Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/16—Sizing or water-repelling agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/20—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof characterised by a particular use or purpose
  • B42D25/29—Securities; Bank notes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
  • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
  • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
  • B42D25/40—Manufacture
  • B42D25/45—Associating two or more layers
  • B42D25/465—Associating two or more layers using chemicals or adhesives
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/71—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes
  • D21H17/72—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes of organic material
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/40—Agents facilitating proof of genuineness or preventing fraudulent alteration, e.g. for security paper

Definitions

• the invention relates to a surface sizing agent for a security paper, a method for surface sizing a security paper substrate material, a method for further processing the security paper substrate material into a security paper or a value document, as well as security paper substrate materials, security papers and value documents which have a surface sizing with the surface sizing agent.
• the value documents are in particular banknotes.
• mass sizing and surface sizing When sizing paper, a distinction is made between mass sizing and surface sizing. While mass sizing agents are added to the fiber mass before the sheet is formed, surface sizing agents are applied to the paper surface after the paper has been produced using suitable application devices such as size presses, doctor blades or spray devices. The surface sizing partially penetrates the paper and also forms a film on the paper surface. Surface sizing reduces the paper's tendency to produce dust, which is mainly caused by fillers, increases the paper's hydrophobicity in order to limit its absorbency and make it easier to write on or print with aqueous or solvent-based inks, and increases the surface strength of the paper and thus its resistance to picking and erasing. Surface sizing also improves the flatness of the paper, which is important for further machine processing, since crooked or curved sheets cannot be processed by machine. Unlike coating colors, surface sizing agents do not contain pigments.
• Valuable documents within the meaning of the present invention are in particular means of payment such as banknotes, but also all other documents for which forgery security plays a role, such as passports and other identification documents, admission tickets, travel tickets, or credit cards.
• Some security papers contain security features and/or security elements that are contained in the fabric, i.e. the security paper substrate material, and are therefore already in the paper before surface sizing.
• security features and security elements are, for example, watermarks and window security threads. These must not be damaged or impaired in their visibility by the surface sizing agent.
• security features and/or security elements must be applied to surfaces of the security paper substrate material, e.g. printed or glued on.
• security elements are glued on with a layer structure with numerous functional layers and auxiliary layers, for example with a holographic security feature, print acceptance, protective and laminating layers, color layers, fluorescent prints, etc.
• the security elements can also have a carrier film in their layer structure. These so-called patches are preferably used on security paper substrate materials with continuous openings to cover the opening. Other embodiments do not have a carrier film and are typically adhered to the security paper substrate material in an area that does not have an opening. The bonding is typically done by heat sealing.
• the security elements can be glued directly onto the glued substrate material, i.e. without prior application of primer.
• the glued substrate material should also retain its bonding ability for as long as possible, since security paper substrate materials are often not processed immediately after surface gluing, but rather numerous rolls of security paper substrate material are first produced and stored, and only at a later point in time are the security elements glued on or the security paper substrate material printed on. The same applies to prints as to security elements to be glued on.
• the security paper substrate material should preferably be easy to print on without pre-treatment and even after storage for a few months, for example.
• the required good and durable bonding ability of the surface-sized security paper substrate material is difficult to reconcile with another important property of security papers, namely a low tendency to soiling.
• Valuable documents such as banknotes are exposed to a wide range of contamination during their circulation, such as solid, liquid, hydrophilic or hydrophobic dirt. They are also subjected to strong mechanical stress, for example they are frequently folded or crumpled, or forgotten in pockets of items of clothing that are to be washed and accidentally washed along with them. In tropical areas, banknotes are permanently exposed to moisture and high temperatures, while in other areas they are exposed to very low temperatures.
• An optimal surface sizing for security paper should be able to withstand all of these stresses without losing the adhesive strength of the prints and applied security elements.
• the surface sizing must of course not change the haptic properties and sound of the special paper, especially in the case of banknotes.
• sizing agents based on different materials are known from the state of the art. Most surface sizing agents contain polymeric compounds, as these seal the pores of paper substrate materials very well.
• DE 40 40 347 C2 A process is known for sizing paper based on cotton or linen or on other plant fibers using a sizing agent that contains a low-viscosity polyvinyl alcohol. Carboxymethylcellulose, starch or alginates can also be added to the sizing agent.
