JP2002338880A - Copolyester resin for forming coating film on metal can interior - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolyester resin for forming such a coating film on a metal can interior that the film is formed without using an epoxy resin, is excellent in retorting resistance, processibility, and corrosion resistance, and does not contain a substance elutable to a beverage, etc.; and a resin composition for forming a coating film comprising the copolyester resin. SOLUTION: This copolyester resin for forming a coating film on a metal can interior comprises glycol residues and polycarboxylic acid residues. At least 50 mol% of the polycarboxylic acid residues are aromatic dicarboxylic residues. The glycol residues contain branched, 3C-chain or lower glycol residues and 4-20C linear glycol residues, the sum of contents of these two kinds of glycol residues being 50 mol% or higher and the molar ratio of the branched glycol residues to the linear glycol residues being (40/60)-(80/20). The intrinsic viscosity of the copolyester resin is 0.2-1.0 dl/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolymerized polyester resin for forming an inner surface coating of a metal can and a copolymerized polyester resin composition.

[0002]

2. Description of the Related Art Metal cans, which are one form of food and beverage packaging containers, have excellent mechanical strength and excellent sealing properties, so that the contents can be stored for a long time, and the contents can be filled at a high temperature. It can be sealed as it is, and sterilization treatment such as retort treatment can be easily performed, so it is highly reliable for safety and health as a packaging container.Furthermore, contents can be stored in a heated state and cans after use In recent years, various types of contents have been filled and used in large quantities because of their many advantages that separation and collection are relatively easy.

[0003] The inner and outer surfaces of a metal can for food and drink are intended to maintain the flavor of the contents and to prevent corrosion of the metal can material, or to improve the aesthetics of the outer surface of the can and to protect the printed surface. Conventionally, a solvent-type resin composition containing a thermosetting resin as a main component has been applied. However, such a paint can has the following problems. (A) When the contents are filled and sealed, and then subjected to a heating treatment such as a retort treatment, low molecular weight substances such as a residual solvent in the film are transferred into the contents, and the flavor (flavor property) of the contents is remarkable. descend. (B) As the diameter of the can lid becomes smaller and the thickness of the can becomes thinner, the workability and impact resistance of the coating are required more than before. On the other hand, the coating whitens after the retort treatment, the coating peels off, etc. However, it is difficult to obtain a coating satisfying these performances.

[0004] Japanese Patent No. 2758 discloses a paint can.
An epoxy resin containing bisphenol A as proposed in Japanese Patent No. 111 has been used. However,
When a composition comprising these is used, bisphenol A
There is a problem that low-molecular-weight substances, which are said to have the potential to affect the human body, are eluted in the contents (beverages, foods, etc.) by retort treatment or long-term storage at high temperatures . For this reason, epoxy resins containing bisphenol A have been shunned in the field of coating the inner surface of cans, and replacement with other materials is in progress.

[0005] Under these circumstances, a metal can inner surface film-forming product which does not use an epoxy resin, has sufficient retort resistance, high workability, excellent corrosion resistance, and has no elution to beverages or the like. I have been asked.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to use an epoxy resin, which has sufficient retort resistance, high workability, excellent corrosion resistance, and no elution to the contents. An object of the present invention is to provide a copolyester resin for forming a film on the inner surface of a metal can and a resin composition for forming a film comprising the same.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a specific proportion of glycol residues constituting the copolymerized polyester is
The retort resistance and processability of the polyester are significantly improved by containing a glycol residue having a branched structure in which the carbon chain between the glycol groups is 3 or less and a linear glycol residue having 4 to 20 carbon atoms. And reached the present invention.

