JPH1024469A - Injection molding method in combination with pressurized fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize forcible supply of pressurized fluid at an early stage after the completion of the injection of molten resin by realizing the full shooting of the molten resin by a method wherein pressurized fluid is forcibly supplied between a cavity surface and a molding article under the state that a mold is slightly opened so as to press the other surface of the molding article against the opposite cavity surface. SOLUTION: After a cavity 1 of a mold 2 is filled with molten resin, the mold 2 is slightly opened. When pressurized fluid is supplied between the two sheets of plate material of an ejector plate 5 after the slight opening of the mold 2, the supplied pressurized fluid is forcibly supplied between one side of a molding article in the cavity 1, the pressure in which is lowered, and a cavity surface 1a opposite to the above-mentioned one side through gaps between the sleeves 4a and the spindle pins 4b of respective ejector pins 4. As a result, the forcibly supplied pressurized fluid presses the other surface, which is opposite to the forcibly supplied side of the pressurized fluid, of a molding article 3 against the corresponding cavity surface 1a.

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, in which after injection of a molten resin, a pressurized fluid is press-fitted between a cavity surface corresponding to one surface of a molded product and the molded product, and the other surface of the molded product is injected. To an injection molding method that uses the pressure of a pressurized fluid in combination with the pressure of a pressurized fluid.

[0002]

2. Description of the Related Art Conventionally, as an injection molding method using a pressurized fluid, a molten resin is injected in an amount smaller than a cavity volume in a state in which a mold is closed with a small clamping force, and then the resin is applied to one side of a molded product. Pressurized gas is injected between the cavity surface and the molded product to slightly spread the mold against the mold clamping force, then clamp the mold again with a strong mold clamping force, and apply pressure inside the cavity. A method is known in which a pressurized gas is compressed and pressurized, and a surface of a molded product on a side opposite to a side on which the pressurized gas is pressed is pressed against a corresponding cavity surface (Japanese Patent Laid-Open No. 6-315947). .

In a general injection molding method using a pressurized fluid, a molten resin is injected and filled into a cavity of a clamped mold, and then a cavity surface corresponding to one surface of the molded product is formed. A pressurized fluid is press-fitted during the pressing to press the other surface of the molded product against the corresponding cavity surface.

[0004] Such a pressurized fluid combined injection molding method,
For example, it is said to be effective for molding a thin molded article having a rib or the like for reinforcement on one side, such as a housing of an electric device. That is, when a molded product having a thin thickness and having a rib or the like on one surface is molded by ordinary injection molding, sink is likely to occur in a rib portion that becomes a partially thick portion, and it is likely to cause poor appearance. According to the method, generation of the sink is prevented by the pressurized fluid pressure, and a molded article having excellent appearance is easily obtained.

[0005]

However, the injection molding method using a pressurized fluid described in Japanese Patent Application Laid-Open No. 6-315947 has a problem that a molded article having a very good appearance cannot be obtained. In other words, since the injection of the molten resin is a short shot of an amount smaller than the cavity volume, the molten resin near the flow end in the cavity is not so strongly pressed against the cavity surface when the injection is completed, whereas the injection near the gate is not so strong. The molten resin is in close contact with the cavity surface. Since the molded product having an uneven contact state with the cavity surface is strongly pressed against the cavity surface by press-fitting the pressurized gas and re-clamping, it is likely to cause uneven gloss on the molded product surface. There's a problem. This can be solved by injecting the molten resin as a full shot that completely fills the cavity, but with a full shot, the mold opens against the mold clamping force before pressurized gas injection. Become.

On the other hand, in the above-mentioned general injection molding method using a pressurized fluid, although the above-mentioned problem does not occur because the shot is a full shot, the pressure in the cavity is not increased even when the pressurized fluid is injected immediately after the injection is completed. Since the pressure is high, the press-fitting cannot be performed immediately, and the press-fitting is performed after the pressure in the cavity is reduced to some extent. Therefore, there is a problem that the cooling of the resin in the cavity proceeds during this waiting time, and it is difficult to obtain a sufficient sinking prevention effect. If the pressure is increased to accelerate the press-fitting time of the pressurized fluid, the press-fitting time is advanced, but the pressurized fluid pressurized into the cavity enters the molded product from, for example, the base of the rib, and the molded product becomes hollow. This causes a defective appearance such as uneven glossiness.

The present invention has been made in view of the above-mentioned conventional problems. After a molten resin is injected into a cavity, a pressurized fluid is injected between the cavity surface corresponding to one surface of the molded product and the molded product. In a pressurized fluid combined injection method in which the other side of the molded product is pressed into the corresponding cavity surface, the injection of the molten resin is made full shot, and the molten resin is injected without excessively increasing the pressure of the pressurized fluid. It is an object of the present invention to be able to press-in a pressurized fluid at an early stage after completion of injection.

