As the demand for plastic flexible packaging increases year by year, plastic packaging is covering the market according to its inherently colorful, novel patterns and easy to use features. However, due to the lack of technical materials for the manufacture and selection of most small and medium-sized packaging color printing companies, the professional knowledge has not been popularized, and the packaging materials have turned south, and the losses are huge, and the packaging business is difficult to expand. I will integrate the theory into practice and make suggestions for many soft packaging industry colleagues.
Generally, the printing method is divided into embossing, gravure, lithography, silk screen printing and the like. Plastic printing is gravure printing, and the commonly mentioned gravure printing machine refers to a unit type (or arranging type) gravure printing machine.
Printing machine
The printing speed of the plastic printing unit is determined by the quality of the paper separation between the printing color groups of the printing press and the effect of the drying box. The longer the interval between the colors and the better the effect of the oven, the faster the printing speed, and vice versa.
The accuracy of the printing press requires not only the synchronization of the various parts before and after the printing machine, but also the stability of the tension control system of each part. Only the tension control design is fair, the material is stable, the winding is stable, and the printing is not Will run the version, in order to maintain the accuracy of the color.
2. Plate
The production of gravure printing plate is divided into two types: corrosion (handmade version) and electric engraving (electric engraving). At present, the manual version is inexpensive, but the printing effect is still good, especially the layered version. In practice, it has been found that the electro-engraving plate has higher requirements on ink. The quality of the printing plate directly affects the quality of the printing.
3. Ink
Plastic gravure inks, solvent-based inks and water-based inks. Solvent inks are further divided into surface printing inks and printing inks (composite inks).
Printed plastic gravure ink: The surface is smooth and shiny, and it is more resistant to friction and odor than the printing ink. When the laminating process is used, one-component glue should be used, which is inferior to the two-component glue, and the amount of glue should not be too large. The printing ink is divided into ordinary ink, ink resistant (beverage packaging ink), label ink (calendar ink), transparent ink and the like. Ink resistant inks are mainly used for printing on milk packaging, beverage packaging and frozen food packaging products. The label ink is very smooth, anti-blocking and scratch-resistant, and is the best ink for printing various labels. Clear ink is a special ink for printing aluminum foil and aluminum foil.
Ink ink (composite ink) is characterized by brilliance, odorless printing, and high peel strength. However, the conjunctiva is soft and not rubbed, and its print is dull, which is beneficial to laminating. If a dry compound is applied, it is advisable to use two-component glue. One is to increase the composite firmness, and the other is to have a small odor. However, when the one-component glue is used for compounding, the finished product of the printed matter is often dissolved or compounded, and the finished product will be contaminated with the harmful smell of the glue, and the composite firmness is poor (note that the alcohol solvent is not allowed to be added). In addition, there is a common composite ink in the printing ink, which is an ink printing of an OPP film (polypropylene film). For printing PET film (polyester film), polyester ink should be used, and the printed pattern is firmer and there is 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 commonly used for printing paper products, including paper-plastic composite products. Its characteristics are that it can meet the ink absorption of paper printing, making the prints full of color. What is more rare is that the solvent is water and ethanol, which is less polluting to the environment and is known as the environmentally friendly green ink.
4. Compound
Composite of plastic flexible packaging, split film extrusion compounding, dry coating compounding and glueless hot pressing compounding. Extrusion compounding refers to the hot melt of PE or PP material, and then extrusion into a film, which is hot-pressed and composited on a printing film to form a composite product. It is characterized by low cost and reduced glue pollution. However, it is better to choose the enthalpy of 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.
Dry glue laminating machine is used to dry the road. Heating method, glue application method, glue amount control, retracting material tension control, hot drum temperature control and whether there is a cooling setting device constitute its price level and grade. In the process of coating and compounding, first of all, the user should understand that if the glue is to be evenly diluted, the glue must be diluted. In order to restore the viscosity of the glue, the solvent on the coating must be volatilized (ie, the concentration process), so that the composite is on the upper side. The amount of glue is the key to composite processing. Special attention should be paid to reducing the amount of glue applied during compounding. Therefore, it is not recommended to use in food packaging.
Because the one-component glue is used with the printed ink, the smell is difficult to eliminate, so it is not recommended to use it in food packaging. Pay special attention to reduce the amount of glue when compounding.
If the two-component glue is used, in addition to the technical requirements of the technical data provided by the manufacturer, the content of the curing agent should be paid attention to, and the amount of glue should be controlled to reduce the odor and glue spots on the laminated product. .
In addition, if you want to use PE film as the laminating lining, pay special attention to the surface tension of PE film, usually should be above 45-52 dynes to ensure the firmness after lamination (it is recommended to install EDM on the laminating machine). machine).
5. Plastic film
Due to the different requirements of the packaged materials, the plastic film required for different packages is also different. The following is a brief introduction to the performance and use of the most commonly used plastic films.
The PE film is also a polyethylene film, which is extremely versatile. It is characterized by low cost, good water resistance, and poor gas barrier properties. The low-pressure polyethylene has small elongation and high tensile strength, and the package bag can be made very thin, but the heat-sealing performance is poor, and it is not suitable for use as a composite inner film. The high-pressure polyethylene film has large elongation and good impact resistance, but it is not suitable for use as a composite film for fried foods and real and retort bags.
PP film is also called polypropylene film, which has high transparency, high strength, good gas barrier and water resistance, but poor oxygen barrier property. This film should not be used as a fabric for vacuum, cooking, medicine, beverages, etc. Among them, CPP uniaxially stretched polypropylene film and heat sealable biaxially oriented polypropylene film are good and most commonly used in vacuum packaging or retort packaging.
PET, also known as polyester film, has high tensile strength, poor impact resistance, high transparency, good resistance to oxygen and gas barrier, but is not resistant to sunlight and water vapor permeability. It can be used as a general vacuum bag, a drug bag and Aluminized bags of fabric and substrate. Not suitable for cooking bags.
Pa film, commonly known as nylon film, is currently used as a fabric for retort pouches. Its cost is high, and vacuum bags are generally not used.
Other films, such as: PE cling film for vegetable and fruit and meat packaging, water-soluble PVa film, PVCD high-resistance film, PVC, PP, PE heat shrink film.
Producers and applicators should select the fabrics and linings necessary for packaging according to the inherent characteristics of various film materials, and strive to produce qualified bags with economical, high quality and low price.
6. Appendix plastic gravure ink commonly used thinner ratio for reference:
First, the printing ratio of the plastic printing gravure ink used in the printing:
Quick drying solvent: ethyl acetate 20%, toluene 80%
Medium dry solvent: butyl acetate 20%, toluene 80 or 100%
Slow drying solvent: butyl acetate 20%, xylene 80%
(Note: alcohol solvents cannot be added)
Second, the ratio of surface printing plastic gravure ink using thinner:
Quick drying solvent: ethyl acetate 20%, toluene 80%, isopropanol 40%
Medium dry solvent: ethyl acetate 25%, toluene 50%, isopropanol 45%
Slow drying solvent: 50% xylene, 50% isopropanol
Very slow dry solvent: 50% xylene, 50% isopropanol, 3% n-butanol
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