Moving Forward Every Day — 3/25/2010

Answer: The drying methods for coatings are generally divided into three types: natural drying, baking drying, and radiation drying. Their respective characteristics are as follows: (1) Natural drying: Natural drying refers to a drying method in which no external heat energy is required, and the material can solidify into a film at room temperature; it is also known as air drying, or simply self-drying. Solvent-evaporating coatings, oxidation-polymerizing coatings, room-temperature cross-linking curing coatings, and others can all be dried naturally. Typically, the painted workpieces are placed in a well-ventilated area to dry through natural ventilation. Drying time is affected by temperature, humidity, and ventilation conditions. During drying, it is advisable to maintain a temperature of 20–30°C and a relative humidity of ≤70%. When working outdoors in winter, do not leave the undry coating on the surface overnight to prevent dew and moisture from damaging it. To accelerate oxidation and the natural drying of polymeric and room-temperature crosslinking coatings, an appropriate amount of drying agent or curing agent can be added, and they can be baked at a temperature below 80°C for a period of time; this improves the adhesion and corrosion resistance of the coating film. After painting many large-scale devices and equipment, as well as precision instruments and meters, they are usually left to dry naturally ； This method is also used when painting outdoors, due to the limitations of heating equipment. (2) Baking drying: The drying method that uses heat to cure the coating into a film is called baking drying, or simply drying. Placing the painted workpiece in a drying room or oven for heating can **significantly reduce the drying time of the paint**, and it also greatly improves the hardness, adhesion, and corrosion resistance of the paint film. Drying by baking can be divided into three types based on temperature: low temperature (below 100°C), medium temperature (100–150°C), and high temperature (above 150°C). Different types of coatings require different baking temperatures; low-temperature baking is suitable for drying the coating on wood and plastics that are prone to deformation when heated (usually not exceeding 80°C), while medium- and high-temperature baking can only be used for drying the coating on metal products. Reducing the baking and drying temperature of coatings helps save energy, lower costs, improve efficiency, and expand the range of applications for coating products; therefore, it is one of the main goals in improving existing coating types and developing new ones. (3) Radiation drying: Radiation drying is a drying method in which the coating is cured into a film through radiation heating or using ultraviolet light and electron beam energy. Radiant heating achieves drying and film formation by heating the painted workpiece through infrared or far-infrared radiation; this is referred to as infrared drying and far-infrared drying, respectively. Ultraviolet curing involves irradiating a photocurable coating containing a photosensitizer with ultraviolet light of a specific wavelength. The photosensitizer decomposes to produce highly reactive free radicals, which then initiate a polymerization reaction that allows the coating to cure into a film within an extremely short time range (from several seconds to a few minutes), thereby achieving drying at room temperature. It is suitable for drying coatings on wood, plastic, and other materials that cannot be heated; it is only used for drying light-curing varnishes, and enamel cannot be dried using this method. Electron beam curing involves irradiating a coated film with high-energy electron beams, which generate active groups within the molecules and trigger a polymerization reaction; the film can thus be cured in 1–2 seconds, achieving rapid drying at room temperature. Its feature is that it can be used for curing opaque paints, but it has blind spots in terms of illumination, and is not suitable for curing the interior of pipes or the inner surfaces of car bodies. It is mainly used for the drying and film formation after coating on wooden sheets, plastics, metal sheets or coils, paper, fabrics, and leather.

Depending on their different film-forming mechanisms, various coatings require different drying conditions and processes. The drying methods for coatings can be classified into natural drying, heat drying, radiation drying, and vapor-phase drying, among others. (1) Natural drying: Natural drying refers to the process of allowing the coated film to dry and cure at room temperature in the atmosphere; it is commonly also referred to as normal drying or air drying. Natural drying is only suitable for volatile, emulsion-coagulated, oxidation-polymerized, and certain polymerized coatings with added curing agents. Factors that affect the quality of naturally dried coatings include temperature, humidity, climate (sunny or cloudy weather, rain, fog, snow, etc.), wind speed, air cleanliness, and light intensity. Generally, free drying is fast and safe under conditions of high temperature, low humidity, high wind speed, and strong light ； Conversely, drying is slow, curing is poor, and it may even affect the quality of the coating film. Natural drying is simple to implement; it requires no energy or special curing equipment. It is particularly suitable for coating surfaces that are not suitable for or cannot be baked, such as buildings, structures in need of repair, plastics, paper, leather, etc. (2) Heating and drying: Heating and drying can be divided into baking drying and forced drying. Baking drying refers to the heat drying of bake-type coatings, that is, the heat drying of coatings that cannot dry without heating. Heating a paint that can dry naturally to accelerate drying and shorten the drying time is called forced drying. Based on the baking temperature, heat drying can be divided into three categories: low temperature (<100°C), medium temperature (100–150°C), and high temperature (>150°C). Classified by heating method, there are three types: convection heating, radiation heating, and induction heating. The drying process conditions (temperature and time) depend on the type of coating, the conditions of the items to be dried, and the heating method. The main process parameters for heat drying are the drying temperature and drying time, which must be specified in the product instructions for coatings. In addition to these two factors, the following process considerations are also important to take into account during heat drying. 1. Except for powder coatings and electrophoretic coatings, conventional solvent-based coatings require a period of time at room temperature before baking, so that the coating film can fully level out and the solvents can evaporate; otherwise, defects such as \"pinholes,\" \"orange peel effect,\" and \"bubbling\" may occur. 2. Certain coatings (such as oil-modified alkyd resins, acrylic resins, etc.) should not be exposed to baking at the specified temperature directly; there should be a gradual increase from room temperature to the specified temperature, so that the temperature of the coating film rises slowly. Otherwise, problems such as bubbling and wrinkling may occur. 3. The temperature inside the drying oven should be kept uniform to prevent localized over-drying or incomplete drying of the coating. 4. The solvents that evaporate during the drying process, as well as the small molecules that decompose, must be removed from the furnace as quickly as possible. 5. The air in the drying rooms and ovens must be filtered and purified. 6. The specified temperature refers to the uniform temperature within the furnace required to dry the coated film or substrate. (3) Radiation curing is further divided into ultraviolet curing and electron beam curing. Electron beam curing has not been widely used due to drawbacks such as high equipment costs, strict requirements, large curing blind spots, and poor curing efficiency on curved surfaces. Compared with ultraviolet curing, its advantage lies in its high energy, which allows it to be used for curing opaque coatings. The light waves used for UV curing are near-ultraviolet rays with wavelengths between 300 and 400 nanometers; when a coating containing a photosensitive initiator is exposed to this light, free radicals are generated. Polymerization of unsaturated monomers or resins is initiated by free radicals, resulting in the cross-linking and curing of the coating layer; this process is very rapid and generally takes just a few minutes to complete. It is widely used for substrates with high requirements for coating quality for which baking is not feasible, such as certain types of wood, paper, and communication fibers. However, it is suitable only for UV-curing coatings and cannot be used to cure opaque paint films. Drying time is related to the coating film thickness, ultraviolet light intensity, and irradiation distance. The higher the light intensity, the closer the irradiation distance, the thinner the film thickness, and the shorter the drying time ； Conversely, the drying time is longer. Ultraviolet light sources used in industry generally include high-pressure mercury lamps, arc lamps, xenon lamps, fluorescent lamps, etc., among which high-pressure mercury lamps are the most widely used. In recent years, to expand the application scope of radiation curing and reduce pollution, methods such as gamma-ray curing and high-frequency oscillation curing have been developed. Their principles are essentially the same as those of ultraviolet curing, with the difference lying in the way in which the initiator is activated. (3) Vapour phase curing: Vapour phase curing refers to two or more prepolymers that have the ability to react with each other. The reaction is carried out in a gasified catalyst atmosphere to cure the coating film. The currently practical vapor curing systems involve reacting isocyanates with resins containing bisphenolic acids in a saturated tertiary amine atmosphere; such coatings belong to the type that undergoes free radical polymerization and cross-linking. The gas-phase curing equipment is very simple; all that is needed is to convert the drying oven of a regular baking line into an amine gas chamber. The coating used for vapor-phase curing is a two-component coating, usually a urethane-modified resin coating.

