EP2978587A1

EP2978587A1 - Printable film

Info

Publication number: EP2978587A1
Application number: EP14715091.6A
Authority: EP
Inventors: Simon Read; David Carruthers; Stephen Langstaff
Original assignee: Innovia Films Ltd
Current assignee: Innovia Films Ltd
Priority date: 2013-03-27
Filing date: 2014-03-27
Publication date: 2016-02-03
Also published as: GB2512358A; JP2016517902A; WO2014155128A1; GB201305632D0

Abstract

This invention concerns aprocess for producing a printable film comprising: providing a web of filmhaving a radiocarbon content;at a first location subjecting at least a first surface of the film web to a modified atmosphere dielectric barrier discharge (MADBD) treatment;winding the film web onto a reel;transporting the wound film web to a second location;unwinding the film web from the reel; and subjecting the first surface of the film to corona treatment. The invention also concerns printed films obtainable by the process of the invention, and articles of packaging and/or labelling made from such films.

Description

PRINTABLE FILM

The present invention is concerned with the surface treatment of substrates, particularly renewable or environmentally sustainable filmic substrates, to improve their printability. There is an increasing demand for filmic materials, such as those used in packaging or labelling for example, to be manufactured at least partly from renewable and/or sustainable sources. WO201 1/140496 discusses the issue in some detail.

There is also an ongoing demand for such materials to be printable.

Modified atmosphere dielectric barrier discharge (MADBD) treatment has been used for many years for the surface treatment of polymeric substrates. US7147758 for example is concerned with such treatments in the presence of a carrier gas, a reducing gas and an oxidising gas. It is not uncommon in the art for MADBD treatment to be called plasma treatment. In this specification no distinction is made between plasma treatment on the one hand and MADBD treatment on the other. However, both are treatments which typically take place in a modified gas atmosphere (i.e. an atmosphere other than air). Corona discharge treatment (also known as corona treatment or D treatment), is another form of dielectric barrier discharge which typically takes place at lower power (and with a larger electrode gap) than MADBD or plasma treatment, and typically takes place in an unmodified atmosphere - i.e. air.

Corona discharge treatment has been used considerably longer than MADBD treatment in the processing of polymeric films, and is an established technique in the industry. However, typically the manufacturers of modified atmosphere MADBD treaters have cautioned against using corona treatment in combination with MADBD treatment, apparently believing that the surface chemistry of MADBD treated film would be adversely affected by corona treatment. Consequently, it has rarely been contemplated to subject film to both MADBD and corona discharge treatment. US5147678 appears to contemplate such combinative treatments, but only in the context of laboratory experimentation and with unproven commercial utility. US7824600 expressly contemplates a two stage treatment in which a monoaxially l oriented film is subjected to a plasma treatment before being laterally stretched and corona treated prior to winding onto a reel. This document fails to appreciate that any benefit may be derived from a further or alternative downstream treatment of the film, and instead concentrates only on multiple treatments taking place before winding of the film onto a reel. On the other hand the benefit of downstream treatment is apparently recognised in US7410675, but only in the context of a repetition of a treatment having already once been conducted on the film.

One problem with MADBD treatment is that whatever surface modification of the film takes place under such treatment, the effect is not permanent, so that a treated film with surface characteristics making it suitable for printing tends to lose those characteristics over time and revert to being unprintable or poorly printable. This causes serious problems in the film industry because film manufacturers are rarely responsible for printing the films they make. Commonly, film manufacturers will instead wind film onto a reel and ship it to their customers, typically printers or converters, who will unwind the film prior to converting and/or printing it. Inevitably in connection with a MADBD treated film, by the time the film is then printed much of the surface characterisation caused by the MADBD treatment has been lost. Hitherto, film manufacturers have consequently sought to guarantee the long-term printability of the film by means other than MADBD treatment - the provision of printable coatings on the film for example.

