JP2011079243A - Blow molding method of flat container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blow molding method of a flat container with a hanger, capable of manufacturing a flat container with a uniform thickness integrally formed with the hanger by using a preform of a general shape. <P>SOLUTION: Before setting the test tube-like general preform 11 in left and right blow molding split molds 31, 32 in an opened state and mold clamping, hanger molding split molds 33, 34 are lowered to hold both sides of a bottom 14 of the preform 11 to pull up it, to stretch the preform 11. After stretching, the blow molding split molds 31, 32 are clamped and free blow is performed by introducing low pressure air into the preform 11. The preform 11 subjected to the free blow is pressed to be formed flat by the blow molding split molds 31, 32, and after clamping, high pressure air is introduced to mold the flat container, and also hanger molding split molds 33, 34 are finally clamped to press-mold the hanger 4 on the bottom of the flat container. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flat container blow molding method used for manufacturing a medical container with a hanging tool such as a drip container having a flat cross-sectional shape by biaxially stretching blow-molding a bottomed cylindrical preform.

  Two types of flat containers with hanging tools, for example, medical containers (infusion containers) enclosing Ringer's solution and physiological saline, are used in the form of bottles and soft bags. Bottle-shaped products are produced by two methods, an injection stretch blow method and an extrusion blow method (direct blow method). In the injection stretch blow method, it is difficult to integrally form the hanging tool to be attached to the bottom part at the time of blow molding, so the hanging tool formed separately after bottle molding is integrated by heat welding, etc. Will increase the cost. In the extrusion blow method, the hanging tool can be integrally formed at the time of blow molding, but burrs appear on the top and bottom of the product, and wasteful materials increase, which also increases the cost. Forming a soft bag type container has an advantage that a hanging tool can be attached at the same time when a bag is first formed by thermally welding a film. However, since the separately molded mouth and bag are thermally welded, the process is complicated and the cost is high. As a method for producing a bottle or soft bag which is a medical container for infusion, a low-cost method is desired in which the number of parts is small and the process is simplified.

  Here, Ringer's solution and physiological saline are infused directly from the blood vessel into the blood, but it is desirable that the infusion rate be constant in order not to give an extra burden on the patient. For this reason, the drip container is designed so that when the liquid content drops and the inside of the container becomes negative pressure, the container itself is deflated so that a large pressure difference from the atmospheric pressure does not occur.

  A container having a large flatness is suitable as a shape that can be easily deflated under a negative pressure. However, from the viewpoint of the blow molded container, it is difficult to uniformly mold the long diameter side and the short diameter side of the blow molded container with a large flatness, and the short diameter side is thick and the long diameter side is thin. Thus, there is a drawback that the container does not always wither easily when the inside of the container becomes negative pressure.

  That is, it is desirable to minimize the difference in wall thickness between the major axis direction and the minor axis direction in order to easily wither when the inside of the container becomes negative pressure. However, in normal blow molding, when a preform having a circular cross section is blow molded so as to have a large circular cross section, a uniform thickness can be obtained in each part in the circumferential direction. In the process of gradually expanding the preform in the blow mold, the portion of the outer peripheral surface of the preform that is on the short diameter side first comes into contact with the inner surface of the blow mold and is cooled, and cannot be stretched any further. Only the portion on the long diameter side of the outer peripheral surface of the preform is stretched to become thin.

  In Patent Document 1, two blow molds are arranged, and the preform is stretched with a primary blow mold so as to have a diameter larger than the minor axis direction of the flat container as the final product, and then the stretched preform is A so-called two-stage blow molding method has been proposed in which, after shrinking, a preform is transferred to a secondary blow mold and blown again. The two-stage blow molding method itself has been put to practical use as a heat-resistant bottle molding method made of PET, and is never a new method. However, in Patent Document 1, a flat container without uneven thickness is obtained by using it for manufacturing a flat container. Yes.

