Method for producing coating film, coating film, and article

Abstract

To provide a method for producing a coating film for obtaining a coating film having excellent adhesion, a coating film, and an article.SOLUTION: The method for producing a coating film includes a preparation step of preparing a water-based coating composition, an application step of applying the water-based coating composition to an object to be coated, and a drying step of heating the applied water-based coating composition to obtain a coating film containing a dried product of the water-based coating composition. The aqueous coating composition contains a resin component. The resin component contains lignin modified with polyethylene glycol. The heating temperature in the drying step is 160 °C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a coating film, a coating film, and an article. [Background technology]

[0002] In recent years, from the viewpoint of environmental friendliness, the use of plant-derived resins as resins has been considered in various industrial fields. As a plant-derived resin, for example, glycol lignin has been proposed.

[0003] Glycol lignin is produced, for example, by solvolyzing lignocellulose using a glycol-based cooking solvent (such as polyethylene glycol) in the presence of an acid catalyst (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-197517 Summary of the Invention [Problem to be solved by the invention]

[0005] The use of glycol lignin as a resin component of aqueous paints is being considered. That is, an aqueous paint composition containing glycol lignin is prepared, applied to a substrate, and dried to obtain a coating film (dried film).

[0006] However, when the aqueous coating composition contains glycol lignin, the coating film (dried film) may not have sufficient adhesion to the substrate.

[0007] The present invention relates to a method for producing a coating film that provides a coating film with excellent adhesion, a coating film, and an article. [Means for solving the problem]

[0008] The present invention [1] includes a method for producing a coating film, which comprises a preparation step of preparing an aqueous coating composition, a coating step of applying the aqueous coating composition to a substrate, and a drying step of heating the applied aqueous coating composition to obtain a coating film containing a dried product of the aqueous coating composition, wherein the aqueous coating composition contains a resin component, and the resin component contains lignin modified with polyethylene glycol, and the heating temperature in the drying step is 160°C or higher.

[0009] The present invention [2] includes the method for producing a coating film according to the above [1], wherein the resin component comprises lignin modified with polyethylene glycol.

[0010] The present invention [3] includes the method for producing a coating film according to the above [1] or [2], wherein the polyethylene glycol has a number average molecular weight of 400 or more.

[0011] The present invention [4] includes a coating film obtained by the method for producing a coating film according to any one of the above [1] to [3].

[0012] The present invention [5] includes an article having the coating film described in [4] above. [Effects of the Invention]

[0013] In the coating film production method of the present invention, the resin component of the aqueous coating composition contains lignin modified with polyethylene glycol, and the aqueous coating composition is heated to a predetermined temperature or higher, so that the coating film obtained by the above method has excellent adhesion.

[0014] The coating film of the present invention is obtained by the above method and therefore has excellent adhesion. Furthermore, the article of the present invention is provided with the above coating film. In the above article, the coating film has excellent adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1. Coating production method 1) Preparation process In the coating film manufacturing method of the present invention, first, an aqueous coating composition is prepared (preparation step). The aqueous coating composition contains a resin component and water.

[0016] (1) Resin component The resin component contains, as an essential component, lignin modified with polyethylene glycol (PEG). The resin component preferably consists of lignin modified with polyethylene glycol (PEG). Hereinafter, lignin modified with polyethylene glycol may be simply referred to as PEG lignin.

[0017] In PEG lignin, lignin is a polymeric phenolic compound. Lignin is a natural product (natural lignin) found in plants. Examples of the basic structure of lignin include guaiacyl lignin (G-type), syringyl lignin (S-type), and p-hydroxyphenyl lignin (H-type).

[0018] Lignin is industrially extracted from plant materials, such as lignocellulose, and includes soda lignin, sulfite lignin, and kraft lignin.

[0019] Examples of methods for extracting lignin include the soda process, the sulfite process, the steam explosion process, the solvolysis process, and the Kraft process.

[0020] More specifically, lignin includes lignin derived from woody plants and lignin derived from herbaceous plants.

[0021] Examples of woody plant-derived lignin include coniferous lignin contained in conifers (e.g., cedar) and hardwood lignin contained in hardwood. Note that woody plant-derived lignin does not contain an H-type basic skeleton. More specifically, among woody plant-derived lignins, coniferous lignin does not contain an S-type basic skeleton but has a G-type basic skeleton. Furthermore, hardwood lignin has both a G-type basic skeleton and an S-type basic skeleton.

[0022] Examples of lignin derived from herbaceous plants include rice lignin, which is contained in grasses. Examples of grasses include wheat straw, rice straw, corn, and bamboo. Lignin derived from herbaceous plants has all of the basic skeletons of H-type, G-type, and S-type.

[0023] These lignins can be used alone or in combination of two or more. As the lignin, preferred is woody plant-derived lignin that does not contain an H-type basic skeleton, more preferred is coniferous lignin that does not contain an S-type basic skeleton and has a G-type basic skeleton, and particularly preferred is coniferous lignin derived from Japanese cedar. PEG lignin obtained from coniferous lignin derived from Japanese cedar has excellent homogeneity.

[0024] In PEG lignin, polyethylene glycol (PEG) improves the solubility of the resin component and also improves the coating film formability and adhesion of the coating film.

[0025] From the viewpoint of the solubility of the resin component, the coating film formability and adhesion of the coating film, the number average molecular weight of polyethylene glycol is, for example, 100 or more, preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more.

[0026] Furthermore, from the viewpoint of the water resistance and adhesion of the coating film, the number average molecular weight of polyethylene glycol is, for example, 1000 or less, preferably 900 or less, more preferably 800 or less, even more preferably 600 or less, and particularly preferably 500 or less.

