JP2019104875A - Polyester resin and coating resin composition - Google Patents

Abstract

To provide a polyester resin that gives a coating film having excellent solubility in general-purpose organic solvent, and excellent metal adhesion, and excellent retort resistance, and particularly suitable for a food and a beverage, and a coating resin composition.SOLUTION: A polyester resin has a dicarboxylic acid component and a glycol component, in which 60 mol% or more of the glycol component is 2-methyl-1,3-propanediol, and an acid value is 20 mgKOH/g or more and a glass transition temperature is 40°C or more.SELECTED DRAWING: None

Description

  The present invention relates to a polyester resin capable of forming a coating on the inner surface of a metal can for food or beverage.

  The paint used on the inner surface of metal cans for food and beverages is used for the purpose of not losing the flavor and flavor of the contents and preventing corrosion of the can material by a wide variety of foods. First of all, it is required to be non-toxic, to withstand heat sterilization (retort) treatment, to be excellent in processability and adhesiveness, and the like. In particular, in recent years, the use of substances such as bisphenol-type epoxy resins containing external factor endocrine disrupting substances (hereinafter, environmental hormones) is being avoided.

At present, epoxy-phenolic resins are widely used as resins for can coatings, but they have the following problems.
Epoxy-phenol resins have a high baking temperature, and are prone to appearance defects such as foaming during baking. Further, as described above, since bisphenol A contained in the epoxy resin is suspected to be an environmental hormone, development of a paint for the inner surface of a can instead of this is desired.

On the other hand, polyester resins are proposed in Patent Document 1 and Patent Document 2 as resins which are easy to paint and bake and have excellent metal adhesion. However, in recent years, the form of food cans and beverage cans has become complicated, and such complicated processing is inferior in processability due to lack of metal adhesion, and further heating by boiling water or steam It is inferior to retort resistance at the time of processing. And as a method of solving these problems, Patent Document 3 and Patent Document 4 propose polyesters containing one or more of propylene glycol and 2-methyl-1,3-propanediol, but metal adhesion It was not possible to satisfy all of the coating film performance such as retort resistance and the solubility in general-purpose organic solvents.
Japanese Examined Patent Publication No. 60-42829 Japanese Examined Patent Publication No. 61-36548 JP 2001-106969 JP 2001-311040

  The present invention solves the problems as described above, polyester having good solubility in general-purpose organic solvents, excellent metal adhesion, and excellent retort resistance, and in particular provides a coating film suitable for food and beverage cans. An object of the present invention is to provide a resin composition for a resin and a paint.

  As a result of intensive studies to solve the problems described above, the present inventors satisfied a specific composition, and by having an acid value of a certain level or more, the solubility in general-purpose organic solvents is good. In the present invention, it has been found that a polyester resin exhibiting high metal adhesion, retort resistance and corrosion resistance can be obtained.

That is, the present invention provides the following (1) to (3) as the gist.
(1) A polyester resin comprising a dicarboxylic acid component and a glycol component, wherein 60 mol% or more of the glycol component is 2-methyl-1,3-propanediol, the acid value is 20 mg KOH / g or more, the glass transition temperature is Polyester resin characterized by having a temperature of 40 ° C. or higher.
(2) A resin composition for a paint, comprising the polyester resin according to (1) and a phenol resin at a mass ratio (polyester resin / phenol resin) of 70/30 to 95/5.
(3) The polyester resin composition according to (2), wherein the phenolic resin is a resol type.

  The polyester resin of the present invention is excellent in solubility in general-purpose organic solvents and can obtain a coating film excellent in metal adhesion, retort resistance and corrosion resistance, and is particularly suitable as an inner coating for food and beverage cans. It can be used.

Hereinafter, the present invention will be described in detail.
The polyester resin of the present invention is a polyester resin comprising a dicarboxylic acid component and a glycol component. And 60 mol% or more of a glycol component needs to be 2-methyl- 1, 3- propanediol, and it is preferable that it is 65 mol% or more especially.