What was realised in our co-pending application PCT/GB2012/052396 is that the surface characterisation of the film caused by MADBD treatment can be revived, improved or reconstituted considerably after (even many months after) initial manufacture and MADBD treatment of the film by the apparently straightforward expedient of corona treating the previously MADBD treated film. The combination of an initial MADBD treatment (normally during manufacture of the film) and a downstream corona treatment to refresh or even augment the surface properties of the MADBD-treated film has not hitherto been recognised in the art. Other combinatory and/or repetitious treatments mentioned in the art which also fail to appreciate this concept are disclosed in EP0947544, US7300859, US7067405, WO2008102408 US4929319, EP1620262, JP1 1256338 and JP9314773. According to the present invention there is provided a process for producing a printable film comprising: a. providing a web of film having a radiocarbon content; b. at a first location subjecting at least a first surface of the film web to a modified atmosphere dielectric barrier discharge (MADBD) treatment; c. winding the film web onto a reel; d. transporting the wound film web to a second location; e. unwinding the film web from the reel; and f. subjecting the first surface of the film to corona treatment. The radiocarbon content of the film is preferably at least about 10pMC, or at least about 20pMC, or at least about 30pMC, or at least about 40pMC, or at least about 50pMC, or at least about 60pMC, or at least about 70pMC, or at least about 80pMC, or at least about 90pMC, or at least about l OOpMC, or at least about 1 10pMC.

"pMC" in this connection means "per cent modern carbon". In this specification we use the term MADBD treatment to refer to a treatment which takes place in a modified atmosphere (i.e. not air). Corona treatment is a treatment that takes place at a lower power, with wider electrode gaps than in MADBD treatment, and in atmosphere (i.e. air). MADBD and corona treatment are, respectively, terms of art which will be understood by skilled addressees such as film manufacturers or the operators of printing, laminating and coating machines.

The invention also provides a process in accordance with the foregoing, wherein the corona treated film obtained at step f) is printed shortly after the said corona treatment. By "shortly after" we mean preferably within 10 days, more preferably within 5 days and most preferably within 1 day. Often printing will take place within hours, if not minutes, of the corona treatment step.

Printing of the film may be by any known process, UV Flexo, screen or combination printing, as well as gravure, reverse gravure, for example. The film may be subjected to the printing step before or after a sheet of the film has been severed from the web.

Optionally, the film may be subjected to other conversion steps - lamination, the provision of an adhesive layer and/or a release liner on the film web, before or after printing of the film and before or after severance of a sheet of film from the film web.

It is contemplated that the film may be subjected to MADBD treatment, and subsequently to corona treatment, only on its first surface or, optionally, on both surfaces. When both surfaces of the film are treated, it is sufficient for the purposes of this invention that only one surface be subjected both to MADBD treatment and, subsequently, to corona treatment. The other surface may be subjected to the same or similar treatment to the first surface, or to different treatment; for example only to MADBD treatment or only to corona treatment.

We have found that there are two primary factors in connection with the properties of the film at its first surface which determine its printability. These are the surface chemistry of the film on the one hand and its surface energy on the other. Surface chemistry is determinative of the ability of the film to bind with an ink applied to the surface, whereas surface energy is determinative of the wetting characteristics of an ink applied to the surface. Both good adhesion and good wettability are considered necessary to achieve a good printable film. The surface energy of the film at its first surface is initially increased by the MADBD treatment. Preferably the surface energy of the film at its first surface immediately after MADBD treatment is at least about 46dynes/cm, preferably at least about 50dynes/cm, more preferably at least about 56dynes/cm and most preferably at least about 60dynes/cm. Preferably the surface energy of the film at its first surface immediately after MADBD treatment is at least about 8dynes/cm, preferably at least about 15dynes/cm, more preferably at least about 20dynes/cm and most preferably at least about 24dynes/cm higher than the surface energy of the film at its first surface immediately before such MADBD treatment. After MADBD treatment the surface energy of the film decreases over time. Generally, by the time the film web is subjected to corona treatment in accordance with the process of the invention, the surface energy has reduced from its high point immediately after MADBD treatment by at least about 10%, often at least about 15%, or even by as much as 20% or 25%. Preferably, the surface energy of the film immediately after the corona treatment is back to within 15%, or at least 10%, of its value immediately after MADBD treatment. In some cases the surface energy of the film immediately after corona discharge treatment may even be above its surface energy immediately after MADBD treatment. The surface chemistry of the film is also affected by the MADBD treatment. Clearly, the affected characteristics will depend not only upon the nature of the film surface but on other factors such as the nature of the modified atmosphere, the energy level of the MADBD treatment, the size of the electrode gap and the duration of the treatment. For the purposes of this invention it is sufficient to state that the surface of the film following MADBD treatment will comprise a number of polar chemical species not present on the film surface prior to MADBD treatment. What we have now discovered is that subsequent corona treatment effects further changes to the surface chemistry of the film.

