GB1585514A

GB1585514A - Plastics net

Info

Publication number: GB1585514A
Application number: GB2120777A
Authority: GB
Original assignee: ELLINIKI BIOMIHANIA
Current assignee: ELLINIKI BIOMIHANIA
Priority date: 1977-05-19
Filing date: 1977-05-19
Publication date: 1981-03-04
Also published as: IT1080116B; ES234299U; ES234299Y; ES462125A1

Description

(54) PLASTICS NET (71) We, ELLINIKI BIOMIHANIA EPEXER GASIAS PLASTIKON ILON "EBEPY" ANONY MOS ETERIA, a Company incorporated under the laws of Greece, of 5 Serbou Street, St. John Rentis, Athens, Greece, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to integral plastics net structures, that is to say nets in which the strands and their joining points are integral with one another and are not connected by knots or the like. Although the invention is particularly applicable to nets of medium gauge suitable for agricultural and horticultural purposes, it may be applied to nets of substantially all gauges.

Although it is usually sufficient for a net to be of relatively fine gauge over most of its area to enable it to perform its function of, for example, supporting crops to be dried or preventing the access or egress of birds or animals, it is frequently the case that certain parts are not sufficiently strong for the function which they are to perform so that it is necessary to use a net which is stronger than is required over most of its area in order to provide adequate strength in those certain parts. For example, nets often have to be anchored around their edges where they frequently have to be doubled. In addition, it is common to use double nets, namely a fine net having the necessary mesh size and a coarse net which acts to provide reinforcement to give sufficient strength to the fine net.

According to the first aspect of the present invention, an integral plastics net structure has reinforcing regions integral therewith, the reinforcing regions consisting of or including isolated thickened anchorage regions spaced around at least a part of the margin of the net structure. Thus, the net structure is not uniform over its entire area but has anchorage regions and possibly other areas which are integral therewith but contain a greater quantity of plastics to provide additional strength. Thus, the structure may comprise a first set of strands extending in a first direction and a second set of strands extending in a second direction, the strands of the two sets being connected at the crossing points, and the reinforcing regions including bands which are of greater crosssection than the strands of the first and second sets and cross at least one of the sets and are connected to the strand which they cross. The reinforcing bands may be of substantially the same thickness as the strands, that is to say their dimensions perpendicular to the general plane of the net n:ay be substantially the same as that of the strands, in which case they will, of course, be substantially wider than the strands to provide the greater cross-section.

Alternatively or in addition, the bands may be thicker than the strands in the said direction perpendicular to the general plane of the net. The cross-sectional area of each of the bands is preferably at least twice (or at least 5, 10 or 20 times) the cross-sectional area of each of the strands.

In a preferred construction the net has a rectangular mesh structure and at least some of the bands extend parallel with one of the parallel pairs of sides of each of the rectangles. In addition, other of the bands may extend parallel with the other of the parallel pairs of sides of each of the rectangles. Alternatively or in addition, there may be bands which extend in a direction which is inclined to the sides of the rectangles.

Each anchorage region may have a hole extending through it from one side of the net structure to the other to provide what may be thought of as an eyelet. The anchorage regions provide reinforcements by which the anchoring loads may be transferred to the main body of the net.

The integral plastics net structure according to the first aspect of the present invention may be produced in various ways and may involve stretching. Thus, according to a second aspect of the present invention, a precursor to a plastics net structure according to the first aspect comprises a plastics sheet having perforations or thinned portions adapted to form the apertures of the structure on stretching in the plane of the sheet and having regions which on stretching will produce the reinforcing regions. The amount of stretching required may vary from case to case. Thus, the precursor may need stretching by only a small amount, for example by less than twice its original dimensions, where the precursor is produced in net-like form and the stretching is only required to adapt the precursor to particular required dimensions. On the other hand, the precursor may be very compact and require streching of its dimensions by many times in order to produce the final net.

The net structure or precursor may be produced in various ways. For example, a sheet of plastics material which is appropriately provided with thickened regions to provide the reinforcing regions may be perforated by any of the ways well known for perforating plastics sheet. The perforated sheet may be ready for use or may be stretched either along a single axis or biaxially. However, according to another aspect of the present invention, a method of manufacturing an integral net structure according to the first aspect of the invention or a precursor according to the second aspect of the present invention comprises passing a sheet of plastics material between a pair of rolls at least one of which has a pattern of recesses and/or projections formed in its surface, the recesses and/or projections being shaped to produce the net or precursor. In many cases, actual apertures can be produced in the product coming from the rolls only if considerable contact pressure between the rolls is maintained.

