PROCESS FOR PREPARING A SEED SUPPORT

Abstract

The invention provides a process for the preparation of a seed support that comprises a biodegradable polymer film having a plurality of seeds at least partially embedded therein, the process comprising the steps of (a) providing a hydrophobic release liner (18); (b) applying a coating of an aqueous dispersion or solution comprising a biodegradable polymer on the hydrophobic release liner (18), wherein the dispersion or solution has a viscosity of from 2000 to 16000 mPa.Math.s and a water content of from 58% to 90% by weight of the coating; (c) depositing a plurality of seeds onto the coating so that the seeds become at least partially embedded in the coating; (d) drying the coating to give a final water content of 1.5% to 15% by weight and thereby form the biodegradable polymer film; and (e) detaching the hydrophobic release liner from the biodegradable polymer film to give the seed support.

Claims

1. A process for the preparation of a seed support that comprises a biodegradable polymer film having a plurality of seeds at least partially embedded therein, the process comprising the steps of (a) providing a hydrophobic release liner; (b) applying a coating of an aqueous dispersion or solution comprising a biodegradable polymer on the hydrophobic release liner, wherein the dispersion or solution has a viscosity of from 4000 to 16000 mPa.Math.s and a water content of from 58% to 90% by weight of the coating; (c) depositing a plurality of seeds onto the coating so that the seeds become at least partially embedded in the coating; (c-i) partially drying the coating and applying a porous reinforcing layer to the coating when the coating has partially dried and while the coating is still sufficiently tacky for the reinforcing layer to adhere to the coating; (d) further drying the coating to give a final water content of 1.5% to 15% by weight and thereby form the biodegradable polymer film; and (e) detaching the hydrophobic release liner from the biodegradable polymer film to give the seed support.

2. A process according to claim 1 wherein the solution or dispersion of biodegradable polymer is coated onto the hydrophobic release liner to give an initial coating thickness in the range from 100-500 μm.

3. A process according to claim 1 wherein, when the final water content of 1.5-15% (w/w) is attained, the thickness of the biodegradable polymer membrane is in the range 20-100 μm.

4. A process according to claim 1 wherein the solution or dispersion of biodegradable polymer is coated onto the hydrophobic release liner using a slot die extruder.

5. A process according to claim 1 wherein the biodegradable polymer is selected from polyvinyl alcohol; polyvinyl acetate; starch; and mixtures thereof.

6. A process according to claim 1 wherein the biodegradable polymer has a water content of from 58% to 89% (w/w) when it is initially coated on to the hydrophobic release layer.

7. A process according to claim 1 wherein the dispersion or solution comprising the biodegradable polymer is other than one which: (a) contains methyl sulphate or wherein methyl sulphate has been used in the preparation of the dispersion or solution; and/or (b) contains styrene-maleic acid copolymer; and/or (c) contains glycerine.

8. A process according to claim 1 wherein the porous reinforcing layer is applied to the coating when the coating has partially dried to a water content in the range from 40% (w/w) to 55% (w/w) and is still sufficiently tacky for the reinforcing layer to adhere to the coating.

9. A process according to claim 1 wherein the reinforcing layer is formed from a woven or non-woven fabric, or a perforated film, or paper.

10. A process according to claim 1 wherein the reinforcing layer has a thickness in the range 25-500 μm.

11. A process according to claim 1 wherein the hydrophobic release layer has a surface constituted by a polymer having a critical surface tension of less than 45 mN/m.

12. A process according to claim 1 wherein the hydrophobic release layer is formed form or has a surface constituted by a polymer selected from polyesters, polyethylene, polypropylene, amorphous polyethylene terephthalate (PET), fluorinated polyolefins, natural or synthetic rubbers, silicones; and polymer films having a surface of polyethylene, polypropylene, PTFE or a nitrile rubber.

13. A process according to claim 1 wherein the hydrophobic release liner is a belt formed from PTFE or a PTFE-coated or silicone-coated polymer.

14. A process according to claim 1 wherein an additive is included in the seed support in an amount of 0-50% by weight, and is selected from plant growth additives; soil-adjustment additives; extender and/or seed protection additives; bio-stimulants; nitrogen containing compounds; inorganic compounds; salt binding agents; micro-nutrients; botanicals; chitosan; biopolymers; biological agents; organic or synthetic fertilizers; biocontrol agents; pH-modifiers; UV-stabilisers; water absorbing and retaining materials; talcum; and pigments.

15. A process according to claim 1 wherein the coating is applied to the hydrophobic release liner as a foam.

16. A process according to claim 2 wherein the solution or dispersion of biodegradable polymer is coated onto the hydrophobic release liner to give an initial coating thickness in the range from 150-400 μm.

