Abstract:
Fabrics having enhanced allergen barrier capabilities are described. The fabrics are woven and calendered, and desirably face finished to provide lightweight, thin fabrics having good aesthetic properties. The fabrics also have good moisture vapor transport characteristics and superior allergen barrier capabilities, and in particular, superior barrier capabilities for cat dander allergen (representing smaller allergen particle size), as well as dust mite allergen. Protective coverings made from the fabrics and methods for their production are also described.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention generally relates to protective fabrics and covers. More specifically, the invention relates to protective fabrics which have enhanced allergen barrier capabilities, rendering them particularly useful as a barrier to allergens and the like.  
         BACKGROUND  
         [0002]    Many people suffer from allergies caused by airborne fine particulate matter such as pollen, dust, house dust mites and their fecal matter, animal and human dander, molds, inorganic dust, and the like. In fact, it has been found that the condition of many asthma sufferers can be exacerbated by, and in some cases even caused as a result of, exposure to common house dust and the dust mites that live in the dust. In addition, the problems associated with human allergies to animal dander are widely known; as a result, many individuals are unable to have dander-producing house pets.  
           [0003]    The house dust mite ( Dermatophagoides pteronyssimus ), which is a member of the spider family, measures about 0.3 mm across and to the naked eye, is indistinguishable from a speck of dust. It accounts for a large percentage of the mite population in samples taken from homes. Because the house dust mites require a moist environment and feed on such things as human skin, they are typically concentrated in high numbers in and around beds and bedding items.  
           [0004]    Due to its relatively large size, it has been found that the dust mite itself does not generally tend to cause an allergic reaction in most individuals. However its fecal pellet, which measures only about 20 microns (20/100 mm) in diameter, is a common cause of allergic reactions in humans. This mite fecal pellet, which is generally referred to as Der p1 in allergen discussions, easily becomes airborne where it can be readily inhaled and deposited on the inner lining of the respiratory tract of a human being. In the case of non-allergic humans, this may go unnoticed, but in those with varying degrees of sensitivity, exposure to the dust mite fecal pellets can cause irritation of the respiratory passages, leading to an itchy stuffy, and/or runny nose, or other similar allergic responses. In the case of an asthmatic person with an allergy to dust mites, the reaction to dust mite fecal matter exposure can be more severe.  
           [0005]    Eradication of these dust mites is virtually impossible in the home environment, due to the tendency of the human skin to shed constantly. As a result, those with allergies to the dust mite fecal matter must typically take efforts to suppress the growth of mites to the extent possible. Generally, this involves removing dust mite host environments such as carpets and other home furnishing items. In addition, doctors treating those individuals with dust mite fecal matter allergies (hereinafter referred to as “dust mite allergies”) generally recommend encapsulation of pillows and mattresses, to prevent the cross-transfer of dust mites from these articles to the allergy sufferer. Furthermore, such individuals are instructed to wash all non-encapsulated bedding articles frequently at the hottest temperatures tolerable, to kill any dust mites which may be living therein.  
           [0006]    Common items for encapsulating the bedding and pillows of an allergic individual generally utilize a plastic coated material, plastic film or similar barrier layer to block the transfer of dust mites. However, such materials can be objectionable to the user, in that they typically have an undesirable hand, poor drape, tend to feel thick, and have poor overall aesthetic characteristics. For that reason, many allergic individuals resist using such barrier materials.  
           [0007]    Other barrier-type covers available on the market include ones which are plain woven from polyester and those which are plain woven from a polyester/cotton blend. These fabrics are typically very tightly woven, to minimize the size of the openings therein through which the dust mites can travel. Although providing barriers for some particles and some superior comfort characteristics as opposed to their plastic coated or film-containing counterparts, such fabrics can fail to prevent the transfer of other common particles, thereby providing ineffective barrier properties for some purposes. Furthermore, they can have poor comfort and aesthetic properties as well due to their plastic feel and thickness.  
