JP2022084172A - Paint for can, and coated metal plate for can - Google Patents

Abstract

To provide paint which is suitably usable for inner and outer surfaces of a metal can, particularly, a beverage can and a food can without using a curing agent derived from bisphenol A, formaldehyde and isocyanate.SOLUTION: Paint for a can is provided which contains a dicarboxylic acid and diol as reaction raw materials, contains 90 mass% or more of an aromatic dicarboxylic acid at a para position in the total component of the dicarboxylic acid, contains 90 mass% or more of propylene glycol and ethylene glycol in the total component of the diol, and has a glass transition temperature of 60°C or higher, and a coated metal plate for a can is also provided.SELECTED DRAWING: None

Description

Beverage cans, metal cans such as food cans, and metal containers are widely and generally used as packaging containers for filling foods, beverages, and the like. On the inner surface side of these metal cans, metal containers, or lids (Easy Open End), the prevention of metal corrosion (corrosion resistance, sulfur resistance) by the contents of foods, etc., and the taste or flavor of the contents are not impaired. Is painted.
Conventionally, as paints for such painting, epoxy paints such as epoxy-phenol paints, epoxy-amino paints, epoxy-acrylic paints, polyester-phenol paints, polyester-amino paints, polyester-poly Polyester-based paints such as isocyanate and vinyl chloride-based paints are widely used.

On the other hand, in research, it has been reported that bisphenol A (BPA), which is a raw material of epoxy resin, may affect estrogenic action and the brain of fetuses and infants. In addition, vinyl chloride-based paints have a problem of generating stabilizers and dioxins when incinerated. Formaldehyde (FA), which is used as a raw material for phenolic resins and amino resins and remains in paints, is harmful to the human body such as carcinogenicity and is known to adversely affect the flavor of the contents. .. As for the polyisocyanate resin, there is a concern that the residual isocyanate monomer, the liberated blocking agent, etc. may adversely affect the human body. In recent years, there has been a demand from the market for paints that do not use these raw materials because of such concerns about adverse effects on the human body.

As a paint for the inner surface of a can that does not use such a material, the acid component is 60 to 100 mol% of terephthalic acid, 0 to 40 mol% of dicarboxylic acid other than terephthalic acid, the glycol component is 40 to 100 mol% of propylene glycol, and other than propylene glycol. Polycarboxylic acid or alicyclic glycol 0 to 60% and 0.1 to 3 mol% trifunctional or higher polycarboxylic acid or polyol with respect to the total acid component or glycol component having a reduced viscosity of 0.3 or more. A polyester resin composition containing the resin (A), a resin composition of a polyester resin having an acid component of 60 to 100 mol% of terephthalic acid and a glycol component of 40 to 100 mol% of propylene glycol, and an alkyl etherified aminoformaldehyde. (See, for example, Patent Documents 1 and 2), the total copolymerization ratio of the terephthalic acid component and the 2,6-naphthalenedicarboxylic acid component is 80 mol% or more, and among the polycarboxylic acid components constituting the polyester resin, 2, The copolymerization ratio of the 6-naphthalenedicarboxylic acid component is 2 to 80 mol%, and the total copolymerization ratio of the ethylene glycol component and the 1,2-propylene glycol component among the polyol components constituting the polyester resin is 50 mol%. As described above, a resin composition of a polyester resin containing a 1,2-propylene glycol component in excess of the ethylene glycol component and a blocked isocyanate is known (see, for example, Patent Document 3).

However, the compositions described in Patent Documents 1 and 2 use alkyl etherified aminoformaldehyde as a curing agent, and the compositions described in Patent Document 3 use isocyanate as a curing agent, both of which use the inner surface of the can. As a paint, it did not meet the market demands of recent years.

Japanese Unexamined Patent Publication No. 05-11275 Japanese Unexamined Patent Publication No. 2001-270935 WO13 / 145992

The present invention has been made to solve at least a part of such a problem, and the inner and outer surfaces of metal cans, especially beverage cans and food cans, without using a curing agent derived from bisphenol A, formaldehyde, and isocyanate. It is an object of the present invention to provide a paint which can be suitably used for.

The present inventors use dicarboxylic acid and diol as reaction raw materials, contain 90% by mass or more of para-aromatic dicarboxylic acid in the total component of dicarboxylic acid, and 90% by mass or more of propylene glycol and ethylene glycol in the total component of diol. It has been found that the problem can be solved by using a polyester resin containing and having a glass transition temperature of 60 ° C. or higher without using the curing agent.

Conventionally, it has been considered that the use of a curing agent reduces the amount of limonene adsorbed, thereby improving the flavor of the contents. On the other hand, the present inventors have good flavor properties and processability without using a curing agent as long as the polyester resin has a specific monomer, a specific monomer ratio, and a glass transition temperature in a specific range. It has been found that a can paint having excellent adhesion can be obtained.

That is, in the present invention, a dicarboxylic acid and a diol are used as reaction raw materials, and a para-aromatic dicarboxylic acid is contained in an amount of 90% by mass or more of the total component of the dicarboxylic acid, and propylene glycol and an ethylene glycol are contained in an amount of 90% by mass or more of the total component of the diol. Further, a paint for a can containing a polyester resin having a glass transition temperature of 60 ° C. or higher is provided.

The present invention also provides a coated metal plate for cans in which the above-mentioned paint for cans is at least on the inner surface side.

According to the paint of the present invention, it is possible to provide a paint that can be suitably used for the inner and outer surfaces of metal cans, particularly beverage cans and food cans, without containing raw materials derived from bisphenol A, formaldehyde, and isocyanate.

(Polyester resin)
The polyester resin used in the present invention contains dicarboxylic acid and diol as reaction raw materials, contains 90% by mass or more of para-aromatic dicarboxylic acid as the total component of dicarboxylic acid, and contains propylene glycol and ethylene glycol as 90% of all components of diol. It is a polyester resin containing% by mass or more and having a glass transition temperature of 60 ° C. or more.

(Dicarboxylic acid)
The dicarboxylic acid used in the present invention requires an aromatic dicarboxylic acid at the para position, but the aromatic dicarboxylic acid at the para position is not particularly limited. For example, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-phenylenedicarboxylic acid and the like can be mentioned.
Of these, terephthalic acid is preferable.

The dicarboxylic acid other than the aromatic dicarboxylic acid at the para position is not particularly limited, and a known dicarboxylic acid can be used. Specific examples of the aromatic dicarboxylic acid include isophthalic acid, orthophthalic acid, 5-sodium sulfoisophthalic acid, and 1,4-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and dimer acid. Examples of the alicyclic dicarboxylic acid include hexahydroterephthalic acid and hexahydrophthalic anhydride.

The para-aromatic dicarboxylic acid is preferably contained in an amount of 90% by mass or more of the total component of the dicarboxylic acid, and most preferably 95% by mass or more of the total component of the dicarboxylic acid from the viewpoint of processability and content resistance. ..

(Glycol)
The diol used in the present invention requires propylene glycol and ethylene glycol, and contains 90% by mass or more of all the components of the diol.

The diol other than propylene glycol and ethylene glycol is not particularly limited, and known diols can be used. Specifically, for example, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol. , 1,4-Cyclohexanedimethanol, p-xylylene glycol, 2,2-dimethylolbutane, 3,3-dimethylolheptan, tricyclodecanedimethanol, 1,9-nonadiol and the like.

The polyester resin used in the present invention may contain a trifunctional or higher functional polycarboxylic acid or a polyol as a reaction raw material in addition to the above-mentioned dicarboxylic acid component and diol component. The trifunctional or higher functional polycarboxylic acid or polyol is preferably in the range of 0.1 to 3.0 mol% with respect to the total acid component or glycol component. Examples of the trifunctional or higher functional polycarboxylic acid include trimellitic anhydride and pyromellitic anhydride. Examples of trifunctional or higher functional polyols include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol.

The polyester resin used in the present invention has a glass transition temperature (hereinafter sometimes referred to as Tg) of 60 ° C. or higher. On the other hand, the upper limit is preferably 120 ° C. or lower. Above all, it is more preferable that the Tg range is 70 ° C. or higher and 110 ° C. or lower. If Tg is less than 60 ° C, flavor and / or water resistance may be poor. Further, when Tg exceeds 120 ° C., it is not preferable from the viewpoint of economic productivity.

(wax)
In the present invention, the effect of the present invention can be exhibited by containing the polyester resin, but it is still preferable to contain the wax because the friction coefficient can be reduced.
Specifically, the wax is SR-16 (microcrystalline wax manufactured by Koyo Chemical Co., Ltd.), HI-DISPER 1250 (microcrystalline wax manufactured by Gifu Seratsk Manufacturing Co., Ltd.), HI-DISPER 1260 (manufactured by Gifu Seratsk Manufacturing Co., Ltd.). ) Gifu Seratsk Manufacturing Co., Ltd., microcrystalline wax), refined palm oil (Nisshin Oillio Group Co., Ltd., palm oil), refined lanolin (CRODA Co., Ltd., lanolin wax). The amount of wax added is preferably in the range of 0.1 to 5.0% by mass, more preferably in the range of 0.2 to 1.0% by mass with respect to the polyester resin.

(solvent)
The paint for cans of the present invention is obtained by dissolving and dispersing the polyester resin and, if necessary, wax in an organic solvent. As the organic solvent, conventionally known ones can be used without particular limitation, for example, aromatic hydrocarbons such as toluene, xylene, Solbesso # 100 and Solbesso # 150, and fats such as hexane, heptane, octane, nonane and decane. Group hydrocarbons, methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, ethyl formate, butyl propionate, etc., ethers, methanol, ethanol, propanol, butanol, etc., acetone, methyl ethyl ketone, cyclohexanone, etc. Ketone-based, ethylene glycol (mono, di) methyl ether, ethylene glycol (mono, di) ethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol (mono, di) methyl ether, diethylene glycol (mono) , Di) Ethyl ether, Diethylene glycol monoisopropyl ether, Diethylene glycol monobutyl ether, Triethylene glycol (mono, di) methyl ether, propylene glycol (mono, di) methyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol Examples thereof include glycol ethers such as (mono, di) methyl ether, and one type or a combination of two or more types can be used.

<Other ingredients>
The paint for cans of the present invention contains the polyester resin and, if necessary, wax, and can be suitably used as a paint for the inner surface of cans. On the other hand, a curing agent such as a phenol resin, an amino resin, or an isocyanate compound can also be used for applications in fields where there is no concern about adverse effects on the human body, not for use on the inner surface of a can. It may also contain an acid catalyst, a pigment, an antifoaming agent, a leveling agent and the like.

Examples of the phenolic resin that can be used as a curing agent include trifunctional phenolic compounds such as coalic acid, m-cresol, m-ethylphenol, 3,5-xylenol, and m-methoxyphenol, or p-cresol, o-cresol, and the like. Bifunctional phenol compounds such as p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, and m-methoxyphenol, and formaldehyde synthesized in the presence of an alkaline catalyst. , Part or all of the methylol group is etherified with lower alcohol. Examples of the amino resin include formalin adducts of urea, melamine and benzoguanamine, and those etherified by the reaction of these with a lower alcohol. Examples of the isocyanate compound include aliphatic and aromatic polyisocyanates, their trimers, and blocked compounds.

While these curing agents improve the reactivity of the paint, if the content is too large, the coating film becomes too hard and the processability may be deteriorated. Therefore, the content of these curing agents is preferably kept at 30% by mass or less of the resin solid content contained in the present invention.

In addition, formaldehyde is used for the synthesis of phenolic resin and amino resin. Formaldehyde may have an effect on the human body such as carcinogenicity, and when used as an inner paint for beverage cans, it may worsen the flavor property. Formaldehyde is completely consumed when synthesizing the resin, and it is harmless if it is incorporated in the resin, and even if unreacted substances remain, the amount may affect the human body and the environment. Although it is suppressed to the extent that it does not exist at all, when the paint of the present invention is used as an inner paint of a beverage can or a food can, it is better if the content of phenol resin or amino resin can be suppressed. There is no such thing. According to the coating material of the present invention, even when a curing agent such as a phenol resin or an amino resin is not used, the reactivity and water resistance are excellent, so that the use of these curing agents can be avoided.

In addition, when an isocyanate compound is used as a curing agent, if unreacted isocyanate remains in the coating film, it may react with water to generate an amine compound that may be harmful to health and be extracted into the contents. be. Normally, such concerns are not so great, but when it is desired to use a paint having a lower health risk, such as when the paint of the present invention is used as an inner paint for beverage cans and food cans. If the content of the isocyanate compound can be suppressed, it is better than that. Even when the coating film of the present invention does not contain such a curing agent, it is possible to obtain a coating film having excellent reactivity and water resistance.

Examples of the acid catalyst include alkylaryl sulfonic acids such as alkyl phosphate, dodecylbenzene sulfonic acid, butylnaphthalene sulfonic acid, dinonylnaphthalene sulfonic acid, paratoluene sulfonic acid and xylene sulfonic acid, and these compounds and sodium, potassium and zinc. Examples thereof include salts with ammonia, triethanolamine and the like. The reactivity can be improved by using these acid catalysts in combination, but if the content is too large, the adhesion between the cured coating film and the substrate may decrease. Therefore, the content of the acid catalyst is preferably 1 part by mass or less, and preferably 0.5 part by mass or less with respect to 100 parts by mass of the resin solid content contained in the coating material. It does not have to contain an acid catalyst.

As the pigment, conventionally known inorganic pigments and organic pigments can be used without particular limitation, and as the inorganic pigments, chromate (yellow lead, chromium vermillion) ferrocyanide (dark blue), sulfide (cadmium ero, cadmium red) can be used. ), Oxide (titanium oxide, red iron oxide, iron black, zinc oxide) Sulfate (barium sulfate, lead sulfate), silicate (ultrablue, calcium silicate), carbonate (calcium carbonate, magnesium carbonate) Phosphate (cobalt violet) Examples thereof include metal powder (aluminum powder, bronze) and carbon (carbon black). Organic pigments include azo (benzidine yellow, hanza ero, vulcan orange, permanent red F5R, carmine 6B, lake red C, chromoftal red, chromoftal ero), phthalocyanine (phthalocyanine blue, phthalocyanine green). , Kenzoku Dye (Induslen Blue, Thio Indigo Bordeaux) Dyed Lake (Eosin Lake, Kinolin Yellow, Rhodamin Lake, Methyl Violet Lake), Kinakudrin (Sincasia Red, Sincasia Violet) Geokidicin (PV Fast Violet) BL) and the like. These pigments can be used alone or in combination of two or more.

Conventionally known defoaming agents, leveling agents and the like can be used, and there is no particular limitation.

The coating material for cans of the present invention can be a steel plate, an aluminum plate for cans, etc. by known means such as various spray coatings such as air spray, airless spray, electrostatic spray, immersion coating, roll coater coating, gravure coater, and electrodeposition coating. It can be applied to a metal substrate, a polyethylene terephthalate (PET) film, or the like. The coating amount may be adjusted so that the film thickness of the cured coating film is about 0.1 to 20 μm. The baking conditions may be appropriately adjusted depending on the intended use, but as an example, when used as a paint for cans, a good coating film can be obtained by baking at 100 ° C. to 280 ° C. for about 1 second to 30 minutes.

