JP2601733B2 - Blow molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding method for forming a hollow body and a method for controlling the thickness of a parison.

[0002]

2. Description of the Related Art Conventional blow molding is generally performed as follows. As shown in FIG. 4, the die 10 is provided with a die slip 14 at the lower end of the housing 12,
The plunger 1 is formed by the core 16 and the die slip 14.
8 forms a die gap 24 for extruding the molten resin 20 to form the parison 22. Core 16
Is axially movably inserted into the housing 12, is connected to the parison control cylinder 26, and is controlled in position by the core position setting device 28 via the parison control cylinder 26 to maintain the die gap 24 at a predetermined value. To control the thickness of the parison 22,
The thickness of the molded product 32 blow-molded in the mold 30 is set to a predetermined value.

However, as described above, the die gap 24
Is controlled to be constant, the characteristics of the draw-down (droop due to its own weight) of the parison 22 change due to ambient temperature changes, disturbance such as waiting time, and the wall thickness easily changes. For this reason, a method has been proposed in which a thickness sensor is attached to the mold 30 to detect the thickness of the molded product 32 and the die gap 24 is controlled so that the thickness of the molded product 32 becomes a predetermined value (actually). JP-A-64-9726).

In conventional blow molding, FIG.
As shown in the figure, a platen 34 for attaching the mold 30;
36, a light emitting unit 38 such as a light emitting diode and a light receiving unit 40 such as a photoelectric tube are provided. A difference between a time when the light receiving unit 40 detects the parison 22 and a time when the parison 22 starts emitting light is obtained. Controlling the gap 24,
There is a method of keeping the length of the parison 22 constant.

[0005]

[Problems to be Solved by the Invention]
In the method described in Japanese Patent No. 9726, since the length of the parison 22 is not taken into account, the length of the parison 22 varies depending on the drawdown state, and the burr generated by blow molding cannot be controlled. It is difficult to improve the molding efficiency due to the increase in generation. In addition, the actual opening 64-972
In the method of controlling the die gap 24 described in Japanese Patent Application Laid-Open No. 6-204, it is difficult to arbitrarily change the position of the thickness sensor because the thickness sensor is disposed in the mold 30, and the thickness of a part of the molded product 32 is reduced. Since the die gap 24 is controlled by detecting the thickness, the overall thickness of the molded article 32 cannot be grasped, and it is difficult to determine whether the molded article 32 has an appropriate thickness. is there.

[0006] The method shown in FIG.
Control the length of the die gap 2
4 controls the parison length, so that the molded product 32
Is not considered, and it is difficult to control the thickness. Moreover, in any of the methods, since the operation of the mold clamping is constant regardless of the state of the drawdown of the parison, when the drawdown of the parison is large,
By the time mold clamping is completed, the parison length increases, the amount of burrs generated on the molded product increases, material loss increases, and molding efficiency deteriorates.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and provides a blow molding method capable of keeping the length of a parison to be blow-molded constant and reducing the occurrence of burrs on a molded product. Is intended to
It is still another object of the present invention to provide a method for controlling the thickness of a parison which can easily obtain a molded product having an appropriate thickness.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, a first aspect of the blow molding method according to the present invention is described.
Detects that the parison ejected from the die has reached the first predetermined length, starts mold closing, and compares the time at which the parison is detected with the time at which the parison has been ejected. If the parison drawdown is large or the amount of resin supplied to the die is large, and the time required to reach the first predetermined length of the parison is earlier than at the end of the parison injection, the swell ratio of the parison is changed. To increase the parison, the injection speed of the parison is increased, and the amount of resin (a weighing value) supplied to the die is reduced to speed up the end of the parison injection.

On the other hand, the drawdown of the parison is small,
Alternatively, when the time at which the parison reaches the first predetermined length is a predetermined time after the end of the parison injection because the resin measurement value is small, the injection speed of the parison is reduced, and the resin measurement value is increased. Then, the end of the parison injection is delayed so that the time from the end of the parison injection to the detection of the parison reaching the first predetermined length is within a predetermined time.

Further, when the time required for the parison to reach the second predetermined length from the first predetermined length is within a predetermined reference time because the drawdown of the parison is large, the injection speed of the parison is increased. , The mold clamping speed of the mold is increased, the length of the parison to be molded is kept constant, and the occurrence of burrs on the molded product is reduced.

