JP3011058B2 - Preform for stretch blow molding and molding method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preform for stretch blow molding and a molding method using the same. The present invention relates to a stretch blow molding preform capable of reducing the weight of a plastic bottle as well as the uniform stretch and thinning of the bottom and a molding method using the same.

[0002]

2. Description of the Related Art Stretch-blow molded plastic bottles, especially polyester bottles, have become popular today, and due to their excellent transparency and moderate gas barrier properties, liquid products such as liquid detergents, shampoos, cosmetics, soy sauce, and sauces. In addition, it is widely used for carbonated drinks such as beer, cola, and cider, and other drink containers such as fruit juice and mineral water.

[0003] In molding a polyester bottle, a bottomed preform, which is considerably smaller in size than the final container and in which the polyester is amorphous, is stretched axially in a blow mold at the stretching temperature by injection molding of the polyester. In addition, a method of performing blow stretching in the circumferential direction is employed.

[0004] The shape of this preform having a bottom is such that the mouth and neck of the bottle, for example, a mouth and neck consisting of an opening end for sealing, a screw for engaging a lid, a support ring, and the like, and the overall shape is a test tube. Things are common. However, on the other hand, attempts have been made to improve the shape of the bottomed preform in order to improve the strength and the degree of stretching of the product.

For example, Japanese Patent Publication No. 62-54696 discloses that the thickness of a bottle bottom portion and a bottle shoulder portion is about 80% to 80% of the thickness of a bottle body portion. A method for forming a biaxially stretched synthetic resin bottle is described, in which the following intermediate material is biaxially stretched so that the stretch ratio of the bottom portion and the shoulder portion is larger than that of the body portion. . It is also described that a biaxially stretched synthetic resin bottle whose bottom and shoulders are sufficiently stretched can be obtained by this method.

Japanese Unexamined Patent Publication (Kokai) No. 2-258214 describes a plastic preform with a bottom having a specific inner wall surface. It is described that a plastic bottle having excellent strength and strength can be obtained.

Further, Japanese Patent Application Laid-Open No. 3-26513 discloses that
A cylindrical preform for biaxial stretch blow molding having a mouth portion, a body portion, and a bottom portion, which has at least a thin band portion in the body portion is described. When this preformed body is heated, the temperature of the thin strip portion decreases more rapidly than the other portions of the thick portion, and this fact can be used to reduce the thickness of a specific portion of the product. Has been described.

Further, Japanese Patent Application Laid-Open No. Hei 4-366604 discloses that an annular stepped portion is provided between a portion corresponding to the bottom of the bottle and a portion corresponding to the body of the bottle so that the portion corresponding to the bottom of the bottle is thick. A preform for blow molding a synthetic resin bottle, characterized in that the preform is made thinner or thinner or narrowed down to a smaller diameter than the body. Extremely uneven thickness and local thinning of the bottom of the bottle body can be achieved by blowing the preformed body, which has a thicker or thinner portion corresponding to the bottom portion or narrowed down to a smaller diameter than the body portion, according to conditions. It states that it can be prevented.

[0009]

On the other hand, in the field of polyester bottles for beverages, the development of new molding methods, new bottle shapes, etc., particularly for the purpose of resource saving, cost reduction, reduction of product weight and volume, etc. In particular, new preform shapes have been attempted by container manufacturers.

In order to achieve such an object, it is conceivable to reduce the wall thickness of the preform. However, this approach is not suitable for bottle performance (eg, strength), moldability, filling lines, handling during transportation, and the like. There is a limit from the viewpoint, and the thickness must be reduced within a range not exceeding the limit. In addition, since there is a standard for the neck and neck of the preform, particularly the nozzle, it is difficult to reduce the weight of the raw resin and the product by changing the shape of the neck and neck of the preform.

Accordingly, an object of the present invention is to reduce the amount of raw material used in the production of a biaxially stretched plastic bottle, to reduce the weight of the plastic bottle as a product, and to further improve the plasticity of the bottom portion by stretching and thinning. An object of the present invention is to provide a stretch blow molding preform capable of producing a bottle and a method for molding a plastic bottle using the preform.

