CZ296574B6 - Razor blade unit - Google Patents

Abstract

In the present invention, there is disclosed a razor blade unit having an elongate blade (15) with a rectilinear sharpened edge, and a skin contacting surface (SC) surrounding the blade edge(s) and including guard and cap surfaces (2, 4) on opposite sides of the blade edge(s), the aspect ratio of the length (L) to width (W) of the skin contacting surface (SC) being in the range of from 1 to 4, as seen in cross section in a plane perpendicular to the blade (15) edge(s) the skin contacting surface (SC) being convex, wherein the razor blade unit edge adjacent to a cap surface (3) is oval or has rounded or obtusangular corners and wherein the overall length (L) of the blade unit at the skin contacting surface (SC) being not greater than 60 mm. The skin-contacting surface (SC) has a circumscribing perimeter (5) confining a footprint area of at least 450 mme2 and with at least one aperture (2) to accommodate said at least one blade (15). The footprint area has a circularity C given by a relation C = (A/Pe2) x 4{pi} x 100, and defined in percentage wherein A is the footprint area and P is the footprint area perimeter, wherein said circularity size is at least equal to the lower value of the Ci65, CiRW values wherein Ci65 = 65 percent and CiRW represents circularity of a substantially rectangular area having the same length and width as the footprint area of the skin contacting surface (SC) and having corner radii of 30 percent of said footprint width.

Description

Razor blade unit

Technical field

The invention relates to razors having a razor blade unit supported by a handle, wherein the razor blade unit comprises an elongate blade or more such edges with parallel edges. A razor blade unit of this type is known, for example, from EP-A-0453906. The razor blade unit may be firmly mounted on the handle, the entire razor being ejected when the blade or edges become dull. Alternatively, the razor blade unit may be detachably attached to the handle to allow the used blade unit to be replaced by a fresh blade unit. Replaceable shaving units are commonly referred to as heads.

BACKGROUND OF THE INVENTION

More recently, it has been a general tendency that the razor blade units have been reduced in size, especially as regards the areal area of the surfaces that are in contact with the skin around the lip during shaving. Most of the cutting units currently available on the market are long and narrow and have substantially rectangular shapes when viewed substantially perpendicular to the skin-contacting surfaces. It has been found that blade shaving units of this shape and size have yielded improved shaving properties compared to larger shaving units.

In particular, the invention is directed to a razor blade for shaving the body, particularly in the armpit region. Shavers for women who are usually shaving underarms have already been available on the market, but, as with other shavers, there has been a strong trend towards shaving units of these narrow-rectangular womens shavers mentioned above. It has become common practice in the art that such narrow-edge razor units are particularly beneficial for underarm shaving, since they more easily reach the relatively deep armpit.

SUMMARY OF THE INVENTION

The present invention provides a razor blade unit comprising at least one elongate blade having a rectilinear sharpened edge and mounted in a substantially rigid carrier and a skin contact surface surrounding said at least one blade and comprising a protective surface and a cover surface on opposite sides of said at least one blade wherein, according to the invention, the aspect ratio of the skin contact area, defined as the ratio of its length, measured between the extreme ends of its outer circumference along the carrier, to its width measured perpendicular to the cutting edge is in the range of 1 to 4; in a cross-sectional plane perpendicular to the cutting edge of the cutting edge convex, the edge of the cutting unit adjacent to the guard surface being rounded or having rounded or obtuse corners, the length of the contact surface being at most 60 mm, a surface having at least one hole for receiving said at least one cutting edge and having a size of at least 450 mm ² , the trace surface having a circularity C given by C = (A / P ² ) x 4π x 100 and expressed as a percentage where A is the area of the footprint area and P is the perimeter of the footprint area, the size of which is at least equal to the lower of C ₆ 5, CRW, where C ₆₅ = 65% and CRW roundness reference surface having the shape of substantially a rectangle having a length equal to the length of the footprint area, and width equal to the width of the footprint, and with rounded corners with radii of curvature of 30% of the footprint width.

