Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
2001-07-20
2004-08-10
Meier, Stephen D. (Department: 2853)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S453110
Reexamination Certificate
active
06774381
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus which continuously applies an electron beam to a filamentary workpiece, and more particularly to an electron beam apparatus for curing a coating material that has been applied to optical fiber. The invention relates also to a method of fabricating optical fiber using such an apparatus.
“Filamentary workpiece,” as used herein, includes slender, continuous workpieces with a circular cross-sectional shape having a diameter of up to 5 mm, and preferably up to 1 mm; as well as slender, continuous workpieces with an elliptical or rectangular cross-sectional shape in which the long axis or horizontal dimension is up to 10 mm, and preferably up to 4 mm, and the short axis or vertical dimension is up to 3 mm, and preferably up to 1 mm.
2. Prior Art
As an electron beam passes through matter, it excites orbital electrons in the matter, triggering chemical reactions and generating secondary electrons and x-rays. Gradually, the electron beam loses energy to the matter and slows down. It also undergoes scattering, causing the radiation to advance in different directions and disperse. This tendency is especially striking in high-density matter such as solids. Electron beams endowed with such characteristics have been used in many diverse industrial applications. Applications in manufacturing industries in particular fall into two broad categories: those involving the use of chemical reactions triggered by electron beams, and those involving the use of heat generated with the loss of kinetic energy by the electrons. Examples of the former type of application include resin crosslinking reactions such as in tire rubber and polyethylene coatings on electrical wire, as well as resin curing reactions in coated paper and printing inks. Examples of the latter type of application include electron-beam melting in smelting operations and electron-beam welding in metalworking operations.
In the first type of application mentioned above, part of the energy of the irradiated electrons is consumed in the chemical reactions. Most of the remaining energy simply passes through, although a portion thereof becomes heat. Such heat is minimized to avoid the deteriorating effect it can have on the resin. By contrast, in the second type of application, substantially all of the kinetic energy of the electron beam is converted to heat when the electrons slow down within the irradiated object, and is thus available for heating the metal to its melting temperature. Hence, the role played by electron beams differs completely from one type of application to another.
At the same time, the systems used in each case for irradiating electron beams share a common feature; each has an electron generating means and an electron accelerating means of some type. However, the electron beam systems used in the first type of application described above are designed to irradiate a broad surface area so as to increase productivity, whereas the electron beam systems used in the second type of application are designed for spot irradiation to increase energy density. Therefore, in connection with the former type of application, relatively low acceleration voltage equipment makes use of a “curtain” system having an electron generating means and an electron accelerating means that produce a broad electron beam band. Relatively high-acceleration voltage equipment makes use of a “scanning” system which has both an electron generating means and an electron accelerating means that together produce a narrow linear beam, and also an electron scanning means which distributes this beam over a broad area. In the latter type of application, the electron beam system typically includes an electron generating means and electron accelerating means that produce a linear beam, and also an electron focusing means that concentrates the beam toward a focal point.
In the first type of application, electron generation and acceleration are carried out in a vacuum, whereas irradiation is generally carried out at atmospheric pressure, which is more conducive to continuous treatment and thus advantageous in terms of productivity. In this type of system, a thin metal foil generally serves as the boundary separating atmospheric pressure from the vacuum, the electron beam being made to pass from the vacuum out to atmospheric pressure through the metal foil. The electron beam is strongly scattered as it passes through the metal foil, and thus diffuses following passage through the foil. However, this has not been a problem because the beam is intended to irradiate a broad area.
On the other hand, in the second type of application, because the electron beam must focus at one point, irradiation is generally carried out in a vacuum in which scattering does not occur. Most equipment of this type uses a batch treatment-type high-vacuum system in which the object to be irradiated is placed in an irradiation chamber and irradiation is carried out following evacuation of the chamber to a high vacuum. However, in a high-vacuum system, evacuation takes a long time, resulting in poor productivity. Hence, low-vacuum systems have been developed and adapted for practical use in which the irradiation chamber is connected to the high-vacuum electron-beam generator by a differential evacuating means, thereby making it possible to carry out irradiation even when the degree of vacuum in the irradiation chamber is low; i.e., even at a short evacuation time.
JP-B 5-50454 discloses art relating to the electron beam irradiation of a filamentary workpiece. While this prior-art reference does not specify the type of apparatus used, the energy of the electron beam or the degree of irradiation, it does describe the electron-beam curing of an optical fiber coating material. However, no technology has previously been arrived at for the continuous application of a focused electron beam to a filamentary workpiece under atmospheric pressure.
A variety of optical fibers are made, including quartz glass fibers, multicomponent glass fibers, and plastic fibers. Of these, large quantities of quartz glass optical fibers are used in a broad range of applications on account of favorable characteristics such as their light weight, low loss, high durability and large transmission capacity. However, the most common quartz glass optical fibers have a diameter of only 125 &mgr;m and thus have a tendency to break with even the slightest scratch. Also, because transmission loss increases when the fiber is subjected to an external stress such as bending, a resin coating composed of a soft primary coating layer and a hard secondary coating layer surrounding the first layer is applied. Coating is typically carried out by using a die-coating process to apply a liquid resin over the bare optical fiber immediately after the fiber has been melt-drawn, then curing the resin by the application of heat or exposure to radiation (generally ultraviolet light). Secondary coating may be carried out by a coating and curing process conducted either subsequent to or concurrent with coating and curing of the primary coating. The coated optical fiber is also commonly colored with an ink for the sake of identification. A number of coated optical fibers, typically four or eight, are gathered into a bundle, which is coated with a liquid resin. The resin is then cured by the application of heat or by exposure to radiation such as ultraviolet light, thereby giving an optical fiber tape.
Coating materials proposed for such use include urethane acrylate-based ultraviolet-curable resin compositions. JP-B 1-19694, JP No. 2522663 and JP No. 2547021 disclose liquid compositions of UV-curable resins composed of a urethane acrylate oligomer, a reactive diluent and a photopolymerization initiator.
Optical fibers are being drawn today at higher speeds to enhance the productivity of the manufacturing process. This rise in speed has been accompanied by an increase in the energy per unit time required to cure the resin coating. But because improvements
Kawada Nobuo
Ohba Toshio
Dudding Alfred
Meier Stephen D.
Shin-Etsu Chemical Co., LTD
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