JP2893046B2 - Method of manufacturing refractive index distribution type plastic optical transmission body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the manufacture of a plastic optical transmission body that can be effectively used as various optical transmission paths such as an optical focusing optical fiber, an optical focusing rod lens, and an optical sensor. It is about the method.

[Prior Art] An optical transmission body having a continuous refractive index distribution from the center to the outer circumference in the cross section of the optical transmission body is disclosed in Japanese Patent Publication No. Sho 47-8.
No. 16, No. 47-28059, European Patent Publication 0208
No. 159 publication.

[Problems to be Solved by the Invention] The refractive index distribution type optical transmission body disclosed in Japanese Patent Publication No. 47-816 is made of glass and made by an ion exchange method, so that its productivity is low. Difficulties with the same shape (especially the same length) and the same performance are difficult to make between different lots, and the length of the graded index optical transmitters with the same performance is not uniform, resulting in poor handling. was there.

Japanese Patent Publication No. 47-28059 discloses a graded-index plastic optical transmitter having a refractive index different from each other and a mixture of two or more transparent polymers having different solubilities in a specific solvent. After shaping into a shape, the polymer is immersed in the solvent and a part of the polymer is extracted from the surface of the molded product, thereby mixing the polymer from the surface of the polymer molded product to the center thereof. It is made by assuming that the proportion has changed. By this method, it is possible to make a graded-index optical transmitter made of plastic, but a mixture of two or more polymers with different refractive indexes has a large fluctuation of the refractive index, and its transparency is reduced. Light scattering is likely to occur, and there is a problem that characteristics as a refractive index distribution type optical transmission body are not sufficient.

EP 0208159 discloses at least one
A kind of thermoplastic polymer (A) and a monomer (B) which is compatible with the polymer (A) when polymerized and which becomes a polymer having a refractive index different from that of the polymer (A) The monomer (B) is volatilized from the surface of the molded product obtained by molding the homogeneous mixture into a rod shape to give a continuous concentration distribution of the monomer (B) from the surface to the inside of the molded product. After that, a method of producing a graded-index-type plastic optical transmission body by polymerizing the unpolymerized monomer in the molded article is disclosed.

The refractive index distribution curve of the graded index optical transmission medium is ideally represented by the following equation, and is said to be the curve indicated by a in FIG.

N = N ₀ (1-ar ² ) However, according to the study of the present inventor, the refractive index distribution curve obtained by measuring the refractive index distribution curve by using an interfaco interference microscope of the refractive index distribution type optical transmitter manufactured by the above method is described below. As shown by b in FIG. 1, the center is 0.5r _{0 to} 0.75r _{0 in the} radial direction.
(The range of c to d in the figure, e indicates the outermost peripheral portion) has a refractive index distribution curve relatively close to an ideal curve section shown by the equation (3), but is outside the range. And the inner refractive index distribution has a large deviation from the ideal curve.

When observing the lattice pattern with such an optical transmission body,
If the refractive index distribution has a refractive index distribution almost exactly following the quadratic curve defined by the equation (1), it is possible to observe a normal lattice image as shown in FIG. However, as shown in FIG. 2 (b), when a lattice image is observed with an optical transmission body whose refractive index distribution is farther from the ideal refractive index distribution, as shown in FIG. 3 (b) or (c), it becomes larger. A distorted lattice image is observed, and accurate image transmission cannot be performed. Further, only a very low modulation transfer function (MTF) showing the resolution of 30% or less was obtained, and it could not be used as a facsimile optical transmitter at all.

Therefore, in the gradient index optical transmission body made by the conventional method having the refractive index distribution as shown in FIG. 2 (b), a portion in the outer peripheral direction is cut away more than in FIG. 2 (d). Alternatively, the portion is eluted with a solvent, and the optical path of the optical transmitter has a relatively ideal refractive index distribution. Therefore, it is difficult to obtain a high-resolution optical transmitter, and However, there is a problem that it is extremely difficult to always produce a uniform product with a very low uniformity.

