Patent Publication Number: US-2016236364-A1

Title: Razor blade assembly with friction surface

Description:
FIELD OF THE INVENTION 
     The present invention relates to razor blades. More particularly, the present invention relates to a razor blade assembly with a friction surface. 
     BACKGROUND OF THE INVENTION 
     A typical modern safety razor includes a disposable cartridge or is entirely disposable. Various components of the razor cartridge or head are intended to increase the closeness of the shave or the comfort of the person being shaved. For example, many razor cartridges include multiple blades. Guards are placed on either side of the blades to prevent cutting of the skin being shaved. 
     Guards of a razor cartridge are often designed to provide other benefits when shaving. For example, a guard may be provided with structure that is designed to stretch the skin prior to shaving with the blades. The guard may include structure that is designed to provide a pleasant sensation during shaving. For example, some guards of razor cartridges are provided with a region filled with narrow rubber projections. A guard may include structure that is designed to dispense a lubricant substance during shaving. For example, a guard may include a strip that is permeated with a lubricant solution. 
     SUMMARY OF THE INVENTION 
     There is thus provided, in accordance with some embodiments of the present invention, a razor blade assembly device including: one or a plurality of razor blades configured to shave a skin surface when drawn across the skin surface in a forward direction; and a friction surface situated in front of the razor blades, the friction surface including an array of raised separated projections, distal ends of the raised projections terminating in substantially flat faces, wherein a total area of the flat faces is greater than 10% of the area of the friction surface. 
     Furthermore, in accordance with some embodiments of the present invention, each of the raised projections is made of an elastomer. 
     Furthermore, in accordance with some embodiments of the present invention, the total area of the flat faces is greater than 20% of the area of the friction surface. 
     Furthermore, in accordance with some embodiments of the present invention, the total area of the flat faces is less than 90% of the area of the friction surface. 
     Furthermore, in accordance with some embodiments of the present invention, an aspect ratio of each of the raised projections is less than 2. 
     Furthermore, in accordance with some embodiments of the present invention, the aspect ratio is less than 1. 
     Furthermore, in accordance with some embodiments of the present invention, adjacent projections of the array of raised projections are separated by channels. 
     Furthermore, in accordance with some embodiments of the present invention, a majority of the channels are oriented such that a long dimension of each channel of the majority is oriented substantially parallel to the forward direction or at an oblique angle to the forward direction. 
     Furthermore, in accordance with some embodiments of the present invention, each of the channels has a substantially rectangular cross-sectional profile. 
     Furthermore, in accordance with some embodiments of the present invention, each of the channels has a substantially V-shaped cross-sectional profile. 
     Furthermore, in accordance with some embodiments of the present invention, each of the channels has a substantially inverted arch cross-sectional profile. 
     Furthermore, in accordance with some embodiments of the present invention, each of the faces has a substantially hexagonal shape. 
     Furthermore, in accordance with some embodiments of the present invention, each of the faces has a substantially parallelogram shape. 
     Furthermore, in accordance with some embodiments of the present invention, each of the faces has a shape that is substantially in the form of a chevron. 
     Furthermore, in accordance with some embodiments of the present invention, each of the faces has shape with a curved side. 
     Furthermore, in accordance with some embodiments of the present invention, each of the faces has a shape that is substantially in the form of an elongated symmetric teardrop. 
     Furthermore, in accordance with some embodiments of the present invention, the device is configured to attach to a handle. 
     Furthermore, in accordance with some embodiments of the present invention, the device further includes a lubricant dispenser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals. 
         FIG. 1  shows a razor that incorporates a razor blade assembly with a friction surface, in accordance with an embodiment of the present invention. 
         FIG. 2  shows a razor blade assembly with a friction surface, in accordance with an embodiment of the present invention. 
         FIG. 3  shows a razor blade assembly with an alternative configuration of a friction surface, in accordance with an embodiment of the present invention. 
