Precoat composition for paint film removal, and film derived therefrom

Abstract

To provide a precoat composition for coated film peeling for efficiently peeling a coated film derived from an aqueous coating, and a film derived from the same.SOLUTION: A precoat composition for coated film peeling contains a polyester resin or a polyacrylic resin, and a solvent, wherein a content ratio of the wax is 10 wt.% or less with respect to the total mass of the polyester resin and the polyacrylic resin, in an FT-IR spectrum obtained when a film derived from the precoat composition for coated film peeling is analyzed using a total reflection measurement method, when a maximum peak height among peaks exhibiting a maximum value in a range of 680-710 cm-1 is represented by A [%T], and a maximum peak height among peaks exhibiting a maximum value in a range of 1710-1740 cm-1 is represented by B [%T], a ratio A / B is 0 or more and less than 1, and a water dissolution ratio of the film derived from the precoat composition for coated film peeling is 0 wt.% or more and 50 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a pre-coat composition for paint film removal and a film derived therefrom. [Background technology]

[0002] Painting of objects to be painted, such as car doors, is usually performed with the object fixed to a painting jig or a movable jig (such as a stopper jig). When painting using such a painting jig, paint tends to adhere to the painting jig after multiple coats. If paint adheres to the painting jig and hardens, it may cause poor conductivity in the painting jig, for example, during electrostatic painting. Therefore, the paint (hereinafter sometimes referred to as "paint film") that adheres to the painting jig needs to be removed periodically.

[0003] Japanese Patent Publication No. 2016-069633 (Patent Document 1) discloses an aqueous primer composition for paint removal characterized by containing a polyester resin or a salt thereof obtained by polycondensation of a dicarboxylic acid component and a glycol component as the main components, and water, wherein the polyester resin has a substituent represented by -SO3M (where M represents hydrogen, alkali metal, ammonium ion, or alkanolamine).

[0004] Japanese Patent Publication No. 2017-066309 (Patent Document 2) discloses a water-soluble primer composition for paint removal that contains an anionic and / or nonionic polyurethane resin (A) and water, and has a thixotropic index (TI value) of 1.25 to 2.00 at 25°C.

[0005] Japanese Patent Publication No. 10-323613 (Patent Document 3) discloses a method for forming a wax film with a melting point of 40 to 150°C on the surface of articles that do not require painting, such as painting jigs, and then, after painting, removing the coating film by applying physical force such as high-pressure water washing.

[0006] International Publication No. 2019 / 044904 (Patent Document 4) discloses a precoat agent for coating film peeling, which contains an acrylic polymer containing an acrylate monomer in part and / or an oil-modified alkyd resin as a binder; and wax.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In recent years, the levels required for coating quality (such as gloss, shine, reduction of coating defects, etc.) have been increasing. For example, the coating film adhering to the coating jig may fall off or scatter and adhere to the object to be coated, and it is required to reduce such coating defects caused by foreign matter mixing. In order to reduce the above coating defects, it is required to clean the coating jig every time the coating is performed, and the development of a coating film peeling agent that can peel the coating film in a shorter time than before, and a precoat composition for coating film peeling is desired.

[0009] On the other hand, for the purpose of coping with the impacts caused by changes in the global environment such as air pollution and global warming, countermeasures are being strengthened in many related technical fields. In the paint field as well, in order to reduce the emission amount of VOC (volatile organic compounds), paints with a low content of VOC such as water-based paints (low VOC paints) are being adopted. Therefore, the development of a precoat composition for coating film peeling that can efficiently peel the coating film derived from water-based paints and the like is desired.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a precoat composition for coating film peeling for efficiently peeling a coating film derived from an aqueous paint or the like, and a film derived therefrom.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that by previously applying a precoat composition for coating film peeling containing a polyester resin or a polyacrylic resin having a specific structure and a solvent to an object to be coated, a coating film derived from an aqueous paint or the like can be efficiently peeled, and completed the present invention. That is, the present invention is as follows.

[0012] [1] A precoat composition for coating film peeling for facilitating peeling of a coating film provided on the surface of a substrate with a coating film peeling agent, comprising: a polyester resin having a structural unit represented by the following formula (1) or a polyacrylic resin having a structural unit represented by the following formula (2); a solvent, the content ratio of wax is 10 wt% or less based on the total mass of the polyester resin and the polyacrylic resin, in the FT-IR spectrum obtained when analyzing the film derived from the precoat composition for coating film peeling using the total reflection measurement method, among the peaks showing a maximum value in the range of 680 to 710 cm -1 when the maximum peak height of the peaks showing a maximum value in the range of 1710 to 1740 cm -1 is defined as B [%T], the ratio A / B is 0 or more and less than 1, the water dissolution ratio of the film derived from the precoat composition for coating film peeling is 0 wt% or more and 50 wt% or less, the precoat composition for coating film peeling.

Chemical Formula

[0013] According to the present invention, it is possible to provide a pre-coat composition for paint film removal that efficiently removes paint films derived from water-based paints, etc., and a coating film derived therefrom. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 shows the FT-IR spectrum obtained when a film derived from a pre-coat composition for paint film removal was analyzed using total internal reflection. [Figure 2] Figure 2 shows the FT-IR spectrum obtained when a film derived from a pre-coat composition for paint film removal was analyzed using total internal reflection. [Modes for carrying out the invention]

[0015] Hereinafter, an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. However, this embodiment is not limited thereto. In this specification, the notation in the form of "A to Z" means the upper and lower limits of the range (that is, A or more and Z or less). When there is no unit description in A and only a unit is described in Z, the units of A and Z are the same.

