Polyester resin, polyester resin composition, coating composition, coating film, and metal can

Abstract

This invention provides a polyester resin that exhibits good reactivity with a curing agent and can form a coating with excellent processability and corrosion resistance. A polyester resin comprising a polycarboxylic acid component and a polyol component as copolymer components, and satisfying the following (1) to (3): (1) Glass transition temperature (Tg) of 60°C or higher; (2) Weight-average molecular weight (Mw) of 50,000 or higher; (3) Containing structural units derived from polycarboxylic acids with three or more functions and / or structural units derived from polyols with three or more functions, wherein when all structural units constituting the polyester resin molecular chain are set to 100 mol%, the total content is 1.0 mol% or more of structural units derived from polycarboxylic acids with three or more functions and structural units derived from polyols with three or more functions.

Description

Technical Field

[0001] This invention relates to a polyester resin. More specifically, it relates to a polyester resin suitable for coating cans, and more particularly to a polyester resin suitable for coating cans containing beverages or food, polyester resin compositions containing the same, coating compositions, coating films, and metal cans. Background Technology

[0002] To prevent metal corrosion caused by food (corrosion resistance) and to preserve the aroma and flavor of the contents (flavor), metal cans such as beverage cans and food cans are coated with organic resins such as polyester. For this coating, the bottle neck forming process requires high-load processing such as necking and threading. Therefore, the coating needs to have durability to withstand such post-processing (processability). Recently, the diversification of can shape designs and can contents has further increased the demand for improved corrosion resistance and processability of can coatings.

[0003] In contrast, for example, Patent Document 1 discloses a can coating with excellent processability and water resistance obtained by increasing the glass transition temperature of polyester resin.

[0004] Existing technical documents

[0005] Patent documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2022-84172 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, the molecular weight of the polyester resin described in Patent Document 1 is insufficient to further improve processability. Furthermore, when increasing the molecular weight to improve processability, the high glass transition temperature of the polyester resin in Patent Document 1 leads to an increase in the melt viscosity of the polymerized resin, making it difficult to remove and resulting in a reduced yield.

[0009] The present invention provides a polyester resin that has good reactivity with a curing agent and can form a coating film with excellent processability and corrosion resistance.

[0010] Methods for solving problems

[0011] After conducting various studies, the inventors discovered that by highly branching the polyester resin, a polyester resin with a high glass transition temperature (Tg) and a high weight-average molecular weight (Mw) can be provided, thus completing the present invention. That is, the present invention comprises the following:

[0012] [1] A polyester resin that uses polycarboxylic acid components and polyol components as copolymer components and satisfies the following (1) to (3).

[0013] (1) The glass transition temperature (Tg) is above 60℃.

[0014] (2) Weight average molecular weight (Mw) is above 50,000

[0015] (3) Contains structural units derived from polycarboxylic acids with more than three functions and / or structural units derived from polyols with more than three functions. When all structural units constituting the polyester resin molecular chain are set as 100 mol%, the total amount of structural units derived from polycarboxylic acids with more than three functions and structural units derived from polyols with more than three functions is more than 1.0 mol%.

[0016] [2] According to the polyester resin of [1], wherein the polycarboxylic acid with three or more functions is selected from one or more of the group consisting of trimellitic acid, pyromellitic acid, 1,3,5-benzotriic acid, benzophenone tetracarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(triellitic anhydride) and 1,2,3,4-butanetetracarboxylic acid.

[0017] The polyol with three or more functions is selected from one or more of the group consisting of glycerol, trimethylolethane, trimethylolpropane and pentaerythritol.

[0018] [3] The polyester resin according to [1] or [2], wherein a structural unit derived from an aromatic dicarboxylic acid is contained as the polycarboxylic acid component.

[0019] [4] According to the polyester resin of [3], wherein when the structural unit derived from an aromatic dicarboxylic acid constituting the polyester resin molecular chain is set to 100 mol%, the total content is 1 mol% or more of structural units derived from at least one component selected from the group consisting of isophthalic acid, phthalic 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 and 2,7-naphthalenedicarboxylic acid.

[0020] [5] According to the polyester resin described in [3] or [4], when the structural unit derived from polycarboxylic acid constituting the polyester resin molecular chain is set to 100 mol%, it contains more than 60 mol% of structural units derived from aromatic dicarboxylic acid.

[0021] [6] The polyester resin according to any one of [3] to [5], wherein at least one of the aromatic dicarboxylic acids selected from the group consisting of terephthalic acid, 2,5-furandicarboxylic acid and 2,6-naphthalenedicarboxylic acid is contained.

[0022] When the structural units derived from aromatic dicarboxylic acids constituting the polyester resin molecular chain are set at 100 mol%, the total content is more than 50 mol% of structural units derived from terephthalic acid, 2,5-furandicarboxylic acid and 2,6-naphthalenedicarboxylic acid.

[0023] [7] The polyester resin according to any one of [1] to [6] has an acid value of 3 eq / ton or more.

[0024] [8] The polyester resin according to any one of [1] to [7], wherein when the structural unit derived from the polyol constituting the polyester resin molecular chain is set to 100 mol%, it contains 50 mol% or more structural units derived from a diol (a) having one primary hydroxyl group and one secondary hydroxyl group.

[0025] [9] According to the polyester resin described in [8], when the structural units derived from polyols constituting the polyester resin molecular chain are set to 100 mol%, the structural units derived from diols (b) other than the diol (a) are 50 mol% or less.

[0026]

[10] The polyester resin according to any one of [1] to [9], wherein when the total of the structural units derived from the polycarboxylic acid with three or more functions and the structural units derived from the polyol with three or more functions is set to 100 mol%, it contains 60 mol% or more of the structural units derived from the polycarboxylic acid with three or more functions.

[0027]

[11] The polyester resin according to any one of [1] to

[10] , wherein when the structural units derived from polycarboxylic acids constituting the polyester resin molecular chain are set to 100 mol%, the structural units derived from aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids are 20 mol% or less.

[0028]

[12] A polyester resin composition comprising any one of [1] to

[11] a polyester resin and a curing agent.

[0029]

[13] A coating composition comprising any one of the polyester resins described in [1] to

[11] .

[0030]

[14] A coating film comprising the coating composition described in

[13] .

[0031]

[15] A metal can having the coating described in

[14] .

[0032]

[16] A method for manufacturing a polyester resin, comprising: a first step of subjecting a polycarboxylic acid component and a polyol component to an esterification reaction or an transesterification reaction, followed by a second step of subjecting a polycondensation reaction.

[0033] In the first step and / or the second step, when all components of the polyester resin raw material are set to 100 mol%, a total of 1.0 mol% or more of a polycarboxylic acid component with three or more functions and / or a polyol component with three or more functions are added, wherein the glass transition temperature (Tg) of the polyester resin is 60°C or more and the weight average molecular weight (Mw) is 50,000 or more.

