JPH03140223A - Injection molding method and device - Google Patents

Abstract

PURPOSE:To greatly reduce the cost of a mold by enabling low mold clamping pressure molding, by a method wherein resin whose viscosity is lowered by generating shearing heat of the molten resin by narrowing an injection nozzle is filled into the mold and the resin is pressed with a movable mold after completion of the filling. CONSTITUTION:A nozzle 20 is screwed into a valve main body 22, a needle pin 21 is fitted slidably into the valve main body 22 and a gap d1 is formed between the tip of the same and the nozzle 20. When resin is passed through this narrow resin passage under a high-shearing speed, viscosity of the molten resin 7 is lowered with shearing heating. The foregoing molten resin 7 is injected and filled into a cavity 36 formed by fitting of a movable mold 32 and stationary mold 35 into each other up to a set position of a screw 1 with a signal of a controller 11. After completion of the filling, the primary mold clamping pressure is lowered and after movement of a wedgy spacer 37 backward further, the gap d1 of a narrowing nozzle 4 is closed and then the mold cavity 36 is compressed with fixed pressure as the secondary mold clamping pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low clamping pressure injection molding method and apparatus for molding plastic products with high dimensional accuracy at low pressure.

(Conventional technology) The filling pressure of a conventional injection molding machine is 50MPa = 100M
Due to the high Pa, there were drawbacks such as large stress distortion in the molded product and lack of dimensional stability, expensive molds, and short mold life. To explain this in more detail, Figure 4 shows the load curve of a conventional injection molding machine during molding. Curve a is the injection pressure, curve A is the mold cavity inlet pressure, and curve C is the mold cavity end pressure. , curve d is the mold clamping pressure. As is clear from the curves a, b+c in Fig. 4, the injection pressure, the mold internal pressure,
Both mold clamping pressure and high pressure are required. This is due to the pressure drop due to the large flow length/l (wall thickness) of the molded product used in boat fishing, and the forced flow of molten resin at a low temperature, therefore with high viscosity and high flow resistance, through a narrow mold cavity. This is because it is large.

(Problem to be Solved by the Invention) However, as can be seen from the mold internal pressure shown by curve c, in the conventional case, there is a large degree of imbalance between the mold internal pressure, that is, the pressure at the entrance and exit of the mold cavity. For this reason, the stress strain of the mold is large and high rigidity is required, so the size and weight of the mold are large and expensive. In addition, in plastic molding, it is necessary to compensate for shrinkage due to cooling of the resin, but in injection molding, when the gate is sealed, the pressure is frozen and no effective pressure acts on the cavity, so the pressure inside the mold remains unbalanced. Cooling solidification progresses and is frozen as internal stress strain in the molded product. As a result, the molded product suffers from large stresses and strains, resulting in a lack of dimensional stability and problems such as warping and sink marks. There is also a problem in terms of energy consumption, as energy is wasted due to pressure drops and the like.

ZAS (zinc alloy) molds, which have traditionally been used as small production molds, have lower mold costs than steel molds (555C, etc.).
Although the production cost is low at approximately 2, it is easy to deform due to its low hardness and low Young's modulus, and the pressure during molding causes the parting surface to open and cracks to occur, causing mold damage and shortening the lifespan. there were. If the deformation of this mold is suppressed to the same degree as carbon steel, mass production using ZAS molds is possible. Since the deformation of steel is proportional to Young's modulus, it is sufficient to keep the mold pressure below Young's modulus. Therefore, as is clear from Table 1,
If the filling pressure is kept below 20 MPa, mass production using ZAS molds is possible.

Table 1 (Young's modulus of mold material and maximum mold internal pressure) Previously published in JP-A No. 5
Twelve injection compression molding methods and injection compression molding apparatuses have been proposed in Japanese Patent Application Laid-open No. 8-167133, Japanese Patent Application Laid-Open No. 60-21225, and Japanese Patent Application Laid-Open No. 61-241114, but these also have the problems described above. there were.

As mentioned above, the purpose of the present invention is to realize low clamping pressure forming where the filling pressure is a Young's modulus ratio of 115 compared to a steel mold, or a maximum mold internal pressure of 20 MPa or less, and to significantly reduce the cost of the mold. The purpose of the present invention is to provide an injection molding method and apparatus.