  In order to improve adhesion to metal, it is preferable to increase the molecular weight, and in order to improve retort resistance and blocking resistance, it is preferable that the glass transition temperature be high. Furthermore, in order to provide solvent solubility, it is preferable to copolymerize the monomer which has a side chain. In consideration of these, in the present invention, a polyester mainly composed of 2-methyl-1,3-propanediol is used. Furthermore, in the case of polyester mainly composed of 2-methyl-1,3-propanediol, the glass transition temperature is lowered, so that the retort resistance becomes inferior. Then, in polyester which has 2 methyl 1, 3- propanediol as a main, it discovers that retort resistance improves by raising an acid value, and completed this invention.

  When the content of 2-methyl-1,3-propanediol in the glycol component is less than 60 mol%, the solvent solubility of the obtained polyester resin is lowered, and the adhesion to metal when it is formed into a coating film is lowered.

  Further, the glass transition temperature of the polyester resin is required to be 40 ° C. or more, and preferably 50 ° C. or more. Retort resistance and corrosion resistance fall that glass transition temperature is less than 40 degreeC. Moreover, since it becomes easy to fall in flavor property when using as a can inner coating material, it is unpreferable.

  The acid value of the polyester resin is required to be 20 mg KOH / g or more, and preferably 25 mg KOH / g or more. When the acid value of the polyester resin is less than 20 mg KOH / g, the coating film after retort treatment becomes white, and the adhesion to metal, retort resistance and corrosion resistance become poor.

  Among glycol components constituting the polyester resin, ethylene glycol, 1,2-propanediol, neopentyl glycol, dipropylene glycol, polypropylene glycol, 2-ethyl, as other than 2-methyl-1,3-propanediol 2-Butylpropanediol, 3-methyl-1,5-pentanediol, 3-ethyl-1,5-pentanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1, 8-octanediol, 4-propyl-1, 8-octanediol, etc. may be mentioned, with preference given to ethylene glycol.

  In the present invention, as the dicarboxylic acid constituting the polyester resin, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, hydrogenated dimer acid And 1,4-cyclohexanedicarboxylic acid, maleic acid, fumaric acid, non-hydrogenated dimer acid, trimellitic acid and the like. Among them, terephthalic acid is preferred.

  The method for producing the polyester resin of the present invention is not particularly limited, and it is produced by a conventional production method by melt polycondensation such as direct esterification or transesterification using the above-mentioned dicarboxylic acid component and glycol component. can do.

  For example, the dicarboxylic acid component, the glycol component and the polycondensation catalyst are charged all at once into the reactor, the air in the system is discharged, and the system is replaced with nitrogen. Thereafter, the temperature is usually raised to 200 to 260 ° C., and the esterification reaction is carried out for 3 to 4 hours while stirring. After completion of the esterification reaction, the temperature is usually raised to 220 to 260 ° C., the system is further depressurized, and the polycondensation reaction is performed under vacuum (5 hPa or less). The reaction time varies depending on the type of polyester resin to be produced, but is usually 4 to 6 hours. After completion of the polycondensation reaction, nitrogen is sealed in the system, and after depressurization is released, there is a method of discharging the obtained resin.

  As the polycondensation catalyst, metal compounds such as tin, titanium, antimony, germanium, cobalt and the like are preferable.

  Under the present circumstances, as a method of giving an acid value to resin, the depolymerization method which adds polyvalent carboxylic acid anhydride in the polycondensation late stage, this is made into a high acid value in the stage of prepolymer, and then a polycondensation reaction is performed, There are a method of obtaining a high acid value resin, a method of mixing with a separately obtained high acid value resin, and the like, but it is preferable to adopt a depolymerization method from the ease of operation.

  As polyvalent carboxylic acid anhydrides used for acid addition in such a depolymerization method, phthalic acid anhydride, tetrahydrophthalic acid anhydride, succinic acid anhydride, trimellitic acid anhydride, pyromellitic acid anhydride, hexahydrophthalic acid anhydride Etc. Preferred is trimellitic anhydride.

  The intrinsic viscosity of the polyester resin is preferably 0.20 or more, and more preferably 0.22 or more. When the intrinsic viscosity is less than 0.20, the resulting coating film becomes brittle and the adhesion to metal becomes poor.

