Appearance improvement solution for acrylic coatings

Abstract

To provide a solution for improving appearance of an acrylic coating film which can perform an improvement treatment of appearance (designability) of an acrylic coating film not by peeling of an acrylic coating film+formation of a new coating film, and formation of a new coating film on an old acrylic coating film but by only wiping the old acrylic coating film, appearance of which has deteriorated, and the like and, which can suppress damages on the acrylic coating film after such an appearance improving treatment.SOLUTION: Provided is a solution for improving appearance of an acrylic coating film, comprising a C1-4 alcohol (A) and water (B).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solution for improving the appearance of an acrylic coating film and a method for improving the appearance of an acrylic coating film. [Background technology]

[0002] Various coating films are formed on the members (substrates) that make up structures in order to impart various functions such as corrosion resistance, stain resistance, weather resistance, scratch resistance, and design properties.

[0003] Coating films formed on substrates often fail to exhibit the desired functions due to coating defects, deterioration over time, etc. Since coating films formed on substrates are required to be endowed with required functions, coating films that have become unable to exhibit their functions in this way are usually peeled off from the substrate, and a new coating film is formed on the peeled area, or a new coating film is formed on the coating film that has become unable to exhibit its function.

[0004] Examples of methods for peeling a coating film from a substrate include a method of peeling the coating film using a power tool such as a disc sander, a method of peeling the coating film by blasting, and a method of peeling the coating film using a stripping agent. Known examples of such stripping agents include the aqueous coating stripper described in Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-203403 Summary of the Invention [Problem to be solved by the invention]

[0006] As the coating film formed on the substrate (top coating film in the case of a multilayer coating film), an acrylic coating film is often used for various substrates. It is known that the appearance (design) of such acrylic coating films deteriorates due to deterioration over time, etc. In particular, if an acrylic paint that forms an acrylic coating film is applied to a substrate and then the applied paint comes into contact with water (due to rain, etc.) before the applied paint dries, the formed acrylic coating film will whiten (deteriorate), impairing the appearance of the coating film.

[0007] One method for improving the appearance of such a deteriorated acrylic coating film is to peel off the deteriorated acrylic coating film and form a new acrylic coating film (hereinafter also referred to as "peeling off the acrylic coating film and forming a new coating film"), as has been conventionally done. However, peeling off the acrylic coating film and forming a new acrylic coating film is time-consuming and labor-intensive, so it is preferable to be able to improve the appearance of the acrylic coating film by a simpler method other than this method.

[0008] As a simple method for improving the appearance of such an acrylic coating film, as described above, it is conceivable to apply a new acrylic paint (for example, the same acrylic paint as the paint used to form the old acrylic coating film) on top of the old acrylic coating film (hereinafter also referred to as "forming a new coating film on an old acrylic coating film"). However, when repainting in this way, the old acrylic coating dissolves, and the new acrylic coating must be dried to a thickness equal to the total thickness of the dissolved old acrylic coating and the newly applied acrylic coating. This requires a longer drying period than when forming a single-layer acrylic coating of the same thickness as the new coating formed when repainting. The longer the drying period, the more likely the applied paint is to come into contact with water before drying, increasing the risk of the resulting coating becoming white. Furthermore, the thicker the acrylic coating, the higher the risk of coating defects such as blisters and cracks. For these reasons, there has been a demand for methods for improving the appearance of acrylic coating films other than forming a new coating film on top of the old acrylic coating film.

[0009] The present invention has been made in view of the above, and aims to provide an appearance improving solution for acrylic coating films that can improve the appearance (design) of acrylic coating films simply by wiping off acrylic coating films with deteriorated appearance, rather than by peeling the acrylic coating film and forming a new coating film or by forming a new coating film on top of an old acrylic coating film, and that can suppress damage to the acrylic coating film after such appearance improvement treatment. [Means for solving the problem]

[0010] As a result of extensive research into methods for solving the above problems, the present inventors have found that the above problems can be solved by the following configuration examples, and have thus completed the present invention. An example of the configuration of the present invention is as follows.

