Polyester resin composition, aqueous dispersion, paint composition, and coating film

Abstract

The present invention is a polyester resin composition comprising a polyester resin (A) and is characterized by satisfying the following requirements. (i) The acid value of the polyester resin (A) is 100 eq / ton or greater. (ii) The polyester resin composition substantially does not contain a curing agent. (iii) A storage elastic modulus E' at 200ºC after the polyester resin composition has been heat treated at 240ºC for 1 hour is 1.0×104 Pa or higher. The polyester resin composition according to the present invention can suppress toxic outgassing and is suitable for a can paint excelling in characteristics such as curability, retort resistance, and processability.

Description

Polyester resin composition, aqueous dispersion, coating composition and coating film

[0001] The present invention relates to a polyester resin composition. More specifically, the present invention relates to a polyester resin composition suitable for use as a can coating, particularly suitable for coating the inner surfaces of cans containing beverages or foods (hereinafter collectively referred to as foods and beverages), as well as an aqueous dispersion, a coating composition, and a coating film containing the same.

[0002] Metal cans, such as beverage cans and food cans, are coated with organic resins to prevent corrosion of the metal by food (corrosion resistance) and to preserve the flavor and taste of the contents (flavorability). These coatings are required to have processability, corrosion resistance, adhesion to the metal substrate, hardening properties, etc. Furthermore, depending on the application, they may be subjected to high-temperature, high-humidity conditions, such as retort sterilization. Even in such cases, the coating film must not only maintain adhesion to the metal substrate, but also must not whiten, especially when applied to the exterior surface of a metal lid, etc.

[0003] Conventionally, epoxy-based paints such as epoxy-phenolic paints, epoxy-amino paints, and epoxy-acrylic paints, polyester-based paints such as polyester-phenolic paints and polyester-amino paints, and vinyl chloride-based paints have been widely used as paints that are corrosion-resistant, flavor-resistant, and durable enough for can molding. However, recent research has shown that bisphenol A, a raw material for epoxy resins, may have estrogenic effects and may affect the brains of fetuses and infants. Furthermore, vinyl chloride-based paints have issues 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 paints, is known to be carcinogenic and harmful to the human body, and to adversely affect the flavor of the contents. Furthermore, there are concerns about environmental pollution and the impact on the working environment caused by the use of organic solvents.

[0004] Due to concerns about these various adverse effects on the human body, there is a demand in the market for water-based paints that do not use these raw materials, but the reality is that they do not provide satisfactory performance for can applications.

[0005] From this perspective, as a resin composition for metal containers or metal lids, for example, an aqueous coating composition has been proposed in which an acrylic-modified polyester resin obtained by graft polymerizing a polymerizable unsaturated monomer component onto a polyester resin having an ethylenic double bond at the resin end, and a β-hydroxyalkylamide crosslinking agent are dispersed in an aqueous medium (Patent Document 1).

[0006] Furthermore, Patent Document 2 proposes a coating composition comprising a polyester polyol and a blocked polyisocyanate curing agent.

[0007] JP 2001-81160 A JP 2006-169535 A

[0008] However, when the high acid value acrylic-modified polyester resin described in Patent Document 1 was used, sufficient processability could not be obtained. Furthermore, unreacted β-hydroxyalkylamide crosslinking agent remained in the coating film, resulting in problems of reduced curability and retort whitening resistance. The coating film obtained by reacting polyester with blocked polyisocyanate described in Patent Document 2 has poor water resistance and is susceptible to whitening when the contents are sterilized.

[0009] An object of the present invention is to provide a polyester resin and a polyester resin composition which can be cured by itself without substantially containing a curing agent, thereby suppressing harmful outgassing and capable of forming a coating film having excellent properties such as adhesion, retort resistance, and processability.

[0010] The present inventors have conducted extensive research into the above and have found that a polyester resin composition containing a polyester resin having a predetermined acid value and exhibiting a specific storage modulus when subjected to a predetermined heat treatment can form a tough coating film using the polyester resin alone, substantially without the use of a curing agent. Furthermore, by specifying the resin composition and controlling the amount of catalyst, it has been found that a polyester resin coating film having an excellent balance between adhesion and processability, no harmful outgassing, and significantly improved retort resistance can be obtained, leading to the present invention.

[0011] That is, the present invention has the following features. [1] A polyester resin composition comprising a polyester resin (A) and satisfying the following requirements (i) to (iii): (i) the acid value of the polyester resin (A) is 100 eq / ton or more; (ii) the polyester resin (A) is substantially free of a curing agent; and (iii) the storage modulus E' at 200°C after heat treatment at 240°C for 1 hour is 1.0 x 10 ４ Pa or more. [2] The polyester resin composition according to [1] above, wherein the polyester resin (A) has a branched structure. [3] The polyester resin composition according to [1] above, wherein the polyol component constituting the polyester resin (A) includes a diol (a) having two primary hydroxyl groups and no alicyclic structure, and further includes one or both of a diol (b) having an alicyclic structure and a diol (c) having one primary hydroxyl group and one secondary hydroxyl group and no alicyclic structure. [4] The polyester resin composition according to [1] above, wherein the polycarboxylic acid component constituting the polyester resin (A) includes a polycarboxylic acid having a benzene skeleton, and further includes at least one selected from the group consisting of an aliphatic polycarboxylic acid, an alicyclic polycarboxylic acid, and an aromatic polycarboxylic acid having a naphthalene skeleton. [5] The polyester resin composition according to [1] above, wherein the polycarboxylic acid component constituting the polyester resin (A) includes an unsaturated dicarboxylic acid (d). [6] The storage modulus E' of the polyester resin (A) at 200°C after heat treatment at 150°C for 30 minutes is 1.0 x 10 ４

[0023] The polyester resin composition according to [1] above, having a viscosity of less than 100 Pa and further containing one or more catalysts (B). [7] A polyester resin aqueous dispersion comprising the polyester resin composition according to any one of [1] to [6] above and an aqueous medium. [8] A coating composition containing either the polyester resin composition according to any one of [1] to [6] above or the polyester resin aqueous dispersion according to [7] above. [9] A coating film containing the polyester resin composition according to any one of [1] to [6] above.

