JPH07137119A - Blow molding method - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the local deformation of the parison due to the air cushion pressure in air cushion blow molding and the uneven thickness due to it. [Structure] The parison 1 is sandwiched by the split molds 12 and 13 from the left-right direction, and gas G ₁ is blown into the parison 1 to bulge the parison 1 toward the cavity surfaces 12a and 13a of the split molds 12 and 13. , Split type 12, 13
In the blow molding method in which the gas G ₂ is ejected from the cavity surfaces 12a, 13a of the parison 1 toward the cavity surfaces 12a, 13a of the parison 1 which are likely to come into early contact, the pressure rise of the gas G ₁ blown inside the parison 1 is increased. Based on the above, the pressure of the gas G ₂ ejected toward the portions of the parison 1 that are likely to come into early contact with the cavity surfaces 12a and 13a is increased.

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 producing a hollow resin molded body, and more particularly to a blow molding method capable of making the thickness of a parison uniform during molding.

[0002]

2. Description of the Related Art Heretofore, an air cushion method has been known in which air is blown from the inner surface of a mold in order to prevent the parison that initially contacts the mold from remaining thick. For example, "Plastic Processing Technology Handbook" December 5, 1969
The first edition, Nikkan Kogyo Shimbun, page 440, describes the air cushion method in vacuum molding, but the same applies to blow molding.

FIG. 12 shows a conventional air cushion method.
An example of blow molding is shown. As shown in FIG.
Blowing air from the cavity surface 53 of the split molds 51 and 52.
A G ₂Allows the parison 50 around the air blowing hole to
Local deformation (dents) easily occurs and uneven thickness is created in that part.
Raise. More specifically, the molten parison 50 has a low viscosity.
Is in the vicinity of the
When a stress is generated by the side, only that part is deformed and the wall thickness
Causes homogenization.

As one of the measures for preventing the nonuniformity of the wall thickness, Japanese Patent Application No. 5-75582 has been previously proposed by the present applicant. In this blow molding method, a main parison and a high-viscosity sub-parison are extruded between split dies, and after the mold is closed, gas is blown from the cavity surface toward the sub-parison for blow molding.
In this case, the load caused by the gas blow is transmitted to a wide range of the high-viscosity auxiliary parison and is received in a wide range, so that the local deformation of the parison and the uneven thickness due to the local deformation are reduced.

[0005]

[Problems to be Solved by the Invention] However, Japanese Patent Application No. 5-7
In the case of the blow molding method of No. 5582, there is a problem that an auxiliary parison is required, the manufacturing process becomes complicated, and the manufacturing equipment becomes expensive. Therefore, it is desired to develop a blow molding method capable of realizing a uniform thickness of the parison at the time of molding without using the auxiliary parison.

The pressure of the gas G ₁ blown into the parison 50 gradually increases as the parison 50 swells, but the gas G ₁ increases in order to enhance the air cushion effect.
_{When the} air cushion pressure due to the jetting of ₂ is set high from the initial stage of molding, as shown in FIG. 13, in the case where the cavity surfaces of the split dies 51 and 52 project toward the parison side, the displacement of the parison 50 inside becomes large. There is a problem that the parison 50 adheres to each other.

It is an object of the present invention to provide a blow molding method capable of reducing the local deformation of the parison due to the air cushion pressure in the air cushion blow molding, reducing uneven thickness due to the local deformation, and eliminating the adhesion between the parison. And

[0008]

A blow molding method according to the present invention for achieving this object is a parison that is sandwiched by a split mold by sandwiching the parison from the left and right directions and blowing gas into the parison. In a blow molding method in which the gas is blown out toward the cavity surface of the split mold and the gas is ejected from the cavity surface of the split mold toward the cavity surface of the parison that is likely to come into early contact, This is a method of increasing the pressure of the gas ejected toward the portion of the parison that is likely to come into early contact with the cavity surface based on the increase in the pressure.

[0009]

In the blow molding thus constructed,
The pressure of the gas ejected from the cavity surface rises as the pressure of the gas supplied to the inside of the parison rises, so when the pressure inside the parison is low, the air cushion pressure due to the ejection of air from the cavity surface is also low. It can be suppressed. Therefore, the parison is not locally deformed by the air cushion pressure, and the thickness of the parison is made uniform. Further, since the air cushion pressure does not become high from the initial stage of molding, even if the cavity surface of the split mold has a shape protruding toward the parison, the adhesion of the parison due to the air cushion pressure is prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the blow molding method according to the present invention will be described below with reference to the drawings.

