JPH0531922U - Injection-molded product protrusion structure - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress waviness due to local "shrink" on the surface of injection-molded products. [Structure] A space S is formed inside the bumper back surface 9 inside.
A rib 2 having a rectangular shape 6 projecting in a direction substantially perpendicular to the back surface 9 and upper and lower sides formed integrally with both the back surface 9 and the rectangular shape portion 6. It is provided with inclined portions 7 and 8. While forming the inclined portions 7 and 8 so as to be smoothly continuous with the back surface 9,
The connection position between the inclined portions 7 and 8 and the back surface 9 is set to a position outside the both ends of the space S so that the thickness dimension does not change suddenly, and the local " To prevent "close-up".

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a projection structure of an injection-molded product, and more particularly to a structure in which a projection is formed on the back surface of the injection-molded product and a space is formed inside the projection.

[0002]

[Prior Art]

 Injection molding has been known as one of the methods for molding a resin molded product. In this injection molding, generally, in a state where a pair of molding dies are closed, a molten resin material is injected into a cavity formed between the two dies and then cooled, and the resin material is made to correspond to the cavity shape. It is performed so as to be molded into a predetermined shape.

As an example of this injection molding, as disclosed in Japanese Patent Publication No. Sho 57-14968, for example, injection molding is proposed in which a space is formed inside the injection molded product. .. More specifically, first, with a pair of molding dies closed, an amount of molten resin material that is insufficient to fill the cavity volume is injected into the cavity formed between the dies. After that, high-pressure air is blown into the injected resin material. As a result, while the inside of the resin material is being filled with air, the resin material spreads over the entire cavity, and the outer surface thereof is formed into a predetermined shape along the inner surface shape of the cavity. After that, an injection-molded product is obtained by cooling and opening the mold. The injection-molded product molded in this manner has an outer shape of a predetermined shape corresponding to the cavity shape, and the inside thereof is hollow.

In addition, British Patent 2158002B has been proposed as a method in which such an injection molding method is used to achieve local reinforcement without increasing the weight of an injection molded product. Specifically, injection molding is performed by using a forming die configured to form a bead-shaped rib on a part of the back surface of the injection-molded product, and a resin material is injected into the cavity of the molding die. After that, high-pressure air is blown into the inside of the rib. In the injection-molded product molded in this way, the rib is reinforced around the molding position and a space is formed inside the rib, which increases the weight of the injection-molded product as a whole. It has nothing to do.

[0005]

[Problems to be solved by the device]

 However, in the structure in which a space is formed inside such a rib, as shown in FIGS. 9 and 10, the rib c protruding from the back surface b of the injection-molded product a is formed. There was a problem that waviness was generated on the surface d of the injection molded product corresponding to the installation position. Explaining the cause of this waviness, the region where the rib c is not formed (region A in FIGS. 9 and 10) has the predetermined thickness (dimension t1) of the injection-molded product a. , The thickness of the injection-molded product a sharply increases around the rising portions e and e of the rib c (increase dimension t2), the heat generated at the portions having different thicknesses is increased. Due to the difference in the amount of contraction, a "shrink" is locally generated on the surface d corresponding to the rising portions e, e, which causes the above-mentioned waviness.

As a countermeasure against this, it is possible to reduce the width dimension of the above-mentioned rib (dimension B in FIGS. 9 and 10) in order to reduce the wavy area as described above. However, it is not possible to suppress the local "shrinkage", and the reinforcing function of the rib c is not sufficiently exerted, which is not practical.

The present invention has been made in view of these points, and it is possible to increase the reinforcing function of the ribs while suppressing waviness due to local "shrinkage" of the surface of the injection molded product. Aim to get.

[0008]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention forms an injection-molded article into a shape such that its thickness dimension does not change suddenly. Specifically, a concave portion having a predetermined shape is formed on the molding surface of the closed molding die, and after the molding material is injected into the cavity of this molding die, gas is fed toward the concave portion. The target is the projection structure of the injection-molded product, which is formed by the above process and has a projection on the back surface with a space formed inside. The projecting portion includes a projecting main body portion that projects in a direction substantially perpendicular to the back surface, and a connecting portion that is integrally formed with both of the back surface and the projecting main body portion. The connecting portion is formed so that the thickness of the molded product gradually increases toward the protruding main body portion continuously and smoothly with respect to the back surface, and the connecting position between the connecting portion and the back surface is formed. Is set outside the end of the space.

