Method of treating cutting edges

Abstract

The present invention is concerned with providing improved cutting edges on cutting instruments such as razor blades by implanting in the cutting edge ions of a metal, reactive non-metal, or an inert gas.

Parent Case Text

This application is a continuation of application Ser. No. 218,824 filed Jan. 18, 1972 now abandoned.

Description

This invention is concerned with a method of improving the properties of cutting edges, such as those of razor blades. Whilst the invention will be described hereinafter with specific reference to razor blades, it is to be understood that the method is equally applicable to other metal cutting edges, both as used in the razor art and also such as are formed as surgical instruments and the like.

Broadly, we have found that properties of a cutting edge can be improved by subjecting the edge to an ion implantation treatment.

The technique of ion implantation is known. Briefly, the equipment used comprises an ion source, an accelerator, an analysing magnet and an implantation chamber. In the method of the invention, one or more, usually a stack, of razor blades is placed in the chamber and the cutting edges are irradiated with a beam of high energy ions from the ion source. The ions enter the material of the cutting edge and cause modification of its properties.

We have found, in particular, that ion implantation can be used (i) to improve the hardness of cutting edges, (ii) to improve the adhesion of metallic and non-metallic coatings on cutting edges, and (iii) to improve the corrosion resistance of the cutting edge material. To obtain all these types of improvement, it is necessary to use the appropriate ion species for implantation and to use the appropriate ion energy and ion dose, that is to say, the total number of ions implanted per unit area. The ion energy will determine the depth of penetration of the ions into the substrate, the higher the energy the greater being the penetration, and the dose will determine the number of ions implanted.

Suitable ions for obtaining the effects referred to will be described below. The optimum values of the other parameters of the process, that is the ion energy and the ion dose, can readily be determined in each particular case by routine trial. The cutting edges are preferably subjected to the ion implantation treatment in their sharpened state and care should be taken that the ion energy and/or the period of irradiation are not so great that physical damage to the cutting edge due to erosion or overheating of the cutting edge material takes place. Useful improvements in cutting edge properties can, however, be obtained in substantially all cases without risk of such erosion or overheating.

I. Cutting edge hardness

In general, it is the case that the harder the material in which a cutting edge, for example that of a razor blade, is formed, the greater is its useful life, other things being equal. The harder the material, the better able the cutting edge is to retain its as-sharpened configuration, provided that the hardness is not accompanied by an undesirably high degree of brittleness. If the latter is present, use of the cutting edge tends to cause the breaking away of portions of the cutting edge, rather than wearing down or deformation of the as-sharpened configuration.

We have found that there are two classes of ions which can be used to improve the hardness of steel cutting edges: (a) ions of non-metallic elements which can form compounds with the metal elements present in the steel, for example, H, B, C, N, O, Si, P and S, and (b) ions of metallic elements which may or may not form alloys or compounds with elements present in the steel, for example strong carbide-forming elements, such as Ti, V, Cr, Fe, Zr, Mo, Hf, Ta, and W, and other transition metals, such as Co, Ni, Cu, Re, Os, Ir, Pt and Au.

With both classes of ions, particular combinations of ion energy and ion dose may lead to the increase in hardness being accompanied by an undesirable increase in brittleness and we have found that this is due to the implanted ions exceeding a threshold concentration at a particular depth from the surface of the substrate. In general this situation can be avoided by using a lower ion dose for the particular ion. For nitrogen ions, for example, this threshold concentration is between 50 and 100 atomic %.

Suitable ion doses are, in general, at least 10.sup.15 ions/cm.sup.2.

The following examples illustrate effective and non-effective ion implantation conditions for certain of the ion species mentioned above.

All these examples, and those given below, were carried out as follows:

A stack of sharpened steel razor blades was placed in the implantation chamber of an ion implantation apparatus. The blades were mounted in a holder so that each blade overlapped the one above it by about 0.005 inch. The holder was placed in the implantation chamber so that one side of the cutting edge bevel was facing the ion beam. The apparatus was then pumped down to a pressure of about 10.sup.-.sup.6 torr. A beam of the ions to be implanted of the required energy was provided from an ion source and analysed by passing through the centre of the pole pieces of the magnet. This beam of ions passed down a flight tube and impinged directly on the blade edges, the number of ions arriving on the blades being closely monitored. When the required does had been received, the implantation chamber was sealed by a baffle valve from the ion beam and the implanted blades removed after admitting air to the chamber.

