WO1996018289A1

WO1996018289A1 - Double-walled thermal plant protector

Info

Publication number: WO1996018289A1
Application number: PCT/AU1995/000369
Authority: WO
Inventors: James Takis Demetriou
Original assignee: James Takis Demetriou
Priority date: 1994-12-15
Filing date: 1995-06-21
Publication date: 1996-06-20

Abstract

A method of and apparatus for making double-walled thermal protective devices is disclosed in which two layers of thermoplastic material (10) joined together along at least one longitudinally extending edge are fed from a roll (11) by feeding rollers (12) through a heat sealing station (14) which forms transversely extending seal lines (22) to create a plurality of transversely extending compartments (24, 124) which are adapted to be filled with water. The heat-sealed layers are then cut transversely by cutting apparatus (18) to create individual lengths (20, 120) of a thermal protective device. The individual lengths (20) may be formed into a tubular thermal protective device (50) by sealing together the ends (28) of the device. Alternatively, the individual lengths (20, 120) may be used as an elongate thermal protective device for a row of plants, with the device incorporating a hose (140) inserted in a longitudinally extending gap (127) between the layers (111, 121) for filling the compartments with water.

Description

DOUBLE-WALLED THERMAL PLANT PROTECTOR

This invention relates to double walled thermal protective devices of the kind which have a plurality of compartments adapted to be filled with a fluid, such as water, and to methods and apparatus for making such devices. Such double-walled devices can provide thermal protection and rapid growing conditions for young plants whether in the form of seeds, bulbs or seedlings.

Various types of thermal protective devices are disclosed in U.S. Patent No. 4,267,665, including a double-walled tubular device in which elongate compartments are formed between inner and outer walls which are adapted to be filled with water. In use, such a device is usually self-supporting and when placed around a growing plant provides thermal protection for the plant thereby stimulating and enhancing growth of the plant.

However, such double walled tubular device can be expensive to manufacture, often requiring complicated and expensive apparatus. It is therefore desirable to provide a more simple, economical method of making such double walled thermal protective devices.

Further, such a double-walled tubular device is usually only suitable for protecting a single individual plant and is not suitable for protecting a plurality of plants which have been planted in a row or other arrangement. It is therefore desirable to provide a thermal protective structure for a row or other arrangement of a plurality of plants.

According to one aspect of the invention there is provided a method of making a double-walled thermal protective device which is divided into a plurality of elongate, substantially parallel compartments which are adapted to be filled with a fluid, such as water, to provide a thermal protective structure for one or more plants, said method comprising the steps of: providing two layers of thermoplastic polymeric material joined together along at least one longitudinally extending edge; feeding the two layers through heat sealing apparatus in a feed direction corresponding to the longitudinal extent of said layers; heat sealing the two layers along a plurality of seal lines at intervals, the seal lines extending transversely across the layers so as to create a plurality of individual compartments; cutting the layers in a direction extending transversely across the layers; and cutting the layers again in a direction extending substantially parallel to the first cut so as to form a double-walled thermal protective device having a plurality of transversely extending compartments which are adapted to be filled with fluid, such as water.

The seal lines may be arranged to extend across the layers substantially perpendicularly to the longitudinally extending joined edges so that the resultant double-walled device has a plurality of parallel transverse compartments which extend upwards when the device is placed on the ground with the longitudinally extending joined edge forming the base. Alternatively, the seal lines may be arranged to extend diagonally across the sheet.

Preferably, the seal lines are made at regular intervals and are substantially equally spaced to form compartments of substantially the same width, although compartments of different widths may be formed if required. A double-walled thermal protective device formed by the method in accordance with the first aspect of the invention may be formed into a tubular thermal protective device by folding the heat-sealed layers so as to bring the two cut ends together and securing said ends to each other. The ends may be secured together by any convenient means, for instance by an adhesive or by securing means such as staples, but preferably the ends are joined together by heat sealing. According to a second aspect of the invention there is provided a double- walled tubular thermal protective device formed by the above-described method. In one embodiment of the present invention, the two layers of thermoplastic sheet material joined together along one edge may be formed from a single sheet of thermoplastic material by folding the sheet along a longitudinal fold line. Alternatively, two separate layers of sheet may be joined together along at least one longitudinally extending edge by securing edges of the separate layers together, e.g. by heat sealing or with an adhesive.

The two layers of the thermal protective device may be of the same width, or one layer of the device may be made slightly wider than the other layer, for instance by folding a single sheet along a longitudinally extending fold line which is slightly closer to one longitudinal edge of the unfolded sheet than the opposite edge.

According to a third aspect of the invention there is provided a method of making a double walled, tubular device which is divided into a plurality of elongate, substantially parallel compartments which are adapted to be filled with water, said method comprising the steps of: providing an elongate sheet of thermoplastic polymeric material and folding the sheet about a longitudinally extending fold line; feeding said folded elongate sheet through heat sealing and cutting apparatus in a feed direction corresponding to the longitudinal extent of said sheet; heat sealing the two layers of the folded sheet along a plurality of seal lines at internals, the seal lines extending transversely across the sheet so as to create a plurality of individual compartments; cutting the heat-sealed, folded sheet in a direction extending transversely across the sheet substantially perpendicularly to the longitudinal fold line; cutting the sheet again in a direction extending substantially parallel to the first cut after feeding the sheet through said cutting apparatus for a predetermined distance so as to form an individual length of heat-sealed folded sheet having a plurality of transversely extending compartments and cut ends extending substantially perpendicularly to the longitudinal fold line; removing said individual length of sheet from the heat sealing and cutting apparatus; folding said individual length so as to bring the two cut ends of the individual length of sheets together; and securing the two ends together to form the double walled tubular device..

In another embodiment of the invention, the transverse seal lines are arranged to extend only partly across the two layers leaving a longitudinally extending unsealed gap between the layers through which the transversely extending compartments formed by the seal lines may be filled with a fluid, such as water. A hose having a plurality of spaced apertures along its length may be inserted into said unsealed gap for filling the transversely extending compartments with a fluid, such as water.

According to a fourth aspect of the invention there is provided a double- walled thermal protective device comprising two layers of thermoplastic material joined together along at least one longitudinally extending edge, said layers being sealed together along a plurality of transversely extending seal lines to form a plurality of transversely extending compartments, wherein said seal lines extend only partly across the layers so that the device has at least one longitudinally extending unsealed gap between the layers adapted to receive filling means for filling the compartments with water or other fluid. The double walled, thermal protective device in accordance with the fourth aspect of the invention may be of any desired length, but preferably is of elongate form so that it can be used to provide thermal protection for a row of plants. For instance, the elongate thermal protective device can be used to provide thermal protection for a row of plants extending alongside a fence, wall or other structure, the elongate thermal protective device being supported at an angle to the vertical with its lower closed edge resting on the ground and the upper edge resting against the fence, wall or other structure. A support frame may be provided for supporting one or more elongate thermal protective devices in accordance with the invention. For example, a structure having one or more support members extending between upwardly extending posts may be provided for supporting one or more elongate thermal protective devices in accordance with the invention.

In one preferred embodiment, the opposite longitudinally extending edges of the layers forming the device are joined together and the longitudinally extending unsealed gap is provided adjacent one of the joined edges of the device which, in use, forms an upper edge of the thermal protective device, the opposite joined edge forming a closed, lower edge of the device.

In another preferred embodiment, the layers forming the device may be joined together along both longitudinally extending edges with at least one unsealed gap extending longitudinally at an intermediate position between the joined, longitudinally extending edges for receiving filling means for filling the compartments with water or other fluid. Such a device may be folded about a central longitudinal fold region over a support frame, such as an A-frame structure, so as to provide thermal protection on opposite sides of a row of plants with a single thermal protective device.

The filling means for filling the compartments may comprise an elongate watering element, such as a hose received in said at least one longitudinally extending gap. When the device is adapted to be folded about a central longitudinal fold region, the device may have a pair of longitudinally extending unsealed gaps on each side of the central fold region, each gap being adapted to receive a respective hose. Alternatively, such a device may have a single intermediate longitudinally extending gap in the central fold region for receiving a single hose having apertures provided in opposite sides thereof. The or each hose preferably has a plurality of apertures spaced along its length, each of said apertures being in register with a respective one of said transversely extending compartments. Preferably, at least one end of the or each hose extends out of the unsealed gap and is provided with connecting means for connecting said hose end to a supply of water or other fluid or to a hose end extending out of another similar double-walled thermal protective device.

