WO2006129172A1

WO2006129172A1 - Preservative device

Info

Publication number: WO2006129172A1
Application number: PCT/IB2006/001425
Authority: WO
Inventors: Willem Jacobus Opperman
Original assignee: Vinguard Limited
Priority date: 2005-05-31
Filing date: 2006-05-31
Publication date: 2006-12-07
Also published as: WO2006129172B1; WO2006129172A8

Abstract

This Invention relates to a method and device for extending the life of cut flowers. Cut flowers are packaged with a preservative device that releases sulphur dioxide at a controlled rate and simultaneously absorbs ethylene. The device includes a layer of a matrix forming material having a sulphur dioxide (SO2) generating compound and an ethylene oxidising compound dispersed therein. The matrix forming material is adhered to a carrier sheet in the form of a layer covering a central area of the carrier sheet so as to form at least one discrete zone (2) , with the peripheral area (3) of the carrier sheet (1) substantially free of such mixture. A cover (4) is sheet secured to the peripheral area to enclose the layer of mixture between the carrier sheet and the cover sheet.

Description

PRESERVATIVE DEVICE

BACKGROUND OF THE INVENTION

This invention relates to a preservative gas generating device for preserving perishable products, such as cut flowers.

During the post harvest storage of cut flowers, ethylene is released. The effects of ethylene are only too well known in the flower industry: petals wilt, buds dry out, flowers open prematurely, leaves yellow and flowers, buds, petals and leaves abscise. To counteract the negative effects of ethylene on cut flowers, so-called scrubbers are used to absorb the ethylene that is produced. These scrubbers can be mechanical devices that circulate the air in storage rooms and filter out the ethylene, or they can be sachets containing chemicals that absorb ethylene and are placed inside packaging containing ihe flowers.

In addition to ethylene, botrytis decay is also a significant probiem during the post harvest handling of cut flowers. Numerous efforts to control botrytis decay on flowers with SO2 gas have failed, as flowers are very sensitive and are easily damaged by too high levels of SO2 gas.

The applicant has therefore identified a need for a new method of preserving cut flowers. SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method of extending the fife of cut flowers, the method including the step of packaging the flowers with a preservative device that releases sulphur dioxide at a controlled rate and simultaneously absorbs ethylene.

According to a second aspect of the invention, there is provided an in package preservative device including: a layer of a matrix forming material having a sulphur dioxide (SO₂) generating compound and an ethylene oxidising compound dispersed therein; the layer of matrix forming material being adhered to a carrier sheet in the form of a layer covering a central area of the carrier sheet so as to form at least one discrete zone, with the peripheral area of the carrier sheet substantially free of such mixture; and a cover sheet secured to said peripheral area to enclose the fayer of mixture between the carrier sheet and the cover sheet; the layer of matrix befπg adapted to permit the generation of SO₂ gas under operative conditions by the SO₂ generating compound at a controiied rate and to permit it to permeate out of the said matrix; the layer of matrix also being adapted to permit the absorption of ethylene, whereby the ethylene can be oxidised by the ethytene oxidising compound within the matrix; and wherein at least one of the carrier sheet and the cover sheet are permeable to the SO₂ gas and ethylene gas.

Further features of the invention provide for the SO₂ generating compound to be a moisture activated compound in which case the layer of matrix is adapted to permit the ingress of moisture at a controlled rate; for the matrix forming material to be a plastisol; far the plastisol to be formed with a multitude of small gas bubbles entrained therein; for the carrier sheet to have a thermoplastic surface to which the cover sheet is thermafly bonded such as, for example, a plastic coating typically of pofyelhyfene carried a support sheet which may be fn the form of a more temperature resistant plastics film such as a polyesteT tiim or a suitable paper in which case the carrier sheet can be impermeable to moisture, SO₂ gas and ethylene gas; and for the cover sheet to be a permeable sheet such as, for example, a non-woven fibrous plastic sheet, typically a non-woven polyester fabric.

The SO₂ generating compound is typically sodium metabisulphϊte and the ethtene oxidising agent is typically potassfum permanganate.

The sodium metabfsulphife is present in an amount of from 3 to 20%, typically 3 to 15% (m/m) of the above matrix forming material, and the sodium metabisulphite is present in an amount of from 3 to 15% (m/m) of the above matrix forming material. Preferably, an equal amount of sodium metabisulphite and potassium permanganate is present in the matrix forming material.

The preservative device may be used for extending the life of cut flowers, and typically during storage and transport thereof.

In the case of roses, the sodium metabisulphite is added in an amount of from 5 to 10% (m/m), and 5 to 10% (m/m) of potassium permanganate is added.

The preservative device may be used as described above by placing one or more of the devices in a package containing cut flowers, or may be joined to another sheet so that the preservative device foτms one side of a bag into which the flowers can be placed.

