Method and a drum coater for coating small items, such as tablets, and a coating system comprising such drum coaters

1. A method for coating tablets, comprising the steps of:

providing a substantially cylindrical drum ( 11 ) having a peripheral drum wall ( 12 ) and a predefined diameter, said drum having a substantially horizontal axis of rotation ( 17 ), a top section ( 20 ) and a bottom section ( 21 ) being defined above and below, respectively, the axis of rotation, and a coating zone which is provided in the top section ( 20 ),

feeding the tablets into said drum ( 11 ),

spinning the drum containing the tablets at a rotational speed such that the tablets are pressed towards, held against, and carried with the peripheral drum wall ( 12 ) utilizing primarily the centrifugal force of the rotating drum, hereby producing a substantially annular bed of tablets extending around the axis of rotation,

providing means for creating a cascade ( 19 ) of tablets at least in a part of said coating zone,

spraying the tablets in said coating zone, and

discharging the tablets from said drum ( 11 ).

2. The method according to claim 1 , whereby the means for creating a cascade ( 19 ) of tablets is provided by loosening means.

3. The method according to claim 2 , whereby said loosening means is provided by at least one deflecting nozzle ( 13 ) directed towards the tablets in said top section ( 20 ), thereby forcing the tablets away from the peripheral drum wall ( 12 ).

4. The method according to claim 3 , whereby said at least one deflecting nozzle ( 13 ) is directed substantially in the radial direction of the drum.

5. The method according to claim 2 , whereby the loosening means is provided by mechanical deflection elements.

6. The method according to claim 1 , comprising the further step of spraying the tablets in said coating zone

at a maximum speed chosen such that the tablets are retained in said cascade ( 19 ).

7. The method according to claim 1 , comprising the further step of spraying the tablets with a suspension or a solution by means of a set of spraying nozzles ( 26 ).

8. The method according to claim 1 , comprising the further steps of providing the drum with perforations, and providing a flow of drying air or gas ( 14 , 15 ) into the bottom section ( 21 ) and out of the top section ( 20 ), by a specific flow rate of said drying flow of air or gas which is relatively high and has a maximum corresponding to the combined force of gravity and centrifugal force acting on the tablets at the bottom section.

9. The method according to claim 1 , comprising the further steps of:

providing the drum ( 11 ) with a cut in the peripheral drum wall creating facing first and second end edge sections ( 24 , 25 ),

deflecting at least one of said first and second end edge sections to create a space ( 23 ) therebetween.

10. The method according to claim 9 , comprising the further step of loading and unloading the tablets through said space ( 23 ).

11. The method according to 1 , whereby a drum having a diameter of below 1 m rotates at a speed of at least 4 rad/s, and a drum having a diameter above 1 m rotates at a speed of at least 3 rad/s.

12. The method according to 1 , whereby a drum having a diameter between 0.75 m and 1.25 m rotates at a speed between 5.11 rad/s and a 3.96 rads/s.

13. The method according to 1 , whereby the rotational speed of the drum is set such that:

the substantially annular bed of tablets completely encircles the axis of rotation, and

a radius of curvature of the substantially annular bed in said coating zone is different from a radius of curvature of the substantially annular bed in portions other than the coating zone.