Polyethylene, polypropylene plastic screen printing ink
First, plastic profile The organic high molecular polymer can be molded into a shape under the conditions of heat and pressure, and a material that can maintain a fixed shape under normal temperature and normal pressure is called a plastic. The main components of plastics are synthetic resins. Synthetic resins are synthetic products obtained by artificially synthesizing organic polymers. Their properties are similar to those of natural resins. In order to change certain properties, some auxiliary materials, such as fillers, can be added. Plasticizers, stabilizers, and colorants, etc., are obtained by uniformly adhering synthetic resin components together. Plastics can be divided into two types, thermoplastics and thermosetting plastics, depending on their performance after being heated. Commonly used polyethylene and polypropylene are two kinds of general plastics, mainly urea-formaldehyde plastics, due to their large output, low price, and a wide range of applications. 1. Polyethylene (PE) plastic Polyethylene plastics are used in many ways and can be made into a variety of finished products through extrusion, injection, and other molding processes. The molecular chain of polyethylene is a long chain of methylene groups containing a certain amount of pendant groups. According to the chemical principle, the longer the number of side groups in the polymer chain, the lower the crystallinity of the polymer, that is, the higher the density of the polyethylene, the more disadvantageous the surface coating is. In general, polyethylene is insoluble in many solvents, but when the temperature exceeds 70°C, the polyethylene can be dissolved in a small amount in solvents such as toluene and amyl acetate. This property of polyethylene provides conditions for surface finishing. We can soak the plastic by heating the solvent to make its surface swell and destroy part of the crystallization to increase the adhesion of the printing ink ink film on the plastic surface. A mixture of concentrated nitric acid, chromic acid, fuming sulfuric acid and sulfuric acid can slowly act on polyethylene at room temperature; a mixture of sulfuric acid and nitric acid at 90 to 100°C can rapidly destroy polyethylene; use potassium dichromate, sulfuric acid, and distilled water The mixed liquid, soaked in polyethylene plastic at 70-75°C, is beneficial to enhance the adhesion of the ink film on the plastic surface. 2. Polypropylene (PP) plastic For many years, polypropylene has been one of the important varieties for plastics development. It is suitable for all molding methods. It can be used for various pipes, building materials, water pipes, various boxes, films, and fibers. Industrial polypropylene has a high degree of crystallinity and its isotactic index is as high as 89% to 95%. At the same time, it also contains a small amount of macromolecular chains of amorphous atactic structure and low crystalline stereoblock structure. When the melting point of the plastic is in the range of 170 to 175°C, the glass transition temperature of the isotactic polymer is -13 to 0°C, while the glass transition temperature of the syndiotactic polymer is 0°C. Concentrated nitric acid and fuming sulfuric acid are capable of attacking polypropylene. At higher temperatures, polypropylene is soluble in aromatics and oxygenated hydrocarbons, but it can only swell at room temperature. Acids and esters also have a certain degree of dissolution, and as the content of isotactic polymers increases, the solvent resistance will increase accordingly. In general, polyethylene and polypropylene are high-molecular materials with high crystallinity and low surface tension and non-polar molecular structures. There is no polar group such as carbonyl group, carboxyl group, hydroxyl group in their molecular structure, however, the surface coating of polypropylene can be easier compared with polyethylene. For polyolefin materials, in order to ensure the adhesion of the ink film, the plastic surface must be treated. One method is to increase the surface tension of the plastic solids by using ultraviolet light to increase the molecular weight of the low molecular layer of the plastic surface in the presence of a photosensitizer and increase the tension on the solid surface. Another method is to oxidize the polyolefin plastic surface molecules to generate polar groups such as carboxyl, hydroxyl, and carbonyl groups on the surface to increase the critical surface tension of the plastic surface and improve the adhesion of inks and coatings to plastic surfaces. Performance, can be used flame, chromic acid mixture, discharge oxidation, ozone oxidation and other treatment methods. Second, polyethylene, polypropylene plastic printing ink Plastic printing inks are also referred to as paints or printing materials. The following is a brief description of the performance requirements of plastic prints for inks and the process requirements of screen printing operations for inks: 1. Performance requirements of inks for plastic prints 1 printing ink ink film appearance smooth light; 2 The ink should have good adhesion on the plastic surface; 3 ink ink film should have greater hardness and wear resistance; 4 ink ink film should have a certain degree of water resistance and hot water resistance; 5 ink film should have a certain degree of alkali resistance, acid resistance, and can resist the erosion of alcohol and other organic solvents; 6 ink ink film has a certain degree of weather resistance, the impact of small changes in temperature and humidity. 2. Screen printing ink process requirements 1Thickening is allowed in the printing process, but the use period should exceed 4h; 2The ink used in the screen printing is easy to operate, and the squeegee operation is convenient. 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