Closed, fully perforated coating drum

The invention relates to a device and method for coating tablets.

Document WO 2005/1 23267 Al discloses a device for coating tablets comprising a horizontally supported, rotatable drum . The drum has perforated segments. The drum comprises an emptying opening and a lockable opening provided at an end side of the drum . The tablets are put into the drum through the lockable opening . The tablets are coated in the drum . The emptying opening is part of the circumference of the drum. If the emptying opening is located at the bottom, the drum can be easily emptied, due to gravity, through this opening .

A mixing mechanism can be provided within the drum . This is made such that the tablets located in the drum are conveyed towards the end side comprising the door upon rotation in a direction opposite to the direction of rotation during mixing or coating, in order to thus be able to remove tablets through the lateral opening, for example.

In a device known from printed publication WO 2005/1 23267 Al , the coating agent to be applied onto the tablets is introduced into the drum via a first feed, as seen from the end side having the lateral opening. In particular, aqueous suspensions or paints, or suspensions or paints provided with organic solvents, are thus introduced into the interior of the mixing container via the first feed . On the inside, the coating agent exits via at least one downwardly directed nozzle. The nozzle is made such that the suspension is sprayed around on the inside of the drum . Thus, the suspension thus reaches the tablets in a nebulized form . The mixing container is slowly rotated about the horizontal axis in the process. The drum typically rotates at up to 25 rotations per minute.

At the same time, or cyclically, conditioned air (i .e. air of a certain temperature, dried and filtered) is introduced into the interior of the mixing drum via a second feed . In a heated state, the air exits in a downward direction in a uniform manner via a punched sheet. The air stream causes the coating agent deposited on a tablet to dry. For this purpose, the punched sheet in the state of the art is arranged above the nozzle and in such a way as to face in the same direction as the nozzle. By this arrangement, it is achieved that the air stream flows uniformly in a downward direction towards the material to be mixed, i .e., in the direction of the tablets. The nebulized suspension also flows towards the tablets in the process. A suspension thus reaches the tablets particularly reliably because of the air stream .

The air stream then exits again through the perforation of the drum segments via a suction device. In one embodiment, the perforation is distributed over the circumference of the drum . For example, four segments of equal size distributed over the circumference may be provided with the perforation .

In an advantageous embodiment known from the printed publication WO 2005/1 23267 Al , coating material for the tablets is fed via an end side of the drum, and air is fed via the opposite side.

If not expressly stated in the following, the features known from the prior art may, individually or in combination, be features of the invention described hereinafter.

Dust is inevitably generated during the coating process in the drum, which can exit unimpeded through the perforation, soiling the surrounding housing. The dust load leads to a correspondingly large cleaning effort with respect to the coating device.

It is the object of the present invention to avoid the dust loads in devices for coating tablets.

In order to achieve the object, a drum for coating tablets is provided, the circumference of which is provided with an inner and an outer wall. The inner wall has perforations. The drum comprises means for suctioning air exiting from the perforation . Dust is suctioned off together with the air. The dust can now be separated from the suctioned-off air and can be disposed of . A dust load and a very laborious cleaning process of the housing of the device for coating tablets and parts located therein can thus be avoided.

The means for suctioning off air exiting the perforation preferably comprise at least one suction opening disposed adjacent the circumference at an end side of the drum . The opening can be combined with a ventilator or a comparable means in order to suction off air from the area between the inner and the outer wall .

The invention is explained below in more detail with reference to figures.

Figure 1 shows a drum 1 for coating tablets. The circumference of the drum is formed by an inner wall 2 and an outer wall 3. Two segments of the outer wall are not shown in Fig. 1 in order to be able to view the segments of the inner wall beneath them . The inner wall 2 is provided with a perforation 4. Between the inner wall and the outer wall, there are partition walls 5 in regular intervals which divide the interspace between the inner and the outer wall into individual chambers 1 0 (see Fig. 2) . Because of the partition walls, air cannot move from one chamber directly to an adjacent chamber. If air enters one of the chambers through the perforation 4, the chamber is preferably screened off by the walls in such a way that the air can only be passed on through a lateral suction opening 6. In a particularly reliable manner, this configuration makes suctioning off the air from the individual chambers via the openings in a controlled manner. The uncontrolled and undesired flow of air from the drum towards the outside can thus be

avoided . Because if, for example, air exits in a downward direction towards the tablets in the drum, the air is preferably only exhausted from the drum via perforated segments beneath it in order to thus coat in a suitable and effective manner. During the rotation of the drum, air is only suctioned off from a chamber if it is located at the bottom . This ensures that the air flows in the intended manner.

