Abstract:
The present invention relates to a process for forming a razor blade. The process includes the steps of: a) providing a substrate, b) forming a wedge-shaped sharpened edge on the substrate that has an included angle of less than thirty degrees and a tip radius of less than 1,000 angstroms, c) placing the substrate in a vacuum chamber, d) placing a first solid target in the vacuum chamber, e) providing a gas to be ionized in the vacuum chamber, and f) generating ions from the first solid target by applying a negative voltage to the first solid target in pulses, the ions forming a thin film coating on the wedge-shaped sharpened edge on the substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to improved razors and razor blades and to processes for producing razor blades or similar cutting tools with sharp and durable cutting edges. 
       BACKGROUND OF THE INVENTION 
       [0002]    A razor blade typically is formed of suitable substrate material such as metal or ceramic. An edge is formed in the razor blade with a wedge-shape configuration having an ultimate edge or tip that has a radius of less than about 1000 angstroms, the wedge shaped surfaces having an included angle of less than 30°. As the shaving action is severe and blade edge damage frequently results, in order to enhance shavability, the use of one or more layers of supplemental coating material has been proposed for shave facilitation, and/or to increase the hardness, strength and/or corrosion resistance of the shaving edge. A number of such coating materials has been proposed, such as polymeric materials, metals and alloys, as well as other materials including diamond and diamond-like carbon material. Diamond and diamond-like carbon materials may be characterized as having substantial sp3 carbon bonding; a mass density greater than 2.5 grams/cm 3 ; and a Raman peak at about 133 cm −1  (diamond) or about 1550 cm −1  (diamond-like carbon). Each such layer or layers of supplemental material desirably provides characteristics such as improved shavability, improved hardness, edge strength and/or corrosion resistance while not adversely affecting the geometry and cutting effectiveness of the shaving edge. However, such proposals have not been satisfactory due to the tendency of the diamond or diamond-like coated edge to have poor adhesion to and to peel off from the wedge-shaped edge of the substrate. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed to a process for forming a razor blade. The process comprises the steps of: 
         [0000]    a) providing a substrate;
 
b) forming a wedge-shaped sharpened edge on said substrate that has an included angle of less than thirty degrees and a tip radius of less than 1,000 angstroms;
 
C) placing said substrate in a vacuum chamber;
 
d) placing a first solid target in said vacuum chamber;
 
e) providing a gas to be ionized in said vacuum chamber; and
 
f) generating ions from said first solid target by applying a negative voltage to said first solid target in pulses, said ions forming a thin film coating on the wedge-shaped sharpened edge on the substrate.
 
         [0004]    The first solid target may be a metal, carbon or boron. The metal may be selected from the group consisting of Al, Nb, Zr, Cr, V, Ta, Ti, W, Ni, Hf, Si, Mo and an alloy comprising any combination of the elements of the group. 
         [0005]    The process may comprise the additional step of g) generating additional ions from said first solid target by applying a second lower negative voltage to said first solid target in pulses, said ions forming a thin film coating on the wedge-shaped sharpened edge on the substrate. 
         [0006]    The process may comprise the additional step of: g) pivoting said substrate about an axis during step f). 
         [0007]    The process may comprise the additional steps of: g) placing a second solid target in said vacuum chamber and h) generating ions from said second solid target by applying a negative voltage to said second solid target in pulses, said ions forming a thin film coating on the wedge-shaped sharpened edge on the substrate. The second solid target may be placed in a different position relative to said substrate than said first solid target. 
         [0008]    The pulses of step f) may be provided in such a way that a peak power density is developed in a pulse in the range of 0.1 kW/cm 2  to 20 kW/cm 2 . The pulses of step f) may be provided at a pulse frequency in the range of 5 Hz to 10,000 Hz. The pulses of step f) may be generated to have a voltage in the range of −100 V to −10000 V. The pulses of step f) may be generated to have a duration in the range of 10 μs to 10000 μs. The pulses of step f) may be generated to have a current density on the target in the range of 0.1 to 10 A/cm 2 . 
         [0009]    The substrate may be biased in the range of −20 V to −1000 V. 14. 
