Strippable paints and protective coatings

Abstract

This invention provides a strippable paint and protective coating material suitable for suppressing temperature-induced fluctuations in adhesion and peelability. [Solution] A strippable paint is provided comprising an aqueous solvent and a first and second acrylic polymer. The first acrylic polymer is a polymer of a first monomer component comprising a first monomer with a relatively high homopolymer Tg and a second monomer with a relatively low homopolymer Tg. The second acrylic polymer is a polymer of a second monomer component comprising a third monomer with a relatively high homopolymer Tg and a fourth monomer with a relatively low homopolymer Tg. The first monomer has a higher homopolymer Tg than the third monomer, or the first and third monomers have the same homopolymer Tg, and the proportion of the first monomer in the first monomer component is greater than the proportion of the third monomer in the second monomer component. The ratio of the tensile storage modulus at 0°C to the tensile storage modulus at 40°C of the cured strippable paint is 350 or less.

Description

[Technical Field]

[0001] The present invention relates to a strippable paint and a protective coating material for forming a protective coating material. [Background technology]

[0002] A technique is known for applying a protective sheet to the surface of an article in order to protect the surface of the article during transportation, storage, curing, and construction. The protective sheet has, for example, a sheet-like base material and an adhesive layer on one side thereof, and the adhesive layer side is attached to the surface of the article to be protected. The protective sheet on the surface of the article is peeled off at a predetermined time. Such a technique for protective sheets is described, for example, in Patent Document 1 below. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-111552 [Patent Document 2] Japanese Patent Publication No. 2004-224874 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, it can be difficult to properly apply protective sheets to articles with non-flat surfaces. Specifically, when applying protective sheets to the non-flat surfaces of articles, wrinkles tend to form in the protective sheet, and air bubbles are likely to form between the protective sheet and the article. If the protective sheet is not properly applied to the article, for example, wind blowing into the wrinkles in the protective sheet during storage or transport of the article may cause the protective sheet to peel off unintentionally.

[0005] On the other hand, it has also been proposed to apply a resin-containing liquid composition to the surface of an article to be protected, and then dry it to form a protective film (a protective coating material as an adhesive resin film). The protective film on the surface of the article is peeled off from the surface at a predetermined time. Technology related to such liquid compositions is described, for example, in the above-mentioned Patent Document 2.

[0006] However, protective films formed from liquid compositions, unlike the protective sheets described above, do not have a substrate. Such protective films tend to have a higher temperature dependence of various physical properties compared to protective sheets, and in addition to the temperature dependence of adhesion to the article surface, the temperature dependence of elongation when pulled during peeling, etc., and the tensile strength are particularly high. The adhesion of the protective film to the article surface is important for ensuring good adhesion to prevent unintended peeling of the protective film from the article surface. The adhesion, elongation, and tensile strength of the protective film have a significant impact on the ease of proper peeling (peelability) of the protective film from the article surface. For such adhesion and peelability of protective films, it is required that there be little variation in the practical temperature range of the protective film.

[0007] The present invention was conceived under the circumstances described above, and aims to provide a strippable paint suitable for suppressing temperature-induced fluctuations in adhesion to and peelability from the surface of an object to be protected. Another object of the present invention is to provide a protective coating material formed from such a strippable paint. [Means for solving the problem]

[0008] According to this specification, a strippable paint for forming a peelable protective coating material is provided. The strippable paint includes an aqueous solvent, a first acrylic polymer and a second acrylic polymer dispersed in the aqueous solvent. The first acrylic polymer is a polymer of a first monomer component. The first monomer component includes a first monomer having a relatively high glass transition temperature of the homopolymer and a second monomer having a relatively low glass transition temperature. The second acrylic polymer is a polymer of a second monomer component and has a different monomer composition from the first acrylic polymer. The second monomer component includes a third monomer having a relatively high glass transition temperature of the homopolymer and a fourth monomer having a relatively low glass transition temperature. The glass transition temperature of the first monomer in the first acrylic polymer is higher than the glass transition temperature of the third monomer in the second acrylic polymer, or the glass transition temperature of the first monomer is the same as the glass transition temperature of the third monomer and the proportion of the first monomer in the first monomer component is larger than the proportion of the third monomer in the second monomer component. The ratio of the tensile storage modulus at 0 °C to the tensile storage modulus at 40 °C after curing of the strippable paint is 350 or less. The strippable paint having such a configuration includes the first and second acrylic polymers whose monomer compositions are different from each other as described above, and since the above ratio of the tensile storage modulus is 350 or less, it is suitable for suppressing the temperature dependence of the adhesion to the article, the ease of elongation and the breaking strength after curing. Specifically, it is as shown in the examples and comparative examples described later. Therefore, this strippable paint is suitable for suppressing fluctuations due to temperature differences in the adhesion to the surface of the object to be protected and the peelability from the surface.

[0009] In some preferred embodiments, the glass transition temperature of the first monomer in the first acrylic polymer is 50 °C or more higher than the glass transition temperature of the second monomer. In some preferred embodiments, the glass transition temperature of the third monomer in the second acrylic polymer is 50 °C or more higher than the glass transition temperature of the fourth monomer. These configurations are suitable for suppressing the temperature dependence of the physical properties of the strippable paint in a relatively wide temperature range defined by two temperatures with a temperature difference of, for example, 50 °C or more. The physical properties include the adhesion of the strippable paint after curing to the article, elongation ease, and breaking strength.

[0010] In some preferred embodiments, at least one of the first monomer in the first acrylic polymer and the third monomer in the second acrylic polymer is acrylonitrile. Acrylonitrile in the acrylic polymer is likely to form a hard segment due to its cohesive force. The formation of a hard segment in the acrylic polymer helps to exhibit the rubber elasticity of the polymer, and thus helps to achieve appropriate elongation ease and ensure breaking strength after the strippable paint containing such an acrylic polymer is cured.

[0011] In some preferred embodiments, the total proportion of the first monomer and the third monomer in the total amount of the first monomer component and the second monomer component is 5% by weight or more. Such a configuration helps to suppress the temperature dependence of the adhesion of the strippable paint after curing to the article, elongation ease, and breaking strength.

[0012] In some preferred embodiments, the loss tangent of the strippable paint after curing has a peak within the range of 23 °C to 40 °C. Such a configuration is suitable for exhibiting good viscoelastic properties for the strippable paint after curing in the temperature region of 23 °C to 40 °C and its vicinity.

[0013] In some preferred embodiments, the tensile storage modulus at 40°C is 1.0 MPa or greater. Such a configuration is suitable for ensuring the adhesion to articles and the breaking strength of the cured strippable paint in the temperature range of 40°C and its vicinity.

[0014] In some preferred embodiments, the tensile storage modulus at 0°C is 1.7 × 10⁻⁶. 3 The pressure is less than or equal to MPa. Such a configuration is suitable for ensuring the adhesion, elongation, and tensile strength of the cured strippable paint in the temperature range of 0°C and its vicinity.

[0015] This specification provides a protective coating material which is a cured product of any of the strippable paints disclosed herein. The protective coating material can be formed, for example, by applying the strippable paint described above to the surface of an article to be protected to form a coating film, and then drying the coating film. The protective coating material may be a dried film of any of the strippable paints disclosed herein.

[0016] Furthermore, combinations of the elements described herein may also be included within the scope of the invention for which patent protection is sought in this patent application. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view showing an example of an object protected by the protective coating material (strippable paint after curing) according to the present invention. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. The embodiments shown in the following drawings are schematic representations intended to clearly illustrate the present invention and do not necessarily accurately represent the size or scale of the actual product offered.

[0019] In this specification, "acrylic monomer" is a comprehensive term referring to monomers having at least one (meth)acryloyl group in one molecule (hereinafter also referred to as "(meth)acryloyl group-containing monomers") and (meth)acrylonitrile. In this specification, "(meth)acryloyl" is a comprehensive term referring to acryloyl and methacryloyl. Similarly, "(meth)acrylate" is a comprehensive term referring to acrylate and methacrylate, "(meth)acrylic" is a comprehensive term referring to acrylic and methacrylic, and "(meth)acrylonitrile" is a comprehensive term referring to acrylonitrile and methacrylonitrile.

[0020] <Strippable Paint> The strippable paints disclosed herein are compositions for forming a peelable protective coating, comprising an aqueous solvent and a first acrylic polymer and a second acrylic polymer dispersed in the aqueous solvent. Typically, the strippable paint is a water-dispersible composition in which the first acrylic polymer and the second acrylic polymer are dispersed in the aqueous solvent. Water-dispersible compositions include aqueous emulsion compositions. Furthermore, the strippable paint contains the first acrylic polymer or the second acrylic polymer in an amount of 50% by weight or more of the polymers in the composition.

[0021] The above-mentioned aqueous solvent refers to water, or a mixed solvent having water as its main component (a component present in more than 50% by weight). The solvents other than water that constitute this mixed solvent may be one or more selected from various organic solvents (such as lower alcohols) that can be uniformly mixed with water. In this specification, the aqueous solvent typically has a water content of 90% by weight or more, preferably 95-100% by weight.

[0022] The above-mentioned first acrylic polymer is a polymer of a first monomer component containing one or more acrylic monomers. The proportion of acrylic monomers in the first monomer component is, for example, 5% by weight or more, preferably 15% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, more preferably 60% by weight or more, and may also be 70% by weight or more, 80% by weight or more, or 85% by weight or more. In some preferred embodiments, the proportion of acrylic monomers in the first monomer component may be 85% by weight or more, 90% by weight or more, 95% by weight or more, or 100% by weight. Also, in some embodiments, the proportion of acrylic monomers in the first monomer component may be 50% by weight or less, 40% by weight or less, or 30% by weight or less.

[0023] In some embodiments, the first monomer component constituting the first acrylic polymer includes at least a (meth)acryloyl group-containing monomer as the acrylic monomer. The (meth)acryloyl group-containing monomer can be used alone or in combination of two or more. The proportion of the (meth)acryloyl group-containing monomer in the first monomer component is, for example, 5% by weight or more, preferably 10% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, more preferably 60% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more. The entirety of the first monomer component (i.e., 100% by weight) may be a (meth)acryloyl group-containing monomer. From the viewpoint of facilitating the formation of a protective coating material with a good balance of properties, in some embodiments, the proportion of the (meth)acryloyl group-containing monomer in the first monomer component is preferably 98% by weight or less, more preferably 90% by weight or less, more preferably 80% by weight or less, and more preferably 70% by weight or less. The technology disclosed herein can also be implemented in which the proportion of (meth)acryloyl group-containing monomers in the first monomer component is 65% by weight or less, 55% by weight or less, 45% by weight or less, or 35% by weight or less.

[0024] The first monomer component preferably contains at least an alkyl (meth)acrylate as the above (meth)acryloyl group-containing monomer. By selecting the type and amount of the alkyl (meth)acrylate used, it can be useful for adjusting the storage elastic modulus, tensile properties, and the like. The alkyl (meth)acrylate can be used alone or in combination of two or more.

[0025] As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used.

[0026] CH2=C(R 1 )COOR 2 (1)

[0027] Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. R in the above formula (1) 2 is a linear alkyl group having 1 to 20 carbon atoms. Hereinafter, such a carbon atom number range may be represented as "C 1-20 ". The linear alkyl group may be linear or branched.

[0028] R 2 being a linear alkyl group of C 1-20 alkyl (meth)acrylate (C 1-20Specific examples of alkyl(meth)acrylates are not limited to, but include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, t-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate. Examples include rilate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc.