[0027] That is, from the viewpoint of the solubility of the resin component, the coating film formability and adhesion of the coating film, the number average molecular weight of the polyoxyethylene glycol is, for example, 100 to 1000, preferably 200 to 900, more preferably 300 to 800, even more preferably 400 to 600, and particularly preferably 400 to 500. The number average molecular weight can be determined as a polyoxyethylene glycol-equivalent molecular weight by a known gel permeation chromatography method.

[0028] In particular, when the heating temperature (described below) in the drying step (described below) is a predetermined value or higher (for example, 220°C or higher), the number average molecular weight of polyethylene glycol (PEG) is preferably 300 or higher, more preferably 400 or higher. When the heating temperature (described below) is a predetermined value or higher and the number average molecular weight of polyethylene glycol (PEG) is a predetermined value or higher, a coating film having particularly excellent adhesion and solvent resistance can be obtained.

[0029] PEG lignin is produced, for example, in accordance with the method described in JP 2017-197517 A.

[0030] In this method, for example, plant material (lignocellulose) that serves as the raw material for lignin is digested using polyethylene glycol. The digestion method is not particularly limited, but for example, the plant material that serves as the raw material for lignin, polyethylene glycol, and an inorganic acid (e.g., hydrochloric acid and sulfuric acid) serving as an acid catalyst are mixed and reacted.

[0031] The mixing ratio of polyethylene glycol relative to 100 parts by mass of the plant material serving as the raw material of lignin is, for example, 200 to 1000 parts by mass, or preferably 300 to 600 parts by mass.

[0032] The mixing ratio of the inorganic acid (100% conversion) relative to 100 parts by mass of polyethylene glycol is, for example, 0.1 to 2.0 parts by mass, or preferably 0.2 to 1.0 part by mass.

[0033] The reaction conditions include normal pressure. The reaction temperature is, for example, 120 to 180° C., or preferably 130 to 150° C. The reaction time is, for example, 60 to 240 minutes, or preferably 80 to 120 minutes.

[0034] After the reaction is complete, an alkali is added to the reaction solution in an appropriate ratio to adjust the pH. Examples of alkali include ammonia and sodium hydroxide. This extracts the PEG lignin into the solution. The adjusted pH is, for example, 8 to 14, preferably 10 to 14, and more preferably 10.5 to 14.

[0035] This method yields pulp as a solid component and PEG lignin as a solution component.

[0036] Next, in this method, the solid component (pulp) is separated from the reaction product by a known separation method (e.g., filtration, pressing, and centrifugation), and the solution component is recovered. In addition, in this method, if necessary, the solid component (pulp) can be washed, and the solution (PEG lignin) impregnated into the solid component can be recovered.

[0037] In this method, an inorganic acid (e.g., hydrochloric acid or sulfuric acid) is then added to adjust the pH to precipitate and decompose the PEG lignin. The pH after adjustment is, for example, 1.5 to 5, preferably 1.5 to 3, and more preferably 1.5 to 2.

[0038] This allows the PEG lignin to be precipitated. The resulting precipitate is then recovered by a known separation method (e.g., filtration, pressing, or centrifugation). This allows the PEG lignin to be obtained as a solid content.

[0039] To improve the solubility in the organic solvent (described below), the PEG lignin solids may be crushed and / or disintegrated as needed before being mixed with the organic solvent (described below). Furthermore, the PEG lignin solids may be heated to an appropriate temperature as needed before being mixed with the organic solvent (described below). Examples of heating methods include a hot water bath and an oil bath.

[0040] The content of the resin component is, for example, 1 to 60 mass%, preferably 5 to 50 mass%, relative to the total amount of the aqueous coating composition. In particular, when the aqueous coating composition is used for electrodeposition coating (described later), the content of the resin component is more preferably 5 to 20 mass%, relative to the total amount of the aqueous coating composition. Furthermore, when the aqueous coating composition is used for physical coating (described later), the content of the resin component is more preferably 25 to 40 mass%, relative to the total amount of the aqueous coating composition.

[0041] (2)Water In the aqueous coating composition, the water dissolves and / or disperses the above-mentioned resin components.

[0042] The water content is, for example, 10 to 99% by mass, preferably 40 to 98% by mass, and more preferably 50 to 95% by mass, based on the total amount of the aqueous coating composition. In particular, when the aqueous coating composition is used for electrodeposition coating (described below), the water content is even more preferably 60 to 90% by mass, and particularly preferably 80 to 90% by mass. Furthermore, when the aqueous coating composition is used for physical coating (described below), the water content is even more preferably 60 to 70% by mass.

[0043] The water content is in the range of, for example, 100 to 10,000 parts by mass, or preferably 200 to 2,000 parts by mass, relative to 100 parts by mass of the resin component.

[0044] (3) Organic solvents The aqueous coating composition may contain an organic solvent as needed, and preferably contains an organic solvent.

[0045] Organic solvents are classified into, for example, organic solvents that readily dissolve PEG lignin and organic solvents that sparingly dissolve PEG lignin.

[0046] The PEG lignin-soluble organic solvent is an organic solvent capable of dissolving the PEG lignin. More specifically, the amount of PEG lignin (specifically, PEG lignin 400 in the Examples described below) that can be dissolved in 100 g of the PEG lignin-soluble organic solvent at 20° C. is, for example, 10 g or more, preferably 30 g or more.

