GB1589181A

GB1589181A - Face mask

Info

Publication number: GB1589181A
Application number: GB7200/77A
Authority: GB
Original assignee: Johnson and Johnson
Current assignee: Johnson and Johnson
Priority date: 1978-03-14
Filing date: 1978-03-14
Publication date: 1981-05-07

Description

(54) FACE MASK (71) We, JOHNSON & JOHNSON, a Corporation organised under the laws of the State of New Jersey, United States of America, of 501 George Street, New Bruns- wick, New Jersey., United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an improved surgical face mask. Surgical face masks have been employed in surgery for some time.

The purpose of these masks is to prevent the bacteria exhaled by the wearer from contaminating the patient undergoing surgery, and also to protect the wearer from bacteria originating from the patient. The original face masks that were used in surgery were multiple plies or layers of gauze fabric which were positioned over the nose and mouth of the surgeon. Multiple plies of linen fabric were also used. These materials are not particularly good bacterial filters and have low bacterial filtration efficiencies. These fabric face masks, although not efficient bacterial filters, were comfortable to the face of the wearer and also had low resistance to air flow through the mask. Air resistance is determined by measuring the pressure drop across the mask when the mask is placed in an air stream. Air could readily flow through the woven fabric masks because of the openness of the fabrics. That is, the interstices formed by the weave of the fabrics were large enough in number and individual size to provide a significant proportion of open or fibre free area in the mask. The low air resistance made these fabric masks quite easy to breathe through. The relatively open arrangement of the fibres in the fabric mask which allowed the ready passage of air throngh the mask also allowed bacteria to penetrate through the mask.

Because of the poor bacterial filtration efficiency of the fabric masks, efforts were directed to the production of a single use disposable mask which would have greater bacterial filtration efficiency than the fabric masks previously used. The single use masks have substantially increased bacterial filters tion efficiency as compared to the fabric masks, attaining efficiencies in the range of 90 per cent or greater, but have created another problem. The new problem of the single use mask is that along with the high bacterial filtration efficiency, air resistance has substantially increased.

Excessive air resistance can lead during exhalation to a build-up of pressure behind the mask, which may tend to lift the mask from the wearer's face and permit bacteria to escape, defeating the purpose of the mask.

Masks with high air resistance can also become uncomfortable to wear, especially if for prolonged periods.

The present invention provides a surgical face mask that has high bacterial filtration efficiency and yet has very low air resistance.

It would normally be expected that as the bacterial filtration efficiency is increased, the air resistance would increase or at least remain at a relatively constant level. The air resistance can be considered to be related to the number of openings in the effective filtration medium of the face mask or the total open area in the mask. As the total open area of the mask increases, the air resistance would decrease but so would the bacterial filtration efficiency. In the mask of the present invention we have obtained a low air resistance but have maintained the level of bacterial filtration efficiency that is at least equivalent to the previously used single use surgical masks. This seemingly contradictory result has been obtained by employing as the filtration medium a non-bonded carded web of textile staple fibres.

It is known for instance from United Kingdom patent Specification No. 892,262 to employ a carded web of fibres between two bonded nonwoven fabrics in a mask but the carded filling was necessarily mechanically bonded within itself by needling to interlock the fibres. United Kingdom Specification No.

966,855 discloses a mask filter material employing a carded fibre web but the web is necessarily bonded within itself by means of thermoplastic fibres activated by heat.

According to the nvention we provide a face mask having a body portion adapted to cover the nose and mouth and having means to secure said body portion over the nose and mouth, said body portion comprising: a face contacting web comprising a nonwoven porous flexible fabric; and a filtration medium composed of a porous non-bonded (as hereinafter defined) carded web comprising substantially uniformly distributed textile staple fibres, having an average fibre linear density not more than 4 Decitex.

By "non-bonded" we mean that the carded web as such is free from binder material and has not been subjected after carding to any treatment, mechanical or otherwise, to bond or lock the fibres together.

Surgical face masks employing a nonbonded carded web of textile staple fibres as filtration medium laminated between facing layers of highly porous nonwoven fabric can exhibit a microbiological filtration efficiency greater than 88 per cent, while also providing acceptable air porosity. They are most comforatable to wear.

The absence of binder from the carded web also contributes to the conformability of the finished face mask. The binder content in mask filtration media used hitherto has a tendency to stiffen the fabrics. In the face mask of the invention, the filtration medium is readily conformable to the contours of the face of the wearer.

The invention is further illustrated with reference to the following drawings in which: Figure 1 is an isometric view of a mask of the present invention folded in the form in which it would appear on the wearer's face; Figure 2 is a plan view of the fabric of the present mask showing folds in the mask; Figure 3 is a schematic cross-sectional view taken along the lines 3-3 in Figure 2 showing the folds in the fabric of Figure 3; Figure 4 is an enlarged cross-sectional view of the mask taken along the lines 14 of Figure 2.

As shown in Figure 1, the face mask, as it appears in use, consists of a main body 10, formed of a laminate to which is attached at the upper edge, a metal nose clip 11. The metal nose clip is made from a metal which can be easily bent to conform to the nose of the wearer, such as aluminium. The mask has attached to the main body, by sewing or heat sealing or other suitable means, a seam binding 13 on the upper and lower edges of the mask. There is also attached to the main body of the mask, on the side edges of the mask, an additional seam binding 12 which is of sufficient length to extend beyond the top and bottom edges of the mask and is employed as the tie string to affix the mask to the head of the wearer. There also appear, in Figure 1, bonding points 14 whose function will be later explained.

Figure 2 shows the configuration of the folds of the mask. The laminate which çon- stitutes the main body of the mask is folded on itself in an accordion shape from the top edge of the mask 15 to the bottom edge of the mask 16. The mask of Figure 2 is shown to be folded in three places at 17, 18 and 19, but the particular folding arrangement or number of folds is not part of the present invention. This particular configuration of the mask has previously been found to provide excellent conformability to the face of the user.

As shown in Figure 4 the outside of the mask is highly porous nonwoven facing fabric 21. The centre portion containing the carded web filtration medium 26 used in the present invention lies between the facing fabric 21 and another layer of facing fabric 23. In practice the complete carded web is composed of a number of individual superimposed layers of carded fibre, depicted by way of example as three layers 27, although any number of layers, for instance up to 10, may be used. Both layers of facing fabric may be constructed of similar or the same highly porous nonwoven fabric. The purpose of the facing fabric portions of the mask is to contain and retain the filtration medium.

The outside layers are a highly porous nonwoven fabric of relatively light weight.

Being highly porous, these materials also offer very little resistance to the flow of air through the mask. The weight of the facing layer of the mask may be between about 200 and 400 grains per square yard. It is advantageous to use extremely light weight facing webs so as not to increase the stiffness and thereby reduce the conformability of the face mask. The facing material can be a carded nonwoven fabric bonded with a thermoplastics binder. A suitable thermoplastics binder is an emulsion polymerized selfcuring acrylic binder.

A suitable facing layer for the inner side of the mask fabric laminate is for instance a 300 grain/square yard white acrylic resin bonded nonwoven fabric and for the outer side a 240 grain/square yard acrylic resin bonded nonwoven fabric.

It has been found to be advantageous to spot bond the three layers of the folded face mask together by heat sealing or other bonding procedures. As each of the individual layers of the laminate are relatively light weight, the layers are bonded together so they may be pleated and the seam binding applied with the minimum possibility of tearing or otherwise disintegrating the webs during the fabrication of the mask. Additionally, the bonding of the inner layer of the face mask to the fabric filtration medium at certain points prevents the inner layer of the mask from moving over the nose or mouth of the wearer as the wearer inhales. If the inner layer is not bonded, it is possible that it could move against the nose or mouth of the wearer when the wearer inhales. Although this does not reduce the efficiency of the mask, it has been found to cause some wearer discomfort. The bonding may be carried out by heat sealing the laminate together at spots 14 with sufficient force to effect the bond through all layers of the mask.

As shown at 14 in Figure 4, the bonded spot may extend through the total depth of the mask. If the filtration medium fabric filaments are thermoplstic, the application of heat and pressure at selected points causes the fila rents to become tacky or to melt; upon cooling, the tacky or melted filaments coalesce and harden to form a permanent bond between the three layers of the mask.

It is also possible to employ hot melt adhesives, or other adhesive materials to effect the spot bonding of the layers of the mask together. It is desirable to make the total bond areas as small as possible. It has been found that six to nine bonded areas located beneath the folds of a typical 4-inch x 7-inch pleated face mask, each area approximately 1/8-inch square, are sufficient to bond the three layers of the mask into a unitary laminate. The total area of the bond points is not critical although it should be recognized that the bond area must be large enough to accomplish the desired result but not so large that it could materially reduce the filtration efficiency or increase the air resistance of the mask. The bond points tend to be impervious areas which prevent passage of air through the mask. A total bonded area covering less than 1 per cent of the total surface area of the mask has been found to be adequate to provide the desired bonded properties. A total bonded area of this order will not measurably reduce the bacterial filtration efficiency or increase the air resistance of the mask.

Although the particular placement of the bond areas on the mask is not critical to the functioning of the mask, we prefer to place the bond area beneath the folds of the mask as shown schematically in Figure 3.

As previously stated, the filtration medium itself is a non-bonded carded web of textile staple fibres. These fibres may be any fibres amenable to carding. Principal examples of interest are cotton, rayon, acrylic, polypropylene, polyethylene terephthalate and polyamide fibres.

Particularly favourable results have been obtained with a filtration medium which is a 45 g/m2 carded web of 1-3 D'tex, 40 mm polypropylene fibre (Montedison); or a 45 g/m2 carded web of 2-4 D'tex, 32 mm staple Sarille viscose rayon (Courtaulds Limited); or a 45 g/m2 carded web of not more than 4 D'tex, e.g. 2 denier, 40 mm Acrilan acrylic fibre (Monsanto Limited).

(The words "Sarille" and "Acrilan" are registered Trade Marks). Laminates and blends of different or mixed carded web materials may be used with advantage. For instance, a laminate of two outer plies of the Sarille viscose rayon with a central ply of the Acrylan acrylic fibre to give a total web weight of 45 g/m2 may be employed. The individual plies may be of any suitable weight per unit area, e.g. from 8 to 30 g/m2, and need not be the same as each other. A basis weight of 45 g/m2 is at present preferred but other weights of web, for instance from 10 g/m2 to 90 g/m2, may be used depending on the fibre material.

The filtration medium is readily produced by carding on a normal carding machine, the fibre taken from a bale being first opened as necessary, for example by a conventional scutching machine to produce a lap for feeding to the card. Other conventional feeds to the card may be used, for instance employing a hopper or chute. A line of several carding machines may be used to lay up the full web of, say 45 g/m2, and the carded material is then laminated between the inner and outer facing fabrics on a simple laminating machine without adhesive bonding other than the abovementioned optional spot bonding. The laminate can then be slit to size and finally made up into masks in known manner.

The microbiological filtration efficiency may be evaluated by an in-vivo test method based on that described by W. Greene and D. Vesley, Method for evaluating effectiveness of surgical masks, J. Bacteriol. 83, 663-667 (1962). The efficiency is expressed as the percentage of bacteria prevented from passing, determined by comparing bacterial counts with and without a mask in place.

In tests in which masks according to the invention are worn for 30 minutes prior to testing, efficiencies of the order of 90 per cent are obtained, i.e., of the same order as prior art masks employing a glass fibre filtration medium.

The air resistance in inches of water pressure differential, may be determined by passing air at a predetermined flow rate (85 litres per minute) through 116 square centimetres of a face mask of the indicated construction. The pressure drop between the upstream and downstream sides of the mask is a measure of the air resistance of the mask.

The standard glass fibre laminate of the prior art should show a pressure drop in the range from 3-8 to 6-3 mm water. Face masks of the present invention do not show a pressure drop in excess of 1-5 mm water.

A typical prior art mask with a glass fibre filtration medium showed a pressure drop of 5-16 mm water. The air resistance of the mask of the present invention is less than that of the prior art mask by a factor of more than 3. The air resistance of the two nonwoven fabric facing layers is of the order of 0 6 mm water.

The filtration web together with the nonwoven fabric facings preferably has a thickness of from 0005 to 0 040 inches after lamination. This thickness is sufficient to prevent the passage of more than 90 per cent of the bacteria that could pass without the mask.

The preferred cardable fibre employed in the invention has a staple length of at least 10 mm, most preferably in the range from 10 mm to 75 mm, and an average linear density from 1 D'tex to 4 D'tex, but it will be appreciated by those skilled in the art that certain other fibres, having an average linear density not more than 4 D'tex, can be carded, and the resulting non-bonded carded webs can be adopted in the invention.

WHAT WE CLAIM IS: 1. A face mask having a body portion adapted to cover the nose and mouth and having means to secure said body portion over the nose and mouth, said body portion comprising: a face contacting web comprising a nonwoven porous flexible fabric; and a filtration medium composed of a porous nonbonded (as hereinbefore defined) carded web comprising substantially uniformly distributed textile staple fibres, having an average fibre linear density not more than 44 Decitex.

2. A mask according to Claim 1, wherein the textile staple fibres have an average linear density of from 1 Decitex to 4 Decitex and a fibre length of at least 10 mm.

3. A mask according to Claim 1 or 2, wherein the carded web is laminated between facing layers of porous nonwoven fabric.

4. A mask according to Claim 3, wherein said body portion is constituted by the carded web and facing layers and said securing means.

5. A mask according to any preceding Claim wherein the pressure drop caused by said filtration web is less than 1 5 mm water when air is passed at a flow rate of 85 litres per minute through 116 square centrimeters of the face mask.

6. A mask according to Claim 5, wherein said filtration web has a weight per unit area of from 10 grams per square metre to 90 grams per square metre.

7. A mask according to any preceding Claim wherein the carded web includes cotton, acrylic, polypropylene, polyethylene terephthalate or polyamide fibres.

8. A mask according to any of Claims 1 to 5, wherein the carded web includes rayon fibres.

9. A mask according to any preceding Claim wherein the carded web is composed of a number of individual superimposed layers of carded fibre.

10. A mask according to any preceding Claim, wherein the body portion is spotbonded and pleated.

11. A face mask substantially as described and shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the present invention do not show a pressure drop in excess of 1-5 mm water. A typical prior art mask with a glass fibre filtration medium showed a pressure drop of 5-16 mm water. The air resistance of the mask of the present invention is less than that of the prior art mask by a factor of more than 3. The air resistance of the two nonwoven fabric facing layers is of the order of 0 6 mm water. The filtration web together with the nonwoven fabric facings preferably has a thickness of from 0005 to 0 040 inches after lamination. This thickness is sufficient to prevent the passage of more than 90 per cent of the bacteria that could pass without the mask. The preferred cardable fibre employed in the invention has a staple length of at least 10 mm, most preferably in the range from 10 mm to 75 mm, and an average linear density from 1 D'tex to 4 D'tex, but it will be appreciated by those skilled in the art that certain other fibres, having an average linear density not more than 4 D'tex, can be carded, and the resulting non-bonded carded webs can be adopted in the invention. WHAT WE CLAIM IS:

1. A face mask having a body portion adapted to cover the nose and mouth and having means to secure said body portion over the nose and mouth, said body portion comprising: a face contacting web comprising a nonwoven porous flexible fabric; and a filtration medium composed of a porous nonbonded (as hereinbefore defined) carded web comprising substantially uniformly distributed textile staple fibres, having an average fibre linear density not more than 44 Decitex.