         SUMMARY  
         [0008]    The instant invention overcomes many of the disadvantages of the prior art barrier fabrics, while providing superior performance characteristics.  
           [0009]    The fabrics of the instant invention are desirably lightweight, thin, have good moisture transport properties, and have superior allergen filtration characteristics. They are desirably tightly woven in a relatively lightweight construction, calendered, then desirably face finished, thereby improving the hand and aesthetic characteristics.  
           [0010]    In one embodiment of the invention, the fabric is woven from substantially all-polyester. In this embodiment of the invention, microdenier polyester yarns are desirably used in at least one of the yarn sets forming the fabric (i.e. the warp or fill direction) while standard-sized polyester yarns are used in the other direction. (For purposes of this application, the term microdenier yarns is intended to describe those yarns made from filaments which are 1 denier per filament in size or less.) Alternatively, microdenier yarns can be provided in both of the yarn sets forming the fabric (i.e. both the warp and fill). In another embodiment of the invention, the fabric is made from a blend of polyester and cotton fibers. For example, polyester yarns can be used to form one of the yarn sets while cotton yarns can be used to form the other of the yarn sets forming the woven fabric.  
           [0011]    The woven fabrics are then desirably calendered on at least one side. If desired, the fabrics can be calendered on both sides by passing the fabric back through the calender a second pass or in some other manner. However, it has been found that calendering a single side of the fabric results in a fabric having barrier properties sufficient to resist the passage of allergens to a significant extent.  
           [0012]    The fabrics are also desirably face-finished, by sanding, sueding or the like. In particular, the fabrics are desirably subjected to a face finishing process which contacts the fabrics at an angle with one or more abrasive rolls, to abrade the fibers on the surface of the fabric.  
           [0013]    Fabrics of the instant invention have been found to be effective barriers from dust mites, as tested both according to airflow and use simulation tests. In addition, the fabrics have been found to have dramatically greater effectiveness as a barrier to cat dander allergen (Fel d1.)  
           [0014]    The fabrics of the instant invention can be used for a variety of purposes, including but not limited to the production of protective covers for upholstered and padded articles such as furniture and bedding items (e.g. mattresses, comforters and pillows.) For example, the fabric can be used to form a cover for covering a portion of a mattress (e.g. in the form of a mattress pad or a regular fitted sheet), a mattress encasing (for surrounding substantially the entire mattress), a pillow encasing or the like. When the fabric forms a mattress covering, it is preferred that the fabric at least form the platform (i.e. the user contacting surface) of the mattress covering. The items can be designed to be used alone or in combination with other bedding articles, such as sheets and the like. In addition, the cover can form a portion of the pillow covering or the mattress ticking, the furniture upholstery, or the like. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a flow diagram of a process which can be used to produce the fabric of the instant invention;  
         [0016]    [0016]FIG. 2 is a schematic representation of the process of FIG. 1 in a batch process; and  
         [0017]    [0017]FIG. 3 is a schematic representation of a continuous process which can be used to produce fabrics according to the instant invention. 
     
    
     DESCRIPTION  
       [0018]    As illustrated in FIGS.  1 - 3 , the fabric  10  is initially passed through a scouring range  12  where the fabric is scoured and dried. From the scouring range, the fabric passes through a set of calender rolls  14  where it is calendered on at least one side. From the calendar rolls  14 , the fabric  10  passes through a face finishing device  16  such as a sander. The face finishing device serves to roughen the fibers on the surface of the fabric; preferably the surface of the fabric opposite that which was calendered is face finished, although it is noted that both surfaces of the fabric can be calendered and/or face finished within the scope of the instant invention. In a preferred form of the invention, the face finishing device contact the fabric at angle in the manner described in commonly-assigned U.S. Pat. No. 5,943,745 to Dischler, the disclosure of which is incorporated herein by reference. It has been found that the use of the face finishing method described in that reference provides a soft hand to the fabric without undesirably destroying its strength and barrier properties. Other types of face finishing processes could also be used such as that described in commonly-assigned U.S. Pat. No. 5,815,896 to Dischler, the disclosure of which is incorporated herein by reference.  