[0009]

[Action]

 According to the present invention having the above-described structure, in injection molding, first, the mold having the recess having the predetermined shape is closed, and the molding material is injected into the cavity of the mold, and then the mold is moved toward the recess. Deliver gas. The injection-molded product molded in this manner has a back surface provided with a protrusion having a space formed inside. Further, since the connecting portion integrally formed with the back surface of the molded product and the protruding main body portion is continuous with the back surface gently, the injection portion is formed at the molded portion of the protruding portion. Since the thickness dimension of the molded product gradually increases due to the continuous portion, the amount of heat shrinkage per unit length during injection molding is small, and the connection position between the connecting portion and the back surface is small. Since the space is set at a position outside the end of the space, the amount of heat shrinkage is less affected by the space, and local shrinkage as in the past does not occur. The surface of the injection molded product will not be wavy, and the appearance will be improved.

[0010]

【Example】

 Next, an embodiment of the present invention will be described with reference to the drawings. Further, in this example, a case where an automobile bumper is adopted as an injection-molded product according to the present invention will be described. FIG. 2 shows a front view of the left half of the automobile bumper 1 according to this example. The bumper 1 is formed by injection molding of a thermoplastic resin such as polypropylene (this injection molding will be described later). In addition, the bumper 1 is provided with a not-illustrated traveling wind introduction port 1a for introducing traveling wind into the engine room and a winker lamp mounting recessed portion 1b to which a winker lamp or the like is mounted when the bumper 1 is assembled to the vehicle body Has been.

Then, the back surface of the bumper 1 is provided with first to fourth reinforcing ribs 2 to 5 as protrusions in the present invention, which extend in the longitudinal direction thereof. Each of the ribs 2 to 5 will be described. The first rib 2 located at the uppermost portion extends in the horizontal direction across the left and right ends of the bumper 1 above the winker lamp mounting recess 1b. The second rib 3 is located below the first rib 2, and both left and right ends thereof extend in the horizontal direction between the inner ends of the recessed lamp mounting recess 1b. The third rib 4 is located further below the second rib 3, and extends horizontally in the left and right ends of the bumper 1 below the turn signal lamp mounting recess 1b. The fourth rib 5 is arranged in the vicinity of the lower end of the bumper 1, and extends in the horizontal direction across the left and right ends of the bumper 1 below the traveling air inlet 1a. Since the ribs 2 to 5 are provided on the back surface of the bumper 1 in this manner, the rigidity of the entire bumper 1 is improved.

A characteristic of this example is the vertical cross-sectional shape of each rib 2-5. Hereinafter, the vertical cross-sectional shapes of the ribs 2 to 5 will be described. Since the vertical cross-sectional shapes of the ribs 2 to 5 are all the same, the first rib 2 will be described as an example here. As shown in FIG. 1, the first rib 2 is provided with a rectangular portion 6 as a protruding main body portion according to the present invention and inclined portions 7 and 8 as connecting portions. The rectangular portion 6 is a portion protruding from the back surface 9 of the bumper 1 in a substantially rectangular shape, and includes an upper surface 6a and a lower surface 6b extending in the horizontal direction in FIG. 1, and a vertical plane between the upper and lower surfaces 6a, 6b. It is made up of 6c. The inclined portions 7 and 8 are composed of an upper inclined portion 7 and a lower inclined portion 8, and the upper inclined portion 7 is formed between the bumper back surface 9 and the upper surface 6a of the rectangular portion 6. On the other hand, the lower inclined portion 8 is formed between the bumper rear surface 9 and the lower surface 6b of the rectangular portion 6. As one of the features of this example, each of the inclined portions 7 and 8 is formed with an inclination angle so as to be smoothly continuous with the back surface 9 of the bumper. Since the ribs 2 to 5 having such a shape are formed, the thickness of the bumper 1 is gradually increased in the bumper 1 where the ribs 2 to 5 are not formed by the inclined portions 7 and 8. It is configured to be continuous with the rectangular portion 6.

