JP2011012265A - Coating resin composition for can and metal plate for can coated with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition which is coated on a metal can for foodstuff and drinks having excellent processability, adhesiveness, retort resistance, resistance to content, extractability, overbake resistance, resistance to deterioration with time, dent resistance, and is particularly suitable for the inner surfaces of cans, and to provide a metal plate coated with the coating resin composition used for the inner surfaces of cans.SOLUTION: The coating resin composition includes: (A) a polyester resin utilizing 40-100 mol.% of terephthalic acid as a polycarboxylic acid component and containing at least one selected from 1, 3-butanediol and 1, 4-cyclohexanedimethanol as a polyalcohol component; (B) an alkoxymethylated resol type phenol resin crosslinker synthesized from a phenol compound; and (C) an acid catalyst.

Description

  The present invention is a paint resin composition comprising a saturated copolymerized polyester resin as an active ingredient, and is applied to food, beverage metal cans, etc., and is processable, overbaked, retort resistant, content resistant (acid, salt The present invention relates to a coating resin composition that is excellent in properties, dent resistance, extractability, and deep drawability, and is particularly suitable for can coating, and a coated metal plate for cans coated with the same.

  Among the can paints, especially the paint for the inner surface of the can is used for the purpose of not impairing the flavor and flavor of the contents and preventing the corrosion of the can material by a wide variety of foods. Resistant to heat sterilization (retort), then excellent processability during molding (workability, deep drawing processability), and resistance to blister and resistance when heat-sterilized contents containing salt and acid Whitening (content resistance), prevention of corrosion with acids and sulfur compounds (sulfur blackening) contained in the contents, no deterioration of workability due to excessive seizure during canning (overbake resistance), retort Later impact resistance (dent resistance) is required. In recent years, the use of substances such as bisphenol-type epoxy resins containing exogenous endocrine disrupting substances (hereinafter referred to as environmental hormones) is being avoided.

  Currently, polyvinyl chloride resins and epoxy-phenol resins are frequently used as paint resins for the inner surface of cans. However, the following serious problems have been pointed out at present.

  First, it is pointed out that polyvinyl chloride resin has excellent retort resistance, content resistance, and processability, but the vinyl chloride monomer remaining in the resin is a material with serious hygiene problems such as carcinogenicity. Has been. Incineration when recycling cans and cans will produce highly toxic and corrosive chlorine gas, hydrogen chloride gas, and highly toxic dioxins from polyvinyl chloride resin, leading to incinerator corrosion and environmental pollution. There is. Furthermore, the polyvinyl chloride resin has insufficient adhesion to the metal which is a can material, and the coating process is complicated, for example, it is necessary to coat it after treating with an epoxy resin.

  Next, the epoxy-phenolic resin has a high baking temperature and is liable to cause appearance defects such as foaming during baking. Moreover, since it was announced that bisphenol-A contained in an epoxy resin acts as an environmental hormone as described above, development of an inner surface coating agent to replace this is desired. Further, in addition to the workability and retort resistance required for the outer surface paint of the can as well as the inner surface paint described above, measures against environmental hormones are becoming necessary.

  In order to solve such problems, painting and baking are easy, workability, adhesion to metal, and retort resistance are excellent. Toxic and corrosive gas is not generated during incineration. In addition to these, attempts have been made to apply polyester resins that do not contain environmental hormones to internal coatings for cans, but in addition to these, content resistance, extractability, overbaking resistance, dent resistance, and deep drawing processability A coating resin and a coating resin composition suitable for cans are not obtained.

  In other words, the can inner surface coating resin with a saturated polyester resin alone, such as JP-B-60-42829 and JP-B-61-36548, has blister resistance and resistance to heat treatment (retort resistance) only with boiling water or steam. It has excellent whitening properties, but it is still insufficient in performance, causing deterioration of the surface condition and gloss of the coating film, and retort treatment (content resistance) in saline and acidic atmospheres assuming the contents. Causes blistering and whitening, resulting in poor appearance.

