GB1572345A - Treating plastics film materials and to materials so treated - Google Patents

Description

(54) TREATING PLASTICS FILM MATERIALS AND TO MATERIALS SO TREATED (71) We, E.T. MARLER LIM1TED, a British Company of Deer Park Road, Wimbledon, London SW19, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to treating plastics film materials and to materials so treated.

In particular the invention relates to the treatment of plastics films to improve their surface properties, e.g. to improve the printing performance of a plastics film and the performance of a plastics film when other compositions are applied to its surface, e.g. adhesives used for laminating the plastics film to other materials. The treatment may also aid in preventing contamination by or of other materials placed in contact with the plastics film, by migration or transfer of migratory or transferable contaminants.

It is known to treat the surface of polythene and polypropylene plastics film to improve the adhesion of printing inks or adhesives to the surface thereof by electric corona treatment or flame impingement, prior to printing or adhesive laminating. This particular treatment is commercially viable because it can be carried out at high speed so the cost is very low. However, the treatment loses its effectiveness on ageing and it is necessary to print the plastics film immediately after treatment to obtain reliable results.

Corona treatment may also reduce the ability to heat-seal the plastics film.

It is also known to apply a coat of lacquer to certain plastics sheet materials to improve the adhesion thereto of printing inks. Such known treatments are costly since the lacquer consumption is very high. For example, to apply the normal dry lacquer thickness of the order of 25 micrometers (pom) a wet coating weight of 125 grams of lacquer per square metre of plastics film is required at 20% v/w lacquer solids. A very large and costly coating and drying plant is required to apply a uniform coat of lacquer even at modest speeds. The material and coating costs are doubled if lacquering of both sides of the plastics film is required since each side must be treated separately.Moreover, lacquering introduces technical disadvantages and may adversely affect certain important mechanical and thermal properties of the plastics film such as sheet flatness, flexibility, elongation, cutting, folding, heat-sealing and high frequency welding, and heat-forming (including vacuum-formingproperties. In addition, the feeding properties of the lacquered sheet on printing, laminating and converting equipment may be made worse, notably as regards the tendency of the plastics film to acquire an electrostatic charge. Generally the lacquer coating, which may amount to a significant propertion of the sheet thickness, has a lower or different feeding performance from that of the base plastics film material.Because of these technical and economic disadvantages, lacquering is seldom used and the majority of plastics film are printed, adhesively laminated, and otherwise used without any pre-treatment. In particular, a great volume of vinyl plastics film produced by high temperature calendering, is printed and adhesively laminated without pretreatment.

For example, the base film used in vinyl selfadhesive plastics films in which the base plastics film is coated with a pressuresensitive adhesive and temporarily laminated to a silicone-coated release paper, is not pretreated.

Vinyl plastics films are normally composed of polyvinyl chloride homopolymer, vinylchloridevinylacetate copolymer, or polyvinyl fluoride.

Such vinyl plastics films after printing or adhesive laminating, are widely used for packaging, publications, display and advertising, stickers, book covers, gramophone record sleeves, lampshades, credit cards, labels, signs, and nameplates.

The printing and adhesive lamination of such untreated plastics film materials presents a number of severe problems which are not experienced in the corresponding processing of paper and paper-board substrates. Printing and adhesive lamination exhibit similar problems because the successful operation of both processes depends on the surface properties of the plastics film. Problems are caused mainly by the poor wetting properties and low adhesive properties of the plastics film surface, migration of plasticiser from the film, surface contaminants, and the smooth, non-porous nature of the surface. Poor printability of the untreated base film leads to low print quality, poor ink adhesion, slow ink drying and production problems regarding sheet-feeding and static electricity generation.

Plastics films which contain plasticiser give rise to problems of plasticiser migration into printing ink, adhesive, or other compositions or materials applied to the plastics film or into materials including foodstuffs which otherwise come into contact with the plastics film. For example, printing inks can be totally prevented from drying by plasticiser migration or an apparently dry ink may subsequently re-soften and smear or block. Vinyl and other plastics films frequently contain surface contaminants which arise from the diffusion into the plastics film surface of additives used in the preparation of the polymeric composition from which the film is produced and also can undergo direct surface contamination by lubricants, such as polyethylene waxes, used on calender rolls and other processing apparatus.Such contaminants will generally also contain plasticiser in the case of the plasticised grades of plastics film.