17. A process according to claim 3 wherein, when the final water content of 1.5-15% (w/w) is attained, the thickness of the biodegradable polymer membrane is in the range 25-70 μm.

18. A process according to claim 4 wherein the slot die extruder comprises a moveable barrier wall (knife) positioned above the liner and being arranged transversely with respect to a direction of travel of the liner, the barrier wall being movable up or down to provide a gap between the barrier wall and the liner, which gap corresponds to a desired thickness of the coating of biodegradable polymer such that the solution or dispersion of biodegradable polymer is deposited onto the liner on an upstream side of the barrier wall and is carried through the gap by the movement of the liner, the lower edge of the barrier wall serving to limit the thickness of the coating as the liner and solution or dispersion pass though the gap.

19. A process according to claim 8 wherein the porous reinforcing layer is applied to the coating when the coating has partially dried to a water content in the range from 45% to 50% (w/w)) and is still sufficiently tacky for the reinforcing layer to adhere to the coating.

20. A process according to claim 5 wherein the biodegradable polymer comprises (or consists of): (i) polyvinyl alcohol; (ii) polyvinyl acetate; (iii) starch or a modified starch; (iv) a mixture of polyvinyl alcohol and polyvinyl acetate; (v) a mixture of starch (or modified starch) and polyvinyl alcohol; (vi) a mixture of starch (or modified starch) and polyvinyl acetate; or (vii) a mixture of starch (or modified starch), polyvinyl alcohol and polyvinyl acetate.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0135] FIG. 1 is a schematic illustration of a production line for the manufacture of a seed support in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0136] An embodiment of the process of the invention will now be described in more detail with reference to the schematic view of the production line shown in FIG. 1.

[0137] Thus, a production line for carrying a process according to one embodiment of the invention comprises a hydrophobic release liner dispensing station (2), a backing support material dispensing station (4), a coating station (6), a seed dispensing station (8), a drying oven (10), a release liner stripping station (12), a used liner collecting station (14) and a seed support collecting station (16). It will be appreciated that the various guide rollers and driving mechanisms for advancing the release liner, backing support material and finished seed support through the production line have been omitted for clarity but it will readily be apparent to the skilled person how and where such components should be located.

[0138] The hydrophobic release liner dispensing station (2) comprises a roll of a hydrophobic release liner belt material which can be, for example, a silicone-coated fibre glass belt or a smooth-surfaced PTFE belt. The hydrophobic release liner material is one which is resistant to the temperatures encountered in the drying oven (10).

[0139] The belt (18) of hydrophobic release liner material is unwound from the roll and is advanced to the coating station (6) which comprises a slot die connected to a supply of an aqueous solution or dispersion of a biodegradable polymer material. The said supply can be held within a reservoir or tank directly connected to the slot die, or it can be fed by means of pipework from a remote tank or reservoir. The slot of the slot die is arranged transversely with respect to the direction of travel of the belt (18).

[0140] The slot die comprises a pair of transverse walls (6a) and (6b) linked by side walls (not shown) to form a generally rectangular hopper which is open at its lower end so that biodegradable polymer material introduced into the hopper will come into contact with the belt (18). The downstream wall (6b) of the hopper is moveable in a vertical axis and can be moved upwards to create a gap (not shown) between its lower edge and the belt (18). The gap between the lower edge of the wall (6b) and the belt (18) constitutes the slot of the slot die.

[0141] As the belt (18) passes through the coating station (6), a solution or dispersion of the biodegradable polymer material is dispensed onto the belt to give an even coating of a desired thickness (e.g. of about 200 μm) which is determined by the size of the gap between the lower edge of the wall (6b) and the belt (18). The thickness of the coating can be varied by moving the wall (6b) up or down to increase or reduce the size of the gap. In this embodiment the coating is a solution of polyvinyl alcohol containing about 65% to about 80% (w/w) of water and having a viscosity of from 5000 to 12000 mPa.Math.s, although it will be appreciated that other biodegradable polymers may be used instead.

[0142] The belt (18) carrying the coating of polyvinyl alcohol solution is then advanced to the seed dispensing station (8) where seeds are deposited onto the coated belt so that they become partially embedded in the coating. The seeds are typically deposited onto the coating in a predefined pattern and the seed dispensing station may therefore be provided with one or more seed dispensing nozzles to provide the desired pattern of seed deposition.

