Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
1998-12-11
2002-08-06
Font, Frank G. (Department: 2877)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
Reexamination Certificate
active
06430348
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flat fiber having the optical-interference function which is formed by alternately laminating individually independent layers of polymers having different refractive indices in parallel with the major axis of its flat cross section, and a use thereof.
BACKGROUND ART
An fiber having the optical-interference function which is formed of alternate laminates of individually independent layers of polymers having different refractive indices interferes with a color having a wavelength of visible light range and develops a color by the reflection interference actions of natural light. This color development has a brightness like a metallic gloss, gives a pure and clear color (monochromatic) having a specific wavelength and has an artificial gracefulness entirely different from a color formed by the light absorption of a dye or a pigment. Typical examples thereof are disclosed in JP-A-7-34324, JP-A-7-34320, JP-A-7-195603 and JP-A-7-331532.
The optical interference effect is greatly influenced by a refractive index difference between two kinds of polymer layers, an optical distance (refractive index x thickness of each layer) of each layer and the number of laminate-forming layers. Above all, a fiber having an excellent optical interference effect is a fiber which is formed by laminating individually independent layers of polymers having different refractive indices in parallel with the major axis direction of its flat cross section and has a flat structure.
In the above flat fiber formed by alternately laminating two kinds of polymers in parallel with the major axis direction of its flat cross section, however, even if layers of polymers having different refractive indices are used only to extrude the polymer layers alternately laminated from a spinneret having a rectangular form, the actual cross-sectional form is deformed to be elliptical or circular. Consequently, the interface of the alternately laminated layers becomes devoid of parallelism and results in the formation of curved laminate interfaces. Moreover, even if alternately laminated polymer layers are extruded through a spinneret having a rectangular form, it is difficult to form a laminate having a uniform optical distance (i.e., having uniform layer thickness), and as a result, there can be obtained only a fiber having sparse color development wavelengths and a low color development intensity and having a cheap texture. Prior art techniques which have been so far proposed neither recognize the above problems nor teach any solution means.
It is an object of the present invention to provide a fiber having the optical-interference function in which the thickness non-uniformity of each laminate and the curvature of laminate interfaces are reduced as much as possible so that color development wavelengths are converged to show a high color development intensity.
DISCLOSURE OF THE INVENTION
It has been revealed that the above problem is easily solved when the ratio of solubility parameter values (SP) of individually independent layers of polymers having different refractive indices is in a specific range.
According to the present invention, therefore, there is provided a flat fiber having the optical-interference function which is formed by alternately laminating individually independent layers of polymers having different refractive indices in parallel with the major axis direction of its flat cross section, characterized in that (a) the ratio (SP ratio) of the solubility parameter value (SP
1
) of high refractive index polymer to the solubility parameter value (SP
2
) of low refractive index polymer is in the range of 0.8≦SP
1
/SP
2
≦1.2.
The fiber having the optical-interference function, provided by the present invention, and the use thereof will be explained further in detail hereinafter.
In the present specification, the term “fiber” generically includes a mono- or single-filament, a multi-filamentary yarn, a spun yarn and a short-cut or chopped fiber.
The fiber having the optical-interference function of the present invention has a characteristic structure in a cross section taken by cutting it at right angles with the lengthwise direction of the fiber. That is, the overall form of the cross section thereof is of a flat form, and the fiber has a structure in which a number of individually independent layers of polymers having refractive indices are laminated in parallel with the major axis direction-of the above flat form.
In the above cross-sectional form, “individually independent layers of polymers” means that layers of polymers having different refractive indices form a boundary plane in a plane where they are in contact with each other. As described above, the cross-sectional form of the fiber of the present invention shows a flat form in which a number of different polymer layers are alternately laminated. In an preferred embodiment, the fiber has a structure in which a protective layer portion is formed on a circumferential portion of the flat cross section. The protective layer may be formed of a polymer of any of the above laminated polymer layers. Further, the thickness of the protective layer portion is preferably greater than the thickness of the polymer layers of the above laminate portion. The cross-sectional form having the protective layer portion on a circumferential portion will be explained in detail later.
The right-angled cross-sectional structure of the fiber of the present invention will be explained with reference to
FIGS. 1 and 2
.
FIGS. 1 and 2
schematically show cross-sectional forms obtained when the fiber of the present invention is cut at right angles with the lengthwise direction thereof.
FIG. 1
shows a flat cross section having an alternate laminate portion formed of polymer layers A and polymer layers B, and
FIG. 2
shows a flat cross section having a protective layer C formed of polymer layer A on the circumferential portion thereof. In each of the cross-sectional forms shown in
FIGS. 1 and 2
, a number of polymer layers A and polymer layers B are alternately laminated in parallel with the major axis direction of the flat cross section (horizontal direction in Figures).
As shown in
FIGS. 1 and 2
, the fiber having the optical-interference function of the present invention has a flat cross section, and polymer layers A and polymer layers B are alternately laminated in parallel with the major axis direction of the flat cross section, whereby an area effective for optical interference is widely formed. And, the parallelism of alternate lamination is particularly important for the optical interference function.
In the above fiber, the thickness of each laminate is generally as ultra-thin as 0.3 &mgr;m or less, and it is therefore very difficult to form a regular alternate laminate portion in view of production process. Meanwhile, when the optical distance of each layer of the alternate laminate portion is entirely uniform both in the major axis direction and the minor axis direction of the flat cross section, the wavelength which is reflected and interfered with the fiber to form a color shows an actually uniform and single-wavelength clear color and has a high color development intensity (relative reflectance).
When a molten polymer is spun and drawn to be formed into a fiber, however, an actual reflection spectrum emitted from the fiber has a width to some extent, and it is very difficult to obtain a fiber having an actually uniform and single wavelength, for the following reason.
That is, in the process of spinning two kinds of molten polymers from a spinneret with these polymers being alternately laminating, and then cooling to solidification and drawing the polymers to form a fiber, laminate members gradually lose uniformity. That is because the flow rates of the molten polymers distributed for the layers change due to inevitable variability in the orifice diameter accuracy, etc., of opening portions for distributing the molten polymers for forming alternately laminated layers, and as a result, there is formed a distribution
Asano Makoto
Kumazawa Kinya
Kuroda Toshimasa
Owaki Shinji
Sakihara Akio
Font Frank G.
Nguyen Tu T
Teijin Limited
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