JP2910931B2 - Blow molding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] In the present invention, when a molten resin is extruded from a die core of a hollow molding machine to form a parison, the extruded molten resin adheres to the die tip and this is formed. A molded product made by baking hardening and suppressing the formation of a die line on the surface of the extruded parison due to baking generated at the tip of the die, holding the parison in a mold, and air blowing. The present invention relates to a hollow molding method and a hollow molding method for preventing the appearance of a die line from appearing on the outer surface and impairing the appearance for a long time.

[Prior Art] When manufacturing a hollow molded article, it is desirable that extrusion of the parison be performed without interruption in order to increase the production efficiency. However, when the parison is formed by extruding the molten resin, the parison is rubbed, and a resin deposit called a die is formed at the tip of the die.

The metal tar is deteriorated and carbonized over time, resulting in a hard burn, which comes into contact with the inner and outer surfaces of the extruded parison and forms a die line in the direction of extrusion on the parison surface. When the parison on which the die line is formed is sandwiched by a mold and air-blown to form a molded product, the surface of the molded product becomes uneven and rough, resulting in a molded product having poor appearance.

Since the deterioration rate at which the above-mentioned eyes are burned is higher for a material having a lower thermal stability, a slip agent or a heat stabilizer is added to the resin to be extruded to adhere the eyes or to burn the eyes. However, it is difficult to completely prevent this.

For this reason, conventionally, when a die line is likely to occur, the parison is temporarily stopped, the tip of the die core is cleaned, and then restarted to prevent the die line from being generated on the parison surface.

[Problems to be Solved by the Invention] However, in order to prevent the occurrence of die lines,
Stopping the operation of the apparatus and cleaning the die core has a problem that the production efficiency is reduced and the cost of the product is increased.

The present inventors have intensively studied to solve this problem.

For example, high-density polyethylene (HDPE), which has the highest market share as a raw material for hollow molded products, is sometimes used without additives, but usually a heat stabilizer is added to prevent thermal deterioration during molding. ing. When this HDPE is measured for the change in resin with a differential thermal analyzer, the pyrolysis temperature is 240 to 250 ° C in the presence of air, whereas when measured in an inert gas, almost all Without measurement, it can reach the resin ignition temperature near 380 ° C.

From this, it was considered that the higher the resin temperature and the longer the time in contact with air, the more the carbonization of the resin was promoted.

SUMMARY OF THE INVENTION The present invention has been made based on the above-described concept, and an object of the present invention is to provide a hollow molding method in which a die line is not generated even when a parison is continuously extruded for a long time, and an apparatus therefor.

[Means for Solving the Problems] In order to achieve the above object, the molding method of the present invention blows an inert gas onto at least the outside near the extrusion port of a parison extruded from the tip of a die core of a hollow molding apparatus. Put on.

Further, the blow molding apparatus is provided with a gas ejector having an ejection port for spraying an inert gas to at least an outer peripheral surface near an extrusion port of a parison to be extruded.

[Operation] Since the present invention is configured as described above, an inert gas is blown from at least outside the vicinity of the parison outlet having the highest temperature, and an inert gas atmosphere is provided near the parison outlet. ,
The occurrence of burning at the lower end of the die is suppressed. This is considered to be based on the effect of preventing oxidation. In particular, it is presumed that a large amount of new air is supplied to the outside and the air is easily oxidized.

EXAMPLES The present invention will be described below with reference to examples.

FIG. 1 shows an embodiment of a die core portion in a hollow molding apparatus of the present invention, and reference numeral 1 in the figure denotes a die. Inside the die 1, a core 2 having a support air hole 2a formed in the center is provided, and a cylindrical resin passage 3 and an extrusion port 3a are formed.

On the outer periphery of the lower part of the die, the inner periphery of the upper part 4a of the ring-shaped gas ejector 4, as shown in the plan view in FIG.
It is attached to the lower periphery of the die 1. This gas ejector 4
The lower part 4b is concentric with the upper part and opens to the extrusion port 3a side. On the inner upper edge of this opened lower part 4b, the extrusion port 3a
It is formed as a slit-shaped gas outlet 4c for blowing an inert gas to the vicinity of the outlet 3a outside the parison 5 extruded from the outlet. The gas ejector 4 is provided with a gas introduction pipe 4d into which an inert gas is introduced and ejected from the ejection port 4c and an ejected gas on the outer peripheral portion through a perforation 4e from a sealed chamber formed by the ejector 4 and the die 1. A gas outlet pipe 4f is attached. However, when the closed chamber is not formed as described above, the perforation is unnecessary.

