JP2009067849A - Antibacterial coating film, cooking container having the same and antibacterial coating agent - Google Patents

Abstract

An antibacterial coating film having excellent antibacterial properties, strong film strength, no limit of thinning, excellent surface smoothness even when thinned, and good appearance, and the antibacterial coating film For example, when used as an inner pot of a rice cooker, when the temperature at the time of heat insulation is lowered from the current level, the generation of odor due to the growth of bacteria is suppressed, and a cooking container that can maintain rice deliciously and various articles An antibacterial coating agent capable of imparting good antibacterial properties and water repellency is provided.
In an antibacterial coating film, metal particles having a 50% cumulative diameter D ₅₀ of a particle size distribution of 100 nm or less are dispersed in a film composed of a large number of resin particles. In the cooking container, at least a part of the inner surface of the container body was covered with the antibacterial coating film. The antibacterial coating agent includes metal particles having a 50% cumulative diameter D _{50 of} particle size distribution of 100 nm or less and at least a part of the surface coated with a dispersant, and resin particles.
[Selection figure] None

Description

  The present invention relates to a novel antibacterial coating film having both antibacterial and water repellency, a cooking container having the antibacterial coating film, and an antibacterial coating capable of imparting antibacterial and water repellency to various articles. It relates to the agent.

  In the field of rice cookers, it has been researched to cook rice more deliciously, mainly by improving the heating means and heating method, but when cooking rice, keeping warm the cooked rice, etc. The fact that the odor generated in the rice deteriorates the taste of rice has not been considered much. However, there was a problem that the odor became stronger and the rice was not delicious, especially as it was kept warm in the rice cooker for a long time. One of the causes of the increase in odor due to heat retention is considered to be Bacillus subtilis, which has high heat resistance in the state of spores (espores), and has a maximum growth rate at around 65 ° C. It is done.

Therefore, conventionally, it has been common to prevent the growth of bacteria by setting the temperature of heat retention to about 72 ° C. In addition, the temperature of the heat retention should be set to about 60 ° C., and the inside of the rice cooker should be pressurized with high-temperature steam, or, for example, heated to a high temperature for a very short period of time to prevent bacterial growth. Has also been done. However, in order to respond to the recent demand for CO ₂ emission reduction for the suppression of global warming, further energy saving has been demanded in the field of rice cookers. There is a need to develop a new technology for lowering the temperature of the plant from the current level and suppressing the generation of odor due to the growth of bacteria.

  The inner surface of the container body of the cooking container, such as the inner pot of a rice cooker, is coated on the inner surface for storing the food to be cooked (rice etc.), imparts water repellency to the surface, and is cooked during cooking Proposal has been proposed to provide antibacterial properties by adding inorganic antibacterial agents that mainly contain silver as a functional component to coat films made of fluororesin that function to prevent objects from sticking or scorching. (See, for example, Patent Documents 1 to 3). The reason why silver exhibits antibacterial properties is that silver ions act on DNA such as viruses, fungi, and molds to cause steric hindrance, function as a catalyst by light irradiation, and have oxygen and antibacterial properties. Changing to active oxygen is considered.

  For example, Patent Document 1 discloses that an inorganic antibacterial agent (registered trademark Novalon AG300 manufactured by Toagosei Co., Ltd.) in which silver is supported on ceramic carrier particles having an average particle size of 0.5 μm is applied to a fluororesin-based paint. It is described that, after blending and coating on the inner surface of the container body, etc., baking is performed to form a coat film having both water repellency and antibacterial properties. In Patent Document 2, first, a base layer made of a fluororesin-based paint not containing an inorganic antibacterial agent is formed on the inner surface of the container main body, and the same inorganic antibacterial agent as described above is included on the base layer. It is described that a fluororesin-based paint is applied and baked to form a surface layer to form a coat film having both water repellency and antibacterial properties, having a two-layer structure of the base layer and the surface layer. Yes.

Furthermore, Patent Document 3 discloses an inorganic antibacterial agent (registered trademark Zeomic manufactured by Sinanen Zeomic Co., Ltd.) in which silver ions and zinc ions are supported on zeolite having an average particle diameter of 2.5 μm as carrier particles. Formulated in a fluororesin-based paint, applied to the inner surface of the container body, etc., and then baked to form a layer containing metal ions, to contain a pyroelectric substance in the layer, the layer, Combining with a layer containing pyroelectric materials is described.
JP-A-6-220391 Japanese Patent Application Laid-Open No. 9-188785 JP 2001-46223 A

  By applying the techniques described in Patent Documents 1 to 3 to give good antibacterial properties to the coating film, when the temperature during the incubation is lowered from the current level, the generation of odor due to the growth of bacteria Suppression is being considered. However, in each of the inventions described in Patent Documents 1 to 3, since an inorganic antibacterial agent having a large particle size is used, there is a limit that can reduce the thickness of the coating film. The smoothness of the surface is lowered, and there is a possibility that an appearance problem may occur. In addition, the inorganic antibacterial agent protruding from the surface of the coat film is likely to fall off due to external force, and there is a possibility that good antibacterial properties cannot be maintained over a long period of time.

