Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Patent
1990-03-16
1991-07-16
Weisstuch, Aaron
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
20429836, 156345, 156643, C23F 404
Patent
active
050322435
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with a method and apparatus for forming or modifying cutting edges by ion bombardment to cause sputter removal of the material of the workpiece. The invention is particularly, but not exclusively, useful in forming very thin ("ultra fine") cutting edges for razor blades.
Theoretical studies and experimental work carried out by us have shown that the shaving performance of razor blades would be significantly improved if the thickness of the cutting edge over a distance back from the ultimate tip was substantially less than that of currently available razor blades. (For the avoidance of doubt the term "cutting edge" is used in this specification to refer to the whole marginal zone of a razor blade which is bounded by tapering surfaces or, in everyday parlance, is sharpened, while "ultimate tip" is used to refer to the final edge or tip of the razor blade; in conventional razor blades, the cutting edge extends some 400-500 .mu.m back from the ultimate tip). The minimum thickness of the cutting edge is determined by the yield or fracture strength of the blade material.
British Specification 2130955A describes such a cutting edge which has a cross-sectional shape, up to a distance of 40 .mu.m from the ultimate tip, defined by the equation: .mu.m, from the ultimate tip, a is a factor of proportionality having a value of .ltoreq.0.8, and n is an exponent having a value in the range 0.65 to 0.75. For actual cutting edges, the values of a and n can be determined by plotting w against d on logarithmic scales, a being given by the intercept on the line d=1 and n by the slope of the straight line. However, it can be seen from the equation that, in effect, a is the calculated thickness, i.e. tip width w, when d is 1 .mu.m.
In practice it is found that for the stainless steels currently used for razor blades, the actual tip width or thickness at 1 .mu.m should be more than 0.7 .mu.m in order to minimize damage to the cutting edge during shaving, but less than 1.0 .mu.m in order to obtain a comfortable shave.
The value of the exponent n is equally or more important than the value of a since it (n) determines the shape of the edge. A value of 0.5 defines a parabola, while a value of 1.0 defines a simple wedge. Previous cutting edges had n values of more than 0.75; the cutting edges defined in the British specification referred to above have n values of from 0.65 to 0.75.
Equation (1) holds for cutting edges made of any material, but to maintain a in the same numerical range as for steels, the equation is modified, for other materials, to: ##EQU1## where m is the ratio of the yield strength of the material in question to that of steel. It follows that for materials with a higher yield strength than steel, the cutting edges will be thinner than the corresponding steel cutting edges.
The above British specification also describes composite cutting edges, that is edges comprising a substrate cutting edge of stainless steel and a coating thereon of a material having a higher yield strength than stainless steel. In this case, the composite cutting edge cross-sectional shape should satisfy two equations ##EQU2## where h is the thickness, in .mu.m, of the coating at the distance d, in .mu.m, from the ultimate tip.
A method of making such composite cutting edges is described in International Application Publication No. WO87/04471 (corresponding to European Application 0255834). This specification describes a process in which a substrate cutting edge having a cross-sectional shape such that strength) than the material of the substrate edge by a vapor deposition or sputtering process, if necessary in the presence of gaseous or vaporized molecules of another element or a compound of another element where it is desired to form the coating of a compound, at a pressure of less than 10.sup.-2 m bar, while simultaneously subjecting the cutting edge to ion bombardment with ions of sufficient mass and energy to cause sputter removal of the deposited material at a rate which is less than the rate of deposition, wh
REFERENCES:
patent: 3740327 (1973-06-01), Lane et al.
patent: 3761374 (1973-09-01), Bromer et al.
patent: 4128765 (1978-12-01), Franks
patent: 4599135 (1986-07-01), Tsunekawa et al.
Bache Roger J.
Parker Colin F.
Morley John P.
The Gillette Company
Weisstuch Aaron
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