JP2006299139A - Method for producing acrylic copolymer for water-borne coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic copolymer suitable as a water-borne coating composition forming a coated film having high processing resistance and excellent retort resistance, scuff resistance and gloss and useful for an outer surface film of a metal can and a polyester film-coated drawn can and to provide an excellent water-borne coating composition. <P>SOLUTION: A method for producing the acrylic copolymer (b) for the water-borne coating composition is carried out as follows. Ether exchange of 20-80 wt.% of an alkoxy moieties in N-alkoxymethyl(meth)acrylamide moieties composing the acrylic copolymer with an ethylene glycol monoalkyl ether, etc., used during polymerization is conducted at a specific temperature under a specified pressure. Thereby, alkoxy moieties of a plurality of alcohols having different boiling points are obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for producing an acrylic copolymer for an aqueous coating composition, and more specifically, an acrylic copolymer that can constitute an aqueous coating composition that is most suitable for the outer surface coating of metal cans and polyester film coated drawn cans. The present invention relates to a method for manufacturing coalescence. More specifically, the present invention relates to a method for producing an acrylic copolymer suitable for an aqueous coating composition capable of forming a coating film excellent in high processability, retort resistance, scratch resistance, transparency (yellowness) and gloss. is there. In addition, the present invention relates to an acrylic copolymer obtained by the above production method and an aqueous coating composition containing the copolymer.

The outer surface of beverage cans that contain soft drinks and food cans that contain foods (hereinafter referred to as beverage cans, etc. together) prevents corrosion of the can material, enhances aesthetic product value, and sterilizes the contents. There has been a need for a coating film that can withstand the hot water (retort) treatment process during treatment.
In recent years, various forms of beverage cans have emerged. For example, a can that has a diamond-cut shape on the can body for the purpose of imparting design characteristics, and a can or logo that gives the image of stripes by beading in the vertical, horizontal, diagonal, etc. Due to the emergence of cans embossed and so on, paints for coating cans require more workability than ever. Furthermore, in order to counter the widespread use of PET bottles, the cans that can be opened and closed with caps are required to have higher workability than ever for the threaded portion.

  The transport speed of beverage cans has been increasing in recent years. As the conveying speed increases, the coating film on the outer surface of the beverage can becomes easily damaged, and troubles that impair the appearance design are frequently generated. Although there is a method of increasing the thickness of the coating film as one means for making the coating film hard to be damaged, if the coating film is thickened, the workability is lowered.

  In recent years, beverage cans have emerged in which gravure-printed films are pasted on cans. The outer surface of a beverage can with a film affixed to the can is generally more glossy than conventional beverage cans that apply ink and finish varnish to the can body. Therefore, it has been demanded that the outer surface of the beverage can of the type in which the ink and the finish varnish are applied to the can body portion is more excellent in gloss and transparency than the conventional beverage can of the same type.

  In addition, when used in 2-piece cans (cans consisting of two parts, a bottomed cylindrical member with a can body and a bottom part integrally formed with a can lid), this metal material, or polyester film material, or An oil-based ink is printed on a base coat of various sizes (white, clear, silver, etc.), and a finish varnish clear is applied on the ink with a wet-on-wet and dried. In this case, in order to improve the ink wet suitability, a means for increasing the ink wet suitability by introducing a long-chain alkyl group such as a lauryl group or a hexyl group into the acrylic resin or the like of the finished varnish paint is common. However, in this method, there is also a problem that a bad odor is adsorbed on the finished varnish coating film in a can distribution process or the like due to the presence of a long-chain alkyl group (low Tg).

For example, Patent Document 1 proposes an aqueous coating composition containing an acrylic copolymer obtained by copolymerizing N-alkoxymethylacrylamide for the purpose of improving processability. However, in the case of the invention described in Patent Document 1, after obtaining an acrylic copolymer and then cooling to 80 ° C., the organic solvent used during the polymerization is distilled off under reduced pressure. At such a low temperature, ether exchange between the alkoxy group part of the N-alkoxymethyl acrylamide part constituting the acrylic copolymer and the organic solvent used in the polymerization hardly proceeds. As a result, most of the alkoxy group part of the N-alkoxymethyl acrylamide part constituting the acrylic copolymer remains as the alkoxy group part derived from the N-alkoxymethyl acrylate used for the copolymerization.
The coating material using such an acrylic copolymer is formed because the detachment of the alkoxy group portion of the N-alkoxymethyl acrylamide portion and the subsequent curing reaction occur simultaneously when the coating film is baked and cured. The coating film has a large curing strain. A coating film having a large curing strain has not been able to sufficiently meet the severe demands on processability in recent years.

