State of the art [0002] Hidden promotional and gaming messages are well introduced in today's world of packaging. Hiding the message in such a way that the consumer can only see the message after having bought the product is generally achieved by inside or reverse printing using very opaque films or covering inks. This is in some cases a limiting factor for flexible packaging.

[0003] A disadvantage of such hidden messages is that they can be read immediately after the pack has been opened. Besides reading the message, no other action is required from the customer to find out whether he/she won.

This takes away the"gaming"experience. This"gaming" experience can be kept by the use of an opaque layer that covers the hidden message. Several possibilities to produce this covering layer exist, non-restrictive examples are strip lamination of a film structure with removable coating, or screen-printed rub-off coatings, such as described in WO 00/31713 A3.

[0004] A series of documents such as documents GB 2185215 A; US Patent 4,299, 637; WO 98/58797 and WO 00/09344 disclose rub-off tickets or cards with hidden information

sandwiched in between a substrate layer and an opaque covering layer able to become transparent by an adequate treatment to enable the viewing of a hidden message through the covering layer when a mask material is removed. In this kind of tickets, an all-over clear varnish underneath a covering mask covers the hidden information. The tickets are furthermore embossed to avoid a relief detection of the hidden information, which stands proud of the surface of the substrate.

[0005] Document WO 03/066344 Al discloses a security label for anti-counterfeit applications having a holographic portion secured to a support layer by a weak adhesive layer such that the first layer can be scratched- off.

[0006] The scratch-off or rub-off layer described in the above-mentioned documents, typically deals with a thickness of 40 to 801im. This high thickness leads to a high cost-price and are not usable for packaging films with a thickness between 20 and 40ym, because in that case, the rub-off coating is proportionally as big as, or even bigger than, the packaging film. In practice, reels of about 1.000 meters are sold to the packaging converters. Those reels have a succession of a few thousand layers. If the packaging web comprises a rub-off layer, on a specific location, with a thickness between 40 and 80ym deposited on a film substrate of about 30pm, this would create an enormous"ghosting effect"because of the accumulation of this specific thickness on a specific location of the reel.

This can lead to loose ends, telescoping, increased thickness of bands in machine direction etc.

[0007] Furthermore, the coatings (opaque masks) described in the above-mentioned documents are not suitable for indirect or direct food contact which is a major issue for food packaging.

[0008] A specific problem to be solved is therefore to create a rub-off layer on a flexible substrate representing substantially not more than 20%, and if possible not more than 10%, of the global thickness of the multilayer substrate to avoid the"ghosting effect".

Furthermore, the thickness of the hidden message should not represent more than 5% of the total thickness of the whole structure in order to avoid the creation of any relief effect revealing the hidden message.

Aims of the invention [0009] The present invention aims to provide a packaging comprising a rub-off area with a rub-off coating layer suitable for direct and indirect food contact and a hidden patterned message of a low thickness with no relief effect.

Summary of the invention [0010] The present invention discloses a multilayer packaging film suitable for direct and indirect food contact comprising a substrate layer, a rub-off layer, a patterned adhesion promotion layer and/or a patterned release promotion layer leading to a selective adhesion of said rub-off layer on patterned areas of said substrate layer, wherein said patterned adhesion promotion layer or release promotion layer allows the rub-off of said rub-off layer on the patterned release promotion layer and/or at the voids of the patterned adhesion promotion layer in order to reveal a hidden message in the form of symbols after the part of the patterned rub-off layer with the lowest adhesion has been rubbed off.

[0011] Moreover, in the multilayer packaging film of the present invention, said substrate layer comprises mono and multilayer polymer films selected from the group

consisting of oriented polyester, oriented polypropylene, oriented polyamide and oriented polystyrene or combinations thereof.

[0012] In addition, the multilayer packaging film of the present invention moreover comprises a metal layer.

[0013] In the present invention, the substrate layer comprise mono and multilayer polymer films of a thickness lower than 50Am.

[0014] The rub-off layer of the present invention advantageously has a thickness lower than 10ym.

