JPH0628885B2 - Injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field Recently, plastic injection molding has come to be made such as lenses and optical disk substrates that require strict shape accuracy in submicron units.

The present invention relates to an injection molding machine capable of injection compression operation that can improve the shape accuracy of these molded products.

Conventional technology In the past, as precision molded products became more precise, the mold was clamped with high pressure, the molten resin was injected from the injection nozzle, and immediately after the mold was filled with molten resin, A general molding method is to apply a high pressure called a holding pressure that does not open the mold to obtain a molded product that is as faithful to the mold shape as possible. In this case, it is necessary to set the holding pressure below the mold clamping pressure and perform molding under the condition that the mold does not open.

Therefore, in this method, as the injection volume is increased and the specific volume of the resin existing in the molten state in the molten state is brought closer to the specific volume in the room temperature state, the shrinkage rate that occurs during cooling becomes smaller and the molding is closer to the mold shape. Is possible.

The problem to be solved by the invention is that in order to actually achieve this condition, the mold and the molding machine must have high rigidity so as not to be mechanically distorted and deformed. It often resulted in a large molding system.

Means for Solving the Problems According to the present invention, since the idea is completely opposite to the conventional example, a member having a small rigidity and elastically deforming with a relatively small stress is used in a certain intended portion of the molding machine. Specifically, the tie bar of the injection molding machine is designed to stretch when it loses the injection pressure.The mold is opened during the injection process, and after the injection is completed, the tie bar expands and the tie bar recovers immediately. The molten resin in the mold is compressed to obtain a molded product that is as faithful as possible to the mold.

Action With such a structure, it becomes possible to give a bending point to the stress-strain curve representing the relationship between the elongation and the stress of the tie bar, and the optimum stress for injection compression molding can be generated.

Embodiment One embodiment of the present invention will be described in detail below with reference to the drawings.

Here, the behavior of the tie bar during each step of injection molding will be described step by step.

Conventional injection molding machines have three to four tie bars, and in practice it was difficult to mount the die plates perfectly parallel so that all tie bars had exactly the same stretch during primary die clamping.

However, if a tie bar having a two-step elastic modulus is used as in the present invention, the primary mold clamping is performed in the region of a where the tie bar having a small elastic modulus extends along the stress-strain line in FIG. For this reason, even if the four tie bars have different elongations at the time of mold clamping, the compression pressures do not differ so much if the stress difference, in other words, a relatively uniform pressure can be generated for all four tie bars. As a result, the mold can be clamped by applying relatively uniform pressure to the four corners of the die plate.

Next, at the stage when the mold is filled with resin and the mold loses this injection stress and opens, the stress and strain of the tie bar are both
Entering the region shown by b in the figure, it becomes possible to store a large stress this time even with a small elongation.

That is, the energy of elongation stored in the tie bar having a large elastic modulus works as a compressive force of the cavity from the time when the injection is completed.

This compressive force acts without inserting hair after the injection process is completed, and ideally the compressive force acts on the resin in the cavity while reducing the displacement, in other words, the pressure along with the compression stroke by the amount determined by the elastic modulus of the tie bar. Compression molding is achieved.

Next, an example in which the injection molding machine having the configuration of the present invention is applied to molding an optical disk substrate will be described.

Generally, the parallelism of the die plate of the molding machine can not be expected so much, and it is general that the parallelism of several tens of microns is misaligned no matter how much the adjustment is made. Therefore, when trying to perform the compression operation after the injection is completed by extending the tie bars, all four tie bars extend the same length, and the elastic recovery causes the same amount of compression force to act on the four corners of the tie bar. If you do not do so, it is not possible to compress the mold while always keeping the mold parallel.

In the present invention, in consideration of this point, the tie bar portion 8 of the injection molding machine shown in the conceptual view of FIG. 1 has a double structure as shown in FIG.

First, the primary mold clamping is performed before injection. In this case, the pressure is generated by the hydraulic cylinder 1 actuating and the hollow tie bar 12 with a small elastic modulus, whose both ends are fixed to the fixed plates 10 and 6, respectively, extending by Δ1 _1. Let From this point, the free end 13 of the tie bar 11 having a large elastic modulus comes into contact with the compression operation starting point adjuster 14 this time. That is, the high pressure generated in the cavity 16 by the injection unit 15 at the stage of shifting to the injection process is divided into the tie bar 11 having a large elastic modulus and the tie bar having a small elastic modulus.
The book will receive it, and the apparent elastic modulus will increase.

Further, the inflection point of this elastic modulus can be freely set by adjusting the gap Δ1 ₁ by the compression operation start point adjuster 14 attached to the fixed platen 10.

Next, the behavior of the tie bar when actually forming an optical disk substrate having a diameter of 130 cm and a thickness of 1.2 mm will be mainly described.

The tie bar 12 uses a tie bar that extends 100 microns under a load of 10 tons, and the first mold clamping is performed at 3 tons.

At this time, the compression operation start point adjuster 14 of the four tie bars attached to the molding machine is set so that Δ1 ₁ becomes zero. Subsequently, a molten polycarbonate resin at 320 ° C. is injected from the nozzle portion at a pressure of 240 kg / cm ² to open the mold by 30 microns.

FIG. 4 shows a state in which the movable side mold 4 and the fixed side mold 5 are opened by ΔL (30 μm in the embodiment) due to the secondary pressure of injection.

In other words, in this state, the injection energy is stored in the form of expansion of the tie bars 11 and 12.

After that, as the gate sealing is completed and the cooling of the disk molded in the cavity progresses, a compressive force acts between the moving mold 4 and the fixed mold 5 without inserting hair, and ideal molding is performed. To be achieved.

As a result, the birefringence of an optical disc having a spiral groove with a groove width of 0.8 μm and a groove depth of 0.01 μm is 12 nm or less in the recording area of the disc, and the groove depth is 0.098 to 0.099 from the inner circumference to the outer circumference. It was possible to mold a disc substrate with micron and very good transferability.

As described above, the most characteristic feature of the present invention is that
The present invention relates to an injection molding machine characterized by having a tie bar in which the apparent elastic modulus of elasticity rapidly changes to a large elastic modulus after a certain strain amount is exceeded.

Therefore, even if the parallelism of the die plate and the mold is a little poor, it is possible to apply a compressive force to the cavity while maintaining the parallelism of the cavity, and accuracy of the submicron unit is required like optical disks and lenses. Precision molding is also possible.

Further, since the elastic modulus of the tie bar and its inflection point can be freely set, even if the molded product has a different thickness or a required shrinkage amount, it is possible to select the elastic modulus and the thickness of the tie bar 11 as desired. It can handle compression force and mold opening amount. Therefore, the injection molding machine having the structure of the present invention has a very simple structure,
Since a complicated and expensive hydraulic control circuit for mold clamping is not required, reliable and always stable molding is possible.

Also, the members forming the molding machine are not limited to steel materials,
For example, for the hollow tie bar 12, it is possible to use a plastic pipe having a small elastic modulus and self-lubricating property.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram of an injection molding machine, FIG. 2 is a configuration diagram showing details of a tie bar structure, FIG. 3 is a graph showing a relationship between elongation and stress of the tie bar, and FIG. 4 is It is a block diagram which shows the state which the mold opened slightly by the secondary pressure of injection. 1 ... compression motor, 2 ... spiral screw for mold clamping, 3 ... movable die plate, 4 ... moving die, 5 ...
… Fixed side mold, 6 …… Front die plate, 7… Mold cavities, 8… Tie bar, 9… Injection nozzle, 10…
… Rear fixed plate, 11 …… Tie bar with large elastic modulus, 12 ……
Tie bar with small elastic modulus, 13 …… Free end of tie bar, 14
...... Compressor start point adjuster.

Front page continuation (72) Inventor Akio Ito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-50-67362 (JP, A) JP-A-56-131060 (JP, A)

Claims (1)

[Claims] 1. An injection molding machine characterized by having a tie bar in which the apparent elastic modulus of elasticity suddenly changes to a large elastic modulus when a certain strain amount is exceeded.