JPS6147180B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester-based coating composition for the inside of a can that is improved in various resistances, particularly boiling resistance. Conventionally, cans for canning have been known to be made of tinplate, various chemically treated steel sheets including tain-free steel, or various metal materials such as aluminum. In some cases, in order to prevent corrosion of metal materials and metal elution into the contents, and maintain the flavor, preservability, and hygiene of the contents at an excellent level,
It is generally necessary to apply a protective coating to the inside surface of the can body. Currently, paints using phenol-epoxy resins, epoxy-urea resins, etc. are used as protective paints. These resins exhibit excellent adhesion to metal materials, act as an effective barrier between the can body and the contents, and have high barrier properties against water and other contents. In this sense, it is suitable as a paint for the inner surface of cans. However, in reality, various external forces are applied during the can manufacturing process, so the resin that serves as the base of the paint must have considerably excellent processability in addition to the above-mentioned properties.
With thermosetting resins such as phenol-epoxy resins and epoxy-urea resins, damage to the paint film occurs during forming processes such as press molding of can lids, flanging of can bodies, and seaming. or partial peeling is observed. In this case, the workability of the coating film is not sufficient, and even the slightest damage causes areas with poor adhesion, and corrosion of the exposed metal progresses. As a result, the original function of the food packaging material, which is to protect the food for a long period of time without impairing the flavor or freshness of the contents, is not fully fulfilled. Therefore, in the actual can manufacturing process, the above-mentioned phenol-epoxy resin or epoxy-urea resin is applied to the metal as an undercoat, and then another paint is applied over it to compensate for the shortcomings of a single coating. is the current situation. In this case, the resin used for surface coating is vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, or the like. In addition, with a single coat of these vinyl chloride paints,
Although it has excellent processability and barrier properties, it has poor adhesion to metals. As a paint for the inside of cans as an alternative to the various paints listed above,
Polyolefins or thermoplastic polyester resins have been proposed. However, polyolefins are soft and do not necessarily have sufficient physical properties as paints for the inside of cans; for example, polyethylene-based paints may whiten after retorting, and polypropylene-based films tend to become cloudy, and both have the disadvantage of being easily scratched. There is. In addition, thermoplastic polyester resin has excellent adhesion to metal materials, inhibits corrosion of metal materials and metal elution, processability of coated metal materials, hygiene properties such as anti-extraction of paint films, and wide applicability to various contents. It is known that it has a wide range of suitability for combinations such as however,
In order to have good properties such as boiling resistance,
Thermoplastic polyester resins with poor workability, that is, poor solubility in organic solvents, must be used;
For example, it is only soluble in solvents such as phenol and tetrachloroethane at room temperature, and it is difficult to satisfy all properties such as adhesion and processability. On the other hand, some thermoplastic polyester resins are known to have excellent solubility or dispersibility in ordinary organic solvents, but it is difficult for these resins to meet the boiling resistance requirements of protective coatings. . Therefore, efforts have been made to meet the performance required for protective coatings by appropriately combining dibasic acids and diols, which are the raw materials for thermoplastic polyester resins, but finding the appropriate combination of raw materials is difficult. Very difficult. The present inventors have focused on the good properties of thermoplastic polyester resin, such as hygiene, adhesion to metals, and processability, and in order to use this resin effectively, we have developed In order to develop a thermoplastic polyester resin with excellent properties such as boiling resistance and boiling resistance, we conducted extensive research and found that we could form a crosslinked structure with a specific compound in a thermoplastic polyester resin that is soluble in organic solvents. The present invention was completed based on the discovery that excellent resistance, especially boiling resistance, can be obtained by using the above method. That is, the present invention provides a thermoplastic polyester resin having a terminal hydroxyl group or a terminal carboxyl group, at least one selected from a chelate compound of aluminum alcoholate and a chelate compound of tetraalkyl titanate, and an organic solvent that dissolves the thermoplastic polyester resin. The present invention relates to a coating composition for the inner surface of a can consisting of the following. Conventionally, a chelate compound of aluminum alcoholate or a chelate compound of tetraalkyl titanate ester forms a chelate bond with an oil-modified alkyd resin, phenol resin, epoxy resin, etc. having a hydroxyl group or carboxyl group, and cures the coating film. It is known that it can be used in thermosetting polyester resins to form a pregel and to improve the formation efficiency of thermosetting polyester resins. In general, thermoplastic polyester resins have excellent physical properties such as adhesion, processability, hygiene, and corrosion resistance.
