KR20040021759A - Process for the production of Preform for Plastic Optical Fiber by Inter diffusion Method - Google Patents

Abstract

PURPOSE: A method for fabricating a plastic fiber preform using an internal diffusion method is provided to form a graded-index type plastic fiber by using the mixture of two monomers. CONSTITUTION: The first monomer having a low refractive index is mixed with an initiator of 0.01 to 0.4 weight percent and a chain transfer agent of 0.01 to 0.4 volume percent. The mixture is inserted into a glass tube. The polymer is fabricated within the glass tube by rotating the glass tube under the temperature of 50 to 150 degrees centigrade. The second monomer having the higher refractive index than the first monomer is mixed with the first monomer in a mixing ratio of 3 to 7. The mixture of the first and the second monomers is inserted into the glass tube. The polymer is swelled by rotating the glass tube under the normal temperature. The mixture of the first and the second monomers is diffused into the inside of the polymer. A plastic fiber preform is fabricated by polymerizing the mixture and the polymer.

Description

Process for the production of Preform for Plastic Optical Fiber by Inter diffusion Method

The present invention relates to a method for producing a preform for a plastic optical fiber having a graded-index type refractive index distribution by the internal diffusion method, and more specifically, using two or more monomers having different refractive indices and copolymerization are possible. The present invention relates to a method for easily producing a preform having a good refractive index distribution by using a copolymerization method by radical polymerization as an internal diffusion method.

In particular, the manufacturing method using the internal diffusion method is introduced in Korea Patent Publication No. 2001-87884.

In this method, the outer diameter of the preform can be increased since the polymer tube forming the cladding with the first monomer is prepared and then a mixed solution of the first monomer and the second monomer is introduced into the tube. There is also a disadvantage that the adjustment of the refractive index distribution is not easy.

Plastic optical fiber is much easier to connect because it can manufacture large-diameter optical fiber than quartz optical fiber, and it is more flexible than quartz-based optical fiber due to the characteristics of plastic. It is suitable to use.

Plastic optical fiber is largely composed of 1) a step-index type consisting of a cladding with a small refractive index and a core with a relatively large refractive index, and 2) a graded refractive index that gradually changes greatly toward the center of the core. Can be divided into graded (indexed) type.

The graded-index type is manufactured by a method using a gel effect using dopants having different refractive indices, a method using ultra-high centrifugal force, or a method by adjusting refractive index by designing a special extrusion die.

The above methods were difficult to control the refractive index distribution and could not produce a preform having a large outer diameter.

An object of the present invention is to provide a method for producing a preform for a graded-index plastic optical fiber having a good refractive index distribution and a large outer diameter of the preform.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for controlling the refractive index distribution of the preform in preparing a graded-index plastic optical fiber, after the tube is made of a first monomer having a relatively low refractive index, the first monomer And a copolymerization with the second monomer having a higher refractive index than that of the second monomer, to prepare a mixed solution having different mixing ratios, and then, into the first prepared polymer tube at room temperature, and to swell the polymer of the tube with the mixture. While the swelling solution allows the mixed solution to be diffused into the polymer, then a gel phase is formed, and the gel phase rises to a polymerizable temperature again when the gel phase affects the next polymerization process, and the polymerization process is repeated. It is characterized by manufacturing a preform forming a hill from the inside.

That is, in the present invention, a mixture of the first monomer having a relatively low refractive index of the first monomer mixed with 0.01 to 0.4% by weight of an initiator and 0.01 to 0.4% by volume of a chain transfer agent is added to a glass tube, and then the glass tube is heated at 50 to 150 ° C. Was polymerized while rotating at 500 to 5,000 rpm on a horizontal axis to prepare a polymer tube, and then the mixing ratio of the first monomer to the second monomer having a relatively high refractive index was 7: 3, 5: 5, 3: 7, 0: After preparing each mixed solution to be 10, the mixed solution was introduced into the tube at room temperature, and then rotated at 500 to 5,000 rpm to swell the polymer in the tube with a copolymerized monomer mixture of the first monomer and the second monomer. While the mixed solution is diffused into the polymer (diffusion) to form a gel phase, the gel phase thus formed is raised to 50 ~ 150 ℃ again at the point of affecting the next polymerization process and then polymerization Is the refractive index by repeating the steps by the mixed solution to a method of making a preform that forms a graded from within.

At this time, if the rotational speed is less than 500rpm, the monomers introduced do not adhere to all of the walls, and if the speed exceeds 5,000rpm, the composition of the device is excessive.

In addition, if the polymerization temperature is less than 50 ℃ polymerization takes too much, if it exceeds 150 ℃ most of the monomer is evaporated, the polymerization is hardly achieved.

As the monomer used in the present invention, methacrylate having a functional group, especially methyl methacrylate (refractive index n = 1.414), benzyl methacrylate (refractive index n = 1.512) is effective, and styrene ( styrene, refractive index n = 1.547), 2,2,2-trifluoroethyl methacrylate (2,2,2-Trifluoroethyl methacrylate, refractive index n = 1.359), and the like.

0.01 to 0.4% by weight of azobis isobutyl nitrate (hereinafter referred to as AIBN) or benzoyl peroxide (hereinafter referred to as BPO) as an initiator to the first monomer having a relatively low refractive index. Is 0.1% by weight, n-butyl mercaptan (hereinafter referred to as n-BMP) as a chain transfer agent, 0.01 to 0.4% by volume, preferably 0.1% by volume into a glass reactor, and then the rotational speed under nitrogen atmosphere After preparing a tube by polymerization at 500 to 5,000 rpm, preferably 3000 rpm, and a polymerization temperature of 50 to 150 ° C., preferably 90 ° C., a volume ratio of each of the second monomers copolymerizable with the first monomer having a relatively low refractive index is obtained. 7: 3, 5: 5, 3: 7, 0: 10 mixed to four, and then the four mixtures were sequentially added to the polymer tube at room temperature and then rotated at 500 ~ 5,000rpm for 12 hours Polymerize step by step.

At this time, if the addition amount and the rotational speed of the initiator, the chain transfer agent is out of the above range, the molecular weight is too low or too high to draw the preform.

In this way, the first polymer produced is swelled by a secondly introduced monomer mixture, and the mixture is diffused into the polymer to form a gel from inside the tube, and the gel is returned to 50 to 150 ° C. When the polymerization is carried out after the temperature is raised, the polymerization reaction proceeds between the gel produced between the first-order polymer and the second monomer mixture.

In this case, as the polymerization proceeds due to the reaction rate difference of each monomer, the distribution of the monomer having a large refractive index increases, and the polymerization proceeds completely to make a tube having a larger refractive index toward the inside.

Subsequently, when a mixed solution having a large mixing ratio of a monomer having a relatively high refractive index is sequentially introduced into a tube and polymerized in the same manner as the above method, a preform in which the refractive index distribution is hilly from the inside can be prepared.

According to the present invention, the size of the preform can be manufactured up to an outer diameter of 50Φ by repeatedly adding and swelling a mixed solution having different mixing ratios, and the refractive index distribution is adjusted by adjusting the mixing ratio of the first monomer and the second monomer. The adjustment can be made easier.

The refractive index distribution index of the preform manufactured in the above process is represented by an α value by the following equation, and the refractive index distribution index of the prepared preform is 1.9 to 2.5, which is not suitable for communication.

Drawing the preform at high temperature produces a plastic optical fiber.

<Formula I>

n; Refractive index of the base material, n ₁ ; Refractive index of the center of the base material, r; Radius of substrate, a; Distance from core, α; Index of Refraction Distribution

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1

In the first process, 370 ml of methyl methacrylate (hereinafter referred to as MMA) is added to a glass tube 50 mm in diameter and 1000 mm in length, 0.1 weight% of AIBN as an initiator, and 0.1 volume% of n-BMP as a chain transfer agent. The polymerization was carried out at 90 ° C. for 12 hours while rotating at 3000 rpm.

After lowering the temperature to room temperature, 260 ml of MMA and 110 ml of benzyl methacrylate (hereinafter referred to as BzMA) were mixed (mixing ratio 7: 3), 0.1 weight% of AIBN as an initiator, and 0.1 volume% of n-BMP as a chain transfer agent. After adding to the polymethyl methacrylate (hereinafter referred to as PMMA) tube prepared in the first step and swelling the PMMA while rotating at 3000rpm for 5 hours on a horizontal axis.

When the mixed solution formed a gel phase after swelling for 5 hours and then diffused into the polymer, the temperature was raised to 90 ° C. and polymerization was performed for 6 hours while rotating the glass tube at 3000 rpm.

After lowering the temperature to room temperature again, the mixture was mixed with 180 ml of MMA and 180 ml of BzMA (mixing ratio 5: 5), and then introduced into the prepared preform tube, followed by swelling while rotating at 3000 rpm for 5 hours on a horizontal axis. After diffusion into the gel phase was formed to rise to 90 ℃ was carried out polymerization for 6 hours while rotating the glass tube at 3000rpm.

In the same manner as described above, the mixture ratio of MMA and BzMA 3: 7 and finally 370ml of BzMA was injected, and finally the preform was prepared through the same manufacturing process.

The preform thus prepared was heat treated at 110 ° C. for 24 hours in a vacuum oven.

The preform thus obtained had a refractive index distribution index of 2.08.

The present invention provides a refractive index distribution by adjusting the refractive index distribution over a total of five stages, unlike a conventional method of preparing a preform prepared by using a two-step process of preparing a tube including a cladding and adding a mixture of two monomers capable of copolymerization. It has the advantage of being able to adjust the index accurately and easily.

Preforms prepared by the present invention can increase the outer diameter and have a refractive index distribution of Graded-Index.

Claims (4)

0.01-0.4% by weight of initiator and 0.01-0.4% by volume of chain transfer agent were mixed in the first monomer having a relatively low refractive index, and then introduced into a glass tube, and the tube was rotated horizontally at a rotational speed of 500-5,000 rpm at a temperature of 50-150 ° C. Preparing a polymer therein, The first monomer and the second monomer having a relatively higher refractive index are mixed at a volume ratio of 7: 3, and then the mixture is introduced into the polymer tube, and then rotated horizontally at 500 to 5,000 rpm at room temperature to swell the polymer. (swelling) while allowing the mixed solution to diffuse into the polymer to form a gel phase, which is then polymerized while rotating again at a rotational speed of 500 to 5,000 rpm at a temperature of 50 to 150 ° C., After preparing a mixed solution in which the volume ratio of the first monomer and the second monomer is 5: 5, 3: 7,0: 10, and then adding the mixed solution to each of the polymer tubes sequentially, the second step is performed. Method of producing a preform for plastic optical fiber by the internal diffusion method characterized in that it is manufactured by repeatedly performing the polymerization step. 2. The method according to claim 1, wherein azobis-isobutyl nitrate or benzoyl peroxide is used as the initiator, and butyl mercaptan is used as a chain transfer agent. The method of claim 1, wherein methyl methacrylate is used as the first monomer and benzyl methacrylate or styrene is used as the second monomer. The preform for plastic optical fiber according to claim 1, wherein 2,2,2-trifluoromethyl methacrylate is used as the first monomer and methyl methacrylate is used as the second monomer. Way.