The outer diameter of the optical fiber is only 100-150um, and glass is a brittle and brittle material. When not coated, the surface defects of the optical fiber will expand due to its exposure in the air, causing stress concentration. Therefore, the strength of the optical fiber is extremely low. Even under tensile force of about 1N (100GF), the optical fiber will fracture. In order to protect the surface of the optical fiber and improve its tensile and bending strength, it is necessary to coat the bare optical fiber once during the drawing process; In addition, the color of the coating material can further distinguish each coated fiber optic cable, which is more conducive to identifying the problem fiber optic cable when it encounters problems.
Fiber optic primary coating material
At present, organic coatings are widely used as primary coating materials. Under high temperature or light, the solvent gradually evaporates, and the remaining functional groups of polymer molecules react with each other, ultimately forming a highly cross-linked thermosetting paint film. There are mainly heat cured and light cured organic silicon, polyurethane, epoxy resin, etc. The fiber optic coating is generally divided into two layers, with the inner layer having small cross-linking and relatively soft properties, which can buffer the micro bending of the fiber optic; The outer layer has strong cross-linking and sufficient mechanical strength to protect the optical fiber, and can resist the swelling of the coating caused by the base oil in the fiber filler.
Basic requirements for coatings: good leveling performance, low coefficient of thermal expansion, small temperature variation, good environmental resistance, suitable strength and modulus, no hydrogen evolution under use conditions, small curing shrinkage, and low moisture absorption. At the same time, it is necessary to consider the adhesive strength between the coating and the optical fiber, as well as the strippability of the coating.
Organic silicon coating
It has the advantages of high temperature resistance, softness, good elasticity, small Young's modulus and little temperature variation, stable high and low temperature performance, UV resistance, ozone resistance, radiation resistance, non-toxic and odorless, and convenient use. It is particularly suitable for military and highly reliable civilian optical fibers. One coat can be either thermally cured or UV cured.
Polyurethane acrylic coating
Polyurethane acrylic coating has strong wear resistance, water resistance, chemical corrosion resistance, heat resistance, and good insulation. It is thinner than organic silicon coating and has a faster curing speed.