A coating machine is a device that wraps a polymer around a tablet core to form a film. That is, the coating solution is sprayed onto the surface of the rolling core, and hot air is introduced to evaporate the solvent on the rolling core to form a continuous polymer film on the surface. The formation of droplets, the movement of droplets to the core, the impact, spreading, coalescence of the droplets on the surface of the core, and the drying of the film are all important factors affecting the coating. These require the designer and operator to understand and control. To achieve a high quality coating.
The characteristics of the coating: (1) overcome the shortcomings of the tablet is not easy to swallow; (2) improve the stability of the tablet to prevent oxidative degeneration caused by light or air; (3) regulate the release of the drug; (4) ) to isolate easily compatible drugs; (5) better appearance.
1 Film formation mechanism and influencing factors After the coating, the structure of the film on the core is not uniform, and the appearance is also different. This heterogeneity is caused by insoluble components (such as colorants) that are intentionally added, while the film is not continuously formed during the coating process. Most coating processes are carried out by adhering the polymer solution to the solid core after spraying, and then taking the next spray. This process needs to be repeated several times until the coating is completed. In order to obtain a good coating effect, it is first necessary to understand the formation mechanism of the film.
1.1 Formation mechanism of the film The formation of the film of the aqueous polymer dispersion is very complicated. It is found that in the wetting stage, the polymer exists in a large amount of discontinuous particles, and as the drying progresses, the water is reduced. The distance becomes small until intimate contact, deformation, and agglomeration, and then melts together to form a discontinuous film in which the surface of the coated core is wetted by the dilute dispersion. In this process, water volatilizes in the form of water vapor and polymer particles are connected to each other. The capillary action of the water film around the particles greatly accelerates the process, and when adjacent particles diffuse into each other, a completely condensed state occurs.
The following processes are involved in several important stages: (1) preparation of the coating solution or suspension; (2) generation of droplets; (3) movement of droplets from the spray gun to the bed; (4) droplets Impact, wetting, spreading, and coalescence on the core surface or particle surface; (5) dry gelation and adhesion film formation. Figure 1 is a schematic illustration of the above stages.
Figure 1. Five Stages of the Coating Process 1.2 Physical Properties of the Coating Solution or Suspension Effect on the Coating Process The physical properties of the coating solution or suspension have an effect on the other four stages of the coating process. It has been found that the particle size of the droplets has a direct influence on the appearance of the garment. Some formulas are summarized to describe the effect on the properties of the droplets, but there are differences between the formulas. The reason for the difference is that there is a very large difference between the selected atomizers. Large differences, so a formula can only be applied to the respective conditions, and when extrapolated to other systems, there will be a large deviation.
Fair (1974) proposed a formula to describe the effect of solution properties on the droplet size in a hydraulic spray:
DVM solution / DVM solvent = {γ solution / γ solvent} 0.5 × {μ solution / μ solvent} 0.2 × {Ï solution / Ï solvent} 0.3
Where DVM - the volume average particle size of the droplets;
γ - the surface tension of the solution;
μ - the viscosity of the solution;
Ï - the density of the solution.
Nukiyama and Tanasawa (1939) proposed a formula for describing the particle size of droplets generated during atmospheric atomization:
Ds={585×103/v}×{γ/Ï}0.5+1683μ0.45{γ×Ï}-0.225{1000/J}1.5
Where Ds - the average surface particle size of the droplets;
Η—the rate of gas relative to the liquid at the outlet of the spray pipe (m/s);
Γ——the surface tension of the liquid (N/m);
Ρ——liquid density (kg/m3);
Μ——the viscosity of the liquid (Pa·s);
J——The volume ratio of gas/liquid at the nozzle.
The above formula shows that the physical properties of the solution will affect the particle size and particle size distribution of the droplets, and then determine the fate of the droplets on the surface of the core, which ultimately affects the quality of the coating. In the physical properties of the solution, the viscosity, surface tension, and density are important for the formulation spray of the coating liquid.
Such as surface tension will affect the formation of droplets. The longer the droplets move toward the core of the coated tablet, the more likely it is to affect the wetting, spreading, penetrating, and adhering processes after reaching the surface of the core, thereby affecting the integrity of the coating, the adhesion of the core surface, and the surface finish; Viscosity affects the evaporation rate of the solvent, affecting the coalescence of droplets suspended in the air. However, in actual engineering, the influence of the actual tension on the quality can be reduced by adjusting the parameters such as the nozzle and the distance.