[0029] Of these, at least C 4-20 Alkyl (meth)acrylate (preferably C 4-14 It is preferable to use alkyl (meth)acrylate, as this can contribute to ensuring the flexibility of the strippable paint after curing by lowering the glass transition temperature (Tg) of the first acrylic polymer, at least C 4-9 It is more preferable to use alkyl acrylates. For example, it is preferable that the first monomer component contains one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA), and more preferably at least BA.

[0030] C 1-20The proportion of alkyl (meth)acrylate is, for example, 5% by weight or more, preferably 10% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, more preferably 60% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more. C 1-20 The proportion of alkyl (meth)acrylate is preferably 98% by weight or less, more preferably 90% by weight or less, more preferably 80% by weight or less, and more preferably 70% by weight or less. The technology disclosed herein involves C among the first monomer components. 1-20 The method can also be implemented in which the proportion of alkyl (meth)acrylate is 65% by weight or less, 55% by weight or less, 45% by weight or less, or 35% by weight or less.

[0031] The first monomer component is C 4-9 In an embodiment comprising alkyl acrylate, among the first monomer components, C 4-9 The proportion of alkyl acrylate is, for example, 5% by weight or more, preferably 10% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, more preferably 60% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more. C 1-20 The proportion of alkyl (meth)acrylate is preferably 98% by weight or less, more preferably 90% by weight or less, more preferably 80% by weight or less, and more preferably 70% by weight or less. The technology disclosed herein involves C among the first monomer components. 1-20 The method can also be implemented in which the proportion of alkyl (meth)acrylate is 65% by weight or less, 55% by weight or less, 45% by weight or less, or 35% by weight or less.

[0032] The first monomer component may contain a combination of alkyl (meth)acrylate and monomers other than alkyl (meth)acrylate. Some examples of monomers other than alkyl (meth)acrylate include carboxyl group-containing monomers, hydroxyl group (OH group)-containing monomers, cyano group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, acid anhydride group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, alkoxysilyl group-containing monomers, and other functional group-containing monomers. Monomers other than alkyl (meth)acrylate can be used individually or in combination of two or more. Appropriate use of functional group-containing monomers can enhance the cohesive strength of the first acrylic polymer. Functional group-containing monomers can also be useful for adjusting the storage modulus, tensile properties, etc.

[0033] Examples of carboxyl group-containing monomers include acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Among these, AA and MAA are preferred.

[0034] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and polypropylene glycol mono(meth)acrylate. Among these, hydroxyalkyl (meth)acrylates in which the alkyl group has 2 to 4 carbon atoms in a linear chain are particularly preferred as hydroxyl group-containing monomers.

[0035] Examples of cyano group-containing monomers include acrylonitrile, methacrylonitrile, and 2-cyanoethyl (meth)acrylate. Of these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0036] Examples of monomers containing an amide group include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, and diacetone(meth)acrylamide.

[0037] Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate.

[0038] Examples of monomers having a nitrogen atom-containing ring include monomers in which a substituent with polymerizable functional groups is bonded to the nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-(meth)acryloylmorpholine. Other examples include maleimide ring-containing monomers such as N-isopropylmaleimide and N-cyclohexylmaleimide.

[0039] An example of an isocyanate group-containing monomer is 2-(meth)acryloyloxyethyl isocyanate.

[0040] Examples of monomers containing acid anhydride groups include maleic anhydride and itaconic anhydride.

[0041] Examples of keto group-containing monomers include diacetone (meth)acrylate, vinyl methyl ketone, vinyl ethyl ketone, allyl acetacetate, and vinyl acetacetate.

[0042] Examples of monomers having an epoxy group include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, and allyl glycidyl ether.

[0043] Examples of monomers containing an alkoxysilyl group include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane.

[0044] The first monomer component may contain other copolymer components other than the monomers mentioned above for purposes such as improving the cohesive strength of the strippable paint after curing. Examples of other copolymer components include vinyl ester monomers such as vinyl acetate (VAc), vinyl propionate, and vinyl laurate; aromatic vinyl compound monomers such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; and aromatic (meth)acrylates such as aryl (meth)acrylate (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylate (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylate (e.g., benzyl (meth)acrylate). Examples include: ring-containing (meth)acrylates; olefin monomers such as ethylene, propylene, isoprene, butadiene, and isobutylene; chlorine atom-containing monomers such as vinyl chloride and vinylidene chloride; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethyl carbitol (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and polyfunctional monomers having two or more (e.g., three or more) polymerizable functional groups (e.g., (meth)acryloyl groups) in one molecule, such as 1,6-hexanediol di(meth)acrylate and trimethylolpropane tri(meth)acrylate.

[0045] In some embodiments, the first monomer component constituting the first acrylic polymer includes a nitrogen atom-containing monomer. Examples of nitrogen atom-containing monomers include at least one of the cyano group-containing monomers, amide group-containing monomers, amino group-containing monomers, and monomers having a nitrogen atom-containing ring, as described above. The nitrogen atom-containing monomer can be used alone or in combination of two or more. The first monomer component preferably contains a combination of alkyl (meth)acrylate and a nitrogen atom-containing monomer, C 4-9 It is more preferable to include a combination of alkyl acrylate and nitrogen atom-containing monomer. Nitrogen atom-containing monomers tend to exhibit relatively high SP values ​​(e.g., higher SP values ​​than alkyl (meth)acrylates) due to the presence of a nitrogen-containing structural moiety. In this specification, SP value refers to the value of the solubility parameter calculated from the basic structure of the compound using the method proposed by Fedors. Appropriate use of nitrogen atom-containing monomers makes it easier to obtain a first acrylic polymer having an SP value above a certain level. A high SP value of the first acrylic polymer can help achieve good peelability in strippable paints. Furthermore, nitrogen atom-containing monomers generally tend to have a high Tg of homopolymer and can be suitably used as the first monomer described later for the first acrylic polymer.

[0046] In embodiments where the first monomer component includes a nitrogen atom-containing monomer, the proportion of the nitrogen atom-containing monomer in the first monomer component can be set to obtain the desired effect. In some embodiments, the proportion of the nitrogen atom-containing monomer in the first monomer component is preferably 10% by weight or more, more preferably 20% by weight or more, more preferably 25% by weight or more, and more preferably 30% by weight or more. This proportion of nitrogen atom-containing monomer is preferable for effectively exhibiting the physical properties resulting from the nitrogen atom-containing monomer in the first acrylic polymer. The proportion of nitrogen atom-containing monomer in the first monomer component is preferably 50% by weight or less, more preferably 45% by weight or less, and more preferably 40% by weight or less.

[0047] In some preferred embodiments, the first monomer component includes at least acrylonitrile as the nitrogen atom-containing monomer. Acrylonitrile in acrylic polymers readily forms hard segments due to its cohesive force (more readily than, for example, styrene). The formation of hard segments in acrylic polymers contributes to the development of rubber elasticity in the polymer, and therefore helps to achieve moderate elongation and ensure tensile strength after curing of strippable paints containing such acrylic polymers. For this reason, including acrylonitrile in the first monomer component makes it easier to realize a strippable paint that can form a protective coating material that balances good peelability and good trace resistance. The proportion of acrylonitrile among the nitrogen atom-containing monomers in the first monomer component is, for example, 25% by weight or more, and may be 50% by weight or more, 75% by weight or more, 95% by weight or more, or 100% by weight.

[0048] In some embodiments, the first monomer component constituting the first acrylic polymer includes an aromatic vinyl compound monomer. Examples of aromatic vinyl compound monomers include at least one of the above-mentioned monomers such as styrene, substituted styrene (α-methylstyrene, etc.), and vinyltoluene. The aromatic vinyl compound monomer can be used alone or in combination of two or more. The first monomer component preferably contains an alkyl (meth)acrylate and an aromatic vinyl compound monomer in combination, C 4-9 It is more preferable to include a combination of alkyl acrylate and aromatic vinyl compound monomer. Aromatic vinyl compound monomers tend to exhibit relatively high Tg (e.g., higher Tg than alkyl (meth)acrylate) due to the inclusion of a structural moiety containing an aromatic ring. Such aromatic vinyl compound monomers can be suitably used as primary monomers for primary acrylic polymers.

[0049] In embodiments where the first monomer component includes an aromatic vinyl compound monomer, the proportion of the aromatic vinyl compound monomer in the first monomer component can be set to obtain the desired effect. In some embodiments, the proportion of the aromatic vinyl compound monomer in the first monomer component is preferably 5% by weight or more, more preferably 8% by weight or more, more preferably 10% by weight or more, more preferably 15% by weight or more, and may be 20% by weight or more or 30% by weight or more. This proportion of aromatic vinyl compound monomer is preferred for effectively exhibiting the properties attributable to the aromatic vinyl compound monomer in the first acrylic polymer. The proportion of aromatic vinyl compound monomer in the first monomer component is preferably 50% by weight or less, more preferably 45% by weight or less, and more preferably 40% by weight or less.

[0050] In some preferred embodiments, the first monomer component includes at least styrene as the aromatic vinyl compound monomer. Styrene in the first acrylic polymer formed from the first monomer component readily forms hard segments due to the superimposed contribution of bulkiness at the benzene ring and intermolecular forces resulting from pi electrons. The formation of hard segments in the acrylic polymer contributes to the development of rubber elasticity in the polymer, and therefore helps to achieve moderate elongation and ensure tensile strength after curing of a strippable paint containing such an acrylic polymer. The proportion of styrene in the aromatic vinyl compound monomer contained in the first monomer component is, for example, 25% by weight or more, and may be 50% by weight or more, 75% by weight or more, 95% by weight or more, or 100% by weight.

[0051] The first monomer component constituting the first acrylic polymer includes a first monomer having a relatively high glass transition temperature for the homopolymer and a second monomer having a relatively low glass transition temperature for the homopolymer. The first and second monomers may each be acrylic monomers or monomers other than acrylic monomers.

[0052] In the technologies disclosed herein, the glass transition temperature of homopolymers shall be the value specified in the publicly available documents. For example, for the monomers listed below, the following value shall be used as the glass transition temperature of the homopolymer of the monomer. n-butyl acrylate -55℃ Acrylonitrile 97℃ Styrene 100℃ Vinyl acetate 32℃ Methyl methacrylate 105℃ Acrylic acid 106℃

[0053] For the glass transition temperature (Tg) of monomer homopolymers other than those exemplified above, the values ​​listed in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. If the Tg of a homopolymer is not listed in publicly available documents, the value obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used. Specifically, 100 parts by weight of monomer, 0.2 parts by weight of azobisisobutyronitrile, and 200 parts by weight of ethyl acetate as the polymerization solvent are added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, and the mixture is stirred for 1 hour while circulating nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Next, the mixture is cooled to room temperature to obtain a homopolymer solution with a non-volatile content of 33% by weight. Next, this homopolymer solution is cast onto a release liner and dried to produce a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is punched out into a 7.9 mm diameter disc shape, sandwiched between parallel plates, and measured using a viscoelasticity tester (manufactured by T.A. Instruments Japan, model name "ARES") in shear mode while applying a shear strain of 1 Hz at a frequency, in a temperature range of -70 to 150°C with a heating rate of 5°C / min. The peak top temperature of tanδ is defined as the Tg of the homopolymer (homopolymer Tg).

[0054] The Tg of the homopolymer of the first monomer is, for example, 30°C or higher, preferably 50°C or higher, more preferably 65°C or higher, more preferably 80°C or higher, more preferably 90°C or higher, more preferably 95°C or higher, and may also be 100°C or higher or 104°C or higher. The higher the Tg of the homopolymer of the first monomer, the higher the cohesive force and high-temperature properties of the strippable paint (containing a first acrylic polymer with the first monomer as a constituent monomer) after curing. These high-temperature properties include, for example, suppression of the decrease in storage modulus in the high-temperature range and peelability at high temperatures in the strippable paint after curing. The Tg of the homopolymer of the first monomer is, for example, 250°C or lower, and may also be 200°C or lower or 150°C or lower.