(Means for Solving the Problems) For this reason, the present invention generates a shear heat wave that reduces the viscosity of the molten resin by narrowing the injection nozzle during injection filling in which the mold is opened slightly and the molten resin is filled by reducing the pressure. This low viscosity resin is then filled into the mold, and after filling is completed, the resin is pressed with a moving mold so that an effective pressing force acts on the resin filled in the mold cavity even after the gate is sealed. It is intended to be used as a means to solve problems.

In addition, the present invention provides fixed positioning means for a movable mold, which maintains the interval between the movable molds at a fixed position by taking into account the compression allowance of the molded product (the reduction in specific volume due to cooling of the resin) with respect to the fixed mold. , an injection flow rate and pressure adjustment means that works in conjunction with a molten resin flow path cross-sectional area variable means of a throttle nozzle during injection filling, and a pressing means that suppresses the resin with a moving mold after filling is completed, and controls the viscosity of the molten resin. The pressure of the molten resin inside the mold cavity is reduced by lowering the...
This is done in such a way as to reduce the problem, and this is done as a means to solve the problem.

(Function) By slightly opening the mold and filling it with molten resin, the pressure drop of the resin flowing inside the mold cavity is reduced, so the filling pressure is reduced.

During injection filling, when the injection nozzle is throttled and the resin passes through a narrow resin passage at high shear rates, the shear heat generation of the resin reduces the viscosity of the molten resin, causing a pressure drop in the mold cavity and, in turn, lowering the filling pressure. do. By pressing the resin with the moving mold after filling is completed, an effective pressing force acts on the resin filled in the mold/cavity even after the gate is sealed, resulting in a molded product with low stress distortion and high density. Can be done.

(Embodiment) Below, embodiments of the present invention will be described based on the drawings.
The figure shows a sectional view of essential parts of an injection molding machine that implements the present invention.

In the figure, l denotes a screw, which is slidably incorporated into a closed space 2a formed by the cylinder 2, end cap 3, and throttle nozzle 4. In addition, the raw resin is transported to hopper 5.
The resin falls into the cylinder 2, is melted and plasticized by heating by a heater (not shown), and rotation of the screw 1 by a hydraulic motor, and is sent to the front of the screw 1 and stored as a molten resin 7.

The hydraulic motor shaft 6a is spline-coupled inside the injection ram 8, and rotates integrally between the two, but can freely slide in the axial direction. In addition, 9 in the figure is the screw l.
, and 10 is an electromagnetic relief valve. Now, the screw 1 is operated by the hydraulic power source 12 based on the command from the controller 11.
The pressurized oil is sent into the injection cylinder 15 via the solenoid valve 13 and the flow control valve 14, and the mold cavity is filled with the molten resin 7.

Details of the aperture nozzle 4 are shown in FIG. In the figure 2
0 is a nozzle, 21 is a needle bottle, and 22 is a valve body, which is connected to the cylinder 2 via an end cap 3. The hydraulic cylinder 2 shown in FIG.
5. Hydraulic cylinder 2
5 is fixed to the cylinder 2 by a bracket 26. A position sensor 27 detects the stroke position of the hydraulic cylinder 25 and, in turn, the forward end or backward end position of the needle bin 21. In addition, 20a in FIG. 2 is a nozzle hole, 2
0b is a resin passage, and 22a is also a resin passage, which is composed of a plurality of holes provided on the circumference. In addition, the valve body 2
2 is attached to the end cap 3 with bolts 28, and the nozzle 2o is screwed into the valve body 22. The needle bottle 21 is slidably fitted into the valve body 22, its tip forms a gap d1 with the nozzle 20, and its rear part is connected to the lever 23 through the hole 21a as described above. 29 is a servo valve, which detects the stroke position of the hydraulic cylinder 25 with a position sensor 27, sends the signal to the controller 11, converts it into a clearance d, and compares it with the set clearance d. An increase/decrease signal is sent to the servo valve 29 to perform servo control of the gap d1.

Further, in FIG. 1, a movable mold 32 fixed to a movable platen 31 is moved back by a mold clamping cylinder 33 and engages with a fixed mold 35 fixed to a fixed platen 34, thereby forming a mold cavity 36. . During molding, this cavity 36 is primarily clamped with a compression allowance δ left in advance, but in order to accurately determine the compression allowance δ, a wedge-shaped spacer 37 is inserted into the drive source 38.
It is interposed between the movable mold 32 and the fixed mold 35.