That is, the present invention provides a copolymerized polyester comprising a glycol residue and a polyvalent carboxylic acid residue, which contains at least 50 mol% of an aromatic dicarboxylic acid residue among all the polyvalent carboxylic acid residues; As a glycol residue,
(A) a glycol residue having a branched structure with 3 or less carbon chains between glycol groups and (B) a linear glycol residue having 4 to 20 carbon atoms, wherein (A) ) + (B) is at least 50 mol%, and (A) /
(B) is 40 / 60-80 / 20 (molar ratio), and the essential viscosity is 0.2-1.0 dl / g.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The copolyester resin for forming a metal can inner surface film of the present invention is a copolyester comprising a glycol residue and a polyvalent carboxylic acid residue, and among all the polyvalent carboxylic acid residues, an aromatic dicarboxylic acid residue. Contains at least 50 mol%,
Of all glycol residues, 3 carbon chains between glycol groups
A glycol residue having a branched structure and a carbon number of 4 to
20 mol% of 20 linear glycols, the ratio of both is 40/60 to 80/20 (molar ratio), and the intrinsic viscosity is 0.2 to 1.0 dl / g. .

The polyvalent carboxylic acid residue constituting the copolymerized polyester resin of the present invention must contain at least 50 mol% of an aromatic dicarboxylic acid residue, more preferably at least 60 mol%. . If the content of the aromatic dicarboxylic acid residue is less than 50 mol%, the retort resistance of the film formed product is insufficient, which is not preferable. Examples of the aromatic dicarboxylic acid residue include, for example, each residue composed of orthophthalic acid, terephthalic acid, isophthalic acid, and the like. Among them, residues composed of terephthalic acid and isophthalic acid are preferably used.

The polyvalent carboxylic acid residue constituting the copolymerized polyester resin of the present invention may contain an aliphatic dicarboxylic acid residue or an alicyclic dicarboxylic acid residue in an amount of less than 50 mol%. it can. When an aliphatic dicarboxylic acid residue or an alicyclic dicarboxylic acid residue is contained in an amount of 50 mol% or more, the retort resistance of the film formed product is insufficient, which is not preferable. As the aliphatic polycarboxylic acid residue,
For example, each residue of adipic acid, sebacic acid, fumaric acid, maleic acid, dimer acid and the like can be mentioned. Examples of the alicyclic polycarboxylic acid residue include, for example, residues such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and maleic acid adduct of terpene. Further, when a carboxylic acid residue having three or more functionalities represented by trimellitic acid or pyromellitic acid is contained, 0.2 to 5 mol% based on the entire carboxylic acid component contained in the polyester resin of the present invention. Is preferred.
When the content is less than 0.2 mol%, the effect of the addition is not exhibited, and when the content exceeds 5 mol%, the gelling point is exceeded and the molecular weight of the copolymerized polyester resin can be sufficiently increased for practical use. Not preferred. These are not necessarily 1
It is not necessary to use them by type, and it is possible to use a mixture of two or more types according to the properties to be imparted to the resin.

Next, the glycol residue constituting the copolymerized polyester resin of the present invention includes (A) a glycol residue having a branched chain structure having 3 or less carbon chains between glycol groups and (B) a glycol residue having 4 carbon atoms. It is necessary to use not less than 50 mol% in combination with -20 linear glycols. In addition to improving the retort resistance and workability of the coating obtained by using both of them, it is possible to maintain the corrosion resistance and flavor properties, and to make the coating suitable for metal can inner surface coating applications. it can. Further, the molar ratio between the component (A) and the component (B) needs to be 40/60 to 80/20. (A)
When the ratio of (A) to + (B) is less than 40 mol%, the retort resistance of the coating film is more than 80 mol%.

Examples of the glycol residue having a branched structure in which the number of carbon chains between the glycol groups is 3 or less include, for example, 1,2-
Propanediol, 1,2-butanediol, 1,3-
Butanediol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-
Amino-2-ethyl-1,3-propanediol, 2-
Amino-2-methyl-1,3-propanediol, 2-
Ethyl-2-methyl-1,3-propanediol, 2-
Each residue such as butyl-2-ethyl-1,3-propanediol and neopentyl glycol is exemplified. Among them, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2- Each residue of ethyl-2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and neopentyl glycol is more preferable.