1.3 Atomization method and principle The generation of droplets is to break the liquid into a mist composed of small droplets. The ideal droplets are required to spread evenly after reaching the surface of the core and form a smooth continuous film of uniform thickness. Air and hydraulics are often used to make fog particles in actual coating equipment. The following are four methods and principles of atomization:
1.3.1 Ultrasonic atomization Ultrasonic atomization is a method of atomizing a liquid by intense high frequency oscillation. The advantage is that the atomization efficiency is high, and most of the energy consumed is used to increase the surface area of ​​the droplets, unlike less than 1% of the other two atomization methods are used to increase the surface area. The disadvantage is that it is difficult to control the rate at which the liquid flows, so that the produced droplets do not have sufficient momentum or are prone to clogging of the nozzle.
1.3.2 Hydraulic airless spray Hydraulic airless spray is in the hydraulic sprayer, the coating liquid passes through a small hole under high pressure, the static pressure energy is converted into kinetic energy, and the coating liquid is dispersed into droplets. Changing the pressure of the liquid or the direction in which the liquid flows into the orifice or using a different nozzle will result in a change in the shape of the droplet. A ribbon or conical mist curtain can be formed. When the polymer is dissolved in an organic solvent, a hydraulic spray method is often selected because no gas is used during the atomization process to prevent premature drying of the droplets. To atomize a solution with a certain viscosity, a higher pressure is required, and a very small pore size is required to ensure the liquid flow rate.
1.3.3 Air Pressure Spray Air pressure spray is to use a high-speed air flow to collide with the solution and rub to form a droplet. The relative shear force generated by the high-speed high-pressure gas stream atomizes the solution because the gas density is small and requires a large volume of high-speed gas to generate sufficient energy to atomize a solution having a certain viscosity and tension.
1.3.4 Centrifugal spray Centrifugal spray is a coating liquid that rotates at a high speed in a centrifugal disk to obtain a high centrifugal force and is scooped out at high speed to form a film, a filament or a droplet, and is also subjected to friction and tearing of the surrounding airflow. Forming droplets.
The above four methods are commonly used in air conditioning sprays and hydraulic sprays in coating equipment. Research has found that factors affecting droplet formation and movement: (1) atomization gas pressure; (2) liquid mist shape; (3) The distance from the spray gun to the bed; (4) the diameter of the liquid nozzle; (5) the radial distance of the center of the liquid mist; (6) the design of the atomizer, ν - the rate of gas relative to the liquid at the outlet of the spray tube (m/ s);
Γ——the surface tension of the liquid (N/m);
Ρ——liquid density (kg/m3);
Μ——the viscosity of the liquid (Pa·s);
J——The volume ratio of gas/liquid at the nozzle.
The above formula shows that the physical properties of the solution will affect the particle size and particle size distribution of the droplets, and then determine the fate of the droplets on the surface of the core, which ultimately affects the quality of the coating. In the physical properties of the solution, the viscosity, surface tension, and density are important for the formulation spray of the coating liquid.
Such as surface tension will affect the formation of droplets. The longer the droplets move toward the core of the coated tablet, the more likely it is to affect the wetting, spreading, penetrating, and adhering processes after reaching the surface of the core, thereby affecting the integrity of the coating, the adhesion of the core surface, and the surface finish; Viscosity affects the evaporation rate of the solvent, affecting the coalescence of droplets suspended in the air. However, in actual engineering, the influence of the actual tension on the quality can be reduced by adjusting the parameters such as the nozzle and the distance.
1.3 Atomization method and principle The generation of droplets is to break the liquid into a mist composed of small droplets. The ideal droplets are required to spread evenly after reaching the surface of the core and form a smooth continuous film of uniform thickness. Air and hydraulics are often used to make fog particles in actual coating equipment. The following are four methods and principles of atomization:
1.3.1 Ultrasonic atomization Ultrasonic atomization is a method of atomizing a liquid by intense high frequency oscillation. The advantage is that the atomization efficiency is high, and most of the energy consumed is used to increase the surface area of ​​the droplets, unlike less than 1% of the other two atomization methods are used to increase the surface area. The disadvantage is that it is difficult to control the rate at which the liquid flows, so that the produced droplets do not have sufficient momentum or are prone to clogging of the nozzle.
