Patent Publication Number: US-2015064415-A1

Title: Agricultural covering

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to woven fabrics, more particularly, to a woven plastic fabric for agricultural use and method for making such. 
     BACKGROUND OF THE INVENTION 
     With the aim of extending the season of various fruits, such as, for example, table grapes, cherries, and soft berry fruits, the use of coverings, such as plastic covers installed to form a canopy, has become very popular and common in agriculture, to the point that it is now considered almost essential for producers looking to satisfy market demand. When placed over the plants in late winter-early spring, such coverings raise the air temperature below the installed coverings, and early fruiting and harvesting can be induced. In late fruit varieties harvesting may be delayed by installing coverings extending the time span the fruits may be offered on the market. Additionally, such a covering protects plants and fruits against damage from rain, hail, or wind. For example, excessive rain during the time approaching harvest can have a seriously deleterious effect on table grapes which may develop a variety of diseases or the grapes itself may burst open if they remain wet for too long. As a result a good crop can be seriously affected, both in quality and quantity. Furthermore, such a covering can reduce the temperature dissipation during night and reduce the plant stress coming from high energetic sunrays through a light diffusion effect and/or light filtering effect. 
     Examples for such coverings are agricultural films, woven fabric sheets, foils, or nets. The coverings are typically tied with tie-down ropes, also called guy ropes or tie-down strings, to structures such as poles or wires or to the ground. In order to do so, the tie-down ropes have to be attached to the plastic cover in a matter that is reliable, inexpensive, and easily done without undue labor. This is currently typically done by integrating holes into the coverings, for example, by moving the strands aside to make a hole, by interweaving an additional and stronger warp thread to position weft threads to form an opening in the fabric (see, for example, JP 10292245), by cutting holes, or by putting eyelets or grommets, such as metal grommets (see, for example, EP1728417), into a border region of the coverings, through which a tie-down rope or other securing element can be placed. Other methods to attach the coverings to a structure or to the ground include using clamps or clips trapping the covering (see, for example, U.S. Pat. No. 5,557,830). While clamps are very effective and distribute the load over a wider range of the covering, they are bulky and expensive. Therefore, clamps typically have to be removed from the covering at the end of each season for storage and then re-attached to the covering at the begin of the following season, which is labor intensive. In order to avoid tearing in the area of the holes or clamps due to the stress induced when the coverings are under tension, the areas of the coverings where the holes or clamps are positioned are often reinforced (see, for example, U.S. Pat. No. 4,044,501). To improve or achieve water impermeability of the coverings and to increase the breaking strength of the coverings, a plastic coating is often applied to at least on side of the covering. But application of such a coating comes with the disadvantage of decreasing the tear resistance and tear propagation resistance of the covering. 
     As problem with existing plant and fruit coverings still remains the attachment or anchoring of the coverings to structures or to the ground that does not lead to tearing of the covering under tension, particularly as a result of wind action on the covering while being practical and inexpensive. A further unsolved problem with known prior art woven coverings is the unlimited (in machine direction) tear propagation of the impermeable part of the cover. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an agricultural covering in form of a woven plastic fabric and a method for making the same. An advantage of embodiments of the present invention is that forming an area having a lower density of warp threads per unit width within an area having a higher density of warp threads per unit width can easily be done during the weaving process and at lower costs. Additionally, the elimination of metal eyelets or grommets facilitates the process of recycling the coverings that have ended their cycle life. The area having a lower density of warp threads per unit width is large enough to allow effortless threading of a securing element, for example a tie-down rope, through the fabric to encircle a plurality of weft threads and at the same time small enough not to cause a substantial loss of overall strength of the fabric. A further advantage of embodiments of the present invention is that due to the elastic nature of, for example, polyethylene, polyamide, polypropylene, ethylene-vinyl acetate, or any other polymer material, the encircled weft threads extend and bunch together when the securing element is under tension. Additionally, the weft threads have a relatively high Youngs modulus and a relatively high elongation at break. Therefore, each of the encircled weft threads contributes to the overall result because the stress and strain are shared between all the weft threads in the bunch. As a result, a stress raising point of neighboring weft and warp threads will not be created. Accordingly, the fabric has an improved resistance to tearing and tensile forces compared to prior art fabrics typically used as agricultural coverings. It is a still further advantage of embodiments of the present invention that once installed the securing elements, for example the tie-down ropes, can be left in place when the covering is rolled for storage, since there is only an insignificant increase in volume. As the fabric sheets of the coverings might be very long, for example about 100 meters, any increase in thickness would accumulate and cause problems. By leaving the tie-down ropes in place there is no need to re-thread them and the covering is ready for the next season once unrolled. 