• a disadvantage of sizing agents that are essentially based on polyvinyl alcohol is their ability to enclose fiber materials. The fiber materials are therefore no longer easily accessible to the printing ink in a subsequent coloring process, for example in a printing process.
• the printing ink can no longer be sufficiently anchored to the fiber materials and the color fastness of the printed paper, such as its washability in particular, but also its wet creasing properties, are impaired.
• the colors can come off even under conditions of use such as high humidity or rain. Even the added alginates, starch and carboxymethylcellulose cannot completely overcome these disadvantages.
• an anionic surface sizing agent for paper in the form of an aqueous colloidal solution of a salt of a copolymer consisting of (meth)acrylic acid, (meth)acrylic acid ester of a C10 to C22 fatty alcohol, styrene, N,N-dimethylaminoethyl acrylate or methacrylate, methyl (meth)acrylate and isobutyl (meth)acrylate. Due to the high proportion of acrylic acid-based monomers, this surface sizing agent forms a good surface film on paper. However, the porosity of paper sized with this surface sizing agent is not sufficiently reduced. As a result, the paper does not achieve sufficiently high strengths, nor are fillers contained in the paper effectively prevented from detaching, known as dusting.
• WO 2019/170287 A1 discloses a surface sizing agent for a paper product comprising at least one polyvinyl alcohol, a dispersion comprising at least one acrylic acid-based polymer and/or at least one acrylic acid-based copolymer, at least one crosslinking agent for the acrylic acid-based polymer and/or the acrylic acid-based copolymer, and at least one solvent.
• This surface sizing agent represents an improvement over the aforementioned sizing agents, but a security paper substrate material sized with the surface sizing agent cannot be bonded to a security element without using a primer. The surface sizing agent does not impart sufficient bonding ability to the security paper substrate material.
• the object of the present invention is to avoid the disadvantages of the prior art and to provide a surface sizing agent optimized for use in security papers.
• the surface sizing agent must be compatible with all materials and techniques used in the production of security papers and valuable documents and must not change the feel and sound of the paper.
• the surface sizing agent should also be as cost-effective as possible.
• a further object of the present invention is to provide value documents with a high circulation stability.
• the surface sizing agent the method for surface sizing a security paper substrate material, the method for producing a security paper or a value document, the security paper substrate material, the security paper and the value document, each with the features as specified in the independent claims.
• Specific embodiments of the present invention are specified in the respective dependent claims.
• a surface sizing agent for a security paper which comprises a binder, a crosslinking agent and a dispersant, wherein the binder comprises a polyvinyl alcohol component and a polyurethane component, the crosslinking agent is a carbodiimide, and the dispersant consists of at least 95% by mass of water.
• the surface sizing agent, the method for surface sizing a security paper substrate material, the method for producing a security paper or a value document, the security paper substrate material, the security paper and the value document represent aspects of the same invention. Therefore, disclosure in connection with one aspect of the present invention applies equally to the remaining aspects of the present invention.
• Fiber paper Both fiber paper and polymer paper and hybrid paper are used as security paper for producing valuable documents.
• Fiber paper as the name suggests, consists of fibers, preferably exclusively of plant fibers. Cotton fibers are particularly preferred for the production of security paper.
• fiber papers can also contain a certain proportion of plastic fibers or even consist entirely of plastic fibers. Suitable plastics are, for example, polyethylene terephthalate, polypropylene and polyethylene.
• Polymer "papers" consist of polymer materials, i.e. they are plastic films, for example made of polyethylene terephthalate, biaxially stretched polypropylene or polyethylene.
• Hybrid papers are fiber papers that have a plastic film on one or both surfaces, as is also used for polymer papers, as well as plastic films that have fiber papers on one or both surfaces.
• fiber papers made from plant fibers Natural fiber substrate materials
• fiber papers made from synthetic fibers synthetic fiber substrate materials
• fiber papers made from a mixture of natural fibers and synthetic fibers mixed fiber substrate materials
• hybrid papers with a film/fiber substrate and fiber substrate/film/fiber substrate structure hybrid substrate materials
• surface sizing is only carried out on the surface of the fiber substrate, while in the case of the other substrate materials, both surfaces are preferably surface-sized.
• a surface sizing agent is understood to mean a composition that essentially has no color-imparting properties, since it is at least largely free of pigments and/or fillers, as are usual for coating colors for paper.
