Coating film and housing

Abstract

A coating film (10A) for protecting an object (20) to be coated that is formed from a resin material, the coating film comprising a heat insulating material and a binder for joining the heat insulating material and the object (20) to be coated, wherein the binder includes inorganic fine particles (11). In the binder, the inorganic fine particles (11) themselves further join the other inorganic fine particles (11) and the object (20) to be coated. The heat insulating material contains thermally expandable graphite (12), and the binder joins the thermally expandable graphite (12) and the object (20) to be coated. The thermally expandable graphite (12) expands upon heating to form a fire-resistant insulating layer.

Description

Coating film and housing

[0001] The present disclosure relates to a coating film that improves fire resistance and heat insulation, and a housing coated with the coating film.

[0002] Resin materials are used in a variety of products and parts due to their light weight and excellent processability. However, from a safety perspective, these products and parts require flame-resistant resin materials, and currently, flame-retardant resin materials containing flame retardants are widely used. However, even flame-retardant resin materials have difficulty withstanding high-intensity flames. Therefore, coating films have been developed that improve fire resistance by coating the surface of resin parts molded from resin materials. For example, Patent Document 1 discloses a heat-insulating fire-resistant paint containing hollow particles formed from an inorganic material, an organic binder formulated as an aqueous emulsion, and an inorganic binder containing at least flaky silica.

[0003] JP 2018-193441 A

[0004] Thermoplastic resin materials are often formed into part shapes using injection molding, which takes advantage of the fact that they become molten and easily flowable at temperatures between 200°C and 400°C. In injection molding, molten resin material is injected into a low-temperature mold in an injection molding machine and solidified into the part shape, so distortion that occurs during rapid cooling inside the mold remains in the resin part.

[0005] If an electronic component such as a capacitor catches fire inside a device having a resin housing molded in this way and the flame comes into contact with the resin housing, the heat of the flame will cause the resin housing to melt, and the residual strain from the injection molding will be released, causing it to shrink due to thermal deformation, which could cause a hole in the resin housing from the point of contact with the flame and spread the fire to nearby devices.Furthermore, if a flame breaks out outside the resin housing and comes into contact with the resin housing, a hole will be made in the resin housing, exposing the electronic components inside the resin housing directly to the flame and causing damage to the electronic components.

[0006] Therefore, in order to prevent fire from spreading to nearby devices due to holes in such plastic housings and damage to electronic components inside the housings, coating films that protect plastic housings used for electrical devices, etc., are required to improve fire resistance and heat insulation, including thermal deformation suppression, by coating the plastic housings. When coated objects molded from resin materials, including these plastic housings, are protected with coating films, the fire resistance and heat insulation of the coated object depend on the combination of the coating film and the material of the coated object.

[0007] When using a coating film to protect an object with little thermal deformation (thermal shrinkage), even if the binder used in the coating film contains a resin binder, the coated object will not be perforated and will have fire resistance and heat insulation properties when exposed to a gas burner flame of about 1800°C for 5 seconds, repeated 5 times at 5-second intervals, as in the UL combustion test according to UL (Underwriters Laboratories Inc.) standards. However, when using a coating film to protect an object with a large thermal deformation, such as an injection-molded plastic casing, if the binder used in the coating film contains a resin binder, the resin binder will soften due to the heat of the flame, and the thermal deformation of the object will not be sufficiently suppressed, which could result in holes being perforated in the object.

[0008] Therefore, even if an attempt is made to protect an injection-molded resin casing that is prone to large thermal deformation using the heat-insulating fire-resistant paint disclosed in Patent Document 1, the heat-insulating fire-resistant paint contains an organic binder, which means that it cannot prevent the resin casing from being thermally deformed by the heat of the flame, and therefore cannot prevent holes from being formed in the resin casing.

[0009] The present disclosure has been made in consideration of the above, and aims to provide a coating film that improves fire resistance and heat insulation properties, including thermal deformation suppression properties, and can prevent holes from being created by the heat of a flame in a coated object molded from a resin material, such as a resin housing.

[0010] In order to solve the above-mentioned problems and achieve the object, the coating film of the present disclosure is a coating film that protects a coated object molded from a resin material, and includes a heat insulating material and a binder that binds the heat insulating material and the coated object together, and is characterized in that the binder is made of inorganic fine particles.

[0011] The coating film according to the present disclosure has the effect of improving fire resistance and heat insulation properties, including thermal deformation suppression properties, by coating an object to be coated that is molded from a resin material.

[0012] 3 is a cross-sectional view schematically showing an example of the structure of a coating film according to the first embodiment; 3 is a cross-sectional view schematically showing an example of the structure of a coating film according to the second embodiment; 3 is a cross-sectional view schematically showing an example of the structure of a coating film according to the third embodiment; 3 is a cross-sectional view schematically showing an example of the structure of a coating film according to the third embodiment, in which the coating film shown in FIG. 3 is heated to form a molten film on at least a part of the surface; 3 is a cross-sectional view schematically showing an example of the structure of a coating film in which the molten film formed on the surface side of the coating film shown in FIG. 3 is expanded; 3 is a cross-sectional view schematically showing an example of the structure of a coating film according to the fourth embodiment;

[0013] The coating film and housing according to the embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments. The shapes and sizes of the particles shown in the drawings are shown schematically to facilitate understanding of the description, and do not represent the actual shapes and sizes.

[0014] Embodiment 1. The coating film according to embodiment 1 is a coating film that protects a coated object molded from a resin material, and includes a heat insulating material and a binder that binds the heat insulating material and the coated object together. The heat insulating material includes thermally expandable graphite, and the binder is made of inorganic fine particles. In other words, the binder contains only inorganic fine particles and does not include any organic components.

[0015] 1 is a cross-sectional view schematically illustrating an example of the structure of a coating film according to a first embodiment of the present disclosure. Fig. 1 shows a state in which a coating film 10A is coated on the surface of a coating target 20 such as a resin housing, and also shows a schematic diagram for easy understanding of the positional relationships of various particles distributed in the coating film 10A.

[0016] The coating film 10A shown in Figure 1 is made of thermally expandable graphite 12 and inorganic fine particles 11. That is, the inorganic fine particles 11 act as a binder, binding the thermally expandable graphite 12, which is a heat insulating material, to the object to be coated 20. The inorganic fine particles 11 themselves also act as a binder, binding other inorganic fine particles 11 to the object to be coated 20. One example of the object to be coated 20 is one made of a thermoplastic resin processed by an injection molding method, but the object to be coated is not limited to this, and may be one processed into a desired shape using a resin material.

[0017] The following describes in detail each component contained in the coating film 10A. The coating liquid for forming the coating film 10A also contains the same components as those contained in the coating film 10A.

[0018] <Inorganic Fine Particles> Examples of inorganic fine particles 11 contained in the coating film 10A according to the first embodiment include metal oxides such as silica, alumina, titanium oxide, zinc oxide, zirconia, and cerium oxide, and one or more types may be used. When the inorganic fine particles 11 are titanium oxide having a catalytic function that promotes deterioration of the resin that is the coated object 20, it is preferable that the surfaces of the titanium oxide fine particles 11 are coated with silica that does not have a catalytic function.

[0019] In the state of the coating liquid before forming the coating film 10A, the surface portions of the inorganic particles 11 in contact with a dispersion medium such as water are partially dissolved in water due to the presence of highly hydrophilic hydroxyl groups, and when the coating liquid is dried, these partially dissolved inorganic particles 11 aggregate, and the inorganic particles 11 themselves act as binders that bind other inorganic particles 11 to the object to be coated 20. Furthermore, because the surfaces of the thermally expandable graphite 12 and the object to be coated 20 also contain hydroxyl groups and carboxyl groups, the inorganic particles 11 also act as binders that bind the thermally expandable graphite 12 to the object to be coated 20. As a result, a coating film 10A can be obtained that is excellent in strength, such as being resistant to cracks, and that also has excellent adhesion to the object to be coated 20.