The drying method of coatings (more accurately, the curing method) is related to the properties of the coatings; the most common methods include self-drying, drying by heat, and curing with ultraviolet light. Self-drying types further include those that dry through solvent evaporation, or cross-linking curing types; in the case of cross-linking curing, it can occur through reaction with moisture and oxygen in the air, or through reaction with specialized curing agents to achieve cross-linking. Generally, exposing it to sunlight can increase the curing speed, and baking has a similar effect. Self-drying coatings include those that cure due to the evaporation of solvents, and those that cure through natural cross-linking with moisture/oxygen in the air. Generally, their overall performance – including mechanical properties such as wear resistance and hardness, as well as physical and chemical properties such as solvent resistance, acid and alkali resistance, and corrosion resistance – is inferior compared to coatings that are cured using drying processes or specialized curing agents; therefore, they are considered low-quality coatings. The biggest advantage of self-drying coatings is their simplicity of use and low cost. Coatings that are cured by baking or specialized curing agents have superior performance, but their application process is complex and the cost is high. Natural drying involves the evaporation of solvents and curing through reaction with water vapor or oxygen in the air; therefore, it has no direct relation to a shaded area. However, sunlight exposure or heating will certainly accelerate the curing process of the paint. Direct sunlight accelerates the aging of paint, as the ultraviolet rays contained in it trigger a series of oxidation reactions in the coating, leading to chain breakdown and powdering.

I. Natural drying: Natural drying refers to the process of allowing the paint to dry and cure at room temperature in the atmosphere; it is commonly also referred to as air drying. Natural drying is only suitable for volatile, emulsion-coagulated, oxidation-polymerized, and certain polymerized coatings with added curing agents. Factors that affect the quality of naturally dried coatings include temperature, humidity, climate (sunny or cloudy, rain, fog, snow, etc.), wind speed, air cleanliness, and light intensity. Generally speaking, free drying is fast and safe under conditions of high temperature, low humidity, high wind speed, and strong light ； Conversely, drying is slow, curing is poor, and it may even affect the quality of the coating. Natural drying is simple to implement; it requires no energy or special curing equipment. It is particularly suitable for coating surfaces that are not suitable or cannot be baked, such as buildings, structural repairs, plastics, paper, leather, etc. II. Heating and Drying Heating and drying can be divided into baking drying and forced drying. Baking drying refers to the heat-based drying of bake-type coatings, that is, the heat-based drying of coatings that cannot dry without heating. Heating a paint that can dry naturally to accelerate its drying and shorten the drying time is known as forced drying. Based on the baking temperature, heat drying can be divided into three categories: low temperature, medium temperature, and high temperature. Classified by heating method, there are three types: convection heating, radiation heating, and induction heating. The main process parameters for heat drying are the drying temperature and drying time, which must be specified in the product instructions for coatings. In addition to these two factors, the following process considerations are also important to take into account during heat drying. 1. Except for powder coatings and electrophoretic coatings, conventional solvent-based coatings require a period of time at room temperature before baking, so that the coating can settle properly and the solvents can evaporate; otherwise, defects such as \"pinholes,\" \"orange peel effect,\" and \"bubbling\" may occur. 2. Certain coatings (such as oil-modified alkyd resins and acrylic resins) should not be exposed to baking at the specified temperature directly; there should be a gradual increase from room temperature to the specified temperature, so that the temperature of the coating rises slowly. Otherwise, problems such as bubbling and wrinkling may occur. 3. The temperature inside the drying oven should be kept uniform to prevent localized over-drying or incomplete drying of the coating. 4. The solvents that evaporate during the drying process, as well as the small molecules that decompose, must be removed from the furnace as quickly as possible. 5. The air in the drying rooms and ovens must be filtered and purified. 6. The specified temperature refers to the uniform temperature inside the furnace required to dry the coating or substrate. III. Radiation curing. Radiation curing is further divided into ultraviolet curing and electron beam curing. Electron beam curing has not been widely used due to drawbacks such as high equipment costs, strict requirements, large radiation blind spots, and poor curing effects on curved surfaces. Compared with ultraviolet curing, its advantage lies in its high energy level, which allows it to be used for curing opaque coatings. The light waves used for UV curing are near-ultraviolet rays with wavelengths between 300 and 400 nanometers; coatings containing photosensitive initiators generate free radicals upon exposure to this light. Polymerization of unsaturated monomers or resins is initiated by free radicals, thereby enabling the cross-linking and curing of the coating; this process is very rapid and generally takes place within a few minutes. It is widely used for substrates that require high painting quality but for which baking is not feasible, such as certain types of wood, paper, and communication fibers. However, it is suitable only for UV-curing coatings and cannot be used to cure opaque paints. Drying time is related to the coating thickness, ultraviolet light intensity, and irradiation distance. The higher the light intensity, the closer the irradiation distance, the thinner the material thickness, and the shorter the drying time ； Conversely, the drying time is longer. Ultraviolet light sources used in industry generally include high-pressure mercury lamps, arc lamps, xenon lamps, fluorescent lamps, etc., among which high-pressure mercury lamps are the most widely used. In recent years, to expand the application scope of radiation curing and reduce pollution, methods such as gamma-ray curing and high-frequency oscillation curing have been developed. Their principles are essentially the same as those of ultraviolet curing, with the difference lying in the way in which the initiator is activated. IV. Vapour Phase Curing Vapour phase curing refers to the use of two or more prepolymers that are capable of reacting with each other. The reaction is carried out in a gasified catalyst atmosphere to cure the coating. The currently practical vapor curing systems involve the reaction of isocyanates with resins containing bisphenol acids in a saturated tertiary amine atmosphere; such coatings belong to the type that undergoes free radical polymerization and cross-linking. The gas-phase curing equipment is very simple; all that is needed is to convert the drying oven of a regular baking line into an amine gas chamber. The coating used for vapor-phase curing is a two-component coating, usually a urethane-modified resin coating.

Depending on their different film-forming mechanisms, various coatings require different drying conditions and processes. The drying methods for coatings can be classified into natural drying, heat drying, radiation drying, and vapor-phase drying, among others. (1) Natural drying: Natural drying refers to the process of allowing the coated film to dry and cure at room temperature in the atmosphere; it is commonly also referred to as normal drying or air drying. Natural drying is only suitable for volatile, emulsion-coagulated, oxidation-polymerized, and certain polymerized coatings with added curing agents. Factors that affect the quality of naturally dried coatings include temperature, humidity, climate (sunny or cloudy weather, rain, fog, snow, etc.), wind speed, air cleanliness, and light intensity. Generally, free drying is fast and safe under conditions of high temperature, low humidity, high wind speed, and strong light ； Conversely, drying is slow, curing is poor, and it may even affect the quality of the coating film. Natural drying is simple to implement; it requires no energy or special curing equipment. It is particularly suitable for coating surfaces that are not suitable for or cannot be baked, such as buildings, structures in need of repair, plastics, paper, leather, etc. (2) Heating and drying: Heating and drying can be divided into baking drying and forced drying. Baking drying refers to the heat drying of bake-type coatings, that is, the heat drying of coatings that cannot dry without heating. Heating a paint that can dry naturally to accelerate drying and shorten the