In accordance with another aspect of the invention there is provided a thermal protective system comprising a plurality of such thermal protective devices adapted to be placed end to end with hoses of adjacent devices being connected together. Such a thermal protective system can therefore provide thermal protection and growth stimulation for a long line or row of plants in which the tubular compartments of the devices can easily be filled at the same time with fluid, such as water, from a single supply. According to a further aspect of the invention there is provided apparatus for making a double-walled thermal protective device in accordance with any of the above-described methods, the apparatus comprising heat sealing means, feeding means for feeding two layers of thermoplastic material joined together along at least one longitudinally extending edge through the heat sealing means in a feed direction corresponding to the longitudinal extent of the layers, the heat sealing means including at least one heat sealing element arranged transversely of said feed direction, and cutting means including at least one cutting device arranged transversely of said feed direction.

In one preferred embodiment, the heat sealing means comprises a single heat sealing element and includes control means for automatically operating the heat sealing element at predetermined intervals as the elongate sheet is continuously fed through the heat sealing means. In an alternative embodiment, the heat sealing means may include a plurality of heat sealing elements which are arranged to operate together to form a plurality of seal lines simultaneously.

The heat sealing element or elements may be arranged to create seal lines which extend completely across the layers of thermoplastic material. Alternatively, the heat sealing element or elements may be arranged to create seal lines which extend only partly across the layers when it is required to provide at least one longitudinally extending unsealed gap between the layers, for example to receive filling means such as a hose or other elongate watering element. The various aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic view of apparatus for making a double walled thermal protective device in accordance with the invention;

Figure 2 is a side view of a heat-sealed individual length of a thermal protective device produced by the apparatus of Figure 1;

Figure 3 is an enlarged sectional view of a heat sealing element of the apparatus of Figure 1;

Figure 4 is an enlarged sectional view of an alternative heat sealing device;

Figure 5 is a sectional view of another heat sealing device for sealing the ends of the individual length of Figure 2 together;

Figure 6 is an isometric view of a double walled, tubular device in accordance with the invention, formed from the individual length of Figure 2;

Figure 7 is a perspective view of a roll of double-walled thermoplastic material for use with the apparatus of Figures 1; Figure 8 is a side view of a double-walled thermal protective device formed from the thermoplastic material of Figure 7; Figure 9 is an end view of a roll of hose for use with the thermal protective device of Figure 8;

Figure 10 is a side view of an extended part of the hose of Figure 9;

Figure 11 is a side view of a thermal protective device incorporating a length of hose from the roll of Figure 9;

Figure 12 is a side view of a heat sealing element for forming the thermal protective device of Figure 8;

Figure 13 is a schematic isometric view from one end of another thermal protective device in accordance with the invention; Figure 14 is a plan view of the device of Figure 13;

Figure 15 is a schematic isometric view from one end of a further thermal protective device in accordance with the invention;

Figure 16 is a plan view of the device of Figure 15; and

Figure 17 is a side view of a heat sealing element for use in forming the thermal protective devices of Figures 13 to 16.

The apparatus shown schematically in Figure 1 comprises a pair of feed rollers 12 for feeding a folded plastics sheet 10 from a roll 11 to a sealing and cutting station 14 which includes heat sealing apparatus 16 and a cutting device 18.

The plastics sheet 10 is preferably formed of ultra violet stabilised polyethylene, but it may be formed from any other convenient thermoplastic material. The plastics sheet is 930mm in width and is folded along a longitudinal fold line 21 to form a double layer sheet having a closed side edge 25 where the fold line 21 extends and an opposite open edge 26. The fold is preferably such that one layer of the sheet is 460mm in width and the other layer of sheet is 470mm in width, but the sheet may be folded such that they layers are of equal width. The folded double-layer plastics sheet may be packaged in the form of a roll which facilitates feeding of the sheet through the apparatus of Figure 1. The roll is strategically loaded at one end of the conveying apparatus shown schematically in