  In JP-A-7-113058, JP-A-7-113059, and JP-A-8-325513, a polyester resin is blended with a bisphenol-A type or phenol novolac type epoxy resin, blended, or an amino resin is used in combination. This suggests the provision of a coating film with excellent retort resistance and content resistance, but this product lacks overbake resistance and dent resistance. Some epoxy resins are difficult to use because they contain bisphenol-A, which is an environmental hormone.

  In JP-A-1-245065 and JP-A-5-112755, a coating composition comprising a saturated polyester resin mainly composed of propylene glycol and an alkyl etherified aminoformaldehyde resin is applied to the coating agent for the inner surface of the can. Therefore, we have proposed to provide a coating film with excellent workability and retort resistance. However, these cannot sufficiently satisfy the overbaking resistance, dent resistance, and acid resistance required for the can inner surface coating.

Japanese Patent Publication No. 60-42829 Japanese Examined Patent Publication No. 61-36548 JP 7-113058 A Japanese Patent Laid-Open No. 7-113059 JP-A-8-325513 Japanese Patent Laid-Open No. 1-245065 Japanese Patent Laid-Open No. 5-112755

  Among these problems, the present inventor has intensively studied over-bake resistance, dent resistance, and acid resistance, which have not been studied particularly in the above-described prior art. It discovered that the coating material which can solve these various problems was obtained by hardening | curing the used polyester resin with the crosslinking agent containing a resol type phenol resin, and reached | attained this invention.

  That is, the present invention includes (A) 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, and 1,4-cyclohexanedimethanol as the polyalcohol component. A polyester resin containing at least one or more, (B) a cross-linking agent comprising an alkoxymethylated resol-type phenol resin synthesized from a phenol compound raw material, (C) a paint resin composition for a can inner surface comprising an acid catalyst, And it is the coating metal plate for can inner surfaces which apply | coated this.

  Paints applied to the inner surface of food and beverage cans are not toxic due to their nature, do not discharge pollutants during disposal or recycling, and can withstand can processing, retort steam, heat, salt of contents, and acids Must be a thing. In recent years, it is also desired to replace paints containing bisphenol compounds, which are exogenous endocrine disrupting substances (environmental hormones) such as epoxy-phenolic paints. The paint resin composition for inner surface of the can of the present invention does not contain or discharge the above-mentioned toxic compounds, does not contain environmental hormones, satisfies processability, retort resistance, and content resistance, and also has acid processability and resistance. Since it is excellent in overbaking and dent resistance, it is suitable for the inner coating of food cans.

  As the polycarboxylic acid component used in the polyester resin (A) used in the present invention, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, Aliphatic dicarboxylic acids such as sebacic acid, dodecanedioic acid, dimer acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, fumaric acid , Unsaturated dicarboxylic acids such as maleic acid and terpene-maleic acid adduct, and the like, and one or more of these can be used. In terms of hygiene, terephthalic acid, isophthalic acid, orthophthalic acid, adipic acid, sebacic acid, dimer acid, 1,4-cyclohexanedicarboxylic acid, fumaric acid and maleic acid are preferred. Preferably terephthalic acid is 40 to 100 mol%, more preferably 60 to 100 mol%.

  The polyester resin (A) used in the present invention includes 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, and 1,4-cyclohexanedimethanol as a polyalcohol component. In addition, at least one or more of these are contained, and the amount contained in combination is preferably 10 mol% or more, more preferably 20 mol% or more. By containing the polyalcohol described above, the flexibility and dent resistance of the coating film after the retort treatment or after the retort treatment after filling the contents (acidic substance, salt) are excellent.