  Next, the resin composition for paints of the present invention will be described. The resin composition for paint of the present invention contains the polyester resin of the present invention and a phenol resin, and the polyester resin and the phenol resin have a ratio of 70/30 to 95/5 in mass ratio (polyester resin / phenol resin) Are preferably contained, and among them, 80/20 to 90/10 are preferable. When the proportion of the phenolic resin is less than the above range, the retort resistance and corrosion resistance of the resulting resin composition for paint decrease. On the other hand, when the proportion of the phenol resin is larger than the above range, the resulting resin composition for coating is inferior in adhesion to metal.

  There are novolak type and resol type as the phenol resin, but it is preferable to use the resol type as the phenol resin used in the resin composition for paint of the present invention. As a specific example of the resol type phenolic resin, Shonol manufactured by Aika SDK Phenol Co., Ltd. can be used.

  The resin composition for paint of the present invention is preferably used by dissolving it in an organic solvent, and the usable organic solvent may be any one that dissolves both the polyester resin and the phenol resin.

Specific examples of usable organic solvents include aromatic solvents such as benzene, toluene and xylene, methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane Chlorinated solvents such as chlorobenzene, o-dichlorobenzene, m-dichlorobenzene and p-dichlorobenzene, ester solvents such as ethyl acetate and γ-butyrolactone, isophorone, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and the like Solvents of ketone series, diethyl ether, butyl cellosolve, ethyl cellosolve, ether solvents such as tetrahydrofuran and 1,4-dioxane, alcohol solvents of methanol, ethanol, propanol, isopropanol, butanol and the like, butane, pentane, Hex Down, cyclohexane, heptane, octane, nonane, Solvesso 100, and a solvent of aliphatic hydrocarbon such as Solvesso 150.
These can be used alone or in combination of two or more. Among these, cyclohexanone, a mixed solvent of cyclohexanone and Solvesso 100, a mixed solvent of toluene and methyl ethyl ketone, ethyl acetate and the like can be mentioned.

  The resin composition for paint of the present invention may contain a polyester resin and a resin other than a phenol resin as long as the characteristics of the present invention are not impaired. For example, alkyd resin, urethane resin, bisphenol structure Epoxy resin which does not have, acrylic resin modified olefin resin, cellulose derivative etc. can be used together. If necessary, a reaction catalyst for accelerating the curing reaction, a repelling inhibitor, a leveling agent, an antifoaming agent, an antiwaist agent, a rheology control agent, a pigment dispersant, a lubricant, a release agent and the like can be used in combination.

  The solid content concentration of the polyester resin in the resin composition for paint of the present invention is preferably 10% by mass or more, and more preferably in the range of 15 to 50% by mass. When the solid content concentration is less than 10% by mass, not only it becomes difficult to form a thick coating film, but also the proportion of the organic solvent in the coating becomes high, and the solvent is distilled off when forming a coating film. Problems, such as a decrease in productivity.

  The resin composition for paints of the present invention is uniformly applied to a metal plate by dip coating method, brush coating method, roll coating method, spray coating method, gravure coating method, curtain flow coating method, various printing methods, etc. .

  Next, a metal plate to which the resin composition for paint of the present invention is applied will be described.

  As a metal plate which is the equipment for application | coating, a sheet-like or strip-like steel plate, an aluminum plate, or those which performed various plating processes and chemical conversion treatment on the surface are mentioned.

  And after apply | coating the resin composition for paints on a metal plate, a coating layer can be formed on a metal surface by baking. The thickness of the coating is preferably 0.2 to 100 μm, and more preferably 1 to 20 μm. If the thickness is less than 0.2 μm, the coating film is broken (peeling or cracking) in the can-forming process, and only cans having poor corrosion resistance and flavor can be obtained. On the other hand, if the thickness exceeds 100 μm, there is a risk that the organic solvent used in the paint may remain, or even if the organic solvent can be completely removed, the process of distilling off the solvent may take a long time, etc. Will occur.

