GB2520040A

GB2520040A - Tablet Tooling surface treatment

Info

Publication number: GB2520040A
Application number: GB1319662.1A
Authority: GB
Inventors: Robert John Blanchard
Original assignee: I Holland Ltd
Current assignee: I Holland Ltd
Priority date: 2013-11-07
Filing date: 2013-11-07
Publication date: 2015-05-13
Anticipated expiration: 2033-11-07
Also published as: GB201319662D0; GB2520040B

Abstract

A method of surface treating the tip of a tablet pressing tool. A mirror finish is applied to provide an Ra of between 0.025 and 0.1 Î¼m. The surface of the pressing tip is then textured by shot blasting to provide an Ra of between 0.35 and 0.55 Î¼m. The textured surface is then coated, and the coated textured surface is then further treated to provide an Ra of between 0.2 and 0.5 Î¼m. The shot blasting may use particles of 0.074 and 0.105 mm at an angle of between 45 and 90 degrees. The coating may be chromium nitride preferably using a physical vapour deposition process, although chemical vapour deposition and electroplating may alternatively be used. The further treatment may be post-polishing using a drag finishing process through particulate media, preferably walnut having a particle size of 0.2 to 0.4 mm and impregnated with a polishing paste. The surface treatments may be applied to the punch tip.

Description

Tablet ToolinQ Surface Treatment This invention concerns a method of treating the surface of tablet tooling, and tooling with a surface treated by this method.

The nature of the surface of tooling used in tablet presses to form tablets from material usually in powder form, and particularly the tips of such tooling, is very significant. It is important that such tooling produces an appropriate finish on the tablets, and does not cause material to stick to the

tablet tooling.

Sticking of powder on tablet tooling has many different causes, and one of the main causes of sticking is moisture content in the formulation and in the production facility.

Liquids react differently with different surfaces and therefore tablet punch tip surfaces can have either a high or a low Contact Angle (CA). The Contact Angle is the angle measured at the intersection between the liquid and the solid surface. The Contact Angle determines whether the surface will be hydrophilic, i.e. attracts water with a CA of less than 900, or hydrophobic i.e. retracts water with a CA greater than 90°. Providing a textured surface on the punch tip has proven to reduce the contact angle creating a more Hydrophilic surface, it is believed that this can help to reduce the chance of formulation sticking to the tablet tooling surface.

The texturing process applies a rough surface to punch tips. This texturing process may create a more consistent uniform tip surface. This tip surface has less severe defects present (such as polishing scratches), which will reduce the ability of the formulation mechanically interlocking to the tip.

The measurement Ra will be used in this specification, which measurement is of surface roughness. The measurement Ra is the average value the profile of a surface departs from a mean line, usually the central point, within a sampling length. The average value is taken for departures below and above the mean line. Ra can be measured for instance by using a profilometry device with a fine stylus which is pulled across the surface with movements of the stylus in a vertical direction being measured.

According to a first aspect of the present invention there is provided a method of treating the surface of tablet tooling, the method comprising polishing the surface to provide a mirror finish with an Ra of between 0.025 and 0.1 pm; a texture is applied to the tablet finish to provide an Ra of between 0.35 and 0.55 pm; a coating is applied to the textured surface; and the coated textured surface is further treated to provide an Ra of between 0.2 and 0.5 pm.

The texture may be applied to the tablet finish to provide an Ra of between 0.35 and 0.45 pm.

The coated textured surface may be further treated to provide an Ra of between 0.2 and 0.35 pm.

The texture may be applied to the surface by shot blasting, the shot blasting may be carried out using media of a particle size of between 0.074mm and 0.105mm. The angle of impingement of the shot blasting media may be between 45° and 90°.A masking fixture may be used so that only the tip of the tablet punch has a texture applied to it.

The coating applied to the surface may be a combination of any of the following elements: Cr, N, Al. Ti, C, Si, B, 0, W, Zr, Ni. The coating may be a combination of Cr and N creating a chromium nitride coating.

The coating may be applied using physical vapour deposition, chemical vapour deposition, or electroplating.

The further treating of the surface may retain the coating intact, and may be a further surface finish modification.

The further surface finish modification may be carried out by dragging the tablet through a particulate media including a polishing paste. The particulate media may act as a carrier for the polishing paste. The particulate media may have a particle size of between 0.2 and 0.4mm. The particulate media may be pre impregnated with polishing paste.

According to a second aspect of the invention there is provided tablet tooling with a surface treated by a method according to any of the preceding five paragraphs.

Embodiments of the present invention will now be described by way of

example only.

