IL43838A - Apparatus for and method of coating a plurality of articles - Google Patents

Abstract

1450435 Coating apparatus PURDUE RESEARCH FOUNDATION 18 Dec 1973 [18 Dec 1972] 58443/73 Heading B2L A device 10 for carrying articles such as tablets 37 through a coating bath 43 and a drier 66 comprises an evacuated rotary cylinder 11 or other conveyor with a plurality of support sites 67 to which vacuum is applied and having means 48 for selectively releasing the vacuum at a predetermined release point. As shown the support sites 67 are at the ends of rows of radial tubes 17 which are rotated about their longitudinal axes by intermeshing gears 44 and a fixed circular face gear 46. Alternative parts 67 may be provided for different tablets. An axially slidable notched bar 48 is provided within the periphery of the cylinder 11 to release the vacuum quickly in each row of tubes 17 when it reaches the bar. A sensor 58 then actuates a motor 56 to slide the bar so that the notches 53, which are preferably connected to an air supply by a tube within the bar, align with the tubes. The tablets may then be removed or remain for further coatings. The dryer 66 may rely on air circulation or contain lamps, wires, radiation, infra-red or microwave heating means. [GB1450435A]

Description

PURDUE RESEARCH POUHDATIQN C:- 41828 Case 118-3328 Coating Apparatus This invention relates to a coating apparatus and, particularly, to an apparatus for coating pharmaceutical solid dosage forms.

Solid, pharmaceutical dosage forms are normally coated in revolving coating pans or by air suspension techniques, for example fluidised bed techniques. However, these operations subject the dosage forms to attrition, which in the case of tablets may result in broken tablets, and which, in any event; are not fully satisfactory for non-spherical tablets, in that they may result in thinner or non-uniform coatings, especially at any edges, which are the points of greatest attrition and film stress.

Tablet attrition may be overcome by increasing the hardness of the tablet, but this, on the other hand, may result in a decrease in drug availability. Non-uniform coatings are detrimental to tablet stability since they do not provide a uniform barrier to the penetration of oxygen and/or water vapour.

To provide adequate protection at the corner boundary of a tablet requires overcoating of the tablet and this may adversely affect drug availability, particularly with coated tablets which release the drug by diffusion through the coating, or by tunnel dissolution - 2 Case 118-3328 of the coating in the body.

Pharmaceutical capsules, in order to be coated by the conventional methods , must first be bonded at the junction of the capsule closure, to prevent their coming apart during coating. This is an expensive and time consuming procedure and, for this reason, capsules have generally not been externally coated but rather the medicament particles within the capsule have been coated.

Because of the disadvantages of the known coating methods, coated dosage forms, particularly tablets, have generally provided variable drug protection and availability. Furthermore, certain coating materials which are of interest, including polymeric materials, eg vinyl polymers, eg polyvinylpyrrolidone or poly (nethyl-vinyl ether/maleic anhydride) and derivatives thereof, have a low glass transition or are inherently tacky, thus making application of these materials by conventional techniques, in which dosage forms contact each other difficult or even impossible.

The present invention, broadly, provides a coating apparatus in which articles, particularly dosage forms, are individually supported, transferred to and immersed in a coating bath of the desired coating material and then released, desirably after passing through a drying zone. The articles may then be reversed and the uncoated portion immersed to secure a completely coated article. In this way, contact between the individual articles during coating, and thus the attrition problem discussed above, is avoided. Furthermore, with the rotary coating apparatuses of the invention, the articles to be coated enter and leave the coating bath at an angle to the horizontal level thereof. This aids in achieving uniform coating, and thus with pharmaceutical dosage forms, improved drug availability.

U.S. Patent 3,192,891 describes an apparatus, somewhat similar to the present apparatus, for transferring ice-cream cones to a plurality of coating stations, the cones being supported and held during transport and coating under vacuum suction. In the apparatus described, however, individual means of releasing the vacuum at each cone support site arriving at a certain point in the operation are provided. In contrast thereto, the apparatus of the present invention incorporates a blocking bar thus enabling the vacuum to be released at a plurality of support sites in a very much simpler and less expensive manner. The apparatus of the U.S. patent would in fact not be adapted to receive, and therefore would in no way suggest, the blocking bar of the present invention, since it also incorporates plungers for ejecting the cones, such ejection means not being required in the present apparatus.

