Anti-fog paint

Abstract

To provide an antifogging coating which enables formation of a coated film that is excellent in antifogging property, moisture resistance, waterproof trace property and appearance.SOLUTION: An antifogging coating contains a resin component (A) which contains a resin component (A) having a constitutional unit based on a specific (meth)acrylamide-based monomer, and a constitutional unit based on at least one hydrophobic monomer selected from the group consisting of a (meth)acrylate monomer having a hydrocarbon group and a styrenic monomer, and amorphous silica (B) having an average primary particle diameter of 60 nm or less, wherein a ratio of the constitutional unit based on the (meth)acrylamide-based monomer with respect to the total constitutional units constituting the resin component (A) is 30-75 mass%, and a ratio of the amorphous silica (B) with respect to the total of the resin component (A) and the amorphous silica (B) is 74-87 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an anti-fog coating. [Background technology]

[0002] Vehicle lighting fixtures, such as automobile headlamps, generally include lenses made of transparent materials. In such vehicle lighting fixtures, high-humidity air can enter the lamp chamber, causing the lens to cool due to external air or rainfall, resulting in condensation of water on the inner surface, resulting in fogging. In particular, when transparent resins such as polycarbonate resins are used as the transparent material, the highly hydrophobic nature of the surface makes the fogging described above more likely to occur. Therefore, a known method for suppressing the occurrence of such fogging involves applying an anti-fog coating to the areas where fogging is likely to occur, forming a coating film.

[0003] Patent Document 1 proposes an anti-fog coating containing a resin for anti-fog coating obtained by living radical polymerization of a polymerizable monomer mixture containing an acrylamide monomer having no hydroxyl groups or alkoxy groups and an acrylamide monomer having either or both of a hydroxyl group and an alkoxy group. This anti-fog coating is said to be capable of forming a coating film with excellent anti-fog properties and water-mark resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-26669 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the coating film formed from the anti-fog coating material of Patent Document 1 may not have sufficient anti-fog properties, moisture resistance, or water drip resistance. An object of the present invention is to provide an anti-fog coating material capable of forming a coating film that is excellent in anti-fog properties, moisture resistance, water drip resistance and appearance. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A polymer composition comprising: a resin component (A) having a structural unit based on a (meth)acrylamide-based monomer represented by the following formula (a) and a structural unit based on at least one hydrophobic monomer selected from the group consisting of a (meth)acrylate monomer having a hydrocarbon group and a styrene-based monomer; and amorphous silica (B) having an average primary particle diameter of 60 nm or less, the proportion of structural units based on the (meth)acrylamide monomer to all structural units constituting the resin component (A) is 30 to 75 mass %, An anti-fog coating material, wherein the proportion of the amorphous silica (B) relative to the total of the resin component (A) and the amorphous silica (B) is 74 to 87 mass %. CH2=CH-CO-NR 1 R 2 (a) where R 1 and R 2 are each independently a hydrogen atom or an alkyl group, or R 1 and R 2 and bond together with N to form a nitrogen-containing heterocyclic group. [2] The anti-fog coating material according to [1] above, wherein the proportion of structural units based on the hydrophobic monomer relative to all structural units constituting the resin component (A) is 25 to 70 mass %. [3] The anti-fog coating material according to [1] or [2] above, wherein the molecular weight dispersity of the resin component (A) is 3.0 or less. [Effects of the Invention]

[0007] The anti-fog coating material of the present invention can form a coating film that is excellent in anti-fog properties, moisture resistance, water drip resistance and appearance. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the present invention, "(meth)acrylic" means acrylic or methacrylic. "(meth)acrylate" means acrylate or methacrylate. "(meth)acrylamide" means acrylamide or methacrylamide. The weight average molecular weight (hereinafter also referred to as "Mw"), number average molecular weight (hereinafter also referred to as "Mn"), and molecular weight dispersity (hereinafter also referred to as "Mw / Mn"), which is the ratio of Mw to Mn, of the resin component (A) are each values ​​calculated in terms of polystyrene measured by gel permeation chromatography (GPC). The average primary particle size of amorphous silica is determined by the BET method. Hereinafter, the average primary particle size will also be referred to simply as "primary particle size." "Water drip marks" refers to streak-like marks that remain on a coating film when water droplets run down the surface of the coating film and the coating film subsequently dries. "Water drip resistance" means that water drips do not easily leave marks.

