The present invention relates to a cutting blade having an asymmetric cross- sectional shape with a first face, a second face opposed to the first face and different from the first face as well as a cutting edge wherein the first face com prises a surface and the second face comprises a primary bevel, a secondary bevel and a tertiary bevel with a first wedge angle qi between the surface on the first face and the primary bevel, a second wedge angle Q2 between the sur face on the first face and the secondary bevel and a third wedge angle Q3 be- tween the surface on the first face and the tertiary bevel. Moreover, the pre sent invention relates to a hair removal device comprising this cutting blade.

The following definitions are used in the present application:

• the rake face is the surface of a cutting blade over which the cut hair slides that is removed in the cutting process

• the clearance face is the surface of a cutting tool that passes over the skin; the angle between the clearance face and the contacting surface to the skin is the clearance angle a • The cutting bevel of a cutting blade is enclosed by the rake face and the clearance face and denoted by the bevel angle Q

• The cutting edge is the line of intersection of the rake face and the clear ance face

Cutting blades, in particular razor blades, are typically made out of a suitable substrate material such as stainless steel in which a symmetric wedge-shaped cutting edge is formed.

With respect to razor blades, the design of the cutting blade has to be optimized to find the best compromise between the sharpness of the blade and the me chanical strength and hence durability of the cutting edge. The fabrication of conventional stainless steel razor blades involves a hardening treatment of the steel substrates before the blade is sharpened from both sides to form a sym metric cutting edge usually by grinding the hardened steel substrate.

A further coating may be applied to the steel blade after sharpening to optimize the mechanical properties of the blades. Hard coating materials such as dia mond, amorphous diamond, diamond-like carbon (DLC), nitrides, carbides, or oxides are suitable to improve the mechanical strength of the cutting edge.

Thus, the harder the cutting edge material, the longer the edge holding prop erty and in consequence the less wear is expected. Other coatings may be ap plied to increase the corrosion resistance or reduce the blade friction.

Most blades in the prior art are focused on blades with a symmetric blade body. However, some approaches exist where blades with an asymmetric blade are taught.

In US 3,606,682, a razor blade with improved cutting ease and shaving comfort is described. The blade has a recessed portion adjacent to the cutting edge which allows an improved shaving comfort. This effect is shown for symmetric and asymmetric blade bodies. US 3,292,478 describes a cutting die knife for textiles, leather and similar sheet materials wherein the knife has suitably inclined surfaces on both sides with the consequence that the cutting edge is not positioned centrally between the side surfaces and the knife has an asymmetric shape.

US 3,514,856 refers to a razor blade construction having defined angular and dimensional limits of the converting surfaces from the cutting edge and an ef fective recessed portion immediately adjacent thereto from proved cutting ease and shaving comfort.

There is a continuing desire to reduce the force needed to cut an object, since this requires less energy and creates less wear of the cutting edge. In the con text of shaving, cutting hairs at lower forces results in less pulling on the hairs and hence less discomfort.

A reduction of the cutting force is achieved by reducing the angle of the wedge- shaped cutting tool. However, making the edge sharper also makes it more fragile and despite the application of hard coatings, the durability of conven tional steel razor blades is still limited today.

The present invention therefore addresses the mentioned drawbacks in the prior art and to provide cutting blades with a design which allow at the same time, a high comfort during the cutting process, i.e. a low cutting force, and a high durability, i.e. a low fragility of the blade.

This problem is solved by the cutting blade with the features of claim 1 and the hair removal device with the features of claim 16. The further dependent claims define preferred embodiments of such a blade.

The term "comprising" in the claims and in the description of this application has the meaning that further components are not excluded. Within the scope of the present invention, the term "consisting of" should be understood as pre ferred embodiment of the term "comprising". If it is defined that a group "com prises" at least a specific number of components, this should also be under stood such that a group is disclosed which "consists" preferably of these com ponents. In the following, the term cross-sectional view refers to a view of a slice through the cutting element perpendicular to the cutting edge (if the cutting edge is straight) or perpendicular to the tangent of the cutting edge (if the cutting edge is curved) and perpendicular to the surface of the substrate of the cutting ele ment.

The term intersecting line has to be understood as the linear extension of an intersecting point (according to a cross-sectional view as in Fig. 3) between dif ferent bevels regarding the perspective view (as in Fig. 1). As an example, if a straight bevel is adjacent to a straight bevel the intersecting point of the cross- sectional view is extended to an intersecting line in the perspective view.

