles) of resin core particles having an average particle diameter of 5 μm and a coefficient of variation in particle diameter of 10% were prepared.

Next, aramid resin particles were pretreated in the same manner as in Example 1. Next, a silver substitution layer was formed by electroless plating on the surface of the aramid resin particles having the tin adsorption layer formed on the surface by the pretreatment. Specifically, first, an aqueous solution containing a complexing agent was prepared by dissolving 369 g of sodium ethylenediaminetetraacetate as a complexing agent in 2 dm ³ of water. Next, a slurry was prepared by immersing the pretreated aramid resin particles in this aqueous solution.

Next, 28 g of silver nitrate, 25% aqueous ammonia, and 284 cm ³ of water were mixed to prepare a silver nitrate-containing aqueous solution having a pH of 10 to 11, and this silver nitrate-containing aqueous solution was dropped while stirring the slurry to obtain a silver substitution layer. Further, 170 cm ³ of formalin (formaldehyde concentration: 37% by mass) as a reducing agent was added to the slurry after the dropwise addition of the silver nitrate-containing aqueous solution, and then the pH was adjusted to 12 by adding a sodium hydroxide aqueous solution to a temperature of 25 ° C. By stirring while being held, silver was deposited on the surface of the resin particles to form a silver coating layer. Thereafter, washing and filtration were performed, and finally, drying was performed at a temperature of 60 ° C. using a vacuum dryer to obtain silver-coated resin particles having a silver amount of 71% by mass with respect to 100% by mass of the silver-coated resin particles. .

<Example 9>
Using the same resin core particle silicone resin particles (PSQ resin particles) having an average particle diameter of 2 μm as in Example 1, this resin core particle was subjected to plasma treatment in the same manner as in Example 1. Hereinafter, in the same manner as in Example 1. Thus, silver-coated resin particles having an amount of silver of 80% by mass relative to 100% by mass of the silver-coated resin particles were obtained.

Next, the silver-coated resin particles and flat silver particles having an average particle diameter of 5 μm are used as conductive fillers in a proportion of 90% by mass of silver-coated resin particles and 10% by mass of silver particles in 100% by mass of the paste. Of the conductive filler so that the proportion of the conductive filler contained in the paste is 70% by mass and the mass ratio of the conductive filler to the binder resin is 75:25 (conductive filler: binder resin). A conductive paste was prepared by adding a conductive filler and kneading with a three-roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 1 except that silver particles were contained.

<Example 10>
Using resin resin core silicone resin particles (PSQ resin particles) having an average particle diameter of 5 μm and a particle diameter variation coefficient of 3%, the resin core particles are acid-treated in the same manner as in Example 2, In the same manner as in Example 2, silver-coated resin particles having 60% by mass of silver with respect to 100% by mass of silver-coated resin particles were obtained.

Next, the silver-coated resin particles and the flat silver particles having an average particle diameter of 2 μm are used as conductive fillers in a proportion of 80% by mass of silver-coated resin particles and 20% by mass of silver particles in 100% by mass of the paste. The conductive material is used so that the non-volatile content in the paste is 60% by mass and the mass ratio of the conductive filler to the binder resin is 80:20 (conductive filler: binder resin). A conductive paste was prepared by adding a filler and kneading with a three-roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 2 except that silver particles were contained.

<Example 11>
In the same manner as in Example 4, resin particles of silicone shell-acrylic core having an average particle diameter of 3 μm were prepared as resin core particles. The silicone shell-acrylic core resin particles are acid-treated in the same manner as in Example 2. Silver-coated resin particles in which the amount of silver is 70% by mass with respect to 100% by mass of the silver-coated resin particles in the same manner as in Example 2. Got.