[0011] <1> An appearance improving solution for acrylic coating films, comprising (A) an alcohol having 1 to 4 carbon atoms and (B) water.

[0012] <2> the mass ratio of the alcohol (A) to the water (B) [(A):(B)] is 65:35 to 95:5; <1> 1. An appearance improving solution for an acrylic coating film according to claim 1. <3> The total content of the alcohol (A) and the water (B) is 95% by mass or more. <1> or <2> 1. An appearance improving solution for an acrylic coating film according to claim 1.

[0013] <4> <1> ~ <3> 1. A method for improving the appearance of an acrylic coating film, using the appearance improving solution for an acrylic coating film according to any one of claims 1 to 9.

[0014] <5> The method includes the following steps [1] or [2]: <4> 1. A method for improving the appearance of an acrylic coating film according to claim 1. [1] <1> ~ <3> a step of wiping the acrylic coating film using a wiping member containing the appearance improving solution for the acrylic coating film according to any one of the preceding claims. [2] On the acrylic coating, <1> ~ <3> and wiping off the appearance-improving solution for the acrylic coating film.

[0015] <6> The acrylic coating film is an outdoor acrylic coating film or a marine acrylic coating film. <4> or <5> 1. A method for improving the appearance of an acrylic coating film according to claim 1. [Effects of the Invention]

[0016] According to the present invention, the appearance (design) of an acrylic coating film can be improved by simply wiping off an acrylic coating film whose appearance has deteriorated, rather than by peeling off the acrylic coating film and forming a new coating film or by forming a new coating film on top of an old acrylic coating film, and damage to the acrylic coating film after the appearance improvement treatment can be suppressed in this way. In particular, according to the present invention, the whitened (deteriorated) portion of the acrylic coating film can be removed, and the whitening can be improved and the gloss lost due to the whitening can be restored while maintaining the unwhitened, healthy acrylic coating film below the whitened portion (on the side of the substrate). Furthermore, by using the appearance-improving solution for acrylic coating films according to the present invention to improve the appearance of an acrylic coating film once, it is possible to obtain an acrylic coating film that is less likely to suffer re-deterioration of its appearance (re-whitening) even if the acrylic coating film after such appearance improvement comes into contact with water or the like. Furthermore, once the appearance of an acrylic coating film is improved using the appearance-improving solution for acrylic coating films according to the present invention, whitening that may occur in the acrylic coating film when the acrylic coating film comes into contact with water after such treatment can be more effectively suppressed than in the case of conventional appearance improvement achieved by forming a new coating film on top of an old acrylic coating film. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram of an appearance-improving treated test plate prepared in the following example. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Appearance improvement solution for acrylic coatings> The appearance improving solution for acrylic coating films according to the present invention (hereinafter also referred to as "the solution") is not particularly limited as long as it contains an alcohol (A) having 1 to 4 carbon atoms and water (B), but may also contain other components described below. Unlike a release agent that peels off an acrylic coating film (that is, peels off and removes the entire acrylic coating film formed on a substrate in the thickness direction), this solution is a solution that can improve the appearance of an acrylic coating film, thereby producing an acrylic coating film with improved appearance (that does not peel off and remove the entire acrylic coating film formed on a substrate in the thickness direction).

[0019] Furthermore, by using this solution to improve the appearance of an acrylic coating film once, it is possible to obtain an acrylic coating film that is less likely to deteriorate again (re-whitening) in appearance even if the improved acrylic coating film comes into contact with water, etc. Furthermore, once the appearance of an acrylic coating film is improved using this solution, whitening that can occur in the acrylic coating film when it comes into contact with water can be more effectively suppressed than when the appearance is improved by conventionally forming a new coating film on top of an old acrylic coating film. Therefore, since this solution has resistance to deterioration (whitening) that can inhibit the deterioration (whitening) of acrylic coating films, it can also be said to be a solution that inhibits the deterioration (whitening) of acrylic coating films.

