JPH03215017A - Blow molding - Google Patents

Abstract

PURPOSE:To prevent melt fracture, poor fusing or the like from developing by a method wherein vibration is given to at least either one of parison forming member and shaping mold so as to mold under the condition that the member or mold is resonated with the given vibration. CONSTITUTION:The predetermined vibration is generated with vibration generating devices 41 and 42 by driving an oscillator 50 so as to bring a die head 21 and a mandrel 22 or a parison forming member 20 under resonant state. On the other hand, since an extrusion orifice 25B is located at the loop of resonance when molding material fed from the nozzle 27 of an extruder to the molding material flow path 25 of a die head 21 is extruded through the extrusion orifice 25B in the form of parison 28, the fluidity of the molding material increases, resulting in realizing smooth forming of the parison 28. After the extrusion of the parison 28 having the predetermined shape, a mold 30 is clamped and, at the same time, ultrasonic vibration is given from a vibration generating device 43 to the mold 30 so as to bring the mold 30 under resonant state, resulting in favorably fusing the part, which is pinched by the mold 30, of the parison 28. Thus, melt fracture, poor fusing of the part pinched by the mold and the like are prevented from developing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a blow molding method for producing a hollow molded product such as a bottle from a molding material such as a polymeric material.

[Background technology]

BACKGROUND ART In recent years, a blow molding method for producing hollow containers such as bottles using molding materials such as plastics has been frequently used.

In this blow molding method, a tube-shaped preform called a parison is made from molding material using parison forming members such as a die and a mandrel, and after this parison is placed in a shaping mold, compressed air is injected into the parison. Inject or
Alternatively, the parison is expanded by reducing the pressure inside the mold, and the molding material is shaped into the shape of the mold to produce a hollow container.

[Problem to be solved by the invention]

However, the above-mentioned blow molding method has the problem of melt fracture, which is a defective phenomenon that occurs during extrusion of the parison, that is, a phenomenon that causes irregular irregularities on the surface of the molded product and loss of gloss. . Such defective phenomena begin to occur when the extrusion speed, that is, the production speed is increased, so conventionally, the production speed has been forced to be reduced.

On the other hand, in order to suppress the occurrence of melt fracture, there is also a means of increasing the resin temperature. However, in this case, drawdown caused by the parison elongating under its own weight became significant, making it difficult to obtain a molded product with a satisfactory shape.

Further, in order to suppress drawdown, resins with high extensional viscosity are sometimes used, but such resins have a problem in that it is difficult to achieve good fusion when the parison is sandwiched between molds.

An object of the present invention is to provide a blow molding method that can improve productivity without causing defects such as melt fracture or poor fusion.

[Means to solve the problem]

The present invention is a molding method in which, when performing hollow molding, molding is performed while applying vibration to at least one of a parison forming member and a shaping mold to cause resonance.

In the present invention, when applying vibration to the parison forming member and/or the forming die, the resonance abdomen due to the vibration substantially coincides with the position of the extrusion port of the parison forming member and/or the joint surface of the forming die. It is preferable to apply it so that

[Effect]

In the blow molding method according to the present invention, when molding the molding material,
Vibration is applied to cause the parison forming member and/or the shaping mold to resonate.

In a resonating balisong forming member, the fluidity of the molding material within the forming member increases significantly under the influence of the vibrations. Therefore, even if the extrusion speed is increased, the occurrence of melt fracture can be suppressed. Furthermore, since the fluidity is increased, sufficient extrusion is possible even if the temperature at which the molding material is melted is lowered, and as a result, drawdown is less likely to occur.

On the other hand, in the shaping mold that resonates, the portion of the parison sandwiched between the shaping molds is well fused due to the vibration.

During molding, if the resonant abdomen is approximately aligned with the position of the extrusion port of the parison forming member, the point where the resonance displacement waveform has the largest amplitude and vibrates most strongly can be used, and the fluidity of the molding material can be maximized. It can be increased efficiently.

In addition, if the resonance abdomen is approximately aligned with the position of the joint surface of the shaping mold, vibration energy can be most efficiently imparted to the molding material sandwiched between the joint surfaces, as described above, and the fusion can be promoted.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. Here, the same reference numerals are used for the same or equivalent components in each embodiment, and the description thereof will be omitted or simplified.