Examples of the linear glycol residue having 4 to 20 carbon atoms include 1,4-butanediol and 1,5-butanediol.
Pentanediol, 1,6-hexanediol, 1,7
-Heptanediol, 1,8-octanediol, 1,
9-nonanediol, 1,10-decanediol, 1,
11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol,
1,16-hexadecanediol, 1,17-heptadecanediol, 1,18-octadecanediol, 1,
Each residue such as 19-nonadecanediol and 1,20-eicosandiol can be exemplified. this house,
1,4-butanediol, 1,5-pentanediol,
Each residue of 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol is more preferable, and 1,4-butanediol, Residues of 1,5-pentanediol and 1,6-hexanediol are more preferred, and residues of 1,4-butanediol are particularly preferred.

[0015] Of the glycol residues constituting the copolymerized polyester resin of the present invention, in addition to the glycols belonging to the above (A) and (B), the properties of the copolymerized polyester resin of the present invention are not impaired. , Other glycol residues. Other glycol residues include, for example, each residue of aliphatic glycol such as ethylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, polyethylene glycol, polytetramethylene glycol, and polypropylene glycol; Cyclohexane dimethanol,
Examples of alicyclic glycol residues such as 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol can be given.

Further, if necessary, a trifunctional or higher functional alcohol can be used in an amount of 5 mol% or less of the glycol component. If it is at least 5 mol%, the gelling point will be exceeded, and the molecular weight of the copolymerized polyester resin cannot be sufficiently increased for practical use. Examples of trifunctional or higher alcohols include glycerol, trimethylolpropane, trimethylolethane, α-methylglucose, mannitol,
Sorbitol. These need not necessarily be used alone, and a plurality of types may be used in combination according to the properties to be imparted to the resin.

The production method for obtaining the copolymerized polyester resin for forming a film on the inner surface of a metal can of the present invention can be produced by a known production method such as a direct esterification method or a transesterification method by a melt polymerization method. .

The production method by the direct esterification method will be described in more detail. The polyhydric alcohol, the polycarboxylic acid and the catalyst, which are the raw materials of the copolymerized polyester resin of the present invention, are charged all at once into a reactor. Is exhausted and replaced with nitrogen. Thereafter, the temperature is raised to the esterification temperature (200 to 240 ° C.), and the reaction is carried out for 2 to 8 hours with stirring. After the completion of the esterification reaction, the temperature is raised to the polymerization temperature (220 to 290 ° C.), and the polymerization reaction is performed under a high vacuum while further reducing the pressure in the system. The reaction time varies depending on the type of resin to be produced, but is usually 3 to 10 hours. After the completion of the polymerization reaction, nitrogen is sealed in the system, the pressure is released, and the resin is discharged to obtain a copolymerized polyester resin.

As a method for controlling the molecular weight of the copolymerized polyester resin of the present invention, a method of terminating the polymerization of a polyester melt at the time of polymerization at a predetermined viscosity or a method of producing a polyester having a high molecular weight once and then adding a depolymerizing agent is used. how to,
Further monofunctional alcohols (eg cetyl alcohol,
Decyl alcohol, lauryl alcohol, myristyl alcohol, octyl alcohol, stearyl alcohol) and benzoic acid. Although the molecular weight of the copolymerized polyester resin of the present invention may be controlled by any of the methods described above, a method of controlling the copolymerized polyester resin melt at the time of polymerization with a predetermined viscosity is suitably used. In addition, when increasing the number of alcoholic hydroxyl groups, it is preferable to proceed the polymerization reaction so that the molecular weight of the copolymerized polyester resin exceeds the target, and depolymerize with a low molecular substance having a polyfunctional alcoholic hydroxyl group.

Examples of catalysts that can be used in producing the copolymerized polyester resin of the present invention include antimony compounds such as antimony trioxide, organic titanate compounds such as tetrabutyl titanate, zinc acetate, magnesium acetate and the like. Organic tin compounds such as alkali metal and alkaline earth metal acetates, and hydroxybutyltin oxide. The amount of the catalyst used is preferably in the range of 0.01 to 1.0% by mass based on the mass of the produced resin. If the amount is less than 0.01% by mass, the polyester may not reach a desired molecular weight. On the other hand, if the amount exceeds 1.0% by mass, the molecular weight of the resin increases to a practically acceptable level. It is not preferable because elution is concerned.