[0020] Furthermore, when this solution is used to wipe an acrylic coating film that has not yet deteriorated in appearance, the gloss of the acrylic coating film tends to improve compared to the state before wiping. This solution is usually used on acrylic coating films whose appearance has deteriorated, but as described above, it has resistance to deterioration (whitening) and can improve gloss, so it can also be used on acrylic coating films whose appearance has not deteriorated. In this way, improving the gloss of an acrylic coating film whose appearance has not deteriorated can be considered an appearance improvement, so a solution used on an acrylic coating film whose appearance has not deteriorated can also be considered an appearance-improving solution for acrylic coating films, and using this solution on an acrylic coating film whose appearance has not deteriorated can also be considered a method for improving the appearance of an acrylic coating film.

[0021] In the present invention, improved appearance means that, when the color difference between an undegraded (before deterioration) acrylic coating film and the acrylic coating film after deterioration is defined as ΔE1, and the color difference between an undegraded acrylic coating film and the acrylic coating film after the appearance improvement treatment has been applied to the deteriorated acrylic coating film is defined as ΔE2, the color difference (ΔE) recovery rate, expressed as (1-(ΔE2 / ΔE1))×100, is preferably 40% or more, and more preferably 50% or more. The ΔE recovery rate (%) can be specifically measured and calculated by the method described in the examples below.

[0022] Furthermore, in the present invention, improved appearance means that, for example, when the 60° specular gloss of an undegraded (before deterioration) acrylic coating film is designated as G1, the 60° specular gloss of a deteriorated acrylic coating film is designated as G2, and the 60° specular gloss of the deteriorated acrylic coating film after appearance improvement treatment has been performed is designated as G3, the gloss recovery rate, expressed as {(G3-G2) / (G1-G2)}×100, is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. Furthermore, in the present invention, improved appearance means that, for example, when the 60° specular gloss of an undegraded (before deterioration) acrylic coating film is taken as G1 and the 60° specular gloss of an acrylic coating film after appearance improvement treatment on a deteriorated acrylic coating film is taken as G3, the gloss retention expressed as (G3 / G1)×100 is preferably 50% or more, more preferably 60% or more, and even more preferably 65% ​​or more. The 60° specular gloss can be specifically measured and calculated by the method described in the examples below.

[0023] [Alcohol (A)] The alcohol (A) is not particularly limited as long as it is an alcohol having 1 to 4 carbon atoms. As the alcohol (A), an alcohol having 1 to 3 carbon atoms, propylene glycol monomethyl ether (PGM), is preferred, and a monohydric alcohol having 1 to 3 carbon atoms, PGM, is more preferred, because it can easily improve the appearance (particularly whitening and gloss) of the acrylic coating film and can easily suppress damage to the acrylic coating film after the appearance improvement treatment. The alcohol (A) used in the present solution may be one type or two or more types.

[0024] Specific examples of the alcohol (A) include methanol, ethanol, 1-propanol, isopropyl alcohol (IPA), ethylene glycol, propylene glycol, and PGM. Of these, ethanol, 1-propanol, IPA, and PGM are preferred, with IPA and PGM being more preferred, because they can easily improve the appearance (particularly whitening and gloss) of the acrylic coating film and can easily suppress damage to the acrylic coating film after the appearance improvement treatment.

[0025] The content of alcohol (A) in the present solution (the amount of alcohol (A) used when preparing the present solution) is preferably 65 to 95% by mass, more preferably 70 to 90% by mass, relative to 100% by mass of the present solution, from the viewpoints that the appearance (particularly whitening and gloss) of the acrylic coating film can be easily improved and damage to the acrylic coating film after the appearance improvement treatment can be easily suppressed.

[0026] [Water (B)] The water (B) is not particularly limited, and tap water or the like may be used, but it is preferable to use pure water or ion-exchanged water.

[0027] The content of water (B) in this solution (the amount of water (B) used when preparing this solution) is preferably 5 to 35 mass %, more preferably 10 to 30 mass %, relative to 100 mass % of this solution, from the viewpoints of adjusting the dissolving power of the alcohol in the acrylic coating film, easily improving the appearance (particularly whitening and gloss) of the acrylic coating film, and easily suppressing damage to the acrylic coating film after the appearance improvement treatment.

