JPH08290465A - Blow molding method - Google Patents

Abstract

PURPOSE: To improve the transfer property of a cavity surface and the dimensional precision of a molded product by a method in which a parison is molded, a side part blow pin is switched from air to hot water, the parison is filled with hot water and pressed on the surface of a mold, and the hot water is switched to cooling water to cool the parison. CONSTITUTION: Male and female molds 24, 26 are opened, a parison 22 is hung, the lower part is pinched, low pressure air is introduced from a preblow pin 32, the parison 22 is expanded, and molds are clamped. Blow pins 28, 30 are inserted, high pressure air is injected, and a cavity surface 41 is shaped. Next, hot water is supplied from the blow pin 28 to discharge air from the blow pin 30, the cavity surface 41 is shaped by hot water with which the cavity is filled, and a surface transfer property is improved by the synergistic effect of a heating medium which is passed through a heating pipe. Hot water is switched to cooling water, and the heating medium is switched to a cooling medium, the container of the parison 22 is cooled from the inside and outside to be solidified, and air is introduced from the blow pin 28 to discharge the cooling medium.

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 in which pre-blow air is switched to warm water at the time of blow molding to press a parison container against a mold surface to improve surface transfer.

[0002]

2. Description of the Related Art Conventionally, resin hollow moldings such as resin fuel tanks for automobiles and resin door panels for office equipment have been manufactured by a hollow molding method. In this hollow molding, a cylindrical parison of thermoplastic resin is made by an extrusion method or an injection method, and a gas such as pressurized air is blown inside the parison between molds by a blow pin attached to a core metal, In this method, a hollow product is formed by expanding and shaping until it comes into close contact with the cavity and then cooling.

[0003]

However, in the conventional blow molding method, the parison is sandwiched between the two molds at the time of blow molding, and air is blown into the parison, and the blown air pressure causes the mold cavity to reach the mold cavity. It is pressed from the inside of the parison to the mold cavity surface until it comes into close contact, but the pressing force is relatively small, so there is the disadvantage that surface transferability is poor.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to arrange slightly larger blow pins on the side and the lower part of the mold to improve the supply and discharge ability of air and hot water and cooling water. At the same time, the present invention provides a blow molding method that improves the transferability of the cavity surface and the dimensional accuracy of the molded product.

[0005]

In order to achieve the above object, according to the present invention, a blow pin is inserted from a side portion and a lower portion of a mold holding a parison to form a container while pressurizing air, and the parison is After pressure molding, while keeping the sealed and pressurized state, the side blow pin of the container is switched from air to hot water and air is discharged from the lower blow pin to fill the container with hot water and press the parison against the mold surface, Subsequently, the hot water was switched to the cooling water to cool the container.

[0006]

[Function] First, high-pressure air is blown into the parison to expand the parison, and then hot water is supplied to replace the hot water with high-pressure air, which is strongly pressed against the cavity surface from inside the parison. And the transferability is improved. In the subsequent cooling process, after switching from hot water to cooling water, the parison container is filled with warm water and then cooled from the inside and outside of the parison container, which improves dimensional accuracy.

[0007]

The blow molding method according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic view of a blow molding apparatus, FIGS. 2 to 9 are explanatory views for explaining a blow molding process according to an embodiment of the present invention, and FIG. 10 is a blow pin used in a blow molding method according to the present invention. FIG. 11 is a sectional view of the tip of the blow pin shown in FIG. 10, and FIG. 12 is an explanatory view showing another embodiment.

In FIG. 1, the die 10 includes a die housing 12 whose outer peripheral surface is formed into a square shape and whose inner peripheral surface is formed into a circular shape. The inner peripheral surface of the die housing 12 is not shown. A mandrel and a core metal 16 composed of a core 14 are fitted to each other, and the die housing 12
An annular resin passage 18 is provided between the resin passage 18 and an inner peripheral surface of the resin passage 18. The resin passage 18 has a slit 20 as a resin discharge port at the lower end portion of the die 10,
The molten resin inside is extruded through the slit 20 to the outside of the die 10 main body to form a parison 22.

