Patent Application
20230051077
The present invention relates to a novel hair removal device including a novel cutting blade with concave bevel.
Cutting blades, in particular razor blades, are typically made out of a suitable substrate material such as stainless steel in which a symmetric wedge-shaped cutting edge is formed.
With respect to razor blades, the design of the cutting blade has to be optimized to find the best compromise between the sharpness of the blade and the mechanical strength and hence durability of the cutting edge. The fabrication of conventional stainless steel razor blades involves a hardening treatment of the steel substrates before the blade is sharpened from both sides to form a symmetric cutting edge usually by grinding the hardened steel substrate.
A further coating may be applied to the steel blade after sharpening to optimize the mechanical properties of the blades. Hard coating materials such as diamond, amorphous diamond, diamond-like carbon (DLC), nitrides, carbides, or oxides are suitable to improve the mechanical strength of the cutting edge.
Thus, the harder the cutting edge material, the longer the edge holding property and in consequence the less wear is expected. Other coatings may be applied to increase the corrosion resistance or reduce the blade friction.
Most blades in the prior art are focused on blades with a symmetric blade body. However, some approaches exist where blades with an asymmetric blade are taught.
In U.S. Pat. No. 3,606,682, a razor blade with improved cutting ease and shaving comfort is described. The blade has a recessed portion adjacent to the cutting edge which allows an improved shaving comfort. This effect is shown for symmetric and asymmetric blade bodies.
U.S. Pat. No. 3,292,478 describes a cutting die knife for textiles, leather and similar sheet materials wherein the knife has suitably inclined surfaces on both sides with the consequence that the cutting edge is not positioned centrally between the side surfaces and the knife has an asymmetric shape.
There is a continuing desire to reduce the force needed to cut an object, since this requires less energy and creates less wear of the cutting edge. In the context of shaving, cutting hairs at lower forces results in less pulling on the hairs and hence less discomfort. However, making the edge sharper also makes it more fragile and despite the application of hard coatings, the durability of conventional steel razor blades is still limited today.
Furthermore, a significant contribution to the cutting force arises from the friction between the tool and the object being cut.
A need exists to provide cutting blades with a design, which allows at the same time, a high comfort during the cutting process, i.e., a low cutting force, and a high durability, i.e., a low fragility of the blade.
The present invention is directed to a cutting blade having a blade body having a first material and a second material joined with the first material, the cutting blade having a first face, a second face opposed to the first face, and a cutting edge, wherein the first face includes a first surface, the second face includes a primary bevel having a convex or straight cross-sectional shape and a secondary bevel having a concave cross-sectional shape with a first line connecting the primary bevel and the secondary bevel, the primary bevel extending from the cutting edge to the first line, and the cutting edge and the primary bevel are shaped in the second material.
In other aspects of the present invention, there is a first wedge angle θ1 between the first surface and the primary bevel or the tangent of the primary bevel through the cutting edge, a second wedge angle θ2 between the first surface and the tangent of the secondary bevel and θ1>θ2.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as forming the present invention, it is believed that the invention will be better understood from the following description which is taken in conjunction with the accompanying drawings in which like designations are used to designate substantially identical elements, and in which:
The following reference signs are used in the figures of the present application.
The present invention relates to a cutting blade having a blade body comprising or consisting of a first material and a second material joined to the first material, the cutting blade having a first face, a second face opposed to the first face, and a cutting edge wherein the first face comprises a first surface and the second face comprises a primary bevel having a convex or straight cross-sectional shape and a secondary bevel having a concave cross-sectional shape. Moreover, the present invention relates to a hair removal device comprising this cutting blade.
The following definitions are used in the present application:
The present invention addresses the mentioned drawbacks in the prior art and provides cutting blades with a design, which allows at the same time, a high comfort during the cutting process, i.e., a low cutting force, and a high durability, i.e., a low fragility of the blade.
This problem is solved by the cutting blade with the features of claim 1 and the hair removal device with the features of claim 15. The further dependent claims define preferred embodiments of such a blade.
The term “comprising” in the claims and in the description of this application has the meaning that further components are not excluded. Within the scope of the present invention, the term “consisting of” should be understood as preferred embodiment of the term “comprising”. If it is defined that a group “comprises” at least a specific number of components, this should also be understood such that a group is disclosed which “consists” preferably of these components.
In the following, the term “cross-sectional view” refers to a view of a slice through the cutting element perpendicular to the cutting edge (if the cutting edge is straight) or perpendicular to the tangent of the cutting edge (if the cutting edge is curved) and perpendicular to the surface of the substrate of the cutting element.
The term “line” or “line intersection” as used herein is understood as the linear extension of a connecting point (according to a cross-sectional view as in
According to the present invention a cutting blade is provided having a blade body comprising or consisting of a first material and a second material joined with the first material, the cutting blade having a first face, a second face opposed to the first face, and a cutting edge, wherein:
It was surprisingly found that a cutting blade with a very stable cutting edge together with a very good cutting performance can be provided when the wedge angles fulfill the following conditions:
θ1>θ2.
The cutting blades according to the present invention have low cutting forces due to a thin secondary bevel with a low wedge angle θ2. This is realized by a reduction of the contact area between the cutting blade in the region of the secondary bevel, which has the function of the penetrating bevel, and the object being cut. According to the present invention the concave cross-sectional shape of the rake face results in a significant reduction of the cutting force.
The second wedge angle θ2 represents the penetration angle of the blade penetrating in the object being cut. The smaller the penetrating angle θ2, the lower the force to penetrate the object being cut.
The cutting blades according to the present invention are strengthened by adding a primary bevel with a first wedge angle θ1 which is greater than the second wedge angle θ2. The primary bevel with the first wedge angle θ1 has therefore the function to stabilize the cutting edge mechanically against damage from the cutting operation which allows a slim blade body in the area of the secondary bevel without affecting the cutting performance of the blade. In consequence, by using a primary bevel with the wedge angle θ1 the second wedge angle θ2 can be reduced. In other words, the wedge angle θ1 has the function to stabilize the cutting edge which allows a slim blade body in the area of the secondary bevel without effecting the cutting performance of the blade.
According to a preferred embodiment, the cutting blade has an asymmetric cross-sectional shape. The asymmetrical cross-sectional shape refers to the symmetry with respect to an axis which is the bisecting line of the primary wedge angle θ2 and anchored at the cutting edge.
According to a further preferred embodiment, the first wedge angle θ1 ranges from 10° to 90°, preferably 12° to 75°, more preferably 15° to 46°, and even more preferably 20° to 45° and/or the second wedge angle θ2 ranges from −5° to 40°, preferably 0° to 30°, more preferably 5° to 25° and even more preferably from 10° to 15° and/or the second wedge angle θ2 ranges from −5° to 30°, preferably 0° to 20°, more preferably −5° to 30°, preferably 0° to 20°, more preferably 5° to 15°, and even more preferably 8° to 12°.
According to a further preferred embodiment, the primary bevel has a length d1 being the dimension projected onto the first surface taken from the cutting edge to the first line from 0.1 to 7 μm, preferably from 0.5 to 5 μm, and more preferably 1 to 3 μm. A length d1<0.1 μm is difficult to produce since an edge of such length is too fragile and would not allow a stable use of the cutting blade. The primary bevel stabilizes the blade body with the secondary bevel which allows a slim blade in the area of the secondary bevel which offers a low cutting force. It has been surprisingly found that the primary bevel does not affect the cutting performance provided the length d1 is not larger than 7 μm.
Preferably, the dimension projected onto the first surface (9) and/or the imaginary extension of the first surface (9′) taken from the cutting edge (4) to a second line (11) has a length d2 which ranges from 1 to 75 μm, more preferably 5 to 50 μm, and even more preferably from 10 to 35 μm. The second line may be the final line of the secondary bevel or, optionally, the intersecting line of the secondary bevel with a tertiary bevel. The length d2 corresponds to the penetration depth of the cutting blade in the object to be cut. In general, d2 corresponds to at least 30% of the diameter of the object to be cut, i.e., when the object is human hair which typically has a diameter of around 100 μm the length d2 is around 30 μm.
The cutting blade is preferably defined by a blade body comprising or consisting of a first material and a second material joined with the first material. The second material can be deposited as a coating at least in regions of the first material, i.e., the second material can be an enveloping coating of the first material, or a coating deposited on the first material on the first face.
The material of the first material is in general not limited to any specific material as long it is possible to bevel this material.
However, according to an alternative embodiment the blade body consists only of the first material, i.e., an uncoated first material. In this case, the first material is preferably a material with an isotropic structure, i.e., having identical values of a property in all directions. Such isotropic materials are often better suited for shaping, independent from the shaping technology.
The first material preferably comprises or consists of a material selected from the group consisting of:
The steels used for the first material are preferably selected from the group consisting of 1095, 12C27, 14C28N, 154CM, 3Cr13MoV, 4034, 40X10C2M, 4116, 420, 440A, 440B, 440C, 5160, 5Cr15MoV, 8Cr13MoV, 95X18, 9Cr18MoV, Acuto+, ATS-34, AUS-4, AUS-6 (=6A), AUS-8 (=8A), C75, CPM-10V, CPM-3V, CPM-D2, CPM-M4, CPM-S-30V, CPM-S-35VN, CPM-S-60V, CPM-154, Cronidur-30, CTS 204P, CTS 20CP, CTS 40CP, CTS B52, CTS B75P, CTS BD-1, CTS BD-30P, CTS XHP, D2, Elmax, GIN-1, H1, N690, N695, Niolox (1.4153), Nitro-B, S70, SGPS, SK-5, Sleipner, T6MoV, VG-10, VG-2, X-15T.N., X50CrMoV15, ZDP-189.
It is preferred that the second material comprises or consists of a material selected from the group consisting of:
The second material may be preferably selected from the group consisting of TiB2, AlTiN, TiAlN, TiAlSiN, TiSiN, CrAl, CrAlN, AlCrN, CrN, TiN, TiCN and combinations thereof.
Moreover, all materials cited in the VDI guideline 2840 can be chosen.
It is particularly preferred to use a second material of nano-crystalline diamond and/or multilayers of nano-crystalline and polycrystalline diamond as second material. It has been shown that production of nano-crystalline diamond, compared to the production of monocrystalline diamond, can be accomplished substantially more easily and economically. Hence, also longer and larger area cutting blades can be produced. Moreover, with respect to their grain size distribution, nano-crystalline diamond layers are more homogeneous than polycrystalline diamond layers, the material also shows less internal stress. Consequently, macroscopic distortion of the cutting edge is less likely.
It is preferred that the second material has a thickness of 0.15 to 20 μm, preferably 2 to 15 μm and more preferably 5 to 10 μm.
It is preferred that the second material has a Young's modulus of less than 1200 GPa, preferably less than 900 GPa, and more preferably less than 750 GPa. Due to the low Youngs' modulus the second material becomes more flexible and less stiff and may be better adapted to the Young's modulus of the substrate to increase mechanical stability of the cutting edge.
The second material has preferably a transverse rupture stress σ0 of at least 1 GPa, more preferably of at least 2.5 GPa, and even more preferably at least 5 GPa.
With respect to the definition of transverse rupture stress σ0, reference is made to the following literature references:
The transverse rupture stress σ0 is thereby determined by statistical evaluation of breakage tests, e.g., in the B3B load test according to the above literature details. It is thereby defined as the breaking stress at which there is a probability of breakage of 63%.
Due to the extremely high transverse rupture stress of the second material the detachment of individual crystallites from the second material, in particular from the cutting edge, is almost completely suppressed. Even with long-term use, the cutting blade therefore retains its original sharpness.
The second material has preferably a hardness of at least 20 GPa. The hardness is determined by nanoindentation (Yeon-Gil Jung et. al., J. Mater. Res., Vol. 19, No. 10, p. 3076).
The second material has preferably a surface roughness RRMS of less than 100 nm, more preferably less than 50 nm, and even more preferably less than 20 nm, which is calculated according to
A=evaluation area
Z(x,y)=the local roughness distribution
The surface roughness RRMS is determined according to DIN EN ISO 25178. The mentioned surface roughness makes additional mechanical polishing of the surface of the second material superfluous.
In a preferred embodiment, the second material has an average grain size d50 of the nanocrystalline diamond of 1 to 100 nm, preferably 5 to 90 nm and more preferably from 5 to 30 nm. The average grain size d50 may be determined using X-ray diffraction or transmission electron microscopy and counting of the grains.
It is preferred that the first material and/or the second material is/are coated at least in regions with a low-friction material, preferably selected from the group consisting of fluoropolymers (e.g., PTFE), parylene, polyvinylpyrrolidone, polyethylene, polypropylene, polymethyl methacrylate, graphite, diamond-like carbon (DLC) and combinations thereof.
The cutting edge has preferably a tip radius of less than 200 nm, more preferably less than 100 nm and even more preferably less than 50 nm, determined e.g., by cross sectional SEM using the method illustrated in
It is preferred that the tip radius r of the cutting edge correlates with the average grain size d50 of the second material. It is hereby advantageous if the ratio between the tip radius r of the second material at the cutting edge and the average grain size d50 of the nanocrystalline diamond hard coating r/d50 is from 0.03 to 20, preferably from 0.05 to 15, and particularly preferred from 0.5 to 10.
In a preferred embodiment, the second face further comprises a straight or concave tertiary bevel with a second line connecting the secondary bevel and the tertiary bevel. The tertiary bevel extends from the second line rearward. Moreover, a third wedge angle θ3 is located between the first surface and the tertiary bevel or its tangent, wherein the third wedge angle θ3 ranges preferably from 1° to 60°, more preferably 10° to 55°, and even more preferably 30° to 46°, and most preferably is 45°.
According to the present invention, the cutting blade are further strengthened by adding a thick and strong tertiary bevel that has a tertiary wedge angle greater than the secondary wedge angle and by employing this tertiary bevel to split the object to be cut, thus reducing the forces acting on the thin secondary bevel. For this function the third wedge angle θ3 has to be larger than the second wedge angle θ2. The tertiary bevel with the third wedge angle θ3 therefore has the function of splitting the object to be cut.
The edge connecting the primary bevel and the secondary bevel is preferably shaped within the second material.
It is further preferred that the edge between secondary and tertiary bevel is arranged at the boundary surface of the first material and the second material which makes the process of manufacture easier to handle and therefore more economic, e.g., the blades can be manufactured according to the process of
The first face preferably further comprises a quaternary bevel which extends from the cutting edge to the first surface. If the first face corresponds to the clearance face this quaternary bevel will improve the comfort of the cutting, i.e., for shaving.
In a preferred embodiment, the first face corresponds to the clearance face and the second face corresponds to the rake face of the cutting blade. However, it is also possible to use the first face as the rake face and the second face as the clearance face.
Hence, according to the present invention also a hair removal device comprising a razor blade as described above is provided.
Turning now to
In
In
In
In
In
In the case of double-sided coating, the diamond layer 104 on the structured second surface 3 has to be removed in a further step 7 prior to the following edge formation steps 9a-9d of the cutting blade. The selective removal of the diamond layer 104 is performed e.g., by using an Ar/O2-plasma (e.g., RIE or ICP mode), which shows a high selectivity towards the silicon substrate. In step 8, the silicon wafer 101 is thinned so that the diamond layer 104 is partially free standing without substrate material and the desired substrate thickness is achieved in the remaining regions. This step can be performed by wet chemical etching in KOH or HF/HNO3 etchants or preferably by plasma etching in CF4, SF6, or CHF3 containing plasmas in RIE or ICP mode.
In a next step 9, (
In
The illustrations presented herein are not intended to be actual views of any particular substrate, apparatus (e.g., device, system, etc.), or method, but are merely idealized and/or schematic representations that are employed to describe and illustrate various embodiments of the disclosure.
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm” or ±10% of the disclosed dimension.
Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20169930.3 | Apr 2020 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2021/059198 | Apr 2021 | US |
| Child | 17966022 | US |
