DE102007026958B4 - Press tool with diffractive microstructure and method for producing such a tool and tableting press - Google Patents

Abstract

Press tool (1, 1a, 1b, 3) for the production of tablets (4), in particular pharmaceutical tablets, by pressing a powder mixture (2) with the press tool (1, 1a, 1b, 3), with the press tool during the pressing process (1, 1a, 1b, 3) a microstructure can be applied to the tablets (4), diffractive grating microstructures (11) being arranged on a pressing surface of the pressing tool (1, 1a, 1b, 3), said grating Microstructures (11) have dimensions which are smaller than the dimensions of the individual crystallites (30) of the material of the pressing surface of the pressing tool (1, 1a, 1b, 3), and wherein the grating microstructures (11) have visible diffraction effects in the visible spectral range , characterized in that the lattice microstructures (11) have a relief with an essentially sinusoidal or rounded profile.

Description

Technical area

The invention relates to a pressing tool for producing tablets with an optical security feature in the form of a diffractive microstructure, and to a method for producing such tools, and to a tableting press with such a tool.

State of the art

Counterfeiting, gray market and illegal re-imports are a big problem for pharmaceuticals. More and more medicines and medicines are being counterfeited, and this is not only a problem in developing countries, where the share of counterfeit products in the supply chain is sometimes over 50%. The problem also exists in industrialized countries, where drug prices are often much higher. For example, for social reasons, the prices of AIDS or cancer drugs in developing countries are often significantly reduced, but this increases the risk of improper re-imports in industrialized countries.

In order to prevent abuse, packaging of medicines is provided with counterfeit-proof features. Holograms, optically variable inks, fluorescent dyes, special printing techniques such as micro-printing and other security features are affixed to the packaging with adhesive labels, laminated to the carton or placed directly on the packaging. The main disadvantage of such labels is that they can be removed from the product or packaging and then reused or analyzed. Some companies put security features on the sealing foil of blister packs, but they have the same drawbacks.

Methods in which forgery-proof signatures, such. B. DNA of known sequence ( US 5,451,505 ), Molecules with a characteristic isotopic composition, or microparticles with a characteristic color layer sequence ( US 6,455,157 ) are extremely critical because these signatures are taken together with the drug. For this reason, registration authorities, such. For example, the US Food and Drug Administration (FDA) has not yet granted approval for such methods.

Some attempts to apply a hologram to edible products have been published. WO 01/10464 A1 discloses the coating of edible products with a thermoformable and embossable layer. However, as the application of this layer alters the composition and manufacturing process of pharmaceutical pills, it needs a new regulatory approval. In addition, heating during the thermoforming steps is problematic for many active agents.

US 4,668,523 shows another approach, in which a polymer solution is brought into contact with a shape with diffractive relief. Subsequently, the polymer is cured during drying. This step can be accelerated by heating. In the end, the cured edible polymer product carries the diffractive relief. This method is limited to polymer solutions and is very slow. In addition, heating the active ingredients used in the manufacture of pharmaceutical tablets is also problematic here. These disadvantages have prevented the market introduction of these techniques.

From the WO 2006/047 695 A2 For example, a pressing tool is known which compresses a powder mixture into a tablet and impresses a diffractive grid microstructure into the tablet during the pressing process. On a pressing surface of the pressing tool is a series of parallel lines engraved with about 500 lines per millimeter. This line arrangement generates a diffraction pattern when pressing the tablet, which has the shape of the letter "Y".

In the WO 01/10464 A1 is a press stamp described which comes after the pressing process used. This ram carries an additional tool attachment, which has a diffractive grating microstructure, which is embossed in an additional shell of the already finished compressed tablet.

In the US 2004/0 163 441 A1 a method for producing a workpiece is described in which a diffractive grating microstructure is introduced into the workpiece solely by means of a stamping process by means of a press die. The microstructure used there has vertical walls.

The prior art is further on the WO 2006/027688 A1 and the US 2005/0232130 A1 referenced, from which a provided with a diffractive grating microstructure pressing tool or a manufacturing method for a press die are known.

Presentation of the invention

The object of the present invention is to provide a pressing tool and a tableting press, with which tablets with integrated security feature can be produced, which have substantially the same composition as conventional tablets and can be produced without elevated temperatures during the manufacturing process, and this without lengthening the production process over the conventional methods, wherein the detachment of the finished tablet is to be facilitated by the pressing tool. Another object of the invention is to provide methods by which such tools can be made.

By the term tablet is meant in this context not only tablets and pills intended for swallowing, sucking, chewing or gulping in the mouth, but also other medicinal forms such as suppositories or suppositories or products which are dissolved in liquids prior to ingestion. Also contemplated are, in addition to pharmaceutical tablets, non-pharmaceutical products such as candies or sweetener tablets.

These and other objects are achieved by a pressing tool according to claim 1, a tabletting press according to claim 9 and by methods of manufacturing such tools according to claims 11 and 16. Preferred variants are given in the dependent claims.

An inventive pressing tool consists of a mold and two press dies. The surface of the press mold facing the powder mixture to be compressed for the tablet and / or one or both of the press dies is provided with a diffractive microstructure. During the pressing process, more specifically during the compression and compression process, this diffractive microstructure is imaged onto the surface of the powder particles. A tablet produced with such a pressing tool according to the invention has on its surface a permanent, diffractive microstructure, which produces perceptible diffraction effects in the optical spectral range, and thus serves as a security feature. The microstructured surface can also be structured macroscopically, for example, to form logos, brand names, etc. The security feature can not be removed from the tablet and can not be subsequently transferred to counterfeit products.

The tools according to the invention can be used in conventional tabletting machines. To prepare the tablets, the conventional temperatures, pressures and processing speeds of known tablet presses can be maintained. In particular, a compression time per tablet of far less than 100 ms is sufficient. The preparation of the tablets is thus compatible with the existing and skilled tablet manufacturing processes, and thus is inexpensive.

