JPH0628884B2 - Molding method for plastic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field In recent years, injection molding of plastics has come to be used for manufacturing lenses and substrates for optical disks, which require strict shape accuracy in the submicron unit. The present invention relates to a plastic molding method capable of improving the shape accuracy of these molded products.

Conventional technology Conventionally, as the precision molded product becomes, the mold is tightened with high pressure, and then the molten resin is injected from the injection nozzle section.
A molding method that gives a molded product that is as faithful to the mold shape as possible by applying a high pressure called a holding pressure that does not open the mold immediately after the mold is filled with resin Met. In this case, the holding pressure is set to be equal to or lower than the mold clamping pressure and molding is performed under the condition that the mold is not opened. Therefore, in this method, the closer the specific volume of the resin present in the mold in the molten state is to the specific volume in the room temperature state, the more locally the localized portion of the "sinker" that occurs during cooling occurs in the commonly called molded product. No shrinkage marks occur.

Problems to be Solved by the Invention However, 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. In many cases, this resulted in a very large molding system.

Means for Solving the Problems According to the present invention, an idea which is completely opposite to the conventional example is formed, and a portion where the rigidity is remarkably lowered is intentionally formed in a certain portion of the molding machine. The tie bar of the machine loses the high pressure immediately before the completion of the injection process, and the tie bar extends by the amount predicted in advance based on the relationship between the volume shrinkage rate of the plastic material to be molded and the mold volume, and the mold can be opened slightly. Specifically, in consideration of the length and thickness of the tie bar, or the elastic modulus of the material, the method is one in which the elastic deformation recovery force of the tie bar is applied while cooling the molded product in the thickness direction. In other words, in other words, when the injection process is completed under the condition that high-pressure energy at high pressure during injection molding is stored in the form of tie bar expansion, and when the gate seal is completed, the cooling of the molded product progresses as the molded product progresses. This is a plastic precision molding method characterized in that the elastic deformation recovery force of a tie bar extending in the thickness direction is applied.

Action The method of the present invention is a kind of injection compression molding method, and is characterized in that, in order to apply the mechanical deformation of the tie bar as a compression force, the shrinkage amount that occurs when the molten resin in the mold is cooled The immediate response is to start the compression operation, so that a molded product very faithful to the mold can be obtained.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a state immediately before injection is completed after mold clamping is completed when molding an optical disk substrate that requires particularly precise molding among plastics. That is, the movable plate 3 is formed by the motor 1 and the spiral screw 2.
The mold is clamped, the clearance between the fixed mold 5 and the movable mold 4 becomes zero, and the mold cavity 7 is formed by tightly adhering. This state corresponds to the stage of low-pressure mold clamping called in normal injection molding, but the feature of this molding machine is that the motor 1 and the spiral screw 2 that are the movable plate drive mechanism have sufficient rigidity, All the pressure applied to the movable plate 3 is absorbed as the extension of the tie bar 8. The total length of the tie bar at this time is Lo
And After that, the injection nozzle 9 advances, the resin is injected into the mold cavity 7, and the state where the secondary injection pressure is applied is shown in FIG.

FIG. 2 shows a state in which the moving side mold 4 and the fixed side mold 5 are slightly opened by ΔL due to the secondary injection pressure acting inside the cavity. That is, the amount of energy stored in the form of tie bar expansion is stored in the amount that the mold is opened by ΔL due to the secondary injection pressure. Thereafter, as the gate seal is completed and the cooling of the molded disc progresses, the elastic deformation recovery force of the tie bar 8 extending in the thickness direction of the disc acts to act on the movable mold 4 and the fixed mold 5. Clearance is reduced. In other words, after the gate seal, the compression operation is started without inserting the hair, so that the molding can be performed extremely faithfully to the mold.

EFFECTS OF THE INVENTION As described above, the present invention is effective for molding, such as an optical disk substrate and a holographic lens, in which a molded product is thin and has a large projected area, and the transfer accuracy of the mold surface is strongly required. In order to realize this injection compression molding, the tie bar of the injection molding machine loses the high pressure immediately before the completion of the injection process and is predicted in advance from the relationship between the volume shrinkage amount of the plastic material to be molded and the mold volume. Designed so that the tie bar can be extended by a certain amount and the mold can be opened slightly. That is, in the present invention, considering the length, thickness, or the elastic modulus of the material of the tie bar, a method of molding while applying the elastic deformation recovery force of the tie bar in the thickness direction when the molded product is cooled, and a method for performing the method. The present invention relates to an injection molding machine, which is characterized in that a molded product extremely faithful to a mold is obtained.

[Brief description of drawings]

FIG. 1 is a front view showing a state where the molding machine is clamped immediately before injecting the resin, and FIG. 2 is a diagram showing a state in which after the mold is clamped, a high-pressure resin is injected into the cavity and loses the injection pressure to slightly open the cavity. It is a front view which shows the opened state. 1 ... Motor, 2 ... Spiral screw for mold clamping, 3
…… Movable plate, 4 …… Movable mold, 5 …… Fixed mold, 6
…… Front fixing plate, 7 …… Mold cavity, 8 …… Tie bar, 9 …… Injection nozzle, 10 …… Rear fixing plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoshio Nakatani Yoshio Nakatani 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-56-131060 (JP, A) JP-A-50-67362 (JP, A) JP-A-62-207612 (JP, A)

Claims (2)

[Claims] 1. A step of injecting high-pressure energy at the time of injection molding under the condition of being accumulated in the form of tie bar elongation, and at the time of completion of gate sealing, cooling of the molded article progresses and the thickness direction of the molded article progresses. And a step of applying elastic deformation recovery force of the tie bar stretched to the outside. 2. The tie bar of an injection molding machine loses the high pressure immediately before the completion of the injection process, and the tie bar is expanded by an amount predicted in advance from the relationship between the volumetric shrinkage ratio of the plastic material to be molded and the mold volume. The length of the tie bar, the thickness, and the elastic modulus of the material are determined so that the mold can be opened slightly, and the elastic deformation recovery force of the tie bar acts in the thickness direction when the molded product is cooled. A method for molding plastic according to item (1).