US3518110A - Razor blade and method of making same - Google Patents

Description

United States Patent Office Patented June 30, 1970 3,518,110 RAZOR BLADE AND METHOD OF MAKING SAME Irwin W. Fischhein, Hyde Park, Mass., assignor to The Gillette Company, Boston, Mass., a corporation of Delaware N Drawing. Filed July 23, 1964, Ser. No. 384,805 The portion of the term of the patent subsequent to June 30, 1984, has been disclaimed Int. Cl. B26b 21/54 US. Cl. 117-93.4 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to safety razor blades, either single edged or double edged, and pertains more specifically to an improved blade having on a cutting edge an adherent coating of a selected type of fluorocarbon polymer, which blade possesses unique shaving characteristics, and to a method for making the same. The fluorocarbon polymer melts between 310 C. and 332 C. and at 350 C. has a melt flow from 0.005 to about 600 grams per ten minutes.

Although it has heretofore been proposed to improve the shaving characteristics of razor blades by applying to the cutting edges thereof adherent coatings of fluorocarbon polymers, and blades having such coatings have exhibited both improved shaving characteristics and longer life, i.e. an increased number of shaves during which the same blade exhibits acceptable shaving effectiveness, those blades which exhibited optimum effectiveness during the first shave have not exhibited maximum blade life.

The present invention, by making use of a fluorocarbon polymer having special characteristics on the cutting edge of a razor blade in the form of an adherent coating having a thickness Within specified limits, makes it possible toachieve not only optimum effectiveness during the first and succeeding shaves but also an unexpected extension of shaving life beyond that previously attainable.

The razor blades which may be treated in accordance with the present invention to provide the new blades having the improved and unique qualities are from about 30 to 375 microns in thickness and have wedged-shaped cutting edges, the included solid angle of which is greater than 14 and less than 35. Although the faces or sides of some such cutting edges extend back from the ultimate edge for a distance up to as much as 0.25 cm. or even more, it is not necessary that each face be a single uninterrupted continuous surface or facet; it may instead 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, may have a width as little as 7.5 microns or even less as compared to the diameter of a beard hair which averages about 100 to 125 microns, while the thickness of the ultimate edge itself is generally less than 0.6 micron and preferably less than 0.25 micron.

The blade on which the coating of the present invention is applied may be razor blade carbon steel or razor blade stainless steel such as Uddeholm AEB or Sandvikens 11R51 or 12C27 or the like, or any other razor blade alloy steel. Uddeholm AEB stainless steel contains, in addition to iron, 13% chromium, 1% carbon, 1% manganese, and 0.15% silicon. Sandvikens 11R51 contains, together with iron, 17% chromium, 8% nickel, 1.3% manganese, 1.2% silicon, 0.7% molybdenum, and 0.09% carbon. Sandvikens 12C27 contains, along with iron, 14%

chromium, 0.6% carbon, 0.3% silicon, and 0.3% manganese, However, the coating may also be applied to blades having cutting edges of (or coated with) metals or metal alloys other than steel or stainless steel. The metal is hardened by any suitable process, as by heattreating or working. Although there is a limit to the extent to which the blade subsequently may be heated, since excessive reheating Will lead to loss of hardness, some softening or tempering of the blades can be tolerated since its disadvantages are more than offset by the improvement in shaving effectiveness produced by the invention.

The remarkable increase in shaving effectiveness manifested by the blades of the present invention is characterized by a decrease in pull as compared to uncoated blades; that is, a decrease in the force required to cut the beard hairs, which becomes apparent in the noticeably increased ease of shaving.

While the coating of solid fluorocarbon polymer may extend over the entire wedge faces back from the ultimate edge or even farther, it need not cover the entire wedge faces. It may, for example, be confined to a zone extending from the ultimate edge for a distance of only about 50 microns. It need not cover that entire zone, but must cover a major part thereof, and although it need not extend to the ultimate edge itself, it must extend at least to a micron or so from the ultimate edge. However, regardless of its extent, the thickness of the coating, within a distance of about 50 microns from the ultimate edge, must be from. about 0.1 to about 0.3 micron, as measured by interference colors in white light as described in U.S. Pat. 2,937,976 assuming a refractive index of 1.4.

Preferably, for optimum results, the coating must be continuous and of the aforesaid thickness from the ultimate edge for a distance of 50 microns from the ultimate edge.

