Clear coating composition and method for repairing concrete structures

Abstract

To provide a clear coating composition which enables provision of a coating film that is excellent in storage stability, sagging resistance and dryness, and has excellent load resistance, and a method for repairing a concrete structure.SOLUTION: A clear coating composition for aerosol product contains a non-reactive acrylic resin, a reactive component, a tin catalyst, and an organic solvent, wherein the reactive component contains at least one of hexamethylene diisocyanate and a derivative thereof, the organic solvent contains a first organic solvent having relative evaporation speed when evaporation speed of n-butyl acetate at 20°C is 100 of 180 or more, the content of the non-volatile content of the reactive component is 55 pts.mass or more and 96 pts.mass or less with respect to 100 pts.mass of the non-volatile content of the clear coating composition, the content of the non-volatile content of the non-reactive acrylic resin is 4 pts.mass or more and 45 pts.mass or less with respect to 100 pts.mass of the non-volatile content of the clear coating composition, and the content of the first organic solvent is 20 pts.mass or more and 50 pts.mass or less with respect to 100 pts.mass of the clear coating composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a clear coating composition and a method for repairing a concrete structure. [Background technology]

[0002] One of the causes of deterioration of concrete structures is corrosion of the reinforcing bars used to reinforce the concrete. Corrosion causes the volume of the reinforcing bars to expand, which can lead to the paint peeling off the surface of the concrete structure and the formation of cracks in the concrete structure.

[0003] Patent Document 1 teaches a resin composition containing an aromatic amine resin and an isocyanate resin. According to Patent Document 1, by applying this resin composition to the surface of a concrete structure, the peeling of concrete pieces can be prevented. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-144401 Summary of the Invention [Problem to be solved by the invention]

[0005] Paints are used to repair large concrete structures such as bridges, highway sidewalls, and tunnels. These paints must be able to cover cracks and / or exposed rebar in concrete structures, form a coating thick enough to prevent rainwater from penetrating into the structure, and have excellent sagging resistance and drying properties. Additionally, the resulting coating must have the ability to prevent concrete spalling due to external vibrations, impacts, and aging (high load-bearing capacity).

[0006] One-component paints containing moisture-curing isocyanate resins are easy to work with because they do not require mixing of the base resin and curing agent. However, the curing reaction of these one-component paints is easily accelerated by the moisture in the air, and they have poorer storage stability than two-component curing reaction urethane paints.

[0007] The present invention has been made in view of the above, and aims to provide a clear coating composition and a method for repairing concrete structures, which is a one-component coating material with high coating workability, has excellent storage stability, sagging resistance, and drying properties, and can produce a coating film with excellent load resistance. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides the following aspects. [1] A clear coating composition for use in an aerosol product, comprising: a non-reactive acrylic resin; A reactive component; a tin catalyst; an organic solvent, the reactive component includes at least one of hexamethylene diisocyanate and its derivatives, the organic solvent includes a first organic solvent having a relative evaporation rate of 180 or more when the evaporation rate of n-butyl acetate at 20°C is set to 100; The content of the nonvolatile content of the reactive component is 55 parts by mass or more and 96 parts by mass or less per 100 parts by mass of the nonvolatile content of the clear coating composition, The content of the nonvolatile content of the non-reactive acrylic resin is 4 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the nonvolatile content of the clear coating composition, A clear coating composition, wherein the content of the first organic solvent is 20 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the clear coating composition. [2] The clear coating composition according to [1] above, wherein the content of the tin catalyst is 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component. [3] A method for repairing a concrete structure, comprising spraying the clear coating composition according to [1] or [2] above onto the concrete structure. [Effects of the Invention]

[0009] According to the present invention, there are provided a clear coating composition which has excellent storage stability, sagging resistance and drying properties, and which can give a coating film having excellent load resistance, and a method for repairing concrete structures. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Clear paint composition] The clear coating composition according to this embodiment is a one-component type and is used in aerosol products. Aerosol products have a mechanism that can release a liquid from a hole (stem hole). The target liquid is released from the container in a spray form, for example, by the force of gas sealed in the container together with the target liquid. The clear coating composition according to this embodiment corresponds to this target liquid.