Preferably, the aspect ratio of the skin contact area is in the range of from 1.5 to 2.8, preferably from 1.5 to 2.8

2.0 to 2.5.

-1 CZ 296574 B6

According to another feature of the cutting unit according to the invention, in its transverse profile, the line intersecting the edges of the guard surface and the covering surface adjacent to the blade or blades away from the blade or blades is inclined at an angle (α) of at least 5 ° relative to the plane tangential to the portions skin contact areas immediately in front of and behind the blade or edges. Preferably, the magnitude of the angle (α) in the region of the shield surface as well as in the region of the cover surface is in the range of 10 ° to 20 °.

According to a further feature of the invention, in the transverse profile of the cutting shaving unit, the contour curve of the skin contact surface touches from the inside at least three points of the circle. Preferably, the contour curve of the skin contact surface is in the region of the guard surface, and the cover surface is substantially identical to the corresponding parts of the circle.

According to another feature of the invention, the trace surface has a circularity in the range of 70 to 85%.

The track surface may have a circularity greater than that of the reference surface, having a substantially rectangular shape with a length equal to the length of the track surface and a width equal to the width of the track surface and with rounded corners with rounding radii of 10% of the track surface length.

According to another feature of the invention, the aspect ratio of the skin-to-skin contact area is less than 3 and its trace surface has a circularity greater than that of said reference surface.

At least one of the leading edge and trailing edge of the cutting unit comprises, according to another feature of the invention, a rectilinear portion disposed along a major portion of the length of the cutting edge and parallel thereto, and a smoothly curved corner portion at both ends of the rectilinear portion.

The skin contact area may have semicircular ends. In another embodiment, the skin contact area is ellipse-shaped.

According to a further feature of the invention, the protective surface and the cover surface are each formed by an elastomeric element. The elastomeric element may be a sheet-like structure with pockets distributed over its area.

According to a further feature of the invention, the cutting unit is provided with at least two cutting edges with cutting edges.

According to a preferred embodiment of the invention, the guard surface has an area of at least 140 mm ² and can occupy at least 18.6% of the footprint.

According to another feature, the protective surface and cover surface each have a surface of at least 140 mm ^2, and at the point where the width of the cutting unit is the largest, the protective surface and cover surface each have a width of at least 4 mm.

It has been summarized in the prior art that there has been a strong trend in the art towards the shaving units of these women's narrow rectangular shavers mentioned above, and that it has become a common practice in the art that such narrow blade units are particularly beneficial for shaving. in the armpit, as they more easily reach the relatively deep armpit.

The invention represents a significant deviation from conventional thinking in the shaving field, and goes directly against the results of the development in this field with respect to the dimensions of the cutting unit. Surprisingly, and in contrast to all expectations, shaving tests have shown that not only can a shaving unit of relatively large size have at least the same shaving efficiency as the known smaller shaver for underarm shaving, but large shaving units can be shaped to fit the body area in the armpit, so overall shaving units have better efficiency than overall shaving

The prior art shaving units and that users prefer them. It turns out that with increased stability delivered by a large skin contact area, the user will have greater confidence in the underarm shaving product when the shaver is not easily visible during the shaving process and that the improved comfort perceived by the user is opposed to any loss of efficiency due to large contact area.

In most adult women, the armpit cavity has a minimum radius of curvature of about 25 to 30 mm. The shaving unit of the invention therefore has a length not exceeding 60 mm, preferably not more than 50 mm, and a length in the range of 40 to 45 mm is preferred. The width of the cutting unit is preferably such that the aspect ratio defined above is in the range of 1 to 4, and in most preferred embodiments of the invention the aspect ratio is in the range of 1.5 to 2.8, and more specifically in the range of 2.0 to 2.5. In preferred embodiments, the width of the cutting unit is from 12 to 23 mm, in particular 15 to 20 mm. A protective surface is defined in front of the blade or blades, and a cover surface is defined behind the blade or blades for skin contact before and behind the blades during shaving, and preferably has both a cover and a cover surface of not less than 4.0 mm in width, at least where the width of the cutting unit is at maximum. Both the guard and cover surfaces have a surface area in contact with the skin, preferably not less than 140 mm ² , and the guard and cover surfaces in combination have a surface area preferably of at least 400 mm ² and most preferably from 450 to 500 mm ² .

