Abstract:
Razors are described herein. In some instances the razors include a safety razor blade unit that includes a guard, a cap, and at least two blades with parallel sharpened edges located between the guard and cap. A first blade defines a blade edge nearer the guard and a second blade defines a blade edge nearer the cap. The first blade has a cutter force greater than the cutter force of the second blade. In some instances the razors provide a comfortable shave having improved closeness.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a divisional of U.S. application Ser. No. 11/392,127, filed on Mar. 29, 2006, now U.S. Pat. No. 7,882,640, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to razor blades. 
     BACKGROUND 
     In shaving, it is desirable to achieve a close shave, while also providing good shaving comfort. Factors that affect shaving performance include the frictional resistance between 
     the blade edge and the skin, the cutter force applied by the blade to the hair. 
     It is common for razor blades used for wet shaving to include a thin polymer coating on the blade edge, which can reduce the frictional resistance between the blade edge and the skin and thereby reduce the cutter force of the blade, greatly improving shaving comfort. Such coatings are described, for example, in U.S. Pat. No. 5,263,256 to Trankiem, the entire disclosure of which is incorporated by reference herein. The polymer coating also helps the blade glide smoothly along the surface of the skin, potentially managing the skin bulge as the razor is pulled along the user&#39;s skin. 
     SUMMARY 
     One method of improving the closeness of a shave is to increase the engagement time of a razor blade with a hair, and thereby improve the ability of the razor blade to pull hair out of the follicle. This can be accomplished by modifying the surface of the blade to provide a blade having increased frictional resistance and increased cutter forces. Cutter force is measured by the wool felt cutter test, which measures the cutter forces of the blade by measuring the force required by each blade to cut through wool felt. The cutter force of each blade is determined by measuring the force required by each blade to cut through wool felt. Each blade is run through the wool felt cutter 5 times and the force of each cut is measured on a recorder. The lowest of 5 cuts is defined as the cutter force. 
     Where a razor has multiple blades, one or more blades can be designed for increased time of engagement with hair, for example by having a higher frictional resistance, while other blades can be designed to reduce cutter forces and improve comfort, for example using a polymer coating such as those described in U.S. Pat. No. 5,263,256. This combination of different blades having differing frictional resistances, in some instances, provides a shave having improved closeness while maintaining comfort. 
     In general, in some aspects, the invention features a razor including a safety razor blade unit that includes a guard, a cap, and at least two blades with parallel sharpened edges located between the guard and cap. A first blade defining a blade edge is positioned nearer the guard and a second blade defining a blade edge is positioned nearer the cap. 
     In one such aspect, the first blade has a cutter force greater than the cutter force of the second blade. 
     In another such aspect, the second blade is coated with a greater amount of a polymer composition than the first blade. 
     In a further aspect, the first and second blades comprise a polymer coating and the polymer coating on the first blade is less lubricious than the polymer coating on the second blade. 
     Some implementations include one or more of the following features. The first blade may have a cutter force at least about 0.1 lbs. greater, e.g., at least about 0.2 lbs greater, than the cutter force of the second blade. For example, the first blade may have a cutter force from about 0.1 lbs. to about 1.0 lbs. greater, preferably about 0.1 to 0.5 lbs greater, than the second blade. The cutter force of the first blade may be between about 1.2 lbs and 1.5 lbs. The blades may be coated with a polymer composition, e.g., a polyfluorocarbon such as polytetrafluoroethylene. The second blade may be coated with a greater amount of polymer composition than the first blade. The first blade and the second blade may be coated with different polymer compositions. For example, the polymer composition coating the first blade may be less lubricious than the polymer composition coating the second blade. In some cases, the first blade may be substantially free of polymer coating. 
     The invention also features methods of treating a razor blade. 
     For example, the invention features a method including disposing a polymer coating on a razor blade, and exposing the coated razor blade to plasma, laser, or electric current, thereby modifying at least a portion of the polymer coating. 
     The invention also features methods of making razors that include a safety razor blade unit comprising a guard, a cap, and at least two blades having parallel sharpened edges located between the guard and cap, a first blade defining a blade edge nearer the guard and a second blade defining a blade edge nearer the cap. One such method includes treating the first or second blade to provide the second blade with a lower cutter force than the first blade. 
