JPH10195372A - Water-base active-energy-ray-curable coating composition for metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-viscosity coating compsn. which forms a cured film excellent in adhesion to a substrate, hardness, surface gloss, and resistances to solvents and water by compounding a water-base reactive resin dispersion prepd. from a carboxylated polymer with an alkylene-oxide-modified polyol polymethacrylate and a photoinitiator. SOLUTION: A (meth)acrylate having at least one carboxyl group is polymerized (or is copolymerized with an ethylenically unsatd. monomer) at 150-310 deg.C to give a polymer having a number average mol.wt. of 1,000-15,000 and an acid value of 100-300mgKOH/g, which is dissolved or dispersed in an aq. alkaline soln. and subjected to the addition reaction with a (meth)acrylate having an epoxy group to given a water-base reactive resin dispersion having an acid value of 20-200mgKOH/g. This dispersion in an amt. of 80-40 pts.wt. is compounded with 20-60 pts.wt. polyol (meth)acrylate having at least two (meth) acryloyl groups and having 1-10mol of added alkylene oxide units and an effective amt. of a photoinitiator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based metal coating composition which is cured by irradiation with an active energy ray such as an electron beam or an ultraviolet ray. More specifically, the present invention relates to a coating composition excellent in both solvent resistance and water resistance. The present invention relates to a water-based active energy ray-curable metal coating composition which forms a cured film having excellent adhesion to a substrate. The composition of the present invention is used for coating metal cans and metal plates, and is particularly suitable as a coating composition for metal cans in which deep drawing is performed after coating. In this specification, acrylate and / or methacrylate are (meth) acrylate, acryloyl and / or methacryloyl are (meth) acryloyl, and acrylic acid and / or methacrylic acid are (meth)
Expressed as acrylic acid. The unit of the acid value is mgKOH / g
All are shown in solid content conversion.

[0002]

2. Description of the Related Art In recent years, organic solvents used in various industries, etc.,
Air pollution on a global scale due to the release of detergents and the like into the atmosphere has progressed, and there is a concern about the effects on living organisms. For this reason, studies have also been made on desolvation of metal coating compositions. One way to solve the above problem is
A coating composition for metal has been studied in which a composition containing no solvent is applied to a metal surface, and then the composition is cured by irradiation with active energy rays. As such a solvent-free active energy ray-curable metal coating composition, a composition comprising an oligoester (meth) acrylate such as polyester acrylate, epoxy acrylate, urethane acrylate and a reactive diluent is known. I have.
For example, Japanese Unexamined Patent Publication No. 53-49027 discloses a coating composition comprising a predetermined oligoester (meth) acrylate, a predetermined epoxy mono (meth) acrylate, and a polymer which can be cured by an active energy ray. A composition is disclosed. On the other hand, as another method for solving the above problems, attempts have been made to remove the solvent by making the composition aqueous, and a composition in which a resin is suspended or emulsified in water is applied to a metal surface, and thereafter, An aqueous metal coating composition for obtaining a dried coating film by a method such as heating and the like is known. For example, JP-A-63-230779 discloses an aqueous paint composition for external painting of cans comprising a predetermined aqueous acrylic resin, a predetermined polyester polyol and an amine formaldehyde condensate.

[0003]

However, according to the above-mentioned conventional solvent-free active energy ray-curable metal coating composition, it is difficult to obtain a cured film having high adhesion (adhesion) to a metal substrate. Met. The cause of such low adhesion is
Compared to compositions that use solvent-dried resins or compositions that use thermosetting resins, which cure gradually while reducing strain by thermal drying and heat curing, active energy ray-curable compositions cure. , The stress strain caused by volume shrinkage during curing tends to accumulate in the cured film. To improve the adhesion, it is also known to reduce the volumetric shrinkage during curing by mixing and dissolving non-reactive substances such as acrylic polymers, polyesters, and petroleum resins in the composition. However, there is a problem that the curability of the composition, the solvent resistance of the cured product and the like are reduced by the addition of the non-reactive substance. Further, such a solvent-free composition generally has a high viscosity, so that a method of applying the composition to a metal surface is limited. For example, it has been extremely difficult to perform spray coating or the like. In addition, according to the conventional aqueous metal coating composition, it is difficult to form a dry coating film having both high solvent resistance and high water resistance and excellent adhesion to metal, especially in such a case. The aqueous composition was apt to have insufficient water resistance. The aqueous coating composition described in JP-A-63-230779 also has insufficient solvent resistance and the like because it contains an amine formaldehyde condensate.

An object of the present invention is to provide a water-based active energy ray-curable metal which is a low-viscosity composition and forms a cured film having excellent adhesion to a metal substrate, solvent resistance and water resistance. An object of the present invention is to provide a coating composition for use.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that an aqueous dispersion of a reactive resin produced by a specific method using a polymer having a specific carboxyl group. And a specific alkylene oxide-modified polyol polyfunctional (meth) acrylate-containing composition were found to be effective, and the present invention was completed.

That is, the water-based active energy ray-curable metal coating composition according to claim 1 comprises one or more (meth) acrylates having one or more carboxyl groups or a compound other than the (meth) acrylate. One or more monomers having one ethylenically unsaturated group and one or more of the (meth) acrylates are polymerized at a polymerization temperature of 150 to 310 ° C to obtain a number average molecular weight of 1,000 to 15.0.
After obtaining a polymer (a) having an acid value of 100 to 300 mgKOH / g and then dissolving or dispersing the polymer (a) in an alkaline aqueous solution, the (meth) acrylate having one epoxy group is converted to the alkaline solution. A reactive resin aqueous dispersion (A _dp ) obtained by subjecting the polymer (a) to an addition reaction in an aqueous solution and having a reactive resin (A) having an acid value of 20 to 200 mgKOH / g dispersed in water; An alkylene oxide-modified polyol polyfunctional (meth) acrylate [hereinafter, referred to as “modified polyfunctional (meth) acrylate”, which is a (meth) acrylate of a polyol having the above (meth) acryloyl group and having 1 to 10 moles of alkylene oxide added thereto.
Acrylate. " ] (B), wherein the modified polyfunctional (meth) acrylate (B) is 20 to 6 with respect to 80 to 40 parts by weight of the reactive resin (A).
It is characterized by containing 0 parts by weight.

