JPS61248708A - Manufacture of fresnel lense - Google Patents

Abstract

PURPOSE:To permit to obtain large size Fresnel lenses, high in the accuracy of configuration and fine in the roughness of surface, by a method wherein a space between a mold and a base body thin sheet is filled with photopolymer and, thereafter is evacuated to contact the base body thin sheet with the protrusion of the mold closely. CONSTITUTION:An acrylic plate 2 is set on the main body 5 of the mold so as to remain the proper space of several mm between the mold 1 and the acrylic plate 2, then, a valve 3 is opened to fill the space with the photopolymer. Subsequently, the valve 3 is closed and the valve 4 is opened to suck the photopolymer by the force of a vacuum pump 7, then, a part of the photopolymer is discharged to a trap 6 and the acrylic plate 2 is contacted with the protrusion of the mold 1 by the flexible property thereof. Further, when the suction is continued, the photopolymer remains only in the corrugated sections of the mold 1, therefore, the acrylic plate 2 returns to a flat plate and the photopolymer remains in the corrugated sections of the mold 1 when the mold 1 is pushed up under this condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a Fresnel lens having a ring-shaped waveform formed on its surface, which is used for projection television, sunlight concentration, and the like.

[Conventional technology]

Conventional Fresnel lenses have been manufactured using injection molding, in which molten plastic is injected into a mold, or compression molding, in which a plastic plate is heated and pressurized in a mold.

Figures 3 and 4 show the molds used for injection molding.

In the mold, a cavity 10 in the form of a Fresnel lens is provided with a gate 11 and a runner 12 on one side for the plastic to enter.

Since the center of the Fresnel lens is an important transmission path for light rays, the Fresnel lens mold has a gate 1 in this area.
If a gate 1 is provided, the transmission of light rays in this portion will be disturbed, so a gate 11 is usually provided in one example of the cavity 10.

The shot cycle of this injection molding is 1 to 2
Since it only takes about a minute, it has the advantage of high productivity.

In addition, in compression molding, a heater and cooling device are installed inside the mold, and the acrylic cast plate is sandwiched between the upper and lower molds, and the acrylic cast plate is heated and pressurized to transform the surface of the acrylic cast plate into the waveform of a Fresnel lens. Then, the mold is cooled to harden the acrylic cast plate, and then taken out.

[Problem that the invention seeks to solve]

In injection molding, as mentioned above, the gate 11 is provided on one side of the cavity 10, so the plastic cools down from the gate 11 to the opposite side of the cavity 10, resulting in poor fluidity and poor transferability of the mold. It will deteriorate.

In response to this, if the temperature of the plastic is raised, the shrinkage during cooling becomes thicker (therefore, the injection pressure must be increased).

At the same time, alignment distortion occurs due to plastic flow, resulting in birefringence of light, which deteriorates the characteristics of the Fresnel lens.

Furthermore, in order to increase productivity, if a large number of molds are used, such as a two-cavity mold as shown in FIG. 4, a large-sized injection molding machine is required, resulting in high equipment costs.

In view of these points, injection molded Fresnel lenses were only used in toys and other items where the characteristics of Fresnel lenses were not important.

In addition, in compression molding, a Fresnel lens with relatively good properties can be produced by heating and cooling the mold, but the heating and cooling required increases the shot cycle, and it usually takes 30 to 40 minutes for one shot. I need.

At the same time, the mold is severely eroded by heating and pressurizing, and the life of the mold is short, resulting in high disposal costs, resulting in a high cost.

[Purpose of the invention]

An object of the present invention is to provide a manufacturing method that eliminates the above-mentioned drawbacks of the conventional Fresnel lens manufacturing method, and that allows a large Fresnel lens with high shape accuracy and fine surface roughness to be obtained at a low cost. shall be.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides a radiation-curable resin (
The gist of this method is to fill the mold with photopolymer (hereinafter referred to as photopolymer), then suck the photopolymer to bring the base thin plate close to the protrusion of the mold, and then irradiate the mold with radiation to harden the photopolymer.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

■ is a mold with a waveform corresponding to the waveform of a Fresnel lens on its surface; 2 is a flexible acrylic plate that transmits ultraviolet rays; 3 is a valve on the filling side that delivers and closes the photopolymer; 4 is a Suction side valve that suctions photopolymer, 5
6 is a mold body connected to these valves 3 and 4, 6 is a trap in which the photopolymer is stored, and 7 is a vacuum pump.

The acrylic plate 2 is set on the mold body 5 so that there is an appropriate gap of several cranes between the mold 1 and the acrylic plate 2,
Valve 3 is opened to fill this gap with photopolymer.

Next, close valve 3, open valve 4, and vacuum pump 7.
When the photopolymer is sucked with a force of , a part of the photopolymer is discharged into the trap 6, and the acrylic plate 2 approaches the protrusion of the mold 1 with its flexibility as shown in FIG.

Furthermore, if the suction is continued, the photopolymer remains only in the corrugated part of the mold 1, as shown in Figure 2 (bl), so if the mold 1 is pushed up in this state, it will become as shown in Figure 2 (C). The acrylic plate 2 returns to a flat surface, and the photopolymer remains in the corrugations of the mold 1, as shown in FIG.

In this state, ultraviolet rays are irradiated from the top surface of the acrylic plate 2,
When the photopolymer is cured, a Fresnel lens in which the waveform of the cured photopolymer is formed on the surface of the acrylic plate 2 is formed.

This Fresnel lens is peeled off from the mold 1 and taken out, and the outer shape of the acrylic plate 2 is cut into the shape of the Fresnel lens to complete the Fresnel lens.

〔Effect of the invention〕

As described above, the present invention utilizes the fluidity of a photopolymer to form the waveform portion of the Fresnel lens with this photopolymer, so the waveform of the Fresnel lens can be accurately transferred with fine surface roughness. , a high-performance Fresnel lens can be obtained.

Furthermore, since there is no heating or pressure applied to the mold as in the conventional compression molding method, there is little corrosion to the mold, the life of the mold is extended, and the amount of wastage is significantly reduced, resulting in lower costs.

Further, by suctioning and discharging the photopolymer, the base thin plate is brought close enough to contact the mold of the Fresnel lens, so that the thickness of one layer of the photopolymer becomes uniform. Furthermore, since the single layer of photopolymer is only the corrugated portion of the Fresnel lens, there is less distortion after curing compared to methods for manufacturing Fresnel lenses that use other photopolymers. Furthermore, since the gap between the mold and the thin base plate is completely filled with the photopolymer at the beginning, the possibility of air bubbles remaining in the photopolymer layer is extremely low.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view showing an example of the manufacturing equipment used in the present invention, Figures 2 (a), (b), and (C) are explanatory diagrams showing the process, and Figures 3 and 4 are FIG. 2 is a plan view of a conventional indie excisine type. l... Mold, 2... Acrylic plate, 3, 4... Valve, 5... Mold body, 6... Trap, 7... Vacuum pump. Patent applicant Pioneer Corporation Figure 1 Figure 2

Claims (1)

[Claims] A sealed space with a gap is formed between the Fresnel lens mold and a thin base plate that transmits radiation such as ultraviolet rays, and this space is filled with a radiation-curable resin that hardens when irradiated with radiation. A Fresnel device characterized in that the thin base plate is brought close to the protruding part of the mold by suction, and then radiation is irradiated to harden the radiation-cured resin to form a Fresnel lens waveform by the radiation-cured resin on the surface of the thin base plate. How to manufacture lenses.