Electronic device housing, method for manufacturing same, and antireflection film

Abstract

The present invention provides a technology which is effective for improving designability and scratch resistance of an antireflection film that is formed on an electronic device housing. According to the present invention, A component is a biner resin, A1 component is a polyvinyl acetal resin, B component is a black material, and B1 component is a composite of a black pigment and a resin. This electronic device housing has an antireflection film on a housing main body. The antireflection film is formed of a resin composition, and contains at least the A component and the B component. The A component includes the A1 component. The B component includes the B1 component that has an average particle diameter of 2 μm to 6 μm inclusive. The mass ratio of the B component to the A component is 7 to 14 inclusive.

Description

Electronic device housing, manufacturing method thereof, and anti-reflection film

[0001] The present invention relates to an electronic device housing, a manufacturing method thereof, and an anti-reflection film.

[0002] Electronic devices such as smartphones, tablets, and personal computers are sometimes coated with a black anti-reflective coating on part or all of their housings for the purposes of improving design, concealing internal wiring, blocking light, and preventing reflections.

[0003] For example, Patent Document 1 discloses a technology for forming a black film on the housing of a portable electronic device such as a smartphone by directly screen printing an insulating material onto the housing, or by in-mold molding a screen-printed film-forming film.

[0004] Japanese Patent Application Laid-Open No. 2007-285093

[0005] However, in recent years, with the demand for improved design of industrial products, there has been a growing demand for coating such products with films that have a more striking black color and a more stylish design.In addition, there is also a demand for ensuring scratch resistance during film production (film formation) and handling.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a technique that is effective in improving the design and scratch resistance of an anti-reflection film formed on the housing of an electronic device.

[0007] After extensive research, the present inventors have found that an anti-reflection film formed on the housing of an electronic device is effective in improving design and scratch resistance by satisfying the following requirements: The film is formed from a resin composition in which a binder resin (element a) containing a specific resin (polyvinyl acetal resin) is mixed with a black material (element b) containing a specific compound (composite of black pigment and resin) having a particle size within a specific range at a specific mass ratio (7 to 14 parts by mass of element a per 1 part a).

[0008] Although the mechanism of action that manifests the above phenomenon is unclear, the inclusion of a specific resin in the a component can impart flexibility and toughness to the resulting film. In addition, because the specific resin itself is crosslinkable, even a small amount of the a component can result in a film with high film strength. This reflective effect allows for an increased relative amount of the b component in the resulting film. By incorporating a specific composite into the b component and incorporating a large amount of the b component into the film, the resulting film exhibits lower gloss compared to films formed from conventional resin compositions (hereinafter also referred to as "conventional films"). In addition, the resulting film exhibits even lower ultra-low reflectivity, ultra-low L values, and high light-blocking properties compared to conventional films. As a result, we believe that a film with excellent designability and excellent scratch resistance can be obtained.

[0009] Based on these new findings, the present inventors have completed the invention provided below and solved the above-mentioned problems. In the following, the binder resin will be referred to as component A, the polyvinyl acetal resin (specific resin) as component A1, the black material as component B, the composite of the black pigment and the resin (specific composite) as component B1, and the dilution solvent as component C.

[0010] One aspect of the present invention is an electronic device housing having an anti-reflection film on a housing body.

[0011] The anti-reflection film of the housing is formed from a resin composition and contains at least an A component and a B component, the A component contains an A1 component, the B component contains a B1 component having an average particle diameter of 2 μm or more and 6 μm or less, and the mass ratio of the B component to the A component is 7 or more and 14 or less.

[0012] Another aspect of the present invention is an anti-reflection film formed on a housing of an electronic device, the anti-reflection film being formed from a resin composition and containing at least an A component and a B component, the A component containing an A1 component, the B component containing a B1 component having an average particle size of 2 μm or more and 6 μm or less, and the mass ratio of the B component to the A component being 7 or more and 14 or less.

[0013] Another aspect of the present invention is a method for manufacturing the above-mentioned electronic device casing, comprising: placing a resin composition containing at least component A, component B, and component C on a casing body; and removing component C by drying to form an anti-reflection film containing at least component A and component B.

[0014] The resin composition used in the method for manufacturing an electronic device casing described above contains at least component A, component B, and component C, and in addition, component A contains component A1, component B contains component B1 having an average particle size of 2 μm or more and 6 μm or less, the mass ratio of component B to component A is 7 or more and 14 or less, and the viscosity at 25°C measured with a Brookfield type viscometer is adjusted to 1 mPa·s or more and 2000 mPa·s or less.

[0015] The electronic device casing may include the following aspects. The glossiness of the outermost surface of the surface on which the film is formed with respect to light incident at an angle of 60° (hereinafter simply referred to as "60° glossiness") may be less than 1%. The glossiness of the outermost surface of the surface on which the film is formed with respect to light incident at an angle of 85° (hereinafter simply referred to as "85° glossiness") may be less than 10%. The reflectance of the outermost surface of the surface on which the film is formed with respect to light with a wavelength of 550 nm (hereinafter simply referred to as "reflectance") may be less than 1.5%. The L value of the outermost surface of the surface on which the film is formed in the CIELAB color system according to the SCE system may be less than 15. The optical density of the outermost surface of the surface on which the film is formed may be 2 or greater.

[0016] The above-described method for manufacturing an electronic device casing may include the following aspects. The resin composition may be applied to the casing body by a spray coating method. In this case, it is preferable to adjust the viscosity of the resin composition to 1 mPa·s or more and 50 mPa·s or less. The resin composition may be applied to the casing body by a dip coating method. In this case, it is preferable to adjust the viscosity of the resin composition to 20 mPa·s or more and 500 mPa·s or less. The resin composition may be applied to the casing body by a dispenser method. In this case, it is preferable to adjust the viscosity of the resin composition to 10 mPa·s or more and 300 mPa·s or less. The resin composition may be applied to the casing body by a method using a paintbrush or brush (brush coating method). In this case, it is preferable to adjust the viscosity of the resin composition to 100 mPa·s or more and 2000 mPa·s or less.

[0017] The above-described electronic device casing, anti-reflection film, and method for manufacturing an electronic device casing may include the following aspects. The content of component A1 in the total amount of component A may be 90 mass% or more. The content of component B1 in the total amount of component B may be 90 mass% or more. The component B1 may contain acrylic resin particles encapsulating carbon black. The anti-reflection film may have a thickness in the range of 2 μm or more and 40 μm or less.

[0018] According to the present invention, it is possible to provide a technique that is effective in improving the design and scratch resistance of an anti-reflection film formed on the housing of an electronic device.

[0019] The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiments. Appropriate modifications and improvements to the following embodiments based on the ordinary knowledge of those skilled in the art are also within the scope of the present invention, as long as they do not deviate from the spirit of the present invention.

[0020] In the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In this specification, the content or amount of each component in a composition means the total content or amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. In this specification, gloss and reflectance evaluate anti-reflection properties, and optical density evaluates light-blocking properties. Design is comprehensively evaluated based on the above evaluations. In this specification, improving design means suppressing light reflection and incidence while achieving high blackness.

[0021] (Explanation of Terms) In this specification, the exterior components of an electronic device are referred to as a "housing." This "housing" may be a single unit or may consist of multiple components, such as a case and a lid, and its shape is not limited. It also includes components attached to the housing body, such as a memory card cover. Examples of electronic devices include electronic devices with a display or input screen, electronic devices equipped with an optical system, etc. Examples of electronic devices with a display or input screen include, but are not limited to, televisions, personal computers, mobile devices (e.g., smartphones, tablets, slate PCs, etc.), digital cameras, digital video cameras, and photo frames. Examples of electronic devices equipped with an optical system include, but are not limited to, digital cameras, digital video cameras, etc.

[0022] 1. <Anti-Reflection Film> The housing of an electronic device according to one embodiment of the present invention has an anti-reflection film on part or all of the outer surface (hereinafter simply referred to as the "outer surface") of the housing body. The "outer surface" includes a case in which the anti-reflection film is formed directly on the outer surface of the housing body of the electronic device housing, as well as a case in which an optional layer (e.g., a primer layer) is interposed between the outer surface of the housing body and the anti-reflection film. The "part or all" includes a case in which the anti-reflection film is formed on part of the outer surface of the housing body. In this case, the outer surface of the housing body itself is exposed on the outer surface of the housing body. The anti-reflection film is formed from a resin composition of a predetermined composition.

