Pressing tool and use of a ceramic foil as a pressing tool

Abstract

Pressing tool (100) formed by a self-supporting ceramic foil (110) or by a press plate (120) coated on one or both sides with a ceramic foil (110), wherein the ceramic foil (110) is formed from a ceramic material containing zirconium dioxide.

Description

[0001] The invention described here relates to a pressing tool which is formed by a self-supporting ceramic foil or by a pressing sheet which is coated on one or both sides with a ceramic foil, and further to a use of the ceramic foil as a pressing tool in a lamination process.

[0002] To produce plastic cards, for example, in the security industry, stacked polymer films are pressed together (laminated) to form a single (monolithic) plastic body that cannot be separated into individual film layers. Laminating systems are used for lamination, in which the polymer film stacks are pressed together at elevated temperatures and under increased pressure. Laminating systems are known, for example, for the production of laminates for multilayer electrical circuits. Multi-stage presses are typically used for their production (DE 30 32 931 A1). Such devices are also used for the production of laminated plastic cards.DE 198 31 377 A1 describes a multi-opening press for producing laminated plastic cards, such as check cards, credit cards, and the like, particularly contactless cards with integrated electronic components. In the multi-opening press, several stacks of foil to be pressed are placed on stacked, vertically collapsible press levels. Each level includes a heater. The pressing process is carried out by raising the levels until they are pressed against each other under pressure.

[0003] There are multi-opening presses in which a large number of stacks are pressed, arranged one above the other, separated from each other by lamination plates. For example, DE 198 31 377 A1 states that the film stacks are separated from each other by press plates to prevent them from sticking together during the pressing process.

[0004] In addition, continuous systems are also used in which the polymer film stacks are successively passed through the system and pressed in the process (for example, as stated in EP 2 236 287 A2 and DE 10 2012 207 174 A1).

[0005] DE 10 2010 040 886 A1 discloses a lamination device for laminating component stacks with a chemical- and / or heat-resistant film that is silicone-free and / or has a thickness of ≤ 1.5 mm.

[0006] EP 2 530 061 A1 discloses a ceramic green film with the following features: The green film comprises a solid component of inorganic material and organic material. The inorganic component includes a binder, plasticizer, and dispersant. The plasticizer consists of a two-component system, with di-n-butyl adipate (DBA) as the first component and an admixture from the group of adipates and / or sebazates and / or carboxylic acid esters as the second component.

[0007] DE 100 30 106 A1 discloses a method for producing layered ceramic composite materials or monolithic structures comprising the following steps: producing a ceramic foil forming a first layer by casting a first slip onto a base, pouring at least one further slip onto the first layer so that a multi-layer ceramic foil is formed, drying at least one uppermost layer of the multi-layer ceramic foil and sintering the dried multi-layer ceramic foil.

[0008] CN 103 920 804 A relates to a wear-resistant punching die that can improve one-sided punching pressure. A smooth resin layer is evenly distributed on the inner surface of a die, a layer of a high-strength elastic compound is symmetrically distributed on the outer surface on two sides of a punch, and the outer diameter, which is jointly composed of the punch and the layer of a high-strength elastic compound, interacts with the inner diameter, which is jointly composed of the resin layer and the opening portion of the die.

[0009] Generally, multiple copies are fed into the presses, from which the individual plastic cards are separated after lamination, for example using a punching process.

[0010] The laminating sheets serve, among other things, to specify the surface finish of the plastic cards. For example, the plastic cards may require a high-gloss or, alternatively, a uniformly matte surface. For this purpose, laminating sheets are used that have the desired surface finish and transfer this finish to the polymer layer surfaces during lamination. Furthermore, it may also be necessary to create a profile in the surface of the plastic cards. For this purpose, the sheets can have the desired embossed profile as a negative. These sheets can also be used after lamination to subsequently emboss an embossed profile into the surface of the plastic cards.For example, DE 10 2008 008 044 A1 describes a method for embossing surface structures in a substrate for producing a card-shaped data carrier, in which laminating sheets which do not have embossed structures are used for producing a laminate consisting of several layers and further sheets (embossing sheets) with embossed structures are used for embossing the surface structures.

