Adhesion is a kind of adhesion between contact layers of plastic film . There are two kinds of adhesion phenomena: one is that the printing surfaces are adhered to each other. The second is that the ink layer of the printed matter adheres to the other contact surface, or the ink adheres to the other contact surface.
The first phenomenon is that the films are adhered to each other, the bag opening is difficult to open, and the user refuses to use it. It can effectively prevent internal stickiness by adding measures such as slipping agent and opening agent in the resin.
The second phenomenon is specifically that the roll material cannot be unrolled smoothly, which seriously hinders the production of high-speed lines or damages the printing pattern or contaminates the contact surface due to ink peeling. In severe cases, the film cannot be opened and cannot be used, resulting in product scrap. Therefore, how to control and improve the anti-stick properties of the ink in the gravure printing process becomes extremely important.
(1) Anti-blocking product characteristics
Anti-adhesion products should have the following characteristics: ① smooth roll unwinding, good machine performance to adapt to the production of high-speed packaging ; ② smooth surface, good packaging opening.
(2) Selection of base material for anti-blocking products
In the gravure printing process, "blocking" is related to a series of factors such as substrate slippage, ink adhesion, solvent evaporation speed, operating environment, printing drying conditions, and printing speed. The selection of the substrate should fully consider the above factors, and it should have the characteristics of good printing adaptability, strong ink adhesion, and good solvent release. Common substrates include BOPP film, BOPET film, aluminum foil, PT film, etc., and the ink, solvent and printing process parameters that match the substrate are selected.
(3) Special technical indicators
In gravure printing, the blocking resistance of printed matter is mainly improved by improving the blocking resistance of ink. Therefore, the anti-blocking requirements must be based on factors such as the type of binder resin in the ink, solvent residues, and printing equipment parameters, and the required anti-blocking requirements must be achieved through the design of materials and performance.
(4) Specific printing process
Taking the anti-blocking printed matter as an example, the following points should be paid attention to when designing the printing process: ① The ink made of high-softening point binder resin should be selected to help prevent blocking. Correspondingly, the solvent has good solubility and release properties for the resin; ② Ensure that the printing ink layer is fully dried to control the solvent residues to reduce the possibility of adhesion between prints; ③ Printing substrates such as cellophane, nylon, or films treated on both sides After the rewinding, the back surface has strong affinity for contact with the ink layer, and the anti-blocking property is poor. Therefore, the corona treatment method should be adjusted during printing, single-sided processing, and slow printing speed. After printing, it must be sufficiently cooled by the cooling roller before being rolled.
(5) Anti-stick test method
The anti-blocking test of gravure printed materials is conducted in accordance with the provisions of GB / T13217.8-2009 "Inspection Methods for Plastic Gravure Inks-Anti-blocking Test".
1) Principle: The prepared ink film print is contacted in a fold in one time within a specified time, and under a certain temperature and pressure, a certain time is passed to observe the print adhesion.
2) Inspection conditions: Inspection should be carried out at (50 ± 1) ℃.
3) Inspection steps: ① make the sample by printing ink on the printing substrate, or scrape printing on the printing substrate with a wire rod; ② leave the printed sample for 2 minutes (such as the printing film is printed with water-based ink, It needs to be dried in a baking box at 59 ~ 61 ℃ for 5min, and then cooled after being taken out. Fold it between the two glasses in the upper and lower circles. Place it in the baking box at 49 ~ 51 ℃ and press 2000g Place the code for 2h; ③ Take it out, open the half-folded part, and check the adhesion.
4) Test result: Cover the pressed part with a translucent millimeter grid paper with a width of 20mm. Count the number of cells occupied by the ink layer and the number of cells occupied by the removed ink layer, respectively. Calculate by
B (%) = B1 / (B1 + B2) × 100
In the formula, B——the degree of ink blocking
B1——Number of cells in the ink layer
B2——the number of cells of the ink layer that has been removed