[0143] After deposition of the seeds, the belt moves into the oven (10) where it is subjected to a temperature in the range from about 40° C. to about 60° C. in order to bring about water removal from the coating. The oven may contain a fan so that the coating is exposed to a stream of warm air to facilitate the drying process. The precise temperature of the oven is selected so as to avoid any damage to the seeds and to ensure that the coating dries as uniformly as possible to maintain a cohesive structure and avoid the formation of cavities and cracks.

[0144] While the coating is still tacky, a backing support material is applied to the coating to form a reinforcing layer. The backing support material is dispensed as a web (20) from a roll at the backing support material dispensing station (4). The backing support material is a biodegradable material which can be, for example, a paper or a woven or non-woven natural fibre material such as jute.

[0145] The belt (18) and the web (20) of backing support material converge at a laminating station (22) inside the oven. Here, the belt (18) and the web (20) pass around a roller (not shown), the tension in the belt (18) providing a source of pressure which compress the belt (18) and web (20) together so that the reinforcing layer becomes firmly bonded to the coating and covers the seeds. As an alternative to using the tension in the belt to provide a source of pressure to assist bonding of the coating and the web (20), a pair of pinch rollers can be used but the surfaces of the rollers and the compression pressures used must be selected so that firm adhesion between the coating and the web (18) occurs but the seeds are not damaged. The rollers may therefore be formed from a rubber or foam to minimize damage to the seeds.

[0146] After the lamination stage, the laminated web and belt are passed through a warmer region of the oven (for example where the air temperature is in the range from 60° C. to 85° C.) where it is dried to its final water content. In order to provide sufficiently drying times of sufficient length (e.g. from 10 to 30 minutes) without needing an oven of excessive length, the laminated web and belt may be guided back and forth several times along a winding through the oven by a series of rollers.

[0147] By the time the laminated web (20) and belt (18) emerge from the oven, the coating has cured to form a laminated seed support comprising a biodegradable polymer membrane having a water content of from 1.5% and 15% (w/w) (more usually from 2% to 5% (w/w)) to which the reinforcing layer is firmly bonded. The laminated seed support has a sufficiently high tensile strength and flexibility to enable it to be removed from the belt (18) at the release liner stripping station (12) and then wound to form a roll at the seed support collecting station (16). The used belt (18) of release liner is then wound onto a roll at collecting station (14) and can subsequently be reused or directly recycled (represented schematically by the dotted line in FIG. 1).

[0148] Although the drying of the coating to its final water content takes place within the oven, the coating may be partially dried before it enters the oven and/or before the seeds are deposited onto the coating. For example, the coating can be exposed to a stream of air which is either at ambient temperature or is heated, so that some removal of water takes place before the seeds are deposited onto the coating. However, the extent of drying must not be so great that the seeds cannot become embedded in the coating.

[0149] In another variation, the backing support material is omitted. It has been found that biodegradable polymers such as those formed from starch, PVOH or PVA or mixtures thereof can form cohesive self-supporting membranes which have sufficient tensile strength and flexibility to enable them to be wound into a roll, without the need for a backing support material.

EXAMPLES

Example 1

[0150] The process described above and illustrated in FIG. 1 can be used to prepare a seed support consisting of a biodegradable polymer film 30 μm in thickness formed from polyvinyl alcohol and containing fescue grass seeds in a density corresponding to from about 20 to about 40 grammes of seed per square metre. The seed support of this Example does not have a reinforcing layer.

Example 2

[0151] The process described above and illustrated in FIG. 1 can be used to prepare a seed support consisting of a biodegradable polymer film 50 μm in thickness formed from polyvinyl alcohol and containing rye grass seeds in a density corresponding to from about 20 to about 40 grammes of seed per square metre. The seed support of this Example does not have a reinforcing layer.

Example 3

[0152] The process described above and illustrated in FIG. 1 can be used to prepare a seed support consisting of a biodegradable polymer film 30 μm in thickness formed from a mixture of 90% (w/w) polyvinyl alcohol and 10% (w/w) polyvinyl acetate and containing fescue grass seeds in a density corresponding to from about 20 to about 40 grammes of seed per square metre. The seed support of this Example does not have a reinforcing layer.

Example 4

[0153] The process described above and illustrated in FIG. 1 can be used to prepare a seed support consisting of a biodegradable polymer film 50 μm in thickness formed from a mixture of 90% (w/w) polyvinyl alcohol and 10% (w/w) polyvinyl acetate and containing rye grass seeds in a density corresponding to from about 20 to about 40 grammes of seed per square metre. The seed support of this Example does not have a reinforcing layer.

Example 5

[0154] The process described above can be used to prepare a seed support containing grass seeds wherein the biodegradable polymer film is formed from a mixture of starch (70% by weight) and vinyl acetate polymer (30% by weight).

