FIELD OF THE DISCLOSURE

This disclosure pertains to curable coating compositions with fast cure speeds. More particularly, this disclosure pertains to curable coating compositions that include acylgermane photoinitiators. Most particularly, this disclosure pertains to curable coating compositions for use as primary and secondary coatings in optical fiber.

BACKGROUND OF THE DISCLOSURE

The transmissivity of light through an optical fiber is highly dependent on the properties of the coatings applied to the fiber. The coatings typically include a primary coating and a secondary coating, where the secondary coating surrounds the primary coating and the primary coating contacts the glass fiber (which includes a central glass core surrounded by a glass cladding). The secondary coating is a harder material (higher Young's modulus) than the primary coating and is designed to protect the glass waveguide from damage caused by abrasion or external forces that arise during processing, handling, and installation of the fiber. The primary coating is a softer material (lower Young's modulus) and is designed to buffer or dissipates stresses that result from forces applied to the outer surface of the secondary coating. Dissipation of stresses within the primary coating attenuates the stress and minimizes the stress that reaches the glass waveguide. The primary coating is especially important in dissipating stresses that arise when the fiber is bent. The bending stresses transmitted to the glass waveguide on the fiber needs to be minimized because bending stresses create local perturbations in the refractive index profile of the glass waveguide. The local refractive index perturbations lead to intensity losses for the light transmitted through the waveguide. By dissipating stresses, the primary coating minimizes bend-induced intensity losses.

In fiber manufacture, primary and secondary coatings are formed on the fiber by applying viscous coating compositions to the fiber and curing the coating compositions with light to induce photochemical reactions that convert the coating compositions to rigid coatings. The fiber manufacture process is a continuous process in which a glass fiber is drawn from a heated glass preform and delivered to a process at a draw speed. The preform includes a central core region surrounded by one or more cladding regions. The drawn fiber is directed through processing units that control the rate of cooling to reduce attenuation. The size and shape of the fiber are also controlled to provide a fiber having a specified diameter and circular cross section. Once the fiber has been cooled sufficiently and sized, it is routed through a series of coating dies and curing stations that apply and cure the primary and secondary coating compositions. In a typical process, the primary coating composition is applied directly to the glass fiber and cured before applying and curing the secondary coating composition.

Driven by the high demand of optical network and cost savings, the draw speed for optical fiber manufacturing has increased significantly over the past few years. Advancements in coating compositions and curing are needed to enable higher draw speeds. The rate of curing of both the primary and secondary coating compositions are important consideration. The primary coating composition needs to be cured sufficiently fast to achieve a degree of cure having the tensile properties needed in a finished fiber before applying the secondary coating composition. Once the secondary coating composition is applied, it absorbs the curing light and attenuates the intensity of curing light transmitted to the underlying primary coating. Similarly, the secondary coating composition needs to cure sufficiently quickly to achieve adequate rigidity in limited process space so that the coated fiber can be wound on a spool for storage at the end of the fiber draw process.

A possible strategy for increasing the cure speed of the primary and secondary coating compositions is to add more curing lamps to the draw tower. This solution, however, is usually not feasible in practice because the space available for curing along the pathway of the draw process is limited and because the implementation of additional curing lamps is complex and costly.

Another strategy for increasing the cure speed is to increase the concentration of photoinitiator in the primary and secondary coating compositions. The photoinitiator initiates the photochemical reaction that leads to curing of the primary coating composition. A higher concentration of photoinitiator in principle should increase the rate of initiation of the curing reaction and the overall rate of curing of primary and secondary coating compositions. This approach, however, has several drawbacks, including solubility limits for the photoinitiator in the primary and secondary coating compositions, a reduction in the molecular weight of the primary and secondary coatings formed upon curing (and the resulting adverse effect on tensile properties), and higher costs.

New strategies are needed for increasing the rate of curing of primary and secondary coating compositions. The cure speeds of existing primary and secondary coating compositions are insufficient to enable meaningful improvements of current draw speeds. There is a need for new primary and secondary coating compositions that cure at faster rates while providing primary and secondary coatings having tensile properties needed for optical fibers.

SUMMARY

The present disclosure provides curable compositions that can be cured at fast rates as well as coatings and cured products formed from the curable compositions. The curable compositions include an acylgermane photoinitiator that leads to fast cure speeds. The curable compositions include primary coating compositions and secondary coating compositions. The primary and secondary coating compositions can be cured to form primary and secondary coatings of optical fibers. The primary coatings feature low Young's modulus and high tear strength. The primary coatings provide good microbending performance and are resistant to defect formation during the fiber draw process and subsequent handling operations. The secondary coatings feature high Young's modulus and good puncture resistance. The primary and secondary coatings can be formed on individual fibers or on each of multiple fibers in a ribbon. The curable compositions also include compositions that can be used to form a matrix for ribbons. The curable compositions can also be used to form cured films and other cured products used in applications outside the field of optical fibers.

The present description extends to:

A coating composition comprising:

a radiation-curable monomer;

an adhesion promoter, the adhesion promoter comprising an alkoxysilane compound or a mercapto-functional silane compound; and

a photoinitiator, the photoinitiator comprising an acylgermane compound having the formula



wherein R6and R7are independently H, an alkyl group, an aryl group, an amine group, or a halogen group; and n=1-4.

The present description extends to:

A method of forming a cured product comprising:

curing a coating composition, the coating composition comprising:a radiation-curable monomer;an adhesion promoter, the adhesion promoter comprising an alkoxysilane compound or a mercapto-functional silane compound; anda photoinitiator, the photoinitiator comprising an acylgermane compound having the formula

wherein R6and R7are independently H, an alkyl group, an aryl group, an amine group, or a halogen group; and n=1-4.

The present description extends to:

A method of forming an optical fiber comprising:

drawing an optical fiber from a preform at a draw speed greater than 35 m/s; and

while the optical fiber is moving at the draw speed,applying a coating composition to the optical fiber, the coating composition comprising: an acylgermane photoinitiator, the acylgermane photoinitiator having the formula

wherein R6and R7are independently H, an alkyl group, an aryl group, an amine group, or a halogen group; and n=1-4; andcuring the coating composition.

The present description extends to:

A coating composition comprising:

a first monomer with a radiation-curable group;

a phosphine oxide photoinitiator; and

an acylgermane photoinitiator, the acylgermane photoinitiator having the formula



wherein R6and R7are independently H, an alkyl group, an aryl group, an amine group, or a halogen group; and n=1-4.

The present disclosure further includes primary and secondary fiber coatings and cured products formed from the curable coating compositions described herein.

The present disclosure further includes an optical fiber coated with a coating formed from a curable coating composition disclosed herein, wherein the optical fiber includes a glass waveguide and the coating surrounds and is in direct contact with the glass waveguide.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings are illustrative of selected aspects of the present disclosure, and together with the description serve to explain principles and operation of methods, products, and compositions embraced by the present disclosure.

