JP2008101077A - Water-based coating material containing polymer emulsion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water-based coating material that does not use a bisphenol A-derived constituent component at all, does not substantially use a surfactant being a causative substance for deteriorating steam sterilization resistance of a cured coating film after baking, forms a polymer emulsion and foams a coating film having excellent steam sterilization resistance, processability and adhesivity and not causing change of fragrance and flavor of beverage and is suitable for can inner surface coating. <P>SOLUTION: The water-based coating material comprises a polymer emulsion obtained by radically polymerizing a component (B) to be emulsified containing an ethylenic unsaturated monomer (B1) but not a polyester in the presence of (1) an aqueous solution or emulsion of a polymer containing a carboxy group-containing polyester (A), a basic compound (C) and water (D). The ethylenic unsaturated monomer (B1) comprises at least one kind of an amide-based monomer as an essential component. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water-based paint, and more particularly to a water-based paint suitably used for coating an inner surface of a can containing a beverage or food. More specifically, the present invention relates to a water-based paint capable of forming a coating film that has excellent hygiene, steam sterilization resistance, processability, adhesion, and low flavor component adsorption ability, and has excellent flavor retention of contents. The present invention relates to a coated can formed by coating the inner surface of the can using the same.

BPA type epoxy resin synthesized from bisphenol A (hereinafter abbreviated as “BPA”) and epichlorohydrin has a function of forming a coating film excellent in steam sterilization resistance, workability and adhesion. It is suitably used for coating materials for inner and outer surfaces.
Conventionally, water-dispersed acrylic-modified epoxy resins in which a BPA type epoxy resin is modified with an acrylic resin and a carboxyl group or the like is introduced into the molecule are mainly used for water-based coatings for can inner surface coating.

Other than BPA type epoxy resins, examples of resins having processability and adhesion similar to those of BPA type epoxy resins include emulsion type acrylic resins synthesized by emulsion polymerization. Emulsion type acrylic resin synthesized by emulsion polymerization method is generally known to have a very high molecular weight compared to acrylic resin synthesized by solution polymerization method. It is thought that processability and adhesion can be obtained.
However, since a surfactant is generally used as an emulsifier in the emulsion polymerization method, the surfactant is contained in the cured coating film. Since this surfactant causes deterioration of the steam sterilization resistance of the cured coating film, at present, the emulsion type acrylic resin synthesized by the emulsion polymerization method using the surfactant is used for the paint for coating the inner surface of the can. Not reached.

Therefore, instead of using a surfactant that causes deterioration of steam sterilization resistance, instead of using a water-based acrylic polymer having a carboxyl group and a crosslinkable functional group other than a carboxyl group and a base compound, a mixture of acrylic monomers Is dispersed in an aqueous medium in advance to obtain an aqueous dispersion of monomer (pre-emulsion), and the aqueous dispersion of monomer is radically polymerized in the presence of a separately prepared aqueous resin having a carboxyl group ( In the following, "Pre-emulsification method") has been proposed (see Patent Document 1: Japanese Patent Laid-Open No. 2002-155234).
That is, Patent Document 1 states that a soap-free acrylic resin emulsion obtained by dropwise polymerization of an aqueous dispersion of an acrylic monomer in the presence of an aqueous resin having a carboxyl group can be used in an aqueous coating composition for cans. It is described that the water-based coating composition can form a coating film excellent in processability, adhesion, and boiling resistance.

However, in can coatings, especially beverage can applications, various processes may be performed on the can body in order to accommodate filling of various contents. In particular, the lid portion is subjected to complicated and advanced processing to prevent deformation of the can body after filling the contents and corrosion caused thereby.
It should be noted that this advanced processing is performed after the cured coating is provided on both sides of the lid. Naturally, the coating does not cause coating defects even under this processing. Sex is required. However, when the aqueous coating composition obtained by the method described in Patent Document 1 is used, the required workability level cannot be ensured.

In addition, Patent Document 1 discloses that it is preferable to form a coating film with a component having a low glass transition temperature from the viewpoint of improving the workability of the cured coating film.
However, when a coating film is formed with a component having a low glass transition temperature, the cured coating film tends to adsorb flavor components other than water contained in the beverage, changing the scent and taste of the beverage, and maintaining the flavor. There is a problem that decreases.
In addition, when a component with a high glass transition temperature is used, the adsorptive capacity of the coating film becomes low, and changes in fragrance and taste can be suppressed. However, the stability of the emulsion is lowered, and it becomes easy to generate flaws, and the cured coating film becomes brittle and the workability is lowered.

Also, an aqueous resin dispersion composed of a polyester having a carboxyl group, a basic compound, and water is used as a polymer emulsifier component, and a polyester and an ethylenically unsaturated monomer are used as an emulsified component. A polymer has been proposed (see Patent Document 2: Japanese Patent Laid-Open No. 2005-60460).
In the method exemplified in Patent Document 2, polyester and ethylenically unsaturated monomers that are to be emulsified are pre-emulsified with a polymer emulsifier, and this is emulsion-polymerized and combined in an aqueous medium with a water-soluble initiator. It is to become.
In general, emulsion polymerization is explained by a special mechanism in which a solubilized monomer reacts in a micelle and the monomer is sequentially supplied from dispersed monomer droplets. From this point of view, it is difficult to say that the polyester and the ethylenically unsaturated monomer are necessarily combined in the reaction, and the composite polymer produced by the method described in Patent Document 2 tends to cause a difference in paint physical properties between production lots. It can be said that the stability is not good.
Furthermore, when the polyester content in the component to be emulsified is increased, the compatibility between the polyester as the component to be emulsified and the ethylenically unsaturated monomer and the polymer thereof is lowered, so that the polymerization stability and obtained are obtained. The problem of lack of dispersion stability of the emulsion arises.

In addition, when crystalline polyester is used as an emulsified component, an operation process for dissolving the polyester in a solvent or a monomer becomes indispensable, and the production process becomes complicated and takes a long time. Become.
JP 2002-155234 A Japanese Patent Laid-Open No. 2005-60460

  An object of the present invention is to use a polymer emulsion without using any component derived from BPA and substantially not using a surfactant that is a causative substance that deteriorates the steam sterilization resistance of a cured coating film after baking. A water-based paint suitably used for coating the inner surface of a can, which is capable of forming a coating film that is excellent in steam sterilization resistance, processability, adhesion, and does not cause a change in the scent or taste of beverages, and It is to provide a coated can formed by coating the inner surface of the can.

