Screen printing technology applied in thermal film

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Wire printing technology applied in the manufacturing process of electrothermal film

in addition to traditional electrothermal materials such as nickel chromium alloy (alloy wire and metal cloth woven from the wire), new electrothermal ceramics and conductive polymer composite systems have begun to be widely used. The core of this electrothermal material is a thin conductive coating. Make the film into a certain resistance, print or spray it on a suitable substrate by means of silk printing or coating, connect the electrode on the film and apply a low-voltage current, and the heat will be immediately released from the film. This kind of electrothermal material has the advantages of convenient processing, no pollution, good safety, high electrothermal conversion efficiency, low power consumption and significant energy saving. It is an ideal electrothermal material and has been widely used in many fields

main features of electrothermal film

electrothermal film is a kind of translucent polyester film that can heat after being powered on. The conductive special ink and metal intercepting strip are printed and hot pressed between two layers of insulating polyester film, which has good heat exchange contact with the heated object. It has high thermal efficiency (the thermal efficiency of the electric heating film heating system can reach more than 90%, which is about 3 ~ 4 times more energy-saving than the electric furnace), its own temperature should be established and improved. The comprehensive evaluation criteria and industry standards for plastic granulator equipment are low (in the case of boiling liquid, the temperature of the heating film itself is only dozens of degrees higher than the liquid), small heat capacity, rapid opening and closing of the heat source, no open fire, and the heating film takes up almost no space, making the appliance extremely light, water-resistant Acid and alkali resistance and high mechanical strength. Some of the electrothermal film itself is transparent. If it is attached to a transparent substrate (such as glass), the whole appliance can be made into a transparent appliance

There are many kinds of electrothermal films. According to their composition, there are two categories: Electrothermal ceramics and conductive polymer composites. The former is generally composed of metal or metal oxide, low melting point glass, etc; The latter is composed of conductive metal, nonmetal or metal coated inorganic particles and organic polymers. If divided according to the temperature difference and property change of the film processing and forming, the electrothermal film can be divided into four types: normal temperature drying type (i.e. non crosslinking type), normal temperature crosslinking type, medium temperature curing type, high temperature sintering type (conductive ceramics)

according to the different properties, morphology, structure and composition of conductive filler and resin binder in electrothermal film, the characteristics after film formation also have great differences. Generally, the properties, morphology, particle size and percentage content of conductive filler in the film affect the molding performance and heating performance of electrothermal film. The different types and structures of polymer binders have a direct impact on the drying and curing conditions of the film, the heat resistance after film formation and its adhesion to the substrate. Some of the following are summarized by the Technology Department of the manufacturer. The film can be dried at room temperature, some are crosslinked and cured at room temperature, and some can only be cured by heating. Moreover, the temperature and time of heating and curing will also vary depending on the nature and structure of the resin

electrothermal film is a composite, which is made of conductive paste composed of conductive filler, binder, additive and solvent, which is constructed on the substrate by spraying or silk printing, and then dried and solidified. The heat resistance of electrothermal films dried and cured under different conditions is also different. The electric heating film dried at room temperature is generally only used below the temperature slightly higher than the human body, while the heat resistance of the electric heating film cured at room temperature is better, and it can usually be used for a long time within 100 ℃. If the electrothermal film needs to be used above 100 ℃, its binder should often choose thermosetting phenolic resin, epoxy resin or silicone resin. When most electric heating films are powered on and heated, the temperature rises, the resistance of the film changes little, and the heating time is extended, and the heating temperature of the film will continue to increase. In order to keep its temperature constant, a temperature controller needs to be added, so it is called non self-control temperature electric heating film. Some electric heating films and the proportional constant of non self longitudinal stress and longitudinal strain are the elastic modulus of the material. On the contrary, when the electric heating film is powered on, the resistance of the film changes at the beginning. In the process of temperature rise, once the film temperature reaches a certain value, the resistance suddenly increases to infinity. In this way, the surface temperature of the film is constant in this state. This kind of electrothermal film with temperature control function is called self-control temperature electrothermal film. The heat resistance of electrothermal film is not only restricted by the film itself, but also related to the substrate on which the electrothermal film is formed. If the polypropylene board with 2mm thick base material is used, the surface of the polypropylene board must be pretreated in order to improve the adhesion of the film on the base material. The method is to roughen by sandblasting first, and then oxidize by plasma technology. Although the adhesion of the film on the pretreated substrate has increased, the heat resistance of polypropylene is not very good because it is a kind of thermoplastic. When the electric heating film heats to 110 ℃, the polypropylene plate will deform when heated, and the stress in the center will be concentrated, and the depression will appear first. Due to the small expansion coefficient of the electrothermal film and the large expansion coefficient of the substrate, the deformation of the whole heating material will bend and sag to the side with the electrothermal film, which will damage the electrothermal film. Therefore, a better base material should be insulating materials with small expansion coefficient and good rigidity, such as phenolic laminate, glass fiber reinforced plastic or inorganic materials. If the inorganic glass plate is used as the base material of the electrothermal film, after the film is formed, it is heated and cured at 140 ℃ for 2h, cooled to room temperature and heat up test is carried out. It can be seen that even if the surface temperature of the film is as high as 160 ℃, the film will not be damaged at all