[0034] Invention Effects

[0035] According to the present invention, a polyester resin that exhibits good reactivity with a curing agent and can form a coating film with excellent processability and corrosion resistance can be provided. Therefore, the polyester resin of the present invention is preferably suitable for use in polyester resin compositions, coating compositions, coating films, and metal cans, etc. Detailed Implementation

[0036] <Polyester Resin>

[0037] 1) Polyester resin

[0038] The present invention relates to a polyester resin, which uses polycarboxylic acid components and polyol components as copolymer components and satisfies the following (1) to (3).

[0039] (1) The glass transition temperature (Tg) is above 60℃.

[0040] (2) Weight average molecular weight (Mw) is above 50,000

[0041] (3) Contains structural units derived from polycarboxylic acids with more than three functions and / or structural units derived from polyols with more than three functions. When all structural units constituting the polyester resin molecular chain are set as 100 mol%, the total amount of structural units derived from polycarboxylic acids with more than three functions and structural units derived from polyols with more than three functions is more than 1.0 mol%.

[0042] The polyester resin of the present invention is characterized by having a high glass transition temperature (Tg) and a high weight-average molecular weight (Mw) (conditions (1) and (2)). Generally, the molecular motion of resins with high glass transition temperatures (Tg) tends to be restricted, and high temperatures are often required to moderate the molecular motion. Therefore, the melt viscosity is high during polymerization, and the equipment load is large, such as increased torque load during stirring, making it difficult to achieve high molecular weight (especially to achieve high Mw). After research, the inventors found that it is effective to make the polyester resin highly branched in order to provide a polyester resin with high glass transition temperature (Tg) and high weight-average molecular weight (Mw) (condition (3)). This is because by making the polyester resin highly branched, the entanglement of molecular chains is reduced, and the melt viscosity can be reduced. As a result, the torque load can be reduced, the equipment load can be reduced, and the yield of polyester resin can be expected to be improved. In addition, since the polyester resin of the present invention is highly branched, it has a large number of reaction points with the curing agent and also has a high glass transition temperature (Tg), so the coating film has good corrosion resistance. In addition, polyester resins have a high weight-average molecular weight (Mw), resulting in good processability of the coating film.

[0043] Furthermore, the ingredients shown below in this specification may be used in combination of one or more.

[0044] Furthermore, in this specification, "branched structure" refers to the branched structure on a polymer chain, specifically, a structure in which three or more branches (molecular chains) branch off from a single structural unit constituting the polyester resin molecular chain. That is, a polyester resin having a branched structure, for example, means that the polymer molecular chain of the polyester resin has a trimer, tetraester, or pentaester structure.

[0045] 2) Polycarboxylic acid components and polyol components

[0046] In polyester resin, polycarboxylic acid components and polyol components are used as copolymer components, and the chemical structure is formed by the condensation polymerization of polycarboxylic acid and polyol.

[0047] In this specification, "all structural units constituting the polyester resin molecular chain" and "structural units derived from A constituting the polyester resin molecular chain" refer to either all structural units derived from the copolymer components or structural units derived from A, excluding structural units derived from compounds containing polycarboxylic anhydride groups that are introduced to the end of the polyester resin after the polycondensation reaction to adjust the acid value of the polyester resin. The proportions of each structural unit constituting the polyester resin can be determined, for example, by the amount of copolymer components added, 1 H-NMR analysis, 13 Determined by various analyses such as C-NMR analysis.

[0048] In this specification, polycarboxylic acids with three or more functions and dicarboxylic acids may be cited as examples. Specifically, polycarboxylic acids with three or more functions refer to polycarboxylic acids having three or more carboxyl groups, preferably with three to five functional groups, more preferably with three to four functional groups. Dicarboxylic acids specifically refer to polycarboxylic acids having two carboxyl groups.

[0049] Examples of polycarboxylic acids with three or more functions include trimellitic acid, pyromellitic acid, 1,3,5-benzotriic acid, benzophenone tetracarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(triellitic anhydride), cyclopentanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 4,4'-oxobisphthalic dianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, and 1,2,3,4-butanetetracarboxylic acid, as well as their anhydrides. Preferably, trimellitic acid, pyromellitic acid, 1,3,5-benzotriic acid, benzophenone tetracarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(triellitic anhydride), and 1,2,3,4-butanetetracarboxylic acid are used, with trimellitic acid being more preferred. As a polycarboxylic acid with three or more functions, it is preferably a substance having an aromatic ring such as a benzene ring or a naphthalene ring within the molecule. By using a polycarboxylic acid with an aromatic ring, a rigid framework can be introduced into the molecule, thereby inhibiting hydrolysis and easily forming a coating film with excellent corrosion resistance.

[0050] Examples of dicarboxylic acids include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids.

[0051] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,5-furandicarboxylic 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, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or their anhydrides.

[0052] Examples of aliphatic dicarboxylic acids (preferably acyclic) include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, dimer acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, or their anhydrides.

[0053] Examples of alicyclic dicarboxylic acids include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, 2,5-norbornanedicarboxylic acid or their anhydrides.

[0054] In this specification, polyols with three or more functional groups and diols may be cited as examples. Specifically, polyols with three or more functional groups refer to polyols having three or more hydroxyl groups, preferably with three to five functional groups, more preferably with three to four functional groups. Diols specifically refer to polyols having two hydroxyl groups.

[0055] Examples of polyols with three or more functions include glycerol, trimethylolethane, trimethylolpropane, mannitol, sorbitol, and pentaerythritol. From the viewpoint of the heat resistance of the monomer itself, glycerol, trimethylolethane, trimethylolpropane, and pentaerythritol are preferred, with trimethylolethane being more preferred.

[0056] Examples of diols include diols having one primary hydroxyl group and one secondary hydroxyl group (a); and diols other than diols (a) (b), etc.

[0057] Examples of diols (a) include 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, and 1,2-hexanediol. Among these, from the viewpoint of improving corrosion resistance, 1,2-propanediol and 1,2-butanediol are preferred, and 1,2-propanediol is more preferred.

[0058] Examples of diols (b) include 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, 1,9-nonanediol, and dimer diol; polyether diols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylenediol; and polyols with cyclic skeletons such as 1,4-cyclohexanediethanol, tricyclodecanediethanol, hydroquinone, catechol, and resorcinol.

[0059] The polycarboxylic acid and polyol components constituting the polyester resin molecular chain can utilize raw materials derived from biomass resources. Biomass resources include: resources stored by converting solar energy into starch, cellulose, etc., through plant photosynthesis; and products obtained from the bodies of animals that grow by consuming plants or from the processing of plants and animals. Among these, plant resources are preferred biomass resources, such as wood, rice straw, rice husks, rice bran, old rice, corn, sugarcane, cassava, coconut, soybean residue, corn cob, cassava residue, sugarcane bagasse, vegetable oil residue, taro, buckwheat, soybeans, oils, waste paper, papermaking residue, aquatic product residue, livestock excrement, sewage sludge, and food waste. Corn, sugarcane, cassava, and coconut are further preferred.

[0060] Specific examples of polycarboxylic acid raw materials derived from biomass resources include adipic acid, sebacic acid, fumaric acid, itaconic acid, terephthalic acid, and 2,5-furandicarboxylic acid.

[0061] Specific examples of polyol feedstocks derived from biomass resources include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,4-butanediol, and 1,4-cyclohexanediol.

[0062] 3) Components with three or more functions

[0063] Polyester resins contain structural units derived from polycarboxylic acids with three or more functionalities and / or polyols with three or more functionalities. When all structural units constituting the polyester resin molecular chain are set at 100 mol%, the total content of structural units derived from polycarboxylic acids with three or more functionalities and structural units derived from polyols with three or more functionalities is at least 1.0 mol%, preferably 1.2 to 6.0 mol%, more preferably 1.5 to 5.0 mol%, and even more preferably 2.0 to 4.0 mol%. The polycarboxylic acids with three or more functionalities and the polyols with three or more functionalities function as branching components in the polyester resin, readily forming branched structures. By setting the content within the above range, the entanglement of molecular chains is reduced, the melt viscosity can be lowered, and the reaction points with the curing agent can be sufficiently ensured, resulting in a coating film with excellent corrosion resistance. Furthermore, the polymerization reaction is easily controlled, allowing for the acquisition of polyester resins with higher molecular weights.

[0064] In this invention, any of the three or more functional polycarboxylic acids and the three or more functional polyols can be used as branching components, but preferably they are mainly derived from the three or more functional polycarboxylic acids. When the total number of structural units derived from the three or more functional polycarboxylic acids and the structural units derived from the three or more functional polyols is set to 100 mol%, it is preferable to contain 60 to 100 mol%, more preferably 75 to 99 mol%, and even more preferably 95 to 98 mol% of structural units derived from the three or more functional polycarboxylic acids.

[0065] 4) Dicarboxylic acid components

[0066] The polyester resin preferably contains structural units derived from aromatic dicarboxylic acids. By containing structural units derived from aromatic dicarboxylic acids, the glass transition temperature increases, and the corrosion resistance of the coating film improves. In this case, when the structural units derived from polycarboxylic acids constituting the polyester resin molecular chain are set to 100 mol%, it is preferable to contain 60-100 mol%, more preferably 65-99 mol%, and even more preferably 70-98 mol% of structural units derived from aromatic dicarboxylic acids. By setting it to the lower limit or above, the glass transition temperature increases, and the corrosion resistance of the coating film improves. Furthermore, the upper limit is not particularly limited, but it is preferably 100 mol% or less, more preferably 99 mol% or less, and even more preferably 98 mol% or less. Industrially, it can also be less than 100 mol%.

[0067] Furthermore, from the viewpoint of improving corrosion resistance, the polyester resin preferably contains at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, 2,5-furandicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. In this case, when the structural units derived from aromatic dicarboxylic acids constituting the polyester resin molecular chain are set to 100 mol%, it is preferable to contain a total of 50 to 100 mol%, more preferably 60 to 95 mol%, and even more preferably 70 to 90 mol% of structural units derived from terephthalic acid, 2,5-furandicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. By setting it within the above range, the corrosion resistance of the coating film is improved.

[0068] Furthermore, from the viewpoint of effectively suppressing gelation during polymerization, the polyester resin preferably contains at least one aromatic dicarboxylic acid selected from the group consisting of isophthalic acid, phthalic 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, and 2,7-naphthalenedicarboxylic acid, more preferably isophthalic acid and / or phthalic acid, and even more preferably phthalic acid. In this case, when the structural units derived from aromatic dicarboxylic acids constituting the polyester resin molecular chain are set to 100 mol%, it is preferable that the total content is 1 to 50 mol%, more preferably 5 to 40 mol%, and even more preferably 10 to 30 mol% of structural units derived from at least one component selected from the group consisting of isophthalic acid, phthalic 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, and 2,7-naphthalenedicarboxylic acid. By setting the content within the above range, gelation during polymerization can be effectively suppressed.

[0069] Polyester resins may contain structural units derived from aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids. In this case, when the structural units derived from polycarboxylic acids constituting the polyester resin molecular chain are set to 100 mol%, it is preferable that the total content is 20 mol% or less, more preferably 19 mol% or less, further preferably 18 mol% or less, even more preferably 15 mol% or less, and particularly preferably 10 mol% or less of structural units derived from aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids. By setting the content below the above-mentioned upper limit, the corrosion resistance of the coating film can be maintained, and the processability of the coating film is improved.

[0070] 5) Diol components

[0071] The polyester resin preferably contains structural units derived from a diol (a) having one primary hydroxyl group and one secondary hydroxyl group. In this case, when the structural units derived from the polyol constituting the polyester resin molecular chain are set to 100 mol%, for example, it contains 50 mol% or more, more preferably 60 mol% or more, further preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more of structural units derived from the diol (a). There is no particular upper limit, but it is preferably 100 mol% or less, for example, it can also be 98 mol% or less, 95 mol% or less, 90 mol% or less, or 80 mol% or less. That is, when the structural units derived from the polyol constituting the polyester resin molecular chain are set to 100 mol%, it is preferable to contain 50 to 100 mol%, 50 to 98 mol%, 50 to 95 mol%, 50 to 90 mol%, 50 to 80 mol%, 60 to 100 mol%, 70 to 100 mol%, 80 to 100 mol%, or 90 to 100 mol% of structural units derived from the diol (a). Because highly branched polyester resins, which typically contain a large number of branched components, undergo rapid gelation during polymerization, it is difficult to achieve high molecular weights (especially high Mw). While the working principle is not limited to the following, it is speculated that by copolymerizing a specific diol (a) with relatively low reactivity in a predetermined amount, the condensation reaction proceeds slowly, thus suppressing gelation while maintaining a high branched content. Therefore, by setting the reaction rate above the aforementioned lower limit, the reaction rate during polyester resin polymerization decreases, making reaction control easier and enabling the suppression of gelation.

[0072] Polyester resins may contain structural units derived from diols (b) other than diols (a) as any component. When the polyol-derived structural units constituting the polyester resin molecular chain are set to 100 mol%, it is preferable to contain 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less of diol-derived structural units (b), or it may be 0 mol%. By setting it to the above-mentioned upper limit value or below, the reaction rate during polyester resin polymerization is reduced, thus making reaction control easier and suppressing gelation.

[0073] 6) Other ingredients

[0074] Polyester resins may contain structural units derived from components other than those mentioned above. For example, polyester resins may contain structural units derived from components with phenolic hydroxyl groups, such as bisphenolic acid, p-hydroxybenzoic acid, p-hydroxyphenylacetic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenylethanol, and 5-hydroxyisophthalic acid. Since phenolic hydroxyl groups do not participate in esterification reactions, it is assumed that when this component is used, the ends of the polyester resin are capped, making it difficult to adjust the weight-average molecular weight (Mw). Therefore, when all structural units constituting the polyester resin molecular chain are set to 100 mol%, structural units derived from components with phenolic hydroxyl groups are preferably 5 mol% or less, more preferably 3 mol% or less, further preferably 1 mol% or less, and most preferably 0 mol%. By setting this to the above-mentioned upper limit value or less, the weight-average molecular weight (Mw) can be set to a preferred range, improving the processability of the coating film.