         FIG. 4A  shows a pattern of hexagonal projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 4B  shows a pattern of parallelogram projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 4C  shows a pattern of chevron projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 4D  shows a pattern of split chevron projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 4E  shows a pattern of teardrop projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 5A  shows a pattern of channels with rectangular cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 5B  shows a pattern of channels with V-shaped cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 5C  shows a pattern of channels with inverted arch cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 5D  shows a pattern of channels with trapezoidal cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
         FIG. 5E  shows a pattern of channels with rounded-corner trapezoidal cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, modules, units and/or circuits have not been described in detail so as not to obscure the invention. 
     In accordance with some embodiments of the present invention, a razor blade assembly, such as a razor cartridge or a head of a disposable razor, includes a friction surface that is configured to stretch the surface of skin that is being shaved by the blades. 
     A razor blade assembly includes one or more razor blades. A typical razor blade assembly is designed to shave a skin surface when drawn across the skin surface such that the motion of the razor blade assembly includes a component of motion in a predefined direction. Typically (but not always), the predefined direction is substantially perpendicular to an orientation of the blades. The predefined direction in which the razor blade assembly is herein referred to as the forward direction. For example, the razor blade assembly may be configured to shave the skin surface when drawn across the skin surface in the forward direction. Similarly, the razor blade assembly may be configured to shave the skin surface when drawn across the skin surface in a diagonal direction that combines motion in the forward direction with motion in a lateral direction (perpendicular to the forward direction). 
     For example, the razor blades in the razor blade assembly may be mounted so as to be inclined relative to the skin surface when the razor blade assembly is positioned for shaving (e.g., with the cutting edges of the blades placed adjacent to the skin surface). The direction toward which the cutting edges are inclined defines the forward direction. 
     In accordance with some embodiments of the present invention, the friction surface is mounted on the razor blade assembly in front of the razor blades. (“In front of” herein refers to placement such that the friction surface passes over a point on the skin surface ahead of the cutting edges of the blades when the razor blade assembly is in use and moving across the skin surface in the forward direction.) Thus, when the razor blade assembly is drawn across the skin surface in the forward direction, the friction surface may engage a region of the skin surface that is ahead of the razor blades. Drawing the razor blade assembly across the skin surface may thus stretch the skin in the vicinity of the razor blades of the razor blade assembly. Stretching the skin in the vicinity of the razor blades may facilitate closer and more efficient shaving of the stretched region of skin by the razor blades. 
     In accordance with an embodiment of the present invention, the friction surface includes structure that is made of, or includes, friction enhancing material, such as, for example, rubber or another elastomer or elastomeric material. The structure includes a plurality of raised projections that are separated from one another. For example, the raised projections may be separated from one another by grooves or channels, or by holes, openings, or spaces. The distal end (from the end of the raised projection that is attached to the remainder of the friction surface) of each raised projection terminates in a face that is substantially flat, or nearly flat. The shape of the flat face may be polygonal, may be bounded by curved boundaries, or may be bounded by a combination of straight and curved segments. 
     The flat distal end of each raised projection is configured to contact the skin surface across which the razor blade assembly is being drawn. The contact between the flat distal end and the skin surface results in a friction force between the raised projection and the skin. 
     The channels between the raised projections may serve to facilitate evacuation of any lubricant or other fluid substance from between the flat distal end and the skin surface. Some or all of the channels may be arranged such that the long dimension of each channel is parallel to, or at an oblique angle to the forward direction. Some of the channels may be oriented such that the long dimension of each of those channels is oriented substantially perpendicular to the forward direction. 
     For example, a majority of the channels may be oriented such that the long dimensions of those channels are either substantially parallel to, or form an oblique angle with, the forward direction. A minority of the channels may be oriented substantially perpendicular to the forward direction. 
     When the flat distal end of a raised projection is pressed against the skin surface and moved in the forward direction, lubricant that is between the flat end and the skin surface may be squeezed out. The squeezed out lubricant may be channeled away via the channels, thus preventing the squeezed out lubricant from entering between a flat face of another raised projection and the skin surface. Some or all of the channels may be preferably oriented in a direction that is not perpendicular to the direction of motion (forward direction) of the friction surface over the skin surface. These (non-perpendicular) channels may convey the lubricant past the raised projection or outward from or around the raised projection. (In some cases, a channel that is oriented perpendicular to the direction of motion could enable lubricant to accumulate or build up in the perpendicular channel ahead of a raised projection, possibly interfering with action of the friction surface in stretching the skin surface.). 
