HEAT SHRINK SYNTHETIC MESH STRUCTURE

Abstract: A mesh structure (10) is formed from a set of a warp strands (12) and a set of intersecting weft strands (14). The warp strands are formed of a knitted synthetic material which shrinks when exposed to heat, and the weft strands pass through the weave of the warp strands at the nodes where the strands intersect. Heat is applied to the mesh structure to shrink the weave of the warp strands tightly around the weft strands at the nodes, thereby co-joining the weft and warp strands to form a high-strength mesh.

Description: HEAT SHRINK SYNTHETIC MESH STRUCTURE FIELD OF THE INVENTION This invention relates to mesh structures such as those used for cargo restraint nets, and to methods for the manufacture of such mesh structures. BACKGROUND OF THE INVENTION Cargo restraint nets are used in many different shipping and transportation applications to prevent undesired shifting of cargo. Such netting is typically made from a high strength mesh structure which may be formed from any of numerous suitable materials and processes. Among the materials commonly used for such nets are synthetic fibers, such as coated polyesters, multi-filament polypropylenes, nylons and mixtures thereof, which are formed into elongated members or strands. These strands are then used to create a mesh structure by various methods such as weaving, knitting, rochelle, or weft insertion. One technique used to form mesh is to knot the warp and weft strands together at their points of intersection. This, however, results in an inherent weakness at the knots due to stress concentrations. In cases where the strands are made of synthetic material, it is also known to bond the warp and weft strands together at the intersections by heat or chemical welding. Welding of synthetic strands can also lead to weakness at the joints. U.S. Patent No. 4,000,344 teaches a netting formed by threading each strand through a hole formed in the other strand at the intersection point. After completion of this weaving process, the net may be impregnated with a binding agent to cause the synthetic fibers of each strand to cohere, thereby promoting the non-slip quality of the intersections. It is known that some types of synthetic materials, such as thermoplastics, shrink when heated to a temperature below the melting temperature of the material. SUMMARY OF THE INVENTION In carrying out this invention in the preferred embodiment described and depicted herein, a mesh structure comprises first and second sets of intersecting elongate members, referred to a weft strands and warp strands respectively. The warp strands are knitted or woven from threads formed from synthetic fibers which shrink when heated, and the weft strands pass through the weave of the warp strands at the points of intersection, hereinafter referred to as "nodes. " Heat is applied to the mesh structure to shrink the weave of the warp strands tightly around the weft strands at the nodes, thereby co-joining the weft and warp strands to form a high-strength mesh. In a preferred embodiment of the invention method for producing a synthetic mesh, the mesh is heated by exposing it to the rays of an ultraviolet lamp. The ultraviolet heating can be precisely controlled in both intensity and time of application, so that the warp strands may be heated just enough to achieve the desired amount of shrinkage without melting either the weft or warp strands. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a section of a mesh structure according to the present invention; and Figure 2 is a detail view of a node of the mesh structure of Figure 1 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in Figures 1 and 2, a representative section of a mesh structure 10 according to the present invention comprises a plurality of elongated warp strands 12 disposed in a generally parallel arrangement, and a plurality of elongated weft strands 14 oriented generally perpendicular to the warp elements. While Figure 1 depicts a mesh wherein all of the strands 1 2, 14 are mutually parallel and perpendicular, the present invention is not limited to such a mesh but rather may be practiced with meshes having any pattern of intersecting weft and warp strands. The warp strands 1 2 are narrow straps knitted or woven from threads composed of synthetic fibers which shrink when heated to a temperature below the temperature at which it begins to melt. Polypropylene is one example of such a material. The weft strands 14 may be made of any suitable material, but are preferably a twisted twine formed of synthetic fibers such as polypropylene. The weft strands 14 pass through the weave of the warp strands 1 2 so that at each node the weft strands are completely surrounded by the threads that make up the weave of the warp strands. This may be achieved by a weft insertion process. The mesh structure 10 is then heated to a temperature below the melting point of the material of the warp strands 1 2, but sufficiently high to cause the weave of the warp strands to shrink and constrict tightly around the weft strands 14 passing therethrough. This constriction of the warp strands 1 2 causes them to grip the weft strands 14 tightly so that the weft strands do not slide relative to the warp strands. The correct temperature and duration of the heating of the warp strands 1 2 to achieve the desired shrinkage depends upon many factors. Among