We have found that we are able to characterise surface chemistry of the film in terms of its functionality - that is to say, in particular the number of polar chemical species present at the surface of the film. Typically, the relative atomic concentration of polar chemical species measurable at the film surface immediately following MADBD treatment and subsequent exposure of the treated film to the atmosphere (whereupon any charged chemical species present on the film surface as a result of the MADBD treatment will be neutralized by the atmosphere) is y %, wherein y is a positive number. Because the effect of MADBD treatment dissipates over time as far as surface functionality is concerned, we generally find that the relative atomic concentration of polar chemical species measurable at the film surface immediately prior to the corona treatment step (after a period of time, generally of a least a few days, but often much longer, has elapsed after the initial MADBD treatment) is y-x %, wherein x is a positive number. Furthermore, because of the restorative or augmentative effect of the corona discharge treatment as concerns the functionality of the film, we then find that the relative atomic concentration of polar chemical species measurable at the film surface immediately after the corona treatment of step f) is y-x+z %, wherein z is a positive number.

Prior to MADBD treatment the surface of the film may, or may not, contain polar chemical species at its surface in any significant or substantial amount (above 1 % relative atomic concentration for example). A polyolefin film for example essentially comprises only carbon-carbon and carbon-hydrogen bonds and is therefore substantially non-polar. On the other hand, a polyester film or an acrylic-coated film for example will already contain polar chemical species, including of course at its surface. In the process of the present invention the relative atomic concentration of polar chemical species measurable at the film surface immediately prior to MADBD treatment is q %, wherein q is zero or a positive number and wherein q is less than y. Preferably y-x+z is at least about 5, preferably at least about 10 greater than q.

In the process of the present invention, y-x+z is preferably at least about 10, more preferably at least about 10.5, still more preferably at least about 1 1 , and most preferably at least about 1 1 .5, or even at least about 12.

The precise nature of the chemical functionality engendered at the surface of the film by MADBD treatment and/or by subsequent corona treatment will depend upon many factors, including the chemical characteristics of the film itself at its surface (meaning or including where applicable the chemical composition of any skin layer or coating or lamination thereon), the nature of the modified atmosphere provided during the MADBD treatment, the power and duration of the MADBD treatment and/or the subsequent corona treatment and other ancillary parameters such as the environment, both physical and chemical, in which the film is treated and/or maintained. Generally speaking, in connection with polymeric films, examples of polar species extant at the surface of the film after or during such treatments will at least include fragments containing carbon-oxygen bonds. Such fragments may derive from the film itself and/or from the atmosphere in which the film is treated. Other polar fragments may derive from the modified atmosphere of the MADBD treatment, alone or in combination with materials from the film. For example, when the modified atmosphere of the MADBD treatment comprises nitrogen gas, there will likely be polar fragments comprising carbon-nitrogen bonds at the film surface after MADBD treatment. (However, with some films - polyurethane for example - the presence of carbon-nitrogen polar fragments at the film surface may not require the use of nitrogen gas in the modified atmosphere of the MADBD treatment.) Generally the polar chemical species at the film surface after MADBD treatment will comprise one or more of the species selected from: nitrile; amine; amide; hydroxy; ester; carbonyl; carboxyl; ether and oxirane.

The technique of ToF-SIMS spectroscopy has been found to be a satisfactory method for measuring in qualitative terms the surface functionality (in terms of the identities of polar species present at the surface) of the film. However, for quantitative characterization (in terms of relative atomic concentration of polar species at the film surface) we have found the technique of XPS spectroscopy to be more useful. Other determinative methods will be apparent to the skilled addressee.

The modified atmosphere of the MADBD treatment will generally contain an inert carrier gas such as a noble gas or nitrogen, and at least one functional or reducing fluid such as acetylene, ethylene, hydrogen or silane for example. Oxidising fluids such as oxygen, ozone, carbon dioxide, carbon monoxide, nitric and nitrous oxides, and sulfur oxide, dioxide or trioxide may also be used.

Suitable film webs which can be used in this invention include webs formed from polymeric films. Polymeric film webs according to the invention can be made by any process known in the art, and the term includes, but is not limited to, cast sheet, cast film, or blown film. The film web may comprise a polyolefin film, for example polyethylene, polypropylene, polybutylene mixtures, blends and copolymers (both block and random) thereof, and/or other known polyolefins. Alternatively, the film web may comprise a polyester film, a polyamide film, a polyurethane film, a polyvinylhalide film, acetate film or a biopolymer film such as a cellulosic film, a PLA film, a starch based film or a PHA film.

