JPH0423618B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing hollow bodies, especially containers of complex shape, by extrusion and blowing of synthetic resin materials.

As is well known, hollow bodies of any shape can be produced from synthetic resin materials by extrusion blowing machines.

One of the most difficult steps in this manufacturing method is the proper feeding of the synthetic resin material, and the well-known extrusion blowing machines automatically set the thickness and length of the parison for this purpose. (i.e., a bubble of synthetic resin material that has been blown but not yet shaped in the mold) and further comprises an ovalized plunger or die, and this ovalization is adjustable by the programmer.

Thus, known devices have one or more dies for extruding synthetic resin material connected to a means for feeding the synthetic resin material, such as an Archimedean screw, the screw being Ensures plasticization of the plastic material in the sleeve and feeding to the extrusion head. Also, means for blowing air into the parison obtained at the exit of the die, means for cutting the parison and joining its base parts, and a mold for receiving the parison and having an internal cavity corresponding to the shape of the hollow body to be cast. at least one blow tube for blowing air into the mold;
It has a device for moving the mold from the extrusion die to the blowing tube and vice versa for the next parison, and a device for ejecting the finished hollow bodies and pieces.

The thickness of the parison at the exit of the extrusion die is programmed vertically, so that a good distribution of the material in the flow direction of the parison, for example between the base and the upper body of the hollow body, is achieved. This technique also allows air to be blown into the already base-joined parison at a relatively low pressure, e.g. 0.3 bar, so that a length of synthetic resin material smaller than the length of the hollow body to be produced It had a kind of foam made of it. The mold is then closed over the parison and high pressure (6-7
Air is blown in with a crowbar), which expands the parson and presses it into the mold cavity.

It has now become clear that when material is fed horizontally into the final product bottle in successive horizontal layers, the material is not fed uniformly. In fact, measurements revealed that there are thin areas and areas that are thicker than necessary. For example, in the case of a 5-liter bottle for household detergents, etc., the vulnerable area is the part that is less than 0.7 millimeters thick. Such weak parts exist at the bottom of the bottle, which is continuous with the crest on the front of the bottle, the shoulder of the bottle, which is continuous with the neck of the bottle, and the handle of the bottle.

The extremely thick parts, over 1.2 millimeters, are at the joint at the bottom of the bottle and at the base on both sides.

This varying thickness of the bottle in its continuous horizontal area leads to the following disadvantages. That is, during container filling and during their storage and handling, the containers are pressed together to a greater or lesser degree in their weak areas. Moreover, the presence of these areas creates a risk of partial rupture and thus leakage during handling operations. Difficulties arise in applying the label due to the fact that the side surface to which the label is applied is not flat.

Harmful irregularities in the distribution of the material within a given horizontal layer or area of the container are caused by the relationship between the hot synthetic resin material and the cold mold walls at about 20°C at the beginning of air blowing into the parison in the mold. This can be explained by the fact that the contact between them does not occur simultaneously at all points of the mold. The contact between the now hot synthetic resin material and the mold cavity wall immediately initiates solidification of the synthetic resin material, which occurs at all points on the outer wall of the less malleable parison. In fact, when analyzing the parison blowing process, the synthetic resin material tries to contact the bottom, the expanded front before the handle, and the neck only after the start of blowing. Therefore, the already cooled material has to be stretched considerably in order to reach the remote point, which causes a reduction in thickness. Furthermore, when the mold is closed, the sides are the earliest to come into contact with the mold. Thus, the synthetic resin material is set and then moved with more difficulty, resulting in the observed excessive thickness.

Various methods have been tried to solve this problem and to provide a sufficient distribution of the synthetic resin material in the horizontal area of the bottle during the blowing process, but none have been able to solve this problem. However, this problem was finally solved in the following way.

The method according to the invention provides that during the formation of a parison joined by two jaw parts, air is blown into the parison through an extrusion die so that the length of the parison is approximately equal to the length of the finished hollow body. characterized in that the parison is highly inflated outside the mold until equalized, then the mold is closed to accommodate the parison, and air is blown into the parison so that the parison is pressed into the cavity of the mold with sufficient pressure. shall be.

According to the invention, excessive thickness and weak spots in each horizontal area of the bottle are reduced by eliminating premature contact between the plastic material and the large-sized cavity of the mold. found.

A feature of the method of the invention is that air is blown outside the mold into the parison until the cross-section of the parison is equal to the cavity cross-section of the mold, so that the material is evenly distributed in each horizontal or transverse section of the parison. . Then, the parison is deflated by stopping the supply of blown air, and the parison is brought into contact with the atmosphere or exposed to a reduced pressure state to become deflated. Additionally, the mold is closed containing the deflated parison, with the walls of the deflated parison being kept from contact with the cold cavity of the mold until the blowing of air into the parison within the mold is resumed. dripping

Thus, the parison, fully tensioned by the previous expansion, reasserts its sagging configuration after contraction, and this contraction allows the parison to position itself within the mold while preventing premature contact with the cold cavity walls of the mold. enable. It will be appreciated that the subsequent expansion of the parison at high pressure ensures that the parison is simultaneously and uniformly pressed into the mold cavity.

