JPH04296524A - Blow molding method - Google Patents

Abstract

PURPOSE:To improve the yield of molding, while the transferring property from a mold is excellent. CONSTITUTION:The die 40 for molding a parison is brought in close contact with the upper aperture of the cavity 14 of a closed mold 10, and molding material is injected into the cavity 14, thereby molding the parison 56. While the parison 56 is injected, air 60 is blown into the parison, and simultaneously the cavity is evacuated (arrow 18) from the cavity surfaces 16a, 16b of the mold 10, and then after the parison 56 has been molded along the whole area of the cavity 14, high pressure-gas is blown into the parison.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a blow molding method in which high-pressure gas is blown into a parison formed into a cylindrical shape. The present invention relates to a blow molding method suitable for obtaining products.

0002

[Prior Art] Conventionally, when blow molding a hollow molded product whose shape changes three-dimensionally, such as a duct, one side of an open mold 1 is placed horizontally or inclined, as shown in FIG. The die 4 for forming the parison 3 is positioned above the upper part of the cavity 2 provided in the mold 1, and the mold 1 is moved so that the parison 3 is along the cavity 2. Pour in. Thereafter, the mold 1 was closed and high-pressure air was blown into the parison 3 to perform blow molding. Alternatively, the mold 1 is arranged horizontally or inclined, the die 4 is moved along the cavity 2,
There is also a method of pouring parison 3 into the cavity.

0003

However, in either method, with the mold 1 open, a large parison 3 that covers the entire cavity surface of the mold is injected into the cavity 2.
Since the mold is then closed and molded, the molding material (resin) forming the parison 3 protrudes from the cavity 2, causing large burrs to occur and significantly reducing the molding yield.

Moreover, in the case of molding a long object with a complicated three-dimensional shape, even if the thickness of the parison 3 injected into the atmosphere is uniform, when the mold 1 is closed, the inside of the cavity 2 In some cases, the parison 3 was stretched locally, causing the parison 3 to become partially thin, or even burst, making it impossible to form the parison 3. In addition, since the parison 3 is injected into the atmosphere and comes into contact with the low-temperature mold cavity surface, the surface of the parison 3 is rapidly cooled, the fluidity of the molten resin that is the molding material is significantly reduced, and the cavity surface is Even if it had a mirror surface, the transferability from the mold 1 was poor and the surface condition of the molded product was deteriorated.

[0005] The present invention has been made in order to eliminate the drawbacks of the prior art, and aims to provide a blow molding method that has excellent transferability from a mold and can improve molding yield. .

In order to achieve the above object, the blow molding method according to the present invention involves bringing a parison-forming die into close contact with the cavity opening of a closed mold, and injecting a molding material into the cavity to form a parison. While blowing gas into the parison, the inside of the cavity is evacuated from the cavity surface of the mold, and after the parison is formed over the entire area of the cavity, high-pressure gas is blown into the parison.

It is desirable that the temperature of the cavity surface be maintained approximately equal to the temperature of the molding material injected into the cavity during the formation of the parison, and cooled after the formation of the parison.

[0008]

[Operation] The present invention configured as described above forms a parison by injecting the molding material directly into the cavity of a closed mold, so the molding material does not protrude from the cavity and the molded product has extremely little burr. Therefore, the molding yield can be greatly improved. In addition, in the present invention, since the parison is injected directly into the mold cavity, unlike when the parison is injected into the atmosphere, the surface of the parison is hardly cooled by the atmosphere, and good transferability can be obtained. , the surface condition of the molded product can be improved.

Furthermore, since the air is exhausted from the cavity surface of the mold, the molding material flows smoothly along the cavity surface, making it possible to make the thickness of the parison almost uniform, thereby preventing the parison from becoming locally thin. This can prevent bursting during blow molding.

[0010] If the temperature of the cavity surface is maintained approximately equal to the temperature of the molding material to be injected during the formation of the parison, and then cooled after the formation of the parison, the parison will be cooled slowly together with the mold, and the temperature will be even better. Transferability is improved, and molded products with extremely good surface properties can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the blow molding method according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an explanatory diagram of a blow molding method according to an embodiment of the present invention.

