JP7478138B2 - Metallic copper fine particle-containing resin composition and method for producing same - Google Patents

Description

The present invention relates to a resin composition containing metallic copper microparticles and a method for producing the same, and more specifically to a resin composition containing metallic copper microparticles in which metallic copper microparticles are uniformly dispersed and which can efficiently exhibit antiviral properties, and a method for producing the same.

Conventionally, silver ions or copper (II) ions have been used as active ingredients in materials having antibacterial or antiviral properties, and various antiviral materials have been proposed in which these metal ions are supported on substances such as zeolite or silica gel or dispersed in a solvent.
However, although the above metal ions can exhibit antiviral activity against viruses having an envelope structure, such as influenza viruses, they are unable to exhibit antiviral activity against viruses that do not have an envelope structure, such as noroviruses.

Monovalent copper compounds are also known as metal compounds capable of exhibiting antiviral properties, regardless of the presence or absence of an envelope structure. For example, Patent Document 1 below describes an antiviral composition that contains monovalent copper compound fine particles, a reducing agent, and a dispersion medium, and has a pH of 6 or less. Patent Document 2 below describes an antibacterial and antiviral composition that contains cuprous oxide particles with a BET specific surface area of 5 to 100 m ² /g, a saccharide having an aldehyde group, and a photocatalytic substance. Patent Document 3 below describes an antiviral coating film that contains a copper-supported oxide having an average secondary particle diameter of 80 nm to 600 nm, in which at least one of copper particles and copper compound particles is supported on an oxide particle, barium sulfate having an average secondary particle diameter of 1 μm to 15 μm, and a water-repellent resin binder.

Patent No. 5194185 JP 2013-82654 A JP 2015-205998 A

However, fine particles of a monovalent copper compound tend to aggregate, making it difficult to uniformly disperse the monovalent copper compound. Thus, when the dispersion liquid is used as an antiviral composition or when it is mixed with a paint and used as a coated antiviral molded body, it has been difficult to efficiently express the antiviral properties of the fine particles of the monovalent copper compound.
In addition, when a monovalent copper compound having a large particle size as described in the above patent document is used, the particle surface area is reduced, and the antiviral properties are reduced due to a decrease in the chance of contact with the virus. In addition, an antiviral molded product coated with a monovalent copper compound having a large particle size has a problem that the haze and light transmittance are deteriorated, resulting in a loss of transparency.
Furthermore, fine particles of a monovalent copper compound can also be obtained by pulverization, but since there is no coating agent or stabilizer, the particles tend to aggregate, and oxidation of cuprous oxide to copper(II) oxide is likely to occur.

In order to solve these problems, the present inventors have conducted intensive research into microparticles that can efficiently exhibit high antiviral properties, and as a result, have found that metallic copper can exhibit higher antiviral properties than monovalent copper compounds, and that by coating the surface of metallic copper microparticles with a fatty acid and an ester compound of the fatty acid, the microparticles can be uniformly dispersed without aggregation even when contained in a low-boiling point solvent at a high concentration.
Since the metallic copper microparticles are provided in the form of a dispersion liquid in a low-boiling point solvent as a dispersion medium, adding this dispersion liquid to a resin and heating and kneading it to uniformly disperse the metallic copper microparticles would be difficult to handle at the manufacturing site because the solvent would easily evaporate and there would be a risk of fire.
Therefore, an object of the present invention is to provide a metallic copper microparticle-containing resin composition in which metallic copper microparticles capable of efficiently exhibiting antiviral properties are uniformly dispersed, and a method for producing the same.

According to the second manufacturing method of the present invention, a method for manufacturing a resin composition containing metallic copper microparticles is provided, which is characterized in that a fatty acid copper is added to a polyol, which is then heated and mixed to prepare a dispersion in which metallic copper microparticles coated with a fatty acid and/or an ester compound of the fatty acid and a polyol are dispersed, the polyol is removed from the dispersion to obtain metallic copper microparticles coated with a fatty acid and/or an ester compound, and the metallic copper microparticles are then added to a resin and kneaded.

According to the fourth manufacturing method of the present invention, a fatty acid and a copper compound are added to a polyol, which is then heated and mixed to prepare a dispersion in which metallic copper fine particles coated with a fatty acid and/or an ester compound consisting of the fatty acid and a polyol are dispersed, the polyol is removed from the dispersion to obtain metallic copper fine particles coated with a fatty acid and/or an ester compound, and the metallic copper fine particles are then added to a resin and kneaded to produce a resin composition containing metallic copper fine particles.