[0011] The clear coating composition according to this embodiment forms a clear coating film on the surface of a concrete structure. The "clear coating film" need only be transparent enough to allow the state or object on one side to be visible through the clear coating film from the other side, but does not need to be transparent enough to allow the other side to be clearly recognized. The clear coating film may be colorless or colored. For example, the visible light transmittance of the clear coating film is 80% or more, and may be 90% or more. The visible light transmittance (total light transmittance in the visible region) can be measured by a method conforming to JIS K 7361-1.

[0012] Aerosol paints allow paint to be applied easily over a wide area and do not require any additional tools, improving paint workability. However, the stem hole is prone to clogging. This clogging occurs, for example, when the paint viscosity increases due to a curing reaction that progresses inside the container during storage.

[0013] In this embodiment, a non-reactive acrylic resin is used that has low or almost no reactivity with isocyanate compounds. By incorporating a non-reactive acrylic resin, the increase in viscosity of the coating composition during storage is suppressed. Therefore, clogging of the stem hole is suppressed. The property of the coating composition, such as viscosity, remaining stable during storage, is called storage stability.

[0014] Furthermore, because an appropriate amount of organic solvent with a high evaporation rate is used, the organic solvent begins to volatilize immediately when the coating composition is released from the container. Therefore, the non-reactive acrylic resin can quickly form a film after being applied to the substrate. In other words, the non-reactive acrylic resin behaves like a lacquer paint. Therefore, the clear coating composition of this embodiment has excellent drying properties and is resistant to sagging. The property of a clear coating composition that is resistant to sagging when applied is called excellent sagging resistance. Since concrete structures have various shapes and often have inclined or even vertical surfaces, a clear coating composition with excellent sagging resistance further improves painting workability.

[0015] Sagging resistance can be evaluated, for example, using a sag tester or a wet film thickness meter as described in the Steel Highway Bridge Corrosion Prevention Handbook (March 2014, Japan Road Association, Public Interest Incorporated Association). Specifically, a painted glass plate is immediately placed upright and the wet film thickness limit at which the coating film does not sag is measured. The higher the limit film thickness, the better the sagging resistance can be evaluated.

[0016] Since it is difficult to achieve load-bearing properties using only non-reactive acrylic resins, reactive components are also used. The reactive components include at least one of hexamethylene diisocyanate (HDI) and its derivatives. HDI and its derivatives crosslink upon reaction with moisture in the air or on the substrate, forming a highly tough cured product. This gives the resulting coating film load-bearing properties. By using a non-reactive acrylic resin and a reactive component together, both sagging resistance and load-bearing properties are achieved.

[0017] The curing reaction of the above-mentioned HDI and its derivatives is unlikely to occur in a sealed container. Therefore, by using the clear coating composition of this embodiment in an aerosol product, storage stability is further improved. In other words, an aerosol product using the clear coating composition of this embodiment has excellent storage stability despite containing reactive components.

[0018] The clear coating composition according to this embodiment further contains a tin catalyst, which accelerates the curing reaction of HDI and its derivatives, improving drying properties (especially dryness to the touch) and sagging resistance.

[0019] The clear coating composition for aerosol products according to this embodiment is a one-component type, yet has excellent storage stability, and can be used even when stored at high temperatures for a long period of time (for example, 3 months at 50°C). Furthermore, this clear coating composition has excellent drying properties and sagging resistance. In addition, the resulting coating film has excellent load resistance.

[0020] The clear coating composition according to this embodiment can easily repair concrete bridges, highway sidewalls, tunnels, and the like. For example, the clear coating composition according to this embodiment can be used for emergency repair of weak spots discovered during inspection. The resulting coating film has excellent load-bearing properties, preventing concrete deterioration and concrete fragments from peeling off. Furthermore, because the formed coating film is clear, the condition of the concrete structure itself can be visually observed through the coating film.

[0021] The load-bearing capacity of the coating is evaluated using a push-out test in accordance with Section 16.2 of the Paint Specifications section of the Metropolitan Expressway Co., Ltd.'s Bridge Painting Guidelines (October 2021 edition). Specifically, the test is conducted as follows: A 100mm diameter hole is drilled vertically into the center of a concrete slab measuring 300mm long x 200mm wide x 60mm thick, or 300mm long x 300mm wide x 60mm thick, leaving a 5mm hole at the bottom (within a tolerance of ±1mm) using a concrete core cutter (also known as "core drilling").

