Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/183—Terephthalic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/185—Acids containing aromatic rings containing two or more aromatic rings
  • C08G63/187—Acids containing aromatic rings containing two or more aromatic rings containing condensed aromatic rings
  • C08G63/189—Acids containing aromatic rings containing two or more aromatic rings containing condensed aromatic rings containing a naphthalene ring
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/199—Acids or hydroxy compounds containing cycloaliphatic rings
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/20—Polyesters having been prepared in the presence of compounds having one reactive group or more than two reactive groups
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
  • C09D167/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
  • B65D25/00—Details of other kinds or types of rigid or semi-rigid containers
  • B65D25/14—Linings or internal coatings

Definitions

• the present invention relates to a crystalline polyester resin. More specifically, the present invention relates to a crystalline polyester resin suitable for use as a paint for cans, and even more specifically, to a crystalline polyester resin suitable for coating cans that contain beverages or foods (hereinafter collectively referred to as "food and beverages"), a paint composition containing the resin, and a coating film and a metal can having the coating film.
• a crystalline polyester resin suitable for use as a paint for cans
• a crystalline polyester resin suitable for coating cans that contain beverages or foods (hereinafter collectively referred to as "food and beverages"), a paint composition containing the resin, and a coating film and a metal can having the coating film.
• Metal cans such as beverage cans and food cans are coated with an organic resin to prevent corrosion of the metal by food (corrosion resistance) and to preserve the flavor and taste of the contents (flavor).
• This coating is subjected to high-stress processing such as necking and threading during the molding process of the mouth of a bottle can. Therefore, the coating needs to be durable against such post-processing (processability). It is also required to have adhesion to metal materials and hardenability.
• the can may be subjected to high temperature and high humidity conditions such as retort sterilization, and even in such cases, the coating needs to maintain adhesion to the metal material and not whiten (retort resistance).
• epoxy-based paints such as epoxy-phenol-based paints, epoxy-amino-based paints, and epoxy-acrylic-based paints
• polyester-based paints such as polyester-phenol-based paints, polyester-amino-based paints, and polyester-isocyanate-based paints
• vinyl chloride-based paints have been widely used as paints that are corrosion-resistant, flavor-resistant, and can withstand the molding process described above.
• bisphenol A a raw material for epoxy resins
• vinyl chloride-based paints have problems with stabilizers and the generation of dioxins during incineration.
• Formaldehyde which is used as a raw material for phenolic resins and amino resins, and remains in the paint, is known to be harmful to the human body, including being carcinogenic, and to have a negative effect on the flavor of the contents.
• isocyanate resins are known to be harmful to the human body, including being carcinogenic.
• Patent Document 1 proposes a resin composition for can coating that uses a crystalline polyester and does not require a curing agent.
• the coating film made of the resin composition for can coating described in Patent Document 1 contains a large amount of non-crystalline polyester resin along with crystalline polyester resin. This is to compensate for the low solubility of crystalline polyester resin in solvents, but it was found that this reduces retort resistance.
• the object of the present invention is to provide a crystalline polyester resin that does not contain a curing agent, and therefore is free of harmful substances such as bisphenol A and formaldehyde, and is capable of forming a coating film that has excellent solvent solubility, processability, and retort resistance properties, as well as a coating composition, coating film, and metal can that contain the same.
• the present inventors have found a specific composition and melting point of a polyester resin based on the idea that, in order to obtain a coating film that satisfies both retort resistance and processability and also satisfies the solvent solubility of the resin when made into a paint, it is necessary to partially destroy the molecular planarity and symmetry while maintaining a certain degree of crystallinity.
• a crystalline polyester resin having copolymerization components of a polycarboxylic acid component and a polyhydric alcohol component, containing 4 to 48 mol % of orthophthalic acid as the polycarboxylic acid component, containing 48 mol % or more of 1,4-butanediol as the polyhydric alcohol component, and containing less than 40 mol % of ethylene glycol, and having a melting point of 120 to 160°C.
• a crystalline polyester resin according to claim 1 in which when the total polyvalent carboxylic acid components and the total polyhydric alcohol components are each taken as 100 mol % and the copolymerization ratio (mol %) of each component is substituted into the following formula, the value of the formula is 95 mol % or more and less than 140 mol %.
