Polyester resin and metal plate coating compositions

Abstract

To provide a polyester resin having excellent curability, and workability, retort resistance and dent resistance, and a composition for metal plate coating using the same.SOLUTION: A polyester resin contains polyvalent carboxylic acid components and polyhydric alcohol components as copolymerization components, and satisfies the following conditions (i) to (iii). (i) The polyester resin has 10 mol% or more of a polyvalent carboxylic acid component having a furane skeleton among the polyvalent carboxylic acid components constituting the polyester resin. (ii) The number of kinds of the polyhydric alcohol components constitutes the polyester resin is two or more. (iii) The acid value is 70 eq / t or more and 400 eq / t or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester resin and a composition for coating metal sheets. More specifically, the present invention relates to a composition for coating metal sheets which mainly contains a polyester resin having furancarboxylic acid as a copolymerization component, and is particularly excellent in curability, as well as excellent in processability and dent resistance.

Background Art

[0002] Polyester resins are widely used as raw materials for resin compositions used in paints, coating agents, adhesives and the like. Polyester resins are generally composed of polyhydric carboxylic acids and polyhydric alcohols. The selection and combination of polyhydric carboxylic acids and polyhydric alcohols, and the molecular weight can be freely controlled, and the resulting polyester resins are used in various applications including paint applications and adhesive applications.

[0003] In addition, metal cans such as beverage cans and food cans are coated with an organic resin to prevent corrosion of the metal by food (corrosion resistance) and not to impair the flavor and taste of the contents (flavor property). These coatings are required to have processability, corrosion resistance, adhesion to metal materials, and the like.

[0004] Patent Document 1 discloses an acid component consisting of 80 to 100 mol% of an aromatic dicarboxylic acid containing 70 to 95 mol% of terephthalic acid and 0 to 20 mol% of a polybasic acid other than aromatic dicarboxylic acid, and 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol as essential components, wherein the content of 2-methyl-1,3-propanediol is 25 to 50 mol%. A polyester resin obtained by reacting the polyester resin with a glycol component, wherein the total weight of terephthalic acid and 1,4-cyclohexanedimethanol is in the range of 45 to 65 wt% of the polyester resin, it is disclosed that the polyester resin for can coating is excellent in processability and stain resistance.

Prior Art Literature

Patent Literature

[0005] Patent Document 1: Japanese Unexamined Patent Publication No. 2008-81617 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, with the recent diversification of can shapes, the performance requirements for can coatings have become more stringent. The polyester for can coatings described in Patent Document 1 had the problem of not being satisfactory in terms of processability and curability. The object of the present invention is to provide a polyester resin having excellent curability, processability, retort resistance, and dent resistance, and a coating composition using the same. [Means for solving the problem]

[0007] The inventors diligently studied and conducted research to achieve the above objective, resulting in the completion of the present invention. That is, the present invention has the following configurations [1] to

[10] . [1] A polyester resin having polycarboxylic acid and polyhydric alcohol components as copolymers and satisfying the following conditions (i) to (iii). (i) The polyester resin contains 10 mol% or more of the polycarboxylic acid components that have a furan skeleton. (ii) The polyester resin contains two or more polyhydric alcohol components. (iii) The acid value is 70 eq / t or higher and 400 eq / t or lower. [2] The polyester resin according to [1], characterized in that it has a reduced viscosity of 0.2 to 0.8 dl / g, a glass transition temperature of 10°C or higher, and no melting point. [3] The polyester resin according to [1] or [2], wherein the polyhydric alcohol component constituting the polyester resin contains 50 to 90 mol% of aliphatic polyhydric alcohol having a side chain and 10 to 50 mol% of polyhydric alcohol having an alicyclic skeleton. [4] The polyester resin according to [3], wherein the aliphatic polyhydric alcohol having the side chain has 6 or fewer carbon atoms, and the polyhydric alcohol having the alicyclic skeleton has 6 or more carbon atoms constituting the alicyclic skeleton. [5] The polyester resin according to any one of [1] to [4] above, wherein, among the polycarboxylic acid components constituting the polyester resin, in addition to the polycarboxylic acid component having a furan skeleton, there is 5 mol% or more of at least one polycarboxylic acid component selected from aromatic polycarboxylic acids, aliphatic polycarboxylic acids and alicyclic polycarboxylic acids. [6] A polyester resin according to any of [1] to [5] above, for use in coating metal plates. [7] A metal plate coating composition comprising the polyester resin and curing agent described in any of [1] to [6] above, wherein the polyester resin / curing agent is contained in a ratio of 98 / 2 to 50 / 50 (by mass). [8] The metal plate coating composition according to [7], wherein the curing agent is at least one curing agent selected from phenol resins and isocyanate compounds. [9] A laminate having a layer containing a reaction product of a polyester resin and a curing agent as described in any of [1] to [6] above.

[10] A coated metal sheet having the metal sheet coating composition described in [7] or [8] laminated on the surface of the metal sheet.

[11] A can containing the painted metal sheet described in

[10] above as a constituent material. [Effects of the Invention]

[0008] The polyester resin of the present invention has extremely high curability, and the resulting coating film has excellent processability, as well as excellent retort resistance and dent resistance, making it suitable as a material for metal plate coatings such as can paints and pre-coated metal paints. In addition, because the resin contains non-petroleum-derived components, it can contribute to solving environmental problems such as suppressing the increase of carbon dioxide. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below.

[0010] The polyester resin of the present invention is characterized by satisfying the following requirements (i) to (iii).