[0047] Examples of organic solvents that readily dissolve PEG lignin include ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monophenyl ether, N-methylpyrrolidone (NMP), formaldehyde, benzyl alcohol, diethylene glycol, diacetone alcohol, and ethyl lactate. These can be used alone or in combination.

[0048] The PEG lignin-slightly soluble organic solvent is an organic solvent that cannot dissolve or can slightly dissolve the PEG lignin. More specifically, the amount of PEG lignin (specifically, PEG lignin 400 in the Examples described below) that can be dissolved in 100 g of the PEG lignin-slightly soluble organic solvent at 20° C. is, for example, less than 10 g, preferably less than 5 g, and more preferably 1 g or less.

[0049] Examples of organic solvents that are poorly soluble in PEG lignin include isopropyl alcohol, normal butanol, and ethylene glycol monomethyl ether. Water is preferred. These can be used alone or in combination of two or more.

[0050] The organic solvent may be used alone or in combination of two or more. From the viewpoint of affinity for the resin component, the organic solvent preferably contains an organic solvent that readily dissolves PEG lignin, and more preferably consists of an organic solvent that readily dissolves PEG lignin.

[0051] Furthermore, PEG lignin-soluble organic solvents are classified, for example, based on AlogP, into relatively hydrophobic PEG lignin-soluble organic solvents (hereinafter referred to as hydrophobic-PEG lignin-soluble organic solvents) and relatively hydrophilic PEG lignin-soluble organic solvents (hereinafter referred to as hydrophilic-PEG lignin-soluble organic solvents).

[0052] The AlogP value is the logarithm of the calculated n-octanol / water partition coefficient (P). More specifically, the AlogP value is calculated using the computer program ALOGPS ver. 2.01 (Virtual Computational Chemical Laboratory).

[0053] The hydrophobic-PEG lignin-soluble organic solvent has an AlogP value of at least a predetermined value. The AlogP value of the hydrophobic-PEG lignin-soluble organic solvent is, for example, at least 1.00, preferably at least 1.05. The AlogP value of the hydrophobic-PEG lignin-soluble organic solvent is usually at most 3.00.

[0054] Among the above-mentioned organic solvents readily dissolving PEG lignin, examples of hydrophobic organic solvents readily dissolving PEG lignin include ethylene glycol monophenyl ether (AlogP: 1.22), ethylene glycol monobenzyl ether (AlogP: 1.06), diethylene glycol monophenyl ether (AlogP: 1.31), diethylene glycol monobenzyl ether (AlogP: 1.03), triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, propylene glycol monophenyl ether (AlogP: 1.7), and benzyl alcohol (AlogP: 1.07). These can be used alone or in combination.

[0055] The hydrophilic PEG lignin-soluble organic solvent has an AlogP value less than a predetermined value. The AlogP value of the hydrophilic PEG lignin-soluble organic solvent is, for example, less than 1.00, preferably less than 0.95. The AlogP value of the hydrophilic PEG lignin-soluble organic solvent is usually -3.0 or more.

[0056] Among the above-mentioned organic solvents readily dissolving PEG lignin, examples of hydrophilic organic solvents readily dissolving PEG lignin include diethylene glycol monomethyl ether (AlogP: -0.67), diethylene glycol monoethyl ether (AlogP: -0.16), diethylene glycol monobutyl ether (AlogP: 0.63), triethylene glycol monomethyl ether (AlogP: -0.55), triethylene glycol monobutyl ether (AlogP: 0.63), tetraethylene glycol monobutyl ether (AlogP: 0.64), propylene glycol monomethyl ether (AlogP: -0.37), N-methylpyrrolidone (AlogP: -0.06), formaldehyde (AlogP: -1.53), diethylene glycol (AlogP: -1.24), diacetone alcohol (AlogP: 0.04), and ethyl lactate (AlogP: 0.17). These can be used alone or in combination.

[0057] The organic solvent readily dissolving PEG lignin preferably contains a hydrophobic organic solvent readily dissolving PEG lignin. That is, from the viewpoint of coating film-forming properties, the aqueous coating composition preferably contains a hydrophobic organic solvent readily dissolving PEG lignin.

[0058] If the aqueous coating composition contains a hydrophobic-PEG lignin-soluble organic solvent, migration of the organic solvent into the aqueous layer during electrodeposition coating (described below) can be suppressed, resulting in excellent coating film-forming properties.

[0059] Furthermore, PEG lignin-soluble organic solvents are classified, for example, based on their boiling points, into organic solvents with relatively high boiling points (hereinafter referred to as high-boiling point organic solvents) and organic solvents with relatively low boiling points (hereinafter referred to as low-boiling point organic solvents).

[0060] The high-boiling organic solvent readily dissolving PEG lignin has a boiling point equal to or higher than a predetermined value. The boiling point of the high-boiling organic solvent readily dissolving PEG lignin is, for example, 200°C or higher, preferably 230°C or higher. The boiling point of the high-boiling organic solvent readily dissolving PEG lignin is usually 400°C or lower.

[0061] Among the above-mentioned organic solvents readily dissolving PEG lignin, examples of high-boiling point organic solvents readily dissolving PEG lignin include ethylene glycol monophenyl ether (boiling point: 242°C), ethylene glycol monobenzyl ether (boiling point: 256°C), diethylene glycol monoethyl ether (boiling point: 202°C), diethylene glycol monobutyl ether (boiling point: 230°C), diethylene glycol monophenyl ether (boiling point: 298°C), diethylene glycol monobenzyl ether (boiling point: 311°C), triethylene glycol monomethyl ether (boiling point: 311°C), and ethylene glycol monomethyl ether (boiling point: 311°C). Examples of suitable solvents include ethyl ether (boiling point: 248°C), triethylene glycol monobutyl ether (boiling point: 276°C), triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, tetraethylene glycol monobutyl ether (boiling point: 304°C), propylene glycol monophenyl ether (boiling point: 243°C), N-methylpyrrolidone (boiling point: 202°C), formaldehyde (boiling point: 210°C), benzyl alcohol (boiling point: 205°C), and diethylene glycol (boiling point: 244°C). These can be used alone or in combination of two or more.