Example 6

[0155] The process described above can be used to prepare a seed support containing grass seeds wherein the biodegradable polymer film is formed from a mixture of starch (50% by weight), PVOH (25% by weight) and PVA (25% by weight).

Example 7

[0156] The process described above can be used to prepare a seed support containing grass seeds wherein the biodegradable polymer film is formed from a mixture of starch (50% by weight) and PVA (50% by weight).

Example 8

[0157] The process described above and illustrated above can be used to prepare seed supports in which the biodegradable polymer films and seed types are as described in Examples 1 to 7 above but where a reinforcing layer of spunlace viscose or cotton or polylactic acid fibre is bonded to the biodegradable polymer film.

[0158] An example of a suitable spunlace viscose is available from Jacob Holm (product specification of 9 Jun. 2015-version 00) which is a finely apertured non-woven fabric having a thickness of about 0.6 mm and a weight of about 50 g/m.sup.2.

Example 9

[0159] Experiments were carried out to determine the moisture content required in a biodegradable polymer film in order to ensure good bonding when the biodegradable polymer film is laminated to the reinforcing layer as described in Example 8.

[0160] An aqueous biodegradable polymer mixture corresponding substantially to Example 5 above was prepared with a solids content of 35.8% (w/w) and a water content of 64.2% (w/w). The aqueous polymer mixture was coated onto a release liner to give an initial coating of 1.285 g/m.sup.2. Samples of the coated release liner were then passed through an infra-red heating oven at varying speeds in order to bring about different degrees of drying of the polymer mixture. After this initial drying step, the weights of the samples were taken and the weights of the partially dried polymer coating (in g/m.sup.2) were recorded. Partially dried samples were then laminated to a reinforcing layer formed from a non-woven fabric having a thickness of about 0.6 mm and a weight of about 50 g/m.sup.2, by pressing the two layers together. The laminated products were then fully dried by passing through the infra red oven again after which the net weights of the fully dried polymer coating were determined. The strength of the bond between the non-woven fabric and the biodegradable polymer film in each sample was then tested qualitatively by attempted manual peeling apart of the layers.

[0161] The results are shown in Table 1 below.

TABLE-US-00001 Strength Weight of Calculated of bond Weight of coating moisture between Speed coating at after content (%) polymer through lamination complete of coating at film and Sample oven - stage drying lamination reinforcing No. mm/sec (g/m.sup.2) (g/m.sup.2) stage layer 1 15 0.605 0.485 19.8 Very poor 2 17.5 0.645 0.505 21.7 Very poor 3 20 0.915 0.495 45.9 Moderate 4 22.5 0.975 0.475 51.3 Good 5 25 1.055 0.505 52.1 Good 6 27.5 1.105 0.455 58.8 Good 7 30 1.175 0.435 60 Good 8 32.5 1.235 0.485 61.7 Good 9 35 1.265 0.465 62.2 Good 10 No IR 1.285 0.485 64.2 Good heating

[0162] The results show that passing the samples through the oven slowly resulted in a much greater proportion of the moisture being lost. Thus, for samples 1 and 2, the moisture contents after the initial drying step were 19.8% and 21.7% respectively. When lamination to the reinforcing layer was attempted with these samples, the degree of adhesion after complete drying was very poor. The bonding between sample 3 (water content of 45.9% at the lamination stage) and the reinforcing layer was moderate, suggesting that the lower limit for the moisture content at the lamination stage needed to achieve an acceptable degree of bonding is at least 40%.

[0163] Samples 4 to 9 having moisture contents at the lamination stage of from 51.3% to 62.2% all showed good bonding, as did sample 10 (moisture content 64.2%) where no initial drying had taken place.

[0164] However, at higher moisture levels, there will be a tendency for the polymer mixture to soak into the reinforcing layer resulting in a brittle product after full drying.

[0165] On the basis of the above experimental results, it is considered that the moisture content of the polymer mixture coating layer at the lamination stage should be in the range from 40% to 55% by weight in order to give good bonding between the layers without giving rise to potential problems of brittleness resulting from the polymer mixture soaking into the reinforcing layer.

Equivalents

[0166] The embodiment described above and illustrated in the accompanying figure is merely illustrative of the invention and is not intended to have any limiting effect. It will readily be apparent that numerous modifications and alterations may be made to the specific embodiment shown without departing from the principles underlying the invention. All such modifications and alterations are intended to be embraced by this application, for example as defined by the claims herein.

[0167] For the avoidance of doubt, it is note that any reference numerals in the claims should not be construed as limiting the scope of the invention.