JP7708543B2 - Gold paste for water-based ink and water-based gold ink made by dispersing said paste - Google Patents

Description

The present invention relates to a gold paste for water-based ink. More specifically, the present invention relates to a gold paste that can be dispersed in a water-based ink vehicle to produce gold ink, and that disperses well in an acrylic water-based ink vehicle and does not gel, and that can produce water-based gold ink with excellent storage stability. When the water-based gold ink is used for printing, the resulting printed matter has an excellent metallic luster, and the gold paste can be used for high-definition printing such as gravure printing and flexographic printing, and can produce water-based gold ink with little environmental impact.

For gold printing ink, flake brass powder is generally used as the metallic pigment.

Flake brass powder is an alloy powder mainly made of copper and zinc, and is commonly called bronze powder or gold powder.

Since the surface of flake brass powder is coated with fatty acids, most gold inks that contain dispersed flake brass powder are organic solvent-based gold inks that use an organic solvent-based ink vehicle.

However, because organic solvents have problems such as air pollution, in recent years there has been an increasing demand for water-based gold inks that use water-based ink vehicles. However, flake brass powder coated with fatty acids is difficult to disperse in water-based ink vehicles, and it also has poor wettability, so there is a problem that water-based gold inks with dispersed flake brass powder cannot produce a gold printing coating with the excellent metallic luster that can be obtained with organic solvent-based gold inks.

A flake brass powder with improved dispersibility in water-based ink vehicles has been developed by coating the fatty acid-coated surface of flake brass powder particles with a surfactant, but previous technology has problems with uneven processing, and the surface of the flake brass powder particles is not sufficiently and firmly coated with the surfactant.

Flaky brass powder whose surface is not sufficiently coated with surfactant may gel if dispersed in an acrylic water-based ink vehicle, etc.

In addition, if flake brass powder whose surface is not sufficiently coated with a surfactant is dispersed in an acrylic water-based ink vehicle or the like and stored for a long period of time (one month or more), the vehicle and the flake brass powder will gradually react, separating into two layers, a flake brass powder layer and a vehicle layer, and then the flake brass powder particles will aggregate together.

Even if the layers separate into flake brass powder and vehicle, they can be mixed again as long as they are not tightly agglomerated. However, if the mixed gold ink is used for printing, the metallic luster of the printed coating may deteriorate.

There is a need for a gold paste that can be dispersed in an acrylic water-based ink vehicle without gelling to produce a water-based gold ink, and that has storage stability and is not easily separated into two layers, a flake brass powder layer and a vehicle layer, and that can be mixed even after separation, and that can produce water-based gold ink that exhibits an excellent metallic luster equivalent to that of organic solvent-based gold ink, not only immediately after the ink is produced but also after long-term storage.

JP 09-165544 JP 09-272817 A Patent Publication 2007-204638

Patent Document 1 describes a water-based gold ink that does not gel even after storage for several months by treating the surfaces of flake brass powder particles with a surfactant and dispersing them in a water-based polyurethane resin.

Patent Document 2 describes flake brass powder for water-based inks, in which the surface of flake brass powder treated with a fatty acid is coated with a nonionic surfactant.

The flake brass powder for water-based inks described in Patent Document 2 exhibits a metallic luster equivalent to that of organic solvent-based gold inks, but has the problem that it gels and becomes unusable when stored for a long period of time.

Patent document 3 describes flake brass powder for water-based printing inks, in which the surface of flake brass powder particles treated with a fatty acid is coated with a nonionic surfactant having an HLB value of 13 to 17 and whose hydrophobic group is composed of fatty acids such as monostearic acid and isostearic acid.

However, the flake brass powder for water-based inks described in Patent Document 3 contains alcohol when coated with a surfactant, and has poor stability over time with certain acrylic water-based ink vehicles, leading to problems such as surface gelation, verdigris, and the generation of air bubbles immediately after ink production, and then the entire ink gelling and becoming unusable.