[0007] In a second aspect of the present invention, there is provided a water-based active energy ray-curable metal coating composition, wherein at least one kind of the monomer having one ethylenically unsaturated group is the same as the first aspect. It is characterized by being styrene or alkylstyrene.

Further, the water-based active energy ray-curable metal coating composition according to claim 3 is the composition according to claim 1 or 2, wherein the modified polyfunctional (meth) acrylate (B) has an Sp value ( Solubility parameter) is 8.5-1.
1.0. In the present invention, “Sp value” refers to KLHoy J. Paint. Technology, 42, p.
Refers to the value calculated according to the calculation formula shown in 76 (1970).

Hereinafter, the present invention will be described in detail. (1) Polymer (a) The aqueous active energy ray-curable metal coating composition of the present invention has one or more carboxyl groups as the polymer (a) serving as the skeleton of the reactive resin (A) ( (Meth) acrylate [hereinafter referred to as “carboxyl group-containing (meth) acrylate”. Or one or more monomers other than the (meth) acrylate and having one ethylenically unsaturated group (hereinafter referred to as “ethylenically unsaturated monomers”). A polymer obtained by polymerizing at least one meth) acrylate under specific conditions is used.

The polymer (a) may be a homopolymer or a copolymer of “carboxyl group-containing (meth) acrylate”. It may be a copolymer with a "saturated monomer". Various kinds of “carboxyl group-containing (meth) acrylate” can be used,
For example, (meth) acrylic acid, crotonic acid, cinnamic acid,
Oligomers of dimer or more by Michael addition of (meth) acrylic acid, ω-carboxypolycaprolactone mono (meth) acrylate, monohydroxyethyl phthalate (meth) acrylate and monohydroxyethyl succinate (meth) acrylate. .

As the "ethylenically unsaturated monomer", various ones can be used as long as they are other than the above-mentioned (meth) acrylate containing a carboxyl group.
-Methylstyrene, (meth) acrylonitrile, vinyl acetate and (meth) acrylate. Specific examples of (meth) acrylate include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate, and cyclohexyl. Alicyclic alkyl (meth) acrylates such as (meth) acrylate, substituted aryl (meth) such as benzyl (meth) acrylate
Alkoxy (meth) acrylates such as acrylate, 2-methoxyethyl (meth) acrylate and 2-ethoxyethyl (meth) acrylate, isobornyl (meth)
Acrylates and hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate.

The copolymerization ratio between the carboxyl group-containing (meth) acrylate and the ethylenically unsaturated monomer is such that the acid value of the resulting polymer (a) is within the following range:
Any percentage is possible. When the polymer (a) having an acid value in this range can be obtained using only one or more carboxyl group-containing (meth) acrylates, the use of the ethylenically unsaturated monomer can be omitted. It is.

[0013] At least one of the ethylenically unsaturated monomers is styrene and alkylstyrene (hereinafter referred to as "styrene").
It is called "styrenic monomer". ) Is preferred. The copolymerization ratio of the styrenic monomer in the polymer (a) is preferably 40 to 85% by weight. This is because, by copolymerizing 40% by weight or more of a styrenic monomer, the glass transition temperature (Tg) of the reactive resin after curing increases, so that a tough cured film can be obtained and the cured film can be obtained. This is because the glossiness becomes better. However, the copolymerization ratio of the styrenic monomer is 8
If the amount exceeds 5% by weight, the cured film becomes too hard, and the physical properties such as bendability tend to decrease. Therefore, the upper limit of the copolymerization ratio is set to 85% by weight. Examples of the “styrenic monomer” include styrene, α-methylstyrene, α-ethylstyrene, β-methylstyrene, 3-methylstyrene,
One or two or more compounds selected from the compounds represented by the structural formula shown below, such as methylstyrene, can be used. Among them, it is particularly preferable to use styrene or α-methylstyrene.

[0014]

Embedded image (However, R ₁ , R ₂ , R ₃ , and R ₄ are each H or an alkyl group having 1 to 6 carbon atoms)

The polymer (a) used in the present invention must have an acid value of 100 to 300, preferably 15 to 300.
0 to 250. If the acid value is less than 100, a (meth) acrylate having one epoxy group described below [hereinafter referred to as “epoxy group-containing (meth) acrylate”. ], The solubility or dispersibility of the polymer (a) in the aqueous alkali solution is poor or the dissolution or dispersion requires time. Here, in order to improve the solubility of the polymer, there is a method of lowering the solid content concentration of the polymer in the aqueous solution. However, according to this method, the reactive resin aqueous dispersion (A _dp ) obtained is dried. It will be inferior. On the other hand, if the acid value is higher than 300, the viscosity of the resulting reactive resin aqueous dispersion (A _dp ) will be high.