Since the blade shaving unit of the invention is fairly wide, in order to facilitate skin contact in the armpit, at least most of the guard surface and cover surface, the skin contact surface is formed in a cross-sectional plane perpendicular to the edges of the blade as convex. It is important to understand the word "convex" in the sense of the invention in that it does not necessarily mean that the skin contact surface is smoothly curved, but that it is only required that the guard and cover surfaces extend upward from their edges remote from the cutting edge or edges the cutting edge or edges are at a level that lies above the mutually facing edges of the cover and guard surfaces. More specifically, the lines connecting the outer and inner edges of the guard and cover surfaces are inclined at an angle of at least 5 ° and possibly up to 25 °, to a plane tangential to the skin contacting surfaces before and behind the blades. In preferred embodiments, the tilt angle is in the range of 10 to 20 °, and more particularly substantially equal to 15 °. Due to the convexity of the skin contact surface, the cutting unit is preferably shaped to form at least a three-point contact with an imaginary circumscribed circle having a diameter of 30 to 100 mm, and preferably about 50 mm, thereby ensuring that the convexity of the cutting unit substantially corresponds armpit shape.

An important feature of the razor blade unit of the present invention is that it delimits a large area in which skin contact during shaving, referred to as the definition of the subject invention, can be formed that defines an outer surface known as a " trace area " of at least 450 mm ² . Most preferably, the trace area is in the range of from 600 to 750 mm ^2, and more particularly from 650 to 720 mm ² .

Since the invention proposes a shaving unit with a long and wide shape, a substantially rectangular shape with sharp corners, at least at the edge adjacent to the guard surface, is inappropriate. For the purpose of describing the invention, an angle less than 120 ° with a radius of curvature less than about 3 mm can be considered a sharp corner. Preferably, the curvature at each corner is at least 5 mm. The edge feature "without sharply rounded corners" is defined in the definition of the subject matter as "rounded or having rounded or obtuse corners".

The unacceptability of a substantially rectangular shape and the goal of creating a large contact area means that the cutting unit must be profiled in plan view perpendicular to the skin contact area to obtain a relatively large area within the overall length and width dimensions. The usual way to relate the area bounded by its perimeter to the length of the perimeter is the 'circularity' of a two-dimensional shape, and in this way it is expressed in the form of

This compares to a circle that always provides the maximum surface area for a given circumferential length.

The circularity for any shape is defined by the equation:

A roundness = - x 4π x 100

P ² where A = area

P = circuit.

The razor shaving units of the invention have a circularity of not less than a lower value of (a) 65% and (b) a circularity substantially rectangular area having the same length and width as the traces of the skin contact area and corner radii of 30% width (such area is referred to as a reference area for purposes of the invention). Preferably, the circularity is greater than that of a rectangle of equal length and width, and with corner radii equal to 10% of the length. For shaving units with a low aspect ratio, i.e. less than about 3, the lower limit (a) will apply, although even with these cutting units it is preferred that the roundness is also greater than the limit (b). Acceptable oval shaving units with an aspect ratio above 3.25 may have a circularity of less than 65%. Preferred embodiments with aspect ratios below about 2.75 have a circularity of greater than 70% and especially about 80%. Typical prior art razor blades have a circularity of less than 65%. A comparatively large circularity of the cutting unit according to the invention can be achieved with rounded corners at the ends of the cutting unit having relatively large radii of curvature of at least 6 mm or with oval, elliptical or polygonal shapes which do not necessarily have to be symmetrical.

