Patent Publication Number: US-2005130525-A1

Title: Nonwoven protective cover for biological organisms

Description:
TECHNICAL FIELD  
      The present invention relates generally to an arrangement for protecting biological organisms, such as aquacultures, as well as agricultural products and other plant life, and more specifically relates to a protective cover for biological organisms formed from nonwoven fabric to protect the organisms against dust, insects, and harmful macro- and micro-bioactivity, while permitting disposable use of the nonwoven cover.  
     BACKGROUND OF THE INVENTION  
      For many types of biological organisms that are kept and nurtured for commercial purposes, it is desirable to protect the cultivated products from dust, insects, and other harmful macro- and micro-bioactivity. In the past, polyethylene films have been employed for protection of crops, but experience has shown that these types of protective covers can be less than satisfactory. In order to allow moisture to evaporate away from the exposed aquacultures and/or agriculture, perforated polyethylene films have typically been used. However, the perforations can undesirably compromise the protection afforded by the covers, permitting ingress of dust and other contaminants.  
      PCT Publication No. WO98/51578 is directed to a bag-like cover for agricultural products, with the construction formed from cellulosic paper. However, the structure disclosed in this publication is not believed to exhibit the desired degree of durability when subjected to harsh or wet environments, and is not believed to provide the desired degree of gas permeability.  
      Greenhouses utilize protective covers as well, so as to prevent insects from damaging plants by borrowing holes through leaves or nesting within the plants. In addition, protective covers protect plants from dust, disease, and harmful environmental conditions. Further, such covers are desirable due to the air and water permeability of the cover material.  
      Where aquacultures are concerned, such as fish, shrimp, and various other shell-fish, it is desirable to protect the cultures against environmental debris, as well as birds, and also protect the cultures from overexposure to sunlight, in addition to other harsh environmental conditions. Further, a proper protective cover is often desired so as to shield aquacultures from splash-overs of bacterial and viral contaminated holding tank waters into uncontaminated holding tanks. Hatcheries with holding tanks that are set up close to one another, or over and under each other, have the potential for spreading problems through drips, sprays, and splashes. The introduction of contaminated water into a clean hatchery tank can have deleterious affects on the entire aquaculture hatchery population. For instance, shrimp hatcheries in Asia and South America are at risk for Taura Syndrome, White Spot Baculovirus (WSBV) or White Spot Syndrome (WSS), thought to be caused by one of several baculoviruses, and Yellow Head Virus (YHV), a rhabdovirus or a paramyxovirus, both of which can be devastating to shrimp hatcheries.  
      The present invention provides an improved form of protective cover for aquacultures and agricultural products which is particularly suited for the protection of aquaculture hatcheries, and which is configured for economical, disposable use.  
     SUMMARY OF THE INVENTION  
      A protective cover embodying the principles of the present invention is configured for protection of aquacultures, as well as agriculture, wherein the nonwoven cover helps control the spread of disease, permits the penetration of light, and allows for a controlled environment due to proper air circulation. The protective cover is positioned generally over the holding container of the aquaculture, whereby the shrimp or fish are substantially enclosed. The cover comprises a fibrous nonwoven fabric formed from fibrous and/or filamentary elements, with the fibrous nonwoven fabric exhibiting sufficient vapor permeability to permit transmission of gasses through the cover, while retarding passage of dust, insects, and contaminated water, thus protecting the aquaculture against potentially detrimental conditions.  
      The fibrous nonwoven fabric of the cover comprises fibrous material selected from the group consisting of thermoplastic polymers, thermoset polymers, natural fibers, and combinations thereof. The fibrous material of the nonwoven fabric can be heat-bonded, adhesive-bonded, or hydroentangled (spunlaced) to provide the fabric with the desired degree of integrity. The fibrous nonwoven fabric may be formed from filamentary elements by providing the fabric in the form of spunbond polymeric material.  
