JP5817409B2 - Method for manufacturing preform and plastic bottle - Google Patents

Description

  The present invention relates to a preform for a plastic bottle and a plastic bottle, and more particularly to a preform shape capable of increasing the strength of the bottom end of the plastic bottle.

  In recent years, it has been desired to reduce the weight of bottles by reducing the materials used for plastic bottles. However, lack of strength is a concern when reducing the weight of plastic bottles. When the strength of a plastic bottle is reduced, the collapse of cargo during loading, clogging of vending machines, and multiple bottles become a problem.

  On the other hand, in order to compensate for the insufficient strength of the plastic bottle, a technique is used in which liquid nitrogen is added after the content liquid is filled, thereby pressurizing the inside of the bottle. In this case, the plastic bottle is pressurized and the inside becomes a positive pressure, but at this time, the bottom of the bottle may be inverted. For this reason, it is necessary to give pressure resistance to the plastic bottle. In general, when the inside is a positive pressure, a plastic bottle having a petaloid-shaped bottom is used.

  However, since the bottom of the petaloid shape has large irregularities, especially when the plastic bottle is thin to reduce weight, the leg tip may become white due to overstretching, which may make blow molding difficult. . Moreover, by making the plastic bottle thin, the thickness of the petaloid bottom tip is also thinned. For this reason, the bottom end of the plastic bottle may be crushed during transportation or transportation despite being pressurized. The plastic bottle may be tilted due to crushing or the like, and as a result, the collapse of the load may occur.

Special table 2008-540185 gazette

  The present invention has been made in consideration of such points, and even when the plastic bottle is thin, the thickness of the bottom end of the plastic bottle can be increased after blow molding, It is an object of the present invention to provide a preform and a plastic bottle capable of preventing the problem that the bottom end of the plastic bottle is crushed at the time of transportation and transportation despite being pressurized.

The present invention provides a preform for a plastic bottle, and the mouth portion, a body portion having an internal diameter D ₁ is connected to the mouth portion, and a concatenated bottom body portion, bottom portion, in its cross section, the radius An outer surface having an outer surface center portion having R ₁ , an outer surface peripheral portion having a radius R ₂ , an inner surface central portion having a radius R ₃ , and an inner surface having an inner surface peripheral portion having a radius R ₄ ; _{) 3.0 ≦ R 1 / R 2} ≦ 9.0, satisfies the relationship _{(b) D 1/2 <} R 3 <R 1, and _{(c) 3.0 ≦ R 3 /} R 4 ≦ 9.0 It is a preform characterized by things.

If the present invention is barrel, which has a large diameter portion of the mouth portion, a small diameter portion of the bottom side, the outer diameter of the small diameter portion and D _2, the outer diameter of the large-diameter portion was set to D _3, 1. A preform characterized by satisfying the relationship of 1.20 <D ₃ / D ₂ <2.40.

In the present invention, the body portion is provided between the large-diameter portion on the mouth side, the small-diameter portion on the bottom side, and the large-diameter portion and the small-diameter portion, and the diameter is reduced from the large-diameter portion side toward the small-diameter portion side. and an inclined portion, the length of the large diameter portion and L _1, the length of the inclined portion and L _2, if the length of the small-diameter portion was set to L _3, relationship L ₁ ≦ L ₂ <L ₃ It is a preform characterized by satisfying.

A method of manufacturing a plastic bottle to produce the plus tics bottle using a preform, a heating step of heating the preform, by blowing a heated preform, a blow molding process to obtain a plastic bottle the provided, bottom tip thickness of the plastic bottles is a method for producing a plastic bottle, wherein it is 0.04Mm～0.25Mm.

According to the present invention, the bottom of the cross-sectional shape has an outer surface central portion with a radius R _1, and an outer surface having an outer surface periphery with a radius R _2, and the inner surface central portion with a radius R _3, the radius R ₄ It has an inner surface having an inner surface peripheral portion satisfies the relation _{(a) R 2 <R 1} , (b) D 1/2 <R 3 <R 1, and _{(c) R 4 <R 3} . By making the shape of the bottom flat in this way, the thickness of the preform corresponding to the thickness of the bottom of the plastic bottle is increased after stretching, so that the thickness of the bottom end of the plastic bottle can be increased after blow molding. In spite of being pressurized, it is possible to prevent the bottom end of the plastic bottle from being crushed during transportation or transportation.