The number average molecular weight of the polymer (a) is 1,000
It must be between 0 and 15,000, preferably between 5,0
00 to 10,000. If the polymer has a value smaller than 1,000, the resulting cured film of the reactive resin (A) has poor adhesion and adhesion to the substrate, and the cured film has insufficient strength. Not something. On the other hand, when this value exceeds 15,000, the solubility or dispersibility of the polymer (a) in an aqueous alkaline solution becomes poor in the addition reaction between the polymer (a) and the epoxy group-containing (meth) acrylate. I will. In this case, in order to improve the solubility or dispersibility of the polymer, there is a method of lowering the solid concentration of the polymer (a) in the aqueous solution or the aqueous dispersion. The dispersion (A _dp ) has poor drying properties. Further, when the solid content concentration of the polymer (a) is reduced as described above, the reactivity between the polymer (a) and the epoxy group-containing (meth) acrylate is reduced, so that the obtained reactive resin (A) The introduction ratio of the (meth) acryloyl group is reduced. Therefore, the reactive resin (A) is inferior in curability, and the cured film has reduced water resistance, solvent resistance and hardness. In the present invention, the number average molecular weight and the weight average molecular weight are values obtained by using tetrahydrofuran as a solvent and converting the molecular weight measured by GPC based on the molecular weight of polystyrene.

The polymer (a) used in the present invention comprises a carboxyl group-containing (meth) acrylate or the (meth) acrylate and an ethylenically unsaturated monomer,
The polymer is polymerized at a high temperature of 0 to 310 ° C., and preferably is polymerized continuously. According to this high-temperature continuous polymerization method, it is not necessary to use a thermal polymerization initiator, or even when a thermal polymerization initiator is used, a polymer having a target molecular weight can be obtained with a small amount of use, so that radical species can be generated by heat or light. A polymer having a high purity and containing almost no impurities that generate the following is obtained. Therefore, the addition reaction between the polymer and the epoxy group-containing (meth) acrylate, which will be described later, can be stably performed, and the finally obtained reactive resin aqueous dispersion (A _dp ) is obtained.
And excellent storage stability of a metal coating composition containing the same,
Furthermore, the cured film of this composition has excellent weather resistance.

As the high temperature continuous polymerization method, Japanese Patent Application Laid-Open No. 57-5
Nos. 02171, 59-6207 and 60-215
007 or the like may be used. For example, after filling a pressurizable reactor with a solvent and setting a predetermined temperature under pressure, a carboxyl group-containing (meth) acrylate, the (meth) acrylate and an ethylenically unsaturated monomer, or an Accordingly, there is a method in which a monomer mixture comprising a polymerization solvent is supplied to the reactor at a constant supply rate, and an amount of the reaction solution corresponding to the supply amount of the monomer mixture is withdrawn. When a polymerization solvent is used, the solvent to be charged into the reactor at the start of the reaction and the polymerization solvent to be mixed with the monomer mixture may be the same or different.

Examples of the solvent or polymerization solvent include aliphatic hydrocarbons, aromatic hydrocarbons such as toluene, xylene, cumene and ethylbenzene, cellosolves such as butyl cellosolve, glycol ethers such as carbitol, glymes such as ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. Ethers such as diglyme, ethyl acetate, butyl acetate, cellosolve acetate, etc.
Acetate esters such as methyl propylene glycol acetate, carbitol acetate and ethyl carbitol acetate, ketones such as acetone and methyl ethyl ketone, hexanol, decanol, ethylene glycol,
Aliphatic alcohols such as propylene glycol and butylene glycol, aromatic alcohols such as benzyl alcohol and toluene alcohol, and poly alcohols such as diethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol and tripropylene glycol Alkylene glycol can be used. The mixing ratio of the polymerization solvent is preferably 200 parts by weight or less based on 100 parts by weight of the monomer mixture.

Further, a thermal polymerization initiator can be added to the monomer mixture, if necessary. The thermal polymerization initiator that can be used in this case is not particularly limited, and examples thereof include an azonitrile initiator and a peroxide initiator.
Azonitrile-based initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile) and 2,2′-azobis (2,4-dimethylvaleronitrile) And the like. Examples of the peroxide-based initiator include hydrogen peroxide, di-t-butyl peroxide and benzoyl peroxide. When the thermal polymerization initiator is blended with the monomer mixture, the amount is preferably 0.001 to 5 parts by weight based on 100 parts by weight of the monomer mixture.

The reaction temperature of the high-temperature continuous polymerization in the present invention is in the range of 150 to 310 ° C. This means that if the reaction temperature is below 150 ° C., the resulting polymer (a)
When the temperature exceeds 310 ° C., on the other hand, when the reaction temperature exceeds 310 ° C., a decomposition reaction occurs, the reaction solution is colored, and the addition reaction described later is not performed. In some cases, the resulting reactive resin (A) becomes unstable. The pressure during the reaction depends on the reaction temperature and the boiling point of the monomer mixture and the solvent used and does not affect the reaction, but may be any pressure that can maintain the reaction temperature. The residence time of the monomer mixture is preferably 2 to 60 minutes. When the residence time is less than 2 minutes, the amount of unreacted monomer increases, and the yield of the polymer (a) may decrease. On the other hand, when the residence time exceeds 60 minutes, the productivity may decrease. May get worse.

(2) Reactive resin (A) The reactive resin (A) of the present invention is obtained by adding an epoxy group-containing (meth) acrylate to a carboxyl group of the polymer (a). “Epoxy group-containing (meth) acrylate” includes glycidyl (meth) acrylate, cyclohexene oxide group-containing (meth) acrylate, and bifunctional or higher epoxy resin with some epoxy groups added with (meth) acrylic acid Etc. can be used. Of these, it is particularly preferable to use glycidyl (meth) acrylate. As a result, the ratio of the (meth) acryloyl group present in the molecule of the obtained reactive resin (A) becomes high, so that the reactive resin (A) is excellent in the curability and the solvent resistance of the cured film. This is because the properties, water resistance and hardness are increased. Further, it is preferable because the reactivity of the addition reaction to the carboxyl group of the polymer (a) is excellent.