[0028] In order to further exert the effects of the present invention, the mass ratio of the alcohol (A) to the water (B) in the present solution (the mass ratio of the alcohol (A) to the water (B) used in preparing the present solution) [(A):(B)] is preferably 65:35 to 95:5, more preferably 70:30 to 90:10. The total content of the alcohol (A) and water (B) in the solution is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 98% by mass or more, with the upper limit being 100% by mass. In other words, the solution preferably consists of only the alcohol (A) and water (B).

[0029] [Other ingredients] If desired, other components such as surfactants, preservatives, pH adjusters, chelating agents, disinfectants, fragrances, and organic solvents may be used in the present solution, provided that the effects of the present invention are not impaired. These other components may each be used alone or in combination of two or more.

[0030] [Surfactants] The surfactant is not particularly limited, and any conventionally known surfactant can be used, such as an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant. A surfactant may be used in this solution, but it is preferable not to use such a surfactant in consideration of costs and the like.

[0031] Examples of the anionic surfactant include fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonates, polyoxyethylene alkyl ether sulfates, and dialkyl sulfosuccinates. Examples of cationic surfactants include alkylamine acetates and quaternary ammonium salts. Examples of amphoteric surfactants include alkyldimethylaminoacetic acid betaine and alkyldimethylamine oxide. Examples of nonionic surfactants include glycerin fatty acid esters, propylene glycol fatty acid esters, polyoxyethylene alkyl ethers, and polyoxyethylene polyoxypropylene ethers.

[0032] [Preservatives] The preservative is not particularly limited, and any conventionally known preservative can be used, including, for example, organic nitrogen-sulfur compounds containing sulfate ions or chloride ions, chlorine compounds, sodium benzoate, etc.

[0033] [pH adjuster] The pH adjuster is not particularly limited, and conventionally known acidic or alkaline substances can be appropriately selected and used. Specific examples of acidic substances include sulfuric acid and p-toluenesulfonic acid, and examples of alkaline substances include sodium hydroxide, potassium hydroxide, ammonia, and alkanolamines.

[0034] [Organic solvents] The organic solvent is not particularly limited as long as it is an organic solvent other than the alcohol (A), and conventionally known organic solvents can be appropriately selected and used.Specific examples include alcohol-based solvents such as benzyl alcohol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monobenzyl ether, ethylene glycol monophenyl ether, and ethylene glycol monohexyl ether, aromatic hydrocarbon-based solvents such as toluene and xylene, ketone-based solvents such as methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK), ester-based solvents such as butyl acetate, and aliphatic hydrocarbon-based solvents such as n-hexane, n-octane, 2,2,2-trimethylpentane, isooctane, n-nonane, cyclohexane, and methylcyclohexane.Among these, organic solvents that are soluble in the alcohol (A) or water (B) are preferred.

[0035] <Acrylic coating> In the present invention, the acrylic coating film whose appearance is to be improved is not particularly limited, and examples thereof include acrylic coating films formed from conventionally known (meth)acrylic resin compositions. By using this solution, the appearance of any acrylic coating film formed from conventionally known (meth)acrylic resin compositions can be improved.

[0036] The (meth)acrylic resin composition refers to a composition in which the content of the (meth)acrylic compound is preferably 20 to 100% by mass, more preferably 40 to 100% by mass, relative to 100% by mass of the resin contained in the composition. Furthermore, the (meth)acrylic resin composition is preferably a composition in which the content of the (meth)acrylic compound is preferably 20 to 100% by mass, more preferably 20 to 80% by mass, and even more preferably 25 to 60% by mass, relative to 100% by mass of the nonvolatile content of the composition.

[0037] The (meth)acrylic compound may be modified. When the (meth)acrylic compound is a (meth)acrylic resin, examples of the modified (meth)acrylic compound include alkyd resin-modified (meth)acrylic resin, fatty acid-modified (meth)acrylic resin, urethane-modified (meth)acrylic resin, fluorine-modified (meth)acrylic resin, and silicone-modified (meth)acrylic resin. That is, the acrylic coating film is any one of an acrylic coating film, a methacrylic coating film, a modified acrylic coating film, and a modified methacrylic coating film.

