JP6834186B2 - Polyester resin composition, painted metal plates for cans and cans - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is a coating having excellent processability, curability, retort resistance, content resistance and dent resistance when used as a resin composition to be blended in a paint to be coated on metal cans for foods and beverages. A film (cured film) can be obtained, and therefore, it relates to a polyester resin composition particularly suitable for can inner surface coating applications. Further, it relates to a painted metal plate for cans and a can.

Generally, the inner surface of metal cans for food and beverages is painted for the purpose of preventing corrosion of the can material by a wide variety of contents. The paint for the inner surface of the can must first be non-toxic, have sufficient curability (curability), then have excellent workability during molding (workability), and withstand heat sterilization (resistant to heat sterilization). Retort pouch), no blisters or whitening when heat sterilizing salt or acidic contents (content resistance), impact resistance after heat sterilization (dent resistance), etc. are required. Further, especially in recent years, the use of substances such as bisphenol type epoxy resins, which are feared to act as exofactor endocrine disruptors (hereinafter, may be abbreviated as environmental hormones), is being avoided.

Polyvinyl chloride-based resins and epoxy-phenol-based resins are currently widely used as base resins for paints on the inner surface of cans, but the following serious problems have been pointed out at present. It is desired to develop an inner coating agent to replace the above.

First, the polyvinyl chloride-based resin has excellent retort resistance, content resistance, and processability, but the vinyl chloride monomer remaining in the resin is a substance having serious hygienic problems such as carcinogenicity. Has been pointed out. In addition, when the can is incinerated, toxic and corrosive chlorine gas, hydrogen chloride gas and highly toxic dioxin may be generated from the polyvinyl chloride resin, which leads to corrosion of the incinerator and environmental pollution. Problems may occur. Further, the polyvinyl chloride resin has insufficient adhesiveness to the metal which is the material of the can, and the coating process is complicated because it is necessary to perform a base treatment with an epoxy resin and then coat the resin.

Next, epoxy-phenolic resins have a high baking temperature and are prone to poor appearance such as foaming during baking. Further, as described above, it is suspected that bisphenol-A contained in the epoxy resin acts as an endocrine disrupter.

Further, in the paint for the outer surface of the can, in addition to the processability and retort resistance required as in the paint for the inner surface of the can described above, measures against environmental hormones are becoming necessary.

In order to solve this problem, an attempt was made to apply a polyester resin that does not generate toxic gas or corrosive gas during incineration and does not contain environmental hormones such as bisphenol-A in the coating film to paint for the inner surface of cans. However, a paint resin and a paint resin composition suitable for cans that simultaneously satisfy processability, curability, retort resistance, content resistance and dent resistance have not been obtained.

Patent Document 1 describes 1,2-propanediol consisting of two types of polyester resins, each containing 80 to 100 mol% of an aromatic dicarboxylic acid component as a dicarboxylic acid component and 50 to 85 mol% of a glycol component. At least one glycol selected from 2-methyl-1,3-propanediol, 1,4-butanediol and ethylene glycol is composed of 50 to 15 mol%, and the hydroxyl value of one of the polyester resins is 20 mgKOH. A resin composition for can paint, which is a blend of two types of polyester resins having a hydroxyl value of 25 to 60 mgKOH / g or less and the other polyester resin having a hydroxyl value of 25 to 60 mgKOH / g, is disclosed.

In Patent Document 2, 50 to 100 mol% of terephthalic acid is contained in the polycarboxylic acid component, 0 to 50 mol% of other polycarboxylic acids are contained, and 2-methyl-1,3-propanediol is contained in the polyalkane component. Disclosed are polyester resins for canned paints, which are 40 to 90%, 1,2-propanediol is 10 to 60 mol%, the ultimate viscosity is 0.45 or more, and the glass transition temperature is 50 ° C. or more.

Patent Document 3 describes an acid component consisting of 80 to 100 mol% of aromatic dicarboxylic acid containing 70 to 95 mol% of terephthalic acid, 0 to 20 mol% of polybasic acid other than aromatic dicarboxylic acid, and 2-methyl-. A polyester resin obtained by reacting 1,3-propanediol with a glycol component containing 1,4-cyclohexanedimethanol as an essential component and having a 2-methyl-1,3-propanediol content of 25 to 50 mol%. A polyester resin for can paint is disclosed in which the total weight of terephthalic acid and 1,4-cyclohexanedimethanol is in the range of 45 to 65% by weight of the polyester resin.

Japanese Unexamined Patent Publication No. 2004-307669 Japanese Unexamined Patent Publication No. 2005-350508 Japanese Unexamined Patent Publication No. 2008-081617

However, the polyester resin according to Patent Document 1 has a problem that the curability is insufficient and the processability and the dent resistance are inferior due to the insufficient mechanical strength of the cured film. Further, the polyester resin according to Patent Document 2 has a problem that it is inferior in retort resistance and content resistance. Further, the polyester resin according to Patent Document 3 has a problem that it is difficult to make the processability, retort resistance, stainability on the contents, and solubility in a solvent parallel.

The present invention has been made against the background of the problems of the prior art. That is, an object of the present invention is a polyester resin capable of forming a coating film (cured film) having extremely high curability, excellent workability, and excellent retort resistance, content resistance, and dent resistance. The purpose is to provide the composition.

The present inventor has completed the present invention as a result of diligent studies to achieve such an object. That is, the present invention has the following configuration.

