JPH0313975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a synthetic resin flat lens in which a gradient index lens portion is provided in a transparent substrate made of synthetic resin.

A refractive index that has a refractive index distribution that changes in a square approximation in the direction of the optical axis in a transparent substrate with parallel planes, and a refractive index distribution that gradually changes in a square approximation as it moves away from the optical axis within at least one cross section that includes the optical axis. A planar lens is known in which a large number of distributed lens portions are formed at intervals in a line shape or in a matrix shape. In such a flat lens,
The lens portion may be a hemispherical or spherical lens that has the above-mentioned refractive index distribution in all cross sections including the optical axis, or it may be a hemispherical or spherical lens that has a refraction that gradually changes as it moves away from the optical axis within one cross section. It may be a lens that has a refractive index distribution and whose refractive index is constant regardless of the distance from the optical axis in a cross section perpendicular to this, that is, a semi-cylindrical or cylindrical lens.

The above-mentioned plane lenses are used as image transmission elements in various applications such as optical systems of copying machines and facsimile machines, or in optical coupling systems between light sources and optical fibers, or for inserting attenuators or branch circuits between optical fibers. It is useful for peripheral devices for optical communication such as parallel light conversion elements.

When manufacturing a plane lens as described above using a synthetic resin, as shown in Figure 1, a monomer (monomer mixture) that produces a network polymer (including copolymer) Pa with a refractive index of Na is used. A transparent gel-like substrate 10 is made by partially polymerizing Ma (including Ma), and a mask 12 with openings 11 corresponding to the pattern of the lens portion to be formed is applied to the surface of this substrate 10.
A monomer (including a monomer mixture) Mb that produces a polymer (including a copolymer) Pb having a refractive index Nb different from the above-mentioned refractive index Na is diffused and polymerized into the substrate through the lens portion 13. There are known methods of forming . In this case, if Na>Nb, the lens portion 13 formed in the substrate has a concave lens effect,
If Na<Nb, it will have a convex lens effect.

Alternatively, as shown in FIG. 2, a transparent gel-like substrate 14 similar to that described above is made, and a mask 15 is applied only to the lens portion of the substrate surface.
There is also a method of diffusing a monomer from the periphery that polymerizes with the substrate 14 to create a polymer having a refractive index of Nb different from that of Na.

In this case, the lens portion 16 formed in the substrate exhibits a convex lens effect if Na>Nb,
If Na<Nb, it exhibits a concave lens effect.

However, in the conventional method shown in FIGS. 1 and 2 as described above, masks 12 and 15 and gel substrates 10 and 14 provided to prevent the diffusion of monomer Mb are
Unless the adhesion between the mask and the gel substrate is very good, monomeric Mb will enter between the mask and the gel substrate, and the monomeric Mb will diffuse over the entire surface of the gel substrate, resulting in a lens with a refractive index distribution. They often had the problem of not being able to form a body.

The present invention solves the above conventional problems and provides a novel method for manufacturing a synthetic resin flat lens that can avoid the problem of adhesion between a mask and a gel substrate in the conventional example when manufacturing a gradient index flat lens. It is intended to.

By the way, in general, in a multicomponent copolymerization reaction,
If the rate constant of the following growth reaction: Mi ^* +Mj→Mj ^* …(1) is kij, then the reactivity ratio rij of any monomer Mi to monomer Mj is rij≡kii/kij …(2) defined. Similarly, monomer for monomer Mi
The reactivity ratio rji of Mj is defined as rji≡kjj/kji (3). There are X (X-1) reactivity ratios in the X element copolymerization. Furthermore, if the mixing ratio of monomers Mi and Mj is (Mi/Mj) _n , the monomer component composition ratio (Mi/Mj) _p of the copolymer produced at this time is expressed by equation (4). It is known.

(Mi/Mj) _p = (Mi/Mj) _n rij (Mi/Mj) _n +1/(Mi/
Mj) _n +rji…(4) Here, rij(Mi/Mj) _n +1/(Mi/Mj) _n +rji≡Q…(5) If Q>1, equation (6) always holds true. .

