JPH0710559B2 - Blow molding method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a blow molding method for ensuring the welding of the outer layer and ensuring the concealment of the inner layer, particularly in the pinch-off portion of the blow-molded hollow molded article by the multi-layer parison. It relates to the device.

(Prior art) Mayonnaise for multi-layer blow molding by blow blow molding,
There are industrial parts such as food containers such as ketchup, automobile ducts, and small tanks.

The strength of the pinch-off portion of these multilayer hollow molded products is inferior to the strength of other portions, and the intermediate layer is exposed at the pinch-off portion.For example, the intermediate layer may be saponified ethylene-vinyl acetate copolymer, nylon, etc. Even in the oxygen barrier layer made of, since these resins have hygroscopicity, they have a drawback that they absorb the moisture of the outside air and deteriorate the oxygen barrier performance.

That is, as shown in FIG. 7, each of the outer layer (a) and the inner layer (b) was made of a polyolefin resin having a small hygroscopic property, and the intermediate layer (c) was made of nylon and Eval (registered trademark) having oxygen barrier properties. In the hollow-molded synthetic resin molded by blow molding a three-layer parison, the intermediate layer (c) is exposed from the welded part of the outer layer (b) at the pinch-off part (d), and the intermediate layer (c) absorbs moisture from the outside air. Further, due to stress concentration in the pinch-off portion (d) or the like, as shown in FIG. 8, the pinch-off portion (d) may be separated from the interface welded portions of the outer layer (a) on both sides of the exposed intermediate layer (c), and the oxygen barrier performance may be deteriorated.

In such a peeling phenomenon, the amount of moisture absorption increases over time, the oxygen barrier performance further deteriorates, and the pinch-off strength also remarkably decreases.

Therefore, as a means for increasing the strength of the pinch-off portion, as shown in FIG. 9, there is a means in which the pinch-off portion (e) is outwardly projecting and a rib (f) is attached. In this case, the pinch-off part (e) is strengthened, but gradually peels from the interface welded part of the outer layer (h) due to moisture absorption due to the exposure of the intermediate layer (g).

Further, as disclosed in Japanese Patent Publication No. 47-4151 and as shown in FIG. 10 for the main part, a separate polyolefin resin piece (n) is welded from the outside to the pinch-off part (i) of the molded product. There is a means for concealing the pinch-off portion by bonding with a wire.

Such means increase the work steps and are inferior in workability.

(Problems to be Solved by the Invention) There is a problem of peeling from the outer layer welding interface at the pinch-off portion of a blown hollow molded article by a multi-layer parison, and means for adhering a separate resin piece is extremely difficult to solve such a point. There were problems such as poor workability.

(Means for Solving the Problems) The present invention provides means for ensuring the welding of the outer layer and ensuring the concealment of the inner layer, particularly in the pinch-off portion of the blown hollow molded article by the multi-layer parison. According to a first aspect of the present invention, a multilayer parison is pinched off by pinching off a portion which is pinched off by a die insert positioned a predetermined distance above the outer bottom forming die surface of a planned hollow molded article. After the first-stage blow molding, the blowing pressure is removed, and then the mold insert is lowered to form a void inside the mountain-shaped portion, and then the outer layer facing portion inside the mountain-shaped portion is formed. A second aspect of the present invention is a blow molding method characterized by performing a second-stage blow molding for welding, wherein the second invention is a left mold insert including a left insert piece and a right insert piece each having a biting part. , Mold consisting of right split mold part The blow molding device is provided with a blow molding mold attached so as to be movable up and down by a predetermined distance corresponding to each of the facing parts, and the blow molding mold is arranged below the extruder.

(Embodiment) The present invention will be described together with an embodiment of the apparatus shown in FIGS. 1 to 6.

As shown in FIG. 1, the blow molding die 2 arranged below the extruder 1 is composed of a left split mold portion 2a and a right split mold portion 2b, which are fixed to mounting plates 3a and 3b, respectively. The boards 3a and 3b can be horizontally reciprocally moved by the rams 4a and 4b of the mold clamping cylinders, and the left split mold part 2a and the right split mold part 2b are provided with the cut-away parts 5a and 5b, respectively. There is.

