BACKGROUND OF THE INVENTION
Surgeons and other healthcare providers often wear an over garment during operating procedures in order to enhance the sterile condition in the operating room and to protect the wearer. The over garment is typically a gown that has a main body portion to which sleeves and a tie cord are attached. The tie cord encircles the wearer at the waist to keep the gown in place. In order to prevent the spread of infection to and from the patient, the surgical gown prevents bodily fluids and other liquids present during surgical procedures from flowing through the gown.
Surgical gowns were originally made of cotton or linen, were reusable and were sterilized prior to each use in the operating room. A disadvantage of the materials used in these types of gowns is that they tend to form lint, which is capable of becoming airborne or clinging to the clothes of the wearer, thereby providing another potential source of contamination. Additionally, costly laundering and sterilization procedures were required before reuse.
Disposable surgical gowns have largely replaced the reusable linen surgical gown and many are now made in part or entirely from fluid repellent or impervious fabrics to prevent liquid penetration or "strike through". Various materials and designs have been used in the manufacture of surgical gowns to prevent contamination in different operating room conditions. Surgical gowns are now available in a variety of different levels of imperviousness and comfort.
Gowns made from completely impervious material provide a high degree of protection, though a surgical gown constructed of this type of material is typically heavy, expensive, and uncomfortably hot to the wearer. In some surgical gowns, certain portions such as the shoulders and back panels may be of a lighter weight material in order to provide for better breathability and help reduce the overall weight of the gown. Generally, however, the higher the breathability of the material, the lower the repellency of the material.
Different types of surgical procedures expose the healthcare provider to different levels of blood and/or fluid exposure, so it is not feasible or economical to use the same type of surgical gown for every surgical procedure conducted by the healthcare provider. New guidelines have recently been created for the rating of the imperviousness of surgical gowns, gloves and the like, to provide guidance to healthcare providers. The Association for the Advancement of Medical Instrumentation (AAMI) has proposed a uniform classification system for gowns and drapes based on their liquid barrier performance. These procedures were adopted by the American National Standards Institute (ANSI) and were recently published as ANSIA/AAMI PB70: 2003 entitled Liquid Barrier Performance and Classification of Protective Apparel and Drapes Intended for Use in Health Care Facilities, which was formally recognized by the U.S. Food and Drug Administration in October, 2004. This standard established four levels of barrier protection for surgical gowns and drapes. The requirements for the design and construction of surgical gowns are based on the anticipated location and degree of liquid contact, given the expected conditions of use of the gowns. The highest level of imperviousness is AAMI level 4, used in "critical zones" where exposure to blood or other bodily fluids is most likely and voluminous. The AAMI standards define "critical zones" as the front of the gown, including the tie cord attachment area, and the sleeves and sleeve seam area up to about 2 inches (5 cm) above the elbow.
The main body portion and the sleeves of a surgical gown are usually produced separately and joined together in some manner at seams in the shoulder area. The sleeves are commonly made from a flat piece of fabric that is folded upon itself and joined together at a seam that runs the length of the sleeve from the shoulder to the wrist, prior to attachment to the main body portion. A single tie cord or a pair of tie cords is also usually attached to the main body portion of the gown. A single tie cord is used to encircle the wearer at the waist and tie to itself in order to keep the gown in position during use. Two tie cords are also used to encircle the wearer at the waist and tie to each other. The seams and the tie cord attachment point are areas where many gowns have been known to fail the AAMI test procedure.
A number of surgical gowns are currently marketed which are assembled through the use of ultrasonic seam sealing. Ultrasonic seam sealing bonds the layers of material together sufficiently for strength but the bonds do not pass ASTM-1671-b; the bacteriophage penetration resistance test, a test that is now required to meet the new AAMI level 4 protection standards. This is particularly true for the sleeve seams and tie cord attachment point.
It is clear that there exists a need for a gown having tie cord attachments bonded in a manner that is more impervious than current methods and that meets AAMI level 4.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an exemplary gown 100 to be worn during a medical procedure as seen from the front.
FIG. 2 illustrates an exemplary gown 100 to be worn during a medical procedure as seen from the back.
FIG. 3 represents a exemplary tie cord for a surgical gown.
SUMMARY OF THE INVENTION
In response to the foregoing difficulties encountered by those of skill in the art, we have successfully used thermal impulse heat welding, aka "bar sealing", to bond thermally sensitive laminate barrier materials made of thermoplastic polymers such that they will pass AAMI level 4 testing (ASTM 1670 and 1671-b). In bar sealing, overlapping layers of thermally sensitive barrier materials composed of thermoplastic polymers are melted and fused together to create a substantially solid bond at the surface of the materials. No substantially un-melted areas remain within the fused seam area on the surface.