  Furthermore, in the inorganic antibacterial agent, since only a trace amount of silver can be supported with respect to the total amount of the carrier particles, in order to impart sufficient antibacterial properties to the coat film, a larger amount of inorganic antibacterial agent is required. In this case, the amount of the fluororesin or the like that forms the coat film is relatively reduced, so that the film strength of the coat film is reduced or, in some cases, a continuous and uniform amount. There is also a possibility that a coat film cannot be formed.

  In a cooking container such as an inner pot of a rice cooker, the film strength of the coat film is an important factor that affects the quality of the product. In other words, in the field of cooking containers, a comparison object is a normal metal cooking container that does not have a coat film. If the coat film is easily damaged or peeled off, these normal cooking dishes are used. In comparison with the container, it is often determined that the durability of the cooking container itself is not sufficient. Therefore, the coating film is required to have as high a film strength as possible in order not to be easily damaged or peeled off.

  An object of the present invention is to provide an antibacterial coating film having excellent antibacterial properties, strong film strength, no limit of thinning, excellent surface smoothness even when thinned, and good appearance. It is in. In addition, the object of the present invention is to provide the antibacterial coating film, so that, for example, it is used as an inner pot of a rice cooker to suppress the generation of odor due to the growth of bacteria when the temperature at the time of heat insulation is lowered from the current level. The object of the present invention is to provide a cooking container capable of maintaining delicious rice at all times. Furthermore, the objective of this invention is providing the antimicrobial coating agent which can provide favorable antimicrobial property and water repellency to various articles | goods.

The present invention is an antibacterial coating film in which metal particles are dispersed in a film made of a large number of resin particles, wherein the metal particles have a 50% cumulative diameter D ₅₀ of a particle size distribution of 100 nm or less. Antibacterial coating film. According to the present invention, instead of the inorganic antibacterial agent having a large particle diameter described above, the metal particles are finely dispersed so that the 50% cumulative diameter D ₅₀ of the particle size distribution in the film falls within the above range. As a result, an antibacterial coating film is formed. Therefore, the antibacterial coating film has no limit for reducing the thickness, and even if it is thinned, it has excellent surface smoothness and a good appearance.

Further, the finely dispersed metal particles can also exhibit high antibacterial properties in the film. That is, since the antibacterial property based on the mechanism described above due to metal ions such as silver ions is mainly expressed on the surface of the metal particles, the smaller the particle size of the metal particles and the larger the specific surface area, the more the metal particles The antibacterial property per unit mass tends to be strong. When the metal particles are finely dispersed so that the 50% cumulative diameter D ₅₀ of the particle size distribution in the film falls within the above range, high antibacterial properties can be expressed with a smaller amount of metal particles. The film strength of the antibacterial coating film can be increased by reducing the content of metal particles.

Therefore, according to the present invention, there is provided an antibacterial coating film having excellent antibacterial properties, strong film strength, no limit to thinning, excellent surface smoothness even when thinned, and good appearance. can do. The metal particles preferably have a ratio D ₈₀ / D ₅₀ of 80% cumulative diameter D ₈₀ and 50% cumulative diameter D ₅₀ of the particle size distribution in the film of 2.0 or less. Thereby, since the particle size is large, the metal particles having a large particle size in which the internal metal does not contribute to the development of antibacterial properties can be eliminated.

  Therefore, when the content of the metal particles is the same, the antibacterial property of the antibacterial coating film can be further increased, and when maintaining the same level of antibacterial property, the content of the metal particles is reduced, The film strength of the antibacterial coating film can be further improved. The content of the metal particles is preferably 1% by mass or less of the total amount of solids constituting the antibacterial coating film. When the content exceeds the above range, the amount of the resin is relatively reduced, so that the film strength of the antibacterial coating film may be lowered. As the metal particles, silver particles having excellent antibacterial properties based on the mechanism described above are preferable.

  As the resin particles forming the antibacterial coating film, in view of imparting good water repellency, film strength, heat resistance, etc. to the antibacterial coating film, fluororesin and polyether ether excellent in these characteristics Particles of at least one resin selected from the group consisting of ketone resins (PEEK) are preferred. The antibacterial coating film of the present invention is preferably formed by applying a coating agent containing metal particles and resin particles to the base surface and then baking it. As a result, an antibacterial coating film having excellent water repellency, film strength, and heat resistance as well as antibacterial properties can be formed by the same operation as that for forming a conventional normal coating film.

