Talking about the offset printing process of gold and silver ink
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Spot color ink refers to a specific color ink pre-mixed, such as fluorescent yellow, pearl blue, metal gold silver ink, etc. It is not mixed by CMYK four colors. The color gamut of CMYK four-color printing ink is narrower than the visible color gamut, while the color gamut of the spot color ink is wider than the color gamut of CMYK four-color printing ink, so it can represent many colors other than CMYK four-color ink. In the design, customers often require gold and silver printing. Since gold and silver printing cannot be realized by four-color printing, its printing technology has special requirements. When printing, gold and silver are treated according to the spot color, that is, printed with gold ink and silver ink. The film should also be a spot color film, a film film alone, and printed separately. The following is the offset printing process of gold and silver ink.
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 blended with aluminum powder and silver oil. Made.
1. Pigment
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, and it 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. It is 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 well 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 powder with a lower mesh number can be used. For example, 400 mesh silver powder to modulate silver ink, which has a high metallic luster after printing.
2. Link material
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 the offset 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 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 dirty.
3. Additives
Adding a small amount of bright paste or transparent yellow to the metal can enhance the ink affinity and transferability of the gold ink; adding a small amount of red dry oil to the gold ink in winter can accelerate the drying speed; adding stearic acid amide surface activity when adjusting the ink The agent can fully wet, disperse and float the gold powder in the binder. Reduce paste and ink accumulation during ink transfer. Adding a small amount of bright light paste to the gold ink can improve the brightness and viscosity of the gold ink while reducing the accumulation of gold ink and improve the fluidity.
Second, the problems that need attention in the production process
1. Process design requirements
Design should avoid gold and silver and the main color or large area overprinting too much, so that gold and silver can not be printed or imprinted. In multi-color printing, gold and silver printing should be placed in the final color sequential printing, because gold and silver inks are surface color forming inks, and if other colors are printed on their surfaces, the metallic luster will be completely lost. As much as possible, the gold and silver are designed on the dark ground such as black, red and blue, giving full play to the metallic brightening effect of gold and silver ink. Gold and silver ink printing lines, text can not be too small, this is because the gold and silver powder particles are large, the transfer performance in the printing ink transfer process is poor, easy to cause stacking, paste, resulting in small lines, text is not blurred clear.
2. Substrate selection
In the offset printing process, gold and silver ink printing needs to select the conforming paper according to the special needs of the product to print to obtain the desired golden and silver printing effect. The better the smoothness of the paper surface, the better the metallic gloss of the printed matter, and the clear dots, rich layers, and bright color; if the surface of the paper is rough and porous, the printing effect of good metallic luster is not obtained. It is generally preferred to use coated paper and calendered white paperboard. The effect of using offset paper is not good, and the effect of using letterpress paper is even worse. To avoid printing gold and silver on acid paper, gold and silver powder will be blackened and discolored by acid.
3. Base ink
Since the metal powder particles of the gold and silver ink are coarse and have poor printability, the adsorptivity to paper is poor, and the oil absorption of the paper is reduced in order to fill the pores on the surface of the paper. Avoid excessive penetration of the binder during printing of gold and silver ink, which affects the fastness and gloss of the ink film, and the neutral base film can separate the gold and silver ink from the acid paper, so that the gloss of the printing is retained for a long time, so the gold and silver are printed on the paper. When printing a ground color first, the background color is mainly yellow ink. The offset paper is mainly made of medium yellow ink, slightly black ink and silver ink, and transparent yellow ink gold and silver ink on the coated paper. Make a base. Special attention should be paid to the drying of the ink layer when printing the ink. The gold and silver ink should be printed on the bottom ink which is not completely dry. The bottom ink is completely dry and the color is good, but the fastness is not enough, affecting the gold and silver. The adhesion of the ink; if the bottom ink is not dry, it must cause the gold and silver ink to be anti-adhesive by the bottom ink, which affects the luster of the gold and silver ink.
4. Control of the suitability of gold and silver ink printing
4.1 The viscosity viscosity of ink 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. There are many problems such as uneven ink on the ground and broken lines of fine lines. 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.
4.2 Dryness of ink The drying speed of the ink should be appropriate. The drying speed of the ink is too fast, and the dry plate is prone to occur, which affects the transfer of the ink. However, the drying speed of the ink cannot be too slow, otherwise the back of the printed matter will 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 being rewinded or stacked before proceeding to the next printing group, but not dried on the printing plate. In the printing process, an appropriate amount of slow-drying solvent or quick-drying solvent can be added to the gold or silver ink according to the specific conditions to adjust the drying speed of the gold and silver ink.
