Abstract:
A stable finely knitted fabric is disclosed which includes a plurality of yarns including filaments of about 1.5 denier or less. The yarns are knitted into a fabric using a right-leaning top triangle (RTT) pattern. The fabric includes a face side having a plurality of parallel and elongated ridges and a back side having a smooth surface without elongated ridges. The fabric exhibits a wicking action from the smooth side to the ridged side of the fabric and excellent absorption. Further, the fabric may be used as a liquid applicator, when an absorbant liquid reservoir layer is added to the back side, as channels of air between the ridges increase liquid flow from the back side to the face side.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to textile fabrics, more specifically to textile fabrics that may be used for cleaning, e.g., mop heads, that include a frictional surface with a series of ribs on at least one side of the fabric and that may be smooth on the other side of the fabric or have ridges on both sides of the fabric. 
       BACKGROUND 
       [0002]    There are three major classes of fabric—woven, non-woven and knitted fabrics. A woven fabric is formed by weaving. In contrast, nonwoven fabrics are fabrics made from fibers, bonded together by chemical, mechanical, heat or solvent treatment. The term nonwoven is used in the textile manufacturing industry to denote fabrics, such as felt, which are neither woven nor knitted. Nonwoven fabrics may lack strength unless densified or reinforced by a backing. When used for cleaning products such as wipes, clothes or mop heads, such nonwoven cleaning products are normally disposable. Compared to the woven and nonwoven fabrics, knitted fabrics are much more elastic, have much greater durability and can range widely in weight and thickness. Knitted fabrics are typically thicker and can be more absorbent than their woven and non-woven counterparts, which accounts for their uses as towels and cleaning cloths. 
         [0003]    For cleaning articles, such as disposable cleaning wipes, nonwoven fabrics have been used frequently. Many nonwoven wipes are made from a composite fabric containing a mixture or stabilized matrix of thermoplastic filaments and at least one additional fabric, often called the “second fabric” or “secondary fabric”. Nonwoven webs with frictional ridges or tufts are also known in the art. For example, nonwoven webs with hollow ridges which extend outward from the surface of the nonwoven web are known. The ridges can be made by a number of processes, but are preferably formed by directly forming the nonwoven web on a surface with corresponding ridges, or by forming the nonwoven on an apertured surface with a pressure differential sufficient to draw the fibers through the apertures, thereby forming the ridges. Nonwoven webs with ridges have also been prepared by bonding a portion of the nonwoven web and leaving a portion of the nonwoven web unbonded using a compaction roll. In some cases, the ridges or tufts of a nonwoven fabric may include a mixture of a thermoplastic polymer and a secondary fabric. 
         [0004]    Such nonwoven webs with frictional tufts, ridges or ribs are used in a variety of applications such as disposable absorbent articles, dry wipes, wet wipes, wet mops and dry mops. However, knitted fabrics with such frictional ridges are not available. Further, knitted fabrics with frictional ridges on one side and a smooth surface on the other side are also not available. 
         [0005]    As concerns about the environment and specifically the overuse of landfills, there is a need for improved cleaning cloths and mops that are not disposable, but that are durable and reusable. Hence, improved cleaning fabrics that are knitted or woven, as opposed to nonwoven fabrics, are needed. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    A knitted fabric with frictional ridges for cleaning devices is disclosed. The knitted structure of the fabric imparts durability and strength as well as softness. The frictional ridges enhance the cleaning/scrubbing ability of the knitted fabric. 
         [0007]    In an embodiment, a stable knitted fabric is disclosed which comprises a face side comprising a plurality of parallel and elongated ridges and a back side comprising a smooth surface without elongated ridges. As an alternative, both sides may include the elongated ridges. 
         [0008]    In another embodiment, a stable, finely knitted fabric is disclosed which comprises a plurality of yarns comprising filaments having thicknesses of about 1.5 denier or less with the yarns having thicknesses ranging from about 50 to about 250 denier. The fibers may be made by any process for making micro-denier fibers including “Island in the Sea”, bicomponent, electrospinning (nanofiber), etc. The yarns are knitted into the fabric using a right-leaning top triangle (RTT) stitch illustrated below. The fabric comprises a face side comprising a plurality of elongated ridges and a back side comprising a smooth surface without elongated ridges. 
