Coating film and coated object

Abstract

 The purpose of the present invention is to provide a coating film having both an attractive metallic appearance and transparency to electromagnetic waves and a coated object including the coating film. A coating film (10) has a layered structure at least including a base coat layer (12) containing a plurality of aluminum flakes of an approximately flat shape which serve as a glitter material (12a). In the base coat layer (12), the areal proportion in which the aluminum flakes occupy is higher than 75% but not higher than 100%. The aluminum flakes have an average longitudinal-direction length (average major-axis length) of the flat plane of 9 μm or less. The coating film (10) has a film thickness greater than 2 μm but less than 9 μm.

Description

Technical Field

[0001] The present invention relates to a coating film having electromagnetic wave permeability such as millimeter waves and a coated article provided with the coating film.

Background Art

[0002] The vehicle body parts constituting a vehicle are painted with a metallic pigment containing, as a brightening agent, aluminum pieces having light reflectivity or the like in order to enhance the design.

[0003] In recent years, research and practical application of vehicle automated driving have been promoted by using radar devices that use microwaves, millimeter waves, etc. that can obtain high resolution. Since this type of radar device is installed on the back side of vehicle body parts (such as front bumpers and rear bumpers), the corresponding vehicle body parts need to keep the attenuation rate of electromagnetic waves low.

[0004] By the way, in order to enhance the design by giving a high contrast feeling of metallic with high design requirements, it is necessary to densely and parallelly spread aluminum as a brightening material on the vehicle body. However, since aluminum has the property that electromagnetic waves such as millimeter waves hardly penetrate, the electromagnetic wave permeability is reduced. On the other hand, in order to improve the electromagnetic wave permeability, the aluminum content in the metallic coating can be reduced or a brightening material other than aluminum can be used, but the contrast feeling is reduced and the design is reduced.

[0005] The following Patent Document 1 discloses a millimeter wave transmissive coating film in order to achieve both design and electromagnetic wave permeability which are the above-described problems.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, Patent Document 1 shows that when the area occupancy rate of aluminum flakes exceeds 75%, the electromagnetic wave transmittance deteriorates rapidly. That is, in the technology of Patent Document 1, the area occupancy rate of aluminum flakes cannot be increased to 75% or more in order to enhance the metallic design, and there is room for improvement. In addition, the technology of Patent Document 1 is mainly a coating technology for emblems. By forming a sea-island structure and an ultra-thin film (1 μm or less) of a brightening material (indium or aluminum), metallic feeling and radar transmittance are achieved simultaneously, but it cannot be adopted for vehicle parts such as bumpers from the viewpoint of quality.

[0008] Although it is conceivable to use a pigment with a low dielectric constant other than aluminum (such as glass or mica) as the brightening material, while the electromagnetic wave transmittance is solved, a decrease in design cannot be avoided.

[0009] As described above, in metallic coating, it is not easy to achieve both metallic design and electromagnetic wave transmittance, which are in a contradictory relationship, and achieving both of these performances has become an important issue in realizing the next-generation metallic coating.

[0010] At least one embodiment of the present invention has been made in view of the above circumstances. Specifically, it is to provide a coating film that achieves both metallic design and electromagnetic wave transmittance, and a coated object provided with the coating film.

Means for Solving the Problems

[0011] The coating film according to this embodiment is a coating film having a laminated structure including at least a base coat layer containing a plurality of substantially flat aluminum flakes. The area occupancy rate of the aluminum flakes exceeds 75% and is 100% or less. The average length in the longitudinal direction on the flat surface of the aluminum flakes is 9 μm or less, and the film thickness of the coating film exceeds 2 μm and is less than 9 μm.

[0012] The coated object according to this embodiment includes the coating film and a base material made of a resin material on whose outer surface the coating film is formed.

Advantages of the Invention

[0013] According to at least one embodiment of the present invention, it is possible to provide a novel coating film and a coated object that achieve both metallic design and electromagnetic wave permeability.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0015] Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings. The embodiments shown here are examples for embodying the technical idea of the present invention and do not limit the present invention. Further, all other possible forms, examples, and operation techniques that can be conceived by those skilled in the art without departing from the gist of the present invention are included in the scope and gist of the present invention, and are included in the invention described in the claims and its equivalent scope.

[0016] Furthermore, the drawings attached to this specification may be schematically represented with appropriate changes in scale, vertical and horizontal dimension ratios, shape, etc. for the sake of illustration and easy understanding, but this is merely an example and does not limit the interpretation of the present invention.

[0017] As shown in FIG. 1, the coated object 1 according to this embodiment is composed of a coating film 10 and a base material 20 which is an object to be coated on whose outer surface the coating film 10 is formed.

[0018] 〈Coating Film〉 The coating film 10 has a laminated structure including at least a primer layer 11, a base coat layer 12, and a top coat layer 13. The coating film 10 is formed by applying the primer layer 11, the base coat layer 12, and the top coat layer 13 one or more times respectively. In order to achieve electromagnetic wave permeability, it is preferable that the layer containing metal is only the base coat layer 12 for the coating film 10.

