The present invention relates to a method for producing a security paper or board product or a security package carrying micro or nano structures such as diffractive optical elements for providing information for authentication. The present inven- tion also relates to a security package containing authentication information in a form of diffractive structures.

Diffractive optical elements are optical components, which contain structures with dimensions of the order of wavelength of light. With diffractive optical elements it is possible to control propagation of light by macroscopically smooth surfaces containing micro or nano structures. These structures are later referred as diffrac- tive structures. A simple example of a diffractive optical component is a one- dimensional diffraction grating consisting of periodic grooves of the order of wavelength. When white light beam is passed through or reflected from a diffrac- tion grating it is dispersed in a spectrum."Diffractive Optics for Industrial and Commercial Applications" (edited by Turunen and Wyrowski, Akademie Verlag 1997, ISBN 3-05-501733-1) discloses diffractive optics and components and their use and design. This source is later referred as"Diffractive Optics".

It is known from prior art to use diffractive structures as well as other optical se- curity elements as watermarks in valuable documents and products for authenti- cation purpose. Diffractive optical security elements are typically embossed on thin foils and applied on articles to be marked as separate adhesives. Optical secu- rity objects can include various elements observable by various methods. Ac- cording to"Diffractive Optics"these observation methods can be divided into first-line, second-line, and third-line inspection levels. First-line inspection is based on the human senses only for instance vision, hearing and the tactile senses.

General public who must be able to distinguish counterfeit and forgery mainly

uses first-line inspection that can be performed by bare eye. In second-line in- spection simple tools are used to reveal hidden security objects. Examples of these tools are magnifiers, barcode scanners, laser pointers, ultraviolet sources and automatic teller machines. Third-line inspection involves forensic investigation of the security element performed by experts using advanced techniques and equip- ment. This kind of equipment is very expensive and is available only in few re- search institutes in the world.

Manufacturing of diffractive structures requires advanced and complex systems, which only are available in advanced laboratories. Therefore diffractive structures are very difficult to forge.

According to"Diffractive Optics"advantages for using diffractive structures as security elements are firstly, that they can not be reproduced with colour copiers or modern desktop publishing equipment. Secondly, production of diffractive structures is quite involved and it requires special equipment and knowledge.

Thirdly, the optically variable effects are generally quite noticeable and therefore they adequately facilitate first line inspection.

Diffractive structures are usually manufactured by microlithographic methods. US 4, 662, 653 discloses an optically diffracting security element comprising a con- tinuous reflecting surface, a dielectric layer formed contiguous with the reflecting surface, and a plurality of non-continuous reflecting surface portions embedded in the dielectric layer in a predetermined arrangement for storing authentication in- formation and a process for forming such element.

US 5, 862, 750 discloses a method for impression microengravings, which repro- duce holograms, kinetic holograms or diffraction patterns, directly on paper through an embossing process. In this method paper is subjected to a pre- treatment step prior to embossing said microengravings to paper. The required pre-treatment is a humidification step, which gives to a paper a degree of humidity

between 60 % and 80 % of relative humidity. The humidified paper is then passed through an embossing group at a certain temperature and pressure. According to said publication it is not possible to impress microengravings directly on untreated paper.

US 5, 871, 615 discloses security paper carrying a surface profile pattern imparted to the paper during its manufacture which requires de-watering of the paper when imparting the profile pattern and drying thereafter. The tactile surface profile pat- tern is visible when viewed under low angle light, which facilitates verification or authentication of security documents made using the patterned paper.

US 5, 981, 040 discloses a holographic image produced of resinous ink comprising metallic particles. This special ink is used for printing to a sensitive document to form a reflective coating, which is embossed by a slum. The embossed area of the reflective coating reflects light in a slight different direction than the remainder of the reflective coating, thereby creating a holographic image.

US 5, 974, 150 discloses an authentication system comprising a medium having a plurality of elements, which are distinctive, detectable and disposed in an irregular pattern or having an intrinsic irregularity. The system provides authentication of an object by providing at least two levels of security, which are a physical level, provided by an observable feature an authentication certificate, and an information level, provided by encoding a unique characteristic of the authentication certifi- cate (such as the observable feature) and/or object to be authenticated in a mark- ing on the certificate.

US 5, 961, 152 discloses security paper which has a filament bonded and embedded into paper which has been previously manufactured. The filament is bonded to the paper by an adhesive, or by heat and pressure. The filament may include a combi- nation of security features, such as reflective filaments, fluorescent filaments, and high tensile strength filaments.

The problems with the prior art security objects are that they are expensive to manufacture, difficult or expensive to integrate on paper and easy to counterfeit if they are applicable as separate adhesive labels. Same applies to laminated package materials containing diffractive foil layers.

The object of the present invention is to provide a security package material and package that is inexpensive and fast to manufacture in amounts.

A further object of the present invention is to provide a method for embossing security elements directly into security package material.

A further object of the present invention is to provide a method for manufacturing security package material using existing machinery equipped with means for inte- grating diffractive structures into package material.

A further object of the present invention is to provide a method for printing secu- rity markings directly on the packaging material by using ink, dye, or other suit- able colored or colorless painting liquids containing diffractive structures.

A further object of the present invention is to provide a manufacturing method for a packaging material containing diffractive structures by using size or paste con- taining diffractive structures in the manufacturing process of paper or board.

A further object of the present invention is to provide a manufacturing method for a packaging material containing diffractive structures by using furnish containing diffractive structures in the manufacturing process of paper or board.

In view of achieving of the objectives stated above and those that will come out later the method for producing a security paper or board product carrying micro or nano structures is mainly characterised in that the diffractive structures comprise

at least a section that is detectable only by inspection tools and the diffractive structures are integrated into the security paper or board product at the manufac- turing process of said product.

A method for producing a security package carrying micro or nano structures such as diffractive optical elements is characterised in that the diffractive structures comprise at least a section that is detectable only by inspection tools and the dif- fractive structures are integrated into the security package at a manufacturing stage of the security package material.

Security package containing authentication information in a form of diffractive structures is characterised in that the diffractive structures comprise at least a sec- tion that is detectable only by inspection tools and the diffractive structures are included in the security package at least in one of the following forms: as em- bossed in the package material, as part of the size or paste or resin used in the manufacturing process of the security package, or as part of the ink used in print- ing the security package or the security package material.

In prior art it is known to transfer diffractive structures to paper when remoistur- ing the paper first. According to the tests by the applicant it has been found out that it is possible to emboss a diffractive structure directly on paper without any additional preparing stages which would require expensive stages to the paper making process. This embossing process can be integrated to several different parts of papermaking, finishing, converting, or printing process.

According to the invention diffractive structures used as security elements are included in the package itself by inserting the elements to the package material in the manufacturing stage. No further stages for adding security information is needed. The security elements can be embossed onto the surface of the package material or they can be integrated as small pieces in paste, size, resin, or furnish of

the paper or board or package material. Diffractive security elements can also be mixed into the ink, dye, or painting liquids used in printing the package.

The advantage of the present invention is the possibility to manufacture security packages with low cost and with high security level. This way forging the package is very difficult and various types of security marks and security levels are easily available. The security information can be included in any part of the package and it can be in visible form or in hidden form. Very large amount of information pos- sible to include in a package when the method of the invention is applied.

Because of the relatively low cost of producing the security packages according to the invention the present invention can be utilized in package industry manufac- turing packages for consumer products liable to forgery, e. g. music CD's, com- puter products, medicines, cigarettes, or generally any brand products.

In a preferred embodiment of the invention a package bearing diffractive struc- tures with all security inspection levels is produced.

In the following the invention will be described in detail with reference of the figures in the accompanying drawing, the invention being however by no means strictly confined to the details of said embodiments or variations.

Figure 1 shows an example of diffractive security structures.

Figure 2 is a side view of a paper machine.

Figure 3 is a schematic illustration of a calender nip for a paper machine.

Figure 4 is a schematic illustration of a Condebelt drying system of a paper ma- chine.

Figure 5 is a schematic illustration of a surface-sizing/pigmenting unit.

Figure 6 is a schematic illustration of an extrusion coating line.

In embossing security elements to the package material in the papermaking proc- ess an embossing surface containing plurality of diffractive structure shims is needed. A diffractive structure shim is a means for embossing the diffractive structures to the desired material, such as paper or board or package material web.

The diffractive structure shims are preferably arranged in a suitably distributed matrix in the embossing surface, which is e. g. a roll in the paper machine or printing unit as described later. For the shim matrix a desired diffractive structure is first originated with an electron beam, a laser beam, an X-ray beam, an ion beam, or other lithographic method to a suitable substrate coated with a proper resist. Thus a microscopic surface relief profile is formed in the resist layer.

Thereafter the said surface is transformed into a negative surface profile in nickel by electroplating. The result is used to generate second and third generation shims for mass production. The process of manufacturing shims is disclosed in detail in "Diffractive Optics". Third generation shims are then used in producing package material integrated with the desired diffractive structures.

The method of embossing diffractive structures in security material is applicable to various kinds of paper, board, or package material grades suitable for printing and packaging. Examples of these are common paper (e. g. newsprint, SC paper, coated mechanical paper, uncoated fine paper, coated fine paper), paperboard (e. g. cartonboards, containerboards, special boards), specialty papers (e. g. cable paper, capacitor tissue, conductive paper, decor paper, photographic paper, building pa- pers, sack kraft, flexible packaging, label paper). See"Paper and Board Grades", part 18 in Papermaking Science and Technology series, ISBN 952-5216-18-7, for detailed information of these grades.

Fig. 1 shows an example of a diffractive security structure divided into different security level elements. In this example the diffractive security structure contains areas for various security inspection levels. In area A there is a figure that can be identified with bare eye i. e. with first line inspection. Area A comprises two secu- rity objects Al, A2. Object Al is a simple wave pattern embossed in the paper and it can be seen by bare eye. Object A2 contains text seen by bare eye at certain view angle when illuminated suitably. Text in object A2 may also contain micro or nano structure information readable only with a second or third level inspection tools.

In area B there is information that can be read with a second-line inspection tool, such as a laser pointer. Area B comprises micro or nano dimensional security structures embossed in the material. A laser pointer LP is used for directing a laser beam to point x in area B. Laser beam light diffracts from the security structure in point x and reveals a security structure B 1.

Area C comprises micro or nano structures, which are only readable by third level inspection, tools i. e. state-of-the-art equipment in research laboratories. An exam- ple of a security object Cl revealed by such an inspection tool is shown. Object Cl is a micro scale bar code, which identifies the security, marked object. Alter- natively, diffractive structures containing second and third line inspection levels can be hidden in various forms within the area covered by the area of the first line inspection level structures.

In the method according to the invention for producing security paper or board or security packages diffractive structures are embossed to the package paper or cardboard as described above. In another embodiment of the present invention diffractive structures are included in the paper or board product or in the security package material as small pieces containing diffractive structures. In this method diffractive structures are embossed in thin sheets of a suitable material, such as aluminium or plastic foil. By grinding, cutting, crushing, or chopping embossed

sheet to small pieces, chopped material with pieces containing diffractive struc- tures is produced and this material can be mixed to a raw material used in paper making or printing process. The chopped material can be mixed for instance to ink, size, paste, resin, or furnish.

When using furnish mixed with pieces containing diffractive structures conven- tional paper and board making machinery can be applied. Using this approach in paper making process the produced paper or cardboard gets a glittering appear- ance, which is typical for diffracting surfaces. Similarly well known sizing and coating methods can be used when mixing pieces containing diffractive structures into size or paste. Also chopped material containing diffractive structures can be added to ink which is then useable in any conventional printing system.

Suitable dimensions for chopped material with pieces containing diffractive structures is of the order of 1 to 10 pm in ink, size, paste and resin and up to 1 mm in furnish. Information contained in the diffractive elements can be read from se- curity paper or board or package according to the invention using special reading device. When using ink containing diffractive structures in printing of the security packages the text or pattern printed with diffractive ink contains information of the diffractive elements and also this information is readable with special reading equipment.

The method of embossing or printing the diffractive structures directly on paper can be carried out e. g. in the following parts of the papermaking or package manufacturing process: -on-or off machine calender unit -drying unit marketed by the applicant by the name Condebelt -impulse drying unit -flexographic, gravure, offset, or other commercially available printing systems -extrusion coating lines

The method of adding chopped material containing diffractive structures is appli- cable in the following parts of the papermaking or package manufacturing proc- ess: -stock preparation unit -sizing unit -coating unit -flexographic, gravure, offset, or other commercially available printing systems -extrusion coating lines -flexible package material lines Fig. 2 shows a side view of a modern paper or board machine. As shown in Fig. 2, stock is fed from a headbox 100 to a wire section 200 followed by a press section 300. The web W is passed from the press section 300 to a dryer section 400 followed by a soft-calendering unit 500. The film-sizing unit 600 is used for treating the web.

Surface-sizing, pigmenting, or coating is performed at this stage typically on both sides of the web at the same time, but the surfaces of the web can also be treated separately in successive units. After that, the paper web is dried by using infrared dryers and airborne web-dryers and a short cylinder group, which follows them.

The web W is coated in coating stations 700,800 which coat the web W on both sides. After that, the web W is calendered in a multi-nip calender 900, in which the linear load in each nip can be advantageously regulated separately. Finally, the web W is passed to a reel-up 1000 in which the web is wound into reels.

Fig. 3 shows an example of applying the method of embossing diffractive structures to paper in a calender. In the calender an extended calendering nip N is formed be- tween an upper roll 550 and a shoe roll 551. The shoe roll 551 comprises a press shoe 524 supported by a stationary beam 525 as well as a calendering belt 520 passed around the press shoe 524 and the beam 525 and formed as an endless loop.

By means of the press shoe 524, the necessary load is produced in the nip N. Ac- cording to the invention the upper roll 550 is coated with the diffractive structure

shims and the diffractive structures are transferred to the paper or cardboard web W passing the nip N. In another embodiment the calendering belt 520 is coated with diffractive structure slums. Although a shoe calender has been described above the present invention can as well be applied into the prior art hard roll cal- enders, soft calenders and supercalenders either on-or off-machine.

Fig. 4 shows a side view of a Condebelt drying system. Condebelt drying system is known e. g. from patent publications FI-54514, FI-61537, and FI-101237. The Condebelt drying system is typically used in cardboard machines. In the Conde- belt drying system the web W carried on a fine-structured wire 43 and a coarse wire 44 is fed through a drying unit 48,49 between two smooth steel belts 41,42.

The upper steel belt 41 contacting the web W is heated while the lower steel belt 42 is cooled. Subject to high pressure and temperature difference the moisture in the web W evaporates and the generated vapour traverses the wires 43,44 to con- dense on the cooler steel belt or the lower belt 42. The condensed water is taken out from the drying zone. This way dried web has very advantageous strength characteristics combined with absence of CD shrinkage. A smooth surface is ob- tained on one side of the web. The method according to the invention of emboss- ing the diffractive structures directly on paper or cardboard is applicable in the Condebelt drying system by providing the heated metal belt wire with the diffrac- tive structure shims.

In an impulse drying process, the web carried on the felt is fed through a pressing nip. The roll contacting the web is heated to temperatures well above 100 °C. In this known process, a very smooth web surface can be obtained. According to one embodiment of the invention, the heated roll is provided with the diffractive structure shims to transfer the diffractive marking directly onto the web surface.

Impulse drying process is disclosed e. g. in US 4,324,613.

Fig. 5 is a schematic illustration of an example of a surface-sizing/pigmenting unit 600, which is used for sizing and coating paper. Surface-sizing/pigrnenting sys-

tems are disclosed e. g. in FI-93885 and FI-81734. The surface-sizing/pigmenting unit 600 comprises rolls 602 and 603 of the size press, so that the first roll 602 and the second roll 603 form a nip N with one another, through which nip the paper or board web W is passed. In the surface-sizing/pigmenting unit 600, a first size film Fi is metered onto the face of the first roll by means of the first coating device 610 and, in a corresponding way, a second size film F2 is metered onto the face 605 of the second roll by means of the second coating device 620. In the roll nip N, the size films Fi and F2 are transferred to the paper or board web W running through the nip.