• the surface sizing agent according to the invention preferably contains no pigments and/or fillers. Due to their high proportion of pigments and fillers, coating colors are not able to penetrate the capillaries of a paper to any significant extent, anchor themselves in the pores of the paper and at the same time improve the printability of the paper.
• the surface sizing agent according to the invention is in the form of a dispersion, that is to say, at least some of the components of the surface sizing agent are dispersed in the dispersion agent. However, some of the components, namely at least the polyvinyl alcohol component, are dissolved therein.
• the invention is based on the finding that the properties of a surface sizing agent, which essentially contains polyvinyl alcohol as a binding agent, can be improved by adding polyurethanes.
• the low ageing resistance of surface sizing agents can be significantly improved by adding polyurethanes.
• This has the advantage that security elements can be glued onto the glued surfaces of prefabricated security paper substrate materials even after a long storage period, and without the use of a primer, which makes the production of the security papers significantly more convenient and comfortable. It also has the advantage that the risk of the security elements becoming detached during the circulation period of a security document due to signs of ageing of the surface sizing is significantly reduced.
• polyvinyl alcohol surface sizing agents are in no way impaired by the addition of polyurethanes, but are partially improved. slightly improved. Polyurethanes are generally more expensive than polyvinyl alcohols, but this price disadvantage is hardly significant, since it has been shown that the advantages of polyurethanes are already apparent when the proportion of polyurethanes in the binder is relatively low.
• the surface sizing agent according to the invention can be prepared from commercially available products.
• the binder contains at least two components, a polyvinyl alcohol component and a polyurethane component.
• the polyvinyl alcohol component consists of a polyvinyl alcohol or a mixture of polyvinyl alcohols, i.e. the polyvinyl alcohol component can contain several polyvinyl alcohols which can differ in their chemical structure, for example in their degree of polymerization, or in one or more physical properties, for example in their viscosity or their solubility properties.
• polyvinyl alcohol or polyvinyl alcohols is essentially not limited. Suitable products include Poval 28-99, Poval 23-88, Poval 26-88, Poval 32-28, Poval 40-28, Poval 47-88 and Poval 23-95 from Kuraray, Japan.
• the polyvinyl alcohol component should preferably dissolve well in the dispersant used, which consists essentially of water. Dissolved components of the surface sizing agent are better able to penetrate into capillaries and pores of the paper substrate material, fill them and close them. This results in a more or less closed surface of the paper substrate material, which reduces the tendency of the paper substrate material to dust and increases its strength.
• Polyvinyl alcohols that are readily soluble in water have a high degree of saponification. Polyvinyl alcohols with a degree of saponification of at least 97 mol% are preferred, and higher degrees of saponification such as at least 98 mol% or at least 99 mol% are more preferred. It is particularly preferred to use fully saponified polyvinyl alcohols. But of course partially saponified polyvinyl alcohols can also be used if they dissolve to the desired extent.
• a further improvement in the capillary and pore-closing properties of the surface sizing agent can be achieved by a particularly suitable viscosity of the polyvinyl alcohol.
• a particularly suitable viscosity is present when a 4% aqueous solution of the polyvinyl alcohol component at 20°C has a viscosity, measured according to DIN 53015 2001:2, in a range from 5 to 35 mPa•s, preferably from 9 to 30 mPa•s.
• the proportion of the polyvinyl alcohol component in the total mass of the surface sizing agent is preferably 2.0 to 5.0 mass%, particularly preferably 2.5 to 3.5 mass%. In this range, an advantageous combination of surface sizing properties (good penetration into the paper substrate material, improvement in printability and the strength and performance properties of the sized paper substrate material), processing properties and storage stability of the surface sizing agent is achieved.
• the polyurethane component of the surface sizing agent according to the invention consists of at least one polyurethane homopolymer or at least one polyurethane-acrylate copolymer or of a mixture of at least one polyurethane homopolymer and at least one polyurethane-acrylate copolymer.
• the binder can also contain a polyacrylate or a mixture of polyacrylates. Other polymers are preferably not contained in the binder.
• the polyacrylate or the mixture of polyacrylates can replace some of the polyurethane components and thus reduce the costs of the surface sizing agent without impairing the positive properties of the surface sizing agent achieved by the polyurethane component.
• Polyurethane homopolymers are polyurethane polymers that consist exclusively of polyurethane units. In contrast, copolymers consist of at least two different types of polymers.
