JPH06226827A - Blow molding method - Google Patents

Abstract

PURPOSE:To prevent a molding malfunction from occurring due to residual air by forming a gap for bleeding the air to be closed at a molding part having a large blowing ratio of a cavity. CONSTITUTION:A pair of split molds 10 for blow molding are formed of a plurality of separably stacked blocks 11, 12, 13. A cavity 19 is so formed that recesses 20, 21 for molding a part having a large blowing ratio of A hollow molded form 2 are disposed at a stacked part of the blocks. Air blowing of a parison 3 is started in a state that an air bleeding gap 15 is formed by separating the blocks, the air is bled from a part having a large blowing ratio from the gap 15, then the blocks 11, 12, 13 are brought into contact with each other before the air blowing is completed, and the gap 15 is closed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding method for hollow synthetic resin moldings which can be used for direct blow molding, injection blow molding, stretch blow molding and the like.

[0002]

2. Description of the Related Art In ordinary blow molding, an extruded or injection molded parison is placed between a pair of vertically divided open / closed blow molds, and a cavity of a hollow molded product is formed by closing the molds of the divided molds. After that, air is blown into the parison located in the center of the cavity to fully expand the cavity, and it is pressed against the cavity surface by the pressure of air to form a hollow molded product.

The air in the cavity is pushed by the pressure caused by the air blow and escapes from the parting surface of the mold. When molding a hollow molded product with a design such as that described above, other parts with a small blow ratio come into contact with the cavity surface prior to that part, blocking the part with a large blow ratio, so there is an escape area for air in that part. It disappears and remains. This residual air causes thermal expansion in contact with the hot parison, causing partial expansion resistance of the parison and causing defective molding or burning.

[0004]

As a means for solving the problem caused by such residual air, an air vent hole is provided at a place where residual air is likely to be generated due to a difference in blow ratio. The resin is pushed inside,
Since the shape of the hole is transferred to the surface of the hollow molded product and becomes an unnecessary pattern and impairs the appearance, the hole diameter of the air vent hole is also limited to a size (0.2 to 0.3 mm) that resin does not enter,
A large number of such holes are opened to correspond.

However, with such a hole diameter, it takes time for the air to escape, and even if air is blown out smoothly in low-pressure air blowing where the blowing speed is slow, even if air blowing is performed at high pressure, it corresponds in terms of speed. However, there is a limit to the elimination of residual air by the air vent hole.

Therefore, as described in Japanese Patent Application Laid-Open No. 1-127728, the air in the cavity is forcibly withdrawn by using a suction with a vacuum pump together. Due to the difficulty of timing and the increase of incidental equipment, the use is limited to a part.

The present invention was conceived in order to solve the above-mentioned problems associated with air bleeding, and its purpose is to:
It is possible to deflate the air with a large blow ratio by simple means, always without being restricted by the air blow speed, and use it not only for direct blow molding but also for injection blow molding or stretch blow molding. It is to provide a new blow molding method that can be performed.

[0008]

The feature of the present invention according to the above object is that a pair of split molds for forming a cavity of a hollow molded product is constituted by a plurality of mold blocks that are stacked in contact with and separated from each other. A parison in the cavity is formed with a cavity formed in the stacking portion of the block so that a concave portion for molding a large blow ratio of the hollow molded product is located, and a required air bleeding gap is formed by separating the mold block. The air blow is started, and the air with a large blow ratio is evacuated from the gap, and before the air blow is completed, the mold blocks are brought into contact with each other to close the air bleed gap.

The stacking of the plurality of mold blocks which can be freely contacted and separated can be easily performed by interposing a spring member between the mold blocks. For the mutual contact of the mold blocks, the blow mold is a lifting mold that can be raised and lowered, and the bottom mold is lifted to push up the lower mold block or insert the blow core in two steps, and the upper part is moved to the second step. It can be done by pushing down the mold block.

[0010]

[Operation] With such a blow molding method, the air bleeding gap in the portion with a large blow ratio can be made large enough so that air bleeding can be performed smoothly even if the blowing speed is fast, and the surface is blown by the blow pressure. The gap is closed before it is pressed hard against the cavity surface, so that no trace of the gap is transferred to the surface.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS This embodiment illustrates a case where a plurality of mold blocks are brought into contact with each other by a bottom mold. In FIG. 1, reference numeral 1 shows a blow mold composed of a pair of split molds 10, 10 which can be freely opened and closed. .