[0062] The low-boiling organic solvent readily dissolving PEG lignin has a boiling point below a predetermined value, such as below 200°C, preferably 150°C or lower, or typically 50°C or higher.

[0063] Among the above-mentioned organic solvents readily dissolving PEG lignin, examples of low-boiling point organic solvents readily dissolving PEG lignin include diethylene glycol monomethyl ether (boiling point: 194°C), propylene glycol monomethyl ether (boiling point: 120°C), diacetone alcohol (boiling point: 168°C), and ethyl lactate (boiling point: 154°C). These can be used alone or in combination of two or more.

[0064] The PEG lignin-soluble organic solvent preferably contains a high-boiling point PEG lignin-soluble organic solvent. That is, from the viewpoint of coating film-forming properties, the aqueous coating composition preferably contains a high-boiling point PEG lignin-soluble organic solvent.

[0065] If the aqueous coating composition does not contain a high-boiling point PEG lignin-soluble organic solvent and only contains a low-boiling point PEG lignin-soluble organic solvent, the organic solvent volatilizes during electrodeposition coating (described below), making it difficult for the organic solvent to remain in the wet film. This can result in a decrease in the coating film-forming properties of the aqueous coating composition. On the other hand, if the organic solvent contains a high-boiling point PEG lignin-soluble organic solvent, the volatilization of the organic solvent can be suppressed during electrodeposition coating (described below), resulting in excellent coating film-forming properties.

[0066] The PEG lignin-soluble organic solvent preferably contains a PEG lignin-soluble organic solvent that has a relatively high boiling point and is relatively hydrophobic (hereinafter referred to as a "high-boiling-point hydrophobic PEG lignin-soluble organic solvent"). Examples of high-boiling-point hydrophobic PEG lignin-soluble organic solvents include ethylene glycol monophenyl ether (AlogP: 1.22, boiling point: 245°C), ethylene glycol monobenzyl ether (AlogP: 1.06, boiling point: 256°C), diethylene glycol monophenyl ether (AlogP: 1.31, boiling point: 298°C), diethylene glycol monobenzyl ether (AlogP: 1.03, boiling point: 311°C), propylene glycol monophenyl ether (AlogP: 1.7, boiling point: 243°C), and benzyl alcohol (AlogP: 1.07, boiling point: 205°C). These solvents can be used alone or in combination. Benzyl alcohol is preferred.

[0067] Alternatively, a high-boiling hydrophobic organic solvent readily dissolving PEG lignin may be used in combination with a hydrophilic organic solvent readily dissolving PEG lignin and / or a low-boiling organic solvent readily dissolving PEG lignin. In such cases, the content of the high-boiling hydrophobic organic solvent is, for example, 1 to 30% by mass, preferably 4 to 20% by mass, based on the total amount of the PEG lignin-soluble organic solvents. The content (total) of the hydrophilic organic solvent readily dissolving PEG lignin and the low-boiling organic solvent readily dissolving PEG lignin is, for example, 70 to 99% by mass, preferably 80 to 96% by mass, based on the total amount of the PEG lignin-soluble organic solvents.

[0068] In the aqueous coating composition, the content of the organic solvent is appropriately set depending on the purpose and application. From the viewpoints of coatability, environmental friendliness, and cost, the content of the organic solvent is preferably adjusted to a relatively low level.

[0069] For example, the content of the organic solvent is, for example, 1 to 30 mass %, preferably 5 to 20 mass %, relative to the total amount of the aqueous coating composition.

[0070] (4) Anionizing agent When the aqueous coating composition is used for anionic electrodeposition coating (described later), the aqueous coating composition preferably contains an anionizing agent that anions the PEG lignin (hereinafter referred to as an anionizing agent).

[0071] The anionizing agent is a modifying agent that anionsize the PEG lignin. Examples of anionizing agents include alkalis, including inorganic and organic alkalis. Inorganic alkalis include sodium hydroxide and potassium hydroxide. Organic alkalis include organic amines. Organic amines include alkylamines, alkanolamines, alkyleneimines, and organic ring-containing amines. Alkylamines include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monobutylamine, dibutylamine, and tributylamine. Alkanolamines include monoethanolamine, diethanolamine, triethanolamine, mono(2-hydroxypropyl)amine, di(2-hydroxypropyl)amine, tri(2-hydroxypropyl)amine, dimethylaminoethanol, and diethylaminoethanol. Examples of alkyleneimines include ethylenediamine, propylenediamine, diethyleneimine, and propyleneimine. Examples of organic ring-containing amines include piperazine, morpholine, pyrazine, and pyridine. These may be used alone or in combination of two or more. Preferred anionizing agents include organic amines. Preferred organic amines include alkylamines and alkanolamines, more preferably triethylamine and dimethylaminoethanol, and even more preferably dimethylaminoethanol.

[0072] By adding an anionizing agent, the PEG lignin can be used more efficiently in anionic electrodeposition coating.