[0020] The average particle size of the inorganic microparticles 11 is preferably 1 nm or more and 50 nm or less, and particularly preferably 3 nm or more and 25 nm or less. Hereinafter, unless otherwise specified, the average particle size refers to the average particle size of primary particles as measured with a laser light scattering or dynamic scattering particle size distribution analyzer. Furthermore, a primary particle is the smallest particle unit and refers to a particle that cannot be further divided. An aggregate of primary particles, which is a cluster of multiple primary particles, is called a secondary particle.

[0021] If the average particle size of the inorganic particles 11 is less than 1 nm, the cohesive force in the coating liquid will be too high, resulting in large secondary particles and poor dispersibility, which may cause sedimentation in the coating liquid or variations in the density of the inorganic particles 11 on the surface of the object to be coated 20. On the other hand, if the average particle size of the inorganic particles 11 is greater than 50 nm, the cohesive force will be low and the particles will not become large secondary particles, but cracks may be more likely to occur in the coating film 10A formed by drying the coating liquid. In addition, the adhesive properties of the inorganic particles 11 as a binder may be reduced. That is, the adhesive properties of the inorganic particles 11 as a binder binding other inorganic particles 11 to the object to be coated 20 and as a binder binding the thermally expandable graphite 12 to the object to be coated 20 may be reduced.

[0022] <Thermal-expandable graphite> The thermal-expandable graphite 12 contained in the coating film 10A according to the first embodiment is formed by inserting an acid such as sulfuric acid, nitric acid, or phosphoric acid between the graphite layers of natural flake graphite. When heated to about 200°C, the acid vaporizes and expands, causing the space between the graphite layers to expand 50 to 350 times its original size, expanding like a worm and forming a fire-resistant, insulating layer.

[0023] The average particle size of the thermally expandable graphite 12 before expansion is preferably 5 μm or more and 300 μm or less. If it is smaller than 5 μm, a sufficient fire-resistant heat insulating layer cannot be formed after thermal expansion. If it is larger than 300 μm, dispersibility in the coating liquid becomes poor.

[0024] The thermal expansion starting temperature of the thermally expandable graphite 12 is preferably about 50°C to 80°C lower than the melting temperature during injection molding of the object to be coated 20. For example, for the object to be coated 20, such as PC / ABS (polycarbonate / acrylonitrile butadiene styrene copolymer) resin or PBT / PC (polybutylene terephthalate / polycarbonate) resin, which is melted at about 240°C to 260°C and then injection molded, the thermal expansion starting temperature is preferably about 160°C or higher and 210°C or lower.

[0025] The preparation of the coating liquid for forming the coating film 10A will be described below.

[0026] <Preparation of Coating Liquid> The coating liquid for forming the coating film 10A is prepared by dispersing inorganic fine particles 11 and thermally expandable graphite 12 in water as a dispersion medium. In the following description, unless otherwise specified, the inorganic fine particles 11 are silica, and in the case of other metal oxides, the content in the coating liquid is converted into true density. True density is a density calculated using only the volume occupied by the substance itself, and is a density measured using a pycnometer method after thoroughly pulverizing the substance so as to eliminate open pores, etc.

[0027] The content of inorganic particles 11 in the coating liquid is preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 2% by mass or less. If the content of inorganic particles 11 in the coating liquid is less than 0.1%, the layer of inorganic particles 11 in the formed coating film 10A becomes too thin, and the desired thermal deformation suppression properties may not be obtained. On the other hand, if the content of inorganic particles 11 in the coating liquid is more than 5% by mass, the thermally expandable graphite 12 in the coating film 10A becomes embedded in the layer of inorganic particles 11, and the desired fire resistance and heat insulation properties may not be obtained.

[0028] The content of thermally expandable graphite 12 in the coating liquid is preferably 0.5% by mass or more and 25% by mass or less, and particularly preferably 2.5% by mass or more and 10% by mass or less. If the content of thermally expandable graphite 12 in the coating liquid is less than 0.5%, the coverage of the object 20 to be coated with thermally expandable graphite 12 is low, and the desired fire-resistant and thermal insulating properties may not be obtained. On the other hand, if the content of thermally expandable graphite 12 in the coating liquid is more than 25% by mass, there will be no problem with fire-resistant and thermal insulating properties, but the number of inorganic microparticles 11 that act as a binder per particle of thermally expandable graphite 12 will be reduced, and thermally expandable graphite 12 will be more likely to fall off from the coating film 10A.

[0029] The method for coating the surface of the object to be coated will be described below.

[0030] <Coating Method for the Surface of the Substrate> The method for coating the surface of the substrate 20 with the coating liquid according to the first embodiment is not particularly limited and can be performed using conventionally known methods. However, a preferred method involves applying the coating liquid to the surface of the substrate 20 by immersion, spraying, brushing, or other methods, and then removing the excess coating liquid using an airflow. If excess coating liquid remains on the surface of the substrate 20, the coating film 10A formed there will become thicker. This can narrow the gap between the substrate 20 with one coating film 10A and the other substrate 20 with another coating film 10A when assembling a device using multiple substrates 20, potentially reducing assembly efficiency. Using an airflow also has the advantage of accelerating drying. However, if the substrate 20 is made of a highly water-repellent resin, a strong airflow can blow away the coating liquid on the surface of the substrate 20. Therefore, the airflow may be adjusted or the substrate may be left to dry as needed. This method allows the coating film 10A to be firmly attached to the surface of the substrate 20.

[0031] The thickness of the coating film 10A is preferably 10 μm or more and 600 μm or less for the following reasons, so it is desirable to adjust the amount of coating liquid to form a coating film 10A of an appropriate thickness. If the thickness is less than 10 μm, the coating film is too thin and cannot achieve the desired fire resistance and heat insulation properties, including thermal deformation suppression. If the thickness is greater than 600 μm, it may become impossible to assemble the coated object 20 having the coating film 10A with other coated objects 20 or coated objects 20 having the coating film 10A.

[0032] As explained above, the coating film 10A of the present embodiment does not contain organic components in the binder, but is composed only of inorganic fine particles 11, and therefore the binder does not soften due to the heat of the flame, thereby improving the rigidity of the coating film 10A and the ability to inhibit thermal deformation of the coated object 20. Therefore, even when the coated object 20 is an injection-molded product made of a thermoplastic resin, coating the coated object 20 with the coating film 10A of the present embodiment improves the fire resistance and heat insulation properties, including the ability to inhibit thermal deformation, and prevents holes from being created in the coated object 20, which is made of a resin material such as a resin housing, due to the heat of the flame.

[0033] In this and other embodiments, an example is shown in which the coating film 10A is coated on one surface of the object to be coated 20, but the coating film 10A may be coated on both surfaces of the object to be coated 20. By coating both surfaces of the object to be coated 20 with the coating film 10A, it is possible to further improve the fire resistance and heat insulation properties, including the ability to inhibit thermal deformation.

[0034] Embodiment 2. In the first embodiment, the case where the heat insulating material contained in the coating film is made of thermally expandable graphite has been described, but the heat insulating material may contain not only thermally expandable graphite but also hollow particles. Explanation of the same parts as in the first embodiment will be omitted, and only the parts different from the first embodiment will be described.

[0035] 2 is a cross-sectional view schematically illustrating an example of the structure of a coating film 10B containing hollow particles 13. The coating film 10B is composed of inorganic fine particles 11, thermally expandable graphite 12, and hollow particles 13. The inorganic fine particles 11 not only bond the thermally expandable graphite 12 to the object 20 to be coated, but also serve as a binder that bonds the hollow particles 13 to the object 20 to be coated. That is, the inorganic fine particles 11 act as a binder to bond the thermally expandable graphite 12, which is a thermal insulator, to the object 20 to be coated, and also to bond the hollow particles 13, which are a thermal insulator, to the object 20 to be coated. Furthermore, the inorganic fine particles 11 themselves serve as a binder that bonds other inorganic fine particles 11 to the object 20 to be coated.

