JP2018024134A - Method for producing synthetic resin container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent molding failure when a molded container is taken out from a blow molding die heated to a heat setting temperature.SOLUTION: A method for producing a synthetic resin container includes: when blow molding a preform P by a blow molding die 1 heated to a heat setting temperature and taking out a blow molded body (synthetic resin container molded into desired container shape) M from the blow molding die 1, jetting high pressure air Ahp of 1-4 MPa from jetting holes 3a opened on a molding surface of the molding die 3, when the molding die 3 provided on the blow molding die 1 is moved to a mold-opening direction.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a synthetic resin container, and more particularly to a method for manufacturing a synthetic resin container to which heat resistance is imparted by heat setting during blow molding.

  Conventionally, a synthetic resin container formed by forming a bottomed cylindrical preform using a thermoplastic resin such as polyethylene terephthalate, and then molding the preform into a bottle shape by biaxial stretch blow molding or the like, It is used in a wide range of fields as containers containing various beverages and various seasonings.

  Moreover, as an example of the method of filling the contents in this type of synthetic resin container, there is a so-called hot pack in which the heat-sterilized contents are filled and sealed at a high temperature. Containers used for hot packs are usually given heat resistance by increasing their crystallinity by heat setting (heat setting) so that they do not deform when filled with hot contents. Yes.

  As a heat set, for example, a method is known in which a preform is blow-molded in a blow mold heated to a predetermined temperature and then brought into contact with the inner surface of the blow mold for a predetermined time (see, for example, Patent Document 1). ).

  In addition, in recent years, this type of synthetic resin container is required to reduce the weight of the container, and at the same time, it is also required to reduce the production cost.

Japanese Patent Laying-Open No. 2005-112440 (paragraph [0037])

  In view of such circumstances, the present applicant has earnestly made it possible to form various containers having different capacities by using the same preform in common in order to reduce the weight of the container and to reduce the production cost. As a result of repeated studies, the following findings were obtained.

  That is, the bottom of the container formed by blow molding tends to remain unstretched without being sufficiently stretched, and when trying to mold various containers having different capacities using the same preform in common. Such a tendency becomes more remarkable as the container has a smaller capacity. And since the unstretched portion is molded in close contact with the details according to the shape of the mold and sticks to the mold more easily than the stretched portion, if the unstretched portion remains at the bottom of the container, the bottom of the container Sticks strongly to the bottom mold of the blow mold, resulting in mold release defects. On the other hand, in a container with a large capacity, the entire container (including the bottom part) is stretched to be thin as a whole, and when the bottom mold of the blow molding mold is released, it is a weak force but is pulled to the bottom mold, The thin shape makes it difficult to maintain the shape, resulting in poor mold release.

  The present invention has been made in view of the circumstances as described above, and is made of a synthetic resin capable of preventing a mold release failure when taking out a molded container from a blow mold heated to a heat setting temperature. It aims at providing the manufacturing method of a container.

  A method for producing a synthetic resin container according to the present invention is a method for producing a synthetic resin container in which a preform is blow-molded by a blow mold heated to a heat setting temperature, and the preform is blow-molded. When taking out the blow molded body from the blow mold, when the bottom mold provided in the blow mold moves in the mold opening direction, high pressure air of 1 to 4 MPa is ejected from the ejection hole opened in the molding surface of the bottom mold. There is a way to make it.

  ADVANTAGE OF THE INVENTION According to this invention, the mold release defect at the time of taking out the shape | molded container (blow molded object) from the blow molding die heated to heat set temperature can be prevented.

It is explanatory drawing which shows one manufacturing process in the manufacturing method of the synthetic resin containers which concern on embodiment of this invention. It is explanatory drawing which shows the outline of one manufacturing process in the manufacturing method of the synthetic resin containers which concern on embodiment of this invention. It is explanatory drawing which shows the outline of one manufacturing process in the manufacturing method of the synthetic resin containers which concern on embodiment of this invention. It is explanatory drawing which shows the outline of one manufacturing process in the manufacturing method of the synthetic resin containers which concern on embodiment of this invention. It is a top view which shows an example of the bottom mold | type of the blow molding die used for the manufacturing method of the synthetic resin containers which concern on embodiment of this invention.