• the polyurethane component can contain polyurethane homopolymers and mixtures of polyurethane homopolymers. These can be homologous mixtures, i.e. homopolymers with only different molecular weights, as well as mixtures of chemically different homopolymers, i.e. mixtures of homopolymers each consisting of different monomers.
• polyacrylates can be polyacrylate homopolymers and mixtures of polyacrylate homopolymers.
• the mixtures can be homologous mixtures and/or mixtures of chemically different homopolymers.
• polyurethane-acrylate copolymers Like homopolymers, the components of the copolymers can be homologous or chemically different.
• the polyurethanes or the polyurethane units of the polyurethane-acrylate copolymers are preferably polyether polyurethanes and/or polyester polyurethanes and/or polyether polyester polyurethanes.
• Polyesters can be both organic and inorganic polyesters, i.e. the polyester polyurethanes or polyether polyester polyurethanes can be polycarbonate polyurethanes or polyether polycarbonate polyurethanes.
• Polyether polyurethanes are particularly preferred.
• the polyurethane polymers are preferably linear, i.e. made up of bifunctional subunits. This is primarily due to the fact that the surface sizing agent according to the invention is an aqueous dispersion.
• Aqueous dispersions are preferable to solutions in organic solvents for environmental reasons, and they also have application-related advantages. They are easy to handle and even at very high molecular weights, the viscosity is only determined by the particle size of the dispersed polymer and by its volume fraction in the dispersion. However, when producing the desired high molecular weights, branched polymers tend to form gels. Minor branching is generally not a problem.
• polyurethane dispersions typically have a solids content of 30 to 50% by mass, although polyurethane contents of up to 60% by mass are also possible.
• the surface sizing agents according to the invention preferably contain pure water as a dispersant.
• Commercially available polyurethane dispersions can However, due to the manufacturing process, they also contain water-dilutable organic solvents, the proportion of which is normally less than 5% by mass.
• the surface sizing agent according to the invention can contain, in addition to the dispersant water, a certain proportion of one or more other dispersants and/or solvents, the proportion of the other dispersants and/or solvents not exceeding 5% by mass, based on the total mass of the dispersant.
• Aliphatic polyurethane homopolymers and polyurethane-acrylate copolymers with aliphatic polyurethane content are preferred over aromatic polyurethane homopolymers and polyurethane-acrylate copolymers with aromatic polyurethane content, since aromatic polyurethanes can yellow when exposed to light. Such a color change can be very disadvantageous for security papers.
• the polyurethane homopolymers contained in the surface sizing agent according to the invention are functionalized by incorporating carboxyl groups.
• the carboxyl groups can be introduced, for example, via chain extenders during the synthesis of the polyurethane homopolymers from their prepolymers.
• the carboxy functionality serves, on the one hand, to stabilize the polyurethane particles in the dispersed state, but above all the carboxyl groups enable the polyurethane homopolymers to be crosslinked to form a film using a suitable crosslinking agent.
• a suitable chain extender for introducing the carboxy functionality is, for example, dimethylolpropionic acid.
• Polyurethane-acrylate copolymers already contain carboxyl groups due to their acrylate units, which allow them to be cross-linked. It is possible, but not absolutely necessary, to incorporate additional carboxyl groups into the polyurethane units.
• Dispersions containing polyurethane homopolymers or polyurethane-acrylate copolymers or polyacrylates are commercially available. Suitable products include the NeoRez ® series (polyurethanes), the NeoPac ® series (polyurethane-acrylate copolymers) and the NeoCryl ® series (polyacrylates), all from Covestro.
• the polyurethane content of the surface sizing agent means that the properties of the sizing agent are determined by the polyurethane component rather than by the polyvinyl alcohol component.
• the binding properties and the aging resistance of the surface sizing are determined to a large extent by the polyurethane component of the binder. It is assumed, without wishing to be bound to theory, that the wetting properties of the surface sizing agent are improved by the polyurethane homopolymers and/or the polyurethane-acrylate copolymers, thereby enabling better penetration of the polymer chains.
• the crosslinking of the polyurethane homopolymers and/or the polyurethane-acrylate copolymers forms a network that includes the polyvinyl alcohol component, with the polyvinyl alcohol component being located more in the pores and capillaries of the security paper substrate material, while the polyurethane component, which, unlike polyvinyl alcohol, is not soluble in the dispersion medium, is located more on the surface of the security paper substrate material, but is anchored excellently to the surface by the network formation and entanglement with the polyvinyl alcohol polymers.
• polyacrylates allow cross-linking via their carboxyl groups.
• polyacrylates do not have the advantageous properties of polyurethanes in terms of improved bonding ability and, in particular, improved resistance to aging of the bonding ability. Therefore, only a limited proportion of the polyurethane component can be replaced by polyacrylates.
• the proportion of the polyurethane component in the surface sizing agent according to the invention is preferably 0.2 to 5.0% by mass, particularly preferably 0.2 to 2.0% by mass. It is also preferred that the proportion of polyurethane homopolymers in the polyurethane component is at least as high as the proportion of polyurethane-acrylate copolymers. Particularly preferably, at least 70% by mass of the polyurethane component consists of polyurethane homopolymers, and very particularly preferably the polyurethane component consists exclusively of polyurethane homopolymers.
• the polyacrylates preferably replace polyurethane-acrylate copolymers, i.e. the proportion of polyurethane homopolymers in the total of polyurethane component and polyacrylate component is at least 50% by mass.
• the mass ratio of polyvinyl alcohol component: polyurethane component or the mass ratio of polyvinyl alcohol component: polyurethane component + polyacrylate component can vary within a wide range and be approximately 95:5 to 5:95, preferably 80:20 to 20:80, particularly preferably 60:40 to 40:60, and in particular 50:50.
• a carbodiimide is used as a cross-linking agent.
• Carbodiimides react with the carboxyl groups built into the polyurethanes and thus cause stable cross-linking of the polyurethane component. They can react in the same way with the carboxyl groups of acrylates, so that they can advantageously cross-link both homopolymers and copolymers of the polyurethane component as well as polyacrylates, which may replace part of the polyurethane component.
• Carbodiimides are also readily available and can be easily dispersed in aqueous media. Highly reactive carbodiimides are available that can be used in small doses. The reaction is typically started by lowering the pH value to the slightly acidic range or by increasing the temperature. Instead of a polycarbodiimide, a mixture of different polycarbodiimides can of course also be used.
• the proportion of the carbodiimide crosslinking agent in the total mass of the surface sizing agent is preferably 0.02 to 0.5 mass%, particularly preferably 0.1 to 0.4 mass%.
• An advantageous mass ratio of polymer to be crosslinked: crosslinking agent is in the range of 20:1 to 5:1, preferably 13:1 to 8:1, particularly preferably 10:1. This achieves an optimal degree of crosslinking with good integration of the polyvinyl alcohol component.
• a suitable carbodiimide crosslinking agent is, for example, Desmodur 2802 from Covestro.
• the surface sizing agent according to the invention can contain, in addition to the above-mentioned components, usual sizing agents, such as defoamers, viscosity modifiers, thickeners, dispersing agents, flow agents, wetting agents and plasticizers.
• usual sizing agents such as defoamers, viscosity modifiers, thickeners, dispersing agents, flow agents, wetting agents and plasticizers.
• pigments, fillers and extenders are preferably not included.
• Polyurethane dispersions have a tendency to foam, which is why the surface sizing agent according to the invention preferably contains a defoamer in an amount of about 0.01 to 0.1% by mass, preferably 0.03 to 0.05% by mass, based on the total mass of the surface sizing agent.
• a defoamer is the mineral oil-free and silicone-free polyoxyalkylene defoamer Agitan 299 from Münzing.
• Plasticizers can be present in larger amounts, i.e. preferably in an amount of 1.0 to 5.0% by mass, particularly preferably in an amount of 2.0 to 4.0% by mass, based on the total mass of the surface sizing agent.
• Preferred plasticizers are neopentyl alcohol, trimethylolpropane, ethylene glycol, diethylene glycol, triethylene glycol and polyethylene glycol.
• the optional plasticizer serves to improve the elasticity of the polymer network formed and thus to reduce the tendency to crack. Smaller molecules that can be integrated into the polymer network or can be placed between the polymer chains are particularly suitable as plasticizers.
• the surface sizing of a security paper substrate material is carried out in accordance with the invention by bringing a surface sizing agent according to the invention into contact with one or both surfaces of the security paper substrate material and then drying the sized security paper substrate material and crosslinking the surface sizing agent, wherein the crosslinking process can be accelerated by heating.