[0011] <Requirement (i)> Requirement (i) will now be explained. The polyester resin of the present invention must contain 10 mol% or more of the polycarboxylic acid components having a furan skeleton among the polycarboxylic acid components constituting the polyester resin. Preferably, it is 15 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more. Setting it above the lower limit improves the mobility of the polyester resin and also increases its polarity, which improves its reactivity with the curing agent and improves the curability of the polyester resin. Furthermore, sufficient coating performance can be obtained even at low temperatures, which contributes to reducing energy in the painting process. In addition, it contributes greatly to reducing the environmental burden due to the non-petroleum component origin. Furthermore, among the polycarboxylic acid components constituting the polyester resin, the polycarboxylic acid components having a furan skeleton are preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less. Setting it below the upper limit improves the flexibility of the polyester resin and improves its dent resistance.

[0012] The polycarboxylic acid component having a furan skeleton can be any component in which the furan structure is contained within the structure of the compound, and there are no particular restrictions, but examples include franzicarboxylic acid. Specifically, 2,5-franzicarboxylic acid is an example. Furthermore, derivatives of these may be used as raw materials in the production of polyester resins, and examples of derivatives include alkyl esters having 1 to 4 carbon atoms, among which methyl esters, ethyl esters, n-propyl esters, and isopropyl esters are preferred, and methyl esters are more preferred. These carboxylic acids having a furan skeleton and / or derivatives thereof may be used individually or as a mixture of two or more.

[0013] <Requirement (ii)> Requirement (ii) will now be explained. The polyester resin of the present invention must consist of two or more polyhydric alcohol components. Having two or more polyhydric alcohol components improves the flexibility and mobility of the polyester resin and improves its processability. In particular, by using a combination of an aliphatic polyhydric alcohol having a side chain and a polyhydric alcohol having an alicyclic skeleton, the polyester resin is given appropriate flexibility, which, along with improved curability, improves processability, and further improves solubility, thereby improving the stability of the paint.

[0014] <Requirement (iii)> Requirement (iii) will now be explained. The acid value of the polyester resin of the present invention must be 70 eq / t or higher, preferably 75 eq / t or higher, more preferably 80 eq / t or higher, and even more preferably 85 eq / t or higher. Setting it above the lower limit improves adhesion to the substrate and reactivity with curing agents, especially with phenol curing agents, without reducing water resistance, resulting in improved curability and, when using isocyanate curing agents, good dent resistance. Furthermore, it must be 400 eq / t or lower, preferably 370 eq / t or lower, more preferably 350 eq / t or lower, and even more preferably 300 eq / t or lower. If it exceeds the upper limit, there will be a large amount of unreacted compounds having carboxylic acid anhydride groups that impart the acid value, which may reduce processability and / or dent resistance, or reduce retort resistance and / or content resistance.

[0015] <Polyester resin> The polyester resin of the present invention may be imparted with an acid value by any arbitrary method. Imparting an acid value may provide effects such as improved curability resulting from increased reactivity with crosslinking agents and curing agents, and improved adhesion to metal materials for cans. Methods for imparting an acid value include a depolymerization method in which a polycarboxylic acid anhydride is added in the late stage of polycondensation, and a method where a high acid value is achieved at the prepolymer (oligomer) stage, which is then subjected to polycondensation to obtain a polyester resin having an acid value. The former depolymerization method is preferred because it is easy to operate and facilitates obtaining a target acid value.

[0016] Examples of the polycarboxylic acid anhydride used for acid addition in such a depolymerization method include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, and ethylene glycol bisanhydrotrimellitate. Trimellitic anhydride is preferred.

[0017] The polycarboxylic acid anhydride used for the aforementioned acid addition may be a carboxylic acid monoanhydride and a carboxylic acid polyanhydride used each alone, or may be used in combination.

[0018] The glass transition temperature (Tg) of the polyester resin of the present invention is preferably 30°C or higher, more preferably 35°C or higher, still more preferably 40°C or higher, and particularly preferably 45°C or higher. If the Tg is lower than the above lower limit, in addition to dent resistance, retort resistance and / or content resistance may become poor. There is no particular upper limit to the glass transition temperature (Tg), but it is usually 130°C or lower, preferably 100°C or lower, more preferably 90°C or lower, and particularly preferably 70°C or lower. The Tg in the present invention is the T specified in JIS K 7121-1987 ig which is substantially consistent, but strictly speaking, it is a value determined by the method described in the Examples.

[0019] The glass transition temperature (Tg) of the polyester resin of the present invention can be adjusted by changing the copolymerization components and the ratios thereof. For example, as the polycarboxylic acid component constituting the polyester resin, increasing the copolymerization ratio of aromatic polycarboxylic acid or alicyclic polycarboxylic acid tends to increase Tg; and as the polyhydric alcohol component constituting the polyester resin, increasing the copolymerization ratio of alicyclic polyhydric alcohol or aliphatic polyhydric alcohol having a main chain with 3 or less carbon atoms tends to increase Tg. On the other hand, increasing the copolymerization ratio of aliphatic polycarboxylic acid as the polycarboxylic acid component constituting the polyester resin tends to decrease Tg, and increasing the copolymerization ratio of aliphatic polyhydric alcohol having a main chain with 4 or more carbon atoms as the polyhydric alcohol component constituting the polyester resin tends to decrease Tg.