[0009] [Anti-fog paint] An anti-fog coating according to one embodiment of the present invention comprises a resin component (A) and amorphous silica (B). The anti-fog coating may further contain a liquid medium, if necessary. The anti-fog coating may, if necessary, further contain other components in addition to the resin component (A), amorphous silica (B) and liquid medium, provided that the properties are not impaired.

[0010] <Resin component (A)> Resin component (A) has a structural unit (hereinafter also referred to as "monomer (a) unit") based on a (meth)acrylamide-based monomer (hereinafter also referred to as "monomer (a)") represented by the following formula (a), and a structural unit (hereinafter also referred to as "monomer (b) unit") based on at least one hydrophobic monomer (hereinafter also referred to as "monomer (b)") selected from the group consisting of (meth)acrylate monomers having a hydrocarbon group and styrene-based monomers: CH2=CH-CO-NR 1 R 2 (a) where R1 and R 2 are each independently a hydrogen atom or an alkyl group, or R 1 and R 2 and bond together with N to form a nitrogen-containing heterocyclic group.

[0011] When the resin component (A) contains the monomer (a) unit, the resin component (A) becomes hydrophilic, and the coating film formed exhibits anti-fogging properties. In the above formula (a), R 1 and R 2 The alkyl group in may be linear or branched. From the viewpoint of anti-fogging properties, the number of carbon atoms in the alkyl group is preferably 1 to 6, and more preferably 1 to 4. R 1 and R 2 Examples of the nitrogen-containing heterocyclic group formed by bonding with N include morpholino and pyrrolidino.

[0012] Examples of the monomer (a) include acrylamide, dimethylacrylamide, isopropylacrylamide, diethylacrylamide, acryloylmorpholine, N-dodecylacrylamide, etc. These monomers may be used alone or in combination of two or more.

[0013] When the resin component (A) contains the monomer (b) unit, the resin component (A) is prevented from becoming excessively hydrophilic, and the moisture resistance is improved. Among the monomers (b), examples of the hydrocarbon group in the (meth)acrylate monomer having a hydrocarbon group include an alkyl group, an alicyclic hydrocarbon group, and an aromatic group. The alkyl group may be linear or branched. The alkyl group preferably has 1 to 18 carbon atoms, more preferably 1 to 4 carbon atoms. The alicyclic hydrocarbon group may be monocyclic or polycyclic. The alicyclic hydrocarbon group has, for example, 5 to 10 carbon atoms. Examples of the aromatic group include aryl groups such as a phenyl group, and aralkyl groups such as a benzyl group.

[0014] Examples of (meth)acrylate monomers having a hydrocarbon group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Examples of styrene-based monomers include styrene, methylstyrene, dimethylstyrene, ethylstyrene, α-methylstyrene, and α-ethylstyrene. These monomers may be used alone or in combination of two or more.

[0015] The resin component (A) may further contain structural units based on monomers other than the monomers (a) and (b) to the extent that the properties are not impaired. The other monomer may be any monomer that is copolymerizable with the monomer (a) and the monomer (b), and examples thereof include a monomer having at least one functional group selected from the group consisting of monomers containing functional groups such as a hydroxyl group, an alkoxy group, a carboxy group, and an amide group (excluding the monomer (a)) (hereinafter referred to as "monomer (c)"). The alkoxy group is preferably an alkoxy group having 1 to 4 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, and an iso-butoxy group.