• the application of the sizing agent can be carried out in a completely conventional manner, for example online in the paper machine in the dipping bath with subsequent size press, or by means of a size press in sump operation, or by means of a coating unit in the paper machine.
• the surface sizing agent can also be applied in a separate process (offline), for example in a coating machine.
• the surface sizing agent according to the invention is basically suitable for surface sizing of any paper, but is specially adapted to the requirements of security paper.
• the substrate materials to be glued in this area are natural fiber papers, in particular papers made of cotton fibers, synthetic fiber papers or mixed fiber papers.
• hybrid papers with a plastic film/fiber substrate structure or a fiber substrate/plastic film/fiber substrate structure can also be glued.
• the fiber substrates of the hybrid papers can in turn consist of natural fibers, synthetic fibers or mixed fibers.
• only the surface of the fiber substrate is glued with the surface sizing agent according to the invention.
• security paper substrate materials can have security features or security elements such as watermarks and window security threads incorporated into the fabric. These security features/security elements must not be damaged or impaired in their visibility by the surface sizing.
• the surface-sized security paper substrate material is further processed into security paper and finally into valuable documents.
• various prints and/or functional layers (layers with security features) and/or security elements are typically applied to the security paper substrate material. applied.
• adhesion-enhancing pretreatments are carried out or a primer layer is applied to conventional surface-glued security paper substrate materials.
• Some surface gluings can also be printed on without adhesion-enhancing pretreatment and/or have security elements stuck to them without prior application of a primer, provided this is done after the gluing process, i.e. without intermediate storage of the glued security paper substrate material.
• security paper substrate material webs are produced, these webs are rolled up onto rolls (tambours), and the rolls are stored until they are further processed.
• the security paper substrate material webs can also be cut into sheets and stored as stacked sheets. The storage time can be several months.
• a tambour with rolled up security paper substrate material or a stack of security paper substrate material sheets is delivered from the paper mill's warehouse to a security paper manufacturer.
• the security paper substrate material is provided with the security features required for a specific security document and then either immediately processed into security documents or stored again in a rolled-up or stacked state.
• individual panels in the form of the desired security documents, such as banknotes, are finally separated from the security paper webs or sheets.
• the surface-sized security paper substrate material can be stored without any problems for a period of several months until it is further processed into security paper and can then be printed on or stuck with security elements of any kind without any adhesion-improving pretreatment or primer application.
• the prints and the glued-on security elements adhere well and permanently to the surface-sized security paper substrate material according to the invention.
• Security paper substrate materials even under the adverse conditions to which, for example, a banknote may be exposed during its life in circulation.
• Known adhesives can be used to stick on the security elements, especially heat-sealing adhesives.
• Preferred adhesives are purely thermally activated heat-sealing adhesives, heat-sealing adhesives that already adhere at room temperature but can be thermally activated, and UV-crosslinkable and LED-crosslinkable heat-sealing adhesives.
• Security paper substrate materials made of cotton vellum with a basis weight of 86 g/m 2 were sized on an Einlehner size press at room temperature with four different surface sizing agents, dried for 10 minutes in a vacuum dryer and for 5 minutes at 120°C in a drying cabinet or allowed to crosslink the surface sizing agents, printed using the intaglio printing process and the steel printing process (color: SICPA blue 9 SL 4752) and then subjected to various paper tests.
• Three of the four surface sizing agents were surface sizing agents according to the invention, each containing a fully saponified polyvinyl alcohol (Poval 28/99 from Kuraray), an aliphatic polyester polyurethane (Liopur 2004-140 from Synthopol), a polyether polyurethane (DU 5055 F from Morchem), a carbodiimide crosslinking agent (Desmodur 2802 from Covestro) and the remainder water as a dispersant.
• a fully saponified polyvinyl alcohol Poval 28/99 from Kuraray
• an aliphatic polyester polyurethane Liopur 2004-140 from Synthopol
• DU 5055 F from Morchem
• carbodiimide crosslinking agent Desmodur 2802 from Covestro
• compositions are given in Table 1 below.
• the fourth surface sizing agent was a comparative sizing agent.
• the composition is given below, with the percentages indicating the solids content based on the total sizing agent mass.