Ways to carry out the invention

The invention will be explained in more detail below with the aid of drawings.

1 shows a simplified schematic representation of the tablet pressing process.

2 shows a schematic cross section of diffractive microstructures on the surface of tablets. Prepared by the method according to the invention, having (a) rectangular, (b) sinusoidal and (c) triangular shaped grid lines;

3 shows a recording of a pressed tablet with a diffractive microstructure, prepared by the method according to the invention.

3a shows a schematic representation of tablets according to the invention with microstructures in wells.

3b shows the schematic representation of a reader for authentication of tablets according to the invention.

4 shows (a) a picture of a microstructured pressing tool for use in the method according to the invention, and (b) a scanning electron microscope (SEM) picture of a tablet produced by the method according to the invention.

5 schematically shows the steps of the ion etching process for producing a pressing tool according to the invention: (a) holographic exposure, (b) chromium asphoric deposition, (c) dry etching, (d) finished microstructured die surface.

6 shows an example of a stress / strain curve.

7 shows a picture of a microstructured by cold stamping aluminum plate.

8th shows the schematic representation of a Hämmerprozesses for imaging a diffractive microstructure on a pressing tool surface.

Powder mixtures for pharmaceutical tablets

Most tablets are made by compressing a powder mixture in a mold. If active powders and fillers are merely mixed and then pressed directly into tablets, this is called direct tableting. This process is mainly a high pressure molding process.

The mixture to be compressed consists of particles of different sizes, the size distribution of the particles being critical for the tablet pressing process. Table 1 shows an example of a typical mixture including excipients for the preparation of a pharmaceutical tablet. Table 2 shows the associated typical particle size distribution. Table 1 Share% by weight substance 72.75 Lactose monohydrate 24 25 Microcrystalline cellulose 1:00 Aerosil (colloidal silica, dried) 1:00 Magnesium stearate 1:00 Sodium salicylate (exemplary active ingredient) Table 2 Diameter of the particles in μm Share in% by weight <75 15-25 75-150 30-50 150-250 15-25 250-500 5-15 > 500 <2

Lactose and cellulose are the most widely used binders and fillers in direct tabletting processes. These substances are particularly suitable for being provided with a diffractive microstructure.

The powder transport in the tablet press apparatuses takes place by gravity. Thus, a good trickling behavior is mandatory. Aerosil improves powder flow.

Magnesium stearate is used as a lubricant. Lubricants work by spreading over the surface of the powder. They reduce the frictional forces between the powder and the pressing tools, thus preventing the tablet from sticking to the pressing tool.

Decomposition agents can be added to the powder mixture to improve the decomposition, ie the dissolution in water. The decomposition time of pills is typically measured in water at 37 ° C. Sometimes a dye is added but only a few dyes are approved for use in medicines. Virtually all pharmaceutical tablets are therefore matt white. Some are bright red or light blue. Thus, all tablets produced in the direct tableting process have a luminous and / or light-scattering surface.

For the pressing process particles are critical, which are greater than 500 microns or less than 75 microns. The former reduce the mechanical stability of the pressed tablet, and the latter are problematic for the flow of particles during the filling of the cavity of the pressing tool. Thus, the proportion of these particles must be kept as small as possible. Overall, it can be stated that virtually all powder particles used in the tablet pressing process are significantly larger than the diffractive microstructures to be introduced into the surface, which typically have structures smaller than 5 μm. In order to prevent undesirable chemical changes of the ingredients during the preparation of the tablets, the temperature should advantageously not exceed 50 ° C, and more preferably 40 ° C. Preferably, the temperature is between 15 ° C and 35 ° C, or room temperature.

Parameters of diffractive microstructures

The reliable and permanent introduction and preservation of typical diffractive microstructures with a period Λ of about 1-2 microns and a depth t in the order of 200-300 nm, as for example in 2 are shown in the surface of a tablet during the direct tableting process is difficult. Of course, the powder blends are not intended to be microstructured, and the size of the microstructures is much smaller than the dimension of the particles. For this reason, the surface of the particles themselves must be microstructured. Last but not least, the tableting process is so fast that the time for microstructuring is extremely short. In order to achieve this, certain parameters of the diffractive microstructure have to be optimized, in particular the diffractive microstructure acting as an embossing pattern on the tool surface. The determined particularly suitable parameter ranges of the microstructures for tablets according to the invention are summarized in Table 2a. Table 2a parameter suitable area preferred range particularly preferred range Period Λ 300-5000 nm 800-2500 nm 1200-2500 nm Depth t 80-1000 nm 100-500 nm 150-300 nm shape rectangular, sinusoidal, triangular or rounded shapes sinusoidal or rounded shapes sinusoidal or rounded shapes

A challenge in the tabletting process is to avoid breaking off the diffractive microstructures protruding from the surface of the tablet according to the invention. Microstructures consisting of linear grid lines (1d gratings) are more suitable than point gratings (2d gratings) because the lines have mechanical greater stability than the points. Crossed gratings with the shape of a grid of holes are similarly suitable thanks to the stability of the connected grid lines.

The microstructuring increases the surface of the pressing tool and thus the contact surface between the pressing tool and the pressed tablet. This leads to increased adhesion and can thus interfere with the detachment of the finished tablet from the tool. To minimize this effect, the microstructure advantageously has a rounded or triangular shape, e.g. B. a sinusoidal grid ( 2 B) , (c)). Less ideal are microstructures with vertical walls, as in 2 (a) , In addition, the depth t of the microstructures should be as low as possible. However, for a visible diffractive effect, a minimum depth t of about 80 nm is needed. The diffraction efficiency of a sinusoidal grating is for example maximal when the grating depth corresponds to 0.3-0.4 grating periods. In addition, the microstructure must be deeper than the lubricant layer between the surface of the die or the mold wall and the tablet mass. Most lubricants have a laminar structure with slip planes that move slightly parallel to the surface of the die or die. For this reason, microstructures that are introduced only in this sliding layer, easily demolished.

