Definition and type of electric heating film
The gist of this lecture: Electric heating film is a sub-category in the electric heating product system, and it is a new type of electric heating product. There is no unified definition and classification of electric heating film at present. The author has written a definition of electric heating film and divided electric heating film into four types according to the material of the heating body. This lecture focuses on the definition and classification of electric heating films involved in the standard discussion draft of the Ministry of Housing and Urban-Rural Development's "Low-temperature Radiation Electric Heating Film", and mainly expounds the definition and classification of electric heating films. The heating materials of four types of electric heating film, such as carbon fiber and polymer", and the corresponding production and processing technology of electric heating film are introduced.
1. Definition of electric heating film
Electric heating film is an electric heating element that directly converts electric energy into heat energy. Like electric heating pipes, electric heating rods, electric heating plates, electric heaters, rice cookers, induction cookers, etc., it is an integral part of a huge family of electric heating products. But the difference is that the electric heating film is still a relatively new product category in China, the application history is only about ten years, and the application field is far less extensive than other electric heating products, so people's knowledge and understanding of the electric heating film have not reached degree of popularity.
Electric heating film, English name "hot film" or "electrothermal film", Japanese name "plane heating body". It is difficult to find the exact definition of electric heating film in textbooks and dictionaries at home and abroad. In the past few years, the definition of electric heating film in China was mostly based on the promotional materials of electric heating film manufacturers, mainly carbon-based printing ink electric heating film, such as: "Electric heating film" The film is a translucent polyester film that can generate heat after being energized. It is made of conductive special ink, metal current-carrying strips, and hot-pressed between insulating polyester films." The name in the project initiation report of the construction industry standard is also "Low Temperature Radiation Polyester Electric Heating Film", which obviously also refers to the carbon-based printing ink electric heating film, which was later changed to "Low Temperature Radiation Electric Heating Film". In recent years, with the technological progress and large-scale production and market application of various types of electric heating films, people have the opportunity to gradually understand and understand various types of electric heating films. one of the issues discussed.
2. Classification of electric heating film
According to incomplete statistics, there are more than a dozen products called electric heating film on the market at present, and there are more than 20 types of electric heating film products in addition to similar products with electric heating film structure and other names. In the 10th issue of "Heating and Refrigeration" in 2006, the author proposed for the first time in China to classify the electric heating film according to the material of the heating element, and divided the electric heating film into "printing ink type, carbon fiber type, metal wire (sheet) type, conductive polymer type. "Material type" and other four types are hereinafter referred to as quartiles). In the "Low Temperature Radiation Electric Heating Film" standard consultation draft, the electric heating film is divided into two categories: metal-based and non-metallic-based (hereinafter referred to as the two-point method), and the non-metal-based electric heating film is subdivided into carbon fiber, carbon-based ink and polymer. Three types.
There is no essential difference between the two-point method and the four-point method of the electric heating film, but the non-metal-based electric heating film is regarded as the first grade, and the other three types of electric heating films except the metal base are regarded as its secondary level, that is, the second grade. There is no error in the logical relationship, but the dichotomy emphasizes metal materials and weakens the status of other materials, while the technological progress of new materials, including electrothermal materials, is very fast. In this way, the future non-metal-based electrothermal The secondary types of membranes will continue to increase, and it is unlikely that metal-based electrothermal membranes will be reclassified for a considerable period of time, which will form two categories
The serious imbalance of members of the electric heating film family, that is, the non-metal-based electric heating film has a huge family and has even reached the third and fourth levels, while the metal-based electric heating film still has only one member. Moreover, the dichotomy method refers to the classification of infrared radiant heaters by radiation matrix in the national standard "Experimental Methods for Infrared Radiant Heaters" (GB/T7287-2008). The classification of infrared radiant heaters is used for electric heating films, and the classification of infrared radiant heaters itself is also debatable. , for example: "Semiconductor heaters" in the type of non-metallic infrared heaters obviously include "ceramic, enamel, high silicon, zircon sand heaters", etc. "Mylar heater" may of course also be an encapsulated metal-based heat-generating material, that is, a "metal-based heater".
In addition to the above two-point method and four-point method, most of the electric heating film manufacturers name their products from different angles, and some define the electric heating film by covering the insulation material of the electric heating film, such as: polyimide electric heating film, silicon (rubber ) glue electric heating film, mica electric heating film, PET electric heating film; some are defined by the power density of the electric heating film, such as low temperature, medium temperature, high temperature electric heating film; some define the electric heating film by emphasizing the concept of radiant heat, such as: radiant electric heating film, far infrared Electric heating film; some emphasize the particle size of the heating body, such as: nano electric heating film, carbon nano electric heating film; there are also "ecological electric heating film", "electric heating film", which define electric heating from the environmental protection characteristics of electric heating film and the application method of floor heating. membrane. In the past two years, the relatively loud "silicon crystal, carbon crystal electric heating film" and the recently appeared "high (super) carbon crystal electric heating film", which have been commonly called in Shanghai, Sichuan, Chongqing, Wuhan and other places, etc., according to the author's investigation and After communicating with relevant manufacturers, it can be concluded that this type of electric heating film is a carbon fiber electric heating film.
Carbon Fiber Infrared Heating Tube--Introduction
Introduction to the classification of electric heating
Definition and type of electric heating film
Structural principle and characteristics of mesh belt dryer
6-step rule for safe use of heavy oil explosion-proof electric heaters
Common sense of electric heating tube
Thermal film". The name of carbon crystal is unscientific.