1.3.2 Hydraulic airless spray Hydraulic airless spray is in the hydraulic sprayer, the coating liquid passes through a small hole under high pressure, the static pressure energy is converted into kinetic energy, and the coating liquid is dispersed into droplets. Changing the pressure of the liquid or the direction in which the liquid flows into the orifice or using a different nozzle will result in a change in the shape of the droplet. A ribbon or conical mist curtain can be formed. When the polymer is dissolved in an organic solvent, a hydraulic spray method is often selected because no gas is used during the atomization process to prevent premature drying of the droplets. To atomize a solution with a certain viscosity, a higher pressure is required, and a very small pore size is required to ensure the liquid flow rate.
1.3.3 Air Pressure Spray Air pressure spray is to use a high-speed air flow to collide with the solution and rub to form a droplet. The relative shear force generated by the high-speed high-pressure gas stream atomizes the solution because the gas density is small and requires a large volume of high-speed gas to generate sufficient energy to atomize a solution having a certain viscosity and tension.
1.3.4 Centrifugal spray Centrifugal spray is a coating liquid that rotates at a high speed in a centrifugal disk to obtain a high centrifugal force and is scooped out at high speed to form a film, a filament or a droplet, and is also subjected to friction and tearing of the surrounding airflow. Forming droplets.
The above four methods are commonly used in air conditioning sprays and hydraulic sprays in coating equipment. Research has found that factors affecting droplet formation and movement: (1) atomization gas pressure; (2) liquid mist shape; (3) The distance from the spray gun to the bed; (4) the diameter of the liquid nozzle; (5) the radial distance of the center of the liquid mist; (6) the design of the atomizer, the radial velocity of the end of the column causes longitudinal vibration, which causes the liquid column to split The length of the liquid column changes with the increase of the liquid flow velocity. When the liquid flow velocity reaches a certain level, the liquid column length becomes shorter due to the longitudinal vibration of the liquid flow. The unstable state of the liquid flow is called the migration flow; when the pressure increases, the flow velocity increases. When large, the end of the liquid column is a wavy flow; if the flow rate continues to increase, a spray flow occurs.
Figure 4 Evolution of the coating liquid atomization In practical applications, due to the action of the surrounding air, there is a relative velocity between the liquid flow and the air, so the spray number je can be used to indicate the degree of atomization.
Je=va2×Ï1×de/σ×{Ïa/Ï1}0.55
Where va is the relative velocity of liquid to air, m/s;
Ρa - the density of air, kg / m3
De——the aperture of the nozzle, mm
Ρ1——density of liquid, kg/m3
Σ——surface tension of liquid, N/m
Je < 0.1, dripping; je ≈ 0.1 ~ 10, smooth flow; je ≈ 10 ~ 400, wavy flow; je > 400, spray flow.
In order to obtain a good droplet, the spray gun and spray pressure suitable for the coating liquid phase should be selected at the beginning of the design. At this time, the peristaltic pump spray speed and the amount of spray are adjusted to match the core and drying parameters. At the same time, the peristaltic pump must be stopped when the temperature of the coating liquid is too low in the equipment.
2.2 Influencing factors of the droplet movement process The parameters that affect the droplet movement process are: atomization pressure, physical properties of the coating liquid itself, and the position and distance of the spray gun relative to the film bed, and the position of the spray gun in the coating drum. Generally facing a position below or on the inner wall of the drum.
During the movement, due to different viscosity and distance, coalescence and evaporation affect the size of the droplet size. In the actual project, the position of the spray gun relative to the bed and the spray direction can be adjusted by the peripheral electrical control system to adjust the polymerization and particle size during the movement of the droplets to the bed.
2.3 Influencing factors in the wetting and drying process This process is the process of the contact between the droplets and the core and the evaporation of the water. After the completion of the * and the two steps, the formation and movement of the droplets are excellent. Adjusting the rotation speed of the drum not only ensures that the core is effectively flipped, but also prevents the core from flying out of the bed or causing debris due to excessive speed. Inlet air temperature, humidity, air intake, and air intake ensure the air circulation required during the drying process, so that the water is discharged from the drum in time, and the exhaust air volume is usually set to be larger than the intake air volume, so that the drum is under negative pressure.
