Conventional PSA formulations are not generally very resistant to UV so can age badly where they are irradiated with UV over long periods. This can be an issue for example when a PSA is applied to an adherend that is substantially transparent or when for example a PSA is used to fix labels or graphic art decals for long periods outdoors. To improve UV resistance it is known to add to PSA formulations small quantities of known additives such as hindered amine light stabilisers (HALS) and/or anti-oxidants as for example described in US 6221198 (Gryska). UVA (UV additives) such as HALS or anti-oxidants act to slow down the degradation of the polymer lattice and rather than absorbing the UV radiation they primary work by reacting with the by-products formed by the UV radiation.

Adding such additives after the PSA latex has been formed has significant disadvantages. The additive (s) are difficult to distribute well within the polymer matrix.

Yet any non-homogeneity produces inconsistent UV resistance in the resultant PSA.

For example. when such PSAs form thin films on application to a substrate, greater discoloration will be seen in those parts of the adhesive film where there is little or no additive (and so less protection from degradation under UV) and a loss of adhesion to the substrate can also be observed. To compensate for this the additive is added at higher levels that is necessary to achieve UV resistance throughout the film. As the additive is also weakly held within the PSA film it tends to leach or bloom out of the film during use.

Instead if such conventional additives are added at an earlier stage for example whilst the PSA latex is formed to be better incorporated this is also unsatisfactory. The presence of such additives can destabilise the latex especially as other ingredients such as surfactants and dispersants are used to help disperse the additives in the aqueous phase so they mix better with the latex.

US 4701962 (Eye Pro Inc) describes eyewear to protect from UV and IR radiation which uses a UV stabilised film comprising known benzotriazoles and benzophenones UV stabilisers. However this reference does not teach how to modify such materials so that might be incorporated into an aqueous dispersion of a polymer latex with minimal effect on other desired properties. The reference is not concerned with optimising the properties of PSA formulations and a person faced with the problems described herein

would have no motivation to refer to this document which is in a distant and unrelated field.

Thus it is difficult to provided enhanced UV resistance to a PSA without having an adverse effect on its performance in other desired areas.

It is an object of the present invention to solve some or all of the above problems with prior art adhesive formulations.

The applicant has found certain UV attenuating species can usefully bind to acrylic polymers used to form PSA lattices.

Therefore broadly in accordance with the present invention there is provided a UV resistant composition suitable for use as a pressure sensitive adhesive, the composition comprising: (a) at least one acrylic polymer latex ; and (b) at least one UV attenuating species bonded to said polymer In the present invention the UV attenuating species is permanently bonded to the polymer backbone and thus low levels (preferably from about 0.1 % to about 2.0 % by total weight of the composition) can be used to achieve the desired good weathering performance and humidity resistance. No additional additives such as surfactants or dispersants are required to hold the UV attenuator in the polymer latex.

As used herein the term UV attenuating species (or UV attenuator) denotes a species which significantly absorbs UV and/or which reacts with other reactive species (such as free radicals) generated when the composition is irradiated with UV and which would otherwise degrade the composition of which the UV attenuator forms a part.

Usefully the UV attenuating species comprise one or more of the general class homopolymers and/or copolymers (e. g. ter-, tetra-and/or penta-polymers and/or multi- monomer compositions) of vinyl-functionalised monomers of benzotriazoles, benzophenones, s-triazines, oxalanilides and/or mixtures thereof.

More usefully benzophenone monomers suitable for use in the present invention may be selected from vinyl functionalised derivatives (whe re necessary) of one or more of the following known UV attenuators : 2,4-dihydroxy-benzophenone, 2-hydroxy-4- acryloxyethoxy-benzophenone, 2-hydroxy-4-methoxy-benzophenone, 2,2'-dihydroxy-4- methoxy-benzophenone, 2,2'-dihydroxy-4, 4'-dimethoxy-benzophenone, 2-hydroxy-4-n-

octoxy-benzophenone, 2,2', 4,4'-tetrahydroxy-benzophenone, and/or 4-dodecyloxy-2- hydroxy-benzophenone.