[0012]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the bottom of a plastic bottle, especially the upper bottom, is made thinner, that is, the bottom equivalent of the preform, particularly the upper bottom equivalent, is reduced. It was thought that the above-mentioned object could be achieved without affecting the bottle performance of the product by reducing the thickness, and various shapes of the bottomed preform were examined. As a result, the present invention succeeded in developing a shape of a preform that can reduce the amount of raw material resin that could not be realized by the above-mentioned conventional technology, and completed the present invention. .

That is, according to the present invention, there is provided a preform for stretch blow molding comprising a trunk, a mouth-and-neck portion provided at one end of the trunk, and a closed bottom provided at the other end of the trunk. The portion is cylindrical or tapered and the bottom is substantially hemispherical, and is smoothly connected on the inner surface side, and is reduced in outer diameter and thickness on the outer surface side toward the bottom. connected to the bottom via a tapered portion which, 該Te
The outer surface of the cross-sectional shape of supermarkets portion is straight, the ratio of the trunk portion of the thickness (d ₁₎ and the bottom of the thickness (d ₂₎ (d ₁ /
The preform for stretch blow molding is provided, wherein d ₂ ) is in the range of 1.1 to 1.5. In the preform of the present invention, the taper angle of the tapered portion (1/2 of the opening angle θ) is preferably in the range of 2 to 12 degrees.

According to the present invention, the preform is heated to a stretching temperature, and the preform is heated so that the hemispherical portion is at the bottom center and the outer diameter reducing taper portion is at the bottom periphery.
Pulling and stretching in the axial direction and blow-extending in the circumferential direction, and then bottoming out the bottom center, the outer diameter reducing taper portion as the ground contact portion and the bottom portion of the outer periphery thereof, and the hemispherical portion as compared to the contact portion. A method is provided for molding a plastic stretched bottle, characterized in that it is molded on the inner top.

[0015]

The present invention is characterized in that a preform for stretch blow molding is provided with a tapered portion of a specific shape in a body near a bottom connecting portion. That is, the preform of the present invention, the substantially hemispherical closed bottom and the cylindrical body,
On the inner surface side, it is connected smoothly and on the outer surface side, it is connected to the bottom through a tapered portion whose outer diameter and thickness decrease toward the bottom , and the outer surface of the tapered portion is cut off.
Surface shape is straight, the ratio of the trunk portion of the thickness _{(d 1)} and the bottom of the thickness _{(d 2) (d 1 /} d 2) is 1.1 to 1.5, in particular 1.1 to 1.4 Is characterized by being in the range of

In the present invention, the preform is heated to a stretching temperature, and the preform is stretched in the axial direction so that the hemispherical portion is at the center of the bottom and the outer diameter reducing taper is at the outer periphery of the bottom. Blow stretching in the circumferential direction,
Then, the center of the bottom is bottomed, and the outer diameter reduction taper portion is used as a ground portion and a bottom portion on the outer periphery thereof, and the hemisphere portion is formed on the upper bottom inside the ground portion.

In the preform for stretch blow molding,
Since the connecting portion between the trunk and the bottom is tapered so that the thickness gradually decreases at the taper angle from the trunk to the bottom, when this is stretched, the stress per unit cross-sectional area gradually increases from the trunk to the bottom. growing. Therefore, it is possible to sufficiently and uniformly stretch and reduce the thickness of the central portion of the bottom portion, which is difficult to stretch, without reducing the buckling resistance and the like, and to uniformly reduce the thickness of the upper bottom portion. The weight per unit area can be reduced to half or less of the conventional one.

The fact that the tapered portion has such a shape that it is smoothly connected on the inner surface side and whose outer diameter is reduced toward the bottom on the outer surface side is also advantageous in terms of moldability of the preform. In addition, there is an advantage in the stretch formability of the preform. In other words, during the injection molding of the resin, the resin can smoothly flow into the body, and further into the mouth via the tapered portion, so that the injection moldability is good, and the mold release from the injection mold is also good. It is. In addition, since the stretching start point gradually shifts to the body by the tapered portion, the stretching operation can be performed smoothly. Further, the outer mold of the injection mold is generally composed of three parts, a slide insert, a cavity, and a gate pad. However, in the present invention, only the gate pad is changed to the one provided with the above-described tapered portion, and the predetermined shape is obtained. A shaped preform can be formed.