  Examples of other polyalcohol components include ethylene glycol, propylene glycol, 1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,4-butanediol, and 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, Aliphatic glycols such as 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, 4-propyl-1,8-octanediol, 1,9-nonanediol, diethylene glycol, triethylene glycol , Polyethylene glycol, polypropylene glycol, polytetramethyle Polyether glycols such as glycol, alicyclic polyalcohols such as 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, tricyclodecane glycols, and water-added bisphenols can be mentioned. One or more can be selected and used. Of these, preferred for hygiene are ethylene glycol, 1,4-butanediol, diethylene glycol and the like, and one or more of these can be selected and used.

  In the polyester resin (A) used in the present invention, a polycarboxylic acid component and / or a polyalcohol component having a tri- or higher functional polycarboxylic acid and / or polyalcohol may be used as long as the processability does not deteriorate. Examples of the trivalent or higher polycarboxylic acid component include trimellitic acid, pyromellitic acid, and benzophenone tetracarboxylic acid. Examples of the trifunctional or higher polyalcohol include glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, and penta. Examples include erythritol and α-methylglucoside. For hygiene, trimellitic acid, trimethylolethane, trimethylolpropane and glycerin are preferable. Preferably, it is used in the range of 0.1 to 3 mol%, and when these trifunctional components exceed 3 mol%, the flexibility of the polyester resin is lost and the processability is lowered.

  Among the properties of the (A) polyester resin used in the present invention, the number average molecular weight is preferably 5,000 to 100,000, more preferably 8,000 to 30,000. If the number average molecular weight is less than 5,000, the coating film becomes brittle and the workability and hot water resistance are poor, and if it exceeds 100,000, the coating workability may be lowered. Moreover, preferable glass transition temperature (Tg) is 0-120 degreeC, More preferably, it is 10-100 degreeC, More preferably, it is 30-100 degreeC. When the glass transition temperature is less than 0 ° C., the retort resistance may be inferior. In particular, Tg of 50 ° C. or higher is desirable for contents that require flavor. When Tg exceeds 120 ° C., workability and coating workability may deteriorate. The number average molecular weight referred to here is measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve, and the glass transition temperature (Tg) is measured by differential thermal analysis (DSC). is there.

The (A) polyester resin used in the present invention may be given an acid value by any method. Examples of the purpose of giving an acid value include acceleration of curing with a crosslinking agent and improvement of adhesion with a metal material for cans. For these purposes, the preferred acid value range is 40 to 200 eq / 10 ⁶ g. If it exceeds 200 eq / 10 ⁶ g, the retort resistance may be reduced, or the acid addition component may be eluted into the contents. As a method for giving an acid value, a depolymerization method in which a polyvalent carboxylic acid anhydride is added in the latter stage of polycondensation, this is made to have a high acid value at the prepolymer (oligomer) stage, and then this is polycondensed to give an acid value. However, the former depolymerization method is preferred because it is easy to operate and a target acid value can be easily obtained.

  Examples of the polyvalent carboxylic acid anhydride used for acid addition in such a depolymerization method include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride and the like. It is done. Trimellitic anhydride is preferable.

  The (B) crosslinking agent used in the can coating composition of the present invention contains a resol type phenol resin synthesized from a phenol compound. Examples of phenol resin compounds include (B-1) trifunctional or higher phenol compounds such as phenol, m-cresol, m-ethylphenol, 3,5-xylenol, m-methoxyphenol, bisphenol-A, and bisphenol-F. (B-2) Examples of the bifunctional phenol compound include o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, and 2,5-xylenol. These are phenol compounds that can be converted into two or more methylols per molecule of phenol compound when methylolated with formaldehyde or the like. These may be used alone or in combination of two or more.

  These blending ratios are blended arbitrarily according to the required coating film, but are preferably (B-1) / (B-2) = 1/99 to 100/0 [wt%]. For example, when hardness and acid resistance are required for the coating film, it is preferable to set (B-1)> 30% by weight. When the coating film needs flexibility and the residual stress after processing is desired to be low Is preferably (B-1) <50 wt%.

  Formaldehydes used when these phenol compounds are used as phenol resins include formaldehyde, paraformaldehyde or trioxane, and one or a mixture of two or more 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. Examples include methanol, ethanol, n-propanol, n-butanol, isopropanol, isobutanol, tert-butanol, etc. (A) n-butanol is used from the viewpoint of compatibility with the polyester resin and reaction curability. preferable.

  The phenol resin crosslinking agent has an average of 0.3 or more, preferably 0.5 to 3, alkoxymethyl groups per phenol nucleus from the viewpoint of reactivity and compatibility with the (A) polyester resin. . If it is less than 0.3, the curability with the polyester resin becomes poor and the workability is lowered.

  As a method for obtaining a phenol resin in which the phenolic compounds (B-1) and (B-2) are mixed, a method in which the phenol resin is mixed at an arbitrary ratio before the phenol resin is formed with formaldehydes or (B-1 ) And (B-2) may be separately converted into a phenol resin and mixed with an arbitrary mixing ratio.

  Examples of optional crosslinking agents that can be used in addition to the (B) phenol crosslinking agent of the present invention include amino resins, isocyanate compounds, and epoxy resins, and amino resins are particularly preferred from the viewpoint of hygiene. These crosslinking agents can be blended and used to such an extent that the performance of the coating film is not deteriorated.

  Examples of the amino resin include methylol obtained by reaction of amino components such as melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, dicyandiamide, and aldehyde components such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. An amino acid resin is mentioned. Those obtained by etherifying the methylol group of this methylolated amino resin with an alcohol having 1 to 6 carbon atoms are also included in the amino resin. Of these, they can be used alone or in combination. In terms of hygiene, amino resins using melamine and benzoguanamine are preferable, and amino resins using benzoguanamine which is excellent in retort resistance and extractability are more preferable.

  Examples of amino resins using benzoguanamine include: methyl ether benzoguanamine resin obtained by etherifying methylol group of methylol benzoguanamine resin partly or entirely with methyl alcohol, butyl ether benzoguanamine resin butyl etherified with butyl alcohol, or methyl alcohol Methyl ether etherified with both butyl alcohol and mixed etherified benzoguanamine resin with butyl ether are preferred. As said butyl alcohol, isobutyl alcohol and n-butyl alcohol are preferable.

  As the amino resin using melamine, a methylol group of the methylolated melamine resin is partially or entirely etherified with methyl alcohol, methyl etherified melamine resin, butyl etherified butyl etherified with butyl alcohol, or methyl alcohol Preference is given to methyl ether etherified with both butyl alcohol and mixed etherified melamine resin with butyl ether.

  Examples of the (C) acid catalyst used in the can coating composition of the present invention include sulfuric acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphorsulfone. Examples include acids, phosphoric acid, and amine blocks (partially neutralized by adding amine), and one or more of these can be used in combination. From the standpoint of compatibility and hygiene, dodecylbenzenesulfonic acid and neutralized products thereof are preferred.

The ratio of the (A) polyester resin, (B) phenol resin cross-linking agent, and (C) acid catalyst used in the can coating composition of the present invention is preferably within the range of the following formula.
(A) / (B) / (C) = 100 / 5-40 / 0.1-5 [weight ratio]
(A) With respect to 100 parts by weight of the polyester resin, if the weight ratio of the (B) phenol resin crosslinking agent exceeds 40 parts by weight, the processability may be inferior. If it is less than 5 parts by weight, curability, retort resistance, Dent properties may be reduced. In addition, if the amount of (C) acid catalyst is less than 0.1 parts by weight, the curability becomes insufficient and the workability and retort resistance may be inferior. Accelerated, workability, curability, retort resistance, dent resistance, etc. may decrease.