  The present invention is a cooking container characterized in that at least a part of an inner surface of a container main body for containing an object to be cooked is covered with the antibacterial coating film of the present invention. According to the present invention, good antibacterial properties can be imparted to the cooking container by the function of the antibacterial coating film. Therefore, for example, in the case of an inner pot of a rice cooker, when the temperature at the time of heat retention is lowered from the current level, the generation of odor due to the growth of bacteria can be suppressed and the rice can always be maintained deliciously.

Further, the present invention is an antibacterial coating agent characterized in that it comprises metal particles having a 50% cumulative diameter D _{50 of} a particle size distribution of 100 nm or less and at least a part of the surface coated with a dispersant, and resin particles. is there. According to the present invention, by applying the antibacterial coating agent to the surface of various articles, it is possible to impart good antibacterial properties and water repellency to the articles.

  According to the present invention, there is provided an antibacterial coating film having excellent antibacterial properties, strong film strength, no limit to thinning, excellent surface smoothness even when thinned, and good appearance. Can do. In addition, according to the present invention, since the antibacterial coating film is provided, for example, as an inner pot of a rice cooker, when the temperature at the time of heat retention is lowered from the current level, the generation of odor due to the growth of bacteria is suppressed. Thus, it is possible to provide a cooking container that can always maintain delicious rice. Furthermore, according to the present invention, an antibacterial coating agent capable of imparting good antibacterial properties and water repellency to various articles can be provided.

<Antimicrobial coating film>
The antibacterial coating film of the present invention is characterized in that metal particles are dispersed in a film composed of a large number of resin particles, and the 50% cumulative diameter D ₅₀ of the particle size distribution of the metal particles is 100 nm or less. To do. As the resin particles forming the antibacterial coating film, various resin particles capable of forming a coating film excellent in water repellency can be used, and in particular, tetrafluoroethylene resin (PTFA), tetrafluoroethylene-par Fluorine resins such as fluoroalkyl vinyl ether resin (PFA), tetrafluoroethylene-hexafluoropropylene resin (FEP), and particles of at least one resin selected from the group consisting of PEEK are preferred.

  In consideration of forming a dense and uniform antibacterial coating film, the resin particles preferably have an average particle size of 0.1 μm or more and 50 μm or less, particularly 0.5 μm or more and 20 μm or less. Further, as the resin particles, it is more preferable to use together the first resin particles having an average particle diameter of 1 μm or more and 20 μm or less and the second resin particles having an average particle diameter smaller than the first resin particles. . When two types of resin particles having different average particle diameters are used in combination, the two types of resin particles can be closely packed, and the denseness of the antibacterial coating film can be further improved.

  The antibacterial coating film of the present invention comprises a coating agent (dispersion) in which the resin particles and metal particles are dispersed in water or an organic solvent in the same manner as a conventional water-repellent coating film. After applying to the base surface on which the antibacterial coating film is formed, such as the inner surface, by a coating method such as spray coating, flow coating, curtain flow coating, roller coating, dip coating, or spin coating, It is formed by baking and integrating a large number of resin particles. The thickness of the antibacterial coating film is 0.1 μm or more, 100 μm or less, especially 1 μm or more in consideration of forming an antibacterial coating film having excellent water repellency, film strength, heat resistance, surface smoothness and good antibacterial properties. 50 μm or less is preferable.

In the present invention, the antibacterial coating film photographed with a scanning electron microscope has the particle size of all the metal particles imaged in the image corresponding to the area of the actual size of 2.8 μm × 4.0 μm. The particle size distribution of the metal particles in the antibacterial coating film is obtained from the result of repeated operations performed by image processing at 10 locations on the same antibacterial coating film. The reason why the 50% cumulative diameter D ₅₀ of the particle size distribution of the metal particles obtained based on the measurement result is limited to 100 nm or less is as follows.

That is, when the 50% cumulative diameter D ₅₀ exceeds the above range, the particle diameter of the individual metal particles is large, and the specific surface area is smaller than that, and the metal inside the particles does not contribute to the development of antibacterial properties. The ratio is high. Therefore, when the content of the metal particles are the same, as compared with the case of 50% cumulative diameter D ₅₀ is in the above range, reduces the antibacterial antimicrobial coating film, tends to maintain the antimicrobial same level As a result, the content of the metal particles increases, causing a problem that the film strength of the antibacterial coating film decreases.