For printable film intended for use as labels or in other types of packaging, polyolefin films are preferred, especially oriented polypropylene films, and still more preferred is an oriented polypropylene film according to EP-A-0202812. The film may have additional layers around the core layer, for example comprising copolymers of ethylene and propylene or terpolymers of propylene, ethylene and butylene. The film may comprise a biaxially orientated polypropylene (BOPP) film, which may be prepared as a balanced film using substantially equal machine direction and transverse direction stretch ratios, or can be unbalanced, where the film is significantly more orientated 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 oven is thereafter used to effect stretching in the transverse direction. Alternatively, simultaneous stretching, for example, using the so-called bubble process, or simultaneous draw stenter stretching may be used.

By "printable" is preferably meant "ink printable" and that in a standard ink pull-off tape test, scratch test, or UV flexo test conducted on a film according to the invention which has been printed on its first surface with a compatible ink and then cured (for example UV cured) and allowed to age for 24 hrs before testing, less than 50%, preferably less than 40%, more preferably less than 30%, still more preferably less than 20% and most preferably less than 10% of the ink is removed from the printed surface in the test. In a particularly preferred embodiment of the invention, less than 5%, or even as low as substantially 0%, of the ink is removed in such testing.

Also by "ink printable" is generally meant that in a standard ink pull-off tape test, scratch test, or UV flexo test conducted on a film according to the invention which has been printed on its first surface with a compatible ink and then tested immediately thereafter, less than 75%, preferably less than 60%, more preferably less than 50%, still more preferably less than 40% and most preferably less than 30% of the ink is removed from the printed surface in the test. In a particularly preferred embodiment of the invention, less than 20%, or even below 10%, of the ink is removed in such testing.

Also provided in accordance with the present invention is a printable film obtained or obtainable by the process of the invention. The invention also concerns a polymer labelstock film in accordance with the above printed on its first surface with at least one ink. The invention also provides a process for ink printing comprising providing a film in accordance with the above and supplying to the first surface of the film by means of screen, flexo, inkjet or other printing means, at least one compatible ink.

The film, or any of its layers in the case of a multi-layer film, may comprise additional materials such as anti-block additives, opacifiers, fillers, UV absorbers, cross-linkers, colourants, anti-static agents, antioxidants, cavitating agents, slip additives and the like.

The films used in accordance with the present invention can be of a variety of thicknesses according to the application requirements. For example they can be from about 8pm to about 240 m, from about 8pm or 20pm to about 200pm, from about 8pm or about 20pm or about 25pm to about 150pm, or from 8pm or 20pm or 25pm to about 75pm or about 100pm or about 125pm thick.

Preferably, the first location and the second location are remote from one another. More preferably the first location is a first factory or manufacturing site and the second location is a second factory or manufacturing site. The process of the invention allows a film manufacturer to operates steps a) and b) of the process to produce a printable film, which film can then be wound onto a reel and shipped to a customer (steps c) and d) of the process), such as a printer or converter, who will then operate steps e) and f) of the process and thereby refresh the film's printability performance following the diminishment in that performance that takes place during steps c), d) and e) of the process.

The invention also provides renewable or sustainable printable or printed webs of film obtainable or obtained by the above described methods.

Consequently, according to the present invention there is provided a printable film having a printable surface, the film comprising a substrate having a radiocarbon content, and at least one polar functional group present at the printable surface, and/or at an opposed surface, of the film and available to bond with an ink, the relative atomic concentration of the at least one polar functional group at the printable and/or opposite surface of the film being at least about 1 % and the concentration of the at least one polar functional group at the printable and/or the opposed surface of the film being at least about 1 % higher than the concentration of any of the same functional group present in the film immediately below the printable and/or opposed surface, wherein the film: a. is an uncoated film; and/or b. is a principally or entirely polyolefinic film; and/or c. is substantially free from acrylic components; and/or d. is substantially free from acrylate components; and/or e. is substantially free from cross-linkers; and/or f. is substantially free from polyurethanes; and/or g. is substantially free from polyesters; and/or h. is substantially free from plasticisers; and/or i. is substantially free from reactive components; and/or j. is substantially free from strong electrophiles.