[0016] Examples of the monomer (c) include hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and N-methylol (meth)acrylamide; alkoxy group-containing monomers such as N-(methoxymethyl) (meth)acrylamide, N-(hydroxymethyl) (meth)acrylamide, N-(2-hydroxyethyl) (meth)acrylamide, N-(ethoxymethyl) (meth)acrylamide, N-(butoxymethyl) (meth)acrylamide, and N-(isobutoxymethyl) (meth)acrylamide; carboxy group-containing monomers such as (meth)acrylic acid, itaconic acid, crotonic acid, and carboxyethyl acrylate; and amide group-containing monomers such as (meth)acrylamide. These monomers may be used alone or in combination of two or more.

[0017] As the other monomer, a reactive ultraviolet absorber or a reactive surfactant may be used. Examples of reactive ultraviolet absorbers include RUVA-93 manufactured by Otsuka Chemical Co., Ltd. Examples of reactive surfactants include Latemul manufactured by Kao Corporation, Adeka Reasoap manufactured by ADEKA Corporation, Aqualon manufactured by Daiichi Kogyo Co., Ltd., styrene-based ammonium styrenesulfonate, and sodium styrenesulfonate.

[0018] The proportion of monomer (a) units relative to all structural units constituting resin component (A) is 30 to 75 mass%, preferably 40 to 60 mass%. When the proportion of monomer (a) units is at least the lower limit, the coating film has excellent anti-fogging properties, and when it is at most the upper limit, the coating film has excellent water mark resistance and moisture resistance.

[0019] The proportion of monomer (b) units relative to all structural units constituting resin component (A) is 70 mass% or less, preferably 25 to 70 mass%, more preferably 25 to 55 mass%. If the proportion of monomer (b) units is at least the above lower limit, the coating film will have better water mark resistance and moisture resistance, and if it is at most the above upper limit, the coating film will have better anti-fogging properties.

[0020] The total proportion of monomer (a) units and monomer (b) units to all structural units constituting resin component (A) is preferably 60 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and may be 100 mass%.

[0021] The Mw of the resin component (A) is preferably from 30,000 to 200,000, and more preferably from 50,000 to 150,000. If the Mw is at least the lower limit, the water mark resistance tends to be better, and if it is at most the upper limit, the coating workability, film-forming properties, and adhesion to substrates of the coating film tend to be better.

[0022] The Mw / Mn of resin component (A) is preferably 3.0 or less, more preferably 2.5 or less. There is no particular restriction on the lower limit of Mw / Mn, but it is, for example, 1.1. When the Mw / Mn of resin component (A) is equal to or less than the above upper limit, the viscosity of the anti-fog coating can be sufficiently reduced, even though the proportion of amorphous silica (B) relative to the total of resin component (A) and amorphous silica (B) is as high as 75 mass% or more, and coating workability is improved.

[0023] Resin component (A) can be produced by polymerizing a monomer mixture containing monomer (a) and monomer (b). The monomer mixture may further contain other monomers.

[0024] The proportion of monomer (a) relative to the total mass of the monomer mixture is 30 to 75 mass%, preferably 40 to 60 mass%. When the proportion of monomer (a) is equal to or greater than the above lower limit, the coating film has excellent anti-fogging properties, and when it is equal to or less than the above upper limit, the coating film has excellent water mark resistance and moisture resistance.

[0025] The proportion of monomer (b) relative to the total mass of the monomer mixture is 70 mass% or less, preferably 25 to 70 mass%, more preferably 25 to 55 mass%. When the proportion of monomer (b) is at least the lower limit, the coating film has better water mark resistance and moisture resistance, and when it is at most the upper limit, the coating film has better anti-fogging properties.

[0026] The total proportion of the monomer (a) and the monomer (b) relative to the total mass of the monomer mixture is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

[0027] The polymerization of the monomer mixture can be carried out by a known method. As a method for polymerizing the monomer mixture, living polymerization is preferred, since it allows the Mw / Mn of the resulting resin component (A) to be easily adjusted to 2.5 or less. Living polymerization includes living cationic polymerization, living anionic polymerization, living radical polymerization, etc. Living radical polymerization includes reversible addition-fragmentation chain transfer polymerization (RAFT polymerization), atom transfer radical polymerization (ATRP polymerization), radical polymerization with nitroxide (NMP polymerization), etc.

