JP2001198943A - Method for manufacturing foamed molded article and injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the appearance of a foamed molded article without generating molding defects such as a sink, short or the like. SOLUTION: In an injection process, a molding material obtained by mixing a foaming material with a resin is injected in a cavity space at a high speed to fill the cavity space and, in the timing just before the completion of the filling of the cavity space with the molding material, the injection process is completed and an injection member is stopped to start a foaming process and, in the foaming process, the foaming material in the molding material is foamed. In this case, since high speed filling is performed and the injection process is completed in the timing just before the filling with the molding material is completed and the foaming material is foamed, the foaming possible quantity in the cavity space becomes large. Therefore, the molding material can be sufficiently expanded and the foaming material is sufficiently foamed accompanied by this to enhance an expansion ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a foam molded article and an injection molding machine.

[0002]

2. Description of the Related Art Conventionally, in an injection molding machine, a molding material is injected from an injection nozzle of an injection device, and is filled into a cavity space via a sprue, a runner and a gate in a mold device. Goods.

[0003] In the method of molding a foamed molded article in which a foamed material is mixed with a resin as the molding material, for example, the foamed material is molded while being foamed. For example, a foamed molded product, for example, a foamed container can be molded.

FIG. 2 is a sectional view of a foam container.

In the drawing, 71 is a foam container, 72 is a substantially cylindrical body formed in a tapered shape, 73 is a bottom formed at the lower end (right end in the figure) of the body 72, and 74 is the body. A leg base portion 75 formed to protrude further downward (to the right in the drawing) from the lower end of 72 is formed to protrude radially outward at an upper end (to the left end in the drawing) of the body portion 72. The flange portion 76 is a storage portion for storing food (not shown).

[0006] The foaming container 71 is formed by filling a molding material into a cavity space in a mold device (not shown). For this purpose, the mold apparatus includes a fixed mold and a movable mold, and the movable mold is brought into and out of contact with the fixed mold to perform mold closing, mold clamping, and mold opening. Then, a cavity space is formed between the fixed mold and the movable mold as the mold is closed and the mold is closed, and the molding material is filled in the cavity space. In the cavity space, a trunk portion, a bottom portion, a leg portion, and a flange portion are formed corresponding to the trunk portion 72, the bottom portion 73, the leg root portion 74, and the flange portion 75, and a gate is formed at the center of the bottom portion. Is formed. Therefore, the molding material enters the cavity through the gate, flows through the bottom portion, the base portion of the leg, and the trunk portion, and then flows into the flange portion formed at the position farthest from the gate in the cavity space. To reach.

When the mold is opened, the foamed container 71 molded in the cavity is released from the fixed mold and the movable mold.

[0008] By the way, the foam container 71 is provided with a foaming container 71 so as to improve the releasability when the mold is opened and to smoothly release the foaming container 71 from the fixed mold and the movable mold.
A draft of 10 to 10 ° is provided. That is, the outer surface S1 common to the body 72 and the leg base 74, and the inner surface S2 common to the body 72 and the flange 75
In any case, the radial dimension decreases as the distance from the upper end of the foaming container 71 increases, and the radial dimension decreases as the inner side surface S3 of the leg-attached root portion 74 moves away from the lower end of the foaming container 71. The leg base 74, especially the leg base 74
A connecting portion R11 between the body 72 and the bottom 73 is made about 20 to 100% thicker than the body 72 and the bottom 73.

A not-shown lid made of paper, aluminum, plastic, film or the like is attached to the flange portion 75 by heat sealing.
The foam container 71 is sealed. For this purpose, the lid is pressed against the flange 75 by a pressing member such as a high-temperature heating element (not shown) or an inductor. Therefore, the flange portion 75 is designed to withstand the pressing force of the pressing member.
It is made thicker than the body 72 by about 20 to 50%.

[0010]

However, in the conventional method of molding a foamed article, the leg base 7 is not used.
Since the thickness of the material 4 is increased, the molding material shrinks with cooling, causing molding defects such as sink marks and shorts.
The appearance of the foaming container 71 is deteriorated.

Since the thickness of the flange portion 75 is also increased, the amount of molding material shrinking with cooling is large.
Since the flange portion 75 is formed at a position farthest from the gate in the cavity space, in the pressure holding step after the filling step is completed, it is not possible to exert sufficient pressure holding on the molding material of the flange portion. Therefore, sink,
Not only does the molding failure such as short-circuiting occur and the appearance of the foam container 71 deteriorates, but also the lid cannot be stably pressed against the flange portion 75 when the lid is attached. As a result, the sealing performance of the foam container 71 is reduced.

The present invention solves the above-mentioned problems of the conventional method of molding a foamed article, and can improve the appearance of the foamed article without causing molding defects such as sink marks and short circuits. An object of the present invention is to provide a molding method of a molded article and an injection molding machine.

[0013]

For this purpose, in the method for molding a foamed molded article of the present invention, in the injection step, a molding material obtained by mixing a foamed material into a resin is injected at a high speed, and the high-speed injection is performed. Filling and filling the cavity space, at the timing immediately before the filling of the molding material is completed, the injection step is completed, the injection member is stopped, and the foaming step is started. The foam material is foamed.

In another molding method of the present invention, the injection speed V _S is set in the range of 200 ≦ V _S ≦ 1000 [mm / s].

In still another method of molding a foamed article according to the present invention, the filling time t _S is set in the range of 0.05 ≦ t _S ≦ 0.2 [s].

In still another method of molding a foamed article according to the present invention, a ratio ζ of a gap formed in the cavity space when the injection step is completed occupies the cavity space. ≤ζ≤5 [%].

In still another method of molding a foamed article of the present invention, the foamed material is a foaming agent.

In still another method for molding a foamed article of the present invention, the foamed material is a gas for foaming.

In the injection molding machine according to the present invention, the cylinder member, the injection member provided to be able to advance and retreat in the cylinder member, the driving means for moving the injection member forward and backward, and A mold device in which a cavity space is formed, and a molding material obtained by mixing a foaming material into a resin in an injection step, is injected at a high speed, and is filled at a high speed to fill the cavity space through a gate. Injection control means and at the timing immediately before the filling of the molding material is completed, the injection process is completed, the injection member is stopped to start the foaming process, and in the foaming process, the foaming material in the molding material is removed. Foaming control means for foaming.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an injection molding machine according to an embodiment of the present invention, FIG. 3 is a time chart showing the operation of the injection molding machine according to the embodiment of the present invention, and FIG. The figure which shows the state of the molding material at the time of a foaming process, FIG. 5 is a relationship diagram between a filling time and a foaming ratio. In addition, in FIG. 3, SG1 is a variable indicating the rotation direction of the screw 12, and SG2 is a variable indicating the moving direction of the screw 12. Each of the variables SG1 and SG2 is assumed for the sake of convenience, and does not represent an actual control amount. In FIG. 5, the horizontal axis represents the filling time t _S and the vertical axis represents the expansion ratio.

In the drawing, reference numeral 11 denotes a heating cylinder as a cylinder member, and 12 denotes a rotatable and advancing / retreating (moving in the left-right direction in FIG. 1) inside the heating cylinder 11.
A screw 13 is a freely disposed injection member, 13 is an injection cylinder as a first drive unit, and 14 is a hydraulic motor as a second drive unit. The heating cylinder 1
1, a hopper 11a is provided at a predetermined position rearward (right side in FIG. 1), and an injection nozzle 2 is provided at a front end (left end in FIG. 1).
0 is formed, and a molding material obtained by mixing a foaming material into a resin or the like is put into the hopper 11a. The molding material is supplied from the hopper 11a to the heating cylinder 11
And injected from the injection nozzle 20. Further, a flight 12a is formed on the surface of the screw 12 in a spiral shape, and a groove 21 is formed along the flight 12a. Note that an electric injection motor can be used in place of the injection cylinder 13 and an electric metering motor can be used in place of the hydraulic motor 14.

The injection cylinder 13 has a piston 13a which can be moved forward and backward. A first oil chamber 16 is provided behind the piston 13a, and a second oil chamber 17 is provided forward (to the left in FIG. 1). The first and second oil chambers 16 and 17 are formed and connected to a hydraulic supply (not shown) via a switching valve (not shown). In this case, the hydraulic pressure is supplied to the first oil chamber 16 and the hydraulic pressure of the second oil chamber 17 is drained to move the screw 12 forward (to the left in FIG. 1), By draining the oil pressure of 16 and driving the hydraulic motor 14, the screw 12 can be rotated to perform weighing. In addition, when measuring, by supplying hydraulic pressure to the first oil chamber 16, back pressure can be applied to the screw 12.

A position sensor 22 connected to the piston 13a for detecting the position of the screw 12, that is, the screw position, detects a back pressure of the screw 12 corresponding to the first oil chamber 16. A pressure detector 24 for detecting the pressure of the molding material is provided in front of the heating cylinder 11. The detection signals of the position sensor 22, the back pressure sensor 23 and the pressure detector 24 are transmitted to the control unit 2
Sent to 6.

Next, the operation of the injection molding machine will be described.

First, at a timing t0, a weighing process is started. In the weighing process, a weighing control means (not shown) of the control unit 26 drives the hydraulic motor 14 to rotate the screw 12 in the forward direction. At this time, the molding material supplied to the hopper 11a is supplied to the molding material supply port Q1.
Is supplied into the heating cylinder 11 through the groove 21 and is advanced in the groove 21 and is stored in front of the screw head 12b, whereby the screw 12 is moved backward (moves rightward in FIG. 1). In the measuring step, a predetermined oil pressure is supplied to the first oil chamber 16 and a back pressure is applied to the screw 12.

At the timing t1, the measuring step is completed and the injection step is started. In the injection step, an injection control unit (not shown) of the control unit 26 drives the injection cylinder 13 to move the screw 12 forward. At this time, the molding material stored in front of the screw head 12b is injected from the injection nozzle 20, and the sprue and the runner 6 (not shown) in the mold device 61.
The cavity space C is filled through the gate 2 and the gate 63. A backflow prevention device (not shown) is provided so that the molding material stored in front of the screw head 12b does not flow backward.

In this case, as a molding material, for example, a resin such as polypropylene resin, polystyrene resin, nylon (trade name) or the like, and as a foaming material, a foaming agent which reacts with heat to generate carbon dioxide gas in an amount of 1 to 5 mass %] By using the mixed material and performing molding while foaming the foaming agent, a foam container 71 (FIG. 2) as a foam molded product containing a large number of cells can be molded. As the foaming agent, for example, a masterbatch-type foaming agent formed by mixing 50% by mass of a polypropylene resin or a polyethylene resin and 50% by mass of sodium bicarbonate can be used.

Also, at a predetermined position in the heating cylinder 11 (for example, at the rear end (right end in FIG. 1) or substantially at the center in the axial direction of the injection nozzle 20), radially inward or at a predetermined position of the screw 12 A gas injection nozzle (not shown) is opened radially outward at a position (for example, approximately the center in the axial direction of the screw 12), and carbon dioxide gas, nitrogen gas, or the like as a foaming material supplied from a gas supply source (not shown) Gas for foaming,
By injecting the mixture into the heating cylinder 11 through the gas injection nozzle and mixing the resin into a resin such as a polypropylene resin, a polystyrene resin, or a nylon, the foaming container 71 containing a large number of air bubbles can be formed. In addition, the gas can be mixed in advance into the resin as a raw material.

Subsequently, at a timing t2 immediately before the filling of the cavity material C with the molding material is completed, the injection step is completed, and the foaming control means (not shown) of the control unit 26 stops driving the injection cylinder 13; Screw 1
2 is stopped, and a foaming step is started. In the foaming step, the foamed material in the molding material is foamed. In the present embodiment, at the timing t2, the leading end of the molding material 90 that has entered the cavity space C, that is, the flow end 91 is connected to the gate 63 in the cavity space C.
Is set in advance just before reaching the position farthest from the camera. In the foaming step, the drive of the hydraulic motor 14 is kept stopped, so that the screw 12 is not not only moved forward and backward but also not rotated.

At the timing t3, the foaming step is completed, and the measuring step is started again.
At timing t4, the weighing process is completed.

The mold apparatus 61 comprises a fixed mold 64 and a movable mold 65. The movable mold 65 is moved toward and away from the fixed mold 64 by a mold clamping device (not shown) to close the mold. , Mold closing and mold opening are performed. Then, a cavity space C is formed between the fixed mold 64 and the movable mold 65 as the mold is closed and clamped.
In the cavity space C, the trunk portion 72, the bottom portion 73,
The trunk portion C1, the bottom portion C2, the leg portion C3, and the flange portion C correspond to the leg portion 74 and the flange portion 75, respectively.
4 are formed, and a gate 63 is formed at the center of the bottom portion C2. Therefore, the molding material 90 is used for the gate 6.
3 into the cavity space C through the bottom portion C
2. After flowing through the foot root portion C3 and the trunk portion C1, it reaches a flange portion C4 formed at a position farthest from the gate 63 in the cavity space C.

When the mold is opened, the foamed container 71 molded in the cavity C is fixed to the fixed mold 6.
4 and the movable mold 65 are released.

Further, in the foaming container 71, the releasability at the time of opening the mold is improved so that the foaming container 71 can be smoothly released from the fixed mold 65 and the movable mold 64. A draft angle of 5 to 10 [°] is provided. That is, as shown in FIG. 2, the outer surface S1 common to the body 72 and the leg base 74 and the inner surface S2 common to the body 72 and the flange 75 are all from the upper end of the foam container 71. The further away, the smaller the radial dimension,
The radial dimension of the inner side surface S3 of the leg base portion 74 decreases as the distance from the lower end of the foam container 71 increases. Therefore,
The connecting portion R11 between the base portion 74 and the trunk portion 72 and the body portion 72 and the bottom portion 73 is more than the body portion 72 and the bottom portion 73.
The wall thickness is about 0 to 100%.

In this case, at the base portion 74,
Since the amount of the molding material 90 shrinking with cooling is large, if the pressure of the molding material 90 at the foot root portion C3 does not become sufficiently high, molding failure such as sinking, short-circuit, and void occurs at the foot root portion 74, The appearance of the foaming container 71 is deteriorated.

A cover (not shown) made of paper, aluminum, plastic, film, or the like is attached to the flange 75 by heat sealing, and the foam container 71 is sealed. For this purpose, the lid is pressed against the flange 75 by a pressing member such as a high-temperature heating element (not shown) or an inductor. In order to withstand the pressing force of the pressing member, the flange portion 75 is attached to the body portion 72.
The thickness is increased by about 20 to 50%.

In this case, also in the flange portion 75, the molding material 90 shrinks greatly with cooling, and the flange portion 75 is formed at the position farthest from the gate 63 in the cavity space C. If the pressure of the molding material 90 in the flange portion C4 is not sufficiently high, molding failure such as sink, short, void, etc. occurs in the flange portion 75, and the appearance of the foam container 71 is deteriorated. Further, when attaching the lid to the foam container 71, the lid cannot be stably pressed against the flange portion 75.
As a result, the sealing performance of the foam container 71 is reduced.

Therefore, in the present embodiment, the speed of the screw 12 during the injection process, that is, the injection speed V _S
Is formed without foaming the foamed material in the molding material 90 so that the molding material 90 is not cooled and the specific volume of the resin melted by the shearing heat generation can be increased. It is set higher than the case, and is set in the range of 200 ≦ V _S ≦ 1000 [mm / s], preferably in the range of 300 ≦ V _S ≦ 600 [mm / s]. Is performed. Further, for example, when the wall thickness of the body 72 and the bottom 73 is 1.0 [mm] or less, the filling time t _S is in the range of 0.05 ≦ t _S ≦ 0.2 [s], preferably, It is set in a range of 0.1 ≦ t _S ≦ 0.15 [s].

Therefore, the molding material 90 stored in front of the screw head 12b is injected from the injection nozzle 20 at a high speed and passes through the sprue and the runner 62 at a high speed due to the high-speed filling performed during the injection process. Then, the cavity space C is filled through the gate 63,
It can be moved at high speed in the cavity space C.

Accordingly, an extremely large shear stress is applied to the molding material 90, and the molding material 90
Is expanded and the volume is increased.

Subsequently, as described above, the flow end 91
However, at a timing t2 immediately before reaching the position farthest from the gate 63 in the cavity space C, the injection step is completed, the foaming step is started, the driving of the injection cylinder 13 is stopped, and the screw 12 is stopped. Can be

At this time, the flow end 91 has not reached the position farthest from the gate 63 in the cavity space C, and the flange portion C4 has a gap C of a predetermined volume.
_B is formed. In this embodiment, when the volume of the cavity C and V _C, the a gap C volume of V _B of _B, the volume V _B is set to a percentage of the volume V _C zeta,
The ratio ζ is set in the range of 1 ≦ ζ ≦ 5 [%].

For this purpose, the screw position is detected by a position sensor 22. When the screw 12 reaches a preset stop position, the foam control means stops the screw 12. The stop position is determined by the clearance C _B when the screw 12 is stopped.
Is calculated in advance so that is formed.

[0044] Thus, the clearance C _B are formed at the time the injection process is completed, the foamable amount in the cavity C (space) is increased, it is possible to sufficiently expand the molding material 90, it Accordingly, the foaming agent can be sufficiently foamed, and the foaming ratio can be increased.

Further, in the foaming step, no shearing stress is applied to the molding material 90 as the high-speed filling is completed, so that the molding material 90 in the cavity space C is cooled and largely contracted. Therefore, the foaming agent can be foamed more sufficiently, and the foaming ratio can be increased.

For example, the mixing amount of the foaming agent is 2%,
When the thickness of the body portion 72 and the bottom 73 is 0.6 mm. As shown in FIG. 5, the fill time t _S is higher expansion ratio becomes higher short filling time t _S is about 0.06
In [s], the expansion ratio becomes 1.15 to 1.2 times and saturates.

The expansion ratio is determined by the filling time t _S , the mold clamping force, the gap of the air vent between the fixed mold 64 and the movable mold 65 when the mold clamping is completed, the heating cylinder 11 The charging time t _S has the largest effect, although it depends on the temperature, the back pressure applied to the screw 12 in the measuring step, the amount of the foaming agent mixed, the composition of the foaming agent, and the like.

As described above, since the expansion ratio can be increased, the weight of the foam container 71 can be reduced, and the weight of the foam container 71 can be reduced to 85% of the weight when the foam material in the molding material 90 is not foamed. [%].

The molding material 9 at the base portion C3 of the leg
Since the pressure of 0 can be sufficiently increased, the molding material 90 is sufficiently pressed against the inner peripheral surface of the cavity space C. Accordingly, molding defects such as sink marks, shorts, voids, etc. do not occur in the base portion 74 of the leg,
Appearance can be improved. The void is
Due to the pressure of the molding material 90, it is sufficiently small (0.1 to
0.5 [mm]).

Further, since the pressure of the molding material 90 in the flange portion C4 can be sufficiently increased, molding failure such as sink, short, void, etc. does not occur in the flange portion 75, and the appearance of the foam container 71 can be improved. Can be better. Further, when attaching the lid to the foam container 71, the lid can be stably pressed against the flange portion 75. As a result, the sealing performance of the foam container 71 can be improved.

Further, since it is not necessary to increase the filling pressure, the mold clamping force of the mold clamping device is reduced to half of the ordinary mold clamping force.
It can be reduced to 1/3. Therefore, not only can the size of the mold clamping device be reduced, but also the cost of the mold clamping device can be reduced.

When an attempt is made to change the design of the foaming container 71, molding defects such as sink marks, shorts, and voids do not occur even if a thick portion is formed due to the change in the design. The degree of freedom in design can be increased.

Furthermore, since the releasability at the time of opening the mold can be improved, not only the draft angle can be reduced, but also the time for cooling the molding material 90 after the completion of the foaming step is shortened. be able to.

The present invention is not limited to the above embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0055]

As described above in detail, according to the present invention, in the method for molding a foamed molded product, in the injection step, the molding material obtained by mixing the foamed material with the resin can be processed at a high speed. Inject, fill the cavity space by performing high-speed filling, at the timing immediately before the filling of the molding material is completed, complete the injection process, stop the injection member and start the foaming process, in the foaming process, The foam material in the molding material is foamed.

In this case, the injection step is completed at a timing immediately before the completion of the filling of the molding material, and the foaming material in the molding material is foamed in the foaming step. The foamable amount increases. Therefore, the molding material can be sufficiently expanded, the foaming agent can be sufficiently foamed, and the expansion ratio can be increased, so that the weight of the foam molded article can be reduced.

Further, the appearance of the foamed molded article can be improved without causing molding defects such as sink marks, shorts, voids and the like.

Since it is not necessary to increase the filling pressure, the clamping force of the clamping device is reduced to 1/2 to 1 of the ordinary clamping force.
/ 3. Therefore, not only can the size of the mold clamping device be reduced, but also the cost of the mold clamping device can be reduced.

When an attempt is made to change the design of the foam molded article, even if a thick portion is formed due to the change in the design, molding defects such as sink marks, shorts, and voids do not occur. The degree of freedom in design can be increased.

Furthermore, since the releasability at the time of opening the mold can be improved, not only the draft angle can be reduced, but also the time for cooling the molding material after the completion of the foaming step can be shortened. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic view of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a sectional view of a foam container.

FIG. 3 is a time chart illustrating an operation of the injection molding machine according to the embodiment of the present invention.

FIG. 4 is a diagram showing a state of a molding material during a foaming step according to the embodiment of the present invention.

FIG. 5 is a relationship diagram between a filling time and an expansion ratio.

[Explanation of symbols]

11 heating cylinder 12 screw 13 injection cylinder 14 hydraulic motor 26 the control unit 61 the mold device 63 gate 71 foam containers 90 molded material C cavity C _B clearance

Claims (7)

[Claims] (A) In an injection step, a molding material obtained by mixing a foaming material into a resin is injected at a high speed, and a high-speed filling is performed to fill a cavity space.
(B) At the timing immediately before the filling of the molding material is completed, the injection step is completed, the injection member is stopped, and the foaming step is started. In the foaming step, the foaming material in the molding material is foamed. A method for molding a foamed molded product. 2. The method according to claim 1, wherein the injection speed V _S is set in a range of 200 ≦ V _S ≦ 1000 [mm / s]. 3. The method according to claim 1, wherein the filling time t _S is set in a range of 0.05 ≦ t _S ≦ 0.2 [s]. 4. The method according to claim 1, wherein the ratio ζ of the gap formed in the cavity space when the injection step is completed in the cavity space is set in the range of 1 ≦ ζ ≦ 5 [%]. Molding method for foam molded products. 5. The method according to claim 1, wherein the foaming material is a foaming agent. 6. The method according to claim 1, wherein the foaming material is a gas for foaming. 7. (a) a cylinder member; and (b) an injection member disposed to be able to advance and retreat in the cylinder member.
(C) a driving means for moving the injection member forward and backward; (d) a mold device in which a cavity space is formed as the mold is closed and closed; and (e) mixing a foaming material into the resin in the injection step. Injection control means for injecting the molding material obtained by the above at a high speed, performing high-speed filling and filling the cavity space through a gate, and (f) at a timing immediately before the completion of the filling of the molding material, An injection molding machine comprising: an injection step, an injection member being stopped, a foaming step being started, and a foaming control means for foaming a foaming material in a molding material in the foaming step.