JPH0524099A - Method for biaxial stretch blow molding and blow mould for the same - Google Patents

Abstract

PURPOSE:To provide a good stretching condition by preventing the deviation between a gate part and a bottom part center by the axial stretching of a primary molding from a stretching rod. CONSTITUTION:An axial stretching of a stretching rod 3 is conducted in the condition in which a bottom part 2a is sandwiched between the stretching rod 3 and a receiving rod 4 placed in face of the stretching rod 3. The deviation of the gate part is prevented by the sandwiching to attain a good stretching condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxial stretch blow molding method used for molding containers such as carbonated drinks and other soft drinks, and a die thereof.

[0002]

2. Description of the Related Art Conventionally, biaxially stretch blow molded synthetic resin bottles have been widely used as containers for carbonated drinks and other soft drinks. In this biaxial stretch blow molding, a heated synthetic resin primary molded product is set in a mold, and a stretch rod axially slidable on the mouth side of the primary molded product is advanced to move the primary molded product. This is done by pressing the bottom from the inside of the molded product to axially stretch the primary molded product, and then blowing a fluid into the interior.

[0003]

However, in the above-mentioned conventional biaxial stretch blow molding, when the stretch rod is pressed, slippage occurs between the stretch rod and the bottom of the primary molded product, so that the gate portion (the stretch rod touches). There is a problem that the center of the bottom part and the contacting part) easily shift. The deviation between the center of the gate and the bottom causes a bias in the stretched state of the primary molded product in the axial direction, resulting in deterioration of stretch formability due to subsequent fluid injection and making the entire stretched state uneven. , Causes unevenness in the orientation degree and the thickness distribution.

Particularly, this unevenness is apt to occur remarkably at the bottom when the leg having a flat lower surface at the edge is swollen to make the obtained bottle self-supporting. This will cause the drop impact strength and pressure resistance of the bottom to be significantly reduced.

Further, instead of the bottom portion having the above-mentioned leg portions, the bottom portion of the bottle itself has a hemispherical swelled shape, and a separate cup is attached to this bottom portion to make it a self-supporting bottle. There is also. The bottom portion in this case is less likely to be affected by unevenness as compared with the bottom portion having the above-mentioned leg portion, but it is the same that the stretched state of the whole tends to be non-uniform, and the physical properties such as the gas barrier property of the bottle are likely to deteriorate. .

The present invention has been made in view of the above problems, and prevents the gate portion and the center of the bottom portion from being displaced from each other when the primary molded article is axially stretched by the stretching rod.
The purpose is to ensure that a good stretched state is obtained.

[0007]

As shown in FIGS. 1 to 3, in the invention of claim 1, in the blow mold 1, the bottom portion 2a is stretched from the inside of the heated primary molded product 2 to the stretched rod 3.
In the biaxial stretch blow molding in which the primary molded product 2 is axially stretched by being pressed with, and the primary molded product 2 is blown with a fluid, the receiving rod 4 and the stretch rod provided at the position facing the tip of the stretch rod 3 3 and the bottom part 2 of the primary molded product 2
The bottom 2a of the primary molded product 2 is pressed by the stretch rod 3 while the receiving rod 4 is retracted while sandwiching a.

According to the second aspect of the present invention, the primary molded product 2 thus set is provided slidably in the axial direction on the side of the mouth 2b, and is extended so as to move forward and press the bottom 2a from the inside of the primary molded product 2. The rod 3 and the bottom 2a side of the set primary molded product 2 are provided so as to be slidable in the axial direction so as to face the tip of the stretching rod 3, and when the stretching rod 3 moves forward,
The blow mold 1 is provided with a bottom rod 2a of the primary molded product 2 and a receiving rod 4 which retracts as the stretching rod 3 advances with the stretching rod 3.