[0020] The reduced viscosity of the polyester resin of the present invention is preferably 0.2 to 0.8 dl / g, more preferably 0.25 to 0.75 dl / g, still more preferably 0.3 to 0.7 dl / g, and particularly preferably 0.35 to 0.6 dl / g. If the reduced viscosity is less than 0.2 dl / g, curability becomes insufficient, and the toughness of the coating film is insufficient, which may reduce workability. On the other hand, if the reduced viscosity exceeds 0.8 dl / g, solvent solubility decreases, which may lead to reduced coating stability and deteriorated coating workability. The reduced viscosity can be adjusted by changing the polymerization time and temperature of the polyester resin, and the degree of pressure reduction during polymerization (in the case of reduced-pressure polymerization). The reduced viscosity in the present invention is a value determined by the method described in the Examples.

[0021] It is preferable that the polyester resin of the present invention has no melting point. Specifically, using a differential scanning calorimeter (DSC), the temperature is increased from -100°C to 250°C at a rate of 20°C / min, and it is preferable that no clear melting peak is exhibited during the temperature increase process. The absence of a melting point improves the stability when dissolved in a solvent. If the polyester resin exhibits a melting point and has crystallinity, solvent solubility and / or coating stability may decrease, and workability and / or dent resistance may deteriorate.

[0022] As described above, the polyester resin of the present invention contains 10 mol% or more of a polycarboxylic acid component having a furan skeleton as a polycarboxylic acid component. In addition to the polycarboxylic acid component having a furan skeleton, it is preferable that the polyester resin of the present invention contains 5 mol% or more of at least one polycarboxylic acid component selected from aromatic polycarboxylic acids, aliphatic polycarboxylic acids, and alicyclic polycarboxylic acids, in addition to the polycarboxylic acid component having a furan skeleton. It is more preferable that it contains 10 mol or more, even more preferable that it contains 20 mol or more, and particularly preferable that it contains 30 mol or more. By setting the value above the lower limit, the solubility of the polyester resin is improved and the workability is improved.

[0023] Examples of polycarboxylic acid components other than those having a furan skeleton include aromatic polycarboxylic acid components such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5-[4-sulfophenoxy]isophthalic acid and alkali metal salts thereof; aliphatic polycarboxylic acid components such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedionic acid, dimer acid, fumaric acid, maleic acid, itaconic acid, and citraconic acid; and alicyclic polycarboxylic acid components such as 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, and 2,5-norbornanedicarboxylic acid. One or more of these can be used. Among these, aromatic polycarboxylic acid components are preferred from the viewpoint of reactivity, water resistance, and heat resistance, and terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid are particularly preferred.

[0024] The polyhydric alcohol component constituting the polyester resin of the present invention is composed of two or more different components as described in <Requirement (ii)> above. In particular, by using a combination of an aliphatic polyhydric alcohol having a side chain and a polyhydric alcohol having an alicyclic skeleton, the polyester resin is given appropriate flexibility, and together with improved curability, processability is improved, and furthermore, solubility is improved, thereby improving the stability as a paint.

[0025] Examples of aliphatic polyhydric alcohols having side chains include 1,2-propylene glycol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 1,4-pentanediol, 1,3-pentanediol, 1,2-hexanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, and 4-propyl-1,8-octanediol. It is preferable that the aliphatic polyhydric alcohol having side chains has 6 or fewer carbon atoms. By limiting the number of carbon atoms to 6 or fewer, flexibility can be imparted to the polyester resin without reducing the resin's cohesive strength, improving processability and retort resistance. In particular, 2-methyl-1,3-propanediol is preferred as an aliphatic polyhydric alcohol having a side chain with 6 or fewer carbon atoms. Of the total polyhydric alcohol components constituting the polyester resin of the present invention, the aliphatic polyhydric alcohol having a side chain is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more. Furthermore, 85 mol% or less is preferred, and 80 mol% or less is more preferred. Keeping it within the above range results in good processability and / or dent resistance.

[0026] Examples of polyhydric alcohols having an alicyclic skeleton include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane glycols, and hydrolyzed bisphenols. It is preferable that the alicyclic skeleton of the polyhydric alcohol has 6 or more carbon atoms. Having 6 or more carbon atoms in the alicyclic skeleton improves the flexibility of the resin, as well as its processability and dent resistance. In particular, it is preferable to use 1,4-cyclohexanedimethanol as the polyhydric alcohol having an alicyclic skeleton with 6 or more carbon atoms. Of the total polyhydric alcohol components constituting the polyester resin of the present invention, the amount of polyhydric alcohol having an alicyclic skeleton is preferably 10 mol% or more, more preferably 20 mol% or more. It is also preferable that it be 50 mol% or less, and more preferably 40 mol% or less. If it is less than the above, dent resistance, retort resistance, and / or content resistance may decrease, and if it exceeds the above, processability and / or dent resistance may decrease, or the crystallinity of the polyester resin may increase, leading to decreased solvent solubility and / or paint stability.

[0027] The polyhydric alcohol component constituting the polyester resin of the present invention may include polyhydric alcohol components other than aliphatic polyhydric alcohols having side chains and polyhydric alcohols having an alicyclic skeleton. Examples include linear aliphatic glycols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,9-nonanediol, and polyether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Two or more of these can be selected and used.