By "substantially free" is meant preferably <0.5 wt %, more preferably <0.25 wt %, even more preferably <0.1 wt% and most preferably 0-0.05 wt % or 0 wt %.

By "immediately below" is preferably meant about 0.5pm below; or about 1 m below; or about 2 m below. Preferably, the concentration of the at least one functional group at the printable surface of the film is at least about 2% higher, more preferably at least about 5% higher and most preferably at least about 10% higher than the concentration of any of the same functional group present in the film immediately below the printable surface. For the avoidance of doubt, there need not be any of the at least one functional group present in the film immediately below its printable surface; although there may be.

The film may be substantially free from cross-linkers, examples of which include acrylate-functional cross-linkers, aziridine cross-linkers and ionomeric cross-linkers for example polyacid cross-linkers and multi-valent metal-containing cross-linkers. The film may be substantially free from reactive components, examples of which include ethylenically unsaturated compounds and imines.

The at least one polar functional group may be a nitrogen-containing functional group, for example a nitrile, amine or amide group; an oxygen-containing group for example a hydroxy, ester, carbonyl, carboxyl, ether, oxirane or silica group; a halogen-containing group wherein the halogen may be fluorine or chlorine for example; and/or a sulphur-containing group for example a thiol group.

Preferably the at least one polar functional group is a nitrogen-containing functional group. Additionally, at least one non-polar functional group may be present at the printable surface and/or at an opposed surface of the film and be available to bond with an ink. In particular, the non-polar functional group may be an ethylenic group.

The substrate may comprise a monolayer or it may comprise multiple layers, one or more of which constitutes a core layer of the film. Also provided in accordance with the invention is a printed film having a radiocarbon content comprising a substrate and an ink bound to the substrate by means of at least one carbon-nitrogen bond.

The invention depends upon the functionalisation of the film at its surface to generate a film which is preferably: a. a polyolefinic film comprising substantially no non-polyolefinic polymeric constituents; b. substantially free from cross-linkers at its printable surface; and/or c. substantially free from acrylic and/or acrylate materials at its printable surface; and/or d. substantially free from polyurethanes, polyesters, plasticisers, reactive components and/or strong electrophiles at its printable surface.

Also provided in accordance with the invention is a sheet of film severed or otherwise separated from such a web. The invention also provides a label or package comprising a sheet of film in accordance with the invention.

Also provided is an article labelled or packaged by a label or package in accordance with the invention. Also provided in accordance with the invention is the use of a sheet of film according to the invention in a labelling or packaging application in which it is necessary for the film to be derived from a renewable or sustainable source.

Consequently, the invention provides a printed polymeric film sheet having a radiocarbon content and comprising at least one ink bound to the surface of the film sheet via a functional group present at the surface of the sheet at a relative atomic concentration of a% but present at a location immediately below the surface of the sheet in an amount of from 0 to b%; b being less than a.

The radiocarbon content of the film is preferably at least about 10pMC, or at least about 20pMC, or at least about 30pMC, or at least about 40pMC, or at least about 50pMC, or at least about 60pMC, or at least about 70pMC, or at least about 80pMC, or at least about 90pMC, or at least about l OOpMC, or at least about 1 10pMC. a may for example be at least about 1 % or at least about, 2% or at least about, 3% or at least about, 4% or at least about 5%. b may for example be at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50% lower than a.

By "immediately below" is preferably meant about 0.5pm below; or about 1 pm below; or about 2pm below.

The invention further provides a printable polymeric film web having a radiocarbon content and a printable surface comprising functional groups at the printable surface capable of binding to an ink, the functional groups comprising a combination of functional groups inducible on the film surface by means of MADBD treatment and of functional groups inducible on the film surface by corona treatment. The functional groups may comprise a combination of functional groups inducible on the film surface by means of sequential treatment of the film by MADBD treatment and subsequently by corona treatment.

Preferably, the subsequent corona treatment is carried out at least 1 week, at least 2 weeks, at least 1 month or at least 3 months after the MADBD treatment.

The invention will now be more particularly described with reference to the following Examples.

Examples

A biaxially oriented polymeric film having a core layer of random polypropylene/polyethylene copolymer wherein the polypropylene has a radiocarbon content, and coextruded skin layers of polypropylene/polyethylene/polybutylene terpolymer is manufactured by means of a bubble process. The film has a total thickness of 55pm, with the skin layers between them constituting less than 1 pm of that thickness. Examples 1 to 6 below all use this film as a starting material.