  The can coating resin composition of the present invention includes known inorganic pigments such as titanium oxide and silica, phosphoric acid and esterified products thereof, curing catalysts such as organotin compounds, surface smoothing agents, antifoaming agents, and dispersions. Known additives such as agents and lubricants can be blended. In particular, a lubricant is added to impart lubricity of a coating film required at the time of molding of DI cans and DR (or DRD) cans. For example, a fatty acid ester wax, which is an esterified product of a polyol compound and a fatty acid, silicon And waxes such as olefin wax, fluorine wax, polyolefin wax such as polyethylene, lanolin wax, montan wax, microcrystalline wax, and carnauba wax. The lubricant can be used alone or in combination of two or more.

  The resin composition for can coating of the present invention is made into a paint in a state dissolved in a known organic solvent. Examples of organic solvents used for coating include toluene, xylene, aromatic hydrocarbon compounds, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoethyl ether acetate, Diethylene glycol monoethyl ether acetate, ethylene glycol monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, etc. considering solubility, evaporation rate, etc., one or more Select to be used.

  For the can coating resin composition of the present invention, other resins for the purpose of modifying the flexibility and adhesion of the coating film can be used. Examples of other resins include ethylene-polymerizable unsaturated carboxylic acid copolymers and ethylene-polymerizable carboxylic acid copolymer ionomers. The effect is obtained by blending at least one resin selected from these. The flexibility and adhesion of the target coating film can be imparted.

  The can coating composition of the present invention can be used by coating the inner and outer surfaces of any metal plate that can be used in beverage cans, cans for cans, lids, caps, etc. Steel, aluminum, etc. can be mentioned. These metal plates should be pretreated with phosphoric acid treatment, chromic acid chromate treatment, phosphoric acid chromate treatment, anticorrosion treatment such as other antirust treatment agents, and surface treatment for the purpose of improving the adhesion of the coating film. May be.

  The coating composition of the present invention can be applied by a known coating method such as roll coater coating or spray coating to obtain the coated metal plate of the present invention. Although a coating film thickness is not specifically limited, It is preferable that it is the range of 3-18 micrometers by dry film thickness, Furthermore, it is the range of 3-10 micrometers. The baking condition for the coating is 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 preferred.

  Hereinafter, the present invention will be specifically described with reference to examples. In the examples, “parts” means “parts by weight”.

Each measurement item followed the following method.
(1) Measurement of resin composition The molar ratio of the acid component and the alcohol component was determined by nuclear magnetic resonance spectroscopy and analysis by gas chromatography after alcoholysis.

(2) Measurement of number average molecular weight The number average molecular weight was measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

(3) Measurement of reduced viscosity 0.10 g of polyester resin 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 It measured with the temperature increase rate of 20 degree-C / min using the differential scanning calorimeter (DSC).

(5) Measurement of acid value 0.2 g of polyester was dissolved in 20 ml of chloroform, and titrated with a 0.1N KOH ethanol solution to obtain the equivalent (eq / 10 ⁶ g) per 10 ⁶ g of resin.

Evaluation item (6) Preparation of test piece The coating composition was applied to an aluminum metal plate (# 5052, 70 mm x 150 mm x 0.3 mm) with a bar coater so as to have a film thickness of 4 to 8 µm, and cured and baked. This was used as a test piece. As the baking conditions, the evaluation was performed at 250 ° C. (PMT, maximum material arrival temperature) × 1 minute.

(7) Workability One metal plate having the same thickness as the test piece is sandwiched and bent in the direction of 180 degrees. This processed part was contacted with a sponge immersed in a 1% NaCl aqueous solution and evaluated by an energization value when a voltage of 5.5 V was applied. The smaller energization value (≦ 1.5 mA) is better.

(8) Overbaking property The test piece was again heat-treated at 210 ° C for 10 minutes, and the workability was evaluated by the same method as in (7).

