Dip coating techniques can be described as a process where the substrate to be coated is immersed in a liquid and then withdrawn with a well-defined withdrawal speed under controlled temperature and atmospheric conditions. The coating thickness is mainly defined by the withdrawal speed, by the solid content and the viscosity of the liquid. If reactive systems are chosen for coatings, as it is the case in sol-gel type of coatings using alkoxides or pre-hydrolyzed systems - the so-called sols - the control of the atmosphere is indispensable. The atmosphere controls the evaporation of the solvent and the subsequent destabilization of the sols by solvent evaporation, leads to a gelation process and the formation of a transparent film due to the small particle size in the sols (nm range). The technique is used for the applications where substrates or objects have large and complicated shape for a two-side coating.
Dip coating processes are used for plate glass by Schott, based on developments made by Schroder2 and Dislich3,4; for solar energy control systems (Calorex®) and for anti-reflective coatings (Amiran®) on windows. The dip coating technique is also used for optical coatings, such as on bulbs, and for optical filters or dielectric mirrors by various small and medium sized enterprises (SMEs) and other companies that must fabricate multilayer systems with up to 30 or 40 coatings with very high precision. A large-scale fused silica dip coating system (FSDCS) has been delivered to Lawrence Livermore National Laboratory (LLNL) to make uniform antireflective sol-gel coatings over large precision optics measuring 44 cm x 44 cm x 41 cm and weighing up to 150 lbs. The FSDCS produces a speed ripple of less than -1% ~ +1% at speeds of 2-20 cm/s, with strict control of vibration for both the optic and the tank.
One dip coating system commonly used for sol-gel coatings incorporates atmosphere control, drying/curing, a programmable dip coating profile (withdraw speed, immersion time, etc.) and solution manageable tanks (temperature, filtration, etc.). Accurate speed control is obtained through the use of a proven precision, offthe-shelf motion system. Vibration control is enhanced by structural rigidity, isolation of the tank and motor drive, and spring mounting supports. Such a system is capable of achieving a uniform coating (-3% ~ +3% thickness variation).
Chemat Dip Coater-DipMasterTM-50: Accommodates substrates up to 2.5" x 2.5", with a withdrawal speed range of 0.5" to 4.0" per minute. It is a compact and bench-top coater. There is an adjustable withdrawal distance, in a controlled environment. Some of the options available are computer interfacing, and dip-tanks with controlled temperatures.
Chemat Dip Coater-DipMasterTM-100: Accommodates substrates up to 12" x 12", with a withdrawal speed range of 0.5" to 4.0" per minute. It has a manual temperature control with a maximum infrared oven temperature of 80 degrees Centigrade. There is an adjustable withdrawal distance, in a Controlled Environment. Some of the options available are computer interfacing, and dip-tanks with controlled temperatures.
Chemat Dip Coater-DipMasterTM-200 :Accommodates substrates up to a size of 12" x 12", with a withdrawal speed range of 0.5" to 4.0"/per minute. It has a maximum thermal oven temperature of 450 degrees Centigrade with programmable temperature control.
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