JPH0753396B2 - Molding method for two-layer molded product and its molding die - Google Patents

Description

TECHNICAL FIELD The present invention relates to the present invention for molding a two-layer molded product having a surface layer and an inner layer, and a molding die used for the same.

[Prior art]

When molding a two-layer molded product such as a so-called sandwich molded product or hollow molded product, a synthetic resin that forms a surface layer in a cavity is injected, and then an injection material that forms an inner layer in the synthetic resin (core layer resin). Alternatively, a hollow portion forming fluid) is injected.

Here, the sandwich molded article refers to a two-layer molded article in which the surface layer and the inner layer (core layer) are formed of different synthetic resins. A hollow molded article is composed of a synthetic resin layer as a surface layer and a hollow portion (for example, gas) as an inner layer.
A layered product.

Conventionally, the molding die for the two-layer molded product has a cavity 91 as shown in FIGS. 3 and 4, for example, and a film gate 92 is provided in communication with the end of the cavity 91. The film gate 92 is connected to a synthetic resin injection device or an injectate injection device via a runner 93 and a sprue 94.

When molding the sandwich molded product, first, the synthetic resin 81 in a softened state is injected from the film gate 92 into the cavity 91. The synthetic resin 81 is for forming the surface layer of a two-layer molded product. Next, film gate 92
Thus, the softened synthetic resin 82 as an injectate is injected into the softened synthetic resin 81 to form the inner layer.

Further, at the time of molding the hollow molded article, a fluid such as gas as an injectate is injected instead of the softened synthetic resin 82 to form the inner layer.

[Problems to be solved]

However, in the conventional molding die for a two-layer molded product, injection defects occur near the gate during molding.

This point will be described with reference to FIGS. 3 and 4.
In general, the flow of the injected material is greatly affected by the molten state of the surface layer and the pressure gradient. Then, a fairly steep pressure gradient exists in the injection direction of the injectate, and a gentle pressure gradient exists in the direction orthogonal thereto.

That is, a considerably steep pressure gradient exists in the longitudinal direction of the cavity 91, and a gentle pressure gradient exists in the width direction of the cavity 91.

Therefore, the synthetic resin 82 as an injectate has a cavity 91
Can only be elongated in the longitudinal direction. As a result, in the two-layer molded product, the thickness of the inner layer does not differ significantly near the gate and inside.

In view of such conventional problems, the present invention can prevent the injection defect of the injection material near the gate.
An object of the present invention is to provide a method for molding a layer molded product and a molding die used therefor.

[Means for solving problems]

The present invention provides a molding method for molding a two-layer molded product by injecting a synthetic resin forming a surface layer into a cavity of a molding die, and then injecting an injection material forming an inner layer into the synthetic resin to mold a two-layer molded article. Has a gate and a cavity for molding a two-layer molded product, and in the vicinity of the gate in the cavity, a pressure gradient in the longitudinal direction of the cavity along a direction orthogonal to the injection direction of the injectate. And a weir for equalizing the pressure gradient in the width direction of the cavity are arranged, and a gap is provided between the weir and the side wall of the cavity. The synthetic resin is injected from the gate into the cavity in front of the weir, and then the injectate is injected from the gate, and the injectate is caused to flow along the weir. , The injectate A portion overlies the weir, and the other portion of the injectate is injected into the synthetic resin through the gap between the weir and the side wall of the cavity. There is a molding method.

What is most noticeable in the present invention is that when forming the two-layer molded product, the weir is provided in the cavity, the synthetic resin for the surface layer is first injected from the gate, and the synthetic resin is provided in front of the weir. After being placed in the cavity, the injectate is allowed to flow along the weir to equalize the pressure gradient in the longitudinal direction of the cavity and the pressure gradient in the width direction of the cavity as described above, and the injectate is synthesized as described above. It is to inject into the resin.

The present invention is applied to two-layer molded products such as so-called sandwich molded products and hollow molded products.

And in the above-mentioned forming die, the injection direction of the injection material,
In order to equalize the pressure gradient in the direction orthogonal to this, a weir is arranged near the gate along the direction orthogonal to the injection direction of the injection material, and the injection material is provided between the weir and the side wall of the cavity. A gap is formed to form the flow path.

The weir is provided on the bottom wall of the cavity, the ceiling wall of the cavity, both the bottom wall and the ceiling wall of the cavity, and the like. Therefore, the injection material injected from the gate gets over the weir and is injected into the surface layer.

Further, the weir may be divided into a plurality of pieces and arranged along the direction orthogonal to the injection direction of the injection material.

Further, as a molding die for carrying out the above-mentioned molding method,
A molding die for molding a two-layer molded article by injecting a synthetic resin forming a surface layer into a cavity and then injecting an injection material forming an inner layer into the synthetic resin, the molding die comprising a gate And a cavity for molding a two-layer molded product, and in the vicinity of the gate in the cavity, a longitudinal direction of the cavity during injection of the injection material along a direction orthogonal to the injection direction of the injection material. For forming a two-layer molded article, characterized in that a weir for equalizing the pressure gradient in the width direction of the cavity and the pressure gradient in the width direction of the cavity is provided, and a gap is formed between the weir and the side wall of the cavity. There is a mold.

[Action]

In the present invention, when the synthetic resin forming the surface layer is injected from the gate into the cavity and then the injection material forming the inner layer is injected into the synthetic resin, the injection material is placed under the pressure of the vicinity of the gate. The flow is temporarily blocked by the weir for adjusting the gradient.

Therefore, the injectate flows along the weir. Then, a part of the injected material flows into the synthetic resin as the surface layer through the gap formed between the weir and the side wall of the cavity.
Further, the other part of the injectate crosses over the weir and flows into the synthetic resin.