[0019] The coating film 10 is not limited to the laminated structure shown in FIG. 1 and may be appropriately changed according to the use of the component. That is, the coating film 10 may include other functional layers in addition to the primer layer 11, the base coat layer 12, and the top coat layer 13.

[0020] The primer layer 11 is formed on the outer surface (coating surface) of the base material 20. The primer layer 11 is a layer for improving the adhesion between the base coat layer 12 and the base material 20. As the material of the primer layer 11, for example, a known resin paint for primer can be adopted. As the resin paint, for example, resinous paints such as modified polyolefin resin, polyester resin, urethane resin, epoxy resin, melamine resin, alkyd resin, phenol resin, and acrylic resin can be adopted. The primer layer 11 may appropriately contain known additives in addition to the resin material.

[0021] The base coat layer 12 is formed on the outer surface (coating surface) of the primer layer 11. The base coat layer 12 is composed of a resin material, a solvent, and a pigment (brightening material). In addition to these materials, the base coat layer 12 may contain, if necessary, for example, organic pigments, inorganic pigments, materials other than aluminum flakes 12a that function as brightening materials (such as mica and glass), ultraviolet absorbers, radical trap agents, etc.

[0022] As the resin material of the base coat layer 12, known resin materials generally used in the paint field can be applied. As the resin material, for example, polyester resin, urethane resin, epoxy resin, melamine resin, alkyd resin, phenol resin, acrylic resin, etc. can be adopted.

[0023] As the solvent, known organic solvents or aqueous solvents (such as water) generally used in the paint field can be applied. Examples of the organic solvents include hydrocarbons such as toluene and xylene, ketones such as acetone, methyl ketone, and methyl ethyl ketone, esters such as ethyl acetate and butyl acetate, and alcohols.

[0024] The pigment is composed of aluminum flakes 12a that function as a brightening material. The aluminum flakes 12a have a substantially flat shape that is non-spherical (including shapes such as flake-like, scaly, plate-like, and lamellar). Here, "flat" means a shape in which the major axis in the width direction orthogonal to the thickness direction of the flat portion (the length of the major axis of the equivalent circle of the "flat plane" where the projected area of the flat portion is the largest) is longer than the length in the thickness direction.

[0025] The base coat layer 12 is formed by mixing a pigment with a resin material and a solvent and then volatilizing the solvent during the drying process, resulting in volume shrinkage. As a result, the orientation of the aluminum flakes 12a is enhanced, and the flat plane of the aluminum flakes 12a can be arranged substantially parallel to the coating surface with respect to the surface of the base coat layer 12. Therefore, the coating film 10 has an increased specular reflectance of reflected light and interference light, and a higher luminance and contrast can be obtained.

[0026] The base coat layer 12 has an area occupancy rate of the aluminum flakes 12a exceeding 75% and being 100% or less, the average length in the longitudinal direction in the flat plane of the aluminum flakes 12a (hereinafter, also simply referred to as "average major axis") being 9 μm or less, and a film thickness exceeding 2 μm and less than 9 μm.

[0027] Here, when the area occupancy rate of the aluminum flakes 12a in the coating film 10 is 75% or less, the base is not concealed, so a contrast feeling cannot be obtained and the design property deteriorates. Further, when the average major axis of the aluminum flakes 12a in the coating film 10 exceeds 9 μm, the adjacent aluminum flakes 12a in the base coat layer 12 are likely to come into contact with each other. Since the contact points between the aluminum flakes 12a act as a dielectric, the dielectric constant increases and the electromagnetic wave permeability decreases. Furthermore, when the film thickness of the coating film 10 is 2 μm or less, the lower layer (primer layer 11 or base material 20) is seen through and the design property deteriorates, and when the film thickness is 9 μm or more, the orientation of the aluminum flakes 12a deteriorates and a contrast feeling cannot be obtained and the design property deteriorates.

[0028] On the other hand, in the coating film 10 according to the present embodiment, when the base coat layer 12 satisfies the above conditions, as shown in FIG. 1, the flat surfaces of the aluminum flakes 12a in the base coat layer 12 are substantially parallel to the coating surface, and the contact with other adjacent aluminum flakes 12a is suppressed so that a gap is formed therebetween. That is, when the base coat layer 12 satisfies the above conditions, the orientation of the aluminum flakes 12a can be controlled, and the metallic design property and the electromagnetic wave permeability can be made compatible. Therefore, the coating film 10 ensures the orientation of the aluminum flakes 12a necessary for obtaining a metallic contrast feeling and an appropriate film thickness, and the metallic design property is improved. Further, as shown in FIG. 1, the contact between the adjacent aluminum flakes 12a in the base coat layer 12 is reduced. Therefore, the coating film 10 has a low attenuation rate of electromagnetic waves and is excellent in electromagnetic wave permeability. As described above, the coating film 10 according to the present embodiment can achieve both metallic design property and electromagnetic wave permeability, which have been difficult in the prior art.

[0029] In the coating film 10 according to the present embodiment, from the viewpoint of improving the electromagnetic wave permeability and the metallic design property, the content ratio (P / B: pigment (aluminum flake) / resin material) of the pigment (aluminum flake 12a) with respect to the resin material in the layer is preferably 45% or less.

