JPH0430324B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a blow molding die that allows the thickness of the parison to be arbitrarily adjusted depending on the molded product. Blow molding can produce hollow molded products at a lower cost than injection blow molding, so it is used in many fields, including detergent bottles and containers such as industrial chemical cans, as well as ducts for automobile parts. It is being used for a wide variety of purposes. However, in blow molding, a parison formed by extruding molten resin through a slit formed between the die and the core is used.
Compared to injection blow molding, which uses a parison obtained by injecting molten resin into a mold, the wall thickness distribution is inferior, and due to the difference in wall thickness distribution, stress during blow molding tends to remain in the molded product, and this residual Stress causes distortion, which often has a negative impact on physical properties such as dimensional stability and environmental stress cracking resistance (ESCR) of molded products. Therefore, in blow molding, a method called parison control is used to adjust the thickness of the parison. This method includes using a tapered die and moving the core up and down during the forming of the parison, thereby changing the slit width of the die, changing the extrusion speed, and changing the withdrawal speed of the parison. However, all of these methods are for adjusting the wall thickness of the parison in the longitudinal direction, but cannot adjust the wall thickness in the cross-sectional direction. Wall thickness adjustment in the cross-sectional direction of the parison is useful not only for making the thickness distribution of the parison uniform, but also for blow molding molded products with partially different blow-up ratios, such as bottles with oval cross sections. It is considered extremely important in this case. Conventionally, this wall thickness adjustment in the cross-sectional direction is performed by shaping. Shaping here refers to changing the shape of a die or part of the core as a whole to increase or decrease a part of the cross-sectional area of the flow path, thereby increasing or decreasing the wall thickness of a part of the parison. Even if it is possible to change the perfect circle and control the vertical direction of the parison by using such shaping together with the parison control described above, the cross-sectional shape will differ depending on the position, such as flat or perfectly round, and the It is considered impossible to mold bottle-shaped containers with different blow-up ratios or molded products with partially uneven parts to a desired weight and with a uniform wall thickness distribution. However, as the range of applications for blow molding expands, the shapes of molded products generally become more complex, and blow molding dies equipped with more effective wall thickness adjustment means than conventional parison control and shaping are required. ing. This invention was conceived in view of the above circumstances, and its purpose is to provide a blow molding die with a new structure that allows the thickness of the parison to be adjusted in both vertical and horizontal directions using only core operation. It is about providing. The features of the present invention for the above-mentioned purpose are that the core is configured to have an inner and outer core, a tapered part is formed at the tip of the outer core, and a shaped part having a desired width and length is formed at the tip of the inner core. At the same time, the tip part protrudes from the tapered part and is provided within the die head so that the outer core and the inner core can move relatively freely in the axial direction, and the straight tip part (hereinafter referred to as the straight part) ) and the axial movement of the inner and outer cores, it is possible to adjust the parison wall thickness in both the vertical and horizontal directions. That is, the cross-sectional shape of the straight portion may not only be the same in the axial direction but may also vary. The core and inner core are moved using a device operated by pneumatic pressure, hydraulic pressure, or the like. In addition, the connections between the inner and outer cores and each moving device are made at the top of the core body, and the wall thickness of the parison can be adjusted in the vertical direction by moving the outer core, which has a tapered part, and the inner core, which forms the straight part, can be moved. It is also possible to adjust the cross-sectional wall thickness of the parison. The cross-sectional shape of the above shaping part is circular,
It can be formed into any shape depending on the cross-sectional shape of the molded product, such as an elliptical shape or a circular shape with chamfered sides. The wall thickness change is greatest when a lip gap is formed.
This is because the lip gap formed between the straight part and the dive bush changes as the straight part moves, and the thickness of the parison can be freely changed within that range. Next, the present invention will be explained in detail using the illustrated blow molding die. In FIG. 1, a die head 1 has a hollow mandrel 2 in the center thereof. This mandrel 2
A double core 5 consisting of an outer core 3 and an inner core 4 is inserted through the die head 1, and a die bush 6 is attached to the lower end of the die head 1 using a die fixing ring 7. The tip of the outer core 3 protrudes above the dive bush 6 from the tip of the mandrel 2, and the circumferential surface of the protrusion is formed into a tapered portion 3a. Further, the tip of the inner core 4 protrudes from the tapered portion 3a into the dive bush 6, and the tip opens the lip gap 8.
A straight portion 4a is formed. The inner core 3 and the outer core 4 are inserted into the mandrel 2 so as to be relatively movable in the axial direction, and hydraulically operated moving devices 9 and 10 move members 11 and 12 at their respective rear ends protruding from the mandrel 2. They are individually connected through. The moving devices 9 and 10 are installed on support stands 13 and 14 provided in upper and lower stages on the top of the die head 1, and are used to move the outer core 3 and inner core 4 through members 11 and 12.
It has the function of moving both individually or simultaneously in the axial direction. In the figure, 15 is an air passage penetrating the center of the inner core 4, and 16 is a resin flow passage. The cross-sectional shape of the shaped portion of the straight portion 4a can be arbitrarily formed depending on the blow-molded product. FIG. 2A shows a case in which both sides of the tip of the straight portion 4a having a circular cross section are shaped in parallel and both sides of the lip gap 8 are enlarged, and FIG. 2B
represents the case where the straight part 4a is formed into an oval shape,
Furthermore, FIG. 2C shows a case in which only one side of the straight portion 4a is shaped. 3 to 6 show the forming state of the parison 17 by the straight part 4a, and the second
In the case of the straight portion 4a shown in FIGS. 3A and 3B, the thickness of both sides of the parison 17 is thickened as shown in FIG.
As shown, even if the outside is circular, the inside is oval. Further, as shown in FIG. 4A, the straight part 4 of the inner core 4 is
When a is moved downward and the lip gap 8 is formed in a circular portion, the cross section of the parison 17 becomes circular both inside and outside as shown in FIG. 4B. This also applies to the case shown in FIG.
As shown in Figure B, only one side is thick, but the 6th
When molding is performed by moving the straight portion 4a downward to the state shown in Figure A, the cross section of the parison 17 is
As shown in Figure B, it has a circular shape with uniform wall thickness. Therefore, if the inner core 4 is moved upward or downward, the lip gap 8 may be formed by the shaped portion of the straight portion 4a or the lip gap 8 may be formed by the circular portion. Parison 1 with different surface thicknesses
7 can be molded. In addition, the longitudinal wall thickness can be adjusted by moving the outer core 3 in the axial direction and adjusting the tapered portion 3a. After adjusting the longitudinal wall thickness uniformly, there is no change in the cross-sectional wall thickness. can be set. Furthermore, the axial movement of the inner and outer cores can be carried out in conjunction with the molding cycle, in which case commonly used control means may be used. Next, the effects of this invention will be illustrated by giving examples. Molding machine used and molding conditions Molding machine Screw 50φmm blow molding machine (continuous extrusion) L/D=27 CR=3.4 Screw rotation speed 40rpm Molding machine setting temperature (℃) C ₁ C ₂ C ₃ A D 150 170 180 180 180 Materials used: High-density polyethylene MFR 0.3g/10min Density 0.950g/cm ^3Example 1 The shape of the straight part is as shown in Figure 2A, and the bottle 18 having the shape shown in Figures 7A, B, and C is blown. Molded. Note that the cross-sectional location B is indicated by Roman numerals. The core diameter is measured at the straight portion, and the product wall thicknesses a and b are determined from the cross section shown in FIG. 7C using the following formula. a=a′+a″/2 b=b′+b″/2

[Table] Example 2 Using the straight portion shown in FIG. 2C, air duct hoses 19 having the shapes shown in FIGS. 8A, B, and C were blow-molded. Note that the cross-sectional location B is indicated by Roman numerals. The core diameter is measured at the straight portion, and the product wall thicknesses a and b are based on the cross section shown in FIG. 8C.

【table】 Comparative example 1 Regular molding, no shaping paricone used. Comparative example 2, 3 Uses shaping paricon.

[Brief explanation of drawings]

The drawings illustrate the blow molding die according to the present invention, and FIG. 1 is a longitudinal sectional view, and FIG.
C is a diagram showing the cross-sectional shape of the straight part, FIGS. 3 to 6 are diagrams showing the molded state of the parison and the cross section of the parison, and FIGS. 7A, B, and C are explanatory diagrams of Example 1.
FIGS. 8A, B, and C are explanatory diagrams of the second embodiment. 1... Die head, 2... Mandrel, 3...
Outer core, 3a...Tapered portion, 4...Inner core, 4a
... Straight part, 5 ... Core, 6 ... Dive bush, 8 ... Lip gap, 9, 10 ... Movement device.

Claims (1)

[Claims] 1. The core is configured to have an inner and outer double structure, a tapered part is formed at the tip of the outer core, a shaping part having a desired width and length is formed at the tip of the inner core, and
A die for blow molding, characterized in that the tip portion thereof protrudes from the tapered portion, and an outer core and an inner core are provided within a die head so as to be relatively movable in the axial direction.