The split molds 10 and 10 are composed of an upper mold block 11, a middle block 12 and a lower mold block 13 which are stacked so as to be able to come into contact with and separate from each other, and a spring member 14 having a required strength is interposed in each stacked part. The spring members 14 keep the mold blocks separated from each other, forming a required gap (2.0 to 3.0 mm) 15 in the stacking portion.

These mold blocks have a gap adjusting space 16
It is housed in a base member 17 so as to be movable up and down, and a bottom mold 18 is attached to the central portion of the lower mold block 13 by a lifting mold that can be raised and lowered.

Reference numeral 19 designates a cavity of the hollow molded product 2, which is a concave portion for molding the shoulder portion 2a and the bottom peripheral edge 2b of the hollow molded product 2 having a large blow ratio and unevenness in the stacked portion of the mold block.
Each mold block 11, 1 so that 1 is located respectively
The upper mold block 11 has a neck portion 22 formed in the center thereof. Reference numeral 23 is a gap adjusting screw.

In order to blow mold the hollow product 2 using such a blow mold 1, first, the parison is placed in the center of the split molds 10, 10 in which the bottom mold 18 is lowered and the mold is open. Position 3. The illustrated example is a case of injection blow molding, and the parison 3 has a blow core 4 also serving as an injection core therein.

Next, the mold is closed to form a cavity 19, and high pressure air is blown from the blow core 4 to the parison 3 at the center of the cavity 19 to expand the cavity to the full extent. At this time, each mold block 11, 12, 13
Are separated by a spring member 14, and a gap 15 is formed in the stacking portion, and the gap 15 is open to the molding recesses 20 and 21 of the cavity 19 having a large blow ratio. Even if the resin forming the small body or the like comes into contact with the cavity surface first, the air smoothly escapes from the gap 15 regardless of such a situation. Therefore, defective molding due to residual air in the cavity is less likely to occur.

The closing timing of the air bleeding gap 15 is detected from the air blow time of the parison 3 and the pressing force against the cavity surface, and the detection signal causes the bottom mold 18 to rise and the lower mold block 13 to rise. As a result, as shown in FIG. 3, the spring member 14 in the stacking portion is compressed, the mold blocks 11, 12, 13 are brought into contact with each other, and the gap 15 is closed. Since the gap is closed before the air blowing is completed, the gap 15 is not transferred to the surfaces of the shoulder 2a and the bottom peripheral edge 2b of the hollow molded product 2 molded therein.

[0018]

As described above, according to the present invention, a pair of split molds for blowing are constituted by a plurality of mold blocks that are stacked so that they can be contacted and separated from each other, and a hollow molded product is blown into the stacked part of the mold blocks. A cavity is formed so that a concave part for molding a large ratio portion is located, and a required air bleeding gap that can be closed is formed in that portion. After going,
Before the air blow is completed, the air bleed gap is closed to prevent defective molding due to residual air and to prevent transfer of the air bleed gap, so even hollow molded products with designs with greatly different blow ratios can be easily used. Can be molded into.

Further, since the air bleeding gap can be easily closed by pressing, there is no technical difficulty in setting the closing timing, and air bleeding can be performed regardless of the blowing speed, so that a hollow molded product in a good molding state can be obtained. Since it can be molded in a high cycle and the structure of the blow mold is simple, it can be used for direct blow molding and stretch blow molding as well as injection blow molding.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a blow mold showing a state immediately after the start of air blowing in a blow molding method of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a schematic vertical sectional view of a blow mold showing a state after completion of air blowing.

[Explanation of symbols]

 1 Blow Mold 2 Hollow Molded Product 3 Parison 10 Divided Mold 11 Upper Mold Block 12 Middle Block 13 Lower Mold Block 14 Spring Member 15 Air Venting Gap 17 Base Member 19 Cavity 20 Shoulder Molding Recess 21 For Molding Bottom Edge Recess

Claims (1)

[Claims] 1. A pair of split molds for forming a cavity of a hollow molded product is constituted by a plurality of mold blocks stacked so as to be freely contactable and separable, and a blow ratio of the hollow molded product is set in a stacked portion of the mold blocks. The cavity is formed so that the concave part for molding a large part is located, and the parison in the cavity is started to blow air with the required air bleeding gap formed by separating the mold block, and the air in the part with a large blow ratio is A blow molding method, characterized in that after the bleeding is performed from the above gap, the mold blocks are brought into contact with each other before the air blowing is completed to close the air bleeding gap.