Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-02-28
2002-03-19
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...
C522S038000, C522S096000, C522S182000, C522S142000, C522S121000, C522S120000, C522S090000
Reexamination Certificate
active
06359025
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radiation-curable liquid resin composition for coating and cabling optical fibers, which compositions exhibit superior curing and a reduced amount of particulate matter, for example crystalline inclusions, and produce cured products which exhibit minimum yellowing, exhibit excellent durability. Hence, the liquid curable resin composition which is particularly suitable for use as a coating material coated on optical fibers or optical fiber ribbon matrices. Furthermore, the resin composition when cured can have stable adhesion, and can be easily removed from the material on which the composition has been coated. Therefore, the composition is particularly suitable for use as a soft coating coated on optical fibers.
DESCRIPTION OF THE RELATED ART
Radiation-curable compositions are extensively used in the optical fiber industry during the production of optical fibers, ribbons, and cables. For example, optical glass fibers are routinely coated with at least one radiation-curable coating (often two coatings) immediately after the glass fiber is manufactured in a draw tower so as to preserve the pristine character of the glass fiber. Immediately after a coating is applied to the fiber, the coating is rapidly cured by exposure to radiation (commonly ultraviolet light). The industry demands faster production speeds, and therefore, faster curing coating compositions.
Radiation-curable matrix and bundling materials can further support and protect the individual strands of coated fiber as individual strands are bundled together into optical fiber ribbons, optical fiber cables, and associated structures. Also, radiation-curable inks can be used to color code individual strands of optical fiber. All of these types of optical fiber-related materials are preferably radiation-curable and can serve as coating and/or cabling materials.
Two radiation-curable coating layers are routinely employed in optical fiber production before ribboning and cabling. One layer is a soft inner primary coating (“primary coating”), which directly contacts the glass fiber and prevents microbending. The other layer is a tougher outer primary coating (“secondary coating”), which provides a more durable exterior for the glass fiber.
Examples of radiation-curable primary coatings are disclosed in U.S. Pat. No. 5,336,563 to Coady et al and secondary coatings in U.S. Pat. No. 4,472,019. Additional aspects of optical fiber coating technology are disclosed in, for example, U.S. Pat. Nos. 5,595,820 to Szum, 5,199,098 to Nolan et al.; 4,923,915 to Urruti et al.; 4,720,529 to Kimura et al.; and 4,474,830 to Taylor et al.
Along with expanding installation of optical fiber cables in recent years causing optical fibers to be exposed under various environmental conditions, higher durability is demanded of soft coatings, hard coatings, coloring materials, and bundling materials for optical fibers. Particularly, a resin used as a soft coating must exhibit stable adhesion to glass over an extended period of time. In addition, expanded use of the optical fiber ribbon structure consisting of a plurality of optical fibers requires improvement in the operation for splicing optical fibers. Specifically, it is strongly desired that all materials in optical fiber ribbons such as soft coatings, hard coatings, coloring materials, ribbon matrixes, and bundling materials be removed in one operation from optical fiber glass. Furthermore, as the demand for optical fibers increases, improvement in the productivity of optical fibers is desired. Specifically, it is strongly desired that the materials have characteristics whereby they may be coated onto glass fibers and cured quickly to constantly produce a coat with an even thickness.
To maximize cure speed in an ultraviolet light cure, at least one photoinitiator is required (photoinitiator may be omitted in an electron beam cure). Several photoinitiators can be used to achieve a suitable balance of surface and through cure. Conventional classes of photoinitiators have been used. Mono-acyl phosphine oxide type photoinitiators can be used such as Lucirin TPO [(2,4,6-trimethylbenzoyl) diphenyl phosphine oxide [commercially available from BASF] which exhibits relatively fast cure speed. However, use of commercial Lucirin TPO can cause undesired crystallization effects in the coatings (e.g., during aging), which can result in inclusions and loss of optical clarity (detected under a light microscope). Attempts have been made to use purified Lucirin TPO, but the purification steps are costly. Other phosphine oxide photoinitiators (e.g., CGI 403, Ciba) can show reduced amounts of harmful crystallization effect, but they may also have slower cure speed. Hence, a need exists to discover photoinitiators which can provide both fast cure speed and good optical clarity. The art, until now, has not provided direction on how to achieve such properties.
In addition, photoinitiators can cause yellowing, particularly during long term aging of cured compositions under photolytic aging conditions (e.g., UV or fluorescent light). Heat may also induce yellowing. Discoloration in general and yellowing in particular is undesired and has become anathema in the industry. Hence, a photoinitiator which would provide for lack of harmful crystalline effects and fast cure, but would result in yellowing, would not sufficiently meet the most stringent industry demands.
The art has not recognized a photoinitiator which provides an excellent balance of these properties. For example, a very large number of phosphine oxide photoinitiators are disclosed in, for example, U.S. Pat. Nos. 5,218,009 to Rutsch et al. and 5,534,559 to Leppard et al. However, these patents do not suggest that any particular species of photoinitiators would solve the above-noted problems and provide an excellent balance of properties. Hence, they do not anticipate or suggest the present invention.
PROBLEMS TO BE SOLVED BY THE INVENTION
The characteristics required for radiation curable resins used as the coating materials for optical fibers include: being a liquid at ordinary temperatures and having a sufficiently low viscosity to be excellently coated; providing good productivity at a high curing rate; having sufficient strength and superior flexibility; exhibiting very little physical change during temperature changes over a wide range; having superior heat resistance and superior resistance to hydrolysis; showing superior long term reliability with little physical changes over time; showing superior resistance to chemicals such as acids and alkalis; exhibiting low moisture and water absorption; exhibiting superior light resistance showing the least discoloration over time; exhibiting high resistance to oils; and producing little hydrogen gas which adversely affects optical fiber characteristics.
High durability and productivity are required for optical fiber along with expanding installation of optical fiber cables in recent years. Specifically, if the durability of a coating material for optical fiber is low and, for example, coloring is conspicuous, the visibility of a color painted for distinguishing optical fiber decreases, exhibiting a problem that the maintenance of the cable is hindered. It has been already confirmed that the reduction of visibility is caused not only by coloring of the bundling material, but also by coloring of the hard coating or the soft coating.
Moreover, an increased demand of optical fibers makes it necessary for the coating materials to cure quickly in a stable manner. A photo-initiator which decomposes fast must be used for the coating materials to cure quickly.
Furthermore, the resin used as the soft coating must exhibit stable adhesion to glass over a long period of time. In addition, when all coating materials are removed from the ribbon structure of optical fibers, there should be no residue remaining on the glass.
Japanese Patent Application Laid-open No. 190712/1989 discloses a composition comprising an acyl phosphine oxide as a photo-curable resin
Bishop Timothy Edward
Ishikawa Miyuki
Komiya Zen
Snowwhite Paul Eugene
Szum David Michael
DSM N.V.
McClendon Sanza L.
Pillsbury & Winthrop LLP
Seidleck James J.
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