     The above objective is accomplished by a system and a method, according to the present invention. 
     Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. 
     According to the advantageous embodiments of the present invention, a plastic fabric woven from warp threads extending in machine direction and weft threads extending in cross-machine direction, the width of the fabric being defined by two border edges running along the machine direction, comprises a waterproof plastic coating applied to at least one surface of the fabric, the coating covering the fabric partially leaving a strip adjacent to each of the borders uncoated. Leaving the strip uncoated is advantageous since a center portion of the fabric is mechanically strengthened in addition to being made impermeable, while the uncoated strip remains un-strengthened allowing the weft threads to bunch together when the securing element encircling the weft threads is under tension resulting in a combination of high tensile strength and high tear propagation resistance of the uncoated strip. The plastic coating is extruded onto the fabric. The plastic fabric has a first area with a first density of warp threads per unit width of the fabric and second areas with a second density of warp threads per unit width of the fabric positioned on either side of the first area and running along with the first ales in machine direction, the second density being lower than the first density, the second areas being located within the uncoated strips, and the second areas extending over the entire length of the fabric. The second density is adapted to allow threading of a securing element through the fabric in machine direction. Utilizing an area having a lower density of warp threads per unit width of the fabric is advantageous for effortlessly threading the securing element through the fabric. By interweaving the weft threads with the warp threads to form the woven fabric, the fabric provides light diffusion, which has typically a positive influence on the regular growth of fruits with improved coloring and ripening. 
     In accordance with a further embodiment of the present invention, the plastic fabric further comprises third areas, the third areas being located between the second areas and the border edges, and the third areas having a higher density of warp threads per unit width of the fabric than the second areas. The density of warp threads per unit width of the fabric in the third areas can be the same as or similar to the one of the first areas. Positioning the third areas between the second areas and the border edges is advantageous since it strengthens the border edges. 
     In further embodiments of the present invention, the second areas are manufactured by omitting warp threads during the weaving process. This is advantages since it is then possible that a securing element is threaded through the weft threads with ease. The securing element is threaded through the weft threads to encircle a plurality of weft threads in the second area. As a result, the weft threads are bunched together by the securing element under tension. This is advantageous because the stress and strain induced by the tension are shared between all the weft threads in the bunch. As a result, a stress raising point of neighboring weft and warp strands will not be created. 
     In still further embodiments of the present invention, the second areas are positioned proximate to the center of the uncoated strips, which is advantageous for strengthening the border edges. 
     In still further embodiments of the present invention, the plastic fabric further comprises multiple spaced reinforced areas extending in the cross-machine direction of the fabric. The reinforced areas are adapted to have improved tear propagation resistance and/or improved weathering resistance and/or improved tensile strength than the non-reinforced areas. Weft threads having a higher density per unit length of the fabric and/or higher ultraviolet resistance and/or higher tensile strength than the weft threads outside the reinforced areas form the reinforced areas. The reinforced areas extend in cross-machine direction over the entire width of the fabric. The reinforced areas are equally distributed over the length of the fabric in machine direction separating the fabric into zones. Integrating the reinforced areas into the fabric is advantageous since it is possible to stop the propagation of a tear in machine direction with the reinforced areas should one occur. 
     In still further embodiments of the present invention, the fabric is used for agricultural and/or horticultural purposes and, more specifically the fabric is used for covering and protecting plants and/or fruits. Installation of the fabric to cover table grapes, cherries and soft berry fruits may be especially advantageous, since not only can rain or wind damage be prevented but also the ripening process can be positively influenced. 
