Anti-adhesion knowledge you must know about flexible packaging
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Adhesion refers to a phenomenon of adhesion between the plastic film contact layers. There are two kinds of sticking phenomena: one is that the bearing surfaces adhere to each other. The second is that the ink layer of the print adheres to the other contact surface (usually the back side of the film) or the ink adheres to the other contact surface. This article will take you from the characteristics of anti-adhesion products, substrate selection, and the use of technology and test methods to understand what is anti-adhesive in flexible packaging.
Adhesion refers to a phenomenon of adhesion between the plastic film contact layers. There are two kinds of sticking phenomena: One is that the printing surfaces adhere to each other. The second is that the ink layer of the print adheres to the other contact surface (usually the back side of the film) or the ink adheres to the other contact surface.
The first phenomenon is specifically manifested by the adhesion of the films to each other, the mouth of the bag is difficult to uncover, and the user refuses to use it. The internal adhesion can be effectively prevented by adding a slip agent, an opening agent, and the like to the resin.
The second phenomenon is manifested in the fact that the coil material cannot be unwinded smoothly, which seriously hinders the production of high-speed lines or damages the printing pattern due to ink peeling and contaminates the contact surface. In severe cases, the film cannot be opened and cannot be used, resulting in product scrapping. Therefore, how to control and improve the anti-stickiness of the ink in the gravure printing process is particularly important.
(1) Anti-blocking product characteristics
Anti-adhesive products should have the following characteristics: 1 smooth roll unwinding, good running performance, to adapt to the production of high-speed packaging; 2 smooth surface, good packaging opening.
(2) Substrate selection of anti-blocking products
In the gravure printing process, "blocking" is related to a series of factors such as substrate smoothness, ink adhesion, solvent volatilization speed, operating environment, printing drying conditions, and printing speed. The selection of the substrate should fully consider the above factors, and 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 matched with the substrate are selected.
(3) Special technical indicators
In gravure printing, the anti-blocking property of printed matter is improved mainly by improving the blocking resistance of the ink. Therefore, in terms of anti-blocking requirements, it is necessary to achieve the anti-sticking requirements to be achieved by designing materials and properties according to factors such as the type of binder resin in the ink, solvent residual amount, and printing equipment parameters.
(4) Specific printing process
Taking anti-blocking prints as an example, you should pay attention to the following matters when designing the printing process: 1 The ink made of high softening point binder resin should be selected to help prevent adhesion. Correspondingly, the solvent has good solubility and release property to the resin; 2 to ensure that the printing ink layer is sufficiently dry to control the solvent residue to reduce the possibility of adhesion between the printed materials; 3 the substrate such as cellophane, nylon or both processed films After the winding, the back side has a strong affinity for contact with the ink layer, and the blocking resistance is poor. Therefore, the corona treatment method, single-sided processing, and slow printing speed should be adjusted during printing. After printing, it must be cooled sufficiently by a chill roll and then wound up.
(5) Anti-stick test method
The anti-adhesion test of gravure printing is carried out in accordance with the provisions of GB/T13217.8-2009 "Intaglio plastic ink inspection method - anti-blocking test".
1) Principle: The obtained ink film is printed in a folded time within a specified time, and under a certain temperature and pressure, after a certain period of time, the adhesion of the print is observed.
2) Test conditions: The test should be carried out at (50 ± 1) °C.
3) Inspection step: 1 by printing the ink on the printing substrate, or by using a wire rod to print on the printing substrate; 2 placing the sample for 2 minutes (if the printing film is printed with water-based ink, It needs to be dried in a baking oven at 59~61 °C for 5 min, taken out and then cooled. It is folded between two glasses with the upper and lower rounds. It is placed in a baking box at 49~51 °C and pressed with 2000 g. The code is placed for 2h; 3 is taken out, and the folded portion is opened, depending on its adhesion.
4) Test results: Cover the pressed portion with a translucent milligram paper having a width of 20 mm. The number of cells occupied by the ink layer and the number of cells occupied by the removed ink layer are respectively counted. Calculated as follows
B(%)=B1/(B1+B2)×100
B in the formula - the degree of ink adhesion
B1 - the number of cells in the ink layer
B2 - the number of cells of the ink layer that has been removed