[0028] In the polyester resin of the present invention, a polycarboxylic acid component and / or a polyhydric alcohol component may be copolymerized with a trifunctional or higher component. Examples of trifunctional or higher polycarboxylic acid components include trimellitic acid, pyromellitic acid, and benzophenonetetracarboxylic acid, while examples of trifunctional or higher polyhydric alcohol components include glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, pentaerythritol, and α-methylglucoside. By using these, the crosslinking density after curing can be increased, and processability can be improved. In particular, from the viewpoint of crosslinking density after curing and processability, it is preferable to use trimellitic acid or trimethylolpropane.

[0029] When copolymerizing a polycarboxylic acid component with three or more functions and / or a polyhydric alcohol component, the copolymerization ratio is preferably 0.1 to 5 mol%, more preferably 0.1 to 4 mol%, even more preferably 0.1 to 3 mol%, and particularly preferably 0.1 to 2 mol% of the polycarboxylic acid component or polyhydric alcohol component. Exceeding the above upper limit may result in loss of flexibility of the polyester resin, reduced processability and / or dent resistance, or gelation during the polymerization of the polyester.

[0030] The polyester resin of the present invention may be given an acid value by any method. By giving an acid value, effects such as improved curability with curing agents and improved adhesion with metal materials for cans may be obtained. Methods for giving an acid value include a depolymerization method in which a polycarboxylic acid anhydride is added in the later stages of polycondensation, and a method in which the prepolymer (oligomer) is given a high acid value and then polycondensed to obtain a polyester resin with an acid value. However, the former depolymerization method is preferred because it is easy to operate and it is easy to obtain the target acid value.

[0031] Examples of polycarboxylic acid anhydrides used for acid addition in this depolymerization method include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, pyromelitic anhydride, hexahydrophthalic anhydride, and ethylene glycol bis-anhydrotrimellitate. Trimellitic anhydride is preferred.

[0032] When producing the polyester resin of the present invention, a polymerization catalyst such as titanium compounds including tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetylacetonate; antimony compounds including antimony trioxide and tributoxyantimony; germanium compounds including germanium oxide and tetra-n-butoxygermanium; and acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum can be used. One or more of these catalysts can be used in combination.

[0033] The polymerization condensation reaction method for producing the polyester resin of the present invention is not particularly limited, but examples include: 1) a method of heating a polycarboxylic acid and a polyhydric alcohol in the presence of any catalyst, and carrying out a dehydration esterification step followed by a depolyhydric alcohol-polycondensation reaction; and 2) a method of heating an alcohol ester of a polycarboxylic acid and a polyhydric alcohol in the presence of any catalyst, and carrying out a transesterification reaction followed by a depolyhydric alcohol-polycondensation reaction. In methods 1) and 2), some or all of the polycarboxylic acid component may be substituted with an acid anhydride. Furthermore, various additives, stabilizers, etc., may be added to the extent that they do not impair the inherent properties of other thermoplastic resins, depending on the intended use and the various properties required.

[0034] The polyester resin of the present invention may optionally contain antioxidants, UV absorbers, stabilizers, etc. While not particularly limited, examples of hindered phenols include 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 1,1,3-tri(4-hydroxy-2-methyl-5-t-butylphenyl)butane, 1,1-bis(3-t-butyl-6-methyl-4-hydroxyphenyl)butane, 3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid, and pentaerythritol tetrakis(3,5-di-t- Examples include butyl-4-hydroxyphenyl)propionate, and while not particularly limited, phosphorus-based materials include, for example, 3,9-bis(p-nonylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, tri(mononylphenyl)phosphite, triphenoxyphosphine, and isodecylphosphite. These can be used individually or in combination. The amount added is preferably 0.1% by mass or more and 5% by mass or less based on the mass of the polyester resin. If it is less than 0.1% by mass, the effect of preventing thermal degradation may be poor. If it exceeds 5% by mass, it may adversely affect the color tone.

[0035] <Composition for coating metal plates> The metal plate coating composition of the present invention is a composition containing the polyester resin of the present invention, and more preferably contains a curing agent. The ratio of polyester resin to curing agent is preferably polyester resin / curing agent = 98 / 2 to 50 / 50 (mass ratio), more preferably 95 / 5 to 60 / 40 (mass ratio), even more preferably 92 / 8 to 70 / 30 (mass ratio), and particularly preferably 90 / 10 to 75 / 25 (mass ratio). If the amount of curing agent is less than 2 parts by mass per 98 parts by mass of polyester resin, sufficient curing may not be obtained, and processability, retort resistance, content resistance and / or dent resistance may decrease. If the amount of curing agent exceeds 50 parts by mass per 50 parts by mass of polyester resin, unreacted curing agent components may remain, and dent resistance, retort resistance and content resistance may decrease.

[0036] <Hardening agent> The curing agent constituting the metal plate coating composition of the present invention is not particularly limited as long as it reacts with the polyester resin of the present invention to form a crosslinked structure, but examples include isocyanate compounds, phenolic resins, amino resins, epoxy resins, etc. Among these, phenolic resins and isocyanate compounds are preferred from the viewpoint of hygiene and processability. Furthermore, blocked isocyanate compounds are even more preferred.

[0037] Examples of the isocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, tetramethylxylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, and 2-nitrodiphenyl Nyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropanediisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl Examples of diisocyanates include aromatic diisocyanates such as -4,4'-diisocyanate, aromatic polyisocyanates such as polymethylene polyisocyanate and crude tolylene diisocyanate, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), decamethylene diisocyanate, and lysine diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated diphenylmethane diisocyanate, as well as biuret derivatives, uretdione derivatives, carbodiimide derivatives, isocyanurate derivatives, uretonimine derivatives, adduct derivatives with polyols, and mixed derivatives thereof. One or more of these can be selected and used. Furthermore, it can also be used in the form of urethane precursors such as prepolymers, modified products, derivatives, and mixtures consisting of isocyanate compounds and active hydrogen compounds such as polyols and polyamines.

