Anti-fog coating

Abstract

An anti-fog coating according to one embodiment of the present invention comprises a resin component (A) and amorphous silica (B) having an average primary particle size of 60 nm or less, wherein the resin component (A) has a CH2=CH-CO-NR 1 R 2 The present invention comprises a structural unit of a (meth)acrylamide monomer represented by , 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, wherein the ratio of the structural unit based on the (meth)acrylamide monomer to all structural units constituting the resin component (A) is 30 to 75% by mass, and the ratio of the amorphous silica (B) to the total of the resin component (A) and the amorphous silica (B) is 74 to 87% by mass. 1 and R 2 are independently a hydrogen atom or an alkyl group, or R 1 With R 2 Bonded to form a nitrogen-containing heterocyclic group together with N.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2021-025146 filed in Japan on February 19, 2021, and uses the contents thereof herein. Background Art

[0003] A lens made of a transparent material is usually provided on a vehicle lamp such as a car headlight. In such a vehicle lamp, high-humidity air enters the lamp chamber, and the lens is cooled by the outside air or rainfall, and moisture condenses on the inner surface, thereby causing fogging. In particular, when a transparent resin such as a polycarbonate resin is used as a transparent material, fogging as described above is likely to occur due to the high hydrophobicity of the surface. Therefore, a method of applying an anti-fog coating to a portion where fogging occurs to provide a coating film is known in order to suppress such fogging.

[0004] Patent Document 1 proposes an antifogging coating comprising an antifouling coating resin obtained by active radical polymerization of a polymerizable monomer mixture, wherein the polymerizable monomer mixture comprises an acrylamide monomer having no hydroxyl group and no alkoxy group and an acrylamide monomer having either or both of a hydroxyl group and an alkoxy group. The antifogging coating can form a coating film having excellent antifogging properties and water drip resistance.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-26669 Summary of the invention

[0008] Technical Problems to be Solved by the Invention

[0009] However, the coating film formed by the anti-fog coating material of Patent Document 1 may have insufficient anti-fog property, moisture resistance, and water drip resistance.

[0010] An object of the present invention is to provide an anti-fog coating material capable of forming a coating film having excellent anti-fog properties, moisture resistance, water drip resistance and appearance.

[0011] Technical means to solve technical problems

[0012] The present invention has the following aspects.

[0013] (1) An anti-fog coating comprising a resin component (A) and amorphous silica (B) having an average primary particle size of 60 nm or less, wherein the resin component (A) has a structural unit based on a (meth)acrylamide 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 monomer,

[0014] The ratio of the structural unit based on the (meth)acrylamide monomer to the total structural units constituting the resin component (A) is 30 to 75% by mass.

[0015] The ratio of the amorphous silica (B) to the total of the resin component (A) and the amorphous silica (B) is 74 to 87% by mass.

[0016] CH2=CH-CO-NR 1 R 2 …(a),

[0017] In formula (a), R 1 and R 2 are independently a hydrogen atom or an alkyl group, or R 1 With R 2 Bonded to form a nitrogen-containing heterocyclic group together with N.

[0018] (2) The anti-fog coating according to (1) above, wherein the ratio of the structural unit based on the hydrophobic monomer to the total structural units constituting the resin component (A) is 25 to 70% by mass.

[0019] (3) The anti-fog coating according to (1) or (2), wherein the molecular weight dispersion of the resin component (A) is 3.0 or less.

[0020] Effects of the Invention

[0021] According to the anti-fog coating of the present invention, a coating film excellent in anti-fog property, moisture resistance, water dripping resistance and appearance can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The cross-sectional schematic diagram shows an example of a substrate with a coating film in which a coating film of an anti-fog coating material is formed on the surface of the substrate.

[0023] Figure 2 The cross-sectional schematic diagram shows another example of a substrate with a coating film in which a coating film of an anti-fog coating material is formed on the surface of the substrate.

[0024] Figure 3 The cross-sectional schematic diagram shows still another example of a substrate with a coating film in which a coating film of an anti-fog coating material is formed on the surface of the substrate. DETAILED DESCRIPTION

[0025] In the present invention, "(meth)acrylic acid" means acrylic acid or methacrylic acid. "(Meth)acrylate" means acrylate or methacrylate. "(Meth)acrylamide" means acrylamide or methacrylamide.

[0026] The weight average molecular weight (hereinafter referred to as "Mw"), number average molecular weight (hereinafter referred to as "Mn"), and molecular weight dispersion which is the ratio of Mw to Mn (hereinafter referred to as "Mw / Mn") of the resin component (A) are polystyrene conversion values ​​measured by gel permeation chromatography (hereinafter referred to as "GPC").

[0027] The average primary particle size of amorphous silica is determined by the BET method. That is, it is calculated from the specific surface area measured by the BET method. Hereinafter, the average primary particle size is simply referred to as “primary particle size”.

[0028] "Drip marks" refer to the streak-like marks left on the coating film when water drops slide down the coating film surface and then the coating film dries.

[0029] The "water dripping mark resistance" refers to the degree to which water dripping marks are unlikely to remain.

[0030] [Anti-fog coating]

[0031] An anti-fog coating according to one embodiment of the present invention comprises a resin component (A) and amorphous silica (B).

[0032] The anti-fog coating may further contain a liquid medium as required.

[0033] If necessary, the anti-fog coating may further contain other components in addition to the resin component (A), the amorphous silica (B) and the liquid medium within a range that does not impair the properties.

[0034] <Resin component (A)>

[0035] The resin component (A) has a structural unit (hereinafter referred to as "monomer (a) unit") based on a (meth)acrylamide monomer (hereinafter referred to as "monomer (a)") represented by the following formula (a) and a structural unit (hereinafter referred to as "monomer (b) unit") based on at least one hydrophobic monomer (hereinafter referred to as "monomer (b)") selected from the group consisting of a (meth)acrylate monomer having a hydrocarbon group and a styrene-based monomer.

[0036] CH2=CH-CO-NR 1 R 2 …(a)

[0037] In formula (a), R 1 and R2 are independently a hydrogen atom or an alkyl group, or R 1 With R 2 Bonded to form a nitrogen-containing heterocyclic group together with N.

[0038] When the resin component (A) has the monomer (a) unit, the resin component (A) becomes hydrophilic, and the formed coating film exhibits antifogging properties.

[0039] In the above formula (a), R 1 and R 2 The alkyl group in may be linear or branched. From the viewpoint of antifogging properties, the number of carbon atoms in the alkyl group is preferably 1 to 6, more preferably 1 to 4.

[0040] As R 1 With R 2 Examples of the nitrogen-containing heterocyclic group formed by bonding with N include a morpholino group and a pyrrolizino group.

[0041] 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.

[0042] When the resin component (A) has the monomer (b) unit, it is possible to suppress the resin component (A) from becoming excessively hydrophilic, thereby improving moisture resistance.

[0043] In monomer (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 number of carbon atoms in the alkyl group is preferably 1 to 18, more preferably 1 to 4. The alicyclic hydrocarbon group may be monocyclic or polycyclic. The number of carbon atoms in the alicyclic hydrocarbon group is, for example, 5 to 10. Examples of the aromatic group include aryl groups such as phenyl and aralkyl groups such as benzyl.

[0044] Examples of the (meth)acrylate monomer having a hydrocarbon group include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearic (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

[0045] Examples of the styrene-based monomer include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, dimethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, α-methylstyrene, α-ethylstyrene, and the like.

[0046] These monomers may be used alone or in combination of two or more.

[0047] The resin component (A) may further have a structural unit based on a monomer other than the monomer (a) and the monomer (b) within a range that does not impair the properties.

