Method for producing alkyd resin, and coating composition containing alkyd resin obtainable thereby

Abstract

To provide a method for producing an alkyd resin that allows an increased amount of polyethylene terephthalate to be used.SOLUTION: A method for producing an alkyd resin comprises: a step for adding a polyhydric alcohol and a fatty acid to polyethylene terephthalate to cause a transesterification reaction to prepare a resin intermediate; and a step for adding a polycarboxylic acid to the resin intermediate to cause an esterification reaction, wherein the alkyd resin contains at least 20 mass% of a structure derived from polyethylene terephthalate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing an alkyd resin, and a coating composition containing the alkyd resin obtained by the method. [Background technology]

[0002] Polyethylene terephthalate is used in large quantities, for example as a material for beverage bottles, and has long been collected and recycled after use.

[0003] The main uses for the recycled polyethylene terephthalate are as a material for beverage bottles, food packaging such as egg cartons and fruit and vegetable trays, and as fiber for use in clothing.

[0004] In order to increase sustainability, there has been an active movement to expand the recycling applications of recovered polyethylene terephthalate. For example, it has been proposed to use recovered polyethylene terephthalate as a raw material for paint resins (e.g., Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-136021 A [Patent Document 2] JP 2004-83695 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the paint resins of Patent Documents 1 and 2, the amount of polyethylene terephthalate actually used is extremely small, and there has been a problem in that polyethylene terephthalate cannot be sufficiently recycled.

[0007] The problem to be solved by the present invention is to provide a method for producing an alkyd resin that allows the amount of polyethylene terephthalate used to be increased. Another problem that the present invention seeks to solve is to provide a coating composition containing an alkyd resin that has a high loading of polyethylene terephthalate. [Means for solving the problem]

[0008] The present invention relates to a method for producing an alkyd resin. 1. A step of adding a polyhydric alcohol and a fatty acid to polyethylene terephthalate and carrying out an ester exchange reaction to prepare a resin intermediate; and a step of adding a polyvalent carboxylic acid to the resin intermediate to carry out an esterification reaction; A method for producing an alkyd resin containing 20 mass% or more of a structure derived from polyethylene terephthalate, comprising: 2. The method for producing an alkyd resin according to 1, wherein the polyethylene terephthalate is recycled polyethylene terephthalate. 3. The method for producing an alkyd resin according to 1 or 2, wherein the polyhydric alcohol is pentaerythritol and / or glycerin. 4. The method for producing an alkyd resin according to any one of 1 to 3, wherein the fatty acid is a vegetable oil fatty acid. 5. The method for producing an alkyd resin according to any one of 1 to 4, wherein the polyvalent carboxylic acid is one or more selected from the group consisting of sebacic acid, succinic acid and phthalic acid. 6. The method for producing an alkyd resin according to any one of 1 to 5, wherein the oil length of the resin intermediate is less than 60%. 7. A method for producing an alkyd resin according to any one of 1 to 6, wherein in the step of preparing the resin intermediate, the amount of polyethylene terephthalate is 20 parts by mass or more when the total amount of the polyethylene terephthalate, the polyhydric alcohol and the fatty acid is 100 parts by mass. 8. The method for producing an alkyd resin according to any one of 1 to 7, wherein in the step of preparing the resin intermediate, the transesterification reaction is carried out without adding a metal compound catalyst. 9. The method for producing an alkyd resin according to any one of 1 to 8, wherein the oil length of the alkyd resin is less than 60%. 10. A coating composition comprising an alkyd resin obtained by the production method according to any one of 1 to 9. 11. The coating composition according to claim 10, which is a paint composition. 12. A coating substrate coated with the coating composition according to 11. Effect of the Invention

[0009] The present invention provides an alkyd resin that allows the amount of polyethylene terephthalate used to be increased. The present invention provides coating compositions containing alkyd resins with high amounts of polyethylene terephthalate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present invention will be described below. The present invention is not limited to the following embodiment, and can be implemented by making appropriate modifications within the scope that does not impair the effects of the present invention. The compounds in the present specification may be derived from fossil resources or biological resources.