[0011] DE 10 2008 058 912 A1 discloses a lamination sheet intended to prevent scratches on documents during the production of layered documents, particularly due to contamination during stacking and / or transport. To achieve this goal, the lamination sheet has first and second regions corresponding to the first and second regions of a layered sheet produced therewith, with the documents being produced from the first regions of the sheet. The second regions of the lamination sheet have recesses opposite the first regions, so that the first regions of the sheets are recessed relative to their second regions, and the document regions are preferably not damaged during handling of the sheets.

[0012] Furthermore, DE 10 2010 031 421 B4 discloses a laminating device for laminating a multi-layer document. This device comprises two laminating plates, between which the document is placed and which are formed from at least one electrically conductive ceramic material. The laminating plates have electrical connections so that the laminating plate and the document can be heated by applying an electrical voltage to the electrical connections. Materials used for all-ceramic laminating plates are aluminum nitride, a III-V compound semiconductor, and silicon nitride, a non-conductor. Compared to metallic laminating plates, such plates have a very low heat capacity due to their relatively low density. The conductivity of the ceramic eliminates the need for a heating cartridge. This allows for very steep temperature increases.

[0013] However, it has been found that handling conventional metal laminating sheets can cause damage to polished sheet surfaces, as scratches or dents are easily created. This damage leads to scrap during lamination, which must therefore be replaced. Another problem after the lamination process is the very strong adhesion of the sheets to the laminated material, making separating the laminates very laborious. The all-ceramic panels mentioned in DE 10 2010 031 421 B4 are also extremely sensitive to damage, as they break or tear easily.

[0014] Therefore, the object of the present invention is to find a tool that can be used in the lamination of polymer films, which is sufficiently resistant to mechanical stress and which also offers the advantage that the laminated product can be easily removed from the tool.

[0015] According to a first aspect of the present invention, these objects are achieved by a pressing tool which is formed by a self-supporting ceramic foil or by a press plate coated on one or both sides with a ceramic foil, wherein the ceramic foil is formed from a ceramic material containing zirconium dioxide (ZrO2).

[0016] According to a second aspect of the present invention, these objects are also achieved by using a ceramic foil containing zirconium dioxide (ZrO2) as a pressing tool in a lamination process.

[0017] The self-supporting ceramic foil containing zirconium dioxide and a press plate coated with one or more such ceramic foils represent extremely robust pressing tools. In particular, it has been found that the mechanical properties of ceramic materials containing zirconium dioxide are very good, as these materials are particularly resistant to scratches, dents, and tearing. For example, the hardness of such materials is very high. The elastic modulus of the matrix materials containing zirconium dioxide or the zirconium dioxide-containing materials is approximately equivalent to that of steel. Against this background, it is particularly advantageous to produce a steel-ceramic composite solution by bonding the self-supporting ceramic foil containing zirconium dioxide to a press plate made of metal (metal sheet), in particular steel, for example, stainless steel.Since the thermal properties of these materials according to the present invention, as in the case of the AlN / Si3N4 material specified in DE 10 2010 031 421 B4, are also favorable for lamination, they are also suitable for use in the production of plastic cards and other laminates. Accordingly, the ceramic materials according to the present invention have advantageous thermal properties, such as low heat capacity, due, among other things, to their low density compared to metallic materials. The advantage of the pressing tools according to the invention therefore leads to a significant increase in the service life of the pressing tools compared to conventional lamination sheets according to the prior art, to a reduction in waste of the plastic laminates produced in the manufacturing process, and to a reduction in the overall process times required for the production of plastic laminates.In addition, the handling during lamination is extremely simple, as the produced laminates can be easily removed from the ceramic films after the lamination process.

[0018] The pressing tool according to the invention is used either for laminating polymer layers to form a plastic body or for subsequently creating surface structures in the plastic body using an embossing process.

[0019] The laminated or embossed plastic body can be used to manufacture a valuable or security product. A valuable or security product includes, for example, a passport, identity card, driver's license or other ID card or access control card, a vehicle registration document, vehicle registration certificate, visa, check, means of payment, in particular a banknote, a check, bank, credit, or cash payment card, a customer card, health card, chip card, a company ID card, proof of authorization, membership card, gift or shopping voucher, waybill or other proof of authorization, tax stamp, postage stamp, ticket, (gaming) token, adhesive label (e.g., for product security), or another ID document. Such products are considered valuable or security documents.A valuable or security product also includes a security element that can be permanently bonded to an object to be protected, such as a sticker, label, or the like. The valuable or security product can be, for example, a smart card. The valuable or security document can be in ID 1, ID 2, ID 3, or any other format, for example, in booklet form, similar to a passport-like object.

[0020] The plastic body can also be a base material for the production of electrical circuit boards or a laminate in the furniture and building materials industry.

[0021] In a first embodiment of the present invention, the pressing tool is formed by a self-supporting ceramic foil. In this case, the pressing tool does not have any structural elements that reinforce the ceramic foil. The ceramic foil could at most be reinforced by an outer frame and / or have a sealing frame for applying a vacuum. In any case, the self-supporting ceramic foil in this embodiment does not have a flat support. This allows the ceramic foil to optimally conform to any unevenness in the plastic material being processed.If the polymer layer stack contains an internal electrical circuit, such as a semiconductor chip and an antenna conductor structure, corresponding local elevations can form on the outside of the polymer film stack. These local elevations would result in a localized pressure peak during lamination with a rigid lamination tool, potentially causing damage to the circuit components in these areas. By conforming the self-supporting ceramic film to the surface of the stack, the risk of such damage is reduced.

[0022] In a second embodiment of the present invention, the pressing tool is formed by a pressing plate coated on one or both sides with a ceramic foil. In this case, the ceramic foil is additionally stiffened by the pressing plate.

[0023] In a further preferred embodiment of the present invention, the ceramic material of the ceramic foil contains tetragonally stabilized zirconium dioxide (TZP). In particular, the tetragonally stabilized zirconium dioxide can be stabilized by yttrium oxide and / or cerium oxide (yttrium-stabilized: Y-TZP; cerium-stabilized: Ce-TZP). This material therefore exhibits high mechanical strength (high Young's modulus, high fracture toughness).

[0024] In a further preferred embodiment of the present invention, the ceramic material is formed from at least two phases, of which the tetragonally stabilized zirconium dioxide forms one of the two phases.

[0025] In a further preferred embodiment of the present invention, the ceramic material contains, in addition to zirconium dioxide, hexagonal platelets, which can form a second of the two phases. These act as internal reinforcement, effectively forming a composite material. The aspect ratio of the platelets (ratio of the dimension parallel to the platelet plane to the dimension perpendicular to the platelet plane) is preferably at least 2. The hexagonal platelets can be formed, for example, by an aluminate phase. The proportion of hexagonal platelets can range from 10 to 75 vol.%, based on the ceramic material.The volume fraction of hexagonal platelets in the ceramic material can be determined in particular by creating a polished cross-section through the ceramic material (polished microstructure) and examining it, for example, with a scanning electron microscope (SEM). The hexagonal platelets are visible as contrasting needle-like structures within the remaining material. The surface fraction of the hexagonal platelets in this polished microstructure, which indicates the volume fraction, is determined. For this purpose, a statistical average is calculated across several polished micrographs. These platelets impart even greater fracture toughness and flexural strength to the already very strong material.

