JPH07195442A - Resin molded item with hole, and method and mold for injection molding - Google Patents

Abstract

PURPOSE:To form the hole of a resin molded item with a hole through injection molding without weld lines. CONSTITUTION:The formation of a hole 10a is achieved such that a cooling process is carried out after the completion of filling molten resin P into a cavity 6 and at the time of the resin P hardened to some extent, i.e., it is not hardened completely. As a core pin 4 is advanced into a cavity 6, the resin P within the cavity 6 is moved backward by the core pin 4 to thereby form a hole 10a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for improving weld strength in a resin molded product with holes, and more particularly to a resin molded product with holes having a weak weld strength, such as a copying machine made of a liquid crystal polyester resin. The present invention relates to a suitable one for a sheet separating claw and the like.

[0002]

2. Description of the Related Art For example, a separating claw 1 for a copying machine shown in FIG.
0 is PPS (polyphenylene sulfide), PAI
(Polyamide imide), PI (polyimide), PEEK
It is manufactured by injection molding a heat resistant resin such as (polyether ether ketone), but it should be attached to a copying machine or stick on a skewer to protect the tip of the nail to improve the transport and workability between processes. Is provided with a hole 10a. In such a separating claw 10 as a resin molded product with a hole, as shown in FIG. 6, a core pin 14 is usually arranged in a protruding state at a predetermined position in a cavity 16 of an injection molding die. Gate 17 from spool (not shown) in cavity 16
It is molded by injecting and filling the molten resin P via. That is, the molten resin P flowing from the gate 17 into the cavity 16 is bifurcated along the core pin 14 arranged in the cavity 16 in a protruding state, and is merged again near the position facing the gate 17. By doing so, the separation claw 10 is molded into a predetermined shape and dimension shown in FIG.

[0003]

According to the above-mentioned injection molding method, the weld line W is unavoidably generated at the confluence of the molten resin P in the cavity 16. The weld line W is a portion that becomes a neck in terms of strength in the resin molded product.

In particular, as a molding material for the separating claw 10, in addition to the above-mentioned resins, a resin having a very weak weld strength such as a liquid crystal polyester resin may be used due to its excellent characteristics. In such a case, The presence of the weld line W causes a structural problem that cracks easily occur from the weld line W.

As means for solving the above problems,
It is possible to improve the weld strength by adding a filler to suppress the orientation of the resin, or by optimizing the molding conditions such as injection speed and injection pressure in injection molding. It cannot be a means for fundamentally solving the problem of weld line formation in a molded product.

[0006] Further, it is also conceivable to remove the core pin that causes weld lines and obtain a molded product having no holes by injection molding, and then separately process holes by a drill or the like to finish the final shape. . According to this means, the generation of weld lines can be prevented, but since it is necessary to separately drill holes, the number of steps is increased and the cost is inevitably increased.

An object of the present invention is to provide an injection molding method and an injection molding die capable of molding a hole of a resin molded product with a hole by injection molding without forming a weld line. .

[0008]

The injection molding method of the present invention uses an injection molding die in which a core pin for molding a hole of a resin molded product having a hole is arranged so as to be movable back and forth with respect to the cavity, and the core pin is a cavity. The molten resin is injected and filled in the cavity in a state of being withdrawn from the cavity, and the core pin is advanced into the cavity to mold the hole after the molten resin is filled and before curing.

The injection molding die of the present invention has a fixed die, a movable die movable back and forth with respect to the fixed die, and a cavity formed at an abutting portion between the fixed die and the movable die. The core pin is driven forward and backward, and the ejector pin is driven forward and backward with respect to the cavity.

[0010]

Since the core pin retreats from the cavity when the molten resin is filled, the molten resin does not split or join due to the core pin. Therefore, the weld line cannot be done.

The holes are formed after the molten resin is filled in the cavities and before the holes are cured. When the core pin advances into the cavity, the resin in the cavity is pushed away by the core pin to form a hole. At the same time, as the core pin advances, the pressure of the resin in the cavity is increased, so that shrinkage after molding is prevented.