electrothermal film is a new type of heating material, which is widely used in many fields because of its many characteristics, such as convenient manufacture, energy saving, less consumables, low price, no pollution and so on. For example, in the fields of industry, agriculture, medical treatment, electronics and electrical appliances, building materials, daily life and so on, electrothermal film has been applied to heating, heat preservation, snow melting, antifreeze and other aspects required by various transmission pipelines and storage tanks, instruments and equipment, greenhouse seedling raising, food processing and so on. It is also widely used in the anti dew and defrosting of glass windows such as aircraft and high-rise buildings, display devices matching with temperature indicating paint, heating and insulation of houses, heating and insulation of daily thermos cups, thermos pots, etc. For example, as a heating method, electric heating film has the advantages of strong controllability (the room temperature and the opening of the system can be adjusted and controlled randomly according to the needs of each room, which meets the personalized needs). Through the infrared direct heat transfer of infrared electromagnetic waves, there is no air circulation, no dust, and low investment costs. Nowadays, intelligent electric heating film has been developed. This kind of electric heating film uses high-tech and can produce specific wavelength infrared ray beneficial to human body under the excitation of external electric field energy. The use of electric heating film can effectively avoid the influence of electromagnetic field on human body and the interference of household appliances. In recent years, the use of electric heating film in electric appliances, such as electric cups, electric hot pots, electric heaters, electric irons, water heaters, etc., has a very good market prospect

The quality of electrothermal film is not only related to the composition of the film, but also the forming process of the film is an important factor. The commonly used process methods are spraying method and silk printing method. Due to the large coating area, small coating thickness, difficult film thickness control and large thickness error of each part of the same coating, the heating temperature is not easy to achieve uniformity. While using silk printing, the film thickness is large, the thickness error of each part of the same film is small, and the heating temperature is relatively uniform. At present, it is an ideal process for expanding the design freedom of portable speaker gaskets and shells

in the use of electrothermal film, it is indispensable to attach electrodes to the film. The electrode can be pasted with steel foil, but it is usually produced by conductive silver paste wire printing. If only from the welding point of view of the lead, the copper foil method is better. However, this kind of pasting process is complex and troublesome, and its reliability is poor. The electrode made of wire printing on the electrothermal film has excellent quality, especially in recent years, using the newly developed silver paste with excellent heat resistance, printing the electrode with wire and then heating and curing, the welding of the lead wire has been very firm. This kind of printing electrode has high quality, good workability, safety and reliability, and is a commonly used process method

although the electric heating film printed with silk has a good overall effect, all parts on the film heat evenly. However, as far as the current conductive paste is concerned, when using wire to print electrothermal film, attention should be paid to some processes, and the technical level needs to be strengthened. For example, there are specific and strict requirements for post press washing, solvent selection, slurry concentration adjustment, etc

in addition, there is no unified standard for how many mesh conductive filler particles should be selected when preparing conductive paste. For the same filler, the smaller the particle size, the larger the surface area, the better the conductivity and the better the printing quality. However, the smaller the particle size, the worse the heat resistance, and the thermal stability under heating conditions will be problematic. The electric heating film made of this kind of filler often cannot stand the test of long-term heating. Therefore, these must be fully observed and summarized in the application practice to find the best solution. The influence of the dispersion state of the conductive filler in the film on the heating characteristics of the electrothermal film can not be ignored. If the dispersion state is good, the heating of the membrane is uniform, otherwise it is not. In order to prevent the settlement of filler in the film, it is particularly important to choose what kind of surfactant in the production process of conductive slurry. Especially for metal fillers with high density, the greater the thickness of the film during silk printing, the easier the filler particles are to settle during the drying and curing process of the film. After the filler particles settle, the lower layer of the film has a higher bulk density than the upper layer, so the volume resistance measured by the film with large thickness is lower than that of the film with small thickness. If you carefully observe the profile of the electrothermal film with thick coating, you can immediately see that there is a large difference in the particle distribution density between the upper and lower layers of the film. For the same film, the thickness of each part is uneven. The resistance value is high where the film is thin and low where the film is thick. When the uneven coating is energized, the surrounding temperature of the thin coating is too high, and the electrical circuit is easy to be burned out. The electrothermal film printed with silk can be considered to be quite uniform. If the surface heating temperature of the electrothermal film is 60 ℃, the temperature difference of each part of the film can be measured to be between 5 ~ 10 ℃, which is within the allowable range in application, and it also shows that the thickness of the electrothermal film is relatively uniform. In order to improve the quality and make it more stable, the concentration of metal slurry and the amount of ink during printing should be strictly controlled

for the non self-control temperature type electric heating film, it is also very important to install the temperature control sensor on what part of the electric heating film. If the installation part is not appropriate, it is impossible to accurately reflect the surface temperature of the electric heating film. In order to make the heat energy generated by the electrothermal film diffuse evenly, it is useful to choose a metal plate with good thermal conductivity as the substrate. Therefore, electrodes must be set to energize and heat the electrothermal film. What kind of material is used for this electrode, what shape it is made of, how to connect the wire end, and how to control the temperature are all highly technical tasks. In order to prevent excessive temperature rise, the setting of switches and the installation of safety components are the key. If you want to obtain the electrothermal film used under high temperature conditions, and

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