According to a third aspect of the invention there is provided a method of manufacturing an in-package preservative device as defined above, the method including the steps of: applying a layer of a matrix forming material having a SO₂ generating compound and an ethylene oxidising compound dispersed therein to an extended carrier sheet, with the layer being arranged in discrete zones thereof spaced apart from each other and each of which is surrounded by an area of carrier sheet material devoid of such matrix; treating the matrix as necessary In order to cure It, dry It, or otherwise stabilize it; covering the extended sheet with a cover sheet; causing the cover sheet to become bonded to the carrier sheet in the said areas devoid of said mixture; and subdividing the extended carrier sheet and associated cover sheet to form in-package preservative devices containing one or more of said discrete zones.

Further features of this aspect of the Invention provide for the mixture to be as defined herein above; for the mixture to be applied to the carrier sheet by an extrusion process in which a layer of mixture is urged under positive pressure out through a nozzle onto a travelling extended carrier sheet, the nozzle conveniently being of a width approximatety equal to the width of the said discrete zones and wherein the spacing of the nozzle from the travelling carrier sheet, at least in part, determines the thickness of the layer; for the carrier sheet to have a thermoplastic surface typicaliy formed as a thermoplastic layer bonded to a support sheet which may be In the form of a more temperature resistant plastics film or a suitable paper- for the matrix forming material to be a plastisol in which case curing thereof is effected by heating, for the SO₂ generating compound to be adapted fo form sulphur dioxide on contact with moisture, and for the matrix to permit ethylene to be absorbed and to be oxidised by the ethylene oxidising compound contained within the matrix.

A further feature of this aspect of the invention for the preservative device to be joined to another portion so as to form a self-contained bag which is capable of generating SO₂ gas and absorbing ethylene.

In its most preferred form the method of the invention is carried out on a substantially continuous basis by extruding a layer of said mixture in discrete zones onto a travelling extended carrier sheet which is then caused to travel past a heating assembly in order to cure the matrix forming material following which thermal bonding of the cover sheet to the carrier sheet is performed along longitudinal and transverse strips between the said discrete zones.

In order that the Invention may be more fully understood, embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTIOM OFTHE DRAWINGS

In the drawings:-

Figure 1 is a partly broken away isometric view of a single in-package preservative device according to a first embodiment of the invention;

Figure 2 is a schematic illustration of the process whereby the gas generating device illustrated in Figure 1 is produced; and

Figure 3 shows a second embodiment of a preservative device according to trie invention.

DETAILED DESCRIPTION OF THE INVENTION

In a first embodiment of the invention an in-package preservative device (Figure 1) includes a carrier sheet (1) which in this particular case vs a polyester film having on one surface thereof a layer or film of a thermoplastic material more appropriate to lower temperature thermal welding such as polyethylene, for exampte. The exact construction of the carrier sheet will depend on requirements. The sheet could, for example, be a co-extruded sheet.

Alternatively, a polyester film may be printed with any one or more of identifying informative and decorative material and thereafter have a fϊfm of polyethylene laminated thereto in known manner in the packaging industry. In either event the construction renders the earner sheet impermeable to moisture, sulphur dioxide (SO₂) gas and ethylene gas. As indicated, the poiyethyfene layer renders that surface, which is directed operatively inwardly (i.e. upwardly in the illustrated orientation), susceptible to thermal welding.

A substantially rectangular discrete zone (2) of a layer of a matrix forming material, in this case in the form of a PVC polymer (plastisol), a sulphur dioxide generating compound in the form of sodium metabisulphite anά an ethylene oxidising compound in the form of potassium permanganate, is adhered to the carrier sheet such that an endless peripheral area (3) is left devoid of any mixture. This matrix mixture is more fully described below,

A cover sheet (4), in this case made of a non-woven fibrous polyester fabric, covers the discrete zone of cured matrix mixture and is thermally bonded to the polyethylene layer or the carrier sheet around the entire periphery as indicated by numeral (5). The bond is, in this case, more a mechanical bond than a true welded fusion bond. As an alternative to the above fabric, a spun bonded polypropylene or polyethylene fabric could be used as the permeable cover sheet.

In use, the in-package preservative device can be used by installing it on top of cut flowers in a plastic bag, usually in a cardboard box. The preservative device is orientated with the cover sheet directed downwards and towards the flowers so that moisture can be received through it to migrate into the matrix to activate the sulphur dioxide generating compound in a controlled manner over a pre-designed period of time. Clearly, there is no wastage of sulphur dioxide gas as the impermeable carrier sheet is directed outwardly and the permeable cover sheet allows the gas generated to pass directly to the flowers. Also, there fs lfttle possfbifity of any part of the layer of mixture coming into contact with the flowers directly or, for that matter, with any part of a person handling the preservative device or the flowers. Alternatively, as shown in Figure 3, the preservative device may itself form part of a bag into which the flowers can be placed. Typically, the preservative device (13) will be Joined to a substantially gas Impermeable sheet (14) so as to define the bag (15). The bag is formed with the cover sheet (16) of the preservative device facing inwards, so ihat moislure and ethylene from the flowers can be absorbed into the matrix, thereby gnerating sulphur dioxide gas and oxidising trie ethylene.