[Means for Solving the Problems] Accordingly, the present inventors use a monochromatic light source such as an LED to obtain a high-resolution, low-chromatic-refractive-index distribution-type plastic optical transmitter that can be used as a facsimile or an image sensor. is obtained by completing the results present invention was investigated for the purpose of, it is an aspect of the present invention is a substance viscosity at the uncured state is 10 ³ to 10 ⁸ poises, the cured product formed by curing a substance N uncured liquid materials having a refractive index n of n ₁ > n ₂ > n ₃ ... _{N N} (N ≧ 3) are arranged in such a manner that the refractive index decreases gradually from the center toward the outer peripheral surface, and are concentric. Shaped into uncured fiber strands laminated in multiple layers,
While performing the material interdiffusion treatment between adjacent layers so that the refractive index distribution between the layers of the strand fiber becomes a continuous refractive index distribution, or after performing the mutual diffusion treatment, it is preferable to cure the uncured strand fiber. The present invention resides in a method of manufacturing a characteristic gradient index type plastic optical transmission body.

According to the manufacturing method of the present invention, it is possible to manufacture an optical transmission body as described below.

The refractive index distribution of the optical transmission of the present invention as shown in Fig. 1 (b), at least 0.25 R ₀ ～0.70R from the central axis _0, is preferably in the range from 0.20r ₀ ~0.75r _0, equation (1 It is preferred that the ideal refractive index distribution curve [FIG. 1 (a)] shown in FIG. The optical transmission body of the present invention in which the range specified above from the central axis of the refractive index distribution type optical transmission body has the ideal refractive index distribution shown in Expression (1) is in a range of 0.25r ₀ from the central axis. Even if each refractive index distribution in the area outside 0.70r _{0 is considerably different} from the refractive index distribution curve shown in the equation (1), the image obtained by observing the lattice image is almost accurate. It can be a lattice image.

N ₀ of the plastic optical transmission medium of the present invention is preferably a range of 1.5 ± 0.1, the refractive index distribution type plastic optical transmission article n ₀ exceeds 1.6 manufacture it becomes difficult its. On the other hand, an optical transmitter having n ₀ less than 1.4 is a plastic optical transmitter having a good resolution characteristic, in which it is difficult to obtain a large difference between the refractive index of the central axis portion and the refractive index of the outer peripheral portion. Can not.

Also, the g value is given by the equation This is a value that defines the lens length of the optical transmission body and its imaging distance. An optical transmitter having a g value exceeding 0.7 mm ^-1 has an extremely short imaging distance, and it is difficult to always produce an optical transmitter having uniform characteristics.

Further, an optical transmitter having a g value of less than 0.3 mm ^-1 has a low resolution, and its performance is insufficient as a gradient index optical transmitter for a facsimile or an image scanner.

When used as an optical transmitter such as a facsimile, the plastic refractive index distribution type optical transmitter of the present invention is used as an array in which many of them are used as a single-row or multi-row bales arrangement rather than using one. Often used, the image obtained with this array is a partially overlapping image of the image from each light transmitter. In order to improve the clarity of the overlapped image, the degree of overlap of these overlapped images has greatly contributed.A factor governing the degree of overlap is the diameter of the optical transmission body, and its radius r ₀ is 0.5 ± 0.1 mm.
Is preferably within the range. If the thickness is smaller, the brightness is insufficient, and it is difficult to efficiently produce an optical transmission body having a uniform refractive index distribution. When an array is formed by arranging a large number of transmitters, the degree of overlap of the images obtained is not uniform, and it is not preferable because the array cannot perform clear image transmission.

The MTF indicating the resolution of the plastic gradient index optical transmission body of the present invention is a grating having a spatial frequency of 4 (line pairs / mm), and a plurality of gradient index optical transmission bodies as shown in FIG. The array and the light sources arranged in this manner are arranged as shown in FIG. 4, and a grid image is read by a CCD line sensor installed on the image plane (FIG. 5). The maximum value (i _max ) of the measured light amount
And the minimum value (i _min ) were measured as shown in FIG. Here, the spatial frequency is, as shown in FIG. 4, a set of a combination of a white line and a black line is defined as one line pair,
This indicates how many lines are provided in a 1 mm width in units of line pairs / mm.

