Patent Application
20060198987
The present invention relates to a multiple layer laminate which can be used, for example, as print substrates, in particular as security paper, but also as packaging material, covering material, card substrate, etc. The multiple layer laminate comprises at least one plastic layer having a top and a bottom, an upper paper layer bonded to the plastic layer and present on the top of the plastic layer, and optionally a lower paper layer bonded to the plastic layer and present on the bottom of the plastic layer.
Combinations of paper and plastic in a laminate have a variety of uses. Particularly, the resistance of paper is increased by such a laminate (tensile strength, resistance to soiling, etc.). Typical uses of such laminates are, for example, packaging materials, printed or unprinted, covering materials, such as tablecloths, inlays for drawers, etc., gift-wrapping paper, etc. However, such laminates are also used as print substrates, for example as cover sheets for journals, as greeting cards, as a substrate for maps and, to date however, in a small quantity, as security paper, particularly as bank notes. Typically, the plastic layer and the paper layer are bonded by means of an adhesion promoter.
The discussion over many years about the advantages and disadvantages of paper and polymer materials as substrates for bank notes has now reached a mature phase. Although even today the polymer substrates do not account for more than a few percent of the market share of the bank note market and their introduction has in some cases been considered as the wrong decision, certain properties of the bank notes comprising polymer material have been regarded as progress and could expediently supplement the property portfolio of the successful paper notes, provided that a synthesis of the two products were to be technically conceivable.
In addition to the security of the novel substrate against falsification, further target parameters are moreover the printability by conventional bank note printing processes and the compatibility with the conventional sorting machines and automatic teller machines, but also further security features which are recognizable without aids or only with simple aids.
A discussion about the advantages and disadvantages of the paper substrate compared with the polymer substrate has taken place in recent years simultaneously with this development. The plastic notes which in particular have their core market in the Australian market have, on the other hand, the advantage of more favorable antiaging behavior in the sense of mechanical stability and antisoiling behavior. In addition, a transparent window, which has not been demonstrated to date in this form in paper notes, is frequently integrated in the polymer notes. The transparent window has been classed in the discussion as a first-level feature of great value but, in the judgment of some experts, is the only polymer-typical security feature of value.
Although the polymer notes have to date won only a few percent of the bank note market, they have exerted a considerable pressure on the market participants and also promoted other manufacturers to launch synthetic or semisynthetic substrates, without however generating a market success to a noticeable extent. In the central banks, there prevails today predominantly the opinion that the future nevertheless belongs to paper, but the latter should in a further stage of evolution additionally acquire certain desirable properties of the polymer. In this context, it should be noted that some bank note publishers have revised their decision regarding the introduction of polymer notes once again in favor of paper. Together with the need for new first-level features, the desire for a paper note with possible integrated transparent window and perhaps further first-level features is clearly evident. Depending on use (frequency of use, climate, etc.), desires for high tensile strength and good antisoiling behavior are also evident.
The conventional bank note papers are traditionally based on cotton as the main fiber raw materials. In addition, flax, synthetic fibers and linen are also admixed for increasing the mechanical strengths. These are not only renewable raw materials; in the case of combed cotton materials, a byproduct of the spinning industry is additionally put to an expedient use, which only reinforces the sustainability of bank note paper production from the ecological point of view. With the aid of additives, the high values for wet strength are achieved.
Since the 70s, multitone watermarks have been customary in the bank note sector and have been constantly refined in the course of the years. Since the introduction of the cylinder mold technology, security filaments in paper have been part of the prior art. Here too, new variants, such as window filaments, broad filaments and personalized filaments were continuously introduced. Security features which can be introduced by simple addition to the fiber in the manufacturing process, such as, for example, pigments or tracer fibers, are easy to integrate into the paper but on the other hand can be imitated in general only with difficulty by the falsification process, which is based on printing processes. This is the reason for the value of paper for security applications and has long made it a preferred substrate for bank notes.
Owing to the open pore structure of the paper substrates, the latter are susceptible to soiling and therefore have a limited life with respect to their circulation time as bank notes. Since the end of the 90s, this problem has been encountered with bank note substrates which have a sealed surface with the aid of a thin coating. A disadvantage is often insufficient matching of printing inks and surface coatings, which in turn also works against a longer life expectancy of the bank notes.
Initial attempts to introduce a polymer-based bank note were made for Haiti. A further attempt is known for the Isle of Man. However, owing to its extremely hydrophobic properties, the material suffers from a considerable susceptibility to soiling with regard to oleophilic substances.
The efforts in Australia, where such bank notes are still in use today, can be regarded as having been successful to a certain extent, but the success would not be conceivable without the printing inks specifically developed for this substrate. However, the additives required for adapting the inks to these specific conditions prevent the provision of certain tones.