[0030] In the coating film 10, when the content ratio of the aluminum flakes 12a to the resin material in the base coat layer 12 exceeds 45%, the gap between adjacent aluminum flakes 12a in the base coat layer 12 becomes narrow and they are likely to come into contact with each other. The contact points between the aluminum flakes 12a act as a dielectric, resulting in an increase in the attenuation rate. However, in the coating film 10, when the content ratio of the aluminum flakes 12a to the resin material in the base coat layer 12 is 45% or less, an appropriate gap is ensured between adjacent aluminum flakes 12a in the base coat layer 12. Therefore, in the coating film 10, it becomes difficult for contact points to be formed between the aluminum flakes 12a, and an effect of improving the electromagnetic wave permeability while ensuring metallic design is obtained.

[0031] In the coating film 10 according to the present embodiment, from the viewpoint of improving the electromagnetic wave permeability and metallic design, the base coat layer 12 preferably has an area occupancy ratio of the aluminum flakes 12a of 99.5% or less, more preferably 77% or more and 89.9% or less.

[0032] In the coating film 10, by setting the area occupancy ratio of the aluminum flakes 12a to 99.5% or less, more preferably 77% or more and 89.9% or less, the orientation of the aluminum flakes 12a can be enhanced with a space between adjacent aluminum flakes 12a without creating poles at the contact points. Therefore, the coating film 10 can further enhance the contrast and improve the metallic design, and can also further improve the electromagnetic wave permeability. Note that as the area occupancy ratio of the aluminum flakes 12a decreases, the contact probability between adjacent aluminum flakes 12a decreases, so that the effect of improving the electromagnetic wave permeability is easily obtained.

[0033] In the coating film 10 according to the present embodiment, from the viewpoint of improving the electromagnetic wave permeability and metallic design, the film thickness may be 6 μm or less, preferably 4 μm or less.

[0034] The coating film 10 can improve the electromagnetic wave permeability while maintaining excellent metallic design properties by making the film thickness of the base coat layer 12 6 μm or less, preferably 4 μm or less, which further improves the orientation of the aluminum flakes 12a.

[0035] In the coating film 10 according to the present embodiment, from the viewpoint of improving the liquid feeling (denseness) without feeling the particle feeling of the pigment (aluminum flakes 12a), the average major axis of the aluminum flakes 12a is 8 μm or more and 9 μm or less. Further, from the viewpoint of achieving both metallic design properties and electromagnetic wave permeability, the average thickness of the aluminum flakes 12a is preferably 0.1 μm or more and 0.7 μm or less, and more preferably 0.1 μm or more and 0.5 μm or less. Also, from the viewpoint of suppressing the deformation of the pigment (aluminum flakes 12a) circulated (circulated) under pressure in the paint piping, the average thickness of the aluminum flakes 12a is preferably more than 0.2 μm. Further, from the viewpoint of further enhancing the effect of suppressing the deformation of the pigment by circulation, the average thickness of the aluminum flakes 12a is preferably 0.25 μm or more, more preferably 0.3 μm or more, still more preferably 0.35 μm or more, and even more preferably 0.4 μm or more.

[0036] When the average thickness of the aluminum flakes 12a is less than 0.1 μm, the rigidity of the aluminum flakes 12a becomes low and they are easily deformed, and the number of overlapping aluminum flakes 12a in the thickness direction of the base coat layer 12 increases, so the contact points between adjacent aluminum flakes 12a increase and the dielectric constant increases, and the electromagnetic wave permeability tends to decrease. Also, when the average thickness of the aluminum flakes 12a exceeds 0.7 μm, the movement of the aluminum flakes 12a is suppressed, so the high orientation due to volume shrinkage cannot be achieved in the process from coating to film formation, and the metallic design further deteriorates. Therefore, from the viewpoint of metallic design properties due to high aluminum orientation, the average thickness of the aluminum flakes 12a is preferably 0.5 μm or less.

[0037] The coating film 10 can improve the electromagnetic wave permeability while maintaining a dense appearance without feeling the graininess of the aluminum flakes 12a and excellent metallic design properties by setting the average major axis of the aluminum flakes 12a to 8 μm or more and 9 μm or less, and further setting the average thickness of the aluminum flakes 12a to 0.1 μm or more and 0.5 μm or less. Also, by adjusting the average thickness of the aluminum flakes 12a to exceed 0.2 μm, the deformation of the pigment during paint stirring can be effectively suppressed, the contact between adjacent aluminum flakes 12a can be suppressed to prevent an increase in the attenuation rate, and further improvement in the electromagnetic wave permeability can be achieved.

[0038] The top coat layer 13 is formed on the outer surface (coated surface) of the base coat layer 12. The top coat layer 13 is a layer for imparting weather resistance, glossiness, scratch resistance, and antifouling properties to the coated article 1. As the top coat layer 13, a conventionally known transparent (regardless of being colored or colorless) resin material having the above performances can be used. Also, for example, a fluororesin may be included in the top coat layer 13. Further, weathering agents, plasticizers, stabilizers, fillers, dispersants, dyes, pigments, solvents, etc. may be appropriately added to the top coat layer 13 as necessary.

