JPS6160404B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to optical filamentary materials having thermoplastic protective jackets, and more particularly to optical filamentary materials containing a core of optically transparent thermoplastic polymeric material. Optical filamentary materials that transmit light along the length of the filament by multiple internal reflections of the light are known in the art. Great care is taken to minimize light loss along the length of the filament. That is, internal reflection is as complete as possible so that light incident on one end of an optical filament-like material is efficiently transmitted to the other end of the material. The light transmitting portion, ie, the core of the optical filament-like material, is surrounded by a sheath having a lower index of refraction that minimizes light escape or absorption along the length of the filament. This sheath is usually transparent since opaque sheaths tend to absorb light. It is also advantageous for the sheath to consist of a substantially amorphous material in order to minimize light scattering and absorption. Optical filamentary materials can be broadly divided into two categories depending on the type of optically transparent core material. The first category of core materials is of thermoplastic nature, while the second category is of glass. The first class is generally superior in toughness and ease of folding, and the second class is generally superior in light transmission. The present invention comprises: (a) a cylindrical core of a substantially amorphous optically transparent thermoplastic polymeric material; (b) a substance for (a) having a refractive index at least 0.1% lower than the core material; (c) an extruded polymer jacket on the outside of (a) and (b); (i) a secondary transition temperature of 80°C to 140°C; (a) using an optically transparent material having a (iv) (c) using a first jacket polymer having a relatively low extrusion temperature and a relatively high The present invention relates to a light transmission cable comprising a second jacket polymer having an extrusion temperature. The cylindrical core referred to in the present invention includes both a cylindrical core and a cylindrical core. There are a variety of substantially amorphous thermoplastic polymeric materials suitable for the optically transparent cylindrical core of the optical filamentary material. As used herein, "optically transparent" means transmission of at least 50% light per 30 cm in the portion of the spectrum from 550 to 1100 nanometers. This degree of transmission does not need to span the entire spectrum. The polymer used as the core has a second order transition temperature, Tg, ranging from 80°C to 140°C. Typical core materials are acrylic and polystyrene homopolymers and copolymers, including those described in GB 1037498, e.g. polyalkyl methacrylates in which the alkyl group has 1 to 6 carbon atoms; Acrylic resins comprising polyalkyl methacrylate copolymers containing at least 70% by weight of units derived from alkyl methacrylates, such as polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, Polyisobutyl methacrylate and polycyclohexyl methacrylate and their interpolymers. Copolymers of units derived from methyl methacrylate with up to 30% by weight of units derived from ethyl acrylate or methyl acrylate and up to 15% by weight of units derived from 2-ethylhexyl acrylate are Examples of useful copolymers. Polymethyl methacrylate and its copolymers containing at least 70% by weight polymethyl methacrylate are preferred because they are readily available at reasonable prices, in high quality, and are very transparent. Also useful are optically transparent polymers in which hydrogen atoms are at least partially replaced with deuterium atoms. Resins suitable as core materials are:
Also described in U.S. No. 3,556,635 and U.S. Pat. No. 3,779,627. The diameter of the cylindrical optically transparent core varies from relatively thin core structures to relatively thick core structures. A suitable diameter is 0.1-2 mm. Thicker core structures can also be used, but tend to add undesirable bulk. Furthermore, in the case of an unduly thick core, attenuation is likely to increase. A relatively thick core has an advantage in its ability to capture large amounts of light when the light source is large, for example from an LED (light emitting diode). However, if the light source is small, such as a laser, a relatively thin core is preferred for capturing the incident light. The sheath material applied to the optically transparent core is substantially amorphous and transparent and has a refractive index that is at least 0.1% lower than the core material. These properties of the sheath reduce light scattering. Without this, the attenuation of transmitted light will increase. Examples of suitable exterior materials include those disclosed in GB 1037498, such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoromethyl trifluorovinyl ether, perfluoropropyl trifluoro Vinyl ether and structure