The SO₂ gas will generally only be generated at relatively high humidity levels within the package, for example, at humidity levels of between 85 and 100 %. The rate at which the SO₂ gas is released from the device can be varied according to specific requirements, and so as to ensure that the SO₂ levels are insufficient to cause damage to the flowers, Generally, the rate is either a "constant" release rate or a "sharp peak" release rate. If the device is configured to generate a constant retease rate, then the SO₂ generally begins to be released within about 12 hours of packaging, and increases until the SO₂ concentration within the package is approximately 30 ppm. Thereafter, the SO₂ concentration will gradually decrease to between 5 to 15 ppm over a six to eight week period. If, however, the device is configured to produce a "sharp peak" release rate, then the SO₂ concentration within the package will rise to about 70 to 80 ppm within 1 to 2 days, and will thereafter decrease to 5 to 10 ppm within a few days, and this lower concentration can be maintained for six to eight weeks.

The potassium permanganate within the matrix acis as an ethylene scrubber. Ethylene gas produced by the flowers is absorbed by the matrix, where it comes into contact with and is oxidised by the potassium permanganate, and is no longer harmful to the flowers. The amount of potassium permanganate contained in the matrix may vary according to many factors, such as the size of the package in which the preservative device is intended to be used and the 1ype of flowers that will be stored within the package.

Typically, the rate at which the SO₂ gas can be released from the matrix, and also the rate at which ethylene can be absorbed into the matrix, can be varied by changing the composition of the PVC polymer. The polymer can be made to form either a dense or open foam structure, with the SO₂ gas being reieased more easily in an open structure.

The preservative device described herein creates a micro-ciimate around stored flowers, ensuring that they remain fresh and disease free for extended periods, thus enabling cut flowers to be stored for the first time for periods longer than four weeks after harvesting. This longer storage period has significant commercial value. For example, the extended shelf life of trie flowers allows for them to be exported by cheaper means of transport.

Turning now to the production of the preservative device described above, and to the composition of the matrix layer, the exact configuration and matrix mixture will depend on requirements, in particular, the targeted shelf or storage life of the flowers concerned, the nature of the fiσwers, the cost allowed for the preservative device, and any other considerations.

Simply by way of example of a plastisol which has proved to be successful in the packaging of grapes the following is given as a preferred formula:

PVC powder having a K value of 80: 58.0%

Epoxidized soya bean oil (ESBO) Plastlcizer 40.0%

(available in South Africa from Chemserve Ltd)

Stablizer in the form of Zinc Stearate in ESBO 1.0% as carrier (available from Chemserve Ltd)

Blowing Agent being Tracel DB145 NER 1.0% (an azodlcarboπamid mixture from Tramanco of Pinneburg Germany)

To this was added sodium metabisulphite and potassium permanganate particles having a particle size of <100 μm. The sodium metabisulphite is added in an amount of from 0.03 to 0.20 kg, typically 0.03 to 0.15 kg (according to the particular application) per kg of the above plasBsol mixture (i.e. in an amount of from 3 to 20%, typically 3 to 15% (m/m)), and 3 to 20%, typically 3 to 15% (m/m) of potassium permanganate is added, depending on the type of flower and storage period. The sodium metabisulphite and potassium permanganate are typically added in equal ammounts. The matrix mixture was blended under a vacuum in a blender.

In the case of roses, the sodium metablsulphite is added rπ an amount of from 5 to 10% (m/m), and an equal amount of potassium permanganate.

The preservative devices described above are preferably made on a substantially continuous basis using an extended carrier sheet in roll form as indicated by numeral (6) in Figure 2, the carrier sheet being transported on a support system through a series of items of processing equipment.

The first of these is an extrusion device (7) which Is adapted to extrude matrix mixture through a series of nozzles in the form of slots extending across the width of the device. The extruded layer of matrix is discontinuous so that rectangular discrete zones (8) of the matrix ave deposited on the travelling carrier sheet.

The sheet is then caused to pass under a series of infrared heaters (9) in order to cure the plastlsol. Thereafter, cover sheet material from a roll (10) thereof is applied over the carrier sheet with the discrete zones of cured matrix mixture thereon.

A welding station (11) causes the cover sheet to become thermally bonded to the piasticteed surface of the carrier sheet along transverse and longitudinal strips.

The final station (12) is a cutting and slitting station which subdivides the substantially continuous web of interconnected preservative devices as described above into the required sizes. It will be understood that numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof. In particular, the formula employed for making the matrix can be varied widely as can the method of producing the in-package preservative devices. It is also envisaged that the preservative device could be used for packaging fruit, such as apples and pears.