A possible reason for the relatively modest market success of the polymer substrate is the small number overall of safety features which have been demonstrated at all with this material. As already mentioned, only the transparent window would be demonstrable here as a significant feature. The window part of the substrate permits novel security features which require transparent areas. On the other hand, the additional cost for printing and the high substrate costs lead to a total cost which can scarcely be justified by the longer life even in the case of notes under considerable stress.
Below, some of the advantages of paper and polymer substrates (in particular biaxially oriented polypropylene PP) for use as bank note substrates are listed in a very compact form:
Advantages of paper:
Advantages of plastic (PP) substrate:
Thus, the polymer has in particular an advantage with respect to the possibility of integratability of a “window”, the mechanical strengths at room temperature and the antisoiling behavior. It is therefore necessary to optimize the paper substrate and to a certain extent to permit the introduction of the positive properties of polymers into the paper substrate.
An attempt to combine the positive properties of paper-based print substrates with the positive properties of plastic film is described in U.S. Pat. No. 5,449,200. It is proposed there to provide a plastic layer between two paper layers, this plastic layer being printed so that the corresponding imprint is visible only in transmitted light but not in reflected light. The bond between plastic layer and the paper layers is produced by laminating the layers, an adhesive being used. The problem with this approach is the unacceptably high risk of delamination of such substrates when they are put into circulation.
It is accordingly the object of the invention to provide a novel multiple layer laminate, for example as a novel print substrate, but in particular not exclusively for security applications but also for other applications, such as, for example, as packaging material, label material, covering material, envelope material, etc. The multiple layer laminate or preferably the print substrate should as far as possible combine at least some of the positive properties of a paper substrate with the positive properties of plastic substrates without exhibiting new disadvantages. A multiple layer laminate or a print substrate in question comprises at least one plastic layer which may optionally have a multilayer form, with a top and a bottom, and at least one upper paper layer on the top of the at least one plastic layer and bonded to the plastic layer. Optionally, a lower paper layer bonded to the plastic layer can also be arranged on the bottom of the plastic layer, i.e. the plastic layer can be surrounded on both sides by paper.
This object is achieved if the plastic layer comprises one (or more) thermoplastic polymeric materials, and if the bond between the paper layer and the plastic layer is ensured substantially without additional adhesion promoter, in each case by penetration zones in which parts of the plastic layer are fused with the material of the fiber composite of the paper layer, the penetration zone substantially not extending completely to the surfaces of the paper layer which face away from the plastic layer. In the case of paper layers arranged on both sides of the plastic layer (upper and lower paper layer), such a fusion with penetration zones to both paper layers is preferably present. The penetration zones can, however, also pass through up to the respective surface of the paper layers and thus in each case more or less completely impregnate the paper layers.
The core of the invention therefore consists in the surprising discovery that paper layers and thermoplastic layers, in spite of their very different chemical behavior (industrial thermoplastic versus cellulose) can be partly fused to one another, an extremely stable and intimate bond forming between paper layer and plastic layer. In this context, fusion means that the thermoplastic flows around the cellulose and embeds this as a matrix. While in fact laminates according to the prior art using reactive adhesives or solvent-based adhesives as adhesion promoter between paper and plastic layer have the problem of delamination in high-stress uses, such as, for example, as packaging material, label material, covering material or envelope material and in particular in the case of the extremely high-stress use as bank notes, this can be prevented by a (multiple layer) laminate according to the invention. The laminate according to the invention provides a bond by virtue of the fact that uppermost layers of the plastic layer are directly fused to lowermost layers of the paper layers, i.e. that the fibers of the paper layers are at least partly embedded in a plastic matrix. The resulting penetration zones in the respective boundary regions between plastic layer and paper layers are adjusted so that the plastic partly penetrates the papers layer but without extending completely to that surface of the paper layer(s) which faces away from the plastic layer. This ensures that the haptic properties of the paper are retained on one side of the resulting print substrate, and that the printing properties of the multiple layer laminate or print substrate are likewise substantially retained on the other side. If in fact plastic penetrates the paper substrate completely to the surface or close to the surface, not only does the handle change but also the porosity (this leads, so to speak, to a seal), which may considerably complicate the adhesion of printing inks or inks and may facilitate the abrasion thereof.
On the other hand, the penetration of the thermoplastic into the paper layers also leads to antisoiling behavior, which is entirely desirable. The antisoiling properties together with the haptic properties and the printing properties can thus be controlled via the degree of penetration of the thermoplastic into the paper matrix.
As already mentioned, the plastic layer may be composed of a single layer of a single material but can also be composed of a multiple layer laminate (multilayer structure), it being possible for individual layers to consist of different thermoplastic materials (differing polymers or identical polymers having different properties). In particular, for example, thermoplastics which have a flow behavior differing from or better than (lower molecular weight, lower glass transition temperature or lower flow temperature) that of the central layers can be used as layers which come into direct contact with the paper.