[0011] [Method of manufacturing alkyd resin] The method for producing an alkyd resin of the present invention includes a step (1) of adding a polyhydric alcohol and a fatty acid to polyethylene terephthalate and carrying out an ester exchange reaction to prepare a resin intermediate, and a step (2) of adding a polyvalent carboxylic acid to the resin intermediate and carrying out an esterification reaction. According to the method for producing an alkyd resin of the present invention, an alkyd resin containing 20% ​​by mass or more of a structure derived from polyethylene terephthalate can be produced. The above steps (1) and (2) will be described below.

[0012] (Process (1)) In step (1), a polyhydric alcohol and a fatty acid are added to polyethylene terephthalate to cause an ester exchange reaction to prepare a resin intermediate.

[0013] The polyethylene terephthalate used in step (1) is preferably recycled polyethylene terephthalate (hereinafter, may be referred to as "recycled PET"). Recycled PET is polyethylene terephthalate in the form of flakes or pellets that is obtained by processing molded PET used as food packaging such as beverage bottles, such as by washing, drying, crushing, remelting, etc. Recycled PET generally has a number average molecular weight in the range of about 10,000 to about 30,000.

[0014] Examples of the polyhydric alcohol used in step (1) include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, tetraethylene glycol, trimethylolethane, trimethylolpropane, trimethylolhexane, triethylolpropane, 1,2,4-butanetriol, and pentaerythritol. The polyhydric alcohols used may be one type alone or two or more types in combination.

[0015] The polyhydric alcohol is preferably pentaerythritol and / or glycerin. Some of these are derived from biomass, and can increase the biomass content of the resulting alkyd resin.

[0016] The fatty acid used in step (1) is preferably a vegetable oil fatty acid, more preferably one or more vegetable oil fatty acids selected from castor oil fatty acids, tall oil fatty acids, palm oil fatty acids, coconut oil fatty acids, soybean oil fatty acids, cocoa fatty acids, corn oil fatty acids, linseed oil fatty acids, cottonseed oil fatty acids, rapeseed oil fatty acids, and rice bran fatty acids.

[0017] In step (1), an oil containing the fatty acid may be used in place of the fatty acid. When an oil is used as the fatty acid in step (1), the oil is preferably a vegetable oil, more preferably one or more vegetable oils selected from castor oil, tall oil, palm oil, coconut oil, soybean oil, cocoa oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, and rice oil. The above vegetable oil is a glyceride in which fatty acids and glycerin are ester-bonded, and the vegetable oil can be used as a mixture of fatty acids and polyhydric alcohols.

[0018] In step (1), the ratio of the polyethylene terephthalate, the polyhydric alcohol, and the fatty acid is adjusted so that the oil length of the resulting resin intermediate is preferably less than 60%. Specifically, when the total amount of the polyethylene terephthalate, the polyhydric alcohol, and the fatty acid is 100 parts by mass, the amount of the fatty acid, calculated as oil, is preferably less than 60 parts by mass.

[0019] The oil length of the resin intermediate obtained in step (1) is preferably 55% or less, 50% or less, and 40% or less, in that order. The lower limit of the oil length of the resin intermediate is not particularly limited, but is, for example, 20%. The oil length of the resin intermediate corresponds to the ratio of the amount of fatty acid charged, calculated as oil, when the total amount of polyethylene terephthalate, polyhydric alcohol and fatty acid is taken as 100 parts by mass.

[0020] In step (1), when the total amount of polyethylene terephthalate, the polyhydric alcohol, and the fatty acid is 100 parts by mass, the amount of polyethylene terephthalate charged is preferably 20 parts by mass or more, preferably 25 parts by mass or more, and more preferably 30 parts by mass or more. The upper limit of the amount of polyethylene terephthalate charged is not particularly limited, but is, for example, 60 parts by mass.

