Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-07-31
2002-12-03
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S090000, C522S097000, C522S040000, C522S120000, C522S121000, C522S150000, C522S151000, C522S152000, C522S181000, C522S182000, C522S077000
Reexamination Certificate
active
06489376
ABSTRACT:
BACKGROUND
The invention relates to a curable composition suitable for coating ribbon matrices and glass surfaces, specifically, coating optical waveguides such as optical fibers, the coating compositions having a faster cure time to achieve greater line speeds.
Optical fibers made from drawn glass have been used as a reliable transmission medium in telecommunications cables. Glass optical fibers are widely used because they have the ability to carry large amounts of information over long distances.
To facilitate these long-distance transmissions, optical fiber waveguides have been coated with plastic compositions of various materials in order to protect the fiber and increase its tensile strength. Generally, to accomplish this optical glass fibers are frequently coated with two superposed coatings. The coating which contacts the glass is a relatively soft, primary coating that must satisfactorily adhere to the fiber and be soft enough to resist microbending especially at low service temperatures. The outer, exposed coating is a much harder secondary coating that provides the desired resistance to handling forces yet must be flexible enough to enable the coated fiber to withstand repeated bending without cracking the coating.
Optical fiber coating compositions, whether they are inner primary or single coatings, generally comprise before cure an ethylenically-unsaturated monomer or oligomer dissolved or dispersed in a liquid ethylenically-unsaturated medium and a photoinitiator. The coating composition is typically applied to the optical glass fiber in liquid form and then exposed to actinic radiation to effect cure.
In practice, the most commonly used coatings have been derived from acrylates. The most widely used acrylates are those which are capable of ultraviolet radiation curing at high speed since the coatings are normally applied immediately after the glass fiber has been drawn from the molten state. Typical of such acrylates are mono- or difunctional (meth)acrylate terminated monomers and oligomers. The outer coatings are most often urethane-acrylate or epoxy-acrylate copolymers which also can be cured by ultraviolet radiation (See Shustack et al, U.S. Pat. No. 6,048,911; Barraud et al, U.S. Pat. No. 5,650,231).
Coatings are applied to the fiber in-line during fiber drawing. As the state of fiber drawing technology has allowed for increased draw speeds to effectuate longer and thinner optical fibers, however, the need for coating compositions that can cure at faster rates coincident with the faster draw speeds has become more urgent. Thus, as draw speeds have increased, a need has developed for materials that cure at faster rates than is currently available with traditional technology.
U.S. Pat. No. 4,663,185 to Eckberg, et al. describes a method of making a UV curable acrylated polymers by blending difunctional acrylate monomers of up to 50 wt % of the total composition to result in a hard, glassy coating to enhance abrasion resistance.
U.S. Pat. No. 4,968,116 to Hulme-Lowe, et al. describes a cladding composition using polyfunctional acrylates being difunctional or higher, at levels ranging from 2-35% in order to crosslink the resin to produce a hard coating.
U.S. Pat. No. 5,188,864 to Lee, et al. describes adhesion promoters for UV curable siloxane compositions that may contain up to 10 wt % multifunctional acrylates being difunctional or higher.
U.S. Pat. No. 6,001,913 to Thames, et al. describes a UV curable, high-gloss coating formulation which uses difunctional acrylates without the use of volatile organic components (VOC). Such coating compositions are poured to approximately a 2 mil thickness.
The present inventors have found that a liquid, non-crosslinked, UV curable composition having an decreased cure time can be provided by adding multifunctional low molecular weight acrylates to a composition comprising a radiation curable oligomer, a free radical photoinitiator, and a reactive diluent.
SUMMARY
There is provided a liquid, radiation curable composition, said composition comprising (a) a radiation curable oligomer, (b) a free radical photoinitiator, and (c) a mixture of reactive diluents comprising (i) at least one mono- or difunctional reactive diluent and (ii) at least one polyfunctional reactive diluent having at least three (meth)acrylate functionalities. The polyfunctional reactive diluent component (ii) increases the cure rate of the composition. A process line speed of at least 1000 mpm may be achieved.
The present curable coating composition may include from 50 wt % to 95 wt %, for example, from 60 wt % to 90 wt %, e.g., from 70 wt % to 85 wt % of radiation curable oligomer (a). The amount of free radical photoinitiator (b) should be sufficient to initiate photopolymerization. The present curable coating composition may include from 5 wt % to 50 wt %, for example, from 10 wt % to 40 wt %, e.g., from 15 wt % to 30 wt % of total reactive diluent (c), which includes both (i) the mono- or difunctional reactive diluent and (ii) the polyfunctional reactive diluent having at least three (meth)acrylic functionalities.
DETAILED DESCRIPTION
Coating compositions in accordance with the present invention may advantageously be utilized for both primary and secondary coatings for optical fibers.
As used herein, the term “primary coating” is defined as that coating which directly contacts the glass portion of the optical fiber. The uncured primary coating should be liquid at room temperature. The uncured primary coating should have a viscosity suitable for high speed processing, and the uncured primary coating should have a high cure speed. The cured primary coating should exhibit good adhesion to glass to prevent premature delamination of the coating from the glass portion of the optical fiber. The cured primary coating should have a low modulus at lower temperatures to minimize the effects of microbend attenuation due to small stresses on the optical fiber itself. The cured primary coating should have a refractive index high enough to ensure that errant signals escaping from the glass core are refracted back to the core of the optical fiber.
As used herein, the term “secondary coating” is defined as the coating which covers the primary coating on the optical fiber. The cured secondary coating should have sufficient modulus to give impact resistance and to provide a protective barrier, and give tensile strength to the optical fiber. The cured secondary coating should exhibit little physical change over a wide temperature range, good resistance to water and solvent absorption and have good color stability.
The uncured liquid primary or secondary coating composition should have a sufficiently low viscosity that the composition will be easily applied to form a continuous protective coating on the glass fibers. Examples of such viscosity are those on the order of magnitude of about 10
3
cP at 45-50° C., e.g., from about 2×10
3
to about 8×10
3
cP at room temperature. There is no particular limitation on viscosity, however, and it can be adjusted to a given application by known methods. For example, viscosity can be adjusted depending on the type of optical fiber material being formulated and the method of application.
Generally, the thickness of the cured primary or secondary coating will be dependent on the intended use of the optical fiber, although thicknesses of about 20 to 35 microns, and in particular thicknesses of about 25 to 30 microns, are suitable.
When used as primary coatings, cured coatings in accordance with the present invention may have a glass transition temperature (T
g
) of from about −60° C. to about 0° C., for example, from about −50 to about −30° C., and, e.g., about −40° C., and a low modulus of elasticity of from about 0.5 to about 3.0 MPa at room temperature (20° C.) and 50% relative humidity, for example, from about 1.0 to about 2.5 MPa.
When utilized as a secondary coating, cured coatings in accordance with the present invention may have a glass transition temperature (T
g
) of from about 40 to about 10
Khudyakov Igor V.
Overton Robert J.
Purvis Michael B.
Alcatel
McClendon Sanza L.
Seidleck James J.
Sughrue & Mion, PLLC
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