Gravure Printing Gold and Silver Ink Practical Experience

With the development of society and the improvement of living standards, people are increasingly demanding the packaging of goods. In the packaging of fine products such as bags and wine labels, gold or silver ink is often printed. Gold and silver inks can exhibit the metallic luster, giving people solemn, magnificent, and colorful feelings that cannot be represented by spectral colors. Therefore, silver ink has been widely used in packaging and decoration printing. The use of gold and silver ink in commodity packaging and trademark labels can not be used to embellish other colors, and it can also enhance the value of the product as a whole. How to improve it? The importance of silver ink printing quality is self-evident.

Composition of gold and silver ink

Like other inks, gold and silver inks are mainly composed of pigments and linking materials. Simply put, gold inks are made of gold powder and gold transfer oil. Silver inks are made of aluminum powder and silver oil. Blended.

1. pigment. We know that pigments are colorants in inks. They give inks a certain color. Pigments in gold and silver inks are made by grinding metal powders, mainly gold powder and silver powder.

The pigment in gold ink is gold powder, which is actually a powder made of copper and zinc alloy. The content of zinc in the gold powder is about 8% to 30%, and the zinc content is 8% to 12%. The gold color of the room is reddish, and it is customarily called the red gold. The color of the gold ink containing 20% ​​to 30% of the zinc rate is partial green. It is generally called the green gold, and is between the red gold and the green gold. For the red gold. In gravure printing, the golden ink used in the deployment of gold ink is generally used for the 800-point gold powder, and the surface of the gold powder particles are mostly coated with a surfactant, and can be better combined with the resin binder.

Silver powder is actually aluminum powder and is composed of 65% aluminum flakes and 35% volatile hydrocarbon solvents. Aluminum pigments have a small specific gravity and are easy to float in liquids. What is used in the gravure silver ink is the floating silver powder that has floating ability in the link material. Silver powder generally uses 400 to 1000 mesh silver powder. If silver ink is printed on a large area, lower mesh silver powder, such as 400 mesh silver powder, can be used to print and have a high metallic luster.

2. Link material. It is the carrier of the pigment, which enables the powdery pigment particles to be uniformly dispersed therein. On the other hand, it also serves as a binder, so that the pigment can finally be fixed on the surface of the substrate material. The binder material largely determines the viscosity, viscosity, flowability and drying performance of the ink. Therefore, the quality of the binder material directly affects the performance of the ink.

The linking material used in gold and silver inks is a special varnish, which is generally called gold transfer oil or silver regulating oil. The main components are oil, resin, and organic solvent auxiliary materials. The linking material for gravure gold and silver ink should meet the following conditions: • Must have enough viscosity to combine well with gold powder or silver powder. The transparency must be high, and it cannot affect the hue of gold and silver ink. • The acidity of gold transfer oil or silver adjustment oil is low, otherwise it will cause chemical reaction of gold powder or silver powder. • The transfer oil or silver transfer oil should also have fast-drying properties and quick fixability to prevent back-scratching of gold or silver ink prints.

The characteristics of gold and silver ink

1. The fineness of the ink. The better the fineness of the ink, the better the dispersibility of the pigment particles. Compared with the pigments in other inks, the pigment particles of the gold and silver inks are coarser, and it is easy to block the printing cylinders during the gravure printing process. Caverns, resulting in blockages and reduced ink transfer rates. Therefore, when deploying gold and silver inks, gold and silver powders with high fineness and good floatability should be selected as far as possible to facilitate uniform deployment and good printing.

2. The gloss of the ink. The glossiness of gold and silver inks is largely related to the particle size of gold powder or silver powder. In general, the larger the particles, the better the gloss of the ink; conversely, the smaller the particles, the less the gloss of the ink. However, it is worth noting that with the increase of metal pigment particles, the printability of gold and silver inks will also decline, the transfer performance will be relatively poor, and printing failures such as stencil printing will easily occur.

3. Heat resistance. Compared with the pigments in other inks, the gold powder and the silver powder in the gold and silver ink have the characteristics of high conductivity and high thermal conductivity, and the golden ink has poor heat resistance and is easily discolored when exposed to heat. Therefore, high temperature and heat accumulation should be avoided during use; silver ink has good light and heat emission performance, good heat resistance, and is not easy to discolor under high temperature conditions.

4. Chemical properties are not determined. The chemical properties of silver inks are relatively well-defined, but silver inks are not acid-resistant and can easily react with acidic substances. As a result, the metallic luster of Indian inks is reduced. Therefore, neutral auxiliary materials should be used for ink transfer during printing. This should be particularly note. The chemical nature of the metal is not enough. Contact with acids, cesium and sulfides will undergo chemical changes to varying degrees, and its metallic luster will be greatly reduced. Gold ink will appear black. Second, gold ink is also very likely to chemically react with air and water vapor. It causes discoloration. Therefore, be sure to seal the container tightly when storing the gold ink.

Some problems that should be noticed in the design process

According to the type of substrate material and the printing process, we can design the layout rationally, not only to be beautiful, but also

To fully take into account the characteristics of gold and silver ink and the printing process, printing failures occur as much as possible.

1. In general, the gold and silver inks are mainly applied to the full-page section or the color blocks, but it is better not to design the gold or silver color for very small texts of Yin, Yang and levels.

2. When printing gold and silver ink on paper, the background ink is usually laid first. For example, when printing silver ink, first lay a light layer of white ink, and then print the silver ink. This can not only improve the gloss of the silver ink layer, but also Strengthen the silver ink adhesion on paper.

3. If the substrate material is aluminum foil or vacuum aluminized paper, transparent yellow can be printed on it to achieve the golden effect; when the plastic film is printed, the composite aluminum foil is printed after the transparent yellow is printed on the OPP plastic film, and the printed ink layer can also be printed. To achieve the golden effect, you can not only save expensive metallic ink, but also achieve the desired effect.

4. In the process of plate design, the order arrangement of gold and silver inks should be taken into consideration to ensure the metallic color.

5. If it is a printed product, after printing gold ink and silver ink, UV coating or water-based coating should also be considered, or the print should be coated to prevent oxidation or discoloration of the gold ink.

Problems that should be noted in the printing process

There are many factors that affect the quality of gravure printing products, such as the type of substrate materials, the characteristics of the printing press, the characteristics of the ink, and the ambient temperature and humidity. Therefore, in the gravure printing process, we must strictly control the technical quality, margin, and silver ink printing quality.

1. Reasonable choice of substrate materials. Reasonable choice of substrate materials. The properties of the substrate materials must be compatible with the printing process characteristics of gold and silver inks. Only by selecting the appropriate substrate materials can the printing effect and metallic luster of gold and silver be highlighted. It is required that the physical and chemical indexes such as whiteness, evenness, smoothness, surface strength and flatness of the substrate materials be good, the stretching rate should be small, and the ink absorption should be moderate. If the substrate material has poor flatness, large flexibility, and poor solidity, it is difficult to maintain a constant printing pressure, and it is easy to have the disadvantages of uneven printing pressure, poor adhesion of the ink layer, and poor quality of the ink color. Therefore, if gold and silver inks are to be printed on paper, substrate materials such as coated paper, glass cardboard, and whiteboard paper can be selected, and the metallic luster of gold and silver inks can be highlighted. If the substrate material is a plastic film, the plastic film must be pre-treated between printing, such as corona treatment, to improve the printability of the plastic film and the adhesion of gold and silver ink.

2. The control of printability of gold and silver inks mainly includes the following aspects: • Viscosity of inks. Viscosity is the most important control index in ink application. It directly affects the transfer performance of ink and the quality of printed materials. Too low viscosity can easily cause the ink to spread. Conversely, if the viscosity is too high, the transfer performance of the ink is relatively poor, and large areas are likely to appear. Inconsistent ink, thin line breaks and other ills. When large areas of gold and silver ink are printed, the viscosity of the ink can be adjusted slightly lower to ensure that the ink layer after printing is uniform; when printing gold and silver ink on lines with smaller areas, the viscosity of the ink should be slightly higher. The dryness of the ink. The drying speed of the ink should be appropriate, the drying speed of the ink is too fast, and the dry plate is liable to occur, which affects the transfer of the ink. However, the drying speed of the ink cannot be too slow, otherwise, the back surface of the printed matter may become dirty. The general principle for selecting the ink drying speed is that under the existing conditions of the printing machine, the ink should be able to be fully dried before the next printing color group and before rewinding or stacking, but it cannot be dried on the printing plate. During the printing process, appropriate amounts of slow-drying solvents or fast-drying solvents can be added to the gold and silver inks to adjust the drying speed of the gold and silver inks.

In addition, the use of gold and silver ink should also follow the principle of follow-up with the printing, the amount of ink each deployment should not be too much, to avoid the excessive deployment of ink to make the powder in the air exposure time is too long, and the oxygen of the air The water vapor undergoes a chemical reaction and loses its golden luster.

3. Press control. Printing pressure. Should be based on the printing methods, ink properties and substrate materials absorb ink and other factors to put the appropriate printing pressure, printing pressure is too large, ink spread, graphic easy to become thicker and wider, and even paste version; printing pressure is too small, Insufficient ink is transmitted, and the picture and text may not be well-balanced. In the printing process of gold and silver ink, if a large area of ​​color blocks can appropriately increase the printing pressure, the ink layer can be uniform and thick; if it is a small line or text, the printing pressure should be reduced appropriately , to avoid the expansion of printing, paste, and other ills. Tension control. The tension should be adjusted according to the type of substrate material and its stretching rate. For example, the stretch rate of the PE film is relatively large, and the tension value should be small; and for a plastic or plastic film with a small stretching ratio such as PET or OPP, the tension can be appropriately Bigger. In addition, the winding tension should not be too large to prevent the back of the hair from sticking. ? Printing speed. When printing gold ink, the speed of the printing machine should not be too fast. Otherwise, the heat generated due to the friction will continue to accumulate. It is easy for the gold ink to oxidize and darken, which will not only affect the gloss of the gold ink, but also cause the paste plate. Drying capacity. The temperature of the drying oven should not be too high, otherwise it will easily cause shrinkage and deformation of the substrate material, especially the PE film. Therefore, when setting the temperature of the drying oven, factors such as the printing speed, the printing tension, the type of substrate material, and the size of the printing pattern must be taken into consideration.

In addition, the printing roller of gold and silver ink should be cleaned in time after printing so as to prevent the dry knot from being formed in the net of the roller and cause the clogging of the cell.

4. Environmental temperature and humidity control. Humidity is too high, the content of water vapor in the air is high, easy to make the metal discolor, but also affect the moisture content of the paper substrate material, the size of the deformation occurs, resulting in overprint and other faults. If the humidity is too low and the air is too dry, static electricity can easily occur. Therefore, the temperature and humidity in the printing plant should be kept as constant as possible. In general, the relative humidity is controlled at 55% to 60%, and the temperature is controlled between 20 and 280C.

Plastic printing gold, silver to common fault

1. The back of the print is dirty. Causes: The drying speed of the ink is too slow to completely dry; The printing speed is too high; The winding tension is too high or the printing product is too high; The operating environment temperature is too high; Solution: Add quick-drying solvent, or change the formula of gold and silver oil; reduce the printing speed; reduce the winding tension or print height; reduce the operating temperature; increase air flow and infrared light intensity.

2. Paste version. Reason: Ink drying is too fast, it has dried in the plate cavity before being transferred to the substrate material; ink particles are too thick; printing plate is not cleaned in time, leaving the residual ink in the mesh cavity, resulting in the network point Blockage; Ink mixed with dust, sand and other impurities. Solution: Slow down the ink drying speed; change the ink; clean the printing plate at any time; filter the ink, stamp the ink residue, and keep the environment of the production workshop.

3. Ink fastness