WO2006079360A1

WO2006079360A1 - Razor blade, razor head, razor and method of manufacturing a razor blade

Info

Publication number: WO2006079360A1
Application number: PCT/EP2005/001522
Authority: WO
Inventors: Vassilis Papachristos; Michalis Karoussis; Dimitris Pissimissis; Cédric Ducros; Frédéric Sanchette
Original assignee: Bic Violex Sa
Priority date: 2005-01-27
Filing date: 2005-01-27
Publication date: 2006-08-03

Abstract

A razor blade (1) comprises a razor blade edge (2) which comprises a substrate and a coating (6) on the substrate. The coating comprises a plurality of superimposed sets of a first (7) and a second (8) layer. The sets comprise nitrogen.

Description

Razor blade , razor head, razor and method of manufacturing a razor blade

FIELD OF THE INVENTION The invention relates to razor blades and methods of manufacturing a razor blade .

BACKGROUND OF THE INVENTION

In particular, the invention is related to a razor blade comprising a razor blade edge which comprises a substrate and a coating on said substrate, said coating comprising a plurality of superimposed sets of at least a first and a second layer .

Such razor blades have been studied for some time , and provide interesting strength properties due to the particular structure of their coatings , which comprise alternating layers of two materials .

SUMMARY OF THE INVENTION

It is an obj ect of the present invention to provide a new razor blade comprising a blade edge with improved combined hardness , wear resistance, strength, durability and shaving performance .

To this end, the invention provides a razor blade comprising a razor blade edge which comprises a substrate and a coating on said substrate, said coating comprising a plurality of superimposed sets of at least a first and a second layer, wherein said sets comprise nitrogen . It has been noticed by the inventors that these particular razor blades provide improved combined hardness , wear resistance, strength, durability and shaving performance .

In particular embodiments of the razor blade according to the invention, one might also use the following features : said first layer comprises a compound of nitrogen and at least a first material taken in the following list for a first material : Chromium, Tungsten,

Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon; said compound of the first layer is a nitride of said first material; said compound of the first layer is a solid solution of nitrogen in said first material; - said compound of the first layer is a supersaturated solid solution of nitrogen in said first material ; said compound of the first layer is a mixture of a nitride of said first material and of a solid solution of nitrogen in said first material ; said second layer includes said first material ; said second layer comprises a compound of nitrogen and at least a second material taken in the following list for a second material : Chromium, Tungsten,

Titanium, Vanadium, Aluminium, Zirconium, Niobium,

Molybdenum, Silicon, Boron or Carbon; said compound of the second layer is a nitride of said second material; - said compound of the second layer is a solid solution of nitrogen in said second material; said compound of the second layer is a supersaturated solid solution of nitrogen in said second material; - said compound of the second layer is a mixture of a nitride of said second material and solid solution of nitrogen in said second material; each set of the plurality of sets is made of only two layers ; - the sets are substantially identical ; said sets form a strengthening coating, said razor blade edge further comprising an interlayer between said substrate and said strengthening coating;

- . said interlayer comprises at least one material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon; said interlayer comprises a content of nitrogen increasing as a distance from the razor blade edge substrate increases ; said sets form a strengthening coating, said razor blade edge further comprising a top layer on said strengthening coating; said top layer comprises at least one material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon; said top layer comprises a content of nitrogen decreasing as a distance from the razor blade edge substrate increases; said razor blade edge further comprises an overcoat PTFE layer; said edge comprises two sides j oining at a tip; - each layer of said sets has a thickness comprised between 0.5 and 10 nm, preferentially comprised between 2 and 5 nm; said substrate is made of stainless steel; said coating comprises alternating Titanium nitride and Chromium nitride layers ; said coating comprises alternating solid solution of nitrogen in Chromium and solid solution of nitrogen in Titanium layers ; said coating comprises alternating solid solution of nitrogen in carbon and solid solution of nitrogen in Titanium layers ;

According to another aspect, the invention provides a razor head comprising at least one such razor blade .

According to another aspect , the invention provides a shaver comprising such a razor head .