         [0019]    From the face finishing device  16 , the fabric desirably passes through a lint extractor  18  to a collection container  20 , from whence it passes through a heat setting range to a take up (not shown.)  
         [0020]    The process illustrated in FIGS. 2 and 3 is similar to that shown in FIG. 1, with FIG. 2 illustrating the fabric being taken up on a roll  24  after scouring and drying and taken up on another roll  26  after calendering. FIG. 3 illustrates the fabric  10  being processed continuously from the supply roll  28  to the take up from the heat setting range  22 .  
         [0021]    In one aspect of the invention, the fabric is made from substantially all-polyester, and has a thickness of less than about 8 mils, and more preferably a thickness of less than about 7 mils. The fabric is also relatively lightweight, preferably weighing less than about 3.5 oz/sq. yd and more preferably, less than about 3 oz/sq. yd. The fabric preferably includes about 130 to about 160 ends per inch, and about 50 to about 80 picks per inch. However, it is noted that other constructions can be used within the scope of the instant invention. In a preferred form of the invention, the fabric is a plain woven fabric, having a yarn made from standard denier polyester filaments in one direction of the weave and a yarn made from microdenier polyester filaments in the other direction of the weave; preferably, the microdenier polyester yarn is provided in the fill direction of the fabric. As the comfort of a fabric is commonly evidenced by its rate of moisture vapor transport (MVTR), the fabric desirably has a moisture vapor transmission rate of at least about 400 g/sq m/24 hrs, and more preferably at least about 425 g/sq m/24 hrs, and even more preferably at least about 430 g/sq m/24 hrs.  
         [0022]    The fabric also desirably has an air permeability of at least about 1, and preferably at least about 2 cfm at 125 pa&#39;s. The fabric also desirably allows an airflow of at least about 15 l/min, and more preferably at least about 20 l/min, and even more preferably at least about 23 l/min. The fabric also desirably allows the passage of less than 1 ng of cat dander allergen when subjected to a Fel d1 cat dander allergen airflow test, more preferably less than about 0.5 ng of Fel d1 cat dander. In a particularly preferred form of the invention, the fabric allows the passage of less than about 0.31 ng of cat dander allergen, as this is generally considered to be an effective barrier to the passage of Fel d1 cat dander allergen. The fabric also desirably allows the passage of less than about 1.3 ng of Der f1 dust mite allergen when subjected to an airflow test, as this is generally considered to be the level at which the fabric functions as a dust mite allergen barrier. The fabric also desirably functions as a dust mite allergen barrier in use simulation testing, by allowing the passage of les than about 3.9 ng of Der p1 and Der f1 dust mite allergen.  
         [0023]    In another embodiment of the invention, the fabric is a polyester/cotton blend. For example, polyester yarns can be provided in one of the yarns sets forming the woven fabric while cotton yarns are provided in the other of the yarn sets. However, other arrangements of the fibers can be used within the scope of the instant invention. The polyester/cotton blended fabric of the invention preferably has a weight which about 4 oz/sq. yd or less, and more preferably less than or equal to about 3.8 oz/sq. yd. In a particularly preferred form of the invention, the fabric is about 3.6 oz/sq. yd or less in weight. Although specific types of polyester and cotton yarns have been described below for purposes of illustration, it is noted that other sizes and compositions of yarn can be used within the scope of the invention. Preferably the fabric has about 130-150 ends per inch and about 50 to about 70 picks per inch. The fabric desirably has an air permeability of at least about 5 cfm at 125 pa&#39;s, and preferably at least about 10 cfm at 125 pa&#39;s. The thickness is preferably less than about 15 mils, and more preferably less than about 10 mils. In addition, the fabric desirably has a moisture vapor transmission rate of at least about 400 g/sq m/24 hrs, more preferably at least about 425 g/sq m/24 hrs, and even more preferably an MVTR of at least about 430 g/sq m/24 hrs.  
         [0024]    The fabric desirably also allows an airflow of at least about 25 l/min, more preferably at least about 30 l/min. The fabric also desirably allows the passage of less than 15 ng of Fel d1 cat allergen when subjected to a cat dander airflow test, more preferably less than about 10 ng, and even more preferably less than about 7.5 ng of Fel d1 cat dander allergen. In addition, the fabric also is an effective dust mite allergen barrier, in that it allows the passage of less than 1.3 ng of Der f1 allergen when subjected to a dust mite allergen airflow test. In addition, the fabric also allows the passage of less than 3.9 ng of Der p1 and Der f1 allergen when subjected to a simulated use test.  
       EXAMPLES  
       [0025]    Commercially available products and those of the instant invention were tested as follows. The fabrics of the invention tested were woven as indicated in the tables and calendered on one side on a BF Perkins woven calender at a speed of 20 (±3) yards per minute at a set point temperature of 300 degrees Farenheit (roll actually heated to 325-340 during processing) and at a pressure of about 1100 (±100) psi. The fabrics were subsequently face finished on the non-calendered side.  
         [0026]    Fabric Weight Fabric weight was tested in accordance with ASTM Designation D3776-96.  
         [0027]    Air Permeability  
         [0028]    Air permeability was tested in accordance with ASTM Designation D 3776-96.  
         [0029]    Thickness  
         [0030]    Thickness was measured according to ASTM Designation D 1777-96.  
         [0031]    Moisture Vapor Transmission  
         [0032]    Moisture vapor transmission (MVTR) was tested in accordance with ASTM Designation E96-93. It is generally considered that variations in MVTR must be ±25 g/sq m/24 hrs to have effective significance in comfort differentiation.  
         [0033]    Mite Allergen and Cat Dander Allergen Airflow Test  
         [0034]    An apparatus based on the design reported by Vaughan, J W et al (JACI 1999; 103:227-231) was used to test allergen barrier properties of the fabrics. Airflow measurements were calibrated against a fabric control with a known airflow rate. Five hundred milligrams of a dust sample with known amounts of the indicated allergens were pulled across each fabric. A filter cassette mounted downstream from the fabric collected any allergen that was able to penetrate the fabric. The filter was extracted in 2.0 mL of 1% BSA in PBS-Tween 20 overnight. The extract was assayed the following day with an ELISA for the relevant allergen. The allergens measured were Mite allergen (Der p1 and Der f1) and Cat allergen (Fel d1). In the tests, the dust samples included 8982 ng of Fel d1 and 1015 ng of Der f1, respectively. It is generally considered that fabrics having a Fel d1 measurement of &lt;0.31 would be an effective barrier to cat dander allergen transfer (smaller particle size) and fabrics with a Der f1 measurement of &lt;1.3 would be an effective barrier to dust mite allergen transfer.  
         [0035]    Mite allergens were again tested using the following use simulation test method:  
         [0036]    Mite Allergen Use Simulation  
         [0037]    A sieved reference dust sample containing a known quantity of the indicated allergen was loaded into one side of the special dual chamber along with two steel bearings. The fabric cloth being investigated was inserted as the barrier between the empty and dust containing sides of this chamber. Each side of the chamber is a glass vial (2.1 cm diameter by 4 cm length) with a transfer surface area between the two vials of 1.13 cm 2 . The chamber was rotated at 25 rotations per minute for 18 hours. The two ⅛″ steel bearings in the allergen vial weighed 132 milligrams each. At the conclusion of the tumbling period, the empty side was tested for the presence of allergen by a sensitive enzyme immunoassay with a limit of detection of 3.9 nanograms of dust mite allergen. When the results of this use simulation test for a fabric are less than 3.9 nanograms transferred, it can generally be concluded that the fabric being tested is an effective barrier to dust mite allergen transfer. The allergen loaded included 0.250 grams of fine dust containing 6250 nanograms of dust mite allergen.  
         [0038]    Sled Friction  
         [0039]    Sled friction was tested according to ASTM Designation Dl 894-93 in both the warp and fill directions, and both static and dynamic coefficients of friction (COF) were recorded.  
                                                                                                         Pristine ® 100               Pristine ®   Allergy Control   Example A-           Allergy Free   Prod.   100%           Houston, TX   Richfield, CT   polyester                        Weight (oz/sq.yd)   2.83   3.8   2.8       Construction   149 × 104 plain   161 × 81 plain   143 × 67           weave 100%   weave 100%   plain weave           polyester   polyester   100%                   polyester       Warp Yam   1/70/34 textured   1/70/34 textured   1/70/34           round polyester   round polyester   textured           2.2 DPF   2.2 DPF   round                   polyester                   2.2 DPF       Fill Yarn   1/70/34 textured   1/175/196   1/140/200           round polyester   hollow core   textured           2.2 DPF   polyester   polyester                   .7 DPF       Air Permeability   12.0   5.9   2.2       (CFM @ 125 pa&#39;s)       Thickness (mils)   7.50   8.75   7.6       + MVTR   443.0   436.1   431.7       (g/sq m/24 hrs)       Airflow (L/Min)   34.4   24.9   23.9       Cat Allergen Fel d1   3.5   1.3   &lt;.31       (ng)       Mite Allergen Der   &lt;1.3   &lt;1.3   &lt;1.3       f1 (ng)       Use Simulation   &lt;3.9   &lt;3.9   &lt;3.9       Mite Allergen Der       p1 and Der f1 (ng)       Sled Friction       Warp Static COF   0.681   0.556   0.333       Warp Dynamic   0.578   0.516   0.274       COF       Sled Friction       Fill Static COF   0.336   0.669   0.457       Warp Dynamic   0.286   0.578   0.339       COF                        Pristine ® Cotton   Example B-           Allergy Solution   40/60           Chadds Ford, PA   polyester/cotton                        Weight (oz/sq.yd)   4.0   3.6       Construction   153 × 85 plain weave   141 × 60           70/30 polyester/cotton   plain weave               40/60               polyester/cotton       Warp Yarn   1/70/34 textured   1/70/34           round polyester   textured           2.2 DPF   round               polyester               2.2 DPF       Fill Yarn   28/1 Open End spun   20.5/1 100%           50/50 polyester/cotton   cotton ring spun       Air Permeability   7.4   11.6       (CFM @ 125 pa&#39;s)       Thickness (mils)   11.30   9.60       + MVTR (g/sq m/24 hrs)   436.1   433.9       Airflow (L/Min)   18.0*   32.8       Cat Allergen Fel d1 (ng)   22.0*   7.1       Mite Allergen Der f1 (ng)   3*   &lt;1.3       Use Simulation Mite   &lt;3.9   &lt;3.9       Allergen Der p1 and Der       f1 (ng)       Sled Friction       Warp Static COF   0.726   0.431       Warp Dynamic COF   0.586   0.365       Sled Friction       Fill Static COF   0.448   0.551       Warp Dynamic COF   0.469   0.417                          
 
         [0040]    As noted above, the fabrics of the instant invention have dramatically improved results as a barrier to cat dander allergen. In fact, the improved barrier was achieved without a reduction in comfort, as evidenced by the comparable moisture vapor transmission rates and airflow properties for the commercial products and those of the instant invention. Furthermore, the lower warp sled friction values suggest it may be easier to install such things as mattress covering made from the fabrics of the invention as compared with those of the prior art, since the warp direction would generally correspond to the direction of fabric installation.