[0021] In step (1), when the total amount of polyethylene terephthalate, the polyhydric alcohol, and the fatty acid is 100 parts by mass, the amount of the polyhydric alcohol charged is preferably in the range of 10 to 30 parts by mass, more preferably in the range of 14 to 26 parts by mass.

[0022] The reaction conditions for the transesterification reaction in step (1) can be any known reaction conditions. For example, the reaction temperature may be set in the range of 100 to 400°C (preferably 200°C or higher and lower than 280°C) and the reaction time may be set in the range of 1 to 20 hours.

[0023] In the transesterification reaction, it is generally known to use, as a catalyst, an oxide, hydroxide, inorganic acid salt, organic acid salt (e.g., carboxylate), halide, sulfide, etc. of a metal (e.g., lithium, zinc, calcium, lead, barium, manganese, cobalt, zirconium, germanium, antimony, titanium, tin). However, in step (1) of the present invention, preferably no metal compound catalyst is added. In the present invention, alcoholysis by polyhydric alcohol and acidolysis by fatty acid are used in combination, and the transesterification effect of the ester compound obtained by the reaction of polyhydric alcohol and fatty acid allows the reaction to proceed sufficiently even when a large amount of polyethylene terephthalate is used. By not adding a metal compound catalyst, the amount of rare metals used can be reduced, which contributes to sustainability.

[0024] The number average molecular weight of the resin intermediate obtained in step (1) is, for example, in the range of 100 to 5,000, preferably in the range of 500 to 3,000, and more preferably in the range of 500 to 2,000. The weight average molecular weight of the resin intermediate obtained in step (1) is, for example, in the range of 500 to 30,000, preferably in the range of 1,000 to 20,000, and more preferably in the range of 1,000 to 12,000. The molecular weight of each resin intermediate is confirmed by the method described in the Examples.

[0025] The acid value of the resin intermediate obtained in step (1) is, for example, in the range of 10 or less. The acid value of the resin intermediate is confirmed by the method described in the Examples.

[0026] (Process (2)) In step (2), a polyvalent carboxylic acid is added to the resin intermediate produced in step (1) to carry out an esterification reaction.

[0027] Examples of the polyvalent carboxylic acid used in step (2) include phthalic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, hexahydrophthalic acid, maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimellitic acid, and pyromellitic acid. The polycarboxylic acid may be a polycarboxylic acid derivative such as an anhydride, etc. The polycarboxylic acid may be used alone or in combination of two or more kinds.

[0028] The polyvalent carboxylic acid is preferably at least one selected from succinic acid, sebacic acid, and phthalic acid (including phthalic anhydride). Some of these are derived from biomass, and can increase the biomass content of the resulting alkyd resin.

[0029] In step (2), the charging ratio of the resin intermediate to the polycarboxylic acid is, for example, resin intermediate:polycarboxylic acid (mass ratio)=60:40 to 100:0, preferably resin intermediate:polycarboxylic acid (mass ratio)=60:40 to 95:5, and more preferably resin intermediate:polycarboxylic acid (mass ratio)=70:30 to 90:10.

[0030] As the reaction conditions for the esterification reaction in the step (2), known reaction conditions can be adopted. For example, the reaction temperature may be set in the range of 100 to 300° C. and the reaction time may be set in the range of 1 to 10 hours. In the esterification reaction, it is advisable to use a solvent that can form an azeotrope with the water produced during the esterification reaction and remove the water from the reaction system, such as xylene.

