It is well known that polymers are generally good electrical insulators, typically having surface resistivities of the order of 1 x 1012 to 1014 Q. Polymer surfaces therefore provide an ideal environment for the build up of static charges, typically by the removal or addition of electrons to their surfaces during initial processing or during downstream operations, such as conveying, assembly or end use. It can therefore be quite common to find polymer surface charges of 5000-10000 V on articles manufactured from commodity polymers, such as polyethylene film, polypropylene fibres, polystyrene mouldings or the like.

There are many detrimental effects associated with such charge build up, and include, for example, the risk of electrical discharge (explosion risk), pick up of dirt/dust and potential damage to sensitive electrical components.

It has therefore been common practice within the plastics industry to try to control the build up of static charges. This has been achieved either by: a) making a polymer article more electrically conductive, for example by the addition of carbon black, or by b) attracting atmospheric moisture to a surface of a polymer article and thus allowing a more conductive path to earth.

Currently available materials for polymer surface charge dissipation include ethoxylated fatty amines, glycerol esters and fatty alkanolamides. These materials are incorporated into the polymer melt during processing and then migrate to the surface of the polymer as it cools.

Such currently available materials suffer however from one or more drawbacks, such as slow migration, poor thermal stability, lack of longevity or can be damaging to substrate materials (for example, amines can cause cracking of printed circuit boards).

There is therefore a need for improved anti-static agents for polymer substrates.

Advantageously, such improved anti-static agents would exhibit the following desirable properties-rapid migration to the polymer surface, good thermal stability at polymer processing temperatures, longevity of anti-static performance, substantially amine free and non-corrosive.

The present invention provides such improved anti-static agents for polymer substrates, and there is provided by the present invention compounds of formula (I) suitable for use as anti- static agents for a polymer substrate RC (O) N (Ri) (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 either hydrogen or {CH2CH20hH; in the case where R, is hydrogen, a = y; in the case where R, is-CH2CH20) bH, a+b = y; wherein y is an integer in the range of 3 to 12.

Preferably a hydrocarbyl group represented by R is an alky ! 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 17 to 21 carbon atoms, and preferred moieties represented by R include any of the following: CH3 (CH2) 16; CH3 (CH2) CH=CH (CH2) 7; and CH3(CH2)7CH=CH(CH2)11.

CH3 (CH2)7 7CH=CH (CH2) 7 and CH3 (CH2) 7CH=CH (CH2) n are especially preferred moieties represented by R as is further illustrated by reference to the accompanying Examples.

Preferably, Ri is hydrogen, and substantially as described above when R, is hydrogen a = y.

Advantageously, y is an integer in the range of 3 to 7. Optimal anti-static properties are observed with compounds according to the present invention where y is an integer in the range to7.of3 It is particularly preferred that the present invention provides a subgroup of compounds of formula (1), namely compounds of formula (la), suitable for use as anti-static agents for a polymer substrate RaC(O)N(H)(CH2CH2O)zH(Ia) where: R@ is an alkyl group, or a monounsaturated alkenyl group, having 17 to 21 carbon atoms; and z is an integer selected from 3 to 7.

Preferred compounds of formula (I) according to the present invention are as follows: R is CH3 (CH2) 6, R, is hydrogen and a = y = 5; R is CH3 (CH2) 7CH=CH (CH2) 7, R, is hydrogen and a = y = 5; and R is CH3 (CH2)@ 7CH=CH (CHZ),, R, is hydrogen and a = y = 5.

Particularly preferred compounds according to the present invention are where: R is CH3 (CH2)7CH=CH(CH2)7,R1 is hydrogen and a = y = 5; and R is CH3 (CH2) 7CH=CH (CH2) u, R, is hydrogen and a = y = 5.

The present invention further provides use of a compound of formula (I) as an anti-static agent for a polymer substrate. It will be understood that reference to a compound of formula (I) herein includes reference to a compound of formula (Ia).

The present invention still further provides a method of dissipating static charge present on a surface of a polymer substrate, which method comprises contacting a compound of formula (I) with a polymer substrate in an amount effective to dissipate static charge present on a surface thereof. A compound of formula (I) may be incorporated into the bulk of the polymer substrate, or by surface application to the polymer substrate, substantially as herein after described in greater detail.

Compounds of formula (I) according to the present invention can be solids, pastes or free flowing liquids. Compounds of formula (I) 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 an anti- static agent for dissipating static charge present on a surface of the polymer substrate, the anti- static agent being selected from a compound according to formula (I). The anti-static agent may be incorporated into the bulk of the polymer substrate or by surface application to the polymer substrate. The polymer substrate may appropriately comprise a polymer film, polymer fibres, polymer mouldings or the like, and the polymer suitably comprises a commodity polymer such as polyethylene, polypropylene, polystyrene or the like.

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 (0) NH2 (II) where R is 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 12, preferably 3 to 7, moles of the ethoxylating agent are reacted with 1 mole of a compound of formula (II).

Compounds of formula (II) are commercially available products, and may be prepared by the reaction of a corresponding carboxylic acid of formula (III) with ammonia RC02H (III) where R is substantially as herein before defined. Carboxylic acids of formula (in) are preferably of vegetable or animal origin. Examples of particularly suitable carboxylic acids of formula (IIn 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). Particularly preferred compounds of formula (in) are erucic acid and oleic acid.

