As the society's demand for plastic flexible packaging increases year by year, plastic packaging is covering the market with its inherently colorful, novel patterns, and easy to use features. However, due to the lack of technical information on manufacturing and material selection for most small and medium-sized packaging color printing companies, professional knowledge has not been popularized, which makes it difficult to package the goods, resulting in huge losses and difficult to expand the packaging business.
Generally, the printing methods are divided into relief printing, gravure printing, offset printing, and silk printing. 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 printing unit is determined by the length of the paper distance between the printing color groups of the printing press 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 go to the canal.
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 machine also requires the stability of the tension control system of each part to be stable. only the reasonable design of the tension control, stable feeding, stable winding and stable printing You can run the version to maintain the accuracy of the register.
2. Printing plate
The production of gravure printing plate is divided into 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 gravure inks are divided into solvent-based inks and water-based inks. Solvent inks are divided into surface printing inks and internal printing inks (composite inks).
Surface printing plastic gravure ink: the surface is smooth and shiny, compared with the inner printing 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. Note that 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 and so on. 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 resistance, is the best ink for printing various labels. Transparent ink is a special ink for printing aluminum-plated foil and aluminum foil.
Ink ink (composite ink) is characterized by bright color, odorless printed products, high peel strength of the film, but the conjunctiva柔软而不耐磨,the printed product is dull, which is conducive to laminating processing. If you use glue-coated dry compound, you should use two-component glue. One is to increase the firmness of the compound, and the other is that the odor is small. However, when compounding with single-component glue, the ink on the printed matter is often dissolved or the finished product will bring the harmful smell of the glue, and the compound has poor firmness (note that alcoholic solvents are not allowed to be added). In addition, there are common 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 stronger and no blocking phenomenon will occur. In short, what type of special ink is used on what film is the principle of plastic gravure ink.
Water-based ink is 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 printed matter plump, and the rare thing is that its solvent is water and ethanol, which has little environmental污染和被称为绿色墨水for environmental protection.
4. Compound
Composite plastic flexible packaging, divided into laminating film extrusion composite, dry glue coating composite and glue-free hot pressing composite, etc. Extrusion compounding refers to extruding PE or PP material to form a film, and hot pressing compounding on the printed film to form a composite product. It is characterized by low cost and reduced glue pollution. However, it is necessary to choose the extrusion material and control the extrusion temperature, and add a small amount of glue or AC agent as a coupling agent between the film formation, the effect will be better.
Dry glue spreading machine drying channel length. The heating method, glue application method, glue application control, tension control of the unwinding and unwinding, temperature control of the hot drum, and whether or not equipped with a cooling and shaping device make up its price and grade. In the compounding process of glue application, users should first understand that if the glue is to be even, the glue must be diluted, and if the viscosity of the glue is to be restored, the solvent on the paint must be volatilized (ie, the concentration process), so the 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.
Single-component glue is used with surface printing inks and the odor 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 ratio 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, if you want to use PE film as the lining of the laminating film, pay special attention to the surface tension of the PE film, which should usually be above 45-52 dynes to ensure the firmness of the laminating film. machine).
5. Plastic film
Due to the different requirements of the packaged objects, the plastic film required for different packaging is also different. The following is a brief introduction to the properties and uses of the most commonly used plastic films.
PE film is also a polyethylene film, which is extremely versatile. It is characterized by low cost, good water resistance, but poor gas barrier. Low-pressure polyethylene has low extensibility and high tensile strength, and can be used to make the packaging bag very thin, but its heat sealing performance is poor, so it is not suitable for use as a composite inner film. 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 and real, 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 and packaging for medicine and beverages should not use this film as a fabric. Among them, CPP uniaxially stretched polypropylene film and heat-sealable biaxially stretched polypropylene film are very good and 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, and good oxygen and gas barrier properties, but it is not resistant to sunlight and has low water vapor permeability. Fabric and base material of aluminum-plated bag. Not suitable for cooking bags.
PA film is commonly known as nylon film, which is currently used as the 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.
Producers and applicators should select the necessary fabrics and linings for packaging materials according to the inherent characteristics of various film materials, and strive to produce affordable, high-quality and affordable packaging bags.