At the bottom of the final plastic bottle,
The grounding portion is provided on the outer periphery of the bottom, and the upper bottom located above the grounding portion is provided at the center of the bottom so that even if the bottom center is slightly deformed, the independence of the bottle is not impaired. However, it is obvious that independence is impaired if the grounding portion is deformed. If the grounding portion is too thin, this portion may be damaged during blow molding or may be deformed during heat sterilization. Further, at the outer peripheral portion of the bottom such as the installation portion, the blow stretch ratio in the circumferential direction is large, so that there is a great tendency to reduce the thickness. In the present invention, since the outer diameter reducing taper portion is the ground portion and the bottom portion on the outer periphery thereof, excessive thinning of these portions can be prevented, and the self-standing stability of the bottle can be enhanced.

In the present invention, the ratio of the thickness (d ₁ ) of the body portion of the preform to the thickness (d ₂ ) of the bottom portion is (d ₁ / d).
It is also important that ₂ ) is in the above range. If this ratio is smaller than the above range, the reduction in the basis weight by high-stretching and thinning of the upper base becomes unsatisfactory. Swelling deformation increases, and the strength also decreases. Further, if the taper angle of the tapered portion is smaller than the above range, it is difficult to achieve the above thickness ratio, and the reduction in the basis weight due to high stretching and thinning of the upper bottom becomes unsatisfactory, while the above range is not satisfied. If it is larger than the above, stress concentration in the tapered portion becomes excessive, and it becomes difficult to perform a smooth stretching operation.

That is, a part of the body is tapered, and the hemispherical bottom connected to the body is made thinner, so that the amount of the raw material resin used can be reduced, and the bottom is made highly stretched and uniformly thinned. Therefore, a plastic bottle having good bottle performance such as strength can be obtained.

[0022]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2, which show an example of the preform of the present invention, this preform is manufactured by injection molding of a thermoplastic resin. For example, it is manufactured in a substantially amorphous state by injection molding and supercooling of polyethylene terephthalate. This preform is roughly divided into a mouth and neck portion 1, a body portion 2, a closed bottom portion 3, and a tapered portion 4 connecting the body portion and the closed bottom portion.

The mouth and neck 1 is provided with an opening end 5 for sealing, a screw 6 for engaging a lid, and a support ring 7. The mouth and neck 1 may exist in an amorphous state, or may be crystallized (whitened) by a heat treatment to impart its rigidity and heat resistance.

The body 2 has a tapered shape in which the diameter is reduced toward the bottom as a whole, and has a small taper angle of about 0.3 to 2 degrees so that the mold can be easily removed. Is desirable. Barrel 3 is smoothly connected to the lower end portion 8 of the neck is substantially constant thickness d ₁ gradually increases the thickness (outer diameter). The thickness d ₁ varies depending on the volume, shape, and use of the plastic bottle, but is generally in the range of 2.5 to 6 mm, particularly 3 to 4.5 mm. The length of the body 2 naturally depends on the size of the container, but generally ranges from 60 to 200 mm, particularly from 90 to 140 mm, including the tapered portion.

The closed bottom 3 is substantially hemispherical, and its thickness d ₂ is substantially constant over the entire hemisphere, and generally varies from 2.5 to 4 depending on the volume, shape and use of the plastic bottle. 0.5mm, especially 3-4m
m. The inner diameter R of the closed bottom portion 3 is to be smoothly connected to the body portion 2 and varies depending on the inner diameter of the body portion 2. However, in general, a range of 6 to 16 mm, particularly 7 to 10 mm is appropriate.

The body 2 and the closed bottom 3 are smoothly connected on the inner surface 9 of the preform, and the tapered portion 4 whose outer diameter decreases toward the bottom on the outer surface of the preform. Connected through. The ratio between the thickness of the body portion 2 _{(d 1)} and the closed bottom of the thickness _{(d 2) (d} 1 /
d ₂ ) is generally in the range of 1.1 to 1.5, particularly 1.1 to 1.4, and the taper angle of the tapered portion is generally in the range of 2 to 12 degrees, especially 3 to 10 degrees.
Range of degrees.

The cross section of the outer surface of the tapered portion 4 is straight . In this case, the connecting portion 10 and the connecting portion 11 may be provided with a curvature portion having a constant radius of curvature (R1). The radius of curvature (R1) is suitably 10 mm or less.