     The contact between the flat ends and the skin surface, together with the channeling action of the channels, enables effective creation of a friction force between the flat ends and the skin surface. The effective creation of friction may thus result in effective stretching of the skin when the friction surface is pulled across the skin surface 
     Each raised projection is characterizable by an aspect ratio. The aspect ratio relates a representative lateral dimension of the raised projection to a representative height of the raised projection. The aspect ratio, as used herein, is defined as the ratio of the representative height to the representative lateral dimension (height divided by the lateral dimension). 
     The representative lateral dimension may be defined in a manner appropriate to the shape of the flat distal end of the raised projection. The representative lateral dimension may include, for example, a representative width, length, diameter, axis length, diagonal distance, or other distance between substantially opposite sides of the flat end. For example, the representative lateral dimension for a rectangular or parallelogram-shaped flat end may include a length, width, diagonal dimension, or other defined length of the flat end. An elliptic flat end may be characterized by a representative lateral dimension in the form of a length of a major axis, minor axis, average diameter, or other representative distance. A polygonal flat end may be characterized by a representative lateral dimension in the form of a distance (e.g., perpendicular distance) between opposite sides, between opposite vertices, or another representative distance. 
     The height of the raised projection may be defined as a distance between the flat distal end of the projection, and a floor of a channel that is adjacent to the raised projection. In a case where the floor of the channel is not flat (in cross section), the height may be defined as an average distance, a maximum distance, or other representative distance between the floor of the channel and the flat end. 
     In accordance with some embodiments of the present invention, the aspect ratio of each raised projection is no greater than 2. In some embodiments, the aspect ratio is no greater than 1. In some other embodiments, the aspect ratio may be less than one half. 
     A low aspect ratio (less than 2) may be advantageous. For example, a low aspect ratio may enable the raised projections to resist bending when sliding over the skin surface. In this manner, the flat ends of the raised projections may remain in contact with the skin surface when the razor blade assembly is drawn over the skin surface. Thus, the friction force between the friction surface and the skin surface may remain approximately constant during shaving. Such friction may stretch the skin being shaved, and thus facilitate cutting of hairs by razor blades of the razor blade assembly. 
     Such raised projections with low aspect ratio may provide greater friction than a strip of projections in the form of (high aspect ratio) narrow cylinders such as is found in some previously described safety razor cartridges. The strips on such safety razor cartridges may not create sufficient friction to stretch the skin in a manner to effectively facilitate shaving. 
     The friction surface, or a portion of the friction surface, may be characterized by an area density of the raised projections. As used herein, the area density of the friction surface is defined as the total area of the flat faces at the distal ends of the raised projections in the friction surface being characterized, divided by the total area of that friction surface (that includes the area of spaces or channels that separate the raised projections, and the projected area of any sloped walls of the raised projections). In accordance with some embodiments of the present invention, the area density is at least 10%. In some other embodiments the area density is at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 80%. In some embodiments, the area density is no larger than 99%. In some embodiments, the area density is no larger than 90%. 
     The area density of the friction surface may be sufficient so as to ensure that the friction between the friction surface and the skin surface is sufficiently large to stretch the skin. The area density is sufficiently small to enable effective channeling of lubricant. 
       FIG. 1  shows a razor that incorporates a razor blade assembly with a friction surface, in accordance with an embodiment of the present invention. 
     Razor  10  includes razor blade assembly  12  that is mounted on handle  14 . Razor blade assembly  12  may be configured to attach to, detach from, and reattach to, handle  14 , or may be permanently attached to handle  14  (e.g., as part of a disposable razor). For example, handle  14  and razor blade assembly  12  may incorporate cooperating structure that enables attachment of razor blade assembly  20  to handle  14 , or detachment of razor blade assembly  20  from handle  14 . 
     Shaving surface  13  of razor blade assembly  12  is designed to be held against a skin surface to be shaved. When shaving surface  13  is placed against the skin surface, the skin surface may be shaved by drawing razor  10  and razor blade assembly  12  in the general direction indicated by forward direction arrow  30 , or across the skin surface in a diagonal direction that includes a component of motion in the direction indicated by forward direction arrow  30 . 