The present invention aims to solve the above problems, and after many prototypes and experiments, it has been found that a water-based ink gold paste containing 100 parts by weight of flake brass powder with a surface coated with fatty acid, 0.5 parts by weight or more and 10 parts by weight or less of a nonionic surfactant with an HLB value of 13 to 17, 15 parts by weight or more and 45 parts by weight or less of a glycol, and 3 parts by weight or more and 10 parts by weight or less of an aqueous wax emulsion solution, can produce a water-based gold ink with excellent storage stability that does not gel for a long period of time of one month or more even in an acrylic water-based ink vehicle and can be mixed even after separation into two layers, a flake brass powder layer and a vehicle layer, and further, the printing coating of the water-based gold ink exhibits a gold color with excellent metallic luster not only immediately after the ink is produced but also after long-term storage, and thus the above technical problem has been achieved.

The above technical problems can be solved by the present invention as follows:

The present invention is a gold paste for water-based ink, which contains 100 parts by weight of flake brass powder whose surface is coated with a fatty acid, 0.5 parts by weight or more and 10 parts by weight or less of a nonionic surfactant having an HLB value of 13 to 17, 15 parts by weight or more and 45 parts by weight or less of a glycol, and 3 parts by weight or more and 10 parts by weight or less of an aqueous wax emulsion solution.

The present invention also relates to the above gold paste for water-based ink, in which the average particle size of the flake brass powder particles is 2 μm or more and 20 μm or less.

The present invention also provides a water-based gold ink obtained by dispersing the above-mentioned gold paste in a water-based ink vehicle.

The present invention also relates to the water-based gold ink, in which the water-based ink vehicle is an acrylic water-based ink vehicle.

The present invention also relates to a method for producing the gold paste for water-based ink.

The present invention contains 0.5 to 10 parts by weight of a nonionic surfactant with an HLB value of 13 to 17 and 15 to 45 parts by weight of glycols per 100 parts by weight of fatty acid-coated flake brass powder, so that unevenness in the treatment of the flake brass powder particle surface is unlikely to occur, and the flake brass powder particle surface can be uniformly and firmly coated with the nonionic surfactant, so that even with an acrylic-based water-based ink vehicle, it is a gold paste that can be used to create a water-based gold ink that does not gel immediately after mixing or during storage.

The present invention also contains 3 to 10 parts by weight of an aqueous wax emulsion solution per 100 parts by weight of flake brass powder, making it a gold paste that can be used to create an aqueous gold ink that has excellent storage stability and can be mixed without gelling for long periods of time.

In addition, if the average particle size of the flake brass powder particles is between 2 μm and 20 μm, it is possible to produce a water-based gold ink that exhibits a superior metallic luster, and it is possible to produce a gold ink that is suitable for use in high-definition printing inks such as gravure printing and flexographic printing.

This invention is a gold paste for water-based inks that contains flake brass powder coated with fatty acids.

Flake brass powder is an alloy of copper and zinc produced by mechanical crushing. In the present invention, an alloy of 75% copper and 25% zinc, which has a gold color close to golden yellow, or an alloy of 90% copper and 10% zinc, which has a slightly reddish gold color, is suitable, but is not limited to these.

The average particle size of the flake brass powder particles is preferably 2 μm to 20 μm.

If the average particle size is less than 2 μm, the flake brass powder will not float uniformly on the surface of the printed coating, and a printed coating with excellent metallic luster will not be obtained. If the average particle size is greater than 20 μm, when used for high-definition printing such as gravure printing or flexographic printing, the powder will not transfer easily to the printing plate in the ink, resulting in poor printability.

The gold paste of the present invention contains a nonionic surfactant with an HLB (hydrophile-lipophile-balance) value of 13 to 17.

The HLB value is a number that indicates the balance between the strength of hydrophilicity and hydrophobicity in a surfactant molecule; the higher the number, the higher the hydrophilicity.

The surfactant used in the gold paste is preferably a non-ionic surfactant that does not ionize when dissolved in water.

Anionic and cationic surfactants, which dissociate into ions, tend to discolor flake brass powder, resulting in a printed coating with poor metallic luster.