Production of tablets with diffractive microstructures

1 shows schematically the manufacturing process of a tablet. The powder to be pressed 2 , a mixture of the powdered ingredients, is placed in a mold 3 brought in. Two axially aligned press punches 1a . 1b exert axial mechanical forces, creating the tablet. The diffractive microstructure to be introduced on the tablet is located on the surface of the press ram 1a . 1b and / or on the inner wall of the mold 3 , Is the wall of the mold 3 provided with a linear diffractive grating as a microstructure, the grid lines are preferably arranged parallel to the axial direction of movement of the press die tools to eject the finished tablet 4 to support. Nevertheless, it is easier with respect to the mechanical stresses occurring in the pressing process, the microstructure on the press dies 1a . 1b to install.

The powder fills the cavity in the mold 3 , which from the lower punch 1b is closed, see 1 (a) , The volume of the mold defines the amount of powder that is pressed into the tablet. This volume can be determined by the position of the lower punch 1b be adjusted during filling of the cavity. The compression force is typically between 5-25 kN. Modern rotary presses achieve maximum compression forces of up to 160 kN. During the pressing process two coherent phenomena take place simultaneously: compression and consolidation (K. Marshall, "Tablet press fundamentals", Tablets & Capsules 2005, p. 6-11). The former leads to a reduction of the mass volume, the latter causes an increase in the mechanical strength of the mass. So if force is exerted on the powder, its volume first decreases, because the air is displaced between the particles, see 1 (b) , This phase is called "repacking phase" and is limited by achieving the highest possible packing density and / or by friction at contact points of the powder particles. Thereafter, most materials are elastically deformed to the plastic limit, see 1 (c) , This phase is called "squeezing phase". Due to the volume reduction, the particles can also suffer brittle fractures. Subsequently, the components can be plastically and / or viscoelastically deformed.

The diffractive microstructure is introduced into the tablet surface mainly by this plastic or viscoelastic deformation. Many materials used for tablet pressing, such as. For example, some polymers used as binders show viscoelastic behavior. If the surface of the particles is coated with a plastic material, the plasticity of a powder can be further improved. Particles may be partially coated with a binder such as polyvinylpyrrolidone (PVP), e.g. B. in wet granulation, whereby the compressibility of the particles is improved. Due to particle-particle interactions, the mechanical strength of the tabletting compound becomes stronger as the applied pressing force increases. In particle-particle interactions bonds are formed on the particle surfaces as the number of points of contact increases. Depending on the chemical composition, the bonds are ionic or covalent bonds, dipole-dipole interactions, and van der Waals forces. Often there is a mixture of these bonds. In addition, solidification of liquid films may occur. The solidification of liquid films can be done in two ways. First, when frictional heat at the points of contact causes a low melting point ingredient to soften or melt, thereby relieving the stress at that point. The ingredient then hardens again via a fusion bond. Second, an ingredient may dissolve at high voltage touch points in the liquid film present on the surface of a particle. Again, the stress is relieved and the material recrystallizes to form a bond. If the hardening occurs near the surface of the microstructured pressing tool, the softened, molten or dissolved ingredient will aid in the replication of the diffractive microstructure.

At the end of the tablet pressing process, the pressure is removed 1 (d) , and the finished tablet 4 ejected, 1 (e) , The subsequent elastic recovery must be kept low in order to achieve a high mechanical stability of the tablet. The recipe is optimized accordingly.

Tablets with diffractive microstructures in their surfaces thus require a formulation which fulfills all the requirements of tablet production and still has sufficiently high plastic deformability in order to be able to introduce the microstructure. As already mentioned, the powders to be pressed consist of a mixture of different substances with different functions. The proportion of plastically deformable materials in the formulation must be as large as possible, but the requirements of the final product as well as the FDA still have to be met. The proportion of microcrystalline cellulose or plastic binder such as PVP can, for. Example, or these materials are used in place of equivalent, but plastically less deformable excipients.

Modern industrial tablet presses are high performance machines that can manufacture tablets at very high speeds. The production speed of state-of-the-art single-rotary presses is approximately 30,000 to 300,000 tablets per hour. In addition, they must offer extreme reliability and accuracy, as all tablets must meet strict specifications regarding thickness, weight, hardness and shape. The machines and all their components must be GMP (Good Manufacturing Process) and FDA compliant.

Table 3 shows examples of speed-specific data for different tablet presses. Further comments can be found in NA Armstrong, "Considerations of Compression Speed in Tablet Manufacture," Pharmaceutical Technology, September 1990, pp. 106-114. The short pressing time is enough to press the powdery raw material into a hard tablet. Table 3 Type of press Speed per mold Lowering time for the last 5 mm hold time eccentric 85 tablets / min. 68.6 ms 0ms Small rotary press 44 tablets / min 61.4 ms 10 84 ms Large rotary press 100 tablets / min 26.7 ms 3.94 ms Large rotary press 121 tabs / min. 19.1 ms 3 16 ms

The settling time plus the hold time is about the same or a little less than the time to heat-roll diffractive microstructures in polymer films in roll-to-roll processes (R2R). Such R2R processes are z. B. used for the production of holograms for banknote security and work with polymer feed rates of about 100 m / min. The polymer substrate, the process parameters and the temperature are optimized for a good replication of the microstructure.

