Analysis of Label Printing and Ink (Part 2)

5. Application of label ink

1. Self-adhesive label ink.

For ordinary self-adhesive labels, flexographic printing is generally used, and then connected with die cutting and slitting devices; for printed products with special requirements, you can also consider adding a screen printing device for some special effect printing . For self-adhesive label products, in fact, more need to consider the issue of production efficiency, therefore, 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 the curing of UV ink is that it is exposed to ultraviolet rays. The photopolymerization initiator in UV ink absorbs photons of a certain wavelength and turns into free molecules, which become free radicals. Then, the energy transfer between the molecules makes the polymerizable prepolymer It becomes excited with photosensitive monomer, and generates charge transfer complexes, which are continuously cross-linked and polymerized and cured into a film. The curing process of UV ink is a process of photochemical reaction, that is, under the action of ultraviolet energy, the prepolymer is cured into a film in a very short time. In addition to causing the surface of the ink to cure, ultraviolet light can penetrate into the liquid ultraviolet curing In the ink, and stimulate the further curing of the deep ink film. The traditional ink is solidified and dried under the action of oxidation, and the ink based on the solvent or water is solidified by the evaporation of water or solvent, and some ink can penetrate into the paper. Therefore, compared with traditional inks, the polymerization and drying of UV-curable inks is more thorough, without any evaporation or solvent-based contaminants, and the ink film is 100% cured.

The main considerations for UV printing are:

(1) For UV inks, ultraviolet rays are relatively easy to pass through yellow and red, and blue and black, especially black, are difficult to transmit. Therefore, if the printing density is increased too much in order to improve the printing effect, it will result in poor curing, ink wiping, poor adhesion, and even the reverse side of the sticky roller. Special attention should be paid to the printing density of black ink in UV printing.

(2) Among the various substrates, there are also a small amount of substrates that have poor adhesion to UV ink, scratch resistance, and bending suitability. In particular, there are quite a variety of substrates for synthetic paper and plastic, and there are also substrate-treated and untreated substrates. The ink has quite different adhesion properties for various substrates, so it is very important to choose a substrate suitable for UV ink or an ink suitable for the substrate. Among UV inks, there are paper and plastic, and there are several types of UV inks for plastic. Be sure to test the adhesion and other properties before use. Even if the substrate is paper, due to different papers, different ink types and different hardening conditions, there may be an accident of poor adhesion performance, so pay attention to pre-testing.

(3) Under normal circumstances, UV inks can be used in principle without adjustment, but depending on the quality of paper, room temperature and printing conditions, 2 to 5% of UV-specific ink adjustment oil or debonding agent can be added appropriately. Another point, if you use auxiliary or cleaning agent, please use the special UV ink.

(4) Do not mix UV inks with oil-based inks. If they must be mixed with other types of inks, the fluidity, adhesion, printing suitability and solidification degree of the mixed inks must be confirmed in advance. When the gold and silver inks of UV are mixed with the general inks of UV, the fluidity deteriorates and solidifies, the speed increases, and the brightness becomes weak. So please do not store the mixed ink for a long time.

(5) If the ink is stored at a high temperature, phenomena such as solidification and hardening will occur, so be sure to keep the UV ink in a dark place below 25 degrees Celsius. Especially gold and silver inks are more prone to solidification and weaker brightness than ordinary UV inks, so do not store them for a long time.

(6) Compared with general oil-based inks, UV inks have a narrower water width, especially when the inks are emulsified, the emulsified inks will accumulate on the inking roller and remain on the plate and blanket, causing dirt. Moreover, when printing is started, the supply of ink in the ink fountain is not very good compared to the oil ink, so there will be a tendency to open the ink fountain too much. The supply of ink on the way gradually increases, and the excess ink on the printing machine causes ink emulsification . So pay special attention to the supply of ink and water.