         [0010]    The gas may be selected from the group consisting of inert gas such as Ar, Ne, Kr, Xe and reactive gasses such as N 2 , CH 4 , C 2 H 2 , O 2  and all possible combinations including inert and reactive gasses. The gas may be at a pressure in the range of 1-10 millitorr. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following description taken in conjunction with the accompanying drawings. 
           [0012]      FIG. 1  is a perspective view of a shaving unit in accordance with the present invention. 
           [0013]      FIG. 2  is a perspective view of another shaving unit in accordance with the present invention. 
           [0014]      FIG. 3  is a diagrammatic view illustrating one example of razor blade edge geometry in accordance with the present invention. 
           [0015]      FIG. 4  is a diagrammatic view of an apparatus for carrying out the process of the present invention. 
           [0016]      FIG. 5  is a diagrammatic view of an alternative apparatus for carrying out the process of the present invention. 
           [0017]      FIG. 6  is a diagrammatic view of another alternative apparatus for carrying out the process of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    With reference to  FIG. 1 , shaving unit  10  includes structure for attachment to a razor handle and a platform member  12  molded of high impact plastic that includes structure defining forward, transversely extending skin engaging surface  14 . Mounted on platform member  12  are leading blade  16  having a sharpened edge  18  and following blade  20  having a sharpened edge  22 . Cap member  24  of molded plastic has structure defining skin engaging surface  26  that is disposed rearwardly of blade edge  22 , and affixed to cap member  24  is shaving aid composite  28 . 
         [0019]    The shaving unit  30  shown in  FIG. 2  is of the type shown in Jacobson U.S. Pat. No. 4,586,255 and includes molded body  32  with front portion  34  and rear portion  36 . Resiliently secured in body  32  are guard member  38 , leading blade unit  40  and trailing blade unit  42 . Each blade unit  40 ,  42  includes a blade member  44  that has a sharpened edge  46 . A shaving aid composite  48  is frictionally secured in a recess in rear portion  36 . 
         [0020]    A diagrammatic view of the edge region of the blades  16 ,  20  and  44  is shown in  FIG. 3 . The blade includes a stainless steel body portion  50  with a wedge-shaped sharpened edge formed in a sequence of edge forming operations that include a grinding operation, a rough honing operation, and a finish honing operation that forms a tip portion  52  that has a radius typically less than 1,000 angstroms with finish hone facets  54  and  56  that diverge at an angle of less than about 30° and merge with rough hone facets  58 ,  60 . More preferably, the tip portion  52  has a radius of less than 750 angstroms and an includes angle of less than about 30° and most preferably, the tip portion  52  has a radius of less than 500 angstroms and an included angle of less than about 25°. Deposited on tip  52  and facets  54 - 60  is thin film layer or coating  62  of chromium nitride that has a thickness of less than about 3000 angstroms, more preferably less than about 2000 angstroms and most preferably less than about 1000 angstroms. Deposited on thin film layer  62  is an optional adherent telomer layer  68 . 
         [0021]    Apparatus  70  for processing blades of the type shown in  FIG. 3  is diagrammatically illustrated in  FIG. 4 . Apparatus  70  includes a stainless steel vacuum chamber  71  with wall structure  72 , door  73  and base structure  74  in which is formed port  76  coupled to a suitable vacuum pumping system (not shown). Mounted in vacuum chamber  71  is support  78  with upstanding support member  80  on which is disposed a stack of razor blades  82  with their sharpened edges  84  in alignment and facing outwardly from support member  80 . Also disposed in vacuum chamber  71  is support structure  85  for target member  86  of chromium (Cr). Target  86  is a vertically disposed plate about twelve centimeters wide and about thirty-seven centimeters long. Support structures  78  and  85  are electrically isolated from vacuum chamber  71  and electrical connections are provided to connect blade stack  82  to a bias power supply  92  through switch  93  and target  86  connected through switch  95  to power supply  98 . Shutter structure  100  is disposed adjacent target  86  for movement between an open position and a position obscuring its adjacent target. 
         [0022]    Support member  80  supports the blade stack  82  with the blade edges  84  spaced about seven centimeters from the opposed target  86 . Support member  80  may be pivotable about an axis such that sharpened blade edge may be positioned at differing angles with respect to target member  86 . 