Analogously, the pressing process in the method according to the invention is adapted to the requirements of microstructuring. Most pharmaceutical pills have a round shape. This facilitates the production process, since the pressing tool is rotationally symmetrical and can rotate freely during the pressing process. For the introduction of the diffractive microstructure, however, it is advantageous if rotation of the press dies is prevented in order to reduce the occurring shear forces, in particular during the detachment of the tool from the tablet, because as the press dies move away from the surface of the tablets, Due to elastic recovery, the tablet and the tool surfaces may remain in contact for a short time.

Protecting the microstructured tablet surface from mechanical damage

For example, in order to protect the microstructure from mechanical stresses during the entire product life cycle, in particular from abrasive forces, the contact of the microstructured surface with other surfaces can be minimized by the diffractive microstructure 11 into a macroscopic depression 12 in the surface of the tablet 4 is arranged (see 3a ).

Such macroscopic pits 12 are common in the conventional direct tableting process. They are mainly used for marketing purposes, z. B. to show the logo of the company, etc. Is the depression 12 deep and small enough so that the sharpest edge of another pill can not touch the microstructured surface (see 3a ), the diffractive structure is well protected against mechanical damage. Even in storage containers, sorting machines or in storage bottles, no abrasion can take place. Less deep wells provide less good protection, but sometimes are unavoidable due to design requirements.

The microstructured tablets may alternatively or additionally also be coated with an additional protective layer without destroying the diffractive effect, provided that the protective layer is transparent in the visible spectral range and has a refractive index which does not correspond to that of the material carrying the microstructure. Such a coating also protects the diffractive microstructure. If the refractive index of this coating is higher, the thickness is less than 1 μm, and the grating period of the microstructure is less than 500 nm, zero-order diffractive color effects can be realized. These color effects are extremely tamper-proof and easy to spot.

Example of a pharmaceutical tablet according to the invention with a diffractive microstructure

A composite according to Table 1 powder mixture was compressed in a simple rotary press of the type 1200i the company Fette, Germany, with 24 pairs of compression punches to tablets. The punches had a diameter of 11.8 mm and a hard chromed surface. In the hard chromium-plated surface, a diffractive microstructure was ion-etched with a period of 1.4 μm and a depth of approximately 500 nm, see 4 (a) , Visible diffractive effects in tablets weighing 540 mg were achieved with a press force of 25 kN and a production rate of 30,000 tablets per hour. 3 shows one of the tablets produced. The diffractive microstructure produces a clearly visible lettering "CSEM". The generated diffraction effects can of course with the black and white shot in 3 not shown. The hardness of the tablet is 154 N, which is a satisfactory value in terms of the solubility of the tablet. 4 (b) shows an SEM image of the microstructured surface of such a tablet. The diffractive microstructure is clearly visible.

Authentication of tablets according to the invention

If tablets according to the invention have a bright and / or luminous color, this strong background may make it more difficult to detect a rainbow effect of the diffractive microstructures. Since the usual powder components in the visible spectral range have a refractive index of approximately 1.5, only a small percentage of the light incident on the tablet surface is deflected back into the first or higher orders of diffraction. The angular distribution of the diffracted light is given by: Λ (sin _{m m} - sin _{l 1} ) = mλ where θ _{m is} the reflection angle of the m-th diffraction order, θ _{1 is} the angle of incidence and λ is the wavelength of the light (see 2 (a) ).

Since higher-order diffraction effects are weaker, recognizing the typical diffraction pattern for a layman may not be easy. However, the deep reflected intensity is not a disadvantage, as strong diffractive color effects could irritate the end user. Many patients are afraid of heavily colored pills. On the other hand, the visibility of the diffraction effect can be easily increased by suitable illumination at an optimized angle of incidence. This makes the effect a so-called second-level security feature. Second- or third-level security is widely used in the pharmaceutical industry as companies do not necessarily want to tell their end-users that counterfeiting is a problem. Under illumination with, for example, a white LED, the rainbow effect of the diffractive microstructure lights up at a certain viewing angle. A skilled person can verify the presence of the diffractive microstructure in less than a second using such a verification device.

The verification of the existence of a diffractive microstructure is a qualitative authentication. A simple and rapid method for quantitatively examining diffractive microstructures is to illuminate the structures with the beam from a laser diode (eg λ = 650 nm) at a fixed angle of incidence. The laser beam is diffracted according to the formula given above into the different diffraction orders. Since the laser wavelength λ and the incident angle θ _{1 are} known, the period Λ of the microstructure can be determined by measuring the diffraction angle of at least one order. This happens z. B. by means of a portable reader, which has a recess in which the pill is fixed and which ensures a fixed angle of incidence of the laser beam (see 3b ). The diffracted laser beams are captured by an array of photodiodes, and the period of the microstructure is calculated based on the positions of the diffracted beams. Such mobile readers can be used for example in pharmacies or by customs authorities.

Producing a pressing tool according to the invention

The material of the tool carrying the microstructure must be very hard to guarantee a long life. At the same time, however, it must be possible to introduce the microstructure into its surface. Suitable materials are for. As hardened steel, hard chromium-plated steel, tungsten carbide or molybdenum carbide. All of these materials are approved by the FDA and can be used for the press dies or dies. However, these materials are not compatible with conventional holographic and lithographic techniques. However, they can be microstructured with other methods, which are described below.

