JP2003103610A - Method for manufacturing heat-resistant bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a heat-resistant bottle by two-stage blow molding, capable of stably performing thermal shrinkage and almost equally performing orientation in the circumferential direction and height direction of the heat-resistant bottle to provide the bottle excellent in mechanical strength. SOLUTION: A preform comprising a thermoplastic polyester is subjected to primary stretch blow molding in a primary blow mold to obtain a primary bottle which is, in turn, heat-treated outside the mold under a condition permitting shrinkage. This secondary bottle is subjected to secondary blow molding in a secondary blow mold to manufacture the heat-resistant bottle. In this manufacturing method, in-mold shrinkage is performed using the heated primary blow mold so that a ratio (R1 ) of heat-treated primary bottle surface area/ primary blow mold surface area becomes 0.6-0.8 and, subsequently, out-mold heat treatment is performed so that a ratio (R2 ) of secondary bottle surface area/heat-treated primary bottle surface area becomes 0.7-0.9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-resistant bottle, more specifically, in a two-stage blow molding method,
A method for producing a heat-resistant bottle that can stably perform heat shrinkage performed before secondary blow molding and that can provide a bottle excellent in mechanical strength by orienting substantially uniformly in the circumferential direction and the height direction. Regarding

[0002]

2. Description of the Related Art Biaxially stretched blow molded containers made of thermoplastic polyester resin such as polyethylene terephthalate have excellent transparency and surface gloss, and also have impact resistance, rigidity and gas barrier property required for bottles. It is used as a bottle for various liquids, that is, a bottle.

In general, in the production of bottled products, it is necessary to heat-fill the contents or to fill the contents with heat and then sterilize by heating or sterilization in order to improve the storability of the contents. However, polyester bottles have the drawback of being inferior in heat resistance, and heat deformation and volume contraction deformation occur when hot filling the contents, so heat setting (heat setting) after molding the biaxially stretched blow container. The operation is being performed.

As a method for manufacturing the heat-set biaxially stretched blow-molded container, there are a one-mold method in which heat-setting is performed simultaneously with blow-molding and a two-mold method in which blow-molding and heat-setting are performed by separate molds. A known two-stage blow molding method is also known, in which the blow-molded product in the first stage is subjected to heat shrinkage and heat fixation, and then final blow-molded. This two-step blow molding method has a short occupation time in the mold and is excellent in productivity.

Japanese Unexamined Patent Publication No. 5-200839 discloses that
(A) The vertical direction is 1.
Using a primary blow molding die having a cavity of 0 to 1.3 times and a lateral direction of 0.6 to 1.0 times, the body and bottom part below the neck part are stretch blown at an area ratio of 4 to 22 times. The heat resistance and the pressure resistance to be formed through the primary blow molding step and (b) the secondary blow molding step in which the primary blow molded article molded by the primary blow molding is heated at 110 to 255 ° C. and then blow molded. A method of molding the provided bottle is described.

[0006]

A container having a hemispherical bottom portion thinned by a drawing process, particularly a crystallized center portion of the bottom portion is excellent in heat resistance and pressure resistance, and contents to which internal pressure of carbonated beverages or the like is applied are contents. It is possible to sufficiently withstand heat sterilization treatment (10 minutes or more at 65 ° C according to the method) in which hot water is poured into the filled product from above, but as described in JP-A-5-200839,
There is the inconvenience of manufacturing a base cup separate from the container and fixing it to the container by adhesion or the like.

Further, since the heat shrinkage is carried out from the blow mold, the workability is inferior and the dimensional stability due to the heat shrinkage is poor. Therefore, the object of the present invention is to
In a method for producing a heat-resistant bottle by two-stage blow molding, it is possible to stably perform heat shrinkage, and to orient almost uniformly in the circumferential direction and the height direction to provide a bottle having excellent mechanical strength. It is to provide a method for producing a heat-resistant bottle to be obtained.

[0008]

According to the present invention, a thermoplastic polyester preform is subjected to primary stretch blow molding with a primary blow mold, and the resulting primary bottle is then removed from the mold under conditions that allow shrinkage. In a method for producing a heat-resistant bottle, which comprises subjecting a secondary blow mold to a secondary blow mold by heat-treating, the heated primary blow mold is used to treat the heat treated primary bottle surface area / primary blow mold. In-mold contraction is performed so that the mold surface area ratio (R ₁ ) is 0.6 to 0.8, and then the secondary bottle surface area / heat treated primary bottle surface area ratio (R ₂ ) is 0.7 to 0. There is provided a method for producing a heat-resistant bottle, which comprises performing heat treatment out of the mold so that the heat resistance becomes 9.

According to the method for producing a heat-resistant bottle of the present invention, (1) the primary blow cavity mold has a temperature (T ₁ ) of Tg + 30 ° C. to Tg + 80 ° C. based on the glass transition point (Tg) of polyester. Being heated, (2) Primary blow bottom mold is 20 ° C to 80 ° C.
Being heated to a temperature (T ₂ ) of ℃, (3)
The heat treatment outside the mold is carried out at a temperature (T ₃ ) at which the surface temperature (T ₃ ) of the bottle body becomes T ₁ + 0 ° C to T ₁ + 120 ° C.
₃ ) and have a relationship of T ₃ > T ₁ .
(4) Heat treatment outside the mold is performed by the surface temperature (T ₄
) Is T ₂ + 40 ° C. to T ₂ + 160 ° C. (T
₄ ) and have a relationship of T ₄ > T ₂ (5)
As a primary blow mold, the primary blow mold surface area / preform outer surface area ratio (R ₀₁ ) is 8 to 14 and the primary blow mold surface area / preform surface area ratio (R ₀₁ ).
₀₂ ) which is 12 to 20, (6)
As the secondary blow mold, one having a ratio of secondary blow mold surface area / heat treated primary bottle surface area (R ₃ ) of 1.0 to 1.3 is used. (7) The primary blow mold is a cavity mold (8) Waist forming portion diameter (D ₁
) And the diameter of the body forming part of the base of the waist forming part (D ₂
The ratio (D ₁ / D ₂ ) with the ratio () is in the range of 0.65 to 0.90, and (9) primary stretch blow molding is performed by thinning the stretch so that the thickness at the center of the bottom is less than 1.5 mm (10) As a preform, a preform whose bottom portion is made thinner than the wall thickness of the body portion is used, and primary stretch blow molding is performed so that the longitudinal stretching ratio is 2.5 times or more. Is preferably performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, in a two-stage blow molding method, a residual thickness due to stretching is relaxed by heat-shrinking the thin-walled primary bottle which is thinned to a highly stretched state in a primary blow molding step. By heat fixing, heat resistance can be improved, and further, the amount of stretching in the secondary blow molding can be reduced, and a bottom shape capable of ensuring heat resistance can be obtained. In the method for producing a heat-resistant bottle of the present invention, the heat treatment of the primary bottle in this two-stage blow molding is carried out by (1) using a heated primary blow mold, the ratio of heat treated primary bottle surface area / primary mold surface area ( R ₁ ) is 0.6
Shrinkage in the mold so as to be 0.8 to 0.8, (2) ratio of secondary bottle surface area / heat treated primary bottle surface area (R ₂ ).
It is an important feature that the out-of-mold heat treatment is performed in two steps such that the heat treatment is 0.7 to 0.9.

In the present invention, after the primary blow is completed, without taking out the primary bottle from the primary blow molding die,
By heating the primary bottle with the heated mold surface, the entire primary bottle can be uniformly heated, and the residual stress caused by stretching can be effectively relaxed and the oriented crystal can be advanced. Moreover,
Since the heat-treated primary bottle having a certain size is obtained by the heat shrinkage performed in the primary blow mold, the heating time and shrinkage amount by the subsequent heat treatment outside the mold can be reduced, and stable shrinkage can be achieved. Moreover, it is possible to obtain a secondary bottle having a shape close to that of the final molded product, and it is possible to stably obtain the final molded product having a uniformly thin bottom.

In the present invention, the in-mold heat treatment carried out in the primary blow mold has a heat treatment primary bottle surface area / primary mold surface area ratio (R ₁ ) of 0.6 to 0.8, particularly 0.65.
It is important to shrink the primary bottle to a value of 0.75 to 0.75. If the ratio of the surface area of the heat-treated primary bottle / the surface area of the primary mold (R ₁ ) is smaller than the above range, it becomes difficult to uniformly heat-shrink the primary bottle due to rapid shrinkage, while the ratio (R ₁ is smaller than the above range. Is large, the amount of shrinkage in the heat treatment outside the mold to be performed later increases, and it becomes difficult to secure stable shrinkage.

In the subsequent out-of-mold heat treatment, the ratio of the surface area of the secondary bottle to the surface area of the heat-treated primary bottle (R ₂ )
It is important to perform the heat treatment outside the mold so that the ratio is 1.0 to 1.3, particularly 1.0 to 1.2. If the ratio (R ₂ ) of the heat-treated primary bottle surface area / primary bottle surface area is smaller than the above range, the amount of stretching in the subsequent secondary blow molding becomes large, making it difficult to make the bottom evenly thin. When the ratio (R ₂ ) is larger than the above range, the heat treatment is insufficient and it becomes difficult to obtain satisfactory heat resistance.

The manufacturing process of the heat resistant bottle of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a manufacturing process of a heat resistant bottle of the present invention, where (A) is a primary blow molding process, (B) is a heat treatment process inside a mold, (C) is a heat treatment process outside a mold, and (D). Shows a secondary blow molding process, and (E) shows a final molded product. Further, FIG. 2 shows an example (a) of a preform used for producing the heat-resistant bottle of the present invention,
And a molded article obtained in each manufacturing step of the present invention,
(B) is a primary bottle after primary blow molding, (c) is a heat-treated primary bottle heat-treated in a primary blow mold,
(D) is a side view showing an example of a secondary bottle heat-treated outside the mold and (e) a final molded product, respectively.

(Preform) The preform used in the present invention has a neck portion 1 and a body portion 2 as shown in FIG.
And a closed bottom portion 3, and the neck portion 1 is provided with a lid fastening mechanism 4 such as a screw and a support ring 5 for holding the container. In the present invention, it is particularly preferable to use, as the preform, a preform whose bottom portion is thinner than the body portion. By making the bottom of the preform thinner than the body, fixing the bottom with a stretch rod and press rod in the primary blow molding process to reduce the thickness of the bottom, which tends to become thicker, to 1 mm or less. Is possible. The degree of thinning of the bottom of the preform is preferably 0.55 to 0.85 times the wall thickness of the body.

In the present invention, a preform whose bottom portion is thinner than that of the body portion is used, and the longitudinal stretch ratio is 2.5 times or more as described later in the primary stretch blow molding. By doing so, it becomes possible to orient almost uniformly in the circumferential direction and the height direction, and it becomes possible to provide a final molded product having excellent mechanical strength. Further, the bottom of the final molded product is sufficiently thinned and highly oriented and crystallized, so that a final molded product excellent in transparency and heat resistance can be obtained. As the preform used in the present invention, any plastic material which can be stretch blow molded and thermocrystallized can be used, and thermoplastic polyester, particularly ethylene terephthalate thermoplastic polyester is advantageous. used. Details of the thermoplastic polyester will be described later. The molding of the thermoplastic polyester into a preform is performed by a conventionally known method, for example, injection molding.

(Primary Blow Molding Step) In the present invention, in the primary blow molding step, the preform is first heated to a drawing temperature of about 85 to 135 ° C. and inserted into the blow mold. The heating of the preform is performed by means known per se such as infrared heating and induction heating. As shown in FIG. 1A, the mold 10 and the mold 11
The preform installed in the blow mold composed of the bottom mold 12 and the bottom mold 12 has a neck supported by the core mold 10, and the movable stretch rod 13 arranged inside the mold and a predetermined pressure installed outside the stretch bar 13. The bottom portion is sandwiched between the press rod 14 and the press rod 14. Next, by raising the drawing rod 13 and introducing high-pressure gas into the preform in synchronism with the movement of the drawing rod 13, the preform is stretched and swelled into a shape along the blow mold. Once formed, the primary bottle is molded.

In general, the draw ratio in primary blow molding is preferably about 4.0 to 5.5 times in the circumferential direction and about 2.5 to 3.5 times in the longitudinal direction. Since the film is also sufficiently stretched in the direction, it can be oriented substantially uniformly in the circumferential direction and the longitudinal (height) direction, and the mechanical strength can be improved by the biaxial stretching effect. In the primary blow molding, the fluid pressure is 15 to 30 kg / cm ² ,
The blowing time is preferably about 2 to 5 seconds.

Further, in the primary blow molding, it is necessary that the obtained primary bottle is stretch-molded so as to satisfy the above-mentioned conditions, but the bottom center of the final molded product is 2 m.
In order to reduce the thickness to m or less, it is preferable to perform stretching and thinning so that the thickness at the bottom center of the primary bottle is less than 1.5 mm.

Examples of primary blow bottles made using various primary blow molds that can be used in the present invention are shown in FIG.
Shown in. In the present invention, it is of course possible to prepare a bottle having no waist portion as shown in FIG. 3 (A), but a bottle having a waist portion formed on the body is preferable. Since the final molded product has a waist portion, it is possible to reinforce the strength by forming the central portion of the bottle body without making it thinner than necessary, and at the same time, the orientation of the body portion of the bottle It becomes possible to adjust the balance as a boundary. In this case, as shown in FIGS. 1 (A) and 3 (C), a waist forming portion 15 having a reduced diameter is formed in the body forming portion of the cavity mold of the primary blow mold, and further, the waist forming portion is formed. Diameter (D
₁ ) and the diameter of the waist forming part of the waist forming part (D
₂₎ the ratio of _(D 1 / _{D 2)} is particularly preferably in the range of 0.65 to 0.90.

(In-mold heat treatment step) In the present invention,
The primary bottle formed by primary blow molding is not immediately taken out of the mold but is subjected to heat treatment in the primary blow mold (FIG. 1 (B)). Therefore, the primary blow cavity mold has a temperature (T ₁ + 30 ° C. to Tg + 80 ° C. (T ₁ ) based on the glass transition point (Tg) of polyester.
In addition, it is desirable that the primary blow bottom mold is heated to a temperature (T ₂ ) of 20 ° C. to 80 ° C. Although the heating time depends on the mold temperature, it is generally preferably 2 to 5 seconds.

Further, in the present invention, in-mold shrinkage is carried out in the primary blow mold so that the ratio (R ₁ ) of the heat-treated primary bottle surface area / primary blow mold surface area is 0.6 to 0.8. This is an important feature. Therefore, as the primary blow mold, the ratio of the primary blow mold surface area / preform outer surface area ( _R01 ) is 8 to 14 and the ratio of the primary blow mold surface area / preform surface area. (R
It is preferable to use those in which ₀₂ ) is 12 to 20. The heat-treated primary bottle thus obtained is shown in FIG.
It has a shape as shown in FIG.

(Outside Mold Heat Treatment Step) In the present invention, as described above, the heat treated primary bottle obtained by primary stretch blow molding and heat shrinkage in the primary blow mold is taken out from the primary blow mold, This is further heat-treated outside the mold (FIG. 1 (C)). The heat-treated primary bottle is held by the core mold 21 and rotates about its axis, and is heated by the infrared radiator 22 installed at the positions corresponding to the body and the bottom, thereby contracting the body and the bottom. A heat shield plate 23 is provided at a portion corresponding to the neck portion.

In the present invention, the heat-treated primary bottle taken out from the primary blow mold is heated so that the heat-treated primary bottle surface area / primary die surface area ratio (R ₁ ) is 0.6 to 0.8. Although contracted, in the present invention, by further heat-treating this heat-treated primary bottle, the residual strain is relaxed, the oriented crystals are advanced, and the heat resistance is improved by heat setting, and the shape is closer to the final molded product. It is possible to reduce the amount of stretching process in the secondary blow molding process to improve the stretching processability by shrinking to the above.

Generally, the heat treatment of the primary bottle is carried out by shrinking the bottom part preferentially and then shrinking the whole bottle, and in the present invention, the heat shrinking of the bottom part is preferentially shrinking the entire bottle. However, since in-mold heat treatment is performed in advance in the out-mold heat treatment step of the present invention, the entire heat-treated primary bottle can be heat-treated without shrinking the bottom first. As a result, the out-of-mold heat treatment process is simplified and the workability is improved. In the out-of-mold heat treatment, the surface temperature (T ₃ ) of the bottle body is T ₁ + 0 ° C. to T ₁ + 120 ° C. (T ₃ ), and T ₃ > T ₁ .
And / or the surface temperature (T ₄ ) at the bottom of the bottle is T ₂ +
It is preferable that the temperature is 40 ° C. to T ₂ + 160 ° C. (T ₄ ), and T ₄ > T ₂ . The secondary bottle thus obtained has a shape as shown in FIG.

(Secondary Blow Molding Step) The secondary bottle contracted to a size close to the final molded product by the above-mentioned outside heat treatment is stretch blown in the secondary blow mold as shown in FIG. 1 (D). The final molded product is obtained. Secondary bottle 31
Has its neck supported by a core mold 32 and is held in a closed secondary blow molding split mold (cavity) 33. A bottom mold 34 that defines the bottom shape of the final container is also arranged on the opposite side of the core mold. In the secondary blow molding step, a fluid is blown into the secondary bottle held in the secondary blow molding die to manufacture a final molded product as shown in FIG. 2 (e). In the secondary blow molding process, the secondary blow mold used must, of course, be larger than the secondary bottle and conform to the dimensions and shape of the final molded product including the self-supporting bottom shape. In the present invention, it is particularly preferable to use one having a ratio (R ₃ ) of the surface area of the secondary mold / the surface area of the heat-treated primary bottle of 1.0 to 1.3.

In the secondary blow molding, since the elastic modulus increases due to crystallization by heat treatment, it is preferable to use a high fluid pressure, generally 15 to 45 kg / cm.
It is preferred to use a pressure of ² . Further, the mold temperature of the secondary blow mold is the cavity mold 140 ° C to 170 ° C,
The bottom mold may be maintained at a temperature of 30 ° C. to 120 ° C. so that cooling is performed immediately after molding, or cooling may be performed by passing cold air or the like into the final molded product. The molded final molded product is taken out from the opened secondary blow mold by a take-out mechanism (not shown) known per se. When forming a waist portion on the final molded product, the waist forming portion 3 in the secondary blow mold is used.
5 is preferably formed at a position that matches the waist portion 36 formed on the secondary molded product. This can prevent the waist portion formed in the final molded product (FIG. 1 (E)) from becoming unnecessarily thin, and can reinforce the bottle body portion.

(Thermoplastic Polyester) As the thermoplastic polyester resin used in the present invention, a polyester resin conventionally used in polyester bottles can be used. The ethylene terephthalate units preferably occupy most of the ester repeating units, generally 70 mol% or more, and have a glass transition point of 50 to 90 ° C., especially 5%.
5 to 80 ° C., melting point (Tm) of 200 to 275 ° C.,
A thermoplastic polyester having a temperature of 220 to 270 ° C. is particularly preferable.

Dibasic acids other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and dodecanedioic acid; 1,4-cyclohexane. One or more combinations of polycarboxylic acid components such as alicyclic dicarboxylic acids such as dicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid are listed, and as diol components other than ethylene glycol. Is propylene glycol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, diethylene glycol. Propylene glycol, 1,4-Si B hexanediol, 1 or more poly alcohol component such as p- xylylene glycol.

The thermoplastic polyester resin used should have at least a molecular weight sufficient to form a film, and an injection grade or an extrusion grade is used depending on the application. This intrinsic viscosity (IV) is generally 0.6 to 1.4 dl / g, especially 0.63 to 1.3.
Those in the range of dl / g are desirable.

(Heat-Resistant Bottle) The heat-resistant bottle molded by the above-mentioned production method of the present invention is measured by X-ray diffraction using a curved PSPC micro diffractometer, particularly in the bottle body, and the following formula (1) is used. Ih / Ic ≧ 0.55 (1) In the formula, Ih is a Bragg angle (2θ) = 1 in the direction perpendicular to the bottle height direction and at the same time when X-rays are incident perpendicularly on the body wall surface.
Orientation that satisfies the diffraction intensity near 6 °, where Ic is the diffraction intensity near the Bragg angle (2θ) = 16 ° in the bottle height direction, with X-rays incident perpendicularly on the body wall. It has a feature that it has a crystallization part.
The heat-resistant polyester bottle obtained by the production method of the present invention having such characteristics is oriented substantially evenly in the circumferential direction and the height direction, so that as a biaxial stretching effect,
In addition to being excellent in mechanical strength, it is also excellent in transparency because the center of the bottom is sufficiently thinned and oriented crystals are formed.

[0032]

According to the method for producing a heat resistant bottle of the present invention
For example, in the method of manufacturing heat-resistant bottles by two-step blow molding
And heat treatment using a heated primary blow mold
Ratio of bottle surface area / primary blow mold surface area (R₁  )But
In-mold contraction is performed so that it becomes 0.6 to 0.8, then
Ratio of secondary bottle surface area / heat treated primary bottle surface area (R
_Two  ) Is 0.7 to 0.9
This enables stable heat shrinkage.
Are evenly oriented in the circumferential and height directions, and
Providing a manufacturing method capable of manufacturing heat-resistant bottles with excellent temperature
I was able to.

[Brief description of drawings]

FIG. 1 is a diagram for explaining each step of the method for producing a heat resistant bottle of the present invention.

FIG. 2 is a diagram for explaining a molded product obtained in each step of the method for producing a heat resistant bottle of the present invention.

FIG. 3 is a diagram for explaining a primary bottle obtained by the primary blow mold used in the present invention.

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Claims (11)

[Claims] 1. A thermoplastic polyester preform is subjected to primary stretch blow molding in a primary blow mold, and then the obtained primary bottle is heat treated outside the mold under conditions that allow shrinkage, and this secondary bottle is subjected to secondary molding. In a method for producing a heat-resistant bottle, which comprises secondary blow molding with a primary blow mold, a heat-treated primary blow mold is used, and the ratio of heat treated primary bottle surface area / primary blow mold surface area (R ₁ ) is 0. .6
In-mold shrinkage is performed so that the ratio becomes 0.8 to 0.8, and then the ratio of the surface area of the secondary bottle / the surface area of the heat treated primary bottle (R ₂ ).
A heat-resistant bottle manufacturing method, characterized in that the heat treatment is performed outside the mold so as to be 0.7 to 0.9. 2. The primary blow cavity mold has a Tg of +30 based on the glass transition point (Tg) of polyester.
The manufacturing method according to claim 1, which is heated to a temperature (T ₁ ) of from 0 ° C to Tg + 80 ° C. 3. The primary blow bottom mold has a temperature of 20 ° C. to 80 ° C.
The method according to claim 1 or 2, wherein the method is heated to a temperature (T ₂ ) of ° C. Heat treatment at 4. A type out, carried out at a surface temperature of the bottle body portion _{(T 3)} is _T 1 + 0 ° C. to _T 1 + 120 ° C. and becomes a temperature _{(T 3),} and _T 3> _{T 1} relationship The manufacturing method according to claim 2 or 3, wherein Heat treatment at 5. A type outside, performed by the bottle bottom portion of the surface temperature _{(T 4)} is _T 2 + 40 ° C. to _T 2 + 160 ° C. and becomes a temperature _{(T 4),} and at _T 4> _{T 2} relationship The manufacturing method according to any one of claims 2 to 4, wherein the manufacturing method is present. 6. A primary blow mold having a ratio of primary blow mold surface area / preform outer surface area (R ₀₁ ) of 8 to 14 and a ratio of primary blow mold surface area / preform inner surface area (R ₀₂ ). The method according to any one of claims 1 to 5, wherein a material having a value of 12 to 20 is used. 7. A secondary blow mold having a secondary blow mold surface area / heat treated primary bottle surface area ratio (R ₃ ) of 1.
7. The manufacturing method according to claim 1, wherein one having a value of 0 to 1.3 is used. 8. The manufacturing method according to claim 1, wherein the primary blow mold has a waist forming portion having a reduced diameter in the body forming portion of the cavity mold. 9. The ratio (D ₁ / D ₂ ) of the diameter (D ₁ ) of the waist forming portion to the diameter (D ₂ ) of the body forming portion of the base of the waist forming portion is 0.65 to 0.90. It exists in the range, The manufacturing method of Claim 8 characterized by the above-mentioned. 10. The manufacturing method according to claim 1, wherein the primary stretch blow molding is performed so that the thickness at the center of the bottom portion is stretched to a thickness of less than 1.5 mm. 11. A preform whose bottom portion is thinner than the wall thickness of the body portion is used as the preform, and primary stretch blow molding is performed so that the longitudinal stretch ratio is 2.5 times or more. The manufacturing method according to any one of claims 1 to 10.