JP4748475B2 - Injection molding preform - Google Patents

Description

  The present invention relates to an injection molded preform for biaxial stretch blow molding.

  Conventionally, synthetic resin casings such as plastic bottles have been widely used in beverage containers and the like. A PET bottle is mainly formed by molding a preform having a test tubular shape by injection molding using polyethylene terephthalate (hereinafter referred to as PET) resin as a raw material, and biaxially stretch-blow molding the preform.

  FIG. 4 shows an example of a preform for a plastic bottle. The preform 101 includes a mouth tube portion 102, a neck ring 105, a cylindrical body portion 103, and a bottom portion 107, which are engraved with threads. Here, the sprue portion 106 that is incidentally formed as a molten resin passage by injection molding is shown in the bottom portion 107 without being cut (so-called gate cut).

  FIG. 5 is a schematic explanatory view showing a main part of an injection molding apparatus used for injection molding of the preform 101 shown in FIG. The nozzle portion 17 is fixed to the mold 11 via a heat insulating ring 19, and the resin flow path of the nozzle portion 17 is opened and closed by the upper and lower sides of the shut-off pin 18 (FIG. 5 shows a closed state). The mold 11 includes a cavity mold 12 and a core mold 13, and the molten resin injected from the tip of the nozzle portion 17 fills the cavity 14 through the sprue 15 and the gate 16, thereby forming the preform 101. Is done.

FIG. 6 is a schematic explanatory view of an apparatus for biaxially stretch blow-molding the preform 101 of FIG. 4 into a casing. In the example shown in FIG. 6 , the mold 21 for blow molding is composed of a blow core mold 22, a main body split mold 23, and a bottom mold 24. The blow core mold 22 is a preform 101. And a blow air hole (not shown in the drawing) and a concentrating rod 25 are provided concentrically at the center, and the upper end of the fitting portion 22a and the main body split mold 23 is provided. And sandwich the bottom portion 107 of the preform 101 so that the stretching center position is not displaced between the stretching rod 25 located on the inner side and the support pin 26 located on the outer side. To do.

  While maintaining this clamping state, the stretching rod 25 is advanced toward the bottom mold 24 and the support pin 26 is retracted to stretch the preform 101 in the vertical direction, and at the same time, it is added into the preform 101. It is blown in the biaxial direction by injecting compressed air and expanding. The support pin 26 may not be used.

Here, the sprue portion 106 of the preform 101 needs to be cut in advance. For example, Patent Document 1 discloses an invention relating to an apparatus for cutting the sprue portion. In addition, for example, various types of injection molding methods of a parison without sprue such as an extended nozzle type or well type injection mold, a pinpoint gate, or a method described in Patent Document 2 have been proposed.
JP 2004-122636 A JP 11-28761 A

  However, the above-described method for cutting a sprue requires a separate process for cutting, and also requires equipment for cutting, resulting in an increase in cost. In addition, the injection molding method of the parison without sprue also makes the structure of the mold more complicated by the mechanism for performing the nozzle touch and the heating mechanism for maintaining the temperature of the gate part, and the resin is fixed to the gate part. There's a problem. Further, in the case of a pinpoint gate, there is a problem that the flow path is blocked, and any method has a difficulty in continuous operation for a long time and is difficult to industrially use.

  Therefore, the present invention can use the conventional injection molding apparatus without greatly changing the nozzle part, the mold, etc., and can create a preform that can be continuously operated and industrially used without gate cut, in particular, the bottom shape. This is a technical issue.

Among the means for solving the technical problem, the means of the invention according to claim 1 is:
An injection molded preform for biaxial stretch blow molding,
In the center of the outer surface of the bottom part, without cutting the sprue part formed in the injection molding with the maximum length 1.5 times the thickness of the bottom part,
At the position facing the sprue portion at the center of the bottom inner surface, the convex shape of the sprue portion is complemented so as to alleviate fluctuations in the thickness of the bottom portion including the sprue portion , and the tip of the drawing lot during biaxial stretch blow molding Forming a recess with a depth shorter than the length of the sprue part that enables centering by inserting the part ,
It is in.

