JP2011178027A - Method for manufacturing resin molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a resin molded product 1 such as a resin gear or a resin pulley with an annular outer peripheral part 11 and a shaft part 13 integrated by a web 14, enhancing dimensional accuracy, particularly circularity, of the resin molded product 1. <P>SOLUTION: In the case of providing a web forming part with pin gates 32 in injection-molding the resin molded product 1, the pin gates 32 are provided to incline the pin gate tips toward the center of the molded product in the case of providing the gates 32 on the outer peripheral side. Injected resin thereby flows deviating toward the center of the molded product. Alternatively, the pin gates are provided to incline the pin gate tips outward in the radial direction of the molded product in the case of providing the gates 33 on the shaft part side. Injected resin thereby flows deviating outward in the radial direction of the molded product. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for injection molding production of synthetic resin molded articles such as resin gears and resin pulleys. In particular, a resin gear or resin in which an annular rim is formed on the outer peripheral portion of the molded product, a shaft portion (such as a boss) is formed in the central portion of the molded product, and the rim and the shaft portion are connected by a disk-shaped web. The present invention relates to a method for manufacturing a pulley with high accuracy by injection molding.

Production of resin gears and pulleys by injection molding of synthetic resin is widely performed. These resin gears are used in office automation equipment such as printer devices, and parts that are required to be produced efficiently by injection molding while high dimensional accuracy is required to improve printing accuracy and prevent noise. There are similar requirements for resin pulleys.

In order to form such resin gears and resin pulleys by injection molding, when pin gates are arranged concentrically on the web portion, it is known that there is a problem in the accuracy of the molded product as described in Patent Document 1. It has been. That is, in the process in which resin is injected and filled into the cavity from pin gates arranged concentrically at regular intervals on the web, as shown in FIG. 7, at the position corresponding to the gate in the circumferential direction on the outer periphery of the molded product The filling timing is increased and the holding pressure is increased. On the other hand, at the position corresponding to the space between the gates in the circumferential direction (that is, the weld portion), the filling timing of the resin is delayed and the holding pressure is also lowered. . As a result, as shown in FIG. 11, dimensional deterioration tends to occur such that the portion corresponding to the gate protrudes outward from the molded product, and the roundness of the outer peripheral portion of the molded product is reduced.

In Patent Document 1, a polymer resin material flow regulation mechanism (a kind of throttle structure capable of regulating resin flow) in which the groove depth and width change continuously or intermittently corresponding to the gate position is a web forming portion. It is disclosed that the above-mentioned problems can be solved by introducing the above.

Further, in Patent Document 2, for the same type of problem, a flow direction restriction that applies a flow component along the circumferential direction to the molten resin injected into the cavity at a portion where the molten resin is injected into the cavity from a plurality of pin gates. It is disclosed that a high-precision molded product is produced by reducing the influence of the generated weld line on the molded product accuracy by providing the portion.

JP-A-8-132542 JP 2006-240038 A

The problem of deterioration of the roundness of the resin molded product when the pin gate is arranged on the web is particularly easily manifested when the pin gate needs to be arranged close to the outer periphery of the resin molded product, Further improvement is required. In FIG. 11, when the pin gate P is arranged close to the outer peripheral part of the resin molded product, the tendency that the outer peripheral part shape of the molded product becomes a polygonal shape and the roundness deteriorates is indicated by a broken line. Further, when it is necessary to place the pin gate close to the shaft portion of the resin molded product, the accuracy of the shaft portion, particularly the inner peripheral surface of the boss hole, is similarly deteriorated, and the improvement is required.

Accordingly, an object of the present invention is to provide a manufacturing method capable of increasing the dimensional accuracy, particularly roundness, of a resin molded product in the manufacture of a resin molded product such as a resin gear or a resin pulley.

As a result of intensive studies, the inventor has provided a pin gate on the web when manufacturing the resin molded product by injection molding, and when the gate is provided near the outer periphery, the tip of the pin gate is inclined toward the center of the molded product. As described above, or when the gate is provided closer to the shaft portion, it has been found that the above object can be achieved by providing the tip of the pin gate so as to be inclined outward in the radial direction of the molded product, and the present invention has been completed.

