It is generally known in the prior art that a wet razor assembled with fluoropolymer coated blades outperforms a razor assembled without fluoropolymer-coated blades. One of the most common fluoropolymers utilized for coating razor blades is polytetrafluoroethylene or PTFE (or a form of TEFLON®). The addition of PTFE (e.g., telomer) coating to the blade cutting edge dramatically reduces the cutting forces for beard hairs or other types of hair fibers. A reduced cutting force is desirable as it significantly improves shaving attributes including safety, closeness and comfort. Such known PTFE-coated blade edges are described in U.S. Pat. No. 3,071,856.
There are many types of coating processes that could be utilized to produce polymer coated (e.g., PTFE) coated blade edges. Some processes involve aqueous dispersion of the PTFE and some involve organic dispersion of the PTFE. Aqueous dispersion processes may include spraying, spin coating and dipping. PTFE may also be deposited on blade edges using vacuum based processes such as sputtering or thermal Chemical Vapor Deposition (CVD). However, when quality, cost and environmental issues are considered, the spraying of an aqueous PTFE dispersion is typically desired. PTFE dispersion in an organic solvent is also a known process in the art. This type of dispersion may include for example, DUPONT'S VYDAX 100 in isopropanol as described in U.S. Pat. No. 5,477,756.
Regardless of whether an aqueous or organic based dispersion is utilized, if a spraying process is utilized along with a subsequent sintering process, a non-uniform surface morphology, on a microscopic scale, is produced on blade edges and in the area proximal to the ultimate blade tips as shown in FIG. 1. This may be caused by the particle size dispersion of PTFE particles and by the wetting and spreading dynamics of dispersion. Typically, the average thickness of PTFE coating produced by a spraying process is about 0.2 μm to about 0.5 μm.
It should be noted that the thinner the PTFE coating becomes on blade edges, the lower the cutting force (assuming the coating is uniform). While this is generally desirable as mentioned above, too thin PTFE coatings on blade edges can give rise to poor coverage and low wear resistance due to intrinsic properties of the PTFE material. Alternatively, a too thick PTFE coating may produce very high initial cutting forces, which generally may lead to more drag, pull, and tug, eventually losing cutting efficiency and subsequently shaving comfort. Thus, there is a technical challenge to balance the attributes of the polymer material with obtaining the thinnest coating possible to provide improved shaving attributes.
This fuels the desire in the art to form a thin, dense and uniform PTFE coating with extremely low coefficient of friction onto the blade edge.
Previous efforts made towards this objective, such as selection of different PTFE dispersions, modification of the surfactant used in the dispersion and/or optimization of spray-sintering conditions have had moderate effectiveness.
Some known solutions for thinning the PTFE on the blade edges include (1) mechanical abrasion, polishing, wearing, or pushing back; (2) a high energy beam (electron, gamma ray or X-ray, synchrotron) or plasma etching; and (3) application of FLUTEC® technology or Perfluoper-hydrophenanthrene (PP11) oligomers.
The disadvantage of the first mechanical abrasion solution is that it is difficult to control, may produce non-uniform thinning and may also cause edge damage. The disadvantage of applying high energy beams to thin the PTFE is that it may change the cross linking and molecular weight of PTFE thereby increasing friction and hence, cutting force.
One relatively successful approach has been the application of FLUTEC® technology as described in U.S. Pat. No. 5,985,459 which is capable of reducing the thickness (e.g., or thinning) a relatively thick PTFE coating produced by a spray and sintering process. This prior art process, as shown in FIG. 1 depicts a flow 10 where blade 12 which has sprayed PTFE particles 11 coated on and around its tip 13 is sintered as shown at step 14 with Argon at about 1 atmospheric pressure (1 atm) and at a temperature of about 330 degrees Celsius (° C.) to about 370° C. to produce a sintered PTFE coating 16. Typically, the average thickness of PTFE coating produced by a spraying process is about 0.2 μm to about 0.5 μm.
The FLUTEC® technology as shown at step 17 is subsequently placed on coating 16 to produce a thinned PTFE coating 18. This typically includes soaking the PTFE coated blades 16 in solvents under elevated temperatures of about 270° C. to about 370° C. and at a pressure of about 3 atm to about 6 atm. In general, the solvents employed in the FLUTEC® process include solvents such as perfluoroalkanes, perfluorocycloalkanes, or perfluoropolyethers.
With the FLUTEC® approach, a more uniform PTFE coating 18 with about 10 nm to about 20 nm in thickness may be achieved consequently resulting in a reduction of the first cutting force of blade edges on wool-felt-fibers of nearly 40% compared to many approaches utilized prior to the knowledge of the FLUTEC® treatment. However, a major drawback to the FLUTEC® process is that even though most of the solvents used are capable of being recycled, some needs to be disposed of as waste.
Another disadvantage of the FLUTEC® technology is that the chemical solvent used in the FLUTEC® process typically removes most of the PTFE materials from the sintered coating 18 which, as mentioned above, provide the improved shaving attributes.
Another disadvantage of the FLUTEC® technology is that generally the resultant FLUTEC® coatings still exhibit porosity since coating molecules are not densely packed. Because of this, a coating with a desirably high molecular weight is difficult to achieve.
Thus, there is a need for an alternative apparatus and method to produce thin, uniform and dense coatings on blade edges.