[0048] As other monomers, any monomer that can copolymerize with monomer (a) and monomer (b) may be used, for example, monomers having functional groups (excluding monomer (a)) (hereinafter referred to as "monomer (c)"). As functional groups in monomer (c), hydroxyl groups, alkoxy groups, carboxyl groups, amide groups, etc. may be listed. As alkoxy groups, alkoxy groups having 1 to 4 carbon atoms are preferred, for example, methoxy groups, ethoxy groups, n-propoxy groups, n-butoxy groups, isobutoxy groups, etc. may be listed. The functional groups possessed by monomer (c) may be one type or two or more types.

[0049] Examples of monomer (c) include hydroxyl-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and N-methylol (meth)acrylamide; alkoxy-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; carboxyl-containing monomers such as (meth)acrylic acid, itaconic acid, crotonic acid, and carboxyethyl acrylate; amide-containing monomers such as (meth)acrylamide, etc. These monomers may be used alone or in combination of two or more.

[0050] As other monomers, a reactive ultraviolet absorber or a reactive surfactant may be used.

[0051] Examples of reactive ultraviolet absorbers include RUVA-93 from Otsuka Chemical Co., Ltd. Examples of reactive surfactants include LATEMUL from Kao Corporation, ADEKA REASOAP from ADEKA CORPORATION, AQUALON from DKS Co. Ltd., and styrene-based ammonium styrene sulfonate and sodium styrene sulfonate.

[0052] The ratio of the monomer (a) unit to the total structural units (100% by mass) constituting the resin component (A) is 30 to 75% by mass, preferably 40 to 60% by mass, and more preferably 45 to 60% by mass. If the ratio of the monomer (a) unit is above the above lower limit, the anti-fogging property of the coating film is excellent, and if it is below the above upper limit, the water drip resistance and moisture resistance of the coating film are excellent.

[0053] The ratio of the monomer (b) unit to the total structural units (100% by mass) constituting the resin component (A) is 70% by mass or less, preferably 25 to 70% by mass, more preferably 25 to 60% by mass, and further preferably 25 to 55% by mass. If the ratio of the monomer (b) unit is above the above lower limit, the coating film has better resistance to dripping marks and moisture resistance, and if it is below the above upper limit, the coating film has better anti-fogging properties.

[0054] The ratio of the total of the monomer (a) unit and the monomer (b) unit to the total structural units (100% by mass) constituting the resin component (A) is preferably 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and may be 100% by mass.

[0055] The Mw of the resin component (A) is preferably 30,000 to 200,000, more preferably 50,000 to 150,000. When the Mw is at least the lower limit, the water drip resistance tends to be more excellent, and when it is at most the upper limit, the coating workability, film-forming property, and adhesion to the substrate of the coating film tend to be more excellent.

[0056] The Mw / Mn of the resin component (A) is preferably 3.0 or less, more preferably 2.5 or less. The lower limit of Mw / Mn is not particularly limited, for example, 1.1. If the Mw / Mn of the resin component (A) is below the above upper limit, the ratio of amorphous silica (B) to the total of the resin component (A) and amorphous silica (B) is as high as 75% by mass or more, and the viscosity of the anti-fog coating can be fully reduced, and the coating operability is good.

[0057] The resin component (A) can be prepared by polymerizing a monomer mixture containing the monomer (a) and the monomer (b). The monomer mixture may further contain other monomers.

[0058] The ratio of monomer (a) to the total mass of the monomer mixture is 30 to 75 mass %, preferably 40 to 60 mass %, and more preferably 45 to 60 mass %. If the ratio of monomer (a) is above the above lower limit, the anti-fogging property of the coating film is excellent, and if it is below the above upper limit, the water drip resistance and moisture resistance of the coating film are excellent.