DETAILED DESCRIPTION OF THE INVENTION
The present invention involves the use of bar sealing technology to meet AAMI level 4 barrier properties in surgical gowns and similar articles formed from thermally sensitive laminate barrier materials that are composed of thermoplastic polymers. In bar sealing, overlapping layers of these thermally sensitive laminate barrier materials are melted and fused together to create a substantially solid bond at the surface of the materials while avoiding damage to regions below the surface of the laminate. No substantially un-melted areas remain within the fused bond area on the surface where heat was applied.
FIG. 1 illustrates a typical gown 100 to be worn during a medical procedure as seen from the front. The gown 100 includes a collar 110, the cuffs 120, the primary tie cord 130 and a primary tie cord attachment area 140. The shoulder seams 150 linking the sleeves 160 to the main body 170 are also visible. FIG. 2 illustrates a typical gown 100 to be worn during a medical procedure as seen from the back. In FIG. 2 the shoulder seams 150 linking the sleeves 160 the main body 170 are visible as are the sleeve seams 180 running from the shoulder seams 150 to the cuffs 120 which are used to produce the sleeves 160. FIG. 2 also shows a secondary tie cord 180 and secondary tie attachment area 190 (not in the AAMI critical zone). FIG. 3 represents the tie cord 130 and shows the end to be bonded to the gown 100 as having, in this case, a "Y" shaped end 200 for attachment to the gown 100. Note that a simple flat shaped end may also be used for attachment to the gown, a "Y" shape is not required.
Many surgical gowns are made from thermally sensitive laminate barrier materials composed of thermoplastic polymers. While such barrier materials may be in the form of thermoplastic polymer spunbond fabrics, thermoplastic polymer meltblown fabrics, and various combinations of such spunbond and meltblown fabrics, a particularly desirable form of these barrier materials incorporate one or more thin, breathable films that provide desirable levels of resistance to penetration by liquids and pathogens while also providing satisfactory levels of breathability and/or moisture vapor transmission.
These thin and breathable films are commonly made from thermoplastic polyolefins like polyethylene and polypropylene and copolymers thereof because of their relatively low cost and ability to be processed. Polyethylene is generally used in the film production and the film is commonly "filled" with calcium carbonate, various kinds of clay, silica, alumina, barium carbonate, soldium carbonate, magnesium carbonate, talc, barium sulfate, magnesium sulfate, aluminum sulfate, titanium dioxide, zeolites, cellulose-type powders, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivatives, chitin and chitin derivatives, to increase breathability. Fillers produce microscopic pores in the film upon stretching to increase porosity. Unfortunately, these thin and breathable films are considered to be thermally sensitive because they have a tendency to become compromised by heat and/or or pressure. When these films are incorporated into laminate barrier materials by sandwiching them together with various combinations of other materials such as, for example, spunbond fabrics, meltblown fabrics and combinations thereof, the resulting laminate barrier materials are generally considered to be thermally sensitive as well. This characterization is particularly important for post-laminate formation processing steps. That is, manufacturing operations that convert the thermally sensitive barrier fabrics after such films are formed into the laminate barrier fabrics. For example, when thermally sensitive barrier materials are converted into gowns or other articles utilizing thermal point bonding and/or ultrasonic bonding techniques or when components such as, for example, tie cords or other features are attached to the articles, the breathable films of barrier laminate are frequently compromised such that they so longer provide desired levels of barrier to liquid penetration and pathogens.
The thin and breathable film laminates described above may be thermally bonded using bar sealing, thus producing a thermal bond for a film layer-containing thermoplastic fabric where the bond joins a thermoplastic material to the fabric to form a fused bonded area, without bonding to the film layer. This bond has no un-melted areas remaining within the fused bond area on the surface.
Spunbond" refers to fabric made from small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and have average diameters (from a sample of at least 10) larger than 7 microns, more particularly, between about 10 and 20 microns.
Meltblown" fabric is formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or is filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. The meltblown fibers are then carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.
Laminates of spunbond and meltblown fabrics, e.g., spunbond/meltblown/spunbond (SMS) laminates and others are disclosed in U.S. Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 5,169,706 to Collier, et al, U.S. Pat. No. 5,145,727 to Potts et al., U.S. Pat. No. 5,178,931 to Perkins et al. and U.S. Pat. No. 5,188,885 to Timmons et al. Such a laminate may be made by sequentially depositing onto a moving forming belt first a spunbond fabric layer, then a meltblown fabric layer and last another spunbond layer and then bonding the laminate in a manner described below. Alternatively, the fabric layers may be made individually, collected in rolls, and combined in a separate bonding step. Such fabrics usually have a basis weight of from about 0.1 to 12 osy (6 to 400 gsm), or more particularly from about 0.75 to about 3 osy. Multilayer laminates may also have various numbers of meltblown layers or multiple spunbond layers in many different configurations and may include other materials like films (F) or coform materials, e.g. SMMS, SM, SFS, etc.