The polyester resin (A) and the curing agent (B) are composed of a polycarboxylic acid component and a polyol component and satisfy the following requirements (i) to (iii), and the polyester resin (A) and the curing agent (B) are A polyester resin composition characterized by containing the polyester resin (A) / curing agent (B) in a ratio of 98/2 to 50/50 (parts by weight).
(I) As a polycarboxylic acid component constituting the polyester resin (A), 95 to 100 mol% of aromatic dicarboxylic acid is contained.
(Ii) As a polyol component constituting the polyester resin (A), 10 to 50 mol of an alicyclic diol containing 50 to 90 mol% of 2-methyl-1,3-propanediol and having 6 or more carbon atoms. %contains.
The polyester resin (A) has a reducing viscosity of 0.3 to 0.7 dl / g, a glass transition temperature (Tg) of 30 to 60 ° C., and an acid value of 0 to 300 eq / t.

A method for producing a coated metal plate for cans, which comprises a step of applying the polyester resin composition to a metal plate and curing it.

A can-coated metal plate in which a layer containing a cured product of the polyester resin composition is laminated on the surface of the metal plate, and a can containing the can-coated metal plate as a constituent material.

The polyester resin composition containing the polyester resin (A) and the curing agent (B) of the present invention has a very high curability and is a coating film excellent in processability, retort resistance, content resistance and dent resistance. (Curing film) can be formed. Therefore, the polyester resin composition of the present invention is suitable for can paint applications.

The polyester resin (A) in the present invention is a polyester resin composed of a polycarboxylic acid component and a polyol component and satisfying the following requirements (i) to (iii).

<Requirement (i)>
The requirement (i) will be described. As the polycarboxylic acid component constituting the polyester resin (A), it is necessary to contain 95 to 100 mol% of aromatic dicarboxylic acid when the total polycarboxylic acid component is 100 mol%. It is preferably 97 mol% or more, more preferably 98 mol% or more, and further preferably 99 mol% or more. If it is less than the above, the retort resistance and / or the content resistance may decrease.

The aromatic dicarboxylic acid component constituting the polyester resin (A) of the present invention includes terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 1,8-naphthalenedicarboxylic acid. Acid is mentioned. These can be used alone or in combination of two or more. Of these, terephthalic acid or isophthalic acid is preferable.

Examples of other polycarboxylic acids constituting the polyester resin (A) of the present invention include aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and unsaturated dicarboxylic acids. Examples of the aliphatic dicarboxylic acid include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecandioic acid, and dimer acid. Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, and 1,2-cyclohexenedicarboxylic acid. Examples of the unsaturated dicarboxylic acid include an unsaturated dicarboxylic acid such as fumaric acid, maleic acid, and a terpene-maleic acid adduct. One or more of these can be selected and used. Among them, an aliphatic dicarboxylic acid is preferable.

<Requirement (ii)>
The requirement (ii) will be described. As the polyol component constituting the polyester resin (A), when the total polyol component is 100 mol%, it contains 50 to 90 mol% of 2-methyl-1,3-propanediol and has 6 or more carbon atoms. It is necessary to contain 10 to 50 mol% of alicyclic diol.

The ratio of 2-methyl-1,3-propanediol in the polyester resin (A) of the present invention is preferably more than 50 mol%, more preferably 55 mol% or more, still more preferably 60 mol% in the total polyol components. That is all. Further, 85 mol% or less is preferable, and 80 mol% or less is more preferable. If it is less than the above, the processability and / or dent resistance may be lowered, and if it exceeds the above, the retort resistance and / or the content resistance may be lowered.

The ratio of the alicyclic diol component having 6 or more carbon atoms in the polyester resin (A) of the present invention is preferably 15 mol% or more, more preferably 20 mol% or more among all the polyol components. Further, 45 mol% or less is preferable, and 40 mol% or less is more preferable. If it is less than the above, the dent resistance, retort resistance and / or content resistance may be lowered, and if it exceeds the above, the processability and / or dent resistance may be lowered, or the crystallinity of the polyester resin may be increased. Solvent solubility and / or paint stability may be reduced.

Examples of the alicyclic polyol component having 6 or more carbon atoms constituting the polyester resin (A) of the present invention include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol. Examples thereof include tricyclodecaneglycols and water-added bisphenols, and one or more of these can be selected and used. Among them, 1,4-cyclohexanedimethanol is preferably used from the viewpoint of processability, dent resistance, retort resistance, and content resistance.

The total amount of 2-methyl-1,3-propanediol and the alicyclic diol component having 6 or more carbon atoms in the polyester resin (A) of the present invention is preferably 60 mol% or more of the total polyol components. It is more preferably 70 mol% or more, further preferably 80 mol% or more, particularly preferably 90 mol% or more, and may be 100 mol% or more.

Examples of other polyol components constituting the polyester resin (A) of the present invention include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, neopentyl glycol, and 3-methyl-1,5-pentanediol. , 1,2-Butandiol, 1,3-Butanediol, 1,4-Butanediol, 1,4-Pentanediol, 1,3-Pentanediol, 2,4-diethyl-1,5-Pentanediol, 1, , 6-Hexanediol, 1-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, Examples include aliphatic glycols such as 4-propyl-1,8-octanediol and 1,9-nonanediol, polyether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol. You can choose one or more of these and use them. Among them, ethylene glycol, 1,2-propylene glycol and neopentyl glycol are preferably used.

