TABLE OF CONTENTS Resins for filter media usually come in one of the three forms: solvent-based solutions, water-based latex emulsions and dispersions, and water-based solution forms. Their main purpose is to strengthen the media; however, they provide for other important properties. These include stiffness, tear strength, modulus, dimensional stability, flex resistance, water resistance, downstream processability, heat and temperature resistance, resistance to chemical and environmental exposure, and durability in the end use application. Resins can also affect filtration properties. For example, some film-forming resins are undesirable because the film may form across a pore and close it to passage of fluid. Resins are available in thermoplastic form or thermosetting form. Very often both properties are desired for processing. For example, a resin may be thermoplastic so that it can be thermally softened for the pleating operation and then afterward heat cured and thermoset to provide for stiff rigid pleats in the end use application. The following is a discussion of some of the various types of resins used as binders for filter media.
Three major forms of formaldehyde resins are phenol formaldehyde and/or pheno-lics, melamine formaldehyde, and urea formaldehyde. In filter medium applications, all three can be used as cross-linkers with other resin systems. Melamine-formalde-hyde, and urea-formaldehyde play important roles as wet strength agents for wet laid media (see Sections 4.4.1.2 and 4.4.1.3). Solvent-based phenol-formaldehyde resin is a very important saturant for wet laid filter paper particularly for engine lube oil filter applications.
Phenol...