Further, the second aspect of the blow molding method according to the present invention is as follows.
If the time at which the parison reaches the first predetermined length is earlier than the end of the parison injection, the injection speed of the parison is increased so that the swell ratio of the parison is increased, and the resin supplied to the die is increased. Even if the weighing value is reduced and the end of the parison injection is advanced by a predetermined amount, or the time required for the parison to reach the second predetermined length from the first predetermined length is within a predetermined reference time. When the parison injection speed is increased to a predetermined speed, the parison drawdown is large, and after the parison is formed in a predetermined number of trials, the parison has a first predetermined length. When the parison is detected earlier than the end of the parison injection, or when the time required for the parison to reach the second predetermined length from the first predetermined length is within a predetermined reference time. , By such as lowering the temperature of the die,
The temperature of the resin forming the parison is reduced, the drawdown of the parison is reduced, the parison length is kept constant, and the burr of the molded product is reduced.

Further, the method for controlling the thickness of a parison according to the present invention comprises detecting the thickness of a molded product taken out of a mold by blow molding, comparing the detected value with a reference thickness, and detecting the detected molding thickness. If the product thickness is larger than the reference thickness, reduce the die gap for injecting the parison.If the detected product thickness is smaller than the reference thickness, increase the die gap, and Make it thick.

[0013] This makes it possible to easily detect the thickness of the molded product taken out of the mold at an arbitrary position, control the thickness of the parison in consideration of the overall thickness of the molded product, and reduce the thickness of the parison. A molded product (product) with small variation can be easily obtained. When detecting the thickness of the molded product taken out of the mold, it is preferable to simultaneously detect the thickness at a plurality of locations using a plurality of detectors.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a blow molding method and a parison thickness control method according to the present invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals are given to portions corresponding to the portions described in the above-described conventional technology, and description thereof is omitted. FIG. 2 is a block diagram showing the configuration of a blow molding machine that embodies the present invention.

In FIG. 2, one of a pair of dies 30a and 30b (for example,
0b), a first light emitting unit 5 such as a light emitting diode is provided.
0 is provided, and a first light receiving unit 52 such as a photoelectric tube is provided at a position corresponding to the light emitting unit 50 in the other mold 30a. The light emitting unit 50 and the light receiving unit 52 are
2 constitutes a first parison sensor for detecting that the length has reached a first predetermined length, for example, molds 30a and 30b
Are arranged on the lower surface of the cavity.

The platen 3 below the first light emitting section 50
6, a second light emitting unit 54 is provided, and the first light receiving unit 5 is provided.
A second light receiving unit 56 is provided on the platen 34 below the second light receiving unit 54 in correspondence with the light emitting unit 54. The light emitting unit 54 and the light receiving unit 56 constitute a second parison sensor that detects that the parison 22 has reached the second predetermined length.
The distance between the first parison sensor and the second parison sensor differs depending on the type of the resin forming the parison 22, the size of the molded product (the molds 30a and 30b), and the like.

The light receiving sections 52 and 56 are connected to a control device 60 which will be described in detail later. When the lower end of the parison 22 falls to the position where the light receiving section is provided, this is detected and the detection signal is controlled. Input to the device 60. A thickness sensor 62 for detecting the thickness of the molded article 32 is connected to the control device 60, and a detection signal is input from the thickness sensor 62.

The thickness sensor 62 is constituted by, for example, an ultrasonic thickness gauge, and is attached to each of the brackets 64 and 66 disposed on both sides of the molded product 32 so that a plurality of the thickness sensors 62 can be adjusted. is there. And bracket 6
Reference numerals 4 and 66 denote actuators 6 such as cylinders, respectively.
8 and 69, and actuators 68 and 69
, The thickness sensors 62 can be brought into contact with the molded product 32 just taken out of the dies 30a and 30b by the clamp device 70, and can be separated therefrom.

The control device 60 receives a detection signal from each sensor and performs a predetermined calculation to control the clamping of the dies 30a and 30b, the measurement of the molten resin 20, the injection speed of the parison 22, and the like. ing. That is, the control device 60 includes platens 34, 36 to which the molds 30a, 30b are fixed.
A mold clamping control section 72 for controlling the mold clamping cylinders 71a and 71b having attached thereto, the molten resin 20 supplied to the die 10
And a parison control cylinder control unit 74 that controls the parison control cylinder 26 connected to the core 16 that changes the die gap 24, and outputs a control signal to these units.

The control device 60 further includes an injection cylinder control unit 76 for controlling the driving of the plunger 18 for injecting the molten resin 20 supplied to the die 10,
Is maintained at a predetermined temperature, a heater control section 78 for controlling a heater (not shown) provided on the die 10 is connected, and a control signal is also output to these control sections. The injection cylinder control unit 76 is provided with an injection sensor, detects the injection speed of the molten resin 20 (parison 22) and the end of injection, and outputs a detection signal to the control device 60.
It is possible to input to. Further, a first light receiving unit 52 is connected to the mold clamping control unit 72, and receives a mold closing start signal of the molds 30 a and 30 b from the first light receiving unit 52.

As shown in FIG. 3, the control device 60 comprises a parison formation control unit 80 and a die gap control unit 100. The parison formation control unit 80 controls the clock 8
2 and a parison detection time calculator 84 connected to the clock 82;
It has a weighing correction circuit 86, an injection correction circuit 88, and a temperature correction circuit 90 connected to the output side of the parison detection time calculator 84.

The parison detection time calculator 84 is connected to the injection sensor 92 provided in the injection cylinder control unit 76 and the first light receiving unit 52 for detecting that the parison 22 has reached the first predetermined length. In response to signals from these sensors, the time from the end of injection of the parison 22 to the detection of the lower end of the parison 22 by the light receiving section 52 is read from the clock 82, and the time is read from the clock 82 and the weighing correction circuit 86 and the injection correction circuit. 8
8 and output. The weighing correction circuit 86 and the injection correction circuit 88 respectively calculate the weighing value of the molten resin 20 and the parison 2 in accordance with the output signal of the parison detection time calculator 84.
A correction value with the injection speed of No. 2 is obtained, and a correction signal is output to the metering control unit 75 and the injection cylinder control unit. Also, the parison detection time calculator 84 makes these corrections,
If the molding of the parison 22 does not satisfy the predetermined condition, a signal is output to the temperature correction circuit 90, and the temperature correction circuit 90 outputs a correction signal for lowering the temperature of the die 10 (die slip 14) to the heater control unit. 78.

The parison formation controller 80 further includes a parison fall time calculator 94, a reference fall time setter 96,
A mold clamping correction circuit 98 is provided. Reference fall time setting device 9
6, the parison 22 includes a first light receiving unit 52 and a second light receiving unit 5;
The reference time required to descend between 6 and 6 is set, and the set reference time is sent to the parison falling time calculator 94. The parison fall time calculator 94 receives the detection signals of the respective light receiving units 52 and 56,
From these detection signals, the parison 22 determines whether the light receiving sections 52, 5
The time required for descending between 6 is determined, and this time is compared with the reference time set in the reference fall time setting device 96,
The comparison result is sent to the injection correction circuit 88 and the mold clamping correction circuit 98. When receiving the signal from the parison fall time calculator 94, the injection correcting circuit 88 and the mold closing correcting circuit 98 generate a signal for correcting the injection speed of the parison 22 and the speed of the mold closing,
The signals are output to the injection cylinder control unit 76 and the mold clamping control unit 72, respectively.

On the other hand, the die gap control unit 100 includes:
A thickness comparison circuit 102, a reference thickness setting circuit 104, and a gap correction circuit 106 are provided. Thickness comparison circuit 102
Receives the output signal of the thickness sensor 62,
Is compared with the reference thickness set in the reference thickness setting circuit 104, and the result is compared with the gap correction circuit 1
06. Then, the gap correction circuit 106
A signal for correcting the die gap 24 is output to the parison control cylinder control unit 74 based on the comparison result of the thickness comparison circuit 102.

The control unit 60 is provided with an input unit such as a keyboard (not shown) and a storage unit such as a memory (not shown).
0 weighing value, die gap 24, molds 30a, 30b
, A correction value output from each correction circuit, a data table for correction, and the like can be input and set. When the operator finishes inputting and setting the initial values and presses the start button, the metering control unit 75 supplies a predetermined amount of the molten resin 20 to the die 10, and the injection cylinder control unit 76 operates the plunger 18. The molten resin 20 is discharged from the die gap 24, and the injection of the parison 22 is started (Step 110 in FIG. 1).

