JPH0358899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a mouth barrel in a primary molded product made of injection molded polyethylene terephthalate resin, which is formed into a bottle by biaxial stretch blow molding. The purpose of this invention is to improve the mechanical strength and heat resistance of the mouth tube of a biaxially stretched blow-molded bottle made of polyethylene terephthalate resin.

Polyethylene terephthalate resin (hereinafter simply referred to as
PET) is used in a wide range of fields because it has many excellent physical properties and characteristics.
Particularly, beneficial effects have been produced when used in bottles as liquid containers.

By the way, in order to make PET products more effectively exhibit the excellent physical properties of PET, it is necessary to form these PET products by biaxial stretching.
Therefore, in the case of PET bottles, without exception, a primary molded product in the shape of a cylinder with a bottom (hereinafter simply referred to as a piece) is molded by injection molding, etc., and this piece is molded into a bottle by biaxial stretching blowing. Measures are being taken.

As is well known, in a bottle molded from this piece by a biaxial stretch blow molding method, the mouth part, which is the part where the piece is assembled into a blow mold, is not subjected to any biaxial stretching and remains as a part of the bottle. Since the bottle is molded into the final shape, the mouth part of the PET bottle is a part where the characteristics of PET are not fully exhibited compared to other parts.

In particular, the mouth part that is not subjected to biaxial stretching has excellent alcohol resistance, mechanical strength, and heat resistance.
This results in inferiority to other parts of the bottle body, and there has been a strong desire for a means to overcome this inferiority in characteristics of the mouth part.

As an effective means for resolving the above-mentioned disadvantages in the mouth part of a biaxially stretched PET bottle, heat treatment is applied to the mouth part of the molded bottle, and the mouth part is shaped by this heat treatment. There is a way to crystallize PET.

Although this method is certainly effective,
Due to the crystallization of PET, the mouth tube becomes opaque and white, and one of the characteristics of PET, its excellent transparency, is lost.

The present invention was devised in order to satisfy the above-mentioned conventional demands without causing the whitening phenomenon, and the mouth part of the bottle is individually stretched in two directions before the other parts of the bottle are biaxially stretched. It is designed to be axially stretched.

The present invention will be explained below with reference to the drawings.

The method for forming the mouth barrel part _P2 of the piece P according to the present invention is to uniformly heat only the mouth barrel part _P2 of the PET piece injection-molded into a bottomed cylindrical shape to a temperature that produces a stretching effect. The piece P is stretched in the axial direction (see FIG. 2), and then the axially stretched mouth tube part _P2 is set in the mouth mold T and stretched in the radial direction to complete the process.

The simplest means to uniformly heat the mouth part _P2 to a temperature that produces a stretching effect is as shown in Fig. 1.
It is also effective to use the heater H that uses electric power because temperature control is easy.

When heating the mouth part _P2 with this heater H,
Since it is necessary to heat the entire mouth tube part P ₂ as uniformly as possible, it is preferable that this piece P is moved while rotating in a closed space where the heater H is placed and the ambient temperature is set to a predetermined temperature. .

At this time, due to the relationship with the stretching process in the axial direction that is performed subsequent to this heating operation, this opening tube part
In order to prevent unnecessary deformation of the body portion P ₁ of the piece P due to the external force acting on P ₂ for stretching in the axial direction, the heating by the heater H is limited to the mouth tube portion.
Must be considered to be added to P ₂ only.

As an example of means for applying heat by the heater H only to the mouth part _P2 , in the case of FIG. 1, a heat shield plate D is provided at the boundary between the body part _P1 and the mouth part _P2 of the piece P. are placed.

That is, in the case of FIG. 1, the heat shield plate D prevents the radiant heat from the heater H that heats the mouth tube portion _P2 from reaching the body portion _P1 .

In addition, in order to facilitate the assembly of the piece P of this heat shield plate D and to create a greater stretching effect on the mouth part _P2 , the outer periphery of the boundary between the body part _P1 and the mouth part _P2 is A stepped portion is formed on the surface, and this stepped portion allows the mouth tube portion _P2 to have a smaller wall thickness than the body portion _P1 .

After the mouth part P ₂ is uniformly heated to a temperature that produces a stretching effect, a mechanical tensile force along the axial direction of the piece P is applied to the mouth part P ₂ to stretch the piece P 2 in the axial direction.

After the mouth tube part P ₂ has been stretched in the axial direction, this mouth tube part P ₂ is set in the mouth mold T (see Fig. 3), and the mold surface formed by this mouth mold T is T ₁
The mouth tube part _P2 is stretched in the radial direction so as to have a shape that follows.

