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Exploration of Application of Water-based Ink in Aluminum Foil Printing
Time: 2014-03-28 Source: Cutting Edge of Packaging Read: 13182 times
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Wenzhou Junchuan Machinery Equipment Co., Ltd.

Abstract: This article describes various aspects of the use of water-based inks in PTP aluminum foil printing, introduces the selection of resins, additives, and pigments for inks in aluminum foil printing, analyzes the application cost, and analyzes the various costs encountered in aluminum foil printing. This kind of problem is analyzed briefly, and the solution is proposed.

With the increase of people's awareness of environmental protection, hygiene, and safety, the requirements for packaging materials are becoming stricter, especially for their health and safety. As a professional company producing pharmaceutical packaging materials, our company serves customers in the pharmaceutical industry. Packaging materials have always had high requirements. As early as 5 years ago, our company has realized all-benzene-free all pharmaceutical packaging materials. In recent years, due to the excellent environmental protection characteristics of water-based inks, the company's R & D team has conducted many experiments and attempts on the use of water-based inks in PTP aluminum foil printing, and has conducted in-depth research on the water-based properties of PTP aluminum foil printing. Now I will discuss some of my company's practices and experiences in the application of ink painting with my colleagues.

First, the production process of PTP aluminum foil for pharmaceutical packaging

Using industrial pure aluminum as the base material, use the gravure printing technology to print the characters and patterns on the medicinal PTP aluminum foil printing and coating machine and apply a layer of protective agent OP to the gravure roll. The words are also printed on the other side of the aluminum foil. And pattern and apply the adhesive VC, after cutting, cut into the required specifications.

The inks used for PTP aluminum foil are special inks for PTP aluminum foil gravure printing. Currently, most of the chemical materials such as OP, VC, and ink used in domestic PTP aluminum foil are solvent-based. During their production and use, a large amount of ethyl acetate, Methyl ethyl ketone even uses organic substances such as toluene as solvents and diluents. Therefore, research on the application of water-based inks for PTP aluminum foil is very urgent.

Water-based inks for PTP aluminum foil

1.Resin system

Resin is the most important component in water-based inks and the main component of the binder. The basic requirements for aluminum foil printing inks are a certain degree of adhesion to aluminum foil and a good heat resistance of resin binders and pigments to prevent them from falling and discoloring during packaging and use. Most of the binders used in traditional solvent-based PTP gravure printing inks are vinyl chloride resin and acrylic resin. These resins can provide good aluminum foil adhesion and good heat resistance.

Chloroacetic acid resin cannot be used directly in water-based systems, but some related technologies of water-based acrylic resins and water-based polyurethanes are relatively mature. With its diversity and good physical and chemical properties, it has become the best choice for the binder of water-based inks. With related applications in water-based inks, the scope of application is getting wider and wider.

Our company tested the water-based acrylic PTP ink and tested its performance after printing. See Table 1 for the situation.

Table 1 Comparison of performance test values of water-based inks and solvent-based inks

kind

Tinting power %

luster

Viscosity / S

Surface tension requirements of aluminum foil

Heat resistance of ink layer

Adhesion to aluminum foil

Initial dryness

D

Solvent-based ink

98

Big

20 18 -20

达因 32 dyne

180-220

宽胶带试验不粘落 25cm wide tape test does not stick

9

Good chroma and satisfactory hue

Water-based ink

100

Big

35 25-35

达因 32 dyne

180-220

宽胶带试验不粘落 25cm wide tape test does not stick

16

Good chroma and satisfactory hue

2.Auxiliaries and pigments for water-based inks

Auxiliaries used in water-based inks are mainly defoamers, surfactants, preservatives, antiwear agents, dispersants, slow drying agents and pH stabilizers. Defoamer is an indispensable component in water-based inks. Otherwise, when the ink has a high viscosity, a low pH value, a high printing speed, or too much water, fine bubbles will be generated on the surface of the substrate. Surfactants can reduce the surface tension of the ink, improve the wettability of the ink, and improve the printability to suit the performance of aluminum foil printing. An adhesion promoter can also be added to the ink and used in aluminum foil printing to improve the adhesion of the ink to the aluminum foil. The use of other additives can improve the weakness of water-based inks and improve the performance of inks. Pigments used in water-based inks are generally alkali-resistant colorants and have good dispersibility in water. Compared with solvent-based pigments, the colorants of water-based inks have higher requirements. They require light weight, softness, and high color saturation, and have good affinity, wettability and dispersibility with the binder. It has coagulated, precipitated and has good fluidity without discoloration and discoloration. For aluminum foil printing, high temperature resistance is a must-have characteristic of pigments, and there are relatively many high temperature resistant varieties of organic and inorganic colorants, which can be widely used in both solvent-based and water-based inks.