       FIG. 2  shows a razor blade assembly with a friction surface, in accordance with an embodiment of the present invention.  FIG. 3  shows a razor blade assembly with an alternative configuration of a friction surface, in accordance with an embodiment of the present invention. 
     Razor blade assembly  12  includes razor blades  22  and friction surface  20 . 
     Razor blades  22  are held and arranged diagonally in razor blade assembly  12 . The diagonal arrangement is such that cutting edge  22   a  of each razor blade  22  is oriented toward leading side  12   a  of razor blade assembly  12 . Thus, when razor blade assembly  12  is pulled across a skin surface in forward direction  30 , cutting edge  22   a  is positioned to shave hairs on the skin surface. 
     Friction surface  20  is positioned adjacent to leading side  12   a  of razor blade assembly  12 . Friction surface  20  includes an array of raised projections  24 . 
     Raised projections  24  may be made of a material with a high coefficient of friction with respect to sliding over skin. Raised projections  24  may be constructed of rubber or another elastomeric material. For example, friction surface  20  with raised projections  24  may be formed by a molding process, or may be otherwise shaped. 
     Raised projections  24  are configured to create a friction force when placed in contact with a skin surface. For example, each raised projection  24  may include, at its end that is distal to razor assembly  12 , a flat face  24   a.  (Flat face  24   a  may be approximately or substantially flat.) Each raised projection  24  has one or more projection walls  24   b.  Projection walls  24   b  of a raised projection  24  may, in some cases, be substantially flat and substantially perpendicular to flat face  24   a  of the same raised projection  24 . In other examples, projection walls  24   b  may be slanted or curved. 
     Flat face  24   a  may be formed in a shape that enables efficient filling of friction surface  20  with a dense array of raised projections  24 . In the example shown in enlarged region  21  of friction surface  20  ( FIG. 2 ), each flat face  24   a  has a regular hexagonal shape. In the example shown in enlarged region  23  of friction surface  20  ( FIG. 3 ), each flat face  24   a  has an elongated symmetric teardrop shape. Other examples of shapes for flat faces  24   a  are described below (in connection with  FIGS. 4A-4E ). 
     Razor blade assembly  20  may include additional structure to facilitate use of razor blade assembly  20  in shaving, or to enhance comfort during shaving. For example, razor blade assembly  20  may include a lubricant dispenser  28 . Lubricant dispenser  28  may include, for example, an absorbent strip that is saturated with a lubricant fluid. Contact between the absorbent strip of lubricant dispenser  28  and the skin surface causes lubricant to be deposited on the skin surface. Additional structure may be configured to hold components of razor blade assembly in place, to prevent accidental cutting of the skin surface by razor blades  22   a,  and to enable attachment of razor blade assembly  12  to a handle of a razor. 
     Each flat face  24   a  may be characterized by a representative lateral dimension. In the example of a regular hexagonal shape (see  FIG. 2 ), the representative lateral dimension may be taken to be a distance between opposite sides of the hexagon, a distance between opposite vertices of the hexagon, a length of each side of the hexagon, or another representative length. In the example of an elongated symmetric teardrop shape (see  FIG. 3 ), the representative lateral dimension may be the distance between the opposite sharp points of the teardrop shape, the maximum width of the teardrop shape, or another representative length. 
     Each pair of adjacent raised projections  24  is separated by a channel  26 . The height of each projection wall  24   b  forms a wall of the channel. The height of the projection wall  24   b  may be defined as perpendicular (to flat face  24   a ) distance between flat face  24   a  and the floor of the adjacent channel  26 . (When the side walls of a channel  26  are not vertical, e.g., not perpendicular to flat face  24   a,  the floor of the channel may be defined as the widthwise midline of the channel, or in another manner.) 
     The aspect ratio of a raised projection  24  may then be defined as the height of a projection wall  24   b  divided by the representative lateral dimension that characterizes flat face  24   a  of that raised projection  24 . In accordance with embodiments of the present invention, the aspect ratio of a raised projection  20  is no greater than 2, or, typically, no greater than 1. A low aspect ratio may inhibit bending of raised projections  24 . 