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

  As an embodiment of the method for producing a synthetic resin container according to the present invention, the outline of the production process is shown in FIG. 1 to FIG. 4. The blow mold 1 shown in these drawings is a body mold 2 and a bottom mold 3. And.

In this embodiment, first, as shown in FIG. 1, a bottomed cylindrical preform P heated to a temperature equal to or higher than the glass transition point (Tg) and ready for blow molding is used as a blow mold 1. set.
Next, as shown by a two-dot chain line in the drawing, the stretching rod 4 is moved downward, and blow air is blown into the preform P from a blow air supply source (not shown) to perform blow molding. As a result, the preform P is stretched in the axial direction (longitudinal direction) by the stretching rod 4 and is also stretched in the circumferential direction (lateral direction) by blow air.

  At this time, the lowering speed of the stretching rod 4 and the pressure of the blow air are appropriately adjusted in consideration of the material used for the preform P, the stretching ratio when the preform P is stretched, and the like. For example, the pressure of blow air can be 3-4 MPa.

  Further, as a material used for the preform P, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, or a copolymer thereof may be blended with these resins or other resins. In particular, ethylene terephthalate-based thermoplastic polyesters such as polyethylene terephthalate are suitable, but not limited thereto.

  The blow molded body M formed by stretching the preform P in this manner is in close contact with the molding surface of the blow mold 1 and the shape of the molding surface is transferred to be molded into a desired container shape (see FIG. 2). . In that case, heat resistance can be provided to the synthetic resin container manufactured by raising the crystallinity degree of the blow molding M by heat set.

  The heat setting can be performed by heating the blow mold 1 to a predetermined heat set temperature and heat-treating the blow molded body M that is in close contact with the molding surface of the blow mold 1.

  As the heat set temperature, the body mold 2 is heated to a temperature of 120 to 170 ° C. On the other hand, since the bottom side of the blow molded body M tends to remain unstretched without being sufficiently stretched, the bottom mold 3 has a range in which whitening due to thermal crystallization of the unstretched portion does not occur. Heat to a temperature of 70 ° C. or higher. If the unstretched portion is heated too much at a high temperature, the bottom die 3 tends to stick to the bottom die 3 more preferably. Therefore, the bottom die 3 is preferably heated to a temperature of 70 to 100 ° C. The heat treatment time for heat setting varies depending on the thickness of the blow molded article M and the heat set temperature, but is generally about 1 to 10 seconds.

  After the heat setting, as shown in FIG. 3, cooling air Ac for cooling is ejected from ejection holes (not shown) provided in the stretching rod 4 to cool the blow molded body M. The cooling time with the cooling air Ac is generally about 0.1 to 2 seconds, although it varies depending on the heat set temperature and the temperature of the cooling air Ac.

  Thereafter, as shown in FIG. 4, the blow molded body (synthetic resin container molded into a desired container shape) M is taken out from the blow mold 1 that has been opened. At this time, in the present embodiment, when the bottom mold 3 moves in the mold opening direction, 1 to 4 MPa of high-pressure air Ahp is ejected from the ejection holes 3 a that open on the molding surface of the bottom mold 3.

  As described above, the bottom side of the blow molded product M tends to remain unstretched without being sufficiently stretched. For this reason, the unstretched part is molded in close contact with the details of the shape of the mold, and the bottom of the blow molded body M is stuck to the bottom mold 3 because it tends to stick to the mold more easily than the stretched part. As a result, mold release defects such as the bottom part of the blow molded body M being pulled and deformed by the bottom mold 3 that moves in the mold opening direction occur. In the present embodiment, such a problem is prevented by prompting the release of the blow molded body M by the high-pressure air Ahp ejected from the bottom mold 3. At this time, if the high-pressure air is smaller than 1 MPa, the mold is not released well and a mold release failure occurs. On the other hand, if it is larger than 4 MPa, the pressure is higher than that of blown air, and the container shape may not be maintained.

  The timing at which the high-pressure air Ahp is ejected from the ejection hole 3a is preferably ejected from when the internal pressure of the blow molded body M starts to decrease until the bottom mold 3 starts moving. In particular, after the cooling air Ac is ejected into the blow molded body M, it is preferable that the blow molded body M be ejected after the internal pressure of the blow molded body M starts to decrease until the bottom mold 3 starts to move. The ejection time of the high-pressure air Ahp is preferably 0.1 to 0.55 seconds.