[0036] By including not only particles of thermally expandable graphite 12 but also hollow particles 13 as a heat insulating material, voids are formed within the hollow particles 13, between the hollow particles 13 and other hollow particles 13, and between the inorganic fine particles 11 and the hollow particles 13 in the coating film 10B as shown in Fig. 2, and the total volume of voids formed in the coating film 10B of Embodiment 2 is greater than the total volume of voids formed in the coating film 10A of Embodiment 1. As a result of the increase in voids, the fire resistance and heat insulation properties are improved in the temperature range up to which the thermally expandable graphite 12 expands.

[0037] Among the components contained in the coating film 10B, the hollow particles 13 will be described in detail below. Note that, among the components contained in the coating film 10B, the inorganic fine particles 11 and the thermally expandable graphite 12 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0038] <Hollow Particles> The hollow particles 13 are particles having a hollow portion inside, and the outer shells forming the particles are formed of an organic material or an inorganic material. The coating film 10B may contain at least one of hollow particles formed of an organic material (hereinafter referred to as "organic hollow particles") and hollow particles formed of an inorganic material (hereinafter referred to as "inorganic hollow particles"). Note that "organic hollow particles" and "inorganic hollow particles" may be collectively referred to as "hollow particles." Examples of organic materials forming organic hollow particles include acrylic, styrene, and imide polymers. Examples of inorganic materials forming inorganic hollow particles include silica and shirasu, which is primarily composed of silica.

[0039] The hollow portions of the hollow particles 13 are preferably non-flammable gases such as air, nitrogen, carbon dioxide, helium, and argon, which have lower thermal conductivity than solids or liquids at room temperature and normal pressure (e.g., standard conditions of 25°C and 106 kPa as recommended in ISO 554:1976), and air is particularly preferred. Because the hollow particles 13 have such hollow portions inside, they expand when heated, improving their fire-resistant and insulating properties. When low-boiling hydrocarbons with a carbon number of 20 or less and a boiling point of approximately 350°C, such as propane or butane, are encapsulated within the hollow particles 13, the expansion of the low-boiling hydrocarbons upon contact with flames causes the hollow particles to expand, improving their insulating properties. However, if the outer shell of the hollow particles 13 is ruptured, the low-boiling hydrocarbons, which have become flammable gases, may ignite in the immediate vicinity of the object to be coated 20, preventing the desired insulating effect from being achieved. Therefore, it is not preferable that the hollow portion of the hollow particle 13 contains low-boiling hydrocarbons having a carbon number of 20 or less and a boiling point of up to about 350° C., such as propane or butane.

[0040] The hollow particles 13 are preferably smaller in size than the gaps between the thermally expandable graphite particles 12, and specifically, the average particle size is preferably 10 nm to 150 μm, and particularly preferably 50 nm to 60 μm. When the hollow particles 13 include both organic and inorganic hollow particles, the average particle sizes of the organic and inorganic hollow particles do not need to be the same. When the average particle size of the hollow particles 13 is less than 10 nm, the outer shell needs to have a certain thickness to maintain the shape of the hollow particle, and therefore the proportion of the hollow portion becomes small, and the insulating effect due to the hollow portion may not be obtained. On the other hand, when the size of the hollow particles 13 is larger than the gaps between the thermally expandable graphite particles 12, the gaps between the thermally expandable graphite particles 12 become larger, and the desired insulating effect due to the thermal expansion of the thermally expandable graphite particles 12 may not be obtained.

[0041] The content of hollow particles 13 in the coating liquid is preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 2% by mass or less. If the content of hollow particles 13 in the coating liquid is less than 0.1%, the desired fire resistance and heat insulation properties of the hollow particles may not be obtained. If the content of hollow particles 13 in the coating liquid is more than 5% by mass, there will be no problem with fire resistance and heat insulation properties, but the number of inorganic fine particles 11 acting as a binder per hollow particle 13 will be reduced, making the hollow particles 13 more likely to fall off the coating film 10B.

[0042] As described above, coating film 10B of the present embodiment contains hollow particles 13 in addition to thermally expandable graphite 12 in the heat insulating material, which increases the number of voids formed in coating film 10B and improves fire resistance and heat insulation in the temperature range up to the expansion of thermally expandable graphite 12. Therefore, when the heat insulating material contains hollow particles in addition to thermally expandable graphite, it is possible to improve fire resistance and heat insulation, including thermal deformation suppression, over a wider temperature range than when the heat insulating material contains only thermally expandable graphite.

[0043] Embodiment 3. In embodiment 2, the case where the heat insulating material contained in the coating film further contains hollow particles in addition to thermally expandable graphite particles has been described, but when the heat insulating material contains organic hollow particles, it may further contain foaming agent particles. Explanation of the same parts as in embodiment 2 will be omitted, and only differences from embodiment 2 will be described.

[0044] 3 is a cross-sectional view schematically illustrating an example of the structure of a coating film 10C containing thermally expandable graphite 12, organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14 as heat insulating materials. The coating film 10C is composed of inorganic fine particles 11, thermally expandable graphite 12, organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14. The inorganic fine particles 11 not only bond the thermally expandable graphite 12 to the object to be coated 20 and the hollow particles to the object to be coated 20, but also serve as a binder that bonds the foaming agent particles 14 to the object to be coated 20. That is, the inorganic fine particles 11 act as a binder to bond the thermally expandable graphite 12, which is a heat insulating material, to the object to be coated 20, and the hollow particles, which are a heat insulating material, to the object to be coated 20, respectively, and also to bond the foaming agent particles 14, which are a heat insulating material, to the object to be coated 20. Furthermore, the inorganic fine particles 11 themselves also function as a binder that binds other inorganic fine particles 11 to the object 20 to be coated.

[0045] When coating film 10C is heated, organic hollow particles 13A thermally expand at or above the softening temperature of the organic material forming the outer shell, melt and flow, and adjacent organic hollow particles 13A connect to form molten film 15. Furthermore, molten film 15 fuses to adjacent inorganic fine particles 11, thermally expandable graphite 12, or inorganic hollow particles 13B, and then expands outward, i.e., in the direction away from object 20 to be coated, due to gas generated by thermal decomposition of foaming agent particles 14, thereby improving fire resistance and heat insulation. That is, when the organic hollow particles 13A are heated to a temperature equal to or higher than the softening temperature of the organic hollow particles, they melt and flow to form a molten film on the surface side of the coating film 10C, and the molten film expands outward, i.e., away from the object to be coated 20, due to the gas generated by the thermal decomposition of the foaming agent particles 14 located between the molten film and the object to be coated 20. As a result, the coating film 10C can improve the fire resistance and heat insulation of the coated object 20.

[0046] As an example, this will be described when a coating film 10C shown in Fig. 3 is heated. When the coating film 10C shown in Fig. 3 is heated, at least the organic hollow particles 13A located on the surface side of the coating film 10C thermally expand at a temperature equal to or higher than the softening temperature of the organic material forming the outer shell, melt, and flow, thereby connecting adjacent organic hollow particles 13A to form a molten film. At this time, it is not necessary for the outer shells of the organic hollow particles 13A to be broken and for the particles 13A to no longer maintain their particle shape.

[0047] Fig. 5 is a cross-sectional view showing an example of the coating film 10C shown in Fig. 3, in which the coating film 10C shown in Fig. 3 is heated to form a molten film 15 on at least a part of the surface. After the molten film 15 is formed on the surface side of the coating film 10C, the foaming agent particles 14 generate gas by thermal decomposition, and the molten film 15 expands as shown in Fig. 6.

[0048] The positional relationship of the particles within the coating film 10C will be explained in detail later, but the organic hollow particles 13A tend to be located in areas of the coating film 10C far from the surface of the object 20 to be coated, in other words, close to the surface of the coating film 10C, i.e., on the surface side of the coating film 10C, and the foaming agent particles 14 tend to be located in areas of the coating film 10C close to the surface of the object 20 to be coated, i.e., on the side of the object 20 to be coated. Therefore, since the organic hollow particles 13A are distributed in greater numbers on the surface side of the coating film 10C and the foaming agent particles 14 are distributed in greater numbers on the side of the object 20 to be coated, when the organic hollow particles 13A are heated to a temperature equal to or higher than the softening temperature of the organic hollow particles, a molten film 15 is likely to be formed on the surface side of the coating film 10C, and the foaming agent particles 14 are likely to be located between the molten film 15 and the object 20 to be coated.