In the production method of the present invention,
1. The copper compound is any one of copper acetate, copper chloride, and copper bromide;
2. The polyol is any one of diethylene glycol, ethylene glycol, triethylene glycol, propylene glycol, and glycerin;
is preferred.

In the resin composition containing metallic copper microparticles of the present invention, the metallic copper microparticles are coated with a fatty acid and/or an ester compound of the fatty acid and a polyol, and are therefore uniformly dispersed in the resin without agglomeration, and molded articles made using this resin composition can exhibit excellent antiviral properties.
Furthermore, the resin composition containing metallic copper fine particles of the present invention has not only antiviral properties, but also properties such as antibacterial properties, electrical conductivity, ultraviolet shielding properties, antifouling properties, etc. In particular, it can exhibit antiviral properties regardless of the presence or absence of an envelope structure, and can also exhibit antiviral properties against viruses that do not have an envelope structure, such as norovirus.
In the method for producing a resin composition containing metallic copper microparticles of the present invention, a resin composition can be efficiently produced in which metallic copper microparticles coated with a fatty acid and/or an ester compound of the fatty acid and a polyol are uniformly dispersed without agglomeration.

(Metallic copper fine particle-containing resin composition)
In the resin composition containing metallic copper microparticles of the present invention, the metallic copper microparticles have their surfaces coated with a fatty acid and/or an ester compound, which makes it possible to suppress aggregation of the microparticles in the resin and allows excellent antiviral properties to be exhibited over a long period of time.
Metallic copper, an active ingredient exhibiting antiviral properties, can adsorb viruses and inactivate them, and can exhibit excellent antiviral properties regardless of the presence or absence of an envelope structure. In other words, the excellent antiviral properties of metallic copper microparticles are believed to be due to the oxidizing power of active oxygen generated from metallic copper, which denatures the proteins of viruses consisting of microproteins, and metallic copper reacts with the thiol groups of the proteins of the viruses to denature the proteins, thereby inactivating the viruses. The mechanism by which metallic copper microparticles coated with fatty acids and/or ester compounds exhibit antiviral properties is not clear, but it is believed that viruses attached to the coating present on the surface of the metallic copper microparticles are replaced by the coating and come into contact with metallic copper.

In addition, as will be seen from the examples described later, Examples 1, 2, and 3 have antiviral properties, whereas Comparative Example 2, to which the ester compound was added later, does not exhibit antiviral properties. This is believed to be because the metallic copper particles are oxidized during kneading. Adding the ester component during kneading has no effect, and it is important that the particles are coated from the beginning.
In the resin composition containing metallic copper microparticles of the present invention, the metallic copper microparticles in the resin are coordinated around the metallic copper microparticles with either a fatty acid or an ester compound, while since the ester compound has an affinity for the fatty acid, it is believed that both the fatty acid and the ester compound are coordinated around the fatty acid or mixed with the fatty acid to the metallic copper microparticles.
In the metallic copper fine particle-containing resin composition, particularly excellent antiviral properties are exhibited by containing a sufficient amount of metallic copper fine particles that are sufficiently coated with an ester compound.

[Metallic copper particles]
Examples of fatty acids that may be used to coat the surface of the metallic copper microparticles include myristic acid, stearic acid, oleic acid, palmitic acid, n-decanoic acid, para-toic acid, succinic acid, malonic acid, tartaric acid, malic acid, glutaric acid, adipic acid, and acetic acid. These may also be used in combination with multiple types of acids, but higher fatty acids having 10 to 22 carbon atoms, and of these, stearic acid, are particularly preferred.
The ester compound coating the surface of the metallic copper microparticles is preferably an ester compound derived from the fatty acids and polyols that are the raw materials in the method for producing metallic copper microparticle powder of the present invention described below, but it is also possible to blend ester compounds other than those derived from the raw materials, and these may be different ester compounds, but it is preferable that they are of the same type as the ester compounds derived from the raw materials.
Suitable ester compounds for coating the surface of metallic copper microparticles include ester compounds of the above-mentioned fatty acids and the polyols described below, such as, but not limited to, diethylene glycol distearate, ethylene glycol distearate, propylene glycol distearate, polyethylene glycol distearate, and polypropylene glycol distearate.