According to a first preferred embodiment of the present invention, at least one of the paper layers is paper which was produced in a vat machine. Alternatively, it is also possible to use a Fourdrinier machine or uphill wire machine. This is preferably, for example, a typical bank note paper, i.e. a paper which was produced using cotton (typically main fiber raw material) and/or flax and/or linen as fiber raw material.
The desired properties with respect to fusion between plastic layer and paper layers can preferably be achieved by using, as material for the plastic layer, a polymeric material having a glass transition temperature or melting point in the range from 50 to 250° C., preferably in the range from 75 to 225° C., or in the range from 100 to 200° C., particularly preferably from 120 to 180° C. In principle, it should be a thermoplastic which begins to melt or soften at a temperature at which the paper is not damaged. For example, in the case of polymeric material, it may be a transparent, for example partly amorphous or completely amorphous polyamide, a polypropylene or polyethylene, particularly preferably a polyamide based on aliphatic and cycloaliphatic building blocks. Transparent polymeric material is advantageous particularly when the possibility of clear transparent windows or at least transparent regions free on one side is intended. However, it is also possible to use as polymeric material a colored or nontransparent material, and semitransparent materials are also conceivable. Such polymers are obtainable, for example, from EMS-CHEMIE (Switzerland) under the trade name GRILAMID®, GRILON® or GRIVORY®. These materials can, if required, be appropriately colored and/or can contain further functional components. Suitable dyes are dyes in the visible range, but also fluorescent or phosphorescent dyes. Moreover, the thermoplastic material may simultaneously contain magnetic components, electrically conductive components, thermochromic or photochromic components, UV absorbers, etc. or a plurality of these components.
In principle, the following polymers constitute suitable material for the plastic layer:
Polymers of monoolefins and diolefins, e.g. polypropylene, polyisobutylene, polybut-1-ene, poly-4-methylpent-1-ene, polyvinylcyclohexane, polyisoprene or polybutadiene, and polymers of cycloolefins, e.g. of cyclopentene or norbornene, polyethylene (which may optionally be crosslinked), e.g. high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), (VLDPE) and (ULDPE).
Copolymers of monoolefins and diolefins with one another or with other vinyl monomers, e.g. ethylene/propylene copolymers, linear low density polyethylene (LLDPE) and blends thereof with low density polyethylene (LDPE), propylene/but-1-ene copolymers, propylene/isobutylene copolymers, ethylene/but-1-ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene copolymers, ethylene/heptene copolymers, ethylene/octene copolymers, ethylene/vinylcyclohexane copolymers, ethylene/cycloolefin copolymers (e.g. ethylene/norbornene, such as COC), ethylene/1-olefin copolymers, the 1-olefin being produced in situ; propylene/butadiene copolymers, isobutylene/isoprene copolymers, ethylene/vinylcyclohexene copolymers, ethylene/alkyl acrylate copolymers, ethylene/alkyl methacrylate copolymers, ethylene/vinyl acetate copolymers or ethylene/acrylic acid copolymers and salts thereof (ionomers) and terpolymers of ethylene with propylene and a diene, such as, for example, hexadiene, dicyclopentadiene or ethylidenenorbornene. Said homopolymers and copolymers may have any desired three-dimensional structure (stereostructure), such as, for example, syndiotactic, isotactic, hemiisotactic or atactic. Stereoblock polymers are also possible.
Polystyrene, poly(p-methylstyrene), poly(α-methylstyrene). Aromatic homopolymers and copolymers derived from vinylaromatic monomers, including styrene, α-methylstyrene, all isomers of vinyltoluene, in particular p-vinyltoluene, all isomers of ethylstyrene, propylstyrene, vinylbiphenyl, vinylnaphthalene and vinylanthracene and blends thereof. Homopolymers and copolymers may have any desired three-dimensional structure, including syndiotactic, isotactic, hemiisotactic or atactic. Stereoblock polymers are also included.
Copolymers, including the abovementioned vinylaromatic monomers and comonomers selected from ethylene, propylene, dienes, nitriles, acids, maleic anhydrides, maleimides, vinyl acetates and vinyl chlorides or acryloyl derivatives and mixtures thereof, for example styrene/butadiene, styrene/acrylonitrile, styrene/ethylene (interpolymers), styrene/alkylmethacrylate, styrene/butadiene/alkyl acrylate, styrene/butadiene/alkyl methacrylate, styrene/maleic anhydride, styrene/acrylonitrile/methyl acrylate; blends having a high impact strength and comprising styrene copolymers and other polymers, e.g. polyacrylates, diene polymers or ethylene/propylene/diene terpolymers; and block copolymers of styrene, such as, for example, styrene/butadiene/styrene, styrene/isoprene/styrene, styrene/ethylene/butylene/styrene or styrene/ethylene/propylene/styrene. Hydrogen-saturated aromatic polymers derived by hydrogen saturation of said polymers, in particular including polycyclohexylethylene (PCHE) prepared by the hydrogenation of atactic polystyrene (frequently designated as polyvinylcyclohexane (PVCH)).