The reaction ratio of the epoxy group-containing (meth) acrylate to the carboxyl group in the polymer (a) is such that the reactive resin (A) after the addition reaction has an essential acid value or a preferable acid value described below. is there.

The acid value of the reactive resin (A) after the addition reaction is as follows:
Must be 20 to 200, preferably 50 to 15
0. When the acid value is less than 20, the dispersibility of the reactive resin (A) in the reactive resin aqueous dispersion (A _dp ) becomes insufficient, so that the reactive resin (A) aggregates,
May precipitate. When the acid value exceeds 200, the reactive resin (A) is dissolved in water. That is, it is impossible to form a reactive resin aqueous dispersion (A _dp ) in which the reactive resin (A) is dispersed in water. Since the aqueous solution in which the reactive resin (A) is dissolved has a high viscosity, the operability is inferior both at the time of producing the metal coating composition and at the time of using the composition.
When the viscosity increases due to the dissolution of the reactive resin (A), the viscosity can be reduced by reducing the solid content of the reactive resin (A) in the aqueous solution. It is not preferable because the drying property of the aqueous solution is reduced.

[0025] (3) a reactive resin water dispersion of the present invention for reactivity resin aqueous dispersion (A _dp) (A _dp) is the polymer (a)
The reactive resin (A) in which an epoxy group of an epoxy group-containing (meth) acrylate is added to a carboxyl group of the above (A) is dispersed in water. In the present invention, after dissolving or dispersing the polymer (a) in an alkaline aqueous solution,
The above addition reaction is performed in an aqueous alkaline solution.

Heretofore, as a method for converting a reactive resin to an aqueous solution, a polymer having a carboxyl group and a compound having an epoxy group and an unsaturated group are subjected to an addition reaction so that the polymer has a reactive group. After producing a reactive resin having a carboxyl group and an unsaturated group by introducing an unsaturated group, the reactive resin is neutralized with an alkali, and in some cases, an emulsifier is used to form an organic compound such as water or alcohol. It is known to suspend or emulsify in an aqueous solution containing a solvent. In this conventional aqueous method, the above-mentioned addition reaction between a polymer having a carboxyl group and a compound having an epoxy group and an unsaturated group is usually carried out in a solvent such as a hydrophilic alcohol or ketone in the presence of a catalyst such as an organic amine. Has been done using

However, in the above-mentioned conventional aqueous method, the reaction requires a long time because the reactivity of the addition reaction is not sufficient. There is also a method of increasing the use amount of a catalyst such as an organic amine in order to increase the reactivity, but in this case, since the amount of the catalyst increases, the catalyst forms a large amount of salt with a polymer having a carboxyl group, There is a problem that the obtained adduct becomes difficult to dissolve in a solvent. In addition, when the obtained reactive resin is made aqueous, it is necessary to use a solvent in which the solvent contained therein is removed by evaporation or the like, but it is difficult to completely remove the solvent from the reactive resin. Therefore, there is a problem that the product has an odor. Further, it takes a long time to completely evaporate the solvent to reduce the odor, so that the productivity is low because the reactive resin is exposed to the anaerobic state for a long time in the evaporating stage. In some cases, storage stability was deteriorated or coloring was caused.

The present invention differs from the conventional method in that the addition reaction is carried out in an alkaline aqueous solution in an organic solvent such as alcohol or ketone. By performing the above addition reaction in an alkaline aqueous solution in this manner, since the alkali component can be present in water at a high concentration, the reaction rate of the addition reaction is remarkably faster than the reaction in an organic solvent. There is an advantage. The reactive resin (A) produced by the addition reaction is obtained as an aqueous dispersion, and the aqueous dispersion of the reactive resin (A _dp ) has a low viscosity and is excellent in coatability. Furthermore, since the reactive resin (A) is obtained as an aqueous dispersion as described above, a conventional production method in which an epoxy group-containing (meth) acrylate is subjected to an addition reaction in an organic solvent, followed by removing the solvent and then dispersing in water. As compared with the above, the aqueous dispersion of the reactive resin (A _dp ) obtained by the present invention has no problems such as odor and coloring.

Various methods can be adopted as a method for obtaining the reactive resin aqueous dispersion (A _dp ) by performing the above addition reaction in an aqueous alkali solution. For example, a method of dissolving or dispersing the polymer (a) in an alkaline aqueous solution, adding an epoxy group-containing (meth) acrylate to the aqueous solution or dispersion, and heating and stirring the mixture is mentioned. The reaction temperature in this case is preferably from 60C to 100C. The carboxyl group in the polymer (a) is consumed by the addition reaction to reduce the acid value, so that the obtained reactive resin (A) is a polymer (a)
The solubility in water is lower than that of. For this reason, the polymer (a) dispersed in the aqueous alkali solution is directly dispersed in water as the reactive resin (A), and the polymer (a) dissolved in the aqueous alkaline solution is also used as the reactive resin (A). Disperse in water. Thus, the aqueous dispersion of the reactive resin (A _dp )
Is obtained.

In the alkaline aqueous solution used as the reaction medium, various types of alkalis can be used, and examples thereof include ammonia, organic amines, and inorganic bases such as sodium hydroxide. Ammonia or a low-molecular-weight organic amine is preferred because it can scatter and maintain the water resistance of the resulting coating film. Examples of the low molecular weight organic amine include trialkylamines such as trimethylamine, triethylamine, and tributylamine, N, N-dimethylethanolamine,
Hydroxyalkylamines such as N-methyldiethanolamine and triethanolamine can be used.

