US 3216415 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Nov. 9, 1965 J. c. LITTLETON 3,216,415
SURGICAL MASK Filed Sept. 4, 1962 N ENTOR JOSEPH 6T IT'TLET'O/V cmfle. ma L A rroR/wsr United States Patent Ofi Frce 3,216,415 Patented Nov. 9, 1965 York Filed Sept. 4, 1962, Ser. No. 221,237 3 Claims. (Cl. 128-146) This invention relates to a new type of surgical mask. In particular it comprises novel breathing means for more elfectively preventing outward passage of bacteria and viruses commonly contained in vapor droplets entrained with expirated air, especially during extended use, while simultaneously providing the following characteristics: free and easy breathing, the portions of the wearers face covered by the mask remain comfortably cool during extended use and no substantial impairment in the sound of the wearers voice as heard by others.
It is the principal object of this invention to provide a surgical mask having the above-mentioned characteristics. These and other objects, which will be apparent to those skilled in the art, are attained in accordance with this invention in which the novel breathing means comprises a plurality of unobstructed air channels, or passages, extending through the breathing means from one side thereof, which is adapted to confront the nose and mouth, to the opposite side thereof, with at least a portion of each channel being disposed in, or forming, a tortuous passage pattern for expirated air passing therethrough. A particularly important characterizing feature of the novel breathing means is that the air channels are defined and separated from one another by appropriately shaped walls, at least the surfaces of which are made of a porous, moisture-absorbent material, or have a layer or coating of moisture-absorbent material thereon. One or more of these breathing means are arranged across one or more openings or apertures in the mask proper, or shield portion of the mask, and within the breathing zone of the wearer.
More particularly, the objects of this invention are best attained with the construction of the novel breathing means comprising a honeycomb body or panel having a plurality of unobstructed air channels extending through it between and terminally opening in a pair of opposed major surfaces thereof. These air channels are defined and separated from one another by thin, porous, moisture absorbent walls, which can be made of one or more suitable materials that are porous and moisture-absorbent, and that can be formed into a honeycomb body, such as paper (e.g. asbestos paper), porous ceramic sheets, and the like. A unitary body comprising multiple layers of corrugated porous ceramic, with or without uncorrugated layers alternating between corrugated layers, sintered together is preferred to provide a strong and rugged construction that is better able to withstand ordinary shock in use and because it is readily sterilizable for reuse without any detrimental effect on the honeycomb body. Another particularly important characterizing feature of this honeycomb breathing means is that at least a portion of each air channel extends through the body or panel in a tortuous pattern, such as at one or more oblique or skew angles to the opposed major surfaces thereof. The term honeycomb is used in this specification and the appended claims in the common generic sense of a thin-walled, multi-channel body without limitation as to the particular geometrical cross-sectional configuration of the individual channels, viz. is not used solely in the more restricted sense of having the channels hexagonal in crosssection.
The effectiveness of the foregoing breathing means in preventing outward passage of bacteria and virus laden droplets entrained with expirated air passing through this means is due in part to the known principle, as stated in US. Patent No. 2,983,271 to W. C. Beck, that as these droplets emanating from the mouth and nose strike a solid object, they will not rebound into the air but will adhere to the object and remain immobilized there. Thus, as expirated air containing the bacteria and virus laden droplets passes through the breathing means of this invention, it impinges on the walls of those portions of the air passages extending in a tortuous pattern or at oblique or skew angles with the result that the droplets are immobilized there.
The greater effectiveness of the mask according to this invention, in preventing the outward passage of bacteria and viruses, particularly for long periods of continuous use, appears to be due, at least in part, to the honeycomb configuration of the breathing means and, in part, to the porous, moisture-absorbent walls or surfaces thereof. One beneficial aspect of the breathing means is that it provides a greatly increased surface area for impingement of the bacteria and virus laden droplets thereby assuring greater immobilization of them. Another important beneficial aspect is the ability of the porous walls or surfaces thereof to absorb and/ or adsorb substantial amounts of moisture. This latter characteristic is believed to be particularly significant to the improved results obtained with the present invention because it appears to allow a greater amount of droplet immobilization per unit of surface area impinged by expirated air of the wearer.