[0026] Such materials are described by way of example in EP 2 086 909 B1. In a particularly preferred embodiment according to the present invention, the ceramic material contains 98 to 50 vol.% zirconium dioxide as matrix material and 2 to 50 vol.% aluminum oxide, of which 5 to 90 vol.%, based on the aluminum oxide, are in the form of hexagonal platelets. The zirconium dioxide is preferably stabilized either with 2 to 3 mol.% yttrium oxide or with 10 to 15 mol.% cerium oxide or with a mixture of yttrium oxide and cerium oxide in the range from 0 to 3 mol.% yttrium oxide and from 0 to 15 mol.% cerium oxide, in each case based on the amount of zirconium dioxide.For example, zirconium dioxide can initially be used to produce the ceramic material in the form of particles with an average particle size of ≤ 0.35 µm (measured using a sedimentation method or laser granulometry). These particles can then be coated with yttrium oxide and / or cerium oxide (coating process). Tetragonal stabilization of the zirconium dioxide particles is then achieved through a diffusion reaction in a sintering process. Alternatively, stabilization can also be achieved by coprecipitation of the zirconium material with the yttrium and / or cerium material. Common compounds of the metals, such as their oxy- or hydroxychlorides, can be used as starting materials for both the coating process and the coprecipitation process.

[0027] In a particularly preferred embodiment of the present invention, the ceramic material contains an aluminate of at least one rare earth metal. The rare earth metals include the elements scandium (Sc), yttrium (Y), lanthanum (La), and the lanthanides, i.e., cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tu), ytterbium (Yb), and lutetium (Lu). Aluminates are generally understood to mean all possible stoichiometries of aluminates of the rare earth metals. The preferred aluminate is the compound ReAl. 11 O 18, where Re is a rare earth metal. Particularly preferred is La as the rare earth metal used to form the aluminate in the form of lanthanum oxide (La2O3). The aluminates preferably form the hexagonal platelets. Additionally, some of the aluminum oxide used in the production of the ceramic material may not be converted into platelets but may be present in the form of unreacted spherical Al2O3.

[0028] The ceramic material may further contain other components, for example, components that generate sufficient electrical conductivity for an erosion process. For example, the ceramic material may contain titanium carbide (TiC) for this purpose. If these additional components are present in the ceramic material, the content of the remaining components (e.g., ZrO2, rare earth metal oxide, Al2O3) decreases proportionally, so that their proportions remain the same as stated above. Titanium carbide, for example, may be present in an amount of 22 vol.% to 40 vol.%, based on the ceramic material.

[0029] With hexagonal plates, for example made of ReAl 11 O 18, tetragonally stabilized ZrO2 exhibits extremely advantageous mechanical properties: The elastic modulus E of this material is preferably at most 250 GPa (measured according to DIN EN 843, Part 2). The elastic modulus E is preferably at least 160 GPa. The Vickers hardness HV 0,5 is preferably 1500 at most (measured according to DIN 50113). The Vickers hardness HV 0,5 is preferably at least 800. The material is above all flexible and therefore has a particularly high bending strength σ 38 of preferably at least 800 MPa (measured according to DIN EN ISO 6872) and a particularly high fracture toughness K lc of preferably at least 6 MPa·m -1 / 2 (measured according to DIN CEN / TS 14425-5). The bending strength σ 38 is preferably not more than 2500 MPa, and the fracture toughness K lc is not more than 30 MPa·m -1 / 2 .

[0030] In a further preferred embodiment of the present invention, the thickness of the ceramic foil is from 10 µm to 5 mm, more preferably from 50 µm to 2 mm, even more preferably from 75 µm to 1.0 mm, and most preferably from 100 µm to 600 µm. The ceramic foil can have any desired (surface) dimensions. In the case of a rectangular semi-finished product, the ceramic foil can, for example, have side lengths in the range of 5 cm to 100 cm. Format sizes with larger or smaller side lengths are also possible.

