JP2017205942A - Molding method and device for foam molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mold a foam molded article having fine and uniform foam cells at high efficiency.SOLUTION: A stock area 34 for storing a molten foamable resin material is arranged in front of screw 16 inside of a barrel 15, measuring of the resin material stored in the stock area 34 is conducted with controlling temperature of the resin material, screw 16 is advanced, the resin material is filled in a mold, the resin material of a predetermined stock amount is left in the stock area and pressure of the resin material remained in the stock area 34 is controlled when injection is completed.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a method and an apparatus for molding a foam molded article.

  There are various molding methods as molding methods in an injection molding machine, and a foam molding method has been attracting attention in recent years. In the foam-molded product, the foamed cell having fine voids is formed into an infinite number of structures, and thus characteristics such as weight reduction and heat insulation of the molded product can be added.

  Recently, against the backdrop of stricter fuel economy regulations for automobiles worldwide, automobile parts have been widely replaced with foam molded products to reduce the weight of automobile bodies. Applying is accelerating.

In foam molding, measurement and injection of a resin material are performed by an injection device.
In the measuring step, the resin material including the foaming agent is melted in the barrel, and the screw is retracted while rotating, whereby the molten resin is stored in front of the screw. In the injection process, the screw advances and the molten resin is filled into the cavity in the mold. Thereafter, in order to foam the filled molten resin, the mold is opened (core back) to expand the cavity volume.

  In order to mold a high quality foamed molded product, it is necessary that the foamed cells constituting the structure of the molded product be fine and uniform. Various methods have been conventionally used to control foaming of a molded product. For example, there are a method of adjusting the timing of core back and a method of adjusting the residence time of the measured molten resin in the heating barrel (Patent Document 1).

JP 2010-162751 A

The temperature and pressure of the molten resin in the heating barrel are important factors for making the foam cells fine and uniform.
The causes of uneven foam cell sizes and reduced quality are related to the lack of heat of the molten resin after measurement and uneven temperature (unstable). For example, when molding with a low resin temperature setting as a countermeasure against molding defects, the generation of foaming gas from the foaming agent is suppressed due to insufficient heat, and uniform foamability in the mold may be hindered. is there.

  In addition, even when a part of the measured molten resin is foamed in the barrel by decompression before the molten resin is injected into the mold, the generated gas inhibits uniform foaming and makes the foam cell non-uniform. Cause it.

  In particular, as seen in the manufacture of automobile parts, it is difficult to make the foam cells fine and uniform in foam molding where the resin temperature is set low to prevent high molding (short cycle) and molding defects (discoloration). There are many cases.

  An object of the present invention has been made in view of the above-described problems of the prior art, and is a method for molding a foam molded product that enables highly efficient molding of a foam molded product in which foam cells are fine and uniform. And to provide an apparatus.

  In order to achieve the above-mentioned object, a method for molding a foam molded product according to the present invention sets a stock area for storing a molten foamable resin material in front of a screw inside a barrel, and stores the stock area in the stock area. The resin material is weighed while controlling its temperature, the screw is advanced, the resin material is filled in a mold, and a predetermined stock amount of resin material is left in the stock region, When the injection is completed, the pressure of the resin material accumulated in the stock region is controlled.

  An injection apparatus for a foam molded product according to the present invention includes a barrel into which a foamable resin material is charged, a screw accommodated in the barrel, a rotation drive unit that rotationally drives the screw, and the screw. A linear drive unit that moves forward and backward in the axial direction, and a stock area for storing a molten foamable resin material is set in front of the screw inside the barrel, and the resin material stored in the stock area And a pressure control means for controlling the pressure of the resin material stored in the stock region.

It is a figure which shows the outline | summary of the injection molding machine used in order to implement the shaping | molding method of this invention. It is a figure which shows the longitudinal cross-section of the front end side of the barrel which the injection apparatus of the injection molding machine of FIG. 1 has. It is a figure which shows the state which accumulated the molten resin in the stock part in front of a screw in the barrel of FIG. It is a figure which shows the change (FIG.4 (a)) of the position of a screw in a measurement process, and the change (FIG.4 (b)) of the pressure of molten resin. It is a figure which shows the position of a check ring while the screw is retracting | retreating in a measurement process. It is a figure which shows the change (FIG. 6 (a)) of the position of a screw in an injection process, and the change (FIG.6 (b)) of the pressure of molten resin. The cross-sectional photograph of the Example of the foaming molded article obtained by implementing the shaping | molding method of this invention is shown.