Thermoplastic polyester resin, which has excellent solubility in organic solvents, has low crystallinity and therefore a low melting point, and its boiling resistance (boiling water resistance) is insufficient for use as a protective coating for the inside of cans, causing whitening and In contrast, thermoplastic polyester resins, which have poor solubility in organic solvents, have good boiling resistance and the like, but have the disadvantage of poor workability. The present invention enables a thermoplastic polyester resin to form chelate crosslinks with a specific compound. Even if the thermoplastic polyester resin has low crystallinity and excellent solubility in organic solvents, it has excellent water resistance and is resistant to boiling. It has thus been discovered that the protective coating for the inner surface of a can can be obtained without causing whitening or blistering, and that the boiling resistance of a highly crystalline thermoplastic polyester resin can be further improved. Furthermore, the obtained protective film for the inner surface of a can has excellent extraction resistance and flavor retention. Suitable dibasic acid components for obtaining the thermoplastic polyester resin of the present invention include aromatic dibasic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and phthalic anhydride, and aliphatic dibasic acids such as adipic acid and sebacic acid. Acids can be mentioned. Similarly, diol components include ethylene glycol, 1,4-
These include butanediol, 1,3-butadiol, propylene glycol, diethylene glycol, neopentyl glycol, and the like. In addition, thermoplastic polyester resins with a composition containing 25 mol% or more of neopentyl glycol in the total diol component can obtain resins with high solubility in organic solvents, and have excellent processability and
Although it is possible to satisfy barrier properties, adhesion properties, and water resistance, there is a problem with extraction resistance to alcoholic contents, and care must be taken when using neopentyl glycol. The composition of a thermoplastic polyester resin with good solubility in organic solvents cannot necessarily be definitively determined depending on the composition of the dibasic acid and diol, but either the dibasic acid or the diol is a thermoplastic polyester resin with low crystallinity. Even when a resin is produced, if either one is used, the result is generally a thermoplastic polyester resin with low crystallinity. Also,
Thermoplastic polyester resin obtained from one type of dibasic acid and one type of diol has a highly regular structure of the resulting resin, and therefore has high crystallinity and poor solubility in organic solvents. Thermoplastic polyester resins obtained from dibasic acids or diols generally impart structural irregularity to the resin, resulting in low crystallinity and a thermoplastic polyester resin with good solubility in organic solvents. Furthermore, it is also effective to use an aliphatic dibasic acid or a diol having a side chain as a copolymerization component. For example, the molar ratio of terephthalic acid/isophthalic acid as a dibasic acid component is
25/75, and thermoplastic polyester resins in which the molar ratio of ethylene glycol/1,4-butanediol/1,3-butanediol as diol components is 20/20/60 usually have a low solubility in organic solvents. It becomes an expensive resin. It is sufficient that the molecular weight of the thermoplastic polyester resin is 5000 or more, and if it is smaller than this, the processability will be poor. The thermoplastic polyester resin according to the present invention must have a terminal hydroxyl group or a terminal carboxyl group, and reacts with a chelate compound of aluminum alcoholate or a chelate compound of tetraalkyl titanate. Thermoplastic polyester resins with terminal hydroxyl groups undergo a normal polycondensation reaction,
It is obtained by a production method carried out under conditions of excess diol. For example, it can be produced by carrying out an esterification reaction between the dibasic acid and a diol, or by carrying out a transesterification reaction between an alcohol ester compound of a dibasic acid and a diol, and then carrying out a polycondensation reaction. Note that in this reaction, a known esterification catalyst or transesterification catalyst may be used. Examples of these catalysts include germanium oxide, antimony trioxide, tetrabutyl titanate, manganese acetate, calcium acetate,
Zinc acetate, lead acetate, etc. can be used. In addition, a known antioxidant or the like may be blended in the production of the thermoplastic polyester resin of the present invention. A thermoplastic polyester resin having a terminal carboxyl group can be produced by reacting the resin having a terminal hydroxyl group obtained by the above method with a required amount of dibasic acid to form a half ester with the terminal hydroxyl group. Note that the method for producing the thermoplastic polyester resin is not limited to the above method, and resins obtained by various production methods may be used. Examples of the aluminum alcoholate according to the present invention include aluminum isopropoxide, aluminum butoxide, and aluminum isobutoxide, and examples of the tetraalkyl titanate include titanium isopropoxide, titanium butoxide, tetraalkyl titanate, and tetraoctadecyl titanate. I can list them. Compounds that can react with aluminum alcoholate or tetraalkyl titanate to form chelate compounds include β-diketones such as acetylacetone, acetylacetone trichloride, and benzoylacetone, and β-keto acids such as ethyl acetoacetate. Esters can be mentioned. A known method is used to convert aluminum alcoholate or tetraalkyl titanate into a chelate compound using these chelating agents. For example, it can be obtained by dissolving a chelating agent in a solution of aluminum alcoholate or tetraalkyl titanate in alcohol, benzene, toluene, etc. and reacting the solution. In the present invention, a chelate compound is used, but when aluminum alcoholate or tetraalkyl titanate is directly added to a thermoplastic polyester resin solution, a reaction occurs rapidly, resulting in thickening or gelation, which improves the storage stability of the coating composition. is extremely bad. However, sufficient storage stability can be obtained by using it as a chelate compound. In the present invention, the chelate compound is used by being added to, mixed and dissolved in an organic solvent solution of a thermoplastic polyester resin. In addition, heating the mixture after mixing and dissolving it to advance the reaction to an extent that does not increase the viscosity can also be effectively used to improve the boiling resistance of the resulting film. In the coating composition of the present invention, the optimum amount of the chelate compound obtained from aluminum alcoholate or tetraalkyl titanate is:
The amount is 0.01 to 3 parts by weight, preferably 0.1 to 2 parts by weight. This quantitative relationship indicates that the amount is sufficient to react with the terminal reactivity or terminal carboxyl group of the thermoplastic polyester resin and exhibit various resistances such as boiling resistance, and if it is less than 0.01 part by weight, a sufficient crosslinking density cannot be obtained. However, blistering occurs during the boiling water test.