According to another aspect, the invention provides a method of manufacturing a razor blade comprising a razor blade edge which comprises a substrate and a coating covering said substrate, said coating comprising a plurality of superimposed sets of at least a first and a second layer, said method comprising a step (a) wherein, in an enclosure comprising at least a first and a second sources respectively comprising a first and a second material, and in which enclosure an atmosphere is established, said razor blade is submitted to a movement relative to said first and second sources so that it subsequently passes in front of said first and second sources , while said first and second sources are operated to release said first and second materials into said enclosure, wherein, at least one of said atmosphere, first and second matter sources includes nitrogen .

In particular embodiments of the method according to the invention, one might also use the following features : said first and second sources are sputter targets each comprising a material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon, wherein said sputter targets are operated by bombardment of argon ions in a nitrogen-containing atmosphere; said first and second sources are sputter targets at least one of which comprises a compound of nitrogen of a material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon, wherein said sputter targets are operated by bombardment of argon ions ;

- during step (a ) , a voltage bias is applied on the razor blade .

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from the following description, drawings and claims . On the drawings :

Fig . 1 is a view of a first embodiment of a razor blade edge ,

Fig . 2 is a view of a second embodiment of a razor blade edge , - Fig . 3 is a view of a third embodiment of a razor blade edge,

Fig . 4 is a view of an apparatus suitable for obtaining a blade edge according to any of Fig . 1 to 3 , and Fig . 5 is a schematic view of a mechanical shaver .

On the drawings , corresponding or similar elements have the same reference numbers . MORE DETAILED DESCRIPTION

Fig . 1 is a sectional view of the edge 1 of a razor blade for a mechanical razor . The razor blade edge is formed from a razor blade edge substrate 2 , of for example stainless steel , ceramic, or other suitable material . The razor blade edge substrate 2 might have previously been submitted to shaping operations , such as grinding operations , in order to provide the shape of a tip, of included angle about 10° to 50 ° , which is located at the j unction of two adj acent sides 4 and 5 , which are for example straight as schematically shown on Fig . 1 , or exhibit a gothic arch configuration . The sides 4 , 5 and tip 3 of the razor blade edge substrate 2 are covered, by a coating 6 which is made of a plurality of superimposed sets of alternating layers 7 , 8 of at least two different materials . Each layer can be between 0.5 and 10 nm thick and more preferably between 2 nm and 5 nm. The coating 6 can be as thin as about 20 to 200 nm thick and yet provide strength, hardness , durability and shaving performance similar or better than those of previous coatings . The coating 6 could be further covered by a PTFE overcoat layer 9 , or another similar coating having lubricating properties .

According to the invention, one or both of first and second layers 7 , 8 will comprise a nitrogen compound .

According to a first example, each set comprises a first layer 7 of a nitride of a first material , said first material being taken in the list Chromium (Cr) , Tungsten (W) , Titanium (Ti ) , Vanadium (V) , Aluminium (Al) , Zirconium ( Zr) , Niobium (Nb) , Molybdenum (Mo) , Silicon ( Si ) , Boron (B) or Carbon (C) . Each set also comprises a second layer 8 of a second material taken in the preceding list . According to a first type of coating, the first material taken for forming the material nitride in the first layer 7 and the second material taken in the second layer 8 are the same . According to a second type of coating, they are different materials . Also, a suitable coating could be obtained with the second layer 8 containing a material nitride, and the first layer 7 containing a material .

According to a second example, the first layer 7 is still a material nitride, while the second layer 8 is also a material nitride, the materials still being taken in the above list , the second material of the second layer 8 being different from the first material of the first layer 7.

According to a third example, the first layer 7 is a solid solution of nitrogen in a first material taken in the above list . The second layer 8 is a second material taken in the above list . Such a solid solution of nitrogen could be supersaturated, if an excess amount of nitrogen is introduced in the layer . In addition, the first layer 7 could include some parts in material nitride phase . The first material forming a compound with nitrogen in the first layer 7 could be the same as the second material of the second layer 8 , or a different one . Also, a suitable coating could be obtained with the second layer 8 containing the solid solution of nitrogen in a material , and the first layer 7 containing a material . According to a fourth example, the first layer 7 includes a solid solution of nitrogen in a first material taken in the above list, and the second layer 8 includes a solid solution of nitrogen in a second material taken in the above list, the second material being different from the first material .