On the other hand, when the 50% cumulative diameter D ₅₀ is within the above range, a high antibacterial property can be expressed by a small amount of metal particles. The film strength of the film can be increased. Incidentally, 50% cumulative diameter D ₅₀ of the metal particles, considering that further enhance the antimicrobial antimicrobial coat film by increasing the specific surface area of the particles, is preferably as smaller within the above range, practically 5nm or more 100 nm or less, preferably 20 nm or more and 50 nm or less.

In addition, the metal particles were obtained based on the measurement results described above in consideration of avoiding as much as possible the particles with a large particle size in which the inner metal does not contribute to the development of antibacterial properties due to the large particle size. The ratio D ₈₀ / D ₅₀ between the 80% cumulative diameter D ₈₀ and the 50% cumulative diameter D ₅₀ of the particle size distribution of the metal particles in the antibacterial coating film is 2.0 or less, particularly 1.1 or more, 1.6 It is preferable that: As a result, the metal particles having a large particle diameter can be eliminated, and therefore, when the content of the metal particles is the same, the antibacterial property of the antibacterial coating film can be further increased, and the same level of antibacterial property can be obtained. In the case of maintaining, the content of the metal particles can be reduced, and the film strength of the antibacterial coating film can be further improved.

  Moreover, it is preferable that more metal particles are dispersed on the side closer to the base surface than the surface of the antibacterial coating film. Since the antibacterial coating film of the present invention has a structure in which a large number of resin particles are bonded as described above, even if the metal particles are not exposed on the surface of the film, The generated metal ions move to the surface of the membrane through minute gaps between the resin particles, and exhibit good antibacterial properties on the surface. Therefore, by dispersing more metal particles on the side of the antibacterial coating film closer to the base surface, the metal particles exposed to the surface of the antibacterial coating film can be easily removed by external force. The antibacterial property can be maintained over a long period of time by suppressing the decrease in the content of the antibacterial agent and the accompanying decrease in the antibacterial property.

  In order to disperse more metal particles on the side closer to the base surface of the antibacterial coating film, the coating agent including the resin particles and the metal particles described above is placed on the base surface maintained horizontally. After coating, it is allowed to stand to allow the metal particles to settle to the base surface side, or after applying electric potential, a magnetic field, etc., to move the metal particles to the base surface side, and then baking to form an antibacterial coating film. . The content of the metal particles in the antibacterial coating film is preferably 1% by mass or less, particularly 0.05% by mass or more and 0.8% by mass or less, based on the total amount of solids constituting the antibacterial coating film. When the content exceeds the above range, the amount of the resin is relatively reduced, so that the film strength of the antibacterial coating film may be lowered.

  As the metal particles, various metal particles capable of exhibiting antibacterial properties based on the mechanism described above can be used. Examples of the metal particles include particles of one or more metals selected from the group consisting of silver, copper, tin, zinc, and nickel, and silver particles are particularly preferable. The metal particles may contain other metals as long as the antibacterial properties are not inhibited. The metal particles can be formed by a high temperature treatment method called an impregnation method, a liquid phase reduction method, a gas phase method, or the like, but it is particularly preferable to form the metal particles by a liquid phase reduction method.

  In the liquid phase reduction method, for example, a liquid phase reaction system is prepared by adding a reducing agent to an aqueous solution containing a water-soluble metal compound as a starting material for metal ions that are the basis of metal particles and a dispersant. The metal particles can be precipitated in the reaction system by preparing and preferably reducing the metal ions in the reaction system with stirring for a certain period of time. The metal particles formed by the liquid phase reduction method are characterized by being spherical or granular in shape, sharp in particle size distribution, and small in particle size.

Examples of the water-soluble metal compound that is a source of metal ions include silver nitrate (I) [AgNO ₃ ] and silver methanesulfonate [CH ₃ SO ₃ Ag] in the case of silver. Copper (II) [Cu (NO ₃ ) ₂ ], copper sulfate (II) pentahydrate [CuSO ₄ .5H ₂ O] and the like can be mentioned. In the case of tin, tin chloride (IV) pentahydrate [SnCl ₄ .5H ₂ O] and the like are listed. In the case of zinc, zinc chloride (ZnCl ₂ ), zinc sulfate heptahydrate (ZnSO ₄ .7H) ₂ O), zinc nitrate hexahydrate [Zn (NO ₃ ) ₂ .6H ₂ O] and the like. Furthermore, in the case of nickel, nickel chloride (II) hexahydrate [NiCl ₂ · 6H ₂ O], nickel nitrate (II) hexahydrate [Ni (NO ₃ ) ₂ · 6H ₂ O] and the like can be mentioned.