[0049] Therefore, when the foaming agent particles 14 thermally decompose at this position and generate gas, the molten film 15 expands outward, i.e., in a direction away from the object to be coated 20, thereby keeping the flame away from the object to be coated 20.In addition, the gas generated from the foaming agent particles 14 reduces the thermal conductivity, causing them to behave like hollow particles, which tends to improve fire resistance and insulation properties.

[0050] Among the components contained in the coating film 10C, the foaming agent particles 14 will be described in detail below. Note that, among the components contained in the coating film 10C, the inorganic fine particles 11, the thermally expandable graphite 12, the organic hollow particles 13A, and the inorganic hollow particles 13B are the same as those described above, and therefore will not be described again.

[0051] <Blowing Agent Particles> Examples of the blowing agent particles 14 include organic blowing agents that generate gas upon thermal decomposition, such as azo compounds such as azodicarbonamide, azodicarboxylate metal salts (e.g., barium azodicarboxylate), azobisisobutyronitrile, and barium azodicarboxylate; nitroso compounds such as N,N'-dinitrosopentamethylenetetramine; and hydrazine derivatives such as 4,4'-oxybis(benzenesulfonylhydrazide) and toluenesulfonylhydrazide; and inorganic blowing agents such as sodium carbonate, calcium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous monosodium citrate. Calcium carbonate is particularly preferred from the viewpoints of thermal decomposition (heat decomposition at or above the softening temperature of the organic hollow particles 13A), availability of fine particles, and safety. These may be used alone or in combination of two or more.

[0052] The foaming agent particles 14 are preferably smaller than the gaps between the thermally expandable graphite particles 12, and specifically, the average particle size is preferably 10 nm to 150 μm, and particularly preferably 50 nm to 60 μm. If the particle size is less than 10 nm, the foaming agent particles aggregate in the coating liquid, resulting in a large particle size and poor dispersibility. If the particle size is greater than 150 μm, the foaming agent particles also have poor dispersibility in the coating liquid.

[0053] The content of the foaming agent particles 14 in the coating liquid is preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 2% by mass or less. If the content of the foaming agent particles 14 is less than 0.1% by mass, the molten film 15 formed from the organic hollow particles 13A may not expand to a sufficient extent due to the gas generated by the thermal decomposition of the foaming agent particles 14, and the desired heat insulating effect may not be obtained. If the content of the foaming agent particles 14 is more than 5% by mass, the amount of gas generated per unit time by the thermal decomposition of the foaming agent particles 14 is too large, and the molten film 15 formed by the melting and flowing of the organic hollow particles 13A may easily break, and the desired heat insulating effect may not be obtained.

[0054] Next, the positional relationship of particles distributed in the coating film 10C will be described. When the average particle size is in the nanometer to micrometer range, Stokes' law can be applied to the settling velocity of particles in water, and the terminal velocity can be expressed by equation (1). In equation (1), ν is the terminal velocity, ρ is the particle density, ρ' is the water density, g is the gravitational acceleration, D is the particle diameter, and η is the viscosity of water.

[0055] If ρ and D are the true density and average particle size of the inorganic microparticles 11, the thermally expandable graphite 12, the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14, respectively, the higher the true density and the larger the average particle size, the faster the terminal velocity, and therefore the more likely they are to be located near the surface of the object to be coated 20.

[0056] The true density was 2.7 g / cm for inorganic microparticles 11, 2.2 g / cm for thermally expandable graphite 12, approximately 1.0 g / cm for organic hollow particles 13A, approximately 1.5 g / cm for inorganic hollow particles 13B, and 2.7 g / cm when the foaming agent particles 14 were calcium carbonate. The true densities of inorganic microparticles 11, thermally expandable graphite 12, and foaming agent particles 14 were close, but because thermally expandable graphite 12 had the largest average particle size, it had the fastest terminal velocity and was likely to be located in a position in coating film 10C where the shortest distance from the surface of object 20 to the surface of thermally expandable graphite 12 was shorter than the shortest distance from the surface of object 20 to the surfaces of other particles. Hereinafter, a short shortest distance from the surface of object 20 to the surface of a particle will be expressed as "close."

[0057] Among the inorganic fine particles 11, the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14, the inorganic fine particles 11 have the smallest average particle size, and therefore have the slowest terminal velocity. However, when the coating liquid is applied to the object to be coated 20 and then dried, the water serving as the dispersion medium evaporates, increasing the concentration of the inorganic fine particles 11, and some of the inorganic fine particles 11 become secondary particles having sizes equal to or larger than those of the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14. As a result, the terminal velocities of the inorganic fine particles 11 range from faster to slower than those of the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14, and the inorganic fine particles 11 are located in the coating film 10C from closer to the surface of the object to be coated 20 to farther from those of the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14. When the organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14 have the same average particle size, the terminal velocities are fastest for the foaming agent particles 14, inorganic hollow particles 13B, and organic hollow particles 13A in that order.

[0058] However, since the inorganic microparticles 11, the thermally expandable graphite 12, the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14 are present randomly in the coating liquid, for example, if the organic hollow particles 13A are located close to the surface of the object to be coated 20 in the coating liquid applied to the object to be coated 20, even if the terminal velocity is slow, the distance to the surface of the object to be coated 20 is short, so that the inorganic microparticles 11, the thermally expandable graphite 12, the organic hollow particles 13A, the inorganic hollow particles 13B, and the foaming agent particles 14 are located somewhat randomly in the coating film 10C, rather than being located in layers.

[0059] For the reasons described above, the particles in the coating film 10C tend to assume the positional relationship shown in Fig. 3. As a result, when the coating film 10C is heated, a molten film 15 tends to form on the surface side of the coating film 10C, as shown in Fig. 5, and the foaming agent particles 14 tend to be positioned between the molten film 15 and the object to be coated 20. When the foaming agent particles 14 thermally decompose in this position and generate gas, the molten film 15 expands to the state shown in Fig. 6, which not only distances the object to be coated 20 from the flame, but also reduces thermal conductivity due to the gas generated from the foaming agent particles 14, thereby improving fire resistance and heat insulation, including thermal deformation suppression.

[0060] Therefore, by adding the above effects to the effects of Embodiments 1 and 2, it is possible to improve fire resistance and heat insulation, including thermal deformation suppression, compared to the coating films of Embodiments 1 and 2. Note that, in this embodiment, the case where the hollow particles contain both organic hollow particles 13A and inorganic hollow particles 13B has been described, but it is sufficient that the hollow particles contain at least organic hollow particles 13A, and similar effects can be achieved even if the hollow particles contain only organic hollow particles 13A and no inorganic hollow particles 13B, as shown in Figure 4.

[0061] Embodiment 4. In the third embodiment, the case where the heat insulating material contained in the coating film includes thermally expandable graphite 12 has been described, but the coating film 10D according to the fourth embodiment differs from the third embodiment in that the heat insulating material does not include thermally expandable graphite 12. Explanation of the same parts as in the third embodiment will be omitted, and only the parts that differ from the third embodiment will be described.

[0062] 7 is a cross-sectional view schematically illustrating an example of the structure of a coating film 10D containing organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14 as heat insulating materials. The coating film 10D is composed of inorganic fine particles 11, organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14. The object to be coated 20 may be a thermoplastic resin processed by injection molding. The inorganic fine particles 11 act as a binder that bonds other inorganic fine particles 11 to the object to be coated 20, a binder that bonds the organic hollow particles 13A to the object to be coated 20, a binder that bonds the inorganic hollow particles 13B to the object to be coated 20, and a binder that bonds the foaming agent particles 14 to the object to be coated 20. That is, the inorganic fine particles 11 act as a binder to bind the hollow particles, which are heat insulating materials, to the object to be coated 20, and to bind the foaming agent particles 14, which are heat insulating materials, to the object to be coated 20. Furthermore, the inorganic fine particles 11 themselves also act as a binder to bind other inorganic fine particles 11 to the object to be coated 20.

[0063] The materials and sizes of the inorganic fine particles 11, organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14 contained in the coating film 10D according to embodiment 4 are the same as those in embodiment 3. In the coating film 10D according to embodiment 4, as in embodiment 3, the organic hollow particles 13A tend to be located on the surface side of the coating film 10D, and the foaming agent particles 14 tend to be located on the side of the object 20 to be coated.

[0064] As a result, when the coating film 10D is heated, a molten film 15 similar to that shown in Figure 5 (not shown) is likely to form on the surface side of the coating film 10D, and the foaming agent particles 14 are likely to be positioned between the molten film 15 and the object to be coated 20. If the foaming agent particles 14 thermally decompose at this position and generate gas, the molten film 15 will expand, distancing the object to be coated 20 from the flame, and the gas generated from the foaming agent particles 14 will reduce thermal conductivity, thereby improving fire resistance and heat insulation. Note that while the coating film 10D shown in Figure 7 has a configuration including inorganic hollow particles 13B, it is sufficient that the hollow particles include at least organic hollow particles 13A, and it is not necessarily required that the inorganic hollow particles 13B be included.

[0065] <Preparation of Coating Liquid> The coating liquid for forming the coating film 10D according to the fourth embodiment is prepared by dispersing inorganic fine particles 11, organic hollow particles 13A, inorganic hollow particles 13B, and foaming agent particles 14 in water as a dispersion medium.

[0066] The content of inorganic particles 11 in the coating liquid is the same as in embodiment 1. The total content of organic hollow particles 13A and inorganic hollow particles 13B in the coating liquid is preferably 0.5% by mass or more and 25% by mass or less, particularly preferably 2.5% by mass or more and 10% by mass or less. If the total content of organic hollow particles 13A and inorganic hollow particles 13B in the coating liquid is less than 0.5%, the coverage of the coated object 20 with the organic hollow particles 13A and inorganic hollow particles 13B is low, and the desired fire-resistant and insulating properties may not be achieved. If the total content of organic hollow particles 13A and inorganic hollow particles 13B in the coating liquid is more than 25% by mass, there will be no problem with fire-resistant and insulating properties, but the number of inorganic particles 11 acting as a binder per particle of organic hollow particles 13A and inorganic hollow particles 13B will be reduced, making the organic hollow particles 13A and inorganic hollow particles 13B more likely to fall off the coating film 10D.

[0067] The content of the foaming agent particles 14 in the coating liquid is preferably 0.5% by mass or more and 25% by mass or less, and particularly preferably 2.5% by mass or more and 10% by mass or less. If the content of the foaming agent particles 14 is less than 0.5% by mass, the molten film 15 formed by the melting and flowing of the organic hollow particles 13A may not expand to a sufficient extent due to the gas generated by the thermal decomposition of the foaming agent particles 14, and the desired insulating effect may not be obtained. If the content of the foaming agent particles 14 is more than 25% by mass, the amount of gas generated per unit time by the thermal decomposition of the foaming agent particles 14 may be too large, and the molten film 15 formed by the melting and flowing of the organic hollow particles 13A may be easily torn, and the desired insulating effect may not be obtained.

[0068] As described above, when the coating film 10D of this embodiment is heated, it forms a molten film 15 on the surface side of the coating film 10D, and the foaming agent particles 14 located between the molten film 15 and the object to be coated 20 undergo thermal decomposition to generate gas, thereby expanding the molten film 15 and distancing the object to be coated 20 from the flame, and the gas generated from the foaming agent particles 14 reduces thermal conductivity, thereby improving fire resistance and heat insulation. As a result, even if the heat insulating material does not contain thermally expandable graphite, it is possible to improve fire resistance and heat insulation, including thermal deformation suppression, and prevent holes from being created by the heat of the flame in the object to be coated molded from a resin material, such as a resin housing.

[0069] Embodiment 5. The coating films according to Embodiments 1 to 4 may further include a reinforcing material that reinforces the coating film. Examples of reinforcing materials for the coating film include carbon nanotubes and carbon nanofibers, but the present invention is not limited to these, and any material that can reinforce the coating film may be used. In Embodiment 5, as an example, a case will be described in which the coating film 10A according to Embodiment 1 further includes carbon nanotubes and carbon nanofibers, but the reinforcing material for the coating film may include at least one of carbon nanotubes and carbon nanofibers. Descriptions of the same parts as in Embodiment 1 will be omitted, and only differences from Embodiment 1 will be described.

[0070] FIG. 8 is a cross-sectional view schematically illustrating an example of the structure of a coating film 10E containing carbon nanotubes 16 and carbon nanofibers 17. The inorganic fine particles 11 function as binders that bind the carbon nanotubes 16 to the object to be coated 20 and also as binders that bind the carbon nanofibers 17 to the object to be coated 20. That is, the inorganic fine particles 11 function as binders that bind not only the thermally expandable graphite 12, which is an insulating material, but also the carbon nanotubes 16, which are reinforcing materials, to the object to be coated 20, and the carbon nanofibers 17, which are reinforcing materials, to the object to be coated 20. Furthermore, the inorganic fine particles 11 themselves also function as binders that bind other inorganic fine particles 11 to the object to be coated 20. By including at least one of the carbon nanotubes 16 and the carbon nanofibers 17, which have a higher aspect ratio than the inorganic fine particles 11, in the coating film 10E, the strength is improved, and the effect of suppressing the formation of holes due to thermal deformation of the object to be coated 20 is enhanced.

[0071] Among the components contained in the coating film 10E, the carbon nanotubes 16 and the carbon nanofibers 17 will be described in detail below. Note that, among the components contained in the coating film 10E, the components other than the carbon nanotubes 16 and the carbon nanofibers 17 are the same as those described above, and therefore description thereof will be omitted.

[0072] <Carbon nanotubes, carbon nanofibers> Carbon nanotubes 16 are a form of carbon based on a structure in which a graphite sheet in which carbon is arranged in the form of a regular hexagon is rolled up into a cylindrical shape. Examples of carbon nanotubes include single-walled carbon nanotubes, which have only one layer, and multi-walled carbon nanotubes, which have multiple layers.

[0073] Both the carbon nanotubes 16 and the carbon nanofibers 17 preferably have a diameter of about 1 nm to 100 nm and a length of 100 nm to 10 μm. If the diameter is less than 1 nm, the contact area with the inorganic fine particles 11 serving as the binder becomes small, and the reinforcing effect of the carbon nanotubes 16 and the carbon nanofibers 17 on the coating film 10E may not be obtained. If the diameter is greater than about 100 nm, the contact area with the inorganic fine particles 11 serving as the binder becomes large, but the aspect ratio (ratio of length to diameter) of the carbon nanotubes 16 and the carbon nanofibers 17 becomes small, and the reinforcing effect of the carbon nanotubes 16 and the carbon nanofibers 17 on the coating film 10E may not be obtained.

[0074] Furthermore, as the diameter increases, the number of carbon nanotubes 16 and carbon nanofibers 17 per unit mass decreases, which may prevent the surface of the coating film 10E from being uniformly reinforced. If the length is less than 100 nm, the aspect ratio of the carbon nanotubes 16 and carbon nanofibers 17 decreases, which may prevent the carbon nanotubes 16 and carbon nanofibers 17 from providing a reinforcing effect to the coating film 10E. If the length is longer than 10 μm, the number of carbon nanotubes 16 and carbon nanofibers 17 per unit mass decreases, which may prevent the surface of the coating film 10E from being uniformly reinforced.