• component (a) is a dicarboxylic acid having a ring structure and a carboxylic acid group at the para-position when the ring is a benzene ring, at the 2- and 6-positions when the ring is a naphthalene ring, or at the 1- and 4-positions when the ring is a cyclohexyl ring;
• component (b) is a dicarboxylic acid having a ring structure and other than component (a);
• component (c) is an aliphatic polyhydric alcohol having a side chain; and each of components (a), (b), and (c) is an optional component.
• a coating composition comprising the crystalline polyester resin according to (1) or (2), and having a curing agent content of less than 1 part by mass per 100 parts by mass of the crystalline polyester resin (solid content).
• the crystalline polyester resin of the present invention is composed of a specified composition, so even without a curing agent, it is possible to form a coating film with excellent solvent solubility, processability, and retort resistance properties, and it is possible to eliminate harmful substances such as bisphenol A and formaldehyde. For this reason, it is suitable for coating compositions, coating films, and metal cans for use in beverage cans and food cans.
• the crystalline polyester resin of the present invention has a chemical structure that can be obtained by polycondensation of a polycarboxylic acid and a polyhydric alcohol, and the polycarboxylic acid and the polyhydric alcohol each consist of one or more selected components.
• the polycarboxylic acid component used in the present invention contains orthophthalic acid.
• orthophthalic acid By including orthophthalic acid as part of the polycarboxylic acid component, the symmetry of the resulting crystalline polyester resin is appropriately disrupted, improving solvent solubility.
• the polyester has a main chain extending in the same direction from each carboxylic acid located at the ortho position, which promotes appropriate orientation and makes it easier to maintain crystallinity. This results in good retort resistance of the coating film.
• the copolymerization ratio of orthophthalic acid must be 4 to 48 mol%, preferably 5 to 45 mol%, more preferably 10 to 44 mol%, even more preferably 20 to 43 mol%, and particularly preferably 30 to 42 mol%.
• the solvent solubility of the resulting polyester is improved.
• the crystallinity of the resulting polyester is high, and the retort resistance of the coating film is improved.
• polycarboxylic acid components other than orthophthalic acid used in the present invention are not particularly limited, but for example, the following polycarboxylic acids or their esters and anhydrides can be used.
• the polyvalent carboxylic acid component other than orthophthalic acid used in the present invention can be a dicarboxylic acid (a) (hereinafter referred to as component (a)) that has a ring structure and, if the ring is a benzene ring, has a carboxylic acid group at the para position, if the ring is a naphthalene ring, has a carboxylic acid group at the 2- and 6-positions, and if the ring is a cyclohexyl ring, has a carboxylic acid group at the 1- and 4-positions. It is preferable that the carboxylic acid group of component (a) is directly bonded to the ring structure.
• component (a) include terephthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. These can be used alone or in combination of two or more kinds.
• the polyvalent carboxylic acid component used in the present invention preferably contains component (a).
• component (a) the crystallinity of the polyester resin is increased, and the coating film has excellent retort resistance.
• dicarboxylic acids having a benzene ring ring and carboxylic acid groups at the para-position or dicarboxylic acids having a naphthalene ring ring and carboxylic acid groups at the 2- and 6-positions are used, since these have small steric hindrance and are particularly highly crystalline. Even more preferably, dicarboxylic acids having a benzene ring ring and carboxylic acid groups at the para-positions are used, since these have smaller steric hindrance in the structure.
• component (a) when component (a) is used as the polycarboxylic acid component, it is preferable that the copolymerization ratio of orthophthalic acid in the polycarboxylic acid component is lower than the copolymerization ratio of component (a).
• the copolymerization ratio (mol%) of component (a) is preferably 40 to 95 mol%, more preferably 45 to 90 mol%, and even more preferably 50 to 80 mol%.
• the crystallinity is high and the retort resistance of the coating film is improved.
• the solvent solubility of the resulting polyester is good.
• the polyvalent carboxylic acid component other than orthophthalic acid used in the present invention has a ring structure, and examples thereof include dicarboxylic acids (b) other than component (a) (hereinafter referred to as component (b)).
• component (b) includes dicarboxylic acids (b) other than component (a) (hereinafter referred to as component (b)).
