JPH0444894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of blow molding a hollow body such as a bottle having an upwardly protruding rib on its inner bottom surface. Before the parison is suspended from the extrusion head, the extrusion head is moved between a mandrel that is movable downward from inside the extrusion head and a bottom mold that moves up and down axially opposite to this mandrel. This method relates to a blow molding method in which the parison is molded in advance, and then the mandrel and the bottom mold are moved downward as the parison droops, the parison including the molded bottom is positioned between the split molds, and the mold is closed and then blow molded. It is something.

Prior Art Prior to suspending the parison from the extrusion head, a mandrel that is movable downward from within the extrusion head and a bottom mold that moves up and down axially opposite the tip of the mandrel are used. The conventional technique for molding the bottom of a hollow body was published in Japanese Patent Publication No. 38-24247.
It is known from the publication No.

In this conventional example, a bottomed parison is preformed within the mandrel by naturally filling the cavity, which is made up of an extrusion head, the tip of the mandrel, and a bottom mold, with plasticized and extruded plastic material. It's becoming like that.

Problems to be Solved by the Invention In the above-mentioned conventional technology, since the preforming in the mandrel is formed by natural filling of the plastic material, it is difficult to actively form thin ribs that protrude upward in the formed part. I couldn't do it. In particular, the synthetic resin used for blow molding must have viscosity because it must be formed into a tubular body, but this viscosity causes the resin to have poor elasticity, and in the conventional molding method described above, a rib protruding upward on the inner bottom surface is required. could not be molded. This is because the pressure of the synthetic resin within the cavity is very small.

Generally, when synthetic resin passes through the extrusion head, the extrusion pressure of the synthetic resin decreases due to pressure loss.This pressure loss depends on the shape of the resin flow path in the extrusion head, but if the extrusion head is the same, the extrusion pressure of the synthetic resin decreases due to pressure loss. Proportional to volume and viscosity. If the viscosity of the synthetic resin used in injection molding is relatively low, the pressure loss will be small.
High viscosity resins used in blow molding have a large pressure loss, and therefore the pressure inside the cavity inside the mandrel is extremely small. I couldn't fill it up.

Means for Solving the Problems The present invention has been made in view of the above-mentioned problems, and provides a blow molding method for a hollow body that can be formed by blow molding into a hollow body having upwardly directed ribs projecting from the inner bottom surface. The gist of the mandrel is to provide a mandrel that is slidably provided at the axial center of the extrusion head and has a rib cavity on its lower end surface. The molten resin is extruded into the space surrounded by the lower end surface of the mandrel and the inside of the lower end of the extrusion head, and then the bottom mold, which is movable coaxially with the mandrel, is inserted. , is inserted into the space surrounded by the mandrel and the extrusion head and raised above at least the side end face of the extrusion head, the molten resin in this space is pressurized and filled into the rib cavity on the lower end face of the mandrel, and then , while extruding the molten resin, the mandrel and the bottom mold are lowered together with respect to the extrusion head, and the parison is placed between the split molds,
The split mold is tightened and pressure fluid is blown into the parison.

Function By inserting the bottom mold above the lower end of the extrusion head, the extruded molten resin is pressurized into the space formed by the lower end surface of the mandrel and the inside of the extrusion head. The molten resin is pressurized and filled into the rib cavity provided on the lower end surface of the mandrel by the pressurizing force.

Example Embodiments of the present invention will be described based on the drawings.

In the figure, 1 is an extrusion head, and this extrusion head 1 includes a die 3 having a resin injection port 2, and an annular flow channel located inside the die 3 and communicating with the resin injection port 2 between the die 3 and the die 3. 4 and a mandrel 6 slidably fitted inside the core 5.
It is becoming more and more. The annular flow path 4 has a tapered shape with a smaller diameter on the lower side, and its extrusion port 7 is directed toward the inside of the die 3. The mandrel 6 is configured to reciprocate from above the extrusion port 7 to below the extrusion head 1 over a predetermined length. The extrusion port 7 is opened at a position above the lower end of the extrusion head 1 by a certain distance l. Moreover, the inner diameter of the die 3 in this period is larger than the diameter of the mandrel 6 that fits into the core 5 by the thickness of the parison.

The mandrel 6 has a step-like shape, and the tip part has a thickness that fits into the inner diameter of the extrusion head, and the other part is tapered. A rib cavity 6a is provided in the lower end surface of this mandrel 6 in the axial direction.
In addition, a positioning rod 8 is attached to the axial center of the mandrel 6.
are slidably fitted. A fluid inlet (not shown) is provided on the side surface of the positioning rod 8.

Reference numeral 9 denotes a bottom mold provided opposite the lower end surface of the mandrel 6, and the top surface of this bottom mold 9 is shaped to mold a part of the outer bottom surface of the molded product, and is similar to the mandrel 6 described above. It is designed to reciprocate in the vertical direction. The outer diameter of the bottom mold 9 is such that it fits tightly into the inner diameter of the die 3 of the extrusion head 1.

10 and 11 are left and right split molds located at the lower end of the extrusion head 1, and 10a and 11a are cavities thereof. The diameter of the upper edge of the split molds 10, 11 is the outer diameter of the positioning rod 8, and the diameter of the lower edge is the outer diameter of the bottom mold 9.

A method for blow molding a hollow body according to the present invention using the apparatus configured as described above will be described below.

The molten resin is extruded from the extrusion port 7 with the lower end of the mandrel 6 positioned above the extrusion port 7.
At this time, since the annular flow path 4 on the upstream side of the extrusion port 7 has a tapered shape with a smaller diameter on the lower side, the parison 12 extruded from the extrusion port 7 is extruded toward the center of the mandrel, and its lower end The parisons 12 gather together to cover the lower end of the extrusion head 1 (FIG. 1).

Next, the bottom mold 9 is raised and inserted into the die 3 of the extrusion head 1, and the parison is extruded below the mandrel 6 between the upper end surface of the bottom mold 9 and the lower end surface of the mandrel 6. Compress the closed part of 12 (Figure 2). At this time, since the bottom mold 9 fits inside the die 3 of the extrusion head 1, the closed part of the parison 12 extruded from the extrusion port 7 is connected to the upper surface of the bottom mold 9, the die 3, and the mandrel 6. Pressure is applied within the space surrounded by the lower surface of the Therefore, the molten resin in this space is pressurized and filled into the rib cavity 6a provided on the lower surface of the mandrel 6. Moreover, the compressed thickness at this time becomes a value close to the thickness of the bottom of the molded body.

Next, the mandrel 6 and the bottom mold 9 are integrated and lowered to a predetermined position between the opposing split molds 10 and 11 (FIG. 3). At this time, the amount of molten resin supplied to the extrusion head 1 is controlled, and an amount of molten resin corresponding to the descending speed of the mandrel 6 and the bottom mold 9 is extruded from the extrusion port 7, and as the mandrel 6 descends, the molten resin is supplied to the mandrel 6. parison 1 formed along the outside of
The wall thickness of 2 is controlled.

With the mandrel 6 and the bottom mold 9 lowered to a predetermined position, the mandrel 6 is divided into molds 10 and 1.
Raise it to a position that deviates from 1. At this time, the positioning rod 8 is left as it is, and its tip is slightly bitten into the inner bottom surface of the parison 12 to position the tip of the parison 12 in the bottom mold 9.

Next, the split molds 10 and 11 are tightened, and pressure fluid is blown into the parison 12 from the positioning rod 8 to perform blow molding (FIG. 4).

In the above molding method, the lower end of the parison 12 may be closed naturally by extrusion from the extrusion port 7 at the initial stage of extrusion of the parison 12 shown in FIG. Alternatively, they may be positioned facing each other with a gap at the bottom, and the molten resin may be extruded into the space between them to close the space.

The inner surface of the bottom of the molded body is molded at the lower end of the mandrel 6, but by chamfering the outer periphery of the lower end of the mandrel 6, the amount of resin for the bottom corner of the molded body increases. Thinning of the corners during blow molding is prevented.

The lower edge portions of the split molds 10 and 11 abut against the outer peripheral surface of the upper edge of the bottom mold 9, and the cavity 10
By making the bottoms of a and 11a substantially coincide with the upper end of the bottom mold 9, the parison 12 at the bottom of the molded body
This eliminates the possibility of pinch-off in this area.

Furthermore, in the above embodiment, the lower edge portions of the split molds 10 and 11 are shown in contact with the outer peripheral surface of the bottom mold 9, but before the clamping process of the split molds 10 and 11, 9 downward and separate the molds 10 and 1.
1 may be brought into direct opposing contact with each other. As a result, the outer bottom surface during blow molding is molded by the split molds 10 and 11. .

Further, in the above embodiment, the molding method is used when the mouth of the molded body is extremely smaller in diameter than the body, but if the diameter of the mouth is not much smaller than the body, the mandrel 6
The entire diameter of the mandrel 6 is the same as that of the tip, and the split mold 10 at the time of mold clamping is attached to the outer diameter of this mandrel 6.
11 may be brought into contact with each other.

By the above molding method, a hollow body 13 as shown in FIG. 5, that is, a hollow body 13 having ribs 14, 14 projecting upwardly on the inner bottom surface of the hollow body 13 is formed. The ribs 14, 14 may have various shapes such as a parallel shape as shown in the figure, an annular shape, and the like.

Effects of the Invention According to the present invention, a hollow body having upwardly extending ribs 14 protruding from the hollow inner bottom surface can be easily formed by blow molding. Furthermore, according to the method of the present invention, the ribs 14 can be formed by being filled under high pressure into the rib cavity, so that even ribs with a large wall thickness to height ratio can be formed into an accurate shape without shrinkage. can do.

[Brief explanation of drawings]

1 to 4 are explanatory diagrams showing the structure and operation of the present invention, and FIG. 5 is a partially cutaway perspective view showing an example of a molded article formed by the method of the present invention. 1 is a pressing head, 6 is a mandrel, 6a is a rib cavity, 9 is a bottom mold, 10 and 11 are divided molds, and 12 is a parison.

Claims (1)

[Claims] 1. A mandrel 6, which is slidably provided at the axial center of the extrusion head 1 and has a cavity for a rib on its lower end surface, is placed in a state where its lower end surface is located above the lower end of the extrusion head 1. Molten resin is extruded into a space surrounded by the lower end surface of the mandrel 6 and the inside of the lower end of the extrusion head 1, and then the bottom mold 9, which is movably provided coaxially with the mandrel 6, is inserted into the space. The molten resin in this space is pressurized and filled into the rib cavity 6a on the lower end surface of the mandrel 6, and then, while extruding the molten resin, the mandrel 6 and the bottom mold 9 are lowered together to place the parison 12 between the split molds 10 and 11, and after the mold is clamped, the parison 1
A blow molding method for a hollow body, characterized in that a pressure fluid is blown into the hollow body.