JPH0788034B2 - Blow molding machine with flat die - Google Patents

Description

TECHNICAL FIELD The present invention relates to a die lip deformation prevention device for a flat die having a flat annular shape in a blow molding machine.

[Prior Art] FIG. 3 shows a plan view of a conventional flat die. Conventionally, when molding a resin hollow container by blow molding, it is easy to adjust the wall thickness in the parison circumferential direction and it is possible to prevent rupture, so flat dies have been adopted for molding deep double wall molded products. There is.

Blow molding apparatuses having this flat die have been widely used for general-purpose resins.

Explaining such a blow molding device conventionally used, there is a mandrel at the center of the die body,
A core is fixedly attached to its lower end.

A die housing surrounds the outer periphery of the core around the core in the lower part of the main body, and a flat annular slit (die lip gap) is formed between the core and the die housing.
The lower end of the molten resin passage is connected to the slit, and when the plunger of the resin injection device is pushed forward, the molten resin in the molten resin passage is pushed out of the main body through the slit, and the parison is formed.

[Problems to be Solved by the Invention] In such a blow molding machine, when attempting to perform high-speed injection using engineering plastic (commonly called engineering plastic), pressure loss in the slit between the lower die housing and the core becomes large. , The resin pressure is, for example, 50
It may be necessary to apply more than 0kg / cm2. Therefore, the lower die housing, which determines the thickness of the parison, also swells in the major axis portion, and there is a problem that the lower die lip gap is not uniform in the circumferential direction.

Therefore, in order to solve these problems, it is necessary to manufacture the die from a material having a high rigidity structure and high strength. In particular, for the die lip portion, the dimension of the die gap finally determines the wall thickness of the parison, so that the rigidity of the die lip portion is particularly important.
However, if the width of the die housing in the horizontal direction is made extremely thick, the weight of the entire die becomes enormous, and in addition, a huge heater capacity is required to heat up the die, and the heating time is long. There was a new problem that it became a thing.

[Means for Solving the Problems] In order to solve such a problem, in the present invention, a core is provided at the center of the lower end of a die housing, and a die lower part is formed apart from the core to form a molten resin passage. The plate is coaxially arranged below the die housing, and the horizontal width dimension of the die lower plate is made longer than the horizontal width dimension of the die housing.

[Operation] The lower part of the die housing forms a die gap with the core arranged at the center of the lower end of the die housing, and a die lower plate having a width dimension larger than the width dimension of the die housing in the horizontal direction is provided in the die housing. It was arranged coaxially with. The horizontal width dimension of the die housing that is difficult to deform is set to 1.5 to 2.5 times the horizontal dimension of the inner minor axis of the die lip area as the reference dimension, and the horizontal width dimension of the die bottom plate that is the most deformable is the above. Standard size 2.5
The weight of the die as a whole is lightened because the structure is set to 4 times.

[Embodiment] FIGS. 1 and 2 show an embodiment of the present invention.
FIG. 1 is a vertical sectional view of the flat die, and FIG. 2 is a plan view in the direction of arrow II-II.

In FIG. 1, the die 1 of the blow molding machine comprises a die housing 2, a mandrel 3, a core 5, a die lower plate 6 and a die gap adjusting device 7.

First, a lower die plate 6 is attached to the lower portion of the die housing 2 by means of studs 10. A mandrel 3 is arranged in the center of the die housing 2, and a core is fixedly arranged below the mandrel 3, and a slit for ejecting the parison 9 between the die lower plate 6 and the core 5 ( A die gap) 20 is formed.

A die gap adjusting device 7 including a bolt box 22, a holding bolt 23, and a lock nut 24 is mounted on the die lower plate 6 at appropriate intervals on the outer periphery of the lower portion of the die housing 2. There is. Bolt box
A screw is engraved on the inner peripheral surface of 22. After engaging with the presser bolt 23, the presser bolts 23 symmetrically arranged with respect to the central axis of the die lower plate 6 are moved as a set. Then, the die gap 20 can be adjusted to a desired one.

When performing blow molding using a resin with a high solidification rate such as engineering plastic, it is necessary to inject the molten resin 12 at a high speed with an injection device. Although the distance between the diamond gaps 20 along the direction did not change, there was a phenomenon that the distance between the die gaps 20 along the direction of the major axis became large.

Therefore, in the present invention, as shown in FIG. 2, a peripheral portion of the lower die plate 6 shown by a chain line facing the core 5 is referred to as a die lip region 21, and a die lip region generated when the molten resin 12 passes through the slit 20 portion. In order to prevent the expansion and deformation of the slit 20 portion along the major axis direction C of 21, the width dimensions of the die housing 2 and the die lower plate 6 and the horizontal width dimension of the die lower plate 6 are determined as follows. To do.

That is, for example, with respect to the width dimension of the die housing 2 (from the end surface on the core 5 side of the die lip area 21 to the outer end surface of the die housing 2), the reference value a (inner minor axis of the die lip area 21 having an elliptical shape) is 1.5 to 2.5 times, preferably 2
Further, regarding the horizontal width dimension of the die lower plate 6 (from the end face on the core side of the die lip area 21 to the outer end face of the die lower plate 6), the standard value a is 2.5 to
It is 4 times, preferably 3 times. At this time, the thickness of the die lower plate in the vertical direction is 0.5 to 1.0 times the reference value a,
The optimum value is 0.7 times.

The dimensional structure of the die lower plate 6 described above is determined by the resin pressure at the time of extrusion when the molten resin 12 is injected at high speed by the injection device. In this case, the die lip plate 21 can be effectively provided with high rigidity and high strength by using the die lower plate 6 having an appropriate size depending on the physical properties of the resin and the resin pressure at the time of extrusion.
The strain of the die gap 20 along the major axis direction C of 21 is 0.
It becomes possible to hold down to 1 mm or less, and the interval of the die gap 20 can be kept constant along the inner peripheral surface of the die lip region 21.

Next, the operation of the blow molding machine thus configured will be described.

The molten resin 12 press-fitted between the mandrel 3 and the die housing 2 by an injection device is extruded as a parison 9 from a slit 20 formed between the core 5 at the lower end of the mandrel 3 and the ends of the die lower plate 6. Under such circumstances, if an attempt is made to perform blow molding using an engineering plastic having a viscosity higher than that of a general-purpose resin as the molten resin 12, the molten resin 12
Causes a large pressure loss when passing through the narrow slit 20, and tries to move the die lip region 21 so as to bulge toward the side opposite to the core 5 by the resin pressure.

Therefore, if the width dimension in the horizontal direction and the thickness dimension in the vertical direction of the die lower plate 6 are set as described above, the molten resin
It is possible to prevent the deformation of the die lip region 21 due to the strain in the direction of the major axis C in 0.1 mm or less by 12 pressure. In this way, the parison 9 having a desired thickness hangs downward from the slit 20 of the die 1 and is blow-molded.

Further, if it is desired to change the wall thickness of the parison 9 so that the parison 9 is not symmetrically symmetrical, the presser bolts 23 arranged symmetrically with respect to the central axis of the die lower plate 6, for example, 23a and 23
After appropriately rotating b, 23c and 23d, and 23e and 23f, respectively, the lock nuts 24a, 24b, 24c and 24d screwed to the holding bolts 23 are respectively rotated to be tightened to obtain a desired die. The gap 20 is easily obtained.

[Effects of the Invention] As apparent from the above description, in the present invention, in order to prevent expansion deformation of the die gap along the major axis direction of the die lip region that occurs when the molten resin passes through the slit portion, Instead of manufacturing the entire die housing with a high-rigidity structure and a high-strength material, it is sufficient to simply attach a separate die lower plate to the lower portion of the die housing at the most deformable portion. Even if the molten resin pressure becomes high, it is not necessary to increase the thickness of the entire die housing, so the weight of the entire die becomes lighter, and the heater capacity when heating up the die does not need to be large, so the temperature rises. It takes less time.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention.
FIG. 1 is a vertical sectional view of a flat die, FIG. 2 is a plan view in the direction of arrows II-II, and FIG. 3 is a plan view of a flat die of a conventional example. 1 ... Die, 2 ... Die housing, 3 ... Mandrel, 5 ... Core, 6 ... Die bottom plate, 7 ... Die gap adjusting device, 9 ... Parison, 12 ... Molten resin, 20 ... slit.

Claims (1)

[Claims] 1. A core is disposed at the center of the lower end of a die housing, and a die lower plate which is separated from the core and forms a molten resin passage is coaxially disposed at the lower portion of the die housing. The blow molding machine having a flat die is characterized in that the horizontal width dimension thereof is longer than the horizontal width dimension of the die housing.