The surface energy of many commodity polymers is fairly low (typically in the region of 30 dynes cm'), whilst the surface energy of water is much higher (typically in the region of 70 dynes cri'). The consequence of this is that water applied to, or condensing from a vapour onto, the surface of a polymer will tend to form spheroidal or lens shaped droplets and will effect the transmission of light through the polymer. This has important consequences for a number of polymer applications, such as films for agricultural use, films for food packaging and the like.

For example, polyethylene mono-layer film and film co-extruded with EVA layers are commonly used as greenhouse film. In a highly humid atmosphere water is prone to condense on the film surface, and fogging can occur. If the water forms spheroidal droplets, total internal reflection of incident light can occur thus reducing the available light to the plants growing in the greenhouse. This can cause a significant drop in crop yield. If the water forms lens shaped droplets a focusing of the light can occur causing burning of plant leaves. As condensation increases the size of droplets increases until they can no longer be supported on the film and they fall onto leaf surface encouraging mould growth.

Fogging is a particular problem where hot food is added to the package which is then sealed and cooled. Water droplets forming on the surface of the package lid will render it effirtively opaque. This then significantly reduces the effectiveness of the polymer as a display packaging material.

The term"fogging"as used herein denotes the formation of either a mist of small spheroidal droplets, or the formation of larger spheroidal or lens-like droplets, both of which can adversely affect the transmission of light through a polymer substrate. Anti-fogging agents which can be provided by the present invention advantageously allow a coherent, transparent film of water to be formed on a polymer surface.

If the surface energy of the polymer can be raised suffìciently it will lower the interfacial tension between the polymer and the water allowing a coherent, transparent film of water to be formed as above, and thus alleviating many of the problems described above. This has previously been achieved by adding a material to the bulk of the polymer during processing which migrates to the surface of the finished article and lowers the interfacial tension between water and the polymer surface. The added material needs to be polar to interact with water and commonly used materials tend to have free hydroxyl groups available. Typical materials which have been used are glycerol esters, sorbitan esters and ethoxylated sorbitan esters.

Drawbacks associated with the use of hitherto employed materials as described above include a limited lifetime and high usage levels often in the region of 4%. There is therefore a need for agents which can alleviate the above problems, which are thermally stable at polymer processing temperatures and in particular which exhibit good anti-fogging performance at low addition levels.

The present invention alleviates the above problems, and provides use of ethoxylated amides substantially as herein after described in modifying the surface energy of a polymer substrate.

In a particularly preferred aspect of the present invention, there is provided use of an ethoxylated amide substantially as herein after described as an anti-fogging agent for a polymer substrate, the term"fogging"being substantially as herein before described. Other uses according to the present invention within the scope of surface energy modification include use of an ethoxylated amide substantially as herein after described as a wetting agent for a polymer substrate, use of an ethoxylated amide substantially as herein after described as a dispersing agent for a polymer substrate, use of an ethoxylated amide substantially as herein after described as a compatiblising agent for a polymer substrate and the like.

In the case where the present invention is concerned with the use of ethoxylated amides as anti- fogging agents, the present invention is particularly applicable in obviating fogging associated either with agricultural films or food packaging films, so as to alleviate the problems referred to above.

More particularly, the present invention provides compounds of formula (1) suitable for use in modifying the surface energy of a polymer substrate RC (O) N (R') (CH2CH20), H (I) where: R is a hydrocarbyl group which may be a straight or branched chain having 8 to 24 carbon atoms; R'is hydrogen, a hydrocarbyl group which may be a straight or branched chain having 1 to 24 carbon atoms, or (CH2CH20); in the case where R'is hydrogen or a hydrocarbyl group, a = y, in the case where R'is- dCH2CH20% EI, a+b = y, where y is an integer in the range of 3 to 50.

Preferably a hydrocarbyl group represented by R is an alkyl or an alkenyl group having 8 to 24 carbon atoms. A suitable alkenyl group may contain one or more double bonds.

Appropriately, the double bond or bonds can exist in either the cis or trans configuration and in the case where more than one double bond is present, the bonds may be conjugated or non- conjugated. Aptly, an alkenyl group represented by R may contain up to three double bonds.

In a preferred embodiment of the present invention, R either represents an alkyl group, or a monounsaturated alkenyl group, having from 12 to 24 carbon atoms. Suitable such preferred moieties represented by R include any of the following: CH3(CH2)16; CH3 (CH2), CH=CH (CH2), ; and CH3 (CH2) 7CH=CH (CH2) 1,- Preferably R'represents hydrogen or a hydrocarbyl group, especially it is preferred that R'represents hydrogen. In the case where R'represents a hydrocarbyl group, W is an alkyi or an alkenyl group having 1 to 24 carbon atoms. A suitable alkenyl group may contain one or more double bonds. Appropriately, the double bond or bonds can exist in either the cis or trans configuration and in the case where more than one double bond is present, the bonds may be conjugated or non-conjugated.

