JP2670240B2 - Method for manufacturing light-focusing optical plastic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a light-focusing plastic optical element.
Manufacturing method, more specifically, a large-diameter, light-focusing plastic rod (LFPR; Light-focu) with excellent imaging characteristics.
sing plastic rod) and the like.

[0002]

2. Description of the Related Art Light-focusing rod (LFR)
rods) are gradient coefficient (GRIN) type optical elements.
The refractive index distribution of LFR is a parabola extending from the central axis to the periphery. Due to these properties, the incident light travels in a zigzag manner within the rod and is focused (focused) in the outer space behind its exit end. This fact makes the LFR act as a concave lens and is commonly referred to as a "light focusing rod".

There are three types of optical elements, which have the above-mentioned parabolic refractive index and are cylindrical. GI type optical fiber, GRIN rod and wood lens. These image transmission principles are the same, but their transmission lengths and categories are different. Of these, GI type optical fibers (eg silica series fibers) are the longest, usually longer than a few hundred meters and even up to a dozen kilometers, and are used as transmission media in optical communication systems. GR
The IN rod is of intermediate length and can be used as an image transmission system, fiber optic coupler and detection sensor. Generally, these devices are longer than the inner diameter, but are not used as optical fibers and are classified as GRIN rods. Wood lenses, on the other hand, take the form of lenses that are shorter and thinner than their inner diameter and are mainly used for image transmission and light focusing.

To date, numerous reports and patents have been issued regarding the manufacture of LFPR. For example, U.S. Pat. No. 3,718,383 (1973), U.S. Pat.
861,160 (1974) and 4,58
No. 1,252 (1986) discloses a non-solvent expansion diffusion method. This method comprises the steps of diffusing various monomers into a plastic rod using a mixture of non-solvent and solvent, and polymerizing these monomers to provide a particular refractive index diffusion. This type of method benefits from the diffusion gradient of the monomers, forming a parabolic diffusion of the refractive index.

Further, the Otsuka literature discloses an ultraviolet-induced copolymerization method. In this method, monomer solvent replenishment is adjusted to avoid bubble formation caused by polymerization shrinkage [Y. Otsuka, Appl. Op.
t., Vol.24, No.24 (1985), 4316]. In addition, Otsuka's group also invented a two-step copolymerization process to produce light-focusing plastic rods. For example, the vapor phase transfer method [Y. Otsuka, Appl. Opt., Vol.22, No.3 (1985),
413] consists of preparing a partially polymerized gel rod, placing the rod in an atmosphere of trifluoroethyl methacrylate vapor, and then subjecting it to heat treatment to create a GRIN rod. .

J. Appl. Polym. Sci., (Vol.26, (1983), 2907-
2915) discloses a method in which a partially polymerized gel rod is treated with 2,2,3,3-tetrafluoropropy methacrylate.
And a heat treatment in a nitrogen atmosphere.
The method disclosed in Appl. Opt., (Vol.20, No.13, (1981), 2319) is also a two-step copolymerization process, and uses diethylene glycol bisallyl carb.
onate) to form a partially polymerized gel rod, and the gel rod is heated under a nitrogen atmosphere to produce fluoroethyl methacrylate.
And a step of immersing in.

All the light-focusing plastic rods obtained by the two-step copolymerization process invented by Otsuka et al. Have a cross-linking structure and therefore cannot be further finished into optical fibers. The interfacial-gel copolymerization method was also reported by Otsuka (Appl.
Opt. Vol.27, No.3, 486). By this method, the copolymer phase is gradually formed from the gel phase formed at the interface between the monomer and the polymer matrix. Gradient rate profiles are obtained from the gel phase formed on the walls of the polymer matrix.

Further, US Pat. No. 4,022,855 (1977) and Japanese Patent Application No. 60-11951
No. 0 (1985) discloses a centrifugal casting method for producing preforms for plastic optical fibers.

The above methods all take different approaches to produce LFR with parabolic index dispersion,
Avoids contraction of the rod. However, all of these methods require complicated processing steps and equipment. For example, in ultraviolet-induced copolymerization, a device that generates ultraviolet rays is required. In addition to this, in order to avoid shrinkage of the manufactured LFR, the diameter of the plastic rod made by the above method is limited and the area available for transmitting images is relatively small, Sometimes the transmitted image is distorted.

[0010]

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a simple method for manufacturing light-focusing optical plastic components.