In the polyester resin (A) of the present invention, a trifunctional or higher functional component may be copolymerized with a polycarboxylic acid component and / or a polyol component. Examples of the trifunctional or higher functional polycarboxylic acid component include trimellitic acid, pyromeritic acid, and benzophenone tetracarboxylic acid, and examples of the trifunctional or higher functional polyol include glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, and pentaerythritol. , Α-Methylglucoside and the like. By using these, the crosslink density when the paint is cured is increased, and the workability can be improved.

The copolymerization ratio of the trifunctional or higher functional polycarboxylic acid component is preferably 0 mol% or more, more preferably 0.5 mol% or more, still more preferably, when the total polycarboxylic acid component is 100 mol%. Is 1 mol% or more. Further, it is preferably 5 mol% or less, more preferably 4 mol% or less, further preferably 3 mol% or less, and particularly preferably 2 mol% or less. The copolymerization ratio of the trifunctional or higher functional polyol component is preferably 0 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol%, when the total polyol component is 100 mol%. That is all. Further, it is preferably 5 mol% or less, more preferably 4 mol% or less, further preferably 3 mol% or less, and particularly preferably 2 mol% or less. If the polycarboxylic acid component and the polyol component each exceed the above, the flexibility of the polyester resin may be lost, the processability and / or dent resistance may be lowered, or gelation may occur during the polymerization of the polyester.

The polyester resin (A) of the present invention may be given an acid value by any method. By imparting an acid value, effects such as improvement of curability with a cross-linking agent or a curing agent and improvement of adhesion with a metal material for cans may be obtained. As a method for imparting an acid value, a depolymerization method in which a polycarboxylic acid anhydride is added in the latter stage of polycondensation, a high acid value is set at the prepolymer (oligomer) stage, and then this is polycondensed to have an acid value. There is a method for obtaining a polyester resin, but the former depolymerization method is preferable because it is easy to operate and a target acid value can be easily obtained.

Among the compounds having a carboxylic acid anhydride group in the molecule for imparting an acid value to the polyester resin (A) of the present invention, examples of the carboxylic acid monoanhydride include phthalic anhydride, succinic anhydride, and maleine anhydride. Acids, trimellitic anhydride, itaconic anhydride, citraconic anhydride, monoanhydrides such as 5- (2,5-dioxotetrahydrofurfuryl) -3-cyclohexene-1,2-dicarboxylic acid anhydride, hexahydrophthalic anhydride , Tetrahydrophthalic anhydride, etc., and one or more of these can be selected and used. Among them, trimellitic anhydride is preferable from the viewpoint of versatility and economy.

Among the compounds having a carboxylic acid anhydride group in the molecule for imparting an acid value to the polyester resin (A) of the present invention, examples of the carboxylic acid polyanhydride include pyromelitoic anhydride, 1,2,3. 4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride Anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, ethylene glycol bistrimericate dianhydride, 2,2', 3 , 3'-diphenyltetracarboxylic dianhydride, thiophen-2,3,4,5-tetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, 4,4'-oxydiphthalic acid dianhydride, 5- (2,5-Dioxotetrahydro-3-furanyl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride and the like are available, and one or two or more of them can be selected and used. Among them, ethylene glycol bistrimeritate dianhydride is preferable.

As the compound having a carboxylic acid anhydride group in the molecule for imparting the acid value, the carboxylic acid monoanhydride and the carboxylic acid polyanhydride can be used alone or in combination. You can also.

<Requirements (iii)>
The requirement (iii) will be described. It is necessary that the reducing viscosity of the polyester resin (A) is 0.3 to 0.7 dl / g, the glass transition temperature (Tg) is 30 to 60 ° C., and the acid value is 0 to 300 eq / t.

Among the characteristics of the polyester resin (A) of the present invention, the lower limit of the reducing viscosity (dl / g) is preferably 0.35, more preferably 0.4. If it is less than the above, the workability and / or dent resistance may decrease. The upper limit of the reduced viscosity (dl / g) is preferably 0.65, more preferably 0.6. If it exceeds the above, the number of functional group terminals that can react with the curing agent is reduced, the curability may be lowered, the solvent solubility and / or the paint stability may be lowered, or the coating workability may be lowered. is there. The reduced viscosity in the present invention is a value determined by the method described in Examples.

Among the characteristics of the polyester resin (A) of the present invention, the acid value is 0 to 300 eq / t. It is preferably 1 eq / t or more, and more preferably 5 eq / t or more. Further, it is preferably 280 eq / t or less, more preferably 260 eq / t or less, and particularly preferably 250 eq / t or less. If it exceeds the above, the amount of unreacted compounds of the compound having a carboxylic acid anhydride group that imparts an acid value increases, and the processability and / or dent resistance is lowered, or the retort resistance and / or content resistance is lowered. I have something to do.

Among the characteristics of the polyester resin (A) of the present invention, the glass transition temperature (Tg) is 30 to 60 ° C. It is preferably 35 ° C. or higher, more preferably 38 ° C. or higher, and even more preferably 40 ° C. or higher. If it is less than the above, the retort resistance and / or the content resistance may be poor. Further, it is preferably 58 ° C. or lower, more preferably 55 ° C. or lower. Exceeding the above is not preferable from the viewpoint of economic productivity. Incidentally, Tg of the present invention is substantially coincident with _{T ig} which is specified in JIS K 7121-1987, strictly to a value determined by the method specified in the examples.

