JP5443089B2 - Plastic molded product - Google Patents

Description

The present invention relates to a resin molded product such as a resin gear or a resin pulley formed by injection molding of a synthetic resin. 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 Regarding pulleys.

Such resin gears and pulleys have come to be widely used as driving parts for, for example, electronic copying machines and printer devices. In these fields of use, the resin gears and pulleys have very high dimensions in order to improve printing quality. Accuracy (for example, roundness of the outer peripheral portion) is required. Such resin gears and pulleys are usually manufactured by injection molding of synthetic resin, and various techniques have been developed so that these resin molded products can be efficiently manufactured while improving accuracy. ing.

The following factors are known as one of the factors causing the accuracy deterioration of such a resin molded product. That is, as shown in FIG. 8, in the case of injection molding a resin gear in which an outer peripheral rim and a central boss are connected by a disk-shaped web, the molten resin is injected into a cavity in a mold. In many cases, a plurality of gates G (pin gates) are provided on the web (in the figure, four gates are provided at equal intervals on a concentric circle with the rim). In this case, the molten resin injected from the gate G fills the cavity while spreading in a circle around the gate. Therefore, at a position (AG position in the figure) that coincides with the gate in the gear circumferential direction, The resin reaches the rim and the tooth tip of the outer peripheral portion faster than at the intermediate position between the gates (AI position in the figure). That is, the timing at which the molten resin reaches the outer periphery of the resin molded product varies depending on the position in the circumferential direction, and there is also a difference in the pressure holding state of the molten resin. As shown by this tendency, the diameter in the circumferential direction AG position tends to be relatively large (indicated by an outward-pointing arrow), and the diameter in the circumferential direction AI position tends to be relatively small (indicated by an inward-pointing arrow). As shown, the resin molded product to be molded tends to have a petal-like accuracy deterioration tendency, and in particular, the roundness of the outer peripheral portion of the molded product tends to decrease.

As techniques for preventing and suppressing such a tendency of deterioration in accuracy, techniques such as those disclosed in Patent Document 1 and Patent Document 2 are known.
Patent Document 1 relates to a resin gear having a tooth portion on the outer periphery and composed of a rim, a web, and a boss. An annular rib is erected on the web, and a gate at the time of resin injection molding is ribbed. It is disclosed that the resin supplied from the gate promotes a large amount of flow in the circumferential direction through the ribs, and the petal-like accuracy deterioration tendency is suppressed by averaging the radial flow. ing.

Further, Patent Document 2 relates to a resin gear having a tooth portion on the outer periphery and including a rim, a web, and a boss, and a gate is disposed on the inner peripheral side of the web, and a rib is provided on the web. It is disclosed that an annular region that is not provided is provided on the outer peripheral side of the gate to prevent deterioration of gear accuracy due to the rib by the annular region.

Japanese Patent Application Laid-Open No. 08-025501 JP 2006-077094 A

The technique disclosed in the above-mentioned patent document averages the flow of the resin, thereby homogenizing the timing and pressure holding state of the resin reaching the outer periphery of the resin molded product, and improving the accuracy of the resin molded product. However, in order to further improve the accuracy, such averaging means may not be able to sufficiently homogenize the resin supply to the outer peripheral portion, and other accuracy improvement techniques are required.

Accordingly, an object of the present invention is to provide a resin molded product having high accuracy of the outer peripheral portion of the molded product in a resin molded product such as a resin gear or a resin pulley manufactured by injection molding.

As a result of intensive studies, the inventor has erected ribs on the outer peripheral side of the web gate, even when using a pin gate, so that the height of the rib corresponds to the gate in the circumferential direction. high, both when such lower at an intermediate position of the gate and the gate, when the offset inner and outer portions of the web in the rotation axis direction, and found that the above problems can be solved, and completed the present invention.

