JPH0431281B2 - - 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 imparting molecular orientation and producing a bottle with excellent appearance characteristics without a lens effect in the shoulder portion.

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 grant However, if the circumferential molecular orientation is not sufficiently imparted to the container body,
The barrel 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 stuck to the barrel 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 subjecting a preform to stretch blow molding where the diameter of the preform body is rather small compared to the diameter of the preform neck, the thickness of the formed bottle varies irregularly at the shoulder from the neck to the body. When observing this bottle, the inside of the bottle will appear to be significantly distorted due to the lens effect caused by the variation in thickness, and the appearance of the bottle itself will be extremely poor, reducing its commercial value. I understood. 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 provide 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 thickness variations at the container shoulder. To provide a polyester bottle stretch-molding preform which can improve the appearance characteristics and commercial value of a container by eliminating the lens effect caused by the lens effect.

Still another object of the present invention is to reduce the lens effect at the final bottle shoulder even though the preform has a considerably smaller body diameter than the preform neck diameter and the diameter decreases rapidly from just below the neck. To provide a preform for stretch blow molding of polyester bottles in which generation is effectively suppressed.

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. a body having an outer peripheral surface smaller in diameter than the surface and a thickness greater than the thickness of the neck, and a connecting portion between the body and the neck has an arc-shaped inner surface that is convex inward when viewed in a vertical cross section; and a convex arcuate outer surface, and the arcuate inner surface has a larger curvature (1/
R) A preform for stretch blow molding is provided.

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 thickness of the neck. In the molded preform, the connection portion between the body and the neck is defined by an inwardly convex arcuate inner surface and an inwardly convex arcuate outer surface, and the arcuate inner surface is larger than the arcuate outer surface. When forming the preform into a shape having a large curvature (1/R), when stretch blow molding the preform into a bottle,
By imparting a large circumferential molecular orientation to the final container body, it is possible to suppress the circumferential expansion of the container body due to internal pressure to a significantly small level, and to almost eliminate the lens effect caused by thickness variations at the container shoulder. This is based on the new knowledge that it is possible to completely eliminate the problem and improve the appearance characteristics and commercial value of the container.

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. According to the present invention, the connecting portion between the neck and the body is formed into an inwardly convex curved shape, so that when this connecting portion has a stepped, tapered, or outwardly convex curved shape, In any case, the occurrence of the lens effect can be significantly suppressed, and this fact will be easily understood by referring to the examples described below.

Although the reason why such effects are achieved by the connection shape of the present invention is not yet fully clear,
It is presumed that this is because the above shape allows the stretching force to be easily transmitted both in the axial direction and in the circumferential direction.

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

The connecting portion 3 is defined by an inwardly convex arcuate inner surface 12 and an inwardly convex arcuate outer surface 13 when viewed in vertical section, and the arcuate inner surface 12 has a larger curvature than the arcuate outer surface 13. (1/R).

In Fig. 2 for explaining various dimensions of the preform having the shape shown in Fig. 1, the ratio of the average inner diameter D ₂ of the body to the average inner diameter D ₁ of the neck, D ₂ /D ₁ , is 0.2 to 0.8, especially 0.3.
It can vary within the range of 0.7 to 0.7. Also, the average thickness of the torso t ₂ and the average thickness of the neck (excluding support ring)
The ratio to t ₁ , t ₂ /t _{1 ,} can vary within the range from 1.3 to 10, in particular from 1.5 to 5. If the ratio of D ₂ /D ₁ is larger than the above range, it may be difficult to increase the stretching ratio in the circumferential direction and produce a container with a large opening that suppresses expansion in the circumferential direction due to internal pressure. If this ratio is smaller than the above range, stretch blow molding becomes difficult. Furthermore, if the ratio of t ₂ /t ₁ is larger than the above range, the final container body tends to become excessively thin and the gas barrier properties deteriorate; on the other hand, if it is smaller than the above range, stretch blow molding becomes difficult. Sexuality decreases.

The ratio of the radius of curvature R ₂ of the arcuate outer surface of the connection part to the radius of curvature R ₁ of the arcuate inner surface, R ₂ /R ₁ is the thickness ratio,
Although it varies depending on t ₂ /t ₁ , it is generally 1.05 to 2,
In particular, it is preferably within the range of 1.1 to 1.5. If this ratio is outside the above range, there will be a tendency for lens effects to occur at the shoulders of the final bottle.

In order to provide effective circumferential molecular orientation to the entire torso without producing a lens effect in the shoulders,
Difference between connection height H ₃ and neck inner diameter and body inner diameter D ₁ −
The ratio to D ₂ , H ₃ /(D ₁ −D ₂ ), is between 0.3 and 2, especially
It is desirable to set it to 0.5 to 1. Also, the radius of curvature
The absolute values of R ₁ and R ₂ are determined under the conditions that the ratio of R ₂ /R ₁ is within the range described above, and H ₃ /(D ₁ - D ₂ ) and t ₂ /t ₁ are within the range described above. To be determined accordingly.

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. Its temperature range is 85~120℃,
In particular, it is preferably in the range of 95 to 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 blowing 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 is due to the fact that the polyester wall of the bottle body was subjected to an in-plane orientation measurement method using fluorescence polarization, and the axial orientation coefficient and circumferential orientation were determined. Confirmed by comparing with the 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 shown in FIG. 2 and were as follows.

H ₁ (Overall height) 155.5mm H ₃ 10.5mm D ₁ 31.5mm D ₂ 15.4mm D ₂ ／D ₁ 0.489 t ₁ 2.0mm t ₂ 4.4mm t ₂ ／t ₁ 2.2mm R ₁ 18 R ₂ 20.5 R ₂ ／R ₁ 1.14 This preform was heated to 100° C., supplied to a stretch blow molding machine, and sequentially stretch blow molded in the axial direction and circumferential direction within the blow mold. 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 by fluorescence polarization method, the circumferential orientation coefficient (l) was 0.284, and the axial orientation coefficient (m) was 0.102, which was significant in the circumferential direction. It was observed that 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 Instead of the preform of Example 1, a preform having the same shape and dimensions as Example 1 except that the inner and outer surfaces of the connection part were made into conical surfaces was used, and stretch blow molding was performed in the same manner as in Example 1. I went to

Of the 100 bottles obtained, 10 had a lens effect on the shoulders, and 5 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 an arc-shaped inner surface that is convex inward when viewed in a vertical cross section, and an inner surface that is convex inward. It is defined by a convex arcuate outer surface, and the arcuate inner surface has a larger curvature (1/1) than the arcuate outer surface.
R) A preform for stretch blow molding.