WO1996019742A1

WO1996019742A1 - Polyolefins as a light transmission medium

Info

Publication number: WO1996019742A1
Application number: PCT/US1995/016537
Authority: WO
Inventors: Michael E. Carter; Aspy K. Mehta
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1994-12-19
Filing date: 1995-12-18
Publication date: 1996-06-27
Anticipated expiration: 1997-06-19
Also published as: AU4523996A

Abstract

A transmission medium for visible light and certain other forms of electromagnetic energy, to which the medium is generally transparent, comprising polyolefin copolymer derived from other than polycyclic olefin monomer.

Description

POLYOLEFINS AS A LIGHT TRANSMISSION MEDIUM

Field of the Invention

This invention relates to the use of polyolefins, particularly those produced by metallocene catalysis, as the transmission medium for visible light and other forms of electromagnetic radiation. Particular applications include "fiber optics" and other light-transmitting applications.

Background of the Invention

It is known that light can be transmitted through high purity glasses formed into optical waveguides. Some waveguides of plastics are known. The general similarities among commonly used waveguides include high purity, high clarity, and comparatively high cost.

Maurer and Schultz describe, in US 3,659,915, optical waveguides having a core with cladding. The core and cladding both employ high purity fused silica, at least one of which is doped to yield enhanced transmittance of light.

Keck et al describe the basic needs for integrated optical circuit optical waveguides in US 3,934,061. High purity glasses are also used in these applications.

Polycarbonate and poly(methyl methacrylate) polymers are known to be useful in forming fiber optics of "plastics". Numerous patents and other publications are available relating to the use of these polymers in this manner. A few which may have distant relation to the materials useful for the practice of our invention are identified.

EP 362 814 A describes a random copolymer of ethylene and a polycyclic olefin which is copolymerized using a vanadium compound and a halogen containing aluminum compound. The polymer has well balanced mechanical properties as well as high transparency, optical homogeneity, and small birefringence. Several publications: EP 446 051 A, US 5,225,503, JP 92-002675/01, JP 92-101584/13, JP 92-101586/13, JP 93-160962/28, and JP 93-400420/58, describe groups of polycyclic polyolefins useful for optical disks and fibers. The polymers are random copolymers of ethylene and specific polycyclic olefins having balanced optical, mechanical, and thermal properties which are apparently formed by catalysis with oxygen-containing vanadium compounds and specific groups of aluminum compounds. The incorporation of polycyclic olefins into the chain backbone renders articles with increased rigidity, which is undesirable for applications requiring soft, flexible light guides.

It would be desirable to develop optical fibers and other light transmission media employing a low cost, highly flexible polymer based on non-cyclic polyolefins, that can be fabricated using standard thermoplastic fabrication techniques (e.g. conventional thermoplastic extrusion).

Summary of the Invention

We have discovered that optical fibers and other light waveguides can be produced from certain grades of single-site catalyzed, non-cyclic polymers, particularly ethylene-alpha-olefin copolymers. The resulting optical fibers are readily processible, highly flexible, soft, smooth, highly transparent to visible light and certain other frequencies of the electromagnetic spectrum, and possess other advantageous properties.

Detailed Description

This invention provides several embodiments of transmission media for electromagnetic energy. The first embodiment affords transmission medium for electromagnetic energy, to which the medium is generally transparent, comprising polyolefin copolymer derived from non-cyclic olefin monomers.

Another embodiment provides transmission media for electromagnetic energy, to which the medium is generally transparent, comprising polyolefin copolymer produced by polymerization in the presence of single-site catalyst other than vanadium compound or a combination of other non-vanadium containing catalyst with vanadium containing catalyst.

A third embodiment provides transmission media for electromagnetic energy, to which the medium is generally transparent, comprising polyolefin copolymer produced by polymerization in presence of single-site catalyst comprising metallocene compound.

Preferred embodiments include those in which the transmission medium is formed into optical waveguides. These waveguides can be used with or without cladding. If cladding is used, the cladding should have a lower refractive index than the transmission medium. Preferably, the cladding will be substantially surrounded with insulation. Of course, in some applications it will not be necessary or desirable to use cladding.

Useful cladding materials include polycarbonate, acrylic or acrylate polymer, as well as furan or furfural polymer, epoxide polymer, or combinations thereof as well as others. Useful characteristics of a good cladding material include lower index of refraction, ability to co-form with the transmission media, and minimal miscibility with the media of choice.