[0016] ≪Precoat Composition for Coating Film Peeling≫ The precoat composition for coating film peeling according to this embodiment is a precoat composition for coating film peeling for facilitating peeling of a coating film provided on the surface of a substrate with a coating film peeling agent, a polyester resin having a structural unit represented by the following formula (1), or a polyacrylic resin having a structural unit represented by the following formula (2), and a solvent, the content ratio of wax is 10 wt% or less with respect to the total mass of the polyester resin and the polyacrylic resin, in the FT-IR spectrum obtained when analyzing the film derived from the precoat composition for coating film peeling using the total reflection measurement method, 680 to 710 cm -1 of the peaks showing a maximum value in the range, taking the maximum peak height as A [%T], and in the range of 1710 to 1740 cm -1 of the peaks showing a maximum value in the range, taking the maximum peak height as B [%T], the ratio A / B is 0 or more and less than 1, the water dissolution ratio of the film derived from the precoat composition for coating film peeling is 0 wt% or more and 50 wt% or less. In formula (1), R 1 represents a divalent saturated hydrocarbon group having 2 to 10 carbon atoms, and m represents a natural number. In formula (2), R 2 represents a monovalent saturated hydrocarbon group having 1 to 4 carbon atoms, R 3 represents a hydrogen atom or a methyl group, and n represents a natural number.

[0017]

Chemical Formula

[0018] The above-mentioned pre-coat composition for paint film removal is used to facilitate the removal of a paint film applied to the surface of a substrate using a paint film remover. More specifically, the above-mentioned pre-coat composition for paint film removal is used to be applied between the surface of the substrate and the paint film. Alternatively, the above-mentioned pre-coat composition for paint film removal is used as an undercoat applied to the surface of the substrate. The above-mentioned substrate may be any substrate material that is commonly used. Examples of the above-mentioned substrate material include metals such as iron, stainless steel (SUS), and aluminum, as well as resins such as polyamide (nylon), polypropylene (PP), polyethylene (PE), acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyetheretherketone (PEEK), polytetrafluoroethylene (Teflon®), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyurethane, and epoxy resin.

[0019] The coating film provided on the surface of the above substrate may be any coating film derived from commonly used paints. Examples of such paints include polyester resin paints, polyurethane resin paints, acrylic resin paints, epoxy resin paints, alkyd melamine resin paints, and nitrocellulose-based paints. In one aspect of this embodiment, it is preferable that the coating film is formed by heating the paint. Examples of paints that form a coating film by heating include polyurethane resin paints, acrylic resin paints, epoxy resin paints, and the like.

[0020] The above-mentioned coating film is provided on the substrate via a film derived from the above-mentioned pre-coat composition for removing coating films.

[0021] <Polyester resin> The above polyester resin may be synthesized from known starting materials by known methods. Alternatively, commercially available polyester resins may be used as is.

[0022] In the above equation (1), R 1R represents a divalent saturated hydrocarbon group with 2 to 10 carbon atoms, and m represents a natural number. 1 is, -(CH2) a It is preferable that the group is a divalent group selected from the group consisting of -(a is an integer from 2 to 10, preferably an integer from 2 to 8), -CH2-C(CH3)2-, and -CH(CH3)-. 1 It is more preferable that the group is a divalent group represented by -CH2-.

[0023] In formula (1) above, m is not particularly limited, but for example, it may be between 20 and 150, or between 40 and 130.

[0024] The above polyester resin preferably contains at least one selected from the group consisting of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), poly(1,2-propylene terephthalate), polytrimethylene terephthalate, poly(2,3-butylene terephthalate), poly(1,3-butylene terephthalate), poly(2-methyl-1,3-propylene terephthalate), polytetramethylene terephthalate, polypentamethylene terephthalate, polyhexamethylene terephthalate, polyheptamethylene terephthalate, polyoctamethylene terephthalate, polynonylmethylene terephthalate, poly(1,3-cyclohexanedimethylene terephthalate), poly(1,4-cyclohexanediethylene terephthalate), poly(1,3-cyclohexanediethylene terephthalate), and polydecamethylene terephthalate. The polyester resin described above more preferably contains polyethylene terephthalate or poly(1,4-cyclohexanedimethylene terephthalate).

[0025] The glass transition temperature (Tg) of the above polyester resin is preferably -40°C to 70°C, and more preferably -25°C to 20°C. This results in a pre-coat composition for paint film removal that has excellent adhesion to the substrate.

[0026] The minimum value of the polarity term (δp) of the solubility parameter for the above polyester resin is 7 [J]. 1 / 2 / cm 3 / 2 ]more than 13[J 1 / 2 / cm 3 / 2 Preferably it is 8[J] or less. 1 / 2 / cm 3 / 2 ] or more 12[J 1 / 2 / cm 3 / 2 It is more preferable that the following conditions are met. This results in a pre-coat composition for paint film removal that exhibits excellent solubility in alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents.

