Label printing and ink analysis (below)
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Fifth, the application of label ink
1. self-adhesive label ink.
For ordinary self-adhesive labels, it is generally based on flexographic printing, and then connected with die-cutting and slitting devices. For printed products with special requirements, it is also possible to consider adding screen printing devices for special effects printing. For self-adhesive label products, in fact, more is to consider the issue of production efficiency, so high-speed flexographic printing equipment has become the first choice. In addition, for ordinary self-adhesive labels, special process units such as super glazing can also be selected to achieve UV glazing such as mirror effect to increase the added value of the product.
The main reason for UV ink curing is the irradiation of ultraviolet rays. The photopolymerization initiator in the UV ink absorbs photons of a certain wavelength and then turns into free molecules, becomes free radicals, and then passes the intermolecular energy to make the polymerizable prepolymer. And the photosensitive monomer becomes an excited state, and a charge transfer complex is generated, and the complex body is continuously cross-linked and polymerized to form a film. The curing process of UV ink is a photochemical reaction process, in which the prepolymer is solidified into a film in a very short period of time under the action of ultraviolet energy. In addition to causing the surface of the ink to be cured, the ultraviolet light penetrates into the liquid ultraviolet curing. In the ink, and stimulate further curing of the deep ink film. Conventional inks are coagulated and dried under oxidation, while solvents or water-based inks are solidified by evaporation of water or solvent, and some inks can penetrate into the paper. Therefore, compared with the conventional ink, the ultraviolet curing ink is more thoroughly polymerized and dried without any evaporation or solvent contaminants, and the ink film is cured 100%.
The main considerations for UV printing are:
(1) For UV inks, UV is generally easier to pass through yellow and red, while blue and black, especially black, are difficult to pass. Therefore, if the printing density is excessively increased in order to improve the printing effect, it may cause poor hardening, ink rubbing, poor adhesion, and even cause the reverse side to stick the roller. Pay special attention to the printing density of black ink in UV printing.
(2) Among the various substrates, there are also a small amount of a substrate which is inferior in adhesion to the UV ink, scratch resistance, and poor bendability. In particular, synthetic paper and plastic substrates are quite versatile, and there are also surface treated and untreated substrates. Ink is quite different for various substrates, adhesion properties, etc., so it is very important to select a substrate suitable for UV inks or to select inks suitable for the substrate. Among the UV inks, there are paper and plastics, and there are several types of UV inks for plastics. Be sure to test for adhesion and other properties before use. Even if the substrate is paper, there are cases where the adhesion performance is low due to the difference in the type of the ink, the difference in the type of the ink, and the hardening conditions, and it is expected to perform the pre-test.
(3) In general, UV inks can be used without adjustment, but depending on the quality of the paper, the temperature of the room, and the printing conditions, 2 to 5% of UV-specific varnish or debonding agent can be added as appropriate. In addition, if using an adjuvant or a detergent, please use UV ink.
(4) UV ink should not be mixed with oily ink. If it must be mixed with other types of ink, it is necessary to confirm the fluidity, adhesion, printability and solidification degree of the ink after mixing. When the UV gold ink is mixed with the UV general ink, the fluidity deteriorates and solidifies, the speed increases, and the brightness becomes weak. Therefore, please do not store the mixed ink for a long time.
(5) If the ink is stored at a high temperature, solidification, hardening, etc. will occur. Be sure to store the UV ink in a dark place below 25 degrees Celsius. In particular, gold and silver inks are more likely to solidify and brighten than the general UV inks, so do not store them for a long time.
(6) Compared with general oily inks, UV inks are relatively narrow in water. Especially when the ink is emulsified, the emulsion ink will accumulate on the inking roller and remain on the plate and the blanket, causing dirt. At the beginning of printing, the ink supply of the ink fountain is not very good compared with the oil ink, so there is a tendency to excessively open the ink fountain. The supply amount of the ink is gradually increased, and the ink on the printing machine is excessively caused to cause the ink to be emulsified. . Therefore, pay special attention to the supply of ink and water.
2. shrink label ink.
For film labels, it is necessary to consider how to eliminate film deformation and static electricity in the configuration of the device. There are two main reasons for the deformation, one is tensile deformation and the other is thermal deformation. To solve the deformation problem of the film, firstly, the material with stable quality and uniformity should be selected. Secondly, in the configuration of the device, the cold UV curing method is preferably used, which not only has a fast curing speed, but also theoretically does not cause deformation of the material. In addition, it is also necessary to consider whether the equipment has a device for dispersing tension, such as a main power transmission roller or a pressure roller device.