Figure 1 and the double layer sheet is fed from the roll and tightly stretched by threading it through the feed rollers 12 which feed the sheet to the sealing and cutting station 14. Referring to Figure 3 of the drawings, the heat sealing apparatus 1 comprises a sealing rod 30 arranged above the plastics sheet 10 and a former 3 disposed below the plastics sheet 10. The sealing rod includes a heating elemen 34 which is arranged to extend transversely of the feed direction along which the sheet 10 is fed through the sealing and cutting station 14. In other embodiments, the sealing rod may be located below the plastics sheet with a former dispose above the plastics sheet, or sealing rods with heating elements may be provided above and below the feed path for the plastics sheet. As the double layered plastics sheet is fed through the sealing chamber, the sealing rod 30 is arranged to move automatically down and up repeatedly to sandwich the sheet between the sealing rod 30 and the former 32 creating transverse seals 22, approximately 2mm wide, at regular intervals which extend across the plastics sheet and which are spaced apart preferably by about 70mm. This creates individual elongate compartments 24 which extend transversely across the sheet in a direction substantially perpendicular to the feed direction. As the sheet continues its passage through the sealing and cutting station 14 the cutting device 18, which also extends transversely in a direction substantially perpendicular to the feed direction, is operated to cut individual lengths 20 of the folded, heat-sealed plastics sheet as illustrated in Figure 2. The cuts are made substantially mid way between two adjacent seal lines 22 to form free ends 28 of the individual lengths 20. In a particularly preferred embodiment, the sheet is cut to produce individual lengths 1.425 metres long and having 18 tubular compartments 24 formed by seal lines at approximately 75 mm intervals, but it will be appreciated that the number and width of tubular compartments, the length and width of the plastics sheet may be varied as required. The individual lengths 20 of the plastics sheet are then transported to end sealing apparatus 36 which is similar to the heat sealing apparatus 16 in that it comprises an upper sealing rod 40 and a lower former 42 as shown in Figure 5. At the end sealing station 36 each individual length 20 of sheet is folded about a transverse fold line so that one end 28 is on top of the other end 28, and the sealing rod 40, which includes a transversely extending heat sealing element 44, is moved down onto the ends 28 to fuse the four layers of plastics material together in an end seal 46. The resultant product 50 may then be opened up as shown in Figure 6 to form a double walled generally cylindrical tubular device 50 which has 18 separate tubular compartments 24. In use, the double walled tubular device 50 can be placed around a plant with each tubular compartment 24 being filled with a fluid, such as water so that the device can thermally protect the growing plant more efficiently.

Referring to Figure 4 of the drawings, there is shown an alternative form of heat-sealing apparatus 56 which may be used instead of the heat sealing apparatus 16 to form the seal lines 22. The heat sealing apparatus 56 comprises an upper member 58 which carries a plurality of sealing rods 60, each of which includes a heating element 64, and a lower member 61 having a number of transverse former sections 62 corresponding to the number of sealing rods 60 and heating elements 64. The upper and lower members 58 and 61 are relatively vertically movable so as to bring all of the sealing rods 60 and heating elements 64 and the former sections 62 together at the same time so as to create a plurality of seals 22 simultaneously for the entire length of the device. Thus, to form the individual length of sheet as shown in Figure 2, the heat sealing station 56 will have 18 sealing rods 60 and corresponding heating elements 64.

Referring to Figure 7 of the drawings there is shown a roll 110 of double layer thermoplastic material which may be used instead of the roll of folded plastics sheet tσ form the elongate thermal protective device as shown in Figure 8. The roll 110 of Figure 7 is formed from two layers 111 and 121 of thermoplastic material placed one on top of another and joined together along opposite longitudinally extending edges 125 and 126. The edges of the layers 111 and 121 may be joined by heat sealing, by an adhesive or by any other continuous joining means. Alternatively, the roll 110 may be formed by extruding a thermoplastic material such as a polyethylene, ultra-violet stabilised plastic film, in flat tubular form without openings at the edges 125 and 126 and rolling the material into a roll. The double layer of thermoplastic material from the roll 110 may be fed through apparatus similar to that of Figure 1 to form the thermal protective device 120 of Figure 8 which is similar to that of Figure 2. The thermal protective device 120 differs from that of Figure 2 in that the layers 111 and 121 are joined togeth along both longitudinally extending edges 125 and 126 and in that the transversel extending seal lines 122, which divide the device into a plurality of transversel extending compartments 124, extend only partly across the width of the device, th seals terminating before they reach the longitudinally extending edge 126 so as t leave a longitudinally extending unsealed gap 127 between the two layers adjace the edge 126. The ends 128 of the device are also sealed leaving a gap of the sam width adjacent the edge 26.

In a preferred embodiment, the width of the thermal protective device 12 and the width of the roll 110 of double layer thermoplastic material from which i is formed is about 930mm, the length of the device 120 is about 2400mm, the sea lines 122 are provided at about 75mm intervals, and the width of the longitudinall extending unsealed gap 127 is about 40mm. It will, however, be appreciated tha each of these dimensions may be varied as and when required for differen applications.