The intrinsic viscosity of the copolymerized polyester resin for forming an inner surface coating of a metal can of the present invention is 0.2 to 1.times.1 measured at 20.degree. C. using a phenol / tetrachloroethane mixed solvent (mass ratio 6/4) as a solvent. It needs to be in the range of 0 dl / g, and more preferably 0.2 to 0.8 dl / g. When the intrinsic viscosity is less than 0.2 dl / g, a low-molecular-weight oligomer is eluted in the content and the flavor may be poor, or the workability may be reduced in a can forming process after baking a steel plate. Therefore, it is not preferable. On the other hand, when the intrinsic viscosity exceeds 1.0 dl / g, it is difficult to produce such a high-viscosity material,
The crosslinking density reacted with the curing agent is undesirably low.

The resin composition for forming a film on the inner surface of a metal can of the present invention comprises a copolymerized polyester resin for forming a film, which is a main component, and a curing agent. The curing agent constituting the resin composition of the present invention is selected from phenol resins, aminoplast resins, melamine resins, polyfunctional isocyanate compounds, blocked isocyanate compounds, and polyfunctional aziridine compounds. The amount of the curing agent to be added is 2 per 100 parts by mass of the base resin.
To 30 parts by mass, more preferably 3 parts by mass.
２５25 parts by mass. If the amount of the curing agent is less than 2 parts by mass, the crosslinking reaction becomes insufficient, and the performance as a can, particularly retort whitening, is not preferred. On the other hand, when the amount exceeds 30 parts by mass, the curing agent becomes excessive and is dissolved in the beverage to deteriorate the flavor property, which is not preferable.

The resin composition for forming an inner surface coating of a metal can of the present invention is composed of a copolymerized polyester resin and a curing agent. However, a reaction catalyst and an accelerator are also required without departing from the spirit of the present invention. They can be used in combination depending on the situation. Further, as other resins, alkyd resin, urethane resin, epoxy resin not containing a bisphenol structure, acrylic resin modified olefin resin, blended with cellulose derivatives,
It is also possible to mix and use resins that have been subjected to block copolymerization and graft copolymerization. Further, as additives, repelling inhibitors, leveling agents, defoaming agents, anti-pecking agents, rheology control agents, pigment dispersants, lubricants, mold release agents, and the like can be used in combination.

The resin composition for forming an inner surface coating of a metal can of the present invention is preferably used after being dissolved in a solvent. The solvent that can be used is not particularly limited as long as it can dissolve both the above-described copolymerized polyester resin and the curing agent, and examples thereof include aromatic solvents such as benzene, toluene, and xylene, methylene chloride, Chlorine solvents represented by chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, acetic acid Ethyl, isophorone,
Ester solvents such as γ-butyrolactone, cellosolve acetate, carbitol acetate, propylene glycol monomethyl ether acetate, ketone solvents represented by acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diethyl ether, butyl cellosolve, ethyl cellosolve , Tetrahydrofuran, ether solvents such as 1,4-dioxane,
Methanol, ethanol, propanol, isopropanol, alcohol solvents such as butanol, butane, pentane, hexane, cyclohexane, heptane, octane, nonane and other aliphatic hydrocarbons, Solvesso 100,
And aromatic hydrocarbons such as Solvesso 150. These may be used alone or in combination of two or more. Among them, a mixed solvent of cyclohexanone and Solvesso 100 or a mixed solvent of carbitol acetate and Solvesso 150 is suitably used.

When the resin composition for forming a coating film on the inner surface of a metal can of the present invention is made into a solution using the above-mentioned solvent, the solid content concentration is 10
It is preferable that the amount is at least mass%. More preferably, 1
5 mass% or more. When the solid concentration is less than 10% by mass, not only is it difficult to form a film having a sufficient thickness, but also the ratio of the solvent in the composition is high,
It takes a long time to evaporate the solvent when forming the coating, which causes a problem that the productivity is reduced.

The solution of the resin composition for forming an inner surface coating of a metal can is prepared by a dip coating method, a brush coating method, a roll coating method, a spray coating method, a gravure coating method, a curtain flow coating method, various printing methods, or the like. Uniformly coated on metal plate.

As the metal plate, a sheet-shaped or band-shaped steel plate and an aluminum plate, or those obtained by subjecting their surfaces to various plating treatments or chemical conversion treatments are preferable.

Particularly, a tin-free steel (TF) having a two-layer structure of metal chromium in the lower layer and chromium hydrated oxide in the upper layer
S) is preferable, and further, one or two or more kinds of multi-layer plating of tin, nickel, zinc, aluminum, etc.
Alloy plating, a film with the above two-layer structure or chromium hydrated oxide film formed on the upper layer, aluminum is subjected to electrolytic chromic acid treatment, immersion chromic acid treatment, etc. Those having an oxide film formed thereon can be used.

After coating the resin composition for forming an inner surface coating of a metal can of the present invention on a metal plate and baking it, a can inner surface coating layer can be formed. The thickness of the coating is 0.2μ
m to 100 μm, more preferably 1 μm to 1 μm.
0 μm. When the thickness is less than 0.2 μm, the coating film is damaged (peeling or cracking) in the can forming step, resulting in a can having inferior corrosion resistance and flavor. On the other hand, when the thickness exceeds 100 μm, the solvent used in the resin composition may remain, or even if the solvent can be completely removed, the solvent removal step takes a long time to impair productivity.

In the baking step, the temperature is from 180 ° C. to 250
It is preferable to perform the reaction in a temperature range of 10 ° C. for 10 minutes to 60 minutes. More preferably, the temperature is from 200C to 240C.
° C, time 20 to 40 minutes. When the temperature is lower than 180 ° C., the distillation of the solvent is incomplete, the curing reaction does not proceed sufficiently, and only a can with poor corrosion resistance can be obtained. On the other hand, when baked at a temperature exceeding 250 ° C., the reaction with the curing agent proceeds sufficiently, but the copolyester resin may be decomposed by heat. If the baking time is less than 10 minutes, the solvent is not distilled off or the curing reaction proceeds insufficiently. On the other hand, when the baking time exceeds 60 minutes, there is no problem with respect to the distillation of the solvent and the curing reaction of the phenol resin, but the productivity is reduced.

As the metal can body to which the resin composition of the present invention can be used, a metal container which has been processed to a form that can be filled with food and drink and used for use, and a part thereof, for example, a tightening process Also included is a can lid molded into a shape that allows for the following. In particular, severe neck-in processing 3
When used as a can body member of a piece can (3P can) or a can body member of a two-piece can (2P can) manufactured by drawing and ironing, excellent workability of the coating on the inner surface of the can of the present invention is exhibited. You.

The metal can body formed with a coating composed of the resin composition mainly comprising the copolymerized polyester resin of the present invention has excellent retort resistance, flavor properties and corrosion resistance. Suitable for filling contents such as food.

[0033]

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples, and various modifications and changes can be made without departing from the spirit of the present invention. Application is possible.

The method for producing the copolymerized polyester resin of the present invention is shown in the following Reference Examples. Reference Example (Production Method of Resin A) Terephthalic acid 166 kg,
104 kg of 1,2-propanediol, 22 kg of 1,4-butanediol and 21 g of hydroxybutyltin oxide as a catalyst were charged into a reactor, and the inside of the system was replaced with nitrogen. While stirring the charged raw materials at 30 rpm, the reactor was pressurized to 0.4 MPa and heated at 240 ° C. to melt the contents. The esterification reaction was allowed to proceed for 4 hours after the temperature in the reactor reached 240 ° C. After the completion of the esterification reaction, the temperature inside the system is raised to 245 ° C. and the pressure is reduced. The polymerization reaction was performed for 7 hours after the inside of the system reached a high vacuum.
After completion of the polymerization reaction, the pressure was returned to normal pressure by filling nitrogen in the system, and the generated resin was discharged out of the system. Hereinafter, copolymerized polyester resins of B to I and J to P were produced in the same manner as in Reference Example. However, the resins I and O are synthesized after synthesizing a copolymer polyester resin having a higher viscosity than desired by the above method,
Before dispensing, add trimethylolpropane and add temperature 2
After the depolymerization reaction was performed at 45 ° C. for 1 hour, the mixture was discharged.