[0031] The alkyd resin obtained by the production method of the present invention (hereinafter, sometimes referred to as "alkyd resin of the present invention") contains 20% by mass or more of a structure derived from polyethylene terephthalate. Here, "containing 20% ​​by mass or more of a structure derived from polyethylene terephthalate" means that the amount of polyethylene terephthalate is 20 parts by mass or more when the total amount of the reaction raw materials (polyethylene terephthalate, polyhydric alcohol, fatty acid, polycarboxylic acid, etc.) used in the production of the alkyd resin is 100 parts by mass. The content of the structure derived from polyethylene terephthalate in the alkyd resin of the present invention is preferably 25% by mass or more, more preferably 30% by mass or more. In the present invention, the term "reaction raw materials" refers to raw materials that constitute the structure of an alkyd resin, and does not include solvents, catalysts, etc. that do not form the structure of an alkyd resin. In addition, the alkyd resin contains 20% by mass or more of a structure derived from polyethylene terephthalate. 1 H-NMR spectrum or 13 This can also be confirmed by C-NMR analysis.

[0032] The upper limit of the polyethylene terephthalate-derived structure in the alkyd resin of the present invention is not particularly limited, but is, for example, 60 mass % or less, preferably 50 mass % or less, and more preferably 45 mass % or less.

[0033] The number average molecular weight of the alkyd resin of the present invention is, for example, in the range of 1,000 to 10,000, preferably in the range of 1,000 to 5,000, and more preferably in the range of 1,000 to 4,000. The weight average molecular weight of the alkyd resin of the present invention is, for example, in the range of 1,000 to 100,000, preferably in the range of 1,000 to 100,000, and more preferably in the range of 8,000 to 100,000. The molecular weight of each alkyd resin is confirmed by the method described in the Examples.

[0034] The acid value of the alkyd resin of the present invention is, for example, in the range of 20 mg KOH / g or less. The acid value of the alkyd resin is confirmed by the method described in the Examples.

[0035] The hydroxyl value of the alkyd resin of the present invention is, for example, in the range of 50 to 300 mgKOH / g. The hydroxyl value of the alkyd resin is confirmed by the method described in the examples.

[0036] The oil length of the alkyd resin of the present invention is, for example, less than 60%, preferably 55% or less, more preferably 50% or less, and further preferably less than 45%. The lower limit of the oil length of the alkyd resin of the present invention is, for example, 20% or more. The oil length of an alkyd resin is the ratio of the amount of fatty acid, converted into oil, to the total mass of the reaction components used in the production of the alkyd resin, expressed as a mass percentage.

[0037] The alkyd resin of the present invention is an alkyd resin containing 20% ​​by mass or more of a structure derived from polyethylene terephthalate, and can promote the recycling of recovered polyethylene terephthalate. In addition, when the polyhydric alcohol is pentaerythritol and / or glycerin, the fatty acid is a vegetable oil fatty acid, and the polycarboxylic acid is sebacic acid and / or succinic acid, the reaction raw materials of the alkyd resin can be only components derived from recycled raw materials (recovered polyethylene terephthalate) and components derived from biomass raw materials (polyhydric alcohol, fatty acid, and polycarboxylic acid), which can greatly contribute to sustainability.

[0038] [Coating composition] The alkyd resin of the present invention can be used, for example, as a binder resin in a coating composition, and is preferably used as a binder resin in a paint composition.

[0039] (hardening agent) When the coating composition of the present invention is used as a paint composition, the paint composition of the present invention contains the alkyd resin of the present invention and a curing agent. As the curing agent, a known one can be used, for example, a melamine resin, an epoxy compound, etc.

[0040] The melamine resin serving as the curing agent is preferably a melamine resin having a structure derived from a melamine compound having a hydroxymethyl group and / or an alkoxymethyl group.

[0041] The melamine resin used as the curing agent may be a commercially available product, and examples of such commercially available products include Cymel 300, Cymel 301, Cymel 303LF, Cymel 350, Cymel 370N, Cymel 771, Cymel 325, Cymel 327, Cymel 703, Cymel 712, Cymel 701, Cymel 266, Cymel 267, Cymel 285, Cymel 232, Cymel 235, Cymel 236, Cymel 238, and Cymel 272. , Cymel 212, Cymel 253, Cymel 254, Cymel 202, Cymel 207, Mycoat 506 (all manufactured by Allnex Japan); Nikalac MW-30M, Nikalac MW-30, Nikalac MW-30HM, Nikalac MW-390, Nikalac MW-100LM, Nikalac MX-750LM, Nikalac MW-22, Nikalac MS-21, Nikalac MS-11, Nikalac MW-24X, Nikalac M S-001, Nikalac MX-002, Nikalac MX-730, Nikalac MX-750, Nikalac MX-708, Nikalac MX-706, Nikalac MX-042, Nikalac MX-035, Nikalac MX-45, Nikalac MX-43, Nikalac MX-417, Nikalac MX-410 (all manufactured by Sanwa Chemical Co., Ltd.); U-Ban 20SB, U-Ban 20SE60, U-Ban 21R, U-Ban 22R, U-Ban 122, Examples of the copolymer include U-ban 125, U-ban 220, U-ban 225, U-ban 228, and U-ban 2020 (all manufactured by Mitsui Chemicals); Amidea J-820-60, Amidea L-109-65, Amidea L-117-60, Amidea L-127-60, Amidea 13-548, Amidea G-821-60, Amidea L-110-60, Amidea L-125-60, and Amidea L-166-60B (all manufactured by DIC).

[0042] The epoxy compound serving as the curing agent is preferably an epoxy compound having two or more epoxy groups in one molecule.

[0043] Specific examples of the epoxy compound as a curing agent include cresol novolac type epoxy resins, phenol novolac type epoxy resins, biphenyl type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, naphthalene type epoxy resins, dicyclopentadiene type epoxy resins, linear aliphatic epoxy resins, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, and the like.

[0044] As the curing agent, in addition to melamine resin and epoxy compound, driers such as isocyanate compounds and metal soaps can also be used. The isocyanate compound as the curing agent is preferably a polyfunctional isocyanate compound, more preferably a polyfunctional isocyanate compound having 2 to 6 reactive isocyanate groups per molecule.

[0045] The curing agent contained in the coating composition may be one type alone or two or more types in combination.

[0046] The content of the curing agent in the coating composition is, for example, in the range of 3 to 40 parts by mass, preferably in the range of 10 to 35 parts by mass, and more preferably in the range of 20 to 30 parts by mass, relative to 100 parts by mass of the total non-volatile components of the coating composition.

[0047] (pigment particles) The coating composition of the present invention preferably contains pigment particles. Specific examples of the pigment particles include titanium oxide (titanium white), zinc oxide (zinc white), lead white, and basic white pigments such as lead sulfate, lead sulfate, lithopone, zinc sulfide, and antimony white; black pigments such as carbon black, acetylene black, lamp black, graphite, iron black (black iron oxide), and aniline black; yellow pigments such as naphthol yellow S, Hansa yellow, Pigment yellow L, benzidine yellow, permanent yellow, and yellow iron oxide; orange pigments such as chrome orange, chrome vermilion, and permanent orange; brown pigments such as iron oxide and amber; red pigments such as red iron oxide, red lead, permanent red, quinacridone red pigments, and diketopyrrolopyrrole red pigments; purple pigments such as cobalt purple, fast violet, and methyl violet lake; blue pigments such as ultramarine, Prussian blue, cobalt blue, phthalocyanine blue, and indigo; and green pigments such as chrome green, pigment green B, and phthalocyanine green.

[0048] The pigment particles may contain an extender pigment. Specific examples of the extender pigment include baryta powder, barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, silica, white carbon, diatomaceous earth, talc, magnesium carbonate, hydrous magnesium silicate, alumina white, gloss white, and mica powder.

[0049] The size (particle diameter, etc.) of the pigment particles is not particularly limited. The size may be appropriately set according to various purposes. The average particle diameter of the pigment particles is preferably 0.1 to 10 μm, more preferably 0.1 to 7 μm.