  As a result of repeated studies by the present inventors on the above problems, a polymer emulsion obtained by radical polymerization of an ethylenically unsaturated monomer in an aqueous medium in the presence of a polyester having a carboxyl group has a BPA-derived component. In addition, it is possible to form a coating film that is excellent in steam sterilization resistance, processability, and adhesion, and does not cause changes in the aroma and taste of beverages, without using a surfactant. It has been found that it can be suitably used as a water-based paint for coating the inner surface of a can, and the present invention has been completed.

  That is, according to the first aspect of the present invention, an ethylenic polymer is used in the presence of an aqueous polymer solution or emulsion (1) containing a polyester (A) having a carboxyl group, a basic compound (C), and water (D). A water-based paint containing a polymer emulsion obtained by radical polymerization of an emulsified component (B) containing a saturated monomer (B1) and not containing polyester, wherein the ethylenically unsaturated monomer (B1) is N- An aqueous paint characterized in that it contains at least one amide monomer selected from the group consisting of alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide as an essential component.

  According to a second aspect of the present invention, there is provided an ethylenically unsaturated monomer in the presence of an aqueous polymer solution or emulsion (1) containing a polyester (A) having a carboxyl group, a basic compound (C), and water (D). Monomer emulsion (2) containing (B1), emulsified component (B) not containing polyester, polyester (A) having carboxyl group, basic compound (C), and water (D) , An aqueous paint containing a polymer emulsion obtained by radical polymerization, wherein the ethylenically unsaturated monomer (B1) is composed of N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide. It is a water-based paint characterized by having at least one selected amide monomer as an essential component.

  3rd invention contains the ethylenically unsaturated monomer (B1) in presence of water (D), the emulsified component (B) which does not contain polyester, polyester (A) which has a carboxyl group, a basic compound (C) and a water-based paint containing a polymer emulsion obtained by radical polymerization of a monomer emulsion (2) containing water (D), wherein the ethylenically unsaturated monomer (B1) is N- An aqueous paint characterized in that it contains at least one amide monomer selected from the group consisting of alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide as an essential component.

  A fourth invention is the water-based paint according to any one of the first to third inventions, wherein the number average molecular weight of the polyester (A) having a carboxyl group is 500 to 10,000.

  A fifth invention is the water-based paint according to any one of the first to fourth inventions, wherein the acid value of the polyester (A) having a carboxyl group is 10 to 400 (mg KOH / g).

  A sixth invention is the water-based paint according to any one of the first to fifth inventions, characterized in that it contains at least one component selected from the group consisting of a phenol resin and an amino resin.

  A seventh invention is the water-based paint according to any one of the first to sixth inventions, characterized in that it is used for coating cans for containing beverages or foods.

  According to an eighth aspect of the present invention, there is provided a coated can characterized in that a can material for containing a beverage or food is coated with the aqueous paint of the seventh aspect.

  The ninth invention relates to an ethylenically unsaturated monomer in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). A method for producing a polymer emulsion in which an emulsified component (B) containing (B1) and not containing polyester is radically polymerized, wherein the ethylenically unsaturated monomer (B1) is N-alkoxyalkyl (meth) acrylamide. And at least one amide monomer selected from the group consisting of N-hydroxyalkyl (meth) acrylamides as an essential component.

  According to a tenth aspect of the present invention, there is provided an ethylenically unsaturated monomer in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). Monomer emulsion (2) containing (B1), emulsified component (B) not containing polyester, polyester (A) having carboxyl group, basic compound (C), and water (D) , A method for producing a polymer emulsion that undergoes radical polymerization, wherein the ethylenically unsaturated monomer (B1) is at least one selected from the group consisting of N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide. A method for producing a polymer emulsion, characterized by comprising an amide monomer as an essential component That.

  The eleventh invention comprises an emulsified component (B) containing an ethylenically unsaturated monomer (B1) and not containing polyester in the presence of water (D), a polyester (A) having a carboxyl group, and a basic compound. (C) and a method for producing a polymer emulsion by radical polymerization of a monomer emulsion (2) containing water (D), wherein the ethylenically unsaturated monomer (B1) is an N-alkoxyalkyl (meta ) A method for producing a polymer emulsion, characterized in that at least one amide monomer selected from the group consisting of acrylamide and N-hydroxyalkyl (meth) acrylamide is an essential component.

  According to the present invention, it can be suitably used for coating the inner surface of a can, which is excellent in hygiene, excellent in steam sterilization resistance, processability, and adhesion, and can form a coating film that does not cause a change in the aroma and taste of beverages. Thus, it is possible to provide a water-based paint having excellent stability.

The polymer emulsion contained in the aqueous paint of the present invention uses a polyester (A) containing a carboxyl group as a polymer emulsifier instead of using a surfactant, contains an ethylenically unsaturated monomer (B1), and contains a polyester. The emulsified component (B) not contained is radically polymerized in an aqueous medium.
And the polymer emulsion contained in the water-based paint of the present invention has three different modes as shown in the first to third inventions due to the difference in the production process.

In the first invention, the “monomer dropping method” in which the emulsified component (B) containing the ethylenically unsaturated monomer (B1) and not containing the polyester is used in an aqueous medium without being predispersed or pre-emulsified. This is the case by what should be said. In this case, the polyester (A) having a carboxyl group is placed in a reaction tank together with the basic compound (C) and water (D) to form an aqueous solution or emulsion (1) of the polymer. ) And radical polymerization to obtain a polymer emulsion.
In the polymerization, radical polymerization can be performed while adding the component to be emulsified (B), or radical polymerization can be started after adding the component to be emulsified (B). The radical polymerization initiator can be contained in the emulsified component (B), can be contained in the reaction tank together with the polyester (A) having a carboxyl group, etc., or the emulsified component (B). When or is added, it may be added separately to the reaction vessel. The polymerization initiator may be added intermittently or continuously, or may be added all at once.