  As the reducing agent, any of various reducing agents capable of reducing metal ions and precipitating them as metal particles in a liquid phase reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, and transition metal ions (trivalent titanium ions, divalent cobalt ions, and the like). However, in order to make the particle size of the metal particles to be precipitated as small as possible, it is effective to reduce the reduction and precipitation rate of the metal ions, and in order to reduce the reduction and precipitation rate, the amount of the reducing agent is reduced. It is preferable to use a reducing agent that is reduced or has a reducing power as weak as possible.

  Examples of the reducing agent having a weak reducing power include alcohols such as methanol, ethanol and 2-propanol, ascorbic acid, and the like, as well as ethylene glycol, glutathione, organic acids (citric acid, malic acid, tartaric acid, etc.), Reducing sugars (glucose, galactose, mannose, fructose, sucrose, maltose, raffinose, stachyose, etc.), aldehydes (formic acid, formaldehyde, acetaldehyde, propionaldehyde, etc.), and sugar alcohols (sorbitol, erythritol, etc.) It is done.

  As the dispersant, various dispersants having a hydrophilic group and having good solubility in water can be used. In the reaction system, the dispersant covers at least a part of the surface of the deposited metal particles to prevent aggregation of the metal particles and to maintain dispersion. The dispersant preferably has a number average molecular weight Mn of 1,000 or more and 800,000 or less, particularly 2,000 or more and 300,000 or less. If the number average molecular weight Mn is less than the above range, there is a possibility that the effect of maintaining the dispersion by preventing aggregation of the metal particles by the dispersing agent may not be obtained.

On the other hand, when the above range is exceeded, the viscosity of the coating agent becomes too high, and there is a possibility that handling at the time of application to the base surface becomes difficult. Examples of the hydrophilic group to be introduced into the dispersant include an oxygen-containing functional group such as an ether bond (—O—), a hydroxy group (—OH), and a carboxyl group (—COOH), an amino group (—NH ₂ ), and an imino group. (> NH), nitrogen-containing functional groups such as ammonium group (—NH ₄ ⁺ ), sulfur-containing functional groups such as sulfanyl group (—SH), sulfanediyl group (—S—), sulfone group (—SO ₃ H), etc. Groups and the like. The dispersing agent may have the said hydrophilic group individually by 1 type, and may have 2 or more types.

  Suitable dispersants include, for example, poval (polyvinyl alcohol), polyethylene oxide, polypropylene oxide, polyethyleneimine, polyvinylpyrrolidone, polyalkanethiol, polyacrylic acid or copolymers thereof, alkali metal salts, ammonium salts, acrylic acid / Maleic acid copolymer or alkali metal salt, ammonium salt thereof, acrylic acid / sulfonic acid copolymer or alkali metal salt thereof, ammonium salt, α-olefin / maleic anhydride copolymer or alkali metal salt thereof, ammonium Examples include salts.

  In addition, when the metal particles are silver particles, the dispersant is likely to be released into the molecule in consideration of preventing the antibacterial property of the antibacterial coating film from being lowered by generating silver sulfide having a low antibacterial property. It is preferable not to contain sulfur in the state. The dispersant can also be added to the reaction system in the state of water or a solution dissolved in a water-soluble organic solvent.

  In order to adjust the particle size of the metal particles, the type and blending ratio of the metal compound, dispersant, and reducing agent are adjusted, and when the metal ions are reduced, the stirring speed, temperature, time, pH, etc. are adjusted. Adjust it. For example, the pH of the reaction system is preferably 7 or more and 13 or less in consideration of forming metal particles having a particle size as small as possible. In order to adjust the pH of the reaction system to the above range, a pH adjusting agent is used. Examples of the pH adjuster include various acids such as nitric acid and various alkalis such as ammonia, depending on the pH value to be adjusted.

Of the metal particles to be deposited in the reaction system, 50% cumulative diameter D ₅₀ of the particle size distribution, 50% of the particle size distribution of an antimicrobial coating film forming cumulative diameter D may be any ₅₀ or less, particularly 60% or more, 100 % Or less is preferable. In the present invention, a metal particle having a 50% cumulative diameter D ₅₀ adjusted within the above range, a dispersing agent that coats at least a part of the metal particle, and a metal that forms a water-soluble metal compound together with the metal. From a liquid phase reaction system containing ions and water, ultrafiltration, centrifugation, washing with water, electrodialysis, etc. are performed to remove impurities such as counterions, and concentration or dilution as necessary. Thus, it is preferable to use, as a raw material for preparing the coating agent, an aqueous dispersion in which metal particles are dispersed in water, the concentration of the metal particles being adjusted.