[0031] The ceramic material can be produced as follows: i) the mixture of the solids used (tetragonally stabilized zirconium dioxide and other materials) is ground, ii) at least one dispersant and at least one binder are added, iii) coarse particles are separated, iv) the dispersion is dried, v) the dried material is sintered and vi) if necessary, hot isostatically densified.

[0032] Dispersants used include solvents commonly used in the relevant field, particularly organic solvents such as toluene. Binders used include binders commonly used in the relevant field, particularly organic binders such as polyvinyl alcohol, polyvinyl acetate, polyvinyl acrylate, cellulose, and the like.

[0033] To produce a ceramic film containing zirconium dioxide, wherein the zirconium dioxide is preferably tetragonally stabilized, a process comprising the following process steps is used: a. Providing a dispersion of ceramic particles, preferably containing tetragonally stabilized zirconium dioxide, in at least one dispersant and further preferably at least one binder (see process steps i, ii, iii above); b. applying the dispersion to a substrate, for example to a polyethylene terephthalate film; c. removing the at least one dispersant from the dispersion, whereby a dried layer of the ceramic particles and optionally the at least one binder is formed on the substrate (see process step iv above); d. removing the dried layer of ceramic particles from the substrate; and e. Sintering the dried layer of ceramic particles to form a ceramic film (see process step v above).

[0034] If the ceramic foil is to be further densified, it is preferably pressed in step e. using a hot isostatic pressing process (see process step vi above).

[0035] A compression or film casting process can be used to apply the dispersion to the substrate. An extrusion process can also be used to produce the ceramic film. For a film casting process, for example, the dispersion is poured onto a polyethylene terephthalate film and then applied with a doctor blade.

[0036] If the ceramic foil is stiffened by a press plate, either a ceramic foil can be applied to one side of the press plate, or a ceramic foil can be applied to both sides of the press plate by applying the method for producing the ceramic foil(s) given above.

[0037] In a further preferred embodiment of the present invention, the at least one ceramic foil is bonded to the press plate by means of an adhesive, for example, a transfer adhesive tape. Alternatively, any other adhesive can be used, for example, a UV-curable or heat-curable adhesive. The tool produced in this way can be used in a lamination or embossing process.

[0038] In a further preferred embodiment of the present invention, the self-supporting ceramic foil or the press plate coated with the at least one ceramic foil is designed either in the form of a rectangular flat product or in the form of a closed belt. Rectangular flat products are used for multi-stage laminating systems or for an embossing process in which the product to be embossed is individually subjected to the embossing process. The product to be processed is clamped between two such flat products. If a continuous system is used for laminating or embossing, a closed belt is preferably used, for example, in a commercial continuous laminating system.

[0039] In a further preferred embodiment of the present invention, the rectangular flat material is thickened at least on one or both sides in one edge region or in two opposing edge regions (on the same side of the flat material or on different sides). Such a flat material or laminating tool is used, for example, to produce a plastic body that is to be sewn into an identity document and for this purpose has a laterally protruding, thinned sew-in flap. The region of the thickening in the at least one edge region corresponds to the thinner region of the sew-in flap, and the adjacent thinner region of the laminating tool corresponds to the thicker region of the plastic body that corresponds to the data side of the document.After production, the plastic body is split in the middle in this thinner area into two parts, forming two sewn-in pages (sheets) for the identity document. An electronic circuit, such as an RFID circuit consisting of an RFID semiconductor chip and an antenna conductor connected to it, can be embedded within the thicker area of ​​each resulting document page.