• the ring structure of component (b) is preferably a benzene ring, a furan ring, a naphthalene ring, or a cyclohexyl ring.
• the carboxylic acid group of component (b) is preferably directly bonded to the ring structure.
• component (b) examples include isophthalic acid, 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, sodium 5-sulfoisophthalate, 2,5-furandicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and hexahydrophthalic acid. These may be used alone or in combination.
• the (b) component is an optional component, and when the total amount of the polyvalent carboxylic acid components is taken as 100 mol%, the copolymerization ratio of the (b) component is preferably 20 mol% or less. More preferably, it is 15 mol% or less, and even more preferably, it is 10 mol% or less, and it may be 0 mol%. By making it 20 mol% or less, the retort resistance of the obtained polyester is improved.
• the total copolymerization ratio (mol %) of orthophthalic acid and component (b) is preferably 15 to 50 mol%, more preferably 20 to 45 mol%, and even more preferably 30 to 45 mol%.
• the solvent solubility of the resulting polyester is improved.
• the retort resistance of the resulting polyester is improved.
• the polycarboxylic acid components other than orthophthalic acid used in the present invention may be aliphatic polycarboxylic acids, alicyclic polycarboxylic acids, aromatic polycarboxylic acids, etc. other than component (a) or (b).
• aliphatic polycarboxylic acids include fumaric acid, adipic acid, sebacic acid, malonic acid, succinic acid, etc.
• alicyclic polycarboxylic acids and aromatic polycarboxylic acids include those with three or more functional groups. Furthermore, one or more of these may be used.
• the polyhydric alcohol component used in the present invention contains 1,4-butanediol.
• the linear chain structure and alkyl chain length of 1,4-butanediol contribute to high crystallinity that satisfies solvent solubility, retort resistance, and processability.
• the copolymerization ratio of 1,4-butanediol must be 48 mol% or more, preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, particularly preferably 80 mol% or more, and even more particularly preferably 90 mol% or more, and may even be 100 mol%.
• the crystallinity of the resulting polyester will be high, and the retort resistance and processability will be good.
• the copolymerization ratio of ethylene glycol must be less than 40 mol%, preferably less than 30 mol%, more preferably less than 20 mol%, and even more preferably less than 10 mol%, and may even be 0 mol%. By making it less than 40 mol%, the solvent solubility and processability of the resulting polyester will be good.
• the polyhydric alcohol component other than 1,4-butanediol used in the present invention is not particularly limited, but specific examples include polyhydric alcohol (c) having a side chain (hereinafter referred to as component (c)).
• Component (c) is preferably a diol having a side chain.
• the side chain in component (c) refers to an atom or atomic group that branches off from a main chain that has a hydrocarbon group (carbon chain) connecting two hydroxyl groups.
• the side chain in component (c) is preferably an alkyl group.
• the number of carbon atoms in the alkyl group is preferably 1 to 50, more preferably 2 to 40, and even more preferably 3 to 35.
• the number of side chains may be 1 or 2 or more.
• the alkyl group may be linear or may have a side chain.
• the component (c) include 1,2-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-hexanediol, 2-methyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-propyl-1,3-propanediol, 2,2-di-n-propyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propane
• Component (c) is an optional component, and when the total amount of the polyhydric alcohol components is taken as 100 mol%, the copolymerization ratio of component (c) is preferably 20 mol% or less. More preferably, it is 15 mol% or less, and even more preferably, it is 10 mol% or less, and it may even be 0 mol%. By making it 20 mol% or less, it is possible to achieve both solvent solubility and retort resistance of the resulting polyester.
• the polyhydric alcohol component other than 1,4-butanediol and ethylene glycol used in the present invention includes a linear polyhydric alcohol (d) (hereinafter referred to as component (d)).
• component (d) examples include 1,3-propylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, etc., and these can be used alone or in combination of two or more.
• Component (d) is an optional component, and when the total amount of the polyhydric alcohol components is taken as 100 mol%, the copolymerization ratio of component (d) is preferably 20 mol% or less. More preferably, it is 15 mol% or less, and even more preferably, it is 10 mol% or less, and it may even be 0 mol%. By making it 20 mol% or less, it is possible to achieve both solvent solubility and retort resistance of the resulting polyester.