More particularly the present invention provides a coating apparatus comprising an evacuable conveyor for transferring individual articles to be coated to and from a coating bath, said conveyor having a plurality of of the conveyor for separately supporting the individual articles , and said conveyor comprising a rotatably mounted vacuum chamber, connectable to a vacuum source, the article to be coated being transferrable to and from a coating bath by rotation of the vacuum chamber, and selective vacuum release means comprising a blocking bar located inside and at a predetermined zone of the rotation of the vacuum chamber, said blocking bar being fixed relative to the rotation of and in slidable contact with the internal wall of the vacuum chamber, and said blocking bar being adapted to block the communication of the vacuum chamber with support sites arriving at the predetermined point in the rotation of the vacuum chamber.

The vacuum chamber is suitably in the form of a hollow cylinder rotatable about its longitudinal axis. 43838/2 - 4 - The support sites desirably comprise a plurality of open-ended tubes opening into and extending radially from the vacuum chamber, in particular the hollow cylinder. Upon evacuation of the vacuum chamber, the articles to, be coated are supported by suction at the ends of the tubes remote from the vacuum chamber.

Preferably, the apparatus also comprises means for rotating the tubes about their longitudinal axes during rotation of the vacuum chamber.

The tubes are preferably provided with removable tips so that tips of appropriate shape may be employed for coating articles of different shape. The support sites, in particular, the radially extending tubes, are preferably arranged around the vacuum chamber, in a plurality of rows parallel with the axis of rotation of the vacuum chamber. In this case, the tubes in a particular row may be rotably connected with each other via a series of interconnected gears, one such gear being mounted on each tube. The gears may suitably be driven to cause rotation of the tubes about their longitudinal axes during rotation - 5 - of the vacuum chamber, by engagement with a stationary face gear mounted on the frame of the apparatus.

The vacuum chamber/ in particular the hollow cylinder, supporting the radially The selective vacuum release means in accordance with the invention may be any device adapted to release the vacuum applied to support sites supporting articles which have already passed through the coating bath, while maintaining the vacuum and, therefore, suction at all other support sites. Once the vacuum is released; the coated articles may easily be removed or may even drop off the support sites. - 6 - The blocking bar is preferably adapted to ^ communicate the support sites arriving at the appropriate point with an air source at the same time as blocking the communication thereof with the vacuum chamber.

Where the vacuum chamber has a plurality of parallel rows of radially extending tubes, as described in the preferred embodiments above/ and comprises a hollow cylinder, the blocking bar is preferably provided with an internal air tube, which communicates at one end with an air source, and communicates with a plurality of points on the surface of the blocking bar which is in slidable contact with the internal wall of the vacuum chamber, said points being arranged to coincide with the tubes as they come into alignment with the blocking bar. In this way, the blocking .bar not only cuts off the vacuum applied to tubes coming into alignment with the blocking bar, but also connects such tubes with an air source, thus allowing easier removal of the coated articles. The blocking bar is also preferably provided with a series of notches on its surface in contact with the - 7 - Case 118-3328 internal circumferential wall of the vacuum chamber.

These notches correspond in number and size to the number of tubes in any row. The vacuum bar is then adapted to be laterally reciprocable, under the action, for example, of an air cylinder itself actuable by means of a suitable sensing device, to bring the notches into and out of alignment v/ith the rov; of tubes and thus open or block the communication between the vacuum chamber and such tubes.

Thus, when a row of tubes carrying coated articles arrives at the zone of the blocking bar the appropriately synchronised sensing device can actuate the lateral movement of the blocking bar to bring the notches out of alignment with the openings of the tubes and thus cut off the vacuum applied to those tubes and, at the same time connecting the tubes to an air source, when the blocking bar is also provided with an internal air tube as described above. The coated articles may then easily be removed and the blocking bar may then be returned to its first position. A blocking bar having a plurality of notches as described has the advantage that it may be actuated to cut off the vacuum as soon as a row of tubes arrives at the appropriate point, while a solid bar would do this only gradually as the vacuum chamber rotates. - 8 - Case 118-3328 The sensing device may suitably comprise a switch having a stationary contact and an appropriate number of contacts, for example in the form of grooves notches or tabs, rotating with the vacuum chamber, and desirably on the outer coaxial chamber.

The apparatus of the invention is preferably provided with a drying chamber through which the articles may pass after immersion in the coating bath and before release of the vacuum applied to the corresponding support sites. The drying chamber may be of the air circulation type or may contain heating elements such as lamps, wires or radiation heating means, eg infra-red or microwave means, _Jor evaporating the solvent from the coating.