[10] A metal can having the coating film according to [9] above.

[0012] The present invention can provide a polyester resin composition and a coating film thereof which do not generate harmful outgassing due to a curing agent, have an excellent balance of curability, adhesion, and processability, and have significantly improved retort resistance.

[0013] Hereinafter, embodiments of the present invention will be described in detail. The polyester resin composition of the present invention is a polyester resin composition containing a polyester resin (A) and characterized by satisfying the following requirements (i) to (iii): (i) the acid value of the polyester resin (A) is 100 eq / ton or more; (ii) it is substantially free of a curing agent; and (iii) the storage modulus E' at 200°C after heat treatment of the polyester resin composition at 240°C for 1 hour is 1.0 x 10 ４ Pa or higher.

[0014] <Requirement (i)> Requirement (i) will be explained. The acid value of the polyester resin (A) must be 100 eq / ton or more. It is preferably 200 eq / ton or more, more preferably 250 eq / ton or more, and even more preferably 300 eq / ton or more. If it is less than the above lower limit, the number of carboxyl groups that serve as crosslinking points will be small, which may result in reduced curability. Furthermore, if the acid value is less than the above lower limit, the thermal decomposition reaction may proceed more predominantly than the curing reaction when heated to 240°C, which may result in reduced processability. In addition, an acid value equal to or greater than the above lower limit facilitates aqueous dispersion. There is no particular upper limit for the acid value, but in order to reduce the amount of unreacted acid components and oligomers during the acid addition reaction, it is preferably 1200 eq / ton or less.

[0015] The acid value of the polyester resin (A) of the present invention can be imparted by any method, such as a method of subjecting a polycarboxylic acid anhydride to an addition reaction in the later stage of polycondensation, or a method of increasing the acid value of a prepolymer (oligomer) and then subjecting it to polycondensation to obtain a polyester resin having an acid value.The former addition reaction method is preferred because of its ease of operation and the ease of obtaining a target acid value.

[0016] Among the compounds having a polycarboxylic acid anhydride group in the molecule for imparting an acid value to the polyester resin (A) of the present invention, examples of carboxylic acid monoanhydrides include phthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, itaconic anhydride, citraconic anhydride, 5-(2,5-dioxotetrahydrofurfuryl)-3-cyclohexene-1,2-dicarboxylic acid monoanhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, etc., and one or more of these can be selected and used. Among these, trimellitic anhydride is preferred from the standpoints of versatility and economy.

[0017] Among the compounds having a polycarboxylic acid anhydride group in the molecule for imparting an acid value to the polyester resin (A) of the present invention, examples of the carboxylic acid polyanhydride include pyromellitic anhydride, 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,2,3,4-pentanetetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, cyclopentanetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6 ... Examples of suitable dianhydrides include phthalene tetracarboxylic dianhydride, ethylene glycol bistrimellitate dianhydride, 2,2',3,3'-diphenyl tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, ethylene tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, and 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride. One or more of these may be selected and used. Among these, ethylene glycol bistrimellitate dianhydride is preferred.

[0018] The compound having a polycarboxylic acid anhydride group in the molecule for imparting the acid value may be a carboxylic acid monoanhydride or a carboxylic acid polyanhydride, which may be used alone or in combination.

[0019] <Requirement (ii)> Requirement (ii) will now be described. The polyester resin composition of the present invention is substantially free of a curing agent. "Substantially free of a curing agent" means that the curing agent content is less than 1 part by mass (solids content equivalent) per 100 parts by mass of polyester resin (solids content equivalent). Here, the curing agent refers to a known curing agent that reacts with the polyester resin (A) of the present invention to form a crosslinked structure. Examples of the crosslinked structure include a reaction in which unsaturated double bonds in the polyester resin react via a radical addition reaction, a cation addition reaction, an anion addition reaction, or the like to form an intermolecular carbon-carbon bond, or a condensation reaction, polyaddition reaction, or transesterification reaction with a polycarboxylic acid group or a polyhydric alcohol group in the polyester resin to form an intermolecular bond. Examples of curing agents include phenolic resins, amino resins, isocyanate compounds, epoxy compounds, β-hydroxylamide compounds, and unsaturated bond-containing resins.

[0020] In the polyester resin composition of the present invention, the content of the curing agent is less than 1 part by mass per 100 parts by mass of the polyester resin (A) (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 contained. If the content of the curing agent is higher than the above range, not only is it inferior in economic efficiency, but there is also a risk of reduced processability due to self-condensation reaction between the curing agents, volatilization of the blocking agent, generation of harmful outgassing such as formaldehyde, and poor long-term storage stability.