A position sensor 39 detects the stroke position of the wedge-shaped spacer 37 and sends a signal to the controller 11 to more accurately control the movement of the wedge-shaped spacer 37.

Further, as shown in FIG. 3, the inclination angle α of the wedge-shaped spacer 37 can be finely adjusted by adjusting the compression distance δ by changing the length of the overlap distance r with the mold. Further, one or more wedge-shaped spacers 37 are arranged in a well-balanced manner between the fixed mold 35 and the movable mold 32. In FIG. 1, 40 is an electromagnetic switching valve, and 41 is an electromagnetic relief valve, which sends pressure oil from the hydraulic source 12 to the mold clamping cylinder 33 in response to a signal from the controller 11, and controls its operation and pressure.

Here, the molten resin 7 plasticized at high temperature is injected and filled into the cavity 36 including the compression allowance δ at high speed up to the set position of the screw l according to a signal from the controller 11. At this time, the mold cavity inlet pressure, ie, the filling pressure, is significantly reduced. After filling is completed, the controller 11 sends a signal to the electromagnetic switching valve 40 and the electromagnetic relief valve 41 to lower the primary mold clamping pressure, and after retracting the wedge spacer 37, sends a signal to the servo valve 29 to close the throttle nozzle 4.
After that, a signal is sent to the electromagnetic switching valve 40 and the electromagnetic relief valve 41 to compress the mold cavity 36 at a predetermined pressure as secondary mold clamping pressure for a predetermined time. After cooling and solidifying, the movable mold 32 is opened and the molded product is taken out.

Next, test results of the present invention will be explained.

1. Filling pressure reduction test (1) Test conditions A sensitivity analysis test for filling pressure reduction was conducted using a 200φ disc mold.

(1) Test machine: Injection machine 900/220?1S
(2) Mold: 200φ disc mold (Fig. 6) Meat
Using a 200φ disc mold with a thickness of 1+3 mm, the mold internal pressure at two points (cavity entrance and cavity end) and resin inflow temperature were measured while changing the molding conditions. Here, the filling pressure is at the completion of filling (terminal pressure O
) is defined as the cavity inlet pressure.

(2) Test results The mold temperature sensitivity was not significant in this test. Using gate dimensions, molded product wall thickness, resin temperature, and injection rate as explanatory variables and filling pressure as a characteristic value, a multiple variable regression analysis was performed on the results at each test level shown in the previous section. By recalculating the characteristic values for changes in each explanatory variable using the obtained multiple regression equation, the sensitivity of each explanatory variable to filling pressure reduction can be determined. Figure 7 shows the sensitivity analysis results for gate dimensions, mold wall thickness, and injection rate. Wall thickness 1m
The process of reducing the actual filling pressure of 50 MPa to 20 MPa based on the gate size of 0.7 mm is as follows.

As is clear from Figure 7, (1) the gate dimension is 0.7
Filling pressure can be increased from 50MPa to 32MPa (■→■) by generating heat from mm to 0,2 +++m.
can be reduced to In addition, (2) by increasing the wall thickness from fan to 1 or 2 carp, the pressure was increased from 32 MPa to 22 MPa (■
→■) (thickness increase effect). Furthermore, (3) by increasing the injection rate from 100 cd/sec to 300 cd/sec, the pressure was increased from 22 MPa to 17 MPa (■→■)
It can be seen that it can be reduced to That is, it becomes 20 MPa or less.

Among the above-mentioned filling pressure reduction effects, terms (]) and (3) are effects of increasing resin temperature due to shear heat generation when the molten resin passes through the gate. Although the above test was carried out by squeezing the mold gate, it is clear that the same effect can be obtained by squeezing the nozzle, and the filling pressure was changed from 50 MPa to 20 Mpa.
It can be reduced to Pa.

2. PvT of resin ABS Tuflex-210 used for compression molding after injection Fig. 8
Show a curve. In the case of injection molding, even if the resin is filled at a temperature of 210'C and held at a holding pressure of 50 MPa, no effective pressure acts on the mold cavity after the gate is sealed, so the specific volume is determined by the gate sealing time, as shown in Figure 6. In the example of 1.03
It is 2cnf/g.