Advantageously, y is an integer in the range of 3 to 20.

It is particularly preferred that the present invention provides a subgroup of compounds of formula (1), namely compounds of formula (Ia), suitable for modifying the surface energy of a polymer substrate R'C (O) N (H) (CH2CH2O)2H (Ia) where: Ra is an alkyl group, or a monounsaturated alkenyl group, having from 12 to 24 carbon atoms; and z is an integer in the range of 3 to 20.

Preferred compounds of formula a) according to the present invention are as follows: R is CH3 (CH2) 1, R'represents hydrogen and a = y = 5; R is CH3 (CH2) 7CH=CH (CH2)7, R1 represents hydrogen and a = y = 5; and R is CH3 (CH2) ? CH==CH (CH2) n. R'represents hydrogen and a = y = 5.

The present invention further provides use of a compound of formula (I) in modifying the surface energy of a polymer substrate. It will be understood that reference to a compound of formula (1) herein includes reference to a compound of formula (la).

In a particularly preferred aspect of the present invention, there is provided use of a compound of formula (1) as an anti-fbgging agent for a polymer substrate, the term"fogging"being substantially as herein before described. Other uses according to the present invention within the scope of surface energy modification include use of a compound of formula (I) as a wetting agent for a polymer substrate, use of a compound of formula (1) as a dispersing agent for a polymer substrate, use of a compound of formula (I) as a compatiblising agent for a polymer substrate and the like substantially as described above.

In the case where the present invention is concerned with the use of compounds of formula as anti-fogging agents, the present invention is particularly applicable in obviating fogging associated either with agricultural filins or food packaging films.

The present invention still further provides a method of modifying the surface energy of a polymer substrate, which method comprises contacting an ethoxylated amide, preferably a compound of formula (n, with a polymer substrate in an amount effective to modify the surface energy of the polymer substrate. Suitably the ethoxylated amide is incorporated into the polymer substrate at a concentration in the range of 400 to 3000ppm. An ethoxylated amide, preferably a compound of formula (1), may be incorporated into the bulk of me polymer substrate substantially as herein after described in greater detail.

Compounds employed according to the present invention can be solids, pastes or free flowing liquids, and may be employed according to the present invention in their original physical form, or may be pre-blended with silica or other suitable solid support to provide a free-flowing admixture.

There is further provided by the present invention a polymer substrate provided with a surface energy modifying agent comprising an ethoxylated amide, preferably a compound according to formula (n. Suitably the ethoxylated amide is incorporated into the polymer substrate at a concentration in the range of 400 to 3000ppm as described above. The polymer substrate preferably comprises a polymer film. Suitably the polymer film may comprise a polyethylene mono-layer film, or a polyethylene film co-extruded with EVA layers, of the types suitable for use as greenhouse films. Alternatively, the polymer film may suitably be of the type generally employed in food packaging.

There is further provided by the present invention a process of preparing a compound of formula (I) substantially as herein before described, which process comprises reacting a compound of formula (II) RC (O) NR'H (II) where R and R'are substantially as herein before defined, with an ethoxylating agent, such as ethylene oxide or the like, so as to yield a compound of formula (I). 3 to 50, preferably 3 to 20, moles of the ethoxylating agent are reacted with 1 mole of a compound of formula aI).

Compounds of formula (II) are commercially available products, and may be prepared by the reaction of a corresponding carboxylic acid of formula (E) with NR'H2 RCO2H (III) where R and Rare substantially as herein before defined. Carboxylic acids of formula (E) are preferably of vegetable or animal origin. Examples of particularly suitable carboxylic acids of formula () include erucic acid (obtainable from high erucic rape seed oil), oleic acid (obtainable from either tallow or vegetable seed oils such as high oleic sunflower oil and low erucic rape seed oil) and stearic acid (obtainable from tallow or plant sources such as palm oil).

The reaction between compounds of formula (In and the ethoxylating agent is typically carried out at a temperature in the range of 130°C and 170°C, and suitably at a pressure of 2 to 3 bar, although it will be appreciated that other appropriate reaction conditions may be employed. A suitable catalyst may also be employed in the reaction between compounds of formula (II) and the ethoxylating agent. Suitable catalysts are, for example, alkali metal hydroxides (such as potassium and sodium hydroxide) and alkali metal alcoholates (such as potassium ethoxide and sodium methoxide), although other catalysts may also be used. Aptly, the amount of catalyst present is in the range of 0.05% to 1% by weight, of the reaction mixture.