After obtaining the acrylic copolymer, the ether exchange between the alkoxy group portion of the N-alkoxymethyl acrylamide portion constituting the acrylic copolymer and the organic solvent used in the polymerization is simply performed at a high temperature without reducing the pressure. There is also a way to make it progress.
However, in this method, the nitrogen atom in the acrylic amide portion is colored to increase the yellowness of the polymer, and it is not possible to provide a coating film having high transparency and excellent gloss.

There is also a method in which the average molecular weight of the acrylic copolymer is increased to improve processability. As a means for increasing the molecular weight, there are a method of reducing a reaction initiator such as a peroxide and a method of lowering the reaction temperature. This method simply increases the number average molecular weight Mn, leading to an increase in resin viscosity, causing problems in paintability, and it is difficult to achieve both workability and paintability.
Japanese Patent Laid-Open No. 05-320564 JP-A-11-106700

  The present invention has been made in view of the above situation, and can form a coating film excellent in workability, retort resistance, scratch resistance, and gloss, and can be coated on the outer surface of a metal can and a polyester film film drawn can. It is an object of the present invention to provide an acrylic copolymer suitable for a water-based paint composition for use, and to provide an excellent water-based paint composition.

As a result of intensive studies in view of the above-mentioned present situation, the present inventors have determined that the alkoxy moieties of the N-alkoxymethyl (meth) acrylamide portion constituting the acrylic copolymer contained in the paint have different boiling points. The present invention has been completed by using the alkoxy moiety of the alcohol as described above and having a specific molecular weight distribution.
That is, the present invention relates to N-alkoxymethyl (meth) acrylamide (1): 15 to 55 in ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher and / or propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher. % By weight, α, β-monoethylenically unsaturated carboxylic acid (2): 3 to 15% by weight, and (meth) acrylates and / or vinyl monomers (3) copolymerizable with the above (1) and (2) ): 40 to 80% by weight is copolymerized (provided that the total of (1) to (3) is 100% by weight), weight average molecular weight (Mw) 7000 to 12000, weight average molecular weight (Mw) / number average Obtaining a copolymer (a) having a molecular weight (Mn) of 2 to 2.5,
Next, under reduced pressure, the copolymer (a) is heated at a temperature 40 ° C. or more higher than the boiling point of the alkyl alcohol leaving the N-alkoxymethyl group constituting the copolymer (a) and at 100 ° C. or higher. 20 to 80% by weight of the N-alkoxy moiety constituting a) is subjected to an ether exchange reaction with the ethylene glycol monoalkyl ether and / or the propylene glycol monoalkyl ether, and N-alkoxymethyl (meth) acrylamide ( 1) Acrylic for water-based paint composition having a weight average molecular weight (Mw) of 15,000 to 25000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 3 to 5, characterized by distilling off the derived alkyl alcohol The present invention relates to a method for producing a copolymer (b).

  Moreover, this invention relates to the water-based coating composition acrylic copolymer (b) obtained by the said manufacturing method.

Furthermore, the present invention provides at least one selected from the group consisting of an amino resin, a compound having an isocyanate group, and a compound having a blocked isocyanate group, and the acrylic copolymer for water-based paint composition (b). A water-based paint characterized by containing
The present invention is also characterized in that the amino resin is a benzoguanamine resin partially etherified with alcohol, and is an amino resin having 0.5 to 2.0 imino groups per benzoguanamine nucleus. The present invention relates to the aqueous coating composition described in the invention.

  Furthermore, the present invention also relates to an article to be coated, which is obtained by applying the aqueous coating composition described in the above invention to a metal can or a polyester film-coated drawn can and heating and curing at 200 ° C. or higher.

  The aqueous coating composition using the acrylic copolymer obtained by the production method of the present invention is less susceptible to curing strain when baked at high temperature, and has excellent workability by having a specific molecular weight distribution. It is a coating film excellent in processability, retort resistance, and scratch resistance suitable for the outer surface coating of metal cans and polyester film coating drawn cans, and can provide a coating film with good gloss.