According to a fifth example, the first layer 7 is a ( supersaturated) solid solution of nitrogen in a first material of the above list . The second layer 8 includes a nitride of a second material of the above list, said second material being the same , or a different material from the first material of the first layer 7. Also, a suitable coating could be obtained with the second layer 8 comprising a solid solution of nitrogen in the material and the first layer 7 comprising a material nitride . In each set, the first layer 7 and the second layer 8 could be of the same thickness , or of different thicknesses . Also, first and second layers of two adj acent sets could have the same or different thicknesses .

When crystalline first and second layers 7 , 8 are formed, a coherent super lattice structure may be obtained by the repetition of the sets of layers . Such super lattice coatings form hard coatings , with their hardness depending on the thickness period, the properties of the individual layers , and of course the parameters of the used deposition method . Such super lattice coatings can also exhibit reduced internal stresses of the whole coating when compared to single layers of the same constituents .

A second embodiment is shown schematically on Fig .

2. As compared with the razor blade described with respect to Fig . 1 , an interlayer 10 is deposited between the razor blade edge substrate and the coating 6. The interlayer 10 is for example 10 to 50 nm thick and is made for example of a material or a mixture of the materials taken in the above list . This interlayer could be totally nitrogen free, or a compound of a material of the above list and nitrogen . If the first layer of the next set contains nitrogen, it can include an increasing content of nitrogen, as the distance from the surface of the razor blade edge substrate increases , so as to form a smooth transition between the interlayer 10 and the nitrogen-containing first layer 7 of the adj acent set of the coating 6.

A third embodiment is shown schematically on Fig .

3. As compared with the coatings 6 described with respect to Fig . 1 , a top layer 11 is deposited between the coating 6 and the PTFE overcoat layer 9. The top layer 11 is for example 5 to 30 nm thick and is made for example of a material or a mixture of the materials taken in the above list . This top layer could be totally nitrogen free, or a nitrogen compound . If the last layer of the last set contains nitrogen, it could include a decreasing content of nitrogen, as the distance from the surface of the razor blade edge substrate increases , so as to form a smooth transition between the ultimate nitrogen-containing layer of the coating 6 and the adj acent PTFE overcoat layer 9. Of course, the embodiments of Fig . 2 and Fig . 3 could be combined in order to obtain a razor blade comprising a razor blade edge substrate coated with an interlayer 10 , coating 6, a top layer 11 and PTFE overcoat layer 9. All coatings could be deposited by a PVD method, such as , for example , magnetron sputtering . Alternately, other suitable techniques could be used . For example, Fig . 4 shows an apparatus that could be used for the deposition . An enclosure 12 comprises two sources , for example first and second sputter targets 13 , 14 , facing each other . The first target 13 comprises a first material to be deposited, and the second sputter target 14 comprises a possibly different second material . Each of the first and second sputter targets 13, 14 can be supported by a respective first and second magnetic device 23 , 24 for example of the type comprising two side magnets 23b, 23c, and a central magnet 23a of opposite polarity, as shown in detail for first magnetic device 23. For example, the second magnetic device 24 can be of opposite polarity, the central magnet 24a being of the same polarity as side magnets 23b and 23c, and the side magnets 24b and 24c being of the opposite polarity of the central magnet 24a . The above description is purely exemplary, and more than two targets could be used . Each sputter target 13 , 14 can be operated by applying a DC current and voltage to the sputter target . A gas source (not shown) delivers argon gas or a mixture of argon and N₂ gas to form an atmosphere in the enclosure . Argon ions Ar+ impinging on the targets will release the material of the target into the enclosure . If the enclosure contains N₂, the released material might at least partially react with the N₂ gas in order to form a nitrogen compound .