Hereinafter, an embodiment of a molding method and apparatus for a foam molded product according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing an outline of the configuration of an injection molding machine (molding apparatus) 10 according to an embodiment of the present invention. In FIG. 1, reference numeral 12 indicates the entire injection apparatus of the injection molding machine. Reference numeral 14 denotes a mold clamping device of an injection molding machine.

  A screw 16 is inserted into the barrel 15 of the injection device 12 so as to be rotatable and movable in the axial direction. The molding material (resin and foaming agent) is put into the barrel 15 from the hopper 17.

  In the injection device 12, the screw 16 is rotated by the metering motor 18, and the resin is accumulated in the front of the barrel 15 while the resin is melted and kneaded. The resin stored in front of the barrel 15 is filled into a cavity formed by the fixed mold 22 and the moving mold 23 from the nozzle 21 by advancing the screw 16 by the injection motor 19 and the ball screw mechanism 20. .

Next, an outline of the mold clamping device 14 will be described with reference to FIG.
A fixed die plate 24 is provided on one end side of the mold clamping device 14, and a link housing 25 is installed on the other end side. A movable die plate 26 is movably installed between the fixed die plate 24 and the link housing 25. A fixed mold 22 is attached to the fixed die plate 24, and a movable mold 23 is attached to the movable die plate 26. The fixed mold 22 and the movable mold 23 constitute a mold 27. A cavity is formed. The fixed die plate 24 and the link housing 25 are connected by a plurality of (for example, four) tie bars (not shown).
In this embodiment, a publicly known toggle link mechanism 30 is used as a mechanism for performing a mold opening / closing operation and a mold clamping operation.

Next, FIG. 2 is a view showing a longitudinal section on the tip side of the barrel 15.
A screw chip 32 is attached to the tip of the screw 16 via a shaft portion 31. A check ring 33 that prevents the backflow of the molten resin is provided outside the shaft portion 31. A spacer ring 35 is provided at the tip of the screw 16, and when the screw 16 advances during injection, the rear end of the check ring 33 is pressed against the spacer ring 35 to close the resin passage and prevent backflow. It has become. The check ring 33 is a check ring having a mechanism that can be closed by reverse rotation of the screw 16.

  As shown in FIG. 2, the space formed in front of the screw tip 32 inside the barrel 15 is a stock portion (stock region) 34 in which molten resin is stored. In the present embodiment, the metering process and the injection process are repeated in the stock section 34 in a state where molten resin for at least one shot, preferably a plurality of shots, is stored as a stock amount. This will be further described later.

  On the outer periphery of the tip of the barrel 15, a stock portion heater 38 that heats the molten resin in the stock portion 34 exclusively is provided separately from the heater 17 that heats the barrel 15 to melt the resin.

  The normal heater 17 is a wide cylindrical heater. On the other hand, the stock portion heater 38 includes a heater group in which a plurality of ring heaters 39 are arranged so as to surround the entire region of the stock portion 34. In addition, temperature detectors 41 including thermocouples for detecting the temperature of the molten resin stored in the stock portion 34 are arranged at a plurality of locations at the tip of the barrel 15.

  The control device 42 of the molding apparatus has a resin temperature control unit 44 that controls the temperature of the molten resin stored in the stock unit 34. The resin temperature control unit 44 feeds back the resin temperature detected by the temperature detector 41 and heats an arbitrary ring-shaped heater 39 to keep the resin temperature at a set temperature.

  Further, the pressure of the molten resin stored in the stock section 34 is detected by a pressure detection section 45 (see FIG. 1) provided in a ball screw mechanism that moves the screw 16 forward and backward. The detected pressure of the molten resin is fed back to the resin pressure control unit 46 of the control device 42, so that the screw 16 can be finely moved through the injection motor 19 so as to become a set pressure. Yes.

  The foam molding product molding apparatus according to the present embodiment is configured as described above. Next, a foam molding product molding method implemented using the molding apparatus will be described.

Here, FIG. 3 is a view showing a state in which the molten resin is stored in the stock portion 34 in front of the screw 16 in the barrel 15.
In the conventional molding method, one shot (one molding) of molten resin is stored in front of the screw 16 in the metering step, and all the molten resin is injected in the injection step.
On the other hand, in the present embodiment, a full-scale molding cycle is started in a state in which at least one shot of molten resin is stored in the stock section 34 in advance.

  Since the stock portion heater 38 for heating the molten resin in the stock portion 34 is disposed in the barrel 15 so as to surround the stock portion 34, the temperature of the molten resin accumulated in the stock portion 34 is By the heating of the partial heater 38, the set injection resin temperature is maintained.