The stainless steel and carbon steel blades referred to in the Examples of this specification were formed, respectively, of a conventional stainless steel containing 12.5-13.5% Cr and 0.6-0.7% C and a conventional carbon steel containing 1.15-1.3% C.

The hardness of the cutting edges, before and after treatment was assessed by an indentation test which, in principle, is similar to a standard indentation hardness determination in which the length of the impression made by a diamond indentor pressed into the material under test is inversely proportional to the hardness of the material. The improvement, if any, in hardness of the blade edges after ion implantation treatment is shown by the percentage decrease in the length of the indentation compared with that of the untreated blades. Because of the nature of the indentation test, small decreases in indent length (that is decreases of more than 2.5%) can represent significant increases in edge hardness (decrease of less than 2.5% are usually not significant).

EXAMPLES 1-15

Stainless steel blades were implanted with nitrogen ions.

______________________________________ Ion Energy Ion Dose % Decrease in Ex KeV ions/cm.sup.2 Indent Length ______________________________________ 1 75 6 .times. 10.sup.17 13.0 2 80 1 .times. 10.sup.16 0 3 80 5 .times. 10.sup.15 0 4 80 1 .times. 10.sup.15 0 5 150 5.5 .times. 10.sup.17 9.4 6 150 2.75 .times. 10.sup.17 7.1 7 150 1.1 .times. 10.sup.17 7.1 8 150 3.6 .times. 10.sup.16 5.2 9 150 7.2 .times. 10.sup.15 0 10 150 3.6 .times. 10.sup.15 5.2 11 250 3.6 .times. 10.sup.17 5.9 12 250 1.4 .times. 10.sup.17 5.3 13 250 3.6 .times. 10.sup.16 2.9 14 250 7.2 .times. 10.sup.15 0 15 250 3.6 .times. 10.sup.15 0 ______________________________________

EXAMPLES 16-22

Carbon steel blades were implanted with nitrogen ions.

______________________________________ Ion Energy Ion Dose % Decrease in Ex KeV ions/cm.sup.2 Indent Length ______________________________________ 16 80 1 .times. 10.sup.16 4.2 17 80 1 .times. 10.sup.15 2.6 18 150 5.5 .times. 10.sup.17 6.7 19 150 2.75 .times. 10.sup.17 2.8 20 150 1.1 .times. 10.sup.17 2.6 21 150 3.6 .times. 10.sup.15 0 22 250 1.4 .times. 10.sup.17 3.4 ______________________________________

EXAMPLE 23

Stainless steel blades were implanted with oxygen ions.

______________________________________ Ion Energy Ion dose % Decrease in KeV ions/cm.sup.2 Indent Length ______________________________________ 15 1.6 .times. 10.sup.17 4.5 ______________________________________

EXAMPLE 24

Stainless steel blades were implanted with titanium ions.

______________________________________ Ion Energy Ion dose % Decrease in KeV ions/cm.sup.2 Indent Length ______________________________________ 250 2 .times. 10.sup.16 7.6 ______________________________________

EXAMPLES 25 and 26

Stainless steel blades were implanted with nickel ions.

______________________________________ Ion Energy Ion dose % Decrease in Ex KeV ions/cm.sup.2 Indent Length ______________________________________ 25 200 3.7 .times. 10.sup.16 6.5 26 400 6.2 .times. 10.sup.16 6.5 ______________________________________

Steel cutting edges which have been coated with thin films of metals, such as Cr, Pt, W, Ti and Al, and mixtures or alloys of two or more of these metals, can also be hardened by ion implantation. For this purpose any of the ions in groups (a) and (b) above can be used; the ion energy used should be such that the majority of the implanted ions remain in the thickness of the metal coating. Suitable ion doses are, in general, at least 10.sup.15 ions/cm.sup.2.