The solid fluorocarbon polymers which are effective in the practice of the present invention are those which melt between 310 C. and 332 C. and which have at 350 C. a melt flow rate from about 0.005 to about 600 grams per ten minutes, as. measured before application to the blades. The beginning of melting is determined by the first appearance of rounding of angular particle edges by visual observation at a magnification of diameters at a heating rate of 0.5 C. per minute; the end of melting is determined by the disappearance of birefringence between crossed polarizers at the same magnification and heating rate. Both the beginning and the end of melting for any given polymer composition must be Within the range 310 C. to 332 C.

The melt flow rates specified herein were measured following the Tentative Method of Test ASTM Designation: D 1238-57T published by the American Society for Testing Materials as modified by R. E. Wiley in his article published in the May 1961 issue of Plastics Technology at pages 4548. All the measurements were made at 350 C. unless otherwise specified and the extrusion pressure was 43.25 pounds per square inch using a micromelt indexer constructed to the specifications in Wileys paper made of 303 stainless steel with a Stellite orifice having a length of 0.1551 inch. Special care was taken to maintain the orifice at 350 C. by means of an auxiliary heater. Measurements on very low viscosity polymers were made using a plug to prevent premature flow from the extrusion orifice as described by Tordella et al., Modern Plastics 31, 146 (1953). All of the flow rate values are reported as the number of grams of material flowing through the orifice during a ten minute period. The term melt flow rate as used in the specification and claims is intended to have the foregoing meaning.

The preferred polymers are those which contain a chain of carbon atoms including a preponderance of CF --CF groups, such as polymers of tetrafiuoroethylene, including copolymers such as those with a minor proportion, e.g. up to 5% by weight of hexafiuoropropylene. These polymers have terminal groups at the ends ofv the carbon chains which may vary in nature, depend ing, as is well known, upon the method of making the polymer. Among the common terminal groups of such polymers are, -H, -COOH, -Cl, CCl

and the like. While the precise molecular weights and distribution of molecular weights of the preferred polymers is not known with certainty, it is believed that they have molecular weights ranging from about 25,000 to about 500,000. The preferred chlorine-containing polymers are those containing from 0.15 to 0.45% by weight of chlorine (which is present in the terminal groups). There may be used mixtures of two or more fluorocarbon polymers, provided the mixtures have melt and melt fiow rate characteristics as specified above, even though the individual polymers making up the mixture do not possess these characteristics. It will be appreciated that in the case of mixtures containing one component of relatively low molecular weight, as well as in the case of polymers containing a fraction of relatively low molecular weight, part or all of the low molecular weight portion may evaporate during the heating or curing step to which the polymer coating is subjected after application to the cutting edge, as described below. This evaporation of a portion of the fluorocarbon polymer coating may result in a finished coating which has a melt flow rate different from that of the polymer initially applied to the blade or even outside of the range specified above.

The polymers are preferably applied to the cutting edges of the razor blades in the form of a dispersion of finely divided particles in an inert volatile liquid such as water, tert-butanol, or a perfluorinated cyclic ether, or the like. For best results it is desirable that the particle size of the dispersion be as small as possible, preferably from 0.1 to 1 micron, any agglomerations of particles in the dispersion being broken up by subjecting the dispersion to the action of a homogenizer shortly before application of the dispersion to the cutting edge.

The dispersion may be applied to the cutting edge in any suitable manner to give as uniform a coating as possible, as, for example, by dipping or spraying; nebulization is especially preferred for coating the cutting edges, in which case, an electrostatic field is preferably employed in conjunction with the nebulizer in order to increase the efiiciency of deposition. Preheat of the dispersion may be desirable to facilitate spraying, the extent of preheating depending on the nature of the dispersion, for example, in the case of a dispersion embodying tert-butanol, preheating to a temperature of 35 C. may be desirable. Preheating of the blades to a temperature approaching the boiling point of the volatile liquid may also be desirable.

