The kraft paper valve pocket is generally composed of three layers of kraft paper and plastic film with moisture-proof effect. Almost all of the outer layers are imported paper, yellow or white, and other colors of kraft paper such as carbon black kraft paper bags are dyed on the dyeing machine.
The inner layer of kraft paper valve pockets is often made of domestic yellow kraft paper. Of course, imported yellow kraft paper is also used in some valve pockets with high requirements. The sandwich plastic film has moisture-proof effect. In addition, it can also be sprayed with a layer of film on the inner kraft paper, that is, the film is covered on the kraft paper, and it can also play a moisture-proof effect. In order to breathe during filling, sometimes a row of holes should be punched on the surface of kraft paper valve pocket to improve filling speed, otherwise the gas can not be discharged quickly with the material entering, which will affect filling speed.
There are two ways to make the pocket valve port of kraft paper valve: inward-facing and outward-facing. The material of imported kraft paper is chosen. Generally, outward-facing valve port is more used, and outward-facing valve port is better sealed. The printing method of kraft paper valve pockets is offset printing basically, and some of the layout design is relatively simple, then the whole volume of relief printing can be color printing. Kraft paper valve pockets belong to high-grade packaging, which is more common abroad. Now they are gradually popularized in China. There are many processing procedures for square bottom valve pockets, and the price is also higher than that of ordinary open pockets.