(Mi/Mj) _p > (Mi/Mj) _n ...(6) In other words, since the content ratio of Mi component in the copolymer to be produced is always higher than the mixing ratio of Mi in the monomer mixture, it increases with the polymerization time. The mixing ratio of Mi in the remaining monomer mixture gradually decreases, and conversely, the mixing ratio of Mj gradually increases. Therefore, although the content ratio of Mi component in the copolymer formed at the initial stage of polymerization is high,
The amount of copolymer produced at that point increases with the polymerization time.
The content ratio of Mi component decreases. On the contrary, the content ratio of the Mj component in the produced copolymer gradually increases as the polymerization progresses. The copolymer thus obtained is a mixture of copolymers having different compositions.

Also, if Q<1, then (Mi/Mj) _p <(Mi/Mj) _n ...(7) Therefore, contrary to the case of Q>1, the content ratio of Mi component in the copolymer is It is always smaller than the mixing ratio of Mi in the monomer mixture.

If Q = 1, (Mi/Mj) _p = (Mi/Mj) _n ...(8), a copolymer with a composition equal to the monomer mixing ratio is produced, and the copolymer has a composition distribution. Not shown.

The present invention takes advantage of the fact that the composition of a copolymer changes as the polymerization progresses, and by selecting two or more monomers that have different refractive indexes when polymerized as components of the copolymer. , a transparent substrate made of synthetic resin is provided with a refractive index distribution that gradually changes in the optical axis direction and a refractive index distribution that gradually changes as the distance from the optical axis increases within at least one cross section including the optical axis. A method of manufacturing a synthetic resin flat lens provided with a single or multiple gradient index lens portions is provided.

That is, the present invention maintains a mixture of at least two types of monomers (including monomer mixtures) whose homopolymers have different refractive indexes in a predetermined shape, and By applying locally non-uniform copolymerization conditions, only a predetermined portion of the mixture locally forms a copolymer having a monomer component ratio different from the mixing ratio, and then Copolymerization progresses gradually from that part to other parts, so that the content ratio of monomer components gradually changes from the predetermined part to other parts inside the copolymer. The present invention relates to a method for manufacturing a synthetic resin flat lens characterized by having a composition distribution.

In the present invention, first, a mixture of X types (X is at least 2) of monomers M ₁ , M ₂ , . . . , M _X is held in a predetermined shape. Since this mixture is usually a liquid, it is held in a predetermined shape, for example, a plate shape, by pouring the mixture into a mold container having a predetermined inner shape.

Next, copolymerization conditions that are locally nonuniform are applied to the monomer mixture held in a predetermined shape. For example, when copolymerization is carried out by heating, it is necessary to provide a non-uniform temperature distribution inside the mixture by using a heat-insulating mask that partially insulates the mixture, and also to protect it from irradiation with ultraviolet rays, visible light, or radiation. Therefore, when performing copolymerization, non-uniform copolymerization conditions can be created by unevenly distributing these irradiations inside the mixture using a light-shielding mask that partially blocks these irradiations. be done. This non-uniform copolymerization condition locally forms a copolymer in which only a predetermined portion of the mixture contains a specific monomer component in a larger amount than the monomer mixing ratio;
Then, the copolymerization is selected so that the copolymerization proceeds gradually from that part to other parts. When irradiating with ultraviolet rays or visible light, it is preferable to mix a sensitizer into the mixture to an extent that does not significantly reduce transparency for sensitization.