[0050] The pigment particles contained in the coating composition may be of one type alone or in combination of two or more types.

[0051] The content of the pigment particles in the coating composition is, for example, in the range of 10 to 70 parts by mass, and preferably in the range of 30 to 60 parts by mass, when the total amount of non-volatile components in the coating composition is 100 parts by mass.

[0052] (solvent) The coating composition of the present invention is usually used after diluting with a solvent. Specific examples of the solvent include aromatic hydrocarbon solvents such as toluene and xylene; alcohol solvents such as methanol, ethanol, isopropyl alcohol, n-butanol, isobutanol, tert-butanol (2-methyl-2-propanol), tert-amyl alcohol, and diacetone alcohol; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as dimethyl carbonate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, butyl cellosolve, and PGMAC; and hydrocarbon solvents such as T-SOL-100FLUID, T-SOL-150FLUID, and Pegasol 3040.

[0053] The coating composition of the present invention may further contain, in addition to the above, a curing accelerator (such as a curing catalyst), a surfactant, a leveling agent, a thixotropic regulator, an ultraviolet absorber, a light stabilizer, a dispersant, and the like.

[0054] The coating composition of the present invention may be in the form of either a one-component type or a two-component type, and may be appropriately selected depending on the purpose and application.

[0055] An article provided with a coating film can be produced by applying the coating composition of the present invention to a substrate, drying the solvent, and then thermally curing the composition. The application method is not particularly limited and may be a spray, a brush, a roller, etc. A coating device or a printing device may be used for application.

[0056] The temperature and time of heat curing may be appropriately set within a range that does not cause deformation of the substrate. The temperature is, for example, room temperature to 180°C, and the time is, for example, 10 minutes to 24 hours. Examples of heat curing methods include using hot air or a drying oven (dryer) attached to a coating machine.

[0057] The amount of the coating composition to be applied is not particularly limited, and may be appropriately adjusted so that the thickness of the coating film falls within the range of, for example, 10 to 1,000 μm. EXAMPLES

[0058] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0059] In the examples of the present application, the acid value and the hydroxyl value are values ​​evaluated by the following methods. [Acid value measurement method] The measurement was performed according to the method of JIS K0070-1992. [Method for measuring hydroxyl value] The measurement was performed according to the method of JIS K0070-1992.

[0060] In the examples of the present application, the number average molecular weight of the alkyd resin is a value calculated in terms of polystyrene based on GPC measurement, and the measurement conditions are as follows. [GPC measurement conditions] Measuring device: Tosoh Corporation HLC-8320GPC Column: TSK-GUARDCOLUMN HXL-H manufactured by Tosoh Corporation +Tosoh Corporation TSK-GEL G5000HXL +Tosoh Corporation TSK-GEL G4000HXL +Tosoh Corporation TSK-GEL G3000HXL +Tosoh Corporation TSK-GEL G2000HXL Detector: RI (differential refractometer) Data processing: Tosoh Corporation HLC-8320GPC EcoSEC-Work Station Measurement conditions: Column temperature 40℃ Developing solvent: Tetrahydrofuran Flow rate: 1.0mL / min Measurement sample: A tetrahydrofuran solution of 0.5% by mass (resin solid content) filtered through a microfilter Sample injection volume: 100 μl Standard sample: In accordance with the measurement manual for the above-mentioned "HLC-8320GPC," the following monodisperse polystyrene with known molecular weight was used. Standard: A calibration curve was prepared using monodisperse polystyrene (A-500, F-2, F-20, F-80, F-288, A-2500, F-10, F-40, F-128, F-380, manufactured by Tosoh Corporation).