The average primary particle size of the metallic copper fine particles in the metallic copper fine particle-containing resin composition of the present invention is preferably in the range of 10 to 500 nm, particularly 10 to 200 nm. By having the average particle size of the metallic copper fine particles in the above range, it is possible to efficiently exhibit excellent antiviral performance. That is, metallic copper fine particles having such a small average primary particle size can efficiently generate active oxygen because the contact rate of the metallic copper fine particles with oxygen is high, and it is possible to exhibit excellent antiviral performance. In addition, the average primary particle size referred to in this specification refers to the average of metallic copper fine particles with no gap between them, which are regarded as one particle. The average primary particle size can be calculated from an image obtained by a scanning microscope using image analysis type particle size distribution measurement software (e.g., Mac-View, etc.).
The amount of the fatty acid and/or ester compound coated on the metallic copper fine particles is preferably in the range of 0.1 to 20% by mass, particularly preferably 0.1 to 10% by mass. If the amount of coating is less than the above range, there is a risk of oxidation or aggregation of the metallic copper fine particles compared to when the amount is within the above range, while if the amount of coating is more than the above range, there is a risk of reduced antiviral properties compared to when the amount is within the above range.

[resin]
In the resin composition containing metallic copper particles of the present invention, examples of the resin containing metallic copper particles include olefin resins such as low-, medium-, and high-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, isotactic polypropylene, syndiotactic polypropylene, propylene-ethylene copolymer, polybutene-1, ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and ethylene-propylene-butene-1 copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamide resins such as nylon 6, nylon 6,6, and nylon 6,10; and polycarbonate resins. Thermosetting resins such as phenolic resins, epoxy resins, urethane resins, melamine resins, urea resins, alkyd resins, unsaturated polyester resins, and silicone resins, as well as conventionally known thermosetting resins such as photocurable acrylic resins.

In the resin composition containing metallic copper particles of the present invention, the metallic copper particles are preferably blended in an amount of 0.01 to 20% by mass, 0.01 to 2% by mass, particularly 0.01 to 0.2% by mass relative to the resin (solid content). If the amount of metallic particles is less than the above range, antiviral properties cannot be fully expressed, while if the amount of metallic particles is more than the above range, not only is the economical efficiency inferior compared to the case in the above range, but moldability and coatability may be impaired. In addition, in the resin composition containing metallic copper particles of the present invention, a high-concentration master batch may be produced and this master batch may be blended with a resin to mold a molded product having a metallic copper particle content in the above range.
Depending on the application, the resin composition containing metallic copper particles of the present invention can be blended with various known compounding agents, such as fillers, plasticizers, leveling agents, thickeners, viscosity reducers, stabilizers, antioxidants, ultraviolet absorbers, dispersants, pigments, etc., in accordance with known recipes.

(First and second manufacturing methods)
The metallic copper particle resin composition of the present invention can be prepared by the following production method.
(1) Preparation of dispersion containing metallic copper microparticles Fatty acid copper is added to a polyol and heated to prepare a polyol dispersion in which metallic copper microparticles having their surfaces coated with fatty acids and/or ester compounds of the fatty acids and polyols are dispersed.
The heating temperature is preferably lower than the decomposition starting temperature of the fatty acid copper used, specifically in the range of 160 to 230° C. The heating and mixing time is preferably 60 to 360 minutes.

The amount of fatty acid copper is preferably in the range of 0.1 to 5% by mass per polyol. If the amount of fatty acid copper is less than the above range, there is a risk that sufficient antiviral properties cannot be imparted to the dispersion liquid compared to when the amount is within the above range. On the other hand, if the amount of fatty acid copper is more than the above range, there is a risk that the economic efficiency is inferior and the coatability and moldability are impaired compared to when the amount is within the above range.
Examples of polyols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and glycerin. In the present invention, glycerin is particularly suitable since it has a high boiling point and reducing property.

