US 3761373 A
Description (OCR text may contain errors)
Sept. 25, 1973 A. s. SASTRI 3,761,373
PROCESS FOR PRODUCING AN IMPROVED CUTTING TOOL v Filed July 9, 1971 HG /34.
I -1 1 E '1 z J [4 L ll' Q United States Patent 3,761,373 PROCESS FOR PRODUCING AN IMPROVED CUTTING TOOL Aiyaswami S. Sastri, Stow, Mass., assiguor to The Gillette Company, Boston, Mass. Filed July 9, 1971, Ser. No. 161,159 Int. Cl. B26b 21/54; C23c 15/ 00 U.S. Cl. 204-192 12 Claims ABSTRACT OF THE DISCLOSURE SUMMARY OF THE INVENTION This invention relates to processes for producing an extremely sharp and durable cutting edge on a razor blade or similar cutting tool, and to improved cutting tools.
The forming of the cutting edges of razor blades by mass production techniques conventionally involves a series of abrading operations (grinding and honing) to produce the desired sharpand durable shaving edge. Each abrading operation forms a facet on the blade edge being sharpened, which facet is modified by subsequent abrading operations of increasing fineness. In general, the blade edge configuration is a Wedge shape, the included solid angle of which is typically 20-30. The faces or sides of such cutting edges may extend back from the ultimate edge a distance up to as much as 0.1 inch or even more. Each face need not be a single uninterrupted continuous surface or facet, but may consist of two or more facets formed by successive grinding or honing operations and intersecting each other along zones generally parallel to the ultimate edge. The final facet, i.e. the facet immediately adjacent the ultimate edge, has a width as low as 7.5 microns or even less compared with the diameter of beard hair which averages about 100 to 125 microns. Through shave test evaluation and measurement of the geometry of such sharpened cutting edges, it has been found that the cutting edge should have an average tip radius of less than 500 Angstroms. A thin adherent layer of a corrosion resistant metal is often applied to the cutting edge of the blade. Further, a shave facilitating layer of polymeric material is also frequently applied to the blade edge. These layers must have adhesion compatibility so that they remain firmly adhered to one another and to the substrate throughout the life of the cutting tool and not adversely affect the edge geometry.
It is a general object of this invention to provide novel and improved cutting implements, the cutting edges of which have improved mechanical properties.
Another object of the invention is to provide novel and improved processes for producing improved cutting tools.
A further object of the invention is to provide novel and improved razor blades which possess superior shaving properties.
In accordance with the invention, the edge geometry of a cutting implement such as a razor blade is modified by a process which includes the steps of forming a cutting edge of dielectric material, depositing a layer of electrically conductive material on said dielectric material, and then subjecting the composite cutting edge to a DC ion bombardment step so that a portion of the deposited 3,761,373 Patented Sept. 25, 1973 ice electrically conductive material is removed so that the dielectric material is exposed at the ultimate tip.
In particular embodiments, the cutting edge is formed in a metal substrate by a suitable procedure such as grinding, honing, strapping, chemical etching, electrolytic sharpening, or forming with an appropriately shaped die; and then the edge is subjected to two successive strengthening material deposition steps, the first step depositing a layer of dielectric material and the second step depositing the layer of electrically conductive material. Preferably the layers are deposited by sputtering on a multiplicity of blade elements while the blade edges are disposed in parallel alignment with one another and in a plane parallel to a target member spaced from the blade edges. A planar target member is used in one embodiment while a cylindrical target rod is used in another embodiment.
A razor blade in accordance with the invention has an average tip radius of less than 500 Angstroms, the exposed tip material is a dielectric, such as A1 0 and added strengthening metal, such as chromium or a chrome-platinum alloy, i on the flanks of the cutting edge. Such razor blades exhibit excellent shaving characteristics and have a long shaving life. A wide range of blade substrate materials may be used, specific razor blade steel compositions with which the invention may be practiced including the following:
COMPOSITION IN PERCENT C Cr M0 Si Ni Other objects, features and advantages of the invention will be seen as the following description of particular embodiments progresses, in conjunction with the drawings in which:
FIG. 1 is a diagrammatic view of apparatus suitable for practice of the invention;
FIG. 2 is a diagrammatic view of the geometry of a razor blade edge sharpened by conventional means; and
FIG. 3 is a diagrammatic view illustrating one example of razor blade edge geometry in accordance with the invention.
DESCRIPTION OF vPARTICULAR EMBODIMENT Diagrammatically shown in FIG. 1 is a sputtering apparatus which includes a stainless steel chamber 10 having wall structure 12 and a base 14 in which is formed a port 16 which is coupled to a suitable vacuum system (not shown). Mounted in chamber 10 is a support 18 on which is disposed a stack of razor blades 20 and support structures 22, 24 for target member 26 of dielectric material and target 28 of electrically conductive material. Support structures 18, 22 and 24 are electrically isolated from chamber 10 and electrical connections are provided to connect blade stack 20 and targets 26, 28 to appropriate energizing apparatus 30, 32, 34. It will be understood that this is a diagrammatic showing of suitable apparatus. In one embodiment the targets 26, 28 are horizontally disposed discs, each six inches in diameter and one-quarter inch thick; and 4 /z-inch long stack of blades 20 is placed on a five-inch diameter aluminum support disc 18 disposed parallel to target discs 26, 28. Disc 18 is movable between a first position aligned with target 26 and a sec- 0nd position aligned with target 28. A coil of razor blade strip may be similarly positioned on such a support with its sharpened edges defining a plane exposed to parallel to targets 26, 28. In another embodiment, target rod that has an exposed length of twenty-nine inches and is 1% inches in diameter is employed. Suitable coolant is circulated through the rod for cooling purposes. A series of stacks of razor blades (either in coil form or in twelve inch long axial extending stacks) are disposed about the target rod at equal distances therefrom.
The geometry of the edge of a typical razor blade of commercial quality sharpened by conventional abrading techniques is shown in FIG. 2 at a magnification of about 100,000 times. The tip 40 has a radius that is typically in the range of 125-500 Angstroms, a typical average radius (the average of radius measurements taken at 5 to points along the length of the blade edge) being about 250 Angstroms. The W1 flank width (at a distance of 1,000 Angstroms from the ultimate edge 40) is typically in the range of 1200 to 1400 Angstroms. The W2 width (at a distance of 2,000 Angstroms from the tip 40) is about 2100 Angstroms; the W4 width (at a distance of 4,000 Angstroms from the tip 40) is about 3200 Angstroms; and the W6 width (at a distance of 6,000 Angstroms) is about 4100 Angstroms; and the W8 width (at a distance of 8,000 Angstroms from the tip) is about 5100 Angstroms.
These measurements were made by a high resolution electron microscopy technique in which a magnified image of a blade edge profile (silhouette) is photographed. The blades are cleaned by immersion in trichloroethylene; subjection to ultrasonic cleaning for two minutes; rinsing in a mixture of one-half acetone and one-half methanol; cleaned in warm air; and then demagnetized in a solenoid coil. A blade specimen in the order of one square millimeter in size with four sides, one of which is the original sharpened razor blade edge, is obtained by abruptly snapping the blade with the help of a suitable instrument such as a watchmakers plier. The blade may be snapped in air or if the blade will not break readily in liquid nitrogen (at a temperature below the ductile to brittle transition value).
A 100 kv. RCA EMU4 electron microscope is used with a standard air lock specimen holder modified to accommodate the small blade edge fragment. The microscope was fitted with a liquid nitrogen cooled bafile valve to reduce contamination during photography. The blade edge profile is held in the path of the electron beam so that a shadow image of the ultimate tip is cast on the final viewing screen. The magnification of the final image is controlled by the strength of the intermediate lens current and the focusing is achieved with control of the objective lens current. The microscope magnification was calibrated in terms of focusing lens current.
The tip radius of the resulting photomicrograph was measured by fitting 90 arcs of circles to the tip profile and selecting as the tip radius that edge profile that best fits the profile of the photomicrograph. The point to point resolution of the microscope is in the order of 5 Angstroms. The variation and average radius of a large nmnber of edges from a particular batch of blades using this technique was within 12.5 Angstroms. The W1, W2 and other dimensions are similarly measured from the photomicrograph.
In operation of the apparatus shown in FIG. 1, sharpened blades 20 are disposed in a stack with their sharpened edges aligned and are placed in chamber 10 on support 18. The chamber is evacuated and the blade edges are subjected to ion bombardment, for example by a glow discharge maintained in argon at a pressure of ten microns to modify the edge geometry as generally indicated by line 42 in FIG. 2 and specifically to reduce the tip radius, a typical radius reduction being about 100 Angstroms.