The concentration of the alkali component in the aqueous alkali solution is preferably such that the alkali component accounts for 30 to 70 mol% based on the total amount of carboxyl groups in the polymer.
When this ratio is less than 30 mol%, the polymer may be difficult to dissolve or disperse in an aqueous alkali solution, while when it exceeds 70 mol%, the obtained reactive resin aqueous dispersion may contain ammonia or ammonia as an alkali. Amine odor may remain. The amount of the aqueous alkali solution used in the addition reaction is
The solid concentration of the obtained reactive resin aqueous dispersion is from 10 to 60.
An amount that results in weight percent is preferred.

This addition reaction proceeds using an alkali component in an aqueous alkali solution as a catalyst, and a catalyst can be further added as necessary. Examples of the catalyst include high molecular weight tertiary amines such as N, N-dimethylbenzylamine and N, N-dimethylaniline; and quaternary ammonium salts such as tetradiethylammonium chloride, tetrabutylammonium bromide and benzyltrimethylammonium chloride. Hydrochlorides of secondary amines such as diethylammonium chloride; and phosphorus compounds such as triphenylphosphine. The preferable addition amount of these catalysts is 0.1 to 10% by weight, more preferably 0.1 to 5% by weight, based on the solid content.

In the addition reaction, it is preferable to add a polymerization inhibitor such as hydroquinone and hydroquinone monomethyl ether or to blow molecular oxygen in order to stably perform the reaction. When a polymerization inhibitor is used, the amount is preferably 10 wtppm to 2% by weight based on the reaction solution.

(4) Modified polyfunctional (meth) acrylate (B) Modified polyfunctional (meth) acrylate (B) in the present invention
Is a (meth) acrylate of a polyol to which 1 to 10 moles of an alkylene oxide is added, and has two or more (meth) acryloyl groups. here,
The reason that the number of acryloyl groups in the modified polyfunctional (meth) acrylate (B) is two or more is that the curability of the composition of the present invention is insufficient when a monofunctional alkylene oxide modified (meth) acrylate is used. This is because the resulting cured film is insufficient in solvent resistance, water resistance and hardness.

The "polyol" includes difunctional, trifunctional and tetrafunctional or higher polyfunctional polyols. Specific bifunctional polyols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, nonanediol, neopentylglycol, cyclohexanediol, cyclohexanedimethanol, bisphenol A, bisphenol F, bisphenol S and alkyl groups thereof. Substitutes and the like.
Examples of the trifunctional polyol include trimethylolpropane, trimethylolethane, glycerin, trihydroxyethyl isocyanurate (THEIC), and alkyl group-substituted products thereof. Examples of tetrafunctional or higher polyols include pentaerythritol, ditrimethylolpropane, dipentaerythritol, diglycerin, and alkyl group-substituted products thereof.

As the alkylene oxide to be added to the polyol, ethylene oxide, propylene oxide, butylene oxide and the like can be used. Among them, it is preferable to use ethylene oxide or propylene oxide. The added mole number of the alkylene oxide needs to be 1 to 10 moles, and preferably 1 to 5 moles. When the number of moles of the alkylene oxide added falls within the above range, the composition of the present invention in which the alkylene oxide is blended with the aqueous dispersion of a reactive resin (A _dp ) has good liquid stability. A smooth coating film is obtained, and the cured film becomes excellent in water resistance, solvent resistance, gloss, and the like. On the other hand, when a polyfunctional (meth) acrylate of a polyol which has not been modified with an alkylene oxide is used, the liquid stability of a composition in which this is blended with an aqueous dispersion of reactive resin (A _dp ) is low, and (A) may be aggregated or the polyfunctional (meth) acrylate may be separated. In addition, the copolymer is not efficiently copolymerized due to poor compatibility with the reactive resin (A), so that a cured film of this composition has poor adhesion to a metal substrate. On the other hand, when the added mole number of the alkylene oxide exceeds 10 moles,
The water resistance and solvent resistance of the cured product of the composition in which this is mixed with the aqueous dispersion of reactive resin (A _dp ) is reduced.
Particularly, it is not preferable because the influence on water resistance is large.

The modified polyfunctional (meth) acrylate (B) of the present invention preferably has an Sp value (solubility parameter) in the range of 8.5 to 11.0, more preferably. 9.0 to 10.0. As a result, the liquid stability of the composition and the smoothness of the coating film are improved, and the cured film is excellent in water resistance, solvent resistance, gloss, and the like.

(5) Mixing ratio of each component The composition of the present invention comprises an aqueous dispersion of a reactive resin (A _dp ) and a modified polyfunctional (meth) acrylate (B). The mixing ratio is such that the modified polyfunctional (meth) acrylate (B) is 20 to 60 parts by weight with respect to 80 to 40 parts by weight of the reactive resin (A) in the aqueous dispersion of reactive resin (A _dp ). More preferably, the modified polyfunctional (meth) acrylate (B) is used in an amount of 25 to 50 parts by weight based on 75 to 50 parts by weight of the functional resin (A). When the amount of the modified polyfunctional (meth) acrylate (B) is less than 20 parts by weight, the curability of the composition tends to be insufficient, and the cured film has good adhesion to a metal substrate, solvent resistance,
It is not preferable because water resistance and hardness become insufficient, and the gloss of the cured film also decreases. On the other hand, metamorphic polyfunctional (meta)
When the amount of the acrylate (B) is more than 50 parts by weight, the liquid stability of the composition is reduced, and the reactive resin (A) is likely to aggregate or the modified polyfunctional (meth) acrylate (B) is likely to be separated. Further, in a coating film from which water has been removed after coating on a substrate, the compatibility between the reactive resin (A) and the modified polyfunctional (meth) acrylate (B) is insufficient, and the coating film may be non-uniform. There is.