[0039] 〈Base material〉 The base material 20 is made of a material that hardly affects the electromagnetic wave permeability and is excellent in impact resistance and weather resistance, and the coating film 10 is formed on its outer surface. As the constituent material of the base material 20, a synthetic resin material is suitable. For example, various synthetic resin materials such as thermoplastic resins including general-purpose plastics (polypropylene (PP), polyvinyl chloride (PVC), acrylic resin (PMMA), acrylonitrile-butadiene-styrene resin (ABS), etc.) and engineering plastics (polycarbonate (PC), etc.) can be mentioned. These synthetic resin materials can be appropriately selected according to the use of the coated article 1. Also, when a resin material is adopted for the base material 20, considering the influence on the electromagnetic wave permeability of the coating film 10 in the coated article 1, it is preferable to adopt a material that does not contain metal or has a metal content that does not adversely affect the electromagnetic wave permeability.

[0040] The method of forming (coating) the coating film 10 on the substrate 20 is not particularly limited, and known coating methods (for example, dipping method, spin coating method, flow coating method, roll coating method, spray coating method, blade coating method, and air knife coating method) can be mentioned. The coating film 10 can be appropriately selected and implemented according to the shape and use of the coated object 1, the composition of the coating film 10 and the substrate 20, etc. Also, the drying process of the coating film 10 can be appropriately selected and implemented, such as natural drying and forced drying.

[0041] In the present embodiment, the coated object 1 has a configuration in which the above-described coating film 10 is provided on the outer surface of the substrate 20. Since the coated object 1 is provided with the coating film 10, it is excellent in electromagnetic wave permeability in addition to metallic design properties. Therefore, the coated object 1 can be suitably used as a constituent material of a vehicle body part that requires metallic design properties and electromagnetic wave permeability, such as a bumper disposed at a position facing the transmission / reception unit 110 of the radar device 100 that transmits and receives electromagnetic waves of a predetermined wavelength such as millimeter waves. Note that the radar device 100 transmits electromagnetic waves (transmission wave W1) of a predetermined wavelength such as millimeter waves to a detection target object X (for example, a vehicle or an obstacle traveling around the own vehicle), and receives the reflected wave W2 to measure physical quantities (such as moving speed and object distance) related to the detection target object X.

[0042] FIG. 2 is a diagram schematically showing a part of a vehicle including a bumper and a radar device 100 which are coated objects 1 according to the present embodiment. As shown in FIG. 2, aluminum pieces 12a in the base coat layer 12 of the coating film 10 are suppressed from contacting other adjacent aluminum pieces 12a, and an appropriate gap is formed. A transmission wave W1, which is an electromagnetic wave transmitted from a transmission / reception unit 110 of the radar device 100, is transmitted toward a detection target X, passes through the base material 20, passes through the spaces between the aluminum pieces 12a, and reaches the detection target X. The transmission wave W1 that has reached the detection target X becomes a reflected wave W2 and returns to the radar device 100 again. At this time, the reflected wave W2 passes through the spaces between the aluminum pieces 12a of the base coat layer 12, passes through the base material 20, and reaches the transmission / reception unit 110 of the radar device 100. In this way, the bumper, which is the coated object 1, can minimize the attenuation amount of the electromagnetic waves (transmission wave W1, reflected wave W2) transmitted and received by the radar device 100 (attenuation rate of 3 dB or less for the normal functioning of the radar device 100). Further, since the bumper, which is the coated object 1, has the coating film 10, it is excellent not only in electromagnetic wave permeability but also in metallic design.

[0043] Note that the use of the coated object 1 is not particularly limited. For example, if it is a vehicle body part, in addition to the bumper described above, it can be applied to other vehicle body parts that require both metallic design and electromagnetic wave permeability. Further, since the coated object 1 has a coating film 10 that achieves both metallic design and electromagnetic wave permeability formed on the outer surface of the base material 20 made of a resin material, it can also be applied to other parts other than vehicle body parts that require metallic design and electromagnetic wave permeability, such as housing a device that transmits and receives electromagnetic waves or covering and protecting at least a part around the device.

[0044] [Operational Effects] As described above, the coating film 10 according to the present embodiment has a laminated structure including at least a base coat layer 12 containing a plurality of substantially flat aluminum pieces 12a, and is formed on the outer surface of the base material 20. In the base coat layer 12 of the coating film 10, the area occupancy rate of the aluminum pieces 12a exceeds 75% and is 100% or less, the average length (average major axis) in the longitudinal direction on the flat surface of the aluminum pieces 12a is 9 μm or less, and the film thickness exceeds 2 μm and is less than 9 μm.

[0045] With such a configuration, the flat surfaces of the aluminum pieces 12a in the base coat layer 12 are substantially parallel to the layer surface, and the orientation can be controlled so as to suppress the contact with other adjacent aluminum pieces and create a gap therebetween. Therefore, both metallic design and electromagnetic wave permeability can be achieved.