The invention will now more particularly be described with reference to the accompanying drawings of which Fig 1 is an axial section through a rotary coating device of this invention, and Fig 2 is a diagrammatic end elevation of the device of Fig. 1, Referring to Figs. 1 and 2, the rotary coating apparatus 10 comprises in combination a cylindrical vacuum chamber 11, a coaxial outer chamber 12 and a circular adapter 13 to maintain the vacuum chamber 11 and outer chamber 12 - 9- - Case 118-3328 in a spaced apart fixed rigid relationship. The vacuum chamber 11 is sealed to the atmosphere at its ends by end walls 14 and 16. Communicating with the vacuum chamber, 11 are tubes 17. These tubes 17 project through and extend beyond the outer chamber 12. The vacuum chamber 11 is rotatable about its longitudinal axis by means of shaft 18, which is secured to end wall 14. Shaft 18 is rotatably mounted in bearing 19, which is mounted on frame 21.

The circular adapter 13 is provided with a flange 22 which is rotatably mounted in a circular bearing housing 23. Within the bearing housing is a circular bearing unit 24, having in combination, an upper race 26, bearings (e.g. ball bearings) 27 and a lower race 28. As the shaft 18 is rotated, flange 22 is supported by the lower race 28 and rotates upon the bearings 27. The upper race 26 is stationary against the bearing housing. The bearing housing 23 is provided with an air tight seal 29, and is supported by frame 21a.

Communicating with the interior of vacuum chamber 11 is a hollow shaft 31, having an orifice 32 which orifice is beyond wall 16 and opens to the interior of vacuum chamber 11. The end of shaft 31 opposite - 10 - Case 118-3328 orifice 32 terminates in conduit 33, which conduit is communicatively connected to a vacuum system (not shown) . Shaft 31 is preferably non-rotatable during the rotation of the vacuum chamber 11.

The tubes 17 are rotatable about their longitudinal axis and are each held in place by bearing seal 34 on the vacuum chamber, bearing seal 35 on the inner surface of the outer chamber, and a spring retaining ring 36 on the outer surface of the outer drum. Seal 34 is an air tight seal. The retaining rings 36 maintain all the tubes in the same relative position on the coating apparatus. The tubes 17 open into the vacuum chamber 11 and extend beyond outer chamber 12.

Although only two rows of five tubes 17 are illustrated it is understood that more or less than five tubes may be used per row depending on length of vacuum chamber 11, and the number of rows is basically limited only by the circumference of the vacuum chamber 11.

In the operation of the coating apparatus of this invention, vacuum chamber 11 is placed under vacuum the vacuum system (not shown) via extension 33, shaft 31, and orifice 32. The articles 37 to be coated (tablets are illustrated) are secured to the external tips of tubes 17 by means of the suction created by the vacuum - 11 - Case 118-3328 in the vacuum chamber 11. The ccating apparatus 10 is rotated by means of motor 38, drive belt 39 and shaft pulley 41. As the apparatus rotates, the tablets 37 are brought into contact with the coating solution (the surface of which is shown by broken lines 42) in reservoir 43. As the coating apparatus rotates, the tablets 37 enter and leave the coating solution 42 at an angle to the horizontal solution surface. The rotation of the coating apparatus also actuates drive gears 44 which rotate the tubes 17 about their lonaidudinal axfis. Th<=> tubes 17 are axially disposed through the center of each gear 44, and may be affixed to the gear by means of a pin or screw.

The gears 44 are driven by engagement with a stationary circular face gear 46, which is affixed to frame 21. Each gear 44 engages its neighbouring gear and thus all the gears in a given tube 17 row are interconnected . When the gear 44 adjacent the circular face gear 46 is rotated by the face gear, all of the gears 44 are thus simultaneously rotated. The rotation of tubes 17 causes the tablets 37 to also rotate, which motion enables the tablets to be evenly coated and to avoid the coating solution being drawn to the lowest part of the tablet as it leaves the coating solution. - 12 - Case 118-3328 As the apparatus 10 rotates, each of the rows of tubes 17 becomes successively aligned with a stationary blocking bar 48. The bar 48 is within the vacuum chamber 11 and slidably engages the inner circumferential wall of the chamber 11 as it rotates.

