JP2017002159A - Polyester resin and resin composition for can coating containing the same - Google Patents

Abstract

[Problem] To provide a polyester resin suitable for a resin composition for can coating and a resin composition for can coating which can form a coating film which is excellent in resistance to contamination of contents and alkali and can hardly be deteriorated in workability after aging.
A polyester resin obtained by reacting a polycarboxylic acid (A) and a polyol (B), wherein terephthalic acids are contained in an amount of 15 to 40 mol% in a total of 100 mol% of the polycarboxylic acid (A). It contains 50 to 85 mol% of isophthalic acid, 10 to 45 mol% of alicyclic diol in the total of 100 mol% of the polyol (B), has primary hydroxyl groups at both ends, and has no side chain. 40 to 80 mol% of linear diol (a) having 4 to 6 carbon atoms, 5 to 35 mol of diol (b) having 3 to 4 carbon atoms having one primary hydroxyl group and one secondary hydroxyl group % Polyester resin.
[Selection figure] None

Description

    The present invention relates to a polyester resin, a resin composition for can coating using the same, a can lid, a coated can, and a beverage can.

Conventionally, BPA type epoxy resin synthesized from bisphenol A (hereinafter also referred to as “BPA”) and epichlorohydrin forms a coating film with excellent steam sterilization resistance (retort resistance), processability and adhesion. As a result, it has been widely used as a coating for coating the inner and outer surfaces of cans.
However, research results have been reported that BPA has the effect of disrupting the endocrine activity of organisms, and it was listed in 67 substances in the list of “chemical substances suspected of having endocrine disrupting activity” published by the Ministry of the Environment. In response to this, BPA eluted into the contents from the coating film covering the inner surface of the can. Therefore, a can coating material that does not use any BPA-derived raw material has been demanded.

Here, the paint that coats the inner surface of the can can be processed at the time of molding of the can member in addition to flavor resistance, corrosion resistance, retort resistance, etc. that do not impair the flavor of the contents. There was a need to be able to form films.
Among the can members, the lid member has a shape with many irregularities and is subjected to advanced molding processing as compared with other members. Therefore, the coating film formed on the lid member requires particularly high workability. .

  Furthermore, due to the type of can contents and the molding process of the can member, the coating film needs to have acid resistance and alkali resistance. In addition to the above required physical properties, a paint satisfying acid resistance and alkali resistance has been demanded. .

Furthermore, beverage cans and food cans may be subjected to a retort treatment at a high temperature for the purpose of sterilization of the contents after filling the contents according to the kind of the contents. Therefore, when the retort resistance of the inner surface coating film is not sufficient, components in the coating film may be eluted in the contents during the retort treatment, which is not preferable for hygiene. In addition, when the retort resistance of the coating film is poor, the coating film component may be eluted into the contents even when the retort treatment is not performed and the film is stored at room temperature. As described above, the inner surface coating film of the can is required to have such resistance that the component hardly dissolves into the contents. In the present invention, the property of the components in the coating film that hardly dissolve into the content is referred to as “content contamination resistance”.
This resistance to content contamination is usually estimated by the amount of organic components eluted from the coating film. The smaller the amount of the organic component to be eluted, the better the resistance to content contamination.

Patent Document 1 discloses a coating composition comprising a mixed polyester resin obtained by mixing two types of polyester resins, a curing agent, and a curing catalyst.

Patent Document 2 discloses a coating composition containing a polyester resin using a specific polyalcohol as a raw material and a curing agent.

Patent Document 3 discloses a can inner surface coating composition containing a polyester resin using a specific polyalcohol as a raw material and a curing agent.

JP 2013-249376 A JP 2004-292664 A JP 2001-172561 A

However, the paint of Patent Document 1 improves the workability after aging after forming a coating film by using a polyester resin having a high glass transition temperature and a polyester resin having a low glass transition temperature. On the other hand, there was a problem that the resistance to contamination of the contents and the alkali resistance deteriorated.
Moreover, although the coating material of patent document 2 improved the content-proof property of the coating film by using the polyester resin characterized by trihydric or more polyalcohol, the high workability required for the lid member, and the content-proof There was a problem of insufficient contamination.
In addition, the paint of Patent Document 3 provides a coating film that is excellent in retort resistance and hardly deteriorates in workability after aging. However, since an amino resin is used as a curing agent, content contamination resistance and There was a problem of insufficient acid resistance.

  The present invention is a polyester resin suitable for a resin composition for can coating that can form a coating film that is excellent in content contamination resistance and alkali resistance and is less likely to deteriorate after the passage of time (hereinafter simply referred to as “processability”). And it aims at provision of the resin composition for can coating | cover.