FIG. 1 shows an embodiment of a blow molding apparatus for carrying out the blow molding method of the present invention.

In the figure, the blow molding apparatus IO of the present embodiment includes a balisong forming member 20 that is fixedly held on a supporting member such as a frame (not shown), and a forming mold that is held movably in relation to the frame etc. It is equipped with 30.

The balisong forming member 20 includes a die head 2l and a mandrel 22. The die head 2l is formed in a cross shape with an intersecting portion displaced to one side, and a mandrel 22 is inserted into the vertically vertical center of the die head 2l so as to be movable up and down. This mandrel 2
2, an air blowing passage 23 is formed, and an air blowing port 24 is connected to the upper end of this passage 23, and a compressed air supply source (not shown) is connected to this air blowing hole 24. Further, the lower end of the passage 23 is an air outlet 23A.

In the die head 2l, a molding material flow path 25 is formed around the mandrel 22 and on the long side of the horizontal portion of the goo head 2l. One end of the horizontal part on the upstream side of this flow path 25 is an inlet 25A for the molding material, and a nozzle 27 of a single-screw or multi-screw extruder (not shown) is connected to this inlet 25A. can be supplied into the flow path 25. On the other hand, the lower vertical end of the flow path 25 on the downstream side is an annular extrusion port 25B formed between the outer periphery of the mandrel 2l, and this extrusion port 25B
The parison 28 is pushed out from there.

The tip of the vertical part of the goo head 2l has a mandrel 2.
A plurality of adjustment bolts 29 that come into contact with the mandrel 22 are screwed together, and by adjusting these adjustment bolts 29, the mandrel 22
The gap between the channels 25 formed around the can be adjusted.

The shaping mold 30 is composed of a pair of mold members 31.32 that can be opened and closed with each other, and these mold members 31.32
The mold 31B of the molded product is placed on the joint surfaces 31A and 32A of each other.
, 32B are carved in half.

Vibration generators 41, 42.4 are provided on the short end surface of the horizontal portion of the die head 2l, the upper end surface of the mandrel 22, and the end surface of one mold member 3l on the side opposite to the mold 31B, respectively.
The three vibrating parts 41A, 42A, and 43A are connected by a connecting member 45 such as a screw. These vibration generators 41
-43 are each coupled to the oscillator 50, and the oscillator 50
Vibration at a predetermined frequency is generated by a signal from the oscilloscope. Further, the vibration generator holder 42 connected to the mandrel 22 is supported by a movable plate 46.
By moving up and down, the tapered mandrel 22
The opening degree of the extrusion port 25B can be adjusted by the shape of the tip.

The oscillator 50 is, for example, of an automatic frequency tracking and automatic power control type, and is used during molding of the die head 21, mandrel 22, and shaping mold 30 (hereinafter sometimes referred to as die head 21 etc. to represent the king). , it is possible to follow changes in resonance frequency due to changes in state. At this time, the resonance frequency of the die head 21 etc. is designed and manufactured in advance to a frequency that can be tracked by the oscillator 50, so the oscillator 50 supplies the molding material from the nozzle 27 of the extruder to the die head 2l, and finally Goui head 21 until the molding material is extruded from the extrusion port 25B or from the support of the parison 28 in the mold 30 until the molding
The system constantly tracks slight changes in the resonant frequency due to moment-by-moment changes in the load applied to the device, etc., and the required power supply is set to supply the necessary amount (less than the maximum output) according to the moment-to-moment changes. has been done.

The vibrations applied to the die head 21 and the like by the vibration generators 41 to 43 have a frequency that causes the die head 2l and the like to resonate. Also, the die head 21 etc. The number of wavelengths to be resonated is n (n−
m/2, where m is a positive integer), so that the die head 21 and the like resonate at so-called n wavelengths. Here, n is preferably 3 or less in order to suppress vibration loss in the die head 21 and the like.

FIG. 2 shows displacement waveforms W when the goo head 2l and mandrel 22 resonate, and FIG. 3 shows displacement waveforms W when the forming mold 30 resonates for one wavelength. In these figures, the point where the displacement waveform W intersects and is not vibrating is defined as a resonance node P.