The bar 48 is affixed at one end by means of brace 49 to the portion of the hollov; shaft 31 which protrudes into the inner tube. At the other end, the bar 48 is supported by a brace 51. Both braces 49 and 51 are interconnected b a cross brace 52, across the inner tube opposite from the bar 48. The bar 48 has on its wall engaging surface a plurality of notches 53. The horizontal dimensions of each notch corresponds to the diameter of the tubes 17. As a row of tubes 17 passes over the blocking bar 48, vacuum may still be maintained in the tubes via the notches 53, which notches match the number and location of the tubes 17. When the row of tubes 17 is aligned with the notches 53 of the blocking bar 48, the bar is rapidly actuated to move the notches 53 away from the corresponding tubes 17 and to position the upper vacuum chamber engaging bar surface 54 over the tubes 17. Thus, the tubes 17 are then rapidly cut off from the vacuum in the vacuum chamber 11 as shown in Fig. 1, the blocking bar 48 is in the cut-off position) . - 13 - Case 118-3328 With the vacuum to the tablets shut off, they are thus able to be removed from the coating device.

The bar 48 is actuated by an air cylinder 56, which is affixed to the external end of shaft 31. When the notches 53 on the bar 48 are aligned with the vacuum tubes, the air cylinder moves the shaft 31 and the interconnected bar 48 to position the upper bar surface 54, over the tubes and thus shut-off the vacuum to the vacuum tubes.

The air cylinder 56 is actuated by a switch 57 via a conventional connection (net shown) . The switch is in communication with an appropriate number of sensors 58 eg tabs on the outer drum 12, which sensors 58 are synchronised with the blocking bar 48 such that when a row of tubes 17 become aligned with the appropriate sensor 58 actuates the switch 57 which in turn actuates the air cylinder 56.

The bar 48 is normally secured at a fixed position on the inner circumference of the inner tube 11 during the rotation of the coating apparatus, by means of a rotational lock assembly 59. A lock collar 61, of the assembly, engages a stationary flange 62 of the end wall 16 and is communicatively secured to the flange by an anti-rotational key 63. When the blocking bar - 14 - Case 118-3328 48 is to be repositioned within the inner tube, the key 63 is removed and the collar 61 disengaged from the flange 62. Shaft 31 (to which the blocking bar 48 is fixed) is then turned on bearing 64 to move the bar 48 to its new position. To lock the blocking bar 43 in position, the above procedure is reversed. The bearing 64 (eg. bronze) also supports the reciprocal movement of shaft 31 when i is moved by the air cylinder 56 to actuate the bar 48.

Bearing 64 is also a vacuum seal for the vacuum chamber.

In a preferred embodiment of the invention, the blocking bar 48 is provided with an internal air tube (not shown) which communicates at one end with an air source, eg. the surroundings, and also communicates with points on the surface 54 thereof in between the notches 53, which points come into alignment with the tubes 17 when the blocking bar is actuated to bring the notches 53 out of alignment with the tubes 17. In this way, the tubes are not only cut off from the vacuum but are also connected to an air source, thus facilitating removal of the coated articles.

Apparatus 10 has affixed to it a drying chamber 66 (see j?ig. 2) , wherein the tablets which have been coat d are dried prior to removal from the coating apparatus.

The drying chamber 66 is of the air circulation type. - 15 - Case 118-3328 Articles to be coated, particularly pharmaceutical tablets or capsules come in a wide variety of shapes and sizes. To accomodate articles of various sizes, the tubes 17 have removable tips 67. These tips are shaped appropriately to accomodate the size and shape of the article to be coated. 43838/3 - 16 -

Claims (24)

1. A coating apparatus comprising an evacuable conveyor for transferring individual articles to be coated to and from a coating bath, said conveyor having a plurality of support sites to which vacuum suction can be applied by evacuation of the conveyor for spearately supporting the indi idual articles , and said conveyor comprising a rotatably mounted vacuum chamber, connectable to a vaccuum source, the article to be coated being transferrable to and from a coating bath by rotation of the vacuum chamber, and selective vacuum release means comprising a blocking bar located inside and at a predetermined zone of the rotation of the vacuum chamber, said blocking -bar being fixed relative to the rotation of and in slidable contact with the internal wall of the vacuum chamber, and said blocking bar being adapted to block the communication of the vacuum chamber with support sites arriving at the predetermined point in the rotation of the vacuum chamber.

2. A coating apparatus according to claim l in which a plurality of open-ended tubes open into and extend radially from the vacuum chamber, the tips of the tubes remote from the vacuum chamber being the support sites for the articles to be coated.