(9) Retort resistance A test piece is placed in a stainless steel cup, and ion-exchanged water is poured into the half of the test piece. This is installed in a pressure cooker and a retort treatment is performed at 125 ° C. for 30 minutes. The evaluation after the treatment is performed for the underwater portion and the steam portion, and the degree of whitening is determined visually as follows.
◎: Good ○: Slightly whitened but no blisters △: Slightly whitened or slightly blistered ×: Significantly whitened or markedly blistered

(10) Resistance to contents The test piece was immersed in an aqueous solution containing 3 wt% of sodium chloride and 3 wt% of lactic acid and treated at 125 ° C. for 30 minutes, and then the whitening of the coating film and the state of the blister were visually determined.
◎: Good ○: Slightly whitened but no blisters △: Slightly whitened or slightly blistered ×: Significantly whitened or markedly blistered

(11) Acid resistance processability After immersing the test piece in an aqueous solution containing 1 wt% citric acid and treating it at 125 ° C. for 30 minutes, the processability was evaluated and judged by the same method as in (7).

(12) Dent resistance The test piece subjected to the retort treatment shown in (11) is faced down, and using a DuPont impact tester, impact is performed at a height of 1/2 inch x 1 kg x 5 cm from the back side. Add Next, the convex portion was brought into contact with a sponge immersed in a 1% NaCl aqueous solution and evaluated by an energization value when a voltage of 5.5 V was applied. The smaller energization value (≦ 1.5 mA) is better.

(13) Extractability The extract after the retort test shown in (10) was titrated with potassium permanganate to quantify the amount of organic matter extracted from the coating film. A smaller number is better.

(14) Deep-drawing workability Using a deep-drawing machine so that the coated surface of the test piece was on the outside, a molding process of L / D (diameter / depth) = 1/1 was performed. The coating film peeling state of the processed side surface portion of this test piece was visually observed and judged.
A: Good B: The coating film has slight scratches.
(Triangle | delta): Some peeling is recognized by the coating film.
X: Severe peeling and damage are observed in the coating film.

Synthesis Example (a) of Synthetic Transesterification Method of Polyester Resin of the Present Invention
890 parts of dimethyl terephthalic acid, 4.4 parts of trimellitic acid, 700 parts of propylene glycol, 100 parts of 1,4-cyclohexanedimethanol and 0.5 part of titanium tetrabutoxide are charged into a 3 L flask and gradually heated to 220 ° C. over 4 hours. The temperature was raised and transesterification was performed. Subsequently, the initial polymerization under reduced pressure was carried out to 10 mmHg over 30 minutes, the temperature was raised to 250 ° C., and the latter polymerization was carried out at 1 mmHg or less for 90 minutes to obtain the polyester resin (a) of the present invention.

Example of synthesis by direct polymerization method (a)
2660 parts of terephthalic acid, 15.5 parts of trimellitic acid, 2450 parts of propylene glycol, 350 parts of 1,4-cyclohexanedimethanol, and 1.8 parts of titanium tetrabutoxide were charged into a 10 L autoclave and added with 3.5 kg / cm · G of nitrogen. The temperature was gradually raised to 235 ° C. over 3 hours under pressure to carry out esterification. Subsequently, the polymerization was carried out under reduced pressure up to 10 mmHg over 1 hour, the temperature was raised to 250 ° C., and the latter polymerization was carried out at 1 mmHg or less for 90 minutes to obtain the polyester resin (a) of the present invention. There is no difference in the performance of the resin (a) obtained by the transesterification method and the direct polymerization method, respectively, and the composition and characteristic values are shown in Table 1. The obtained resin was cyclohexanone / solvesso-150 = 1/1 solvent to make a resin varnish having a solid content of 40%, and this was used to prepare the coating composition of the present invention.

