JPH0745169B2 - Injection blow molding method for containers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of the injection blow molding method for a container of the present invention, particularly the injection blow molding method for forming a hollow synthetic resin container from a cylindrical bottomed parison.

[Prior Art] An injection blow molding method is well known in which a cylindrical bottomed parison is formed by injection molding, and a gas is blown into the bottomed parison to expand it to form a synthetic resin container having a predetermined shape. It is used to form various hollow containers such as cosmetics and detergent containers and beverage bottles.

In this injection molding method, it is extremely important to control the expansion ratio of each part of the bottomed parison during blow molding in order to make the wall thickness distribution of the hollow container formed uniform.

That is, when the cylindrical hollow container is formed from a cylindrical bottomed parison, the thickness distribution of the container has a constant expansion ratio as long as the thickness and temperature distribution of the bottomed parison are constant. Since there is no difference in the extension of each part, it is said that the parts are uniform throughout.

However, when a hollow container with a rectangular cross section or a flat hollow container such as a flat circle or an ellipse is formed from a cylindrical bottomed parison, a difference occurs in the linear expansion coefficient of each part of the parison.
The thickness distribution of the container, in particular, the thickness distribution of the peripheral surface (side surface) of the container becomes uneven, resulting in uneven thickness.

This uneven thickness appears only as a slight difference when the container is formed to be thick, but when the container is formed to be thin, the thickness is significantly different, and in an extreme case, the peripheral surface has a small difference. The part may be thinly formed like a film and the function as a container may be impaired at all.

In order to solve such a problem, conventionally, there has been proposed a method for injection blow molding of a flat container (Japanese Patent Publication No. 59).
-42925 gazette). In this molding method, air is blown into a bottomed parison 1 having a circular cross section as shown in FIG. 11 to form a flat container 2 having significantly different vertical and horizontal expansion ratios in a flat cross section, as shown in FIG. .

At this time, as shown in FIG. 13, the bottomed parison 1 has a circular plane section and the facing portions 1a, 1a are formed to be slightly thicker than the other portions 1b, 1b. This thick part 1a, 1a
As shown in FIG. 14, the flat container 2 forms front and rear surfaces 2a, 2a having a large expansion ratio, and the other portions 1b, 1b form both peripheral surfaces 2b, 2b having a small expansion ratio of the flat container 2. To do.

That is, since the thick portions 1a, 1a of the bottomed parison 1 have a larger heat capacity than the other portions 1b, 1b, even in blow molding with different vertical and horizontal expansion ratios, there is a difference in heat capacity between the expansion ratios. The difference is compensated for, resulting in uniform expansion. As a result, the flat hollow container 2 having a uniform wall thickness distribution can be formed even though the cylindrical bottomed parison 1 is used.

[Problems to be Solved by the Invention] However, in this conventional method, it is necessary to form the parison 1 having a slightly different wall thickness distribution. Therefore, there has been a problem that processing of a mold used for injection molding becomes complicated.

Particularly, in the above-mentioned conventional technique, there is a problem that a complicated process for forming the core die of the injection molding die into a flat shape in conformity with the inner shape of the parison is required, and the whole manufacturing apparatus becomes expensive.

In such a conventional technique, the bottomed parison 1 injection-molded is often sent to a heating furnace to adjust the parison temperature, and then the flat container is often blow-molded. In this case, the temperature control core type provided in the heating furnace also requires complicated processing according to the inner shape of the bottomed parison, which also causes a problem of increasing the cost of the entire manufacturing apparatus. there were.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a container injection blow molding method capable of forming a container having a good wall thickness distribution by solving the problems described above. To provide.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for blow molding a bottomed parison injection-molded using an injection mold to form a hollow container, wherein the injection mold By providing a gate for injecting resin into the resin as a resin flow control gate for controlling the resin flow from the bottom surface of the bottomed parison to the peripheral surface during injection molding,
The bottomed parison is formed so as to have a retained heat quantity distribution according to the shape of the final molded product, and the wall thickness distribution of the peripheral surface of the hollow container during blow molding is controlled.

[Operation] Next, the operation of the present invention will be described.

The bottomed parison is formed by injecting a molten resin from a runner through a gate into an injection mold. At this time, the resin present in the gate formed in the injection mold is cooled and solidified on the bottom surface of the bottomed parison, and a projection called a gate portion is formed.