     The invention further features methods of shaving. One such method includes (a) providing a safety razor blade unit comprising a guard, a cap, and at least two blades with parallel sharpened edges located between the guard and cap, a first blade defining a blade edge nearer the guard and a second blade defining a blade edge nearer the cap, in which the first blade has a cutter force greater than the cutter force of the second blade and/or the second blade is coated with a greater amount of a polymer composition than the first blade; and (b) contacting a skin surface with the safety razor blade unit. 
     In other aspects, the invention features razors including the blade units described herein. 
     In some instances, the razors described herein provide a shave having improved closeness relative to a control razor, e.g., a similar razor in which all of the blades have substantially the same frictional resistance. In some instances, the razors described herein provide greater shaving efficiency relative to the control razor, increasing the number of hairs cut per unit stroke. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1   a - c  represent a schematic diagram depicting the cutting of a hair extended from a hair follicle. 
         FIGS. 2 ,  3   a - b ,  4 , and  5   a - c  depict razors having multiple blades where one or more blades have relatively higher cutter forces than another blade positioned in the razor. 
         FIG. 6  depicts a schematic of a plasma formation process. 
         FIGS. 7   a  and  7   b  depict modification of a portion of a blade using plasma. 
         FIG. 8  depicts an atomic force microscope (AFM) image of a blade tip etched with plasma. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Pulling a hair prior to cutting it with a razor can result in a close shave of that hair. In the case of a multiblade razor a first blade can be used to pull the hair away from the follicle and cut the hair to a first length while a second blade, positioned behind the first blade, can cut the hair to a second, shorter length. Referring to  FIG. 1 , a hair is pulled in both an upward and forward direction by a first blade. While the hair is in this position, it will be cut by the first blade to a first length. The hair will retreat into the follicle relatively slowly, and thus while the hair remains extended from the follicle, the second blade is able to cut the hair to a second, shorter length. Upon relaxation, the cut hair settles below the surface of the skin to provide a close shave and a smooth feel to the user&#39;s skin. 
     Razors Having Blades with Varied Frictional Resistance 
     Referring to  FIG. 2 , a razor cartridge  100  includes a guard  10 , a cap  12 , and two blades  14  and  16 . The first blade  14  has higher cutter forces than the second blade  16 , and is positioned between the guard and the second blade. Thus, when the razor is in use, the first blade  14  will contact the hair before the second blade  16 . As the first blade  14  passes the user&#39;s skin, it engages a hair, pulling it and thereby extending the hair outside of the hair follicle, and cutting the hair to a first length. Before the hair has retracted fully back into its original position, the second blade  16  passes the user&#39;s skin and it cuts the hair again, to a shorter length. Subsequent to cutting, the hair settles back into the hair follicle below the surface of the skin. 
     As used herein in both the text and the figures the term “first blade” refers to a blade having relatively higher cutter forces, which correspond to a higher frictional resistance than the blade referred to as the second blade. Likewise, the term second blade refers to a blade having relatively lower cutter forces, which correspond to a lower frictional resistance than the blade referred to as the first blade. 
     Referring to  FIGS. 3   a - b ,  4 , and  5   a - c , other razors can include the guard  10 , the cap  12 , and the multiple blades  14 ,  16  (three, four, or five blades respectively). In each instance a first blade  14  having higher cutter forces than a second blade  16  is positioned between a guard  10  and the second blade  16 . As depicted in  FIGS. 3   a  and  3   b , where the razor has three blades, the first blade  14  can be the blade closest to the guard (i.e., in the principal position) ( FIG. 3   a ), or it can be positioned after the principal position, where the third blade  18  is in the principal position ( FIG. 3   b ). The third blade can have any desired cutter force, typically within a 0.8 to 1.5 pound range. 
     Although  FIGS. 3   a  and  3   b  both depict razor cartridges  200 A and  200 B, respectively, where the first and second blades  14  and  16  are positioned adjacent to each other, other instances are envisioned where the first and second blade  14  and  16  are not positioned adjacent to each other. For example, in some instances (not shown) the first blade  14  is positioned nearest the guard  10  with the third blade  18  positioned between the first and second blade  14  and  16 . In general, any positioning of the multiple blades is acceptable provided that the first blade  14  is positioned closer to the guard than the second blade  16 . 