In the embodiment shown in Fig. 1 , the drum comprises one suction opening 6 as well as a conduit 7 per chamber, via which the air is suctioned from the respective chamber.

A discharge helix 8 can be provided in the interior of the drum . After the coating process, the direction of rotation of the drum is changed in such a way that the coated tablets are transported towards the opening provided in an end wall by the helices. The tablets can now be easily removed through the opening . This embodiment avoids a greater technical effort which would otherwise be necessary for a removal opening through the inner and outer wall.

Fig. 2 shows a device for coating tablets having a drum 1 shown in Fig. 1 . Air and the coating means are directed in a downward direction towards the tablets to be coated, namely in particular in the way known from the printed publication WO 2005/1 23267 Al . If a conduit 7 of the drum is located at the bottom, its outer opening is adjacent to a suction opening 9 which is adjacent to the drum, via which opening the air is suctioned from the corresponding chamber 1 0. In that case, such a suction opening 9 adjacent to the drum is provided only in the bottom area in order to thus achieve the air only being suctioned from a chamber 1 0 if the chamber is located at the bottom . Thus, air, together with the dust, can be suctioned from the drum in a controlled manner in such a way that coating can be done effectively.

Preferably, a suspension used for the coating process is fed laterally via a first side of the drum, and the air is fed laterally at the opposite side. It is thus accomplished that there is more room at the side from which the operation is carried out by the user as compared to the case where suspension and air is fed through an end wall .

The feed as well the nozzle via which the suspension is fed must be cleaned from time to time. It is therefore advantageous to provide this feed from the front side, i .e. from the side of the operator. This reduces the cleaning effort. No or a significantly smaller cleaning effort is required for the air feed . Therefore, the air feed is preferably carried out from the rear, which is comparatively hard to access.

In an advantageous embodiment of the device, the suspension is being fed to the drum beneath or at the level of its axis of rotation. The air is fed to the drum entirely or predominantly above the axis of rotation. Thus, the air, coming from above, can be directed towards the material to be mixed, and it can transport the nebulized suspension towards the material to be mixed or the tablets in the process.

Because the material to be mixed, that is, the tablets, roll around in the interior of the drum, they are, on average, not located at the lowermost point during the coating process, but slightly displaced laterally from this lowermost point, depending on the speed of rotation of the drum . Advantageously, this is taken into account when arranging the feeds of air and suspension by the means for feeding air and suspension being oriented such that the suspension as well as the air are being directed towards this laterally displaced point. If a punched plate for feeding air and a nozzle for feeding a coating agent are used, the punched plate as well as the nozzle are preferably oriented not exactly vertically, but correspondingly obliquely. The punched plate is then oriented in an approximately parallel direction to the surface which the tablets form during coating . In that case, air and suspension exit in the same direction from the respective feeding means. The direction of discharge of air and suspension then enclose an angle with

the vertical that is larger than 0° and smaller than 90°. As a rule, this angle is between 1 0° and 60°, in particular between 25° to 50°, at the common speeds of rotation of up to 25 revolutions per minute. Therefore, one or more suction openings 9, which are adjacent to a conduit 7 of the drum from the outside, are provided correspondingly offset from the lowermost point. In that case, there are preferably no further suction openings 9 beyond that.

Air can be fed, for example, via an annular recess at the front side of the drum . Preferably, however, the drum at its rear comprises a circular plate which is rotatably connected to the rest of the drum . Advantageously, the rotatable connection is formed to be sealing . During the mixing process, the drum rotates, and not the circular plate. The air is passed, via an appropriate passage, through this circular plate. The technical area of the device, for example, electronic controllers, motors etc, is then arranged behind the rear of the drum . This technical area is thus separated from the production area, which is an advantage with respect to a trouble-free operation .