JPH0576602B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a gradient index optical transmission body made of synthetic resin. [Technical Background of the Invention] As is well known, a gradient index optical transmission body consists of a transparent body with a distribution in which the refractive index gradually changes from the center to the periphery in a direction perpendicular to the optical axis, and is composed of a rod-shaped lens. It is widely used as optical transmission fiber. The above self-focusing optical transmitter has a refractive index N at a distance of X from the central axis, where the refractive index on the central axis is No and A is a constant, as expressed by the formula N-No (1-1/2AX ² ) (1) It has a distribution expressed as . 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. [Description of Prior Art] A typical method for producing such a gradient index optical transmission body using synthetic resin is to use a mixture of a plurality of monomers having different polymer refractive indexes and monomer reactivity ratios. There is a method in which a predetermined container is filled with the mixture, and light is irradiated from the outside of the container to gradually advance the polymerization reaction from the outer layer of the mixture in the container to form a copolymer distribution of monomer units, that is, a refractive index distribution. The prior art will be explained in detail below. First, a light-transmissive mold is filled with a monomer mixture. The relationship between the reactivity ratios of the monomers in the monomer mixture is as follows. Generally, 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). 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. Furthermore, if the mixing ratio of monomers Mi and Mj is (Mi/Mj)m, the monomer component composition ratio (Mi/Mj)p of the copolymer produced at this time is as follows (4)
It is known that it can be expressed by the formula. (Mi/Mj)p=(Mi/Mj)mRij(Mi/Mj)m+1/
(Mi/Mj)m+Rji(4) Here, Rij(Mi/Mj)m+1/(Mi/Mj)m+Rji≡Q (5) If Q>1, the following equation (6) always holds true. (Mi/Mj)p>(Mi/Mj)m (6) In other words, the content ratio of Mi component in the resulting copolymer is always higher than the mixing ratio of Mi in the monomer mixture, but if Q≧1.1. It is preferable that there be. 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, Mj in the copolymer produced
The content ratio of the components 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 The content ratio of the Mi component 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 shows a composition distribution. do not have.
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 ... _M
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, the _M3 component, and so on. The Mx component takes a maximum value at the center. Therefore, polymerization of monomers M ₁ , M ₂ ...M _X P ₁ , P ₂ ...
...If the refractive indices N ₁ , N ₂ ...N _X of P _X are different, some kind of refractive index distribution can be obtained in the radial direction. [Problem to be solved by the invention] However, when the temperature inside the system is room temperature or low temperature, it is possible to create a synthetic resin optical transmitter having the refractive index distribution of formula (1) in a two-component system by simply irradiating light. However, only the area near the central axis has the refractive index distribution expressed by equation (1), and the gradient of the refractive index becomes gentler toward the periphery. This is because the refractive index of the copolymer that precipitates with polymerization increases, but at the beginning of polymerization, the refractive index of the copolymer that precipitates in the peripheral region increases slowly, but in the late stage of polymerization, that is, in the central region, the refractive index increases rapidly. This is to do so. This phenomenon will be explained below. It may be assumed that if the inside of the system is at room temperature or low temperature, thermal polymerization is negligible and polymerization proceeds only by light. Copolymerization begins upon irradiation with light, and the reaction system gradually becomes viscous, forming a polymer layer on the inner wall of the tube. This is because the intensity of the ultraviolet rays is stronger the closer you get to the inner wall of the tube, so the closer you get to the inner wall, the more radicals are generated and polymerization is initiated, producing copolymer radicals. However, at first, the radicals can easily diffuse through the reaction system, so the reaction proceeds throughout the system.
The viscosity of the system increases uniformly. As the viscosity increases, the diffusion of radicals slows down, and the radicals grow near the inner walls, resulting in a high molecular weight copolymer. The copolymer layer becomes thicker over time until it solidifies to the center. Here, the mechanism by which the above-mentioned refractive index distribution is formed will be explained. Examples include MMA (methyl methacrylate), VB
(vinyl benzoate) binary copolymerization (MMA/VB
Figure 6 shows the change in the refractive index of the precipitated copolymer as the conversion rate P increases. The refractive index of the precipitated copolymer does not increase much from the early stage to the middle stage of polymerization, but shows a sharp increase in the late stage of polymerization. Here, the copolymer precipitated near the inner wall of the polymerization tube was precipitated during the early to middle stages of polymerization, so the refractive index distribution in the peripheral region has a gentle slope, and the refractive index distribution in the late stage of polymerization, that is, the central region, is steep. It becomes a gradient. Therefore, it is impossible to obtain a synthetic resin optical transmission body having a uniform refractive index distribution throughout. [Means for Solving the Conventional Problems] The gist of the present invention for solving the above problems is to improve the reactivity ratio of any monomer Mi to the monomer Mj among multiple types of monomers having different polymer refractive indexes. Let Rji be the reactivity ratio of monomer Mj to monomer Mi,
If the mixing molar ratio of monomers Mi and Mj is (Mi/Mj)m, then the value of Rij(Mi/Mj)m+1/(Mi/Mj)m+Rji is 1.1 or more or 1/1.1 or less. A mixture of multiple types of monomers is filled into a predetermined container, and the temperature applied to the predetermined container is set to 40° C. or higher, preferably 150° C. or lower. The above heat treatment can be carried out, for example, by placing the polymerization container through a thermostatic chamber maintained at a predetermined temperature and moving either the thermostatic chamber or the polymerization container relative to the other, as shown in the Examples below. Therefore, it is desirable to limit the heating range to only a portion of the polymerization container and to gradually advance the heating from one end of the container. Due to such progressive heating, even if the liquid mixture near the center of the container contracts during the polymerization reaction process, the liquid mixture above the heating area flows down one after another to fill the shrinkage, and the inner and outer peripheries of the container shrink. Even in cases where polymerization progresses gradually in the axial direction of the container, the inner and outer peripheries of the container solidify first over the entire length of the container, leaving no voids inside. A rate distribution polymer can be obtained. In carrying out the present invention, it is preferable to carry out light irradiation, but it is also possible to produce a synthetic resin optical transmission body having a uniform refractive index distribution over the entire diameter by thermal polymerization alone. In addition, in the present invention, as a polymerization container, a monomer with the highest monomer reactivity ratio, that is, a monomer that is the same as or has affinity with the polymer of the monomer that is most contained in the copolymer precipitated on the inner wall of the container. It is desirable to use containers made of synthetic resin with good quality. If a container made of such a material is used, the copolymer will precipitate on the inner wall at a lower conversion rate than in a container with poor affinity due to its good affinity, and the refractive index of the surrounding area will decrease, resulting in a refractive index difference. becomes larger and the numerical aperture NA becomes larger. The monomers used in the present invention include prior patent applications filed by the present inventors, such as Japanese Patent Application No. 11723/1986, Japanese Patent Application No. 53920/1983,
The monomer groups listed in Japanese Patent Application No. 58-11954 and Japanese Patent Application No. 58-11956 can be used, and by using these monomers, a self-focusing optical transmission body having a convex lens action can be manufactured. . As an example, examples of suitable monomers M ₁ and M ₂ when carrying out the present invention using a binary monomer mixture are listed below.
M ₁ is an aliphatic titacrylic ester such as methyl methacrylate, ethyl methacrylate, torfluoroethyl methacrylate, methacrylic anhydride, ethylene dimethacrylate, or a mixture thereof. _M2
Vinyl aromatic carboxylates such as vinyl benzoate, vinyl O-chlorobenzoate, vinyl P-chlorobenzoate, vinyl α-naphthoate, vinyl β-naphthoate, acrylonitrile, pentachlorostyrene, or mixtures thereof. M ₁ is an acrylic ester such as methyl acrylate or ethyl acrylate, or a mixture of these and the above methacrylic ester. Vinyl styrene aromatic carboxylates or mixtures thereof as M ₂ above. Methyl methacrylate/methacrylonitrile as _M1 . α-methylstyrene as _M2 . In the above example of the combination of M ₁ -M ₂ , M ₁ is a monomer that becomes a low refractive index polymer, and M ₂ is a monomer that becomes a high refractive index polymer. For the combination of two types of monomers selected from these combinations, the monomer reactivity ratio, the refractive index of the polymer, and the above Q value are 1.1 or more or 1/1.1
To give an example of a range of mixing ratios as follows,
As shown in the table. [Effects of the invention] In a two-component system, when the temperature of the polymerization system is increased to 40°C or higher, the effect of thermal polymerization increases, and after radicals are generated, the viscosity of the reaction system increases rapidly, causing copolymerization. It takes a short time for the combined radicals to become difficult to diffuse. Furthermore, a copolymer containing a large amount of monomers with a high monomer reactivity ratio is produced near the inner wall of the container, but at this time, the conversion rate of the remaining monomer mixture is also increased due to the effect of thermal polymerization. And the conversion rate increases with time. That is, unlike the case where thermal polymerization is negligible as described above, the copolymer precipitated near the inner wall of the polymerization tube has already reached a conversion rate at which the refractive index in FIG. 6 rises rapidly. Accordingly

【table】

[Embodiments of the invention]

First, a predetermined amount of monomers M ₁ , M ₂ , M ₃ . inside diameter (e.g. approx.
2.9mm) and fill it into a polymerization tube with one end closed.
Photocopolymerization is carried out using the apparatus shown in the figure. The polymerization tube 1 is installed vertically passing through the compartment 2, and is rotated by a drive mechanism 3 while moving vertically at a low speed. A through hole 6 is provided in the ceiling wall and bottom wall of the compartment 2, and a guide tube 7 whose inner diameter approximately matches the outer diameter of the polymerization tube 1 is inserted into these holes.
7 is installed, and this guide tube 7,7
The polymerization tube 1 moves inside. By adjusting the length of the guide tube protruding into the compartment, it serves to limit the light irradiation range to the polymerization tube 1 to a constant length l in the length direction of the polymerization tube. The interior of the compartment 2 is partitioned into a thermostatic chamber 2A and a light source housing chamber 2B by a partition wall having a transparent window 8, and the light source lamp inside the light source housing chamber is The light beam from 10 is arranged to illuminate the transparent window 8. Air conditioner device 1 is installed on one side wall of constant temperature room 2A.
3 are connected via an air supply pipe 14 and an intake pipe 15, and the gas that is collected from the temperature controlled room 2A through the intake pipe 15 and then controlled to a constant temperature by the air conditioner 13 passes through the air supply pipe 14 to the temperature controlled room 2A. As a result, the atmosphere surrounding the polymerization tube 1 in the light irradiation range is always maintained at a constant temperature of 40° C. or higher. In the above apparatus, the polymerization tube 1 is fed from above to below at a constant speed through the thermostatic chamber 2A, whereby the monomer mixture within the tube 1 is gradually heated and irradiated with light from the lower end. Copolymerization occurs from the bottom of the polymerization tube 1. Although the volume contracts during polymerization, no voids are created inside the polymer because the monomer mixture is always supplied from the unpolymerized portion at the top of the polymerization tube. As the polymerization tube 1 moves, the portion to be polymerized gradually moves upward, and finally all of the monomer mixture in the polymerization tube 4 solidifies. The polymerization tube 4 is removed from the apparatus after a predetermined period of time, for example, about 10 hours, from the start of heating and irradiation, and heated to, for example, 80° C. for 24 hours to polymerize as much of the remaining monomer as possible. Then, the copolymer rod is taken out. The refractive index distribution constant A exhibits a constant value throughout the rod except for the ends thereof. Although heating and light irradiation are used in combination in the above embodiment, the light irradiation of the polymerization tube 4 by the light source lamp 10 may be omitted and only heating may be used. Next, it is stretched using a hot stretching device whose principle is shown in FIG. That is, the above synthetic resin rod is attached to the support member 22 as a preform 21, and the speed
The film is lowered at a speed of V ₁ (mm/sec), passed through a constant temperature heater 23 at a constant temperature Td, and pulled and stretched by a lower drive roll 24 at a speed of V ₂ mm/sec.
V ₂ /V ₁ is the stretching ratio. The obtained synthetic resin optical fiber 25 is cut and polished to form a rod lens having a length of 1 to 2 mm, and the refractive index distribution constant A of equation (1) is determined from the lens action. In addition, a synthetic resin optical fiber is wrapped around a drum, a 6328 Å laser beam is applied from one end, and the intensity of the light emitted from the other end is measured. Transmission loss is determined from the relationship between the length of the fiber and the intensity of the emitted light. Next, numerical examples of the present invention will be described. (Example 1) MMA (methyl methacrylate) as a monomer,
VPAC (phenyl vinyl acetate) was mixed at a weight ratio of 5:1, and 0.5wt% was added as a polymerization initiator.