  On the other hand, when a medical container such as an infusion container, which is a flat container with a hanging tool, is blow-molded, how to form the hanging tool becomes a problem. As described above, in the medical container for infusion by the conventional injection biaxial stretch blow molding method, the hanging tool cannot be molded integrally with the container main body, so that another part is attached later. This method is costly because the hanging tool must be formed in a separate process and integrated with the container body.

  Patent Document 2 discloses a method in which an extension portion for forming a hanging tool is integrally formed in advance on the bottom of a preform, and the extending portion is pressed into a hanging tool at the time of blow molding or after the preform. Has been proposed.

JP 2007-21619 A JP 2003-89147 A

  The two-stage blow molding method disclosed in Patent Document 1 is effective as a method for equalizing the thickness of each portion in the circumferential direction in the flat cross section when a flat container is formed. Compared with the molding method, a blow mold is required twice, and an additional mold clamping device of the molding machine is also required, resulting in a high manufacturing cost. Also, the heat resistance is not always satisfactory. The reason is that after shrinking the primary blow true circular molded product molded by the primary blow mold, blow molding in the secondary blow flat mold, the thermal contraction rate of the resulting flat molded product can be satisfied. It is not a thing.

  On the other hand, in the method for forming a container with a hanging tool disclosed in Patent Document 2, it is necessary to integrally form an extension portion during injection molding of a preform, so a general test tubular preform is molded as an injection mold. There is a problem that it is necessary to make it different from what is to be done and the cost becomes high. In addition, when a plate-like object is integrally formed with the preform as the extending portion, the extending portion is always in a certain direction so that the extending portion of the preform set in the blow mold can be pressed. Thus, it is necessary to set the preform in the mold. For this reason, there also exists a problem that the process of setting a preform in a blow mold becomes complicated. Furthermore, the preform with the extension part formed integrally needs to be handled more carefully than a general test tube preform so that the extension part is not damaged. A lot of space is required.

  In view of these points, an object of the present invention is to propose a flat container blow molding method capable of manufacturing a flat container free of uneven thickness by performing a single biaxial stretch blow on a preform.

  Another object of the present invention is to propose a blow molding method of a flat container with a suspension capable of manufacturing a flat container without uneven thickness, in which the suspension is integrally formed using a preform having a general shape. is there.

In order to solve the above-mentioned problems, the present invention biaxially stretches a portion other than the mouth of a bottomed cylindrical preform, and the cross-sectional shape orthogonal to the central axis of the preform is a flat cross-sectional shape. A blow molding method for producing a flat container,
A set step of setting the preform heated to a temperature capable of blow molding to the left and right blow mold split molds in an open state;
A mold clamping step for performing a mold clamping operation of the blow molding split mold;
Performed in parallel with the mold clamping step, a free blow step of free blowing the preform by introducing blow air into the preform from the mouth of the preform at a first pressure;
In the middle of the mold clamping step, the blow molding split is started while the blow molding split mold comes into contact with the free blown preform, and the introduction of blow air of the first pressure is continued. A constraining blow step of press-molding the preform so as to have the flat cross-sectional shape by a mold;
A final blow step, which is performed after completion of the mold clamping step and introduces blow air having a second pressure higher than the first pressure into the preform to form the preform into the flat container. And
At the end of the free blow step, the outer diameter of the preform cross-sectional shape orthogonal to the central axis of the preform is orthogonal to the central axis in the cavity defined by the blow mold split mold Free-blow of the preform is performed so that it is larger than the minor axis of the cavity sectional shape and smaller than the major axis of the cavity sectional shape, and the circumference of the preform sectional shape is shorter than the circumference of the cavity sectional shape. It is characterized by that.

  In the present invention, the preform is free blown in the free blow process to swell to a predetermined size, and after contacting the left and right blow molding split molds, the left and right blow moves to move toward each other in the restraining blow process. The preform after free blow is press-molded so as to have a flat cross-section by a molding split mold. At the end of the free blow, the outer diameter of the preform cross-sectional shape is larger than the minor axis of the cavity cross-sectional shape perpendicular to the central axis of the cavity defined by the mold for mold-clamping blow molding, and the cavity cross-sectional shape is It is set to be smaller than the major axis. The circumference of the preform cross-sectional shape is set to be shorter than the circumference of the cavity cross-sectional shape.