2. Shrink label ink.

For film labels, the device configuration needs to consider how to eliminate film deformation and static electricity. There are two main reasons for deformation, one is tensile deformation, and the other is thermal deformation. To solve the problem of deformation of the film, first of all, materials with stable quality and good uniformity must be selected. Secondly, in the configuration of the equipment, it is best to use the cold UV curing method, which not only cures fast, but also theoretically does not deform the material. In addition, it is necessary to consider whether the equipment is equipped with a device for dispersing tension, such as the main power transmission roller or 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 due to the fact that the main customers in the shrinking label market are large companies, and their requirements are often large-volume, long-term jobs. In fact, solvent-based gravure inks are best suited for long-type live printing, which makes solvent-based inks the best choice for the shrink label market. However, with the development of the shrink label market, some small customers have also shown great interest in this. The increase in small batches and short-run activities has driven the growth in the demand for water-based inks and free radical UV inks. The cationic UV ink is less expensive because of its high price and troublesome printing.

The ink for shrink label printing needs to have strong adhesion, flexibility, and considerable heat resistance. The pigment in the ink cannot change color or fade at high temperatures. In the selection, the main considerations are ink friction coefficient, shrinkage rate, adhesion, chemical residue and migration and other performance indicators.

3. RFID label ink.

The conductive ink used for RFID tags is composed of fine conductive particles or other special materials (such as conductive polymers, etc.). After printing on the substrate, it acts as a wire, an antenna and a resistor. This ink is printed on a flexible or hard substrate to make a printed circuit, and an antenna printed with conductive ink can receive RFID-specific radio signals.

Conductive ink saves the cost of RFID tags in two ways. First, in terms of material cost, ink is cheaper than stamping or etching metal coils; second, in terms of material consumption, stamping or etching consumes a lot of metal, and conductive ink printing antennas or circuits have high speed and low cost. efficient. In the past, conductive inks were only screen printed, but now they have expanded to offset printing, flexographic printing, and gravure printing.

6. Attentions for label printing site management

At present, there are many deficiencies in label printing inks on the market. The most prominent problem is the hue deviation of inks: on the one hand, the hue of the same ink produced by different ink manufacturers is different; In different batches, the hue will deviate, sometimes even very large. For this reason, printing factories often have to shut down for debugging, which is very unfavorable to the stability of printing quality, which brings great inconvenience to production and seriously hinders the improvement of printing quality.

We repeatedly recommend: use the same brand of ink produced by the same ink manufacturer to avoid printing failures of different manufacturers and different types of ink. The ink should be fully stirred before use, and it should be stirred frequently during the printing process to ensure that the ink system is evenly dispersed. It is not advisable to use too much ink every time. It should follow the principle of "less addition and diligent addition", which is not only conducive to the stability of ink performance, but also can effectively avoid waste; in addition, for special color inks, it should also be well prepared. In the printing process, in order to ensure the quality of the label prints and the smooth production, certain additives should be added to the ink, such as antistatic agents, defoamers, debonding agents, etc., pay attention to the amount must be controlled within the specified range Inside.

In order to achieve a better preservation effect, the label printing ink should be stored in a sealed container under normal temperature, cool, dry, dark and ventilated environment. During the storage and management of label printing inks, the following issues should also be noted:

1. Keep the ink away from fire and heat as far as possible. It is best to maintain a constant temperature in the ink warehouse, and the temperature difference with the printing workshop should not be too wide. If the temperature difference between the two is large, the ink should be put into the printing workshop in advance, which is not only conducive to the stability of the ink performance, but also ensures the high efficiency of production.

2. In winter in the north, avoid storing ink outdoors to prevent gelation. Once gelation occurs, it should be transferred to a warehouse with high temperature 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 storage period is one year. If it is stored for too long, 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 filter mesh of more than 100 mesh before re-use, mix it thoroughly and use it with new ink.

4. The label printing factory shall set up a special material management department to be responsible for the unified management of raw and auxiliary materials including ink, establish a perfect material management system, formulate reasonable feeding and picking procedures, and implement strict storage, Outbound procedures. That is, a person in charge is responsible for the management of the ink, and the ink products are partitioned to avoid misleading and misuse. In addition, make a detailed record of the type, origin, batch, quantity and use of ink to ensure product traceability.

7. Conclusion

Due to the diverse needs of label products in terms of aesthetics, anti-counterfeiting, and personalization, the advantages of combining various printing methods are the best choices to reflect the printing effect. Therefore, the design and application of combined printing machines with multi-functions of flat, convex, flexible and mesh 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 all new opportunities and challenges faced by label printing companies. For our ink manufacturers, the development and production of various types of label inks that meet the needs of the market are also the only way to survive and re-develop.

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