[0038] The weight average molecular weight (Mw) of the acrylic resin constituting the acrylic coating film, as measured by gel permeation chromatography (GPC), is not particularly limited, but is preferably 20,000 to 70,000 in terms of making it easier to achieve the effects of the present invention. Specifically, the Mw can be measured by the method described in the examples below.

[0039] The iodine value of the acrylic resin constituting the acrylic coating film is not particularly limited, but from the viewpoint of making it easier to exhibit the effects of the present invention, it is preferably 0 to 50, more preferably 0 to 35, even more preferably 0 to 20, and particularly preferably 0 to 15. Specifically, the iodine value can be measured by the method described in the examples below.

[0040] The glass transition temperature (Tg) of the acrylic resin constituting the acrylic coating film is not particularly limited, but is preferably 0 to 70°C in terms of making it easier to achieve the effects of the present invention. The glass transition temperature (Tg) of the acrylic coating film is not particularly limited, but is preferably 10 to 45°C in view of the fact that the effects of the present invention can be more easily exhibited.

[0041] The Tg can be measured by DSC (differential scanning calorimetry), but can also be approximately calculated using the following Fox formula described in Fox TG, Bull. Am. Physics Soc. 1, 3, p. 123 (1956). In this specification, Tg is specifically a value measured by the method described in the examples below.

[0042]

number

[0043] Tg n For example, the values ​​described in Polymer Handbook 2nd Edition, J. Wiley & Sons, New York (1975) can be used as reference.

[0044] The present invention is particularly effective for acrylic coating films that are prone to deterioration, particularly whitening. Examples of acrylic coating films that are prone to such deterioration, particularly whitening, include acrylic coating films for ships (particularly acrylic coating films for ship decks) and acrylic coating films for outdoor use (for example, acrylic coating films that are in an environment where the coating film comes into contact with water (particularly an environment exposed to rain) after coating film formation), and examples thereof include acrylic coating films formed from conventionally known (meth)acrylic resin compositions for ship coating and conventionally known (meth)acrylic resin compositions for outdoor coating, respectively. Among these, the present invention is particularly effective for acrylic coating films for ship decks.

[0045] The thickness of the acrylic coating film (acrylic coating film before the appearance is improved) is not particularly limited, and there are recommended thicknesses depending on the substrate on which the acrylic coating film is formed and the application, but the thickness of one layer of acrylic coating film (new coating film) formed on a substrate is usually about 30 to 200 μm. According to the present invention, the appearance of a new acrylic coating film formed on an old acrylic coating film can also be improved. Therefore, taking into consideration the use of the present invention on a laminate of such an old coating film and a new coating film, the thickness of the acrylic coating film (new coating film or old coating film and new coating film) at which the effects of the present invention are likely to be exhibited is, for example, about 30 to 2000 μm.

[0046] <<Method for improving the appearance of acrylic coatings>> The method for improving the appearance of an acrylic coating film according to the present invention is not particularly limited as long as the present solution is used, but it preferably includes the following step [1] or [2]. [1] A process of wiping the acrylic coating film using a wiping material containing this solution. [2] A process of applying the solution onto the acrylic coating and wiping the solution off.

[0047] The wiping member containing the present solution in the step [1] specifically includes a wiping member impregnated with the present solution. In the step [2], when wiping the present solution provided on the acrylic coating film, the wiping may be performed using a wiping member that does not contain the present solution, or using a wiping member that contains the present solution.

[0048] Examples of wiping members used in the steps [1] and [2] include waste cloths, dustcloths, mops, sponges, pads, and brushes. When wiping the acrylic coating film in steps [1] and [2], the wiping may be performed by hand using the wiping member, or by using equipment equipped with the wiping member (e.g., floor cleaning equipment, automatic floor cleaning machine).

[0049] Methods for applying the present solution onto the acrylic coating film in the step [2] include spraying the present solution onto the acrylic coating film by spraying, showering, etc., and immersing the substrate on which the acrylic coating film has been formed in the present solution. [Example]

[0050] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0051] [Example 1] An appearance improving solution was prepared by placing 80 parts by mass of isopropyl alcohol (IPA) and 20 parts by mass of water in a container and stirring them.