The chamber is again evacuated and argon at a pressure p of 58 microns is placed in the chamber. With the blade stacks and chamber grounded, an RF potential is applied to dielectric target 26 and argon ions are produced which bombard target 26 and release atoms of the target material. The released atoms of dielectric material are deposited on exposed surfaces, including the sharpened blade edges. This layer is applied uniformly to the thickness of less than 500 Angstroms. The support 18 is then aligned with the target 28 and an RF potential applied to that target to cause deposition of an electrically conductive layer on the dielectric layer. The RF power supply is then disconnected from the target 28 and the blades are subjected to DC ion bombardment which removes electrically conductive but not dielectric material, more material being removed from the tip region of the blades than the flanks. The resulting blades have a cutting edge geometry of the nature diagrammatically indicated in FIG. 3 in which the exposed tip 44 is dielectric material and its average radius is about 250 Angstroms and two layers 46, 48 are on the flanks at the W6 dimension.
As a specific example, a 4 /2-inch long stack of stainless steel razor blades having the following composition:
Percent Carbon .5462
Manganese .20.50 Silicon .20.50 Phosphorus, max .025 Sulphur, max. .020 Nickel, max .50 max. Iron Remainder sharpened to the edge geometry as indicated in Feb. 2, and sharpened to the edge geometry as indicated in FIG. 2, were placed on a five-inch diameter aluminum disc support 18 in an RF sputtering unit. Two targets were employed, an A1 0 target 26, and a Cr Pt target 28. The A1 0 target 26 was a sintered compact disc six inches in diameter and inch thick, and the Cr Pt target 28 was a pure chromium disc six inches in diameter and A1 inch thick that had squares of pure platinum foil one centimeter on a side and 0.002 inch thick spot welded on its surface. The foil squares were spaced on the surface so that 23% of the chromium surface was covered with platinum. The target surfaces were disposed parallel to the sharpened blade edges at a distance of 2 /2 inches from those edges.
Pressure in the vacuum chamber 10 was reduced to 0.1 micron of mercury and then pure argon gas was bled into the chamber to a pressure of ten microns of mercury. The aluminum support disc 18 was then connected to a DC source of power and with the chamber 10 grounded the blade edges were subjected to ion bombardment at a voltage of 1800 volts and a current of 35 milliamperes for seven minutes. The targets 26, 28 were covered by metal shields during this step. A 13.56 megahertz RF source was connected to A1 0 target 26 and that target was sputtered for thirty minutes while maintaining ten microns of mercury pressure of argon gas in the chamber. The shield was then removed from between the blades 20 and the target 26 and 0.4 kilowatts of powder (with a DC negative bias of about 3400 volts and a superimposed RF signal of about 4500 volts peak to peak) was applied for 10 minutes while maintaining argon at 10 micrions pressure. The edges of the blades facing target 26 received an aluminum oxide layer 46 to a thickness of about 250 Angstroms. Application of RF power was then terminated and support 18 was aligned with the Cr Pt target 28. The Cr Pt target 28 was connected to the RF source and cleaned for five minutes and then a layer 48 of chromium-platinum alloy 250 Angstroms in thickness was deposited by application of 0.4 kilowatts of power for seconds. The blade stack was then connected to the DC source and subjected to ion bombardment for seven minutes at 1800 volts at a current of milliamperes to remove the chromium-platinum film from the tip region but not the flank region of the blades to provide a blade edge geometry as shown in FIG. 3. The resulting blades have an average tip radius of 250 Angstroms, an average W1 dimension of about 1400 Angstroms, aWZ dimension of about 2500 Angstroms, a W4 dimension of about 4,000 Angstroms, and a W6 dimension of about 5150 Angstroms. A coating of polytetrafluoroethylene telomer was then applied to the edges of the blades in accordance with the teaching in U.S. Pat. 3,518,110. This processing involved heating the blades in an argon environment and provided on cutting edges of the razor blades an adherent coating of solid PTFE. These blades exhibited excellent shaving properties and long shaving life.