The present invention is a method for manufacturing a resin molded product integrally formed by an annular outer peripheral portion, a shaft portion serving as a rotating shaft, and a disc-shaped web by injection molding, and a cavity corresponding to the shape of the resin molded product And a step of preparing a mold in which a pin gate for supplying resin to the cavity is disposed in the web molding region, and after the resin is injected from the pin gate into the cavity and cured, the resin molded product is removed from the mold. An injection molding step of taking out, and in the mold preparation step, the pin gate is arranged in a region near the outer peripheral portion of the web, and the tip end portion of the pin gate is inclined toward the center direction of the molded product. A method for producing a resin molded product, characterized in that the resin injected in the injection molding step flows in the cavity in a direction deflected toward the center of the molded product A.

Further, the present invention is a method for manufacturing a resin molded product integrally formed by an annular outer peripheral portion, a shaft portion serving as a rotating shaft, and a disc-shaped web by injection molding, and corresponds to the shape of the resin molded product A mold having a pin gate for supplying resin to the cavity and a pin gate arranged in the web molding region, and injecting resin from the pin gate into the cavity to cure the resin and then molding the resin from the mold An injection molding step for taking out the product, and in the mold preparation step, the pin gate is arranged in a region near the shaft portion of the web, and the central axis of the tip portion of the pin gate is inclined toward the outside in the radial direction of the molded product. The resin composition is characterized in that the resin injected in the injection molding process flows in the cavity while being deflected radially outward of the molded product. It is a manufacturing method of goods (claim 2).

According to the first aspect of the present invention, the central axis of the tip of the pin gate is provided so as to incline toward the center of the molded product, and the resin injected in the injection molding process is deflected in the center of the molded product within the cavity. As a result, the resin arrival timing and holding pressure level are made uniform between the circumferential gate position and the circumferential weld position in the outer periphery of the molded product, and the pin gate is closer to the outer periphery of the molded product. Even if it is provided, accuracy degradation such as roundness of the outer peripheral portion of the resin molded product can be suppressed or prevented.

According to the second aspect of the present invention, the center axis of the tip of the pin gate is provided so as to incline toward the outside in the radial direction of the molded product, and the resin injected in the injection molding process is injected into the molded product within the cavity. By deflecting radially outward and flowing, the resin arrival timing and holding pressure level are made uniform between the circumferential gate position and circumferential weld position in the molded product shaft, and the pin gate is molded. Even in the case of being provided closer to the product shaft portion, it is possible to suppress or prevent accuracy deterioration such as roundness of the resin molded product shaft portion.

It is a figure which shows the resin gear manufactured by the manufacturing method of this invention. It is a schematic diagram which shows the structure of the metal mold | die used for the manufacturing method of this invention. It is a schematic diagram which shows the shape of the pin gate front-end | tip part of the metal mold | die used for the manufacturing method of this invention. It is a schematic diagram which shows the state which opened the mold after injection | pouring of resin in the injection molding process of the manufacturing method of this invention. It is a schematic diagram which shows the state which took out the molded article in the injection molding process of the manufacturing method of this invention. It is a figure which shows the filling process of resin in the injection molding process of the manufacturing method of this invention. It is a figure which shows the filling process of the resin in the injection molding process of the conventional manufacturing method. It is a schematic diagram which shows the structure of the metal mold | die used for the manufacturing method of 2nd Embodiment of this invention. It is a schematic diagram which shows the shape of the pin gate front-end | tip part of the metal mold | die used for the manufacturing method of 2nd Embodiment of this invention. It is a schematic diagram which shows another shape of the pin gate front-end | tip part of the metal mold | die used for the manufacturing method of this invention. It is a schematic diagram which shows the tendency of the precision deterioration in the conventional manufacturing method.

