Carbon coating composition for spraying and method for forming carbon coating film

Abstract

A carbon coating composition for spraying contains (A) a resin, (B) a carbon-based filler, and (C) a solvent. The component (B) contains (B1) graphite and (B2) carbon black. The component (C) contains (C1) at least one selected from the group consisting of propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate. The blending amount of the component (C) is from 30 mass% to 70 mass% relative to 100 mass% of the carbon coating composition.

Description

Spray carbon coating composition and method for forming carbon coating film

[0001] The present invention relates to a carbon coating composition for spray application and a method for forming a carbon coating film.

[0002] Metal plates or sheets are generally used as electromagnetic wave shielding materials. For example, in the case of a current sensor, a stainless steel plate that has been processed by sheet metal or bending is installed on the bottom or other surface of the component housing. If the electromagnetic wave shielding layer is installed on the side as well as the bottom, it will be even more effective in reducing noise, but it is difficult to bend metal to fit the component shape.

[0003] Therefore, for example, Patent Document 1 proposes providing an electromagnetic wave shielding layer inside a component housing using a carbon coating composition (such as carbon paste). Typical methods for applying carbon paste include screen printing and brush coating. However, screen printing makes it difficult to apply the carbon paste to surfaces that are not flat, such as component housings. Furthermore, when attempting to apply carbon paste directly to a component housing using a brush, unevenness is likely to occur, making it difficult to achieve a uniform finish. Therefore, there is a demand for applying the carbon coating composition by spraying.

[0004] Japanese Patent Application Laid-Open No. 2023-179994

[0005] However, when attempting to apply a typical carbon coating composition for use in screen printing or the like by spraying, there is a problem that the viscosity is too high and therefore the composition cannot be applied properly. On the other hand, it is conceivable to increase the amount of solvent blended in order to adjust the viscosity within an appropriate range. However, if the amount of solvent blended is too high, sagging occurs after application by spraying. Furthermore, if the amount of solvent blended is too high, there is a problem that the carbon-based filler precipitates during storage in the spray coating liquid container. Furthermore, there is also a problem that the carbon coating composition clogs the spray nozzle. As such, when applying a carbon coating composition by spraying, it has been extremely difficult to sufficiently suppress sagging while ensuring sufficient applicability.

[0006] An object of the present invention is to provide a carbon coating composition for spray application that has sufficient application properties and can sufficiently suppress sagging when applied by spraying, and a method for forming a carbon coating film.

[0007] According to the present invention, there are provided the following carbon coating composition for spray application and a method for forming a carbon coating film. [1] A carbon coating composition containing (A) a resin, (B) a carbon-based filler, and (C) a solvent, wherein the component (B) contains (B1) graphite and (B2) carbon black, and the component (C) contains (C1) at least one selected from the group consisting of propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate, and the blending amount of the component (C) is 30% by mass or more and 70% by mass or less, relative to 100% by mass of the carbon coating composition. [2] The carbon coating composition for spray application described in [1], wherein the component (A) contains a phenolic resin. [3] The carbon coating composition for spray application described in [1] or [2], wherein the component (C) further contains (C2) a glycol-based solvent having a boiling point of 170°C or higher. [4] The carbon coating composition for spray application according to any one of [1] to [3], wherein the blending amount of the component (C1) is 30% by mass or more and 80% by mass or less, relative to 100% by mass of the component (C). [5] A method for forming a carbon coating film, comprising applying the carbon coating composition for spray application according to any one of [1] to [4] by spraying to form a carbon coating film.

[0008] According to one aspect of the present invention, it is possible to provide a carbon coating composition for spray application that has sufficient application properties and can sufficiently suppress sagging when applied by spraying, and a method for forming a carbon coating film.

[0009] [Carbon Coating Composition for Spraying] First, a carbon coating composition for spraying according to this embodiment (hereinafter sometimes referred to as a "coating composition") will be described. The coating composition according to this embodiment contains (A) a resin, (B) a carbon-based filler, and (C) a solvent, which will be described below.