The tapered part 4 and the hemispherical closed bottom part 3
As shown in FIG. 1, it may be directly connected, or as shown in FIG. 2, a straight portion 12 having a constant thickness and a short length may be provided between the two. The length of the straight portion 12 is 1 times or less of the bottom thickness d _2, in particular is preferably 0.5 times or less.

As the plastic for preform molding of the present invention, any thermoplastic resin that can be molded can be used. Such resins include thermoplastic polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate; polycarbonates;
Butadiene-styrene copolymer (ABS resin); polyacetal resin; nylons such as nylon 6, nylon 66, and their copolymerized nylons; acrylic resins such as polymethyl methacrylate; isotactic polypropylene; -, Medium- or high-density polyethylene, ethylene-propylene copolymer, ethylene-butene-1 copolymer, styrene-butadiene thermoplastic elastomer and the like. These plastics, various additives within a range that does not impair the quality of the product, such as a coloring agent, an ultraviolet absorber, a release agent, a lubricant,
A nucleating agent and the like can be blended.

In particular, it is preferable to use a polyester as the thermoplastic resin. In this case, the intrinsic viscosity (η) of the polyester may be a bottle molding grade,
Those having a content of 5 dl / g or more, particularly 0.70 to 0.90 dl / g, and a diethylene glycol unit content of 1.60% by weight or less, particularly 1.50% by weight or less are suitable. used.

The preform according to the present invention is manufactured by an injection molding method. In FIG. 3 showing a mold used for the injection molding, the mold includes a core mold 20 for defining the inner surface of the preform, a slide insert mold 21 for defining the outer surface of the preform, a cavity mold 22, and a gate pad. 23. Slide insert mold 21
Is mainly for molding the mouth and neck of the preform, through which the core mold 20 is inserted and withdrawn while sliding into the cavity. The cavity mold 22 forms the body of the preform. The shapes of the slide insert mold 21 and the cavity mold 22 are known per se.

The gate pad 23 forms a taper portion and a closed bottom portion of the preform, and has a gate 24 for injecting resin into the cavity.

Using the above device, the gate pad 23
By simply changing the shape shown in FIG. 3, it is possible to manufacture a preform for manufacturing a bottle in which the upper bottom weight is significantly reduced.

In order to impart heat resistance and rigidity to the mouth of the obtained preform, the mouth and neck may be crystallized by heat treatment at the preform stage and may be whitened. After molding the preform into a bottle,
The mouth and neck of the obtained plastic bottle may be crystallized and whitened.

The preform is heated to a stretching temperature, and the preform is stretched in the axial direction such that the hemispherical portion is at the bottom center and the outer diameter reducing taper portion is at the bottom outer periphery, and is also blow stretched in the circumferential direction. Then, the center of the bottom is bottomed, and the outer diameter reduction taper portion is formed as a ground contact portion and a bottom portion of the outer periphery thereof, and the hemisphere portion is formed on the upper bottom inside the ground contact portion.

Prior to stretch blow molding, the preform is preheated to a suitable stretching temperature by means such as hot air, an infrared heater, or high-frequency induction heating. Its temperature range is 85
The temperature is preferably in the range of from 120 to 120 ° C, particularly from 95 to 110 ° C.

The preform is supplied to a known stretch blow molding machine, set in a mold, and stretched in the axial direction by pushing a stretching rod, and is blown in the circumferential direction by blowing a fluid. After stretching, the bottom is finally bottomed with a bottoming die to form an upper bottom. At this time, by the above-described operation, the desired strength can be obtained by sufficiently stretching the upper bottom portion while reducing the weight thereof.

The stretching ratio in the final container is suitably from 8 to 12 times in area ratio. Among them, the stretching ratio in the axial direction is 1.8 to 2.7 times and the stretching ratio in the circumferential direction is 3.0.
It is good to make it 4.5 times. The height of the center of the upper bottom from the grounding portion is suitably 10 to 18 mm.

FIG. 4 (front view), FIG. 5 (side view), FIG. 6 (plan view), FIG. 7 (bottom view), FIG. 8 (AA) showing an example of a bottle manufactured by the method of the present invention. Sectional view), FIG.
(BB sectional view), FIG. 10 (CC sectional view), FIG.
In (D-D sectional view), this bottle is
0, a frustum-shaped shoulder 31, an upper body 32, a lower body 33, and a bottom 34.