At this resonance node P, the nozzle 27
1 by means of attachment means such as screws, thereby minimizing vibration transmission to the nozzle 27 side and minimizing vibration fatigue of the attachment portion. At this time, in order to further suppress the transmission of vibration to the nozzle 27, it is necessary to
It is preferable to incorporate a cushioning material such as titanium alloy fibers into the contact portion with l.

In addition, the screwing position of the adjustment bolt 29 that adjusts the mounting position of the mandrel 22 with respect to the goo head 2l is also
In order to prevent loosening of the displacement waveform W, it is made to almost coincide with the node P of the displacement waveform W.

Further, it is preferable that the position where the Goo head 2l, the forming mold 30, etc. are held on a support member such as a frame by a holding member such as a bolt or flange (not shown) is also set at a node P of the displacement waveform W. By doing so, it is possible to prevent vibrations from being transmitted to the outside at the holding portion and damage caused by vibration fatigue.

On the other hand, in order to transmit the vibrations generated by the vibration generators 41 to 43 to the die head 21 etc. with high efficiency and easily, the contact portion between the vibration generators 41 to 43 and the die head 21 etc. should be connected to the resonating state of the guide head 2l. It is preferable to match the part where the oscillator etc. vibrate with the largest amplitude, that is, the resonance abdomen Q.

In addition, the molding material extrusion port 25B in the die head 2l
And the point where the vibration is strongest at the resonance belly Q, that is, the farthest part of the displacement waveform W, so as to coincide with the joint surfaces 31A, 32A of both mold members 31, 32 in the shaping mold 3o. It is preferable to set This improves the fluidity of the molding material at the extrusion port 25B, thereby reducing the occurrence of melt fractures. Also,
The part of the parison 28 sandwiched between the joint surfaces 31A and 32A of both mold members 31 and 32 can be well fused.

Furthermore, as is clear from FIGS. 2 and 3, the wavelength between the resonant node P and the abdomen Q is 1/4.

In the vertically extending portion of the die head 2l,
Vibration direction conversion mechanism called LL converter (not shown)
Due to the action of this L-L converter, vibrations are transmitted even in a direction where the direction of vibration transmission is changed by 90 degrees at that part. Therefore, the vibration generator 4l
The transmission direction of the vibration oscillation applied to the die head 2l is perpendicular to the extrusion direction of the molding material extruded from the extrusion port 25B.
Due to the 0 degree conversion, the actual vibration transmission direction at the extrusion port 25B is the same as the extrusion direction of the molding material.

In addition, the vibration direction conversion mechanism is not limited to the L-L converter described above, but when ultrasonic vibration is used, the conventionally used L-R converter, L-L-L converter, etc. 21
It can also be equipped with At this time, die head 2
The extrusion direction of the molding material extruded from the extrusion port 25B and the direction of vibration transmitted through the extrusion port 25B are not limited. However, when dispersing and stirring the molding material by vibration at the extrusion port 25B, it is preferable that the extrusion direction and the vibration direction are perpendicular.

The method of generating vibration in the vibration generators 41 to 43 is not particularly limited, but includes, for example, an ultrasonic vibration method using an ultrasonic vibrator, a mechanical method such as a cam crank method, an unbalanced weight method, etc. An electromagnetic electric system such as an electrodynamic vibrator, an electrohydraulic system, or the like can be used.

In addition, the frequency of vibration is from several tens of Hz to several tens of MHz.
A range of z can be used. At this time, the vibration frequency is set at 10KHz to 10KHz in order to obtain the vibration effect in a short time and to suppress excessive heat generation of the molding material.
z ultrasound is preferred.

Further, as the vibration mode, other than longitudinal vibration, known vibration modes such as lateral vibration, torsional vibration, radial vibration, and flexural vibration can be used.

It is also possible to incorporate a vibration transmitter for transmitting vibration between the die head 21 etc. and the vibration generators 41 to 43, and if the shape of the vibration transmitter is appropriately selected, the vibration generators 41 to 43 can It becomes possible to easily increase or decrease the amplitude of the generated vibration. At this time, the number of vibration generators 41 to 43 coupled to the Goo head 21 etc. or the number of vibration transmitters via them is not particularly limited, but when a plurality of them are coupled, the timing of the vibrations may be adjusted. , die head 2
It is necessary to prevent the 1st class resonance state from being disturbed.