According to the present invention a cutting blade is provided having a first face, a second face opposed to the first face and different from the first face as well as and a cutting edge wherein

• the first face comprises a first surface and

• the second face comprises a primary bevel, a secondary bevel and a ter tiary bevel with

• the primary bevel extending from the cutting edge to the second ary bevel,

• the secondary bevel extending from the primary bevel to the tertiary bevel

• a first intersecting line connecting the primary bevel and the sec ondary bevel, and

• a second intersecting line connecting the secondary bevel and the tertiary bevel,

• a first wedge angle qi between the first surface and the primary bevel and

• a second wedge angle Q2 between the first surface and the sec ondary bevel and

• a third wedge angle Q ₃ between the first surface and the tertiary bevel, and

• the primary bevel having a length di being the dimension pro jected onto the first surface (9) and/or the imaginary extension of the first surface (9') taken from the cutting edge (4) to the first intersecting line (10) from 0.1 to 7 miti,

• a length d2 being the dimension projected onto the first surface taken from the cutting edge to the second intersecting line from 1 to 75 pm.

It was surprisingly found that a cutting blade with a very stable cutting edge together with a very good cutting performance can be provided when the wedge angles fulfill the following conditions:

0i > Q2 and Q2 < 03-

The cutting blades according to the present invention have low cutting force due to a thin secondary bevel with a low wedge angle.

The cutting blades according to the present invention are strengthened by add ing a primary bevel with a primary wedge angle greater than the secondary wedge angle. The primary bevel with the first wedge angle qi has therefore the function to stabilize the cutting edge mechanically against damage from the cutting operation which allows a slim blade body in the area of the secondary bevel without affecting the cutting performance of the blade.

The cutting blades according to the present invention are even mechanically stronger by reducing the length of the thin secondary bevel to a fraction of the thickness of the object to be cut and employing the secondary wedge for pen etrating the object to be cut which allows a reduction of the cutting force of the cutting blade. The secondary bevel with the second wedge angle Q2 therefore has the function of penetrating the object to be cut. By using the primary bevel with the wedge angle qi to stabilize the cutting edge the second wedge angle Q2 can be reduced.

The cutting blades according to the present invention are further strengthened by adding a thick and strong tertiary bevel that has a tertiary wedge angle greater than the secondary wedge angle and by employing this tertiary bevel to split the object to be cut, thus reducing the forces acting on the thin second ary bevel. For this function the third wedge angle Q3 must be larger than the second wedge angle Q2. The third wedge angle Q3 represents the splitting angle, i.e. the angle necessary to split the object to be cut. For this function the third wedge angle Q3 must be larger than the second wedge angle Q2.

According to a preferred embodiment, the cutting blade has an asymmetric cross-sectional shape. The asymmetrical cross-sectional shape refers to the symmetry with respect to an axis which is the bisecting line of the secondary wedge angle Q2 and anchored at the cutting edge.

In a preferred embodiment of the invention the primary and secondary bevel are formed within a hard coating material to increase their mechanical strength further and the tertiary bevel is formed from a substrate material. Such an asymmetric cutting edge may lower the friction at the bevel side (conical shape) due to a reduction of the contact area between the second face and the hair.

According to a first preferred embodiment, the first wedge angle qi ranges from 5° to 75°, preferably 10° to 60°, more preferably 15° to 46°, and even more preferably 20° to 45° and/or the second wedge angle Q2 ranges from -5° to 40°, preferably 0° to 30°, more preferably 5° to 25°, even more preferably 10 to 15° and/or the third wedge angle Q3 ranges from 1° to 60°, preferably 10° to 55°, more preferably 19° to 46°, and most preferably is 45°.

According to a further preferred embodiment, the primary bevel has a length di being the dimension projected onto the first surface and/or the imaginary extension of the first surface taken from the cutting edge to the first intersect ing line from 0.5 to 5 pm, and preferably 1 to 3 pm. A length di < 0.1 pm is difficult to produce since an edge of such length is too fragile and would not allow a stable use of the cutting blade. It has been surprisingly found that the primary bevel stabilizes the blade body with the secondary and tertiary bevel which allows a slim blade in the area of the secondary bevel which offers a low cutting force. On the other hand, the primary bevel does not affect the cutting performance provided the length di is not larger than 7 pm.