The bottom portion 34 is formed of a grounding portion 35 and an upper bottom 36 which rises upward from the grounding portion, and the tapered portion (4) of the preform whose diameter is reduced becomes the grounding portion 35, so that the thickness of the preform is reduced. The hemispherical bottom (3) is the upper bottom 36. It should be understood that the upper bottom 36 is provided with radial ribs 37 for the purpose of reinforcing the bottom.

The neck and neck portion 30 of the bottle has the same shape and dimensions as the neck and neck portion (1) of the preform, and the shoulder portion 31 has a lower portion of the neck and neck portion (8) of the preform or a thicker portion (8).
a).

The upper body 32 and the lower body 33 of the bottle include:
The panel portion (mirror portion) 38 for absorbing the reduced pressure deformation is a rib 39
Is formed through. In addition, the upper trunk 32 and the lower trunk 3
3, a circumferential concave bead 40 for reinforcement is formed.

FIGS. 12 (front view), 13 (side view), and FIG. 14 show another example of a bottle manufactured by the method of the present invention.
In FIG. 15 (bottom view), FIG. 15 (bottom view), FIG. 16 (AA cross section), and FIG. 17 (BB cross section), the bottle has a mouth-neck portion 30, a frustum-shaped shoulder 31, The upper body portion 32, the lower body portion 33, and the bottom portion 34 are the same as those in FIGS. 4 to 11, but in this example, the upper bottom 36 is formed to bulge in a dome shape.

A large number of circumferential concave beads 41 for reinforcement are arranged on the upper body 32 at small intervals, and a panel 38 is provided on the lower body 33 via a rib 39. ,
The panel portion 38 is also formed with fine uneven beads 42.

In each of these examples, the ground contact portion 35 is formed from the diameter-reduced tapered portion (4) of the preform, and the upper base 36 sufficiently extended from the thinned hemispherical bottom portion (3) of the preform is formed. Due to the formation, the weight of the bottom portion can be reduced, the material cost can be reduced, and the container can be reduced in weight while maintaining the strength of the bottom portion sufficiently high and maintaining the self-standing stability of the container.

[0046]

The present invention will be described with reference to the following examples.

Example 1 The same injection mold as that shown in FIG. 3 was used, and polyethylene terephthalate was injection-molded into the shape shown in FIG.
A preform having the following dimensions was produced. Total length 152mm Mouth / neck opening inner diameter 20mm Body taper angle 1 ゜ Body thickness 4.5mm Bottom thickness 3.6mm Bottom inner surface radius of curvature 9mm Distance from opening to start end of thickness reduction taper 128mm Taper of thickness reduction taper Square 8mm Preform weight 57g

The preform was preheated to a temperature of 105 ° C. and stretch blow-molded by a known biaxial stretch blow molding machine at a longitudinal stretch ratio of 2.1 times and a transverse stretch ratio of 4.4 times. It was molded into a bottle having the shape shown in FIG.

For comparison, a similar bottle was formed using a preform having a thickness of 4.5 mm, which is the same as the thickness of the body, without the thickness reduction taper portion.

The upper bottom of the obtained bottle was cut out and its weight was measured.
In comparison with 0.2 g, the bottle of this example weighed 5.5 g. In addition, 45k necessary for heat-resistant bottle
g or more, and the self-sustainability was extremely satisfactory.

Example 2 The same injection mold as that shown in FIG. 3 was used, and polyethylene terephthalate was injection-molded into the shape shown in FIG.
A preform having the following dimensions was produced. Total length 158mm Mouth / neck opening inner diameter 21mm Body taper angle 1.1 ゜ Body thickness 4.5mm Bottom thickness 3.6mm Bottom inner surface radius of curvature 9mm Distance from opening to start end of thickness reduction taper 137mm Thickness reduction taper Taper angle 10mm Length of straight part under taper part 2mm Preform weight 65g

The mouth was crystallized by heating only the mouth and neck of the preform. This preform is 105 ° C
, And stretch blow-molded with a known biaxial stretch blow molding machine at a longitudinal stretch ratio of 2.1 times and a transverse stretch ratio of 4.4 times to form bottles having the shapes shown in FIGS. .

