Discussion on the UV screen printing process of th

Discussion on the UV printing process of plastic bottles (Part 2)

UV printing process of plastic bottles

the specific working process of printing is as follows: the printed matter is positioned on a rotating part printing support in the center of the printing table, and the rear of the support is equipped with a conical plug that matches the diameter of the container. The pipe head is connected with the compressed air pump to inflate the soft plastic container during printing, so that it has a force to compete with the printing pressure. There is a set of backup rollers in the middle of the support that coincides with the outer diameter of the container, and there is a chuck in the front that coincides with the bottom of the container and belongs to the open-loop control system. The chuck is equipped with a positioning pin that matches the positioning pin groove injected at the bottom of the container. The taper plug, backup roller, chuck and the scraping movement of the printing plate do synchronous linear speed transfer printing. After printing a plate, the positioning pin of the chuck still returns to the positioning point

1. In theory, in order to obtain good printability on the plastic surface, its surface tension should be higher than that of the ink

pp and PE plastics are non-polar polymer materials with stable chemical properties and low surface tension. In addition, they are difficult to bond firmly with ink due to the influence of opening agent, antistatic agent and anti-aging agent added in the synthesis of resin. In order to improve the printability of PP, the vision, touch, hearing and taste of passengers and PE plastic must be treated so that its surface tension is not less than 3.8 × Ｎ/m。

(1) flame treatment

flame treatment is applicable to the surface treatment of small plastic containers. Its principle is to decontaminate the plastic surface through high temperature, melt the film surface, and improve the adhesion of its surface to ink. It has the most powerful independent research and development and technical solution ability in China year-on-year

the specific operation is: put the container to be treated into the gas flame, control the length of the inner core of the flame within 6 ~ 19mm, the distance between the top of the flame core and the surface of the container is 6 ~ 25mm, the contact time is 0.1 ~ 1.0s, and the rotation speed is 100 ~ 150 rpm

the flame contains free radicals such as -oh and -nh in the excited state, which can combine with hydrogen on the surface of polymer plastic, and introduce some polar oxygen-containing groups to produce chain breaking reaction, so that the wettability and adhesion of plastic surface can be improved

(2) detection of treatment effect

the simplest method is to use a surface tension test pen for detection. Select 3.8 × For the n/m surface tension test pen, if the liquid mark is evenly spread and does not shrink at the place where the test stroke passes, it indicates that the treatment effect is good; If the liquid mark shrinks, or part of the liquid mark shrinks and part does not shrink, it indicates that the treatment is insufficient

2. Key points of UV printing process for plastic bottles

(1) production of silk plate

① yellow, high strength and low elongation polyester yarn with mesh number greater than 355 mesh/inch should be selected

the tension of ② version is controlled at (1. The full load is only 5n8 ~ 2.5) × 103N/m。

③ use ordinary washing water to clean the plate, and use photosensitive glue direct method or capillary photosensitive diaphragm indirect method to make silk plate, and the film thickness is controlled within 15 ~ 25 μ m。

(2) printing

① printing scraper. The polyurethane double pointed edge printing scraper with hardness of hs80 shall be selected when printing with the printing machine, and the printing scraper with hardness of hs70 shall be selected for manual printing

② fully stir the ink before printing

③ curing conditions. Using medium and high pressure mercury lamps, the wavelength range of the emitted light wave is 280 ~ 380nm, the peak value is 365nm, and the power is 80 ~ 120W/cm; The curing speed is adjusted according to the demand of light curing energy

(3) printing environment

the viscosity of UV ink changes greatly under the influence of temperature. When the temperature is high, the viscosity of UV ink becomes low. After printing, it is easy to produce hairy teeth and paste plate. Low temperature, high viscosity of UV ink, easy to produce incomplete curing phenomenon. Therefore, UV ink needs to be refrigerated in summer, and the temperature in the printing workshop cannot be too high. In winter, the UV ink should be taken out of the cold air chamber in advance, and the curing speed should be appropriately reduced

the temperature of the printing workshop is generally controlled at 15 ~ 25 ℃

source: printing technology - packaging printing

Jin Yinhe, Beijing Institute of printing