[0028] The RAFT polymerization of a monomer mixture will be described in more detail below. In RAFT polymerization, a monomer mixture is polymerized in the presence of a polymerization initiator using a chain transfer agent (hereinafter, the chain transfer agent used in RAFT polymerization is also referred to as a "RAFT agent").

[0029] The polymerization initiator used in RAFT polymerization is not particularly limited, and any initiator capable of initiating radical polymerization may be used. Examples of such polymerization initiators include peroxide-based polymerization initiators and azo-based polymerization initiators, such as 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and dimethyl-2,2'-azobis(2-methylpropionate). These polymerization initiators may be used alone or in combination of two or more.

[0030] The RAFT agent is not particularly limited, and known RAFT agents can be used. Examples include thiocarbonylthio compounds such as dithioesters, trithiocarbonates, dithiocarbamates, and xanthates. Among these, dithioesters and trithiocarbonates are preferred. Specific examples include 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid and 2-[(dodecylsulfanylthiocarbonyl)sulfanyl]propanoic acid. These RAFT agents may be used alone or in combination.

[0031] The polymerization method in RAFT polymerization is not particularly limited, and known methods can be used, such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. The solvent (polymerization solvent) used during polymerization is also not particularly limited, and known solvents can be used. The polymerization conditions are also not particularly limited, and examples include conditions of 40 to 100°C for 2 to 24 hours. Thereafter, the reaction is stopped by cooling or the like, to obtain resin component (A). In RAFT polymerization, the molecular weight of the resulting resin depends on the concentration of the RAFT agent, not the concentration of the polymerization initiator.

[0032] <Amorphous Silica (B)> The primary particle size of the amorphous silica (B) is 60 nm or less, preferably 40 nm or less, and more preferably 20 nm or less. The lower limit of the primary particle size is not particularly limited, but is, for example, 5 nm. If the primary particle size of the amorphous silica (B) is the above upper limit or less, the coating film will have excellent antifogging properties and transparency.

[0033] The surface state of the amorphous silica (B) may be silanol type, anionic type, cationic type, etc. The surface state of the amorphous silica (B) may be any of the above types, but the anionic type is preferred from the viewpoint of exhibiting particularly good anti-fogging properties.

[0034] <Liquid medium> The liquid medium is used to dissolve or disperse the resin component (A) and disperse the amorphous silica (B). Examples of liquid media include water and organic solvents. Examples of organic solvents include alcohol-based solvents such as methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and isobutanol; glycol-based solvents such as dibutyl glycol, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate; cellosolve-based solvents such as butyl cellosolve; ester-based solvents such as ethyl acetate and butyl acetate; ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and diacetone alcohol. These organic solvents may be used alone or in combination of two or more. Of the above, water, alcohol-based solvents, and glycol-based solvents are preferred as the liquid medium. Water and alcohol-based solvents dissolve the resin component (A) well. Glycol-based solvents improve the film-forming properties of the coating film.

[0035] <Other ingredients> Other components include various known additives, such as surface conditioners, coupling agents, acid catalysts, ultraviolet absorbers, surfactants, and the like. Examples of the surface conditioner include polyether-modified polydimethylsiloxane, polyether-modified polymethylalkylsiloxane, and polyether-modified polysiloxane. Examples of the coupling agent include an aluminum-based coupling agent, a titanate-based coupling agent, and a silane coupling agent. Examples of the acid catalyst include paratoluenesulfonic acid, dinonylnaphthalenemonosulfonic acid, dinonylnaphthalenedisulfonic acid, and alkylphosphoric acid.

[0036] In the anti-fog coating, the proportion of amorphous silica (B) relative to the total of resin component (A) and amorphous silica (B) is 74 to 87 mass%, preferably 75 to 85 mass%. If the proportion of amorphous silica (B) is at least the above lower limit, the coating film will have excellent anti-fog properties and water-stain resistance, and if it is at most the above upper limit, the coating film will be less likely to crack.

