WO2014167313A1

WO2014167313A1 - Uv protected films

Info

Publication number: WO2014167313A1
Application number: PCT/GB2014/051093
Authority: WO
Inventors: Simon James Read; Jonathan Hewitt; Philipp MAYDANNIK; Kimmo LAHTINEN; David Cameron
Original assignee: Innovia Films Limited; Lappeenranta University Of Technology
Priority date: 2013-04-09
Filing date: 2014-04-08
Publication date: 2014-10-16
Also published as: GB201306427D0; GB2514539A

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.

Description

UV PROTECTED FILMS

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

UV barrier films are well known in the art. 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 ΤΙΟζ, ZnO, SiOa and AI2O3, TiOa is widely used as a UV blocker and has been added to polymers to improve their UV resistance. Inorganic UV blockers, such as TsG₂, provide UV protection by both scattering the UV rays and by the absorption of UV rays, Erdem si a/. (Journal of Applied Polymer Science, Vol.115, 152-157 (2010)) discusses the UV protective properties of nano- Ti0₂~doped polypropylene filaments in which the TiOa 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 nature of inorganic UV protecting agents or due to organic UV protecting agents degrading over time following exposure to UV radiation. This is unsatisfactory, particuiar!y where the polymer film is used in signage and packaging, where the optical clarify 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, with a desired compound in a continuous process (a so called "roii~to-roH" system). WO2008/057625 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. US8304019 discloses a system for ALD In a roi!-to-rol! manufacturing environment. At least a first portion of a substrate from a first roil is deposited in a chamber, A first ALD half reaction is performed on the portion of the substrate while the portion is within the chamber. A second ALD half 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 reaction chambers.

Polymeric films are used in a number of applications. Polypropylene films, particularly biaxially oriented polypropylene (BOPP) films, are often used in food packaging due to their transparency, high stiffness, thermal stability and low cost. However, problems may occur when the film is exposed to UV radiation. The photodegradation of BOPP 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 critically reduce its mechanical properties. Of the solar wavelengths, the UV-B component is particularly effective in photo-damaging materials.

Attempts to improve the UV resistance of polymers have been carried out, such as 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! (J, Am. Ceram. Soc 92[3] 849-654 (2009)) discusses the incorporation of ΤΊ0₂ onto high density polyethylene particles (HOPE) using ALD. The particles are extruded into films such that the Ti0₂ is integrated within the polymer material and not coated onto a polymer film. However, the method disclosed in Liang et al, and other prior art methods such as nanoparticle doping and chemical vapour deposition, are not appropriate for improving the UV resistance of flexible polymeric films 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 low hazing and high clarity.

Aspects and embodiments of the invention were devised with the foregoing in mind.

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 deposit UV-blocking compositions on the polymeric films. This is contrary to expectations since adding UV blocking 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 fiim without resulting in, or not least reducing, the hazing effects observed 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 resistance to degradation following exposure to UV radiation. The use of ALD to deposit a UV barrier 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 UV 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 diffusion 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 ALD is that it 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 nonuniform profile comprising a myriad of molecular intersticies on their surfaces, ALD 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 <100nm, more preferably <75nm, still more preferabl <50nm and most preferably <40nm. 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 composition may comprise one or more organic additives such as triazines, hindered amines, oxanilides, cyanoacry!ates, benzotriazoies, benzop enones 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 film is formed. However, the organic additives have a tendency to bloom or migrate from within the polymer material to the film surface over time, causing deterioration in the optical properties of the film. The use of the ALL) process avoids such blooming effects.

The flexible polymer film substrate may be a multilayer structure formed by any suitable method (such as co-extrusion and/or lamination) with one or more UV protecting layers provided on the susface of an outermost layer of the structure. The numbers of UV protecting layers 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 controlled by controlling the number of AID deposition/purge cycles. Each layer of deposited UV protecting material deposited by AID gsves rise to a thin (sub- nanometer thickness), amorphous, clear layer and therefore multiple layers may be applied until the substrate is 100% UV absorptive and/or blocking, and protected indefinitely. Typically, the total thickness of the multiple layers of deposited UV protecting material is around iOOnm or less. Nanopartide coatings deposited by chemical vapour deposition typically require organic adhesives to stick the nanoparticies 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 ALD 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 typicall exhibits a gloss at 45° angle of from 95% or more, preferably from 95% to 99%.

The UV protected flexible polymeric film may be clear. By 'clear' what is preferably meant is that the UV protected flexible polymeric film is transparent. For example, the UV protected flexible polymeric film may be transparent to light in the visible region of the spectrum.