Corona treatment of the film involves an electrical process using ionized air to increase the surface tension of non-porous substrates. Corona treatment converts the substrate surface from a normally non-polar state to a polar state. Oxygen molecules from the corona discharge area are then free to bond to the ends of the molecules in the substrate being treated, resulting in an increase in surface tension. Generally a film to be treated would pass under a filament where a streaming discharge through the air would earth on the film at speeds appropriate for a printing process.

MADBD treatment of the film differs from corona treatment in that the rate at which electron bombardment occurs is up to 100 times greater. This increased cross- linking activity forces a greater ion bombardment onto the substrate surface. This result increases etching of the substrate's surface, and stronger bonding attributes across the length of the film. In addition to these surface reactions, plasma also facilitates the use of chemical gases which can produce controlled chemical reactions on the surface as well. Generally a film to be treated would pass under a series of solid electrodes where a glow discharge through the modified atmosphere would earth on the film at speeds appropriate for a coating process.

Examples 1 to 6 The following film samples are used:

Example 1 : untreated film (control; comparative).

Example 2: film treated with MADBD at 50w/cm² in an atmosphere of N₂ and acetylene; 100ppm acetylene.

Example 3: film treated with MADBD at 55w/cm² in an atmosphere of N₂ and acetylene; 75ppm acetylene.

Example 4: film treated with MADBD at 45w/cm² in an atmosphere of N₂ and acetylene; 100ppm acetylene.

Example 5: film treated with MADBD at 75w/cm² in an atmosphere of N₂ and acetylene; 100ppm acetylene. Example 6: film treated with MADBD at 65w/cm² in an atmosphere of N₂ and acetylene; 100ppm acetylene.

Two samples of each film are prepared and each sample is left without further treatment for a 10 day period. At the end of that period of time, one sample of each film is corona treated at 50m/min; the other is not. All films are subjected to an ink adhesion test using a Sericol ink in a UV Flexo process followed by a scratch test. The scratch test is conducted using a nickel coin held at approximately 45 degrees and dragged away from the tester.

Table 1 shows the results that are achieved. Ink adhesion is measured on a scale of 1 to 3 (1 being relatively good and 3 being relatively poor). "N/A" indicates complete non-adhesion of the ink.

Table 1 Film Sample Ink adhesion score for the non- Ink adhesion score for the corona treated sample corona treated sample

Example 1 3 3

(control)

Example 2 3 1 .5

Example 3 3 1 .5

Example 4 N/A 1 .5

Example 5 N/A 1

Example 6 N/A 1

The results demonstrate that in relation to the control sample, corona treatment of the film makes no marked difference to the film's ink adhesion performance. In contrast, films treated by MADBD and then aged (by 10 days) show a marked improvement in ink adhesion performance upon corona treatment.

Examples 7 and 8

The film of example 1 is taken and MADBD treated in an atmosphere of nitrogen/acetylene; 200ppm acetylene at 65w/cm². The resulting film after brief exposure to the atmosphere (Example 7) is then surface characterised by XPS spectroscopy to determine the relative atomic concentration of polar species at its surface. The film is then re-tested by the same technique after being aged for 2 weeks (Example 8).

Table 2 shows the results that are achieved.

Table 2

Example 8 77.2 6.8 2 1 .1 0.6 - 12.5

^*Does not include any substantial amount of polar species

The total relative atomic concentration of polar species measurable at the film surface by XPS spectroscopy is 1 1.4% immediately after MADBD treatment, and 10.5% after aging of the film for two weeks, representing a significant deterioration in the ability of the film to bind a UV flexo ink, for example.

Subsequent corona treatment of the aged film causes the relative atomic concentration of polar species measurable at the film surface to rise to 1 1.2%.

Examples 9 and 10 The film of example 1 is taken and MADBD treated in an atmosphere of nitrogen/acetylene; 75ppm acetylene at 65w/cm². The treated film is aged for a period of approximately 2 months (Example 9) and then the resulting film is surface characterised by XPS spectroscopy to determine the relative atomic concentration of polar species at its surface. The film is then re-tested by the same technique after being aged for approximately 10 months (Example 10).

Table 3 shows the results that are achieved.

Table 3

^*The C-O bonds are likely to be surface C-OH bonds. *^*Does not include any substantial amount of polar species. Examples 11 and 12 A film sample of the same type as used as the control sample in Examples 1 to 6 is taken and subjected to MADBD at 65w/cm² in an atmosphere of N₂ and acetylene; 75ppm acetylene.

The treated film is aged for a period of six months and then its surface energy is measured using dyne solutions from Sherman.

The aged film is then corona treated at 0.3kW and 20meters per minute and its surface energy measured again.

Table 4 shows the results that are achieved.

Table 4

The results indicate that the surface energy of the film following MADBD treatment and subsequent aging can be re-boosted following corona treatment.

Example 13

A biaxially oriented polymeric film having a core layer of polypropylene with a radiocarbon content, and co-extruded polyolefin skin layers is manufactured by means of a bubble process. The film is MADBD treated in an atmosphere of nitrogen/acetylene; 200ppm acetylene at 65 kW/m².min. The resulting film is aged for 6 weeks and subsequently corona treated at 0.5kW and 30m/min. Samples of the film are printed by one of three methods: i. UV Flexo using an Optiflex^® ink ii. UV Screen using an Optiscreen^® ink iii. UV Flexo/Screen Combination Each printed sample is subjected to an ink pull-off tape test and scratch test (as previously described); a ruckle test wherein opposite edges of the sample are manually held and the sample is scrunched and then rubbed together at speed in a motion akin to pedals on a bike, for several seconds; and an appearance assessment. These tests are carried out as soon as the printed sample comes off the press i.e. 0 hours after printing, and 24 hours thereafter.

Table 5 shows the results that are achieved. Each of the parameters tested is measured on a scale of 1 to 3 (1 being relatively good and 3 being relatively poor).

Table 5

From the results it can be seen that good print quality is achieved using all three printing methods on the polypropylene-based film.

Claims

A process for producing a printable film comprising: a. providing a web of film having a radiocarbon content; b. at a first location subjecting at least a first surface of the film web to a modified atmosphere dielectric barrier discharge (MADBD) treatment; c. winding the film web onto a reel; d. transporting the wound film web to a second location; e. unwinding the film web from the reel; and f. subjecting the first surface of the film to corona treatment.

A process according to claim 1 wherein the radiocarbon content of the film is at least about 10pMC, or at least about 20pMC, or at least about 30pMC, or at least about 40pMC, or at least about 50pMC, or at least about 60pMC, or at least about 70pMC, or at least about 80pMC, or at least about 90pMC, or at least about 10OpMC, or at least about 1 10pMC.

A process according to claim 1 or claim 2 wherein the surface energy of the film at its first surface immediately after MADBD treatment is: i. at least about 46dynes/cm; ii. at least about 50dynes/cm; iii. at least about 56dynes/cm; or iv. at least about 66dynes/cm.

A process according to any one of claims 1 to 3 wherein the surface energy of the film at its first surface immediately after MADBD treatment is: i. at least about 8dynes/cm; ii. at least about 15dynes/cm; iii. at least about 20dynes/cm; or iv. at least about 24dynes/cm higher than the surface energy of the film at its first surface immediately before such MADBD treatment.

5. A process according to any one of claims 1 to 4 wherein after MADBD treatment the surface energy of the film decreases over time.

6. A process according to claim 5 wherein the time during which the surface energy of the film decreases is the time that elapses during steps c), d) and e) and any other intermediate or additional optional steps which take place prior to step f).

7. A process according to claim 5 or claim 6 wherein by the time the film web is about to be subjected to corona treatment in accordance with step f), the surface energy has reduced from its amount immediately after MADBD treatment by: i. at least about 10%; ii. at least about 15%; iii. at least about 20%; iv. at least about 25%; or v. at least about 50%.

8. A process according to claim 7 wherein immediately after the corona treatment of step f) the surface energy of the film returns to at least within: i. 20%; ii. 15%; or iii. 10% of its value immediately after MADBD treatment.

9. A process according to claim 8 wherein the surface energy of the film immediately after corona discharge treatment is above its surface energy immediately after MADBD treatment.

10. A process according to any one of claims 1 to 9 wherein the surface of the film immediately following MADBD treatment comprises a number of polar chemical species not present on the film surface prior to MADBD treatment.

1 1 . A process according to claim 10 wherein the relative atomic concentration of polar chemical species measurable at the film surface immediately following MADBD treatment is y %, wherein y is a positive number.