In FIG. 1, a mold 10 is divided into two molds 10a and 10b by a parting line 12. As shown in FIG. A cavity 14 whose shape changes three-dimensionally is formed on the dividing surface of both molds 10a and 10b. In addition, the cavity surface 16 of each mold 10a, 10b
A, 16b are provided with a large number of minute exhaust holes (not shown), and these exhaust holes are connected to a vacuum pump, etc. (not shown), and as shown by arrow 18, the cavity surfaces 16a, The inside of the cavity 14 can be exhausted from the cavity 16b.

Furthermore, the molds 10a, 10b are provided with heaters 20 for maintaining the cavity surfaces 16a, 16b at a predetermined temperature, and cavity surfaces 16a, 16b at appropriate locations along the cavity surfaces 16a, 16b. A cooling hole 22 is provided through which cooling water is passed. The cavity 14 is open at the upper and lower ends of the mold 10.
Mounts 24, 26 are formed in this opening.

A circular lid 28 is in close contact with the lower mount 26 of the mold 10, and this lid 28 is raised and lowered in the direction of an arrow 32 by, for example, a cylinder (not shown) to cover the cavity 14. Open and close the bottom opening. On the other hand, the lower end surface of the die 40, which moves up and down as shown by the arrow 34, is brought into close contact with the upper mount 24.

The die 40 has a cylindrical mandrel 44 disposed inside a cylindrical die housing 42 . The mandrel 44 is connected to the constricted portion 46 of the die housing 42.
It is located above and has a conical lower end corresponding to the constricted part 46, and has an outer diameter smaller than the inner diameter of the die housing 42, and has a molten material, which is a molding material (not shown), between the die housing 42 and the die housing 42. A channel 48 through which resin flows is formed.

A mandrel core 50 is inserted into the center hole of the mandrel 44. This mandrel core 50 is
A skirt-like die lip 52 is formed at the lower end, and the upper end is connected to a parison control cylinder (not shown), and is moved up and down by the parison control cylinder to form an injection port 54 between it and the die housing 42. By changing the opening degree (opening area) of the parison 56, the thickness of the parison 56 shown by the two-dot chain line injected into the cavity 14 can be adjusted.

The outer diameter of the injection port 54, ie, the inner diameter of the lower end of the die housing 42, is approximately equal to the opening diameter of the upper end of the cavity 14. Further, the die lip 52 is provided with a blow hole 58 at the center along the axis.
Air 60 is blown into the parison 56 to enable so-called pre-blowing.

When performing blow molding, the mold 10a,
10b is closed, the lower end opening of the cavity 14 is closed with the lid 28, and the die 40 is lowered to bring the lower end surface of the die 40 into close contact with the mount 24. At this time, the die 40 is pressed against the mount 24 by a pressing device (not shown) to prevent molten resin from leaking from the contact surface. The molds 10a and 10b are heated by the heater 20 to maintain the temperature of the cavity surfaces 16a and 16b at the same level as the die 40, that is, approximately the temperature of the molten resin.

On the other hand, molten resin injected from an accumulator or the like (not shown) flows into the die 40, and the resin is injected from an injection port 54 to form a parison 56. When forming the parison 56, air 60 is blown from the blow hole 58 to perform pre-blowing, and the inside of the cavity 14 is evacuated through exhaust holes provided in the cavity surfaces 16a and 16b. Note that the amount of air 60 blown, the pressure, etc. are determined in advance through experiments, calculations, etc. As a result, the inside of the cavity 14 has a higher pressure than the outside, and the parison 56 is brought into close contact with the cavity surfaces 16a, 16b.
The molten resin flows down smoothly while forming a parison 56.

When the parison 56 reaches the lower end of the cavity 14, injection of resin from the die 40 is stopped. The stopping of this injection, that is, the completion of injection, can be accomplished by (a) performing molding several times in advance to ascertain the condition of the molded product (underfilling or overfilling), and determining an appropriate measurement value for the injection device; (b) Near the bottom end of the cavity 14, a resin pressure gauge,
This is carried out by a method in which a sensor such as a resin thermometer or a capacitive proximity switch is provided, and the sensor detects that the parison 56 has reached the lower end of the cavity 14, and then stops the injection.

When the injection of the parison 56 is completed, high-pressure air is blown through the blow hole 58 provided in the mandrel core 50, the power supply to the heater 20 is stopped, and cooling water is introduced into the cooling hole 22 to cool the cavity surface 16a, 16b is lowered to cool the molded product. And cavity 14
The vacuum inside is stopped at an appropriate time during the cooling process of the molded product.