Next, the above silver-coated resin particles and flat silver particles having an average particle diameter of 5 μm are used as conductive fillers in a proportion of 80% by mass of silver-coated resin particles and 20% by mass of silver particles in 100% by mass of the paste. Of the conductive filler so that the proportion of the conductive filler contained in the paste is 60% by mass and the mass ratio of the conductive filler to the binder resin is 80:20 (conductive filler: binder resin). A conductive paste was prepared by adding a conductive filler and kneading with a three-roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 2 except that silicone core-acrylic core resin particles were used as the resin core particles and silver particles were contained.

<Example 12>
Using the same resin core particle silicone resin particles (PSQ resin particles) having an average particle diameter of 2 μm as in Example 1, this resin core particle was subjected to plasma treatment in the same manner as in Example 1, and silver in the same manner as in Example 1. Silver-coated resin particles in which the amount of silver was 80% by mass with respect to 100% by mass of the coated resin particles were obtained.

Subsequently, a conductive paste was prepared using the silver-coated resin particles as a conductive filler at a predetermined ratio. Specifically, in addition to the conductive filler, a thermosetting phenol resin composition (manufactured by DIC, product name: PR15) was prepared as a phenol resin constituting an organic vehicle.

Next, the phenol resin having a nonvolatile content concentration of 40% by mass (solvent PGMEA) has a mass ratio of the conductive filler to the binder resin so that the nonvolatile content contained in the prepared paste is 70% by mass. However, the said conductive filler was added so that it might become 80:20 (conductive filler: binder resin), and the electrically conductive paste was prepared by knead | mixing with a 3 roll mill and making it into a paste.

<Example 13>
Using silicone rubber particles (silicone rubber powder) of resin core particles having an average particle diameter of 2 μm, the resin core particles are subjected to plasma treatment in the same manner as in Example 1 and 100 masses of silver-coated resin particles in the same manner as in Example 1. Silver-coated resin particles having an amount of silver of 80% by mass with respect to% were obtained.

Subsequently, a conductive paste was prepared using the silver-coated resin particles as a conductive filler at a predetermined ratio. Specifically, in addition to the conductive filler, a phenylmethyl silicone resin composition (manufactured by Toray Dow Co., Ltd., product name: 805 RESIN) was prepared as a silicone resin constituting the organic vehicle.

Next, the silicone resin (non-volatile content: 50% by mass, solvent xylene) has a mass ratio of the conductive filler to the binder resin so that the non-volatile content in the prepared paste is 80% by mass. , 80:20 (conductive filler: binder resin), the conductive filler was added, and the conductive paste was prepared by kneading with a three-roll mill to make a paste.

<Example 14>
Using resin resin core silicone resin particles (PSQ resin particles) having an average particle diameter of 0.1 μm and a particle diameter variation coefficient of 8%, the resin core particles are subjected to plasma treatment in the same manner as in Example 1. In the same manner as in Example 1, silver-coated resin particles having an amount of 90% by mass with respect to 100% by mass of the silver-coated resin particles were obtained.

<Example 15>
The same silver-coated resin particles as in Example 1 and flat silver-coated inorganic particles having an average particle diameter of 3 μm were prepared. The flat silver-coated inorganic particles had a core particle of graphite having an aspect ratio of 10, and the silver coating ratio was 90% by mass. The silver-coated resin particles and the flat silver-coated inorganic particles are used as conductive fillers at a ratio of 70% by mass of silver-coated resin particles and 30% by mass of silver-coated inorganic particles in 100% by mass of the paste. The above-mentioned conductive filler is binder resin so that the non-volatile content contained is 80% by mass and the mass ratio of the conductive filler to the binder resin is 75:25 (conductive filler: binder resin). And a conductive paste was prepared by kneading with a three-roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 1 except that it contained flat silver-coated inorganic particles.

<Example 16>
The same silver-coated resin particles as in Example 1 and flat silver-coated inorganic particles having an average particle diameter of 5 μm were prepared. In the flat silver-coated inorganic particles, the core particles were talc having an aspect ratio of 20, and the silver coating ratio was 80% by mass. The silver-coated resin particles and the flat silver-coated inorganic particles are used as conductive fillers at a ratio of 70% by mass of silver-coated resin particles and 30% by mass of silver-coated inorganic particles in 100% by mass of the paste. The conductive filler is added so that the nonvolatile content ratio is 75% by mass, and the mass ratio of the conductive filler to the binder resin is 80:20 (conductive filler: binder resin). A conductive paste was prepared by kneading with a three-roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 1 except that it contained flat silver-coated inorganic particles.

<Example 17>
The same silver-coated resin particles as in Example 1 and flat silver-coated inorganic particles having an average particle diameter of 10 μm were prepared. The flat silver-coated inorganic particles had a core particle of mica having an aspect ratio of 30 and a silver coating ratio of 80% by mass. The silver-coated resin particles and the flat silver-coated inorganic particles are used as conductive fillers in a ratio of 90% by mass of silver-coated resin particles and 10% by mass of silver particles in 100% by mass of the paste, and contained in the prepared paste. The conductive filler is added so that the nonvolatile content ratio is 70% by mass, and the mass ratio of the conductive filler to the binder resin is 80:20 (conductive filler: binder resin). A conductive paste was prepared by kneading with this roll mill to form a paste. A conductive paste was prepared in the same manner as in Example 1 except that it contained flat silver-coated inorganic particles.

<Comparative Example 1>
Acrylic resin particles (PMMA resin particles) having an average particle diameter of 2 μm and a coefficient of variation in particle diameter of 5% were prepared as resin core particles. The resin core particles were not surface modified. Except this, it carried out similarly to Example 1, and obtained the silver covering resin particle whose quantity of silver is 80 mass% with respect to 100 mass% of silver covering resin particles. Next, using only the silver-coated resin particles as a conductive filler, the mass ratio of the conductive filler and the binder resin is such that the nonvolatile content contained in the prepared paste is 60% by mass, The conductive paste was added in the same manner as in Example 1 by adding the conductive filler so as to be 80:20 (conductive filler: binder resin), kneading with a three-roll mill, and forming a paste. Prepared.

<Comparative example 2>
Styrene resin particles having an average particle diameter of 3 μm and a coefficient of variation in particle diameter of 3% were prepared as resin core particles. The resin core particles were surface-treated by acid treatment in the same manner as in Example 2. Except this, it carried out similarly to Example 2, and obtained the silver covering resin particle whose quantity of silver is 70 mass% with respect to 100 mass% of silver covering resin particles. Next, using only the silver-coated resin particles as a conductive filler, the mass ratio of the conductive filler and the binder resin is such that the non-volatile content contained in the prepared paste is 60% by mass, The conductive paste was added in the same manner as in Example 1 by adding the conductive filler so as to be 80:20 (conductive filler: binder resin), kneading with a three-roll mill, and forming a paste. Prepared.

<Comparative Example 3>
Melamine resin particles having an average particle diameter of 3 μm and a coefficient of variation in particle diameter of 7% were prepared as resin core particles. The resin core particles were surface-modified by silane coupling treatment as in Example 3. Except this, it carried out similarly to Example 2, and obtained the silver covering resin particle whose quantity of silver is 70 mass% with respect to 100 mass% of silver covering resin particles. Next, using only the silver-coated resin particles as a conductive filler, the mass ratio of the conductive filler and the binder resin is such that the nonvolatile content contained in the prepared paste is 60% by mass, The conductive paste was added in the same manner as in Example 1 by adding the conductive filler so as to be 80:20 (conductive filler: binder resin), kneading with a three-roll mill, and forming a paste. Prepared.

<Comparative example 4>
Using the silicone resin particles (PSQ resin particles) of the resin core particles having an average particle diameter of 12 μm and a coefficient of variation of the particle diameter of 4%, the resin core particles are subjected to plasma treatment in the same manner as in Example 1. In the same manner as in Example 1, silver-coated resin particles having an amount of silver of 80% by mass with respect to 100% by mass of silver-coated resin particles were obtained. Next, the above silver-coated resin particles and flat silver particles having an average particle diameter of 2 μm are used as conductive fillers in a proportion of 80% by mass of silver-coated resin particles and 20% by mass of silver particles in 100% by mass of the paste. The above conductive material is used so that the non-volatile content in the later paste is 70% by mass and the mass ratio of the conductive filler to the binder resin is 80:20 (conductive filler: binder resin). A conductive paste was prepared by adding a conductive filler and kneading with a three-roll mill to form a paste.

<Comparative Example 5>
A silicone resin (PSQ resin particle) having an average particle diameter of 2 μm as in Example 1 was prepared as a resin core particle. The resin core particles were not surface modified. Except for this, silver coated resin particles having an amount of silver of 80% by mass with respect to 100% by mass of silver coated resin particles were obtained in the same manner as in Example 1, but when pretreatment was performed with an aqueous stannous chloride solution, The resin first floated with the aqueous stannous chloride solution, and the resulting silver-coated powder had a sparse silver coating. Next, using only the silver-coated resin particles as a conductive filler, the mass ratio of the conductive filler and the binder resin is such that the nonvolatile content contained in the prepared paste is 70% by mass, The conductive paste was added in the same manner as in Example 1 by adding the conductive filler so as to be 80:20 (conductive filler: binder resin), kneading with a three-roll mill, and forming a paste. Prepared.

<Comparative Example 6>
Silicone resin particles (PSQ resin particles) as resin core particles having an average particle size of 2.0 μm and a particle size variation coefficient of 7% are pulverized for 5 hours with a dry ball mill (media uses zirconia), Resin core particles having an average particle diameter of 0.05 μm were obtained. The resin core particles were subjected to plasma treatment in the same manner as in Example 1 to obtain silver-coated resin particles in which the amount of silver was 90% by mass with respect to 100% by mass of the silver-coated resin particles as in Example 1. Next, using only the above-mentioned silver-coated resin particles as a conductive filler, the mass ratio of the conductive filler to the binder resin is 80% so that the proportion of non-volatile components contained in the prepared paste is 70% by mass. : The conductive paste was prepared in the same manner as in Example 1 by adding the above conductive filler so as to be 20 (conductive filler: binder resin), and kneading with a three-roll mill to make a paste. did.

Types of resin core particles of Examples 1 to 17 and Comparative Examples 1 to 6, average particle diameter thereof, surface modification method, silver content in silver-coated resin particles, and average particle diameter of silver particles as a conductive filler Tables 1 to 3 show the ratios. In Table 1, the core-shell resin particles mean silicone shell-acrylic core resin particles.

<Comparison test and evaluation>
As a result of differential thermal analysis and thermogravimetry of the silver-coated resin particles obtained in Examples 1 to 17 and Comparative Examples 1 to 6, the conductive pastes obtained in Examples 1 to 14 and Comparative Examples 1 to 6 were applied. Tables 4 and 5 show the volume resistivity and appearance of the conductive film after firing and firing, and the volume resistivity and appearance and comprehensive evaluation after the conductive film is subjected to atmospheric heat treatment.

(1) Differential thermal analysis and thermogravimetric measurement of silver-coated resin particles Using a differential thermal / thermogravimetric measurement device (TG-DTA), silver coating from room temperature in the air at a rate of 5 ° C / min. When the resin particles were heated, the exothermic peak temperature was measured. At the same time, the weight reduction rate of the silver-coated resin particles when heated to 300 ° C. was measured.

(2) Volume resistivity and appearance of the conductive film after firing The conductive paste was applied on a glass substrate using a screen printing method and dried, and then the coating film (conductive film) was 180 ° C. in the atmosphere. It was baked for 1 hour and cured. The volume resistivity of this conductive film was measured by the four-probe four-terminal method of JIS K 7197. The appearance of the conductive film was evaluated by visual observation of the conductive film surface layer.