On the other hand, in the compression molding after low-pressure filling of the present invention, the effective pressure acts on the cavity up to near the heat distortion temperature, so the compression pressure is
For example, even at a low pressure of 10M1'a, if pressure is applied to a heat-resistant ABSO heat distortion temperature of 110°C, the specific volume at the final stage of compression molding will be 1. oc++I/g, and a molded product with higher density than injection molded products can be obtained.

(Effects of the Invention) Since the present invention is configured as explained in detail above,
The mold cavity inlet pressure decreased significantly, and the load curve during molding became as shown in Figure 5 (e is the injection pressure, r is the mold cavity population pressure, g is the mold cavity flow end pressure, and 11 is the mold clamping pressure). As per the pressure drop in the mold cavity Δ
P2 is significantly reduced compared to the conventional ΔP1 due to a decrease in the viscosity of the molten resin. Moreover, the imbalance between the pressure at the cavity entrance and the end is almost eliminated. When the movable mold (pressing means) presses the entire cavity with a predetermined pressure after filling is completed, the difference between the inlet pressure r and the flow end pressure g is small, and no unreasonable pressure imbalance occurs in the mold. Moreover, the average pressure at the inlet and the end is low, so the pressing force can be low and energy consumption is low. From the above, according to the present invention, the mold cavity inlet pressure also
This means that molding can be performed with low pressing force after filling.
It can be sufficiently molded using a ZAS mold.

Furthermore, during injection filling, the filling pressure is increased from 50 MPa to 17 MPa due to the mold wall thickness increase effect by opening the mold and injection filling, the resin temperature increase effect due to the heat generated by the nozzle throttle, and the resin temperature increase effect due to high-speed filling. A significant reduction is possible. In addition, in compression molding after filling, 10MI'a
Molded products with good dimensional accuracy can be obtained even at low pressures, and the mold clamping force can be much smaller than conventional molds. Therefore, according to the present invention, low filling pressure molding and low mold clamping pressure molding are possible, and mass production using ZAS (zinc alloy), which has traditionally been used as a small-volume production mold, is possible, and mold costs are significantly reduced. can. Furthermore, low-pressure filling and low-pressure mold clamping can significantly reduce the energy consumed per molded product. Furthermore, since a low mold clamping pressure is required, the injection molding apparatus can be made smaller and occupy less space.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a cross section and piping of an injection molding apparatus according to a first embodiment of the present invention, FIGS. 2 and 3 are sectional views of main parts in FIG. Figure 5 is a load curve diagram for the injection molding machine, Figure 5 is a load curve diagram for the molding machine of the present invention, Figure 3 is a cross-sectional view of the test molded product, Figure 7 is the filling of wall thickness, gate size, and injection rate. FIG. 8 is a pressure reduction sensitivity characteristic curve diagram. ε: B is a PvT curve diagram of BS resin. Explanation of main parts in the figure 1 - Screw 4 - Throttle nozzle 11 - Controller 21 - Needle bin 27 - Position sensor 33 - Clamping cylinder 36 - Cavity 2 - Cylinder 5 - Hub 20 - Nozzle 22 - Valve body 32 - - Movable mold 35...Fixed mold 37--Wedge-shaped spacer Fig. 6 f Restraint mold (φ200 circle set child mold) ,': f-to size 2 bird devised rod's original month U11 &Wei's βV (Figure 4 4L Izumi's Murayama molding machine's negative technique Lffi and 5 figure Wood's molding machine's negative combi V (Figure 8 Temperature ('(1)

Claims (2)

[Claims] (1) Open the mold slightly and fill the molten resin by reducing the filling pressure.During injection filling, the injection nozzle is narrowed to reduce the viscosity of the molten resin by generating a shear heat, and this low-viscosity resin is transferred to the mold. An injection molding method characterized by filling a mold and pressing the resin with a movable mold after filling is completed so that an effective pressing force acts on the resin filled in the mold cavity even after gate sealing. (2) fixed positioning means for the movable mold, which maintains the interval between the movable molds at a fixed position with respect to the fixed mold, taking into account the compression allowance of the molded product (reduction in specific volume due to cooling of the resin); At the time of filling, the injection flow rate and pressure adjusting means is interlocked with the means for varying the cross-sectional area of the molten resin flow path of the throttle nozzle, and after the filling is completed, a pressing means is provided that presses the resin using a moving mold to lower the viscosity of the molten resin. An injection molding device characterized by reducing pressure loss of molten resin within a mold cavity.