Popular Science: Anti-sticking knowledge of flexible packaging is here!

Adhesion refers to a phenomenon of adhesion between plastic film contact layers. There are two kinds of sticking phenomenon: One is that the printing surfaces stick to each other. The second is that the ink layer of the printed matter adheres to another contact surface, or the ink adheres to the other contact surface.

The first phenomenon manifests itself in that the films are stuck to each other, the bag mouth is difficult to open, and the user refuses to use it. Adding slip agent, opening agent and other measures to the resin can effectively prevent internal sticking.

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 printed patterns due to ink peeling and pollutes the contact surface. In severe cases, the films cannot be torn apart and cannot be used, resulting in product scrapping. Therefore, how to control and improve the ink's anti-sticking in the gravure printing process is extremely important.

(1) Anti-blocking product characteristics

Anti-blocking products should have the following characteristics: â‘  The material roll is unwinding smoothly, and the machine performance is good to adapt to the production of high-speed packaging; â‘¡ The surface is smooth and the packaging opening is good.

(2) Selection of base materials for anti-blocking products

In the gravure printing process, "blocking" is related to a series of factors such as substrate slip, ink adhesion, solvent volatilization speed, operating environment, printing drying conditions, and printing speed. The choice of 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 select the ink, solvent and printing process parameters that match the substrate.

(3) Special technical indicators

In gravure printing, the anti-blocking properties of printed products are mainly improved by improving the anti-blocking properties of ink. Therefore, the anti-blocking requirements must be based on factors such as the type of binder resin in the ink, the amount of residual solvent, printing equipment parameters, etc., through the design of materials and performance to achieve the anti-blocking requirements to be achieved.

(4) Specific printing process

Taking the anti-blocking printed matter as an example, you should pay attention to the following items when designing the printing process: â‘  inks made of high-softening point connecting material resin should be selected to help prevent blocking. Correspondingly, the solubility and release of the solvent to the resin are better; â‘¡Ensure that the printing ink layer is sufficiently dry to control the residual of the solvent to reduce the possibility of adhesion between printed products; After winding, the back surface has strong affinity with the ink layer and poor blocking resistance. Therefore, the corona treatment method, single-sided treatment, and slow printing speed should be adjusted during printing. After printing, it must be fully cooled by the cooling roller before rewinding.

(5) Anti-sticking test method

The anti-blocking test of the gravure printed matter shall be conducted in accordance with the provisions of GB / T13217.8-2009 "Testing Methods for Gravure Plastic Ink-Anti-blocking Test".

1) Principle: Fold the ink film imprint in half contact within a specified time, and observe the adhesion of the imprint after a certain time under a certain temperature and pressure.

2) Inspection conditions: The inspection should be carried out at (50 ± 1) ℃.

3) Inspection steps: ①Sample is prepared by printing ink on the printing substrate, or using a wire rod to print on the printing substrate; ②After placing the printing 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 ℃ for 5 minutes, and then cooled after being taken out), relatively folded between the upper and lower round glass, placed in a baking oven at 49 ~ 51 ℃, and pressed with a 2000g weight Place the code for 2h; ③ Take it out and open the folded part, depending on its adhesion.

4) Test result: cover the pressed part with translucent millimeter paper with a width of 20mm. Count the number of grids occupied by the ink layer and the number of grids occupied by the stripped ink layer, respectively. Calculate by

B （％） = B1 / (B1 + B2) × 100

In the formula B-the degree of ink adhesion

B1——The number of ink layers

B2-the number of ink layers removed