[0012]

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

FIG. 1 shows a cross section of the main part of an injection mold used in the injection molding method of this embodiment. This injection molding die is for injection molding the separation claw 10 for a copying machine shown in FIG. 5, and includes a fixed die 1, a movable die 2 that can move forward and backward with respect to the fixed die 1, and a fixed die. The mold 1 is provided with a fixed side ejector pin 3 slidably arranged, a movable mold 2 slidably arranged with a core pin 4 and a plurality of movable side ejector pins 5. Fixed ejector pin 3,
The core pin 4 and the movable ejector pin 5 are respectively
It is slidably driven by a driving means such as a hydraulic cylinder (not shown).

At the abutting portion A between the fixed mold 1 and the movable mold 2, a cavity 6 corresponding to the shape and size of the separation claw 10 is formed. The molten resin P is injected and filled into the cavity 6 from the sprue 8 through the gate 7. Molten resin P
Is a liquid crystal polyester resin (LCP) melted, for example.

The core pin 4 has a diameter corresponding to the diameter of the hole 10a of the separating claw 10 and is arranged at a position corresponding to the molding position of the hole 10a. The core pin 4 is normally retracted to a position where its tip is flush with the end surface of the cavity 6 on the movable mold 2 side.

The plurality of movable ejector pins 5 are distributed near the edge of the cavity 6 and are synchronously driven by the same driving means. Like the core pin 4, the movable ejector pin 5 is also normally retracted to a position where the tip of the movable ejector pin 5 is flush with the end face of the cavity 6 on the movable mold 2 side.

The fixed ejector pin 3 is the core pin 4
And the cavities 6 are sandwiched between them and they are arranged at opposite positions. The fixed side ejector pin 3 has the same diameter as the core pin 4 and is slidably driven by the driving means like the movable side ejector pin 5, but the tip end portion 3a thereof is interposed between the rear side portion 3b and the coil spring 3c. It has a structure capable of sliding movement against the elastic force of. The fixed-side ejector pin 3 is normally retracted to a position where its tip is flush with the end surface of the cavity 6 on the fixed mold 1 side. The fixed position of the tip of the fixed-side ejector pin 3 is set at a position where the fixed-side ejector pin 3 is pulled in from the end surface of the cavity 6 on the fixed mold 1 side by a predetermined amount (a range that does not hinder the flow direction of the molten resin P in the cavity 6), Alternatively, it may be a position protruding by a predetermined amount (a range in which a weld line cannot be formed).

FIG. 2 shows a state in which the molten resin P is filled from the sprue 8 through the gate 7 into the cavity 6. At the time of filling, since the core pin 4 is retracted to a position where it is flush with the end surface of the cavity 6 on the movable mold 2 side, the hole 10a of the separation claw 10 is not yet formed at this point. Instead, no splitting or joining of the molten resin P occurs in the cavity 6.

FIG. 3 shows a state in which the core pin 4 is advanced into the cavity 6 and the hole 10a of the separating claw 10 is formed. The hole 10a is formed at the time when the resin P is cured to some extent (melted state which is not completely cured) by performing cooling work after the filling work of the molten resin P into the cavity 6 is completed. When the core pin 4 is advanced into the cavity 6, the resin P in the cavity 6 is pushed away by the core pin 4 to form the hole 10a. At the same time, the pressure of the resin P in the cavity 6 is increased as the core pin 4 advances. A part of the resin P whose pressure has increased flows toward the edge of the cavity 6 and contributes to preventing the occurrence of shrinkage after molding, and the remaining part of the resin P is fixed by the internal pressure of the resin to the fixed side ejector pin 3. Coil spring 3 with tip 3a
It becomes the discharged resin portion S by retracting against c. Then, the resin P is completely cured.

FIG. 4 shows a state in which, after the resin P is completely cured, the movable mold 2 is moved to open the mold and the completed product 10 'is discharged from the injection mold. When the resin P hardens, the core pin 4 first retracts to its original position. At this point, the hole 10a is formed into a predetermined size and shape.
Next, when the movable mold 2 moves and the mold is opened, the movable side ejector pin 5 advances into the cavity 6, presses the cured molded product 10 ′, and discharges it from the movable mold 2. The discharged completed product 10 ′ is cut into the gate 7 or the like to be finished as the separation claw 10. On the other hand, the discharged resin portion S remaining on the fixed mold 1 is driven by the restoring force of the coil spring 3c to move the fixed side ejector pin 3 forward.
Alternatively, they are discharged from the fixed mold 1 by both actions.

According to the injection molding method of this embodiment, when the molten resin P is filled, the core pin 4 is retracted to a position flush with the end surface of the cavity 6 on the movable mold 2 side. As described above, splitting and joining of the molten resin P due to the core pin does not occur. Therefore, a weld line cannot be formed on the separation claw 10 which is an injection molded product. Further, since the core pin 4 is advanced into the cavity 6 to form the hole 10a after filling the molten resin P and before hardening, it is not necessary to separately perform hole machining after the molding. Furthermore, with the advance of core pin 4,
Since the pressure of the resin P in the cavity 6 is increased, shrinkage after molding is unlikely to occur. Therefore, the separation claw 10 as a resin molded product with a hole molded by the injection molding method of this embodiment is excellent in weld strength and cost efficiency.

In this embodiment, the present invention is applied to the injection molding of the separating claw 10 for a copying machine, but the present invention is not limited to this, and resin sleeves, washers, gears, etc. can be used. It can be generally applied to resin molded products with holes, and in that case, the same operational effect is obtained. Further, the present invention exerts a particularly remarkable effect when a resin molded product with a hole such as the separating claw 10 is injection-molded using a liquid crystal polyester resin (LCP) or the like, which has a weak strength in a weld line. However, in addition, polyimide (PI), polyamide (P
A), polyamideimide (PAI), polyetherimide (PEI), polyetherketone (PEK), polyetheretherketone (PEEK), polyethernitrile (PEN), polyphenylene sulfide (PP)
S), polyacetal (POM), polyethylene (P
It also exerts a great effect when injection molding is performed using E) or the like. The liquid crystal polyester resin (LCP) has a particularly remarkable effect for the following reasons. That is, the liquid crystal polyester resin is excellent in self-reinforcement because the molecules are oriented in respective directions when melted, but the molecules are aligned in a fixed direction when cured. However, in the weld line part, the resin flow direction is divided,
Since they merge, such self-reinforcing effect cannot be expected. Therefore, in the molded product of the liquid crystal polyester resin, the strength at the weld line is significantly reduced. Therefore,
In a molded product made of a resin having such a liquid crystal property, it is possible to remarkably improve its strength by preventing the occurrence of weld lines.

[0023]

According to the present invention, since the core pin retreats from the cavity during the filling of the molten resin, the splitting and joining of the molten resin due to the core pin does not occur unlike the conventional case. Therefore, the weld line cannot be formed in the injection molded product. Further, since the core pin is advanced into the cavity to form a hole after the molten resin is filled and before the resin is cured, it is not necessary to separately perform hole processing after the molding. Furthermore, since the pressure of the resin in the cavity is increased as the core pin advances, shrinkage after molding is unlikely to occur.

Therefore, the resin molded product with holes molded by the injection molding method of the present invention is excellent in weld strength and cost performance.

[Brief description of drawings]

FIG. 1 is a view showing a cross section of a main part of an injection molding die used in an injection molding method of an example.

FIG. 2 is a cross-sectional view showing a state when a molten resin is filled in the cavity.

FIG. 3 is a cross-sectional view showing a state when forming a hole.

FIG. 4 is a cross-sectional view showing a state when a molded product is discharged from an injection molding die.

FIG. 5 is a plan view showing a separating claw for a copying machine as a resin molded product with holes.

FIG. 6 is a view showing a conventional method of injection molding a separation pawl.

[Explanation of symbols]

 1 Fixed mold 2 Movable mold 3 Fixed side ejector pin 4 Core pin 5 Movable side ejector pin 6 Cavity 10 Separation claw (resin molded product with hole) 10a hole

Claims (3)

[Claims] 1. An injection molding die in which a core pin for molding a hole of a resin molded product with a hole is arranged so as to be movable back and forth with respect to a cavity, and a molten resin is put in the cavity with the core pin retracted from the cavity. Is injected and filled, and the core pin is advanced into the cavity to mold the hole after the molten resin is filled and before the resin is cured, the method of injection molding a resin molded product with a hole. 2. An injection molding mold used in the injection molding method according to claim 1, comprising a fixed mold, a movable mold movable forward and backward with respect to the fixed mold, and a fixed mold and a movable mold. A core pin that is driven forward and backward with respect to the cavity formed in the abutting portion,
An injection mold for a resin molded product with a hole, comprising: an ejector pin that is driven forward and backward with respect to the cavity. 3. A resin molded product having a hole, which is molded by the injection molding method according to claim 1.