(2) Preparation of resin composition using metallic copper microparticle dispersion Next, a polyol dispersion in which metallic copper microparticles coated with a fatty acid and/or an ester compound of the fatty acid and a polyol are dispersed is added to a resin and kneaded to prepare a metal microparticle-containing resin composition.
When a dispersion liquid containing metallic copper particles in which a polyol is used as a solvent is used, either the thermoplastic resin or the thermosetting resin described above can be used.
When using a thermoplastic resin such as polyolefin, polyester, or polyamide, a twin-screw extruder is used, and while the resin is melt-kneaded, a dispersion liquid containing metallic copper particles is added to disperse the metallic copper particles in the resin, thereby preparing a molten metallic copper particle-containing resin composition.
The melt-kneaded resin composition containing metallic copper microparticles can be extruded into a strand shape and cut into a pellet-shaped molded product, or it can be molded into a film-shaped molded product using a T-die, or it can be spun into a nonwoven fabric-like molded product, or it can be molded into any of the conventionally known molded product shapes.
When a thermosetting resin is used, a dispersion containing metallic copper particles is added together with the thermosetting resin and a curing agent, and then heated and cured to form a coating film or a molded article.

(3) Preparation of resin composition using metallic copper microparticle powder In the second manufacturing method of the present invention, a metallic copper microparticle powder in a dry state recovered by removing the dispersion medium from the metallic copper microparticle-containing dispersion liquid described above is used and added to a resin to prepare a metallic copper microparticle-containing resin composition.
The recovery of metallic copper microparticles from a metallic copper microparticle-containing dispersion liquid in which a polyol is used as a dispersion medium can be carried out by a conventionally known separation method such as membrane separation, centrifugation, evaporation, decantation, etc., but it is preferable to recover metallic copper microparticles having an adjusted coating amount of a fatty acid and/or an ester compound with particularly excellent antiviral properties by carrying out the method described below.

That is, the above-mentioned polyol dispersion containing metallic copper particles and a low boiling point solvent are mixed to prepare a mixed liquid.
The mixed liquid is allowed to stand for 30 to 120 minutes at a temperature of 0 to 40° C. to cause phase separation of the polyol and the low-boiling point solvent. When the mixed liquid is phase-separated, excess fatty acid copper, free fatty acid or fatty acid ester compound, or impurities present in the mixed liquid are extracted into the low-boiling point solvent side, and metallic copper fine particles coated with fatty acid and/or ester compound of said fatty acid and polyol remain in a precipitated state in the polyol.
Next, the low boiling point solvent is removed from the phase-separated mixture to obtain a dispersion in which metallic copper particles coated with fatty acid and/or ester compound of fatty acid and polyol are precipitated in polyol. In order to obtain a dispersion in which metallic copper particles are dispersed in polyol, it is important not to add a dispersant when mixing with the low boiling point solvent. The removal of the low boiling point solvent can be performed by a conventionally known separation method such as simple distillation, reduced pressure distillation, precision distillation, thin film distillation, extraction, etc.

The low boiling point solvent is preferably added to the polyol dispersion in an amount of 10 to 200% by mass based on the polyol.
Examples of low-boiling point solvents include esters such as methyl acetate, ethyl acetate, and butyl acetate, hydrocarbons such as hexane, heptane, toluene, xylene, and cyclohexane, and ketones such as methyl isobutyl ketone, methyl ethyl ketone, and cyclohexanone, but ester solvents are preferred, and among them, butyl acetate, ethyl acetate, and methyl isobutyl ketone can be preferably used. It is important that the low-boiling point solvent is not miscible with the polyol, and it is preferable to combine the polyol and the low-boiling point solvent so that the difference in solubility parameter (Sp value) between them is 3 or more.
Preferably, when diethylene glycol (Sp value: 12.6) is used as the polyol, butyl acetate (Sp value: 8.4) is used as the low boiling point solvent.

When preparing a resin composition containing metallic copper microparticles using the metallic copper microparticle powder obtained in this way, it is preferable to mix the thermoplastic resin and the metallic microparticle powder and feed them into a twin-screw extruder. The thermoplastic resin and the metallic microparticle powder fed into the extruder can be melt-kneaded while dispersing the metallic copper microparticles in the resin to prepare a molten metallic copper microparticle-containing resin composition. The prepared metallic copper microparticle-containing resin composition can be molded into a molded body in the same manner as when using a metallic copper microparticle-containing dispersion. In addition, when the metallic copper microparticles are directly mixed with the thermoplastic resin, it is preferable to use a polyolefin, since it is desirable for the thermoplastic resin to have a low melting point.
When a thermosetting resin is used, metallic copper fine particle powder can be added to and mixed with the thermosetting resin and curing agent, and then heated and cured, in the same manner as in the case where the metal fine particle-containing dispersion liquid described above is used.
Heat curing conditions for coatings, resin molded products, etc. cannot be generally defined depending on the type of thermosetting resin or curing agent used, but can be set based on the curing temperature and curing time of the thermosetting resin used.