[0027] The number-average molecular weight of the above polyester resin is preferably 5,000 to 30,000, and more preferably 10,000 to 20,000. The number-average molecular weight of the above polyester resin can be determined by high-performance liquid chromatography under the following conditions. High-performance liquid chromatography analytical conditions Equipment: Preparative HPLC system PLC761 (manufactured by GL Sciences Co., Ltd.) Separation method: Size exclusion chromatography

[0028] Specific examples of the above-mentioned polyester resins include the following: Poly(1,4-cyclohexanedimethylene terephthalate) has a glass transition temperature (Tg) of -25°C and a number-average molecular weight of 17,000. Polyethylene terephthalate with a glass transition temperature (Tg) of 8°C and a number-average molecular weight of 17,000. Polyethylene terephthalate with a glass transition temperature (Tg) of 15°C and a number-average molecular weight of 13,000.

[0029] <Polyacrylic resin> The above polyacrylic resin may be synthesized from known starting materials by known methods. Alternatively, commercially available polyacrylic resins may be used as is.

[0030] In equation (2) above, R2 This represents a monovalent saturated hydrocarbon group having 1 to 4 carbon atoms, and R 3 R represents a hydrogen atom or a methyl group, and n represents a natural number. 2 H-(CH2) a It is preferable that the group is a monovalent group selected from the group consisting of -(a is an integer from 1 to 4, preferably an integer from 1 to 3), CH3-C(CH3)2-, and CH2(CH3)-. 2 It is more preferable that the group is a monovalent group represented by H-(CH2)-.

[0031] In equation (2) above, R 3 R represents a hydrogen atom or a methyl group. 3 It is more preferable that it be a hydrogen atom.

[0032] In equation (2) above, n is not particularly restricted, but for example, it may be between 30 and 350, or between 50 and 330.

[0033] The above polyacrylic resin preferably contains at least one selected from the group consisting of polymethyl methacrylate, polyethyl methacrylate, poly-n-propyl methacrylate, poly-iso-propyl methacrylate, poly-n-butyl methacrylate, poly-sec-butyl methacrylate, poly-iso-butyl methacrylate, poly-tert-butyl methacrylate, polymethyl acrylate, polyethyl acrylate, poly-n-propyl acrylate, poly-iso-propyl acrylate, poly-n-butyl acrylate, poly-sec-butyl acrylate, poly-iso-butyl acrylate, and poly-tert-butyl acrylate. The above polyacrylic resin more preferably contains polymethyl methacrylate or polyethyl methacrylate.

[0034] The glass transition temperature (Tg) of the above polyacrylic resin is preferably -40°C to 70°C, and more preferably -25°C to 20°C. This results in a pre-coat composition for paint film removal that has excellent adhesion to the substrate.

[0035] The minimum value of the polarity term (δp) of the solubility parameter for the above polyacrylic resin is 4 [J]. 1 / 2 / cm 3 / 2 ]more than 9[J 1 / 2 / cm 3 / 2 It is preferable that it be less than or equal to 6[J 1 / 2 / cm 3 / 2 ]more than 9[J 1 / 2 / cm 3 / 2 It is more preferable that the following conditions are met. This results in a pre-coat composition for paint film removal that exhibits excellent solubility in alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents.

[0036] The number-average molecular weight of the above polyacrylic resin is preferably 5,000 to 30,000, and more preferably 10,000 to 20,000. The number-average molecular weight of the above polyacrylic resin can be determined by the high-performance liquid chromatography described above.

[0037] Specific examples of the polyacrylic resins mentioned above include the following: Polymethyl methacrylate with a glass transition temperature (Tg) of 5°C and a number-average molecular weight of 20,000. Polyethyl methacrylate with a glass transition temperature (Tg) of 10°C and a number-average molecular weight of 20,000.

[0038] In one aspect of this embodiment, the pre-coat composition for paint removal may contain either the polyester resin or the polyacrylic resin, or both. The total content of the polyester resin and the polyacrylic resin is preferably 2 to 50% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 10% by mass, based on the total amount of the pre-coat composition for paint removal. This results in a pre-coat composition for paint removal that is not affected by aqueous paints and has excellent solubility in alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents. The total content of the polyester resin and the polyacrylic resin can be determined by analysis using high-performance liquid chromatography and FT-IR. The conditions for analysis using high-performance liquid chromatography and FT-IR are as follows. High-performance liquid chromatography analytical conditions Equipment: Preparative HPLC system PLC761 (manufactured by GL Sciences Co., Ltd.) Separation method: Size exclusion chromatography

[0039] FT-IR analysis conditions Equipment: FT-IR spectrometer Frontier (manufactured by Perkin Elmer) Measurement method: Total reflection measurement method

[0040] <Solvent> The above-mentioned pre-coat composition for paint film removal contains a solvent. In this embodiment, "solvent" is a concept that includes not only a medium for dissolving a substance but also a medium for dispersing a substance. Examples of the solvent include water, alcohol-based solvents, ether-based solvents, ketone-based solvents, aprotic polar solvents, ester-based solvents, and the like. The solvent preferably contains water.

[0041] The solvent is preferably contained in an amount of 50 to 97% by mass, more preferably 70 to 95% by mass, and even more preferably 80 to 95% by mass, relative to the total amount of the pre-coat composition for paint film removal. This results in a pre-coat composition for paint film removal with excellent applicability.