Materials for forming the die head 21, mandrel 22, shaping mold 30, that is, the die head 21, etc. include metal materials conventionally used for extrusion molding dies, etc.
Various materials such as ceramics and graphite can be used, but among these materials, the vibration transmission loss of the vibration generators 41 to 43 at the molding temperature is small, and even if the vibration amplitude is increased, fatigue is small. It is preferable to use materials such as titanium alloy, K-monel, phosphor bronze, duralumin, and graphite.

In addition, the surface of the die head 21 etc. may be subjected to various plating or coating treatments, or even graining, to improve wear resistance and corrosion resistance, or to lower the coefficient of friction with the molding material, as necessary. Processing such as processing may also be performed. Furthermore, the goo head 2l can be divided into three or more parts, but in this case, the divided surfaces should be in surface contact as much as possible or in order to improve the transmission of vibrations by the vibration generators 41 to 43. It is preferable to position it near the abdomen Q of the patient.

In addition, when the die head 21 etc. are composed of a plurality of members,
The die head 21 and the like may be made of the same material or may be made of different materials.

Furthermore, when heating the die head 2l and the mold 30, when the die head 21 or the mold 30 is resonating, the die head 21 or the mold 30 is heated.
Most parts of the heater vibrate, so when a conventional plate-shaped heater is installed, the wiring inside the plate-shaped heater may be broken due to the vibration. Therefore, for heating the goo head 21 or the mold 30, it is preferable to use a far-infrared heater that can heat the goo head 2l or the mold 30 without coming into contact with it. In this case, make sure that the heater comes into contact only with the non-vibrating part of the die head 2l or the mold 30 that is in a resonant state, that is, the resonant node P, and use a screw or the like to connect the die head 2l or The mold 30 and the far-infrared heater may be fixed.

Next, the operation of this embodiment configured as above will be explained.

The oscillator 50 is driven to generate predetermined vibrations from the vibration generators 41 and 42, and the die head 2l and mandrel 22
That is, the parison forming member 20 is excited at a resonant frequency,
The parison forming member 20 is brought into a resonant state.

On the other hand, from the nozzle 27 of the extruder (not shown)
The molding material is supplied to the molding material flow path 25 of l, and the extrusion port 2
Extrude parison 28 from 5B.

At this time, as shown in FIG. 2, the extrusion port 25B has a resonant abdomen Q, so the fluidity of the molding material is increased, and the parison 28 is molded very smoothly. In addition, when extruding the parison 28, the shaping mold 3
Each mold member 31, 32 of No. 0 is in an open state.

After the balisong 28 is extruded into a predetermined shape, the mold 30 is clamped and ultrasonic vibrations are applied to the mold 30 from the vibration generator 43 to bring it into a resonant state. Due to this resonance, the portion of the parison 28 supported by the mold 30 is well fused.

In addition, after the mold clamping, the air outlet 23 of the mandrel 22
Air is blown into the parison 28 from A, and the parison 28
Mold 31B of mold 30. Shaping is performed by bringing it into close contact with 32B. After this, the mold is opened to obtain a molded product.

According to this embodiment as described above, there are the following effects.

That is, since the vibrations of the vibration generators 41 to 43 are transmitted as resonance to the die head 2l, mandrel 22, and mold 23, that is, the die head 21, etc., it is possible to efficiently transmit the vibrations to the die head 21, etc. can. In addition, the vibration generating units 41A to 43 of the vibration generators 4l to 43
Since the abdomen Q of the resonance displacement waveform W is set to be located at the joint surface between A and the die head/sod 2l, etc., the vibration effects of the vibration generators 41 to 43 can be maximized. The fluidity or fusion properties of the molding material can be improved.

At this time, as shown in FIG. 2, if the abdomen Q of the displacement waveform W is located at the position of the extrusion port 25B, the resonance within the parison forming member 20 as a whole will occur, and the The fluidity of the molding material can be further improved. Therefore, even if the extrusion speed is significantly increased compared to conventional molding techniques, melt fracture does not occur, and productivity can be significantly improved. Furthermore, since the fluidity is improved, extrusion is possible even if the temperature of the molding material is lower than before, and drawdown is less likely to occur.

On the other hand, as shown in FIG.
A. By locating the abdomen Q of the displacement waveform W at the position 32A, the portion of the parison 28 held between the molds 30 can be better fused.