[0038] As the isocyanate compound, it is preferable to use a blocked isocyanate compound obtained by blocking the terminal NCO group of an isocyanate compound. Suitable blocking 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 dityl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; and acetanilic acid. Examples include acid amide compounds such as acetic acid amide, lactam compounds such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam, imidazole compounds such as imidazole and 2-methylimidazole, urea compounds such as urea, thiourea, and ethyleneurea, oxime compounds such as formamide oxime, acetaldehyde oxime, acetone oxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, and cyclohexanone oxime, and amine compounds such as diphenylaniline, aniline, carbazole, ethyleneimine, and polyethyleneimine. These can be used individually or in combination.

[0039] The reaction between such a blocking agent and the isocyanate curing agent component can be carried out, for example, at 20 to 200°C, using known inert solvents or catalysts as needed. It is preferable to use 0.7 to 1.5 times the molar amount of the blocking agent relative to the terminal isocyanate group.

[0040] The phenolic resin is preferably a resol-type phenolic resin synthesized from a phenolic compound. Examples of trifunctional or more functional phenolic compounds include phenol, m-cresol, m-ethylphenol, 3,5-xylenol, m-methoxyphenol, bisphenol-A, and bisphenol-F. Examples of bifunctional phenolic compounds include o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol. These have two or more functional groups capable of methylolation per molecule of phenolic compound and can be synthesized by methylolation with formaldehyde or the like. These can be used individually or as a mixture of two or more.

[0041] The blending ratio of these trifunctional or higher phenolic compounds to the bifunctional phenolic compounds is arbitrarily determined according to the required coating film (cured film), but it is preferably 1 / 99 to 100 / 0 (parts by mass). For example, when hardness and acid resistance are required for the coating film, it is preferable to use more than 30 parts by mass of the trifunctional or higher phenolic compound, and when flexibility is required for the coating film and residual stress after processing is to be low, it is preferable to use less than 50 parts by mass of the trifunctional or higher phenolic compound.

[0042] Examples of formaldehydes used when these phenolic compounds are used to make phenolic resins include formaldehyde, paraformaldehyde, or trioxane, and can be used individually or in combination of two or more.

[0043] As the alcohol used to alkyl etherify some of the methylol groups in the methylolated phenol resin, a monohydric alcohol having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, can be used. Examples include methanol, ethanol, n-propanol, n-butanol, isopropanol, isobutanol, and tert-butanol. From the viewpoint of compatibility with polyester resin and reaction curing properties, n-butanol is preferred.

[0044] The phenolic resin has an average of 0.3 or more, preferably 0.5 to 3, alkoxymethyl groups per phenolic nucleus, in terms of reactivity and compatibility with the polyester resin. If the number is less than 0.3, the curing properties with the polyester resin will be poor, and the processability may decrease.

[0045] As a method for obtaining a phenolic resin containing a mixture of these trifunctional or more phenolic compounds and bifunctional phenolic compounds, one may mix them in any ratio before phenolic resinification with formaldehydes, or one may separately phenolic resinify the trifunctional or more phenolic compounds and the bifunctional phenolic compounds, and then mix them in any ratio before using the resulting mixture.

[0046] Examples of amino resins include methylolated amino resins obtained by the reaction of amino components such as melamine, urea, benzoguanamine, acetoganamine, steroguanamine, spiloganamine, and dicyandiamide with aldehyde components such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Amino resins obtained by etherifying the methylol group of these methylolated amino resins with an alcohol having 1 to 6 carbon atoms are also included in the above-mentioned amino resins. These can be used individually or in combination of two or more. Amino resins using benzoguanamine or melamine are preferred.

[0047] Preferred amino resins using benzoguanamine include methyl etherified benzoguanamine resin, in which some or all of the methylol groups of methylolated benzoguanamine resin are etherified with methyl alcohol; butyl etherified benzoguanamine resin, in which some or all of the methylol groups of methylolated benzoguanamine resin are etherified with butyl alcohol; or mixed etherified benzoguanamine resin with methyl ether and butyl ether, in which some or all of the methylol groups of methylolated benzoguanamine resin are etherified with methyl alcohol and butyl alcohol. Isobutyl alcohol and n-butyl alcohol are preferred as the butyl alcohol.

[0048] As amino resins using melamine, methyl etherified melamine resins in which some or all of the methylol groups of methylolated melamine resin are etherified with methyl alcohol, butyl etherified melamine resins in which some or all of the methylol groups of methylolated melamine resin are etherified with butyl alcohol, or mixed etherified melamine resins of methyl ether and butyl ether are etherified with both methyl alcohol and butyl alcohol.

[0049] <Additives> The metal plate coating composition of the present invention preferably further contains a catalyst. The inclusion of a catalyst improves the performance of the cured film. Examples of catalysts when the curing agent is a phenolic resin or amino resin include sulfuric acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphor sulfonic acid, phosphoric acid, and amine-blocked versions of these (with added amine for partial neutralization). One or more of these can be used in combination. Dodecylbenzenesulfonic acid and its neutralized form are preferred due to their compatibility with polyester resins and hygienic properties. When the curing agent is an isocyanate compound, examples include organotin compounds such as stannous octylate and dibutyltin dilaurate, triethylamine, zinc compounds, and aluminum compounds. One or more of these can be used in combination.

