JPS6220006B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a primary molded product of a polyethylene terephthalate resin laminate, and more specifically, the present invention relates to a method for forming a primary molded product of a polyethylene terephthalate resin laminate. The purpose is to prevent a portion of a primary molded product made of terephthalate resin, particularly a gate portion, from whitening due to injection molding of other synthetic resin materials.

Polyethylene terephthalate resin (hereinafter simply referred to as
Products molded from PET) and copolymer resins mainly composed of PET, especially stretch-blow molded bottles, have good transparency, excellent content resistance, and relatively good gas barrier properties. It is used in large quantities in the fields of food, cosmetics, detergents, etc., as it has many advantages, such as being tall and rigid, and its mechanical strength is significantly improved by stretching, and it is also hygienic and excellent as a food container. There is.

However, PET products, which have many of the excellent features mentioned above, are not completely free from drawbacks; for example, in the case of stretch-blow molded products, it is difficult to apply stretch to the mouth or bottom, and the product Due to the design, it is not possible to stretch the product uniformly like a film, and the design of the product also makes it impossible to achieve sufficient heat fixation.

These above-mentioned drawbacks are not problems with the material of PET itself, and can be solved relatively easily by changing the molding method, the shape of the product, and even heat treatment. A serious drawback is that the barrier properties, especially the gas barrier properties against oxygen, are not sufficient.

The gas barrier property of PET is simply lower than that of other synthetic resins with high gas barrier properties, and it can be used without any problem in fields where normal gas barrier properties are sufficient. be.

However, when used as a storage container for the contents of juice, etc., which are easily affected by oxygen, or the contents of beer, etc., whose taste changes due to the leakage of gas, the storage period is extremely short, and it is not suitable for practical use. There is anxiety.

As described above, PET products have a variety of excellent characteristics as containers, but their range of use has been greatly limited due to their insufficient gas barrier properties.

In order to eliminate the above-mentioned drawbacks of PET products, a configuration has been devised in which the PET product has a laminated structure of PET and a synthetic resin with high gas barrier properties.

The above-mentioned laminated structure maintains the various excellent features of PET and only improves its low gas barrier properties, so it has a high gas barrier property.
Although this is an extremely excellent method for obtaining PET products, the following problems occurred when actually molding this type of laminated structure product.

In other words, when molding this type of PET laminate product, it is necessary to perform biaxial stretching molding in the same way as ordinary PET products, so the primary molded product is injected and extruded, and this primary molded product is then biaxially stretched. Blow mold.

When this primary molded product is injection molded, an inner layer body in the shape of a cylinder with a bottom is first molded from PET, and then the outer surface of this inner layer body is covered, and the inner layer body is used as a gas barrier as part of the mold. The barrier layer is insert molded by injection molding using a resin with high properties.

When injection molding this barrier layer, a part of the inner layer becomes white due to the injection pressure and heat of the molten resin used to mold the barrier layer.

Through various experiments and observations, the inventor of the present application has found that
It has been found that the whitening of the inner layer described above is limited to the vicinity of the gate portion when the inner layer is injection molded.

In other words, since PET is a crystalline resin,
It is necessary to rapidly cool the gate immediately after molding, but the cooling effect of the gate part is poor, and it is susceptible to crystallization due to the influence of pressure during injection molding. It seems that many microcrystals are generated.

Therefore, when the barrier layer is ignition-molded with a gate section provided in the cylindrical part opposite to the gate section of the inner layer, the heat and injection pressure of the molten resin for forming the barrier layer will cause the inner layer to It is thought that the areas near the gate that are prone to crystallization crystallize and easily cause whitening.

In this way, the reason why the gate part of the inner layer body and the gate part of the barrier layer body coincide is that both the inner layer body and the barrier layer body have a cylindrical shape with a bottom. This is because it is advantageous to provide a gate at the bottom when injection molding a bottomed cylindrical body from the viewpoint of die cutting, flow of molten resin, and thermal control.

The present invention prevents the heat and injection pressure of the molten resin for molding the barrier layer from directly acting on the vicinity of the gate of the inner layer, thereby preventing whitening of the vicinity of the gate of the inner layer.