Referring to Figure 12, there is shown a side view of a modified heat sealin rod 130 suitable for producing the seal lines 122 in the device of Figure 8. Th lower part 131 of the sealing rod 130 has a cut away section 132 at one end wit a heating element 134 provided on the lower surface of the remaining section 13 of the rod 130. The total length of the sealing rod 130 in a preferred embodimen is about 1000mm with the length of the heating element 134 being about 890mm corresponding to the required length of the seal lines 122 in the thermal protectiv device of Figure 8.

The longitudinally extending unsealed gap 127 in double-walled heat-seale device 120 of Figure 8 is adapted to receive an elongate filling element in the for of a length of plastic hose 140 as illustrated by Figure 11. The plastic hose 14 may comprise a commercially available flat plastic tube provided with a pluralit of apertures 142 spaced at 75mm intervals along its length. The hose 140 may b supplied from a roll 141 and typically the internal cross-sectional dimensions of th flat hose are 2mm x 25mm.

The flat plastic hose 140 is threaded into the longitudinally extending ga 127 between the two layers 111 and 121 of the thermal protective device 120 as shown in Figure 11. The spaced apertures 142 are each arranged to be disposed in line with the centre of a respective tubular compartment 124 and with the apertures 142 facing the open ends of the compartments 124 where the seal lines 122 terminate. The apertures are preferably 1/16 inch in diameter. One or both of the ends of the flat plastic hose 140 projecting out of the gap 127 may be provided with standard hose connections 144 enabling the flat plastic hose 140 to be connected to a water supply by means of a standard commercially available garden hose or the like. In use, the elongate thermal protective device is placed alongside a row of young plants, seedlings or the like requiring thermal protection and growth stimulation. For this purpose, a support structure, for instance a frame having one or more horizontal support members extending between A-shaped frame members at the ends of the support frame, may be provided for the device to lean on. Alternatively, a support structure may not be necessary in some instances, such as if the device is to provide protection for a row of plants alongside a fence, wall or other structure against which the device may lean. The hose 140 within the gap 127 is then connected to a water supply and, once water pressure is applied, the plastic hose 140 increases in cross-sectional area releasing water through the apertures 142 which then flows into the individual compartments 124 of the device. The thermal protective device 140 of Figure 10 is therefore a self-filling device which may be readily installed and rapidly filled with water in contrast to devices with open upper edges such as the devices of Figures 2 and 6 which require the compartments to be filled individually by manual means. Furthermore, if co-operating connecting means such as complementary male and female connectors 144, are provided on opposite ends of the flat plastic hose 140, a plurality of thermal protective devices 120 such as illustrated in Figure 11 may be placed end to end with adjacent male and female connectors of adjacent devices being connected together to form a thermal protective system for a long line or row of plants. In such a system it will be appreciated that the tubular compartments 124 of the plurality of devices can be readily filled with a fluid, such as water, at the same time from a common supply.

Referring to Figures 13 and 14, there is shown a single thermal protective device 200 which can be placed over a support structure, such as an A-frame structure, to provide thermal protection on both sides of a row of plants or the like. The thermal protective device 200 is formed from two layers 201 and 202 of thermoplastic material joined together along its longitudinally extending edges 225. The device has two side regions 220 and a central region 210. The layers of the device 200 are sealed together along a plurality of transversely extending seal lines 222. The transverse seal lines 222 divide each side of the device into a plurality of transversely extending compartments 224. The central region 210 of the device has a central longitudinally extending seal or fold line 221. The transverse seal lines 222 on both sides of the central seal or fold line 221 extend only partly across the layers so that the device has a longitudinally extending gap 227 on each side of the central seal or fold line 221. The ends 228 of the device are also sealed together to leave a gap on each side of the central seal or fold 221. Each gap 227 is adapted to receive filling means in the form of an elongate filling element for filling the compartments 224. Each filling element preferably comprises a length of hose 240 of similar form to the hose 140 of Figures 9 to 11 having spaced apertures 242 along one side which are arranged to face the upper open ends of the compartments 224 where the seal lines terminate. One or both of the ends of the hose 240 may be provided with a hose connection 244 enabling the length of hose 240 to be connected to a water supply.