[0073] The mechanism by which PEG lignin can be used in anionic electrodeposition coating is thought to be as follows. When an anionizing agent is added to PEG lignin, the phenolic hydroxyl groups in the PEG lignin are anionized. This improves the water solubility and / or water dispersibility of the PEG lignin. Then, in anionic electrodeposition coating, the PEG lignin migrates to the anode by electrophoresis, where it is electrically neutralized, decreasing its water solubility and / or water dispersibility. As a result, a coating film of PEG lignin is deposited on the anode. In other words, PEG lignin can be used as an anionic electrodeposition coating.

[0074] The content of the anionizing agent relative to the total amount of the aqueous coating composition is, for example, 0.1 to 20 mass %, preferably 0.5 to 10 mass %, or more preferably 1 to 5 mass %.

[0075] For example, the content of the anionizing agent is, for example, 0.5 to 10 parts by mass, or preferably 0.8 to 5 parts by mass, relative to 100 parts by mass of the PEG lignin.

[0076] More specifically, from the viewpoint of improving the water solubility and / or water dispersibility of the PEG lignin, the lower limit of the content of the anionizing agent is, for example, 0.5 parts by mass or more, preferably 0.8 parts by mass or more, relative to 100 parts by mass of the PEG lignin. From the viewpoint of suppressing redissolution of the PEG lignin during electrodeposition coating to obtain excellent deposition efficiency, and from the viewpoint of suppressing gas generation due to electrolysis during electrodeposition coating to obtain excellent appearance, the upper limit of the content of the anionizing agent is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, relative to 100 parts by mass of the PEG lignin.

[0077] (5) Method for preparing aqueous coating composition The method for preparing the aqueous coating composition is not particularly limited. For example, the aqueous coating composition can be obtained by mixing the resin component and the water in the above ratio. Preferably, the aqueous coating composition can be obtained by mixing the resin component, the water, and the organic solvent in the above ratio. If necessary, the anionizing agent can be added at an appropriate timing. The mixing order is not particularly limited.

[0078] More specifically, for example, the resin component and the organic solvent are mixed in the above ratio to obtain a solution and / or dispersion of the resin component. Preferably, the resin component and the organic solvent that readily dissolves PEG lignin are mixed to obtain a solution of the resin component.

[0079] Next, the solution and / or dispersion of the resin component is mixed with water. In other words, the solution and / or dispersion of the resin component is diluted with water. In this way, an aqueous coating composition containing the resin component, water, and organic solvent is prepared.

[0080] Furthermore, when an anionizing agent is added, for example, from the viewpoint of efficiently anionizing the PEG lignin, the anionizing agent is added before the water is added, i.e., to the mixture of the resin component and the organic solvent.

[0081] The aqueous coating composition is pretreated as needed. For example, when the aqueous coating composition is used for electrodeposition coating (described later), the aqueous coating composition is preferably subjected to ion exchange treatment. That is, the above-mentioned aqueous coating composition may contain an acid and / or an alkali, and in electrodeposition coating (described later), the acid and / or alkali may reduce the uniformity of the coating film. Therefore, the aqueous coating composition for electrodeposition coating is preferably subjected to ion exchange treatment to remove the acid and / or alkali.

[0082] The solids concentration of the aqueous coating composition is adjusted depending on the application of the aqueous coating composition. For example, when the aqueous coating composition is used for electrodeposition coating (described later), the solids concentration of the aqueous coating composition is, for example, 1 to 60 mass%, preferably 5 to 50 mass%, more preferably 10 to 20 mass%. When the aqueous coating composition is used for physical coating (described later), the solids concentration of the aqueous coating composition is, for example, 1 to 60 mass%, preferably 5 to 50 mass%, more preferably 30 to 40 mass%.

[0083] 2) Coating process Next, in this method, the aqueous coating composition is applied to the substrate (application step).

[0084] The coating method is not particularly limited, and known coating methods can be used. More specific examples of coating methods include physical coating, electrostatic coating, and electrodeposition coating. Examples of physical coating include brush coating, bar coating, air spraying, airless spraying, and dip coating. Preferred coating methods include physical coating and electrodeposition coating, and more preferred are bar coating and electrodeposition coating. From the viewpoint of coating film uniformity, electrodeposition coating is even more preferred.

[0085] Examples of electrodeposition coating include anionic electrodeposition coating and cationic electrodeposition coating, and preferably anionic electrodeposition coating. A known method is used for electrodeposition coating. Specifically, in a known electrodeposition coating device, the substrate is immersed in the aqueous coating composition and a current is applied between the electrodes.

[0086] The substrate is not particularly limited, but a substrate appropriate for the coating method is used. For example, when electrodeposition coating is employed, conductive materials can be used as the substrate. Examples of conductive materials include substrates with conductive films (e.g., ITO films and FTO films), substrates with semiconductor films (e.g., silicon wafers), metal plates (e.g., copper, aluminum, and stainless steel), electrode materials with anodized films, and materials with conductive paint coatings. These can be used alone or in combination of two or more types.

[0087] The coating conditions are not particularly limited and are set appropriately depending on the coating method.

[0088] For example, when electrodeposition coating is employed, the applied voltage and current application time are appropriately set. The applied voltage is, for example, 1 to 250 V, preferably 5 to 150 V. The current application time is, for example, 0.1 to 10 minutes, preferably 0.5 to 5 minutes. When the applied voltage is relatively high, the current application time is preferably adjusted to be relatively short. When the applied voltage is relatively low, the current application time is preferably adjusted to be relatively long. The voltage application method may be, for example, either a method in which a set voltage is applied simultaneously with current application (hard start), or a method in which the voltage is gradually increased to the set value during current application (soft start).

