JPS61134222A - Blow molding method - Google Patents

Abstract

PURPOSE:To improve adhesive strength of a pinch-off part, by performing blow molding within inactive-gaseous atmosphere. CONSTITUTION:As inactive gas may be good if it does not oxidize the surface of resin, carbon dioxide (CO2), helium (He) and argon (Ar) other than N2 gas are used. Blow molding resin such as high-density polyethylene or polyamide is in a molten state at the time of either injection or extrusion of a parison and oxidization progresses already from the time of the extrusion or injection of the parison so long as atmosphere is within aerial atmosphere. Although it is necessary to perform the title method within inactive-gaseous atmosphere from the time of the extrusion or injection of the parison, an improvement is sufficient adhesive strength is observed even if inactive gas is blown into at the time of only blowing. A container W is molded by a method wherein simultaneously with extrusion of the parison P at a resin temperature of 210 deg.<= N2 gas is blown off through a blow pin B by making use of a single-layer blow molding machine and the N2 gas is blown off by inserting the parison P between molds M.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a blow molding method that is often used for molding hollow containers.

As is well known in the art, a single layer of high density polyethylene (HDP) or high density polyethylene and polyamide (FA)
Multilayer blow-molded containers are used in a wide variety of applications.

Particularly with regard to automobile fuel tanks, the use of resin using blow-molded containers as described above is being actively promoted, and it is an essential condition for tanks to have impact strength that prevents fuel leakage in the event of a collision. It has become. - Due to the special nature of the molding method, the pinch-off part (see Figure 1) of blow-molded containers is generally prone to breakage or peeling, so improving the adhesive strength of the pinch-off part is an important issue. It has become.

For this reason, various methods have been proposed, for example, as shown in Japanese Patent Publication No. 57-2579 and Japanese Patent Application Laid-Open No. 59-87132, but these methods all involve, for example, impregnating polyamide with a certain percentage of a compound. The basic idea is to change one's identity.

Problems to be Solved by the Invention However, the quality of the adhesive strength at the pinch-off portion depends not only on internal factors such as the above-mentioned towability, but also on external factors.

For example, according to the ordinary law! D When blow molding is performed by extruding molten resin at 200°C or higher into a cylinder in the vertical direction, the resin on the surface of the υ pinch-off portion is oxidized by oxygen in the air. This oxidation phenomenon is also an external factor that causes the adhesive strength of the pinch-off portion to decrease. That is, the oxidized layer is interposed between the bonded resins.

The present invention aims to provide a blow molding method that prevents the above-mentioned oxidation phenomenon and improves the adhesive strength of the pinch-off portion.

Means for Solving the Problems The present invention is characterized in that blow molding is performed in an inert gas atmosphere such as nitrogen gas coffin 6) as a molding condition.

The inert gas only needs to be one that does not oxidize the resin surface, so in addition to N2 gas, carbon dioxide (CO),
Gold such as helium (He) and argon (Ar) can be used. .

Normally, resins for blow molding such as high-density polyethylene and polyamides (such as nylon) are in a molten state when the parison is injected or extruded, and the atmosphere is in an air atmosphere when the parison is extruded or injected. Oxidation has already progressed.

Therefore, it is preferable to carry out parinone extrusion or injection in a non-oxidizing atmosphere, that is, in an inert gas atmosphere, but even if an inert gas is blown in instead of air only during the blowing stage, sufficient bond strength can be improved. is recognized.

Moreover, it does not matter whether the container to be molded has a single layer or multiple layers.

Examples 1 to 3 A pellet of high-density polyethylene (manufactured by Showa Denko ■, registered trademark Nijiyo Rex Super 4551H) was molded using a single-layer blow molding machine (manufactured by Japan Steel Works ■, model NB-120) shown in FIG. At the same time as extruding parison Pt at a resin temperature of 210°C and an extrusion amount of 3#/-, N2 is applied from blow pin B.
Gas was blown out, and a container w6 having a thickness of 4 mm and an internal volume of 50 t was formed by blowing N2 gas between the parison Pf and gold ff1M.

Furthermore, as Examples 2 and 3, only an inert gas was used under the same conditions as above. Molding was performed by replacing gas and He gas.

Example 4 Under the same conditions as in Examples 1 to 3 above, parison extrusion was performed in an air atmosphere, and only blowing was performed using N and gas.

Comparative Example 1 Under the same conditions as in Examples 1 to 3 above, molding was carried out in an air atmosphere without using any inert gas from extrusion to blowing.

Then, dumbbell-shaped samples were cut out from each container molded in Examples 1 to 4 and Comparative Example 1, and JIB
Tension speed 50 m/in accordance with K6760
- The adhesive strength of the pinch-off portion PO was measured under -. The measurement results are shown in Table-1.

Effects of the Invention As described above, according to the present invention, the adhesive strength at the pinch-off portion is significantly improved compared to conventional methods, and is particularly suitable for molding containers that require high adhesive strength such as automobile fuel tanks. It is.

In addition, in the past, in order to ensure the strength of the pinch-off part, it was necessary to consider various pinch-off shapes depending on the container shape, etc., but with the present invention, sufficient adhesive strength can be obtained, so the final pinch-off shape can be determined. It has the advantage of not requiring much effort.

[Brief explanation of drawings]

FIG. 1 (Al (B) (0) is a process explanatory diagram showing an example of the molding method of the present invention. P... parison, Pa... pinch-o-y part, s...
・Blow pin.

Claims (4)

[Claims] (1) A blow molding method in which a parison is preformed by extrusion molding or injection molding, and a gas is blown into the inside of the preformed parison, and the blow molding is characterized by molding in an inert gas atmosphere. Method. (2) The blow molding method according to claim 1, wherein at least extrusion or injection of the parison, which is preforming, is performed in an inert gas atmosphere. (3) The blow molding method according to claim 1, characterized in that the molding is carried out by blowing an inert gas into at least the preformed parison. (4) The blow molding method according to claim 1, 2, or 3, wherein the inert gas is any one of nitrogen, carbon dioxide, helium, and argon.