First Embodiment FIGS. 1 to 9 show a first embodiment of the present invention.
First, a blow molding device to which the present invention is applied will be described. In FIG. 1, reference numeral 11 denotes a die head of a molding machine in which molten resin is extruded. Below the die head 11, split dies 12 and 13 are arranged. Split type 1
2 and 13 are parisons 1 extruded from the die head 11.
Are arranged so as to face each other. Split type 1
Reference numerals 2 and 13 are connected to a drive device (not shown). The split molds 12, 13 are adapted to be horizontally closed and opened by a driving device. Each of the split molds 12 and 13 has a cooling pipe.

A blow nozzle 21 is arranged between the split mold 12 and the split mold 13. The blow nozzle 21
A lifting device (not shown) is used to move up and down. When the blow nozzle 21 is raised, the upper end of the blow nozzle 21 enters the split molds 12 and 13. With the blow nozzle 21 lowered,
The upper end of the blow nozzle 21 is adapted to come out of the split dies 12, 13. An air supply source (not shown) for supplying compressed air G ₁ is connected to the blow nozzle 21.

A plurality of air ejection holes 15 are formed in the split molds 12 and 13. The air ejection hole 15 is a split mold 1
The openings 2 and 13 are opened in the cavity surfaces 12a and 13a. The air ejection hole 15 is formed on the cavity surface 12 of the parison 1.
It is arranged so as to face a portion where early contact with a and 13a is easy. That is, the air ejection hole 15 is arranged at a position on the cavity surfaces 12a and 13a where the parison 1 is supposed to come into contact with the earliest. In addition, the split mold 12,
An air vent hole 16 is formed in 13. The air bleeding hole 16 is arranged at a position where the parison 1 is considered to come into contact most lately.

An air passage 17 connected to the air ejection hole 15 is connected to the split dies 12, 13. Air passage 1
An air supply source (not shown) for supplying compressed air G ₂ is connected upstream of 7. The blow nozzle 21 is provided with a pressure gauge 31 for measuring the pressure of the compressed air G ₁ blown inside the parison 1. That is, the pressure inside the parison 1 is measured by the pressure gauge 31. The pressure gauge 31 has a function of converting the measured pressure into an electric signal.

A control valve 32 is provided in the middle of the air passage 17. The control valve 32 is connected to the control means 33. An electric signal from the pressure gauge 31 is input to the control means 33. The control means 33 has a function of increasing the pressure of the compressed air G ₂ ejected from the air ejection holes 15 of the cavity surfaces 12a and 13a based on the increase of the pressure of the compressed air G ₁ blown inside the parison 1. is doing. A pressure gauge 34 for measuring the pressure of the compressed air G ₂ controlled by the control valve 32 is attached to the air passage 17.

FIG. 4 shows the cavity surface 1 of the air ejection hole 15.
The opening to 2a is shown. A sintered metal 18 is fitted in the opening of the air ejection hole 15. Sintered metal 18
As shown in FIG. 5, is formed in a disk shape having a diameter of 12 mm, for example, and has about 340 pores having a diameter of 0.5 mm. The compressed air G ₂ from the control valve 32 is designed to be jetted from the cavity surfaces 12 a and 13 b toward the surface of the parison 1 via the sintered metal 18. In addition,
Similarly, a sintered metal 18 is fitted in the opening of the air vent hole 16.

Next, the blow molding method and its operation in the first embodiment will be described. At the start of molding,
The split molds 12 and 13 are opened, and the die head 11
The parison 1 is extruded downward. When the parison 1 is extruded by a predetermined length, the blow nozzle 21 rises,
The blow nozzle 21 enters the inside of the parison 1. When the insertion of the blow nozzle 21 into the parison 1 is confirmed, the compressed air G ₁ is blown into the parison 1 from the blow nozzle 21. At the same time, the mold closing of the split molds 12 and 13 is started.

Even after the mold closing of the split dies 12, 13 is completed, the supply of the compressed air G ₁ from the blow nozzle 21 into the parison 1 is continued, and the parison 1 is divided into the split dies 12, 13.
Bulges toward the cavity surfaces 12a and 13a. The pressure inside the parison 1 rises as the parison 1 expands, and the pressure inside the parison 1 is measured by the pressure gauge 31. At the beginning of bulging of parison 1, pressure gauge 3
Since the pressure inside the parison 1 measured by 1 is also low, the pressure of the compressed air G ₂ ejected from the air ejection hole 15 opening in the cavity surfaces 12a and 13b is also controlled to a low value by the control valve 32. Therefore, even if the parison 1 has a low viscosity, it is not locally deformed by the ejection of the compressed air G ₂ .