A left nesting piece 6a and a right nesting piece 6b are attached to the lower facing portions of the left split mold portion 2a and the right split mold portion 2b, respectively, to form a mold nest 6, and the left nest piece 6a, The right nesting pieces 6b each have a cutting portion 7a, 7b. The left nesting pieces 6a and the right nesting pieces 6b of the mold nesting 6 are attached at their lower ends to the mounting board 9 of the mold nesting up / down mechanism 8 so that they can be moved up and down by a predetermined distance. In addition, it is reciprocally movable in the horizontal direction.

As shown in FIG. 2, the left nesting piece 6a and the right nesting piece 6b are formed by facing each other with the bite-cutting portions 7a, 7b facing each other, and the back surface portions 6a ', 6b' are converged inward with each other. And, when the left split mold part 2a, the right split mold part 2b are brought close to each other and the cutting parts 5a, 5b are made to act, at the same time when the cutting parts 7a, 7b act to cut the cutting, The upper end surfaces of the portions 7a and 7b are in the same horizontal plane, and the lower end portions 6 of the rear surface portions 6a 'and 6b' are
a ″ and 6b ″ are located above the outer bottom forming surfaces 2a ′ and 2b ′ of the planned molded product of the left split mold part 2a and the right split mold part 2b by a predetermined distance (s), and the mold nesting vertical mechanism 8 descends. Lower end 6a ″, 6 when fully lowered
The b "is formed to have the same horizontal plane as the outer bottom forming surfaces 2a 'and 2b'.

With such an apparatus, a hollow molded article is molded as follows. A three-layer parison (A) including an outer layer 10, an intermediate layer 11, and an inner layer 12 was extruded from a hollow molding crosshead die 1a mounted on the extruder 1 to raise a left nest piece 6a and a right nest piece 6b by a predetermined distance. Left split mold part 2a, right split mold part
2b, then the left split mold part 2a and the right split mold part 2b are brought close to each other, the parison is cut by the cutting parts 5a, 5b and the cutting parts 7a, 7b, and attached to the crosshead die 1a. 2-30 kg / cm ² , preferably 3-6 kg / cm ² of pressurized air is blown into the parison (A) from the air nozzle 1b to form the parison (A).
Is expanded and brought into close contact with the cavity wall defined by the blow molding die 2 and the die insert 6 to form the first stage. At this time, at the bottom of the cavity wall, as shown in FIG. 3, the parison (A) is extended upward along the mountain-shaped portion formed by the upper portions of the left nesting piece 6a and the right nesting piece 6b, and the pinch-off is performed. The formed portion becomes a mountain-shaped portion (α) inward.

Then, once the blowing pressure is eliminated, the mold insert 6 is lowered to form a gap (β) as shown in FIG. 4, and then the blowing pressure is applied again as shown in FIG. The outer layer facing portion on the inner side of the mountain portion (α) is welded to form a steeply inclined mountain portion (γ) with the pinch-off portion projecting inward, and the mold insert 6 is lowered to form the blow molding mold 2. Open and take out the bottle-shaped hollow molded article (B).

In the center of the inner bottom (C) of the hollow molded product (B) thus molded, as shown in FIG. 6, a pinch-off portion (D) is formed which is inwardly projecting and has a steeply inclined chevron shape. In the pinch-off part (D), the welded part of the outer layer 10, the welded part of the intermediate layer 11 and the welded part of the inner layer 12 are firmly welded, and in the outer surface side concave part (E) of the pinch-off part (D), the intermediate layer 11 is formed.
The intermediate layer 11 is surely hidden by the outer layer 10 without being exposed.

In this case, the temperature of the mold insert in the first stage molding is set to about ± 10 ° C. of the parison resin temperature, and the mold insert in the second stage molding is cooled in the same manner as the mold. In order to prevent the sticking of the parison, the surface of the mold insert is coated with Teflon or the like.

Furthermore, the blowing pressure is the same in both the first-stage molding and the second-stage molding, and a heat insulating material is provided in the left split mold portion of the mold, the left nesting piece of the right split mold portion, or the mounting portion of the right nesting piece, or a space is provided. Good to have formed,
The vertical movement distance of the mold insert is about 3 mm to 10 mm.

Application examples of the present invention will be described below.