In both the second and third inventions, an “emulsified component (B) containing an ethylenically unsaturated monomer (B1) and not containing a polyester is pre-dispersed and pre-emulsified in an aqueous medium. It is the case by the method which should be called "the law".
In the second invention, the polyester (A) having a carboxyl group is placed in a reaction tank together with the basic compound (C) and water (D) to form an aqueous solution or emulsion (1) of the polymer. This is a case where a monomer emulsion (2) containing a polyester (A) having an emulsion, the emulsified component (B), a basic compound (C), and water (D) is added, and a polymer emulsion is obtained by radical polymerization. . In the monomer emulsion (2), the polyester (A) having a carboxyl group functions as a polymer emulsifier for emulsifying the component to be emulsified (B).
In the polymerization, radical polymerization can be performed while adding the monomer emulsion (2), or radical polymerization can be started after the monomer emulsion (2) is added. Further, the radical polymerization initiator can be contained in the monomer emulsion (2), can be contained in the reaction tank together with the polyester (A) having a carboxyl group, etc., and the monomer emulsion (2). When or is added, it may be added separately to the reaction vessel. And various addition methods can be illustrated similarly to the case of the said 1st invention.

In the third invention, the emulsified component (B) is pre-dispersed and pre-emulsified using the polyester (A) having a carboxyl group, the basic compound (C), and water (D) to form a monomer emulsion (2). Is obtained, and this is added to water in the reaction vessel and radical polymerization is performed to obtain a polymer emulsion.
In the polymerization, radical polymerization can be performed while adding the monomer emulsion (2), or radical polymerization can be started after the monomer emulsion (2) is added. Further, the radical polymerization initiator can be contained in the monomer emulsion (2), can be contained in the reaction tank together with water, or when or after the monomer emulsion (2) is added. It can also be added separately to the reaction vessel. And various addition methods can be illustrated similarly to the case of the said 1st invention.

Next, various components used in the present invention will be described in detail.
<Polyester (A) having carboxyl group>
The polyester (A) having a carboxyl group contains an emulsified component (B) containing an ethylenically unsaturated monomer (B1) and not containing a polyester in the presence of the basic compound (C) and water (D). Functions as a polymer emulsifier to emulsify. Further, at the time of radical polymerization, the ethylenically unsaturated monomer is uniformly and stably dispersed in an aqueous medium as oil droplets, and the inside of the emulsion is provided as a reaction field. Moreover, after reaction, it will contribute to the dispersion stability of the obtained polymer emulsion.
Accordingly, the polyester (A) having a carboxyl group is most important for the present invention because it greatly affects the polymerization rate of the monomer, the molecular weight of the reaction product, the size of the emulsion particles, the stability of the emulsion, and the physical properties of the coating film. Positioned as one of the components.
In general, in order to emulsify a hydrophobic component in an aqueous medium, the polymer emulsifier needs to have both a hydrophobic part and a hydrophilic part in its molecular structure. In the case of the polyester (A) having a carboxyl group, the molecular structure has an alkylene skeleton, an aromatic ring or the like as a hydrophobic portion, and a carboxyl group derived from a polybasic acid described later as a hydrophilic portion.

The emulsifier in the polymer emulsion has a great influence on the physical properties of the coating film, and the influence becomes larger as the emulsifier content in the emulsion increases. In particular, when a polymer emulsifier is used, various physical properties such as the resin type, molecular weight, and glass transition temperature are reflected in the physical properties of the emulsion to be produced. .
For example, when an acrylic copolymer having a carboxyl group is used as a polymer emulsifier for the purpose of forming a coating film having excellent processability and adhesion, the resin component has a low glass transition temperature and a relatively high value. It is necessary to adopt a molecular weight. However, a polymer emulsion obtained using such an acrylic copolymer as a polymer emulsifier has a high viscosity, and the cured coating film easily causes changes in the taste and aroma of the beverage.
On the other hand, when the polyester (A) having a carboxyl group is used as a polymer emulsifier, the resulting polymer emulsion has a low viscosity, the cured coating film has excellent workability and adhesion, and the taste and aroma of the beverage. It will not cause any change.
That is, in the polymer emulsion formed by radical polymerization, the polymeric emulsifier, which is a component of the polymer emulsion, is a polyester that is generally excellent in processability, thereby satisfying both the reduction of taste and aroma adsorption and the improvement of the processability of the coating film. Make it possible.

The polyester (A) having a carboxyl group can be obtained by a reaction between a polyhydric alcohol component and a polybasic acid component according to a conventional method.
In the raw material, as an example of the polyhydric alcohol component,
Ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, glycerin, trimethylolpropane, trimethylol Ethane, pentaerythritol and the like can be mentioned. In the reaction, these may be used alone or in combination of two or more.
Moreover, as an example of a polybasic acid component,
Orthophthalic acid, isophthalic acid, terephthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, (anhydrous) maleic acid [maleic acid and maleic anhydride Together with the acid, it is expressed as “(maleic anhydride)”. The same applies below. ], (Anhydrous) trimellitic acid. In the reaction, these may be used alone or in combination of two or more.

  It is preferable that the number average molecular weight of the polyester (A) which has a carboxyl group which consists of the said raw material is 500-10000, More preferably, the number average molecular weight is 800-5000. When the number average molecular weight is less than 500, the stability of the polymer emulsion obtained by polymerizing the component to be emulsified (B) is inferior, and there is a possibility of occurrence of bumps or sedimentation of the emulsion. When the number average molecular weight exceeds 10,000, the viscosity of the aqueous solution or emulsion (1) of the polyester (A) having a carboxyl group is increased, the polymerization itself becomes non-uniform, and a gel is easily generated. Moreover, since the polyester (A) having a carboxyl group having a number average molecular weight exceeding 10,000 is difficult to synthesize and it is difficult to provide an acid value, production stability may not be ensured.

  The polyester (A) having a carboxyl group in the present invention requires the presence of a carboxyl group in its molecular structure. As a means for introducing a carboxyl group, a method such as reacting an excess amount of polybasic acid in a molar ratio with respect to the polyhydric alcohol, or adding an acid anhydride to the hydroxyl group after the reaction is effective. Become.

  The acid value of the polyester (A) having a carboxyl group is preferably 10 to 400 (mgKOH / g). More preferably, it is 100-300 (mgKOH / g). When the acid value is less than 10 (mgKOH / g), the emulsifying power is lowered, and the radical polymerization of the emulsified component (B) becomes unstable. In particular, when the acid value is less than 5 (mgKOH / g), it becomes difficult to make the polyester resin itself water-soluble or water-dispersed, making it impossible to use it as a polymer emulsifier. Moreover, when an acid value is larger than 400 (mgKOH / g), it exists in the tendency for the water resistance of the coating film obtained to fall.