The number average molecular weight of the polyester resin (A) of the present invention is preferably 5,000 or more, more preferably 6,000 or more, and even more preferably 7,000 or more. Further, it is preferably 30,000 or less, more preferably 28,000 or less, and further preferably 25,000 or less.

The polyester resin (A) of the present invention can be produced by a known polycondensation method for polyester. For example, a direct polymerization method in which an oligomer is obtained by transesterifying a polycarboxylic acid component and a polyol component and then melt-polycondensed at a high temperature under reduced pressure, or a lower alkyl ester having 1 to 2 carbon atoms of the polycarboxylic acid. Examples thereof include an ester exchange method in which an oligomer is obtained by transesterifying a polyol component and then melt-polycondensed at a high temperature under reduced pressure. Since there is no difference in the characteristics of the polyester resin of the present invention produced by these methods and the performance of the resin composition for can paint, it does not matter which method is used.

As a characteristic of the polyester resin (A) of the present invention, it is preferable that a clear peak indicating a melting point (Tm) is not observed by differential thermal analysis (DSC) from the viewpoint of solvent solubility and paint stability. When the polyester resin exhibits a melting point and has crystallinity, solvent solubility and / or paint stability may decrease, and processability and / or dent resistance may decrease.

<Curing agent (B)>
The curing agent (B) preferably reacts with the polyester resin (A) of the present invention to form a crosslinked structure, and examples thereof include a phenol resin, an amino resin, and an isocyanate compound. Among them, a phenol resin and / or an amino resin is preferable from the viewpoint of hygiene, and a phenol resin is more preferable. In the case of an amino resin, an amino resin using melamine or benzoguanamine is preferable for hygiene, and more preferably an amino resin using benzoguanamine having excellent retort resistance and extractability.

The phenol resin is preferably a resol type phenol resin synthesized from a phenol compound. For example, examples of the trifunctional or higher functional phenol compound include phenol, m-cresol, m-ethylphenol, 3,5-xylenol, m-methoxyphenol, bisphenol-A, and bisphenol-F. Examples of the bifunctional phenol compound 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 the phenol compound, and can be synthesized by methylolation with formaldehyde or the like. These can be used alone or in combination of two or more.

The blending ratio of the trifunctional or higher functional phenol compound and the bifunctional phenol compound is 1/99 to 100/0 (part by weight), although it is arbitrarily blended according to the required coating film (cured film). Is preferable. For example, when the coating film requires hardness and acid resistance, it is preferable to use more than 30 parts by weight of a trifunctional or higher functional phenol compound, the coating film needs to be flexible, and the residual stress after processing is low. If this is desired, the amount of the trifunctional or higher functional phenol compound is preferably less than 50 parts by weight.

Examples of formaldehydes used when these phenol compounds are used as phenol resins include formaldehyde, paraformaldehyde or trioxane, and one type or a mixture of two or more types can be used.

As the alcohol used for alkyl etherifying a part of the methylol group of the methylolated phenol resin, a monohydric alcohol having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms can be used. , For example methanol, ethanol, n-propanol, n
Examples thereof include -butanol, isopropanol, isobutanol, and tert-butanol, and n-butanol is preferable from the viewpoint of compatibility with the polyester resin (A) and reaction curability.

From the viewpoint of reactivity and compatibility with the polyester resin (A), the phenol resin has an average of 0.3 or more alkoxymethyl groups per phenol nucleus, preferably 0.5 to 3. If the number is less than 0.3, the curability with the polyester resin is poor and the processability may be lowered.

As a method for obtaining a phenol resin in which these trifunctional or higher functional phenol compounds and bifunctional phenol compounds are mixed, a method of mixing them in an arbitrary ratio before converting them into phenol resins with formaldehyde or a trifunctional method The above phenol compounds and bifunctional phenol compounds may be separately converted into phenol resins, which may be mixed at an arbitrary mixing ratio.

As the amino resin, for example, methylol obtained by reacting an amino component such as melamine, urea, benzoguanamine, acetguanamine, steloganamin, spiroganamin, dicyandiamide, and an aldehyde component such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Examples include formaldehyde resin. The amino resin also includes a methylolated amino resin in which the methylol group is etherified with an alcohol having 1 to 6 carbon atoms. These can be used alone or in combination of two or more. Amino resins using benzoguanamine or melamine are preferred.

Examples of the amino resin using benzoguanamine include methyl etherified benzoguanamine resin obtained by etherifying a part or all of the methylol groups of the methylolated benzoguanamine resin with methyl alcohol, butyl etherified benzoguanamine resin obtained by butyl etherifying with butyl alcohol, or methyl alcohol. Methyl ether etherified with both butyl alcohol and mixed etherified benzoguanamine resin with butyl ether are preferable. As the butyl alcohol, isobutyl alcohol and n-butyl alcohol are preferable.

Examples of the amino resin using melamine include methyl etherified melamine resin in which some or all of the methylol groups of the methylolated melamine resin are etherified with methyl alcohol, butyl etherified melamine resin obtained by butyl etherifying with butyl alcohol, or methyl alcohol. Methyl ether etherified with both butyl alcohol and mixed etherified melamine resin with butyl ether are preferable.