Hereinafter, the present invention will be described in detail.
In the production method of the present invention, after obtaining the acrylic copolymer (a), a part of the N-alkoxymethyl (meth) acrylamide portion constituting the acrylic copolymer (a) was used during the polymerization. An ether exchange reaction with ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher and propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher to obtain an acrylic copolymer (b) having a specific molecular weight distribution. In other words.
The N-alkoxymethyl (meth) acrylamide (1) used in obtaining the acrylic copolymer (a) before the ether exchange is obtained by reacting (meth) acrylamide with formalin to form N-methylol ( A (meth) acrylic amide is obtained, and this N-methylol (meth) acrylic amide is reacted with an alcohol. Specific examples include N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide and the like. It is important to use 15 to 55% by weight of these monomers (1) based on the total amount of the copolymer (a) when obtaining the acrylic copolymer (a), and 20 to 45% by weight is used. Things are preferable. If it is less than 15% by weight, the retort resistance and hardness of the coating film are reduced, and if it exceeds 55% by weight, not only gelation is likely to occur during the reaction, but even if a copolymer is obtained without gelation, the copolymer is obtained. When a polymer is used, the processability of the coating film decreases.

  The α, β-monoethylenically unsaturated carboxylic acid (2) used for obtaining the acrylic copolymer (a) before ether exchange includes acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid In particular, acrylic acid and methacrylic acid are preferable. It is important that the α, β-ethylenically unsaturated carboxylic acid (2) is used in an amount of 3 to 15% by weight based on the total amount of the copolymer (a) when obtaining the acrylic copolymer (a). It is preferable to use ˜7% by weight. If it is less than 3% by weight, it is difficult to make the acrylic copolymer (a) water-based, and if it exceeds 15% by weight, the water resistance of the coating film becomes poor.

The (meth) acrylate monomer and / or vinyl monomer copolymerizable with the above (1) and (2) used for obtaining the acrylic copolymer (a) before ether exchange are the above (1), ( 2) Any monomer that can be copolymerized with the monomer, and (meth) acrylate monomers include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Alkyl (meth) acrylates such as n-hexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, caprolactone modified acrylate (Daicel Chemical Industries ( Product name "Placcel FA-1," Lacceric FA-3 ") hydroxyl group-containing monomers, and the like.
As the latter, aromatic vinyl monomers such as styrene and vinyltoluene, and vinyl carboxylate monomers such as vinyl acetate can be used.

The acrylic copolymer (a) can be obtained by ordinary solution polymerization in an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher or a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher.
Examples of the polymerization initiator used for obtaining the acrylic copolymer (a) include peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, and t-butylperoxybenzoate, or 2 An azo compound such as 2-azobisisobutylnitrile is used, and radical polymerization of (1) to (3) is performed using this azo compound.
Solid content at the time of polymerization, that is, the ratio of the solvent medium such as ethylene glycol monoalkyl ether and the monomer, monomer / (monomer + solution medium such as ethylene glycol monoalkyl ether) × 100 is 40 to 55% by weight. It is preferable.

The organic solvent used when synthesizing the acrylic copolymer (a) is an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher and a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher. You can also use both.
The ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher is one in which one end of ethylene glycol or ethylene glycol condensate is a hydroxyl group and the other is etherified with an alkyl group. A propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher is a propylene glycol or a propylene glycol condensate having one end of a hydroxyl group and the other etherified with an alkyl group. From the viewpoint of making the acrylic copolymer (b) after ether exchange aqueous, that is, dissolving or dispersing in an aqueous medium, as a solvent for these polymerizations, which is also a raw material for ether exchange, an ethylene glycol type having a boiling point of 120 ° C. or higher Monoalkyl ethers are preferred. The boiling point is more preferably 140 to 230 ° C.

Examples of the ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher include ethylene glycol monomethyl ether (boiling point 124 ° C., the same applies hereinafter), ethylene glycol monoethyl ether (135 ° C.), ethylene glycol monoisopropyl ether (144 ° C.), ethylene Examples include glycol monobutyl ether (171 ° C.), ethylene glycol monoisobutyl ether (160 ° C.), diethylene glycol monomethyl ether (194 ° C.), diethylene glycol monoethyl ether (202 ° C.), and diethylene glycol monobutyl ether (230 ° C.).
Examples of the propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher include propylene glycol monomethyl ether (121 ° C.), propylene glycol monoethyl ether (133 ° C.), propylene glycol monobutyl ether (170 ° C.) and the like.

The acrylic copolymer (a) thus obtained is important to have a weight average molecular weight Mw of 7000 to 12000, a number average molecular weight of Mn of 3000 to 7000, and Mw / Mn = 2 to 2.5. When Mn> 2.5, the acrylic copolymer (b) after the ether exchange has Mw / Mn> 5 and high viscosity, resulting in poor paintability when the aqueous coating composition is formed. When Mw / Mn <2, the acrylic copolymer (b) in the range of Mw / Mn = 3 to 5 cannot be obtained, and the desired high workability cannot be obtained.
The acid value is preferably 10 to 150 (mg KOH / g), the hydroxyl value is 0 to 150 (mg KOH / g), and the glass transition temperature is preferably 0 to 80 ° C., the acid value is 30 to 70 (mg KOH / g), the hydroxyl value is 0 to 80 ° C. It is more preferable that they are 60 (mgKOH / g) and glass transition temperature 20-60 degreeC.

Next, the acrylic copolymer (b) and the ether exchange reaction for obtaining it will be described.
As described above, the acrylic copolymer (b) is an ethylene glycol having a boiling point of 120 ° C. or higher in which a part of the N-alkoxymethyl (meth) acrylamide part constituting the acrylic copolymer (a) is used during the polymerization. It is obtained by ether exchange reaction with a monoalkyl ether or a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher.
The ether exchange reaction is carried out under reduced pressure, preferably 200 to 60 mmHg, and the boiling point of the alkyl alcohol desorbed from the N-alkoxymethyl group constituting the copolymer (a) is 40. It is performed at a temperature higher than 100 ° C. and 100 ° C. or higher. Preferably it carries out at 110-130 degreeC.
That is, 20 to 80% by weight of the N-alkoxy moiety constituting the copolymer (a) under the above conditions is an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher or a propylene glycol monoalkyl having a boiling point of 120 ° C. or higher. The acrylic copolymer (b) having a specific molecular weight distribution can be obtained by distilling off the alkyl alcohol derived from the N-alkoxymethyl (meth) acrylamide (1) until the ether is exchanged with ether. . The ether exchange rate of the alkoxy group moiety derived from N-alkoxymethyl (meth) acrylamide (1) is preferably 30 to 60% by weight. The ether exchange rate can be determined from ¹ H-NMR data.
When ether exchange is performed at a temperature lower than 100 ° C., ether exchange of the resulting copolymer (b) occurs, but condensation of amides does not occur, and the intended molecular weight distribution cannot be obtained.

  For example, when N-alkoxymethyl (meth) acrylamide (1) constituting the acrylic copolymer (a) is N-butoxymethyl acrylate, the alkyl alcohol derived from the N-butoxy group and distilled off is Since it is butanol and has a boiling point of 84.3 ° C. at 200 mmHg, it is carried out at 130 ° C. above + 40 ° C.

The acrylic polymer (b) thus obtained is important to have a weight average molecular weight Mw of 15000 to 25000 and Mw / Mn = 3 to 5, and a weight average molecular weight of Mw 15000 to 22000 and Mw / Mn = 3. It is more preferable that the average molecular weight Mn is 4000 to 6000. When Mw / Mn <3 or less, high workability that can withstand the threaded portion processing of cap opening and closing type cans is not achieved, and when Mw / Mn> 5, the viscosity becomes high and the paint is made into an aqueous coating composition. Cause sexual defects.
The acid value is preferably 10 to 150 (mg KOH / g), the hydroxyl value is 0 to 150 (mg KOH / g), and the glass transition temperature is preferably 0 to 80 ° C., the acid value is 30 to 70 (mg KOH / g), the hydroxyl value is 0 to 80 ° C. It is more preferable that they are 60 (mgKOH / g) and glass transition temperature 20-60 degreeC.

When the coating containing the acrylic copolymer having an N-alkoxymethyl group is cured, (a) first, an alkyl alcohol is eliminated from the N-alkoxymethyl group to produce a methylol group, and (i) the methylol. The groups react with each other, or the methylol group reacts with an amino resin or the like described later to form a cured coating film.
In the step (a), the easier the alkyl alcohol is eliminated, that is, the lower the boiling point of the alkyl alcohol to be eliminated is, the faster the methylol group is generated, and the faster the curing is. However, although the curing reaction proceeds rapidly if alkyl alcohol that is too easily desorbed at once, there is no time to alleviate the shrinkage associated with curing, and the formed coating film has a large curing strain. .
On the other hand, the more difficult the alkyl alcohol is eliminated, that is, the higher the boiling point of the alkyl alcohol, the slower the production of methylol groups, and the longer the reaction of the step (a).

As described above, the N-alkoxymethyl part in the acrylic copolymer (b) includes a part derived from the N-alkoxymethyl (meth) acrylamide (1), an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher, N-alkoxymethyl moieties ether-exchanged with a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher are mixed. Alkyl alcohol is relatively easily detached from the N-alkoxymethyl moiety derived from N-alkoxymethyl (meth) acrylamide (1). On the other hand, from the N-alkoxymethyl moiety ether-exchanged with an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher or a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher, the ethylene glycol monoalkyl ether or propylene glycol monoalkyl Ether is relatively difficult to desorb.
A coating composition containing an acrylic copolymer (b) having a functional group that has different easiness of elimination of alcohol, that is, different easiness of generation of a methylol group, can be rapidly produced while suppressing the occurrence of curing strain. Can be cured.

Furthermore, the N-alkoxymethyl moiety ether-exchanged with an ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher and a propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher is derived from N-alkoxymethyl (meth) acrylamide (1). It is richer in lipophilicity than the N-alkoxymethyl moiety. Accordingly, the coating composition containing the acrylic copolymer (b) is improved in wet suitability with the ink, resulting in excellent gloss, compared with the acrylic copolymer (a) not subjected to ether exchange. Coating film can be provided.
Moreover, ethylene glycol monoalkyl ethers with a boiling point of 120 ° C. or higher and propylene glycol monoalkyl ethers with a boiling point of 120 ° C. or higher, which contributed to improving the affinity with ink, are desorbed during baking and do not remain on the coating after curing. Excellent off-flavor adsorption.

Add volatile base such as ammonia or organic amine to water and water after adding volatile base such as ammonia or organic amine to the obtained acrylic copolymer (b) solution. By neutralizing all or part of the carboxylic acid in the blend (b), the acrylic copolymer (b) can be dissolved or dispersed in the aqueous medium.
The volatile base preferably has a boiling point of 400 ° C. or lower, and examples of the organic amine include monoethanolamine, dimethylamine, diethylamine, triethylamine, triethanolamine, diethylethanolamine, dimethylethanolamine and the like.

  Next, the amino resin that can be used in combination with the acrylic copolymer (b) will be described. As the amino resin, it is formed by adding formaldehyde to methylol to a part or all of amino groups such as benzoguanamine, melamine, spiroguanamine, acetoguanamine, phthaloguanamine, etc., and then condensing the imino group, methylol group, or An alkoxy group obtained by etherifying a part or all of a methylol group with an alcohol, and also having these groups. As the amino resin, a benzoguanamine resin is preferable.

The benzoguanamine resin is obtained by condensing a methylol compound obtained by adding formaldehyde to an amino group in benzoguanamine, or by etherifying a part or all of the methylolated product with an alcohol or an alcohol solvent.
Specific examples include methyl etherified benzoguanamine and butyl etherified benzoguanamine.

In the present invention, it is preferable to have 0.5 to 2.0 imino groups per benzoguanamine nucleus.
When the number of imino groups is 2.0 or more, the temporal stability of the paint is poor, and when it is 0.5 or less, the curing reactivity is inferior. The imino group is usually ═NH and not a ring skeleton, but the imino group referred to here is two —NH ₂ —NH groups existing in the benzoguanamine skeleton, which are usually used in the amino resin industry. In the field, the —NH ₂ moiety is added with formaldehyde to form a methylol group, and then etherified with alcohol (ROH), and the —NH portion of the nitrogen-containing group having a structure of —NH—CH ₂ —O—R is called an imino group. . And, the industry dealing with amino resin, -NH ₂ (amino group) of formaldehyde unmodified portion also 2.0 or count imino group. Therefore, the functional group of benzoguanamine before formaldehyde modification is counted as 4.0 imino groups.