There is further provided by the present invention a process of preparing a polymer substrate provided with an ethoxylated amide (preferably a compound according to formula (I)), capable of modifying the surface energy of a polymer substrate, which process comprises contacting the polymer substrate with the ethoxylated amide so as to incorporate the latter into the polymer substrate. Appropriately, the polymer may be ground to a powdered form or the like, and the ethoxylated amide can then be blended therewith. Altematively the ethoxylated amide can be adsorbed onto a porous polymer substrate.

The present invention will now be further illustrated by the following Examples, which do not limit the invention in any way.

Examples Example 1 Preparation of Samples For the incorporation of anti-fogging additives into a polymer film, the following procedure was adopte.

The base polymer was ground to a powder and additive concentras (3% w/w) produced by adding the ethoxylated amide directly to the polymer powder and tumble blending.

Alternatively the ethoxylated amide was adsorbed onto a porous substrate, such as silica or open cell polymer foam, at 50 % wfw and then blended back into the polymer pellets to give a 3% w/w concentrate. To ensure good dispersion the concentrate was extruded using a twin screw extruder through a rod die, into a cooling bath followed by cutting to give an easily handledpellet form.

The concentrate was blended back with virgin polymer to give the reqmred film concentrations (e. g. 0.05,0.1,0.25% w/w) and extruded into film under the appropriate conditions. For laboratory evaluation purposes LDPE film was produced by extrusion on a 35 mm 24: 1 LJD single screw extruder fitted with a 50 mm annular die, 0.9 mm die gap and blown film haul off tower. Extruder temperatures between 160-200 °C were employed.

Example 2 Foe testing Hot fog testing Water (50 cm3) was placed in a 250 cm3 Pyrex (trade mark) beaker and equilibrated to 60°C in a water bath. A piece of film or polymer plaque was placed on top covering the opening of the beaker (as shown in figure 1) and the build up of water droplets observed every minute for 5 minutes. This was repeated at various times after fabrication of the polymer article. The observations were graded (1-5) as follows: 5) an opaque mist of small spheroidal droplets, 4) spheroidal droplets coalescing to form larger droplets than (5), 3) larger lens-like droplets with some see through clarity, 2) almost complete film of water with a few large droplets, 1) complete transparent film of water.

Co ! d Foe Testine Water (200 cm3, 23°C) was placed in a 250 cm3 Pyrex (trade mark) beaker and covered with the test sample. This assembly was then placed in a temperature controlled cabinet at 4°C.

The sample was observe at regular intervals over at least a 3 hour period and at various times after fabrication. Observations on the fogging of me article were made as described in the hot fog test above.

Example 3 Short foggingperformanceofLDPEcontainingethorvlatedamideshot at 2500 ppm A comparison of the 5 minute hot fog test readmgs for some ethoxylated amides in LDPE films at various times after fabrication. Time after extrusion (hours) Ethoxylated amide O 24 168 Noadditive 5 5 5 5 5 Mole EO 1 1 1 1 lauramide 5 mole EO 1 1. 5 3 2 Stearamide 5 Mole EO 1 1 1 1 oleamide 5 Mole EO 1 1 1-1.5 1 erucamide EOoleyl4.543.535mole palmitamide (EO as used herein represents ethoxylated). Examo ! e 4 Effect of concentration on the hot fogging oerformwnce of ethoxylated<BR> in LDPE blown film Comparison of the 5 minute hot fog readings for ethoxylated amides at 500,1000 and 2500 ppm at various times after extrusion are shown in Figure 2.

Ethoxylated amides were clearly effective at low (500ppm) concentrations, higher concentrations giving anti-fogging effects almost immediately after extrusion.

Example 5 Comparison of the cold fog oerformance of ethoxvlated amide in LDPE film Ethoxylated amides at 2500 ppm in LDPE 2 hours after extrusion Timeon test Ethoxylated 10min15min30min1hr2hr3hr20hrmin amide EO111111115mole oleamide 5 mole EO 1 1 1 1 1 1 1 1-2 stearamide Both the 5 mole ethoxylated oleamide and 5 mole ethoxylated stearamide demonstrated excellent anti-fogging performance throughout the period of the test.

Example 6 Comparison of the hot foe performance of ethoxvlated amides with some commonlv used anti-fogging agents The anti-fogging agents were compared at 1000 ppm in LDPE film Time after extrusion Anti-fog 0 3 hr 1 day 7 days 14 days 11112Glycerolmono- oleate Glycerol mono-1 2 2 2 4 Sorbitan monoleate 5 4 4 4 3 EO sorbitan mono-5 5 5 5 5 oleate 5 mole EO oleamide 1 1 1 1 The ethoxylated amide showed excellent performance at 1000 ppm when compared with other materials that are used as anti-fogging agents.