         [0023]    In a particular processing sequence, a stack of blades  82  (thirty centimeters high) is secured to support member  80 . Vacuum chamber  71  is evacuated. Target  86  is cleaned by high power impulse magnetron sputtering (HIPIMS) for five minutes. HIPIMS is a short pulse (impulse) sputtering method utilizing high powers. Cleaning of target  86  is carried out in an argon environment at a pressure of 3 millitorr. Switch  95  is opened, power is supplied by power source  98  at a voltage of −1200V, a current of 1600 A and a peak power of 1.6 kW/cm 2  increased gradually during the process. Pulse frequency is set at 100 Hz, with a pulse duration of 40 μs. 
         [0024]    The cleaning of target  86  may be carried out at other settings such as at a pressure in the range of 1 to 5 millitorr, a voltage in the range of −500 V to −2500 V, a current in the range of 500 A to 2500 A, a peak power in the range of 0.1 kW/cm 2  to 20.0 kW/cm 2 , a pulse frequency in the range of 50 Hz to 200 Hz, and a pulse duration in the range of 10 μs to 500 μs. 
         [0025]    Blades  82  are then pre-treated or ion etched in an argon environment at a pressure of 1 millitorr for 5 minutes. Shutter  100  is in open position. Power is supplied to target  86  by power source  98  at a voltage of −1000 V, a pulse current of 1500 A and a peak power of 1.25 kW/cm 2  increased gradually during the process. Pulse frequency is set at 105 Hz, with a pulse duration of 50 μs. The blades are biased by power supplied from power source  92  to a high voltage that may be ramped from a low value up to the range of −500 V to −1000 V and an average current of 2.5 A. Shutter  100  remains opened. In these conditions the ion current density to the blades is 0.2 Acm −2  in the peak. A substantial portion of the sputtered metal flux is ionized with metal ion fractions reaching 30%. A significant fraction of metal ions are doubly-ionized. Under these conditions high-energy metal ion bombardment of the blade edges occurs. The ion bombardment has the effect of incorporation of the etching metal, i.e., chromium, into the blade edge to depths of about 30 nm. Such incorporation leads to better adhesion of the coating to the blade edge via a mechanism of epitaxial coating growth localized on individual grains of the blade edge. Switches  93  and  95  are then closed at the end of the ion etching cycle. 
         [0026]    The ion etching may be carried out at other settings such as at a pressure in the range of 0.5 to 5 millitorr for 1-10 minutes. Power may be supplied to target  86  by power source  98  at a voltage in the range of −500 V to −3000 V, a current in the range of 500 A to 3000 A, a peak power in the range of 0.1 to 20 kW/cm 2 , a pulse frequency in the range of 50 to 300 Hz, and pulse duration in the range of 1 to 1000 μs. The blades may be biased by power supplied from power source  92  to a high voltage that may be ramped from a low value up to the range of −500 V to −1000 V and a current in the range of 1.0 to 2.5 A. The peak ion current density to the blades may be from 0.01 to 0.5 Acm −2 . 
         [0027]    Blades  82  are then coated with a thin film coating of CrN in an argon and nitrogen environment. After the substrate cleaning cycle, the shutter remains opened, 200 sccm of nitrogen gas and 150 sccm of argon gas starts flowing into chamber  71 , the cathode power and bias voltage are switched on at the same time. Argon is at a partial pressure of 2 millitorr and nitrogen is at a partial pressure of 1 millitorr. Shutter  100  in front of chromium target  86  is in a open position. Power is supplied to chromium target  86  by power source  98  at a voltage of −700 V, a current of 700 A and a peak power of 0.5 MW constant during the process. Pulse frequency is set at 200 Hz, with a pulse duration of 100 μs. The blades are biased by power supplied from power source  92  to a high voltage in the range of −50 V to −1000 V and an average current of 1 A. In these conditions the peak ion current density to the blades is 0.4 Acm −2 . A substantial portion of the ion flux is ionized with metal ion fractions reaching 15%. A significant fraction of metal ions are doubly-ionized and significant fraction of nitrogen molecules are dissociated. Under these conditions high-energy metal ion bombardment of the blade edges occurs. The ion bombardment coats the metal onto the blade edge. The thickness of the metal coating on the blade edge may be from 50 to 5000 angstroms. 