[0015] Additionally, the adhesion promotion layer is selected from the group consisting of urethanes, EVA's, PVB's, EBA's, water-based acrylic polymers, styrene acrylic polymer, EAA copolymer, polyurethane, epoxy, polyethyle- neimine, polyester, silane and its derivatives, and vinyl amine.

[0016] Furthermore, the adhesion promotion layer further comprises a crosslinker selected from the group of isocyanates and aziridines.

[0017] In the multilayer of the present invention, the release promotion layer is selected from the group consisting of polymers and/or waxes of the following families: polyethylene, amides, silicone, acryl, fluoro- carbons, melamine, ionizing radiation-curable type poly- functional acrylates, polyester, epoxy, catalyst-, light- and heat-curable amino modified silicone oils, polydimethyl silicone rubber, phenyl-modified silicone rubber, epoxy- modified silicone rubber, and urethane-modified silicone rubber, acrylate-acrylonitrile copolymer, acrylic acid- alkyl acrylate copolymer, polyvinyl chloride resin, polyvinyl N-octadecyl carbamate, polyethylene based wax, polyamide based wax, polysiloxane, polyvinyl ester, polyethylene imine, alkyl substituted amine, chromium complex, fatty acids, and mixtures thereof.

[0018] As a further advantage, the rub-off layer (4) is selected from the group consisting of natural or synthetic rubber latex dispersions comprising polychloroprene, polyurethane, styrene-isoprene copolymers, styrene-butadiene copolymer, polyimide; polyvinyl chloride; nitrocellulose, polyisoprene, acrylonitrile-butadiene- isoprene terpolymer, butadiene/methacrylonitrile, poly- ethylene vinyl acetate, polyacrylates, ethyl acrylate/vinyl acetate/methacrylic acid terpolymers and mixtures thereof.

[0019] In the multilayer of the invention, the rub- off layer is coloured to enhance the promotional message.

[0020] In a particular embodiment of the invention, the patterned adhesion promotion layer keeps an optical contrast versus the substrate layer after the rub-off layer has been taken away.

[0021] Moreover, said rub-off layer comprises colour pigments that are able to migrate into the adhesion promotion layer or into the release promotion layer.

[0022] In another particular embodiment of the present invention, the adhesion promotion layer or the release promotion layer represents less than 5% of the total thickness of the multilayer.

[0023] Moreover, the invention discloses a method for the production of the multilayer according to the present invention comprising the following steps: - extrusion of a first mono or multilayer polymer film; - application of a patterned adhesion or release promotion layer on said mono or multilayer packaging film in register with a printing layer; - application of a rub-off layer in register, covering the patterned adhesion or release promotion layer.

Short description of the drawings [0024] Fig. 1 shows a multilayer comprising a substrate layer, a patterned adhesion promotion layer and a rub-off layer as a covering. In this case, the patterned adhesion promotion layer represents the hidden message.

[0025] Fig. 2 shows the same multilayer as in Fig. 1 after the rub-off layer has been rubbed off in the areas where no patterned adhesion promotion layer was applied.

Almost the entire rub-off layer remains visible where the adhesion promotion layer was applied and reveals thereby the hidden message.

[0026] Fig. 3 shows the same multilayer as in Fig. 1 and 2 after the rub-off layer has almost totally been rubbed off with only a very thin coating of rub-off layer remaining on the adhesion promotion layer, thus creating a differential optical reflection compared to the areas where no adhesion promotion layer was applied and still leaving a clearly visible promotional message.

[0027] Fig. 4 shows the particular case of the invention where the colour pigment of the rub-off layer has migrated into the patterned adhesion promotion layer.

[0028] Fig. 5 shows a multilayer substrate comprising a substrate layer, a patterned release promotion layer and a rub-off layer.

[0029] Fig. 6 shows the same multilayer substrate as in Fig. 4 after the rub-off layer has been rubbed off and where the rub-off layer only disappeared on the patterned surfaces where the patterned release promotion layer was applied.

[0030] Fig. 7 shows a top view of a multilayer substrate of the present invention.

[0031] Fig. 8a and 8b show a particular multilayer substrate of the present invention with an aluminium vacuum

coated BOPP film. The hidden messages can be positioned on the recto side or/and the verso side.

[0032] Fig 8a shows the recto version of a BOPP film printed with a patterned adhesion promotion layer (hidden message).

[0033] Fig 8b shows the verso version of a metallized BOPP film printed all over with an adhesion promotion layer.

Detailed description of the invention [0034] The present invention is based on a differential adhesion effect between an opaque rub-off layer 4 and a substrate layer 1. This differential adhesion is achieved by an adhesion promotion layer 2 (primer) or by a release promotion layer 3 printed on a substrate.

[0035] The use of a patterned adhesion promotion layer 2 or a patterned release promotion layer 3 allowing a differential adhesion of the rub-off layer makes it unnecessary to entirely remove the rub-off layer to reveal the hidden message. The hidden message is revealed by the remaining rub-off layer itself.

[0036] The"hidden message"should be understood as an information of any kind and can be a positive or a negative text, logo, number,...; this can be achieved by alternatively playing with an adhesion promotion layer and/or a release promotion layer to favour the adhesion of some patterned surfaces or to favour the release of other patterned surfaces.

[0037] Some rub-off layer compositions comprising particular colour pigments are suitable to favour the migration of those colour pigments into the adhesion promotion layer 2 or the release promotion layer 3. This always creates an optical contrast, even if the rub-off layer is entirely rubbed off, as shown in Fig. 3.

[0038] In a first embodiment of the present invention, shown in Fig. 1,2 and 3, an adhesion promotion layer 2 is printed in pattern and contains a hidden message in form of a positive or negative text. The adhesion between the adhesion promotion layer 2 and the substrate layer 1 on one hand and the rub-off layer 4 on the other hand is better than the adhesion between the rub-off coating layer 4 and the substrate 1. These adhesion properties allow the consumer to rub away the part of the rub-off coating layer which is not printed on the adhesion promotion layer 2. The part of the rub-off coating layer which is printed on the adhesion promotion layer cannot be rubbed-off easily, as shown in Fig. 2 or only partly rubbed off with a remaining optical effect in form of residues, as shown in Fig. 3. After rubbing away the rub-off layer 4, the promotional message becomes visible.

[0039] In a second embodiment of the present invention, shown in Fig. 4 and 5, a release promotion layer 3 is printed in pattern on a substrate layer 1 and the printed pattern contains a positive or negative picture of a hidden message. In this case, the adhesion between the substrate layer and the rub-off layer is better than the adhesion between the rub-off layer and the release promotion layer 3. This allows to rub away the rub-off layer 4 on the areas where the release promotion layer 3 is applied, revealing a promotional message.

[0040] In a third embodiment of the present invention, the rub-off layer 4 is coloured with a particular pigment that is able to migrate into the adhesion promotion layer 2 or into the release promotion layer 3. This embodiment is represented in Fig. 4 and allows to rub off the total thickness of the rub-off layer 4 without losing the message which still appears on the

adhesion promotion layer 2 or on the release promotion layer 3.

[0041] Non-restrictive examples of substrate layers are mono or multilayer plastic films or bottles, glass, paper, cellophane, non-woven, metallic layers or combinations thereof. As far as the plastic film is concerned, all different flexible packaging films well- known by those skilled in the art can be used, non- restrictive examples are extruded and/or laminated polyolefins, polyesters, polyamide, polystyrene, PVC or their copolymers or combinations thereof.

[0042] Non-restrictive examples of the adhesion promotion layer 2 are EVA-, PVB-or EBA-based polymer coatings, acrylics, styrene acrylics, ethylene-acrylic acid copolymer, polyurethane, epoxy, polyethyleneimine, polyester, silane and its derivatives, and vinyl amine. The adhesion promotion layer may comprise a crosslinker like isocyanate or aziridine.

[0043] Non-restrictive examples of the release promotion layer 3 are generally waxes. Examples of release agents usable as the release promotion layer include waxes such as polyethylene wax, amide wax, Teflons powder, silicone wax, carnauba wax, acryl wax, and paraffin wax, fluorocarbon resins, melamine resins, polyolefin resins, ionizing radiation-curable type polyfunctional acrylate resins, polyester resins, epoxy resins, catalyst-, light- and heat-curable silicone oils modified with amino, epoxy, OH, and COOH, silicone resins such as polydimethyl silicone rubber, phenyl-modified silicone rubber, epoxy-modified silicone rubber, and urethane-modified silicone rubber.

[0044] Other examples are ethyl acrylate- acrylonitrile copolymer, acrylic acid-alkyl acrylate copolymer, polyvinyl chloride resin, polyvinyl N-octadecyl

carbamate, polyethylene based wax, polyamide based wax, polysiloxane, fluorocarbon polymer, polyvinyl ester, polyethylene imine, alkyl substituted amine, chromium complex, fatty acid based wax, and mixtures thereof.

[0045] The rub-off layer 4 generally are latex dispersions of synthetic or natural rubber. Non-restrictive examples of such dispersions are polymeric materials such as natural latex, polychloroprene; polyurethane (including aqueous polyurethanes), styrene-isoprene copolymers (including terpolymers, tetrapolymers, etc. ), styrene- butadiene copolymer, polyimide; polyvinyl chloride, nitrocellulose, polyisoprene, acrylonitrile-butadiene- isoprene terpolymer, butadiene/methacrylonitrile, poly- ethylene vinyl acetate, polyacrylates, including a carboxyl modified acrylic emulsion, ethyl acrylate/vinyl acetate/ methacrylic acid terpolymers and mixtures thereof.

[0046] The position of the rub-off areas within the packaging wrap can be chosen according to marketing criteria's and can be placed inside longitudinal or cross- seal as well as inside or outside the packaging. Since the messages are automatically hidden by the nature of the system, they can be positioned both on the recto and the verso side of the wrap, as well as in the seal area.

[0047] When the rub-off layer is located in the seal area, the consumer can only rub off the rub-off layer 4 after opening the seal. Since the adhesion promotion layer 2 or the release promotion layer 3 are situated in the seal area, special care is required. In the case of a cold seal area, the adhesion/release promotion layer (2,3) and the rub-off layer 4 can be positioned in a cold-seal free area.

In the case of a heat-seal version, the adhesion/release promotion layer (2,3) and the rub-off layer 4 can be positioned in a heat-seal free area. In order to achieve

this, the heat-seal jaws have been designed in such a way that the adhesion/release promotion layer (2,3) and the rub-off layer 4 are not heat-sealed. In the case of peelable seals, the rub-off layer can also be automatically removed when the seal is peeled open. This is possible because the rub-off layer 4, which covers the message within the adhesion/release promotion layer (2,3) on one side of the seal, is removed towards and onto the rub-off layer 4 on the other side of the seal. This is possible because of the differential adhesion properties of the rub- off layer versus the substrate in the presence of said adhesion/release promotion layer (2,3).

[0048] When the rub-off layer 4 with the hidden promotional message is inside the packaging and in contact with the product, in the case of a food product, the rub- off layer needs to enjoy food-contact status. Moreover, since the message is"written"on the inside of the packaging, the printed substrate needs to be sufficiently opaque in order to avoid that the message can be read from the outside. This is given by the extremely low thickness of the adhesion/release promotion layer (2,3) which is substantially lower than that of the printing used on ticketing of the prior art and is generally lower than 1, 4.

[0049] The types of rub-off layers related to the invention are typically, but not limited to latex based dispersion coatings with reduced stickiness. Generally they can be considered as a cold sealing adhesive that is sensitive to contact and pressure. They can stick in a "permanent"way to the surface of many materials by means of mere contact and pressure.

[0050] Different types of cold-seal can be classified e. g. in a range from dry (limited stickiness) to soft (increased stickiness).

[0051] In a reel of flexible packaging material, adhesion (BLOCKING) between cold-seal and the other side of the'flexible packaging material can be avoided by the right choice of material on the other side, for instance the homopolymer side of a co-extruded biaxially-oriented polypropylene film NND of TrespaphanX, MB 200 from Mobil Films, by a coating, or by the choice of cold-seal (dry cold-seal).

[0052] When the substrate opaqueness is sufficient, the choice of substrate material is only restricted by practical machinability considerations such as thickness and stiffness (e. g. substrates between 15 and 150Am) consisting of polypropylene, polyester, polyethylene, polyamide multilayers as well as different types of paper, non-wovens, aluminium foil and in general, any known structure in the field of packaging can be used.

[0053] Particularly preferred embodiments are represented in fig 8a and fig 8b. Fig 8a shows the recto version (layers not to scale), the metallized side 12 of the BOPP film 1 is printed with a patterned adhesion promotion layer (hidden message) 2. In general, the design (ink) 9 is printed onto an adhesion promotion layer 13, which in some cases can be the same coating as the patterned adhesion promotion layer 2. A protective or a release lacquer 10 is printed all over except on the hidden message and the surrounding part to protect the inks and to avoid blocking between the inks on the recto side and the cold-seal (if any) on the verso side. The patterned adhesion promotion layer (hidden message) 2 and the surrounding part are covered with the rub-off layer 4. If the pack is to be closed by a cold-seal, a cold-seal coating 7 will be printed in pattern on the verso side of the substrate.

[0054] The verso version represented in fig 8b where the layers are not to scale, the metallized (recto) side 12 of the BOPP film 1 is printed with an adhesion promotion layer all over. The design (inks) 9 is printed onto an adhesion promotion layer 13. A protective or a release lacquer 10 is printed all over to protect the inks and to avoid blocking between the inks on the recto side and the cold-seal (if any) on the verso side. The patterned adhesion promotion layer (hidden message) 2 is printed on the verso side covered with a rub-off coating 4. If the pack is to be closed by a cold-seal, a cold-seal coating 7 will be printed in pattern on the verso side of the substrate.

[0055] The following examples shows different preferred embodiments of the present invention with adhesion and/or release promotion layer on different substrates.

[0056] Example 1 cover varnish: Siegwerk# 10-6093445-3P, lym printing inks: Siegwerk# MRH range, 3µm adhesion promotion layer: SunSwale 122879, lym rub-off layer: SunSwale 8076 substrate: BOPP metallised 30ym VifanX CY coldseal: SunSwale# IP 8025, 3Am [0057] Example 2 cover varnish: Siegwerk 10-6093445-3P, lAm printing inks: Siegwerk# MRH range, 3µm adhesion promotion layer: SunSwale 12289, lym release promotion layer: Michelman emulsion 61335,2gsm rub-off layer: SunSwale 8076 substrate: BOPP metallised 30ym VifanX CY coldseal: SunSwale IP 8025, 3Am

[0058] Example 3 cover varnish: Siegwerk# 10-6093445-3P, lum printing inks: Siegwerk# MRH range, 3Am adhesion promotion layer : SunSwale# 12289 rub-off layer: SunSwale# 8076 substrate: BOPP metallised 30pm VifanO CY coldseal: SunSwale# IP7956, 4Am [0059] Example 4 cover varnish: Siegwerk# 10-6093445-3P, lAm printing inks: Siegwerk# MRH range, 3Am adhesion promotion layer: SunSwale@ 200160, lAm rub-off layer: SunSwale# 8076, 4µm substrate: Tyvec# type 1059B, 64.4gsm [0060] Legend 1. Substrate layer 2. Adhesion promotion layer 3. Release promotion layer 4. Rub-off layer 5. Residues of the rub-off layer 6. Coloured adhesion/release promotion layer 7. Cold-seal areas 8. Rub-off area 9. Printing ink 10. Transparent cover varnish 11. BOPP film 12. Aluminium layer 13. Ink adhesion promotion layer