  The baking step is preferably performed at a temperature of 180 to 250 ° C. for 5 to 60 minutes, and more preferably for 7 to 20 minutes. When the temperature is lower than 180 ° C., the removal of the organic solvent is incomplete and the curing reaction does not proceed sufficiently, so that only cans with poor corrosion resistance can be obtained. On the other hand, when baking is carried out at a temperature exceeding 250 ° C., although the reaction with the curing agent proceeds sufficiently, the polyester resin may be thermally decomposed. In addition, when the baking time is less than 7 minutes, the removal of the organic solvent is incomplete, the curing reaction does not sufficiently proceed, and only a can having poor corrosion resistance can be obtained. On the other hand, when the baking time exceeds 60 minutes, the productivity is reduced.

  By using the metal plate on which the resin film thus obtained is formed, the heat resistance is excellent, and high temperature processing such as retort processing is possible, and even if severe processing is performed, pinholes, micro cracks, etc. No metal defects occur, and a metal can having excellent corrosion resistance and impact resistance can be manufactured.

  The metal plate having the coating film obtained as described above can be used as a member that requires workability, such as a two-piece can barrel and an upper lid, and a three-piece can barrel and a bottom lid.

Next, the present invention will be more specifically described by way of examples.
Each measurement and evaluation item were implemented by the following method.
(1) Measurement of polyester resin composition The obtained polyester resin is dissolved in a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform in a volume ratio of 11: 1, and JNM-ECZ-400R type NMR apparatus manufactured by JEOL Ltd. 1 H-NMR was measured, and from the integrated intensity of the proton peak of each component of the obtained chart, the amount of copolymerization was determined to determine the composition.
(2) Measurement of Intrinsic Viscosity ([η]) of Polyester Resin The obtained polyester resin was measured at a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent.
(3) Measurement of Glass Transition Temperature (Tg) of Polyester Resin The obtained polyester resin was measured using a differential scanning calorimeter (DSC 7 manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. .
(4) Measurement of Acid Value of Polyester Resin 0.5 g of the obtained polyester resin was weighed, completely dissolved in 25 ml of 1,4-dioxane, and several drops of cresol red were added as an indicator. The resulting solution was titrated with KOH methanol solution with a concentration of 0.1 mol / l. A value obtained by converting the number of mg of KOH consumed for neutralization into an amount per 1 g of resin was determined as an acid value.

(5) Solvent Solubility The obtained polyester resin was dissolved in cyclohexanone to make 30% by mass, and then the dissolution stability after leaving for 1 week at 25 ° C. was evaluated as solubility.
○: Good, ×: White turbidity, solidification or insoluble (6) Metal adhesion The test on the obtained coated metal plate was carried out in accordance with JIS K5400-8.5 (adhesion-grid test).
:: no peeling, x: peeling (7) Retort resistance The obtained coated metal sheet is immersed in distilled water and treated with a retort processor for 30 minutes at 125 ° C., and then the hue L value of the coating is measured. It was measured.
○: L value <50, ×: L value 50 50
(8) Corrosion resistance A crosscut was applied to the base of the coating film using the obtained coated metal sheet, and then the metal sheet was subjected to salt spray treatment with a 5% aqueous solution of sodium chloride at 35 ° C. for 3 weeks. . The evaluation was carried out on the basis of the following criteria visually for the metal plate after the test.
○: Rust width is less than 2 mm on one side from cut part Δ: Rust width is more than 2 mm on one side and less than 5 mm from cut part ×: Rust width is more than 5 mm on one side from cut

Example 1
(Preparation of polyester resin)
87.2 parts by weight of terephthalic acid and 44.0 parts by weight of ethylene glycol were charged in the esterification reactor, and the esterification reaction was carried out by a conventional method. The obtained polyester oligomer is transferred to a polymerization reactor, and 96.6 parts by weight of 2-methyl-1,3-propanediol and 0.1 parts by weight of tetrabutyl titanate are charged, and then the reaction system takes 60 minutes. The pressure was gradually reduced to 0.4 hPa, and then a polycondensation reaction was performed at a temperature of 260 ° C. for 4 hours. After completion of the polycondensation reaction, 9.0 parts by weight of trimellitic anhydride was added, and a depolymerization reaction was carried out at 260 ° C. for 2 hours to obtain a polyester resin.
(Preparation of resin composition for paints)
The obtained polyester resin was dissolved in cyclohexanone to prepare a solution having a solid content concentration of 30% by mass. As a curing agent, a phenol resin (manufactured by Aika SDK Phenol Co., Ltd., Shonol PC-TS-490) was mixed at a polyester resin / phenol resin = 90/10 (mass ratio) to obtain a resin composition for paint.
(Preparation of painted metal plate)
The obtained resin composition for paint was applied on an aluminum steel plate (A5052P, 1 mm × 70 mm × 150 mm) using a coater (slit width: 100 μm) so that the coating film would be 10 to 20 μm and air dried at normal temperature . Thereafter, drying and baking were performed for 7 minutes in a hot air circulation type oven adjusted to 215 ° C., to obtain a coated metal plate on which a 10 μm coating film was formed.