[0021] <Requirement (iii)> Requirement (iii) will be described. The polyester resin composition of the present invention has a storage modulus E′ of 1.0×10 at 200° C. after heat treatment at 240° C. for 1 hour. ４ The storage modulus E' at 200°C must be 1.0 x 10 Pa or more. ４ By setting the storage modulus E' at 200°C to 1.0 x 10 Pa or more, a polyester resin composition and a coating film thereof having an excellent balance between retort resistance and processability can be obtained. 5 Pa or more, more preferably 5.0 × 10 5 Pa or more, and more preferably 1.0 × 106 Pa or more. 1.0 x 10 ４ If the storage modulus E' at 200°C is less than 2.0 x 10 Pa, the curing will be insufficient, the toughness of the coating film will be insufficient, and the retort resistance and adhesiveness will be reduced, and the coating may not be able to withstand the forming process into a can after being coated on a metal plate. ７ Pa or less, and more preferably 8.0 × 10 ６ Pa or less, and more preferably 5.0 × 10 6 Pa or less. 2.0 x 10 7 If the storage modulus exceeds 10 Pa, the workability of the coating film may be insufficient, and the coating film may not be able to withstand molding into a can after being coated on a metal plate. Here, the "storage modulus E' at 200°C after heat treatment of the polyester resin composition at 240°C for 1 hour" refers to the storage modulus E' at 200°C calculated by applying the polyester resin composition to a copper foil so that the thickness after drying is 10 μm, heating at 240°C for 1 hour, etching the copper foil with an aqueous ferric chloride solution, and measuring the dynamic viscoelasticity of the resulting coating film using a dynamic viscoelasticity measuring device (DVA-220, manufactured by IT Measurement & Control Co., Ltd.) under conditions of a frequency of 10 Hz, a heating rate of 4°C / min, a chuck distance of 15 mm, and a sample width of 4 mm.

[0022] [Polyester Resin (A)] Next, the polyester resin (A) of the present invention will be described. The polyester resin (A) in the present invention is composed of a polycarboxylic acid component and a polyol component.

[0023] The polyester resin (A) of the present invention preferably contains, as a polyol component, a diol (a) having two primary hydroxyl groups and no alicyclic structure (hereinafter sometimes referred to as component (a)). Examples of the diol (a) having two primary hydroxyl groups and no alicyclic structure in the polyester resin (A) of the present invention include aliphatic glycols such as ethylene glycol, 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,4-butanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, and 1,9-nonanediol; polyether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; and the like. One or more of these can be selected and used. Among these, it is preferable to use ethylene glycol, 2-methyl-1,3-propanediol, and 1,6-hexanediol.

[0024] In the polyester resin (A) of the present invention, the copolymerization ratio of the diol (a) having two primary hydroxyl groups and no alicyclic structure is preferably 20 to 80 mol %, more preferably 20 to 60 mol %, and even more preferably 20 to 40 mol % of the total polyol components. When it is within the above range, good curability and retort resistance are obtained.

[0025] The polyester resin (A) of the present invention preferably contains a diol (b) having an alicyclic structure as a polyol component. The inclusion of the diol (b) having an alicyclic structure (hereinafter sometimes referred to as component (b)) facilitates achieving both processability and retort resistance. Examples of the diol (b) having an alicyclic structure that constitutes the polyester resin (A) of the present invention include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane glycols, and hydrogenated bisphenols, and one or more of these can be selected and used. Among these, the use of 1,4-cyclohexanedimethanol is preferred from the viewpoints of curability, processability, and retort resistance.

[0026] The copolymerization ratio of the diol (b) having an alicyclic structure constituting the polyester resin (A) of the present invention is preferably 5 to 50 mol %, more preferably 10 to 40 mol %, and even more preferably 20 to 30 mol %, of the total polyol components. When it is within the above range, processability is improved.

[0027] The polyester resin (A) of the present invention preferably contains, as a polyol component, a diol (c) (hereinafter sometimes referred to as component (c)) that has one primary hydroxyl group and one secondary hydroxyl group and does not have an alicyclic structure. Examples of the diol (c) in the polyester resin (A) of the present invention that has one primary hydroxyl group and one secondary hydroxyl group and does not have an alicyclic structure include 1,2-propylene glycol and 1,2-butanediol, and one or more of these can be selected and used. Of these, the use of 1,2-propylene glycol is preferred.

[0028] In the polyester resin (A) of the present invention, the copolymerization ratio of the diol (c) having one primary hydroxyl group and one secondary hydroxyl group and no alicyclic structure is preferably 5 to 75 mol %, more preferably 10 to 65 mol %, and even more preferably 15 to 50 mol %, of the total polyol components. When it is within the above range, good curability and retort resistance are obtained.

[0029] The polyester resin (A) of the present invention preferably contains, as the polyol component, the above-mentioned component (a) and either or both of the component (b) and the component (c). Component (a) easily forms ester bonds, while the ester bonds of components (b) and (c) are more easily cleaved than those of component (a). Therefore, it is presumed that the presence of component (a) together with components (b) and (c) promotes the rearrangement and recombination of ester bonds during heat treatment, increases the crosslink density, and thereby increases the storage modulus E', enabling the formation of a coating film that combines curability, retort resistance, adhesion, and processability.

[0030] The polycarboxylic acid component constituting the polyester resin (A) of the present invention is not particularly limited, but examples include polycarboxylic acids having a benzene skeleton, such as terephthalic acid, isophthalic acid, and orthophthalic acid, and polycarboxylic acids having a naphthalene skeleton, such as 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. These can be used alone or in combination of two or more. In particular, the combined use of a polycarboxylic acid having a benzene skeleton and a polycarboxylic acid having a naphthalene skeleton is preferred in terms of achieving both processability and retort resistance. When a polycarboxylic acid having a benzene skeleton and a polycarboxylic acid having a naphthalene skeleton are used in combination, the molar ratio of polycarboxylic acid having a benzene skeleton to polycarboxylic acid having a naphthalene skeleton is preferably 95 / 5 to 70 / 30, more preferably 90 / 10 to 75 / 25. By keeping the ratio within the above range, better processability and retort resistance are achieved, which is preferred. Furthermore, terephthalic acid is preferred as the polycarboxylic acid having a benzene skeleton, and 2,6-naphthalenedicarboxylic acid is preferred as the polycarboxylic acid having a naphthalene skeleton.

[0031] Other polycarboxylic acid components constituting the polyester resin (A) of the present invention include aliphatic polycarboxylic acid components and alicyclic polycarboxylic acid components. Examples of aliphatic polycarboxylic acid components include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and dimer acid. Examples of alicyclic polycarboxylic acid components include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, and 1,2-cyclohexenedicarboxylic acid. One or more of these can be selected and used. The inclusion of an aliphatic polycarboxylic acid component or an alicyclic polycarboxylic acid component can improve processability. Among these, adipic acid and 1,4-cyclohexanedicarboxylic acid are preferred in terms of reactivity and economy.

