US3508957A - Coated razor blades - Google Patents

Description

United States Patent 01 Rice 3,508,957 Patented Apr. 28, 1970 3,508,957 COATED RAZOR BLADES Walter Bliichl, Karlsruhe, Germany, assignor to Laura Noss, trading as Firma T ondeo-Werk Adolf Noss No Drawing. Filed Oct. 21, 1965, Ser. No. 500,194 Claims priority, application Germany, Oct. 23, 1964,

Int. Cl. B26b 21/54; B44d N36 US. Cl. 117132 8 Claims ABSTRACT OF THE DISCLOSURE The invention relates to razor or safety razor blades provided With a coating which improves the shaving characteristics of the blades, protects the edges from corrosion, and imparts oil-repellant, anti-adhesive properties to the blades. The invention also relates to a method of applying the coating.

Razor blades provided with a coating for improving their shaving properties, particularly for the purpose of giving a smooth shave, are already known in the art. However, these known razor blades have several drawbacks, principally that whenever such blades are very keen they generally lose this property after a very few shaves, whereas blades which remain keen for a longer time have an initial keenness which is inferior to that of those which in use preserve their keenness for only a short length of time.

In the first case, i.e., when the blades are very keen to start with, the known coating consists of a silicon-containing organic polymer, whereas in the second case the known coating on the edge consists of polytetrafluoroethylene.

The application of a polytetrafiuoroethylene (PTFE) coating presents difliculties because PTFE lacquers demand high stoving temperatures. Such a coating can therefore be provided only on the more expensive highly alloyed chrome steels which are more difficult to work.

It has been found that blades which have been provided for instance with coatings of a silicon-containing organic polymer by the application of a temperature of 340 C. deteriorate to the quality of an uncoated blade very quickly, in fact halfway through the first shave. If higher temperatures are applied, carbon steel blades become useless for shaving because of the annealing they suffer during the process of applying the coating. Even the more expensive chrome steel razor blades lose much of their hardness at such high temperatures and this impairs the life of the edge.

It in such a process a reasonably satisfactory final hardness is to be achieved chrome steel blades must be used in which the residual austenite can be precipitated by quenching at low temperatures after the hardening process has been performed. This calls for the provision of low temperatures, a necessity which adversely affects the economy of production and raises the cost. Furthermore, this particularly hard and tough razor blade steel is expensive to work. For instance, costly hard metal stamping tools must be used which suffer considerable wear. Moreover, the stoving process requires the provision of a protective gas atmosphere.

If, according to a proposal known in the art the protective gas atmosphere is dispensed with, as is usual for stoving PTFE lacquers, then the razor blades thus obtained very rapidly lose their keen edge, halfway through the first shave. The protective gas atmosphere is therefore indispensable.

This again necessitates the performance of an uneconomical, relatively unproductive batch process or the use of extremely complicated air lock devices for running an automated production line.

It has now been discovered that these drawbacks can be avoided if the blades are treated or rather coated with polyperfiuoropropylene.

Polyperfluoropropylene can be produced by the method described in published German application 1,137,218.

The success of this step was quite unexpected, since the effect of a polymer in the form of a coating depends not alone upon its chemical structure but also upon a well defined degree of cross linkage and branching. For instance, even PTFE is unsuitable for treating razor blades if its molecular weight is excessive or too low. This is borne out by the properties of blades which according to prior proposals have been treated with a thermally degraded PTFE. If other fluorocarbon polymers are used, such as those known under the name Scotchgard impregnation P68 (3M Company, Messrs. Pfersee) or polymerised perfiuorophenylene, Kel-F Viton or copolymers of tetrafiuoroethylene and trifluoroethylene or vinylidene fluoride, the results are consistently negative. Both polymers which are soluble in solvents have nearly the same linear structure as PTFE without branching. The only difference is that the polymer chain bears a chlorine or two hydrogen atoms instead of a fluorine atom at shorter or longer intervals. The effect of these polymers on razor blades, irrespectively as to how applied and subsequently treated, is to produce edges on treated blades that are inferior to those of untreated blades despite the presence of the polymer chain with a multitude of CF -CF groups.

It was therefore not to be expected that polyperfluoropropylene, which differs so radically from polyfluoroethylone in its properties, its highly branched structure and many side chains, should be a highly effective substance for improving the keenness of the blades. Polyperfluoropropylene (PPFP) has three times the stiffness of PTFE (131 kg./sq. mm. as against 43 kg./sq. mm., measured by the Tinius Olsen-ASTM standard D747). In contrast to PTFE, PPFP is fusible and a pronounced thermoplastic. It is soluble in specific solvents, a fact which permits the inference that the crystalline and geometrical configuration of its chains is different. The variation of its mechanical properties with temperature is also different.