Insulation is useful for protecting the integrity of the waveguide and, if present, its cladding. Such protection will be from impact, heat, damaging radiation, and other hazards to which the waveguide may be exposed. Useful insulation may include carbon, furan or furfural derivatives, epoxide polymer, vinyl or vinyl chloride derivatives, other polyolefins, latex, rubber, and urethane derivatives as well as other suitable materials, or combinations thereof. Of course, in many applications it will not be necessary or desirable to use an insulating material.

These embodiments will be useful in various forms, including planar waveguides, generally round fibers or filaments, films, and others. The transmission media, particularly fibers will find use in communications transmissions, particularly for short distances. They are also useful in illumination devices, visual displays, medical diagnostic and/or treatment devices, toys, entertainment devices, and other novelty items.

With the advent of commercially available polyolefins which are produced by single-site catalysts (SSC), particularly transition metal metallocenes or their analogues, it is now possible to make polyolefins with exceptional clarity. This is possible since such catalysts typically have extremely high polymer conversion efficiencies. Thus, they leave minimal catalyst residue in the final polymer. Their clarity is also enhanced by the narrow molecular weight distribution (MWD) and the narrow composition distribution (CD) of such products. The narrow MWD provides homogeneity in the length of the polymer molecules which assures minimal optical interference from high and low weight molecules. The narrow composition distribution provides relatively homogeneous distribution of the comonomers throughout the polymer which helps minimize crystallization, and keep any existing crystallites small. Useful polyolefins for the practice of this invention will include those produced by single site catalysis, particularly copolymers. For the purpose of this application, the term "copolymers" includes polymers derived from two or more monomers.

While any high clarity non-polycyclic derived polyolefin may be used in the practice of our invention, some may be more useful, particularly in some applications, than others. As a general "rule of thumb", olefinic polymers of lower densities will have comonomers incorporated into the polymer backbone; comonomers which disrupt the polymer crystalhnity will tend to make the structure less dense. While it is the successful disruption of crystallinity which is of interest, polymer density may be used as a crude measure of crystallinity. In the practice of our invention, lower density polymers are generally preferred over those having higher density.

Another general trend among these polymers is that the longer or bulkier comonomers will tend to disrupt crystalline polymer structure more effectively than will the shorter chain or more compact comonomers. This may be noted in the series of ethylene copolymers with propylene, butene-1, hexene-1, and octene- 1 as comonomers. On a molecule-for-molecule basis, inclusion of the same amount of each comonomer in each of the four different binary copolymers will demonstrate lower density, and lower crystallinity, as the length of the comonomer chain moves from three through four and six to eight carbons in the chain.

In light of the preference for polymers with minimal interfering structures, including crystals, preferably polymers useful in the practice of our invention will include copolymers. Such copolymers will be derived from other than polycyclic

-} olefins and will preferably be of densities in the range of about 0.85 g/cm to about

0.92 g/cm for ethylene based linear polymers. Even more preferably, the copolymers will have densities in the range of about 0.86 g/cm to about 0.90 g/cm 3 , those in the range of about 0.865 g/cm 3 to about 0.89 g/cm 3 will be found to be particularly useful.

Preferably, the copolymer used in producing the transmission media of the present invention has a substantially narrow composition distribution. The composition distribution of a polymer may be measured in a number of manners. For the purposes of the present application and the appended claims, composition distribution shall be measured by the "composition distribution breadth index" (CDBI) or the "solubility distribution breadth index" (SDBI) of the polymer. A description of these measurement parameters can be found in WO 93/03093.

Generally, particularly with ethylene copolymers, as the concentration of comonomer which interferes with crystallinity of the copolymer increases, the clarity will increase. With enhanced clarity, light transmittance will increase. Of course, disruption of crystal formation by copolymerization of non-polycyclic comonomers will reach an upper limit of usefulness at which point further comonomer incorporation will not enhance clarity or may actually, and undesirably, increase interference. Such a limit will likely vary with comonomer.

Generally, the fewer impurities and fewer crystallites in the materials, the better for high light transmission. This makes sense since the inclusion of such items will tend to scatter light or otherwise attenuate the intensity of the light by the end of the transmission. Impurities may be reduced by care in the manufacturing process and by enhancement of the reaction efficiency to reduce non-polymer residue.