[0075] The content of at least one of the carbon nanotubes 16 and the carbon nanofibers 17 in the coating liquid is preferably 0.1% by mass or more and 5% by mass or less, and particularly preferably 0.5% by mass or more and 2% by mass or less. If the content of at least one of the carbon nanotubes 16 and the carbon nanofibers 17 is less than 0.1%, the effect of improving the strength of the coating film 10E by the carbon nanotubes 16 and the carbon nanofibers 17 may not be obtained. If the content of at least one of the carbon nanotubes 16 and the carbon nanofibers 17 is more than 5% by mass, the effect of improving the strength of the coating film 10E by the carbon nanotubes 16 and the carbon nanofibers 17 will not be a problem, but the dispersibility in the coating liquid will be poor.

[0076] The true density of the carbon nanotubes 16 is 1.3 to 1.4 g / cm for single-walled carbon nanotubes. ３ , multi-walled carbon nanotubes 2.1 g / cm ３ The true density of the carbon nanofiber 17 is 2.2 g / cm ３ If the diameter of a sphere having the same volume as the volume of a fibrous substance such as the carbon nanotubes 16 and the carbon nanofibers 17 is defined as the equivalent sphere diameter, the equivalent sphere diameter of the carbon nanotubes 16 and the carbon nanofibers 17 is several nm to several hundred nm, and the terminal velocities of the carbon nanotubes 16 and the carbon nanofibers 17 range from slower than the inorganic fine particles 11 to faster than the secondary particles of the inorganic fine particles 11. Therefore, the carbon nanotubes 16 and the carbon nanofibers 17 are located farther from the surface of the object to be coated 20 than the inorganic fine particles 11 and are located closer to the surface of the object to be coated 20 than the secondary particles of the inorganic fine particles 11.

[0077] As described above, the coating film 10E of the present embodiment contains, as a reinforcing material, at least one of the carbon nanotubes 16 and the carbon nanofibers 17, which have a higher aspect ratio than the inorganic particles 11, thereby improving the strength of the coating film 10E and improving the effect of suppressing holes caused by thermal deformation of the coated object 20. Therefore, the fire resistance and heat insulation properties, including the ability to suppress thermal deformation, can be improved, and it is possible to prevent holes from being generated by the heat of a flame in the coated object 20, which is made of a resin material, such as a resin housing.

[0078] Sixth Embodiment A housing coated with a coating film according to the first to fifth embodiments of the present disclosure will be described below. Fig. 9 is a cross-sectional view schematically illustrating an example of the structure of a housing 40 having improved fire resistance and heat insulation properties by using any one of coating films 10A, 10B, 10C, 10D, and 10E according to the first to fifth embodiments. Hereinafter, coating films 10A, 10B, 10C, 10D, and 10E will be collectively referred to as coating film 10.

[0079] The housing 40 shown in FIG. 9 includes a resin housing 41 molded from a resin material and a coating film 10 coated on the surface of the resin housing 41. The housing 40 contains, for example, a printed circuit board 43 equipped with electronic components such as a capacitor 42. In FIG. 9, the resin housing 41 corresponds to the object to be coated 20. While FIG. 9 shows an example in which the coating film 10 is coated on both surfaces of the resin housing 41, the coating film 10 may be coated on only one surface of the resin housing 41. When the coating film 10 is coated on the inner surface of the resin housing 41, the effect of suppressing thermal deformation of the resin housing 41 in the event of a flame occurring inside the housing is high. When the coating film 10 is coated on the outer surface of the resin housing 41, the effect of suppressing thermal deformation of the resin housing 41 in the event of a flame occurring outside the housing is high. Furthermore, when the coating film 10 is coated on both surfaces of the resin housing 41, the effect of suppressing thermal deformation of the resin housing 41 can be further enhanced compared to when the coating film 10 is coated on only one surface.

[0080] As described above, the housing 40 of this embodiment is a resin housing having a surface coated with the coating film 10 that has improved fire resistance and heat insulation properties, including thermal deformation suppression properties, so that even if an electronic component such as a capacitor inside the housing catches fire and the flames reach the housing, it is possible to prevent a hole from opening in the housing and the fire from spreading to nearby devices. Furthermore, even if a flame comes from outside the housing, it is possible to prevent a hole from opening in the housing and directly exposing the electronic components inside the housing to the flames.

[0081] Hereinafter, the embodiments of the present disclosure will be described more specifically based on examples, but the present disclosure is not limited to these examples.

[0082] <Preparation of the object to be coated> A PC / ABS resin was injection molded into a flat plate measuring 150 mm (length) × 150 mm (width) × 2.0 mm (thickness) to prepare the object to be coated. The molding conditions were a molding temperature of 240°C and a mold temperature of 60°C.

[0083] Example 1 A coating liquid was prepared by blending colloidal silica containing silica microparticles with an average particle size of 12 nm (NH4+-stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200°C (GRAFGUARD 200-100, 120 mesh residue, manufactured by Tomoe Engineering Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water. This coating liquid contained 1% by mass of silica microparticles, 5% by mass of thermally expandable graphite, 0.5% by mass of dispersant, and the remainder was deionized water. The coating liquid was applied to a substrate using a bar coater and then dried at 25°C for 24 hours. The silica microparticles functioned as an inorganic binder, adhering the coating film to the substrate.

[0084] Example 2 A coating liquid was prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200° C. (GRAFGUARD 200-100, 120 mesh residue, manufactured by Tomoe Engineering Co., Ltd.), organic hollow particles with an average particle size of 80 nm (TECHPOLYMER NH, XX-255AA, manufactured by Sekisui Plastics Co., Ltd.), inorganic hollow particles with an average particle size of 75 nm (THRULYA, 5320, manufactured by JGC Catalysts and Chemicals Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water as water, followed by mixing and stirring. In this coating liquid, the content of silica fine particles is 1 mass%, the content of thermally expandable graphite is 5 mass%, the content of organic hollow particles is 0.5 mass%, the content of inorganic hollow particles is 0.5 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. The coating liquid is applied to the substrate using a bar coater, and then dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder, fixing the coating film to the substrate.

[0085] Example 3 A coating liquid is prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion starting temperature of 200° C. (120 mesh residue of GRAFGUARD 200-100, manufactured by Tomoe Engineering Co., Ltd.), organic hollow particles with an average particle size of 80 nm (TECHPOLYMER NH, XX-255AA, manufactured by Sekisui Plastics Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water as water, followed by mixing and stirring. In this coating liquid, the content of silica fine particles is 1 mass%, the content of thermally expandable graphite is 5 mass%, the content of organic hollow particles is 1 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. The coating liquid is applied to the substrate using a bar coater, and then dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder, fixing the coating film to the substrate.

[0086] Example 4 A coating liquid was prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (Nissan Chemical Industries, Ltd., NH4+ stable alkaline sol, ST-N), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200° C. (Tomoe Engineering Co., Ltd., GRAFGUARD 200-100, 120 mesh residue), inorganic hollow particles with an average particle size of 75 nm (JGC Catalysts and Chemicals Co., Ltd., THRULYA, 5320), a dispersant (MP Gokyo Food & Chemical Co., Ltd., Echo Gum), and deionized water. The coating liquid contained 1% by mass of silica fine particles, 5% by mass of thermally expandable graphite, 1% by mass of inorganic hollow particles, 0.5% by mass of dispersant, and the remainder was deionized water. The coating solution is applied to the object to be coated using a bar coater, and then dried for 24 hours at 25° C. The silica fine particles function as an inorganic binder, fixing the coating film onto the object to be coated.