  Alcohols used for etherifying methylol groups include, in addition to methanol and butanol, alkyl alcohols such as n-propyl alcohol, isopropyl alcohol, ethanol, isobutyl alcohol, s-butyl alcohol, t-butyl alcohol, and alcohols. Examples of the solvent include cellosolves such as butyl cellosolve, hexyl cellosolve, butyl carbitol, 3-methyl-3-methoxybutanol, 3-methoxybutanol, ethylene glycol monoisopropyl ether, and methylpropylene glycol. It doesn't matter.

  The aqueous coating composition of the present invention comprises 40 to 70% by weight of the acrylic copolymer (b) and 100% by weight of the amino resin in a total of 100% by weight of the acrylic copolymer (b) and the amino resin (benzoguanamine resin). It is preferable to contain 30 to 60 weight%.

The acrylic copolymer (b) can be used in combination with a compound having an isocyanate group in addition to the amino resin.
As the compound having an isocyanate group, various known polyisocyanates which are aromatic, aliphatic or alicyclic can be used. For example, 1,5-naphthylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethane diisocyanate, 4,4′-dibenzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3- Phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4- Diisocyanate, xylylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, disi B hexyl methane over 4,4'-diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, methylcyclohexane diisocyanate, norbornane diisocyanate, m- tetramethylxylylene diisocyanate iso eye sulfonates, and the like. Furthermore, an isocyanate compound formed by blocking the above compound having an isocyanate group with a blocking agent such as active methylene, MEK oxime, or ε-caprolactam can be used in combination with the acrylic copolymer (b).

In the aqueous coating composition of the present invention, an acid catalyst, or an amine block thereof, for example, p-toluenesulfonic acid, dodisylbenzenesulfonic acid, dinolylnaphthalenesulfonic acid, etc. 0.05-4 parts by weight of the amine block can be added to 100 parts by weight in total of the acrylic copolymer (b) and amino resin.
Further, if necessary, a conventionally known leveling agent, slip agent, antifoaming agent, WAX and other lubricants may be added. Further, a pigment such as titanium oxide, aluminum pigment, quinacridone and the acrylic copolymer (b) are kneaded with a known disperser such as a sand mill or a disper, and can be made into a paint by the same method as described above.

  In the aqueous coating composition of the present invention, a commonly used water-soluble resin or water-dispersed resin such as polyester resin, polyether polyol resin, polyester polyol resin, maleated fatty acid, ethylene oxide or propylene oxide of bisphenol A is added. It is also possible to add an epoxy resin in which an amine or phosphoric acid is added to the glycidyl group of the product resin or epoxy resin and the terminal is converted to a phosphate ester.

The aqueous coating composition of the present invention can be applied to various substrates by known means such as roll coating, spraying, and brush coating.
For example, the aqueous coating composition of the present invention is applied to an electroplated tin steel plate, an aluminum steel plate, a stainless steel plate, or a laminated steel plate obtained by laminating a polyester film such as polyethylene terephthalate or polybutylene terephthalate on these metal plates, heated and cured. A painted product can be obtained. In particular, the aqueous coating composition of the present invention is most suitable for coating and coating the outer surface of metal cans for beverages and polyester film coated cans.

  Hereinafter, the present invention will be described by way of examples. In the examples, “parts” represents parts by weight, and “%” represents percent by weight.