There are four main types of inks used for shrink label printing: solvent based inks, water based inks, cationic UV inks and free radical UV inks. From the current application situation, solvent-based inks have the largest market share, followed by water-based inks and free-radical UV inks. This is mainly because the main customers in the current shrink label market are large companies, and their requirements are often long-running in large quantities. In fact, solvent-based gravure inks are best suited for long-run printing, making solvent-based inks the best choice for shrink label markets. However, with the development of the shrink label market, some small customers have shown great interest in this. The increase in small-volume and short-run activities has led to an increase in demand for water-based inks and free-radical UV inks. The cationic UV ink is less expensive in application in the field of shrink film because of its higher price and more troublesome printing.
Shrink label printing inks need to have strong adhesion, flexibility, and considerable heat resistance, and the pigments in the ink cannot be discolored or faded at high temperatures. In the selection, the performance index of the friction coefficient, shrinkage, adhesion, chemical residue and migration of the ink is mainly considered.
3. RFID label ink.
Conductive inks for RFID tags are composed of fine conductive particles or other special materials (such as conductive polymers, etc.), which are printed on the substrate and act as wires, antennas and resistors. Such inks can be printed on flexible or rigid substrates to form printed circuits, and antennas printed with conductive inks can receive RFID-specific radio signals.
Conductive inks save the cost of RFID tags in two ways. First, in terms of material cost, ink is less expensive than stamping or etching metal coils. Secondly, in terms of material consumption, stamping or etching consumes a large amount of metal, while conductive inks print antennas or circuits with high speed and low cost. efficient. In the past, conductive inks were only screen printed, and today they have expanded to offset, flexographic, and gravure.
Six, label printing site management considerations
At present, there are many shortcomings in label printing inks on the market. The most prominent problem is the problem of ink hue deviation: on the one hand, the hue of the same kind of ink produced by different ink manufacturers is different; on the other hand, even the same kind of ink produced by the same manufacturer Different batches, the hue will be biased, sometimes even large. For this reason, the printing plant often has to stop the debugging, which is very unfavorable to the stability of the printing quality, which brings great inconvenience to the production and seriously hinders the improvement of the quality of the printed matter.
We have repeatedly suggested: use the same brand of ink produced by the same ink manufacturer to avoid printing failures of different manufacturers and different types of inks. The ink is thoroughly stirred before use, and it is also frequently stirred during the printing process to ensure uniform dispersion of the ink system. The ink to be dispensed should not be too much each time. The principle of “less addition and diligence” should be followed, which is beneficial to the stability of the ink performance and can effectively avoid waste. In addition, for the spot color ink, the preparation record should also be made. In the printing process, in order to ensure the quality of the label print and the smooth production, some additives should be added to the ink, such as antistatic agents, defoamers, debonding agents, etc., the amount of addition must be controlled within the specified range. Inside.
In order to achieve better preservation results, the label printing ink should be stored in a closed container in a normal temperature, cool, dry, dark, and ventilated environment. The following issues should also be noted during the storage and management of label printing inks:
1. Keep the ink away from fire and heat sources as much as possible. It is best to keep the temperature in the ink warehouse, and the temperature difference between the printing workshop and the printing workshop should not be too great. If the temperature difference between the two is large, the ink should be put into the printing workshop in advance, which not only helps the stability of the ink performance, but also ensures the high efficiency of production.
2. In the winter in the north, avoid storing the ink outdoors to prevent gelation. Once gelation occurs, it should be transferred to a high temperature warehouse or placed in hot water to restore the insoluble matter to its original state.
3. The principle of “first in, first out” should be followed in ink storage and management. The ink also has a certain shelf life. The general shelf life is one year. If the storage is too long, the various components in the ink will separate and precipitate. The remaining ink after printing must be sealed and stored in a dark place. Filter it with a mesh of 100 mesh or more before reuse, mix well and mix with new ink.
4. The label printing factory shall set up a special material management department to carry out unified management of raw and auxiliary materials including ink, establish a complete material management system, formulate reasonable feeding and picking procedures, and implement strict warehousing, Exit procedures. That is, the person in charge is responsible for the management of the ink, and the ink product is partitioned and stored to avoid misuse and misuse. In addition, detailed records should be made on the type, origin, batch, quantity and availability of the ink to ensure traceability of the product.
Seven, the conclusion
Due to the diversified needs of label products in terms of aesthetics, anti-counterfeiting and personalization, the advantages of combining various printing methods are the best choice for printing effects. Therefore, the design and application of flat presses with flat, convex, flexible and mesh functions will be more and more. This is also the development direction of label equipment manufacturers.
Every enterprise is facing more and more severe tests. Tomorrow's market will put forward higher requirements for today's label printing: multiple printing process combinations, flexible and diversified production, new varieties, high printing quality, high production efficiency, low Production costs, etc. These are the new opportunities and challenges facing label printing companies. For our ink manufacturers, the development and production of various types of label inks suitable for the market is also the only way to survive and re-development.