In the composition of the present invention, in addition to the above essential components, if necessary, inorganic fillers such as barium sulfate, silicon oxide, talc, clay and calcium carbonate, phthalocyanine blue, phthalocyanine green, titanium oxide And various additives such as a dye or pigment such as carbon black, a viscosity modifier, a treating agent, a UV blocking agent, an adhesion promoter and a leveling agent, and hydroquinone, hydroquinone monomethyl ether, phenothiazine and N-nitrosophenylhydroxylamine aluminum A polymerization inhibitor such as a salt may be added. When these are blended, the total amount is preferably 100 parts by weight or less based on 100 parts by weight of the solid content of the composition. When the polymerization inhibitor is compounded, the compounding ratio is preferably 10 wtppm to 2% by weight based on the solid content of the composition.

(6) Curing Method When ultraviolet rays are used as active energy rays for curing the composition of the present invention, a photopolymerization initiator is added to the composition. When an electron beam is used as the active energy ray, it is not necessary to particularly incorporate a photopolymerization initiator. Preferred examples of the photopolymerization initiator include Irgacure 2959 and Darocur 11 which are water-soluble or hydrophilic photopolymerization initiators.
73, 1116, Irgacure 184 (manufactured by Ciba Geigy Co., Ltd.), Kantacure ABQ, BTC, QTX
[Manufactured by Shell Chemical Co., Ltd.]. Further, benzoin, benzoin methyl ether, benzophenone, benzyldimethyl ketal, 2,4-dimethylthioxanthone, and the like, which are usually used in a solvent system or a non-solvent system, can also be used. If necessary, two or more photopolymerization initiators may be used in combination. The photopolymerization initiator is preferably added in an amount of 0.1 to 10% by weight based on the solid content of the composition according to the present invention. As a method for adding the photopolymerization initiator, when a photopolymerization initiator having low solubility in water is used, the photopolymerization initiator is preliminarily dissolved in the modified polyfunctional (meth) acrylate (B), and then the modified polyfunctional (meth) acrylate is used. ) It is preferably added together with the acrylate (B). When a water-soluble or hydrophilic photopolymerization initiator is used, it can be directly added to and mixed with the composition by a method such as heating and stirring.

As a method for irradiating the composition of the present invention with an active energy ray for curing, a general method known as a method for curing a radically polymerizable compound may be employed. For example, it is preferable to apply the composition to a metal substrate, remove water as a dispersion medium by a method such as heating, and then irradiate an active energy ray. This is because if moisture remains in the cured film, the strength of the cured film may be insufficient or the transparency of the film may be impaired. When ammonia or a low-molecular-weight organic amine is used as the alkali component, it is preferable that the ammonia or the low-molecular-weight organic amine be evaporated and scattered together with water during this heating in order to reduce the odor of the cured film.

(7) Method of Use Metal substrates to which the composition of the present invention can be applied include cut or coiled iron plates, hot-rolled steel plates, cold-rolled steel plates, alloy-plated steel plates, electro-galvanized steel plates, hot-dip zinc. Examples thereof include a plated steel sheet, or a sheet obtained by subjecting these to chemical conversion treatment such as chromic acid treatment or phosphoric acid treatment, an aluminum sheet, a stainless steel sheet, a tinplate and a tin-free steel sheet. Further, a pretreatment or the like may be performed on the above-described metal base material as necessary. For example, when using a substrate that has already been subjected to a chemical conversion treatment in the manufacturing process as described above, it is possible to simply use a substrate that has been subjected to a cleaning treatment, or to use a substrate that has not been subjected to a chemical conversion treatment. May be pre-processed according to the material. Further, as the steel sheet, a steel sheet having a surface coated with a primer may be used. By applying the primer to the surface of the steel sheet in this manner, the corrosion resistance of the steel sheet and the adhesion to the cured film of the coating composition can be improved. Various primers can be used, and examples thereof include an epoxy resin, a modified epoxy resin, a bisphenol resin, an epoxy acrylate, and a polyester.

As a method of applying the composition of the present invention to a metal substrate, a conventionally known method such as direct coating or printing may be used. Then, preferably after removing water, the composition can be cured by irradiating with active energy rays. When the composition is directly applied, a method such as curtain flow coating and roll coating may be used. Furthermore, according to the present invention, a low-viscosity composition can be obtained, so that direct coating by spray coating is also possible. When applying by printing,
A normal printing method such as an offset method, a gravure offset method, a gravure method, and a flexo method can be used. The composition of the present invention may be formed into a desired shape after forming a cured film on a metal substrate in advance, or may be formed on a metal substrate that has been subjected to bending or extrusion in advance. The composition of the present invention may be applied and cured.
The composition of the present invention can be used for cans such as two-piece cans or three-piece cans using the above-mentioned metal base material, or for precoated steel sheets for home appliance outer panels or tunnel interiors.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples and comparative examples are shown below,
The present invention will be described more specifically. In the following, parts and% are based on weight.

Reference Examples 1 and 2 A method for producing an aqueous dispersion of a reactive resin (A _dp ) used in Examples of the present invention will be described. (1) Production of copolymer by high-temperature continuous polymerization A 300-ml pressurized stirred tank reactor equipped with an electric heater was filled with diethylene glycol monoethyl ether, the temperature was raised to 250 ° C, and the pressure was gauged by a pressure controller. The pressure was maintained at 25-27 kg / cm ² . Then
While keeping the pressure of the reactor constant, acrylic acid (AA) as a carboxyl group-containing (meth) acrylate, styrene (St) as an ethylenically unsaturated monomer and α-methylstyrene (Reference Example 2) MSt),
And a monomer mixture having a composition and a weight ratio shown in Table 1 consisting of tertiary butyl peroxide (TBPO) as a thermal radical initiator at a constant feed rate (23 g /
Min, residence time: 14 minutes), and the reactant corresponding to the supply amount of the monomer mixture was continuously extracted from the outlet from the raw material tank. Immediately after the start of the reaction, after the reaction temperature once decreased, a rise in temperature due to the heat of polymerization was observed.
It was kept at 271 ° C.