[0055] In some preferred embodiments, the homopolymer Tg of the first monomer is 50°C or higher than the homopolymer Tg of the second monomer. Such a configuration is suitable for suppressing the temperature dependence of the properties of the strippable paint over a relatively wide temperature range defined by two temperatures with a temperature difference of, for example, 50°C or more. These properties include the adhesion to articles, elongation, and tensile strength of the strippable paint after curing. The difference in homopolymer Tg between the first and second monomers is more preferably 70°C or higher, more preferably 90°C or higher, more preferably 110°C or higher, more preferably 130°C or higher, and more preferably 150°C or higher.

[0056] The proportion of the first monomer in the first monomer component is preferably 10% by weight or more, more preferably 20% by weight or more, more preferably 25% by weight or more, and more preferably 30% by weight or more. This proportion of the first monomer is preferable for effectively exhibiting the physical properties attributable to the first monomer in the first acrylic polymer. The proportion of the first monomer in the first monomer component is preferably 50% by weight or less, more preferably 45% by weight or less, and more preferably 40% by weight or less. This proportion of the first monomer is preferable for exhibiting a good balance between the physical properties attributable to the first monomer and the physical properties attributable to the second monomer in the first acrylic polymer.

[0057] The first monomer is preferably a nitrogen atom-containing monomer or an aromatic vinyl compound monomer, and more preferably acrylonitrile or styrene.

[0058] The homopolymer Tg of the second monomer described above is, for example, 40°C or lower, preferably 20°C or lower, more preferably 0°C or lower, more preferably -20°C or lower, more preferably -40°C or lower, more preferably -50°C or lower, and may also be -60°C or lower or -70°C or lower. The lower the homopolymer Tg of the second monomer, the more helpful it is in ensuring the flexibility of the strippable paint after curing. The homopolymer Tg of the second monomer is, for example, -100°C or higher, and may also be -90°C or higher or -80°C or higher.

[0059] The proportion of the second monomer in the first monomer component is preferably 10% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, and more preferably 60% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more. This proportion of the second monomer is preferred for effectively exhibiting the physical properties attributable to the second monomer in the first acrylic polymer. The proportion of the second monomer in the first monomer component is preferably 98% by weight or less, more preferably 90% by weight or less, more preferably 80% by weight or less, and more preferably 70% by weight or less. This proportion of the second monomer is preferred for exhibiting a good balance between the physical properties attributable to the second monomer and the physical properties attributable to the first monomer in the first acrylic polymer.

[0060] The second monomer is preferably C 4-20 Alkyl (meth)acrylate, more preferably C 4-14 Alkyl (meth)acrylate, more preferably n-butyl acrylate (BA) or 2-ethylhexyl acrylate (2EHA).

[0061] In some preferred embodiments, the first monomer is the monomer with the highest homopolymer Tg in the first monomer component forming the first acrylic polymer. In some preferred embodiments, the second monomer is the monomer with the second highest homopolymer Tg in the first monomer component. In some preferred embodiments, the first monomer component consists of two components: the first monomer and the second monomer. These configurations are suitable for effectively forming a first acrylic polymer with the first and second monomers that has significant physical properties different from the second acrylic polymer described later. In some embodiments, the first monomer component may include one or more monomers other than the first and second monomers.

[0062] The above-mentioned second acrylic polymer is a polymer of a second monomer component containing one or more acrylic monomers, and its monomer composition differs from that of the first acrylic polymer. The proportion of acrylic monomers in the second monomer component is the same as that of acrylic monomers in the first monomer component as described above.

[0063] In some embodiments, the second monomer component constituting the second acrylic polymer includes at least a (meth)acryloyl group-containing monomer as the acrylic monomer. The (meth)acryloyl group-containing monomer can be used alone or in combination of two or more. The proportion of the (meth)acryloyl group-containing monomer in the second monomer component is the same as that described above for the proportion of the (meth)acryloyl group-containing monomer in the first monomer component.

[0064] The second monomer component preferably contains at least an alkyl (meth)acrylate as the above (meth)acryloyl group-containing monomer. As the alkyl (meth)acrylate, as described above with respect to the first monomer component, for example, the compound represented by formula (1) above can be suitably used, and at least C 4-20 It is preferable to use alkyl (meth)acrylates (specific examples are as described above), and at least C 4-9 It is more preferable to use alkyl acrylates. The second monomer component preferably contains one or both of BA and 2EHA as alkyl (meth)acrylates, as described above with respect to the first monomer component. 1-20 Regarding the proportion of alkyl (meth)acrylate, C in the first monomer component 1-20 The proportion of alkyl (meth)acrylate is the same as described above. The second monomer component is C 4-9 In embodiments comprising alkyl acrylate, the C in the second monomer component 4-9 Regarding the proportion of alkyl acrylate, C in the first monomer component 4-9 The proportion of alkyl acrylate is the same as described above.

[0065] The second monomer component may, like the first monomer component described above, contain a combination of alkyl (meth)acrylate and monomers other than alkyl (meth)acrylate. Examples of monomers other than alkyl (meth)acrylate in the second monomer component include the monomers described above as examples of monomers other than alkyl (meth)acrylate in the first monomer component.

[0066] The second monomer component may contain other copolymer components other than the monomers mentioned above, for purposes such as improving the cohesive strength of the strippable paint after curing. Examples of such copolymer components include the components mentioned above as other copolymer components in the first monomer component.

[0067] In some embodiments, the second monomer component constituting the second acrylic polymer includes a nitrogen atom-containing monomer. Examples of nitrogen atom-containing monomers include at least one of the above-mentioned cyano group-containing monomers, amide group-containing monomers, amino group-containing monomers, and monomers having a nitrogen atom-containing ring. The nitrogen atom-containing monomer can be used alone or in combination of two or more. The second monomer component preferably contains a combination of alkyl (meth)acrylate and a nitrogen atom-containing monomer, C 4-9 It is more preferable to include a combination of alkyl acrylate and nitrogen atom-containing monomer. Nitrogen atom-containing monomers tend to exhibit relatively high SP values ​​(for example, higher SP values ​​than alkyl (meth)acrylates) due to the presence of a nitrogen-containing structural moiety. Appropriate use of nitrogen atom-containing monomers makes it easier to obtain a second acrylic polymer having an SP value above a predetermined level. A high SP value of the second acrylic polymer can help achieve good peelability in strippable paints. Furthermore, nitrogen atom-containing monomers generally tend to have a high Tg of homopolymer and can be suitably used as a third monomer for the second acrylic polymer, as described later.

[0068] In embodiments where the second monomer component includes a nitrogen atom-containing monomer, the proportion of the nitrogen atom-containing monomer in the second monomer component can be set to obtain the desired effect. In some embodiments, the proportion of the nitrogen atom-containing monomer in the second monomer component is preferably 2% by weight or more, more preferably 4% by weight or more, and may be 6% by weight or more, 8% by weight or 10% by weight or more. This proportion of nitrogen atom-containing monomer is preferred for effectively exhibiting the physical properties resulting from the nitrogen atom-containing monomer in the second acrylic polymer. The proportion of nitrogen atom-containing monomer in the second monomer component is preferably 30% by weight or less, more preferably 20% by weight or less, more preferably 10% by weight or less, and more preferably 7% by weight or less.

[0069] In some preferred embodiments, the second monomer component includes at least acrylonitrile as the nitrogen atom-containing monomer. Including acrylonitrile in the second monomer component makes it easier to realize a strippable paint that can form a protective coating material that balances good peelability and good trace resistance. The proportion of acrylonitrile in the nitrogen atom-containing monomer contained in the second monomer component is, for example, 25% by weight or more, and may be 50% by weight or more, 75% by weight or more, 95% by weight or more, or 100% by weight.

[0070] The above-mentioned second monomer component includes a third monomer with a relatively high homopolymer Tg and a fourth monomer with a relatively low homopolymer Tg. The third and fourth monomers may each be acrylic monomers or monomers other than acrylic monomers.

[0071] The Tg of the homopolymer of the third monomer is, for example, 30°C or higher, preferably 50°C or higher, more preferably 65°C or higher, more preferably 80°C or higher, more preferably 90°C or higher, more preferably 95°C or higher, and may also be 100°C or higher or 104°C or higher. The higher the Tg of the homopolymer of the third monomer, the higher the cohesive force and high-temperature properties of the strippable paint (containing a second acrylic polymer that includes the third monomer as a constituent monomer) after curing. The Tg of the homopolymer of the third monomer is, for example, 250°C or lower, and may also be 200°C or lower or 150°C or lower.

[0072] In some preferred embodiments, the homopolymer Tg of the third monomer is 50°C or higher than the homopolymer Tg of the fourth monomer. Such a configuration is suitable for suppressing the temperature dependence of the properties of the strippable paint over a relatively wide temperature range defined by two temperatures with a temperature difference of, for example, 50°C or more. The difference in homopolymer Tg between the third monomer and the fourth monomer is more preferably 70°C or higher, more preferably 90°C or higher, more preferably 110°C or higher, more preferably 130°C or higher, and more preferably 150°C or higher.

[0073] The proportion of the third monomer in the second monomer component is preferably 2% by weight or more, more preferably 4% by weight or more, and may be 6% by weight or more, 8% by weight or 10% by weight or more. This proportion of the third monomer is preferable for effectively expressing the physical properties attributable to the third monomer in the second acrylic polymer. The proportion of the third monomer in the second monomer component is preferably 30% by weight or less, more preferably 20% by weight or less, more preferably 10% by weight or less, and more preferably 7% by weight or less. This proportion of the third monomer is preferable for expressing a good balance between the physical properties attributable to the third monomer and the physical properties attributable to the fourth monomer in the second acrylic polymer.

[0074] The third monomer is preferably a nitrogen atom-containing monomer, and more preferably acrylonitrile.

[0075] The homopolymer Tg of the fourth monomer described above is, for example, 40°C or lower, preferably 20°C or lower, more preferably 0°C or lower, more preferably -20°C or lower, more preferably -40°C or lower, more preferably -50°C or lower, and may also be -60°C or lower or -70°C or lower. The lower the homopolymer Tg of the fourth monomer, the more helpful it is in ensuring the flexibility of the strippable paint after curing. The homopolymer Tg of the fourth monomer is, for example, -100°C or higher, and may also be -90°C or higher or -80°C or higher.

[0076] The proportion of the fourth monomer in the second monomer component is preferably 10% by weight or more, more preferably 30% by weight or more, more preferably 45% by weight or more, and more preferably 60% by weight or more, and may be 65% by weight or more, 75% by weight or more, or 85% by weight or more. This proportion of the fourth monomer is preferred for effectively exhibiting the physical properties attributable to the fourth monomer in the second acrylic polymer. The proportion of the fourth monomer in the second monomer component is preferably 98% by weight or less, more preferably 90% by weight or less, more preferably 80% by weight or less, and more preferably 70% by weight or less. This proportion of the fourth monomer is preferred for exhibiting a good balance between the physical properties attributable to the fourth monomer and the physical properties attributable to the third monomer in the second acrylic polymer.

[0077] The fourth monomer is preferably C 4-20 Alkyl (meth)acrylate, more preferably C 4-14 Alkyl (meth)acrylate, more preferably BA or 2EHA.