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 multilayer 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 substantially equal machine direction and transverse direction stretch ratios, or can be unbalanced where the film is significantly more oriented in one direction {MD or TD). Sequential stretching can be used in which heated rollers effect stretching of the film 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 particularly from 6:1 to 8:1.

Many suitable benzotriazoles may be contemplated for use in one or more embodiments in accordance with the present invention, of which 2-(2'- hydroxy~3\ 5'~di~t~amyiphenyl) benzoiriazole, available under the trade name Cyasorb UV-2337 from Cytec Industries Inc. and under the trade name Lowilite 28 from Great Lakes Chemical Corporation, and 2-{5-chloro-2H- benzotriazole-2-yl)-8-(1 ,1-dimethylethyl)-4-methyl- phenol available under the trade name Tinuvin 326 and 2-{2H~benzotriazol-2~yl)-4_!8-bis{1~methyl-1~ phenylethyl)phenol available 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_s 2-hydroxy-4~(octy1oxy)~phenyl available under the trade name Chimassorb 81 from BASF Schweiz AG and 2-[4_!6-bis{2,4-dimethylphenyl)-1 ,3.5-thazln~2~yl]~ 5-{octyloxy)phenol available under the trade name Cyasorb UV-1184 from Cytec Industries Inc. may be mentioned as examples.

Many suitable 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 Shelfplus UV 1400 available from BASF Schweiz AG may be mentioned as an example.

Commercially available materials may also comprise a blend of one or more organic UV absorbers, together with one or more inorgansc UV absorbers, of which Shelfplus UV 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 available for example under the trade name Bayoxsde from Borchers GmbH.

The polypropylene substrate or the skin layers of the film may comprise additional materials such as anti-block additives, opacifiers, fillers, cross- linkers, 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 directly since, in the case of TIG₂, the surface energy of the protecting layer is sufficient to bind ink directly without any further treatment. The polymer film substrate may be reverse printed which would have the advantage of 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 UV light on the polypropylene substrate. The presence of a coating, such as TI0_2l 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 ceils and modules known as dye-sensitized solar cells (DSSCs) on flexible substrates, buffer layers are necessary to reduce the

1 ! interaction between the absorbing and the transparent conducting layer. UV protected flexible polymer films may be used as such buffer layers.

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 ΊΠ02 coatings. The coating thicknesses are 38 and 87 nm.

Figure 4 shows the apparent absorbance of visual light for BOPP films with atomic layer deposited T1O2 coatings. The coating thicknesses are 36 and 67 nm.

Figure 5 shows an IR spectra of BOPP films with atomic layer deposited TiO₂ 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.

Figure 8 shows atomic force microscopy (AFIWi) images of BOPP films coated with Ti0₂ 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.

Figure 10 shows UV reflectance spectra for a Ti0₂ coated sample, a ZnO coated sample and a control sample.

Figure 1 1 shows UV transmitlance spectra for a Ti0₂ coated sample, a ZnO coated sample and a control sample.

ΊΊ0₂ coating of BOPP using ALD

TiOa was deposited on BOPP film (Rayoface™ C58 supplied by Innovia Films Ltd) by ALD. Rayoface™ C58 is a three-iayer structure film having heat set laminated core in the middle sandwiched with two polyolefin top layers. The thickness of the film is 58 μτα. One side of the film is corona-treated for printing purposes. The film has relatively low additive levei. Both corona and non-treated sides of the film were equally used for the ALD depositions.

The ALD- TiOa coatings were deposited using a Beneq TFS 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 metai clips leaving an area of 1010 cm² inside the frames and to be ALD coated. Each batch included three sets of frames, i.e. six BOPP films were one-side coated with ALD in each batch performed. Teirakis(dimethylamino)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 1 mbar. Approximately 38, 87 and 97 nm thick Ti0₂ layers were obtained on the BOPP surface. The thicknesses were estimated using a spectroscopic ellipsometer from the surface of silicon pieces deposited in the same process as the polymer samples.