The term "generally transparent" for the purpose of this description means that the chosen electromagnetic energy will pass through a substantial amount of the material with minimal interference, attenuation, or loss, of intensity. This will occur in a manner such that a relatively high fraction of the radiation will be received at the distal end of the transmission. The desirable or useful intensities will be determined by the application in which the guides of this invention are used.

Currently, useful means of producing the materials, preferably copolymers, used in the practice of this invention involves polymerizing proper combinations of monomers with single site catalyst systems. Particularly useful catalyst systems include metallocene, metallocene-type, amine or amido, or combinations, of transition metals with an activator, combinations of activators, scavengers, or combinations thereof. Some of these systems are described in EP A 129 368, EP A 277 003, EP, A 277 004, US patent numbers 5,153,157, 5,057,475, 5,318,935, and WO 92/00333. As it is now known in the art, suitable activators for these families of catalytic transition-metal compounds include various aluminum compounds including alumoxanes, particularly trimethyl alumoxane, and bulky labile anionic activators. These catalyst systems may be used in numerous manufacturing processes including high pressure, liquid phase, and gas phase systems. Care must be used to recognize that some of these catalyst systems, particularly when used in supported form (e.g., in gas phase reactors) may appear to act as other than single-sited in light of variations in conditions during polymerizations. Such polymerization reaction systems are useful but may make catalyst systems which are inherently single-sited appear otherwise.

Single-site catalyst systems, particularly the metallocene-type systems, produce polyolefins of notable clarity. This derives from the consistency of the length of the polymer molecules, as demonstrated in their narrow molecular weight distribution, and the efficiency of the catalyst systems to incorporate comonomer, thereby reducing crystallinity. Clarity of the polymer as well as optical transmittance characteristics are improved by the lack of non-polymer residue, or "ash". Generally, traditionally produced linear polyolefins are catalyzed by less efficient systems and thus include more ash which will tend to scatter and diffuse light transmission.

Numerous monomers and comonomers may be used in the practice of our invention; these will include ethylene, propylene, butene-1, pentene-1, 4- methylpentene-1, hexene-1, octene-1, cyclohexene, cyclopentene, cyclooctene, and many others, as well as combinations of these. Generally, comonomers which interfere with the crystallization of the resulting polymer will be found to be useful. Any such comonomer including the cyclic olefins, with the exception of the polycyclic olefins, with specific exceptions, will find use in the practice of our invention. The exceptions for the polycyclic olefin- derived polymers will be those produced by non-vanadium containing, particularly metallocene-type, single-site catalysts.

The usefulness of the media of this invention may be tailored and enhanced for specific applications, including tinting or dying the medium to provide transmittance selectivity for specific areas of the electromagnetic, particularly the visible range, spectrum. Such coloring may be accomplished by addition of any number of polymer-compatible dyes, tints or other such non-blocking, non- scattering, or interfering agents. This will find particular application in visual displays and novelty items.

The transmitting ability of these media may be enhanced by assuring higher, preferably complete, or approaching complete, internal reflectance. Internal reflectance is enhanced by known techniques including use of a cladding layer around the transmission medium. Useful methods include securing refractive index relationships between the transmission medium and the cladding such that the index of refraction of the transmission medium is greater than that of the cladding layer. This may be accomplished by increasing the index of the transmission medium or by decreasing the index of the cladding medium; use of different copolymers for the differing media, or use of an entirely different polymer or other materials, may be useful approaches here.

In some applications, it will be desirable to thermally fuse the cladding to the transmission medium. Metallocene catalyzed polymers will be particularly useful for such cladding and/or transmission medium, because such polymers have advantageous heat seal properties, including a relatively low seal initiation temperature.

Internal reflectance, or retention of the radiation, particularly visible light, within the waveguides or light guides of this invention may be improved by provision of a refractive index barrier, often a cladding layer, at the boundary of the transmission medium. Preferably, a diminishment of refractive index should occur when crossing out of the transmission media. While other cladding layers are preferred, such a diminishment can be arranged with a bare item of acceptable medium alone in air. Far better waveguides may be created, though, by use of a cladding layer of an acrylic, acrylate, polycarbonate, or other suitable polymer with a melting range near that of the polyolefin and with, preferably, low miscibility with the polyolefin.