If less pressure is maintained, thin films will remain over those areas of the product from the rolls which are to provide the mesh openings in the finished net but such films provide weak points which can be converted to actual apertures during a subsequent stretching process.

The rolls may form part of a calender on which the plastics sheet is produced and may be the penultimate or the last roll of the calender. Preferably, both the rolls of the said pair have surfaces differing from the smooth cylindrical surface and thus the second roll may have recesses in its surface which may coincide at the nip between the two rolls with recesses in the first roll or may not so coincide; in a preferred arrangement one of the pair has recesses and the other has projections. For example, one of the rolls may have a pattern of fine projections in the nature of pins to provide fine depressions or apertures in the resulting sheet which is a precursor for a net, the depressions or apertures producing the meshes of the net on stretching. The stretching is preferably biaxial stretching and is performed with the precursor hot.

Various plastics materials may be used for making the net structure, including polypropylene, polyethylene, polyester and nylon.

The invention may be carried into practice in various ways but an integral plastics net structure in accordance with the invention and precursors for such net structures and methods of producing such precursors and net structures will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of a section of net structure; Figure 2 is a detail view to a larger scale of an edge portion of the net structure shown in Figure 1; Figure 3 is a detail view similar to Figure 1 showing how the net structure may be supported; Figure 4 is an end elevation of a calender for the production of a precursor for the net structure; Figure 5 is a somewhat simplified front elevation of the penultimate roll of the calender shown in Figure 4; Figure 6 is a simplified longitudinal section of the roll shown in Figure 5 taken on the plane VI-VI in Figure 5; Figure 7 is a simplified cross-section of the roll taken on the plane VII-VII in Figure 5; Figure 8 is an enlarged detail of the portion indicated by the ring VIII in Figure 7; Figure 9 is a diagrammatic view of a calender similar to that shown in Figure 4 used to produce another precursor to a net structure; Figure 10 is a detail view to an enlarged scale of the area indicated by the ring X in Figure 9; Figure 11 is a diagrammatic plan view of the precursor produced by the calender shown in Figure 9; Figure 12 is a detail cross-section to an enlarged scale of the precursor shown in Figure 11 taken on the plane XII-XII in Figure 11; and Figure 13 is a cross-section similar to Figure 12 of another form of precursor.

The net structure shown in Figures 1, 2 and 3 is of integral plastics construction and is made of polypropylene. In the central section it is composed of a first set of parallel strands 1 and a second set of parallel strands 2 which cross the strands of the first set at right-angles to produce a mesh, the strands of the two sets being connected to each other at their crossing points at integral junction zones. The strands of the two sets lie in the same plane and are of the same cross-section but in modified nets they lie in slightly spaced parallel planes and they are of different cross-sections. At intervals both across and along the net there are integral reinforcing bands 3, 4 which extend parallel with the strands 1 and 2 respectively and, as can be seen in Figure 2, these reinforcing bands are both wider and thicker than the strands 1 and 2 and have cross-sectional areas which are approximately five times that of the strands 1, 2. The bands have one surface (the undersurface as seen in Figure 2) which lies in the same plane as the corresponding surface of the strands 1 and 2 but they project above the plane containing the upper surfaces of the strands 1 and 2. In a modified net the reinforcing bands extend beyond the planes containing the strands on both sides of the net. The bands are, of course, integrally connected to the strands where they cross them. At the upper edge as seen in Figure 1 there is a reinforcing band 5 along the edge of the net but on the right-hand edge as seen in Figure 1 there is a reinforcing band 6 which is spaced from the extreme edge of the net by three of the strands 1. It will also be seen that adjacent the band 6 the strands 1 are closer together to provide a marginal area 20 in which the mesh is rectangular.

Spaced at intervals around the edges of the net are reinforcing regions 7 which can be seen in greater detail in Figure 2. Each reinforcing region 7 comprises a square zone which is substantially thicker than the strands and the bands and is connected integraily therewith. The reinforcing regions project upwardly above the level of the reinforcing bands. Each region 7 has a hole 8 extending therethrough by which the net can be anchored. One method of anchoring can be seen in Figure 3 where one of four vertical corner posts 9 is shown. These corner posts are connected by straining wires 11, 12 to which the net is connected by double hooks 13, one hook end of which engages a straining wire and the other hook end of which passes through the aperture 8 of one of the reinforcing regions 7.

Figure 1 may be considered to show only part of a complete net which is produced in one piece or alternatively may be considered to show a section which is joined, for example by ultrasonic welding, to similar sections to produce the final product.