[0032] When the polyester resin (A) of the present invention contains an aliphatic dicarboxylic acid component and an alicyclic dicarboxylic acid component as constituent units, the copolymerization ratio thereof is preferably 5 to 40 mol % of the polycarboxylic acid component, more preferably 10 to 30 mol %. If the copolymerization ratio is outside the above range, the glass transition temperature of the polyester resin (A) may be significantly reduced, and the retort resistance may be reduced.

[0033] It is also preferable that the polycarboxylic acid component constituting the polyester resin (A) of the present invention contains an unsaturated dicarboxylic acid (d) as a structural unit. The presence of the unsaturated dicarboxylic acid (d) can improve curability by a reaction that generates an intermolecular carbon-carbon bond due to cleavage of the unsaturated bond during heat treatment. Examples of the unsaturated dicarboxylic acid (d) include fumaric acid, maleic acid, itaconic acid, citraconic acid, 2,5-norbornanedicarboxylic acid, and tetrahydrophthalic acid, as well as acid anhydrides thereof, and these can be used alone or in combination.

[0034] When the polyester resin (A) of the present invention has an unsaturated dicarboxylic acid (d) as a constituent unit, the copolymerization ratio of the unsaturated dicarboxylic acid (d) in the polycarboxylic acid component is preferably 5 to 20 mol %, more preferably 10 to 15 mol %. By being within this range, both processability and retort resistance can be achieved.

[0035] The polyester resin (A) of the present invention preferably has a branched structure. Having a branched structure refers to the presence of a branched structure in the polyester main chain. An example of a method for introducing a branched structure into the polyester resin (A) is to copolymerize a trifunctional or higher functional component as part of the polycarboxylic acid component and / or polyol component in the polyester polycondensation reaction. Examples of trifunctional or higher functional polycarboxylic acid components include trimellitic acid, pyromellitic acid, and benzophenone tetracarboxylic acid. Examples of trifunctional or higher functional polyols include glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, pentaerythritol, and α-methyl glucoside. The branched structure of the polyester resin (A) increases the crosslink density when rearrangement and recombination of ester bonds occur during heat treatment, thereby increasing the storage modulus E' and improving curability, retort resistance, adhesion, and processability.

[0036] The copolymerization ratio of the tri- or higher functional polycarboxylic acid component, when the total polycarboxylic acid components are taken as 100 mol%, is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, and even more preferably 1 mol% or more. It is also preferably 7 mol% or less, more preferably 6 mol% or less, even more preferably 5 mol% or less, and particularly preferably 4 mol% or less. The copolymerization ratio of the tri- or higher functional polyol component, when the total polyol components are taken as 100 mol%, is preferably 0.1 mol% or more, more preferably 0.5 mol% or more, and even more preferably 1 mol% or more. It is also preferably 5 mol% or less, more preferably 3 mol% or less, even more preferably 2 mol% or less, and particularly preferably 1 mol% or less. If the polycarboxylic acid component and the polyol component each exceed the above range, the flexibility of the polyester resin may be lost, processability may be reduced, or the polyester may gel during polymerization.

[0037] The polycarboxylic acid component and polyol component constituting the polyester resin (A) of the present invention can be derived from biomass resources. Biomass resources include the stored materials obtained by converting solar energy into starch, cellulose, etc. through plant photosynthesis, animals that grow by eating plants, and products made by processing plants or animals. Among these, plant resources are more preferred, including wood, rice straw, rice husks, rice bran, used rice, corn, sugarcane, cassava, sago palm, soybean pulp, corn cob, tapioca dregs, bagasse, vegetable oil cakes, potatoes, buckwheat, soybeans, oils and fats, waste paper, papermaking residues, seafood residues, livestock excrement, sewage sludge, and food waste. Corn, sugarcane, cassava, and sago palm are even more preferred.

[0038] Next, a method for producing the polyester resin (A) of the present invention will be described. In the esterification / exchange reaction, all monomer components and / or their oligomers are heated and melted to react. The esterification / exchange 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 until the subsequent polycondensation reaction. In the polycondensation reaction, the polyol 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 polycondensation reaction temperature is preferably 220 to 280°C, more preferably 240 to 275°C. The degree of vacuum is preferably 130 Pa or less. Insufficient vacuum tends to prolong the polycondensation time, which is undesirable. The time required for the pressure to reach 130 Pa or less from atmospheric pressure is preferably gradual, taking 30 to 180 minutes.

[0039] In the esterification / exchange reaction and polycondensation reaction, polymerization is carried out as necessary using an organic titanate compound such as tetrabutyl titanate, or an organic tin compound such as germanium dioxide, antimony oxide, or tin octoate. From the viewpoint of reactivity, organic titanate compounds are preferred, and from the viewpoint of resin coloration, germanium dioxide is preferred.

[0040] The glass transition temperature of the polyester resin (A) thus obtained is preferably 40° C. or higher, more preferably 60° C. or higher, from the viewpoint of water resistance, particularly retort resistance of the coating film. There is no particular upper limit to the glass transition temperature, but it is usually 130° C. or lower.

[0041] The reduced viscosity of the polyester resin (A) of the present invention is preferably 0.2 to 0.6 dl / g, more preferably 0.3 to 0.5 dl / g. If the reduced viscosity is 0.2 dl / g or less, the curing property will be insufficient, and the toughness of the coating film will be insufficient, which may result in the resin not being able to withstand the molding process into a can after being coated on a metal plate. On the other hand, if the reduced viscosity is 0.6 dl / g or more, the melt viscosity and solution viscosity will be high, which will not only reduce workability but also may make it difficult to impart a sufficient acid value due to the reduced number of hydroxyl terminal groups.

