There are three commonly used printing processes in the production process of plastic bags
Plastic packaging bags are generally printed on various plastic films and then combined with barrier layers and heat-sealing layers to form composite films, which are cut and bagged to form packaging products.
Among them, printing is the first line of products and the most important process. To measure the grade of a packaging product, printing quality is the first.
Therefore, understanding and controlling the printing process and quality have become the key to flexible packaging production.
1. Gravure printing
The printing of plastic film is mainly based on the gravure printing process. The plastic film printed with gravure has the advantages of high printing quality, thick ink layer, bright color, clear and crisp pattern, a rich picture layer, moderate contrast, vivid image, and strong three-dimensional sense. Gravure printing requires that the registration error of each color pattern is not more than 0.3mm, and the indicators such as product same-color density deviation and same-batch same-color deviation meet the requirements of GB7707-87. The printing plate of gravure printing has strong printing resistance and is suitable for long-form jobs. However, gravure printing also has shortcomings that cannot be ignored, such as complex pre-press plate-making process, high cost, long cycle, and large pollution.
The gravure printing process is divided into surface printing and inner printing
1. Surface printing process
The so-called surface printing refers to the process in which the printed graphics and texts are displayed on the surface of the finished product after printing on the plastic film and after the bag-making process.
The "surface printing" of the plastic film is made of white ink as the laying background, which is used to set off the printing effect of other colors. It mainly has the following advantages.
First of all, the plastic white ink has a good affinity with PE and PP film, which can improve the adhesion fastness of the ink layer of the printed matter.
Secondly, the background color of white ink is a total reflection, which can make the color of the printed product more vivid. Thirdly, printing the background color can increase the thickness of the ink layer of the printed product, making the printed product richer in layers and rich in the visual effect of embossing.
Therefore, the printing color sequence of the plastic film printing process is generally determined as white→yellow→magenta→cyan→black.
The surface printing plastic film requires good ink adhesion and has considerable wear resistance, light fastness, freezing resistance, and temperature resistance.
In recent years, some ink merchants have developed special high-temperature cooking alcohol-soluble inks for surface printing, which are excellent in abrasion resistance, light fastness, adhesion, and color gloss.
2. Inside printing process
Inner printing refers to a special printing method that uses a printing plate with a reverse image and text to transfer the ink to the inner side of the transparent printing material, thereby showing the positive image on the front of the substrate.
In order to get the same visual effect as "surface printing", the printing color sequence of the inner printing process should be opposite to that of "surface printing", that is, the white ink background color should be placed in the last printing so that the white ink background color can be seen from the front of the printed product. To set off the role of various colors. Therefore, the printing color sequence of the inner printing process should be black→cyan→magenta→yellow→white.
Printing plastic bag manufacturers
1. Flexographic printing
Flexographic printing primarily utilizes flexographic and fast-drying letterpress inks. The equipment is simple, the cost is low, the plate material is light in weight, the printing pressure is small, the plate material and mechanical loss are small, the printing noise is small, and the speed is fast.
The flexo plate has a short plate change time and high work efficiency. The flexo plate is soft, elastic, and has good ink transfer performance.
It has a wide range of printing materials, and the cost of printing small batches of products is lower than that of gravure printing.
However, flexographic printing has higher requirements on ink and plate materials, so the printing quality is slightly lower than that of the gravure process.
2. Screen printing
During printing, through the extrusion of the squeegee, the ink is transferred to the substrate through the mesh of the graphic part to form the same graphic as the original.
Screen printing products have rich ink layers, bright colors, full colors, strong covering power, a wide selection of ink varieties, strong adaptability, low pressure during printing, easy operation, simple plate-making process, and low equipment investment, so the cost is low, Good economic benefits, a wide variety of printing materials.
Packaging promotes the overall image of commodities as much as advertising.
It has many functions such as beautifying commodities, protecting commodities and facilitating commodity circulation.
Printing plays an important role in the production of packaging bags.