The coated web is denoted with the reference W'. The size films Fi and F2 are spread onto the faces 604 and 605 of the size press rolls 602,603 using bar coaters, which are equal to one another in this example of a surface-sizing/pigmenting unit 600. In the coating devices 610,620 the coating agent is introduced into a pressurized coat- in-agent chamber 616,626 placed before the coating bar 611,621. The coating bar 611,621 is fitted in a cradle 612,622 supporting the coating bar 611,621 over its entire length and is rotated in directions opposite to the directions of rotation of the rolls 602,603. According to the invention chopped material containing diffractive structures is added to size or paste which is then transferred to the web in the sur- face-sizing/pigmenting unit 600.

Extrusion is a process that transfers thermoplastics from a solid to a melted state and compresses them against a substrate using the pressure in a die. Figure 6 shows an example of an extrusion coating line 1200. A web (paper, aluminium or film) W is unwound from a main unwinder 1210. The pre-treatment unit 1220 is used for pre-treating the web W in a way depending on the material e. g. in order to increase the adhesion. In the extrusion coating unit 1230 a melted resin (LDPE, PP, or other) is extruded on the web W with the extruder 1231. The resin is melted in the extruder 1231 and through a flat die it is extruded on the web and immedi- ately cooled. The extrusion coating unit 1230 comprises a chill roll 1232 with chromium plated surface, a pressure roller 1233 with a rubber surface, and a back- up roller 1234 with chromium plated surface.

In the nip between the pressure roller 1233 and the chill roll 1232 the extruded resin comes in contact with the web. The purpose of the chill roll 1232 is to re- duce the temperature of the resin (normally extruded at temperature ranging from 250°C to 300°C) to a value below the melting point in order to prevent the stick- ing on the chill roll surface 1232.

As alternative it is possible to laminate two different webs in the extrusion coating unit 1230 using the resin as adhesive. In this case the second web is coming from the secondary unwinder 1240. It is possible to use more than one extruder if the product structure requires different layers. Ill this case the resins extruded from the extruders are collected to the die through a feedblock. The purpose of the feedblock is to collect the materials from the extruders maintaining the different layers. The coated or laminated material obtained with this process is rewound on the rewinder 1290. A thickness gauge 1250 is normally placed before the re- winder 1290 to measure thickness variation of the final product to be rewound. An automatic control system can be used to manage the extrusion die in order to con- trol the thickness of the extruded material.

The method according to the invention is applicable in an extrusion line prefera- bly in the nip between the pressure roller 1233 and the chill roll 1232. Either of the pressure roller 1233 or the chill roll 1232 is provided with diffractive structure shims according to the invention. Alternatively, chopped material containing dif- fractive structures is mixed with the extrusion coating resin.

The method according to the invention is also applicable in the printing process of the security paper, board, or package. The printing process can be carried out in flexographic, gravure, offset, or other commercially available printing systems. A printing machine is optionally provided with an embossing unit, which is prefera- bly placed in the printing line after the last printing unit. According to the present invention said embossing unit is provided with the diffractive structure shims to transfer the diffractive marking directly onto the web surface in the printing line.

In another embodiment of the present invention chopped material containing dif- fractive structures is added to ink and then transferred to the printed material.

Alternatively, the method of embossing diffractive structures directly on paper or board or package material according to the invention is applicable to sheet mate- rial also. Sheets of paper, board, or package material can be embossed by stamp- ing with a stamping device. A stamping device can be installed e. g. in connection with a sheet cutter in paperiboard machine, printing machine, or such.

Laser pointers are preferable tools for inspecting the authenticity of the security paper or board products or security packages according to the invention. Laser pointers are relatively inexpensive and easy to carry along so they are available to public. When pointing a security marking according to the invention with a laser beam special effects not seen with bare eye are revealed. These can be e. g. a com- pany or brand logo appearing at or coming out from the security marking.

The method according to the invention can be fully integrated to the existing pa- per and cardboard machines and coating and printing lines. No auxiliary systems need to be built. hi addition of using the method according to the invention for producing security marked material for authentication purpose the same method is applicable for decorative use.

In the following the patent claims will be given and various details of the inven- tion may show variation within the scope of the inventive idea defined in the pat- ent claims and differ from the details disclosed above for the sake of example only.