Since the ribs 2 to 5 having such a shape are molded, the mold used in the injection molding described later has a mold structure that forms a concave cavity matching this rib shape. Is becoming In this injection molding, high-pressure air is blown into the molding portions of the ribs 2-5, and the high-pressure air causes a substantially triangular shape inside the ribs 2-5. The space portion S is formed.

As another feature of this example, the connection position between each of the inclined portions 7 and 8 and the bumper back surface 9 is set outside the space S. That is, the connection position between the upper inclined portion 7 and the bumper rear surface 9 is set further above the upper end of the space S in FIG. 1, and the connection position between the lower inclined portion 8 and the bumper rear surface 9 is 1 is set further below the lower end of the space S in FIG. As a result, the sloped portions 7 and 8 ensure a change in thickness such that the thickness of the bumper 1 gradually increases.

Next, injection molding when molding the bumper 1 will be described. First, a molten resin material is poured into a pair of molding dies that form a cavity around a rib as shown in FIG. 1 over the entire inner space of the cavity. After the operation of injecting the molten resin material, high-pressure air is blown from the same inlet as the inlet of the molten resin material. The air blowing pressure is set to, for example, 100 kg / cm ² . Such air blowing fills the inside of the rib 2 with air throughout, and as shown in FIG. 1, the rib 2 has a substantially triangular space at the central portion in the vertical cross section. The part S is formed. Then, the resin material is cooled by, for example, circulating cooling water through a pool passage (not shown) formed in the molding die, and the mold is opened to obtain the bumper 1 having a predetermined shape. The characteristic operation of this example is when the resin material is cooled. When this resin material is cooled, the amount of heat shrinkage differs in each part depending on the thickness of the resin material, and in particular, in the conventional case, a local "shrinkage" occurs on the bumper surface 10 at the molded part of the rib 2. Although waviness may have occurred on the front surface 10, according to the configuration of the present example, as described above, the slanted portion 7, which is formed with a slanting angle that smoothly continues to the bumper rear surface 9, Since the ribs 2 are formed, the thickness of the bumper 1 in the formed portion of the rib 2 is gradually increased by the inclined portions 7 and 8, so that the heat shrinkage amount per unit length is small. Therefore, there is no occurrence of local “shrinkage” as in the conventional case, and therefore no waviness occurs on the bumper surface 10. Further, since the connection positions of the inclined portions 7 and 8 and the bumper back surface 9 are set to positions outside the both ends of the space portion S, the heat shrinkage amount is less affected by the space portion S. This also suppresses the occurrence of the above-mentioned "closing". Therefore, the bumper surface 10 corresponding to the molded portion of the rib 2 is formed as a smooth continuous surface, and its appearance is greatly improved as compared with the conventional one. Further, in such a rib shape, in addition to the rectangular portion 6 having the same shape as that of the conventional rib shape, the inclined portions 7 and 8 are formed at the upper and lower ends thereof. The improvement in the rigidity of the bumper 1 due to No. 5 will be further improved.

As described above, according to the configuration of this example, the rib 2 formed on the back surface 9 of the bumper is formed with the inclined portions 7 and 8 that are smoothly continuous with the back surface 9 of the bumper. Therefore, the appearance of the bumper surface 10 can be improved and the bumper rigidity can be further improved, and an extremely highly practical configuration can be obtained.

(Experimental Example) Next, an experiment conducted by the inventors of the present invention to confirm the above effect will be described. In this experiment, various types of the shapes of the inclined portions 7 and 8 described above were adopted for each portion of the bumper 1, and the wavy state of the bumper surface 10 at the time of injection molding in each case was measured. As the type of the inclined portion shape, in addition to the A type as shown in FIG. 1 described above, B to E types shown in FIGS. 3 to 6 are respectively adopted at the a to i positions of the bumper 1 in FIG. The surface shape of the bumper at the time of injection molding was measured. Explaining each type, in the A, B, and C types, the slanted portion length L1 is 10 mm, 5 mm, and 2 mm, respectively, and the slanted portion height L2 is set to 2 mm. Further, the D type employs only the lower inclined portion 8 of the type B and does not include the upper inclined portion 7. Further, the E type has a conventional rib shape having no inclined portion. The results of each experiment are shown in Table 1 below. Each position of α, β, γ in Table 1 corresponds to each part shown in FIGS. 1, 2 to 6 and each part shown in FIG. 7, and Table 1 shows each part α, β, γ The "closed" dimensions are shown.

[0018]

[Table 1]

As can be seen from Table 1, the smaller the inclination angle of the upper and lower inclined portions 7 and 8 with respect to the bumper back surface 9, that is, the smoother the connecting portion between the bumper back surface 9 and the inclined portions 7 and 8. It was confirmed that the "shrink" size of each part was small, and in particular, the effect of suppressing "shrink" was exhibited to the extent that "shrink" could not be measured in Type A.

(Modification) Next, a modification of the present invention will be described. As shown in FIG. 8, the ribs 11 of the bumper 1 in this example extend in a direction perpendicular to the extension direction of the bumper back surface 9 with a larger dimension than the ribs of the above-described embodiment. The base end of the rib 11, that is, the connecting portion with the bumper rear surface 9 is integrally formed with a curved portion 12 having a curved surface and smoothly continuing to the bumper rear surface 9.

Even with such a configuration, the unmolded portion of the rib 11 of the bumper 1 is continuous with the rib 11 while the thickness dimension of the bumper 1 gradually increases due to the curved portion 12. Therefore, it is possible to improve the appearance of the bumper surface 10 and further improve the bumper rigidity by the same operation as that of the above-described embodiment.

In this embodiment, the case where the automobile bumper 1 is used as the injection molded product has been described, but the present invention is not limited to this, and it is also adopted for various other injection molded products. can do. In addition, the injection molding described in this embodiment is one in which a molten resin material that sufficiently fills the cavity volume is injected into the cavity (generally called full shot molding). After injecting an insufficient amount of molten resin material, it can be used for injection molding (generally called short shot) in which this molten resin material is spread throughout the cavity by supplying air. Good.

[0023]

[Effect of the device]

 As described above, according to the present invention, the projecting portion provided on the back surface of the injection-molded product is provided on the projecting body portion projecting in a direction substantially perpendicular to the back surface, and on the back surface and the projecting body portion. And a connecting portion integrally formed with both of them, and the connecting portion is smoothly continuous to the back surface and gradually increases in thickness of the molded product toward the protruding main body portion. In addition, since the connection position between the connecting part and the back surface is set to a position outside the both ends of the space part, the injection molded product is There is no sudden change in thickness, there is no local "shrinkage" as in the past, and there is no waviness on the surface of the injection molded product. Is improved. Further, since the connecting portion increases the volume of the protruding portion, the rigidity of the injection molded product can be improved by the protruding portion.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view of a type A rib.

FIG. 2 is a front view showing the left half of the bumper.

FIG. 3 is a view corresponding to FIG. 1 in type B.

FIG. 4 is a diagram corresponding to FIG. 1 in type C.

FIG. 5 is a view corresponding to FIG. 1 in type D.

FIG. 6 is a view corresponding to FIG. 1 in a type E.

FIG. 7 is an enlarged view showing the curvature of the bumper surface in order to show the position where “shrinkage” occurs.

FIG. 8 is a view corresponding to FIG. 1 showing a modified example of the rib peripheral structure.

FIG. 9 is a view corresponding to FIG. 1 in the prior art.

FIG. 10 is a view corresponding to FIG. 9 when the shape of the space portion is different.

[Explanation of symbols]

 1 Bumper (injection-molded product) 2, 3, 4, 5 Rib (projection part) 6 Rectangular part (projection main body part) 7, 8 Inclined part (connecting part) 9 Back surface S Space part

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Claims (1)

[Scope of utility model registration request] 1. A mold having a predetermined shape is formed with a concave portion on the molding surface of a closed mold, and after a molding material is injected into the cavity of the mold, gas is fed toward the concave portion. A projection body structure of an injection-molded article, comprising a projection section having a space formed inside formed on the back surface, wherein the projection section projects substantially vertically to the back surface. And a connecting portion integrally formed with the rear surface and the protruding main body portion, the connecting portion being smoothly continuous with respect to the rear surface of the protruding main body. It is formed so that the thickness dimension of the molded product gradually increases toward the portion, and the connection position between this connecting portion and the back surface is set to an outer position than the end portion of the space portion. The structure of the protruding part of the injection molded product.