A) Evaluation method of characteristic value of resin 1) Composition analysis The composition of the resin was analyzed by using a proton NMR (manufactured by JEOL Ltd., apparatus name: JOEL LAMDBA300WB). 2) Glass transition temperature DSC7 manufactured by PerkinElmer was used as an apparatus, and the temperature was raised at a rate of 20 ° C / min. 3) intrinsic viscosity phenol / tetrachloroethane mixed solvent (mass ratio 6 /
4) and dissolved at a measurement temperature of 20 ° C., and indicated in units of dl / g. A list of characteristic values of the obtained resin is shown in Table 1 below.
Shown in

[0036]

【table 1】

B) Method for Forming and Evaluating Can Body 1) Method for Forming Two-Piece Metal Can Body 1) -1 Method for Producing Resin Composition for Forming Coating Copolymer polyester resin 100 obtained as described above
By mass, a predetermined amount of a curing agent described in Table 2 was mixed with the curing agent and dissolved in a mixed solvent of cyclohexanone / solvesso 100 (mixing volume ratio: 5/5) so as to be 30% by mass. A resin composition for forming a metal can inner surface coating was prepared. 1) -2 Coating method on metal plate and production of metal can body On a roll-shaped tin-free steel (TFS, temper degree T-4) having a thickness of 0.24 mm and a width of 22 cm, 1)
The composition prepared in -1 was continuously applied using a gravure coater, followed by drying and baking for 30 minutes in a hot-air circulation type oven adjusted to 200 ° C. Using the obtained coated metal plate, drawing and ironing is performed under the following forming conditions, and then neck-in processing and trimming are performed to obtain a 202P 2P can (outer diameter 56 mm, trunk height 100 mm).
I got Blank diameter: 139 mm Drawing condition: First drawing ratio 1.85, Second drawing ratio 1.42 Ironing punch diameter: 52.65 mm Total ironing rate: 35% 2) Evaluation method of coating liquid 1) -1 The prepared coating solution was applied at 5 ° C. × 1 day, room temperature × 1 day,
In a cycle of 50 ° C. × 1 day, the presence or absence of alteration such as thickening and cloudiness was visually confirmed. 3) Metal can body evaluation method 3) -1 Workability The metal can body is formed and processed, and the presence or absence of damage such as peeling, cutting, and cracking of the coating after the forming is visually observed and observed with a fluorescence microscope (80x magnification). And evaluated according to the following criteria. ：: 95 or more of the 100 cans were not damaged. Δ: 80 to 94 out of 100 cans were not damaged. C: Out of 100 cans, 21 or more can be damaged. 3) -2 Retort-resistant metal can body was autoclaved (BS-3, manufactured by Tommy Seiko)
25), and subjected to a retort treatment in steam at 120 ° C. for 60 minutes, and visually observed whitening and the occurrence of water spots (white spots) as an index of retort resistance. ：: good. Δ: Some change was observed in less than 5% of the surface area of the coating. X: Some change was seen in 5% or more of the coating surface area. 3) -3 Corrosion resistance For metal cans evaluated as having good moldability, the cans were filled with an aqueous solution in which 3% by mass of sodium chloride, malic acid, and citric acid were dissolved, and sealed. , 60 ° C
For 2 weeks, and opened, and the state of rust generation in the can was evaluated according to the following criteria. ：: Almost no rust is visually observed. Δ: Rust is scattered, and the total area is less than 5% of the film surface area. ×: Rust is generated on almost the entire surface, and the total area is 5% or more of the film surface area. 3) -4 Flavorability Fill a metal can body with distilled water and use commercially available 206 diameter or 2
A 02-diameter aluminum EO lid was tightly wound and sealed, and retort treatment was performed in the same manner as described above. Next, after sufficiently cooling to room temperature, the contents were tasted by 100 panelists, and whether or not the odor, taste, etc. were different from that of distilled water was determined, and the results were flavored according to the following criteria. The index was used. In addition, it was previously confirmed that the aluminum EO lid had no adverse effect on the taste test. ：: Less than 5 people sensed the difference between the two. Δ: The number of persons who sense the difference between the two is 5 or more and less than 20. ×: The number of people who sensed the difference between the two was 20 or more. Table 2 shows the evaluation results of the two-piece metal cans manufactured by the above method.

