Editor's note: Flexible packaging is widely used in the outer packaging of commodities due to its many superior properties. This article focuses on the analysis of the printing characteristics and printability of flexible packaging materials, and points out the printing skills of various flexible packaging materials.
Plastic films commonly used plastic films are: PE, PP, PVC, PS, PVA, PC, PET, CA, NY, the printing characteristics of these plastic films are:
â‘ Plastic film is a non-polar polymer compound, which has poor adhesion to printing ink. In order to make the plastic film surface have good ink adhesion and enhance the firmness of the printed product, surface activation treatment is performed before printing:
â‘¡The hygroscopicity is mostly affected by the relative humidity of the surrounding air and expands and contracts, resulting in poor overprinting;
â‘¢Due to the change of tension, in the printing process, in the allowable range of strength, the elongation rate increases with the increase of tension, which makes the accuracy of color printing overprint difficult:
â‘£The surface is smooth, there is no capillary holes, the ink layer is not easy to fix or is not fixed firmly, after the first color is printed, it is easy to be stuck by the ink of the next color overprint, which makes the pattern and text incomplete and causes defects;
⑤ The oil layer on the surface oozes out. Films made with additives can easily bleed out during the printing process, forming an oily layer, ink layer, paint or other adhesives on the surface of the film.
â‘¥Since the plastic film is a non-polar material, there are no capillary holes, and the ink is not easy to dry. These characteristics are not conducive to printing, so the plastic film must be surface-treated before printing.
The characteristics of cellophane cellophane are: high transparency, strong glossiness, exceptionally bright color after printing graphics, which is not achieved by plastic film; good printability, no need to undergo any treatment before printing, cellophane also has antistatic treatment performance , It is not easy to attract dust, avoiding printing failures such as graphic sticky dust. However, the moisture resistance is poor, and the film is easily deformed by the influence of temperature and humidity, which makes it difficult to register the graphics during printing.
The characteristics of aluminum foil aluminum foil are:
â‘ Light weight, with metallic luster, good light shielding, high reflectivity to heat and light, metallic luster and reflective capacity can improve the brightness of printed colors;
â‘¡Good isolation, strong protection, airtight body and water vapor, to prevent moisture absorption and vaporization of the contents, and not easy to be attacked by bacteria and insects;
â‘¢Good shape stability, not affected by humidity changes. Easy to process, printing, color difference, embossing, surface coating, gluing and painting of aluminum foil;
â‘£ Cannot be stressed, without sealing, pinholes and wrinkles, so it is generally not used alone, usually processed into composite materials with paper and plastic film, which overcomes the shortcomings of no sealing and its isolation Sex and other advantages have also been fully exerted.
Aluminum foil is widely used in packaging fields such as food and medicine. Aluminum foil is combined with plastic film, which effectively utilizes the characteristics of high temperature cooking and complete shading. It is made into a cooking bag, which can be used to package cooked food. Multi-layer composite film is also used. Used for packaging small food such as biscuits, snacks, beverages, etc.
Vacuum aluminized film The main function of the vacuum aluminized film is to replace the aluminum foil compound, so that the flexible plastic packaging also has a silver-white beautiful luster, improve the barrier light-shielding properties of the flexible packaging film bag, and thus reduce costs. The substrate film to be vacuum-plated aluminum is a polypropylene film with a relatively high melting point, including CPP, IPP, and BOPP. PET film, NY film and paper can also be directly vacuum-plated after pretreatment or humidity adjustment. PE film and PT can adopt indirect aluminum plating process. In order to provide the fastness of aluminum plating, the method of coating the bottom layer on the substrate film to be plated is adopted abroad, while the domestic generally has no bottom coating surface, and only performs corona treatment on the surface. There are two methods of vacuum aluminum plating of the film, which can be reverse printed on the mask of the film, that is, inside printing, and then vacuum aluminum plating and then combined with the bottom film. It can also be reverse printed on the mask, and then dry compounded with the vacuum aluminized base film. The latter's base film must be CPP or IPP with good heat resistance and heat sealability.