[0010] [Component (A)] Examples of the resin (A) used in this embodiment include polyester resins, urethane resins, acrylic resins, epoxy resins, phenolic resins, and alkyd resins. These may be used alone or in combination of two or more. Among these, phenolic resins are preferred from the viewpoint of the performance of the carbon coating film.

[0011] The blending amount of component (A) is preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 25% by mass or less, relative to 100% by mass of the coating composition. When the blending amount of component (A) is equal to or more than the lower limit, the smoothness of the carbon coating film can be further improved. When the blending amount of component (A) is equal to or less than the upper limit, the spray applicability can be further improved.

[0012] [Component (B)] The carbon-based filler (B) used in this embodiment must contain graphite (B1) and carbon black (B2). If the coating composition does not contain component (B1), clogging of the spray nozzle occurs when the coating composition is applied by spraying. Furthermore, if the coating composition does not contain component (B2), sagging cannot be suppressed when the coating composition is applied by spraying.

[0013] Component (B1) is a carbon-based filler that has been graphitized. Graphitization refers to a process in which the filler is heated at a high temperature, for example, around 3000°C, while being shielded from air. The average particle size of component (B1) is preferably 1 μm or more and 50 μm or less, and more preferably 3 μm or more and 40 μm or less. Component (B2) is carbon black powder. The average particle size of component (B2) is preferably 10 nm or more and 1000 nm or less, and more preferably 15 nm or more and 100 nm or less.

[0014] From the viewpoint of spray application properties, the blending amount of component (B1) is preferably 40% by mass or more and 74% by mass or less, more preferably 50% by mass or more and 72% by mass or less, and particularly preferably 60% by mass or more and 70% by mass or less, relative to 100% by mass of the total of components (B1) and (B2).

[0015] Component (B) may contain a carbon-based filler (hereinafter also referred to as component (B3)) other than components (B1) and (B2) as long as the effects of the present invention can be achieved. Examples of component (B3) include carbon nanotubes. However, from the viewpoint of spray applicability, component (B) preferably consists solely of components (B1) and (B2). Furthermore, the combined amount of components (B1) and (B2) is preferably 75% by mass or more, more preferably 85% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of component (B). From the viewpoint of spray applicability, the coating composition according to this embodiment preferably does not contain conductive particles other than component (B).

[0016] From the viewpoint of the performance of the carbon coating film, the blending amount of component (B) is preferably 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 35% by mass or less, and particularly preferably 20% by mass or more and 30% by mass or less, relative to 100% by mass of the coating composition.

[0017] [Component (C)] The solvent (C) used in this embodiment must contain at least one selected from the group consisting of (C1) propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate. If the coating composition does not contain component (C1), sagging cannot be suppressed when the coating composition is applied by spraying.

[0018] The blending amount of component (C1) is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 75% by mass or less, and particularly preferably 45% by mass or more and 70% by mass or less, relative to 100% by mass of component (C). When the blending amount of component (C1) is equal to or more than the lower limit, the smoothness of the carbon coating film can be further improved. When the blending amount of component (C1) is equal to or less than the upper limit, the spray applicability can be further improved.

[0019] Component (C) preferably further contains (C2), a glycol-based solvent with a boiling point of 170°C or higher. Component (C2) can improve leveling during spray application. Examples of component (C2) include butyl cellosolve acetate (boiling point 191°C), ethyl carbitol (boiling point 202°C), ethyl carbitol acetate (boiling point 217°C), and butyl carbitol acetate (boiling point 247°C). These may be used alone or in combination of two or more. The blending amount of component (C2) is preferably 20% by mass or more and 70% by mass or less, more preferably 25% by mass or more and 60% by mass or less, and particularly preferably 30% by mass or more and 55% by mass or less, relative to 100% by mass of component (C).

