Background of the invention Polyethylene based films are used extensively in greenhouse structures where they provide an economical method of providing a protected environment for horticultural production.

It has been established that use of such films can be effective in changing the spectral quality of solar radiation reaching plants so that the choice of film can influence plant growth, the effect being dependent on the type of plant. For example a shortening of the stem height has been observed by either increasing the amount of blue or red light, or by reducing the amount of far red light in the 700 nm to 800 nm wavelength band.

Therefore, to avoid inhibiting natural light effects, useful films would transmit at least about 60% of the available light, particularly visible and phytosensitive wavelengths useful in controlling and promoting plant growth, including the recognised photosynthetically active radiation (PAR) that has a wavelength of from 400 nm to 700 nm approximately. Such films are very popular for commercial tunnel greenhouses for example.

There is, though, an increasing concern over the flammability of such films which, as a potential hazard, prevents their use in structures to which members of the public have access-for example garden centres and similar retail areas. There is also the possibility of restrictions being placed on the use of flammable films over areas where any individual might be required to work for a period of time on crop planting, harvesting or packing.

Materials which are currently used in forming structures which are subject to fire regulations are typically fabrics coated with a flame retardant material often based on polyvinyl chloride (PVC). However, these transmit less light than do polyethylene-based films, and are therefore generally less suitable for growing or maintaining the quality of plants. Such materials are used in garden centres or the like, but present problems in maintaining the quality of growing plants.

There is also a problem with discolouration and shrinkage over the lifetime of such fabrics. Furthermore, they do not share the economics of polyethylene film production, and therefore are not available in large widths suitable for covering large structures. This means that to cover such structures necessitates the sheets being joined by sewing or welding.

Moreover such fabric does not have the degree of flexibility which makes polyethylene film suitable for stretching over supporting structures.

Compositions for preparing fire-retardant PVC films are described in US-A-3 983 290. These compositions comprise a blend of about 40-55% PVC, about 7-20% of chlorinated polyethylene, about 4-20% of a phosphate ester plasticizer, about 3-7% of magnesium hydroxide filler, about 3-6% zinc borate and about 3-6% of antimony trioxide fire-retardant with optional lubricants, pigments and stabilisers.

Polyethylene films which can satisfy regulations concerning flammability are well known, typically using combinations of additives such as halogenated hydrocarbons and antimony oxide, (see for example CN-A-1 134 432) but these do not have the essential requirements of light transmission and are not sufficiently resistant to sunlight and weathering to allow them to be used in applications which involve long term exposure.

A fireproof plastic film is described in DE A 4 421 420, e. g. a polyolefin film, especially adhesive polyolefin film based on polyethylene, polypropylene or EPDM, in which the required level of fire resistance is obtained without using any halogen- containing fire retardants. Instead fire resistance is addressed by using additives such as sulphur, phosphorus or phosphorus derivatives or inorganic fillers such as Al (OH) 3, Mg (OH) 2 or Si hydroxide. However, its weathering and light transmission characteristics are unknown. Additionally, such heavy loadings of inorganic materials (some of which may be temperature sensitive) limit the ability of the composition to be processed into a useful film product.

Flame retardant compositions including a fluorinated polyolefin, preferably with a halogenated flame retardant, for use in retarding a polymeric substrate, which may be a blown film, are described in WO 03/016388. Such compositions also include, as synergists, N-hydroxycarbyloxy substituted hindered amines ("NOR-HALS"). Such NOR-HALS additives are also described in W099/00450 for use together with heavy metal oxides such as antimony oxides in fire retardant compositions. EP 0 792 911 also describes use of NOR-HALS for enhancing the performance of halogenated phosphate flame retardants, in flame resistant polyolefin compositions including antimony oxides for production of fibres and fabrics. Use of antimony compounds is not entirely satisfactory because of concerns about the potential for production of toxic combustion products, especially if a halogenated flame retardant material is also present in the composition.