(Third and fourth manufacturing methods)
The metallic copper particle resin composition of the present invention can be prepared by the following method in addition to the first and second production methods described above.
That is, in the first and second manufacturing methods described above, by carrying out the same procedures as the first and second manufacturing methods except that a combination of a fatty acid and a copper compound is added instead of the fatty acid copper used as a raw material, a dispersion liquid in which metallic copper particles coated with a fatty acid and/or an ester compound are dispersed can be prepared, and the resulting dispersion liquid can be used in the same manner as the first and second manufacturing methods.
Examples of copper compounds include oxides, acetates, chlorides, bromides, hydroxides, and cyanides, with copper acetate, copper chloride, and copper bromide being particularly preferred.
The amount of the fatty acid and the copper compound to be blended is preferably 0.1 to 5% by mass, respectively, based on the polyol.

(Uses of the resin composition containing metallic copper particles)
More specific applications of the metallic copper microparticle-containing composition of the present invention include molded articles obtained by directly molding molded articles such as films, sheets, nonwoven fabrics, fibers, or pellets as resin compositions based on thermoplastic resins. In addition, in the case of a thermosetting resin base, examples of the coating composition include molded articles obtained by applying a coating film to the surface of a substrate such as a nonwoven fabric, a resin film, or a fiber product.

(Preparation of metallic copper particle dispersion)
2.5% by mass of copper stearate was added to diethylene glycol, and the mixture was heated with stirring. After heating for 2 hours from the time when the temperature reached 190°C, the diethylene glycol dispersion was cooled to 120°C or less. After cooling, butyl acetate was added and the mixture was stirred for about 1 minute. After the mixture was left to stand and the diethylene glycol layer and the butyl acetate layer were separated, the butyl acetate layer was removed to obtain diethylene glycol dispersion 1 containing metallic copper fine particles.
In addition, butyl acetate in which 1.0% by mass of dispersant DISPERBYK-2090 (manufactured by BYK-Chemie) and 1.0% by mass of diethylene glycol distearate were dissolved was added to the prepared dispersion 1 and stirred. After leaving it to stand for about 1 hour, the butyl acetate layer was collected to obtain butyl acetate dispersion 2.

Example 1
A master batch was prepared using a twin-screw extruder (manufactured by Technovel Co., Ltd.) under molding conditions of an extrusion molding machine set temperature of 230° C. and Q (discharge rate)/N (screw rotation speed)=4/100=0.04, while adding the prepared dispersion 1 so that metallic copper became 0.5% by mass.
Next, the master batch was blended into polypropylene resin (S119 manufactured by Prime Polypro) so that the metallic copper content was 0.05% by mass, and the mixture was kneaded in a twin-screw extruder at a secondary molding temperature of 200° C., extruded from a nozzle diameter of 600 μm, and stretched with an air ejector to produce polypropylene fibers, which were then heated and pressed with an embossing roll to obtain a nonwoven fabric.

(Preparation of metallic copper fine particle powder)
The prepared dispersion liquid 1 was suction filtered through a membrane filter having a pore size of 10 μm, washed with water, and then dried at 50° C. for 2 hours to obtain metallic copper fine particle powder 1.
The solvent in the prepared dispersion liquid 2 was dried to obtain metallic copper fine particle powder 2.

Example 2
The obtained metallic copper microparticle powder 1 was blended in an amount of 0.5% by mass into polypropylene resin (WMG03 manufactured by Japan Polypropylene), and a master batch was prepared using a twin-screw extruder (manufactured by Technovel Co., Ltd.) under molding conditions of an extrusion molding machine set temperature of 230°C and Q (discharge rate)/N (screw rotation speed) = 4/100 = 0.04.
Next, the master batch was blended into polypropylene resin (S119 manufactured by Prime Polypro) so that the metallic copper content was 0.05% by mass, and the mixture was kneaded in a twin-screw extruder at a secondary molding temperature of 200° C., extruded from a nozzle diameter of 600 μm, and stretched with an air ejector to produce polypropylene fibers, which were then heated and pressed with an embossing roll to obtain a nonwoven fabric.

