In the daily chemical label self-adhesive market, although the market share of paper labels is as high as 75%, in recent years, the heat transfer film labels also show a high growth trend. For heat transfer film materials, good printability is absolutely necessary, but the commonly used PE and PP films can not meet the requirements. In order to ensure that there are few problems or no problems in the printing process of this kind of label materials, it is very important to change the film surface properties.
There are many methods that can be used to modify the surface of thin films, including corona pretreatment, plasma pretreatment, flame pretreatment, chemical pretreatment/fluorination and coating pretreatment. Among them, corona pretreatment and coating pretreatment are the most commonly used surface treatment methods in printing industry.
Corona pretreatment is realized by high frequency and high voltage discharge of electrodes. After corona pretreatment, the surface energy of PP film can be increased to nearly 50mN/m, but this effect is short, because the following processes counteract the effect of corona pretreatment: polar functional groups rotate inward in plastic film polymer; The functional groups react and lose polarity; Additives in the film migrate to the surface and cover polar functional groups. The longer the film material is stored, the more serious this situation is, so corona pretreatment must be carried out again before printing.
The effect of corona pretreatment will be different with different materials of heat transfer film. In addition, the additives in the film and the aging of the material will also have a certain impact on the corona treatment effect. That is to say, when corona treating aging films containing more additives (such as lubricants), it will be difficult to obtain sufficiently high surface energy due to the barrier of additives migrating to the film surface.