[0022] A 200mm x 200mm coating is applied to the surface of the concrete slab opposite the surface where the core cutter was applied, facing the cored area, and then dried to form a coating film (wet film thickness 250μm to 350μm). The sample is placed, coated side down, on a test table that can support the periphery of the sample. The cored area is clamped on both sides with a spherical seat or the like, and a uniform load is applied vertically to the center to perform a push-out test. The push-out test is carried out at a loading rate of 1mm / min until the core breaks. When the core breaks, it is observed whether the coating film has broken or not. If the core breaks but the coating film has not, it can be evaluated as having excellent load-bearing properties.

[0023] The viscosity η of the clear coating composition measured by the flow cup method at 23°C is, for example, 25 seconds or more. This can improve sagging resistance. The viscosity η is that of the clear coating composition immediately after preparation, for example, that of a clear coating composition that does not contain a propellant. The viscosity η may be 45 seconds or less. The viscosity η may be 30 seconds or more. The viscosity η may be 40 seconds or less. In one embodiment, the viscosity η is 25 seconds or more and 45 seconds or less. Because the clear coating composition has excellent storage stability, the viscosity of the clear coating composition can satisfy the above range even after long-term storage at high temperatures.

[0024] The viscosity of the clear coating composition is measured at 23°C using a No. 4 Ford cup in accordance with JIS K5600-2-2:1999, Section 3, Flow Cup Method. The viscosity is the average value of the viscosities of five different coating compositions with the same composition.

[0025] (Non-reactive acrylic resin) Non-reactive acrylic resins have low reactivity with isocyanate compounds (typically, HDI and its derivatives) or barely react with isocyanate compounds. In other words, non-reactive acrylic resins do not contain hydroxyl groups, carboxyl groups, or amino groups that react with isocyanate groups in their molecules, or contain them to such an extent that they cannot undergo a curing reaction with isocyanate compounds. Specifically, the hydroxyl value of non-reactive acrylic resins is 1 mgKOH / g or less, and may be 0 mgKOH / g. The acid value of non-reactive acrylic resins is 1 mgKOH / g or less, and may be 0 mgKOH / g.

[0026] Non-reactive acrylic resins can be obtained, for example, by polymerizing (meth)acrylic acid ester-based monomers (raw material monomers) that do not have hydroxyl groups, carboxyl groups, or amino groups. Examples of raw material monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth)acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and ethyl dimethacrylate. The above raw material monomers can be used alone or in combination of two or more.

[0027] Other polymerizable monomers may be used in addition to the above raw material monomers, such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, N-vinyl-2-pyrrolidone, acrylonitrile, and divinylbenzene.

[0028] The content of the non-volatile content of the non-reactive acrylic resin is 4 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the non-volatile content of the clear coating composition. This improves drying properties and sagging resistance. The content of the non-reactive acrylic resin may be 10 parts by mass or more, or 12 parts by mass or more, per 100 parts by mass of the non-volatile content of the clear coating composition. The content of the non-reactive acrylic resin may be 40 parts by mass or less, or 35 parts by mass or less, per 100 parts by mass of the non-volatile content of the clear coating composition.

[0029] The number average molecular weight of the non-reactive acrylic resin is not particularly limited. The number average molecular weight of the non-reactive acrylic resin may be, for example, 3,000 or more, or 5,000 or more. The number average molecular weight of the non-reactive acrylic resin may be 50,000 or less, or 30,000 or less. In one embodiment, the number average molecular weight of the non-reactive acrylic resin is 3,000 or more and 50,000 or less.

[0030] Number average molecular weight is determined by gel permeation chromatography (GPC) using polystyrene standard sample standards.

[0031] (Other non-reactive resins) The clear coating composition may further contain a non-reactive resin other than the acrylic resin. The hydroxyl value of the non-reactive resin is 1 mgKOH / g or less, and may be 0 mgKOH / g. The acid value of the non-reactive resin is 1 mgKOH / g or less, and may be 0 mgKOH / g.

[0032] Examples of non-reactive resins other than acrylic resins include urethane resins and epoxy resins. From the viewpoint of weather resistance, the content of other non-reactive resins may be, for example, 60 parts by mass or less per 100 parts by mass of the non-volatile content of the clear coating composition.