Graft copolymers of vinylaromatic monomers, such as, for example, styrene or α-methylstyrene, for example styrene on polybutadiene, styrene on polybutadiene-styrene or polybutadiene-acrylonitrile copolymers; styrene and acrylonitrile (or methacrylonitrile) on polybutadiene; styrene, acrylonitrile and methyl methacrylate on polybutadiene; styrene and maleic anhydride on polybutadiene; styrene, acrylonitrile and maleic anhydride or maleimide on polybutadiene; styrene and maleimide on polybutadiene; styrene and alkyl acrylates or methacrylates on polybutadienes; styrene and acrylonitrile on ethylene/propylene/diene terpolymers; styrene and acrylonitrile on polyalkyl acrylates or polyalkyl methacrylates, styrene and acrylonitrile on acrylate/butadiene copolymers.
Halogen-containing polymers, such as, for example, polychloroprene, chlorinated rubbers, chlorinated and brominated copolymers of isobutylene-isoprene (halobutyl rubber), chlorinated or sulfochlorinated polyethylene, copolymers of ethylene and chlorinated ethylene, epichlorohydrin homo- and copolymers, in particular polymers of halogen-containing vinyl components, e.g. polyvinyl chlorides, polyvinylidene chlorides, polyvinyl fluorides, polyvinylidene fluorides, and copolymers thereof, such as, for example, vinyl chloride/vinylidene chloride, vinyl chloride/vinyl acetate or vinylidene chloride/vinyl acetate copolymers.
Polymers derived from α,β-unsaturated acids and derivatives thereof, such as, for example, polyacrylates and polymethacrylates; polymethyl methacrylates, polyacrylamides and polyacrylonitriles, made impact-resistant with butyl acrylate, copolymers of said monomers with one another and with other unsaturated monomers, such as, for example, acrylonitrile/butadiene copolymers, acrylonitrile/alkyl acrylate copolymers, acrylonitrile/alkoxyalkyl acrylates or acrylonitrile/vinyl halide copolymers or acrylonitrile/alkyl methacrylate/butadiene terpolymers.
Polymers derived from unsaturated alcohols and amines or from acyl derivatives or acetals thereof, for example polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate or polyallylmelamine; and copolymers thereof with olefins.
Homopolymers and copolymers of cyclic ethers, such as, for example, polyalkylene glycols, polyethylene oxide, polypropylene oxide or copolymers thereof with bisglycidyl ethers.
Polyacetals, such as, for example, polyoxymethylene and those polyoxymethylenes which contain ethylene oxide as a comonomer; polyacetals modified with thermoplastic polyurethanes, acrylates or MBS.
Polyphenylene oxides and sulfides.
Polyurethanes derived from hydroxyl-terminated polyethers, polyesters or polybutadienes on the one hand and aliphatic or aromatic polyisocyanates on the other hand, and precursors thereof.
Polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or the corresponding lactams, for example polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11, polyamide 12, aromatic polyamides starting from m-xylenediamine and adipic acid; polyamides prepared from hexamethylenediamine and isophthalic and terephthalic acid as starting materials and with or without an elastomer as a modifier, for example poly-2,4,4-trimethylhexamethyleneterephthal-amide or poly-m-phenyleneisophthalamide; and also block copolymers of said polyamides with polyolefins, olefin copolymers, ionomers or chemically bonded or grafted elastomers; or with polyethers, for example with polyethylene glycol, polypropylene glycol or polytetramethylene glycol; and also polyamides or copolyamides modified with EPDM or ABS; and polyamides condensed during the preparation (RIM polyamide systems).
Polyureas, polyimides, polyamidoimides, polyetherimides, polyesterimides, polyhydantoins and polybenzimidazoles.
Polyesters derived from dicarboxylic acids and diols and/or from hydroxycarboxylic acids or the corresponding lactones, for example polyethylene terephthalate, polybutylene terephthalate, poly-1,4-dimethylolcyclohexane terephthalate, polyalkylene naphthalate (PAN) and polyhydroxybenzoate, and also block copolyetheresters derived from hydroxyl-terminated polyethers.
Polycarbonates and polyestercarbonates, polyketones, polysulfones, polyethersulfones and polyetherketones.
Crosslinked polymers derived from aldehydes on the one hand and phenols, ureas and melamines on the other hand, such as, for example, phenol/formaldehyde resins, urea/formaldehyde resins and melamine/formaldehyde resins.