[0078] In some preferred embodiments, the third monomer is the monomer with the highest homopolymer Tg in the second monomer component forming the second acrylic polymer. In some preferred embodiments, the fourth monomer is the monomer with the second highest homopolymer Tg in the second monomer component. In some preferred embodiments, the second monomer component consists of two components: the third monomer and the fourth monomer. These configurations are suitable for effectively forming a second acrylic polymer with significantly different physical properties from the first acrylic polymer described above, using the third and fourth monomers. In some embodiments, the second monomer component may include one or more monomers other than the third and fourth monomers.

[0079] In some embodiments, the combined proportion of the first and third monomers in the total amount of the first and second monomer components is preferably 5% by weight or more, more preferably 10% by weight or more, more preferably 15% by weight or more, and more preferably 20% by weight or more. This combined proportion of the first and third monomers is preferred for effectively exhibiting the properties derived from the first and third monomers in the strippable paint. In some embodiments, the combined proportion of the first and third monomers in the total amount of the first and second monomer components is preferably 50% by weight or less, more preferably 40% by weight or less, more preferably 33% by weight or less, and more preferably 30% by weight or less. This combined proportion of the first and third monomers is preferred for exhibiting the properties derived from the first to fourth monomers in a balanced manner in the strippable paint.

[0080] In the strippable paint disclosed herein, the homopolymer Tg of the first monomer is higher than the homopolymer Tg of the third monomer (first configuration), or the homopolymer Tg of the first monomer is the same as the homopolymer Tg of the third monomer, and the proportion of the first monomer in the first monomer component is greater than the proportion of the third monomer in the second monomer component (second configuration). With respect to the second configuration, when the homopolymer Tg of the first monomer and the third monomer are the same, this includes cases where the first monomer and the third monomer are the same type of monomer or different types of monomers.

[0081] In the first configuration described above, the proportion of the first acrylic polymer in the polymer in the strippable paint is preferably 5% by weight or more, more preferably 10% by weight or more, more preferably 17% by weight or more, and more preferably 20% by weight or more. This proportion of the first acrylic polymer is preferable for effectively exhibiting the physical properties derived from the first acrylic polymer in the strippable paint. In the first configuration described above, the proportion of the first acrylic polymer in the polymer in the strippable paint is preferably less than 70% by weight, more preferably 60% by weight or less, more preferably 50% by weight or less, more preferably 40% by weight or less, and more preferably 35% by weight or less. This proportion of the first acrylic polymer is preferable for exhibiting a balanced expression of the physical properties derived from the first and second acrylic polymers in the strippable paint.

[0082] In the first configuration described above, the proportion of the second acrylic polymer in the polymer in the strippable paint is preferably more than 30% by weight, more preferably 40% by weight or more, more preferably 50% by weight or more, more preferably 60% by weight or more, and more preferably 65% ​​by weight or more. This proportion of the second acrylic polymer is preferable for effectively exhibiting the physical properties derived from the second acrylic polymer in the strippable paint. In the first configuration described above, the proportion of the second acrylic polymer in the polymer in the strippable paint is preferably 95% by weight or less, more preferably 90% by weight or less, and more preferably 80% by weight or less. This proportion of the second acrylic polymer is preferable for exhibiting a balanced expression of the physical properties derived from the first and second acrylic polymers in the strippable paint.

[0083] In the case of the second configuration described above, the proportion of the first acrylic polymer in the polymer in the strippable paint is preferably 10% by weight or more, more preferably 25% by weight or more, more preferably 35% by weight or more, more preferably 45% by weight or more, and more preferably 50% by weight or more. This proportion of the first acrylic polymer is preferable for effectively exhibiting the physical properties derived from the first acrylic polymer in the strippable paint. In the case of the second configuration described above, the proportion of the first acrylic polymer in the polymer in the strippable paint is preferably 95% by weight or less, more preferably 90% by weight or less, more preferably 87% by weight or less, more preferably 80% by weight or less, and more preferably 75% by weight or less. This proportion of the first acrylic polymer is preferable for exhibiting a balanced expression of the physical properties derived from the first and second acrylic polymers in the strippable paint.

[0084] In the case of the second configuration described above, the proportion of the second acrylic polymer in the polymer in the strippable paint is preferably 5% by weight or more, more preferably 15% by weight or more, more preferably 25% by weight or more, more preferably 35% by weight or more, and more preferably 40% by weight or more, and may be 45% by weight, 55% by weight or 65% by weight or more. This proportion of the second acrylic polymer is preferable for effectively exhibiting the physical properties due to the second acrylic polymer in the strippable paint. In the case of the second configuration described above, the proportion of the second acrylic polymer in the polymer in the strippable paint is preferably 90% by weight or less, more preferably 80% by weight or less, more preferably 75% by weight or less, more preferably 65% ​​by weight or less, more preferably 55% by weight or less, and more preferably 50% by weight or less. This proportion of the second acrylic polymer is preferable for exhibiting a balanced expression of the physical properties due to the first and second acrylic polymers in the strippable paint.

[0085] The strippable paint disclosed herein may optionally contain various additives. Examples of such additives include known thickeners, thixotropes, dispersants, defoamers, and inorganic powders.

[0086] By incorporating inorganic powder into strippable paint, a protective coating material containing inorganic powder can be formed from such strippable paint. With such a protective coating material, the inorganic powder blocks light such as ultraviolet rays, and photodegradation of the coating material itself and the coating film protected by the coating material can be suppressed. Suitable inorganic powders include oxides such as titanium dioxide, zinc oxide, magnesium oxide, alumina, and silica; carbonates such as calcium carbonate; sulfates such as barium sulfate; and the like. Inorganic powder that can color the strippable paint white is preferred. With white strippable paint, for example, the deterioration of the protective coating material and the coating film can be better suppressed by suppressing the temperature rise caused by sunlight irradiation.

[0087] The amount of inorganic powder used per 100 parts by weight of total polymer (including the first and second acrylic polymers described above) in the strippable paint can be, for example, 0.5 parts by weight or more, and from the viewpoint of light shielding effect, it is appropriate to be 1 part by weight or more, preferably 2 parts by weight or more, more preferably 3 parts by weight or more, and may also be 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, or 40 parts by weight or more (for example, 45 parts by weight or more). Furthermore, the amount of inorganic powder used per 100 parts by weight of total polymer in the strippable paint can be, for example, 100 parts by weight or less, and from the viewpoint of the strength and film-forming properties of the protective coating material, it is appropriate to be 80 parts by weight or less, advantageous to be 60 parts by weight or less, preferably 50 parts by weight or less, and may also be 40 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less.

[0088] In several preferred embodiments, the inorganic powder contains at least titanium dioxide (TiO2). Titanium dioxide may be used in combination with one or more other inorganic powders (e.g., calcium carbonate). The type of titanium dioxide is not particularly limited, and any crystalline form of titanium dioxide, such as rutile, anatase, or brookite, can be used. Rutile titanium dioxide is preferred. Titanium dioxide with a coating applied to the particle surface may also be used. The material used to coat the titanium dioxide particles is not particularly limited and can be an inorganic oxide such as silica, alumina, or zinc oxide. A preferred example is a highly weather-resistant type of titanium dioxide (typically rutile titanium dioxide) with the particle surface coated with Si-Al2O3 or the like.

[0089] The amount of titanium dioxide used per 100 parts by weight of total polymer in the strippable paint can be, for example, 0.1 parts by weight or more, and from the viewpoint of light shielding effect, it is appropriate to use 0.5 parts by weight or more, preferably 1 part by weight or more, more preferably 2 parts by weight or more, and may also be 3 parts by weight or more. In addition, the amount of titanium dioxide used per 100 parts by weight of total polymer in the strippable paint can be, for example, 30 parts by weight or less, appropriate to use 20 parts by weight or less, preferably 15 parts by weight or less, may also be 10 parts by weight or less, and may also be 8 parts by weight or less.

[0090] The average particle size of the inorganic powder is not particularly limited. For example, from the viewpoint of obtaining a good light shielding effect, the average particle size of the inorganic powder is preferably 150 nm or more, more preferably 180 nm or more, and may also be 220 nm or more, or 250 nm or more. On the other hand, from the viewpoint of dispersibility in the resin component, the average particle size of the inorganic powder is suitable to be 3000 nm or less (e.g., 2000 nm or less), preferably 1500 nm or less, more preferably 1000 nm or less (e.g., 800 nm or less), and may also be 500 nm or less, 400 nm or less, or 350 nm or less. For example, titanium oxide particles with an average particle size of about 250 to 350 nm can be preferably used.

[0091] Thickeners can be used to adjust the viscosity properties of strippable paints. Known thickeners such as urethane-based thickeners, cellulose-based thickeners, polyether-based thickeners, and acrylic-based thickeners can be used. Thickeners can be used individually or in combination of two or more as appropriate.

[0092] Examples of commercially available urethane-based thickeners include BYK's product names "RHEOBYK-H 3300VF," "RHEOBYK-T 1010," and "RHEOBYK-L 1400," ADEKA's product names "Adekanol UH-450VF," "Adekanol UH-420," "Adekanol UH-462," "Adekanol UH-472," "Adekanol UH-540," "Adekanol UH-756VF," and "Adekanol UH-814N," and Sunnopco's product names "SN Thickener 612," "SN Thickener 621N," "SN Thickener 625N," "SN Thickener 627N," and "SN Thickener 660T." In some embodiments, urethane association type thickeners can be preferably used as urethane-based thickeners. Suitable examples of urethane-associated thickeners include BYK's product names "RHEOBYK-H 3300VF," "RHEOBYK-T 1010," and "RHEOBYK-L 1400," and ADEKA's product names "Adekanol UH-450VF," "Adekanol UH-420," and "Adekanol UH-756VF."

[0093] Examples of cellulose-based thickeners include hydroxyethylcellulose, carboxymethylcellulose, and methylcellulose. A commercially available example is "SANHEC L" manufactured by Sansho Co., Ltd.

[0094] Examples of polyether-based thickeners include polyethylene glycol, polyether dialkyl esters, polyether dialkyl ethers, and polyether epoxy modified products. A commercially available example is "POLYOX WSR N-80" manufactured by Dow Chemical.

[0095] Examples of acrylic thickeners include acrylic acid polymers such as sodium polyacrylate. Commercially available products include, for example, "Primal ASE-60," "Primal TT-615," and "Primal RM-5" from Rohm & Haas, and "SN Thickener 613," "SN Thickener 618," "SN Thickener 630," "SN Thickener 634," and "SN Thickener 636" from Sunnopco.

[0096] The amount of thickener used is not particularly limited and can be adjusted as appropriate to obtain the desired viscosity characteristics. From the viewpoint of suppressing excessive influence on film properties, in some embodiments, the amount of thickener used per 100 parts by weight of total polymer in the strippable paint is appropriate to be 15 parts by weight or less, preferably 10 parts by weight or less, more preferably 5 parts by weight or less (e.g., 3 parts by weight or less), may be 2.5 parts by weight or less, 2 parts by weight or less, 1.0 part by weight or less, or 0.50 parts by weight or less. The lower limit of the amount of thickener used is not particularly limited and may be 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more (e.g., 0.10 parts by weight or more), or 0.20 parts by weight or more per 100 parts by weight of total polymer.

[0097] Thixotropes can be useful for adjusting the viscosity properties of strippable paints. Inorganic materials such as bentonite, modified bentonite, montmorillonite, and hectorite can be used as thixotropes. Thixotropes can be used individually or in combination of two or more.

[0098] The amount of thixotropin used is not particularly limited and can be adjusted as appropriate to obtain the desired viscosity characteristics. From the viewpoint of suppressing excessive influence on film properties, in some embodiments, the amount of thixotropin used per 100 parts by weight of total polymer in the strippable paint is appropriate to be 10 parts by weight or less, preferably 5 parts by weight or less, and may also be 3 parts by weight or less, 2.5 parts by weight or less, or 2 parts by weight or less. The lower limit of the amount of thixotropin used is not particularly limited and may be 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more per 100 parts by weight of total polymer. Alternatively, no thixotropin may be used.