Examples of the isocyanate compound 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, 2-nitrodiphenyl-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'- Aromatic diisocyanates such as dimethoxydiphenyl-4,4'-diisocyanate, aromatic polyisocyanates such as polymethylene polyisocyanate and crude tolylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), decamethylene diisocyanate, lysine diisocyanate and the like Diisocyanates such as aliphatic diisocyanates, isophorone diisocyanates (IPDI), hydrogenated tolylene diisocyanates, hydrogenated xylene diisocyanates, hydrogenated diphenylmethane diisocyanates and other alicyclic diisocyanates, and biuret, uretdione modified and carbodiimide modified versions of the isocyanates. Examples thereof include isocyanurate modified products, uretonimine modified products, adduct products with polyols, and mixed modified products thereof, and one or more of these can be selected and used. It can also be used in the form of a urethane precursor such as a prepolymer, a modified product, a derivative or a mixture composed of an isocyanate compound and an active hydrogen compound such as a polyol or a polyamine.

As the isocyanate compound, it is preferable to use a blocked isocyanate compound in which the terminal NCO group of the isocyanate compound is blocked. Examples of the blocking agent include phenolic compounds such as phenol, cresol, ethylphenol and butylphenol, 2-hydroxypyridine, butyl cellosolve, propylene glycol monomethyl ether, benzyl alcohol, methanol, ethanol, n-butanol, isobutanol, 2-ethylhexanol and the like. Alcohol compounds, active oxime compounds such as dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylaeton, mercaptan compounds such as butyl mercaptan and dodecyl mercaptan, acid amides such as acetoanilide and acetate amide. Systems compounds, lactam compounds such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, imidazole compounds such as imidazole and 2-methylimidazole, urea compounds such as urea, thiourea and ethyleneurea, formamide oximes and acet. Examples thereof include oxime compounds such as aldoxime, acetone oxime, methyl ethyl keto oxime, methyl isobutyl keto oxime and cyclohexanone oxime, and amine compounds such as diphenylaniline, aniline, carbazole, ethyleneimine and polyethyleneimine. These can be used alone or in admixture of two or more.

Such a reaction between the blocking agent and the isocyanate compound can be carried out, for example, at 20 to 200 ° C., if necessary, using a known inert solvent or catalyst. The blocking agent is preferably used in a molar amount of 0.7 to 1.5 times the terminal isocyanate group.

The blending ratio of the polyester resin (A) and the curing agent (B) in the polyester resin composition of the present invention is polyester resin (A) / curing agent (B) = 98/2 to 50/50 (parts by weight). More preferably, the polyester resin (A) / curing agent (B) = 95/5 to 60/40 (parts by weight). If the blending ratio of the curing agent (B) is less than 2 parts by weight with respect to 98 parts by weight of the polyester resin (A), sufficient curability cannot be obtained, and workability, retort resistance, content resistance and / or resistance Dentability may decrease. When the compounding ratio of the curing agent (B) exceeds 50 parts by weight with respect to 50 parts by weight of the polyester resin (A), the unreacted curing agent (B) component remains, and the workability, dent resistance, and retort resistance are retorted. Properties and / or content resistance may be reduced.

The polyester resin composition preferably further contains a catalyst. By containing a catalyst, the performance of the cured film can be improved. When the curing agent (B) is a phenol resin and an amino resin as the catalyst, for example, sulfuric acid, p-toluene sulfonic acid, dodecylbenzene sulfonic acid, naphthalene sulfonic acid, dinonylnaphthalene sulfonic acid, dinonylnaphthalenedisulfonic acid, and cerebral brain. Examples thereof include sulfonic acid, phosphoric acid, and amine blocks (partially neutralized by adding amine) thereof, and one or more of these can be used in combination. Dodecylbenzenesulfonic acid and its neutralized product are preferable from the viewpoint of compatibility with the polyester resin (A) and hygiene. When the curing agent (B) is an isocyanate compound, for example, an organic tin compound such as stannous octylate or dibutyltin dilaurylate, triethylamine, etc. can be mentioned, and one or more of these can be used in combination. ..

Among the characteristics of the cured film obtained from the polyester resin composition of the present invention, the glass transition temperature (Tg) is preferably 45 ° C. or higher, more preferably 48 ° C. or higher, still more preferably 50 ° C. or higher. is there. Further, 100 ° C. or lower is preferable, 95 ° C. or lower is more preferable, and 90 ° C. or lower is further preferable. If it is less than the above, the retort resistance and / or the content resistance may be poor, and if it exceeds the above, the workability and the dent resistance may be poor.

Among the characteristics of the cured film obtained from the polyester resin composition of the present invention, the tensile elastic modulus at 25 ° C. is preferably 1 GPa or more, more preferably 1.1 GPa, and further preferably 1.3 GPa. Yes, especially preferably 1.4 GPa. Further, 2 GPa or less is preferable, 1.9 GPa or less is more preferable, and 1.8 GPa or less is further preferable. If it is less than the above, the mechanical strength of the cured film is insufficient and the curability may be poor, and if it exceeds the above, the workability and dent resistance may be poor.

