Cutlery – Razors – Curved edge
Reexamination Certificate
2003-02-28
2004-10-19
Goodman, Charles (Department: 3724)
Cutlery
Razors
Curved edge
C030S050000, C030S346550
Reexamination Certificate
active
06804886
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC
Not Applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention is concerned with safety razors of the kind in which a blade unit assembly is carried by a handle and includes at least one blade with a sharp cutting edge which is moved across the surface of the skin being shaved by means of the handle. A blade unit may be mounted detachably on a razor handle to enable the blade unit to be replaced by a fresh blade unit when the blade sharpness has diminished to an unsatisfactory level, or it may be fixedly attached to the handle with the intention that the entire razor be discarded when the blade or blades have become dulled. Detachable and replaceable blade units are commonly referred to as shaving cartridges. The present invention is particularly concerned with the blades of safety razor blade units, and relates specifically to elongate blades having cutting edges which extend along the blades.
(2) Description of Related Art
Safety razor blade units generally include, in addition to the at least one blade, a guard which defines a surface for contacting the skin ahead of the blades as the blade unit is moved across the skin in the performance of a shaving stroke, and a so-called cap defining a surface for contacting the skin behind the blade(s). It is well known that to achieve the best possible performance the or each blade must be orientated with respect to the cap and guard surfaces so that it is inclined to a plane which is tangential to those surfaces (the “tangent plane”). By the blade being inclined it is meant that the mid-plane of the sheet material of the blade, which plane bisects the angle defined between the edge facets that form the cutting edge at the blade tip, is at an angle, sometimes called the “blade tangent angle”, to the tangent plane. A blade can be fixed in position so that the blade tangent angle does not vary to any significant extent when the razor is being used, but it is also known to mount blades movably within the frame so that their blade tangent angles may change as a consequence of blade movements in the performance of a shaving stroke. In either case it has been the prior practice to support the or each blade in safety razor blade units so that a substantially planar blade element which includes the cutting edge and a blade section extending back from the faceted edge for at least several millimeters, lies at an appropriate angle to the tangent plane. In one well known construction planar blade elements are mounted on bent blade supports which have a forwardly and upwardly inclined portion on which the blade elements are carried, and upright rear portions which are slidably guided. in the frame in which the blades are mounted. The need to set the blade tangent angles by correct positioning of the blades during blade unit assembly is inconvenient and has a tendency to complicate the construction of the blade units as well as the assembly procedures themselves. Furthermore, in modern safety razors it is common to have two or three blades with parallel edges, and having a plurality of such blades lying in respective planes inclined to the tangent plane can inhibit blade unit flexibility should that be desired.
There have been proposals for safety razors with blade elements having circular cutting edges which extend around holes in the elements. Examples of such safety razors are those described in U.S. Pat. Nos. 5,201,253 and 5,490,329. Unlike a straight-edged blade, the blade elements with circular cutting edges can not be inclined to the sharpened edge at a desired angle and position with respect to the skin during shaving. Therefore, these blade elements need to be made to ensure the required shape and inclination of the edges, such as by special grinding techniques as taught by U.S. Pat. No. 5,490,329, and/or the required shape can be imparted to the circular edges by deforming the edges after sharpening, as described in U.S. Pat. No. 5,201,253. These proposals have been addressed specifically to overcome problems inherent with blade elements with circular cutting edges, and they have no obvious application to blades with straight edges which do not present the same difficulties.
In U.S. Pat. No. 5,010,646 there is described a safety razor blade unit incorporating blades which are bent so that a cutting portion along which the sharpened edge extends is at an angle of about 112° to a base or guide portion, both portions also being corrugated for stress relieving purposes. Blades bent in this way have substantially reduced flexibility and do not offer any solution to the above mention drawbacks of the hitherto known planar blades.
There is described in U.S. Pat. No. 3,938,250 a composite blade assembly for a safety razor, which composite blade assembly includes a planar blade and a supplementary blade member fastened to the underside of the planar blade, the supplementary blade member being bent to increase the span between the cutting edges respectively provided on the planar blade and the supplementary blade member. Also, the blade tangent angle of the supplementary blade member is reduced by this, blade member being bent. The bent blade member is specifically adapted to the production of a composite tandem blade and it does not offer any obvious solution to the drawbacks of the known arrangements which limit flexibility by requiring the blades to be set at certain inclinations to provide the desired blade tangent angles.
With a blade of this form a relatively small tip section can be bent to achieve the desired blade tangent angle with the major part of the blade being substantially planar and lying parallel to the tangent plane, thereby enabling enhanced flexibility, especially in blade units equipped with multiple blades.
BRIEF SUMMARY OF THE INVENTION
The present invention has for its objective to eliminate, or at least substantially alleviate the limitations of the prior art blade arrangements. The invention is directed particularly to a blade for a safety razor blade unit, comprising an elongate blade element with upper and lower surfaces, a forward edge section having a sharp cutting edge extending therealong and defined by surface portions which taper towards the tip of the cutting edge, and a substantially planar blade section extending rearwardly from the edge section and over which the upper and lower surfaces are parallel, wherein in a transition region between the planar blade section and the forward edge section the lower surface has a convex curvature and the upper surface is non-convex and is preferably concave.
According to an aspect of the invention there is provided a blade of the form described above wherein, along at least most of the length of the blade, the blade cross-section has a minimum second moment of area not greater than 1.0×10
−4
mm
4
.
The second moment of area of the blade cross-section is dependent on the size and shape of the cross-section and is a measure of blade flexibility. Although flexibility is dependent on the Young's modulus of the blade material, razor blade materials currently used have Young's moduli close to one another so the second moment of area is a good indicator of blade flexibility. The second moment of area is measured with respect to an axis, and by the minimum second moment of area it is meant the moment of area determined with respect to that axis which results in the lowest value for that blade cross-section. It is preferable that the minimum second moment of area does not exceed 0.5×10
−4
mm
4
and blades having a minimum second moment area less than 0.35×10−
4
mm
4
, and even less 0.20×10−
4
mm
4
, e.g. around 0.14×10
4
mm
4
or lower are possible.
In accordance with another aspect the invention provides a blade of the form defined above wherein a plane bisecting the tip of the blade edge is inclined to the mid plane of the planar blade section
Goodman Charles
The Gillette Company
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