MTF of the gradient index optical transmission body made of plastic of the present invention
Is preferably 40% or more. An optical transmitter having an MTF of less than 40% has a low resolution, and when used as an optical transmitter for a copying machine such as a facsimile, a clear image cannot be formed. Therefore, the MTF is preferably set to 45% or more. .

Hereinafter, the method for producing a graded-index plastic optical transmission body of the present invention will be further described.

Viscosity prepared the N uncured material refractive index n is _{n 1> n 2> n 3} ... n N becomes N ≧ 3 when cured is 10 ³ to 10 ⁸ poise in the unhardened center From a plurality of layers to form a rod-shaped body or a fiber-shaped shaped article laminated concentrically so that the refractive index of each layer is gradually reduced, and diffusion treatment is performed so that the refractive index distribution between each layer becomes a continuous refractive index distribution. It is manufactured by performing a hardening treatment during or after a diffusion treatment.

When N is 2, if the difference n ₁ -n ₂ between the center layer and the outermost layer of the graded index optical transmitter is increased, the difference between the center and the center is set at 0.
It is difficult to make the refractive index distribution within the range of 25r ₀ -0.70r ₀ approximate to the curve of the equation (1), and it cannot be used as the optical transmitter of the present invention. Therefore, N is in the range of 3 or more, and preferably in the range of 3 to 5.

The uncured material used in practicing the invention is
It must have a viscosity of 10 ³ to 10 ⁸ poise and be curable. If the viscosity is less than 10 ³ poise, thread breakage occurs during the shaping, and it is difficult to form a thread. On the other hand, if the viscosity is more than 10 ⁸ poise, the shaping operability is poor, and concentricity of each layer is impaired, or a shaping material having a large unevenness in thickness tends to be unfavorable.

As the curable substance that can be used in carrying out the present invention, a radical polymerizable vinyl monomer or a composition comprising the monomer and a polymer soluble in the monomer can be used.

Specific examples of the radical polymerizable vinyl monomer that can be used include methyl methacrylate (n = 1.49), styrene (n =
1.59), chlorostyrene (n = 1.61), vinyl acetate (n
= 1.47), 2,2,3,3-tetrafluoropropyl (meth)
Acrylate, 2,2,3,3,4,4,5,5-octafluoropropyl (meth) acrylate, 2,2,3,4,4,4-hexafluoropropyl (meth) acrylate, 2,2, Fluorinated alkyl (meth) acrylates such as 2-trifluoroethyl (meth) acrylate (n = 1.37 to 1.44), refractive index 1.43
1.62 (meth) acrylates such as ethyl (meth)
Acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, hydroxyalkyl (meth)
Acrylate, alkylene glycol di (meth) acrylate, trimethylolpropane di or tri (meth) acrylate, pentaerythritol di, tri or tetra (meth) acrylate, diglycerin tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, etc. And diethylene glycol bisallyl carbonate and fluorinated alkylene glycol poly (meth) acrylate.

The uncured material is soluble in the vinyl monomer to adjust the viscosity of the uncured material used for shaping these uncured materials into a thread and to provide a refractive index distribution from the center to the outside in the resulting filamentous material. It is preferable to be composed of a polymer. The polymer which can be used here preferably has good compatibility with the polymer formed from the above-mentioned radical polymerizable vinyl monomer. For example, polymethyl methacrylate (n = 1.49), polymethyl methacrylate copolymer (n = 1.47) -1.50), poly-4-methylpentene-1 (n = 1.46), ethylene / vinyl acetate copolymer (n = 1.46-1.50), polycarbonate (n = 1.50-1.
57), polyvinylidene fluoride (n = 1.42), vinylidene fluoride / tetrafluoroethylene copolymer (n = 1.42-1.
46), vinylidene fluoride / tetrafluoroethylene / hexafluoropropene copolymer (n = 1.40-1.46), polyalkyl fluoride (meth) acrylate polymer and the like.

It is preferable to use a polymer having the same refractive index for each layer in order to adjust the viscosity, since a plastic optical transmission body having a continuous refractive index distribution from the center toward the surface can be obtained. In particular, polymethyl methacrylate has excellent transparency and a high refractive index of itself, so that it is suitable as a polymer to be used for producing the gradient index optical transmitter of the present invention.

In order to cure the thread-like material formed from the uncured material, it is preferable to add a thermosetting catalyst or a photocuring catalyst in the uncured material, and a peroxide catalyst is usually used as the thermosetting catalyst. . Benzophenone, benzoin alkyl ether, 4'-isopropyl-2-hydroxy-2-methyl-propiophenone, 1
-Hydroxycyclohexyl phenyl ketone, benzyl methyl ketal, 2,2-diethoxyacetophenone, chlorothioxanthone, thioxanthone-based compound, benzophenone-based compound, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, N-methyldiethanolamine, Triethylamine and the like.

Next, in order to cure the uncured thread, the ultraviolet ray is preferably applied from the periphery in the curing section, and the thread containing the thermosetting catalyst and / or the photocuring catalyst is subjected to heat treatment or light irradiation treatment.

The optical transmission body of the present invention can be manufactured by using, for example, the yarn forming apparatus shown in FIG. FIG. 6 is a process diagram schematically showing the yarn forming apparatus, in which only the interdiffusion section and the hardening section are formed in a longitudinal sectional view, in which 61 is a concentric composite nozzle, and 62 is an extruded part. Uncured thread, 63 is a mutual diffusion part for diffusing the monomers of each layer of the thread to give a refractive index distribution, and 64 is a curing part for curing the uncured material. , 65 is a take-off roller, 66
Is a manufactured refractive index distribution type plastic optical transmission body, 7 is a winding section, 68 is an inert gas inlet, and 69 is an inert gas outlet. In order to remove volatile substances released from the thread 62 from the interdiffusion section 63 and the curing section 64, an inert gas such as a nitrogen gas is introduced from the inert gas inlet 68.

Examples of light sources used for photopolymerization include a carbon arc lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a low-pressure mercury lamp, a chemical lamp, a xenon lamp, and a laser beam that emit light having a wavelength of 150 to 600 nm.

The plastic graded-index optical transmission body of the present invention preferably has the above-mentioned features, and a plurality of such optical transmission bodies are arranged in one or more rows as shown in (41) in FIG. By using an integrated optical transmitter array,
It can be usefully used as an image transmitter for a copier or a facsimile. Its lens length when used as an optical transmission article array (Z _n) is 5 to 15 mm, good properly is 6 to 12 mm, that the imaging distance (T _c) is 10 to 40 mm, the good properly to 13~25mm As a result, an optical transmitter array having a uniform performance and a uniform array length can be obtained, and the MTF measured using a grating of 4 line pairs / mm is preferably a high-resolution optical transmitter array of 40% or more. It can be.

Graded index plastic optical transmission medium according to the present invention a method [Effect of the invention] is compared with the optical transmission of the same kind that have been previously developed, preferably the refractive index distribution of at least 0.25r ₀ ~0.70r ₀ range of the center Has a distribution very similar to the distribution curve in equation (1), so that the lens has extremely good lens characteristics without cutting the outer periphery thereof, and has a high resolution. It is extremely useful as a required optical transmitter for facsimile and image sensors.

In addition, the method of the present invention is the first to succeed in efficiently manufacturing an optical transmission body by using a multi-layer extrusion method of forming three or more concentric circles of an uncured material.

Hereinafter, the present invention will be described in more detail by way of examples. The measurement of the lens performance and the refractive index distribution in the examples was performed by the following methods.

I. Measurement of lens performance Evaluation device The lens performance was measured using an evaluation device shown in FIG.

The optical transmission body obtained in the preparation example of a sample, the He-Ne laser undulation of light is determined from synchronization (lambda) of the cut to be substantially the length of _^1/4 (λ / ₄₎ passing through Then, the sample was polished using a polishing machine such that both end surfaces of the sample became parallel planes perpendicular to the long axis, to obtain an evaluation sample.