Hereinafter, an embodiment of the present invention will be described using a resin gear as an example. FIG. 1 is a view showing the shape of a resin gear 1 manufactured by the first embodiment of the manufacturing method according to the present invention. The resin gear 1 is formed by injection molding of a synthetic resin and is used for a gear transmission mechanism such as a printer, a copier, or a meter.
An annular rim 11 is formed on the outer peripheral portion of the resin gear 1, and a tooth portion 12 of a helical gear is formed on the outer peripheral portion of the rim 11. Further, a boss 13 is provided at a shaft portion provided in the central portion of the resin gear 1, and a rotation shaft of the resin gear 1 is configured by fitting a shaft (not shown) on the inner peripheral surface of the boss 13. The boss 13 as the shaft portion and the rim 11 as the outer peripheral portion are integrated with each other by a substantially disk-shaped web 14.

The rim 11 and the boss 13 have a larger thickness dimension in the rotation axis direction than the web 14, and the annular rim 11 and the boss 13 protrude from the disc-shaped web 14 in the rotation axis direction. In other words, a portion of the web 14 has been stolen. On one surface of the web 14 (upper surface side in the figure), there is a trace (gate mark 16) of a gate portion where the resin is injected when the resin gear 1 is injection molded. In the resin gear 1, the gate marks 16, 16 are concentric in a region closer to the rim 11 that is the outer peripheral portion than the substantially central portion in the radial direction of the web 14, in other words, in a region closer to the outer peripheral portion than the shaft portion. It is provided on the top at equal intervals.

The gate traces 16 and 16 are traces of a pin gate from which resin is injected in the injection molding process, and are preferably arranged concentrically at regular intervals for the purpose of accurately molding the resin gear 1. Has six gate marks. The number of gate marks, that is, pin gates, is preferably larger from the viewpoint of improving the accuracy of a molded product, but is usually about 2 to 20 in consideration of restrictions on mold manufacturing.

The resin gear 1 is formed of a thermoplastic resin suitable for injection molding, for example, a general-purpose synthetic resin such as polyethylene resin, polypropylene resin, or polyamide resin, or engineering plastic such as polyacetal resin or polybutylene terephthalate resin. A filler or reinforcing fiber may be kneaded into these resin materials.

Hereinafter, the process of the manufacturing method of the present invention for injection molding the resin gear 1 will be described.
First, a mold used for injection molding is prepared. FIG. 2 is a schematic diagram showing the structure of a molding die used in the injection process. The molding die is composed of a pair of an upper die 2 and a lower die 3 that can be opened in the vertical direction of the drawing. The resin gear 1 has a side surface opposite to the one side surface by these molds. FIG. 2 shows a state in which the pair of molds 2 and 3 are closed.

The upper mold 2 is a mold that forms the outer peripheral surface (tooth portion) of the resin gear 1, the upper half of the side surface, and the inner peripheral surface of the boss 13, so that the mold matches the shape of the resin gear 1. The shape of the inner surface is formed. The upper die 2 is configured by integrating a pin 22 and the like with an upper die body 21, and ejector pins 23 and 23 are slidably provided at positions facing the web 14 of the resin gear.

On the other hand, the lower mold 3 is a mold that forms the remaining outer surface (lower half side surface) of the resin gear 1, and the inner surface of the mold is formed so as to match the shape of the lower surface of the resin gear 1. Yes. In the lower mold 3, pin gates 32, 32 for injecting resin are provided in the lower mold main body 31. The pin gates 32 and 32 are located closer to the portion for molding the rim than the substantially central portion in the radial direction of the portion for molding the web (that is, the web molding region), in other words, closer to the outer peripheral portion than the shaft portion of the molded body. It is provided at equal intervals on a concentric circle in a near area.

The pin gate is such that the pin gate tip is inclined toward the center of the molded product at the portion where the pin gates 32 and 32 are connected to the cavity C of the mold (ie, the pin gate tip), that is, the central axis of the pin gate. Is inclined so as to go in the direction of the central axis of the molded product from the inside of the pin gate toward the cavity of the mold. FIG. 3 is an enlarged view of the tip of the pin gate shown on the left side of FIG.