Examples

To aid in explaining and clarifying this invention, examples are provided below. These are intended solely for exemplification, not for limitation of the scope of this invention.

Example 1

T'\λ

A sample of EXACT 5009 type material was obtained from Exxon ^rV\Λ

Chemical Company in Houston, Texas; EXACT 5008 would work equally as well. Both materials are ethylene/butene-1 copolymers with about 31% butene rt copolymerized, nominal density about 0.865 g/cm , and melt indices (MI) about 10 and 20, respectively. The polyolefin was extruded into strands about 2 mm in diameter through a two-hole die using an extruder made by Modern Plastic Machinery Corporation (MPM) of Clifton, New Jersey with an approximately 2.5 cm (1 in) barrel having a screw with an LJD ratio of 20: 1. Such strands were made using a temperature profile which would typically be about 88°C/110^oC/110^oC/99°C (190°F/230° F/230°F/210°F) with the screw speed being about 70 rpm and the melt temperature about 132°C (270°F).

The strands were cleanly cut into about 15 cm (6 in) lengths, placed in a bundle, and placed with their cut ends flush against the lens of a low voltage light source. Opaque tape was wrapped around the bundle and the end of the light source to exclude a wash of light from the area around the bundle of strands. When the light was turned on in a darkened environment, the ends of the fibers distal from the light source became illuminated.

Example 2

Different colors may be obtained. This could be accomplished by use of colored filters or gels between the light source and the fibers or strands.

Example 3

Another method of obtaining different colors would be through incorporation of non-blocking or interfering dyes, stains, tints, or other coloring means within the waveguide itself prior to or during formation. By combining fibers which preferentially transmit different colors, a single light source would be able to be used to provide illuminated displays with different colors. This would have use in advertising and artistic applications.

Example 4

Olefinic optical waveguides would have application with toys. Since the materials useful in the practice of this invention are generally soft and pliable, there would not be the same danger of embedding minute glass shards or fragments within the skin as there might be with the more rigid and brittle glass waveguides. The generally lower densities of olefinic waveguides would be of benefit here also, as with other applications, in that shipping and handling costs, as well as overall product weight, would be lowered over the glass waveguides which would generally have specific gravities more than about 2.5 times that found in the optical material of our invention. Other benefits may accrue from the practice of our invention when SSC-produced, non-polycyclic monomer derived polyolefins are used; these materials, with their narrow molecular weight distributions will have relative consistency in the length of the polymer molecules and will tend not to include the longer molecules which tend to serve as nuclei for crystal formation and growth. The reduction of such nucleating species will enhance the ability to draw fine, high-transmitting waveguides, particularly fibers.

Example 5

In consideration of the softness, flexibility, low density and low cost of the materials useful in the practice of this invention, such waveguides, particularly in the form of strands or fibers, would find use in medical applications. They would provide disposable visual probes useful for accomplishing less intrusive exploration and also be useful in providing a source of illumination in surgeries.

Example 6

Such probes would also find use in delivery of specific electromagnetic energy to local spots. This would include ultraviolet, infra-red and other frequency lights, including lasers, capable of healing lesions or destroying tissue in a localized and minimally invasive fashion.

Example 7

Fibers of these materials would also be useful in medical applications involving light therapy. Recognizing the softness and pleasant feel of these materials when formed into fibers or fabrics, as noted in US 5,322,728, fiber-type waveguides could be useful in forming light-delivering fabric. By providing numerous ends of fibers within the fabric, or abrading the fibers of a fabric on one side and having the other ends of such fibers communicate with a light source, light may be delivered to a large area. Such a fabric or blanket could be useful for wrapping, for example, jaundiced infants with high bilirubin counts. This would provide a more comfortable and less traumatizing means of delivering light, particularly, metered amounts of ultraviolet light, to the entire body of an infant or other individual, to aid the body's ability to process excess bilirubin.

Example 8

Such illuminated, or illuminatable fabric would also find use in advertising, artistic, and other such displays.

Example 9

Bundled fibers, including those capable of transmitting different or varying colors, could be made into novelty lamps taking the form of a "light fountain".

Example 10

Illuminated fabrics, as described earlier would also be capable of providing pleasant, diffuse light for area lighting. Depending upon intensity of the source and the makeup of the fabric or bundle ends, such lighting could be generalized for wide area or limited for localized illumination.

