FIELD OF THE DISCLOSURE

This disclosure pertains to optical fiber coating dies and methods of coating optical fiber.

BACKGROUND OF THE DISCLOSURE

Optical fibers, commonly used in telecommunications, are typically coated with one or more generally concentric polymeric coatings to protect the optical fiber from damage, such as from abrasion or moisture. These protective coatings, typically radiation curable (e.g., UV-curable), are applied as the fiber is being drawn. The drawn fiber is passed through one or more coating (or sizing) dies having a cylindrical land portion having a diameter greater than the diameter of the optical fiber. A liquid curable coating composition disposed above the cylindrical land portion is entrained by the fiber and pulled through the cylindrical land portion. It is important that the coating or multiple coatings are concentric with the fiber and have a uniform thickness (or diameter) along the length of the fiber. These attributes contribute to ease in splicing and connectorization of the fiber, thereby providing lower losses in an installed fiber application. Market demands place increasingly stringent tolerances on the diameter and concentricity of optical fiber coatings.

SUMMARY OF THE DISCLOSURE

Cone-only coating die designs are disclosed which have wetted length L5(defined as the distance between the exit of the guide die and entrance of the cone-only coating die) such that 1 mm≤L5≤5 mm, coating chamber inner radius L6such that 3 mm≤L6≤10 mm, cone half angle between 2°≤α≤25°, cone height L1between 0.25 mm and 2 mm; and a cylindrical land portion having an inner diameter of d2such that 0.1 mm≤d2≤0.5 mm, and length L2such that 0.05 mm≤L2≤1.25 mm. Such a die design results in a coating system having a smaller and more stable gyre that improves the stability of the coating application process.

As fiber draw speeds increase or the diameter of the sizing die decreases, more coating is rejected in the sizing die taper, and the gyre in the sizing die bell gets stronger. This leads to both increased instability of the fiber position, which causes an increase in coating offset, and increased incidence of flooding, which causes fiber breaks and increased costs. Reducing the size of the gyre by reducing the wetted length also reduces the amount of coating rejected by the die. Reducing the strength and size of the gyre suppresses the random motion of the fiber, allowing the centering forces to improve the offset. Cone-only die designs disclosed herein with the described wetted length and coating chamber inner diameter characteristics result in increased stability and reduced strength of the gyre, thereby resulting in a more stable and reliable coating application process in manufacturing, particularly for applications at draw speed≥50 mps (meters per second).