[0033] (reactive resin) The clear coating composition may further contain a reactive resin as long as the effects of the present invention are not impaired. The reactive resin can react with an isocyanate compound. The reactive resin has active hydrogen that reacts with an isocyanate group. The hydroxyl value of the reactive resin is, for example, more than 1 mgKOH / g. The acid value of the reactive resin is, for example, more than 1 mgKOH / g. Examples of the reactive resin include resins other than the above non-reactive acrylic resin and other non-reactive resins. Examples of the reactive resin include an acrylic resin having a hydroxyl value of more than 1 mgKOH / g, a polyester resin, and a polyol resin.

[0034] The content of the non-volatile matter of the reactive resin is, for example, 1 part by mass or less, 0.5 part by mass or less, and 0.1 part by mass or less with respect to 100 parts by mass of the non-volatile matter of the clear coating composition.

[0035] (Reactive component) The reactive component is a moisture-curing reaction type compound that reacts with moisture contained in the air or the object to be coated to crosslink. Thereby, a cured product with high toughness is formed, and high toughness is imparted to the coating film.

[0036] The content of the non-volatile matter of the reactive component (typically, HDI and / or its derivative) is 55 parts by mass or more and 96 parts by mass or less with respect to 100 parts by mass of the non-volatile matter of the clear coating composition. Thus, by blending a large amount of the reactive component, the load resistance of the coating film is improved. The content of the reactive component may be 60 parts by mass or more, and may be 65 parts by mass or more with respect to 100 parts by mass of the non-volatile matter of the clear coating composition. The content of the reactive component may be 92 parts by mass or less, and may be 85 parts by mass or less with respect to 100 parts by mass of the non-volatile matter of the clear coating composition.

[0037] <HDI and / or its derivative> The reactive component includes at least one of hexamethylene diisocyanate (HDI) and its derivatives, such as HDI polymers (biuret, nurate, adduct, and tetramer or higher prepolymers), copolymers of HDI with other isocyanates, and alcohol-modified versions of these.

[0038] The reactive component may include an HDI polymer. The reactive component may include an HDI polymer in which a portion of the isocyanate groups has been modified with an alcohol. The reactive component may include a copolymer of HDI and another isocyanate in which a portion of the isocyanate groups has been modified with an alcohol. The alcohol modification imparts further flexibility to the resulting coating film. Therefore, the load-bearing capacity may be further improved.

[0039] Other isocyanates that can be copolymerized include, for example, aliphatic diisocyanates such as tetramethylene diisocyanate, pentamethylene diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate, lysine diisocyanate, and trioxyethylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and norbornene diisocyanate; and aromatic polyisocyanates such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and metaxylylene diisocyanate.

[0040] The alcohol used for alcohol modification is not particularly limited. Examples of the alcohol include those having a hydrocarbon group with 4 to 16 carbon atoms and one or more hydroxy groups. The hydrocarbon group may be an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or may have an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear or branched. From the viewpoint of flexibility, the hydrocarbon group may be a linear or branched aliphatic hydrocarbon group. Similarly, the number of carbon atoms in the hydrocarbon group may be 6 or more, or 8 or more. The number of carbon atoms in the hydrocarbon group may be 12 or less, or 10 or less.

[0041] From the viewpoint of toughness, the mass proportion of HDI and / or its derivatives may be 80 mass% or more, 90 mass% or more, 95 mass% or more, or 100 mass% of the total mass of the reactive components.

[0042] <Other isocyanate compounds> The clear coating composition may contain isocyanates other than HDI and their derivatives (hereinafter referred to as "other isocyanate compounds") as reactive components. A portion of the HDI and / or its derivatives may be replaced with other isocyanate compounds.

[0043] The other isocyanate compounds include the above-mentioned other isocyanates that can be copolymerized and derivatives thereof.

[0044] <Other reactive ingredients> The clear coating composition may contain reactive components other than the isocyanate compound, such as silicone resins and oxazolidines.

[0045] From the viewpoint of load resistance, it is desirable that the content of other reactive components is small. The content of other reactive components may be 10 mass % or more, 5 mass % or more, or 3 mass % or more of the total mass of the reactive components.

[0046] (tin catalyst) Tin catalysts accelerate the curing reaction of isocyanate compounds such as HDI, improving drying and sagging properties.

[0047] The tin catalyst is an organic catalyst containing tin. Examples of the organic tin catalyst include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. The organic tin catalyst may be dibutyltin dilaurate.