In the polyester resin composition of the present invention, known inorganic pigments such as titanium oxide and silica, phosphoric acid and its esterified products, surface smoothing agents, defoaming agents, dispersants, lubricants and the like are known according to the required properties. Additives can be blended. In particular, the lubricant is important for imparting the lubricity of the coating film required for molding DI cans, DR (or DRD) cans, etc., for example, fatty acid ester wax, which is an esterified product of a polyol compound and a fatty acid. Examples of suitable lubricants include silicon wax, fluorine wax, polyolefin wax such as polyethylene, lanolin wax, montan wax, microcrystallin wax, and carnauba wax. The lubricant may be used alone or in admixture of two or more.

The polyester resin composition of the present invention can be made into a paint in a state of being dissolved in a known organic solvent. Examples of the organic solvent used for coating 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, and ethylene. Examples thereof include glycol monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and solvent. From these, one kind or two or more kinds are selected and used in consideration of solubility, evaporation rate and the like.

The polyester resin composition of the present invention can be blended with other resins intended for modification such as imparting flexibility and adhesion to the coating film. Examples of other resins include ethylene-polymerizable unsaturated carboxylic acid copolymer and ethylene-polymerizable carboxylic acid copolymer ionomer, and at least one resin selected from these is blended. As a result, the flexibility and / or adhesion of the coating film may be imparted.

The polyester resin composition of the present invention can be applied to one or both sides of a metal plate made of a metal material that can be used for beverage cans, cans, lids, caps, etc., and also to end faces if necessary. Can be painted. Examples of the metal material include tinplate, tinfree steel, aluminum and the like. The metal plate made of these metal materials was previously subjected to phosphoric acid treatment, chromic acid chromate treatment, phosphoric acid chromate treatment, anticorrosion treatment with other rust preventive treatment agents, and surface treatment for the purpose of improving the adhesion of the coating film. You may use the one.

The coated metal plate for cans of the present invention can be obtained by coating the metal plate with the polyester resin composition of the present invention by a known coating method such as roll coater coating or spray coating and curing it. The coating film thickness is not particularly limited, but the dry film thickness is preferably in the range of 3 to 18 μm, more preferably 3 to 10 μm. The baking conditions of the coating film are usually about 5 seconds to about 30 minutes in the range of about 100 to 300 ° C., and further about 1 to about 15 minutes in the range of about 150 to 250 ° C. Is preferable.

Examples of cans containing the coated metal plate for cans as a constituent material include beverage cans, canning cans, and lids or caps thereof.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples. The characteristic values in each example were evaluated by the following methods. The term "part" simply indicates the part by weight, and the term "%" indicates the percentage by weight.

<Polyester resin (A)>
(1) Measurement of Resin Composition A sample of the polyester resin (A) was dissolved in deuterated chloroform, and ^{1 1} H-NMR analysis was performed using an NMR apparatus 400-MR manufactured by VARIAN. The molar ratio was calculated from the integrated value ratio.

(2) Measurement of number average molecular weight A sample of polyester resin (A) is dissolved and / or diluted with tetrahydrofuran so that the resin concentration becomes about 0.5% by weight, and is made of polytetrafluoride ethylene having a pore size of 0.5 μm. The sample filtered through the membrane filter was used as the measurement sample. The molecular weight was measured by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase and a differential refractometer as a detector. The flow velocity was 1 mL / min and the column temperature was 30 ° C. Showa Denko KF-802, 804L, and 806L were used as columns. Monodisperse polystyrene was used as the molecular weight standard.

(3) Measurement of Reducing Viscosity (Unit: dl / g) 0.1 g of a sample of polyester resin (A) was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (weight ratio 6/4) and measured at 30 ° C.

(4) Measurement of glass transition temperature (Tg) Measurement was performed by a differential scanning calorimeter (SII, DSC-200). A 5 mg sample of the polyester resin (A) was placed in an aluminum holding lid type container, sealed, cooled to −50 ° C. using liquid nitrogen, and then heated to 150 ° C. at 20 ° C./min. In the endothermic curve obtained in this process, the temperature at the intersection of the baseline before the endothermic peak appears and the tangent line toward the endothermic peak was defined as the glass transition temperature (Tg, unit: ° C.).

(5) A sample 0.2g of acid value measurement polyester resin (A) was dissolved in chloroform 40 ml, and titrated with potassium hydroxide solution in ethanol 0.01 N, equivalents per carboxyl group-containing resin 10 ⁶ g (eq / 10 ⁶ g) was calculated. Phenolphthalein was used as an indicator.

<Cured film of polyester resin composition>
(6) Preparation of Cured Film of Polyester Resin Composition The polyester resin composition was applied onto a copper foil so that the thickness after drying was 10 ± 2 μm, and dried with hot air at 120 ° C. for 5 minutes. Then, the cured film of the polyester resin composition is formed by immersing the polyester resin composition in an aqueous solution of ferric chloride at room temperature until the copper foil is completely removed visually, washing with water, and drying at 50 ° C. for 60 minutes. Obtained (hereinafter referred to as a cured film). Using the obtained cured film, the following glass transition temperature and elastic modulus were measured.

(7) Measurement of glass transition temperature (Tg) of cured film The cured film obtained as described above was subjected to a frequency of 10 Hz and a temperature rise rate using a dynamic viscoelasticity measuring device DVA-220 manufactured by IT Measurement Control Co., Ltd. The dynamic viscoelasticity was measured at 4 ° C./min, and the glass transition temperature (Tg) of the cured film was determined from the temperature at which Tan δ was maximized.