When cooling of the molded product is completed, the blowing of high-pressure air is stopped, and the high-pressure air inside the molded product is exhausted from the blowing hole 58 to bring the inside of the molded product to atmospheric pressure, and then a pressing device (not shown) is pressed. is operated in reverse to raise the die 40 and separate the molded product from the die 40. That is, when the die 40 rises, the molded product (parison 56) is torn off at the heated portion of the lower surface of the die 40. Thereafter, the mold clamping cylinder is operated to open the molds 10a and 10b, and the lid 28 is lowered to take out the molded product from the mold 10.

As described above, in the embodiment, the parison 56 is directly discharged into the cavity 14 of the closed mold 10, and the air 60 is blown into the parison 56 for pre-blowing. Since the air is evacuated, the parison 56 does not have its outer surface brought into contact with the atmosphere and its temperature is lowered, and the parison 56 is brought into close contact with the cavity surfaces 16a and 16b, and the mold 10
The transferability from the paper is greatly improved. Further, in the embodiment, since the parison 56 is injected into the closed mold 10, not only is there almost no burr generation and the molding yield is improved, but also the parison 56 is locally elongated.
The thickness of the parison may become uneven, or the parison 5 may become uneven during blow molding.
6 can be prevented from bursting.

In addition, the mold 10 is provided with the heater 20 and the cooling holes 22 are formed so that the cavity surface 16 is not exposed until the formation of the parison 56 in the cavity 14 is completed.
Since the temperatures of a and 16b are maintained almost equal to the temperature of the parison 56 and the mold 10 is cooled after forming the parison 56 to cool the parison 56 slowly, transferability is further improved and molding with extremely good surface condition is achieved. Goods can be obtained. In the embodiment, the die 40 is brought into close contact with the mold 10, and in order to separate the molded product, it is only necessary to raise the die 40. Therefore, the parison pinch directly below the die 40, which was conventionally required, can be omitted. Not only does space for pinching become unnecessary, but also burrs do not occur at the pinching portion, improving molding yield. Moreover, the cavity 14 is
Since the opening at the lower end is opened and closed by the lid 28, the molded product can be released from the top and bottom at the time of mold release, making mold release easy.

In the above embodiment, the case where the die 40 is raised and lowered by the pressing device has been described, but the mold 10 side may be raised and lowered. Further, in the above embodiments, a case has been described in which air is used as the pre-blowing gas and the high-pressure gas for molding, but other gases such as nitrogen may also be used. In the above embodiments, the case where the cavity 14 changes three-dimensionally has been described, but it goes without saying that the present invention can also be applied to blow molding of a straight tube-shaped molded product.

FIG. 2 shows another embodiment of the mold used in the present invention. The mold 10 of this embodiment is formed so that the lower end of the cavity 14 is closed. The mold 10 of this embodiment also provides the same effects as described above.

[0027]

As explained above, according to the present invention, since the parison is formed by directly injecting the molding material into the cavity of a closed mold, the molding material does not protrude from the cavity, and the molding The burrs on the product are extremely reduced, and the molding yield can be greatly improved. In addition, in the present invention, the parison is injected directly into the mold cavity, so unlike the parison that is injected into the atmosphere,
There is almost no cooling of the surface of the parison by the atmosphere, good transferability is obtained, and the surface condition of the molded product can be improved.

Moreover, since the parison is injected into the cavity of a closed mold, the molding material flows smoothly along the cavity surface with an almost uniform thickness, causing local thinning and blow molding. This can prevent it from bursting in the event of an accident. Note that if the temperature of the cavity surface is maintained approximately equal to the temperature of the injected molding material during the formation of the parison, and then cooled after the formation of the parison, the parison will be cooled slowly together with the mold, resulting in better transferability. You can improve your performance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the blow molding method according to the present invention.

FIG. 2 is an explanatory diagram of another embodiment of a mold applied to the present invention.

FIG. 3 is an illustration of a conventional blow molding method for obtaining a molded article whose shape changes three-dimensionally.

[Explanation of symbols] 10 Mold 14
Cavities 16a, 16b
cavity surface

Claims (1)

[Claims] 1. A parison-forming die is brought into close contact with the cavity opening of a closed mold, and a molding material is injected into the cavity to form a parison, while gas is blown into the parison. A blow molding method characterized in that after evacuating the inside of the cavity from a surface and forming the parison over the entire area of the cavity, high-pressure gas is blown into the parison.