JP2003062866A - Injection-molding method and injection mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin injection-molding method for enhancing the strength of the fusion-bonded part generated in a molded article by a simple method, and an injection mold used therein. SOLUTION: In a resin filling method at the time of injection molding, a plurality of resin streams come into contact with each other to be fusion-bonded and, thereafter, the core inserted in the mold is moved to the outside of the mold to expand the volume of a cavity and the resin is allowed to flow in the expanded cavity to allow other resin stream to flow in one of the resin streams forming the fusion-bonded part. By this constitution, the shape of the core layer part of the fusion-bonded part is changed to improve the bonding strength of the fusion-bonded part.

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 and an injection molding die for preventing deterioration of appearance of a weld line portion and deterioration of mechanical strength such as tensile strength in injection molding.

[0002]

2. Description of the Related Art In injection molding, when molten resin is injected and filled through a plurality of gate portions into the same cavity in a mold, a plurality of resin streams are not completely fused. In, a linear weld line is generated at the resin joint portion. The occurrence of this weld line is
Not only the external appearance such as V-grooves and color unevenness is impaired, but also the internal resin-bonded portion is not completely fused, which often results in a defective portion in terms of strength, which is a major cause of defective molding.

In order to solve this problem, Japanese Patent Laid-Open No. 2-2
The prior art disclosed in Japanese Patent No. 02414 uses a mold equipped with a plurality of valve gates that can be driven to open and close, and causes one resin flow to flow into the other resin flow, thereby increasing the bonding strength of the fusion-bonded portion. An improved injection molding method is disclosed. And, in this publication, after the tips of a plurality of resin streams are in contact with each other and fused and integrated in the resin filling process,
A method is described in which the filling pressures of a plurality of resin flows are made different by performing opening / closing operations of a valve gate, and one of the resin flows flows into the other to improve the strength of the fused portion.

Another prior art is Japanese Patent Laid-Open No. 7-27.
In the Japanese Patent No. 6410, two injection molding machines are used, and a resin is injected from a plurality of gates at different pressures so that a resin flow has a pressure difference. An injection molding method is disclosed in which a weld line is made to flow into a stream to make it inconspicuous.

[0005]

However, in the above-mentioned Japanese Unexamined Patent Publication No. 2-202414, it is necessary to use a mold having a plurality of valve gates that can be opened and closed in the practice of the invention. Has a complicated structure and becomes an expensive material, and in addition, a precise controller is required to perform the opening / closing operation of the valve gate precisely, and its control is easy. There was a problem such as not.

[0006] Another prior art is Japanese Patent Laid-Open No. 7-27.
In Japanese Patent No. 6410, there is a problem that it is difficult to carry out only with a special molding machine having two injection units, and since the two injection molding machines are used, the device is There were problems such as enlargement, complexity, and cost.

In view of the above problems, the present invention does not require an expensive and complicated device or the like required in the prior art, and is equipped with a single injection molding machine and a simple structure without a valve gate or the like being operated. It is intended to improve the appearance of the weld line portion and the mechanical strength such as the tensile strength by using the mold.

[0008]

In order to solve the above-mentioned problems, the injection molding method according to the present invention comprises: (1) injection molding in which a cavity of a mold is filled with resin through gate portions arranged at a plurality of positions. In the method, when the resin is filled, a plurality of resin flows filled from the gate portions at a plurality of positions come into contact with each other to form a fused portion, and then the core inserted in the cavity is moved to form the fused portion. Expand the volume of the cavity filled with one of the resin flow to
The other resin flow is introduced into one of the resin flows forming the fused portion.

(2) In the injection molding method described in (1), the resin is a filler-based reinforcing resin mixed with a filler.

Further, the injection molding die according to the present invention comprises: (3) A plurality of gate portions are arranged in the cavity, and a removable core is provided in a part of the cavity. An injection mold for partially enlarging the volume of the cavity by moving it from the state of being inserted into the inside of the cavity, wherein a plurality of resin flows filled from the gate portions at a plurality of positions at the time of resin filling. Form a fused portion in contact with each other, move the core inserted in the cavity to expand the volume of the cavity portion filled with one of the resin streams forming the fused portion, The other resin flow is introduced into one of the resin flows forming the part.

(4) In the injection-molding die according to (3), the core has a shape which divides the cavity of the die into two sections in a state of being inserted into the cavity, and the gate portions at the plurality of locations. Were concentrated in one of the two compartments.

