As the society's demand for plastic flexible packaging increases year by year, plastic flexible packaging is covering the market due to its inherently colorful, novel patterns, and convenient use. Generally, the printing methods are divided into relief printing, gravure printing, offset printing, screen printing and so on. Plastic printing is gravure printing. The commonly mentioned gravure printing machine refers to the unit type (or arrangement type) gravure printing machine.
1 printing machine
The printing speed of the plastic flexible packaging printing unit is determined by the length of the paper distance between the printing color groups of the printing machine and the effect of the drying box. The longer the distance of each color and the better the effect of the oven, the faster the printing speed, otherwise the printing speed will not be up.
In addition to requiring the synchronization of the front and rear parts of the printing machine, the precision of the printing plate of the printing press also requires the stability of the tension control system of each part to be stable. You can run the version to maintain the accuracy of the register.
2 plates
The production of gravure printing plate is divided into two types: corrosion (manual version) and electric engraving (electric engraved version). At present, the price of manual version is low, but the printing effect is still good, especially the layered version. It has been found in practice that electro-engraving plates have higher requirements on inks. The quality of the printing plate production directly affects the quality of the printing effect.
3 ink
Plastic flexible packaging gravure ink is divided into solvent ink and water-based ink.
Solvent ink is divided into surface printing ink and inside printing ink (composite ink).
Surface printing plastic gravure ink: the surface is smooth and shiny, compared with the Indian ink, it is resistant to friction and smell. One-component glue should be used in laminating process, which has poor combination with two-component glue, and the amount of glue should not be too large. Surface printing ink is divided into ordinary ink, water-resistant ink (drink packaging ink), label ink (calendar ink), transparent ink, etc. Water-resistant ink is mainly used for printing on milk packaging, beverage packaging and frozen food packaging products; label ink is very smooth, anti-blocking, scratch-resistant, is the best ink for printing various labels; transparent ink is used for printing Special ink for aluminum foil and aluminum foil.
The characteristics of the inner printing ink (composite ink) are bright color, odorless printing, and high peeling strength, but the conjunctiva is soft and not abrasion-resistant. Observing the printed matter is matt, which is conducive to laminating processing. If using glue-coated dry compound, it is advisable to use two-component glue, the main purpose is to increase the firmness of the compound, and its odor is small. However, when compounding with a single-component glue, the ink on the printed matter is often dissolved or the finished product will bring a harmful smell of the glue, and the compound has a poor firmness (note that alcoholic solvents are not allowed to be added).
In addition, there are ordinary compound inks in the Indian ink, which is the ink printing of OPP film (polypropylene film). When printing PET film (polyester film), polyester ink should be used, and its printing pattern is firmer, and there will be no blocking phenomenon. In short, what type of special ink is used on what film is the principle of plastic gravure ink.
Water-based inks are usually used for printing paper products including paper-plastic composite products. Its characteristic is that it can meet the ink absorption of paper printing, making the prints full-color, and the rare thing is that its solvent is water and ethanol, which has little environmental pollution and is known as the green ink for environmental protection.
4 compound
Compounding of plastic flexible packaging, laminating film extrusion compounding, dry glue compounding and glue-free hot pressing compounding, etc. Extrusion compounding means that PE or PP material is melted and extruded into a film, and then hot-pressed compounded on the printed film to form a composite product. It is characterized by low cost and reduced glue pollution. However, it is better to select the extrusion materials and control the extrusion temperature, and add a small amount of glue or AC agent as a coupling agent between the film formation.
The length of the drying tunnel, heating method, gluing method, gluing amount control, tension control of the unwinding and unwinding, temperature control of the hot drum and the availability of cooling and shaping devices make up its price and grade.
During the compounding process, the user should first understand that if the glue is to be uniform, the glue must be diluted, and if the viscosity of the glue is to be restored, the solvent on the paint must be volatilized (that is, the concentration process), so the upper surface of the compound The amount of glue is the key to compound processing. Special attention should be paid to reducing the amount of glue when compounding. So it is recommended not to use it in food packaging.
Since the one-component glue is used with surface printing inks, the smell is difficult to eliminate, so it is recommended not to use it in food packaging. Special attention should be paid to reducing the amount of glue when compounding. If you use a two-component glue compound, in addition to the glue according to the technical data provided by the manufacturer, you should also pay attention to the content of the curing agent, and you should reasonably control the amount of glue to reduce the odor and glue points on the film product. .
In addition, when using PE film as the lining of the laminating film, pay special attention to the surface tension of the PE film, usually it should be above 45-52 dyne to ensure the firmness after laminating (it is recommended to install an EDM on the laminating machine ).
5 Plastic film
Due to the different requirements of the objects to be packaged, the plastic films required for different packages are also different. The following is a brief description of the properties and uses of the most commonly used plastic films.
PE film is also called polyethylene film, and its uses are extremely wide. It is characterized by low cost, good water resistance, but poor gas barrier. Low-pressure polyethylene has low extensibility and high tensile strength, which can make the packaging bag very thin, but the heat sealing performance is poor, so it is not suitable for use as a composite inner film. The high-pressure polyethylene film has great elongation and good impact resistance, but it should not be used as a composite inner film for fried foods, vacuum bags and cooking bags.
PP film is also called polypropylene film. It has high transparency, high strength, good gas barrier and water barrier, but poor oxygen barrier. Vacuum, cooking, medicine, beverage and other packaging should not use this film as a fabric. Among them, CPP uniaxially oriented polypropylene film and BOPP heat-sealable biaxially oriented polypropylene film are very good, and are the most commonly used compound linings for vacuum packaging or retort packaging.
PET, also known as polyester film, has extremely high tensile strength, poor impact resistance, high transparency, good oxygen and gas barrier properties, but it is not resistant to sunlight and has low water vapor permeability. It can be used as ordinary vacuum bags, medicine bags and The fabric and base material of the aluminized bag. Not suitable for cooking bags.
PA film is commonly known as nylon film, and is currently used as a fabric for cooking bags. Its cost is relatively high, and vacuum bags are generally not used.
Other films, such as: PE cling film for vegetable, fruit and meat packaging, water-soluble PVA film, PVCD high barrier film, PVC, PP, PE heat shrink film ...
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