[0020] Component (C) may contain a solvent other than components (C1) and (C2) (hereinafter also referred to as component (C3)) as long as the effects of the present invention can be achieved. Examples of component (C3) include ketones such as methyl ethyl ketone; aromatic hydrocarbons such as toluene, phenol, and xylene; alcohols such as methanol, n-propanol, isopropanol, cyclohexanol, and propylene glycol monomethyl ether; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and esters such as ethyl acetate. These may be used alone or in combination of two or more. However, from the viewpoint of spray application properties, the combined amount of components (C1) and (C2) is preferably 75% by mass or more, more preferably 85% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of component (C).

[0021] The blending amount of component (C) needs to be 30% by mass or more and 70% by mass or less, based on 100% by mass of the coating composition. If the blending amount of component (C) is less than 30% by mass, the viscosity will be too high and proper application by spraying will be impossible. On the other hand, if the blending amount of component (C) is more than 70% by mass, precipitation of the carbon-based filler will occur during storage in the spray coating liquid container. From the same viewpoint, the blending amount of component (C) is preferably 40% by mass or more and 65% by mass or less, and more preferably 50% by mass or more and 62% by mass or less, based on 100% by mass of the coating composition.

[0022] [Other Components] In addition to components (A), (B), and (C), other additives may be added to the flux composition used in this embodiment as needed. Examples of other additives include thixotropic agents, antifoaming agents, modifiers, curing catalysts, extender pigments, flame retardants, matting agents, and foaming agents. The amount of these additives added is preferably 0.01% by mass or more and 5% by mass or less relative to 100% by mass of the coating composition.

[0023] [Method for producing a carbon coating composition for spray application] The method for producing the coating composition according to this embodiment is not limited to a specific method. For example, the coating composition can be produced by blending the above components in a predetermined ratio and then kneading or mixing them at room temperature using a kneading device such as a triple roll mill, a ball mill, or a sand mill, or a stirring device such as a super mixer or a planetary mixer. Furthermore, pre-kneading or pre-mixing may be performed as necessary before kneading or mixing. Furthermore, after kneading or mixing, a solvent may be appropriately added.

[0024] [Method for forming a carbon coating film] Next, a method for forming a carbon coating film according to this embodiment will be described. The method for forming a carbon coating film according to this embodiment is a method for forming a carbon coating film by applying the coating composition according to this embodiment described above by spraying. Examples of objects to be coated include component housings for electronic devices. By applying the coating composition according to this embodiment by spraying, a uniform carbon coating film can be formed without unevenness even on component housings with complex shapes.

[0025] Specifically, the coating composition according to this embodiment is first applied to the coating target, and then dried to form a carbon coating film. The drying conditions vary depending on the type of coating composition and are not particularly limited, but may be, for example, heating at a temperature in the range of 60°C to 80°C for 15 minutes to 60 minutes. This drying volatilizes the solvent and the like in the coating composition, forming a carbon coating film. The thickness of the carbon coating film (dry film thickness) is not particularly limited, but is usually 5 μm to 200 μm, and preferably 10 μm to 70 μm.

[0026] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0027] (Component (A)) Resin: resol type phenolic resin, trade name "Phenolite 5010", manufactured by DIC Corporation (Component (B1)) Graphite powder: trade name "Graphite AT" (average particle size 5 to 25 μm), manufactured by Oriental Sangyo Co., Ltd. (Component (B2)) Carbon black powder: trade name "Printex" (average particle size 10 to 50 nm), manufactured by Degussa (Component (C1)) Solvent A: propylene glycol monomethyl ether (boiling point 120°C) Solvent B: propylene glycol monomethyl ether acetate (boiling point 146°C) (Component (C2)) Solvent C: butyl cellosolve acetate (boiling point 191°C) Solvent D: ethyl carbitol (boiling point 202°C)

[0028] [Example 1] 24 parts by mass of resin, 18 parts by mass of graphite powder, 8 parts by mass of carbon black powder, 16 parts by mass of solvent C, and 11 parts by mass of solvent D were charged into a container and premixed using a stirrer, and then mixed and dispersed at room temperature using a three-roll mill, after which 23 parts by mass of solvent A was charged and mixed to obtain a coating composition.

