JPS615913A - Mold assembly of discoid recording medium base - Google Patents

Abstract

PURPOSE:To obtain a mold assembly capable of forming a resin discoid plate poor in residual strain and suitable for an optical disk by giving a very thin clearance around a mold cavity and deforming the very thin clearance so that it becomes smaller by the mold clamping pressure within the elastic limit of mold material. CONSTITUTION:Discoid cavities 4 are formed along the divided surfaces 3 on the movable mold 1 and on the fixed mold 2 and a very thin clearance 9 in a disk form is formed along the divided surface 3 on the whole outer circumferences of this discoid cavity 4. These molds are made deformable so that the discoid very thin clearance 9 is made smaller within the elastic limit. Resin pressure sensors 14, 15 are provided on the cavity surface. In the mold clamping stage the mold clamping pressure is made so low that resin does not leak from between the divided surfaces. When the resin pressure in the cavity has taken a specified value, the resin injecting pressure is reduced, the resin is cooled, hardened and mold clamping pressure is reduced, the resin is cooled, hardened and the mold clamping force is enlarged to give uniform push force to the resin in the cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molding apparatus that combines a mold for molding disk-shaped recording medium substrates such as video disks and an injection molding machine.

A disc-shaped recording medium (hereinafter referred to as a medium) substrate is an extremely high-quality, ultra-precision molded product that requires not only excellent optical properties but also high dimensional accuracy. In particular, the birefringence (phase difference) of the substrate is a very important characteristic for the quality of the medium, and is required to have a small value overall and to have very little difference between different parts of the medium.

In addition, the dimensions must be highly accurate in terms of usage conditions, optical characteristics, etc., and must have little change over time.

A factor that greatly affects these characteristics is the tendency of residual strain during the engraving process, and the need to reduce residual strain.

The present invention is a molding device invented to obtain a high-quality media substrate by operating just-in-time electrically and mechanically related to both the mold structure and the injection molding machine in order to reduce this residual strain. be.

The feature of the present invention is that the mold clamping force is lower than the final pressure applied in advance in the mold clamping stage, and the mold is small enough to prevent the mold from opening due to the injection pressure of the resin injected into the cavity. After pressurizing with clamping force, resin is injected into the cavity, and at the same time the resin pressure reaches a preset pressure value by the action of a resin pressure sensor installed in the cavity or the passage through which the resin passes. Decrease the injection pressure and injection speed of the molding machine.

At the same time, as the resin cools and solidifies, the mold clamping force is increased and pressure is reapplied to the final predetermined mold clamping force, and the molding machine is operated so that a uniform pressing force is applied to the entire area of the cavity.

In addition, in order to compensate for the volumetric contraction that occurs when the resin cools and solidifies inside the cavity, an extremely thin disc-shaped gap is created along the outer periphery of the cavity so that it can easily change within the elastic deformation limit of the mold material. This is a molding device characterized by using a mold provided therein.

Fig. 4 shows an outline of the most commonly used device in the past, which is a disk-shaped device that molds a media substrate between the opposing dividing surfaces 3 of a movable mold 1 and a fixed mold 2. Cavity 4
A mold is constructed from a sprue 5 which is directly connected to the nozzle 6 of the plasticizing cylinder 8 from the center thereof, and the movable mold 1 is used to open and close the mold and apply pressure. It is fastened and fixed to a mold clamping ram 11 that fits into and slides on the hydraulic cylinder 10 of an attached molding machine, and operates in accordance with the movement of the ram 11 of the molding machine, that is, opens and closes the mold with the dividing surface 3 as a border. The structure is such that

After the movable mold 1 clamps the stationary mold 2 under high pressure by the advancement of the ram 11 of the molding machine, the plasticizing cylinder 8
The plasticized and molten resin is injected as the screw 7 moves forward.

The injected resin passes through the nozzle 6 and sprue 5, is injected and filled into the cavity 4, and is then cooled and solidified to form a media substrate.

Describing in detail the process in which the resin filled in the cavity cools and solidifies, after the cavity 4 is completely filled, cooling and solidification begins, and as the volume shrinks, it is necessary to replenish the resin. Even after the resin is completely filled, the injection pressure is maintained and resin replenishment continues.

In this case, the injection pressure applied to the media substrate is due to the fact that the outer periphery of the media substrate is a distance from the sprue 5, the thickness of the media substrate itself is thin, and the resin in contact with the mold surface of the cavity 4 is cooled during the filling process. This results in a skin layer with high viscosity, which causes a phenomenon in which the transmission of injection pressure is extremely reduced.