The degree of atomization of the coating solution in the operation directly affects the appearance quality, and the atomization effect of the spray liquid is directly determined by the atomization pressure and the atomization system. At the beginning of atomization, the control principle of atomization speed and dry hot air temperature is to make the surface of the sheet slightly moist, and to prevent the surface from sticking, and the temperature should not be too high or too low. If it is too high, the drying will be too fast, the film formation will be rough and the film color will be uneven; if it is too low or the atomization amount is too large, the humidity in the coating drum will be too high, and the adhesion of the core will soon appear.
In addition, the relationship between the rotation speed of the drum and the coating operation: the rotation speed is low, the adhesion of the film is strong; the rotation speed is high, the adhesion of the film is poor, and the film is easily peeled off. During the coating process, if the drying temperature is too low, the amount of atomization is too large, or the flow of the film is retained, there is a possibility that the sticking phenomenon may occur.
3 Conclusion In summary, it is necessary to understand and according to the physical properties of the coating liquid, the core physical properties, the physical environment of the coating environment and the controllable parameter processing after the equipment design and manufacture, optimize the conditions affecting the quality of the coating, and set according to the mutual constraint relationship. Equipment operating parameters.
[references]
[1]Jin Guojun. Drying Equipment [M]. Beijing: Chemical Industry Press, 2005.8
[2] Yu Caiyuan, Wang Baohe, Wang Xizhong. Design Manual for Drying Device [M]. Beijing: Chemical Industry Press, 2005.5
[3] Zhu Hongji, Zhang Mingxian. Pharmaceutical equipment and engineering design [M]. Beijing: Chemical Industry Press, 2004
[4] Liu Guangwen. Practical Technology of Spray Drying [M]. Beijing: China Light Industry Press, 2001.10
[5] Cole Hogan Alton. Process and principle of tablet coating [M]. Zhang Junmin translation. Beijing: China Medical Science and Technology Press, 2001
[6]TIAN Yaohua. Discussion on the Influence Factors of Operating Parameters and Film Coating Quality of High-efficiency Coating Machine[J].Electromechanical Information,2006(4):25～29
The characteristics of the coating: (1) overcome the shortcomings of the tablet is not easy to swallow; (2) improve the stability of the tablet to prevent oxidative degeneration caused by light or air; (3) regulate the release of the drug; (4) ) to isolate easily compatible drugs; (5) better appearance.
1 Film formation mechanism and influencing factors After the coating, the structure of the film on the core is not uniform, and the appearance is also different. This heterogeneity is caused by insoluble components (such as colorants) that are intentionally added, while the film is not continuously formed during the coating process. Most coating processes are carried out by adhering the polymer solution to the solid core after spraying, and then taking the next spray. This process needs to be repeated several times until the coating is completed. In order to obtain a good coating effect, it is first necessary to understand the formation mechanism of the film.
1.1 Formation mechanism of the film The formation of the film of the aqueous polymer dispersion is very complicated. It is found that in the wetting stage, the polymer exists in a large amount of discontinuous particles, and as the drying progresses, the water is reduced. The distance becomes small until intimate contact, deformation, and agglomeration, and then melts together to form a discontinuous film in which the surface of the coated core is wetted by the dilute dispersion. In this process, water volatilizes in the form of water vapor and polymer particles are connected to each other. The capillary action of the water film around the particles greatly accelerates the process, and when adjacent particles diffuse into each other, a completely condensed state occurs.
The following processes are involved in several important stages: (1) preparation of the coating solution or suspension; (2) generation of droplets; (3) movement of droplets from the spray gun to the bed; (4) droplets Impact, wetting, spreading, and coalescence on the core surface or particle surface; (5) dry gelation and adhesion film formation. Figure 1 is a schematic illustration of the above stages.
