JPH0153615B2 - - Google Patents

Description

[Detailed description of the invention] When molten resin is injected into a mold cavity at a high injection rate in an injection molding machine, if the air in the mold cavity is not exhausted, it will become high pressure air, which will have an unfavorable effect on the appearance of the molded product. give. For this reason,
BACKGROUND ART Deaerators for discharging air from mold cavities have been invented and devised.

Jitsugoku 48-41333, Jitsubishi 49-18135, Unexamined Japanese Patent Publication 1977 52
-123450, JP-A-56-123841, JP-A-56-139940
describes a mold cavity degassing device.
In injection molding of video disks, particularly optical video disks, a disk made of acrylic or the like is required to have a uniform birefringence. In this case, when the thickness of the disk is injection molded to be thinner than the diameter, it is necessary to mold at a high injection rate. When the filling speed of the molten resin increases, if the air in the mold cavity is not discharged quickly, air will remain in the mold cavity and become high pressure, which will cause residual stress on the outer periphery of the disk and cause fluctuations in the birefringence, which is undesirable. . The mold shown in FIG. 1 was used to mold video disk discs, but the air in the cavity was not sufficiently discharged and a molded product of good quality could not be obtained. Furthermore, due to variations in the thickness of the stamper 9, the degassing gap 101 naturally varies accordingly, and in order to keep the degassing gap constant, which changes every time the stamper is replaced, 3 to 4 expensive stamper holders 100 of different thicknesses are used. I also needed to prepare some.

A conventional device and the present invention will be explained by comparing FIG. 1 and FIG. 2. 1 is a fixed plate fixed to the machine base 2, and 3 is a movable plate that reciprocates along the stay 4. 5 is a heating cylinder having a nozzle 5a fixed to its tip. Reference numeral 6 denotes a ram whose tip end is fixed to the movable platen 4 and inserted into a mold clamping cylinder (not shown). 7 is a stationary side mold fixed to the stationary platen 1. 8 is movable plate 3
The movable mold is fixed to the 9 is the movable side mold 8
It is a stamper installed on the cavity surface of
is a stamper holder fixed to the outer periphery of the stamper 9 with a plurality of bolts. 101 is stamper holder 10
102 is a degassing gap provided between 0 and the surface of the stationary mold 7, and 102 is a degassing passage provided in the split surface of the movable mold. When the molten resin is injected into the mold cavity, the molten resin spreads out from the sprue hole 10 into a circular shape and fills the mold cavity. At this time, the outer circumferential end surface of the disk in the mold cavity becomes R-shaped, and the air on the degassing gap side of the stationary mold 7 is exhausted, but on the other side there is a space formed by the resin, the stamper 9, and the stamper holder 100. Air cannot escape and may be compressed. For this reason, the disk is partially compressed due to the influence of high-pressure air on the outer circumference of the disk, causing an undesirable effect of changing the birefringence index. Therefore, as shown in FIG. 2, when the mold is closed, the present invention creates a degassing gap 12A that communicates with the cavity 20 formed by the sloped wall surface 11A of the stamper holder 11 and the sloped wall surface 7A of the stationary mold 7. , stamper holders 1 facing each other and communicating with the degassing gap 12A.
1 and the outer surface of the stationary mold 7 form a degassing gap 1
2, and a degassing gap e is provided between the stamper holding surface of the stamper holder and the surface of the stamper 9, and the annular inner circumferential surface of the stamper holder 11 and the annular inner circumferential surface communicate with the degassing gap e. A plurality of gap grooves 30 are provided between the outer peripheral surface of the fitting convex portion of the member 8a of the movable mold to which the movable side mold member 8a is fitted.

In this example, the plurality of gap grooves 30 are provided on the member 8a, but they may be provided on the stamper holder 11 side.

Furthermore, a deaeration groove 13 communicating with the gap groove 30 is provided on the contact surface of the member 8a that contacts the bottom surface of the stamper holder 11 via the shim 16, and the outer circumferential surface of the stamper holder 11 communicates with the deaeration groove 13. A gap 14 is provided between the movable mold 8 and the inner circumferential surface of the inner hole 40 of the movable mold 8. As described above, in this example, the outer circumferential surface of the fitting convex portion of the member 8a and the inner circumferential surface of the annular portion of the stamper holder 11 are fitted, and as a result, the member 8a and the movable mold 8 into which the member 8a is fitted are fitted. In contrast, the stamper holder 11 is positioned for centering, but it is of course possible to perform the same centering positioning by fitting the outer periphery of the stamper holder 11 into the inner hole 40 of the movable mold 8. In this case, the above-mentioned gap groove 30 becomes a continuous gap, and the gap 14 becomes a gap groove.

The degassing gap 12 and the gap 14 configured as described above merge and communicate with the degassing passage 15.

Here, the effect of the shim 16 will be explained in detail.

For the stamper 9, which normally has a thickness variation of about 10 μm, by adjusting the shim 16, the degassing gap e can be kept constant, and the change in the gap in the degassing gap 12A can be reduced to the extent that it can be virtually ignored.

That is, if the thickness t (not shown) of the shim 16 is increased, the degassing gap e increases by t, and the degassing gap 12 decreases by that amount, but since the degassing gap 12A is provided at an angle, the change in the gap is This is because it remains at t×sinα.

Here, α is the inclination angle of the inclined wall surface 7A of the stationary mold 7 (same as the inclination angle of the inclined wall surface 11A of the stamper holder 11). With this structure, even if the mold cavity is filled with resin, the present invention makes it possible to exhaust the air from both sides of the circumferential end surface of the resin, and prevents air from accumulating on one side and causing high pressure. I was able to. In addition, the amount of air to be discharged is further increased by 2.
By dividing the air in the direction, the air degassing gap 12A
Even if the deaeration gap e is narrowed, the same amount of air can be exhausted as in the conventional device, so it is possible to prevent molten resin from overflowing from the gap during injection. Furthermore, the structure allows the degassing gap in two directions to be kept constant simply by adjusting the shims 16 to account for variations in the thickness of the stamper 9, so a number of expensive stamper holders are prepared to hold the stamper. There is no longer a need to deal with variations in thickness.

[Brief explanation of drawings]

FIG. 1 is a partially cross-sectional front view of a conventional device, and FIG. 2 is a partially cross-sectional front view of the present invention. 1... Fixed plate, 3... Movable plate, 7... Fixed side mold, 8... Movable side mold, 9... Stamper, 10...
... Sprue hole, 7A ... Slanted wall surface, 11 ... Stamper holder, 11A ... Slanted wall surface, 12 ... Degassing gap, 12A ... Degassing gap, 15 ... Degassing passage, 1
6... Shim, 20... Cavity, e... Degassing gap.

Claims (1)

[Claims] 1. A fixed plate is fixed to the machine base, a movable plate is provided that moves close to and away from the fixed plate, a fixed side mold is fixed to the fixed plate, and a sprue hole connected to the inner hole of the nozzle is provided in the fixed side mold. On the other hand, a movable side mold is fixed to the movable platen, a mold cavity formed by the fixed side mold and the movable side mold is provided, and a stamper 9 is installed on the cavity surface of the movable side mold facing the sprue hole. A stamper holder 11 is provided and fixed to the outer periphery of the stamper 9, and when the mold is closed, a release plate is provided that communicates with the cavity formed by the inclined wall surface 11A of the stamper holder 11 and the inclined wall surface 7A of the stationary mold 7. An air gap 12A is provided, and a deaeration gap 12 is formed by the outer surfaces of the stamper holder 11 and the stationary mold 7, which communicate with the deaeration gap 12A and face each other. A degassing gap e is provided between the bottom surface of the stamper holder 11 and the movable mold, and a shim adjustment means is provided between the bottom surface of the stamper holder 11 and the movable mold to keep the degassing gap e constant. A mold device for an injection molding machine, characterized in that the degassing passage 15 joins the degassing gap 12 and communicates with a degassing passage 15 that opens the merged degassing gap to the outside of the mold.