Nonionic surfactants with an HLB value of less than 13 are difficult to disperse in printing ink vehicles that are nearly completely aqueous, and are difficult to transfer to the printing plate, resulting in a printing coating with poor hiding power.

Also, when the HLB value exceeds 17, the amount of solid nonionic surfactant increases, and solid surfactants are difficult to disperse in the ink.

There are nonionic surfactants that have been prepared as aqueous solutions, but these do not mix well with the fatty acid coating on the surface of the flake brass powder particles, and there is a risk that the resulting printed coating will not exhibit an excellent metallic luster.

There are no particular limitations on the nonionic surfactant as long as its HLB value is in the range of 13 to 17.

Examples of nonionic surfactants in the present invention include polyoxyalkylene alkyl ether, polyoxyethylene sorbitan monolaurate, and polyoxyethylene coconut oil fatty acid sorbitan.

The content of the nonionic surfactant is preferably 0.5 to 10 parts by weight, and more preferably 3 to 7 parts by weight, per 100 parts by weight of the flake brass powder.

If the amount is less than 0.5 parts by weight, it will be difficult to coat the flake brass powder uniformly, which will reduce dispersibility in the water-based ink vehicle; if the amount is more than 10 parts by weight, the foaming will increase, which will reduce the coating performance and may also reduce printing suitability, such as drying speed.

The gold paste of the present invention preferably contains 15 to 45 parts by weight of glycols per 100 parts by weight of flake brass powder, and more preferably 25 to 35 parts by weight.

In the present invention, it is preferable to mix the flake brass powder in a solution of a mixture of glycols, a nonionic surfactant, and an aqueous wax emulsion, and then stir the mixture to coat the surface of the flake brass powder particles with the nonionic surfactant. However, if the amount of glycols is less than 15 parts by weight, the nonionic surfactant may not coat the surface of the flake brass powder particles uniformly and firmly.

In addition, water-based gold ink containing gold paste with more than 45 parts by weight of glycols has poor drying properties.

The glycols are not particularly limited, but low molecular weight glycols such as ethylene glycol, propylene glycol, and diethylene glycol are preferred.

This is because polymeric glycols such as polyethylene glycol may reduce the metallic luster and storage stability of the printed coating of water-based gold ink.

From the standpoint of safety and environmental impact, propylene glycol is preferred.

The gold paste for water-based ink in this invention contains a water-based wax emulsion.

The aqueous wax emulsion is a wax emulsion of copolymer and water-based solvent, which creates steric hindrance in the aqueous gold ink, improving the dispersibility of the flake brass powder and suppressing sedimentation.

The aqueous wax emulsion is not particularly limited, but examples include emulsions of ethylene vinyl acetate copolymer and AQUATIX (registered trademark) 8421 (manufactured by BYK Corporation).

The content of the aqueous wax emulsion in the present invention is preferably 3 to 10 parts by weight, and more preferably 5 to 8 parts by weight, per 100 parts by weight of the flake brass powder.

If the content is less than 3 parts by weight, the settling of the flake brass powder may not be sufficiently suppressed, and if the content exceeds 10 parts by weight, the flake brass powder may not rise to the surface of the printed coating, resulting in a decrease in the metallic luster of the printed matter.

The present invention is a gold paste for water-based inks in which the surfaces of flake brass powder particles are uniformly and firmly coated with a nonionic surfactant, so that the gold paste disperses well in water-based ink vehicles and can be mixed without gelling.

The aqueous ink vehicle in which the gold paste of the present invention is dispersed is not particularly limited.

Examples of water-based ink vehicles include urethane-based water-based ink vehicles and acrylic-based water-based ink vehicles.

In addition, the gold paste of the present invention has excellent dispersibility, so it does not gel even when dispersed in an acrylic water-based ink vehicle, and can be stored for a long period of time, such as one month or more, in a state that allows the flake brass powder layer and the vehicle layer to be mixed.

The gold paste for water-based inks of the present invention can be mixed with the vehicle for water-based inks in any desired weight ratio, but the gold paste:vehicle ratio is preferably 3:7 to 5:5.

The following are examples of the present invention, but the present invention is not limited to these.