[0023] 2. <Resin Composition> A resin composition according to one embodiment of the present invention (hereinafter also referred to as "the composition") is used to form a film on the outer surface of the housing body (hereinafter also referred to as "substrate") of an electronic device housing according to one embodiment of the present invention. The composition comprises a film-forming component (solid content) and a volatile component. The film-forming component refers to the components remaining after excluding the volatile components from all components constituting the composition, and is the component that will ultimately form the anti-reflective film. In this specification, the components remaining when the resin composition is dried at 120°C for 3 minutes are considered to be the film-forming component.

[0024] The film-forming components include a binder resin (component A) and a black material (component B), and the volatile components include a diluent solvent (component C). Component A includes a polyvinyl acetal resin (component A1). Component B includes a composite of a black pigment and a resin (component B1) having a predetermined particle size range. A film formed from this composition containing the above components A, B, and C exhibits lower gloss (60° gloss less than 1%, 85° gloss less than 10%) than conventional films, and also exhibits ultra-low reflectance (less than 1.5%) and ultra-low L value (less than 15), which are lower than conventional films, while also exhibiting high film strength. Although the reason for this is unclear, by including component A1, which is tough, flexible, and self-crosslinkable, in component A, the film formed exhibits high film strength even when a small amount of component A is added. The reflective effect of this (a small amount is sufficient) allows for an increase in the relative amount of B component, including B1 component, in the film formed. By including B1 component in B component and incorporating a large amount of B component in the film, the film formed has a lower gloss than conventional films, and in addition, it exhibits ultra-low reflectivity, ultra-low L value, and high light-blocking properties that are lower than conventional films. As a result, the film formed is thought to exhibit high designability and excellent scratch resistance.

[0025] 2-1. <Binder Resin (Component A)> Component A included in the present composition is a fixing agent for the coating surface and also a binder for Component B. Component A contains a thermoplastic resin. Examples of thermoplastic resins include polyacrylic ester resin, polyvinyl chloride resin, polyvinyl acetal resin, and styrene-butadiene copolymer resin. Among these, it is preferable to contain a polyvinyl acetal resin (Component A1) from the viewpoints of achieving low gloss, ultra-low reflectance, and ultra-low L value on the formed film surface, as well as film strength. One type of thermoplastic resin may be used alone, or two or more types may be used in combination.

[0026] By including Component A1 in the thermoplastic resin contained in Component A, flexibility and toughness can be imparted to the film formed. In addition, because it is crosslinkable itself, high film strength (scratch resistance) can be achieved even with a small amount of Component A1 in the composition (and therefore in the film).

[0027] 2-1-1. <Polyvinyl acetal resin (component A1)> Component A1 is a polymer having a structural unit having an acetal group in the molecule, and is preferably a polymer having a structural unit having an acetal group and a structural unit having a hydroxy group. Examples of component A1 include polyvinyl formal, polyvinyl acetoacetal, polyvinyl propylal, and polyvinyl butyral. More specifically, a polymer represented by the following formula (1) is preferred.

[0028]

[0029] In formula (1), R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. x represents the content (mol %) of structural units having a vinyl acetal group, and is expressed as the total content (mol %) of structural units derived from acetalized vinyl alcohol. y represents the content (mol %) of structural units derived from vinyl alcohol, and z represents the content (mol %) of structural units derived from vinyl acetate. x and y are greater than 0, and z may be 0.

[0030] R 1is preferably a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and most preferably a propyl group. 1 A polyvinyl butyral resin having a structural unit in which is a propyl group is most preferred.

[0031] Polyvinyl butyral resin can be obtained by acetalizing polyvinyl alcohol (PVA) with butyraldehyde under acidic conditions. When acetalizing PVA, it is difficult to completely acetalize the PVA, so some hydroxyl groups remain irreversibly. Furthermore, PVA is usually produced by saponifying polyvinyl acetate. Since a small amount of acetyl groups often remains during the saponification process in the PVA production process, polyvinyl butyral resin generally contains some acetyl and hydroxyl groups remaining irreversibly.

[0032] From the viewpoint of heat resistance, the glass transition temperature (Tg) of the polyvinyl butyral resin may be 40°C or higher and 130°C or lower, preferably 60°C or higher and 120°C or lower. When the glass transition temperature (Tg) is within the range of 40°C or higher and 130°C or lower, merits such as improved coating film strength when formed into a coating film can be exhibited. The higher the glass transition temperature (Tg), the more improved the coating film strength can be expected when formed into a coating film. The glass transition temperature (Tg) can be determined by measuring the change in heat quantity by differential scanning calorimetry (DSC method).

[0033] The x of component A1, i.e., the content of structural units having acetal groups (hereinafter also referred to as the "acetal group amount" or "degree of acetalization"), may be preferably 60 mol% or more, more preferably 65 mol% or more, and even more preferably 70 mol% or more, from the viewpoint of the slipperiness of the coating surface when formed into a coating film. Furthermore, from the viewpoint of the dispersibility of the black material (component B) in the composition, it may be preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less. The acetal group amount (x) is the molar fraction calculated by dividing the amount of ethylene groups to which acetal groups are bonded by the total amount of ethylene groups in the main chain, and corresponds to the content (mol%) of structural units having acetal groups. The amount of ethylene groups to which acetal groups (particularly butyral groups) are bonded can be measured using JIS K6728 "Test Methods for Polyvinyl Butyral."

[0034] From the viewpoint of adhesion between the coating film and the substrate when formed into a coating film, the y of component A1, i.e., the content of structural units having hydroxy groups (hereinafter also referred to as "hydroxy group amount"), may be preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and may be preferably 50 mol% or less, more preferably 45 mol% or less, even more preferably 40 mol% or less. When component A1 contains structural units having acetyl groups, the content thereof (hereinafter also referred to as "acetyl group amount") may be preferably 0.0001 mol% or more, more preferably 0.001 mol% or more, and may be preferably 15 mol% or less, more preferably 10 mol% or less, even more preferably 8 mol% or less, from the viewpoint of increasing the content of the black material (component B).

[0035] The number average molecular weight of component A1 is not particularly limited, but from the viewpoint of the strength of the coating film when formed into a coating, it is preferably 8,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, still more preferably 20,000 or more, and preferably 300,000 or less, more preferably 200,000 or less, even more preferably 150,000 or less. The higher the number average molecular weight of component A1, the more improved the coating film strength when formed into a coating film can be expected. The number average molecular weight of component A1 can be determined as a calculated molecular weight based on the degree of polymerization of the polyvinyl acetal resin used in the reaction. The number average molecular weight refers to a calculated molecular weight.

[0036] Component A1 typically contains an unmodified polyvinyl acetal resin, but from the viewpoint of increasing the cohesive strength of the coating film when formed into a coating film, it may contain a modified polyvinyl acetal resin containing a structural unit having a modifying group other than an acetal group, a hydroxy group, or an acetyl group. Examples of the structural unit having a modifying group include one or more structural units selected from the group consisting of a structural unit having an imine structure, a structural unit having an acid-modified group, and a structural unit having an amino group or an amide structure. When the modified polyvinyl acetal resin contains a structural unit having an imine structure (a structure having a C═N bond), the content thereof is preferably 0.1 mol% or more, more preferably 1 mol% or more, and preferably 20 mol% or less, more preferably 15 mol% or less. Examples of the acid-modified group include a carboxy group, a sulfonic acid group, a maleic acid group, a phosphate group, etc., and salts thereof. When the modified polyvinyl acetal resin contains a structural unit having an acid-modified group, the content thereof is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and preferably 5 mol% or less, more preferably 3 mol% or less. The contents of the structural unit having an imine structure and the structural unit having an acid-modified group can be measured, for example, by NMR. In the modified polyvinyl acetal resin, the imine structure, the acid-modified group, the amino group, or the amide structure may be directly bonded to a carbon atom constituting the main chain or side chain of the modified polyvinyl acetal resin, or may be bonded via a linking group such as an alkylene group.

[0037] The molecular weight, structure, hydroxyl group content, etc. of the polyvinyl acetal resin (modified or unmodified) can be appropriately adjusted by the polymerization degree of the PVA used and the acetalization reaction conditions. In the component A1, it is preferable that the sum of x, y, and z in the formula (1) is 100 mol %.

[0038] Commercially available examples of polyvinyl acetal (butyral) resins include Sekisui Chemical Co., Ltd.'s S-LEC product lines: BL (low molecular weight type) series: BL-1, BL-1H, BL-S, BL-2H; BM (medium molecular weight type) series: BM-1, BM-2(Z), BM-5, BM-S(Z); BH (high molecular weight type) series: BH-S, BH-A; BX (heat resistant type) series: BX-1, BX-5(Z); KS (high heat resistant type) series: KS-6Z, KS-5Z; and the like, as well as Kuraray Co., Ltd.'s Mobital series products. Component A1 may be used singly or in combination of two or more types.

