# Patent

## Title
Razor blades

## Abstract

A razor blade having a substrate with a cutting edge being defined by a sharpened tip. The substrate has thicknesses of 1.60-1.75 micrometers and 9.25-10.00 micrometers measured at a distance of four and forty micrometers from the blade tip, respectively. A ratio of the thickness measured at four micrometers to the thickness measured at forty micrometers is between 0.165-0.185. The substrate thickness is about 2.70-3.00 micrometers at eight micrometers from the blade tip, about 4.44-5.00 micrometers at sixteen micrometers from the blade tip with a thickness ratio measured at four micrometers and eight micrometers between 0.56-0.62, and a thickness ratio measured at four micrometers and sixteen micrometers between 0.32-0.40. The blade edge shape is defined by equation w=adn where “a” is between 0.50-0.62 and “n” is between 0.76-0.80. An included angle of less than 7° is measured at a distance of forty micrometers or greater from the blade tip. A nitrided substrate may also be provided.

## Background
TECHNICAL FIELD
This invention relates to razors and more particularly to razor blades with sharp and durable cutting edges.
BACKGROUND
A razor blade is typically formed of a suitable substrate material such as stainless steel, and a cutting edge is formed with a wedge-shaped configuration with an ultimate tip having a radius. Hard coatings such as diamond, amorphous diamond, diamond-like carbon-(DLC) material, nitrides, carbides, oxides or ceramics are often used to improve strength, corrosion resistance and shaving ability, maintaining needed strength while permitting thinner edges with lower cutting forces to be used. Polytetrafluoroethylene (PTFE) outer layer can be used to provide friction reduction. Interlayers of niobium, chromium, or titanium containing materials can aid in improving the binding between the substrate, typically stainless steel, and hard carbon coatings, such as DLC.
It is desirable to improve the shape of the razor blade substrate to reduce the cutter force needed to cut hair. Such a reduction in cutter force will lead to a more comfortable shave.
SUMMARY
The present invention provides a razor blade comprising a substrate. The substrate has a cutting edge being defined by a sharpened blade tip. The substrate has a thickness of between about 1.60 and 1.75 micrometers measured at a distance of four micrometers from the blade tip, and a thickness of between about 9.25 and 10.00 micrometers measured at a distance of forty micrometers from the blade tip. The substrate has a ratio of the thickness measured at four micrometers to the thickness measured at forty micrometers between 0.165 and 0.185. The substrate has a thickness of between about 2.70 and 3.00 micrometers measured at a distance of eight micrometers from the blade tip, a thickness of between about 4.44 and 5.00 micrometers measured at a distance of sixteen micrometers from the blade tip, a ratio of thickness measured at four micrometers to the thickness measured at eight micrometers between 0.56 and 0.62, and a ratio of thickness measured at four micrometers to the thickness measured at sixteen micrometers between 0.32 and 0.40.
The razor blade of the present invention comprises a cross-sectional shape of the blade edge defined by the equation w=adn, in which “w” is the thickness in micrometers of the blade tip at a distance “d” in micrometers from the blade tip, wherein “a” is a proportionality factor in the range of 0.50 to 0.62, and “n” is in the range of 0.76 to 0.80.
Preferably, the substrate has a tip radius of from about 125 to about 500 angstroms.
The razor blade may comprise an interlayer joined to the substrate. The interlayer preferably comprises niobium, chromium, platinum, titanium, or any combination or alloys thereof. The razor blade may comprise a coating layer joined to the interlayer. The coating layer may comprise a material containing carbon or aluminum magnesium boride. The razor blade may or may not comprise an overcoat layer joined to the coating layer. The overcoat layer preferably comprises chromium. The razor blade may comprise an outer layer joined to the overcoat layer or to the hard coating. The outer layer preferably comprises a polymer, which may comprise polytetrafluoroethylene.
The razor blade may comprise an included angle that is less than 7 degrees. The included is measured at a distance of forty micrometers or greater from the blade tip.
The razor blade substrate may include only two facets on each side of said cutting edge.
The razor blade may include a nitride region disposed at or beneath a surface of the substrate which may be formed by plasma nitriding. One or more layers may be joined to the nitrided substrate.



