JPH0437962B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a synthetic resin optical transmitter having a refractive index distribution in which the refractive index gradually changes and has a low optical transmission loss. Synthetic resin optical transmitters whose refractive index distribution is expressed by equation (1) are disclosed in Japanese Patent Publication No. 54-30301 (Patent Application No. 11723-1981) and Japanese Patent Application Laid-open No. 1986-11723.
-21937 (Patent Application 1982-96795), and Japanese Patent Application 1986-
149004 (Patent Application No. 55-53920). N=No(1-1/2A r ² ) (1) Here, No is the refractive index of the central axis, N is the refractive index of a point at a distance of r from the central axis, and A is the constant of the refractive index distribution. . The patent utilizes the fact that the composition of a copolymer changes as the polymerization progresses, and monomers M ₁ and M ₂ have different refractive index values when they become a polymer, and are transparent. Copolymerization is started from a predetermined portion of the monomer mixture kept in a predetermined shape, and then copolymerization is carried out so that the formed copolymer is continuously precipitated within the reaction system. By selecting polymerization conditions, an optical transmission body having a refractive index gradient can be manufactured. The patent describes a method for producing a synthetic resin light transmitting material having a refractive index gradient, in which two types of monomers (monomeric M ₁ and M ₂ (including a mixture of monomers), and the monomer reaction characteristic ratios of the monomers M ₁ and M ₂ in their copolymerization reactions are r ₁ and r ₂ , respectively, and the monomer M ₁ If the mixing molar ratio of monomer M ₂ and monomer M 2 is (M ₁ /M ₂ )m, then the value of r ₁ (M ₁ /M ₂ )m+1/(M ₁ /M ₂ )m+r ₂ (2) is Holding a mixture of monomer M ₁ and monomer M ₂ in a predetermined shape, such as a cylinder, such that the ratio is 1/1.1 or more or 1/1.1 or less, and the location of the mixture with respect to the predetermined shape of the mixture By applying copolymerization conditions that are non-uniform in terms of copolymerization, only a predetermined portion of the mixture, for example, the outer circumferential portion of a cylindrical mixture, differs from the mixing ratio of the _M1 component and the _M2 component.
A copolymer having the same ratio of components is formed locally, and the copolymerization is gradually progressed from that part to other parts, such as the central part, so that the copolymerization is carried out from the predetermined part to other parts inside the copolymerized body. A method for producing a synthetic resin light transmitting body having a refractive index gradient is described, which includes providing a concentration gradient such that the content ratio of the M ₁ component and the M ₂ component gradually changes toward a certain area. Examples of combinations of monomers M ₁ and M ₂ include methyl methacrylate and vinyl benzoate, and methacrylic acid alkyl ester and phenyl vinyl acetate. However, the optical transmission material obtained from the monomer combinations listed above has a refractive index distribution expressed by equation (1) only near its central axis, and the refractive index gradient increases toward the periphery. becomes very gradual. This is because the refractive index of the copolymer increases with polymerization, and although the increase is gradual at first, it increases sharply in the latter half of polymerization. In order to obtain a rod-shaped convex lens using this method, it was necessary to remove the peripheral portion and use only the portion near the center. The present inventor has conducted intensive research to obtain an optical transmission body that follows the distribution of equation (1) up to the peripheral portion, and has thus arrived at the present invention. That is, a mixture of three types of monomers M ₁ , M ₂ , and M ₃ that satisfies the following conditions is polymerized to obtain a light transmitting material by the polymerization method described in the above patent.