Taking into account the above, the invention consists in a razor blade unit comprising at least one elongated blade having a rectilinear sharpened edge and housed in a substantially rigid carrier, and a skin contact area surrounding the lip edge (s) and comprising a protective and cover cap. the area on opposite sides of the cutting edge or edges, wherein the aspect ratio of the skin contact surface (as defined above) is in the range of 1 to 4, wherein the skin contact surface is cut perpendicular to the cutting edge or edges convex, total length (i.e., the length measured between the extreme ends of its outer perimeter along the carrier) of the cutting unit in the skin contact area is at most 60 mm, the skin contact area has a circumscribed circumference defining a trace area of at least 450 mm ² , and the circumscribed circumference is shaped the trace area delimited by this circumference has a circularity (as as defined above) not less than a lower value of (a) 65%; and (b) a substantially rectangular area having the same length and width as the traces of the skin contact area and corner radii of 30% of said width; the cutting unit adjacent to the guard surface is free of sharply angled corners.

A razor with a razor blade unit as described above has been shown to exhibit markedly improved overall shaving efficiency in the armpits in shaving tests and has also been shown to be very effective in shaving other body parts such as legs.

It is to be understood that unless stated otherwise, all length and area dimensions herein are measured in the plane of plan view, so that the effect of the convex curvature of the skin contact surface has not been taken into account in determining the appropriate dimensional quantities.

According to a further independent claim, the invention further provides a razor blade unit comprising at least two elongated blades with longitudinally elongated sharpened edges permanently spaced from one another on a carrier comprising a plastic molding, and a skin contact area surrounding the sharpened edges and comprising a protective surface and a covering surface. of which the guard surface is on the front of the cutting unit and the cover surface is on the back

The cutting edges of the lip shaving unit and the blades lie between the guard surface and the cover surface, the blades having sharpened edges oriented in the same direction towards the guard surface, so that during shaving engagement the guard surface, sharpened edges of the blades then gradually touch the skin wherein, according to the invention, the aspect ratio of the skin contact area, defined as the ratio of its length, measured between the extreme ends of its outer perimeter along the carrier, to its width measured perpendicular to the edges is in the range of 1 to 4; is not more than 60 mm, the contact surface defining a circumferential surface with at least one aperture for receiving the at least one cutting edge and having a surface area of at least 450 mm ² , the protective surface having an area of at least 140 mm ² and at least 18,6% areas. Preferably, the guard surface and the cover surface each have a surface of at least 140 mm ^2, and at the point where the width of the cutting unit is the largest, the guard surface and the cover surface each have a width of at least 4 mm.

According to a third independent claim, the invention further provides a razor blade unit for attachment to a razor handle, wherein the razor unit comprises at least two elongated blades with longitudinally elongated rectilinear sharpened edges spaced apart in a carrier comprising a plastic molding, and a skin contact area surrounding sharpened edges of the blades and comprising a front surface and a rear skin engagement surface, the front skin engagement surface lying on the front of the razor blade and the rear skin engagement surface lying on the back of the razor blade, and the blades lying between the front surface for engaging the skin and the rear engaging surface, wherein the blades have sharpened edges oriented in the same direction towards the front surface so that during shaving engagement the front surface, sharp edges of the blades and the back surface the skin, the edges, the carrier, and the front and rear skin engagement surfaces are attachable as a unit to the razor handle, the present invention being the aspect ratio of the skin contact surface, defined as the ratio of its length (L) measured between the extreme ends of its outer periphery along the carrier, to its width (W), measured perpendicular to the blades, in the range of 1: 1 to 2.8: 1, wherein the blade shaving unit is substantially rigid for most of its longitudinal dimension during shaving, wherein the contact surface defines at its outer circumference a track surface of at least 450 mm ² , the front surface having a surface of at least 140 mm ² and at least 18.6% of the track surface, the track surface having a circularity C given by C = (A / P) ⁽² ) x 4π x 100, and expressed as a percentage, where A is the area of the footprint and P is the circumference of the footprint, of at least 70%.

BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is explained in more detail below with reference to the accompanying drawings, in which: FIGS. 1 to 9 show schematic plan views showing the cutting units according to the invention; FIG. Fig. 10 is a diagram showing the circularity plotted in relation to the aspect ratio and showing the results for the razor blade units of Figures 1 to 9 and for some prior art razor blade units; Fig. 11 a schematic cross-section of the razor blade unit of Fig. 1; 1, FIG. 13 shows a perspective view of the shaving unit housing shown in FIG. 1, FIG. 14 is a perspective view of the cutting shaving unit of FIG. an area similar to that shown in Figures 13 and 15 and 16 14 is a view corresponding to FIG. 14 showing the razor blade units with two and three forward facing blades.