Figure 1. Five Stages of the Coating Process 1.2 Physical Properties of the Coating Solution or Suspension Effect on the Coating Process The physical properties of the coating solution or suspension have an effect on the other four stages of the coating process. It has been found that the particle size of the droplets has a direct influence on the appearance of the garment. Some formulas are summarized to describe the effect on the properties of the droplets, but there are differences between the formulas. The reason for the difference is that there is a very large difference between the selected atomizers. Large differences, so a formula can only be applied to the respective conditions, and when extrapolated to other systems, there will be a large deviation.
Fair (1974) proposed a formula to describe the effect of solution properties on the droplet size in a hydraulic spray:
DVM solution / DVM solvent = {γ solution / γ solvent} 0.5 × {μ solution / μ solvent} 0.2 × {Ï solution / Ï solvent} 0.3
Where DVM - the volume average particle size of the droplets;
γ - the surface tension of the solution;
μ - the viscosity of the solution;
Ï - the density of the solution.
Nukiyama and Tanasawa (1939) proposed a formula for describing the particle size of droplets generated during atmospheric atomization:
Ds={585×103/v}×{γ/Ï}0.5+1683μ0.45{γ×Ï}-0.225{1000/J}1.5
Where Ds - the average surface particle size of the droplets;
Η—the rate of gas relative to the liquid at the outlet of the spray pipe (m/s);
Γ——the surface tension of the liquid (N/m);
Ρ——liquid density (kg/m3);
Μ——the viscosity of the liquid (Pa·s);
J——The volume ratio of gas/liquid at the nozzle.
The above formula shows that the physical properties of the solution will affect the particle size and particle size distribution of the droplets, and then determine the fate of the droplets on the surface of the core, which ultimately affects the quality of the coating. In the physical properties of the solution, the viscosity, surface tension, and density are important for the formulation spray of the coating liquid.
Such as surface tension will affect the formation of droplets. The longer the droplets move toward the core of the coated tablet, the more likely it is to affect the wetting, spreading, penetrating, and adhering processes after reaching the surface of the core, thereby affecting the integrity of the coating, the adhesion of the core surface, and the surface finish; Viscosity affects the evaporation rate of the solvent, affecting the coalescence of droplets suspended in the air. However, in actual engineering, the influence of the actual tension on the quality can be reduced by adjusting the parameters such as the nozzle and the distance.
1.3 Atomization method and principle The generation of droplets is to break the liquid into a mist composed of small droplets. The ideal droplets are required to spread evenly after reaching the surface of the core and form a smooth continuous film of uniform thickness. Air and hydraulics are often used to make fog particles in actual coating equipment. The following are four methods and principles of atomization:
1.3.1 Ultrasonic atomization Ultrasonic atomization is a method of atomizing a liquid by intense high frequency oscillation. The advantage is that the atomization efficiency is high, and most of the energy consumed is used to increase the surface area of ​​the droplets, unlike less than 1% of the other two atomization methods are used to increase the surface area. The disadvantage is that it is difficult to control the rate at which the liquid flows, so that the produced droplets do not have sufficient momentum or are prone to clogging of the nozzle.
1.3.2 Hydraulic airless spray Hydraulic airless spray is in the hydraulic sprayer, the coating liquid passes through a small hole under high pressure, the static pressure energy is converted into kinetic energy, and the coating liquid is dispersed into droplets. Changing the pressure of the liquid or the direction in which the liquid flows into the orifice or using a different nozzle will result in a change in the shape of the droplet. A ribbon or conical mist curtain can be formed. When the polymer is dissolved in an organic solvent, a hydraulic spray method is often selected because no gas is used during the atomization process to prevent premature drying of the droplets. To atomize a solution with a certain viscosity, a higher pressure is required, and a very small pore size is required to ensure the liquid flow rate.
1.3.3 Air Pressure Spray Air pressure spray is to use a high-speed air flow to collide with the solution and rub to form a droplet. The relative shear force generated by the high-speed high-pressure gas stream atomizes the solution because the gas density is small and requires a large volume of high-speed gas to generate sufficient energy to atomize a solution having a certain viscosity and tension.
1.3.4 Centrifugal spray Centrifugal spray is a coating liquid that rotates at a high speed in a centrifugal disk to obtain a high centrifugal force and is scooped out at high speed to form a film, a filament or a droplet, and is also subjected to friction and tearing of the surrounding airflow. Forming droplets.
The above four methods are commonly used in air conditioning sprays and hydraulic sprays in coating equipment. Research has found that factors affecting droplet formation and movement: (1) atomization gas pressure; (2) liquid mist shape; (3) The distance from the spray gun to the bed; (4) the diameter of the liquid nozzle; (5) the radial distance of the center of the liquid mist; (6) the design of the atomizer, ν - the rate of gas relative to the liquid at the outlet of the spray tube (m/ s);
Γ——the surface tension of the liquid (N/m);
Ρ——liquid density (kg/m3);
Μ——the viscosity of the liquid (Pa·s);
J——The volume ratio of gas/liquid at the nozzle.
The above formula shows that the physical properties of the solution will affect the particle size and particle size distribution of the droplets, and then determine the fate of the droplets on the surface of the core, which ultimately affects the quality of the coating. In the physical properties of the solution, the viscosity, surface tension, and density are important for the formulation spray of the coating liquid.
Such as surface tension will affect the formation of droplets. The longer the droplets move toward the core of the coated tablet, the more likely it is to affect the wetting, spreading, penetrating, and adhering processes after reaching the surface of the core, thereby affecting the integrity of the coating, the adhesion of the core surface, and the surface finish; Viscosity affects the evaporation rate of the solvent, affecting the coalescence of droplets suspended in the air. However, in actual engineering, the influence of the actual tension on the quality can be reduced by adjusting the parameters such as the nozzle and the distance.
1.3 Atomization method and principle The generation of droplets is to break the liquid into a mist composed of small droplets. The ideal droplets are required to spread evenly after reaching the surface of the core and form a smooth continuous film of uniform thickness. Air and hydraulics are often used to make fog particles in actual coating equipment. The following are four methods and principles of atomization:
1.3.1 Ultrasonic atomization Ultrasonic atomization is a method of atomizing a liquid by intense high frequency oscillation. The advantage is that the atomization efficiency is high, and most of the energy consumed is used to increase the surface area of ​​the droplets, unlike less than 1% of the other two atomization methods are used to increase the surface area. The disadvantage is that it is difficult to control the rate at which the liquid flows, so that the produced droplets do not have sufficient momentum or are prone to clogging of the nozzle.
1.3.2 Hydraulic airless spray Hydraulic airless spray is in the hydraulic sprayer, the coating liquid passes through a small hole under high pressure, the static pressure energy is converted into kinetic energy, and the coating liquid is dispersed into droplets. Changing the pressure of the liquid or the direction in which the liquid flows into the orifice or using a different nozzle will result in a change in the shape of the droplet. A ribbon or conical mist curtain can be formed. When the polymer is dissolved in an organic solvent, a hydraulic spray method is often selected because no gas is used during the atomization process to prevent premature drying of the droplets. To atomize a solution with a certain viscosity, a higher pressure is required, and a very small pore size is required to ensure the liquid flow rate.
1.3.3 Air Pressure Spray Air pressure spray is to use a high-speed air flow to collide with the solution and rub to form a droplet. The relative shear force generated by the high-speed high-pressure gas stream atomizes the solution because the gas density is small and requires a large volume of high-speed gas to generate sufficient energy to atomize a solution having a certain viscosity and tension.
1.3.4 Centrifugal spray Centrifugal spray is a coating liquid that rotates at a high speed in a centrifugal disk to obtain a high centrifugal force and is scooped out at high speed to form a film, a filament or a droplet, and is also subjected to friction and tearing of the surrounding airflow. Forming droplets.
The above four methods are commonly used in air conditioning sprays and hydraulic sprays in coating equipment. Research has found that factors affecting droplet formation and movement: (1) atomization gas pressure; (2) liquid mist shape; (3) The distance from the spray gun to the bed; (4) the diameter of the liquid nozzle; (5) the radial distance of the center of the liquid mist; (6) the design of the atomizer, the radial velocity of the end of the column causes longitudinal vibration, which causes the liquid column to split The length of the liquid column changes with the increase of the liquid flow velocity. When the liquid flow velocity reaches a certain level, the liquid column length becomes shorter due to the longitudinal vibration of the liquid flow. The unstable state of the liquid flow is called the migration flow; when the pressure increases, the flow velocity increases. When large, the end of the liquid column is a wavy flow; if the flow rate continues to increase, a spray flow occurs.
