US 3605291 A
Description (OCR text may contain errors)
Sept. 20, 1971 F. c. MOORE em 3,605,291
DISPOSABLE FOOT COVERING.
Filed July 27. 1970 IN'IORSJ I6 FRANCIS C. MOORE LEON R. PERKINSON 0 (1137, awn/ug United States Patent Ofiice 3,605,291 DISPOSABLE FOOT COVERING Francis C. Moore and Leon R. Perkinson, Indianapolis,
Ind., assignors to Moore-Perk Corporation, Indianapolis, Ind.
Filed July 27, 1970, Ser. No. 58,404 Int. Cl. A43b 3/16 US. Cl. 367.1R 21 Claims ABSTRACT OF THE DISCLOSURE A disposable foot covering comprising a pair of superimposed layers of film or sheet material marginally sealed together, the upper of such layers being formed of a high elongation elastomer film and being provided with a small but greatly expandable opening for the insertion of a wearers foot. A fused marginal bead about the opening prevents tearing as the material about the opening is stretched. Breathability of the cover, where necessary, is insured by forming the covers lower layer from a porous moisture-resistant film or sheet.
BACKGROUND Despite considerable effort in the past to develop disposable shoe covers suitable for use by surgeons, nurses, and others, prior products have all been found to have major shortcomings. For example, paper shoe covers are commonly used and have the advantages of low cost, disposability (by incineration), and breathability. However, such covers do not normally fit snugly over a wearers shoes without some additional means (such as tie bands or elastic bands) which are designed to take up slack and which require additional manipulation by a user when the covers are donned. Furthermore, paper tears easily and, because of its porosity, offers only limited protection against penetration by fluids.
In our prior Pat. 3,442,034 we have disclosed an improved shoe cover formed largely of plastic foam. While the sole of such cover incorporates a non-porous moisture barrier, the top layer was left porous in order to achieve a breathable product which could be worn for extended periods in surgery without discomfort to the wearer. Because of such porosity, however, the foam top layer provides only limited protection when exposed to liquids. Furthermore, such liquids, many of which may be contaminating and dangerous, might readily contact a wearers foot because of the gaps created by the top opening of the cover which must be relatively large to permit insertion of a wearers foot without causing tearing of the foam upper layer.
SUMMARY It is an object of one form of the present invention to provide a shoe cover which is breathable and is therefore comfortable to wear indoors for extended periods, and yet one which has a top barrier layer which fully covers the top of a wearers foot and which will block the penetration of liquids impinging on that layer. It is a specific object to provide a shoe or foot covering which is easily fitted upon a wears foot and which fits snugly over the foot and about the wearers ankle without the use of ties, elastic bands, or the like. The result is an inexpensive disposable shoe or foot cover which aifords ample protection, is comfortable to wear, and, in general, overcomes the defects and disadvantages of prior constructions.
In accordance with this invention, a disposable foot covering is provided including a top layer of a nonporous thermoplastic elastomer having a modulus of elongation of at least about 300 percent, such layer being 3,605,291 Patented Sept. 20, 1971 marginally sealed to a bottom layer of the same or different material and having an opening in the top layer that is relatively small in relation to the surface area of such layer by a ratio of about 1:10. A tear resistant bead extends about the opening to prevent tearing of the top layer despite the extensive stretching of the material about the opening as a foot is inserted into the cover. By forming the lower layer of a tough compatible sheet material which is porous and is therefore permeable to air (but resistant to the passage of liquids), a covering is provided which is particularly effective for use in surgery and elesewhere. In a preferred form of the invention, the lower layer is formed of a tough and relatively non-stretchable material; however, despite such non-stretchability of the lower layer, the cover fits snugly and is comfortable to wear, without the joined edge portions of the upper and lower layers extending beneath a wearers foot and causing objectionable ridges (which might also interfere with good electrical grounding should a conductive strip be provided) because of the elasticity of the upper layer and the size of the cover relative to the area defined by the outline of a wears foot.
DRAWINGS FIG. 1 is a perspective view of a covering embodying the invention, such covering being illustrated upon a wearers foot;
FIG. 2 is a top plan view of the covering;
FIG. 3 is a somewhat schematic sectional view taken along line 33 of FIG. 2;
FIG. 4 is an enlarged view illustrating the bead and opening forming the operation.