The outer and inner layers are high-density polyethylene "BZ50A" (MFR 0.25g / 10 minutes) manufactured by Mitsubishi Petrochemical Co., Ltd., and the intermediate layer is saponified product "Eval" of ethylene-vinyl acetate copolymer manufactured by Kuraray Co., Ltd. and parison resin. Using a blow molding die with a temperature of 200 ° C and a die insert with a thickness of 15 mm and a length of 80 mm for the left insert piece and the right insert piece, the mold temperature is 40 ° C, Nesting temperature is 200 at the first stage molding
℃, 40 ℃ in the second stage molding, the first stage injection pressure 5kg / cm ²
After shaping for 1.5 seconds and then eliminating the blowing pressure, lower the mold insert by 5 mm and shape at the second stage blowing pressure of 5 kg / cm ² for 25 seconds to form an outer layer of 0.2 mm, an intermediate layer of 0.1 mm, A bolt-shaped hollow molded product having an inner layer thickness of 0.3 mm, a body diameter of 100 mm, a body height of 130 mm, and an overall height of 180 mm was manufactured.

The pinch-off strengths of the method according to the present invention and the comparative example in which the pinch-off portion is not formed as in the method of the present invention are compared as follows.

The drop strength is represented by the altitude at which 5 out of 10 pieces were broken by being filled with 70% aqueous solution of ethylene glycol that does not freeze in an atmosphere of -30 ° C and dropped vertically onto the concrete floor surface.
The tensile strength was determined by the JISK-6760 tensile breaking strength point test.

Regarding the oxygen barrier property, the following table shows the measurement results of the oxygen permeation amount per bottle (cc / 1 atm, 23 ° C, 24 hours).

(Effect of the invention) The present invention reliably welds the outer layer of the pinch-off portion of the blown hollow molded product by the multi-layer parison through the mold nest attached to the mold, and does not expose the intermediate layer, so the strength of the pinch-off portion is remarkably high. And the function of the intermediate layer can be sufficiently fulfilled.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of an apparatus of the present invention, FIG. 2 is a sectional view showing an essential part in a state where a mold nest is raised and a parison is hung, and FIG. 3 is a first stage molding in the method of the present invention. 4 is a sectional view of a main part of the same when the mold insert is lowered, and FIG. 5 is a sectional view of a main part of the same when molding the second stage,
FIG. 6 is an enlarged explanatory view of a pinch-off portion according to the method of the present invention, FIG. 7 is a cross-sectional view of an essential portion showing a state of a pinch-off portion of a multi-layer parison hollow molded product by conventional means, and FIG. FIG. 9 is an explanatory view showing an example of conventional means for strengthening the pinch-off portion, and FIG. 10 is an explanatory view showing the same or another example. 1 ... Extruder, 2 ... Blow molding die, 2a ... Left split mold part, 2b ... Right split mold part, 2a, 2b ... Outer bottom forming surface, 6 ... Mold nest, 6a ... … Left nesting piece, 6b …… Right nesting piece, 7a, 7
b ... Elimination part, 8 ... Mold nesting up / down mechanism, 10 ... Outer layer, 11 ... Middle layer, 12 ... Inner layer, (A) ... Three-layer parison, (B) ... Hollow molded product, (Α) …… Mountain shape part,
(Β) ... void, (γ) ... steeply sloped mountain portion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takefumi Uematsu 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Oil Chemicals Co., Ltd. Resin Research Laboratory (56) References Japanese Patent Publication Sho 53-15432 (JP, B2)

Claims (2)

[Claims] 1. A first part in which a multi-layered parison is pinched off by being cut off by a mold insert positioned a predetermined distance above the outer bottom forming mold surface of a predetermined hollow molding product to form a mountain-shaped part inward.
Step-blow molding, and then, after eliminating the blowing pressure, the mold insert is lowered to form a void inside the mountain-shaped portion, and then the outer layer facing portion inside the mountain-shaped portion is welded. A blow molding method characterized in that step blow molding is performed. 2. A mold insert comprising a left nesting piece and a right nesting piece each having a biting part can be moved up and down by a predetermined distance in correspondence with the facing parts of the left split mold part and the right split mold part, respectively. 1. A blow molding apparatus, comprising: a blow molding die attached to a base, and the blow molding die being disposed below an extruder.