An exemplary method of forming a film includes a co-extrusion film apparatus that forms the film with multiple layers consisting of skin and core layers. Typically the apparatus will include two or more polymer extruders. In one method of fabrication, the film is extruded into a pair of nip or chill rollers. In another method the film is extruded onto a chilled roll which can have a smooth or matte finish. Typically, the film as initially formed will have an overall thickness of approximately 25 to 60 micrometers with, in the case of multilayer films, the total skin or bonding layer having an initial thickness that may be about 3% to 30% of the total thickness. Other film making processes known to those skilled in the art may be used as well, including cast embossing, chill and flat casting and blown film processes.
From the coextrusion film apparatus the film is directed to a film stretching unit such as a machine direction orienter (MDO), which is a commercially available device from vendors such as the Marshall and Williams Company of Providence, R.I. Such an apparatus has a plurality of paired stretch rolls that move at predetermined speeds that may rotate faster, slower or at the same speed relative to each other. Typically the stretch rolls move at a progressively faster speeds to progressively stretch and thin the film in the machine direction of the film, which is the direction of travel of the film through the process. The stretch rolls are generally heated for processing advantages.
The temperatures to which the film is heated while stretching will depend on the composition of the film as well as the breathability and other desired end properties of the laminate. In most cases the film will be heated to a temperature no higher than 5 degrees ° C. below the melting point of the core or "B" layer in the film. The purpose for heating the film is to allow it to be stretched quickly without causing film defects. The amount of stretching will depend on the polymeric composition, but, in general, the film may be stretched to about 300% or more of its original length (that is, a one cm length, for example, will be stretched to 3 cm) but less than the amount that tends to result in film defects. For most applications, for example, the stretch will be to at least 200% of the original film length and, frequently, in the range of about 250% to 500%.
The multilayer stretch-thinned film may be attached to one or more support layers to form a multilayer film/nonwoven laminate as described above. For example, a conventional fibrous nonwoven web forming apparatus, such as a pair of spunbond machines, may be used to form the support layer. The long, essentially continuous fibers are deposited onto a forming wire as an unbonded web and the unbonded web is then sent through a pair of bonding rolls to bond the fibers together and increase the tear strength of the resultant web support layer. One or both of the rolls are often heated to aid in bonding. Typically, one of the rolls is also patterned so as to impart a discrete bond pattern with a prescribed bond surface area to the web. The other roll is usually a smooth anvil roll but this roll also may be patterned if so desired.
Once the multilayer film has been sufficiently thinned and oriented and the support layer has been formed, the two layers are brought together and laminated to one another using a pair laminating rolls or other means. As with the bonding rolls, the laminating rolls may be heated. Also, at least one of the rolls may be patterned to create a discrete bond pattern with a prescribed bond surface area for the resultant laminate. Generally, the maximum bond point surface area for a given area of surface on one side of the laminate will not exceed about 50 percent of the total surface area.
The process described above may be used to create a three layer laminate. The only modification to the previously described process is to feed a supply of a second fibrous nonwoven web support layer into the laminating roll on a side of the multilayer film opposite that of the other fibrous nonwoven web support layer. Alternatively, as with the other layers, the support layer may be formed directly in-line. In either event, the second support layer is fed into the laminating rolls and is laminated to the multilayer film in the same fashion as the other support layer.
Exemplary processes and materials for forming thin films and laminates may be found in commonly assigned U.S. Pat. Nos. 5,188,885, 5,213,881, 5,271,883, 5,464,688, 5,695,868, 6,037,281, 6,309,736, 6,653,523 and 6,764,566, incorporated herein in their entirety.
Multilayer film laminates may have various numbers of meltblown layers or multiple spunbond layers in many different configurations and may include other materials like coform materials. These include, for example, spunbond/film/spunbond (SFS) laminates, spunbond/film/meltblown (SFM) laminates, spunbond/meltblown/film (SMF) laminates and laminates having a greater number of layers like spunbond/film/spunbond/meltblown/spunbond (SFSMS) and spunbond/meltblown/film/meltblown/spunbond SMFMS, coform/meltblown/film (CMF) etc.