     The area density of a region of friction surface  20  may be defined as the area of all flat faces  24   a  of all raised projections  24  in that region, divided by the total area of that region. (The total area includes the area of all flat faces  24   a  in the region, plus the area of all channels  26  in that region.) In accordance with embodiments of the present invention, the area density of a friction surface  20  is at least 10%, or typically, at least 20%. On the other hand, the area density of a friction surface  20  is no greater than 99%, and typically less than 90%. An area density in this range may ensure sufficient friction (e.g., to stretch the skin) when friction surface  20  is slid over a skin surface, while ensuring sufficient channels to effectively channel lubricant away from friction surface  20 . 
     Some or all of channels  26  may be arranged such that those channels  26  are not oriented perpendicular to forward direction  30 . Examples of patterns of projections  24  that are densely packed, and with no channels  26  that are oriented perpendicular to forward direction  30 , are shown in  FIGS. 4A-4E  for differently shapes of flat faces  24   a . A non-perpendicular orientation of channels  26  may facilitate channeling a lubricant out of friction surface  20  when friction surface  20  is moved in forward direction  30 . 
       FIG. 4A  shows a pattern of hexagonal projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. Hexagonal faces  32   a,  as shown, are oriented such that all channels  26  formed by sides of hexagonal faces  32   a  are either substantially parallel to forward direction  30 , or are oriented at an oblique angle to forward direction  30 . For example, each hexagonal face  32   a  may be oriented such that a line connecting opposite vertices is oriented substantially parallel to forward direction  30 . 
     In some embodiments of the present invention, the pattern may be rotated by about 30° so that two of the six channels  26  that surround each hexagonal face  32   a  are substantially perpendicular to forward direction  30 . In this case, the zigzag pattern formed by the remaining channels  26  may effectively channel the lubricant. 
       FIG. 4B  shows a pattern of parallelogram projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. Parallelogram faces  32   b  (in the illustrated example, square faces) are oriented in a diamond pattern such that channels  26  formed by sides of square faces  32   b  are oriented at an oblique angle (e.g., 45°) with respect to forward direction  30 . For example, a diagonal of each parallelogram face  32   b  may be oriented substantially parallel to forward direction  30 . Other orientations may be used. 
       FIG. 4C  shows a pattern of chevron projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. Chevron faces  32   c,  as shown, are oriented such that all channels  26  formed by sides of chevron faces  32   c  are either substantially parallel to forward direction  30 , or are oriented at an oblique angle to forward direction  30 . Chevron faces  32   c  are oriented such that the central convex vertex faces forward direction  30 . Other orientations may be used. 
       FIG. 4D  shows a pattern of split chevron projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. A split chevron pattern may be considered to be composed of a pattern of pairs of rhombus faces  32   d,  arranged in a pattern of rows and columns. For example, all rhombus faces  32   d  in a single column of the column are oriented the same. Along each row, adjacent rhombus faces  32   d  exhibit reflectional symmetry with respect to one another. Rhombus faces  32   d,  as shown, are oriented such that all channels  26  formed by sides of rhombus faces  32   d  are either substantially parallel to forward direction  30 , or are oriented at an oblique angle to forward direction  30 . For example, columns of the pattern may be oriented substantially parallel to forward direction  30 . In this manner, a side of each rhombus face  32   d  is substantially parallel to forward direction  30 . Other orientations may be used. 
     In accordance with some embodiments of the present invention, a face may have a shape with one or more curved sides. 
       FIG. 4E  shows a pattern of teardrop projections for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. Each elongated symmetric teardrop face  32   e  includes curved sides meeting at two points. The channels  26  formed between elongated symmetric teardrop faces  32   e  may be described as a pattern of osculating sinuous curves. The curves in the pattern of channels  26 , as shown, are either substantially parallel to (momentarily tangent to the direction of) forward direction  30 , or are oriented at an oblique angle to forward direction  30 . For example, a line connected the pointed opposite ends of each elongated symmetric teardrop face  32   e  may be oriented substantially parallel to forward direction  30 . Other orientations may be used. Faces may have other shapes with curved sides. 