  Therefore, in the constrained blow process, the preform swelled to a uniform thickness by free blow is crushed in the minor axis direction in the flat cross-sectional shape of the flat container of the final product, and is extruded in the major axis direction as a whole. Deformed. If the circumference of the preform is slightly shorter than the circumference of the cavity of the flat cross section, the thickness of the preform does not substantially change due to biaxial stretching, and the preform has a flat cross section without sagging. Deform. That is, it is press-molded into a flat cross-sectional shape with the uniform thickness obtained by free blow molding. Thereafter, in the final blow step, high-pressure blow air is introduced, and the outer peripheral surface of the preform is pressed against and closely adhered to the inner peripheral surface of the cavity, so that a flat container having a uniform thickness is obtained.

  Here, if the inner peripheral surface of the blow mold is heated to a predetermined temperature, the tightly pressed preform pressed against the inner peripheral surface of the cavity in the final blow process is heated (heat treatment), so that heat resistance Can be obtained.

  In the mold clamping step, the mold clamping operation of the split mold can be performed continuously. Instead of this, it is also possible to intermittently perform the mold clamping operation such that the movement of the blow molding split mold is stopped during mold clamping and the movement is resumed after a certain time.

Next, in order to produce a flat container with a hanging tool, the blow molding method of the present invention,
After the setting step, a sandwiching step of sandwiching the bottom portion of the preform from both sides of the central axis with left and right hanging tool forming split molds;
A stretching step of stretching the preform by pulling up the hanging mold forming mold sandwiching the bottom in the direction of the central axis;
A hanging tool forming step of forming a part to be a hanging tool on the bottom by performing final mold clamping of the hanging tool forming mold that has been pulled up to a position that does not interfere with the blow molding tool,
The free blow step is performed in parallel with the stretching step, and in the free blow step, a body portion between the mouth portion of the preform and the bottom portion sandwiched by the split mold for hanging tool is free blown. It is characterized by doing.

  In the present invention, the preform is stretched in the direction of the central axis by sandwiching the bottom of the preform set in the blow mold split mold in an open state from both sides. Further, a hanging tool forming split mold is used as a member for clamping, and after stretching, the bottom portion sandwiched by the hanging tool forming split mold is press-molded so as to become a hanging tool. Therefore, it is possible to manufacture a flat container with a suspension using a general test tube-shaped preform without using a preform integrally formed with a portion such as an extending portion for forming a suspension. Is possible.

  Here, the stretching step may be performed so that the hanging tool split mold does not interfere with the blow molding split mold to be clamped. For example, the mold clamping operation may be started after the lifting operation by the hanging tool forming split mold is completed. Alternatively, the stretching process and the clamping process may be performed in parallel so that the lifting tool split mold does not interfere with the blow molding split mold (ie, the movement of the lifting tool split mold and the blow molding splitting). The mold may be moved in parallel.)

  According to the flat container blow molding method of the present invention, the preform set in the mold for blow molding in an open state is blown free by low-pressure blow air so as to be inflated in a uniform thickness state. Clamp the thick preform with a blow molding split mold so that it has a flat cross-sectional shape, and after the mold clamping, introduce high-pressure blow air into the preform for final blow molding ing. Therefore, a flat container having a uniform thickness can be manufactured at a low cost by a single-stage blowing process.

  Further, the bottom of the preform set in the blow molding split mold is sandwiched by the lifting tool split mold and the preform is stretched in the central axis direction. After stretching, the sandwiched bottom is stretched by the lifting mold split mold. The hanging tool is formed by pressing. Therefore, it is possible to manufacture a flat container in which a hanging tool is integrally formed using a preform having a general shape.