• the polyhydric alcohol component other than 1,4-butanediol used in the present invention includes polyhydric alcohol (e) having an aromatic ring skeleton or an alicyclic skeleton (hereinafter referred to as component (e)).
• component (e) examples include 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydroquinone, catechol, resorcinol, etc., and these can be used alone or in combination of two or more.
• Component (e) is an optional component, and when the total amount of the polyhydric alcohol components is taken as 100 mol%, the copolymerization ratio of component (e) is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less, and may even be 0 mol%. By keeping it 30 mol% or less, it is possible to achieve both solvent solubility and retort resistance of the resulting polyester.
• the copolymerization ratio is preferably less than 5 mol%, more preferably less than 1 mol%, and most preferably does not contain isosorbide. By making it less than 5 mol%, the solvent solubility and retort resistance of the resulting polyester can be improved.
• the copolymerization ratio (mol %) of the crystalline polyester resin in the present invention is preferably such that, when the total polyvalent carboxylic acid components and the total polyhydric alcohol components are each taken as 100 mol %, and the copolymerization ratio (mol %) of each component is substituted into the following formula, the value of the formula is 95 mol % or more and less than 140 mol %.
• the crystalline polyester resin has particularly good solvent solubility, coating film processability and retort resistance.
• the above performance is more preferably 98 mol% or more, even more preferably 100 mol% or more, and particularly preferably 110 mol% or more. It is more preferably 135 mol% or less, even more preferably 130 mol% or less, and particularly preferably 120 mol% or less.
• the polyvalent carboxylic acid component and polyhydric alcohol component constituting the crystalline polyester resin in the present invention can be made from raw materials derived from biomass resources.
• Biomass resources include the stored solar energy converted into starch or cellulose by the photosynthetic action of plants, the bodies of animals that grow by eating plants, and products made by processing plants or animals.
• biomass resources are plant resources, but examples of such resources include wood, rice straw, rice husks, rice bran, old rice, corn, sugar cane, cassava, sago palm, soybean pulp, corn cobs, tapioca waste, bagasse, vegetable oil residue, potatoes, buckwheat, soybeans, oils and fats, waste paper, papermaking residues, marine product residues, livestock waste, sewage sludge, and food waste. More preferred are corn, sugar cane, cassava, and sago palm.
• polycarboxylic acid raw materials derived from biomass resources include adipic acid, sebacic acid, fumaric acid, itaconic acid, terephthalic acid, and 2,5-furandicarboxylic acid. These may be used alone or as a mixture of two or more.
• polyhydric alcohol raw materials derived from biomass resources include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. These may be used alone or as a mixture of two or more.
• the crystalline polyester resin in the present invention preferably has a branched structure. Having a branched structure means that the polyester has a branched structure in its main chain.
• a method of copolymerizing a trifunctional or higher component as part of a polycarboxylic acid component and/or a polyhydric alcohol component in a polyester polycondensation reaction can be mentioned.
• the trifunctional or higher polycarboxylic acid component the following polycarboxylic acids or their esters and polycarboxylic anhydrides can be used. Specific examples include trimellitic acid, pyromellitic acid, and benzophenone tetracarboxylic acid.
• the trifunctional or higher polyhydric alcohol component glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, and pentaerythritol can be mentioned, and one or more of these can be used.
• the crystalline polyester resin has a branched structure, the processability of the resulting coating film is improved.
• the tri- or higher functional polycarboxylic acid component and/or tri- or higher functional polyhydric alcohol component is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, and even more preferably 1 mol% or more, when the entire crystalline polyester resin is taken as 100 mol%. Also, it is preferably 5 mol% or less, more preferably 3 mol% or less, even more preferably 2 mol% or less, and particularly preferably 1.5 mol% or less. If the polycarboxylic acid component and/or polyhydric alcohol component exceed the above amounts, the crystallinity of the crystalline polyester resin decreases, the retort resistance deteriorates, or gelation may occur during polyester polymerization.
• the crystalline polyester resin of the present invention can be given an acid value by any method.
• Methods for giving an acid value include a method of adding a compound having a polyvalent carboxylic anhydride group in the molecule in the later stage of polycondensation, and a method of giving a high acid value to the prepolymer (oligomer) stage and then polycondensing this to obtain a polyester resin having an acid value.
• the former method of adding a reaction is preferred because of the ease of operation and the ease of obtaining the target acid value.
• carboxylic acid monoanhydrides include phthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, itaconic anhydride, and citraconic anhydride, and one or more of these can be selected and used.
• trimellitic anhydride is preferred from the standpoint of versatility and economy.
• carboxylic acid polyanhydrides include pyromellitic anhydride, 1,2,3,4-butane tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, ethylene glycol bistrimellitate dianhydride, 2,2',3,3'-biphenyl tetracarboxylic acid dianhydride, etc., and one or more of these can be selected and used.
• ethylene glycol bistrimellitate dianhydride is preferred from the standpoint of versatility and economy.
• the compound having a polyvalent carboxylic acid anhydride group in the molecule to impart the acid value can be a carboxylic acid monoanhydride or a carboxylic acid polyanhydride, which can be used alone or in combination.
• the acid value of the crystalline polyester resin in the present invention is preferably 400 eq/t or less, more preferably 300 eq/t or less, and even more preferably 200 eq/t or less, and even 0 eq/t is acceptable. By making it below the upper limit, the molecular weight can be increased, resulting in good processability.
• the concentration of the metal sulfonate salt in the crystalline polyester resin of the present invention is preferably less than 50 eq/t. More preferably, it is 20 eq/tg or less, even more preferably 10 eq/tg or less, and particularly preferably 5 eq/tg. By making it less than 50 eq/tg, the hydrophilicity of the resulting polyester is reduced and the retort resistance is improved.
• the esterification/exchange reaction all monomer components and/or their oligomers are heated and melted to react.
• the esterification/exchange reaction temperature is preferably 180 to 250°C, more preferably 200 to 250°C.
• the reaction time is preferably 1.5 to 10 hours, more preferably 3 to 6 hours.
• the reaction time is the time from when the desired reaction temperature is reached to when the subsequent polycondensation reaction is started.
• the polyhydric alcohol component is distilled off from the esterified product obtained in the esterification reaction under reduced pressure at a temperature of 220 to 280°C, and the polycondensation reaction is continued until the desired molecular weight is reached.
• the reaction temperature for polycondensation is preferably 220 to 280°C, more preferably 240 to 275°C.
• the degree of reduced pressure is preferably 130 Pa or less. If the degree of reduced pressure is insufficient, the polycondensation time tends to be long, which is not preferable. It is preferable to gradually reduce the pressure from atmospheric pressure to 130 Pa or less over a period of 30 to 180 minutes.
• organic titanate compounds such as tetrabutyl titanate, or organic tin compounds such as germanium dioxide, antimony oxide, and tin octylate. From the standpoint of reaction activity, organic titanate compounds are preferred, and from the standpoint of resin coloration, germanium dioxide is preferred.
• the glass transition temperature of the crystalline polyester resin in the present invention is preferably 10°C or higher, more preferably 15°C or higher, from the viewpoint of water resistance, particularly retort resistance of the coating film. Also, from the viewpoint of processability, it is preferably 50°C or lower, more preferably 40°C or lower.
• the melting point (Tm) of the crystalline polyester resin in the present invention is the temperature at the apex of the endothermic peak with the largest heat of fusion during the heating process, which is performed by aging the polyester resin at 100°C for 30 hours and then heating it from -50 to 200°C at 20°C/min using a differential scanning calorimeter (DSC).
• the melting point (Tm) of the crystalline polyester resin in the present invention is in the range of 120 to 160°C, preferably 125 to 155°C, more preferably 130 to 150°C, and even more preferably 135 to 145°C.
• crystallinity refers to the melting point (Tm) exhibited by the polyester resin when it is measured under the above-mentioned conditions. Also, high crystallinity means that the polyester resin has a high melting point.
• the reduced viscosity of the crystalline polyester resin of the present invention is preferably 0.2 to 0.8 dl/g, more preferably 0.4 to 0.8 dl/g, and even more preferably 0.6 to 0.8 dl/g.
• the reduced viscosity is 0.2 dl/g or more, the toughness and processability of the coating film are good.
• the reduced viscosity is 0.8 dl/g or less, the solvent solubility is good.
• the coating composition of the present invention contains at least the above-mentioned crystalline polyester resin and organic solvent.
• the crystalline polyester resin is contained as the main component.
• the component with the highest content (mass ratio) among the solid components (non-volatile components excluding volatile substances such as water and organic solvents) that form the coating film in the coating composition is defined as the main component.
• the coating composition of the present invention is capable of forming a coating film using the crystalline polyester resin alone without the addition of a curing agent. Therefore, it is preferable that the coating composition of the present invention does not substantially contain a curing agent, that is, the curing agent content is preferably less than 1 part by mass (solids content equivalent) per 100 parts by mass (solids content equivalent) of the crystalline polyester resin.
• the content of the curing agent is preferably less than 1 part by mass per 100 parts by mass of the crystalline polyester resin (solid content). Less than 0.5 parts by mass is more preferable, less than 0.1 parts by mass is even more preferable, and it is most preferable that no curing agent is included. If the content of the curing agent is higher than the above range, not only is it less economical, but there is also a risk of reduced processability due to self-condensation reactions between the curing agents, volatilization of the blocking agent, generation of harmful outgassing such as formaldehyde, and poor stability during long-term storage.
• curing agent refers to a known curing agent that reacts with polyester resin to form a crosslinked structure.
• the form of the crosslinked structure include a reaction in which the unsaturated double bonds in the polyester resin react through a radical addition reaction, a cationic addition reaction, or an anionic addition reaction to generate intermolecular carbon-carbon bonds, or a condensation reaction, polyaddition reaction, or transesterification reaction with polyvalent carboxylic acid groups or polyhydric alcohol groups in the polyester resin to form intermolecular bonds.
• curing agents include phenolic resins, amino resins, isocyanate compounds, epoxy compounds, ⁇ -hydroxylamide compounds, and unsaturated bond-containing resins.
• the coating composition of the present invention can be blended with known additives such as known inorganic pigments such as titanium oxide and silica, phosphoric acid and its esters, surface smoothing agents, defoamers, dispersants, lubricants, crystal nucleating agents, plasticizers, etc., according to the required characteristics.
• known additives such as known inorganic pigments such as titanium oxide and silica, phosphoric acid and its esters, surface smoothing agents, defoamers, dispersants, lubricants, crystal nucleating agents, plasticizers, etc.
• Lubricants are particularly important for imparting the lubricity of the coating film required when molding DI cans, DR (or DRD) cans, etc.
• suitable examples of lubricants include fatty acid ester waxes which are esters of polyol compounds and fatty acids, silicone waxes, fluorine waxes, polyolefin waxes such as polyethylene, lanolin waxes, montan waxes, microcrystalline waxes, etc.
• Lubricants can be used alone or in combination of two or more types.
• Organic solvents used in the coating composition of the present invention include, for example, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, Solvesso, etc. From these, one or more types are selected and used, taking into consideration solubility, evaporation rate, etc.
• the coating composition of the present invention can be blended with other resins for the purpose of modifying the coating film, such as by imparting flexibility or adhesion.
• other resins include amorphous polyesters, crystalline polyesters, ethylene-polymerizable unsaturated carboxylic acid copolymers, and ethylene-polymerizable carboxylic acid copolymer ionomers. Blending at least one resin selected from these may impart flexibility and/or adhesion to the coating film.
• the crystalline polyester resin of the present invention can be made into a powder coating by a known pulverization method.
• Known pulverization methods include, for example, the pulverization method.
• a mixture of the polyester resin composition of the present invention, and optionally anti-rust pigments and additives is dry-mixed in a mixer such as a tumbler mixer or a Henschel mixer, and then melt-kneaded in a kneader.
• a mixer such as a tumbler mixer or a Henschel mixer
• melt-kneaded in a kneader melt-kneaded in a kneader.
• a general kneader such as a single-shaft or twin-shaft extruder, a triple roll, or a lab blast mill can be used.
• the kneaded mixture is cooled and solidified, and the solidified product is coarsely pulverized and finely pulverized to obtain a pulverized product.
• a jet-type pulverizer that uses a supersonic jet stream to pulverize, and an impact-type pulverizer that introduces a solidified product into the space formed between a rotor and a stator (liner) rotating at high speed to pulverize it, can be used. If necessary, additives may be further added to the pulverized product.