Claims

1. A method of extending the life of cut flowers, the method Including the step of packaging the flowers with a preservative device that releases sulphur

5 dioxide at a controlled rate and simultaneously absorbs ethylene.

2. A preservative device including: a layer of a matrix forming material having a sulphur dioxide (SO₂) generating compound and an ethylene oxidising compound dispersed therein; ϊθ the layer of matrix forming material being adhered to a carrier sheet in the form of a layer covering a centra? area of the carrier sheet so as to form at least one discrete zone, with the peripheral area of the carrier sheet substantially free of such mixture; and a cover sheet secured to said peripheral area to enclose the layer of 15 mixture between the carrier sheet and the cover sheet; the layer of matrix being adapted to permit the generation of SO₂ gas under operative conditions by the SO₂ generating compound at a controlled rate and to permit it to permeate out of the said matrix; the layer of matrix also being adapted to permit tie absorption of 20 ethylene, whereby the ethylene can be oxidised by the ethylene oxidising compound within the matrix; and wherein at least one of the carrier sheet and the cover sheet are permeable to the SO₂ gas and ethylene gas.

25 3. The device of claim 2, wherein the SO₂ generating compound is a moisture activated compound, and the layer of matrix is adapted to permit the ingress of moisture at a controlled rate.

4. The device of claim 2 or 3, wherein the matrix forming materia! Js a 30 plastisol.

5. The device of cfaim 4, wherein the pfastisoi is formed with a multitude of small gas bubbles entrained therein.

6. The device of any one of claims 2 to 5, wherein the carrier sheet has a thermoplastic surface to which the cover sheet is thermally bonded,

7. The device of claim 6, wherein the carrier sheet has a plastic coating carried a support sheet.

8. The device of claim 7, wherein the piastic coating is polyethylene.

9. The device of claim 7 or 8, wherein the support sheet is in the form of a temperature resistant plastics film or a suitabfe paper.

10. The device of any one of claims 2 to 9, wherein the carrier sheet is impermeable to moisture, SO₂ gas and ethylene gas; and the cover sheet is permeable to moisture, SO₂ gas and ethylene gas.

11. The device of claim 10, wherein the cover sheet is a non-woven fibrous plastic sheet.

12. The device of cfaim 11 , wherein the cover sheet is a non-woven polyester fabric.

13. The device of any one of claims 2 to 12, wherein the SO₂ generating compound is sodium metabisulphite.

14. The device of claim 13, wherein sodium metabisulphite is present in an amount of from 3 to 20% (m/m) of the matrix forming material.

15. The device of claim 14, wherein sodium metabisulphite is present in an amount of from 3 to 15% (m/m) of the matrix forming material.

16. The device of any one of claims 2 to 15, wherein the ethylene oxidising agent is potassium permanganate.

17. The device of claim 16, wherein the potassium permanganate is present in an amount of from 3 to 20% (m/m) of the matrix forming material.

18. The device of claim 17, wherein the potassium permanganate is present In an amount of from 3 to 15% {m/m) of the matrix forming material.

19. The device of any one of claims 16 to 18, wherein an equal amount of sodium metabisulphite and potassium permanganate is present in the matrix forming material.

20. The device of any one of claims 2 to 19, to be used for extending the life of cut flowers.

21. The device of claim 20, wherein the cut flowers are roses and the sodium metabisulphite is present in an amount of from 5 to 10% (m/m), and an equal amount of potassium permanganate is present in the matrix forming materia!.

22. A bag for storing flowers, the bag including a preservative device as defined in any one of claims 2 to 21 forming a side or part thereof of the bag.

23. A method of manufacturing an in-package preservative device as defined in claim 2, the method including the steps of: applying a layer of a matrix forming material having a SO₂ generating compound and an ethylene oxidising compound dispersed therein to an extended carrier sheet, with the layer being arranged in discrete zones thereof spaced apart from each other and each of which is surrounded by an area of carrier sheet material devoid of such matrix; treating the matrix as necessary in order to cure it, dry it, or otherwise stabilize it; covering the extended sheet with a cover sheet; causing the cover sheet to become bonded to the carrier sheet in the said areas devofd of said mixture; and subdividing the extended carrier sheet and associated cover sheet to form in-package preservative devices containing one or more of said discrete zones.

24. A method of manufacturing a preservative device, the method including the steps of: preparing a matrix mixture including a plastisol, sodium metabisulphite and potassium permanganate; applying the mixture to a carrier sheet by an extrusion; and heating the mixture to cure the mixture and form a matrix, for the matrix to form sulphur dioxide on contact with moisture, and for the matrix to permit ethylene to be absorbed and to be oxidised by the potassium permanganate contained within the matrix,