That is, when a dispersion type coating agent is prepared by blending the aqueous dispersion with a dispersion in which resin particles are dispersed in water or an organic solvent compatible with water, at least the metal particles are mainly used. Antibacterial coating film formed by preventing the aggregation of metal particles in the adjusted coating agent or when the coating agent is applied to the base surface and baked by the function of the dispersing agent that partially coats The 50% cumulative diameter D ₅₀ of the metal particles inside can be maintained at 100 nm or less. In addition to the above components, the coating agent may further contain various additives such as carbon black.

  As in the prior art, two or more antibacterial coating films may be laminated. In order to improve the adhesion of the antibacterial coating film to the ground surface, the ground surface may be roughened or a primer may be used. An antibacterial coating film may be formed on the layer. Further, on the formed antibacterial coating film, a clear coating film containing the same or different resin particles and not containing metal particles may be further laminated. Like the antibacterial coating film, the coating film has a structure in which a large number of resin particles are bonded, so that metal ions generated on the surface of the metal particles in the antibacterial coating film are separated from minute gaps between the resin particles. It can be moved to the surface of the membrane through it, and good antibacterial properties can be expressed on the surface.

《Cooking container》
The cooking container of the present invention is characterized in that at least a part of the inner surface of the container main body for storing the food to be cooked is covered with the antibacterial coating film of the present invention. Examples of the cooking container include an inner pot such as a rice cooker, a tray such as an oven, and a cooking plate such as a hot plate. A coating agent is applied to the entire inner surface or a part (for example, the bottom surface) of the container body formed into a three-dimensional shape of the cooking container by the above-described coating method, dried as necessary, and then baked. Thus, the cooking container of the present invention is manufactured by forming an antibacterial coating film having a single layer structure or a laminated structure of two or more layers described above.

In addition, the cooking container of the present invention is a composite material in which the antibacterial coating film having the single-layer structure or the laminated structure is formed on the entire surface or a part of one surface of a flat metal substrate that is a base of the container body. It can also be manufactured by processing into a three-dimensional shape of the cooking container. According to the present invention, good antibacterial properties can be imparted to the cooking container by the function of the antibacterial coating film of the present invention. Therefore, for example, in the case of an inner pot of a rice cooker, when the temperature at the time of heat retention is lowered from the current level, the generation of odor due to the growth of bacteria can be suppressed and the rice can always be maintained deliciously. Therefore, it is possible to sufficiently meet the demand for further energy saving in order to meet the demand for CO ₂ emission reduction for the purpose of suppressing global warming.

<Antimicrobial coating agent>
The antibacterial coating agent of the present invention is characterized in that it comprises metal particles having a 50% cumulative diameter D _{50 of} a particle size distribution of 100 nm or less and at least part of the surface coated with a dispersant, and resin particles. It is. The antibacterial coating agent can be prepared in the same manner as the coating agent that forms the antibacterial coating film described above. That is, from the liquid phase reaction system in which metal particles have been deposited by the liquid phase reduction method, treatments such as ultrafiltration, centrifugation, water washing, and electrodialysis are performed to remove impurities, and concentration or concentration is performed as necessary. Mixing the aqueous dispersion in which the metal particles are dispersed in water, the concentration of the metal particles being adjusted by dilution, is added to the dispersion in which the resin particles are dispersed in water or an organic solvent compatible with water. Thus, a dispersion type coating agent is prepared.

  When the antibacterial coating agent of the present invention is applied, for example, in the form of a wax to an automobile body and then dried, the body is given good water repellency and antibacterial properties, and stains due to scales, etc. It can be suppressed over a period of time. Moreover, as a spray coating agent, it is possible to impart good water repellency and antibacterial properties to these articles by spray-coating on an umbrella, shoes, etc. and then drying. In the present invention, the particle size distribution of the metal particles to be added to the antibacterial coating agent is determined using a particle size distribution measuring apparatus to which the laser Doppler method is applied.

Example 1
At least a part of the surface is coated with a polycarboxylic acid-based anionic polymer surfactant as a dispersant, the 50% cumulative diameter D _{50 of} the particle size distribution is 100 nm, and the 80% cumulative diameter D ₈₀ is 50%. the ratio D ₈₀ / D ₅₀ between the cumulative diameter D ₅₀ aqueous dispersion containing silver particles is 1.6 to prepare a coating agent in addition to the fluororesin dispersion of the water-based. The silver particle content in the coating agent was 1% by mass of the total amount of solids constituting the antibacterial coating film. Further, a fluororesin dispersion, a fluororesin particle having an average particle diameter of 7 μm and a fluororesin particle having an average particle diameter of 0.7 μm was used.

