Plastics film and production thereof

Abstract: A semi-matt plastics film has a regular embossed pattern, preferably of depth 0.5 to 10 microns and repeat distance 20 to 400 microns. The regularity of the embossed pattern is such that when the plastics film is rubbed, for example against itself it emits a noise of characteristic frequency, or is sufficient that the embossed film is capable of giving rise to diffraction patterns. The above can be used as distinctive features in security packaging when the embossed film is used as the outermost layer in such packaging.

Description: This invention relates to plastics film useful for example for packaging or for lamination to paper or board to form packaging or promotional material. In particular, it relates to matt or semi-matt film, that is film having a 60° gloss of 5 (a full matt film) to 30 (a light semi-matt film) and having surprising additional properties. It also relates to laminated products containing such film as exterior layer, to the preparation of such products and of such film and to use of the film in a process for testing the authenticity of packaged goods. Most plastics film, for example polyolefin, polyester or regenerated cellulose film, is made by extrusion; some, such as cellulose acetate film, is made by casting from solution. The process of the present invention is particularly suitable as a treatment of cast film but can also be applied to extruded film. Most cellulose acetate film sold commercially is clear film of 60° gloss greater than 100. This clear film is produced by casting a solution of cellulose acetate, generally in acetone as solvent, onto a polished stainless steel endless belt or a chrome-plated drum. The cast film is dried (hardened) on the belt or drum until it is coherent enough to be stripped from the belt or drum, and it is then dried (hardened) further by passage around rollers in an oven to remove substantially all solvent. Matt film can be produced similarly by casting onto a roughened, for example shot-blasted, surface. Some semi-matt film is available commercially; it is believed to be produced by casting onto a lightly roughened surface. Semi-matt film preferably has a 60° gloss in the range 10 to 25, most preferably 12 to 20. Embossing of plastics film is known for example from GB-A-2104847, GB-A-1493512, EP-A-604685, GB-A-995591, GB-A-1168490 and US-A-3316825. None of these patents relates to the treatment of cast cellulose acetate film. GB Patent Application No 2,104,847 describes and claims an embossed thermoplastic polyolefin film having an embossed matt pattern, the thickness of the film being within the range of about 0.5 to about 1.5 mils and the embossed depth being about 0.5 to about 2.5 mils wherein the embossed pattern comprises a series of embossed lines parallel to free lengthwise edges of the film and a series of embossed transverse lines intersecting the parallel lines to provide an overall general network of the lines surrounding raised bosses on one side of the film, wherein the bosses and lines overlie on the opposite side of the film corresponding depressions and ridges, the embossed lines numbering within the range of about 150 to 300 lines per inch. GB Patent No 1,493,512 describes and claims an embossed thermoplastic film wherein one surface thereof is provided with two groups of rows ofprotuberances, the first group of said rows extending substantially perpendicular to the second group of said rows, each of the first group of rows being separated from the next row of said first group by a continuous valley extending from one edge of the film to the opposite edge thereof, each of the second group of rows being separated from the next row of said second group by a plurality of aligned valleys, each of the aligned valleys having a length substantially equal to the dimension of the base of an adjacent protuberance in a direction perpendicular to the direction of the continuous valleys. Published PCT Patent Application No WO89/03760 relates to a method of decoration of paper or plastic sheeting by providing a coating and then embossing the coated substrate. The coated sheet is heated to soften the coating by use of a heated platen or heated cylinders and infrared heaters. The softened sheet surface is then decorated using an embossing member to provide a diffraction pattern or hologram. The embossment pattern has a lesser depth than the surface roughness of the sheet before embossing. In a process according to the invention for the preparation of a laminated product having a surface which is highly resistant to finger marking, clear plastics film in an unhardened condition is embossed by an embossing cylinder and is thereafter allowed to harden, the embossing according to one aspect of the invention being in a pattern of such depth, repeat distance and regularity that when the plastics film is rubbed it emits a noise of characteristic frequency and according to another aspect of the invention being in a pattern of such depth, repeat distance and regularity that the embossed plastics film is capable of giving rise to diffraction patterns, and the hardened, embossed film is laminated to paper or board with its embossed surface as the exterior layer of the resulting laminated product. For best results, clear plastics film is embossed by an embossing cylinder having a regular embossing pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns, and the invention includes laminated products in which such a plastics film is laminated to paper or board substrate. The invention also includes the use of a semi-matt plastics film as the outermost layer of laminated packaging on packaged goods, characterised in that the film has a regular embossed pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns, the regularity of the embossed pattern being such that when the plastics film is rubbed, for example against itself, it emits a noise of characteristic frequency. Alternatively or additionally, the regularity of the embossed pattern is sufficient that the embossed film is capable of giving rise to a diffraction pattern. The invention further includes a process as defined in claim 20 for the preparation of a matt or semi-matt plastics film. The noise emitted by the film when rubbed, particularly when rubbed against itself, is highly distinctive and has been variously described as a wailing noise or as a twittering or crying noise. As far as we know, no other plastics film produces a noise of this type when rubbed. The characteristic frequency (pitch) of the noise is dependent on the embossed pattern of the film, most particularly on the repeat distance of the pattern. The distinctive noise is repeatable and reproduceable whenever the film is rubbed. The characteristic pitch is essentially the same whether the film is rubbed against itself or against other rigid or semi-rigid plastics material, wood, paperboard, metal or similar materials under a range of conditions. This distinctive noise means that the film can be used as a security packaging for expensive goods when applied as the exterior layer of the packaging, for example as a laminate over paperboard. If access to the film is restricted to reputable luxury goods manufacturers only, packages of genuine goods can be distinguished from fakes by gently rubbing the package, for example by rubbing two packages together. If supply of a film of particular embossed pattern is limited to one luxury goods manufacturer, the pitch of the noise generated is characteristic of the packaged goods of that manufacturer. One or both surfaces of the film can be embossed; usually it is preferred that only one surface is embossed, and this surface is arranged to be the outermost surface of any packaging material incorporating the film. The capability of the embossed film to give rise to diffraction patterns can also be used in security packaging for testing the authenticity of packaged goods. In this case a laminated packaging material comprises a reflective layer with the embossed film of the invention being laminated outside the reflective layer so that the reflective layer is visible through the film. The reflective layer can for example be a metallised layer. If only one surface of the film is embossed, the opposite surface can be metallised. Alternatively, the metallised layer can be a substantially rigid layer such as metallised paperboard. The reflective layer can alternatively be a metallic foil, preferably laminated to a substantially rigid layer such as paperboard. Diffraction patterns can be seen if a patterned transparent material having a pattern of closely spaced lines, for example 0.5 to 0.02 mm apart, is placed over the package. The diffraction pattern observed is characteristic of the plastics film having a particular regular embossed pattern combined with the patterned transparent material used. The patterned transparent material can for example be a line grating used to measure the count of fabrics. The clear plastics film used as starting material can for example be a cast film such as cast cellulose acetate film or can be an extruded film such as a polyolefin film, for example polyethylene or polypropylene, or a polyester film, for example polyethylene terephthalate, or a regenerated cellulose film. The film can contain any of the additives known for incorporation in clear film. Cellulose acetate film can for example contain a plasticiser, for example 10 to 25% by weight of a phthalate ester plasticiser such as diethyl phthalate. The process of the invention can be carried out as an in-line process following casting or extrusion of the clear film or can be carried out as a separate process on clear film which has been reeled up after production. The thickness of the film is generally in the range 5 to 200 microns, more usually 10 or 15 microns up to 50 or 100 microns. For example, film for lamination over print, e.g. for lamination over paperboard packaging, may have a thickness of 10 to 25 or 40 microns and film for other uses such as labels and seals may have a thickness of 25 to 75 microns. The film in its unhardened condition is preferably softened, for example by applying a solvent or volatile plasticiser for the plastics to the film. For cellulose acetate film the preferred softener is acetone. The acetone content of the film as it is embossed is preferably in the range 1 to 5% by weight, most preferably 1.0 or 1.5% up to 2 or 4% by weight. The plastics film in its unhardened condition can alternatively be obtained by retaining sufficient solvent in a cast film so that it is still soft when contacted by the embossing cylinder, but it is generally preferred to dry and thereby harden the cast film and then rewet with solvent or plasticiser since this gives a more manageable process. A controlled amount of solvent can for example be sprayed onto the film just before it contacts the embossing cylinder, or the solvent or plasticiser can be carried on the surface of the embossing cylinder before it contacts the film, for example the solvent or plasticiser can be applied by lick roller to that part of the cylinder which is not pressed against the film. An extruded film can also be softened by application of a solvent or volatile plasticiser to the film before or just as it contacts the embossing cylinder. A polyolefin film, for example, can be softened by a hydrocarbon solvent. An extruded thermoplastics film can alternatively be softened by heat, for example by radiation heating of the film surface which is to contact the embossing cylinder or by radio-frequency induction heating. Softening may be achieved by a combination of heat treatment and application of solvent or plasticiser. The film is usually embossed on only one surface. It is pressed against the embossing cylinder, preferably by one or more rollers forming a nip with the embossing cylinder. The film can alternatively be embossed on both surfaces by passing it through a nip between two embossing cylinders. The pattern which is embossed on the film is generally a regular pattern. For example, there may be a pattern of raised lines or grooves on the embossing cylinder arranged as parallel lines or as a grid, such as a grid of intersecting raised lines producing separated raised lines on the film surface, or as a grid of intersecting grooves producing a grid of intersecting raised lines on the film surface. The pattern on the embossing cylinder can alternatively be a regular pattern of raised spots such as lines or dots or a geometrical pattern of dots, producing a pattern of circular depressions in the film surface. Alternatively, the embossing cylinder can have a regular pattern of pits, for example circular pits, so that the embossing surface of the cylinder is formed by the raised areas between the pits, producing a pattern of raised dots on the film surface. The depth of the embossing pattern (the height difference between the embossing members and the lowest surface of the embossing cylinder) is preferably in the range 0.5 to 20 microns, most preferably 1 to 5 or 10 microns, and the depth of pattern embossed on the film surface is preferably in the range 0.5 to 10 microns, most preferably 1 to 5 microns when producing semi-matt film. The width of the embossing features is preferably in the range 10 to 200 microns, most preferably 20 to 125 microns, and these features are preferably spaced apart by a centre-to-centre distance of 20 to 400 microns, most preferably 35 to 260 microns. For example, the embossing pattern can be a series of raised lines 1 to 10 microns high and 20 to 80 microns wide arranged 35 to 260 microns apart, or it can be a pattern of raised dots or circular depressions 1 to 10 microns high and 20 to 125 microns in diameter arranged in lines 35 to 260 microns apart with the centre-to-centre spacing in each line being 35 to 260 microns. In a further embodiment the embossing pattern comprises a regular series of raised dots or circular depressions of depth 0.5 to 10 microns and diameter 20 to 125 microns arranged in lines 20 to 260 microns apart, the dots in each line being spaced apart by a centre-to-centre distance of 35 to 260 microns. Where the embossing pattern is a pattern of raised dots or circular depressions (pits), these can be contiguous, that is with a centre-to-centre distance equal to their diameter, or they can be spaced further apart. The circular features can be arranged in a square, rectangular or hexagonal or other regular geometric pattern, which can be arranged on the embossing cylinder surface at any desired angle to the axis of the cylinder. The embossing features are preferably sharp-edged, that is the sides of each embossing feature are at a high angle to the surface of the embossing cylinder. The surface of the embossing cylinder is preferably of a particularly hard material, for example a hard metal or ceramic material. The regular pattern can be formed on the embossing cylinder surface in the required micron dimensions by laser etching, which can be computer controlled to give a very regular pattern. Although the pattern on most of the surface area of the embossing cylinder is the regular pattern which gives rise to the noise when the film is rubbed, specific areas of the roller may carry a different emboss pattern or might even be unembossed. The different emboss pattern can for example be a decorative feature or a security mark such as the logo of the perfume house or other luxury goods manufacturer who is to use the film for packaging. After the film has been embossed it is allowed to harden, for example by drying if it has been softened by solvent or volatile plasticiser or by cooling if it has been softened by heat. One embodiment of the invention will now be described with reference to the accompanying drawings, of which Figure 1 is a diagrammatic side elevation of apparatus for casting and embossing a film; and Figure 2 is a diagrammatic side elevation of the embossing cylinder of Figure 1. Referring to the drawings, cellulose acetate solution from a reservoir 11 is passed through a pipe 12 to a manifold 13 from which it is cast on a polished stainless steel endless belt 14 travelling in the direction shown. The belt 14 is enclosed within a housing (not shown) from which solvent evaporated from the cast solution can be recovered. At a roller 15 the cellulose acetate film 16 formed is stripped from the belt 14. The film 16 at this stage is clear and transparent. The film 16 is passed around transfer rollers 18 enclosed within a drying oven and as it leaves the last transfer roller 18z it is similar to commercially sold clear cellulose acetate film. The film 16 then passes around a counter-balanced tension roller 19 to an embossing cylinder 20, shown in more detail in Figure 2. The film 16 passes around a pressure roller 22 which forms a nip with the embossing cylinder 20, rotating in the direction shown. Before the embossing cylinder 20 contacts the film 16 it is contacted by a lick roller 23 which rotates in a bath 24 of softening agent, for example acetone solvent, applying a controlled amount of softening agent to the surface of the cylinder 20. As the film 16 contacts the cylinder 20 it is softened by the solvent carried on the cylinder and is embossed by the cylinder 20. The film 16 is carried around the cylinder 20 in contact with the embossing pattern on its surface until it reaches a stripping roller 26, which does not form a nip with the cylinder 20 but is a swinging roller free to move a short way back and forth around the cylinder 20 in response to changes in tension. At the roller 26 the film, which is now a semi-matt film 27, is lifted off the cylinder and passes to rollers 28, which are enclosed within a drying oven, for hardening the film. After re-drying, the film 27 is wound up on a reel 29. The semi-matt plastics film of the invention is particularly suitable for laminating over printed paperboard, with its embossed surface outermost, for use in packaging. It can alternatively be used as a packaging material without lamination or as a label material, for example for pressure-sensitive labels and seals. As well as the distinctive noise which can be used as a security packaging feature as described above, and the ability to generate diffraction patterns when laminated over a reflective layer, the semi-matt plastics film can be written on clearly and easily and is highly resistant to finger marking (much more resistant than the semi-matt film presently sold). The invention is illustrated by the following Example:- Example 100 parts by weight cellulose acetate and 20 parts by weight diethyl phthalate were dissolved in acetone. The solution was degassed and was cast onto a polished stainless steel belt using the apparatus of Figures 1 and 2. The clear film produced was stripped from the belt and dried to an acetone content of about 1.5% by weight before it contacted the embossing cylinder 20. The thickness of the dry film was 15 microns. Acetone solvent was applied by the lick roller 23 to the surface of the embossing cylinder and hence to the film in an amount of 2 to 3% by weight based on the film. The pattern on the embossing cylinder 20 comprised rows of circular (frusto-conical) pits each 7 microns deep and 20 microns in diameter at the embossing surface. The pits were arranged in rows 40 microns apart in a square pattern. The embossing surface of the cylinder is thus the land area between the pits, producing a pattern of raised dots on the film surface. After embossing, the film was re-dried (allowed to harden) to an acetone content of 0.8% by weight before being reeled. The resulting semi-matt film had a 60° gloss of 15. The film was laminated to paperboard with its embossed surface outermost. The film emitted a characteristic wailing noise of reproduceable pitch when rubbed against itself before and after being laminated and was highly resistant to finger marking. Another sample of the embossed film was laminated to metallised paperboard, forming an attractive package material. When a transparent line grating was placed over the laminated packaging material a distinctive diffraction pattern could be seen. No diffraction pattern was seen when the same line grating was placed over clear film laminated to metallised paperboard or over conventional semi-matt film laminated to metallised paperboard.

Claims: A process for the preparation of a laminated product having a surface which is highly resistant to finger marking, characterised in that clear plastics film in an unhardened condition is embossed by an embossing cylinder and thereafter allowed to harden, the embossing being of such depth and repeat distance that either the plastics film is capable of giving rise to diffraction patterns or when the plastics film is rubbed it emits a noise of characteristic frequency, and the hardened, embossed film is laminated to paper or board with its embossed surface as the exterior layer of the resulting laminated product. A process according to claim 1, characterised in that the film to be embossed is softened by applying a solvent or volatile plasticiser for the plastics to the film. A process according to claim 2, characterised in that the solvent or plasticiser is carried on the surface of the embossing cylinder before it contacts the film so that the film is simultaneously softened and embossed as it is pressed against the cylinder. A process according to any of claims 1 to 3, characterised in that the clear plastics film is cast film. A process according to claim 4, characterised in that the clear plastics film is cellulose acetate film. A process according to claim 1, characterised in that the clear plastics film to be embossed is a thermoplastic film and is softened by heat. A process according to any of claims 1 to 6, characterised in that the embossing cylinder has an embossing pattern of depth 1 to 10 microns and repeat distance 20 to 260 microns. A process according to claim 7, characterised in that the embossing pattern comprises a series of raised dots or circular depressions of depth 0.5 to 10 microns and diameter 20 to 125 microns arranged in lines 35 to 260 microns apart, the dots in each line being spaced apart by a centre-to-centre distance of 35 to 260 microns. A process according to any of claims 1 to 8, characterised in that the pattern on the embossing cylinder is formed by computer controlled laser etching. Use of a matt or semi-matt plastics film as the outermost layer of laminated packaging on packaged goods, characterised in that the film has a regular embossed pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns, either the regularity of the embossed pattern being such that when the plastics film is rubbed it emits a noise of characteristic frequency, or the regularity of the embossed pattern being sufficient that the embossed film is capable of giving rise to a diffraction pattern. Use according to claim 10, characterised in that the regularity of the embossed pattern is such that when the plastics film is rubbed it emits a noise of characteristic frequency and specific areas of the film carry a different emboss pattern or are unembossed so that those specific areas form a decorative feature or a security mark. Use according to claim 10, characterised in that the regularity of the embossed pattern is sufficient that the embossed film is capable of giving rise to a diffraction pattern and only one surface of the film is embossed, the opposite surface of the film being metallised. Use according to claim 10, characterised in that the regularity of the embossed pattern is sufficient that the embossed film is capable of giving rise to a diffraction pattern and the laminating packaging includes a reflective layer visible through the film. Use according to any of claims 10 to 13, characterised in that the plastics material is cellulose acetate. Use according to any of claims 10 to 14, characterised in that the regular embossed pattern comprises a series of raised dots or circular depressions of depth 0.5 to 10 microns and diameter 20 to 125 microns arranged in lines 35 to 260 microns apart, the dots in each line being spaced apart by a centre-to-centre distance of 35 to 260 microns. A laminated product comprising plastics film laminated to paper or board substrate, characterised in that the film has an embossed pattern of depth 0.5 to 10 microns and centre-to-centre repeat distance 20 to 400 microns and is laminated to the substrate with its embossed surface as the outermost layer of the resulting laminated product, so that when the plastics film is rubbed it emits a noise of characteristic frequency and the laminated product is highly resistant to finger marking. A laminated product according to claim 16, characterised in that the plastics material is cellulose acetate. A laminated product according to claim 16 or claim 17, characterised in that the embossed pattern comprises a regular series of raised dots or circular depressions of depth 0.5 to 10 microns and diameter 20 to 125 microns arranged in lines 35 to 260 microns apart, the dots in each line being spaced apart by a centre-to-centre distance of 35 to 260 microns. A process according to claim 1 for the preparation of a laminated product which is highly resistant to finger marking, characterised in that a clear thermoplastics film is softened by heat and the softened film is embossed by means of an embossing cylinder, the embossing being in a regular pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns, the embossed softened film is allowed to harden, whereby the hardened embossed film is capable of emitting a noise of characteristic frequency when the film is rubbed against itself and the hardened embossed film is highly resistant to finger marking, and the hardened embossed film having a semi-matt surface is laminated to paper or board with its embossed semi-matt surface as the exterior layer of the resulting laminated product. A process for the preparation of a matt or semi-matt plastics film, characterised in that clear plastics film is softened by applying a solvent or volatile plasticiser for the plastics to the film and is embossed by an embossing cylinder and thereafter allowed to harden, the embossing being in a pattern of such depth, repeat distance and regularity that the embossed plastics film is capable of giving rise to diffraction patterns and/or that when the plastics film is rubbed it emits a noise of characteristic frequency. A process according to claim 20, characterised in that the solvent or plasticiser is carried on the surface of the embossing cylinder before it contacts the film, so that the film is simultaneously softened and embossed as it is pressed against the cylinder. A process according to claim 20 or claim 21, characterised in that the clear plastics film is cast film. A process according to claim 22, characterised in that the clear plastics film is cellulose acetate film. A process according to any of claims 20 to 23, characterised in that the embossing cylinder has a regular embossing pattern comprising raised dots or pits of depth 1 to 10 microns and diameter 20 to 125 microns arranged in lines 35 to 260 microns apart, with the dots or pits in each line being spaced apart by a centre-to-centre distance of 35 to 260 microns. A process according to any of claims 20 to 24, characterised in that the regular pattern on the embossing cylinder is formed by computer-controlled laser etching. A process for testing the authenticity of packaged goods, either characterised in that the goods are packaged in a laminated packaging material having a matt or semi=matt plastics film as its outermost layer, the film having a regular embossed pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns and the regularity of the embossed pattern being such that when the plastics film is rubbed it emits a noise of characteristic frequency, and the package is rubbed to test whether it emits the noise of characteristic frequency, or characterised in that the goods are packaged in a laminated packaging material comprising a reflective layer and a matt or semi-matt plastics film outside the reflective layer, the film having a regular embossed pattern of depth 0.5 to 10 microns and repeat distance 20 to 400 microns and the regularity of the embossed pattern being sufficient that the embossed film is capable of giving rise to a diffraction pattern, and a patterned transparent material having a pattern of closely spaced lines is placed over the package for the purpose of observing whether a diffraction pattern characteristic of the plastics film and the patterned transparent material is visible. A process according to claim 26, characterised in that the laminated packaging material includes a layer of substantially rigid paperboard. A process according to claim 26, characterised in that the laminated packaging material comprises a reflective layer comprising metallisation on the opposite surface of the film to the embossed surface. A process according to claim 26, characterised in that the laminated packaging material comprises a reflective layer comprising metallised paperboard or a metallic foil laminated to paperboard.

Inventors: BRAUN FRANCOIS, FRENCH DAVID, HYMAN ALAN, WESSON DAVID, WILLINS GORDON, BRAUN, FRANCOIS, FRENCH, DAVID, HYMAN, ALAN, WESSON, DAVID, WILLINS, GORDON
Applicants: ACORDIS ACETATE CHEMICALS LTD, ACORDIS ACETATE CHEMICALS LIMITED
Application year: 1997
Main classification: B42D15
IPC codes: B29C59, B29C43