One hour after the start of the supply of the monomer mixture having a stable temperature, the starting point for extracting a reaction solution as a raw material for the next esterification reaction was defined as a starting point. As a result of continuing the reaction for 3 hours, about 4140 g of the monomer mixture was supplied, and about 4130 g of a reaction product was recovered. Thereafter, the reaction solution is introduced into a thin film evaporator to separate volatile components such as unreacted monomers,
About 3800 g of a copolymer concentrate was obtained. As a result of analysis by gas chromatography, no unreacted monomer was present in the concentrate. For this copolymer, the number average molecular weight Mn and the weight average molecular weight Mw were determined by liquid chromatography using tetrahydrofuran as a solvent, and the polydispersity Mn / Mw was calculated from this. Further, the acid value AV of this copolymer was measured. The above results are also shown in Table 1.

[0047]

[Table 1]

(2) Production of Reactive Aqueous Resin Dispersion (A _dp ) Copolymer 50 was placed in a flask equipped with a stirrer and a condenser.
g, 25% aqueous ammonia 6.0 g and water 186 g were added, heated to 70 ° C., and stirred to dissolve the copolymer. After the copolymer was completely dissolved, 13.9 g of glycidyl methacrylate (GMA) and 32 mg of hydroquinone monomethyl ether (MQ) were charged and stirred at 75 ° C. for 2 hours to obtain about 256 g of a reactive resin aqueous dispersion. Table 2 shows the above reaction conditions. Table 2 also shows the viscosity, solid content, and acid value in terms of solid content of the obtained reactive resin aqueous dispersion.

[0049]

[Table 2]

As shown in Table 2, each of the aqueous dispersions of the reactive resin had a low viscosity, and the workability was good when preparing the composition and applying it to the metal surface in Examples described later. . Further, these reactive resin aqueous dispersions were prepared at 40 ° C. for 2 hours.
When the dispersion was left for 00 hours, no increase in viscosity or generation of aggregates or precipitates was observed in any of the dispersions, and the dispersion was excellent in liquid stability.

Examples 1-4 The modified polyfunctional (meth) acrylate (B) and photoinitiator were added to the aqueous dispersion of reactive resin (A _dp ) obtained in Reference Examples 1 and 2 at the composition ratios shown in Table 3. The agent was added and mixed by stirring for 60 minutes using a three-one motor to prepare a coating composition. At this time, each of the adjusted compositions had a low viscosity so that it could be used for spray coating. In Table 3, the “solid content ratio” refers to the solid content (that is, the reactive resin (A)) in the reactive resin aqueous dispersion (A _dp ), the modified polyfunctional (meth) acrylate (B), Means the weight ratio of The substances used are as follows. M-350: Trimethylolpropane ethylene oxide 3 mol modified triacrylate (Toagosei Co., Ltd., trade name "Aronix M-350", SP value 9.74) M-220: Tripropylene glycol diacrylate (Toagosei Co., Ltd.) , Brand name "Aronix M-2
20 ", SP value 9.13) M-310; Trimethylolpropane propylene oxide 3 mol modified triacrylate (manufactured by Toagosei Co., Ltd., trade name" Aronix M-310 ", SP value 9.2)
0) Photoinitiator DC1173; 2-hydroxy-2-methyl-1-phenyl-propan-1one (manufactured by Nippon Ciba Geigy Co., Ltd., trade name “Darocur 1173”) Photoinitiator Irg2959; 1- [4- (2- [Hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one (trade name “Irgacure 2959” manufactured by Ciba-Geigy Japan KK)

Comparative Examples 1 to 6 Except for using the compositions shown in Table 3, coating compositions were prepared in the same manner as in Examples 1 to 4. The substances used are as follows. M-400: dipentaerythritol hexaacrylate (trade name “Aronix M-
400 ", SP value 10.02) M-270; polypropylene glycol diacrylate (trade name" Aronix M-2 "manufactured by Toagosei Co., Ltd.)
70 ", SP value 8.80) M-101; phenol ethylene oxide 2 mol modified acrylate (trade name" Aronix M-101 ", manufactured by Toagosei Co., Ltd., SP value 10.21)

[0053]

[Table 3]

[Evaluation of Performance] The compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 6 and their cured films were evaluated by the following methods. Table 4 shows the results.

(1) Curable Bonderite steel plate PB-144 (manufactured by Nippon Test Panel Co., Ltd.) and aluminum plate H-4000 (manufactured by Nippon Test Panel Co., Ltd.) were used as base materials, and a bar coater # 2 was used.
Each composition was applied using No. 0 and heated in a dryer at 80 ° C. for 5 minutes to remove water from the coating film. Thereafter, the coating material was repeatedly passed under an ultraviolet lamp under the following conditions. UV irradiation conditions; Lamp: 80 W / cm condensing high-pressure mercury lamp Lamp height: 10 cm Conveyor speed: 10 m / min At this time, the curability is determined in the following three stages by the number of passes until the tack disappears from the surface of the coating film. Was evaluated. ：: Within 2 passes △: Within 3 or more and 5 passes ×: No loss of surface tack after 5 passes. Also, for a cured film which has passed under an ultraviolet lamp 5 times under the above irradiation conditions, The following evaluations (2) to (5) were performed.