When the part to be copolymerized first includes a part through which the optical axis of the plane lens passes, the copolymer formed earlier contains a monomer that contains more monomer components whose refractive index is higher than that of the homopolymer. If you choose a combination of
The resulting plane lens becomes a convex lens. On the other hand, if a combination of monomers is selected in which the copolymer produced earlier contains more monomer components whose refractive index is lower than that of the homopolymer, the resulting plane lens will be a concave lens. That is, when the refractive index of the respective homopolymers of arbitrary two types of monomers Mi and Mj is Ni and Nj, in the above formula (5), Q>1.1 and Ni>Nj, or Q<1/ 1.1 and Ni <Nj, a convex lens is formed. Also, Q＞
1.1 and Ni<Nj, or Q<1/1.1 and Ni>Nj, a concave lens is formed. When the value of Q is 1/1.1 or more and 1.1 or less, the resulting copolymer shows no compositional distribution at all, or even if it does show a compositional distribution, it is not sufficient. Also, the difference between Ni and Nj is
It is preferably 0.005 or more, because if the difference in refractive index is less than 0.005, it is difficult to obtain a refractive index gradient sufficient to function as a lens.

In addition, if the part to be copolymerized last includes a part through which the optical axis of the plane lens passes, contrary to what was mentioned above, the refractive index of the homopolymer will be smaller as the copolymer is formed earlier in the polymerization. If a combination of monomers is selected so as to contain a large amount of monomer components, the resulting plane lens becomes a convex lens. On the other hand, if the combination of monomers is selected so that the copolymer formed early in the polymerization contains more monomer components with a higher refractive index than the homopolymer, the resulting plane lens will be a concave lens. become. That is, Q>1.1 and Ni<
If Nj or Q<1/1.1 and Ni>Nj, a convex lens is formed, and if Q>1.1 and Ni>Nj or Q<
If 1/1.1 and Ni<Nj, a concave lens is formed.

Next, a case of binary copolymerization in which copolymerization is performed using a monomer mixture consisting of two types of monomers M ₁ and M ₂ will be specifically explained.

In this case, the following four 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 ₂ ^* +M ₁ →M ₁ ^* (〃 k ₂₁ ) M ₂ ^* M ₂ →M ₂ ^* ( 〃 k ₂₂ ) The monomer reaction ratios r ₁₂ and r ₂₁ are defined by equation (9).

r ₁₂ ≡k ₁₁ /k ₁₂ r ₂₁ ≡k ₂₂ /k ₂₁ (9) Also, Q is expressed by equation (10).

Q≡{r ₁₂ (M ₁ /M ₂ ) _n + 1} / {(Mi / Mi) _n + r ₂₁ }...
(10) Here, (M ₁ >M ₂ ) _n is the mixing molar ratio of monomer M ₁ and monomer M ₂ .

At this time, if Q>1.1 or Q<1/1.1, a desired composition distribution will be formed in the copolymer. Therefore, when performing copolymerization from a location including the part where the optical axis of the plane lens passes, Q > 1.1 and N ₁ > N ₂
(N ₁ and N ₂ are the refractive indexes of the homopolymers of monomers M ₁ and M _2, respectively), or a combination of monomers such that Q < 1/1.1 and N ₁ < N ₂ is used to form a convex lens. is formed, and if Q>1.1 and N ₁ <N ₂ or Q<1/1.1 and N ₁ >N ₂ , a concave lens is formed. Further, when copolymerization is performed from a part other than the part including the optical axis, a concave lens is formed if Q>1.1 and N ₁ <N ₂ or Q<1/1.1 and N ₁ >N ₂ , Q>
1.1 and N ₁ >N ₂ or Q<1/1.1 and N ₁ <N ₂ , a concave lens is formed. Here |N ₁ −N ₂
| is preferably 0.005 or more.

In ternary copolymerization, in which copolymerization is carried out using a monomer mixture consisting of three types of monomers M ₁ , M ₂ and M ₃ , 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 ^* (rate constant 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 ^* (〃 h ₃₃ ) The monomer reactivity ratio is defined by equation (11).

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 …( 10) Also, Q can be expressed by the following three equations.