[0075] Polyester resins, for example, may contain structural units derived from components with a molecular weight of 500 or higher. Components with a molecular weight of 500 or higher specifically include dimer acids, dimer glycols, polytetramethylene glycol, polyethylene glycol, polypropylene glycol, hydroxyl-terminated polybutadiene, hydroxyl-terminated polyisoprene, and hydroxyl-terminated polyolefins. In this invention, the copolymerization amount is preferably low. When all structural units constituting the polyester resin molecular chain are set to 100 mol%, the structural units derived from components with a molecular weight of 500 or higher are preferably 5 mol% or less, more preferably 3 mol% or less, further preferably 1 mol% or less, and most preferably 0 mol%. By setting this to the above upper limit or below, the branched structures (reaction sites) in the polymer molecular chain of the polyester resin are positioned close to each other, resulting in a resin with a higher crosslinking density.

[0076] 7) Properties of polyester

[0077] The weight-average molecular weight (Mw) of the polyester resin, determined by gel permeation chromatography (GPC) analysis using polystyrene standard samples, is 50,000 or higher, preferably 50,000 to 400,000, more preferably 51,000 to 400,000, more preferably 55,000 to 350,000, even more preferably 60,000 to 300,000, and even more preferably 70,000 to 280,000. By setting it within the above range, the reactivity with the curing agent is improved, and a coating film with excellent corrosion resistance and processability can be obtained.

[0078] The number-average molecular weight (Mn) of the polyester resin, as determined by gel permeation chromatography (GPC) analysis using polystyrene standard samples, is preferably 8,000 to 25,000, more preferably 9,000 to 20,000, and even more preferably 10,000 to 18,000. By setting it within the above range, the reactivity with the curing agent is improved, and a coating film with excellent corrosion resistance and processability can be obtained.

[0079] The molecular weight distribution (Mw / Mn) of the polyester resin, as determined by gel permeation chromatography (GPC) analysis using polystyrene standard samples, is preferably 5.0 to 30.0, more preferably 5.5 to 25.0, and even more preferably 6.5 to 20.0. By setting it within the above range, the reactivity with the curing agent is improved, resulting in a coating film with excellent corrosion resistance and processability. Furthermore, the polyester resin of the present invention has a particularly high weight-average molecular weight (Mw), thus the molecular weight distribution (Mw / Mn) tends to increase.

[0080] The hydroxyl value of the polyester resin is preferably 50-800 eq / ton, more preferably 150-600 eq / ton, and even more preferably 200-400 eq / ton. By setting it within the above range, the reactivity with the curing agent is improved, resulting in a coating film with excellent corrosion resistance and processability. Furthermore, adjusting the copolymerization amount of the branching components (trifunctional or higher polycarboxylic acids and / or trifunctional or higher polyols) is effective in increasing the hydroxyl value. By copolymerizing the branching components, a polyester resin with both high weight-average molecular weight (Mw) and high hydroxyl value can be easily manufactured.

[0081] The acid value of the polyester resin is, for example, 3 eq / ton or higher, preferably 3 to 600 eq / ton, more preferably 70 to 600 eq / ton, even more preferably 80 to 500 eq / ton, further preferably 90 to 400 eq / ton, and even more preferably 100 to 350 eq / ton. In particular, by setting it to 70 eq / ton or higher, more reaction sites with the curing agent can be introduced, increasing the crosslinking density. By setting it below the above upper limit, the reaction during polymerization is easily controlled, and polyesters with higher molecular weights can be obtained.

[0082] In polyester resins, an acid value can be acquired by any method. Methods for acquiring an acid value include addition reactions of compounds with polycarboxylic anhydride groups in the late stage of polycondensation; and methods that achieve a high acid value in the prepolymer (oligopolymer) stage and then polycondense it to obtain a polyester resin with an acid value. However, for ease of operation and to easily obtain the target acid value, the former addition reaction method is preferred.

[0083] Among compounds containing intramolecular polycarboxylic anhydride groups used to impart acid value to polyester resins, monocarboxylic anhydrides, for example, include phthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, itaconic anhydride, citraconic anhydride, etc., among which trimellitic anhydride is preferred for its versatility and economy.

[0084] Among compounds containing intramolecular polycarboxylic anhydride groups used to impart acid values ​​to polyester resins, examples of polycarboxylic anhydrides include pyromellitic anhydride, 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, ethylene glycol dipreptyltriacyl dianhydride, and 2,2',3,3'-biphenyltetracarboxylic dianhydride. Ethylene glycol dipreptyltriacyl dianhydride is preferred for its versatility and economy.

[0085] Carboxylic acid monohydric anhydrides and carboxylic acid polyhydric anhydrides can be used in combination of one or more types.

[0086] The polyester resin has a glass transition temperature (Tg) of 60°C or higher, preferably 60-100°C, more preferably 62-100°C, more preferably 65-95°C, and even more preferably 70-90°C. Setting it to the lower limit or higher results in good corrosion resistance of the coating. Setting it to the upper limit or lower results in good processability of the coating. Furthermore, the polyester resin can be either a crystalline resin or an amorphous resin, preferably an amorphous resin.

[0087] The specific viscosity of the polyester resin is preferably 0.30~0.70 dl / g, more preferably 0.35~0.65 dl / g, and even more preferably 0.4~0.60 dl / g. By setting it to the upper limit below the above values, the toughness of the coating film is improved, and the processability becomes better. By setting it to the lower limit above the above values, gelation during polymerization can be suppressed.

[0088] Polyester resins can be dispersed in aqueous media using known dispersion methods, and used as aqueous dispersions of polyester resins. Examples of known methods include dispersion methods using emulsifiers.

[0089] 8) Manufacturing method

[0090] The manufacturing method of the polyester resin will be described. The polyester resin of the present invention can be appropriately manufactured by conventional methods from copolymer components that can constitute the structural units of the above-described polyester resin. The manufacturing method of the polyester resin of the present invention is expected to include a first step of performing an esterification reaction or transesterification reaction on a polycarboxylic acid component and a polyol component, followed by a second step of performing a polycondensation reaction. Furthermore, in the first step and / or the second step, when all components as raw materials for the polyester resin are set to 100 mol%, a total of 1.0 mol% or more of a trifunctional or more polycarboxylic acid component and / or a trifunctional or more more polyol component is added. By this method, the polyester resin of the present invention that satisfies a glass transition temperature (Tg) of 60°C or higher and a weight-average molecular weight (Mw) of 50,000 or higher can be easily manufactured.