The present invention is a resin molded product that is integrally formed by injection molding of resin and in which an annular outer peripheral portion and a shaft portion that is a rotating shaft are connected by a web, and the web has a plurality of gate marks on the shaft. parts so as to surround the are arranged on the shaft portion and the outer peripheral portion and concentrically, to the outer peripheral side of the gate remain of the web, along cormorants ribs erected on the shaft portion and the outer peripheral portion and concentrically in the circumferential direction, the rib, the rib height in the circumferential positions corresponding to the gate marks, gate mark and gate mark formed higher than the rib height in which circumferential position corresponding to between the Rutotomoni, the radial position of a rib The resin molded product is characterized in that the web is divided into an inner peripheral portion and an outer peripheral portion as a boundary so as to be offset from each other in the rotation axis direction . (Claim 1)

In the present invention, it is preferable that the ribs are intermittently provided in the circumferential direction (Claim 2 ), and the rib height is preferably continuously changed in the circumferential direction (Claim 3 ).

According to the present invention, the portion of the rib disposed between the gate and the outer peripheral portion of the molded product serves as a buffer region for diverting the resin flow flowing from the gate toward the outer peripheral portion at the time of injection molding. The timing at which the flow reaches the outer periphery of the molded product can be delayed, and at the circumferential position corresponding to the gate, the rib is provided high, the delay time is increased, and the corresponding circumferential direction between the gate and the gate At the position, the rib is provided low and its delay time is reduced, so that the dispersion of the resin arrival timing to the outer peripheral part of the molded product that has appeared in the conventional resin molded product can be compensated and made uniform. A resin molded product having roundness is obtained. In addition, the web is divided into an inner peripheral portion and an outer peripheral portion with the radial position where the rib is provided as a boundary, and the roundness is more effective by being configured to be offset from each other in the rotational axis direction. Enhanced.

Furthermore, as described in claim 2 and claim 3 , by making a resin molded product having a more preferable configuration, the effect of adjusting and compensating the resin arrival timing by the rib is more effectively exhibited, and high roundness is achieved. A resin molded product having the above can be obtained effectively.

It is a perspective view of the resin gear of a 1st embodiment of the present invention. It is the front view and sectional drawing of a resin gear of a 1st embodiment of the present invention. It is a schematic diagram which shows the flow of the molten resin at the time of performing the injection molding of the resin gear of this invention. It is a figure which shows the example of the rib shape in this invention. It is a perspective view of the resin gear of 2nd Embodiment of this invention. It is the front view and sectional drawing of the resin gear of 2nd Embodiment of this invention. It is a front view which shows other embodiment of this invention. It is a figure which shows the tendency of the roundness fall in the conventional resin gear.

Hereinafter, an embodiment of the present invention will be described using a resin gear as an example. 1 and 2 are views showing the shape of the resin gear 1 according to the first embodiment of the present invention. FIG. 1 shows a perspective view, and FIG. 2 shows a front view and a sectional view (A-A section). 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 (the detailed shape of the tooth portion 12 is not shown). ing). 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 that is the shaft portion and the rim 11 that is the outer peripheral portion are connected and integrated with each other by a substantially disc-shaped web 14. In the present embodiment, the web 14 is concentrically divided into two parts, and includes a first web 141 on the inner peripheral side and a second web 142 on the outer peripheral side. And the 1st web 141 and the 2nd web 142 are mutually offset and provided in the rotating shaft direction of the resin gear, and the space | interval is connected by the annular connection part 143.

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, the portion of the web 14 has a resin gear shape in which the meat is stolen. On one surface of the web 14, there are a plurality of traces (gate traces 16) of the gate portion that injected the resin when the resin gear 1 is injection-molded. The gate traces 16, 16 are the first web 141 on the inner peripheral side. Are arranged on a concentric circle surrounding the shaft portion 13. In the present embodiment, the four gate marks 16, 16 are arranged at equal intervals on a circle centered on the gear central axis.