  As the substrate, a surface of an aluminum plate having a diameter of 30 cmφ × thickness of 1 mm was roughened by electrochemical etching. Immediately after the coating agent was applied to one side of the substrate by a spin coating method, It was dried and then baked at 400 ° C. for 10 minutes to form an antibacterial coating film having a thickness of 30 μm.

Example 2
At least a part of the surface is coated with a polycarboxylic acid type anionic polymer surfactant as a dispersant, the 50% cumulative diameter D _{50 of} the particle size distribution is 50 nm, and the 80% cumulative diameter D ₈₀ is 50%. A coating agent was prepared by adding an aqueous dispersion containing silver particles having a ratio D ₈₀ / D ₅₀ of 1.6 to the cumulative diameter D ₅₀ to the same aqueous fluororesin dispersion used in Example 1. . The silver particle content in the coating agent was 1% by mass of the total amount of solids constituting the antibacterial coating film. Then, an antibacterial coating film having a thickness of 30 μm was formed in the same manner as in Example 1 except that the coating agent was used.

Example 3
At least a part of the surface is coated with a polycarboxylic acid type anionic polymer surfactant as a dispersant, the 50% cumulative diameter D _{50 of} the particle size distribution is 20 nm, and the 80% cumulative diameter D ₈₀ is 50%. A coating agent was prepared by adding an aqueous dispersion containing silver particles having a ratio D ₈₀ / D ₅₀ of 1.6 to the cumulative diameter D ₅₀ to the same aqueous fluororesin dispersion used in Example 1. . The silver particle content in the coating agent was 1% by mass of the total amount of solids constituting the antibacterial coating film. Then, an antibacterial coating film having a thickness of 30 μm was formed in the same manner as in Example 1 except that the coating agent was used.

Example 4
At least a part of the surface is coated with a polycarboxylic acid type anionic polymer surfactant as a dispersant, the 50% cumulative diameter D _{50 of} the particle size distribution is 50 nm, and the 80% cumulative diameter D ₈₀ is 50%. A coating agent was prepared by adding an aqueous dispersion containing silver particles having a ratio D ₈₀ / D ₅₀ of 2.2 to the cumulative diameter D ₅₀ to the same aqueous fluororesin dispersion used in Example 1. . The silver particle content in the coating agent was 1% by mass of the total amount of solids constituting the antibacterial coating film. Then, an antibacterial coating film having a thickness of 30 μm was formed in the same manner as in Example 1 except that the coating agent was used.

Example 5
The same coating agent as used in Example 1 was applied by spin coating, allowed to stand for 60 minutes and then dried, and then baked at 400 ° C. for 10 minutes to form an antibacterial coating film having a thickness of 30 μm.

<< Examples 6 and 7 >>
The amount of the aqueous dispersion was adjusted so that the silver particle content in the coating agent was 0.5% by mass (Example 6) and 0.05% by mass (Example) of the total amount of solids constituting the antibacterial coating film. An antibacterial coating film having a thickness of 30 μm was formed in the same manner as in Example 1 except that 7).

<< Comparative Example 1 >>
At least a part of the surface is coated with a polycarboxylic acid type anionic polymer surfactant as a dispersant, the 50% cumulative diameter D _{50 of} the particle size distribution is 200 nm, and the 80% cumulative diameter D ₈₀ and 50%. A coating agent was prepared by adding an aqueous dispersion containing silver particles having a ratio D ₈₀ / D ₅₀ of 1.6 to the cumulative diameter D ₅₀ to the same aqueous fluororesin dispersion used in Example 1. . The silver particle content in the coating agent was 1% by mass of the total amount of solids constituting the antibacterial coating film. Then, an antibacterial coating film having a thickness of 30 μm was formed in the same manner as in Example 1 except that the coating agent was used.

<< Silver particle size distribution measurement 1 >>
The actual dimensions of the antibacterial coating film formed in Examples and Comparative Examples were taken with a scanning electron microscope under the condition of an acceleration voltage of 2 kV in a state where the surface of the antibacterial coating film was covered with a vacuum deposition film of platinum. From the result of repeating the operation of measuring the particle diameter of all silver particles imaged in the image of the 0.0 μm region by image processing at 10 locations on the same antibacterial coating film, The particle size distribution of silver particles was determined. From the particle size distribution, 50% cumulative diameter D ₅₀ , 80% cumulative diameter D ₈₀ , and ratio D ₈₀ / D ₅₀ of both cumulative diameters were determined. The results are shown in Table 1.

  Table 1 confirms that the particle size distribution of the silver particles dispersed in the film is almost the same as the particle size distribution of the silver particles in the aqueous dispersion used as a raw material in any of the examples and comparative examples. It was done.