As shown in Figure 14, the transverse seal lines 222 do not extend completely across the sides 220 of the device to the side edges 225 and 226 and so they leave a longitudinally extending unsealed space 226 adjacent each side edge 225 which is in communication with each transversely extending compartment 224. The transverse seals at the ends 228 of the device also terminate short of the side edges 225 to form outlets 229 which may be conveniently closed by plugs or fluid release valves 250. In use, the thermal protective device 200 of Figure 14 is placed over a suitable support structure in such a manner that its side regions 220 extend downwardly from its central region 210 at an angle to the vertical to form a "tunnel" having an inverted "V" shape in end view as illustrated by Figure 13. The support structure is not shown in Figure 13, but it will be appreciated that the support structure may take a variety of forms. One convenient form of support structure may comprise a framework having A-frame members at its end and one or more generally horizontally members such as railings extending between the A- frame members. The support structure may be formed from any convenient material, such as plastics or metal material, including wire-mesh tubing or reinforcement steel sheeting. When the thermal protective device 200 is placed over the support structure or frame and the tubular compartments 224 are filled with water or other fluid, the weight of the fluid will assist in holding the device to the frame, and so it is possible that no retaining clips or clamps will be required to hold the device 200 in position on the frame.

When placed over a support structure and filled with water the thermal protective device 200 of Figure 14 forms a thermal protective tunnel for providing thermal protection to a row of plants within the tunnel. The device may be formed in panels of any desired length, or a continuous sheet of double layer thermoplastic material sealed together by seal lines 222 to form the transverse compartments 224 on either side of the central region 210 may be manufactured, with lengths of the sheet being cut off as required to form individual thermal protective devices.

When it is desired to provide a thermal protective tunnel of extended length, a plurality of thermal protective panels or devices 200 may be positioned end to end over a suitable support structure. The hose connectors 224 at opposite ends of each device are preferably complementary male and female connectors which enable the hose lengths 240 of adjacent thermal protective devices 200 to be connected together. In such a thermal protective tunnel or system comprising a plurality of devices 200 connected end to end, the devices may conveniently be filled simultaneously with a fluid, such as water, from a common supply.

The plugs or fluid release valves 250 at the bottom edges of the ends 228 of the device 200 allow the user of the device to release water or other fluid from the tubular compartments of the thermal protective device 200 when it is required to disassemble the device for removal to another location or for storage. The plugs or fluid release valves 250 may take any convenient form, such as commercially available pull-type plugs or screw-type release valves. The plugs or fluid release valves may be connectable to irrigation means, such as an irrigation hose, for irrigating plants in the neighbourhood of the device. Alternatively, additional irrigation means, such as a hose, may be provided alongside the filling hose or hoses 240. The irrigation hoses may be fitted with nozzles or spraying heads of known type for irrigating the plants within the tunnel device.

Referring to Figures 15 and 16, there is shown a thermal protective device 200, similar to that of Figures 13 and 14 and corresponding reference numerals have been applied to corresponding parts. The device 200' differs from the device 200 of Figures 13 and 14 in that there is no central seal or fold line 221 and there is only one filling device or hose 240' in a longitudinally extending gap 227' in the central region 210. The filling hose 240' differs from the filling hoses 240 in that it is provided with apertures 242' on opposite sides. The apertures 242' are located adjacent the upper open ends of the compartments 224 where the transversely extending seal lines 222 on each side 220 of the device terminate.

It will be appreciated that the thermal protective device 200' may be placed over a support frame or structure and used in a similar manner to the device 200 of Figures 13 and 14, but that there is only one filling hose 240' which has to be connected to a supply of water or other fluid for filling the tubular compartments 224. Like the device 200, the thermal protective device 200' of Figures 15 and 16 also has longitudinally extending unsealed spaces 226 adjacent its joined side edges 225 and outlets 229 in its end edges 228 adjacent the side edges 225 which may be closed by plugs or fluid release valves 250.

Referring to Figure 17, there is shown a side view of a modified heat sealing rod 230 suitable for producing the seal lines 222 in the devices of Figures 13 to 16. The lower part 231 of the sealing rod 230 has a central cut away section 232 and a pair of cut away sections 233 at opposite ends with heating elements 234 provided on the lower surface of the rod 230 between the central cut away sections 232 and the end cut away sections 233. When the heat sealing rod 230 is applied transversely to a double layer of thermoplastic material with longitudinally extending sealed edges, the heating elements 234 will create the seal lines 222 which extend only partially across the device and the cut-away regions 232 and 233 will correspond to the central unsealed region 210 and the unsealed spaces 226 respectively of the device 200 or 200'.