<Emulsified component (B)>
The emulsified component (B) is a component emulsified with the polyester (A) having a carboxyl group in the presence of the basic compound (C) and water (D). The emulsified component (B) is mainly composed of an ethylenically unsaturated monomer (B1) and is insoluble or hardly soluble in water. Usually, solution polymerization using an organic solvent or a surfactant is used. Subject to emulsion polymerization.
In the present invention, the emulsified component (B) does not contain polyester. The reason is to improve polymerization stability, dispersion stability and industrial stability, as described in the background section.
In the present invention, the emulsified component (B) insoluble or hardly soluble in water is obtained by using a polyester (A) having a carboxyl group as an emulsifier without using a surfactant having a low molecular weight. It is characterized by radical polymerization.

  As the ethylenically unsaturated monomer (B1), an ethylenically unsaturated monomer that is emulsified when an acrylic emulsion polymerization is performed using an ethylenically unsaturated monomer or a surfactant used in normal acrylic solution polymerization. The thing similar to a monomer can be used.

In particular, in the case of the present invention, the ethylenically unsaturated monomer (B1) must contain at least one amide monomer selected from the group consisting of N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide. Ingredients.
Examples of the above amide monomers include
N-hydroxyalkyl (meth) acrylamide, such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide, and
N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide N-alkoxyalkyl (meth) acrylamides such as N- (n-, iso) butoxyethyl (meth) acrylamide.

The amide monomers are all self-crosslinking monomers and can be easily self-condensed under heating or acidic conditions. Further, it is known to react with these functional groups in the presence of a carboxyl group or a hydroxyl group. That is, a polymer emulsion obtained by radical polymerization of the emulsified component (B) containing the amide monomer can have self-crosslinking properties in the particles.
In the present invention, the crosslinking reaction of the polymer emulsion having self-crosslinking property proceeds in the baking process at the time of radical polymerization and coating. The crosslinking reaction at the time of radical polymerization contributes to high molecular weight and three-dimensional structure in the emulsion particles, and improves the workability and corrosion resistance of the resulting coating film. Moreover, in a baking process, it contributes to bridge | crosslinking between polymer emulsion particles, can improve film forming property, and can form a firm coating film.

As an example of the ethylenically unsaturated monomer (B1) other than the amide monomer used in the present invention,
Ethylenically unsaturated monomers having a carboxyl group such as (meth) acrylic acid, (anhydrous) itaconic acid, (anhydrous) maleic acid, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl Alkyl (meth) acrylates such as (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate, hydroxymethyl (meth ) Acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) Ethylenically unsaturated monomer having a hydroxyl group such as acrylate, styrene, and aromatic monomers such as methylstyrene.

<Basic compound (C)>
The basic compound (C) is used for neutralizing a part or all of the carboxyl groups in the polyester (A) having a carboxyl group, so that the polyester (A) having a carboxyl group is water-soluble or dispersed in water. Is.

Examples of the basic compound (C) used in the present invention include organic amine compounds, ammonia, alkali metal hydroxides, etc. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, and monoethylamine. , Diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl- 1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, etc. That.
Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
These basic compounds (C) are preferably used in an amount of 10 to 150 mol% with respect to 100 mol% of the carboxyl groups in the polyester (A) having a carboxyl group.

<Water (D)>
When water (D) obtains a polymer emulsion by radical polymerization of the emulsified component (B), an aqueous solution or emulsion (1) of the polymer together with the polyester (A) having a carboxyl group and the basic compound (C). Form.
Water (D) is preferably 100 to 1000 parts by weight and more preferably 200 to 600 parts by weight with respect to 100 parts by weight of the emulsified component (B).

<Monomer emulsion (2)>
As described above, the monomer emulsion (2) is prepared by radical polymerization of the emulsified component (B), which essentially contains the ethylenically unsaturated monomer (B1), which is essentially hydrophobic. ) In the presence of a carboxyl group is used as an emulsifier, so that it is pre-emulsified and used to obtain a polymer emulsion.
In obtaining the pre-emulsion, (B), (C), (D) and (A) can be mixed together, but the polyester (A) having a carboxyl group is previously prepared with a basic compound (C). It is preferable to neutralize and dissolve or disperse in water (D), and emulsify the emulsified component (B) with this neutralized aqueous solution or dispersion. At the time of emulsification, from the viewpoint of the stability of the dispersion state of the monomer emulsion (2), it is preferable to stir at high speed or to apply a high share.

  A water-soluble solvent may be added for the purpose of assisting emulsification when the monomer emulsion (2) is obtained.

  Next, the polymerization initiator used in obtaining the polymer emulsion in the present invention will be described. The polymerization initiator is roughly classified into a water-insoluble initiator and a water-soluble initiator.

Examples of the water-insoluble initiator used in the present invention include ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, and acetylacetone peroxide;
1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (tert-butylperoxy) cyclohexane, 2,2-bis (tert-butylperoxy) octane, n- Peroxyketals such as butyl-4,4-bis (tert-butylperoxy) valerate, 2,2-bis (tert-butylperoxy) butane;
Di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, α, α'-bis (tert-butylperoxy-i-propyl) benzene, 2,5-dimethyl-2,5-di ( dialkyl peroxides such as tert-butylperoxy) hexane, 2,5-dimethyl2,5-di (tert-butylperoxy) hexyne-3;
Acetyl peroxide, i-butyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, oxalic acid peroxide, benzoyl peroxide, 2,4-dichloro Diacyl peroxides such as benzoyl peroxide;
Di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis- (4-tert-butylcyclohexyl) peroxydicarbonate, dimyristyl peroxydi Peroxydicarbonates such as carbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxy-i-propyl peroxydicarbonate, di (3-methyl-3-methoxybutyl) peroxydicarbonate, diallyl peroxydicarbonate ;
tert-butyl peroxyacetate, tert-butyl peroxy-i-butyrate, tert-butyl peroxypivalate, cumylperoxyneodecanoate, tert-butylperoxylaurate, tert-butylperoxybenzoate, cumylper Various peroxide-based initiators such as peroxyesters such as oxyoctate, tert-hexylperoxypivalate, cumylperoxyneohexanoate,
Further, azobis-i-butyronitrile, azobismethylbutyronitrile, azobis- (2,4-dimethylvaleronitrile), 2,2′-azobis- (4-methoxy-2,4-dimethylvaleronitrile), 1 , 1′-azobis- (cyclohexane-1-carbonitrile), various azo initiators such as dimethyl 2,2′-azobisisobutyrate are used, and peroxide initiators are preferable.