Example 1 (Production of acrylic copolymer b1 solution)
A four-necked flask equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas blowing tube was charged with 100 parts of the reaction solvent ethylene glycol monoisopropyl ether, and the temperature was maintained at 105 ° C. while stirring while introducing nitrogen gas. What melt | dissolved 5 parts of benzoyl peroxide in the mixture of the following monomer from the tank was dripped over 3 hours.
・ Nn-butoxymethyl acrylic amide 30 parts
・ Acrylic acid 5 parts
・ Styrene 20 parts
・ Methyl methacrylate 15 parts
-Ethyl acrylate 30 parts Then, it kept at 105 degreeC, it reacted for 1 hour, 1 part of benzoyl peroxide was added, and it was made to react for 1 hour further, and the acrylic copolymer a1 solution of Mn: 4400 and Mw10500 was obtained.
The resulting acrylic copolymer a1 solution was distilled at 130 ° C. under a reduced pressure of 200 mmHg to remove butanol and ethylene glycol monoisopropyl ether to a non-volatile content of 70% (solvent removal), and the butoxy group of N-butoxymethylacrylamide. And ethylene glycol monoisopropyl ether are subjected to ether exchange and condensation reaction between amides to obtain an acrylic copolymer of Mn4700, Mw19200, Mw / Mn = 4.08, and then cooled to 80 ° C. or lower to dimethyl 5.2 parts of ethanolamine and water were added to obtain an aqueous solution of aqueous acrylic copolymer b1 having a solid content of 50%.
Table 1 shows the results of calculating the ether exchange rate of the weight average molecular weight Mw, the number average molecular weight Mn, and the butoxy moiety of Nn-butoxymethylacrylamide with ethylene glycol monoisopropyl ether by GPC.

Examples 2 to 8 and Comparative Examples 1 to 3 (Production of aqueous solution of acrylic copolymer b2 to 11)
Polymerization and ether exchange were similarly carried out according to the monomer composition and reaction conditions shown in Table 1 according to Example 1, and aqueous solutions of aqueous acrylic copolymers b2 to 11 having a solid content of 50% were obtained.
Table 1 shows the result of NMR calculation of the ether exchange rate between the alkoxy moiety derived from N-alkoxymethyl acrylamide and the solvent during polymerization. The reaction solvent IPC in Table 1 is an abbreviation for ethylene glycol monoisopropyl ether.

Production Example 1 (Production of benzoguanamine resin c1)
A four-necked flask equipped with a thermometer, a stirrer, a reflux cooling device, a dropping tank, and a nitrogen gas blowing tube was charged with 187 parts of benzoguanamine, 281 parts of 80% paraformaldehyde, and 320 parts of methanol, and 0.5% of 25% sodium hydroxide solution. After adding 7 parts, it heated at 60 degreeC for 3 hours. Thereafter, a 60% nitric acid solution was charged until the solution became pH 3.5, and the reaction was continued for 4 hours. After completion of the reaction, the reaction mixture was neutralized with 25% sodium hydroxide solution, and methanol water was removed under reduced pressure at 70 ° C. or lower, followed by filtration under reduced pressure, added with ethylene glycol monoisopropyl ether, and benzoguanamine resin having a solid content of 75%. The c1 solution was prepared. Table 2 shows the results of NMR calculation of the number of imino groups and methylol groups per benzoguanamine nucleus.
The imino group was counted according to the definition in the 31st paragraph.

Production Examples 2 and 3 (Production of benzoguanamine resins c2 and c3)
According to Production Example 1, the reaction was carried out in the amounts of benzoguanamine, paraformaldehyde and methanol shown in Table 2 to obtain benzoguanamine resins c2 and c3. Table 2 shows the results of NMR calculation of the number of imino groups and methylol groups per benzoguanamine nucleus. The imino group here shows the result counted by the method described in the 31st paragraph.

Example 10
60 parts by weight (solid content) of the acrylic copolymer (b1) obtained in Example 1, 40 parts by weight (solid content) of the benzoguanamine resin (c1) obtained in Production Example 1, and p-toluenesulfonic acid amine as an acid catalyst 0.2 parts by weight of a salt and 0.3 parts by weight of a silicone leveling agent are mixed, and ethylene glycol monoisopropyl ether and ion-exchanged water are added to and mixed with this to make a non-volatile content of 40% and an organic solvent amount of 20%. An aqueous coating composition was obtained.

Examples 11-19, Comparative Examples 4-6
According to the formulation (parts by weight) shown in Table 3, Examples 11 to 19 and Comparative Examples 4 to 6 were obtained according to Example 10 for each component.

Table 3 shows the results of examining the stability of the water-based paint composition and the physical properties of the coating film prepared in Examples and Comparative Examples.
Each test method is as follows.

[Film performance test]
An aluminum can body for a two-piece can is opened and flattened, and ink (2 μm) containing oil-modified polyester resin as the main component of the vehicle is printed, and the above-mentioned water-based paint composition is left in an undried state. An object was coated (film thickness after baking: 4 to 5 μm) and baked in a gas oven at an ambient temperature of 220 ° C. for 1 minute was evaluated as a test coating plate.

<Retort resistance test>
After the retort process (pressurized steam process at 130 ° C. for 30 minutes) was performed on the coated plate, the whitening state of the coating film was visually evaluated.
Evaluation (whitening area): 0% (◎), 0 to less than 2% (◯), 2 or more to less than 10% (△, rejected), 10% or more (×, rejected)

<High processing adhesion test>
The coated plate is punched into a cap shape with a diameter of 25 mm and a height of 10 mm, and a cellophane tape is adhered to the coating film on the body of the cap before and after the retort treatment (pressure steam treatment at 130 ° C. for 30 minutes). The tape was peeled off, and the peeled area of the coating film was visually evaluated.
Evaluation (peeling area): 0% (◎), 0 to less than 1% (◯), 1 to less than 5% (△, rejected), 5% or more (x, rejected)

<Hardness in hot water>
The coated plate was immersed in 80 ° C. hot water for 30 minutes, and then the pencil hardness was measured in 80 ° C. hot water.
Evaluation: F or more (◎), HB (◯), B (△, rejected), 2B or less (×, rejected)

<Scratch resistance>
130 ° C-30 minutes retorted coated plate using Tritogear HEIDON-22H type made by Shinto Kagaku Co., Ltd., sliding on the coating film while changing the load applied to the sapphire needle, the largest without scratches The load was determined.
Measurement conditions: Continuous load method Scratching speed: 300 mm / min Scratching needle: Sapphire 100 μm
Measurement temperature: 25 ° C
Evaluation (g): 300 g or more (◎), 250 g or more to less than 300 g (◯), 200 g or more to less than 250 g (Δ, fail), less than 200 g (x, fail)

<Glossy>
The gloss of the test plate was measured with a gloss meter Σ-80, VG-1D (manufactured by JEOL Ltd.) under conditions of a light source incident angle of 60 °, and after retorting at 130 ° C. for 30 minutes.
Evaluation: 90 or more (◎), less than 90 to 85 or more (◯), less than 85 to 80 or more (Δ, reject), less than 80 (×, fail)

Claims (5)

In ethylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher and / or propylene glycol monoalkyl ether having a boiling point of 120 ° C. or higher, N-alkoxymethyl (meth) acrylamide (1): 15 to 55% by weight, α, β -Monoethylenically unsaturated carboxylic acid (2): 3 to 15% by weight, and (meth) acrylates and / or vinyl monomer (3) copolymerizable with the above (1) and (2): 40 to 80% by weight % (Where the total of (1) to (3) is 100% by weight), weight average molecular weight (Mw) 7000 to 12000, weight average molecular weight (Mw) / number average molecular weight (Mn) = 2 -2.5 copolymer (a) is obtained,
Subsequently, under reduced pressure, at a temperature 40 ° C. or higher than the boiling point of the alkyl alcohol desorbed from the N-alkoxymethyl group constituting the copolymer (a) under the reduced pressure, and at 100 ° C. or higher,
20 to 80% by weight of the N-alkoxy moiety constituting the copolymer (a) is subjected to an ether exchange reaction with the ethylene glycol monoalkyl ether and / or the propylene glycol monoalkyl ether, and N-alkoxymethyl ( An aqueous solution having a weight average molecular weight (Mw) of 15,000 to 25000 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 3 to 5, characterized by distilling off the alkyl alcohol derived from (meth) acrylamide (1) A method for producing an acrylic copolymer (b) for a coating composition. The acrylic copolymer (b) for water-based coating compositions obtained by the manufacturing method of Claim 1. An acrylic resin (b) for an aqueous coating composition according to claim 2, comprising at least one selected from the group consisting of an amino resin, a compound having an isocyanate group and a compound having a blocked isocyanate group A water-based coating composition characterized by comprising: 4. The aqueous resin according to claim 3, wherein the amino resin is a benzoguanamine resin partially etherified with alcohol and has 0.5 to 2.0 imino groups per benzoguanamine nucleus. Paint composition. An article to be coated, which is obtained by applying the water-based coating composition according to claim 3 or 4 to a metal can or a polyester film coated drawn can and heating and curing at 200 ° C or higher.