In general, multicomponent copolymerization reactions are as follows. If the rate constant of the growth reaction ~~~ _{M 1} * +Mj-→Mj* is Kij, the reactivity ratio rij is defined as rij≡Kii/Kij, and X (X-1) reactions are required for X-element copolymerization. There is a sex ratio. The monomer combinations of the present invention indicate the conditions to be satisfied. Now, two integers i and j are 1≦i, j≦X,
When there is a relationship i>j (1) Regarding the reactivity ratio (rij (Mi/Mj) _n +1)/{(Mi/Mj) _n +rij}>
1.1 Here, (Mi/Mj) _n is the mixing molar ratio of monomer Mi and monomer Mj. (2) Regarding the refractive index, it is necessary that ni (refractive index of Mi homopolymer) > nj (refractive index of Mj homopolymer). The case where X=3 will be specifically explained. In ternary copolymerization, the following nine types of growth reactions occur in competition. 〜〜〜M ₁ ※ ＋M ₁ →〜〜〜M ₁ ※ (rate constant
K ₁₁ ) ～～～M ₁ * +M ₂ →～～～M ₂ * ( 〃
K ₁₂ ) ～～～M ₁ * +M ₃ →～～～M ₃ * (〃
K ₁₃ ) ～～～M ₂ * ＋M ₁ → ～～～M ₁ * ( 〃
K ₂₁ ) ～～～M ₂ * ＋M ₂ →～～～M ₂ * (〃
K ₂₂ ) ～～～ _{M 2} * ＋M ₃ →～～～M ₃ * ( 〃
K ₂₃ ) ～～～M ₃ * +M ₁ →～～～M ₁ * ( 〃
K ₃₁ ) ～～～M ₃ * +M ₂ →～～～M ₂ * ( 〃
K ₃₂ ) ～～～M ₃ * +M ₃ →～～～M ₃ * ( 〃
K ₃₃ ) Monomer reactivity ratio is defined by equation (3). r ₁₂ ≡K ₁₁ ／K ₁₂ r ₂₁ ≡K ₂₂ ／ _{K 21} r ₁₃ ≡K 11 ／K 13 r _{31 ≡K 33} ／K ₃₁ r ₂₃ ≡K ₂₂ ／K ₂₃ r ₃₂ ≡K ₃₃ ／K ₃₂ (3 ) The conditions that the combination of monomers M ₁ , M ₂ , and M ₃ of the present invention must satisfy are (1) Regarding the reactivity ratio (r ₁₂ (M ₁ /M ₂ ) _n +1)/{(M ₁ /M ₂ ) _n + r ₂₁ }＞
1.1(4) (r ₁₃ (M ₁ /M ₃ ) _n + 1) / {(M ₁ /M ₃ ) _n + r ₃₁ }＞
1.1(5) (r ₂₃ (M ₂ /M ₃ ) _n + 1) / {(M ₂ /M ₃ ) _n + r ₃₂ }＞
1.1(6) where (Mi/Mj) _n is the mixing molar ratio of monomer Mi and monomer Mj. (2) Regarding the refractive index, n ₁ (refractive index of M ₁ homopolymer) < n ₂ (refractive index of M ₂ homopolymer) < n ₃ (refractive index of M ₃ homopolymer). Here, both (n ₃ −n ₂ ) and (n ₂ −n ₁ ) are preferably at least 0.005. Condition (1) is that as the terpolymerization progresses, the initial monomer
M ₁ polymerizes rapidly, then monomer M ₂ polymerizes,
It shows that monomer M ₃ polymerizes most slowly. In other words, the copolymer formed at the initial stage of polymerization contains a large amount of monomer _M1 , but as the polymerization progresses, the content of _M1 rapidly decreases until the content of monomer _M2 decreases. To increase. As the polymerization progresses further, the content of M ₂ also decreases, and the content of monomer M ₃ increases. If condition (2) is satisfied here, the refractive index of the copolymer produced will increase as the polymerization progresses, but by adjusting the type of monomer and the monomer charging ratio, the refractive index of the copolymer will increase as the polymerization proceeds. The refractive index of the polymer can be gradually increased over a wide conversion range along with the polymerization conversion rate, and a sudden rise in the refractive index can be avoided. Table 1 lists examples of combinations of ternary monomers used in the present invention. The mixing ratio of monomers varies depending on the type of monomer, the diameter of the optical transmitter, the refractive index distribution, polymerization conditions, etc., but is usually M ₁ 20-90, M ₂ 2-40, M ₃ 5. ~60
It is selected from within each weight % range. Next, the present invention will be explained in detail. First, a predetermined amount of monomers M ₁ , M ₂ , M ₃ are mixed,
Add to this a predetermined amount of a photopolymerization initiator (e.g. benzoyl peroxide (BPO), benzoin methyl ether, etc.)

