JPH0530845B2 - - Google Patents

Description

[Detailed description of the invention]

3-1 Industrial Application Field The present invention relates to a method for manufacturing a synthetic resin ball lens having a refractive index distribution in which the refractive index changes in the normal direction from the center of the sphere to the periphery. 3-2 Description of the Prior Art As a lens having a refractive index distribution, a transparent rod-shaped body having a refractive index distribution that decreases in the radial direction approximately in proportion to the square of the distance from the central axis is known. This transparent rod-shaped body has a convex lens effect, and its refractive index distribution is approximated by equation (1). n(r)=n _p (1-1/2Ar ² ) (1) In the formula, n(r) is the refractive index at the distance r from the central axis, n _p is the refractive index at the central axis, and A is the positive Each represents a constant. The light beam propagates in a meandering manner in such a transparent rod-shaped body, and its period L is expressed by equation (2). L=2π/√ (2) Also, as approximated by equation (3), if the transparent rod-like body has a refractive index distribution that increases approximately in proportion to the square of the distance from the central axis, it will act as a concave lens. It becomes an optical transmission body with n(r)=n _p (1+1/2Br ² ) (3) In the formula, n(r) and n _p are the same as above, and B is a positive constant. A method for manufacturing a synthetic resin optical transmission body having such a refractive index distribution is described in Japanese Patent Publication No. 52-5857 and Japanese Patent Application Laid-Open No.
It is described in JP-A No. 51-16394, Japanese Patent Application Laid-open No. 119939-1980, etc. 3-3 Problems to be Solved by the Invention As described above, a cylindrical rod lens having a refractive index distribution in the radial direction is attracting attention as a light condensing and imaging element in the field of optoelectronics. However, if the optical axis of the rod lens is slightly shifted from the optical axis of the optical system, skew rays (stray light) cause large aberrations, which is currently a problem. However, in the case of a spherical lens, since there is no optical axis of such a lens, there is no skew ray due to axis misalignment. A ball lens whose refractive index decreases from the center to the outer circumference in an approximately square law distribution is embedded in a medium with an appropriate refractive index, or a cladding with a uniform refractive index is placed around such a ball lens. If you use the attached one as a condensing element, it is possible to condense light with almost no aberration. However, with the prior art, it is extremely difficult to control the refractive index distribution spherically, and such a spherical lens has not yet been obtained. In order to manufacture a synthetic resin ball lens with a refractive index gradient, it is first necessary to obtain a spherical base material. However, if a polymerized base material is used as the base material, monomers with different refractive indexes will be formed later. In the process of diffusing the metal, it is extremely difficult to diffuse it to the center of the base material. Therefore, as a base material,
Partially polymerized spherical transparent gel particles are used, but even if one attempts to obtain spherical transparent gel particles by bulk polymerization, it is difficult to obtain perfect spheres, and a large number of gel particles are produced at once. Since it is impossible to obtain it stably, it is not suitable for mass production. 3-4 Means for Solving Conventional Problems Suspension polymerization is used as a method for producing spherical transparent gel particles that serve as the base material of a gradient refractive index spherical lens. 3-5 Effects of the invention If suspension polymerization is adopted as a method for producing spherical transparent gel particles, completely spherical gel particles can be obtained, and they can be produced in large quantities at once. Through the subsequent diffusion and heat treatment steps, it is possible to mass-produce a synthetic resin ball lens having a refractive index distribution in which the refractive index changes in the normal direction from the center to the periphery as described above. 