It will be understood that a variety of dielectric materials including other metal oxides may be used for the dielectric layer 46 and that other metals and metal alloys may be used for the electrically conductive layer 48. Ion bombardment between the application of the dielectric and conductive layers is optional. For example, such ion bombardment may be desirable when the process is employed with separate deposition chambers with a single target in each chamber.
The invention provides an improved cuting implement such as a razor blade in which the tip radius of the implement is within the optimum range for cutting effectiveness, the exposed tip is of dielectric material and substantial amounts of edge strengthening materials have been added to the flanks of the cutting edge.
While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention.
What is claimed is:
1. A process for treating a cutting implement comprising the steps of forming a cutting edge in dielectric material on the implement having an average tip radius of less than about 500 Angstroms, depositing a layer of electrically conductive material on said dielectric material, said layer of electrically conductive material having a total thickness at the W6 dimension of said cutting implement of at least 100 Angstroms, and subjecting said cutting edge to DC ion bombardment to remove a portion of the deposited electrically conductive material so that said dielectric material is exposed at the tip of the cutting edge of said implement and other portions of the deposit edelectrically conductive material remain on the flanks of said cutting edge adjacent said tip.
2. The process as claimed in claim 1 wherein said dielectric material is a metal oxide and said electrically conductive material is metal.
3. The process as claimed in claim 2 wherein said dielectric material is aluminum oxide.
4. The process as claimed in claim 2 wherein said metal includes chromium.
5. The process as claimed in claim 1 wherein said cutting implement is a razor blade.
6. The process as claimed in claim 1 wherein said dielectric material cutting edge is formed by the steps of forming a cutting edge on a metal substrate and then depositing a layer of dielectric material on said substrate cutting edge.
7. The process as claimed in claim 6 wherein said layer of dielectric material is deposited to a total thickness at the W6 dimension of said cutting implement of at least Angstroms.
8. The process as claimed in claim 6 wherein said dielectric and electrically conductive materials are deposited by sputtering.
9. The process as claimed in claim 6 and further including the step of subjecting said cutting edge on said metal substrate to an initial ion momlv substrate to an initial ion bombardment step to reduce the average tip radius of said cutting edge on said metal substrate at least about 100 Angstroms, and wherein said dielectric material is deposited to a thickness in the range of about 100-300 Angstroms.
10. The process as claimed in claim 6 wherein said dielectric and electrically conductive strengthening materials are deposited by sputtering techniques on a multiplicity of razor blade elements while the blade edges are disposed in parallel alignment with one another and in a plane parallel to a target member spaced from said blade edges.
11. The process as claimed in claim 10 and further in cluding the step of subjecting said cutting edges to an initial ion bombardment step to reduce the average tip radius of said cutting edges at least about 100 Angstroms, and wherein said dielectric material is deposited to a thickness in the range of about 100-300 Angstroms.
12. The process as claimed in claim 11 wherein said dielectric material is a metal oxide and said electrically conductive material is metal.
References Cited UNITED STATES PATENTS 3,345,202 10/1967 Kiss et al 74-106 R 2,843,542 7/1958 Callahan 204-192 3,562,140 2/ 1971 Skinner'et al 204-298 3,479,269 11/1969 Byrnes et a1 204-192 3,652,443 3/1972 Fish et al 204-192 3,480,483 11/1969 Wilkinson 204-192 3,682,795 8/ 1972 Fischbein et al 204-192 JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner U.S. Cl. X.R.
nmrnn STATES PATENT oFrrcE QETWKCATE M @QEUHQN Patent No. 3751 7 Dated September 25, 1973 Inventor(s) Aiye swami S. iiastr'i It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 3, line 20, delete and--;
Column 4, ,line 28, delete line, beginning with "sharpened" and ending with "Felon 2,";
Column i, line 56, change powder to "g;ower--; v
Jolumn 5, line 19, change outing" to ---cutting;-;
tolumn 5 lines H t- 15, change deposit delectr'ically to --deposited e1ectrically5 Jolumn 6," (Claim 9), delete line 15 starting ,with' "'siaubstrate" and ending with, "momlv".
Signed and sealed this 5th day of March 19714.,
EDWARD M F'LETCHERJR, v c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 (169) USCOMM-DC scans-pas fi U.5 GOVERNMENT PRINTING OFFICE 2 I955 0-355-334