Unsaturated polyester resins derived from copolyesters of saturated and unsaturated dicarboxylic acids, polyhydric alcohols and vinyl components as crosslinking agents, and also halogen-containing modifiers thereof having low flammability.
Crosslinked acrylic resins derived from substituted acrylates, e.g. epoxyacrylates, urethaneacrylates or polyesteracrylates.
Alkyd resins, polyester resins and acrylate resins crosslinked with melamine resins, urea resins, isocyanates, isocyanurates, polyisocyanates or epoxy resins.
Crosslinked epoxy resins derived from aliphatic, cycloaliphatic, heterocyclic or aromatic glycidyl components, for example products of diglycidyl ethers of bisphenol A and bisphenol F, which are crosslinked with conventional curing agents, such as, for example, with anhydrides or amines, with or without an accelerator.
Cellulose acetates, cellulose propionates and cellulose butyrates, or cellulose ethers, such as methylcellulose.
Blends of two or more of said polymers or copolymers are also possible.
As stated, the flowability of the thermoplastic used is important. Accordingly, it is alternatively also possible to use thermoplastics whose glass transition temperature or melting point is below the abovementioned glass transition temperature but which are in the solid state at the temperature of use of a product (e.g. bank note) and whose flow temperature is in the range from 50 to 250° C., preferably in the range from 75 to 225° C. or in the range from 100 to 200° C., particularly preferably from 120 to 180° C. Thus, for example in the case of polypropylene (PP), polyethylene (PE), polyvinylidene chloride (PVDC) or polyvinylidene fluoride (PVDF).
A further preferred embodiment is distinguished by the fact that the paper layers have a basis weight in the range from 50 to 500 g/m2 or even from 5 to 500 g m2, preferably in the range from 20 to 80 g/m2, or from 10 to 80 g/m2, particularly preferably in the range from 20 to 50 g/m2. Preferably, the plastic layer has a thickness in the range from 5 to 500 μm, preferably in the range from 10 to 80 μm, particularly preferably in the range from 20 to 50 μm. The print substrate as a whole should have a basis weight in the range from 15 to 1500 g/m2 or from 50 to 500 g/m2, preferably in the range from 80 or 60 to 180 or to 200 g/m2, particularly preferably in the range from 90 to 120 g/m2 or from 80 to 150 g/m2.
Very particularly advantageous in relation to the proposed multiple layer laminate or print substrate is the fact that it can be combined with the multiplicity of security features known from the area of the pure paper substrates. For this purpose, such security features can be simply incorporated into at least one of the paper layers either before, during or after the lamination process. Suitable security features are a very wide range of methods and types, very generally, for example, security features comprising corresponding information media of an optical, electronic, electrical or magnetic nature, for example watermarks, in particular gray step watermarks, security filaments, so-called optically variable devices (OVDs), colored fibers, security pigments, iridescent color applications, microperforations, microprints, offset, gravure printing, magnetic stripes, chips, etc. The plastic layer may also be provided with security features. In the simplest embodiment, this may be an imprint which is not visible in reflected light owing to the paper layers present on top (and accordingly, for example, also cannot be reproduced using a copier), but which can be recognized in transmitted light. However, in the case of the plastic layer, other security features, in particular in the region of the below-mentioned windows, are suitable, for example fluorescent regions, polarizing regions, polarized fluorescent regions, polarized absorbent regions, photochromic regions, holograms, embossing, etc.
The multiple layer laminate according to the invention or the print substrate according to the invention has the unusual advantage that, in spite of appearance and handle like paper, it offers the possibility of incorporating additional information as security features, in particular security features in the form of or incorporated in windows.
In this context, a window is understood as meaning not exclusively a transparent region which is bounded all round (by paper); a window in the context of the present invention can be bounded all round but, in the final intended multiple layer laminate or print substrate, may also be arranged at the edge in such a way that the window region directly borders the edge. A window is in principle also to be understood as meaning not exclusively a cut-out which contains a transparent region but also cut-outs which expose colored and, for example, nontransparent or partly transparent, fluorescent, phosphorescent, polarizing, optically refractive or holographic plastic regions. Also possible in the case of multiple layer laminates which have paper on both sides are cut-outs in which only the paper is exposed on one side of the plastic layer(s). Also possible are corresponding combinations in which, for example, the cut-outs in the two paper webs do not coincide so that, on the one hand, regions in which the plastic layer is accessible from both sides form, and, on the other hand, at least one further region in which the plastic layer is accessible only from one side.
The window itself and many of the information media or security features integrated in the window constitute so-called first-level security features since they can be easily verified by the human eye on the street without the aid of technical devices. Such security features, if they are virtually impossible to reproduce, have an extremely high value. In the case of a print substrate according to the invention, it is possible to provide a window by virtue of the fact that at least one of the paper layers has a cut-out right through so that the plastic layer is exposed in this region (one-sided window, for example, for a view of a safety feature of the plastic layer). A properly transparent window with the use of a transparent plastic layer is provided by virtue of the fact that both paper layers have such a cut-out in at least a partly overlapping manner with formation of a window. It proves to be interesting from the point of view of security to enable such cut-outs to have an irregular edge and/or fluid transitions without edges between paper and window. Surprisingly, in the case of the print substrate according to the invention, the problems of delamination of paper layers from the plastic layer in the edge region, which otherwise occur particularly in relation to windows having a complex contour, are virtually completely absent.
In order to be able to ensure a homogeneous thickness of the multiple layer laminate or print substrate, it is also possible to insert a further plastic layer having the same or a similar contour as the window into the window in the region of the cut-out during production.
It is found that in principle in particular the region of the window and the cut-out on one side are particularly suitable for the arrangement of security features in the plastic film. Thus, for example, security features having polarized properties can be incorporated into these regions. Such windows are also very suitable for so-called “self-verifying” properties, i.e. the verification of other security features with the aid of the window. Thus, for example, polarizing properties of a security feature can be verified by placing a window region which likewise has polarizing transmission properties above the security feature by folding the bank note.
Further preferred embodiments of the printed substrate according to the invention are described in the dependent claims.
The present invention furthermore relates to a process for the production of a multiple layer laminate, such as, for example, of a print substrate, as described above. In a preferred procedure, the at least one paper layer is at least partly fused to the plastic layer in a laminator, a temperature in the range from 50 to 250° C., preferably in the range from 75 to 225° C., or in the range from 100 to 200° C., particularly preferably from 140 to 180 degrees, being used. Preferably, a pressure in the range from 10 Pa to 10 MPa, preferably from 1 kPa to 10 MPa, or from 1 kPa to 5 MPa, particularly preferably in the range from 0.5 MPa to 2 MPa, is also used. It is possible to run a program by first increasing the temperature and then pressure, or vice versa. The process either can take place batchwise in presses or can be carried out continuously. In the continuous procedure, the individual substrates are appropriately fed by means of rollers, and the laminator is a roller laminator, the plastic layer and optionally also security features, such as security filaments, being fed centrally and the two paper layers from the top or from the bottom.
If a window is to be made, a cut-out unit in which the cut-outs are made in the paper webs in register, for example by means of a laser, water jet, punching or the like, must be installed in the process.
Further preferred embodiments of the process according to the invention are described in the further dependent claims.
In addition, the present invention relates to the use of such a print substrate as security paper, in particular as bank note, check, ticket, certificate, share document or bond document, documents, identity papers, packaging material, label material, envelope material, covering material, etc.
The invention is to be explained in more detail below with reference to embodiments in relation to the drawings.
a)-c) shows sections from multiple layer laminates comprising different penetration depths, d) a section through a multiple layer laminate comprising locally different penetration depths;
a), b) shows sections through multiple plastic layers;
The paper layers 11 and 12 are, for example, a bank note-like paper having a basis weight of 40 g/m2, but in principle a weight in the range from 20 to 50 g/m2 or from 5 to 500 g/m2 is possible. The papers layers 11 and 12 accordingly contain cellulosic materials, such as cotton, as main fiber material and are produced, for example, on a vat machine. The paper of these layers contains, for example, a gray step watermark, and particularly high security can optionally be ensured by arranging different watermarks in a registered manner in the two paper layers 11 and 12.
The plastic layer 22 is a film, for example having a thickness of 40 μm and comprising completely amorphous, transparent polyamide. Such films can be obtained, for example, from EMS-CHEMIE (Switzerland) under the trade name GRILAMID® TR90 LX or under the name GRIVORY® G21.
The multiple layer laminate or security paper according to
In a continuous roller process, a nip pressure in the range of 1-500 N/mm can be employed.
A comparison of the mechanical properties of the security paper according to
It is evident that in particular the number of folds of the new security paper is considerably superior, and with respect to the appearance and the mechanical properties after complete wetting (washing machine test).
Such windows also permit extremely interesting combinations of security features. Thus, for example, it is possible to design the plastic film 22 to be polarizing. If the bank note 10 is now folded so that the window 15 comes to rest above the character 17 (fold line parallel to the short side of the bank note), it is possible to see through both windows since the two polarization directions are parallel. If, however, the window 15 is placed above the window 16 by folding the upper left corner obliquely toward the bottom right, the two polarization directions are orthogonal and accordingly the two windows appear dark in transmitted light. More complex effects can be achieved if in addition different colors are brought into play, and if in addition different polarization directions are formed in the regions of different windows.