In any event the blades carrying the deposited polymer particles on their cutting edges must be heated at an elevated temperature above the melting range of the polymer to form an adherent coating on the cutting edge. The period of time during which the heating is continued may vary widely, from as little as a few minutes to as long as several hours, depending upon the identity of the particular polymer used, the nature of the cutting edge, the rapidity with which the blade is brought up to the desired temperature, the temperature achieved, and the nature of the atmosphere in which the blade is heated. While the blades may be heated in an atmosphere of air, it is preferred that they be heated in an atmosphere of inert gas such as helium, nitrogen, etc., or in an atmosphere of reducing gas such as hydrogen, or in mixtures of such gases, or in vacuo. The heating must be sufficient to permit the individual particles of polymer to coalesce and spread into a substantially continuous film of the proper thickness and to cause it to become firmly adherent to the blade edge material.

The heating conditions, i.e. maximum temperature, length of time, etc., obviously must be adjusted so as to avoid substantial decomposition of the polymer and/or excessive tempering of the metal of the cutting edge. Preferably the temperature should not exceed 430 C.

The following specific examples illustrate the nature of the present invention. The quality of the first shave obtained with blades of each of the following examples is equal to the best quality obtained with the fluorocarbonpolymer-coated blades hitherto known; and the decrease in quality with successive shaves in the case of blades of each particular example is less than the decrease in quality in the case of the blades previously known, i.e. the shaving life of the present blades is greater than that of those previously known, even when the latter blades were such that the quality of the initial shave was substantially inferior to that of the present blades.

EXAMPLE 1 There was dispersed in a perfluorinated cyclic ether having a molecular weight of 416 (PC 75, Minnesota Mining and Manufacturing Co.), 0.5% by weight of a finely divided solid polymer of tetrafiuoroethylene containing a minor proportion of chlorine and hydrogen atoms in the terminal groups (about 0.26% chlorine and about 0.01% hydrogen by weight) having a melting range from 318.5 C. to 323.5 C. as determined visually between crossed polarizers and melt flow rate measured at 350 C. of 230 grams per ten minutes. This dispersion was sprayed by means of a nebulizer onto the cutting edges of a stainless steel razor blade previously cleaned by thorough washing in trichloroethylene. The ether evaporated and the coated blade was then heated at 330 C. for five minutes in an atmosphere of hydrogen gas. The coating was substantially continuous in the zone extending for a distance of about 50 microns from the ultimate edge and it had a thickness in that zone, as measured by interference colors when viewed in white light at 750 diameters magnification, from 0.12 to 0.27 micron.

EXAMPLE 2 There was prepared an aqueous dispersion containing 0.5 by weight of a polymer of tetrafiuoroethylene containing a minor proportion of chlorine and hydrogen atoms in the terminal groups (about 0.44% chlorine and about 0.06% hydrogen by weight). The polymer had a melting range of 318 C. to 324 C. and a melt flow rate at 350 C. of 300 grams per ten minutes. There was employed as a stabilizer for the dispersion 0.5% by weight of an alkylarylpolyether alcohol (Triton X-l00). Stainless steel safety razor blades were cleaned and preheated in air to 99 C., then coated on their cutting edges with the foregoing dispersion by means of a nebulizer in a 40 kv. electrostatic field. The coated blades, which dried almost immediately by evaporation of the water, were then heated to 370 C. in five minutes in an atmosphere of hydrogen gas and were held at that temperature in the hydrogen atmosphere for eighteen minutes. The blades displayed a coating which was substantially continuous throughout the zone extending about 50 microns from the ultimate edge. The coating had a thickness throughout the zone of approximately 0.12 micron, when measured as in Example 1.

EXAMPLE 3 There was prepared in the cyclic ether of Example 1 a dispersion of 1.0% by weight of a finely divided polymer of tetrafiuoroethylene containing a minor proportion of chlorine and hydrogen atoms in the terminal groups (about 0.18% chlorine and 0.02% hydrogen by weight). The polymer had a melting range of 320 C. to 325 C. and a melt flow rate at 350 C. of 40 grams per ten minutes. This dispersion was sprayed as described in Example 1 in a 40 kv. electrostatic field on the cutting edge of a stainless steel safety razor blade. The blade was then heated as described in Example 2. The blade had a substantially continuous and uniform coating extending for a distance of about 50 microns from the ultimate edge, which coating had a thickness of approximately 0.27 micron throughout the zone, when measured as in EX- ample 1.

A carbon steel razor blade was coated in the same manner with the same dispersion except that the blade was heated in vacuo instead of in hydrogen. The finished blade had a coating substantially identical with that produced on the stainless steel blade.