In the present invention, ribs 15 and 15 are erected on the outer peripheral side of the web 14 with respect to the gate marks 16 and 16 along the circumferential direction. In the present embodiment, the ribs 15 and 15 are provided along the connecting portion 143 at the boundary between the first web 141 and the second web 142, and the four ribs 15 and 15 are connected to the rim 11 and the boss 13. It is provided concentrically. In the following description, the height of the rib 15 refers to the dimension of the rib in the gear rotation axis direction, the thickness of the rib 15 refers to the dimension of the rib in the gear radial direction, and the length of the rib 15 refers to the rib in the gear circumferential direction. Dimension shall be referred to.

The ribs 15, 15 provided along the circumferential direction have a relatively high height at a position corresponding to the gate mark 16 (AG position in the drawing) with respect to the position in the circumferential direction of the gear. It is provided so as to be relatively low at an intermediate position (AI position in the figure) of the gate mark 16. In particular, in the present embodiment, the rib height is substantially zero at the intermediate position between the gate mark 16 and the gate mark 16 (the AI position in the figure), and the ribs 15 and 15 are intermittently present in the circumferential direction. In addition, the rib height of each of the ribs 15 becomes an arc shape when viewed from the radial direction such that the AG position is the highest and the height gradually decreases toward the AI position. It is said that the height. The ribs 15 are formed to have a constant thickness, preferably about the same as or thicker than the thickness of the second web 142 in the gear central axis direction.

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.

The resin gear 1 is formed by resin injection molding in which a molten resin is injected into a cavity using a mold capable of forming a cavity that matches the outer shape of the gear. The resin is injected through a plurality of pin gates provided at positions corresponding to the gate marks 16 of the molded product.

The function and effect of the present invention will be described. In the present invention, the ribs having a height change in the circumferential direction are arranged along the circumferential direction on the outer circumferential side of the web with respect to the gate trace, thereby exhibiting the following effects. FIG. 3 is a schematic diagram showing the flow of the molten resin injected from the gate in the cavity when the resin gear 1 is injection-molded. The upper half of the figure corresponds to the position (AG The lower half of the figure is a figure at a position (AI position) corresponding to the gate and the middle of the gate in the circumferential direction. In addition, the code | symbol which attached | subjected C to the head in the figure means that it is a cavity part which forms the part to which each number was attached | subjected in the resin molded product.

The resin injected from the pin gate flows in the outer circumferential direction and the inner circumferential direction while spreading in the cavity forming the web. In the flow toward the outer circumferential direction, the first web portion C141, the connecting portion C143, 2 It flows with the web part C142 and reaches the rim part C11 and the tooth part C12. At that time, at the circumferential position (for example, AG position) where the rib portion C15 is provided so as to be continuous with the connecting portion C143, the resin also flows into the rib portion C15 side, and the resin is secondly increased by that amount. The flow into the web portion C142, the rim portion C11, and the tooth portion C12 is delayed. On the other hand, in the circumferential position (AI position) where the rib portion C15 is not provided as shown in the lower side of FIG. 3, the resin flows without being separated, and the first web portion C141, the connecting portion C143, It flows with the second web portion C142 and reaches the rim portion C11 and the tooth portion C12. As a result, at the circumferential position where the rib portion C15 is provided, the speed at which the resin reaches the rim portion C11 from the gate can be delayed by the amount that the resin flows into the rib portion C15. The delay effect is larger as the rib height is higher, and the delay effect is smaller as the rib height is lower.

In the present invention, the rib 15 in the molded product 1 (that is, the rib portion C15 in the cavity) is high at the circumferential position (AG position) corresponding to the gate, and the circumferential position (AI position) between the adjacent gates. In the AG position, the timing of filling the rim portion C11 with the resin is delayed, and in the AI position, the timing of filling the rim portion C11 with the resin is reduced. Compensating for the time difference between the resin reaching the rim portion from the gate, the timing at which the rim portion C11 is filled with the resin can be made uniform in the circumferential direction.