It will be appreciated that to form the devices 200 and 200' either a single sealing head 230 which operates repetitively may be provided in apparatus similar to the apparatus described with reference to Figure 3 or multiple sealing elements 230 may be provided in apparatus similar to that of Figure 4.

Also, it will be appreciated that the lengths of the heat sealing rod 230, the cut-away portions 232 and 233 and of the heating elements 234 may be varied to produce devices which have compartments and unsealed gaps and spaces of different lengths and widths for different applications. The present invention therefore provides, in its various aspects, a simple method of manufacturing double-walled thermal protective devices which does not require expensive apparatus to form the devices from either a single, folded sheet or two layers of thermoplastics material joined together along at least one edge, apparatus for performing the method to make thermal protective devices, self-filling thermal protective devices which may be made from the method and a thermal protective system comprising a plurality of such devices. It will, however, be appreciated that various modifications and/or alterations may be made to the process, apparatus and/or devices described with reference to the accompanying drawings without departing from the scope or spirit of the invention.

Claims

CLAIMS:

1. A method of making a double-walled, thermal protective device which is divided into a plurality of elongate, substantially parallel compartments which are adapted to be filled with fluid, such as water, to provide a thermal protective structure for one or more plants, said method comprising the steps of: providing two layers thermoplastic polymeric material joined together along at least one longitudinally extending edge; feeding the two layers through heat sealing and cutting apparatus in a feed direction corresponding to the longitudinal extend of said layers; heat sealing the two layers along a plurality of seal lines at intervals, the seal lines extending transversely at least partly across the layers so as to create a plurality of individual compartments; cutting the layers in a direction extending transversely across the layers; and cutting the layers again in a direction extending substantially parallel to the first cut so as to form a double- walled, thermal protective device having a plurality of transversely extending compartments which are adapted to be filled with fluid, such as water.

2. A method according to claim 1 wherein the transverse seal lines are arranged to extend across the layers substantially perpendicularly to said at least one joined edge.

3. A method according to claim 1 or claim 2 wherein the seal lines are formed by heat sealing the layers at regular intervals and are substantially equally spaced to form compartments of substantially the same width.

4. A method according to any one of claims 1 to 3 wherein the two layers are formed by folding a single sheet of thermoplastic material along a longitudinal fold line to form the longitudinal joining edge which joins said sheets together.

5. A method according to any one of claims 1 to 3 wherein two separate layers of thermoplastic material are joined together along at least one longitudinally extending edge before the layers are passed through the heat sealing apparatus.

6. A method according to claim 4 or claim 5 wherein one layer of the thermal protective device is slightly wider than the other layer.

7. A method according to any one of the preceding claims further comprising the further steps of: folding the heat sealed layers so as to bring the two cut ends together; and securing the two cut ends together to form a double-walled tubular thermal protective device.

8. A method of making a double-walled tubular thermal protective device which is divided into a plurality of elongate, substantially parallel compartments which are adapted to be filled with fluid, such as water, to provide a thermal protective structure for one or more plants, said method comprising the steps of: providing a single elongate sheet of thermoplastic polymeric material and folding the sheet along a longitudinally extending fold line; feeding the folded elongate sheet through heat sealing and cutting apparatus in a feed direction corresponding to the longitudinal extent of said sheet; heat sealing the two layers of the folded sheet along a plurality of seal lines at intervals, the seal lines extending transversely across the sheet so as to create a plurality of individual compartments; cutting the heat-sealed, folded sheet in a direction extending transversely across the sheet substantially perpendicularly to the longitudinal fold line; cutting the heat-sealed folded sheet again in a direction extending substantially parallel to the first cut so as to form an individual length of double- walled, heat-sealed folded sheet having a plurality of transversely extending compartments which are closed at one end open at the other end; removing the individual length of sheet from the heat sealing and cutting apparatus; folding said individual length so as to bring the two cut ends together; and securing the two ends together to form the double walled, tubular thermal protective device.

9. A method according to claim 7 or claim 8 wherein the two cut ends are joined together by heat sealing.

10. A method according to claim 7 or claim 8 wherein the two cut ends of the individual length of double-walled, heat sealed folded sheet are joined together by an adhesive.

11. A double-walled tubular thermal protective device formed by a method in accordance with any one of claims 7 to 10.

12. A method according to any one of claims 1 to 5 wherein the transverse seal lines are arranged so as to extend only partly across the layers thereby leaving at least one longitudinally extending unsealed gap or space between the layers.