In particular, in the present embodiment, as shown in FIG. 3, the gate tip portion is formed in a tapered surface shape, and the surface 32a on the inner side in the molded product radial direction of the gate tip portion is substantially perpendicular to the molding surface of the web. At the same time, the surface 32b on the outer side in the radial direction of the molded product at the tip of the gate is a surface inclined so as to go inward in the radial direction toward the web molding surface. The gate tip is tapered so that the cross section gradually decreases toward the connection with the cavity.
The above mold is prepared and used for the injection molding process.

In the injection molding process, as shown in FIG. 2, with the upper mold 2 and the lower mold 3 being closed, a cavity C corresponding to the outer shape of the resin gear 1 is formed, and in this state, Injection molding of the resin gear 1 is performed by injecting molten resin into the cavity through the gates 32 and 32. After resin injection, cooling and solidification are performed, and then the resin gear 1 is taken out.

When taking out the resin gear 1, first, the upper mold 2 and the lower mold 3 are relatively moved to open the mold. When the mold is opened, the release resistance between the upper mold 2 and the resin gear 1 is increased so that the resin gear 1 remains on the upper mold 2 side (FIG. 4).

After opening the mold, the ejector pins 23, 23 provided on the upper mold 2 are slid to take out the resin gear 1 from the upper mold 2 (FIG. 5). As described above, the resin gear 1 can be smoothly taken out from the molds 2 and 3 by injection molding the resin gear 1.

The function and effect of the present invention will be described.
In the resin molded body manufacturing method of the present invention, since the pin gate tip is provided at a specific position and inclined in a specific direction, the flow state of the resin when the resin is injected into the cavity is controlled, It is possible to homogenize the timing at which the outer peripheral portion and the shaft portion are filled with resin and the pressure holding state.

In other words, in this embodiment, the tip of the pin gate is formed so as to be inclined inward in the radial direction, so that the resin flow injected from the pin gate 32 into the cavity C is directed inward in the radial direction of the molded product. The resin flow as emphasized. In this embodiment, since such a pin gate is provided in a region near the outer peripheral portion, the flow and filling of the resin in the cavity C are in the form as shown in FIG. In FIG. 6, the situation in which the resin spreads is schematically shown as the tip line of the resin at each time of the resin filling process. Such a line may be observable on the surface of the molded product.

On the other hand, FIG. 7 shows the flow and filling of the resin in the cavity by the conventional pin gate connected to the web forming region straight without tilting the gate tip.

As is clear from the comparison between the two figures, in this embodiment (FIG. 6), the flow of the resin is emphasized toward the inside in the radial direction of the molded product so as to be deflected and flow toward the center of the molded product in the cavity. Therefore, in particular, the flow of the resin filling the outer peripheral side of the molded product becomes slow, the timing of filling in the circumferential direction on the outer peripheral side is also aligned, and variation in holding pressure is suppressed. On the other hand, according to the conventional form of FIG. 7, since the resin spreads concentrically from the gate, the resin arrives quickly at the circumferential gate position G at the outer periphery of the molded product, whereas at the circumferential weld position W, The arrival of the resin is delayed, and the filling timing and holding pressure of the resin vary.

Therefore, according to the present embodiment, the timing of the resin arrival and the degree of holding pressure are homogenized between the circumferential gate position (G) and the circumferential weld position (W) in the outer peripheral portion of the molded product, and the pin gate is Even when it is provided closer to the outer periphery of the molded product, it is possible to suppress or prevent accuracy deterioration such as roundness of the outer periphery of the resin molded product.

The present invention is not limited to the above embodiment, and can be implemented with various modifications. Other embodiments of the present invention will be described below. However, in the following description, portions different from the above embodiment will be mainly described, and detailed descriptions of the same portions will be omitted.

FIG. 8 shows an example in which pin gates 33 and 33 are provided closer to the shaft as another embodiment of the present invention. In this embodiment, the pin gates 33 and 33 are provided at positions closer to the shaft side in the web forming region of the molded product, and the central axis of the pin gate tip 33a is inclined outward in the radial direction of the molded product. That is, it differs from the first embodiment (FIG. 2) in that the central axis is inclined so as to go radially outward from the pin gate side toward the cavity side. The point is similar.