         [0009]    A covered sponge is also disclosed which comprises a sponge enclosed within a knitted cover. The knitted cover is at least partly fabricated from a stable knitted fabric comprising a face side comprising a plurality of parallel and elongated ridges and a back side comprising a smooth surface without elongated ridges. The smooth back side may enhance wicking between the sponge and the ridged front side. 
         [0010]    In any one or more of the embodiments described above, the fabric comprises a right-leaning top triangle (RTT) stitch illustrated below. 
         [0011]    In any one or more of the embodiments described above, the fabric may comprise fibers made from polymers consisting of, for example, polyesters, polyamides, polyethylene terephthalate and combinations thereof. 
         [0012]    A method of making a knit fabric is also disclosed which comprises forming a plurality of yarns of dissimilar weights, wherein each yarn is formed by spinning fibers comprising approximately 1.50 denier or less. The method also includes forming the fabric by knitting the plurality of yarns of dissimilar weights to have ridges extending in the direction of the knitting. 
         [0013]    In a refinement, the forming of the fabric further comprises knitting the plurality of yarns of dissimilar weight to provide the knitted ridges. 
         [0014]    In another refinement, the forming of the plurality of yarns of dissimilar weights further comprises forming at least some yarns of dissimilar weights from bi-component splittable filaments. 
         [0015]    In another refinement, the forming of the plurality of yarns of dissimilar weights comprising forming a plurality of yarns of dissimilar weights from micro-denier fibers. 
         [0016]    In another refinement, the knitting of the plurality of yarns of dissimilar weights to have knitted ridges further comprises knitting the yarns at imaginary intersection points of a grid such that a first yarn skips the grid and is knitted every other grid, a second yarn is knitted every grid, and a third yarn is knitted in rows along the grid to form the ridges on the front side of the fabric. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic line diagram illustrating a prior art knitted stitch or pattern. 
           [0018]      FIG. 2  is a schematic line diagram illustrating a disclosed RTT knitted stitch or pattern. 
           [0019]      FIG. 3  is a plan view of a disclosed fabric made with the RTT pattern of  FIG. 2 . 
           [0020]      FIG. 4  is another plan view of the disclosed fabric of  FIG. 3 . 
           [0021]      FIG. 5  is a flow diagram illustrating the knitting of disclosed cleaning articles using the RTT pattern of  FIGS. 2-4 . 
           [0022]      FIG. 6  is a more detailed flow diagram illustrating the knitting of disclosed cleaning articles using the RTT pattern of  FIGS. 2-4 . 
           [0023]      FIG. 7  illustrates the face side of the disclosed knitted fabric. 
           [0024]      FIG. 8  illustrates both the face and back sides of the disclosed knitted fabric. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 1 and 2  provide a convenient comparison of a prior art weft pattern  10  ( FIG. 1 ) and the disclosed, more complex RTT pattern fabric  20  ( FIG. 2 ). The fabric  20  of  FIG. 2  is a warp structure. The warp structure of  FIG. 2  can be fabricated using the methods of  FIGS. 5-6  and the detailed description of  FIGS. 2-4  provided below. 
         [0026]    A fine microfiber fabric  20  with low drag is accomplished using ridges  26  (FIGS.  4  and  7 - 9 ) on one side  28  of the microfiber fabric. The ridges  26  allow a wipe cloth or mop head to avoid dragging or sticking to a surface when wiped on a surface. The poor absorbency of polyesters and other polymer fibers has also been addressed. The ridges  26  in the micro-denier fiber fabric  20  enhance the absorbency of the fabric  20 . 
         [0027]    Specifically, it has been discovered by applicant that a capillary action results from spaces between the knit filaments. Specifically, a smaller tube has more capillary action. And smaller tubes allow more tubes on a fabric of a given size. The ridges  26  reduce the drag caused by suction or capillary suction or the possible drag caused by the micro-denier fibers binding or snagging on irregularities in the surface. Without being bound by any particular theory, it is believed these ridges  26  reduce the surface tension of any liquid being wiped on a surface by the fabric  20 . It is also believed that the ridges  26  might break the surface tension of any liquid. Channels  27  for air are provided between the ridges  26  ( FIG. 4 ) so that any suction does not cause as much drag since the fabric  20  and liquid is riding on some of the air in the channels  27 . Previously there was little or no air. This is particularly true when wiping in the direction of the ridges  26 , rather than wiping against the ridges  26  (perpendicular to the ridges  26 ). 
         [0028]    The disclosed fabric  20  is an improved liquid applicator. Specifically, the ridges  26  on the fabric  20 , when placed against a dry surface, may create channels  27  of air that urge an increased flow of liquid from the fabric  20  to the surface being cleaned. As an alternative embodiment, an absorptive layer, such as a sponge  36  ( FIGS. 7-9 ) may be added on the back side  35  opposite the ridges  26  to act as a fluid reservoir. By placing the ridges  26  in a microfiber fabric  20 , both high absorption and low drag when wiping are achieved. 
         [0029]    A microfiber is defined as approximately 1.0 denier or below but greater than 0.3 denier. Example applications are towels, upholstery, flat mops, isolator covers and wipers or cleaning cloths. An additional problem addressed by the disclosed fabric  20  is that, by reducing friction, the pad is not twisted or pulled off of a mop frame as prior art mop pads are prone to do. Further, while the fabric  20  made of micro-denier blended yarn has significantly greater effective surface area, the ridges  26  reduce the amount of micro-denier fiber in contact with the surface being cleaned or prepared. The fabric  20  also has less effective surface area as a pad or surface in contact with a sterile instrument. 
         [0030]      FIG. 2  illustrates a line diagram of an example of the disclosed fabric of three types of yarns  21 ,  22  and  33  according to an embodiment. In  FIG. 2 , each yarn  21 - 23  is illustrated by a single line. A matrix of horizontal gridlines  24  and vertical gridlines  25  are also illustrated for reference purposes and form no part of the fabric  20 . The illustrated exemplary fabric  20  exhibits high performance characteristics. The three yarns  21 - 23  are intertwined in a knit configuration. The yarn  21  is thicker than yarns  22  and  23 . The yarns  21 - 23  each have a micro-denier fiber content. The yarns  21 - 23  are knitted at the intersection points of the horizontal gridlines  24  and vertical gridlines  25 . The yarn  22  skips the grid and is knitted every other grid. The yarn  23  is knitted every grid. The thickest yarn  21  is knitted in rows along the grid to form the ridges  26  on the front side  28 . This places more of the micro-denier fibers in yarn  23  on the back side  35  ( FIG. 9 ) than the front side  28 , thereby improving fluid transfer. 
         [0031]    The fabric  20  can be knitted using a wide variety of knitting machine technologies including, but not limited to, warp knit, circular knit, superpol, and/or Jacquard or even woven on a loom. The thickest yarn  21  may be a 200 denier 384 filaments yarn of all polyester filament thickness of (0.52 denier). The medium thickness warp yarn  22  may be a bi-component, splittable filament yarn  150  with the split filaments having a thickness of about 0.13-1.00 denier or less. The yarn  23  may be a 75 denier  36  filaments (filament thickness of about 0.5 denier). 
         [0032]    After splitting, each filament of yarn  22  results in about eight to sixteen micro-denier fibers each of about 0.13 to about 0.2 denier. The two fabrics of the bi-component yarn  22  are polyester and polyamide which is the generic name for Nylon®. The bi-component filament made of two dissimilar materials allows it to be split into micro-denier fibers. 
         [0033]    The yarn  21  is knitted to form a ridge while the yarn  22  is knitted to form a smooth top side surface between the ridges. The yarn  22  is knitted within the fabric in a zigzag pattern and forms a smooth backside surface. The yarn  23  is knitted to form a base fabric that holds all yarns including yarns  21  and  22 . This means that the ridges  26  consist of one line each of yarn  21  and yarn  23 . The yarn  22  runs zigzag (to left and right) for 3 needle spaces. The yarn  23  runs zigzag for one (1) needle space knotting three (3) microfibers at a time. The yarn  21  runs straight circling each microfiber. Ridges are formed by placing the yarn  21  on every 5th needle and at the back side of the fabric. The yarn  23  also runs the ridged parts and knots microfiber and ridged fibers together. Microfiber loops are longer on the surface than at the back. This is one reason there are ribs or ridges  26  only on the top surface. However, as will be appreciated by those skilled in the art, ridges  26  can also be placed on both the top surface  28  and the bottom surface  36 . 
         [0034]      FIG. 3  is a hatched diagram and plan view of the fabric  20 .  FIG. 3  illustrates the same yarns  21 - 23  of  FIG. 2  except the drawing is a hatched diagram rather than a line diagram. In  FIG. 2 , each yarn  21 - 23  is illustrated by a single line. In  FIG. 3 , the yarns  21 - 23  are each illustrated by a series of hatches. 
         [0035]      FIG. 4  illustrates a plan view of the surface of the ridged fabric  20 . In  FIG. 4 , the ridges  26  generally contain the yarn  21  and the areas between the ridges  27  generally contain the yarns  22  and  23 . The ridged, microdenier surface  28  of the disclosed knitted fabric  20  is effective at removing viruses, vegetative bacteria, bacterial spores, mold spores and other organic matter. Not only can bacteria be removed, but also high levels of endotoxins can be removed from a wiped surface as well. Endotoxins are the waste from bacteria. This is useful for example in a critically controlled environment in a sterile clean room manufacturing facility, such as a pharmaceutical manufacturing plant, a baby formula facility, a research laboratory or food preparation or compounding plant. 
         [0036]      FIG. 5  is a flow diagram of an exemplary method of making the knitted fabric  20 . In step  31  a plurality of yarns is formed of different, dissimilar or varying weights. Each yarn is formed in step  32  by spinning a fiber of approximately 1.50 denier or below. In step  33  the fabric  20  is formed by knitting the plurality of yarns of dissimilar (different or varying) weights to have knitted ridges  26  as shown in  FIG. 4 . Optionally, a refinement of steps  31 - 34  can be made as shown in  FIG. 6 . The steps  132 - 133  usually are performed at the same time as steps  31 - 33  but can be done separately. Also steps  31  and  32  or  31  and  132  can be performed at the same time. In step  132  the plurality of yarns of different weights is formed by spinning only fibers of the same fabric. In step  133  the fabric is formed by knitting only the yarns of the same material produced above in step  132 . The yarns are knitted at imaginary intersection points of a grid, such as the horizontal gridlines  24  and vertical gridlines  25  illustrated in  FIG. 2 . 
         [0037]    A first yarn  22  ( FIG. 2 ) skips the grid and is knitted every other grid. A second yarn  23  ( FIG. 2 ) is knitted every grid. A third yarn  21 , the thickest yarn of the three ( FIG. 2 ) is knitted in rows along the grid to form the ridges  26  on a front side  28  ( FIG. 4 ). To achieve the desired properties, the fabric  20  is knitted and not woven. Knitting involves tying knots and weaving uses a warp and a weft. A ridge  26  can be formed in the fabric  20  by yarn that has been knitted around itself. 
       INDUSTRIAL APPLICABILITY 
       [0038]    Exemplary applications for the knit fabric  20  with ridges  26  are mop heads, sponges, applicators for disinfectants, and wipes. The improved fabric  20  transports fluid from one side  28  to an opposite side  35  of the fabric  20 , wherein the direction of flow is away from the smooth side  28 . The wetter side  35  may include a sponge  36  ( FIG. 9 ), terry cloth or denser microfiber fabric. 
         [0039]    Although certain embodiments have been described and illustrated in the above description and drawings, it is understood that this description is by example only, and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of this disclosure. Although the examples in the drawings depict only example constructions and embodiments, alternate embodiments are available given the teachings of this disclosure.