Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2002-01-11
2004-03-30
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C260S001000, C385S123000
Reexamination Certificate
active
06714712
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to coated optical fibers and to radiation curable compositions, which are adaptable for use as a covering layer in optical fiber technology, such as a primary coating, secondary coating, upjacketing or tight-buffer coating, bundling material, ribbon matrix material, each of which can be colored or not, or ink composition for optical fibers.
BACKGROUND OF THE INVENTION
Glass optical fibers are provided with protective coatings immediately after spinning the molten glass. Generally, two coatings are applied, a primary coating of a relatively soft, flexible resin directly on the glass surface, and a harder resin, a secondary coating, on the primary coating. The individual fibers generally are combined in larger structures such as cables. Cables may comprise individual fibers, or fiber ribbon structures. The optical fiber ribbon generally is made from 2, 4, 6, 8 or 12 optical fibers, generally arranged in a plane, and bonded together with a so-called matrix material. Several ribbons can be bundled together using bundling materials. Further, individual fibers often are provided with a coloring or ink layer to be able to identify individual fibers. In certain cases, the individually coated fibers that have a thickness of about 250 &mgr;m are provided with a further coating layer to make a thicker and thereby more easy to handle fiber. Such a coating is denoted as an upjacketing coating. All of the materials presently in use for these applications are preferably radiation curable compositions.
In many of these compositions, use is made of a urethane oligomer having reactive termini and a polymer backbone. Further, the compositions generally comprise reactive diluents, photoinitiators to render the compositions UV-curable, and suitable additives.
As polymer backbone for the urethane oligomer, many materials have been suggested. In the synthesis of the oligomer backbone, polyols have been used such as hydrocarbon polyols, polyether polyols, polycarbonate polyols and polyester polyols. Polyester polyols are particularly attractive because of their commercial availability, oxidative stability and versatility to tailor the characteristics of the coating by tailoring the backbone. Polyester polyols used as the backbone polymer in a urethane acrylate oligomer are described for use in optical fiber coatings in e.g. U.S. Pat. No. 5,146,531 and EP-A-539030. However, polyester polyols in general are susceptible to hydrolysis.
Urethane-free polyester acrylate oligomers have also been used in radiation-curable coating compositions for optical glass fibers.
For example, JP-5792552 (Nitto Electric) discloses a coating material for optical glass fibers comprising a polyester di(meth)acrylate, the polyester backbone having an average molecular weight of 300 or more. The polyesters are synthesized by reacting saturated polybasic acids and polyalcohols by standard esterification reactions and polyester polyols are produced by using an excess of polyalcohols in this reaction. Next, the polyol is reacted with acrylic acid or methacrylic acid. The coating compositions disclosed in JP-5792552 typically contain said polyester di(meth)acrylate oligomer, a (meth) acrylate ester monomer, a radical photoinitiator and additives. This coating is used as a so-called single coating for optical glass fibers.
The disadvantage of the coatings disclosed in JP-5792552 is their susceptibility to hydrolysis. It appears that, after aging, the coating integrity is lost. Thus, the coated optical fiber will not be adequately protected from the environment, resulting in signal attenuation. Moreover, the single coatings disclosed in JP-5792552 appeared to not have the appropriate mechanical properties, such as modulus and Tg, necessary for low signal attenuation. Furthermore, the coatings of JP-5792552 appeared to show an insufficient cure speed.
From DE-A1-4126860 (Bayer), a matrix material for a three-fiber ribbon is known consisting of a polyester acrylate oligomer, 2-(N-butyl-carbamyl)-ethylacrylate as reactive diluent and 2-hydroxy-2-methyl-1-phenyl-propan-1-one as photoinitiator. The matrix material disclosed in DE-A1-4126860 appeared not to have the required mechanical properties. It appears that the modulus of the matrix material exemplified in DE-A1-4126860 is too low to be acceptable as a matrix material. Moreover, said matrix material appeared to show insufficient hydrolytic stability.
From JP-243227/1998 a liquid curable resin composition is known comprising a polyester acrylate oligomer which consists of a polyether diol endcapped with two diacids or anhydrides and terminated with hydroxy ethyl acrylate. However, the polyester acrylate disclosed and the resulting resin composition appeared to show insufficient hydrolytic stability.
It is an object of the present invention to provide a coating, ink or matrix composition comprising a polyester and/or alkyd (meth)acrylate oligomer having greater utility and better stability and which is adapted for use as a coating, composition or matrix material for an optical glass fiber.
It is a further object of the present invention to provide a primary coating, secondary coating, upjacketing coating, ink, matrix or bundling composition for an optical fiber comprising a polyester and/or alkyd (meth)acrylate oligomer having good mechanical properties.
It is a further object of the invention to obtain an optical fiber or optical fiber ribbon, or optical fiber cable comprising at least one of said coating, ink or matrix as defined above.
SUMMARY OF THE INVENTION
Surprisingly, one or more of the above objects can be obtained by the radiation-curable coating composition, ink composition or matrix material comprising a polyester and/or alkyd (meth)acrylate oligomer.
The present invention provides a radiation-curable coating, ink or matrix composition comprising:
(A) a polyester and/or alkyd (meth)acrylate oligomer comprising a polyacid residue or anhydride thereof,
(B) optionally, a reactive diluent, and
(C) optionally, a photoinitiator,
wherein said composition when cured and aged under 85° C. and 85% Relative Humidity conditions for 10 days is hydrolytically stable to such an extent that the coating maintains mechanical integrity. Mechanical integrity means that the coating sample remains intact to such an extent that the coating sample can be measured in a DMA measurement as described in more detail in the description of test methods. Preferably, the coating composition does not fall apart when a sample thereof is prepared for the DMA-measurement. The term polyacid is used to refer to di- as well as polyacid.
Preferably, the polyester (meth)acrylate oligomer according to the present invention comprises more than about 1 mole of diacid.
In particular, the Mn, functionality and/or building blocks of said oligomer and/or the other components of the composition and/or the method of preparation of the oligomer and/or the curing conditions can be chosen such as to achieve the required hydrolytic stability.
The present invention further relates to said composition for use as an optical fiber primary coating having a modulus of about 5 MPa or less; for use as an optical fiber secondary coating or ink composition; and for use as an optical fiber matrix material having a modulus of at least about 5 MPa.
The present invention further provides a radiation-curable coating, ink or matrix composition comprising:
(A) a polyester and/or alkyd (meth)acrylate oligomer comprising a polyacid residue or anhydride thereof,
(B) optionally, a reactive diluent, and
(C) optionally, a photoinitiator,
wherein said composition when cured and submitted to 200° C. for 40 minutes in a Thermogravimetric Analysis (TGA) measurement shows a weight loss of about 10% or less.
Preferably, the polyester (meth)acrylate oligomer according to the present invention comprises more than about 1 mole of diacid.
The present invention further relates to a coated optical fiber comprising a glass optical fiber having a primary coating, a secondary coating, upjacketing coating and
Bishop Timothy E.
Derks Franciscus J. M.
Tortorello Anthony
DSM N.V.
Healy Brian
Lin Tina M
Pillsbury & Winthrop LLP
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