Coating Materials: What they are and how they work
Coatings are protective layers applied directly to the glass during the fiber draw process. Buffers and cabling strength members are added later. A particular coating material may serve different functions depending on its mechanical properties and how it is ultimately applied to the base fiber. For instance, a coating may sometimes be used as a fiber buffer and it may sometimes be used as a cabling material. The customer’s application and environmental demands as well as the characteristics of the material will determine what function it ultimately performs.
A coating or combination that works ideally for one application may not be appropriate for another environment. The dual acrylate coating used on standard telecommunications grade fibers, for example, is not suitable for many of the increasing number of harsh environment applications in oil and gas, defense, medical, and industrial markets. These applications require a careful choice of materials to offer resistance to abrasion, chemicals, water vapor, hydrogen ingression, mechanical bend and more, and to ensure the fiber’s optical performance over the lifetime required. OFS specialty coating options–such as carbon, HCS® fiber coating, PYROCOAT® polyimide, and silicone/high-temperature acrylate–can provide solutions to these requirements.
When additional protection is needed, the coated fiber can be buffered with another material. This might be a high-temperature fluoropolymer, such as PFA (-200 to +260°C) or ETFE (-125 to +150°C), which offer excellent chemical and UV resistance plus flame retardance. Alternatively, a PEEK buffer (-55 to +240°C), which offers excellent abrasion resistance and flame retardance might be chosen.
Complete cables involve an outer jacket, often applied over strength members, such as aramid yarn, for a high level of protection. The material chosen for the cable jacket should offer protection in response to specific conditions the cable will experience. If you application is a utility substation, oil refinery, or subway data link where cables must meet stringent requirements for smoke emission, flame and toxicity, you may find a solution using our LSZH material. Aircraft cables having to pass rigorous qualifications and a high-temperature performance requirement of 150°C may use ETFE for the cable jacket.
OFS has many options for coating, buffer, and cabling materials, and we have the expertise to combine them into a unique solution for your application. The standard options are listed below, and one of our product design experts will help guide you through the ones that will best meet your requirements.
Standard telecommunications fibers use a dual urethane acrylate coating—a softer, inner layer that cushions the fiber during bending and that strips easily for connectorizing; and a higher modulus (harder) outer layer for protection from abrasion. Single-layer usage is also possible for smaller form factor applications.
In addition to 15 higher degrees of temperature tolerance, this version of acrylate offers enhanced delamination resistance (US Patent 5,908,484) and is resistant to steam and cable gels. It is easy to strip mechanically.
Fluoroacrylate can be used as either a cladding or a coating. It is USP Class VI Biocompatible and non-toxic for use in medical applications. Its exceptional ruggedness and bend performance as a cladding lower the probability of laser output “hot spots” by distributing lost power over a greater area.
This material cushions the fiber for low microbending loss and provides superior low-temperature performance, temperature stability to 200°C. Silicone is resistant to water vapor and many chemicals and is easy to strip mechanically. Silicone is applied in a thicker layer than fluoroacrylate; and because of its softness, it must be upbuffered for protection, usually with a thermoplastic such as ETFE, PFA, or FEP.
This advantage of this combination is its bend performance with resistance to abrasion and handling while maintaining a standard 250 µm fiber size.
Our PYROCOAT® polyimide brand is a heat and cold resistant polymer with high strength, abrasion- and chemical-resistance. It is applied to a compact thickness of only 15 µm over the fiber cladding; smaller size allows for better bend performance. It is strong and hard enough to be used in down-hole or aerospace applications.
Carbon, as a primary coating, extends fiber lifetime dramatically. It is applied to a thickness of less than 400Å in a reactive process during fiber draw, hermetically sealing the fiber surface. Carbon can be applied under acrylate, silicone, or polyimide coatings, depending on application temperature requirements.
As a class, these fluoropolymer buffering and cabling materials have several common properties: low- and high-temperature functionality, low flammability and smoke-generation properties, excellent chemical resistance, low friction coefficient, flexibility, and UV resistance for applications exposed to direct sunlight. The particulars vary according to the exact type, and selection depends on your application.
PEEK offers superior resistance to chemicals, steam, moisture, and radiation. It is used as an optical fiber buffer where toughness and both high- and low-temperature performance is required. PEEK is a highly flame retardant and very low smoke generating material. It is commonly used in medical applications and will survive all accepted forms of commercial steriliziation. The superior chemical resistance, high-temperature performance, and mechanical toughness also make it an ideal optical fiber buffering material for geophysical applications.
Aramid yarn is a tough, synthetic and heat-resistant (to 160°C--glass yarn can be substituted when temperatures go as high as 300°C) filament that provides high strength and flexibility to optical fiber cables. It can be applied between layers in cables either in a straight served or braided construction. Both types of yarn can be used to relieve strain on the optical fiber in connector termination processes.