these factors are the type and denier of the synthetic fibers which make up the threads, and the size and thread density of the strands 12. The mesh 10 may be heated by any suitable means, such as radiant heat, convection heat, or by ultrasonic waves. In the preferred embodiment, however, the mesh structure 10 is heated by exposing it to the rays of an ultraviolet lamp. It has been found that ultraviolet heating of the mesh may be very precisely controlled in both intensity and time of application so that the warp strands 1 2 are heated just enough to provide an sufficient shrinkage to co-join the strands but are not overheated to the point where they begin to melt or otherwise negatively affected. Only the warp strands 12 of the invention mesh structure 10 need to shrink in order to co-join the weft strands 14 and warp strands. Accordingly, it may be desirable to form the warp strands 1 2 of a first material which shrinks when heated to a given temperature, and form the weft strands 14 of a second material that does not shrink at the given temperature. It is also possible to achieve differential heating of the weft strands 14 and warp strands 1 2 by using differently colored materials for the two strands. Specifically, the warp strands 1 2 may be formed of a relatively dark colored material and the weft strands 14 of a relatively light colored material. When the mesh structure 10 is exposed to a radiant heat source, the darker colored warp strands 1 2 will heat more quickly than the lighter colored weft strands 14 so that the warp strands 1 2 reach the temperature at which the desired shrinkage occurs prior to the weft strands 14 reaching the same temperature. Although it is not necessary to shrink the weft strands 14, heating the mesh to shrink the warp strands 1 2 may have a beneficial effect on weft strands formed from synthetic fibers. For example, if the weft strands 14 are of a twisted construction, the application of heat may bond or fuse the exterior fibers of each weft strand together, making the exterior of the strand more resistant to abrasion and less likely to fray. The warp and weft strands may be of any desired size, and they may be spaced from one another to create a mesh of any desired size depending on the intended usage of the mesh. In a preferred embodiment of the invention, the warp strands 1 2 are approximately 4 mm. wide and 2 mm. thick and are spaced approximately 25 mm. apart. The twisted weft strands 14 are approximately 2 mm. in diameter and are arranged in closely spaced pair relative to the overall mesh size. The weft strands 14 of each pair are spaced approximately 3 mm. apart, and the pairs are approximately 25 mm. apart. This arrangement results in a mesh having generally equal strengths in both the weft-wise and warp- wise directions. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims: The invention claimed is: 1 . A mesh structure comprising: a set of warp strands formed of a knitted synthetic material which shrinks when subjected to heat; and a set of weft strands intersecting the warp strands at nodes, the warp strands and the weft strands co-joined at the nodes by passing the weft strands through the warp strands and heating the mesh structure to shrink the warp strands around the weft strands. 2. The mesh structure of claim 1 wherein the weft strands are a twisted twine formed of synthetic fibers. 3. The mesh structure of claim 1 wherein the weft strands are arranged in relatively closely spaced pairs. 4. The mesh structure of claim 1 wherein the weft strands and the warp strands are composed of polypropylene. 5. The mesh structure of claim 1 wherein the weft strands have a relatively light colored exterior surface and the warp strands have a relatively dark colored exterior surface. 6. The mesh structure of claim 1 wherein the weft strands and the warp strands are formed of different materials having differing physical responses to a given level of heating. 7. A method of making a mesh structure comprising the steps of: providing a plurality of warp strands formed of a knitted synthetic material which shrinks when subjected to heat; providing a plurality of weft strands intersecting the warp strands and passing through the warp strands at nodes; and heating the mesh structure to shrink the warp strands around the weft strands to co-join the warp and weft strands at the nodes. 8. The method according to claim 7 wherein the step of heating the mesh is performed by exposing the mesh to ultrasonic waves. 9. The method according to claim 7 wherein the step of heating the mesh is performed by exposing the mesh to ultraviolet rays. 10. The method according to claim 7 wherein selective heating of the mesh structure is achieved by providing weft strands having a relatively light colored exterior surface and warp strands having a relatively dark colored exterior surface. 1 1 . The method according to claim 7 wherein the weft strands and the warp strands are formed of different materials having differing physical responses to a given level of heating. 1 2. The method according to claim 7 wherein the weft strands are passed through the warp strands by a weft insertion process after the warp strands have been knitted.

Inventors: MOORE DONAL, MOORE, DONAL
Applicants: POLYTECH NETTING L P, POLYTECH NETTING, L.P.
Application year: 2000
Main classification: D03D15
IPC codes: B60P7, D03D9, D03D15, D04C1