[0059] The ratio of monomer (b) to the total mass of the monomer mixture is 70% by mass or less, preferably 25 to 70% by mass, more preferably 25 to 60% by mass, and further preferably 25 to 55% by mass. If the ratio of monomer (b) is above the above lower limit, the coating film has better resistance to dripping marks and moisture resistance, and if it is below the above upper limit, the coating film has better anti-fogging properties.

[0060] The ratio of the total amount of the monomer (a) and the monomer (b) to the total mass of the monomer mixture is preferably 60 mass % or more, more preferably 80 mass % or more, further preferably 90 mass % or more, and may be 100 mass %.

[0061] The polymerization of the monomer mixture can be carried out by a known method.

[0062] As a method for polymerizing the monomer mixture, living polymerization is preferred because the Mw / Mn of the obtained resin component (A) can be easily adjusted to 2.5 or less.

[0063] Examples of living polymerization include living cationic polymerization, living anionic polymerization, and living radical polymerization. Examples of living radical polymerization include reversible addition fragmentation chain transfer polymerization (RAFT polymerization), atom transfer radical polymerization (ATRP polymerization), and nitroxide stabilized radical polymerization (NMP polymerization).

[0064] Hereinafter, the case of subjecting the monomer mixture to RAFT polymerization will be described in more detail.

[0065] 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 referred to as “RAFT agent”).

[0066] The polymerization initiator used for RAFT polymerization is not particularly limited, and any polymerization initiator can be used as long as it can initiate free radical polymerization. As such a polymerization initiator, a peroxide polymerization initiator, an azo polymerization initiator, etc. are generally used, for example, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl azobisisobutyrate, etc. can be listed. Any one of these polymerization initiators can be used alone, or two or more can be used simultaneously.

[0067] As RAFT agent, there is no particular limitation, and known RAFT agents can be used. For example, thiocarbonylsulfide compounds such as dithioesters, trithiocarbonates, dithiocarbamates, and xanthates can be listed. Among them, dithioesters and trithiocarbonates are preferred. As specific examples, 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid, 2-[(dodecylsulfanylthiocarbonyl)sulfanyl]propionic acid, etc. can be listed. Any one of these RAFT agents can be used alone, or two or more can be used simultaneously.

[0068] The polymerization method in RAFT polymerization is not particularly limited, and a known method can be used, for example, solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, etc. There is no particular limitation on the solvent (polymerization solvent) used during the polymerization, and a known solvent can be used. The polymerization conditions are also not particularly limited, and for example, conditions at 40 to 100° C. for 2 to 24 hours can be cited. Thereafter, the reaction is stopped by cooling, etc., to obtain the resin component (A).

[0069] In addition, in RAFT polymerization, the molecular weight of the obtained resin depends on the concentration of the RAFT agent, but does not depend on the concentration of the polymerization initiator.

[0070] <Amorphous silicon dioxide (B)>

[0071] The primary particle size of 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, for example, 5 nm. If the primary particle size of amorphous silica (B) is below the above upper limit, the anti-fogging property and transparency of the coating film are excellent.

[0072] The surface state of amorphous silica (B) includes silanol type, anionic type, cationic type, etc. The silanol type has a silanol group on the surface. The anionic type has an arbitrary anionic group on the surface. The cationic type has an arbitrary cationic group on the surface. The surface state of amorphous silica (B) can be any of the above types, and the anionic type is preferred from the perspective of showing particularly good anti-fogging properties.

[0073] <Liquid medium>

[0074] The liquid medium is used to dissolve or disperse the resin component (A) and disperse the amorphous silica (B).

[0075] Examples of the liquid medium include water and organic solvents. Examples of the organic solvent include alcohol solvents such as methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and isobutanol; glycol solvents such as ethylene glycol dibutyl ether, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate; cellosolve solvents such as butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and diacetone alcohol. Any one of these organic solvents may be used alone, or two or more thereof may be used simultaneously.

[0076] As the liquid medium, water, alcohol solvents, and glycol solvents are preferred among the above. Water and alcohol solvents can dissolve the resin component (A) well. Glycol solvents can improve the film-forming property of the coating film.