It should be noted that, when vacuum aluminum plating is performed on the printed mask, although it is back-printed, it does not need to use back-printed ink, but only needs to be an ink with excellent heat resistance. If the printed product becomes dark after vacuum aluminum plating, it loses its luster due to the poor heat resistance of the ink. Vacuum aluminum plating on the printing surface, because the adhesive resin in the ink is a good primer layer, the fastness of aluminum plating is relatively good, especially when the full plate is printed on the ground, the fastness of the aluminum plating layer is better.
Compared with aluminum foil, vacuum aluminum plating greatly saves the amount of aluminum used. The former is only 1 / 100-1 / 200 of the latter, but it has the gloss and isolation of metal. Because the thickness of the vacuum aluminum plating layer is relatively thin, only O. 4 one O. 6¨m, can not be used to replace aluminum foil composite films that require high barrier properties, such as vacuum packaging and high temperature cooking bags. The cost of vacuum aluminum plating is lower than that of aluminum foil, and it will be greatly developed in the field of food trademarks. In recent years, vacuum aluminum plating paper is gradually replacing aluminum foil in the packaging of cigarettes, cold food cartons, chewing gum and other packaging.
Composite film Composite film is widely used in food packaging, such as fast food, quick-frozen food, puffed food, etc. in shopping malls. These are made of composite films, which can maintain the excellent characteristics of single-layer films, but also have their own shortcomings. After compounding, they have new characteristics to meet the different requirements of commodities for films. For example, food packaging requires films to have moisture resistance, It has excellent performances such as gas-proof, light-proof, oil-resistant, high-temperature resistance, good heat-sealability, etc. At the same time, it also has good printability and decorative art effects. The performance and requirements are difficult to achieve with a single film. Take the most widely used PE film, although it has excellent transparency, moisture resistance, heat resistance, and chemical stability, it has limited oil resistance and oxygen resistance, and poor printability. PET and PA films have high tensile strength and fatigue strength, but the former has poor moisture resistance, and the latter has poor heat sealability and chemical resistance. PE (glass) has excellent transparency, no static electricity, no pollution and easy adhesion, but toughness, water resistance and moisture resistance are poor. Aluminum foil has a shiny metallic luster and thermal conductivity. It has good barriers to moisture, steam, light, and grease, but it has the disadvantages of easy cracking, lack of flexibility, and no thermal adhesion.
The layers of desert are compounded together, and have excellent properties such as moisture-proof, gas-proof, light-proof, heat-resistant, oil-resistant, and good heat-sealability, making them ideal packaging materials. For example: the current high-end RP-H cooking bag is a three-layer composite film with a plastic film as the base material. Its middle is aluminum foil, which has good insulation performance and is conducive to the storage of food for a long period of time; the outer layer uses BOPP film, which has Excellent dimensional stability, intaglio printing on the back, compounded with aluminum foil with adhesive and pulling agent, ensuring the firmness and smoothness of the printed color. The inner layer uses PE film to take advantage of its heat resistance, softness and easy sealing. After the three are combined, it can withstand 120 ° C high temperature sterilization treatment, and the microorganisms will not be immersed, which plays a role in freshness and taste preservation.
There are many types of composite films, common ones include cellophane and plastic film, plastic film and plastic film, aluminum foil and plastic film, aluminum foil, glass, paper and plastic film, various papers and their printed materials and various There are as many as 30-40 kinds of plastic film compounding, etc. The number of compound layers is generally 2-5 layers. The basic structure of various composite films is to use PT, BOPP, NY, PET and other non-thermoplastic or high-melting point films as the outer layer, and PP and PE as the inner layer for comprehensive application. The commonly used composite film structure is composed of many uses. When selecting the composite film, it is necessary to consider the printing performance in order to obtain a beautiful trademark pattern.
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