More usefully benzotriazoles monomers suitable for use in the present invention may be selected from vinyl functionalised derivatives (where necessary) of one or more of the following known UV attenuators : 2 (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (3,3', 5'-di-t-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole, 2- (3'-t-butyl-2'-hydroxy-5'- methylphenyl)-5-chlorobenzotriazole, 2 (2'-hydroxy-3', 5'-di-t-butylphenyl) benzotriazole, 2 (2'-hydroxy-3', 5'-di-t-amylphenyl) benzotriazole, and/or 2- (2'-hydroxy-5-t- octylphenyl) benzotriazole.

Preferably the UV attenuator comprises at least one monomer of Formula 1: Formula 1 where R1 is H or methyl, optionally methyl R2 is a divalent organo linking group, optionally optionally-substituted C, 4alkylene, more optionally ethylene ; R3 is a divalent organo linking group or a direct covalent bond betwen Z at the ring carbon, optionally a bond, a divalent carbonyl or a C1salkylenylcarboxy, such as ethylenylcarboxy X is independently C1 10alkyl, OH, OMe or SOn (where n is 1 or 2), optionally OH and/or t-butyl, more optionally 2'-OH (i. e. the OH is attached to the carbon atom on the benzene ring labelled 2 in Formula 1) and/or 3'-t-butyl ; p is 1 to 4, optionally 1 or 2; and where the circle Rg denotes either an optionally substituted phenyl ring or a ring of formula 1a : Formula 1 a where each Z is independently is N or CH, optionally all are N; Y is H, OH, OMe or SOn (where n is 1 or 2), optionally H; and qis1to4.

Conveniently the UV attenuating species comprises (meth) acrylate functionalised benzotriazoles or benzophenones, more conveniently those such as: 2-(2'-hydroxy-5'-methacryloxyethyi phenyl)-2H-benzotriazole ; 2- (2'-hydroxy-3'-tertbutyl-5'-methacryloxyethyl phenyl propionate)-2H-benzotriazole ;

2-hydroxy-4-acryloxyethoxy benzophenone.

A particularly convenient UV attenuator for use in the present invention is 2- (2'- hydroxy-5'-methacryloxyethylphenyl)-2H-benzotriazole (CAS No. 96478-09-0 and 73790-28-0) that is available commercially from Janssen Pharmaceutica under the trade designation NorBloc 7966 or from Ciba Speciality Chemicals under the trade name Tinuvin R-796.

Preferably the UV attenuating species is present in the polymer of the invention in an amount of less than about 10% more preferably from about 0.1 % to about 5% by weight of the total polymer.

Most preferably the UV attenuating species is a vinyl functional benzotriazole or benzophenone monomer comprising less than 10% by weight of the total vinyl monomers in the acrylic polymer of the invention.

Acrylic polymers for use in the present invention are those obtainable from conventional i. e. non UV attenuating) monomers generally selected to impart desired

performance characteristics to the final PSA for parameters such as Tg,, peel, shear strength and/or tack. Preferred non-UV attenuating monomers are vinyl functional monomers such as (meth) acrylic acids and esters thereof, hydroxy and/or carboxy vinyl compounds, vinyl aromatics, cyano compounds, vinyl acids, vinyl esters, cross-linking monomers and/or any suitable mixtures thereof.

More preferred acrylic polymers are those obtainable from one or more of the following monomer (s): methyl methacrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2- ethyhexyl (meth) acrylate, decyl methacrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, carboxyethyl acrylate, styrene, acrylonitrile, acrylamide, maleic acid, maleic anhydride, acrylic acid, vinyl acetate, vinyl formal, vinyl butryral, glycidyl methacrylate, allyl methacrylate, diallyl maleate"butylene diacrylate and/or suitable mixtures thereof. Most preferred polymers are those obtained by predominately (meth) acrylate monomers for example those obtained from methyl methacrylate, acrylic acid, butyl acrylic and/or vinyl acetate monomers.