drying time is called forced drying. Based on the baking temperature, heat drying can be divided into three categories: low temperature (<100°C), medium temperature (100–150°C), and high temperature (>150°C). Classified by heating method, there are three types: convection heating, radiation heating, and induction heating. The drying process conditions (temperature and time) depend on the type of coating, the conditions of the items to be dried, and the heating method. The main process parameters for heat drying are the drying temperature and drying time, which must be specified in the product instructions for coatings. In addition to these two factors, the following process considerations are also important to take into account during heat drying. 1. Except for powder coatings and electrophoretic coatings, conventional solvent-based coatings require a period of time at room temperature before baking, so that the coating film can fully level out and the solvents can evaporate; otherwise, defects such as \"pinholes,\" \"orange peel effect,\" and \"bubbling\" may occur. 2. Certain coatings (such as oil-modified alkyd resins, acrylic resins, etc.) should not be exposed to baking at the specified temperature directly; there should be a gradual increase from room temperature to the specified temperature, so that the temperature of the coating film rises slowly. Otherwise, problems such as bubbling and wrinkling may occur. 3. The temperature inside the drying oven should be kept uniform to prevent localized over-drying or incomplete drying of the coating. 4. The solvents that evaporate during the drying process, as well as the small molecules that decompose, must be removed from the furnace as quickly as possible. 5. The air in the drying rooms and ovens must be filtered and purified. 6. The specified temperature refers to the uniform temperature within the furnace required to dry the coated film or substrate. (3) Radiation curing is further divided into ultraviolet curing and electron beam curing. Electron beam curing has not been widely used due to drawbacks such as high equipment costs, strict requirements, large curing blind spots, and poor curing efficiency on curved surfaces. Compared with ultraviolet curing, its advantage lies in its high energy, which allows it to be used for curing opaque coatings. The light waves used for UV curing are near-ultraviolet rays with wavelengths between 300 and 400 nanometers; when a coating containing a photosensitive initiator is exposed to this light, free radicals are generated. Polymerization of unsaturated monomers or resins is initiated by free radicals, resulting in the cross-linking and curing of the coating layer; this process is very rapid and generally takes just a few minutes to complete. It is widely used for substrates with high requirements for coating quality for which baking is not feasible, such as certain types of wood, paper, and communication fibers. However, it is suitable only for UV-curing coatings and cannot be used to cure opaque paint films. Drying time is related to the coating film thickness, ultraviolet light intensity, and irradiation distance. The higher the light intensity, the closer the irradiation distance, the thinner the film thickness, and the shorter the drying time ； Conversely, the drying time is longer. Ultraviolet light sources used in industry generally include high-pressure mercury lamps, arc lamps, xenon lamps, fluorescent lamps, etc., among which high-pressure mercury lamps are the most widely used. In recent years, to expand the application scope of radiation curing and reduce pollution, methods such as gamma-ray curing and high-frequency oscillation curing have been developed. Their principles are essentially the same as those of ultraviolet curing, with the difference lying in the way in which the initiator is activated. (3) Vapour phase curing: Vapour phase curing refers to two or more prepolymers that have the ability to react with each other. The reaction is carried out in a gasified catalyst atmosphere to cure the coating film. The currently practical vapor curing systems involve reacting isocyanates with resins containing bisphenolic acids in a saturated tertiary amine atmosphere; such coatings belong to the type that undergoes free radical polymerization and cross-linking. The gas-phase curing equipment is very simple; all that is needed is to convert the drying oven of a regular baking line into an amine gas chamber. The coating used for vapor-phase curing is a two-component coating, usually a urethane-modified resin coating.

