JP5170726B2 - Water-based paint composition for outer surface of can lid and can lid - Google Patents

Description

The present invention relates to a water-based coating composition for can lid outer surfaces and tabs that require severe processability.

Conventionally, metals such as aluminum, tin, and tin-free steel are used as the metal can material. For these metals, a coating film is usually formed on the outer surface of the can, can lid, and tab for formability, designability, and surface protection. An epoxy / urea-based paint is usually used as a paint for can outer surfaces because it is excellent in adhesion and moldability.

However, since the paint as described above contains an organic solvent, it has a risk of air pollution, deterioration of working environment and fire and explosion, and epoxy resin is used as a means to avoid these problems. Various methods have been proposed in which a so-called self-emulsifiable epoxy resin in which a segment having emulsifying power is introduced into a molecule by being modified with an acrylic resin is dispersed in water. As the water-based paint, an epoxy-modified acrylic resin-based water-based paint obtained by reacting or mixing an epoxy resin and a carboxyl group-containing acrylic resin has been proposed (for example, see Patent Document 1).

Conventionally, the surface of a metal can material has been subjected to printing or painting in order to add surface protection and design properties. In the case of lids for cans, especially lids such as beverage cans, there is a risk that coating film fragments may be mixed into beverages when opening cans. It was. As described above, a paint containing a self-emulsifying epoxy resin containing a carboxyl group has been introduced as a paint for can lids. Moreover, the cover material which bonded the resin film containing a color pigment is disclosed (for example, refer patent document 2). In addition, paints containing colorants are considered to improve design, but colored paints with excellent adhesion and workability within the range of materials whose possibility of affecting beverage safety is below a specific standard Has not been put to practical use.

In recent years, a demand for safety has been increasing, and coloring paints considering safety have not been put into practical use even in colorants and dispersants thereof.

JP-A-5-9431 JP-A-9-277477

An object of the present invention is an outer surface of a can lid containing a colorant that is excellent in adhesion, processability, and abrasion resistance within the range of registered raw materials of the US Food and Drug Administration (FDA). It is another object of the present invention to provide a water-based paint composition and a can lid having a cured coating film of the paint.

As a result of intensive studies, the present inventors have found that by using a specific acrylic dispersion resin, it is possible to sufficiently disperse not only the dispersant-treated pigment but also a specific pigment that has been registered in the FDA, resulting in the present invention. It was.

That is, the present invention is an aqueous coating composition for can lid outer surface containing a pigment dispersion and a binder resin, wherein the pigment dispersion comprises a pigment, methacrylic acid, styrene and ethyl acrylate as constituent components. The acrylic copolymer is an acrylic copolymer having 30 to 60% by mass of methacrylic acid, 20 to 50% by mass of styrene, and 20 to 50% by mass of ethyl acrylate as constituents. There, the ratio of the pigment and the acrylic copolymer is 95: 5 to 60: a 40, wherein the binder resin is an aqueous coating composition for can end an outer surface which is a self-water-dispersible acrylic-modified epoxy resin And a can lid having a cured coating film of the aqueous coating composition.

The present invention can provide a water-based coating composition for can lid outer surfaces which is excellent in adhesion, workability, and abrasion resistance, while containing a colorant, by the above means.

The water-based paint composition for can lid outer surface of the present invention is a water-based paint composition for can lid outer surface containing a pigment, a pigment dispersion resin, and a binder resin, and the pigment dispersion resin contains methacrylic acid (MAA), styrene ( It is characterized by being an acrylic copolymer having St) and ethyl acrylate (EA) as essential components. Each component requirement is explained in full detail below.

Arbitrary materials can be used as a pigment used for the water-based coating composition for can lid outer surfaces of this invention. However, when used in can lids of beverage cans, it is desirable to use pigments that are listed in the FDA list, which is a US standard for food hygiene. Among these, as an indigo pigment, C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, etc., iron oxide is preferable as a red (red) pigment, and Tartazine lake is preferable as a yellow pigment. For other colors, C.I. I. In the case of Pigment Green 7 or black pigment, Carbon black or the like is preferably used.

