JPS61255903A - Formation of refractive index gradient in plastic - Google Patents

Abstract

PURPOSE:To exactly form a refractive index gradient of a desired pattern in a plastic, by polymerizing a metal-containing monomer composition under an applied electric field and thereby forming a region of a varied refractive index by concentrating the metal on the area near the region of the electric field. CONSTITUTION:A mixture formed by adding a polymerization initiator to a metal-containing monomer composition is sealed between quartz plates each having a transparent tin oxide electrode membrane (ITO membrane) 17. These are heated in a dryer under an applied DC voltage from an electric power source 20, whereupon the monomer composition is completely polymerized and crosslinked to obtain a transparent plastic. The measurement of the surface resistance of this plastic manifests that the metal is concentrated on the surfaces contiguous to ITO membranes 17. Namely, the larger the amount of the metal concentrated on the surface of the plastic, the larger the amount of atmospheric moisture adsorbed by the metal and the more the surface resistances decreases. Therefore, a relationship that the more the surface resistance decreases, the more the refractive index of the given area decreases can hold.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a method for forming a refractive index distribution in plastics, and in particular to optical components K or flat plate micros such as optical fibers and optical waveguides used in optical communication or optical data link systems. The present invention relates to a method for appropriately forming a refractive index distribution in a lens or the like.

[Snowscape of invention]

In recent years, new communication methods such as optical communication or optical data link systems that use optical components such as optical fibers and optical waveguides have been put into practical use.

The structural feature of this optical fiber is that it transmits light by utilizing the refractive index produced by having a constant refractive index distribution in a highly transparent material. Furthermore, optical waveguides constitute simple optical circuits that have optical wiring functions such as optical distribution and coupling, and are components that have been in demand with the development of new communication methods.

Conventionally, the methods for forming the refractive index distribution of plastics have been the diffusion polymerization method described in the document titled "Plant microlens and its application to laminated circuits" published in Denki Gakkai Journal, Vol. 103, No. 2, p. 127, and the special method. It can be broadly classified into the photopolymerization method described in Japanese Patent Publication No. 56-3522.

First, the diffusion polymerization method will be explained with reference to FIG.

A monomer 1 to form a high refractive index polymer to which a number of polymerization initiators made of peroxides have been added is placed in a container 2 with a lid.c
(corresponds to figure A). Next, the monomer 1 is heated to undergo semi-polymerization to form a semi-polymer 3 as shown in Figure B. A mask 4 made of a glass plate cut into an arbitrary shape is attached to this semi-polymer 3,
(corresponds to Figure 10, immersed in low refractive index monomer 5). After heating this and diffusing the low refractive index monomer 5 into the semi-polymer 7 to create a compositional distribution, C is taken out from the low refractive index monomer 5.
(corresponds to figure D). and compositionally distributed semi-polymers7.
Completely polymerize 3 while heating to obtain a refractive index distribution of 7A, 3
(corresponds to Figure 18 where A is made of plastic).

As mentioned above, in the diffusion polymerization method, a mask is placed on a semi-polymer and it is immersed in a low refractive index monomer, and the low refractive index monomer is diffused into the semi-polymer to create a composition distribution, that is, a refractive index distribution. be. However, because the adhesion between the mask and the semi-polymer is not sufficient, the low refractive index monomer may enter the gap between the semi-polymer and the mask, resulting in a refractive index distribution that is different from the shape of the mask. The problem was that it was easy to create.

Next, a photopolymerization method, which is another method for forming a refractive index distribution for plastics, will be explained with reference to FIG.

According to the figure, a casting solution 8 made of a transparent photopolymerizable material is placed in a casting container 7 for producing a sheet-like polymer film as shown in FIG. Then, by partially evaporating the organic solvent 9 in the casting solution 8, a semi-solid polymer film 8A is obtained (corresponding to FIG. 13). Next, a photomask 10 having an arbitrary shape is placed on the polymer film 8A, and by irradiating ultraviolet rays 11 from above, photopolymerization is selectively caused in the area outside the shift mask. A portion that reduces the refractive index is formed in the portion (corresponding to Figure 0). Then, by heating, the low refractive index monomer 12 contained in the non-photopolymerized portion 14 under the photomask is removed. This makes it possible to form a polymer film in which the refractive index of the non-photopolymerized portions 14 is larger than that of the photopolymerized portions 13 (corresponding to Figure D). Next, when the front and back surfaces of the polymer film thus obtained are coated with a low refractive index resin 15, the high refractive index portion 1
(corresponding to Fig. 18) to obtain a plastic having a refractive index distribution whose periphery is covered with a low refractive index portion 13.15).