EXAMPLE 4 A polymer dispersion was prepared as described in Example 1, except that the polymer employed contained about 0.36% chlorine and about 0.02% hydrogen by weight and had a melting range of 323.5 C. to 326.5 C. and had a melt flow rate at 350 C. of 2.3 grams per ten minutes. This dispersion was applied to the cutting edge of a stainless steel razor blade, as described in Example 1, the blade was heated to 370 C. in five minutes in an atmosphere of hydrogen gas and held at that temperature in that atmosphere for eighteen minutes. The blade displayed a substantially continuous coating in the zone extending approximately 50 microns from the ultimate edge and the coating had a thickness ranging from 0.12 to 0.27 micron throughout the zone, when measured as in Example 1.

EXAMPLE 5 Tetrafluoroethylene was polymerized in a diluent consisting of a cyclic dimer of hexafiuoropropylene using ditertiary-butyl peroxide as a catalyst. The polymer contained terminal groups derived from the cyclic dimer and also contained in the terminal groups about 0.03% hydrogen by weight. The polymer had a melting range of 321.5 C. to 325.5" C. and a melt flow rate at 350 C. of 2.2 grams per ten mintes. A dispersion of this polymer was prepared and applied to a stainless steel safety razor blade as described in Example 1, except that the coated blade was heated to a temperature of 370 C. in five minutes in an atmosphere of hydrogen gas and was held at that temperature for eighteen minutes in the same gas. The coating on the cutting edge of the blade was substantially continuous in the zone extending from the ultimate edge for a distance of about 50 microns and the thickness of the coating in that zone, was from 0.12 to 0.27 micron, when measured as in Example 1.

EXAMPLE 6 A finely divided solid polymer of tetrafluoroethylene containing a minor proportion of chlorine and hydrogen atoms in the terminal groups (about 0.03% chlorine and 0.01% hydrogen by weight) with a melting range of 323.5 C. to 330.5 C. and :a melt flow rate at 350 C. of 0.4 gram per ten minutes was dispersed in the ether of Example 1 to form a 0.05% weight dispersion. This dispersion was sprayed by means of a nebulizer and a 40 kv. electrostatic field onto the cutting edge of a clean stainless steel razor blade. The blade was heated to 370 C. in five minutes in a hydrogen gas atmosphere and held at 370 C. for eighteen minutes in this atmosphere. The blade displayed a continuous coating in the zone extend ing from the ultimate edge for about 50 microns, the coating having a thickness from 0.12 to 0.27 micron throughout the zone, when measured as in Example 1.

EXAMPLE 7 A finely divided solid polymer of tetrafluoroethylene containing about 0.06% chlorine and 0.01% hydrogen by weight in the terminal groups with a melting range of 325 C. to 328.5 C. and amelt flow rate at 350 C. of 0.001 gram per ten minutes was mixed with an equal 6 Weight of a finely divided solid polymer of tetrafiuoroethylene containing about 1.0% chlorine and 1% hydrodrogen by weight in the terminal groups, with a melting range of 265 C. to 295 C. and a melt flow rate at 350 C. much greater than 600 grams per ten minutes. The melting range of the mixture was 313.5 C. to 322.5 C. and the melt flow rate of the 50-50 solid mixture at 350 C. was 0.8 gram per ten minutes. This mixture was dispersed in the ether of Example 1 to form a 0.35% by weight dispersion which was sprayed by means of a nebulizer and a 40 kv. electrostatic field onto the cutting edge of a clean stainless steel razor blade. The blade was heated to 370 C. in five minutes in a hydrogen gas atmosphere and held at 370 C. in that atmosphere for eighteen minutes. The blade displayed a coating like that of Example 6.

EXAMPLE 8 Tetrafluoroethylene was polymerized in aqueous dispersion with methyl alcohol as the telogen using ammonium persulfate as the catalyst. The terminal groups of the polymer included hydroxymethyl and carboxyl groups. The polymer had a melting range of 323.5" C. to 328.5 C. and a melt flow rate at 350 C. of 0.008 gram per ten minutes. An aqueous dispersion containing 0.5% by weight of this polymer was prepared using 0.1% by weight of an alkylarylpolyether alcohol as dispersing agent. The dispersion was applied to the cutting edges of stainless steel razor blades as described in Example 2. The finished blades possessed a substantially continuous coating on their cutting edges extending from the ultimate edge for a distance of about 50 microns, the thickness of which was from 0.12 to 0.27 micron in that zone, when measured as in Example 1.

