Note: Descriptions are shown in the official language in which they were submitted.
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5606-04-CWA
IMPROVED BLADE EDGE
Background of the Invention
I . Field of the Invention
This invention relates to the forming and coating of blade edges to modify the
cutting performance of the blade edge.
2. Description of Related Art
Razor blade m~nllf~ctllrers have over the years attempted various means of
improving shave performance. The primary goal of the m~nllf~Gtl,rers has been toimprove shave pe,~ lance and comfort by redllcing the required cut force and increasing
the life of the blade edge. Generally, efforts at improving shave pc. îol ...~-ce and reducing
cut force have focused on providing edges with thinner, and lI.eG.elically sharper, edge
profiles than prevailing blades. Since the thinner edges are weaker than their thicker
counterparts, there have been efforts to simult~neously increase the ~ nglh of the edge.
With regard to cut force, one means of reduçing cut force is to modify the geometry of the
razor blade edge. It has been found that reducing the width of the blade edge for some
~i~t~nce back from the tip will improve shave pcl~llllance by cut force reduction.
However, reduction in the edge width also weakens the edge and leads to more rapid
deterioration due to mecll~nical deformation during cutting.
A typical razor blade edge has a wedge shape with a pr~,fc"ed inrh~ded angle of
appro~i".~lely 20 degrees. This wedge may be further characterized by its tip radius,
which is the radius of curvature of the I ~Itim~te cutting tip, and the thickness of the edge
for a ~ t~nce back from the ultim~te tip. Typically, the tip radius is specified as being less
than 500 A. The edge thickness is a function of ~ Ance from the ultim~te edge. For
example T2 and T 10 may be defined as the width of the edge 2 microns and 10 microns
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back from the ultimate edge respectively. Typical razor blades have T2 values in the range
of from 0.85 ~ and T10 values in the range of 3.3-4.0 ,u. Standard mechanicalgrinding and honing operations give the edge a bit of a convex shape which has been
described as a '~gothic arch" shape. Most razor blades have a thin layer of chromium on
the cutting edge to increase the blade's corrosion resistance and to provide a good base
for the application of a lubricating polymer such as polytetrafluoroethylene (PTFE).
PTFE has an extremely low coefficient of friction and its use has become virtually
universal in the razor blade industry. PTFE (an example of which is sold by duPont under
the name KRYTOX 1000) is deposited on the blade edge as a fine powder which is heated
above the melt point so that it flows and bonds to the blade edge. The lubricating polymer
reduces the force required for the edge to cut through hair. Standard felt cutting tests
demonstrate the large reduction in cut force for a PTFE coated edge compared to an
uncoated chromium edge.
While the addition of a polymer to the blade edge reduces the cut force, a closelook at the ultimate edge of the blade reveals that the ultimate tip is not fully covered by
PTFE. Scanning electron microscope (SEM) micrographs show that the molten polymer
has a tendency to pull back slightly from the edge. Con~eq~lently, polymer coated razor
blades contain an uncoated region e~ctending up to a few microns back from the tip of the
blade. Therefore, the ~ltim~te tip and cutting point does not benefit from the lubricating
effect of the PTFE. It is an object of this invention to improve the lubrication of this small
but critical area. It is a further object of this invention to improve the ~llengl}1 of the
ultimate tip of the razor blade.
Various means to streng~hçn the edge, from using harder substrates for blades tothe use of hard coatingc to ~Llen~,lhen the edge, have been proposed. An ~,~al.,ple of a
substrate that is inhe~el.lly stronger than the prese~llly used grade of stainless steel is
described in U.S. patent 5,121,660 issued to Kramer. Kramer discloses a blade made of a
polycrystalline ceramic material which is significantly harder than steel. However, this
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material is difficult to process and has not yet found commercial application for ra~or
blades.
Hard coatings have been described numerous times as a means of increasing edge
strength. For example, U.S. patent 4,933,058 issued to Bache~ et. al. describes the use of
ion bombardment during hard coating deposition to achieve a prescribed tip shape. This
tip is narrower than standard blades, but retains its strength due to the presence of a thick
hard coating on the tip. U.S. patent 5,295,305, issued to Hahn~ et. al. discloses the use of
a diamond-like carbon (DLC) coating over various adhesion interlayers. The DLC coating
is said to provide strength and high quality shaving performance. U.S. patents 5,142,785,
issued to Grewal and 5,232,568, issued to Parent. et. al. both describe the use of DLC
coatings over a molybdenum adhesion layer. Other patents have similarly disclosed a
variety of ceramic coatings applied to strengthen the blade edge.
The modification of edge shape to provide a suitable substrate for hard coatings is
disclosed in U.S. patent 5,032,243, issued to Bache. et. al. This patent discloses a method
for modifying edge shape through ion beam bo~"bard.nenl. The ion beam removes
material from both sides of the &cet thus red~lc.ing its width. The ion beam method is
proposed due to the difficulty in obtaining such blade profiles using ~..ech~l-ical grinding
means. However, the ion beam method has its own difficulties and such an arrangement
remains to be commercialized.
A somewhat di~I~renl means of increasing blade life is disclosed in U. S. patent5,488,774, issued to Janowski. This patent discloses the use of a diamond or DLCcoating to reduce shaving degradation due to possible loss of the lubricating polymer
during shaving. It is claimed that the PTFE is gradually removed from the edge and that
the presence of a low friction coating will ll~;n.lll;~.Ç the effect of the PTFE removal.
As can be seen, extensive effort has gone into producing thinner and stronger blade
edges that ",;ni",i7e cut force while providing normal or extended life. Most ofthese
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methods employ sophisticated means of shaping the blade edge followed by a thickcoating of a hard material to strengthen the edge. These methods are difficult to
implement and it would be advantageous to produce a blade that has the benefits of a
thinner blade edge, i.e. Iow cut force, but without the attendant strength and production
difficulties.
Consequently, it is an object of the present invention to describe such a razor blade
and a means for production that avoids much of the difficulty associated with prior
designs. Such a blade would advantageously have enhanced strength and durability and
exhibit reduced cut forces compared to standard razor blades.
Summary of the Invention
The present invention is directed to a blade edge with improved shave pel rOI .llance
and a method of m~m~facturing such blades. To achieve the desired result the tipthickness, tip radius and cut force are increased, either by application of a first, non-
polymeric coating or by some other means, and then the blade is coated with a second
non-polymeric adherent coating having a very low coefficient of friction. Suitable
materials for the second coating include the class of carbon films which include diamond,
amorphous diamond, and diarnond like carbon (DLC). Another material with a suitably
low coefficient of friction is Molybdenum disulfide. The thickness of the coating need
only be such that a continuous film, typically less than 500 ~, is forrned over the blade
edge up to and incllJding the ultimate tip. The aspect ratio of this film is approximately
1:1, there is no need for the high aspect ratios claimed in previous disclosures. The blade
is then coated with a lubricating polyrner, such as PTFE, as is standard practice in the
industry. The resulting blades cut with a signicantly lower cut force than comparable
blades without the low coefficient of friction film. The blade pe~ Çol Ills as if the edge were
sharper and thinner while ret~ining the original edge geometry. Because the edge is of at
least standard thickness it retains the ha~dness and durability of a regular edge
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A preferred embodiment of the invention emphasizes edge durability. In this casethe edge is made thicker than usuaJ via coating or grinding. Normally the thickening
would have the effect of increasing the cut force and compromising shave performance.
However, the addition of the coating of this invention reduces the cut force to a nominal
level thus restoring shave comfort. Such coated blades last significantly longer and
provide better shave performance than their uncoated counterparts by virtue of their
thicker and stronger edge.
Brief Description of the Drawings
Figure I is a chart illustrating the indent depths of blade edges having di~e-encoatings. A smaller indent signifies a stronger edge.
Figure 2 is a chart illustrating the effect of the coating of this invention on average
cut force for 20 cuts.
Detailed Description of the ~lefel led Embodiments
Rerelence will now be made in detail to the presently plefe-,ed embor~im~nts ofthe
invention.
The blade edge of the present invention comprises a razor blade having an
increased tip thir~ness and tip radius, a reduced cutting force and a longer usable life. In
order to provide these desireable pl ope. lies, a substrate is provided in which the portion
which is to be the cutting edge is prepared with a profile either nominal to or thicker than
that of prevailing blades, res.llting in increased tip thicl~nçss. tip radius, cut force and
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coefficient of friction. The increased thickness may be achieved in various manners, but a
preferred method for achieving this shape is by appropriately grinding or stropping the
edge. A further preferred method of producing this shape is by depositing an inner
coating of suitable thickness onto the edge of the blade. This coating may consist of of
virtually any compatible material inclucling oxides, carbides, nitrides, borides, metals and
any combinations thereof, preferred materials include ceramics, chromium,
chromium/platinum, and chrome nitride The primary criteria for this coating are that it
adhere to the steel substrate and that the coating of this invention adheres to it. In the
p, ~ ,ed embodiment a coating of up to 1500 angstroms of chromium is applied to the
edge of a ground blade The actual thickness of the coating may vary depending on a
number of variables, inclu~in~ the starting edge shape, and a thicker or thinner coating
may be used as desired. The result of the initial thickening step is a blade edge which has
increased tip thickness, increased ~le~ h, increascd tip radius, is less sharp than before
and exhibits a correspondingly higher cut force For eAal",.,lc, such a thickened blade edge
would be less desireable for cutting hair in that it would tend to "pull" the hair and thus
prove uncomfortable during wet shaving
Once a suitable blade edge is obtained, the edge is coated with an outer coating of
a thin film of a non-polymeric material which has a very low coefficient of friction. The
outer coating may be deposited by ion beam sputtering, m~gnetron sputtering, laser beam
ablation, vacuum arc deposition, or any other suitable process. The thickness of this non-
polymeric coating is preferably less than about 1500 an~ o-l,s and an aspect ratio (tip
thickness/flank thickness) of about 1:1 is plefel~bly obtained. In an especially p~efe~ ~ed
embodiment, the thickness of the non-polymeric coating is in the range of from 100 - 1000
angstroms A prel~,.ed value for the low coeffiriçnt of friction is less than about 0 3 and
preferably less than 0 2 Pl~ftllc;d materials having such a low coefficient for the thin film
coating are amorphous diamond, diamond-like carbon (DLC), molybdenum dislllfide~ or
any other similar material. The prefellcd thin film coating material is amorphous diamond.