  Examples of the water-soluble initiator used in the present invention include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate, azobisisobutyronitrile hydrochloride, 2,2′-azobis (2 -Amidinopropane) dihydrochloride, 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1, 3- Diazepin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis [ 2- (5-Hydroxy- 4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} 2 Hydrochloride, 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis [2-methyl-N- ( Azo initiators such as 2-hydroxyethyl) propionamide] and peroxide initiators such as hydrogen peroxide and tert-butyl hydroperoxide.

  Further, redox polymerization can be carried out using these radical initiator and reducing agent in combination. Examples of the reducing agent that can be used in combination include sodium pyrosulfite and L-ascorbic acid.

The polymer emulsion in the present invention is mainly composed of one or more kinds of polyester (A) having a carboxyl group and an emulsified component (B) which contains an ethylenically unsaturated monomer and does not contain a polyester. It is formed by radical polymerization in a medium.
In the case of the present invention, the composition ratio of the polyester (A) having a carboxyl group with respect to 100 parts by weight of the emulsified component (B) is preferably 5 to 300 parts by weight, and 10 to 200 parts by weight. More preferably, it is more preferably 20 to 100 parts by weight.
When the amount of the polyester (A) having a carboxyl group is less than 5 parts by weight as compared with 100 parts by weight of the emulsified component (B), the emulsified component (B) and the polymer emulsion after polymerization tend to be difficult to be emulsified. . Moreover, when there are more than 300 weight part of polyester (A) which has a carboxyl group with respect to 100 weight part of to-be-emulsified components (B), the processability improvement of the coating film after baking hardening cannot be expected so much. Water resistance tends to be inferior.
The emulsified component (B) is a component having a very high molecular weight by radical polymerization, and this contributes to the improvement of the workability of the cured coating film. Accordingly, when the total amount of the polyester (A) having a carboxyl group as an emulsifier component is more than 300 parts by weight, the component to be emulsified (B) is relatively decreased, and as a result, the processability of the cured coating film is not expected to be improved. become unable. In addition, increasing the polyester (A) having a carboxyl group increases the content of the carboxyl group, which is a hydrophilic group, in the cured coating film, and thus tends to cause a decrease in water resistance.

  In addition to the polymer emulsion described above, the water-based paint of the present invention further improves the curability and adhesion of the coating film as required, such as phenol resin, amino resin, polyvinyl alcohol, polyvinyl alcohol derivatives, etc. One or more curing agents can be added.

  A phenol resin and an amino resin can react with a carboxyl group in the polyester (A) having a carboxyl group in addition to a self-crosslinking reaction. Further, when the emulsified component (B) or the polyester (A) having a carboxyl group has a hydroxyl group, the phenol resin or amino resin can also react with the hydroxyl group. Furthermore, since the ethylenically unsaturated monomer (B1) has a crosslinkable functional group derived from an amide monomer, it can also react with these crosslinkable functional groups.

Examples of the phenol resin used in the present invention include trifunctional phenol compounds such as carboxylic acid, m-cresol, and 3,5-xylenol, and bifunctional phenol compounds such as o-cresol, p-cresol, and p-tert-butylphenol, and formaldehyde. And the like in the presence of an alkali catalyst.
Examples of the amino resin used in the present invention include urea, melamine, and benzoguanamine added with formalin.
As the phenol resin and amino resin, those obtained by etherifying some or all of the methylol groups generated by addition of formalin with alcohols having 1 to 12 carbon atoms are also preferably used.
When using a phenol resin or an amino resin, it is preferable to add 0.5 to 20 parts by weight, and more preferable to add 2 to 10 parts by weight with respect to 100 parts by weight of the resin solid content of the polymer emulsion.

If necessary, a lubricant such as wax may be added to the water-based paint of the present invention for the purpose of preventing the coating film from being damaged in the can-making process.
Examples of waxes include animal and plant waxes such as carnauba wax, lanolin wax, palm oil, candelilla wax, and rice wax, petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum, polyolefin wax, and Teflon (registered trademark) wax. A synthetic wax or the like is preferably used.

A hydrophilic organic solvent can be added to the water-based paint of the present invention for the purpose of improving paintability.
Examples of hydrophilic organic solvents include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, ethylene glycol mono (iso) propyl ether, ethylene glycol di (iso) propyl ether, ethylene glycol mono (iso ) Butyl ether, ethylene glycol di (iso) butyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, 1,3-butylene glycol-3-monomethyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol , Diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl Ether, diethylene glycol diethyl ether, diethylene glycol mono (iso) propyl ether, diethylene glycol di (iso) propyl ether, diethylene glycol mono (iso) butyl ether, diethylene glycol di (iso) butyl ether, diethylene glycol monohexyl ether, diethylene glycol dihexyl ether, triethylene glycol dimethyl ether, Propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono (iso) propyl ether, propylene glycol mono (iso) butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di (iso) propyl ether, Pyrene glycol di (iso) butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono (iso) propyl ether, dipropylene glycol mono (iso) butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether Various ether alcohols or ethers such as diethylene glycol di (iso) propyl ether and dipropylene glycol di (iso) butyl ether;
Alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, furfuryl alcohol;
Ketones such as methyl ethyl ketone, dimethyl ketone, diacetone alcohol;
Glycols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol;
Examples include alkoxy esters such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, 1-methoxy-2-propyl acetate, propylene glycol monomethyl ether acetate, etc. These may be used alone or 2 Can be used in combination with more than one species.

  In addition, for the purpose of improving the paintability, the water-based paint of the present invention may contain various auxiliary agents such as a hydrophobic organic solvent, a surfactant, and an antifoaming agent.

The water-based paint of the present invention can be widely used not only for the following cans, but also for general metal materials or metal products, etc., but is suitably used as a paint for coating the inner and outer surfaces of cans that contain beverages and foods. Suitable for can inner surface coating.
As the material of the can, aluminum, tin-plated steel plate, chrome-treated steel plate, nickel-treated steel plate or the like is used, and these materials may be subjected to surface treatment such as zirconium treatment or phosphoric acid treatment.

As a coating method of the water-based paint of the present invention, spray coating such as air spray, airless spray, electrostatic spray or the like is desirable, but roll coater coating, dip coating, electrodeposition coating, or the like can also be applied.
Although the water-based paint of the present invention can form a film only by volatilization of volatile components after coating, it is better to add a baking step in order to obtain excellent steam sterilization resistance, processability and adhesion. As conditions for baking, baking at a temperature of 150 ° C. to 280 ° C. for 10 seconds to 30 minutes is desirable.