Many fire retardant additives can interfere with the stabilisation effects of hindered amine light stabilisers and/or contribute to the photo-degradation of a polymeric film. Thus, hitherto it has proved difficult to produce a durable, photo- stable film of a width and thickness suitable for use as a cover

film for horticultural applications and retail areas such as garden centres.

It is also known in the agricultural film industry that polyethylene-based colourless film offering an extended useful life can be obtained by including W light stabilisers such as nickel compounds or hindered amine stabilisers. Certain of these products can exhibit a distinctive and persistent odour which is disadvantageous during processing and subsequent use.

Presently there is no known commercial product that satisfies current needs for a commercially viable fire-retardant light- transmissive film suitable for use in the aforementioned applications as cover materials for greenhouses.

Accordingly an object of the present invention is to provide compositions useful in producing fire-retardant film using conventional extrusion technology, and improved films which obviate or mitigate the abovementioned disadvantages.

Summary of the invention It is now found that the objectives of the invention are surprisingly achievable by using a polymeric or oligomeric hindered amine light stabiliser (HALS) that has as a substituent pendant morpholine group (s), as fire retardant synergist in a composition that is useful for producing a fire-retardant plastics film suitable for use as a cover material for greenhouses or areas provided for cultivation display or retail of plants. The preferred film provided according to the invention typically also provides at least about 60% transmission of light particularly visible and phytosensitive wavelengths useful in controlling and promoting plant growth, including photosynthetically active radiation (PAR) of wavelength 400 nm to 700 nm approximately.

Thus according to the invention there is provided, a fire- retardant composition for use in producing a plastics film suitable for use as a cover material providing at least about 60% transmission of light, particularly visible and phytosensitive wavelengths useful in promoting plant growth, wherein the composition comprises an extrudable polyolefinic film-forming polymer, a fire retardant component, and a polymeric or oligomeric hindered amine light stabiliser (HALS)- based component that has a synergistic effect with respect to the fire retardant component in promoting fire retardant properties, wherein the HALS-based synergistic component comprises a polymeric or oligomeric HALS having substituted piperidyl groups and substituted triazine groups wherein at least one of the substitutions is a morpholine group.

It is observed that the radical group NC5HIO-derived from piperidine is often referred to in the commercial and technical literature as"piperidinyl", but the correct radical name according to IUPAC is"piperidyl". The commercial sources of the additives used herein use"piperidinyl"to identify the radical group NCgHio-, and so that usage is retained in the examples. Similarly, some sources prefer the term"morpholino" instead of"4-morpholinyl"as used in the examples herein.

Advantageously from 1000 ppm to 5000 ppm of the morpholinyl substituted HALS fire-retardant synergist is present in the composition.

The HALS fire-retardant synergist may be a 1,6-hexane- diamine, N, N'-bis (2,2, 6,6-tetramethyl)-4-piperidinyl)-polymer with 2, 4-Dichloro-6- (4-morpholinyl)-1, 3, 5-triazine [CAS No. 082451-48-7] or an alkyl substituted variant such as the methylated form [CAS No. 193098-40-7]. Materials of this type are commercially available as UV light stabilisers from Cytec Industries, Inc.

The composition may be an extrudable film-forming polyolefin such as a polyethylene or a copolymer thereof, or a polypropylene or copolymer thereof. Suitable film-forming polymers include polymers of ethylene with vinyl acetate, butyl acrylate, or a C4-C8 or higher unsaturated hydrocarbons, such as butene, hexene, octene etc.

The fire retardant component of the film may be selected from halogenated phosphonate esters, preferably a poly-brominated phosphonate ester such as tris (tribromoneopentyl) phosphate, otherwise known as [1-propanol, 3-bromo-2,2-bis (bromomethyl)] 3 phosphate, or tris [3-bromo-2,2-bis (bromomethyl) propyl] phosphate i. e. O=P-(OCH2-C3H4Br2-CH2Br) 3, available under the trade names CR-900, Flame Cut 175R (Tosoh Corp. , Japan), TBP 3070, FR370 and FR372. Whilst this flame retardant was readily to hand, it is considered that other halogenated flame retardant materials will also be acceptable for this purpose, provided that they do not interfere with the transparency of the finished film. Known polybrominated flame retardants include tetrabromobisphenol A i. e. 4, 4'- (l-methylethylidene) bis [2, 6-dibromo-] phenol (Derakane) ; tris (2, 3-dibromopropyl) phosphate ; tris (tribromophenyl) triazine ; bis (2, 3-dibromopropyl) phosphate ; tetradecabromo (p-diphenoxy-benzene) (Saytex 120); the group consisting of deca-, nona-, octa-, hexa-, penta-, tetra-, and tri-bromodiphenyl ethers; 2-propenoicacid (pentabromophenyl- methyl) ester, homopolymer ; 1, 2-bis (2,4, 6-tribromophenoxy) ethane (Firemaster 680) and bis (2,4, 6-tribromophenyl) carbonate, disodium tetrabromophthalate; hexabromocyclododecane and various polybrominated alkylphenyl derivatives.

The following examples of flame retardant additives are known including phosphorus-based plasticizers such as cyclic phosphates, phosphites, and phosphate esters, exemplified by Pliabrac TCP (tricresyl phosphate), Pliabrac TXP (trixylenyl phosphate), Antiblaze N (cyclic phosphate esters), Antiblaze TXP

(tar acid, cresol, xylyl, phenol phosphates), and Antiblaze 524 (trixylyl phosphate) from Albright & Wilson Americas; Firemaster BZ 54 (halogenated aryl esters) from Great Lakes Chemicals; chlorinated biphenyl, 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, p-t-butylphenyl diphenyl phosphate, triphenyl phosphite, and the like. Other examples of phosphorus-based plasticizers include halogenated alkyl phosphate esters such as Antiblaze 100 (chloro alkyl diphosphate ester) from Albright & Wilson Americas; alkyl phosphates and phosphites such as tributyl phosphate, tri-2-ethylhexyl phosphate, and triisoctyl phosphite; other organophosphates and organophosphites such as tributoxy ethylphosphate ; other phosphates and phosphonates such as chlorinated diphosphate and chlorinated polyphosphonate; and the like.

According to this invention, there is provided a preferred film- forming polyolefinic polymer composition containing both (a) a morpholine substituted polymeric or oligomeric HALS comprising piperidyl groups and triazine groups, and (b) a halogenated phosphonate ester, especially a brominated phosphonate ester.

Preferably the HALS polymer/oligomer is selected from the group consisting of 1, 6-hexadiamine, N, N'-bis (2,2, 6, 6-tetramethyl)-4- piperidyl-polymers with 2, 4-dichloro-6- (4-morpholinyl)-1, 3,5- triazine ; 1, 6-hexadiamine, N, N'-bis (2,2, 6, 6-tetramethyl)-4- (1-methylpiperidyl) -polymers with 2, 4-dichloro-6- (4- morpholinyl)-1, 3, 5-triazine and the like morpholine-substituted polymeric or oligomeric HALS comprising piperidyl groups and triazine groups; and the brominated phosphonate ester is tris (tribromoneopentyl) phosphate.

Further according to this invention there is provided a method of producing a fire retardant plastics film providing at least about 60% transmission of light, particularly visible and phytosensitive wavelengths useful in promoting plant growth,

said method comprising introducing a fire retardant component, and a hindered amine light stabiliser (HALS) component which has a synergistic effect with respect to the fire retardant component, said HALS being a polymeric or oligomeric hindered amine light stabiliser having substituted piperidyl groups and substituted triazine groups wherein at least one of the substitutions is a morpholine group, to an extrudable polyolefinic film-forming polymer, to form an extrudable fire retardant film-forming composition, and extruding said composition to form a film.

Preferably, the extrusion is carried out through a multi-layer co-extrusion system.

The extrusion temperature is preferably in the range of from 180 to 250 deg. C.