[0050] The metal plate coating composition of the present invention may be formulated with known inorganic pigments such as titanium dioxide and silica, known additives such as phosphoric acid and its esters, surface smoothers, defoamers, dispersants, and lubricants, according to the required properties. In particular, lubricants are important for providing the lubricity of the coating film required during the molding of DI cans and DR (or DRD) cans, etc. Suitable lubricants include fatty acid ester waxes, which are esters of polyol compounds and fatty acids, silicone waxes, fluorine waxes, polyolefin waxes such as polyethylene, lanolin waxes, montan waxes, microcrystalline waxes, and carnauba wax. One or more lubricants can be used in combination.

[0051] The metal plate coating composition of the present invention can be made into a paint when dissolved in a known organic solvent. Examples of organic solvents used for paint formation 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 are selected and used, taking into consideration solubility, evaporation rate, etc.

[0052] The metal plate coating composition of the present invention may contain other resins for the purpose of modifying the coating film, such as by imparting flexibility and adhesion. Examples of other resins include ethylene-polymerizable unsaturated carboxylic acid copolymers and ethylene-polymerizable carboxylic acid copolymer ionomers, and by incorporating at least one resin selected from these, flexibility and / or adhesion of the coating film may be imparted.

[0053] The metal plate coating composition of the present invention can be applied to various known substrates. The substrates are not particularly limited and include, for example, tinplate steel, tinplate, bonded steel, galvanized steel, aluminum, and stainless steel. Metal plates made of these metal materials may be used that have been pre-treated with phosphate treatment, chromate treatment, phosphate treatment, or other rust-preventive treatments, or surface treatments aimed at improving the adhesion of the coating film.

[0054] The method of coating the substrate is not particularly limited and includes, for example, bar coating, curtain flow, roll coating, dipping, spraying, and brush coating. The amount of coating is not particularly limited, but the thickness of the coating film after drying is usually adjusted to about 1 to 30 μm, preferably about 5 to 15 μm.

[0055] The baking conditions for the coating film are typically in the range of approximately 100 to 300°C for about 5 seconds to about 30 minutes, and more preferably in the range of approximately 150 to 250°C for about 20 seconds to about 15 minutes.

[0056] The metal sheet coating composition of the present invention can be laminated onto the surface of a metal sheet and suitably used as a painted metal sheet. The painted metal sheet can be used as a component material for cans, and cans containing the painted metal sheet as a component material include beverage cans, canned food cans, and their lids or caps. [Examples]

[0057] 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 refers to parts by mass, and % refers to mass percent.

[0058] <Polyester resin> (1) Measurement of resin composition Polyester resin samples were dissolved in deuterated chloroform and subjected to 1H-NMR analysis using a VARIAN 400-MR nuclear magnetic resonance (NMR) spectrometer. The molar ratio was determined from the ratio of the integrated values.

[0059] (2) Measurement of reduced viscosity (ηsp / c, unit: dl / g) A 0.1 g sample of polyester resin was dissolved in 25 cc of a phenol / tetrachloroethane mixed solvent (mass ratio 6 / 4) and measured at 30°C.

[0060] (3) Measurement of glass transition temperature (Tg) and melting point (Tm) Measurements were taken using a differential scanning calorimeter (SII, DSC-200). A 5 mg sample of polyester resin was placed in an aluminum container with a retaining lid, sealed, cooled to -50°C using liquid nitrogen, and then heated to 250°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 line toward the endothermic peak was defined as the glass transition temperature (Tg, in °C). The maximum peak temperature of the heat of fusion was defined as the melting point (Tm, in °C). If no maximum peak of heat of fusion was observed, the melting point was considered to be absent (indicated as "-" in Table 1).

[0061] (4) Measurement of acid value Dissolve 0.2 g of polyester resin sample in 40 ml of chloroform and titrate with 0.01 N potassium hydroxide ethanol solution. 6 The equivalent weight per gram (eq / t) was calculated. Phenolphthalein was used as the indicator.

[0062] <Preparation of compositions for metal plate coatings> According to the formulations shown in Table 2, the polyester resin, curing agent, and catalyst were dissolved in cyclohexanone / Solvesso-150 at a ratio of 1 / 1 (by mass) to obtain a solid content of approximately 35% by mass, thereby obtaining a metal plate coating composition.

[0063] (5) Evaluation of hardening properties The curability of the polyester resin was evaluated by applying a metal plate coating composition onto copper foil to a dry thickness of 10 μm, curing and baking under conditions of 200°C (PMT: maximum substrate temperature) for 10 minutes or 190°C (PMT: maximum substrate temperature) for 30 seconds, and measuring 10 cm in length and 2.5 cm in width. The mass of the sample before immersion in THF (tetrahydrofuran) was (X), and the mass of the sample after immersion in 60 ml of THF at 25°C for 1 hour, followed by drying at 100°C for 10 minutes was (Y), and the following formula was used to determine the mass. Gel fraction (mass%) = [{(Y)-copper foil mass} / {(X)-copper foil mass}]×100 (judgement) ○: Gel fraction of 85% by mass or more △: Gel fraction is 76% by mass or more and less than 85% by mass. ×: Gel fraction less than 76% by mass

[0064] <Preparation of test specimens> The metal plate coating composition was applied to one side of a tinplate (JIS G 3303 (2008) SPTE, 70 mm × 150 mm × 0.3 mm) using a bar coater to achieve a dry film thickness of 10 ± 2 μm. The plate was then cured and baked at 200°C (PMT: maximum temperature reached by the substrate) for 10 minutes or at 190°C (PMT: maximum temperature reached by the substrate) for 30 seconds, and this was used as a test specimen (hereinafter referred to as the test specimen).