As a result of intensive studies, the present inventors have reached the present invention.
That is, the present invention is a polyester resin obtained by reacting a polycarboxylic acid (A) and a polyol (B), and 15 to 40 mol of terephthalic acids in a total of 100 mol% of the polycarboxylic acid (A). %, Containing 50 to 85 mol% of isophthalic acid, and 10 to 45 mol% of alicyclic diol and 4 to 6 carbon atoms in a total of 100 mol% of the polyol (B). A diol (b) having 40 to 80 mol%, 3 to 4 carbon atoms, and having one primary hydroxyl group and one secondary hydroxyl group. ) To 5 to 35 mol% of a polyester resin.

The present invention also relates to the polyester resin, wherein the alicyclic diol is 1,4-cyclohexanedimethanol.

The present invention also relates to the polyester resin, wherein the diol (b) is at least one selected from the group consisting of propylene glycol, 1,2-butanediol and 1,3-butanediol.

The present invention also relates to a can coating resin composition comprising the polyester resin and a phenol resin.

Moreover, this invention relates to the said resin composition for can coating | covers for can inner surfaces.

The present invention also relates to a can lid formed by coating at least one surface of a can lid member with the can coating resin composition.

The present invention also relates to a coated can in which a can body is coated with the can coating resin composition.

The present invention also relates to a beverage can comprising the can lid and a can body member.

The present invention also relates to a beverage can comprising the coated can.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polyester resin and a can coating resin composition that can form a coating film that is excellent in resistance to content contamination and alkali resistance and is less likely to deteriorate in workability after time.

FIG. 1 is a schematic diagram illustrating a method for creating a test piece for a bending workability test.

Before describing the present invention, terms are defined. The polycarboxylic acid (A) includes a compound in which a carboxyl group in the polycarboxylic acid is esterified with a monoalcohol such as methanol or ethanol, and an acid anhydride of the polycarboxylic acid.
In the present specification, “terephthalic acid” means terephthalic acid which may be substituted with an alkyl group, and “isophthalic acid” means isophthalic acid which may be substituted with an alkyl group.
When the above esterified compound is used as the polycarboxylic acid (A), the “number of carboxyl groups of the polycarboxylic acid (A)” is “—COOH” and “—COOR” (R is an alkyl alcohol). Is the alkyl group of the alkyl alcohol used for the esterification).
In addition, since an acid anhydride group is generated by dehydration from two carboxyl groups, in the present invention, one acid anhydride group corresponds to two carboxyl groups. For example, trimellitic anhydride is regarded as a compound having three carboxyl groups. The content resistance property refers to the property that the coating film is not easily damaged by the contents of the can, and the contents are acidic food, salt, fish meat and the like. Acidic foods corrode iron, the material of cans, and salt oxidizes iron. Fish meat also contains trace amounts of sulfur compounds, which react with iron and turn the can black.

The polyester resin of the present invention is synthesized by reacting the polycarboxylic acid (A) and the polyol (B).
Of the total 100 mol% of the polycarboxylic acid (A), terephthalic acids are 15 to 40 mol%, isophthalic acids are 50 to 85 mol%, and the total of 100 mol% of the polyol (B) is alicyclic. Linear diol (a) having 10 to 45 mol% type diol, 4 to 6 carbon atoms, having primary hydroxyl groups at both ends, and having no side chain, 3 to 3 carbon atoms 4 and it is important that it is 5 to 35 mol% of the diol (b) having one primary hydroxyl group and one secondary hydroxyl group. If the ratio of the polycarboxylic acid (A) and the polyol (B) is within the above range, it does not contain any BPA-derived components, and when used as a resin composition for can coating, It is possible to obtain a polyester resin that is excellent in alkali resistance and difficult to process.

In a more preferred embodiment of the polyester resin of the present invention, terephthalic acids are 15 to 35 mol%, isophthalic acids are 55 to 85 mol% in a total of 100 mol% of the polycarboxylic acid (A), and a polyol ( B) A linear diol (a) having 10 to 40 mol% of alicyclic diol and 4 to 6 carbon atoms, having a primary hydroxyl group at both ends, and having no side chain. ) 40 to 70 mol%, 3 to 4 carbon atoms, diol (b) having 5 to 30 mol% of one primary hydroxyl group and one secondary hydroxyl group.

The polyester resin of the present invention can be preferably used as a resin composition for can coating. More specifically, it is preferably used as an aspect of a paint. This paint is used for coating metal cans such as aluminium, tinplate, iron, etc., film-laminated metal cans made by laminating plastic films such as PET (polyethylene terephthalate) films on the above metals, and can bodies of plastic cans. It is preferable to do.
Moreover, the resin composition for can coating | cover of this invention can be preferably used also as an aspect of the adhesive agent which bonds a plastic film and a metal in a film laminated metal can. If necessary, a coating layer may be further provided on the surface of the plastic film of the film laminated metal can.
Any of the above-described embodiments, that is, use as a paint and use as an adhesive, can produce a coated can in which the can body is coated with the can coating resin composition of the present invention.