<< Silver particle size distribution measurement 2 >>
The surface of the antibacterial coating film formed in Examples 1 and 5 was covered with a platinum vacuum deposition film and photographed with an operation electron microscope under conditions of acceleration voltages of 0.5 kV, 1 kV, 2 kV, and 5 kV, The operation of measuring the particle size of all silver particles imaged in the image of the actual dimension of 2.8 μm in length × 4.0 μm in width by image processing is repeated at 10 locations on the same antibacterial coating film. From the results, the distribution of silver particles in the thickness direction in the antibacterial coating film was determined. The results are shown in Table 2. In addition, the substantial abundance ratio in the table is determined from the abundance ratio of silver particles (cumulative abundance ratio) in the region from the surface of the antibacterial coating film to the depth measurable by the acceleration voltage, obtained at a specific acceleration voltage. The abundance ratio of silver particles at a specific depth is obtained by subtracting the abundance ratio of silver particles obtained up to that stage.

  From Table 2, in Example 1, silver particles are distributed almost uniformly in the thickness direction, whereas in Example 5, silver particles are not present on the surface of the antibacterial coating film and are close to the base surface. It was confirmed that there was more distribution on the side.

<Antimicrobial evaluation>
The antibacterial activity value of the antibacterial coating film formed in Examples and Comparative Examples is that Japanese Industrial Standard JIS Z2801: 2000 "Antimicrobial Processed Products-Antibacterial" except that Bacillus subtilis (storage number NBRC3134) was used as bacteria. Measured according to the “Testing method / antibacterial effect”. That is, an aluminum plate formed by coating a water-based fluororesin dispersion without adding a silver particle dispersion to form a coat film (unprocessed test piece), an antibacterial coating in Examples and Comparative Examples Prepare a 5 cm square aluminum plate with a membrane, inoculate each with a predetermined amount of Bacillus subtilis, place it in an incubator, leave it in a dark room at a predetermined temperature for a predetermined time, and then count the number of bacteria. Counted.

And the average value A (number) of the number of viable bacteria immediately after inoculation of the unprocessed test piece, the average value B (number) of the number of viable bacteria after 24 hours of the unprocessed test piece, and the antibacterial of Examples and Comparative Examples From the average value C (cells) of the number of viable cells after 24 hours of the coating film, the formula (1):
R = [log (B / A) -log (C / A)] = [log (B / C)] (1)
Was used to determine the antibacterial activity value R. As the antibacterial activity value R is higher, the antibacterial coating film is more excellent in antibacterial effect. Here, if the antibacterial activity value R is 2.0 or more, the antibacterial activity is assumed to be present. Changes in the antibacterial activity value R at the test temperatures of 35 ° C., 50 ° C., 55 ° C., 60 ° C., 65 ° C., and 75 ° C. in Examples and Comparative Examples are shown in Table 3 and FIG.

  From Table 3 and FIG. 1, it was found that in Comparative Example 1, the maximum antibacterial activity value did not reach 2 within the measurement temperature range, and the antibacterial property was insufficient. In contrast, in Examples 1 to 7, the maximum antibacterial activity value exceeded 2 and it was confirmed that the antibacterial property was exhibited.

It is a graph which shows the relationship between the antibacterial activity value with respect to Bacillus subtilis, and the test temperature of the antibacterial coating film of the Example of this invention, and a comparative example.

Claims (8)

An antibacterial coating film in which metal particles are dispersed in a film composed of a large number of resin particles, wherein the metal particles have a 50% cumulative diameter D ₅₀ of a particle size distribution of 100 nm or less. . 2. The antibacterial coating film according to claim 1, wherein the ratio D ₈₀ / D ₅₀ of the 80% cumulative diameter D ₈₀ of the particle size distribution to the 50% cumulative diameter D ₅₀ of the metal particles is 2.0 or less.   The antibacterial coating film according to claim 1 or 2, wherein the content of the metal particles is 1% by mass or less of the total amount of solids constituting the antibacterial coating film.   The antibacterial coating film according to any one of claims 1 to 3, wherein the metal particles are silver particles.   The antibacterial coating film according to any one of claims 1 to 4, wherein the resin particles are particles of at least one resin selected from the group consisting of a fluororesin and a polyether ether ketone resin.   The antibacterial coating film according to any one of claims 1 to 5, which is formed by applying a coating agent containing metal particles and resin particles and then baking the coating agent.   A cooking container characterized in that at least a part of an inner surface of a container main body for containing an object to be cooked is covered with the antibacterial coating film according to any one of claims 1 to 6. An antibacterial coating agent comprising: metal particles having a 50% cumulative diameter D _{50 of} a particle size distribution of 100 nm or less, wherein at least a part of the surface is coated with a dispersant, and resin particles.

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