【table】

[Table] Melt it and make it into a specified inner diameter (for example, about 2.9 mm).
A glass tube with one end closed is filled with the above-mentioned materials, and photocopolymerization is carried out using the apparatus shown in FIG. A tubular ultraviolet lamp 1 is located at the center of the device, and cylindrical light-shielding plates 2 are attached to the upper and lower parts of the lamp 1. A mixture of these is irradiated. Reference numeral 11 denotes a brim-shaped auxiliary light-shielding plate provided so that the light from the lamp 1 is emitted only at an interval of 70 mm between the light-shielding plates 2. The ultraviolet light intensity is monitored with a silicon photocell 3. A plurality of glass tubes 4 filled with the above-mentioned monomer mixture are mounted on a support member 5 at a predetermined distance, for example, 10 cm from the ultraviolet lamp 1, and a motor 6 is used to speed up the rotation at a rate of, for example, 40 cm per minute.
Keep it spinning. First, the ultraviolet lamp 1 is placed at a position lower than the lower end of the glass tube 4, and ultraviolet rays are irradiated while the lamp 1 is moved upward by the motor 7 at a constant speed V (mm/min). Air at a constant temperature is fed into the inside of the device from an inlet 8 by a fan 9 and is discharged from an outlet 10. Although the temperature rises due to the heat generated by the lamp 1, it remains at a temperature that is somewhat higher than the inlet air temperature. becomes constant. Photocopolymerization occurs from the bottom of the glass tube 4. Although the volume shrinks 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 glass tube. As the lamp 1 moves, the portion to be polymerized gradually moves upward, and finally all of the monomer mixture in the glass tube 4 solidifies. After a predetermined period of time, for example about 10 hours, from the start of irradiation, the glass tube 4 is removed from the apparatus and heated to, for example, 80° C. for 24 hours to polymerize as much of the remaining monomer as possible. Then, the glass tube 4 is crushed and the copolymer rod is taken out. The refractive index distribution constant A exhibits a constant value throughout the rod except for the ends thereof. The obtained light transmitting body is heated and stretched to obtain a light-focusing fiber. Prior to heating and stretching the rod, the rod was heated at 50℃3 under a reduced pressure of 10 ^-3 to 10 ^-4 mmHg to remove trace amounts of volatile substances contained in the rod.
Leave for ~4 days. 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. Examples are shown below. Examples 1 to 4 Methyl methacrylate (MMA) with a refractive index of 1.492 as monomer M ₁ , acrylonitrile (AN) with a refractive index of 1.52 as M ₂ , and vinyl benzoate with a refractive index of 1.578 as M ₃ Lenses were manufactured using the ternary system consisting of (VB) using the apparatus shown in the drawings under the conditions shown in Table 2, and the results shown in the table were obtained. In addition, the monomer reactivity ratio in equation (3) is r ₁₂ =
1.34, r ₁₃ = 8.52, r ₂₁ = 0.12, r ₂₃ = 5.0, r ₃₁ = 0.07,
r ₃₂ =0.05, and (4), (5), (6) for Example 1
The values on the left side of the equation were 1.56, 8.62, and 5.68, respectively, and all satisfied equations (4), (5), and (6). Examples 2 to 4 also satisfied formulas (4) to (6).

【table】

【table】

[Table] Table 3 shows the refractive index distribution of Example 4. For comparison, the dotted line in FIG. 3 shows the refractive index distribution when an optical transmission body having the same dimensions as in Example 4 was manufactured using 75 parts of MMA and 25 parts of VB without using AN. The rod of Example 1 was hot-stretched 100 times at 270° C. to obtain an optical fiber having a diameter of 0.29 mm, a refractive index distribution constant A=0.563 mm ⁻² , and a transmission loss of 1.2 dB/m. Examples 5 to 10 Table 3 shows the manufacturing conditions and results of optical transmission bodies manufactured using ternary systems other than MMA-AN-VB.

[Brief explanation of drawings]

FIG. 1 is a partially sectional side view showing an example of a manufacturing apparatus for explaining the present invention, and FIG. 2 is a side view showing an example of an apparatus for carrying out the present invention following the apparatus shown in FIG. . FIG. 3 is a graph showing an example of the refractive index distribution of the optical transmission body obtained by the present invention.

Claims (1)

[Claims] 1 The refractive index when the monomer Mi becomes a polymer is
If ni is a mixture of three different monomers (including monomer mixtures) M ₁ , M ₂ , M ₃ that are different from each other, the mixture is held in a predetermined shape, and the mixture object of the predetermined shape is By applying locally non-uniform copolymerization conditions, only a predetermined portion of the mixture is locally coated with a copolymer having a ratio of monomer components different from the mixing ratio. Once formed, the copolymerization proceeds gradually from that part to other parts, so that the monomer components gradually change from the predetermined part to other parts inside the copolymerized body. In the method of manufacturing a synthetic resin optical transmitter having a refractive index gradient that has a concentration gradient, a combination of monomers is selected such that the monomer Mi with a lower ni is easier to copolymerize. A method of manufacturing a synthetic resin light transmitting body in which the refractive index decreases over the entire light transmitting body in proportion to the square of the distance from the central axis.