[0052] [Examples 2 to 8 and Comparative Examples 1 and 2] An appearance improving solution was prepared in the same manner as in Example 1, except that the components shown in the raw material column of Table 1 were used in the amounts (parts by mass) shown in Table 1.

[0053] <Preparation of test plate (substrate with acrylic coating)> Paint 1 (acrylic resin paint) in Table 2 below was applied to the surface of the substrate (tin plate) using an applicator with a gap of 0.5 mm so that the thickness of the acrylic coating film obtained after drying would be 120 μm. Next, the coating was dried at room temperature (23°C) for 3 hours to prepare a substrate (test plate) with an acrylic coating film. The numerical values ​​shown in Table 2 indicate parts by mass, and the explanation of each component shown in Table 2 is shown in Table 3.

[0054] The weight average molecular weight (Mw) of the acrylic resin shown in Table 3 was measured by GPC under the following conditions. Apparatus (Tosoh Corporation, HLC-8220GPC) Column (SuperH2000 + SuperH4000 (Tosoh Corporation, inner diameter 6 mm / length 15 cm each)) Column temperature (40℃) Eluent (tetrahydrofuran) Flow rate (0.50mL / min.) Detector (RI) Standard material (polystyrene)

[0055] The iodine values ​​of the acrylic resins shown in Table 3 were measured by the following method. 0.2-5 g of acrylic resin was accurately weighed into a stoppered flask, and 10 ml of carbon tetrachloride was added to dissolve the resin. 25 ml of Wiess's solution was then added. After the stopper was placed, the flask was left in the dark at room temperature for 30 minutes. Next, 20 ml of 10% w / v potassium iodide solution and 100 ml of water were added and shaken. The solution was titrated with N / 10 sodium thiosulfate solution until it turned slightly yellow. A few drops of starch solution were added, and titration was continued while shaking thoroughly. The end point was the disappearance of the blue color due to the starch. A blank test similar to the main test was also conducted in parallel with the main test, except that no resin was used. The iodine value was calculated by the following formula: Iodine value = ((AB) × f × 1.269) / S (A: Amount (ml) of N / 10 sodium thiosulfate aqueous solution used in blank test, B: Amount (ml) of N / 10 sodium thiosulfate aqueous solution used in main test, f: Factor of N / 10 sodium thiosulfate aqueous solution, S: Mass of resin (g))

[0056] The Tg of the acrylic coating film shown in Table 2 was measured by the following method. The acrylic resin paints listed in Table 2 below were applied using an applicator with a 0.2 mm gap so that the thickness of the acrylic coating film obtained after drying would be 50 μm. The acrylic coating film was then prepared by drying at 50°C for 24 hours. The prepared coating film was cut into a round shape weighing 0.8 to 2.0 mg, and a precisely weighed sample was used to perform DSC (differential scanning calorimetry) under the following conditions. Equipment: DSC Q2000 (TA Instruments) Container: Aluminum (Standard Pan, Standard Lid, manufactured by TA Instruments) Measurement temperature: -20℃~80℃ Heating rate: 20°C / min

[0057] <Preparation of test plate (substrate with white acrylic coating) after water immersion> The test plate prepared as described above was immersed in tap water for 24 hours, with the lower half of the plate immersed in tap water at room temperature contained in a container. Thereafter, the test plate was removed from the container, and the water adhering to the test plate was wiped off with a waste cloth (JK Wiper 100-S [manufactured by Nippon Paper Crecia Co., Ltd.]), thereby preparing a test plate (substrate with a whitened acrylic coating film) after water immersion. After the water immersion, the acrylic coating film in the water-immersed portion of the test plate was whitened compared to the acrylic coating film in the upper half of the test plate that had not been immersed in water. In the following description, the lower half of the test plate immersed in water will also be referred to as the "water-immersed portion," and the upper half of the test plate not immersed in water will also be referred to as the "non-water-immersed portion."