[0039] 2-1-2. <Other A Components> Component A may contain, in addition to Component A1, other thermoplastic resins or thermosetting resins other than Component A1. By including a thermosetting resin in Component A, improved adhesion between the coating film and the substrate upon formation of a coating film is expected. Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, melamine resins, urea resins, diallyl phthalate resins, unsaturated polyester resins, epoxy resins, and alkyd resins. One type of thermosetting resin may be used alone, or two or more types may be used in combination. When Component A contains a thermosetting resin, the mass ratio of the thermosetting resin in Component A may be preferably 0.1% by mass or more, and preferably 0.5% by mass or more, relative to the total amount (100% by mass) of resin solids in Component A1, from the viewpoint of adhesion between the coating film and the substrate upon formation of a coating film. Also, the mass ratio may be preferably 1.5% by mass or less, and more preferably 1% by mass or less.

[0040] 2-1-3. <Total Amount of Component A1> The content (total amount) of component A1 in component A may be any amount that can exhibit the effects of the present invention. From the viewpoint of expecting the strength of the formed film to be exhibited, the content may be, for example, 90% by mass or more, or 95% by mass or more, relative to the total amount (100% by mass) of component A. The upper limit is not particularly limited, and is 100% by mass.

[0041] 2-1-4. <Total Amount of Component A> The content (total amount) of Component A in the total solid content of the composition may be any amount that can exhibit the effects of the present invention. From the viewpoint of maintaining the strength of the formed film, the content may be, for example, 1% by mass or more, or may be 5% by mass or more, relative to the total amount of all solid content (100% by mass). The upper limit may be, for example, 25% by mass or less, or may be 20% by mass or less, from the viewpoint of expecting an improvement in the design of the formed film.

[0042] 2-2. <Black Material (Component B)> Component B included in this composition is dispersed in a matrix containing component A to impart predetermined optical properties to the film that is formed. Component B includes a composite of black pigment and resin (component B1). By including component A1 in component A, even with a small amount of component A blended, the film that is formed exhibits high film strength due to the reflective effect, making it possible to increase the relative blend amount of component B. By including component B1 in component B and blending a large amount of component B, the film that is formed has low gloss and can exhibit ultra-low reflectivity, ultra-low L value, and high light-blocking properties.

[0043] 2-2-1. <Composite of Black Pigment and Resin (Component B1)> Examples of resins constituting the composite of component B1 with the black pigment include epoxy resins, acrylic resins, urethane resins, styrene resins, ethylene resins, phenolic resins, urea resins, amide resins, melamine resins, and benzoguanamine resins. Among these, from the viewpoint of dispersibility in the composition, acrylic resins or urethane resins are preferred, and acrylic resins are more preferred. These may be used alone or in combination of two or more. Note that the name of the resin particles can be partially omitted by adding the name of the resin before the name of beads. For example, resin particles made of acrylic resin are sometimes called acrylic beads.

[0044] The black pigment constituting the composite with the resin of component B1 is not particularly limited, but it is preferable to use carbon black (hereinafter also simply referred to as "CB"), which has a great effect of blackening the composite and is also advantageous in terms of cost. By using CB, the formed film is colored, which further improves the antireflection effect and provides good antistatic effect.

[0045] Examples of the composite form of the black pigment and resin in component B1 include (1) a form in which the black pigment is coated with the resin (including a form in which the black pigment is encapsulated in resin particles), or (2) a form in which the resin is bonded to the surface or interior of the black pigment, or a composite form of these.

[0046] Examples of methods for coating the surface of a black pigment with a resin include the microencapsulation method, and more specifically, the interfacial polymerization method, in-situ polymerization method, liquid curing coating method (orifice method), phase separation from an aqueous solution, and liquid drying method. In addition to the microencapsulation method, there are also methods for bonding or adhering a resin to a dispersed black pigment. One example is a method in which the black pigment serves as a core, the surface of which is covered with numerous colloidal resin particles. When using a colorant in which the black pigment core is covered with colloidal resin particles, it is desirable that the size of the surrounding resin particles be sufficiently small compared to the black pigment core. Furthermore, it is desirable that the colloidal resin particles coat the black pigment core with almost no gaps. However, this does not exclude cases in which the black pigment core is directly exposed to the outside.

[0047] Component B1 may be a black pigment bonded to a resin of approximately the same size as the black pigment particles. Alternatively, the black pigment or black dye may be kneaded into a thermoplastic or thermosetting resin and then pulverized to form a composite of the black pigment and the resin.

[0048] In one embodiment, the composite form is preferably form (1), and more preferably form of resin particles encapsulating a black pigment, from the viewpoint of improving dispersibility in the composition. In the resin particles encapsulating a black pigment, the black pigment is encapsulated in resin particles with a larger diameter, and therefore aggregates are less likely to occur in the composition compared to when a small-diameter black pigment is directly blended into the composition, contributing to improved dispersibility.

[0049] The content of black pigment (particularly CB) in component B1 (the total amount of black pigment contained therein when the total amount of component B1 is taken as 100% by mass) may be, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, with the upper limit being, for example, 50% by mass or less, 40% by mass or less, or 30% by mass or less.

[0050] Component B1 may contain aggregated secondary particles formed by aggregation of primary particles (single particles) of component B1. Aggregated secondary particles are formed by aggregation of multiple (two or more) primary particles due to intermolecular forces or the like. Component B1 does not have to be entirely in the form of aggregated secondary particles, and some may be primary particles.

[0051] The average particle size (D50) of component B1 is 2 μm or more, preferably 3 μm or more. The D50 of component B1 is 6 μm or less, preferably 5 μm or less. For primary particles of the same size, the larger the aggregated secondary particle size, the greater the degree of aggregation. In this regard, component B1 has an average particle size of 6 μm or less, and can be said to have a relatively small degree of aggregation. The smaller the degree of aggregation of component B1, the lower the L value of the formed film tends to be (ultra-low L value), so the D50 value of component B1 is an important indicator. If the D50 of component B1 is too small (e.g., smaller than 2 μm), the proportion of aggregated secondary particles in the composition increases, making dispersion difficult. If the D50 of component B1 is too large (e.g., larger than 6 μm), the tinting power tends to decrease. "Average particle size (D50)" is the volume-based cumulative 50% diameter of particles or fillers, determined by laser diffraction / scattering. That is, the particle size distribution is measured by a laser diffraction / scattering method, a cumulative curve is calculated assuming the total volume of the particle group to be 100%, and D50 is the particle diameter at the point on the cumulative curve where the cumulative volume is 50% (= the cumulative 50% diameter (D1) in the volume cumulative distribution). D50 of component B1 is determined by dispersing component B1 in water and analyzing it by a laser diffraction / scattering method using a laser diffraction / scattering particle size distribution analyzer (LA-920 measuring instrument, manufactured by Horiba, Ltd.).

[0052] The B1 component preferably has a cumulative 50% diameter (D2) in the number cumulative distribution of primary particles measured with an electron microscope of 1 μm or more and 20 μm or less, and more preferably 2 μm or more and 10 μm or less. The cumulative 50% diameter (D2) is the median diameter of the primary particles of the B1 component observed with an electron microscope. If the cumulative 50% diameter (D2) is in the above range, the D50 (= cumulative 50% diameter (D1)) of the B1 component described above is likely to fall within the desired value (6 μm or less), which is preferable. The cumulative 50% diameter (D2) of the B1 component refers to the cumulative 50% diameter when the B1 component is observed with a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation), the diameters (longest diameters) of 100 randomly selected primary particles are measured, and these are expressed as the number cumulative distribution of primary particles.

[0053] The ratio (D1 / D2) of D1 to the cumulative 50% diameter (D2) of the primary particles of the B1 component is preferably 1 or more and 9 or less, more preferably 1 or more and 5 or less, even more preferably 1 or more and 4 or less, and most preferably 1 or more and 2 or less. The ratio (D1 / D2) of D1 to D2 indicates the degree of aggregation of the B1 component when the size of the primary particles is also taken into consideration, and the smaller the value, the lower the degree of aggregation (in other words, the closer it is to primary particles and the closer it is to a monodispersed state). As mentioned above, there is a correlation between the degree of aggregation of the primary particles of the B1 component and the L value of the film formed, and by reducing the value of D1 / D2 (specifically, preferably 9 or less), the L value of the film formed can be further reduced (realization of an ultra-low L value).