5. Control of the printing press
5.1 printing pressure in the gold, silver ink printing process, if the large area of the solid color block can 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 appropriate Reduce it to avoid the occurrence of defects such as blotting and paste.
5.2 Printing speed When printing gold ink, the speed of the printing machine should not be too fast. It should be slowed down gradually, generally 3500~4000 sheets/hour. Otherwise, the heat generated by friction will accumulate, it is easy to make The oxidation of black ink to black will not only affect the luster of gold ink, but also may cause paste.
5.3 Correctly select and use dampening solution Dampening solution should not be acidic, because gold and silver powder is easy to turn black when it meets acidic dampening solution. The gold-silver ink offset printing is preferably an alcohol-based fountain solution, because the alcohol-based fountain solution uses ethanol and isopropyl alcohol as main components, has small surface tension, good wettability, and is neutral, and can reduce the water consumption of the printing plate. Prevent gold and silver ink from emulsification and affect gloss. At the same time, the alcohol dampening solution is volatile, can reduce the temperature of the plate, and improve the printing durability of the printing plate without ensuring that the blank portion is not dirty, and does not react with the gold and silver powder. At present, the most used in printing plants are polyoxypropylene, polyoxyethylene ether and alkyl alcohol amide, which can reduce the surface tension of the fountain solution.
5.4 Choosing the right lining Because the lithographic offset printing speed is fast, the contact time between the plate cylinder and the blanket cylinder, the blanket cylinder and the paper is short, and the transfer performance of the gold and silver ink is poor, and the ink layer is required to be thick, so it is necessary to increase the printing. Stress to solve. However, the printing pressure soft lining is easy to compress and deform, causing the gold and silver dots to expand and paste, so the medium and rigid lining is generally used to achieve the purpose of reducing the compression deformation of the lining and increasing the pressure.
5.5 Ink volume under the ink fountain The control of the ink volume should be small and then gradually increased, and it should be added less and diligently, so that the ink volume of the ink fountain can be kept evenly to achieve the ink balance.
6. Temperature and humidity control
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 as constant as possible. Generally speaking, the relative humidity is controlled between 55% and 60%, and the temperature is controlled between 20 and 28 °C.
Third, gold and silver ink offset printing common faults and elimination
1. Stacking ink
Trouble phenomenon: gold and silver ink accumulates more on the rubber roller, and it is very smooth when rotating, but the gold and silver ink on the printing plate is not enough, the product is printed with thin flowers, or the ink layer of the printing plate and the blanket is very good. Thick, and the product is printed with thin flowers.
The cause of the failure: the fluidity of the gold and silver ink is too poor, or the storage time is too long; the quality of the gold and silver ink toner is poor, the particles are coarse, and the blocking property is poor, resulting in low transferability.
Remedy: Add an appropriate amount of thin varnish to the ink to reduce the viscosity of the ink and improve fluidity.
2. Paste
Trouble phenomenon: the printing plate dot or the edge of the graphic is spread, the blank word is dead, not fine.
The cause of the failure: the gold and silver powder particles are coarse and the thermal conductivity is poor. After the friction, the thermal expansion occurs together with the connecting material, causing the spread of the graphic and text.
Remedy: Appropriately reduce the speed of the printing machine, the machine speed is controlled within 4000 sheets/hour; use the wetting syrup suitable for printing with gold and silver ink, and add 5% to 10% alcohol (isopropyl alcohol) to the original dampening solution. ).
3. Pulling hair
Fault phenomenon: the product is not solid in color, there are light colored plush.
The cause of the failure: the ink is too thick, the viscosity is large, the fluidity is low; the water roller is lost: the rubber roller is aged.
Remedy: Appropriate amount of varnish and ink additive can be added to the ink; the water velvet cloth is wrapped on the water roller, and the rubber roller with good printing property is selected.
4. The back is dirty
Symptom: The front side of the product sticks to the back of the previous one, and the product is hairy.
Cause of failure: Excessive addition of auxiliary materials affects the fixing speed of the ink; the ink layer is too thick.
Remedy: increase the proportion of red dry oil, so that the ink drying speed is faster; control the amount of thin ink, you can add 5% offset anti-adhesive agent; spray powder, drying rack and other methods.
5. Imprinted
Fault phenomenon: gold and silver ink imprinted unevenly, imaginary.
Fault reason: improper printing pressure adjustment, the plate version is not uneven, the ink volume is too small or the local ink volume is uneven, the gold oil content is too much, the paper surface is too rough or the background color printing is not ideal.
Remedy: Appropriately increase the printing pressure, and fine-tune from light to heavy; reduce the gold-adjusting oil; print gold and silver on the flat-bottomed ink layer. At the same time, the printing pressure and the amount of ink are appropriately increased.