[0091] The amount added in step 1 and / or step 2 above refers to the total amount added in steps 1 and 2. Furthermore, the amount of copolymer component added is related to the proportion of each structural unit constituting the polyester resin to a certain extent. Therefore, referring to the above description, the amount of each copolymer component added can be adjusted to be the same as the content of the aforementioned structural units (for example, replacing the content of the aforementioned structural units with the amount added in step 1 and / or step 2 above).

[0092] In the esterification / exchange reaction, all monomer components and / or their oligomers are heated and melted to allow them to react. The esterification / exchange reaction temperature is preferably 180~250°C, more preferably 200~250°C. The reaction time is preferably 1.5~10 hours, more preferably 3 hours~6 hours. Furthermore, the reaction time refers to the time from reaching the desired reaction temperature to the subsequent polycondensation reaction.

[0093] In the polycondensation reaction, under reduced pressure and at a temperature of 220–280°C, the polyol component is removed by distillation from the esterified product obtained through esterification, and the polycondensation reaction continues until the desired molecular weight is reached. The reaction temperature for polycondensation is preferably 220–280°C, more preferably 240–275°C. The reduced pressure is preferably 150 Pa or less. Insufficient reduced pressure leads to prolonged polycondensation time, which is therefore undesirable. A slow reduction of pressure from atmospheric pressure to below 150 Pa over 30–180 minutes is preferred.

[0094] During esterification / exchange and polycondensation reactions, organotitanate compounds such as tetrabutyl titanate, tetraisopropyl titanate, and acetylacetonate titanium oxide are used as needed; germanium compounds such as germanium dioxide and tetra-n-butoxygermanium; antimony compounds such as antimony oxide and tributoxyantimony; organotin compounds such as tin octoate; and metal acetates such as magnesium, iron, zinc, manganese, cobalt, and aluminum are used for polymerization. In terms of reactivity, organotitanate compounds are preferred, while germanium dioxide is preferred for resin coloring.

[0095] <Polyester Resin Composition>

[0096] The polyester resin composition of the present invention contains at least the above-mentioned polyester resin and a curing agent. By compounding the curing agent, the polyester resin composition can be used as an adhesive, coating, or coating agent, and a cured coating film with excellent processability and corrosion resistance can be obtained.

[0097] Here, "curing agent" refers to a known curing agent that reacts with polyester resin to form a cross-linked structure. The morphology of the cross-linked structure can be, for example, through reactions such as free radical addition, cationic addition, or anionic addition, which react the unsaturated double bonds in the polyester resin to form intermolecular carbon-carbon bonds; or based on condensation reactions, stepwise addition polymerization, or transesterification reactions with polycarboxylic acid groups or polyol groups in the polyester resin to form intermolecular bonds. Examples of curing agents include, for example, polyols, polycarboxylic acids, and resins containing unsaturated bonds such as phenolic resins, amino resins, epoxy compounds, isocyanate compounds, or β-hydroxyamide compounds. Among these, phenolic resins, amino resins, epoxy compounds, and isocyanate compounds are soluble in water and organic solvents, readily yielding cured coatings with high cross-linking density, and are therefore preferred.

[0098] Examples of phenolic resins include trifunctional phenolic compounds such as phenol, m-cresol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol, or difunctional phenolic compounds such as p-cresol, o-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, and m-methoxyphenol, as well as substances synthesized with formaldehyde in the presence of an alkaline catalyst, or substances in which the hydroxymethyl group is partially or completely etherified with a lower alcohol.

[0099] Examples of amino resins include urea, melamine, formaldehyde addition products of benzoguanamine, or substances that are etherified by reaction of these with lower alcohols.

[0100] As an epoxy compound, there are no particular limitations as long as it is a compound having two or more epoxy groups in one molecule. Specifically, examples include bisphenol A glycidyl ethers and their oligomers, diglycidyl phthalate, diglycidyl isophthalate, diglycidyl terephthalate, diglycidyl p-hydroxybenzoate, tetrahydrophthalic acid diglycidyl ether, hexahydrophthalic acid diglycidyl ether, diglycidyl succinate, diglycidyl adipate, diglycidyl sebacate, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and 1,4-butanediol. Diglycidyl alcohol esters, 1,6-hexanediol diglycidyl esters, as well as polyalkylene glycol diglycidyl esters, trimellitic acid triglycidyl esters, isocyanuric acid triglycidyl esters, 1,4-diglycidyloxybenzene, diglycidyl acrylate, glycerol triglycidyl ether, trimethylolethane triglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol tetraglycidyl ether, and triglycidyl ethers of glycerol alkylene oxide addition products, etc. These can be used in combination of one or more. Among them, the addition products of glycidyl groups with sorbitol, glycerol, and pentaerythritol are soluble in aqueous and organic solvents, readily yielding high crosslinking density cured coatings, and are therefore preferred. Various amine catalysts are effective as curing catalysts.

[0101] Examples of isocyanate compounds include, for example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, tetramethylxylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, terephthalene diisocyanate, 1,4-naphthalene diisocyanate, 1,5-naphthalene diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'- Aromatic diisocyanates such as diisocyanates, aromatic polyisocyanates such as polymethylene polyphenyl isocyanates and crude toluene diisocyanates, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), decamethylene diisocyanate, and lysine diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate (IPDI), hydrogenated toluene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated diphenylmethane diisocyanate, as well as biuret, ureidone-modified, carbodiimide-modified, isocyanurate-modified, uretonimine-modified, adducts with polyols, and mixed modified forms of the above isocyanates, may be used in combination of one or more. In addition, it can also be used in the form of polyurethane precursors such as prepolymers, modifiers, derivatives, and mixtures composed of isocyanate compounds and polyols, polyamines, and other compounds containing active hydrogen.

[0102] From the viewpoint of stability after compounding with a curing agent, end-capped isocyanate compounds that have undergone end-capping treatment of the terminal NCO groups of the isocyanate compound are particularly preferred as curing agents. Examples of end-capping agents include phenolic compounds such as phenol, cresol, ethylphenol, and butylphenol; alcoholic compounds such as 2-hydroxypyridine, butyl cellosolve, propylene glycol monomethyl ether, benzyl alcohol, methanol, ethanol, n-butanol, isobutanol, and 2-ethylhexanol; active methylene compounds such as dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; thiol compounds such as butyl mercaptan and dodecyl mercaptan; and acetanilide, ethyl... Amide compounds such as amides, lactam compounds such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam, imidazole compounds such as imidazole and 2-methylimidazolium, urea compounds such as thiourea and ethyleneurea, oxime compounds such as formamide oxime, acetaldehyde oxime, acetone oxime, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, and cyclohexanone oxime, and amine compounds such as diphenylaniline, aniline, carbazole, ethyleneimine, and polyethyleneimine. These can be used alone or in combination of two or more.

[0103] The reaction between such a capping agent and the isocyanate curing agent can, for example, be carried out at 20–200°C using a known inert solvent and catalyst as needed. The capping agent is preferably used in a molar amount of 0.7–1.5 times the terminal isocyanate group.