[0099] The thixotropic agent may also function as a thickening agent. The thickening agents and thixotropic agents described above may be used in combination, or one of them may be used alone. When the thickening agents and thixotropic agents are used in combination, the total amount used may be, for example, 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, 4 parts by weight or less, 2.5 parts by weight or less, 1.5 parts by weight or less, or 1.0 part by weight or less, or 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more (for example, 0.10 parts by weight or more), or 0.20 parts by weight or more, based on 100 parts by weight of the total polymer in the strippable paint.

[0100] Methods for applying strippable paint to a coating on an object to be protected include, for example, application by a coater such as a die coater or spray coater, roller application, or dip coating. The application by a die coater may be performed by a coating system including a robotic arm equipped with a slit die. For example, by controlling the robotic arm so that the slit die moves along the shape of the object to be protected while discharging the strippable paint in a continuous liquid film (ribbon shape), the strippable paint can be applied efficiently and accurately to the object to be protected even if the object has a non-planar shape (for example, a complex three-dimensional shape such as the exterior of an automobile).

[0101] Drying the applied strippable paint is preferably carried out under heating, from the viewpoint of improving the efficiency and precision of protective coating material formation. The drying temperature can be, for example, around 40°C to 100°C, and is usually preferably around 60°C to 90°C.

[0102] While not particularly limited, from the viewpoint of ease of coating and film thickness control, the solid content of strippable paint is appropriately 25 to 75% by weight, and preferably 30 to 70% by weight (for example, 45 to 55% by weight). The solid content can be adjusted by the amount of solvent (e.g., aqueous solvent) used. For example, the solid content of strippable paint can be adjusted by adjusting the amount of water used in emulsion polymerization described later, or by adding water after the emulsion polymerization is completed.

[0103] (BH viscosity) In some embodiments, the viscosity V1 of the strippable paint, as measured by a BH-type viscometer at 2 rpm, is appropriately 20 Pa·s or higher, preferably 40 Pa·s or higher, and more preferably 55 Pa·s or higher. As the viscosity V1 measured under such low shear rate conditions increases, the anti-sagging properties of the strippable paint applied to the object to be protected (for example, anti-sagging properties when applied to a vertical surface) tend to improve. On the other hand, from the viewpoint of the defoaming and leveling properties of the strippable paint, the viscosity V1 of the strippable paint is appropriately 200 Pa·s or less, preferably 150 Pa·s or less, and more preferably 100 Pa·s or less (for example, 80 Pa·s or less).

[0104] The viscosity V2 of the strippable paint described above, measured using a BH-type viscometer at 20 rpm, is not particularly limited and may be, for example, around 5 Pa·s to 50 Pa·s. When viscosity V2 is within this range, the viscosity V1 described above is easily obtained. The viscosity of the strippable paint measured using a BH-type viscometer (BH viscosity) is measured using a BH-type viscometer at 30°C under conditions of 2 rpm and 20 rpm. The rotor used for measurement is appropriately selected according to the viscosity. For example, it can be measured using a No. 6 rotor, and if the use of a No. 6 rotor is inappropriate, it can be measured using another rotor of a suitable number.

[0105] The ratio of viscosity V1 to viscosity V2 (hereinafter also referred to as the "Ti value") may be, for example, 2.0 or more, preferably 3.0 or more, and more preferably 3.5 or more. Furthermore, the Ti value may be, for example, 9.0 or less, preferably 8.0 or less, more preferably 7.0 or less, and may also be 6.0 or less, or 5.5 or less. Strippable paints having such a Ti value tend to have coating properties suitable for slot die coating.

[0106] (Rheometer viscosity) In some embodiments, the strippable paint has a shear rate of 100 sec measured by a cone-plate rheometer. -1The viscosity V3 is preferably 1.0 Pa·s or higher, more preferably 1.3 Pa·s or higher, and may also be 1.5 Pa·s or higher, 2.0 Pa·s or higher, or 2.3 Pa·s or higher. By setting the viscosity V3 measured under such high shear rate conditions to a predetermined level or higher, the coating properties (die coating properties) by the slot die can be improved. There is no particular upper limit to the viscosity V3, but from the viewpoint of ease of compatibility with defoaming properties and ease of liquid transfer, it is appropriate to be 15 Pa·s or lower, preferably 10 Pa·s or lower, and may also be 8.5 Pa·s or lower, or 6.0 Pa·s or lower. The viscosity (rheometer viscosity) of the strippable paint was determined using a commercially available rheometer (for example, Haacke's "Rheo Stress 1" rheometer viscometer or equivalent) with a cone-type rotor (Cone Diameter: 35 mm, Cone Angle: 0.5 deg.) at 30°C, with a shear rate of 0.1 to 2000 sec. -1 From the viscosity when continuously changed, the shear rate 100 sec -1 The viscosity can be measured by reading the viscosity in the sample.

[0107] (Tensile storage modulus) The strippable paint disclosed herein has a ratio of the tensile storage modulus at 0°C (second tensile storage modulus) to the tensile storage modulus at 40°C (first tensile storage modulus) after curing of 350 or less, preferably 220 or less, more preferably 100 or less, more preferably 50 or less, more preferably 30 or less, and more preferably 20 or less. Such a strippable paint contains first and second acrylic polymers with monomer compositions different from each other as described above, and because the above ratio of tensile storage moduli is 350 or less, it is suitable for suppressing the temperature dependence of adhesion to articles, elongation, and breaking strength after curing. Specifically, this is shown in the examples and comparative examples below. Therefore, this strippable paint is suitable for suppressing fluctuations in adhesion to article surfaces and peelability from those surfaces due to temperature differences (for example, a temperature difference between approximately 0°C and approximately 40°C). The above ratio is, for example, 0.5 or more, 1.0 or more, 2.0 or more, or 3.0 or more. The tensile storage modulus of a cured strippable paint is determined by dynamic mechanical analysis. This measurement can be performed using the RSA-G2 dynamic mechanical analysis device manufactured by TA Instruments. In this measurement, the measurement mode is set to tensile mode, the measurement temperature range is -70°C to 150°C, the heating rate is 5°C / min, and the frequency is 1 Hz. The method for measuring the tensile storage modulus is specifically described in the examples below. Methods for adjusting the above ratio of tensile storage modulus include, for example, adjusting the monomer composition, molecular weight, glass transition temperature, degree of crosslinking, and blending amount of each acrylic polymer in the strippable paint. Other methods for adjusting the above ratio of tensile storage modulus include selecting and blending amounts of components other than polymers in the strippable paint.

[0108] The first tensile storage modulus (at 40°C) of the cured strippable paint is preferably 1.0 MPa or higher, more preferably 3.0 MPa or higher, more preferably 5.0 MPa or higher, more preferably 10 MPa or higher, more preferably 20 MPa or higher, more preferably 30 MPa or higher, and more preferably 40 MPa or higher. Such a configuration is suitable for ensuring the adhesion to articles and the breaking strength of the cured strippable paint in the temperature range of 40°C and its vicinity. The first tensile storage modulus (at 40°C) is preferably 100 MPa or lower, more preferably 80 MPa or lower, and more preferably 70 MPa or lower. Methods for adjusting the first tensile storage modulus include, for example, adjusting the monomer composition of each acrylic polymer in the strippable paint, adjusting the molecular weight, adjusting the glass transition temperature, adjusting the degree of crosslinking, and adjusting the blending amount. Methods for adjusting the first tensile storage modulus also include selecting and adjusting the blending amount of components other than polymers in the strippable paint. These adjustment methods are also applicable to the second tensile storage modulus, loss tangent, elongation at break, and breaking strength described later.

[0109] The second tensile storage modulus (0°C) of the strippable paint after curing is preferably 1.7 × 10⁻⁶. 3 MPa or less, more preferably 1.5 × 10 3 MPa or less, more preferably 1.0 × 10⁻⁶ 3 MPa or less, more preferably 0.8 × 10⁻⁶ 3 MPa or less, more preferably 0.7 × 10 3 It is less than or equal to MPa. Such a configuration is suitable for ensuring the adhesion to articles, elongation, and tensile strength of the cured strippable paint in the temperature range of 0°C and its vicinity. It is preferable that the cured strippable paint is not too hard, as this facilitates operations to form an edge for peeling the cured strippable paint from a predetermined location (for example, scratching the edge of the cured strippable paint with a fingernail or the like to lift it from the surface of the object to be protected). The second tensile storage modulus (0°C) is preferably 0.1 × 10⁻⁶. 3 MPa or higher, more preferably 0.2 × 10 3 MPa or higher, more preferably 0.3 × 103 MPa or higher, more preferably 0.4 × 10 3 MPa or higher, more comfortable 0.5 × 10 3 It is above MPa.

[0110] (loss tangent) The strippable paint disclosed herein preferably has a loss tangent peak in the range of 23°C to 40°C after curing. Such a configuration is suitable for exhibiting good viscoelasticity in the strippable paint after curing in the temperature range of 23°C to 40°C and its vicinity. More preferably, the strippable paint has a further peak in the loss tangent in the range of -15°C to 5°C after curing. Such a configuration helps suppress the temperature dependence of the adhesion to the article, elongation, and fracture strength of the strippable paint after curing, and therefore helps suppress temperature-dependent variations in the adhesion of the strippable paint to and peelability from the surface of the protected object. The loss tangent is determined by the dynamic viscoelasticity measurement described above. The method for measuring the loss tangent is specifically described later with reference to examples.

[0111] (Elongation at break) The strippable paints disclosed herein, after curing, have an elongation at break at 40°C, as measured by a tensile test described later for each example, preferably 100% or more, more preferably 150% or more, more preferably 180% or more, more preferably 250% or more, more preferably 300% or more, more preferably 350% or more, and more preferably 400% or more. Such strippable paints (after curing) can distribute stress by deforming appropriately when peeled off from a protected object at temperatures of 40°C or nearby, thus suppressing tearing due to localized stress concentration. The above elongation at break at 40°C is preferably 550% or less, more preferably 510% or less, and may also be 500% or less, 480% or less, or 460% or less. Such strippable paints (after curing) can suppress excessive deformation when peeled off from a protected object at temperatures of 40°C or nearby. Having an elongation at break that is not too large can be advantageous from the viewpoint of improving work efficiency during peeling.

[0112] After curing, the strippable paint has a break elongation at 0°C, as measured by a tensile test described later for each example, preferably 100% or more, more preferably 120% or more, more preferably 150% or more, more preferably 200% or more, more preferably 240% or more, and may also be 250% or more or 270% or more. Such a strippable paint (after curing) can distribute stress by deforming appropriately when peeled off from the protected object at temperatures of 0°C or near 0°C, thus suppressing tearing due to localized stress concentration. The break elongation at 0°C is preferably 550% or less, more preferably 450% or less, more preferably 300% or less, and may also be 280% or less, 260% or less, or 250% or less. Such a strippable paint (after curing) can suppress excessive deformation when peeled off from the protected object at temperatures of 0°C or near 0°C.

[0113] (Breaking strength) The strippable paints disclosed herein, after curing, have a breaking strength at 40°C, as measured by a tensile test described later with respect to the examples, preferably 10 N / 25 mm or more, more preferably 15 N / 25 mm or more, more preferably 18 N / 25 mm or more, and may be 20 N / 25 mm or more or 24 N / 25 mm or more. The breaking strength is, for example, 40 N / 25 mm or less, 60 N / 25 mm or less, or 100 N / 25 mm or less. A high breaking strength helps to suppress the tearing of the protective coating material formed from the strippable paint on the object to be protected when the coating material is peeled off the object to be protected.