On the other hand, below the die 10, there are provided a male die 24 and a female die 26 which are located on a machine head (not shown) and are moved forward and backward by a mold clamping cylinder (not shown). The parison 22 is configured to be clamped and opened by means of the pair of left and right male dies 24 and female dies 26 provided with respect to the center line of the parison 22. It is configured to be typed into.

As shown in FIG. 1, holes 29 and 31 for inserting the blow pins 28 and 30 are formed in the side portion and the lower portion of the female die 26. Further, a pre-blow pin 32 is arranged along the axial direction of the core metal 16, and the tip of the pre-blow pin 32 is projected from the core metal 16. Then, from the lower end of the pre-blow pin 32, the die 10
² to 3 kg / cm ² of low-pressure air is blown into the parison 22 that is drooped from the front end of the parison 22 and pinched in a bag shape by the pinch device 34 to expand the parison 22.

On the other hand, a blow pin 28 can be inserted into the female die 26 from a side portion of the female die 26, and another blow pin 30 can be inserted into the lower portion of the female die 26. There is.

The blow pin 30 is considerably longer than the blow pin 28, and the blow pin 2
Both of the tips of 8 and 30 are located on the upper part of the container of the parison 22, and the two blow pins 28 and 30 are
Is designed not to interfere.

By arranging the tips of the two blow pins 28 and 30 above the container of the parison 22, the replacement of the air with the super-water or the cooling water can be performed completely.

The rear ends of the blow pins 28 and 30 are connected to the flexible tubes 36 and 37, respectively, and when the blow pins 28 and 30 are mounted on the female die 26, the blow pins 28 and 30 are moved forward and backward. Are available.

Further, the rear ends of the flexible tubes 36 and 37 are connected to two-way switching valves 38 and 39, respectively, and are appropriately switched between compressed air sent from an air compressor or pump (not shown) or hot water or cooling water. It is designed to be used.

A heating or cooling pipe 40 that circulates a heating medium such as oil for heating the male mold 24 and the female mold 26 is arranged in both molds 24 and 26, and both molds 2 and
Indentations such as letters and patterns are engraved on the cavity surfaces 41 of Nos. 4 and 26.

As shown in FIGS. 10 and 11, the blow pins 28 and 30 have sharp tips. In addition to the tips of the blow pins 28 and 30, a large number of supply / discharge holes 28a for air, warm water, etc. are formed. This is because when the supply / discharge holes 28a are formed at the tips of the blow pins 28, 30, the ends of the blow pins 28, 30 are easily clogged with resin when the parison 22 is shaped, and therefore the supply / discharge holes 28a are not formed. is there.

Further, the supply / discharge hole 28a is large so that the supply / discharge of air, warm water and cooling water can be smoothly performed.

Next, a molding procedure by the blow molding device will be described.

First, a mold opening process for opening both the male and female molds 24, 26 is performed. Next, as shown in FIG.
After the parison 22 is hung between 6 and the lower part of the parison 22 is pinched by the pinch device 34, low pressure air is blown into the parison 22 from the pre-blow pin 32 to expand the parison 22.

Further, the male and female molds 24 and 26 are opened and the parison 22 is hung down to an appropriate length (parison 2
(The position where the pinch part of 2 comes out from the lower end parts of both molds 24 and 26)
During the parison feeding process until completion, the heating or cooling pipe 40 is first caused to flow a heating medium to heat both molds 24 and 26 to, for example, 130 ± 20 ° C.

In this embodiment, as the resin, polypropylene resin (PP), polyethylene resin (PE), AB
S resin and modified PPO resin are used.

Then, as shown in FIG. 3, a mold clamping process for clamping the male and female molds 24, 26 is performed, and both molds 24, 2 are performed.
Close the parison 22 above and below 6.

Further, after that, the blow pin insertion hole 2
While inserting the blow pins 28 and 30 into 9 and 31, respectively, switching the two-way switching valves 38 and 39, respectively, the high pressure air (5 to 7 kg / cm ² ) from the compressor (not shown) is put into the container of the parison 22. Molds 24 and 2 which were blown and clamped
6 is formed on the cavity surface 41 (FIG. 4).

Next, the two-way switching valve 38 is switched to switch the high pressure air blown from the blow pin 28 into the container of the parison 22 to warm water (70 to 90 ° C.). On the other hand, the two-way switching valve 39 does not switch, and only blows high pressure air (FIG. 5).

