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Analysis of label printing and ink (Part 2)

IV. self adhesive materials

the application scope of self-adhesive labels mainly includes decoration materials and related adjustments by manufacturers, which can meet the requirements of ASTM, ez3, iso148 and other national and international standards at the same time; Due to the principle of one broaching process, the standard material. The decoration materials are mainly films, which are mainly used for decorative decals on cars and motorcycles, logo words on trademark windows, reflective films on highways, marks on containers, etc. Trademark materials are mainly paper and film, which are subdivided into basic labels and variable information labels according to the scope of application. Basic labels mainly include labels for food and beverages, chemical products, drugs, office supplies, toys, shampoo, electrical appliances, sanitary supplies and other commodities. Variable information labels include batch number, sequence code, bar code, production date, expiration date, price, information processing in the mailing process, distribution, warehouse management, inventory data, etc

the self-adhesive material consists of three parts: surface material, adhesive and backing paper. Choosing a suitable self-adhesive product for customers is by no means an easy task. According to the experience of professional workers, we should understand the following aspects:

1 The permanence and removability of the adhesive. In terms of the performance of adhesives, they can be divided into two categories: permanent and removable

2. Emphasize the significance of the label surface. Labels processed with self-adhesive materials may be labeled on the surface of various materials, and different labeling surfaces have a great impact on performance

3. Surface structure and shape of labeling substrate. Intuitively speaking, the rough label surface needs glue with strong viscosity. The surface of the label base material can be divided into plane and curved surface. If the label surface has a certain radian (for example, the surface of a medicine bottle with a diameter of less than 3 cm), it may need a face paper with good adaptability or a glue with strong viscosity

4. The cleanliness of the label surface. Self adhesive materials are most suitable for label substrates with clean, dry surfaces and free of oil and dust

5. The adverse effect of plasticization on rubber, that is, the requirements of climate resistance. For example, whether the adhesive viscosity needs to be pasted under cold, hot, humid or room temperature conditions; Whether the self-adhesive label is exposed to the environment below the freezing point; Whether it is used outdoors, under high temperature, humidity or ultraviolet light, and whether it is close to the car engine with higher temperature

6. Requirements of printing and processing methods for self-adhesive materials. After selecting different printing methods (such as flexographic printing, letterpress printing, offset printing, heat transfer and laser printing) and processing methods (such as roll to roll, roll to sheet, folding paper feeding method, sheet to sheet), the printing materials can be determined

v. application of label ink

1. Self adhesive label ink

for ordinary self-adhesive labels, flexographic printing is generally the main method, and then wiring is combined with die cutting and slitting devices; For printing materials with special requirements, printing devices can also be considered to be added for printing with some special effects. For self-adhesive label products, in fact, it is more necessary 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 realize UV glazing of mirror effect, so as to increase the added value of products

the main reason for the curing of UV ink is that it is irradiated by ultraviolet rays. The photopolymerization initiator in UV ink absorbs photons of a certain wavelength and turns into free molecules, which become free radicals. Then, through the transfer of energy between molecules, the polymeric prepolymer and photosensitive monomer become excited, generating charge transfer complexes. The complexes are continuously crosslinked and polymerized, and solidified into films. The curing process of UV ink is a photochemical reaction process, that is, under the action of UV energy, the prepolymer solidifies into a film in a very short time. In addition to causing the surface curing of the ink, UV can penetrate into the liquid UV curing ink and stimulate the further curing of the deep ink film. Traditional inks solidify and dry under oxidation, while solvent or water-based inks solidify by evaporation of water or solvent, and some inks can penetrate into paper. Therefore, compared with traditional inks, if there is still doubt, the polymerization and drying of UV curing inks are more thorough, without any evaporation or solvent pollutants, and the ink film is 100% cured

the main precautions during UV printing are:

(1 semi-automatic impact tester) for the poor resistance of UV ink to weather, UV, ozone and heat, UV is generally easier to penetrate yellow and red, while blue and black, especially black, are difficult to penetrate. Therefore, if the printing concentration is excessively increased in order to improve the printing effect, it will cause poor hardening, ink wiping off, poor tightness, and even cause the reverse side to stick to the drum. Pay special attention to the printing concentration of black ink in UV printing

