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

Abstract

A carbon coating composition for spraying is a carbon coating composition containing (A) resin, (B) carbon filler and (C) solvent, wherein the (B) component contains (B1) graphite and (B2) carbon black, and the (C) component contains at least one selected from (C1) propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate, wherein the amount of the (C) component relative to 100% by mass of the carbon coating composition is 30% by mass or more and 70% by mass or less.

Description

Technical Field

[0001] This invention relates to a carbon coating composition for spraying and a method for forming a carbon coating film. Background Technology

[0002] Electromagnetic wave shielding materials typically use metal plates or sheets. For example, in current sensors, components made of stainless steel sheets through sheet metal processing or bending are often placed on the bottom surface of the component housing. If the electromagnetic wave shielding layer is placed not only on the bottom surface but also on the sides, the noise reduction effect is even greater. However, it is difficult to bend metal to follow the shape of the component.

[0003] Therefore, for example, Patent Document 1 proposes to use a carbon coating composition (carbon paste, etc.) to provide an electromagnetic wave shielding layer inside the component housing.

[0004] Carbon paste is typically applied using methods such as screen printing or brushing. However, screen printing is difficult to apply to non-planar surfaces like component housings. Furthermore, brushing often results in uneven application, making it difficult to achieve a uniform coating. Therefore, a technique for applying carbon coating compositions via spraying is required.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2023-179994 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, when attempting to apply conventional carbon coating compositions used in methods such as screen printing via spraying, problems arise due to excessive viscosity, preventing proper coating. On the other hand, increasing the amount of solvent can be considered to adjust the viscosity to an appropriate range. However, excessive solvent can cause sagging after spraying. Furthermore, excessive solvent can lead to the precipitation of carbon fillers during storage in the coating container. Additionally, there is a problem of the carbon coating composition clogging the spray nozzle.

[0010] Thus, when applying carbon coating compositions by spraying, it is very difficult to adequately suppress sagging while ensuring sufficient coatability.

[0011] The object of the present invention is to provide a carbon coating composition for spraying that has sufficient coatability and can effectively suppress sagging when applied by spraying, and a method for forming a carbon coating film.

[0012] Problem Solving Methods

[0013] According to the present invention, a carbon coating composition for spraying and a method for forming a carbon coating film as shown below can be provided.

[0014] [1] A carbon coating composition for spraying, comprising (A) a resin, (B) a carbon filler, and (C) a solvent.

[0015] Component (B) contains graphite (B1) and carbon black (B2).

[0016] The (C) component contains at least one selected from (C1) propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate.

[0017] The amount of component (C) is 30% to 70% by mass relative to 100% by mass of the carbon coating composition.

[0018] [2] According to the carbon coating composition for spraying described in [1], wherein,

[0019] Component (A) contains phenolic resin.

[0020] [3] The carbon coating composition for spraying according to [1] or [2], wherein,

[0021] The (C) component further contains (C2) a diol solvent with a boiling point of 170°C or higher.

[0022] [4] The carbon coating composition for spraying according to any one of [1] to [3], wherein,

[0023] The amount of component (C1) is 30% or more and 80% or less relative to 100% by mass of component (C).

[0024] [5] A method for forming a carbon coating film, the method comprising:

[0025] A carbon coating film is formed by applying the carbon coating composition for spraying as described in any one of [1] to [4] by spraying.

[0026] According to one aspect of the present invention, a carbon coating composition for spraying that has sufficient coatability and can sufficiently suppress sagging when applied by spraying, and a method for forming a carbon coating film, can be provided. Detailed Implementation

[0027] [Carbon coating composition for spraying]

[0028] First, the carbon coating composition for spraying (hereinafter, as may be referred to as "coating composition") of the embodiment will be described.

[0029] The coating composition of the embodiments contains (A) resin, (B) carbon filler, and (C) solvent as described below.

[0030] [(A)Component]

[0031] Examples of resins used in embodiment (A) include polyester resins, urethane resins, acrylic resins, epoxy resins, phenolic resins, and alkyd resins. These can be used individually or in combination. From the viewpoint of carbon coating performance, phenolic resin is preferred.

[0032] The amount of component (A) relative to 100% by mass of the coating composition is preferably 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 25% by mass or less. When the amount of component (A) is at or above the lower limit mentioned above, the smoothness of the carbon coating film can be further improved. In addition, when the amount of component (A) is at or below the upper limit mentioned above, the spray coating properties can be further improved.

[0033] [(B) Component]

[0034] The carbon filler (B) used in this embodiment needs to contain both (B1) graphite and (B2) carbon black. If the coating composition does not contain component (B1), nozzle clogging will occur 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.

[0035] (B1) is a carbon filler that has undergone graphitization treatment. Graphitization treatment refers to a process in which the material is heated at a high temperature of around 3000°C in an air-isolated environment.

