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

Abstract

To provide a carbon coating composition for spraying that exhibits adequate coating performance in spray application and effectively suppresses sagging.SOLUTION: 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.SELECTED DRAWING: None

Description

[Technical Field]

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

[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 (carbon paste or the like). Common methods for applying carbon paste include screen printing and brush coating. However, it is difficult to apply carbon paste to surfaces that are not flat, such as component housings, using screen printing. Furthermore, when attempting to apply carbon paste directly to component housings 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 paint composition by spraying. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-179994 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when attempting to apply a typical carbon coating composition for 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 possible 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 described above, when applying a carbon coating composition by spraying, it has been extremely difficult to sufficiently prevent 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. [Means for solving the problem]

[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 comprising (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 (C) component is 30% by mass or more and 70% by mass or less with respect to 100% by mass of the carbon coating composition. A carbon coating composition for spray application. [2] In the spray carbon coating composition according to [1], The component (A) contains a phenolic resin. A carbon coating composition for spray application. [3] In the spray carbon coating composition according to [1] or [2], The component (C) further contains (C2) a glycol-based solvent having a boiling point of 170°C or higher. A carbon coating composition for spray application. [4] In the spray carbon coating composition according to any one of [1] to [3], The blending amount of the (C1) component is 30% by mass or more and 80% by mass or less, relative to 100% by mass of the (C) component. A carbon coating composition for spray application. [5] The spray carbon coating composition according to any one of [1] to [4] is applied by spraying to form a carbon coating film. A method for forming a carbon coating. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Carbon coating composition for spray application] First, the spray carbon coating composition according to this embodiment (hereinafter sometimes referred to as the "coating composition") will be described. The coating composition according to this embodiment contains (A) a resin, (B) a carbonaceous filler, and (C) a solvent, which will be explained below.

[0010] [Component (A)] Examples of the resin (A) used in this embodiment include polyester resin, urethane resin, acrylic resin, epoxy resin, phenol resin, and alkyd resin. These may be used alone or in combination of two or more. Among these, phenol resin is 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, based on 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] [(B) Component] 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 carbonaceous filler that has been graphitized. Graphitization refers to a process in which the filler is heated to a high temperature, for example, around 3000°C, while being shielded from air. The average particle size of the component (B1) is preferably from 1 μm to 50 μm, and more preferably from 3 μm to 40 μm. 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 the (B1) component 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 combined total of the (B1) component and the (B2) component.

[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. Component (B3) includes carbon nanotubes. However, from the viewpoint of spray application properties, it is preferable that component (B) consists of only 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, based on 100% by mass of component (B). From the viewpoint of spray coating properties, it is preferable that the coating composition according to this embodiment 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] [(C) component] The solvent (C) used in this embodiment must contain at least one selected from the group consisting of propylene glycol monomethyl ether (C1) 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, based on 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. On the other hand, when the blending amount of component (C1) is equal to or less than the upper limit, the spray applicability can be further improved.

[0019] The component (C) preferably further contains (C2) a glycol solvent having a boiling point of at least 170° C. The component (C2) can improve leveling during spray application. Examples of the 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 total amount of the (C1) component and the (C2) component 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 the (C) component.

[0021] The amount of component (C) must be 30% by mass or more and 70% by mass or less, based on 100% by mass of the coating composition. If the 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 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, relative to 100% by mass of the coating composition.

[0022] [Other ingredients] 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 based on 100% by mass of the coating composition.

[0023] [Method of manufacturing a spray carbon paint composition] 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 carbon coating] 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 the coating target 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, first, the coating composition according to this embodiment is applied to an object to be coated, 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. By drying in this manner, the solvent and the like in the coating composition are evaporated, and a carbon coating film can be formed. The thickness of the carbon coating film (dry film thickness) is not particularly limited, but is usually from 5 μm to 200 μm, and preferably from 10 μm to 70 μm. [Example]

[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, product name "Phenolite 5010", manufactured by DIC Corporation ((B1) component) Graphite powder: Trade name "Graphite AT" (average particle size 5-25 μm), manufactured by Oriental Sangyo Co., Ltd. ((B2) component) Carbon black powder: Trade name "Printex" (average particle size 10-50 nm), manufactured by Degussa ((C1) component) Solvent A: Propylene glycol monomethyl ether (boiling point 120°C) Solvent B: Propylene glycol monomethyl ether acetate (boiling point 146°C) ((C2) component) 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 placed in a container and premixed using a stirrer, then mixed and dispersed at room temperature using a three-roll mill, after which 23 parts by mass of solvent A were added and mixed to obtain a coating composition.

[0029] [Examples 2 to 4] A coating composition was obtained in the same manner as in Example 1, except that the materials were mixed according to the composition shown in Table 1. [Comparative Examples 1 to 5] A coating composition was obtained in the same manner as in Example 1, except that the materials were mixed according to the composition shown in Table 1.

[0030] [Evaluation of coating composition] The coating compositions were evaluated (spray applicability (nozzle clogging, dripping, leveling, liquid pooling at bottom corners), and liquid properties) using the following methods. The results are shown in Table 1. (1) Spray application (nozzle clogging, dripping, leveling, liquid accumulation at the 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 resulting coating composition was placed in a spray device with a nozzle that could be inserted into the housing, and spray coating was carried out under conditions such that the thickness of the carbon coating film would be 20 μm. At this time, the presence or absence of nozzle clogging was observed, and the nozzle clogging was evaluated according to the following criteria. ○: No nozzle clogging occurs. ×: Nozzle clogging occurred, making normal spray application impossible. The surface of the carbon coating was also observed and evaluated for sagging according to the following criteria. ○: There is no sagging on the surface of the carbon coating. ×: Drooping occurred on the surface of the carbon coating film. The surface of the carbon coating was also observed, and the leveling ability was evaluated according to the following criteria. ◯: The surface of the carbon coating is smooth. ×: The surface of the carbon coating film is not smooth or has an orange peel appearance. The corners of the bottom surface were also observed for the presence or absence of liquid accumulation, and the liquid accumulation at the corners of the bottom surface was evaluated according to the following criteria. ○: No liquid pooling at the bottom corners. ×: Liquid pools were observed at the corners of the bottom surface. (2) Liquid properties The resulting coating composition was placed in a container and left to stand for 24 hours at a temperature of 25° C. The properties of the liquid were then evaluated according to the following criteria. ○: No precipitation occurs in the coating composition. ×: Precipitation occurred in the coating composition.

[0031] [Table 1]

[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. [Industrial Applicability]

[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 comprising (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 (C) component is 30% by mass or more and 70% by mass or less with respect to 100% by mass of the carbon coating composition. A carbon coating composition for spray application.

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

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

4. The carbon coating composition for spraying according to claim 1 or 2, 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). A carbon coating composition for spray application.

5. The spray carbon coating composition according to claim 1 or 2 is applied by spraying to form a carbon coating film. A method for forming a carbon coating.

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