[0114] After curing, the strippable paint has a breaking strength at 0°C, as measured by a tensile test described later for each example, which is preferably 15 N / 25 mm or more, more preferably 20 N / 25 mm or more, and more preferably 23 N / 25 mm or more, and may also be 25 N / 25 mm or more or 30 N / 25 mm or more. The breaking strength is, for example, 50 N / 25 mm or less, 70 N / 25 mm or less, or 100 N / 25 mm or less.

[0115] (Peel strength) The strippable paint disclosed herein preferably has a peel strength at 40°C, measured by the method described later with respect to the examples, of 6.5 N / 25 mm or less, more preferably 5.8 N / 25 mm or less, and may also be 5.0 N / 25 mm or less, 4.0 N / 25 mm or less, or 3.0 N / 25 mm or less, from the viewpoint of obtaining good peelability at temperatures of 40°C and nearby. A low peel strength is preferable from the viewpoint of reducing the workload during peeling, and is also advantageous from the viewpoint of suppressing tearing and chipping of the strippable paint (after curing) during peeling. Furthermore, from the viewpoint of obtaining appropriate adhesion of the strippable paint (after curing) to the object to be protected at temperatures of 40°C and nearby, the above peel strength is preferably 0.1 N / 25 mm or more, 0.2 N / 25 mm or more, 0.3 N / 25 mm or more, and may also be 0.5 N / 25 mm or more or 0.7 N / 25 mm or more. It is preferable that the peel strength is not too low, from the viewpoint of preventing the strippable paint (after curing) from unintentionally peeling off the object being protected. Methods for adjusting the peel strength include, for example, adjusting the monomer composition of each acrylic polymer in the strippable paint, adjusting the molecular weight, adjusting the glass transition temperature, adjusting the degree of crosslinking, and adjusting the amount of each polymer. Another method for adjusting the peel strength is to select and adjust the amount of components other than polymers in the strippable paint. Another method for adjusting the peel strength is to adjust the thickness of the strippable paint after curing.

[0116] From the viewpoint of obtaining good peelability at temperatures of 0°C and nearby, the peel strength at 0°C measured by the method described later with respect to the examples of the strippable paint is preferably 3.0 N / 25 mm or less, more preferably 2.8 N / 25 mm or less, and may also be 2.0 N / 25 mm or less, 1.5 N / 25 mm or less, or 1.0 N / 25 mm or less. A low peel strength is preferable from the viewpoint of reducing the workload during peeling, and is also advantageous from the viewpoint of suppressing tearing and chipping of the strippable paint (after curing) during peeling. Furthermore, from the viewpoint of obtaining appropriate adhesion of the strippable paint (after curing) to the object to be protected at temperatures of 0°C and nearby, the above peel strength is preferably 0.1 N / 25 mm or more, 0.2 N / 25 mm or more, 0.3 N / 25 mm or more, and may also be 0.5 N / 25 mm or more or 0.7 N / 25 mm or more. It is preferable that the above peel strength is not too low, from the standpoint of preventing the strippable paint (after curing) from unintentionally peeling off the object being protected.

[0117] <Synthesis of acrylic polymers> The method for obtaining the first acrylic polymer from the first monomer component described above, and the method for obtaining the second acrylic polymer from the second monomer component described above, are not particularly limited. As methods for obtaining each acrylic polymer (first acrylic polymer, second acrylic polymer), known polymerization methods such as emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization can be appropriately employed. Alternatively, active energy ray irradiation polymerization, such as photopolymerization performed by irradiating with light such as UV (typically performed in the presence of a photopolymerization initiator) or radiation polymerization performed by irradiating with radiation such as beta rays and gamma rays, may be employed. Since it is easy to prepare a composition in the form of an aqueous emulsion in which the acrylic polymer is dispersed in an aqueous solvent, in some preferred embodiments, the acrylic polymer is obtained by emulsion polymerization of monomer components (first monomer component, second monomer component) having the above-described composition. As a monomer supply method in the emulsion polymerization method, a batch supply method in which all monomer raw materials are supplied at once, a continuous supply (dropping) method, a divided supply (dropping) method, etc., can be appropriately employed. Some or all of the monomer components may be pre-mixed with water and an emulsifier to create an emulsified solution, which can then be supplied to the polymerization vessel.

[0118] The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc. A polymerization temperature of approximately 20°C or higher is appropriate, preferably approximately 40°C or higher, more preferably approximately 50°C or higher, and may also be approximately 60°C or higher, approximately 65°C or higher, and even more preferably approximately 70°C or higher. Furthermore, a polymerization temperature of approximately 170°C or lower (typically approximately 140°C or lower) is appropriate, and preferably approximately 95°C or lower (for example, approximately 85°C or lower). In emulsion polymerization, it is preferable to set the polymerization temperature to approximately 95°C or lower (for example, approximately 85°C or lower).

[0119] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene (typically aromatic hydrocarbons), acetic acid esters such as ethyl acetate, and aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane are preferably used.

[0120] During polymerization, known or conventional thermal polymerization initiators or photopolymerization initiators may be used depending on the polymerization method and polymerization mode. Polymerization initiators can be used individually or in appropriate combinations of two or more types.

[0121] While not particularly limited, thermal polymerization initiators can be used, for example, azo polymerization initiators, peroxide initiators, redox initiators consisting of a combination of peroxide and reducing agent, substituted ethane initiators, etc.

[0122] Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride.

[0123] Examples of peroxide initiators include persulfates such as potassium persulfate and ammonium persulfate; benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, dilauroyl peroxide, di-n-octanoyl peroxide, di(4-methylbenzoyl) peroxide, t-butyl peroxybenzoate, t-butyl peroxyisobutyrate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(2-ethylhexyl Examples include sil)peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butylperoxydicarbonate, t-butylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 1,1-bis(t-hexylperoxy)cyclohexane, hydrogen peroxide, etc.

[0124] Examples of redox initiators include combinations of peroxides and ascorbic acid (such as hydrogen peroxide and ascorbic acid), combinations of peroxides and iron(II) salts (such as hydrogen peroxide and iron(II) salts), and combinations of persulfates and sodium bisulfite.

[0125] While not particularly limited, the following can be used as photopolymerization initiators: ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and the like.

[0126] The amount of polymerization initiator used can be the usual amount depending on the polymerization method and polymerization mode, and is not particularly limited. For example, approximately 0.001 to 5 parts by weight (typically approximately 0.01 to 2 parts by weight, for example, approximately 0.01 to 1 part by weight) of polymerization initiator can be used per 100 parts by weight of the monomer to be polymerized.

[0127] During polymerization, various conventionally known chain transfer agents (which may also be understood as molecular weight modifiers or degree of polymerization modifiers) can be used as needed. Chain transfer agents can be used individually or in combination of two or more. Mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, and thioglycolic acid can be used as chain transfer agents. Alternatively, chain transfer agents that do not contain sulfur atoms (non-sulfur chain transfer agents) may be used. Specific examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; compounds having a benzylidenyl group such as dibenzylideneacetone, cinnamyl alcohol, and cinnamyl aldehyde; hydroquinones such as hydroquinone and naphthohydroquinone; quinones such as benzoquinone and naphthoquinone; olefins such as 2,3-dimethyl-2-butene and 1,5-cyclooctadiene; alcohols such as phenol, benzyl alcohol, and allyl alcohol; and benzyl hydrogens such as diphenylbenzene and triphenylbenzene. When a chain transfer agent is used, the amount used can be approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer component. The technology disclosed herein can also be preferably implemented in a form that does not use a chain transfer agent.

[0128] Emulsification polymerization is usually carried out in the presence of an emulsifier. The emulsifier used for emulsion polymerization is not particularly limited, and known anionic emulsifiers, nonionic emulsifiers, etc., can be used. The emulsifier can be used alone or in combination of two or more.

[0129] Non-limiting examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate. Non-limiting examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers. Emulsifiers having reactive functional groups (reactive emulsifiers) may also be used. Examples of reactive emulsifiers include radical polymerizable emulsifiers, which have a structure in which radical polymerizable functional groups such as propenyl groups and allyl ether groups are introduced into the above-mentioned anionic or nonionic emulsifiers.

[0130] The amount of emulsifier used in emulsion polymerization may be, for example, 0.2 parts by weight or more, 0.5 parts by weight or more, 1.0 part by weight or more, or 1.5 parts by weight or more, per 100 parts by weight of monomer components. From the viewpoint of suppressing foaming during emulsion polymerization and in compositions containing the obtained emulsion, in some embodiments, the amount of emulsifier used is usually appropriate to be 10 parts by weight or less, preferably 5 parts by weight or less, and may be 3 parts by weight or less, per 100 parts by weight of monomer components.

[0131] Emulsion polymerization may be carried out in the presence of a protective colloid. Examples of protective colloids include polyvinyl alcohol-based polymers such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and modified polyvinyl alcohol; cellulose derivatives such as hydroxyethylcellulose, hydroxypropylcellulose, and carboxymethylcellulose salts; and natural polysaccharides such as guar gum. The degree of saponification of partially saponified polyvinyl alcohol is typically less than 95 mol%, but may also be less than 92 mol% or less than 90 mol%. There is no particular lower limit to the degree of saponification of partially saponified polyvinyl alcohol, but from the viewpoint of emulsion stability, it is appropriate to have a degree of 65 mol% or higher, preferably 70 mol% or higher, and more preferably 80 mol% or higher (e.g., 85 mol% or higher). Examples of the above-mentioned modified polyvinyl alcohol include anionic modified polyvinyl alcohol into which anionic groups such as carboxyl groups and sulfonic acid groups have been introduced; and cationic modified polyvinyl alcohol into which cationic groups such as quaternary ammonium salts have been introduced. The degree of saponification of the modified polyvinyl alcohol may be, for example, less than 98 mol%, but may also be less than 95 mol%, less than 92 mol%, or less than 90 mol%. Furthermore, the lower limit of the degree of saponification of the modified polyvinyl alcohol may be, for example, 55 mol% or more, and from the viewpoint of emulsion stability, 65 mol% or more is appropriate, 70 mol% or more is preferred, and 80 mol% or more (for example, 85 mol% or more) is more preferred. The protective colloid can be used alone or in combination of two or more types.

[0132] The amount of protective colloid used is appropriately about 0.1 parts by weight or more per 100 parts by weight of monomer component, preferably 0.5 parts by weight or more (for example, 0.7 parts by weight or more), and preferably 10 parts by weight or less, and preferably 5 parts by weight or less (for example, 3 parts by weight or less, or 2 parts by weight or less). The protective colloid is preferably used in combination with the emulsifier as described above, but is not limited thereto, and the protective colloid may be used without an emulsifier. For example, emulsion polymerization can be carried out by placing water and protective colloid in a polymerization container, and supplying an emulsion to the polymerization container in which some or all of the monomer component has been pre-mixed with water and an emulsifier. When using an anionic protective colloid (for example, anionic modified polyvinyl alcohol) in combination with an emulsifier, it is preferable to use one or more types selected from the group consisting of anionic emulsifiers and nonionic emulsifiers as the emulsifier, from the viewpoint of polymerization stability, etc.