Examples of the polycarboxylic acid (A) include the following compounds in addition to terephthalic acids and isophthalic acids.
Examples of the aromatic dibasic acid include orthophthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid.
Examples of the aliphatic dibasic acid include sebacic acid, adipic acid, succinic acid, azelaic acid, dodecanedioic acid, and dimer acid.
Examples of the alicyclic dibasic acid include 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, and the like.
Other examples include α, β-unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid.
In addition, the alkyl ester of these compounds and an acid anhydride can also be used as polycarboxylic acid (A).

In order to introduce a branched structure into the polyester resin, a tri- or higher functional acid may be used in addition to the dibasic acid. As an example thereof, for example, (anhydrous) trimellitic acid [trimellitic acid and trimellitic anhydride are collectively referred to as “(anhydrous) trimellitic acid”. The same applies below. ], (Anhydrous) pyromellitic acid, ethylene glycol bis trimellitate dianhydride, etc. are mentioned.
Furthermore, a monofunctional acid may be used as necessary.

In the polyol (B), it is important to use at least 10 to 45 mol% of the alicyclic diol out of 100 mol% in total of the polyol (B), and it is preferable to use 10 to 40 mol%. This polyol provides processability, retort resistance, and alkali resistance.
As the alicyclic diol, 1,4-cyclohexanedimethanol is preferable.

The polyol (B) is a linear diol (a) having at least 4 to 6 carbon atoms in the total 100 mol% of the polyol (B), having primary hydroxyl groups at both ends, and having no side chain. ) Is important to use in an amount of 40 to 80 mol%, preferably 40 to 70 mol%. This polyol provides processability, resistance to content contamination, and adhesion of the coating film.
The linear diol (a) is preferably an alkanediol in which two hydroxyl groups are bonded to a linear alkylene group, such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and the like. Can be mentioned.

The polyol (B) has at least 3 to 4 carbon atoms in a total of 100 mol% of the polyol (B), and 5 to 35 diols (b) having one primary hydroxyl group and one secondary hydroxyl group. It is important to use mol%, and it is preferable to use 5 to 30 mol%. With this polyol, the production stability of the polyester resin and the solubility in the solvent can be further improved, and the content contamination resistance and alkali resistance can be obtained.
As the diol (b), propylene glycol, 1,2-butanediol and 1,3-butanediol are preferable.

As the polyol (B), the following compounds can be used in addition to the alicyclic diol, the linear diol (a), and the diol (b).
Examples of the aliphatic diol having 2 to 10 carbon atoms include ethylene glycol, 1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-methyl-1, Examples include 3-propanediol and 2-ethyl-2-butyl-1,3-propanediol.
Examples of the diol containing an ether bond include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

In order to introduce a branched structure into the polyester resin, a trifunctional or higher functional alcohol may be used in addition to the diol. Specific examples include trimethylolpropane, glycerin, trimethylolethane, mannitol, sorbitol, pentaerythritol, and α-methylglucoside.
Furthermore, you may use monofunctional alcohol as needed.

  The polyester resin in the present invention can be obtained by subjecting polycarboxylic acid (A) and polyol (B) to a condensation reaction or a transesterification reaction at a high temperature. When an acid anhydride is used, an addition reaction occurs partly. The end point of the reaction is usually determined by the acid value.

When the polycarboxylic acid (A) does not contain an esterified product, the compounding ratio of the polycarboxylic acid (A) and the polyol (B) is the number of hydroxyl groups (N _B ) in the polyol ( _B ) and the polycarboxylic acid (A preferably) the ratio of the number of carboxyl groups (N _a) in is N _B / N _a = 1.10~1.40, more preferably 1.15 to 1.35.
Further, when the polycarboxylic acid (A) comprises ester is preferably N _B / N _A = 1.10~2.40, more preferably 1.20 to 2.10.
If the ratio of the N _B and N _A is within the above range, acid resistance when used in can coating resin composition, alkali resistance, retort resistance and workability more excellent, and workability is decreased more with time It is possible to obtain a polyester resin that is difficult to do.

The number average molecular weight of the polyester resin of the present invention is preferably 5,000 to 30,000, more preferably 8,000 to 25,000. If the number average molecular weight is in this range, the solubility in a solvent can be further improved, and a coating film with more excellent workability and retort resistance can be formed.
In addition, the number average molecular weight in this specification is the value of standard polystyrene conversion by GPC (gel permeation chromatography).