Preferably, the length d2 being the dimension projected onto the first surface and/or the imaginary extension of the first surface taken from the cutting edge to the second intersecting line ranges from 5 to 100 miti, and more preferably from 10 to 75 pm and even more preferably from 15 to 50 pm. The length d2 corresponds to the penetration depth of the cutting blade in the object to be cut. In general, d2 corresponds to at least 30% of the diameter of the object to be cut, i.e. when the object is human hair which typically has a diameter of around 100 pm the length d2 is around 30 pm.

The cutting blade is preferably defined by a blade body comprising or consisting of a first material and a second material joined with the first material. The sec ond material can be deposited as a coating at least in regions of the first mate rial, i.e. the second material can be an enveloping coating of the first material or a coating deposited on the first material on the first face.

The material of the first material is in general not limited to any specific mate rial as long it is possible to bevel this material.

However, according to an alternative embodiment the blade body comprises or consists only of the first material, i.e. an uncoated first material. In this case, the first material is preferably a material with an isotropic structure, i.e. having identical values of a property in all directions. Such isotropic materials are often better suited for shaping, independent from the shaping technology.

The first material preferably comprises or consists of a material selected from the group consisting of

• metals, preferably titanium, nickel, chromium, niobium, tungsten, tan talum, molybdenum, vanadium, platinum, germanium, iron, and alloys thereof, in particular steel,

• ceramics comprising at least one element selected from the group con sisting of carbon, nitrogen, boron, oxygen or combinations thereof, preferably silicon carbide, zirconium oxide, aluminum oxide, silicon ni tride, boron nitride, tantalum nitride, AITiN, TiCN, TiAISiN, TiN, and/or TiB ₂ ,

• glass ceramics; preferably aluminum-containing glass-ceramics, • composite materials made from ceramic materials in a metallic matrix (cermets),

• hard metals, preferably sintered carbide hard metals, such as tungsten carbide or titanium carbide bonded with cobalt or nickel,

• silicon or germanium, preferably with the crystalline plane parallel to the second face, wafer orientation <100>, <110>, <111> or <211>,

• single crystalline materials,

• glass or sapphire,

• polycrystalline or amorphous silicon or germanium,

• mono- or polycrystalline diamond, nano-crystalline and/or ultranano- cystalline diamond like carbon (DLC), adamantine carbon and

• combinations thereof.

The steels used for the first material are preferably selected from the group consisting of 1095, 12C27, 14C28N, 154CM, BCrlBMoV, 4034, 40X10C2M, 4116, 420, 440A, 440B, 440C, 5160, 5Crl5MoV, 8Crl3MoV, 95X18, 9Crl8MoV, Acuto+, ATS-34, AUS-4, AUS-6 (= 6A), AUS-8 (= 8A), C75, CPM-10V, CPM-3V, CPM-D2, CPM-M4, CPM-S-30V, CPM-S-35VN, CPM-S-60V, CPM-154, Cronidur- 30, CTS 204 P, CTS 20CP, CTS 40CP, CTS B52, CTS B75P, CTS BD-1, CTS BD-30P, CTS XHP, D2, Elmax, GIN-1, HI, N690, N695, Niolox (1.4153), Nitro-B, S70, SGPS, SK-5, Sleipner, T6M0V, VG-10, VG-2, X-15T.N., X50CrMoV15, ZDP-189.

It is preferred that the second material comprises or consists of a material se lected from the group consisting of

• oxides, nitrides, carbides, borides, preferably aluminum nitride, chromium nitride, titanium nitride, titanium carbon nitride, ti tanium aluminum nitride, cubic boron nitride

• boron aluminum magnesium

• carbon, preferably diamond, poly-crystalline diamond, nano crystalline diamond, diamond like carbon (DLC), and

• combinations thereof. The second material may be preferably selected from the group consisting of TiB ₂ , AITiN, TiAIN, TiAISiN, TiSiN, CrAI, CrAIN, AICrN, CrN, TiNJiCN and combi nations thereof.

Moreover, all materials cited in the VDI guideline 2840 can be chosen for the second material.

It is particularly preferred to use a second material of nano-crystalline diamond and/or multilayers of nano-crystalline and polycrystalline diamond as second material. Relative to monocrystalline diamond, it has been shown that produc tion of nano-crystalline diamond, compared to the production of monocrystal line diamond, can be accomplished substantially more easily and economically. Moreover, with respect to their grain size distribution nano-crystalline diamond layers are more homogeneous than polycrystalline diamond layers, the mate rial also shows less inherent stress. Consequently, macroscopic distortion of the cutting edge is less probable.