12. A process according to claim 1 1 wherein the relative atomic concentration of polar chemical species measurable at the film surface immediately prior to the corona treatment of step f) is y-x %, wherein x is a positive number.

13. A process according to claim 12 wherein the relative atomic concentration of polar chemical species measurable at the film surface immediately after the corona treatment of step f) is y-x+z %, wherein z is a positive number.

14. A process according to claim 13 wherein y-x+z is: a. at least about 10%; b. at least about 10.5%; c. at least about 1 1 %; d. at least about 1 1 .5%; and/or e. at least about 12%.

15. A process according to any one of claims 1 1 to 14 wherein the relative atomic concentration of polar chemical species at the film surface is measurable, or is measured by the technique of XPS spectroscopy.

16. A process according to any one of claims 1 to 15 wherein the film web comprises a filmic material selected from: polyolefins; polyesters; polyamides; polyurethanes; polyvinylhalides; acetates; biopolymers, including cellulose and cellulosic derivatives, PLA and PHA; and compatible mixtures, blends or copolymers of two or more thereof.

17. A process according to any one of claims 1 to 16 additionally comprising: g. printing the film web, or a film sheet severed therefrom.

18. A process according to any one of claims 1 to 17 wherein first location and the second location are remote from one another.

19. A process according to claim 18 wherein the first location is a first factory or manufacturing site and the second location is a second factory or manufacturing site.

20. A process according to claim 19 wherein a film manufacturer operates steps a) and b) of the process and a customer in the form of a printer or converter operates steps e) and f) of the process.

21 . A film obtained or obtainable by means of the process of any one of claims 1 to 19.

22. An article of packaging or labelling comprising the film of claim 20.

23. A printable film having a printable surface, the film comprising a substrate having a radiocarbon content, and at least one polar functional group present at the printable surface, and/or at an opposed surface, of the film and available to bond with an ink, the relative atomic concentration of the at least one polar functional group at the printable and/or opposite surface of the film being at least about 1 % and the concentration of the at least one polar functional group at the printable and/or the opposed surface of the film being at least about 1 % higher than the concentration of any of the same functional group present in the film immediately below the printable and/or opposed surface, wherein the film: a. is an uncoated film; and/or b. is a principally or entirely polyolefinic film; and/or c. is substantially free from acrylic components; and/or is substantia ly free from acrylate components; and/or is substantia ly free from cross-linkers; and/or is substantia ly free from polyurethanes; and/or is substantia ly free from polyesters; and/or is substantia ly free from plasticisers; and/or is substantia ly free from reactive components; and/or j. is substantially free from strong electrophiles.

24. A printed film having a radiocarbon content comprising a substrate having a printable surface and an ink bound to the printable surface by means of at least one carbon-nitrogen bond.

25. A printed film according to claim 24 which is: a. a polyolefinic film comprising substantially no non-polyolefinic polymeric constituents; b. substantially free from cross-linkers at its printable surface; and/or c. substantially free from acrylic and/or acrylate materials at its printable surface; and/or d. substantially free from polyurethanes, polyesters, plasticisers, reactive components and/or strong electrophiles at its printable surface.

26. A printed polymeric film sheet having a radiocarbon content and comprising at least one ink bound to the surface of the film sheet via a functional group present at the surface of the sheet at a relative atomic concentration of a% but present at a location immediately below the surface of the sheet in an amount of from 0 to b%; b being less than a.

27. A label or package comprising a sheet of film according to any one of claims 23 to 26.

28. An article labelled or packaged by a label or package according to claim 27.

29. Use of a sheet of film according to any one of claims 21 or 23 to 26 in a labelling or packaging application in which it is necessary for the film to be derived from a renewable or sustainable source.

30. A printable polymeric film web having a radiocarbon content and a printable surface comprising functional groups at the printable surface capable of binding to an ink, the functional groups comprising a combination of functional groups inducible on the film surface by means of MADBD treatment and of functional groups inducible on the film surface by corona treatment.

31 . A printable polymeric film web according to claim 30 wherein the functional groups comprise a combination of functional groups inducible on the film surface by means of sequential treatment of the film by MADBD treatment and subsequently by corona treatment.

32. A printable polymeric film web according to claim 30 or claim 31 wherein the functional groups comprise a combination of functional groups inducible on the film surface by means of sequential treatment of the film by MADBD treatment and subsequently after a period of at least 1 week, at least 2 weeks, at least 1 month or at least 3 months, by corona treatment.