During the radial stretch forming of this mouth part _P2 ,
It goes without saying that the temperature of the mouth tube part _P2 is the temperature at which the stretching effect is produced, and therefore, after stretching in the axial direction, the temperature of the mouth tube part _P2 is lower than the temperature value at which the stretching effect is produced. If it is stored away, it is necessary to reheat the opening part _P2 to a temperature that produces a stretching effect prior to the radial stretching operation.

This radial stretching of the mouth tube part _P2 involves the injection of pressurized air into the piece P, and the radial expansion and deformation of a special member formed from an elastic material within the mouth tube part _P2 . , and even achieved by using a dedicated core or the like.

In addition, the radial stretching of the mouth part _P2 is as follows:
This is also the final forming operation for the bottle opening, so
By stretching the mouth part _P2 in the radial direction with the mouth mold T heated to about 80 to 120°C, heat setting can be performed simultaneously with this radial stretching. Therefore, higher heat resistance can be imparted to the mouth barrel portion _P2 .

In addition, when forming a screw in the mouth part of the bottle which is the final molded product, when the mouth part _P2 is stretched in the radial direction, as in the illustrated example, the mouth part mold T is It is sufficient to set the mold surface T ₁ to a shape that allows molding of the screw.

In addition, when forming the opening part P ₂ in the radial direction in this way, if a screw is also formed at the same time, in order to improve the formability of this threaded part, the material of the opening part mold T should be made with porous holes. It is effective to use a quality material.

In this way, the molding of the mouth part _P2 of the piece P is completed, but as in the embodiment shown in _FIG . If an unnecessary attached part P ₂ ' is formed on the top, as shown in Fig. 5,
After the molding of P ₂ is completed, this attached portion P ₂ ′ may be cut out by appropriate means.

In this way, the mouth barrel formed according to the present invention
Since P ₂ is biaxially stretch-molded, when piece P is biaxially stretch-blow-molded into a bottle,
This means that the excellent properties of PET can be exhibited in the same way as the body of this bottle, and this eliminates the issue of the inferiority of the physical properties of the neck of this type of bottle to the body of this type of bottle, as has been the case in the past. There isn't.

Further, the mouth barrel portion P ₂ formed according to the present invention is 2
Since it is formed by axial stretching, the wall thickness is naturally thinner, which reduces the amount of PET material required to form one bottle. The weight of the cylinder can be reduced.

As is clear from the above description, the present invention improves the mechanical strength, heat resistance, and alcohol resistance of the mouth of the bottle when it is finally formed into the body of the bottle. This makes it possible to significantly expand the scope of use of PET bottles, and to significantly reduce restrictions on handling PET bottles. It can be molded while maintaining high transparency, and it takes longer than conventional methods to mold one identical bottle.
Not only is it economical because the amount of PET material is reduced, but the weight of the mouth tube is also reduced, which stabilizes the standing posture of the large, lightweight PET biaxially stretched blow-molded bottle when it is empty. It has many excellent functions and effects, such as improved properties and thus easier handling before filling with the liquid.

[Brief explanation of drawings]

The drawings show specific examples of each step in the molding method of the present invention, and FIG. 1 shows the heating process of the mouthpiece, FIG. 2 shows the stretching process of the mouthpiece in the axial direction, and FIG. The figure shows the state in which the mouthpiece part stretched in the axial direction is set in the mouth mold, Figure 4 shows the state in which the mouthpiece part is stretched in the radial direction, and Figure 5 shows the state in which the mouthpiece part is stretched in the radial direction. FIG. 6 is a vertical cross-sectional view of the main part showing a state in which attached portions formed on the completed mouth barrel portion are cut away. Explanation of symbols, P... Piece, P ₁ ... Body part,
P ₂ ... Mouth tube part, P ₂ ′ ... Attached part, H ... Heater,
D...Heat shield plate, T...Mouth mold, _T1 ...Mold surface.

Claims (1)

[Claims] 1. A method for molding the mouth part of a primary molded product made by injection molding of a biaxially stretched blow-molded bottle made of polyethylene terephthalate resin, in which only the mouth part of the primary molded product is heated uniformly to a temperature that produces a stretching effect. A method for forming a mouth barrel part of a primary molded product, which comprises stretching the mouth barrel part in the axial direction in a heated state, and then stretching the axially stretched mouth barrel part in the radial direction in a mouth mold.