The can paint of the present invention is a paint for coating various metal materials such as can bodies and lids of beverage cans and food cans, inner and outer surfaces of caps, aluminum and tin-plated steel plates, pretreated metals, and steel. It can be used as a coating agent for wood, film and other processed products. Above all, it can be preferably used as a paint for the inner and outer surfaces of beverage cans and food cans.

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The composition and other values are based on mass unless otherwise specified.

<Polyester resin>
According to a known synthesis method, polyester resins A1 to A2 and B1 to B7 having the compositions shown in Table 1 were obtained.

(1) Measurement of number average molecular weight The number average molecular weight of the polyester resin is made of polytetrafluoride ethylene having a pore size of 0.5 μm by dissolving and / or diluting it with tetrahydrofuran so that the polyester resin concentration is about 0.5% by weight. The sample filtered through a membrane filter was used as a measurement sample, and the measurement was performed by gel permeation chromatography (GPC) using tetrahydrofuran as a mobile phase and a differential refractometer as a detector. The flow rate was 1 mL / min and the column temperature was 30 ° C. Showa Denko's KF-802, 804L, and 806L were used as columns. Monodisperse polystyrene was used as the molecular weight standard.

(2) Measurement of glass transition temperature (Tg) The glass transition temperature of the polyester resin was measured by a differential scanning calorimeter (SII, DSC-200). A 5 mg polyester resin sample was placed in an aluminum capped container, sealed, cooled to −50 ° C. using liquid nitrogen, and then heated to 150 ° C. at 20 ° C./min. In the endothermic curve obtained in this process, the temperature at the intersection of the baseline before the endothermic peak appears and the tangent line toward the endothermic peak was defined as the glass transition temperature (Tg, unit: ° C.).

(3) Measurement of acid value To measure the acid value of polyester resin, 0.2 g of a polyester resin sample is dissolved in 40 ml of chloroform and titrated with a 0.01 N potassium hydroxide ethanol solution, and the acid value is measured per 106 g of carboxyl group-containing resin. The equivalent (equivalent / 106 g) was determined. Phenolphthalein was used as an indicator.

(Example: How to adjust the paint for cans)
In the formulation shown in Table 2, weigh and mix the raw materials with an electronic balance using an organic solvent (cyclohexanone, Solbesso # 150, etc.) so that the solid content is 20%, and then use a dispersion stirrer at a temperature of 25 ° C. The coating material for cans of Examples 1 to 4 was prepared by stirring at a rotation speed of 3000 rpm for 1 minute. Similarly, the paints for cans of Comparative Examples 1 to 7 were prepared according to the formulations shown in Table 3. The details of the raw materials used for adjusting the paint are as follows.

<Wax>
(Wax C1)
HI-DISPER 1260 (microcrystalline wax manufactured by Gifu Seratsk Manufacturing Co., Ltd., solid content 10%) was used.
(Wax C2)
Refined palm oil (manufactured by Nisshin Oillio Group Co., Ltd., palm oil, 100% solid content) was used.

(Evaluation method)
[Creation of test paint plate]
On an aluminum plate made of 5182 material having a thickness of 0.26 mm, the respective paints obtained in each example were applied using a bar coater so that the weight of the dry coating film was 45 mg / dm2. After baking under the oven condition that the passing time in the oven was 22 seconds and the PMT was 250 ° C., the plate was cooled to room temperature to obtain a test coating plate.

[Workability]
The test coating plate was cut into 40 mm x 50 mm, and a test coating plate was folded in half in a V shape using a bending tester so that the coating film surface was on the outside. A weight of 3 kg was dropped from a height of 50 cm to obtain a test piece. The outside of the bent portion of this test piece is pressed against a sponge soaked with 1% saline solution, the test piece is energized for 6 V × 3 seconds, and the current value is measured using a SENCON enamel heater (energization tester), and then the current value is measured. Evaluation was made on a 4-point scale as shown.
◎ ………… Current value is less than 1mA ○ ………… Current value is 1mA or more and less than 5mA △ ………… Current value is 5mA or more and less than 10mA × ………… Current value is 10mA or more ..