Another object of the present invention is to provide a method of manufacturing a light focusing plastic rod having a large diameter and excellent imaging characteristics.

[0012]

To achieve the above objects, the method of the present invention comprises the steps of a) providing a prepolymer transparent preform; and b) having different reactivity from each other. two or more of the monomers is immersed in a solution containing a part of the monomer is diffused with infiltrating the preform, whereby the step of inflating the preform; c) the preform is fully expanded And then copolymerizing the diffused monomers in the preform after molding the plastic member; and more preferably, d) forming the plastic member into an optical element.

According to the invention, the prepolymer may be a linear polymer, so that the plastic product produced can be further made into optical fibers.

Also according to the present invention, due to the gel action of each monomer and the different reaction ratio, after the prepolymer preform is completely expanded and homogenized, the monomer having a large reaction ratio is outside the expansion zone. In the expansion zone of the preform at an earlier stage than it is first polymerized with more rapid consumption,
Alternatively, it is copolymerized. This action causes the monomer to undergo a greater reaction outside the expansion zone to continuously supplement the expansion zone. This mechanism causes polymerization to proceed from the center of the preform towards its periphery, which is the opposite of the Otsuka process. Therefore,
A parabolic refractive index profile is formed from the center to the periphery, and an optical plastic device having a large transmission range and excellent imaging characteristics can be obtained.

Hereinafter, the present invention will be described in detail.

According to the method of the present invention, the prepolymer has excellent permeability and becomes a linear prepolymer or a cross-linked prepolymer. For example, PMMA (poly methyl methacrylate), PEGDMA (poly
Ethylene / glycol / dimethyl / acrylate), P
ST (polystyrene) and PVB (polyvinyl benzoate) are suitable for use as the prepolymer of the present invention. If an optical fiber is desired, it is of course necessary to choose a prepolymer (such as polymethylmethacrylate) with a linear structure as the preform material. The prepolymer preform may be rod, plate or spherical in shape. The preform is preferably rod-shaped when it is desired to finish it into an optical fiber. The method for producing the prepolymer / preform can be, for example, an injection molding method or a casting method, but is not limited to these two methods.

The monomers of the solution used for soaking preferably have different reaction ratios and very close density and solubility parameters. When using a two-element monomer system, it is preferred that the reaction ratio of one monomer be> 1 and the reaction ratio of the other monomer be <1. The weight ratio of the monomers used should be in the given range.
However, different weight ratios are used for different monomers.

[0018]

The preferred embodiment for carrying out the method of the present invention will now be described.

In this embodiment, a polymethylmethacrylate (PMMA) rod is used as a prepolymer preform, and a solution containing only methyl methacrylate (MMA) and vinyl benzoate (VB) as monomers is used as a prepolymer. -Used to soak the preform.

Referring to FIG. 1A, the PMMA prepolymer rod 13 has a comonomer (MMA / VB =
4/1; weight ratio) and AIBN (α,
α'-azobisisobutyronitrile (α, α'-azobisiso
butyronitrile), 1% concentration). All of these members are placed in the glass tube 15, sealed with a silicon stopper 12 and sealed with a tape 11.

During the expansion step shown in FIG. 1 (B), which is processed at the expansion temperature (T ₁ ), the PMMA rod 13 gradually disappears and the expanded gel 16 increases. When the PMMA rod 13 disappears completely and the expanded gel 16 increases to the maximum, the temperature rises to the copolymerization temperature (T ₂ ) for complete copolymerization (FIG. 1 (C)). The LFPR (FIG. 1 (D)) obtained by cutting the two ends and polishing the both end faces is composed of a clouded part 18 and a transparent part 17 with a gradient rate diffusion.

The LFPR prepared according to the preferred embodiment described above has a large image-carrying area, namely a high Rc / Rp (> 90%) (where Rc is the active radius of the LFPR and its refractive index is two. Presents a quadratic curve variance and Rp is LFPR
Radius) and a low A (refractive index dispersion constant). Therefore, the transmitted image is not distorted.

The method of the present invention will be described more specifically based on the following examples, but the present invention is not limited to these examples.