• the comparative sizing agent contained 3 wt.% polyvinyl alcohol (Poval 28/99 from Kuraray), 1.2 wt.% polyamidoamine-epichlorohydrin crosslinker (Kycoat from Solenis) and the remainder water as a dispersant.
• Test pieces were cut from the security paper substrate materials of all examples and the comparative example, each of which had been surface-glued on both surfaces. The following paper tests were carried out on the test pieces:
• the test pieces were printed using the steel printing process and subjected to a reproducible crease, partly in a dry state and partly in a wet state.
• the crease process imitates the stress on a banknote in circulation.
• a test piece is rolled up, pushed into a sleeve and compressed using a stamp. The crumpled test piece is then removed, unrolled and smoothed out. This process is repeated eight times.
• test pieces are placed in distilled water for 15 minutes before the test and then couched with blotting paper. Four creasing processes are then carried out, the test piece is placed in distilled water again for 1 minute, couched and another four creasing processes are carried out.
• test pieces are soiled with a defined dirt mixture (mixture of solid and liquid hydrophilic and hydrophobic dirt) and then visually evaluated.
• the test simulates the circulation properties of banknotes.
• the test consists of placing a sample in a container, adding glass beads (7 mm diameter) and the dirt mixture, and moving the container back and forth for 20 minutes. The sample is then removed and cleaned as thoroughly as possible with paper towels.
• the brightness level L is then measured and compared with the brightness level L before contamination.
• test pieces are used that are not only surface-glued but also printed, partly using the steel printing process, partly using the offset printing process. The print is always directly on the surface glue.
• One test piece is put into a linen bag, fixed in place and washed in a washing machine with detergent. Some of the test pieces are washed at 60°C, the other part at 95°C.
• the wash test is intended to imitate an unintended but conceivable stress that a banknote may be subjected to in daily circulation. It is also referred to as a wet ink adhesion test.
• test pieces After spinning, the test pieces are removed, allowed to dry and visually assessed using a grading scale from 0 to 4, as described above for the crease test.
• the double fold number was determined in the longitudinal and transverse directions of the test pieces according to ISO 5626-1993. The results are given in Table 2 below together with the calculated mean values.
• the ultimate load was determined in both the dry and wet condition (wet ultimate load) in the longitudinal and transverse directions of the test pieces according to ISO 1924-2. The results are given in Table 2 below, together with the calculated mean values.
• the roughness was determined on the wire side (SS) and on the felt side (FS) of the test pieces according to ISO 8791-2. The results are given in Table 2 below together with the calculated mean values.
• Porosity was determined by flowing air from the screen side to the felt side of the test pieces according to ISO 5636/3. The results are given in Table 2 below.
• the drying time is determined to test the absorption behavior and drying time of printing inks on the paper in question.
• a drying time tester from excbau was used. The results are shown in Table 2 below.
• Test pieces containing T-LEAD and L-LEAD security elements were used for the test.
• the security elements were bonded directly to the surface-glued security paper substrate materials using a heat-seal adhesive, without the use of a primer.
• Half of the test pieces had security elements that had been bonded immediately after surface gluing, while the other half of the test pieces had the security elements bonded after three months of storage.
• Tesa test In the Tesa test, one end of a strip of Tesa tape is folded over and stuck to the other end to form a loop, with the adhesive side facing outwards. The Tesa strip is then stuck to a test piece so that it covers the security element on it and is pressed firmly into place. It is then torn off the test piece with a jerk at an angle of around 45° and stuck next to it.
• test was carried out on dry and wet test pieces.
• the test pieces were placed in water for 30 minutes after the Tesa tape had been stuck on, and the Tesa tape was torn off immediately after being removed from the water.
• the dry test was carried out on test pieces with freshly bonded security elements as well as on test pieces three days after bonding of the security elements; the wet test was carried out only on test pieces three days after bonding of the security elements.
• the adhesive strip used was Tesafilm from Beiersdorf, type no. 4104.
• the assessment is done visually according to a grading scale with grades from 0 to 4 as indicated above in the crease test.
• Example 3 which was sized with a surface sizing agent with a polyurethane:polyvinyl alcohol mass ratio of 6:94, was rated with the top grade of 4 in all Tesa tests if the security elements were glued on immediately after surface sizing.
• the paper of Example 2 in which only 17% by mass of the polyvinyl alcohol had been replaced by polyurethane, was rated with the top grade of 4 in all Tesa tests.

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