[0037] The total content of the resin component (A) and the amorphous silica (B) is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass, relative to 100% by mass of the nonvolatile content of the anti-fog coating material. The non-volatile content of an anti-fog paint is the sum of all components other than the liquid medium (resin component (A), amorphous silica (B), and other components).

[0038] The nonvolatile content of the anti-fog coating can be appropriately set taking into consideration the coating method of the anti-fog coating, and can be, for example, 3 to 20% by mass relative to the total mass of the anti-fog coating.

[0039] The anti-fog coating material can be prepared, for example, by mixing a solution or dispersion of the resin component (A) with a dispersion of amorphous silica (B), and in this case, other components or additional liquid media may be mixed in as necessary. As the dispersion of amorphous silica (B), colloidal silica is preferred. The dispersion of amorphous silica (B) can be a commercially available product, such as the "Quattron PL" series from Fuso Chemical Industries, Ltd. or the "Snowtex" series from Nissan Chemical Industries, Ltd.

[0040] Anti-fog paints are used to impart anti-fog properties to any substrate. Anti-fog properties are imparted by applying the anti-fog paint to the surface of the substrate to form a coating film (anti-fog coating film). The material of the substrate is not particularly limited, and examples thereof include resins such as polycarbonate and polymethyl methacrylate, glass, etc. Transparent resins such as polycarbonate and polymethyl methacrylate are preferred because they are highly hydrophobic and therefore prone to fogging due to condensation, and imparting anti-fogging properties is highly effective. The anti-fog coating can be applied by any known coating method such as dipping, spraying, roller coating or flow coating. The applied anti-fog coating is thermally cured to form a coating film. There are no particular restrictions on the thermal curing conditions, but examples include conditions of 60 to 150°C for 5 to 60 minutes. There are no particular limitations on the thickness of the coating film that is formed (thickness after curing), but it can be, for example, 0.5 to 8 μm. [Example]

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, "parts" means "parts by mass."

[0042] The symbols used below represent the following compounds. DMAA: dimethylacrylamide. iPAA: isopropylacrylamide. MMA: methyl methacrylate. St: styrene. ABN-E: 2,2'-azobis(2-methylbutyronitrile), manufactured by Japan Finechem Co., Ltd. RAFT-1: A compound represented by formula (1) described in the examples of JP 2019-26669 A. IPA: 2-propanol. PL-1D: Fuso Chemical Industries' "Quartolone PL-1-D", colloidal silica in which amorphous silica is dispersed in a dispersing medium (water), amorphous silica concentration 20% by mass, surface state: anionic type, primary particle diameter 15 nm. ST-OS: Nissan Chemical Industries' "Snowtex OS", colloidal silica in which amorphous silica is dispersed in a dispersing medium (water), amorphous silica concentration 20% by mass, surface state: anionic type, primary particle diameter 9 nm. ST-YL: Nissan Chemical Industries' "Snowtex YL", colloidal silica in which amorphous silica is dispersed in a dispersing medium (water), amorphous silica concentration 40% by mass, surface state: anionic type, primary particle diameter 60 nm. ST-ZL: Nissan Chemical Industries' "Snowtex ZL", colloidal silica in which amorphous silica is dispersed in a dispersing medium (water), amorphous silica concentration 40% by mass, surface condition: anionic type, primary particle diameter 80 nm.

[0043] <Manufacturing example A-1> 70 parts of iPAA, 30 parts of MMA, 0.3 parts of RAFT-1, 0.18 parts of ABN-E, 100 parts of ethyl acetate, and 30 parts of methanol were placed in a two-neck flask, and the flask was heated to 70°C while being purged with nitrogen gas. A polymerization reaction was carried out for 10 hours with stirring to obtain a solution of Resin A-1 (non-volatile content approximately 40% by mass).

