Automated spray guns are widely used in fully integrated pan-coating systems. Such pan-coating systems are used by the pharmaceutical/food industries to apply aqueous film, solvent and sugar coating for tablets, confectioneries, and a variety of other products.
Bullows proposes a method that includes analysis of the critical elements of atomizer testing, consisting of layout and overlap optimizOur Product Basket includes,ation to reduce the errors commonly associated with spray manifold application, such as uneven spray distribution, heavy edges and poor overlap.
Furthermore, this approach will also consider the effects of “normal” operating parameters such as fluid flow rate, automization pressure and gun-to-target distance on spray pattern uniformity, drop size, and velocity .
Aqueous film coating is one of the most important operations in the pharmaceutical industry.
The process is very demanding and is not as forgiving as other coating applications such as solvent coating.
A successful process greatly depends on controlling many of the variables with little or no allowance for significant variation.
There are many governing parameters that relate to the processing conditions such as the type of tablet coater (conventional/side-vented), the air and tablet movement, and temperature. The dynamics of the tablet also affect the process; these include dimensional changes due to expansion and contraction in the moisture absorption and final drying stages. From a spray application standpoint, the problem can be analyzed by evaluating the steps in the coating process. As shown in Figure 1, these steps include the formation of drops, the contact of drops with the solid surface, droplet expansion, droplet coalescence, droplet penetration and finally droplet evaporation.
Early research and field experiments indicate the need for a narrow span droplet size distribution with a limited number of small drops (or fines). Small drops have a tendency to drift off-target, therefore, the number of “fines” must be reduced in order to provide uniform coating. Tablet coating machines are equipped with automated spray guns specifically designed to deliver the coating solution.
The general delivery method includes a manifold system that is fitted with multiple spray guns; the tablet coating machine control system controls these guns.
Typically, these machines are designed and optimized for a specific process. As the process is modified, the operator alters the gun settings to accommodate the new process. However, frequently these changes do not produce the expected results due to a lack of standardized procedures that can be used to optimize the guns settings.
The Mechanism of Tablet Coating
The main function of the spray gun is to divide the coating liquid stream (as delivered by the pumping device) into very fine droplets. This division is known as atomisation and is achieved by forcing a fine stream of liquid through a fine nozzle into the pressurised zone (achieved by compressed air). The droplet size depends on the nozzle size and available air pressure. These fine droplets, after leaving the nozzle, travel certain distance in the drying air zone where part of the solvent present in the droplet gets evaporated. These semi-dried droplets get deposited on the tablet surface. As the droplet still contains some amount of solvent, it spreads on the tablet surface and fuses or coalesces with neighbouring droplets, thus, making a continuous film. Now, if the atomisation is extremely fine, the amount of solvent in the droplet (at the time of leaving the spray nozzle) will be very less causing the droplet to dry completely before reaching the tablet surface. This situation is known as spray drying and as the droplet is hitting the tablet surface in the dry powder form and it will not be able to make a continuous film. On the other hand, if the atomisation is coarse, the amount of solvent left in the larger droplets will still be very high at the time it hits the tablet bed. This extra solvent can cause surface wetting (causing problems like sticking) and this solvent may also get adsorbed into the core tablet causing the degradation of the active drug. Thus the uniform atomisation of the coating solution significantly affects the coating quality. The uniformity of atomisation very much depends on the accuracy of spray nozzle shape and size.
Bullows Solution To Tablet Coating
Bullows have evaluated a method that includes an analysis of the critical elements of atomizer testing. This method consists of layout and overlap optimization to reduce the errors commonly associated with spray manifold application, such as uneven spray distribution, heavy edges and poor overlap. This approach will document a baseline condition for an existing setup in a tablet coater and will proceed in optimizing the flux/density distribution to obtain the optimal spray setup and overlaps.
Optimization will be accomplished by using a patternation technique that involves collecting liquid flux density data at various gun spacing and gun to – target distances.
Data will be collected at various feed rates that are typically used in tablet coating applications. The patternation data is then correlated with drop size and velocity data in order to determine the effects of “normal” operating parameters such as liquid flow rate, automization air pressure, and gun-totarget distance on spray-pattern uniformity, drop size, and velocity. Drop size data is collected using an Aerometric Inc. Phase Doppler Particle Analyzer (PDPA). The sampling method consists of collecting data at various radial locations throughout the spray. Information such as volume flux and velocity are correlated with the D32 measured at these locations. Results will demonstrate the variation in drop size as a function of spray distance and the sampling location within the spray.
|Atomizing Air||Max – 70 psi|
|Piston Air Min||50 psi|
|Tip & Needle Size||0.8 mm to 2.5 mm|
|MOC||Fluid Passage In SS|
|Paint Connection||1/8” BSP|
|Air Connection||Automation – 1/8” BSP|
Bullows is known for its system excellence in terms of quality, innovation and customization. We have extended our wings & specialized ourselves into Spray Painting Solutions & pre-treatment systems & solutions with help & support from our associate concern M/s Triologics Surface Coating Private Limited. Bullows had pioneered spray painting technology in India, from conceptualization to application, for achieving best surface finish, fast productivity and in compliance with environmental protection norms, keeping operator safety at prime focus.
Our Product Basket includes:
- Bullows Spray Gun – Model 230 & 630
- Spray painting equipment -Conventional, HVLP, Compliant, Electrostatic, Airless, Air Assisted Airless
- Bullows Pressure Feed Paint Containers
- Paint Agitation Air Motor
- Paint Filters and Regulators
- Air Filters and Regulators
- Paint and Air Hoses
- Paint Circulation System with Paint Kitchen
In recent years Bullows have also established name in providing total turnkey solutions (manual / automatic) to various industrial applications which starts from last activity of manufacturing to first activity of packing (pre-treatement process + painting process + loading / unloading).