This material permits even carbon steel blades to be treated, because a stoving temperature in the region of 200 C. can be chosen. This low stoving temperature also permits the treatment to be performed in the absence of a protective gas atmosphere. Another advantage is that it may not be necessary to use dispersions and that solutions can also be used. Cheaper carbon steel blades can thus be employed and the more expensive raw materials saved.

Razor blades coated according to the invention are anti-adhesive, dirt repellant and their edges are corrosion resistant. Whereas a normal carbon steel blade keeps its edge for only about two shaves, blades treated as herein proposed keep their keen edges for more than five to eight shaves.

The procedure adopted for applying the coating will be hereunder described.

The finished ground and polished blades are very carefully degreased. Possibly they may be thoroughly rewashed with water with the addition of a detergent and/ or perfiuorodetergent. The blades are sprayed with an aqueous emulsion of a PPFP solution in a perfluoroalkane or, after having been previously dried, they may be dipped into the pure solution or its emulsion. Alternatively the pure solution or its emulsion may be sprayed on the blades. The blades are then dried and preferably heated for five minutes toseveral hours at temperatures exceeding 190 C. In the case of carbon steel blades it is best to keep the temperature under 250 C. A protective gas atmosphere is unnecessary until the temperatures exceed 250 C. if such high temperatures are to be used. Otherwise the blades are simply heated in air. The safety razor blades thus obtained give a shave that is decidedly smooth and this remains so for a large number of shaves.

The invention is illustrated by the following examples.

EXAMPLE 1 (A) An 0.5% solution of PPFP in perfluoro-l,3-dimethylocyclobutane is emulsified with the aid of an Ultratnrrax (mechanical high frequency apparatus for dispersing, dissolving, homogenising and emulsifying for the performance of physical and chemical material changes) in twice the quantity of Water containing a perfluorinated emulsifier, such as perfluorocaprylic acid or its ammonium salt, in a dilution of 0.01%. This produces a sprayable emulsion. I

(B) A batch of carbon steel razor blades and ice hardened chrome steel razor blades was degreased with benzene in a Soxhlet apparatus for two days. After being dried, the cutting edge side of this batch was sprayed with the suspension prepared as set out in Example 1A, from a spray gun. The blades were then dried. The carbon steel blades were heated for one hour at 210 C., whereas the chrome steel blades were heated at 260 C. for fifteen minutes.

EXAMPLE 2 A batch of blades was degreased as described in Example 1B and sprayed with a solution of PPFP in perfiuorooctane. Stoving was as described in Example 1B.

EXAMPLE 3 A dried chrome steel blade which had been sprayed as described in Examples 113 or 2 was tempered in a protective gas atmosphere at 350 C. for ten minutes.

4 EXAMPLE 4 Blades that had been degreased in the manner described in Example 1B were washed with an aqueous 0.05% solution of ammonium salt of perfluorocarbylic acid and dried. The blades were then further treated in the same way as in Examples 113, 2 or 3.

The finished coated blades of the above examples had an excellent keenness and gave a very smooth shave for a relatively large number of shaves.

I claim:

1. The process for improving the shaving properties of carbon steel razor blades wherein the cutting edge or edges of mechanically completed and cleaned blades are coated with a solution of polyperfiuoropropylene and then heated at a temperature between about C. to 250 C.

2. The process of claim 1 in which said solution is applied to said blade as an emulsion.

3. The method of claim 2 in which said emulsion includes a perfluorinated emulsifier.

4. The method of claim 1 wherein said blade is heated in an atmosphere of air.

5. The method of claim 1 wherein said blade is heated for five minutes to several hours.

6. The method of claim 1 wherein said solution of said polyperfluoropropylene comprises a perfluoroal-kane as a solvent for said perfluoropropylene.

7. The method of claim 1 wherein said solution of polyperfluoropropylene is sprayed on to said blade as a suspension.

8. A razor blade made by the method of claim 1.

References Cited UNITED STATES PATENTS 2,958,685 11/1960 Eleuterio 260-921 3,071,856 1/1963 Fischbein 117-161 X 3,203,829 8/1965 Seyer et al 117132 3,206,344 9/ 1965 Elkins 15-6-86 X 3,341,348 9/1967 Letendre 1178 3,376,183 4/1968 Flynn et a1. 156t244- RALPH I. KENDALL, Primary Examiner US. Cl. X.R.