[0042] (water) The water mentioned above is not particularly limited as long as it is water used as a raw material for various industrial products, tap water, well water, etc. The water may be distilled water or deionized water. In one aspect of this embodiment, the electrical conductivity of the water may be 1 to 300 μS / cm or 1 to 100 μS / cm.

[0043] If the solvent contains water, the water content is preferably 5 to 97% by mass, more preferably 70 to 95% by mass, and even more preferably 80 to 95% by mass, relative to the total amount of the pre-coat composition for paint removal. This results in a pre-coat composition for paint removal that is excellent in terms of work safety and environmental safety. The water content can be determined by analysis using a Karl Fischer moisture meter. The conditions for analysis using a Karl Fischer moisture meter are as follows. Analytical conditions for Karl Fischer moisture meter Equipment: Karl Fischer moisture meter MKS-500 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.) Measurement method: volumetric titration method Measurement temperature: 20℃

[0044] Examples of the alcohol-based solvents mentioned above include benzyl alcohol, tetrahydrofurfuryl alcohol, and isopropyl alcohol.

[0045] Examples of the ester-based solvents mentioned above include dimethyl succinate, dimethyl glutarate, and dimethyl adipate.

[0046] Examples of the above-mentioned aprotic polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, and dichloromethane.

[0047] Examples of the ether-based solvents mentioned above include triethylene glycol dimethyl ether, diethylene glycol monomethyl ether, and butyl cellosolve (ethylene glycol monobutyl ether).

[0048] Examples of the ketone solvents mentioned above include acetophenone, cyclohexanone, and acetone.

[0049] <Wax content percentage> In this embodiment, the wax content of the pre-coat composition for paint film removal is 10 wt% or less, preferably 0 wt% to 10 wt%, and more preferably 0 wt% to 5 wt%, relative to the total mass of the polyester resin and the polyacrylic resin. This results in a pre-coat composition for paint film removal that exhibits excellent solubility in alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents.

[0050] In this embodiment, "wax" refers to an oily substance that is solid at room temperature and melts into a liquid when heated. The wax is not particularly limited, but examples include plant-based waxes, animal-based waxes, mineral waxes, petroleum-based waxes, and synthetic waxes.

[0051] Examples of plant-based waxes include wood wax, sumac wax, white wax, carnauba wax, candelilla wax, rice wax, and jojoba oil. Examples of animal-based waxes include beeswax, privet wax, lanolin, and whale wax.

[0052] Examples of mineral-based waxes include montan wax, ozokerite, and ceresin. Examples of petroleum-based waxes include paraffin wax and petrolatum.

[0053] Examples of synthetic waxes include hydrogenated waxes (montan wax derivatives, paraffin wax derivatives, and hydrogenated castor oil and its derivatives), 12-hydroxystearic acid-based waxes, stearamide-based waxes, phthalimide anhydride-based waxes, and polyethylene wax.

[0054] The content ratio of the above waxes can be determined by high-performance liquid chromatography and FT-IR. The conditions for analysis by high-performance liquid chromatography and FT-IR are as follows. Analytical conditions for high-performance liquid chromatography Equipment: Preparative HPLC system PLC761 (manufactured by GL Sciences Co., Ltd.) Separation method: Size exclusion chromatography

[0055] FT-IR analysis conditions Equipment: FT-IR spectrometer Frontier (manufactured by Perkin Elmer) Measurement method: Total reflection measurement method

[0056] <Other ingredients> The pre-coat composition for paint film removal according to this embodiment may further contain other components, insofar as the effects of the present invention are achieved. Examples of these other components include defoaming agents, surface modifiers, viscosity modifiers, pH adjusters, preservatives, and rust inhibitors.

[0057] <Characteristics of pre-coat compositions for paint film removal> (FT-IR spectrum) In this embodiment, when the film derived from the above-mentioned pre-coat composition for paint film removal is analyzed using total internal reflection, the FT-IR spectrum obtained is 680-710 cm⁻¹. -1 Let A[%T] be the highest peak height among the peaks showing maximum values ​​within the range of 1710-1740 cm. -1When B[%T] is defined as the highest peak height among the peaks showing maximum values ​​within the specified range, the ratio A / B is preferably between 0 and 0.8, more preferably between 0 and 0.5, and even more preferably between 0 and 0.1. This results in a pre-coat composition for paint film removal that exhibits excellent solubility in alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents. The procedure and conditions for analysis using total internal reflection are as follows.

[0058] The pre-coat composition for paint film removal is placed in a glass container and dried in a circulating air oven at 80°C until a constant weight is reached. Then, the extracted resin component (film) is subjected to FT-IR spectral measurement under the following conditions. From the obtained FT-IR spectrum, the region between 680 and 710 cm⁻¹ is determined. -1 Among the peaks showing maximum values ​​within the range, the highest peak height A[%T] is 1710~1740cm. -1 Identify the peak with the largest peak height B[%T] among the peaks showing a maximum value within the range, and calculate the ratio A / B. Equipment: FT-IR spectrometer Frontier (manufactured by Perkin Elmer) Measurement method: Total reflection measurement method

[0059] Figures 1 and 2 are FT-IR spectral diagrams obtained when a film derived from a pre-coat composition for paint film removal was analyzed using total internal reflection. As shown in Figure 1, resins containing an aromatic ring of styrene within the molecule, such as styrene-acrylic resin, have a total internal reflection of 680-710 cm² derived from the aromatic ring. -1 A peak is observed. However, in the polyacrylic resin shown in Figure 1 and the polyester resin shown in Figure 2, the 680-710 cm peak originates from the aromatic ring. -1 No peak is observed. On the other hand, the peak originating from the carbonyl group is 1710-1740 cm. -1The peak is observed in all three resins: styrene-acrylic resin, polyacrylic resin, and polyester resin. Focusing on the above points, the inventors have found that if the above ratio A / B is 0 or more and less than 1, the above pre-coat composition for paint film removal can exert the desired effect even if it contains a "resin having an aromatic ring of styrene in its molecule".

[0060] Examples of "resins having an aromatic ring of styrene in their molecule" include styrene-acrylic resin and copolymers of vinyl ester and styrene.

[0061] The paint film removal precoat composition according to this embodiment has been described above. The above paint film removal precoat composition can efficiently remove paint films derived from water-based paints, etc., by being applied as a primer to the object to be painted in advance. Therefore, there is no need to use dangerous chemicals such as strong alkaline chemicals or hydrogen peroxide that have been used in the past, and the above paint film removal precoat composition is excellent in safety. Even when alkaline chemicals are used, paint films derived from water-based paints, etc., can be removed efficiently. Because the water solubility of the film derived from the above paint film removal precoat composition is low, the film is not affected by water-based paints and can fully perform its original function as a precoat. Furthermore, because the above paint film removal precoat composition has a low wax content, the film is not melted by heating above the melting point of the wax and can fully perform its original function as a precoat.

[0062] ≪Coating≫ The coating according to this embodiment is derived from the above-mentioned pre-coat composition for paint removal. Here, "derived from the pre-coat composition for paint removal" means that the above-mentioned pre-coat composition for paint removal is used as the starting material. In other words, the coating is formed by applying the above-mentioned pre-coat composition for paint removal to a substrate (such as an object to be painted) and then heat-treating it.

[0063] (Water solubility of the coating) In this embodiment, the water solubility of the film derived from the above pre-coat composition for paint removal is 0 wt% to 50 wt%, preferably 0 wt% to 30 wt%, more preferably 0 wt% to 20 wt%, and even more preferably 0 wt% to 10 wt%. This results in a pre-coat composition for paint removal that has excellent resistance to water-based paints. The water solubility of the above film is determined as follows.

[0064] First, a double-sided grid blast of SPCC-SD (JIS G3141:2017) (size, 1cm x 7cm) is immersed in acetone for 20 minutes to degrease it. After degreasing, each pre-coat composition is immersed in the degreased SPCC-SD double-sided grid blast and dried in a circulating oven at 80°C for 20 minutes to obtain a test piece. The obtained test piece is immersed in water for 10 minutes (at room temperature, under stirring conditions (500 rpm)), and then dried in a circulating oven at 80°C for 20 minutes. The solubility of the coating in water is calculated from the mass of the SPCC-SD double-sided grid blast before application of the pre-coat composition (a), the mass of the test piece after application of the pre-coat composition and drying (b), and the mass of the test piece after immersion in water and drying (c), according to the following formula. The dissolution rate of the film in water (wt%) = 100 × {(b) - (c)} / {(b) - (a)}

[0065] ≪Method for producing a pre-coat composition for paint film removal≫ The method for producing the pre-coat composition for paint film removal according to this embodiment includes the steps of preparing the polyester resin or polyacrylic resin and the solvent, and adding the polyester resin or polyacrylic resin to the solvent. Any method may be used for the addition step. Examples of the addition step include adding the polyester resin or polyacrylic resin to the solvent in a flask, and adding the polyester resin or polyacrylic resin to the solvent on an industrial scale in a chemical plant or the like.

[0066] ≪Method for removing paint film≫ In one aspect of this embodiment, the method for removing the coating film is: A method for removing a coating film provided on the surface of a substrate, comprising bringing a coating film remover into contact with the coating film, The above coating film is provided on a film provided on the above substrate, The above-mentioned film is derived from the above-mentioned pre-coat composition for removing coatings.

[0067] In another aspect of this embodiment, the method for removing the coating film is: A method for removing a coating film applied to the surface of a substrate, A step of applying the above-mentioned pre-coat composition for removing coatings to the surface of the above-mentioned substrate to form a film, A step of forming a coating film on the surface of the above-mentioned film, The process includes the step of bringing a paint remover into contact with the paint film.

[0068] The method for applying the above-mentioned pre-coat composition for removing the coating film to the surface of the above-mentioned substrate is not particularly limited, and known methods can be used, such as application by spraying, application by roller, application by dip method, application by bar coating, application by mist, application by brush, etc.

[0069] The pre-coat composition for removing coatings applied to the surface of the substrate can then be formed into a film by heat treatment or room temperature drying. The method of heat treatment is not particularly limited, but examples include methods using a circulating oven or methods using infrared heating.

[0070] The method for forming a coating on the surface of the above-mentioned film is not particularly limited, and examples include applying paint to the surface of the film and then heat-treating it. The method for applying the paint is not particularly limited, and known methods can be used, such as spray application, roller application, dip application, bar coating, mist application, and brush application. The method for heat treatment can be the same as the method used to form the above-mentioned film.