Measuring method A trial evaluation sample (78) is set on a sample stage (76) placed on an optical bench (71) in FIG. 7, and a stop (74) is adjusted to adjust a light source (72). After passing through the condenser lens (73), the diaphragm (74), and the glass plate (75), the light is incident on the entire end surface of the sample, and the position of the sample (78) and the polaroid camera (77) is changed to Polaroid. (Polaroid) The film was adjusted to focus on the film, a square grid image was taken, and the grid distortion was observed. Glass plate (7
For 5), a chrome coating of chromium-plated glass for photomasks was precisely processed into a 0.1 mm square lattice pattern.

II. Measurement of refractive index distribution It was measured by a known method using an Interfaco interference microscope manufactured by Carl Zeiss.

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 Polymethyl methacrylate ([η] = 0.56 in MEK, 25
46 parts by weight, 44 parts by weight of benzyl methacrylate, 10 parts by weight of methyl methacrylate, 0.2 part by weight of 1-hydroxycyclohexyl phenyl ketone and 0.1 part by weight of hydroquinone are kneaded at 70 ° C. to form the first layer (center). Part) Stock solution. 50 parts by weight of polymethyl methacrylate ([η] = 0.41, measured at 25 ° C. in MEK), 50 parts by weight of methyl methacrylate, 0.2 parts by weight of 1-hydroxycyclohexyl phenyl ketone and 0.1 part of hydroquinone 0.1 part by weight
A weight part was heated and kneaded at 70 ° C. to prepare a stock solution for forming a second layer, and polymethyl methacrylate ([η] = 0.34, 25% in MEK)
C) 45 parts by weight, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate 35 parts by weight, methyl methacrylate 20 parts by weight, 1-hydroxycyclohexyl phenyl ketone 0.2 part by weight and hydroquinone 0.1 parts by weight to 70
The mixture heated and kneaded at a temperature of ° C was used as a stock solution for forming a third layer. These three types of stock solutions were attached to the molding apparatus shown in FIG. 6 with a concentric three-layer composite spinning nozzle, arranged in order from the center so that the refractive index of the uncured material became lower, and simultaneously extruded strand fibers. The viscosity of the first layer is 4.
5 × 10 ⁴ poise, the second layer was 2.0 × 10 ⁴ poise, and the stock solution of the third layer was 2.2 × 10 ⁴ poise. The temperature of the composite spinning nozzle was 55 ° C.

Then, each layer of 90 cm in length is passed through the interdiffusion processing section, and then 120 fluorescent lamps of 120 cm in length and 40 W are passed through the center of the light irradiating sections arranged at equal intervals in a circular shape through a strand fiber.
It was picked up by a nip roller at a speed of 50 cm / min. The light transmitting body obtained with the discharge ratio of (first layer) :( second layer) :( third layer) = 1: 1: 1 has a radius (r ₀ ) of 0.50 mm and a refractive index distribution of the central part. (N ₀ ) is 1.512, the peripheral portion is 1.470, and the refractive index distribution constant (g) is 0.52. As shown in FIG. 1, the range of 0.25r ₀ to 0.75r ₀ from the center to the outer surface is approximately ( 1)
It had a refractive index distribution almost consistent with the equation.

Further, the MTF measured by using a grating of 4 lP / mm with both ends of this optical transmission body polished to a lens length of 7.2 mm and 57 lP / mm was 57%,
The conjugate length at this time was 15.4 mm. The image of the obtained lattice was a clear image with little distortion.

Furthermore, an MTF measured using a grating of 4 lP / mm was prepared using the plurality of optical transmitters to form an optical transmitter array having a structure as shown in 41 in FIG. became. Using this optical transmitter array, an image scanner using LEDs as a light source and a CCD as a light receiving element was assembled. This image scanner was able to transmit clear images with high resolution.