[0048] The content of the tin catalyst is, for example, 0.1 to 1 part by mass per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component. When the content of the tin catalyst is 0.1 parts by mass or more, drying properties are improved and sagging is easily suppressed. When the content of the tin catalyst is 1 part by mass or less, storage stability is less likely to decrease.

[0049] The content of the tin catalyst may be 0.12 parts by mass or more, or 0.15 parts by mass or more, per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component, and 0.95 parts by mass or less, or 0.90 parts by mass or less, per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component.

[0050] (Other catalysts) The clear coating composition may contain a curing catalyst other than the tin catalyst. Examples of other curing catalysts include bismuth compounds. Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, and bismuth carboxylate.

[0051] From the viewpoint of curability, the content of the other curing catalyst may be 0.5 parts by mass or less per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component.

[0052] (organic solvent) The organic solvent contains a first organic solvent having a relative evaporation rate (hereinafter simply referred to as relative evaporation rate) of 180 or more when the evaporation rate of n-butyl acetate at 20°C is set to 100. This improves sagging resistance and drying properties.

[0053] The relative evaporation rate at 20°C can be calculated using the following formula, based on the description in the book "Paint Flow and Pigment Dispersion" (Kyoritsu Publishing). Relative evaporation rate E=kpM (In the formula, k is 0.11, p is the vapor pressure (mmHg) of the organic solvent at 20°C, and M is the molecular weight of the organic solvent.)

[0054] The first organic solvent is not particularly limited as long as it has a relative evaporation rate of 180 or higher and does not react with isocyanate groups. Examples of the first organic solvent include hydrocarbon solvents such as n-hexane (1000), n-heptane (386), and methylcyclohexane (320); ester-based solvents such as methyl acetate (1182), ethyl acetate (615), and isopropyl acetate (500); ketone-based solvents such as acetone (1160) and methyl ethyl ketone (572); and aromatic solvents such as benzene (630) and toluene (240). The relative evaporation rate is indicated in parentheses. These solvents may be used alone or in combination of two or more. From the viewpoint of sagging resistance, ester-based solvents and aromatic solvents are preferred.

[0055] The content of the first organic solvent is 20 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the clear coating composition. This provides excellent storage stability and load resistance. The content of the first organic solvent may be 23 parts by mass or more, or 25 parts by mass or more per 100 parts by mass of the clear coating composition. The content of the first organic solvent may be 48 parts by mass or less, or 46 parts by mass or less per 100 parts by mass of the clear coating composition.

[0056] The clear coating composition may further contain a second organic solvent having a relative evaporation rate of less than 180, provided that the effects of the present invention are not impaired. The content of the second organic solvent is preferably less than 50 mass %, more preferably less than 40 mass %, of the total organic solvents. The content of the second organic solvent may be 5 mass % or more of the total organic solvents.

[0057] The second organic solvent is not particularly limited, and any organic solvent other than those mentioned above can be used. Typical examples include n-butyl acetate and xylene.

[0058] From the viewpoint of storage stability, it is desirable that the clear coating composition is substantially free of water. "Substantially free" means that the content is below the detection limit. For example, the water content is 0.1 parts by mass or less, and 0.05 parts by mass or less, per 100 parts by mass of the clear coating composition.

[0059] (others) The clear coating composition may contain additives that are typically added to coating compositions. Examples of additives include pigments, plasticizers, antioxidants, light stabilizers, UV absorbers, viscosity control agents, organic cosolvents, and surfactants. The clear coating composition may contain pigments to the extent that the transparency is not impaired. The type of pigment is not particularly limited, and pigments typically used in aerosol products can be used.

[0060] [Aerosol products] The clear coating composition according to this embodiment is suitable for aerosol products. The aerosol product includes, for example, a container containing the above-mentioned clear coating composition and propellant, a stem having a stem hole communicating with the container, a valve for opening and closing the stem hole, and an actuator having a nozzle that fits onto the stem.

[0061] Normally, the stem hole is blocked by a valve. When the actuator is pressed down, the stem moves down and the stem hole opens. This reduces the pressure inside the container, increasing the volume of the propellant. The clear coating composition is pushed up by the propellant, enters the stem through the stem hole, and is then sprayed out through the nozzle.

[0062] The form of ejection of the aerosol product is not particularly limited. For example, it may be a mist spray, a jet spray, a foam spray, or a gel spray. A mist spray is preferred because it can be sprayed uniformly over a wide area.

[0063] The shape, material, and size of the container, stem, valve, and actuator are not particularly limited, and in this embodiment, those that are normally used for aerosol products can be used.

[0064] (propellant) The type of propellant is not particularly limited. Propellants include those typically used in aerosol products. Propellants typically include liquefied gases and compressed gases. Liquefied gases include, for example, liquefied petroleum gas (LPG), dimethyl ether, and fluorocarbons (typically, alternatives to chlorofluorocarbons). LPG includes, for example, butane, propane, and mixtures thereof. Compressed gases include, for example, carbon dioxide, nitrogen, compressed air, oxygen, helium, and nitrous oxide. In terms of compatibility, the propellant may be dimethyl ether.

[0065] The amount of propellant is not particularly limited. From the viewpoint of coating workability, the mixing ratio (by mass) of the clear coating composition and the propellant: clear coating composition / propellant may be 60 / 40 to 30 / 70, or 55 / 45 to 65 / 35.

[0066] [Methods for repairing concrete structures] The clear coating composition according to this embodiment is suitable for repairing concrete structures. Repairing concrete structures is carried out by spraying the above-mentioned clear coating composition onto the concrete structure. As a result, a strong and uniform clear coating film is quickly formed on the surface of the concrete structure.

[0067] Repair of concrete structures can be carried out more easily by using the aerosol product according to this embodiment.

[0068] The amount of spraying of the clear coating composition is not particularly limited. The clear coating composition is sprayed, for example, so that the dry film thickness of the clear coating film is 300 μm or less. Even with such a thin film, excellent load resistance can be exhibited. The dry film thickness of the clear coating film may be 280 μm or less, or may be 250 μm or less. The dry film thickness of the clear coating film may be 150 μm or more. Even with such a film thickness, a uniform coating film is formed without sagging. The dry film thickness of the clear coating film may be 180 μm or more, or may be 200 μm or more. [Example]

[0069] The present invention will be described below with reference to examples, but the present invention is not limited to the examples described below.

[0070] (Production of non-reactive acrylic resin A1) A reaction vessel equipped with a stirrer, nitrogen inlet tube, temperature controller, condenser, and dropping funnel was charged with 75 parts of xylene and heated to 120°C while stirring under a nitrogen atmosphere. A monomer mixture of 50 parts of methyl methacrylate, 25 parts of 2-ethylhexyl acrylate, and 25 parts of n-butyl methacrylate was separately prepared. This monomer mixture was added dropwise to the reaction vessel over 3 hours along with an initiator solution prepared by dissolving 1 part of Kayaester O (manufactured by Kayaku Akzo Co., Ltd., tert-butylperoxy-2-ethylhexanate) in 20 parts of xylene. After the dropwise addition was completed, the mixture was maintained at 120°C for 0.5 hours, and then an initiator solution prepared by dissolving 0.5 parts of Kayaester O in 6 parts of xylene was added dropwise over 0.5 hours as a post-shot. The mixture was further stirred at 120°C for 1 hour to obtain acrylic resin A1. The non-volatile content of the obtained acrylic resin A1 was 50%.

[0071] The hydroxyl value and acid value of acrylic resin A1 calculated based on the nonvolatile content, calculated from the monomer composition, were 0 mgKOH / g and 0 mgKOH / g, respectively. The number average molecular weight of acrylic resin A1 was 10,000.

[0072] (Production of non-reactive acrylic resin A2) Acrylic resin A2 was obtained in the same manner as above, except that 57 parts of methyl methacrylate, 5 parts of styrene, 28 parts of n-butyl acrylate, and 10 parts of 2-ethylhexyl methacrylate were used as raw material monomers.

[0073] The hydroxyl value and acid value of acrylic resin A2 calculated based on the nonvolatile content, calculated from the monomer composition, were 0 mgKOH / g and 0 mgKOH / g, respectively. The number average molecular weight of acrylic resin A2 was 12,000.

[0074] (Production of reactive acrylic resin B1) Acrylic resin B1 was obtained in the same manner as above, except that 48.72 parts of methyl methacrylate, 25 parts of 2-ethylhexyl acrylate, 25 parts of n-butyl methacrylate, and 1.28 parts of acrylic acid were used as raw material monomers.

[0075] The hydroxyl value of the acrylic resin B1 calculated from the monomer composition was 0 mgKOH / g, the acid value was 10 mgKOH / g, and the number average molecular weight of the acrylic resin B1 was 10,000.

[0076] (Production of reactive acrylic resin B2) Acrylic resin B2 was obtained in the same manner as above, except that 47.68 parts of methyl methacrylate, 25 parts of 2-ethylhexyl acrylate, 25 parts of n-butyl methacrylate, and 2.32 parts of hydroxyethyl methacrylate were used as raw material monomers.

[0077] The hydroxyl value of acrylic resin B2 calculated from the monomer composition, calculated on a nonvolatile basis, was 10 mgKOH / g, the acid value was 0 mgKOH / g, and the number average molecular weight of acrylic resin B2 was 10,000.

[0078] (Production of Curing Agent 1) A four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube was charged with 500 parts by mass of HDI, 20 parts by mass of 2-octanol, 0.3 parts by mass of 2,6-di(tert-butyl)-4-methylphenol, and 0.52 parts by mass of tridecyl phosphite, and the mixture was reacted at 80 ° C. for 2 hours. The reaction mixture was then cooled to 45 ° C., and 0.05 parts by mass of N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate was added as an isocyanurate catalyst. The mixture was then reacted for 20 minutes, and then 0.12 parts by mass of o-toluenesulfonamide was added at 95 ° C. The resulting reaction mixture was passed through a thin-film distillation apparatus and distilled at a vacuum of 0.09 KPa and a temperature of 150 ° C., and unreacted HDI was removed. Thereafter, 0.02 parts by mass of o-toluenesulfonamide was added to 100 parts by mass of the obtained high-boiling-side composition (the residue after removing unreacted HDI) to obtain 100 parts by mass of curing agent 1, which is an HDI derivative.

[0079] (Production of hardener 2) A four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube was charged with 450 parts by mass of HDI, 150 parts by mass of isophorone diisocyanate, 25 parts by mass of 2-octanol, 0.3 parts by mass of 2,6-di(tert-butyl)-4-methylphenol, and 0.52 parts by mass of tridecyl phosphite, and in the same manner as for curing agent 1, 100 parts by mass of curing agent 2, which is a copolymer of HDI and isophorone diisocyanate, was obtained.

[0080] [Examples 1 to 12, Comparative Examples 1 to 8] (1) Preparation of clear coating composition Clear coating compositions were prepared by mixing and stirring acrylic resin, curing agent, tin catalyst, and organic solvent in the compositions shown in Tables 1 to 4. The masses of the curing agent and acrylic resin shown in Tables 1 to 4 are all non-volatile components.

[0081] (2) Preparation of aerosol products An aerosol product was prepared comprising a container, a stem, a valve, and an actuator. The container contained the clear coating composition prepared in each Example and Comparative Example and dimethyl ether in a mass ratio of 50 / 50.

[0082] (3) Painting on concrete panels The centre of a concrete slab measuring 300mm in height, 300mm in width and 60mm in thickness was cored vertically using a concrete core cutter with a diameter of 100mm, leaving 5mm (tolerance range ±1mm) at the bottom.

[0083] The prepared aerosol product was used to paint an area of ​​200 mm x 200 mm on the side of the concrete slab opposite to the side where the core cutter was applied, facing the cored area. The wet film thickness was 300 μm.

[0084] The painted concrete slab was then dried in accordance with JIS K 5600-1-1 (1999) 4.3.4 a) Room temperature drying. Specifically, the concrete slab was held horizontally with the painted surface facing upwards and dried under standard conditions of 23±2°C and 50±5% relative humidity.

[0085] [evaluation] The clear coating composition and the coated concrete plate were evaluated for the following performance characteristics. The evaluation results are shown in Tables 1 to 4.

[0086] (1) Load-bearing capacity Evaluation was performed using a push-out test in accordance with Section 16.2 of the Paint Specifications section of the Metropolitan Expressway Co., Ltd.'s Bridge Painting Guidelines (October 2021 edition). Specifically, the concrete slab prepared above was placed, painted side down, on a test bench capable of supporting the periphery. The cored area was clamped between spherical seats on both sides, and a uniform vertical load was applied to the center to perform the push-out test. The push-out test was performed at a loading rate of 1 mm / min until the core broke. When the core broke, it was evaluated whether the paint film had broken or not. The evaluation criteria are as follows: (Evaluation criteria) Good: The coating is not broken when the core is broken. Poor: The coating was broken when the core was destroyed.

[0087] (2)Drying property As described above, when drying was performed in accordance with JIS K 5600-1-1(:1999) 4.3.4 a) room temperature drying, the time until the coating film reached semi-hardened dryness in accordance with JIS K 5600-1-1(:1999) 4.3.5 b) was measured.

[0088] b) Semi-dry is the state where the center of the coating surface is gently rubbed with a fingertip and no scratches remain. If the time to semi-dry is within 24 hours, it can be said that the coating has drying properties suitable for practical use. If the time to semi-dry is within 16 hours, it can be said that the coating has good drying properties. If the time to semi-dry is within 24 hours, it also has excellent dryness to the touch. Dryness to the touch is specified in JIS K 5600-1-1(:1999)4.3.5 a) Dry to the touch, and refers to the state where the fingertip does not get dirty when lightly touched with the center of the coating surface.

[0089] (3) Storage stability The aerosol products were stored at 50°C for three months. The appearance and paintability of the aerosol products after storage were compared with those before storage. Paintability was evaluated by observing the amount of spray, the degree of scattering, and the degree of foaming. Good: No change in appearance or paintability was observed before and after storage. Acceptable: The amount of sprayed water decreases after storage, but the change before and after storage is not a problem for practical use. Defective: Cannot be aerosol painted after storage

[0090] (4) Sagging resistance The aerosol product was applied to a concrete plate, and the critical wet film thickness at which sagging occurs was evaluated using a wet film thickness meter (described on page II-91 of the Steel Highway Bridge Corrosion Prevention Handbook (March 2014, Japan Road Association, Public Interest Incorporated Association) under the environment of 4.2 of JIS K 5600-1-6 (:1999). The higher the critical wet film thickness, the higher the sagging resistance.

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] As shown in Tables 1 to 4, the clear coating compositions of Examples 1 to 12 have excellent storage stability and drying properties. Furthermore, the resulting coating films have excellent load resistance and are resistant to sagging.

[0096] On the other hand, as shown in Table 1, the clear coating composition of Comparative Example 1 has poor load resistance because it contains a small amount of curing agent (HDI derivative).The clear coating composition of Comparative Example 2 does not contain acrylic resin, so it is poor in drying properties, storage stability, and sagging resistance.

[0097] As shown in Table 2, the clear coating composition of Comparative Example 3, which did not contain the first organic solvent and contained only the second organic solvent, had poor storage stability. Conversely, the clear coating composition of Comparative Example 4, which contained an excess of the first organic solvent, had poor sagging resistance, and the resulting coating film had poor load resistance.

[0098] As shown in Table 3, the clear coating composition of Comparative Example 5 uses only a second organic solvent, and therefore has poor sagging resistance. Comparative Example 6 does not contain a tin catalyst, and therefore has poor drying properties and sagging resistance.

[0099] As shown in Table 4, Comparative Examples 7 and 8 have poor storage stability because they use a reactive acrylic resin. [Industrial Applicability]

[0100] The clear coating composition of the present invention is particularly suitable for repairing concrete structures because it has excellent storage stability, sagging resistance and drying properties, and can provide a coating film with excellent load resistance.

Claims

1. A clear coating composition for concrete structures used in an aerosol product, comprising: a non-reactive acrylic resin; A reactive component; a tin catalyst; an organic solvent, the reactive component includes at least one of hexamethylene diisocyanate and its derivatives, the organic solvent includes a first organic solvent having a relative evaporation rate of 180 or more when the evaporation rate of n-butyl acetate at 20°C is taken as 100; The content of the nonvolatile content of the reactive component is 55 parts by mass or more and 96 parts by mass or less per 100 parts by mass of the nonvolatile content of the clear coating composition, The content of the nonvolatile content of the non-reactive acrylic resin is 4 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the nonvolatile content of the clear coating composition, A clear coating composition, wherein the content of the first organic solvent is 20 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the clear coating composition.

2. 2. The clear coating composition according to claim 1, wherein the content of the tin catalyst is 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the total of the non-volatile content of the non-reactive acrylic resin and the non-volatile content of the reactive component.

3. A method for repairing a concrete structure, which comprises spraying the clear coating composition according to claim 1 or 2 onto the concrete structure.

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