[0071] The method for bringing the above-mentioned paint remover into contact with the above-mentioned paint film is not particularly limited. Such methods include, for example, immersion, application, and spraying or showering, in air, under reduced pressure, or under pressure, at room temperature or under heating. When bringing the above-mentioned paint remover into contact with the above-mentioned paint film by immersion, operations such as ultrasonic treatment, bubbling, and agitation may be performed as needed. In this method, it is preferable to immerse the substrate having the paint film in a paint remover tank into which the heated above-mentioned paint remover has been introduced, and to remove the paint film. At this time, it is preferable to stir the above-mentioned paint remover so that the aqueous phase and the organic phase are uniformly dispersed. The immersion time is preferably 1 minute to 60 minutes.

[0072] The above-mentioned coating remover preferably includes at least one selected from the group consisting of, for example, alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents.

[0073] Examples of the alcohol-based solvents mentioned above include benzyl alcohol and tetrahydrofurfuryl alcohol.

[0074] Examples of the ester-based solvents mentioned above include dimethyl succinate, dimethyl glutarate, and dimethyl adipate.

[0075] Examples of the above-mentioned aprotic polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, and dichloromethane.

[0076] Examples of the ether-based solvents mentioned above include triethylene glycol dimethyl ether and diethylene glycol monomethyl ether.

[0077] Examples of the ketone solvents mentioned above include acetophenone and cyclohexanone.

[0078] Examples of the above-mentioned paint stripper composition include a composition of 40 wt% benzyl alcohol and 60 wt% water. Furthermore, the following compositions are also possible for the above-mentioned paint stripper composition. 1) Dichloromethane 100 wt%, 2) Benzyl alcohol 50 wt%, monoethanolamine 20 wt%, diethylene glycol monomethyl ether 10 wt%, potassium hydroxide 1 wt%, water 19 wt% 3) Benzyl alcohol 50 wt%, water 33 wt%, sodium toluenesulfonate 15 wt%, potassium hydroxide 2 wt%

[0079] In the coating removal method of this embodiment, the temperature of the coating remover is preferably 20 to 120°C, more preferably 30 to 100°C, and even more preferably 40 to 80°C.

[0080] Afterward, the paint remover can be removed from the substrate from which the paint film has been removed by normal washing and drying. For example, the substrate from which the paint film has been removed can be washed with water, acetone, isopropyl alcohol, etc., and then dried at room temperature.

[0081] The pre-coat composition for paint film removal according to this embodiment can be suitably used not only for the painting jigs described above, but also for removing paint films from painted surfaces of automobile parts, bicycle parts, precision equipment, and electronic components. [Examples]

[0082] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0083] ≪Raw materials≫ The names of the raw material compounds used in this example are shown below. The Tg values ​​are those listed in the catalog. <Polyester resin> Poly(1,4-cyclohexanedimethylene terephthalate) (Tg = -25℃, number average molecular weight 17,000) Polyethylene terephthalate (Tg=8℃, number-average molecular weight 17,000) Polyethylene terephthalate (Tg=15℃, number average molecular weight 13,000) <Polyester resin (containing a sulfonate structure in the resin's molecular structure)> Polyester resin (Tg=47℃, number average molecular weight 14,000) <Styrene acrylic resin> Copolymer of polymethyl methacrylate and styrene (Tg=15℃) Copolymer of polymethyl methacrylate and styrene (Tg=22℃) Copolymer of polymethyl methacrylate and styrene (Tg=30℃) Copolymer of polymethyl methacrylate and styrene (Tg=53℃)

[0084] <Polyacrylic resin (containing carboxyl groups in the molecular structure of the resin)> Polyacrylic resin (Tg=65℃, weight-average molecular weight 10,000) <Polyacrylic resin> Polyethyl methacrylate (Tg=10℃, number average molecular weight 20,000) Polymethyl methacrylate (Tg=5℃, number-average molecular weight 20,000) <Other> Epoxy melamine resin Epoxy resin (Tg=50℃, number average molecular weight 20,000) Polypropylene resin (melting point 80°C, weight-average molecular weight 75,000) Cellulose acetate resin (Tg=170℃, degree of polymerization 150) Paraffin wax (melting point 60℃)

[0085] <<Experiment: Comparison of the performance of various pre-coat compositions for paint film removal>> <Preparation of pre-coat compositions for paint film removal> First, based on the formulations (mass%) shown in Tables 1 to 4, pre-coat compositions for paint film removal were prepared by adding each raw material to a solvent, as in Examples 1, 2, 3a to 3c and 4 to 11, and Comparative Examples 2 to 15. In Tables 1 to 4, a "-" indicates that the corresponding component was not added. Comparative Example 1 is a comparative example in which the evaluation described later was performed without using a pre-coat composition for paint film removal. Comparative Examples 2 to 8 and Comparative Example 11 used water as the solvent. Comparative Example 9 used methylcyclohexane as the solvent, and Comparative Example 10 used acetone as the solvent (Table 2).