As a result, in the resin gear of the present invention, in the injection molding process, the resin filling time difference with respect to the outer peripheral portion and the tooth portion can be reduced, and the difference in the resin shrinkage rate is reduced. It is possible to compensate for the deterioration tendency of the petal-like roundness that has occurred, and to improve the accuracy of the resin gear, particularly the roundness.

In order to obtain the above effect, the present invention is characterized in that the height of the rib 15 is high at the AG position and low at the AI position. Can be provided. In FIG. 4, the example of the shape of the rib 15 in this invention is shown. In FIG. 4, the rib shape seen from the radial direction of the gear is shown, the center of the figure is the AG position (position corresponding to the gate), and both sides of the figure are the AI position (circumferential position between the gate and the gate). The shape which developed the rib so that it may become is shown. Moreover, the surface of the web used as the foundation which the rib 15 stands with respect to the web 14 is shown with the dotted line. FIG. 4A shows the shape of the rib shown in the first embodiment. The rib 15 has a maximum height at the AG position and substantially zero at the AI position. It is provided intermittently in the direction. The rib height is monotonously and continuously (gradually) decreased from the AG position to the AI position, and the top of the rib is convex toward the outside of the resin molded product when viewed from the radial direction. It is designed to form a circular arc.

FIG. 4B shows another shape of the rib. In the present embodiment, the rib is provided in an annular shape over the entire circumference of the gear without having a height of zero even at the AI position. The height of the rib is continuously and linearly changed along the circumferential direction so that the height is maximum at the AG position and minimum at the AI position. Even if the ribs are continuous in the circumferential direction as in this embodiment, if the height is different between the AG position and the AI position (high at the AG position), in the resin injection filling process, the rib portion It is possible to compensate so that the resin flows in and the timing at which the resin reaches the rim portion C11 is aligned.

FIG. 4C shows still another shape of the rib. In this embodiment, the rib is provided at a constant height near the AG position, and the height is zero near the AI position. , Provided intermittently. Even if the rib height is abruptly changed as in the present embodiment, if the rib height is different between the AG position and the AI position (high at the AG position), the resin is near the AG position. Can reach the rim portion C11 and can be compensated in such a direction that the resin reaches the rim portion C11.
In addition, in order to compensate so that the timing at which the resin reaches the rim portion C11 is more evenly aligned, from the AG position to the AI position as in the rib shape shown in FIGS. 4A and 4B. It is more preferable that the rib height is continuously and gradually changed.

Further, the present invention is intended to increase the roundness of the outer peripheral portion of the resin gear and the pulley by uniformly aligning the timing when the resin is filled into the rim portion C11 and the tooth portion C12 of the cavity of the molding die. However, for this purpose, the gate marks 16 and 16 (that is, the gate position in the injection process) are arranged at equal intervals on the circumference concentric with the boss 13 and the rim 11, and the ribs 15 and 15 are also formed. More preferably, the bosses 13 and the rim 11 are provided in the same shape at equal intervals on the circumference concentric with the boss 13 and the rim 11. By doing so, it is easier to design and manufacture a resin molded product having a high roundness.

Further, as described in the resin gear 1 of the first embodiment, the web 14 is configured to be concentrically divided into a first web 141 that is an inner peripheral portion and a second web 142 that is an outer peripheral portion. The first web 141 and the second web 142 are offset from each other in the gear rotation axis direction, and it is true that the ribs 15 and 15 are erected at the boundary portion (that is, the connecting portion 143). It is more preferable in increasing the circularity. Thus, if the ribs 15 and 15 are provided in the part where the first web 141 and the second web 142 are stepped, the molten resin flowing through the web part of the cavity effectively flows into the rib part C15. Therefore, the timing adjustment effect by the rib portion C15 is more effectively exhibited, which is more preferable in increasing the roundness.

In the first embodiment (FIGS. 1 and 2), the form in which the rib 15 is erected from the portion where the connecting portion 143 and the second web 142 are connected has been described. However, the first web 141 and the connecting portion are described. Even if the rib 15 is erected from the portion to which the 143 is connected (that is, the erected from the opposite surface of the web as compared to the first embodiment), the first web 141 and the second web are If they are offset and provided in steps, the resin is promoted to flow into the rib portion C15, which is similarly preferable in increasing the roundness.

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 the same portions will be denoted by the same reference numerals and detailed description thereof will be omitted. To do.

5 and 6 show a resin gear according to a second embodiment of the present invention. In the present embodiment, the web 14 is configured such that the inner circumferential side and the outer circumferential side of the rib 15 are flush with each other without being offset in the gear rotation axis direction, and the ribs 15 and 15 are on both sides of the web. Although different from the first embodiment in that it is provided in the above, it is the same in other points. Even if there is no step between the inner peripheral side and the outer peripheral side of the web as in the present embodiment, the resin injected from the gate flows into the spaces forming the ribs 15 and 15, and the rim 11 is made accordingly. As in the first embodiment, the timing of flowing into the space to be formed is delayed, and the timing at which the resin flows into and fills the rim portion C11 is made uniform, thereby obtaining the effect of improving the roundness of the molded product. Note that, as in the first embodiment, it is more preferable that the web 14 is offset at the portion where the ribs 15 and 15 are provided and is stepped because the timing delay effect due to the portion of the rib 15 is more reliably exhibited. This is as described above.

Further, the surface on which the rib 15 is provided on the web 14 may be on the same side as the gate mark 16, may be on the opposite side, or may be provided on both sides as in the present embodiment.

FIG. 7 shows still another embodiment of the present invention. In this embodiment, there are six gate marks 16, 16 and a substantially straight 6 extending in a direction perpendicular to the radial direction of the gear. Two ribs 15 ′, 15 ′ are provided so as to surround the gate marks 16, 16. In other words, in the present invention, the ribs erected along the circumferential direction of the gear as shown in the first embodiment of FIGS. 1 and 2 and the second embodiment of FIGS. In the front view, the ribs are not limited to ribs that are curved in an arc shape and are arranged in the circumferential direction. As shown in the present embodiment in FIG. 7, substantially straight ribs 15 ′ and 15 ′ are formed as a whole. It also includes the form of ribs arranged along the circumferential direction so as to form a series of circular shapes (in the present embodiment, hexagonal shapes).

Moreover, in the description of the above embodiment, the embodiment has been described by taking the resin gear as an example, but the present invention is not limited to this, and can be applied to a resin pulley having no tooth portion.

According to the present invention, when resin pulleys and resin gears are molded by injection molding, the timing at which the resin reaches the outer periphery of the molded product can be made uniform, and the accuracy of the resulting resin molded product can be improved. it can. The obtained resin molded product can be used as a component of a gear transmission mechanism or a belt transmission mechanism, and has high industrial utility value.

1 Resin Gear 11 Rim 12 Teeth 13 Boss 14 Web 15 Rib 16 Gate Trace

Claims (3)

A resin molded product that is integrally molded by resin injection molding, and an annular outer peripheral portion and a shaft portion that is a rotating shaft are connected by a web,
The web is arranged concentrically with the shaft and outer periphery so that a plurality of gate marks surround the shaft ,
On the outer peripheral side of the gate remain of the web, along cormorants ribs erected on the shaft portion and the outer peripheral portion and concentrically in the circumferential direction,
The rib, the rib height in the circumferential positions corresponding to the gate mark is higher is than the rib height in the corresponding circumferential position between the gate mark and gate mark Rutotomoni,
A resin molded product characterized in that the web is divided into an inner peripheral side portion and an outer peripheral side portion with a radial position where the rib is provided as a boundary so as to be offset from each other in the rotation axis direction . 2. The resin molded product according to claim 1 , wherein the ribs are intermittently provided in the circumferential direction. The resin molded product according to claim 1 , wherein the rib height continuously changes in the circumferential direction.

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