However, in this photopolymerization method, a semi-solid polymer film is produced by a casting method, so it is difficult to control the amount of solvent evaporated, and it is difficult to produce a film with a thickness of about 200 μm or more. This is because the solvent near the surface evaporates easily, but the solvent near the back surface is difficult to evaporate, making it easier for the polymer film to swell or ripple during the subsequent process of removing the low refractive index monomer. be.

In addition, when exposing to ultraviolet light, if the film thickness exceeds approximately 150 μm, the intensity of the ultraviolet light transmitted to the back surface of the film decreases, resulting in insufficient photopolymerization within the polymer film, resulting in the same refraction as the photomask shape. There was also the problem that it was not possible to obtain a rate distribution.

[Purpose of the invention]

An object of the present invention is to provide a method for forming a refractive index distribution of plastic, which can accurately form a refractive index distribution of a predetermined shape in plastic, and can form a refractive index distribution without being affected by the thickness of the plastic. It's about doing.

[Summary of the invention]

The method of forming a refractive index distribution has been studied the most, and in the case of glasses that are already commercially available as optical components such as optical fibers and optical waveguides, two-step electric field application ion exchange method and ion electric field transfer are used to form the refractive index distribution. Laws are being enforced in a negative way.

In each of these methods, a glass substrate having a mask with an opening of an arbitrary shape attached to one side of the glass surface is immersed and heated in a molten salt containing ions that increase the refractive index. Ions that increase the refractive index in the molten salt are diffused into the glass substrate through the opening of the mask by an electric field applied in the thickness direction of the glass substrate.

After removing the mask, the glass is immersed in a high-temperature molten salt containing ions that reduce the refractive index of the glass, and an electric field is applied to diffuse the ions to form a refractive index distribution.

In this way, according to the above method, ions that increase the refractive index are implanted into the glass to create a refractive index distribution that matches the shape of the mask. We have come to believe that a refractive index distribution can be formed by selectively increasing the ion content. That is, the present invention was made based on the above knowledge, and its structure is that by applying an electric field during the polymerization process of a monomer composition containing a metal, metal ions gather near the electrode to which the electric field is applied. This is a method for forming a refractive index distribution of plastics that can form a refractive index distribution according to the content of.

In the configuration of the present invention described above, the metal is bonded to the monomer composition in an ionic state during the monomer polymerization process. That is, the metal cation and the substituent group having a negative orientation in the monomer composition are ionically bonded, and by applying an electric field during the polymerization process of these monomer compositions, the metal ion is concentrated near the electrode. We will gather together.

Depending on the type of metal, there are those that increase the refractive index of plastic and those that decrease it. An example of a metal that increases the refractive index is thallium.

Examples include sodium, cesium, lead, barium, and cadmium. For example, boron can be used as a metal that reduces the refractive index.

By blending 10 to 70% by weight of these metals into the monomer composition, the refractive index of the plastic can be increased to about +0.09. Since the monomer composition is used as an optical component, it is generally desirable that the monomer composition be a transparent material. The following monomers can be used as this transparent material. Methyl methacrylate, styrene,
O-chlorostyrene, r-chlorostyrene, vinylnaphthalene, vinylthiophene, O-methoxystyrene.

O-methylstyrene, vinylfuran, vinyl benzoate, ethyl methacrylate, propyl methacrylate,
isobutyl methacrylate, lauryl methacrylate,
Tridecyl methacrylate.

stearyl methacrylate, benzyl methacrylate,
Methacrylic acid, methyl acrylate, ethyl acrylate, vinyl methacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, cininamil methacrylate, lead methacrylate,
Hexyl methacrylate, α-naphthyl methacrylate, 0-chlorobenzyl methacrylate e Ter-butyl methacrylate, methyl-α-glomoacrylate.

Trimethylolpropane trimethacrylate etc.

The size of the refractive index distribution in plastic changes depending on the content of metal that gathers near the electrode.