The feature of the present invention is that the gate is provided as a resin control gate for controlling the resin flow from the bottom surface of the bottomed parison to the peripheral surface during injection molding, so that the bottom surface of the bottomed parison or this bottom surface to the peripheral surface, The purpose is to give the distribution of heat quantity possessed according to the shape of the hollow container which is the final molded product. This makes it possible to control the wall thickness distribution of the peripheral surface (side surface) of the hollow container during blow molding.

That is, when the resin is injected from the gate of the injection mold, the injected resin passes through the resin flow control gate and wraps around from the portion corresponding to the bottom surface of the bottomed parison to the portion corresponding to the peripheral surface. At this time, the gate formed in the injection molding die is formed, for example, as an elliptical, star-shaped, or flat-shaped resin flow control gate so that the runner passes through the resin flow control gate. The flow of the resin flow flowing into the mold is controlled according to the shape of the resin flow control gate, so that the bottomed parison can be provided with an arbitrary distribution of heat quantity.

Thus, according to the present invention, by forming the shape of the control gate into a shape that gives a retained heat quantity distribution according to the shape of the container to be blow molded, a rectangular hollow container,
The oblong or elliptical flat hollow container can be formed so that the peripheral surface thereof has a substantially uniform wall thickness distribution.

In particular, in the present invention, the thickness of the peripheral surface of the bottomed parison is not controlled as in the prior art to give the retained heat quantity distribution, but the gate of the injection mold is provided with a resin that controls the flow of resin during injection molding. It was formed based on a completely new idea of forming a flow control gate and giving the distribution of heat quantity retained by the flow of this resin. Therefore, the injection mold and the temperature control mold are not required to have complicated processing corresponding to a complicated wall thickness distribution as in the conventional case, and the cost of the entire apparatus can be reduced.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

1 to 7 show a first preferred embodiment of the present invention.

In the injection blow molding method of this embodiment, air is blown into the cylindrical bottomed parison 10 shown in FIG. 1 to form a flat hollow synthetic resin container 110 as shown in FIG.

FIG. 3A shows an injection mold 20 used for injection molding the bottomed parison 10. This injection mold 20
Has an injection core mold 24 and an injection mold 22. A hot runner nozzle 40 is connected to the resin injection gate 26 of the injection mold 20 via a heat insulating agent 42.

Then, the injection mold 2 is passed from the runner 40a through the gate 26.
By injecting molten resin into 0, bottomed parison 10
Is formed. At this time, the resin existing in the gate 26 formed in the injection mold 20 is cooled and solidified, and a projection called a gate portion 12 is formed.

The feature of the present invention is that the flow of the molten resin injected into the mold 20 is controlled by using the gate 26, and the bottomed parison 10, particularly the synthetic resin container as the final molded product from the bottom surface 16 to the peripheral surface 17 thereof.
The purpose is to give a distribution of heat quantity possessed according to the shape of 110.
As a result, even when air is blown into the parison 10 to blow-form the flat synthetic resin container 110 having different vertical and horizontal expansion ratios, it is possible to compensate for the difference in expansion ratio with the retained heat quantity distribution. As a result, the cylindrical bottomed parison
Despite the use of 10, it is possible to obtain a flat synthetic resin container 110 having a uniform thickness distribution on the peripheral surfaces 110a and 110b.

As shown in FIGS. 3B and 3C, the gate 26 of the embodiment is shown.
Is composed of a pore gate 26a as an initial injection port and a resin flow control gate 26b following the pore gate 26a.
On the bottom surface 16 of the bottomed parison 10, a protrusion-shaped initial gate portion 26a and a plate-shaped control gate portion 26b connected to the protrusion-shaped initial gate portion 26a are formed corresponding to the gates 26a and 26b.

With the above configuration, the molten resin flow injected into the mold from the initial gate 26a through the resin flow control gate 26b passes through the bottom forming space 28a and the peripheral surface forming space 28b, and is deep inside the mold. It flows toward. It is estimated that the resin flow at this time is controlled as shown in FIG.

That is, the molten resin flow that has flowed from the control gate 26b into the bottom surface forming space 28a directly enters from the both ends of the control gate 26b toward the peripheral surface forming space 28b as shown by the arrow 100a. The resin flow that has flowed into the bottom surface forming space 28a near the center of 26b collides with the injection core mold 24 as shown by the arrow 100b, flows once laterally, and then flows into the peripheral surface forming space 28b.

Fig. 5 (a) shows an estimated diagram of the resin flow in the cross section Va-Va of Fig. 4, and Fig. 5 (b) shows Va-Va of Fig. 5.
The estimated diagram of the resin flow in the cross section of Vb-Vb orthogonal to is shown. As can be understood from these estimation diagrams, the bottomed parison 10 formed by the injection molding of the embodiment has a large amount of heat retained in the 10a and 10a regions where the resin flow directly enters, and the resin flow hardly flows in. It is estimated that the amount of heat retained in the 10b and 10b regions will be low. Because 100a
The resin flow of 10b is cooled by the mold in the process of wrapping around to the resin flow of 100b.
This is because it is estimated that the amount of heat retained is higher in the region of 0a.

Therefore, it will be understood that in the regions 10a, 10a having a large retained heat amount, the resin easily expands in the blow molding process described later, and in the regions 10b, 10b having a small retained heat amount, the resin hardly expands in the blow molding process.

The bottomed parison 10 is a blow mold shown in FIG.
At 30, a flat synthetic resin container 110 is blow-molded. At this time, the transfer to the blow mold 30 is performed by the bottomed parison 10
After being released from the injection mold 20, there are cases where it is immediately transferred to the blow mold 30 and cases where it is transferred to the one-end heating furnace to readjust the parison temperature and then transferred to the blow mold 30. Can adopt any of these.

FIG. 6 shows the position of the bottomed parison 10 in the blow mold 30. The bottomed parison 10 in the embodiment is
Located in the center of the flatly formed cavity 32, the mold surfaces 32a and 32a forming the front and rear peripheral surfaces 110a and 110a of the flat container 110 are exposed to the regions 10a and 10a having a high retained heat amount. Then, by blowing air into the bottomed parison 10, the areas 10a, 10a having a high retained heat amount are brought into contact with the mold surfaces 32a, 32a, and the areas 10b, 10b having a low retained heat amount are provided on the left and right sides of the flat container 110. Both sides 110b, 1
10b is expanded in a direction in which it contacts the mold surfaces 32b, 32b for molding.

At this time, the area 10a where the bottom parison 10 has a large amount of heat,
The area 10a is sufficiently elongated as compared with the areas 10b and 10b having a small heat quantity. As a result, from the cylindrical bottomed parison 10 as shown in FIG. 1, it is possible to obtain a flat hollow container 110 having a uniform wall thickness distribution on the peripheral surfaces 110a, 110b as shown in FIG.

In particular, according to the present invention, both peripheral surfaces 110b, 110b of the flat container 110 are thinly formed like a film and have insufficient strength as in the conventional case, or stress whitening does not significantly impair aesthetics. Therefore, a good flat synthetic resin container can be obtained.

In addition, after forming the synthetic resin container 110 in this way,
The gate portions 112a and 112b on the bottom surface 116 may interfere. In this case, these gate portions 112a, 1
12b may be crushed, and after that, the gate portion 112a,
Only 112b may be excised.

Further, the resin flow control gate portion 112b on the bottom surface 116 of the synthetic resin container 110 may be positively utilized, for example, as a suspending tool for suspending the container 110 by making a hole 120 or the like in the control gate portion 112b. Can also be used.

In the present embodiment, the case where the considerably large control gate portion 12b is formed on the bottom surface of the bottomed parison 10 has been described as an example, but even if the control gate portion 12b is not so large, for example, Even a small one as shown in FIG. 7 can obtain a sufficient effect.

In the present embodiment, the resin flow control gate 26b is described as an example in which the plate-shaped control gate portion 12b is provided on the bottom surface 16 of the bottomed parison, but the present invention is not limited to this. , According to the shape of the synthetic resin container 110 to be formed,
The resin flow control gate 26b may be formed so that the control gate portion 12b has an arbitrary shape, for example, a star shape or an elliptical shape.

For example, a prismatic hollow synthetic resin container as shown in FIG.
When forming 110, the gate 26b for resin flow control may be used to form a star-shaped control gate portion 12b having a cross shape on the bottom surface as shown in FIG. As a result, as shown in FIG. 8 (c), the resin flow easily flows into the bottomed parison 10 and particularly the bottom surface 16 thereof, and the area 10a having a large amount of heat is retained.
And the regions 10b in which the resin flow is less likely to flow and the amount of heat retained is low are formed alternately. Therefore, by blowing air into the bottomed parison 10, the region 10a having a high retained heat amount forms the peripheral surface 110a of the synthetic resin container 110, and the region 10b having a low retained heat amount forms the corner portion 110b of the container 110. Will be done.

In particular, when forming such a rectangular hollow container 110 in the past, the corner portion 110b tended to be easily stretched during blow molding, resulting in insufficient strength, but according to the present invention, the meat of the corner portion 110b is The thickness can be kept good.

Further, in the above-mentioned embodiment, the gate 26 is composed of the fine pore gate 26a as the initial injection port and the resin flow control gate 26b subsequent thereto.
Although the present invention is not limited to this, the present invention is not limited to this, and may be configured such that only the resin flow control gate 26b is provided without providing the fine pore gate 26a if necessary. In this case, for example, the control gate portion 12b of the bottomed parison 10 is
The resin flow control gate 26b may be formed to have the shape shown in FIG.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.

[Effects of the Invention] As described above, according to the present invention, the gate for injecting the resin into the injection mold is for resin flow control for controlling the resin flow from the bottom surface of the bottomed parison to the peripheral surface during injection molding. By providing it as a gate, it is possible to form a bottomed parison so as to have a retained heat quantity distribution according to the shape of the final molded product, which allows good control of the wall thickness of the peripheral surface of the hollow container during blow molding. be able to.

In particular, according to the present invention, the thickness of the peripheral surface of the hollow container during blow molding can be controlled without using a bottomed parison whose peripheral surface thickness is accurately controlled. The mold does not need to be complicatedly processed as in the past, and the cost of the injection molding apparatus itself can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a bottomed parison used in the present invention. FIG. 1 (a) is an explanatory view of a peripheral surface thereof, and FIG. 1 (b) is a peripheral surface of the same shown in FIG. Explanatory drawing, the same figure (c) is an explanatory bottom view of the same figure (a) seen from the arrow c direction, and FIG. 2 is a flat hollow synthetic resin formed by blowing air into the bottomed parison shown in FIG. It is an explanatory view of a container,
1A is a perspective view thereof, FIG. 1B is a bottom view thereof, and FIG. 3 is an illustration of an injection mold used for molding the bottomed parison shown in FIG. FIG. 1A is an explanatory view of a longitudinal section of the whole, FIG.
FIG. 4C is a vertical cross-sectional explanatory view in a direction orthogonal to FIG. 4B, and FIGS. 4A and 4B are explanatory views showing the flow of resin in the mold shown in FIG. FIGS. 5 (a) and 5 (b) are explanatory views of the flow of resin in the mold shown in FIGS. 3 (b) and 3 (c), and FIG. 6 is the position of the bottomed parison and the blow mold. FIG. 7 is a cross-sectional explanatory view showing the relationship, and FIG. 7 is an explanatory view showing an example in which the resin flow control gate portion formed on the bottom surface of the bottomed parison is formed smaller, and FIG. FIG. 8B is an explanatory view of the resin flow control gate portion viewed from the lateral direction, FIG. 8B is an explanatory view of the resin flow control gate portion viewed from the front direction, and FIG. FIG. 4A is an explanatory view of the peripheral surface thereof, FIG. 3B is a perspective explanatory view of the bottomed parison as seen obliquely from below, and FIG. The illustration of the bottom surface thereof, FIG. 9 is an explanatory view of a hollow synthetic resin container formed rectangular with a bottomed parison shown in FIG. 8, FIG. (A)
Is a perspective explanatory view thereof, FIG. 10B is an explanatory view of the bottom surface thereof, FIG. 10 is an explanatory view of a bottomed parison having only a control gate portion formed on the bottom surface, and FIGS. 11 to 14 are conventional drawings. It is explanatory drawing which shows an example of the injection blow molding method of this. 10: bottomed parison, 10a, 10b: area, 12b: control gate, 16: bottom, 26: gate, 26b: resin flow control gate, 110: synthetic resin container.

Claims (1)

[Claims] 1. A method for blow molding a bottomed parison injection-molded using an injection mold to form a hollow container, wherein a gate for injecting resin into the injection mold is provided with the bottomed parison during injection molding. By providing it as a resin flow control gate that controls the resin flow from the bottom surface to the peripheral surface,
An injection blow molding method for a container, which comprises forming a bottomed parison so as to have a retained heat quantity distribution according to the shape of the final molded product, and controlling the wall thickness distribution of the peripheral surface of the hollow container during blow molding.