FIG. 9 is an enlarged view of the vicinity of the tip of the pin gate 33 on the left side of FIG. 8, but in this embodiment, the pin gate tip 33a is formed in a substantially cylindrical shape, and its inner diameter is that of the tip. It is the same over the length direction.

In the present embodiment, since the tip of the pin gate is formed so as to be inclined outward in the radial direction, the flow of the resin injected from the pin gate into the cavity is emphasized outward in the radial direction of the molded product. In this way, the flow of the resin filling the molded part shaft side becomes slow, and the circumference of the shaft part side is reduced. The resin filling timing in the direction is also aligned, and variation in holding pressure is suppressed.

Therefore, according to the second embodiment, the resin arrival timing and holding pressure level are homogenized between the circumferential gate position (G) and the circumferential weld position (W) on the molded product shaft side, Even when the pin gate is provided closer to the molded product shaft, it is possible to suppress or prevent deterioration in accuracy such as roundness of the resin molded product shaft.

The present invention can be implemented with further modifications. For example, the inner diameter change of the pin gate tip can be a tapered shape that decreases in diameter from the pin gate side toward the cavity side as in the first embodiment, or as in the second embodiment. Also, it can be a cylindrical shape whose diameter does not change. Alternatively, as shown in FIG. 10, the pin gate tip 33 a ′ may be tapered so that the diameter increases from the pin gate side toward the cavity C side. In addition, the shape of the tip of the pin gate can be an elliptical cross section instead of a circular cross section, or a polygonal cross section.

Since the effect of the present invention can be obtained if the center axis of the pin gate tip is inclined toward the outside in the radial direction of the molded product or toward the center, the shape of the pin gate tip is easy to gate cutting and gate processing. An appropriate selection may be made in consideration of easiness.

The resin used in the practice of the present invention is not limited to a thermoplastic resin, and may be a thermosetting resin or a rubber material.

Also, the resin molded product produced according to the present invention can take various forms such as resin gears and resin pulleys of various shapes, and in particular, an annular shape in which roundness is important. If it is the form of the resin molded product which has the outer peripheral part and axial part of this invention, this invention is applied effectively.

According to the present invention, it is possible to prevent deterioration of dimensional accuracy such as roundness when molding a resin pulley or a resin gear by injection molding. The obtained resin molded product can be used as a component part of a gear transmission mechanism or a belt transmission mechanism of a printer device or a copier, and has high industrial utility value.

1 Resin gear 11 Rim 12 Tooth part 13 Boss 14 Web 16 Gate mark 2 Upper die 21 Mold body 23 Ejector pin 3 Lower die 32 Pin gate 33 Pin gate C Cavity

Claims (2)

A method of manufacturing a resin molded product integrally formed by an annular outer peripheral portion, a shaft portion serving as a rotation shaft, and a disk-shaped web by injection molding,
Preparing a mold having a cavity corresponding to the shape of the resin molded product and a pin gate for supplying resin to the cavity disposed in the web molding region;
An injection molding process of taking out a resin molded product from a mold after injecting resin into a cavity from a pin gate and curing the resin,
In the mold preparation step, the pin gate is arranged in a region near the outer peripheral portion of the web, and the tip end portion of the pin gate is provided so that its central axis is inclined toward the center direction of the molded product, and is injected in the injection molding step. A method for producing a resin molded product, characterized in that the resin flows in the cavity in a direction deflected toward the center of the molded product. A method of manufacturing a resin molded product integrally formed by an annular outer peripheral portion, a shaft portion serving as a rotation shaft, and a disk-shaped web by injection molding,
Preparing a mold having a cavity corresponding to the shape of the resin molded product and a pin gate for supplying resin to the cavity disposed in the web molding region;
An injection molding process of taking out a resin molded product from a mold after injecting resin into a cavity from a pin gate and curing the resin,
In the mold preparation process, the pin gate is disposed in a region near the shaft portion of the web, and the tip end portion of the pin gate is provided so that its central axis is inclined outward in the radial direction of the molded product. A method for producing a resin molded product, characterized in that the molded resin flows while being deflected radially outward of the molded product in the cavity.

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