Amorphous diamond comprises a nonhydrog~nqted version of DLC with at least 40% sp3
carbon bonding, a hardness of at least 45 gigaracc~l~ and a modulus of at least 400
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gigapascals. In contrast, standard DLC has a hardness of only about 30 gigapascals. The
resultant blade edge has a further increased tip radius and tip thickness over the blade edge
having no coating or the inner coating alone, and has a cut force which is significantly
lower than that of the blade edge having the first coating alone. In an especially prefel I ~d
embodiment, the blade edge may be further coated with a lubricious polymer to fi~rther
reduce the cut force. Because this coating has been shown to pull back from the edge the
presence of the hard, thin film of low coefficient of friction causes the blade to show a
significant reduction in cut force over blades having only chromium or other conventional
materials on the edge. This superiority of cut force is evident even over sharper blades
using conventional coatings. In an especially p,~fe-~ed embodiment, the blade edge is first
coated with a thin film having a low coefficient of friction, such as amorphous diamond,
and then with a lubricious polymer such as low molecular weight PTFE or KRYTOX
1000 to provide a shave exhibiting minim~l cut force. The resulting razor blade is
especially advantageous for use with a wet shave razor, and one or more of such blades
may be employed in a razor. The blades may be employed in a wet shave razor which is
either disposable, i.e. the entire razor is discarded after a certain amount of usage, or
pe""anenl which requires disposal and repl~ce~ 1 of only the razor cartridge, but not the
handle, after a certain number of uses.
A variety of methods are available for depositing the coating of this invention.One method uses pulsed laser deposition to generate a plume of vaporized carbon ions
from a solid carbon source. These ions can be directed to the edge of a blade where they
will condense as a hard solid film with a suitable low coefficient of friction. Another
method is the use of sputtering, either RF or DC, to provide a vapor of carbon atoms
which similarly condense onto the blades fo~ g carbon films. Typically, the sputtered
films are not as hard as coatings prepared by other means but they may be used due to
their low coefficient of friction. CVD methods can be utili7çd, using a gaseous
hydrocarbon gas as the source, but these must be done under conditions where the blades
do not exceed 350 C for periods oftime as this will soften the blade steel. A plefe.led
method of depositing the carbon films is by the cathodic arc method. Such a method is
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described fully in patent 5,458,754, assigned to Multi Arc Inc. in New Jersey and the
disclosure of that patent is incorporated herein by reference. In this method carbon ions
are produced with the arc vaporization of a solid graphite target. The patented method
described pro-duces amorphous diamond films with a very low coefficient of friction.
As illustrated in Figure 1, the blade edge which is coated with chromium has
significantly increased strength over the uncoated blade edge. Specifically, an unused,
standard blade edge will be indented to a depth of approximately 650 nanometers by a 4
gram load applied normal to the blade edge. Coating with 300 A of chromium increases
the edge strength as shown by a reduction in indent depth to about 610 nm, while 600
angstroms of chromium coating further reduces the indents to about 595 nm. A 600angstrom chromium coating in combination with an amorphous diamond coating of 200-
300 angstroms significantly reduces the indent range to apploxillldlely 540 nm, thus
illustrating that the blade of the present invention is significantly stronger than a standard
blade.
Figure 2 illustrates the cut force of a standard blade, a less sharp blade made
according to this invention, and a similar less sharp blade including the amorphous
diamond coating. All blades are coated per standard process with PTFE. The standard
blade edge exhibits a cut force of 2.64 Ib. The less sharp blade exhibits an average cut
force of 2.96 Ib. The addition of 250 angstroms of amorphous diamond to the less sharp
blade results in a cut force of 2.46 Ib, a significant reduction over the uncoated blade.
Consequently, blades made according to this invention are exceedin~ly durable and will
continue to exhibit advantages over conventional blades for hundreds of cuts.
While there have been described what are p,escnlly believed to be the p,~;rel,cdembodiments of the present invention, those skilled in the art will realize that various
ch~nges and modifications may be made to the invention without d~pa, ling from the spirit
of the invention, and it is intended to claim all such ch~nges and modifications as fall
within the scope of the invention.