[0133] In some preferred embodiments, emulsion polymerization is carried out in the presence of a polyvinyl alcohol-based polymer. The aqueous emulsion of the acrylic polymer obtained by such emulsion polymerization tends to exhibit a thickening effect when a thickener is added. By using such an aqueous emulsion of the acrylic polymer, a strippable paint exhibiting good viscosity characteristics suitable for slot die coating can be suitably prepared. Anion-modified polyvinyl alcohol is a preferred example of the polyvinyl alcohol-based polymer. For example, sulfonic acid group-modified polyvinyl alcohol or carboxy-modified polyvinyl alcohol can be preferably used. A combination of the polyvinyl alcohol-based polymer and an emulsifier may also be used.

[0134] For example, a first acrylic polymer and a second acrylic polymer can be formed by emulsion polymerization as described above. Then, an aqueous emulsion (polymerization reaction solution) of the first acrylic polymer obtained by emulsion polymerization and an aqueous emulsion (polymerization reaction solution) of the second acrylic polymer obtained by emulsion polymerization are mixed to obtain a mixed emulsion, and then the above-mentioned additives are added to this emulsion to prepare an aqueous emulsion type strippable paint. Alternatively, the mixed emulsion may be used as is, or the mixed emulsion may be pH adjusted (for example, by adding aqueous ammonia to adjust the pH to about 6-8) and / or concentration adjusted (for example, by adding water to adjust the solid content to about 40-60% by weight) before being used as a strippable paint. It is preferable from the viewpoint of environmental hygiene that the strippable paint is of the aqueous emulsion type.

[0135] <Protective coating material> The protective coating material disclosed herein can be formed using the strippable paint described above. For example, the protective coating material can be formed by applying the strippable paint (preferably by applying it with a slot die) onto an object to be protected to form a coating film, and then drying the coating film.

[0136] Figure 1 is a schematic cross-sectional view showing an example of an object protected by a protective coating material. In Figure 1, the protective coating material 10 formed from the strippable paint is applied to the object 20. The object 20 has a coating film 22 on its surface. The protective coating material 10 protects the object 20 by covering its surface (the coating film 22 in Figure 1). The protective coating material 10 can be peeled off from the object 20 at a desired time, for example, after it has finished its protective function (e.g., by tearing).

[0137] The thickness of the protective coating material is not particularly limited, but from the viewpoint of enhancing the protective effect, it is appropriate to have a thickness of 20 μm or more, and from the viewpoint of strength and peelability, it is preferable to have a thickness of 50 μm or more, and more preferably 70 μm or more (e.g., 85 μm or more). The thickness of the protective coating material can be adjusted by the amount of strippable paint applied and the solid content. From the viewpoint of drying properties and preventing sagging of the applied composition, the thickness of the protective coating material is appropriate to have a thickness of 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0138] The protective coating material disclosed herein has a ratio of the tensile storage modulus at 0°C (second tensile storage modulus) to the tensile storage modulus at 40°C (first tensile storage modulus) after curing of 350 or less, preferably 220 or less, more preferably 100 or less, more preferably 50 or less, more preferably 30 or less, and more preferably 20 or less. Such a protective coating material (the above-mentioned strippable paint after curing) is suitable for suppressing the temperature dependence of adhesion, elongation, and tensile strength to the object to be protected, and is therefore suitable for suppressing the above-mentioned adhesion and peelability due to temperature differences (for example, a temperature difference between about 0°C and about 40°C). The above ratio is, for example, 0.5 or more, 1.0 or more, 2.0 or more, or 3.0 or more.

[0139] The first tensile storage modulus (40°C), second tensile storage modulus (0°C), loss tangent, elongation at break and breaking strength at 40°C and 0°C, and peel strength at 40°C and 0°C for the protective coating material are the same as those described above for the first tensile storage modulus (40°C), second tensile storage modulus (0°C), loss tangent, elongation at break and breaking strength at 40°C and 0°C, and peel strength at 40°C and 0°C for the strippable paint after curing.

[0140] <Protected objects> The strippable paints and protective coatings disclosed herein can be used to protect a variety of articles (objects to be protected). For example, they are suitably used to protect articles having a coating on their surface. Examples of such coated articles include painted automobiles and their parts, painted metal sheets (e.g., painted steel sheets used in housing materials, building materials, ships, railway vehicles and other transportation equipment) and their molded products, and synthetic resin sheets and their molded products with a coating. Examples of objects to be protected other than those mentioned above include resin members (e.g., resin sheets and resin molded products), glass sheets, and metal members (e.g., metal sheets and metal molded products).

[0141] The matters disclosed in this specification include the following: [1] A strippable paint for forming a peelable protective coating, The solution comprises an aqueous solvent and a first acrylic polymer and a second acrylic polymer dispersed in the aqueous solvent. The above-mentioned first acrylic polymer is a polymer of a first monomer component comprising a first monomer having a relatively high glass transition temperature for the homopolymer and a second monomer having a relatively low glass transition temperature for the homopolymer. The above-mentioned second acrylic polymer is a polymer of a second monomer component containing a third monomer with a relatively high glass transition temperature of the homopolymer and a fourth monomer with a relatively low glass transition temperature of the homopolymer, and its monomer composition differs from that of the above-mentioned first acrylic polymer. The glass transition temperature of the first monomer is higher than the glass transition temperature of the third monomer, or the glass transition temperature of the first monomer is the same as the glass transition temperature of the third monomer and the proportion of the first monomer in the first monomer component is greater than the proportion of the third monomer in the second monomer component. A strippable paint in which the ratio of the tensile storage modulus at 0°C to the tensile storage modulus at 40°C after curing is 350 or less. [2] The strippable paint according to [1], wherein the glass transition temperature of the first monomer is 50°C or higher than the glass transition temperature of the second monomer. [3] The strippable paint according to [1] or [2] above, wherein the first monomer is the monomer in the first monomer component that has the highest glass transition temperature of the homopolymer. [4] The strippable paint according to [3], wherein the second monomer is the monomer in the first monomer component that has the second highest glass transition temperature of the homopolymer. [5] The strippable paint according to any one of [1] to [4] above, wherein the glass transition temperature of the third monomer is 50°C or higher than the glass transition temperature of the fourth monomer. [6] The strippable paint according to any one of [1] to [5] above, wherein the third monomer is the monomer in the second monomer component that has the highest glass transition temperature of the homopolymer. [7] The strippable paint according to [6], wherein the fourth monomer is the monomer in the second monomer component that has the second highest glass transition temperature of the homopolymer. [8] The strippable paint according to any one of [1] to [7] above, wherein at least one of the first monomer and the third monomer is acrylonitrile. [9] The strippable paint according to any one of [1] to [8] above, wherein the proportion of the first monomer in the first monomer component is 3% by weight or more.

[10] The strippable paint according to any one of [1] to [9] above, wherein the proportion of the first monomer in the first monomer component is 50% by weight or less.

[11] The strippable paint according to any one of [1] to

[10] above, wherein the total proportion of the first monomer and the third monomer in the total amount of the first monomer component and the second monomer component is 5% by weight or more.

[12] The strippable paint according to any one of [1] to

[11] above, wherein the total proportion of the first monomer and the third monomer in the total amount of the first monomer component and the second monomer component is 50% by weight or less.

[13] A strippable paint according to any one of [1] to

[12] above, wherein the loss tangent after curing has a peak in the range of 23°C to 40°C.

[14] The strippable paint according to

[13] above, wherein the loss tangent has a further peak in the range of -15°C to 5°C.

[15] A strippable paint according to any of [1] to

[14] above, wherein the elongation at break at 0°C after curing is 100% or more.

[16] A strippable paint according to any of [1] to

[15] above, wherein the elongation at break at 40°C after curing is 550% or less.

[17] A strippable paint according to any one of [1] to

[16] above, wherein the above-mentioned first tensile storage modulus at 40°C is 1.0 MPa or more.

[18] The second tensile storage modulus at 0°C is 1.7 × 10⁻⁶ 3 A strippable paint as described in any of the above [1] to

[17] , having a pressure of MPa or less.

[19] A protective coating material which is a cured product of any of the strippable paints described in [1] to

[18] above. [Examples]

[0142] The following describes several experimental examples related to the present invention, but the present invention is not intended to be limited to these specific examples. In the following description, "parts" and "%" used to express amounts and content are based on weight unless otherwise specified. Also, unless otherwise specified, the amount of each material used is based on the amount of active ingredient.

[0143] <Polymer emulsion used> E1: Emulsion containing acrylic polymer P1 with a monomer composition of 66% butyl acrylate (BA) and 34% acrylonitrile (AN) (preparation method is as described below). E2: Emulsion containing acrylic polymer P2 with a monomer composition of 96% BA and 4% AN (DOW Corporation, product name "ELATENE 2468 Acrylic Emulsion") E3: Emulsion containing acrylic polymer P3 with a monomer composition of 83% BA and 17% styrene (St) (DOW Corporation, product name "ELATENE 2471 Emulsion") E4: Emulsion containing acrylic polymer P4 with a monomer composition of 61% BA and 39% St (DOW Corporation, product name "ELATENE 1500 Emulsion") E5: Emulsion containing acrylic polymer P5 with monomer composition of BA 70.4% and AN 29.6% (preparation method is as described below).

[0144] <Method for preparing polymer emulsion E1> First, a surfactant solution was prepared by dissolving 2 parts of polyoxyalkylene alkenyl ether (manufactured by Kao Corporation, product name "Latemul PD-420") and 0.5 parts of sodium dodecylbenzenesulfonate (manufactured by Kao Corporation, product name "Neoperex G-65") in 25 parts of deionized water in a container. Next, 100 parts of a monomer component consisting of 66 parts of n-butyl acrylate (BA) and 34 parts of acrylonitrile (AN) were added to the same solution, and the resulting mixture was emulsified in an emulsifier (homomicker) to prepare a monomer emulsion. Meanwhile, in a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirring device, 2.0 parts of anionically modified polyvinyl alcohol (manufactured by Mitsubishi Chemical Corporation, product name "Gosenex L-3266"; saponification degree 86.5-89.0 mol%) was dissolved in 75 parts of deionized water while introducing nitrogen gas, and the solution was heated to 70°C. Next, to the obtained solution, the above monomer emulsion (containing 100 parts of monomer components), 0.3 parts of aqueous sodium metabisulfite solution (based on solid content), and 0.3 parts of aqueous ammonium persulfate solution (based on solid content) were added over 5 hours while maintaining the reaction system at around 70°C to carry out the emulsion polymerization reaction. After the addition was complete, the reaction mixture was aged for another 3 hours at 70°C. Then, the obtained reaction mixture was cooled to room temperature, and the pH of the mixture was adjusted to 7.5 by adding 10% ammonium water. In this manner, polymer emulsion E1 (solid content approximately 47%) as an aqueous emulsion containing acrylic polymer P1 was prepared.

[0145] <Method for preparing polymer emulsion E5> Polymer emulsion E5 was prepared in the same manner as the preparation method for polymer emulsion E1 described above, except that 100 parts of a monomer component consisting of 70.4 parts BA and 29.6 parts AN were used as the monomer component to be mixed with the surfactant solution.

[0146] <Example 1> Polymer emulsion E1 and polymer emulsion E2 were mixed to obtain a mixed emulsion containing acrylic polymer P1 and acrylic polymer P2 in a weight ratio of 85:15. To this mixed emulsion, 38.7 parts of inorganic particle dispersion, 0.3 parts of a thickener (ADEKA, trade name "ADEK-1770"), and 0.1 parts of an antifoaming agent (BYK, trade name "BYK-1770") were added and mixed. The inorganic particle dispersion described above was obtained by mixing 8.7 parts of a solution (8.2 parts) of 100 parts of the acrylic polymer in the above mixed emulsion with 8.2 parts of water and 0.5 parts of a dispersant (manufactured by Nisshin Chemical Industry Co., Ltd., trade name "Orphine PD-201"), 5.0 parts of titanium dioxide (rutile-type titanium dioxide manufactured by Ishihara Sangyo Co., Ltd., trade name "TIPAQUE CR-95", average particle size 280 nm), and 25 parts of calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., trade name "Softon 3200"). The strippable paint of Example 1 was prepared in the manner described above.

