JPH0469218A - Molding die for lens with uneven surface - Google Patents

Abstract

PURPOSE:To prevent a change in the shape of a molded product without application of an excessive force during a mold-parting process by providing an annular gap through which a gas for thrusting a molded product formed in a cavity, is blown out of the cavity between inserted pieces. CONSTITUTION:One mold 2 which finishes the uneven surface of a lens is constituted by an inserted piece 22 arranged coaxially. Next, an annular gap 24 through which a gas for thrusting out a lens molded by a cavity 23 is blown out of the cavity, is provided between the inserted pieces 22a, 22b. After that, the lens part of a molded product is parted from a mold by pressure of the gas. Thus it is possible to prevent a change in the shape during a mold-parting process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a mold for molding a lens having an uneven surface, such as a Fresnel lens.

(Prior Art) A Fresnel lens used as a condensing lens for a general nitrogen head projector is as shown in Fig. 2.
The front side of the planar back surface (1) has an uneven surface (3) consisting of a plurality of concentric step inclined surfaces (2) with fine pitches.
), and is formed in a structure that condenses light incident from the back surface (1) onto a single point on the front surface. Such Fresnel lenses are used not only as condensing lenses for overhead projectors, but also in infrared sensor lenses, camera lenses, and the like.

Conventionally, this Fresnel lens has good workability, so
It is mainly molded from plastic, and molding methods include injection molding, heat compression, and casting.

FIG. 3 shows an example of an injection mold.

This mold has a pair of molds consisting of a fixed mold (4) and a movable mold (5), and the movable mold ( 5) Formed on the side. Also, on the movable mold (5) side, the peripheral part of the molded product molded in the cavity (7) is pressed,
A plurality of ejector turbines (8) are provided for ejecting the molded article from the cavity (7). (9) is an ejector plate for integrally driving the plurality of ejector turbines (8).

Molding of Fresnel lens with this mold is fixed type (4)
The sprue (10) provided on this sprue (lO)
The cavity (7) is filled with molten resin through the gate (11) communicating with the molded product, and after cooling to a predetermined temperature, an ejector turbine (8) is pressed against the periphery of the molded product. 7) It is done by protruding from. FIG. 4 is a diagram of the molded product, in which (12) is the Fresnel lens part and (13) is the trace of the ejector turbine.

However, when a Fresnel lens is molded using the above method,
The bottom surface (6) of the cavity (7) on the side of the movable mold (5) has an uneven surface consisting of a sloped surface with concentric steps, and the height of the peaks of the unevenness is approximately 0.001 to B+a+s. The molded product bites into the surface, and it is necessary to press the peripheral part of the molded product with a fairly strong pressing force to push it out. Moreover, since the mold is released at a considerably high temperature during production, there is a problem in that the molded product warps and the shape of the Fresnel lens is impaired.

Such problems also occur in hot compression and casting processes other than injection molding.

(Problems to be Solved by the Invention) As described above, conventional Fresnel lenses made of plastic have been molded by molding methods such as injection molding, hot compression, and casting. However, when molding is performed using the above method, the conventional molding mold has a structure in which the ejector turbine is pressed against the periphery of the molded product molded in the cavity to protrude, so the uneven surface on the bottom of the cavity on the movable mold side In order to eject the molded product that has been bitten into the mold by the pressure of the ejector turbine, a fairly strong pressing force is required.Moreover, during production, the mold is released at a fairly high temperature, which causes the molded product to warp and cause Fresnel. There is a problem that the shape of the lens is damaged.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to construct a molding die that can release a lens having an uneven surface without damaging its shape.

[Structure of the Invention] (Means for Solving the Problems) In a mold for molding a lens having an uneven surface, one of a pair of molds constituting a cavity for molding a lens having an uneven surface. One of the molds for molding the uneven surface of the lens is composed of a plurality of concentric inserts, and between the plurality of inserts, the molded product formed in the cavity is blown out from the cavity. A gap was created.

(Function) As described above, one of the molds for molding the uneven surface of the lens is composed of a plurality of concentric inserts, and between the inserts, a gas is blown to protrude the lens molded in the cavity from the cavity. When an annular gap is provided, the lens portion of the molded product is pressed with gas and released from the mold, thereby preventing the shape from changing when the molded product is released.

(Example) Hereinafter, the present invention will be described based on an example with reference to the drawings.