An injection sensor 92 provided in the injection cylinder control section 76 detects the end of injection of the parison 22 from the amount of hydraulic oil for operating the plunger 18 and the stroke amount of the plunger 18, and outputs an injection end signal to the control device. It is sent to the parison detection time calculator 84 of 60. When the lower end of the parison 22 ejected from the die slip 14 reaches between the first light emitting unit 50 and the first light receiving unit 52 having the first predetermined length, the light receiving unit 52 detects the parison 22. The detection signal is input to the mold clamping control unit 72 and the parison detection time calculator 84 and the parison fall time calculator 94 of the control device 60. When receiving the detection signal from the light receiving unit 52, the mold clamping control unit 72 operates the mold clamping cylinders 71a and 71b to start closing the molds 30a and 30b.

On the other hand, when a detection signal is input from the light receiving section 52, the parison detection time calculator 84 checks whether or not the injection sensor 92 provided in the injection cylinder control section 76 has output the end of injection (step S1). 112). When the parison detection time calculator 84 receives the detection signal from the light receiving unit 52 before receiving the injection end signal from the injection sensor 92,
A signal to that effect is sent to the weighing correction circuit 86 and the injection correction circuit 88.

The metering control unit 75 and the injection correction circuit 88, which have received the signal from the parison detection time calculator 84, output corrected values of the measured value and the injection speed as shown in step 114, and the injection of the parison 22 is completed. Hurry, parison 22
Is set to a predetermined length. That is, when the parison 22 reaches the first predetermined length before the end of the injection of the parison 22 and is detected by the light receiving unit 52, the weighing correction circuit 86 determines that the amount of the molten resin 20 supplied to the die 10 is large. A correction signal for reducing the measured value of the resin is sent to the metering control unit 75 to reduce the amount of the molten resin 20 to be supplied to the die 10 next time, so that the injection of the parison 22 is completed earlier, and the parison length is reduced. Adjust.

The injection correction circuit 88 includes the parison 22
If the lower end of the parison 22 is detected by the light receiving unit 52 before the end of the injection of the parison 22, the drawdown of the parison 22 is assumed to be large, the injection speed of the parison 22 is increased to shorten the injection time, and the thickness of the parison 22 is reduced. The parison length is adjusted by increasing the thickness to reduce the drawdown and making the injection of the parison 22 faster.

The correction to accelerate the end of injection based on the measured value and the injection speed is previously stored in a memory (not shown) of the control device 60 in accordance with the difference between the detection time of the light receiving section 52 and the injection end time. It is advisable to store a quantity table and read the correction values from the table. Further, either the correction of the measurement value or the correction of the injection speed may be performed. The correction to accelerate the end of the injection is to make the next injection time 3 to 10% shorter than the current parison injection time.

When the weighing value and the injection speed are corrected by the weighing correction circuit 86 and the injection correction circuit 88, the controller 60 controls the trial injection of the parison 22 as in step 116. Then, the control device 60 determines whether the time when the parison 22 ejected from the die slip 14 reaches the position of the first light receiving unit 52 having the first predetermined length is after the end of the ejection of the parison 22. (Step 11
8) If the detection time of the light receiving unit 52 is after the end of the injection,
Proceeding to step 142, the injection of the next shot is started.

However, if the detection time of the light receiving section 52 is before the end of the injection of the parison 22 by the test injection, the control device 60 proceeds to step 120 from step 118, and performs the test injection a predetermined number of times (for example, 10 times). ) Is determined, and if the predetermined number has not been reached, the routine returns to step 116 to perform the next trial injection. If the time of detection of the light receiving unit 52 is before the end of injection even though the test injection has been performed a predetermined number of times, the parison detection time calculator 84 outputs a signal to the temperature correction circuit 90, The correction temperature is read from a previously determined table so that the resin temperature is lowered according to the time difference, and a correction signal for lowering the temperature by, for example, 1 to 3 degrees is output to the heater control unit 78 (step 122), and the process proceeds to step 142. When the temperature is corrected, the test injection can be performed again.

In step 112, the metering correction circuit 86 and the injection correction circuit 88 detect the first light receiving section 52 after the injection sensor 92 outputs an injection end signal from the signal received from the parison detection time calculator 84. If it is determined that the signal has been output, the process proceeds to step 124. That is, the weighing correction circuit 86 and the injection correction circuit 88 determine the time from receiving the parison injection end signal obtained by the parison detection time calculator 84 until the detection signal of the light receiving unit 52 is input.
It is determined whether or not the time is within a predetermined time (for example, 10 seconds). If the time difference obtained by the parison detection time calculator 84 exceeds a predetermined time, the process proceeds to step 12.
Proceeding to 6, the measurement value of the resin is increased, the injection speed of the parison 22 is reduced, and correction is made so that the injection end time is delayed, so that the parison length becomes a predetermined length.