The following examples illustrate suitable conditions for ion implantation into coated razor blades.

EXAMPLE 27

Stainless steel blades having a sputtered coating of aluminium 40 nm thick were implanted with oxygen ions so that the majority of the ions remained within the coating thickness.

______________________________________ Ion Energy Ion Dose % Decrease in KeV ions/cm.sup.2 Indent Length ______________________________________ 15 1.6 .times. 10.sup.17 7.4 ______________________________________

EXAMPLE 28

Stainless steel blades having a sputtered coating of titanium 100 nm thick were implanted with nitrogen ions so that the majority of the ions remained within the coating thickness.

______________________________________ Ion Energy Ion Dose % Decrease in KeV ions/cm.sup.2 Indent Length ______________________________________ 100 1.1 .times. 10.sup.17 5.7 ______________________________________

ii. Coating adhesion

We have found that the adhesion of metallic and metallic compound, such as metallic oxide, coatings on cutting edges can be improved by implanting ions with energies such that the ions penetrate the substrate/coating interface. The coatings in question are, for example, W, Ta, Ti, Au, V, Mo, Pt and Al.sub.2 O.sub.3 ; they may be formed on the cutting edge by any procedure that gives a thin uniform coating, for example, sputtering.

There are two classes of ions which can be used to bring about such increase in coating adhesion (a) ions of inert gases, that is He, Ne, A, Kr and Xe, and (b) ions of elements which are capable of reacting with the substrate material and/or the coating material, for example Cr.

As indicated above, the ion energy should be such that a substantial proportion of the implanted ions penetrate the substrate/coating interface and suitable ion energies will, of course, depend on the ion species used and the nature of the coating and substrate materials. The ion dose required will normally be at least 10.sup.14 ions/cm.sup.2.

The following examples illustrate suitable conditions for ion implantation to obtain increased adhesion of coatings of the kind referred to.

In these examples, the coated blades were used in a standard shaving test, some without having been subjected to ion implantation and the others after this treatment, and the degree of coating loss was estimated by microscopical examination of 500.times. magnification on a 1 to 10 scale, where 10 = complete loss of coating and 1 = no loss.

EXAMPLES 29-33

Stainless steel blades with various sputtered coatings were implanted with 5 .times. 10.sup.15 argon ions per cm.sup.2 using ion energies such that the distribution peak of the implanted ions lay just beyond the interface between the sputtered coating and the blade surface.

__________________________________________________________________________ Coating Thickness Energy of Degree of coating Degree of coating Ex material of coating A ions loss on blade with- loss on blade after nm KeV out argon implant- argon implantation ation __________________________________________________________________________ 29 W 50 200 7 3 30 Ta 100 300 6 4 31 Ti 50 100 3 1 32 Au 40 200 4 3 33 V 100 200 7 2 __________________________________________________________________________

EXAMPLES 34-37

Stainless steel blades with various sputtered coatings were implanted with Cr ions so that a substantial proportion of the implanted ions penetrated beyond the substrate/coating interface

Coating Coating Energy of Dose of Degree of coat- Degree of coating Ex Material Thickness Cr ions Cr ions ing loss without loss after nm KeV Ions/cm.sup.2 Cr implant Cr implant __________________________________________________________________________ 34 Al.sub.2 O.sub.3 50 125 2 .times. 10.sup.15 6 4 35 W 35 340 1 .times. 10.sup.16 9 2 36 Mo 40 150 5 .times. 10.sup.15 5 2.5 37 Pt 25 150 5 .times. 10.sup.15 6 2 __________________________________________________________________________

We have also found that the adhesion of polymer coatings to cutting edges can be improved by ion implantation of the substrate with ions of elements which are capable of reacting with the substrate material and/or the polymer which is subsequently applied. The polymer coating may be directly on a steel cutting edge or on a thin metal or metallic compound coating previously applied to the cutting edge, examples of suitable metal or metallic compound coatings being as mentioned above. The polymer coating most widely used on razor blade cutting edges is polytetrafluoroethylene and suitable ions for increasing the adhesion of polytetrafluoroethylene coatings are Cr and F.

The ion energy used should be such that a substantial proportion of the implanted ions are within 100A of the substrate surface. The ion dose required will normally be at least 10.sup.15 ions/cm.sup.2.

The following examples illustrate suitable conditions for ion implantation to obtain increased adhesion of polytetrafluoroethylene coatings. In these examples the adhesion of the polymer was assessed as described for Examples 29-37.

EXAMPLES 38-41

Stainless steel blades having sputtered coatings of W or Mo and carbon steel blades were implanted with Cr or F ions, and then coated with polytetrafluoroethylene. The ion energies used were such as to implant the majority of ions within 100A of the substrate surface.

Ex Blade Implanted Ion Energy Ion Dose Av. degree of polymer Av. degree of polymer ion KeV ions/cm.sup.2 loss without implant loss after implant __________________________________________________________________________ 38 Carbon Steel Cr 10 5 .times. 10.sup.15 3.6 2.9 39 Stainless steel Cr 30 5 .times. 10.sup.15 10 5.5 with 50 nm W coating 40 Stainless Steel Cr 10 5 .times. 10.sup.15 4.9 3.9 with 50 nm Mo coating 41 Stainless steel F 10 5 .times. 10.sup.15 5.5 3.0 with 10 nm Mo coating __________________________________________________________________________

iii. Corrosion resistance

We have found that the corrosion resistance of steel cutting edges, more particularly that of carbon steel razor blades, can be improved by implanting ions of elements which are capable of imparting corrosion resistance when incorporated as alloying elements into carbon steels, for example, Cr, Ta, Mo, W, Au, and Pt. Suitable ion energies are determined by substantially the same factors as referred to in the first part of section (i) above; the ion dose required will normally be at least 10.sup.15 ions/cm.sup.2.

The following examples illustrate suitable conditions for ion implantation to obtain improved corrosion resistance in carbon steel blades.

In these examples, the blades were used in a standard shaving test, some without having been subjected to ion implantation and the others after this treatment, and the degree of corrosion of the blade edges and facets was assessed on a 1-10 scale by microscopical examination at 500.times. magnification. On this scale, 1 = no corrosion, 10 = 100% corrosion.

EXAMPLES 42 and 43

Carbon steel blades were implanted with Cr ions.

__________________________________________________________________________ Ion Energy Ion Dose Av. degree of Av. degree of Ex KeV ions/cm.sup.2 corrosion without corrosion after implantation implantation __________________________________________________________________________ 42 250 1 .times. 10.sup.16 9 6.5 plus 125 2.5 .times. 10.sup.15 43 400 1 .times. 10.sup.16 plus 280 7 .times. 10.sup.15 4 2 plus 200 5 .times. 10.sup.15 __________________________________________________________________________

Claims

What we claim is:

1. A process for improving a coated or uncoated steel cutting edge, said process comprising implanting ions selected from the group consisting of metals, reactive non-metals and inert gases into said cutting edge, said ions being propelled at said cutting edge in the form of an ion beam at energies of between about 10 to 400 KeV until a dose of between about 1 .times. 10.sup.14 ions/cm.sup.2 to 6 .times. 10.sup.17 ions/cm has been implanted.

2. A process as defined in claim 1 in which said cutting edge is a razor blade.

3. A process as defined in claim 2 in which metallic or non-metallic ions which will improve the hardness or corrosion resistance of the steel cutting edge are implanted.

4. A process as defined in claim 2 in which a thin metal coating is on the cutting edge and metallic or non-metallic ions which will improve the hardness or corrosion resistance of the coating are implanted at energies at which a substantial proportion of the ions will be in the coating.

5. A process as defined in claim 2 wherein a thin metallic coating is on the cutting edge and metallic, non-metallic or inert gas ions are implanted at energies such as to penetrate through the cutting edge-coating interface to improve the adhesion of said coating.

6. A process as defined in claim 2 in which the cutting edge is coated with a polytetrafluoroethylene coating and ions will improve the adhesion of the polyethylene are implanted at energies such that a substantial proportion of said ions are implanted within 100A of the polytetrafluoroethylene substrate surface.

7. A process as defined in claim 6 in which said ions are selected from chromium and fluorine.