Silicone rubber masks

The coating apparafus consisfs of a silk screen mesh fixed to a frame with sufficient tension to squeeze the ink through the screen and onto the blank substrate (e.g., polyimide). The substrate is fixed on an XY fable wifh adhesion fape, and fhe silken screen mesh is masked, wifh an open window in the center for screen printing. The silicon rubber squeeze is a fixed support and can be moved in both X and Y directions. A hot-air or IR ramp is used to dry the coating for solvenf removal. 

An important question of mask design is the composition of the elastic material used to cover the face the faceblank. The first masks introduced in World War I were made of rubberized cloth or leather. Subsequent masks used natural rubber, but recently, sophisticated synthetic polymers using silicone, butyl, and perfluorocarbon rubbers have been used.6 Silicone rubber has the advantage of making possible a tight fit or seal between the mask and skin, with a correspondingly decreased potential for leaking (a factor said to be responsible for about 5% of mask failures).12... 

Unfortunately, silicone rubber offers rather low resistance to the penetration of common chemical agents. Perfluorocarbon rubber is very impermeable but is expensive and tears easily. Butyl rubber offers both good protection and seal and has therefore become the material of choice.7 Even this description of materials used to construct the faceblank underestimates the complexity of actual mask design. In today s standard U.S. military masks, the faceblank consists of two separate layers an inner later made of silicone rubber (for maximum seal) and an outer layer made of butyl rubber for maximum protection (Figure 16-2). 

Fig. 16-2. The M45 protective mask facepiece has two skins. The inner skin is composed of silicone rubber, and the outer skin is composed of butyl rubber. This arrangement maximizes both mask-to-skin seal and chemical agent impermeability. A similar design is used in the M40 protective mask. Photograph Courtesy of Visual Information Division, US Army Chemical and Biological Defense Command, Aberdeen Proving Ground, Md.

The MCU-2/P Chemical-Biological Mask is used by U.S. Air Force ground crews and aircrews when not in flight. This protective mask is constructed of molded silicone rubber facepiece material, and an integral, molded, polyurethane, one-piece panoramic lens is bonded to it (Figure 16-9). 

Some of the applications Include contact lenses, medical tubing and protective gas masks. The silicone rubber for these applications is optically clear because the silicone polymer and the reinforcing silica used to prepare the rubber are isorefractive at a specified temperature, usually about 25 C. The polymers which have been used are copolymers with sufficient phenyl substitution to raise the refractive index, from 1.4023 (for PDMS) to approximately 1.43 which is the refractive index of tri methyl si lyl treated fumed silica (e.g., Cabosll S-17). Such copolymers are prepared by copolymerizing (Me2S10)x and (PhMeSiO) or (Ph2S10)x using equilibrium conditions. 

With a nylon plastic visor, polycarbonate lens, polypropylene chin guard and cotton shroud, Allegro s new Supplied Air Shield is perfect for use with grinding, chipping, spray painting and auto body repair. The Full Mask Supplied Air Respirator is made of silicone rubber for durability. Allegro Industries, (800) 622-3530, www.allegrosafety.com. 

Silicone rubber is often used in medical devices as it offers good flexibility, a degree of softness (for face masks, etc.) and good resistance to both EtO and gamma radiation sterilisation processes. Silicone rubber can be bonded with the aid of a primer (see Section 10.6). 

Devine AT, et al. Bonding Lexan Polycarbonate to Silicone Rubber for Gas Masks. Picatinny Arsenal Technical Report... 

The benefit of such a LAPS sandwich structure consists in a easy manufacturing process, where no patterning and masking as well as encapsulation of conducting tracks are needed (see Fig. 5.1). In the measurement set-up, the LAPS structure itself will be embedded in a measurement chamber. The flat uniform surface of the LAPS assists a proper sealing by, e.g., an O-ring, silicone or rubber material. Finally, only the sensitive membrane will stay directly in contact with the analyte under test. 

These masks can be found in hardware stores or online shops and are safe for use once they have been properly gassed out. They are not immediately safe because they are made using rubber, silicone and other synthetic substances. But, once they are out-gassed, all you have to do is screw on the filter and it s ready to go. Wearing these masks for a long time is not comfortable, so if it gets to the point where... 

Conformal coatings are used for PCAs that require exceptional resistance to moisture, solvents, or abrasion. A wide variety of polymers are used to perform this function, including phenolic, silicone and urethane lacquers and sUicone rubber, polystyrene, epoxy, and paraxylylene coatings. Epoxy and polyurethane-based coatings are the most commonly used. H conformal coatings are used in conjunction with a solder mask, they must be chemically compatible. - ... 

Secondary contamination is common and persormel should wear aprons, rubber gloves, and masks as needed. Contaminated items can be washed in cold water (hot water will cause residual gas to vaporize) with soap or allow nonwashable items to air out for a few days. Most lacrimators dissipate quickly, but CS may be micronized and mixed with an antiagglomerant agent (CSl), which remains active for up to 5 days. A similar formulation mixed with silicone (CS2) remains in the environment for up to 45 days (Hu et al., 1989). 

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