[0089] When physical coating is employed, the environmental temperature and humidity of the coating environment are set appropriately. The environmental temperature is, for example, 10 to 40° C., preferably 20 to 30° C. The environmental humidity (relative humidity) is, for example, 20 to 80% RH, preferably 40 to 70% RH.

[0090] By the above coating, the aqueous coating composition is applied to the substrate, and a wet coating film (wet film) is formed.

[0091] 3)Drying process In this method, the aqueous coating composition applied to the substrate is then heated to obtain a coating film (dried film) containing the dried aqueous coating composition (drying step).

[0092] That is, in this step, the aqueous coating composition applied to the substrate (i.e., the wet film) is heated and dried using a known heating device. In this step, the heating temperature (drying temperature) in the heating device is adjusted from the viewpoint of the adhesion of the coating film.

[0093] More specifically, from the viewpoint of obtaining excellent adhesion, water resistance, and solvent resistance, the lower limit of the heating temperature (drying temperature) is 160° C. or higher, preferably 180° C. or higher. In particular, when electrodeposition coating is used as the coating method, the lower limit of the heating temperature (drying temperature) is more preferably 200° C. or higher, even more preferably 220° C. or higher, and particularly preferably 240° C. or higher.

[0094] In order to prevent deterioration of the resin component, the upper limit of the heating temperature (drying temperature) is, for example, 300°C or less, or preferably 260°C or less.

[0095] That is, the heating temperature (drying temperature) is, for example, 160 to 300° C., or preferably 180 to 260° C. In particular, when electrodeposition coating is used as the coating method, the heating temperature (drying temperature) is more preferably 200 to 260° C., even more preferably 220 to 260° C., and particularly preferably 240 to 260° C.

[0096] The heating time is appropriately selected depending on the heating temperature (drying temperature). More specifically, the heating time is, for example, 10 to 50 minutes, and preferably 20 to 40 minutes.

[0097] The heating described above forms a dried product of the aqueous electrodeposition coating composition on the surface of the substrate. That is, a coating film (dried film) is formed on the surface of the substrate. The heating also forms an article comprising the substrate and the coating film.

[0098] 2. Coatings and articles The coating film is obtained by the above-mentioned coating film manufacturing method. The coating film contains a dried product of the aqueous coating composition, and preferably consists of a dried product of the aqueous coating composition. That is, the coating film contains PEG lignin as the resin component.

[0099] In the coating film, the PEG lignin may be cross-linked. That is, the coating film may or may not contain cross-linked PEG lignin. Preferably, the coating film contains cross-linked PEG lignin.

[0100] More specifically, the PEG lignin has self-crosslinking properties, and the PEG lignin can self-crosslink by heating the aqueous coating composition at the above-mentioned heating temperature (preferably 220°C or higher). In other words, the coating film preferably contains self-crosslinked PEG lignin. If the coating film contains self-crosslinked PEG lignin, excellent adhesion, solvent resistance, and chemical resistance can be obtained.

[0101] The PEG lignin may also be crosslinked with a curing agent. That is, the above-mentioned aqueous coating composition can contain a curing agent. In such a case, the PEG lignin can be crosslinked by the curing agent when the aqueous coating composition is heated at the above-mentioned heating temperature. That is, the above-mentioned coating film preferably contains PEG lignin crosslinked with a curing agent. If the coating film contains PEG lignin crosslinked with a curing agent, excellent adhesion, solvent resistance, and chemical resistance can be obtained.

[0102] From the viewpoint of obtaining excellent adhesion, solvent resistance, and chemical resistance easily and at low cost, the coating film preferably contains self-crosslinked PEG lignin.

[0103] The article comprises the above coating film, and preferably comprises the above substrate and a coating film covering the substrate.

[0104] 3. Effects In the method for producing a coating film, the resin component of the aqueous coating composition contains lignin modified with polyethylene glycol, and the aqueous coating composition is heated to a predetermined temperature or higher, so that the coating film obtained by the method has excellent adhesion.

[0105] The coating film described above is obtained by the method described above and therefore has excellent adhesion. The article described above is provided with the coating film described above. In the article described above, the coating film has excellent adhesion.

[0106] Furthermore, in the coating film production method, coating film, and article described above, the resin component contains PEG lignin, and therefore the coating film production method, coating film, and article described above have excellent environmental friendliness.

[0107] Therefore, the coating film manufacturing method, coating film, and article described above are suitable for use in various industrial fields where environmental friendliness and adhesion are required. More specifically, the coating film manufacturing method, coating film, and article described above are suitable for use in physical coating and electrodeposition coating. [Example]

[0108] Next, the present invention will be described based on examples, but the present invention is not limited to the following examples. Note that "parts" and "%" are by mass unless otherwise specified. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical property values, and parameters used in the following description can be substituted with the corresponding upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than" or "exceeding") of the blending ratios (content ratios), physical property values, parameters, etc. described in the above "Form for Carrying Out the Invention."

[0109] 1. Resin component Preparation Example 1 (PEG400 lignin, GL-400M) Lignin modified with polyethylene glycol having a number average molecular weight of 400 was produced by the following method.