Furthermore, it is an essential requirement of the method according to the invention that the parison is pre-expanded outside the mold. This is because it is possible to supply material uniformly in the cross direction within the horizontal cross section obtained.
This is due to the expansion of this parison at the appropriate pressure in the outer contour of the mold. It will be appreciated that the thickness of successive horizontal sections can be programmed appropriately.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The apparatus shown in Figures 1 and 2 produces hollow bodies, especially containers of complex shapes, such as polyethylene bottles of various sizes, for holding detergents, etc., by extruding and blowing synthetic resin material. It is for manufacturing.

Conventionally, this device consists of a horizontal screw for plasticizing the material introduced into the extruder through a hopper 2, and two extrusion dies placed vertically into which the plasticized material is fed by the extruder 1. 3, means 15 for cutting a continuous parison, and two half molds 6 forming two semi-cavities 7 corresponding to the desired shape of the hollow body to be molded.
a main mold 6 formed by a, two pipes 8 for blowing air into the mold 6, and (not shown) the main mold 6 formed by a die below the blowing pipes 8. 3 to the blowing tube 8 and vice versa, and consists of an extruder 1 with means for removing the finished hollow body 9 and waste (not shown). . The waste is received by a conveyor 11 and returned to the extruder 1 in a known manner.

All of the previously mentioned component parts are on a fixed frame 12. The device further includes a mold 13 for receiving the container 9a formed in the mold 6;
A plunger arranged in a well-known manner is attached to a parison 5.
A ram 14 associated with each extrusion die for movement within the extrusion die to adjust the wall thickness.
and a pneumatic ram 16 combined with an insufflation tube 8
and a hydraulic ram 17. The device has a motor 18 connected to a speed reducer 19 for rotating the screw of the extruder 1, electronic programming means and a ram (not shown). This ram is used to move the two half molds 6a away from each other or closer to each other for the purpose of closing the molds, and also has an extrusion die 3 and a blowing pipe 8.
The purpose is to move the mold between the mold and the mold so that the parison is accommodated and the mold is closed.

According to the invention, the device has two solenoid valves, as shown in FIG.
They are connected to each other to an air blowing means for blowing air into them. These valves are automatically controlled by a solenoid valve 23, which itself is controlled by a programmable time relay.
Electrically controlled. Each solenoid valve 21, 22 controls the air passage according to its position. This air passage is for inflating the corresponding parison 5 through the plungers 24, 25 of the connected extrusion die 3 by the path of the axial passages 26, 27 represented diagrammatically in FIG. It is.

What should be noted in the method of the present invention is that each step is shown in FIG.
This is carried out by a control device for the blowing air blown into the parison through the extrusion die by the extrusion die 23, and the operation of this control device will therefore first be described.

At the positions of the solenoid valves 21 to 23 indicated by solid lines, an electric control device Y configured by two time relays (not shown) of the solenoid valve 23 controls the start and stop of communication with the atmosphere. , which is in the rest position, so that the return device X is in a position to block the solenoid valve 23 from the passage of pressure P ₁ indicated by the solid arrow. Pressure P ₂ applied on pushbuttons (not shown) of the solenoid valves 21 and 22 causes the solenoid valves to be placed in a position for direct communication of the inflation air pressure P into the parison through the axial passages 26 and 27 and the plungers 24 and 25. Hold 22.

In the second position of the solenoid valves 21-23, shown in dotted lines, the parison is communicated with the atmosphere in the following manner. That is, the electric control device Y
P ₁ air passes through the solenoid valve 23, and the solenoid valve 21,
22 signals the parison to move to a position where it is retracted. Arrow P indicates that the supply of inflation air to passages 26, 27 is blocked.

When a new parison is to be inflated, the relay automatic programming device described above places the electric control device Y in the rest position and the cycle described above is carried out.

Referring to FIG. 3, the method of the present invention is illustrated in further detail.

The two flat molds 6a are separated, and the synthetic resin material is supplied from the extrusion die 3 into the parison 28 together with blown air. This synthetic resin material is extruded through the extrusion die 3.
It is automatically controlled by a solenoid valve 21 (or 22) connected to the solenoid valve 21 (or 22), and is itself operated by the solenoid valve 22 as described above.

Air is blown into the parison 28 and the parison gradually expands at an air pressure of, for example, 0.6 bar.
The beginning of this process is shown in Figure a.

This pneumatic blowing continues until the length of the parison is substantially the length of the final container 9 and its cross section is equal to the cross section of the cavity when the mold is closed. This step is illustrated in FIG. b, and when the parison assumes the shape indicated by reference numeral 29 during step b, the air blow-in is shut off by the action of the solenoid valve 23.

Therefore, during this process, the synthetic resin material is uniformly supplied to the horizontal section of the parison 29, so that the thickness of the parison is constant within the resulting section.

Thereafter, the air blowing is stopped (step c) and the parison is evacuated to the sagging condition shown at 31 by communicating with the atmosphere or low atmospheric pressure. As mentioned above, the shutoff of air injection is achieved by a signal issued by the electric control device Y of the solenoid valve 23.