[0046] Further, in the coating film 10 according to the present embodiment, preferably, the content ratio of the aluminum pieces to the resin material in the base coat layer may be 45% or less.

[0047] With such a configuration, a gap between adjacent aluminum pieces 12a in the base coat layer 12 is appropriately ensured, making it difficult to form contacts between the aluminum pieces 12a. Therefore, the effect of improving the electromagnetic wave permeability while ensuring the metallic design can be obtained.

[0048] Further, in the coating film 10 according to the present embodiment, preferably, the area occupancy rate of the aluminum pieces may be 99.5% or less, more preferably 77% or more and 89.9% or less.

[0049] With such a configuration, the coating film 10 can further enhance the contrast and improve the metallic design, and can also enhance the orientation of the aluminum pieces 12a and improve the electromagnetic wave permeability.

[0050] Further, in the coating film 10 according to the present embodiment, preferably, the film thickness may be 4 μm or less.

[0051] By adopting such a configuration, the coating film 10 has the effect that the orientation of the aluminum pieces 12a is further improved, and while maintaining excellent metallic design properties, the electromagnetic wave permeability is improved.

[0052] Further, in the coating film 10 according to the present embodiment, preferably, the average length (average major axis) in the longitudinal direction on the flat surface of the aluminum pieces 12a is 8 μm or more and 9 μm or less, and the average thickness of the aluminum pieces 12a is 0.1 μm or more and 0.5 μm or less.

[0053] By adopting such a configuration, the coating film 10 has the effect that while maintaining a dense appearance without feeling the particle sense of the pigment (aluminum pieces 12a) and excellent metallic design properties, the electromagnetic wave permeability is improved.

[0054] Further, in the coating film 10 according to the present embodiment, preferably, the average thickness of the aluminum pieces 12a may exceed 0.2 μm.

[0055] With such a configuration, in the coating film 10, the deformation of the pigment during paint stirring is effectively suppressed, the contact between adjacent aluminum pieces 12a is suppressed to prevent an increase in the attenuation rate, and further improvement in electromagnetic wave permeability can be achieved.

[0056] Further, the coated object 1 according to the present embodiment includes the above-described coating film 10 and a base material 20 made of a resin material on the outer surface of which the coating film 10 is formed.

[0057] By adopting such a configuration, in the coated object 1, since the coating film 10 that achieves both metallic design properties and electromagnetic wave permeability is formed on the outer surface of the resin material, for example, it can be applied to components that require both metallic design properties and electromagnetic wave permeability, such as those that house devices for transmitting and receiving electromagnetic waves or cover and protect at least a part of the surroundings.

[0058] Further, the coated object 1 according to the present embodiment may be configured to be arranged opposite to the transmission and reception unit 110 of the electromagnetic wave W in the radar device 100 that transmits and receives the electromagnetic wave W and measures the physical quantity with the detection object in front.

[0059] With such a configuration, when the coated article 1 is adopted as a bumper attached to the front or rear of a vehicle, even if the radar device 100 is disposed on the back side of the bumper, since it has both metallic design properties and electromagnetic wave permeability, the design property of the vehicle can be improved without inhibiting the function of the radar device 100.

Example

[0060] Hereinafter, the present invention will be specifically described by way of examples, but the scope of the present invention is not limited to the following examples.

[0061] Examples and comparative examples of the coated article 1 provided with the coating film 10 according to the embodiment of the present invention will be described.

[0062] [Adjustment of paint] The adjustment methods of the paints to be coating films in Examples 1 to 7 and Comparative Examples 1 to 9 were adjusted as follows, respectively.

[0063] <Examples 1 to 7> The paints used in Examples 1 to 7 were obtained by uniformly mixing the following materials and sufficiently stirring them with a disperser. 〈Raw materials〉 · Resin material (Protouch Nigori Clear, solid content 23%: manufactured by Rock Paint Co., Ltd.) · Solvent (Protouch thinner: manufactured by Rock Paint Co., Ltd.) · Pigment A (GX-3109, solid content 74%: manufactured by Asahi Kasei Corporation) 〈Mixing ratio〉 · Example 1 Resin material: 28% by mass, Solvent: 70% by mass, Pigment A: 2% by mass · Example 2 Resin material: 28% by mass, Solvent: 70% by mass, Pigment A: 2% by mass · Example 3 Resin material: 28% by mass, Solvent: 70% by mass, Pigment A: 2% by mass · Example 4 Resin material: 28% by mass, Solvent: 70% by mass, Pigment A: 2% by mass · Example 5 Resin material: 28% by mass, Solvent: 70% by mass, Pigment A: 2% by mass · Example 6: Resin material: 25% by mass, solvent: 72% by mass, Pigment A: 3% by mass · Example 7: Resin material: 28% by mass, solvent: 70% by mass, Pigment A: 2% by mass <Comparative Examples 1 - 9> The paints used in Comparative Examples 1 - 9 were obtained by uniformly mixing the following materials and sufficiently stirring them with a disperser. 〈Raw materials〉 · Resin material (Protouch Nigori Clear, solid content 23%: manufactured by Rock Paint Co., Ltd.) · Solvent (Protouch Thinner: manufactured by Rock Paint Co., Ltd.) · Pigment A (GX - 3109, solid content 74%: manufactured by Asahi Kasei Corporation) · Pigment B (GX - 3160, solid content 74%: manufactured by Asahi Kasei Corporation) · Pigment C (EMRS - 910, solid content 10%: manufactured by Toyo Aluminum Co., Ltd.) · Pigment D (EMR - DZ460, solid content 60%: manufactured by Toyo Aluminum Co., Ltd.) 〈Mixing ratio〉 · Comparative Example 1: Resin material: 28% by mass, solvent: 70% by mass, Pigment A: 2% by mass · Comparative Example 2: Resin material: 25% by mass, solvent: 72% by mass, Pigment A: 3% by mass · Comparative Example 3: Resin material: 25% by mass, solvent: 72% by mass, Pigment A: 3% by mass · Comparative Example 4: Resin material: 96% by mass, solvent: 0% by mass, Pigment B: 4% by mass · Comparative Example 5: Resin material: 90% by mass, solvent: 4% by mass, Pigment B: 5% by mass · Comparative Example 6: Resin material: 87% by mass, solvent: 6% by mass, Pigment B: 7% by mass · Comparative Example 7: Resin material: 71% by mass, solvent: 0% by mass, Pigment C: 29% by mass · Comparative Example 8: Resin material: 84% by mass, solvent: 6% by mass, Pigment D: 10% by mass · Comparative Example 9: Resin material: 28% by mass, solvent: 70% by mass, Pigment A: 2% by mass