In addition, if the attachment position of the nozzle 27 and adjustment bolt 29 to the die head 2l, and furthermore the connection position of the die head/rod 2l etc. and a holding member (not shown) are set to the node P of the resonance displacement waveform W, the connection part Not only can damage to the engine be reduced, but also the leakage of vibrations to the outside can be reduced.

FIG. 4 shows a parison forming member 20 used in the present invention.
Another example is shown.

In this embodiment, the die head 2l constituting the parison forming member 20 extends only in the horizontal direction, and an extrusion port 25B for the molding material is formed on the lower surface of the die head 2l.

Therefore, in this embodiment, the vibration transmission direction near the extrusion port 25B in the die head 20 is perpendicular to the extrusion direction of the molding material.

Also in this embodiment, substantially the same functions and effects as those of the parison forming member 20 in the previous embodiment can be achieved.

FIG. 5 shows a parison forming member 20 used in the present invention.
Still other embodiments are shown.

In this embodiment, the die head 21 is divided into two parts, a stationary part 21A and a resonant part 21B equipped with an L-L converter.
Only B is resonated by the vibration generator 4l, and the stationary part 21
A is not resonated.

At this time, the position of the joint between the stationary part 21A and the resonant part 21B is preferably set at a resonance node.

In this embodiment as well, almost the same functions and effects as in the embodiment shown in FIG. There is an effect that it can be done.

FIG. 6 shows another embodiment of the shaping mold 30 used in the present invention.

In the mold 30 of this embodiment, one mold member 3l has a linear shape similar to the embodiment of FIG. 1, while the other mold member 32 has a cross shape. A vibrating section 43A of a vibration generator 43 is connected to the upper end surface of this cross-shaped mold member 32 by a connecting member 45.

The mold member 32 in this embodiment is equipped with a vibration direction conversion mechanism, and the joint surface 31 of both mold members 3l, 32 is
A. The direction of vibration transmission at 32A is converted by 90 degrees from the direction of vibration transmission emitted from vibrator 43A.

Furthermore, the bonding surfaces 3IA and 32A are used as resonant regions, so that vibrations can be transmitted efficiently.

Also in this embodiment, substantially the same functions and effects as those of the mold 30 in the embodiment shown in FIG. 1 can be achieved.

In addition, in the present invention, moldable molding materials include:
Examples include organic materials such as plastics, rubber, and elastomer pitch, inorganic materials such as inorganic polymers, ceramics, metals, and glass, other foods, and mixed materials thereof.

Further, blow molding in the present invention includes extrusion blow molding, injection blow molding, stretch blow molding, and multilayer blow molding.

Moreover, a cross head, a spider head, an accumulator head, etc. can be applied to the die head 2l.

Furthermore, in the above embodiment, the parison forming member 20 was explained as an extrusion method including a die head 2l and a mandrel 22, but this is usually an injection method comprising a core mold, a neck mold, a cavity mold, etc. The shaping mold may also be an injection method consisting of a core mold, a neck mold, a blow mold, etc. instead of the mold 30 in the extrusion method. Further, the shaping method is not limited to the method of pressurizing the inside of the parison 28, but may also be a method of reducing the pressure inside the mold 30.

(Experimental Example) Hereinafter, the results of an experiment conducted to confirm the effects of the above-mentioned example will be explained while comparing with a comparative example.

-3! Using the blow molding apparatus lO shown in Fig. 1, the die head 2l
The diameter of the extrusion port 25B was set to 30 mm, and the gap was set to 1.

The oscillator 50 is an ultrasonic oscillator with a fundamental frequency of 19.15 KHz (SONOPET manufactured by Seidensha Electronics Industry Co., Ltd.
1200-8), both the gooey head 2l and the mandrel 22 were caused to resonate so as to have a vibration displacement waveform W shown in FIG. 2, and the amplitude was set to 11 μm.

As the molding material, linear low density polyethylene (LLDPE, manufactured by Idemitsu Petrochemical Co., Ltd., 0154H) was used.

The molding conditions were 170° C. for both the molding material temperature and the die head temperature.

Molding was performed under the above-mentioned conditions while causing the die head 2l and mandrel 22 to resonate with ultrasonic waves, and the critical extrusion speed at which melt fracture occurred was determined.

Experimental example l except that no ultrasonic waves are applied to the mandrel 22
The experiment was conducted under the same conditions.