[Formula] (wherein, X is selected from the group consisting of F, H or Cl, and n is 2
-10, m is an integer from 1 to 6, and Y is CH ₃ or H). The thickness of the sheath is generally not important since the sheath material reflects the light traveling through the core. Typically used is a thickness that is at least twice the wavelength of the light traveling through the core. An example of a suitable range of jacket thickness is 2 to 500 microns. Excessive thickness of the sheath reduces the flexibility of the final product cable. Formation of the optical filamentary material of the core and its sheath is generally by coextrusion techniques well known in the art, as disclosed, for example, in US Pat. Nos. 3,458,615 and 3,646,186. An optical filamentary material having an optically transparent core and a lower index of refraction sheath is protected by a jacket. This is because the filament-like material will be damaged if it is not protected during handling and use in various applications. Such damage can result in increased attenuation of the transmitted light or, even worse,
resulting in destruction of the optical filamentary material. In the present invention, the jacket consists of a polymer applied by extrusion at a temperature at least equal to the second order transition temperature of the core material. It has been found that direct application of such polymers to optical filament-like materials consisting of an optically transparent core and a lower index of refraction sheath increases the attenuation of light transmitted through the core. The extrusion temperature required to apply the polymer adversely affects the light transmission ability of the optical filamentary material. In order to overcome this thermal effect, it is necessary according to the invention to use a thermal shield that thermally protects the filamentary material during extrusion of the jacket polymer. The thermal shield can be applied to the optical filament-like material without applying excessive heat (i.e., at a temperature below the Tg of the core) and can remain solid at the extrusion temperature of the jacket polymer. Consists of materials.
Preferably, the thermal shield is applied as a preformed material, meaning that the thermal shield is in a solid state before, during and after application to the optical filament-like material. The preformed material can be shaped at the time of application to the optical fiber material, for example, by weaving the fibers onto a sheath. As another method,
A tube can be disposed around the optically transparent filamentary material. The thickness of the preformed material is sufficient to protect the thermoplastic optically clear core from excessive heat during application of the jacket polymer until it is cooled from the exterior surface. Suitable materials of construction for forming the thermal shield include polyesters, polyamides including aramids, polyolefins (homopolymers and copolymers), acrylics, and cellulosic materials. Nylon, wool, cotton, polyethylene and polypropylene are examples. The factors that govern the selection of materials used for thermal shields are the degree of protection from heat provided by the thickness of the shield, and the final product cable, including its strength, elongation, flammability and ease of stripping. This is a desirable characteristic. Thermal shield is the sheath (or outer jacket layer)
It is understood that there is no need for contact with The thermal shield can be bonded to the sheathing through the use of adhesives. A jacket is disposed on the exterior of the thermal shield, which is applied by extrusion at a temperature at least equal to the second order transition temperature of the thermoplastic core. Since the primary purpose of the jacket polymer is to protect the optical filament-like material, the factors that govern the selection of the appropriate polymer are the extrusion method (at least the core
is the applicability of the polymer at high temperatures equal to Tg). Extrusion methods for applying such polymers are conventional and well known in the art. Polymers suitable as jackets include:
Polyamides, polyurethanes, copolyetheresters, polycarbonates, polyolefins (homopolymers and copolymers including ionomers) such as polyethylene and polypropylene, and melt-extrudable fluorocarbons such as tetrafluoroetherene/hexafluoropropylene copolymers. . Another factor that influences the selection of jacket polymer is the desired properties of the final product cable. These factors include factors of material selection for the thermal shield, such as strength, elongation, burn rate, and ease of stripping. For example, good stripability is necessary for ease of cable-to-cable bonding and connection of the cable to a light source or detector. In the cable of the invention, more than one layer of jacket is applied outside the thermal shield.
For example, a first jacket polymer having a relatively low extrusion temperature is applied to the thermal shield, followed by a second jacket polymer being applied at a relatively high extrusion temperature. In such cases, the first jacket polymer would serve to provide thermal protection to the optical filamentary material during extrusion of the second polymer. To further illustrate the invention, the following reference examples:
Examples and comparative examples are shown. Reference Example A lower refractive index substantially amorphous transparent polymeric outer shell consisting of a core of polymethyl methacrylate and a fluorinated ester of methyl methacrylate and methacrylic acid (Tg at 50°C and 6% lower than the core) A starting optical filamentary material was used consisting of a refractive index of The attenuation of this optical filamentary material was 490 dB per kilometer at 655.3 nm. A 2.5 cm extruder was equipped with a crosshead tube type die having a 1.05 mm inner diameter, a 2.32 mm outer diameter guide, and a 3.75 mm die. A 22 tex (195 denier) zero-twist yarn of poly(p-phenylene terephthalamide) fiber was stretched using six yarn stretchers equally spaced around a 7 cm circle above the guide hole. This thread was threaded through a stainless steel needle with an inner diameter of 1.2 mm and an outer diameter of 1.62 mm. The needle was inserted into the inlet of the guide and the thread was pulled through the hole in the guide, through the water bath, and into the variable speed puller. The extruder was heated to 175 °C and 15% containing 20% carboxylic acid groups neutralized with ethylene and zinc ions.
Ionic copolymer consisting of methacrylic acid (melt flow index 14, ASTMD-
1238, 190° C., 2.60 g, condition E) was introduced into the extruder at low speed. When this ionic copolymer appeared at the exit of the extruder, the puller was started. The die was adjusted to center the thread within the ionic copolymer extruded as a tube. A tube with an outer diameter of about 0.9 mm was prepared by increasing the take-off speed to 58 m/min and adjusting the extruder speed. At this point the temperature of the melt was 160°C. Poly (p-
An optical filamentary material surrounded by fibers of (phenylene terephthalamide) was fed into the needle and introduced into the center of the ionic copolymer tube. per kilometer at 655.3nm.
It showed an attenuation of 500dB. EXAMPLE By extrusion using a melt temperature of 185°C,
The reference material was overcoated with a copolyetherester (described in Example 1 of US Pat. No. 3,651,014). This cable had an outer diameter of approximately 1.25 mm. Attenuation was 490 dB per kilometer at 655.3 nm. Comparative Example The procedure of the Reference Example was followed except that poly(p-phenylene terephthalamide) fiber yarn was not used. The attenuation of this product was 1800 dB per kilometer at 655.3 nm.

Claims (1)

Claims: 1. (a) a cylindrical core of a substantially amorphous optically transparent thermoplastic polymeric material; (b) a refractive index of at least 0.1% lower than the core material; (c) an extruded polymeric jacket on the outside of (a) and (b); (a) using an optically transparent material with a transition temperature of (a); (ii) using a thermal shield between (b) and (c); (i) using a polymer extruded at a temperature at least equal to the second order transition temperature of the material used in (i); and (iv) (c) using a first jacket polymer having a relatively low extrusion temperature; A light transmission cable comprising a second jacket polymer having a relatively high extrusion temperature.