4. Label application
In-mold label technology actually consists of raw materials printing and processing technology and label application technology. The latter refers to the technology of adhering the label to the bottle through blow molding (or injection molding). Label application technology is much more important than printing and processing technology. Perfect as the label is, inferior application can turn it into a waste product. During recent years, inferior label application has resulted in tremendous waste and many complaints, and many printing presses have been obliged to give up in-mold label business. Those persisting in this business are being tortured by the lingering worries of being informed of the existence of defective products among the finished labels.
In-mold label application is a new technology in its exploration stage. There exists no systematic theory or practice summarization, and even no book or literature is available. Every bottle blowing mill is acting on the basis of their own habit and experience. Therefore, in case of a change in bottle shape or raw materials type, inferior label application quality often arises, including slanting, bubbling, winkling, local shrinkage, surface discoloration, malfunction of the adhesive, etc. Adjustment must be carried out repeatedly to eliminate these problems.
For these reasons, usually bottle blowing mills will not change their label supplier or try new materials. Therefore, those printing presses and other raw materials suppliers which want to initialize in-mold label projects will face a difficult situation. As a final result, the whole industry may be confined to a limited scope, insulated and less competitive.
In fact, in-mold label application technology has a considerable tolerance. During blow forming (injection forming), many parameters of the equipment are adjustable. Reasonable adjustment will eliminate faults and adapt the equipment to different raw materials. Several years ago, on an plastics printing equipment exhibition, Hong Kong Yaqi Co., Ltd. delivered an on-the-spot presentation of the in-mold label bottle forming process. Three kinds of in-mold label raw materials have been used in sequence to manufacture labels. During the transition from one material to the following one, the label on the surface of the bottle indicated some problems, to an extent more or less. However, after the operator' s adjustment, the fault was soon eliminated. Finally, 3 kinds of raw materials all brought about qualified in-mold label bottles.
Currently, there exist 3 major kinds of in-mold raw materials in the market, that is, PE, PP and PE+PP. These materials differ in such indicators as density, stiffness, resin content in the adhesive, melting point, thickness, etc. To make full use of these materials, one needs to adjust relevant parameters of the bottle blowing equipment, including mat temperature, bottle blowing time, bottle blowing pressure, cooling time, mold temperature, etc.
Conclusion
On the whole, the application of in-mold label is undergoing a difficult period. It may take a long time to wait for new opportunities, and current technology should be assimilated and innovated by the relevant industries. The difficulties have brought down the growth rate; however, development is an eternal truth. The whole in-mold label industry chain, including raw materials suppliers, label printing mills, bottle blowing mills using labels, and even terminal users, should do their best to overcome all the adverse factors existing in the preliminary stage, and ultimately realize the rapid development of the in-mold label in our country.
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