DESCRIPTION OF DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the present invention, it is believed that the invention will be more fully understood from the following description taken in conjunction with the accompanying drawings.
FIG. 1 is a diagrammatic view illustrating a blade substrate.
FIG. 2 is a graph illustrating the edge profile of a razor blade.
FIG. 3 is a diagrammatic view illustrating a blade substrate.
FIG. 4 is a diagrammatic view illustrating a blade substrate with coatings disposed thereon in an embodiment of the present invention.
FIG. 5 is a diagrammatic view illustrating a blade substrate with coatings disposed thereon in an alternate embodiment of the present invention.
FIG. 6 is a diagrammatic view illustrating a blade substrate with a nitrided region in an alternate embodiment of the present invention.



DETAILED DESCRIPTION
Referring now to FIG. 1, there is shown a razor blade 10. The razor blade 10 includes stainless steel body portion or substrate 11 with a wedge-shaped sharpened edge (or cutting edge) having a tip 12. Tip 12 preferably has a radius of from about 125 to about 500 angstroms with facets 14 and 16 on each edge that diverge from tip 12. The substrate 11 has a thickness 21 of between about 1.60 and 1.75 micrometers measured at a distance 20 of four micrometers from the blade tip 12.
The substrate 11 has a thickness 23 of between about 2.7 and 3.00 micrometers measured at a distance 22 of eight micrometers from the blade tip 12.
The substrate 11 has a thickness 25 of between about 4.44 and 5.0 micrometers measured at a distance 24 of sixteen micrometers from the blade tip 12.
The substrate 11 has a thickness 27 of between about 9.25 and 10.00 micrometers measured at a distance 26 of forty micrometers from the blade tip 12.
The substrate 11 has a ratio of thickness 21 measured at four micrometers from the tip 12 to the thickness 27 measured at forty micrometers from the tip 12 of between 0.165 and 0.185.
The substrate 11 has a ratio of thickness 21 measured at four micrometers from the tip 12 to the thickness 23 measured at eight micrometers from the tip 12 of between 0.56 and 0.62.
The substrate 11 has a ratio of thickness 21 measured at four micrometers from the tip 12 to the thickness 25 measured at sixteen micrometers from the tip 12 of between 0.32 and 0.40.
Table 1 below outlines the values contemplated in the present invention. The units for distance and thickness are micrometers.