[0042] The polyester resin (A) of the present invention has a storage modulus E' of 1.0 x 10 at 200°C after heat treatment at 150°C for 30 minutes. ４ It is preferable that the viscosity is less than 1.0×10 Pa. More preferably, it is less than 1.0×10 ３ Pa, more preferably less than 1.0 × 10 ２ Pa, and is less than 1.0 × 10 １ Under relatively low-temperature heating conditions of about 150°C, if the storage modulus E' at 200°C is less than the above value, it is possible to suppress the generation of aggregates when the polymer is dissolved in a solvent or dispersed in water.

[0043] [Catalyst (B)] The polyester resin composition of the present invention preferably further contains a catalyst (B). The inclusion of catalyst (B) promotes self-crosslinking of the polyester resin (A) during heat treatment, increases the storage modulus E', and improves the performance of the cured film. Examples of catalysts include acid catalysts such as sulfuric acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphorsulfonic acid, and phosphoric acid, as well as amine-blocked catalysts thereof (partially neutralized by adding an amine), organotin compounds such as dibutyltin dilaurate, titanium compounds such as titanium tetrabutoxide, zinc compounds such as zinc acetate, hafnium compounds such as hafnium chloride-THF complex, and rare earth compounds such as scandium triflate. One or more of these may be used in combination. Among these, dodecylbenzenesulfonic acid and its neutralized products are preferred in terms of compatibility with the polyester resin (A) and hygiene.

[0044] The blending ratio of the polyester resin (A) and the catalyst (B) used in the present invention is preferably (A) / (B)=100 / 0.01 to 0.5 (parts by mass), more preferably 100 / 0.05 to 0.4 (parts by mass), and most preferably 100 / 0.1 to 0.3 (parts by mass). By being within this range, the storage modulus E' of the polyester resin composition can be improved.

[0045] In the polyester resin composition of the present invention, the catalyst (B) may be contained in the polyester resin (A) or may be added later. From the viewpoint of avoiding gelation during polymerization of the polyester resin (A), the catalyst (B) is preferably added after the production of the polyester resin (A).

[0046] A radical polymerization inhibitor (C) may be added to the polyester resin composition of the present invention. It is primarily used to prevent gelation due to unsaturated bond cleavage during polymerization of the polyester resin (A), but may also be added after polymerization to improve the storage stability of the polyester resin. Examples of the radical polymerization inhibitor (C) include known antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, and inorganic compound-based antioxidants.

[0047] Examples of phenolic antioxidants include 2,5-di-t-butylhydroquinone, 4,4'-butyldenbis(3-methyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-tris-methyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-t-butyl-4-hydroxyphenyl)isocyanurate, and derivatives thereof.

[0048] Examples of the phosphorus-based antioxidant include tri(nonylphenyl)phosphite, triphenyl phosphite, diphenylisodecyl phosphite, trioctadecyl phosphite, tridecyl phosphite, diphenyldecyl phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenylditridecyl phosphite), distearyl-pentaerythritol diphosphite, trilauryl trithiophosphite, and derivatives thereof.

[0049] Examples of the amine antioxidant include phenyl-beta-naphthylamine, phenothiazine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-beta-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, aldol-alpha-naphthylamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and derivatives thereof.

[0050] Examples of sulfur-based antioxidants include thiobis(N-phenyl-beta-naphthylamine), 2-mercaptobenziazole, 2-mercaptobenzimidazole, tetramethylthiuram disulfide, nickel isopropyl xanthate, and derivatives thereof.

[0051] Examples of the nitro compound-based antioxidant include 1,3,5-trinitrobenzene, p-nitrosodiphenylamine, p-nitrosodimethylaniline, 1-chloro-3-nitrobenzene, o-dinitrobenzene, m-dinitrobenzene, p-dinitrobenzene, p-nitrobenzoic acid, nitrobenzene, 2-nitro-5-cyanothiophene, and derivatives thereof.

[0052] Inorganic compound antioxidants include FeCl ３ , Fe(CN) ３ , CuCl ２ , CoCl ３ , Co(ClO ４ ) ３ , Co(NO ３ ) ３ , Co ２ (SO ４ ) ３ etc.

[0053] As the radical polymerization inhibitor (C) used in the present invention, among the above antioxidants, phenol-based antioxidants and amine-based antioxidants are preferred in terms of thermal stability, and those having a melting point of 120° C. or higher and a molecular weight of 200 or higher are more preferred, and those having a melting point of 170° C. or higher are even more preferred. Specific examples include phenothiazine and 4,4′-butyldenbis(3-methyl-6-t-butylphenol).

[0054] The blending ratio of the polyester resin (A) and the radical polymerization inhibitor (C) used in the present invention is preferably (A) / (C)=100 / 0.001 to 0.5 (parts by weight), more preferably 100 / 0.01 to 0.1 (parts by weight), and most preferably 100 / 0.02 to 0.08 (parts by weight). By keeping the ratio within this range, gelation during the production of the polyester resin (A) can be suppressed.

[0055] The polyester resin 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, antifoaming agents, dispersants, and lubricants, depending on the required properties. 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-based waxes, polyolefin waxes such as polyethylene, lanolin waxes, montan waxes, and microcrystalline waxes. Lubricants can be used alone or in combination.

[0056] The polyester resin composition of the present invention can be made into a coating material in a state where it is dissolved in a known organic solvent. Examples of organic solvents used for making coating materials include 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, and Solvesso. One or more of these solvents are selected and used, taking into consideration solubility, evaporation rate, and the like.