DETAILED DESCRIPTION OF THE INVENTION

Each of the cutting units shown in FIGS. 1 to 9 will comprise a lip housing that includes a substantially rigid frame carrier of plastic. The housing defines the contact

A skin area surrounding an elongated rectangular aperture 2 in which a cutting edge (not shown in Figures 1 to 9) is mounted, with a sharp cutting edge. A single cutting edge may be used, but preferably two or more cutting edges with parallel sharpened edges are provided in the aperture 2. In the particular embodiment shown in Fig. 14, three blades 15 are used, two forward and one backward, so that the shaving blade unit will shave in both directions, although moving forward through the skin will yield a slightly better result. Giant. 15 shows an embodiment with two edges 15 in tandem, and FIG. 16 shows another embodiment with three edges 15 with parallel edges, all of which face forward.

Each of the razor blade units of Figures 1 to 9 may be considered to fit two or three blades disposed similarly to the blades 15 in Figure 14 or all in tandem. The housing has, in each of the embodiments shown in Figures 1 to 9, a guard surface 3 located in front of the cutting hole 2 (below) and a cover surface 4 behind the cutting hole 2 (above).

In the figures, the skin-contacting surface SC is further defined, defining a trace surface with its outer periphery 5. Figures 7 and 8 show the length L of the skin contact surface SC, measured between the extreme ends of its outer perimeter along the carrier, and the width W of the skin, measured at its widest point or at its widest perpendicular to the blade 15. aspect ratio of the SC contact area with the skin.

The cutting unit of FIG. 1 is oval and has a rectangular shape with semicircular ends. The dimensions measured in plan view are as follows:

length L width W

42,0 mm

18,0 mm end radius guard surface 3 cover surface 4

9,0 mm

206.0 mm ²

277 mm ² total area of contact surface SC with leather 504 mm ² total trace area inside perimeter 686 mm ²

The cutting unit of FIG. 2 is approximately rectangular with corners with a large radius of curvature. Specific dimensions for this embodiment are:

length L 41,0 mm width W 18,0 mm corner radius corner surface 3 cover surface 4

6.0 mm

213 mm ²

286 mm ² total area of contact surface SC with skin 520 mm ² total trace area inside perimeter 703 mm ²

-6GB 296574 B6

Giant. 3 shows an asymmetrically shaped cutting unit. At the ends of the front edge of the shaving unit housing there are rounded corners of a large radius (as in Fig. 2) and the corners at the ends of the rear edge are rounded with a substantially larger radius of curvature. Specific dimensions are:

length L width W corner radius before, ends corner end radius of rear end guard surface area cover surface area 4

40,0 mm

18,0 mm

6.0 mm

10,0 mm

185 mm ²

283 mm ² total area of contact area SC with skin 488 mm ² total trace area inside perimeter 668 mm ²

Giant. Figures 4 to 6 show cutting units with shells of the same overall shape and size as shown in Figure 1, but the position of the cutting hole 2 is different. In Fig. 4, the opening 2 is positioned such that the size of the guard surface 3 and the cover surface 4 are the same, while in Fig. 5 it is positioned such that the size of the guard surface 4 is substantially smaller than the size of the guard surface 3 at least 140 mm ²⁾ and FIG. 6 is located so that the guard area 3 is substantially smaller than the cap area 4 (but still at least 140 mm ^2).

Giant. 7 shows a polygonal razor blade shaped substantially as a rectangle with chamfered corners 7 with surfaces inclined at 135 ° to the longitudinal front, the back, and the ends. In the case of a cutting unit of a total length of 42 mm and an overall width of 18 mm, the bevels may be arranged along diagonals of squares of 5 mm x 5 mm.