[0061] (Example 1: Production of alkyd resin and preparation and evaluation of coating composition) 106.4 parts by mass of rice bran fatty acid, 75.6 parts by mass of tall oil fatty acid, 161.2 parts by mass of polyethylene terephthalate, and 90.8 parts by mass of pentaerythritol (biomass-derived) were charged into a four-necked reaction vessel and reacted at 250°C for 3 hours to produce a resin intermediate. The acid value of the obtained resin intermediate was 2 mgKOH / g, the oil length was 47%, and the number average molecular weight was 800.

[0062] The polyethylene terephthalate used in Example 1 was recycled PET (manufactured by FPCO Corporation).

[0063] The reaction system containing the above resin intermediate was once cooled to 160° C., and then 65.3 parts by mass of sebacic acid was added and reacted for 10 hours at 180° C. A process analysis was carried out on an alkyd resin / xylene = 50 / 50 (mass ratio) solution, and the reaction was terminated when the acid value became 6 mgKOH / g or less, and the obtained alkyd resin was diluted with butyl acetate to prepare an alkyd resin solution (non-volatile content 65 mass%). The resulting alkyd resin had an oil length of 38%, an acid value of 8 and a number average molecular weight of 2,100.

[0064] To the obtained alkyd resin solution, melamine resin (DIC Corporation's "Amidair L-109-65") was added as a curing agent so that the alkyd resin:melamine resin (mass ratio) was 75:25, and titanium oxide (Chemours Corporation's "Ti-Pure R-960") was further added to prepare an enamel paint (non-volatile content 71 mass%, pigment mass concentration 60%).

[0065] The obtained enamel paint was applied with an applicator onto a 0.5 mm thick hot-dip galvanized chromate-treated steel sheet to form an enamel coating film with a thickness of 76 μm. The steel sheet with the enamel coating film formed was heated in an oven at 130°C for 20 minutes to obtain a steel sheet with a topcoat layer with a dry thickness of 26 μm. The obtained coated steel sheets were evaluated as follows, and the results are shown in Table 1.

[0066] (gloss value) The 60 degree specular reflectance of the resulting coated steel sheets was measured.

[0067] (Adhesion to substrate) The obtained coated steel sheets were evaluated for substrate adhesion according to JIS K-5600. Specifically, 1 mm-wide cuts were made on the coating film with a cutter to make 100 squares, and cellophane tape was applied so as to cover all the squares, which were then quickly peeled off. The number of squares remaining in contact after the test was expressed as a percentage. In terms of substrate adhesion, 100% means that no coating peeled off, and 0% means that the entire coating peeled off. Adhesion of 95% or more can be considered to be sufficient for practical use.

[0068] (Pencil hardness) The pencil hardness of the painted portion of the painted steel plate was measured in accordance with JIS K-5600.

[0069] (DuPont Impact) Based on JIS K5600, a die with a hemispherical tip with a radius of 6.3 mm was placed on the coated surface of the resulting coated steel sheet, and a weight of 500 g was dropped onto the die from heights of 30 cm, 35 cm, 40 cm, 45 cm, and 50 cm. The heights at which cracks occurred are shown in Table 1. If no cracks occurred in the sheet even after dropping from 50 cm, it is recorded as >50 cm.

[0070] (Example 2: Production of alkyd resin and preparation and evaluation of coating composition) 106.4 parts by mass of rice bran fatty acid, 75.6 parts by mass of tall oil fatty acid, 161.2 parts by mass of recycled PET, and 96.5 parts by mass of pentaerythritol (biomass-derived) were charged into a four-necked reaction vessel and reacted at 250°C for 3 hours to produce a resin intermediate. The acid value of the obtained resin intermediate was 3 mgKOH / g, the oil length was 45%, and the number average molecular weight was 700.