[0104] The amount of curing agent in the polyester resin composition is preferably 1 to 50 parts by weight relative to 100 parts by weight of polyester resin, more preferably 5 to 40 parts by weight, and even more preferably 8 to 30 parts by weight. By setting it within the above range, a coating film with excellent corrosion resistance and excellent processability can be obtained.

[0105] Furthermore, the reactivity of the polyester resin with the curing agent can be evaluated by the gel (solvent-insoluble component) fraction. The gel fraction measured by the method described in the examples is preferably 50-100%, more preferably 60-100%, further preferably 70-98%, even more preferably 80-98%, with an upper limit of 100%, and may also be below 98%. By setting it within the above range, the reactivity with the curing agent is improved, resulting in a coating film with excellent corrosion resistance and processability.

[0106] <Coating Composition>

[0107] The coating composition contains at least the polyester resin of the present invention, and may further contain organic solvents. The coating composition contains polyester resin as the main agent. In the coating composition, the component with the highest content (by mass ratio) of the solid components (excluding non-volatile components such as water and organic solvents) that form the coating film is defined as the main agent.

[0108] Examples of organic solvents 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. Considering solubility, evaporation rate, etc., one or more of these can be used in combination.

[0109] In coating compositions, known inorganic pigments such as titanium dioxide and silica, phosphoric acid and its esters, surface leveling agents, defoamers, dispersants, lubricants, nucleating agents, and plasticizers can be added according to the required properties. Lubricants are particularly important because they impart the necessary film lubrication during the forming process in DI cans, DR (or DRD) cans, etc. Examples of preferred lubricants include fatty acid ester waxes (esters of polyol compounds and fatty acids), silicone waxes, fluorinated waxes, polyolefin waxes such as polyethylene, lanolin waxes, lignite waxes, and microcrystalline waxes. One or more lubricants can be used in combination.

[0110] In coating compositions, other resins may be blended to impart modifications such as flexibility and adhesion to the coating film. Examples of other resins include amorphous polyesters, crystalline polyesters, ethylene-polymerizable unsaturated carboxylic acid copolymers, and ethylene-polymerizable carboxylic acid copolymer ionomers. By blending at least one resin selected from these, it is sometimes possible to further impart flexibility and / or adhesion to the coating film.

[0111] The coating composition can be applied to metal sheets using known coating methods such as roller coating or spray coating. The coating film thickness is not particularly limited, but a dried film thickness of 3–18 μm is preferred, and more preferably, 5–15 μm. The sintering conditions for the coating film are typically in the range of approximately 120–260°C for approximately 5 seconds to 30 minutes, and more preferably, in the range of approximately 140–240°C for approximately 10 seconds to 20 minutes.

[0112] Coating

[0113] The coating of the present invention contains at least the above-described coating composition. Specifically, the coating refers to a polyester resin layer formed by applying the coating composition of the present invention to a substrate. The coating may also be configured such that a coating layer made of a resin other than the polyester resin of the present invention overlaps with either the upper or lower surface of the polyester resin layer. That is, the present invention includes laminated structures such as substrate / polyester resin layer, substrate / coating layer / polyester resin layer, substrate / polyester resin layer / coating layer, and substrate / coating layer / polyester resin layer / coating layer.

[0114] Metal Can

[0115] The metal can of the present invention has at least the aforementioned coating. The metal can, for example, can be obtained by forming a coating on one or both sides of a metal sheet made of a metal material suitable for beverage cans, canned goods, can lids, caps, etc., and, if necessary, also on the end faces. Examples of such metal materials include tinplate, stainless steel, and aluminum. The metal sheet made of these metal materials can also be a metal sheet that has undergone a surface treatment based on phosphoric acid treatment, chromate treatment, chromate phosphate treatment, or other rust-inhibiting agents to improve the adhesion of the coating.

[0116] The polyester resin of the present invention can be powder coated using a known pulverization method. Examples of known pulverization methods include, for instance, the pulverization method. In the pulverization method, the polyester resin composition of the present invention, a mixture of desired anti-rust pigments and additives, etc., are dry-mixed using a rotary mixer, Henschel mixer, or similar mixer, and then melt-mixed using a compounding mill. Examples of compounding mills include, for instance, a single-shaft or twin-shaft extruder, a three-roll extruder, a Labo Plastomill, or other common compounding mills. The compound is cooled and solidified, and the solidified material is coarsely and finely pulverized to obtain a powdered material. Examples of compounding mills include, for instance, an airflow pulverizer that utilizes supersonic airflow for pulverization, and an impact pulverizer that introduces and pulverizes the solidified material into the space formed between a high-speed rotating rotor and a stationary rotor. Furthermore, additives can be added to the powdered material as needed. The powdered material is graded, and the powder is adjusted to a desired particle size and particle size distribution to obtain a powder coating composition. Grading can be performed using known classifiers that remove excessively finely pulverized toner master particles through centrifugal force and wind grading, such as rotary wind classifiers.

[0117] This application claims the benefit of priority based on Japanese Patent Application No. 2024-013100, filed on January 31, 2024. This application incorporates the entire contents of the specification of Japanese Patent Application No. 2024-013100, filed on January 31, 2024.

[0118] Example

[0119] The following examples illustrate the present invention in detail, but the present invention is not limited by the following examples. Of course, it can be implemented with appropriate modifications within the scope of the foregoing and following spirit, and all such modifications are included within the technical scope of the present invention. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0120] (1) Determination of resin composition

[0121] The polyester resin sample was dissolved in deuterated chloroform and analyzed using a Bruner AVANCE-NEO600 nuclear magnetic resonance (NMR) instrument. 1 H-NMR analysis or 13 C-NMR analysis. The molar ratio is determined from the ratio of their integral values.

[0122] (2) Determination of specific viscosity (unit: dl / g)

[0123] 0.1 g of the polyester resin sample was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4), and the viscosity was measured using an Ubbelohde viscometer at 30 °C. In the evaluation described later in (7), this measured value is designated as (X).

[0124] (3) Determination of acid value

[0125] Dissolve 0.2 g of polyester resin sample in 40 ml of chloroform, and titrate with 0.01 N potassium hydroxide ethanol solution to determine the per 10 g of polyester resin. 6 g corresponds to the equivalent amount (eq / ton). Phenolphthalein is used as the indicator.

[0126] (4) Determination of hydroxyl value

[0127] The polyester resin was pulverized and dried under reduced pressure at 50°C for at least 24 hours on a TEFLON (registered trademark) substrate. Then, approximately 0.5 g of the sample was accurately weighed, and 10 ml of acetylation agent (0.5 mol% / L pyridine acetic anhydride solution) was added. The sample was then immersed in a water bath at 95°C or higher for 1.5 hours, followed by the addition of 10 ml of pure water and cooling to room temperature. Titration was then performed with N / 5-NaOH using phenolphthalein as an indicator. The same procedure was performed on a blank control group without adding the sample, and the hydroxyl value (eq / ton) was calculated according to the following formula.