Application cost

Our company has compared the cost of using water-based inks and solvent-based inks. The main comparison is shown in Table 2:

Table 2 Cost comparison of water-based inks and solvent-based inks

kind

unit price

(Yuan / kg )

Solid content

( % )

Ink amount

( G / m 2 )

Product usage per ton

( Kg )

Unit cost

吨) (Yuan / ton)

Solvent-based production

Solvent-based ink

40.00

20 ~ 25

(干量) 0.8 (dry)

60.0

2400

2463

Ethyl acetate

7.00

100.0

Thinner

9.0

63

Water-based production

Water-based ink

55.00

30 ~ 35

(干量) 0.8 (dry)

50.0

2750

2758

Demineralized water

1.00

100.0

Thinner

8.0

8

Note: This table is a comparison of black inks. The prices of solvent inks and water-based inks for other colors are basically the same.

It can be seen from Table 2 that the price of water-based ink is much higher than that of solvent-based ink in terms of unit price. However, due to the characteristics of water-based ink pigments, the amount of water-based ink is usually only about 80% of the amount of solvent-based ink. In summary, although the cost of using water-based ink is slightly higher than that of solvent-based ink, the price difference is not large.

Third, the main points of water-based ink printing quality control

1.Effect of oil residue on the surface of medicinal aluminum foil on water-based ink

PTP aluminum foil for pharmaceutical packaging generally uses rigid aluminum foil as the substrate, and rigid aluminum foil is made in an aluminum factory without multilayer annealing after multiple layers of rolling. During the rolling process, some of the rolling oil will remain on the surface of the aluminum foil. Therefore, the surface of the aluminum foil will often carry sporadic oil stains, and sometimes there are pieces of oil stains that are not well controlled. The main component of the oil stain is kerosene, which is a mixture of a series of hydrocarbons. A large area of oil stain on the surface of the aluminum foil is not allowed to appear in large quantities in the packaging raw materials.

In PTP aluminum foil printing, when the surface tension of the ink is less than the surface tension of the aluminum foil substrate, the ink can wet the substrate and it is possible to provide adhesion.

Table 3 Surface tension of commonly used liquid materials in PTP production

Solvent

Ethyl acetate

Butanone

Toluene

Ethanol

Pure water

Water-based material

kerosene

dyn/cm ) Surface tension (25 ° C, dyn / cm )

23.5

23.97

27.92

22.1

71.8

25-30

23-32

The surface tension of the aluminum foil substrate is not less than 32dyn / cm, so that all kinds of solvents and water-based materials can wet the aluminum foil. However, when oil stains remain on the aluminum foil surface, the surface tension of the oil stains will drop to 23 ~ 32dyn / cm, so the wettability of the ink to oil stained aluminum foils will decrease. When using solvent-based inks, the surface tension of the solvent is close to that of kerosene, and kerosene and organic solvents have a certain compatibility. Therefore, there will be no obvious defects in appearance when there is a slight oil stain, and it will not significantly affect the coating. The adhesion and strength of the layer and the ink. However, the presence of a large amount of oil pollution will also be affected. This problem is even more prominent when using water-based ink materials. Because the surface tension of water at 25 ° C is about 71.8 dyn / cm, the surface tension of water-based inks after deployment is reduced to about 25 to 30 dyn / cm, and water-based materials It is incompatible with kerosene itself. The oil and water-based materials on the surface of the aluminum foil are not wetted, and the water-based coating and ink will not spread and form a film on the surface of the aluminum foil carrying the oil. In actual production, we also found this kind of phenomenon. If there is a large amount of oil on the surface of the aluminum foil, the phenomenon of unclear ink printing, shrinkage and uneven coating will appear. Although we can also use additives and a small amount of co-solvent to reduce The surface tension of water-based materials reduces the above phenomenon. But to solve the problem fundamentally, the oil on the surface of the aluminum foil must be removed. Our general approach is to let the aluminum foil first pass through an oven at about 90-100 ° C before printing, and dry it by hot air for about 1 second to reduce the residual oil on the surface of the aluminum foil to increase printability.

2.Effect of water drying speed on water-based ink

For water-based ink to be used for PTP aluminum foil, it must be adapted to the existing basic printing and coating process conditions of PTP aluminum foil, that is, to be printed and coated under the process parameter conditions normally used by conventional solvent-based inks. Generally, the drying temperature of solvent-based ink is 90 ~ 100 ℃, and the drying time is about 1s; the linear speed is generally controlled at 80 ~ 90m / min.

Drying of water-based ink is a very complicated process. In the printing industry, hot air drying is usually used. In hot air drying, the transfer of thermal energy, the evaporation of liquids such as water and solvents, and the barrier properties of solids to fluid evaporation will affect the drying speed of the ink. The speed and temperature of hot air as the main drying body are the key factors that determine the drying efficiency. . During the drying and filming process of the ink, the diluent must be completely evaporated, and the evaporation of this part of the diluent will consume a lot of energy. Compared with solvent-based materials, due to the large amount of water used in water-based materials, the evaporation heat of water is much higher than that of commonly used organic solvents (see Table 4), so it takes more energy to dry the same quality of water. However, in the production, we did not find too much energy loss (see Table 4-1). This is because in the coating process of solvent-based materials, if the solvent is completely dried in a short time, a large amount of heat and blowing must be provided. A large amount of hot air is entered, and the energy is completely surplus. Therefore, when using water-based materials, the energy is also completely sufficient and is also surplus.

Table 4 Evaporation heat of common solvents in PTP production

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    • Solvent

      Ethyl acetate

      Butanone

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