(8) Measurement of elastic modulus of cured film The cured film obtained as described above is adjusted to a width of 10 mm and a measurement length of 40 mm, and a tensile speed of 20 mm / min at room temperature of 25 ° C. using Tensilon manufactured by Toyo Baldwin. The elastic modulus of the cured film was measured with.

<Test piece>
(9) Preparation of test piece A polyester resin composition was dried on one side of a tin plate (JIS G 3303 (2008) SPTE, 70 mm × 150 mm × 0.3 mm) with a bar coater so that the film thickness after drying was 10 ± 2 μm. The coating was applied and cured and baked under a baking condition of 200 ° C. (PMT: maximum temperature reached by the substrate) for 10 minutes, and this was used as a test piece (hereinafter referred to as a test piece).

(10) Evaluation of Workability The obtained test piece was bent 180 ° in the direction in which the cured film was on the outside, and the cracking of the cured film generated in the bent portion was evaluated by measuring the energization value. Prepare a sponge (width 20 mm, depth 50 mm, thickness 10 mm) on which a sponge (width 20 mm, depth 50 mm, thickness 10 mm) soaked in a 1% NaCl aqueous solution is placed on an aluminum plate electrode (width 20 mm, depth 50 mm, thickness 0.5 mm). The vicinity of the central portion of the bent portion of the test piece was brought into contact with the sponge so as to be parallel to the side of 20 mm. A DC voltage of 5.0 V was applied between the aluminum plate electrode and the unpainted portion on the back surface of the test plate, and the energization value was measured. The smaller the energization value, the better the bending characteristics.
(Judgment)
⊚: less than 0.5 mA ○: 0.5 mA or more and less than 1.0 mA Δ: 1.0 mA or more and less than 2.0 mA ×: 2.0 mA or more

(11) Evaluation of Curability A gauze felt soaked with methyl ethyl ketone ^{was pressed against the cured film surface of the test piece so as to make contact with 1 cm 2} and a rubbing test was performed with a load of 500 g. The number of times until the cured film was peeled off (one round trip) was evaluated according to the following criteria.
(Judgment)
⊚: The coating film did not peel off even after 50 times or more, and no change was observed in the cured film. ○: The cured film peeled off at 25 to 49 times, and the tin plate was exposed. Δ: The cured film peeled off at 16 to 24 times. The tin plate was exposed ×: The cured film was peeled off after 15 times or less, and the tin plate was exposed.

(12) Evaluation of retort resistance A test piece is placed upright in a stainless steel cup, ion-exchanged water is poured into the test piece until it is half the height of the test piece, and this is poured into a retort tester (ES-made by Tommy Kogyo Co., Ltd.). It was installed in the pressure cooker of 315) and retorted at 130 ° C. for 60 minutes. The evaluation after the treatment was carried out at the steam contact portion, which is generally considered to be exposed to more severe conditions for the cured film, and the whitening of the cured film and the state of the blister were visually judged as follows.
(Judgment)
◎: Good (no whitening or blisters)
◯: Slight whitening but no blisters Δ: Some whitening and / or some blisters ×: Significant whitening and / or significant blisters

(13) Evaluation of content resistance A test piece is placed upright in a stainless steel cup, and an aqueous solution containing 3% by weight of salt and 3% by weight of acetic acid is poured into the test piece until the entire test piece is immersed, and this is poured into a retort tester (Tommy Industries). It was placed in a pressure cooker of ES-315 manufactured by Co., Ltd., and after treatment at 130 ° C. for 60 minutes, the whitening of the cured film and the state of the blister were visually judged as follows.
(Judgment)
◎: Good (no whitening or blisters)
◯: Slight whitening but no blisters Δ: Slight whitening and / or some blisters ×: Significant whitening and / or significant blisters

(14) Evaluation of dent resistance Using a DuPont impact tester, the painted surface of the test piece subjected to the retort treatment shown in (12) was turned down, and the diameter of the unpainted surface of the steam contact portion of the test piece was 1 /. A 2-inch ball head striking punch was pressed against it, and a 1 kg weight was dropped from a height of 50 cm to apply an impact. Next, a sponge (width 20 mm, depth 50 mm, thickness 10 mm) dipped in a 1 wt% NaCl aqueous solution was placed on an aluminum plate electrode (width 20 mm, depth 50 mm, thickness 0.5 mm). The convex portion of the impacted test piece was brought into contact with the sponge. A DC voltage of 5.0 V was applied between the aluminum plate electrode and the unpainted portion on the back surface of the test plate, and the energization value was measured. The smaller the energization value, the better the bending characteristics.
(Judgment)
⊚: less than 0.5 mA ○: 0.5 mA or more and less than 1.0 mA Δ: 1.0 mA or more and less than 2.0 mA ×: 2.0 mA or more