The glass transition temperature of the polyester resin of the present invention is preferably 20 to 70 ° C, more preferably 25 to 60 ° C. When the glass transition temperature is within this range, a polyester resin having more excellent resistance to content contamination, alkali resistance, retort resistance and processability when used in a can coating resin composition can be obtained.

  The polyester resin of the present invention gives an acid value by a method of adding a polycarboxylic acid anhydride after or during the polymerization reaction in order to improve adhesion to metals and plastics and reactivity with a curing agent. May be. Examples of the polycarboxylic acid anhydride used for imparting an acid value include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, ethylene glycol bistrimellitic dianhydride, and the like.

The acid value of the polyester resin of the present invention is preferably 30 mgKOH / g or less, and more preferably 20 mgKOH / g. When the acid value is within this range, the content contamination resistance, retort resistance, acid resistance and alkali resistance are further improved. The lower limit of the acid value is 0 mgKOH / g.

  The resin composition for can coating | cover of this invention contains the polyester resin and phenol resin of this invention. The phenol resin is a curing agent for crosslinking the polyester resin when the coating film is baked and cured. The phenol resin is a resin synthesized by an addition condensation reaction between a phenol monomer and an aldehyde such as formaldehyde.

Examples of the phenol monomer include phenol, o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-nonylphenol, 2,3-xylenol, 2,5-xylenol, m-cresol, 3,5. -Xylenol, resorcinol, bisphenol A, bisphenol F, bisphenol B, bisphenol E, bisphenol H, bisphenol S, catechol, hydroquinone and the like. Among these, phenol, o-cresol, m-cresol, p-cresol and the like which are excellent in curability and reactivity are preferable, and m-cresol is more preferable.
A phenol monomer may be used independently and may use 2 or more types together.

  In the phenol monomer, the ortho-position and the para-position serve as reaction sites with respect to the phenolic hydroxyl group. Therefore, o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-nonylphenol, 2,3-xylenol, 2,5-xylenol, etc. have two reactive sites in one molecule. , A phenol monomer having an equivalent number of 2 and a functional group of 2. In addition, phenol, m-cresol, 3,5-xylenol, resorcinol, and the like have three reactive sites in one molecule, and thus are phenol monomers with an equivalent number of 3 and have a functional group of 3. Also, bisphenol such as bisphenol A, bisphenol F, bisphenol B, bisphenol E, bisphenol H, bisphenol S, catechol, hydroquinone, etc. are phenol monomers with 4 equivalents because there are 4 reactive sites in one molecule. , The functional group is 4. When a phenol monomer having an equivalent number of less than 4 is used, it is easy to obtain a phenol resin having an appropriate molecular weight. Therefore, when such a phenol resin is used, the solubility with respect to a solvent improves and it is hard to produce the defect derived from a phenol resin on the coating-film surface.

In the present invention, the phenol resin is preferably a resin obtained by reacting m-cresol and an aldehyde. Since this phenol resin has high reactivity with the polyester resin and excellent curability, a coating film in which retort resistance and alkali resistance are excellent and workability is hardly lowered can be obtained.
Commercially available products that can be preferably used include, for example, Sumitrite Resin PR-55317 (metacresol phenol resin, non-volatile content 50%) manufactured by Sumitomo Bakelite Co., Ltd., Shounol CKS-3898 (metacresol phenol manufactured by Showa Denko KK). Resin, nonvolatile concentration 50%) and the like. In addition, metacresol type | system | group shows using m-cresol for the raw material of a phenol resin.

The weight ratio of the polyester resin to the phenol resin is preferably polyester resin / phenol resin = 95/5 to 75/25, and more preferably 90/10 to 85/15. If the weight ratio between the two is within this range, the workability, retort resistance and the like are further improved.

The resin composition for can coating according to the present invention contains, as necessary, additives such as a lubricant such as wax, a curing catalyst and a leveling agent, and an organic solvent for the purpose of preventing the coating film from being scratched in the can manufacturing process. Can be blended.
The wax is animal or vegetable wax such as carnauba wax, lanolin wax, palm oil, candelilla wax, rice wax;
Petroleum waxes such as paraffin wax, microcrystalline wax, petrolatum;
Examples thereof include synthetic waxes such as polyolefin wax and Teflon (registered trademark) wax.
Examples of the curing catalyst include dodecylbenzenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, and phosphoric acid compounds, and neutralized products thereof.

The resin composition for can coating of the present invention can be used regardless of the inner and outer surfaces of the can, and is preferably used as an inner coating of the can by taking advantage of its high workability, particularly the inner surface of the can lid member. It is preferable to use it for paints. In addition, it cannot be overemphasized that the resin composition for can coating | cover of this invention can be used also for the outer surface coating material of the member for can lids. The can lid of the present invention can be obtained by providing a coating layer made of a can coating resin composition on at least one surface of the can lid member.
Furthermore, since the resin composition for can coating of the present invention has good adhesion to a plastic film in addition to the above properties, as an adhesive for laminating a plastic film and a metal in a film laminated metal can. Can also be preferably used.

