JPH0434925B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a preform for stretch blow molding, and more specifically to a preform for stretch blow molding. The present invention relates to a preform shape capable of producing a bottle to which molecules can be applied, the shoulder part is also effectively stretched and oriented, and the shoulder part has no lens effect and has excellent appearance characteristics.

PRIOR ART AND TECHNICAL PROBLEMS OF THE INVENTION Stretch-blow-molded polyester bottles are common today, and due to their excellent transparency and appropriate gas barrier properties, they are widely used in liquid products such as liquid detergents, shampoos, cosmetics, soy sauce, and sauces. beer outside,
Widely used in containers for carbonated drinks such as cola and cider, and other beverages such as fruit juice and mineral water.

When molding polyester bottles, a preform with a bottom that is much smaller in size than the final container and in which the polyester is in an amorphous state is manufactured by injection molding of polyester, and this preform with a bottom is then placed in a blow mold at the stretching temperature range. A method of stretching in the axial direction and blow stretching in the circumferential direction is employed.

The shape of the bottomed preform is generally one that has a neck that corresponds to the neck of the bottle, such as a neck that consists of an opening end for sealing, a screw for engaging the lid, a support ring, etc., and that the overall shape is similar to a test tube. However, the axial and circumferential dimensions must be determined in relation to the axial and circumferential stretch ratios in the final container. Although the inner axial dimension of these preform dimensions can be arbitrarily set according to the stretching ratio, it is often difficult to arbitrarily set the circumferential direction dimension (diameter) depending on the circumferential stretching ratio.

For example, if the neck diameter of the final container is relatively large compared to the container body diameter, making the preform neck diameter and preform body diameter the same will result in an effective circumferential molecular orientation in the final container body. It is often difficult to assign However, if sufficient molecular orientation is not imparted to the container body in the circumferential direction,
The body wall expands in the circumferential direction due to the internal pressure caused by the carbon dioxide gas filled as the contents, and this expansion causes problems such as the label attached to the body wall coming off.

Thus, in order to overcome the above disadvantages for polyester bottles with relatively large diameters,
The diameter of the preform body should be smaller than the diameter of the preform neck in order to obtain a sufficient circumferential stretch ratio for the bottle body.

However, when a preform is subjected to stretch blow molding, the diameter of the preform body is rather small compared to the diameter of the preform neck, the stretching of the connection part occurs irregularly, and the neck of the bottle is formed. There is always a part where the thickness varies irregularly at the shoulder, and when this bottle is observed, the inside of the bottle appears to be significantly distorted due to the lens effect caused by the variation in thickness, and the appearance of the bottle itself is affected. It was found that the product became extremely defective and the product value decreased. This tendency is particularly noticeable in preforms in which there is a large step difference between the neck and the body, and in preforms in which the diameter decreases from just below the neck to a large extent.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a preform for stretch blow molding polyester bottles, which overcomes the above-mentioned drawbacks of conventional preforms.

Another object of the present invention is to impart a large circumferential molecular orientation to the final container body, thereby suppressing circumferential expansion of the container body due to internal pressure to a small level, and also to prevent strong stretching of the container shoulder. The object of the present invention is to provide a polyester bottle stretch-molding preform that can improve the appearance characteristics and commercial value of a container by eliminating the lens effect caused by thickness variations in this portion.

Yet another object of the invention is that the preform neck diameter is relatively small. To provide a preform for stretch blow molding of a polyester bottle, in which the occurrence of a lens effect at the shoulder of the final bottle is effectively controlled despite the body having a large body diameter and the diameter decreasing rapidly from just below the neck. There is something to do.

Structure of the Invention According to the present invention, there is provided a preform for stretch blow molding having a neck, a body, and a closed bottom formed by injection molding of polyethylene terephthalate, the inner circumferential surface having a smaller diameter than the inner circumferential surface of the neck, and the outer circumference of the neck. The trunk has an outer circumferential surface having a smaller diameter than the surface and a thickness greater than the neck thickness, and the connecting portion between the trunk and the neck has a thickness gradient in which the thickness gradually decreases from the trunk to the neck. Provided is a stretch blow molding preform characterized in that it has a shape such that stress per unit area during stretching gradually increases from the body toward the neck.

Features and Effects of the Invention The present invention provides polyester injection molding having a body having an inner circumferential surface having a smaller diameter than the inner circumferential surface of the neck, an outer circumferential surface having a smaller diameter than the outer circumferential surface of the neck, and a thickness greater than the neck thickness. In the molded preform, the connecting portion between the body and the neck has a thickness gradient in which the thickness gradually decreases from the body to the neck, and the stress per unit area gradually increases from the body to the neck. When this preform is stretch-blow-molded into a bottle, a large circumferential molecular orientation is imparted to the final container body, thereby significantly reducing the circumferential expansion of the container body due to internal pressure. Based on the new knowledge that it is possible to suppress the lens effect caused by the thickness variation at the shoulder part of the container to almost completely by applying strong stretching to the connection part, thereby improving the appearance characteristics and commercial value of the container. It is based on

Lensing effects in the shoulders of polyester bottles occur when there are circumferential thickness variations or when there are axial thickness variations, as well as in poorly formed glass bottles. If the diameter of the body is larger than the diameter of the neck of the preform, a portion whose diameter increases from the body to the neck is necessarily formed at the connection, and this connection becomes the shoulder of the polyester bottle. It now corresponds to the department. Since the diameter of this connection part is necessarily larger than the diameter of the body part, the cross-sectional area of the connection part is larger than the cross-sectional area of the body part, and the stress per cross-sectional area applied during stretching is applied to the body part. In comparison, it is smaller at the joint, and this reduction in stress per unit cross-sectional area would result in insufficient stretching of the joint, which would cause thickness variations to occur at the shoulder of the bottle.

On the other hand, according to the present invention, a thickness gradient is provided in the connecting portion such that the thickness gradually decreases from the trunk to the neck, and the stress per unit area during stretching is transferred from the trunk to the neck. By forming the connecting portion into a shape that gradually increases in size, the stretching of the connecting portion is forcibly and uniformly performed prior to stretching of the body, and the occurrence of the lens effect can be significantly suppressed. This fact will be easily understood by referring to the example described below.

According to the present invention, furthermore, by adopting the above-mentioned connection shape, the preform has a shape in which stretching in the circumferential direction to the body is most likely to occur effectively, that is, the body has a diameter considerably smaller than the diameter of the preform neck. Even when the diameter decreases rapidly from just below the neck, the lens effect at the final bottle shoulder is effectively suppressed.

Preferred Embodiments of the Invention The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing an example of the preform of the present invention, this preform P is manufactured in a substantially amorphous state by injection molding and supercooling of polyethylene terephthalate. This preform P
It is roughly divided into a neck part 1, a body part 2, and a connecting part 3 between them. The neck 1 has an open end 4 for sealing, a lid engaging screw 5 and a support ring 6. The body 2 has at its lowermost end a closed bottom 7, for example in the form of a rounded bottom.

The neck 1 and the body 2 have a body inner circumferential surface 9 smaller in diameter than a neck inner circumferential surface 8, a body outer circumferential surface 11 smaller in diameter than a neck outer circumferential surface 10, and a body smaller in diameter than the neck 1. The relationship is such that the thickness of the portion 2 is large.

In this specific example, the connecting portion 3 is defined by an inwardly convex arc-shaped inner surface 12 and an inwardly convex arc-shaped outer surface 13, and the arc-shaped inner surface 12 is defined by an arc-shaped outer surface 13. polarity larger than (1/
R).

Since the curvature of the inner surface 12 is greater than the curvature of the outer surface 13, it will be understood that the thickness of the connecting portion 3 has a thickness gradient that gradually decreases from the trunk toward the neck.

In FIG. 2 for explaining the principle of the present invention, when the tensile load applied during stretch forming is F, the stress in the body is as follows, where the wall thickness of the body is t ₀ and the center diameter of the wall thickness is D ₀ . It is expressed as σ ₀ =F/πD ₀ t ₀ (1).

On the other hand, the stress at the connection part is calculated as follows: σ=F/cosθπDt, where t is the wall thickness at a certain position of the connection part, D is the center diameter of the wall thickness, and θ is the center inclination angle at this position... (2) It is expressed as

According to the present invention, this stress σ is larger than σ ₀ , that is, the formula σ−σ ₀ =F/π(D ₀ t ₀ −cosθDt/cosπDtD ₀ t ₀ )>
0...(3) is satisfied, and the difference gradually increases from the torso to the neck.

For this purpose, the dimensions described above should be determined to satisfy the following formula cosθ<D ₀ t ₀ /Dt (4), and the thickness t of the connection portion should be reduced and the inclination angle θ should be increased. It will be understood that this is effective.

As a practical example, when the thickness of the connecting part directly under the neck is t ₁ , the thickness ratio t ₀ /t ₁ is in the range of 1.0 to 4.0, particularly 1.5 to 3.0, and θ is 5 to 60.
If the angle is within the range of 15 to 35 degrees, the stress applied to the joint can be increased, making it possible to forcibly stretch the joint and make the thickness uniform.

Stretch blow molding from a preform according to the invention is carried out under conditions known per se, except for using this preform.