[0012]

In the present invention, after a plurality of resin streams are in contact with each other and fused in the resin filling process, the volume of the cavity is expanded, and the resin is flown to the enlarged portion to form the fused portion. By changing the shape of the core layer portion of the fusion-bonded portion to improve the bonding strength of the fusion-bonded portion, it is possible to change the shape of the core layer portion of the fusion-bonded portion by inflowing the other resin flow into one of the flows (sometimes called press-fitting). One

The details of the operation will be described. In the first step of molding, when the resin is injected and filled into the cavity of the mold through the gate portions arranged at a plurality of positions, the tips of the plurality of resin flows are in contact with each other and melted, and then the tips of the resin flows are balanced by pressure Flow stops.

At this time, the resin in contact with the inner wall of the mold (the inner surface of the mold cavity) is partially solidified, but in the inner core layer, the resin is still in a melted and flowable state. In the pressure-holding step, the solidified layer of resin gradually develops, and the whole is solidified. That is, in the state where the flow is temporarily stopped, although the molten resin is solidifying in the vicinity of the inner wall surface of the mold of the cavity, the internal core layer is still in the molten state and can flow.

Here, when the core inserted into the cavity is moved to the outside of the cavity, the volume of the cavity portion filled with one of the resin streams forming the fusion-bonded portion is increased. , The resin begins to reflow as the resin tries to flow into the enlarged part.

As a result, an underflow phenomenon occurs in which one resin flow flows into the other resin flow. At the time point when the underflow phenomenon is completed, one of the resin streams has a shape deeply flowing into the other resin stream at the fused portion of the core layer. After that, the mixture is cooled and solidified in the state of inflow, and the bonding of the fusion-bonded portion is strengthened, so that the mechanical strength of the molded product increases.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred example of an embodiment according to the present invention will be described below with reference to FIGS. Figure 1
FIG. 3 is a sectional view illustrating a structure of an injection molding die device according to an embodiment of the present invention. FIG. 2 shows a process of changing the shape of the fusion-bonded portion formed by a plurality of resin streams in contact with each other in the resin filling process of the injection molding method according to the embodiment of the present invention.
It is a figure explaining in order of (4). 3A and 3B are views for explaining the orientation state of the glass fiber of the molded product, FIG. 3A shows the case of the molded product according to the present invention, and FIG. 3B shows the case of the conventional molding method. FIG. 4 is a conceptual diagram illustrating the structure of the injection molding die apparatus and the movement of the core according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view for explaining the structure of an injection molding die apparatus according to another embodiment of the present invention, and FIG. 6 is an injection molding die apparatus according to another embodiment of the present invention. It is a conceptual diagram explaining a structure and movement of a core.

A preferred example of the embodiment of the mold according to the present invention will be described below. An embodiment of a mold according to the present invention is a mold in which a plurality of gate parts are provided for one cavity, and a weld line is generated. As shown in FIG. 1 and FIG. It has a core 5A that is insertable and removable and that is arranged so as to cross the cavity. Then, the core 5A is shown in FIG.
By inserting into the cavity as shown in Fig. 4, the cavity can be divided into two sections, and the core 5A shown in Fig. 4 (B) is inserted into the cavity. The mold is configured such that the volume of the cavity is partially expanded by moving the core 5A from the above state to the direction shown in FIG.

Further, the fixed mold 3 is provided with two gates, and in order to explain the arrangement of the gates provided on the fixed mold 3, the position of the movable mold 2 facing the gate position is referred to as a gate facing position. Is shown in FIG. As shown in FIG. 4, the two gates are concentrated in one of the two sections. As shown in FIG. 1, the core 5A is fixed to a piston rod of a hydraulic cylinder, and a line A and a line B for supplying hydraulic pressure to the hydraulic cylinder are connected to a hydraulic source (not shown).

A preferred example of the injection molding method in this embodiment will be described below. As the first step, FIG.
As shown in (1), the mold apparatus 10 is clamped, the hydraulic cylinder is driven by a hydraulic source (not shown), and the core 5A is inserted into the cavity so that the cavity is divided into two. punctuate. Next, the cavity is filled with resin from the two gates provided on the fixed mold 3. In this embodiment, the resin used is a glass fiber reinforced nylon resin mixed with glass fibers as a filler.

The two resin streams are injected and filled from the gate into the cavity as shown in FIG. 2 (2). At the stage when the filling is advanced, the tips of the two resin streams are shown in FIG. 2 (3). The parts come into contact with each other, and the flow at the tip part is once stopped to form a fused part. After forming the fusion-bonded portion, as shown in FIG. 2 (4), by moving the core 5A in the direction of removing it from the state of being inserted into the cavity, the cavity volume is expanded in one direction, The volume of the cavity portion filled with one of the resin streams forming the fused portion is expanded.