(2) Adhesion The obtained cured film was cut in a grid with a width of 1 mm using a cutter knife to form 100 square sections, and a commercially available cellophane tape (manufactured by Nichiban Co., Ltd.) was pressed on the surface. After being peeled off, it was evaluated according to the following four grades based on the number of grids remaining. ：: No peeling (residual rate 100/100) Δ: Partial peeling (residual rate 1/100 to 99/10)
0) ×: The entire surface is peeled off (residual rate 0/100)

(3) Pencil hardness Measured in accordance with JIS K 5400.

(4) Water Resistance The surface condition of the cured film, which was immersed in warm water of 80 ° C. for 1 hour and dried at 60 ° C. for 2 hours, was visually observed and evaluated according to the following three grades. ：: No abnormality Δ: Slight peeling and / or whitening occurred X: Clear peeling and / or whitening occurred

(5) Solvent resistance Using a cotton swab impregnated with acetone, a load of 500
g, the surface of the cured film obtained under the condition of one reciprocation per second was rubbed, and the number of times until the surface of the cured film caused an abnormality such as whitening or peeling was evaluated in the following three grades. ○: No abnormality in cured film after 20 reciprocations △: Abnormality in cured film after 10 reciprocations and less than 20 reciprocations ×: Abnormality in cured film after less than 10 reciprocations

[0060]

[Table 4]

As can be seen from Table 4, the compositions of Examples 1 to 4 all have good curability, and the cured films have excellent adhesiveness, hardness, water resistance and solvent resistance. Performance was shown. On the other hand, Comparative Example 1 is an example in which the modified polyfunctional (meth) acrylate (B) is not used, and the curability of the composition is low, and the cured film has adhesion, hardness, water resistance and solvent resistance. Was bad. Comparative Example 2 was an example in which the amount of the modified polyfunctional (meth) acrylate (B) was small, and the effect of improving the adhesion, hardness, water resistance and solvent resistance of the cured film was insufficient. On the other hand, Comparative Example 3 is an example in which the amount of the modified polyfunctional (meth) acrylate (B) is excessively large, and the liquid stability of the composition was low and the modified polyfunctional (meth) acrylate (B) was separated. Was not able to evaluate the curability and the performance of the cured film. Comparative Examples 4 to 6 are examples in which the modified polyfunctional (meth) acrylate (B) different from the modified polyfunctional (meth) acrylate (B) of the present invention was added to the reactive resin aqueous dispersion (A _dp ). That is, Comparative Example 4 is an example using M-400, which is a polyfunctional acrylate of hexaol that is not modified by alkylene oxide, and has insufficient adhesion, so that the adhesion of the cured film to the metal substrate is insufficient. It was bad. Comparative Example 5 is an example in which a modified polyfunctional (meth) acrylate having an excessively large number of added moles of alkylene oxide of 11 mol was used, and the cured film was too high in hydrophilicity and thus poor in water resistance. In addition, the curability of the composition, the hardness of the cured film, and the solvent resistance were insufficient. Comparative Example 6 is an example in which a monofunctional modified (meth) acrylate was used. Since the crosslink density of the cured film was low, the solvent resistance and water resistance of the cured film were poor, and the curability of the composition was low. The hardness of the cured film was also insufficient.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application.

[0063]

The metal coating composition of the present invention is an aqueous composition comprising an aqueous dispersion of a reactive resin (A _dp ) and a modified polyfunctional (meth) acrylate (B), and therefore does not contain a solvent. It has a significantly lower viscosity than active energy ray-curable metal coating compositions and compositions using aqueous reactive resin solutions.
For this reason, it is excellent in workability at the time of producing the aqueous dispersion of reactive resin (A _dp ), at the time of preparing a coating composition for metal, and at the time of applying the composition. In addition, since the metal coating composition of the present invention is an active energy ray-curable type, it can form a cured film having excellent hardness, solvent resistance and water resistance. Furthermore, since the reactive resin (A) is dispersed in water in the composition, the reactive resin (A) having a relatively high molecular weight can be used without being restricted by viscosity. By using the high-molecular-weight reactive resin (A) in this way, the curing shrinkage of the coating film during irradiation with active energy rays is suppressed, so that a cured film having excellent adhesion to a metal substrate and the like can be obtained.

Claims (3)

[Claims] (1) one or more (meth) acrylates having one or more carboxyl groups, or one or more monomers other than the (meth) acrylate but having one ethylenically unsaturated group; One or more meth) acrylates are polymerized at a polymerization temperature of 150 to 310 ° C to form a number average molecular weight of 1,000 to 15,000 and an acid value of 10
After obtaining the polymer (a) of 0 to 300 mgKOH / g, and then dissolving or dispersing the polymer (a) in an alkaline aqueous solution, the (meth) acrylate having one epoxy group is subjected to the above-mentioned method in the alkaline aqueous solution. An acid value of 20 to 200 m, obtained by an addition reaction to the polymer (a)
gKOH / g of a reactive resin (A) dispersed in water, a reactive resin aqueous dispersion (A _dp ), and a polyol having two or more (meth) acryloyl groups and adding 1 to 10 mol of an alkylene oxide And a polyfunctional (meth) acrylate (B), which is an alkylene oxide-modified polyol that is a (meth) acrylate of the above, wherein the alkylene oxide-modified is based on 80 to 40 parts by weight of the reactive resin (A). An aqueous active energy ray-curable metal coating composition comprising 20 to 60 parts by weight of a polyol polyfunctional (meth) acrylate (B). 2. The aqueous active energy ray-curable metal coating composition according to claim 1, wherein at least one kind of the monomer having one ethylenically unsaturated group is styrene or alkylstyrene. 3. The aqueous active energy ray-curable metal coating composition according to claim 1, wherein the solubility parameter of the alkylene oxide-modified polyol polyfunctional (meth) acrylate (B) is 8.5 to 11.0. Stuff.