According to the above configuration of the present invention, since the length dimension of the sprue portion is at most 1.5 times the thickness of the bottom portion, a convex shape by the sprue portion is provided at a position facing the sprue portion at the center of the bottom inner surface. By forming the recess so as to compensate for the fluctuation of the thickness at the bottom due to the presence of the sprue portion can be mitigated,
Since it is possible to easily center with high precision by inserting the tip of the extending rod into this recess,
Regardless of the presence of the sprue portion, it is possible to smoothly achieve stretching in the vertical direction and the horizontal direction at the bottom.
For this reason, the gate cut process for cutting a sprue part becomes unnecessary.

Here, the thickness of the bottom of the preform is usually about 2 to 7 mm. However, if the length of the sprue in the injection molding apparatus is set to such a dimension, the nozzle portion and the mold in the injection molding machine By using a heat insulating plate in between, the nozzle part can be prevented from being affected by the mold temperature, and the resin can be prevented from solidifying near the tip of the nozzle part. Use is possible.
Here, if the length dimension of the sprue part exceeds 1.5 times the thickness of the bottom part, the convex shape of the sprue part cannot be supplemented by the concave part, and uniform stretching cannot be performed. .
On the other hand, the minimum value of the length of the sprue portion can be determined based on whether or not continuous operation is possible.

Further, since the posture of fixing the preform to the mold usually has some variation, it is not always easy to achieve centering before stretching related to the preform of the stretching rod with high accuracy. Further, in the stretching stage, it is difficult to keep the centered state constant by applying some frictional force between the preforms, and a deviation occurs for each molding batch, resulting in defective products.
Here, in the above-described configuration of the present embodiment, the centering state can be stably maintained by using the recesses and during stretching as well as before stretching.

  According to a second aspect of the present invention, in the first aspect of the present invention, the shape of the recess is substantially complementary to the shape of the sprue portion.

  According to the above configuration of the second aspect, it is possible to more effectively mitigate fluctuations in the thickness distribution of the preform bottom portion including the sprue portion. Here, when the length dimension of the sprue part is a dimension close to the thickness of the bottom part, if the depth dimension of the concave part is set to a value close to the thickness of the bottom part, an extremely thin part will be formed at the bottom part. In such a case, the depth dimension of the recess is set smaller than the length dimension of the sprue part.

The present invention is the method described above, and has the following effects.
In the invention according to claim 1, by forming the concave portion so as to complement the convex shape by the sprue portion, it is possible to reduce fluctuations in the thickness at the bottom due to the presence of the sprue portion, Since the leading end of the stretching rod can be fitted into the recess and easily centered with high accuracy, stretching in the vertical and lateral directions of the bottom can be smoothly achieved regardless of the presence of the sprue portion.

  In the invention according to claim 2, by making the shape of the concave portion substantially complementary to the shape of the sprue portion, the variation in the thickness distribution of the preform bottom portion including the sprue portion can be more effectively performed. Can be relaxed

Embodiments of the present invention will be described below with reference to the drawings.
1 to 3 illustrate a first embodiment of the preform of the present invention.
FIG. 1 is a longitudinal front view of a preform, and FIG. 2 is an enlarged vertical sectional view of a main part showing the vicinity of the bottom. This preform 1 is made of PET resin, and is a test tube having a mouth tube portion 2, a neck ring 3, a cylindrical body portion 4, and a bottom portion 5, each of which has a height of 170 mm, The body part has an outer diameter of 40 mm and a bottom part thickness of 3.5 mm.

The bottom 5 is in a state where a sprue portion 6 that is incidentally formed by a sprue serving as a passage for the molten resin of the injection mold remains. The sprue portion 6 has a truncated cone shape. The length L is 3.5 mm, the diameter of the distal end 6a is 4 mm, and the diameter of the proximal end 6b is 5 mm. (See Figure 2)
Incidentally, the length of the sprue portion 6 of the conventional preform 101 shown in FIG. 4 is 7 mm, the tip diameter is 4 mm, and the base end diameter is 6 mm.