[0057] The polyester resin composition of the present invention can be made into a powder coating by a known pulverization method. Examples of known pulverization methods include grinding. In this method, a mixture of the polyester resin composition of the present invention, optionally including an anticorrosive pigment and additives, is dry-mixed in a mixer such as a tumbler mixer or Henschel mixer, and then melt-kneaded in a kneader. Examples of kneaders that can be used include common kneaders such as single- or twin-screw extruders, triple-roll mills, and lab blast mills. The kneaded mixture is cooled and solidified, and the solidified product is coarsely and finely pulverized to obtain a pulverized product. Examples of pulverizers include jet pulverizers that utilize a supersonic jet stream to pulverize the mixture, and impact pulverizers that introduce and pulverize the solidified product into the space formed between a rotor and a liner rotating at high speed. If necessary, additives may be added to the pulverized product. The pulverized product is classified to adjust the powder to the desired particle size and particle size distribution, thereby obtaining a powder coating composition. For classification, a known classifier capable of removing over-pulverized toner base particles by classification using centrifugal force and wind force can be used, for example, a rotary wind classifier (rotary wind classifier) ​​or the like.

[0058] The polyester resin composition of the present invention can be blended with other resins for the purpose of improving the coating film by imparting flexibility, adhesion, etc. Examples of other resins include amorphous polyesters, crystalline polyesters, ethylene-polymerizable unsaturated carboxylic acid copolymers, and ethylene-polymerizable carboxylic acid copolymer ionomers, and blending at least one resin selected from these may impart flexibility and / or adhesion to the coating film.

[0059] The polyester resin composition of the present invention can be applied to one or both sides, and if necessary, the end faces, of metal sheets made of metal materials that can be used for beverage cans, food cans, their lids, caps, etc. Examples of such metal materials include tinplate, tin-free steel, and aluminum. Metal sheets made of these metal materials may be previously subjected to a phosphate treatment, a chromate chromate treatment, a chromate phosphate treatment, or other corrosion prevention treatment using a rust prevention agent, or a surface treatment for improving the adhesion of a coating film.

[0060] The polyester resin composition of the present invention can be applied to a metal plate by a known application method such as roll coating or spray coating, and then cured. The thickness of the applied film is not particularly limited, but a dry film thickness of 3 to 18 μm, preferably 5 to 15 μm, is preferred. The baking conditions for the coating film are typically in the range of about 180 to 260°C for about 10 minutes to 2 hours, and more preferably in the range of about 200 to 240°C for about 5 minutes to 1 hour.

[0061] [Polyester Resin Water Dispersion] The polyester resin composition of the present invention can also be dispersed in an aqueous medium and used as a polyester resin water dispersion. Methods for preparing a water dispersion of the polyester resin (A) of the present invention include (a) dissolving the polyester resin (A) in a water-soluble organic solvent that dissolves the polyester resin (A), and then adding a basic compound and water as needed to disperse the polyester resin; and (b) adding the polyester resin (A), water, a water-soluble organic solvent that dissolves the polyester resin (A), and a basic compound as needed, and then heating and dispersing the mixture. Furthermore, if it is desired to reduce the amount of organic solvent or to completely remove the organic solvent to prepare a water dispersion, it is also possible to disperse the resulting mixture in an organic solvent having a boiling point of 100°C or less, and then remove the solvent by heating or under reduced pressure. In the case of the polyester resin (A) of the present invention, the former method (a) is preferred from the viewpoint of film-forming properties.

[0062] In this case, the temperature at which the polyester resin (A) is dissolved is preferably 40 to 160°C, more preferably 50 to 140°C, even more preferably 60 to 120°C, and most preferably 70 to 100°C. At temperatures below 40°C, the polyester resin (A) may not be sufficiently dissolved, making it difficult to sufficiently disentangle the molecular chains, while at temperatures above 160°C, the polyester resin (A) may be more likely to deteriorate. Examples of organic solvents that can dissolve the polyester resin (A) by heating within a temperature range of 40 to 160°C include methyl ethyl ketone, dimethylacetamide, dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, 1,3-dioxane, 1,3-dioxolane, 1,2-hexanediol, methyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and triethylene glycol monobutyl ether. Of these, methyl ethyl ketone, butyl cellosolve, propylene glycol monopropyl ether, propylene glycol monobutyl ether, etc. are preferred.

[0063] When the polyester resin (A) is dissolved at 100°C or higher, it is necessary to cool the temperature of the polyester resin solution to 100°C or lower, and then gradually add water and, if necessary, a basic compound while stirring the resin solution to cause phase inversion, thereby obtaining an aqueous dispersion.

[0064] The basic compound used when dispersing the polyester resin (A) of the present invention in water is preferably a compound that volatilizes during the drying or baking process during coating film formation, and ammonia and / or an organic amine compound having a boiling point of 250°C or less are preferably used. Preferred examples include triethylamine, N,N-diethylethanolamine, N,N-dimethylethanolamine, aminoethanolamine, N-methyl-N,N-diethanolamine, isopropylamine, iminobispropylamine, ethylamine, diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, N-methylmorpholine, and N-ethylmorpholine. These basic compounds must be added in an amount that allows at least partial neutralization of the carboxyl groups of the polyester resin (A); specifically, it is desirable to add 0.5 to 1.5 equivalents per carboxyl group equivalent.

[0065] The average particle size of the polyester resin aqueous dispersion according to the present invention is very important because it significantly affects the coating appearance and storage stability, and is preferably 30 to 250 nm. It is more preferably 50 to 200 nm, and particularly preferably 70 to 150 nm. If the average particle size exceeds 250 nm, not only is dispersion stability significantly reduced, but film-forming properties are also reduced, resulting in a poor appearance of the resulting coating. Conversely, if the average particle size is less than 30 nm, film-forming properties tend to be significantly improved, but this is undesirable because fusion and aggregation between dispersed particles are more likely to occur, resulting in increased viscosity and poor dispersion.