Synthesis example (b)
380 parts of dimethyl terephthalic acid, 255 parts of 2-methyl-1,3-propanediol, 159 parts of neopentyl glycol, 3 parts of trimethylolpropane, and 0.2 part of titanium butoxide are charged into a 2 L flask and 220 for 4 hours. The temperature was gradually raised to 0 ° C. to perform transesterification. Next, after cooling to 200 ° C. or lower, 45 parts of sebacic acid was added, and the temperature was raised again to 230 ° C. to conduct an esterification reaction. Next, this was subjected to reduced pressure initial polymerization to 10 mmHg over 30 minutes and the temperature was raised to 250 ° C., and then the latter polymerization was performed at 250 ° C. and 1 mmHg or less for 90 minutes. Then, one end resin was cooled to 220 degreeC under nitrogen stream, and 3.4 parts of trimellitic acid was added to this, and the polyester resin (b) of this invention was obtained. The composition and characteristic values of the obtained resin are shown in Table 1. The obtained resin was cyclohexanone / solvesso-150 = 1/1 solvent to make a resin varnish having a solid content of 40%, and this was used to prepare the coating composition of the present invention.

Polyester resin synthesis examples (c) to (f)
Polyester resins (c) to (f) of the present invention as shown in Table 1 in the transesterification method or direct polymerization method of synthesis example (a) and synthesis example (b), and their A resin varnish having a solid content of 40% was obtained.

＊１：１，４−シクロヘキサンジメタノール

* 1: 1,4-cyclohexanedimethanol

Synthesis examples for comparative examples (g) to (k)
Comparative Example polyester resins (g) to (k) having a resin composition as shown in Table 2 were obtained in the same manner as in Synthesis Example (a) or (b). The obtained resin was cyclohexanone / solvesso-150 = 1/1 solvent to make a resin varnish having a solid content of 40%, and a coating composition was prepared using the resin varnish.

＊１：１，４−シクロヘキサンジカルボン酸

* 1: 1,4-cyclohexanedicarboxylic acid

Synthesis example (l)
Synthesis of Resol Type Phenolic Resin 100 parts of m-cresol, 180 parts of 37% formaldehyde aqueous solution and 1 part of sodium hydroxide were added and reacted at 60 ° C. for 3 hours, and then dehydrated at 50 ° C. for 1 hour under reduced pressure. Subsequently, 100 parts of n-butanol and 6 parts of phosphoric acid were added and reacted at 110 to 120 ° C. for 2 hours. After completion of the reaction, the resulting solution was filtered to obtain an m-cresol-based resol type phenol resin crosslinking agent (l) having a solid content of about 50%. The synthetic formulation is shown in Table 3.

Other resol type phenol resins (m) to (p) were obtained as other resol type phenol resins in the same manner as in Synthesis Example (l). The synthetic formulation is shown in Table 3. Furthermore, PL-4523 (manufactured by Gunei Chemical Co., Ltd.) was used.

種類の欄の略号
ｍ−ＣＳ：ｍ−クレゾール
ｐ−ＣＳ：ｐ−クレゾール
Ｘｙｌ：３，５−キシレノール
Ｐｈ：フェノール
＊：フェノール型 ブチルエーテル化レゾール型フェノール樹脂（群栄化学（株）製）

Abbreviation of column of type m-CS: m-cresol p-CS: p-cresol Xyl: 3,5-xylenol Ph: phenol *: phenol type butyl etherified resol type phenol resin (manufactured by Gunei Chemical Co., Ltd.)

Example (1)
After blending 20 parts of resin varnish (a), 3.2 parts of phenolic resin (l), 0.028 part of dodecylbenzenesulfonic acid and 0.08 part of carnauba wax, coating with cyclohexanone / solvesso-150 = 1/1 It diluted until it became a suitable viscosity, and obtained the coating composition (1) of this invention. This was applied and baked by the method described above to obtain a test piece of the coated metal plate of the present invention. Table 4 shows the composition and the results of evaluating the test pieces.