This geometrical arrangement of a security feature having polarizing properties and its verification means on a bank note is an independent innovation as such and independently of the laminate described here. It could also be used, for example, with the aid of a laminate having adhesive for fastening the paper webs.
For further illustration, FIGS. 4 to 11 show different possibilities of the multiple layer laminates and the arrangement of the windows in a wider context.
Alternatively, it is also possible to produce such a substrate in a continuous manner and then to cut it into appropriate pieces (for example into individual bank notes, greeting cards, etc.). This cutting can take place either with the use of elevated temperature (hot cutting tool) or optionally in combination with the use of elevated pressure. This is done so that, in the edge regions, the plastic layer 22 is pressed out slightly from the region of the paper layers 11 and 12, and an edge fusion 23 results.
Furthermore, it is possible to carry out an additional lamination of the edge after cutting to size in a separate process, once again parts of the plastic layer 22 being pressed out between the paper layers and giving rise to the edge fusion 23.
A further special feature is shown in
Further embodiments were produced and measured in order to illustrate the subject according to the invention. The following materials were used:
Paper:
Polymers:
In general, the following processes were used:
Polymer films: The films were produced in a pressure melting process at the following temperatures:
A Carver press, model M 25T, was used for this purpose. The applied pressure was 2 MPa during a time of 5 min, followed by cooling to room temperature. Films having a thickness of about 80 μm were obtained.
Paper/polymer/paper laminates: Layer structures comprising layers of paper/polymer/paper were assembled and were placed between two copper plates in the heated Carver press and initially left for 30 sec without application of pressure. Different pressures were then applied for different periods. The temperature during the pressure phase in the various example was in the range from 125° C. to 250° C. The examples were then cooled to room temperature.
Characterization: Tensile strength, modulus of elasticity and elongation at break of selected examples were determined from stress-strain diagrams which were obtained by tensile tests at room temperature (23° C.). An Instron tensile tester (model 4464) was used for this purpose. The sample length at the beginning was 12.5 mm, the width was 2 mm and the speed of the crosshead was 10 mm/min. Bursting pressure (DIN ISO 2758), breaking force, number of double folds (Tappi T423), tensile strength (DIN EN 21974) and stiffness (DIN 53121) were measured by standard methods for some selected samples, in each case according to the standard stated in brackets.
20 mm×100 mm samples of paper A were cut out, and a hole of 5 mm diameter was punched out in each case at one end of each piece. A piece of polymer film measuring 20 mm×40 mm×0.1 mm was then cut out and was placed between the two paper layers A, the two paper layers having been placed one on top of the other in such a way that the holes coincided (cf.
In all cases, a strong bond was obtained between the paper layers and the polymer. The two regions of the paper which were not bonded by the polymer layer were torn apart (cf.
Example 1 was repeated, except that a larger piece of Grilamid® TR 90 LX measuring 24 mm×44 mm×0.1 mm was cut out. Once again, this piece was placed between two paper layers comprising paper A, a small region of the polymer film projecting in each case beyond the edge of the paper layers (
Example 1 was repeated, but windows having a diameter up to 16 mm were produced instead of a window of 5 mm. In all cases, satisfactory multiple layer laminates having excellent mechanical properties were obtained.
Example 1 was repeated, but a structure in which the two paper layers were not continuous was produced instead of a window of 5 mm (cf.
Paper/polymer/paper laminates were produced as described under example 1, but with the use of paper B from Grilamid®TR 90 LX at 200° C. Thereafter, the multiple layer laminate was immersed in boiling water and kept there for 30 minutes with vigorous stirring. As a reference, a sheet of paper (paper B) was also exposed to the same conditions. This reference sheet decomposed completely under these conditions, whereas the multiple layer laminate remained intact and showed no delamination either during the treatment or thereafter.
Paper C/Grivory® G21 30 μm film/paper D laminates measuring 80 mm×150 mm were produced as described under example 1, lamination being effected at 150° C. and 0.5 MPa for 1, 2 and 10 min. The tensile strength of the multiple layer laminates was then measured as stated above. Substantially no differences between the different multiple layer laminates were found, and tensile strengths of about 11 km were measured, which substantially corresponds to a value of paper D and is 50% higher than in the case of the polymer film alone and 30% higher than in the case of paper C. The various multiple layer laminates had different visual appearances and different surface structures. Thus, multiple layer laminates which had been produced in the lamination time of 10 min exhibited a polymer on the surface of the paper, which indicates that the molten polymer at least partly diffuses through the paper under these conditions. This manifested itself in a glossy appearance and in a smoother surface and in smoother haptic properties.