[0054] The shape of component B1 is not particularly limited, but from the viewpoint of matte finish, a spherical shape is preferred. Furthermore, in order to achieve a low gloss, low reflectance, and low L value on the surface of the film to be formed, it is preferable to use particles with a narrow particle size distribution (sharp particles) as component B1. Examples of particles with a narrow particle size distribution include particles with a CV (Coefficient of Variation) value of, for example, 15 or less, preferably 13 or less, and more preferably 11 or less. The CV value is a numerical representation of the degree of spread of particle size distribution (particle size variation) relative to the average particle size (arithmetic mean particle size), and represents the uniformity of the particle size. The smaller the CV value, the more uniform the particle size. A CV value of 15 or less can be said to be particles with a uniform particle size (also referred to as single-diameter particles). To achieve a CV value of 15 or less, a method of appropriately selecting a manufacturing method for component B1 can be used. For example, a method of producing the material by slurrying and spray-drying it can easily achieve a CV value of 15 or less. The method for determining the CV value includes the Coulter method. By using particles with such a narrow particle size distribution, they are uniformly contained in the film, forming fine irregularities on the film surface, which makes it easier to achieve a film surface with even lower gloss, lower reflectivity, and a lower L value. In addition, in order to further reduce the gloss of the formed film surface, amorphous particles may be used as component B1. By using amorphous particles as component B1, when a film is formed, light is repeatedly refracted on the surface and inside of component B1, which can further reduce the gloss of the film surface.

[0055] Commercially available products can be used as component B1. Examples of products containing urethane beads include Art Pearl C800 Black (average particle size 6.5 μm, CB content 7.5%, Negami Chemical Industrial Co., Ltd.). Examples of products containing acrylic (acrylic copolymer) beads include Art Pearl GR-004BK (average particle size 3-5 μm, CB content 35-39%, Negami Chemical Industrial Co., Ltd.) and Labcolor 224 (SMD) Black (average particle size 2-3 μm, CB content 18%, Dainichiseika Color & Chemicals Mfg. Co., Ltd.). Component B1 may be used alone or in combination of two or more.

[0056] 2-2-2. <Other Components B> Component B may contain, together with component B1, other black materials (such as black sulfide compounds, porous carbon, carbon black, etc.) other than component B1.

[0057] 2-2-3. <Total Amount of Component B1> The content (total amount) of component B1 in component B may be any amount that can exhibit the effects of the present invention. From the viewpoint of expecting an improvement in the design of the formed film, the content may be, for example, 90% by mass or more, or 95% by mass or more, relative to the total amount (100% by mass) of component B. The upper limit is not particularly limited, and is 100% by mass.

[0058] 2-2-4. <Total Amount of Component B> The content (total amount) of Component B in the total solid content of the composition may be any amount that can exhibit the effects of the present invention. From the viewpoint of avoiding problems with the formed film (increased gloss, insufficient optical density), the content may be, for example, 60% by mass or more, 65% by mass or more, or 75% by mass or more, relative to the total amount of all solid content (100% by mass). The upper limit may be, for example, 90% by mass or less, 85% by mass or less, or 80% by mass or less, from the viewpoint of avoiding problems with the substrate (film detachment due to poor adhesion or insufficient strength) that occur due to a small amount of Component A in the formed film.

[0059] 2-2-5. <Mass Ratio of Component B to Component A> The mass ratio of component B to component A (component B / component A) is 7 or more, preferably 8 or more, and more preferably 9 or more. From the viewpoint of improving the design of the film to be formed, the higher the ratio, the better. From the viewpoint of maintaining the strength of the film to be formed, the upper limit is 14 or less, preferably 12 or less. By blending component B in such a mass ratio range, it is possible to achieve improved design (low gloss, low reflectivity, low L value, high light blocking) while maintaining the strength of the film to be formed. The "mass ratio of component B to component A" refers to the total amount of component B when the total amount of component A is 1.

[0060] 2-3. <Diluting Solvent (Component C)> Component C is included in the present composition for the purpose of adjusting the viscosity of the present composition. The inclusion of Component C improves the uniformity of the present composition. In addition, the viscosity of the present composition can be appropriately adjusted, which can greatly contribute to improving the operability of the present composition and the uniformity of the applied thickness when applying the present composition to a coating surface.

[0061] The component C is not particularly limited as long as it is a solvent that can adjust the viscosity of the composition. Examples include water, an organic solvent, or a mixture of water and an organic solvent. Examples of organic solvents that can be used include methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, butyl acetate, methanol, ethanol, isopropyl alcohol, and butanol. One type of component C may be used alone, or two or more types may be used in combination. The amount of component C may be appropriately determined to adjust the solids concentration of the composition.

[0062] 2-4. <Optional Component (Component D)> In addition to the above-described components (Component A, Component B, and Component C), the present composition may contain an optional component (Component D) to the extent that the effects of the present invention are not impaired. Examples of Component D include leveling agents, thickeners, pH adjusters, lubricants, dispersants, antifoaming agents, curing agents, and reaction catalysts. When Component D is included, the blending amount may be 100 parts by mass or less, or may be 30 parts by mass or less, per 100 parts by mass of Component A.

[0063] 2-4-1. <Curing Agent> By incorporating a curing agent as Component D, the hydroxyl groups contained in Component A1 can be utilized to promote crosslinking of Component A. Examples of curing agents that react with hydroxyl groups include epoxy compounds, methylol compounds, isocyanate compounds, and titanium chelate compounds. Of these, isocyanate compounds are particularly preferred.

[0064] The isocyanate compound preferably used as a curing agent can be any compound having two or more isocyanate groups in the molecule. Examples include at least one of aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, and derivatives thereof. Here, araliphatic polyisocyanates refer to polyisocyanates having a structure in which an isocyanate group is bonded to an aromatic ring via an aliphatic carbon atom.

[0065] Examples of aromatic polyisocyanates include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, p-phenylene diisocyanate, triphenylmethane triisocyanate, tris(isocyanatophenyl)thiophosphate, etc. Examples of aliphatic polyisocyanates include hexamethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc. Examples of alicyclic polyisocyanates include isophorone diisocyanate, dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, bis(isocyanatomethyl)norbornane, etc. Examples of aromatic aliphatic polyisocyanates include xylylene diisocyanate, tetramethylxylylene diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, etc. Examples of derivatives of polyisocyanate compounds include multimers such as trimers, dimers, pentamers, etc., such as the isocyanurates of the isocyanate compounds, adducts obtained by reacting the isocyanate compounds with polyol compounds such as trimethylolpropane, and modified polyisocyanates such as allophanate compounds and biuret compounds.

[0066] From the viewpoint of further improving the adhesion of the formed film to the substrate, it is preferable to use an isocyanate compound having a structure in which the nitrogen atom of the isocyanate group is bonded to an aliphatic carbon atom, and at least one selected from aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, and derivatives thereof is preferably used. Among these, from the viewpoint of improving the adhesion and strength of the formed film to the substrate, isocyanurates of aliphatic polyisocyanates, xylylene diisocyanate, and modified polyisocyanates thereof are preferably used as the isocyanate compound. One type of curing agent may be used alone, or two or more types may be used in combination.

[0067] 2-4-2. <Ratio of Curing Agent> When a curing agent is included in the composition, the ratio may be 10 to 70 mass % relative to 100 mass % of Component A. By including a curing agent in this range, it is possible to impart greater strength to the film formed, resulting in a film with greater scratch resistance and allowing the excellent properties of the film surface (improved design) to be maintained over a long period of time.

[0068] 2-4-3. <Reaction catalyst> When a curing agent is included in the composition, a reaction catalyst can be used in combination to promote the reaction between Component A and the curing agent. Examples of reaction catalysts include ammonia and ammonium chloride. When a reaction catalyst is included in the composition, the amount of the reaction catalyst may be 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the curing agent.

[0069] 2-5. <Preparation> The present composition can be prepared (manufactured) by adding component A, component B, and, if necessary, component D to component C, and mixing and stirring them. The order in which the components are mixed is not particularly limited, as long as these components are mixed uniformly.

[0070] 3. <Method for Producing an Anti-Reflection Film> The composition is applied to the surface of a desired portion (in this example, the outer surface; the same applies hereinafter) of an object to be coated (in this example, the housing body of an electronic device housing; the same applies hereinafter), and the dilution solvent (component C) is removed by drying, thereby allowing a film (anti-reflection film) formed from the composition to be applied to the desired portion of the object to be coated. There are no particular limitations on the method for applying the composition to the object to be coated (application method), and examples include application methods (brush coating, etc.), droplet discharge methods (dispenser method, spray coating, etc.), and immersion methods (dip coating, etc.).

