Commonly used plastic films are polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polyester film (PET), polypropylene (PP), nylon and so on. The properties of various plastic films are different, the difficulty of printing is also different, and the use as packaging materials is also different.
Polyethylene film is a colorless, odorless, odorless, translucent and non-toxic insulating material, which is used in large quantities as packaging bags; food bags, and can also be used to make various containers. It is an inert material, so it is more difficult to print, and it must be processed to print better results.
The polyvinyl chloride film has good light resistance and aging resistance, and has good tear resistance. It is breathable. It is a clean, colorless, and transparent film. Generally, plasticizers are added. It is soluble in acetone. Solvents such as cyclohexanone. Therefore, it can be printed with an ink made of polyvinyl chloride resin. Suitable for packaging bags, book covers, etc.
Polystyrene film is a soft and tough film, clean, colorless and transparent. When it does not contain plasticizers, the film is always soft, resistant to freezing, and does not age when stored. When printing, it uses oxidative polymerization synthetic binder ink to make The imprinting fastness is better.
Polyester film is colorless, transparent, moisture-resistant, airtight, soft, strong, resistant to acids, alkalis, oils, esters and solvents, and is not afraid of high and low temperatures. After electric spark treatment, it has relatively good surface fastness to ink . Used in packaging and composite materials.
Polypropylene film has good gloss and good transparency, heat-resistant acid and alkali, solvent-resistant, friction-resistant, tear-resistant, breathable, and cannot be heat-sealed below 160°C.
Nylon film is stronger than polyethylene film. It is odorless, non-toxic, impervious to bacteria, oil-resistant, ester-resistant, boiling water and most solvents. It is generally used for load-bearing and wear-resistant packaging, as well as cooking packaging (reheating of food) , It can be printed without surface treatment.
There is basically no polar group on the polyethylene molecule, which is a kind of non-polar imprint. In the polypropylene molecule, each structural unit contains a methyl group, which is a weak polar group, basically They are also non-polar polymers. Therefore, they have poor affinity for inks. Therefore, they must be processed before printing to obtain satisfactory prints.
The treatment method is mostly through oxidation to increase the polarity and change the surface structure. Specific treatment methods include discharge (commonly known as corona, electric spark) method, flame method, ultraviolet radiation method, acid (sulfuric acid, chromic acid) treatment method, etc. The discharge method is relatively simple and popular.