         [0028]    The blade coating may be carried out at other settings such as 25 to 500 sccm of nitrogen gas, 25 to 500 sccm of argon gas, argon pressure in the range of 1 to 10 millitorr, nitrogen pressure in the range of 1 to 10 millitorr. Power may be supplied to chromium target  86  by power source  98  at a voltage in the range of −100 V to −10000 V, a current in the range of 100 A to 5000 A, and a peak power in the range of 0.1 to 20 kW/cm 2 , pulse frequency in the range of 5 to 10000 Hz, and a pulse duration in the range of 10 to 10000 μs. The blades may be biased by power supplied from power source  92  to a high voltage in the range of −20 V to −1000 V and a current in the range of 0.1 A to 10 A. The ion current density to the blades may be in the range of 0.01 to 0.5 Acm −2  in the peak. 
         [0029]    The target member  86  may be comprised of metal, carbon or boron. Metals for the target member  86  may be selected from the group consisting of Al, Nb, Zr, Cr, V, Ta, Ti, W, Ni, Hf, Si, Mo, and an alloy comprising any combination of elements of the group. 
         [0030]    An optional coating of polytetraflouroethylene (PTFE) telomer may be applied to the CrN coated edges of the blades in accordance with the teaching of U.S. Pat. No. 3,518,110. The process involves heating the blades in a neutral atmosphere of argon and providing on the cutting edges of the blades an adherent and friction reducing polymer coating of solid PTFE. The telomer coating may have a thickness in the range of 100 to 2000 angstroms. 
         [0031]    Referring now to  FIG. 5  there is shown an alternative apparatus  170  for processing blades of the type shown in  FIG. 3 . Apparatus  170  includes a stainless steel vacuum chamber  171  with wall structure  172 , door  173  and base structure  174  in which is formed port  176  coupled to a suitable vacuum system (not shown). Mounted in vacuum chamber  171  is support  178  with upstanding support member  180  on which is disposed a stack of razor blades  182  with their sharpened edges  184  facing outwardly from support member  180 . Also disposed in vacuum chamber  171  is support structure  185  for target member  186 . Target  186  is a vertically disposed plate about twelve centimeters wide and about thirty-seven centimeters long. Support structures  178  and  185  are electrically isolated from vacuum chamber  171  and electrical connections are provided to connect blade stack  182  to a bias power supply  192  through switch  193  and target  186  connected through switch  195  to power supply  198 . Shutter structure  200  is disposed adjacent target  186  for movement between an open position and a position obscuring its adjacent target. 
         [0032]    Support member  180  supports the blade stack  182  with the blade edges  184  spaced about seven centimeters from the opposed target  186 . Support member  180  is pivotable about pivot axis  179  such that sharpened blade edge can be positioned at differing angles with respect to target member  186 . Arrows  202  and  203  indicate the direction of pivotal movement of support member  180  carrying blade stack  182  with blade edges  184  about pivot axis  179 . By pivoting the blade edges  184  about pivot axis  179  multiple facets of the wedge-shaped sharpened edge can be coated with a thin film coating of CrN. The pivoting may take place in one or both of the ion etching or thin film coating operations. 
         [0033]    Referring now to  FIG. 6  there is shown an alternative apparatus  270  for processing blades of the type shown in  FIG. 3 . Apparatus  270  includes a stainless steel vacuum chamber  271  with wall structure  272 , door  273  and base structure  274  in which is formed port  276  coupled to a suitable vacuum system (not shown). Mounted in vacuum chamber  271  is support  278  with upstanding support member  280  on which is disposed a stack of razor blades  282  with their sharpened edges  284  facing outwardly from support member  280 . Also disposed in vacuum chamber  271  are two support structures  285  for target members  286 . Each target  286  is a vertically disposed plate about twelve centimeters wide and about thirty-seven centimeters long. Support structures  278  and  285  are electrically isolated from vacuum chamber  271  and electrical connections are provided to connect blade stack  282  to a bias power supply  292  through switch  293  and targets  286  connected through switch  295  to power supply  298 . Shutter structures  300  are disposed adjacent each target  286  for movement between an open position and a position obscuring its adjacent target. 
         [0034]    Each target  286  is placed in different positions within chamber  271  relative to blade stack  282  so as to be at different angles with respect to the facets of the wedge-shaped sharpened edge. Both targets are utilized in both the ion etching and thin film coating operations. 
         [0035]    The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” 
         [0036]    All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
         [0037]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.