[0036] The average particle size of component (B1) is preferably 1 μm or more and 50 μm or less, more preferably 3 μm or more and 40 μm or less.

[0037] (B2) is composed of carbon black powder.

[0038] The average particle size of component (B2) is preferably 10 nm or more and 1000 nm or less, more preferably 15 nm or more and 100 nm or less.

[0039] From the viewpoint of spray coating properties, the amount of component (B1) is preferably 40% or more and 74% or less, more preferably 50% or more and 72% or less, and particularly preferably 60% or more and 70% or less, relative to 100% by mass of the total components (B1) and (B2).

[0040] (B) may contain carbon fillers other than (B1) and (B2) (hereinafter also referred to as (B3) component) within the range that enables the effects of the present invention. Examples of (B3) component include carbon nanotubes, etc.

[0041] From the viewpoint of spray coating properties, component (B) is preferably composed only of components (B1) and (B2). Furthermore, the total amount of components (B1) and (B2) relative to 100% by mass of component (B) is preferably 75% by mass or more, more preferably 85% by mass or more, and particularly preferably 95% by mass or more.

[0042] It should be noted that, from the viewpoint of spray coating properties, the coating composition of the embodiment preferably does not contain conductive particles other than component (B).

[0043] From the viewpoint of the performance of the carbon coating, the amount of component (B) relative to 100% by mass of the coating composition 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.

[0044] [(C) Component]

[0045] The solvent (C) used in this embodiment needs to contain at least one selected from (C1) propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate. When the coating composition does not contain the (C1) component, sagging cannot be suppressed when the coating composition is applied by spraying.

[0046] The amount of component (C1) relative to 100% by mass of component (C) 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. When the amount of component (C1) is at or above the lower limit mentioned above, the smoothness of the carbon coating film can be further improved. In addition, when the amount of component (C1) is at or below the upper limit mentioned above, the spray coating properties can be further improved.

[0047] Component (C) preferably further contains a diol solvent (C2) with a boiling point of 170°C or higher. Component (C2) can improve the leveling properties during spray coating.

[0048] Examples of (C2) components include butyl carbitol 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 can be used individually or in combination.

[0049] The amount of component (C2) relative to 100% by mass of component (C) 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.

[0050] Within the scope of achieving the effects of this invention, component (C) may contain solvents other than components (C1) and (C2) (hereinafter also referred to as component (C3)). 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.

[0051] From the viewpoint of spray coating properties, the total amount of (C1) and (C2) components relative to 100% by mass of component (C) is preferably 75% by mass or more, more preferably 85% by mass or more, and particularly preferably 95% by mass or more.

[0052] The amount of component (C) relative to 100% by mass of the coating composition needs to be between 30% by mass and 70% by mass. If the amount of component (C) is less than 30% by mass, the viscosity is too high, and therefore proper coating by spraying is not possible. On the other hand, if the amount of component (C) exceeds 70% by mass, carbonaceous filler will precipitate during storage in the coating container after spraying.

[0053] From the same point of view, the amount of component (C) relative to 100% by mass of the coating composition is preferably 40% by mass or more and 65% by mass or less, more preferably 50% by mass or more and 62% by mass or less.

[0054] [Other ingredients]

[0055] In addition to components (A), (B), and (C), other additives may be added to the flux composition used in the embodiments as needed. Examples of other additives include: thixotropic agents, defoamers, modifiers, curing catalysts, extender pigments, flame retardants, matting agents, and foaming agents. The amount of these additives in the formulation is preferably 0.01% by mass or more and 5% by mass or less relative to 100% by mass of the coating composition.

[0056] [Method for manufacturing carbon coating composition for spraying]

[0057] The method for manufacturing the coating composition of this embodiment is not limited to a specific method. For example, the above-mentioned components can be combined in a given ratio and then mixed or blended at room temperature using a mixing apparatus such as a three-roll mill, ball mill, or sand mill, or a stirring apparatus such as a high-speed mixer or planetary mixer. Furthermore, pre-mixing or blending can be performed as needed before mixing or blending. Additionally, solvent can be added appropriately after mixing or blending.

[0058] [Methods for forming carbon coatings]

[0059] Next, the method for forming the carbon coating film according to the embodiment will be described.

[0060] The carbon coating film formation method of this embodiment is a method of forming a carbon coating film by spraying the coating composition of this embodiment described above.

[0061] Examples of coating targets include component housings of electronic devices. When the coating composition of the embodiment is applied by spraying, a uniform carbon coating film can be formed without uneven coating, even for component housings with complex shapes.

[0062] Specifically, first, the coating composition of the embodiment is applied to the object to be coated, and then dried to form a carbon coating film.

[0063] The drying conditions vary depending on the type of coating composition and are not particularly limited. For example, heating can be carried out at a temperature ranging from 60°C to 80°C for a period of 15 minutes to 60 minutes. Through such drying, solvents and other components in the coating composition can evaporate to form a carbon coating film.