The razor blade substrates are stacked in bayonets on a rotating carousel 17 which can be moved so that the edge of the razor blade substrates are subsequently displaced in the vicinity of the two matter sources . The released material and/or nitrogen compounds deposit on the razor blade edge substrates .

A voltage bias of up to 1000 V can be applied on the razor blades in a DC mode or pulsed DC mode . Thus , it is possible that some of the sputter targets 13, 14 hold one of the nitrogen-containing material to be deposited, or that targets are sputtered in a nitrogen-containing atmosphere, or both .

For applying an interlayer or a top layer, the sputter targets comprising the material ( s ) to be part of the interlayer or top layer are operated . By changing the nitrogen flow rate into the enclosure, the concentration of nitrogen in the interlayer or top layer can be varied .

In general , the values of the applied current or power intensities on the targets , the relative speed of the blades with respect to the targets , the bias voltage applied and the N₂ partial flow will define the properties of the coating .

Of course , only an exemplary deposition method is given here . Another in-line PVD apparatus could be used, wherein the razor blade substrates are stacked in a razor blade holder that is moved back and forth along a linear track passing in front of two or more sputter targets of the above-mentioned type . Prior to the deposition of the coating, a sputter etching step could be applied in order to clean the tip of the blade substrates . Another sputter-etching step could again be applied after the deposition of the coating 6 or top layer 11 , when appropriate, and before the application of PTFE .

Other deposition methods are believed to be of possible use in order to obtain razor blades as exemplified on Fig . 1 to 3 , and including for example RF sputtering, ion plating, ion beam assisted deposition, or other deposition methods .

After the coatings 6, and possibly 10 and 11 have been applied, a PTFE overcoat layer 9 can be applied, for example by spraying PTFE on the coated blade , or by other suitable method . As shown on Fig . 5 , the obtained blades could be mounted in a razor head containing one , two, three or more blades . The razor head could be held fixedly or removably on a mechanical razor handle 16 in order to form a shaver 18. Three exemplary detailed embodiments are described below with reference to Fig . 4 :

Example 1 - ( solid solution Cr (N) /Ti (N) coating) After loading the bayonets containing the blade substrates into the enclosure , the enclosure 12 is evacuated down to a base pressure . First , a sputter etching step is performed . Ar gas is inserted into the chamber up to a pressure suitable for sputter etching . Motion of the bayonets begins at a constant speed that brings the bayonets repeatedly in front of Cr 13 and Ti 14 targets . Both Cr and Ti targets are operated under DC current control and a DC voltage is applied on the blade substrates for 4 minutes .

After the end of the sputter etching step the enclosure pressure is adj usted for the interlayer deposition step . The Cr and Ti targets are operated under DC current control at 3 A while a DC voltage of 300 V is applied on the blade substrates . Adj usting the deposition time and the traveling speed of the blade bayonets , a Cr-Ti alloy interlayer 10 of 20 nm is deposited on the edges . After the deposition of the Cr-Ti alloy interlayer, the current on Cr and Ti targets is adj usted to 6 and 10 A respectively, while at the same time N₂ is inserted inside the chamber . The partial flow of N₂ (N₂ flow / total flow in seem) is adj usted to 0.16. A negative DC voltage of 300 V is applied on the blade substrates moving at about 1.5 rpm. Adj usting the deposition time and traveling speed a Cr (N) /Ti (N) coating consisting of a plurality of sets of alternate layers of crystalline Cr (N) and Ti (N) solid solutions is deposited on the Cr-Ti alloy layer . The total thickness of the Cr (N) /Ti (N) coating is 72 nm and the combined thickness of a Cr (N) and a Ti (N) layer in the coating is 12 nm. On top of the Cr (N) /Ti (N) coating, a fluoropolymer overcoat layer ( PTFE) of 500 nm is deposited, mainly to provide a lower friction of the blade surface . Grazing incidence XRD on coupons of Si-wafer coated with a Cr (N) /Ti (N) coating deposited under identical conditions yielded a crystalline structure with broad peaks corresponding to a stressed lattice, with a lattice parameter between the lattice parameters of Cr and Ti . Results of tests used for investigation of blade cutting performance and strength, showed an improvement for blades coated with the new Cr (N) /Ti (N) coating as compared with standard production Cr-Pt single-layered coated blades . In a series of trials, a test involving the repeating cutting action of the blade on a moving felt using a load cell for measuring the load on the blade for each cut, resulted in load ranges for the first 10 cuts that were at least 5 % lower than the load range of blades with standard production Cr-Pt coating . This result shows that the blades with the Cr (N) /Ti (N) coating preserve their cutting ability (i . e . shape and integrity) in a more effective manner during cutting action .

