Printing plastic film printing substrate

As far as plastic films are concerned, there are two main types of PE printing technology that are currently used in China: PE and PP. Other types of films, such as PVC, PET, etc., generally use a gravure process because of their small tensile deformation. In addition, so far, there is no domestically applicable flexographic ink for such films. In the past, the author printed the relevant product on the PVC soft film, and he stopped because he could not find the flexo ink that met the standard in printing fastness. Therefore, the control of printed substrates is mainly the control of PE and PP printed films.
The PP film is divided into two kinds, CPP and OPP. The control of the CPP film is exactly the same as that of the gravure printing process, and will not be described here. The more OPP film used in flexo printing is the label film, the film density is relatively small, generally 0.6 ~ 0.7, compared with the original density of OPP film 0.90 ~ 0.91, obviously a lot smaller. The most widely used is the beverage labels used by the two major companies, Coca Cola and Pepsi. Due to the environmental protection and production costs of PVC heat-shrinkable bottles, many beverage suppliers have gradually changed their labels, and the market for OPP labels has become increasingly popular.
Gravure printing dominates the label printing process, but savvy business operators have evolved to use a flexo printing process to print beverage labels that are less costly and require at least half the ink consumption compared to gravure printing. Therefore, the potential of flexo-printed OPP beverages on the market will be enormous.
The OPP label film, which is to be controlled before printing, except for the same physical properties as the gravure process such as film flatness, vertical and horizontal tensile strength, surface friction coefficient, and wet tension of the film surface, we feel that the film should be emphasized. BaiDu. Because the flexible process is different from the gravure process, the OPP label films with different brightness have different effects under the same printing process parameters.
The use of fixed-point film supply in control has been proven to be a simple and effective method. Of course, we must pay more attention to this issue when we use other brands of film under the requirement of continuously reducing the cost of film supply. Because, for gravure, even if the color difference of the film is larger, the depth of the printing plate can be adjusted and masked with the saturation of the color. However, the flexo printing process uses less ink and has a thin ink layer. It is difficult to achieve the purpose of masking. The whiteness of the OPP label film is directly related to the color masterbatch used in the production process of the film, and it is necessary to pay attention to this problem when feeding the film.
PE film is the leading product of flexographic printing materials. In the past, the main purpose of the PE film was to use the film as a heat resistant film and used as a composite film. Therefore, in general production companies, the product standards for the product are basically determined by the standards of the composite film. But now the situation is different. Whether it is transparent PE or milky white PE, it has gradually been used in flexo printing products. Therefore, if we continue to use the original parameters, we will not be able to meet the requirements of the flexo printing process. Two parameters are emphasized here, one is the crystal point problem of the film and the other is the printability problem of the film surface.
Crystal spots, also known as dead spots, are known in foreign professional books as "fish eyes" or "arrow heads." This is a process in which the polyethylene resin undergoes cross-linking after being oxidized during processing, thereby generating a gel. Such gel particles can form macroscopic aggregates in film articles. Our training on this issue is gradually deepening. Initially, during the printing process, we often encountered the squeezing of the flexographic printing plate due to the crystal point on the PE film. Therefore, the product that was provided to us for the printing film was put on the control before the film was blown. Replace the new filter beforehand. However, the accident continues.
This prompted us to find ways to avoid such accidents and further control the cause of the crystal spot. In fact, a large crystal point may be caused by a bad filter, but a small crystal point can not be solved by changing the filter again. Of course, this belongs to the problem of film production. It cannot be solved by temperature regulation alone. The control of the crystal point of the printed film is a very important part. For a printing company, it is necessary to formulate an acceptance standard, that is, the size of a single crystal spot and the number of crystal spots per unit area. Crystal points that exceed a certain "degree" will be unacceptable, and it is directly related to the protection of the quality of printing plates and printed products.
For the printability of plastic films, it has long been specified only 38-42 dyne of surface wetting tension. Once this value is reached, it is generally considered to pass. However, we have encountered some problems in our production practice. When using a company's PE film, the production speed can only reach 150-160m/min, and then go up, you will find the pinhole phenomenon in the field printing more and more serious, in order to ensure the density of the field, we have to The speed is maintained at around 150m/min.
The same production process (subsidiary materials and process parameters are completely the same) in the author's current company, only with a different film, the speed can be mentioned above 200m/min, our production speed is 230 ~ 250m/min, on-site density Basically unaffected. This prompted us to consider a problem, in addition to the condition of wetting tension on the surface of the film, there are still other factors that affect the ink transfer characteristics. These factors are collectively referred to as printability. Therefore, the printability of the film should also be one of the parameters that we must control. This is directly related to the quality of the product and also to the benefits of the company.