The mold 6 closes on the evacuated parison 31 (step d), but the walls of the parison are thus not in contact with the cold walls of the cavity 7. Type 6
(In the embodiment shown in FIG. 1, two containers 9a
) is then moved so as to be placed below the air blowing tube 8. At high pressure, for example 7 bar, air is blown through the tube 8 as indicated by the arrow in FIG.

The air trapped between the parison 31 and the cavity 7 is uniformly supplied and blown between the two mold halves 6a by passages (not shown) provided for this purpose in a known manner. Has a screen from which air is excluded.

During blowing, the material is consequently uniformly and rapidly pressed over the entire surface of the cavity 7, including the point furthest from the axis of the parison 9a. The reason is that the required expansion has already largely been achieved outside the mold 6.

After cutting off the included air, the mold 6 is removed from the cast container 9.
The container 9 is opened to remove it, the burrs and flashes are removed by a known method, and the completed container 9 is taken out.

The mold 6 is in a waiting position below the die 3 and the cycle is restarted for the next parison.

As mentioned above, the wall thickness of the container 9 is precisely uniform within a given lateral area from one end of the container to the other. This effect is made possible by the pre-expansion of the parison outside the mold (steps a and b) and by the deflation of the parison before the mold confines it (step c). This prevents premature contact between the cavity 7 and the parison and thus prevents premature local solidification of the material which would otherwise disturb its uniform tension or tension.

It has been unexpectedly discovered that the method according to the invention makes it possible to slightly reduce the weight of the bottle and, as a result, to reduce the amount of synthetic resin material required.

Furthermore, the strength of the various bottles that can be produced by the method of the invention is clearly improved over that of bottles obtained by conventional methods, especially since the bottles are slightly lighter. This is a useful point.

[Brief explanation of drawings]

FIG. 1 shows a simplified front view of an extrusion blowing unit of synthetic resin material for producing hollow bodies by the method of the invention. 2 is a simplified side view of the unit of FIG. 1; FIG. FIG. 3 represents the successive steps of the method for producing the hollow bodies of the invention by means of the units of FIGS. 1 and 2; FIG. 4 is a diagram of one embodiment of a device for controlling the blowing air into the parison at the exit of the extrusion head when the parison is outside the mold. 1: extruder, 2: hopper, 3: extrusion die,
5: parison, 6: mold, 6a: half mold, 7: cavity, 16, 17: ram, 21, 22: solenoid valve,
24, 25: Plungeya.

Claims (1)

[Claims] 1. For adjusting the wall thickness of the screw for plasticizing the material and the hollow body in a method of manufacturing a hollow body such as a container with a particularly complicated shape by extrusion and blowing of a synthetic resin material. A synthetic resin material is supplied to an extruder having an extrusion die equipped with a movable plunger, a parison giving the general shape of the hollow body is obtained at the outlet of the die, and the parison is extracted from the synthetic resin material extruded at the upstream end. The parison is expanded by blowing air into a mold which forms a cavity of the hollow body to be manufactured inside, and the mold is removed in order to remove the hollow body cast into the cavity of the mold. opening and blowing air into the parison through the extrusion die to expand the parison outside the mold until the length of the parison is approximately equal to the final length of the hollow body to be produced; A method for manufacturing a synthetic resin hollow body, comprising: closing the mold to accommodate the parison, and blowing air into the parison with sufficient pressure to press the parison into the cavity of the mold. 2 Blowing air into the parison outside the mold until the cross section of the parison is equal to the cross section of the cavity of the mold so that the material in each cross section of the homogeneous hollow body is evenly distributed; The parison is contracted by cutting off the air to be blown into the parison so as to make it sag, and communicating the parison with atmospheric pressure or a reduced pressure state, and blowing air into the parison housed in the mold. closing the mold and accommodating the parison so that the walls of the parison do not come into contact with the cold cavity walls of the mold until the
A manufacturing method according to claim 1. 3 Air is outside the mold and inside the parison at a rate of 0.6
3. Process according to claim 2, characterized in that it is blown into the parison at a pressure of ~0.7 bar, and inside the mold it is blown into the parison at a pressure of about 7 bar. 4 at least one extrusion die connected to means for supplying plastic material and for extruding synthetic resin material; means for cutting said parison and joining the bases of said parison; means for blowing air into the parison; a mold having a cavity accommodating said parison and corresponding to the shape of the hollow body to be cast; at least one tube for blowing air into said mold;
means for moving the mold relative to each other between the extrusion die and the blowing tube, and means for ejecting finished hollow bodies and pieces, the ejecting means for blowing air into the extrusion die. a first solenoid valve connected to means, said extrusion die being controlled and connected by a second solenoid valve for communicating said corresponding parison to atmosphere after expansion;
A manufacturing device for synthetic resin hollow bodies that shuts off communication with the atmosphere after a predetermined period of time and allows the next parison to expand. 5. The deflation of the parison is programmable by a time relay which electrically controls a second solenoid valve which pneumatically controls a first solenoid valve. Device.