[0071] The reaction system containing the above resin intermediate was once cooled to 160° C., and then 80.8 parts by mass of phthalic anhydride was added and reacted for 10 hours at 180° C. A process analysis was carried out using an alkyd resin / xylene = 50 / 50 (mass ratio) solution, and the reaction was terminated when the acid value of the alkyd resin became 6 mgKOH / g or less, and the obtained alkyd resin was diluted with xylene to prepare an alkyd resin solution (non-volatile content 65 mass%). The resulting alkyd resin had an oil length of 40%, an acid value of 9 mgKOH / g, and a number average molecular weight of 1,700.

[0072] The polyethylene terephthalate used in Example 2 was recycled PET (manufactured by Utsumi Recycle Systems Co., Ltd.).

[0073] The obtained alkyd resin was used to prepare an enamel paint in the same manner as in Example 1, and a coated steel panel was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0074] (Comparative Example 1: Production of alkyd resin and preparation and evaluation of coating composition) 106.4 parts by mass of rice bran fatty acid, 67.7 parts by mass of tall oil fatty acid, 120.6 parts by mass of glycerin, 7.7 parts by mass of pentaerythritol (derived from biomass), and 189.7 parts by mass of phthalic anhydride were charged into a four-necked reaction vessel and reacted for 6 hours at 210° C. Process analysis was performed on an alkyd resin / xylene = 50 / 50 (mass ratio) solution, and the reaction was terminated when the acid value of the alkyd resin became 3 mg KOH / g or less, and the obtained alkyd resin was diluted with xylene to prepare an alkyd resin solution (non-volatile content 60% by mass). The resulting alkyd resin had an oil length of 40%, an acid value of 4 mgKOH / g and a number average molecular weight of 2,400.

[0075] The obtained alkyd resin was used to prepare an enamel paint in the same manner as in Example 1, and a coated steel panel was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0076] [Table 1]

[0077] The results in Table 1 show that, although the alkyd resins in the paints of Examples 1 and 2 contain a high proportion of PET-derived structures, they provide practical performance that is comparable to that of Comparative Example 1, which uses an alkyd resin that does not contain any PET-derived structures. In particular, the alkyd resin of Example 1 is composed only of reactive components derived from biomass and recycled components, and is therefore excellent in terms of sustainability.

Claims

1. A step of adding a polyhydric alcohol and a fatty acid to polyethylene terephthalate and carrying out an ester exchange reaction to prepare a resin intermediate; and a step of adding a polyvalent carboxylic acid to the resin intermediate to carry out an esterification reaction; A method for producing an alkyd resin containing 20 mass% or more of a structure derived from polyethylene terephthalate, comprising:

2. The method for producing an alkyd resin according to claim 1, wherein the polyethylene terephthalate is recycled polyethylene terephthalate.

3. 3. The method for producing an alkyd resin according to claim 1, wherein the polyhydric alcohol is pentaerythritol and / or glycerin.

4. The method for producing an alkyd resin according to claim 1 or 2, wherein the fatty acid is a vegetable oil fatty acid.

5. 3. The method for producing an alkyd resin according to claim 1, wherein the polyvalent carboxylic acid is at least one selected from the group consisting of sebacic acid, succinic acid and phthalic acid.

6. The method for producing an alkyd resin according to claim 1 or 2, wherein the oil length of the resin intermediate is less than 60%.

7. 3. The method for producing an alkyd resin according to claim 1 or 2, wherein in the step of preparing the resin intermediate, the amount of polyethylene terephthalate is 20 parts by mass or more when the total amount of the polyethylene terephthalate, the polyhydric alcohol and the fatty acid is 100 parts by mass.

8. The method for producing an alkyd resin according to claim 1 or 2, wherein in the step of preparing the resin intermediate, the transesterification reaction is carried out without adding a metal compound catalyst.

9. 3. The method for producing an alkyd resin according to claim 1, wherein the oil length of the alkyd resin is less than 60%.

10. A coating composition comprising an alkyd resin obtained by the process according to claim 1 or 2.

11. 11. The coating composition of claim 10 which is a paint composition.

12. A coating substrate coated with the coating composition of claim 11.

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