JPH07100907A - Novel extrusion blow molding method - Google Patents

Abstract

PURPOSE:To obtain an excellent mold surface-reproducibility and uniform surface glossiness by coating the mold surface forming the cavity of a main mold having specific conductivity with a heat insulating layer composed of a heat resistant polymer and having specific heat conductivity and specific thickness and cooling the main mold to temp. lower than the softening temp. of a resin by specific temp. CONSTITUTION:In a mold consisting of main molds 1, 2 composed of a metal whose heat conductivity at room temp. is 0.05cal/cm.sec. deg.C or more, the mold surfaces forming the cavities 3, 4 of the main molds 1, 2 are coated with heat insulating layers 5, 6 each composed of a heat-resistant polymer with heat conductivity of 0.002cal/cm.sec. deg.C or less and having a thickness of 0.05-2mm. The main molds 1, 2 are cooled to temp. lower than the softening temp. of a resin by 20 deg.C or lower and the thickness of each of the heat insulating layers 5, 6 is set so as to make the surface temp. of a molded product obtained by pressing an extruded heated parison to the mold surfaces by high pressure blow gas lower than the softening temp. of the resin by 10 deg.C or lower. Then, the parison is extruded to be set to the cavity 3 and the molds are clamped to perform the blow molding of the parison.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to extrusion blow molding of a thermoplastic resin, and in particular, it uses a mold in which a mold wall forming a cavity of a main mold used in extrusion blow molding is covered with a heat insulating layer. And extrusion blow molding.

[0002]

2. Description of the Related Art In extrusion blow molding of a thermoplastic resin, it is usually necessary to improve the reproducibility in imparting the shape condition of the mold surface to the molded product and to improve the luster of the molded product. It can be achieved to some extent by selecting molding conditions such as increasing the temperature and increasing the blow gas pressure.

The mold temperature has the greatest effect among these factors, and the higher the mold temperature, the better.
However, if the mold temperature is increased, the cooling time required for the cooling and solidification of the plasticized resin becomes longer, and the molding efficiency is lowered.
Therefore, there is a demand for a method that improves the reproducibility of the mold surface without increasing the mold temperature and that does not increase the required cooling time even if the mold temperature is increased. There is also a method in which heating and cooling holes are attached to the mold and heating and cooling of the mold are repeated by alternately flowing a heat medium and a refrigerant, but this method also consumes a lot of heat, Cooling time becomes longer.

A method for improving mold surface reproducibility by coating a mold wall forming a mold cavity with a substance having a low thermal conductivity is disclosed in US Pat. No. 3,544,518 for injection molding. Also in extrusion blow molding, a method of coating the mold wall surface with a substance having a small thermal conductivity is disclosed in US Pat. No. 5,041,247.

In extrusion blow molding, compared with injection molding,
The resin temperature of the extruded parison is low, the viscosity of the parison is high, the pressure that pushes the parison against the mold wall is much lower than the injection pressure, or a part of the parison contacts the mold. The effect of coating the mold wall surface with a substance having a small thermal conductivity is unlikely to appear due to the reason that it takes a long time to apply pressure to the mold wall surface.

In the conventional extrusion blow molding, the parison has a shape in which the parison hangs straight downward. It will stick out. For example, when molding a complicated deformed long duct with severe irregularities such as automobile air-conditioning parts for which demand has recently been increasing, a large amount of flash occurs due to the above reasons, and the effective utilization rate of materials is extremely poor. The parison follows the required path on the lower mold of the mold that has been opened according to the NC control device, etc., and lays the parison laterally along the lower mold cavity. Occurrence can be suppressed to a minimum, and such a molding method is used.

When a circular blow molding product such as a circular bottle or a circular drum is blow-molded from the circular parison, the parison is blown and comes into contact with the mold, and at the same time, the high pressure of the blow pressure is applied, and the resin is applied to the mold wall at a high pressure. It is pressed.
In such a case, the effect of coating the mold wall surface with a substance having a small thermal conductivity is remarkable. However, when a molded product with a more complicated shape, which is generally called a three-dimensional blow molded product, is molded, a part of the extruded parison is molded before the mold is closed. Contact the wall. That is, a parison is extruded from above along the mold cavity of the lower mold, and the parison is laid in the mold cavity and then, when blow molding is performed, the parison that is extruded onto the mold and comes into contact with the mold. Begins cooling immediately. Even if the mold wall surface is coated with a substance having a small thermal conductivity, in such a case, the effect is difficult to appear in a well-balanced manner. That is, it is difficult to obtain a molded product having a uniform appearance.

In recent years, as blow molded products, three-dimensionally bent pipe-shaped molded products such as air intake ducts around automobile engines have been formed. As this molding method, the parison is laid down along the mold cavity of the lower mold, then the mold is clamped, and blow molding is performed. In such a case, a part of the extruded parison comes into contact with the mold wall surface when the mold is closed. Then, the contacted parison immediately begins cooling. In such a case, it is difficult to obtain a molded product having a uniform appearance simply by covering the mold wall surface with a heat insulating layer having a uniform thickness.
The present inventors arrived at the present invention as a result of repeated research on a blow molding method for solving this problem.

In blow molding in which the parison is laid in the lower mold cavity, it takes about 5 to 10 seconds after the parison comes into contact with the mold and before it is pressed against the mold wall surface by the high pressure gas for blowing. The time the parison comes into contact with the lower die earliest becomes longer. Also, the larger the blow-molded product, the longer the time. Therefore, the time required for a part of the parison placed in the mold cavity of the lower mold to be pressed against the mold wall surface by the high pressure gas for blowing is 5
It will take about 10 seconds. The surface of the part of the parison receives cooling from the mold in 5 to 10 seconds and is pressed against the mold wall surface in a cooled state, so that the mold surface reproducibility of the part deteriorates.

[0010]

PROBLEM TO BE SOLVED: To provide a method for obtaining a blow-molded product having excellent mold surface reproducibility and excellent surface gloss even in a three-dimensional blow-molded product in an extrusion blow molding method. It is in.

[0011]

Means for Solving the Problems In the extrusion blow molding of a thermoplastic resin according to the present invention, (1) a metal having a thermal conductivity of 0.05 cal / cm · sec · ° C. or more at room temperature is used. The heat conductivity of the mold wall forming the mold cavity of the main mold is 0.002 cal / cm · sec · ° C.
Insulating layer consisting of the following heat-resistant polymer 0.05-2mm
Using a thickly coated mold, (2) the temperature of the main mold is cooled to a temperature lower than the softening temperature of the resin by 20 ° C. or lower,
(3) The thickness of the heat insulating layer is such that the surface temperature of the molded product immediately after being pressed against the mold wall surface by the high pressure gas for blowing in the mold where the extruded heated parison is clamped is 10 ° C. higher than the softening temperature of the resin. (4) The thickness of the parison is not less than a low temperature, and (4) the parison is extruded from above along the mold cavity of the opened lower mold and placed in the mold cavity, and then the mold is clamped and blow-molded for extrusion molding. It is a molding method. Furthermore, the present invention provides the extrusion blow molding method as described above, wherein the difference in the surface temperature distribution of the molded product is within 30 ° C. immediately after the extruded parison is pressed against the mold wall surface by the high pressure gas for blowing in the clamped mold. Is. Further, the present invention is the above extrusion blow molding method for molding a three-dimensionally bent pipe-shaped molded article.

The present invention will be described in detail below. The synthetic resin that can be used in the extrusion blow molding of the present invention is a thermoplastic resin that can be used in general extrusion blow molding. For example, in general, extrusion blow molding of styrene polymer, ABS resin or its copolymer, olefin polymer such as polyethylene and polypropylene, modified polyphenylene ether resin, vinyl chloride polymer or its copolymer, polycarbonate, polyamide, polyester and the like. The thermoplastic resin used can be used.

When these resins are mixed with various reinforcing materials or various fillers, or when they are polymer alloys or the like, a particularly great effect is obtained. For example, in the above resin,
One or more kinds of rubber, glass fiber, asbestos, calcium carbonate, talc, calcium sulfate, wood powder and the like can be blended. The heat-resistant polymer used in the heat insulating layer in the present invention has a glass transition temperature of 150 ° C. or higher, preferably 19
It is a heat resistant polymer having a temperature of 0 ° C. or higher and / or a melting point of 250 ° C. or higher, preferably 280 ° C. or higher. The heat conductivity of the heat resistant polymer is 0.002 cal / cm · sec · ° C. or less, and that of a general polymer is less than this heat conductivity. A tough polymer having a breaking elongation of 10% or more is preferable. The breaking elongation is measured according to ASTM D638, and the tensile speed at the time of measurement is 5 mm / min.

