CA1041753A - Shaving foil - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

This invention concerns a foil for electrically or mechanically operated dry shavers.
More especially the invention concerns a foil made from a sheet having perforations and bars between the perforations, the bars being dished in cross-sectional profile, the base of the dished profile being flat and of uniform thickness (t) while the edges extend at an obtuse angle .alpha. to the base, terminating in coplanar faces parallel to the base, the width of the face (w) being not greater than the thickness (t).
The foils are especially suitable for battery operated razors, in which the reduced width (w) leads to reduced power consumption and longer battery life.

Description

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FIELD OE` THE INVENTION
This invention concerns perforated foils for dry shavers.

': STATEMENT OF PRIOR ART
: - _ The cutting head of a dry shaver conventionally com- ;
prises a perforated stationary outer shear foil and an inner movable cutter contacting the rear face of the shear foil.
The cutter can eitller comprise a plurality of separate blades or it can itself be made from a perforated foil.
Various forms of foil have been proposed in the literature, or employed in practice. For instance, British Patent Specification No. 845,832 describes a foil whose thickness (from front to rear surfaces) immediately adjacent to the apertures exceeds the thickness of those portions between apertures.
There has, however, been a continued search for new and improved types of foil.
U.S. Patent No. 3,409,984 to Fùtterer describes a ~ foil with a thin coating of a hard material on a backing -. ~o of softer material which is intended to contact the blade ~ of a shaver. The exposed edge of the hard coating pro-., vides a hard cutting edge around the rims of the perfor-ations in the foil.
, An example of a more recent type of foil is des-,i cribed in German Offenlegungsschrift 2,537,6071 which ~ ;
, describes foils in which the central zone of bars between -4 perforations is surrounded by raised edges (as in the above-mentioned British Patent No. 845,832), but the metal is thinner in the central zone than it is at the edges, This reduction in thickness is provided to improve the .
flexibility o~ the foil. The width of -the edges, however, is maintaincd to ensure a good cutting action.
OBJECT OF THE INVENTION
The object of the present invention is to provide a novel form of perforated foil for a dry shaver.
STATEMENT OF THE INVENTION
According to the present invention there is provided a shearing foil for a dry shaver, made from a sheet oi metal or alloy, having perforations extending through the sheet with bars between the perforations, the bars being dished in transverse cross-sectional profile, the base of the dished profile being substantially flat and of uniform thickness (t), and the edges of the dished profile extending at an obtuse angle cL to the base to terminate with coplanar -~
faces disposed parallel to the base, said face having a width (w) in the transverse direction which is not greater than the thickness (t).
DESCRIPTION OF DRAWINGS
The invention will be more particularly described with reference to the accompanying drawings, in which:
Eig. 1 is a cross-section through a bar on a foil of conventional construction;
Fig. 2 is a cross-section through a bar on a foil according to the invention; and Figs. 3 and 4 are cross-sections illustrating two stages during a technique by which it is possible to produce a foil according to the invention.
PARTICULAR DESCRIPTION OF THE INVENTION
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Referring now to Figs. 1 and 2, a foil has apertures 1 and bars 2 between the apertures. The bars 2 are dished `
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in cross-sectional profile, with a substantially flat base 3 of thickness t and edges 4 extending at an angle d~ to the base. The edges 4 terminate in faces 5 which are coplanar and parallel to the base 3, and have a width w The bars therefore, have recessed portions 6.
In accordance with the conventional construction, w is greater than t, and the angle o~ is substantially a right angle.
In accordance with the present invention, w is not greater than t. In other words, w can be substantially the same as t, or it can be less than t. Preferably _ is not greater than 0.9 t, and more preferably not greater - than 0.75 t. The minimum value for w is governed by the properties of the metal from which the foil is constructed.
Generally w will be greater than 0.25 t. Most preferably w is about 0.6 t.
j Also in accordance with the present invention, the angle 5~ between the base 3 and the edges 4 is an obtuse angle. Conveniently it will lie in the range from 120 to 160, more preferably from 130 to 150. The most pre~
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ferred value for ~C is around 140.
The material from which the foils according to the invention are made is a single metal or alloy (e.g. steel), which advantageously and conveniently can be worked by an etching technique. One convenient etching technique for ;
Canall d n A the purpose forms the subject of our copending~Application ~EF30) No.~6,~0 . This technique will be described with refer- l ence to Figs. 3 and 4 of the accompanying drawings.

In accordance with this method~ a strip 10 of a r suitable metal, e.g. laminated steel, is cleaned to remove _4_ ':

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grease and other contaminants from its sùrfaces, and is then pro-vided by dip-coa-ting with a layer oE a suitable negative or positive photoresist on each surface. A preferred negative photoresist is sold by the Philip A. Hunt Chemical Corporation under the trade mark Waycoat-450 which is a photosensitive poly-mer. Another suitable negative photoresist is sold by Eastman ICodak Co~pany under the trade mark ~R which is also a photo-sensitive polymer, and a suitable positive photoresist is sold by Shipley Chemicals I.td. under the trade mark AZ 111. The layers o~ photoresist 11 and 12 are hardened by baking. The strip 10 at this stage is shown in Fig. 3. Both layers are then exposed to ultraviolet radiation through appropriate masks, such as exposed and developed photographic film having transparent areas and opaque areas. In the case of a negative photoresist, the mask adjacent the layer 11 will have opaque areas in corres-pondence to the desired position of the apertures 1, whilst the mask adjacent the layer 12 will have opaque areas in corres-pondence to the recessed portions t. Care must of course be .,. -taken to ensure that the masks are precisely registered, so that `~

the positions of the apertures 1 and recessed portions 6 in the .
finished product will be accurate. After the exposure, the photo-resist is developed and baked. The strip 10 will have on one side masking areas lla and on the other side, masking areas 12a (see Fig. 4).
The face of the workpiece pro~ided with the masking areas 12a is then subjected to spray etching, in order to form -the recessed portions 6. Once these have been etched to the correct depth, the workpiece is rinsed and dried, and the newly etched - face is protected by a protective film 13, for instance of adhesive tape.
The face of the workpiece provided with masking ,;.

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areas lla is then spray etchecl, the etching being halted when the metal has been eaten away to position 14, shortly before the apertures are completely formed.
After rinsing, the masking areas lla are removed, leaving the areas 12a and protective film 13 in place.
Alternatively, both the masking areas lla and 12a and the protective film 13 are removed, and a furkher protective film, for instance a layer of shellac, is applied over the face bearing the recessed portions. Further etching of the unprotected face removes more metal, leaving a foil with apertures 1 and bars 2. Finally, after an optional r ch~mical polishing step, the protective film is removed, and the finished foil is rinsed and dried.
The foils according to the invention offer several advantages. Clean shaving requires the application of pressure between the outer foil and the movable cutter.
The area between these two parts is proportional to w, so that the smaller the value of w, the smaller the total -force F which must be employed to produce the desired pressure. Since power consumption in use is substantially proportional to F, it must therefore decrease with a decrease in w. A lower power consumption leads to a longer shaving facility between successive charges of the battery in battery-operated shavers. f The following Example illustrates one preferred manner in which a shaving foil according to the invention can be made. L
EXAMPLE ' ~, , .
~ A steel strip is subjected to an intensive cleaning ~
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involving firstly ultrasonic cleaning in a chlorinated .

solvent, such as trichloroethylene, or preferably trichloro-ethane, at room te~perature, followed by blow drying. This is followed by alkaline cleaning in a hot degreasing salt -solution, with agitation, followed by rinsing with water. A
suitable degreasing salt for this purpose is sold by MacDermid Company under the trade mark Metex TS40A which can be con-veniently employed at a temperature of about 40C. The plate is then subjected to electrolytic cleaning in a cold alkaline ;~
cyanide-free solution, e.g, one available ~rom Oxy Metal ~
10 Finishing Co. identified by their trade mark Oxyprep 285, ;
followed by water-rinsing. After neutralizing wi$h dilute 18% hydrochloric acid, washing with wa~er deionized water and isopropyl alcohol, the plate is finally dried in a vapour of a chlorinated solvent, such as trichloroethane.
Both faces of the plate are now provided with a layer of Waycoat* 450 photoresist by dip-coating in Waycoat* 450 thinned with ~aycoat* PF thinner (a halogenated hyrdocarbon solvent) to a viscosity providing the required thickness of photoresist. After optional air-drying of the coated plate, the photoresist is provided with a pre-exposure baking, for 10 minutes at 95-100C in a convection oven, or for 2 minutes at 350C in an infra-red unit. The photoresist on each side of the plate is then exposed to ultraviolet light through masks made from exposed photographic film having transparent areas and opaque areas. On the side provided with layer 11 (see Fig. 3) the transparent areas wlll correspond to areas lla ~see Fig. 4), and on the side provided with layer 12 the trans-parent areas will correspond to areas 12a. Optimum exposure is achieved by holding 6 to 7 steps after exposure through a Stauf~er 21 step sensitivity guide or a Kodak #2 step wedge (Kodak is a trade mark of the Eastman Kodak Company).

* Waycoat is a trade mark of the Philip A. Hunt Chemical Corp.

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~ 4~7~3 After exposure, development can be carried out by spray~
ing and immersion. It involves contacting the exposed photo-resist with Waycoat* PF Developer, ~aycoat* PF Thinner, and water, followed by air drying. The developed photoresist is then baked for 10 minutes at 120C in a convection oven or for

2 minutes at 350~C in an infra-red unit.
Etching is then carried out, advantageously using a double-sided spray-etching apparatus, for instance, the apparatus sold by Chemcut Corporation. Etching can be carried out using Waycoat* PF Etchant, but it is advantageous to employ a 48 Beaume solution of ferric chloride, heated to a temperature of 52C.
The first etching stage is carried out for 20 to 40 seconds to provide the recessed portlons 6, followed by rinsing with deionized water and blow-drying with nitrogen.
A protective layer of adhesive cellulose acetate tape 13 - is then applied. ~he second etching stage is then carried :`
out to remove metal down to position 14. This involves etching for 100 to 140 seconds, followed by washing with 20 deionized water and blow-drying with nitrogen. "rz ~.,1 The masking areas lla are then removed using Kodak** ~!' .
_ ~P Stripper 13 LS, the recesses 6 and masking areas l~a being protected by the protective layer 13. The final etch-ing is carried out using the same etching solution as before, ~;
at the same tempexature as before. This final etching takes about 40 seconds, followed by washing with deionized water and blow-drying with nitrogen.
A chemical polishing step can then be carried out using a polishing solution suitable for the metal of the ;;~
- 30 strip 10. Suitable solutions are described for instance ;~

* Waycoat is a trade mark of the Philip A. Hunt Chemical Corp.
** Kodak is a tra~e mark of the Eastman Kodak Company.

., , 7~3 in Band l/2 of "~landbuch der Galvano technik" by De-ttner and Elze, Carl ~lauser Verlag, Munchen.
Finally the protective layer 13 is removed and the remaining masking areas 12a are stripped off using Kodak*
LS 13 stripper. After a final washing with water and blow-drying wi-th nitrogen, the manufacture of the foil is complete. , .. ~." ~
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* Kodak is a trade mark of the Eastman Kodak Company.

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Claims (3)

The embodiments of the invention in Which an exclusive property or privilege is claimed are defined as follows:

1. A shearing foil for a dry shaver, made from a sheet of metal or alloy, having perforations extending through the sheet with bars between the perforations, the bars being dished in transverse cross-sectional profile, the base of the dished profile being substantially flat and of uniform thickness (t), and the edges of the dished profile extending at an obtuse angle .alpha. to the base to terminate with coplanar faces disposed parallel to the base, said face having a width (w) in the transverse direction which is not greater than the thickness (t).

2. A shearing foil as claimed in claim 1, wherein w has a value from 0.25 t to 0.9 t.

3. A shearing foil as claimed in claim 1 or 2, wherein the obtuse angle .alpha. is from 120 to 160°.