According to another aspect of the present invention there is provided a fire retardant plastics film for use in greenhouse cladding or plant cover comprising an extruded film of polyolefin polymer or copolymer, said film including a fire retardant component and at least one synergistic stabiliser therefor in the form of a polymeric or oligomeric hindered amine light stabiliser having substituted piperidyl groups and substituted triazine groups wherein at least one of the substitutions is a morpholine group.

Preferably the film is made from an extrudable film-forming olefinic polymer or copolymer optionally incorporating additional stabilisers to enhance the lifetime of the film.

Films suitable for this purpose are those based on polyolefins, especially polyethylene and copolymers of ethylene with vinyl compounds such as vinyl acetate, or a C4-C8 or higher unsaturated hydrocarbon, such as butene, hexene, octene etc.

The fire retardant component is preferably present in the extrudable polymer composition in an amount of 4-12%. Such a

component may be an ester such as a halogenated phosphonate ester, e. g. a brominated phosphonate ester, or another similar compound. The most preferred brominated phosphonate ester is (tribromoneopentyl) 3 phosphate.

Additionally, the film may also comprise additional UV stabilisers, such as other hindered amine light stabilisers and/or UV absorbers if desired.

Optionally other minor components can be incorporated, such as processing aids such as anti-block agents, slip additives and anti-oxidants as required.

A fire retardant plastics film adapted to allow light transmission of more than 60% therethrough, is provided in accordance with the invention by extruding, a film-forming olefinic polymer or copolymer having a fire retardant component included therein and at least one synergistic component in the form of a polymeric or oligomeric hindered amine light stabiliser having substituted piperidyl groups and substituted triazine groups wherein at least one of the substitutions is a morpholine group.

The film produced thereby, is generally made from an extrudable film-forming polyolefinic polymer or copolymer and it may incorporate additional stabilisers to enhance the lifetime of the film. The film can be produced using conventional blown film extrusion or co-extrusion processes. For a wide film, it is common to use a three layer co-extrusion processes; in such a case it is particularly preferred that all layers have fire retarding and stabilising components as described herein.

Films suitable for this purpose are those based on film-forming polyolefins, especially polyethylene, polypropylene, and olefinic copolymers, e. g. of ethylene with vinyl compounds such as vinyl acetate. Preferably the films of the present invention are made from film-forming polyolefins in the form of one or

more polyethylene polymers or copolymers. Such polymers may include polymers of ethylene with vinyl acetate, butyl acrylate, butene, hexene or octene.

Additionally the film is produced from an extrudable composition containing a fire retardant component which is present in an amount of from 4-12%. An example of a suitable fire retardant component is a halogenated phosphonate ester such as a brominated phosphonate ester or similar component. Most preferred is (tribromoneopentyl) 3 phosphate.

The film of the invention is particularly characterised by the fact that the effectiveness of the fire retardant component (s) is improved by the presence of a polymeric or oligomeric hindered amine light stabiliser having substituted piperidyl groups and substituted triazine groups wherein at least one of the substitutions is a morpholine group. Thus contrary to the detrimental effects upon films hitherto observed with use of some fire retardant additives together with HALS stabilisers, the present proposal to utilise a morpholine-substituted HALS, shows good results.

Generally 1000 ppm to 5000 ppm of the morpholine substituted hindered amine light stabiliser (HALS) is present in the composition to be extruded into a film. The film may also comprise additional UV stabilisers, such as other hindered amine light stabilisers and/or UV absorbers if desired. The purpose of these further additives is to increase the light stability of the film structure and not to contribute to the fire retardant properties of the material. Optionally other minor components can be incorporated, such as processing aids and process anti- oxidants as required.

Those skilled in this art will be aware that it is easier to make thin films exhibit flame retardancy, but production of thicker films is a more demanding task due to the additional

additives normally used which are not easily compatible with retaining good mechanical or optical properties.

However, a fire retardant film having the desired properties outlined above can be produced by a conventional extrusion process to provide a wide, durable film with fire retardant properties and translucent or transparent properties. Such film is suitable for covering structures to provide shelter and weather protection for plants, animals and people. Accordingly by using such a standard process it is possible to produce sheets of film of sufficient width to be of use in covering large areas. Generally the sheets produced are 4. Om or more in width with a thickness of 125 to 225 microns.