BPO was dissolved in a bath, filled into a transparent polymerization tube 1 made of acrylic resin (PMMA) with an inner diameter of 5.3 mm and closed at one end, and the system was heated to three different temperatures using the apparatus shown in Figure 1. Copolymerized. The gap between the light shielding plates is 70 mm, the distance from the ultraviolet lamp 10 to the polymerization tube 1 is 10 cm, and the rotation speed of the polymerization tube is
Experiments were conducted under three conditions: 40 rpm, ramp rising speed 0.3 mm/nin, and constant temperature in constant temperature room 2A at 30°C, 50°C, and 60°C. When the refractive index distribution of the synthetic resin light transmitting body obtained under three types of temperature conditions is measured using an interference microscope, the result is as shown in FIG. 3. Here, the vertical axis is the refractive index difference from the refractive index of the central axis, and the horizontal axis is the normalized radius. As is clear from FIG. 3, as the temperature inside the system increases, the region exhibiting a uniform refractive index distribution corresponding to equation (1) spreads over almost the entire diameter. (Example 2) MMA and VPAC were mixed at a weight ratio of 4:1, 0.5 wt% BPO was dissolved as a polymerization initiator, and a Pyrex glass polymerization tube with an inner diameter of 7 mm was filled with the mixture. This time, copolymerization was carried out only by thermal polymerization without UV irradiation. The temperature of constant temperature room 2A is 60℃,
The polymerization time was 20 hours, and the other conditions were the same as in Example 1. The refractive index distribution of the obtained synthetic resin optical transmission body was
As shown in the figure. By setting the temperature in the system to 60℃,
We were able to expand the region with a refractive index distribution corresponding to equation (1). However, since the Pyrex glass tube has a poor affinity with MMA, which has a high monomer reactivity ratio, the copolymer containing a large amount of MMA that precipitates inside the tube does not easily precipitate into the polymerization tube, and only aggregates to a certain extent and then precipitates. Therefore, the refractive index of the periphery increases, and the refractive index difference becomes smaller. (Example 3) MMA and VPAC were mixed at a weight ratio of 8:1, 0.5 wt% BPO was dissolved as a polymerization initiator, and an acrylic resin polymerization tube with an inner diameter of 14.3 mm was filled with the mixture. This time as well, copolymerization was carried out only by thermal polymerization without UV irradiation. The temperature inside constant temperature room 2A is 60
℃, polymerization time was 24 hours, other conditions were as in Example 1.
It is similar to The refractive index distribution of the obtained synthetic resin transmission body is shown in FIG. By increasing the temperature in the system to 60°C, we were able to obtain a refractive index distribution corresponding to equation (1) over the entire diameter. Moreover, it has a high monomer reactivity ratio.
Since we used a polymer tube made of the same material as MMA,
Because it has good affinity with MMA, the copolymer precipitates on the inner wall at a lower conversion rate than in the case of Pyrex glass tubes, which have poor affinity, and the refractive index of the surrounding area decreases, resulting in a large refractive index difference. Summer. Therefore, the numerical aperture NA was 0.22, which is higher than before.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of an apparatus for carrying out the present invention, and FIG. 2 shows a step of hot-stretching a base material rod obtained by the apparatus of FIG. 1 to form a gradient index optical fiber. The vertical cross-sectional views, FIGS. 3, 4, and 5 are graphs showing various examples of radial refractive index distribution states in optical transmission bodies obtained by the method of the present invention, and FIG. It is a graph showing a refractive index distribution state of a transmission body. 1... Polymerization tube, 2... Compartment, 2A... Temperature chamber,
2B...Light source storage chamber, 3...Polymerization tube drive mechanism, 6
...Through hole, 7...Guide tube, 8...Translucent window, 10...Light source lamp, 13...Air conditioner device, 14...Air supply pipe, 15...Intake pipe.

Claims (1)

[Claims] 1. Rij is the reactivity ratio of any monomer Mi to monomer Mj among multiple types of monomers having different polymer refractive indexes, and Rij is the reactivity ratio of monomer Mj to monomer Mi. If the ratio is Rji and the mixing molar ratio of monomers Mi and Mj is (Mi/Mj)m, then the value of Rij(Mi/Mj)m+1/(Mi/Mj)m+Rji is 1.1 or more or 1/ 1.1 or less is filled into a predetermined container, and the container is heated to 40°C or higher to advance the polymerization reaction from the outer layer of the mixture in the container to the inside. A method of manufacturing a synthetic resin optical transmission body. 2. In the method described in claim 1,
The container to be used should be one that has the highest monomer reactivity ratio in the monomer mixture, that is, one that is the same as or has good affinity with the polymer of monomer Mk that polymerizes in the outermost layer of the monomer mixture. A method for manufacturing a synthetic resin optical transmission body, characterized by: 3. In the method described in claim 1,
A method for manufacturing a synthetic resin light transmitting body, characterized in that heating is performed gradually from one end side of the container.