Q ₁ ≡{r ₁₂ (M ₁ /M ₂ ) _n + 1} / {(M ₁ /M ₂ ) _n + r ₂₁ } Q ₂ ≡ {r ₂₃ (M ₂ /M ₃ ) _n + 1} / 1 {(M ₂ /M ₃ ) _n + r ₃₂ } Q ₃ ≡ {r ₁₃ (M ₁ /M ₃ ) _n + 1} / {(M ₁ /M ₃ ) _n + r ₃₁ }...
(12) Here, (M ₁ /M ₂ ) _n , (M ₂ /M ₃ ) _n and (M ₁ /M ₃ ) _n are the mixing molar ratios, respectively.

If Q ₁ , Q ₂ , and Q ₃ expressed by formula (12) are all larger than 1.1, the content ratio of M ₁ component becomes larger in the early stage of polymerization, and the content ratio of M ₂ and M ₃ components increases sequentially. A compositional distribution is formed. If Q ₁ , Q ₂ , and Q ₃ are all smaller than 1/1.1, a composition distribution will be formed in which the content ratio of M ₃ component is higher in the early stages of polymerization, and the content ratio of M ₂ and M ₁ components increases sequentially. be done. When copolymerizing from the part through which the optical axis of the plane lens passes, Q ₁ , Q ₂ , Q(3)C > 1.1 and N ₁ > N ₂ > N ₃
(N ₁ , N ₂ , N ₃ are the refractive indices of homopolymers of monomers M ₁ , M ₂ , M ₃ respectively), or Q ₁ , Q ₂ , Q ₃ <1/1.1 and N ₁ <N ₂ A convex lens is formed using a monomer combination such that <N ₃ and Q ₁ , Q ₂ , Q ₃ > 1.1
If N ₁ <N ₂ <N ₃ or Q ₁ , Q ₂ , Q ₃ <1/1.1 and N ₁ >N ₂ >N ₃ , a concave lens is formed. In addition, if the area where the copolymerization is performed first does not include the area through which the optical axis passes, Q ₁ , Q ₂ , Q ₃ >1.1 and N ₁
If <N ₂ < N ₃ or Q ₁ , Q ₂ , Q ₃ <1/1.1 and N ₁ > N ₂ > N ₃ , a convex lens is formed, and Q ₁ , Q ₂ ,
Q ₃ > 1.1 and N ₁ > N ₂ > N ₃ or Q ₁ , Q ₂ , Q ₃ <
If 1/1.1 and N ₁ <N ₂ <N ₃ , a concave lens is formed. Here, |N ₁ −N ₂ |, |N ₂ −N ₃ | are both
It is preferably 0.005 or more.

Similar conditions hold true for quaternary or higher copolymers.

Any monomer that can be used in the present invention can be used as long as it produces a transparent polymer, and includes not only a monomer that produces a linear polymer but also a monomer that produces a network polymer. Any monomer may be used as long as it satisfies the above-mentioned conditions. For example, acrylic esters such as methyl acrylate, ethyl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, trifluoroethyl methacrylate, benzyl methacrylate, and -1,1,3-trihydroperfluoropropyl methacrylate. Methacrylic acid esters such as methacrylic anhydride; ethylene dimethacrylate; vinyl benzoate, vinyl 0-chlorobenzoate, vinyl p-chlorobenzoate, divinyl phthalate, divinyl isophthalate, divinyl terephthalate, vinyl naphthoate , vinyl naphthoate, vinyl acetate,
Vinyl carboxylates such as vinyl phenyl acetate; diallyl esters such as diallyl phthalate, diallyl isophthalate, diallyl terephthalate, diethylene glycol bisallyl carbonate; triallyl esters such as triallyl trimellidate, triallyl phosphate, triallyl phosphite, allyl methacrylate , unsaturated acid allyl esters such as allyl acrylate; acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl chloride, butadiene, and mixtures thereof. The above-mentioned conditions may be satisfied by appropriately combining these monomers.

Next, the present invention will be explained in more detail with reference to the drawings.

First, a predetermined amount of monomers M ₁ , M ₂ , ... _M
dissolve. The obtained solution of the monomer mixture is sealed in, for example, a flat transparent cell 20 as shown in FIG. 3A. Next, the cell 20 is irradiated with ultraviolet light through the photomask 21. As will be described in detail later, the photomask 21 has a predetermined pattern formed by a transparent portion 22 that transmits ultraviolet rays and a light shielding portion 23 that blocks ultraviolet rays.

The monomer mixture 24 in the cell 20 irradiated with ultraviolet light through the photomask 21 is exposed to the photomask 2
Polymerization starts from the exposed portion 25 corresponding to the transparent portion of No. 1. At this time, the ease of copolymerization of monomers is
M ₁ >M ₂ >... _M When the value of Q expressed by the above formula (5) is larger than 1.1, first the monomer M ₁ is mainly polymerized, and thereby the monomer M ₁ of mixture
content decreases. As the polymerization further progresses, from the exposed part 25 to the deep part of the cell 20 and the unexposed part 26
Copolymers are formed radially toward the surface.
At the same time, the resulting copolymer sequentially contains monomers M ₁ ,
A composition distribution is formed in which M ₂ , . . . M _X are the main components.

Ease of copolymerization of monomers is M ₁ <M ₂ <...
When Q<1/1.1 in M _X , the relationship is opposite to that described above.

For example, when manufacturing a flat lens in which a large number of hemispherical lens parts are arranged in a substrate, the photomask is a photomask 21 having a circular transparent part 22 as shown in FIG. 4A, or a photomask 21 having a circular transparent part 22 as shown in FIG.
A photomask 21 having a circular light-shielding portion 23 as shown in the figure can be used.

When using a photomask as shown in FIG. 4A, a hemispherical lens portion is formed whose optical axis passes through the center of the exposed portion where the copolymer is first produced. Therefore, by choosing a combination of monomers in which the easier the monomers are to copolymerize, the higher the refractive index of the homopolymer is, and the more difficult the monomers are to copolymerize, the lower the refractive index of the homopolymer, a convex lens can be formed. , in the opposite case a concave lens is formed. In this case, the diameter of the lens portion to be formed is wider than the diameter R of the exposed portion 25, that is, the transparent portion 22 of the photomask, so the diameter R is made smaller than the diameter of the lens portion to be formed.

When using the photomask shown in FIG. 4B, a substantially hemispherical lens portion whose optical axis passes through the center of the non-exposed portion 26 is formed. In this case, if you select a combination of monomers in which the easier the monomer is to copolymerize, the lower the refractive index of the homopolymer, and the more difficult the monomer is to copolymerize, the higher the refractive index of the homopolymer, the convex lens will be created. is formed, and in the opposite case a concave lens is formed. The diameter of the obtained lens portion is approximately equal to the diameter R of the non-exposed portion 26, that is, the light-shielding portion 23 of the photomask.

Further, when making a semi-cylindrical lens, it is preferable to use a photomask having a slit-shaped transparent portion as shown in FIG.

After copolymerizing the monomer mixture as described above to form a lens portion having a refractive index distribution in which the refractive index changes from the center to the periphery, the polymerization is completed as necessary. Heat treatment may be added for this purpose.

Examples of the present invention will be described below.

Example 1 Diethylene glycol bis(allyl carbonate) (CR-39) and benzyl methacrylate (BzMA) were mixed at a ratio of 9:1 by weight, and 3% by weight of benzoyl peroxide and 4% by weight were added to the mixture. After adding % of benzophenone, it was sealed in the cell. The fetish mask shown in FIG. 4A was used, and the diameter R of the transparent part was 1.0 mm. This was irradiated with ultraviolet rays from an ultra-high pressure mercury lamp through a photomask for 24 hours, and then left at 80°C for 15 hours. After the block consisting of the CR-39/BzMA copolymer that had been completely polymerized was taken out from the cell, the surface was polished. In this block, convex lenses with a diameter of about 4 mm were arranged in a 5 x 5 matrix.