For comparison, a similar bottle was formed using a preform having a thickness of 4.5 mm, which is the same as the thickness of the body portion, without the thickness reduction taper portion.

The upper bottom of the obtained bottle was cut out and its weight was measured.
In comparison with 0.2 g, the bottle of this example weighed 5.5 g. In addition, when oolong tea was hot-filled at 85 ° C. and sealed, there was no swelling deformation of the container bottom, and the self-sustainability was extremely satisfactory.

[0055]

According to the present invention, a thickness reducing taper portion having a specific size is provided near a connecting portion between a body portion and a bottom portion of a preform, and a ground contact portion of a bottle is formed from the thickness reducing taper portion of the preform. Since the upper bottom which is sufficiently extended from the thinned hemispherical bottom of the preform is formed, the weight of the bottom is reduced while maintaining the strength of the bottom sufficiently high and maintaining the self-standing stability of the container. The cost can be reduced and the container can be reduced in weight.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a preform of the present invention.

FIG. 2 is a sectional view showing another example of the preform of the present invention.

FIG. 3 is a partial sectional view showing an example of an injection mold of a preform of the present invention.

FIG. 4 is a front view showing an example of a bottle manufactured by the method of the present invention.

FIG. 5 is a side view of the bottle of FIG. 4;

FIG. 6 is a plan view of the bottle of FIG. 4;

FIG. 7 is a bottom view of the bottle of FIG.

FIG. 8 is a cross-sectional view taken along the line AA of the bottle of FIG.

FIG. 9 is a sectional view of the bottle of FIG. 4 taken along line BB.

FIG. 10 is a sectional view taken along the line CC of the bottle of FIG.

FIG. 11 is a sectional view taken along the line DD of the bottle of FIG. 4;

FIG. 12 is a front view showing another example of the bottle manufactured by the method of the present invention.

FIG. 13 is a side view of the bottle of FIG.

FIG. 14 is a plan view of the bottle of FIG.

FIG. 15 is a bottom view of the bottle of FIG.

FIG. 16 is a cross-sectional view taken along the line AA of the bottle of FIG.

FIG. 17 is a cross-sectional view taken along the line BB of the bottle of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mouth and neck part 2 Body part 3 Closed bottom part 4 Tapered part 5 Sealing open end 6 Screw for lid engagement 7 Support ring 8 Lower end of mouth and neck part of preform 9 Inner surface of preform 10 Large diameter connection part 11 Small diameter Connection 12 Straight part 20 Core mold 21 Slide insert mold 22 Cavity mold 23 Gate pad 24 Gate 30 Bottle neck and neck 31 Truncated shoulder 32 Upper torso 33 Lower torso 34 Bottom 35 Grounding 36 Upper bottom 37 Reinforcing rib 38 Panel part (mirror part) 39 Rib 40 Circular concave bead 41 Circular concave bead 42 Irregular bead

Claims (3)

(57) [Claims] 1. A stretch blow molding preform comprising a trunk, a mouth and neck provided at one end of the trunk, and a closed bottom provided at the other end of the trunk, wherein the trunk is cylindrical or tapered. And the bottom portion is substantially hemispherical, and is smoothly connected on the inner surface side, and is connected to the outer surface side via a tapered portion whose outer diameter and thickness are reduced toward the bottom portion. connected to the bottom, the cross-sectional shape of the outer surface of the tapered portion is straight, the ratio of the trunk portion of the thickness (d ₁₎ and the bottom of the thickness (d ₂₎ (d ₁
/ D ₂ ) is in the range of 1.1 to 1.5. 2. The stretch blow molding preform according to claim 1, wherein a taper angle of the tapered portion is in a range of 2 to 12 degrees. 3. The preform according to claim 1 or 2 is heated to a stretching temperature, and the preform is stretched in the axial direction such that the hemispherical portion has a bottom center and an outer diameter reducing taper portion has a bottom outer periphery. Stretch and blow stretch in the circumferential direction,
Then, the center of the bottom is bottomed, and the outer diameter reduction taper portion is used as a ground portion and a bottom portion of the outer periphery thereof, and a hemisphere portion is formed on the upper bottom inside the ground portion. Bottle molding method.