The damage imposed on the blade edge after 10 cuts during the above-described test was also evaluated with the aid of an optical microscope . The damage on the blade edge was quantified in terms of area of missing material (i . e . material that has been broken and removed from the edge) . Cr (N) /Ti (N) coated blades resulted in 80 % decrease of the missing material area as compared with blades with standard production Cr-Pt coating . This result shows the increased durability of the blades with the new Cr (N) /Ti (N) coating .

Shaving tests in a panel experienced in shaving performance evaluation has shown that the shavers comprising the new blades have performed better than current production shavers in comfort, closeness, irritation, number of nicks/cuts and overall opinion .

Example 2 - ( solid solution Ti (N) /C (N) coating) After loading the bayonets containing the blade substrates into the enclosure, the enclosure is evacuated down to a base pressure . Then Ar gas is inserted into the chamber up to a pressure suitable for sputter etching . Motion of the bayonets begins at a constant speed that brings the bayonets repeatedly in front of the Ti 13 and C 14 targets for a preliminary sputter etching step . Ti target is operated under DC current control and a DC voltage is applied on the blade substrates for 4 minutes .

After the end of the _^ sputter etching step, the enclosure pressure is adj usted for the interlayer deposition step . The Ti targets are operated under DC current control at 3 A while a DC voltage of 300 V is applied on the blade substrates . Adj usting the deposition time a Ti interlayer 10 of 20 nm is deposited on the edges .

After the deposition of the Ti interlayer, the current on Ti target is adj usted to 10 A and the C target is switched on at 12 A . At the same time N₂ is inserted inside the enclosure . The partial flow of N₂ (N₂ flow / total flow in seem) is adjusted to 0.2. A negative DC voltage of 300 V is applied on the blade substrates rotating at about 1.5 rpm. Adj usting the deposition time and traveling speed a Ti (N) /C (N) coating consisting of alternate layers of Ti (N) and C (N) solid solutions is deposited on the Ti interlayer . The total thickness of the Ti (N) /C (N) coating is 70 nm and the combined thickness of a Ti (N) layer and a C (N) layer in the coating is 10 nm. On top of the C (N) /Ti (N) coating, a fluoropolymer overcoat layer ( PTFE) of 500 nm is deposited, mainly to provide a lower friction of the blade surface .

Grazing incidence XRD on coupons of Si-wafer coated with a Ti (N) /C (N) coating deposited under identical conditions yielded a spectrum with broad peaks corresponding only to Ti (N) . This result characterizes an overall structure of low crystallinity confined in the Ti (N) layers . Results of tests used for investigation of blade cutting performance and strength, showed an improvement for blades coated with the new Ti (N) /C (N) coating as compared with standard production Cr-Pt single layered coated blades . In a series of trials , a test involving the repeating cutting action of the blade on a moving felt using a load cell for measuring the load on the blade for each cut, resulted in load ranges for the first 10 cuts that were at least 3% lower than the load range of blades with standard production Cr-Pt coating . This result shows that the blades with the new Ti (N) /C (N) coating preserve their cutting ability ( i . e . shape and integrity) in a more effective manner during cutting action .

The damage imposed on the blade edge after 10 cuts during the above-described test was also evaluated with the aid of an optical microscope . The damage on the blade edge was quantified in terms of area of missing material ( i . e . material that has been broken and removed from the edge ) . C (N) /Ti (N) coated blades resulted in 90 % decrease of the missing material area as compared with blades with standard production Cr-Pt coating . This result shows the increased durability of the blades with the new Ti (N) /C (N) coating .