[0087] Example 5 A mixture of colloidal silica containing silica fine particles with an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion starting temperature of 200° C. (GRAFGUARD 200-100, manufactured by Tomoe Engineering Co., Ltd., 120 mesh residue), and organic hollow particles with an average particle size of 80 nm (TECHPOLYMER, manufactured by Sekisui Plastics Co., Ltd.) was used. A coating solution was prepared by blending and stirring a mixture of silica particles (NH, XX-255AA), inorganic hollow particles with an average particle size of 75 nm (THRULYA, 5320, manufactured by JGC Catalysts and Chemicals Co., Ltd.), blowing agent particles with an average particle size of 80 nm (TecoCell, manufactured by Trexel Japan Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water. This coating solution contained 1% by mass of silica fine particles, 5% by mass of thermally expandable graphite, 0.5% by mass of organic hollow particles, 0.5% by mass of inorganic hollow particles, 0.5% by mass of blowing agent particles, 0.5% by mass of dispersant, and the remainder was deionized water. The coating solution was applied to the substrate using a bar coater and then dried at 25°C for 24 hours. The silica particles function as an inorganic binder, adhering the coating film to the surface of the coating object.

[0088] Example 6 A coating liquid is prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200° C. (GRAFGUARD 200-100, 120 mesh residue, manufactured by Tomoe Engineering Co., Ltd.), organic hollow particles with an average particle size of 80 nm (TECHPOLYMER NH, XX-255AA, manufactured by Sekisui Plastics Co., Ltd.), foaming agent particles with an average particle size of 80 nm (TecoCell, manufactured by Trexel Japan K.K.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water as water, followed by mixing and stirring. In this coating liquid, the content of silica fine particles is 1 mass%, the content of thermally expandable graphite is 5 mass%, the content of organic hollow particles is 1 mass%, the content of foaming agent particles is 1 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. The coating liquid is applied to the substrate using a bar coater and then dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder, adhering the coating film to the substrate.

[0089] Example 7 A coating liquid was prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (Nissan Chemical Industries, Ltd., NH4+ stable alkaline sol, ST-N), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200°C (Tomoe Engineering Co., Ltd., GRAFGUARD 200-100, 120 mesh residue), carbon nanotubes with a diameter of 25 nm and a length of 340 nm (KJ Specialty Paper Co., Ltd., TMB060), a dispersant (MP Gokyo Food & Chemical Co., Ltd., Echo Gum), and deionized water. The coating liquid contained 1% by mass of silica fine particles, 5% by mass of thermally expandable graphite, 1% by mass of carbon nanotubes, 0.5% by mass of dispersant, and the remainder was deionized water. The coating solution is applied to the object to be coated using a bar coater, and then dried for 24 hours at 25° C. The silica fine particles function as an inorganic binder, fixing the coating film onto the object to be coated.

[0090] Example 8 A coating solution was prepared by blending colloidal silica containing silica microparticles with an average particle size of 12 nm (Nissan Chemical Industries, Ltd., NH4+ stable alkaline sol, ST-N), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion onset temperature of 200°C (Tomoe Engineering Co., Ltd., GRAFGUARD 200-100, 120 mesh residue), carbon nanofibers with a diameter of 80 nm and a length of 10 μm (Showa Polymer Co., Ltd., VGNF), a dispersant (MP Gokyo Food & Chemical Co., Ltd., Echo Gum), and deionized water. The coating solution contained 1% by mass of silica microparticles, 5% by mass of thermally expandable graphite, 1% by mass of carbon nanofibers, 0.5% by mass of dispersant, and the remainder was deionized water. The coating solution is applied to the object to be coated using a bar coater, and then dried for 24 hours at 25° C. The silica fine particles function as an inorganic binder, fixing the coating film onto the object to be coated.

[0091] Example 9 A coating liquid is prepared by blending colloidal silica containing silica fine particles with an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), thermally expandable graphite with an average particle size of 140 μm and a thermal expansion starting temperature of 200° C. (GRAFGUARD200-100, manufactured by Tomoe Engineering Co., Ltd., 120 mesh residue), carbon nanotubes with a diameter of 25 nm and a length of 340 nm (TMB060, manufactured by KJ Specialty Paper Co., Ltd.), carbon nanofibers with a diameter of 80 nm and a length of 10 μm (VGNF, manufactured by Showa Polymer Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water. In this coating liquid, the content of silica fine particles is 1 mass%, the content of thermally expandable graphite is 5 mass%, the content of carbon nanotubes is 0.5 mass%, the content of carbon nanofibers is 0.5 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. The coating liquid is applied to the object to be coated using a bar coater, and then dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder, fixing the coating film to the object to be coated.

[0092] Example 10 A coating liquid is prepared by blending colloidal silica containing silica fine particles having an average particle size of 12 nm (NH4+ stable alkaline sol, ST-N, manufactured by Nissan Chemical Industries, Ltd.), organic hollow particles having an average particle size of 80 nm (TECHPOLYMER NH, XX-255AA, manufactured by Sekisui Plastics Co., Ltd.), inorganic hollow particles having an average particle size of 75 nm (THRULYA, 5320, manufactured by JGC Catalysts and Chemicals Co., Ltd.), foaming agent particles having an average particle size of 80 nm (TecoCell, manufactured by Trexel Japan Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water as water, followed by mixing and stirring. In this coating liquid, the content of silica fine particles is 1 mass%, the content of organic hollow particles is 2.5 mass%, the content of inorganic hollow particles is 2.5 mass%, the content of foaming agent particles is 2.5 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. After applying the coating liquid to the object to be coated with a bar coater, it is dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder to fix the coating film on the object to be coated.

[0093] Example 11 Colloidal silica containing silica fine particles with an average particle size of 12 nm (Nissan Chemical Industries, Ltd., NH4+ stabilized alkaline sol, ST-N) and organic hollow particles with an average particle size of 80 nm (Sekisui Plastics Co., Ltd., TECHPOLYMER NH, XX-255AA), inorganic hollow particles having an average particle size of 75 nm (THRULYA, 5320, manufactured by JGC Catalysts and Chemicals Co., Ltd.), foaming agent particles having an average particle size of 80 nm (TecoCell, manufactured by Trexel Japan Co., Ltd.), carbon nanotubes having a diameter of 25 nm and a length of 340 nm (TMB060, manufactured by KJ Specialty Paper Co., Ltd.), carbon nanofibers having a diameter of 80 nm and a length of 10 μm (VGNF, manufactured by Showa Polymer Co., Ltd.), a dispersant (Echo Gum, manufactured by MP Gokyo Food & Chemical Co., Ltd.), and deionized water are blended and mixed and stirred to prepare a coating liquid. In this coating liquid, the content of silica fine particles is 1 mass%, the content of organic hollow particles is 2.5 mass%, the content of inorganic hollow particles is 2.5 mass%, the content of foaming agent particles is 2.5 mass%, the content of carbon nanotubes is 0.5 mass%, the content of carbon nanofibers is 0.5 mass%, the content of dispersant is 0.5 mass%, and the remainder is deionized water. The coating liquid is applied to the substrate using a bar coater, and then dried at 25°C for 24 hours. The silica fine particles function as an inorganic binder, adhering the coating film to the substrate.

[0094] Comparative Example 1 A coating liquid is prepared in the same manner as in Example 1, except that a core-shell type styrene-acrylic emulsion (Seiko PMC Corporation, water-based styrene-acrylic emulsion X-436) is used instead of colloidal silica containing silica fine particles, and the styrene-acrylic content is set to 1 mass %. Also, in the same manner as in Example 1, the coating liquid is applied to an object to be coated using a bar coater, and then dried at 25°C for 24 hours.

[0095] 10 is a cross-sectional view schematically showing an example of the structure of a coating film 10F according to Comparative Example 1. Core-shell type microparticles, each having a core made of styrene acrylic and a shell made of a water-soluble polymer encapsulating the core, are fused with other core-shell type microparticles to form a continuous film 18 of shell-core microparticles, which serves as a binder that bonds other core-shell type microparticles to the object to be coated 20, and also as a binder that bonds thermally expandable graphite 12 to the object to be coated 20. That is, in Comparative Example 1, the core-shell type microparticles function as an organic binder.

