Patent Application
20240042637
The present invention relates to a cutting element comprising a substrate with at least one aperture which comprises a cutting edge along at least a portion of an inner perimeter of the aperture, wherein the cutting edges have an asymmetric cross-sectional shape with a first face, a second face opposed to the first face and a cutting edge at the intersection of the first face and the second face. Moreover, the present invention relates to a hair removal device comprising such cutting elements.
Conventional shaving razors contain a plurality of straight cutting edges aligned parallel to each other and these razors are moved in a direction perpendicular to the cutting edges over the user's skin to cut body hair. Typically, a handle is attached to the plurality of cutting edges at this perpendicular angle to facilitate easy operation of the razor. However, this limits these razors to being used only in this single perpendicular direction. Shaving in any other direction requires the user to change the orientation of the hand and arm holding the razor or to change the grip of the handle within the hand. As a result, it is possible to shave back and forth over the body surface but still limited to a direction that is perpendicular to the elements. Shaving sideways and in any other kind of motion, e.g. circular or in the shape of an “8” is very difficult.
It is also known that moving conventional straight cutting edges parallel to the skin result in slicing action that severely cuts the skin, because the skin bulges into the gaps between the cutting edges and hence is presented to the full length of the cutting edge as it moves parallel to the bulge (like cutting a tomato with a knife).
This can be overcome by providing a cutting element that comprises cutting edges that are shorter and surrounded on all sides by solid material to create cutting edges that are located on the inside perimeter of an aperture. An array of such apertures containing cutting edges gives better support to the skin during shaving, flattens the skin and reduces bulging of the skin into the apertures, which result in a much safer cutting element.
Furthermore, cutting edges that are located on the inside perimeter of apertures only present a very short section of cutting edge that is parallel to any direction of motion and therefore considerably reduces the slicing action and risk of cutting the user's skin.
There is therefore a need for cutting elements and hair removal devices that can be used anywhere on the body's skin surface in any form of back and forth, sideways, circular, “8”-shaped or any other motion. For instance, it is easier and more natural to remove hair from under the arm in a circular motion. It is also easier not to be constraint to up and down shaving on some difficult to reach and hard to see areas of the body.
To enable multi-directional shaving, hair removal devices consisting of a sheet of material containing circular or other shaped apertures with cutting edges provided along the internal perimeter of these apertures have been previously proposed. However, fabricating these devices from sheets of e.g. metal requires the cutting edge to protrude from the plane of the sheet material and hence point towards the skin of the user (US 2004/0187644 A1, WO2001/08856 A1, EP 0 917 934 A1, U.S. Pat. No. 5,293,768 B1). This causes severe issues with the safety of these shaving devices and this is the reason for why no such devices are available on the market today.
To improve the safety and prevent the skin from being cut by the cutting edges, it has been proposed to fabricate apertures with cutting edges along the internal perimeter that do not protrude beyond the shaving surface by etching apertures with beveled edges along the internal perimeter into e.g. silicon wafers (U.S. Pat. No. 7,124,511 B1, JP 2004/141360 A1, EP 1 173 311 A1, DE 35 26 951 A1).
It has been found that all silicon cutting edges, even with hard coatings such as DLC, are too brittle to provide for a durable shaving device, which is the reason that no such devices are available on the market today.
There is therefore a need to provide a cutting element and a hair removal device that can be used safely in a multi directional motion without much skin bulging into the apertures and with cutting edges that efficiently remove hair but not cut into the skin. This requires cutting edges along the internal perimeter of an array of apertures that lie within the plane of the array while having cutting edges with a bevel of less than 20° that is sufficiently durable to withstand frequent usage.
The present invention therefore addresses the problem to overcome the mentioned problems and to provide a cutting element which is efficient and safe to handle in multi-directional shaving, i.e. to cut the hair without cutting the skin.
This problem is solved by the cutting element with the features of claim 1 and the hair removal device with the features of claim 16. The further dependent claims define preferred embodiments of such a cutting element.
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 has to be understood as the linear extension of an connecting point (according to a cross-sectional view as in
According to the present invention a cutting element is provided which comprises a substrate with at least one aperture which comprises a cutting edge along at least a portion of an inner perimeter of the aperture, wherein the cutting edges have an asymmetric cross-sectional shape with a first face, a second face opposed to the first face and a cutting edge at the intersection of the first face and the second face.
The first face comprises a first surface. 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.
The second face comprises a first line which connects the primary bevel and the secondary bevel. The primary bevel extends from the cutting edge to the first line. The second face has a first wedge angle θ1 between the first surface and the primary bevel or its tangent at the cutting edge and a second wedge angle θ2 between the first surface and the tangent of the secondary bevel at the first line. The secondary bevel extends from the first line to a second line which may be the final line of the secondary bevel or, optionally, the intersecting line of the secondary bevel with a tertiary bevel.
Preferably, the substrate has a plurality of apertures, e.g. more than 5, preferably more than 10, more preferably more than 20 and even more preferably more than apertures.
According to a preferred embodiment the cutting edge is shaped along the inner perimeter of the apertures resulting in a circular cutting edge. However, according to another preferred embodiment the cutting edge is only shaped in portions of the inner perimeter of the apertures.
The substrate of the inventive cutting element has preferably a thickness of 20 to 1000 μm, more preferably from 30 to 500 μm, and even more preferably 50 to 300 μm.
According to a preferred embodiment of the cutting element the substrate comprises a first material, more preferably essentially consists of or consists of the first material.
According to another preferred embodiment the substrate comprises a first and a second material which is arranged adjacent to the first material. More preferably, the substrate essentially consists of or consists of the first and second 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. It is preferred that the first material is different from the second material, more preferably the second material has a higher hardness and/or a higher modulus of elasticity and/or a higher rupture stress than the first material.
However, according to an alternative embodiment the blade body comprises or 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 for the second material.
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. Relative to monocrystalline diamond, 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. Moreover, with respect to their grain size distribution nano-crystalline diamond layers are more homogeneous than polycrystalline diamond layers, the material also shows less inherent stress. Consequently, macroscopic distortion of the cutting edge is less probable.
It is preferred that the second material has a thickness of 0.15 to 20 μm, preferably 2 to 15 μm and more preferably 3 to 12 μm.
It is preferred that the second material has a modulus of elasticity (Young's modulus) of less than 1200 GPa, preferably less than 900 GPa, more preferably less than 750 GPa and even more preferably less than 500 GPa. Due to the low modulus of elasticity the hard coating becomes more flexible and more elastic. The Young's modulus is determined according to the method as disclosed in Markus Mohr et al., “Youngs modulus, fracture strength, and Poisson's ratio of nanocrystalline diamond films”, J. Appl. Phys. 116, 124308 (2014), in particular under paragraph III. B. Static measurement of Young's modulus.
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 hard coating, 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 Rids 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 Rids is determined according to DIN EN ISO 25178. The mentioned surface roughness makes additional mechanical polishing of the grown second material superfluous.
In a preferred embodiment, the second material has an average grain size d50 of the nano-crystalline diamond of 1 to 100 nm, preferably 5 to 90 nm more preferably from 7 to 30 nm, and even more preferably 10 to 20 nm. The average grain size d50 is the diameter at which 50% of the second material is comprised of smaller particles. The average grain size d50 may be determined using X-ray diffraction or transmission electron microscopy and counting of the grains.
According to a preferred embodiment, the first material and/or the second material are coated at least in regions with a low-friction material, preferably selected from the group consisting of fluoropolymer materials like PTFE, parylene, polyvinylpyrrolidone, polyethylene, polypropylene, polymethyl methacrylate, graphite, diamond-like carbon (DLC) and combinations thereof.
Moreover, the apertures have preferably a shape which is selected from the group consisting of circular, ellipsoidal, square, triangular, rectangular, trapezoidal, hexagonal, octagonal or combinations thereof.
The area of an aperture is defined as the open area enclosed by the inner perimeter. The aperture area preferably ranges from 0.2 mm2 to 25 mm2, more preferably from 1 mm2 to 15 mm2, and even more preferably from 2 mm2 to 12 mm2.
According to a first preferred embodiment, the first wedge angle θ1 ranges from 10° to 90°, preferably 12° to 75°, more preferably 15° to 45° and/or the second wedge angle θ2 ranges from 0° to 30°, preferably 5° to 20°, more preferably 8° to 15°.
It is preferred that the wedge angles fulfill the following conditions:
θ1≥θ2.
This condition provides a cutting element with a very stable cutting edge combined with very good cutting performance. The cutting elements according to the present invention have a low cutting force due to a thin secondary bevel with a small second wedge angle θ2.
The cutting elements according to the present invention are strengthened by adding a primary bevel with a primary wedge angle greater than the secondary wedge angle. 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 element body in the area of the secondary bevel without affecting the cutting performance of the element.
According to a further preferred embodiment, the primary bevel has a length d1 being the dimension projected onto the first surface and/or the imaginary extension of 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 element. It has been surprisingly found that the primary bevel stabilizes the element body with the secondary and tertiary bevel which allows a slim element in the area of the secondary bevel which offers a low cutting force. On the other hand, the primary bevel does not affect the cutting performance as long as the length d1 is not larger than 7 μm.
Preferably, the length d2 being the dimension projected onto the first surface and/or the imaginary extension of the first surface taken from the cutting edge to the second line ranges from 5 to 150 μm, preferably from 10 to 100 μm, and more preferably from 20 to 80 μm. The length d2 corresponds to the penetration depth of the cutting element 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 at least 30 μm. The cutting elements according to the present invention have therefore a low cutting force due to a thin secondary bevel with a low second wedge angle θ2
The cutting edge micro geometry ideally has a round configuration which improves the stability of the element. 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.
It is preferred that the tip radius r is coordinated to the average grain size d50 of the hard coating. It is hereby advantageous in particular 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.
According to a preferred embodiment, the second face further comprises a straight or concave tertiary bevel with:
It is preferred that the cutting edge, the primary bevel, and the secondary bevel are shaped in the second material.
It is further preferred that the second line 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.
According to a further preferred embodiment, the first face comprises a quaternary bevel with:
The cutting element according to the present invention may be used in the field of hair or skin removal, e.g. shaving, dermaplaning, callus skin removal, but also in other fields where cutting elements are used, e.g. as a kitchen knife, vegetable peeler, slicer, wood shaver, scalpel and composite fiber material cutter.
According to the present invention also a hair removal device comprising at least one cutting element as described above is provided.
The present invention is further illustrated by the following figures which show specific embodiments according to the present invention. However, these specific embodiments shall not be interpreted in any limiting way with respect to the present invention as described in the claims in the general part of the specification.
The following reference signs are used in the figures of the present application.
In
In
In
In
In
In a next step 9, (
In
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.”
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 |
|---|---|---|---|
| 21169482.3 | Apr 2021 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/060373 | Apr 2022 | US |
| Child | 18380718 | US |
