Printing compound process
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1. Corona treatment of plastic film surface:
The surface corona treatment of the substrate PE, PP, and even aluminum foil must be carried out before printing and compounding. The purpose is to improve the printing composite firmness to achieve the desired effect and ensure the critical surface tension during printing and compounding. More than 38 millinewtons/meter; for composite films used for cooking, the inner substrate thickness should be greater than 70μ to ensure adequate heat seal strength.
2, composite process:
The composite film can improve various properties of a single film and can improve the protection of the contents, including moisture resistance, oil repellency, barrier property, light blocking property and air tightness. According to different substrates and different uses, the processing methods of composite films can be roughly divided into the following five categories:
A, dry composite method
This method is a method in which a binder is applied to a surface of a substrate by a laminating machine and laminated by a heat roller to be attached to another film. This method can be applied to almost all substrates, and many layers can be compounded, and has been widely used in various fields of packaging materials. The equipment cost is cheaper than the extrusion compound machine. Recently, the packaging function is more stringent due to the retort treatment and boiling sterilization, and the adhesive is often made of a polyurethane series having excellent adhesion. In addition, in the dry compounding method, the residual solvent causes dangerous problems such as pollution, fire, explosion, etc. In order to solve such problems, a composite system of different organic solvents should be developed, which has the following advantages:
· No solvent, reduce environmental pollution.
· No fire or explosion hazard.
· No solvent drying process is required to save energy and equipment footprint.
• No solvent etches the printing ink.
· No need to recycle solvent plant investment.
· Reduced costs due to increased production speed.
B, wet composite method
The method is mainly used for the composite of aluminum foil and porous materials such as paper, sheet paper and ordinary cellophane. A water-soluble binder (gelatin, starch), a water-dispersible binder (vinyl acetate latex, etc.) is applied to the surface of the substrate in a wet state to be composited with other materials, and then pressed and dried by a roll. This method is simple to operate and can be compounded with a small amount of adhesive. The extremely thin aluminum foil (5~6μ) can also be compounded. Compared with other composite methods, it is fast and can be processed in a large amount, and the processing cost is very low. It does not use organic solvents, it is very safe, there is no residual solvent, and the market centered on paper-based materials is relatively stable.
C, extrusion compounding method
This is the most common method used in composite processing. Extrusion machine is used to extrude PP, PE, EVA (ethylene-vinyl acetate copolymer) ionic resin into a film, and is coated with a processing agent (polyethyleneimine, Various films of polyurethane resin, etc. are compounded, cooled and solidified. This method saves labor due to the use of an adhesive resin (maleic anhydride-modified olefin-based resin, block-modified olefin resin such as maleic anhydride, etc.). Therefore, it is possible to reduce the cost of the process without using an adhesive.
D, hot melt compounding method
The method is to mix rosin, xylene resin, styrene resin, etc. in a base resin such as EVA (ethylene-vinyl acetate copolymer), EEA (ethylene-ethyl acrylate copolymer), PE, or butyl rubber. A hot melt agent such as an adhesive and a paraffin-based adhesive lowering agent is applied to a film, a paper surface, or an aluminum foil surface, and is immediately compounded on another substrate to be cooled.
It is mainly used for producing cover materials for various containers, and is required to have retort resistance. The adhesive is mixed in a base resin such as EVA, and extrusion coating is applied to the substrate to improve heat resistance.
E, coextrusion compounding method
The method is a two-layer or more film obtained by simultaneous molding of two or three extruders, and has a T-die method and a blow molding method, and can perform various kinds of compounding to produce an ultra-thin film. Japan's annual output is nearly 10,000 tons, and more than a quarter of the US composite film is coextruded. Representative membranes are: PE/PVDC/PE, PE/PP/PE, PP/PE/PVA, PE/EVA, N/PE, etc.
This method has no problem in the same kind of resin bonding, but it cannot be bonded to nylon or EVAL by polyolefin. It can be made by using modified polyolefin with ionic resin-maleic anhydride. Good composite film. These coextruded films have an absolute advantage in the field of food packaging and have a high market share.