JPH04327919A - Injection molding method for thick walled product - Google Patents

Abstract

PURPOSE:To injection mold a thick walled product without the generation of sink marks in a short molding cycle. CONSTITUTION:A cavity unit 1 is constituted by molds 2 and 3 and a clamping component 6 for clamping the mold opening sections of molds 2 and 3. The cavity unit 1 is set in a molding machine, and molten resin is injected in the state of being mold clamped by the molding machine. After that, the cavity unit 1 is released from the molding machine in the state that the clamping component 6 is clamped, and the resin is cooled and solidified. The mold is deflected by the expansion force of the resin in a cavity 4, and as the resin is solidified while compensating the shrinkage of resin following cooling by means of elastic recovery force of the mold, sink marks can be controlled, and as injection is carried out by setting another cavity unit after releasing the cavity unit 1, the molding cycle can be shortened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection molding thick-walled products, which allows high-precision thick-walled products to be molded in a short cycle.

0002

2. Description of the Related Art When injection molding a thick-walled product such as a plastic lens, cooling is required to prevent sink mark deformation, resulting in a long molding cycle. As a method for solving this problem, the injection molding method described in Japanese Patent Application Laid-Open No. 64-36421 is known. This injection molding method uses a U-shaped mold clamping member to clamp the cavity unit, heats the clamped cavity unit above the glass transition temperature, injects the molten resin, closes the gate, and then heats the cavity unit. The mold is gradually cooled to the deformation temperature, and then, while the mold clamp of the cavity unit is self-retained, it is released from the mold clamping mechanism of the molding machine and allowed to cool independently.

0003

[Problems to be Solved by the Invention] However, in the conventional injection molding method, the mold clamping member must be held so that the mold does not open against the pressure of the resin injected into the cavity. A clamping force is required, which increases the size of the entire cavity unit including the mold clamping member, which hinders the original function of shortening the molding cycle. In other words, in the conventional injection molding method, the cavity unit is once isolated from the mold clamping mechanism of the molding machine during the cooling process.
The purpose is to shorten the molding cycle by setting and injecting another cavity unit in the meantime, and if the cavity unit becomes large, it may be necessary to move, replace, or
This is because not only does the device become bulky for attaching and detaching, but also the temperature control ability deteriorates, impairing the quality of the molded product.

The present invention was made in view of these problems, and not only can the cavity unit be made smaller and lighter, but also the entire molding process from injection to completion of cooling can be simplified by compensating for the sinkage. An object of the present invention is to provide an injection molding method for thick-walled products that can mold a molded product of better quality than the usual molding method in which the mold is molded in a state where the mold is clamped by a machine.

[0005]

[Means for Solving the Problems] The injection molding method for thick-walled products of the present invention includes a pair of molds forming a cavity, and a method for opening the molds by removably engaging the outer edge of the molds. A cavity unit is formed by a fastening member that fastens the faces, and after injecting molten resin with this cavity unit clamped in a molding machine, the molding machine is moved with the mold opening face of the mold fastened by the fastening member. The mold clamping force is released, the cavity unit is separated from the mold clamping mechanism of the molding machine, the mold is deflected by the expansion force of the resin volume in the cavity, and the elastic restoring force of the mold causes the resin to cool as it cools. Solidify the resin while compensating for shrinkage.

FIGS. 1 and 2 show the basic configuration of a cavity unit 1 applied to the present invention. The cavity unit 1 consists of a pair of molds 2 and 3, and a cavity 4 is formed by clamping the molds 2 and 3. A spool 5 is formed in one of the molds 2 to guide molten resin from an injection nozzle of a molding machine into a cavity 4.

This cavity unit 1 is provided with a fastening member 6 that fastens the mold opening surfaces of the molds 2 and 3, and the fastening member 6 is rotatably supported on the other mold 3 by a pin 6a. By rotating in the direction of the mold, the hook portion 6b at the tip engages with the outer edge of one of the molds 2, and by rotating in the opposite direction, this engagement is released. . This fastening member 6 is connected to the molds 2 and 3 as shown in FIG.
These are provided at multiple locations on the outer edge of the

[0008]

[Operation] Molten resin is injected into the cavity 4 while the cavity unit 1 is clamped by the mold clamping mechanism of the molding machine. Thereafter, the cavity unit 1 is removed from the mold clamping mechanism of the molding machine with the mold opening surfaces of the molds 2 and 3 fastened together by the fastening member 6 and cooled.

[0009] To explain the action at this time in order, first, the molten resin filled into the cavity 4 under high pressure is somewhat compressible, and the specific volume (cm3/g) is reduced by an amount commensurate with the pressure. Contained within 4. When this cavity unit 1 is separated from the mold clamping mechanism and released from the mold clamping force F of the mold clamping mechanism, at the same time as this release, in conjunction with the restoring force (expansion force) of the resin and the action of the fastening member 6,
A deflection Δx is generated around the cavity 4. This Δx tends to increase as the filling pressure of the resin increases, as the projected area of the cavity increases, and as the thickness of the molds 2 and 3 decreases. However, as the resin gradually cools and solidifies, its volume shrinks, but the elastic restoring force caused by this deflection Δx acts on the cavity surface to push back the resin, causing the resin inside the cavity 4 to expand as the resin gradually cools and solidifies. Can be kept compressed. In this way, the molded product can be molded without causing defects such as sink marks on the surface, and of better quality than when normal mold clamping force is constantly applied.

0010

Embodiment FIGS. 3 to 5 show a first embodiment of the present invention. 3 and 4, the cavity 13 is closed by mold clamping.
The fixed side template 11 and the movable side template 12 forming a A cavity unit 10 is configured. A spool 15 communicating with the cavity 13 is formed on the fixed side mold plate 11, and this spool 15 is connected to a heating cylinder 16 of a molding machine that injects molten resin. 17 in Figure 3
and 18 are platens of the molding machine, which hold the cavity unit 10 within the molding machine by a holding mechanism (not shown). Among these, the tip of a mold clamping device 19 is connected to the platen 18 on the side of the movable mold plate 12, and the mold plate 11, 1
2 are pressed in parallel, and a predetermined mold clamping force is applied to the mold plates 11 and 12.

Next, a method for molding thick products such as lenses using the above structure will be explained. With the mold clamping device 19 clamping the cavity unit 10, the heating cylinder 1
6 injects the molten resin into the cavity 13. Then, the cavity unit 10 is removed from the molding machine while being clamped by the fastening member 14, and the cavity unit 10 is cooled and the resin is solidified. After this cavity unit 10 is removed, another cavity unit is newly set in the molding machine and injection is performed. Therefore, by replacing the cavity units 10 one after another, continuous molding can be performed and the molding cycle can be shortened.

FIG. 5 is an explanatory diagram for setting the deflection amount δ of the template 12 (same as the template 13) to an optimum value in the case of molding in this manner. In the figure, L is the length of the template (mm), h is the thickness of the template (mm), p is the resin pressure acting on the template (kgf/cm2), and E is Young's modulus (E= 2.1×106 kgf/cm2), B is the width of the template (mm), b is the width of the molding pressure receiving surface (mm), c is the length of the molding pressure receiving surface (mm), I is the mold When the second moment of area of the plate is (I=Bh3/R), the amount of deflection δ (mm) of the template when resin pressure P acts is δ=5Pb
It can be obtained from L4/384EI. Therefore, for example, B=150, h=25, L=150, b=20, c
=50 and P=400, it is possible to design δ=0.13 (mm). In this case, this δ is molding into a convex lens with a thickness of about 3 mm, and the molding pressure is P = 40
Although it was set to 0 kgf/cm2, in the case of a thicker lens, the molding pressure is increased, so the template must also be thicker. Specifically, for lenses with a thickness of 1 to 3 mm, P = 400.
kgf/cm2, P=50 for lenses with a thickness of 4 to 5 mm
Lenses of 0 to 700 kgf/cm2 and 6 to 10 mm thick are molded at P=800 to 1000 kgf/cm2, but as the thickness of the lens increases, the amount of resin shrinkage also increases, so it is not recommended to increase the value of δ too much. This is not preferable due to the relationship with the life of the mold. Therefore, based on the above formula, δ is at most δ<0.2m
m is good.