Example 1
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the water-based gold ink was stored at 25°C for two months, it did not gel and could be mixed even after separation. In addition, when gravure printing was performed with the gold ink after two months, it was confirmed that the gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 2
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene sorbitan monolaurate (Kao Corporation) having an HLB value of 17, and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 3
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyalkylene alkyl ether (Sanyo Chemical Industries, Ltd.) having an HLB value of 13, and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 4
15 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 5
45 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 6
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (90% by weight copper, 10% by weight zinc) with an average particle size of 6 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

(Example 7)
10 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan (manufactured by Nippon Emulsion Co., Ltd.) having an HLB value of 16 was added and mixed to 30 parts by weight of propylene glycol (manufactured by Kanto Chemical Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, manufactured by BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (90% by weight copper, 10% by weight zinc) with an average particle size of 2 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

(Example 8)
To 30 parts by weight of propylene glycol (manufactured by Kanto Chemical Co., Ltd.), 3 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan (manufactured by Nippon Emulsion Co., Ltd.) having an HLB value of 16 was added and mixed, and then 7 parts by weight of an aqueous wax emulsion solution (product name: AQUATIX (registered trademark) 8421, manufactured by BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (90% by weight copper, 10% by weight zinc) with an average particle size of 12 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

(Example 9)
0.5 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan (manufactured by Nippon Emulsion Co., Ltd.) having an HLB value of 16 was added and mixed with 30 parts by weight of propylene glycol (manufactured by Kanto Chemical Co., Ltd.), and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, manufactured by BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (90% by weight copper, 10% by weight zinc) with an average particle size of 20 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

(Example 10)
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 3 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

Example 11
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan having an HLB value of 16 (Nihon Emulsion Co., Ltd.), and then 10 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection confirmed that the resulting gold print had the same metallic luster as an organic solvent-based gold ink.

When the gold ink was stored at 25°C for two months, it did not gel and could still be mixed even after separation. It was also confirmed that when gravure printing was performed with the gold ink after two months, the resulting gold print had a good metallic luster similar to that of the ink immediately after it was made.

(Comparative Example 1)
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene glyceryl isostearate (Nihon Emulsion Co., Ltd.) having an HLB value of 12, and then 7 parts by weight of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

60 parts by weight of the acrylic water-based ink vehicle was mixed and stirred with 40 parts by weight of the gold paste obtained to produce a water-based gold ink, which was then gravure printed. Visual inspection revealed that the gold print had the same metallic luster as the organic solvent-based gold ink. However, after storing the gold ink for two months at 25°C, the surface of the ink completely hardened and could not be mixed, making it unusable for printing.

(Comparative Example 2)
30 parts by weight of propylene glycol (Kanto Chemical Co., Ltd.) was mixed with 7 parts by weight of polyoxyethylene alkyl ether (Kao Corporation) having an HLB value of 18, and then 7 parts by weight of an aqueous solution of an aqueous wax emulsion (product name: AQUATIX (registered trademark) 8421, BYK Corporation) was added and thoroughly mixed with a mixer to obtain a gold paste solution.

100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) with an average particle size of 9 μm was added to the resulting solution and mixed in a mixer for 10 minutes to produce a gold paste.

40 parts by weight of the gold paste obtained was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection revealed that the print had a gold color, but the metallic luster of the printed coating was poor.

Furthermore, when the gold ink was stored at 25°C for two months, no gelation occurred, and the flake brass powder layer and vehicle layer were able to be mixed even after separation. However, the metallic luster of the printed coating after gravure printing was poor, just as it was immediately after the ink was made.

(Comparative Example 3)
To 100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) having an average particle size of 9 μm, 5.5 parts by weight of polyoxyethylene coconut oil fatty acid sorbitan (manufactured by Nippon Emulsion Co., Ltd.) with an HLB value of 16 and 5.5 parts by weight of isopropyl alcohol (manufactured by Kanto Chemical Co., Ltd.) were added and mixed thoroughly in a mixer to prepare a gold paste.

60 parts by weight of the acrylic water-based ink vehicle was mixed and stirred with 40 parts by weight of the gold paste obtained to produce a water-based gold ink, which was then gravure printed and visually observed. Immediately after the ink was produced, the gold print exhibited a metallic luster equivalent to that of organic solvent-based gold ink, but when the gold ink produced was stored at 25°C for one day, a film formed on the ink surface, and subsequently, when stored at 25°C for one week, gelation occurred and printing became impossible.

(Comparative Example 4)
100 parts by weight of flake brass powder (75% by weight copper, 25% by weight zinc) having an average particle size of 9 μm was mixed with 2 parts by weight of polyoxyethylene nonylphenyl ether (manufactured by Sanyo Chemical Industries, Ltd.) having an HLB value of 11, and the mixture was thoroughly mixed in a mixer to obtain a gold paste.

40 parts by weight of the obtained gold paste was mixed and stirred with 60 parts by weight of an acrylic water-based ink vehicle to produce a water-based gold ink, which was then gravure printed. Visual inspection of the printed matter revealed that a gold print could be produced immediately after the gold ink was produced, but when the gold ink was stored at 25°C for a day, a film formed on the ink surface, and subsequent storage at 25°C for a week caused gelation, making it impossible to print.

The results of the examples are shown in Table 1, and the results of the comparative examples are shown in Table 2.

In the table, in the "Gloss" column immediately after the ink was made, prints that exhibited the same metallic luster as organic solvent-based gold ink were marked with ◎, prints that exhibited slightly inferior metallic luster to organic solvent-based gold ink were marked with ◯, and prints that exhibited significantly inferior metallic luster were marked with ×.

Regarding changes over time, in the "Condition" column, if no gelling was observed after two months and the flake brass powder layer and vehicle layer were able to mix, an O was given, and if the ink surface had hardened or gelled, an X was given. In the "Gloss" column, if the metallic luster was the same as immediately after printing, an O was given, if the metallic luster was poor, an X was given, and if printing was no longer possible, an "Unacceptable" was given.

The gold paste of the present invention exhibits good dispersibility in acrylic water-based ink vehicles and does not gel. It is also possible to mix the flake brass powder layer with the vehicle layer even after two months, proving that it is possible to produce a water-based gold ink that retains a good metallic luster even after printing.

The present invention is a gold paste that can be dispersed in an aqueous ink vehicle to prepare an aqueous gold ink, and which exhibits good dispersibility even in acrylic aqueous ink vehicles and does not cause gelation.The gold paste can also be used to prepare an aqueous gold ink with excellent storage stability, in that the flake brass powder layer and the vehicle layer can be mixed for a long period of time, such as over one month.
Furthermore, printed matter printed using the aqueous gold ink obtained by dispersing the gold paste of the present invention exhibits an excellent metallic luster equivalent to that of conventional organic solvent-based gold inks, and the printed coating of the aqueous gold ink exhibits a gold color with excellent metallic luster not only immediately after the ink is made but even after storage, and this gold paste can be used to make an aqueous gold ink that is suitable for high-definition printing such as gravure printing and flexographic printing.
Moreover, since a vehicle for water-based inks is used, it is possible to prepare a water-based gold ink that is highly safe and has a low environmental impact.
Therefore, the present invention has high industrial applicability.

Claims (5)

A gold paste for water-based ink, comprising 100 parts by weight of flake brass powder whose surface is coated with a fatty acid, 0.5 parts by weight or more and 10 parts by weight or less of a nonionic surfactant having an HLB value of 13 to 17, 15 parts by weight or more and 45 parts by weight or less of a glycol, and 3 parts by weight or more and 10 parts by weight or less of an aqueous wax emulsion solution. The gold paste for water-based ink according to claim 1, wherein the average particle size of the flake brass powder particles is 2 μm or more and 20 μm or less. An aqueous gold ink obtained by dispersing the gold paste according to claim 1 or 2 in an aqueous ink vehicle. The water-based gold ink according to claim 3, wherein the water-based ink vehicle is an acrylic water-based ink vehicle. A method for producing the gold paste for water-based ink according to claim 1 or 2.