JP3238830B2 - Injection molding method of flat plate with lattice rib - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for a flat plate with a grid-like rib, and can be used for forming a molded product having a grid-like rib such as a paper supply part of a copying apparatus.

[0002]

2. Description of the Related Art When injection-molding a synthetic resin flat plate having a grid-like rib formed on one surface of a flat portion to improve surface rigidity,
Due to the molding shrinkage inherent in synthetic resin, the flat part shrinks, and the contraction rate of the lattice ribs is different from the flat part,
In addition, since the grid-like ribs serve as a structure and are restrained by the shrinkage of the rib portions, the plane portion generally has a warp.

[0003]

[0005] Such a warp is caused by
The holding pressure (holding pressure) for the resin injected into the mold cavity can be suppressed by lowering the holding pressure. However, when the holding pressure is lowered, there is a problem that the sink of the ribs particularly becomes large and conspicuous. On the other hand, if excessive holding pressure is applied to the resin injected into the mold cavity in order to prevent sink marks, there is a problem that excessive holding pressure is applied to the flat portion, causing warpage deformation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above contradictory problems and to prevent sinking of a rib portion when injection-molding a flat plate with lattice ribs, and to prevent warpage of a flat portion. An object of the present invention is to provide an injection molding method for a flat plate with lattice ribs, which can eliminate distortion and can be molded with high precision.

[0005]

Injection molding process of the grid-shaped ribbed flat of the present invention, in order to solve the problem] is the injection molding process for molding a flat plate having ribs arranged in a grid on at least one surface of the flat portion, the dies after closing, when the mold of the molten resin a molten resin is filled into the cavity is in the state being cooled and solidified, the compressed fluid is injected between the cavity surface and the resin in the grating portion surrounded by the rib , The molten resin is cooled
After solidification, the mold is released and the molded product is taken out .

At this time, it is preferable that the compressed fluid is injected into all the grid portions of the flat plate with the grid-like ribs so that the entire surface of the flat plate is pressurized and held. Further, when injecting the compressed fluid into the cavity, it is desirable to inject the compressed fluid from the clearance of the protruding pin (the gap between the protruding pin and the die through hole into which the protruding pin is inserted) for releasing the molded product. . Here, it is preferable that the clearance at the tip of the protruding pin on the cavity side (portion opened on the cavity surface) is set to 1/100 to 8/100 mm (10 to 80 μm).

Furthermore, when the compressed fluid is injected under pressure into the cavity, a low-pressure compressed fluid is injected at the initial stage of injection, and then a high-pressure compressed fluid is injected to perform multi-stage pressure control of the compressed fluid. Is desirable. Further, a concave portion for erecting a barrier on the back surface side of the molded product may be formed on the cavity surface around the protruding pin as necessary.

[0008]

According to the present invention, since the molten resin injected into the cavity is being cooled and solidified, a compressed fluid such as nitrogen gas is injected into the grid portion surrounded by the ribs. , The molten resin (flat plate) in the cavity
The flat portion is cooled and solidified while being pressed against the inner surface of the cavity, and sink is prevented. Furthermore, injection molding at a low pressure can be performed without the need to apply an excessive holding pressure to the molten resin, and since the compressed fluid acts not only on the flat portion but also on the rib portion, the pressure distribution between the rib portion and the flat portion can be improved. Is eliminated and the distribution of molding shrinkage disappears, so that a flat plate with excellent surface accuracy and without warpage is formed. At this time, if the compressed fluid is injected into all the lattice parts, the entire flat part is uniformly pressed against the cavity surface, so that sinks are reliably prevented, and a flat plate with even more excellent surface accuracy and no warping deformation is obtained. Molded.

Also, if the compressed fluid is injected using the clearance of the protruding pins provided in the mold, it is not necessary to newly provide a mechanism for injecting the compressed fluid into the mold, and the structure of the mold is reduced. It is simplified and easy to manufacture.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an injection molding apparatus 1 of the present embodiment. The injection molding device 1 includes a screw 2
Injection device 3 that has resin and melts and kneads the resin, and fixed mold 4
And a mold clamping device 6 to which the movable mold 5 is attached. The movable die 5 is provided with a push-out pin 9 which is pushed through the protrusion plate 7 and whose tip projects into the cavity 8 to take out a molded product through the through hole 10 of the movable die 5.

A gas supply path 11 is formed in the movable mold 5 so as to communicate with the through hole 10. The gas supply path 11 is connected to a gas injection controller 12. The gas injection controller 12 is driven by driving air from the compressor to increase the pressure of the nitrogen gas for injection into a compressed fluid, thereby increasing the pressure of the nitrogen gas for injection. An opening / closing valve 14 for controlling the supply of nitrogen gas to the apparatus and a control device 15 for controlling the operation of the pressure intensifier 13 are provided. Therefore, the gas supply path 11 and the gas injection control device 12 constitute a compressed fluid supply unit.

The opening / closing valve 14 includes a supply electromagnetic valve 16 for controlling the supply of nitrogen gas, an exhaust electromagnetic valve 17 for exhausting the injected nitrogen gas, and an electromagnetic valve 18 for controlling the pressure of the supplied nitrogen gas. These valves 16, 17, and 18 are individually controlled to open and close by the control device 15.

As shown in FIG. 3, the cavity 8 of this embodiment forms a flat plate 90 having a grid-like rib 91 on one side of a flat portion 94. Groove 19 is formed.

As shown in FIG. 2, the through holes 10 of the movable mold 5 are formed between the concave grooves 19, that is, the grid-like ribs 9 of the flat plate 90.
1 is formed at a portion where the grid portion 98 is formed, which is surrounded in four directions or three directions. In this embodiment, the through-holes 10 are not formed in the mold portions that form the four corners (the lattice portions 99 in which the ribs 91 are formed in only two directions) of the flat plate 90 shown in FIG. , This lattice part 9
The through-hole 10 may be formed also in the portion where 9 is formed.

As shown in FIG. 2, the tip of the through hole 10 has a small diameter at the cavity 8 side so that the clearance A with the protruding pin 9 is 1/100 to 8/100 mm (10 to 80 μm). Is set. Also, the protruding plate 7 of the through hole 10
On the side (opposite side of the cavity 8), a sealing material 21 such as an O-ring for sealing a gap with the protruding pin 9 is provided.

Next, the procedure of injection molding in this embodiment will be described. First, using the mold clamping device 6, the mold 4,
5 is closed, and the injection device 3 injects a predetermined amount of the molten resin into the cavity 8. At this time, the resin pressure applied to the protruding pin 9 increases with the resin filling, but the clearance A at the tip of the through hole 10 on the cavity 8 side becomes 1/100 to 8/100.
Since the width is reduced to mm, the resin is prevented from flowing into the through-hole 10, and the resin is filled without clogging the clearance.

When a predetermined amount of the molten resin is charged and a signal indicating the end of the charging is sent from the injection device 3 to the gas injection control device 12, the pressure intensifier 13 is operated and the supply valve 16 is opened to supply the gas. Through hole 10 through road 11
Is injected with nitrogen gas. At this time, the molten resin is being cooled and solidified, so that a gap is formed between the molten resin and the cavity 8.
Therefore, the nitrogen gas injected into the through-hole 10 is injected into the cavity 8 through the clearance of the protruding pin 9.

The nitrogen gas injected into the cavity 8 is
Each grid portion 9 surrounded by a rib 91 having an open through hole 10
8 is injected. The gas pressure of this nitrogen gas is
4 acts against the inner surface of the cavity 8 of the fixed mold 4 and also acts in the direction of each of the ribs 91 orthogonal to the direction, whereby a sufficient holding pressure is applied until the flat plate 90 is cooled and solidified. The surface of the flat plate 90 is pressed against the inner surface of the cavity 8 of the fixed mold 4 to prevent sink marks. Further, since the gas pressure is applied to both the rib 91 and the flat portion 94, the pressure distribution disappears and the distribution of the molding shrinkage disappears, so that the flat plate 90 having excellent surface accuracy and without warpage can be obtained.

When the molten resin has cooled and solidified, the exhaust valve 17 is opened to release the gas in the cavity 8, the molds 4 and 5 are released, and the protruding pins 9 are protruded to take out the molded product 90. One cycle of injection molding is completed. By repeating the above molding cycle, molded article 9
0 is sequentially formed.

According to this embodiment, the following effects can be obtained. In forming the flat plate 90 with the grid-like ribs 91, the nitrogen gas is injected into the grid portion 98 surrounded by the ribs 91 in the cavity 8, so that the gas pressure of the nitrogen gas is only in the direction of the flat portion 94. The rib 91 also acts in the direction of the ribs 91, so that the compression action can be performed on the flat plate 90 not only from the flat portion 94 but also from the entirety including the rib 91. For this reason, the pressure distribution of the flat plate 90 is eliminated, the distribution of molding shrinkage can be eliminated, and the flat plate 90 with excellent surface accuracy and without warpage can be formed.

Further, since the molten resin is pressed against the inner surface of the cavity 8 by the injected nitrogen gas, the state of close contact between the resin surface and the inner surface of the cavity 8 can be maintained until the molten resin is cooled and solidified. Even when a flat plate 90 having ribs 91 is formed, sinkage can be prevented,
It is possible to simultaneously solve the problems of preventing sink marks and warpage that have not been compatible with each other.

In the above embodiment, since the nitrogen gas is injected into all of the grid portions 98 other than the grid portions 99 at the four corners of the flat plate 90, a compression action can be exerted from the entire back surface of the flat plate 90 to the front surface side. The sink of the entire plate 90 can be surely prevented, and the surface accuracy of the entire plate 90 can be improved, and an excellent flat plate 90 without warpage can be manufactured.

By injecting nitrogen gas into the cavity 8, the flat plate 90 can be prevented from warping or sinking. Therefore, it is not necessary to perform high-pressure injection molding to prevent sinking as in the prior art. Molding can be realized. Therefore, the molding cycle can be shortened, and the productivity can be improved without lowering the quality of the flat plate 90.

The cavity 8 is formed through a clearance between the protrusion pin 9 and the through hole 10 which are usually provided in the mold 5.
Since the nitrogen gas is injected into the inside, there is no need to newly form a gas injection hole, so that the structure of the mold 5 can be simplified and provided at a low cost. At this time, the clearance A around the protruding pin 9 is 1/100 to 8/100 mm.
Therefore, it is not necessary to arrange a porous member or the like having a fine hole for preventing the molten resin from flowing into the through hole 10 in the clearance portion, and the mold structure can be further simplified, Since the molten resin can be reliably prevented from flowing into the through-hole 10 and does not hinder the flow of the nitrogen gas into the cavity 8, a sufficient gas can be supplied smoothly, and the holding pressure by the nitrogen gas can be maintained. And the sink and warpage of the flat plate 90 can be reliably prevented.

Since non-combustible nitrogen gas is used as the compressed fluid, there is no danger of explosion even if it is expanded or heated by injection into the cavity 8, and the safety of injection molding can be ensured.

Since a gap is formed by injecting nitrogen gas between the back side of the flat plate 90 and the movable mold 5, the flat plate 90 can be easily released, and in particular, the ribs 91 are large and are difficult to release. Even when the flat plate 90 is formed, it is possible to prevent troubles due to poor mold release, and to perform efficient injection molding.

Next, a description will be given of an experimental example conducted to confirm the effect of the present invention. In this experimental example, a square flat plate 90 having a grid-like rib 91 as shown in FIG.
And, as shown in Table 1, various conditions were changed to obtain a flat plate 9.
The sink and warpage amounts of 0 are evaluated.

In molding the flat plate 90, IS-200 manufactured by Toshiba Machine Co., Ltd. was used as an injection molding machine, and MFR was used as a resin.
(Melt flow ratio) [230 ℃, 2.16kgf] = 10g / 10min
Block PP (polypropylene) was used. Flat plate 90
Has a side length of 250 mm, and as shown in FIG. 4, the general thickness d other than the rib 91 is 2.5 mm and the rib 9
The base thickness (width) b of 1 is set to 2 mm. In FIG. 4, the thicknesses of the rib 91 and the flat member 95 are made larger than the actual dimensional ratio for easy understanding.

The mold clamping pressure was set to 200 t, and the resin temperature and the mold temperature were set as shown in Table 1. Then, Experimental Examples 1 to 4 were performed by changing the dimensions of the pin clearance A and the gas pressure, and the sink condition of the flat plate 90 was detected using a surface roughness meter (Surfcoder SE-30D manufactured by Kosaka Laboratories). And the amount of warpage was measured. On the other hand, as Reference Examples 1 to 4, experiments were also conducted when the pin clearance A was smaller (Reference Examples 1 and 2) or larger (Reference Examples 3 and 4) than in the experimental examples.

[0030]

[Table 1]

As shown in Table 1, the pin clearance A
(Experimental example: 1/100 to 8 / 100mm) If the gas pressure is set appropriately according to the type of resin, the shape of the molded product, the size of the molded product, the molding conditions, etc., the sink and warpage are extremely small. Thus, it was confirmed that a flat plate 90 having excellent surface accuracy can be formed. On the other hand, if the clearance A of the protruding pin 9 is too small as in Reference Examples 1 and 2, the inflow of nitrogen gas is hindered, and a sufficient gas cannot be supplied into the cavity 8, so that both the sink and warpage amounts increase. understood. Also, if the clearance A is too large as in Reference Examples 3 and 4, the molten resin will be in the clearance portion (through hole 10).
It has been found that both the sink and the warpage increase because the gas flows backward and is clogged and cannot supply gas.

As described above, if nitrogen gas is injected into the lattice portion 98 in the cavity 8 through the clearance of the protruding pin 9 which is appropriately set according to the type of resin, etc., the flat plate 90 having the lattice ribs 91 can be formed. High quality, high precision, and high strength flat plate 9
0 was found to be moldable, confirming the usefulness of the present invention.

Although the present invention has been described with reference to preferred embodiments, the present invention is not limited to these embodiments, and various modifications and changes in design can be made without departing from the spirit of the present invention. Is possible. For example, in the above-described embodiment, the compressed fluid (nitrogen gas) is injected from the clearance of the protruding pin 9, but as shown in FIG.
May be provided. That is, the through hole 22 is formed in the movable mold 5, the gas supply path 11 is connected to the through hole 22, the fixed pin 30 is disposed in the through hole 22, and the compressed fluid is injected from the clearance around the pin 30. May be. In this way, a compressed fluid such as nitrogen gas can be injected into the portion where the protrusion pins 9 are not provided (the lattice portion 99 in the above embodiment), and sink and warpage can be reliably prevented over the entire surface of the flat plate 90. There are advantages that can be.

At this time, as shown in FIG. 5, a flat plate 9 is provided outside the concave groove 19 on the inner surface of the cavity 8 of the movable mold 5.
It is preferable that a groove 20 having a triangular cross section for forming the barrier wall 92 is formed along the concave groove 19. That is, the grid portion 9 that is not entirely surrounded by the ribs 91
In the case of injecting the compressed fluid into the portions 8 and 99, if the barrier 92 is formed in a portion where the rib 91 is not provided, the injected compressed fluid is held in the lattice portions 98 and 99 and does not leak out. Can be sufficiently maintained. The shape of the groove 20 is not limited to a triangular cross section, but may be a rectangular cross section similar to a thin rib, for example. The depth of the groove 20 (the height of the barrier 92)
Is preferably set to about 2 to 10 mm in consideration of the holding capacity of the compressed fluid and the increased amount of the resin used.

The compressed fluid is not limited to nitrogen gas, but other gases such as compressed air may be used. However, since the temperature of the compressed fluid in contact with the molten resin increases, there is an advantage that the use of a nonflammable gas such as nitrogen gas provides higher safety.

When supplying the compressed fluid, the pressure of the compressed fluid to be injected may be controlled in two stages by using the pressure control valve 18 of the opening / closing valve 14. That is,
At the initial stage of the injection of the compressed fluid, the valve 18 is opened and a part of the compressed fluid is evacuated to lower the pressure, and the compressed fluid at a low pressure (for example, the pressure in the intensifier 13 is 0.5 to 3 MPa) is supplied for a predetermined time (for example, 0.2 to 3 seconds), and then the valve 18 may be closed to inject a high-pressure (for example, 3.5 to 20 MPa) compressed fluid for a predetermined time (for example, 2 seconds or more).
As described above, if the low-pressure compressed fluid is injected at the initial stage of injection, the solidified layer is compressed by the pressure of the compressed fluid at the initial stage of cooling and solidification immediately after the injection of the molten resin, that is, when the solidified layer on the resin surface is in a thin state. Thus, a flat plate 90 of high quality and high strength can be manufactured without breaking and breaking gas inside the resin.

The pressure of the compressed fluid to be injected is not limited to two-stage control, but may be controlled to three or more stages or a pressure value to be changed continuously. The value may be constant. The pressure value at this time is
What is necessary is just to set suitably according to the kind of resin to be used, etc. Further, the pressure control method is not limited to the method in which the pressure control valve 18 is provided as in the above embodiment, and a known appropriate pressure control method using a pressure reducing valve or the like may be used.

A porous member made of heat-resistant metal or ceramic may be arranged in the clearance of the protruding pin 9. If this porous member is arranged, the through hole 1
0 can be injected into the cavity 8 and the molten resin in the cavity 8 can be prevented from flowing into the through hole 10. For this reason, even when the clearance of the protruding pin 9 is larger than the optimum range particularly in the existing mold 5 or the like, the porous member is disposed in the clearance so that the porous member is suitable for gas injection and resin inflow. Can be prevented. In addition,
The pore diameter of the porous member may be appropriately set according to the type of resin used, etc., for example, 1/100 to 8/100 m, which is the same as in the above embodiment.
It should be set to m.

As shown in FIG. 6, when the resin is injection-filled by partially cutting out the leading end of the concave groove 19 for the rib 91 of the mold 5, a thickened portion is formed at the base of the rib 91 on the flat plate 90. 96
May be formed. In the present invention, the back side of the flat plate 90 is recessed and recessed by an amount corresponding to the prevention of sink on the front side. However, if the thickened portion 96 is formed, the cutout missing portion is replenished by the thickened portion 96 and the strength is reduced. Can be prevented. At this time, if the amount of resin in the thickened portion 96 is set to about 20 to 70% of the volume of the cooling delay portion 97 generated in the center of the rib 91, the required strength is secured without significantly increasing the amount of resin. can do. In addition, since the fillet portion 96 is eliminated by being replenished to the missing portion, the fillet portion 96 does not stand out on the flat plate 90.

The present invention is not limited to the flat plate 90 of the above embodiment, but can be used for forming various flat plates having a grid-like rib on one or both sides.

[0041]

According to the present invention, when a flat plate having a grid-like rib is injection-molded, sink and warpage of the flat plate can be prevented, and a flat plate of high precision, high quality and high strength can be prevented. There is an effect that can be molded.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a central portion of a mold according to the embodiment.

FIG. 3 is a perspective view showing a flat plate with a grid-like rib formed in the embodiment.

FIG. 4 is a diagram illustrating a warped state of a flat plate with lattice ribs in an experimental example.

FIG. 5 is an enlarged sectional view showing a main part of a modification of the present invention.

FIG. 6 is an enlarged sectional view showing a main part of another modification of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection molding device 3 Injection device 4 Fixed die 5 Movable die 6 Mold clamping device 8 Cavity 9 Protrusion pin 10 Through hole 11 Gas supply path 12 Gas injection control device 13 Pressure booster 14 Open / close valve 15 Control device 19 Concave groove 20 Groove 22 Through-hole 90 Flat plate 91 Rib 92 Wall 94 Flat part 98, 99 Grid part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-254924 (JP, A) JP-A-6-254912 (JP, A) JP-A-11-245267 (JP, A) JP-A-5-254267 301257 (JP, A) JP-A-11-268083 (JP, A) JP-A-10-503719 (JP, A) European Patent Application Publication 593308 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (5)

(57) [Claims] In an injection molding method for forming a flat plate having ribs arranged in a lattice pattern on at least one surface of a flat portion, a molten resin is filled in a cavity of the die after closing a die. When the resin is in a state of being cooled and solidified, a compressed fluid is injected between the cavity surface in the lattice portion surrounded by the ribs and the resin, and the molten resin is cooled and solidified.
A method for injection-molding a flat plate with a grid-like rib, comprising releasing a mold and removing a molded product . 2. The method of injection molding a flat plate with grid ribs according to claim 1, wherein the compressed fluid is injected into all the grid portions of the flat plate with grid ribs to hold the entire surface of the flat plate under pressure. An injection molding method of a flat plate with a grid-like rib. 3. The method according to claim 1, wherein the compressed fluid is injected from a clearance of a protruding pin for releasing the molded product. Flat plate injection molding method. 4. The injection molding method of a flat plate with a grid-like rib according to claim 3, wherein a clearance of at least a tip of the protrusion pin on the cavity side is 1/100 to 8 /.
An injection molding method for a flat plate with a grid-like rib, which is set to 100 mm. 5. The injection molding method of the grid-shaped ribbed flat according to any one of claims 1, 2, 3, 4, when injecting the compressed fluid in the cavity, the injection pressure injection early An injection molding method for a flat plate with a grid-like rib, characterized in that the pressure is controlled to a low pressure and then to a high pressure.