[0128] Hydroxyl value = {(BA) × 0.2 × f × 1000 / W} + Acid value

[0129] (A = titration volume (ml), B = titration volume of blank group (ml), f = factor of N / 5-NaOH, W = weight of sample (g))

[0130] (5) Determination of glass transition temperature (Tg)

[0131] The glass transition temperature (Tg) was determined using a Seiko Instruments DSC-220 differential scanning calorimeter (DSC). A 5 mg sample of polyester resin was placed in an aluminum capped container and sealed. The container was cooled to -50°C using liquid nitrogen and then heated to 200°C at a rate of 20°C / min. In the endothermic curve obtained during this process, the temperature at the intersection of the baseline before the endothermic peak and the tangent towards the endothermic peak was defined as the glass transition temperature (Tg, unit: °C).

[0132] (6) Determination of number-average molecular weight (Mn), weight-average molecular weight (Mw), and molecular weight distribution (Mw / Mn)

[0133] The polyester resin sample was dissolved and / or diluted in tetrahydrofuran to a resin concentration of approximately 0.5% by weight. The sample filtered through a 0.5 μm PTFE membrane filter was used as the analytical sample. Molecular weight was determined using gel permeation chromatography (GPC) with tetrahydrofuran as the mobile phase and a differential refractometer as the detector. The flow rate was set to 1 mL / min, and the column temperature to 30 °C. Showa Denko KF-802, 804L, and 806L columns were used. Monodisperse polystyrene was used as the molecular weight standard; the portion of the standard polystyrene with a molecular weight less than 1000 was omitted during calculation.

[0134] (7) Evaluation of aggregation

[0135] A 10g sample of polyester resin was placed on TEFLON (registered trademark) and heated at 230°C for 1 hour in a nitrogen atmosphere. The specific viscosity (Y) of the polyester resin after heat treatment was then measured using the same procedure as described above. The determination was performed using the calculated specific viscosity (X) before and after heat treatment (Y), as described below.

[0136] (determination)

[0137] ◎: (X) - (Y) is 0.1 or higher (the viscosity is reduced compared to concentrated viscosity).

[0138] ○: (X) - (Y) is greater than 0.05 and less than 0.1 (slightly less than the viscosity of concentrated viscous material).

[0139] △: (X) - (Y) is greater than 0 and less than 0.05 (the specific viscosity remains almost unchanged).

[0140] ×: (X) - (Y) is less than 0 (the viscosity increases over time, making it easier to gel during polymerization.)

[0141] (8) Determination of gel fraction

[0142] The gel fraction was used as an evaluation index for curability. A coating composition was applied to a copper foil to a thickness of 10 μm after drying. The sample was heated at 200 °C for 10 minutes. The mass of the sample before THF impregnation (X) was 10 cm long and 2.5 cm wide. The mass of the sample after THF impregnation (Y) was defined as the mass of the sample after THF impregnation (Y) after immersion in 60 ml of THF at 25 °C for 1 hour and drying at 100 °C for 10 minutes. The mass of the sample was calculated using the following formula.

[0143] Gel fraction (mass%) = [{(Y) - copper foil mass} / {(X) - copper foil mass}] × 100

[0144] (9) Evaluation of processing

[0145] The obtained test piece was bent 180° with the coating facing outwards. Coating cracks generated at the bend were evaluated by measuring the electrical conductivity. Furthermore, the bending process was performed without any objects being held in between (i.e., 0T). A test substrate (20mm wide, 50mm long, 0.5mm thick) soaked in a 1% NaCl aqueous solution was placed on an aluminum plate electrode (20mm wide, 50mm long, 0.5mm thick). The test piece was placed near the center of the bend, parallel to the 20mm edge of the sponge, in contact with the sponge. A 5.0V DC voltage was applied between the aluminum plate electrode and the uncoated area on the back of the test substrate, and the electrical conductivity was measured. A lower electrical conductivity indicates better bending characteristics.

[0146] (determination)

[0147] ◎: Less than 0.5mA

[0148] ○: Above 0.5mA and below 2.0mA

[0149] ×: 2.0mA or more

[0150] (10) Evaluation of corrosion resistance

[0151] The obtained test piece was placed upright in a stainless steel cup, and an aqueous solution containing 1% by weight of salt and 5% by weight of acetic acid was poured into it until it reached half the height of the test piece. The cup was then placed in a pressure vessel of a steam retort tester (TOMY Industrial Co., Ltd. ES-315) and subjected to a steam retort treatment at 125°C for 90 minutes. Evaluation of the treated film was performed on the steam contact areas, which are typically considered to be exposed to more stringent conditions. The whitening and blistering status of the cured film were visually assessed as described below.

[0152] (determination)

[0153] ◎: Good (no whitening or bubbling)

[0154] 〇: Minor whitening and / or blistering.

[0155] ×: Significant whitening and / or significant blistering.

[0156] <Examples 1-17, Comparative Examples 1-2>

[0157] <Production of Polyester Resin>

[0158] Synthetic example (a)

[0159] 570 parts of dimethyl terephthalate, 14 parts of trimellitic anhydride, 330 parts of 1,2-propanediol, 300 parts of neopentyl glycol, and 0.4 parts of tetrabutyl titanate (hereinafter, sometimes abbreviated as TBT) as a catalyst (0.03 mol% relative to the total acid content) were added to a 3L four-necked flask. The transesterification reaction was carried out while the temperature was slowly increased to 240°C over 3 hours. Then, the temperature was lowered to 160°C, and 100 parts of phthalic acid were added. The esterification reaction was carried out while the temperature was slowly increased to 240°C over 3 hours. After the esterification reaction, the system was slowly depressurized, and the pressure was reduced to 10 mmHg for 1 hour for depressurized polymerization. Simultaneously, the temperature was increased to 240°C, and further late-stage polymerization was carried out under a vacuum of less than 1 mmHg for 90 minutes. When the target molecular weight was reached, the resin was removed to obtain the polyester resin (Synthesis Example (a)).

[0160] Synthetic examples (b) to (s)

[0161] Similar to Synthesis Example (a), Synthesis Examples (b) to (e), (g) to (i), (k) to (m), and (r) produced polyester resins with the following resin compositions by changing only the feed composition through transesterification and esterification reactions.

[0162] In addition, synthetic example (f) was carried out in the same way as synthetic example (a) as transesterification and esterification, except that the late polymerization time was set to 50 minutes to produce polyester resin.

[0163] Synthetic Examples (n) to (p) were polymerized in the same manner as in Synthetic Example (a). After the polycondensation reaction was completed, the mixture was cooled to 220°C under a nitrogen atmosphere, and then a specified amount of trimellitic anhydride was added. The reaction was continued for 30 minutes under a nitrogen atmosphere and at 220°C. After the reaction was completed, the mixture was removed to obtain the polyester resin.