Further, in order to make the mold release from the bottom mold 3 better, the mold release force received by the blow molded body M by the high-pressure air Ahp ejected from the ejection hole 3a is 0.3 to 6 kgf. It is preferable to appropriately adjust the pressure of the high-pressure air Ahp to be ejected and the opening area of the ejection hole 3a. The opening area of the ejection hole 3a is 0. From the viewpoint that a release force can be reliably obtained, clogging hardly occurs, and the trace of the ejection hole 3a remaining in the molded container is not conspicuous. It is preferably 03 to 0.2 cm ² . If the ejection hole 3a is smaller than this, a reliable mold release force cannot be obtained, and if it is larger, the resin may enter the hole and the mold release may be deteriorated.

Further, the release of the blow molded body M is performed by peeling off the blow molded body M attached to the bottom mold 3, and at that time, shear stress acts on the blow molded body M. For this reason, for example, if only one ejection hole 3 a is provided in the center of the bottom mold 3, the blow molded body M is peeled in one direction from the center of the bottom 3 toward the outer periphery. Thus, if excessive shear stress acts locally in the process, there is a possibility that inconveniences such as distortion occur in the molded container.
In order to effectively avoid such inconvenience, the bottom mold 3 is provided with a plurality of ejection holes 3a so as to be rotationally symmetric about the central axis thereof, as shown in FIG. It is preferable that release of the blow molded body M is promoted by the high-pressure air Ahp ejected from the air so that excessive shear stress does not act locally on the blow molded body M.

  Hereinafter, the present invention will be described in more detail with reference to specific examples.

[Examples 1-8, Comparative Examples 1-5]
A container having a capacity (500 mL, 320 mL, 280 mL) shown in Table 1 was formed using the same preform (weight: 22 g) in common. The bottom mold is provided with ejection holes having the opening area shown in Table 1 in the arrangement shown in FIG. 5 (arrangement that is rotationally symmetric around the center axis of the bottom mold). Air was ejected from each ejection hole. Table 1 also shows the release force that the blow molded body receives by the high-pressure air ejected from each ejection hole.
The releasability was evaluated according to the following criteria.
○: Good mold release ×: Poor mold release (Drag was pulled to the bottom mold)

  From these results, it was confirmed that when releasing high pressure air of 1 to 4 MPa was ejected from the ejection holes opened on the molding surface of the bottom mold, mold release failure was not caused.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. Nor.

  In the present invention, when the preform P is blow-molded by the blow mold 1 heated to the heat setting temperature, and the blow molded body M is taken out from the blow mold 1, the bottom mold 3 provided in the blow mold 1 is opened. When moving in the direction, the high pressure air Ahp of 1 to 4 MPa may be ejected from the ejection hole 3a opened in the molding surface of the bottom mold 3, and other matters are not limited to the above-described embodiment. It can be changed as appropriate. In addition, the items described in the above-described embodiments can be appropriately selected and combined.

  INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a synthetic resin container to which heat resistance is imparted by heat setting during blow molding.

DESCRIPTION OF SYMBOLS 1 Blow molding type | mold 3 Bottom type | mold 3a Ejection hole P Preform M Blow molding (synthetic resin container shape | molded in the desired container shape)
Ahp high pressure air

Claims (4)

A method of manufacturing a synthetic resin container in which a preform is blow-molded by a blow mold heated to a heat set temperature,
When a blow molded body formed by blow-molding the preform is taken out from the blow mold, an ejection hole opened in the molding surface of the bottom mold when the bottom mold included in the blow mold moves in the mold opening direction. A method for producing a synthetic resin container, characterized in that high-pressure air of 1 to 4 MPa is ejected from the container.   2. The method for producing a synthetic resin container according to claim 1, wherein a release force received by the blow molded body by high-pressure air ejected from the ejection holes is 0.3 to 6 kgf. Method for manufacturing a synthetic resin container according to claim 1 or 2 opening area of the ejection hole is 0.03～0.2Cm ^2.   The method for producing a synthetic resin container according to any one of claims 1 to 3, wherein high-pressure air is ejected from the plurality of ejection holes provided so as to be rotationally symmetric around the center axis of the bottom mold.

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