The pigment dispersion resin used in the water-based paint composition for the outer surface of the can lid of the present invention is an acrylic copolymer having methacrylic acid, styrene and ethyl acrylate as essential components. Generally, a pigment is not easily dispersed in an aqueous resin as a binder component as it is. Accordingly, surfactants and pigment dispersants are used. In many cases, however, there is a concern about the safety of such active agents and dispersants to foods. The pigment-dispersed resin used in the water-based paint composition for the outer surface of the can lid of the present invention is synthesized within the range of raw materials described in the FDA list.

The acrylic copolymer described above preferably has 30 to 60% by mass of methacrylic acid, 20 to 50% by mass of styrene and 20 to 50% by mass of ethyl acrylate as constituent components.

The aforementioned acrylic copolymer is produced, for example, by the following method. A prescribed amount of a solvent such as n-butanol is charged in the flask in advance and heated to the reaction temperature (about 100 to 120 ° C.). Into the solvent kept at the reaction temperature, a prescribed amount of monomer, initiator and diluent solvent weighed in a separate container are added dropwise over a certain period of time (1-3 hours). Furthermore, the reaction temperature is maintained for 3 to 5 hours. During this time, a small amount of initiator (additional catalyst) is added. After the holding, it is cooled to obtain an acrylic copolymer which is the target pigment-dispersed resin.

The ratio of the pigment and the acrylic copolymer described above is preferably 95: 5 to 60:40 in terms of mass ratio. If the ratio of the pigment-dispersing acrylic copolymer exceeds 50 with respect to the pigment, the pigment-dispersing acrylic copolymer may be separated when mixed with the binder resin.

The water-based paint composition for the outer surface of the can lid of the present invention comprises a pigment dispersion in which a pigment is dispersed in an acrylic copolymer as a dispersion resin, and an aqueous dispersion of, for example, a self-water-dispersible acrylic-modified epoxy resin as a binder resin. Prepared by mixing the body.

Below, the manufacturing method of a pigment dispersion is described. The above-mentioned pigment and acrylic copolymer are mixed at a ratio of 95: 5 to 60:40, more preferably 90:10 to 70:30, and dispersed with a disperser such as a bead mill together with an FDA compatible dispersant and solvent. Let As the solvent for dispersion, a hydrophilic solvent is preferable, and for example, butyl cellosolve, butyl carbitol and the like are used.

It is essential that the binder resin used in the water-based coating composition for the outer surface of the can lid of the present invention is a self-water dispersible acrylic-modified epoxy resin.

The self-water-dispersible acrylic-modified epoxy resin used as a binder resin in the water-based paint composition for the outer surface of the can lid of the present invention is (1) a resin obtained by reacting an acrylic resin and an epoxy resin in the presence of an amine catalyst. A resin obtained by water dispersion after neutralization with an amine, or (2) a resin obtained by grafting an acrylic monomer component to an epoxy resin in the presence of an initiator and then water dispersion after amine neutralization. Resin.

A general production method of the self-water dispersible acrylic-modified epoxy resins (1) and (2) described above will be described below.

Manufacturing method (1)
Aromatic epoxy resin (A) and carboxyl group-containing acrylic resin (B) are partially esterified in an organic solvent under an amine catalyst at a reactive group concentration in which the carboxyl group is excessive with respect to the epoxy group. It is obtained by reacting. Thereafter, the acrylic-modified epoxy resin obtained by the esterification reaction is neutralized with an amine and dispersed in an aqueous medium, whereby the aqueous resin composition used as a binder resin component in the aqueous coating composition for the outer surface of the can lid of the present invention. Things can be easily obtained. Although it does not specifically limit as an amine catalyst, Dimethylethanolamine can be used conveniently.

Manufacturing method (2)
An acrylic resin is grafted by dropping a monomer solution containing an initiator into an aromatic epoxy resin solution at a reaction temperature (about 110 ° C.) over a certain period of time (1 to 3 hours) and grafting the acrylic monomer onto the epoxy resin. An epoxy resin is obtained. By neutralizing with amine and dispersing in an aqueous medium, an aqueous resin composition used as a binder resin component in the aqueous coating composition for can lid outer surface of the present invention can be easily obtained. Although it does not specifically limit as an amine catalyst, Dimethylethanolamine can be used conveniently.