Films according to the invention are able to withstand weathering without loss of such properties for 2 years or more whilst still allowing an overall transmission of light >60%.

The invention will now be described more fully below by way of example.

Modes for Carrying out the invention Production Example : A cover film was manufactured using a Dolci three layer co- extrusion system. The same material composition was used in each layer of the film, i. e.

60% of a ethylene vinyl acetate co-polymer, with 4% vinyl acetate, Melt Flow Index (MFI) 0.25 (AG0358, from Exxon Chemical) 20% of a linear low density copolymer of ethylene and butene, density 0.92. MFI 0.9 (LL0209AA from BP Chemicals) 17% of a masterbatch containing low density polyethylene and linear low density polyethylene with 40% of (tribromo- neopentyl) 3 phosphate and 2% of a 1, 6-hexane-diamine, N, N'-

bis (2,2, 6,6-tetramethyl)-4-piperidinyl)-polymer with 2,4- Dichloro-6- (4-morpholinyl)-1, 3,5-triazine, as a synergist 3% of an additional HALS stabiliser masterbatch containing 20% of a polymer of 2,2, 4,4-tetramethyl-7-oxa-3, 20- diazadispiro (5.1. 11.2)-heneicosan-21-on and epichlorohydrin (Hostavin N30), together with 8.7% 2-hydroxy-4-octoxybenzo- phenone (UV absorber as a co-stabiliser) and 1. 5% of a process stabiliser.

The concentration of active stabilising components were: 6. 8% brominated phosphonate ester 3400 ppm polymeric HALS synergist 6000 ppm additional HALS stabiliser 2600 ppm benzophenone co-stabiliser Physical characteristics of product : The film produced was 9.2m wide and 180 microns in thickness.

Extrusion temperatures were in the region 180 to 250 deg. C.

Performance Testing: Fire Resistance The film was tested for fire resistance with the following results: Limiting Oxygen Index: 27% Flammability The test was conducted according to BS5438 : 1898 Test 2B using a 10 second flame application time to the bottom edge of a test specimen : In six tests there was no incidence of flaming continuing after the removal of the flame, no afterglow and no flaming debris from the sample. The material met the requirements of BS7837: 1996

Weathering Samples of the film were exposed in a QUV accelerated ageing machine (UVA fluorescent tubes, test cycle 8hrs light at 60 deg C, 4hrs dark condensation cycle at 40 deg C). After 2000hr total exposure, the properties of the films remained unchanged.

Comparative testing In a series of comparative tests using a variety of commercially available stabiliser additives in polyolefin films, the flame retardant properties thereof were evaluated. Table A shows polyolefin films which showed no flame retardant properties and thus such films failed to achieve the objectives of the invention. On the other hand a film produced in accordance with the invention exhibited flame retardant properties and thus satisfied the objectives of the invention.

Table A Polymer Film Thickness Additive Assessment Low density 180 microns NOR-HALS 116 Fail polyethylene EVA polymer, 180 microns NOR-HALS 116 Fail (4% VA) Low density 100 microns NOR-HALS 116 Fail polyethylene EVA polymer, Exolit 5073* + (4% VA) 150 microns Fail HALS N30 EVA polymer, Brominated (4% VA) 180 microns phosphonate Pass ester + HALS with morpholine substitution Exolit 5073 is a brominated compound

The advantages offered by the present invention are such that the provision of a film having the combined properties described hereinbefore enables use of such film in retail areas and greenhouses. This is because although the films are fire retardant, and thus safe for use in areas visited by the public, the films also allow enough transmission of light to enable growth and maintenance of plants. Furthermore, such films may be produced in sufficient size as they are able to be made by a conventional extrusion process thus obviating the need for a large number of joins by welding or sewing.

Industrial Applicability The compositions, films and methods of the invention are useful in the agricultural and horticultural industries wherever cover films are required over growing or display areas.