The coated can of the present invention includes a can body and a coating layer formed on the can body portion with the resin composition for can coating.
In the coated can, a coating layer is formed by coating a metal or plastic can body, and further, coating the resin composition for can coating of the present invention on the inner surface or outer surface of the film-laminated metal can and curing it.
In the present invention, an adhesive layer formed when used as an adhesive for bonding a plastic film and a metal in a film-laminated metal can is also included in the category of the coating layer.
The metal is preferably a metal plate such as aluminum, tin-plated steel plate, chrome-treated steel plate, or nickel-treated steel plate.
The plastic can is preferably made of polyolefin, polyester or the like.
As the plastic film used in the film laminated metal can, polyester, particularly PET is preferable.
In using as a paint and an adhesive, known methods such as spray coating such as air spray, airless spray, and electrostatic spray, roll coater coating, immersion coating, and electrodeposition coating can be used.
When coating on a metal, baking at a temperature of 200 to 300 ° C. for 10 seconds to 2 minutes is preferable, and 20 to 40 seconds is more preferable.

The coated can of the present invention contains beverages, soft drinks, beverages such as coffee, tea, beer, Chuhai, sake, whiskey, and water split as contents, fish meat, livestock meat, vegetables, fruits, oil, sauces, etc. Although the use which stores foodstuffs etc. is preferred, things other than food uses, such as engine oil, can also be stored.

One aspect of the beverage can of the present invention includes the can lid of the present invention and a can body member. In another aspect of the beverage can of the present invention, the can body member is coated with the can coating resin composition of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, “parts” represents “parts by weight” and “%” represents “% by weight” unless otherwise specified. “Mn” represents the number average molecular weight, and “Mw” represents the weight average molecular weight. “Polycarboxylic acid (A)” and “polyol (B)” may be abbreviated as “(A)” and “(B)”, respectively.

(Measurement conditions for number average molecular weight and weight average molecular weight)
Measurement was performed using a high-speed GPC apparatus 8020 series (tetrahydrofuran solvent, column temperature 40 ° C., polystyrene standard) manufactured by Tosoh Corporation. Specifically, it is a measured value obtained by connecting four columns of G1000HXL, G2000HXL, G3000HXL, and G4000HXL manufactured by Tosoh in series and measuring at a flow rate of 1.0 ml / min.

(Measurement conditions of glass transition temperature (Tg))
It measured with the temperature increase rate of 10 degree-C / min using the differential scanning calorimeter (DSC) ("DSC6220" made by SII).

(Measurement conditions of acid value)
0.2 g of the polyester resin was dissolved in 20 ml of THF (tetrahydrofuran) and titrated with a 0.1N KOH ethanol solution to determine the acid value (mgKOH / g) of the polyester resin.

First, examples of the polyester resin of the present invention are shown as production examples below.
[Production Example A (transesterification method)]
In a reaction vessel, 134.1 parts of dimethyl terephthalic acid (19.8 mol% in (A)), 52.5 parts of propylene glycol (16.5 mol% in (B)), 1,4-butanediol 248.8 Parts (66.1 mol% in (B)), 99.5 parts of 1,4-cyclohexanedimethanol (16.5 mol% in (B)), 4.6 parts of trimethylolpropane (0. 9 mol%), 0.1 part of zinc acetate, and 0.01 part of titanium butoxide were added, and the temperature was gradually raised to 220 ° C. to conduct a transesterification reaction. After distilling off the theoretical amount of methanol, 413.0 parts of isophthalic acid (71.3 mol% in (A)), 47.5 parts of 1,4-cyclohexanedicarboxylic acid (7.9 mol% in (A)) ) Was added and the temperature was gradually raised to 250 ° C. over 3 hours to carry out the esterification reaction. Next, after cooling to 230 ° C. under a nitrogen stream, the pressure was reduced to 5 mmHg or less over 30 minutes, and a polymerization reaction was carried out in that state for 3 hours. Thereafter, the resin was cooled to 200 ° C. under a nitrogen stream, and 6.6 parts of trimellitic anhydride (1.0 mol% in (A)) was added thereto and reacted for 2 hours. From the above, the polyester resin of the present invention was obtained. The obtained resin was adjusted with a mixed solvent of Flexisolv DBE esters (manufactured by Invista) / xylene = 1/1 (weight ratio) so that the nonvolatile content concentration was 40% to obtain a resin varnish.
The ratio of each monomer used in the above polymerization is shown as a molar ratio in Table 1. In addition, the trimellitic anhydride (acid addition) in Table 1 represents that the acid value was added to the polyester resin by adding and adding trimellitic anhydride at the latter stage of the polymerization reaction.