[0110] That is, 230 parts by mass of commercially available polyethylene glycol (hereinafter, PEG400) with a number average molecular weight of 400 and 0.69 parts by mass of sulfuric acid as an acid catalyst (0.3 parts by mass per 100 parts by mass of PEG400) were placed in a reaction vessel and stirred. Next, 46 parts by mass of bone-dried cedar wood flour was added to the reaction vessel, and the temperature was raised to 140°C under normal pressure, and the reaction was carried out for 90 minutes with stirring. Next, the reaction vessel was cooled, and after confirming that the temperature had reached 40°C or less, 280 parts by mass of sodium hydroxide (0.2 mol / L) was added and stirred for 30 minutes. Next, the obtained solid component (pulp) was removed using a filter press, and the solution component was recovered. Next, sulfuric acid was added to the obtained solution component, and the pH was adjusted to 2.0.

[0111] As a result of the above, lignin modified with polyethylene glycol having a number average molecular weight of 400 (hereinafter referred to as PEG400 lignin, abbreviated as GL-400M) was obtained. The PEG400 lignin was collected by centrifugation.

[0112] Preparation Example 2 (PEG600 lignin, GL-600M) Lignin modified with polyethylene glycol having a number average molecular weight of 600 (hereinafter referred to as PEG600 lignin, abbreviated as GL-600M) was obtained in the same manner as in Preparative Example 1, except that polyethylene glycol having a number average molecular weight of 600 (hereinafter referred to as PEG600) was used instead of polyethylene glycol having a number average molecular weight of 400.

[0113] Preparation Example 3 (PEG200 lignin, GL-200M) Lignin modified with polyethylene glycol having a number average molecular weight of 200 (hereinafter referred to as PEG200 lignin, abbreviated as GL-200M) was obtained in the same manner as in Preparative Example 1, except that polyethylene glycol having a number average molecular weight of 200 (hereinafter referred to as PEG200) was used instead of polyethylene glycol having a number average molecular weight of 400.

[0114] Preparation Example 4 (Sodium Lignosulfonate) Commercially available sodium lignosulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared.

[0115] Preparation Example 5 (Lignin (dealkalized)) Commercially available lignin (dealkalized) (manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared.

[0116] 2. Painting A) Electrodeposition coating (1) Production of aqueous coating composition Manufacturing Example A1 A 1-liter flask equipped with a stirrer was charged with 46 parts by mass of propylene glycol monomethyl ether (organic solvent) and 2 parts by mass of benzyl alcohol (organic solvent).

[0117] Next, while stirring the contents of the flask, 50 parts by mass of PEG400 lignin (GL-400M) was added little by little to the flask and stirred. Next, the PEG lignin adhering to the inner wall of the flask was washed off with 1 part by mass of propylene glycol monomethyl ether (organic solvent).

[0118] The contents of the flask were then stirred for 10 minutes, and then 1 part by mass of dimethylaminoethanol (anionizing agent, organic amine) was added to the flask, and the contents of the flask were stirred for 30 minutes.

[0119] Next, 400 parts by mass of deionized water was added to the flask, and the contents of the flask were stirred for 30 minutes. Thereafter, the contents of the flask were subjected to ion exchange treatment with an anion exchange resin. This resulted in an aqueous coating composition. The solids concentration of the aqueous coating composition was 10% by mass.

[0120] Manufacturing Example A2 PEG600 lignin (GL-600M) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example A1.

[0121] Manufacturing Example A3 PEG200 lignin (GL-200M) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example A1.

[0122] Manufacturing Example A4 When washing off the PEG lignin adhering to the inner wall of the flask, the amount of propylene glycol monomethyl ether (organic solvent) used was changed from 1 part by mass to 2 parts by mass. Also, the amount of deionized water blended was changed from 400 parts by mass to 399 parts by mass. Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example A1.

[0123] Manufacturing comparison example A1 Sodium lignin sulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example A1.

[0124] Manufacturing comparison example A2 Lignin (dealkalized) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example A1.

[0125] (2) Coating production Example A1 The aqueous coating composition obtained in Production Example A1 was used to coat an aluminum plate with anionic electrodeposition.

[0126] More specifically, the aqueous coating composition was placed in a 1 L container for electrodeposition coating. A stainless steel plate (SUS304) was placed as the cathode. An aluminum plate (A-6063) with an anodized coating was placed as the anode. A DC power source was connected to the anode and cathode. The liquid temperature was adjusted to 25°C. A voltage of 100 V was applied between the electrodes for 2 minutes, forming a wet film of the aqueous coating composition on the anode (aluminum plate).

[0127] Next, the aluminum plate and the wet film were washed with water and drained. Thereafter, the aluminum plate and the wet film were heated and dried. The heating temperature was adjusted to 250°C. The drying time was set to 30 minutes. In this way, the aluminum plate was electrodeposited to obtain a coating film (dried film).

[0128] Examples A2 to A4 and Comparative Examples A1 to A2 The aqueous coating compositions of Production Examples A2 to A4 and Production Comparative Examples A1 and A2 were used instead of the aqueous coating composition of Production Example A1, according to the formulations shown in Table 2. Except for the above, an aluminum plate was electrodeposition coated in the same manner as in Example A1 to obtain a coating film (dry film).

[0129] However, in Comparative Examples A1 and A2, no wet film was formed even when a current was passed between the electrodes, and no coating film (dried film) was obtained.

[0130] Examples A5 to A8 and Comparative Examples A3 to A5 The aqueous coating composition shown in Table 3 was used, and the wet film was dried at the heating temperature shown in Table 3. Except for the above, an aluminum plate was electrodeposition coated in the same manner as in Example A1 to obtain a coating film (dried film).

[0131] (3) Evaluation [Coating film formation] The formability (film-forming properties) of the coating film of the aqueous coating composition was evaluated according to the following criteria.

[0132] ◯: The coating film was formed and was not powdery. ×: No coating film was formed, or a powdery coating film was formed.