Examples 2 to 4 and Comparative Examples 1 to 4
The procedure of Example 1 was repeated except that the amounts of terephthalic acid, ethylene glycol, 2-methyl-1,3-propanediol and trimellitic anhydride added were changed to obtain a polyester resin of the composition shown in Table 1. A polyester resin was obtained.
A resin composition for coating was produced in the same manner as in Example 1 except that the obtained polyester resin was used, to produce a coated metal plate.

Comparative example 5
A polyester resin was obtained in the same manner as in Example 1 except that 1,2-propanediol was changed instead of 2-methyl-1,3-propanediol to be a polyester resin having the composition shown in Table 1. .
A resin composition for coating was produced in the same manner as in Example 1 except that the obtained polyester resin was used, to produce a coated metal plate.

Examples 5 to 6, Comparative Example 6
A polyester resin was obtained in the same manner as in Example 1 except that adipic acid or sebacic acid was used as the dicarboxylic acid component to obtain a polyester resin having the composition shown in Table 1.
A resin composition for coating was produced in the same manner as in Example 1 except that the obtained polyester resin was used, to produce a coated metal plate.

Comparative example 7
A resin composition for coating was produced in the same manner as in Example 1 except that the polyester resin of Example 1 was used and the curing agent was melamine resin (Cymel 303 manufactured by Mitsui Cytec Co., Ltd.), and a coated metal plate was produced. .

Examples 7-8, Comparative Examples 8-9
A resin composition for paint was produced in the same manner as in Example 1 except that the mass ratio of the polyester resin to the phenol resin was changed as shown in Table 1 using the polyester resin of Example 1, and a coated metal plate was produced. .

  As is clear from Table 1, the polyester resins of Examples 1 to 6 have good solubility, and the obtained resin compositions also exhibit aluminum adhesion, retort resistance, and corrosion resistance as a coating film. It was good. Furthermore, the resin compositions of Examples 7 to 8 were also excellent in performance when used as a coating film.

On the other hand, since the polyester resin of Comparative Examples 1 to 3 had a low acid value of the polyester resin, the obtained resin composition was inferior in aluminum adhesion, retort resistance and corrosion resistance.
The polyester resin of Comparative Example 4 was poor in solubility because the amount of copolymerization of 2-methyl-1,3-propanediol was small. For this reason, the resin composition containing a phenol resin was not able to be obtained.
Since the polyester resin of the comparative example 5 used propylene glycol instead of 2-methyl- 1, 3- propanediol, the obtained resin composition was inferior to retort resistance.
Since the polyester resin of Comparative Example 6 had a low glass transition temperature of the resin, the obtained resin composition was inferior in retort resistance and corrosion resistance.
The resin composition of Comparative Example 7 was inferior in retort resistance because a melamine resin was used as a curing agent when obtaining the resin composition.
The resin composition of Comparative Example 8 was inferior in retort resistance and corrosion resistance because it did not contain a curing agent.
The resin composition of Comparative Example 9 was poor in aluminum adhesion because the content of the phenol resin was large.

Claims (3)

A polyester resin comprising a dicarboxylic acid component and a glycol component, wherein 60 mol% or more of the glycol component is 2-methyl-1,3-propanediol, the acid value is 20 mg KOH / g or more, and the glass transition temperature is 40 ° C. or more Polyester resin characterized by being. A resin composition for a paint comprising the polyester resin according to claim 1 and a phenol resin at a mass ratio (polyester resin / phenol resin) of 70/30 to 95/5. The resin composition for paints according to claim 2, wherein the phenolic resin is a resol type.