80 mm×150 mm laminates of paper C/Grilamid® TR 90 LX 60 μm film/paper D (laminate I) and of paper C/Grilamid® ELY 60/paper D (laminate II) were produced as described under example 1, lamination being effected at 180° C. and a pressure of 0.75 MPa during a time of 1 min. A number of different parameters was measured using the methods described above. For comparison, the same properties were measured in the case of a paper as used in the production of a conventional 100 SFr. bank note (reference).
Test conditions: 23° C. and 50% relative humidity (test room conditions)
The data show that the multiple layer laminates actually have outstanding properties, and in some respects surpass the properties of a bank note according to the prior art, for example with respect to the bursting pressure, the breaking force and the stiffness. Particularly remarkable is the increase or improvement in the values for the number of folds for the multiple layer laminate.
Example 7 was repeated and multiple layer laminates comprising paper C/Grilamid® TR 90 LX 60 μm film/paper D were produced. They had a transparent window having a size of 10 mm×10 mm. A number of double folds was determined in a range in which the window was arranged. For this purpose, a test strip was cut out (or was positioned) so that the fold occurred in the window and in the surrounding paper (corresponding to Tappi T 423). The resulting value of the number of double folds was 7510.
Example 8 was repeated and multilayer laminates comprising paper C/Grilamid® TR 90 LX 60 μm film/paper D were produced. They had a transparent window having a size of 10 mm×10 mm. The laminates were then subjected to a standard crumple test, an IGT crumpling tester being used 1, 4 or 8 times. The multiple layer laminates withstood these tests substantially unchanged, and no delamination was observed, even in the region of the windows. Moreover, the windows remained transparent.
Example 9 was repeated, paper C containing a watermark this time while paper D had no watermark. The multiple layer laminate thus produced showed the watermark in paper C in surprising clarity and detectability. Surprisingly, the watermark appeared more sharply in the multiple layer laminate than was produced in paper C in the unlaminated state. This was particularly true on viewing in reflected light.
Example 9 was repeated. In this test, the multiple layer laminate was subjected to a hot washing machine test, this test being carried out at a temperature of 95° C. for a time of 1 hour in 4 l of water, and 50 ml of a standard detergent (Omo) being added to this water. The multiple layer laminate withstood this test substantially unchanged, and no delamination was observed, even in the region of the window. The window withstood the test without becoming opaque.
Aqueous dye solutions having a concentration of 0.25 mg/g of Congo Red (Aldrich Chemicals Co., Milwaukee) and Chicago Sky Blue (Sigma Chemical Co., St. Louis) were prepared by dissolving in each case 12.5 mg of the dye in 50 ml of distilled water. 10 g of polyvinyl alcohol (PVA, 98-99% hydrolyzed, weight average molecular weight of 105 g/mol, Aldrich Chemicals Co., Milwaukee) were stirred for 2 h in 490 ml of boiling distilled water, a 2% w/w PVA solution being obtained. The solution was then allowed to cool to room temperature. Three PVA/dye blend films were produced by mixing a certain amount of corresponding dye solution with 10 g of the 2% w/w PVA solution, and the water was evaporated in a solution casting process in Petri dishes having a diameter of 9 cm at room temperature.
The films thus produced had the following compositions:
The dried PVA/dye blend films were cut into 2 cm wide strips and then uniaxially oriented on a hot shoe (Wagner & Munz, model WME) with a stretching ratio (ratio of the length after orientation to the length before orientation) of 6 at a temperature of 200° C. The polarizing filters obtained had dichroic ratios of more than 50 (determined at the absorption maxima in the spectrum) and had a thickness of, typically, 15 μm.
Multiple layer laminates having a size of 80 mm×150 mm and consisting of paper C and D, Grivory® G21 film having a thickness of 30 μm were produced using the dichroic filters described above (cf.
The stack was laminated at a temperature of 120° C. during a time of 1 min and at a pressure of 0.5 MPa. Thus, a multiple layer laminate having three windows #1, #2 and #3 which all had a lavender gray color was obtained. When window #3 is viewed through the window #1 (by folding the multiple layer laminate along the line #a), the window #3 has a blue color. In contrast, a red coloration of window #3 is observed when window #3 is viewed through window #2 (by folding the multiple layer laminate along the line #b). Thus, a self-verifying object can be produced in a simple manner.
An object according to
If the object is now folded so that the points a and c are placed on the points b and d, respectively, the cross and the number appear nontransparent and light gray. If, on the other hand, point a is folded onto point d, a black window appears as a result of the crossed polarization directions. The same applies to a folding of point c onto point b.
Example 6 was repeated, but paper E was used on both sides of the various polymer films instead of the papers C and D. In this case too, excellent multiple layer laminates were obtained, which shows that such multiple layer laminates are obtainable using different papers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 301/03 | Feb 2003 | CH | national |
| 963/03 | May 2003 | CH | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CH03/00850 | 12/30/2003 | WO | 2/21/2006 |