FIG. 1 shows an injection mold for a Fresnel lens, which is one embodiment of the invention. This mold has a pair of molds consisting of a fixed mold (20) and a movable mold (21), and in particular, the movable mold (21) has two concentric optical inserts <22a),
(22b), and the central optical insert (22a) is formed into a cylindrical shape. Then, the two optical inserts (22a) and (22b) are placed on the mold mating surface of the fixed mold (20) and the movable mold (21) consisting of these two optical inserts (22a) and (22b). A cavity (23) is formed on the side thereof, the bottom surface of which is an uneven surface consisting of a concentric stepped inclined surface. The center of this cavity (23) coincides with the centrally located optical insert (22a). Furthermore, the boundaries of the two optical inserts (22a) and (22b) coincide with the boundary between the peaks and valleys at the bottom intermediate portion of the cavity (23), that is, the stepped portion of the stepped slope. The two optical nests (22a) and (22b
), there is an annular gap of approximately 2 to 20 μm (
24), and is formed in a structure capable of blowing out the gas supplied through the gas supply hole (25) formed in the optical insert (22b) toward the cavity (23). Further, the fixed mold (20) is connected to the cavity (23) through a gate (27) formed on the mold matching surface.
) is provided with a sprue (28) for filling with molten resin.

Molten resin is molded by this mold into the cavity (23) through a sprue (28) provided on the fixed mold (20) and a gate (27) communicating with this sprue (28). Fill and mold, open the mold after cooling to a predetermined temperature, and then open the gas supply hole (25).
This is carried out by supplying pressurized gas to the gap (24) between the two optical inserts (22a) and (22b) through the gas, and the pressure of the gas causes the molded product to be ejected from the cavity (23).

Therefore, like the above mold, the movable mold (21) is composed of two optical inserts (22a) and (22b), and the boundary between the two optical inserts (22a) and (22b) is the cavity. (23) so as to match the boundary between the peaks and valleys of the bottom intermediate part, and the two optical inserts (2
2a).

(22b) is provided with an annular gap (24) of about 2 to 20 μ- in size, and the molded product is moved into the cavity (23) by the pressure of the pressurized gas supplied to this gap (24).
When configured to protrude from the molded product, the Fresnel lens part of the molded product is directly pressed and released from the mold, so there is no need to apply excessive force to the molded product, unlike ejection using a conventional ejector turbine, and this prevents warpage. A Fresnel lens with a predetermined shape without any cracks can be obtained. Moreover, the gap (24) between the two optical inserts (22a) and (22b) is 2
~20 μm, and the position of the gap (24) was made to coincide with the boundary between the peaks and valleys at the bottom of the cavity (23), so that no trace of the gap (24) was left on the Fresnel lens to be molded. There's nothing left. Therefore, by applying this mold to injection molding with excellent mass productivity, a desired Fresnel lens can be easily molded.

In the above embodiment, the movable mold is divided into two optical nests, but the movable mold may be composed of two or more concentric optical nests,
A gap may be provided between each of the optical inserts, and the molded product may be released from the mold by gas supplied to each of the gaps.

Furthermore, although the above embodiments have been described with respect to injection molding molds, this Fresnel lens molding mold can also be applied to heating compression molds and casting molds.

Further, in the above embodiment, a mold for molding a Fresnel lens was described, but the present invention can also be applied to molding other lenses having an uneven surface, such as a lens having a diffraction grating.

[Effects of the invention] Among a pair of molds forming a cavity for molding a lens whose one surface is an uneven surface, one mold for molding the uneven surface of the lens is composed of a plurality of concentric nests. However, if an annular gap is provided between the plurality of inserts from which gas is blown out to protrude the molded product formed in the cavity, the lens part of the molded product can be pressed with gas and released from the mold. Unlike ejection using a conventional ejector turbine, this method does not apply excessive force to the molded product, prevents shape changes during mold release, and allows lenses with the desired uneven surface to be easily molded. .

[Brief explanation of drawings]

FIG. 1 shows the structure of an injection mold for a Fresnel lens according to an embodiment of the present invention, and FIGS. 2(a) and (
b) is a plan view showing the shape of a Fresnel lens and its cross-sectional view, FIG. 3 is a view showing the configuration of a conventional injection mold for a Fresnel lens, and FIG. 4 is a plan view showing the molded product. It is. 20...Fixed type, 21...Movable type, 22a
, 22b... optical insert, 23... cavity,
24...gap, 27...gate, 28
... Sprue agent Patent attorney Norio Ogo

Claims (1)

[Claims] It has a pair of molds forming a cavity for molding a lens whose one surface has an uneven surface, and one mold for molding the uneven surface of the lens is composed of a plurality of concentric inserts, and 1. A mold for molding a lens having an uneven surface, characterized in that an annular gap is provided between a plurality of inserts, through which gas blows out the molded product molded in the cavity from the cavity.