JP6544022B2 - Blow molding die for thermoplastic resin bottle and manufacturing method - Google Patents

Description

  The present invention relates to a blow molding die for a thermoplastic resin bottle and a method for producing a thermoplastic resin bottle using the same.

  Thermoplastic resin bottles such as polyethylene and polypropylene resin are generally manufactured by blow molding. In blow molding, the parison extruded from the extruder is held in a pair of molds (split molds), the blow nozzle is inserted into the parison, and a fluid such as blow air is blown to blow the parison into the mold cavity. The molded product is pressed into a desired shape and cooled in a mold to a shape-retainable temperature, and then the mold is opened to take out the molded product (bottle).

  A blow molding mold for manufacturing a bottle is known in which a mouth mold, a body mold and a bottom mold are separately configured (see Patent Document 1 below). Moreover, as a shape of a bottle, what provided the undercut (recessed part) which makes the center of a bottom part project toward the inner side of a container (upwardly) is generally known (refer following patent document 2).

Japanese Patent Application Laid-Open No. 7-276483 JP-A-8-25469

  The undercut provided at the bottom of the thermoplastic resin bottle is provided concavely to ensure the self-supporting property of the bottle, and after blow molding is completed, the mold is opened to release the bottle. On the other hand, the shape from the mouth of the bottle to the body is various, and there are those having a shoulder whose diameter gradually increases from the mouth.

  In the blow molding of such thermoplastic resin bottles, in the case of a bottle having an undercut at the bottom, the upward convex portion of the bottom forming mold provided for forming the undercut at the time of mold opening at the completion of the blow molding. However, the bottom outer peripheral portion of the bottle is pushed upward, and while the mouth forming mold and the barrel forming mold are opened, the pushed up bottle is used for the mouth forming mold and the barrel forming metal. The phenomenon of touching the mold occurs. In particular, in the case of a bottle shape having a shoulder portion whose outer diameter sharply expands from the mouth portion, the shoulder portion of the bottle contacts the corner portion of the lower end portion of the parting line of the mouth portion forming mold This may increase the resistance of the bottle, or may cause slight marks on the shoulder of the bottle.

  The present invention takes an example of the problem to address such a problem. That is, it is an object of the present invention to eliminate a defect that occurs at the time of mold opening when manufacturing a bottle having an undercut at the bottom by blow molding.

In order to achieve such an object, the present invention has the following configuration.
A blow molding mold for molding a thermoplastic resin bottle having a mouth mold and having an undercut projecting toward the inside of the bottle at the bottom, the lower end of the parting line of the mouth mold. A blow molding die for a thermoplastic resin bottle characterized by having a chamfered portion in the portion.

  In the present invention having such features, when the blow molding die is opened and the molded bottle is taken out, the upward convex portion of the bottom molding die that forms an undercut at the bottom of the bottle pushes up the bottle Even if the shoulder of the bottle comes in contact with the lower end of the parting line of the mouth mold, the chamfered part is formed at the lower end of the parting line, so a large resistance is received when the mold is opened. Also, there is no noticeable rub mark on the shoulder of the bottle.

It is sectional drawing (longitudinal cross section of 90 degrees direction with respect to a parting surface) which showed the blow molding die of the thermoplastic resin bottle which concerns on embodiment of this invention. It is an explanatory view showing a mouth part forming mold in a blow molding mold of a thermoplastic resin bottle according to an embodiment of the present invention. It is an explanatory view showing a cornering part of a mouth part forming mold. It is an explanatory view showing a manufacturing method of a bottle using a blow molding die concerning an embodiment of the present invention. ((A) shows the step of holding the parison in the molding die, (b) shows the step of blowing blow air into the parison, and (c) shows the step of removing the bottle by mold opening.)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, a blow molding die 1 according to an embodiment of the present invention is for molding a thermoplastic resin bottle by blow molding.

  The blow molding mold 1 shown in FIG. 1 includes a body molding mold 2, a mouth molding mold 3, and a bottom molding mold 4. Here, the respective molds are separately configured, but the body molding mold 2 and the bottom molding mold 4 may be an integral mold. In the figure, the X and Y directions indicate the horizontal direction, and the Z direction indicates the vertical (vertical) direction. The body molding die 2, the mouth molding die 3 and the bottom molding die 4 are a pair of split dies in which the parting surfaces face each other.

  Although the form of the bottle molded by the blow molding mold 1 is arbitrary, here, the bottom mold 4 has a convex molding surface 4A which protrudes upward (in the Z direction in the figure), and is molded At the bottom of the bottle, an undercut is formed by the convex molding surface 4A and protrudes toward the inside of the bottle. Further, the body molding die 2 directly below the mouth molding die 3 is provided with an enlarged diameter portion 2A for molding a shoulder whose outer diameter sharply increases from the mouth.

  The mouth part forming mold 3 provided in the blow molding mold 1 is provided with a groove 3B for forming an external thread on the forming surface 3A as shown in FIGS. 1 and 2, and a body forming mold Engage with 2 to shape the mouth of the bottle. The mouth portion forming mold 3 is provided with a chamfered portion 30 at the lower end portion of the parting line 31.

  As shown in FIGS. 2 and 3, the chamfered portion 30 is chamfered with respect to the edges of the parting surface 3P, the molding surface 3A and the bottom surface 3C of the mouth molding die 3. That is, it has a curved surface 30R in contact with all of the parting surface 3P, the molding surface 3A and the bottom surface 3C. The curved surface 30R is, for example, a curved surface in contact with three axes in the Z direction, which is a direction perpendicular to the X and Y directions which are horizontal directions, and the curvature of the curved surface 30R is gradually changed. That is, with respect to the radius of curvature R1 of the part in contact with the edge of the parting surface 3P, the molding surface 3A, and the bottom surface 3C, the radius of curvature R2 of the part away therefrom gradually decreases.