Examples (2) and (6), Reference Examples (3) to (5) and (7)
After obtaining the coating resin compositions (2) to (7) of the present invention in the same manner as in Example (1), coating and baking were performed in the same manner as described above to obtain a test piece of the coated metal sheet of the present invention. . Table 4 shows the composition and the results of evaluating the test pieces.

＊１：フェノール型、ブチルエーテル化レゾール型フェノール樹脂（群栄化学（株）製）
＊２：メチルエーテル化ベンゾグアナミン樹脂（三井サイテック（株）製）
＊３：メチルエーテル化メラミン樹脂（三井サイテック（株）製）
＊４：フェノールノボラック型エポキシ樹脂（油化シェルエポキシ（株）製）ドデシルベンゼンスルホン酸
＊５：ドデシルベンゼンスルホン酸＊６：ドデシルベンゼンスルホン酸系硬化触媒（キングインダストリイズ社製）

* 1: Phenol type, butyl etherified resol type phenol resin (manufactured by Gunei Chemical Co., Ltd.)
* 2: Methyl etherified benzoguanamine resin (Mitsui Cytec Co., Ltd.)
* 3: Methyl etherified melamine resin (Mitsui Cytec Co., Ltd.)
* 4: Phenol novolac-type epoxy resin (Oilized Shell Epoxy Co., Ltd.) dodecylbenzenesulfonic acid * 5: Dodecylbenzenesulfonic acid * 6: Dodecylbenzenesulfonic acid-based curing catalyst (King Industries)

Comparative Examples (8) to (15)
In the same manner as in Example (1), after obtaining paint resin compositions (8) to (14) of comparative examples, coating and baking were similarly performed by the methods described above to obtain test pieces of comparative examples. Table 5 shows the composition and the results of evaluating the test pieces. Incidentally, (15) is a reproduction of an epoxy-phenol resin paint.

＊１：フェノール型、ブチルエーテル化レゾール型フェノール樹脂（群栄化学（株）製
＊２：メチルエーテル化ベンゾグアナミン樹脂（三井サイテック（株）製）
＊３：メチルエーテル化メラミン樹脂（三井サイテック（株）製）
＊４：フェノールノボラック型エポキシ樹脂（油化シェルエポキシ（株）製）
＊５：ビスフェノール型エポキシ樹脂（油化シェルエポキシ（株）製）
＊６：ドデシルベンゼンスルホン酸＊７：ドデシルベンゼンスルホン酸系硬化触媒（キングインダストリイズ社製）

* 1: Phenol type, butyl etherified resol type phenol resin (manufactured by Gunei Chemical Co., Ltd.) * 2: Methyl etherified benzoguanamine resin (manufactured by Mitsui Cytec Co., Ltd.)
* 3: Methyl etherified melamine resin (Mitsui Cytec Co., Ltd.)
* 4: Phenol novolac type epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd.)
* 5: Bisphenol epoxy resin (Oilized Shell Epoxy Co., Ltd.)
* 6: Dodecylbenzenesulfonic acid * 7: Dodecylbenzenesulfonic acid-based curing catalyst (manufactured by King Industries)

As is apparent from Tables 4 to 5, the metal plate coated with the resin composition for can coating of the present invention has its workability, retort resistance, content resistance (acid, salt) resistance, overbaking resistance, and acid resistance processing. Excellent in properties, extractability, dent resistance, and deep drawability.

Claims (3)

(A) is 40 to 100 mole% terephthalic acid used as the polycarboxylic acid component, 1 to polyalcohol component, 3-butanediol, 1, of the 4-cyclohexanedimethanol, containing at least one or more among these A can resin composition comprising a polyester resin, (B) an alkoxymethylated phenolic resin cross-linking agent synthesized from a phenol compound, and (C) an acid catalyst.   The can coating resin composition according to claim 1, wherein (A) / (B) / (C) is 100/5 to 40 / 0.1 to 5 in a weight ratio. Resin composition. A coated metal sheet for cans, wherein the resin composition for can paints according to claim 1 or 2 is applied and cured.