1, corona treatment of plastic film surface:
Before the printing and compounding, surface corona treatment must be performed on the substrate PE, PP, and even aluminum foil. The purpose is to improve the printing composite fastness so that it can achieve the desired effect and ensure the critical surface tension during printing and compounding. Greater than 38 millinewtons/meter; for composite films used for cooking, the thickness of the inner substrate should be greater than 70Î¼ to ensure adequate heat seal strength.
2, composite process:
The composite film can improve various characteristics of a single film and can improve the protection of the contents, including moisture resistance, oil resistance, barrier properties, light-shielding properties, and airtightness. According to different substrates and different uses, the composite film processing methods can be roughly divided into the following five categories:
A. Dry compound method
In this method, the adhesive is applied to the surface of the substrate through a laminator, and the heat roller is pressed against the other film to form a composite. This method can be applied to almost any substrate, how many layers can be compounded, and has been widely used in various fields of packaging materials. Its equipment cost is cheaper than extrusion machine. Recently, retort treatment and boiling sterilization have imposed more stringent requirements on the functional requirements of the packaging. Polyurethanes with excellent adhesiveness are used in many adhesives. In addition, the residual solvents in the dry composite method lead to hazards such as hazards, fires, and explosions. In order to solve such problems, a composite system of different organic solvents should be developed, which has the following advantages:
Â· No solvent, reduce environmental pollution.
â€¢ No risk of fire and explosion.
â€¢ No solvent drying process is needed to save energy and equipment footprint.
â€¢ There is no solvent for the printing ink.
â€¢ No need to recycle solvent plant investment.
â€¢ Lower costs due to higher production speeds.
B. Wet compound method
This method is mainly used for the compounding of porous materials such as aluminum foil and paper, sheet paper, and ordinary glass paper. A water-soluble binder (gelatin, starch), a water-dispersible binder (vinyl acetate latex, etc.) is applied to the surface of the base material in a wet state and is compounded with other materials, and then roll-bonded and dried. This method is easy to handle and can be compounded with a small amount of adhesive. The extremely thin aluminum foil (5-6Î¼) can also be compounded. Compared with other compounding methods, it is fast and can be processed in a large amount. The processing cost is very low. Without organic solvents, the safety is very good, there is no residual solvent, and the market centered on paper-based materials is relatively stable.
C, extrusion composite method
This is the most common method used in composite processing. Extrusion of PP, PE, EVA (ethylene-vinyl acetate copolymer) ionic resin, etc. into films is performed using an extruder, and a process agent (polyethylene imine, Polyurethane-based resins, etc., are compounded on various films, cooled and cured. This method saves labor because of the use of an adhesive resin (maleic anhydride-modified olefin-based resin, maleic anhydride and other block-modified olefin resins). Therefore, no adhesive can be used, and the process can be reduced to reduce the cost.
D, hot melt composite method
The method is to mix rosin, xylene resin, styrene resin, etc. in base material resins such as EVA (ethylene-vinyl acetate copolymer), EEA (ethylene-ethyl acrylate copolymer), PE, and butyl rubber that are heated and melted. Hot-melt adhesives such as adhesives and wax-based adhesive base-reducing agents are applied to the surface of the film, paper, and aluminum foil, and are immediately compounded and cooled on other substrates.
It is mainly used to produce cover materials for various containers, and it is required to be resistant to retort. Adhesives are mixed in EVA and other base materials, and extrusion coating is used as a base material to improve heat resistance.
E, co-extrusion compound method
The method consists of two or three extruders simultaneously forming and processing two or more layers of film. There are T-die method and blow molding method, which can perform a variety of composites and can produce ultra-thin films. Japan's annual production reaches nearly 10,000 tons, while over a quarter of US composite membranes are co-extruded membranes. Representative membranes are: PE/PVDC/PE, PE/PP/PE, PP/PE/PVA, PE/EVA, N/PE, etc.
This method has no problem in the adhesion of the same kind of resin, but it cannot be bonded to nylon or eval by polyolefin, and the adhesive can be prepared by using a modified polyolefin having an ionic resin, maleic anhydride Good composite film. These co-extruded films have an absolute advantage in the field of food packaging and have a high market share.
Reproduced from: Wins
Yixing Linchang Technology Co., Ltd. , http://www.kamado-link.com