[0038]

[Table 2]

In Examples 1 to 11, the stability, workability, retort resistance, corrosion resistance, and flavor of the coating solution were all good. Comparative Example 1 was inferior in processability because the content of the glycol residue of (B) in the copolymerized polyester was low. In Comparative Example 2, the ratio of (A) + (B) in the copolymerized polyester was low, and at the same time, the content of the glycol residue in (A) was low, so that the overall performance was low, and particularly the retort resistance was poor. It became. Comparative Example 3
Was poor in retort resistance because the ratio of (B) in the copolymerized polyester was high. Comparative Example 4 was poor in processability because the ratio of (A) in the copolymerized polyester was high. In Comparative Example 5, since the amount of the aromatic dicarboxylic acid residue in the copolymerized polyester was less than 50 mol%, the retort resistance was poor. Comparative Example 6
Used a copolymerized polyester having an intrinsic viscosity of less than 0.2, resulting in inferior flavor. In Comparative Example 7, the performance was low as a whole because the ratio of (A) + (B) in the copolymerized polyester was low.

[0040]

The copolymerized polyester resin of the present invention has a high solubility in a solvent, so that a coating film can be easily formed by a casting method or a calendering method as a coating liquid. The polymerized polyester resin does not use an epoxy resin, and not only solves the problem of the canning process which has been regarded as a problem such as sufficient retort resistance and high workability, but also uses the polyester resin and a curing agent together. Resin for forming film on the inner surface of metal cans (beverage cans, food cans), because it also satisfies the characteristics such as corrosion resistance and lack of elution of low molecular weight substances that impair the flavor properties, which are essential performances of cans. It can be used as a composition.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AB01A AK31B AK31H AK33B AK33H AK36B AK36H AK42B AK42K AK51B AK51H AK53B AK53H BA02 CA02B GB16 JB02 JB07 JL00 4J029 AA03 BA01 BA01 BA03 BA01 BA01 BA04 BH01 CA02 CA06 CB04A CB05A CB06A CD03 DA02 GA13 GA14 GA22 GA73 JA091 JB131 JB171 JE181 JF131 JF181 JF321 JF371 JF471 KD02 KD07 KE02 KE03 KE05 4J038 DA042 DA112 DD001 DD061 DG262 DG302 JB26 KA302

Claims (3)

[Claims] 1. A copolymerized polyester comprising a glycol residue and a polycarboxylic acid residue, wherein at least 50 mol% of an aromatic dicarboxylic acid residue is contained in all the polyvalent carboxylic acid residues, and (A) a glycol residue having a branched structure with a carbon chain between glycol groups of 3 or less and (B) a linear glycol residue having 4 to 20 carbon atoms. The ratio of (A) + (B) is 50 mol% or more, and (A) / (B) is 40/60 to 8
0/20 (molar ratio), and the intrinsic viscosity is 0.2 to 1.0.
dl / g copolymerized polyester resin for forming an inner surface coating of a metal can. 2. A phenol resin, an aminoplast resin, a melamine resin, a polyfunctional isocyanate compound, a blocked isocyanate compound, and the like, based on 100 parts by mass of the copolymerized polyester resin for forming an inner surface coating of a metal can described in claim 1.
2-30 curing agents selected from polyfunctional aziridine compounds
A resin composition for forming a metal can inner surface coating compounded by mass. 3. A resin film comprising the resin composition for forming an inner surface film of a metal can according to claim 2.