(A) is a top view of a flat container with a hanger, (b) is a side view showing a side shape of the flat container with a hanger together with a longitudinal sectional shape of the preform, and (c) is a bottom surface of the flat container with a hanger. FIG. It is explanatory drawing which shows the heating process of a preform. It is explanatory drawing which shows the setting process which set the preform to the split mold for blow molding. It is explanatory drawing which shows the clamping process which clamped the bottom part of the preform. It is explanatory drawing which shows the extending | stretching process which extends | stretches a preform in a center axis direction. It is explanatory drawing which shows the mold clamping process of the split mold for blow molding, a restraint blow process, and the last blow process. It is explanatory drawing which shows the change of the cross-sectional shape of the preform in the process shown in FIG.

  Below, the blow molding method of the flat container with a hanging tool which applied this invention with reference to drawings is demonstrated.

(Flat containers with preforms and preforms)
1A, 1B, and 1C are a plan view, a side view, and a bottom view showing an example of a flat container with a suspension that can be manufactured by the blow molding method of the present invention. In FIG. 1B, the longitudinal section of the preform used for manufacturing the flat container with the hanging tool is also indicated by an imaginary line.

  The illustrated flat container 1 with a hanging tool is a flat container for drip, for example, and is obtained by biaxially stretching blow-molding a general test tube-shaped preform 11. The preform 11 is an injection-molded product of PET or other thermoplastic resin that can be blow-molded. The cylindrical mouth portion 12 of the preform 11 remains as it is without being stretched and blown, and remains as the mouth portion 2 of the flat container 1.

  A cylindrical body 13 that is continuous with the mouth 12 of the preform 11 is biaxially stretched and blown in the direction of the central axis 11a and in the direction perpendicular to the central axis 11a to form the body 3 of the flat container. is doing. The body portion 3 has an oval side profile shape that is vertically long as a whole, and the cross-sectional shape in a direction perpendicular to the central axis thereof has a major axis in one direction and a minor axis in the direction perpendicular thereto. It has a flat elliptical shape with both ends of the major axis sharpened. For example, the minor axis is substantially the same as the outer diameter of the preform 11 and the major axis is approximately three times as long as the minor axis.

  A hemispherical bottom portion 14 at the lower end of the body portion of the preform 11 is press-molded to form a hanger 4 integrally formed with the bottom portion of the flat container 1. The hanging tool 4 has a structure in which a circular through hole 4b for hanging is formed at the center of a substantially rectangular plate-like piece 4a having a constant thickness.

(Blow molding procedure)
With reference to FIGS. 2-7, the procedure which manufactures the flat container 1 with a hanging tool from the preform 11 by blow molding is demonstrated. The procedure described below applies the present invention to the cold parison method in which the preform 11 is injection-molded in advance and heated to a temperature suitable for blow molding to perform blow molding. Of course, it can be similarly applied to a one-stage (hot parison method) molding method.

  First, as shown in FIG. 2, the preform 11 is carried on a carrier 21 in an inverted state, and is conveyed via a heating station 23 in which a heater 22 is disposed in this state. During the conveyance, the preform 11 is rotated around its central axis 11a, and the whole is uniformly heated to a temperature suitable for blow molding. Such a heating process is generally employed.

  Next, as shown in FIG. 3, the preform 11 heated to a temperature suitable for blow molding is set coaxially in the center of the left and right blow molding split dies 31, 32 in the mold open state (set). Process). Concave molding surfaces 31a and 32a capable of forming a cavity having an inner peripheral surface shape corresponding to the contour shape of the flat container 1 in the clamped state are formed on the opposing surfaces of the blow molding split dies 31 and 32. Yes. Right and left lifting tool forming split molds 33 and 34 are arranged right above the centers of the blow molding split molds 31 and 32, and can be opened and closed by a mold clamping mechanism (not shown). It can be moved up and down by the lifting mechanism. The hanging tool forming split molds 33 and 34 are press molds, and press forming surfaces 33a and 34a for press forming the hanging tool 4 are formed on the opposing surfaces thereof.