[0009]

In the present invention, when the bottom portion 2a of the primary molded product 2 is pressed by the stretching rod 3, the bottom portion 2a is sandwiched between the stretching rod 3 and the receiving rod 4 and is pressed in a fixed position. Since the stretching rod 3 and the bottom portion 2a of the primary molded product 2 do not slip, the positional relationship between the gate portion 5 and the bottom portion 2a with which the stretching rod 3 contacts can be reliably maintained. .

[0010]

First, an embodiment of the blow mold 1 will be described with reference to FIG.

As shown in the drawing, the blow mold 1 has a drawing rod 3 and a receiving rod 4.

The stretch rod 3 is axially slidably provided on the side of the opening 2b of the primary molded product 1 set in the blow mold 1. In addition, the receiving rod 4 has its tip end faced with the tip end of the stretching rod 3, and thus the primary molded product 2
It is provided on the bottom portion 2a side so as to be slidable in the axial direction.

The mechanism for sliding the stretching rod 3 and the receiving rod 4 may be an air cylinder type, a cam type, or a combination of both.

The stretching rod 3 advances in the primary molded product 2 and presses the bottom portion 2a of the primary molded product 2 from the inside to stretch it in the axial direction. The receiving rod 4 is the extension rod 3
When the bottom part 2a of the primary molded product 2 is pressed, the bottom part 2a is sandwiched between the bottom part 2a and the stretching rod 3, and in that state, the bottom part 2a moves backward as the stretching rod 3 advances.

The pressing force A of the stretching rod 3 is 1 to 6 kg / c.
m ² is preferable, and more preferably 2 to 5 kg / cm ² . The pressing force B of the receiving rod 4 on the side of the stretching rod 3 (the force that clamps the bottom portion 2 a) needs to be smaller than the pressing force of the stretching rod 3 so as not to impair the forward movement of the stretching rod 3. The difference between the pressing force A of the stretching rod 3 and the pressing force B of the receiving rod 4 is preferably 0.2 to 5.5 kg / cm ² , and more preferably 0.5 to 3.0 kg / cm 2.
^{Is 2} . If this pressure difference is too large, it is difficult to obtain a sufficient force to pinch the bottom portion 2a of the primary molded product 2, and the gate portion 5 tends to shift from the center of the bottom portion 2a. On the other hand, if it is too small, the sandwiched bottom portion 2a is excessively crushed, and pinholes and the like are likely to occur.

In particular, when the slide mechanism of the receiving rod 4 is of the air cylinder type, the pressing force B of the receiving rod 4 is adjusted by the flow rate of air escaped from the air cylinder, so it is necessary to determine this appropriately. The flow rate of the air escape depends on the size of the air cylinder, etc., but is usually 10 to 1
00 cm ³ / sec is preferable, and more preferably 30 to
It is 70 cm ³ / sec.

The deviation between the gate 5 and the center of the bottom 2a is
It is also affected by the distance C between the receiving rod 4 and the bottomed primary molded product 2 when the primary molded product 2 is set. This distance C is -5
-20 mm is preferable, and 0-10 mm is more preferable.

The biaxial stretch blow molding is performed as follows using the blow mold 1 having the receiving rod 4 as described above.

First, as shown in FIG. 1, a primary molded product 2 made of synthetic resin heated to a temperature suitable for molding is set in a blow mold 1.

Then, as shown in FIG.
Is pushed forward to sandwich the bottom portion 2a of the primary molded product 2 between the receiving rod 4 and the bottom portion 2a and press the bottom portion 2a from the inside. The stretching rod 3 is further advanced while being sandwiched between the bottom portion 2a and the receiving rod, and the receiving rod 4 is retracted accordingly, and the primary molded product 2 is axially stretched.

After the primary molded product 2 has been stretched in the axial direction, a fluid such as blow air is blown into the primary molded product 2 to stretch it in the circumferential direction as shown in FIG.
And After the completion of the stretching in the circumferential direction, the stretching rod 3 is retracted, the pressing of the receiving rod 4 in the direction of the stretching rod 3 is released, and the secondary molded product 6 is taken out from the blow mold 1 to perform one cycle of molding. finish.

When the molding is further continued, the blow mold 1 is closed, the receiving rod 4 is returned to the position shown in FIG. 1, the primary molded product 2 is set, and the same operation is performed.

In the case of molding the primary molded bodies 2 having different axial lengths, it can be easily dealt with by adjusting the advancing position of the receiving rod 4.

Next, the results of examining the influence of the adjustment items around the receiving rod 4 will be shown. Table 1 shows the results of examining the influence of the gap C between the receiving rod 4 and the primary molded product 2 on the shift of the gate portion 5, and Table 2 shows the pressing force of the receiving rod 4 and the shift of the gate portion 5 and the gate portion 5. It is the result of investigating the effect on the wall thickness of.

[0025]

[Table 1]

[0026]

[Table 2] Furthermore, the results of examining the wall thickness distribution of the bottom portion 2, the drop impact strength, and the moldability of the bottle molded by the method of the present invention and the bottle manufactured by the conventional method are shown. However, in the method of the present invention, the distance C between the receiving rod 4 and the primary molded product 2 is 0 mm, the pressing force of the receiving rod 4 is 2 kg / cm ² , the sliding mechanism of the receiving rod 4 is an air cylinder system, and the air release flow rate is = 50 cm ³ / sec, pressing force of the stretching rod 3 = 2.
It was carried out at 5 kg / cm ² . Moreover, each survey item was investigated as follows.

(1) Thickness Distribution of Bottom Part 2 The thickness of the valley line part 7 in the bottom part 2 was measured at the site as shown in FIG. The results are shown in Table 3. still,
Reference numeral 8 in FIG. 4 is a leg portion.

(2) Drop impact strength After being filled with 4.0 vol of pseudo-carbonated water, it was stored in a constant temperature bath at 38 ° C.
It was dropped vertically and examined for its damage rate. The results are shown in Table 4.

(3) Moldability It was carried out by examining the complete molding rate and the yield. The results are shown in Table 5.
Shown in.

[0030]

[Table 3]

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

The present invention is as described above, and since the gate portion 5 can be formed so as to coincide with the center of the bottom portion 2a, it is possible to perform good stretching without unevenness in the degree of orientation and the thickness distribution. The state is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a primary molded product is set in a blow mold.

FIG. 2 is a cross-sectional view showing a state in which a stretching rod is advanced to stretch a primary molded product in an axial direction.

FIG. 3 is a cross-sectional view showing a state in which a fluid is blown into a primary molded product to form a secondary molded product.

FIG. 4 is an explanatory diagram of a thickness measurement site.

[Explanation of symbols]

1 blow mold 2 Primary molded products 2a bottom 2b neck 3 Stretching rod 4 Receiving rod 5 gates 6 Secondary molded products 7 valley line part 8 legs

Continued front page    (72) Inventor Teruhiko Sugiura             3-5-1, Asahi-cho, Machida-shi, Tokyo Electrification             Gakkou Co., Ltd.

Claims (2)

[Claims] 1. A biaxial stretching in which, in a blow mold, the bottom of the heated primary molded product is pressed from the inside by a stretching rod to axially stretch the primary molded product and then a fluid is blown into the primary molded product. In blow molding, with the bottom part of the primary molded product sandwiched between the receiving rod and the stretching rod that are provided at the position facing the tip of the stretch rod, while retracting the receiving rod, press the bottom part of the primary molded product with the stretch rod. A biaxial stretch blow molding method comprising: 2. A stretch rod provided axially slidably on the mouth side of the set primary molded product and for moving forward to press the bottom from the inside of the primary molded product, and the bottom of the set primary molded product. Is provided so as to be slidable in the axial direction facing the tip of the stretching rod on the side, and when the stretching rod advances, a receiving rod that retreats as the stretching rod advances with the bottom of the primary molded product sandwiched between the stretching rod and the stretching rod. A blow mold characterized by having.