[0096] <Fire Resistance Evaluation Method> The coated objects 20 having the coating films prepared in Examples 1 to 11 and Comparative Example 1 were used as plate test specimens, and a horizontal flammability test of the plate test specimens was performed based on UL94-5V by Underwriters Laboratories. First, the plate test specimens were conditioned under two conditions. For the first condition, two sets of three plate test specimens were prepared and conditioned for 48 hours at a temperature of 23°C and a relative humidity of 50%. For the second condition, two sets of three plate test specimens were prepared and aged for 168 hours at a temperature of 70°C in an air-circulating oven, followed by cooling in a desiccator for 4 hours. A 50 mm x 50 mm, 6 mm thick absorbent cotton rug was conditioned for 24 hours in a desiccator before use. The temperature and relative humidity during the horizontal flammability test of the plate-shaped test specimens were 23°C and 50%, respectively. Using a clamp on a ring stand, one plate-shaped test specimen was fixed horizontally with the coating film facing downward relative to the object to be coated 20. The distance from the bottom end of the plate-shaped test specimen to the surface of the horizontally placed absorbent cotton was 300 mm.

[0097] The burner, fueled by methane gas, was adjusted to a total flame height of 125 mm and an internal blue flame height of 40 mm. The burner tube was tilted 20° from the vertical axis so that the tip of the internal blue flame struck the lower surface of the test plate at approximately the center. The flame was applied to each test plate for 5 seconds, followed by a 5-second release of the burner flame. This cycle was repeated five times. A flame contact test was conducted on all three test plate specimens conditioned for 48 hours at 23°C and 50% relative humidity, as well as on all three test plate specimens aged for 168 hours at 70°C. The flame contact test for the test plate specimens aged for 168 hours at 70°C was completed within 30 minutes of removing both the test plate specimens and the absorbent cotton pad from the desiccator to the test environment of 23°C and 50% relative humidity. If even one test piece was penetrated by flame according to the criteria described below, an additional flame contact test was conducted using the remaining set of three plate-shaped test pieces that had been conditioned in the same way.

[0098] <Fire Resistance Evaluation Criteria> The evaluation criteria consist of four individual criteria: one individual criterion unique to the present disclosure, which is the presence or absence of thermally expandable graphite or the like falling off when the plate-shaped test specimen is fixed to the clamp of the ring stand, and three individual criteria in accordance with the UL94-5V evaluation criteria. The three individual criteria in accordance with the UL94-5V evaluation criteria consist of two individual criteria related to the penetration of flames into the test specimen, and one individual criterion related to objects falling from the plate-shaped test specimen onto absorbent cotton. The individual criteria are shown below. If all four individual criteria are met, the evaluation criteria are met.

[0099] [Individual Criterion 1] Regarding the presence or absence of thermally expandable graphite or other materials falling off when the plate test specimen is fixed to the clamp of the ring stand, if no falling off occurs, it is deemed to have passed the test. [Individual Criterion 2] If no visible flame is observed on the surface of the plate test specimen opposite the flame-contact surface during the flame contact test, it is deemed to have passed the test. [Individual Criterion 3] After the flame contact test is completed, the plate test specimen is allowed to cool for 30 seconds or more, and if there are no openings, or if there are openings, they are 3 mm or less, it is deemed to have passed the test. [Individual Criterion 4] It is deemed to have passed the test if there are no molten or flaming falling objects from the plate test specimen that can ignite the absorbent cotton mat.

[0100] <Fire Resistance Evaluation Results> The obtained evaluation results are shown in Figure 11. In Examples 1 to 11, no holes were formed in the coating film 10 or the coated object 20 even after flame contact, and all four individual criteria were met, so they met the evaluation criteria. On the other hand, in Comparative Example 1, holes were formed during flame contact in the first flame contact test, and holes were also formed during flame contact in the additional flame contact test, so that it did not meet individual criteria 2 and 3, and therefore did not meet all four individual criteria, so it did not meet the evaluation criteria. In other words, Examples 1 to 11, which used only an inorganic binder as the binder, met the evaluation criteria, while Comparative Example 1, which used an organic binder as the binder, did not meet the evaluation criteria.

[0101] As described above, according to the present invention, it is possible to impart fire resistance and heat insulation properties, including thermal deformation suppression properties, to injection-molded resin housings and the like that have a high degree of thermal shrinkage.

[0102] The configurations shown in the above embodiments are examples of the contents of the present disclosure. The configurations of each embodiment can be combined with other known technologies. The configurations of each embodiment can also be combined as appropriate. Part of the configuration of each embodiment can be omitted or modified without departing from the gist of the present disclosure.

[0103] 10, 10A, 10B, 10C, 10D, 10E, 10F coating film, 11 inorganic fine particles, 12 thermally expandable graphite, 13 hollow particles, 13A organic hollow particles, 13B inorganic hollow particles, 14 foaming agent particles, 15 molten film, 16 carbon nanotubes, 17 carbon nanofibers, 18 continuous film, 20 coated object, 40 housing, 41 resin housing, 42 capacitor, 43 printed circuit board.

Claims

1. A coating film for protecting a coated object molded from a resin material, comprising: a heat insulating material; and a binder that binds the heat insulating material and the coated object together, wherein the binder is made of inorganic fine particles.

2. The coating film according to claim 1, characterized in that the binder is an inorganic fine particle that further binds other inorganic fine particles to the object to be coated.

3. A coating film according to claim 1 or claim 2, characterized in that the heat insulating material contains thermally expandable graphite, and the binder binds the thermally expandable graphite to the object to be coated.

4. The coating film according to claim 3, wherein the thermally expandable graphite expands when heated to form a fire-resistant heat-insulating layer.

5. A coating film according to claim 3 or 4, characterized in that the heat insulating material further contains hollow particles having a hollow portion inside, and the binder further bonds the hollow particles to the object to be coated.

6. The coating film according to claim 5, wherein the hollow particles contain air in the hollow portions and expand when heated.

7. The coating film according to claim 5 or 6, characterized in that the hollow particles include organic hollow particles made of an organic material or inorganic hollow particles made of an inorganic material.

8. The coating film according to claim 7, characterized in that the heat insulating material, when containing the organic hollow particles, further contains particles of a foaming agent, and the binder further binds the particles of the foaming agent to the object to be coated.

9. The coating film described in claim 8, characterized in that the organic hollow particles are distributed more on the surface side of the coating film than on the side of the object to be coated, and the foaming agent particles are distributed more on the side of the object to be coated than on the surface side of the coating film.

10. The coating film according to claim 9, characterized in that when the organic hollow particles are heated to a temperature above their softening temperature, they melt and flow to form a molten film on the surface of the coating film, and the molten film expands due to gas generated by thermal decomposition of the foaming agent particles located between the molten film and the object to be coated.

11. A coating film according to claim 1 or claim 2, characterized in that the heat insulating material is made of hollow particles having a hollow portion inside and particles of a foaming agent, the binder bonds the hollow particles to the object to be coated and the particles of the foaming agent to the object to be coated, and the hollow particles include organic hollow particles formed from an organic material.

12. The coating film described in claim 11, characterized in that the organic hollow particles are distributed in greater numbers on the surface side of the coating film than on the object to be coated, and the foaming agent particles are distributed in greater numbers on the object to be coated than on the surface side of the coating film.

13. The coating film described in claim 12, characterized in that when the organic hollow particles are heated to a temperature above their softening temperature, they melt and flow to form a molten film on the surface of the coating film, and the molten film expands due to gas generated by thermal decomposition of the foaming agent particles located between the molten film and the object to be coated.

14. A coating film according to any one of claims 1 to 13, further comprising a reinforcing material, wherein the binder further binds the reinforcing material to the object to be coated.

15. The coating film according to claim 14, characterized in that the reinforcing material contains carbon nanotubes or carbon nanofibers, and the binder bonds the carbon nanotubes to the coated object when the reinforcing material contains the carbon nanotubes, or bonds the carbon nanofibers to the coated object when the reinforcing material contains the carbon nanofibers.

16. A coating film according to any one of claims 1 to 15, characterized in that the binder contains inorganic fine particles whose average particle size is 3 nm or more and 25 nm or less.

17. A housing comprising: a resin housing molded from a resin material; and a coating film according to any one of claims 1 to 16 coated on the surface of the resin housing.

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