Preferred acrylic polymers for use in the present invention are those obtained from one or more conventional vinyl functional monomers such as those described herein with one or more UV attenuating species such as those described herein.

Preferably the conventional vinyl functional monomer (s) are present in the polymer in an total amount of at least about 50% by weight of the total polymer.

Most preferred UV attenuating polymers of the invention are penta-polymers of methyl methacrylate, acrylic acid, butyl acrylic and/or vinyl acetate with a vinyl functionalised UV attenuating species such as 2- (2'-hydroxy-5'-methacryloxyethylphenyl)-2H- benzotriazole.

The preferred use of compositions of the invention is as pressure sensitive adhesives (PSAs) and thus preferably the acrylic polymer latex is selected and designed for such a use. More preferably the PSA formulated to be particularly suitable for marking and labelling applications including where the PSA is designed to be either permanent or removable. The compositions of the present invention are particularly useful for PSAs applied to a substrate as a thin clear film or coloured coating where some UV protection is required for either a short or extended time. For example PSA of present invention can be advantageous used for outdoor applications such as graphic arts.

The UV attenuating polymers of the invention may be prepared by conventional emulsion polymerisation of monomers such as those described herein using well known techniques. The polymers of the invention may be aqueous lattices comprising

colloidal particles of the UV attenuating polymer suspended in a substantially aqueous medium. The lattices may be adapted to form an adhesive polymer film. The lattices may be stabilised by suitable surfactants such as non-ionic alkaryl polyether alcohols and/or anionic alkaryl polyether sulfonates.

To form the polymer lattices of the invention, polymerisation of suitable monomer mixtures (dispersed by suitable surfactants) may be initiated by any suitable means such as reaction of a radical initiator such as potassium persulfate.

Polymers of the invention may conveniently have a Tg from about-50°C to about 50°C.

A further aspect of the invention provides use of a composition of the present invention employed in a film.

Other additives may be added to UV resistant PSAs of the present invention such as: thickeners, defoamers, plasticizers, wetting agents, slip and mar agents (e. g. silicones) biocides, fire retardants, pigments, dyes, and/or (at low level s) dispersants.

Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

" r, r The term"comprising"as used herein will be understood to mean that the li st following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature (s), component (s), ingredient (s) and/or substituent (s) as appropriate.

The terms'effective','acceptable''active'and/o r'suitable' (for example with reference to any process, use, method, application, preparation, product, material, formulation, compound, monomer, oligomer, polymer precursor, and/or polymers of the present invention and/or described herein as appropriate) will be understood to refer to those features of the invention which if used in the correct manner provide the required properties to that which they are added and/or incorporated to be of utility as described herein. Such utility may be direct for example where a material has the required properties for the aforementioned uses and/or indirect for example where a material has use as a synthetic intermediate and/or diagnostic tool in preparing other materials of direct utility. As used herein these terms also denote that a functional group is compatible with producing effective, acceptable, active and/or suitable end products.

The preferred utility of the compositions of the present invention is as adhesives preferably as pressure sensitive adhesives.

The terms'optional substituent'and/or'optionally substituted'as used herein (unless followed by a list of other substituents) signifies the one or more of following groups (or substitution by these groups): carboxy, sulpho, formyl, hydroxy, amino, imino, nitrilo, mercapto, cyano, nitro, methyl, methoxy and/or combinations thereof. These optional groups include all chemically possible combinations in the same moiety of a plurality (preferably two) of the aforementioned groups (e. g. amino and sulphonyl if directly attached to each other represent a sulphamoyl group). Preferred optional substituents comprise: carboxy, sulpho, hydroxy, amino, mercapto, cyano, methyl, halo, trihalomethyl and/or methoxy.

The synonymous terms'organic substituent'and"organic group"as used herein (also abbreviated herein to"organo") denote any univalent or multivalent moiety (optionally attached to one or more other moieties) which comprises one or more carbon atoms and optionally one or more other heteroatoms. Organic groups may comprise organoheteryl groups (also known as organoelement groups) which comprise univalent groups containing carbon, which are thus organic, but which have their free valence at an atom other than carbon (for example organothio groups). Organic groups may alternatively or additionally comprise organyl groups which comprise any organic substituent group, regardless of functional type, having one free valence at a carbon atom. Organic groups may also comprise heterocyclyl groups which comprise unival ent- ;-, groups formed by removing a hydrogen atom from any ring atom of a heterocyclic compound: (a cyclic compound having as ring members atoms of at least two different elements, in this case one being carbon). Preferably the non carbon atoms in an organic group may be selected from: hydrogen, halo, phosphorus, nitrogen, oxygen, silicon and/or sulphur, more preferably from hydrogen, nitrogen, oxygen, phosphorus and/or sulphur.

Most preferred organic groups comprise one or more of the following carbon containing moieties: alkyl, alkoxy, alkanol, carboxy, carbonyl, formyl and/or combinations thereof; optionally in combination with one or more of the following heteroatom containing moieties: oxy, thio, sulphinyl, sulphonyl, amino, imino, nitrilo and/or combinations thereof. Organic groups include all chemically possible combinations in the same moiety of a plurality (preferably two) of the aforementioned carbon containing and/or heteroatom moieties (e. g. alkoxy and carbonyl if directly attached to each other represent an alkoxycarbonyl group).

The term'hydrocarbo group'as used herein is a sub-set of a organic group and denotes any univalent or multivalent moiety (optionally attached to one or more other moieties) which consists of one or more hydrogen ato ms and one or more carbon

atoms and may comprise one or more saturated, unsaturated and/or aromatic moieties.

Hydrocarbo groups may comprise one or more of the following groups. Hydrocarbyl groups comprise univalent groups formed by removing a hydrogen atom from a hydrocarbon (for example alkyl). Hydrocarbylene groups comprise divalent groups formed by removing two hydrogen atoms from a hydrocarbon, the free valencies of which are not engaged in a double bond (for example alkylen). Hydrocarbylidene groups comprise divalent groups (which may be represented by"R2C=") formed by removing two hydrogen atoms from the same carbon atom of a hydrocarbon, the free valencies of which are engaged in a double bond (for example alkylidene).

Hydrocarbylidyne groups comprise trivalent groups (which may be represented by "RC="), formed by removing three hydrogen atoms from the same carbon atom of a hydrocarbon the free valencies of which are engaged in a triple bond (for example alkylidyne). Hydrocarbo groups may also comprise saturated carbon to carbon single bonds (e. g. in alkyl groups); unsaturated double and/or triple carbon to carbon bonds (e. g. in respectively alkenyl and alkynyl groups); aromatic groups (e. g. in aryl groups) and/or combinations thereof within the same moiety and where indicated may be substituted with other functional groups The term'alkyl'or its equivalent (e. g.'alk') as used herein may be readily replaced, where appropriate and unless the context clearly indicates otherwise, by terms encompassing any other hydrocarbo group such tas those described herein (e. g. comprising double bonds, triple bonds, aromatic moieties (such as respectively alkenyl, alkynyl and/or aryl) and/or combinations thereof (e. g. aralkyl) as well as any multivalent hydrocarbo species linking two or more moieties (such as bivalent hydrocarbylene radicals e. g. alkylen).

Any radical group or moiety mentioned herein (e. g. as a substituent) may be a multivalent or a monovalent radical unless otherwise stated or the context clearly indicates otherwise (e. g. a bivalent hydrocarbylene moiety linking two other moieties).

However where indicated herein such monovalent or multivalent groups may still also comprise optional substituents. A group which comprises a chain of three or more atoms signifies a group in which the chain wholly or in part may be linear, branched and/or form a ring (including spiro and/or fused rings). The total number of certain atoms is specified for certain substituents for example C organo, signifies a organo moiety comprising from 1 to N carbon atoms. In any of the formulae herein if one or more substituents are not indicated as attached to any particular atom in a moiety (e. g. on a particular position along a chain and/or ring) the substituent may replace any H and/or may be located at any available position on the moiety which is chemically suitable and/or effective.

Preferably any of the organo groups listed herein comprise from 1 to 36 carbon atoms, more preferably from 1 to 18. It is particularly preferred that the number of carbon atoms in an organo group is from 1 to 12, especially from 1 to 10 inclusi ve, for example from 1 to 4 carbon atoms.

As used herein chemical terms (other than IUAPC names for specifically identified compounds) which comprise features which are given in parentheses-such as (alkyl) acrylate, (meth) acrylate and/or (co) polymer-denote that that part in parentheses is optional as the context dictates, so for example the term (meth) acrylate denotes both methacrylate and acrylate.

Certain moieties, species, groups, repeat units, compounds, oligomers, polymers, materials, mixtures, compositions and/or formulations which comprise and/or are used in some or all of the invention as described herein may exist as one or more different forms such as any of those in the following non exhaustive list : stereoisomers (such as enantiomers (e. g. E and/or Z forms), diastereoisomers and/or geometric isomers); tautomers (e. g. keto and/or enol forms), conformers, salts, zwitterions, complexes (such as chelate, clathrates, crown compounds, cyptands/cryptades, inclusion compounds, intercalation compounds, interstitial compounds, ligand complexes, organometallic complexes, non-stoichiometric complexes, rr-adducts, solvates and/or hydrates); isotopically substituted forms, polymeric configurations [such as homo or copolymers, random, graft and/or block polymers, linear and/or branched polymers (e. g. star and/or side branched), cross-linked and/or networked polymers, polymers obtainable from di and/or tri-valent repeat units, dendrimers, polymers of different tacticity (e. g. isotactic, syndiotactic or atactic polymers)] ; polymorphs (such as interstitial forms, crystalline forms and/or amorphous forms), different phases, solid solutions; and/or combinations thereof and/or mixtures thereof where possible. The present invention comprises and/or uses all such forms which are effective as defined herein.

Polymers of the present invention may be prepared by one or more suitable polymer precursor (s) which may be organic and/or inorganic and comprise any suitable (co) monomer (s), (co) polymer (s) [including homopolymer (s) ] and mixtures thereof which comprise moieties which are capable of forming a bond with the or each polymer precursor (s) to provide chain extension and/or cross-linking with another of the or each polymer precursor (s) via direct bond (s) as indicated herein.

Polymer precursors of the invention may comprise one or more monomer (s), oligomer (s), polymer (s); mixtures thereof and/or combinations thereof which have suitable polymerisable functionality.

A monomer is a substantially monodisperse compound of a low molecular weight (for example less than one thousand daltons) which is capable of being polyme rised.

A polymer is a polydisperse mixture of macromolecules of large molecular weight (for example many thousands of daltons) prepared by a polymerisation method, where the macromolecules comprises the multiple repetition of smaller units (which may themselves be monomers, oligomers and/or polymers) and where (unless properties are critically dependent on fine details of the molecular structure) the addition or removal one or a few of the units has a negligible effect on the properties of the macromolecule.

A oligomer is a polydisperse mixture of molecules having an intermediate molecular weight between a monomer and polymer, the molecules comprising a small plurality of monomer units the removal of one or a few of which would significantly vary the properties of the molecule.

Depending on the context the term polymer may or may not encompass oligomer.

The polymer precursor of and/or used in the invention may be prepared by direct synthesis or (if the polymeric precursor is itself potymerie) by polymerisation. If a polymerisable polymer is itself used as a polymer precursor of and/or used in the invention it is preferred that such a polymer precursor has a low po lydispersity, more preferably is substantially monodisperse, to minimise the side reactions, number of by- products and/or polydispersity in any polymeric material formed from this polymer precursor. The polymer precursor (s) may be substantially un-reactive at normal temperatures and pressures.

Except where indicated herein polymers and/or polymeric polymer precursors of and/or used in the invention can be (co) polymerised by any suitable means of polymerisation well known to those skilled in the art. Examples of suitable methods comprise: thermal initiation; chemical initiation by adding suitable agents; catalysis; and/or initiation using an optional initiator followed by irradiation, for example with electromagnetic radiation (photo-chemical initiation) at a suitable wavelength such as UV; and/or with other types of radiation such as electron beams, alpha particles, neutrons and/or other particles.

The substituents on the repeating unit of a polymer and/or oligomer may be selected to improve the compatibility of the materials with the polymers and/or resins in which they may be formulated and/or incorporated for the uses described herein. Thus the size and length of the substituents may be selected to optimise the physical entanglement

or interlocation with the resin or they may or may not comprise other reactive entities capable of chemically reacting and/or cross-linking with such other resins as appropriate.

Many other variations embodiments of the invention will be apparent to those skilled in the art and such variations are contemplated within the broad scope of the present invention. Further aspects of the invention and preferred features thereof are given in the claims herein.

Examples The present invention will now be described in detail with reference to the following non limiting examples which are by way of illustration only.

Standard latex formulation The standard aqueous latex formulation described in Table 1 was used to prepare the following PSAs using the same conventional acrylic comonomers. The differences in the PSA formulations related to the UV attenuator.

Table 1 Ingredient Amount/q Initial charge Water 224.38 NaHCO3 1.43 KOS04 3.10 Pre emulsion Water 86.57 Abex EP-120 8.38 Triton X-305 3.48 Aerosol OT 3.00 Monomers Glacial acrylic acid (AA) 6.57 Vinyl acetate (VA) 21.80 Methyl methacrylate (MMA) 60.17 Butyl acrylate (BA) 561.23 Tinuvin R 796 13.26 Stop solution TBHP (70% aq soln) 0.21 Parolite 0.19 Nofoam 1976 3.10 The following ingredients listed in Table 2 are identified by their trade names:

Table 2 Trade name Chemical description Primarv Function Suitable source Abex EP-120 ethoxylated nonylphenol sulfate ionic surfactant Rhone- ammonium salt Poulenc.

Triton X-305 octylphenol ethoxylate non-ionic surfactant Dow (average no. of ethoxy groups per mol = 30) Aerosol OT Sodium salt of 1,4-bis (2-ethyl dispersing agent Cytec hexyl) sulfosuccinate, Tinuvin R-796- (2-hydroxy-5-methacryloxyethyl UV attenuator Ciba phenyl)-2H-benzotriazole TBHP t-butyl hydroperoxide polymerisation Various initiator Parolite Zinc formaldehyde sulfoxylate, reducing agent Royce Zn (HSO2CH20) 2 International Nofoam1976 proprietary mixture of defoamer Oil Chem Tech.

Surfactants Inc.

Method The initial charge of water, sodium bicarbonate, and potassium persulfate was added to one litre glass reactor equipped with an overhead agitator with two delay feeding pumps and was heated to 82°C. In a metal vessel the pre-emulsion of surfactant was prepared by mixing under high agitation for 15 minutes the water, Abex EP-120, Triton X-305, and Aerosol. The monomers (AA, VA, MMA, BA and Tinuvin R796 where present) were mixed in a glass container until a clear solution was obtained. The monomer mixture was then added to the pre-emulsion slowly and mixed for 30 minutes as the agitator speed was increased from 200 to 900 rpm. When the temperature of this mixture reached 77°C it was slowly added to the reactor via the delay pumps at a rate of about 3.2 g per minute over 4 hours with the reactor temperature at 82°C and the agitator set to 200 to 250 rpm. The reactor was held at 82°C for a further 30 minutes and then cooled to 65°C after which the stop solution was added and the mixture held at 60°C for 10 minutes. The reaction was cooled to 30°C whilst mixing at 300 to 350 rpm and then a suitable biocide was added (such as Kathon LX from Rohm & Haas) and the mixing was continue for a further 10 minutes. The product was collected by filtration through a 5 pm filter..

Examples 1 to 4 and Comp A & B Comp A contains no UV attenuator Comp B contains 0.5 % HAL & 1. 0% benzotriazole by weight of polymer which were added to the latex post polymerisation.

Examples 1 to 4 contain the amounts shown in table 3 of Tinuvin R-796 as a UV attenuating (co) monomer. This is bound to the polymer backbone of the resultant latex.

Table 3 Ex % of R-796 (as weight % of total monomer) 1 0. 5 2 1.0 3 2.0 4 5.0 Each of these examples was tested for UV resistance as described above.

Testing for UV resistance A sample of the adhesive latex was cast directly (at a coat weig ht of 1 mil) onto a Mylar film of thickness 1 mil and then dried under ambient conditions in air for 10 minutes and then at 90°C for 5 minutes. The dried coated Mylar film was then laminated onto a silicone release liner and cut into 2 inch by 4 inch strips. The strips of coated Mylar were removed from the release liner and carefully bonded to a white pigmented PET (nylon) film of 2 mil thickness ensuring no air bubbles were formed. This PET/Mylar laminate was in turn attached to a stainless steel substrate for use in the UV exposure tests.

The steel mounted laminate was mounted in an accelerated weather meter and exposed to UV radiation from a carbon arc (model Atlas GI 65A-GB 2413) as described in standard test method for marking and labelling systems UL 969 section 7.5 (7 June 1989). The degree of yellowing as a function of exposure time to UV was assessed periodically (weekly) both visually and also measured quantitatively as a Yellowing Index (YI) using a BYK Chemie colour measuring apparatus type 4411, calibrated with a BaS04 standard. The higher the yellowing index the worst the degree of yellowing.

The results are given in table 4.

Table 4 (Yellowing Index) UV exposure Comp A Comp B Ex 1 Ex 2 Ex3 Ex4 time/hours<BR> 0 0 0 0 0 0 0 168 3.57 2.06 2.19 0.71 0.53 0.36 355 12.16 2.60 2.81 2.51 1.43 0.97 522 18.72 5.08 5.41 4.03 4.48 3.45 722 22.69 6.63 7.09 6.48 6.55 5.27 PSA performance Those properties desirable in a PSA were also measured for each of these formulations as follows (data in Table 5).

The percentage by weight of solids was determined by placing a known amount of latex into a pre-weighed aluminium tin then dried at 150°C for 60 minutes and reweighed to calculate the latex solids.

The average particle size was measured using a Horiba laser scattering particle size distribution (PSD) analyser model LA 910.

The pH of the un-neutralized latex was measured using an Orion model 250 pH meter.

If desired the pH of the latex can be subsequently adjusted to between 6 to 9 using either NH40H or 2-amino-1-methylpropanol.

The Brookfield viscosity is measured using a Brookfield viscometer model LV ll+ with spindle #3 and #4 at 40 rpm.

Table 5 (PSA properties) Example % wt solids av PSD pH Visc 1% lum/cps Comp A 67.15 0.526 4.10 1488 Ex 1 67.24 0.560 4.18 3908 Ex 2 67.35 0.528 4.16 5240 Ex 3 67.79 0.502 4.09 7620 Ex 4 67.31 0.520 4.21 2292 Comp B 59.94 0.532 6.65 720 The data in Tables 4 and 5 show that PSAs of the invention (Examples 1 to 4) have enhanced UV resistance compared to a conventional PSA (Comp A) without having a significant effect on desired PSA properties compared to a PSA when UV additives are post mixed into the latex (Comp B).