The reaction between compounds of formula (D) 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 l % by weight, of the reaction mixture There is further provided by the present invention a process of preparing a polymer substrate provided with an anti-static agent selected from a compound according to formula (I) substantially as herein before described, which process comprises contacting the polymer substrate with a compound of formula (1), whereby a compound of formula (1) can be either (a) incorporated into the bulk of the polymer substrate or (b) applied to the surface of the polymer substrate. According to (a), the polymer may be ground to a powdered form or the like, and a compound of formula (1) can then be blended therewith. Alternatively according to (a), a compound of formula (I) can be adsorbed onto a porous polymer substrate. According to (b) a compound of formula (I) can be applied to the surface of a polymer substrate so as to provide 1 to 3 mg/m2 of a compound of formula (I) on the polymer surface 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 Samnles for Testine For the incorporation of the anti-static additives into a polymer film, the following procedure was adopted.

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

Altematively the ethoxylated amide was adsorbed onto a porous polymer substrate at 50 % w/w 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 cooling bath followed by cutting to give an easily handled pellet form.

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

Example 2 Measurement of static charge decav time The time for the charge to decay to 1/e (approx. 37% of its original value) was recorded using a JCI 155 (John Chubb Ind.) static charge decay test unit. The sample was charged to 5000 V by corona discharge and the decay recorded after removal of the charging assembly. The decay time was defined as the time between the peak voltage (not the charging voltage) immediately after removal of the electrode and the time to reach 1/e of this voltage. All tests were carried out in a Faraday cage and at constant temperature and humidity (23°C/50% RH). Testing was carried out immediately after extrusion and at 72,168,336 hours after extrusion after conditioning for 1 hour in the humidity cabinet (where possible). Longer-term tests were also performed.

Example 3 LDPE film samples were sprayed separately with a solution of anti-static additives, including compounds of formula (I), in 2-propanol to give a level of 2mg/m2 of active ingredient on the polymer surface. In practice 10 cm3 of solution was sprayed onto a 20 X 20 cm sample of polymer film. Charge decay times were measured as described in Example 2 following conditioning for 3 hours at 23°C/50 % RH ....................................................... _-vs :...... le EO, :.. _.- : : : : : :, : :,- : : v : _ : : v : : : : v :' : : : =ti : 4 : : : : : : T : : : : = : : : : : : v : : : : : :.-. : : v : : = : : : :, r_ := : = : : : :,. ; i : 5 mole EO laurazùde Q 5-7 .y ' : 5 mole EO lauiamiiie :-. 0 : 5 :...- a- mole EO eiucamide...-" ; ; : 0. 33.... :- :.

(EO as used herein represents ethoxylated).

These results demonstrated the exceptional anti-static performance the 5 mole ethoxylates of fatty amides particularly those derived from the C 18 monounsaturated amide (oleamide) and the C22 monounsaturated amide (erucamide).

The 15 mole EO adduct of lauramide was ineffective as an anti-static agent, and is outside the scope of the present invention.

Example 4 Separate LDPE formulations containing 2500ppm of ethoxylated containing 3,5 and 15 moles of ethylene oxide were produced as described in Example 1. The charge decay times were measured after conditioning for 24 hours post extrusion. 3 rnole EO lauramide 3 insole EO lauramide 1 15 mole EO lauramide 500 Both the 3 and 5 mole adducts were effective anti-static additives whereas the 15 mole variant (outside the scope of the present invention) gave an unacceptablyhigh static decay time.

Example 5 Separate LDPE formulations containing 500ppm of 5 mole ethoxylates of four fatty amides of varying chain length and structure were produced as described in Example 3.

Charge decay times were measure at various time intervals after extrusion of the films. Addffive7'0 hours""" 3. 1irs ; : %'"""" :24hrs :''"''"""ICT.Iirs ;''''336hil : ; ; :'" ; ; 600'hrs||J>l (Mff|l .ilgli ;, ;.. :,. : :,31B. :. ;. : :,. : ; :|i.. (ida ; :- ; ; :. (T : !'.'xilClilE : ; ; :... (2i (aa||| 600 | s AdEvë~ O hõuis 3 firs :-24 hrsf-168 hri-336 hìi-~ 60û hriVÛig................ "-His"IBiHB SHBBHBEiH-HB BBBHiRBHHB MBpHBHB iyMil|iB MBSffiB saSWs SvsEO"18000 800 9. 0 1, 4 1-o.4.."'"'""'"..'O.Sjg enxcamide'Itooo 9. 0 t. 4 ; All products were effective anti-static agents but demonstrated differing migration and longevity characteristics.

Example 6 Separate LDPE formulations containing either 2500ppm of 5 mole ethoxylated oleamide or 2500ppm of various proprietary anti-static additives were produced.

Charge decay times were measured as a function of time after extrusion and the results are shown in Figure 1.

The 5 mole ethoxylated oleamide gave comparable anti-static performance to the lauric diethanolamide and was faster acting than the commercial ethoxylated tallow amine.

Example 7 The thermal stabilities of ethoxylated amide samples according to the present invention were compared with those of proprietary anti-static agents based on lauric diethanolamide and ethoxylated tallow amine.

The samples were assessed by Thermo-gravimetric Analysis, and the results are shown in Figure 2.

The 5 mole ethoxylated amides according to the present invention were clearly more thermally stable than current commercial anti-static agents. This renders them more suitable for use at high polymer processing temperatures than the conventional anti-static agents.