Experimental example 1 except that no ultrasonic waves were applied to the die head 2l.
The experiment was conducted under the same conditions.

The results of Experimental Examples 1 to 3 are shown in Table-1.

ht- Except for stopping the ultrasonic oscillation. The experiment was conducted under the same conditions.

The results of Comparative Example 1 are shown in Table 1l.

Experimental Example 1 and Table 1 According to Experimental Examples 1 to 3, if resonance vibration is applied to at least one of the goo head 2l and the mandrel 22 constituting the parison forming member 20, a critical temperature at which melt fracture occurs is generated. It can be seen that the extrusion speed is significantly increased compared to Comparative Example 1 in which no vibration is applied. In this case, the extrusion speed can be made the highest when vibration is applied to both the die head 2l and the mandrel 22, and then the amount of increase in extrusion speed decreases in the order of only the die head 2l and only the mandrel 22.

-1t4 The experiment was conducted under the same conditions as Experimental Example 1, except that the extrusion speed was 5 kg/m and the material temperature was changed by controlling the die head temperature. At this time, the material temperature (# die head temperature) at which melt fracture does not occur and the drawdown state at that time were investigated.

Experimental example 4 except that no ultrasonic waves were applied to the first J1 raw i-mandrel 22.
The experiment was conducted under the same conditions.

The results of Experimental Example 4.5 are shown in Table-2.

Step 4 An experiment was conducted under the same conditions as Experimental Example 4, except that no ultrasonic waves were applied to either the die head 21 or the mandrel 22.

The results of Comparative Example 2 are shown in Table-2.

(The following is a blank space) Table 2 According to Experimental Example 4.5, it can be seen that melt fracture does not occur even if the material temperature is significantly lowered compared to Comparative Example 2. As a result, the state of drawdown becomes very small, and it is also possible to save energy.

1st ffi The forming mold 30 shown in Fig. 1 was heated to 50°C, and the parison 28 formed and extruded under the conditions of Experimental Example 5 was sandwiched while resonating with ultrasonic waves. The thickness of the fused portion was examined. Balison 2 at 20am above the fusion part
The wall thickness of 8 is 1. It was 08m.

The results of Experimental Example 6 are shown in Table-3.

One! The experiment was conducted under the same conditions as in 6 except that no ultrasonic waves were applied to the mold 30.

The results of Comparative Example 3 are shown in Table 3.

Experimental Example According to Experimental Example 6, the thickness of the fused portion sandwiched between the molds 30 was approximately four times thicker than in Comparative Example 3, indicating that sufficient fusion was achieved.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to increase the extrusion speed without causing melt fracture or poor fusion of the mold clamping portion, and there is an effect that productivity can be improved.

[Brief explanation of drawings]

FIG. 1 is a front view showing a schematic configuration of an embodiment of a blow molding apparatus for carrying out the method of the present invention, with main parts cut away, and FIGS. 2 and 3 show the parison forming member and mold shown in FIG. 1, respectively. FIGS. 4 and 5 are explanatory diagrams of displacement waveforms and wavelengths during resonance, respectively, and are cross-sectional views of essential parts showing other different embodiments of parison forming members used in blow molding equipment that implements the method of the present invention. FIG. 6 is a cross-sectional front view showing another embodiment of a mold used in a blow molding apparatus for carrying out the method of the present invention. lO...Blow molding, 20...Parison forming member, 2
l... Die head, 21A... Fixed part, 21B...
- Resonance part, 22... Mandrel, 23... Air blowing passage, 23A... Air blowing port, 25... Molding material flow path, 25B... Extrusion port, 27... Nozzle, 28 ...Parison, 30...Shaping mold, 31.3
2... Mold member, 31A. 32A...Joint surface, 41
, 42.43... Vibration generator, 50... Oscillator,
W...Displacement waveform, P...Node, Q...Abdomen.

Claims (2)

[Claims] (1) In a hollow molding method in which a parison is formed by a parison forming member and then shaped by a shaping mold, the hollow molding method is characterized in that molding is performed while causing the parison forming member and/or the shaping mold to resonate by vibration. Molding method. (2) The blow molding method according to claim 1, characterized in that the molding is performed while resonating so that the resonance abdomen substantially coincides with the position of the extrusion port of the parison forming member and/or the joint surface of the mold.