• the pulverized product can be classified to adjust the powder to a desired particle size and a desired particle size distribution to obtain a powder coating composition.
• the powder coating composition does not contain an organic solvent.
• a known classifier that can remove over-pulverized toner base particles by classification using centrifugal force and wind force can be used, such as a rotary wind classifier (rotary wind classifier).
• the crystalline polyester resin of the present invention can be dispersed in an aqueous medium by a known dispersion method and used as a crystalline polyester resin aqueous dispersion.
• Known methods include a dispersion method using an emulsifier.
• the coating composition of the present invention can be applied to a metal plate by a known coating method such as roll coater coating or spray coating.
• the coating thickness is not particularly limited, but the dry thickness is preferably in the range of 3 to 18 ⁇ m, and more preferably 5 to 15 ⁇ m.
• the coating is usually baked at a temperature in the range of about 160 to 260°C for about 1 minute to 2 hours, and more preferably in the range of about 180 to 240°C for about 1 minute to 1 hour.
• the coating film made of the crystalline polyester resin of the present invention is baked within the above range and then aged. By aging, crystallization in the coating film is further promoted, resulting in good retort resistance.
• the crystalline polyester resin of the present invention can be melt extrusion coated by known methods.
• One known method is, for example, the T-die method.
• T-die method a number of extruders corresponding to the type of crystalline polyester resin of the present invention, or other resins as necessary, are used to extrude the polyester through a die, which is then extruded onto a metal substrate and thermally bonded to form an extrusion coating and film.
• Melt extrusion coating has the advantage that the process of making the polyester resin into a paint and the drying process can be omitted, improving productivity.
• the coating film of the present invention is a substrate coated with a crystalline polyester resin (two layers: substrate/crystalline polyester resin). It may also be configured such that a layer made of another resin is superimposed on either the top or bottom of the crystalline polyester resin layer. In this case, the layer made of another resin is referred to as a coating layer.
• the coating film of the present invention can be obtained by laminating the crystalline polyester resin of the present invention on various substrates according to conventional methods, and further laminating another resin layer on top of it.
• the metal can of the present invention has the above-mentioned coating film.
• Metal cans can be obtained by coating one or both sides, and if necessary, the end faces, of a metal plate made of a metal material that can be used for, for example, beverage cans, canned food cans, their lids, caps, etc.
• the metal material include tinplate, tin-free steel, aluminum, etc.
• Metal plates made of these metal materials may be treated in advance with phosphate treatment, chromate chromate treatment, chromate phosphate treatment, or other anticorrosion treatment using an antirust treatment agent, or a surface treatment for the purpose of improving the adhesion of the coating film.
• Tm melting point
• Tg glass transition temperature Measurement was performed using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc.
• the aging treatment of the crystalline polyester resin was performed under the aging treatment conditions of 100°C x 30 hours, and 5 mg of the sample of the crystalline polyester resin after the treatment was placed in an aluminum clamped lid type container and sealed, and nitrogen gas was flowed at 30 ml/min to create a nitrogen atmosphere, and then the sample was cooled to -50°C using liquid nitrogen, and then heated to 200°C at 20°C/min.
• the temperature of the apex of the maximum peak of the heat of fusion obtained in this process was determined as the melting point (Tm, unit: °C).
• the sample was heated to 200°C under the same conditions, then rapidly cooled to -50°C, and heated again to 200°C at 20°C/min.
• Tg glass transition temperature
• ⁇ Preparation of crystalline polyester resin coating composition 100 parts by mass (solid content) of the crystalline polyester resin was dissolved in cyclohexanone to obtain a crystalline polyester resin coating composition (solid content: approximately 10% by mass).
• test specimen A crystalline polyester resin coating composition was applied to one side of a tinplate (JIS G 3303 (2008) SPTE, 70 mm x 150 mm x 0.3 mm) using a bar coater so that the film thickness after drying would be 10 ⁇ 2 ⁇ m, and the coating was baked under baking conditions of 200°C x 30 seconds to prepare a test specimen (hereinafter referred to as the test specimen).