That is, when the time difference obtained by the parison detection time calculator 84 exceeds a predetermined time, the weighing correction circuit 86 determines that the amount of resin supplied to the die 10 is small and determines the weighing value of the resin. Since the drawdown of the parison 22 is small, the injection correction circuit 88 reduces the injection speed of the parison 22 and adjusts the parison length. Then, when these corrections are completed, the control device 60 proceeds to step 142 and starts the next shot.

If the time from the end of the injection calculated by the parison detection time calculator 84 to the detection of the light receiving section 52 is within a predetermined time, the control device 60 proceeds to step 128 from step 124, and the parison 22 From the predetermined length to the second predetermined length. That is, the parison fall time calculator 94 of the control device 60
The first light receiving unit 5 set in the reference fall time setting unit 96
2 is a reference time from when the parison 22 is detected to when the second light receiving unit 56 detects the parison 22 (for example, the reference time when the interval between the light receiving units 52 and 56 is 10 cm is 3).
Second) and whether the time from when the light receiving unit 52 outputs the detection signal to when the light receiving unit 56 outputs the detection signal is within the reference time set in the reference fall time setting unit 96. Is monitored (step 128). Then, if the difference between the detection times of the light receiving units 52 and 56 is within the reference time, the parison fall time calculator 94 calculates the time difference and sends it to the injection correction circuit 88 and the mold clamping correction circuit 98.

When the output signal of the parison falling time calculator 94 indicates that the difference between the detection times of the light receiving section 52 and the light receiving section 56 is within the reference time, the injection correction circuit 88 lowers the drawdown of the parison 22. In order to reduce the parison length, a correction value for increasing the injection speed of the parison 22 is output to the injection cylinder control unit 76 (step 130) so as to shorten the parison length. When the output signal of the parison falling time calculator 94 indicates that the difference between the detection times of the light receiving unit 52 and the light receiving unit 56 is within the reference time, the mold closing correcting circuit 98 corrects the mold closing speed. A signal is output to the mold clamping controller 72 to prevent the parison length from increasing during mold clamping due to the large drawdown, thereby preventing the burr amount from increasing (step 130).

Next, when the injection speed is corrected in step 130, the control unit 60 performs the same test injection control as in steps 116 to 122 described above, and performs the first predetermined length of the parison 22. It is determined whether or not the time from when the time reaches the second predetermined length exceeds the reference time. If not, the temperature of the dice 10 is lowered and the next shot in step 142 is started.

Further, the control device 60 controls the first light receiving section 5
If the detection signal of the second light receiving unit 56 is not input within the reference time set in the reference fall time setting unit 96 after receiving the detection signal of No. 2, the process proceeds from step 128 to step 134. , The output signal of the thickness sensor 62 is taken in. Then, the thickness comparison circuit 102 of the control device 60
The thickness of the molded product 32 detected by the thickness sensor 62 is compared with the reference thickness set in the reference thickness setting circuit 104, and the comparison result is sent to the gap correction circuit 106.

The gap correction circuit 106 receives the comparison result from the thickness comparison circuit 102, and if the detected thickness is within the set value range, starts the next shot of step 142 (step 134). However, when the detected thickness is out of the range of the set value, the detected thickness of the molded article 32 is larger than the set value,
It is determined whether it is thin (step 136). Then, when the detected thickness is larger than the set value, the gap correction circuit 106
A correction signal for reducing the die gap 24 so as to reduce the thickness of the parison 22 is output to the parison control cylinder controller 74 (step 138), and the next shot is started (step 142). If the detected thickness is smaller than the set value, a correction signal for increasing the die gap 24 is output to the parison control cylinder controller 74 in order to increase the thickness of the parison 22 (step 140). Start the next shot.

As described above, in the embodiment, the injection end time of the parison 22 is compared with the time when the parison 22 reaches the first predetermined length, and the time difference between the two is controlled so as to be within a predetermined range. Therefore, the parison length can be kept constant. Moreover, the time required for the parison 22 to reach the second predetermined length from the first predetermined length is controlled, and the mold clamping speed of the molds 30a and 30b is changed according to this time. Even if the drawdown is relatively large, the length of the parison 22 to be molded can be made constant, the burr of the molded product 32 can be reduced, material loss can be reduced, and molding efficiency can be improved.

Further, in the embodiment, the mold 30a,
The thickness of the molded product 32 taken out of the molded product 30b is detected to facilitate the detection of the thickness of the molded product 32 at an arbitrary position or at a plurality of locations, and the die gap 24 is determined based on the detected value.
Is controlled, the parison 22 having a proper thickness and a small thickness is obtained as a whole, and the quality of the molded product 32 can be improved.

In the above embodiment, parison 2 was used.
Although the case where the photoelectric tube is used to detect that 2 has reached the predetermined length has been described, it may be detected by a magnetic sensor, a capacitive proximity switch, or the like. Further, in the above embodiment, the case where the ultrasonic thickness gauge is used as the thickness sensor 62 has been described, but the thickness may be detected by a change in capacitance or a change in magnetic field. In the above-described embodiment, the thickness of the bracket 6 is adjusted so that the thickness sensor 62 can simply change the mounting length with a nut or the like.
Although the description has been given of the case where the thickness sensor 62 is attached to the molded product 32, the elastic member is interposed in the attachment portion of the thickness sensor 62 so that the thickness sensor 62 is securely brought into close contact with the molded product 32.

Further, in the above embodiment, the die 1
Although the case where the present invention is applied to a blow molding machine that is a so-called in-die type accumulator that stores the molten resin 20 in the inside of the die is described, a so-called external die accumulator blow molding machine that stores the molten resin 20 outside the die is described. Can also be applied.

[0044]

As described above, according to the blow molding method of the present invention, the time when the parison has been injected and the time when the parison has reached the first predetermined length are compared, and the time difference between the two is determined. Since the parison length is controlled to be within the range, the parison length can be made constant, the burr of the molded product can be reduced, and the molding efficiency can be improved.

The parison is moved from the first predetermined length to the second
Since the time required to reach the predetermined length is controlled and the injection speed of the parison and the mold closing speed of the mold are changed in accordance with this time, the parison to be formed can be formed even if the drawdown of the parison is relatively large. The length can be made constant, the burr of the molded product can be reduced, the material loss can be reduced, and the molding efficiency can be improved.

Further, in the method for controlling the thickness of a parison according to the present invention, the thickness of a molded product taken out of a mold is detected, and the thickness of an arbitrary position or a plurality of locations of the molded product is easily detected. As a result, the die gap is controlled on the basis of the detected value, so that a parison having an appropriate thickness and a small thickness can be obtained as a whole, and the quality of a molded product can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an embodiment of the present invention.

FIG. 2 is an explanatory view of a blow molding machine to which the present invention is applied.

FIG. 3 is a detailed block diagram of the control device shown in FIG. 2;

FIG. 4 is an explanatory view of a conventional blow molding method.

FIG. 5 is an explanatory diagram of a conventional method for controlling the parison length.

[Explanation of symbols]

 Reference Signs List 10 die 14 die slip 16 core 18 plunger 22 parison 24 dice gap 26 parison control cylinder 32 molded product 52 first light receiving unit 56 second light receiving unit 62 wall thickness sensor 71a: 71b mold clamping cylinder

Claims (2)

(57) [Claims] In a blow molding method, wherein a parison injected from a die is housed in a mold and high-pressure gas is blown into the parison in the mold to form the parison into a predetermined shape, the parison has a first predetermined length. When the parison is detected and the parison is detected, the time at which the parison is detected is compared with the time at which the parison is completed. If the parison is detected earlier than the time at which the parison is completed, the parison is completed. When the parison detection time is a predetermined time after the end of the parison injection, the end of the parison injection is delayed, and the time from the end of the parison injection to the detection of the parison is within the predetermined time, When the time required for the parison to reach the second predetermined length from the first predetermined length is within a predetermined time, the injection speed of the parison is increased. Both increase the clamping speed of the mold, a blow molding process, characterized in that. 2. The blow molding method according to claim 1, wherein when the parison reaching the first predetermined length is detected earlier than the end of the parison injection, the end of the parison injection is advanced by a predetermined amount. After that, or when the time until the parison reaches the second predetermined length from the first predetermined length is within a predetermined reference time, the injection speed of the parison is increased by a predetermined amount. Thereafter, the parison is trial-formed a predetermined number of times, and when the parison having reached the first predetermined length after the trial formation is detected earlier than the end of the parison injection, or the parison has a first predetermined length. The resin temperature for forming the parison is reduced when the time from when the resin reaches a second predetermined length is within a predetermined reference time.