[0133] [Coating appearance] The appearance of the dried film was visually evaluated according to the following criteria.

[0134] ◯: The coating film was smooth and glossy. ×: The coating film was not smooth and had no gloss.

[0135] [water resistance] Absorbent cotton soaked in deionized water was passed back and forth 100 times over the surface of the coating film, and the condition of the coating film was then visually evaluated. The evaluation criteria are as follows:

[0136] ⊚: No scratches or scuffs were found on the coating (no abnormalities). ○: Scratches and / or abrasions were observed on the coating film. ×: Peeling and / or dissolution of the coating film was observed.

[0137] [Solvent resistance] A cotton ball soaked in acetone was rubbed back and forth on the surface of the coating film 50 times. The condition of the coating film was then visually evaluated. The evaluation criteria are as follows:

[0138] ⊚: No scratches or scuffs were found on the coating (no abnormalities). ○: Scratches and / or abrasions were observed on the coating film. ×: Peeling and / or dissolution of the coating film was observed.

[0139] [Adhesion (primary adhesion)] The adhesion of the coating film was evaluated by cross-cut testing in accordance with JIS K 5600-5-6, and the evaluation criteria are as follows:

[0140] ⊚: The result of the peel test was 25 / 25, and no chipping was observed in the grid. ◯: The result of the peel test was 25 / 25, and slight chipping was observed in the grid. ×: The result of the peeling test was 25 / 25, and large chips or peeling was observed in the grid.

[0141] The formulation of the aqueous coating composition used for electrodeposition coating is shown in Table 1. The production conditions and evaluation results of the coating film are shown in Tables 2 and 3.

[0142] [Table 1]

[0143] [Table 2]

[0144] [Table 3] B) Physical painting (1) Production of aqueous coating composition Manufacturing Example B1 A 1-liter flask equipped with a stirrer was charged with 48 parts by mass of propylene glycol monomethyl ether (organic solvent).

[0145] Next, while stirring the contents of the flask, 50 parts by mass of PEG400 lignin (GL-400M) was added little by little to the flask and stirred. Next, the PEG lignin adhering to the inner wall of the flask was washed off with 1 part by mass of propylene glycol monomethyl ether (organic solvent).

[0146] The contents of the flask were then stirred for 10 minutes, and then 1 part by mass of dimethylaminoethanol (organic amine) was added to the flask, and the contents of the flask were stirred for 30 minutes.

[0147] Next, 66.7 parts by mass of deionized water was added to the flask, and the contents of the flask were stirred for 30 minutes. The contents of the flask were then subjected to ion exchange treatment with an anion exchange resin. Thus, an aqueous coating composition was obtained. The solids concentration of the aqueous coating composition was 30% by mass.

[0148] Manufacturing Example B2 PEG600 lignin (GL-600M) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example B1.

[0149] Manufacturing Example B3 PEG200 lignin (GL-200M) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example B1.

[0150] Manufacturing comparison example B1 Sodium lignin sulfonate (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example B1.

[0151] Manufacturing comparison example B2 Lignin (dealkalized) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of PEG400 lignin (GL-400M). Except for the above, an aqueous coating composition was obtained in the same manner as in Production Example B1.

[0152] (2) Coating production Example B1 The aqueous coating composition obtained in Production Example B1 was used to physically coat a stainless steel plate (SUS304).

[0153] More specifically, the aqueous coating composition was applied to a degreased stainless steel plate (SUS304) using a bar coater #16 to form a wet film of the aqueous coating composition.

[0154] The stainless steel plate and the undried film were then heated and dried. The heating temperature was adjusted to 180°C. The drying time was set to 30 minutes. In this way, the stainless steel plate was physically coated, and a coating film (dried film) was obtained.

[0155] Examples B2 to B3 and Comparative Examples B1 to B2 The aqueous coating compositions of Production Examples B2 and B3 and Comparative Production Examples B1 and B2 were used instead of the aqueous coating composition of Production Example B1, according to the formulations shown in Table 5. Except for the above, a stainless steel plate was physically coated in the same manner as in Example B1 to obtain a coating film (dry film).

[0156] Example B4 and Comparative Example B3 The aqueous coating composition shown in Table 5 was used, and the wet film was dried at the heating temperature shown in Table 5. Except for the above, the stainless steel plate was physically coated in the same manner as in Example B1 to obtain a coating film (dried film).

[0157] (3) Evaluation The coating film-forming properties, appearance, water resistance, solvent resistance, and adhesion (primary adhesion) were evaluated in the same manner as above.

[0158] The formulation of the aqueous coating composition used for physical coating is shown in Table 4. The production conditions and evaluation results of the coating film are shown in Table 5.

[0159] [Table 4]

[0160] [Table 5]

Claims

1. a preparation step of preparing an aqueous coating composition; a coating step of applying the aqueous coating composition to an object to be coated; a drying step of heating the applied aqueous coating composition to obtain a coating film containing a dried product of the aqueous coating composition; Equipped with The aqueous coating composition contains a resin component, The resin component contains lignin modified with polyethylene glycol, The method for producing a coating film, wherein the heating temperature in the drying step is 160°C or higher.

2. The method for producing a coating film according to claim 1, wherein the resin component comprises lignin modified with polyethylene glycol.

3. The method for producing a coating film according to claim 1, wherein the polyethylene glycol has a number average molecular weight of 400 or more.

4. A coating film obtained by the coating film manufacturing method according to any one of claims 1 to 3.

5. An article comprising the coating of claim 4.

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