Synthesis example of polyester resin (A) (1)
140 parts by weight of terephthalic acid, 553 parts by weight of isophthalic acid, 8 parts by weight of trimellitic anhydride, 393 parts by weight of 2-methyl-1,3-propanediol, 118 parts by weight of neopentyl glycol, 118 parts by weight of 1,4-cyclohexanedimethanol , 0.3 part by weight (0.02 mol% with respect to the total acid component) of tetra-n-butyl titanate (hereinafter, may be abbreviated as TBT) as a catalyst is charged in a 3 L four-necked flask and takes 3 hours. The esterification reaction was carried out while gradually raising the temperature to 235 ° C. Next, the pressure inside the system was gradually reduced, polymerization was carried out under reduced pressure to 10 mmHg over 1 hour, the temperature was raised to 250 ° C., and late polymerization was carried out for 50 minutes under a vacuum of 1 mmHg or less. When the target molecular weight was reached, it was cooled to 220 ° C. under a nitrogen atmosphere. Next, 8 parts by weight of trimellitic dianhydride and 9 parts by weight of ethylene glycol bistrimericte dianhydride were added one after another, and stirring was continued at 200 to 230 ° C. for 30 minutes under a nitrogen atmosphere. This was taken out to obtain the polyester resin of the present invention (Synthetic Example (1)). The obtained polyester resin had a number average molecular weight of 12,500, a reduced viscosity of 0.47 dl / g, a glass transition temperature (Tg) of 52 ° C., and an acid value of 145 eq / t.

Synthesis Examples (2) to (8), and Comparative Synthesis Examples (1) to (8)
Similar to Synthesis Example (1), the polyester resin of the present invention (Synthesis Examples (2) to (8)), wherein the charged composition is changed by the direct polymerization method and the resin composition is as shown in Tables 1 and 2. And comparative synthesis examples (1) to (6)) were produced.

Examples of production of resin varnish The polyester resins of Synthesis Examples (1) to (8) and Comparative Synthesis Examples (1) to (8) are dissolved in cyclohexanone / Solbesso-150 = 1/1 (weight ratio) to have a solid content of 40% by weight. % Resin varnish was prepared.

Example (1) (Polyester resin composition (1))
63 parts of the resin varnish of Synthesis Example (1), 4 parts of a resole-type phenol resin (manufactured by Allnex, PR-371, solid content 70% by weight) as a curing agent (B), and dodecylbenzenesulfonic acid (manufactured by King Industries) as a catalyst. , Varnish 5076, solid content 70% by weight) 0.04 part, diluted with cyclohexanone / sorbesso-150 = 1/1 (weight ratio) until the viscosity suitable for coating is obtained, and the polyester resin composition of the present invention is prepared. (Paint composition) (1) was obtained. This was applied and baked by the method described above to obtain a cured film of the polyester resin composition (1) of the present invention and a test piece of a coated metal plate. Tables 3 to 4 show the results of the formulation of the polyester resin composition (1) and the evaluation of the cured film and the test piece.

Example (2) , Reference Example (3), Example (4), Reference Example (5)-(7), Example (8), Reference Example (9)-(10) (Polyester resin composition (2) )-(10), Comparative Examples (1)-(10) (Comparative Polyester Resin Compositions (1)-(10))
The polyester resin composition of the present invention was obtained in the same manner as in Example (1), except that the formulation was changed according to Tables 3 to 4. Next, coating and baking were carried out by the same method as described above to obtain a test piece of the coated metal plate of the present invention. Tables 3 to 4 show the results of evaluating the composition of the polyester resin composition and the test pieces.

PR-371: Allnex, Resol-type phenol resin PR-899: Allnex, Resol-type phenol resin PR-521: Allnex, Resol-type phenol resin Cymel (registered trademark) 303LF: Allnex, methylated melamine Cymel (registered trademark) 1123: Allnex, methyl / ethylated benzoguanamine DESMODUR (registered trademark) VP LS 2078/2: Covestro, IPDI-based blocked isocyanate Nace (registered trademark) 5076: King Industries, dodecylbenzene sulfonate Acid Name (registered trademark) 5925: Made by King Industries, amine-neutralized dodecylbenzenesulfonic acid DBTL: Dibutyltin dilaurate

As is clear from Tables 3 to 4, the cured film (coating film) obtained from the polyester resin composition using the polyester resin (A) of the present invention has its processability, curability, retort resistance, and content resistance. Both physical properties and dent resistance are excellent.

The product of the present invention is a polyester resin composition having excellent processability, curability, retort resistance, content resistance, and dent resistance, and a coated metal plate for cans coated with the polyester resin composition, which is a metal can for foods and beverages. It is suitable as a main agent for paints to be painted on.

Claims (4)

It is composed of a polycarboxylic acid component and a polyol component, contains a polyester resin (A) and a curing agent (B) that satisfy the following requirements (i) to (iii), and the curing agent (B) is a phenol resin, and the polyester. A polyester resin composition comprising a resin (A) and a curing agent (B) in a ratio of polyester resin (A) / curing agent (B) = 98/2 to 90/10 (parts by weight).
(I) As a polycarboxylic acid component constituting the polyester resin (A), 95 to 100 mol% of aromatic dicarboxylic acid is contained.
(Ii) As a polyol component constituting the polyester resin (A), 20 to 50 mol of an alicyclic diol containing 50 to 80 mol% of 2-methyl-1,3-propanediol and having 6 or more carbon atoms. %contains.
(Iii) The reducing viscosity of the polyester resin (A) is 0.3 to 0.7 dl / g, the glass transition temperature (Tg) is 30 to 60 ° C., and the acid value is 0 to 300 eq / t. A method for producing a coated metal plate for cans, which comprises a step of applying the polyester resin composition according to claim 1 to a metal plate and curing it. A coated metal plate for cans in which a layer containing a cured product of the polyester resin composition according to claim 1 is laminated on the surface of the metal plate. A can containing the coated metal plate for cans according to claim 3 as a constituent material.