The timing at which the core 5A is moved in the direction in which it is removed from the state of being inserted into the cavity can be calculated in advance from the cavity volume of the mold apparatus 10, the gate arrangement, the resin filling speed, and the like. Also, it is possible to accurately calculate by a flow analysis method using a computer. In particular, it is preferable to design the mold cavity and the gate so that the fusion portion is completed to be formed at the same time when the resin is almost completely filled in the cavity before expansion, and in this case, it will be described later. Since the underflow phenomenon of the resin effectively occurs, there is an advantage that the strength of the weld portion is greatly improved.

Further, the timing of forming the fusion-bonded portion can be determined by examining a molded sample obtained by performing a molding test, even if it is not calculated in advance. In actual molding, it is possible to accurately determine an appropriate timing for moving the core 5A by performing a molding test with the timing slightly changed and examining the strength and appearance of the weld portion of the molded sample obtained in the molding test. ,preferable.

Then, the resin begins to flow into the portion of the expanded cavity volume, and a flow of the resin tends to flow into one side of the resin forming the fused portion. Although the fused portion where the flow once stopped has a skin layer, the inner core layer is still in a melted and flowable state.
As shown in (B), the other molten resin flows into one of the resin streams, and the fusion-bonded portion that can flow without being solidified bends and an underflow phenomenon occurs.

The underflow phenomenon is a phenomenon in which, after the resin in contact with the inner wall surface of the mold cavity is cooled and solidified, the molten resin in the core layer still inside the resin flows into the other resin. After that, when the resin is completely filled in the expanded cavity volume part and the cooling progresses and the solidification proceeds, one of the core layer parts of the fusion-bonded part is cooled and solidified while the other is difficult to fit due to the underflow phenomenon. The joint strength of the joint is increased.

As described above in the section of the prior art, the weld line as shown in FIG. 3A, which occurs when a plurality of resin streams are not completely fused, not only impairs the appearance but also exists inside. Since the resin joint portion of the core layer portion is not completely fused, it becomes a defective portion in terms of strength. Particularly in the case of a resin filled with a filler such as glass fiber,
As shown in (A), the glass fibers are arrayed in the thickness direction (short axis side direction) of the molded product at the weld portion by the fountain flow, and the orientation of such glass fibers is the tensile strength in the longitudinal direction of the molded product. , Greatly reduces bending strength.

According to the present invention, as described above, the core layer portion of the fusion-bonding portion is deeply flown into the low-pressure side resin flow, whereby the bonding strength of the fusion-bonding portion can be increased.
Further, the V-grooves on the surface of the molded body are not noticeable, which brings about an effect of improving the appearance. Therefore, the present invention can exert a great effect on the production of weld lines, for example, products that cannot be molded without using a mold having a large number of gates, products with openings, or thin products. it can.

In particular, the application of the present invention to a resin filled with glass fiber is as shown in FIG. 3 (B), as shown in FIG. 3 (B), the glass fiber is formed in the thickness direction (short axis side direction) of the molded product at the weld portion. Are prevented from being arranged, so that the bonding strength of the fused portion can be greatly increased, which is preferable. Further, the effect of improving the strength due to the orientation according to the present invention is not limited to the case of using glass fiber as a filler, and other inorganic fibers, carbon fibers, flat-plate-like fillers such as talc, and the like among resins. It is effective for filler-based reinforced resins filled with various fillers whose strength changes depending on the orientation.

Other embodiments according to the present invention will be briefly described below, focusing on the points different from the above-described embodiments.

A preferred example of another embodiment of the mold according to the present invention will be described below. Another embodiment of the mold according to the present invention is a mold in which a plurality of gate portions are provided for one cavity as in the above-described embodiment, and a weld line is generated. Then, as shown in FIG. 5, a removable core 5B is arranged on the side wall portion of the cavity, and the core 5B is shown in the state shown in FIG. 6A and shown in FIG. 6B. The volume of the cavity can be reduced by inserting it into the cavity in such a manner, and the volume of the cavity can be changed by inserting and removing the core 5B into the cavity. It is a mold.

The core 5B is fixed to the piston rod of the hydraulic cylinder as shown in FIG. 5, and a line A for supplying hydraulic pressure to the hydraulic cylinder and a hydraulic source (not shown) are connected to the line B. ing.