When such an extreme pressure drop occurs, it is necessary to set a high injection pressure in advance to account for the rounding, which appears as defects in appearance and dimensions, and the pressure drop.

When a high injection pressure is set, the inner circumference near the sprue 5 has a smaller pressure drop than the outer circumference, so an unnecessary excess injection pressure is applied to the outer circumference, which is more than the pressure necessary to compensate for the volumetric contraction. Since the wall thickness is larger than that of the main body, large stress and strain remain.

This strain not only causes deformation of the medium substrate, but also causes deterioration of birefringence, and also causes deformation over time.

In order to solve these drawbacks, the method according to the present invention can be said to be revolutionary and excellent.

The present invention will be explained in detail below.

1 to 3 relate to the present invention, and FIG. 1 schematically shows the mold structure and the mold clamping mechanism of the molding machine.

FIG. 2A shows a state W4 of the mating portion of the fixed side and movable side of the mold just before the mold is closed, and FIG. 2B shows the state where resin is injected in the first mold clamping.

FIG. 2C shows the state when the mold is pressurized with the second mold clamping force, that is, the final mold clamping force.

Figure 3 is an outline of the relationship between the movement (operation) and time of the mold clamping mechanism and injection mechanism in the molding process, the relationship between mold clamping pressure and injection pressure and time, and the mutual relationship with the resin pressure in the mold. The movements of the mold clamping mechanism and injection mechanism are shown in solid lines.
The mold clamping pressure and injection pressure are shown by dotted lines, and the resin pressure inside the mold is shown by a dashed line.

The general structure of the mold according to the present invention is shown in FIG.
Compared to the commonly used mold structure shown in FIG. A pressure sensing bottle 5 communicating with the pressure sensor 4 is provided.

The other structure is roughly the same as that in FIG. 4.

The gap Ps9 is provided so as to be located between the through-mold dividing surface 3 and the cavity 4 shown in FIG. 2A, and communicates with the cavity 4, and the detection bin 15 is provided so as to be a part of the cavity.

That is, it is provided so that it directly contacts the injected resin 16 and the resin pressure is transmitted to the resin pressure sensor 14 via the detection bottle 15.

The molding process involves a ram 11 to which the movable mold 1 is fastened and fixed.
moves forward (FIG. 3A), and the movable mold 1 and the stationary mold 2 are brought together along the mold dividing surface 3 to perform primary mold clamping (FIG. 3B).

In this case, the clamping force on the mold is maintained at a low pressure (FIG. 3C) in which the mold is not opened at the dividing surface 3 due to the pressure of the injected resin.

When this pressure (Fig. 3 c) K mold clamping force is reached, the injection screw gourd-7 moves forward (Fig. 3 H) and the resin u-screw z-7, which has been heated and melted in advance in the plasticizing cylinder 8, is moved forward (Fig. 3 H). As shown in Fig. 2B, the injected resin passes through the nozzle 6, the crow 7', and the hole 5 and is injected into the cavity 4. The gap 9 is also filled to some extent.

When the injected resin 16 fills the cavity 4, the resin pressure within the cavity 4 gradually increases (FIG. 3D).

The rising resin pressure (FIG. 3D) is transmitted to the resin pressure sensor 14 through the detection bottle 15.

The transmitted resin pressure is set to a preset pressure (third
When reaching the pressure point (Fig. 3E), an electrical signal is sent from the resin pressure sensor 4 to the operation control circuit of the molding machine, and the movement of the screw 7 is stopped (Fig. 3F). At the same time, the injection pressure decreases (Fig. 3F).
Start Figure G).

Coupled with the start of this pressure drop (Fig. 3 G), the mold clamping ram 11 moves forward to re-pressurize (Fig. 3 H), and the L mold clamping pressure begins to rise again (Fig. 3 J), reaching the final predetermined level. The pressure increases to (K in Figure 3) and the second mold clamping (K and L in Figure 3) occurs.

At this point, as shown in FIG.
Due to the increase in mold clamping pressure, the mold material undergoes elastic deformation and the first
The distance y of the gap 9 at the time of the next mold clamping is narrowed to the distance y', that is, close to zero j, by the second mold clamping.

At this time, the resin 16Vi filled in the gap 9 is cooled by the sides 12 and 13 of the mold, and is cooled and solidified.