[0071] 3-1. <Viscosity of Resin Composition> The viscosity of the composition cannot be generalized because the appropriate range varies depending on the application method, but it is sufficient if it is approximately 1 mPa·s or more and 2000 mPa·s or less. When the viscosity is within this range, the composition has excellent coatability and is easy to form a film (anti-reflection film) of any thickness on the desired portion of the substrate. Furthermore, when the composition has a viscosity within this range, the film formed therefrom is likely to exhibit predetermined characteristics (gloss, reflectance, L value, optical density) and film properties (adhesion, scratch resistance). For example, when the application method is a method using a paintbrush or brush (brush application method), the viscosity is preferably approximately 100 mPa·s or more and 2000 mPa·s or less. When the application method is a dispenser method, the viscosity is preferably approximately 10 mPa·s or more and 300 mPa·s or less. When the application method is a spray coating method, the viscosity is preferably approximately 1 mPa·s or more and 50 mPa·s or less. When the application method is a dip coating method, the viscosity is preferably about 20 mPa·s or more and 500 mPa·s or less. The viscosity of the composition is determined by measuring the composition using a Brookfield viscometer at 25°C and a rotation speed of 60 rpm. The measurement is repeated three times, and the average value of the three measured values ​​is used.

[0072] In the case of brush application, if the viscosity of the composition is too low, the problem of dripping may occur. If the viscosity of the composition is too high, the problem of smearing may occur. In the case of dispenser application, if the viscosity of the composition is too low, the solution may splash or drip, potentially resulting in the application of the solution to areas not intended for application. If the viscosity of the composition is too high, the solution may not come out of the nozzle, or if it does come out, the surface shape may tend to be flat, resulting in a glossy finish. In the case of spray coating, if the viscosity of the composition is too low, it may be impossible to form a film thick enough to achieve the desired performance. If the viscosity of the composition is too high, the solution (the composition) may not come out of the nozzle, or even if it does come out, it may not be atomized. In the case of dip coating, if the viscosity of the composition is too low, the solution may drip excessively, resulting in unevenness and the inability to form a clean film. If the viscosity of the composition is too high, the liquid may not drain well when the substrate is pulled out of the liquid (composition), resulting in the formation of burrs, or the surface of the film formed from the composition may tend to be flat, resulting in a glossy appearance.

[0073] The viscosity of the composition varies depending on the type and molecular weight of the solids (component A, component B) contained in the composition. When component D is blended in addition to components A and B, the viscosity of the composition also varies depending on the type and molecular weight of component D. The viscosity of the composition can be easily adjusted by appropriately determining the amount of component C in the composition.

[0074] The present composition may be a one-component type or a two-component type. When a curing agent is blended, the present composition may be, for example, a two-component type having a first component containing components other than the curing agent and a second component containing the curing agent.

[0075] When the composition is applied by spray coating, even if the desired part of the object to be coated has protrusions or steps, a film with a uniform thickness and specific performance can be formed over the entire surface.

[0076] The coating conditions using the spray coating method are preferably a spray gun diameter of about 0.2 to 1.2 mm, a discharge rate of about 0.2 to 10 (g / min), a shortest distance between the spray gun and the surface of the object to be coated of about 30 to 500 mm, a coating speed of about 30 to 300 (mm / sec), an overlap pitch of about 1.5 to 10 mm, and an atomizing air pressure of about 0.03 to 0.2 MPa. In terms of the number of spray guns, in addition to operating a single gun, multiple guns may be arranged according to the size of the object to be coated from the viewpoint of coating efficiency.

[0077] When this composition is applied by brush coating, the thickness of the film formed on the desired part of the substrate tends to vary depending on the location, but the performance of the resulting film is equivalent to that of other coating methods. The reason for this is not clear, but it is thought to be because the appropriate amount of pigment content forms unevenness.

[0078] 3-2. <Example of Process> After the composition is applied to the desired portion of the substrate, it is heated and dried to remove the component C, forming a film (film formation). The heating to remove the component C may be carried out, for example, at a temperature of 80°C to 120°C for 5 to 30 minutes. If necessary, the formed film may be irradiated with UV light or EB light. When the composition contains a curing agent, the film formed by heating and drying may be further heated to cure the film. In this case, it is not necessary to completely remove the component C during the heating to remove the component C. The heating conditions for curing the film may be adjusted appropriately depending on the thickness of the film before heating, the heat resistance of the substrate, the type of component C used, and the like. For example, the heating conditions may be at 70°C to 150°C for 1 to 30 minutes, or at 100°C to 130°C for 2 to 10 minutes.

[0079] 4. <Thickness of Anti-Reflection Film> The thickness of the anti-reflection film is not particularly limited as long as it provides good adhesion strength to the substrate and does not impede the improvement of design. An example of a suitable film thickness is preferably 2 μm or more, more preferably 5 μm or more. The upper limit is preferably 40 μm or less, more preferably 25 μm or less. The film thickness of the anti-reflection film refers to the height from the desired portion of the surface of the substrate to the portion protruding due to component B of the film. The film thickness can be measured by a method in accordance with JIS K7130.

[0080] 5. <Characteristics of Anti-Reflection Film> The characteristics of the film formed from the present composition are as follows.

[0081] 5-1. <Optical Properties (Gloss, Reflectance, L Value, Optical Density)> It is preferred that a film formed from the present composition has a 60° gloss of less than 1%, an 85° gloss of less than 10%, a reflectance of less than 1.5%, an L value of less than 15, and an optical density of 2 or greater on the film surface.

[0082] Here, when a film formed from the present composition is exposed on the outermost surface of an electronic device housing, it is preferable that the 60° gloss, 85° gloss, reflectance, L value, and optical density of the film surface are literally within the above-mentioned ranges. When another film is coated on the film formed from the present composition, it is preferable that the 60° gloss, 85° gloss, reflectance, L value, and optical density of the surface of the other film (i.e., the outermost surface of the housing body of the electronic device housing) are within the above-mentioned ranges. Hereinafter, these surfaces are collectively referred to as the "outermost surface of the film."

[0083] The film formed from this composition preferably has an outermost surface with a 60° gloss of less than 1%, an 85° gloss of less than 10%, a reflectance of less than 1.5%, an L value of less than 15, and an optical density of at least 2. When the optical properties of the outermost surface of the film are within the above ranges, the outermost surface of the film can achieve low gloss, low reflectance (excellent antireflection properties; the same applies hereinafter), high blackness, and high light-blocking properties, which in turn tends to significantly improve design.

[0084] The upper limit of the 60° gloss is preferably less than 1%, more preferably less than 0.7%, and even more preferably less than 0.5%. When the upper limit of the 60° gloss is less than 1%, it is easy to effectively prevent the phenomenon in which the film appears whitish due to diffuse reflection of light, and the design is likely to be significantly improved. The lower limit of the 60° gloss is not particularly limited, and the lower the better. The upper limit of the 85° gloss is preferably less than 10%, and more preferably less than 5%. When the upper limit of the 85° gloss of the outermost film surface is less than 10%, together with the 60° gloss, it is easy to effectively prevent the phenomenon in which the film appears whitish due to diffuse reflection of light, angle dependency is eliminated, and the benefit of improved design is likely to be obtained. The lower limit of the 85° gloss is not particularly limited, and the lower the better.

[0085] The upper limit of the reflectance is preferably less than 1.5%, more preferably less than 1.25%, and even more preferably less than 1.0%. By making the upper limit of the reflectance less than 1.5%, it is easy to effectively prevent the phenomenon in which the film appears whitish due to diffuse reflection of light, and it is easy to significantly improve the design. The lower limit of the reflectance is not particularly limited, and the lower the better.

[0086] The upper limit of the L value (blackness) is preferably less than 15, more preferably less than 12, and even more preferably less than 10. The lower limit of the L value is not particularly limited, but from the perspective of achieving a more intense black appearance, the lower the value, the better. The film may be installed in a location visible to the user, resulting in a requirement for a higher appearance quality. Specifically, a more sophisticated black-painted film (e.g., a textured film) may be required. By setting the L value to less than 15, the above requirements are more easily met. The L value refers to the lightness L* value of the outermost film surface in the CIE 1976 L*a*b* (CIELAB) color system according to the SCE method. The SCE method refers to a specular reflection removal method, which is a method of measuring color by removing specular reflection. The definition of the SCE method is specified in JIS Z8722 (2009). Since the SCE method removes specular reflection during measurement, the color obtained is closer to the actual color seen by the human eye. CIE stands for Commission Internationale de l'Eclairage, which stands for International Commission on Illumination. The CIELAB color system is a uniform color space recommended in 1976 to measure color differences due to differences in perception and devices, and is specified in JIS Z8781 (2013). The three coordinates of CIELAB are L*, a*, and b*. L* indicates lightness and ranges from 0 to 100. An L* value of 0 indicates black, while an L* value of 100 indicates diffuse white. The a* value indicates a color between red and green. A negative a* value indicates a color leaning toward green, while a positive value indicates a color leaning toward red. The b* value indicates a color between yellow and blue. A negative b* value indicates a color leaning toward blue, while a positive value indicates a color leaning toward yellow.

[0087] The lower limit of the optical density is preferably 2 or more, more preferably 2.5 or more, and even more preferably 3.2 or more. By setting the lower limit of the optical density to 2 or more, the light-blocking property can be further improved, which is effective in improving the design. The upper limit of the optical density is not particularly limited, and the higher the value, the better.

[0088] The glossiness, reflectance, L value, and optical density can be measured by the methods described below.

[0089] 5-2. <Film Properties (Adhesion, Scratch Resistance)> In addition to exhibiting the above optical properties, it is preferable that the film formed from the present composition further exhibit good adhesion to the substrate and high film strength (scratch resistance). As shown in the adhesion evaluation in the Examples described later, the adhesion of the film formed from the present composition to the substrate is such that the film remains at 90% or more, or even 95% or more, or even 100%. Such good adhesion to the substrate can prevent the film from falling off the substrate. As shown in the evaluation of Scratch Resistance 1 in the Examples described later, the film strength of the film formed from the present composition is such that the number of scratches according to JIS K5600-5-10 ISO 7784-3 is 10 or less, or 2 or less, or even 0. Such high film strength makes it easier to ensure scratch resistance during film production (film formation) and handling.

[0090] (Other Embodiments) In the above-described embodiment, the anti-reflection film may be formed on the outer surface of the housing body of the electronic device housing directly without pre-treatment or via a pre-treatment layer, but is not limited to this. For example, a sheet for an anti-reflection film may be prepared by forming an anti-reflection film on an ultra-thin plastic film (such as a PET film) by a spray coating method, and the sheet may be cut to fit the shape of the outer surface of the housing body of the electronic device housing to obtain a sheet piece. The sheet piece may then be attached to the housing body of the electronic device housing via an adhesive layer, and finally, an anti-reflection film may be formed on the outer surface of the housing body of the electronic device housing.

[0091] The present invention will be specifically described below based on experimental examples (including examples and comparative examples), but the present invention is not limited to these experimental examples. In the following description, "parts" means "parts by mass" and "%" means "% by mass".

[0092] [Constituent Components of Resin Composition] As the binder resin (component A), the following polyvinyl acetal resins (component A1) (A1a to A1e) and a non-polyvinyl acetal resin (component A2) were prepared. A1: Polyvinyl acetal resin (S-LEC, Sekisui Chemical Co., Ltd.) A1a: BL-S (degree of acetalization: approximately 72 mol%, amount of hydroxyl groups: approximately 23 mol%, amount of acetyl groups: 4 to 6 mol%, calculated molecular weight: approximately 23,000, Tg: 66°C) A1b: BM-S(Z) (degree of acetalization: approximately 72 mol%, amount of hydroxyl groups: approximately 23 mol%, amount of acetyl groups: 4 to 6 mol%, calculated molecular weight: approximately 55,000, Tg: 67°C) A1c: BH-S (degree of acetalization: approximately 72 mol%, amount of hydroxyl groups: approximately 23 mol%, amount of acetyl groups: 4 to 6 mol%, calculated molecular weight: approximately 66,000, Tg: 67°C) A1d: BX-5(Z) (Degree of acetalization: about 72 mol%, amount of hydroxyl groups: about 27 mol%, amount of acetyl groups: 3 mol% or less, calculated molecular weight: about 130,000, Tg: 92°C) A1e: KS-5Z (Degree of acetalization: about 74 mol%, amount of hydroxyl groups: about 25 mol%, amount of acetyl groups: 3 mol% or less, calculated molecular weight: about 130,000, Tg: 113°C) A2: Thermosetting acrylic resin (Acrydic A801, DIC Corporation) (Resin Tg 67°C, resin solids content 34%, molecular weight 15,000, acid value 1 mgKOH / g, hydroxyl value 5 mgKOH / g)

[0093] As the black material (B component), the following were prepared: a composite of black pigment and resin (B1 component) with an average particle size in the range of 2 μm to 6 μm (Ba); a composite of B1 component but with an average particle size outside the range of 2 μm to 6 μm (Bb); and a composite of B1 component but not with an average particle size in the range of 2 μm to 6 μm (Bc to Bf). Ba: Black acrylic beads (average particle size 3-5 μm) (Art Pearl GR-004BK, Negami Chemical Industrial Co., Ltd., CB content 35-39%) Bb: Black acrylic beads (average particle size 14-16 μm) (Art Pearl GR-400BK, Negami Chemical Industrial Co., Ltd., CB content 6-10%) Bc: CB (average particle size 150 nm) (MHI Black #273, Mikuni Shikishokusha, CB content 9.5%) Bd: Composite silica (average particle size 3 μm) (Vexia ID, Fuji Silysia Chemical Ltd.) Be: Transparent acrylic beads (average particle size 3 μm) (Unipowder MNB0320C, ENEOS Corporation) Bf: Transparent acrylic beads (average particle size 2 μm) (Unipowder MNB0220C, ENEOS Corporation)

[0094] The "Art Pearl GR-004BK" used for Ba and the "Art Pearl GR-400BK" used for Bb are both spherical acrylic resin particles containing CB, and are a type of composite of CB and acrylic resin. The "MHI Black #273" used for Bc (CB) is a CB dispersion, with 9.5% of the total solids content of the dispersion of 18% being CB and the remaining 8.5% being other compounds. Of the 8.5% other compounds, 3% is a copper compound and 5.5% is an acrylic resin. The "Vexia ID" used for Bd (composite silica) is a composite particle of CB and silica with a CB / silica ratio of approximately 25 / 75 (mass ratio).

[0095] The following dilution solvents (component C) were prepared: C1: methyl ethyl ketone C2: butyl acetate

[0096] As an optional component (component D), an isocyanate compound (Takenate D110N, Mitsui Chemicals, Inc., solid content 75%) was prepared.

[0097] [Substrate] A smartphone housing (plastic outer box) was prepared as the substrate.

[0098] [Experimental Examples 1 to 20, 24 and 5a to 16a, 24a] 1. Preparation of resin composition (paint) Each component for each experimental example was added to a predetermined amount of component C (mixed solvent of C1 and C2) shown in Tables 1 to 3 so that the total solids content (mass%) and the solids content ratio of each component were the values ​​shown in Tables 1 to 3, and the paint was prepared by stirring and mixing.

[0099] 2. Preparation of Evaluation Samples Evaluation samples (films 1 and 2) were prepared using the paints obtained in each experimental example as follows: 2-1. Formation of Film 1 Using the spray coating method in the same manner as in (3-3-1) Coatability 1 below, the paint was sprayed onto the outer surface of the substrate to form a coating film, and then the coating film was dried by heating at 120°C for 3 minutes, thereby forming Film 1 by the spray coating method with an average film thickness of 10 μm on the coated surface of the substrate.

[0100] 2-2. Formation of Film 2 A coating film was formed on the substrate by brush coating in the same manner as in (3-3-2) Coating Property 2 below, and then the coating film was dried by heating at 120°C for 3 minutes, thereby forming Film 2 by brush coating on the coated surface of the substrate with an average film thickness of 10 μm.

[0101] 3. Evaluation The paints obtained in each experimental example were evaluated for various properties (viscosity, pourability, applicability, dripping) using the methods described below (paint evaluation). In addition, the films formed from the paints obtained in each experimental example were evaluated for various properties (characteristics) using the methods described below (film evaluation). The results are shown in Tables 1 to 3.

[0102] [Paint Evaluation] (3-1-1) Viscosity 1 The viscosity 1 of the paint was measured using a Brookfield viscometer (VISCOMETER BM2: Toki Sangyo Co., Ltd.) under the conditions of 25°C, 60 rpm, 1 minute, and No. 1 rotor. This measurement was repeated three times, and the average of the three measured values ​​was calculated. The evaluation criteria are as follows:

[0103] ◯: Viscosity is 1 mPa·s or more and 50 mPa·s or less (good viscosity) ×: Viscosity exceeds 50 mPa·s (excessively high viscosity) (3-1-2) Viscosity 2 The viscosity 2 of the paint was measured using a Brookfield viscometer (VISCOMETER BM2: Toki Sangyo Co., Ltd.) under the conditions of 25°C, 60 rpm, 1 minute, and No. 2 rotor. This measurement was repeated three times, and the average of the three measured values ​​was calculated. The evaluation criteria are as follows:

[0104] Good: Viscosity is 100 mPa·s or more and 2000 mPa·s or less (good viscosity) Bad: Viscosity is more than 2000 mPa·s (excessive viscosity)

[0105] (3-2) Injectability The injectability of the paint was evaluated by observing how it was injected into the air sprayer. Using an air sprayer consisting of an air can (Spraywork Air Can 420D, Tamiya) and an airbrush (Spraywork HG Single Airbrush, Tamiya), the injectability was evaluated by visually observing how each paint entered the nozzle from the cup of the airbrush. The evaluation criteria were as follows:

[0106] ◯: No clogging at all, and the paint entered the nozzle smoothly. △: No clogging, but the speed at which the paint entered the nozzle was a little slow. ×: There was clogging, and the paint did not enter the nozzle.

[0107] (3-3-1) Coatability 1 Coatability 1 of the paint was evaluated by observing coating unevenness after application by spray coating. Each paint was poured into the air spray used in (3-2) above and sprayed toward the outer surface of the substrate from a distance of 10 cm from the tip of the airbrush for 10 seconds, and the formed coating film (before drying) was visually evaluated for coating unevenness. (3-3-2) Coatability 2 Coatability 2 of the paint was evaluated by observing coating unevenness after application by brush coating. Each paint was applied to the tip of a brush and a 10 cm line was drawn on a SUS plate, and the formed coating film (before drying) was visually evaluated for coating unevenness.

[0108] The evaluation criteria for both Coatability 1 and Coatability 2 are as follows: ⊚: No coating unevenness (uneven thickness) was observed ◯: Coating unevenness was observed in a small area ×: Coating unevenness was observed over a large area

[0109] (3-4) Dripping property The dripping property of the paint was evaluated by observing dripping from the substrate after application by spray coating. As in (3-3-1) above, each paint was poured into the air spray used in (3-2) above and sprayed toward the outer surface of the substrate from a distance of 10 cm from the tip of the airbrush for 10 seconds, and then the dripping property of the droplets adhering to the substrate was evaluated. The evaluation criteria are as follows:

[0110] ◯: No dripping occurred even when the coated object was placed vertically after application. △: When the coated object was placed vertically after application, the liquid gradually began to drip. ×: When the coated object was placed vertically after application, the liquid immediately began to drip.

[0111] [Film Evaluation] (3-5) Properties - Glossiness - The glossiness of the surface of the film formed on each substrate with respect to measurement light at an incident angle of 60° (60° specular glossiness) and with respect to measurement light at an incident angle of 85° (85° specular glossiness) was measured at nine points using a gloss meter (VG 7000: Nippon Denshoku Industries Co., Ltd.) according to a method in accordance with JIS Z8741, and the average value was taken as the glossiness. The evaluation criteria are as follows:

[0112] (60° specular gloss) ◎: Less than 0.5% (extremely excellent low gloss) ◯: 0.5% or more and less than 0.7% (excellent low gloss) △: 0.7% or more and less than 1% (good low gloss) ×: 1% or more (insufficient low gloss)

[0113] (85° specular gloss) ◎: Less than 5% (extremely excellent low gloss) ◯: 5% or more but less than 10% (excellent low gloss) ×: 10% or more (insufficient low gloss)

[0114] (Overall evaluation of glossiness) ◎: All evaluations of 60° specular glossiness and 85° specular glossiness were ◎ (extremely excellent low glossiness) ◯: At least one evaluation of 60° specular glossiness and 85° specular glossiness was ◯, and none was × (excellent low glossiness) ×: At least one evaluation of 60° specular glossiness and 85° specular glossiness was × (insufficient low glossiness)

[0115] -Reflectance- The reflectance of the surface of the film formed on each substrate to light with a wavelength of 550 nm (550 nm reflectance) was measured at nine points using a spectrophotometer (CM-5: Konica Minolta) according to a method conforming to JIS Z8722, and the average value was taken as the reflectance. The evaluation criteria were as follows:

[0116] ◎: Reflectance is less than 1% (extremely excellent low reflectance) ◯: Reflectance is 1% or more but less than 1.25% (excellent low reflectance) △: Reflectance is 1.25% or more but less than 1.5% (good low reflectance) ×: Reflectance is 1.5% or more (insufficient low reflectance)

[0117] -Blackness- The blackness of the surface of the film formed on each substrate was evaluated by measuring the lightness L* value of the film surface in the CIE 1976 L*a*b* (CIELAB) color system according to the SCE method. The lightness L* value was measured using a spectrophotometer (CM-5: Konica Minolta) in accordance with JIS Z8781-4:2013. The evaluation criteria are as follows. In the measurement, the CIE standard illuminant D65 was used as the light source, and the L* value was determined in the CIELAB color system according to the SCE method at a viewing angle of 10°. CIE standard illuminant D65 is specified in JIS Z8720 (2000) "Illuminates (standard light) and standard light sources for colorimetry," and the same specification is also found in ISO 10526 (2007). CIE standard illuminant D65 is used to display the color of objects illuminated by daylight. The 10° viewing angle is specified in JIS Z8723 (2009) "Method for visual comparison of surface color," and the same specification is found in ISO / DIS 3668.

[0118] ◎: L value is less than 10 (extremely excellent blackness) ◯: L value is 10 or more and less than 12 (excellent blackness) △: L value is 12 or more and less than 15 (good blackness) ×: L value is 15 or more (insufficient blackness)

[0119] - Light-blocking property - The light-blocking property of the film formed on each substrate was evaluated by calculating the optical density of the film. The optical density of the film formed on each substrate was calculated using an optical densitometer (X-rite 361T (ortho filter: Nippon Heihan Kizai Co., Ltd.) by irradiating the film side of the substrate with a perpendicular transmitted light beam and expressing the ratio to the state without the film in log (logarithm). An optical density of 6.0 or higher is the upper detection limit for measurement. The evaluation criteria are as follows:

[0120] ◎: Optical density is 3.2 or more (extremely excellent light-blocking properties) ◯: Optical density is 2.5 or more and less than 3.2 (excellent light-blocking properties) △: Optical density is 2 or more and less than 2.5 (good light-blocking properties) ×: Optical density is less than 2 (insufficient light-blocking properties)

[0121] Adhesion: The adhesion of the film formed on each substrate to the surface of the substrate was evaluated by making grid-shaped cuts in the film with a commercially available cutter, sticking cellophane tape (Nichiban Co., Ltd.) to the cuts, then peeling it off and visually checking the state of the film remaining. The evaluation criteria are as follows:

[0122] ◎: 100% of the film remains (extremely excellent adhesion) ◯: 95% or more but less than 100% of the film remains (excellent adhesion) △: 90% or more but less than 95% of the film remains (good adhesion) ×: Less than 90% of the film remains (insufficient adhesion)

[0123] -Abrasion Resistance 1- The abrasion resistance 1 of the film formed on each coated object was evaluated by measuring scratches on the film surface using an abrasion resistance tester (Suga Abrasion Tester NUS-ISO3: Suga Test Instruments Co., Ltd.) in accordance with JIS K5600-5-10 ISO 7784-3. The measurement conditions were a load of 100 g (corresponding to a weight of 100 g to 3 kg), and a test piece (one form of a coated object on which a film has been formed; the same applies hereinafter) 1 cut to a size that fit the jig was reciprocated 10 times against a test piece 2 wrapped around a rotating wheel positioned below the test piece 1 and sized to fit the rotating wheel, causing abrasion. The abrasion resistance 1 was evaluated by checking whether scratches were formed on the film surface of the test piece 1. The rotating wheel rotated 0.9° for each reciprocation of the test piece 1, so that the newly worn surface of the test piece 2 was always abrading the test piece 1. The evaluation criteria were as follows.