It is preferred that the second material has a thickness of 0.15 to 20 pm, pref erably 2 to 15 pm and more preferably 3 to 12 pm.

It is preferred that the second material has a modulus of elasticity (Young's modulus) of less than 1200 GPa, preferably less than 900 GPa, more preferably less than 750 GPa and even more preferably less than 500 GPa. Due to the low modulus of elasticity the hard coating becomes more flexible and more elastic and may be better adapted to the object or the contour to be cut. The Young ^' s modulus is determined according to the method as disclosed in Markus Mohr et al., "Youngs modulus, fracture strength, and Poisson ^' s ratio of nanocrystal line diamond films", J. Appl. Phys. 116, 124308 (2014), in particular under par agraph III. B. Static measurement of Young ^' s modulus.

The second material has preferably a transverse rupture stress oo of at least 1 GPa, more preferably of at least 2.5 GPa, and even more preferably at least 5 GPa.

With respect to the definition of transverse rupture stress oo, reference is made to the following literature references: • R. Morrell et al., Int. Journal of Refractory Metals & Hard Materials, 28 (2010), p. 508 -515;

• R. Danzer et al. in "Technische keramische Werkstoffe", published by J. Kriegesmann, HvB Press, Ellerau, ISBN 978-3-938595-00-8, chapter 6.2.3.1 "Der 4-Kugelversuch zur Ermittlung der biaxialen Biegefestigkeit sproder Werkstoffe"

The transverse rupture stress oo is thereby determined by statistical evaluation of breakage tests, e.g. in the B3B load test according to the above literature details. It is thereby defined as the breaking stress at which there is a probability of breakage of 63%.

Due to the extremely high transverse rupture stress of the second material the detachment of individual crystallites from the hard coating, in particular from the cutting edge, is almost completely suppressed. Even with long-term use, the cutting blade therefore retains its original sharpness.

The second material has preferably a hardness of at least 20 GPa. The hardness is determined by nanoindentation (Yeon-Gil Jung et. al., J. Mater. Res., Vol. 19, No. 10, p. 3076).

The second material has preferably a surface roughness RRMS of less than 100 nm, more preferably less than 50 nm, and even more preferably less than 20 nm, which is calculated according to

A = evaluation area

Z(x,y) = the local roughness distribution The surface roughness RRMS is determined according to DIN EN ISO 25178. The mentioned surface roughness makes additional mechanical polishing of the grown second material superfluous.

In a preferred embodiment, the second material has an average grain size dso of the nano-crystalline diamond of 1 to 100 nm, preferably 5 to 90 nm more preferably from 7 to 30 nm, and even more preferably 10 to 20 nm. The average grain size dso is the diameter at which 50% of the second material is comprised of smaller particles. The average grain size dso may be determined using X-ray diffraction or transmission electron microscopy and counting of the grains.

It is preferred that the first material and/or the second material is/are coated at least in regions with a low-friction material, preferably selected from the group consisting of fluoropolymers (like PTFE), parylene, polyvinylpyrrolidone, polyethylene, polypropylene, polymethyl methacrylate, graphite, diamond-like carbon (DLC) and combinations thereof.

The intersecting line connecting the primary bevel and the secondary bevel is preferably shaped within the second material.

It is further preferred that the intersecting line between secondary and tertiary bevel is arranged at the boundary surface of the first material and the second material which makes the process of manufacture easier to handle and there fore more economic, e.g. the blades can be manufactured according to the pro cess of Fig. 7.

The cutting edge ideally has a round configuration which improves the stability of the blade. The cutting edge has preferably a tip radius of less than 200 nm, more preferably less than 100 nm and even more preferably less than 50 nm, determined e.g. by cross sectional SEM using the method illustrated in Fig. 8.

It is preferred that the tip radius r of the cutting edge correlates with the aver age grain size dso of the hard coating. It is hereby advantageous if the ratio be tween the rounded radius r of the second material at the cutting edge and the average grain size dso of the nano-crystalline diamond hard coating r/dso is from 0.03 to 20, preferably from 0.05 to 15, and particularly preferred from 0.5 to 10.

The first face preferably further comprises a quaternary bevel which extends from the cutting edge to the first surface. If the first face corresponds to the clearance face this quaternary bevel will improve the comfort of the cutting, i.e. for shaving.

In a preferred embodiment, the first face corresponds to the clearance face and the second face corresponds to the rake face of the cutting blade. However, it is also possible to use the first face as the rake face and the second face as the clearance face.

In particular, the cutting blade can be configured as a knife blade, razor blade, scalpel, knife, machine knife in slitting-, burst- and crash cutting systems, scis sors or shear cutting systems or can be used as such. Likewise, it is possible that the cutting blade is configured as a shaving system, i.e. as a head with a plurality of razor blades or can be used as such. All the razor blades are thereby config ured as a cutting blade according to the present invention.

Hence, according to the present invention also a hair removal device compris ing a cutting blade as described above is provided.

The present invention is further illustrated by the following figures which show specific embodiments according to the present invention. However, these spe cific embodiments shall not be interpreted in any limiting way with respect to the present invention as described in the claims in the general part of the spec ification.

FIG. 1 is a perspective view of a first cutting blade in accordance with the present invention

FIG. 2 is a cross-sectional view of the cutting blade according to Fig. 1

FIG. 3 is a cross-sectional view of a further cutting blade in accordance with the present invention FIG. 4 is a cross-sectional view of a further cutting blade in accordance with the present invention with a second material

FIG. 5 is a cross-sectional view of a further cutting blade in accordance with the present invention with an additional bevel on the first face

FIG. 6 is a perspective view of a further cutting blade in accordance with the present invention with a non straight cutting edge consisting of curved segments

FIG. 7 are flow charts of the process for manufacturing the cutting blades

Fig. 8 is a schematic cross sectional view of a round tip showing the deter mination of the tip radius

Fig. 9 is a microscopic image of a cutting blade according to the present invention

The following reference signs are used in the figures of the present application.

Reference sign list

1 blade

2 first face

3 second face

4 cutting edge

5 primary bevel

6 secondary bevel

7 tertiary bevel

9 first surface

9 ^' imaginary extension of the first surface

10 first intersecting line

11 second intersecting line

15 blade body

18 first material 19 second material

20 boundary surface

60 bisecting line

61 perpendicular line

62 circle

65 construction point

66 construction point

67 construction point

260 bisecting line

Fig.l is a perspective view of the cutting blade according to the present inven tion. This cutting blade 1 has a blade body 15 which comprises a first face 2 and a second face 3 which is opposed to the first face 2. At the intersection of the first face 2 and the second face 3 a cutting edge 4 is located. The cutting edge 4 is shaped straight or substantially straight. The first face 2 comprises a plane first surface 9 while the second surface 3 is segmented in different bevels. The second face 3 comprises a primary bevel 5, a secondary bevel 6 and a tertiary bevel 7. The primary bevel 5 is connected via a first intersecting line 10 with the secondary bevel 6 which on the other end is connected to the tertiary bevel 7 via a second intersecting line 11. In Fig. 2, the cross-sectional view of the cutting blade of Fig. 1 is shown.

In Fig. 3, a further cross-sectional view of the cutting blade according to the present invention is shown. This cutting blade 1 has a blade body which com prises a first face 2 and a second face 3 which is opposed to the first face 2. At the intersection of the first face 2 and the second face 3 a cutting edge 4 is located. The first face 2 comprises a plane first surface 9 while the second face 3 is segmented in different bevels. The second face 3 of the cutting blade 1 has a primary bevel 5 with a first wedge angle qi between the first surface 9 and the primary bevel 5. The secondary bevel 6 has a second wedge angle Q2 be tween the first surface 9 and the secondary bevel 6 with a bisecting line 260 of the secondary wedge angle Q ₂ and anchored at the cutting edge 4. Q ₂ is smaller than qi. The tertiary bevel 7 has a third wedge angle Q ₃ which is larger than Q ₂ . The primary bevel 5 has a length di being the dimension projected onto the first surface 9 which is in the range from 0.5 to 5 pm. The primary bevel 5 and the secondary bevel 6 together have a length d2 being the dimension projected onto the first surface 9 which is in the range from 1 to 150 miti, preferably 5 to 100 pm.

In Fig. 4, a further sectional view of a cutting blade of the present invention is shown where the blade body 15 comprises a first material 18, e.g. silicon, with a second material 19, e.g. a diamond layer on the first material 18 at the first face 2. The primary bevel 5 and secondary bevel 6 are located in the second material 19 while the tertiary bevel 7 is located in the first material 18. The first material 18 and the second material 19 are joined along a boundary surface 20.