3-6 Examples Hereinafter, a method for manufacturing a synthetic resin ball lens according to the present invention will be described based on examples. First, monomers (including monomer mixtures) forming a network polymer (including copolymers) with a refractive index of Na
Ma is placed in a predetermined container together with an initiator, a solvent, and a dispersant at a predetermined temperature T ₁ ℃, time t ₁ and rotation speed r ₁
Suspension polymerization is carried out at (rpm) and partially polymerized to produce a large amount of spherical transparent gel particles at once. At this time, the gel particles are left in an uncompleted polymerized state containing 20 to 90% by weight of a component (reticular polymer) insoluble in the solvent. Since the spherical transparent gel particles produced as described above are dispersed in the polymerization system in a predetermined container, the polymerization system is suction-filtered to separate the transparent gel particles. Next, the separated particles are mixed with a polymer (including a copolymer) having a refractive index Nb different from that of the Na.
The monomer Mb (including a monomer mixture) forming the sphere is added into a container containing Mb, and at a predetermined temperature T ₂ °C and time t ₂ , the monomer Mb is added from the surface of the sphere to the center.
is diffused and polymerized to form a refractive index distribution in the transparent gel particles in which the refractive index changes continuously in the normal direction from the center to the periphery of the sphere. After that, the transparent gel particles after diffusion are mixed with the monomer.
Suction filtration is performed again to separate it from Mb. Then, in order to finally complete the polymerization, the particles are dispersed in water heated to a predetermined temperature T ₃ °C in a predetermined container, and heat treated at a predetermined time t ₃ and rotation speed r ₃ (rpm). Let's do it. All synthetic resin ball lenses obtained in large quantities in this way have a refractive index distribution that changes continuously in the normal direction from the center to the periphery, and this lens has a normal refractive index. Compared to a uniform spherical lens, not only spherical aberration but also comatic aberration is corrected. The monomer Ma that should be the raw material for the transparent gel object as the lens base material in the above example is as follows:
A monomer having two or more types of groups selected from allyl group, acrylic group, methacrylic acid group, and vinyl group can be used. Next, a specific example of monomer Ma will be given. (1) Allyl compounds Diallyl phthalate, diallyl isophthalate,
Diallyl esters such as diallyl terephthalate and diethylene glycol bisallyl carbonate; triallyl esters such as triallyl trimellitate, triallyl phosphate, and triallyl phosphite; unsaturated acid allyl esters such as allyl methacrylate and allyl acrylate. (2) Compound represented by R ₁ −R ₂ −R ₃ R ₁ and R ₃ are both vinyl group, acrylic group,
A compound in which either R ₁ or R ₃ is a vinyl ester group or a methacrylic group;
A compound in which one of the four groups is an acrylic group, a methacrylic group, and a vinyl ester group, and the other is one of the remaining three groups. Here, R ₂ can be selected from the divalent groups shown below. −(CH ₂ CH ₂ O)m−CH ₂ CH ₂ − (m=0 to 20) -( _CH2 )P- (P=3~15) (3) A mixture of the monomers (1) and (2) above, or at least one of the five monovinyl compounds, vinyl esters, acrylic esters, and methacrylic esters and the above (1) or A mixture with the monomer (or mixture thereof) of (2). Further, examples of monomeric Mb include the following. (Four)