  The present invention will be described below with reference to synthesis examples, comparative synthesis examples, examples, and comparative examples. In the examples, “parts” represents parts by weight, and “%” represents percent by weight.

[Synthesis Example 1]
Synthesis of polyester (A) having a carboxyl group 30 parts of isophthalic acid, 27 parts of 1,4-dicyclohexanedicarboxylic acid, ethylene in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas introduction pipe 17 parts of glycol, 13 parts of diethylene glycol, and 13 parts of trimethylolpropane were charged, stirred under normal pressure and nitrogen atmosphere, dehydrated while raising the temperature, and slowly heated to 230 ° C. Then, pressure reduction was performed for 30 minutes at 230 degreeC. Thereafter, the temperature is lowered to 180 ° C., 24 parts of trimellitic anhydride is added, and the mixture is stirred for 1 hour under normal pressure and nitrogen atmosphere, and has a carboxyl group having a number average molecular weight of about 1000 and an acid value of 225 (mgKOH / g). Polyester (A) was obtained.
Next, 4.2 parts of dimethylethanolamine was added and stirred for 10 minutes, and then 270 parts of ion-exchanged water was added and stirred to obtain an aqueous polyester solution having a carboxyl group having a nonvolatile content of 25%. Let this be the polyester (A) aqueous solution which has a carboxyl group.
In addition, the number average molecular weight was measured using GPC (gel permeation chromatography), and the number average molecular weight in terms of polystyrene was calculated.

[Comparative Example 1 for Comparative Example]
Synthesis of Acrylic Copolymer (E) Having Carboxyl Group In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank and nitrogen gas inlet tube, 50 parts of ethylene glycol monobutyl ether and 50 parts of ion-exchanged water Was stirred under normal pressure and a nitrogen atmosphere, and the temperature was raised to 90 ° C. While maintaining the temperature in the reaction vessel at 90 ° C., a mixture comprising 52 parts of methacrylic acid, 25 parts of styrene, 17 parts of ethyl acrylate, 6 parts of N-butoxymethylacrylamide and 1 part of benzoyl peroxide was added from the dropping tank over 4 hours. Continuous dripping.

After 1 hour and 2 hours from the end of dropping, 0.1 part of benzoyl peroxide was added, and the reaction was continued for 3 hours from the end of dropping. The number average molecular weight was about 55000, the acid value was 338 (mgKOH / g), the solid content was 50 % Acrylic copolymer solution was obtained.
Next, after adding 13.5 parts of dimethylethanolamine and stirring for 10 minutes, 200 parts of ion exchange water was added to obtain an acrylic copolymer aqueous solution having a carboxyl group having a nonvolatile content of 25%. Let this be the acrylic copolymer (E) aqueous solution which has a carboxyl group.

[Comparative Example 2 for Comparative Example]
Synthesis of polyester (F) 32 parts of isophthalic acid, 32 parts of 1,4-cyclohexanedicarboxylic acid, 19 parts of ethylene glycol, diethylene glycol in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank and nitrogen gas introduction pipe 12 parts and 5 parts of trimethylolpropane were charged, stirred under normal pressure and nitrogen atmosphere, dehydrated while raising the temperature, and slowly heated to 230 ° C. Thereafter, the pressure was reduced at 230 ° C. for 30 minutes to obtain a polyester insoluble in water and soluble in an organic solvent having a number average molecular weight of about 1300 and an acid value of 4 (mgKOH / g). This is designated as polyester (F).

[Example 1]
70 parts of the aqueous solution of the polyester (A) having a carboxyl group obtained in Synthesis Example 1 and 55 parts of ion-exchanged water were mixed, and 35 parts of styrene, 27.5 parts of ethyl acrylate, and N-butoxymethylacrylamide 7.5 were mixed therewith. A monomer emulsion was prepared by adding a portion of the ethylenically unsaturated monomer mixture and stirring.
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction tube, 50 parts of an aqueous polyester (A) solution having a carboxyl group obtained in Synthesis Example 1 and 40 parts of ion-exchanged water were added. The temperature was raised to 90 ° C. while stirring and introducing nitrogen gas.
Next, the monomer emulsion is charged into the dropping tank 1, and 0.2 part of benzoyl peroxide dissolved in 6 parts of toluene is charged into the dropping tank 2, and the temperature in the reaction vessel is increased to 90 ° C. over 3 hours at the same time. The polymer emulsion was obtained by adding dropwise with stirring.
Thereafter, 109 parts of ion-exchanged water, 50 parts of n-butanol and 50 parts of ethylene glycol monobutyl ether were added, and the contents were taken out by filtration through a 5 μm filter to obtain an aqueous paint (1) having a nonvolatile content of 20%. .

[Example 2]
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction tube was charged with 120 parts of an aqueous polyester (A) solution having a carboxyl group obtained in Synthesis Example 1 and 95 parts of ion-exchanged water. The temperature was raised to 90 ° C. with stirring under normal pressure and a nitrogen atmosphere.
Next, a dropping tank 1 is charged with a mixture of 35 parts of styrene, 27.5 parts of ethyl acrylate and 7.5 parts of N-butoxymethylacrylamide, and 0.2 part of benzoyl peroxide is added to 6 parts of toluene in the dropping tank 2. The dissolved ones were charged and dropped simultaneously with stirring while maintaining the temperature in the reaction vessel at 90 ° C. over 3 hours, thereby obtaining a polymer emulsion.
Thereafter, 109 parts of ion-exchanged water, 50 parts of n-butanol and 50 parts of ethylene glycol monobutyl ether were added, and the content was taken out by filtration through a 5 μm filter to obtain an aqueous paint (2) having a nonvolatile content of 20%. .

[Example 3]
Example 1 Except that 0.2 parts of ammonium persulfate, which is a water-soluble radical polymerization initiator, was dissolved in the monomer emulsion prepared in Example 1 and charged into a dropping tank, and benzoyl peroxide and toluene were not used. In the same manner, an aqueous paint (3) having a nonvolatile content of 20% was obtained.

[Example 4]
As a polymerization initiator, a solution obtained by dissolving 0.2 part of ammonium persulfate, which is a water-soluble radical polymerization initiator, in 6 parts of water was charged into the dropping tank 2 and polymerized in the same manner as in Example 2. A water-based paint (4) having a nonvolatile content of 20% was obtained.

[Example 5] (Phenolic resin added)
8 parts of a 20% butanol solution of “PR-C-101” (manufactured by Sumitomo Bakelite Co., Ltd., phenol resin) was added to 200 parts of the water-based paint (1) obtained in Example 1 with stirring. The content was removed by filtration to obtain an aqueous paint (5) having a nonvolatile content of 20%.

[Example 6] (Amino resin added)
Under the stirring of 200 parts of the aqueous coating composition (1) obtained in Example 1, “My Coat 106” (manufactured by Nippon Cytec Co., Ltd., amino resin solution) was diluted with ethylene glycol monobutyl ether to obtain a solid content of 20%. 8 parts of the solution was added, and the content was removed by filtration through a 5 μm filter to obtain an aqueous paint (6) having a nonvolatile content of 20%.

[Comparative Example 1]
70 parts of an aqueous solution of an acrylic copolymer (E) having a carboxyl group obtained in Synthesis Example 1 for Comparative Example and 55 parts of ion-exchanged water were mixed, and 35 parts of styrene, 27.5 parts of ethyl acrylate, N A monomer emulsion was prepared by adding a mixture of ethylenically unsaturated monomers consisting of 7.5 parts of butoxymethylacrylamide and stirring.
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction tube, 50 parts of an acrylic copolymer (E) aqueous solution having a carboxyl group obtained in Synthesis Example 1 for Comparative Example, 40 parts of ion-exchanged water was charged, and the temperature was raised to 90 ° C. with stirring while introducing nitrogen gas.
Next, the monomer emulsion is charged into the dropping tank 1, and 0.2 part of benzoyl peroxide dissolved in 6 parts of toluene is charged into the dropping tank 2, and the temperature in the reaction vessel is increased to 90 ° C. over 3 hours at the same time. The polymer emulsion was obtained by adding dropwise with stirring.
Thereafter, 109 parts of ion-exchanged water, 50 parts of n-butanol and 50 parts of ethylene glycol monobutyl ether were added, and the content was removed by filtration through a 5 μm filter to obtain an aqueous paint (7) having a nonvolatile content of 20%. .

[Comparative Example 2]
70 parts of the polyester (A) aqueous solution having a carboxyl group obtained in Synthesis Example 1 and 55 parts of ion-exchanged water are mixed, and a mixture of ethylenically unsaturated monomers composed of 40 parts of styrene and 30 parts of ethyl acrylate is added thereto. The monomer emulsion was then prepared by stirring.
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction tube, 50 parts of an aqueous polyester (A) solution having a carboxyl group obtained in Synthesis Example 1 and 40 parts of ion-exchanged water were added. The temperature was raised to 90 ° C. while stirring and introducing nitrogen gas.
Next, the monomer emulsion is charged into the dropping tank 1, and 0.2 part of benzoyl peroxide dissolved in 6 parts of toluene is charged into the dropping tank 2, and the temperature in the reaction vessel is increased to 90 ° C. over 3 hours at the same time. The polymer emulsion was obtained by adding dropwise with stirring.
Thereafter, 109 parts of ion-exchanged water, 50 parts of n-butanol and 50 parts of ethylene glycol monobutyl ether were added, and the content was taken out by filtration through a 5 μm filter to obtain an aqueous paint (8) having a nonvolatile content of 20%. .

[Comparative Example 3]
70 parts of an aqueous polyester (A) solution having a carboxyl group obtained in Synthesis Example 1 and 55 parts of ion-exchanged water were mixed, and ethylenic composed of 28 parts of styrene, 22 parts of ethyl acrylate, and N-butoxymethylacrylamide 6 A monomer emulsion was prepared by adding and stirring 14 parts of a polyester (F) soluble in an organic solvent and insoluble in water obtained in Synthesis Example 2 for Comparative Example and a mixture of unsaturated monomers. .
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas introduction tube was charged with 50 parts of the aqueous polyester (A) solution having a carboxyl group obtained in Synthesis Example 1 and 40 parts of ion-exchanged water. The temperature was raised to 90 ° C. with stirring while introducing nitrogen gas.
Next, a solution prepared by dissolving 0.2 part of ammonium persulfate in the above monomer emulsion was charged into a dropping tank, and the polymer emulsion was obtained by dropping with stirring while maintaining the temperature in the reaction vessel at 90 ° C. over 3 hours. It was.
Thereafter, 109 parts of ion-exchanged water, 50 parts of n-butanol and 50 parts of ethylene glycol monobutyl ether were added, and the contents were taken out by filtration through a 5 μm filter to obtain an aqueous paint (9) having a nonvolatile content of 20%. .

[Evaluation of coating film]
Each water-based paint obtained in Examples 1 to 6 and Comparative Examples 1 to 3 was applied to an aluminum plate having a thickness of 0.26 mm so that the dry film thickness was 5 to 6 μm. A test panel for evaluation was obtained by baking at 200 ° C. for 3 minutes, and the performance of the coating film was evaluated as follows. The results are shown in Table 1.
Each evaluation method will be described below.

<Appearance of coating film>
Visually evaluate the test panel.
(Double-circle): A coating film is smooth and there is no fuzz and foaming.
○: Slightly fine but has no problem in practical use.
Δ: There are many irregularities in the coating film, and there is a problem in practical use.
X: Remarkably uneven on the entire surface of the coating film.

<Curing property>
A gauze is wound around a 2-lb hammer, impregnated with methyl ethyl ketone, reciprocated on the coating film of the test panel, and the number of times until the underlying aluminum is exposed is determined.
◎: 200 times or more ○: 100 times or more and less than 200 times Δ: 50 times or more and less than 100 times x: Less than 50 times

<Corrosion resistance>
After cutting the test panel to 40 x 80 mm, applying the DuPont impact (1/2 inch, 500 g, 30 cm) with the coating film on the outside (convex), the test panel was immersed in a commercial sports drink and retort Retort treatment was performed at 125 ° C. for 30 minutes in the kettle. Then, it preserve | saved at 50 degreeC for 3 days with being immersed. After 4 days, it was taken out and evaluated for blisters on the flat surface portion and DuPont impact portion.
◎: No blister occurred ○: Blister occurred in the DuPont impact area, less than 50% of the processed area △: Blister occurred in the DuPont impact area, 50% or more of the processed area ×: Blister occurred in the flat area