Although the honeycomb configuration of the breathing means according to this invention may have a plurality of air channels of only limited opening size or cross-sectional area, expirated air is found to freely pass through the honeycomb body or panel thereby affording free and easy breathing for the wearer. This beneficial result occurs because the collective cross-sectional areas of the air passages of the thin-called body constitute a very substantial portion of the total cross-section area of the body generally perpendicular to the direction of air flow. Thus, the structural configuration provides a generally negligible pressure drop in the, air flow through the breathing means, i.e. generally negligible back presur e.
A benefit provided by the free air flow characteristic of the present invention, which is particularly important when a surgical mask has to be worn for extended periods of time, is that exhaled air is not reflected back against the covered portions of the wearers face to thereby create the feeling of being in a hot, humid, unventilatedroom. Thus, unlike 16-ply, or even 8-ply, gauze masks, the present invention is very comfortable to the wearer.
Another factor providing comfort to the wearer, similar in this respect to common gauze masks, is that the mask of the present invention can be made lightweight. This is mainly due to the use of a thin-walled body of porous materials which is very light in weight.
The breathing means of the present invention also affords the advantages of being able to clearly hear and understand the wearers speech while the mask is being worn.
It is contemplated that the breathing means according to this invention can be made integral with the mask proper or in the form of a replaceable and/or reusable cartridge that can be readily removed and another one inserted in its place. Moreover, it is contemplated that the novel breathing means, with or without the mask proper, can be disposable after one period of use (e.-g. when constructed of corrugated paper) or reusable after sterilization (e.g. when constructed of porous ceramic).
The invention will be more readily understood from the following detailed description in conjunction with the attached drawing in which:
FIG. 1 is a front elevational view of one embodiment of a mask according to the present invention, with part of the honeycomb panel and of the retaining cover broken away; and
FIG. 2 is a cross-sectional view of FIG. 1.
As shown in the drawing, a mask comprises a shield portion 1 and a honeycomb breathing body or panel 2 mounted across an opening or aperture in the shield 1. The shield 1 is attached about the wearers head by any conventional means so that the mask remain-s mounted before his face and usually with the breathing panel 2 positioned in the breathing zone of the wearer before his mouth and his nose. Preferably the shield 1 is made in any suitable or conventional design so that the mask covers only the nose and mouth portions of the wearers face. The shield 1 can be made of any suitable material used by the art for these purposes for example, aluminum, fiber glass, paper, polyethylene or polypropylene. The latter material is presently preferred for steam sterilizing of the complete mask.
In the embodiment illustrated in the drawing, the shield 1 is provided with a forward extending housing portion 56 surrounding the opening or aperture in the shield 1 formed by the rear retaining lip 7. The housing 6 forms the means for mounting the honeycomb panel 2 across the opening in shield 1, and lip 7 prevents the honeycomb panel 2 from sliding rearwardly out of housing 6. Retaining cover 8 is placed over the forward portion of housing 6 and has a forward retaining lip 9 to hold panel 2 inside the housing 6. The opening in cover 8 formed by lip 9 allows the expirated air passing through panel 2 to freely exit therefrom. Cover 8 customarily can be made of the same material as shield 1 (including housing 6 and lip 7) and preferably of a resilient material such as polyethylene or polypropylene for reasons given below.
In order to retain the cover 8 in place during use, two opposite sides of the cover 8 are extended further back than the other two opposite sides and the ends of these extended sides are curved outwardly to form latch release levers 10. The sides of housing 6 underlying these extended sides of cover 8 are provided with latch ribs 11 and the adjacent portions of cover 8 are provided with complementary or mating notch-forming portions 12 that engage the ribs 11. By virtue of making cover 8 of a resilient material, the levers can be lifted forwardly and outwardly to disengage notches '12 from ribs 11 for emoval of cover 8.
Honeycomb panel 2 is characterized by a large number of unobstructed air channels 15 that extend from the rear surface 1-7 of the panel 2 through .to the front surface 18. These unobstructed air passages are defined and separated from one another by thin, porous, moisture absorbent walls 20. By unobstructed, I mean that no structure exists within the air passages that would prevent air flow. The walls defining these air passages can be arranged in triangular, circular, or other geometric shape as'desired, the former being shown in FIG. -1.
In the particular embodiment shown in the drawings (note especially FIG. 2), panel 2 is made up of three panel sections which are bonded together by means of a thin layer 22 of a cement covering the periphery or sides of the three abutting panel sections. This cement layer is bonded to all three sections thereby forming .a unitary panel unit or cartridge 2 that is removable from'the mask and can be thrown away or reused in the mask after being sterilized. As shown, each of the three panel sections has its air channels 15 extending in an oblique or skew angular direction opposite that of the sections adjacent to it to obtain maximum impingement of the bacteria and virus laden droplets on the walls 20. The abutting surfaces of adjacent sections are mated so that the air channel ports in one section are substantially in register or alignment with the air channel ports in the adtaken through line 22 jacent section to maximize the freedom of air flow through the unobstructed air channel 15.
While the particular illustrated embodiment has three panel sections with different oblique or skew angular directions for the air passages 15 in each, the honeycomb panel can be made with more or less than three sections and only one can be used if desired. Where two or more sections are used, one section can be made to have its air passages 15 extending generally perpendicular to the major surfaces 17 and 1 8 instead of on an oblique or skew angle. Moreover/the panel 2 can be made up of one section with its air passages 15 having varying angular direction across the width of the panel 2 by appropriate manufacturing techniques. Also, it is not essential that the panel 2 be of a rectangular shape as shown in the drawing, but it can also be made circular, triangular, square or any appropriate geometrical shape as desired, with appropriate changes in other parts of the mask structure to accommodate these'other shapes for pariel'Z'. Further, if it is desired, the panel 2 can be made unre- -rnovable from the mask by bonding the panel 2 to the shield 1 and housing 6 by any suitable mean-s, eg, by injection molding of the shield portion 1 and housing 6 around the panel 2 or by plastic welding of a plastic rimmed panel 2 into a plastic housing 6.
Honeycomb bodies or panels having the preferred thin; porous, moisture absorbent ceramic walls that are usefulin accordance with the teachings of this invention can be prepared by several processes. For example, a pulverized ceramic material can be admixed with a suitable binder and then extruded to a ribbon form. The resulting ribbon can be further shaped, if desired, and assembled, either by itself or with other ribbons of this material to the desired honeycomb shape. The resulting assembly is then sintered to a unitary structure. Preferably, howthe ceramic honeycomb body is prepared by coating a: suitable carrier with a mixture of a pulverized ceramic and a binder, crimping the resulting coated carrier and then assembling it to the desired shape, alone or with another coated carrier that'need not be crimped. The assembled body is then heated to a temperature sufiicient to sinter it to a unitary structure as more fully detailed hereinafter. This latter procedure is, generally, the process set forth in the co-pending application of Robe'rtZ. Hollenbach, Serial No. 759,706, filed September 8, 1958, now Patent No. 3,112,184, to which reference can be made.
The purpose of the binder is to bond the unfired ceramic material to the carrier, to impart green strength to the coated carrier and to retain the formed unfired article in the desired shape after forming and prior to sintering. It is preferred to use an organic binder, especially those that are heat curable or' thermosetting, that can be removed by decomposition and/or volatilization when the article is fired and in particular an epoxy resin. Among the many other materials having the requisite, well-known characteristics of binders, that can be used in the process are those listed in the aforementioned Hollenbach patent.
The purpose of the carrier is to provide support for the unfired coating to allow it to be formedt'o'the desiredl shape prior to sintering the ceramic coating. Tea bag: paper is a preferred carrier and a list of other suitable materials is disclosed in the aforementioned Hollenbach patent. Tea bag paper, as well as other organic film materials, substantially decompose upon firing and thus result in a honeycomb body consisting almost entirely of porous, moisture absorbent, ceramic material.
Any known sinterable ceramic material is suitable for the present purpose. By sinterable ceramic material, I means an inorganic substance in the crystalline or amorphous state which can be compacted or agglomerated by heating to a temperature near, but below, the temperature at which it melts or has low enough viscosity to deform. Many suitable examples are disclosed in the aforementioned Hollenbach patent, but I prefer to use mixtures of petalite and a glass-ceramic with the latter generally amounting to about to 40 weight percent and the remainder petalite. Glass-ceramics are those crystalline materials made from glass generally by heat treatment, for example, those disclosed in US. Patent No. 2,920,971 to Stookey. These materials normally are used in a particle size of about minus 200 mesh (Tyler) or finer, depending on the wall thickness desired in the resulting honeycomb body.
Honeycomb structures are assembled from ceramic coated carriers in a variety of ways. These structures can be assembled from multiple layers of coated carriers corrugated with the same pattern with alternate layers laterally displaced a distance equal to half of the width of the individual corrugation pattern so that layers do not nest with each other. The honeycomb structure can also be formed from rolling alternate layers of crimped and uncrimped coated carriers until the desired shape is formed. A structure can also be formed by assembling to a stack alternate crimped and uncrimped coated carriers until the desired dimensions are attained. If it is desired to make a panel 2 in one section but having its air passages varying in angular direction, i.e. following a tortuous path, across the thickness of the panel, each of the layers in the foregoing assembly methods are shaped into an appropriate zig-zag, sinusoidal or the like pattern generally normal to the corrugation pattern. Other ways of assembling these honeycombs will be apparent to those skilled in the art.
The firing of the green honeycomb structure, however formed, is accomplished in the normal manner for ceramic firing by placing the article in a furnace and heating it at a rate slow enough to prevent distortion or breakage to a tempertaure high enough to cause the ceramic particles to sinter. While the firing schedule, including heating rates and sintering temperature, will vary depending upon the ceramic material utilized, the size and shape of the structure formed, and the atmosphere used, the details of such schedules are not critical and suit-able conditions are readily determinable by one skilled in the art of firing ceramic articles.
When the panel 2 is constructed of two or more individual sections, as shown in FIG. 2, any suitable ceramic cement that will bond or fuse to the ceramic material of the honeycomb sections can be used. For honeycomb sections made from my preferred mixtures of petalite and glass-ceramic, I have obtained good results by using a cement having a composition by weight, of 1-16% of lead oxide, 115% of a flux, 16% of silicon carbide, 1-6% of sulfur trioxide, and substantially all the remainder, but amounting to at least 70%, a lithium-aluminosilicate such as petalite. Typical flux materials include the fluorides and oxides of magnesium, calcium, strontium, barium, zinc, cadmium, lead, lithium, sodium and potassium. Generally a mixture of oxide and fluoride fluxes is used. The sulfur trioxide and part or all of the lead oxide and/or fluxes is provided by, for example, compounds such as lead sulfate, calcium sulfate, barium sulfate, lithium sulfate, etc. The cement is used by coating (e.g. brushing or painting it on) the sides of the panel sections, while they are held in appropriate abutting relation and then firing the abutting coated sections to a temperature of at least about 1050 C. and generally not higher than 1150 C. until the cement layer and the sections are completely sintered to a unitary structure. Thereafter, the composite panel structure is cooled to handling temperature. The foregoing ceramic cement and firing procedure is the subject of the copending application of Guy E. Stong, Serial No. 164,993, filed January 8, 1962., and assigned to the assignee of the present application.
The honeycomb breathing means of the invention will be described further in conjunction with the following 6 specific example in which the details are given by way of illustration and not by way of limitation.
In this example, a ceramic composition is made of 75 parts by weight of petalite and 25 parts by weight of a glass-ceramic having the following approximate composition by oxide analysis in weight percent: 70% SiO 18% A1 0 5% TiO 3% Li O, 3% MgO and 1% ZnO. The composition is ball-milled to a minus 200 mesh (Tyler) particle size. A solution of the following composition is added to 2160 grams of the ceramic material in the ball mill:
cc. Isopropanol 640 Ethyl acetate 860 Versamid 180 Hysol 611 480 Versamid 115 is the trade name of a thermoplastic polymer supplied by General Mills, Inc. It is prepared by condensation of polymerized unsaturated fatty acids, such as dilinoleic acid, with aliphatic amines such as ethylene diamine. Hysol 611 is the trade name of an epoxy resin solution, supplied by Houghton Laboratories, Inc., containing 57% by weight of epoxy resin having a viscosity of about 2.5-4.0 poise at 25 C., an epoxide equivalent (grams of resin containing 1 g. chemical equivalent of epoxy) of 595 i 50, and a melting range of 73- 85 C.
The ceramic material and the binder are further ballmilled for about three hours to produce a uniform suspension. A porous natural cellulose paper, commonly known as 3 /2 pound tea bag paper, cut to a width of 4 inches is then dipped into the suspension and dried by heating to C. for 2 minutes. The dried, coated paper is then heated to C. and crimped to produce a corrugated pattern, taken in cross-section, in the shape of an isosceles triangle with legs about 0.07 inch long and an open base about 0.1 inch wide. The crimped, unfired, coated paper is rolled up simultaneously with a sheet of tea bag paper of the same width, which has been coated in the same manner but not crimped, upon a 2 inch diameter reel until an annular cylinder with an outside diameter of about 20 inches in obtained. Preferably, the uncrimped coated paper is not dried prior to the roll-up operation, but this paper is dried by forcing air heated to about 120 C. through the channels of the annular cylinder as they are formed during the roll-up operation.
The unfired honeycomb body is then placed in a furnace chamber and heated in accordance with the following schedule:
Temperature range: Firing rate Room temp. to 700 C 350 C./hr. Hold at 700 C 1 hr. 700 C. to 1220 C Furnace rate. Hold at 1220 C 30 minutes. Cool to room temp Furnace rate. Refire at 1240 C 300 C./hr. Hold at 1240" C 7 hours.
Thereafter the body is cooled to handling temperature.
Three sections for panel 2 are sawed from the fired honeycomb body, as made above, in a size appropriate to nt housing 6, e.g. each about A" thick x 1%" high x 2" wide. These sections are cut from the fired honeycomb block in such a maner that the air passages extend through the A" dimension of each section at an angle of about 20 to 25 to a vertical plane, or horizontal plane, perpendicular to the planes of the two parallel major surfaces of the section. As shown in FIG. 2, the air passages 15 extend through the sections at an angle to a vertical plane perpendicular to the major surfaces 17, 18, and those in abutting relation. Then the three sections are arranged and clamped together so that the air passage 15 extends through the assembly with three different changes of angular direction as discussed above and shown in FIG. 2. T hena cement having the following composition, by weight, is used to join these sections as described above: 8.72% ZriO, 1.3% CaF 3.46% SiC, 1.93% S 6.81% PbO and the remainder glassy petalite. A batch of this cement composition, in granular form, is dispersed in a mixture containing 75 weight percent of butyl alcohol and 25 weight percent of toluene and is wet ballmilled to thoroughly mix the batch prior to coating it on the side of the assembled sections. The coated assembly of sections is then placed in a furnace and heated to 100 C. at a rate of 2 C./min. After 2 hours at 100 C., the temperature is raised at 5 C./min. to 1150 C. and is held at 1150 C. for one hour and 15 minutes to assure complete sintering and bonding. It is then furnace cooled at a rate of 5 C./min. to handling temperature.
Honeycomb panels made according to the foregoing example have been found to absorb as much as about 0.25 ml. of water per gram of ceramic. The wall thicknes'ses are generally about 0.004 to 0.008 inch, although suitable panels have been made with wall thicknesses somewhat less than 0.004 inch and even as great as about 0.015 inch or more. The collective or aggregate crosssectional areas of all the air passages in the panel unit comprise a total open area of generally about 70% to 80% of the total cross-sectional area of the panel. However, suitable honeycomb panel can be made with a total open area of 50%, or even as low as 30%, of the total cross-sectional area, as when thicker walls or smaller corrugation patterns are used.
In accordance with'the provisions of the patent statute,
I have explained the principle of my invention and have illustrated .and described what I now consider to be its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.
What is claimed:
1. Ina surgical mask comprising means attachable to the head for forming a shield and having a portion adapted to be disposed in alignment with the nose and mouth, said portion having at least one opening therein, and breathing means across said opening for allowing air expirated from the nose and mouth to pass therethrough, the improvement comprising a honeycomb body, as breathing means, across said opening and having a pair of opposed surfaces, one of said surfaces forming part of the rear surface of said mask for confronting relation to the nose and mouth and the other of said surfaces forming part of the front surface of said mask, a plurality of unobstructed air channels extending through said body and terminally opening in said surfaces, said channels being defined and separated from one another by thin ceramic walls having porous, moisture absorbent surfaces, said body comprising a plurality of consecutive sections between said surfaces with at least a portion of each of said channels extending through each section disposed at an oblique angle to said surfaces different from the oblique angular disposition of the channels in an adjacent section.
2. In a surgical mask according to claim 1, the improvement further comprising thin ceramic walls that are porous and moisture absorbent throughout.
3. In a surgical mask according to claim 2, the improvement further comprising three of said consecutive sectlons.
References Cited by the Examiner UNITED STATES PATENTS 1,781,254 11/30 Stelzner --523 X 1,821,996 9/31 Willson 128146 2,019,186 10/35 Kaiser 55278 2,079,297 5/37 Manning 55488 2,261,362 11/41 Gill 128146 2,408,659 10/46 Lamb 55485 2,838,132 6/58 Markham et al. 55278 X 2,952,333 9/60 Bush 55523 2,973,828 3/61 Engle 55278 2,983,271 5/61 Beck 128--146 RICHARD A. GAUDET, Primary Examiner.
. I ORDAN FRANKLIN, Examiner.