Analysis of printing technology of spray aluminum paper (board)

Aluminized paper (board) is a high-grade packaging printing paper that is deep-processed from normal white paper (board). Many of its advantages have long been known to those in the industry. However, due to the structural relationship of aluminum spray paper (board), such as the non-absorbent surface, it is different from the printing process conditions of ordinary white paper (board). The user often encounters some problems, and the attention points of the aluminum spray paper (board) at the time of printing are described below for reference and hopefully useful to the printing operator.

offset printing:

1. All-oxidation dry ink should be used. (Special ink for plastic and aluminum foil)

2. Anti-adhesion dusting must be kept to a minimum. Excessive dusting can cause wear on the printed surface. Makes the surface rough and dark.

3. The stacking height of printed paper is kept at about 300 mm, and the stacking pressure can be reduced to avoid blocking before the ink is completely dried after printing.

4. To facilitate drying, it is recommended that the ink layer be thinned. Some prints require an ink layer with strong hiding power. This thick ink layer printing can be achieved by using two colors (overprinting) in one color.

5. If possible, use damp water (deionized water or distilled water). If using fountain solution, do not use it too acidic (pH = 5.5) and use it sparingly, as this will affect drying. It may sometimes be necessary to add up to 15% isopropyl alcohol to the fountain solution to reduce the surface tension and reduce the amount of water that is drawn to the paper (board).
6. Generally, it can be used according to the viscosity of the ink supplied by the manufacturer. If viscosity adjustment is required, the supplier's instructions must be followed. Mineral oils and paste thinners should be avoided.

7. Additives can be added to the fountain solution to aid in drying but everything is ink manufacturer's recommendation. The dampening must cross the width to avoid excessive moisture on the paper (board) edge. It is recommended to add an appropriate amount of desiccant to the ink to ensure it is solid and dry.

The fountain solution temperature is generally controlled at 10°C-15°C to control the temperature and amount of the fountain solution so as to prevent the ink from emulsifying excessively, thereby preventing the problem of causing imprinting break marks and printing instability.

8. In general, the viscosity of the ink of the second color is slightly lower than the viscosity of the ink of the first color. (The so-called surface absorption of aluminum spray paper, strictly speaking, there is still a small amount of absorption). Excessive increase in printing pressure can cause aluminum to fall off, which is undesirable.

9. The surface of the sprayed aluminum paper is relatively smooth, and there is sometimes a slight degree of paper adhesion. When the paper is fed, the hair is blown moderately for smooth paper feeding.

UV ink printing: UV curing inks are suitable for printing on aluminum paper (plate). The use of ultraviolet light to achieve instant rapid drying effect (actually absorbs UV energy and initiates monomer polymerization to make the liquid ink form a solid), while radiating UV energy, it will also bring heat to the surface of the printing material, and be careful when printing. The surface of the paper is overheated, as it will lose the metallic luster on the surface of the aluminum spray paper. It is recommended that the long-term surface temperature of the paper (plate) is less than 40°C. That is, before the paper is piled after printing, the paper (board) must be sufficiently cooled.

UV coating: The quality of UV oil can be quite different. Some UV oils contain a certain amount of fatty amines and surfactants. In order to reduce potential problems, you should select the best quality coating inks to ensure transparency and surface quality. With good protection, it is better to apply a small amount of varnish, and it will also be beneficial to reduce costs. When aluminum-sprayed paper (board) is used as a packaging material, when the glazing layer is too thick, it may cause the problem that the crease line of the package is too shallow. At this time, if the depth of the crease line is to be maintained, fine cracks or ink bursts will be caused. View questions.

Sometimes coating operations can be better done 24 hours after printing.

Screen printing: It is advisable to contact the ink manufacturer to perform printing production tests in advance for the establishment of processing parameters. The same precautions must be taken when printing to avoid transferring excessive heat to the surface of the aluminum spray paper.

Gravure printing and flexo printing: Traditional printing inks can be used. Due to the non-absorption of the ink on the surface of the material, the degree of drying needs to be adjusted. Drying oven temperature should not be too high, the temperature is too high will cause excessive drying of the paper base and loss of water, causing changes in the dimensional stability of the material, resulting in overprinting problems, the general drying temperature should be less than 75 °C, 50 °C Drying temperatures are frequently used (high proportions of fast-drying solvents can be used). When the length of the drying box is short, the printing speed should be slower, and when the drying box length is longer, the printing temperature can be lower. It should be noted that the time for the substrate to pass through the drying oven should not be too short.

The ink should be allowed to dry in the factory, otherwise the residual solvent in the ink will penetrate the surface coating of the aluminum spray paper-(board) to cause problems such as surface coating damage such as surface battering, cracking and the like.

Use oven drying printing ink, the degree of drying can be combined with the following points to consider:

1. Printing speed

2. Oven drying temperature and number of temperature zones

3. Dry wind speed

4. Oven length

5. Printed coating properties (solvent type and solvent release properties of ink resin, solids content)

6. Thickness of the print coating (wet coating print volume, ie depth and number of lines of the printed screen roller, print area)

7. Paper base thickness

Of course, the adjustment of the degree of drying is mainly based on the characteristics of the print coating and the thickness change, and the thickness of the paper base to determine the speed of the printing speed and the level of drying temperature.

It is also advisable to use an ink with a small amount of plasticizer (eg DOP), which can prevent some adhesion problems.

Special gravure inks for plastics and foils are suitable for printing on aluminum foil (board).

Environmental conditions:

In order to avoid edge deformation, 24 hours before printing, the paper and the paper roll are equilibrated to the temperature of the printing shop, and then the package is unpacked before printing. The greater the temperature difference, the longer the required equilibrium time, sometimes reaching several days. The temperature and humidity of the printing shop are kept at 20-25°C, and 50-60% RH is good. During storage and printing processes (such as ink printing drying, cutting, hot stamping, die cutting, finishing processes, etc.), excessive or low temperature and humidity must be avoided. If the time interval between work processes is longer, it is necessary to temporarily seal moisture-proof semi-finished products, which will play a good role in the smooth processing of subsequent processes.

Printing on aluminum paper (plates) is like printing on plastics and aluminum foils. Drying of the ink requires volatilization and/or oxidation. Due to the non-absorbency of the surface, during offset printing, its ink drying is slower than that of normal white paper (board). The increase of the ambient temperature or the decrease of the humidity is of course beneficial to the oxidation and drying of the printing ink on the aluminum spray paper, but it is not favorable for the paper. smooth.

In addition, when the sprayed aluminum paper (board) before printing is stored, the height of the stack should be a knife; when the two sheets of a roll, the aluminum spray paper is stored with the end face down (so-called upturned eyes) to prevent the paper from causing adhesion or surface Damage problem. Because the aluminum spray paper (plate) has a good metallic luster, the surface of the paper is affected more by the external world than ordinary paper, and the surface of the sprayed aluminum paper (plate) is very conspicuously damaged, so the sprayed aluminum paper ( Board) to prevent excessive pressure during transport storage.

Recommendation: There is a process of exploration, familiarization and experience for the printing of aluminum spray paper (board). In addition to the above mentioned, in summary, pay special attention to the following two points.

1. temperature:

During the printing process, the surface temperature of the sprayed aluminum paper (board) is improper (or too high), and its staying heat will soften the surface resin coating of the sprayed aluminum paper (board) and cause deformation, resulting in loss of metallic luster texture.

The use of sprayed aluminum paper (board) metal texture, appropriate mix and use of transparent and opaque inks will make the printed image with a three-dimensional sense, of course, this need to maintain the metal luster in the printing process without loss, in order to achieve beautiful Effect.

2. humidity:

Environmental humidity affects the retention and loss of moisture in the sprayed aluminum paper, which causes curling of the sprayed aluminum paper. If the ambient humidity is too low, moisture in the aluminum spray paper will be lost, and the sprayed aluminum paper will curl toward the reverse side of the aluminum surface. Conversely, excessively high ambient humidity can cause increased moisture in aluminum spray paper, which will curl toward the aluminum surface.

Generally, the relative water content of aluminum spray paper is 4.5-5.5%. With the drying of ink (such as gravure and flexo printing), the aluminum spray paper is affected by the drying. Generally, the relative moisture content of the paper after printing. Will be lower than 4.5%, at this time can be properly filled with water to the paper, the relative moisture content of spray aluminum paper to maintain the level of 4.5-5.5% before printing, in order to prevent the general environment The paper curls toward aluminum and affects the use.

Compared to aluminum spray paper, aluminum spray paperboard stiffness will be larger and less likely to be affected by environmental humidity curling phenomenon (the same 1 gram of moisture changes, 1% for 100 grams of paper, 200 grams of cardboard only accounted for 0.5%).

Conclusion: The printing company uses aluminum-sprayed paper (board) to obtain good packaged printing products, in addition to well-equipped printing machinery and good printing technology; the characteristics of the two raw materials, aluminum spray paper (board) and ink Familiar with understanding, to choose the appropriate ink, combined with the above mentioned points of attention will certainly play a multiplier role in improving the printing quality and reduce costs.