[0064] The thickness of the carbon coating (DRY film thickness) is not particularly limited, but is usually 5 μm or more and 200 μm or less, preferably 10 μm or more and 70 μm or less.

[0065] Example

[0066] The present invention will now be described in further detail through examples and comparative examples, but the present invention is not limited to these examples in any way.

[0067] ((A) ingredient)

[0068] Resin: Form-A phenolic resin, trade name "PHENOLITE 5010", manufactured by DIC Corporation.

[0069] ((B1) component)

[0070] Graphite powder: Trade name "Graphite AT" (average particle size 5~25μm), manufactured by Orient Sangyo.

[0071] ((B2) component)

[0072] Carbon black powder: Trade name "Printex" (average particle size 10~50nm), manufactured by Degussa.

[0073] (C1 component)

[0074] Solvent A: Propylene glycol monomethyl ether (boiling point 120℃)

[0075] Solvent B: Propylene glycol monomethyl ether acetate (boiling point 146℃)

[0076] (C2 component)

[0077] Solvent C: Butyl cellosolve acetate (boiling point 191℃)

[0078] Solvent D: Ethyl carbitol (boiling point 202℃)

[0079] [Example 1]

[0080] 24 parts by weight of resin, 18 parts by weight of graphite powder, 8 parts by weight of carbon black powder, 16 parts by weight of solvent C and 11 parts by weight of solvent D were put into a container and premixed with a mixer. Then, they were mixed at room temperature using a three-roll mill to disperse them. Finally, 23 parts by weight of solvent A were added and mixed to obtain the coating composition.

[0081] [Examples 2-4]

[0082] The materials were formulated according to the composition shown in Table 1, and otherwise, the coating composition was obtained in the same manner as in Example 1.

[0083] [Comparative Examples 1-5]

[0084] The materials were formulated according to the composition shown in Table 1, and otherwise, the coating composition was obtained in the same manner as in Example 1.

[0085] [Evaluation of Coating Compositions]

[0086] The coating compositions were evaluated using the methods described below (spray application properties (nozzle clogging, sagging, leveling, liquid accumulation at bottom corners), liquid properties). The results are shown in Table 1.

[0087] (1) Spray coating properties (nozzle clogging, sagging, leveling, liquid accumulation at bottom corners)

[0088] For the test piece used as the coating target, a shell (internal size: 4cm × 3cm, internal depth: 1.5cm) was prepared. The obtained coating composition was fed into a spraying device with a nozzle that could be inserted into the shell, and spraying was performed to achieve a carbon coating thickness of 20μm.

[0089] Observe whether nozzle clogging occurs at this time, and evaluate nozzle clogging according to the following criteria.

[0090] A: No nozzle blockage occurred.

[0091] C: Nozzle blockage has occurred, preventing normal spraying and coating.

[0092] In addition, the surface of the carbon coating was observed, and the sag was evaluated according to the following criteria.

[0093] A: The carbon coating has no dripping or sagging on its surface.

[0094] C: Sagging occurred on the surface of the carbon coating.

[0095] In addition, the surface of the carbon coating was observed, and the leveling properties were evaluated according to the following criteria.

[0096] A: The surface of the carbon coating is smooth.

[0097] C: The surface of the carbon coating is not smooth, or it has an orange peel-like texture.

[0098] In addition, observe whether there is fluid accumulation at the bottom corners, and evaluate the fluid accumulation at the bottom corners according to the following criteria.

[0099] A: There is no liquid accumulation at the bottom corner.

[0100] C: There is fluid accumulation at the corner of the bottom surface.

[0101] (2) Liquid properties

[0102] The obtained coating composition was placed in a container and left at 25°C for 24 hours. Then, the liquid properties were evaluated according to the following criteria.

[0103] A: No precipitation occurred in the coating composition.

[0104] C: Precipitation occurred in the coating composition.

[0105]

[0106] As can be clearly seen from the results shown in Table 1, when using the carbon coating composition for spraying according to the present invention (Examples 1-4), all results regarding nozzle clogging, sagging, leveling, liquid accumulation at the bottom corner, and liquid properties are excellent. Therefore, it is confirmed that, according to the present invention, a carbon coating composition for spraying that has sufficient coatability when applied by spraying and can adequately suppress sagging can be obtained.

[0107] Industrial applicability

[0108] The carbon coating composition for spraying of the present invention can be suitably used as a technique for forming an electromagnetic wave shielding layer in the housing components of electronic devices such as current sensors.

Claims

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

2. The carbon coating composition for spraying according to claim 1, wherein, Component (A) contains phenolic resin.

3. The carbon coating composition for spraying according to claim 1 or 2, wherein, The (C) component further contains (C2) a diol solvent with a boiling point of 170°C or higher.

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

5. A method for forming a carbon coating film, the method comprising: A carbon coating film is formed by applying the carbon coating composition for spraying as described in claim 1 or 2 by spraying.

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