Example 11

With proper optical electronic interfaces and optical amplifiers, a communication system comprising transmission media derived from single-site catalyzed polyolefins derived from olefins other than those which are polycyclic will be possible. Such interfaces and amplifiers, or "repeaters", are known from work with glass waveguides. Such communications systems would be useful for

- u - data transmission, voice communications, as well as other applications such as computer networking.

Example 12

Selected optical fibers within a visual display such as a billboard or artistic presentation may be made to move because of their inherent flexibility. By such action, the display, or portions of it, will provide a sense of movement, and likely, depth. It will therefore be possible to provide "moving" displays with, for example, walking or dancing people, speeding trains, charging animals, or other desirable "movement". Such movement of the fibers may be caused by any suitable means including mechanical means, creation of a thermal differential across the fiber including through application of heat or cold, or combinations to specific fibers. Differential application of heat, cold, or combinations may cause a temporal change in refractive index within the fiber which may also provide a sense of movement, by altering the distal fiber end receipt of light energy.

Example 13

Formation of fiber-type optical waveguides of our invention may be accomplished by coextrusion of the transmission medium, or core, the cladding layer, and optionally insulation. This may be accomplished by use of relatively unsophisticated multi-orifice coextrusion dies of the type known in the art. To obtain very thin fibers, the coextruded fibers may be drawn down under proper conditions of temperature, pressure, use of draw-down dies, or combinations thereof.

Example 14

Other means of producing such fiber optics would include draw-down of a preformed "billet". The round billet could be extruded such that the thicknesses of the desired layers are in proportion to their final desired thicknesses. Under proper conditions of temperature, pressure, use of draw-down dies, or combinations thereof the final desired fibers may be obtained. Such a billet could also be made by pouring molten material to desired thicknesses in successive molds.

Example 15

The billet of Example 15 may also be produced by successive deposition of the desired layers. This may be accomplished by vapor deposition, sputtering, or even in a polymerization reactor. Vapor deposition or sputtering under vacuum would provide a high purity method of deposition which may be used, beneficially, to remove undesirable residual low molecular weight polymer impurities.

* * *

Those skilled in the art will appreciate that the invention may take many forms not expressly described above. To the extent the description above was specific, this was by way of illustration and not limitation. The scope of the invention shall be limited only by the following claims.

Claims

CLAIMSWe claim:

1. A transmission medium for electromagnetic energy, to which the medium is generally transparent, comprising a waveguide, said waveguide comprising a metallocene catalyzed polyolefin copolymer derived from other than polycyclic olefin monomers.

2. An optical waveguide, comprising an elongated light transmitting element, said element being composed of at least 50%, preferably 80% by weight of an olefinic copolymer, said copolymer having a density in the range of 0.85 - 0.92 g/cm³, preferably in the range of 0.86 - 0.90 g cm³, a MWD not exceeding 3.5, and wherein said copolymer was produced utilizing metallocene catalysis.

3. A light transmitting system, comprising a light source and a waveguide, said waveguide having an elongated member substantially transparent to at least one frequency of the light produced by said light source, said elongated member being at least 80 weight percent, preferably at least 95 weight percent polyethylene copolymer, said copolymer having a MWD < 3.5, a CDBI > 50 and said copolymer being produced utilizing metallocene catalysis.

4. The transmission medium of claim 1, wherein said waveguide comprises a communication system, a medical or therapeutic device or an illuminating device.

5. The waveguide as set forth in any of the preceding claims, wherein said waveguide is colored to selectively transmit narrow frequency ranges of visible light.

6. The waveguide as set forth in any of the preceding claims wherein said waveguide is substantially surrounded by cladding of lower refractive index than said waveguide, which cladding is optionally substantially surrounded by insulation.

7. The transmission medium as set forth in claim 1 wherein said waveguide comprises an ethylene based copolymer having a density in the range of about 0.865 g/cm³ through about 0.92 g/cm³ preferably in the range of 0.865 g/cm³ through 0.90 g/cm³, and more preferably in the range of 0.865 g/cm³ through 0.888 g/cm³.

8. The optical waveguide as set forth in claim 2, wherein said elongated light transmitting element takes the form of a fiber, filament, strand, planar, film, or combinations thereof.

9. The light transmitting system as set forth in claim 3, wherein said waveguide is a fiber having a thickness not exceeding 2mm.