DESCRIPTION In the illustration given, the numeral 10 generally designates a foot covering having a pair of flat superimposed upper and lower sheets of layers 11 and 12, respectively. The layers are of the same size and, as illustrated most clearly in FIG. 2, are generally oval or almond-shaped in configuration. Each of the layers has a surface area substantially larger than the area defined by the outline of wearers foot; specifically, the area of each layer should be approximately 30 to percent greater and the margins of the layers should extend Well beyond the margins or limits of the foot upon which the cover is to be fitted.
While the covering is referred to herein as a foot covering, it is to be understood that the product would ordinarily be worn over a wearers shoes. Under those circumstances, the terms foot and shoe are used interchangably herein. Thus, in speaking of the differential in area between the outline of the covering and the outline of a wearers foot, the term foot should be understood to mean shoe in those instances where the covering is to be worn over a shoe. Such usage is illustrated in the drawings with the foot outline 13 in FIG. 3 actually being the outline of the sole and heel of a wearers shoe, such shoe being designated by the numeral 14 in FIG. 1.
The top layer or sheet 11 is formed of a non-porous high-elongation thermoplastic elastomer. Such elastomer should be capable of at least 300 percent, and preferably 500 percent, elongation. While various plastic materials might be used, particularly effective results have been obtained with films formed of block copolymers of styrene and butadiene. Elastomeric films of polyurethane may also be used.
A relatively small ankle opening 15 is provided in top layer 11. The opening is defined by a continuously curved edge in either circular or oval configuration and is substantially smaller (when the layer is in an untensioned state) than the dimensions of a wearers ankle. Depending on the foot size of the intended wearer, the
area of opening 15 should fall within the range of approximately 1 to 4 square inches and, in any event, should be no greater than one tenth the area defined by the outline of the cover as a whole. For a covering adapted to be fitted over the foot of an adult, particularly effective results have been obtained where the area of opening 15 falls within the range of 1.5 to 3.0 square inches.
While lower layer 12 may be formed of the same material, the advantages of the invention are more completely realized if such layer is formed from a material which, in addition to being strong, tough and pliable, is also porous. Such porosity permits the flow of air through the covers to prevent the buildup of heat and moisture which would otherwise render the covers uncomfortable to wear for the extended periods that are frequently encountered in surgery, etc. At the same time, such material should byeither treatment or composition be resistant to the passage of liquids therethrough. While tough paper materials which have been treated to be liquid resistant may be used, porous plastic materials such as spun-bonded polyethylene have been found especially effective.
The superimposed layers have their marginal portions secured together by heat sealing or lay any other suitable means. Heat sealing is particularly advantageous because the integrity of non-porous character of the upper layer 11 is thereby maintained; however, somewhat similar results might be achieved by utilizing a suitable cement or adhesive to bond the edges of the layers together or by sewing or otherwise securing them to each other.
In the illustration given, a flexible strip 16 is secured by heat-sealing, adhesive, or stitching to the undersurface of bottom layer 12 along the longitudinal midline thereof. Preferably the conductive strip is composed of a fabric-reinforced foil which has been folded longitudinally as illustrated in FIG. 3, such strip being fabricated as disclosed in our co-pending application, Ser. No. 58,403, filed July 27, 1970. The strip has a free end portion 16a which projects beyond the rear end of the cover and which is intended to be brought into contact with a wearers leg or foot. Thus, the end portion of the conductive strip may be tucked in the opening of a wearers sock or shoe to provide an electrically conductive path for preventing static buildup in locations where a spark or static discharge might ignite explosive gases or highly combustible fluids.
Because of the dimensions of the cover and the elasticity of upper layer 11, the sealed edge portion 17 of the cover tends to be pulled upwardly out of contact with a floor surface when the foot cover is worn (FIG. 1). The double-thickness edge portion 17 is therefore displaced away from beneath the foot where such increased thickness might otherwise interfere with proper contact between conductive strip 16 and a floor surface. Stated differently, the size of the cover and the tension of upper layer 11 when the cover is worn insure that conductive strip 16 will be exposed for direct and forceful contact with a floor surface and that the marginal zone 17 of double thickness will not interfere with that contact.
Despite the substantial tension imposed on upper layer 11 when the cover is worn, the edge of opening 15 fits snugly about the wearers ankle 19. Thus, as illustrated in FIG. 1, a wearers shoe is completely covered. Of particular importance in achieving a snug fit about the ankle is the especially small size of opening 15 when the upper layer is in an untension state. Even though the upper layer must undergo substantial stretching and tensioning when the cover is worn, such tensioning does not increase the size of the opening to the point where a snug fit and adequate protection are lost.
FIG. 3 illustrates that a bead or marginal enlargement 15a is provided about opening 15. At the time that the opening is cut into the upper thermoplastic layer 11 uring fabrication of the cover, the cutting blade 18 is heated to produce retraction and fusion along the edge. Nicks or slight irregularities of even microscopic size, which might otherwise be the starting points of tearing when the opening is later stretched over a wearers foot, are thereby eliminated. In addition, the enlarge heat-retraction bead 15a provides reinforcement for the edge because of its increased thickness. FIG. 4 illustrates in somewhat schematic fashion the manner in which the material retracts to form the reinforcing head when the opening 15 is cut by hot knife 18.
The temperature of the knife will of course vary depending upon the material being cut and the duration of the cutting step. In general, it has been found that if the blade is heated to approximately the melt temperature of the thermoplastic material and is in contact with the film no longer than approximately one second then an effective bead 15a will be formed. Higher temperatures may be used if the interval of contact is shorter and somewhat lower temperatures may be used for longer contact periods.
From the foregoing, it is believed apparent that the article of the present invention constitutes a highly effective foot covering which is especially suitable for use by surgeons, nurses, etc. The wearer is protected against contamination by liquids often present during surgery because of hte non-porous liquid-impermeable material of upper layer 11 and because of the snug fit of opening 15 about the wearers ankle. Nevertheless, the cover is comfortable to wear, even for extended periods, because of the air permeability of the sole or bottom portion 12. Comfort is also increased because of the tensioned fit of the cover as a whole resulting from the stretched and tensioned nature of the top layer when the cover is worn. In that connection, it is to be observed that the tensioning of the upper layer or sheet 11 will result in a snug comfortable fit of any given cover over a range of shoe sizes.
In general, a foot covering embodying the present invention, constructed as described above, may be formed where the upper layer 11 is formed of a thermoplastic elastomer exhibiting the following properties.
Property: Value Tensile strength, p.s.i 625-3000 300% modulus, p.s.i 200-970 Elongation, percent 300-1350 Hardness, shore A 35-77 Tear strength -460 Specific gravity 0.93-1.02
The invention is further illustrated by the following specific examples:
EXAMPLE I A shoe cover embodying the invention may be made utilizing for the upper layer of film of 4 mil (0.004 inch) in thickness of a butadiene-styrene copolymer marketed under the trademark Kraton 2109 by Shell Chemical Company, New York, N.Y. To fit size 9-11 shoe, the outline of the cover defined an area of approximately 83 square inches and the area of the ankle opening in the untensioned upper layer was approximately 3 square inches. The lower layer was formed of spun-bonded polyethylene marketed under the designation Tyvek by E. I. du Pont de Nemours, Wilmington, Del., and the two layers were heat sealed together about the periphery of the cover. A conductive strip of fabric-reinforced aluminum foil was adhesively secured to the underside of the cover along the longitudinal midline thereof.
EXAMPLE II Another cover embodying the invention may be formed utilizing the porous spun-bonded polyethylene described in Example I for the bottom layer and using for the upper layer an elastomeric polyurethane film marketed under the designation Tuftane by B. F. Goodrich Chemical Company, Cleveland, Ohio.
EXAMPLE 1 11 As a further illustration of the invention, a shoe cover may be formed utilizing for the upper layer a film of 3 mil (0.003 inch) in thickness of the butadienestyrene copolymer identified in Example I and using for the bottom layer a scrim-reinforced paper marketed under the designation Kaycel by Kimberly-Clark Corporation, Neenah, Wis. The layers of the cover may be heat sealed together and the cover may be otherwise formed as described in Example I. Because of the porosity of the soft reinforced paper bottom layer, such cover is breatheable and comfortable to wear despite the non-porous character of the top layer.
In the preceding description and examples, the shoe covers embodying the invention have been characterized as having upper layers of a non-porous and highly stretchable thermoplastic elastomer to protect the surgeon, nurse, or other wearer against contaminating contact with spilled liquids while, at the same time, because of the porosity of the lower layers, such covers provide for breathability and wear comfort. It is to be understood, however, that where such protection against possible contamination or injury from spilling liquids is not required, the upper layers might be provided with small vents or openings to further increase the circulation of air through the covers.
While in the foregoing We have disclosed embodiments of the invention in considerable detail for purposes of illustration, it will be understood by those skiled in the art that many of these details may be varied without departing from the spirit and scope of the invention.
1. A protective foot covering comprising a pair of flat superimposed upper and lower sheets having curved peripheral edges defining an area approximately 30 to 100 percent larger than that defined by the outline of a wearers foot; said upper sheet being formed of an essentially non-porous and high-elongation thermoplastic elastomer having at least 300 percent elongation and said lower sheet being formed of a tough porous moisture-resistant material; the peripheral edge portions of said sheets being sealed together to define a space between said sheets for receiving a wearers foot; said upper sheet having an opening therein for insertion of a wearers foot into said space; said opening when said upper layer is untensioned having an area less than one tenth the area defined by the outline of said superimposed sheets.
2. The foot covering of claim 1 in which said sheets are of the same size and are generally oval in shape.
3. The foot covering of claim 1 in which said lower sheet is relatively non-stretchable.
4. The foot covering of claim 1 in which said upper and lower sheets have their peripheral edge portions heat sealed together.
5. The foot covering of claim 1 in which said opening is defined by an edge of generally continuous concave curvature, that opening being defined by an edge having an enlarged heat-fused bead.
6. The foot covering of claim 1 in which said upper sheet is formed from a butadiene-styrene copolymer.
7. The foot covering of claim 1 in which said upper sheet is formed from a urethane film.
8. The foot covering of claim 1 in which said lower sheet is formed of spun-bonded polyethylene fibers.
9. A protective shoe cover for use in surgery comprising a pair of flat superimposed upper and lower sheets having an outline defining an area approximately 30 to 100 percent larger than the outline of a wearers shoe; said upper sheet being formed of an essentially non-porous and high-elongation thermoplastic elastomer having at least 300 percent elongation; said lower sheet being formed of a tough, porous, moisture-resistant, and relatively non-stretchable material capable of being heat sealed to said upper sheet; said upper and lower sheets having their peripheral edge portions heat sealed together along their entire extent; said upper sheet having an opening therein defined by an edge of concave curvature and having an area when said upper sheet is untensioned of less than one tenth the area defined by the outline of said superimposed sheets; and a conductive strip secured to the underside of said lower sheet and having an end portion adapted to be placed in conductive contact with a wearer.
10. The shoe cover of claim 9 in which said sheets are of substantially the same size and are generally oval in shape.
11. The shoe cover of claim 9 in which said upper and lower sheets have their peripheral edge portions heat sealed together.
12. The shoe cover of claim 9 in which said opening is defined by an edge having an enlarged continuous heatfused bead.
13. The shoe cover of claim 9 in which said upper sheet is formed from a butadiene-styrene copolymer.
14. The shoe cover of claim 9 in which said upper sheet is formed from a urethane film.
15. The shoe cover of claim 9 in which said lower sheet is formed of spun-bonded polyethylene fibers.
16. A protective foot cover comprising a pair of flat superimposed upper and lower layers having curved peripheral edges defining an area at least 30 percent larger than that defined by the outline of a wearers foot; said upper layer being formed of an essentially non-porous and high-elongation thermoplastic elastomer having at least 300 percent elongation and said lower layer being formed of a thermoplastic material capable of being heatsealed to said upper layer; the peripheral edge portions of said upper and lower layers being heat-sealed together along their entire extent; said upper layer having an opening of rounded outline therein for insertion of a wearers foot between said upper and lower layers; said opening when said upper layer is untensioned having an area no greater than one tenth the area defined by the outline of said superimposed sheets.
17. The foot cover of claim 16 in which said opening is defined by a thickened continuous bead formed integrally with said upper layer.
18. The foot cover of claim 16 in which said opening is generally oval in outline.
19. The foot cover of claim 16 in which said lower layer is formed of a non-porous high-elongation thermoplastic elastomer having at least 300 percent elongation and capable of being heat-sealed to said upper layer.
20. The foot cover of claim 16 in which said lower layer is formed of a tough porous moisture-resistant thermoplastic material.
21. The foot cover of claim 20 in which said lower layer is formed of spun-bonded polyethylene fibers.
References Cited UNITED STATES PATENTS 3,308,562 3/1967 Zimmon 367.1R 3,359,658 12/1967 Price 36-7.1R
PATRICK D. LAWSON, Primary Examiner US. Cl. X.R. 3 17-2 (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,605,291 Dated September 20, 1971 Inventor-(s) Francis C. Moore and Leon R. Perkinson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Claim 1, line 6, the word "thermoplastic" should be deleted.
Claim 4, line 1, after "said" insert upper sheet is formed of a thermoplastic elastomer, said Claim 5, line 1, after "said" insert upper sheet is formed of a thermoplastic elastomer, said line 2, delete "is" and substitute being Signed and sealed this 21 st day of March 1972.
EDWARD M.FLETCHER, JR. Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents