JPH0357442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a gradient index lens array in which gradient index plastic lenses are arranged in one or more rows.

Recently, in copiers, a refractive index gradient rod lens called a self-occurring lens, which has a parabolic refractive index distribution axially symmetrical from the center, has been used as an optical element to form a projected image on a photoreceptor. Copying machines using gradient index lens arrays arranged in one or more rows have become commercially available. [Reference 1: "Optics" Vol. 10 No. 2 (April 1981)
), pp. 111-117] However, the gradient index lens arrays currently on the market all use glass rod lenses, which are relatively difficult to manufacture and therefore expensive. It has the disadvantage of becoming boring.

In order to solve these drawbacks, an inexpensive gradient index lens array using plastic rod lenses has been considered.

Several methods are already known for forming a refractive index distribution on a plastic lens, one example of which is described in Reference 2 (Appl. Phys.
Lett. Vol. 23, No. 5, pages 247-248).

In this method, diallyl isophthalate, which is a monomer that becomes a polymer with a high refractive index by polymerization (hereinafter referred to as a high refractive index monomer), is first filled into a tube of a predetermined shape, and then half-polymerized to form a gel. A rod is made, and then this rod is immersed in methyl methacrylate, which is a monomer that becomes a low refractive index polymer by polymerization (hereinafter referred to as a low refractive index monomer), and the low refractive index monomer is added to the gel rod. It copolymerizes while permeating and diffusing. As a result, the diffusion concentration of the low refractive index monomer becomes lower from the outer periphery toward the center of the rod, so that an axially symmetrical refractive index distribution is formed.

The manufacturing method for such graded index plastic lenses is called a two-step copolymerization method, and in addition to the high refractive index and low refractive index monomers mentioned above, diallyl phthalate and diethylene glycol bis are used as high refractive index monomers. It is known that a similar refractive index distribution can be formed using a divinyl monomer such as allyl carbonate or a vinyl monomer such as butyl methacrylate or methyl acrylate as a low refractive index monomer. [Refer to Document 3: "Optics" Vol. 10, No. 2 (April 1981), pp. 105-110] Conventionally, the gradient index rod lens produced in this way was cut to a predetermined length. After polishing and grinding the surface, a predetermined number of lenses are arranged in one or more rows and fixed with resin, adhesive, etc. to obtain a gradient index lens array.

However, such conventional manufacturing methods require (1) cutting the rod lens to a predetermined length;
The surface of each book was polished and ground, which required a huge amount of man-hours.

(2) Resin, adhesive, etc. are required to fix each rod lens.

For this reason, the production cost increased and the price was not as low as expected.

In order to solve these drawbacks, the present inventor previously proposed in Japanese Patent Application No. 56-81364 that a gel rod made by semi-polymerizing a high refractive index monomer was placed in a predetermined device, and the gel rod was placed inside the container. By filling the rod with a low refractive index monomer and polymerizing and solidifying it, the low refractive index monomer is diffused into the gel-like rod to form a refractive index distribution, and each rod is bonded and solidified by the low refractive index monomer. We proposed a method for manufacturing lenses.

This makes it possible to provide an extremely inexpensive gradient index lens array, but since no special measures are taken to block light between each rod, a small amount of light leaks from each rod to the adjacent rods, impairing image formation. It had the disadvantage of being distorted.

An object of the present invention is to provide a lens manufacturing method that can realize an inexpensive gradient index lens array that solves these drawbacks.

In order to achieve the above object, the lens manufacturing method of the present invention is a lens manufacturing method for manufacturing a gradient index lens array in which gradient index plastic lenses are arranged in one or more rows.
By arranging and storing a predetermined number of semi-polymerized rods of high refractive index monomers in a predetermined device, and filling the device with low refractive index monomers and polymerizing and solidifying them, the low refractive index monomers can be added to the rods. The method is characterized in that the rods are bonded and fixed together while being diffused.

As described in Document 3, a divinyl monomer such as diallyl isophthalate can be used as a high refractive index monomer, and a vinyl monomer such as methyl methacrylate can be used as a low refractive index monomer. As the black pigment, it is preferable to use activated carbon or a black pigment made of an inorganic substance insoluble in the low refractive index monomer so that it is attached only to the surface without diffusing into the rod.

Moreover, as described in Document 2, a polymerization initiator such as benzoyl peroxide can also be used if necessary.

The present invention will be described in detail below based on Examples.

Example 1 A monomer solution was prepared by dissolving 4% by weight of benzoyl peroxide in commercially available diallyl isophthalate. This monomer solution was filled into a polyethylene tube with an inner diameter of 3 mm, placed in a constant temperature bath, and polymerized at 80° C. for 90 minutes.

Thereafter, the semi-polymerized rod was taken out from the polyethylene tube and cut into a length of 4 cm. This 4cm
The five rods cut into strips were arranged and stored in a device as shown in FIG.

The spacer 2 in this case was made of silicone rubber with a thickness of 3 mm, and the substrate 1 had a Teflon plate on one side and a glass substrate on the other side. Next, these Teflon plates and glass substrates were joined to the spacer 2, and methyl methacrylate containing and dispersing 10% by weight of activated carbon as a low refractive index monomer was filled from the injection port 3.

The device was placed in a constant temperature bath at 80° C. and allowed to react for 2 hours while being careful not to generate air bubbles while looking through the glass substrate.

After the reaction, the device was disassembled, the polymerized and solidified lens array was taken out, cut into 3.5 cm lengths, and the surface was polished.

Thereafter, when the end face of each rod was inspected, it was confirmed that there was no evidence that the activated carbon had penetrated into the inside of the rod, and that it was only attached to the surface of the rod.

The results of the optical characteristics of the lens array thus obtained and the single lens constituting the lens array are as follows.

[Characteristics of lens array]

Number of lines: 5 Length: 3.5cm Resolution: 6-7 lines/mm [Single lens characteristics] Diameter: 3mm N ₀ (center refractive index): 1.570 A (refractive index gradient constant): 0.0153mm ^{- 2} Δn (difference in refractive index between the center and the outer periphery): 0.027 Period: 51.1mm In addition, a lens array consisting of five single lenses mentioned above is applied from one end surface of the lens array to a document consisting of five characters. 5 of the manuscript at a distance of A
The letters and the end surfaces of the five single lenses arranged in the array were arranged so as to face each other, and a projected image of the original consisting of five letters was formed at a position separated by a distance A from the other end surface of the lens array. However, an erect, same-size image with almost the same shape as the five characters on the original was obtained.

As described above, the performance of the above-mentioned lens array was equivalent to that of a conventional gradient index lens array using glass rod lenses that are commercially available.

Furthermore, the bonding strength due to methyl methacrylate was also sufficient.

As described above, according to the present invention, there is no need for resin or adhesive to join each rod as in the past, and the rods can be cut while being joined.
Since only polishing is required, the number of man-hours can be greatly reduced compared to conventional methods, and an extremely low-cost gradient index lens array can be realized.

Further, by a simple method of incorporating a black dye into a low refractive index monomer, it is possible to realize a high-performance lens array that does not leak light from each rod.

It goes without saying that the present invention is not limited to the examples, and that similar effects can be obtained by using other monomers. Furthermore, the diameter of the rods is not limited to the embodiments, and it is also possible to produce a lens array consisting of rod lenses with extremely small diameters, which could not be achieved by the conventional method of polishing one rod at a time.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an apparatus used for manufacturing a lens in an example of the present invention. 1...Substrate, 2...Spacer, 3...Injection port,
4...Rod in a semi-polymerized state.

Claims (1)

[Claims] 1 1 graded index plastic lens
In a lens manufacturing method that creates a gradient index lens array arranged in a row or multiple rows, a predetermined number of half-polymerized high refractive index monomer rods are arranged and housed in a predetermined device, and a low By filling the low refractive index monomer containing a refractive index monomer and an insoluble black pigment and polymerizing and solidifying it, the low refractive index monomer is diffused into the rod and the black pigment is attached around the rod. and, at the same time, bonding and fixing the rods.