[0164] Synthesis Example (j) produces a polyester resin with the resin composition shown in the table by direct polymerization (omitting the transesterification reaction step in Synthesis Example (a)).

[0165] Synthetic example (q) only carried out transesterification, but gelation occurred when the late polymerization time was 90 minutes. Therefore, the late polymerization time was set to 50 minutes to produce polyester resin.

[0166] Synthesis Example (s) was carried out in the same manner as Synthesis Example (a) with transesterification and esterification reactions, except that the late polymerization time was set to 50 minutes to produce polyester resin.

[0167] <Preparation of Coating Compositions>

[0168] 100 parts (solids content) of the obtained polyester resin were dissolved in cyclohexanone to obtain a polyester resin solution (solids content approximately 40%). Then, relative to 212.5 parts of the polyester resin solution, 25 parts of IPDI-based terminal isocyanate (manufactured by Covestro, DESMODUR VP LS 2078 / 2, 60% by weight solids content) as a curing agent and 0.1 parts of DBTL (dibutyltin dilaurate) as a catalyst were mixed, and the mixture was diluted with cyclohexanone to a viscosity suitable for coating to obtain a coating composition. The gel fraction, processability, and corrosion resistance of the obtained coating composition were evaluated.

[0169] <Preparation of Experimental Pieces (Coatings)>

[0170] The coating composition was coated on one side of a tinplate (JIS G 3303 (2008) SPTE, 70mm × 150mm × 0.3mm) with a dried film thickness of 10±2μm using a rod coater. The coating was then sintered at 200℃ for 10 minutes and used as a test piece (coating film).

[0171] Table 1

[0172]

[0173] Table 2

[0174]

[0175] In Examples 1-17, the coatings containing polyester resin exhibited excellent processability and corrosion resistance.

[0176] On the other hand, in Comparative Example 1, although the glass transition temperature (Tg) was high, the amount of components with three or more functions was low, making it difficult to increase the weight-average molecular weight (Mw). In Comparative Example 1, the low weight-average molecular weight (Mw) of the polyester resin resulted in poor processability of the coating film. Furthermore, due to the low amount of branched components, the reaction sites with the curing agent were insufficient, resulting in a lack of reactivity of the polyester resin with the curing agent and poor corrosion resistance of the coating film.

[0177] In Comparative Example 2, the coating film had poor processability because the polyester resin had a low weight-average molecular weight (Mw).

[0178] Industrial availability

[0179] This invention relates to a polyester resin that exhibits good reactivity with a curing agent and can form a coating film with excellent processability and corrosion resistance. Polyester resin compositions containing the polyester resin of this invention are suitable for various applications. In particular, the polyester resin of this invention can be effectively utilized in the form of coating compositions, adhesive compositions, coating compositions, etc., and is preferably suitable as a main agent in coatings for metal cans containing beverages and food.

Claims

1. A polyester resin, characterized in that, Polycarboxylic acid components and polyol components are used as copolymer components, and the following conditions are met (1) to (3). (1) The glass transition temperature Tg is above 60℃. (2) The weight-average molecular weight Mw is above 50,000. (3) Contains structural units derived from polycarboxylic acids with more than three functions and / or structural units derived from polyols with more than three functions. When all structural units constituting the polyester resin molecular chain are set to 100 mol%, the total contains more than 1.0 mol% of structural units derived from polycarboxylic acids with more than three functions and structural units derived from polyols with more than three functions.

2. The polyester resin according to claim 1, wherein, The polycarboxylic acid with three or more functions is selected from one or more of the group consisting of trimellitic acid, pyromellitic acid, 1,3,5-benzotriic acid, benzophenone tetracarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(triellitic anhydride), and 1,2,3,4-butanetetracarboxylic acid. The polyol with three or more functions is selected from one or more of the group consisting of glycerol, trimethylolethane, trimethylolpropane and pentaerythritol.

3. The polyester resin according to claim 1, wherein, The polycarboxylic acid component contains structural units derived from aromatic dicarboxylic acids.

4. The polyester resin according to claim 3, wherein, When the structural units derived from aromatic dicarboxylic acids constituting the polyester resin molecular chain are set at 100 mol%, the total content includes more than 1 mol% of structural units derived from at least one component selected from the group consisting of isophthalic acid, phthalic 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, and 2,7-naphthalenedicarboxylic acid.

5. The polyester resin according to claim 3, wherein, When the structural units derived from polycarboxylic acids constituting the polyester resin molecular chain are set at 100 mol%, the resin contains more than 60 mol% structural units derived from aromatic dicarboxylic acids.

6. The polyester resin according to claim 3, wherein, The aromatic dicarboxylic acid contains at least one selected from the group consisting of terephthalic acid, 2,5-furandicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. When the structural units derived from aromatic dicarboxylic acids constituting the polyester resin molecular chain are set at 100 mol%, the total content is more than 50 mol% of structural units derived from terephthalic acid, 2,5-furandicarboxylic acid and 2,6-naphthalenedicarboxylic acid.

7. The polyester resin according to claim 1, wherein the acid value is 3 eq / ton or higher.

8. The polyester resin according to claim 1, wherein, When the structural units derived from polyols constituting the polyester resin molecular chain are set at 100 mol%, the product contains more than 50 mol% of structural units derived from diols (a) having one primary hydroxyl group and one secondary hydroxyl group.

9. The polyester resin according to claim 8, wherein, When the structural units derived from polyols constituting the polyester resin molecular chain are set to 100 mol%, the structural units derived from diols (b) other than the diol (a) are 50 mol% or less.

10. The polyester resin according to claim 1, wherein, When the total of the structural units derived from the polycarboxylic acid with three or more functions and the structural units derived from the polyol with three or more functions is set to 100 mol%, the structure contains 60 mol% or more of the structural units derived from the polycarboxylic acid with three or more functions.

11. The polyester resin according to claim 1, wherein, When the structural units derived from polycarboxylic acids constituting the polyester resin molecular chain are set at 100 mol%, the structural units derived from aliphatic dicarboxylic acids and / or alicyclic dicarboxylic acids are less than 20 mol%.

12. A polyester resin composition comprising the polyester resin according to any one of claims 1 to 11 and a curing agent.

13. A coating composition comprising the polyester resin according to any one of claims 1 to 11.

14. A coating film comprising the coating composition of claim 13.

15. A metal can having the coating of claim 14.

16. A method for manufacturing a polyester resin, characterized in that, It has a first step of performing an esterification or transesterification reaction on polycarboxylic acid components and polyol components, followed by a second step of performing a polycondensation reaction. In the first step and / or the second step, when all components of the polyester resin raw material are set to 100 mol%, a total of 1.0 mol% or more of a trifunctional or higher polycarboxylic acid component and / or a trifunctional or higher polyol component are added, wherein the glass transition temperature Tg of the polyester resin is 60°C or higher and the weight-average molecular weight Mw is 50,000 or higher.

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