     As depicted in  FIG. 4 , the razor cartridge  300  can include four blades.  FIG. 4  depicts a razor cartridge  300  having two first blades  14  with higher cutter forces and two second blades  16  having lower cutter forces. The first blades  14  with higher cutter forces are positioned to alternate with the second blades  16  having lower cutter forces. The first blades  14  having the higher cutter forces are positioned closest to the guard  10  (i.e., the principal position) and in the third position from the guard  10 . The second blades  16  having lower cutter forces are positioned in the second and fourth positions from the guard  10 . 
       FIGS. 5   a - 5   c  all depict razor cartridges  400 A-C, respectively, each razor cartridge  400 A-C having five blades. In these razor cartridges  400 A-C, the position of the first and second blades  14  and  16  is varied. In  FIG. 5   a , the first blade  14  is in the principal position and the second blade  16  is in the third position from the guard  10 . The razor cartridge  400 A also includes three additional blades  18 ,  20 , and  22 . Typically, these blades will have cutter forces less than 1.6 pounds, e.g., in the range of 0.8 to 1.5 pounds. 
       FIG. 5   b  depicts an example of a razor cartridge  400 B in which the first blade  14  is not in the principal position, but instead is in the second position from the guard  10 . The second blade  16  is positioned directly behind the first blade, in the third position. Like  FIG. 5   a , the razor cartridge  400 B also includes additional blades  18 ,  20 , and  22 .  FIG. 5   c  depicts a razor cartridge  400 C having two first blades  14  and two second blades  16 . The razor cartridge  400 C also includes a blade  18  in the position nearest the cap  12 . 
     In some instances, the first blade has a cutter force at least about 0.1 lbs greater than the cutter force of the second blade. In general, the cutter force of the first blade is between about 0.1 and 1.0 lbs. (e.g., at least about 0.2, 0.3, 0.4, or 0.5 lbs. and at most about 1.0, 0.9, 0.8, 0.7 and 0.6 lbs.) greater than that of the second blade. Preferably, the first blade  14  has a higher cutter force of about 0.2 lbs. relative to the second blade  16 . 
     Providing a blade having higher cutter forces can be accomplished in a variety of ways. In some instances, it is desirable to provide a first blade having a modified polymer coating. For example, the blade may include a Teflon coating that is modified, for example using plasma etching, to incrementally increase its surface friction. Exposure of the coated blade to plasma under suitable conditions can cause both chemical and physical changes to occur on the polymer coating. The changes can affect a variety of properties of the coating, including but not limited to roughness, wettability, cross-linking, and molecular weight, each of which can affect the cutter force of the blade. 
     In some instances, a blade can be used that is substantially free of polymer coating. However, a blade without any polymer coating can result in an undesirable decrease in comfort. For example, it may pull the hair too aggressively. 
     Polymer Coating a Blade 
     Methods of coating razor blade edges with polyfluorocarbons are known in the art and are disclosed, for example, in U.S. Pat. No. 5,263,256 to Trankiem. A polyfluorocarbon-coated blade edge can be prepared by any process known in the art. For example, the blade edge can be coated with a polyfluorocarbon dispersion. 
     Examples of polyfluorocarbons include MP1100, MP1200, MP1600, and LW1200 brand polytetrafluoroethylene powders manufactured by DuPont. 
     Polyfluorocarbon dispersions generally include from 0.05 to 5% (wt) polyfluorocarbon, preferably from 0.7 to 1.2% (wt), dispersed in a dispersant media. The polymer can be introduced into a flow stream or mixed directly into an agitated reservoir and then homogenized. When injected into the flow stream, a static mixer downstream is generally used. 
     The dispersing medium generally includes one or more of a fluorocarbon (e.g. Freon brand from DuPont), water, a volatile organic compound (e.g. isopropyl alcohol), and/or supercritical CO 2 . 
     The dispersion can be applied to the cutting edge in any suitable manner, as for example, by dipping or spraying the dispersion onto the blade edge. Where nebulization is used, an electrostatic field can be employed in conjunction with the nebulizer in order to increase the efficiency of deposition. The coating is generally heated upon application to provide improved adhesion. 
     The coated blade is then heated to drive off the dispersing media and sinter the polyfluorocarbon onto the blade edge. Alternatively, the blade can be coated using chemical vapor deposition, laser, or sputtering deposition. 
     Modifying the Blade Coating 
     Low surface friction and hard to wet materials, such as Teflon, can be modified, for example, using plasmas to incrementally increase surface friction. Examples of plasmas include, for example radiofrequency (RF) plasma or direct current (DC) plasma. Exposure of the coated blade to plasma under suitable conditions can cause both chemical and physical changes to occur on the polymer coating. The changes can affect a variety of properties (e.g., polymer properties) including but not limited to roughness, wettability, cross-linking, and molecular weight, each of which can affect the cutter forces of the blade. 
     An RF plasma deposition system like that schematically illustrated in  FIG. 6  can be employed for carrying out the modification process. As will be recognized by those skilled in the art, other conventional plasma systems can also be employed. The example system  30  includes an air-tight vacuum chamber  32  formed of, e.g., steel, and includes a powered electrode  34  and a ground electrode  36  each formed of, e.g., aluminum. 
     The powered electrode  34  is preferably configured with connection to a feed gas source  38  such that the gas  40  is introduced into the chamber, e.g., through tubes in the powered electrode in a conventional shower-head configuration. Preferably, the shower-head tubes provide a reasonably equal flow of gas per unit area of the upper electrode. Accordingly, the shower-head tubes should be spaced such that the concentration of the gas injected out of the shower-head is relatively uniform. The number and spacing of the tubes is dependent upon the specific pressure, electrode gap spacing, temperature, and other process parameters, as will be recognized by those skilled in the art. 
     A flow rate controller  42  is preferably provided to enable control of the flow of gas through the powered electrode into the chamber. The powered electrode is also connected electrically to a radio frequency (RF) power source  44 , or other suitable power source, for producing a plasma of the feed gas in the chamber. 
     The grounded electrode  36  is connected electrically to a ground  46  of the vacuum chamber system. Preferably, the grounded electrode  36  provides a surface  48  for supporting a substrate or other structure. The grounded electrode and its support surface are preferably cooled by way of a cooling system including, e.g., a coolant loop  50  connected to cooling coils  51  and a temperature controller  52 , enabling a user to set and maintain a desired electrode temperature by way of, e.g., water cooling. 
     A pump  54  is provided for evacuating the chamber to a desired pressure; the pressure of the chamber is monitored by way of, e.g., a pressure gauge  56 . Also preferably provided is an analysis port  76  for enabling a user to monitor progress of the process. 
     Suitable gasses to provide plasma include, for example, oxygen, argon, nitrogen, and a variety of fluorocarbons. Varying the type of gas, the plasma power, the gas pressure and the geometry of the blades can affect the degree and kind of modification to the blade or polymer coating. Accordingly, it is possible to provide blades having a range of different frictional properties (i.e., cutter forces). 
     Plasma, for example, high ion bombardment plasma, e.g., RF or DC plasma, can selectively remove polymer, for example, at the tip of the blade. Accordingly, where a blade is coated with a polymer, the blade, or a portion of the blade, can be exposed to a plasma (e.g., argon, oxygen, or a mixture thereof) that will physically etch away a portion of that polymer. In general, the composition of the plasma (e.g., reactivity of the elements) can be varied depending on the desired result of the exposure to the plasma. For example, where the polymer is being etched to physically modify the polymer, a mixture of argon and oxygen is generally preferred (e.g., a 90/10 mixture of argon/oxygen). The higher the oxygen content, the faster the etching rate will be. Other suitable gases include neon and nitrogen. 
     In some instances, referring to  FIGS. 7   a  and  7   b , only the tip  84  of the blade  86  is etched with plasma  88 . Selectively etching only a portion of the blade  86  can be accomplished in a variety of ways. For example, using a mask  90  to cover a portion of the blade  86  that is not modified (See  FIG. 7   a .), or placing blades  86  in the stream of the plasma  88  with a geometry that favors exposure of a only portion of the blade, for example the tip  84  of the blade  88  (See  FIG. 7   b .), provides selective exposure of a desired portion of the blade  86 . 
     In instances where a coated blade is exposed to plasma, the plasma can etch away the entire thickness of the polymer, providing portions of the blade (e.g., the blade tip) that are substantially free of polymer coating. Alternatively, the plasma can instead etch only a portion of the thickness of the polymer to thin or change the texture of the polymer coating. For example, the polymer coated blade can be exposed to plasma under conditions to provide a coating having a rough texture, which can increase the cutter forces of the blade. 