An embodiment of the present invention will be described below with reference to the drawings.

First, as shown in FIG. 1, an inner layer body 2 made of PET is injection molded using a core 7 assembled to a core base 8 and a cavity 9.

At this time, the gate portion 3 of the inner layer body 2 is located at the bottom.

This injection molded inner layer body 2 is cooled while being assembled to the core 2, and the cavity 9 is removed.

Next, a new cavity 9' is assembled to the core 7 with the inner layer 2 still assembled, and the barrier layer 5 is injection molded. A protector 4 is attached and fixed in a form that covers the outer surface of the gate portion 3 of the body 2.

This protector 4 is intended to prevent the heat and injection pressure of the molten resin molding the barrier layer 5 from directly acting on the gate portion 3 of the inner layer 2, and is made of aluminum foil, thin aluminum plate, or It is made of a heat resistant material such as polyester film, and has a certain degree of heat insulation and rigidity.

In this way, the protective body 4 is attached to the gate portion 3 of the inner layer body 2.
Once deposited, the barrier layer 5 is injection molded using the inner layer 2 as part of the mold by clamping the mold with the cavity 9' as shown in FIG.

At this time, the gate part 6 of the barrier layer body 5 is located opposite to the gate part 3 of the inner layer body 2, and the above-mentioned protector 4 is located between the gate parts 3 and 6. Therefore, when the molten resin for forming the barrier layer 5 is injected, the heat and injection pressure of this molten resin do not directly act on the gate portion 3 due to the protection body 4. Therefore, this gate portion 3 portion does not become white at all.

By the way, as is clear from FIG. 3, the protector 4 is
The protective body 4 remains in the wall of the molded primary molded part 1, in particular in the bottom wall in the illustrated embodiment, so that the primary molded part 1 is not molded into a product. This may damage the appearance of this product.

Therefore, when a synthetic resin film or thin synthetic resin plate is used as the protector 4, it is desirable that the protector 4 be transparent.

In addition, when using an opaque thin aluminum plate or aluminum foil as the protector 4, it is advisable to stamp the company's mark on the protector 4 in advance or to provide a suitable decorative effect. desirable.

As is clear from the above description, the present invention can prevent whitening of the gate portion 3 portion of the inner layer body 2 due to the influence of injection pressure and heat during injection molding of the barrier layer body 5, and can Since the gate part can be located at the bottom of the molded body, which is most advantageous for injection molding of the shaped body, injection molding can be achieved satisfactorily, and the mold equipment used for molding is conventional. Since it can be used as is, it is inexpensive and easy to implement, and has many excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the process of injection molding the inner layer. FIG. 2 is a longitudinal cross-sectional view showing a molding process in which a barrier layer is insert-molded to complete a primary molded product. FIG. 3 is an enlarged longitudinal sectional view of the main part of the primary molded product. Explanation of symbols, 1; primary molded product, 2; inner layer body,
3; gate part, 4; protection body, 5; barrier layer body,
6; gate part, 7; core, 8; core base, 9,
9′; Cavity.

Claims (1)

[Claims] 1. A method for forming a laminate molded product made of polyethylene terephthalate resin that is biaxially stretch blow molded, in which an inner layer body 2 in the shape of a cylinder with a bottom is molded from polyethylene terephthalate resin by injection molding, and the inner layer body 2 is placed in a mold. A barrier layer body 5 is insert-molded by injection molding using a synthetic resin such as a polyamide resin with high gas barrier properties so as to cover the outer surface of the inner layer body 2 as a part, and the gate part 6 of the barrier layer body 5 is inserted into the inner layer body 2. 2, and when injecting the barrier layer 5,
Aluminum foil or thin aluminum plate that prevents the injection pressure and heat of the molten resin for molding the barrier layer 5 from directly acting on the outer surface of the gate portion 3 of the inner layer 2. Furthermore, the method for forming a primary molded product of a polyethylene terephthalate resin laminate molded product is characterized in that a heat-resistant, relatively heat-insulating and rigid protector 4 such as a polyester film is attached to the attached position.