That is, when metals that increase the refractive index gather near the electrode, the more metals gather, the larger the refractive index becomes compared to other parts. Further, in #1 where the electric field strength is increased, more metals are collected, and the refractive index becomes larger.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an apparatus for carrying out the present invention. In the figure, a pair of quartz glass plates 16 are provided facing each other, and a spacer 1 is provided between these quartz glass plates 16.
Place 8. The inner facing surface of the quartz glass plate 16 has an IT
An O film (tin oxide transparent electrode film) is formed, this ITO film 17 is connected to an ICIJ-domain wire 19, and a DC current source 20 is provided in the middle.

The ITO film has a width of 5 m/m and a length of 20 m/m. The spacer 18Fi has a thickness of 4 m/m. The portion where these quartz glass plates 16 face each other is connected to a dryer (not shown).
located within.

Next, the operation of this embodiment will be explained.

I is a monomer composition containing a metal with a polymerization initiator added.
It is sealed between quartz glass plates having a TO film 17. Then, while applying DC power from the current source 20 to these, they are heated in a dryer to completely polymerize and crosslink the monomer composition,
Obtain clear plastic.

It was revealed by measuring the surface resistance of the plastic that metal was gathered on the surface of the plastic that was in contact with the ITO film 17. In other words, as the amount of metal collected on the plastic surface increases, the metal will adsorb more moisture in the air, and its public surface resistance will decrease. Therefore, the lower the surface resistance, the lower the refractive index of the plastic in that area.

The actual surface resistance was measured using JIS standard insulation resistance test electrodes (conductor width 0.635 m/m% conductor gap 1.27 m/
m and an overlapping width of 20.0 m/m on the transparent plastic obtained according to the embodiment shown in FIG. 1 above, and the values are measured at 300 V DC.

The refractive index of the obtained plastic surface is measured by the edge reflection method (Journal of the Institute of Electrical Engineers of Japan, Vol. 97, No. 11, Item 967 (1978)).

Note that the ITO film explained in the above example has a width of 5 m/m.
Although the ITO film was a straight line with a length of 20 m/m, combinations of shapes such as circular and branched shapes can also be used as the ITO film.

Next, a specific experimental example will be explained.

C Experimental Example 1) Add 6 g of IL acrylic acid and 15.5 g of cinnamic acid to 50 td of benzene, and heat to 40±20 td while stirring.

Add 15 g of barium hydroxide-water salt little by little to this. After the reaction is completely completed, 17.2 g of chlorstyrene (a mixture of ortho and para) and 10 g of hydroxyethyl acrylate are added dropwise and thoroughly stirred. Subsequently, benzene, by-products, and product water are completely removed azeotropically. This is 0.2
A barium-containing monomer composition is obtained through a μ-m filter.

To this monomer composition, 0.5% by weight of a polymerization initiator such as similystyl peroxydicarbonate was added,
The monomer composition was sealed between quartz glass plates having an ITO film 17 and heated at 601:l'/3 hours, 100G/1 hour, and 120C/1 hour while applying a DC voltage from a current source 20 to completely polymerize the monomer composition. A transparent plastic containing barium was obtained by crosslinking.

Next, the surface resistance of this plastic was measured.

The results are shown in FIG.

According to FIG. 2, it can be seen that the higher the applied voltage applied between the IT'O films, the more the surface resistance decreases linearly.

Next, the refractive index of the transparent plastic was measured by the edge reflection method. The results are shown in FIG.

The refractive index shown in FIG. 3 is the value measured on the surface that was in contact with the negative ITO film. As can be seen from the characteristic diagram in FIG. 3, it can be seen that the higher the electric field, the higher the refractive index. Further, when the refractive index distribution was measured in detail, it was found that the refractive index distribution had a shape similar to that of the ITO film.

C Experimental Example 2) 11.8 g of methacrylic acid, 7 g of 3-phenylpropionic acid
．． Add 5g of lead monoxide to 50ml of benzene, heat to 40±2C, and add 15g of lead monoxide little by little while stirring. After the reaction is completed, 117.2 g of chlorstyrene (a mixture of ortho and para) is added and stirred. Then, benzene and water are removed, and a monomer composition containing lead is obtained through a 0.2 μm filter. This monomer composition Similystyl peroxydicarbonate and 063 polymerized dicarbonate were added to the above Experimental Example 1.
A transparent plastic containing lead was obtained by applying an electric field in the same manner as above. When the refractive index of this plastic was measured, it was found to be 20V.
The refractive index changed by 0.017 when 0.009.40V was applied. The surface resistance was about 10"" when 20V was applied compared to a place where no voltage was applied, and about 10-4 when 40V was applied.