Furthermore, if 3 parts by weight or more is used, the amount tends to be excessive relative to the hydroxyl group or carboxyl group, and unreacted products may remain in the coating film, and when used as a paint for the inside of a can, there is a risk that it may be eluted into the food contents. be. The organic solvents used in the present invention are ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, cyclic ethers such as tetrahydrofuran and dioxane, halogenated hydrocarbons such as chloroform and dichloroethane, and aliphatic hydrocarbons such as cyclohexane and methylcyclohexane. , amides such as N/N-dimethylformamide and N/N-dimethylacetamide, ethyl acetate,
It is a mixed solvent of one or more of esters such as butyl acetate and aromatic hydrocarbons such as benzene, toluene, and xylene, and is an organic solvent commonly used in paints. An organic solvent that dissolves at least the thermoplastic polyester resin used is appropriately selected and used. A solution of a thermoplastic polyester resin in an organic solvent is obtained by heating and stirring in a conventional manner to completely dissolve the resin, and then cooling the resin. In the coating composition of the present invention, the concentration of the thermoplastic polyester resin is 5 to 60% by weight, preferably 5 to 60% by weight, although it depends on the coating method, the type of organic solvent, etc.
It is 15-30% by weight. The paint for the inside of a can of the present invention can also contain commonly used additives. In manufacturing cans using the paint for the inside of cans of the present invention, a phenol-epoxy resin paint is used as an undercoat (primer layer) for metal materials, and on top of the coating film of this undercoat, Of course, it can be applied as a top coat agent,
Because it has excellent adhesion to metal materials, it can be applied directly as a single coat to the surface of metal materials for cans without a primer layer. On the other hand, the paint for the inside of a can is applied to the can body by coating methods such as dip coating, electrostatic coating, electrophoretic coating, spray coating, and roll coating, and spray coating and roll coating are generally used. The paint of the present invention applied to the surface of the metal material for cans is then baked. Baking can be carried out using commonly used infrared heaters, hot air heating furnaces, high frequency heating, etc. It is recommended to bake at 150-250℃ for 3-20 minutes. The paint film of the present invention obtained as described above has good boiling resistance, consumes less potassium permanganate due to water extraction, and is excellent as a paint for the inside of a can. The present invention will be specifically explained below using Examples and Comparative Examples. In the examples, "parts" are parts by weight. Example 1 90.1 parts of dimethyl terephthalate, 90.1 parts of dimethyl isophthalate, 93.1 parts of ethylene glycol, 1.
67.6 parts of 4-butanediol and 67.6 parts of 1,3-butanediol were placed in a four-necked flask equipped with a thermometer, a nitrogen inlet tube, a distillation device, and a stirring device, and 0.4 parts of calcium acetate was used as a catalyst at 180°C. The reaction was carried out by heating and stirring for 3 hours. After a predetermined amount of methanol had been distilled off, 0.2 part of antimony trioxide was added and polycondensation was further carried out at 260° C. under reduced pressure of 1 to 0.5 mmHg for 2 hours to obtain thermoplastic polyester resin 1. 20 parts of the resin 1 was added to 80 parts of cyclohexanone and dissolved with heating and stirring.
Two thermoplastic polyester resin solutions obtained in this manner were prepared. Next, 2 parts and 0.2 parts of a 10% by weight toluene solution of a chelate compound obtained by adding and reacting 3 moles of acetone ethyl acetate to a toluene solution of 1 mole of aluminum isopropylate were added to each thermoplastic polyester resin solution,
Paints 1 and 2 were created. All paints exhibited stable solubility even when stored at room temperature. Example 2 Thermoplastic polyester resin 1 obtained in Example 1
A 10% by weight n-butanol solution of a chelate compound obtained by reacting 1 mole of tetra n-butyl titanate and 2 moles of ethyl acetoacetate with a resin solution of 20 parts of cyclohexanone and 80 parts of cyclohexanone was added to each resin solution.