[0086] <Evaluation of film-soluble water solubility> The water solubility of the coating was evaluated using the following procedure. First, SPCC (JIS G3141:2017) (size, 1cm x 2cm) was immersed in acetone for 20 minutes to degrease it. Each precoat composition was dropped onto the degreased SPCC. Then, the SPCC with the precoat compositions was dried in a circulating oven at 80°C for 20 minutes to form a coating. 1 μL of water was dropped onto the formed coating and allowed to air dry. After air drying, the presence or absence of water droplet marks on the coating was checked. If no water droplet marks were observed on the coating, it could be evaluated as a coating that is not affected by water-based paints. The results are shown in Tables 1 and 2.

[0087] <Evaluation of the solubility of the film in water> SPCC-SD double-sided grid blast (JIS G3141:2017) (size, 1 cm × 7 cm) was immersed in acetone for 20 minutes for degreasing. After degreasing, the SPCC-SD double-sided grid blast was immersed in each precoat composition and dried at 80°C for 20 minutes using a circulating air oven to obtain test pieces. The obtained test pieces were immersed in water for 10 minutes (at room temperature, under stirring conditions (500 rpm)) and then dried at 80°C for 20 minutes using a circulating air oven. From the mass (a) of the SPCC-SD double-sided grid blast before applying the precoat composition, the mass (b) of the test piece after applying and drying the precoat composition, and the mass (c) of the test piece after immersion in water and drying, the dissolution ratio of the film in water was calculated according to the following formula. However, for Comparative Example 9 and Comparative Example 11, the temperature and time when using the circulating air oven were 40°C and 40 minutes. The lower the dissolution ratio in water, the better the film can be evaluated as having excellent resistance to aqueous paints. The results are shown in Table 1 and Table 2. Dissolution ratio of the film in water (wt%) = 100 × {(b) - (c)} / {(b) - (a)}

[0088] <Evaluation of benzyl alcohol solubility and swelling of the film> 1 μL of benzyl alcohol was dropped onto the film formed in the same manner as the method described in <Evaluation of film water solubility> above. After 10 minutes of dropping, the benzyl alcohol was absorbed with a Kimwipe, and it was confirmed visually and by palpation whether the film was dissolved or swollen. The case where the film was dissolved or swollen was ranked as A, and the case where the film did not change was ranked as E. The fact that the film was dissolved or swollen means that the film can be peeled off with a paint stripper containing benzyl alcohol. The results are shown in Table 1 and Table 2.

[0089] <FT-IR spectrum measurement> The precoat composition for coating film peeling was placed in a glass container and dried in a circulating air oven at 80°C until it reached a constant weight. Then, for the resin component (film) taken out, FT-IR spectrum measurement was carried out under the following conditions. From the obtained FT-IR spectrum, 680 - 710 cm -1Among the peaks showing maximum values ​​within the range, the highest peak height A[%T] is 1710~1740cm. -1 Among the peaks showing local maximums within the specified range, the highest peak height B[%T] was identified, and the ratio A / B was calculated. The results are shown in Tables 1 and 2. Equipment: FT-IR spectrometer Frontier (manufactured by Perkin Elmer) Measurement method: Total reflection measurement method

[0090] <Evaluation of peelability of the coating film> (Preparing the test pieces) Test pieces for evaluating peelability were prepared using the following procedure. Specifically, first, a double-sided grid blast of SPCC-SD (JIS G3141:2017) (size, 2cm x 7cm) was immersed in acetone for 20 minutes to degrease it. After degreasing, each precoat composition was immersed in the SPCC-SD double-sided grid blast and dried in a circulating oven at 80°C for 20 minutes to form a film. A water-based paint (acrylic resin paint) was spray-coated onto the SPCC-SD double-sided grid blast with the film formed on it and dried in a circulating oven at 80°C for 40 minutes. Subsequently, a solvent-based paint (acrylic resin paint) was spray-coated onto the dried water-based paint and dried in a circulating oven at 80°C for 40 minutes, and then dried further at 120°C for 60 minutes to obtain the test piece.

[0091] (Evaluation test of peelability) The peelability of the paint remover was evaluated using the following procedure. First, each prepared test piece was immersed in the paint remover (40 wt% benzyl alcohol, 60 wt% water) (at 50°C, under stirring conditions (500 rpm)). After 10 minutes, each test piece was removed from the paint remover and wiped with a cloth, and the peelability of the paint film was visually confirmed. The evaluation was performed according to the following criteria based on the area ratio of the portion where the paint film was peeled off on the test piece. The evaluation results are shown in Tables 1 to 4.

[0092] Criteria for evaluation ranking A Rank: 99% or higher, 100% or lower Rank B: 90% or more but less than 99% Rank C: 70% or more but less than 90% Rank D: 40% or more but less than 70% E rank: Less than 40%

[0093] [Table 1]

[0094] [Table 2]

[0095] From the results in Tables 1 and 2, the pre-coat compositions for paint removal (Examples 1, 2, 3a-3c and 4-7) that contained a predetermined polyester resin or a predetermined polyacrylic resin and a solvent, had a wax content of 10 wt% or less relative to the total mass of the polyester resin and the polyacrylic resin, and in the FT-IR spectrum obtained when the pre-coat composition for paint removal was analyzed using total internal reflection, the ratio A / B was 0 or more and less than 1, and the water solubility of the film derived from the pre-coat composition for paint removal was 0 wt% or more and 50 wt% or less showed a peelability of rank A or B. On the other hand, the pre-coat compositions for paint removal that did not meet the above requirements (Comparative Examples 2-11) showed a peelability of rank D or E. From the above results, it was found that the pre-coat compositions for paint film removal of Examples 1, 2, 3a-3c and 4-7 are suitable as pre-coat compositions for efficiently removing paint films derived from water-based paints, etc.