[0077] <Other ingredients>

[0078] Examples of other components include various known additives, such as a surface conditioner, a coupling agent, an acid catalyst, an ultraviolet absorber, and a surfactant.

[0079] Examples of the surface conditioner include polyether-modified polydimethylsiloxane, polyether-modified polymethylalkylsiloxane, and polyether-modified polysiloxane.

[0080] Examples of the coupling agent include aluminum coupling agents, titanate coupling agents, and silane coupling agents.

[0081] Examples of the acid catalyst include p-toluenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalene disulfonic acid, and alkylphosphoric acid.

[0082] In the anti-fog coating, the ratio of amorphous silica (B) to the total of the resin component (A) and the amorphous silica (B) is 74 to 87% by mass, preferably 75 to 85% by mass. If the ratio of amorphous silica (B) is above the above lower limit, the anti-fog property and water drip resistance of the coating film are excellent, and if it is below the above upper limit, cracks are not easily generated on the coating film.

[0083] 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 based on 100% by mass of the nonvolatile components of the anti-fog coating.

[0084] The nonvolatile component of the anti-fog coating is the total of the components (resin component (A), amorphous silica (B), and other components) excluding the liquid medium.

[0085] The concentration of the nonvolatile component of the antifog coating can be appropriately set in consideration of the coating method of the antifog coating, and can be set to, for example, 3 to 20% by mass relative to the total mass of the antifog coating.

[0086] The anti-fog coating can be prepared, for example, by mixing a solution or dispersion of the resin component (A) with a dispersion of amorphous silica (B). In this case, other components or additional liquid media may be mixed as needed.

[0087] As the dispersion liquid of amorphous silica (B), colloidal silica is preferred.

[0088] A commercially available product can be used as the dispersion liquid of amorphous silica (B). Examples of the commercially available product include "Quartron PL" series from FUSOCHEMICAL CO., LTD. and "SNOWTEX" series from Nissan Chemical Corporation.

[0089] The anti-fog coating can be used to impart anti-fog properties to any substrate. The anti-fog properties are imparted by coating the anti-fog coating on the surface of the substrate to form a coating film (anti-fog coating film).

[0090] Figure 1 1 shows an example of a substrate with a coating film having an anti-fog coating formed on the surface of the substrate. The substrate with a coating film 1 of this example includes a substrate 3 and a coating film 5 with an anti-fog coating formed on the surface of the substrate 3. In this example, the substrate 3 is in a flat plate shape, and the coating film 5 is formed on one surface thereof.

[0091] Figure 2 Another example of a substrate with a coating film having an anti-fog coating formed on the surface of the substrate is shown in FIG. The substrate with a coating film 1 of this example is different from the substrate 3 except that the shape of the substrate 3 is different. Figure 1 The same as the substrate 1 with coating film shown in . In this example, the surface of one side of the substrate 3 is concavely curved, and the surface of the other side is convexly curved. The coating film 5 is formed along the surface of one side of the substrate 3, and the surface of the coating film 5 is also concavely curved.

[0092] Figure 3 2 shows another example of a substrate with a coating film having an anti-fog coating formed on the surface of the substrate. The substrate with a coating film 1 of this example is different from the substrate 3 in shape. Figure 1 The same as the substrate 1 with coating film shown in . In this example, the surface of one side of the substrate 3 is convexly curved, and the surface of the other side is concavely curved. The coating film 5 is formed along the surface of one side of the substrate 3, and the surface of the coating film 5 is also convexly curved.

[0093] In addition, although Figures 1 to 3 2 shows an example in which the coating film 5 is formed on one surface of the substrate 3 , but the coating film 5 may be formed on both the one surface and the other surface of the substrate 3 .

[0094] The shape of the substrate 3 is not limited to the illustrated example, and may be other shapes.

