JPS6113201B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a plastic light guide sheet. More specifically, it is an object of the present invention to provide a novel method for producing a light guide sheet according to a mask pattern by polymerizing an ultraviolet ray polymerizable monomer in a plastic transparent film. Light guide sheets made of transparent plastic sheets are used for branch paths for optical communication or fiber sheets for abstraction. As shown in the figure, this light guide sheet consists of a part with a high refractive index (light guide part) 1 and a part with a low refractive index (clad part) 2,
It is configured such that light propagates through the light guide portion 1 while undergoing total reflection or refraction. In such a light guide sheet, if the difference in refractive index between the light guide section 1 and the cladding section 2 is small, the incident light will not be able to travel freely in the case of an optical path bent at a large angle. In order to integrate the provided light guide paths, it is necessary to increase the difference in the refractive index to allow light to travel freely. Conventionally, this kind of plastic light guide sheet is made by dispersing a low refractive index monomer in a high refractive index plastic transparent sheet, then placing a mask pattern in close contact with the sheet and irradiating it with ultraviolet rays to polymerize the monomers present outside the light guide. A manufacturing method has been adopted in which the monomer remaining in the light guide portion is then evaporated and removed in a vacuum. In this production method, in order to disperse a low refractive index monomer in a high refractive index plastic transparent sheet, a monomer that is compatible with the solvent is dissolved in the solvent when the sheet is produced by the casting method, and the monomer and the solvent are dissolved in the solvent. This method utilizes the difference in boiling point between the The mask pattern was printed in a short time while preventing However, in this monomer simultaneous dissolution method, it is very difficult to know when the cast sheet is completed, and if the sheet drying time is too long, even the monomer will evaporate and be removed, and the light guide portion and cladding portion will be separated. On the other hand, if the drying time is too short, problems such as deformation of the sheet during mask pattern printing may occur due to insufficient hardness of the sheet surface, resulting in a satisfactory guide sheet. It was difficult to obtain an optical path sheet. A vapor phase diffusion method of monomers has also been proposed as a method of dispersing monomers in transparent plastic sheets. In this method, a transparent sheet of high refractive index plastic in which an ultraviolet sensitizer is dispersed is manufactured by a film forming method such as a casting method or melt extrusion method, and this sheet is left in a container filled with saturated vapor of monomer. A method is used in which a monomer is diffused into a sheet and then a mask pattern is printed using the same process as the monomer simultaneous dissolution method described above. This vapor phase diffusion method has the drawback that the monomer tends to collect on the sheet surface or in a portion close to the surface layer, and the finished light guide sheet is prone to cracking. The inventors of the present application have conducted extensive research in order to solve all of the drawbacks of the above processes at once, and as a result, they have created a polymer film on the sheet surface by pre-polymerizing a part of the end-polymerized monomer. By wrapping the monomer, it is possible to connect the light guide portion and the cladding portion without causing any hindrance to the mask pattern printing operation and the removal of unreacted monomers remaining in the light guide after superimposing monomers existing outside the light guide. We have completed a method to obtain a light guide sheet with a large refractive index difference. That is, the gist of the present invention is that when forming a light guide path in a plastic transparent sheet, first, a low refractive index monomer is selectively polymerized on the surface of a high refractive index sheet containing a low refractive index monomer, and then a low refractive index polymer is formed. The method is characterized in that a thin film layer is formed to confine the terminally reactive monomer inside the sheet, a desired mask pattern is printed, and then the terminally reactive monomer remaining in the portion that will become the light guide path is removed by evaporation. Note that the low refractive index polymer thin film layer has almost no problem in evaporating and removing the reactive monomer after the mask pattern is baked. The plastic for manufacturing the light guide sheet used in the present invention can be arbitrarily selected based on its refractive index, but the compatibility of the polymer with the monomer or polymer/monomer/solvent, and the film-forming ability of the solution of each of these components are important. ,
In particular, it is necessary to find a combination of a high refractive index polymer and a low refractive index polymer, taking into consideration the ability to form a transparent film. Therefore, the plastic polymers for the sheet that can be used here include, for example, polygarbonate, polystyrene, polymethyl methacrylate, diallyl phthalate, di. Glycol.
J. Allyl carbonet (CR-39), poly-4.methylpentene. 1. Transparent plastics such as polyvinyl butyral, cellulose acetate butyrate, polymethyl acrylate, etc., each having a light transmittance of 80% or more are preferable, and as monomers, they have a relatively low boiling point and a small refractive index. Excellent compatibility and transparency of UV-polymerized polymers.For example, methyl acrylate, methyl methacrylate, ethyl acrylate, isobutyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, acrylic acid. 2
- Cyanoethyl, cyclohexyl acrylate, ethyl methacrylate, etc., which have a boiling point of 120°C or less and a refractive index of 1.50 or less are preferred. The present invention provides high refractive index polymers in which one or more high refractive index polymers and low refractive index monomers arbitrarily selected from the above polymers and monomers are dispersed by a monomer simultaneous dissolution method or a vapor phase diffusion method. A plastic sheet is prepared, a low refractive index monomer on the surface of the sheet is first polymerized to form a low refractive index polymer thin film layer, and then a mask pattern baking process is performed on the plastic transparent sheet provided with the low refractive index polymer thin film layer. A light guide sheet is manufactured by polymerizing a low refractive index monomer that will become a cladding portion, and then removing unreacted monomers remaining in the light guide portion in a vacuum container. In the present invention, in order to form a thin film layer of a low refractive index polymer on the surface of a high refractive index plastic sheet in which a low refractive index monomer is dispersed, a method of uniformly irradiating low-intensity ultraviolet rays is adopted. An ultraviolet lamp with a lamp input of 100 W/cm or less is suitable for low-intensity ultraviolet rays, and the irradiation time cannot be unconditionally specified because the sensitive wavelength range varies depending on the type of monomer, the type of sensitizer, and the concentration. Although this is not possible, it is usually desirable to complete within a few minutes. In addition, the film thickness of the high refractive index plastic sheet that becomes the base sheet is 20
μ~250μ is suitable, and desirably 50μ~120μ is suitable. If an excessively thin base sheet is used, the monomer will easily volatilize and the coating effect of the low refractive index polymer thin film layer formed on the surface will not be obtained sufficiently. Using a thick sheet is undesirable because it tends to cause spots when irradiating with a mask on. The proportion of low refractive index monomers contained in the base sheet depends on transparency during film formation, reduction of monomer during film formation, influence of film thickness, and mechanical properties of the base sheet at the end of film formation, mainly hardness and flexibility. The monomer concentration should be determined by taking into consideration the expected refractive index difference, and usually the monomer concentration should be 60% or less of the base polymer, preferably 60% or less of the base polymer.
It is preferably in the range of 10 to 50%. When using a monomer concentration in this range, the refractive index difference between the light guide portion and the cladding portion will be 10% or more, usually 15% or more, of the refractive index difference between the high refractive index polymer and the low refractive index polymer, respectively. . The ultraviolet light for mask baking may be the same as the ultraviolet light for forming the surface layer, but it is preferable to prepare a different one if possible, and usually a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, or an ultraviolet laser is used. As described above, according to the present invention, a low refractive index polymer thin film layer in which a low refractive index monomer is selectively polymerized is formed on the surface of a plastic sheet in which a low refractive index monomer is dispersed, and a mask pattern is baked by ultraviolet irradiation. The attaching process suppresses monomer evaporation during film formation and mask pattern baking, and effectively polymerizes low refractive index monomers.
As a result, a light guide sheet with a large refractive index is obtained,
Since there is a large difference in refractive index between the light guide section and the cladding section, it is possible to construct a light guide path that can bend at a large angle, which is impossible to achieve with ordinary glass fibers such as branch circuits, direction conversion circuits, and crossover circuits. Application circuits can be easily created.
In addition, cracks, which were a drawback of light guide sheets produced by the vapor phase diffusion method, are reinforced by the low refractive index polymer thin film layer on the surface, making it possible to obtain a good light guide sheet that is stable over time without any cracks. Next, specific examples of the present invention will be explained. A light guide sheet was made using bisphenol polycarbonate (manufactured by Bayer) as a high refractive index polymer. In order to obtain a sheet by the casting method, a polymer solution having the composition shown in Table 1 was prepared.

[Table] Polished stainless steel container (20 x 15
cm), the entire container was placed in a sealed container, and dry nitrogen was flushed at 200 c.c./min to evaporate the methylene chloride. After about 3 hours, a transparent sheet with a thickness of 50 μm was obtained. This sheet contains monomers, sensitizers,
Polymerization inhibitor is uniformly dispersed. A high-pressure mercury lamp (lamp input: 80
Microscopic observation of the cross section of the sheet after 60 seconds of irradiation with (W/cm) revealed that a thin film layer of polymethyl methacrylate was formed on the sheet surface. After this treatment, the interior of the sheet is filled with highly concentrated reactive monomers. This sheet is closely attached to a light guide pattern made by etching a chromium film on the surface of Pyrex glass, and is attached to an ultra-high pressure mercury lamp (lamp input:
120W/cm) for 180 seconds. Next, the unreacted monomer remaining in the light guide was removed in a vacuum container maintained at 10 ^-5 mmHg. For comparison, we created a sample under the same irradiation conditions that did not undergo the process to form a low refractive index polymer thin film layer during the process, and compared the two.As shown in Table 2, a large difference in the optical properties of the two was observed. The effects of the present invention were demonstrated. As is clear from the results in Table 2, according to the present invention, a device with a large refractive index difference can be obtained, and the NA of the light guide path is
It is possible to obtain a sheet with a large value, a large elastic modulus, and a small loss.

[Table] *Refractive index difference, measured using an interference microscope.

[Brief explanation of the drawing]

The figure is an explanatory diagram of the structure of the light guide sheet. 1: Light guide portion, 2: Clad portion.

Claims (1)

[Claims] 1. After forming a low refractive index polymer thin film layer in which the low refractive index monomer is polymerized on the surface of a high refractive index plastic transparent film in which a low refractive index monomer is dispersed, a desired mask pattern is used to block light and the inside of the thin film layer is formed. 1. A method for producing a plastic light guide sheet, which comprises selectively polymerizing low refractive index monomers dispersed in the light guide with ultraviolet light, and then removing unreacted monomers present in the light guide portion.