[0096] The polyester resins used in Examples 1, 2, 3a-3c and 4 are obtained by polycondensation of terephthalic acid and an alkanediol having 2 to 10 carbon atoms. The polyester resins exemplified in the <Polyester Resin> section above have the same chemical structure characteristics as the polyester resins used in Examples 1, 2, 3a-3c and 4. Therefore, the inventors believe that the polyester resins exemplified in the <Polyester Resin> section above have similar properties to the polyester resins used in Examples 1, 2, 3a-3c and 4 and can be used as components of a pre-coat composition for efficiently removing coatings derived from water-based paints, etc.

[0097] The polyacrylic resins used in Examples 5 and 6 are obtained by polymerizing vinyl monomers with ester groups and a molecular weight of 86 to 142. The polyacrylic resins exemplified in the <Polyacrylic Resin> section above have the same chemical structure characteristics as the polyacrylic resins used in Examples 5 and 6. Therefore, the inventors believe that the polyacrylic resins exemplified in the <Polyacrylic Resin> section above have similar properties to the polyacrylic resins used in Examples 5 and 6 and can be used as components of a pre-coat composition for efficiently removing coatings derived from water-based paints, etc.

[0098] [Table 3]

[0099] From the results in Table 3, it was found that the pre-coat composition for paint film removal (Example 3a), in which the wax content is 10 wt% or less relative to the total mass of the polyester resin and the polyacrylic resin, exhibits superior peelability compared to the pre-coat compositions for paint film removal (Comparative Examples 11-15), in which the wax content exceeds 10 wt%.

[0100] [Table 4]

[0101] The results in Table 4 show that pre-coat compositions for paint film removal (Examples 8-11) containing butyl cellosolve (ether-based solvent), isopropyl alcohol (alcohol-based solvent), N-methyl-2-pyrrolidone (aprotic solvent), or acetone (ketone-based solvent) as solvents in addition to water exhibited excellent peelability, similar to the pre-coat composition for paint film removal containing only water as a solvent (Example 3a).

[0102] As described above, embodiments and examples of the present invention have been explained, but it is also intended from the outset that the configurations of each of the above embodiments and examples may be combined as appropriate.

[0103] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the meaning and scope of the claims are intended to be included.

Claims

1. A pre-coat composition for paint film removal, which facilitates the removal of a coating film applied to the surface of a substrate using a paint film remover, Polyester resin or polyacrylic resin, A solvent is included, The wax content is 10 wt% or less relative to the total mass of the polyester resin and the polyacrylic resin. In the FT-IR spectrum obtained when the film derived from the aforementioned pre-coat composition for paint film removal is analyzed using total internal reflection, the range is 680 to 710 cm⁻¹. －１ Let A[%T] be the highest peak height among the peaks showing maximum values ​​within the range of 1710–1740 cm. －１ If B[%T] is the highest peak height among the peaks showing a maximum value within the range, then the ratio A / B is between 0 and 1. The water solubility of the film derived from the aforementioned pre-coat composition for paint film removal is 0 wt% or more and 50 wt% or less. The polyester resin includes at least one selected from the group consisting of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), poly(1,2-propylene terephthalate), polytrimethylene terephthalate, poly(2,3-butylene terephthalate), poly(1,3-butylene terephthalate), poly(2-methyl-1,3-propylene terephthalate), polytetramethylene terephthalate, polypentamethylene terephthalate, polyhexamethylene terephthalate, polyheptamethylene terephthalate, polyoctamethylene terephthalate, polynonylmethylene terephthalate, poly(1,3-cyclohexanedimethylene terephthalate), poly(1,4-cyclohexanediethylene terephthalate), poly(1,3-cyclohexanediethylene terephthalate), and polydecamethylene terephthalate. The polyacrylic resin comprises at least one selected from the group consisting of polymethyl methacrylate, polyethyl methacrylate, poly-n-propyl methacrylate, poly-iso-propyl methacrylate, poly-n-butyl methacrylate, poly-sec-butyl methacrylate, poly-iso-butyl methacrylate, poly-tert-butyl methacrylate, polymethyl acrylate, polyethyl acrylate, poly-n-propyl acrylate, poly-iso-propyl acrylate, poly-n-butyl acrylate, poly-sec-butyl acrylate, poly-iso-butyl acrylate, and poly-tert-butyl acrylate, and is a pre-coat composition for paint film removal.

2. The coating film removal precoat composition according to claim 1, wherein the precoat composition for coating film removal is used so as to be provided between the surface of the substrate and the coating film.

3. The solvent comprises water, the pre-coat composition for paint film removal according to claim 1 or claim 2.

4. The coating remover comprises at least one selected from the group consisting of alcohol-based solvents, ester-based solvents, aprotic polar solvents, ether-based solvents, and ketone-based solvents, according to any one of claims 1 to 3.

5. The coating film is a coating film formed by heating paint, according to any one of claims 1 to 4, a pre-coat composition for removing coating films.

6. A film derived from the pre-coat composition for paint film removal according to any one of claims 1 to 5.

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