All of the embodiments of Figures 1 to 7 have straight front and rear edge portions that are parallel to the edges of the cutting edges for at least a major part of the cutting edge length. This may be desirable to facilitate orientation of the cutting unit and to assist the user in knowing in which direction the cutting unit should move over the skin. However, this is not essential and the dimensional criteria of the cutting unit of the invention can be achieved by other shapes. Giant. 8 shows, for example, the cutting unit of an elliptical contour, and a circular shape as shown in FIG. 9 is also possible, although this is not the most desirable embodiment.

FIG. 10 is a diagram showing the circularity plotted against the aspect ratio L: W or the ratio L of length to width W of the skin contact area SC. The points representative of the razor blade units of Figures 1 to 9 are indicated (1). . . . (9), the points representative of the prior art three-blade shaving units currently available on the market are labeled A, B and C, and the point representative of the square is labeled S for comparison purposes. The line R _w , arranged diagonally in the graph, is representative of rectangles with a corner radius of 30% of the width of the rectangle. The dotted line R _L is representative of rectangles with corner radii of 10% of the length of the rectangle. The horizontal line applies to a circularity of 65%.

It is evident from the graph that all preferred embodiments of the invention shown in the graph have aspect ratios between 1.5 and 2.8, and that for most aspect ratios it is in the range of 2.0 to 2.5. Further, embodiments of the invention have a circularity greater than that of a reference surface in the form of a corresponding rectangle with the same aspect ratio and corners rounded at a radius of 10% of the length of the rectangle (line RL) or 30% of the width of the rectangle (line RW). Further, embodiments of the invention have greater roundness than prior art razor units, and the embodiments shown in the graph have all values above 60%, and more particularly above 70%. FIG. 10 further illustrates two points (8) for displaying two alternative elliptical shapes.

-7EN 296574 B6

In all embodiments of the invention, the skin contact surfaces SC are non-planar, and Figures 1 to 9 are plan views only. Preferably, the surfaces are shaped so as to form at least three-point and ideally at least four-point contact with an imaginary circumscribed circle of 25 mm radius. Giant. 11 illustrates this preferred relationship for the cutting unit, which could be, for example, the cutting unit of FIG. 1. The imaginary circle S is shown in dotted shape and it can be seen that the surfaces of the cover surface 4 and the guard surface 3 correspond substantially (in FIG. In Fig. 11, the cap and cover surfaces are substantially flat, but may be convexly curved for even closer adaptation, for example as schematically illustrated in Fig. 12. The cap and cover surfaces 4, 3 are inclined relative to plane P, which is a "shaving surface", tangential to the skin contact surface SC with the skin immediately in front of and behind the blades, in the present embodiment at an angle α of 15 °. In particular cases, the most appropriate angle α of inclination will depend on the width of the cutting unit and will be selected accordingly, but at least in most embodiments of the invention the angle α will be in the range of 10 ° to 20 ° to ensure conformation to a near-imaginary circle. In the case of a convex guard and / or cover surface, as in Fig. 12, it will be appropriate to consider the inclination of the chord intersecting the edges of the respective surface at a location closest and furthest to the adjacent blade. Said chord is shown in Fig. 12 as a line L1 intersecting the edge of the cover surface 4 at point P2 and a plane P tangent to the skin contact areas SC immediately preceding and behind the cutting edges U5 at point P1.

FIG. 13 shows a preferred housing shape of the cutting unit. It has a frame 10 defining an opening 2 for accommodating the blades and the components that fix them in the frame 10. The frame 10 is provided with guard and cover members having each elastomeric surface element 12 defining a skin contact surface formed with a group of cylindrical pockets 13, evenly distributed over the entire surface area. For ease of manufacture and assembly, the elastomeric element 12 is formed on a support 14 fixedly mounted in the frame 10.

Giant. 14, 15 and 16 show a modified structure in which the elastomeric elements 12 are supported directly by the frame of the cutting unit. These figures also illustrate the blades 15 mounted in the frames and one of the safety clips 16 mounted at each end of the blade shaving unit to hold the blades 15 in place. The blades 15 have sharpened cutting edges.