(2) among various substrates, there are also a small number of substrates with poor adhesion, scratch resistance and bending adaptability to UV ink. In particular, there are a wide variety of substrates for synthetic paper and plastics, and there are also substrates with and without surface treatment. Ink for a variety of substrates, adhesion properties are also quite different, so it is very important to choose the substrate suitable for UV ink, or choose the ink suitable for the substrate. Among UV inks, there are paper and plastic, and there are also several kinds of UV inks for plastic. Be sure to test the tightness and other properties before use. Even if the base material is paper, due to different paper, different ink types and different hardening conditions, there may be accidents of low adhesion performance. Please pay attention to the prior test

(3) generally, UV ink can be used without adjustment in principle, but according to the quality of paper, indoor temperature and printing conditions, 2 to 5% of UV special inking oil or adhesive remover can be appropriately added. Also, if you use auxiliary agents or cleaning agents, please use UV ink special

(4) UV ink should not be mixed with oily ink. If it must be mixed with other kinds of ink, the fluidity, adhesion, printability and solidification degree of the mixed ink must be confirmed in advance. After UV gold silver ink and UV general ink are mixed, the fluidity will deteriorate and solidify, the speed will increase, and the brilliance will become weak. Therefore, do not store the mixed ink for a long time

(5) if the ink is stored at a high temperature, solidification, hardening and other phenomena will occur. Be sure to keep the UV ink in a dark place below 25 ℃. In particular, gold and silver ink is easier to solidify and weaken its brilliance than ordinary UV ink, so don't store it for a long time

(6) compared with general oily inks, UV inks have a narrow water range. Especially when the ink is emulsified, the emulsified ink will accumulate on the ink roller and remain on the layout and blanket, causing dirt. And at the beginning of printing, compared with oily ink, the supply of UV ink in the ink bucket will not be very good, so there will be a tendency to open the ink bucket too much. The supply of ink on the way will gradually increase, and the excess ink on the printing machine will cause ink emulsification. So 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 equipment. There are two main reasons for deformation, one is tensile deformation, the other is thermal deformation. To solve the deformation problem of thin films, we must first choose materials with stable quality and good uniformity; Secondly, in terms of equipment configuration, it is best to choose the cold UV curing method, which not only has fast curing speed, but also theoretically will not cause material deformation. In addition, it is also necessary to consider whether the equipment has a device to disperse tension, such as the driving roller or pressing roller device of the main force

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 account for 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 of the shrinking label market are large companies, whose requirements are often large quantities of long version activities. In fact, solvent based gravure inks are most suitable for long version live printing, which makes solvent based inks the best choice in the shrinking label market. However, with the development of the shrink label market, some small customers have also shown great interest in this. The increase of small batch and short version activities has driven the growth of the demand for water-based inks and free radical UV inks. Cationic UV ink is less used in the field of shrink film due to its high price and troublesome printing

shrink label printing ink needs to have strong adhesion, flexibility and considerable heat resistance. The pigment in the ink cannot change color or fade under high temperature. In the selection, we mainly consider the friction coefficient, shrinkage, adhesion, chemical residue and migration and other performance indicators of the ink

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 plays the role of wires, antennas and resistors. This kind of ink can be printed on a flexible or hard substrate to make a printed circuit, and the antenna printed with conductive ink can receive radio signals dedicated to RFID

conductive ink saves the cost of RFID tags from two aspects. First of all, in terms of material cost, the price of ink is lower than that of stamping or etching metal coils; Secondly, in terms of material consumption, stamping or etching consumes a lot of metal, while conductive ink printing antenna or circuit has high speed, low cost and high efficiency. In the past, conductive ink was printed only with silk, but now it has been extended to offset printing, flexographic printing and gravure printing

VI. precautions for label printing site management

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

we have repeatedly suggested that the same brand of ink produced by the same ink manufacturer should be used to avoid the printing failure of mixing different manufacturers and different types of ink. The ink shall be fully stirred before use and frequently during the printing process to ensure that the ink system is evenly dispersed. The ink should not be mixed too much each time, and the principle of "less and more" should be followed, which is not only conducive to the stability of ink performance, but also can effectively avoid waste; In addition, for spot color inks, deployment records should also be made. In the printing process, in order to ensure the quality of label prints and the smooth progress of production, some additives should be added to the ink, such as antistatic agent, defoamer, adhesive remover, etc., and the amount must be controlled within the specified range

in order to achieve better preservation effect, label printing ink should be stored in a closed container in a normal temperature, cool, dry, dark and ventilated environment. Printing ink on label

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