As used herein, the term "thermally sensitive materials" means fabrics and webs which have a tendency to become compromised by heat and/or or pressure. These materials have a relatively narrow range of temperature (the bonding window) at which they can be bonded and can be damaged to a great degree when conditions fall outside of these ranges.
A "substantially solid bond" is one in which there are no substantially un-melted areas within the bond footprint. This means that the thermoplastic fibers on the surface have been melted to a degree sufficient to produce a film. The surface film thus produced is the material which results in a bonding together of the two layers that are desired to be bonded.
Previous tie cord sealing methods tended to damage the layers of the gown and to impair the liquid resistance of the bond to a point that the gown failed the MMI level 4 test at the bond, or to be prohibitively expensive. These methods included ultrasonic or thermal point bonding and adhesive bonding. The inventors believe, though do not wish to bound by that belief, that the former methods tend to bond materials through their entire thickness, thus disrupting the structure to a relatively high degree. Since many surgical gowns include a film layer in order to increase the penetration resistance of the gown and because film layers tend to be relatively weak, the robust bonding used previously tended to damage this layer and increase liquid penetration. In the case of adhesive bonding the manufacturing challenges and expense are relatively great since adhesives tend to be expensive and time consuming to apply and can have detrimental effects on manufacturing facility cleanliness. The inventors believe, though do not wish to bound by that belief, that bar sealing can bond a thermoplastic material to a second thermoplastic material that has a film layer within it, without damaging the barrier properties of the film layer. Bar sealing is also substantially less expensive and less challenging in a manufacturing environment than is adhesive bonding.
Bar sealing uses heat, pressure and dwell time to thermally bond thermoplastic materials together. According to the present invention, these variables are adjusted so that the thermal bonding takes place substantially at or adjacent the surface of the thermally sensitive barrier laminate materials while avoiding degradation of the thermally sensitive film component in an interior region of the barrier laminate.
Bar sealing devices generally have a press with a set of jaws that open (vertically), into which the materials to be bonded are placed. The jaws are heated by, for example, electric resistance heating and the temperature of each may be controlled separately. The pressure at which the jaws come together may also be adjusted for optimal bonding. Lastly, the time for which the jaws are together (the "dwell" or "hover" time) may also be adjusted. A dwell time of zero indicates that the jaws were brought together for an instant and immediately moved apart, i.e., they were not held together.
Different applications may require different jaw sizes, but the size of jaw is generally about a 1.75 cm (a half inch) wide, producing a bond width of about 0.635 cm (1/4 inch), by about 3.8 cm long (1.5 inches) to about 6.35 cm (2.5 inches) long. The jaw size may be as small as a half centimeter by a centimeter, depending on the materials to be joined.
An exemplary bar sealing device is available from Therm-O-Seal.RTM. Corporation of Mansfield, Tex. One such device is a Vertrod.RTM. Style Steel frame sealer that has jaws about 1.75 cm wide and 2.54 cm in length and uses electrical resistance heating and water cooling. Another is a Vertrod.RTM. style hand-held heat sealer that can produce a bond of 2, 4, 8 or 12 inches (5.1, 10.16, 20.3 and 30.5 cm) in length and 1/8, 3/16, 1/4 and 3/8 inch (0.32, 0.48, 0.64 and 0.95 cm) in width. Yet another example of a bar sealing device is a Vertrod.RTM. style table-top vacuum heat sealer producing seals 9, 14, 20, 24 and 30 inches (22.9, 35.6, 50.8, 61 and 76.2 cm) in length and 1/8, 3/16, 1/4 and 3/8 inch in width.
As noted above, the process conditions will vary depending on the materials of construction. For example, the current thermoplastic polymeric materials commonly used in disposable gowns and for components such as, for example, tie cords that are presently attached to such disposable gowns, are typically nonwoven fabrics formed from polypropylene and/or polyethylene and have a basis weight typically ranging from about 0.5 (17 gsm) to about 1.5 osy (51 gsm).
Desirably, the tie cord material may be a folded 1.0 osy (34 gsm) SMS material made as described above. Fabric for the fabrication of gowns may be, for example, made of random copolymer spunbond, a three layer (Catalloy.RTM./polyethylene/Catalloy.RTM.) or "ABA" calcium carbonate filled film, and a spunbond/meltblown/spunbond (SMS) layer. This "SFSMS" may bonded together to form the gown with the SMS against the skin. The spunbond layer and film may have a basis weight of between 0.2 and 1.0 osy (7 and 34 gsm) or more particularly about 0.6 osy (20.3 gsm). The SMS layer may have a basis weight of between 0.5 and 1.5 osy (17 and 51 gsm) or more particularly about 0.75 osy (25.4 gsm).
When these materials are used, the temperature of the bar sealer should be between 240 and 320° F. (116 and 160° C.), the pressure should be between 40 and 80 psi (276 and 552 kPa) and the dwell time should be between 0 and 5 seconds. More particularly, the temperature should be between 260 and 290° F. (127 and 143° C.), the pressure should be between 50 and 60 psi (345 and 414 kPa) and the dwell time should be between 1 and 3 seconds.
ASTM tests 1670 and 1671-b, procedure A: These tests are identical except that 1670 uses synthetic blood and 1671 uses Phi-X174 bacteriophage.
The test uses a penetration test cell available from Wilson Road Machine Shop, Rising Sun, Md. The cell has a capacity of about 60 ml. In the test cell, the specimen acts as a partition separating the challenge fluid from the viewing side of the penetration cell. An annular flange cover with an open area to allow visual observations of the specimen, and a transparent cover are included. The cell body has top port for filling and a drain valve for draining the penetration test cell. The penetration cell is further specified in Test Method F903.
The fabric specimen is placed in the penetration cell with the layer that is normally outermost facing the back (solid flange) part of the cell where the challenge fluid is placed. The cell is filled through the top port with the challenge fluid and observed for 5 minutes. Air is then supplied to the top port and the sample held at 13.8 kPa (2 psig) for 1 minute and the pressure released. If liquid penetration is not yet seen, the sample is allowed to stand for 54 minutes and observed. If bacteriophage is the test fluid, the sample is subsequently assayed using a 0.5 ml sample size onto agar for 6 to 18 hours at 35 to 37° C. to test for passage of fluid that is not observable to the unaided eye.
Kimberly-Clark MicroCool.RTM. surgical gowns are made of random copolymer spunbond, a three layer (Catalloy.RTM./polyethylene/Catalloy.RTM.) calcium carbonate filled film, and a spunbond/meltblown/spunbond (SMS) layer. This "SFSMS" is bonded together to form the gown with the SMS against the skin. The random copolymer of which the outermost layer of spunbond material is made is a 2.5 weight percent ethylene-propylene copolymer known as R532-35R, from the Dow Chemical Company of Midland, Ml. No treatments are applied to the fabric.
The spunbond layer and film each had a basis weight of 0.6 osy (20.3 gsm). The SMS layer had a basis weight of 0.75 osy (25.4 gsm).
The tie cord to be bonded to the gown was a folded 1.0 osy (34 gsm) SMS material. The material was folded either once for a double layer of fabric, or twice for a triple layer of fabric. The outer layer (spunbond) was made from a 2.5 weight percent ethylene-propylene copolymer known as R532-35R, from the Dow Chemical Company and the outer layer is treated with an antistat and a fluorochemical to reduce surface tension. Prior to bonding to the gown, a additional piece of tie cord material was bonded to the tie cord near an end to produce a "Y" shaped end for bonding to the gown on both upper end of the Y. The Y was flattened out onto the gown for bonding at two points on the branches of the Y but near the stem of the Y.
A bar sealing device from Therm-O-Seal.RTM. of Mansfield, Tex. was used. It was a Vertrod.RTM. model number 2PF-ST-12004-55HT-WC-CRF-TC-KY-SP. This device had jaws about 1.75 cm wide and 2.54 cm in length and used electrical resistance heating and water cooling. Only the jaw in contact with the tie cord was heated.
A double folded SMS tie cord was bonded to a MicroCool.RTM. surgical gown at a temperature of 275 to 282° F. (135 to 139° C.) at a zero dwell time and 56 psi pressure (386 kPa). The bonded area was tested according to ASTM 1670. Nine out of 11 samples passed and two failed.
A double folded SMS tie cord was bonded to a MicroCool.RTM. surgical gown at a temperature of 280 to 286° F. (138 to 141° C.) at a zero dwell time and 56 psi pressure (386 kPa). The bonded area was tested according to ASTM 1670. All 11 samples passed
A double folded SMS tie cord was bonded to a MicroCool.RTM. surgical gown at a temperature of 290 to 296° F. (143 to 147° C.) at a zero dwell time and 56 psi pressure (386 kPa). The bonded area was tested according to ASTM 1670. Nine out of 11 samples passed and two failed.
The samples from Example 2 were tested according to ASTM 1671-b using bacteriophage. Eleven of 11 samples passed.
As will be appreciated by those skilled in the art, changes and variations to the invention are considered to be within the ability of those skilled in the art. Examples of such changes are contained in the patents identified above, each of which is incorporated herein by reference in its entirety to the extent it is consistent with this specification. Such changes and variations are intended by the inventors to be within the scope of the invention. It is also to be understood that the scope of the present invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the foregoing disclosure.