Example 1 A glass tube (internal diameter 4 mm) of a mixture of MMA monomer (Mark Company, Federal Republic of Germany; EP grade) and 0.2% by weight of AIBN (Hanawa Company, Japan; EP grade). Placed inside, 4 in the water bath
Heated at 2 ° C. for 20 hours. The obtained PMMA prepolymer rod was taken out, and the comonomer [MMA / VB (manufactured by Tokyo Caustic Co., Ltd., Japan; R grade) = 4/1] was used.
It is placed in another glass tube (inner diameter 14 mm) containing a mixture with a polymerization initiator AIBN (0.05% by weight), and 36
Heat at ℃ for about 10 hours, expand the PMMA rod,
The temperature was raised to 0 ° C. to allow complete polymerization. The obtained plastic rod was taken out, cut into an appropriate length, and the cut end face was polished to prepare LFPR. This LFP
The optical characteristics of R are shown in Table 1.

Example 2 A process similar to that described in Example 1 was used. However, the only difference is that the AIBN concentration is changed to 0.075% by weight. Table 1 shows the optical characteristics of the LFPR prepared here.

Example 3 A process similar to that described in Example 1 was used. However, the only difference is that the AIBN concentration is changed to 0.1% by weight. Table 1 shows the optical characteristics of the LFPR prepared here.

[0027]

[Table 1]

As shown in Table 1, the value of Rc / Rp is 9
LFPR formed by the present invention greater than 0%
Have excellent image transmission characteristics.
Further, it is shown that the concentration of the polymerization initiator does not affect the optical characteristics of LFPR.

FIG. 2 shows the refractive index dispersion in the LFPR of the above-mentioned three examples. As shown in FIG. 2, the refractive index dispersion has a substantially parabolic shape extending from its central axis to the periphery. FIG. 3 shows the three-dimensional refractive index dispersion of LFPR prepared according to Example 3.

Example 4 A mixture of MMA monomer (Mark Company, Federal Republic of Germany; EP grade) and 0.2% by weight of AIBN (Hanawa Company, Japan; EP grade) in a glass tube (inner diameter 4 mm). Placed inside, 4 in the water bath
Heated at 2 ° C. for 20 hours. The obtained PMMA prepolymer rod was taken out, and a mixture of a comonomer [MMA / VB (manufactured by Tokyo Caustic Co., Ltd., Japan; R stage) = 4/1] and a polymerization initiator AIBN (0.075% by weight) was used. It is placed in another glass tube (internal diameter 14 mm), and the temperature is 36 ° C.
And heat the PMMA rod for about 10 hours to expand the PMMA rod.
The temperature was raised to 5 ° C. for complete polymerization. The obtained plastic rod was taken out, cut into an appropriate length, and the cut end face was polished to prepare LFPR. This LF
Table 2 shows the optical characteristics of PR.

Example 5 A process similar to that described in Example 4 was used. However, the only difference is that the expansion temperature (T ₁ ) is changed to 40 ° C. The optical properties of the LFPR prepared here are shown in Table 2.
Shown in

Example 6 A process similar to that described in Example 4 was used. However, the only difference is that T ₁ is changed to 44 ° C. Table 2 shows the optical characteristics of the LFPR prepared here.

[0033]

[Table 2]

As shown in Table 2, the value of Rc / Rp is 9
LFPR formed by the present invention greater than 6%
Have excellent image transmission characteristics.
Further, it is shown that the expansion temperature does not affect the optical characteristics of LFPR.

Example 7 A glass tube (inner diameter: 4 mm) of a mixture of MMA monomer (Mark Company, Germany; EP grade) and 0.2% by weight of AIBN (Hanawa Company, Japan; EP grade). Placed inside, 4 in the water bath
Heated at 2 ° C. for 20 hours. The obtained PMMA prepolymer rod was taken out, and the comonomer [MMA / VB (manufactured by Tokyo Caustic Co., Ltd., Japan; R grade) = 4/1] was used.
It is placed in another glass tube (inner diameter 14 mm) containing a mixture with a polymerization initiator AIBN (0.05% by weight), and 40
Heat at ℃ for about 10 hours, expand the PMMA rod,
The temperature was raised to 7.5 ° C. for complete polymerization. The obtained plastic rod was taken out, cut into an appropriate length, and the cut end face was polished to prepare LFPR. Table 3 shows the optical characteristics of this LFPR.

Example 8 A process similar to that described in Example 7 was used. However, the only difference is that the polymerization temperature (T ₂ ) is changed to 60 ° C. Table 3 shows the optical characteristics of the LFPR prepared here.

Example 9 A process similar to that described in Example 7 was used. However, the only difference is that T ₂ is changed to 62.5 ° C. Table 3 shows the optical characteristics of the LFPR prepared here.