(3) Volume resistivity of conductive film after atmospheric heat treatment and its appearance,
The conductive film was placed in an electric oven at 300 ° C. for 30 minutes, then removed from the oven, and the volume resistivity of the conductive film was measured by the four-probe four-terminal method of JIS K7197. As for the appearance of the conductive film, the cross section of the conductive film before and after the atmospheric heat treatment was observed with a scanning electron microscope (SEM), and the presence or absence of the change was evaluated.

(4) Comprehensive evaluation All the results of (1) to (3) above were judged as “excellent”, partly inferior as “good”, and partly bad as “bad”.

As apparent from Table 4 and Table 5, regarding the exothermic peak temperature when the silver-coated resin particles were subjected to differential thermal analysis, the silver-coated resin particles of Comparative Examples 1 to 3 were 245 to 259 ° C. and had low heat resistance. In contrast, the silver-coated resin particles of Examples 1 to 17 and Comparative Examples 4 to 6 had a high heat resistance of 265 to 546 ° C. This is due to the use of resin core particles with high heat resistance. In addition, regarding the weight reduction rate of the silver-coated resin particles when heated to 300 ° C. in thermogravimetry, the silver-coated resin particles of Comparative Examples 1 to 3 were 11 to 23% and the heat resistance was low, The silver-coated resin particles of Examples 1 to 17 and Comparative Examples 4 to 6 were 9% or less and had high heat resistance. This is because the resin core particles having high heat resistance are used.

In addition, regarding the volume resistivity of the conductive films after firing made of the conductive paste using silver-coated resin particles, the conductive films of Comparative Examples 1 to 4 have 0.1 × 10 ⁻⁵ to 9.0 × 10 ⁻⁵ Ω. The conductive film of Examples 1 to 17 was 0.6 × 10 ⁻⁵ to 9.0 × 10 ⁻⁵ Ω · cm, which was different between the comparative example and the example. There was no. On the other hand, the conductive films of Comparative Examples 5 to 6 had a volume resistivity of 80 × 10 ⁻⁵ to 200 × 10 ⁻⁵ Ω · cm and a high volume resistivity. This is because the surface modification treatment was not performed in Comparative Example 5 and thus the silver coating was poor. In Comparative Example 6, the particle size of the silver-coated resin particles was small, so that aggregation occurred and the paste was poorly dispersed. Caused by

Furthermore, regarding the volume resistivity of the conductive film after the heat treatment of this conductive film, the conductive films of Examples 1 to 17 and Comparative Example 5 are 1.0 × 10 ⁻⁵ to 10 × 10 ⁻⁵ Ω · cm. While the conductivity was not changed, the conductive films of Comparative Examples 1 to 3 were 100 × 10 ⁻⁵ to 1000 × 10 ⁻⁵ Ω · cm, and the conductivity was high. This is because in Comparative Examples 1 to 3, the resin was decomposed by atmospheric firing.