[0065] (6) Evaluation of processability The aforementioned test specimen was bent 180° in the direction where the hardened film faces outward, and the cracking of the hardened film occurring at the bend was evaluated by measuring the current flow. The bending was performed without anything being inserted between the specimen and the specimen (so-called 0T). An aluminum plate electrode (20mm wide, 50mm deep, 0.5mm thick) was placed on top of a sponge (20mm wide, 50mm deep, 10mm thick) soaked in a 1% NaCl aqueous solution, and the central part of the bend of the test specimen was brought into contact with the sponge so as to be parallel to the 20mm side of the sponge. A DC voltage of 5.0V was applied between the aluminum plate electrode and the unpainted area on the back of the test specimen, and the current flow was measured. A smaller current flow indicates better bending characteristics. (judgement) ○: Less than 0.5mA △: 0.5mA or more and less than 2.0mA ×: 2.0mA or more

[0066] (7) Evaluation of retort resistance The aforementioned test specimen was placed upright in a stainless steel cup, and deionized water was poured into it until it reached half the height of the specimen. This was then placed in the pressure vessel of a retort testing machine (ES-315, manufactured by Tommy Industries Co., Ltd.) and subjected to retort treatment at 125°C for 30 minutes. Post-treatment evaluation was performed on the steam contact area, which is generally expected to be subjected to more severe conditions for the cured film, and the whitening and blistering of the cured film were visually judged as follows. (judgement) ○: Good (No whitening or blistering / Slight whitening but no blistering) △: Slight whitening and / or slight blistering present. ×: Significant whitening and / or significant blistering present.

[0067] (8) Evaluation of dent resistance Using a DuPont impact tester, the painted side of the retort-treated specimen (as shown in (7)) was placed face down, and a 1 / 2-inch diameter spherical impact punch was pressed against the unpainted surface of the vapor-contact portion of the specimen. A 1 kg weight was then dropped from a height of 50 cm to apply impact. Next, a sponge (20 mm wide, 50 mm deep, 10 mm thick) soaked in a 1 mass% NaCl aqueous solution was placed on top of an aluminum plate electrode (20 mm wide, 50 mm deep, 0.5 mm thick). The convex portion of the impacted specimen was brought into contact with the sponge, and a 5.0 V DC voltage was applied between the aluminum plate electrode and the unpainted back surface of the specimen. The current flow value was measured. A smaller current flow value indicates better bending characteristics. (judgement) ○: Less than 0.5mA △: 0.5mA or more and less than 2.0mA ×: 2.0mA or more

[0068] Examples of polyester resin synthesis Synthesis of polyester resin (Synthesis Example 1) In a 3L flask equipped with a stirrer, condenser, and thermometer, 250 parts by mass of 2,5-franzicarboxylic acid, 427 parts by mass of isophthalic acid, 8 parts by mass of trimellitic anhydride, 622 parts by mass of 2-methyl-1,3-propanediol, 219 parts by mass of 1,4-cyclohexanedimethanol, and 0.3 parts by mass of tetra-n-butyl titanate (hereinafter sometimes abbreviated as TBT) as a catalyst (0.02 mol% of the total polycarboxylic acid components) were charged, and the esterification reaction was carried out while raising the temperature from 160°C to 235°C over 4 hours. Next, the pressure in the system was gradually reduced, and initial polymerization was carried out by reducing the pressure to 5 mmHg over 20 minutes, while the temperature was raised to 250°C, and further late polymerization was carried out for 80 minutes under a vacuum of 1 mmHg or less. Once the target molecular weight was reached, it was cooled to 220°C under a nitrogen atmosphere. Next, 8 parts by mass of trimellitic anhydride were added, and stirring was continued for 30 minutes at 200-230°C under a nitrogen atmosphere to obtain a polyester resin (Synthesis Example 1). The reduced viscosity of the obtained polyester resin was 0.52 dl / g, the acid value was 110 eq / t, the glass transition temperature (Tg) was 53°C, and no melting point was observed.

[0069] Synthesis of polyester resin (synthesis example 2), (comparative synthesis example 1) to (comparative synthesis example 5) Similar to (Synthesis Example 1), but with a different composition, polyester resins (Synthesis Example 2), (Comparative Synthesis Examples 1) to (Comparative Synthesis Examples 5) were produced with resin compositions as shown in Table 1.

[0070] [Table 1]

[0071] The obtained polyester resin was used to prepare a metal plate coating composition, and its curability, processability, retort resistance, and dent resistance were evaluated. The formulation of the metal plate coating composition and the evaluation results are shown in Table 2.

[0072] The following were used as hardening agents. Phenodur PR521: Manufactured by Ornex, phenolic curing agent. Desmodur BL 2078 / 2: Manufactured by Sumika Covestro Urethane Co., Ltd., isophorone diisocyanate-based blocked isocyanate.

[0073] The following were used as curing catalysts. Nacure5076: Dodecylbenzenesulfonic acid, manufactured by King Industries. K-KAT XK-626: Non-tin urethane curing catalyst manufactured by King Industries.