[0066] The polyester resin aqueous dispersion of the present invention is preferably prepared with a resin solids concentration of 10 to 45% by mass. It is more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass. If the resin solids concentration exceeds 45% by mass, the viscosity of the aqueous dispersion increases and aggregation between resin particles is more likely to occur, resulting in a significant decrease in dispersion stability. Furthermore, if the resin solids concentration is less than 10% by mass, it is difficult to say that it is practical from the standpoint of both production and application.

[0067] The polyester resin aqueous dispersion of the present invention is ideal for use as an inner coating for food and beverage cans. To produce an inner coating for food and beverage cans, various additives may be blended depending on the purpose. Leveling agents and surfactants for improving coatability, coating film smoothness, and appearance, lubricants for preventing scratches on the coating film, coloring pigments, and, in some cases, polyester resins other than the polyester resin of the present invention, and resins other than polyester resins, such as acrylic resin emulsions and polyurethane resin emulsions, may be blended within a range that does not impair the object of the present invention, such as food hygiene and flavor properties.

[0068] A coating material using the polyester resin aqueous dispersion of the present invention can be applied to metal substrates for cans, such as aluminum, stainless steel, and tinplate, using a gravure roll coater, a comma coater, or a spray method. There are no particular limitations on the film thickness, but a dry film thickness of 3 to 18 μm is generally preferred, with a range of 5 to 15 μm being preferred. The coating film is typically baked at a temperature in the range of about 180 to 260°C for about 10 minutes to 2 hours, preferably at a temperature in the range of about 200 to 240°C for about 5 minutes to 1 hour.

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Various properties were evaluated according to the following methods. Parts simply indicate parts by mass, and % indicates % by mass.

[0070] <Polyester Resin (A)> (1) Measurement of Resin Composition A sample of polyester resin (A) was dissolved in deuterated chloroform and subjected to H-NMR analysis using a nuclear magnetic resonance (NMR) apparatus 400-MR manufactured by VARIAN Corp. The molar ratio was determined from the ratio of integral values.

[0071] (2) Measurement of reduced viscosity (unit: dl / g) A 0.1 g sample of polyester resin (A) was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4), and the reduced viscosity was measured at 30°C.

[0072] (3) Measurement of Glass Transition Temperature (Tg) Measured using a differential scanning calorimeter (DSC-200, manufactured by SII). A 5 mg sample of polyester resin (A) was placed in an aluminum container with a clamped lid, sealed, cooled to -50°C using liquid nitrogen, and then heated to 150°C at a rate of 20°C / min. In the endothermic curve obtained in this process, the glass transition temperature (Tg, unit: °C) was determined as the temperature at the intersection between the baseline before the endothermic peak and the tangent line to the endothermic peak.

[0073] (4) Measurement of Acid Value 0.2 g of a sample of polyester resin (A) was dissolved in 40 ml of chloroform, and titrated with a 0.01 N potassium hydroxide ethanol solution to obtain 10% of the polyester resin. ６ The equivalent weight per gram (eq / ton) was calculated. Phenolphthalein was used as an indicator.

[0074] <Preparation of Polyester Resin Composition> 100 parts by weight (solid content) of polyester resin (A) was dissolved in cyclohexanone / Solvesso-150 = 1 / 1 (weight ratio) to a viscosity suitable for coating. A polyester resin composition (solid content: approximately 35 mass %) was obtained according to the formulations in Tables 2 and 3.

[0075] (5) Measurement of Storage Modulus E' The storage modulus E' at 200°C after 1 hour of heat treatment at 240°C was measured by applying a polyester resin composition to a copper foil to a dried thickness of 10 μm, heating at 240°C for 1 hour, and then etching the copper foil using an aqueous ferric chloride solution. The dynamic viscoelasticity of the resulting coating was measured using a dynamic viscoelasticity measuring device (DVA-220, manufactured by IT Measurement & Control Co., Ltd.) under conditions of a frequency of 10 Hz, a heating rate of 4°C / min, a chuck distance of 15 mm, and a sample width of 4 mm, and the storage modulus E' at 200°C was calculated. The storage modulus E' at 200°C after 30 minutes of heat treatment at 150°C was determined in the same manner as above, except that the heat treatment conditions were 150°C and heating for 30 minutes. It should be noted that the storage modulus E' was 1.0 x 10 ４ When the pressure was below 100 Pa, the coating film broke during the measurement, and the value could not be calculated.

[0076] <Preparation of Test Piece> The polyester resin composition was applied to one surface of a tinplate (JIS G 3303 (2008) SPTE, 70 mm × 150 mm × 0.3 mm) using a bar coater so that the film thickness after drying would be 10 ± 2 μm, and the coating was cured and baked under baking conditions of 240°C (PMT: maximum temperature reached by substrate) × 1 hour to prepare a test piece (hereinafter referred to as test piece).

[0077] (6) Evaluation of Workability The obtained test specimen was bent 180° so that the cured film was facing outward, and the cracks in the cured film at the bent portion were evaluated by measuring the current value. The bending was performed without any interposition (so-called 0T). An aluminum plate electrode (width 20 mm, depth 50 mm, thickness 0.5 mm) was placed on top of a sponge (width 20 mm, depth 50 mm, thickness 10 mm) soaked in 1% NaCl aqueous solution. The test specimen was placed in contact with the sponge near the center of the bent portion so that it was parallel to the 20 mm side of the sponge. A DC voltage of 5.0 V was applied between the aluminum plate electrode and the uncoated portion on the back of the test specimen, and the current value was measured. A smaller current value indicates better bending properties. (Judgment) ◎: Less than 0.5 mA ○: 0.5 mA or more but less than 1.0 mA △: 1.0 mA or more but less than 2.0 mA ×: 2.0 mA or more

[0078] (7) Evaluation of curing property A gauze felt soaked in methyl ethyl ketone was placed on the cured film surface of the test piece to a thickness of 1 cm. ２ The rubbing test was carried out by pressing the film against the surface so that it was in contact with the surface, and applying a load of 500 g. The number of times until the cured film peeled off (one back and forth counted as one rub) was evaluated according to the following criteria. (Evaluation) ◎: The coating film did not peel off even after 50 or more rubs, and no change was observed in the cured film. ○: The cured film peeled off after 25 to 49 rubs, exposing the tin plate. △: The cured film peeled off after 16 to 24 rubs, exposing the tin plate. ×: The cured film peeled off after 15 rubs or less, exposing the tin plate.