<Retort resistance>
While the test panel was immersed in water, retort treatment was performed in a retort kettle at 130 ° C. for 1 hour. After cross-cutting the coated film surface with a cutter, a cellophane pressure-sensitive adhesive tape was stuck and peeled strongly, and the coated film surface was evaluated.
A: No peeling at all ○: Less than 5% peeling Δ: 5-50% peeling ×: More than 50% peeling

<Processability>
The test panel is cut into a size of 30 mm × 50 mm, the coating is on the outside, the test part is folded in advance by hand so that the width of the test part is 30 mm, and the thickness of 0.26 mm is between the two folded test pieces. Two aluminum plates were sandwiched, and a load of 1 kg was dropped from a height of 40 cm onto the bent portion and completely bent.
Next, the bent tip of the test piece was immersed in a 1% strength saline solution, and 6.0 V × 6 seconds was passed between the metal part of the test piece not immersed in the saline solution and the saline solution. The current value was measured.
When the processability of the coating film is poor, the coating film in the bent portion is cracked, the underlying metal plate is exposed, and the conductivity is increased, so that a high current value can be obtained.
A: Less than 1.0 mA B: 1.0 mA or more and less than 10 mA Δ: 10 mA or more and less than 20 mA ×: 20 mA or more

<Processability after retort>
While the test panel was immersed in water, retort treatment was performed in a retort kettle at 130 ° C. for 1 hour.
Using the treated test panel, the current value was measured in the same manner as in the above <workability>.
◎: Less than 10 mA ○: 10 mA or more and less than 20 mA Δ: 20 mA or more and less than 50 mA ×: 50 mA or more

<Water flavor properties>
Each aqueous paint was coated on both sides of an aluminum foil having a thickness of 0.1 mm and cured by heating at 200 ° C. for 2 minutes (film thickness 5 to 6 μm), and the obtained test panel (2) was 10 cm × 25 cm (both sides 500 cm ^2). ). The test panel (2) after cutting is put into a heat-resistant bottle together with 500 g of tap water treated with activated carbon, sealed and subjected to a retort treatment at 125 ° C. for 30 minutes, and then a flavor test is performed. As a comparison for the flavor test, tap water without a coated plate is also treated as a blank at the same time.
◎: tasteless (same as blank)
○: Slightly tastes △: Tastes x: Slightly tastes

<Flavor-resistant adsorption>
Place a 100 mm x 160 mm test panel (2) and 100 µg of limonene dissolved in diethyl ether in a 12 liter desiccator so as not to touch the test panel (2), and cover the desiccator. And then let stand at 25 ° C. for 24 hours.
After standing, the test panel (2) was taken out, immediately put in carbon disulfide and allowed to stand for 1 hour, limonene adsorbed on the coating surface was extracted, and the amount of adsorption (μg) was measured by gas chromatography.
A: Less than 100 μg ○: 100 μg or more and less than 500 μg Δ: 500 μg or more and less than 2000 μg x: 2000 μg or more

Claims (11)

  An ethylenically unsaturated monomer (B1) is contained in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). , An aqueous paint containing a polymer emulsion obtained by radical polymerization of an emulsified component (B) not containing polyester, wherein the ethylenically unsaturated monomer (B1) is N-alkoxyalkyl (meth) acrylamide, and A water-based paint comprising at least one amide monomer selected from the group consisting of N-hydroxyalkyl (meth) acrylamide as an essential component.   An ethylenically unsaturated monomer (B1) is contained in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). The monomer emulsion (2) containing the emulsified component (B) not containing polyester, the polyester (A) having a carboxyl group, the basic compound (C), and water (D) is radically polymerized. A water-based paint containing a polymer emulsion, wherein the ethylenically unsaturated monomer (B1) is at least one selected from the group consisting of N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide. An aqueous paint comprising an amide monomer as an essential component.   In the presence of water (D), an emulsified component (B) containing an ethylenically unsaturated monomer (B1) and not containing polyester, polyester (A) having a carboxyl group, basic compound (C), and water A water-based paint containing a polymer emulsion obtained by radical polymerization of a monomer emulsion (2) containing (D), wherein the ethylenically unsaturated monomer (B1) is N-alkoxyalkyl (meth) acrylamide And at least one amide monomer selected from the group consisting of N-hydroxyalkyl (meth) acrylamides as an essential component.   The water-based paint according to any one of claims 1 to 3, wherein the number average molecular weight of the polyester (A) having a carboxyl group is 500 to 10,000.   The water-based paint according to any one of claims 1 to 4, wherein the acid value of the polyester (A) having a carboxyl group is 10 to 400 (mg KOH / g).   6. The water-based paint according to claim 1, comprising at least one component selected from the group consisting of a phenol resin and an amino resin.   The water-based paint according to any one of claims 1 to 6, wherein the water-based paint is used for covering a can material for containing a beverage or food.   A coated can comprising a can material for containing a beverage or a food, which is coated with the aqueous paint according to claim 7. An ethylenically unsaturated monomer (B1) is contained in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). , A method for producing a polymer emulsion in which an emulsified component (B) not containing polyester is radically polymerized, wherein the ethylenically unsaturated monomer (B1) comprises N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl. A method for producing a polymer emulsion, comprising at least one amide monomer selected from the group consisting of (meth) acrylamide as an essential component.   An ethylenically unsaturated monomer (B1) is contained in the presence of an aqueous solution or emulsion (1) of a polymer comprising a polyester (A) having a carboxyl group, a basic compound (C), and water (D). Polymer emulsion for radical polymerization of monomer emulsion (2) containing emulsified component (B) not containing polyester, polyester (A) having carboxyl group, basic compound (C), and water (D) The ethylenically unsaturated monomer (B1) is at least one amide monomer selected from the group consisting of N-alkoxyalkyl (meth) acrylamide and N-hydroxyalkyl (meth) acrylamide. A method for producing a polymer emulsion, characterized by comprising an essential component.   In the presence of water (D), an emulsified component (B) containing an ethylenically unsaturated monomer (B1) and not containing polyester, polyester (A) having a carboxyl group, basic compound (C), and water A method for producing a polymer emulsion in which a monomer emulsion (2) containing (D) is radically polymerized, wherein the ethylenically unsaturated monomer (B1) is N-alkoxyalkyl (meth) acrylamide, and N- A method for producing a polymer emulsion, comprising as an essential component at least one amide monomer selected from the group consisting of hydroxyalkyl (meth) acrylamides.