JPH0148135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a blow molding method suitable for shortening the cooling time after mold clamping and shortening the molding cycle time in blow molding of thermoplastic resin.

[Conventional technology]

Blow molded products are molded using thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene polycarbonate, and are used in many fields such as detergent bottles, cosmetic bottles, milk containers, and kerosene cans. In blow molding, the melt-extruded parison is sandwiched between cavity molds and the molds are clamped, and pressurized gas is blown into the parison from an air pin to expand the parison and press it against the inner surface of the cavity mold to form the mold, leaving the mold clamped. After cooling and solidifying, the mold is opened to remove the blow molded product.

In blow molding, the entire inside of the cavity mold is cooled by passing a refrigerant (usually water) at the same temperature, and the inside of the cavity mold is kept at a low temperature in order to shorten the cooling time and molding cycle time. In this case, moisture in the air condenses during the mold opening and roughens the outer surface of the blow-molded product, so the temperature of the inner surface of the cavity mold must often be kept at about 20°C or higher.

[Problems to be solved by the present invention]

As mentioned above, in conventional technology, there is a conflict between the desire to shorten the molding cycle time by keeping the inner surface of the mold as low as possible and the desire to eliminate roughening of the outer surface of the molded product due to dew condensation during mold opening. It has been hoped that a solution will emerge.

[Means to solve the problem]

The present invention was arrived at as a result of various studies to improve this situation, and its gist is to provide a cavity mold that is cooled to an extent that no condensation occurs on the inner surface, and a cavity mold that is cooled to a lower temperature than the cavity mold. This is a blow molding method in which a parison made of thermoplastic resin is sandwiched between a rear mold which is isolated from the cavity mold during mold opening and is in close contact with the cavity mold during mold closing, and gas is blown into the parison to expand and cool the mold.

The contents of the present invention will be explained below using the drawings.

FIG. 1 and FIG. 2 are perspective cutaway views showing a mold closed state and a mold open state, respectively, of a mold used in the blow molding method of the present invention, and FIG. 3 is a cavity mold of the same mold, It is a sectional view showing an example of the connection state of a rear part mold and a mold mounting plate. 1 is a cavity mold in which a parison (not shown) into which pressurized gas is blown is expanded and tightly adheres to its inner surface; 2 is a rear mold; both molds are cavity molds as shown in Fig. 3; They are connected by a guide rod 30 so as to be isolated during mold opening in step 1 and in close contact with each other during mold clamping.
A stopper 31 is fixed to the top surface with a business 32, and a spring 33 is further arranged around the guide rod 30. A rear mold 2 is provided between the cavity mold 1 and a mold mounting plate 3 to which a guide rod 30 is fixed, and the mold is opened while the cavity mold 11 is being clamped by the back and forth movement of the mold mounting plate 3. When the mold is opened, a gap is created between the cavity mold 1 and the rear mold 2 by the spring 33, and when the mold is closed, the cavity mold 1, the rear mold 2, and the mold mounting plate 3 are tightly packed together. .

Normally, it is preferable that the stopper 31 is not open on the inner surface of the mold, but if it is open, the inner surface of the mold and the outer surface of the stopper will be flush with each other when the two are in close contact, which will affect the surface formation of the molded product. There isn't.

The cavity mold 1 has a cooling water flow path 11, and the inner surface of the cavity mold is kept at a temperature (20
Cooling water (~60℃) is flowing. On the other hand, the rear mold 2 also has a cooling water flow path 21, but this cooling water needs to be at a sufficiently low temperature necessary for molding. In this way, the rear mold 2 is cooled to a lower temperature than the cavity mold 1, but during the mold opening before sandwiching the parison, both molds 1 and 2 are separated and the cavity mold 1 is cooled to a lower temperature than the cavity mold 1. By keeping the temperature low, moisture in the air can be prevented from condensing on the inner surface of the cavity mold and roughening the outer surface of the blow-molded product. The mold 2 is brought into close contact with the mold 2 to promote the cooling effect of the cavity mold 1 on the blow-molded product, shortening the cooling time and shortening the molding cycle time.

In the present invention, the temperature of the cavity mold 1 is approximately 20 to 60°C during the mold opening, and the temperature rises as it receives heat from the parison that expands and is crimped by blowing immediately after the mold is closed, causing the molded product to solidify. Although it takes a considerable amount of time to cool down, the cooling time is shortened because the rear mold 2 at a low temperature, for example, 5°C, is in close contact with the mold.

Since the blowing is carried out immediately after the mold is clamped, even if the temperature of the inner surface of the cavity mold 1 drops due to the close contact of the rear mold 2, there is no chance of condensation and the outer surface of the blow-molded product will not become rough.

The present invention has been described in detail above, but by dividing the mold into two parts each having the size necessary for blow molding and creating a constant low temperature part, the mold is cooled to the temperature required for molding. This succeeded in preventing dew condensation and shortening the cooling cycle time.

〔Example〕

The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

Example 1 Figures 1 to 3 were installed in a blow molding machine with a screw diameter of 90 mm.
Install the blow molding mold shown in the figure, and the density is 0.947g/
cc, using high-density polyethylene with a melt index of 0.3 g/10 min, internal volume 400 c.c., average wall thickness 2
mm bottles were molded.

Both the cavity mold and the rear mold are made of aluminum alloy, and water at 20°C is constantly passed through the cavity mold and water at 5°C is passed through the rear mold, and both molds are kept running for the entire mold clamping time. The mold was closed in just 15 seconds, and the mold was opened and the outer surface temperature reached 40°C.
A blow molded article was obtained.

Comparative Example 1 The same procedure as in Example 1 was carried out except that nothing was flowed into the cooling water channel of the rear mold and the temperature was kept at room temperature (20°C) without any particular cooling or heating, and the mold clamping time was as long as 48 seconds. A blow molded product with a firm outer surface temperature of 40°C was obtained.

Comparative Example 2 The same procedure as in Example 1 was carried out, except that water at 5°C was constantly passed through the cavity mold, nothing was flowed into the cooling water channel of the rear mold, and the temperature was kept at room temperature (20°C) without any particular cooling or heating. When the mold was opened, dew condensation was observed on the inside of the cavity mold, and although a blow molding method with a short mold closing time of 10 seconds and an external surface temperature of 40°C was developed, a pock-like pattern appeared on the external surface. This caused the appearance of the product to be inappropriate.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway perspective view showing a mold used in the blow molding method of the present invention in a closed state, Fig. 2 is a partially cutaway perspective view showing the same mold in an open state, and Fig. 3 is a partially cutaway perspective view showing the mold in an open state. It is a sectional view showing a connection state of a cavity mold, a rear mold, and a mold mounting plate of the same mold. 1... Cavity mold, 2... Rear mold, 3...
...Mold mounting plate, 11...Cooling water flow path, 30...Guide rod, 31...Stopper, 32...Screw, 33...Spring.

Claims (1)

[Claims] 1. A cavity mold that is cooled to an extent that no condensation occurs on the inner surface, and a rear mold that is cooled to a lower temperature than the cavity mold, is isolated from the cavity mold during mold opening, and is in close contact with the mold during mold closing. A blow molding method that is characterized by sandwiching a thermoplastic resin parison between two cylinders, blowing gas into it, expanding it, and cooling it.