〔water resistant〕
Put the test coating plate upright in a beaker, and put ion-exchanged water into it to half the height of the test piece. This is boiled at 100 ° C. for 30 minutes and visually evaluated.
◎ ………… Good ○ ………… Slight bleaching but no blister △ ………… Slight bleaching or some blister × ………… Whitening or blister.

[Adhesion]
On the coating film formed on the test coating plate, 100 1 × 1 mm grids were prepared with a cutter, and the sample pieces were treated with hot water at 100 ° C. for 30 minutes. After that, an adhesive tape was attached to the grid portion, the adhesive tape was rapidly peeled off, the peeled state of the coating film was observed, and the evaluation was made in the following four stages.
◎ ………… No peeling ○ ………… 1 to 2% of the whole peeled △ ………… 3 to 10% of the whole peeled × ………… 11 to 100% of the whole peeled.

[TOC]
After immersing the above test coating plate of 500 cm ² in 500 mL of purified water and treating it with hot water at 100 ° C. for 30 minutes, the amount of organic matter in the water was measured based on the amount of carbon, and is shown below. It was evaluated according to the following four stages.
◎ ………… The amount of organic matter is less than 3 ppm ○ ………… The amount of organic matter is 3 ppm or more and less than 7 ppm △ ………… The amount of organic matter is 7 ppm or more and less than 15 ppm × ………… The amount of organic matter is 15 ppm or more. ..

[Flavor]
Ten pieces of test coating plate cut into 50 mm x 50 mm were prepared, immersed in 250 mL of a 2 ppm limonene aqueous solution (containing 5% ethanol), and stored at 30 ° C. for 1 week to measure the limonene retention rate, and then It was evaluated on a 4-point scale as shown.
◎ ………… The sorption rate is less than 2ppm ○ ………… The sorption rate is 2ppm or more and less than 5ppm △ ………… The sorption rate is 5ppm or more and less than 10ppm × ………… The sorption rate is It is 10 ppm or more.

The results are shown in Tables 2 and 3.

In the table, the abbreviations are as follows.
90% or more of the p-position aromatic dicarboxylic acid: 〇 is the one containing 90% by mass or more of the para-position aromatic dicarboxylic acid of all the components of the dicarboxylic acid, and × is the one not containing the para-aromatic dicarboxylic acid.
PG / EG 90% or more: 〇 indicates that propylene glycol and ethylene glycol are contained in an amount of 90% by mass or more of all diol components, and × indicates that the PG / EG does not contain propylene glycol and ethylene glycol in an amount of 90% by mass or more.
Tg 60 ° C. or higher: ◯ has a glass transition temperature of 60 ° C. or higher, and x has no glass transition temperature.
C1: Wax C1 "HI-DISPER 1260 (manufactured by Gifu Seratsk Manufacturing Co., Ltd., microcrystalline wax, solid content 10%)"
C2: Wax C2 "Refined palm oil (manufactured by Nisshin Oillio Group Co., Ltd., palm oil, 100% solid content)"

As a result, it is clear that the paint for cans satisfying the constitution of the present application is excellent in all of workability, water resistance, adhesion, TOC and flavor property.

Claims (3)

Using dicarboxylic acid and diol as reaction raw materials, para-aromatic dicarboxylic acid is contained in an amount of 90% by mass or more of the total component of the dicarboxylic acid, propylene glycol and ethylene glycol are contained in an amount of 90% by mass or more of the total component of the diol, and the glass transition is performed. A paint for cans, which comprises a polyester resin having a temperature of 60 ° C. or higher.
The can paint according to claim 1, which contains a wax.
A coated metal plate for cans, wherein the paint for cans according to claim 1 or 2 is at least on the inner surface side.