Polymers that can be favorably used as the heat insulating layer in the present invention are heat-resistant polymers having an aromatic ring in the main chain, and various amorphous heat-resistant polymers soluble in organic solvents, various polyimides and the like are favorably used. Can be used. As the non-crystalline heat resistant polymer, polysulfone, polyether sulfone, polyallyl sulfone, polyarylate, polyphenylene ether,
Examples thereof include polybenzimidazole. The repeating units of these typical heat resistant polymers are shown below.

[0015]

[Chemical 1]

[0016]

[Chemical 2]

[0017]

[Chemical 3]

[0018]

[Chemical 4]

[0019]

[Chemical 5]

Although there are various kinds of polyimide, a straight chain type high molecular weight polyimide can be favorably used. Generally, a straight chain type high molecular weight polyimide has a large breaking elongation and excellent durability.
Examples of linear high molecular weight polyimides that can be favorably used in the present invention are shown in Table 1. In addition, Tg is a glass transition temperature,
Also, n represents the number of repeating units.

[0021]

[Table 1]

The Tg of the straight-chain polyimide differs depending on the constituents, examples of which are shown in Tables 2 and 3. Tg is 15
A polymer of 0 ° C. or higher is used, preferably 190 ° C. or higher, more preferably 230 ° C. or higher.

[0023]

[Table 2]

[0024]

[Table 3]

Table 4 shows various soluble polyimides which can be favorably used in the present invention and can be dissolved in a solvent.

[0026]

[Table 4]

Injection molding has an economic value in that a molded product having a complicated shape can be obtained by molding once. In order to coat the surface of this complicated mold with the heat-resistant polymer and firmly adhere it, the heat-resistant polymer solution and / or the heat-resistant polymer precursor solution is applied and then heated to heat-resistant polymer. Most preferably, a coalescence is formed. Therefore, it is preferable that the heat resistant polymer or the heat resistant polymer precursor of the present invention can be dissolved in a solvent.

The above-mentioned non-crystalline heat-resistant polymer, soluble polyimide, or polyimide precursor is tetrahydrofuran, dimethylformamide, dimethylacetamide,
It is dissolved in various solvents such as N-methylpyrrolidone and used in the present invention. The linear polyimide precursor is synthesized, for example, by subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction.

[0029]

[Chemical 6]

These polyimide precursors are heated to undergo a dehydration cyclization reaction to form a polyimide. The most preferable linear polyimide precursor is polyamic acid, and the repeating unit of a typical example thereof and the repeating unit of polyimide obtained by imidizing the same are shown below.

[0031]

[Chemical 7]

[0032]

[Chemical 8]

[0033]

[Chemical 9]

[0034]

[Chemical 10]

The polymer of the above polyimide precursor is N-
It is dissolved in a solvent such as methylpyrrolidone and applied on the wall surface of the mold. These heat-resistant polymer solution, or heat-resistant polymer precursor solution, to adjust the viscosity at the time of coating,
Additives for adjusting the surface tension of the solution and thixotropy can be added, and / or a small amount of additives for improving the adhesion to the mold can be added.

As the heat-resistant polymer used for the heat insulating layer, in addition to the amorphous heat-resistant polymer and polyimide, an epoxy resin and a silicone resin having flexibility are used depending on molding conditions. It is preferable that the heat-resistant polymer film of the present invention and the main mold have a large adhesive force, and 0.5 k at room temperature.
g / 10mm width or more, preferably 0.8kg / 10mm
The width is more than or equal to the width, and more preferably the width is 1 kg / 10 mm or more. This is the peeling force when the adherent heat insulating layer is cut into a width of 10 mm and pulled at a speed of 20 mm / min in the direction perpendicular to the adhesive surface. Although the peeling force varies considerably depending on the measurement place and the number of times of measurement, it is important that the minimum value is large, and it is preferable that the peeling force is stable and large. The adhesion force described in the present invention is the minimum value of the adhesion force of the main part of the mold.

In order to further improve the smoothness of the surface of a thin layer of a heat insulating material such as polyimide, to further improve the scratch resistance of the surface, or to improve the releasability.
If necessary, another material thinner than about 1/10 of the thickness of the polyimide layer can be applied to the polyimide surface,
Included in the present invention. On the surface of synthetic resin sheets and molds,
A paint generally referred to as a hard coat, which is used to improve scratch resistance, can also be applied. For example, a thermosetting type silicone hard coating agent, in particular, a hard coating agent having excellent adhesiveness in which an epoxy substance is mixed with a silicone type hard coating agent can be favorably used.
It is also possible to apply a fluororesin or a silicone-based polymer in order to improve the releasability.

In the extrusion blow molding of the present invention, the parison is extruded from above along the mold cavity of the lower mold to lay it in the mold cavity, and then the mold is clamped for blow molding. By appropriately moving the mold and / or the parison, the extruded parison is laid down along the mold cavity of the lower mold (the mold cavity is facing up).

The softening temperature of the resin in the present invention is the temperature at which the synthetic resin can be easily deformed. For the amorphous resin, the Vicat softening temperature (ASTM D1525) and for the hard crystalline resin, the heat deformation temperature (ASTM D648). Load 18.
6 kg / cm ² ), the heat distortion temperature (A
STM D648 load 4.6 kg / cm ² ) and the temperature shown in each. The hard crystalline resin is polyoxymethylene, nylon 6, nylon 66, etc., and the soft crystalline resin is various polyethylene, polypropylene, etc.

In the present invention, a heat insulating layer is provided only on the surface of the main mold so that the surface temperature of the molded product immediately after the parison is pressed against the mold wall surface by the high pressure gas for blowing is 10 ° C. or more lower than the softening temperature of the resin. To be installed. The surface temperature of the molded product described here is, of course, the surface temperature of the molded product in contact with the mold wall surface. This is a molding method in which the wall surface of the lower mold is thickly covered with a heat insulating layer so that the mold surface temperature immediately after the parison is pressed against the mold wall by the high-pressure gas for blowing is above the softening temperature of the resin. . After the parison is blown and comes into contact with the mold wall surface to stop the deformation, the blow gas pressure in the mold rises sharply. By measuring the blow gas pressure, it can be detected that the parison is blown and pressed against the mold wall. Therefore, the time from the contact of the parison to the mold wall surface when the parison is in contact with the mold wall surface until it is pressed against the mold wall surface with high pressure can be expressed as the time until the blow gas pressure in the mold rises sharply. it can.

The term "immediately after being pressed against the mold wall surface by the high pressure gas for blowing" in the present invention means a time point when the blow gas pressure in the mold reaches 80% or more of the set blow gas pressure. Before the mold is closed, the parison does not come into contact with the mold. The mold wall portion of the upper mold comes into contact with the parison due to mold clamping and is immediately pressed with high pressure gas.
It is pressed at a high pressure in a short time after about 4 seconds, so that the surface temperature of the molded product is kept above the softening temperature even if the thickness of the heat insulating layer is thin. In the present invention, the parison is pressed against the mold wall surface at a high pressure by adjusting the thickness of the heat insulating layer on the surface of the main mold by the time from the contact with the mold wall surface until the parison is pressed against the mold wall surface by the blowing high pressure gas. Immediately after that, the appearance of the blow-molded product is made uniform by keeping the difference in temperature distribution of the parison surface within 30 ° C.

In the present invention, the numerical value calculated by calculation is used as the parison surface temperature or the mold surface temperature. The mold surface temperature is the surface temperature of the heat insulating layer coated on the surface of the main mold, and coincides with the parison surface temperature. The surface temperature can be calculated from the initial temperature of the main mold, resin, heat insulating layer, etc., specific heat, thermal conductivity, latent heat of crystallization, etc., and the calculated value is used. The calculation method can be calculated by heat conduction analysis by the finite element method (a method of solving a physical problem represented by a general partial differential equation as a multidimensional simultaneous equation by using the variational principle).

At the time of blow molding, air may remain between the resin layer and the heat insulating layer to form a pool of air (hereinafter referred to as an air trap).
It is possible to reduce air traps by adjusting the blowing gas blowing method and the like, or by using a vacuum cavity, and in the present invention, these methods are used as necessary. Further, a method in which a large number of fine pores are opened in the heat insulating layer and the gas in the air trap is discharged out of the mold can be used as required.

The smaller the difference in the surface temperature distribution of the molded product immediately after the extruded parison is pressed against the mold wall surface by the high pressure gas for blowing in the clamped mold, the more uniform the appearance of the molded product is. In the present invention, the heat insulating layer is made thicker in the lower mold and the heat insulating layer is made thinner in the upper mold in which the parison comes into quick contact with the wall surface of the mold to reduce the difference in surface temperature distribution of the molded product. or,
Even in the same lower mold, thicken the heat insulating layer in the part where the parison contacts quickly. The difference in surface temperature distribution is preferably within 30 ° C, more preferably within 20 ° C.

The present invention will be described with reference to the drawings. FIG. 1 shows a diagram in which a three-dimensionally bent pipe-shaped molded article is extrusion blow molded by the method of the present invention. FIG. 2 shows only a cross section of a portion of the extrusion blow molding die shown in FIG. 1 according to the present invention.

In FIGS. 1 and 2, the heat-insulating layers 4 and 5 made of a heat-resistant polymer are formed on the mold wall surfaces forming the mold cavities 3 and 4 of the main molds 1 and 2 made of a metal by 0.05. ~
Using a mold coated to a thickness of 2 mm, the main mold temperature is cooled to 20 ° C or lower than the softening temperature of the resin, and the heated parison is pressed against the mold wall surface by the high pressure gas for blowing in the clamped mold. Immediately after the molding, the mold cavity 3 of the lower mold 1 is used, in which the mold is covered with the heat-insulating layers 5 and 6 having a thickness of 10 ° C. or more lower than the softening temperature of the resin. Extrude the parison 7 from above along the die 8
It is extrusion blow molding in which it is further extruded, laid down in the mold cavity 3 and then clamped and blow molded. In the lower mold 1, the extruded parison 7 is blown by the high pressure gas after being in contact for a longer time. Therefore, the heat insulating layer 5 of the lower mold 1 is thicker than the heat insulating layer 6 of the upper mold 2, and is generally 1.5 times or more thicker.

3 to 6 are calculated values of changes with time in temperature near the mold surface when the resin comes into contact with the mold wall surface. 70
The change in temperature distribution near the mold surface when the ABS resin at 220 ° C. comes into contact with the main mold at ° C. is shown. FIG. 7 shows the relationship between the contact time and the polyimide thickness necessary to bring the mold surface (polyimide surface) temperature to the softening temperature of the ABS resin when the ABS resin contacts the steel mold covered with polyimide.

FIG. 3 shows the change over time in the temperature distribution near the mold surface when the ABS resin directly contacts the steel main mold. The numbers in the figure indicate the number of seconds after contact. FIG. 4 shows the change over time in the temperature distribution near the mold surface when the ABS resin contacts the mold in which the surface of the steel main mold is coated with 0.2 mm thick polyimide. Figure 5 shows 0.4mm on the surface of the steel main mold
The time-dependent change of the temperature distribution near the mold surface when the ABS resin contacts a mold coated with a thick polyimide is shown.

FIG. 6 shows the temperature change of the mold surface (polyimide surface) when the ABS resin comes into contact with the mold in which the surface of the steel main mold is coated with polyimide. The numbers in the figure indicate the thickness of the polyimide. FIG. 7 shows the mold surface (polyimide surface) temperature near the softening temperature of the ABS resin (105 ° C., 9 ° C., 9 ° C. when the ABS resin comes into contact with the steel mold coated with polyimide).
The relationship between the contact time and the thickness of the polyimide, which is necessary to reach 5 ° C), is shown.

FIGS. 3 to 7 show ADINA and ADI.
It is a value calculated by unsteady heat conduction analysis by a nonlinear finite element method using NAT (software developed at Massachusetts Institute of Technology). The value of each curve in the figure is the time (seconds) after the heated resin comes into contact with the cooled mold wall.
Indicates. From these figures, the thickness of the heat insulating layer that covers the mold wall surface can be determined. By appropriately adjusting the thickness of the heat insulating layer, the difference in the mold surface temperature distribution immediately after the parison is pressed against the mold wall surface by the high pressure gas for blowing is reduced to 30.
It can be within ℃.

In the lower mold, the time from the contact of the parison to the pressing against the mold wall surface by blow molding of the high pressure gas becomes long, and the thickness of the heat insulating layer is increased. It is molded high. If the heat insulating layer is not covered, the temperature of the main mold needs to be remarkably increased, which results in shortening the molding cycle time in the present invention.

[0052]

EXAMPLE Extrusion blow molding is performed with the mold shown in FIGS. The main mold has a thermal conductivity of 0.2 cal / cm
Pipe-shaped cavity 3 that is mirror-like and is three-dimensionally bent and hard-chrome plated with a steel material (S55C) of sec.
Have. As a heat insulating layer, the surface of the main mold is covered with polyimide. As the polyimide, a linear PMDA polyimide precursor solution "Treney # 3000" (trade name of Toray Industries, Inc.) is applied and then heat-cured to form a polyimide, and then the surface is polished to form a mirror-like polyimide layer. Then, the surface is polished to form a mirror-like polyimide layer. The upper mold has a thickness of 0.25 mm, and the lower mold has a thickness of 0.
Form a 4 mm thick polyimide. Tg of the polyimide
Is 300 ° C, thermal conductivity is 0.0007 cal / cm · s
ec · ° C.

As the thermoplastic resin, ABS resin, Stylak ABS A4593 (trade name of Asahi Chemical Industry Co., Ltd.) (Vicat softening temperature 105 ° C.) was used. Main mold upper temperature 7
0 ℃, main mold lower temperature 80 ℃, ABS resin extrusion temperature 22
At 0 ° C., blow molding gas pressure of 6 kg / cm ² G, a circular parison is extruded, laid down along the mold cavity of the lower mold, and immediately clamped for blow molding.

After the high pressure blow gas pressure is blown into the mold, the time for the blow gas pressure in the mold to reach 5 kg / cm ² or more is set to about 0.4 seconds, and after the mold is closed, the blow gas in the mold is blown. time pressure reaches 5 kg / cm ² or more is about 4 seconds, the parison is time to mold the blow gas pressure reaches 5 kg / cm ² or more from the contact with the lower mold was about 8 seconds. The blow-molded article had a good and uniformly glossy surface throughout.

[0055]

According to the method of the present invention, a blow molded product such as a three-dimensionally bent pipe-shaped molded product having excellent mold surface reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a view showing extrusion blow molding of a three-dimensionally bent pipe-shaped molded product by the method of the present invention.

FIG. 2 shows a cross section of the extrusion blow molding die shown in FIG.

[Fig. 3] Time-dependent change in temperature distribution when the ABS resin contacts the steel mold (the numbers in the figure are the number of seconds after the resin contacts the mold wall).

FIG. 4 Time-dependent change in temperature distribution when ABS resin contacts a steel mold coated with 0.2 mm thick polyimide (the numbers in the figure are the number of seconds after the resin contacts the mold wall surface)

FIG. 5: Time-dependent change in temperature distribution when ABS resin contacts a 0.4 mm thick polyimide-coated steel mold (the numbers in the figure are the number of seconds after the resin contacts the mold wall surface)

[Fig. 6] Temperature change of mold surface (polyimide surface) of temperature distribution when ABS resin comes into contact with a steel mold covered with polyimide (the numbers in the figure indicate the thickness of polyimide)

FIG. 7 shows the mold surface (polyimide surface) temperature AB when the ABS resin comes into contact with a steel mold coated with polyimide.
Relationship between contact time and polyimide thickness required to reach the softening temperature of S resin (105 ° C, 95 ° C)

Claims (3)

[Claims] 1. In extrusion blow molding of a thermoplastic resin, (1) the thermal conductivity at room temperature is 0.05 cal / c.
The heat conductivity is 0.002 cal on the mold wall forming the mold cavity of the main mold made of metal of m · sec · ° C or higher.
Using a mold coated with a heat-insulating layer made of a heat-resistant polymer having a temperature of not more than / cm · sec · ° C to a thickness of 0.05 to 2 mm, (2) the temperature of the main mold is 20 ° C lower than the softening temperature of the resin (3) The thickness of the heat insulating layer is such that the surface temperature of the molded product immediately after the extruded heated parison is pressed against the mold wall surface by the high pressure gas for blowing in the mold where the mold is clamped. (4) The parison is extruded from above along the mold cavity of the lower mold with the mold opened and placed in the mold cavity, and then the mold is clamped. Extrusion blow molding method for blow molding. 2. The extrusion according to claim 1, wherein the difference in the surface temperature distribution of the molded product immediately after the extruded parison is pressed against the mold wall surface by the high pressure gas for blowing in the clamped mold is within 30 ° C. Blow molding method. 3. The extrusion blow molding method according to claim 1, wherein a pipe-shaped molded product bent in three dimensions is molded.