In the production method (1), the use ratio of the aromatic epoxy resin (A) and the carboxyl group-containing acrylic resin (B) is a solid mass ratio when the total weight is 100 parts by mass. The range of (A) / (B) = 95/5 to 70/30 is preferable, and a reactive group concentration range in which the carboxyl group is excessive with respect to the epoxy group is preferable.

In the production method (2), the use ratio of the aromatic epoxy resin (A) and the total monomer amount (C) is a solid content mass ratio when the total weight is 100 parts by mass, A) / (C) = 95/5 to 70/30 is preferable.

The aromatic epoxy resin (A) used for preparing the self-water dispersible acrylic-modified epoxy resin used as the binder resin in the aqueous coating composition of the present invention has a number average molecular weight of 2000 or more and an epoxy equivalent of 9, 000 or less epoxy resin. This number average molecular weight is measured by gel permeation chromatography (GPC) and determined in terms of polystyrene. The epoxy equivalent is a value obtained by multiplying the reciprocal of the epoxy value, which is a value indicating the amount of the epoxy group present in 100 g of the epoxy resin, by 100.

The range of the number average molecular weight of the epoxy resin is preferably 2000 to 18000, and more preferably 3000 to 10,000 in terms of processability and adhesion. As for the range of the epoxy equivalent of an epoxy resin (A), 2000-7000 are preferable from a viewpoint of sclerosis | hardenability and prevention of the coating film whitening phenomenon after a hot water process.

As these epoxy resins, any of bisphenol A type, bisphenol B type, and bisphenol F type can be used.

Examples of commercially available products include HM101 manufactured by Dainippon Ink & Chemicals, Inc., Epicoat 1010 and Epicoat 1256 manufactured by Japan Epoxy Resin Co., Ltd., ZX1449-8 manufactured by Tohto Kasei Co., Ltd., and the like.

Examples of organic solvents used for the preparation of self-water-dispersible acrylic-modified epoxy resins are only typical, and methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol Various hydrophilic properties such as dibutane, dimethylformamide or diacetone alcohol, as well as isobutanol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, methyl cellosolve acetate or ethyl cellosolve acetate Organic solvents: various lipophilic organic solvents such as ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene or xylene. These may be used alone or in combination of two or more thereof, and if necessary, water and these organic solvents may be used in combination.

As the basic compound that can be used for neutralizing the carboxyl group of the self-water dispersible acrylic-modified epoxy resin obtained by the above-described method, ordinary ammonia or organic base can be used.

Of these, alkyl amines such as trimethylamine, triethylamine or butylamine: alcohol amines such as dimethylaminoethanol, diethylisopropanolamine, diethanolamine or aminomethylpropanol; Etc. Polyvalent amines such as ethylenediamine and diethylenetriamine can also be used. Among these, dimethylaminoethanol is preferable because it does not remain in the coating film and tends to improve water resistance. The amount of the basic compound used is preferably such that the pH of the dispersion is 5 or more.

In the present invention, the aqueous medium means water alone or a mixture of water and a hydrophilic organic solvent in which at least 5% by mass or more is water. Examples of hydrophilic organic solvents that can be used in the present invention include methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, and isobutanol. Alkyl alcohols such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, hexyl cellosolve, glycol ethers such as methyl carbitol, ethyl carbitol, butyl carbitol; or glycol ether esters such as methyl cellosolve acetate, ethyl cellosolve acetate And dioxane, dimethylformamide, tetrahydrofuran, methyl ethyl ketone, diacetone alcohol and the like.

If necessary, it is safe to use a lipophilic organic solvent. When it is necessary to reduce the organic solvent contained therein from the aqueous resin composition thus obtained, an organic solvent that has a low boiling point and azeotropes with water when producing an acrylic-modified epoxy resin, for example, , Acetone, methyl ethyl ketone, n-butanol, butyl cellosolve, etc. are dispersed in an aqueous medium in combination with water and then distilled at normal pressure or reduced pressure to stably stabilize the self-water with a low organic solvent content. An aqueous dispersion of a dispersible acrylic-modified epoxy resin can be easily obtained. If necessary, additives such as an antifoaming agent and wax can be added to the aqueous dispersion.

The aqueous coating composition for can lid outer surface of the present invention comprises a pigment dispersion in which a pigment is dispersed in an acrylic copolymer as a dispersion resin, and an aqueous dispersion of a self-water dispersible acrylic modified epoxy resin as a binder resin. Prepared by mixing. The self-water dispersible acrylic-modified epoxy resin (solid content) as the pigment dispersion / binder resin is preferably about 1/99 to 50/50. The amount of the pigment dispersion is not limited because it is adjusted according to the desired color tone. Before mixing, weigh the aqueous dispersion of the self-water-dispersible acrylic-modified epoxy resin as the required amount of binder resin in the vat in advance, then slowly add the specified amount of pigment dispersion at room temperature while thoroughly stirring with a dispersion stirrer To do.

The viscosity range of the water-based paint composition for the outer surface of the can lid of the present invention varies depending on the coating method, but is preferably 15 to 120 seconds (Ford Cup # 4, 25 ° C.), but in the case of coating with a reverse roll coater Is preferably 20 to 60 seconds.

The coating method using the aqueous resin composition of the present invention is preferably a reverse roll coater, but besides this, various spray coatings such as air spray, airless spray or electrostatic spray, dip coating, Roll coater coating and electrodeposition coating are also possible.

The baking conditions are preferably 120 to 280 ° C. and 10 seconds to 30 minutes.

The coating amount is preferably 10 to 100 mg / dm2.

Hereinafter, the present invention will be specifically described with reference to examples. The numbers represent mass% or parts by mass.

(Preparation of dispersion resin A)
(A) n-butanol 416
(B) MAA 120
(C) St 90
(D) EA 90
(E) BPO 4
(F) n-butanol 30
Total 750 (parts by mass)
(A) was charged into a four-necked flask purged with nitrogen gas, kept at 110 ° C. with stirring, and a solution in which (b) to (f) were mixed and dissolved therein was gradually added dropwise over 2 hours. . After completion of the dropping, the mixture was further stirred at the same temperature for 3 hours to obtain a dispersion resin A having a solid content of 40%.

Similarly, a dispersion resin B having a relative ratio of MAA / St / EA of 40/59/1 and a dispersion resin C having a relative ratio of MAA / St / EA of 10/45/45 were prepared.

(Preparation of pigment dispersion A)
(1) Preparation of Premix Blue Pigment (IRGALITE Blue BSP) 45
(Ciba Specialty Chemicals Co., Ltd.)
Dispersing resin A (nonvolatile content 40%) 37.5
Surfinol 465 6
Diethylene glycol monobutyl ether (BDG) 11.5
Total 100.0 (parts by mass)
After stirring the above with a dispersion stirrer, aging was performed at 40 ° C. for 12 hours to obtain a premix (A).

(Pigment dispersion process)
Premix (A) 33.3
Dimethylethanolamine (DMEA) 1.0
Ion exchange water 65.7
Bead 150
The above was treated with a paint conditioner for 3 hours to obtain a pigment dispersion (A) having a pigment content of 15% and a resin solid content of 5%.

(Preparation of self-water dispersible acrylic modified epoxy resin (R))
[Synthesis of carboxyl group-containing acrylic resin]
(A) n-butanol 670 parts (b) styrene 250 parts (c) ethyl acrylate 10 parts (d) methacrylic acid 190 parts (e) benzoyl peroxide 10 parts First, a four-necked flask in which (a) is replaced with nitrogen gas The solution prepared by mixing and dissolving (b) to (e) was gradually added dropwise over 2 hours. After completion of dropping, the mixture was further stirred at the same temperature for 3 hours to obtain a carboxyl group-containing acrylic resin solution having a solid content of 40%.

[Synthesis and water dispersion of self-water dispersible acrylic modified epoxy resin]
(F) ZX-1449-8 135 parts (g) Epicoat 1010 15 parts (h) Carboxyl group-containing acrylic resin solution 66 parts (i) n-butanol 225 parts (j) Dimethylethanolamine 3 parts (k) Dimethylethanol Amine 5 parts (l) Ion-exchanged water 530 parts First, (f) to (i) were charged into a four-necked flask purged with nitrogen gas and completely dissolved by stirring at 110 ° C. for 2 hours. Cooled to. To this solution, (j) was charged and stirred for 120 minutes to obtain a carboxyl group-containing self-emulsifying epoxy resin solution having a solid content of 40%, and at the same time, a part of (k) and (l) were charged. The esterification reaction is substantially stopped by lowering the temperature, and while further stirring, the remainder of (l) is dropped over 30 minutes, phase-inversion emulsification, and a carboxyl group-containing self-emulsifying epoxy resin having a solid content of 18% An aqueous dispersion of was obtained. From the measurement of the acid value and the epoxy equivalent, about 56% of the epoxy groups were reacted in the esterification reaction for 120 minutes.

ZX-1449-8 used here is a bisphenol A type epoxy resin having a number average molecular weight of 13,000 and an epoxy equivalent of 8500 manufactured by Toto Kasei Co., Ltd., and Epicoat 1010 is a number average molecular weight of 6800 and an epoxy equivalent of 3900 manufactured by Japan Epoxy Resin. The bisphenol A type epoxy resin. Furthermore, n-butanol and water were distilled off by azeotropic distillation under reduced pressure to obtain an aqueous dispersion of a carboxyl group-containing self-emulsifying epoxy resin containing no solvent and having a nonvolatile content of 37%. Further, in the following manner, the viscosity is adjusted with dimethylethanolamine so that the FC # 4 viscosity at 25 ° C. becomes 30 seconds, and an aqueous dispersion of a self-water dispersible acrylic-modified epoxy resin (R) (non-volatile content: 27%) )
(1) The aqueous dispersion 73 parts (2) Butyl cellosolve 7 parts (3) Butyl carbitol 5 parts (4) 7700 LB 1 part (5) Hydisper 3028 3 parts (6) Ion-exchanged water 11 parts 7700 LB used here Is a phenol resin with a non-volatile content of 70% manufactured by Bakelite AG. High Disper 3028 is an aqueous dispersion of 10% carnauba wax component from Gifu Shellac Factory.

(Painting)
91.5 parts by mass of the aqueous dispersion (27% non-volatile content, clear type) of the above self-water-dispersible acrylic-modified epoxy resin (R) and 8.5 parts by mass of the pigment dispersion (A) are mixed to form a resin. The aqueous coating composition (A-1) for can lid outer surfaces according to the present invention having a pigment content of 5% based on the solid content was obtained.

Similarly, a pigment dispersion was prepared using each pigment described below and dispersion resins B and C. Furthermore, it mixes with the water dispersion (non-volatile content 27%) of the above-mentioned self-water-dispersible acrylic-modified epoxy resin (R), and the aqueous coating composition (A-2), (B- 1), (C-1) and water-based paint compositions (X-1) and (X-2) for can lid outer surfaces as comparative examples were prepared. The water-based paint composition for outer surface of can lid of Comparative Example 1 (X-1) is a self-water-dispersible acrylic-modified epoxy that uses the same pigment as that used in Examples 1 to 4 as a binder resin without using a dispersion resin. It means mixing with the aqueous dispersion of resin (R). Table 1 shows the formulation and evaluation results for the blue pigment.

Each pigment in Table 1 and Table 2 represents the following.
Blue pigment BSP: IRGALITE Blue BSP (manufactured by Ciba Specialty Chemicals)
Red pigment L3920: Paliogen Maroon L3920 (BASF)
Green pigment GLPO: IRGALITE Green GLPO (manufactured by Ciba Specialty Chemicals)
Yellow Pigment 2RLT: IRGAZIN Yellow 2RLT (manufactured by Ciba Specialty Chemicals)
The red pigment L3920 and the yellow pigment 2RLT are FDA compatible and have a 1% limit on the resin solid content, so the amount added for both pigments is 1% of the solid content.

The following aqueous processed pigments are pigments manufactured by Ciba Specialty Chemicals Co., Ltd. processed with FDA unregistered dispersion resin.
Blue pigment B GS: UNISPERSE Blue GS
Red pigment TR-S: UNISPERSE DPP Rubine TR-S
Green pigment G GS: UNISPERSE Green GS
Yellow Pigment 2RLT-S: UNISPERSE Yellow 2RLT-S

Below, the evaluation method of each characteristic is demonstrated.
(Stability over time)
Each pigment dispersion described above was added to the water dispersion (non-volatile content 27%) of the self-water-dispersible acrylic-modified epoxy resin (R) described above to prepare an aqueous coating composition for the outer surface of the can lid, and then 40 ° C. × 3 Let stand for days. It was visually determined whether pigment sedimentation or dispersion resin separation had occurred.

(Color development degree)
Using the same pigment as the standard, the color development degree of the aqueous processed pigment processed with a dispersion resin not registered in FDA is used as a reference, and the color development degree of the coating film to which the pigment dispersion using the dispersion resin produced this time is added. It evaluated by (circle) x.

(Color fading: Molding oil)
Absorbent cotton containing molding oil (for tab molding) used in the molding process was attached to a 2-pound hammer, and a fixed portion of the coating film was reciprocated 50 times to visually determine the transfer (color loss) of the pigment to the absorbent cotton.

(Color fading: 10% ethanol)
Assuming an alcoholic beverage, absorbent cotton containing 10% ethanol was attached to a 2-pound hammer, and a certain portion of the coating film was reciprocated 50 times to visually determine the transfer (color loss) of the pigment to the absorbent cotton.

(Color fading: Tissue)
In order to confirm the color fading under practical conditions when it actually becomes a can, a commercially available tissue paper is attached to a 2-pound hammer, and a certain portion of the coating is reciprocated 50 times to transfer the pigment to the tissue paper ( (Color loss) was judged visually.

(Paintability: pinhole)
The coating was applied to an A4 size aluminum plate with a bar coater so as to have an application amount of 40 mg / dm ² , and determination was made based on the number of pinholes in the coated film after curing.
No pinhole: ◎
1-3 pinholes: △
4 pinholes or more: ×

(Press workability)
By press molding, scratches on the surface of the coating film when processed and molded up to the shell process were visually determined.
No scratch: ◎
Scratches on part of shell circumference: △
Most scratches on the shell circumference: ×

From the above results, the can-coating outer surface aqueous coating composition of the present invention using a specific dispersion resin can form a cured film having excellent adhesion and workability using each raw material registered in the FDA.

The aqueous coating composition for can lid outer surface of the present invention forms a cured film having excellent adhesion and workability, and can be usefully developed for can lid and tab applications.

Claims (4)

An aqueous paint composition for can lid outer surface containing a pigment dispersion and a binder resin, wherein the pigment dispersion was prepared from a pigment and an acrylic copolymer having methacrylic acid, styrene and ethyl acrylate as constituent components The acrylic copolymer is a dispersion, and the acrylic copolymer has 30 to 60% by mass of methacrylic acid, 20 to 50% by mass of styrene and 20 to 50% by mass of ethyl acrylate as constituent components , It said ratio of the acrylic copolymer is 95: 5 to 60: a 40, wherein the binder resin is, the can end an outer surface for aqueous coating composition, which is a self-water-dispersible acrylic-modified epoxy resin. The water-based paint composition for can lid outer surfaces according to claim 1 , wherein the pigment is an FDA registered pigment. The self-water-dispersible acrylic-modified epoxy resin is a resin obtained by reacting an acrylic resin and an epoxy resin in the presence of an amine catalyst, and water-dispersed after amine neutralization (1), or The aqueous coating composition for can lid outer surfaces according to claim 1 or 2 , which is a resin (2) obtained by grafting an acrylic monomer component to an epoxy resin in the presence of an initiator. A can lid comprising a cured coating film of the water-based paint composition for an outer surface of a can lid according to any one of claims 1 to 3 .