A preferred example of the injection molding method in this embodiment will be described below. As a first step, the mold apparatus 10 is clamped, the hydraulic cylinder is driven by a hydraulic power source (not shown), and the core 5B is inserted into the cavity, thereby reducing the volume of the cavity. next,
As in the above-described embodiment, the cavity is filled with resin from the two gates provided in the fixed mold 3. The two resin streams are injected and filled from the gate into the cavity,
When the filling is advanced, the tips of the two resin streams come into contact with each other, and the flow at the tips is temporarily stopped to form a fused portion. After forming the fused portion, the cavity 5 is expanded by moving the core 5B in a direction away from the state of being inserted into the cavity.

As a result, the other molten resin flows into one resin flow which is still in a molten state, and the melted portion which can flow without being solidified bends to cause an underflow phenomenon. For the reason described above in the above embodiment, the bonding strength of the fused portion is increased.

In another embodiment, the core 5B is used.
Was driven by a hydraulic cylinder, but it is not limited to this. If the core 5B is inserted into the cavity by a spring,
Since the core 5B is pressed and spontaneously disengages from the inside of the cavity, it is not necessary to control the drive timing of the hydraulic cylinder, which is preferable in that the control is simple.

Further, a more preferable mode of the present invention will be described. When the underflow phenomenon occurs, the gate supplying resin to the cavity portion side to be enlarged is closed before the cavity is enlarged. Since the other resin flow largely flows in, a large underflow phenomenon occurs and the effect becomes large. As a means for closing the gate, it is effective to adjust the gate seal timing by using, for example, a valve gate.

[0037]

According to the present invention, after a plurality of resin streams are in contact with each other and fused in the process of filling the resin, the volume of the cavity is enlarged and the resin is flown to the enlarged portion to form the fused portion. By injecting the other resin flow into one of the resin flows, the shape of the core layer portion of the fusion-bonded portion is changed, the bonding strength of the fusion-bonded portion is improved, and the V-groove on the surface portion of the molded body is also made conspicuous. It has the effect that it does not exist.

Therefore, the appearance improvement that makes the weld line inconspicuous at low cost by using one injection molding machine and a mold having a simple structure without the need for expensive and complicated equipments required in the prior art And the strength can be improved.

When the present invention is applied to a filler-based reinforced resin, the filler such as glass fiber in the fused portion is
Since the resin is oriented along the inflowing resin flow and the resin flow pushed back by the underflow and arranged in the strengthening direction of the molded product, the tensile strength and bending strength of the molded product in the longitudinal direction can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the structure of an injection molding die device according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating a process of changing the shape of a fusion-bonded portion formed by a plurality of resin streams in contact with each other in the resin filling process of the injection molding method according to the embodiment of the present invention.

FIG. 3 is a diagram for explaining the orientation state of glass fibers of a molded product, (A) showing the case of the molded product according to the present invention,
(B) shows the case of the conventional molding method.

FIG. 4 is a conceptual diagram illustrating the structure of the injection molding die device and the movement of the core according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating the structure of an injection molding die device according to another embodiment of the present invention.

FIG. 6 is a conceptual diagram illustrating the structure of an injection molding die device and the movement of a core according to another embodiment of the present invention.

[Explanation of symbols]

2 movable 3 fixed type 5A core 5B Nakako 10A mold equipment 10B mold equipment

Claims (4)

[Claims] 1. An injection molding method for filling a resin into a cavity of a mold through gate portions arranged at a plurality of positions,
When the resin is filled, a plurality of resin flows filled from the gate portions at a plurality of positions come into contact with each other to form a fused portion, and then the core inserted into the cavity is moved to form the fused portion. 2. An injection molding method, characterized in that the volume of a cavity portion filled with one of the two is expanded, and the other resin flow is made to flow into one of the resin flows forming the fused portion. 2. The injection molding method according to claim 1, wherein the resin is a filler-based reinforced resin mixed with a filler. 3. A plurality of gate portions are arranged in the cavity, and a removable core is provided in a part of the cavity, and the core is moved in a direction to be removed from the state of being inserted in the cavity. A mold for injection molding for partially enlarging the volume of the cavity by the method, wherein a plurality of resin flows filled from the gate portions at a plurality of positions come into contact with each other at the time of resin filling to form a fused portion, and then the cavity is formed. By moving the core inserted therein, the volume of the cavity portion filled with one of the resin streams forming the fusion-bonded portion is expanded, and the resin flow of one of the resin streams forming the fusion-bonded portion is added to the other resin flow. A mold for injection molding, characterized in that 4. The core has a shape that divides a mold cavity into two sections in a state where the core is inserted into the cavity, and the gate portions at a plurality of locations are concentrated in one of the two sections. The mold for injection molding according to claim 3, wherein