13. A method according to claim 12 wherein the layers are joined together along opposite longitudinally extending edges and a longitudinally extending unsealed gap is disposed adjacent one of said longitudinally extending joined edges to receive filling means for filling the compartments formed between the transversely extending seal lines.

14. A method according to claim 12 wherein the layers are joined together along opposite longitudinally extending edges and said at least one longitudinally extending unsealed gap is disposed in a central region between said joined longitudinally extending edges to receive filling means for filling the compartments formed between the transversely extending seal lines.

15. A method according to claim 13 or claim 14 wherein said filling means comprises a hose or other elongate filling element inserted into said at least one unsealed gap for filling the transversely extending compartments with water or other fluid.

16. A method according to claim 15 wherein the hose or other elongate filling element has a plurality of apertures spaced along its length, each of said apertures being in register with a respective one of the transversely extending compartments.

17. A double-walled thermal protective device formed by a method in accordance with any one of claims 1 to 6 or 13 to 17.

18. A double-walled thermal protective device comprising two layers of thermoplastic material joined together along at least one longitudinally extending edge, said layers being sealed together along a plurality of transversely extending seal lines extending across the layers to form a plurality of transversely extending compartments, wherein said seal lines extend only partly across the layers so that device has at least one longitudinally extending unsealed gap between the layers.

19. A thermal protective device according to claim 18, wherein opposite longitudinally extending edges of the layers forming the device are joined together, and the at least one longitudinally extending unsealed gap is provided adjacent one of the longitudinally extending edges of the device.

20. A thermal protective device according to claim 18 wherein opposite longitudinally extending edges of the layers forming the device are joined together and at least one longitudinally extending unsealed gap is provided in a central region of the device which is adapted to be folded over a support structure to form a thermal protective tunnel for a row of plants.

21. A thermal protective device according to claim 19 or claim 20 including a hose received in said at least one longitudinally extending unsealed gap, said hose having a plurality of apertures spaced along its length, each of said apertures being in register with a respective one of said transversely extending compartments.

22. A thermal protective device according to claim 21 wherein at least one end of the hose extends out of said unsealed gap and is provided with connecting means for connecting said hose end to a supply of water or to another similar double-walled thermal protective device.

23. A thermal protective system comprising a plurality of devices in accordance with claim 22 adapted to be placed end-to-end with hoses of adjacent devices being connected together.

24. A thermal protective device according to any one of claims 18 to 22 wherein a longitudinally extending unsealed space in addition to the longitudinally extending gap is provided adjacent to at least one longitudinally extending edge of the device which, in use, is adapted to form a lower edge of the device, and at least one outlet for fluid is provided from said longitudinally extending space.

25. A thermal protective device according to claim 24 wherein said at least one outlet is closed by a plug or a fluid release valve.

26. Apparatus for making a double-walled thermal protective device in accordance with the method of any one of claims 1 to 10 or 12 to 16, the apparatus comprising heat sealing means, feeding means for feeding two layers of thermoplastic material joined together along at least one longitudinally extending edge through the heat sealing means in a feed direction corresponding to the longitudinal extent of the layers, the heat sealing means including at least one heat sealing element arranged transversely of said feed direction, and cutting means including at least one cutting device arranged transversely of said feed direction.

27. Apparatus according to claim 26 wherein the heat sealing means comprises a single heat sealing element and includes control means for automatically operating the heat sealing element at predetermined intervals as the layers are continuously fed through the heat sealing means.

28. Apparatus according to claim 27 wherein the heat sealing means comprises a plurality of heat sealing elements which are arranged to operate together to form a plurality of seal lines simultaneously.

29. Apparatus according to any one of claims 26 to 28 wherein said at least one heat sealing element is arranged to create seal lines which are extended completely across the layers of thermoplastic material.

30. Apparatus according to any one of claims 26 to 28 wherein said at least one heat sealing element is arranged to create seal lines which extend only partly across the layers leaving at least one longitudinally extending unsealed gap between the layers.

31. Apparatus according to claim 30 wherein said at least one sealing element comprises an elongate sealing rod having at least one heating surface which extends longitudinally along the rod for only part of the length of the rod.

32. Apparatus according to claim 31 wherein said at least one sealing element comprises an elongate sealing rod having at least one cut-away portion between heating surfaces which extend longitudinally along the rod for only part of the length of the rod.