Shaving tests in a panel experienced in shaving performance evaluation has shown that the shavers comprising the new blades have performed better than current production shavers in comfort, closeness , irritation, number of nicks/cuts and overall opinion .

BEST MODE

Example 3 - (CrN/TiN nitride coating) After loading the bayonets containing the blade substrates into the enclosure , the enclosure is evacuated down to a base pressure . Then Ar gas is inserted into the enclosure up to a pressure suitable for sputter etching step . Motion of the bayonets begins at a constant speed that brings the bayonets repeatedly in front of the Cr 13 and Ti 14 targets for a preliminary sputter etching step .

Both Cr and Ti targets are operated under DC current control and a DC voltage is applied on the blade substrates for 4 minutes . After the end of sputter etching step the enclosure pressure is adj usted for the interlayer deposition step . Cr and Ti targets are operated under DC current control at 3 A while a negative DC voltage of 300 V is applied on the blade substrates . Adjusting the deposition time and the traveling speed of the blade bayonets a Cr-Ti alloy interlayer of 20 nm is deposited on the edges

After the deposition of the Cr-Ti alloy interlayer, the current on Cr and Ti targets is adj usted to 6 and 10 A respectively, while at the same time N₂ is inserted into the chamber . The partial flow of N₂ (N₂ flow / total flow in seem) is adjusted to 0.38. A negative DC voltage of 300 V is applied on the blade substrates rotating at about 1.5 rpm. Adj usting the deposition time and traveling speed a CrN/TiN coating consisting of alternate layers of crystalline CrN and TiN is deposited on the Cr-Ti alloy interlayer . The total thickness of the CrN/TiN coating is 70 nm and the combined thickness of a CrN layer and a TiN layer in the coating is 5 nm. On top of the CrN/TiN coating, a fluoropolymer overcoat layer ( PTFE) of 500 nm is deposited, mainly to provide a lower friction of the blade surface .

Grazing incidence XRD on coupons of Si-wafer coated with a CrN/TiN coating deposited under identical conditions yielded a well-defined crystalline structure with a lattice parameter between the lattice parameters of CrN and TiN . Results of tests used for investigation of blade cutting performance and strength, showed an improvement for blades coated with the CrN/TiN coating as compared with standard production Cr-Pt single layered coated blades . In a series of trials , a test involving the repeating cutting action of the blade on a moving felt using a load cell for measuring the load on the blade for each cut, resulted in load ranges for the first 10 cuts that were at least 8 % lower than the load range of blades with standard production Cr-Pt coating . This result shows that the blades with CrN/TiN coating preserve their cutting ability ( i . e . shape and integrity) in a more effective manner during cutting action .

The damage imposed on the blade edge after 10 cuts during the above-described test was also evaluated with the aid of an optical microscope . The damage on the blade edge was quantified in terms of area of missing material ( i . e . material that has been broken and removed from the edge) . CrN/TiN coated blades resulted in a 90 % decrease of the missing material area as compared with blades with standard production Cr-Pt coating . This result shows the increased durability of the blades with CrN/TiN coating .

Shaving tests in a panel experienced in shaving performance evaluation has shown that the shavers comprising the new blades have performed better than current production shavers in comfort , closeness , irritation, number of nicks/cuts and overall opinion .

Claims

1. A razor blade comprising a razor blade edge which comprises a substrate and a coating on said substrate, said coating comprising a plurality of superimposed sets of at least a first and a second layer, wherein said sets comprise nitrogen .

2. Razor blade according to claim 1 , wherein said first layer comprises a compound of nitrogen and at least a first material taken in the following list for a first material : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon .

3. Razor blade according to claim 2 , wherein said compound of the first layer is a nitride of said first material .

4. Razor blade according to claim 2 , wherein said compound of the first layer is a solid solution of nitrogen in said first material .

5. Razor blade according to claim 2 , wherein said compound of the first layer is a supersaturated solid solution of nitrogen in said first material .

6. Razor blade according to claim 2 , wherein said compound of the first layer is a mixture of a nitride of said first material and of a solid solution of nitrogen in said first material .

7. Razor blade according to any of claims 2 to 6, wherein said second layer includes said first material .

8. Razor blade according to any of the preceding claims , wherein said second layer comprises a compound of nitrogen and at least a second material taken in the following list for a second material : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon .

9. Razor blade according to claim 8 , wherein said compound of the second layer is a nitride of said second material .

10. Razor blade according to claim 8 , wherein said compound of the second layer is a solid solution of nitrogen in said second material .

11. Razor blade according to claim 8 , wherein said compound of the second layer is a supersaturated solid solution of nitrogen in said second material .

12. Razor blade according to claim 8 , wherein said compound of the second layer is a mixture of a nitride of said second material and of a solid solution of nitrogen in said second material .

13. Razor blade according to any of the preceding claims, wherein each set of the plurality of sets is made of only two layers .

14. Razor blade according to any of the preceding claims , wherein the sets are substantially identical .

15. Razor blade according to any of the preceding claims, wherein said sets form a strengthening coating, said razor blade edge further comprising an interlayer between said substrate and said strengthening coating .

16. Razor blade according to claim 15 , wherein said interlayer comprises at least one material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon .

17. Razor blade according to any of claims 15 and 16, wherein said interlayer comprises a content of nitrogen increasing as a distance from the razor blade edge substrate increases .

18. Razor blade according to any of the preceding claims, wherein said sets form a strengthening coating, said razor blade edge further comprising a top layer on said strengthening coating .

19. Razor blade according to claim 18 , wherein said top layer comprises at least one material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon .

20. Razor blade according to claim 18 or claim 19 , wherein said top layer comprises a content of nitrogen decreasing as a distance from the razor blade edge substrate increases .

21. Razor blade according to any of the preceding claims , wherein said razor blade edge further comprises an overcoat PTFE layer .

22. Razor blade according to any of the preceding claims , wherein said edge comprises two sides j oining at a tip .

23. Razor blade according to any of the preceding claims wherein each layer of said sets has a thickness comprised between 0.5 and 10 nm, preferentially comprised between 2 and 5 nm.

24. Razor blade according to any of the preceding claims wherein said substrate is made of stainless steel .

25. Razor blade according to claim 1 , wherein said coating comprises alternating Titanium nitride and Chromium nitride layers .

26. Razor blade according to claim 1 , wherein said coating comprises alternating solid solution of nitrogen in

Chromium and solid solution of nitrogen in Titanium layers .

27. Razor blade according to claim 1 , wherein said coating comprises alternating solid solution of nitrogen in carbon and solid solution of nitrogen in Titanium layers .

28. Razor head comprising at least one razor blade according to any of claims 1 to 27.

29. Shaver comprising a razor head according to claim 28.

30. A method of manufacturing a razor blade comprising a razor blade edge which comprises a substrate and a coating on said substrate, said coating comprising a plurality of superimposed sets of at least a first and a second layer, said method comprising a step (a) wherein, in an enclosure comprising at least a first and a second sources respectively comprising a first and a second material , and in which enclosure an atmosphere is established, said razor blade is submitted to a movement relative to said first and second sources so that it subsequently passes in front of said first and second sources , while said first and second sources are operated to release said first and second materials into said enclosure, wherein, at least one of said atmosphere, first and second matter sources includes nitrogen .

31. A method according to claim 30 , wherein said first and second sources are sputter targets each comprising a material taken in the following list : Chromium, Titanium, Tungsten, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon, wherein said sputter targets are operated by bombardment of argon ions in a nitrogen-containing atmosphere .

32. A method according to claim 30 , wherein said first and second sources are sputter targets at least one of which comprises a compound of nitrogen of a material taken in the following list : Chromium, Tungsten, Titanium, Vanadium, Aluminium, Zirconium, Niobium, Molybdenum, Silicon, Boron or Carbon, wherein said sputter targets are operated by bombardment of argon ions .

33. Method according to claim 30 , wherein during step (a) , a voltage bias is applied on the razor blade .