The author believes that it is more scientific to classify and name the electric heating film with the heating material as the main body, because the heating material determines the characteristics of the electric heating film, and the definition of the electric heating film by the heating material can be used by people with certain science and engineering knowledge and other non-professionals. It is easier to understand and understand the basic characteristics of different types of electric heating films from the root, and it also avoids the attempts of manufacturers to achieve their own goals through vague concepts. Of course, just like the definition of the electric heating film, after the "Low Temperature Radiation Electric Heating Film" standard is approved, the manufacturer will naturally follow the classification of the electric heating film on the standard to name its own products.
The confusion of thermal film classification will also be curbed to a certain extent.
The following are the basic performance characteristics of the four types of electrothermal film heating materials, production and processing technology and the corresponding electrothermal film that appear together in the dichotomous method and the four-point method. An introduction.
Carbon-based printing ink type electric heating film Heating material: graphite, metal powder, metal oxide
The production process of carbon-based printing ink electric heating film is to make the above-mentioned heating material together with other fillers into ink-like slurry, and quantitatively print it on the polyester film pre-bonded with metal current-carrying strips (as electrodes) by screen printing process. , and then covered with polyester film to form an insulating structure, so it is also called a printing ink electric heating film. The power control of this type of electric heating film is mainly realized through the composition of the paste, the thickness and spacing of the ink strips.
The technical core of the carbon-based printing ink electric heating film is the production and processing technology of the paste. At present, there are many carbon-based ink paste manufacturers and more than a dozen carbon-based printing ink electric heating film manufacturers in China. Foreign brands are dominated by the United States and South Korea.
Metal heating film Heating material: pure metal or metal alloy material
The production process of the metal-based electric heating film is to first make the metal or metal alloy material of the heating element into a metal foil, bond it on the polyester film to make a resistance circuit, and then coat it with a layer of polyester film to form an insulating structure. Commonly used metal electric heating materials are copper, nickel, copper-nickel, iron-chromium-aluminum and so on. Different metals and metal alloy materials have different resistivities, that is, electrical conductivity. According to this, different metal heating materials can be selected and different resistance circuits can be designed according to different working voltages and power requirements per unit area. The difference in metal materials will also directly affect the performance of the heating element (such as anti-oxidation ability)
and cost.
Carbon fiber heating film Heating material: carbon fiber
Carbon fiber is made of raw material fiber with high carbon content (usually more than 90 percent ), placed in an inert gas, and subjected to thermal stable oxidation at 200-300 degree , carbonization and graphitization at 1000-2000 degree . According to different basic raw materials, carbon fibers can be divided into polyacrylonitrile (PAN)-based, pitch-based and viscose-based carbon fibers. Among them, PAN-based carbon fibers account for 90 percent of the world's carbon fiber production. At present, the world's carbon fiber technology is mainly mastered in Japan. , while the production processes of most other carbon fiber companies are still in the process of continuous improvement. The main carbon fiber raw materials used in the production of carbon fiber electric heating film in China
Imported from Japanese company.
Carbon fiber has high temperature resistance, abrasion resistance, electrical conductivity, thermal conductivity and corrosion resistance. Carbon fiber can be combined with resin, metal, ceramics and other matrices to form a variety of composite materials, which are used in aerospace, automobile, oil drilling, sports and medical equipment and other fields.
Using the conductive properties of carbon fiber to make it into an electric heating material, it can be divided into two types: carbon fiber heating cable and carbon fiber heating film according to the structure of the heating body. Among them, carbon fiber electric heating film is divided into non-uniform linear carbon fiber electric heating film produced by textile process directly using carbon fiber filament (small tow or large tow) as warp or weft through textile process, and the carbon fiber filament is cut into Disturbed short fibers are mixed with pulp to form carbon fiber electric heating paper by papermaking process. Different power densities can be obtained by adjusting the carbon fiber ratio. According to the application and insulation grade requirements, the carbon fiber electric heating film is formed by covering with different insulating materials.
Polymer electric heating film Heating material: conductive polymer material.
The production process is to first synthesize functional polymer conductive composite materials using different molecular design methods, and uniformly coat the above conductive polymer materials on the pre-implanted electrode substrate by spraying or comma coating process to form a naked electric heating film. The polymer electric heating film is formed by covering with different insulating materials.
The polymer electric heatin
g film was born in Japan. The power density of the polymer electric heating film is realized by adjusting the polymerization degree of the heating body material, the number and proportion of positive and negative polar groups, and the number of free charges, rather than adding or subtracting the coating amount.
Although the types of electric heating films are different, they all contain three common parts, such as heating element, electrode and insulating layer. The difference is that the metal-based electric heating film and the carbon-based ink electric heating film are directly hot-pressed between the insulating polyester films, while the carbon fiber and polymer electric heating films are coated with the heating material on the substrate, and then covered with insulating materials.
Different types of electrothermal films have different electrothermal properties and application properties due to their different heating materials and different production and processing techniques, such as: the limit value of power density, the thermal stability and thermal uniformity of the heating element, and the resistance to heat. Oxidation and aging ability, power attenuation, cracking and swelling, etc., and these characteristics directly determine the most suitable application field of the product and the technological requirements for application and construction as a heating element material.