Fig. 5 shows an embodiment according to the present invention of a cutting blade 1 with a first face 2 and a second face 3. The second face 3 has a primary bevel 5, a secondary bevel 6 and a tertiary bevel 7. On the first face 2 between the surface 9 and the cutting edge 4, a further quaternary bevel 8 is located. The angle between the quaternary bevel 8 and the surface 9 is 0 ₄ . The wedge angle 0 ₂ between the primary bevel 5 and the surface 9 is smaller than the wedge angle 0i between the secondary bevel 6 and the surface 9. Moreover, the wedge angle 0 ₃ between the tertiary bevel 7 and the surface 9 is larger than 02

In Fig. 6 a perspective view of a further cutting blade according to the present invention is shown. The cutting blade 1 has a blade body 15 which comprises a first face 2 and a second face 3 which is opposed to the first face 2. A cutting edge 4 is located at the intersection of the first face 2 and the second face 3 and is shaped not straight but consisting of curved segments. The first face 2 comprises a planar surface 9 while the second surface 3 is segmented in a pri mary bevel 5, a secondary bevel 6 and a tertiary bevel 7. The primary bevel 5 is connected via an intersecting line 10 with the secondary bevel 6 which on the other end is connected to the tertiary bevel 7 via an intersecting line 11. The intersecting lines 10 and 11 follow the shape of the cutting edge 4 and are therefore shaped not straight but consisting of curved segments as well.

In Fig. 7 a flow chart of the inventive process is shown. In a first step 1, a silicon wafer 101 is coated by PE-CVD or thermal treatment (low pressure CVD) with a silicon nitride (S INU) layer 102 as protection layerforthe silicon. The layerthick ness and deposition procedure must be chosen carefully to enable sufficient chemical stability to withstand the following etching steps. In step 2, a photo resist 103 is deposited onto the S13N4 coated substrate and subsequently pat terned by photolithography. The (S13N4) layer is then structured by e.g. CF4- plasma reactive ion etching (RIE) using the patterned photoresist as mask. After patterning, the photoresist 103 is stripped by organic solvents in step 3. The remaining, patterned S13N4 layer 102 serves as a mask for the following pre structuring step 4 of the silicon wafer 101 e.g. by anisotropic wet chemical etch ing in KOH. The etching process is ended when the structures on the second face 3 have reached a predetermined depth and a continuous silicon first face 2 remains. Other wet- and dry chemical processes may be suited, e.g. isotropic wet chemical etching in HF/HNO3 solutions or the application of fluorine con taining plasmas. In the following step 5, the remaining S13N4 is removed by, e.g. hydrofluoric acid (HF) or fluorine plasma treatment. In step 6, the pre-struc- tured Si-substrate is coated with an approx. 10 pm thin diamond layer 104, e.g. nano-crystalline diamond. The diamond layer 104 can be deposited onto the pre-structured second surface 3 and the continuous first surface 2 of the Si- wafer 101 (as shown in step 6) or only on the continuous fist surface 2 of the Si-wafer (not shown here). In the case of double-sided coating, the diamond layer 104 on the structured second surface 3 has to be removed in a further step 7 prior to the following edge formation steps 9-11 of the cutting blade. The selective removal of the diamond layer 104 is performed e.g. by using an Ar/0 ₂ - plasma (e.g. RIE or ICP mode), which shows a high selectivity towards the silicon substrate. In step 8, the silicon wafer 101 is thinned so that the diamond layer 104 is partially free standing without substrate material and the desired sub strate thickness is achieved in the remaining regions. This step can be per formed by wet chemical etching in KOH or HF/HNO3 etchants or preferably by plasma etching in CF4, SF ₆ , or CHF3 containing plasmas in RIE or ICP mode. Add ing O2 to the plasma process will yield in a cutting edge formation of the dia mond film (as shown in step 9). Process details are disclosed for instance in DE 198 59 905 Al.

In Fig. 8, it is shown how the tip radius can be determined. The tip radius is determined by first drawing a line 60 bisecting the cross-sectional image of the first bevel of the cutting edge 1 in half. Where line 60 bisects the first bevel point 65 is drawn. A second line 61 is drawn perpendicular to line 60 at a dis- tance of 110 nm from point 65. Where line 61 bisects the first bevel two addi tional points 66 and 67 are drawn. A circle 62 is then constructed from points 65, 66 and 67. The radius of circle 62 is the tip radius of the cutting edge 4.