Figure 4 Evolution of the coating liquid atomization In practical applications, due to the action of the surrounding air, there is a relative velocity between the liquid flow and the air, so the spray number je can be used to indicate the degree of atomization.
Je=va2×Ï1×de/σ×{Ïa/Ï1}0.55
Where va is the relative velocity of liquid to air, m/s;
Ρa - the density of air, kg / m3
De——the aperture of the nozzle, mm
Ρ1——density of liquid, kg/m3
Σ——surface tension of liquid, N/m
Je < 0.1, dripping; je ≈ 0.1 ~ 10, smooth flow; je ≈ 10 ~ 400, wavy flow; je > 400, spray flow.
In order to obtain a good droplet, the spray gun and spray pressure suitable for the coating liquid phase should be selected at the beginning of the design. At this time, the peristaltic pump spray speed and the amount of spray are adjusted to match the core and drying parameters. At the same time, the peristaltic pump must be stopped when the temperature of the coating liquid is too low in the equipment.
2.2 Influencing factors of the droplet movement process The parameters that affect the droplet movement process are: atomization pressure, physical properties of the coating liquid itself, and the position and distance of the spray gun relative to the film bed, and the position of the spray gun in the coating drum. Generally facing a position below or on the inner wall of the drum.
During the movement, due to different viscosity and distance, coalescence and evaporation affect the size of the droplet size. In the actual project, the position of the spray gun relative to the bed and the spray direction can be adjusted by the peripheral electrical control system to adjust the polymerization and particle size during the movement of the droplets to the bed.
2.3 Influencing factors in the wetting and drying process This process is the process of the contact between the droplets and the core and the evaporation of the water. After the completion of the * and the two steps, the formation and movement of the droplets are excellent. Adjusting the rotation speed of the drum not only ensures that the core is effectively flipped, but also prevents the core from flying out of the bed or causing debris due to excessive speed. Inlet air temperature, humidity, air intake, and air intake ensure the air circulation required during the drying process, so that the water is discharged from the drum in time, and the exhaust air volume is usually set to be larger than the intake air volume, so that the drum is under negative pressure.
The degree of atomization of the coating solution in the operation directly affects the appearance quality, and the atomization effect of the spray liquid is directly determined by the atomization pressure and the atomization system. At the beginning of atomization, the control principle of atomization speed and dry hot air temperature is to make the surface of the sheet slightly moist, and to prevent the surface from sticking, and the temperature should not be too high or too low. If it is too high, the drying will be too fast, the film formation will be rough and the film color will be uneven; if it is too low or the atomization amount is too large, the humidity in the coating drum will be too high, and the adhesion of the core will soon appear.
In addition, the relationship between the rotation speed of the drum and the coating operation: the rotation speed is low, the adhesion of the film is strong; the rotation speed is high, the adhesion of the film is poor, and the film is easily peeled off. During the coating process, if the drying temperature is too low, the amount of atomization is too large, or the flow of the film is retained, there is a possibility that the sticking phenomenon may occur.
3 Conclusion In summary, it is necessary to understand and according to the physical properties of the coating liquid, the core physical properties, the physical environment of the coating environment and the controllable parameter processing after the equipment design and manufacture, optimize the conditions affecting the quality of the coating, and set according to the mutual constraint relationship. Equipment operating parameters.
[references]
[1]Jin Guojun. Drying Equipment [M]. Beijing: Chemical Industry Press, 2005.8
[2] Yu Caiyuan, Wang Baohe, Wang Xizhong. Design Manual for Drying Device [M]. Beijing: Chemical Industry Press, 2005.5
[3] Zhu Hongji, Zhang Mingxian. Pharmaceutical equipment and engineering design [M]. Beijing: Chemical Industry Press, 2004
[4] Liu Guangwen. Practical Technology of Spray Drying [M]. Beijing: China Light Industry Press, 2001.10
[5] Cole Hogan Alton. Process and principle of tablet coating [M]. Zhang Junmin translation. Beijing: China Medical Science and Technology Press, 2001
[6]TIAN Yaohua. Discussion on the Influence Factors of Operating Parameters and Film Coating Quality of High-efficiency Coating Machine[J].Electromechanical Information,2006(4):25～29
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