Thereafter, the weighing process shown in FIGS. 4 and 5 and the injection process shown in FIG. 6 are performed as follows.
Here, FIG. 4 is a diagram showing a change in the position of the screw 16 (FIG. 4A) and a change in the pressure of the molten resin (FIG. 4B) in the measuring step.

In FIG. 4A, the one-dot chain line indicates the measurement start position of the screw 16, and the solid line indicates the measurement completion position of the screw 16.
As the screw 16 rotates, the molten resin is fed forward, and the molten resin is accumulated in the stock portion 34. The screw 16 is retracted by the pressure of the accumulated molten resin, and measurement is performed based on the retracted amount.

FIG. 5 is a view showing the position of the check ring 33 while the screw 16 is retracted.
A gap S is formed between the rear end of the check ring 33 and the spacer ring 35 so that the molten resin is fed forward by the positively rotating screw 16. The molten resin flows through the inside of the check ring 33 from the gap S and is sent forward as indicated by an arrow. During this time, measurement is performed so that the resin pressure is maintained at a preset resin pressure Pc.

Thereafter, the screw 16 reaches the measurement completion position and the measurement is completed. If the gap S remains open between the rear end of the check ring 33 and the spacer ring 35 at the time of completion of measurement, molten resin may leak from the gap S and the pressure may drop. Therefore, in this embodiment, the screw 16 is rotated in the reverse direction and the gap is closed by the check ring 33. Thus, the pressure of the molten resin stored in the stock portion can be maintained even after the completion of measurement.
In addition, when the measurement is completed, the resin pressure may decrease when the check ring 33 is closed. In that case, the screw 16 may be slightly advanced and controlled to be kept constant at the resin pressure Pc.

On the other hand, while the weighing process is performed, in addition to the amount of resin that has been accumulated up to that point, a new resin flows into the stock section 34. During the measurement process, the heating by the stock portion heater 38 continues, and the stock portion 34 as a whole is managed so as to be constant at the temperature T1 of the molten resin.
In the molding cycle, the molded product is cooled, the mold is opened, and the molded product is taken out in parallel with the above-described measurement process.

Next, the injection process will be described with reference to FIG.
FIG. 6 is a diagram showing a change in the position of the screw 16 (FIG. 6A) and a change in the pressure of the molten resin (FIG. 6B) in the injection process. In FIG. 6B, the time on the horizontal axis advances from the right to the left in accordance with the direction of position change of the screw 16 in FIG.

In FIG. 6A, the screw 16 moves forward from the completion of the measurement, and the injection process is started. As a result, the molten resin stored in the stock portion 34 is filled into the mold 27 (see FIG. 2). While the screw 16 is moving forward, the gap between the rear end of the check ring 33 and the spacer ring 35 is closed, and the backflow of the molten resin is prevented. When the screw 16 moves forward to the position indicated by the one-dot chain line, one shot of molten resin is filled into the mold 27, and the injection process is completed.
A change in the resin pressure in the stock portion 34 in such an injection process is indicated by a curve 100. The resin pressure continues to rise and the injection pressure peaks at the completion of injection. Thereafter, the mold 27 is opened and core back is performed. The moving mold 23 is slightly retracted, the resin pressure is rapidly reduced, and the filled resin is foamed.

  Simultaneously with the completion of injection, the shut-off valve 47 (see FIG. 2) provided in the nozzle 21 is closed, but the pressure of the molten resin accumulated in the stock portion 34 is still lowered. If the pressure is too low, a part of the molten resin in the stock part 34 may foam.

  Therefore, the resin pressure is maintained as follows. In the present embodiment, the screw 16 is not stopped completely at the time of completion of injection, and the molten resin in the stock portion 34 is pushed by the screw 16 so that the resin pressure becomes constant at a preset resin pressure Pi that can suppress foaming. Hold. At this time, the shutoff valve 47 in the nozzle 21 is closed. Thus, after the injection process is completed, the pressure of the molten resin accumulated in the stock portion 34 is kept constant, and it is possible to reliably prevent a part of the molten resin from foaming.

Further, during and after the injection process, the heating by the stock portion heater 38 continues, and the temperature of the molten resin accumulated in the stock portion 34 is controlled to be constant T1.
In addition, while the resin pressure of the stock part 34 is maintained as described above, in the mold, the molded product is cooled, the mold is opened, and the molded product is taken out.