[0064] [Manufacture of samples] For each sample of Examples 1 to 7 and Comparative Examples 1 to 9, first, as a base material, a raw material obtained by mixing a polypropylene base material (MX01HX: manufactured by Sun Allomer Co., Ltd., blended with 2 wt% of TET0CA129: manufactured by Toyo Color Co., Ltd.) was injection-molded to produce a black propylene flat plate of 150 mm × 150 mm × 3 mm. For the coating film, a conductive primer (PLYMAC No.1501 (N6): manufactured by BASF Japan Ltd.) was spray-coated on the produced base material at a film thickness of 4 μm to 5 μm to form a primer layer. Then, the paint adjusted for each sample was spray-coated on the surface of the primer layer in a wet-on-wet manner to form a base coat layer with a predetermined film thickness. Further, a two-component clear (Multi Top Clear SF, Multi Top S hardener: both manufactured by Rock Paint Co., Ltd., mixed at a ratio of 2:1) was applied on the surface of the base coat layer in a wet-on-wet manner. After setting for 5 minutes, it was forced to dry at 60 °C for 35 minutes to obtain the product.

[0065] [Measurement Method] In the examples and comparative examples, the constituent dimensions, ratios, etc. were measured by the methods shown below. 〈Area Occupancy Ratio〉 The area occupancy ratio of the aluminum flakes was obtained by forming a base coat layer on a transparent polypropylene base material under the film thickness conditions set for each of the examples and comparative examples, forming a top coat layer on the base coat layer, baking at 85 °C for 20 minutes, photographing the sample through transmission at 500 times magnification with an optical microscope, and analyzing the obtained microscope photograph with image analysis software "Microstudio". · Optical microscope: LEICA DMLM · Camera: WRAYMER VEX120 · Image analysis software: Microstudio · Magnification: Camera 0.63×2 / 3, Objective 10× · Measurement part: Area without pigment (aluminum flakes) · Measurement method: Based on the RGB of the selected position, the area of the same color was extracted. When the entire void position was selected, counting was performed, and the ratio was calculated as (count number / total number of pixels) × 100. 〈Aluminum Major Axis〉 The major axis length of aluminum (average major axis length of aluminum flakes) was obtained by measuring the median diameter of the volume-based particle size distribution using a laser diffraction scattering method with a particle size distribution measuring device. 〈Thickness of the base coat layer and thickness of aluminum flakes〉 The thickness of the base coat layer and the thickness of the aluminum flakes were obtained by observing TEM photographs of cross-sections of the samples of the examples and comparative examples using a transmission electron microscope, respectively.

[0066] [Performance evaluation] The results of the performance evaluations of the examples and comparative examples are shown in Tables 1 and 2 below.

[0067]

Table 1

[0068]

Table 2

[0069] [Evaluation indicators] In the performance evaluations in Tables 1 and 2, the evaluation indicator for electromagnetic wave permeability was "attenuation rate (dB)", and the evaluation indicator for metallic designability was "luminance (FF value)".

[0070] 〈Attenuation rate (dB)〉 The attenuation rate was determined as follows. An electromagnetic wave absorption measurement device (transmission attenuation measurement jig with a dielectric lens, manufactured by Keycom Co., Ltd.) was used indoors (temperature: 26°C, humidity: 60%). An electromagnetic wave of 76.5 GHz was incident on each sample from the transmitter of a millimeter-wave module (WR12-VNAX, manufactured by Virginia Diodes, Inc.) at an incident angle of 0 degrees. The electromagnetic wave transmitted through the sample was received by the receiver of the millimeter-wave module facing the sample with the sample in between. After measuring the transmission attenuation amount with a network analyzer (N5222B, manufactured by Keysight Technologies, Inc.), the value was doubled to obtain the attenuation rate based on the transmission attenuation amount of the round-trip electromagnetic wave. For example, in a radar device mounted on a vehicle, if the attenuation rate is "3 dB or less", the radar device functions normally, and if it is "2 dB or less", more accurate measurement is possible. Also, if it is "3 dB or less", it is a value at which the radar device mounted on the vehicle can detect the rear of the vehicle, and if it is "2 dB or less", it is a value at which the front and sides of the vehicle can be detected. Based on the above, if the evaluation index of electromagnetic wave permeability is "3 dB or less", it can be evaluated that the product has sufficient performance as a product.

[0071] 〈Glossiness〉 The glossiness was measured using a metallicity measurement device (Alcope LMR-200, manufactured by Kansai Paint Co., Ltd.) to measure the FF (Flip Flop) value. The FF value quantifies the degree of change in the intensity of light due to the difference in the reflection angle with respect to the incident light from the light source in the painting of automobiles. A larger value indicates that the brightness of the highlight and shade is greater and the contrast is stronger. If it is "1.7 or more", it can be evaluated that the product has good metallic design.

[0072] [Results] As shown in Table 1, the samples of Examples 1 to 7 had an area occupancy rate of the aluminum flakes exceeding 75% and being 100% or less, the average major axis of the aluminum flakes being 9 μm or less, the film thickness of the base coat layer exceeding 2 μm and being less than 9 μm, and the attenuation rate and FF value meeting the passing criteria of the evaluation indicators. From these results, "setting the area occupancy rate of the aluminum flakes to exceed 75% and be 100% or less", "setting the average major axis of the aluminum flakes to 9 μm or less", and "setting the film thickness of the base coat layer to exceed 2 μm and be less than 9 μm" indicate that they are important factors for achieving both electromagnetic wave transparency and metallic design in the coating film and the coated article provided with the coating film.

[0073] On the other hand, in Example 6, P / B was 45% or less, and it was confirmed that the attenuation rate was lower than that of Example 7 (P / B: 56.2%) and it had excellent brilliance. From these results, "setting P / B to 45% or less" indicates that it is a factor for improving electromagnetic wave transparency and metallic design in the coating film 10 and the coated article 1 provided with the coating film.

[0074] Both Example 4 and Example 5 had an area occupancy rate of 99.5% or less, and it was confirmed that the attenuation rate was lower than that of Example 6 (area occupancy rate: 100%) and they had excellent brilliance. From these results, "setting the area occupancy rate to 99.5% or less" indicates that it is a factor for improving electromagnetic wave transparency and metallic design in the coating film 10 and the coated article 1 provided with the coating film.

[0075] Examples 1 to 3 had an area occupancy rate of 77% or more and 89.9% or less, and the film thickness was further 4 μm or less. It was confirmed that the attenuation rate was lower than that of Example 4 and they had excellent brilliance. From these results, "setting the area occupancy rate to 77% or more and 89.9% or less" and "setting the film thickness to 4 μm or less" indicate that they are factors for improving electromagnetic wave transparency and metallic design in the coating film 10 and the coated article 1 provided with the coating film.

[0076] In Examples 1 to 7, the average thickness of the aluminum flakes was 0.5 μm, and the attenuation rate and FF value met the acceptance criteria of the evaluation indicators. From these results, "the average thickness of the aluminum flakes is 0.1 μm or more and 0.5 μm or less" indicates that it is a factor for improving electromagnetic wave permeability while maintaining a dense and excellent metallic design without feeling the particle sensation of the pigment (aluminum flakes). Also, "the average thickness of the aluminum flakes exceeds 0.2 μm" indicates that it is a factor for effectively suppressing the deformation of the pigment during paint stirring and further improving electromagnetic wave permeability.

[0077] As shown in Table 2, in Comparative Example 1, the area occupancy rate was 70%, the film thickness was 1.8 μm, and it was confirmed that the attenuation rate met the standard, but the brilliance did not meet the standard. From these results, it is presumed that in Comparative Example 1, the film thickness was too thin to conceal the substrate, and the lower layer was transparent, resulting in a decrease in brilliance.

[0078] As shown in Table 2, in Comparative Example 2, the film thickness was 9.0 μm, and it was confirmed that the attenuation rate met the standard, but the brilliance did not meet the standard. From these results, it is presumed that in Comparative Example 2, the film thickness was too thick, the orientation of the aluminum flakes was disrupted, and the brilliance decreased.

[0079] As shown in Table 2, in Comparative Example 3, the film thickness was 10.0 μm, and it was confirmed that the attenuation rate and brilliance did not meet the standard. From these results, it is presumed that in Comparative Example 3, the film thickness was too thick, the attenuation rate deteriorated, and furthermore, the orientation of the aluminum flakes was disrupted, resulting in a decrease in brilliance.

[0080] As shown in Table 2, in Comparative Example 4, the average major axis was 15.0 μm, the film thickness was 18.5 μm, the average thickness of the aluminum flakes was 1.0 μm, and it was confirmed that the attenuation rate met the standard, but the brilliance did not meet the standard. From these results, it is presumed that in Comparative Example 4, the contact between adjacent aluminum flakes was suppressed due to the thick film thickness, but the film thickness was too thick, the orientation of the aluminum flakes was disrupted, and the brilliance decreased.

[0081] As shown in Table 2, in Comparative Example 5, the average major axis was 15.0 μm, the film thickness was 14.8 μm, the average thickness of the aluminum flakes was 1.0 μm, and it was confirmed that the attenuation rate met the standard, but the luster did not meet the standard. From this result, it is presumed that in Comparative Example 5, similar to Comparative Example 4, the contact between adjacent aluminum flakes was suppressed due to the thick film thickness, but the film thickness was too thick, resulting in the disorder of the orientation of the aluminum flakes and the decrease in luster.

[0082] As shown in Table 2, in Comparative Example 6, the average major axis was 15.0 μm, the film thickness was 14.6 μm, the average thickness of the aluminum flakes was 1.0 μm, and it was confirmed that the attenuation rate and the luster did not meet the standards. From this result, it is presumed that in Comparative Example 6, the film thickness was too thick, resulting in the disorder of the orientation of the aluminum flakes and the decrease in luster. Also, since the P / B in Comparative Example 6 was nearly twice as much as 25.5% compared to Comparative Example 4, the contact points between adjacent aluminum flakes with disordered orientation increased, resulting in an increase in the dielectric constant, and as a result, it is presumed that the attenuation rate deteriorated.

[0083] As shown in Table 2, in Comparative Example 7, the average major axis was 11.0 μm, the average thickness of the aluminum flakes was 0.03 μm, and it was confirmed that the luster met the standard, but the attenuation rate did not meet the standard. The paint circulates (circulates) under pressure in the paint piping to suppress the sedimentation of the pigment. In Comparative Example 7, since the average thickness of the aluminum flakes was 0.1 μm or less, the stability during circulation was poor (the aluminum flakes were easily deformed), and also, as the number of aluminum flakes per unit mass increased, the contact points between adjacent aluminum flakes after layer formation increased, resulting in an increase in the dielectric constant and a decrease in the electromagnetic wave permeability.

[0084] As shown in Table 2, in Comparative Example 8, the film thickness was 10.0 μm, the average thickness of the aluminum flakes was 0.14 μm, and the attenuation rate met the standard, but it was confirmed that the luster did not meet the standard. From this result, in Comparative Example 8, since the average thickness of the aluminum flakes was 0.1 μm or more, the electromagnetic wave permeability was ensured due to the effect of achieving both metallic design and electromagnetic wave permeability. However, it is presumed that the film thickness was too thick, the orientation of the aluminum flakes was disturbed, and the luster decreased.

[0085] As shown in Table 2, in Comparative Example 9, the film thickness was 15.0 μm, the attenuation rate met the standard, but it was confirmed that the luster did not meet the standard. From this result, in Comparative Example 9, since the average thickness of the aluminum flakes exceeded 0.2 μm, the electromagnetic wave permeability was superior to that of Comparative Example 8. However, similar to Comparative Example 8, it is presumed that the film thickness was too thick, the orientation of the aluminum flakes was disturbed, and the luster decreased.

Explanation of Signs

[0086] 1 Coated object, 10 Coating film, 11 Primer layer, 12 Base coat layer (12a Aluminum flakes), 13 Top coat layer, 20 Substrate, 100 Radar device, 110 Transmitting and receiving section, W1 Transmitted wave (electromagnetic wave), W2 Reflected wave (electromagnetic wave), X Detection object.

Claims

1. A coating film having a laminated structure including at least a base coat layer containing a plurality of substantially flat aluminum pieces, wherein in the base coat layer, the area occupancy rate of the aluminum pieces exceeds 75% and is 100% or less, and the average length in the longitudinal direction on the flat surface of the aluminum pieces is 9 μm or less, the film thickness exceeds 2 μm and is less than 9 μm, and the average thickness of the aluminum pieces exceeds 0.2 μm.

2. The coating film according to claim 1, wherein the content ratio of the aluminum pieces to the resin material in the base coat layer is 45% or less.

3. The coating film according to claim 1 or 2, wherein the area occupancy rate of the aluminum pieces is 99.5% or less.

4. The coating film according to any one of claims 1 to 3, wherein the area occupancy rate of the aluminum pieces is 77% or more and 89.9% or less.

5. The coating film according to any one of claims 1 to 4, wherein the film thickness is 4 μm or less.

6. The coating film according to any one of claims 1 to 5, wherein the average length in the longitudinal direction on the flat surface of the aluminum pieces is 8 μm or more and 9 μm or less, and the average thickness of the aluminum pieces is 0.7 μm or less.

7. A coated article comprising the coating film according to any one of claims 1 to 6, and a base material made of a resin material having the coating film formed on an outer surface thereof.

8. The coated article according to claim 7, wherein the base material is arranged to face the electromagnetic wave transmitting and receiving part in a radar device that transmits and receives electromagnetic waves and measures a physical quantity with a detection object in front.

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