Surface contaminants further increase the risk of contamination of any material which comes into contact with the plastics film surface; if the contaminant is non-polar in character, it further reduces the wetting properties of the plastics film, even to the extent of causing repellency of printing inks.

The poor wetting and adhesion properties of most untreated plastics films and of surface contaminated plastics films usually make it impossible satisfactorily to apply inexpensive water-based inks or adhesives to the plastics film, and expensive special products are required which often contain strong, toxic, or inflammable solvents.

According to the present invention there is provided a method of treating a supported to unsupported vinyl or polyester plastics film to improve the adhesion properties thereof, which method comprises forming on one or both surfaces of the film a flexible, block-resistant and stable polymer base layer with a thickness of from 0.1 to 5 ijm and a peel bond of over 200 g/cm by applying a liquid coating composition comprising a solution or dispersion of an acrylic or methacrylic polymer or copolymer or a mixture thereof in a volatile liquid, or a liquid photopolymerisable ethylenically unsaturated material containing acrylate or methacrylate monomers or a mixture thereof, and respectively removing said volatile liquid from the composition or subjecting the composition to the action of actinic radiation to provide a dry coating.

The invention also includes vinyl or polyester plastics film material produced by the treatment method just defined.

By keeping the application rate of polymer to the low level just defined, it is found that considerable advantages may be obtained in terms of certain properties of the plastics film without incurring the disadvantages associated with prior art coating methods, or incurring such disadvantages only to a greatly reduced extent. Additionally, any important properties of the plastics film material, e.g. mechanical and thermal properties, can be retained unchanged.

Advantages in terms of improved properties may be obtained in, for example: the adhesion properties of the plastics film, the wetting, electrostatic and contaminating properties of the plastics film, the printability of the film including improved ink wetting, improved transfer print quality, increased ink adhesion, faster ink drying, reliable sheet feeding, and improved anti-static properties.

Important mechanical and thermal properties of the plastics film which may remain substantially unchanged include sheet flatness, stiffness, elongation and the abilities of the film to be folded, cut, heat-sealed, high frequency welded and heat-formed including vacuum formed.

Parallel improvements in adhesive coating and the performance of other compositions coated on the plastics film may be obtained, particularly improved wetting properties, ad- hesion and drying.

The low final coating weight of the composition may be obtained by applying to the plastics film surface a very thin layer of the coating composition, which may contain the polymeric material as a solution or dispersion, followed by a rapid drying operation or by applying a photopolymerisable coating composition which is preferably substantially free from volatile solvents. The average dry thickness of the layer is 0.1 to 5.0 micrometres with the preferred range being 0.1 to 2.0 micrometres, more preferably 0.2 to 1.0 micrometres.

To produce a layer of say 0.2 um. average dry thickness from a solvent solution of the polymer a wet coating weight of only 1 gram of coating composition per square metre of film is required at 20% vlw solids polymer concentration. These thin surface coated layers may cause coloured light interference patterns when viewed by reflected light and the coatings frequently exhibit such coloured interference patterns in the thickness range of 0.1-1.0 micrometres.

The plastics film may be treated in the form of separate sheets or as a continuous film (i.e.

in web form). Any thickness of film may be treated and the film may be unsupported film or may be supported on a paper, textile, foil or other plastics film support.

The apparatus used for applying the coating composition may consist, for example, of a roller coater using a single or multiple rubber rolls, a gravure roll coater, a reverse roll coater, or an air knife coater. The apparatus is usually adjusted to apply a very low wet coating weight.

Since the coating is applied at a very low coating weight it can be dried in a few seconds and very high coating speeds may accordingly be obtained, so reducing the cost of the treatment. Photopolymerisable compositions can be cured to a dry state at very high speeds typically at a conveyor speed of 30-120 metres per minute corresponding to an exposure time of 1/10 secorid or less to the Wradiation.

If required, the coating composition can be applied simultaneously to both sides of unsupported plastics film since drying is so rapid that both sides of the sheet can be dried before making mechanical contact, with parts of the apparatus, e.g. the conveyor of the drier.

Much commercially available plastics film material is surface contaminated, for example, by plasticiser, processing lubricants and additives which diffuse to the surface during processing. When treating such material according to the present invention high adhesion of the applied composition thereto may be achieved by incorporating in the coating composition a solvent for the surface contaminant.

Some plastics are so heavily contaminated that it is necessary to apply a pre-treatment prior to the treatment according to the invention in order to obtain high adhesion of the layer to the plastics film surface. In addition, it is difficult to obtain high adhesion of the coating to polyesters and pre-treatment is preferable with such materials.

Such a pre-treatment is preferably an electronic corona discharge treatment. It is an important advantage that whereas such elec tronic.treatment normally gives only a temporary improvement in the adhesion and wetting properties of a plastic film treated thereby, if treatment according to the present invention is applied shortly after such electronic pre-treatment, a permanent, and consistent improvement in adhesion and wetting properties is obtained. In addition, the treatment according to the invention provides the film surface with a barrier which can prevent plasticiser migration and contamination by or of materials placed in contact with the plastics film.

A further disadvantage of known corona treatments is the alteration of the thermal properties of the plastics film; for example, the ability to heat-seal such films is reduced. The corona pre-treatment followed by coating according to the present invention can lead to heat-sealing properties in the final film which are equal or even superior to those of the untreated plastics film.

Owing to the short life of corona treatment and the adverse effect on heat-sealing, it has previously been necessary to carry out the treatment immediately prior to printing and to localise the treatment.

Corona treatment followed by treatment according to the method of the invention enables the corona treatment to be carried out at the time of manufacturing of the plastics film, for example, when producing calendered vinyl plastics. Such corona treatment should preferably raise the wetting tension of the plastics film surface to at least 35 x 1(r3 N/M (ASTM 257847).

The applied layer of dried coating composition may be a glossy continuous film or textured by control of the coating process, for example, using a gravure roller. Texture consists of thickness variations of the layer and includes physical discontinuities; these increase the apparent surface area of the plastics film without producing a loss of clarity and gloss.

The applied layer of polymer has a negligible effect on the mechanical and thermal properties of the plastics film particularly if the layer is textured with physical discontinuities. This enables plastics to plastics contact in heat-sealing or heat-welding. Heat-sealing properties of the plastics film may be Improved by the use of a thermoplastics polymer in the applied layer.

The coating composition may also contain dispersed solid particles of materials which may produce a matt or semi-matt finish in the dried layer. If the solid particles have a refractive index close to that of the polymer, the effect on the clarity of the treated plastics film is very small. A semi-matt finish is useful in some printing work as it improves ink transfer and ink drying; the peaks in the layer reduce the pressure between the sheets or laps in stacks or reels produced by the printing machine and allows air retention between adjacent sheets or laps, which aids hardening of inks which dry by oxidation.

The retention of a film of air between sheets or laps in this way also aids sheet separation or unreeling and feeding on sheet or web-fed printing presses. Feeding unsupported plastics film glossy both sides, is extremely difficult and sometimes impossible in sheet fed printing machines, and in many cases it is necessary to edge gum a sheet of paper to each plastics sheet and feed and print this assembly. This procedure is expensive and the paper must subsequently be stripped from each plastics sheet after printing.

The dry polymer layer should possess high adhesion to the plastics film and this may be obtained by physical and/or chemical bonding.

Physical bonding relies on polar, induced polar, or other secondary valency forces using an unreactive polymer and chemical bonds are produced by a covalent link between a reactive polymer and the plastics film. Physical bonding may be achieved by applying an unreactive polymer, or a polymer reactive only with itself, whereas a chemical bond can be obtained by applying a coating composition containing a reactive monomer or polymer which subsequently reacts chemically with existing functional groups in the plastics film surface.

The adhesion of the polymer layer to the plastics film surface should be such that it is retained when printing ink or adhesive is applied and dried on the plastics film. If ink or adhesive to be subsequently applied contains organic solvents or water, then the layer must have appropriate resistance to these in order to retain its adhesion. It is possible, of course, to select non-reactive polymers particularly those of high molecular weight which still adhere to the film surface in the presence of organic solvents and/or water. Also monomer containing compositions if used can develop resistance to a wide range of solvents because of cross-linking in the photo-polymerisation reaction.Certain polymers, particularly acrylic polymers or copolymers of high molecular weight, are resistant to solvents at room temperature and are only soluble in some solvents at about 60 OC. Such polymers are particularly useful because they may be dissolved in solvents at 60 OC., coated on the plastics film and, after drying, acquire excellent resistance to solvent-containing inks. Inks which are solvent free, such as paste inks used in litho or letterpress, do not present problems of solvent attack and it is relatively easy to select polymers in which adhesion to the plastics film is not reduced by the varnish media used in these inks.Preferably the polymer in the layer should keep its adhesion to the plastics film on application thereto of a wide range of conventional printing inks including solvent and water-based inks used in screen, gravure and flexographic printing, paste inks, quick -set inks, organosol and plastisol inks, two pack catalytic inks, thermoplastic inks, ultra-violet curing inks and electron beam curing inks.

Analogous considerations apply to the application of adhesives and other compositions to the treated plastics film.

The polymer will possess satisfactory adhesion to both ink polymer and plastics film if it is compatible with both materials. Compatibility can be determined by mixing a solution of the polymer for the coating composition with a solution of the plastics film.or of the ink polymer at a mixing ratio of 1:1 by weight.

The mixture is examined for clarity, cast on a glass plate, and the dry cast layer again examined for clarity and gloss. If both mixed solutions and cast film are clear, and the cast film is glossy, compatibility is established.

Soluble or dispersible polymers suitable for use as the polymeric material of the coating composition used in the method of the present invention are acrylic or methacrylic polymers and copolymers and mixtures thereof.

For example, there may be used an acrylic copolymer prepared from two or more of methyl methacrylate, ethyl acrylate and acrylic acid. Preferably the polymer used is one which is insoluble in liquid hydrocarbons e.g. those normally regarded as solvents for inks, more preferably, one which is soluble in a liquid glycol ether or glycol ether ester.

Photopolymerisable liquid coating compositions which cure to a dry state by exposure to actinic radiation such as ultra violet or electron beam radiation comprise monomers or mixtures of monomers as defined above e.g. photopolymerisable acrylate ester monomers, optionally together with oligomers and/or prepolymers. A photoinitiator may be incorporated in the liquid composition to accelerate photopolyinerisation and nonpolymerisable components such as polymers, plasticisers, matting agents and anti-static agents can also be incorporated. A minor proportion of an organic solvent or solvent mixture may also be included to control viscosity and increase adhesion to the plastics film by solvent attack on its surface.

Suitable monomers are 1,6-hexane diol diacrylate, pentaerythritol tetra-acrylate, tinnethylol propane tri-acrylate, tetraethyleneglycol diacrylate, diethyleneglycol diacrylate and ethylene glycol methacrylate.

Suitable oligomers and prepolymers are acrylated polyurethane, unsaturated polyester, acrylated polyester, epoxy methacrylate, and acrylated epoxy oligomers and prepolymers.

Suitable photoinitiators are benzophenone, chlorinated ketones, aromatic ketals, anthraquinone derivatives, thioxanthene derivatives and Michler's ketone.

The monomers, oligomers or prepolymers may contain reactive groups such as hydroxyl, amide, carboxyl or isocyanate groups to increase the adhesion of the dry treated plastics film surface to the printing ink, adhesive or other coatings such as magnetic tape coatings and photosensitive coatings.

In any practical application, a polymer for the coating may be selected on grounds of solubility, and adhesion. The practical test for surface improvement of plastics film is to apply a layer of the composition and after drying applying printing ink to the sheet in both treated and untreated areas so that a side by side control is obtained. The uniformity of ink wetting and transfer in solid areas, and fine detail, ink set-off, rate of ink hardening and adhesion of the dry ink are then all easily compared on the adjacent treated and untreated areas of plastics film. Similar tests may be used for evaluating the treated plastics film for adhesive laminating and other uses, using simple test procedures.

Adhesion of the dry polymer to the plastics material is measured by peel bond value. Pressure sensitive adhesive tapes are applied to the treated plastics material and peeled off at 900 to the surface. The polymer is notremoved by a peel of over 200 g/cm. of tape width and preferably should exceed a peel of 500 g/cm.

The inter-film adhesion of the dry printing ink to the polymer treated plastics film is tested similarly and should also preferably have an adhesion in excess of 200 g/cm.

There are a number of general properties of the polymer in the coating composition which are desirable to impart suitable surface properties to the plastics film including clarity, light fastness, flexibility, scratch resistance, and stain resistance, as well as blocking resistance.

These should all be considered in the selection of the polymer, as also should its properties in thin layer form regarding plasticiser or surface contaminant migration across the layer. Barrier properties can be tested, for example, by incubating printed plastics films e.g. at 48 OC and 70% RH and then testing ink scratch hardness, block resistance and adhesion. Coating compositions containing polymers which are reactive and cross-link after coating tend to give layers with the best barrier properties.

Also a reactive polymer layer which has a chemical action on the subsequently applied ink can produce very plasticiser-resistant ink films.

The layer may contain metallic driers, oxidising agents, isocyanates, acid catalysts or photoinitiators which assist curing of the subsequently applied ink and of subsequently applied adhesives for laminating work.

The layer may contain components which impart antistatic properties to the plastics film.

This assists sheet or web feeding in printing and converting operations and aids in avoiding printing defects such as ink feathers and in avoiding dirt attraction to the plastics film.

Antistatic properties can be obtained by the incorporation of a quantity of an antistatic agent, usually a highly polar material in the coating composition. Quaternary ammonium salts containing long alkyl chains are useful anti-static additives and are particularly effective.

It is useful if the anti-static additive is incompatible with the dry polymer so that it concentrates as an extremely thin surface layer when the coating composition dries. The antistatic properties are readily tested by rubbing two sheets of plastics film together and then measuring electrostatic potential produced using a meter. At normal values of relative humidity a low or zero potential is obtained on the treated material whereas a potential of over 8000 volts can frequently be observed on untreated plastics films. The antistatic additive is preferably used to the extent that the decay half-life of charge generated in this way is less than 1 second.

Many untreated or contaminated plastics films have a low energy surface and wetting problems are caused with liquid inks and adhesives. Consequently, the polymer treated plastics films of the present invention preferably should have a wetting tension of 35 x 1(T N/M or higher to give a spreading with a wide range of liquid inks and adhesives. The wetting tension of the treated plastics film may be determined by examining the wetting proper- ties of a range of liquids of known surface tension values (ASTM 2578-67).

The following examples will serve to illustrate the invention. All parts and percentages are by weight unless otherwise stated, and all of the treated films prepared according to the method of this invention had a peel bond of over 200 g/cm.

EXAMPLE I An acrylic copolymer consisting of 95% methyl methacrylate and 5% ethyl acrylate with a Vicat softening point of 103 OC which is insoluble in water, alcohols and aliphatic hydrocarbons is used to prepare a coating composition as follows: Acrylic copolymer 9.00 parts Ethoxy ethanol acetate 8.36 parts Butoxy ethanol 8.36 parts Ethoxy ethanol 74.28 parts 100.007 The copolymer is dissolved in a mixture of the first two solvents by high speed stirring, and the third solvent is then added as a diluent. This composition is applied using a rubber roller coater simultaneously to both sides of unsupported calendered unplasticised polyvinyl chloride homopolymer film at a wet coating weight of 2.5 grams per square metre on each side of the film. This gives an average dry thickness of 0.22 micrometres.In appearance the dried film has a clear glossy surface, the surface layer being visible by viewing the specular reflection in white light and giving rise to multicoloured interference patterns with predominantly yellow or red reflections.

Polyvinyl chloride film treated as above was printed using a cellulose nitrate based screen printing ink including a solvent mixture which does not destroy the applied layer, e.g. a 1:1 mixture of ethoxy ethanol and aromatic hydrocarbon b.pt. 150-180 OC, in both solid and fine detail ink areas. After drying the adhesion of the ink to the film is tested by means of the adhesive tape test. The ink is completely removed from the untreated film whereas no ink is removed from the treated film. The print quality of the treated film shows uniform solid ink areas and excellend reproduction of fine detail. The printing on the un treated film shows mottle in the solid ink areas and ragged edges in the fine detail areas.

EXAMPLE 2 There is dissolved in the acrylic copolymer coating composition of Example 1, OA parts by weight of a highly polar anti-static additive, alkyl tri-methyl ammonium chloride in which the alkyl group consists mainly of C18 carbon chain.

This composition is coated under the same conditions as Example 1, and after drying the electrostatic properties are measured by vigorously rubbing two sheets of the treated plastics film together. The electrostatic charge developed on the surface of the plastics film is very small (less than 500 volts) and rapidly falls to zero. Untreated plastics film under the same conditions develops an electrostatic charge of 12,000 volts which is persistent for a consider- - able time and the plastics sheets generally always retain some electrostatic charge.

EXAMPLE 3 A photopolymerisable coating composition consists of Unsaturated polyester resin 36.0 Hexane diol diacrylate 35.0 Acrylated benzophenone 15.0 Acrylated amine 15.0 100.0 This composition is coated by multiple rubber rollers to give an average coating thickness of 1 tun to polyvinylchloride -film immediately after calendering and dried by exposure to two medium pressure mercury vapour tubular lamps rated at 80 watts per centimetre of lamp length.

Screen printing ink based on cellulose nitrate polymer and a lithographic printing ink based on a linseed drying oil varnish both print with excellent quality on such treated plastics film and when dry the ink film does not become tacky or soft due to plasticiser migration on long ageing.

Both dry inks are resistant to the tape adhesion test.

If the same cellulose nitrate ink is applied and dried on untreated plastics film, it can be completely removed by adhesive tape and after a few hours ageing the ink becomes tacky due to plasticiser migration. If a lithographic ink is applied to the untreated plastics film, the ink does not dry and remains permanently soft due to plasticiser migration before the ink has oxidised to a hard film.

EXAMPLE 4 Polyethylene terephthalate film is electronically pretreated using a high intensity corona discharge at a frequency of 25 KHz and output voltage of 14 KV. The film is coated with the coating composition used in Example 3 and dried as in Example 3. Compared to the uncoated film wetting, adhesion and antistatic properties of the film are all greatly improved, and the improvement is stable and not reduced on ageing or exposure of the film to the atmosphere. Conventional printing inks used for paper printing which fail the tape test or have poor scratch resistance on the untreated film exhibit extremely high adhesion to the treated film. The antistatic properties permit the film to be sheet fed on printing machines and the printed film retains its antistatic properties and does not become rapidly discoloured by dust attraction.

EXAMPLE 5 A semi-gloss coating composition is prepared as follows from polyvinyl formal polymer containing 45% polyvinyl acetate groups and 6% polyvinyl alcohol groups: Polyvinyl formal 8.74 parts Cyclohexanone 21 A0 parts Ethoxyl ethanol acetate 67.86 parts Silica aerogel 2.00 parts 100.00 This composition is applied with a gravure roller at a wet coating weight of 2.5 grams per square metre to one side of a clear, unplasticised, glossy calendered polyvinyl chloridepolyvinyl acetate copolymer plastics film of 100 micrometre thickness. Simultaneously an anti-static clear, glossy coating of the composition set out in Example 2 is applied as in Example 2 to the other side of the plastics film by a smooth rubber roller.On drying, the plastics film has excellent printability by off-set litho on the gloss surface and can be fed at high speed by reason of the anti-static coating and gloss/semi gloss surface finishes of the plastics film. The litho ink dries to give very high adhesion, and is free from set-off even on deep pile delivery.

EXAMPLE 6 An acrylic copolymer is prepared from methyl methacrylate, ethyl acrylate and acrylic acid to give an acid value of 62-66 OC, Koffler Bar softening Point of 125 OC, and SG of 1.18. A coating composition is prepared from this Polymer as follows: Acrylic polymer 12.00 parts N-Butoxyl Ethanol 10.00 parts Demineralised water 78.00 parts 100.00 To the above suspension of polymer, triethanolamine is added until the pH reaches 8 and high speed stirring continued until the polymer is dissolved.

The coating composition is applied at a high viscosity by rubber rollers to a corona treated polyvinyl chloride glossy clear homopolymer plastics film of .025 mm gauge. On drying, the coating imparts a texture pattern to the film which appears as a very fine orange-peel or reticulated effect, and which has very little effect on sheet clarity. The dried coating was between 0.1 and 5 Erm thick.

Lithographic printing applied to this surface by 4-colour process inks show excellent ink transfer and adhesion and the sheets may be deep-piled without set-off due to the cushioning i.e. air trapping effect of the applied coating EXAMPLE 7 A coating composition was prepared from the following ingredients: Polyester diacrylate prepolymer 34.8 Trimethylol propane tri-acrylate 19.0 N-vinyl-2-pyrrolidone 30.0 1,6-Hexane diol diacrylate 10.0 Aromatic ketal 3.0 Benzophenone 2.0 Michler's Ketone 0.2 100.0 This liquid composition was applied as a very thin layer by transfer from rubber roller to rubber roller using a sequence of 6 rollers and the last roller applied the composition to a plastics film to give a coating weight of 1.0 gsm.

The plastics film was highly plasticised vinyl film and the treated film was cured by a dry state by exposure to UV radiation from a medium pressure tubular mercury vapour lamp.

The coating polymerised and cross-linked to a hard film which did not become soft or tacky on ageing by plasticizer migration.

WHAT WE CLAIM IS: 1. A method of treating a supported or unsupported vinyl or polyester plastics film to improve the adhesion properties thereof, which method comprises forming on one or both surfaces of the film a flexible, block-resistant and stable polymer base layer with a thickness of from 0.1 to 5 elm and a peel bond of over 200 g/cm by applying a liquid coating composition comprising a solution or dispersion of an acrylic or methacrylic polymer or copolymer or a mixture thereof in a volatile liquid, or a liquid photopolymerisable ethylenically unsaturated material containing acrylate or methacrylate monomers or a mixture thereof, and respectively removing said volatile liquid from the composition or subjecting the composition to the action of actinic radiation to provide a dry coating.

2. A method according to claim 1, wherein the coating rate is such as to provide a dry coating thickness of from 0.1 to 2.0 sun.

3. A method according to claim 1 or claim 2, wherein the vinyl plastics film is polyvinyl chloride homopolymer or a vinylchloridevinylacetate copolymer film.

4. A method according to claim 1 or claim 2, wherein the surface of the plastics film to be coated is pre-treated by exposure to corona discharge.

5. A method according to any one of the preceding claims, wherein the coating composition is selected to provide a treated film having a wetting tension of at least 35 x 1 (T3 N/M.

6. A method according to any one of the preceding claims, wherein the coating composition is selected to provide a glossy coating when dry.

7. A method according to any one of claims 1 to 5, wherein the coating composition contains dispersed solid particles to produce a matt or semi-matt dry coating.

8. A method according to any one of the preceding claims, wherein the coating composition is applied so as to provide a continuous dry coating.

9. A method according to any one of claims 1 to 7, wherein the coating composition is applied so as to provide a texturised or discontinuous dry coating.

10. A method according to any one of the preceding claims wherein the coating composition comprises photopolymerisable acrylate ester monomers.

11. A method according to claim 10, wherein the coating composition comprises photopolymerisable acrylate ester monomers in admixture with acrylated polyurethane or acrylated epoxy oligomers or prepolymers or mixtures thereof.

12. A method according to any one of the preceding claims, wherein the photopolymerisable composition contains a photoinitiator.

13. A method according.to any one of the preceding claims, wherein the coating composition includes an anti-static agent.

14. A method according to claim 13 wherein the anti-static agent is a quaternary ammonium salt.

15. A method according to any one of the preceding claims, wherein a second liquid coating composition is applied to the ilrst dry coating and the second liquid coating composition contains a solution or dispersion of a cellulose nitrate polymer.

16. A method according to any one of the preceding claims, wherein a second liquid coating composition is applied to the first dry coating by printing and the polymer of the second composition is selected to provide a peel bond adhesion in excess of 200 g/cm to the first dry composition.

17. A method according to claim 1 and substantially as hereinbefore described with ref- erence to any one of the specific Examples.

18. A vinyl or polyester plastics film when treated by a method according to any one of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. EXAMPLE 7 A coating composition was prepared from the following ingredients: Polyester diacrylate prepolymer 34.8 Trimethylol propane tri-acrylate 19.0 N-vinyl-2-pyrrolidone 30.0 1,6-Hexane diol diacrylate 10.0 Aromatic ketal 3.0 Benzophenone 2.0 Michler's Ketone 0.2 100.0 This liquid composition was applied as a very thin layer by transfer from rubber roller to rubber roller using a sequence of 6 rollers and the last roller applied the composition to a plastics film to give a coating weight of 1.0 gsm. The plastics film was highly plasticised vinyl film and the treated film was cured by a dry state by exposure to UV radiation from a medium pressure tubular mercury vapour lamp. The coating polymerised and cross-linked to a hard film which did not become soft or tacky on ageing by plasticizer migration. WHAT WE CLAIM IS:

1. A method of treating a supported or unsupported vinyl or polyester plastics film to improve the adhesion properties thereof, which method comprises forming on one or both surfaces of the film a flexible, block-resistant and stable polymer base layer with a thickness of from 0.1 to 5 elm and a peel bond of over 200 g/cm by applying a liquid coating composition comprising a solution or dispersion of an acrylic or methacrylic polymer or copolymer or a mixture thereof in a volatile liquid, or a liquid photopolymerisable ethylenically unsaturated material containing acrylate or methacrylate monomers or a mixture thereof, and respectively removing said volatile liquid from the composition or subjecting the composition to the action of actinic radiation to provide a dry coating.

2. A method according to claim 1, wherein the coating rate is such as to provide a dry coating thickness of from 0.1 to 2.0 sun.

3. A method according to claim 1 or claim 2, wherein the vinyl plastics film is polyvinyl chloride homopolymer or a vinylchloridevinylacetate copolymer film.

4. A method according to claim 1 or claim 2, wherein the surface of the plastics film to be coated is pre-treated by exposure to corona discharge.

5. A method according to any one of the preceding claims, wherein the coating composition is selected to provide a treated film having a wetting tension of at least 35 x 1 (T3 N/M.

6. A method according to any one of the preceding claims, wherein the coating composition is selected to provide a glossy coating when dry.

7. A method according to any one of claims 1 to 5, wherein the coating composition contains dispersed solid particles to produce a matt or semi-matt dry coating.

8. A method according to any one of the preceding claims, wherein the coating composition is applied so as to provide a continuous dry coating.

9. A method according to any one of claims 1 to 7, wherein the coating composition is applied so as to provide a texturised or discontinuous dry coating.

10. A method according to any one of the preceding claims wherein the coating composition comprises photopolymerisable acrylate ester monomers.

11. A method according to claim 10, wherein the coating composition comprises photopolymerisable acrylate ester monomers in admixture with acrylated polyurethane or acrylated epoxy oligomers or prepolymers or mixtures thereof.

12. A method according to any one of the preceding claims, wherein the photopolymerisable composition contains a photoinitiator.

13. A method according.to any one of the preceding claims, wherein the coating composition includes an anti-static agent.

14. A method according to claim 13 wherein the anti-static agent is a quaternary ammonium salt.

15. A method according to any one of the preceding claims, wherein a second liquid coating composition is applied to the ilrst dry coating and the second liquid coating composition contains a solution or dispersion of a cellulose nitrate polymer.

16. A method according to any one of the preceding claims, wherein a second liquid coating composition is applied to the first dry coating by printing and the polymer of the second composition is selected to provide a peel bond adhesion in excess of 200 g/cm to the first dry composition.

17. A method according to claim 1 and substantially as hereinbefore described with ref- erence to any one of the specific Examples.

18. A vinyl or polyester plastics film when treated by a method according to any one of the preceding claims.