When the amount of expansion of the parison 1 increases, the pressure inside the parison 1 also increases, and the pressure of the compressed air G ₂ ejected from the air ejection hole 15 is also increased by the control valve 32. Therefore, the cavity surfaces 12a and 13b can be quickly replaced.
The bulging of the part of the parison 1 which is supposed to come into contact with is suppressed, and the extension of the part of the parison 1 which is not directly hit by the compressed air G ₂ is promoted. Therefore, the entire parison 1 stretches uniformly, and the parison 1 is a split type 1 without local deformation.
It comes into close contact with the cavity surfaces 12a and 13a of the two and thirteen.

In FIG. 3, the parison 1 is moved into the cavity surface 12 by blowing compressed air G ₁ from the blow nozzle 21.
It shows a state where they are in close contact with the entire surfaces of a and 13a. When the parison 1 is in close contact with the entire surfaces of the cavity surfaces 12a and 13a, the ejection of the compressed air G ₂ from the air ejection hole 15 is stopped. After the parison 1 is cooled and solidified by heat exchange with the split molds 12 and 13, the split molds 12 and 13 are opened and the molded product is taken out.

FIG. 6 shows the relationship among the working steps of blow molding in the first embodiment. As shown in FIG. 6, the application of the air cushion pressure by the compressed air G ₂ is started before the pre-expansion of the parison 1 is started and is performed until the parison 1 comes into close contact with the cavity surfaces 12 a, 13 a of the split molds 12, 13. . FIG. 7 shows the relationship between the pressure inside the parison 1 (the pressure inside the parison) and the air cushion pressure.
As shown in FIG. 7, as the parison internal pressure increases,
It can be seen that the air cushion pressure is set high. Although the air cushion pressure is increased stepwise in the present embodiment, the air cushion pressure may be increased linearly.

FIG. 8 shows a molded product obtained by a test for confirming the action and effect of the present invention. The molded product is
As shown in FIG. 8, 500 mm × 430 mm × 250 m
m and a corner portion R200 mm in a box shape. Resin is high molecular weight high density polyethylene resin (B5732V manufactured by Tonen Kagaku)
X) was used. The pre-stretching gas pressure was 150 KPa, and the gas pressure during main molding was 540 KPa.

The test results are shown in FIG. The horizontal axis of FIG. 9 is the thickness measured at a 1 cm pitch from the side center A of FIG.
The wall thickness was measured at the position of cm and moved to the top through the corner, and at the position of 37 cm, the thickness up to the center B of the top was measured. Figure 9
The vertical axis indicates the wall thickness (mm). Characteristic (a) of Figure 9
Is the present invention, characteristic (b) is the conventional method shown in FIG. 12, and characteristic (c) is due to the double parison of Japanese Patent Application No. 5-75582. As can be seen from FIG. 9, the conventional method of the characteristic (b) has a large variation in wall thickness, and the characteristic (a) of the present invention and the characteristic (c) of Japanese Patent Application No. 5-75582 have almost the same results. . Therefore, the present invention, which does not use the sub-parison, is easier to manufacture and is excellent as blow molding.

Second Embodiment FIG. 10 shows a second embodiment of the present invention. The second embodiment differs from the first embodiment only in the shape of the cavity surface of the split mold, and the other parts are in conformity with the first embodiment. Therefore, the corresponding parts are designated by the same reference numerals as in the first embodiment. Therefore, the description of the corresponding parts will be omitted, and only different parts will be described. The same applies to other embodiments described later.

In the first embodiment, the cavity surfaces 12a and 13a of the split dies 12 and 13 are flat, but in this embodiment, the convex portions 13b are formed on a part of the cavity surface 13a of the split dies 12.
Are formed. A plurality of air ejection holes 15 are formed in the convex portion 13b. Air ejection hole 15 of the convex portion 13b
Is connected to an air passage 17 for supplying compressed air G ₂ . A control valve 35 is provided in the middle of the air passage 17 on the convex portion 13b side. The control valve 35 is connected to a pressure gauge 31 that measures the pressure inside the parison 1 and is connected to the control means 3
It is controlled by 3.