      The protective cover of the present invention can be provided with additional features to facilitate its effective use for protection of agricultural products, as well as greenhouse plants. If desired, the nonwoven fabric may comprise a reinforcing scrim, which may be integrated into the fabric by hydroentanglement. When the fibrous nonwoven fabric comprises polymeric material, the polymeric material may incorporate one or more protection enhancing agents selected from the group consisting of insecticidal, fungicidal, algaecidal, decay-inhibiting, and UV-protected, agents. Such protection-enhancing agents can be provided in the form of a melt-additive in the polymer, as a fiber surface treatment, and/or as a topical treatment applied to the nonwoven fabric. The protective cover may further incorporate means for controlling the ripening of agricultural products during growth so as to obtain optimum product value, wherein the protective cover may either be in a sheet form that is secured about the entire or partial element of the agricultural product, or be constructed so as to have a tubular configuration sized to permit the cover to be positioned generally about an associated agricultural product, whereby the product is essentially enclosed.  
      Pigmenting agents may also be employed. A method of protecting aquacultures, as well as agriculture in accordance with the present invention comprises the steps of providing at least one piece of nonwoven fabric formed from fibrous and/or filamentary elements. The present method further includes positioning the protective cover generally about the opening of a holding tank so as to protect the aquaculture from dust, insects, and/or transfer of disease. The protective cover may be permanently, semi-permanently or temporarily affixed along one or more edges of a holding tank by such representative means as adhesives and adhesive tapes, hook and loop fasteners, staples, zippers, snaps, buttons, and ties. Further, the cover is useful in protecting various field crops, in addition to nursery or greenhouse plants. The nonwoven fabric may comprise heat-bonded polymeric staple length fibers, or adhesive-bonded fibrous material. When the fabric is formed from spunbond polymeric material, the fabric comprises substantially continuous polymeric filaments.  
      The nonwoven fabric employed in the protective cover of the present invention can, for some applications, be non-apertured, with the fabric itself providing the desired breathability or vapor permeability. For some applications, it can be desirable to form the protective cover with a polymeric film layer applied to the nonwoven fabric. For these applications, the resultant laminate structure can be apertured to provide the desired vapor permeability.  
      Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagrammatic view of a forming apparatus for forming a nonwoven fabric for use as a protective cover for aquacultures and agriculture in accordance with the principles of the present invention;  
       FIG. 2  is a diagrammatic view of a hydroentangling forming surface for formation of a nonwoven fabric as a protective cover for agriculture in accordance with the present invention; 
    
    
     DETAILED DESCRIPTION  
      While the present invention is susceptible of embodiment in various forms, there is shown in the drawings, and will hereinafter be described, a presently preferred embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.  
      The present invention is directed to a protective cover for aquacultures and agriculture, which is particularly suited for use as covers for holding compartments that house fish, shrimp, and other various shell-fish. During cultivation of many aquacultures, it is desirable to protect the products from dust, insects, and/or disease, while at the same time providing vapor permeability or breathability to assure that the aquacultures maintain ideal living conditions. The protective cover further provides the aquaculture with a controlled environment due to the ability of air to readily pass through the cover, thus providing adequate air circulation to the aquaculture.  
      The protective cover embodying the principles of the present invention is provided in a general configuration sized to permit the cover to be positioned generally about an associated aquatic holding compartment. The protective cover may be permanently, semi-permanently or temporarily affixed along one or more edges of a holding tank by such representative means as adhesives and adhesive tapes, hook and loop fasteners, staples, zippers, snaps, buttons, and ties. The cover comprises a fibrous nonwoven fabric formed from fibrous and/or filamentary elements. The fibrous nonwoven fabric is selected to exhibit sufficient vapor permeability to permit transmission of gasses through the cover, while retarding passage of dust, insects, and/or contaminated waters.  
      The fibrous nonwoven fabric comprises fibrous material selected from the group consisting of thermoplastic polymers, thermoset polymers, natural fibers, and combinations thereof. The fibrous nonwoven fabric may be formed from filamentary elements when the fabric is provided in the form of a spunbond polymeric material. The nonwoven fabric preferably has a basis weight from about 10 to 50 gm/m 2 , and in one especially preferred form, comprises polypropylene staple length fibers that are heat-bonded.  
      The present protective cover can be differently configured to facilitate its cost-effective use for protection of aquacultures and agricultural field crops or nursery plants. For some applications, it can be desired to incorporate a reinforcing scrim in the fabric, with formation of the fibrous nonwoven fabric by hydroentanglement (spunlacing) facilitating incorporation of such a scrim. While it is contemplated that the nonwoven fabric may be non-apertured, for some applications, it can be desirable to apply a polymeric film layer to the nonwoven fabric, with the cover being apertured to provide the desired vapor permeability.  