Depending on their different film-forming mechanisms, various coatings require different drying conditions and processes. The drying methods for coatings can be classified into natural drying, heat drying, radiation drying, and vapor-phase drying, among others. (1) Natural drying: Natural drying refers to the process of allowing the coated film to dry and cure at room temperature in the atmosphere; it is commonly also referred to as normal drying or air drying. Natural drying is only suitable for volatile, emulsion-coagulated, oxidation-polymerized, and certain polymerized coatings with added curing agents. Factors that affect the quality of naturally dried coatings include temperature, humidity, climate (sunny or cloudy weather, rain, fog, snow, etc.), wind speed, air cleanliness, and light intensity. Generally, free drying is fast and safe under conditions of high temperature, low humidity, high wind speed, and strong light ； Conversely, drying is slow, curing is poor, and it may even affect the quality of the coating film. Natural drying is simple to implement; it requires no energy or special curing equipment. It is particularly suitable for coating surfaces that are not suitable for or cannot be baked, such as buildings, structures in need of repair, plastics, paper, leather, etc. (2) Heating and drying: Heating and drying can be divided into baking drying and forced drying. Baking drying refers to the heat drying of bake-type coatings, that is, the heat drying of coatings that cannot dry without heating. Heating a paint that can dry naturally to accelerate drying and shorten the drying time is called forced drying. Based on the baking temperature, heat drying can be divided into three categories: low temperature, medium temperature, and high temperature. Classified by heating method, there are three types: convection heating, radiation heating, and induction heating. The main process parameters for heat drying are the drying temperature and drying time, which must be specified in the product instructions for coatings. In addition to these two factors, the following process considerations are also important to take into account during heat drying. 1. Except for powder coatings and electrophoretic coatings, conventional solvent-based coatings require a period of time at room temperature before baking, so that the coating film can fully level out and the solvents can evaporate; otherwise, defects such as \"pinholes,\" \"orange peel effect,\" and \"bubbling\" may occur. 2. Certain coatings (such as oil-modified alkyd resins, acrylic resins, etc.) should not be exposed to baking at the specified temperature directly; there should be a gradual increase from room temperature to the specified temperature, so that the temperature of the coating film rises slowly. Otherwise, problems such as bubbling and wrinkling may occur. 3. The temperature inside the drying oven should be kept uniform to prevent localized over-drying or incomplete drying of the coating. 4. The solvents that evaporate during the drying process, as well as the small molecules that decompose, must be removed from the furnace as quickly as possible. 5. The air in the drying rooms and ovens must be filtered and purified. 6. The specified temperature refers to the uniform temperature within the furnace required to dry the coated film or substrate. (3) Radiation curing: Radiation curing is further divided into ultraviolet curing and electron beam curing. Electron beam curing has not been widely used due to drawbacks such as high equipment costs, strict requirements, large curing blind spots, and poor curing efficiency on curved surfaces. Compared with ultraviolet curing, its advantage lies in its high energy level, which allows it to be used for curing opaque coatings. The light waves used for UV curing are near-ultraviolet rays with wavelengths between 300 and 400 nanometers; when a coating containing a photosensitive initiator is exposed to this light, free radicals are generated. Polymerization of unsaturated monomers or resins is initiated by free radicals, resulting in the cross-linking and curing of the coating layer; this process is very rapid and generally takes just a few minutes to complete. It is widely used for substrates with high requirements for coating quality for which baking is not feasible, such as certain types of wood, paper, and communication fibers. However, it is suitable only for UV-curing coatings and cannot be used to cure opaque paint films. Drying time is related to the coating film thickness, ultraviolet light intensity, and irradiation distance. The higher the light intensity, the closer the irradiation distance, the thinner the film thickness, and the shorter the drying time ； Conversely, the drying time is longer. Ultraviolet light sources used in industry generally include high-pressure mercury lamps, arc lamps, xenon lamps, fluorescent lamps, etc., among which high-pressure mercury lamps are the most widely used. In recent years, to expand the application scope of radiation curing and reduce pollution, methods such