Therefore, the pressure gradient in the injection direction of the injectate and the pressure gradient in the direction orthogonal thereto are made uniform. Therefore, the injected material is widely and uniformly injected into the synthetic resin as the surface layer from the vicinity of the gate toward the front. Therefore, the defective injection of the injected material unlike the conventional case does not occur. That is, it is possible to obtain a two-layer molded product having an inner layer having a substantially uniform thickness in the vicinity of the gate and in the inner part.

〔effect〕

Therefore, according to the present invention, it is possible to provide a method for molding a two-layer molded product and a molding die used for the same, which can prevent defective injection of the injected material in the vicinity of the gate.

〔Example〕

A method of molding a two-layer molded product and a molding die used therefor according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. This example is applied to a so-called sandwich molded product.

In this example, in the vicinity of the film gate 92 in the cavity 91 shown in the conventional example, along the direction orthogonal to the injection direction of the softened synthetic resin 82 as the inner layer forming injectate, the longitudinal direction of the cavity A weir 1 is provided to make each pressure gradient in the width direction uniform. A gap 2 is formed between the weir 1 and the side wall of the cavity 91.

The weir 1 has a width dimension larger than that of the film gate 92 and is integrally formed so as to protrude from the bottom wall of the cavity 91. The gap 2 as a flow path is formed between the weir 1 and the side wall of the cavity 91, and the gap 3 as a flow path is also formed between the weir 1 and the ceiling wall of the cavity 91. Is formed.

Others are the same as the above-mentioned conventional example.

Next, when molding a sandwich molded product as a two-layer molded product, first use a sprue 9 from a synthetic resin injection device.
1, runner 93, cavity 91 through film gate 92
A synthetic resin 81 in a softened state for forming a surface layer is injected therein.

Next, sprue 94 and runner 9
3. The softened synthetic resin 82 for forming the inner layer is injected into the synthetic resin 81 in the cavity 91 through the film gate 92.

What is important here is that, as shown in Figs. 1 and 2,
The synthetic resin 82 injected from the film gate 92 is temporarily blocked from flowing in the straight direction by the weir 1 arranged near the film gate 92.

Then, the synthetic resin 82 flows in the width direction of the cavity 91 along the weir 1. Then, a part of the synthetic resin 82 flows into the synthetic resin 81 in the cavity 91 through the gap 2 formed on the side of the weir 1. Further, the other part of the synthetic resin 82 flows into the synthetic resin 81 through the gap 3 formed above the weir 1 over the weir 1.

As a result, the pressure gradient in the longitudinal direction of the cavity 91 which is the injection direction of the synthetic resin 82 and the pressure gradient in the width direction of the cavity 91 which is the direction orthogonal to the injection direction are made uniform. Therefore, the synthetic resin 82 is uniformly injected into the synthetic resin 81.

The two-layer molded product molded in this manner is in a state where the synthetic resin 82 as the inner layer (core layer) is injected and molded into the synthetic resin 81 as the surface layer having a uniform thickness.

Therefore, according to this example, it is possible to mold a sandwich molded product as a two-layer molded product having a substantially uniform inner layer thickness without causing a defective injection of a conventional injected product.

If a fluid such as gas is injected instead of the synthetic resin 82, a hollow molded article as a two-layer molded article having a substantially uniform surface layer thickness can be molded.

[Brief description of drawings]

1 and 2 show a molding die for a two-layer molded product according to an embodiment, FIG. 1 is a plan sectional view of the molding die in a molding state, FIG. 2 is a side sectional view thereof, FIG. FIG. 4 shows a conventional example, FIG. 3 is a plan sectional view of a molding die in a molding state, and FIG. 4 is a side sectional view thereof. 1 …… Weir, 2,3 …… Gap, 81,82 …… Synthetic resin, 91 …… Cavity, 92 …… Film gate,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohisa Ikukawa 1 Ochiai, Ochiai, Kasuga-cho, Nishikasugai-gun, Aichi Toyoda Gosei Co., Ltd. (56) Reference JP-A-63-69613 (JP, A) JP Sho 59-187425 (JP, A)

Claims (2)

[Claims] 1. A molding method for molding a two-layer molded article by injecting a synthetic resin for forming a surface layer into a cavity of a molding die, and then injecting an injection material for forming an inner layer into the synthetic resin to form a two-layer molded article. The mold has a gate and a cavity for molding a two-layer molded product, and a pressure in the longitudinal direction of the cavity is provided in the vicinity of the gate in the cavity along a direction orthogonal to the injection direction of the injection material. A weir for equalizing the gradient and the pressure gradient in the width direction of the cavity is provided,
There is a gap between the weir and the side wall of the cavity. When molding a two-layer molded product, first, the synthetic resin is injected from the gate to move the synthetic resin in the cavity in front of the weir. And then injecting the injectate through the gate, causing the injectate to flow along the weir, causing a portion of the injectate to pass over the weir, and another portion of the injectate. Is a method for molding a two-layer molded article, characterized in that the above-mentioned injection material is injected into the above-mentioned synthetic resin through a gap between the weir and the sidewall of the cavity. 2. A molding die for molding a two-layer molded article by injecting a synthetic resin forming a surface layer into a cavity and then injecting an injection material forming an inner layer into the synthetic resin, The mold has a gate and a cavity for molding a two-layer molded product, and in the vicinity of the gate in the cavity, during injection of the injection material along a direction orthogonal to the injection direction of the injection material. In the two-layer structure, a weir is provided for equalizing the pressure gradient in the longitudinal direction of the cavity and the pressure gradient in the width direction of the cavity, and a gap is formed between the weir and the side wall of the cavity. Mold for molding molded products.