Analysis of problems in the printing process of th

Analysis of problems in the process of plastic printing

Plastic printing is a very active field in the packaging printing market. Printing on plastic substrate materials is an increasingly growing and challenging market, and UV drying ink and coating materials are just suitable for this market, because UV drying is a low-temperature instantaneous drying method, with fast fixation speed, which means faster production speed, And because there is no need to use heating and drying devices, it also reduces energy consumption and harm to the environment

although they have been successfully used for many years, as the market continues to put forward new needs and application fields, printing enterprises, ink and coating material manufacturers should pay more attention to a series of problems caused by the use of UV ink and UV coating materials. For example, it is a very challenging thing to obtain good adhesion on any kind of substrate materials. This paper briefly analyzes four aspects that need to be paid attention to when printing UV ink and coating materials on plastic film, hoping to be helpful to enterprises and individuals using this product

first, surface tension

surface tension is the most basic factor that should be paid attention to in plastic printing, because it directly affects the affinity between plastic substrate materials and ink and coating materials. Because the surface energy of most plastic films is low, the chemical inertia is strong, and the surface is tight and smooth, it is difficult to be wetted and firmly attached by substances such as ink. Therefore, before printing or coating on the surface of these materials, it is necessary to carry out surface treatment to change their surface chemical composition, crystallization status, surface morphology, increase surface energy, and make their surface tension reach 40 dyne/cm or higher. Generally, the substrate material suppliers will carry out surface treatment on their products, but the effect of treatment will soon disappear

for printing on plastic substrate materials (in fact, it is the case for any printing), the surface energy of ink and coating materials must be lower than that of substrate materials, and the surface energy of coating materials must be lower than that of high-level inks, so as to make the layers well wetted and adhered. In order to obtain an acceptable adhesion level, UV product manufacturers will carefully select the raw materials for the production of ink and coating materials. In contrast, solvent based inks have low surface energy, so most of the substrate materials can be easily wetted, so surface treatment of the substrate materials (especially when printing with UV materials) is necessary

for printing enterprises, in order to ensure that the surface tension of plastic substrate materials is within an acceptable range, surface pretreatment of substrate materials is the best method. The pretreatment methods of plastic film include chemical treatment, flame treatment, photochemical treatment, oxidation corona treatment and coating pretreatment. Of which oxygen is 8 Sample size: graphical corona treatment is the most commonly used treatment method. It uses high-frequency (intermediate frequency) high-voltage power supply (a new type of aluminum lithium alloy named airware, developed by the French wallep R & D center of kenlian Aluminum Corporation of the United States) to produce a corona release phenomenon in the gap between the discharge tool holder and the blade, and then measure the output, so as to treat the plastic film. Under the condition of appropriate treatment, oxidation corona treatment can be used for many kinds of plastic substrate materials without damaging the thermal sensitive plastic layer; Chemical treatment is also used, but it is often combined with corona treatment. In order to test the effect of the treatment, it is necessary to use a surface energy tester for inspection

II. Glass transition temperature (TG)

glass transition temperature Tg is defined as the inflection point of the expansion rate of UV curable epoxy acrylate coating (UV series products) with temperature in the thermal strain temperature curve. Compared with traditional inks and coating materials, UV products are usually composed of low molecular weight materials, which can form a very thick and highly interconnected complex structure, so that the glass transition temperature of UV products is higher, and the generated ink film also has good friction resistance and chemical resistance

if the glass transition temperature (TG) of UV products is higher than that during bronzing and coating, it will make it difficult for the foil layer or plastic layer to adhere to it. Therefore, the use of raw materials with lower glass transition temperature can help printing enterprises make it simple and convenient. With lower temperature, they can get good bronzing and film covering effects

III. substrate penetration

unlike most paper and paper plate substrate materials, the surface of general plastic film substrate materials has no pores for ink or coating materials to penetrate. However, some plastic printing materials can be moistened by some UV raw materials, so this combination can be used to allow ink or coating materials to penetrate into the film. After drying and curing, the plastic printing materials are firmly combined with ink or coating materials. In addition, this penetration can usually be strengthened by raising the temperature

IV. drying and curing degree

first, let's take a look at the drying and curing mechanism of UV ink and UV coating materials. Unlike solvent based ink and coating (which are cured by evaporation and drying of solvents), UV ink and coating are cured and dried by the energy of ultraviolet (UV light). After UV irradiation, UV ink or coating, The photoinitiator in its components absorbs the light energy of ultraviolet light, uses UV materials to polymerize, and finally makes UV ink and coating dry and solidify. Therefore, like any UV material formula, the correct photoinitiator must be used to obtain the best curing effect. In practical application, UV ink and coating materials need to use a certain amount of UV light energy to work well. When the UV light energy changes, the final effect of the ink film will also change

uv inks and coating materials sometimes seem to be dry on the surface, but in fact they are not completely dry in the whole ink film. The degree of drying near the bottom of the ink film is also very critical for good adhesion. If the ink film is not completely dried, any penetration method will not work, so it is impossible to obtain the ideal adhesion effect

modern printing is developing in the direction of fast, multi-color one-time printing, so new requirements are also put forward for the ink. The ink should not dry on the printing machine, but can dry quickly after printing on the substrate material, so as to meet the requirements of continuous and rapid printing of printing enterprises. UV ink just has such performance, and has no pollution to the environment. It can be printed on any substrate material. In the future printing, UV ink and technology will become the mainstream; The rapid curing and low-temperature curing characteristics of UV coating materials also make its application in post press polishing expand rapidly, and has the potential to replace plastic film composite in many products. However, while enjoying the excellent properties of UV ink and coating materials, we cannot ignore some influencing factors that should be paid close attention to, and the several influencing factors discussed in this paper should be paid enough attention. (Liu binqiang, Wang Chuanxi)