• a tinplate JIS G 3303 (2008) SPTE, 70 mm x 150 mm x 0.3 mm
• the obtained test piece was bent 180° in the direction in which the coating film was on the outside, and the cracks in the coating film that occurred at the bent part were evaluated by measuring the electric current value.
• the bending process was performed without sandwiching anything between the test piece and the aluminum plate electrode (width 20 mm, depth 50 mm, thickness 0.5 mm), and a sponge (width 20 mm, depth 50 mm, thickness 10 mm) soaked in 1% NaCl aqueous solution was placed on the aluminum plate electrode (width 20 mm, depth 50 mm, thickness 0.5 mm).
• the sponge was placed near the center of the bent part of the test piece so that it was parallel to the 20 mm side of the sponge.
• a direct current voltage of 5.0 V was applied between the aluminum plate electrode and the uncoated part on the back side of the test plate, and the electric current value was measured.
• a smaller electric current value means better bending characteristics. (judgement) ⁇ : Less than 0.5 mA ⁇ : 0.5 mA or more and less than 1.0 mA ⁇ : 1.0 mA or more and less than 2.0 mA ⁇ : 2.0 mA or more
• Synthesis Example of Crystalline Polyester Resin 105 parts by mass of dimethyl 2,6-naphthalenedicarboxylate, 130 parts by mass of 1,2-propylene glycol, 505 parts by mass of 1,4-butanediol, 150 parts by mass of 1,4-cyclohexanedimethanol, 0.4 parts by mass of tetra-n-butyl titanate (hereinafter sometimes abbreviated as TBT) as a catalyst (0.03 mol% relative to the total acid component) were charged into a 3L four-neck flask, and the temperature was gradually raised to 240 ° C. over 3 hours, while carrying out an ester exchange reaction.
• TBT tetra-n-butyl titanate
• the temperature was lowered to 160 ° C., and 535 parts by mass of terephthalic acid, 70 parts by mass of isophthalic acid, and 35 parts by mass of orthophthalic acid were added, and the temperature was gradually raised to 240 ° C. over 3 hours, while carrying out an esterification reaction.
• the pressure in the system is gradually reduced, and reduced pressure polymerization is carried out to 10 mmHg over 1 hour, and the temperature is raised to 250 ° C., and further post-polymerization is carried out for 90 minutes under a vacuum of 1 mmHg or less.
• the resin was taken out to obtain a crystalline polyester resin (Synthesis Example (1)).
• the reduced viscosity of the obtained crystalline polyester resin was 0.75 dl/g, the glass transition temperature (Tg) was 40° C., the crystalline melting point (Tm) was 135° C., and the acid value was 3 eq/t.
• polyester resins having the resin compositions shown in Table 1 were produced by the transesterification method in the same manner as Synthesis Example (1), except that the charged compositions were changed. In the other Synthesis Examples, polyester resins having the resin compositions shown in Table 1 were produced by the direct polymerization method (the transesterification reaction step in Synthesis Example (1) was omitted).
• the resulting crystalline polyester resin was used to create a crystalline polyester resin coating composition, and the solvent solubility, processability, and retort resistance were evaluated.
• the coating films obtained from the crystalline polyester resins of the present invention in Examples 1 to 9 are excellent in solvent solubility, processability, and retort resistance.
• the crystalline polyester resin did not have orthophthalic acid as a polyvalent carboxylic acid component, and therefore had poor solvent solubility.
• the copolymerization ratio of orthophthalic acid in the polyvalent carboxylic acid component was high, and the melting point was lowered, and therefore the retort resistance was poor.
• Comparative Example 4 the copolymerization ratio of 1,4-butanediol in the polyhydric alcohol component was low, and the melting point was lowered, and therefore the retort resistance was poor.
• Comparative Example 5 the copolymerization ratio of ethylene glycol in the polyhydric alcohol component was high, and therefore the solvent solubility and processability were poor.
• Comparative Example 6 the melting point of the crystalline polyester resin was high, and therefore the solvent solubility and processability were poor.
• the product of the present invention is a crystalline polyester resin with excellent solvent solubility, processability, and retort resistance, as well as a paint composition and coating film that contain the same, and is suitable as a base agent for paints applied to metal food and beverage cans, etc.

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• 2023
  • 2023-12-21 JP JP2024572899A patent/JPWO2024157682A1/ja active Pending
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