ion etching

• 1. Eine dünne, lichtempfindliche Schicht 20, ein so genannter Photoresist, wird auf die Oberfläche des Presswerkzeuges aufgetragen, welche mikrostrukturiert wird. In 5(a) ist dies ein Pressstempel 1. Die Beschichtung wird in einem speziellen Raum ohne Blau- und UV-Strahlung vorgenommen. Geeignete Photoresist-Materialien sind z. B. ma-N440 (MRT) Microposit S1800 (Röhm & Haas) und AZ1500 (Clariant). Die optimale Dicke der Schicht 20 liegt im Bereich von 300 nm bis 2000 nm. Die Beschichtung kann, falls das Werkzeug angemessen fixiert wird, durch Spin-Coaten (Convac 1001 s) oder durch Spray-Coaten (EFD MicroCoat MC780S) erfolgen. Letzteres muss für eine gute Homogenität im gewünschten Dickebereich optimiert sein. Nach der Beschichtung wird bei 100 bis 120°C während 1–60 min (je nach Dicke und Material der Schicht) gehärtet (sog. Soft Bake).
• 2. Als nächstes wird die Photoresist-Schicht 20 in einem holographischen Belichtungs-Aufbau mit zwei interferierenden Laserstrahlen 21 belichtet (siehe 5(a)). Gekreuzte Gitter werden durch zwei orthogonale Belichtungen realisiert. Die integrierte Leistung wird durch eine Photodiode kontrolliert und hängt vom Photoresist-Material und den gewünschten Gitterparametern ab. Der Laser ist beispielsweise ein HeCd-Laser mit einer Wellenlänge λ = 441.6 nm. Je nach Einfallswinkel Θ der beiden Strahlen sowie den optischen Komponenten des verwendeten Holographie-Aufbaus sind Gitterperioden Λ von 270 nm bis zu 16'000 nm möglich, A = λ/(2n sin Θ). n ist der Brechungsindex des Materials, durch welches die Laserstrahlen die Photoresistoberfläche beleuchten. Findet die Beleuchtung in Luft statt, ist n = 1. Um die Form der Gitterfläche zu definieren, können Schattenmasken benutzt werden. Auf diese Weise können z. B. Logos, Markennamen etc. realisiert werden.
• 3. Nach der Belichtung wird die Photoresist-Schicht in einer geeigneten Entwicklungslösung entwickelt. Dafür können z. B. der Grundentwickler S303 (Microposit) oder Konzentrat (Microposit) verwendet werden. Die Entwicklungszeit hängt von den herzustellenden Gitterparametern ab. Sofort nach der Entwicklung wird das Werkzeug in ein Stoppbad mit reinem Wasser gelegt. Die Temperaturen beider Bäder liegen bei 30°C und werden auf ±0.2°C kontrolliert. Am Ende des Entwicklungsschrittes verfügt die Photoresist-Schicht auf dem Pillenpresswerkzeug über ein Gitter mit der gewünschten Periode und Tiefe (siehe 5(b)). Die Form kann wie gezeigt sinusförmig oder auch komplexer sein.
• 4. Um das Gitter in der Werkzeugoberfläche trockenätzen zu können, muss ein Kontrast in der Ätzrate von mindestens 2:1 realisiert werden. Dies wird erreicht, indem eine Metallhaube, vorzugsweise eine Chromhaube, mit einer Massendicke von 10 nm bis 200 nm auf die erhöhten Stellen des Gitters auf der Photoresist-Schicht 20 aufgetragen wird. Die optimale Dicke hängt von der Gittertiefe und -periode ab. Das Tablettenpresswerkzeug mit der entwickelten Photoresist-Schicht 20 wird so in einer Vakuumkammer (Balzers BAK550) angeordnet, dass die aufgedampften Atome die Vertiefungen des Gitters nicht erreichen können. Diese Schiefbedampfung wird in 5(b) schematisch dargestellt. Der Einfallswinkel α der Metallatome liegt dabei je nach Gittertiefe und -periode zwischen 3° bis 45°. Falls nötig wird die Schiefbedampfung von zwei oder mehr Seiten her vorgenommen, um symmetrische Metallkappen zu erhalten.
• 5. Nun wird die Photoresist-Schicht 20 geöffnet, womit eine Maske 22 resultiert. Wie in 5(c) gezeigt, werden die Teile des Polymer-Resistmaterials ohne Chromkappen mit O₂-Plasma (Oxford-RIE) geätzt. Die kinetische Energie der reaktiven Sauerstoffionen liegt im Bereich von 500 eV. Die Ätzrate hängt darüber hinaus vom Druck in der Vakuumkammer ab. Das Ende dieses Öffnungsschrittes wird durch ein Endpunktdetektionssystem festgestellt, welches auf Laser-Interferometrie basiert.
• 6. Die geöffnete Maske 22 wird anschliessend dazu benutzt, die Gitterstruktur 11 durch einen weiteren Trockenätzschritt in die Werkzeugoberfläche zu transferieren. Diese Ätzung in die harte Oberfläche des Pillenpresswerkzeugs erfolgt durch Beschießung mit Argon-Ionen (Veeco RF 350) mit einer kinetischen Energie in der Größenordnung von 500 eV. Bei 500 eV ist die Energie niedrig genug, um eine hohe Eindringtiefe der Quellionen in die Probe zu verhindern, ohne jedoch die Ätzrate zu vermindern. In Tabelle 4 werden für verschiedene Elemente und Verbindungen typische Ätzraten r für eine solche Argon-Beschießung bei einer Ionenstromdichte von 1 mA/cm², einer kinetischen Energie der Ionen von 500 eV und bei senkrechtem Beschuss aufgelistet.

Tabelle 4 Element oder Verbindung Argon-Atzrate r [nm/min] Al 73 C 44 Cr 58 Cu 110 Fe 53 Mo 54 Ni 66 Si 38 SiC 35 SiO₂ 40 Ta 42 TaC 10 Ti 38 V 37 W 38 Zr 62 Hardened steel, hard chromium-plated steel, tungsten carbide or molybdenum carbide may be microstructured using a special ion etching technique. This technique includes the following steps, which are in 5 (a) bis (d) are shown schematically:

• 1. A thin, photosensitive layer 20 , a so-called photoresist, is applied to the surface of the pressing tool, which is microstructured. In 5 (a) This is a press stamp 1 , The coating is done in a special room without blue and UV radiation. Suitable photoresist materials are for. Ma-N440 (MRI) Microposit S1800 (Rohm & Haas) and AZ1500 (Clariant). The optimal thickness of the layer 20 is in the range of 300 nm to 2000 nm. If the tool is adequately fixed, the coating can be done by spin coating (Convac 1001s) or by spray coating (EFD MicroCoat MC780S). The latter must be optimized for good homogeneity in the desired thickness range. After coating, hardening takes place at 100 to 120 ° C. for 1-60 minutes (depending on the thickness and material of the layer) (so-called soft bake).
• 2. Next, the photoresist layer 20 in a holographic exposure setup with two interfering laser beams 21 exposed (see 5 (a) ). Crossed grids are realized by two orthogonal exposures. The integrated power is controlled by a photodiode and depends on the photoresist material and the desired lattice parameters. The laser is, for example, a HeCd laser with a wavelength λ = 441.6 nm. Depending on the angle of incidence Θ of the two beams and the optical components of the holography structure used, grating periods Λ of 270 nm to 16,000 nm are possible, A = λ / (2n sin Θ). n is the refractive index of the material through which the laser beams illuminate the photoresist surface. If lighting is in air, n = 1. Shadow masks can be used to define the shape of the grid surface. In this way, for. B. logos, brand names, etc. can be realized.
• 3. After exposure, the photoresist layer is developed in a suitable developing solution. For z. For example, the basic developer S303 (Microposit) or concentrate (Microposit) can be used. The development time depends on the grid parameters to be produced. Immediately after development, the tool is placed in a stop bath of pure water. The temperatures of both baths are at 30 ° C and are controlled at ± 0.2 ° C. At the end of the development step, the photoresist layer on the pill press tool has a grid of the desired period and depth (see 5 (b) ). The shape may be sinusoidal or more complex as shown.
• 4. In order to be able to dry etch the grid in the tool surface, a contrast in the etching rate of at least 2: 1 must be realized. This is achieved by placing a metal cap, preferably a chrome cap, with a bulk thickness of 10 nm to 200 nm on the raised areas of the grating on the photoresist layer 20 is applied. The optimum thickness depends on the grid depth and period. The tablet press tool with the developed photoresist layer 20 is placed in a vacuum chamber (Balzers BAK550) so that the vapor deposited atoms can not reach the wells of the grid. This slate evaporation is in 5 (b) shown schematically. The angle of incidence α of the metal atoms is between 3 ° and 45 °, depending on the grating depth and period. If necessary, the oblique evaporation from two or more sides is made to obtain symmetrical metal caps.
• 5. Now the photoresist layer is 20 opened, bringing a mask 22 results. As in 5 (c) The parts of the polymer resist material without chromium caps are etched with O ₂ plasma (Oxford-RIE). The kinetic energy of the reactive oxygen ions is in the range of 500 eV. The etch rate also depends on the pressure in the vacuum chamber. The end of this opening step is detected by an endpoint detection system based on laser interferometry.
• 6. The opened mask 22 is then used to the grid structure 11 to transfer into the tool surface by another dry etching step. This etch into the hard surface of the pellet press tool is by bombardment with argon ions (Veeco RF 350) with a kinetic energy of the order of 500 eV. At 500 eV, the energy is low enough to prevent a high penetration of the source ions into the sample, but without reducing the etch rate. Table 4 lists typical etch rates r for such elements and compounds for such argon bombardment at an ion current density of 1 mA / cm ² , a kinetic energy of the ions of 500 eV, and normal bombardment.

Table 4 Element or connection Argon etch rate r [nm / min] al 73 C 44 Cr 58 Cu 110 Fe 53 Not a word 54 Ni 66 Si 38 SiC 35 SiO ₂ 40 Ta 42 TaC 10 Ti 38 V 37 W 38 Zr 62

Once the desired grid depth has been reached, the remaining chromium and photoresist material is removed, leaving behind the finished, microstructured surface of the press tool according to the invention (see 5 (d) ).

For cost-effective production of the diffractive microstructures on the pressing tools according to the invention, a plurality of such tools are produced in parallel in the time-consuming steps of oblique deposition and dry etching.

With the ion etching method mentioned, coated pressing tools can also be microstructured, such as galvanic hard chrome coatings. 4 (a) shows an image of a press ram according to the invention 1a with a galvanically deposited hard chrome surface. into the surface became a diffractive microstructure according to the method described above 11 brought in. 4 (b) shows an SEM image of the microstructured surface of a pressed tablet with this pressing tool.

embossing

Another method for introducing a diffractive microstructure on a pressing die according to the invention is to hammer the desired microstructure into the surface of the pressing tools according to the invention by means of an embossing process with the aid of a main tool. This main tool can be microstructured by the ion etching method described above.

It is known macroscopic structures such. For example, chassis number or brand name, hammer in metal. Such structures are typically a few millimeters in the smallest case. The required accuracy of the structuring is low, since the only requirement is to be able to read the numbers and letters. The hammering of diffractive microstructures with periods in the order of 1 .mu.m in pressing tools according to the invention is of course considerably more complicated. The required accuracy is very high in order to obtain the interference effect of the microstructures. In addition, the microstructures are smaller than the internal structures of metals (grain size), and the tools are made of very hard metal alloys.

To facilitate understanding of this method, some characteristic mechanical properties of metals are summarized below. Metals tend to have high melting points because of the strength of the metallic bond. The bond strength differs from metal to metal and depends, among other things, on the number of electrons that each atom emits into the so-called free electron gas. In addition, it depends on the packing density. Each metal consists of a large number of individual grains or crystallites, ie perfectly ordered microcrystalline regions. The average diameter of such grains is typically between 10 μm and 100 μm. At the grain boundaries, also called dislocations, the atoms are misaligned. Special treatments enable smaller particle sizes and thus harder metals.

If a small mechanical stress acts on a metal, individual metal layers begin to slide over one another. Once the tension is released, the atoms fall back to their original position (elastic deformation). When the tension is greater, the atoms slide into a new position; the metal is permanently deformed (plastic deformation). The movement of the dislocations leads to the disruption of a limited number of atomic bonds. The power required to simultaneously break the bonds of all the atoms in a crystal plane is very large. The movement of the dislocations, however, allows atoms in crystal planes to pass each other at much lower voltages. Since the energy needed to move along the densest crystal planes is lowest, the dislocations within a metal grain have a preferred direction of motion. This results in sliding displacements along parallel planes within the grain. The diameter of such slip lines is typically in the range of 10 nm to 1000 nm. These slip lines cluster and form slip strips. The latter are already visible under an optical microscope. As will be described below, the slip lines and slip lines support the replication of microstructures. The shift of the atomic layers on top of each other is hampered by grain boundaries, which are due to an inappropriate constellation of the atomic series. This means that the more grain boundaries a piece of metal has, ie the smaller the individual crystal grains, the harder the metal. Since the grain boundaries are areas where the atoms do not make good contact with each other, metals tend to break at grain boundaries. Thus, by increasing the number of grain boundaries, the metal is not only harder but also more brittle. The harder a metal is, the harder it is to deform. Table 5 lists Vickers hardness (HV), material density ρ, and modulus of elasticity or Young's modulus E for various materials (not just metals and alloys). Table 5 material ρ [g / cm ³ ] Hardness [HV] E [GPa] σ _y [MPa] σ _u [MPa] Diamond (C) 3:52 10060 1000 - - Polycrystalline diamond / diamond-like carbon DLC (C) 2.8-4.1 3000-12000 150-800 - - Cubic boron nitride (c-BN) 3:48 4500 680 - 50 Silicon carbide (SiC) 3.22 3300 480 - 140 Boron carbide (B ₄ C) 2.5 3200 450 - 380 Titanium carbide (TiC) 4.93 3200 460 - 330 Vanadium carbide (VC) 5.4 2940 420 - - Aluminum nitride (AlN) 3.2 2500 350 - 500 Tungsten carbide (W ₂ C) 15.6 2400 ≈700 - 530 Titanium nitride (TiN) 5.22 2100 260 - - Corundum (Al ₂ O ₃ ) 3.97 2060 ≈400 - 320 Molybdenum carbide (Mo ₂ C) 8.2 1950 550 - - Tantalum carbide (TaC) 13.9 1800 ≈340 - - Silicon nitride (Si ₃ N ₄ ) 3.2 1400-1700 ≈340 - 580 Zirconium oxide (ZrO ₂ ) 5.6 1400-1600 240 - 1000 Chrome (Cr) 6.9-7.2 750-1050 289 360 690 Hardened nickel 7.9-81 600-950 214 - - Hardened steel ≈7.8 500-900 190-214 520 860 nickel 8.91 550 214 940 1010 Unhardened steel ≈7.8 100-500 190-214 365 900 aluminum 2.7 25 ≈70 260 290

The modulus of elasticity is independent of the degree of hardness. The degree of hardness is a measure in which the plastic deformation begins by mechanical stress. The Young's modulus E = dσ / dε is the slope of the linear part of the stress / strain curve σ (ε). 6 shows an example of such a curve for a ductile material such as steel. The greater the resistance of a material to elastic deformation, the greater the value of the Young's modulus. Above the elastic limit ( 40 ) the plastic deformation takes place. The yield strength σ _y measures the resistance to plastic deformation. Any increase in stress over the yield strength ( 40 ) causes a permanent deformation of the material. In this so-called flow zone, the deformation is relatively large even with small increases in voltage. This process, characterized by a very small slope of the stress / strain curve, is often referred to as "perfect plasticity". After flow, the stress is increased to the breaking strength or ultimate tensile stress σ _u at which the material breaks ( 41 ). With brittle materials, the flow zone practically does not exist. Brittle materials often have relatively high Young's moduli and ultimate tensile stresses compared to ductile materials. Table 5 shows maximum values for σ _y and σ _u , respectively. All values in Table 5 are only reference values. The data of proper samples may differ significantly. In particular, values of coatings of such materials depend, among other things, on the process parameters and the growth mechanism.

• 1. Die Härte des Hauptwerkzeugs muss größer sein als diejenige des Presswerkzeugs.
• 2. Der Young'sche Modul muss für beide so hoch wie möglich sein, um die elastische Deformation zu minimieren.
• 3. Die angewandte Spannung muss höher als die Streckgrenze, jedoch tiefer als die ultimative Zugspannung des Presswerkzeugs sein. Außerdem muss sie niedriger sein als die Streckgrenze (falls vorhanden) und die ultimative Zugspannung des Hauptwerkzeugs.

In order to be able to hammer the diffractive microstructure with a main tool into a pressing tool according to the invention, the following conditions must be met:

• 1. The hardness of the main tool must be greater than that of the pressing tool.
• 2. The Young's modulus must be as high as possible for both to minimize elastic deformation.
• 3. The applied stress must be higher than the yield strength but lower than the ultimate tensile stress of the press tool. In addition, it must be lower than the yield strength (if any) and the ultimate tensile stress of the main tool.

Optionally, the crimping tool or its surface may be hardened after hammering the microstructure by subsequent heat treatment or ion implantation.

8th Figure 12 shows schematically how the microstructures of the main tool are replicated on the die in the stamping step by filling the cavities with the slip planes in the metal grains.