[0095] The material of the substrate is not particularly limited, and examples thereof include resins such as polycarbonate and polymethyl methacrylate, glass, etc. Since the substrate is highly hydrophobic and easily fogged by condensation, transparent resins such as polycarbonate and polymethyl methacrylate are preferred from the perspective of high effectiveness in imparting anti-fogging properties.

[0096] As a coating method of the anti-fog coating, a known coating method such as a dipping method, a spraying method, a roll coating method, a flow coating method, etc. can be adopted.

[0097] After coating, the applied anti-fog coating may be thermally cured as required. The thermal curing conditions are not particularly limited, and examples thereof include conditions of 60 to 150° C. for 5 to 60 minutes.

[0098] The thickness of the formed coating film (thickness after curing) is not particularly limited, and can be, for example, 0.5 to 8 μm.

[0099] Example

[0100] Hereinafter, the present invention will be described in further detail using Examples, but the present invention is not limited thereto. Hereinafter, "parts" means "parts by mass".

[0101] Each abbreviation used below represents the following compound.

[0102] DMAA: dimethylacrylamide.

[0103] iPAA: isopropylacrylamide.

[0104] MMA: methyl methacrylate.

[0105] St: Styrene.

[0106] ABN-E: 2,2'-azobis(2-methylbutyronitrile), manufactured by Japan Finechem Inc.

[0107] RAFT-1: A compound represented by formula (1) described in Examples of JP-A-2019-26669.

[0108] IPA: 2-propanol.

[0109] PL-1D: "Quartron PL-1-D" produced by FUSO CHEMICAL CO., LTD., colloidal silica in which amorphous silica is dispersed in a dispersion medium (water), the amorphous silica concentration is 20% by mass, the surface state is anionic, and the primary particle size is 15 nm.

[0110] ST-OS: "SNOWTEX OS" manufactured by Nissan Chemical Corporation, colloidal silica in which amorphous silica is dispersed in a dispersion medium (water), amorphous silica concentration is 20% by mass, surface state: anionic, primary particle size is 9 nm.

[0111] ST-YL: "SNOWTEX YL" from Nissan Chemical Corporation, colloidal silica in which amorphous silica is dispersed in a dispersion medium (water), amorphous silica concentration is 40% by mass, surface state: anionic, primary particle size is 60 nm.

[0112] ST-ZL: "SNOWTEX ZL" from Nissan Chemical Corporation, colloidal silica in which amorphous silica is dispersed in a dispersion medium (water), amorphous silica concentration is 40% by mass, surface state: anionic, primary particle size is 80 nm.

[0113] <Preparation Example A-1>

[0114] Into a two-necked flask were added 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. The atmosphere in the flask was replaced with nitrogen and the temperature was raised to 70°C. A polymerization reaction was carried out under stirring for 10 hours to obtain a solution of resin A-1 (non-volatile content: approximately 40% by mass).

[0115] <Preparation Examples A-2 to A-7>

[0116] Except that the materials added to the flask were changed according to the ratio shown in Table 1, solutions of resins A-2 to A-7 (all containing about 40% by mass of nonvolatile components) were obtained in the same manner as in Preparation Example A-1.

[0117] The polymerization rate (%) in each preparation example was calculated by nonvolatile content (%) of the obtained resin solution / theoretical nonvolatile content (%) of the resin solution×100 (nonvolatile content of the obtained resin solution / theoretical nonvolatile content of the resin solution×100). The results are shown in Table 1.

[0118] The "non-volatile content of the obtained resin solution" (actually measured value) was obtained as the ratio of the mass after heating to the mass before heating when about 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 monomer amount (parts) + RAFT amount (parts) + polymerization initiator amount (parts)) / total added amount (parts) × 100.

[0119] In addition, for the resins (A-1 to A-7) contained in the resin solutions obtained in each preparation example, the number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight dispersion (Mw / Mn) in terms of polystyrene were determined by gel permeation chromatography (GPC). The measurement conditions of GPC are as follows. Mw and Mw / Mn are shown in Table 1.

