JP2006264035A - Blow molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable blow molding method for keeping the posture of the intermediate molded product, which is fed into a blow mold, upright without adding a special mechanism. <P>SOLUTION: In the blow molding method of a heat-resistant container 206 for performing blow molding at least twice, the intermediate molded product 202 having a recessed bottom part is moved to a final blow mold 144 and compressed air is subsequently blown out to the bottom part of the intermediate molded product 202 from a bottom mold 150 in synchronous relation to the advance of the bottom mold 150 to the bottom part to correct the posture of the intermediate molded product 202. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for molding a heat-resistant container, and particularly to a method for molding a heat-resistant container obtained by molding a synthetic resin such as polyethylene terephthalate (hereinafter referred to as PET).

  Generally, a container called a biaxial stretch blow molded container is a preform obtained by injection molding placed in a blow mold and stretched in the longitudinal direction by a stretch rod, and high pressure air is blown into the preform. It is stretched in the horizontal axis direction and formed into a container shape.

  In such a PET container, there is a heat resistance problem that the container is deformed when filled with high-temperature sterilized contents. Accordingly, various molding methods for imparting heat resistance to PET containers have been proposed (see, for example, Patent Document 1 and Patent Document 2).

  The applicant has also proposed a blow molding apparatus for heat-resistant containers (see, for example, Patent Document 3). In this molding apparatus, a preform heated to an appropriate temperature for stretching is blown primarily in a heated primary molding die to be expanded to form an intermediate molded product, and after the intermediate molded product is heated, the intermediate molded product is The intermediate molded product taken out from the primary molding die and contracted and softened is secondarily blown in the secondary molding die to be re-expanded.

  According to this heat-resistant container forming apparatus, a desired heat treatment can be performed in a short time, and a container having excellent heat resistance can be easily formed.

  However, in the above-mentioned apparatus, the center position of the bottom and the center of the final blow mold may not exactly match due to the inclination or misalignment of the intermediate molded product, which affects the quality and appearance of the final product. was there.

  For example, when one side of the body portion is formed thin, the strength of that portion is reduced. If the inclination is further increased, when the blow mold is closed, the body part and the bottom part of the intermediate molded product are slightly sandwiched, which may cause a leak after filling the container.

  The causes of tilt and misalignment are considered as follows. First, the intermediate molded product is tilted by the acceleration / deceleration of conveyance. In the above-described blow molding apparatus, the intermediate molded product is conveyed into the blow mold and stopped at a proper position, and then the blow mold is closed and blow molding is performed. Thereafter, the blow mold is opened and conveyed again to the next step. Therefore, intermittent operation of the transport device is necessary, and the container may be shaken each time. However, it is not preferable to slow the conveyance speed or lower the acceleration / deceleration characteristics because it immediately affects the cycle time and productivity.

  The above-mentioned tendency appears more prominently for a large container of about 2 L than for a small container of about 500 mL in internal capacity, for example. This is because the larger the container, the higher the overall height of the intermediate molded product, the higher the center of gravity, and the greater the mass, which is greatly affected by acceleration and deceleration.

Another cause is due to deformation of the molded product itself. As described above, since the intermediate molded product is in a softened and contracted state by heating, the shape thereof is often not a fixed shape as in the completed container. The surface of the torso is rich in undulations, and the cross section may be elliptical or bend in the middle of the torso. In some cases, only the peripheral part of the bottom part is inclined. In either case, it is more difficult to correctly position the container and the center of the blow mold.
Japanese Patent Publication No. 61-29858 Japanese Patent Publication No. 1-56891 JP 2003-231170 A

  An object of the present invention is to provide a stable blow molding method by keeping the posture of an intermediate molded product conveyed into a blow mold upright without adding a special mechanism.

In order to achieve the above object, the blow molding method of the present invention is a blow molding method for a heat-resistant container that performs blow molding at least twice.
After the intermediate molded product having the concave bottom is moved into the final blow mold, compressed air is blown from the bottom mold to the bottom of the intermediate molded product in synchronization with the advancement of the bottom mold with respect to the bottom. Thus, the posture of the intermediate molded product is corrected.

  According to the present invention, even if the intermediate molded product is bent or inclined, the center of the bottom can be easily aligned at the time of final blow molding.

  In the blow molding method of the present invention, when the final product is taken out from the final blow mold after final blow molding, compressed air is blown out from the bottom mold to the bottom of the final product.

  According to the present invention, the above-mentioned effect can be obtained by utilizing the compressed air circuit and the nozzle originally provided for another purpose, which is very economical.

  In the heat-resistant container, in order to minimize the distortion generated during the final blow, it is customary that the intermediate molded product is as close as possible to the shape of the final product. The same applies to the bottom, and the bottom of the intermediate molded product has a concave bottom shape that is substantially the same as the final shape.

  Therefore, it has a concave bottom shape when viewed from the bottom. When the bottom is out of the center by blowing compressed air to the center of the bottom when it is transported into the final blow mold, for example, the intermediate molded product may be lifted from the transport member due to transport acceleration / deceleration. Even if it tilts, it can be firmly pressed against the conveying member by the air blown to the bottom, and the posture can be restored.

  Thereby, the final blow mold can always be closed with a good posture. Further, even if the body portion of the intermediate molded product is bent, at least the bottom portion is positioned at the center position by blowing compressed air to the bottom portion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view showing an overall configuration of a blow molding apparatus according to an embodiment of the present invention. This blow molding apparatus 100 manufactures a heat-resistant container as a final product, and a preform supply unit 102, a heating station 104, a transfer unit 106, and a blow conveyance path 134 are arranged in the conveyance direction A of the preform. It is arrange | positioned linearly along.

  This heat-resistant container molding method is roughly divided into the following steps. First, the preform 200 is supplied from outside the machine to the preform supply unit 102. The preform 200 is sent to the heating station 104 and heated to an appropriate molding temperature by a heater. The preform is mounted on the conveyance member 128 via the transfer unit 106 and the blow conveyance path 134. As it is, it is conveyed to the primary blow / heat treatment molding die 142 to perform biaxial stretch blow molding. At the same time, the blow mold is heated in the same mold to perform heat treatment.

  Due to the primary blow molding, the intermediate molded product swells much larger than the final product, but then shrinks by the heat treatment that it undergoes. As a result, the overall height of the intermediate molded product 202 settles to the same level as the final product 206 or slightly higher (approximately 0.5 mm to 1 mm). The intermediate molded product 202 is conveyed into the final blow molding die 144 and blow molded to obtain a final product 206.

  The present invention relates to the positioning of the intermediate molded product 202 in the final blow molding part 146 among the above steps. The intermediate molded product 202 is conveyed toward the final blow molding unit 146 by the conveying member 128. At this time, the final blow molding die 144 is in a fully opened state, and the final blow bottom die 150 is also in the retracted position (the rising end in this embodiment). Although not shown, temperature adjusting oil piping is provided inside the final blow molding die 144 and the final blow bottom die 150 so that the intermediate molded product 202 is heat-treated.

  After the intermediate molded product 202 is positioned at the normal stop position, the final blow bottom mold 150 first moves forward. A compressed air outlet 152 is provided at the center of the final blow bottom mold 150. In the present embodiment, one compressed air outlet 152 is provided with the center facing downward, and four slanted downwards are provided at equal intervals around the periphery. At the same time as the final blow bottom mold 150 moves forward, for example, compressed air blows out from the outlet 152. As described above, since the bottom shape of the final product 206 and the bottom shape of the intermediate molded product 202 are substantially close to each other, if the intermediate molded product 202 is correctly upright and the center is aligned, the final blow bottom mold 150 is When it stops at the forward end position, it just fits in the bottom of the intermediate molded product 205. The compressed air blowing start time is not necessarily limited to the time when the bottom mold 150 is moved forward, but may be intermediate when the final blow bottom mold 150 stops at the forward end position as long as the bottom mold 150 is synchronized with the forward movement. Since the molded product can be positioned, it may be before or after the bottom mold 150 starts to advance.

  Thus, after the final blow bottom mold 150 has been advanced and the intermediate molded product 202 has been fixed, the final blow molding mold 144 is closed. A blow-type guide is attached to the lower portion with a spring or the like, and the caliber portion of the intermediate molded product 202 is sandwiched from both sides. Subsequently, the final blow molding die 144 is closed from both sides, and the closing of the die is completed. Subsequently, the mold clamping mechanism is switched to high pressure mold clamping, and a high pressure blow is blown into the intermediate molded product 202 to perform final blow molding and final heat treatment.

  In the blow molding apparatus for heat-resistant containers manufactured by the applicant, a compressed air outlet provided in the central portion of the final blow bottom mold 150 for mold release (a step of taking out the product from the mold) after completion of the final blow molding. 152 is used again. By blowing out compressed air even when the mold is opened, the final product is prevented from sticking to the final blow bottom mold 150.

  In the embodiment of the present invention, this air blowing is also used for positioning and posture correction of the intermediate molded product 202. The bottom of the intermediate molded product 202 has substantially the same concave shape as that of the bottom of the finished container (final product 206). Is done. It fits in the correct position and posture according to the closing of the blow mold and the advance of the bottom mold, and can avoid tilting and pinching.

  As described above, in the present invention, a great effect can be obtained in correcting the posture of the intermediate molded product without adding a special device. The optimum air pressure setting for mold release is about 0.7 MPa, and this set pressure is used as it is for the posture stabilization blowout. If the compressed air is blown out simultaneously with the advance of the final blow bottom mold 150, it is not necessary to extend the cycle time. The actual blowing time was about 1 second, and good results were obtained. In the final blow molding, the temperature control in the mold is also an important factor, but this air blowing did not affect the molding.

It is a top view of the whole blow molding apparatus. It is the schematic which shows the mode of the molded article mounted in the conveyance member 128 in each step of blow molding. From the left, a preform 200, an intermediate molded product 202 by primary blow, and a final product 206 are shown. It is the schematic which shows a mode that the intermediate | middle molded product 202 bent at the trunk | drum by the inclination at the time of conveyance or heat contraction. It is the schematic which shows each element when the type | mold of the final blow molding part 146 opens, and the mode of the intermediate molded product 202 conveyed there. It is sectional drawing which shows a mode when the type | mold of the last blow molding part 146 has closed. It is the schematic which shows the final blow bottom mold | type 150 and the air blowing port 152 provided in the center part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Blow molding apparatus 102 Preform supply part 104 Heating station 106 Transfer part 128 Conveying member 134 Blow conveyance path 140 Primary blow / heat treatment molding part 142 Primary blow / heat treatment molding die 144 Final blow molding die 146 Final blow molding part 148 Container Extraction unit 150 Final blow bottom mold 152 Outlet A Conveying direction 200 Preform 202 Intermediate molded product 204 Heat-shrinked intermediate molded product 206 Final product / heat-resistant container

Claims (2)

In a blow molding method of a heat-resistant container that performs blow molding at least twice,
After the intermediate molded product having the concave bottom is moved into the final blow mold, compressed air is blown from the bottom mold to the bottom of the intermediate molded product in synchronization with the advancement of the bottom mold with respect to the bottom. Thus, the blow molding method is characterized by correcting the posture of the intermediate molded product. In claim 1,
A blow molding method characterized in that compressed air is blown from the bottom mold to the bottom of the final product when the final product is taken out from the final blow mold after final blow molding.

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