[0058] <Preparation of Appearance Improvement Treatment Test Panel> A cloth (JK Wiper 100-S [manufactured by Nippon Paper Crecia Co., Ltd.]) was impregnated with the appearance-improving solution prepared in the Examples and Comparative Examples, and the cloth containing the obtained appearance-improving solution was then passed back and forth eight times (to wipe the acrylic coating surface) over the acrylic coating surface of the right half (water-immersed portion + non-water-immersed portion) of the test plate prepared as described above after immersion in water, thereby performing an appearance improvement treatment.The appearance-improving solution remaining on the appearance-improved portion was then wiped off with a dry cloth (JK Wiper 100-S [manufactured by Nippon Paper Crecia Co., Ltd.]), thereby producing an appearance-improved test plate.

[0059] An explanatory diagram of the appearance-improved test plate prepared in this manner is shown in Figure 1. The upper left part A of the test plate is the part not immersed in water and is the part that was not subjected to the appearance-improving treatment (hereinafter also referred to as the "healthy part"). The upper right part B of the test plate is the part not immersed in water and is the part that was subjected to the appearance-improving treatment. The lower left part C of the test plate is the part that was immersed in water and is the part that was not subjected to the appearance-improving treatment (hereinafter also referred to as the "deteriorated part"). The lower right part D of the test plate is the part that was immersed in water and is the part that was subjected to the appearance-improving treatment (hereinafter also referred to as the "treated part").

[0060] <Preparation of decorative coating test panels> Paint 1 (acrylic resin-based paint) in Table 2 below was applied to the acrylic coating film on the right half (water-immersed part + non-water-immersed part) of the test plate prepared as described above after water immersion, using an applicator with a gap of 0.1 mm, so that the thickness of the acrylic coating film (new coating film) obtained after drying would be 20 μm, and the test plate was dried at room temperature for 3 hours to prepare a decorative coating-treated test plate.

[0061] <Color difference change (ΔE recovery rate)> The color difference (ΔE1) of the acrylic coating film between the healthy and deteriorated areas of the appearance improvement treated test panels prepared as described above, and the color difference (ΔE2) of the acrylic coating film between the healthy and treated areas were measured using a Spectrophotometer CM-3700A (light source: C, field of view: 2°) manufactured by Konica Minolta Japan, Inc., and the color difference (ΔE) recovery rate was calculated using the following formula. The results of ΔE1 and ΔE recovery rate are shown in Table 1. Note that ΔE1 in Examples 1 to 8 and Comparative Examples 1 and 2, which were tested under the same conditions, was taken as the average value of each appearance improvement treated test panel. ΔE recovery rate (%)=(1-(ΔE2 / ΔE1))×100

[0062] <Gloss retention> Using a BYK micro-TRI-gloss, the 60° specular gloss (G1) of the acrylic coating film in the healthy area, the 60° specular gloss (G2) of the acrylic coating film in the deteriorated area, and the 60° specular gloss (G3) of the acrylic coating film in the treated area were measured, and the gloss recovery rate and gloss retention rate were calculated using the following formula. The results are shown in Table 1. Gloss recovery rate (%) = {(G3-G2) / (G1-G2)} x 100 Gloss retention rate (%)=(G3 / G1)×100

[0063] <Damage Assessment> The acrylic coating film and the waste cloth after the appearance improvement treatment performed when preparing the appearance improvement treated test plate were visually inspected, and the evaluation was made as follows: if there were no scratches on the acrylic coating film in the treated area and no acrylic coating film was attached to the waste cloth, it was marked with ○; if there were scratches on the acrylic coating film in the treated area or the acrylic coating film was attached to the waste cloth, it was marked with ×. The results are shown in Table 1.