as gamma-ray curing and high-frequency oscillation curing have been developed. Their principles are essentially the same as those of ultraviolet curing, with the difference lying in the way in which the initiator is activated. (4) Vapour phase curing: Vapour phase curing refers to two or more prepolymers that have the ability to react with each other. The reaction is carried out in a gasified catalyst atmosphere to cure the coating film. The currently practical vapor curing systems involve reacting isocyanates with resins containing bisphenolic acids in a saturated tertiary amine atmosphere; such coatings belong to the type that undergoes free radical polymerization and cross-linking. The gas-phase curing equipment is very simple; all that is needed is to convert the drying oven of a regular baking line into an amine gas chamber. The coating used for vapor-phase curing is a two-component coating, usually a urethane-modified resin coating. 1# Green Hand

The drying methods for coatings can be classified into natural drying, heat drying, radiation drying, and vapor-phase drying, among others. 1. Natural drying: Natural drying refers to the process of allowing the coated film to dry and cure at room temperature in the atmosphere; it is commonly also referred to as normal drying or air drying. Natural drying is only suitable for volatile, emulsion-coagulated, oxidation-polymerized, and certain polymerized coatings with added curing agents. Factors that affect the quality of naturally dried coatings include temperature, humidity, climate (sunny or cloudy weather, rain, fog, snow, etc.), wind speed, air cleanliness, and light intensity. Generally, free drying is fast and safe under conditions of high temperature, low humidity, high wind speed, and strong light ； Conversely, drying is slow, curing is poor, and it may even affect the quality of the coating film. Natural drying is simple to implement; it requires no energy or special curing equipment. It is particularly suitable for coating surfaces that are not suitable for or cannot be baked, such as buildings, structures in need of repair, plastics, paper, leather, etc. 2. Heating drying: Heating drying can be divided into baking drying and forced drying. Baking drying refers to the heat drying of bake-type coatings, that is, the heat drying of coatings that cannot dry without heating. Heating a paint that can dry naturally to accelerate drying and shorten the drying time is called forced drying. Based on the baking temperature, heat drying can be divided into three categories: low temperature, medium temperature, and high temperature. Classified by heating method, there are three types: convection heating, radiation heating, and induction heating. The main process parameters for heat drying are the drying temperature and drying time, which must be specified in the product instructions for coatings. In addition to these two factors, the following process considerations are also important to take into account during heat drying. 3. Radiation curing. Radiation curing is further divided into ultraviolet curing and electron beam curing. Electron beam curing has not been widely used due to drawbacks such as high equipment costs, strict requirements, large curing blind spots, and poor curing performance on curved surfaces. Compared with ultraviolet curing, its advantage lies in its high energy level, which allows it to be used for curing opaque coatings. The light waves used for UV curing are near-ultraviolet rays with wavelengths between 300 and 400 nanometers; when a coating containing a photosensitive initiator is exposed to this light, free radicals are generated. Polymerization of unsaturated monomers or resins is initiated by free radicals, resulting in the cross-linking and curing of the coating layer; this process is very rapid and generally takes just a few minutes to complete. It is widely used for substrates with high requirements for coating quality for which baking is not feasible, such as certain types of wood, paper, and communication fibers. However, it is suitable only for UV-curing coatings and cannot be used to cure opaque paint films. Drying time is related to the coating film thickness, ultraviolet light intensity, and irradiation distance. The higher the light intensity, the closer the irradiation distance, the thinner the film thickness, and the shorter the drying time ； Conversely, the drying time is longer. Ultraviolet light sources used in industry generally include high-pressure mercury lamps, arc lamps, xenon lamps, fluorescent lamps, etc., among which high-pressure mercury lamps are the most widely used. In recent years, to expand the application scope of radiation curing and reduce pollution, methods such as gamma-ray curing and high-frequency oscillation curing have been developed. Their principles are essentially the same as those of ultraviolet curing, with the difference lying in the way in which the initiator is activated. 4. Vapour curing: Vapour curing refers to two or more prepolymers that have the ability to react with each other. The reaction is carried out in a gasified catalyst atmosphere to cure the coating film. The currently practical vapor curing systems involve reacting isocyanates with resins containing bisphenolic acids in a saturated tertiary amine atmosphere; such coatings belong to the type that undergoes free radical polymerization and cross-linking. The gas-phase curing equipment is very simple; all that is needed is to convert the drying oven of a regular baking line into an amine gas chamber. The coating used for vapor-phase curing is a two-component coating, usually a urethane-modified resin coating. bs.hcbbs.com/redirect.php?goto=findpost&pid=3665565&ptid=638440]1# Green Hands