A precursor for a net similar to that shown in Figure 1 may be produced on the apparatus shown in Figures 4 to 8. Figure 4 shows a calender 30 consisting of three heated rolls 31, 32 and 33 arranged one above the other and a fourth heated roll 34 arranged alongside the roll 33. A supply of plastics material is maintained above the nip between the rolls 33 and 34 and a continuous plastics sheet is formed which passes between the rolls 33 and 32 and between the rolls 32 and 31 where it is modified to form the precursor which is finally taken off to the left of the machine to pass to ancillary equipment for producing the net from the precursor. The penultimate roll 32 of the calender is shown to a larger scale in Figures 5, 6 and 7 where some parts are shown distorted for clarity and to an even larger scale in Figure 8. It will be seen that, in contrast with the normal roll of a calender which is smooth and has a substantially constant diameter, the roll 32 has recesses ground into it, these recesses converting the sheet to the net precursor. Thus, the roll has circumferential grooves 35 to produce the reinforcing bands 3 and 6 and longitudinal grooves 36 to produce the reinforcing bands 5. Extending parallel with these grooves and omitted for clarity from Figures 5 to 7 are shallow grooves 37 and 38 corresponding to the strands 1 and 2.

Adjacent the ends of the roll and in way of the outermost grooves 35 there are deeper square recesses 39 to produce the reinforced anchorage regions 7.

The sheet which is produced between the rolls 33 and 34 and passes between the rolls 33 and 32 will be squeezed between the rolls 32 and 31 so that the material fills all the recesses in the roll 32 and the material is either completely squeezed out of the remaining portions of the nip or is reduced to a very thin film depending upon the pressure between the rolls 32 and 31.

The resulting sheet which is either perforated or heavily recessed is taken from the calender along the line 40 and while still hot is passed to a biaxial stretching machine where it is stretched in two directions at right angles, i.e. along the strands 1 and the strands 2, to produce a net structure as shown in Figure 1.

Although recesses are shown in only the roll 32, there may also or alternatively be recesses in the roll 31. Also, although it is suggested that the precursor should be passed directly to the stretching machine, this is not essential and stretching can be performed on a machine remote from the calender with reheating if necessary.

The calender shown in Figure 9 has four rolls 41, 42, 43 and 44 corresponding to the rolls 31 to 34 of the calender shown in Figure 4. In this case the roll 42 has circumferential grooves 45 and longitudinal grooves 46 which provide bands in the precursor which ultimately will provide the reinforcing bands in the finished net structure.

The rolls 41 and 42 are not passed together so close that in the areas in which there are no grooves the plastics material is squeezed out completely from the nip but an unperforated sheet is allowed to pass from the nip and around the roll 41. The surface of the roll 41 is covered with a plurality of needles arranged on a square pattern, these needles being arranged in square blocks so that circumferential and longitudinal strips free of needles register with the grooves 45 and 46 of the roll 42, as can be seen more clearly in Figure 10. The resulting sheet can be seen in Figures 11 and 12 and has on one side ribs 48, 49 corresponding to the grooves 45, 46 and on the other side recesses 51 produced by the needles 47. After the sheet forming the precursor has left the calender as indicated by the arrow 52, it is biaxially stretched while still hot so that the thin film portions 53 between the recesses 51 are stretched to breaking point and open out to form the meshes of the net. The portions between the recesses 51 are stretched to form the crossing strands of the net while the ribs 48 and 49 are stretched to form the reinforcing bands. The resulting net structure is similar to that shown in Figure 1. It will be appreciated that if the plastics material for making the precursor is appropriately selected this stretching opeartion will result in an orientation of the molecules along the lengths of the strands and reinforcing bands thus strengthening the resulting net.

In the calender shown in Figure 9 the needles are placed on the roll 41 but it is possible for the needles to be on the roll 42 and for the roll 41 to be smooth or for the roll 42 to be smooth and for the roll 41 to have both the grooves and the needles.

A precursor resulting from the latter arrangement is shown in Figure 13.

Although the manufacture of net structures has been described only via precursors, it will be appreciated that the manufacturing method described with reference to Figures 5 to 8 can be modified to produce the final net structure directly. All that is required is for the pattern of recesses on the roll 32 to be appropriate. Thus, the grooves will have to be much shallower and spaced much further apart than is indicated in Figure 8.

WHAT WE CLAIM IS: 1. An integral plastics net structure having reinforcing regions integral therewith, the reinforcing regions consisting of or including isolated thickened anchorage regions spaced around at least a part of the margin of the net structure.

2. An integral plastics net structure as claimed in Claim 1 in which each anchorage region has a hole extending through it from one side of the net structure to the other.

3. An integral plastics net structure as claimed in Claim 1 or Claim 2 in which the structure comprises a first set of strands extending in a first direction and a second set of strands extending in a second direction, the strands of the two sets being connected at the crossing points, and the reinforcing regions include bands which are of greater cross-section than the strands of the first and second set and cross at least one of the sets and are connected to the strands which they cross.

4. An integral plastics net structure as claimed in Claim 3 in which the net has a rectangular mesh structure and at least some of the bands extend parallel with one of the parallel pairs of sides of each of the rectangles.

5. An integral plastics net structure as claimed in Claim 4 in which other of the bands extend parallel with the other parallel pair of sides of each of the rectangles.

6. An integral plastics net structure as claimed in Claim 3 or Claim 4 or Claim 5 in which at least some of the bands extend in a direction which is inclined to the sides of the rectangles.

7. An integral plastics net structure as claimed in any of Claims 3 to 6 in which the cross-sectional area of each band is at least five times the cross-sectional area of each strand.

8. An integral net structure as claimed in any of Claims 2 to 7 in which each thickened region has at least one reinforcing band terminating therein or passing there through.

9. An integral plastics net structure sub stantially as described herein with reference to Figures 1 to 3 of the accompanying draw ings.

10. A precursor to a plastics net struc ture as claimed in any of the preceding claims which comprises a plastics sheet having perforations or thinned portions adapted to form the apertures of the structure on stretching in the plane of the sheet and having regions which on stretching will pro duce the reinforcing regions.

11. A precursor to a plastics net structure as claimed in Claim 1, the precursor being substantially as described herein with reference to Figures 11 and 12 or to Figures 11 and 13 of the accompanying drawings.

12. A method of manufacturing an integral plastics net structure as claimed in any of Claims 1 to 9 or a precursor as claimed in Claim 10 or Claim 11 which comprises passing asheet of plastics material between a pair of rolls at least one of which has a pattern of recesses and/or projections formed in or on its surfaces, the recesses and/or projections being shaped to produce the net or precursor.

13. A method as claimed in Claim 12 in which the rolls form part of a calender on which a plastics sheet is produced.

14. A method as claimed in Claim 13 in which the penultimate roll of the calender has the recesses and/or projections and the remaining rolls are smooth.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. needles being arranged in square blocks so that circumferential and longitudinal strips free of needles register with the grooves 45 and 46 of the roll 42, as can be seen more clearly in Figure 10. The resulting sheet can be seen in Figures 11 and 12 and has on one side ribs 48, 49 corresponding to the grooves 45, 46 and on the other side recesses 51 produced by the needles 47. After the sheet forming the precursor has left the calender as indicated by the arrow 52, it is biaxially stretched while still hot so that the thin film portions 53 between the recesses 51 are stretched to breaking point and open out to form the meshes of the net. The portions between the recesses 51 are stretched to form the crossing strands of the net while the ribs 48 and 49 are stretched to form the reinforcing bands. The resulting net structure is similar to that shown in Figure 1. It will be appreciated that if the plastics material for making the precursor is appropriately selected this stretching opeartion will result in an orientation of the molecules along the lengths of the strands and reinforcing bands thus strengthening the resulting net. In the calender shown in Figure 9 the needles are placed on the roll 41 but it is possible for the needles to be on the roll 42 and for the roll 41 to be smooth or for the roll 42 to be smooth and for the roll 41 to have both the grooves and the needles. A precursor resulting from the latter arrangement is shown in Figure 13. Although the manufacture of net structures has been described only via precursors, it will be appreciated that the manufacturing method described with reference to Figures 5 to 8 can be modified to produce the final net structure directly. All that is required is for the pattern of recesses on the roll 32 to be appropriate. Thus, the grooves will have to be much shallower and spaced much further apart than is indicated in Figure 8. WHAT WE CLAIM IS:

1. An integral plastics net structure having reinforcing regions integral therewith, the reinforcing regions consisting of or including isolated thickened anchorage regions spaced around at least a part of the margin of the net structure.

15. A method as claimed in Claim 13

in which one of the pair of rolls has recesses and the other has projections.

16. A method as claimed in Claim 13 or Claim 14 or Claim 15 in which a precursor is produced on the calender and is passed while still hot to a biaxial stretching machine on which it is stretched to produce an integral plastics net structure.

17. A method of manufacturing an integral plastics net structure as claimed in Claim 1, the method being substantially as described herein with reference to Figures 4 to 8 or to Figures 9, 10, 11 and 12 or to Figures 9, 10, 11 and 13 of the accompanying drawings.