JPH0241001B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a synthetic resin optical transmission body having a refractive index distribution in which the refractive index gradually changes. [Prior Art] As is well known, a gradient index optical transmission body consists of a transparent body whose refractive index gradually changes from the center to the periphery in the direction orthogonal to the optical axis. Widely used as transmission fiber, etc. The self-focusing optical transmitter described above has a refractive index on the central axis of No and a constant of A, and the refractive index N at a distance of X from the central axis is N=No (1-1/2AX ² )...(1) It has a distribution expressed by the formula. When the constant A is positive, the transmitter has a convex lens effect, and when A is negative, the transmitter has a concave lens effect. In addition, a refractive index distribution type optical transmission body having a refractive index distribution of A>0 in equation (1) near the center, and a distribution in which the refractive index gradually increases outwards at the outer periphery side. has also been proposed. The following two methods are typical methods for manufacturing such a refractive index distribution type optical transmission body using synthetic resin. One method is to polymerize a portion of a monomer that forms a three-dimensional network structure to create, for example, a cylindrical base material made of a transparent gel-like material. This is a method in which the polymerization is completed after diffusing another monomer having a refractive index different from that of the above monomer. Another method is to fill a transparent tube with a mixture of multiple monomers with different polymer refractive indexes and monomer reactivity ratios, and then perform molding by irradiating light and/or heating from the outside of the mold. There is a method of gradually advancing the polymerization reaction from the outer layer of the mixture in the mold to form a distribution of monomer units, that is, a refractive index distribution. The present invention relates to improvements in the latter method. The method using light irradiation will be explained in detail below, taking as an example. First, a light-transmissive mold is filled with a monomer mixture. The relationship in reactivity ratio between monomers in a monomer mixture is as follows. In general, in a multicomponent copolymerization reaction, if the rate constant of the following growth reaction Mi ^* + Mj→Mj ^* is Kij, then the reactivity ratio Rij of any monomer Mi to monomer Mj is Rij≡Kii/Kij...(2 ) is defined as Similarly, monomer for monomer Mi
The reactivity ratio Rji of Mj is defined as Rji≡Kjj/Kji (3). There are X (X-1) reactivity ratios in the X element copolymerization. Also, the mixing ratio of monomers Mi and Mj is (Mi/Mj)
It is known that the copolymer component composition ratio (Mi/Mj)p produced at this time is expressed by the following formula (4), where m is represented by the following formula (4). (Mi/Mj)p=(Mi/Mj)mRij(Mi/Mj)m+1/(M
i/Mj)m+Rji...(4) Here, Rij(Mi/Mj)m+1/(Mi/Mj)m+Rji≡Q...(5) If Q>1, the following equation (6) is always satisfied. To establish. (Mi/Mj)p>(Mi/Mj)m...(6) That is, the content ratio of the Mi component in the resulting copolymer is always higher than the mixing ratio of Mi in the monomer mixture, but Q≧1.1 It is preferable that As the polymerization time increases, the mixing ratio of Mi in the remaining monomer mixture gradually decreases, and conversely, the mixing ratio of Mj gradually increases. Therefore, the content ratio of the Mi component in the copolymer produced at the initial stage of polymerization is high, but as the polymerization time increases, the content ratio of the Mi component in the copolymer produced at that point decreases. Conversely, the content ratio of the Mj component in the produced copolymer gradually increases as the polymerization progresses. The copolymer thus obtained is a mixture of copolymers having different compositions. Also, if Q<1 (preferably Q≦0.9), (Mi/Mj)p<(Mi/Mj)m...(7), so contrary to the case of Q>1, the copolymer The content ratio of Mi components in the monomer mixture is always smaller than the mixing ratio of Mi in the monomer mixture. If Q=1, (Mi/Mj)p=(Mi/Mj)m...(8), a copolymer with a composition equal to the monomer mixing ratio is produced, and the copolymer has a composition distribution. does not indicate.
Therefore, when Q in the above formula (5) is a number other than 1 (preferably Q≧1.1 or Q≦0.9) and such a monomer mixture is filled in a transparent tube and irradiated with light from the outside. If polymerization proceeds from the outside toward the central axis, a monomer composition distribution will be formed that is more biased toward the outside as the monomer has a larger reactivity ratio. For example, if a monomer mixture contains monomers M ₁ , M ₂ ...Mx
It is composed of X types of monomers, and 1≦i<j≦X
When i and j are selected such that if Q in the above formula (5) is a larger number than 1, the portion where the amount of the Mi component in the copolymer is maximum or maximum is the amount of the Mj component. It is located in the part that polymerized earlier than the part that is the largest or local maximum. In other words, in this case, when the composition distribution of the copolymer is investigated from the outside toward the center, the _M1 component reaches its maximum or local maximum value first, then the _M2 component, and the _M3 component.
The maximum values of the components are seen in order, and the Mx component takes the maximum value at the center. Therefore, monomers M ₁ , M ₂ ... polymers P ₁ , P ₂ of Mx
...If the refractive indices N ₁ and N ₂ of Px are different, some kind of refractive index distribution can be obtained in the radial direction. The monomers used in the above photocopolymerization method are:
Prior application patent application No. 50-11723 by the present inventors;
55-53920, patent application 1982-11954, patent application 1982-11956
The monomer groups listed in can be used, and by using these monomers, a self-focusing light transmission body having a convex lens action can be manufactured. Furthermore, by using the monomer described in Japanese Patent Application No. 58-11955, an optical transmission material with a W-shaped refractive index distribution in which the refractive index initially decreases from the center to the periphery and then increases again can be produced. can get. Although the case where polymerization is carried out by light irradiation has been described above, the same effect can be obtained by heating instead of light irradiation. However, if light irradiation or heating is applied simultaneously over the entire length of the monomer mixture filled tube, a solid polymer will initially form from the inner circumferential wall of the tube, and the mixture inside it, which is still in a liquid phase, will form. shrinks in volume over time, but because its outer periphery is solidified (gelled), polymerization proceeds without filling the voids caused by shrinkage, and eventually a void forms in the center over a considerable length. The problem arises that it is generated. As an improved method that solves the above problem, the monomer mixture filled tube is moved relatively through a polymerization treatment chamber that has a built-in light irradiation light source or is maintained at a constant temperature necessary for polymerization. A method has also been proposed in which light irradiation or heating is gradually applied from the lower end side. [Problems to be Solved by the Invention] However, even with the above improved method, the following problems remain. In other words, if the entire formed tube is filled with a monomer mixture from the beginning and is passed through the aforementioned polymerization treatment chamber, the polymer component produced by the polymerization reaction will be transferred to the unused material above the outside of the polymerization treatment chamber. There is a problem of diffusion into the monomer mixture of the reaction, contamination of the monomer mixture by the polymer component, and the refractive index distribution of the shaped light transmitter becoming non-uniform along its length. [Means for solving the problem] By sequentially supplying a monomer mixture into the tube from the outside in accordance with the moving speed of the tube, the liquid level in the tube is brought to near the entrance of the light irradiation area or the heating area. I tried to keep it constant. [Function] During the movement of the forming tube, the unreacted monomer mixture existing in the forming tube is constantly removed near the boundary between the area where no light irradiation (or heating) is applied and the area where light irradiation (or heating) is applied. Only a small amount of the monomer mixture is contaminated by the polymer component, and the monomer mixture is confined to the vicinity where polymerization is occurring. That is, as the polymerization reaction progresses, fresh unreacted monomer mixture is supplied to the front end of the polymerization tube in the axial direction. Thereby, contamination by the polymer component of unreacted monomers is suppressed to a minimum, and a light transmitting body having a constant refractive index distribution in the length direction can be obtained. [Embodiments] The present invention will be described in detail below with reference to embodiments shown in the drawings. First, a predetermined amount of complementary monomers M ₁ , M ₂ , . Dissolve benzoin methyl ether etc. Monomers that can be used in the present invention include:

[Formula]

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[Formula] CH ₂ = CH−CH ₂ −X

【formula】

[Formula] CH ₂ = C-CH ₂ -X | CH ₃ Acrylonitrile, methacrylnitrile, vinyl chloride, N-vinylcarbazole, N-vinylphthalimide, N-vinylpyrrolidone, vinylthiophene, vinylfuran, vinylphenyl sulfide, R =-CnH _2o+1 (n=1 to 10) -C ₆ H ₁₁ or fluorine-containing aliphatic group

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〔Effect of the invention〕

According to the method of the present invention, the monomer mixture in an unreacted state is almost never contaminated by polymer components, and the dispersion in the refractive index distribution of the lens due to this contamination is greatly reduced. A refractive index distribution type synthetic resin light transmitting body having uniform optical properties in the transverse direction and between products can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of an apparatus for implementing the present invention, and FIG. 2 is a schematic vertical cross-sectional view showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Monomer mixture, 2... Molded tube, 3... Polymerization treatment chamber (light irradiation area), 7... Light source lamp, 9...
...Air conditioner device, 10...Storage tank,
11...Liquid level detection sensor, 13...Opening/closing valve, 15...Copolymer with refractive index gradient.

Claims (1)

[Claims] 1 A mixture of a plurality of monomers having different polymer refractive indexes and monomer reactivity ratios is filled into an elongated molded tube, and the tube is moved relative to a light irradiation source or (and) a heating element to cool the tube. Light irradiation or (and) heating is applied gradually from the lower end to advance the polymerization reaction from the outer layer of the mixture inside the tube and in the direction of the tube axis, and the refractive index changes from the outer periphery toward the center. In a method for manufacturing an optical transmission body, a monomer mixture is sequentially supplied into the tube from the outside in accordance with the moving speed of the tube, and the liquid level in the tube is brought to approximately near the upper end of the light irradiation area or the heating area. A method for manufacturing a synthetic resin optical transmission body having a refractive index distribution that is maintained constant.