Example 2 50 parts by weight of polymethyl methacrylate ([η] = 0.40, measured at 25 ° C. in MEK), 20 parts by weight of methyl methacrylate, benzyl were added to the first layer of the stock solution of the first layer used in Example 1. 30 parts by weight of methacrylate, 0.2 part by weight of 1-hydroxycyclohexyl phenyl ketone and 0.1 part by weight of hydroquinone were heated and kneaded at 65 ° C. to obtain a stock solution for forming a second layer. Also, the stock solution for forming the second layer used in Example 1 was used as the stock solution for the third layer, and polymethyl methacrylate ([η] = 0.40, MEK
Medium, measured at 25 ° C) 50 parts by weight, methyl methacrylate 30
Parts by weight, 20 parts by weight of 2,2,3,3-tetrafluoropropyl methacrylate, 0.2 parts by weight of 1-hydroxycyclohexyl phenyl ketone and 0.1 part by weight of hydroquinone were heated and kneaded at 65 ° C. to obtain a stock solution for forming a fourth layer. The four kinds of stock solutions were simultaneously extruded using a concentric four-layer composite nozzle in the same manner as in Example 1 to obtain strand fibers. The viscosity at the time of extrusion was 4.5 × 10 ⁴ poise for the stock solution of the first layer, 4.0 × 10 ⁴ poise for the stock solution of the second layer, 2.0 × 10 ⁴ poise for the stock solution of the third layer,
The stock solution of the fourth layer was 2.2 × 10 ⁴ poise. The temperature of the composite nozzle was 60 ° C.

Then, it was cured in the same manner as in Example 1 and had a radius (r ₀ ) of 0.48 mm
Was obtained. The discharge ratio is (first layer): (second layer):
(Third layer): (Fourth layer) = 2: 1: 1: 1 The refractive index distribution of the optical transmission medium measured by an interfaco interference microscope was 1.513 at the center (n ₀ ) and 1.513 at the periphery. 1.479, the refractive index distribution constant (g) is 0.53 and 0.2r from the center to the outer peripheral surface.
₀ ～0.8R an approximation in the range of ₀ (1) had the equation Ho Isuzu matched refractive index distribution. The MTF measured using a 4 lP / mm grating was 60% at a lens length of 7.1 mm and a conjugate length of 14.9 mm.
Further, an optical transmitter array was prepared in the same manner as in Example 1 by combining a plurality of the optical transmitters. As a result, the MTF was 53%.
The image scanner using this array was able to transmit a high-resolution image similarly to the image scanner of Example 1.

Example 3 Undiluted solution for forming the first to fourth layers used in Example 2,
Further, the stock solution for forming the fifth layer was used as the stock solution for forming the third layer in Example 1, and the stock solutions from the first layer to the fifth layer were simultaneously extruded using the concentric composite nozzle in the same manner as in Example 1. Strand fiber was used. Thereafter, an optical transmitter having a radius (r ₀ ) of 0.48 mm was obtained in the same manner as in Example 1.

An optical transmission body obtained by setting the discharge ratio to (first layer) :( second layer) :( third layer) :( fourth layer) :( fifth layer) = 3: 1: 1: 1: 2 is used as an interface. The refractive index distribution measured by a faco interference microscope was 1.514 at the center (n ₀ ) and 1.469 at the periphery, and the refractive index distribution constant (g) was 0.57, which was 0.15r ₀ from the center toward the outer peripheral surface.
Refractive index distribution in the range of ～0.85R ₀ is approximately (1) and Ho Isuzu coincides, the MTF lens length 8.0 mm, a conjugate length 15.9mm
Was 65%. Furthermore, the MTF of the optical transmitter array prepared in the same manner as in Example 1 was 60% (measured with a 4 lP / mm grid), and the image scanner was able to transmit a high-resolution image using this array.

Comparative Example 1 60 parts by weight of 2,2,3,3-tetrafluoropropyl methacrylate polymer ([η] = 2.268, measured in MEK at 25 ° C.)
A mixture of 40 parts by weight of methyl methacrylate, 0.1 part by weight of 1-hydroxyhexyl phenyl ketone and 0.1 part by weight of hydroquinone was heated to 80 ° C. and extruded through a kneading section through a nozzle having a diameter of 2.0 mm. At this time, the viscosity of the kneaded composition at the time of extrusion was 1 × 10 ⁴ poise.

