Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
2000-04-18
2001-04-10
Ngo, Hung N. (Department: 2874)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S901000, C385S128000, C385S145000, C362S559000, C362S551000
Reexamination Certificate
active
06215947
ABSTRACT:
This invention relates to an improved composition for cladding and sheathing a flexible light-conducting core to form a flexible light pipe (“FLP”) having improved side-lighting performance, and the improved side-lighting FLP composition which results.
U.S. Pat. Nos. 5,406,641 and 5,485,541, both herein incorporated by reference, teach a process for preparing a flexible light pipe, preferably from a crosslinked poly(alkyl acrylate) core, which core is enclosed in a polymeric cladding and further protected by a polymeric sheathing. These applications teach a variety of cladding materials with refractive indices lower than the polyacrylate core, preferring fluorinated polymers and teaching or exemplifying terpolymers of perfluoroalkyl vinyl ether/tetrafluoroethylene/hexafluoropropylene (FEP) and of vinylidene fluoride/ tetrafluoroethylene/hexafluoropropylene (THV). THV has advantages in highly flexible applications, but is somewhat harder to process when curing is desired than FEP. These cited applications further teach a number of polymers useful as sheathing, such as polyethylene, linear low density polyethylene, polypropylene, and polystyrene.
The major use for such lighting has been in end-lit applications, where it is desired to conduct the light effectively and with few losses from the source to the desired area of illumination. However, a second area of use exists where the light is allowed to issue as uniformly as possible from the side or walls of the light pipe. The side-light emitting flexible pipe has many potential uses, such as advertising signs, exit path illuminators, swimming pool surrounds, entertainment and amusement uses, architectural uses, and the like, where the combination of flexibility, decoupling from the light source for safety reasons, ability to use various colors, ability to produce even illumination, and the like produce advantages over neon tubing or over rigid plastic pipe or fibers.
Robbins et al., U.S. Pat. No. 5,067,831, describe the general concept of a core/fluoropolymer clad/transparent or translucent sheath composite for use in side-lighting applications. However, Robbins relies on the leakage of light from the clad combined with the passage and issuance of light through the transparent or translucent sheath to produce his side-lighting effects. He does not teach or suggest altering the nature of the clad material to enhance the amount of light issued from the composite.
Japanese Kokai JP 08-094862-A teaches an optical waveguide tube with good optical transmission comprising a transparent core and a fluororubber cladding which contains a trapping agent for a halogen compound, which remains in the clad, such as activated carbon, silica, silica gel, alumina, or molecular sieves, a zeolite-based adsorbent, an ion exchange resin, magnesium oxide(which has a high reactivity toward halogen), calcium carbonate, or silver sulfate. However, the transparent core is a silicone liquid, which is far less useful for a flexible light pipe in terms of avoidance of kinking and in handling and installation than a solid flexible polymer. Further, the particles are present in the clad purely to stabilize the clad against decreases in transmission due to the halogen compounds, and at amounts significantly higher than the optimum level for effective light enhancement, so that they would contribute opacity. Kokai JP 08-094862 neither teaches or suggests the use of selected particulate addition to the clad to enhance the side-lighting capabilities of the composite.
Orcutt, U.S. Pat. No. 4,422,719 teaches a transparent semi-solid core with a clad or sleeve which is designed to transmit light from the core as it travels the length of the pipe. Orcutt teaches the use of titanium dioxide (TiO
2
) but at high levels of 2 to 10%, which will produce a light pipe which, although not totally opaque, will not pass through enough of the light introduced by the illuminator to give the brilliant illumination desired.
Thus, the need still exists for an improved flexible light pipe which delivers light from the side in a uniform manner along the length of the pipe, and which uses the delivered light effectively so as to give optimum illumination effects from the specific light intensity supplied at one or both ends of the flexible light pipe. More specifically, we have discovered an improved process for producing light pipe suitable for side-lit applications, comprising the steps of:
a) concurrently and coaxially extruding:
i.) a molten fluoropolymer through an annular channel of a coextrusion die to form an extruded tubular fluoropolymer cladding, and
ii.) a crosslinkable core mixture through a core mixture delivery tube of the coextrusion die to form an extruded crosslinkable core mixture within the circumference of the extruded tubular fluoropolymer cladding;
b) filling the extruded tubular fluoropolymer cladding with the extruded crosslinkable core mixture; and
c) curing the extruded crosslinkable core mixture within the extruded tubular fluoropolymer cladding wherein the cured extruded crosslinkable core mixture and the extruded tubular fluoropolymer cladding are in substantially complete contact, the improvement which comprises:
d) adding to the molten fluoropolymer, prior to feeding to the annular channel, from 50 to 4000 parts per million, preferably 200 to 2000 parts per million, of at least one light-scattering additive. Here the additive may be finely-divided, where finely-divided is defined as preferably from 0.1 to 10 microns, but it may also be larger in particle size, such as several millimeters in length. Preferably steps a), b), and c) are continuous.
Preferably the light-scattering additive when finely-divided is titanium dioxide, which may be treated, such as with a stearate salt, to improve dispersion, and preferably the titanium dioxide is of particle size from 0.2 to 0.5 microns. Calcium carbonate of similar particle size, but including preferred sizes of 8-10 microns, is also effective.
The core polymer may be any of those taught in the art, such as in U.S. Pat. No. 5,485,541, for light pipe or optical fiber uses, such as a poly(alkyl acrylate), poly(methyl methacrylate), a polyglutarimide, a silicone polymer, and the like. It will be transparent, preferably flexible, and preferably processable in melt form, then later cured or crosslinked to form the final core. However, by use of other manufacturing techniques such as filling cladding with monomer and polymerizing by a batch process, the need for delayed curability may be removed, although such processes are much harder to run in a continuous mode.
U.S. Pat. No. 5,485,541 also teaches many polymers other than fluoropolymers suitable for cladding of flexible light pipe or fibers; it is preferred for the present invention that the clad be of lower refractive index than the core, that the clad and the core bond at the surface in a uniform manner, and that the clad without additives be transparent. It is further preferred that the clad be readily co-extrudable with a co-extruded crosslinkable core.
Separately preferably, the crosslinkable core mixture comprises:
a) from about 90 to about 99.9 weight percent, based on the crosslinkable core mixture weight, of an uncrosslinked copolymer having weight average molecular weight from about 10,000 to about 150,000 daltons, the uncrosslinked copolymer comprising:
i) from about 80 to about 99.9 weight percent, based on the uncrosslinked copolymer weight, of polymerized units of a C
1
-C
18
alkyl acrylate, a C
1
-C
18
alkyl methacrylate, or mixtures thereof,
ii) from about 0.1 to about 20 weight percent, preferably about 0.5 to about 12 weight percent, based on the uncrosslinked copolymer weight, of polymerized units of a functionally reactive monomer, preferably selected from 2-methacryloxyethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, or mixtures of these, and
iii) from 0 to about 10 weight percent, based on the uncrosslinked copolymer weight, of polymerized units of a
Abramowicz Mark A.
Daecher Jeffrey L.
Hallden-Abberton Michael P.
Bruzga Charles E.
Fiberstars Incorporated
Ngo Hung N.
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