Influence of environmental temperature and humidity on plastic flexible packaging printing composite

by:Nanxin Print & Packaging     2020-03-04
The influence of temperature and humidity on composite flexible packaging

Summer has arrived, and high temperature and humidity weather has also followed. Since summer, the temperature and humidity of the environment have increased significantly, and there are many quality problems in film printing and composite processing. So, when high temperature and high humidity weather, composite flexible packaging enterprises should pay attention to what?

The influence of temperature and humidity on printing:

1. Influence on printing effect: under the condition of high temperature and humidity in summer, during plastic intaglio printing, due to the volatilization of solvent, the condensation of water vapor in the surrounding air makes the surface of the printing ink film form fog. Due to the short printing oven and fast printing speed, the ink layer loses its luster and the overall printing effect is foggy.

2. Influence overprinting: it mainly affects paper and NY Film. Paper is composed of plant fibers, which are porous and hydrophilic and very sensitive to water. The temperature and humidity of the environment change slightly, and the water content of the paper will change. The influence of air relative humidity on paper water content is generally the increase of relative humidity and paper water content. The change of paper water content will cause the paper to expand and contract (Including local deformation) When printing multi-color overprint products, the water content of the paper decreases and the horizontal size shrinks every time it passes through an oven unit. When this shrinkage is relatively large, the overprint of the product will be inaccurate. However, if the water content is too low, the paper will become brittle, hard and easy to tear, and static electricity and material breakage will easily occur during printing. Especially in the north, the humidity changes greatly in winter and summer, and this influence is more obvious. Therefore, paper printing needs to control the water content of the paper.

BOPA film is made of polyamide 6 (Nylon 6)Made for raw materials. Polyamide molecules contain polar amide groups (-CO-NH-) The amide group in the polyamide molecular chain can coordinate with the water molecule, so the nylon membrane has strong water absorption. However, after nylon absorbs water, the size will change and overprint will always be affected.

3, printing knife line, floating dirty and other problems: humidity is too large, ink dispersion becomes worse, the affinity between ink and plate roller increases, the plate is not easy to scrape clean; However, if the humidity is too small, both of them will cause knife lines because of electrostatic adsorption of dust.

4. Anti-sticking phenomenon: 'Anti-sticking '(Back sticky, back sticky) It refers to the phenomenon that the printing layer adheres to the back of the film or the printing layer adheres to each other in the process of compounding or bag making after the plastic film is printed and rolled. 'Anti-sticking' phenomenon is easy to occur in high temperature, especially in high humidity environment. Due to the high temperature in summer and the high viscosity of ink, it is easy to cause high residual solvent or 'false dry' phenomenon. In addition, too much humidity increases the acting force of ink and non-printing surface to a certain extent.

Therefore, the control of temperature and humidity is very critical for the printing process. To ensure good printing effect, the temperature is usually controlled at room temperature 20- 25 degrees is appropriate, humidity control at about 40%, which is conducive to the true reproduction of color and reduce the appearance of quality defects. Some large-scale and standardized enterprises will definitely control the environment of the printing workshop. In summer, central air conditioning is used to control the temperature and humidity of the environment, and humidifier is used for humidification in winter.

However, due to the conditions of the workshop, some manufacturers have limited ability to adjust the temperature and humidity. At this time, we need to adjust our own technology in time to reduce the occurrence of quality problems.

The influence of temperature and humidity on the composite

The influence of environmental temperature and humidity on the composite is mainly in the environment of adhesive, high temperature and high humidity, and the condensation phenomenon will occur at the network roller and the rubber roller, this will increase the tension of the adhesive and affect the leveling of the glue; Under the environment of high temperature, the reaction speed of the glue will be accelerated, and the reaction speed of the water and the curing agent will be faster, which will cause the viscosity of the glue to rise quickly, causing the adhesive to become turbid and white, greatly affecting the coating effect, thereby appearing spots, bubbles and other phenomena. In addition, moisture will consume the curing agent in the adhesive, which will never cause incomplete curing and will never affect the peel strength and the temperature resistance of the adhesive

. What are the countermeasures for the compound process of high temperature and high humidity?

1, high temperature and high humidity season with glue, must be done with less frequently, it is best to use up within two hours. At the same time according to product curing situation appropriate increase curing agent (5-About 10%).

2. For materials that are easy to absorb moisture and oxidize, such as NY, EVOH, AL and other surplus materials, wrap the film with aluminum foil or aluminum-plated composite film and place it in a wooden frame or other dry environment.

3. Because it is relatively difficult to control the influence of water in the environment, the amount of water and alcohol in the solvent ethyl acetate used is strictly controlled.

4. Check whether there are water drops on the guide roller and the composite roller, and wipe them with a dry towel.

5. Properly isolate and protect the coating unit to reduce air circulation and never reduce the volatilization of ethyl ester in the rubber tank. In addition, the rubber barrel must be covered.

6. The trough is heated to provide the heat required for the volatilization of ethyl ester. Due to the increase of the trough and roller temperature, the condensation of water vapor is reduced.

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