  When such a chamfered portion 30 is provided, the bottle is pushed upward by the convex molding surface 4A of the bottom molding die 4 at the time of mold opening, and the shoulder portion of the bottle is the parting line of the mouth molding die 3. Even if the lower end portion of 31 is in contact, this chamfered portion 30 will be in contact, so that it is possible to prevent the formation of a marked rubbing mark on the shoulder surface, and also at the time of mold opening by this contact There is no possibility of problems such as increased resistance.

  When the chamfered portion 30 is provided at the lower end portion of the parting line 31 of the mouth part forming mold 3, a small groove is formed in the mating part of the parting surface 3P, and the groove lowers the bottle lower end by the groove As described above, by gradually changing the curvature of the curved surface 30R of the chamfered portion 30, the protrusion can be made as inconspicuous as possible.

  Each step in the method for producing a thermoplastic resin bottle using the blow molding die 1 will be described with reference to FIG. As shown in FIG. 4A, in the first step, the extruded parison 5 is held in the blow molding die 1. In the illustrated example, hollow parisons 5 to be extruded are supplied into the pair of blow molds 1 while being gripped by the pickup chucks 6A and 6B. At this time, the upper pickup chuck 6A holds the upper end of the parison 5 in the open state.

  As shown in FIG. 4 (b), in the second step, blow air is blown into the parison 5 held in the blow molding die 1. In this example, the blow nozzle 7 is inserted into the upper end opening of the parison 5 and blow air is blown into the blow molding die 1 while the upper opening of the blow molding die 1 is sealed by the blow nozzle 7.

  As shown in FIG. 4C, in the third step, after the parison 5 is brought into close contact with the molding surface of the blow molding die 1, the cooled blow molding die 1 is opened, and the bottle W is taken out. At this time, the bottle W is held by the pickup chucks 6A and 6B, and the bottle W is separated from the blow molding die 1 by opening the blow molding die 1 to the left and right. In this mold opening step, the bottle W is pushed upward by the convex molding surface 4A provided on the bottom mold 4 and the lower end of the parting line 31 in the mouth mold 3 is a bottle It may touch the shoulder of W.

  In the molding die 1 according to the embodiment of the present invention, as described above, the chamfered portion 30 (curved surface 30R) is provided at the lower end of the parting line 31 of the mouth molding die 3 Even if the shoulder of the bottle W comes in contact with the lower end of the mouth forming mold 3, no major problems occur. Therefore, the manufacturing method of the bottle using the blow molding die 1 according to the embodiment of the present invention can solve the problem at the time of mold opening and obtain the bottle W of good quality.

Although it is conceivable to move the separately formed bottom molding die 4 downward at the time of mold opening as a method of solving the problem at the time of mold opening described above, according to this, the mold of the blow molding mold 1 The opening operation becomes complicated, and it becomes difficult to secure the alignment accuracy in the continuous operation. According to the embodiment of the present invention, since the bottom molding die 4 can be integrally opened with the barrel molding die 2, the complexity of the opening operation and the alignment adjustment during the continuous operation can be achieved. Can be eliminated, which can contribute to the improvement of productivity.
Further, the above-described chamfered portion 30 prevents parting marks on the mouth above the shoulder, for example, the parting line 31 of the molding surface 3A of the portion including the groove 3B of the mouth molding die 3 It may further be provided on the upper end portion, the lower end portion or the like of

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and changes in design etc. within the scope of the present invention are not limited. Are included in the present invention.

1: Blow molding mold,
2: Barrel molding die, 2A: enlarged diameter portion,
3: Mouth forming mold, 3A: molding surface, 3B: groove, 3C: bottom surface,
3P: Parting plane,
30: Corner removal part, 31: Parting line, 30R: Curved surface,
4: Bottom molding die, 4A: convex molding surface,
5: Parison, 6A, 6B: Pickup chuck, 7: Blow nozzle,
W: Bottle,

Claims (5)

It is a blow molding mold for molding a thermoplastic resin bottle provided with a mouth part molding mold and having an undercut protruding toward the inside of the bottle at the bottom,
1. A blow molding mold for a thermoplastic resin bottle, wherein a chamfered portion is provided at the lower end of the parting line of the mouth molding mold.   The thermoplastic resin according to claim 1, wherein the chamfered portion is chamfered with respect to an edge of each of the parting surface, the molding surface and the bottom surface of the mouth part forming mold. Bottle blow mold.   The blowout of the thermoplastic resin bottle according to claim 1 or 2, wherein the chamfered portion has a curved surface in contact with the parting surface, the molding surface, and the bottom surface of the mouth part forming mold. Mold.   The mold for blow molding a thermoplastic resin bottle according to claim 3, wherein the curvature of the curved surface is gradually changed. A method for producing a thermoplastic resin bottle having an undercut protruding toward the inside of the bottle at the bottom thereof,
Holding the molded parison in a blow mold;
Blowing blow air into the parison held in the blow mold;
Opening the cooled blow mold and taking out the bottle;
The method for producing a thermoplastic resin bottle, wherein the blow molding die comprises a mouth portion molding die provided with a chamfered portion at the lower end portion of the parting line.

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