(1) Natural drying: Natural drying refers to a drying method in which no external heat is required; the material can solidify into a film at room temperature. It is also known as air drying, or simply self-drying. Solvent-evaporating coatings, oxidation-polymerizing coatings, room-temperature cross-linking curing coatings, and others can all be dried naturally. Typically, the painted workpieces are placed in a well-ventilated area to dry through natural ventilation. Drying time is affected by temperature, humidity, and ventilation conditions. During drying, it is advisable to maintain a temperature of 20–30°C and a relative humidity of ≤70%. When working outdoors in winter, do not leave the undry coating on the surface overnight to prevent dew and moisture from damaging it. To accelerate oxidation and the natural drying of polymeric and room-temperature crosslinking coatings, an appropriate amount of drying agent or curing agent can be added, and they can be baked at a temperature below 80°C for a period of time; this improves the adhesion and corrosion resistance of the coating film. After painting many large-scale devices and equipment, as well as precision instruments and meters, they are usually left to dry naturally ； This method is also used when painting outdoors, due to the limitations of heating equipment. (2) Baking drying: The drying method that uses heat to cure the coating into a film is called baking drying, or simply drying. Placing the painted workpiece in a drying room or oven for heating can **significantly reduce the drying time of the paint**, and it also greatly improves the hardness, adhesion, and corrosion resistance of the paint film. Drying by baking can be divided into three types based on temperature: low temperature (below 100°C), medium temperature (100–150°C), and high temperature (above 150°C). Different types of coatings require different baking temperatures; low-temperature baking is suitable for drying the coating on wood and plastics that are prone to deformation when heated (usually not exceeding 80°C), while medium- and high-temperature baking can only be used for drying the coating on metal products. Reducing the baking and drying temperature of coatings helps save energy, lower costs, improve efficiency, and expand the range of applications for coating products; therefore, it is one of the main goals in improving existing coating types and developing new ones. (3) Radiation drying: Radiation drying is a drying method in which the coating is cured into a film through radiation heating or using ultraviolet light and electron beam energy. Radiant heating achieves drying and film formation by heating the painted workpiece through infrared or far-infrared radiation; this is referred to as infrared drying and far-infrared drying, respectively. Ultraviolet curing involves irradiating a photocurable coating containing a photosensitizer with ultraviolet light of a specific wavelength. The photosensitizer decomposes to produce highly reactive free radicals, which then initiate a polymerization reaction that allows the coating to cure into a film within an extremely short time range (from several seconds to a few minutes), thereby achieving drying at room temperature. It is suitable for drying coatings on wood, plastic, and other materials that cannot be heated; it is only used for drying light-curing varnishes, and enamel cannot be dried using this method. Electron beam curing involves irradiating a coated film with high-energy electron beams, which generate active groups within the molecules and trigger a polymerization reaction; the film can thus be cured in 1–2 seconds, achieving rapid drying at room temperature. Its feature is that it can be used for curing opaque paints, but it has blind spots in terms of illumination, and is not suitable for curing the interior of pipes or the inner surfaces of car bodies. It is mainly used for the drying and film formation after coating on wooden sheets, plastics, metal sheets or coils, paper, fabrics, and leather.

Natural drying has the advantage of saving energy. Baking drying is fast, resulting in a membrane with good hardness and adhesion. Ventilated drying falls somewhere in between the two? :lol

Cure by cooling and cure by heat. Generally, cold curing takes longer and is mostly used in engineering applications. The thermal curing time is fast, and the curing effect is good.