3. A coating apparatus according to claim 2 43838/3 - 17 - in which the tips of tubes remote from the vacuum chamber are removable .

4. A coating apparatus according to claim 2 or 3r in which the tubes are arranged in a plurality of rows around the vacuum chamber and parallel to the axis of rotation thereof.

5. · Λ coating apparatus according to claim 2 or 4, which comprises means for rotation of the radially extending tubes about their longitudinal axes, during rotation of the vacuum chamber.

6. A coating apparatus according to claim 5 in which the means for rotation comprises a series of inter-connected gears, each gear being mounted on a radially extending tube, and at least one of which is engaged by a stationary face gear.

7. , A coating apparatus according to claim 1 in which the blocking bar is adapted to communicate the support sites arriving at the predetermined point in the rotation of the vacuum chamber, with an air source, at the same time as blocking the communication thereof with the vacuum chamber.

8. A rotary coating apparatus comprising a cylindrical vacuum chamber rotatably mounted for rotation about its longitudinal axis and connectable to a vacuum source, a plurality of rows of open ended tubes opening into and extending radially from the vacuum chamber, the rows being arranged around the circumference of the vacuum chamber and parallel to the longitudinal axis there 43838/3 - 18 - being adapted to support, by suction, individual articles to be coated, and a blocking bar located at a predetermined zone of the vacuum chamber, fixed relative to the rotation thereof and in slidable contact with the internal circumferential wall thereof, being adapted to block the communication between the vacuum chamber and a row of radially extending tubes coming into alignment with the blocking bar .

9. · Λ rotary coating apparatus according to claim 8 , in which the blocking bar is adapted to communicate the row of radially extending tubes coming into alignment therewith, with an air source at the same time as blocking the communication thereof with the vacuum chamber.

10. A rotary coating apparatus according to claim 9, in which the blocking bar is provided with an internal air tube which communicates at one end with an air source and which communicates with a plurality of points on that surface of the blocking bar which is in slidable contact with the internal circumferential wall of the vacuum chamber, said points being arranged to coincide with the ends of the row of tubes when the blocking bar blocks the communication thereof with the vacuum chamber.

11. A rotary coating apparatus according to 43838/3 - 19 - claims 8, 9 or 10, in which the blocking bar is provided, on its surface in contact with the internal circumferential wall of the vacuum chamber, with a series of notches corresponding to the number and size of tubes in a row, the blocking bar being reciprocatable to bring the notches into and out of alignment with the openings of a row of tubes to open and block communication between the vacuum chamber and the rows of tubes.

12. A rotary coating apparatus according to any one of claims 8 or 11, comprising an outer cylindrical chamber coaxial with and connected to the vacuum chamber and through which the radial extending tubes project.

13. . 13. A rotary coating apparatus according to any one of claims 8 to 12 ? which comprises means for rotation of the radially extending tubes about their longitudinal axes during rotation of the vacuum chamber.

14. A rotary coating apparatus according to claim 13, in which the means for rotation comprises a series of interconnected gears associated with each row of tubes, each gear being mounted on a tube, an end gear in each row being engaged by a stationary face gear.

15. A rotar coating apparatus according to any one of claims 8 to 14 , in which the tip of each tube remote from the vacuum chamber is removable. 43838/3 - 20 -

16. A coating apparatus according to any one of the preceding claims, comprising a chamber for drying the articles after coating and prior to their removal from the support sites.

17. A coating apparatus according to claim 1, substantially as herein described with reference to the accompanying drawings. ■

18. A continous method of coating a plurality of articles, comprising separately supporting individual articles to be coated at a plurality of support sites by vacuum suction, immersing the articles n a coating bath one or more times, and selectively releasing the vacuum applied at support sites supporting articles which have been immersed in the coating bath. as aforesaid, while maintaining the vacuum suction applied at the remaining support sites.

19. A method according to claim 1, in which the articles are immersed in the coating bath such that they enter and leave the coating bath at an angle to the horizontal level thereof.

20. A method according to claim 18 or 19, in which the articles are dried after each immersion in the r-coating bath.

21. A method according to claim 18, 19 or 20, in which the articles to be coated are pharmaceutical 43838/3 - 21 - solid dosage forms.

22. A method according to claim 21, in which the solid dosage forms are tablets or capsules.

23. A method according to claim 18, substantially as herein described. i

24. Articles, whenever coated by a method according to any one of claims 18 to 23. HE/ss