[0044] <Manufacturing examples A-2~A-7> Solutions of Resins A-2 to A-7 (non-volatile content: approximately 40% by mass each) were obtained in the same manner as in Production Example A-1, except that the materials placed in the flask were changed according to the formulations shown in Table 1.

[0045] The polymerization rate (%) in each production example (non-volatile content of the obtained resin solution / theoretical non-volatile content of the resin solution × 100) was calculated by the formula: non-volatile content (%) of the obtained resin solution / theoretical non-volatile content (%) of the resin solution × 100. The results are shown in Table 1. Here, the "non-volatile content of the obtained resin solution" (actual measured value) was calculated as the ratio of the mass after heating to the mass before heating when approximately 1 g of the resin solution was taken and heated at 135°C for 60 minutes. The "theoretical non-volatile content of the resin solution" was calculated by (total amount of monomer (parts) + amount of RAFT agent (parts) + amount of polymerization initiator (parts)) / total amount charged (parts) × 100.

[0046] Furthermore, the polystyrene-equivalent number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight dispersity (Mw / Mn) of the resins (A-1 to A-7) contained in the resin solutions obtained in each Production Example were determined by gel permeation chromatography (GPC). The GPC measurement conditions were as follows. Mw and Mw / Mn are shown in Table 1. GPC apparatus: GPC-101 (manufactured by Shoko Tsusho Co., Ltd.). Column: Shodex A-806M × 2 connected in series (Showa Denko K.K.). Detector: Shodex RI-71 (Showa Denko K.K.). Mobile phase: tetrahydrofuran. Flow rate: 1mL / min.

[0047] [Table 1]

[0048] Example 1 A container was charged with 8.2 parts of PL-1D in terms of amorphous silica, 1.5 parts of a solution of resin A-2 in terms of nonvolatile matter, and 90.3 parts of a liquid medium, and the mixture was stirred using a Chemistirer (manufactured by Tokyo Rikakikai Co., Ltd.) to obtain an anti-fog coating material.

[0049] <Examples 2 to 12 and Comparative Examples 1 to 6> Anti-fog coating materials were obtained in the same manner as in Example 1, except that the materials placed in the container were changed according to the formulations shown in Tables 2 and 3. The liquid medium columns in Tables 2 and 3 show the total composition of the dispersion medium for colloidal silica (PL-1D, etc.), the solvent for the resin solution, and the liquid medium blended when preparing the anti-fog coating.

[0050] <Evaluation> For the anti-fog paints obtained in each example, test materials were prepared according to the following procedure, and the paintability, initial appearance, anti-fog properties, and water drip resistance were evaluated. The results are shown in Tables 2 and 3.

[0051] (Preparation of test materials) The anti-fog paint was sprayed onto the surface of a polycarbonate plate so that the thickness after drying was 3 μm, and the plate was dried by heating at 120° C. for 15 minutes to form a coating. The resulting coated polycarbonate plate was used as the test material.

[0052] (Painting workability) The test pieces thus prepared were visually inspected for the presence or absence of swelling (sagging) at the bottom end of the coating film, and the coating workability was evaluated according to the following criteria. ○: No sauce. △: There is sauce.

[0053] (initial appearance) The prepared test materials were visually inspected for transparency of the coating film and the occurrence of cracks, and the initial appearance was evaluated according to the following criteria. ◯: The coating film is transparent and no cracks are observed. Δa: Cracks are observed at the edge of the coating film. △b: The transparency of the coating film is slightly low. ×a: Cracks are observed over the entire surface of the coating film. ×b: The coating film is opaque.

[0054] (Anti-fogging) The prepared test material was placed upright so that water droplets would run off the coating surface, and steam at 40°C was applied to the coating for 3 minutes. The appearance of the coating was then visually observed and the anti-fogging properties were evaluated according to the following criteria. ○: The coating film does not become cloudy during steaming. △: The coating becomes cloudy during steaming, but the cloudiness disappears within 5 seconds after the steam is stopped. ×: The coating film becomes cloudy during steaming, and the cloudiness does not disappear even after 5 seconds have passed since the steam was stopped.

[0055] (Water-resistant) After applying steam to the test pieces to evaluate the anti-fogging properties, the test pieces were left to dry for 12 hours in an environment with a temperature of 25±2°C and a humidity of 55±5%RH. The appearance of the dried coating was visually observed, and the water mark resistance was evaluated according to the following criteria. ○: No traces of water dripping on the coating film. ×: There are traces of water dripping on the coating film.

[0056] (moisture resistance) The test material was left in an environment of 65°C and 95% RH for 10 days, after which the appearance of the coating film was visually observed and the moisture resistance was evaluated according to the following criteria. ○: No change in the appearance of the coating film. △: Slight changes such as whitening were observed in the coating film. ×: The coating film was whitened or dissolved.

[0057] [Table 2]

[0058] [Table 3]

[0059] Coating films with good appearance, anti-fogging properties, and moisture resistance were formed using the anti-fog coatings of Examples 1 to 12. The anti-fog coatings of Examples 1 to 8 and 10 to 12, in which the Mw / Mn of the resin component was 2.5 or less, also had excellent coating workability. On the other hand, the coating film of the anti-fog coating of Comparative Example 1, in which the proportion of amorphous silica relative to the total of the resin component and amorphous silica was more than 87 mass %, had cracks all over its surface and was poor in appearance. The coating films of the anti-fog coatings of Comparative Examples 2 and 6, in which the primary particle size of the amorphous silica exceeded 60 nm, were opaque and had poor appearance. The coating film of the anti-fog coating material of Comparative Example 3, in which the proportion of monomer (a) units relative to all structural units constituting the resin component was less than 30 mass %, was poor in anti-fog properties. The coating film of the anti-fog coating material of Comparative Example 4, in which the proportion of amorphous silica to the total of the resin component and amorphous silica was less than 74 mass %, was poor in anti-fog properties and water mark resistance. The coating film of the anti-fog coating of Comparative Example 5, in which the proportion of monomer (a) units relative to all structural units constituting the resin component was more than 75 mass %, was poor in water mark resistance and water resistance. [Industrial Applicability]

[0060] By applying the anti-fog coating material of the present invention to a substrate, a coating film that is excellent in anti-fog properties, moisture resistance, water drip resistance and appearance can be formed. Substrates having a coating film of the anti-fog coating of the present invention formed thereon can be used for, for example, vehicle lighting fixtures such as automobile headlamps, meter covers for motorcycles, and visor covers for helmets.

Claims

1. An anti-fog coating material for a vehicle lamp, a meter cover, or a visor cover, comprising: a resin component (A) having a structural unit based on a (meth)acrylamide-based monomer represented by the following formula (a) and a structural unit based on at least one hydrophobic monomer selected from the group consisting of a (meth)acrylate monomer having a hydrocarbon group and a styrene-based monomer; and amorphous silica (B) having an average primary particle diameter of 60 nm or less: the proportion of structural units based on the (meth)acrylamide monomer relative to all structural units constituting the resin component (A) is 30 to 75 mass %, a ratio of the amorphous silica (B) to the total of the resin component (A) and the amorphous silica (B) is 74 to 87 mass%, The anti-fog coating material, wherein the total content of the resin component (A) and the amorphous silica (B) is 90% by mass or more relative to 100% by mass of the non-volatile content of the anti-fog coating material. Here, the nonvolatile content of the anti-fog coating is the total of the components other than the liquid medium. CH ２ =CH-CO-NR １ R ２ ・・・(a) Here, R １ and R ２ are each independently a hydrogen atom or an alkyl group, or R １ and R ２ and bond together with N to form a nitrogen-containing heterocyclic group.

2. 2. The anti-fog coating according to claim 1, wherein the proportion of structural units based on the hydrophobic monomer relative to all structural units constituting the resin component (A) is 25 to 70 mass %.

3. 3. The anti-fog coating material according to claim 1, wherein the molecular weight dispersity of the resin component (A) is 3.0 or less.

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