[0008]

According to the present invention, there is provided:
As shown in FIG. 2, after injecting and filling the molten resin into the cavity 1, the mold 2 is slightly opened, and a space between the cavity surface 1 a corresponding to one surface of the molded product 3 and the molded product 3 is formed. The pressurized fluid is press-fitted, and the other surface of the molded product 3 is pressed against the corresponding cavity surface 1b.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the present invention will be described with reference to FIGS.

As shown in FIG. 1, the mold 2 used in the method of the present invention is not particularly limited as long as the cavity 1 is not opened even when the mold 2 is slightly opened. Because it is easy to prevent pressurized fluid leakage from the parting surface,
It is preferable to have a cavity 1 that forms a concave shape in the opening and closing direction of the mold 2. The cavity 1 forming the concave shape is a mold 2
A molded product 3 (see FIG. 2) having a shape in which one end of the mold 2 is open and the other end of the mold 2 in the open / close direction and the periphery thereof are enclosed, for example, a molded product 2 such as a packaging box or a housing of an electric device. For molding. The prevention of pressurized fluid leakage from the parting surface of the mold 2 will be described later.

The mold 2 will be further described. As shown in FIG. 1, a cavity 1 is formed between a movable mold 2a and a fixed mold 2b. In the drawings, the core mold is the movable mold 2a and the mold is the fixed mold 2b. However, the core mold may be the fixed mold 2b and the mold may be the movable mold 2a.

On the movable mold 2a side, an ejector pin 4 penetrating the movable mold 2a has its tip end face facing the cavity 1. The ejector pin 4 has a tubular sleeve 4
a, and a shaft pin 4b inserted into the sleeve 4a, and a gap serving as a passage for a pressurized fluid, which will be described later, is left between the sleeve 4a and the shaft pin 4b. The rear end of the ejector pin 4 is connected to the ejector plate 5. In particular, the ejector plate 5 is constituted by two plate members, and the ejector pins 4 are held in a state where they enter the joint of the two plate members.

In the vicinity of the rear end of each ejector pin 4, a pressurized fluid is supplied to a joint between two plate members constituting the ejector plate 5. The supplied pressurized fluid is supplied from the rear end of each ejector pin 4 into the cavity 1 from the front end of the ejector pin 4 through the gap between the sleeve 4a and the shaft pin 4b. Here, 6a to 6f are sealing materials.

First, in the mold clamping state shown in FIG.
A molten resin is injected into the cavity 1. As resin,
Thermoplastic resins used in general injection molding and extrusion molding can be widely used. Further, a thermosetting resin can be used if necessary. Further, in these resins, for example, fillers such as fillers and reinforcing fibers and various additives (eg, plasticizers, lubricants, ultraviolet absorbers, dyes, pigments, antifogging agents, antistatic agents, flame retardants, etc.) Can be added.

In addition to the above-described injection in the mold-clamped state, injection is started with the mold 2 slightly opened, and the mold 2 is closed while being injected (the movable mold 2a is advanced). If the cavity 1 is filled when the mold is clamped, the mold 2 is slightly open, so that the flow resistance in the cavity 1 is reduced, and the pressing force due to the mold clamping can be applied. Even when the product 3 (see FIG. 2) is thin, it is preferable because the cavity 1 can be filled with a relatively low injection pressure while the molten resin is in close contact with the cavity surfaces 1a and 1b.

As described above, even if the pressurized fluid is supplied immediately after the cavity 1 of the mold 2 is filled with the molten resin, the pressure in the cavity 1 is high and the pressurized fluid is difficult to be injected. . Therefore, in the present invention, as shown in FIG. 2, the mold 2 is slightly opened. That is, immediately after the injection of the molten resin into the cavity 1 is completed, the movable mold 2
a is slightly retracted. The opening of the mold 2 can be easily performed by an injection compression molding machine of a type capable of stopping and holding the advance and retreat of the movable mold at an arbitrary position. Also,
For example, a spring may be interposed between the movable mold 2a and the fixed mold 2b to loosen the mold clamping force, so that the movable mold 2a can be retracted by the repulsive force of the spring. In this case, it is preferable to provide a mechanical stopper for locking the movable mold 2a at a proper position so that the mold 2 does not open more than necessary.

Preferably, the mold 2 is slightly opened by retracting the movable mold 2a by about 0.05 to 0.5 mm from the clamped state. If the retreat amount of the movable mold 2a is too small,
The meaning of opening the mold 2 becomes less significant, and the waiting time until the pressurized fluid can be press-fitted becomes longer, making it difficult to sufficiently prevent sinking. Conversely, if the retreat amount of the movable mold 2a is too large, it takes time to increase the pressure by pressurizing the pressurized fluid, and as a result, it is difficult to sufficiently prevent sinking.

When the mold 2 is slightly opened, the volume in the cavity 1 increases, and the pressure in the cavity 1 decreases. Therefore, a pressurized fluid can be injected even at a very low pressure of about 7 kg / cm ² G. That is, when the pressurized fluid is supplied between the two plate members of the ejector plate 5 after the mold 2 is slightly opened, the supplied pressurized fluid is supplied to the sleeve 4a of the ejector pin 4 and the shaft pin 4b.
One side of the molded product in the cavity 1 in which the pressure is reduced through the gap between the cavity surface 1 and the cavity surface 1 corresponding to the one side.
a. Then, the pressurized fluid that has been press-fitted presses the other surface of the molded article 3 opposite to the press-fitted side of the pressurized fluid against the corresponding cavity surface 1b.

As the pressurized fluid, for example, a gas such as nitrogen gas, carbon dioxide gas, air, or the like, or a liquid such as oligomer or liquid paraffin can be used. Activated gas is preferred.

Although the pressurized fluid is press-fitted through the ejector pins 4 in the illustrated example, the present invention is not limited to this, and a separate pressurized fluid passage is formed in the mold 2. You may go. Further, the inlet of the pressurized fluid into the cavity 1 is formed so that the pressurized fluid can be reliably injected between the molded product 3 and the cavity surface 1a without being protruded or retracted from the cavity surface 1a. 1
It is preferable to be located on the same plane as a.

After the pressurized fluid is injected, the molded article 3 is cooled while the inside of the mold 2 is closed (usually, the supply of the pressurized fluid is also stopped) in the same manner as in normal injection molding with pressurized fluid. After the necessary cooling of the molded product 3, the pressurized fluid in the cavity 1 is discharged, and then the mold 2 is opened to take out the molded product 3. Further, after the press-fitting of the pressurized fluid is completed, the supply line of the pressurized fluid is closed, and the opened mold 2 is urged in the mold clamping direction, so that the pressure of the press-fitted pressurized fluid can be increased. . In this case, the molded article 3 on the non-press-in side of the pressurized fluid can be used without preparing a pressurized fluid having a high pressure.
This is preferable because the surface can be pressed strongly against the cavity surface 1b and the molding cost can be reduced.

As in the present invention, if the pressurized fluid is pressed immediately after the mold 2 is opened after the injection is completed, the molded product 3
At a stage where the cooling has not progressed so much, the pressing of the pressurized fluid against the cavity surface 1b can be started. Therefore, full-scale cooling of the molded article 3 is performed under pressure by the pressurized fluid, and it is possible to prevent sinks due to cooling. In particular, in the molded product 3 having the ribs and bosses for reinforcement on one side, the portion provided with the ribs and bosses is a thick portion. The sink is likely to occur at the position corresponding to the boss. According to the present invention, if a pressurized fluid is pressed into the rib or boss formation surface at an early stage after the injection is completed, it is possible to prevent sink marks due to the presence of the rib or boss.

According to the present invention, the surface condition of the molded article 3 on the non-press-in side of the pressurized fluid is particularly improved. In the example shown in the drawings, the surface condition of the molded product 3 on the side pressed against the cavity surface 1b by the press-fitting of the pressurized fluid is improved. Therefore, it is preferable that the side which is hard to be seen by the user when using the molded article 3 is the press-in side of the pressurized fluid. For example, in the housing of an electric device, it is preferable that the inner surface side is the press-in side of the pressurized fluid.

When the pressurized fluid is pressed into the mold 2 as shown in FIG. 2, the pressurized fluid pressurized between the molded product 3 and the cavity surface 1a is applied to the end of the molded product 3. There is a problem that it easily escapes to the parting surface of the mold 2 through the interface between the resin and the cavity surface 1a in the portion (the left end portion of the molded product in FIG. 2). When this pressurized fluid escapes, the molded product 3 cannot be pressed strongly against the cavity surface 1b, and it becomes difficult to sufficiently prevent sinking. In order to prevent this, the end of the molded product 3 is set as parallel to the opening and closing direction of the mold 2 as possible, and even if the mold 2 is slightly opened, the close contact between the resin and the cavity surface 1a at this portion is maintained. It is preferable to be able to maintain.

In order to prevent the pressurized fluid from escaping, as shown in FIG. 3, the undercut portion 7 extending over the entire periphery of the end portion of the molded product 3 is provided with the cavity surface 1 on the press-in side of the pressurized fluid.
a. The illustrated undercut portion 7 is convex with respect to the cavity surface 1a on the press-in side of the pressurized fluid, but may be concave. When the undercut portion 7 is provided, as shown in FIG. 4, when the mold 2 is slightly opened, one side of the undercut portion 7 cuts into the molded product 3 as indicated by a dotted line in the drawing. And the boundary between the cavity surface 1a and the resin is meandering, and the flow of the pressurized fluid along the boundary line is generated. Can be difficult.

However, in the above case, as shown in FIG. 4, since the volume of the end portion of the molded product 3 is also enlarged by the opening of the mold 2, the undercut portion 7 bites into the molded product 3 on one side. Power is easily weakened. Therefore, as shown in FIG. 5, it is preferable to use a mold 2 having a slide core 8 that defines at least the end surface of the molded product 3. The slide core 8 is a mold-type fixed type 1b.
, Which can be slid in a direction perpendicular to the opening and closing direction of the mold 2 to open the cavity 1. The shape of the cavity 1 (the shape of the molded product 3)
Is divided into two or more in accordance with.

When the mold 2 having the slide core 8 as described above is used, as shown in FIG. 5, when the mold 2 is slightly opened, the volume at the end of the molded product 3 does not increase, and One surface of the cut portion 7 is strongly pressed against the resin to form a seal portion, thereby reliably preventing the pressurized fluid from escaping through the interface between the resin and the cavity surface 1a at the end of the molded product 3. be able to.

The size of the undercut portion 7 has an elastic modulus of resin used may vary depending the thickness or the like of the physical properties and molded articles of elongation at break, etc., the entire perimeter of the molded article end L _1, undercut 7 top portion or the entire perimeter of the bottom portion when the L ₂ of, it is preferable that satisfy the following formula.

0.3% ≦ | {(L ₂ −L ₁ ) / L ₁ } |
× 100 ≦ 3% If the undercut portion 7 is too large, not only is it difficult to release the mold, but it also causes whitening and partial breakage of the molded article 3 when it is forcibly released. If the undercut portion 7 is too small, the meaning of providing the undercut portion 7 is lost.

[0030]

Example 1 Using a mold as shown in FIG. 1, a box-shaped molding having a flat rectangular shape, a thickness of 2 mm, and a width 3 mm and a height 3 mm in a diagonal direction on the inner side of the bottom surface and reinforcing ribs. The product was molded. High impact polystyrene was used as the resin, and nitrogen gas was used as the pressurized fluid. The pressure of nitrogen gas is 30, 5
0 and 100 kg / cm ² G. As a molding machine, an injection molding machine "IP-1050" manufactured by Komatsu, which can freely move and hold a movable mold during molding was used.

The molten resin was injected into the cavity while the mold was clamped to fill the cavity, and the movable mold was immediately retracted by 0.1 mm to slightly open the mold. Immediately after the mold is opened, nitrogen gas is injected between one side of the molded product (the inner surface of the box-formed product) and the corresponding cavity surface. After 40 seconds, the supply of nitrogen gas is stopped, and the state is maintained for 20 seconds. Cooling was performed while pressing.
After the cooling, the nitrogen gas in the cavity was completely discharged (to atmospheric pressure), the mold was opened, the molded product was taken out, and the occurrence of sink marks was visually observed.

At each of the nitrogen gas pressures, almost no sink marks were observed, but nitrogen gas escaped from the end of the molded article to the parting surface of the mold, and the nitrogen gas injection time was reduced. Was set to 30 seconds or less, the tendency for sink marks to easily occur was recognized.

Example 2 The same molding as in Example 1 was performed except that the injection time of nitrogen gas was set to 30 seconds and the dwell time was set to 10 seconds using a mold as shown in FIG. And the presence or absence of sink marks was observed. The size of the undercut portion is determined by the value of | {(L ₂ −L ₁ ) / L ₁ } | × 100.
The size was set to 0%.

At any of the pressures of the nitrogen gas, almost no sink marks were observed. However, when the injection time of the nitrogen gas was set to seconds or less, the sink tended to occur.

Example 3 The same molding as in Example 1 was carried out except that the injection time of nitrogen gas was 15 seconds and the dwell time was 10 seconds using a mold as shown in FIG. And the presence or absence of sink marks was observed. The size of the undercut portion is 0.3, 0.5, 1.0, 3,... (100) (undercut value) | カ ッ ト (L ₂ −L ₁ ) / L ₁ ｝ | × 100. 0,
6.0 types.

In any of the molds having the nitrogen gas pressure and the undercut value, almost no sink marks were observed.

Table 1 shows the results obtained by examining the sealing performance and the release failure due to the undercut portion. In the column of “Sealability” in Table 1, “」 ”indicates a case where the pressure half-time by escape of nitrogen gas from the parting surface of the mold is 20 seconds or more, and“ △ ”indicates a pressure half-time of 10 seconds. Indicates the case of less than. Further, in the column of “whitening at the time of release” in Table 1,
“○” indicates a case where no whitening occurred in the molded article released, and “△” indicates a case where slight whitening occurred in some of the molded articles.

Comparative Example 1 A molded product similar to that of Example 1 was molded using the mold shown in FIG. 5 and the same molding machine and resin as those of Example 1.

After a short shot (injecting an amount of molten resin substantially filling the cavity in the mold-clamped state) with the mold opened slightly, nitrogen gas having a pressure of 50 kg / cm ² G is injected for 20 seconds. The mold was further opened slightly, the supply of nitrogen gas was stopped, the mold was closed to the original mold half-open state, and cooling was performed while maintaining the pressure for 10 seconds. After this cooling, the nitrogen gas in the cavity is completely exhausted (to atmospheric pressure),
The mold was opened, the molded product was taken out, and the glossiness of the surface was visually observed.

As a result, on the surface of the molded product on the side pressed against the cavity surface by the pressure of the nitrogen gas, the gloss near the gate and the rib portion is inferior to the portion far from the gate as compared with the case where the gloss is rich. It was observed that gloss unevenness was present as a whole.

Comparative Example 2 A molded article was molded in the same manner as in Example 1 except that the mold was not slightly opened, using a mold as shown in FIG. Observed.

As a result, it was not possible to sufficiently prevent sinking of the molded article at any nitrogen gas pressure.
This is based on the fact that the pressure in the mold immediately after the injection was completed was high, and it took 4 seconds or more before nitrogen gas was injected.

[0043]

[Table 1]

[0044]

The present invention is as described above. After a molten resin is injected into a cavity, a pressurized fluid is press-fitted between the cavity surface corresponding to one surface of the molded product and the molded product. In the pressurized fluid combined injection molding method of pressing the other surface of the molded product against the corresponding cavity surface, despite the fact that the injection of the molten resin is a full shot, without excessively increasing the pressure of the pressurized fluid, Since the pressurized fluid can be injected at an early stage after the completion of the injection of the molten resin, the occurrence of sink marks can be reliably prevented without causing uneven gloss on the molded product.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a mold used in the present invention.

FIG. 2 is a cross-sectional view showing a state in which a mold is opened in the present invention.

FIG. 3 is a sectional view showing another example of a mold used in the present invention.

FIG. 4 is an explanatory diagram of an operation of an undercut portion in the mold of FIG. 3;

FIG. 5 is a sectional view showing another example of a mold used in the present invention.

6 is an explanatory diagram of an operation of an undercut portion in the mold of FIG.

[Description of Signs] 1 cavity 1a, 1b cavity surface 2 mold 2a movable mold 2b fixed mold 3 molded product 4 ejector pin 4a sleeve 4b shaft pin 5 ejector plate 6a to 6f sealing material 7 undercut portion 8 slide core

Claims (6)

[Claims] After a molten resin is injected and filled into a cavity, a mold is opened and a pressurized fluid is press-fitted between the cavity surface corresponding to one surface of the molded product and the molded product. A method for injection molding with pressurized fluid, characterized in that the other surface of the product is pressed against a corresponding cavity surface. 2. After the mold is slightly opened and pressurized fluid is injected,
2. The injection molding method using a pressurized fluid according to claim 1, wherein the mold is urged in a mold clamping direction. 3. The injection molding method using a pressurized fluid according to claim 1, wherein a mold having a cavity having a concave shape in the opening and closing direction of the mold is used. 4. A mold according to claim 3, wherein a mold provided with an undercut portion on one side of the molded product on the press-fit side of the pressurized fluid and around the entire periphery near the end of the molded product is used. Pressurized fluid combined injection molding method. 5. A method in which a mold having a cavity surface against which the other surface of a molded product, which is a non-pressurized side of a pressurized fluid, is pressed, is provided with a slide core for defining an end surface of the molded product. The injection molding method using a pressurized fluid according to claim 4, characterized in that: 6. The injection molding method using a pressurized fluid according to claim 1, wherein the mold is closed and the cavity is filled with the molten resin while injecting the molten resin while the mold is slightly opened. .