[0013]

Embodiment 2 FIG. 6 shows a molding apparatus applied to Embodiment 2 of the present invention. In this molding apparatus, two cavity units 10, 10 are arranged in parallel. The movable mold plate 12 of each cavity unit 10 can be slid laterally on the movable mold base 20. For this reason, a dovetail-shaped guide slit 21 is provided on the front side of the mold base 20.
are formed in the lateral direction, and a guide protrusion 22 is formed on the opposing surface side of each movable template 12 to be inserted into the guide slit 21 in an engaged state. In addition, the mold base 20
An actuator 23 such as a hydraulic cylinder is attached to one side of the movable mold plate 12 , and a rod 24 of the actuator 23 is connected to the movable mold plate 12 . In this embodiment as well, a fastening member 14 for fastening the mold opening surface is attached to each cavity unit 10, 10. This fastening member 14 fastens and releases the mold plates 11 and 12 by an actuator (not shown) attached to the mold base 20. Further, a stationary mold base 25 is disposed opposite to such a movable mold base 20. The stationary mold plate 11 is fixed to the stationary mold base 25 by a fixture (not shown), but a relief is formed by a stepped portion having a dimension t.

When injection molding is performed using such an apparatus, injection of resin and cooling of the cavity unit 10 are performed in the same manner as in the first embodiment, but the cavity unit 10 is slid along the guide slit 21 by the actuator 23. Therefore, resin can be injected into one cavity unit 10, and the cavity unit 10 can be evacuated while being clamped by the fastening member 14, and the other cavity unit 10 can be set, allowing quick replacement of the cavity unit. be able to. In this case, when the other cavity unit 10 is clamped, the dimension t
Due to the action of the stepped portion 26, no mold clamping force is applied to one of the retracted cavity units 10.

[0015] Therefore, when injection molding is carried out with the above configuration, it is possible to mold a molded product of high quality with no shrinkage as in Example 1, but in addition, since the cavity unit is replaced only inside the mold, there is no need for additional equipment. This has the advantage that the entire device can be made very compact, and the cavity units can be switched continuously and smoothly.

[0016]

Effects of the Invention The present invention has the following effects because the cavity unit into which resin has been injected in the mold-clamped state is removed from the molding machine and cooled with the mold opening surface in the fastened state.

(1) High-quality molded products with no sink marks on the surface can be molded. It is particularly suitable for molded products such as lenses that are thick and require highly accurate transferability, and lenses with good surface accuracy can be molded.

(2) During the cooling process, the mold clamping force is released and molding can be performed in a separate cavity unit, so it is possible to
It is possible to perform multiple shots during the cycle, making it possible to shorten the molding cycle.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the basic configuration of a cavity unit applied to the present invention.

FIG. 2 is a plan view of a cavity unit applied to the present invention.

FIG. 3 is a sectional view of a molding machine applied to Example 1 of the present invention.

FIG. 4 is a perspective view of a cavity unit applied to Example 1 of the present invention.

FIG. 5 is a sectional view illustrating the operation of Example 1 of the present invention.

FIG. 6 is a perspective view of a molding machine applied to Example 2 of the present invention.

[Explanation of symbols]

1 Cavity unit 2 Mold 3 Mold 4 Cavity 6 Fastening members

Claims (1)

[Claims] [Claim 1] A pair of molds forming a cavity;
A cavity unit was constituted by a fastening member that removably engaged with the outer edge of the mold and fastened the mold opening surface of the mold, and the molten resin was injected with this cavity unit clamped in a molding machine. After that, with the mold opening surface of the mold fastened by the fastening member, the mold clamping force of the molding machine is released, the cavity unit is separated from the mold clamping mechanism of the molding machine, and the mold is tightened by the expansion force of the resin volume in the cavity. A method for injection molding thick-walled products, which is characterized by bending the mold and solidifying the resin while compensating for shrinkage of the resin due to cooling using the elastic restoring force of the mold.