JPH0340362B2 - - 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. A synthetic resin optical transmitter whose refractive index distribution is expressed by equation (1) has been proposed in Japanese Patent Publication No. 54-30301 (Patent Application No. 11723, No. 50) and Japanese Patent Application No. 149004 (No. 56, No. 55). . N=N ₀ (1-1/2Ar ² ) (1) Here, N ₀ is the refractive index of the central axis, and N is the distance r from the central axis.
is the refractive index of a point at a distance of , where A is a 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 reactivity 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 ) _n , then r ₁ (M ₁ /M ₂ ) _n + 1/(M ₁ /M ₂ ) _n + r ₂ (2) Holding a mixture of monomer M ₁ and monomer M ₂ such that the value is 1.1 or more or 1/1.1 or less in a predetermined shape, such as a cylinder, and for a mixed object of the predetermined shape. By applying copolymerization conditions that are locally nonuniform, first, only a predetermined portion of the mixture, for example, the outer peripheral portion of a cylindrical mixture, has a mixture ratio of _M1 and M that differs from the above mixing ratio. ₂
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 motyl methacrylate, vinyl benzoate and others, and alkyl methacrylate 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 gradient of the refractive index decreases toward the periphery. It becomes very gradual. The distribution will look like curve ABC in Figure 1. Note that r _p is the radius of the optical transmission body. This is because the refractive index of the copolymer increases with polymerization, but the increase is gradual at first, but sharply increases in the latter half of polymerization. In order to obtain a rod-shaped convex lens using this method, it was necessary to shave off the peripheral portion until the radius r _c was reached. The present invention provides an optical transmission body that follows the distribution of equation (1) up to the peripheral portion. That is, three types of monomers M ₁ , M ₂ and
A mixture of M ₃ (the refractive index of each homopolymer is n ₁ , n ₂ and n ₃ ) is polymerized to obtain a light transmitting material by the polymerization method described in the above patent. Generally, in a ternary copolymerization reaction, 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 ) The 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 +r ₃₂ }＞1.1 (6) where (Mi / Mj) _n is monomer Mi and monomer Mj
The mixing molar ratio of (2) Regarding the refractive index, n ₁ < n ₃ < n ₂ (7). Here, the value of (n ₂ − _{n 1} ) is at least 0.005 and the value of (n ₂ − n ₃ ) is at least
Preferably it is 0.001. Condition (1) is that as the terpolymerization progresses, the initial monomer
M ₁ rapidly polymerizes, 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, the refractive index of the copolymer produced in the early stage of polymerization is the lowest, the refractive index of the copolymer produced in the middle stage of polymerization is the highest, and the refractive index of the copolymer produced in the late stage of polymerization is the lowest. has a medium refractive index. Since the M ₁ -M ₃ system also satisfies the conditions of the patent, the refractive index distribution is of the ABC curve type shown in FIG. When M ₂ monomer is added to this system, the refractive index near B increases. _M1 , _M2 , _M3
By adjusting the combination and the preparation ratio, it is possible to push B up to D and create a square distribution to the periphery as shown by the straight line ADC in the figure. Examples of combinations of ternary monomers used in the present invention are listed below. (A) Vinyl benzoate is used for M ₂ , vinyl phenyl acetate is used for M ₃ , and the following monomers are used for M ₁ . (A1) CH ₂ =C (CH ₃ )COOR R = -C _o H _2o+1 (n = 1 to 10), -C ₆ H ₁₁ , furfuryl group (C ₅ H ₅ O), or (A2) CH ₂ = CHCOOR R = C _o H _2o+1 (n = 1 to 6), or -
C ₂ H ₄ Cl (A3) CH ₂ =C(Cl)COOR R=C _o H _2o+1 (n=1~6) or (A4)

【formula】

【formula】

[Formula] or CH ₂ = C (CH ₃ ) CN (B) M ₂ is benzyl acrylate or chloroethyl acrylate, M ₃ is vinyl chloroacetate, M ₁
The following monomers are used. (B1) CH ₂ = C (CH ₃ ) COOR R = C _o H _2o+1 (n = 1 to 10), or -
C ₆ H ₁₁ (B2)

[Formula] R=C _o H _2o+1 (n=1 to 6) or (B3)

[Formula] (C) Combination of M ₁ , M ₂ , and M ₃ shown in the table. The mixing ratio of each monomer varies depending on the type of monomer, the diameter of the optical transmitter, the refractive index distribution, polymerization conditions, etc., but usually M ₁ 40-80, M ₂ 5-30, M ₃ =10~
Selected from a range of 40% by weight. According to the present invention, an optical transmission body having a parabolic refractive index distribution up to the peripheral portion is manufactured, and the present invention

According to [Table], a rod-shaped or fibrous optical transmission body can be easily manufactured, and by heating and stretching it, a fibrous optical transmission body with a small diameter can be manufactured. Next, details of embodiments of the present invention will be described.
First, monomers M ₁ , M ₂ and M ₃ are mixed, and a predetermined amount of a photopolymerization initiator (for example, benzoyl peroxide (BPO), benzoin methyl ether, etc.) is mixed.
and melt it to a specified inner diameter (for example, about 2.9 mm).
A glass tube with one end closed was filled with the above-mentioned mixture, and photocopolymerization was 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 monomer mixture are mounted on a support member 5 at a specific distance, for example, 10 cm from the ultraviolet lamp 1, and are rotated by a motor 6 at, for example, 40 revolutions per minute. First, the ultraviolet lamp 1 is placed at a position lower than the lower end of the glass tube 4, and the lamp 1 is moved at a constant speed V (mm/mm/mm) by the motor 7.
irradiate with ultraviolet rays while moving upward at a speed of min). Air at a constant temperature is fed into the device from an inlet 8 by a fan 9 and is discharged from an outlet 10, but the temperature rises due to the heat generated by the lamp 1.
The temperature is kept constant at a certain level higher than the inlet air temperature. 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 rod is an optical transmission body with a constant refractive index distribution constant A over the entire rod except for the ends. To heat and stretch the rod, first the rod is heated to 10 -3 to 10 ^-3 to remove trace amounts of volatile substances contained in the rod.
Place at 50°C under reduced pressure of 10 ^-4 mmHg for 3 to 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/min), 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. Benzoyl peroxide in a mixture of 30 parts of methyl methacrylate with a refractive index of 1.492 as M ₁ , 6 parts of vinyl benzoate with a refractive index of 1.578 as M ₂ , and 10 parts of phenyl vinyl acetate with a refractive index of 1.567 as M ₃ . Dissolve 0.46 parts and photocopolymerize using the method described above. The reactivity ratio of each monomer is r ₁₂ = 8.30, r ₂₁ =
0.049, r ₁₃ = 22.76, r ₃₁ = 0.00494, r ₂₃ = 4.54, r ₃₂
=0.17, and the values on the left side of equations (4), (5), and (6) are 8.32, 22.9, and 4.82, respectively, and satisfy each equation.
The UV lamp feed speed is 0.6 mm/min. A transparent rod (radius 1.45 mm) was obtained. The refractive index distribution constant A=2.6×10 ^-3 mm ^-2 , and the refractive index had a quadratic distribution up to the periphery. The numerical aperture is 0.113. The rod is hot-stretched 100 times at 220℃ and has a diameter of 0.29mm.
obtained fibers. Transmission loss was 0.8 dB/m.

[Brief explanation of drawings]

FIG. 1 is a graph explaining the refractive index distribution according to the present invention, FIG. 2 is a partially cross-sectional side view showing an embodiment of the present invention, and FIG. 3 is an example of implementing the present invention following FIG. 2. FIG.

Claims (1)

[Claims] 1. Different refractive indexes when formed into polymers 3.
holding a mixture of seed monomers (including monomer mixtures) M ₁ , M ₂ and M ₃ in a predetermined shape;
By applying copolymerization conditions that are locally non-uniform to the mixed body of a predetermined shape, only a predetermined portion of the mixed body is initially copolymerized with monomer components different from the mixing ratio. By forming a polymer locally, and then gradually copolymerizing it from that part to other parts, the monomer is In a method for manufacturing a synthetic resin optical transmitter having a refractive index gradient that has a concentration gradient in which the body components gradually change, if the refractive index of a monomer homopolymer is n _p , then n _p is the highest value. A combination of monomers such that a monomer with a low n p is the easiest to copolymerize, a monomer with the highest n _p is the second easiest to copolymerize, and a monomer with an intermediate n _p is the most difficult to copolymerize. A method of manufacturing a synthetic resin optical transmitter in which the refractive index decreases over the entire optical transmitter in proportion to the square of the distance from the central axis. 2 The mixture of the three types of monomers described above has a monomer reactivity ratio of Mj to Mi (i, j = 1, 2, 3)
is expressed as rij, and the mixing molar ratio of Mi and Mj is expressed as (Mi/Mj) _n , then the mixture of monomers is {r ₁₂ (M ₁ /M ₂ ) _n +1}/{(M ₁ / M ₂ ) _n + r ₂₁ }＞1.1 {r ₁₃ (M ₁ /M ₃ ) _n +1}/{(M ₁ /M ₃ ) _n +r ₃₁ }＞1.1 {r ₂₃ (M ₂ /M ₃ ) _n +1} A method for manufacturing a synthetic resin optical transmission body according to claim 1, which satisfies all of the following expressions: /{(M ₂ /M ₃ ) _n + r ₃₂ }>1.1.