[0079] (8) Evaluation of Adhesion A cutter knife was used to make 100 grids at 1 mm intervals on the cured film surface of the test piece, and cellophane adhesive tape was adhered to the grids and peeled off at a 60° angle. The metal adhesion was evaluated based on the percentage of no peeling. 100% indicates no peeling, and 0% indicates complete peeling. (Judgment) ◎: 100% (no peeling) ○: 75% or more but less than 100% △: 30% or more but less than 75% ×: Less than 30%

[0080] (9) Evaluation of retort resistance A test specimen was placed upright in a stainless steel cup, and ion-exchanged water was poured into it up to half the height of the test specimen. This was then placed in the pressure cooker of a retort tester (ES-315, manufactured by Tomy Kogyo Co., Ltd.) and subjected to retort treatment at 125°C for 30 minutes. Evaluation after treatment was performed at the steam contact point, which is generally considered to be the most severe condition for a cured film, and the whitening and blistering of the cured film were visually evaluated as follows: (Evaluation) ◎: Good (no whitening or blisters) ○: Slight whitening but no blisters △: Slight whitening and / or slight blisters ×: Significant whitening and / or significant blisters

[0081] Synthesis example of polyester resin (A) (a) 670 parts by mass of dimethyl terephthalate, 100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 50 parts by mass of fumaric acid, 8 parts by mass of trimellitic anhydride, 190 parts by mass of ethylene glycol, 330 parts by mass of 1,2-propanediol, 190 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) was charged into a 3 L four-neck flask, and the temperature was gradually raised to 230 ° C. over 3 hours, while the esterification reaction was carried out. Next, the pressure in the system was gradually reduced, and reduced-pressure polymerization was carried out to 10 mmHg over 1 hour, and the temperature was raised to 250 ° C., and further post-polymerization was carried out for 50 minutes under a vacuum of 1 mmHg or less. Once the target molecular weight was reached, it was cooled to 210 ° C. under a nitrogen atmosphere. Next, 26 parts by mass of trimellitic anhydride was added, and stirring was continued for 30 minutes at 200 to 230°C under a nitrogen atmosphere. The mixture was removed to obtain a polyester resin of the present invention (Synthesis Example (a)). The resulting polyester resin had a reduced viscosity of 0.33 dl / g, a glass transition temperature (Tg) of 65°C, and an acid value of 300 eq / ton.

[0082] Synthesis Examples (b) to (s) Polyester resins of the present invention (Synthesis Examples (b) to (s)) having the resin compositions shown in Table 1 were produced by the direct polymerization method similar to that of Synthesis Example (a), except that the charged compositions were changed.

[0083]

[0084] The polyester resin was used to prepare a polyester resin composition, and the composition was evaluated for processability, curability, adhesiveness, and retort resistance. The formulation of the polyester resin composition and the evaluation results are shown in Tables 2 and 3.

[0085]

[0086]

[0087] As is clear from Table 2, the cured film (coating film) obtained from the polyester resin composition using the polyester resin (A) of the present invention is excellent in all of its processability, curability, adhesion, and retort resistance.

[0088] The present invention relates to a polyester resin composition and an aqueous polyester resin dispersion that are excellent in processability, curability, adhesion, and retort resistance, as well as a paint and coating film containing the same, which are suitable as a base agent for paints to be applied to metal cans for food and beverages, etc.

Claims

1. A polyester resin composition comprising a polyester resin (A) and satisfying the following requirements (i) to (iii): (i) The acid value of the polyester resin (A) is 100 eq / ton or more. (ii) It is substantially free of a curing agent. (iii) The storage modulus E' at 200°C after heat treatment of the polyester resin composition at 240°C for 1 hour is 1.0 x 10 ４ It is equal to or greater than Pa.

2. The polyester resin composition according to claim 1 , wherein the polyester resin (A) has a branched structure.

3. 2. The polyester resin composition according to claim 1, comprising, as a polyol component constituting the polyester resin (A), a diol (a) having two primary hydroxyl groups and no alicyclic structure, and further comprising either or both of a diol (b) having an alicyclic structure and a diol (c) having one primary hydroxyl group and one secondary hydroxyl group and no alicyclic structure.

4. 2. The polyester resin composition according to claim 1, wherein the polycarboxylic acid component constituting the polyester resin (A) contains a polycarboxylic acid having a benzene skeleton and further contains at least one selected from the group consisting of an aliphatic polycarboxylic acid, an alicyclic polycarboxylic acid, and a polycarboxylic acid having a naphthalene skeleton.

5. The polyester resin composition according to claim 1, further comprising an unsaturated dicarboxylic acid (d) as a polycarboxylic acid component constituting the polyester resin (A).

6. The storage modulus E' at 200°C after heat treatment at 150°C for 30 minutes is 1.0 x 10 ４ The polyester resin composition according to claim 1, further comprising one or more catalysts (B).

7. A polyester resin water dispersion comprising the polyester resin composition according to any one of claims 1 to 6 and an aqueous medium.

8. A coating composition comprising the polyester resin composition according to any one of claims 1 to 6.

9. A paint composition containing the polyester resin aqueous dispersion described in claim 7.

10. A coating film comprising the polyester resin composition according to any one of claims 1 to 6.

11. A metal can having the coating film according to claim 10.