For example, in order to be able to microstructure a pressing tool with a hard chromium-plated surface, a tungsten carbide main tool is necessary, and an embossing force of approximately 400-500 MPa. Alternatively, the main tool also made of hardened steel, with a coating z. As tungsten carbide, Si ₃ N ₄ or ZrO ₂ , which carries the microstructure. The latter variant is more cost-effective, since only the coating must consist of the very hard and break-resistant material. 7 shows an example of a microstructure on a metal surface produced in this way using an embossing method. A block of aluminum 61 with a thickness of about 4 mm was made with a round nickel shim 60 microstructured with a diameter of about 12 mm. The nickel shim 60 located in 7 on the metal block 61 , The shim has a diffraction grating with a period of 1400 nm and a depth of about 300 nm, which shows the four letters CSEM in mirror image. This shim was pressed at room temperature with a pressure of 3 tons for about 0.5 sec. On the aluminum block. How out 7 As can be seen, the diffractive microstructure was well imitated on the aluminum block.

LIST OF REFERENCE NUMBERS

1, 1a, 1b

press die

2

powder mixture

3

mold

4

tablet

10

grid line

11

Lattice microstructure

12

deepening

20

Photoresist layer

21

Interfering laser radiation

22

mask

30

Grains, crystallites

40

Elastic border

41

fracture

50

laser

51

photodiodes

60

Nickel shim

61

metal block

Λ

period

t

depth

.theta..sub.M

Reflection angle of the mth diffraction order

θi

angle of incidence

m

diffraction order

Claims (19)

Pressing tool ( 1 . 1a . 1b . 3 ) for the production of tablets ( 4 ), in particular pharmaceutical tablets, by pressing a powder mixture ( 2 ) with the pressing tool ( 1 . 1a . 1b . 3 ), during the pressing process with the pressing tool ( 1 . 1a . 1b . 3 ) a microstructure on the tablets ( 4 ) is applied, wherein on a pressing surface of the pressing tool ( 1 . 1a . 1b . 3 ) diffractive grating microstructures ( 11 ), said grating microstructures ( 11 ) Have dimensions which are smaller than the dimensions of the individual crystallites ( 30 ) of the material of the pressing surface of the pressing tool ( 1 . 1a . 1b . 3 ), and wherein the grating microstructures ( 11 ) have visible diffraction effects in the visible spectral range, characterized in that the grating microstructures ( 11 ) have a relief with a substantially sinusoidal or rounded profile. Crimping tool according to claim 1, characterized in that the microstructures ( 11 ) are present only on a part of the press surface. Crimping tool according to claim 1 or 2, characterized in that the grating microstructures ( 11 ) are linear gratings or pitch grid. Press tool according to one of claims 1 to 3, characterized in that the period length Λ of the grid microstructure ( 11 ) is between 300 nm and 5000 nm. Press tool according to one of claims 1 to 4, characterized in that the depth t of the relief between the grid lines ( 10 ) of the lattice microstructure ( 11 ) is at least 80 nm, preferably 300 nm, and particularly preferably 400 nm. Press tool according to one of claims 1 to 5, characterized in that the depth t of the relief between the grid lines ( 10 ) of the lattice microstructure ( 11 ) is at most 1000 nm. Press tool according to one of claims 1 to 6, characterized in that the depth t of the relief between the grid lines ( 10 ) of the lattice microstructure ( 11 ) between 0.3 and 0.4 period lengths Λ of the lattice microstructure ( 11 ) is. Press tool according to one of the preceding claims 1 to 7, characterized in that the pressing tool is a pressing punch ( 1 . 1a . 1b ). Tableting press with at least one pressing tool ( 1 . 1a . 1b . 3 ) according to one of claims 1 to 8. The tableting press of claim 9, wherein the tableting press is a rotary press. Process for the production of microstructures ( 11 ) on the surface of a tool, in particular a pressing tool ( 1 . 1a . 1b . 3 ) according to any one of claims 1 to 8, comprising the steps of: - applying a photoresist layer ( 20 ) on the surface; Exposing the photoresist layer ( 20 ) with a microstructure; Developing the photoresist layer ( 20 ) - Transferring the microstructure on the photoresist layer ( 20 ) on the surface of the tool by dry etching; and - removing the photoresist layer ( 20 ). A method according to claim 11, characterized in that the exposure of the photoresist layer ( 20 ) by interfering laser beams ( 21 ) he follows. Method according to claim 11 or 12, characterized in that by means of a shadow mask a macroscopic structure of the microstructure ( 11 ) is produced. Method according to one of claims 11 to 13, characterized in that, before the dry etching (the projecting parts of the microstructure of the photoresist layer 20 ) A metal cap is applied, preferably by Schiefevampfung. A method according to claim 14, characterized in that prior to the dry etching the non-metal-coated portions of the photoresist layer ( 20 ) are removed by an oxygen plasma. Process for the production of microstructures ( 11 ) on the surface of a pressing tool ( 1 . 1a . 1b . 3 ) according to one of claims 1 to 8 for the production of tablets ( 4 ), in particular pharmaceutical tablets, by pressing a powder mixture ( 2 ) with the pressing tool ( 1 . 1a . 1b . 3 ), during the pressing process with the pressing tool ( 1 . 1a . 1b . 3 ) a microstructure on the tablets ( 4 ), the microstructures ( 11 ) with one the inverse form of the microstructures ( 11 ) carrying main tool into the surface of the tool ( 1 . 1a . 1b . 3 ). A method according to claim 16, characterized in that the hardness in Vickers degrees of hardness of the microstructures ( 11 ) carrying surface of the main tool is greater than that of the tool ( 1 . 1a . 1b . 3 ). Method according to claim 16, characterized in that during the impressing of the microstructure ( 11 ) applied stress is greater than the yield strength and lower than the ultimate tensile stress of the material of the tool ( 1 . 1a . 1b . 3 ), and at the same time lower than the yield strength and the ultimate tensile stress of the material of the main tool. Method according to one of claims 16 to 18, characterized in that after the impressing of the microstructure ( 11 ) the microstructured surface of the tool ( 1 . 1a . 1b . 3 ) is hardened.

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