Coating 3 and Coating 4 were prepared by adding 0.2 parts and 0.2 parts. All paints exhibited stable solubility even when stored at room temperature. Example 3 72.1 parts of dimethyl terephthalate, 108.1 parts of dimethyl isophthalate, 93.1 parts of ethylene glycol and 135.2 parts of 1,3-butanediol were reacted according to the method of Example 1 to obtain thermoplastic polyester resin 2. Add 20 parts of the resin 2 to cyclohexanone.
80 parts was dissolved while heating. Two thermoplastic polyester resin solutions obtained in this manner were prepared.
Then, to this resin solution, 3 mols of ethyl acetoacetate was added to a toluene solution of 1 mol of aluminum n-butyrate.
10 of the chelate compound obtained by reacting by adding mole
2 parts and 0.2 parts of a wt% toluene solution were added to obtain paints 5 and 6. All paints exhibited stable solubility even when stored at room temperature. Example 4 180.2 parts of dimethyl terephthalate, 37.2 parts of ethylene glycol, 162.2 parts of 1,3-butanediol and 63.7 parts of diethylene glycol were reacted according to the method of Example 1 to obtain thermoplastic polyester resin 3. Next, a chelate compound was added by the method of Example 2 to obtain paints 7 and 8. It remained stable even when stored at room temperature. Comparative Example 1 20 parts each of thermoplastic polyester resins 1, 2, and 3 obtained in Examples 1, 3, and 4 were added to cyclohexanone.
Each was added to 80 parts, heated to dissolve, and then cooled to prepare a paint. Each paint was rated 9, 10, and 11. Comparative Example 2 Butylated melamine resin (trade name: Melan 20, manufactured by Hitachi Chemical Co., Ltd.) and benzobunamine resin (trade name: Super Betsucomin TA-126) were added to 100 parts of a 20% by weight solution of thermoplastic polyester resin 1 in cyclohexanone in Example 1. , manufactured by Dainippon Ink & Chemicals Co., Ltd.) were added to prepare paints 12 and 13. Using the paints obtained in the above Examples and Comparative Examples, a tin plate (ET) or an aluminum plate (Al) was coated with a No. 38 bar coater and baked at 165°C or 195°C for 5 minutes, respectively. Each coated board or paint was tested for adhesion, workability, boiling resistance, flavor retention, and storage stability of the paint under the conditions shown below. The results are shown in Table 1. The coating was applied immediately after the paint was manufactured and after being stored at 40°C for 30 days, but there was almost no change in each test except for the comparative example. (1) Adhesion: Approximately 1.5mm using a knife on the coating surface
Make 10 vertical and horizontal cuts in the width of the goban. When a 24mm wide cellophane adhesive tape is applied and strongly peeled off, the number of unpeeled parts of the goblin area is expressed in the numerator. (2) Processability: Using a special folding type Dupont impact tester, place a sample folded in half at the bottom, and then drop a 1 kg iron weight with a flat contact surface from a height of 50 cm. The length of cracks in the paint film was measured. 0 to 10 mm......○ mark 10 to 20 mm......△ mark 20 mm or more......Indicated by × mark. (3) Boiling resistance (boiling water resistance): After treatment in water at 100°C for 30 minutes, the painted surface is judged visually and by peeling off the cellophane adhesive tape. (4) Potassium permanganate consumption: Ministry of Health and Welfare notification
In accordance with No. 434, an aluminum plate (Al) coated on both sides and baked at 195℃ was used as a sample, and after immersing it in distilled water at a rate of 2ml per ^1cm2 of surface area at 60℃ for 30 minutes, the immersion liquid was diluted to 0.01N. (N) Measurement was performed using a sodium oxalate aqueous solution and a 0.01N potassium permanganate aqueous solution. Display the obtained results in PPm. (5) Storage stability of paint: It was kept in a furan vessel at 50°C and evaluated by periodically examining its appearance and boilability. (Measurement for 1 month) Good storage stability ……〇 Abnormalities in the dispersion state such as kelization, sedimentation, and separation occur during storage ……Indicated by ×. 【table】

Claims (1)

[Claims] 1. A thermoplastic polyester resin having a terminal hydroxyl group or a terminal carboxyl group, and at least one selected from a chelate compound of aluminum alcoholate and a chelate compound of tetraalkyl titanate ester and the thermoplastic polyester resin are dissolved. A paint composition for the inside of a can, comprising an organic solvent. 2 0.01 to 3 parts of at least one selected from a chelate compound of aluminum alcoholate and a chelate compound of tetraalkyl titanate to 100 parts by weight of a thermoplastic polyester resin having a terminal hydroxyl group or a terminal carboxyl group.
The coating composition for the inner surface of a can according to claim 1, which is used in parts by weight.