In addition, regarding the appearance of the conductive films after firing made of the conductive paste using silver-coated resin particles, the conductive films of Comparative Examples 4 to 6 have poor smoothness, and the conductive films of Examples 3, 9, 11 and 14 Slightly inferior in smoothness. In contrast, the conductive films of Examples 1 to 8, 10, 12, 13, 15 to 17 and Comparative Examples 1 to 3 were good. This is because the average particle size of the silver-coated resin particles used is large in Comparative Example 4 and small in Comparative Example 6. In Comparative Example 5, the silver coating was sparse, and at the same time, the particles were self-precipitated in the plating process, the silver coating layer was peeled off from the resin core particles, and the silver fine powder was agglomerated. In Example 3, the particle diameter of the silver-coated resin particles was as large as 10 μm, and the particle filling property in the coating film was lowered. Further, Examples 9 and 11 are because the silver particles used are slightly large at 5 μm. Further, in Example 14, the particle diameter of the silver-coated resin particles was as small as 0.1 μm, and many agglomerates were contained, resulting in a decrease in surface smoothness. In addition, regarding the appearance of the conductive film after firing in the air made of a conductive paste using silver-coated resin particles, the conductive films of Comparative Examples 1 to 3 were significantly decomposed and changed. Although only a part of the conductive films of Examples 7 and 8 was decomposed, it could not be said that there was a change. In contrast, Examples 1 to 6, Examples 9 to 17, and Comparative Examples 4 to 6 were not changed. This is considered because the heat resistance of the resin core particles is different. Comprehensively evaluating the above, Examples 1, 2, 4 to 6 were excellent, Examples 3 and 7 to 17 were good, and Comparative Examples 1 to 6 were bad.

The silver-coated resin particles of the present invention are mounted on an automobile, a conductive paste that forms external terminal electrodes of chip-type electronic components such as chip inductors, chip resistors, chip-type multilayer ceramic capacitors, chip-type multilayer ceramic capacitors, and chip thermistors. It can be used for heat conductive paste for heat dissipation and other conductive film paste to be soldered. In addition, since the silver-coated resin particles of the present invention have a high antibacterial action, they can be developed for applications having antibacterial properties.

Claims

A resin core particle having heat resistance and a silver coating layer formed on the surface of the resin core particle,
Resin core particles having an average particle size of 0.1 to 10 μm,
The amount of silver contained in the silver coating layer is 60 to 90 parts by mass with respect to 100 parts by mass of the silver coated resin particles, and the exothermic peak temperature when the differential thermal analysis of the silver coated resin particles is 265 ° C. or more. Silver-coated resin particles characterized by that.
The silver-coated resin particles according to claim 1, wherein the resin core particles having heat resistance are particles of silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber, or silicone shell-acrylic core resin.
The silver-coated resin particles according to claim 1 or 2, wherein the weight-decreasing rate of the silver-coated resin particles when the silver-coated resin particles are heated to 300 ° C in thermogravimetry is 10% or less.
A step of modifying the surface of the resin particles by subjecting the resin core particles having heat resistance to plasma treatment, ozone treatment, acid treatment, alkali treatment or silane treatment;
Adding a resin core particle comprising the surface-modified resin particles to an aqueous solution of a tin compound kept at 25 to 45 ° C. to form a tin adsorption layer on the surface of the resin particles;
The tin adsorption layer formed on the surface of the resin core particle is brought into contact with an electroless silver plating solution containing no reducing agent, and the tin adsorption layer formed on the surface of the resin core particle and the silver in the electroless plating solution Forming a silver substitution layer on the surface of the resin core particles by a substitution reaction with
Adding a reducing agent to the electroless silver plating solution and forming a silver coating layer on the surface of the silver substitution layer of the resin core particles.
5. The method for producing silver-coated resin particles according to claim 4, wherein the resin core particles having heat resistance are particles of silicone resin, silicone rubber, polyimide resin, aramid resin, fluororesin, fluororubber, or silicone shell-acrylic core resin. .
A conductive paste comprising the silver-coated resin particles according to any one of claims 1 to 3 and one or more binder resins of epoxy resin, phenol resin, or silicone resin.
A conductive paste comprising the silver-coated resin particles according to any one of claims 1 to 3, silver particles, and one or more binder resins of epoxy resin, phenol resin, or silicone resin.
A silver-coated resin particle according to any one of claims 1 to 3, a flat silver-coated inorganic particle in which a flat inorganic core particle is silver-coated, and one or two of an epoxy resin, a phenol resin, or a silicone resin A conductive paste comprising at least a binder resin.
A method for forming a thermosetting conductive film by applying the conductive paste according to any one of claims 6 to 8 to a substrate and curing the paste.