     In still further embodiments of the present invention, a method for making a fabric comprises the steps of weaving a plastic fabric from warp threads extending in machine direction and weft threads extending in cross-machine direction, the plastic fabric having first areas with a first density of warp threads per unit width of the fabric and having two border edges extending in machine direction and defining a width of the fabric; and forming second areas having a second density of warp threads per unit width of the fabric that is lower than the first density, the second areas extending over the entire length of the fabric, the second density being adapted to allow threading of a securing element through the fabric to encircle a plurality of weft threads in the second areas such that the encircled weft threads are bunched together with the securing element under tension. The step of omitting a plurality of warp threads during the weaving process to form the second areas is advantageous for easy installation of the securing element. 
     In still further embodiments of the present invention, the method for making a fabric comprises the step of partially applying a plastic coating to one surface of the fabric leaving a strip adjacent to each of the border edges that is uncoated, the second areas being located within the uncoated strips. This is advantageous since the majority of the surface of the fabric is mechanically strengthened and made impermeable while the areas close the border edges remain uncoated enabling secure attachment of the securing elements while having a relatively high breaking load. A further advantage of leaving the strips adjacent to each of the border edges uncoated is an increase in tear resistance and tear propagation resistance. The decrease in breaking strength in the uncoated strips is compensated by the bunches of weft threads formed by the securing element under tension. 
     In still further embodiments of the present invention, the method for making a fabric comprises the steps of separating the fabric into zones by integrating a plurality of reinforced areas adapted to have improved tear propagation resistance, improved weathering resistance, and/or improved tensile strength than the non-reinforced areas and extending over the width of the fabric in cross-machine direction; and forming the reinforced areas spaced along the machine direction of the fabric by using weft threads having a higher density per unit length of the fabric and/or higher ultraviolet resistance and/or higher tensile strength. Integrating the reinforced areas into the fabric is advantageous since it is possible to stop the propagation of a tear in machine direction and/or deflect the tear in cross-machine direction at the reinforced areas should a tear occur. 
     The above and other characteristics, features, and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of woven plastic fabric, in accordance with an embodiment of the present invention; and 
         FIG. 2  is a sectional plan view of the woven plastic fabric under tension, in accordance with an embodiment of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates exemplary embodiments of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term “comprising” is used in the present description and claims, it does not exclude other elements or steps. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. 
     A woven plastic fabric in accordance with embodiments of the present invention includes, close to each border edge, an area having a lower density of warp threads per unit width compared to the adjacent areas that is large enough to allow effortless threading of a securing element, for example a tie-down rope, through the fabric to encircle a plurality of weft threads and at the same time small enough not to cause a substantial loss of overall strength of the fabric. Furthermore, the fabric includes multiple reinforced areas extending in a cross-machine direction of the fabric to improve the tear propagation resistance, the weathering resistance, and/or the tensile strength of the fabric. A plastic coating applied to at least one surface of the fabric makes the fabric impermeable and increases the mechanical strength of the fabric. The plastic coating is applied to the fabric such that a strip adjacent to each of the border edges is left uncoated to ensure easy and effective attachment of a securing element, such as a tie-sown rope. The woven plastic fabric in accordance with embodiments of the present invention can be used as a covering for agricultural and/or horticultural purpose, for example, for covering and protecting plants and/or fruits. The fabric is suitable for covering, for example, table grapes, cherries, and soft berry fruits, to protect the plants and fruits against damage from rain, hail, or wind and to extend the season of the fruits. 
     Referring to  FIG. 1 , a woven plastic fabric  10  is schematically illustrated in accordance with an embodiment of the present invention. The fabric  10  is woven from a plurality of warp threads  12  extending in machine direction  120  and a plurality of weft threats  14  extending in cross-machine direction  140 . The weft threads  14  interweave with the warp threads  12  to form the woven fabric  10 . The width  160  of the fabric  10  is defined by two border edges  16  running along the machine direction  120 . The border edges  16  are adapted to prevent fraying and/or raveling of the fabric  10 . The fabric  10  includes a first area  24  having a first density of warp threads  12  per unit width of the fabric, two second areas  25 , one positioned on either side in machine direction  120  of the first area  24 , having a second density of warp threads  12  per unit width of the fabric, wherein the second density is lower than the first density, and two third areas  26  each positioned between a second area  25  and a border edge  16  and having the same density of warp threads  12  per unit width of the fabric as the first area  24 . The first area  24 , the second areas  25 , and the third areas  26  extend in machine direction  120  over the entire length of the fabric. The second areas  25  are preferably positioned proximate to the center of the uncoated strips  22 . The second density of warp threads  12  per unit width of the fabric is preferably zero, which means that no warp threads  12  are present in the second areas  25 . 