Subsequently, the strand fiber obtained by extrusion was
C., and nitrogen gas was passed through a volatilizing section at a flow rate of 10 l / mm over 13 minutes to partially evaporate methyl methacrylate from its surface.
The center part of a 500 W ultra-high pressure mercury lamp was passed through the strand fiber, irradiated with light for about 0.5 minutes, and taken out with a nip roller at a speed of 20 cm / mm.

The radius (r ₀ ) of the obtained optical transmission body was 0.35 mm, the refractive index measured by an interfaco interference microscope was 1.441 at the center (n ₀ ), 1.427 at the periphery, and the refractive index distribution constant ( g) is 0.48, and 0.35 from the center toward the outer surface.
refractive index distribution in the range of r ₀ ~0.5r ₀ was which was consistent with the approximate equation (1). The MTF measured using a 4 lP / mm grating was 23% with a lens length of 6.6 mm and a conjugate length of 13.8 mm, and the combined image of the obtained grating had large distortion.

Further, an optical transmitter array was prepared using a plurality of these optical transmitters in the same manner as in Example 1, and as a result, the MTF (4 lP / mm) was 1
3%. The image scanner using this array had a remarkably low resolution and was unsuitable for image transmission.

Example 4 Polymethyl methacrylate ([η] = 0.45 in MEK, 25
50 parts by weight, 40 parts by weight of methyl methacrylate, 10 parts by weight of phenyl methacrylate, 0.2 parts by weight of 1-hydroxycyclohexyl phenyl ketone, and 0.1 parts by weight of hydroquinone were heated and kneaded at 60 ° C. to obtain an uncured substance.
As a stock solution for forming a layer, polymethyl methacrylate ([η]
= 0.40, MEK, 25 ° C) 48 parts by weight, methyl methacrylate 40
2 parts by weight of a 2,2,3,3-tetrafluoropropyl methacrylate, 12 parts by weight of 1-hydroxycyclohexyl phenyl ketone, and 0.1 part by weight of hydroquinone at 60 ° C. are heated and kneaded at 60 ° C. to prepare a second layer stock solution. 40 parts by weight of polymethyl methacrylate ([η] = 0.34, MEK, 25 ° C.), 40 parts by weight of 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 20 parts by weight of methyl methacrylate , 1
An uncured product obtained by heating and kneading 0.2 part by weight of hydroxycyclohexylphenyl ketone and 0.1 part by weight of hydroquinone at 60 ° C. was used as a third layer forming stock solution, and these stock solutions were simultaneously extruded using a concentric composite nozzle. The viscosity at the time of extrusion at this time was 5.0 × 10 ⁴ poise for the first layer component, 3.5 × 10 ⁴ poise for the second layer component, and 2.4 × 10 ⁴ poise for the third layer component. The temperature of the composite nozzle was 60 ° C.

The discharge ratio is (first layer) :( second layer) :( third layer) = 2: 1:
As in Example 1, the fiber strand subjected to the diffusion treatment in the same manner as in Example 1 was cured to obtain an optical transmitter having r ₀ = 0.52. The refractive index distribution of this optical transmission medium measured by an interfaco interference microscope was 1.495 at the center (n ₀ ) and 1.461 at the periphery, the refractive index distribution constant (g) was 0.41 mm ⁻¹ , and the outer peripheral surface from the center. , The refractive index distribution in the range of 0.18r _{0 to} 0.75r ₀ approximately matches the equation (1), and the MTF is the lens length.
It was 60% at 9.1 mm and conjugate length of 19.8 mm. Furthermore, the MTF of the optical transmitter array prepared in the same manner as in Example 1 was 56% (measured with a grid of 4 line pairs / mm). When this array was incorporated in an image scanner, a high-resolution image was transmitted. We were able to.