[Production Example B (direct polymerization method)]
In a reaction vessel, 115.6 parts of terephthalic acid (19.8 mol% in (A)), 416.2 parts of isophthalic acid (71.3 mol% in (A)), 47.9 1,4-cyclohexanedicarboxylic acid Parts (7.9 mol% in (A)), 58.2 parts propylene glycol (17.6 mol% in (B)), 257.0 parts 1,4-butanediol (65.6 mol in (B)) %), 1,4-cyclohexanedimethanol 100.3 parts (16.0 mol% in (B)), trimethylolpropane 4.7 parts (0.8 mol% in (B)), titanium butoxide 0 .01 part was charged into a polymerization reactor, the temperature was gradually raised to 250 ° C. in a nitrogen atmosphere, and an esterification reaction was carried out over 6 hours. Next, after cooling to 230 ° C. under a nitrogen stream, the pressure was reduced to 5 mmHg or less over 30 minutes, and a polymerization reaction was carried out in that state for 2 hours. Thereafter, the resin was cooled to 200 ° C. under a nitrogen stream, and 6.6 parts of trimellitic anhydride (1.0 mol% in (A)) was added thereto and reacted for 2 hours. From the above, the polyester resin of the present invention was obtained. The obtained resin was adjusted with a mixed solvent of Flexisolv DBE esters (manufactured by Invista) / xylene = 1/1 (weight ratio) so that the nonvolatile content concentration was 40% to obtain a resin varnish.

[Production Example I (direct polymerization method)]
In a reaction vessel, 146.1 parts of terephthalic acid (25.0 mol% in (A)), 368.3 parts of isophthalic acid (63.0 mol% in (A)), 14.2 parts of sebacic acid ((A) 2.0 mol%), 1,6-cyclohexanedicarboxylic acid 60.6 parts (10.0 mol% in (B)), propylene glycol 53.5 parts (16.6 mol% in (B)), 1 , 4-butanediol 253.5 parts (66.4 mol% in (B)), 1,4-cyclohexanedimethanol 101.4 parts (16.6 mol% in (B)), trimethylolpropane 2.4. Parts (0.4 mol% in (B)) and 0.01 parts of titanium butoxide are gradually charged to 250 ° C. in a nitrogen atmosphere and subjected to esterification over 6 hours. It was. Next, after cooling to 230 ° C. under a nitrogen stream, the pressure was lowered to 5 mmHg or less over 30 minutes, and a polymerization reaction was performed for 2 hours in this state to obtain the polyester resin of the present invention. The obtained resin was adjusted with a mixed solvent of Flexisolv DBE esters (manufactured by Invista) / xylene = 1/1 (weight ratio) so that the nonvolatile content concentration was 40% to obtain a resin varnish.

[Production Examples C to H]
Except having changed the raw material of manufacture example B into the raw material shown in Table 1, respectively, the polyester resin was synthesize | combined by carrying out similarly to manufacture example B, and the resin varnish of manufacture example CH was obtained, respectively.

[Comparative Production Examples J, K, M, O, P, Q]
A polyester resin was synthesized in the same manner as in Production Example B, except that the raw materials of Production Example B were changed to the raw materials shown in Table 1, and Comparative Production Examples J, K, M, O, P, and Q were respectively used. A resin varnish was obtained.

[Comparative Production Examples L, N, R]
A polyester resin was synthesized in the same manner as in Production Example I except that the raw materials of Production Example I were changed to the raw materials shown in Table 1, and resin varnishes of Comparative Production Examples L, N, and R were obtained.

[Example 1]
483.4 parts of the polyester resin varnish obtained in Production Example A, Sumilite resin PR-55317 (metacresol phenol resin, n-butanol solution having a nonvolatile concentration of 50%, manufactured by Sumitomo Bakelite Co., Ltd.) as the phenol resin 43.1 As a curing catalyst, 153.2 parts of Flexisolv DBE esters (Invista), 191.0 parts of xylene, 23.6 parts of butyl cellosolve, 28.4 parts of n-butanol and 76.8 parts of cyclohexanone are mixed as a solvent. 0.5 parts of dodecylbenzenesulfonic acid was added to obtain a paint (resin composition for can coating) having a nonvolatile content concentration of 21.5%. In Table 2, the compounding quantity (part) of a polyester resin, a phenol resin, and a curing catalyst is shown.

[Examples 2 to 9]
Example 1 except that the polyester resin varnish obtained in Production Example A was changed to the polyester resin varnish obtained in Production Examples Production Examples B, C, D, E, F, G, H, and I, respectively. The paint was obtained for each.

[Example 10]
429.8 parts of the polyester resin varnish obtained in Production Example B instead of 483.4 parts of the polyester resin varnish obtained in Production Example A, Sumilite Resin PR-55317 (metacresol phenol resin, non-volatile content concentration 50% The n-butanol solution (manufactured by Sumitomo Bakelite Co., Ltd.) was applied in the same manner as in Example 1 except that 86.0 parts were used instead of 43.1 parts and 201.7 parts were used instead of 191.0 parts of xylene. Obtained.

[Example 11]
Instead of 483.4 parts of the polyester resin varnish obtained in Production Example A, 499.7 parts of the polyester resin varnish obtained in Production Example B, Sumilite Resin PR-55317 (metacresol phenolic resin, nonvolatile content concentration 50% The n-butanol solution (manufactured by Sumitomo Bakelite Co., Ltd.) was used in the same manner as in Example 1 except that 30.1 parts were used instead of 43.1 parts, and 187.7 parts were used instead of 191.0 parts of xylene. Obtained.

[Comparative Examples 12 to 20]
Instead of the polyester resin varnish obtained in Production Example A, Examples were changed to the polyester resin varnish obtained in Comparative Production Examples J, K, L, M, N, O, P, Q, and R, respectively. In the same manner as in No. 1, paints were obtained.

[Comparative Example 21]
Instead of 483.4 parts of the polyester resin varnish obtained in Production Example A, 376.1 parts of the polyester resin varnish obtained in Production Example J, Sumilite Resin PR-55317 (metacresol phenol resin, nonvolatile content concentration 50% The n-butanol solution (manufactured by Sumitomo Bakelite Co., Ltd.) was applied in the same manner as in Example 1 except that 128.9 parts were used instead of 43.1 parts and 212.5 parts were used instead of 191.0 parts of xylene. Obtained.

[Comparative Example 22]
Instead of 483.4 parts of the polyester resin varnish obtained in Production Example A, 521.2 parts of the polyester resin varnish obtained in Production Example J, Sumilite Resin PR-55317 (metacresol phenol resin, nonvolatile content concentration 50% The n-butanol solution (manufactured by Sumitomo Bakelite Co., Ltd.) was used in the same manner as in Example 1 except that 12.9 parts were used instead of 43.1 parts and 183.4 parts were used instead of 191.0 parts of xylene. Obtained.

[Production of test panel]
The paints obtained in Examples 1 to 11 and Comparative Examples 12 to 22 were each coated with a bar coater on an aluminum plate having a thickness of 0.26 mm so that the dry weight was 80 mg / dm ² . A test panel provided with a coating film was produced by passing through a double-type conveyor oven in which the temperature in one zone was 286 ° C. and the temperature in the second zone was 326 ° C. in 24 seconds, followed by drying and curing. The obtained test panel was evaluated as follows.

<Bending workability test>
The test panel was prepared in a size of 30 mm in width and 50 mm in length. Next, as shown in FIG. 1 (a), the test panel 1 was coated on the outside, and a round bar 2 having a diameter of 3 mm was attached to a position of 30 mm in length. Next, as shown in FIG. 1B, the test panel 2 was folded in two along the round bar 2 to prepare a test piece 3. Two 0.26 mm thick aluminum plates (omitted) are sandwiched between the test specimens 3 folded in half, and 1 kg of a rectangular parallelepiped having a width of 15 cm, a height of 5 cm and a depth of 5 cm as shown in FIG. The weight 4 was dropped from a height of 40 cm onto the bent portion of the test piece 3 and completely bent.
Next, after removing the aluminum plate, the bent part of the test piece 3 was immersed in a saline solution having a concentration of 1%. Next, the current value was measured by applying a current of 6.0 V × 6 seconds between the metal portion of the flat portion of the test piece 3 not immersed in the saline solution and the saline solution.
When the processability of the coating film is poor, the coating film in the bent portion is cracked, the underlying metal plate is exposed, and the conductivity is increased, so that the current value is increased. Evaluation was performed according to the following evaluation criteria.
A: Less than 5 mA (good)
○: 5 mA or more and less than 10 mA (usable)
Δ: 10 mA or more and less than 20 mA (unusable)
X: 20 mA or more (defect)

<Openness test>
A test panel was prepared in a size of 50 mm long × 50 mm wide. Using a press machine, a mold was formed into a shape of a general steion tab opening with a beverage can on the painted surface of the test panel, and used as a sample. Next, the aluminum plate was peeled off along the shape of the opening from the uncoated surface side of the sample, and the opening was magnified with a microscope and visually judged. When the opening property is poor, the coating film tends to remain in the peripheral part of the opening, and the width of the film protruding into the opening becomes large. “Openness is good” means that the coating film does not protrude into the opening at all, or even if it protrudes, its protruding width is very small. As a specific determination method, the width of the protruding coating film was measured and evaluated according to the following evaluation criteria.
A: The maximum width of the protruding coating film is less than 100 μm (good)
○: The maximum width of the protruding coating is 100 μm or more and less than 200 μm (can be used)
Δ: The maximum width of the protruding coating film is 200 μm or more and less than 400 μm (unusable)
×: The maximum width of the protruding coating film is 400 μm or more (defect)

<Retort resistance test>
While the test panel was immersed in water, retort treatment was performed at 125 ° C. for 30 minutes in a retort kettle, and the appearance of the coating film was visually evaluated according to the following evaluation criteria.
A: Untreated coating and no change (good)
○: Very thin whitening (can be used)
Δ: Slightly whitened (cannot be used)
×: Remarkably whitened (defect)

Corrosion resistance was evaluated by acid resistance test and alkali resistance test.
<Acid resistance test>
While the test panel was immersed in an aqueous solution having a pH of about 2 containing 2% by weight of citric acid, the retort treatment was performed in a retort kettle at 125 ° C. for 30 minutes, and the appearance of the coating film was visually evaluated according to the following evaluation criteria.
A: Untreated coating and no change (good)
○: Very thin whitening (can be used)
Δ: Slightly whitened (cannot be used)
×: Remarkably whitened (defect)

<Alkali resistance test>
While the test panel was immersed in an aqueous solution adjusted to pH 12 using sodium hydroxide, a retort treatment was performed in a retort kettle at 125 ° C. for 30 minutes, and the appearance of the coating film was visually evaluated according to the following evaluation criteria.
A: Untreated coating and no change (good)
○: Very thin whitening (can be used)
Δ: Slightly whitened (cannot be used)
×: Remarkably whitened (defect)

<Content contamination resistance test>
A test panel was placed in a retort kettle and immersed in water. Next, a retort treatment was performed at 125 ° C. for 30 minutes. The ratio of the area of the test panel (that is, the area of the coating film) and water was such that water was 100 mL with respect to 100 cm ² of the test panel.
The water after retort treatment is analyzed using “TOC-L CPH” (manufactured by Shimadzu Corporation),
The total organic carbon (TOC) amount was measured. In addition, the amount of TOC is the total amount of organic matter present in water expressed as the amount of carbon in the organic matter. Evaluation was performed according to the following evaluation criteria.
A: Less than 1 ppm (good)
○: 1 ppm or more and less than 1.5 ppm (can be used)
Δ: 1.5 ppm or more and less than 2 ppm (unusable)
X: 2 ppm or more (defect)

<Aging processability test>
The test panel was left in a constant temperature bath at 37 ° C. for 60 days, then the panel was processed in the same manner as in the bending workability test, and the current value was measured. Next, the difference between the current value obtained in the bending workability test and the current value after panel aging (current value after panel aging−current value before panel aging) was determined to evaluate the workability over time. Evaluation was performed according to the following evaluation criteria.
A: Less than 1 mA (good)
○: 1 mA or more and less than 5 mA (can be used)
Δ: 5 mA or more and less than 10 mA (unusable)
X: 10 mA or more (defect)

Table 2 shows the physical property evaluation results of each coating composition.

1 Test panel 2 Round bar 3 Test piece 4 Weight

Claims (9)

  A polyester resin obtained by reacting a polycarboxylic acid (A) with a polyol (B), wherein terephthalic acids are 15 to 40 mol% and isophthalic acids are 50 in a total of 100 mol% of the polycarboxylic acid (A). In the total of 100 mol% of the polyol (B), the alicyclic diol is 10 to 45 mol%, the carbon number is 4 to 6, and each has a primary hydroxyl group at both ends. 40 to 80 mol% of a linear diol (a) having no chain, 3 to 4 carbon atoms, and 5 to 35 mol of a diol (b) having one primary hydroxyl group and one secondary hydroxyl group % Polyester resin.   The polyester resin according to claim 1, wherein the alicyclic diol is 1,4-cyclohexanedimethanol.   The polyester resin according to claim 1 or 2, wherein the diol (b) is at least one selected from the group consisting of propylene glycol, 1,2-butanediol and 1,3-butanediol.   A resin composition for can coating comprising the polyester resin according to any one of claims 1 to 3 and a phenol resin.   The resin composition for can coating according to claim 4, which is used for an inner surface of a can.   A can lid formed by coating at least one surface of a can lid member with the resin composition for can coating according to claim 4 or 5.   A beverage can comprising the can lid according to claim 6 and a can body member.   A coated can in which a can body is coated with the resin composition for can coating according to claim 4 or 5.   A beverage can comprising the coated can according to claim 8.

Images