C Experimental Example 3) Add 8 g of IL methacrylic acid to 60 ± of benzene and add 40 ±
Add 14 g of thallium oxide little by little while heating and stirring at 2 CVc. After the reaction is completed, 8 g of hydroxyethyl acrylate and 17.2 g of chlorostyrene (a mixture of ortho and para) are added and stirred. Next, benzene and water are completely removed, and a monomer composition containing thallium is obtained through a 0.2 μm filter. 0.5% by weight of cimilistyl peroxydicarbonate was added to this monomer composition to obtain a transparent plastic containing barium in the same manner as in Experimental Example 1 above. When the refractive index of this plastic was measured, it changed by 0.023 when 20V was applied, ois, and 0.023 when 40V was applied. Also, the surface resistance is approximately 2X10-2 when 20V is applied.
It was about 10-3 when 40V was applied.

(Experimental Example 4) Acrylic acid 5.6g% 3-phenylpropionic acid 5.3
Add the ears to dichloromethane Zoowt and reflux.

Add 18 g of cesium chloride little by little to this.

After the reaction is complete, 4 g of hydroxyethyl acrylate and 15.4 g of chlorostyrene (a mixture of ortho and para) are added and the mixture is refluxed. Next, after completely removing dichloromethane and water, a monomer composition containing cesium is obtained through a 0.2 μm filter. 0.5% by weight of cimilistyl peroxydicarbonate was added to this monomer composition to obtain a transparent plastic containing cesium in the same manner as in Experimental Example 1 above. When the refractive index of this plastic was measured, it changed by 0.025 when 20V was applied and α02.40V was applied. Further, the surface resistance was about 2 x 10-'' when 20V was applied, and about 2 x 10-'' when 40V was applied.

(Experimental Example 5) Next, a resin having a thickness of 1+w and a thickness of 3 cm were manufactured using the same resin as in Experimental Example 1, and the refractive index of each was measured. As a result, the refractive index values were the same in both cases.

Therefore, any refractive index distribution portion can be formed regardless of the thickness of the plastic.

〔Effect of the invention〕

As explained above, according to the method for forming a refractive index distribution of plastic according to the present invention, it is possible to accurately form a refractive index distribution shape that is the same as the shape of the % electric field applying section.

Therefore, by changing the shape of the electrolytic application section, a refractive index distribution section having a predetermined shape can be obtained.

Further, the refractive index can be reliably adjusted by adjusting the intensity of the electric field or the amount of metal contained in the monomer.

Furthermore, since an electric field is used to form the refractive index distribution portion, unlike the case where ultraviolet light is used, the refractive index distribution portion can be formed satisfactorily regardless of the thickness of the plastic.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of an apparatus for carrying out the method for forming a refractive index distribution of plastic according to the present invention, and FIG.
The figure shows the relationship between the applied voltage and the surface resistance of the plastic. Figure 3 is a graph showing the applied voltage and the refractive index of the plastic. Figure 4 is a process diagram for forming the refractive index distribution of the plastic using the conventional diffusion polymerization method. , FIG. 5 is a process diagram of forming a refractive index distribution of plastic by photopolymerization. 16... Quartz glass plate, 17... ITO film, 18.
...Spacer, 19...Lead wire, 20...Current source.

Claims (1)

[Claims] 1. A metal-containing monomer composition is polymerized while applying an electric field to the monomer composition, and the metal is aggregated in the vicinity of the electric field region to form a refractive index changing portion. Method for forming refractive index distribution of plastic. 2. A method for forming a refractive index distribution of plastic according to claim 1, wherein the metal forms a refractive index change portion higher than that of the plastic. 3. A method for forming a refractive index profile for plastics according to claim 2, wherein the metal is at least one member of the group consisting of thallium, sodium, cesium, lead, barium, and cadmium. 4. In any one of claims 1 to 3, the metal is present in the monomer composition in an amount of 10 to 70% by weight.
A method for forming a refractive index distribution of plastics, characterized in that: 5. A method for forming a refractive index distribution of plastics according to claim 1, wherein the monomer composition is a transparent material.