[0074] [Table 2]

[0075] As is clear from Table 2, in Examples 1 and 2, which used phenolic resin as the curing agent, the curing performance was better than in Comparative Examples 1 and 2, which used polyester resin without a furan skeleton, and the processability / retort resistance and dent resistance were also improved. In Comparative Example 3, the acid value of the polyester resin was low, resulting in poor reactivity with the phenolic resin and insufficient curing performance. In Comparative Example 4, the acid value of the polyester resin was high, resulting in insufficient processability / retort resistance / dent resistance. In Examples 3 and 4, which used isocyanate-based curing agents, the curing performance was excellent, and the processability / retort resistance / dent resistance were all good. In contrast, in Comparative Example 5, which used polyester resin without a furan skeleton, the curing performance and dent resistance were insufficient. In Comparative Example 6, the acid value of the polyester resin was low, resulting in poor reactivity with the isocyanate curing agent and weak coating strength, thus insufficient dent resistance. Furthermore, in Comparative Example 7, which used a polyester resin with only one type of glycol, the polyester resin exhibited a melting point and insufficient solubility in the solvent, making it impossible to dissolve it in the solvent and evaluate the coating performance. Thus, the metal plate coating composition using the polyester resin of the present invention exhibits excellent reactivity with the curing agent, and the resulting cured film (coating film) has excellent processability, retort resistance, and dent resistance. [Industrial applicability]

[0076] The present invention relates to a polyester resin with excellent curability, processability, retort resistance, and dent resistance, as well as a metal plate coating composition and painted metal plate containing the same, and is suitable as a main component in metal plate coating compositions used for metal cans for food and beverages and pre-coated metal coatings.

Claims

1. A polyester resin having a polycarboxylic acid component and a polyhydric alcohol component as copolymer components, satisfying the following conditions (i) to (v). (i) The polyester resin contains 30 to 80 mol% of the frangic acid component among the polycarboxylic acid components. (ii) The polyester resin contains 50 to 90 mol% of an acyclic aliphatic dihydric alcohol having a side chain, and 10 to 50 mol% of a polyhydric alcohol having an alicyclic skeleton, wherein the polyhydric alcohol having an alicyclic skeleton does not contain an aromatic ring. (iii) The acid value is 70 eq / t or higher and 400 eq / t or lower. (iv) Contains a polycarboxylic acid component with three or more functionalities and / or a polyol component with three or more functionalities, When a polycarboxylic acid component with three or more functions is contained, the polycarboxylic acid component with three or more functions is present in an amount of 0.1 to 5 mol% of the polycarboxylic acid component constituting the polyester resin. When a polyhydric alcohol component with three or more functions is included, the amount of the polyhydric alcohol component with three or more functions is 0.1 to 5 mol% of the polyhydric alcohol component constituting the polyester resin. (v) Among the polycarboxylic acid components constituting the polyester resin, in addition to the frangic acid component, there is at least 20 mol% or more of one polycarboxylic acid component selected from aromatic polycarboxylic acids, aliphatic polycarboxylic acids, and alicyclic polycarboxylic acids.

2. The polyester resin according to claim 1, wherein, in (v) above, the polyester resin comprises 20 mol% or more of aromatic polycarboxylic acid in addition to the frangic acid component.

3. The polyester resin according to claim 1, wherein, in (v), the polyester resin comprises 30 mol% or more of aromatic polycarboxylic acid in addition to the frangic acid component.

4. The polyester resin according to claim 3, wherein the aromatic polycarboxylic acid other than the frangic acid component is at least one selected from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

5. The polyester resin according to claim 4, wherein the aromatic polycarboxylic acid other than the frangic acid component is at least one selected from terephthalic acid and isophthalic acid.

6. The polyester resin according to claim 1, wherein in (iv) above, the component comprises a trifunctional or polyhydric carboxylic acid component or a trifunctional or polyhydric alcohol component.

7. The polyester resin according to claim 1, wherein the polyhydric alcohol having an alicyclic skeleton is at least one selected from the group consisting of 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane glycols, and hydrogenated bisphenols.

8. The polyester resin according to claim 1, wherein the polyester resin contains 50 to 80 mol% of an acyclic aliphatic dihydric alcohol having the side chain and 20 to 50 mol% of a polyhydric alcohol having the alicyclic skeleton as a polyhydric alcohol component constituting the polyester resin.

9. The polyester resin according to claim 1, having a reduced viscosity of 0.2 to 0.8 dl / g, a glass transition temperature of 30°C or higher, and no melting point.

10. The polyester resin according to claim 1, wherein the acyclic aliphatic dihydric alcohol having the side chain has 6 or fewer carbon atoms, and the polyhydric alcohol having the alicyclic skeleton has 6 or more carbon atoms constituting the alicyclic skeleton.

11. The polyester resin according to claim 1, for use in coating metal plates.

12. A metal plate coating composition comprising the polyester resin and curing agent according to any one of claims 1 to 11, wherein the polyester resin / curing agent is contained in a ratio of 98 / 2 to 50 / 50 (by mass).

13. The metal plate coating composition according to claim 12, wherein the curing agent is at least one curing agent selected from amino resins, phenolic resins, and isocyanate compounds.

14. A laminate having a layer containing a reaction product of a polyester resin and a curing agent according to any one of claims 1 to 11.

15. A coated metal plate having the metal plate coating composition described in claim 12 laminated on the surface of the metal plate.

16. A can containing the painted metal plate described in claim 15 as a constituent material.

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