TABLE 1









distance from the




blade tip
blade thickness







 4
1.60-1.75



 8
2.70-3.00



16
4.44-5.00



40
 9.25-10.00














ratio of distances




from tip
ratio of thickness







T4/T8 
0.56-0.62



T4/T16
0.32-0.40



T4/T40
0.165-0.185










The thicknesses and ratios of thicknesses provide a framework for improved shaving. The thicknesses and ratios of thickness provide a balance between edge strength and low cutting force or sharpness. A substrate having smaller ratios will have inadequate strength leading to ultimate edge failure. A substrate having greater thicknesses will have a higher cutting force leading to an increased tug and pull and increased discomfort for the user during shaving.
In accordance with the present invention, a cross-sectional shape of blade 10 in the region described in FIG. 1 may be defined by the equation w=adn, in which “w” is the thickness in micrometers of the substrate at a distance “d” in micrometers from the blade tip 12 and in which the variable “a” is a proportionality factor that has a value in the range of 0.50 to 0.62, and the variable “n” is an exponent that has a value which may be in the range of 0.76 to 0.80 for improved edge attributes such as strength, durability, and cutting performance.
A graph 30 of the w=adn equation with “a” in the range of 0.50 to 0.62 and “n” in the range of 0.76 to 0.80 of the present invention is shown in FIG. 2 applying the range of values of thicknesses and distances of FIG. 1 as discussed above.
Area 32 represents the edge profile of the present invention, while the remaining lines 34 illustrate the different edge profiles described in prior art ranges of “a” and “n” and in particular, U.S. Pat. No. 4,720,918. As can be seen from the graph 30, area 32 represents a novel shape over the prior art.
Substrate 11 may be a stainless steel material of any type to facilitate producing an appropriately sharpened edge. The stainless steel of the present invention may preferably be a martensitic stainless steel comprising about 0.35% to about 0.6% Carbon (C) and about 13% to about 14% Chromium (Cr). The martensitic steel may desirably comprise about 1.1% to about 1.5% Molybdenum (Mo).
Additionally, the martensitic stainless steel may contain smaller, more finely distributed carbides, but with similar overall carbon weight percent. A fine carbide substrate provides for a harder and more brittle after-hardening substrates, and enables the making of a thinner, stronger edge. An example of such a substrate material is a martensitic stainless steel with a finer average carbide size with a carbide density of at least about 200 carbides per square micrometer, more preferably at least about 300 carbides per square micrometer and most preferably at least about 400 carbides or more per 100 square micrometers as determined by optical microscopic cross-section.
As discussed above, facets 14 and 16 of FIG. 1 of the wedge-shaped edge of blade 10 diverge from tip 12. In accordance with an alternate preferred embodiment of the present invention, each edge of the wedge-shaped edge of the razor blade of the present invention may also include an additional facet. Turning to FIG. 3, blade 40 of the present invention is shown having a substrate 31 with just two facets on each side or edge. First facets 44, 45 on either edge may generally initially be formed and by known methods (e.g., grinding). Similarly, second facets 42, 43 may subsequently be formed such that they define the final blade tip 41 (e.g., the facets 42, 43 diverge from tip 41). The second facets 42, 43 may have a distance 42a back from the blade tip 41 of about 12 to 50 micrometers. It is noted that a two-stage grinding process may more preferably produce the first and second facets of the present invention. In some applications, a three-stage grinding process, producing a third facet, may be used.
Thus, the present invention contemplates that a sixteen and/or forty micrometer distance from the blade tip 41 may either be disposed within the second facets 42, 43 or within the first facets 44, 45.
First facets 44, 45 generally define an included angle 46 (or 49) which may preferably be below 7 degrees, more preferably between 4-6 degrees, and most preferably about 6 degrees. Included angle 49, as shown, may be determined as half the angle formed between the intersection 47 of extended lines 48 (shown as extending from facets but 44, 45 in dotted lines) of first facets 44, 45 prior to second facets 42, 43 being formed. It should be noted that lines 48 are not part of the substrate 31, serving only to illustrate how the included angle is determined. Included angle 46 may alternately be determined by the angle disposed between a perpendicular or line extension 50 of the blade body 51 to the first facet 44 or 45. Though illustrated at two different locations in the razor, included angle is intended to be substantially identical (e.g., included angle 46 is the same value as angle 49) as they generally represent the same geometry.
The first facets 44, 45 may generally extend a distance 44a of about 175 to about 400 micrometers back from the blade tip 41.
Thus, the present invention contemplates an included angle of less than 7 degrees in the region of the blade having a distance greater than or equal to 40 micrometers back from the blade tip.
Alternately, the present invention preferably contemplates an included angle of less than 7 degrees where the razor blade includes only two facets on each side or edge of the razor blade.
A reduced included angle allows the blades to be slimmer further back on the blade from the tip (e.g., at or beyond the 16 micrometers back from the blade tip region and particularly in the region of 40 to 100 micrometers range back from the blade tip). This, with the geometry (e.g., thicknesses and ratios of thicknesses, etc.) described above, provides a unique combination of sharpness and strength, not recognized in the art.
Referring now to FIG. 4, there is shown a finished first blade 50 of the present invention including a substrate (e.g., substrate 11 of FIG. 1 depicted), interlayer 54, hard coating layer 56, overcoat layer 58, and outer layer 52. The substrate 11 is typically made of stainless steel though other materials can be employed. An example of a razor blade having a substrate, interlayer, hard coating layer, overcoat layer and outer layer is described in U.S. Pat. No. 6,684,513.
Interlayer 54 is used to facilitate bonding of the hard coating layer 56 to the substrate 11. Examples of suitable interlayer material are niobium, chromium, platinum, titanium, or any combination or alloys thereof. A particular interlayer is made of niobium greater than about 100 angstroms and preferably less than about 500 angstroms thick. The interlayer may have a thickness from about 150 angstroms to about 350 angstroms. PCT US92/03330 describes use of a niobium interlayer.
Hard coating layer 56 provides improved strength, corrosion resistance and shaving ability and can be made from fine-, micro-, or nano-crystalline carbon-containing materials (e.g., diamond, amorphous diamond or DLC), nitrides (e.g., boron nitride, niobium nitride, chromium nitride, zirconium nitride, or titanium nitride), carbides (e.g., silicon carbide), oxides (e.g., alumina, zirconia) or other ceramic materials (including nanolayers or nanocomposites). The carbon containing materials can be doped with other elements, such as tungsten, titanium, silver, or chromium by including these additives, for example in the target during application by sputtering. The materials can also incorporate hydrogen, e.g., hydrogenated DLC. Preferably coating layer 56 is made of diamond, amorphous diamond or DLC. A particular embodiment includes DLC less than about 3,000 angstroms, preferably from about 500 angstroms to about 1,500 angstroms. DLC layers and methods of deposition are described in U.S. Pat. No. 5,232,568. As described in the “Handbook of Physical Vapor Deposition (PVD) Processing, “DLC is an amorphous carbon material that exhibits many of the desirable properties of diamond but does not have the crystalline structure of diamond.”
Overcoat layer 58 is used to reduce the tip rounding of the hard coated edge and to facilitate bonding of the outer layer to the hard coating while still maintaining the benefits of both. Overcoat layer 58 is preferably made of chromium containing material, e.g., chromium or chromium alloys or chromium compounds that are compatible with polytetrafluoroethylene, e.g., CrPt. A particular overcoat layer is chromium about 100-200 angstroms thick. Overcoat layer may have a thickness of from about 50 angstroms to about 500 angstroms, preferably from about 100 angstroms to about 300 angstroms. Razor blade 10 has a cutting edge that has less rounding with repeated shaves than it would have without the overcoat layer.
Outer layer 52 is generally used to provide reduced friction. The outer layer 52 may be a polymer composition or a modified polymer composition. The polymer composition may be polyfluorocarbon. A suitable polyfluorocarbon is polytetrafluoroethylene sometimes referred to as a telomer. A particular polytetrafluoroethylene material is Krytox LW 2120 available from DuPont. This material is a nonflammable and stable dry lubricant that consists of small particles that yield stable dispersions. It is furnished as an aqueous dispersion of 20% solids by weight and can be applied by dipping, spraying, or brushing, and can thereafter be air dried or melt coated. The layer is preferably less than 5,000 angstroms and could typically be 1,500 angstroms to 4,000 angstroms, and can be as thin as 100 angstroms, provided that a continuous coating is maintained. Provided that a continuous coating is achieved, reduced telomer coating thickness can provide improved first shave results. U.S. Pat. Nos. 5,263,256 and 5,985,459, which are hereby incorporated by reference, describe techniques which can be used to reduce the thickness of an applied telomer layer.
Razor blade 50 is made generally according to the processes described in the above referenced patents. A particular embodiment includes a niobium interlayer 54, DLC hard coating layer 56, chromium overcoat layer 58, and Krytox LW2120 polytetrafluoroethylene outer coat layer 52. Chromium overcoat layer 58 is deposited to a minimum of 100 angstroms and a maximum of 500 angstroms. Razor blade 50 preferably has a tip radius of about 200-400 angstroms, measured by SEM after application of overcoat layer 58 and before adding outer layer 52.
Another embodiment depicted in FIG. 5 shows a finished blade 60 of the present invention having a substrate (e.g., substrate 11 of FIG. 1, depicted, or substrate 31 of FIG. 3) having an interlayer 62, preferably chromium, a hard coating layer, which may or may not include dopants, and a polytetrafluoroethylene outer coat layer 66 (e.g., Krytox LW2120). Hard coatings such as aluminum magnesium boride based coatings are described in U.S. Patent Publication No. 2013/0031794, assigned to the Assignee hereof and incorporated by reference herein. In FIG. 5, the outer layer 66, which generally is comprised of the same type of material as outer layer 52, described above in FIG. 4, is deposited directly on the hard coating layer 64, as no overcoat layer is present in this embodiment.
The substrate profile of the razor blade of the present invention provides an improvement in blade sharpness. The blade sharpness may be quantified by measuring cutting force, which correlates with sharpness. Cutting force may be measured by a Single Fiber Cutting test, which measures the cutting forces of the blade by measuring the force required by each blade to cut through a single hair. The cutting force of each blade is determined by measuring the force required by each blade to cut through a single human hair. Each blade cuts the hair greater than 50 times and the force of each cut is measured on a recorder. A control blade population is often used with intermittent cuts, to determine a more reliable cutting force comparison. The hair being cut is fully hydrated. Cut speed is 50 millimeters per second. The blade tip offset from the “skin plane” is 100 micrometers. The blade angle relative to the “skin plane” is generally about 21.5 degrees. The hair orientation relative to the “skin plane” is 90 degrees. The data acquisition rate is 180 kHz. This type of cutting force testing process is described in US Patent Publication No. 20110214493, assigned to the Assignee hereof, and incorporated herein by reference.
The finished or coated blades of the present invention (e.g., blades 50 or 60) have a cutting force of less than about 40 milliNewtons and preferably less than about 35 milliNewtons, for a hair with a diameter near 100 microns. This is considered herein to be a relatively sharp blade.
FIG. 6 depicts an alternate embodiment of the present invention showing a finished blade 70 having a blade substrate 71, facets 72 and 74, with the geometries described above in conjunction with FIG. 1-3, and a nitride region 76 at or beneath the surface of the substrate which is formed as a result of a nitriding process step. The nitriding process step may comprise plasma nitriding to form the nitride region 76. The nitride region provides a strengthening to the substrate close to the edge and this extra strength is particularly useful with the blade profile of the present invention. If desired, one or more layers 78 may be joined to the nitrided substrate 71. One layer 78 is shown in FIG. 6. Layer 78 may comprise a polymer much like outer layer 52 or outer layer 66 described above. One type of nitriding process is described in U.S. Patent Publication No. 2010/0299931A1, assigned to the Assignee hereof and incorporated by reference herein.
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 micrometers” is intended to mean “about 40 micrometers.”
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.
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.

## Claims

1. A razor blade comprising:
a substrate with a cutting edge being defined by a sharpened tip, said substrate having a thickness of between 1.60 and 1.75 micrometers measured at a distance of four micrometers from the sharpened tip, and a thickness of between 9.25 and 10.00 micrometers measured at a distance of forty micrometers from the sharpened tip.

2. The razor blade of claim 1, further comprising a ratio of the thickness measured at four micrometers to the thickness measured at forty micrometers between 0.165 and 0.185.

3. The razor blade of claim 1, wherein said substrate has a thickness of between 2.70 and 3.00 micrometers measured at a distance of eight micrometers from the sharpened tip, a thickness of between 4.44 and 5.00 micrometers measured at a distance of sixteen micrometers from the sharpened tip, a ratio of the thickness measured at four micrometers to the thickness measured at eight micrometers between 0.56 and 0.62, and a ratio of the thickness measured at four micrometers to the thickness measured at sixteen micrometers between 0.32 and 0.40.

4. The razor blade of claim 1, wherein a cross-sectional shape of the blade is defined by the equation w=adn, where “a” is in the range of 0.50 to 0.62, and “n” is in the range of 0.76 to 0.80.

5. The razor blade of claim 1, wherein the substrate comprises a martensitic stainless steel of between 0.35% and 0.6% C and between 13% and 14% Cr.

6. The razor blade of claim 5 wherein said substrate further comprises between 1.1% and 1.5% Mo.

7. The razor blade of claim 1 wherein the substrate is a martensitic stainless steel having a carbide density of at least 200 carbides or more per 100 square micrometers as determined by optical microscopic cross-section.

8. The razor blade of claim 1 wherein the substrate has a tip radius of in the region of 125 to 500 angstroms.

9. The razor blade of claim 8 further comprising an interlayer joined to said substrate.

10. The razor blade of claim 9 wherein said interlayer comprises niobium, chromium, platinum, titanium, or any combination or alloys thereof.

11. The razor blade of claim 10, further comprising a coating layer joined to said interlayer.

12. The razor blade of claim 11 wherein said coating layer comprises carbon or aluminum magnesium boride.

13. The razor blade of claim 12 further comprising an overcoat layer joined to said coating layer.

14. The razor blade of claim 13 wherein said overcoat layer comprises chromium.

15. The razor blade of claim 13 further comprising an outer layer joined to said overcoat layer.

16. The razor blade of claim 15 wherein said outer layer comprises a polymer.

17. The razor blade of claim 16 wherein said outer layer comprises polytetrafluoroethylene.

18. The razor blade of claim 12 further comprising an outer layer joined to said coating layer.

19. The razor blade of claim 1, further comprising an included angle that is less than 7 degrees.

20. The razor blade of claim 19 wherein said included angle is measured at a distance of forty micrometers or greater from the sharpened tip.

21. The razor blade of claim 19 wherein said substrate has only two facets on each side of said cutting edge.

22. The razor blade of claim 1, further comprising a nitride region disposed at or beneath a surface of the substrate.

23. The razor blade of claim 22 wherein said nitride region is formed by plasma nitriding.

24. The razor blade of claim 23 further comprising one or more layers joined to said nitride region.