In the second embodiment thus constructed, when the parison 1 is expanded by the compressed air G ₁ , the air ejection holes 15 on the cavity surface 12a side and the cavity surface 13 are formed.
Compressed air G ₂ is ejected toward the surface of the parison 1 from the air ejection holes 15 on the a side. In this embodiment, for example, the control characteristic of the air cushion pressure by the control valve 32 on the split mold 12 side and the control characteristic of the air cushion pressure by the control valve 35 on the split mold 13 side are different, and the convex portion 13b of the cavity surface 13a is different. The contact of parison 1 with is delayed. Therefore, the extension of the parison 1 at the portion not facing the convex portion 13b on the cavity surface 13a side is promoted, and the thickness of the parison 1 can be made uniform.

Third Embodiment FIG. 11 shows a third embodiment of the present invention. As shown in FIG. 11, one split mold 12 is provided with a movable insert 40. The movable insert 40 is slidably fitted to the split mold 12, and can be reciprocated by a drive device (not shown). An air ejection hole 15 is formed in the movable insert 40. The air ejection hole 15 is connected to the air passage 17. The operation timing of the movable insert 40 is set in consideration of the shape of the movable insert itself, the shape of the split mold, and the blow pressure. In this embodiment, the movable insert 40 is operated simultaneously with the start of the main molding. The start timing of the air cushion may be any time until the parison 1 comes into contact with the movable insert 40, but in the present embodiment, it is the same as the start of movement of the movable insert 40.

In the third embodiment thus constructed, the compressed air G ₂ is ejected from the air ejection hole 15 of the movable insert 40 at the start of the movement of the movable insert 40 toward the parison 1, so that the parison is formed. The contact between 1 and the movable insert 40 is delayed. Therefore, the extension of the other parts of the parison 1 is promoted, and the wall thickness of the parison 1 in close contact with the cavity surfaces 12a and 13b can be made uniform. Japanese Patent Application No. 5-7
In the blow molding method of No. 5582, since the viscosity of the outer parison is low, the parison may be broken during the movement of the conventional movable insert. However, the compressed air is ejected from the movable insert 40 as in this embodiment. By doing so, blow molding with a deeper shape is possible.

[0029]

According to the present invention, the following effects can be obtained. (1) The pressure of the gas blown inside the parison is increased based on the pressure rise of the gas blown inside the parison, so that the pressure of the gas ejected toward the part of the parison that is likely to come into early contact with the cavity surface is increased. When is low, the air cushion pressure due to the gas ejected from the cavity surface is also kept low, the parison is not locally deformed by the air cushion pressure, and the wall thickness can be made uniform. (2) Since the air cushion pressure does not increase from the initial stage of molding, even if the cavity surface of the split mold projects to the parison side, the parison will not be excessively deformed by the air cushion pressure, and the parison will not be deformed by the air cushion pressure. It is possible to prevent mutual adhesion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state immediately after starting preforming in a blow molding method according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state immediately after the start of main molding in the blow molding method of FIG.

FIG. 3 is a cross-sectional view showing a state immediately after the end of the air cushion in the blow molding method of FIG.

FIG. 4 is an enlarged cross-sectional view near an air ejection hole in FIG.

5 is a perspective view of the sintered metal in FIG.

FIG. 6 is a time chart in the blow molding method of FIG.

FIG. 7 is a characteristic diagram showing a relationship between the parison internal pressure and the air cushion pressure in FIG.

FIG. 8 is a perspective view of a resin molded product used in the test of the present invention.

9 is a wall thickness distribution diagram when the molded product of FIG. 8 is blow molded by the method of the present invention and the conventional method.

FIG. 10 is a sectional view showing a molding state in the blow molding method according to the second embodiment of the present invention.

FIG. 11 is a cross-sectional view showing a molding state in the blow molding method according to the third embodiment of the present invention.

FIG. 12 is a cross-sectional view of a main molding step of a conventional blow molding method.

FIG. 13 is a cross-sectional view showing a bonded state of a parison by a conventional blow molding method.

[Explanation of symbols]

 1 Parison 12 Split Type 12a Cavity Surface 13 Split Type 13a Cavity Surface 15 Air Jet Hole 21 Blow Nozzle 31 Pressure Gauge 32 Control Valve

Claims (1)

[Claims] 1. A parison is sandwiched by a split mold from the left-right direction, and gas is blown into the parison to bulge the parison toward the cavity face of the split mold, and the cavity of the parison is extended from the cavity face of the split mold. In a blow molding method in which gas is ejected toward a portion that is likely to come into early contact with a surface, based on a pressure increase of gas blown inside the parison, toward a portion that is likely to come into early contact with the cavity surface of the parison. A blow molding method comprising increasing the pressure of ejected gas.