Spray coating, control

The properties of thermal-sprayed coatings vary as a function of processing parameters such as temperature and particle velocity. Generally, such coatings have greater porosity than CVD or PVD coatings and thickness control is more difficultto achieve. Yet the process is economical and undemanding. It can be applied in any location. 

Formation of free milk fat in DWM powder particles as a result of atomization and drying may also contribute significantly to poor solubility and dispersibility. Free milk fat, which is extractable from the powder by a 50 50 mixture (v/v) of ethyl and petroleum ether (Brunner, 1974), probably coats the powder particles and prevents their rehydration. The physical state of the milk fat, as controlled by the liquid-to-solid ratio and the presence of free milk fat on the particle surface, strongly influences DWM particle dispersibility. Spray coating of DWM particles with lecithin or other surfactants and dispersion in warm water improve their dispersibility. 

Chen MC, Liang HE Chiu YL, et al. A novel drug-eluting stent spray coated with multi-layers of collagen and sirolimus, J Control Release 2005 108 178-189. 

Spray coating is used before and after a product is assembled particularly if already assembled and has complex shaped and curved surfaces. Many different types of spray equipment are in use to handle the different forms of paints used. They are classified by their method of atomization (airless, air, rotary, electrostatic, etc.) and by their deposition assist (electrostatic or nonelectrostatic, flame spray, etc.). Spraying techniques may fall into several of these categories. They range from simple systems with one manual applicator to highly complex, computer-controlled, automatic systems. They can incorporate hundreds of spray units. Automatic systems may have their applicators mounted on fixed stands, on reciprocating or rotating machines, on robots, and so on. 

Polyamic acid (PAA) solutions are deposited by either spinning or spraying. They are cured by heating at a controlled rate from 50 C to 350-420 C to evaporate solvents and reaction products (primarily H2O) and convert the PAA to PI. Multiple coats are deposited to achieve the thick (20-40 pm) planarized dielectric layers required for high Impedance TFML interconnects. Figure 3 shows a cross-section of 5 pm thick conductor lines planarized with 25 pm (three coatings) of spray-coated PI. 

In order to compare the relative extent of the damaged surface corrosion and of the pitting corrosion, the percentage of the corroded area in the tested surface is used, and summarized in Table 28.2. It is important to note that pitting corrosion was found only on chromate conversion-coated controls (one with chromated spray primer and another with E-coat). It is also important to note that E-coat directly... 

Prohesion salt spray-tested panels in Figure 31.24 show that [7B] (Alk/AH)/T/ E and [7B] (Alk/0)/TH/E systems performed comparably to the controls. Deft primer-coated control panels ([7B] CC/A) displayed extensive pitting corrosion away from the scribe in both tests, indicating that Deft primer may have poor barrier properties. This pitting corrosion away from the scribe was observed on both controls when examined by scanning electron microscopy (SEM). 

The corrosion widths of Prohesion salt spray-tested IVD Al-coated Al panels were calculated and are summarized in Figure 32.6. As is evident from the data, after 12 weeks of Prohesion salt spray testing, IVD/plasma polymer/spray paint systems showed better corrosion protection overall than IVD/plasma polymer/E-coat systems. All the IVD/plasma polymer/spray paint systems outperformed the cathodic E-coated controls and showed corrosion test results comparable to those of the Deft primer oated controls. 

Tablet cores may also be spray-coated with either aqueous or organic solutions of highly substituted low-viscosity grades of methylcellulose to mask an unpleasant taste or to modify the release of a drug by controlling the physical nature of the granules. Methylcellulose coats are also used for sealing tablet cores prior to sugar coating.

The addition of sodium chloride to aqueous spray-coating solutions containing hydroxypropyl cellulose or hypromellose suppresses the agglomeration of crystalline cellulose particles. Sodium chloride can also be used to modify drug release from gels and from emulsions.It can be used to control micelle size, and to adjust the viscosity of polymer dispersions by altering the ionic character of a formula-... 

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