As hot water is supplied from the blow pin 28 into the container of the parison 22, hot water is stored in the container of the parison 22 and air is naturally discharged from the blow pin 30 (FIG. 6) (FIG. 7).

As described above, the container of the parison 22 is filled with warm water to shape the parison 22 on the cavity surface 41, and the surface transferability is improved by the synergistic action of the heating medium flowing through the heating pipe 40. is there.

In the cooling step, the warm water is switched to the cooling water and the cooling medium is circulated through the cooling pipe 40 to cool the parison 22 from inside and outside.

After switching from hot water to cooling water in the container of the parison 22, the cooling efficiency by the cooling water increases after an appropriate time, and the container of the parison 22 is cooled and solidified.
At this time, the cooling medium flowing through the cooling pipe 40 is 50 ± 10.
Adjust the temperature to be ° C.

During the cooling process, hot water is introduced from the blow pin 28, and at the same time the cooling water stored in the container of the parison 22 is easily discharged through the blow pin 30. The tip of the blow pin 30 is the container of the parison 22. It is moved so that it is located below (Fig. 8). next,
When hot water is switched to cooling water and the cooling process is completed, air is continuously introduced from the blow pin 28 and cooling water is drained from the blow pin 30. In this way, the cooling water in the container of the parison 22 is almost completely discharged (FIG. 9).

In this embodiment, the blow pin 30 inserted from the bottom is made longer than the blow pin 28 inserted from the side of the female die 26, and the tips of both blow pins 28, 30 are placed in the container of the parison 22. The air and hot water were supplied and discharged in the state of being positioned above, but if a short blow pin 30 is used as shown in FIG. 12, the replaceability of air and hot water at the time of hot water supply will be improved. Parison 22 to improve
Another blow pin 42 may be inserted into the upper part of the container.

[0033]

As is apparent from the above description, according to the present invention, the blow pin is inserted from the side and the lower part of the mold holding the parison to mold the container while pressurizing the air and molding the parison. After pressure molding, switch the side blow pin of the container from air to hot water while keeping the sealed and pressurized state, discharge air from the lower blow pin and fill the container with hot water, press the parison against the mold surface, and continue. By switching from hot water to cooling water to cool the container, the air inside the parison container can be replaced with hot water while keeping the pressurized state in the parison, so the parison can be smoothly shaped on the cavity surface and the surface property is improved. And the transferability is improved. In addition, since cooling water is supplied into the parison in the cooling step, cooling is performed inside and outside the parison to shorten the cooling cycle and improve dimensional accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a blow molding device.

FIG. 2 is an explanatory diagram illustrating a blow molding process.

FIG. 3 is an explanatory diagram showing a continuation of the operation of FIG.

FIG. 4 is an explanatory diagram showing a continuation of the operation of FIG.

5 is an explanatory diagram showing a continuation of the operation of FIG. 4. FIG.

FIG. 6 is an explanatory diagram showing a continuation of the operation of FIG.

7 is an explanatory diagram showing a continuation of the operation of FIG.

8 is an explanatory diagram showing a continuation of the operation of FIG. 7. FIG.

9 is an explanatory diagram showing a continuation of the operation of FIG.

FIG. 10 is a tip outline drawing of a blow pin used in the blow molding method according to the present invention.

11 is a cross-sectional view of the blow pin shown in FIG.

FIG. 12 is an explanatory diagram showing another embodiment.

[Explanation of symbols]

 10 dies 12 dies housing 14 core 16 core metal 18 resin passage 20 slit 22 parison 24 male mold 26 female mold 28, 30 blow pin 28a supply / discharge hole 29, 31 blow pin insertion hole 32 pre-blow pin 34 pinch device 36, 37 flexible Tube 38, 39 Two-way switching valve 40 Heating or cooling pipe 41 Cavity surface 42 Blow pin

Claims (1)

[Claims] 1. When molding a container while inserting a blow pin from the side and bottom of a mold holding a parison and pressurizing air, after the pressure molding of the parison, the container is kept in a sealed and pressurized state. Switch the side blow pins from air to warm water, discharge the air from the lower blow pins, fill the container with warm water, press the parison against the mold surface, and then switch from warm water to cooling water to cool the container. A blow molding method characterized by the above.