Example 3
The obtained metallic copper microparticle powder 2 was mixed in an amount of 0.5% by mass into polypropylene resin (WMG03 manufactured by Japan Polypropylene), and a master batch was prepared using a twin-screw extruder (manufactured by Technovel Co., Ltd.) under molding conditions of an extrusion molding machine set temperature of 230°C and Q (discharge rate)/N (screw rotation speed) = 4/100 = 0.04.
Next, the master batch was blended into polypropylene resin (S119 manufactured by Prime Polypro) so that the metallic copper content was 0.05% by mass, and the mixture was kneaded in a twin-screw extruder at a secondary molding temperature of 200° C., extruded from a nozzle diameter of 600 μm, and stretched with an air ejector to produce polypropylene fibers, which were then heated and pressed with an embossing roll to obtain a nonwoven fabric.

(Comparative Example 1)
A nonwoven fabric was prepared in the same manner as in Example 2, except that the metallic copper fine particle powder used was changed from Powder 1 to commercially available metallic copper fine particle powder 3 (manufactured by Sigma-Aldrich).

(Comparative Example 2)
A nonwoven fabric was prepared in the same manner as in Example 2, except that the metallic copper fine particle powder used was changed from Powder 1 to commercially available metallic copper fine particle powder 3 (manufactured by Sigma-Aldrich) and 0.5% by mass of diethylene glycol distearate was added.

(Method for evaluating antiviral properties of nonwoven fabric)
1. Host cells are infected with a virus, cultured, and then centrifuged to remove cell debris to obtain a virus suspension.
2. The virus suspension obtained in step 1 above is diluted 10-fold with sterile distilled water to prepare the test virus suspension.
3. Inoculate a 0.4 g test piece of nonwoven fabric with 0.2 mL of the test virus suspension.
4. After leaving the specimen at 25°C for 2 hours, 20 mL of SCDLP medium is added and stirred with a vortex mixer to wash out the virus from the specimen.
5. The viral infectivity is measured by the plaque assay method, and the antiviral activity value is calculated.
6. If the antiviral activity value is 3.0 or more, it can be determined that the product has sufficient antiviral properties against the virus.

The antiviral evaluation results of the nonwoven fabric prepared are shown in Table 1.

The resin composition containing metallic copper microparticles of the present invention can be used to produce textile products such as paper products, masks, wet tissues, air conditioner filters, air purifier filters, clothing, work clothes, curtains, carpets, automotive parts, packaging parts, freshness-preserving agents, sheets, towels, bath mats, diaper covers, stuffed animals, slippers, shoe insoles, and cleaning supplies such as wipers, making it possible to impart antiviral properties to these products.
In addition, the material can be used for medical equipment, packaging films for medical equipment, waste containers, garbage bags, wall materials and floor materials in nursing homes or public facilities such as hospitals and schools, wax coating materials, and vomit disposal tools.
Furthermore, in addition to sanitary products, the composition can be used for a variety of applications, including conductive films, films, metal plates, glass plates, marine paints, heat exchanger fins, ceramic products such as tableware, rubber products, metal products such as faucets, additives for humidifiers, liquid detergents, ion adsorbents, and deodorants.

Claims (4)

A method for producing a resin composition containing metallic copper particles, comprising: adding fatty acid copper to a polyol, heating and mixing the mixture to prepare a dispersion in which metallic copper particles coated with a fatty acid and/or an ester compound of the fatty acid and a polyol are dispersed; removing the polyol from the dispersion to obtain metallic copper particles coated with a fatty acid and/or an ester compound; and then adding the metallic copper particles to a resin and kneading the resulting mixture. A method for producing a resin composition containing metallic copper particles, comprising: adding a fatty acid and a copper compound to a polyol, heating and mixing the mixture to prepare a dispersion in which metallic copper particles coated with a fatty acid and/or an ester compound consisting of the fatty acid and a polyol are dispersed; removing the polyol from the dispersion to obtain metallic copper particles coated with a fatty acid and/or an ester compound; and then adding the metallic copper particles to a resin and kneading the resulting mixture. 3. The method for producing a resin composition containing metallic copper particles according to claim 2 , wherein the copper compound is any one of copper acetate, copper chloride and copper bromide. 3. The method for producing a resin composition containing metallic copper particles according to claim 1 , wherein the polyol is any one of diethylene glycol, ethylene glycol, triethylene glycol, propylene glycol and glycerin.