Film forming mechanism of the hottest Polish 0

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Film forming mechanism of glazing oil

in the packaging and printing industry, in order to improve the high added value of packaging and printing products, finishing technologies such as post press film covering and surface finishing (spraying or printing) glazing oil are used. After leveling, drying and pressing the handle and various buttons, whether they can operate normally and control the light, a thin and uniform transparent bright layer is formed on the surface of the print, Its mechanism is to use the main reflection light of the picture characteristics of the printed matter and the surface reflection light of the surface performance of the printed matter to improve its quality to make up for the deficiencies in the early stage of packaging and printing products. At present, there are many factors involved in the polishing process, such as packaging and printing materials, inks, varnish, raw materials (including adhesion, viscosity, surface tension, etc.) and the environmental conditions of the polishing production process (mainly in the plum rain season of high temperature and high humidity), which can cause the peeling of the base oil and surface oil on the print, and even the fog fault after surface polishing, and lead to the scrap of the product, Caused the imbalance of finishing technology. The reason for this failure is:

1. The purpose of glazing:

the purpose of producing and using base oil and surface (gloss) oil is to obtain the coating varnish film required for compounding. The film-forming process directly affects whether the glazing oil can give full play to the predetermined effect, and whether it can get the economy, durability and convenience shown by the glazing oil in the coating. The film-forming of varnish includes two processes: varnish coating (spraying, coating, printing) on the surface of packaging and printing substrate to form a solid (body) continuous varnish film. At present, the popular way of finishing and polishing: first apply primer (alcohol soluble or water-soluble), and then apply UV oil. Its finishing process almost covers the field of paper products and even flexible packaging products. Of course, the mechanical and optical properties of the varnish film layer can be determined in the process of coating varnish. For the film-forming properties of two different solidification and drying forms and properties of base oil and surface oil, the ultimate goal is how to choose the correct and reasonable operation and production process skills, which will not affect the quality changes in the post-processing process and obtain the best finishing artistic effect under the condition of ensuring the quality

2. Mechanism of film formation:

the base oil and surface oil sold in the market are liquid (state) linked polish. When the polish is on the surface of packaging and printing products, it only completes the first step of finishing and polishing. Because the "wet film" of liquid varnish turns into a dry film, which is the inevitable morphological change process of glazing, that is, from a liquid (state) that can flow to a liquid (state) that is not easy to flow. This series of changes is also the change of liquidity or viscosity defined by academia. The viscosity of liquid primer or glazing oil in finishing processing is about 0.03-0.07pa S. Therefore, after the liquid varnish is coated on the surface of packaging and printing products, the viscosity of the "wet film" is very low. And to become a "dry film" with certain mechanical properties, that is, when people often say the "full dry" stage of bottom oil or surface oil, at this time, the viscosity must reach at least 10mpa S or more. In the viscosity change process from "wet film" to "dry film", it can be considered that the drying or curing process of any liquid (state) base oil or gloss (surface) oil must go through the viscosity change process of the product, that is, solid (state) base oil or gloss (surface) oil, because it is mostly powdery, but after finishing and adhering to the surface of the coated packaging and printing products, It is impossible to form a continuous process into a solid (state) continuous varnish film immediately. Only when certain conditions are met can the whole process from varnish coating to drying film formation be completed

3. Factors causing the atomization of varnish film:

under normal circumstances, the varnish generally does not produce atomization. For example, users often coat the surface of cigarette boxes with a layer of polyolefin film. When the humidity is high, especially when the temperature is high to a certain condition, when the primer is coated, the surface oil often has poor adhesion fastness due to extremely short air mist, The polyolefin film covered on the surface of the varnish will appear thick and uniform mist like small steam, which will reduce or cause the internal quality change of the commodity brand at this time

liquid varnish is coated on the surface of packaging and printing products to form a liquid (state) thin layer that can flow, generally becoming a "wet film". It is mainly a continuous "dry film" that turns into a solid (state) through different ways (infrared drying box, ultraviolet curing and drying) according to different mechanisms. This can get the required coating varnish film. This process from "wet film" to "dry film" is usually called "drying" or "curing". This is the core stage of the film-forming process after the coating of primer and surface (gloss) oil in the process of drying or curing drying, which we often say. This is because of the morphological change of the other liquid/that is, the film formation process can be realized by agglutinating the dispersed particles into a continuous varnish film. Whether the primer, varnish or solid primer or varnish, the drying speed of the process often referred to as "drying" or "curing" is determined by the composition of the varnish itself, the conditions of film formation (including temperature, humidity, oil film thickness, etc.) and the material of the coated packaging and printing products, especially the moisture content

different forms and compositions of base oil and gloss oil have their own film-forming mechanism, which is determined by the properties of the film-forming substances used in the finishing materials. For example, the film-forming of base oil can be defined as the physical film-forming method - that is, the volatile film-forming of solvents or dispersion media, while the film-forming of UV surface oil can be defined as the chemical film-forming method - that is, the film-forming process of polymers dried by the polymerization reaction of gloss oil caused by UV irradiation. The former is often divided into solvent type or dispersion type, but the base oil must go through a form in the film-forming process, such as non conversion base oil. The solvent or dispersion medium in the coated "wet film" volatilizes into the atmosphere, so that the viscosity gradually increases to a certain degree and forms a solid (that is, the whole process of the base oil film-forming is completed). If the converted base oil is volatilized by solvent or dispersion medium and then formed by chemical method, this film-forming method is the reverse process of production in liquid base oil or dispersed base oil