As described above, while repeating the metering and injection in the molding cycle, at least one shot of molten resin is always stored in the stock portion 34 in front of the barrel 15, so that the molten resin is in a stable state in both temperature and pressure. Is injected into the mold 27.
This prevents the molten resin from being injected into the mold 27 while the temperature is not uniform or the amount of heat is insufficient, and it is also possible to avoid a part of the molten resin from foaming in the barrel 15. Therefore, in the mold 27, the resin can be foamed under favorable conditions, and a high-quality molded product in which uniform and fine foamed cells are formed can be obtained.

(Example)
Next, an embodiment of a foam molded article obtained by carrying out the present invention will be described with reference to FIG.
In the example, a document case having a wall thickness (1.8 → 2.7 mm) was molded using a material obtained by adding 3.5% by weight of a foaming agent (sodium hydrogen carbonate) to polypropylene.

The molding conditions are as follows.
Injection speed 160 [mm / s]
Molding cycle 35 [s]
Expansion ratio 1.5 times
Injection machine Toshiba Machine EC350SX-17A (screw φ60)
FIG. 7 shows a photograph of a cross-section of a molded product formed by molding the resin temperature of the stock portion under each temperature condition of 200 ° C., 220 ° C., and 240 ° C.
In addition, what was shape | molded by the conventional method (method to shape | mold without accumulating in a stock part) on the same temperature conditions is given as a comparative example for the comparison.
In addition, the results of measuring the temperature distribution of the molded product using thermography are also shown.

  Comparing the examples and comparative examples as described above, in the examples, the cells were fine and uniform, and a good foamed molded product was obtained. The occurrence of cracks was observed. From this, it was confirmed that the present invention is more advantageous than foam molding at a low resin temperature.

  Further, regarding the temperature distribution of the molded product, it was confirmed that the variation in the temperature distribution was small at the same temperature, which is considered to contribute to a good foamed state.

  DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 12 ... Injection apparatus, 14 ... Clamping apparatus, 15 ... Barrel, 16 ... Screw, 17 ... Hopper, 18 ... Measuring motor, 19 ... Injection motor, 21 ... Nozzle, 22 ... Fixed mold , 23 ... Moving mold, 30 ... Toggle link mechanism, 32 ... Screw tip, 33 ... Check ring, 34 ... Stock part, 38 ... Stock part heater, 39 ... Ring heater, 42 ... Control device

Claims (9)

Set the stock area to store the molten foamable resin material in front of the screw inside the barrel,
Measuring the resin material while controlling the temperature of the resin material stored in the stock area,
Advance the screw, fill the mold with resin material, leave a predetermined stock amount of resin material in the stock area,
A method for molding a foam molded article, comprising: controlling a pressure of a resin material accumulated in the stock region when injection is completed.   During the measurement, the resin material is measured while keeping the temperature of the resin material accumulated in the stock region constant, and when the measurement is completed, the pressure of the resin material is held so as not to decrease. The method for molding a foam molded article according to claim 1.   When injection is completed, the pressure of the resin material accumulated in the stock region is maintained so as not to decrease, and the temperature of the resin material accumulated in the stock region is kept constant until the next measurement starts. The method for molding a foam molded article according to claim 1.   3. A plurality of heaters are arranged at the tip of the barrel so as to surround the stock region, and the temperature is maintained by heating the resin material in the stock region with the heater. 3. A method for molding a foam molded article according to 3.   3. When the measurement is completed, a check ring for preventing backflow provided at the tip of the screw is closed by reverse rotation of the screw, and the pressure of the resin material in the stock region is maintained. Or the molding method of the foaming molded article of 3.   4. The method for molding a foam molded product according to claim 2, wherein the screw is finely moved forward when the measurement is completed or the injection is completed, and the pressure of the resin material in the stock region is maintained.   The method for molding a foam molded product according to any one of claims 1 to 6, wherein at least one shot of the resin material is accumulated in the stock region when the injection is completed. A barrel into which a foamable resin material is charged;
A screw housed in the barrel;
A rotational drive unit for rotationally driving the screw;
A linear drive unit for moving the screw forward and backward in the axial direction, and
A stock area is set in front of the screw inside the barrel to store the molten foamable resin material.
Heating means for controlling the temperature of the resin material stored in the stock region;
And a pressure control means for controlling the pressure of the resin material stored in the stock region. A pair of molds consisting of a fixed mold and a moving mold;
A mold clamping device to which the pair of molds are attached;
An injection device according to claim 8;
An apparatus for forming a foam molded product, comprising: