JP4335040B2 - Blow molding method for plastic containers - Google Patents

Description

  The present invention relates to a blow molding method for a plastic container made of PET, PEN, PC, and the like, and more particularly, to a blow molding method for a plastic container capable of producing a plastic container that is flatter than the axial length of a preform that is a primary molded product thereof. Is.

  A plastic bottle such as a PET bottle is manufactured by heating a bottomed cylindrical preform which is an injection-molded product, and biaxially stretching and blowing in a blow mold. A general preform has a test tube shape, and the mouth portion is not stretched and is directly used as the mouth portion of the bottle. Also, in blow molding, a preform is stretched at a predetermined draw ratio in the longitudinal direction, which is the axial direction thereof, and in the transverse direction orthogonal to the inside of the blow mold, and is a plastic container having a size larger than the axial length of the preform. It is said.

  Here, when producing a product with low longitudinal stretching by blow molding, or a flat plastic container having a large transverse stretching ratio compared to the longitudinal stretching ratio, each part of the preform is biaxially formed to have a uniform thickness. It was difficult to stretch and blow. In particular, the part that becomes the neck lower part of the plastic container that continues to the mouth that remains unstretched and the part that becomes the bottom of the plastic container hit the inner peripheral surface of the blow mold earlier than other parts and cool down. As a result, stretching does not proceed sufficiently. Therefore, it is very difficult to adjust the thickness of such a part. For this reason, it is impossible to produce a large flat plastic container by a biaxial stretch blow molding method using a flat plastic container shorter than the axial length of the preform or a thick preform having a thickness of 5 mm or more. It was thought to be.

  In addition, in order to produce a flat plastic container by a biaxial stretch blow molding method, conventionally, the shape and thickness of the preform are adjusted for each part, and the heating state of the preform is also changed for each part. Such a method had to be adopted, and it was not a method that could withstand practical use.

  Furthermore, when a plastic container such as a flat rectangular parallelepiped shape is manufactured by the biaxial stretch blow molding method, the corner portion has a high stretch ratio, so the thickness of the portion becomes thin, and sufficient strength is provided. A corner portion having a predetermined thickness could not be accurately formed.

  In view of these points, an object of the present invention is to propose a plastic container blow molding method capable of manufacturing a flat plastic container so as to have a uniform thickness by a biaxial stretch blow molding method. .

  Another object of the present invention is to propose a plastic container blow molding method capable of producing a flat plastic container shorter than the axial length of the preform so as to have a uniform thickness by a biaxial stretch blow molding method. It is in.

  Furthermore, an object of the present invention is to propose a plastic container blow molding method capable of producing a plastic container having a body portion having a flat polygonal cross section with a uniform thickness by a biaxial stretch blow molding method. There is.

  A further object of the present invention is to propose a plastic container blow molding method capable of producing a flat thick plastic container with a uniform thickness from a thick preform by a biaxial stretch blow molding method. It is in.

In order to solve the above problems, the plastic container blow molding method of the present invention,
A free blow step of blowing air into a bottomed cylindrical preform heated to a predetermined temperature and stretching it in an unrestricted state to obtain a substantially spherical free blow molded product;
A compression molding step of compressing the free blow molded product from a predetermined direction with a compression mold to obtain a plastic container having a final shape;
It is characterized by including.

  Here, instead of the free blow process, it is also possible to employ a partial free blow process in which a preform is stretched in a partially restricted state to obtain a partially free blow molded product.

  In the method of the present invention, the preform is free-blowed or free-blowed with only a part of it being restricted, so that the preform can be stretched so that the thickness of each part is substantially uniform. it can. Because the final product plastic container is obtained by compressing a free blow molded product or partially free blow molded product that has been stretched with a uniform thickness with a compression mold, it has a uniform thickness and has a target shape. The container can be manufactured. For example, a flat plastic container with a polygonal cross section can be manufactured to have a uniform thickness.

  Here, it is difficult to obtain a free blow molded product or a partially free blow molded product having a target size by a conventional blow molding method for controlling the air blowing pressure and the blowing time. In the present invention, a predetermined amount of air is blown in the free blow process or the partial free blow process. In the present invention, the pressure of air blown into the preform is controlled in the free blow process or the partial free blow process. In the air pressure control, it is desirable to gradually reduce the air pressure from the start point of air blowing to the end point of blowing. In this way, by controlling the air blowing amount and the blowing pressure, it is possible to reliably obtain a free blow molded product or a partial free blow molded product having a target size without a decrease in yield due to rupture or the like. .

  In order to appropriately control the air blowing amount and the blowing pressure, air is blown into the preform from an air tank filled with a predetermined amount of air in a predetermined pressure state in the free blow process or the partial free blow process. What should I do? The air pressure in the air tank is initially in the highest state, and when the preform is stretched and blown and expanded by being supplied to the preform, the pressure in the air tank decreases as the volume increases. Accordingly, a balanced state between the tensile stress generated in the stretched resin and the pressure of the blown air is automatically formed, and the stretching stops in that state. If an appropriate supply amount of blown air and an air pressure are set based on the heating temperature, the draw ratio, etc., a free blow molded product or a partial free blow molded product having a target size can be obtained with certainty.

  In the free blow step or the partial free blow step, the free blow of the target thickness and size is mainly controlled by controlling the heating temperature, stretch ratio, air pressure, air supply amount, etc. of the preform. A molded product or a partially free blow molded product can be obtained.

  Next, in the compression molding step of the present invention, the free blow molded product or the partial free blow molded product can be compression molded from a direction parallel to the axial direction of the preform. Thereby, a flat plastic container having a uniform wall thickness, for example, a flat plastic container shorter than the axial length of the preform can be obtained.

  Further, in the compression molding step, the body having a polygonal cross section such as a rectangular parallelepiped shape is formed by compression molding the free blow molded product or the partial free blow molded product from a direction orthogonal to the axis of the preform. A plastic container can be obtained in which the thickness of the corner portion is the same as that of the other portions.

  Here, in the compression molding step, it is desirable to perform compression molding in a state where the free blow molded product or the partial free blow molded product is maintained at a predetermined temperature. In order to perform compression molding with high accuracy, it is desirable to control the internal pressure of the free blow molded product or the partial free blow molded product in the compression molding step. In general, compression molding may be performed in a state where the internal pressure of the free blow molded product or the partial free blow molded product is maintained at a predetermined pressure.

  The preform generally has a configuration including a non-stretching mouth portion that is directly used as the mouth portion of the plastic container without being stretched, and other stretching portions. Therefore, the free blow process or the partial free blow process and the compression molding process may be performed in a state where the non-stretch port portion of the preform is held.

  According to the experiments by the present inventors, it has been confirmed that the method of the present invention makes it possible to produce a plastic container with a uniform thickness that is flatter than the preform axial length, which has been difficult in the past. Further, it was confirmed that a thick plastic container having a thickness of 0.5 mm or more can be produced with a uniform thickness from a thick preform having a thickness of 5 mm or more, which has been considered difficult in the past. In addition, it was confirmed that plastic containers can be appropriately molded from thick preforms with a wall thickness of up to 50 mm.

  Next, the method of the present invention includes a heating step of heating the preform to a temperature suitable for biaxial stretching prior to the free blow step or the partial free blow step, and this heating step is a first heating step. In the first heating step, moisture contained in the preform is removed, and the preform is heated in a state where a temperature difference does not substantially occur on the inner and outer surfaces of the preform. As described above, by placing the preform in an atmosphere at a first temperature for a first time, the preform is heat-dried. In the second heating step, the preform is more than the first time. During the short second time, the preform is heated to a second temperature suitable for blow molding higher than the first temperature.

  If the heating process of the present invention is employed, the temperature difference is substantially reduced by appropriately setting the first time and the first temperature in the first heating process according to the material and thickness of the preform. Thus, the preform can be heated in a state where it is not generated, and moisture absorbed inside can be released to the outside so as not to remain as bubbles. Further, the preform heated uniformly in the first heating step can be heated to a temperature suitable for blow molding in the second heating step in a short time without causing a temperature difference.

  Therefore, compared with the conventional method, a thicker preform can be heated to a temperature suitable for blow molding without any temperature difference, and the harmful effect of moisture remaining as bubbles can be avoided reliably. .

  Here, it is desirable to set the first temperature in the first heating step to a value within a range from the glass transition point of the preform to a temperature 20 ° C. lower than the glass transition point. Moreover, it is desirable that the first time of the first heating step be at least 2 hours. That is, by gradually heating to a temperature that does not crystallize, moisture can be efficiently released from the inside of the preform and the preform can be dried.

  The heating process of the present invention is suitable for heating a preform made of a highly hygroscopic polycarbonate resin or PEN resin. The heating step of the present invention is suitable for heating a thick preform, that is, a preform having a maximum thickness of at least 5 mm. In particular, it was confirmed that a preform having a thickness of 13 mm or more, which was conventionally considered not suitable for blow molding, can be heated in an appropriate state.

  As described above, in the plastic container blow molding method of the present invention, a preform is subjected to free blow or partial free blow to form a spherical free blow molded product or partial free blow molded product, and then free blow molding A product or a partially free blow molded product is compression-molded vertically and horizontally to form a plastic container as a final product. Therefore, a flat plastic container or a plastic container having a corner portion is compression-molded from a free blow molded product or a partial free blow molded product having a uniform thickness in each part obtained by free blow or partial free blow.

  Therefore, according to the method of the present invention, a plastic container that is flatter than the preform, a thick plastic container, or a plastic container having a corner portion can be manufactured with a uniform thickness.

  Below, with reference to drawings, the manufacturing method of the flat thick plastic container to which this invention is applied is demonstrated.

  FIG. 1 shows a cross section of a thick preform used in the method to which the present invention is applied, a cross section of a free blow molded product formed by free blowing the preform, and a compression molding of the free blow molded product. It is explanatory drawing which shows the cross section of the plastic container of the final shape obtained. The preform 1 is an injection-molded product having a bottomed cylindrical shape made of plastic, and includes a non-stretched mouth portion 1a that remains as a mouth portion of the final product without being stretched, and a body portion 1b that is biaxially stretched. Yes. The body portion 1b has a thickness of, for example, 5 mm or more.

  In the method to which the present invention is applied, the preform 1 having this shape is heated to a temperature suitable for biaxial stretching blow (heating step), and then free blow is performed to form a substantially spherical free blow molding as shown in the figure. Product 2 is manufactured (free blow process). Subsequently, the free blow molded product 2 is subjected to compression molding to produce a flat thick plastic container 3 having a flat rectangular cross section as shown in the figure (compression molding process). The flat and thick plastic container 3 is a container having a rectangular parallelepiped shape that is flatter than the axial length of the preform 1, and the substantially spherical free-blow molded product 2 includes a vertical direction parallel to the axis 1A and a horizontal direction perpendicular thereto. Are compressed to form a flat rectangular parallelepiped shape.

  FIG. 2 is a schematic configuration diagram of a manufacturing apparatus for manufacturing the flat thick plastic container 3. The manufacturing apparatus 10 includes a preform holding unit 11 that holds the mouth portion 1a of the preform 1, a free blow mechanism 12 that free blows the preform 1, and a compression molding mechanism that compresses the free blow molded product 2. 13 and a control panel 14 for driving and controlling the mechanisms 12 and 13.

  The free blow mechanism 12 includes an air tank 21 and a blow air supply circuit 22 that supplies blow air to the inside of the preform 1 held by the preform holding unit 11. The air tank 21 is filled with a constant amount of air at a constant pressure. The blow air supply circuit 22 includes an open / close valve 23 and a three-way valve 24, and an air discharge port of the air tank 21 is formed in the preform holding unit 11 through the open / close valve 23 and the three-way valve 24. It is possible to communicate with. The blow air inlet 11 a can be opened to the atmosphere via the three-way valve 24 and the regulator 25. The on-off valve 23 and the three-way valve 24 are switched and controlled by the control panel 14. Further, a portion between the three-way valve 24 and the on-off valve 23 in the blow air supply circuit 22 can communicate with a high-pressure air supply side of a high-pressure compressor (not shown) via an on-off valve 26. When the on-off valve 26 is opened by the control panel 14, high-pressure air can be supplied to the blown air inlet 11a via the three-way valve 24.

  The compression molding mechanism 13 includes an upper mold 31 and a lower mold 32, left and right open / close molds 33 and 34, and a pair of open / close molds (not shown) facing each other in a direction orthogonal to the open / close molds 33 and 34 (FIG. Opening and closing molds 35 and 36) shown in b) are provided. The upper mold 31 is a fixed mold, and the preform holding part 11 is mounted at the center thereof. The lower mold 32 can be moved up and down between positions 32A and 32B by an air cylinder type lifting mechanism 37. The lower position 32A of the lower mold 32 indicated by a solid line in the drawing is a position that does not hinder the free blow of the preform 1. The open / close molds 33 and 34 can also be opened and closed by air cylinder type open / close mechanisms 38 and 39, and the open position shown by the solid line in the drawing is a position that does not hinder the free blow of the preform 1. Similarly, a pair of open / close molds 35 and 36 (not shown) can be opened and closed by an air cylinder type open / close mechanism, and their open positions are positions that do not hinder the free blow of the preform 1. The elevating mechanism 37 of the upper and lower molds 31, 32 and the opening / closing mechanisms 38, 39 of the open / close molds 33, 34 are driven and controlled by the control panel 13 via the pneumatic circuit 40.

  With reference to FIG. 2 and 3, the manufacturing process of the flat thick plastic container 3 by the manufacturing apparatus 10 is demonstrated. First, as shown in FIG. 2, inside the compression molding mechanism 12 in which the lower mold 32 is in the lowered position 32A and the open / close molds 33 to 36 are in the open position, the mold heated to a temperature suitable for biaxial stretch blow molding is used. The reform 1 is held in the preform holding unit 11. Next, the on-off valve 23 is opened, and the compressed air in the air tank 21 is blown into the preform 1 from the air blowing port 11a. As a result, the preform 1 is free blown and gradually expands into a spherical shape.

  In this free blow process, the preform 1 is stretched to increase its internal volume. Since the air tank 21 is filled with a certain amount of compressed air, the pressure of the blow air supplied from the air tank 21 decreases as the internal volume of the preform 1 increases. As a result, an opportunity to stretch the thick preform 1 by high pressure is created at the start of blowing, and the pressure is reduced at the final blow time to balance the tensile force generated in the stretched preform and its internal pressure. The preform 1 becomes a free blow molded product 2 having a certain size. Therefore, unlike the case of controlling the pressure and time of the blow air as in the conventional biaxial stretch blow molding, the target size of the free blow molded product 2 can be reliably obtained without rupturing. Further, a molded product 2 having a constant thickness is obtained.

  After the free blow molded product 2 is obtained, the on-off valve 23 is closed and the three-way valve 24 is switched to the regulator 25 side. As a result, the internal pressure of the free blow molded product 2 communicating with the regulator 25 through the air blowing port 11a is maintained at a constant pressure defined by the regulator 25.

  In this state, first, the lower mold 32 is raised as shown in FIG. 3A to compress the free blow molded product 2 in the vertical direction. As a result, the spherical free-blow molded product becomes a flat molded product 2A. Subsequently, the left and right open / close molds 35 and 36 are moved in the closing direction, and the molded product 2A is compressed from the left and right as shown in FIG. 3B to obtain the molded product 2B. Next, the other left and right open / close molds 33 and 34 are moved in the closing direction to compress the molded product 2B from the direction orthogonal to each other as shown in FIG. By switching the valve 24, high-pressure air is introduced into the molded product 2B from the high-pressure compressor side to obtain the final shape. As a result, a flat thick plastic container 3 is obtained.

  In the free blow molding process and the compression molding process, it is desirable to keep the molded product in a heated state at a predetermined temperature or higher. When a desired heating state cannot be maintained with the amount of heat retained by the molded product, an external heating source such as a heater may be disposed to hold the molded product at a predetermined temperature state.

  Moreover, what is necessary is just to select the optimal pressure and capacity | capacitance of the air tank 21 according to the container of a shaping | molding object, the shape and thickness of the preform to be used, the resin material of a preform, its heating temperature, a draw ratio, etc. . Of course, instead of the air tank, a free blow mechanism having a high pressure air supply source, a pressure control mechanism for high pressure air supplied therefrom, and an air amount adjusting mechanism for adjusting the amount of air supplied therefrom is used. It is also possible.

  Furthermore, in the above description, a free blow process for free blowing the preform body 1b is performed, but instead, a partial free blow process for performing blow in a partially restricted state may be employed. it can. When there are few restricted portions, a partially free blow molded product having a uniform thickness can be obtained by the same process as the free blow process.

  A flat rectangular parallelepiped thick plastic container was manufactured using the manufacturing apparatus 10 described above. The preform 1 used is made of PEN and weighs 700 g. As shown in FIG. 1, the length of the mouth portion 1a in the axial direction is 30 mm, the length of the trunk portion 1b in the axial direction is 110 mm, and the inner diameter. Having a maximum thickness of 25 mm. Further, as the air tank 21 of the free blow mechanism 12, a tank having a capacity of 6 liters and a pressure of 3 MPa was used.

  First, the thick preform 1 was placed in a high-temperature tank maintained at a temperature in the vicinity of the glass transition temperature for a predetermined time and dried by heating (first heating step). Specifically, the temperature of the high-temperature tank was set to 110 to 120 ° C., and the thick preform 1 was put into this for 2 to 4 hours. As a result, it was confirmed that the thick preform 1 at room temperature around 20 ° C. was heated to a temperature exceeding 105 ° C. with substantially no temperature gradient between the inner and outer surfaces. Moreover, the generation | occurrence | production of the bubble by the water | moisture content absorbed inside the preform was not confirmed.

  Next, the thick preform 1 was transferred from the high-temperature tank to a heating device, and rapidly heated from the outside to a temperature of about 130 to 150 ° C. suitable for biaxial stretch blow molding using a heat source such as an infrared heater (second) Heating step). It was confirmed that the thick preform 1 was heated in a state in which no temperature difference substantially occurred between the inner and outer surfaces, and it was confirmed that no bubbles were generated.

  In the free blow process, when blow air is supplied from the air tank 21 to the preform 1 heated as described above, biaxial stretching is performed for approximately 3 seconds. As shown in FIG. The barrel portion 1b was stretched to obtain a substantially spherical free blow molded product 2 having a height of 240 mm and a barrel portion outer diameter of 320 mm. The internal pressure of the free blow molded product 2 in the final stage of free blow, and thus the internal pressure of the air tank 21 was about 1 MPa. Moreover, the average thickness was 1.8 mm, and it was confirmed that the thickness was uniform throughout. The draw ratio was about 14 times, 2 times in length and 7 times in width.

  In the compression molding process, the internal pressure of the molded product was always kept at 0.8 MPa by the regulator 25. In this compression molding step, first, as shown in FIG. 3A, the free blow molded product 2 was compressed in the vertical direction to 80 mm. As a result, a flat molded product 2A having a barrel outer diameter of 350 mm was obtained.

  Next, as shown in FIG.3 (b), the trunk | drum of 2A of molded products was compressed from the horizontal direction, and the width | variety was 240 mm. As a result, a molded product 2B was obtained in which the dimension in the orthogonal width direction was expanded to 400 mm. Thereafter, as shown in FIG. 3 (c), the molded product 2B is compressed in the lateral direction to compress the width dimension of 400 mm to 350 mm, and finally the high pressure air is introduced to set the internal pressure to 3 MPa to obtain the final shape. .

  As a result, the thick plastic container 3 having a rectangular parallelepiped shape that is flatter than the preform 1 and has a rectangular shape with an inner diameter of 45 mm, a weight of 700 g, an average thickness of 1.8 mm, a body depth of 80 mm, and a body section of 240 mm × 350 mm. was gotten. It was confirmed that the thickness of each portion of the plastic container 3 is uniform, and in particular, the thickness of the corner portion of the trunk portion is also constant. In addition, it was confirmed that the corner portion was accurately formed.

Cross section of a thick preform used in the method to which the present invention is applied, a cross section of a free blow molded product formed by free blowing the preform, and a final shape obtained by compression molding the free blow molded product It is explanatory drawing which shows the cross section of this plastic container. It is a schematic block diagram of the manufacturing apparatus for manufacturing the flat thick plastic container 3. FIG. It is explanatory drawing for showing the operation | movement which compression-molds a free blow molded product using the manufacturing apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Preform 1A Axis 1a Mouth part 1b Body part 2 Free blow molded product 2A, 2B Compression molded product 3 Flat thick plastic container 10 Manufacturing apparatus 11 Preform holding part 11a Air blowing port 12 Free blow mechanism 13 Compression molding mechanism 14 Control Panel 21 Air tank 23 Open / close valve 24 Three-way valve 25 Regulator 31 Upper mold 32 Lower mold 33-36 Open / close mold 37 Lift mechanism 38 Open / close mechanism 39 Pneumatic circuit

Claims (14)

A free-blow process in which air is blown into a bottomed cylindrical preform heated to a predetermined temperature and stretched in an unrestricted state to obtain a substantially spherical free-blow molded product, and a bottomed cylinder heated to a predetermined temperature Any one of the partial free blow processes to blow a part of the air-shaped preform to obtain a partially free blow molded product by stretching in a partially unrestricted state;
A compression molding step of compressing the free blow molded product or the partial free blow molded product from a predetermined direction with a compression mold to obtain a final shape plastic container ,
In the free blow step or the partial free blow step, a blow molding method for a plastic container, wherein the pressure of the air blown into the preform is controlled to gradually reduce the air pressure from the start point of the blow to the end point of the blow. A free-blow process in which air is blown into a bottomed cylindrical preform heated to a predetermined temperature and stretched in an unrestricted state to obtain a substantially spherical free blow molded product, and a bottomed cylinder heated to a predetermined temperature Any one of the partial free blow processes to blow a part of the air-shaped preform to obtain a partially free blow molded product by stretching in a partially unrestricted state;
A compression molding step of compressing the free blow molded product or the partial free blow molded product from a predetermined direction with a compression mold to obtain a final shape plastic container,
In the compression molding step, a plastic container blow molding method for controlling an internal pressure of the free blow molded product or the partial free blow molded product. In claim 2,
In the compression molding step, a plastic container blow molding method for performing compression molding in a state where an internal pressure of the free blow molded product or the partial free blow molded product is maintained at a predetermined pressure. A free-blow process in which air is blown into a bottomed cylindrical preform heated to a predetermined temperature and stretched in an unrestricted state to obtain a substantially spherical free blow molded product, and a bottomed cylinder heated to a predetermined temperature Any one of the partial free blow processes to blow a part of the air-shaped preform to obtain a partially free blow molded product by stretching in a partially unrestricted state;
A compression molding step of compressing the free blow molded product or the partial free blow molded product from a predetermined direction with a compression mold to obtain a final shape plastic container,
The preform is provided with a non-stretching mouth portion that is directly used as the mouth portion of the plastic container without being stretched, and other stretched portions,
With the non-stretching mouth portion of the preform held, the free blow step or the partial free blow step and the compression molding step are performed,
In the free blow step or the partial free blow step, a plastic container blow molding method in which only a part of the stretched portion is stretched in an unrestricted state. A free-blow process in which air is blown into a bottomed cylindrical preform heated to a predetermined temperature and stretched in an unrestricted state to obtain a substantially spherical free blow molded product, and a bottomed cylinder heated to a predetermined temperature Any one of the partial free blow processes to blow a part of the air-shaped preform to obtain a partially free blow molded product by stretching in a partially unrestricted state;
A compression molding step of compressing the free blow molded product or the partial free blow molded product from a predetermined direction with a compression mold to obtain a final shape plastic container,
A plastic container blow molding method for producing a plastic container flatter than an axial length of the preform from the preform. A free-blow process in which air is blown into a bottomed cylindrical preform heated to a predetermined temperature and stretched in an unrestricted state to obtain a substantially spherical free blow molded product, and a bottomed cylinder heated to a predetermined temperature Any one of the partial free blow processes to blow a part of the air-shaped preform to obtain a partially free blow molded product by stretching in a partially unrestricted state;
A compression molding step of compressing the free blow molded product or the partial free blow molded product from a predetermined direction with a compression mold to obtain a final shaped plastic container;
A heating step of heating the preform to a temperature suitable for biaxial stretching prior to the free blow step or the partial free blow step,
The heating step includes a first heating step and a second heating step,
In the first heating step, the preform is heated so that moisture contained in the preform is removed and the preform is heated in a state where a temperature difference does not substantially occur on the inner and outer surfaces of the preform. The preform is heat-dried by placing it in an atmosphere at a first temperature for 1 hour,
In the second heating step, a plastic container that heats the preform to a second temperature suitable for blow molding higher than the first temperature during a second time shorter than the first time. Blow molding method. In claim 6,
The plastic container blow molding method, wherein the first temperature in the first heating step is a value within a range from a glass transition point of the preform to a temperature 20 ° C. lower than the glass transition point. In claim 7,
The method for blow molding a plastic container, wherein the first time of the first heating step is at least 2 hours. In any one of claims 1 to 6,
A plastic container blow molding method for blowing a predetermined amount of air in the free blow step or the partial free blow step. In any one of claims 1 to 6,
In the free blow step or the partial free blow step, a plastic container blow molding method in which air is blown into the preform from an air tank filled with a predetermined amount of air in a predetermined pressure state. In any one of claims 1 to 6,
In the compression molding step, a plastic container blow molding method in which the free blow molded product or the partial free blow molded product is compression molded from a direction parallel to the axial direction of the preform. In any one of claims 1 to 6,
In the compression molding step, a blow molding method for a plastic container, wherein the free blow molded product or the partial free blow molded product is compression molded from a direction orthogonal to the axis of the preform. In any one of claims 1 to 6,
In the compression molding step, a blow molding method for a plastic container, in which compression molding is performed while the free blow molded product or the partial free blow molded product is held at a predetermined temperature. In any one of claims 1 to 6 ,
A plastic container blow molding method for producing a plastic container having a maximum wall thickness of 0.5 mm or more from the preform having a maximum wall thickness of 5 mm or more.

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