Example 2 Diallylisophthalate (DAIP) and 1,1,
After mixing 3-trihydroperfluoropropyl methacrylate (4FMA) in a ratio of 9:1 by weight and adding 3% by weight of benzoyl peroxide and 4% by weight of benzophenone to the mixture, this was enclosed within the cell. A photomask with an radius of 4.0 mm as shown in FIG. 4B was used. This was irradiated with ultraviolet rays from an ultra-high pressure mercury lamp through a photomask for 29 hours, and then left at 80°C for 15 hours. Polymerization is completed
After the block made of DAIP/4FMA copolymer was removed from the cell, the surface was polished. In this block, convex lenses with a diameter of about 4 mm were arranged in a 5 x 5 matrix.

Example 3 Three types of monomers, methyl methacrylate (MMA), acrylonitrile (AN), and vinyl benzoate (VB), were mixed in a ratio of 6:1:3 by weight, and 3% by weight was added to the mixture. % of benzoyl peroxide was added and then sealed into the cell. A photomask with an radius of 2.0 mm as shown in FIG. 4B was used. This was irradiated with ultraviolet rays from an ultra-high pressure mercury lamp through a photomask for 30 hours, and then left at 80°C for 15 hours.
After the block made of the MMA/AN/VB ternary copolymer that had been completely polymerized was taken out from the cell, the surface was polished. In this block, convex lenses with a diameter of about 2 mm were arranged in a 5 x 5 matrix.

Example 4 Three types of monomers, methyl methacrylate (MMA), vinyl benzoate (VB), and vinyl phenyl acetate (VPA), were mixed in a ratio of 6:2:2 by weight.
Mix in a ratio of 3 to that mixture.
% by weight of benzoyl peroxide was added.
This was sealed in a cell and covered with a photomask as shown in FIG. The width of the transparent part of this photomask is 200 μm, and the width of the light-blocking part is 1 mm. This was irradiated with ultraviolet rays from an ultrasonic mercury lamp through a photomask for 35 hours, and then left at 80°C for 16 hours. After the completed block of MMA/VB/VPA ternary copolymer was removed from the cell, the surface was polished. This block has a width of
It was a lenticular lens plate with ten 110μm semi-cylindrical lenses lined up.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing conventional examples of the method for manufacturing synthetic resin optical circuits, and FIG.
3C is a series of sectional views showing the method of manufacturing a synthetic resin optical circuit according to the present invention, and FIG. 4A,
FIGS. 4B and 5 are plan views of photomasks that can be used in the present invention, respectively. In the symbols used in the drawings, 20... transparent cell, 21... photomask, 22... transparent portion, 23... light shielding portion, 24... monomer mixture.

Claims (1)

[Claims] 1. A refractive index distribution that gradually changes in the optical axis direction in a transparent substrate made of synthetic resin, and a refractive index that gradually changes as the distance from the optical axis increases within at least one cross section that includes the optical axis. A method for manufacturing a synthetic resin flat lens provided with a single or a plurality of gradient index lens portions each having a gradient index, the homopolymer comprising at least two monomers whose refractive indexes differ from each other. By holding a mixture of monomers (including a monomer mixture) in a predetermined shape and applying locally non-uniform copolymerization conditions to the predetermined shape of the mixture, first A copolymer is formed by locally forming a copolymer having a monomer component ratio different from the above-mentioned mixing ratio only in a predetermined portion of A method for manufacturing a synthetic resin flat lens, characterized in that the composition distribution is such that the content ratio of monomer components gradually changes from the predetermined portion to the other portion within the lens. 2 A mixture of two or more monomers shall consist of X monomers, and any two or more monomers constituting this mixture
The monomer reaction ratio in the copolymerization reaction of seed monomers Mi and Mj is expressed as rij and rji, respectively, and the monomer
When the mixing molar ratio of Mi and Mj is expressed as (Mi/Mj) _n , the formula; {rij (Mi/Mj) _n +1}/{(Mi/Mj) _n +rji}≡Q (1≦i≦X, 1≦j≦X, i≠j, i, j, and X are all natural numbers) is larger than 1.1 or smaller than 1/1.1. How to manufacture lenses.