[0064] <Whitening resistance> The appearance-improving treated test panels and decoratively painted test panels prepared as described above were dried at room temperature for 3 hours, and then the dried appearance-improving treated test panels and decoratively painted test panels were immersed in tap water for 24 hours, with the lower halves of the panels immersed in tap water at room temperature contained in a container.The test panels were then removed from the container, and the water adhering to the test panels was wiped off with a rag (JK Wiper 100-S [manufactured by Nippon Paper Crecia Co., Ltd.]), thereby preparing test panels that had been re-immersed in water. The color difference (ΔE3) of the acrylic coating film between the part corresponding to the healthy part (A in Figure 1) and the part corresponding to the treated part (D in Figure 1) of the appearance improvement treated test board prepared after re-immersion in water, and the color difference (ΔE4) of the acrylic coating film between the part corresponding to the healthy part (A in Figure 1) and the part corresponding to the treated part (D in Figure 1) of the decorative coating treated test board prepared after re-immersion in water were measured in the same manner as above. The results are shown in Table 1.

[0065] Furthermore, ΔE3 of the test plate after re-immersion in water was smaller than ΔE1. ​​This indicates that the water-immersed portion of the test plate after re-immersion in water, which was subjected to the appearance improvement treatment, i.e., the portion that had been subjected to the appearance improvement treatment once, was inhibited from whitening that can occur in the acrylic coating film, even when immersed in water. Furthermore, ΔE3 of the test panel after re-immersion in water was smaller than ΔE4. This shows that compared to the conventional simple method of improving the appearance (whitening) of acrylic coating films, which involves forming a new coating film on top of the old acrylic coating film, the appearance improvement method of the present invention can suppress whitening that can occur in the acrylic coating film even if the acrylic coating film comes into contact with water after these treatments.

[0066] [Table 1]

[0067] Furthermore, when thinners (xylene, toluene, or butyl acetate) were used in the above-mentioned appearance improvement treatment, the acrylic coating film dissolved and softened, causing defects such as blisters and cracks in the acrylic coating film after the appearance improvement treatment.

[0068] In preparing the test panels and decoratively painted test panels, the same tests as those in Example 2 were carried out, except that Paint 2 (acrylic resin-based paint), Paint 3 (acrylic resin-based paint) or Paint 4 (acrylic resin-based paint) in Table 2 below was used instead of Paint 1 (acrylic resin-based paint) in Table 2 below. The results were the same as those in Example 2. In other words, regardless of the type of acrylic coating film, this solution can improve the appearance of acrylic coating films simply by wiping them with a deteriorated appearance, and can also suppress damage to the acrylic coating film after appearance improvement treatment.Furthermore, even if the acrylic coating film after appearance improvement treatment comes into contact with water or the like, it is possible to obtain an acrylic coating film that is less likely to suffer re-deterioration in appearance (re-whitening), and compared to the conventional method of forming a new coating film on top of an old acrylic coating film, whitening that can occur in the acrylic coating film can be suppressed.

[0069] [Table 2]

[0070] [Table 3]

Claims

1. An appearance improving solution for an acrylic coating film, comprising an alcohol (A) having 1 to 4 carbon atoms and water (B), The content of the alcohol (A) is 65 to 95% by mass relative to 100% by mass of the appearance improving solution, The appearance improving solution is a solution for removing deteriorated portions of deteriorated acrylic coating films. A solution that improves the appearance of acrylic coatings.

2. 2. The appearance improving solution for acrylic coating films according to claim 1, wherein the mass ratio of the alcohol (A) to the water (B) [(A):(B)] is 65:35 to 95:

5.

3. The appearance improving solution for an acrylic coating film according to claim 1 or 2, wherein the total content of the alcohol (A) and the water (B) is 95 mass% or more.

4. A method for improving the appearance of an acrylic coating film, using the appearance improving solution for an acrylic coating film according to any one of claims 1 to 3.

5. The method for improving the appearance of an acrylic coating film according to claim 4, comprising the following steps [1] or [2]: [1] A step of wiping an acrylic coating film using a wiping member containing the appearance improving solution for an acrylic coating film according to any one of claims 1 to 3. [2] A step of applying an appearance improving solution for an acrylic coating film according to any one of claims 1 to 3 onto the acrylic coating film and wiping off the appearance improving solution.

6. 6. The method for improving the appearance of an acrylic coating film according to claim 4 or 5, wherein the acrylic coating film is an outdoor acrylic coating film or an acrylic coating film for ships.

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