     Channels  26  may have be formed with different cross-sectional profiles, depending on the form of walls of the raised projections. For example, channels  26  with one cross-sectional profile may be effective for channeling one type of lubricant, but less effective in channeling a different type of lubricant. Different channel profiles may also contribute to stiffness or another property of the raised projections. Various channel profiles are illustrated in  FIGS. 5A-5C . 
       FIG. 5A  shows a pattern of channels with rectangular cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     Rectangular section channels  34   a  separate raised projections  36   a  with vertical walls. Length  40  schematically represents a representative lateral dimension of raised projection  36   a.  Height  42  represents a representative height of raised projection  36   a.    
       FIG. 5B  shows a pattern of channels with a V-shaped cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     V-shaped section channels  34   b  (or inverted triangular channels) separate raised projections  36   b  with sloped walls (and trapezoidal profile). Length  40  schematically represents a representative lateral dimension of raised projection  36   b.  As shown, length  40  represents a length that characterizes the upper base of the trapezoidal profile. Other lengths (e.g., the length of the lower base or at half the height) may be used as the representative lateral dimension. Height  42  represents a representative height of raised projection  36   a,  here taken from the bottom of V-shaped section channel  34   b  to the top of raised projection  36   b.    
       FIG. 5C  shows a pattern of channels with inverted arch cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     Inverted arch section channels  34   c  separate raised projections  36   c  with concavely curved walls. Length  40  schematically represents a representative lateral dimension of raised projection  36   c.  As shown, length  40  represents a length that characterizes the top (flat) upper surface of raised projection  36   c.  Other lengths (e.g., the lateral length of raised projection  36   c  at a particular fraction of the height of raised projection  36   c ) may be used as the representative lateral dimension. Height  42  represents a representative height of raised projection  36   c,  here taken from the bottom of inverted arch section channel  34   c  to the top of raised projection  36   c.    
       FIG. 5D  shows a pattern of channels with trapezoidal cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     Trapezoidal section channels  34   d  separate raised projections  36   d  with sloped walls (and trapezoidal profile). Length  40  schematically represents a representative lateral dimension of raised projection  36   d.  As shown, length  40  represents a length that characterizes the upper base of the trapezoidal profile of raised projection  36   d.  Other lengths (e.g., the length of the lower base or at half the height) may be used as the representative lateral dimension. Height  42  represents a representative height of raised projection  36   a,  here taken from the bottom of trapezoidal section channel  34   d  to the top of raised projection  36   d.    
       FIG. 5E  shows a pattern of channels with rounded-corner trapezoidal cross section for a friction surface of a razor blade assembly, in accordance with an embodiment of the present invention. 
     Rounded trapezoidal section channels  34   e  separate raised projections  36   e  with similarly rounded-corner trapezoidal profiles. Length  40  schematically represents a representative lateral dimension of raised projection  36   e.  As shown, length  40  represents a length that characterizes the top (flat) upper surface of raised projection  36   e.  Other lengths (e.g., the lateral length of raised projection  36   e  at a particular fraction of the height of raised projection  36   e ) may be used as the representative lateral dimension. Height  42  represents a representative height of raised projection  36   e,  here taken from the bottom of rounded trapezoidal section channel  34   e  to the top of raised projection  36   e.    
     Patterns having raised projections with other profiles, and channels with other forms of cross section, may be used. A pattern may mix several types of raised projections or channels. Raised projections may have irregular faces, or faces that vary from one raised projection to another. 
     Measurements have been made comparing performance of a razor blade assembly with a friction surface, in accordance with embodiments of the present invention, with commercially available safety razor cartridges. The friction surface included raised projections with hexagonal flat faces. The diameters of each hexagonal face in different measurements were approximately 50 μm in some cases, and 700 μm in other cases. The coefficient of dynamic friction of each type of razor blade assembly (safety razor cartridge) was measured when the assembly was slid against human (inner forearm) skin lubricated with commercially available shaving foam. The measurements demonstrated that the razor blade assembly with a friction surface in accordance with an embodiment of the present invention has a significantly larger coefficient of dynamic friction than the coefficient of dynamic friction that was measured with commercially available safety razor cartridges.