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INDUSTRIAL ORGANIC SOLVENTS
Published in Nicholas P. Cheremisinoff, Industrial Solvents Handbook, Revised And Expanded, 2003
Solvent-based coatings can be classified as conventional low-solids and high-solids ( 60% solids) coatings. Glycol ethers and acetates act as active solvents to dissolve the film-forming resins and to suspend pigments and additives. Conventional low-solids coatings contain alkyd, epoxy, nitrocellulose, polyester, and polyurethane-type resins and find use in coil coating, metal and wood furniture, automotive coatings, and machinery finishes. These coatings can be classified as thermoplastic or thermoset. Evaporation of the solvents yields the thermoplastic film while the thermoset coating is cured by a chemical cross-linking reaction or by air oxidation in a high temperature oven. Selection of the proper glycol ether depends on how the coating is cured. Ambient cured coatings often utilize EB, PM, and DPM glycol ethers and propylene glycol methyl ether acetate (PMA). For thermally cured coatings the above mentioned glycol ethers as well as blends can be used. In high temperature coil coating processes the diethylene glycol n-butyl ether and dipropylene glycol methyl ether acetate (DPMA) are often used as tailing solvents (these solvents prevent pinholes and other film defects during the last stages of cure).
SU-8 Photolithography and Its Impact on Microfluidics
Published in Sushanta K. Mitra, Suman Chakraborty, Fabrication, Implementation, and Applications, 2016
Rodrigo Martinez-Duarte, Marc J. Madou
SU-8 is an acid-catalyzed negative photoresist,* made by dissolving EPON® SU-8 resin (a registered trademark of Shell Chemical Company) in an organic solvent such as propylene glycol methyl ether acetate (PGMEA), cyclopentanone, or gamma-butyrolactone (GBL) and adding up to 10 wt% of triarylsulfonium hexafluoroantimonate salt as a photoinitiator. Commercial formulations also include 1–% propylene carbonate. In a chemically amplified resist such as SU-8, one photon produces a photoproduct that, in turn, causes hundreds of reactions to change the solubility of the film. Because each photolytic reaction results in an “amplification” via catalysis, this concept is dubbed “chemical amplification” (Ito, 1996). The viscosity of the photoresist and hence the range of thicknesses accessible are determined by the ratio of solvent to SU-8 resin. The EPON resist is a multifunctional, highly branched epoxy derivative that consists of bisphenol-A novolac glycidyl ether. On an average, a single molecule contains eight epoxy groups that explain the 8 in the name SU-8 (Figure 8.1). The material has become a major workhorse in miniaturization science because of its low UV absorption (up to thicknesses of 2 mm), high chemical and thermal resistance, and good mechanical properties that make it suitable as a structural material. For example, Abgrall et al. (2007) fabricated SU-8 microfluidic devices with different techniques, including the successive lamination and patterning of SU-8 layers on existent topographies. The use of SU-8 photoresists allows for the coating of thick layers (up to 500 μm) on a single spin coat, or thicker layers in multiple spin coatings, and high-aspect-ratio structures with nearly vertical side walls.
High-efficiency large-angle reflective composite polarization grating
Published in Liquid Crystals, 2020
Zhi-Wei Zhao, Cheng-Miao Wang, Song-Zhen Li, Wan Chen, Yong-Gang Liu, Quan-Quan Mu, Zeng-Hui Peng, Qi-Dong Wang, Li Xuan, Ru-dong Wei
In this article, we use ROF dissolved in solvent propylene-glycol-methyl-ether-acetate (PGMEA) with a concentration of 50% by weight. The reactive mesogen-PEMGA solution is spin coated at the LPP layer at 500 rpm for 10 s and 2000 rpm for 40 s after the holographic exposure. During subsequent exposure to UV lamps for 2 min in an -rich environment, the LCmonomers form a cross-linked polymer. The process continues until the polarisation gratings meet the half-wave retardation. In this article, we spin three-layer ROF-PGMEA solution to achieve the half-wave retardation (532 nm). Another substrate is aluminium mirror. Polyimide is spin coated at aluminium mirrors and another substrate surface with ITO thin film at 1000 rpm for 10 s and 6000 rpm for 40 s, then dried at 150°C for 10 min and 235°C for 30 min. The polyimide film gets parallel orientation by rubbed. Two substrate surface with ITO thin film opposite are assembled together separated by 4-um spacers. The cell was filled by capillary action with the LC mixture Mo16 (from DIC) above the clearing temperature (120) and slowly cooled down into the nematic phase.