     The second density of the second areas  25  is adapted to allow threading of a plurality of securing elements  30  through the fabric  10 . Preferably, each securing element  30  is threaded through the weft threads  14  to encircle a plurality of the weft threads  14  in the second area  25 . 
     The second areas  25  are preferably manufactured by omitting warp thread during the weaving process, which can be easily done not only without extra cost but at a lower cost, since warp threads  12  are omitted. If enough warp threads  12  are left out during the weaving process, for example, such that each second area  25  covers a distance of about 5 mm to 20 mm or even less depending on the thickness of the securing element  30 , the dimensions are such that a regular person does not have difficulties in threading the securing elements  30  through the weft threads  14  in area  25 . However, a loss of, for example two times 20 mm for both second areas  25  in a width of about 2.5 m to 3 m, which is a typical size for agricultural coverings, is not a great loss of overall strength. 
     The plastic fabric  10  in accordance with embodiments of the present invention is preferably made from a polyethylene material. For example, the warp threads  12  and/or the weft threads  14  can be made from a high-density polyethylene material in form of flat tapes. The high-density polyethylene material is preferably clear to allow a relatively high visible light transmittance. Other materials such as polyamide, polypropylene, ethylene-vinyl acetate or any other polymer materials can be used instead of the polyethylene material. 
     A plastic coating  18  is applied, preferably by extrusion, to at least one surface of the fabric  10 , covering almost the entire first area  24 , thereby leaving a strip  22  adjacent to each of the border edges  16  uncoated. By doing so, the center and majority of the fabric  10  is coated and, thus, made water-resistant or waterproof and also mechanically strengthened, while the strips  22  including the second areas  25  and the third areas  26  are left mechanically un-strengthened. The plastic coating  18  can be made of, for example, a low-density polyethylene material. The low-density polyethylene material is preferably clear to allow a relatively high visible light transmittance. If desired, the color and thickness of the coating can be adjusted to optimize light transmittance and temperature characteristics of the fabric for a specific plant and/or fruit. Other materials such as polyamide, polypropylene, ethylene-vinyl acetate or any other polymer materials can be used for the plastic coating. 
     A plurality of reinforced areas  28  extending in cross-machine direction  140  over the entire width  160  is formed from weft threads  29  having a higher density per unit length of the fabric and/or higher ultraviolet resistance and/or higher tensile strength than the weft threads  14  outside the reinforced areas  28 . The reinforced areas  28  are adapted to have improved tear propagation resistance and/or improved weathering resistance and/or improved tensile strength than the non-reinforced areas  24 ,  25 , and  26 . By extending over the entire length  160  of the fabric  10  and by being spaced, preferably equally, over the entire length of the fabric  10 , the reinforced areas  28  separate the fabric  10  into zones. The securing elements  30  are placed preferably within these zones. This has the advantage that should a tear in machine direction  120  originate from an attachment location of a securing element  30 , the propagation of the tear in machine direction can be stopped and/or deflected in cross machine direction at a reinforced area  28 . For example, the weft threads  29  can be made from a high-density polyethylene material in form of flat tapes. The high-density polyethylene material has preferably a higher tensile strength and/or a higher ultraviolet resistance that the material used for weft threads  14 . When using a black material for weft strands  29 , the reinforced areas may also provide some shade. Accordingly the length of the reinforced areas  28  can be adapted to the desired visible light transmittance of the entire fabric. Other materials such as polyamide, polypropylene, ethylene-vinyl acetate, or any other polymer materials can be used for the weft thread  29 . 
     Referring to  FIG. 2 , a section of the woven plastic fabric  10  under tension is illustrated in accordance with an embodiment of the present invention. As can be seen the securing element  30  is threaded through the weft threads  14  to encircle a plurality of weft threads  14  in the second area  25 . The encircled weft threads  14  are bunched together by the securing element  30  under tension  32 . This is advantageous since due to the elastic nature of polyethylene or any other polymer material the encircled weft threads  14  extend and bunch together when the securing element  30  is under tension  32 . Additionally, the weft threads  14  have a relatively high Youngs modulus and a relatively high elongation at break. Therefore, each of the encircled weft threads  14  contributes to the overall result because the stress and strain induced by the tension  32  are shared between all the weft threads  14  in the bunch. As a result, a stress raising point of neighboring weft threads  14  and warp threads  12  will not be created and the force that can be withstood before ripping or tearing (breaking load) is increased significantly compared to typical prior art agricultural covering. Accordingly, the fabric  10  is, especially in the uncoated strip  22 , mechanically stronger and has an improved resistance to tearing and tear propagation, and tensile forces  32  compared to prior art fabrics typically used as agricultural coverings. This is achieved by embodiment of the present invention without reinforcing the border region of the fabric as often done in the prior art. In the uncoated strip  22 , the decrease of breaking strength due to being uncoated is compensated by the bunches of weft threads  14  formed by the securing element  30  under tension. 
     A method for making the fabric  10  as illustrated in  FIGS. 1 and 2  includes the steps of weaving the plastic fabric  10  from warp threads  12  extending in machine direction  120  and weft threads  14  extending in cross-machine direction  140  such that the plastic fabric  10  has a first area  24  with a first density of warp threads per unit width of the fabric and two border edges  16  extending in machine direction and defining a width of the fabric. In a further step second areas  25  having a second density of warp threads per unit width of the fabric that is lower than the first density are formed such that the second areas  25  extend over the entire length of the fabric and such that the second density is adapted to allow threading of a securing element  30  through the fabric  10  to encircle a plurality of weft threads  14  in the second areas  25  such that the encircled weft threads  14  are bunched together with the securing element  30  under tension. This leads to an increased breaking strength of the second areas  25 . In a still further step, the second areas  25  are formed by omitting a plurality of warp threads  12  during the weaving process. In a still further step, a plastic coating  18  is partially applied to one surface of the fabric  10  leaving a strip  22  adjacent to each of the border edges  16  that is uncoated. The plastic coating provides impermeability to the fabric  10  and increases the breaking strength. The second areas  25  are located within the uncoated strips  22 . In a still further step the fabric  10  is separated into zones by integrating a plurality of reinforced areas  28  adapted to have improved tear propagation resistance, and/or improved weathering resistance, and/or improved tensile strength than the non-reinforced areas and extending over the width  160  of the fabric in cross-machine direction  140 . In a still further step, the reinforced areas  28  are spaced along the machine direction  120  of the fabric and are formed using weft threads  29  having a higher density per unit length of the fabric and/or higher ultraviolet resistance and/or higher tensile strength than weft threads  14 . The fabric  10  in accordance with embodiments of the present invention can be attached to structures, such as poles and/or wires, using the pre-installed securing elements  30  to form a canopy or covering for agricultural and/or horticultural purposes. 
     By providing a woven plastic fabric  10  that includes, close to each border edge  16 , an area  25  having a lower density of warp threads  12  per unit width compared to the adjacent areas  24 ,  26 , effortless threading of a securing element  30 , for example a tie-down rope, through the fabric  10  to encircle a plurality of weft threads  14  in the area  25  is enabled, while the overall mechanically strength of the fabric is maintained. When the securing element  30  is under tension, the encircled weft threads  14  bunch together increasing the breaking strength of the strips  22  located at the border edges  16  without creating a single stress point. By providing a woven plastic fabric  10  that includes multiple reinforced areas  28  spaced in machine direction  120  and extending in a cross-machine direction  140  of the fabric, the tear propagation resistance, and/or the weathering resistance and/or the tensile strength of the fabric  10  is improved. By applying a plastic coating  18  to at least one surface of the fabric  10 , the fabric is made impermeable and the mechanical strength of the fabric is increased. By applying the plastic coating  18  such that a strip  22  adjacent to each of the border edges  16  is left uncoated, easy and effective attachment of a securing element  30  is enabled. By attaching the securing element  30  to the fabric  10  in the uncoated strip  22  by encircling a plurality of weft threads  14 , the force that can be withstood before ripping or tearing (breaking load) is increased compared to typical prior art agricultural coverings. 
     It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention. For example, the various profiles may be constructed to form a framework that supports and secures panels of various sizes and functions. 
     The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention. 
     Other arrangements for accomplishing the objectives of embodiments of the present invention will be obvious for those skilled in the art.