EXAMPLE 9 A dispersion was prepared as described in Example 1 of a copolymer of tetrafiuoroethylene with a small proportion of hexafiuoropropylene (about 2.5% by Weight). The copolymer contained about 0.1 chlorine and about 0.02% hydrogen by weight in the terminal groups. The copolymer had a melting range of 320.5 C. to 328.5 C. and a melt flow rate at 350 C. of 0.1 gram per ten minutes. The dispersion was applied to the cutting edge of a stainless steel razor blade, cleaned as described in Example l, by means of a nebulizer and employing a 40 kv. electrostatic field. The blade was heated to 370 C. in five minutes in an atmosphere of helium gas and held at that temperature in that atmosphere for eighteen minutes. The blade possessed a substantially continuous coating in the zone extending from the ultimate edge for a distance of about 50 microns, the coating having a thickness of 0.12 to 0.27 micron in that zone, Where measured as in Example 1.

EXAMPLE 10 The polymer described in Example 3 was mixed with an equal weight of a finely divided solid polymer of tetrafluoroethylene containing about 1% chlorine and 1% hydrogen by weight in the terminal groups, with a melting range of 265 C to 295 C. and a melt flow rate at 350 C. much greater than 600 grams per ten minutes. The melting range of the mixture was 314 C. to 321.5 C. and the melt flow rate of the 5050 solid mixture at 350 C. was 600 grams per ten minutes. This mixture was dispersed in the ether of Example 1 to form a 0.5 by Weight dispersion which was sprayed by means of a neblizer and a 40 kv. electrostatic field onto the cutting edge of a clean stainless steel razor blade. The blade was heated to 370 C. in five minutes in a hydrogen gas atmosphere and held at 370 C. in that atmosphere for eighteen minutes. The blade displayed a coating like that of Example 9.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the variations and modifications which suggest themselves to persons skilled in the art.

What is claimed is:

1. A safety razor blade having on its cutting edge an adherent coating consisting essentially of a solid fluorocarbon polymer melting between 310 C. and 332 C. and having at 350 C. a melt fiow rate from about 0.005 to about 600 grams per ten minutes as defined herein, said coating being cured in situ by heating above its melting range and having a thickness from about 0.1 to about 0.3 micron in the zone extending from the ultimate edge for a distance of about 50 microns.

2. A safety razor blade as claimed in claim 1 in which said polymer contains a chain of carbon atoms including a plurality of CF CF groups.

3. A safety razor blade as claimed in claim 1 in which said blade is stainless steel.

4. A safety razor blade as claimed in claim 3 in which said polymer is a homopolymer of tetrafiuoroethylene.

5. A safety razor blade as claimed in claim- 3 in which said polymer is a copolymer of tetrafluoroethylene with up to 5% by weight of hexafiuoropropylene.

6. A safety razor blade as claimed in claim 3 in which said polymer contains from 0.15 to 0.45% by weight of chlorine.

7. A method of making a razor blade which comprises depositing on its cutting edge a composition comprising a solid fluorocarbon polymer melting between 310 C. and 332 C. and having at 350 C. a melt flow rate from about 0.005 to about 600 grams per ten minutes as defined herein, and heating the deposited polymer to a temperature above its melting range to form an adherent coating on said cutting edge which has a thickness from about 0.1 to about 0.3 micron in the zone extending from the ultimate edge for a distance of about 50 microns.

8. A method as claimed in claim 7 in which said heating is carried out in a reducing atmosphere.

9. A method as claimed in claim 7 in which said heating is carried out in an inert atmosphere.

10. A method as claimed in claim 7 in which said blade is stainless steel.

11. A method as claimed in claim 7 in which said deposition is carried out by spraying in an electrostatic field.

References Cited UNITED STATES PATENTS 3,019,126 1/1962 Bartholomew 11793.4 X 3,071,856 1/1963 Fischbein l17132 X 3,203,829 8/1965 Seyer et al. 117--132 3,283,117 11/1966 Holmes et al 117-1052 3,402,468 9/1968 Kiss et al. 117--132 OTHER REFERENCES Brenner et al.: High Temperature Plastics, 1962, Reinhold Pub. Corp., TP986A2B75, pp. 113-116.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R.