     In general, a physical modification of a coated blade can be accomplished by exposing the coated blade to plasma for between 5 seconds and about 10 minutes (e.g., between about 1 and 8 minutes, preferably about 5 minutes). The pressure is generally between about 1 and about 100 mtorr (e.g., between about 10 and about 75 mtorr, preferably between about 20 and about 40 mtorr). In general, the plasma is supplied at an energy between about 1 and about 100 Watts (e.g., between about 5 and about 80 Watts, between about 10 and about 50 Watts, or about 20 Watts). 
     An example of a blade tip  84  etched with plasma is depicted in  FIG. 8 . The blade was coated with MP 1600 polymer and exposed to plasma of 90% Ar/10% O 2  for 5 minutes at 20 W and a pressure between 20 and 40 mtorr. Upon exposure, about 3 μm of the polymer was removed from the tip to provide a tip portion of the blade substantially free of polymer coating. 
     While in some instances a coated blade can be exposed to plasma to remove, thin, or roughen the polymer coating, in other instances the coated blade can be exposed to plasma to chemically modify the polymer coating. For example, where it is desirable to increase the cutter forces of the blade, the polymer coating can be exposed to a plasma that will reduce the lubricity of the polymer coating, for example by reducing the degree of fluorination of a polymer, e.g., a PTFE polymer. RF or DC plasma may be used, and exposure time can range from a few seconds to 20 minutes. 
     In general, for chemical modification of the coated blade, the plasma is provided at a pressure of between about 1 and about 100 mtorr, (e.g., at least about 1, 5, 10, 15, 20, 25, 30, or 40 mtorr and at most about 100, 95, 90, 85, 80, 75, 50, or 40 mtorr). Although the conditions of plasma exposure can vary depending on the nature of the desired modification (e.g., plasma etching or plasma deposition), in general, the blades are exposed to plasma for between about 5 seconds and about 30 minutes (e.g., about 15 seconds, 30 seconds, 1 minute, 2 minutes, 50 minutes, 10 minutes, etc.). The plasma is generally provided at between about 1 and about 100 W (e.g., about 5, 10, 15, 20, 25, 30, 40, 45, 50, 60, 70, 80, 90, or 100 W). Preferably, the base vacuum (pressure prior to deposition) is greater than 10 −6  Torr, and during deposition is at least 10 −3  Torr. It is also preferred that heating be limited to less than the melting temperature of the polymer, typically less than 300° C. The preferred conditions will vary depending on the gas used. 
     Applying a Blade Coating Using Plasma 
     In some instances a blade not coated with polymer is exposed to a plasma that deposits a coating thereon. For example, an uncoated blade having high cutter forces can be modified to have lower cutter forces by using plasma to deposit a fluorine containing moiety (e.g., a CF 2  species) directly onto the blade (e.g., onto a hard coating such as diamond like carbon). The use of plasma deposition, e.g., high ion bombardment plasma, can provide blades having different physical properties than those coated with a polymer (e.g., a PTFE polymer) using the methods described above. 
     Preferably, the monomer gas includes hexafluoropropylene oxide, and the heat source preferably is a resistively-heated conducting filament suspended over the structure surface or a heated plate having a pyrolysis surface that faces the structure. The heat source temperature is preferably greater than about 500 K and the structure surface is preferably substantially maintained at a temperature less than about 300 K. Where it is desirable to have a blade with higher cutter forces than a polymer coated blade, the blade can be exposed to a CF 2  containing plasma for a time sufficient to lower the cutter forces relative to the uncoated blade while still having higher cutter forces than a polymer coated blade. 
     The conditions of plasma exposure can vary depending upon the desired blade properties. For example, the blade can be exposed for a greater length of time if a higher amount of plasma deposition is desired. In general, deposition of a film having properties similar to bulk PTFE can be accomplished with the described methods. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. 
     For example, while modification of the blades using plasma has been described, other blade modification methods are also envisioned. In some instances a polymer coated blade is exposed to electric current to chemically and physically modify the blade surface. In some instances the polymer coating is exposed to a laser or electron beam to chemically and physically modify the blade surface. 
     In some instances a blade (e.g., a polymer coated blade) is subjected to additional modifications, for example a blade can be exposed to a solvent to modify the amount or thickness of polymer coating on the blade. The additional modification can occur, for example, either before the blade is exposed to plasma, laser, or electric current, or after the blade is exposed to plasma, laser, or electric current. 
     Accordingly, other embodiments are within the scope of the following claims.