[0120] GPC apparatus: GPC-101 (manufactured by SHOKO CO., LTD.).

[0121] Chromatographic column: Shodex A-806M×2 connected in series (manufactured by Showa Denko KK).

[0122] Detector: Shodex RI-71 (manufactured by Showa Denko KK).

[0123] Mobile phase: tetrahydrofuran.

[0124] Flow rate: 1 mL / min.

[0125] [Table 1]

[0126]

[0127] <Example 1>

[0128] 8.2 parts of PL-1D calculated as amorphous silica, 1.5 parts of a solution of resin A-2 calculated as non-volatile components, and 90.3 parts of a liquid medium were added to a container, and stirred using a pressure-proof explosion-proof stirrer (ケミスターラー) (manufactured by TOKYO RIKAKIKAI CO., LTD.) to obtain an anti-fog coating.

[0129] <Examples 2 to 12, Comparative Examples 1 to 6>

[0130] An anti-fog coating was obtained in the same manner as in Example 1 except that the materials added to the container were changed according to the ratios shown in Tables 2 to 3.

[0131] In the column of liquid medium in Tables 2 and 3, the compositions of the dispersion medium of colloidal silica (PL-1D, etc.), the solvent of the resin solution, and the entire liquid medium blended when preparing the anti-fog coating are shown.

[0132] <Evaluation>

[0133] For the anti-fog coating obtained in each example, a test sample was prepared according to the following procedure, and the coating workability, initial appearance, anti-fog property, and water dripping mark resistance were evaluated. The results are shown in Tables 2 and 3.

[0134] (Preparation of test samples)

[0135] The anti-fog coating was applied on the surface of the polycarbonate plate by spraying so as to have a thickness of 3 μm after drying, and then dried by heating at 120° C. for 15 minutes to form a coating film. The obtained polycarbonate plate with the coating film was used as a test sample.

[0136] (Coating workability)

[0137] The prepared test samples were visually observed to see if there was a bulge (sagging) at the lower end of the coating film, and the coating workability was evaluated based on the following criteria.

[0138] G: No sagging.

[0139] P: There is sagging.

[0140] (Initial appearance)

[0141] The transparency and crack generation state of the coating film of the prepared test sample were observed with the naked eye, and the initial appearance was evaluated according to the following criteria.

[0142] G: The coating film was transparent and no cracks were observed.

[0143] Pc: Cracks were observed at the edge of the coating film.

[0144] Pt: The transparency of the coating film is slightly low.

[0145] VPc: Cracks were observed over the entire surface of the coating film.

[0146] VPt: The coating film is opaque.

[0147] (Anti-fog)

[0148] The prepared test sample was stood up to allow water drops to slide down the coating surface, and the coating was exposed to 40° C. steam for 3 minutes. The appearance of the coating was observed with the naked eye, and the antifogging property was evaluated according to the following criteria.

[0149] G: The coating film does not fog in steam.

[0150] P: Although the coating film was fogged in the steam, the fog disappeared within 5 seconds after the steam was stopped.

[0151] VP: The coating film was fogged in the steam, and the fogging did not disappear even after 5 seconds had passed after the steam was stopped.

[0152] (Water drip resistance)

[0153] The test sample exposed to steam in the anti-fogging evaluation was placed in an environment of 25±2°C and 55±5%RH for 12 hours to dry the coating film. The appearance of the dried coating film was observed visually, and the water drip resistance was evaluated according to the following criteria.

[0154] G: There is no trace of water dripping on the coating film.

[0155] VP: There are traces of water dripping on the coating film.

[0156] (moisture resistance)

[0157] The test sample was left to stand in an environment of 65° C. and 95% RH for 10 days. Then, the appearance of the coating film was observed with the naked eye, and the moisture resistance was evaluated according to the following criteria.

