What is the basic structure and function of self-adhesive materials?
Pressure-sensitive adhesive mainly consists of surface coating, facestock, undercoat, adhesive, release coating, liner paper, and back coating or back printing.
(1) Surface coating
It is used to change the surface properties of surface material, such as improving the surface tension, changing the color, and increasing the protective layer, so that it can better accept ink and easier to print. And it achieves the purpose of preventing dirt, increasing ink adhesion and preventing printed graphics from falling off. Surface coating is mainly used for non-absorbent materials, such as aluminum foil, aluminized paper and various film materials.
Adhesive is the medium between label material and bonded substrate, playing a bonding role. According to its characteristics, it can be divided into two types: permanent and removable. It has a variety of formulations, suitable for different facestocks and occasions. Adhesive is the most important component in the technology of self-adhesive materials and the key to the application of label technology.
(3) Release coating (Silicon coating)
That is to coat silicon oil layer on the surface of the liner paper. Silicone oil coating can make the liner paper a very smooth surface with low surface tension. Its function is to prevent the adhesive from sticking to the liner paper.
(4) Liner paper
The function of the liner paper is to accept the coating of release agent, protect the adhesive on the back of the surface material, and support the surface material so that it can be die-cut, discharged and labeled on the labeling machine.
This refers to surface material. It is the material that receives printed graphic on the front and adhesives on the back, and eventually be applied to the objects to be pasted. Generally speaking, all flexible deformable materials can be used as the facestock of self-adhesive materials, such as commonly used paper, film, composite foil, all kinds of textiles, thin metal sheets and rubber, etc. The types of facestock depend on the final application and printing process. It should be able to adapt to printing and stamping, have good inking property, and have enough strength to accept various processing, such as die cutting, waste discharge, vertical cutting, punching and labeling.
(6) Back coating or back printing
Back coating is a protective coating on the back of the liner paper to prevent the adhesive around the label from sticking to the liner paper after discharging and rewinding; another function is to make multi-layer labels. The function of back printing is to print the registered trademark or pattern of the manufacturer on the back of the liner paper, which plays the role of propaganda and anti-counterfeiting.
It is the same as the surface coating, but it is applied to the back of the facestock. The main purpose of undercoat is:
To protect facestock from the penetration of adhesives;
To increase the opacity of surface;
To increase the cohesion between adhesives and facestocks;
To prevent plasticizers in plastic facestock from penetrating into the adhesives, which will affect the properties of the adhesives, resulting in the decrease of the bonding force of the labels and the drop of them.