Abstract:
This invention concerns a drum-like container made of a discontinuously extruded hose-like perform of thermoplastic in a blow molding process. The drum-like container has a wall consisting of an inner layer, an outer layer, and at least one intermediate layer. To make it possible to monitor the fill level of the fill material, the wall has a visual indicator strip of translucent plastic running in the axial direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention pertains to a drum-like container produced by blow-molding from a discontinuously extruded tubular preform of thermoplastic material, with a wall consisting of an inner layer, an outer layer, and at least one middle layer. 
     2. Description of the Related Art 
     A process and a device for the production of a large-capacity hollow body, such as a drum, out of plastic with a multi-layer wall are known from European Patent Publication 0,326,584. The device consists of an annular piston, acting as a co-extrusion head, which can slide axially in a housing; this piston has a flow channel bore extending approximately in the radial direction for each layer of the wall and thus for each plastic melt; each of these bores opens out into a ring-shaped distributor. The ring-shaped distributor then leads to a common flow channel, into which the individual plastic melts flow one after the other. The flow channel located approximately in the center of the annular piston gradually expands to the cross section of a ring-shaped reservoir upon which the annular piston acts. 
     In the case of storage or transport containers such as drums with a multi-layer wall, the outer layer of the wall, and thus also the layer of the preform which is blow-molded to form the drum-like container, is colored in a special way to provide protection against UV rays, for example, or to give a certain visual appearance. At the same time, however, it is also desirable to have the ability to determine at any timed, without any special measuring devices, how much liquid is still in the drum-like container simply by looking at it from the outside. 
     A device for the discontinuous production of a tubular, multi-layer, co-extruded preform of thermoplastic material, out of which a drum-like container is formed by the blow-molding process, is known from DE-GM 91-07,812, in which a connecting channel is provided between the ring-shaped channel for the plastic melt of the inner layer, which consists of clear or transparent plastic, and the ring-shaped channel for the outer layer, which consists of a colored plastic composition. As a result of this connecting channel, a so-called “view strip” can be produced in the outer layer, which makes it possible to see how much liquid is left in the finished container. If the wall of the container has more than two layers, however, it is impossible by means of this device to produce a preform for a drum-like container which has a view strip to allow the determination of the amount of liquid left in the container. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the task of creating a drum-like container which has walls consisting of at least three layers and which makes it possible to determine the degree to which the container is filled at any time. 
     To accomplish this task, it is proposed in accordance with the invention that the wall of a drum-like container of the general type described above has a view strip of translucent plastic extending in the axial direction. 
     By means of the view strip, it is possible for the amount of material present in a container designed in this way to be monitored or checked regularly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is explained in greater detail below on the basis of an exemplary embodiment, which is illustrated in simplified form in a drawing: 
     FIG. 1 shows a perspective view of a container according to the invention; 
     FIG. 2 shows a cross section through a device according to the invention for producing a container such as that shown in FIG. 1; and 
     FIG. 3 shows an enlarged section of the device of FIG. 2 in the area where the view strip is formed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 of the drawing shows a drum-like container  1 , which is produced from a tubular preform of thermoplastic material by blow-molding. The wall of the preform consist of at least three different layers, and a view strip  2  extending in the axial direction is incorporated into this wall. The tubular preform out of which drum-like container  1  is made is produced by means of a device with an annular piston reservoir  3  or ring-shaped retaining head as shown in FIG. 2 of the drawing. Annular piston reservoir  3  consists, first, of a reservoir jacket  4 , which is connected in a manner known in itself (not shown) to a housing, known in itself. In the exemplary embodiment shown, stationary reservoir jacket  4  holds an axially movable annular piston  5 , through which a mandrel  6  with a mushroom-shaped nozzle tip  7  can be moved in the axial direction. Between reservoir jacket  4  and mushroom-shaped nozzle tip  7  there is a nozzle gap  8 , which can be opened and closed by the axial displacement of mandrel  6 . For this movement, mandrel  6  is provided with a drive (not shown), designed as, for example, a piston-cylinder unit. 
     In the part extending outside reservoir jacket  4 , annular piston  5  has three flow channel bores  9 ,  10 ,  11 , to each of which an extruder for a different plastic melt is connected. Through flow channel bore  10 , for example, a clear or transparent plastic melt is supplied, which forms the so-called inner layer of the tubular preform to be produced and thus the inner layer of container  1  ultimately obtained. Flow channel bore  9  is supplied with a plastic melt which consists of recycled plastic. It is advantageous for this recycled plastic to consist of the so-called slug material, which accumulates during the blow-molding of container  1 . The plastic melt supplied through flow channel bore  9  forms the so-called middle layer of the preform and thus of ultimate container  1 . This middle layer is opaque. Via flow channel bore  11 , finally, a third plastic melt arrives in annular piston  5 ; this melt is colored and consists of a material resistant to UV radiation. This plastic layer forms the outside layer of the preform and thus the outside layer of ultimate blow-molded container  1 . 
     Each of flow channel bores  9 ,  10 ,  11  leads first to an encircling, ring-shaped distributor  12 ,  13 ,  4 , to each of which a slanting, ring-shaped channel  12   a ,  13   a ,  14   a  is connected. These ring-shaped channels  12   a ,  13   a ,  14   a  open out in succession into a common ring-shaped channel  15 , which gradually expands to the width of a ring-shaped reservoir  16  in reservoir jacket  4 . Because the individual plastic melts are supplied in succession to common ring-shaped channel  15  and because this channel expands gradually to the cross section of ring-shaped reservoir  16 , it is ensured that the individual layers of the multi-layer plastic melt are not changed in their structure, but rather remain intact. This also applies to container  1 , which is made from the tubular preform produced in annular piston reservoir  3 . 
     In the exemplary embodiment shown in FIG. 2, another flow channel bore  17  is provided on the right side of annular piston  5 ; this bore is connected to an extruder, which supplies a translucent plastic melt to annular piston  5 . If needed, this flow channel bore  17  can also be connected to the extruder which is connected to flow channel bore  9 . It is necessary, however, to install upstream of flow channel bore  17  a device which can accurately control the pressure and flow rate of the translucent plastic melt being supplied. 
     The opening of flow channel bore  17  is a certain distance away from slanting ring-shaped channels  12   a ,  13   a ,  14   a  and is directed radially into the common ring-shaped channel  15 . In the area where this flow channel bore  17  opens into the common channel, a flow-control element (FIG.  3 ), designed as a torpedo  18 , is inserted into ring-shaped channel  15  to divide the outer layer and the middle layer of the multi-layer plastic melt and thus to allow the infeed of the translucent plastic melt. Torpedo  18  extends up as far as the plastic melt forming the inner layer of the preform, which is not colored. The translucent plastic melt supplied through flow channel bore  17  produces a transparent strip in the opaque plastic melts of the outer layer and middle layer; this strip later forms view strip  2  in blow-molded container  1 . It is thus possible to see through this strip to check or monitor visually the degree to which the drum-like container  1  is filled; that is, there is no need for any special measuring device. It is advantageous, however, for the translucent plastic melt not to pass continuously through flow channel bore  17 , but rather only just long enough to extend all the way along the area which later forms the lateral surface of container  1 . It is known, after all, that there is no need for a view strip  2  in either the bottom or the top of container  1 . 
     In the case that the plastic melt forming the inner layer of the wall of container  1  or of the tubular preform is opaque, the translucent plastic melt supplied through flow channel bore  17  must extend all the way to the opposite wall of common ring-shaped channel  15 . This means that torpedo  18  must be long enough to interrupt all three layers of the multi-layer plastic melt and allow the infeed of the translucent plastic melt for view strip  2 .