The tip of a tablet pressing tool is treated in the following manner. The tool may be made of stainless steel, and could for instance be HPGP® such as Bolher K340®, HPGSS® such as Bolher M340®, or an equivalent martensitic stainless steel which can be heat treated.

A mirror finish is applied to the tip of the tool in a conventional manner to provide an Ra of between 0.025 and 0.1 pm.

The surface of the tablet tip is then textured by shot blasting. A grit with a particle size of 0.074 to 0.105mm is fired at the tip at an impingement angle of between 45° and 90°. An annular mask is provided around the tip such that this is the only part of the tablet surface which is textured. The texture is applied so as to provide an Ra of between 0.35 and 0.55pm.

The textured surface is then coated with chromium nitride using a physical vapour deposition process. The coated textured surface is then post polished using a drag finishing process to alter the surface topography. The tablet tools are mounted in holders, lowered into a drum filled with a polishing media and then rotated about two axes, typically at a speed of around 70rpm for instance for a forty minute period. The finished textured tip has an Ra of between 0.2 and O.5pm.

The polishing media includes a particulate material and a polishing paste. In this instance the particulate material is walnut of a particle size between 0.2 and 0.4mm. The walnut may be preimpregnated with an appropriate polishing paste, and will require subsequent application of polishing paste after a number of polishing cycles, for instance every 10 hours. The post polishing process decreases the surface roughness by reducing the average peak to valley height, thereby creating a more uniform and unique surface finish.

This has been found to provide tablet tooling with a tip which has a finish which provides significantly reduced amounts of sticking of tablet material relative to prior tablet tooling, to positively affect punch performance during tablet production.

It is to be realised that a range of modifications may be made without departing from the scope of the invention. For instance different parameters may be used in the shot blasting, or other texturing processes could be used.

Different coatings may be applied, and the coating may comprise a combination of any of the elements Cr, N, Al. Ti, C, Si, B, 0, W, Zr, Ni.

Chromium nitride has been found to be a particularly good coating, but titanium based coatings are another possibility. The coating may be applied by a different process to physical vapour deposition, such as for instance electroplating or chemical vapour deposition.

The parameters used for post polishing may be different, and for instance different polishing media may be used such as maize or plastics material.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A method of treating the surface of tablet tooling, the method comprising polishing the surface to provide a mirror finish with an Ra of between 0.025 and 0.1 pm; a texture is applied to the tablet finish to provide an Ra of between 0.35 and 0.55 pm; a coating is applied to the textured surface; and the coated textured surface is further treated to provide an Ra of between 0.2 and 0.5 pm.
2. A method according to claim 1, in which the texture is applied to the tablet finish to provide an Ra of between 0.35 and 0.45 pm.
3. A method according to claims 1 or 2, in which the coated textured surface is further treated to provide an Ra of between 0.2 and 0.35 pm.
4. A method according to any of the preceding claims, in which the texture is applied to the surface by shot blasting.
5. A method according to claim 4, in which the shot blasting is carried out using media of a particle size of between 0.074mm and 0.105mm.
6. A method according to claims 4 or 5, in which the angle of impingement of the shot blasting media is between 45° and 90°.
7. A method according to any of claims 4 to 6, in which a masking fixture is used so that only the tip of the tablet punch has a texture applied to it.
8. A method according to any of the preceding claims, in which the coating applied to the surface is a combination of any of the following elements: Cr, N, Al. Ti, C, Si, B, 0, W, Zr, Ni.
9. A method according to claim 8, in which the coating is a combination of Cr and N creating a chromium nitride coating.
10. A method according to any of the preceding claims, in which the coating is applied using physical vapour deposition.
11. A method according to any of claims 1 to 9, in which the coating is applied using chemical vapour deposition.
12. A method according to any of claims 1 to 9, in which the coating is applied using electroplating.
13. A method according to any of the preceding claims, in which the further treating of the surface retains the coating intact.
14. A method according to any of the preceding claims, in which the further treating of the surface is a further surface finish modification.
15. A method according to any of the preceding claims, in which the further surface finish modification is carried out by dragging the tablet through a particulate media including a polishing paste.
16. A method according to claim 15, in which the particulate media acts as a carrier for the polishing paste.
17. A method according to claim 16, in which the particulate media is pre impregnated with polishing paste.
18. A method according to any of claims 15 to 17, in which the particulate media has a particle size of between 0.2 and 0.4 mm.
19. Tablet tooling with a surface treated by a method according to any of the preceding claims.
20. A method of treating the surface of tablet tooling, the method being substantially as hereinbefore described.
21. Tablet tooling substantially as hereinbefore described.
22. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.