The application of gravure gold and silver ink and the problems that should be paid attention to
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With the development of society and the improvement of living standards, people are increasingly demanding the packaging of goods. In some fine products, such as cigarette packets and wine labels, gold ink or silver ink is often printed. Gold ink and silver ink can present the luster of metal, giving people a solemn, luxurious, colorful and colorful feeling, which cannot be expressed by spectral color. Therefore, gold and silver inks have been widely used in packaging and decoration printing. The use of gold and silver inks on commodity packaging and trademark labels can not only embellish and highlight other colors, but also enhance the grade of the products as a whole. The importance of improving the quality of silver ink printing is self-evident.
First, the composition of gold and silver ink
Like other inks, gold and silver inks are mainly composed of two parts: pigment and binder. In short, gold ink is made up of gold powder and gold oil. Silver ink is made of aluminum powder and silver oil. Blended.
1. pigment. We know that pigment is a coloring agent in ink, which gives the ink a certain color. The pigment in gold and silver ink is made of metal powder, mainly gold powder and silver powder.
The pigment in the 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 generally about 8% to 30%, and the zinc content is between 8% and 12%. The color of gold ink is reddish, which is customarily called red gold. The color of gold ink with a zinc content between 20% and 30% is greenish, generally called green gold, which is called between red gold and green gold. Green red gold. In gravure printing, gold ink is generally used for 800-mesh gold powder, and the surface of the gold powder particles is mostly coated with a surfactant, which can be better combined with the resin binder.
Silver powder is actually aluminum powder, which is composed of 65% flake aluminum powder and 35% volatile hydrocarbon solvent. Aluminum powder pigments have a small specific gravity and are easy to float in liquids. What is used in the gravure silver ink is a floating silver powder having a floating ability in the binder. Silver ink generally uses 400-1000 mesh silver powder. If silver ink is printed on a large area, silver ink can be prepared with a lower mesh number of silver powder, such as 400 mesh silver powder, which has a high metallic luster after printing.
2. Link material. The binder is a liquid component in the ink. On the one hand, it is a carrier of the pigment, so that the powdery pigment particles can be uniformly dispersed therein, and on the other hand, it acts as a binder to finally fix the pigment. The surface of the substrate material. The binder determines the viscosity, viscosity, fluidity and drying properties of the ink to a large extent. Therefore, the quality of the binder directly affects the performance of the ink.
The binder used in gold and silver ink is a special varnish, generally called gold or silver oil. The main components are oil, resin and organic solvent auxiliary materials. The binder of gravure gold and silver ink should meet the following conditions: 1 It must have sufficient viscosity to be well combined with gold powder or silver powder. 2 Transparency must be high, and it cannot affect the hue of gold and silver ink. 3 The acidity of the gold or silver oil should be low, otherwise the gold powder or silver powder will react chemically. 4 Gold oil or silver oil should also have fast drying and fast fixing, to prevent the back of the gold ink or silver ink prints from sticking.
Second, the characteristics of gold and silver ink
1. The fineness of the ink. The finer the fineness of the ink, the better the dispersibility of the pigment particles. Compared with the pigments in other inks, the pigment particles of gold and silver ink are coarser, and it is easy to block the cylinder on the plate during the gravure process. The cells, which cause blockage and reduce the transfer rate of the ink. Therefore, when blending gold and silver ink, it is necessary to select gold powder and silver powder with high fineness and good floatability to facilitate uniform distribution and good imprinting.
2. The gloss of the ink. The gloss of gold and silver ink is largely related to the particle size of gold powder or silver powder. Generally speaking, the larger the particle size, the better the gloss of the ink; on the contrary, the smaller the particle size, the lower the gloss of the ink. However, it is worth noting that as the amount of metallic pigment particles increases, the printability of gold and silver inks also decreases, and the transfer performance is relatively poor, which is prone to printing failures such as paste.
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 electrical conductivity and high thermal conductivity, and the gold ink has poor heat resistance and is easily discolored by heat. Therefore, high temperature and heat accumulation should be avoided during use; silver ink has good reflection performance against light and heat, and has good heat resistance, and is not easily discolored under high temperature conditions.
4. Unstable chemical properties. The chemical properties of silver ink are relatively stable, but silver ink is not resistant to acid, and it is easy to chemically react with acidic substances, so that the metallic luster of the imprint is reduced. Therefore, neutral auxiliary materials should be used for printing ink during the printing process. . The chemical properties of gold ink are not stable enough. Different degrees of chemical changes occur when contact with acid, alkali and sulfide, so that its metallic luster is greatly reduced, gold ink will appear black; secondly, gold ink is easy. It reacts with air and water vapor to cause discoloration. Therefore, it is necessary to seal the container tightly when storing the gold ink.
