GB2514539A - UV protected films - Google Patents

Abstract

The present invention provides a UV protected flexible polymeric film comprising a flexible polymeric film substrate and one or more ALD deposited monolayers of a UV-protecting composition supported by the polymeric film substrate. Also provided is a method of manufacturing a UV protected flexible polymeric film using an ALD process (atomic layer deposition). The preferred UV protecting composition comprises an inorganic mineral and/or metal oxide, preferably zinc oxide (ZnO) or titanium dioxide (TiO2), which is deposited by the alternating exposure of the surface to tetrakis(dimethylamino)titanium (TDMAT) and ozone (O3). The preferred material for the polymer film is biaxially oriented polypropylene (BOPP), and the UV protective layer may be deposited in film thicknesses between 36 and 97 nm. Organic UV protectors may also be used, e.g. triazines, hindered amines, oxanilides, cyanoacrylates, benzotriazoles or benzophenones. The resulting films may be used in food packaging requiring low hazing and high clarity.

Description

UV PROTECTED FILMS

The present invention concerns a flexible polymer film having an ultra-violet radiation ((N) absorbing composition deposited thereon by atomic layer deposition (ALD).

UV barrier films are well known in the ad. Such films may comprise organic or inorganic UV blockers. The organic blockers are also called UV absorbers more generally UV protecting compositions because they mainly absorb, and thereby protect the film substrate, from the effects of UV rays. Inorganic UV blockers are usually certain semiconductor oxides such as Ti02, ZnO, 8102 and A1203. Ti02 is widely used as a UV blocker and has been added to polymers to improve their UV resistance. Inorganic 1W blockers, such as Tl02, provide UV protection by both scattering the UV rays and by the absorption of UV rays. Erdem et at (Journal of Applied Polymer Science, Vol.115, 152-157 (2010)) discusses the UV protective properties of nano-Ti02-doped polypropylene filaments in which the TiC)2 is integrated within the polymer structure by melt compounding from a polypropylene/Ti02 master batch mix.

TypIcally, polymer films have had UV protecting functionality imparted to them by nanoparticle doping or coating of the polymer film with a UV protecting compound or chemical vapour deposition. However, these processes generally result In a decrease in the optical clarity due to the UV protecting compound Imparting a hazy appearance to the film due to the particulate

I

nature of inorganic UV protecting agents or due to organic UV protecting agents degrading over time following exposure to UV radiation. This is unsatisfactory, particularly where the polymer film is used In signage and packaging, where the optical clarity of the film Is required, sometimes over long periods of time.

ALD is a process in which thin films of material are deposited on to a substrate in a controlled manner one atomic layer of film at a time. For example, to coat a substrate with a compound AB, the substrate is exposed to a precursor of A, PA. A monolayer of PA is absorbed on to the surface and excess PA Is then purged away. The substrate is then exposed to the precursor B, PB. PB reacts to form a layer AB, and any excess of PB Is purged away. This cycle is repeated as many times as required such that the deposited film is built up one layer per cycle. A typical ALD process is shown schematically in Figure 1.

ALD has been used widely in the electronics industry to coat silicon chips but less so in the plastics industry and, in particular, less so for coating polymer films. A number of ALD systems have been developed to coat flexible substrates, such as metal foils, polymer films or textiles, wtth a desired compound In a continuous process (a so called "roll-to-roll" system).

W02008057625 discloses a roll-to-roll ALD device. The device includes mechanisms to enable relative movement between a substrate to be deposited upon and various chambers containing ALD precursor gases.

US5304019 discloses a system for AU) in a roikordU manufacturing environment. At east a first porfion of a substrate from a first roll is deposited in a chamber, A first ALD half reaction is performed on the portion of the substrate whUe the portion is within the chamber, A second ALD heW reaction may be performed on the same portion of the substrate to form a layer of materiaL Multiple ALD sequences may be performed by passing the substrate through a sequence of ALD reaction chambers or by passing the substrate through one or more ALD reacflon chambers.

Polymeric fllms are used in a number of appflcations. Polypropylene films, particularly biaxially oriented polypropyiene (BOPP) films, are often used in food packaging due to theft transparency, high stiffness, thermal stability and ow cost. However, problems may occur when the film is exposed to UV radiation. The photodegradation of 60FF is an oxygen diffusion controlled process. The irradiation is strong at the surface of the polymer but falls off in the interior, In generaL UV irradiation causes chain scission, void formation and other structural changes in BOPP which crifically reduce its mechanical properfles. Of the solar waveiengths, the UV-B component is particularly effective in photo-damaging materials.

Attempts to improve the UV resistance of polymers, such polyesters used in fabrics and polypropylene filaments in the art have used nanoparticle doping of the polymer with a UV blocking composition or incorporation of a UV blocking composition into the polymer by chemical vapour deposition. Liang et a! (I Am. Ceram. Soc 92[3] 649654 (2OO)) discusses the incorporation of Ti02 onto high den&ty polyethylene particles (HDPE) using ALD. The paffides are extruded into tUrns such that the 1102 s integrated wfthin the polymer material and not coated onto a polymer tUrn. However, the method cflsclosed in Liang at aL and other prior art methods such as nanoparUcle doping and chemical vapour deposition, are not appropriate for improving the UV resistance of flexible polymeric tUrns since such techniques cause an increase in hazing in a flexible polymeric film which is unsatisfactory for applications such as signage and food packaging which require ow hazing and high Clarity Aspects and embodiments of the invention were devised wIth the foregoing in m nd.

The inventors have found that the hazing effect observed as an effect of the nanodoping and chemical vaporisation techniques used to coat flexible polymeric films in the art may be significantly reduced, and even avoided, by using ALD to deposft UV-bbcking compo&tions on the polymeric tUrns, This is contrary to expectations since adding UV hiocking functionality to polymeric films in the prior art has resulted in hazing and decreased optical clarity.

Consequently, the use of an ALD process may provide substantial UV barrier functionality that can be added to a target flexible polymeric film without resulting in, or not least reducing, the hazing effects obseed in other techniques such as nano-doping or chemical vapour deposition. Films of the present invention display enhanced optical properties compared to UV protected films formed by other means whilst also showing re&stance to degradation following exposure to UV radiation. The use of ALD to depo&t a UV baffler on a flexible polymeric film may also smooth out the profile of the film such that the UV protected film has acceptable optical clarity required for applications such as the use of the film in signage and packaging. Without wishing to be bound by theory, it is thought that an ALD deposited U'! barrier follows the contours of the surface of the substrate such that there Is a mInimum or no inclusions or particle diffraction centres. This results in a reduction in a contribution to light scattering and light diftkjsion compared to other deposition techniques such as sputtering, chemical vapour deposition or evaporative techniques.

Viewed from a first aspect, there is provided a UV protected flexible polymeric film comprising a flexible polymeric film substrate and one or more ALD deposited monolayers of a UV-protecting composition supported by the flexible polymeric film substrate.

Viewed from a second aspect, there is provided a method of manufacturing a UV protected flexible polymeric film comprising depositing one or more monolayers of a UV-protecting composition on the surface of a flexible polymeric film substrate by ALD.

A feature of AL!) is that is lays down a desired coating on a substrate on an atom by atom basis which can give an extremely homogenous and smooth surface. Typically, substrates, such as flexible polymer films, have a non-uniform profile comprising a myriad of molecular intersticies on their surfaces.

AID deposits a small amount of material such that the initial layer or layers of the deposited UV protecting composition tend to sit in the molecular intersticies of the substrate and consequently become embedded in the surface of the substrate at a molecular level. The deposition of subsequent layers may build up a profile on a substrate which is extremely smooth in its surface characteristics.

The flexible polymeric film substrate may be a web based material such as paper, a polymer film or flexible laminate material comprising one or more polymeric film substrates. The flexible polymer film substrate may be a polymer material such as polypropylene or polyethylene. In particular, the polymer material may be biaxially orientated polypropylene (BOPP).

The UV-protecting composition used to coat the polymeric film substrate may comprise an inorganic additive, organic additive or mixture thereof. The inorganic additive may be selected from one or more mineral oxides such as metal oxides, for example from non-aggregated zinc and/or titanium oxides or mixtures thereof. Smaller particle sizes result in a smoother profile of the flexible polymeric substrate when the particles are deposited by ALD.

Consequently, the mean particle size of the inorganic additive is preferably clOOnm, more preferably cl5nm, still more preferably c5Onm and most preferably c4Onm. Typically, the metal oxide composition is non-aggregated and this may be achieved by means known in the art such as coating or dispersion. Non-aggregation of the UV-protecting composition is inherent to the ALD coating process.

The UV-protecting composlUon may comprise one or more organic additives such as tdazines, hindered amines, oxaniUdes, cyanoacylates, benzotriazoes, benzophenones or mixtures thereof, In the context of polymeric films in the prior art, such organic additives have been incorporated within the polymeric material from which the flm is formed. However, the organic additives have a tendency to bloom or migrate from wfthin the poymer material to the ifim surface over fime, causing deterioration in the optical properties of the film. The use of the ALD process avoids such blooming effects.

The flexible polymer film substrate may he a multilayer structure formed by any suitable method (such as coextrusion andlor lamination) with one or more UV protecting layers provided on the surface of an outermost layer of the structure. The numbers of UV protecting ayers provided on the polymer film substrate depends on the end application in which the polymer film is used, The number of UV protecting layers may be easily controUed by controlilng the number of ALD deposition/purge cycles. Each layer of deposited UV protecting materia deposited by ALD gives rise to a thin (sub-nanometer thickness), amorphous, clear layer and therefore multiple layer may be applied until the substrate is 100% UV reflective and protected indefinitely. TypicaUy, the total thickness of the multiple layers of deposited UV protecting material is around lOOnm or less.

Nanoparticle coatings deposited by chemical vapour deposition typically require organic adhesives to stick the nanoparticles to a flexible polymeric substrate film and this can increase hazing of the flexible polymeric substrate film. A UV protected flexible polymeric film coated by an AID process does not require such organic adhesives.

The UV protected flexible polymeric film typically exhibits wide angle haze (WAH) of 1.3% or less, and particularly 1.1 to 1.3%.

The UV protected flexible polymeric film typically exhibits a gloss at 450 angle of from 95% or more, preferably from 95% to 99%.

The flexible polymeric substrate can be of a variety of thicknesses according to the application requirements. For example, the flexible polymeric substrate may be typically from about 10 to about 240 microns thick, particularly from about 20 to about 60 microns thick.

In the case where the polymeric substrate is a muitilayer film having one or more skin layers, the skin layers typically have a thickness of from about 0.05 microns to about 2 microns, from about 0.1 microns to about 1.5 microns, from about 0.2 microns to about 1.25 microns or particularly from about 0.3 microns to about 0.9 microns.

in one embodiment the polymeric film substrate is a polypropylene film comprising biaxially oriented polypropylene (BOPP). The BOPP film may be prepared with substantially balanced physical properties, for example as can be produced using substanUally equal machine direction and transverse direcflon stretch rafios, or can be unbaianced where the film is signfficanfly more oriented in one direction (MD or TD). Sequential stretching can be used in which heated rollers effect stretching of the tUrn in the machine direction and a "stenter over' is then used to effect stretching in the transverse direction, or simultaneous stretching, for example using the so-called bubble process. The machine direction and transverse direction stretch ratios are typically in the range of from 4:1 to 10:1, and particifiarly from 6:1 to 8:1.

Many suitable benzotdazoies may he contempiated for use in one or more embodiments in accordance with the present invention, of which 2-(2-hydroxy-3, 5'di-t-amylphenvF) benzotriazole, available under the trade name Cyasorb UV-2337 from Cytec Industries Inc. and under the trade name Lowte 28 from Great Lakes Chemical Corporation, and 2-(5-chloro-2H-benzotriazole-2-y-6-( t-dimnethylethy-4--methyi-phenol avallahie under the trade name Tinuvin 326 and 2-(2H-henzotriazol-2-yb)-46-bis(1 methyl-I -phenylethyl)phenol avaUable under the trade name Tinuvin 234 from BASF Schweiz AG may be mentioned as examples.

Many suitable benzophenones may be contemplated for use in one or more embodiments in accordance with the present invention of which methanone, 2-hydroxy4(octyioxy)-phenyl available under the trade name Chiniassorb 81 from BASE Schweiz AG and 2-[4,6-bis(24--dimethylphenyl)--1 3,5-triazin-2-yl]- 5(octytoxy)phenoi availabie under the trade name Cyasorb UV-1164 from! Cytec Industries Inc. may be menfioned as examples.

Many suftable combinations of benzotriazole(s) and benzophenone(s) may be contemplated for use in one or more embodiments in accordance with the present invention, of which Shelfpius UV 1400 avaUable from BASF Schweiz AG may be mentioned as an example.

CommercUy avaabie materials may aiso comprise a blend of one or more organic UV absorbers! together with one or more inorganic UV absorbers, of which Sh&fplus U'J 1400 is also an example.

Examples of UV absorbers are micronised metal oxides such as zinc and titanium oxides, and mixtures thereof. Suitable zinc oxide UV additives are commercially avaabie for example under the trade name Bayoxde from Borchers GmhH.

The polypropylene substrate or the skin layers of the film may comprise additional materials such as anti-block additives, opacifiers, fillers, cross-tinkers, colourants, waxes and the like.

ink may be printed on to the flexible polymeric films for applications such as signage or posters. The ink may be printed on to the UV protecting layer directiy since, n the case of 1102, the surface energy of the protecting layer is sufficient to bind ink directiy without any further treatment. The polymer film substrate may be reverse printed which would have the advantage of 1 0 shielding the ink itself from UV light once the end product is in use. The polymer film may be further treated, by corona discharge, for example. to improve ink receptivity of the film before the UV protecting layer is applied.

Flexible polymeric films may be used in posters, advertising hoardings and shop signs which currently, when the substrate is polypropylene, have about only a two year lifetime outdoors because of the deleterious effects of IN light on the polypropylene substrate. The presence of a coating, such as Ti02, laid down by ALD, produces extremely clear, non-hazy films ideal for the same purpose but with an extended lifetime in respect of exposure to UV light.

Flexible polymeric films are useful in the packaging industry since they have reduced oxygen and water permeation and prevent harmful gas/vapour transmission through the packaging material. The layers of UV protecting compositions deposited on the polymer film substrate act as a barrier to oxygen and water which helps preserve the packaged food whilst also protecting the food and the packaging from degradation by UV.

In thin film photovoltaic cells and modules known as dye-sensitized solar cells (DSSCs) on flexible substrates, buffer layers are necessary to reduce the interaction between the absorbing and the transparent conducting layer. UV protected flexible polymer films may be used as such buffer layers. I I.

One or more embodiments in accordance with the Invention will now be more particularly described by way of example only with reference to the following Examples and Figures in which: FIgure 1 shows schematically a typical ALD process.

Figure 2 shows a UV and visible radiation spectrum of the fluorescent lamp used in the study. The spectrum was measured from a distance of 155 mm.

Figure 3 shows UV absorbance spectra of BOPP films with atomic layer deposited Ti02 coatings. The coating thicknesses are 36 and 67 nm.

Figure 4 shows the apparent absorbance of visual light for BOPP films with atomic layer deposited 1102 coatings. The coating thicknesses are 36 and 67 nm.

Figure 5 shows an lR spectra of BOPP films with atomic layer deposited Ti02 coatings after six-week exposure to UV light.

Figure 6 shows the tensile strengths of the BOPP films as a function of UV exposure time.

Figure 7 shows the elongations at break of the BOPP films as a function of UV exposure time. 1.2

Figure 8 shows atomic force microscopy (AFM) images of BOPP films coated with 1102 deposIted by ALD and uncoated films.

Figure 9 shows the oxygen transmission rate of BOPP films coated with Ti02 deposited by ALD and uncoated films.

Ti02 coating of BOPP using ALD T102 was deposited on BOPP film (Rayofac&' C58 supplied by Innovia Films Ltd) by ALD. Rayoface C58 Is a three-layer structure film having heat set laminated core in the middle sandwiched with two polyolefin top layers. The thickness of the film is 58 pm. One side of the film is corona-treated for printing purposes. The film has relatively low additive level. Both corona and non-treated sides of the film were equally used for the ALD depositions.

The ALE)-T102 coatings were deposited using a Beneq IFS 500 ALD tool with a 3D batch reactor. Two polymer films were pressed together and sealed against each other with two rectangular polycarbonate frames laminated with aluminium foil. The frames were attached with metal clips leaving an area of 1010 cm2 inside the frames and to be AW coated. Each batch included three sets of frames, i.e. six BOPP films were one-side coated with ALD in each batch performed. Tetrakis(dlmethylamino)titanium (TDMAT) and ozone (03) were used as titanium and oxygen precursors, respectively. Nitrogen was used as a purge gas. The reactor temperatures used were 80 and 130°C and the pressure was approximately I mbar. Approximately 36, 67 and 97 nm thick 1102 layers were obtained on the BOPP surface. The thicknesses were 1! estimated using a spectroscopic ellipsometer from the surface of silicon pieces deposited in the same process as the polymer samples.

Characterisatlon of TiO coated BOPP UV block characteristics of the coatings were measured by using UV-Vis and IR spectrometry, and differential scanning calorimetry, According to the results, the 36 and 67 nm coatings provided considerable decrease in the photodegradation of the I3OPP film during UV exposure. PR spectra showed that during a six-week UV exposure, the 67 nm titanium oxide coating was able to almost completely prevent the formation of photodegradatlon products in the film, The mechanical properties of the film were also protected by the coating, but unlike the IR study suggested they were still compromised by the UV light. After a six-week exposure the tensile strength and elongation at break of the 67 nm titanium oxide coated film decreased to half of the values measured before the treatment, There was degradation of the uncoated base sheet after just four weeks of treatment, but no degradation was detected for the 67 nm coated film after the same period.

UV spectrum of lamp used in UV performance testing The sample exposure for UV radiation was conducted with an UV fluorescent lamp (UVP, Upland). The power of the lamp was 8W (230 V, 50 Hz, 0.16 A) and the distance of It from the samples was 155 mm. No mask was covering the fluorescent bulb. The radiation spectrum of the light was measured with an optical spectrometer from the same distance. The spectrum measured is shown in Figure 2. Treatment durations were from two to six weeks.

UV and vi&ble light absorbance of samples The UV absorbance spectra of the ALDThO2 coated and uncoated BOPF films are shown in Figure 3. The ALD process temperature was 80°C and the coating thicknesses for the samples were 3$ and 67 nm as measured on sificon samples deposited at the same time as the polymer samples. Each spectrum of Figure 3 is based on the average of the absorbance of three sampies. The absorbance levei of BOPP film increases as a function of the TO2 coating thickness. The absorbance increase in the films is nol linear with thickness suggesting that the sample thickness on the BOFP is not the same as on the silicon. This may be because of a longer nucleation period on the polymer or an initial period where there is diffusion of the ALD precursors into the polymer forming a mixed polymer-oxide ayer. The 36 nrn TO2 coating is able to cause a modest increase in absorbance whereas with the 67 nm coating the increase is significant.

It was visually observed that, in general, the higher the coating thickness the more the grey colour is emphasised in the is caused by the change in the reflectance of the sample because of the higher refractive index of the coating compared to the polymer. The phenomenon can be seen from the apparent absorbance of the samples in the visible region shown in Figure 4. The 67 nm coating in particular, causes a clear increase in the apcarent absorhance.

The absorbance is defined as a logarithmic ratio bePween the ntensfties of the radiation before and after it has passed through the materiaL The absorbance at a particular wavelength can be caicuted according to equation (1), in which AA is the absorbance, and log ratio of the intensity of radiation passed through the material / and the initial radiation I. A, :, ori1 (1) 2s The fraction of the radiation transmitted through the material, so known as transmittance, is shown in Table I. which shows the absorbances, transmittances and percent transmittances measured for the ALDJiQ2 coated and uncoated I3OPP ifirns at various wavelengths. The table iflustrates the significant UV NockabiUty of the 1102 coating especiaUy in the case of 67 nm coating thickness. The lower the wavelength the higher the absorption ahihty is. In the UV8 region, the 67 nm coating is able to block 68 95 % of the UV light intensity. This can be a highly useful feature when exposing the 80FF fHm to outdoor conditions.

\Vavelength Base thee 36 nmiiO2 coating 67 wnTiO! coatth8 (tiol) A LI 1009170 A I i00*Lft, A 1ootI; 250 0078 0,84 84 0.465 0.3 34 1.647 0.023 2.3 280 0086 0S 8) 0392 041 41 fl4 0049 49 300 0.058 0.87 87 0.276 0.53 53 0.843 0.14 14 315 0.053 0.89 89 0.199 0.63 63 0.493 032 32.

340 0.061 0.87 87 0.136 0.73 73 0.178 0.66 66 400 0.049 089 89 0.083 022 82 0.159 0.69 69 500 0.048 0.90 90 0.06 0.86 86 0.166 0.68 68 600 29 90 7.....i

Table I

Degradation of BOPP following exposure to UV The degradation of the U'J exposed BOPF samples was investigated by measuring the infrared spectra of them after individual exposure times. The spectra for the samples after six-week exposure are shown in Figure 5. Each spectrum represents an average absorption performance from two separate measurements, In the figure, the spectra are compared to the spectrum of unexposed BOPP film. The spectra show that the uncoated BOPP film had experienced a significant amount of degradation during the sixweek UV exposure. This can be seen from the main products of polypropy photodegradaflon which are carhonyls (1700-1300 cm') and hydroperoxides (3300-3600 cm5. The 36 nm ALD-Ti02 coating was able to moderately decrease the carbonyl spike for the BOPP film whereas there is no spike at aU with the 67 nm coating.

According to Nagai et aL the background peak at 1000-1300 cm" is due to CO stretch and OH-bend in polypropylene. This can also he seen from the spectra of Figure 5 as a background increase of the exposed base sheet at the same frequency. However, the background increase is found to be smaer for 36 nm coated film and even disappears for the 67 nrn coated film. This also indicates the UV block feature of the ALD-T102 coating.

The spectrum of the 67 nm ALD-TiO2 coated film generafly foflows the spectrum of unexposed BOPP film across the frequency area. Together with specific features, this supports the conclusion of prevented UV degradation in .7 the BOPP film provided by the coating. The ALD-T102 coatings as such did not have any influence on the IR spectrum of the film.

Differential Scanning Calorimetry (DSC) examination Table Ii shows the melting point and enthalpy data for the base sheet and the 67 nm Ti02 coated BOPP film before and after the six-week UV exposure.

According to the results, no clear glass transition temperature could be found for the samples. Neither the ALD coating nor the UV treatment caused a significant effect on the enthalpy of the film which suggests that the crystallinity of the sample as not changed. UV treatment significantly decreased the melting point of the uncoated BOPP, which indicates degradation of the polymer. Two clearly separated peaks were seen in the second heating run. The ALO coated samples also showed some changes after the UV treatment in the form of smaller shoulders in the melting peaks, but the peak of the second heating run was always identical with the untreated film. According to the DSC examination, the ALD-T102 coating provided clear protection for the BOPP film against the UV induced effects.

Table II. Melting temperatures (t). crystallisation temperatures (To) and enthalpies (AR) of uncoated and 67 inn TiO! coated BOPP Suns before and after the sixweek UV exposurt T°C(1.run AHJ!g T°C(1.nin bJlJ/g T°C(2.mi AHVg _________ up) -___ down) ___ up) ___ Basesheet,Oweeks 161.61169.5 -96.5 10&0 92.2 165.6 -89.0 Base sheet, 6 weeks 151.6 -101.2 110.0 8&0 148.81151.4 -90.0 6mm TiOj, 0 weeks 168.5 -97.3 108.8 92.6 165.4 -90,0 ölumTiO1,6weeks 158.2(sh)! -98.3 108.3 93.0 165.4 *92.1 __________________ 165.9Il693(sh) _______ ______________ _______ ____________ _______ tsh = shoulder peak 1 g Mechanica properties of I3OPP films foflowbig UV exposure Tense strengths and elongations at break for the UV exposed BOPP fHm sampes with various exposure times and TO2 coatings are shown in Table ILL Figures 6 and 7 further iUustrate the resufts. The results show that after six-week UV exposure, the mechanica properties of the base sheet were completely degraded. After six-week exposure the tensile strength of the 67 nm 1102 coated sample had decreased by approximatSy 60%. Thus, the TO2 coatings were able to protect the film from photodegradation.

The protection oF the 67 nm coating was considerably better than that for the 36 rim coating. The TO2 coatings had no considerable influence on the mechanical properties of the unexposed film. A shght improvement can be seen in both the tense strength and the elongation at break probably due to the thermal load of the ALD process. Once the UV exposure started, the mechanical properties of the sampLes began to decrease rapidly. A two-week exposure already shows a significant decrease in the properties. The 67 nm coated film could protect the BOPP for longer than the other coatings. For the 67 nm coated sample, similar characteristics were found after a four-week exposure than for the uncoated sample after a two-week exposure. For the uncoated and 36 nm coated samples, the dramatic decrease in properties occurred between two and four weeks of exposure. The similar kind of complete degradation was not detected at all for the 67 nm coated sample. 1 9

Table III. Tensile sengths aud elongations at break for the 11W exposed BOP? films vith and ithont the ALD.Ti02 coatings.

Teth strength (MPa) Etongáoo at break () ______ Noexp. lweeks 4weeks 6weeks Notip. lweeks Iweeks öweeh Baseslicet 115 63.2 24.6 03 30.8 15.7 13 1.3 36mnTiO2 140 10.5 33.1 24.0 40.6 16.9 6.3 1.9 dlnmTiO, 128 98,9 64.1 523 33.2 30.0 13.5 11.0 The results obtained indicate that the ALD-Ti02 coatings are able to protect the BOPP film from UV degradation.

Surface characteristics of BOPP toilowing ALt) deposition Generally, differences in the topography of a surface are indicated by larger roughness average (Ra). This value therefore provides a measure of the "smoothness" of a surface. Atomic Force Microscopy (AFM) of the surfaces of the T102 ALD coated BOPP film was conducted using a CP-ll Atomic Force Microscope fitted with a 2ONm cantilever, operated in intermittent contact mode. The feedback gain was set between 0.3 and 0.4. The images obtained are shown in Figure 8.

Generally, average surface roughness values positively correlate with poor optical clarity of BOPP films. Coating BOPP with Tb.2 did not cause a significant change in Ra values compared to uncoated films and no significant difference was seen in the Ra values comparing corona treated samples and non-corona treated samples. In other words, coating BOPP with T102 using and ALD method did not adversely affect the optical clarity of the film.

Oxygen transmissOfl rate The oxygen transmission rate of the T102 ALD coated BOPP was determined at 23°C and 0% r&ative humidity. The resuts are shown in Figure 9. The resufts show the oxygen transmission rate of the E3OPP film is decreased when 1102 is deposited on the surface of the BOPP film by ALD.

Haze characteristics The wide angle haze characterisfics and gioss characteristics of hO2 ALO coated BOPF were determined using standard measurement techniques known in the art for determining each characteristic. Various optic characteristics of Ti07 chemical vapour deposition coated BOPF were also determined using standard techniques known in the art. The results are shown in Tables IV and V b&ow. *ihe Wide Angie Haze (WAH) of a specimen is the percentage of transmftted light which, in passing through the specimen, deviates from the incident beam by more than 2.5 degrees by forward scattering, it is measured using a test method described in ASTM 01003.

Table IV: Gloss and Haze characteristics of hO2 ALD coated BOPP 98.0. Li 1.2 95.0 1.3 Avz97.3 Avgl.2 ____ Table V: optical charactehsflcs of Ti02 chemical vapour deposition coated BOPP.

Tl'ransrnission Haze (1⁄4) Clarity (1⁄4) (q/) _______________________ _______________________ 91.0 1.4 ____ 94.5 93M _____ lÀ 95.9 92.0 13 96.1 Ay" 920 Avgi S &v 95 5 -----.--.-.-.- -fl --As used herein any reference to one embodiment or "an embodiment' means that a particular element, feature, structure, or charactedstic described in connection with the embodiment is included in at least one embodiment.

The appearances of the phrase "in one embodiment" in various places in the specfticatior are not necessarily all referring to the same embodiment.

As used herein, the terms comprises,' comprising,' includes,' "induding," "has,' having or any other variation thereof, are intended to cover a non exclusive inclusion.. For example, a process, method, article, or apparatus that comprises a hst of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method; article, or apparatus. Further, unless expressly stated to the contrary, "or refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the foHowing: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of the "a' or "an" are employed to describe elements and components of the invention. This is done merely for convenience and to give -, 1 a general sense of the nvention This description should be read to indude one or at east one and the singular also includes the plural uniess it is obvious that t is meant otherwise.

In view of the foregoing descñption it wUl be evident to a person skified in the art that various modifications may be made within the scope of the invention.

rhe scope of the present disdosure includes any novel feature or combination of Features disclosed therein either expUcifly or implicitly or any generahsation thereof irrespective of whether or not it relates to the claimed invention or mitigate against any or all of the problems addressed by the present invention.

The appcant hereby gives notice that new claims may be formulated to such features during proseoLmon of this application or of any such further application derived therefrom, in particular, with reference to the appended dairns, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in specific combinations enumerated in the claims.

Claims (12)

1. CLAIMS1. A UV protected flexible polymeric film comprising a flexible polymeric film substrate and one or more ALt) deposited monolayers of a UV-protecting composition supported by the flexible polymeric film substrate.
2. 2. The UV protected flexible polymeric film of Claim 2, wherein the flexible polymeric film substrate is a polyolefin film.
3. 3. The UV protected flexible polymeric film of Claim I or Claim 2, wherein the flexible polymeric film substrate is a polypropylene film.
4. 4. The UV protected flexible polymeric film according to Claim 3, wherein the polypropylene film substrate comprises BOPP.
5. 5. The UV protected flexible polymeric film according to any preceding Claim, wherein the UV-protecting composition is an inorganic addItive, an organic additive or mixtures thereof.
6. 8, The UV protected flexible polymeric film according to Claim 5, wherein the inorganic additive is comprises one or more mineral and/or metal oxides. 2.4
7. 7, The UV protected flexible polymeric film according to Claim 5 or Claim 6, wherein the inorganic additive comprises zinc andlor titanium oxides.
8. 8. The LIV protected flexible polymeric film according to Claim 5, wherein the organic additive is selected from triazines, hindered amines, oxanilides, cyanoacrylates, benzotriazoles, benzophenones or mixtures thereof or mixtures thereof.
9. 9. The UV protected flexible polymeric film according to any preceding Claim which exhibits a wide angle haze (WAH) of 1.3% or less preferably between 1.1% and 1.3%.
10. 10. The UV protected flexible polymeric film according to any preceding Claim, which exhibits a gloss at 450 angie of from 95% or more, preferably from 95% to 99%.
11. 11. A method of manufacturing a WV protected flexible polymeric film comprising depositing one or more monolayers of a WV-protecting composition on the surface of a flexible polymeric film substrate by ALD.
12. 12. The method according to Claim 11, wherein the UV protected flexible polymeric film is as defined in any of claims I to 10.