      The fibrous nonwoven fabric may comprise polymeric material incorporating one or more protection-enhancing agents selected from the group consisting of insecticidal, fungicidal, algaecidal, decay-inhibiting, and UV-protective agents. The protective cover may further incorporate means for controlling the ripening of agricultural products during growth so as to obtain optimum product value, wherein the protective cover may either be in a sheet form that is secured about the entire or partial element of the agricultural product, or be constructed so as to have a tubular configuration sized to permit the cover to be positioned generally about an associated agricultural product, whereby the product is essentially enclosed. It is also contemplated that the polymeric material of the fabric may comprise a pigmenting agent. The protection-enhancing agents may be provided in the form of a melt-additive in the polymer from which the nonwoven fabric is formed, or may comprise a fiber surface treatment applied to the fibrous material from which the fabric is formed, prior to fabric formation. It is within the purview of the present invention that one or more of the protection-enhancing agents may comprise a topical treatment applied to the nonwoven fabric after it is formed.  
      In the following Examples, various techniques are described for formation of the nonwoven fabric from which the present protective cover is formed. The protective cover is positioned generally about an associated aquaculture holding tank, a row of field crops or individual plants, to protect them from dust, insects, and/or disease.  
     EXAMPLE 1  
     Thermal Bonded Carded Staple Fiber  
      The present protective cover was formed from nonwoven fabric comprised of a conventional carded staple length polypropylene fiber of 9.0 denier by 2.0 inch staple length. The basis weight of the carded lap was 45 grams per square meter. The carded batt was thermally bonded by calender nip at a pressure of 450 pounds per linear inch, a calender anvil roll surface temperature of 300° F. to 310° F., a calender embossing roll surface temperature of 300° F. to 310° F., and a point pattern of 9% bond area relative to total surface area. The overall line speed for manufacturing the representative nonwoven fabric was approximately 400 feet per minute.  
     EXAMPLE 2  
     Spunbond Filamentary Elements  
      A bonded precursor web may be produced on a commercial spunbond production line using standard processing conditions. In particular, a polyester filament precursor web may be employed having a basis weight of 20 grams per square meter, and a filament denier of 1.8. The precursor web is bonded by calender at a calender temperature of 200 to 220 degrees C., and a nip pressure of 320 PLI.  
      Optionally, a bonded precursor web may incorporate the use of nano-fibers or sub-denier fibers of infinite length, wherein the average fiber diameter of the nano-fiber is in the range of less than or equal to 1000 nanometers, and preferably less than or equal to 500 nanometers. Further, the precursor filamentary web may be subsequently subjected to hydraulic jets so as to interengage the continuous filaments.  
     EXAMPLE 3  
     Spunlace Fabric  
      Using a forming apparatus as illustrated in  FIG. 1 , a nonwoven fabric was made in accordance with the present invention by providing a precursor web comprising 100 percent by weight polyester fibers as supplied by Wellman as Type T-472 PET, 1.2 dpf by 1.5 inch staple length. The precursor fibrous batt was entangled by a series of entangling manifolds such as diagrammatically illustrated in  FIG. 1 .  FIG. 1  illustrates a hydroentangling apparatus for forming nonwoven fabrics in accordance with the present invention. The apparatus includes a foraminous forming surface in the form of belt  12  upon which the precursor fibrous batt P is positioned for pre-entangling by entangling manifold  14  including a plurality of sub-manifolds. In the present examples, each of the sub-manifolds of the entangling manifolds  14  included three orifice strips including 120 micron orifices spaced at 42.3 per inch, with three of the sub-manifolds successively operated at 100, 300, and 600 pounds per square inch, with a line speed of 45 feet per minute. The precursor web was then dried using two stacks of steam drying cans at 300° F. The precursor web had a basis weight of 1.5 ounce per square yard (plus or minus 7%).  
      The precursor web the received a further 2.0 ounce per square yard air-laid layer of Type-472 PET fibrous batt. The precursor web with fibrous batt was further entangled by a series of entangling sub-manifolds, with the sub-manifolds successively operated at 100, 300, and 600 pounds per square inch, with a line speed of 45 feet per minute. The entangling apparatus of  FIG. 1  further includes an imaging drum  18  comprising a three-dimensional image transfer device for effecting imaging of the now-entangled layered precursor web. The image transfer device includes a moveable imaging surface which moves relative to a plurality of entangling manifolds  22  which act in cooperation with three-dimensional elements defined by the imaging surface of the image transfer device to effect imaging and patterning of the fabric being formed. The entangling manifolds  22  included 120 micron orifices spaced at 42.3 per inch, with the manifolds operated at 2800 pounds per square inch each. The imaged nonwoven fabric was dried using two stacks of steam drying cans at 300° F.  
      The three-dimensional image transfer device of drum  18  was configured with an image forming surface consisting of a pattern, as illustrated in  FIG. 2 .  
     EXAMPLE 4  
     Spunlace with Scrim  
      A composite nonwoven fabric was formed with the arrangement of  FIG. 1 . The entangled layer was produced using 1.5 denier polyester staple fibers at 1.5 inch staple length which were carded, cross-lapped and entangled using a Perfojet 2000 Jetlace entangler. The PET scrim layer  16  was a 7×5 mesh, 70 denier scrim available from Conwed Plastics of Minneapolis, Minn. A thermally bonded, 2.0 denier polyester thermally bonded fibrous layer was used as the bonded layer  20 , with a 50 gsm target basis weight.  
      The fibrous layers were unwound at 40 feet per minute and impinged with three successive manifolds  22  each operating at 4000-psi pressure. Each manifold  22  had 120-micron diameter orifices spaced at 42.3 orifices per inch.  
     EXAMPLE 5  
     Spunbond with Film Extrusion  
      A base material was supplied in the form of a prewound roll of 85 gram per square meter (gsm) spunbond polypropylene having been previously hot calendered with a 14% land area pattern. To this base material a co-polyester film extrusion was applied by the use of a five zone extruder system. The co-polyester polymer blend was comprised of an ethyl methyl acrylate at 65% (w/w) and a co-polyester polymer at 35% (w/w). The five zone extruder was operated with each successive zone at 3501 F., 450° F., 485° F., 525° F., and 515° F. The melt temperature of the molten film extrusion was 477° F. The cast station temperatures were 80° F. for the nip roll, 65° F. for the cast roll, and 70° F. for the stripper roll. The cast station roll pressures were 75 pounds per square inch for the nip roll and 60 pounds per square inch for the stripper roll. Overall line speed during the processing of this material was 51 feet per minute.  
     EXAMPLE 6  
     Mechanical Compaction of Nonwoven Fabric  
      Nonwoven fabrics may be further treated by mechanical compaction should the protective article require enhanced conformability.  
      —Sanforizing— 
      In order to enhance softness and drapeability of the present nonwoven fabric, the fabric may be subjected to slight mechanical compaction, such as by sanforizing (Sanforized® is a registered trademark of Cluett, Peabody &amp; Co., Inc.). Such treatment has been found to enhance hand and drapeability of the fabric, without adversely affecting the mechanical characteristics of the fabric or being deleterious to the image imparted therein.  
      —Micrexing— 
      The nonwoven fabric used for the present invention can be subjected to mechanical compaction by a microcreping process. The particular microcreping process employed was that as is commercially available from the Micrex Corporation of Walpole, Mass., and is referred to by the registered mark of the same company as “MICREX”. The apparatus for performing MICREXING is described in U.S. Pat. Nos. 3,260,778; 3, No. 416,192; No. 3,810,280, No. 4,090,385; and No. 4,717,329, hereby incorporated by reference. In such an apparatus, a means for imparting pressure applies a predetermined amount of pressure through a substructure, and extending across the path of a continuously supplied sheet of nonwoven fabric. The nonwoven fabric is carried by a rotating drive roll on which the pressure is imparted through the nonwoven fabric and against the rotating drive roll. While the nonwoven fabric is under applied pressure it then further impinges upon a retarding surface. This retarding surface in combination with the applied pressure induces the fabric into a creped form, with a resulting distortion of constituent fibrous components out of the planar aspect of the original nonwoven fabric.  
      From the foregoing, numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiment disclosed herein is intended or should be inferred. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.