JPH0741632B2 - Double injection molded body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a box-shaped double injection-molded article having a substantially U-shaped cross section, and more specifically, it suppresses shrinkage of the primary resin and causes burrs of the secondary resin. The present invention relates to a double injection molded body that prevents

[Prior Art and Problems] Conventionally, a double injection molded body made of a synthetic resin having a substantially U-shaped section is often used for a timing gear cover of an automobile engine mainly due to a demand for weight reduction.

For example, in the case of a timing gear cover, for the purpose of weight reduction,
The main part of the cover is made of high-rigidity hard synthetic resin,
A soft synthetic resin is formed by secondary injection molding in a portion that receives vibration and a portion that requires packing.

However, as shown in Fig. 10, the primary resin 11 is fixed after molding.
It is inevitable that the cavities of 10 contract due to cooling, and the rising portion falls inward in the cavity C of the fixed mold to form a gap G between the outer mold surface and the secondary resin 12. At the time of injection, there is a tendency that the secondary resin wraps around the gap G to generate burrs B and impair the appearance of the product.

This state is as shown in FIGS. 10 and 11. That is, FIG. 10 is a sectional view showing a state in which the gap G is generated, and FIG. 11 is a sectional view showing a state in which the secondary resin is injected into the flange of FIG.

Therefore, in order to reduce the gap generated when the primary resin is cured, it is necessary to provide a waste bone S extending to the outside of the flange as shown in FIGS. 12 and 13 so as not to generate a gap at least outside the flange. It has been proposed by people (Japanese Patent Application No. Sho 63-192949). In this case, the flange part is a waste bone S
Since it is pulled outwards by G, the gap G occurs inside the molded body, and thus the burr B also occurs inside, which is advantageous because it does not impair the appearance.

A plurality of these discarded bones are provided in a part of the fixed mold in which a gap is apt to be generated due to contraction, a secondary resin is injection-molded, the mold is opened to take out a double injection-molded body, and then it is manually broken.

However, this work of breaking away the discarded bone is surprisingly troublesome, and unless it is properly ground with a disc sander or the like after breaking, the aesthetics will be spoiled and the resin material will be wasted.

Therefore, the present inventors have found that the problem can be solved by providing a convex portion or a concave portion on the back surface of the flange itself,
The present invention has been reached.

[Object of the Invention] An object of the present invention is to provide a double injection molded article that reduces shrinkage gaps that occur during curing of a primary resin, reduces burrs that occur when a secondary resin is injected, and improves product aesthetics. It is in.

Another object of the present invention is to provide a double injection molded body which does not require manual removal of waste bone for suppressing shrinkage of the primary resin as in the prior art.

[Structure of the Invention] According to the present invention, a double-sided injection-molded product having a box-shaped section having a substantially U-shaped cross-section formed by injection-molding a secondary resin having a different color and hardness on a surface of a flange formed of a primary resin. Further, there is provided a double injection-molded article having a box-shaped substantially U-shaped section, characterized in that a plurality of projections and / or recesses are intermittently formed along the outer periphery of the flange when viewed from the die cutting direction.

The present invention will be described in detail below with reference to examples.

[Embodiment] FIGS. 1 and 2 are perspective views of an embodiment of the present invention, in which FIG. 1 shows a plurality of recesses on the back surface of the flange, and FIG. 2 shows a plurality of projections on the back surface of the flange. Prepared intermittently.
The recesses or protrusions may be provided intermittently along the peripheral edge of the flange, but the recesses and protrusions may be alternately or selectively used as required.

3 is a sectional view taken along the line III-III 'in FIG. 1, and FIG. 4 is a sectional view taken along the line IV-IV' in FIG.

In FIGS. 3 and 4, 1 is a convex portion (projection) and 2 is a concave portion (square hole). When the primary resin is injected, the convex portion 1 and the concave portion 2 suppress the shrinkage of the primary resin during cooling, and the gap G
Is unlikely to occur.

5 is a sectional view taken along line VV 'of FIG. 1, and FIG. 6 is a sectional view taken along line VI-VI' of FIG.

FIG. 7 is a front view of the timing gear cover of the SOHC engine. FIG. 8 is a sectional view taken along the line VIII-VIII ′ of FIG.
FIG. 9 is an enlarged sectional view taken along line IX-IX ′ in FIG. 7. FIG. 9 shows a state in which the concave portion shown in FIG. 3 or the convex portion shown in FIG. 4 suppresses the shrinkage of the primary resin.

[Effects of the Invention] By carrying out the present invention, all of the above objects can be achieved.

That is, by adopting the double injection molded body structure of the present invention, a gap between the outside of the primary resin flange and the fixed die is extremely reduced. Therefore, since the secondary resin does not enter the gap as in the conventional case, the appearance of the molded product becomes good. Moreover, the effect of not particularly impairing the appearance can be obtained even if the convex portions and concave portions are left as they are. Furthermore, there is no extra step of manually scraping away the discarded bone,
Secondary synthetic resin materials can be saved.

[Brief description of drawings]

1, 2, 3, 4, 5 and 6 are respectively a perspective view of a concave type embodiment, a perspective view of a convex type embodiment, a III-III 'sectional view, an IV-IV' sectional view,
FIG. 6 is a sectional view taken along line VV ′ and a sectional view taken along line VI-VI ′. Figures 7, 8 and 9 are front views of the timing gear case, respectively.
FIG. 6 is a sectional view taken along line I-VIII ′ and an enlarged sectional view taken along line IX-IX ′. 10, 11 and 12 are cross-sectional views showing a conventional primary resin contraction state, respectively, and FIG. 13 is a perspective view of a conventional molded body with waste bone. 1 ... convex part, 2 ... concave part, 3 ... flange, 3A ... flange surface, 3B ... flange back surface, 10 ... fixed type, 11 ...
Primary resin, 12 ... Secondary resin, B ... Burr, C ... Cavity, G ... Gap, 100 ... Double injection molding.

Claims (1)

[Claims] 1. A double injection molded body having a box-shaped section having a substantially U-shaped cross-section formed by injection-molding a secondary resin having a different color and hardness on a surface of a flange formed of a primary resin. A double injection-molded body having a box-shaped section with a substantially U-shaped cross-section, characterized in that a plurality of convex portions and / or concave portions are formed intermittently along the outer circumference of the flange.