A compound represented by the formula, where X is a hydrogen atom or a methyl group,
Y is

【formula】

[Formula] -CH=CH ₂ , -(CH ₂ )lH (l=1-8), i-propyl group, i-butyl group, s-butyl group, t-
butyl group,

【formula】

[Formula] (h=0~2) and -(CH ₂ CH ₂ O)p-CH ₂ CH ₃ (p=1~
6) a group selected from the group consisting of, or -
(CF ₂ ) a-F (a = 1 to 6), -CH ₂ (CF ₂ ) bH
(b=1 to 8), -CH ₂ CH ₂ O・CH ₂ CF ₃ , -
(CH ₂ CH ₂ O)c CF ₂ CF ₂ H (c = 1 to 4), -
CH ₂ CH ₂ O・CH ₂ (CF ₂ )aF (a=1 to 6), -
_CH2 ( _CF2 )dO( _CF2 )lF(d=1~2, l=1
~4) and -Si( _{OC2H5 )3 .} (Five)

Compound represented by [Formula] However, in the formula, R ₄ is -(CH ₂ )f-CH ₃ (f=
0-2), -( _CH2 )gH (g=1-3),

[Formula] and

[Formula] represents a group selected from the group consisting of (h=0-2). (6) A mixture of monomers (4) and (5). Any of the above (1) to (3) as the monomer Ma and (4) to (6) as the monomer Mb can be combined. In addition, in order to adjust the gelation state of the transparent gel object, as mentioned in section (3), a monomer having one unsaturated group is added to the crosslinkable monomer Ma;
A method of adding a chain transfer agent such as CBr ₄ , CCl ₄ or mercaptans, or a method of using both in combination is effective. Next, test examples of the present invention will be explained. Test example 1 DAI (diallyl isophthalate) as monomer Ma
(Na=1.569) 10g, BPO (benzoyl peroxide) 0.30g as an initiator, water 200g as a solvent, and PVA (polyvinyl alcohol) 0.30g as a dispersant.
was added into a flask equipped with a stirrer, and heated at a temperature T ₁ = 80°C and a rotation speed r ₁ = 250 (rpm) for a time t ₁ =
Suspension polymerization was carried out for 6 hours to produce a large amount of partially polymerized spherical transparent gel particles at once. These transparent gel particles consist of 75% by weight of methanol-insoluble components (reticular polymer portion and linear polymer portion) and 25% by weight of methanol-soluble components (monomer and low molecular weight prepolymer portion). Ta. Next, the transparent gel particles produced above are suction-filtered to separate them from the polymerization system, and then the separated particles are heated to _3FMA (methacrylic acid- 2, 2, 2-
trifluoroethyl) (Nb=1.4210) and held for t ₂ =0.5 hours to diffuse 3FMA into the particles and simultaneously polymerize. Thereafter, the particles after diffusion are again filtered by suction in order to separate them from 3FMA. And finally the temperature T ₃ =
Add to 200 g of water in a container heated to 80℃, complete polymerization at rotation speed r ₃ = 250 rpm, time t ₃ = 18 hours, and continue in the normal direction from the center of the sphere to the periphery. A synthetic resin ball lens with a diameter of 2 mm and whose refractive index changes over time was obtained. When the refractive index distribution formed in the obtained ball lens was measured using an interference microscope, it was as shown in FIG. In FIG. 1, the horizontal axis represents the ratio of the distance r to the radius Rp of the sphere, and the vertical axis represents the refractive index at the same point. Test example 2 DAI 5g as monomer Ma, as initiator
Using 0.05 g of BPO and 0.05 g of DBPO (ditertiary butyl peroxide), 200 g of water as a solvent, and 1.5 g of PVA as an aqueous dispersion, the mixture was added into a flask equipped with a stirrer, and the temperature was set at T ₁ = 90°C and the number of revolutions.
Suspension polymerization was carried out at r ₁ =350 rpm for a time t ₁ =3 hours to produce a large amount of partially polymerized spherical transparent gel particles at once. The transparent gel particles consist of 75% by weight of methanol-insoluble components (reticular polymer part and linear polymer part) and 25% by weight of methanol-soluble components (monomer and low molecular weight prepolymer part). Ta. Next, the transparent gel particles produced above were filtered by suction to separate them from the polymerization system, and then the separated particles were added to 3FMA in a container heated to a temperature of T ₂ =70° _C . hold for 100 minutes,
3FMA is diffused into the particles and simultaneously polymerized. Thereafter, the particles are suction filtered again to separate them from 3FMA after diffusion. and finally the temperature
T ₃ = PVA1.5 in a container heated to 90℃
The polymerization was completed at rotation speed r ₃ = 350 rpm time t ₃ = 13 hours, and the refractive index changed continuously in the normal direction from the center to the periphery of the sphere. A synthetic resin ball lens of mmφ was obtained. When the refractive index distribution formed in the obtained ball lens was measured using an interference microscope, it was as shown in FIG. In FIG. 2, the vertical axis indicates the difference between the refractive index n at a distance r/Rp from the center and the refractive index n _p at the center point.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the refractive index distribution within the cross section of a spherical lens obtained by the method of the present invention, and FIG. 2 is a graph showing another example of the refractive index distribution.

Claims (1)

[Claims] 1. Network polymer (including copolymer) with a refractive index of Na
Monomers (including monomer mixtures) forming Pa Ma
A step of partially polymerizing the gel by suspension polymerization to form spherical transparent gel particles. 2 Add the spherical transparent gel particles into a monomer (including a monomer mixture) Mb that forms a polymer (including a copolymer) Pb having a refractive index Nb different from that of the Na, and A step of diffusing monomer Mb toward the center and polymerizing it to form a refractive index distribution in the transparent gel particles in which the refractive index changes continuously from the center to the periphery of the sphere. 3. A method for manufacturing a synthetic resin gradient index ball lens having a refractive index distribution, which includes a step of fixing the refractive index distribution by completing polymerization by heating or the like.