Third, some problems should be paid attention to during the design process
According to the type of substrate material and the printing process, the layout should be reasonably designed. It is necessary to be aesthetically pleasing, and must fully consider the characteristics of gold and silver ink and the printing process, and print defects should occur as much as possible.
1. In general, gold and silver inks are mainly applied on the solid parts or color blocks, and it is best not to design gold or silver for very fine intaglio, yang and gradation transitions.
2. When printing gold and silver ink on paper, it is usually necessary to lay a ground color ink. For example, when printing silver ink, firstly apply a layer of light white ink, and then print silver ink, which can improve the gloss of the silver ink layer. Enhance the adhesion of silver ink to paper.
3. If the substrate material is aluminum foil or vacuum aluminized paper, transparent yellow can be printed on it, and the golden effect can be achieved; in the plastic film composite printing process, after printing transparent yellow on the OPP plastic film, the aluminum foil is printed, and the ink layer is printed. It also achieves a golden effect, which saves expensive metal inks while achieving the desired results.
4. In the process of plate making, the color sequence of gold and silver ink should be taken into consideration to ensure the color of the metal.
5. If it is a printed product, after printing gold ink or silver ink, UV glazing or water glazing should also be considered, or the printed matter should be coated to prevent oxidative discoloration or falling off of the gold ink.
Fourth, the problem should be paid attention to during the printing process
There are many factors that affect the quality of gravure products, such as the type of substrate material, the characteristics of the printer, the characteristics of the ink, and the temperature and humidity of the environment. Therefore, in the gravure printing process, the process technology must be strictly controlled to ensure the printing quality of gold and silver ink.
1. Reasonable choice of substrate materials. The performance of the substrate material must be compatible with the printing process characteristics of gold and silver ink. Only the selection of suitable substrate materials can highlight the printing effect and metallic luster of gold and silver. It is required that the physical properties of the substrate material such as whiteness, uniformity, smoothness, surface strength and flatness are good, the expansion ratio is small, and the ink absorption is moderate. If the flatness of the substrate material is not good, the stretchability is large, the firmness is poor, and it is difficult to maintain a constant printing pressure, and it is easy to cause uneven printing pressure, poor adhesion of the ink layer of the blotting ink, and the quality of the ink color. Therefore, if you want to print gold and silver ink on paper, you can choose substrate materials such as coated paper, glass cardboard, and white paper, which can highlight the metallic luster of gold and silver ink. If the substrate material is a plastic film, the plastic film must be pretreated 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 the suitability of gold and silver ink printing. The control of the performance of gold and silver ink mainly includes the following aspects: 1 viscosity of the ink. Viscosity is the most important control index in ink application. It directly affects the transfer performance of ink and the quality of printed matter. If the viscosity is too low, it will easily cause ink to spread. On the contrary, if the viscosity is too high, the transfer performance of ink is poor, and it is easy to appear in large area. Part of the ink is uneven, thin lines and other defects. When printing gold and silver ink in a large area, the viscosity of the ink can be adjusted slightly lower to ensure uniformity of the ink layer after printing; when printing gold or silver ink on a small area, the viscosity of the ink should be slightly higher. 2 Dryness of the ink. The drying speed of the ink should be appropriate, the drying speed of the ink is too fast, the dry plate is prone to occur, and the transfer of the ink is affected, but the drying speed of the ink cannot be too slow, otherwise the back of the printed matter may be dirty. The general principle for selecting the drying speed of the ink is that under the existing conditions of the printing press, the ink should be sufficiently dry before the next printing color set and before rewinding or stacking, but not dry on the printing plate. During the printing process, an appropriate amount of slow-drying solvent or fast-drying solvent may be added to the gold or silver ink according to the specific conditions 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 printing, the amount of ink should not be too much each time, avoiding too much ink blending, so that the gold powder is exposed to the air for too long, and the oxygen and air Water vapor reacts chemically and loses golden luster.
3. Control of the printing press. 1 printing pressure. Appropriate printing pressure should be set according to the printing method, ink performance and ink absorption performance of the substrate material. The printing pressure is too large, the ink spreads, the image is easy to become thicker and wider, and even the paste; the printing pressure is too small, pass Insufficient ink, the graphics may be uneven. In the printing process of gold and silver ink, if the large-area solid color block can appropriately increase the printing pressure, the ink layer can be made uniform and thick; if it is a small line or text, the printing pressure should be appropriately reduced. To avoid the emergence of defects such as blotting and paste. 2 tension control. The tension should be adjusted according to the type of substrate material and its expansion ratio. For example, the stretch ratio of PE film is relatively large, and the tension value should be smaller. For plastic film with small stretch ratio such as paper or PET, OPP, the tension can be appropriately large. some. In addition, the winding tension should not be too large to prevent the back side from getting dirty. 3 printing speed. When printing gold ink, the speed of the printing machine should not be too fast. Otherwise, the heat generated by the frictional action will accumulate, it is easy to make the gold ink oxidize and blacken, which will not only affect the luster of the gold ink, but also may cause the paste. . 4 drying ability. The temperature of the drying oven should not be too high, otherwise it will easily cause shrinkage deformation of the substrate material, especially the PE film. Therefore, when setting the temperature of the drying oven, it is necessary to comprehensively consider factors such as the printing speed, the printing tension, the type of the substrate material, and the size of the printed pattern.
In addition, the plate roller of gold and silver ink should be cleaned in time after printing to prevent the dry knot from being trapped in the mesh of the plate roll.
4. Control of ambient temperature and humidity. If the humidity is too high, the content of water vapor in the air is high, which easily causes discoloration of the gold ink, and also affects the water content of the paper substrate material, causing dimensional deformation, which causes malfunctions such as overprinting. If the humidity is too low, the air is too dry and static electricity is likely to occur. Therefore, the temperature and humidity in the printing workshop should be kept constant. Generally speaking, the relative humidity is controlled between 55% and 60%, and the temperature is controlled between 20 and 28 °C.
Five, plastic gold, silver, common faults
1. The back of the print is dirty.
Reason:
(1) The drying speed of the ink is too slow, it can not be completely dried;
(2) The printing speed is too fast;
(3) The winding tension is too large or the printed product stack is too high;
(4) The operating environment temperature is too high;
(5) The printing machine has low drying ability.
Solution:
(1) add quick-drying solvent, or replace the formula of gold and silver oil;
(2) reduce the printing speed;
(3) reduce the winding tension or the stacking height of the printed product;
(4) reduce the operating environment temperature;
(5) increase the air volume and far Infrared light intensity.
2. Paste.
Reason:
(1) The ink dries too fast, and it has been dried in the plate cell before being transferred to the substrate material;
(2) the ink particles are too thick;
(3) the plate is not cleaned in time, so that the residual ink is dried in the cell, resulting in The cell is clogged;
(4) the ink is mixed with impurities such as dust and sand.
Solution:
(1) slow down the drying speed of the ink;
(2) replace the ink;
(3) clean the printing plate at any time;
(4) filter the ink, and cover the ink tank, and also maintain the environmental sanitation of the production workshop.
3. The ink layer has poor fastness, and the gold and silver inks are easy to fall off.
Reason:
Gold silver powder and gold, silver, silver oil, solvent.
Solution:
Replace the formula of the gold-plated silver oil.
4. Gold or silver ink is discolored or dull.
Causes:
(1) The oxidation time has occurred for a long time, or chemical reactions have occurred in contact with chemicals such as acid and alkali:
(2) printing speed is too fast;
(3) coloration occurs with other inks.
Solution:
(1) gold ink with the use, can not be deployed too much each time;
(2) reduce the printing speed;
(3) to prevent cross-color, once the color, immediately replace the ink.
5. The large area produces a speckle pattern and the gloss is extremely poor.
Reason:
(1) ink is too thin;
(2) plate mesh is too deep;
(3) a large amount of static charge accumulated on the plastic film.
Solution:
(1) reduce the amount of solvent;
(2) reduce the shallow plate mesh;
(3) anti-static treatment of the plastic film.
6. Some of the thin lines are not clearly printed or printed.
Reason:
(1) ink viscosity is too high;
(2) ink drying too fast;
(3) printing speed is too slow.
Solution:
(1) reduce the viscosity of the ink;
(2) add a slow-drying solvent such as butanol;
(3) appropriately increase the printing speed.
7. Gold ink overprint is not real gold.
Reason:
(1) ink drying is not enough;
(2) printing pressure is too small or too large;
(3) the depth of the cell on the plate cylinder is not enough.
Solution:
(1) Add an appropriate amount of fast-drying solvent to the gold ink, add a slow-drying agent to the spot color;
(2) adjust the printing pressure appropriately;
(3) appropriately increase the depth of the cell.