Characterisation of Ti0₂ coated! BOPP

UV block characteristics of the coatings were measured by using UV-Vis spectroscopy. The effects on the films before and following UV irradiation were then studied using IR spectrometry and differential scanning calorimetry. According to the results, the 38 and 67 nm coatings provided considerable decrease in the photodegradation of the BOPP film during UV exposure. IR spectra showed that during a six-week UV exposure, the 87 nm titanium oxide coating was able to almost completely prevent the formation of photodegradation 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 87 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 8 W (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 visible light absorbance of samples

The UV absorbance spectra of the ALD~Ti02 coated and uncoated BOPP films are shown in Figure 3. The ALD process temperature was 80°C and the coating thicknesses for the samples were 38 and 87 nm as measured on silicon samples deposited at the same time as the polymer sampies. Each spectrum of Figure 3 is based on the average of the absorbance of three samples. The absorbance level of BOPP film increases as a function of the Τί(¾ coating thickness. The absorbance increase in the films is not linear with thickness suggesting that the sample thickness on the BOPP 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 layer. The 38 nm Ti0₂ coating is able to cause a modest increase in absorbance whereas with the 87 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 sampies. This 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 apparent absorbance.

The absorbance is defined as a logarithmic ratio between the intensities of the radiation before and after it has passed through the material. The absorbance at a particular wavelength can be calculated according to equation (1 ), in which A_¾ is the absorbance, and log ratio of the intensity of radiation passed through the material IQ and the initial radiation /?,

The fraction of the radiation transmitted through the material, also known as transmittance, is shown in Table I, which shows the absorbances, transmittances and percent transmittances measured for the ALD-TIOg coated and uncoated BOPP films at various wavelengths. The table illustrates the significant UV blockability of the Ti(¾ coating especially in the case of 87 nm coating thickness. The lower the wavelength the higher the absorption ability is. In the UV-B region, the 87 nm coating is able to block 68 - 95 % of the UV light intensity. This can be a highly useful feature when exposing the BOPP film to outdoor conditions.

The degradation of the UV exposed BOPP 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, n 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 six-week UV exposure. This can be seen from the main products of pofypropyl photodegradation which are carbonyls (1700-1800 cm^"1) and hydroperoxides (3300-3800 cm^"1). The 38 nm ALD-TIOa coating was able to moderately decrease the carbony! spike for the BOPP film whereas there is no spike at all with the 87 nm coating.

According to agai at ai the background peak at 1000-1300 cm^"1 is due to CO stretch and OH-bend in polypropylene. This can also be 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 smaller for 38 nm coated film and even disappears for the 87 nm coated film. This also indicates the UV block feature of the ALD-TiOs coating.

The spectrum of the 87 nm ALD~TiQ₂ coated film generally follows the spectrum of unexposed BOPP film across the frequency area. Together with specific features, this supports the conclusion of prevented UV degradation in the BOPP film provided by the coating. The ALD-T1O2 coatings as such did not have any influence on the IR spectrum of the film.

Differential Scanning Ca!orimetry (DSC) examination

Table I! shows the melting point and enthalpy data for the base sheet and the 67 nm TiG₂ 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 ALD 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-TiOa coating provided clear protection for the BOPP film against the UV induced effects. 3ase sheet, 0 week ai

^!echansca! properties of BOPP films following UV exposure

Tensile strengths and elongations at break for the UV exposed BOPP film samples with various exposure times and Ti0₂ coatings are shown in Table N!. Figures 6 and 7 further Illustrate the results. The results show that after six- week UV exposure, the mechanical properties of the base sheet were completely degraded. After six-week exposure the tensile strength of the 67 nm Ti0₂ coated sample had decreased by approximately 60%. Thus, the TiC¾ coatings were able to protect the film from photodegradation.

The protection of the 87 nm coating was considerably better than that for the 38 nm coating. The Ti<¾ coatings had no considerable influence on the mechanical properties of the unexposed film. A slight improvement can be seen in both the tensile 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 38 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 87 nm coated sample.

Table 1, Te sile strengths and elongations attreak folk OT exposed BOPP fifcts iili end wilbtit the MQi coatings.

The results obtained indicate that the ALD- iOa coatings are able to protect the BOPP film from UV degradation.

Surface characteristics of BOPP following ALD 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 (AF ) of the surfaces of the Ti0₂ ALD coated BOPP film was conducted using a CP-!I Atomic Force Microscope fitted with a 20Nm 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 ΤΊΟ2 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 Ti0₂ using and ALD method did not adversely affect the optical clarity of the film.