This phenomenon occurs because the size of the gap 7 is very small, so it cools and solidifies faster than other parts, and the resin 16 filled in the cavity 4 flows out outside the cavity 4 along the outer periphery of the medium and becomes dry. prevent.

When the second mold clamping is performed, the resin 16 filled in the cavity 41C is heated to a preset resin pressure (Fig. 3E) after injection injection.
), the injection pressure (Fig. 3 M) decreases (Fig. 3 M).
Since the injection pressure is not maintained by the conventional method, there is no need to apply injection pressure to the filled resin 16 over a long period of time to cool and solidify it, and it is almost unnecessary. Cooling and solidification begins in a state close to the pressure, but at the same time as the injection pressure shifts to (G in Figure 3), the mold clamping force gradually increases (J in Figure 3) to correspond to the cooling and solidification of the resin 16. Since the method of This results in the replenishment of

Therefore, a surface medium substrate with good appearance can be obtained, and at the same time, a second
The pressure increase when moving to the next mold clamping (Fig. 3 J) means that a uniform pressurizing force is applied to the entire area of the medium, so there is less distortion on the outer periphery and more distortion on the inner periphery as in the conventional method. It is possible to obtain a media substrate that is homogeneous on both the outer and inner peripheries without producing a non-uniform media substrate, and the pressurizing force at the time of secondary mold clamping (Fig. 3 K)
#: This is a rational and innovative invention because it allows selection of a wide range of arbitrary conditions to satisfy the appearance, birefringence, etc. of the medium.

In addition, in order to prevent the deformation of the parts 3 and 9 that cause elastic deformation in the mold structure from affecting the cavity 4, the cavity 4 is formed separately from the movable mold 1 and the fixed mold 2 to be formed. It is also possible to adopt a nesting method.

In addition, in order to obtain precision molded products such as media substrates using the mold according to the present invention, the mold must be integrated with an injection molding machine that has a mechanism that satisfies the requirements described above. .

When molded using the molding apparatus according to the present invention, a molded product with almost no molding distortion and stable birefringence was obtained, and a medium substrate of unprecedented high quality was obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a mold clamping mechanism of a molding machine according to the present invention.゛ Fig. 2A is a diagram showing the mold structure of the present invention. FIG. 2B is a diagram showing the state immediately after the resin is injected and filled into the mold. tJS2C is a diagram showing the state when the mold is pressurized with the final mold clamping pressure. Figure 3 schematically shows the relationship between the movement of the mold clamping mechanism and the injection mechanism and time in the molding process, the relationship between mold clamping pressure and injection pressure and time, and the mutual relationship with the resin pressure in the mold. It is a line diagram. FIG. 4 is a diagram showing a conventional mold clamping mechanism. In Figures 1.2A, 2B, 2C and 4, each number indicates the following. 1: Movable side mold 2: Fixed side mold 5; Sprue 6: Nozzle 7; Screw 8 Niji ring - 9: Ultra-thin gap 14; Resin pressure sensor] 5: Pressure detection bin In Figure 3, the solid line indicates mold clamping It shows the movement of the mechanism and injection mechanism. The dotted lines indicate clamping pressure and injection pressure. The dashed line indicates the resin pressure within the mold.

Claims (3)

[Claims] (1) In a mold for molding a disc-shaped recording medium substrate made of thermoplastic resin, a disc-shaped part along the entire outer circumference of the mold cavity, along the mold dividing surface and communicating with the mold cavity. This mold has an ultra-thin gap and can be deformed by clamping pressure so that the disk-shaped ultra-thin gap becomes smaller within the elastic limit of the mold material.The resin pressure sensor is installed on the mold cavity surface or when the resin is injected. A mold for forming a disk-shaped recording medium substrate is provided at an appropriate position on the path. (2) An injection molding machine used to perform molding using the amount of gold as claimed in claim (1), which adjusts the resin injection pressure based on a signal from a resin pressure sensor installed on the mold cavity surface or resin injection path A disc-shaped recording medium substrate molding apparatus characterized by comprising a mechanism that interlocks mold clamping pressure, resin injection speed, and mold clamping speed. (3) In claims (1) and (2), the mold clamping pressure is set so that the mold dividing surface does not open due to the resin pressure injected into the mold cavity, and the resin injection is completed. A disk-shaped recording medium substrate molding apparatus designed to reduce post-injection pressure and simultaneously increase mold clamping pressure at a set speed to a final predetermined pressure.