[0124] ◎: 0 scratches (extremely excellent scratch resistance) ◯: 1 to 2 scratches (excellent scratch resistance) △: 3 to 10 scratches (good scratch resistance) ×: 11 or more scratches (insufficient scratch resistance)

[0125] - Scratch Resistance 2 - Scratch resistance 2 of the film formed on each coated object was evaluated by observing the presence or absence of scratches using a melamine sponge (Gekiochikun, Melamine Foam, LEC Corporation). 2 The sample was rubbed 30 times with a load of 200 g, and then visually inspected for the presence or absence of scratches to evaluate the sample. The evaluation criteria were as follows:

[0126] ◎: No change (extremely excellent scratch resistance) ◯: 1-2 thin scratches (excellent scratch resistance) △: 3-10 thin scratches (good scratch resistance) ×: 11 or more thin scratches (insufficient scratch resistance) XX: Sharp scratches on the entire surface of the rubbed surface (poor scratch resistance)

[0127] - Overall Evaluation - The glossiness, reflectance, blackness, light blocking property, adhesion, and scratch resistance 1 and 2 were evaluated overall. The evaluation criteria were as follows:

[0128] ◎: All evaluations of glossiness, reflectance, blackness, light-blocking property, adhesion, and scratch resistance 1 and 2 were ◎. 〇: At least one of the evaluations of glossiness, reflectance, blackness, light-blocking property, adhesion, and scratch resistance 1 and 2 was 〇, and none was ×. ×: At least one of the evaluations of glossiness, reflectance, blackness, light-blocking property, adhesion, and scratch resistance 1 and 2 was ×.

[0129]

[0130]

[0131]

[0132] 4. Discussion As shown in Table 1, when component A1 was included in the paint as component A, and component B of the paint included a component B1 (Ba) that belonged to component B1 and had an average particle size within a predetermined range, and the mass ratio of component B to component A in the paint was 7 or more and 14 or less (Experimental Examples 5, 12-15), all of the paint characteristics and film characteristics (optical characteristics (gloss, reflectance, L value, light-blocking properties), film physical properties (adhesion, scratch resistance 1, 2)) could be satisfied. In contrast, when component A1 was not included in the paint as component A (Experimental Examples 1-4), one or more of the film characteristics, optical characteristics, and film physical properties could not be satisfied. Even when component A1 was included in the paint as component A (Experimental Examples 5-10, 24), or when component B of the paint was replaced with component B1 (Ba) that belonged to component B1 but had an average particle size outside the specified range (Bb) (Experimental Example 6), one or more of the film characteristics, optical characteristics, and film physical properties could not be satisfied. Even when component A1 was included in the paint as component A (Experimental Examples 5-10, 24), or when component B of the paint was replaced with component B1 (Ba) that belonged to component B1 and had an average particle size within the specified range (Bc-Bf), one or more of the film characteristics, optical characteristics, and film physical properties could not be satisfied. Even when the B component of the coating material contained a B1 component (Ba) having an average particle size within a predetermined range (Experimental Examples 5, 11 to 16), when the mass ratio of the B component to the A component in the coating material was less than 7 (Experimental Example 11) or more than 14 (Experimental Example 16), one or more of the film characteristics, optical characteristics, and film physical properties could not be satisfied.

[0133] As shown in Table 2, when the paint contained component A1 as component A, and the paint's component B included a particle (Ba) belonging to component B1 and having an average particle size within a predetermined range, and the mass ratio of component B to component A in the paint was 7 to 14 (Experimental Examples 5a, 12a to 15a), all of the paint's properties and film properties were satisfactory. In contrast, even when the paint contained component A1 as component A (Experimental Examples 5a to 10a, 24a), when the paint's component B included a particle (Bb) belonging to component B1 but having an average particle size outside the predetermined range instead of a particle (Ba) belonging to component B1 and having an average particle size within the predetermined range, one or more of the film properties, optical properties, and physical properties could not be satisfied. Even when component A1 was included in the paint as component A (Experimental Examples 5a to 10a, 24a), or when components not belonging to component B1 (Bc to Bf) were included in component B of the paint instead of components belonging to component B1 and having an average particle size within a predetermined range (Experimental Examples 7a to 10a, 24a), one or more of the film characteristics, optical properties, and film physical properties could not be satisfied.Even when component B of the paint contained components belonging to component B1 and having an average particle size within a predetermined range (Ba) (Experimental Examples 5a, 11a to 16a), one or more of the film characteristics, optical properties, and film physical properties could not be satisfied when the mass ratio of component B to component A in the paint was less than 7 (Experimental Example 11a) or more than 14 (Experimental Example 16a).

[0134] As shown in Table 3, when the amount of component A was fixed and the type of component A1 included in component A was changed (Experimental Examples 5, 17 to 20), it was also confirmed that the film strength (scratch resistance 1, 2) improved as the molecular weight and glass transition temperature increased.

[0135] [Experimental Example 21] A paint was prepared with the same composition as in Experimental Example 5, except that Ba (i.e., a compound belonging to the B1 component and having an average particle size within a predetermined range) was used as the black pigment and resin composite (B1 component) included as the black material (B component), and black acrylic beads (average particle size 5 to 6 μm), which are spherical acrylic resin particles encapsulating CB like Ba but have a slightly larger average particle size, were used. A film was then formed in the same manner as above and evaluated in the same manner, and it was confirmed that the same evaluation as in Experimental Example 5 was obtained.

[0136] [Experimental Example 22] A coating material was prepared with the same composition as in Experimental Example 5, except that the content of polyvinyl acetal resin (component A1) relative to the total amount (100 mass%) of binder resin (component A) was 90 mass%, and the remaining 10 mass% was an acrylic resin (molecular weight of 10,000 or more, Tg of 30°C or more) that belongs to component A but does not belong to component A1. A film was then formed in the same manner as above, and the same evaluation was carried out, confirming that the same evaluation as in Experimental Example 5 was obtained.

[0137] [Experimental Example 23] A paint was prepared with the same composition as in Experimental Example 5, except that the content of Ba (i.e., Ba belonging to component B1 and having an average particle size within a predetermined range) relative to the total amount (100% by mass) of the black material (component B) was set to 90% by mass, and the remaining 10% by mass was black acrylic beads (average particle size 0.5 to 1.5 μm) belonging to component B1 but having an average particle size outside the predetermined range. A film was then formed in the same manner as above, and the same evaluation was carried out, confirming that the same evaluation as in Experimental Example 5 was obtained.

Claims

1. An electronic device casing having an anti-reflection coating on the casing body, the anti-reflection coating being formed from a resin composition and containing at least component A and component B, component A containing component A1, component B containing component B1 having an average particle size of 2 μm or more and 6 μm or less, and the mass ratio of component B to component A being 7 or more and 14 or less. (Component A) Binder resin (Component A1) Polyvinyl acetal resin (Component B) Black material (Component B1) Composite of black pigment and resin 2. The electronic device casing according to claim 1, wherein the anti-reflection film has a thickness in the range of 2 μm to 40 μm.

3. An electronic device casing according to claim 1 or 2, wherein the outermost surface on which the film is formed has a glossiness of less than 1% for incident light at an incident angle of 60°, a glossiness of less than 10% for incident light at an incident angle of 85°, a reflectance of less than 1.5% for light with a wavelength of 550 nm, an L value of less than 15 in the CIELAB color system according to the SCE method, and an optical density of 2 or more.

4. An anti-reflection film formed on the housing of an electronic device, which is formed from a resin composition and contains at least component A and component B, where component A contains component A1, component B contains component B1 having an average particle size of 2 μm or more and 6 μm or less, and the mass ratio of component B to component A is 7 or more and 14 or less. (Component A) Binder resin (Component A1) Polyvinyl acetal resin (Component B) Black material (Component B1) Composite of black pigment and resin 5. A method for producing an electronic device casing according to claim 1, comprising disposing a resin composition containing at least components A, B and C, wherein component A includes component A1, component B includes component B1 having an average particle size of 2 μm or more and 6 μm or less, the mass ratio of component B to component A being 7 or more and 14 or less, and the viscosity at 25°C measured with a Brookfield viscometer being adjusted to 1 mPa·s or more and 2000 mPa·s or less, on a casing body, and removing component C by drying to form an anti-reflection film containing at least components A and B. (Component C) Dilution solvent 6. A method for manufacturing an electronic device casing according to claim 5, comprising applying a resin composition, the viscosity of which is adjusted to 1 mPa·s or more and 50 mPa·s or less at 25°C as measured by a Brookfield viscometer, by a spray coating method to form an anti-reflection film on the casing body.

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