It is important to note, as mentioned above, that all dimensions mentioned in the description and claims are based on the skin contact surface profile SC projected on a plane parallel to the plane of the shaving surface, i.e. the plane P in Fig. 11. that, when calculating roundness, account should be taken of any minor irregularities in the circumference, for example resulting from small gears, such as narrow indentations or projections, which can substantially change the circumference without substantially changing the area.

Claims (22)

PATENT CLAIMS A razor blade unit comprising at least one elongate blade (15) having a linear sharpened edge and mounted in a substantially rigid carrier, and a skin contact area (SC) surrounding said at least one blade (15) and comprising a protective surface (3) ) and a cover surface (4) on opposite sides of said at least one cutting edge (15), characterized in that the side ratio of the skin contact surface (SC), defined as the ratio of its length (L) measured between the extreme ends of its outer the circumference along the carrier, to its width (W), measured perpendicular to the cutting edge (15), is in the range of 1 to 4, 296574 B6 wherein the skin contact surface (SC) is cross-sectional in a plane perpendicular to the cutting edge (15) of the cutting edge (15), the edge of the cutting unit adjacent to the guard surface (3) being rounded or having rounded or obtuse corners; the length (L) of the contact surface (SC) is at most 60 mm, the contact surface (SC) defining a track surface with at least one opening (2) for receiving said at least one cutting edge (15) and having a size of at least 450 mm ² , the trace surface having a circularity C, given by C = (A / P ² ) x 4π x 100, and expressed as a percentage, where A is the trace surface area and P is the trace surface circumference (5), is at least equal to the lower of C ₆₅ , C _RW where C ₆₅ = 65% and C _RW is the circularity of the reference surface having a substantially rectangular shape with a length equal to the length of the track surface and a width equal to the width of the track surface, and with rounded corners with radii of curvature of 30% of the track surface width. A razor blade unit according to claim 1, characterized in that the aspect ratio of the skin contact area (SC) ranges from 1.5 to 2.8. A razor blade unit according to claim 1, characterized in that the aspect ratio of the skin contact area (SC) is in the range of 2.0 to 2.5. A razor blade unit according to any one of claims 1 to 3, characterized in that in its transverse profile a line (L1) intersecting the edges of the guard surface (3) and the cover surface (4) adjacent the blade (15). or blades (15) and remote from the blade (15) or blades (15) inclined at an angle (α) of at least 5 ° to the plane (P) tangent to the skin contact area (SC) immediately preceding and beyond the cutting edge (15) or cutting edges (15). A razor blade unit according to claim 4, characterized in that the amount of angle (α) is in the range of 10 ° to 20 ° in the area of the guard surface (3) and in the area of the cover surface (4). A razor blade unit according to any one of claims 1 to 5, characterized in that, in its transverse profile, the contour curve of the skin contact surface (SC) touches from the inside at least three points of the circle (S). A razor blade unit according to claim 6, characterized in that the contour curve of the skin-to-skin contact area (SC) in the region of the guard surface (3) and the cover surface (4) is substantially identical to the corresponding parts of the circle (S). A razor blade unit according to any one of claims 1 to 7, characterized in that its trace surface has a circularity C in the range of 70 to 85%. A razor blade unit according to any one of claims 1 to 8, wherein its trace surface has a circularity C greater than the circularity C of the _RW reference surface, having a substantially rectangular shape with a length equal to the length of the tracking surface and a width equal to the width of the tracking surface. and with rounded corners with rounding radii of 10% of the trace surface length. -9EN 296574 B6 10. A razor blade unit according to any one of claims 1 to 9, wherein the aspect ratio of the skin contact surface (SC) is less than 3 and its trace surface has a circularity C greater than the circularity C _{RW of} said reference surface. A razor blade assembly according to any one of claims 1 to 10, wherein at least one of the leading edge and trailing edge of the cutting unit comprises a rectilinear portion extending along a greater portion of the length of the cutting edge and parallel thereto, and smoothly curved corner portions on both. the ends of this straight part. A razor blade unit according to any one of claims 1 to 11, characterized in that the skin contact surface (SC) has semicircular ends. A razor blade assembly according to any one of claims 1 to 11, characterized in that the skin contact surface (SC) has an ellipse shape. 14. The razor blade assembly of any one of claims 1 to 13, wherein the guard surface (3) and the cover surface (4) are each formed by an elastomeric element (12). A razor blade unit according to claim 14, characterized in that the elastomeric element (12) is formed by a sheet-like structure with pockets (13) distributed over its surface. A razor blade unit according to any one of claims 1 to 15, characterized in that it is provided with at least two cutting edge edges (15). A razor blade unit according to any one of claims 1 to 16, characterized in that the guard surface (3) has an area of at least 140 mm ² . The razor blade assembly of claim 17, wherein the guard surface (3) occupies at least 18.6% of the footprint. A razor blade unit according to claim 1 to 6, characterized in that the guard surface (3) and the cover surface (4) each have a surface of at least 140 mm ² and have a guard surface (3) where the width of the blade unit is greatest. a cover surface (4) of at least 4 mm width. A razor blade unit comprising at least two elongated blades (15) with longitudinally elongated sharpened edges, permanently spaced from one another on a carrier comprising a plastic molding, and further comprising a skin contact surface (SC) surrounding the sharpened edges and comprising a protective surface ( 3) and a cover surface (4) of which the guard surface (3) lies on the front side of the razor blade and the cover surface (4) lies on the rear side of the razor blade, and the blades (15) lie between the guard surface (3) and a cover surface (4), the blades (15) having sharpened edges oriented in the same direction towards the guard surface (3), so that during shaving engagement the guard surface (3), the sharp edges of the blades (15) and then the cover surface (4) successively touching the skin, characterized in that the aspect ratio of the contact area (SC) to the skin, defined as the ratio of its length (L), measured zi the extreme ends of its outer circumference along the carrier, to its width (W), measured perpendicular to the edges (15), is in the range of 1 to 4, the length (L) of the skin contact area (SC) being at most 60 mm; the contact surface (SC) defines, with its outer periphery (5), a track surface with at least one opening (2) for receiving said at least one cutting edge (15) and having a size of at least 450 mm ² , Wherein the guard surface (3) has an area of at least 140 mm ² and is at least 18.6% of the footprint. 21. The razor blade assembly of claim 20, wherein the guard surface (3) and the cover surface (4) each have a surface of at least 140 mm ² and have a guard surface (3) and a cover at the point where the width of the cutting unit is greatest. Area (4) each width of at least 4mm. A shaving unit for attaching to a razor handle, the shaving unit comprising at least two elongated blades (15) with longitudinally elongated rectangular sharpened edges, spaced apart from each other in a carrier comprising a plastic molding, and a skin contact area (SC) surrounding sharpened edges of the blades and comprising a front surface and a back skin engaging surface, the front skin engaging surface lying on the front side of the razor blade and the back skin engaging surface lying on the rear side of the razor blade, and the blades lying (15) between the front skin engagement surface and the rear skin engagement surface, wherein the blades (15) have sharpened edges oriented in the same direction towards the front surface, such that during shaving engagement the front surface, sharp edges of the blades and the rear surface come into contact with skin, wherein the blades (15), the carrier and the front and rear skin engagement surfaces are attachable as a unit to the razor handle, characterized in that the aspect ratio of the skin-to-skin contact area (SC), defined as the ratio of its length (L), measured between the extreme ends its outer periphery along the carrier, to its width (W), measured perpendicular to the blades, is in the range of 1: 1 to 2.8: 1, wherein the blade shaving unit is substantially rigid for most of its longitudinal dimension during shaving, the contact surface (SC) defines, by its outer periphery (5), a track surface of at least 450 mm ² , the front surface having a surface of at least 140 mm ² and at least 18.6% of the track surface, the track surface having a circularity C given by C = (A / p ² ) x 4 π x 100, and expressed as a percentage, where A is the footprint area and P is the footprint circumference (5), of at least 70%.