in a word, the drying speed and degree of the primer film are directly related to the volatilization ability of the solvent or dispersion medium used, as well as the diffusion degree of the solvent (including water) in the oil film, as well as the molecular structure, molecular weight and glass transition temperature of the film-forming material. For example, most of the base oil with thermoplastic acrylic resin as the main body first forms a film in the way of solvent volatilization. It is inevitable that in the process of changing from liquid to solid, in addition to the water content of the packaging and printing substrate, or how many solvents will still remain. In addition, polymer particles agglomerate to form a film. This film-forming method of bottom oil depends on the polymer particles as film-forming substances agglomerate with each other under certain conditions to form a continuous solid (state) light oil film. This is the film forming method of dispersing and forming bottom oil energy. Dispersed base oil containing volatile dispersion medium, such as lotion base oil, non-aqueous dispersion base oil and organic sol, will aggregate and form a continuous varnish film when the dispersion medium volatilizes

if it is composed of transforming film-forming substances, it is forming the primer film chemically. At present, the film formation of "water-soluble bottom oil" also depends on the condensation of polymer particles as the main film formation method, while the plastic sol contains nonvolatile dispersion medium, and its film formation is through the swelling, condensation and film formation of polymer particles in the dispersion medium. Usually, the solid bottom oil forms a film through the hot melting and condensation of polymer particles under heating conditions, and the film can be formed only after the thermosetting resin is composed by chemical reaction. The UV light (surface) oil of the latter is usually called chemical film-forming method. Chemical film formation follows the mechanism of polymer synthesis reaction and is divided into two types: chain polymerization and step-by-step polymerization

at present, UV varnish used in packaging and printing products, in addition to the formation of oxidized polymer, generally adopts two forms of initiation polymerization and energy initiation polymerization (both are called photosensitive resin, that is, the photosensitive resin of the varnish system, which is formed by the polymerization of the resin under UV irradiation, is called UV curing varnish). Initiation polymerization is to polymerize a typical unsaturated polyester resin liquid varnish into a film by using an initiator. Its mechanism is to use the material to contain unsaturated groups, and when the initiator boundary produces a chain reaction to form a macromolecular facial mask

the form of energy initiated polymerization is often favored by packaging, printing and finishing technology, and its main body is mostly cheap epoxy acrylic resin. This uses the covalent bond contained in the material to form a gloss facial mask through energy initiated polymerization. This is because the covalent bond homolysis requires a large amount of energy, so one of the main forms caused by the radiant energy of UV light is selected. For this reason, people usually call it UV gloss. In the presence of photosensitizer, the free radical addition reaction of the film-forming material of the varnish is very rapid, and the whole team is composed of more than 210 domestic and foreign composite professionals to cure into a film in a few seconds. There is also the use of electronic radiation film-forming varnish called electronic curing varnish. Because the monomer or polymer containing covalent bond can be directly excited to generate free radicals, the addition reaction can be completed and cured into a film in a few seconds. Therefore, electron beam curing varnish is one of the forms of energy initiated polymerization in film formation in the finishing technology of packaging and printing products at present

looking at the materials and film-forming mechanism of the bottom oil and gloss (surface) described above, we will find that the glazing system uses the easily emulsified resin as the material of the gloss film-forming material. When the temperature rises or the humidity is high during the production, storage and use of the gloss, the water vapor in the commodity and package will continue to condense on the inner surface of the polyethylene film on the top layer, generating a lot of fine water droplets, A layer of opaque fog like white water film is formed, which greatly reduces the light transmittance. With the temperature in the film rising, the emulsified acidic water causes the instability of the glazing oil, releasing white fog like gas, which affects the surface performance of the UV oil material coated after packaging and printing. When it is serious, it causes users to reduce the price of packaged printed matter and return it, and even be sued for compensation

4. Ways and means to prevent glazing ink and polyolefin mist:

in the face of mist failure, we should clearly identify that the mist is caused by the defects of varnish film and polyolefin film, and can even be extended to the packaging and printing substrate containing too much water. According to the experience, the solution is:

first, add antifogging agent to the varnish or polyolefin film system, make full use of the surface activity of antifogging agent, make the above materials hydrophilic, and the generated fine water droplets gradually condense into large water droplets on the surface of the varnish film or polyolefin film, so that the water droplets flow down the film or return to the packaging and printing products, or even commodities, so as to restore the transparency of the film, Through the action mechanism of antifogging agent, glazing oil and polyolefin film - (1) use hydrophilic polymer materials; (2) Crosslinking agent; (3) Surfactants are used to absorb moisture. It can not only prevent and suppress the serious failure of frosting and atomization of packaging and printing products, but also greatly increase the glazing oil

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