  Next, as shown in FIG. 4, after the preform 11 is set at the center of the left and right blow molding split molds 31 and 32 in the mold open state, the left and right hanging tool molding split molds 33 and 34 are molded. Descent in the open state. These molding surfaces 33a, 34a stop descending at a height position facing the bottom portion 14 of the preform 11 in the inverted posture, and the left and right lifting tool molding split dies 33, 34 are moved by a mold clamping mechanism (not shown). The bottom portion 14 of the preform 11 is closed and clamped with a predetermined force from both sides of the central axis 11a. The bottom portion 14 is sandwiched between the left and right lifting tool forming split dies 33 and 34 in a state of being crushed into a plate shape (a clamping step).

  Next, as shown in FIG. 5, the lifting tool forming split molds 33 and 34 that sandwich the bottom portion 14 of the preform 11 are pulled up in the state in the direction of the central axis 11 a by a lifting mechanism (not shown). As a result, the preform 11 is stretched in the direction of the central axis 11a (stretching step). Here, simultaneously with extending the preform 11 in the direction of the central axis 11 a, low-pressure blow air 41 is introduced into the preform 11 from below through a through-hole formed in the center of the carrier 21. The blow air 41 free blows the preform 11 in a direction perpendicular to the central axis 11a (free blow process). That is, the cylindrical body portion 13 between the mouth portion 12 of the preform 11 and the bottom portion 14 sandwiched by the hanging tool forming split molds 33 and 34 is restrained in a direction orthogonal to the central axis 11a. It swells in a cylindrical shape. In addition, since the extending | stretching force is acting in the up-down direction, when it sees from a side, it swells in the shape of a spindle as a whole.

  Here, it is desirable to manage the amount of blown air blown into the preform 11 in the free blow process. For example, it is desirable to fill the fixed tank 41A with blow air, supply blow air from the fixed tank, and introduce it into the preform 11. Alternatively, a certain amount of blow air stored in a quantitative container such as an air cylinder may be pushed out by a piston or the like and supplied into the preform 11. By supplying a certain amount of blow air into the preform 11, the preform 11 can be freely blown with high accuracy so as to have a target shape.

  The stretching of the preform 11 by the lifting tool forming split molds 33, 34 is such that the lower end surfaces 33b, 34b of the lifting tool forming split molds 33, 34 are the upper end jaw surfaces 31b of the left and right blow molding split molds 31, 32, This is done until the height position is 32b. When the lifting tool forming split molds 33 and 34 are raised to this height position, they will not interfere with the blow molding split molds 31 and 32 to be clamped. When the lifting tool forming molds 33 and 34 reach this height position, they are stopped and held at that position, and the mold clamping operation of the left and right blow molding molds 31 and 32 is started (mold clamping). Process).

  The mold clamping operation of the left and right blow molding split molds 31 and 32 can be performed in parallel with the lifting operation of the hanging tool molding split molds 33 and 34. In this case, the lifting tool forming molds 33 and 34 may be pulled up so as not to interfere with the blow molding molds 31 and 32 to be clamped.

  Even after the mold clamping operation is started, free blow of the body portion 13 of the preform 11 by the low-pressure blow air 41 is continuously performed. The process continues until the molding surfaces 31a and 32a of the left and right blow molding split molds 31 and 32 to be clamped come into contact with the preform 11 being blown free.

  Here, as shown in FIG. 7, at this time, the outer diameter L of the cylindrical preform cross-sectional shape orthogonal to the central axis 11a of the preform 11 is the mold molds 31 and 32 in the mold-clamped state. Is larger than the minor axis L1 of the cavity cross-sectional shape in the direction orthogonal to the central axis 11a in the cavity 35, and smaller than the major axis L2 of the cavity sectional shape. Further, the circumference of the preform cross-sectional shape is slightly shorter than the circumference of the cavity cross-sectional shape. In order to form this state, the pressure of low-pressure blow air, the supply amount, the lifting speed of the lifting tool forming split molds 33 and 34, the clamping speed of the blow molding split molds 31 and 32, etc. should be set. Good. Moreover, it is also possible to carry out by the intermittent operation | movement form which stops for a fixed time on the way, without performing the mold clamping of the blow molds 31 and 32 continuously.

  Thereafter, as shown in FIGS. 6 and 7, while the introduction of the low-pressure blow air 41 is continued, the body portion 13 (C) of the preform 11 expanded by the pre-blow is the left and right blow-molding split molds 31, 32. Is pressed so as to have a flat cross-sectional shape (restraint blow process). In these figures, the movement positions of the blow molding split mold 31 are indicated by reference numerals 31 (A) to 31 (E), and preforms at the respective positions 31 (C), 31 (D), and 31 (E). The shape of the eleven trunk portions 13 is indicated by reference numerals 13 (C), 13 (D), and 13 (E).

  As described above, in the restraining blow process in which the low pressure blow air is introduced into the preform while being flattened by the left and right blow molding dies 31, 32, the blow-off is a cylinder which is inflated into a cylindrical shape with a uniform thickness by free blow. The reform 11 is deformed as a whole so that it is crushed in the minor axis direction in the flat sectional shape of the flat container 1 of the final product and extruded in the major axis direction. Since the circumference of the preform 11 is slightly shorter than the circumference of the cavity of the flat cross section, the preform 11 is deformed into a flat cross section without substantially changing the wall thickness due to biaxial stretching. That is, it is formed into a flat cross-sectional shape with a uniform thickness obtained by free blow molding.

  As shown by the thick solid line in FIG. 7, after the mold clamping operation of the blow molding split molds 31 and 32 is completed, the high-pressure blow air 42 is introduced so that the outer peripheral surface 13a of the body portion 13 of the preform 11 becomes a cavity. The flat container 1 having a uniform thickness is obtained by being pressed against and closely adhered to the inner peripheral surfaces 35 (molding surfaces 31a and 32a) (final blowing step). Here, if the inner peripheral surface of the blow mold is heated to a predetermined temperature, the tightly pressed preform pressed against the inner peripheral surface of the cavity in the final blow process is heated (heat treatment), so that heat resistance Can be obtained. For example, by making the main body of the blow molds 31 and 32 heated by a cartridge heater or a heat medium, the finally formed flat container 1 can be heat treated to improve heat resistance.

  At the same time as this final blow step, the final mold clamping operation of the lifting tool forming split dies 33 and 34 is performed to press the bottom 14 sandwiched between them, and the suspension provided with the circular through hole 4b. The tool 4 is molded (hanger molding process).

  Through the above steps, the hanging tool 4 is integrally molded and a drip medical container having high heat resistance can be stably produced.

(Other embodiments)
The above example is a case where the present invention is applied to a flat container with a hanging tool. The method of the present invention can also be used in the manufacture of flat containers that are not equipped with a hanger. In this case, the split mold for hanging tool formation is unnecessary, and the flat container is blow-molded by the following process.
(1) introducing a preform heated to a predetermined temperature into a blow mold.
(2) Almost simultaneously with the start of closing the blow mold, low pressure blow air is introduced into the preform and free blow is started.
(3) After a certain period of time, the preform in the middle of the free blow starts to contact the surface of the blow mold for mold forming during the mold clamping. The preform diameter swelled in a circular shape at that time is larger than the short diameter of the blow molding split mold and smaller than the long diameter. In addition, the preform circumference during blowing is shorter than the circumference of the cavity formed by the blow molding split mold.
(4) Next, when the blow mold is continuously closed, the preform blown in a restrained state gradually approaches the final flat shape while being pressed. After the blow mold split mold is completely closed, high pressure blow air is introduced into the preform and shaped into a mold shape to obtain a finished product (flat container).

  The blow molding split mold may be continuously driven until the final mold clamping, or may be temporarily stopped in the middle of mold clamping and clamped after a certain time.

Next, the blow molding method of the present invention can also be used to manufacture a container with a hanging tool having a general cylindrical cross section that is not a flat cross section. In this case, the container with a hanging tool is blow-molded by the following process.
(A) After setting the preform after heating to the mold for blow molding in the mold open state, after sandwiching the tip of the preform with a bottom split mold (split mold for hanging tool formation) that forms the hanging part, While gradually raising the bottom split mold (i.e., stretching the preform), a low pressure blow air is introduced into the preform and free blow is performed. At this time, if the amount of the fine pressure blow air introduced into the preform is regulated, a result that the shape is stable and good can be obtained.
(B) After raising the bottom split mold to a predetermined position (or you may start closing the blow mold split mold while pulling up the bottom split mold) and then continue inside the preform while closing the blow mold split mold Then introduce the fine pressure blow air.
(C) When the blow mold split mold is finally closed, the bottom split mold that forms the hanger is also finally clamped to form the hanger.

  In addition, by making the blow mold split mold heated by a cartridge heater or a heat medium, the finally molded container with a hanging tool can be heat treated to improve heat resistance.

DESCRIPTION OF SYMBOLS 1 Flat container 2 Mouth part 3 Trunk part 4 Hanging tool 4a Plate-like piece 4b Circular through-hole 11 Preform 11a Center axis 12 Mouth part 13 Body part 14 Bottom part 22 Carrier 22 Heater 23 Heating station 31, 32 Blow molding split mold 31a , 32a Molding surfaces 33, 34 Splitting molds 33a, 34a Molding surface 35 Cavity 41 Low pressure blow air 41A Metering tank 42 High pressure blow air

Claims (5)

A blow molding method for producing a flat container having a flat cross-sectional shape with a cross-sectional shape orthogonal to the central axis of the preform by biaxially stretching and blowing a portion other than the mouth of the bottomed cylindrical preform,
A set step of setting the preform heated to a temperature capable of blow molding to the left and right blow mold split molds in an open state;
A mold clamping step for performing a mold clamping operation of the blow molding split mold;
Performed in parallel with the mold clamping step, a free blow step of free blowing the preform by introducing blow air into the preform from the mouth of the preform at a first pressure;
In the middle of the mold clamping process, the blow molding split mold is started from the time when the blow mold split mold comes into contact with the preform that has been blown freely. A constraining blow step for forming the preform so as to have the flat cross-sectional shape;
A final blow step, which is performed after completion of the mold clamping step and introduces blow air having a second pressure higher than the first pressure into the preform to form the preform into the flat container. And
At the end of the free blow step, the outer diameter of the preform cross-sectional shape orthogonal to the central axis of the preform is orthogonal to the central axis in the cavity defined by the blow mold split mold Free blow of the preform so as to be larger than the minor axis of the cavity sectional shape in the direction and smaller than the major axis of the cavity sectional shape, and the circumference of the preform sectional shape is shorter than the circumference of the cavity sectional shape. A method for blow-molding a flat container. In claim 1,
In the mold clamping step, the mold clamping operation of the split mold is performed continuously or intermittently. In claim 1 or 2,
After the setting step, a sandwiching step of sandwiching the bottom portion of the preform from both sides of the central axis with left and right hanging tool forming split molds;
A stretching step of stretching the preform by pulling up the hanging mold forming mold sandwiching the bottom in the direction of the central axis;
A hanging tool forming step of forming a part to be a hanging tool on the bottom by performing final mold clamping of the hanging tool forming mold that has been pulled up to a position that does not interfere with the blow molding tool,
The free blow step is performed in parallel with the stretching step, and in the free blow step, a body portion between the mouth portion of the preform and the bottom portion sandwiched by the split mold for hanging tool is free blown. A blow molding method for a flat container. In claim 3,
The clamping process is started after the stretching process is completed, or the stretching process and the clamping process are performed in parallel so that the lifting tool split mold does not interfere with the blow molding split mold. A method for blow molding a flat container. In any one of claims 1 to 4,
A blow molding method of a flat container, wherein the blow mold split mold is heated to a predetermined temperature in order to increase heat resistance by heat-treating the flat container in the final blowing step.

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