Example 5 Using the three kinds of stock solutions used in Example 4, the discharge ratio was set to (first layer) :( second layer) :( third layer) = 2.2: 1: 0.8 in the same manner as in Example 4. After making a fiber strand, it was cured to obtain an optical transmitter having a radius (r ₀ ) of 0.60 mm. The refractive index distribution of this optical transmission medium measured by an interfaco interference microscope was 1.494 at the center and 1.463 at the periphery, and the refractive index distribution constant (g) was 0.34 mm ^-1. 0.
The refractive index distribution in the range of 19r _{0 to} 0.76r ₀ approximately matches the equation (1), and its MTF is 11.3 mm in lens length and 2 in conjugate length.
It was 57% at 2.1 mm. Furthermore, the MTF of the optical transmitter array prepared in the same manner as in Example 1 is 50% (measured with a grid of 4 line pairs / mm). When this array is incorporated in an image scanner, an image with high resolution is transmitted. We were able to.

Comparative Example 2 Using the three kinds of stock solutions prepared in Example 4, the discharge ratio was set to (first layer) :( second layer) :( third layer) = 4.0: 1.0: 3.0. Cured in the same way, radius (r ₀ ) 0.50
mm optical transmission body was obtained. The refractive index distribution of this optical transmission medium measured by an interfaco interference microscope was 1.498 at the center and 1.449 at the periphery, and the refractive index distribution constant (g) was 0.46 mm ^−1.
, And the refractive index distribution in the range of 0.30r ₀ ~0.65r ₀ toward the outer circumference from the center was almost consistent with the approximate equation (1). At this time, the MTF of the optical transmitter is 8.4 mm in lens length, conjugate length
It was 35% at 16.0 mm. Further, the MTF of the optical transmitter array prepared in the same manner as in Example 1 was 30%. When this array was incorporated in an image scanner, the resolution was low and the image was distorted or the edges were blurred.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of measurement of the refractive index distribution of one example of the gradient index optical transmission body of the present invention, and FIG. 2 is the refractive index distribution of a gradient index plastic optical transmission body made by a conventional method. FIG. 3 is a diagram showing an example of a lattice image combined image of these optical transmitters, FIG. 4 is a diagram schematically showing a resolution measuring device of the optical transmitter, and FIG. 5 is a CCD sensor. 5 is a graph of which the resolution was measured by using FIG. FIG. 6 is a schematic view of a manufacturing apparatus which can be preferably used to produce the gradient index plastic optical transmission body of the present invention, and FIG. 7 is a schematic view of a lens performance measuring apparatus.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshihiro Uozu 20-1, Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Masaaki Oda 20-1, Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Inside Rayon Co., Ltd. (72) Inventor Keita Ishimaru 20-1 Miyukicho, Otake City, Hiroshima Pref. Inside Mitsubishi Rayon Co., Ltd. (56) References JP-A-62-25705 (JP, A) Kaisho 64-68702 (JP, A) JP-B 47-28059 (JP, B1) Terutsu Kose "Optical Engineering Handbook", Asakura Shoten, 4th Edition 556-558 (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 6/00, 6/18

Claims (2)

(57) [Claims] 1. A substance having a viscosity of 10 ³ to 10 ⁸ poise in an uncured state, and a cured product obtained by curing the substance has a refractive index n ₁ > n ₁ .
The N uncured liquid materials of n ₂ > n ₃ ... _{N N} (N ≧ 3) are arranged in such a manner that the refractive index decreases gradually from the center toward the outer peripheral surface, and are concentrically laminated. Shaped into a cured fiber strand, while performing the material interdiffusion treatment between adjacent layers so that the refractive index distribution between each layer of the strand fiber becomes a continuous refractive index distribution, or after performing the interdiffusion treatment, A method for producing a graded-index plastic optical transmission body, comprising curing an uncured strand fiber. 2. A graded-index plastic optical transmission body according to claim 1, wherein the uncured liquid material comprises a mixture of polymethyl methacrylate and a radically polymerizable vinyl monomer. Production method.