In order to perform hollow molding using the hollow molding apparatus having the above configuration, a molten thermoplastic resin is extruded using an extruder (not shown), and extruded from an extrusion port 3a through a resin passage 3 of a die core. A parison 5 is formed. At this time, an inert gas is introduced from the gas introduction pipe 4d and is ejected from the ejection port 4c on the inner upper edge of the lower part 4b, so that the vicinity of the extrusion port 3a outside the parison 5 becomes an inert atmosphere, and burning occurs at the die tip. Is suppressed. Further, if necessary, an inert gas is introduced separately from the air from the support air hole 2a, attached to the tip of the die, and a slit for ejecting the inert gas is provided, so that the inner surface of the parison becomes the same. If the shape of the parison is maintained by introducing an inert gas instead of air, the inside of the parison 5 also becomes an inert gas atmosphere, and the occurrence of burning at the tip of the core 2 is suppressed.

Due to this operation, the vicinity of the extrusion port 3a on the outer surface of the parison 5 becomes an inert gas atmosphere, so that the burning of the die is suppressed, and the die line is prevented from being formed on the surface of the parison for a long time. .

As the inert gas, any ordinary inert gas such as argon and nitrogen can be used. In particular, N ₂ is inexpensive and is suitable as the inert gas used in the present invention.

Further, even if an inert gas is introduced into the support air hole 2a so that no line is formed on the inner surface of the parison 5,
Since it becomes the inner surface of the molded product, it does not affect the outer surface gloss, but in the case of a transparent molded product, the line on the inner surface can be seen through, so introduce an inert gas from the support air hole 2a. Has a great effect on improving the appearance.

Example 1 Using a 90 mm screw blow molding machine as a molding machine, a hollow molded product of HDPE (Showa Denko, Shorex 5003) having a density of 0.944 g / cm ³ and an MFR of 0.3 g / 10 min was produced.

Molding conditions are: resin temperature: 200 ° C, screw rotation speed: 50r
pm, mold temperature: 20 ° C. ± 2 ° C., die shape: a cylindrical bottle 500 ml, the N ₂ gas pressure of 0.1 kg / m ² as an inert gas to be introduced into the gas ejector at a rate of 1000 cc / min Air was supplied to the support air holes.

The occurrence of die lines on the outer surface of the parison when the molded article was manufactured as described above was examined over time.

Comparative Example 1 Example 1 except that no inert gas was supplied to the ejector
Same as.

 Table 1 shows the results of Example 1 and Comparative Example 1 collectively.

Example 2 A random polypropylene having a density of 0.9 g / cm ³ and an MFR of 1.0 g / 10 min (Showa Denko KK, Show Allomer EG110) was used as a molding machine using a screw blow molding machine of φ90 mm.
Made a hollow molded product.

Molding conditions are: resin temperature: 220 ° C, screw rotation speed: 50r
pm, mold temperature: 20 ° C. ± 2 ° C. Mold shape: 500 ml round bottle, the N ₂ gas pressure of 0.1 kg / m ² as an inert gas supplied to the gas ejector and fed at a rate of 1000 cc / min, Also, 0.2 kg / m ² of N ₂ gas was supplied from the support air hole at a rate of 1000 cc / min instead of air.

The occurrence of die lines on the outer surface and inner surface of the parison when the molded article was manufactured as described above was examined over time.

Comparative Example 2 Example 2 was the same as Example 2 except that no inert gas was supplied to the gas ejector and air was introduced into the support air holes.

 Table 2 summarizes the results of Example 2 and Comparative Example 2.

[Effects of the Invention] As described above, in the blow molding method and apparatus of the present invention, burns due to an inert atmosphere caused by a tar on which a parison extruded from a die core is rubbed and adhered to a die are suppressed. As a result, molded products with excellent appearance can be obtained, and die lines do not occur for a long time, and the number of times of stopping the molding machine and removing burns is greatly reduced, so that production efficiency is improved, and efficiency is reduced. Is obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a blow molding apparatus according to the present invention, and FIG. 2 is a plan view of a gas ejector. 1 ... die, 2 ... core. 2a …… Support air holes, 3…
... Resin passage, 3a ... Extrusion port, 4 ... Gas ejector, 4a ...
Upper part, 4b lower part, 4c gas outlet, 4d gas inlet pipe, 4e perforated, 4f gas outlet pipe, 5 parison.

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) B29C 49/00-49/80 B29B 11/10 B29C 47/08 B29C 47/12-47/32 B29C 47/88

Claims (2)

(57) [Claims] 1. A hollow molding method, wherein an inert gas is blown onto at least the outside near the extrusion opening of a parison extruded from the tip of a die core of a hollow molding apparatus. 2. A blow molding apparatus having a die core for extruding a parison, wherein a gas ejector having an ejection port for blowing an inert gas to at least an outer peripheral surface near an extrusion opening of the parison extruded from the die core is provided at a die tip portion. A hollow molding apparatus, which is attached to a hollow molding apparatus.