JPH1058502A - Injection compression molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce warp and strain and, further, prevent flow marks, hesitation marks, etc., by constructing an outer peripheral portion of a movable side separately from an inside portion thereof, controlling an outside core of the movable side mold by a hydraulic cylinder, and making an inside core freely playable to embed elastic members therein. SOLUTION: A core plate 5 at an outer peripheral portion of a movable side mold and a core 7 at an inside portion thereof are provided on the movable side of the mold, and the core 7 is allowed to play, whereby a plurality of elastic members 8 such as springs are embedded between the core 7 and a back plate 9. A resin material is packed into a cavity through a hot runner 2 and a gate 3. At the time of the packing of the resin material, the core 7 is in an advanced state by means of the pressure regulating elastic members 8, and the balance between the injection pressure of the resin and the pressure of the pressure regulating elastic members is temporarily kept, thereby preventing the drooling of the molten resin. At the same time as the packing of the molten resin is finished, the gate 3 is closed to enter a secondary step of clamping a mold, and the molten resin in the cavity is compressed under pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICABILITY The present invention can be used for molding relatively flat molded articles such as refrigerator shelves by injection compression molding.

2. 2. Related Art and Problems Thereof Conventionally, many refrigerator food shelves are made of AS resin, but in recent years, polystyrene resin has been increasingly used as a measure against inexpensive manufacturing. When the PS resin has the same shape as the AS resin, the PS resin is inferior in load strength, causing problems such as cracks, structural changes such as thickening of the product, and ultra high molecular weight. It was necessary to change to a molecular PS resin. In addition, increasing the wall thickness to maintain the product strength increases the product weight and reduces the production cost reduction effect.
The use of 000 / melt flow 0,2) has low fluidity and requires high-speed, high-pressure blasting power, and as a result, there are many molding defects such as burnt bubbles, uneven color, insufficient filling, and the like. Was. As a countermeasure when using a material with low fluidity, the gate diameter is increased, the number of gate points is increased, and the flow cross-sectional area is increased.However, the residual stress around the gate is large and the appearance is poor. . In order to reduce these problems, it has become necessary to anneal the injection molded article. As a method for solving the above problems and the like, an injection compression molding method capable of low pressure molding has been conventionally developed,
Although the shape of the molded product was relatively flat, compression molding was not possible on the entire surface due to the undercut portion and the like on the side surfaces, and the partial compression of a small area did not solve the problem due to insufficient compression capacity. . Also, since the cavity volume including the mold opening before the compression process becomes larger than the final product volume, in the case of a large-sized molded product, the injected resin droops in the direction of gravity, and the filling amount is not sufficient. Uniform compression molding resulted in problems such as the occurrence of burrs, defects in appearance such as flow marks of resin wrinkles from the time of filling to the time of compression, and stable molding conditions could not be set.

3. Object of the present invention An object of the present invention is to provide an injection compression molding method capable of improving design, shape and precision and reducing man-hours, excluding the above-mentioned disadvantages of the prior art.

4. Means for Solving the Problems In the present invention, a hot runner specification is used in order to perform injection filling in a short time and facilitate gate sealing before reaching a glass transition point of the resin.

In order to enhance the injection compression effect, the movable side has an outer peripheral portion (including a slide core) and an inner portion having different structures, thereby enabling a partial compression method in which the inner portion is expanded in area.

In order to equalize the cavity volume during the injection process from injection to compression, the outer peripheral core of the movable mold is controlled by a hydraulic cylinder, the inner core is made to float, and an elastic body inside the floating core to respond to the injection pressure Was buried.

5. EXAMPLE The operation of the molding machine from the closing of the primary mold to the compression step through the injection step will be described with reference to the drawings. The first figure is before the compression step, and the second figure is after the compression step. The operation of the injection molding machine having an injection compression function using the present mold will be described with reference to FIGS.
The mold closing operation starts and several millimeters to several millimeters /
The width opened by an arbitrary thickness (11) of 100 is the width between the core plate (5) and the back plate (9) in FIG. Therefore, there is no gap between the cavity plate (4) and the core plate (5). This gap is due to the operation of the hydraulic cylinder (10) under the control of the molding machine sequence that has received a signal by detecting the primary mold closing position. At that time, the core (7) is also pushed forward by a plurality of elastic members (8) such as springs embedded between the core (7) and the back plate (9), and the volume of the cavity at this time is the same as the final desired cavity volume. . Next, the resin material plasticized by the molding machine (1) passes through the hot runner (2) and reaches the gate (3). Gate (3) at the same time as injection
Is released and the molten resin material is filled into the cavity. At that time, the core (7) is advanced by the pressure adjusting elastic body (8), and the pressure balance between the injection resin pressure and the pressure adjusting elastic body is temporarily maintained. By maintaining this pressure balance, the dripping phenomenon of the molten resin in the direction of gravity is prevented and reduced. When the injection pressure exceeds the repulsion pressure of the pressure regulating elastic body (8), the floating core (7) retreats. The gate (3) is closed at the same time as the filling of the molten resin is completed. The holding pressure step in the ordinary molding step is not required in the present molding method.
When the closing step of the gate (3) is completed, the second mold closing step of the molding machine is started, and the molten resin in the cavity is compressed and compressed. At this time, since the gate (3) has been completely closed, there is no backflow of the molten resin to the injection cylinder side due to pressurization and compression, and the product shape accuracy is determined. When the pressurizing and compressing step is completed, a cooling step is started, and a molded article is obtained through a releasing step.

6. Effect of the Invention As described above, according to the present invention, even for a product having a complicated shape having an undercut portion, it is possible to perform partial injection compression molding in an area close to full compression, and maintain a pressure balance between a floating core and an injection pressure. As a result, the compression pressure is uniformly applied to the surface of the molded product, so that the concentrated residual stress around the gate is reduced. Warpage and distortion were small, the load strength was increased, the amount of deflection was reduced, and a molded article having excellent transparency without flow marks, hesitation marks, etc. was obtained. Since the floating core structure was installed to prevent the molten resin from sagging due to gravity, it was possible to obtain a molded article having a good appearance without resin burrs.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state before injection molding of a molten resin in an injection compression molding die applied as one embodiment of the present invention, and FIG. 2 is a schematic view showing a state after completion of compression molding. Injection molding machine Hot runner Gate Cavity plate Core plate Slide core Core Elastic body for pressure adjustment Back plate ▲ 10 ▼ Hydraulic cylinder ▲ 11 ▼ Dimension of gap for primary mold closing

Claims (1)

[Claims] Replaces AS resin shelves in household electric refrigerator food shelves. Injection molded refrigerator shelves made of transparent polystyrene resin, using runner-less from conventional cold runner molding, warping, distortion, residual stress, etc. An injection compression molding method in which, in addition to the conventional injection compression molding method, in order to reduce molding defects, the resin injected into the cavity has a reduced drooping phenomenon in the direction of gravity.