Film coating, also known as laminating, is the processing technique of applying adhesive to plastic film and bonding it to paper printed products through heating and pressure, forming a paper plastic composite product. The printed products produced by the laminating machine have a thin and transparent plastic film on the surface, which makes the surface smoother and brighter, thereby improving the glossiness and fastness of the printed products. The graphic and text colors are more vivid, giving a sense of three dimensionality, and also playing a role in waterproofing, stain resistance, wear resistance, folding resistance, chemical corrosion resistance, etc.

With the development of printing technology, there are increasingly more methods for laminating. There are three types of film coating processes: dry, wet, and oily. According to the different raw materials and equipment selected, it can be divided into instant coating film and pre coating film processes. Let’s briefly introduce the basic concepts and characteristics of these methods below.
1. Apply instant film coating
During the operation of the instant film coating process, adhesive is first applied to the film, and then hot pressed, but the production process is prone to fire.

2. Pre coated film
This process greatly simplifies the laminating process because the laminating equipment does not require a heating and drying system for adhesives, and the operation is very convenient. It can be used and started at any time, with high production flexibility, no solvent odor, no environmental pollution, and more importantly, it can completely avoid faults such as bubbles and delamination. Its product has extremely high transparency, broad prospects for use, and practical value.
The pre coating structure consists of a substrate and a glue layer. The substrate is usually PET and BOPP film. Considering material cost and processing technology, the vast majority of pre coating substrates use BOPP film with a thickness of 12-20 microns and a glue layer thickness of 5-15 microns. According to different processing equipment and process conditions, different thicknesses of adhesive layers are selected, which are divided into hot melt adhesive and organic polymer low-temperature resin. The difference between the two is that hot melt adhesive is made by blending and modifying several materials, including main adhesive resin, tackifiers, and adjusters, while organic polymer resin is a single low-temperature polymer copolymer.
Due to limitations in skills, production equipment, and raw materials, pre coated films produced by domestic equipment (mostly hot-melt adhesives) still have quality defects. Because there is a production process that relies on a process similar to instant film coating, where the colloid is dissolved in organic solvents and the rubber roller is coated onto the substrate film using a concave mesh roller, there may be insufficient solvent evaporation, odor during operation and use, solvent evaporation after film coating, and easy foaming on the surface. Meanwhile, due to the blending of several polymer materials in hot melt adhesive, poor temperature control during use can cause degradation and cross-linking of the polymer inside the hot melt adhesive, resulting in poor coating appearance. Some pre coated colloids are prone to sticking to the surface of the substrate, resulting in poor coiling. Due to the thin adhesive layer and lack of activation treatment on the surface, defects such as insufficient adhesion to printed materials are prone to occur. Because hot melt adhesive is made by mixing several materials, its transparency after coating is significantly lower than that of low-temperature pure resin pre coating.

3. Water based film coating
It is a method of processing the appearance of printed materials to improve their glossiness, strength, and enhance their aesthetic appeal. To measure the quality of film coating, it is also necessary to consider its brightness, strength, adhesion, etc. Water based wet laminating is highly favored by customers for its high strength, easy retrieval, and pollution-free properties in laminated printed products.

4. Curved surface coating film
It is a new transfer printing skill that can handle complex shaped workpieces and is suitable for different raw materials. It greatly increases the added value of products due to vivid patterns and colors. This skill is achieved by using a specially chemically treated film, which is printed with a certain color pattern and then placed flat on the surface of water. Using water pressure, the pattern is evenly written on the surface of the product, while the coating film automatically dissolves. After cleaning and drying, a layer of clear protective coating is applied, and the product presents a completely different visual effect.
The laminating process can be divided into cold (cold pressed) laminating, hot (hot activated) laminating, and liquid laminating methods according to the temperature, pressure conditions, and materials.