Oxygen transmission rate

The oxygen transmission rate of the TIQ₂ ALD coated BOPP was determined at 23°C and 0% relative humidity. The results are shown in Figure 9. The results show the oxygen transmission rate of the BOPP film is decreased when TiC»2 is deposited on the surface of the BOPP film by ALD,

Haze characteristics

The wide angle haze characteristics and gloss characteristics of Ti0₂ ALD coated BOPP were determined using standard measurement techniques known in the art for determining each characteristic. Various optical characteristics of TiOa chemical vapour deposition coated BOPP were also determined using standard techniques known in the art. The results are shown in Tables IV and V below. The Wide Angle Haze (WAH) of a specimen is the percentage of transmitted 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 AST D1003. Table IV: Gloss and Haze characteristics of TsC ALD coated BOPP

Table V: optical characteristics of TsG₂ chemical vapour deposition coated BOPP.

Preparation of film samples with different UV-protecting compositions Two UV protected film samples were prepared.

The first UV protected film sample was prepared by depositing T\0₂ onto a Rayoface™ C58 film in the manner previously described under the section TiOa coating of BOPP using ALD', The resulting Τ!{¾ layers on the C58 film surface were approximately 80 nm thick. The thickness was estimated using a spectroscopic eliipsometer from the surface of silicon pieces deposited in the same process as the UV protected film sample.

The second UV protected film sample was prepared by depositing ZnO onto a Rayoface™ C58 film using the same method as that used for preparing the first UV protected film sample. The resulting ZnO layers on the C58 film surface were approximately 67 nrn thick. Again, the thickness was estimated using a spectroscopic ellipsometer from the surface of silicon pieces deposited in the same process as the UV protected film sample.

UV-Vis spectrometry was used to measure the reflectance of the two coated samples, as weli as the reflectance of an uncoated Rayoface^{i M} C58 film sample (the control sample).

The UV reflectance spectra of the two coated samples and the control sample are shown in Figure 10. From the results it can be seen that the ZnO coated sample is less reflective than the control sample across the majority of the wavelength range. The Ti0₂ coated sample is more reflective than the control sample at wavelengths between approximately 350 nm to 900 nm. However, below 350 nm, the ΤΊΟ₂ coated sample is less reflective than the control sample.

UV-Vis spectrometry was used to measure the transmittance of the two coated samples, as well as the transmittance of an uncoated Rayoface™ C58 film sample (the control sample). The UV transmsttance spectra of the two coated samples and the control sample are shown in Figure 11. From the results it can be seen that both the Ti0₂ coated sample and the ZnO coated sample have lower % transmission across the entire wavelength range compared to the % transmission of the control sample. Thus, with reference to Equation (1 ), it can be deduced that both the TiOa coated sample and the ZnO coated sample absorb more light than the control sample, particularly at wavelengths below 300 nm for the Τίί¾ coated sample and at wavelengths below 400 nm for the ZnO coated sample.

The results suggest that the TI02 and ZnO coatings preferentially absorb the deleterious UV radiation rather than the more sensitive GPP layer underneath.

As used herein any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic 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 specification are not necessarily all referring to the same embodiment.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a nonexclusive inclusion. For example, a process, method, article, or apparatus that comprises a list 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 following: 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 a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

The scope of the present disclosure includes any novel feature or combination of features disclosed therein either explicitly or implicitly or any generalisation 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 applicant hereby gives notice that new claims may be formulated to such features during prosecution of this application or of any such further application derived therefrom. In particular, with reference to the appended claims, 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

CLAI S

1. 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.

2, The UV protected flexible polymeric film according to Claim 1„ which is clear. ti The UV protected flexible polymeric film according to Claim 1 or Claim 2_S wherein the flexible polymeric film substrate is a polyolefin fi^m.

4, The UV protected flexible polymeric film according to any preceding claim, wherein the flexible polymeric film substrate is a polypropylene film.

5 The UV protected flexible polymeric film according to Claim 4, wherein the polypropylene film substrate comprises BOPP.

6, 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.

7. The UV protected flexible polymeric film according to Claim 8, wherein the inorganic additive is comprises one or more mineral and/or metal oxides.

8. The UV protected flexible polymeric film according to Ciaim 8 or Claim 7, wherein the inorganic additive comprises zinc and/or titanium oxides.

9_* The UV protected flexible polymeric film according to Claim 8, wherein the organic additive is selected from triazines, hindered amines, oxanilides, cyanoacryiates, benzotriazoles, benzophenones or mixtures thereof or mixtures thereof.

10. The UV protected flexibie 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%.

11. The UV protected flexible polymeric film according to any preceding Ciaim, which exhibits a gloss at 45° angle of from 95% or more, preferably from 95% to 99%.

12. 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. e method according to Ciaim 12, wherein the UV protected xible polymeric film is as defined in any of claims 1 to 11.