[0158] G: There is no change in the appearance of the coating film.

[0159] P: A slight change such as whitening of the coating film was observed.

[0160] VP: The coating film turns white or dissolves.

[0161]

[0162]

[0163] The antifog coatings of Examples 1 to 12 can form coating films having good appearance, antifogging properties, water drip resistance and moisture resistance. The antifog coatings of Examples 1 to 8 and 10 to 12 having a resin component Mw / Mn of 2.5 or less also have excellent coating workability.

[0164] On the other hand, the anti-fog coating of Comparative Example 1, in which the ratio of amorphous silica to the total of the resin component and amorphous silica was greater than 87% by mass, had cracks on the entire surface of the coating film and had a poor appearance.

[0165] The anti-fog coatings of Comparative Examples 2 and 6, in which the primary particle size of the amorphous silica was larger than 60 nm, had opaque coating films and poor appearance.

[0166] The anti-fog coating of Comparative Example 3, in which the ratio of the monomer (a) unit to the total structural units constituting the resin component was less than 30% by mass, had poor anti-fog properties in the coating film.

[0167] The anti-fog coating of Comparative Example 4, in which the ratio of amorphous silica to the total of the resin component and amorphous silica was less than 74% by mass, had poor anti-fog properties and water dripping mark resistance in the coating film.

[0168] The anti-fog coating of Comparative Example 5, in which the ratio of the monomer (a) unit to all structural units constituting the resin component was greater than 75% by mass, had poor water drip resistance and moisture resistance.

[0169] Industrial Applicability

[0170] By applying the anti-fog coating of the present invention on a substrate, a coating film having excellent anti-fog properties, moisture resistance, water drip resistance and appearance can be formed.

[0171] The substrate on which the coating film of the antifog coating of the present invention is formed can be used, for example, for vehicle lamps such as automobile headlights, instrument covers of motorcycles, helmets, and the like.

[0172] Description of Reference Numerals

[0173] 1: substrate with coating; 3: substrate; 5: coating of anti-fog coating.

Claims

1. An anti-fog coating, comprising a resin component (A), amorphous silica (B) having an average primary particle size of 60 nm or less, and a liquid medium for dissolving the resin component (A), wherein the resin component (A) is composed of a structural unit based on a (meth)acrylamide 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 monomer, or is composed of a structural unit based on the (meth)acrylamide monomer, a structural unit based on the hydrophobic monomer, and a structural unit based on other monomers, wherein the other monomer is at least one selected from the group consisting of hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, N-methylol (meth)acrylamide, N-(methoxymethyl) (meth)acrylamide, N-(hydroxymethyl) (meth)acrylamide, N-(2-hydroxyethyl) (meth)acrylamide, N-(ethoxymethyl) (meth)acrylamide, N-(butoxymethyl) (meth)acrylamide, N-(isobutoxymethyl) (meth)acrylamide, (meth)acrylic acid, itaconic acid, crotonic acid, carboxyethyl acrylate, (meth)acrylamide, a reactive ultraviolet absorber, and a reactive surfactant, The ratio of the structural unit based on the (meth)acrylamide monomer to the total structural units constituting the resin component (A) is 30 to 75% by mass. The ratio of the amorphous silica (B) to the total of the resin component (A) and the amorphous silica (B) is 74 to 87% by mass. CH2=CH-CO-NR 1 R 2 …(a), In formula (a), R 1 and R 2 are independently a hydrogen atom or an alkyl group, or R 1 With R 2 Bonded to form a nitrogen-containing heterocyclic group together with N.

2. The anti-fog coating according to claim 1, wherein: The ratio of the structural unit based on the said hydrophobic monomer with respect to the total structural units which comprise the said resin component (A) is 25-70 mass %.

3. The anti-fog coating according to claim 1 or 2, wherein: The molecular weight dispersion of the resin component (A) is 3.0 or less.

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