FIG. 1 is a partial sectional view showing a preform according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view (an enlarged view of a portion II in FIG. 1) showing a bottom portion of the preform according to the embodiment of the present invention. FIG. 3 is a perspective view showing a plastic bottle manufactured by a preform according to an embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a heating apparatus for heating a preform. FIG. 5 is a partial cross-sectional view showing a comparative example (Comparative Example 1) of a preform. FIG. 6 is a partial sectional view showing a comparative example (Comparative Example 2) of a preform. FIGS. 7A and 7B are perspective views showing another example of the bottom of a plastic bottle manufactured by a preform according to an embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 are views showing an embodiment of the present invention.

  First, an outline of a preform according to the present embodiment will be described with reference to FIGS.

  A preform 10 shown in FIG. 1 includes a mouth portion 11 having an opening portion 11 a, a trunk portion 20 connected to the mouth portion 11, and a bottom portion 30 connected to the trunk portion 20.

  Among these, on the outer periphery of the mouth portion 11, there is provided a screw portion 16 for screwing a cap (not shown) after the preform 10 is biaxially stretch blow-molded to produce a plastic bottle 40 (FIG. 3). . An annular support ring 12 projects from the lower portion of the mouth portion 11.

  The trunk portion 20 includes a large diameter portion 21 on the mouth portion 11 side, a small diameter portion 23 on the bottom portion 30 side, and an inclined portion 22 provided between the large diameter portion 21 and the small diameter portion 23.

Inclined portion 22 is formed of a shape that gradually decreases in diameter toward the small diameter portion 23 side from the large diameter portion 21 side, and has a length L _2.

The small-diameter portion 23 has a cylindrical shape, and has an outer diameter D ₂ smaller than the outer diameter of the large-diameter portion 21 and a length L ₃ . The small diameter portion 23 has the inner diameter D _1. In the present specification, the inner diameter of the body portion 20 refers to the inner diameter D ₁ in the small diameter portion 23.

In this case, the outer diameter D ₂ of the small diameter portion 23, between the outer diameter D ₃ of the large diameter portion 21, preferably be established relation of _{1.20 <D 3 / D 2 <} 2.40, 1 More preferably, the relationship of 30 <D ₃ / D ₂ <1.85 holds. That is, the body portion 20 of the preform 10 in the present embodiment has a diameter that is more reduced toward the center than the body portion 92 (see FIG. 6) of a general preform 90 shown as a comparative example. It has become.

If the value of D ₃ / D ₂ is smaller than 2.40, the angle for gradually reducing the diameter from the large diameter portion 21 side toward the small diameter portion 23 side does not become steep, so that the injection moldability deteriorates or the short circuit occurs. Or the like can be prevented from occurring.

On the other hand, if the value of D ₃ / D ₂ is greater than 1.20, it is easy to reduce the weight of the preform 10. In addition, when the diameter of the small diameter part 23 is too large with respect to the large diameter part 21, when heating the preform 10 with the heater 52 (refer FIG. 4 mentioned later) before blow molding, the small diameter part 23 becomes a heater relatively. It will approach. In this case, since the small diameter portion 23 is excessively warmed, the small diameter portion 23 is easily stretched during blow molding, and as a result, the thickness of the body portion 42 (FIG. 3) of the plastic bottle 40 becomes thin.

Further, the length L ₁ of the larger diameter portion 21, the length L ₂ of the inclined portion 22, between the length L ₃ of the small-diameter portion 23, to satisfy the relationship of L ₁ ≦ L ₂ <L ₃ preferable. The length L ₁ of the larger diameter portion 21, the length L ₂ of the inclined portion 22, the length L ₃ of the small-diameter portion 23 by satisfying the above relationship, blow moldability and injection moldability is improved. Note that when L ₁ > L ₂ ≧ L ₃ , the resin volume from the large diameter portion 21 to the small diameter portion 23 increases, which may make it difficult to reduce the weight of the preform 10.

  As shown in FIGS. 1 and 2, the bottom 30 has an outer surface 31 and an inner surface 32 in its cross-sectional shape. Of these, the outer surface 31 includes an outer surface central portion 35 positioned on the center side and a pair of outer surface peripheral portions 36 positioned on the peripheral side of the outer surface central portion 35 and continuously extending to the outer surface central portion 35. Each outer peripheral edge portion 36 is continuous with the lower end of the outer surface of the small diameter portion 23. The inner surface 32 includes an inner surface central portion 37 positioned on the center side, and a pair of inner surface peripheral portions 38 positioned on the peripheral side of the inner surface central portion 37 and continuously extending to the inner surface central portion 37. Each inner peripheral edge 38 is continuous with the lower end of the inner surface of the small diameter portion 23.

As shown in FIG. 2, the outer surface central portion 35, the outer surface peripheral edge portion 36, the inner surface central portion 37, and the inner surface peripheral edge portion 38 are arcs having a radius R ₁ , a radius R ₂ , a radius R _3, and a radius R ₄ , respectively. . In this case, the radius R ₁ of the outer surface center portion 35 is larger than the radius R ₂ of the outer surface periphery portion 36 (R ₂ <R ₁ ), and the radius R ₃ of the inner surface center portion 37 is the radius of the inner surface periphery portion 38. It is larger than R ₄ (R ₄ <R ₃ ). Further, the radius R ₁ of the inner diameter D _1, the radius R ₃ of the inner surface central portion 37, and an outer surface center portion 35 of the small-diameter portion 23 satisfy the relation of _{D 1/2 <R 3 <} R 1.

  That is, the entire bottom portion 30 is not uniformly curved, but has a shape in which the central portion of the bottom portion 30 is relatively flat while the peripheral portion of the bottom portion 30 is relatively greatly curved. It has become flat. Therefore, the bottom portion 30 of the preform 10 in the present embodiment has a shape that is retracted upward (toward the mouth portion 11 side) as compared with a bottom portion 93 (see FIG. 6) of a general preform 90 shown as a comparative example. ing.

Further, the radius R ₂ of the radius R ₁ and outer surface peripheral edge 36 of the outer surface center portion 35 preferably satisfies the relationship of _{3.0 ≦ R 1 / R 2 ≦} 9.0, 4.5 ≦ R 1 / More preferably, the relationship of R ₂ ≦ 7.0 is satisfied. Further, the radius R ₃ of the inner surface central portion 37, the radius R ₄ of the inner surface rim portion 38 preferably satisfies the relationship of _{3.0 ≦ R 3 / R 4 ≦} 9.0, 4.5 ≦ R 3 It is more preferable that the relationship / R ₄ ≦ 6.0 is satisfied.

If the value of R ₁ / R ₂ (R ₃ / R ₄ ) is larger than the above value, the outer peripheral edge portion 36 of the bottom 30 is close to a right angle, so the preform 10 is manufactured by injection molding. At this time, it becomes difficult for the molten plastic to flow to the body 20 side. On the other hand, if the pressure of the molten plastic is increased, the in-core of the injection mold is displaced in one direction from the central axis due to this pressure, so that the thickness of the body portion 20 may not be uniform in the circumferential direction. On the other hand, when the value of R ₁ / R ₂ (R ₃ / R ₄ ) is smaller than the above value, the draw ratio of the bottom 30 at the outer peripheral edge 36 increases, and the bottom tip of the bottle (eg, petaloid in FIG. 3). It is difficult to obtain the effect of increasing the thickness of the leg 45).

In FIG. 1, the total length L _{4 of the} preform 10 is preferably 35 mm to 140 mm. In this case, the ratio of the total length L ₄ of the preform 10 to the outer diameter D ₂ of the small diameter portion 23 (L ₄ / D ₂ ) is preferably 1.5 ≦ L ₄ / D ₂ ≦ 5.5.

  The bottom wall thickness of the bottom of the plastic bottle can be set to 0.04 mm to 0.25 mm, and the weight can be reduced as compared with the prior art.

  In addition, it is preferable to use a thermoplastic resin, especially PE (polyethylene), PP (polypropylene), PET (polyethylene terephthalate), PEN (polyethylene naphthalate) as the main material of the preform 10, and a biomass-based plastic derived from plants. For example, PLA (polylactic acid) can also be used.

  Next, an example of a plastic bottle produced by biaxially stretching blow molding such a preform 10 will be described with reference to FIG. Needless to say, the plastic bottle manufactured using the preform 10 is not limited to this. However, the present invention is not limited to this, and there are also bottles as shown in FIGS.

  In FIG. 3, the plastic bottle 40 includes a mouth part 41, a cylindrical body part 42 provided below the mouth part 41, and a bottom part 43 provided continuously to the body part 42. A neck portion 44 is provided between the mouth portion 41 and the body portion 42. A shoulder portion 48 is formed between the neck portion 44 and the trunk portion 42.

  Further, on the outer periphery of the mouth portion 41, a screw portion 46 (corresponding to the screw portion 16 of the preform 10 described above) for screwing a cap (not shown) is provided, and in the outer periphery of the mouth portion 41, on the lower portion of the screw portion 46. Is formed with an annular support ring 47 projecting outward (corresponding to the support ring 12 of the preform 10 described above).

  The bottom 43 has a so-called petaloid bottom shape. That is, the bottom 43 has a plurality of petaloid legs 45 that are arranged at equal intervals in the circumferential direction and project downward. The number of petaloid legs 45 is preferably 5 to 9 from the viewpoint of stably erecting the plastic bottle 40 and improving the moldability of the lightweight bottle.

  The size (capacity) of the plastic bottle 40 is not limited, and may be any size bottle, but may be 500 ml to 600 ml, for example. The thickness of the plastic bottle 40 can be set to 0.04 mm to 0.25 mm at the petaloid leg 45 of the bottom 43, and the plastic bottle 40 can be reduced in weight.

  Next, the operation (method for manufacturing a plastic bottle) of the present embodiment having such a configuration will be described.

  First, pellets made of thermoplastic resin such as PET (polyethylene terephthalate) are put into an injection molding machine (not shown), and the pellets are heated and melted and pressurized by the injection molding machine. Thereafter, the pellets become pressurized molten plastic and are injected into an injection mold having an internal shape corresponding to the preform 10.

  After a predetermined time has elapsed, the molten plastic is cured in the injection mold, and the preform 10 is formed. Thereafter, the injection mold is separated, and the preform 10 shown in FIG. 1 is taken out from the injection mold.

  Next, the preform 10 is heated in the heating unit 50 in the blow molding machine (heating process: see FIG. 4). In this heating process, the preform 10 is conveyed by the mandrel 51 with the mouth portion 11 facing downward, and is uniformly heated in the circumferential direction by the heater 52 of the heating device 50 while rotating around the central axis. . Reference numeral 53 is a reflecting plate for reflecting the heat from the heater 52 toward the preform 10, and reference numeral 54 is a shielding member for preventing the heat from the heater 52 from escaping to the outside of the heating device 50. is there. In addition, the heating process mentioned above is an example, and depending on the structure of the mandrel 51 or the blow molding machine, the mouth part 11 may be conveyed in a state of facing upward.

  In this heating step, the preform 10 is heated to a temperature of, for example, 80 ° C. to 140 ° C. by the heater 52 of the heating unit 50.

Incidentally in this embodiment, the body portion 20 has a large-diameter portion 21 and the small diameter portion 23 and the inclined portion 22, between the outer diameter D ₃ of outer diameter D ₂ and the large diameter portion 21 of the small diameter portion 23 In addition, a relationship of 1.20 <D ₃ / D ₂ <2.40 is established. Therefore, in FIG. 4, the small diameter portion 23 is located farther from the heater 52 than the large diameter portion 21 and the inclined portion 22 and is not easily heated. For this reason, the small diameter part 23 is hard to be warmed compared with the large diameter part 21 and the inclination part 22, and is hard to be extended | stretched in a subsequent blow molding process.

  On the other hand, after the heating step, the heated preform 10 is sent to a blow molding unit (not shown) by a transport device (not shown).

  The preform 10 sent to the blow molding part is inserted into the blow molding die of the blow molding part. Thereafter, high-pressure air is supplied into the preform 10 from the stretching rod inserted into the preform 10, and the preform 10 is stretched by stretching the stretching rod to perform biaxial stretching blow molding (blow molding). Process). The plastic bottle 40 shown in FIG. 3 is obtained by such blow molding. At this time, the outer peripheral edge portion 36 of the bottom portion 30 of the preform 10 extends to mainly become the petaloid leg 45 of the plastic bottle 40.

  The plastic bottle 40 molded in the blow molding process is transported from a blow molding unit into a filling machine (not shown) by an air transport unit or a neck transport unit.

  Thereafter, the beverage (contents) is filled into the plastic bottle 40 in the filling machine. After the beverage is filled in this way, an inert gas such as liquid nitrogen is sealed in the plastic bottle 40, sealed with a cap (not shown), and further labeled. It is more preferable that each process until the cap is sealed is aseptic. In this way, a product bottle composed of the plastic bottle 40, the contents, and the cap is manufactured.

Incidentally in this embodiment, the bottom 30 radius R ₁ of the outer surface center portion 35, the radius R ₂ of the outer surface periphery 36, the radius R ₃ of the inner surface central portion 37, the inner surface peripheral edge portion 38 of radius R ₄ and a small-diameter portion 23 the inner diameter D ₁ is provided with _{(a) R 2 <R 1} , (b) D 1/2 <R 3 < satisfies the relationship of R _1, and _{(c) R 4 <R 3} , bottom 30 is flat shape It has become. As a result, the preform thickness corresponding to the thickness of the bottom of the plastic bottle is increased after stretching, so that the outer peripheral edge 36 is less likely to be stretched than the outer central portion 35 during blow molding. Therefore, the thickness of the tip of the bottom 43 of the plastic bottle 40 (that is, the tip of the petaloid leg 45) can be increased after blow molding, and the tip of the bottom 43 is crushed during transportation or transport despite being pressurized. It can be effectively prevented.

  In the present embodiment, as described above, the small-diameter portion 23 is located farther from the heater 52 than the large-diameter portion 21 and the inclined portion 22 in the heating unit 50, and the large-diameter portion 21 and the inclined portion 22 In comparison, it is relatively difficult to heat. Therefore, in the blow molding process shown in FIG. 5, the large diameter portion 21 and the inclined portion 22 can be sufficiently stretched, and there is little influence on the strength of the entire plastic bottle 40 out of the plastic bottles 40. The shoulder 48 that is difficult to be stretched can be made thin.

  On the other hand, the small diameter portion 23 is not heated as compared with the large diameter portion 21 and the inclined portion 22. Therefore, in the blow molding process, the stretching amount of the small diameter portion 23 is suppressed from the stretching amounts of the large diameter portion 21 and the inclined portion 22. As a result, among the plastic bottles 40, it is possible to increase the thickness of the body portion 42, which has a great influence on the strength of the entire plastic bottle 40, and to maintain the strength of the entire plastic bottle 40.

  Such an effect is particularly remarkable when the thickness of the plastic bottle 40 is reduced to reduce the weight (for example, when the weight of the preform 10 for the plastic bottle 40 of 500 ml to 600 ml is 7 g to 19 g). I can get it.

  Next, specific examples of the present embodiment will be described.

  First, the following seven types of preforms (Examples 1 to 5 and Comparative Examples 1 to 2) were produced by injection molding.

Example 1
A preform 10 (Example 1) according to the present embodiment shown in FIG. 1 was produced. In this preform 10 (Example 1), the radius R ₁ of the outer surface central portion 35 is 0.83D ₁ , R ₂ is 0.17D ₁ , and the radius R ₃ of the inner surface central portion 37 is 0.67D ₁ , R ₄ . It was 0.17D _1. The outer diameter D ₃ of the large diameter portion 21 was set to 1.50 the ratio (D ₃ / D ₂₎ to the outer diameter D ₂ of the small-diameter portion 23. Further, the length L ₁ of the larger diameter portion 21, the length L ₂ of the inclined portion 22, between the length L ₃ of the small-diameter portion 23 satisfy the relation of L ₁ ≦ L ₂ <L ₃ . The weight of the preform 10 was 12 g.

(Example 2)
It has the R ₃ and 0.95D _1, except in the same manner as in Example 1 to prepare a preform 10 (Example 2).

(Example 3)
A preform 10 (Example 3) was produced in the same manner as in Example 1 except that R ₃ was set to 0.30D ₁ .

Example 4
A preform 10 (Example 4) was produced in the same manner as in Example 1 except that the value of D ₃ / D ₂ was 1.20.

(Example 5)
A preform 10 (Example 5) was produced in the same manner as in Example 1 except that the value of D ₃ / D ₂ was 2.40.

(Comparative Example 1)
As a comparative example, a preform 80 (Comparative Example 1) shown in FIG. 5 was produced. This preform 80 (Comparative Example 1) is the same as Example 1 except that the bottom 83 has a round shape, and the outer surface 84 and the inner surface 85 are each formed of a single radius arc. It is. In this case, the outer diameter D ₃ of the large diameter portion, is 1.50 the ratio (D ₃ / D ₂₎ to the outer diameter D ₂ of the small diameter portion. In FIG. 5, reference numerals 81 and 82 indicate the mouth portion and the trunk portion of the preform 80, respectively. The weight of the preform 10 was 12 g.

(Comparative Example 2)
As a comparative example, a preform 90 (Comparative Example 2) shown in FIG. 6 was produced. In this preform 90 (Comparative Example 2), the bottom portion 93 has a round shape, and the outer surface 94 and the inner surface 95 are each composed of an arc having a single radius. The value of D ₃ / D ₂ was 1.10. In this case, the ratio (R ₁ / D ₁ ) of the radius R ₁ of the outer surface 94 of the bottom portion 93 to the inner diameter D ₁ of the small diameter portion 23 is 0.56. In FIG. 7, reference numerals 91 and 92 denote a mouth portion and a trunk portion of the preform 90, respectively. The weight of the preform 90 was 24 g.

  As a result, for the preforms 10 of Examples 3 and 5, the shapeability deteriorated when the preform 10 was produced by injection molding. On the other hand, when the injection pressure of the molten plastic at the time of injection molding was increased, the thickness of the preform 10 was biased in the circumferential direction (referred to as uneven thickness).

  Preforms other than Examples 3 and 5 had good injection moldability.

  Then, each preform 10, 80, 90 is heated using the heating unit 50 (see FIG. 4), and then each heated preform 10, 80, 90 is biaxially stretch blow molded by the blow molding unit. Thus, a plastic bottle 40 having a petaloid bottom shape shown in FIG. 3 was produced.

  As a result, in the plastic bottle 40 manufactured using the preform 10 of Example 4 and the preform 80 of Comparative Example 1, the bottom 43 was whitened due to overstretching.

  The preform 10 of Example 1 and Example 2 and the preform 90 of Comparative Example 2 had good blow moldability.

  Each bottle was filled with green tea at 30 ° C., and liquid nitrogen was added to close the bottle so that the internal pressure of the bottle became 80 kPa. Using the bottle, a loading test was conducted to verify the presence or absence of collapse.

  The bottles of Example 1 and Comparative Example 2 were good without collapsing. On the other hand, in the bottle of Example 2, the collapse of the load occurred because the thickness at the bottom end was 0.03 mm.

  The above results are summarized in Table 1.

DESCRIPTION OF SYMBOLS 10 Preform 11 Mouth part 12 Support ring 16 Thread part 20 Body part 21 Large diameter part 22 Inclined part 23 Small diameter part 30 Bottom part 31 Outer surface 32 Inner surface 35 Outer surface center part 36 Outer surface peripheral part 37 Inner surface central part 38 Inner surface peripheral part 40 Plastic bottle 50 Heating unit 80, 90 Preform

Claims (4)

In preforms for plastic bottles,
The mouth,
A barrel having an inside diameter D ₁ is connected to the mouth portion,
A bottom connected to the body,
The bottom portion has, in cross-sectional shape, an outer surface center portion having a radius R ₁ , an outer surface having an outer surface periphery portion having a radius R ₂ , an inner surface center portion having a radius R _3, and an inner surface periphery portion having a radius R ₄ And having an inner surface
(A) 3.0 ≦ R ₁ / R ₂ ≦ 9.0 ,
_{(B) D 1/2 <} R 3 <R 1, and _{(c) 3.0 ≦ R 3 /} R 4 ≦ 9.0
Preform characterized by satisfying the relationship. The trunk has a large-diameter portion on the mouth side and a small-diameter portion on the bottom side,
When the outer diameter of the small diameter portion is D ₂ and the outer diameter of the large diameter portion is D ₃ ,
1.20 <D ₃ / D ₂ <2.40
The preform according to claim 1, wherein: The trunk portion includes a large-diameter portion on the mouth side, a small-diameter portion on the bottom side, and an inclined portion that is provided between the large-diameter portion and the small-diameter portion and decreases in diameter from the large-diameter portion side toward the small-diameter portion side. Have
If the length of the large diameter portion and L _1, the length of the inclined portion and L _2, and the length of the small diameter portion and L _3,
L ₁ ≦ L ₂ <L ₃
The preform according to claim 1 or 2, wherein the following relationship is satisfied. A method of manufacturing a plastic bottle to produce the plus tics bottle using a preform of any one of claims 1 to 3,
A heating step of heating the preform;
A blow molding process for obtaining a plastic bottle by blow molding a heated preform,
A method for producing a plastic bottle , wherein the thickness of the bottom end of the plastic bottle is 0.04 mm to 0.25 mm.

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