  Moreover, a truncated cone-shaped concave portion 8 having a shape substantially complementary to the shape of the sprue portion 6 is formed on the inner surface of the bottom portion 5 facing the sprue portion 6, and the depth D thereof is 2 mm. The diameter of the bottom 8a is 4 mm, and the diameter of the base end 8b is 5 mm. (See Figure 2)

  FIG. 3 is a schematic explanatory view showing the injection molding apparatus for molding the preform 1 of the present embodiment in a longitudinal section. The basic structure of this injection molding apparatus is the same as that of the apparatus of FIG. 5 described above, but the tip of the nozzle portion 17 is brought close to the gate 16 so that the length of the sprue 15 is half (7 → 3.5 mm). And the convex part 13a for forming the concave part 8 of the preform 1 mentioned above in the front-end | tip of the core metal mold | die 13 shall be formed.

  Here, if the nozzle portion 17 is too close to the gate, the influence of the mold temperature reaches the tip portion of the nozzle portion, causing problems such as solidification of the resin. The minimum value of the length dimension of the sprue 15 can be set as much as possible. When the sprue length is about 3.5 mm as in this embodiment, continuous operation for a long time was possible.

Next, the biaxial stretch blow molding of the preform 1 of the present embodiment is basically performed by the method described above with reference to FIG. As shown in 2. That is, biaxial stretch blow molding is performed according to the above-described method in a state in which the distal end portion 25a of the stretching rod 25 is fitted into the recess 8 and the support pin 26 is in contact with the surface of the distal end 6a of the sprue portion 6.
At this time, the recess 8 can easily and accurately center the preform 1 with the stretched rod 25 before stretching, and the distal end of the stretched rod 25 is fitted into the recessed portion 8 even when it is stretched and deformed. Therefore, since the centering state is maintained, biaxial stretch blow molding can be stably performed with high productivity.

  As mentioned above, although the aspect of this invention was demonstrated along the Example, this invention is not limited to these Examples. For example, in addition to the PET resin of the present invention, an injection molded preform such as a polypropylene resin can be used for biaxial stretch blow molding.

  As described above, the preform of the present invention can omit the gate cutting step, can provide a biaxial stretch blow molded container with high productivity and low cost, and can be expected to develop a wide range of applications. Further, the shape of the preform is not limited to a test tube, and may be a small cup for molding a cup container, for example.

It is a vertical front view which shows 1st Example of the preform of this invention. FIG. 2 is an enlarged longitudinal sectional view of a main part of the preform of FIG. 1. It is a schematic explanatory drawing which cuts and shows the principal part of the injection molding apparatus for shape | molding the preform of FIG. It is a partial vertical front view which shows the conventional preform (before cut of a sprue). It is a schematic explanatory drawing which cuts and shows the principal part of the injection molding apparatus for shape | molding the preform of FIG. It is a schematic explanatory drawing which shows a biaxial stretch blow molding apparatus longitudinally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Preform 2; Mouth part 3; Neck ring 4; Trunk part 5; Bottom part 6; Sprue part 6a; Tip 6b; Base end 8; Recessed part 8a; Bottom 8b: Base end L: (Sprue part) Length D ; (Concave) depth 11; injection mold 12; cavity mold 13; core mold 13a; convex 14; cavity 15; sprue 16; gate 17; nozzle part 18; shut-off pin 19; Blow molding die 22; blow core die 22a; fitting portion 23; main body split die 24; bottom die 25; stretching rod 25a; tip portion 26; support pin 101; preform 102; mouth tube portion 103; ; Bottom part 105; neck ring 106; sprue part

Claims (2)

An injection-molded preform (1) for biaxial stretch blow molding, with the length (L) at the maximum at the center of the outer surface of the bottom (5) 1.5 times the wall thickness of the bottom (5) The bottom part including the sprue part (6) at the position facing the sprue part (6) at the center of the inner surface of the bottom part (5) without cutting the sprue part (6) formed in the injection molding. ( 5 ) A concave portion that complements the convex shape by the sprue portion (6) so as to alleviate the wall thickness variation and that can be centered by inserting the end portion of the drawn lot during biaxial stretch blow molding ( A preform made of synthetic resin, characterized in that 8 ) is formed with a depth dimension (D) shorter than the length dimension (L) of the sprue portion (6) . The preform according to claim 1, wherein the shape of the concave portion (8) is substantially complementary to the shape of the sprue portion (6).

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