JPH0624756B2 - Parison stretching method in stretch blow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a parison for molding a container such as a bottle by axially stretching an injection-molded bottomed parison, or after air blown with the stretching. The present invention relates to a stretching method.

[Prior Art] Since an injection-molded parison is stretched while holding a mouth portion with a thread formed on the outer periphery, the mouth portion is not stretched, and the mouth portion of the container remains in the injection-molded state. Becomes

Because of this, the mouth of a normal parison is formed thinner than the body and bottom that are stretched as the mouth of the container, and it is formed thicker from the bottom to the bottom of the mouth. There is.

[Problems to be Solved by the Invention] However, when the stretching rod is inserted into the parison and the stretching is performed by pressing the inner bottom surface, the stretching of the body is remarkable,
The bottom of the mouth, which is closest to the supporting point, and the bottom, which is the force point, have little stretching. Similarly, even when the body is expanded by blowing air, the body is well expanded, but the lower side of the mouth and the bottom are not expanded so that the body is formed thick. Such a phenomenon is more remarkable as the parison is longer.

Unlike the thin-walled body, this thick-walled part is under insufficient biaxial orientation, so it is inferior in pressure resistance, heat resistance, etc., and is not suitable for liquid containers such as bottles. Subject to restrictions.

Therefore, improvements have been made to solve the difficult stretchability on the lower side of the mouth, but this problem has not been solved because it is still insufficient.

The present invention has been conceived in view of the above circumstances, and an object thereof is to improve the method for stretching a parison so that a new method for stretching a parison in a stretch-blow molding that allows the lower side of the mouth to be sufficiently stretched. To provide.

[Means for Solving the Problem] The feature of the present invention according to the above-mentioned object is to extend the injection-molded bottomed parison in the axial direction and blow-mold it into a container such as a bottle. Is formed to be thinner than that of the above portion, and a step is formed on the inner wall at the boundary between the lower side of the mouth and the body, and the thin portion above the step is temporarily blown from the air hole on the side of the tubular member. The drawn air is stretched while preventing the tubular member on the lower side of the mouth from sticking to the tubular member due to the diameter reduction due to the stretched air, and then the other thick portion is stretched.

Further, the stretching is performed after heating the thin wall portion and cooling the thick wall portion to adjust the parison temperature.The thin wall portion is stretched by connecting the tip of the tubular member connected to the blow core to the stepped portion. On the other hand, the stretching of the other portion is performed by pressing the parison bottom with the stretching rod inserted into the blow core.

[Operation] In the above stretching method, even if the thin portion is reduced in diameter by stretching,
The lower side of the mouth does not stick to the tubular member due to the temporary blowing of air. Further, the thin portion is further thinned by stretching, and the temperature of the portion is lowered.

Therefore, when the next thick portion is stretched, the thin portion is slightly stretched due to the temperature difference, and most of the stretching until it comes into contact with the bottom of the mold is the thick portion, which is thinned similarly to the lower side of the mouth. It As a result, the stretching extends entirely from the lower side of the mouth to the bottom, and the difficult stretchability on the lower side of the mouth is eliminated.

[Embodiment] FIG. 1 An injection mold 11 and a neck mold 12 which also serves as a holding member for the parison 1 are closed, and an injection core 14 is inserted into the cavity 13 through the neck mold 12.

The injection core 14 is formed with a small diameter about 20 to 30 mm below the neck mold 12 from the lower side to the tip with a step 15 as a boundary, and a thread is formed between the large diameter part 16 and the neck mold 12. The cavity of the mouth portion 2 having is formed.

A cavity 13 is injection-filled with a material resin such as polyethylene terephthalate or polypropylene from the bottom of the injection mold 11 to form a bottomed parison 1 having a total length of 124 mm. The molded parison 1 has a large diameter portion 16 and a mouth portion 2
From the bottom to the mouth portion 4 which reaches the step portion 15, it is formed to be thinner by 0.5 to 1.0 mm than the body portion 3 having a wall thickness of 4 mm, and a step portion 5 is formed inside the boundary.

FIG. 2 After opening the injection mold 11, the injection core 14 and the neck mold 13, the mouth 2 is held by the neck mold 12,
The parison 1 is transferred to the temperature control pot 17 to control the temperature.

This temperature control pot 17 has a structure in which the temperature of the lower part 4 of the parison 1, the body part 3 and the bottom part can be individually adjusted. By inserting the temperature control rod 17a into the temperature control pot, the lower part 4 of the thin wall can be adjusted. While heating, the thick body 3 is cooled to adjust the temperature of the entire parison.

FIG. 3 After the parison temperature control, the parison 1 is transferred to the blow mold 18 by the neck mold 12. The blow mold 18 is a split mold, and the blow core 20 having the extending rod 19 inserted therethrough is inserted from above.

The blow core 20 penetrates the neck mold 12, and a tubular member 21 that engages with the step portion 5 of the parison 1 is continuously provided as an outer tube of the stretch rod 19. Further, an annular engaging projection 22 having a diameter substantially the same as the inner diameter of the mouth portion is provided on the outer periphery of the distal end of the tubular member 21, and an air hole 23 is provided on the side portion.

When the blow core 20 is inserted into the neck mold 12 after the mold is clamped, the engaging protrusion 22 of the tubular member 21 is located on the step 5.

FIG. 4 When the blow core 20 is pushed in until the lower end comes into contact with the inner bottom surface of the neck mold 12, the engaging projection 22 pushes the step portion 5. As a result, the lower part 4 of the mouth is pulled in the axial direction and stretched,
The temperature decreases as it becomes thinner. At this time, air is blown in primarily. A part of the blown air enters between the mouth lower side 4 and the tubular member 21 through the air hole 23, and prevents the mouth lower side 4 from sticking to the tubular member 21 due to the diameter reduction accompanying the stretching.

FIG. 5 Subsequently, when the extension rod 19 is extended under the blown air,
The parison 1 is pulled in the axial direction by the tip of the rod in contact with the inner bottom. Since the temperature of the trunk 3 is higher than that of the mouth lower side 4 which is thinned, the stretching is performed only for the thick trunk 3, and the lower side of the step 5 is stretched to be thin.

Further, in the process of stretching the body portion 3, the temperature of the body portion 3 is increased by 4 below the mouth portion.
When the temperature becomes equal to, the lower mouth side 4 is also stretched together with the body 3 from that point.

Fig. 6 After the stretching of the entire parison with the stretching rod is completed, secondary blowing of air is performed as usual to expand the stretching parison into the cavity of the blow mold 18 and mold it into a container 6 such as a bottle. To do.

Due to this expansion, the lower side 4 of the mouth also comes into contact with the cavity surface and is molded without any step.

[Effects of the Invention] As described above, the present invention forms the lower portion of the mouth portion thinner than the other portions, and forms the step portion on the inner wall at the boundary between the lower portion of the mouth portion and the body portion. The upper thin portion is stretched by air blown temporarily from the air holes on the side of the tubular member while preventing sticking to the tubular member on the lower side of the mouth due to the diameter reduction due to stretching. Since the other part of the meat pressure forming the is stretched, the stretching obstacle due to the sticking on the lower side of the mouth is removed,
As in the case of the body, the lower side of the mouth is sufficiently stretched to be biaxially oriented, and the pressure resistance, heat resistance, impact resistance and the like are also improved on the lower side of the mouth. As a result, it is extremely effective for containers such as heat-resistant crush.

In addition, since the amount of resin required under the mouth is reduced due to the thinning and the stretching is performed by utilizing the step portion that is generated inside the boundary with the body, the injection molding of the parison becomes particularly complicated as compared with the conventional method. However, since it is possible to perform stretching by individually adjusting the temperature of the mouth side and the body side, it is possible to arbitrarily set the amount of stretching on the mouth side under the shape of the container to be molded, In a neck-long container in which the lower side of the mouth is formed as a neck, the neck is also formed to have a uniform thin wall, so that the thickness distribution of the entire container is adjusted.

Further, since the lower part of the mouth can be stretched by using the blow core, there is also an advantage that the stretch blow device of the past can be used by only changing a part of the blow core.

[Brief description of drawings]

The drawings show one embodiment of a parison stretching method in stretch blow molding according to the present invention. FIG. 1 is a sectional view during parison molding, FIG. 2 is a sectional view during temperature control, and FIG. 3 is a blow core. FIG. 4 is a cross-sectional view at the time of insertion, FIG. 4 is an enlarged cross-sectional view at the time of lower extension of the mouth portion, FIG. 5 is a cross-sectional view at the time of body extension, and FIG. 1 ... Parison, 2 ... Mouth section, 3 ... Body section, 4 ... Mouth section lower side, 5 ... Step section, 6 ... Container, 11 ... Injection mold, 14 ... Injection core, 16 ... Large diameter section , 17 ... Temperature control pot 18 ... Blowing die, 19 ... Stretching rod 20 ... Blowing core, 21 ... Tubular member 22 ... Engaging ridge, 23 ... Air hole

Claims (3)

[Claims] 1. When the injection-molded bottomed parison is axially stretched and blow-molded into a container such as a bottle, the lower side of the mouth of the parison is formed to be thinner than the other portions, and the lower side of the mouth is formed. A step is formed on the inner wall between the body and the body, and a thin portion above the step is stretched while temporarily blowing air through the air holes on the side of the tubular member. A parison stretching method in stretch blow molding, which comprises stretching a portion. 2. The method for stretching a parison in stretch blow molding according to claim 1, wherein the stretching is performed after heating the thin portion and cooling the thick portion to adjust the parison temperature. 3. The thin portion is stretched by engaging the tip of a tubular member connected to the blow core with the step, and the other portions are stretched by a stretch rod inserted into the blow core. The parison stretching method in stretch blow molding according to claim 1, wherein the bottom portion is pressed.