[0029] [Examples 2 to 4] Coating compositions were obtained in the same manner as in Example 1, except that the materials were blended according to the formulation shown in Table 1. [Comparative Examples 1 to 5] Coating compositions were obtained in the same manner as in Example 1, except that the materials were blended according to the formulation shown in Table 1.

[0030] [Evaluation of Coating Compositions] Evaluation of the coating compositions (spray coatability (nozzle clogging, sagging, leveling, liquid pooling at bottom corners), and liquid properties) was performed using the following methods. The results obtained are shown in Table 1. (1) Spray coatability (nozzle clogging, sagging, leveling, liquid pooling at bottom corners) A housing (internal dimensions: 4 cm × 3 cm, internal depth: 1.5 cm) was prepared as a test piece to be coated. The obtained coating composition was placed in a spray device having a nozzle that could be inserted into the housing, and spray coating was performed under conditions such that the carbon coating film would have a thickness of 20 μm. The presence or absence of nozzle clogging was observed at this time, and the nozzle clogging was evaluated according to the following criteria: A: No nozzle clogging occurred. C: Nozzle clogging occurred, making normal spray coating impossible. The surface of the carbon coating was also observed, and sagging was evaluated according to the following criteria: A: No sagging occurred on the surface of the carbon coating. C: Sagging occurred on the surface of the carbon coating. The surface of the carbon coating was also observed, and the leveling ability was evaluated according to the following criteria. A: The surface of the carbon coating was smooth. C: The surface of the carbon coating was not smooth or had an orange peel appearance. The corners of the bottom surface were also observed for the presence or absence of liquid pooling, and the liquid pooling was evaluated according to the following criteria. A: No liquid pooling was observed in the corners of the bottom surface. C: Liquid pooling was observed in the corners of the bottom surface. (2) Liquid Properties The resulting coating composition was poured into a container and left to stand at 25°C for 24 hours. The liquid properties were then evaluated according to the following criteria. A: No precipitation occurred in the coating composition. C: Precipitation occurred in the coating composition.

[0031]

[0032] As is clear from the results shown in Table 1, when the carbon coating composition for spraying of the present invention was used (Examples 1 to 4), it was confirmed that all of the results regarding nozzle clogging, sagging, leveling, liquid accumulation at the bottom corners, and liquid properties were good. Therefore, it was confirmed that according to the present invention, a carbon coating composition for spraying can be obtained which has sufficient applicability when applied by spraying and can sufficiently suppress sagging.

[0033] The spray carbon coating composition of the present invention can be suitably used as a technique for forming an electromagnetic wave shielding layer on the housing parts of electronic devices such as current sensors.

Claims

1. A carbon coating composition for spray application, comprising (A) a resin, (B) a carbon-based filler, and (C) a solvent, wherein the component (B) comprises (B1) graphite and (B2) carbon black, the component (C) comprises (C1) at least one selected from the group consisting of propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate, and the blending amount of the component (C) is 30% by mass or more and 70% by mass or less, relative to 100% by mass of the carbon coating composition.

2. The carbon coating composition for spray application according to claim 1, wherein the component (A) contains a phenolic resin.

3. A carbon coating composition for spray application according to claim 1 or 2, wherein the component (C) further contains (C2) a glycol-based solvent having a boiling point of 170°C or higher.

4. A carbon coating composition for spray application according to claim 1 or 2, wherein the blending amount of the component (C1) is 30% by mass or more and 80% by mass or less, relative to 100% by mass of the component (C).

5. A method for forming a carbon coating film, comprising applying the spray carbon coating composition according to claim 1 or 2 by spraying to form a carbon coating film.

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