First, in stretch blow molding, a preform is preheated to a temperature suitable for stretching by means of hot air, an infrared heater, high frequency dielectric heating, or the like. The temperature range is preferably between 85 and 120°C, particularly between 95 and 110°C.

This preform is fed into a stretch blow molding machine known per se, set in a mold, and stretched in the axial direction by pushing a stretch rod.
Blow stretching in the circumferential direction by suctioning fluid. At this time, the stretching ratio in the circumferential direction is larger than the stretching ratio in the axial direction, so that the molecular orientation in the circumferential direction is performed to a higher degree than the molecular orientation in the axial direction. The fact that the molecular orientation in the circumferential direction occurs more highly than the molecular orientation in the axial direction can be confirmed by subjecting the polyester wall of the bottle body to an in-plane orientation measurement method using fluorescence polarization method. This is confirmed by comparing with the orientation coefficient.

The invention is illustrated by the following example.

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 1.0 was supplied to an injection machine and injected into an injection mold to produce an amorphous polyethylene terephthalate preform having the shape shown in FIG.

The dimensions of this preform were as follows.

H ₁ Overall height 155.5mm H ₃ Connection height 10.5mm D ₁ Neck inner diameter 31.5mm D ₂ Body inner diameter 15.4mm D ₂ /D ₁ 0.489 t ₁ Connection thickness (just below the neck) 2.0mm t ₀ Body thickness 4.4mm t ₀ / t ₁ 2.2 R ₁ Inner radius of curvature 18 R ₂ Outer radius of curvature 20.5 R ₂ / R ₁ 1.14 θ Inclination angle 25.7 For this preform, the positions at the top of the body, 4 mm from the top of the body, and 6 mm from the top of the body When the stress values were calculated for each, they were as follows.

σ ₀ = F/3.05cm ² σ ₁ = F/2.26cm ² σ ₂ = F/2.11cm ² This preform is heated to 100°C, supplied to a stretch blow molding machine, and axially molded in a blow mold. Stretch blow molding was carried out sequentially in the direction and circumferential direction. The stretching ratio was set to 2.75 times in the axial direction and 3.47 times in the transverse direction.

When the orientation coefficient of the body of the obtained polyester bottle was measured using a fluorescence polarization method, the orientation coefficient in the circumferential direction (l) was 0.284, the orientation coefficient in the axial direction (m) was 0.102, and the orientation coefficient in the circumferential direction was 0.284. It was observed that significant molecular orientation occurred.

After wrapping and pasting a label on this bottle, it was filled with water containing 4 gas volumes of carbon dioxide gas, the lid was sealed tightly, and the bottle was left in an atmosphere at 40°C for 3 months, but expansion in the circumferential direction was ignored. What you get (expansion rate 0.5%)
Therefore, no separation of the label was observed.

In addition, when the shoulder portions of the bottles were visually observed after molding and after filling, none of the 100 molded bottles showed any lens effect, and the appearance characteristics were extremely excellent.

Comparative Example 1 A preform was manufactured in the same manner as in Example 1, except that the thickness of the connection part was 4.4 mm, which was the same as the body part, instead of the preform of Example 1. Regarding this preform, stress values were calculated at the upper end of the body, at positions 4 mm from the upper end of the body, and at positions 6 mm from the upper end of the body, and the results were as follows.

σ ₀ =F/3.05cm ² σ ₁ =F/3.27cm ² σ ₂ =F/3.52cm ² Using this preform, stretch blow molding was performed in the same manner as in Example 1.

Of the 100 bottles obtained, 50 had a lens effect on the shoulders, and 13 of them had a significantly poor appearance.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an example of a preform according to the present invention, and FIG. 2 is an explanatory diagram showing various dimensions of the preform of FIG. 1. 1 is a neck portion, 2 is a body portion, 3 is a connecting portion, 12 is an arc-shaped inner surface, 13 is an arc-shaped outer surface, R ₁ is a radius of curvature of the inner surface 12, and R ₂ is a radius of curvature of the outer surface 13.

Claims (1)

[Scope of Claims] 1. A preform for stretch blow molding having a neck, a body, and a closed bottom formed by injection molding of polyethylene terephthalate, the preform having an inner circumferential surface smaller in diameter than the inner circumferential surface of the neck and an outer circumferential surface of the neck. The body has an outer circumferential surface with a small diameter and has a thickness greater than the thickness of the neck, and the connecting portion between the body and the neck has a thickness gradient in which the thickness gradually decreases from the body to the neck. Also, a preform for stretch blow molding, characterized in that it has a shape such that stress per unit area during stretching gradually increases from the body toward the neck.