Example 10 A process similar to that described in Example 7 was used. However, the only difference is that T ₂ is changed to 65 ° C. Table 3 shows the optical characteristics of the LFPR prepared here.

[0039]

[Table 3]

As shown in Table 3, the value of Rc / Rp is 9
LFPR formed by the present invention greater than 7%
Have excellent image transmission characteristics.
It also shows that the polymerization temperature does not affect the optical properties of LFPR.

Example 11 The image transmission characteristics of the LFPR formed in Example 1 are shown in FIG.
Further testing was done using the equipment shown in. In FIG. 4, 44 is a camera, 43 is LFPR, 45 is a light beam, 42
Is a slide, and 41 is a light source. When the object is attached to the slide 42, its image is taken by the camera 44. Figure 5 shows the LFPR with a length of 29 mm and a diameter of 9 mm.
The image of the check pattern of 7 mm square through is shown.
As shown in FIG. 5, the LFPR of the present invention has excellent image characteristics and the transmitted image is not distorted.

Comparative Example In this comparative example, LFPR formed by the UV-induced copolymerization method was obtained and tested using the same equipment as described in Example 11. The image is shown in FIG.

The preferred embodiments of the present invention are summarized below.

(1) a) preparing a prepolymer transparent preform; and b) immersing the prepolymer preform in a solution containing one or more monomers having different reactivities from each other to obtain the monomers. Infiltrating and diffusing a portion of the preform into the preform, thereby expanding the prepolymer preform; and c) after the preform has fully expanded to form the plastic member and then diffused into the preform. A step of copolymerizing the above-mentioned monomer;

(2) The method according to (1) above, wherein the prepolymer is a linear polymer.

(3) The linear polymer is polymethyl
The method of (1) above, which is a methacrylate.

(4) The method according to (1) above, wherein the monomers are methyl methacrylate and vinyl benzoate in a weight ratio of 4: 1.

(5) The method according to (1) above, wherein the preform is rod-shaped.

(6) The method according to (1) above, wherein the preform is spherical.

(7) The method according to (1) above, wherein the solubility parameter of each monomer is close to the solubility parameter of another monomer.

(8) The method of (1) above, wherein the preform is formed by injection molding.

(9) The method according to (1) above, wherein the prepolymer is a cross-linked prepolymer.

[0053]

Since the prepolymer used in the present invention may be a linear polymer, there is an effect that an optical fiber can be further produced from the produced plastic product.

[Brief description of the drawings]

FIG. 1 is a process diagram showing an example of the method of the present invention, (A) is a diagram showing a process of immersing a prepolymer rod in a comonomer solution, and (B) is a solution containing a comonomer and AIBN at an expansion temperature. Diagram showing the step of expanding the prepolymer,
(C) is a diagram showing copolymerization at a polymerization temperature, (D)
FIG. 4 is a diagram showing LFPR obtained after polishing the end face.

FIG. 2 is a diagram showing the relationship between the refractive index and the radius ratio (r / Rp) ^{2 of} LFPR obtained in Example 1-3 at various AIBN concentrations.

FIG. 3 is a diagram showing a three-dimensional refractive index dispersion of LFPR prepared in Example 3.

FIG. 4 is a schematic diagram of an apparatus used to test images transmitted over LFPR.

FIG. 5 shows an image transmitted by LFPR manufactured according to the present invention.

FIG. 6 is a diagram showing an image transmitted by LFPR manufactured by an ultraviolet copolymerization method.

FIG. 7 is a diagram showing the meaning of the maximum allowable angle of an SI type optical fiber.

[Explanation of symbols]

 11 Tape 12 Silicon Stopper 13 PMMA Prepolymer Rod 14 Mixture 15 Glass Tube 16 Expanding Gel 17 Clear Area 18 Cloudy Area 41 Light Source 42 Slide 43 LFPR 44 Camera 45 Light Ray

Claims (1)

(57) [Claims] 1. A a) preparing a prepolymer transparent preform; a b) said preform is immersed in a solution containing two <br/> one or more monomers having different reactivity from each other, Infiltrating and diffusing a portion of the monomer into the preform, thereby expanding the preform; and c) diffusing into the preform after the preform has fully expanded to form a plastic part. A step of copolymerizing the obtained monomer, and a method for producing a light-focusing optical plastic element comprising: