Composite process of the hottest printing

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Composite process method of printing

release date: Source: China paper

in the packaging and printing industry, this is one of the largest integrated robots in history, and a variety of printing processes are often used. Today, China paper industry takes you into compliance process and introduces the relevant contents in detail

1. Corona treatment of plastic film surface:

before printing and compounding, the substrate PE, PP, and even aluminum foil must be corona treated. The purpose is to improve the firmness of printing and compounding, make it achieve the desired effect, and ensure that the critical surface tension during printing and compounding is greater than 38 Mn/M; For the composite film used for cooking, the thickness of the inner substrate should be greater than 70 μ, To ensure sufficient heat sealing strength

2. Composite process:

composite film can improve various characteristics of a single film and improve the protection of internal contents, including moisture resistance, oil resistance, barrier, shading 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 compounding method

this method is a way of coating adhesive on the surface of substrates through a compounding machine, and compounding by heating, rolling and attaching it to other films. This method can be applied to almost all substrates, and can be compounded in any number of layers. It has been widely used in all fields of packaging materials. The equipment cost is cheaper than that of the extruder. Recently, due to cooking treatment and boiling sterilization, the packaging function requirements are more stringent, and the adhesives are mostly polyurethane series with excellent adhesion. In addition, the residual solvent in the dry compounding method leads to hazardous problems such as public hazard, fire, explosion, etc. in order to solve these problems, a compounding system of different organic solvents should be developed, which has the following advantages:

· solvent free, reducing environmental pollution

· no danger of fire and explosion

· no solvent drying process is required, which can save energy and equipment area

· no solvent erosion of printing ink

· there is no need to recover the solvent unit investment

· cost reduction due to increased production speed

b, wet compounding method

this method is mainly used for compounding aluminum foil and porous materials such as paper, sheet paper and ordinary cellophane. Water soluble adhesives (gelatin, starch) and water dispersible adhesives (vinyl acetate latex, etc.) are coated on the surface of the substrate and compounded with other materials in a wet state, and then rolled and dried. This method is simple to operate, and it can be compounded with a small amount of adhesive. Aluminum foil with extremely thin thickness (5-6 μ) It can also be compounded. Compared with other compounding methods, it is fast and can be processed in a large number. The processing cost is very low. There is no organic solvent. It has good safety. There is no residual solvent. The market centered on paper-based materials is relatively stable

c, extrusion compounding method

this is the most commonly used method in composite processing. PP, PE, EVA (ethylene vinyl acetate copolymer) ionic resin and other resins are extruded into thin films by extruder, coated and adhered to various films mixed with processing agents (polyethyleneimine, polyurethane resin, etc.) for compounding, and then cooled and cured. This method saves labor due to the use of adhesive resins (maleic anhydride modified olefin resins, maleic anhydride and other block modified olefin resins). Therefore, no adhesive can be used, and the process can be reduced to achieve the purpose of reducing costs

d, hot melt compounding method

this method is to mix rosin, xylene resin and benzene into heated molten EVA (ethylene vinyl acetate copolymer), EEA (ethylene ethyl acrylate copolymer), PE, butyl rubber and other base resins, and the testing equipment required by the textile industry: the hot-melt agent of adhesive such as ethylene resin and adhesive base reducing agent such as paraffin is coated on the surface of film, paper and aluminum foil, A method of immediately compounding and cooling on other substrates

it is mainly used to produce the cover materials of various containers, and it is required to have cooking resistance. Mixing adhesive in EVA and other base resin, and extruding it as the base material for coating can improve the heat resistance

e, coextrusion compounding method

this method is formed and processed by two or three extruders at the same time to obtain two layers of films that have experienced more than three 10-year development stages, including the planned R & D reserve period, the scope industry period and the integration expansion period. There are T-die method and blow molding method. In some fields and even at the world advanced level, it can carry out a variety of compounding and produce ultra-thin films. The annual output of Japan is nearly 10000 tons, while more than a quarter of the composite membranes in the United States are coextruded membranes. Representative films include PE/PVDC/PE, PE/PP/PE, PP/PE/PVA, PE/EVA, N/PE, etc

although this method has no problem in the bonding of the same kind of resin, it cannot bond nylon or Eval with polyolefin. A composite membrane with good bonding can be prepared by using modified polyolefin with ionic resin maleic anhydride palace group. These coextruded films have absolute advantages in the field of food packaging and have a high market share

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