[0147] In the strippable paint of Example 1, the proportion of acrylonitrile (AN), which has the highest homopolymer glass transition temperature (homopolymer Tg) among acrylic polymers P1, is greater than the proportion of AN, which has the highest homopolymer Tg among acrylic polymers P2. In such a strippable paint, acrylic polymer P1 is the first acrylic polymer, and acrylic polymer P2 is the second acrylic polymer. Table 1 shows the proportion (by weight) of each monomer type in the total amount of monomers forming the entire acrylic polymer in the strippable paint (the same applies to the other examples and comparative examples described later).

[0148] <Examples 2-6 and Comparative Examples 1-6> The strippable paints for each example were prepared in the same manner as the strippable paint preparation in Example 1, except that the type and amount of acrylic polymer used were changed as shown in Table 1.

[0149] In each of the strippable paints in Examples 2 to 4, similar to the strippable paint in Example 1, acrylic polymer P1 is the first acrylic polymer and acrylic polymer P2 is the second acrylic polymer. In the strippable paint of Example 5, styrene (St), which has the highest homopolymer Tg in acrylic polymer P3, has a higher homopolymer Tg than AN, which has the highest homopolymer Tg in acrylic polymer P1. In such a strippable paint, acrylic polymer P3 is the first acrylic polymer and acrylic polymer P1 is the second acrylic polymer. In the strippable paint of Example 6, styrene (St), which has the highest homopolymer Tg in acrylic polymer P4, has a higher homopolymer Tg than AN, which has the highest homopolymer Tg in acrylic polymer P1. In such a strippable paint, acrylic polymer P4 is the first acrylic polymer and acrylic polymer P1 is the second acrylic polymer. In the strippable paint of Comparative Example 6, St, which has the highest homopolymer Tg among acrylic polymers P4, has a higher homopolymer Tg than AN, which has the highest homopolymer Tg among acrylic polymers P2. In such a strippable paint, acrylic polymer P4 is the first acrylic polymer, and acrylic polymer P2 is the second acrylic polymer.

[0150] <Measurement and Evaluation> [Tensile test] For each strippable paint in the examples and comparative examples, a measurement sample for tensile testing was prepared as follows. First, a painted steel plate, coated with an acid epoxy crosslinked acrylic paint (manufactured by Kansai Paint Co., Ltd., product name "KINO1210TW"), was held horizontally with the painted surface facing upwards. Next, the strippable paint was applied to the painted surface (on the paint film) of this painted steel plate using an applicator manufactured by TP Giken Co., Ltd., and dried and cured at 80°C for 3 minutes to form a film (protective coating material). The amount of strippable paint applied was set so that the thickness in terms of solid content was 100 μm. Next, the formed film was peeled off the painted steel plate at room temperature and cut into strips with a width of 25 mm and a length of 100 mm. This obtained a measurement sample for tensile testing.

[0151] Under conditions of 0°C and 50%RH, the above-mentioned sample was placed in a tensile testing machine (Shimadzu Corporation, machine name "Tensilon"), and a tensile test was performed at a gauge length of 50 mm and a tensile speed of 0.3 m / min to measure the breaking strength [N / 25 mm] and elongation at breaking [%] at 0°C. Similarly, the breaking strength [N / 25 mm] and elongation at breaking [%] of the sample at 40°C were measured using the same procedure, except that the temperature condition was changed from 0°C to 40°C. These results are shown in Table 1.

[0152] [Dynamic viscoelasticity measurement] For each of the strippable paints in the examples and comparative examples, a measurement sample for dynamic viscoelasticity measurement (10 mm wide x 30 mm long x 100 μm thick) was prepared in the same manner as the measurement sample for tensile testing described above, except for the size. For the measurement samples, the storage modulus G' (tensile storage modulus) and loss modulus G'' (tensile loss modulus) were measured using a dynamic viscoelasticity analyzer (TA Instruments, product name "RSA-G2"). In this measurement, the initial chuck distance of the sample holding chuck was set to 10 mm, the measurement mode was set to tensile mode, the measurement temperature range was set to -70°C to 150°C, the heating rate was set to 5°C / min, the frequency was set to 1 Hz, the dynamic strain was set to 0.05%, and the data measurement interval was set to 1°C intervals (1 data per 1°C). For each example of strippable paint (after curing), the tensile storage modulus at 40°C (MPa), the tensile storage modulus at 0°C (MPa), the ratio of the tensile storage modulus at 0°C to the tensile storage modulus at 40°C (modulus ratio), and the peak temperature (°C) and magnitude of the loss tangent tanδ (tensile loss modulus / tensile storage modulus) are shown in Table 1.

[0153] [Peel strength] For each of the strippable paints in the examples and comparative examples, a 100 μm thick film was formed on the painted steel plate in the same manner as in the preparation of the film for the tensile test described above. Next, the painted steel plate was placed in a constant temperature chamber at 70°C and held for 7 days. After removing the painted steel plate from the constant temperature chamber and holding it in an environment of 23°C and 50% RH for at least 30 minutes, two straight cuts (25 mm apart, 90 mm long) and one cut perpendicular to the first cut were made in the film on the coating. The film was partially peeled off from the latter cut and set in a tensile testing machine with a constant temperature chamber (Shimadzu Corporation, machine name "Tensilon"). After 30 minutes, the film was peeled off in the 180-degree direction at a tensile speed of 0.3 m / min to measure the peel strength [N / 25 mm] of the film from the painted steel plate. In this measurement, the temperature inside the constant temperature chamber of the tensile testing machine was set to 0°C beforehand. Furthermore, the peel strength [N / 25mm] of the film from the above-mentioned painted steel plate was measured under the same conditions, except that the temperature was changed from 0°C to 40°C. These results are shown in Table 1. For each of the films in Comparative Examples 2 and 3, the peel strength could not be measured because they were too soft at 40°C and tore when pulled continuously.

[0154] [Evaluation of peelability] For each of the example and comparative example strippable paints, a 100 μm thick film (protective coating material) was formed on the painted steel sheet in the same manner as the film preparation for the tensile test described above, except for the thickness of the formed film. Next, the painted steel sheet with the film attached was placed in a constant temperature chamber at 0°C, and the film was peeled off the painted steel sheet at 0°C. During this process, the ease with which the peeled edge of the film on the painted steel sheet could be raised by rubbing the edge with a fingertip, and the ease with which the film could be peeled off by pulling the peeled edge after it had been raised, were evaluated. For the ease with which the peeled edge could be raised, it was evaluated as "good" if it was easy to raise the peeled edge, and as "poor" if it was not. For the ease with which the film could be peeled off after it had been raised, it was evaluated as "good" if it was easy to peel off, and as "poor" if it was not. Furthermore, the ease with which the peeled edge of the film could be raised from the painted steel sheet and the ease with which the film could be peeled off after it had been raised were evaluated in the same manner, except that the temperature conditions were changed from 0°C to 40°C. These results are shown in Table 1. The "poor" ratings for the strippable paints in Comparative Examples 1-6 are specifically for the following reasons.

[0155] The film of Comparative Example 1 was too hard and difficult to deform at 0°C, making it difficult to stand up and sometimes cracking when standing up. The films of Comparative Examples 2 and 3 were too soft at 40°C, stretching excessively when pulled and making them difficult to peel off, and tearing if pulled continuously. The films of Comparative Examples 4 and 6 were soft, stretched easily when pulled, and difficult to peel off. The film of Comparative Example 5 was too hard and difficult to deform at 0°C, making it difficult to stand up.

[0156] [Table 1]

[0157] As shown in Table 1, each of the strippable paints in Examples 1 to 6 contains first and second acrylic polymers with different monomer compositions, and the ratio of tensile storage moduli is 350 or less. As a result, the temperature dependence of the peel strength (adhesion), elongation at break (ease of stretching), and breaking strength after curing is suppressed. Therefore, each of the strippable paints in Examples 1 to 6 after curing showed suppressed variations due to temperature differences in both adhesion to the surface of the article and peelability (removability) from the same surface. In contrast, each of the strippable paints in Comparative Examples 1 to 6 after curing showed significant differences in peelability due to temperature differences.

[0158] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above. [Industrial applicability]

[0159] The strippable paint provided by the technology described in this specification is suitable as a strippable paint for forming a protective coating material that is applied to a predetermined surface of an object to be protected to protect the surface from damage and deterioration such as scratches and dirt, and is peeled off from the object after it has finished its protective role. The strippable paint can be used for surface protection of objects to be protected that have surfaces made of various materials (e.g., resin, metal, glass, etc.), and is suitable for use, for example, to protect the surface of a coating when the object to be protected has a coating on its surface. The object to be protected may be, for example, a painted metal sheet (e.g., painted steel sheet used in housing materials, building materials, ships, railway vehicles, automobiles and other transportation equipment), a synthetic resin sheet with a coating, or molded products thereof. The protective coating material formed from the above-mentioned strippable paint can be preferably used to protect the coating of an article to be protected (an article having a coating formed by the above-mentioned coating treatment, such as a metal plate such as a steel plate or a molded product thereof) that has been coated with paints of various compositions, such as acrylic paints, polyester paints, alkyd paints, melamine paints, urethane paints, acid epoxy crosslinked paints, or composites thereof (e.g., acrylic melamine paints, alkyd melamine paints). [Explanation of Symbols]

[0160] 10 Protective coating material 20 Protected Objects 22 Coating film

Claims

1. A strippable paint for forming a peelable protective coating, The solution comprises an aqueous solvent and a first acrylic polymer and a second acrylic polymer dispersed in the aqueous solvent. The first acrylic polymer is a polymer of a first monomer component comprising a first monomer having a relatively high glass transition temperature for the homopolymer and a second monomer having a relatively low glass transition temperature for the homopolymer. The second acrylic polymer is a polymer of a second monomer component containing a third monomer having a relatively high glass transition temperature for the homopolymer and a fourth monomer having a relatively low glass transition temperature for the homopolymer, and its monomer composition differs from that of the first acrylic polymer. The glass transition temperature of the first monomer is higher than the glass transition temperature of the third monomer, or the glass transition temperature of the first monomer is the same as the glass transition temperature of the third monomer and the proportion of the first monomer in the first monomer component is greater than the proportion of the third monomer in the second monomer component. A strippable paint in which the ratio of the tensile storage modulus at 0°C to the tensile storage modulus at 40°C after curing is 350 or less.

2. The strippable paint according to claim 1, wherein the glass transition temperature of the first monomer is 50°C or higher than the glass transition temperature of the second monomer.

3. The strippable paint according to claim 1, wherein the glass transition temperature of the third monomer is 50°C or higher than the glass transition temperature of the fourth monomer.

4. The strippable paint according to claim 1, wherein at least one of the first monomer and the third monomer is acrylonitrile.

5. The strippable paint according to claim 1, wherein the total proportion of the first monomer and the third monomer in the total amount of the first monomer component and the second monomer component is 5% by weight or more.

6. The strippable paint according to claim 1, wherein the loss tangent after curing has a peak in the range of 23°C to 40°C.

7. The strippable paint according to claim 1, wherein the tensile storage modulus at 40°C is 1.0 MPa or more.

8. The tensile storage modulus at 0°C is 1.7 × 10⁻⁶. ３ The strippable paint according to claim 1, wherein the pressure is less than or equal to MPa.

9. A protective coating material which is a cured product of a strippable paint according to any one of claims 1 to 8.

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