[0040] If the pressing tool according to the invention is also to be suitable for forming surface structures on the top and / or bottom of a plastic body, three-dimensional structures corresponding to these surface structures must be formed as negatives on the pressing tool. Their production can be realized, for example, in process step d. of the process using a suitable pressing tool by molding. The sintered ceramic foil can also be machined to produce the structures with significantly more precision than introducing these structures into the dried layer of ceramic particles using a molding process. An erosion process, in particular a spark erosion process, can be used for this. For the latter to be applicable, the ceramic foil must be electrically conductive. For this purpose, the foil contains electrically conductive particles, for example SiC or TiC particles.These are added to the layer of ceramic particles during the layer's production. For spark erosion, a stamp made of a highly electrically conductive material, such as copper, is preferably used as a matrix. This stamp has three-dimensional structures in the form of a negative corresponding to the structures to be formed on the ceramic particle layer. During spark erosion, the stamp serves as a counter electrode to the ceramic foil.

[0041] The press tool according to the invention can be used in a lamination process. For this purpose, a stack of several polymer films is formed, which are then fused together using heat and pressure. Typically, the material of the polymer films softens and flows during the lamination process, thus achieving a material-to-material bond between the films. The level of the lamination pressure and, in particular, the lamination temperature depend on the type of material of the individual polymer films, their thicknesses, and other parameters. The maximum temperature to which the lamination press tools are heated is selected depending on the type of material from which the polymer films are made. In the case of polycarbonate (PC) and PC blends (mixtures of PC with other polymers), the maximum temperature in the lamination press can be in the range of 170-200°C, preferably 180-190°C.During the lamination process, the polymer film stacks are subjected to pressure between the laminating press tools, preferably perpendicular to the stack surfaces. This pressure should be sufficiently high to expel any air trapped between the polymer films as the layers soften. To further promote the escape of air, an additional vacuum can be applied to the polymer film stack. The pressure can range from 25 to 700 N / cm. 2 , preferably in a range of 50 to 100 N / cm 2 , lay.

[0042] A plastic body to be produced by lamination is created from several polymer films. These films are formed from a polymer that is preferably selected from a group comprising polycarbonate (PC), in particular bisphenol A polycarbonate, polyethylene terephthalate (PET), and their derivatives, such as glycol-modified PET (PETG), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polyimide (PI), polyvinyl alcohol (PVA), polystyrene (PS), polyvinylphenol (PVP), polypropylene (PP), polyethylene (PE), thermoplastic elastomers (TPE), in particular thermoplastic polyurethane (TPU), acrylonitrile-butadiene-styrene copolymer (ABS), and their derivatives, and / or paper and / or cardboard and / or glass and / or metal and / or ceramic. Furthermore, the product can also be made from several of these materials. It is preferably made of PC or PC / TPU / PC. The polymers can be either filled or unfilled.In the latter case, they are preferably transparent or translucent. If the polymers are filled, they are opaque. The above information applies both to films that are to be bonded together and to liquid formulations that are applied to a precursor, such as a protective or topcoat. The product is preferably made from 3 to 12, preferably 4 to 10 films, whereby the individual films can be made of the same material or of different materials. Overlay layers formed in this way protect a security feature arranged underneath and / or provide the document with the required abrasion resistance.

[0043] For the production of valuable or security products, the polymer film stacks for the lamination process are formed from polymer films corresponding to several valuable or security products, thus creating multiple uses during lamination. The valuable or security products are then manufactured from the laminated plastic bodies by separating them, for example, by punching.

[0044] The plastic body to be manufactured for a valuable or security product can have an embedded electronic circuit, for example an RFID (radio frequency identification device) circuit consisting of an RFID semiconductor chip and an antenna conductor connected to it. The RFID semiconductor chip can in particular be mounted unpackaged on the antenna conductor, preferably using flip-chip technology, very preferably by means of an anisotropic conductive adhesive. The semiconductor chip is preferably thinned. For this purpose, the electronic circuit can be mounted on a carrier layer. Above the carrier layer in the polymer film stack to be laminated, there can be a compensating film layer which has cutouts at the locations where electronic components such as a semiconductor chip are located, so that these protrude into the cutouts.Above the compensating film layer in the polymer film stack there may also be a flow film layer whose glass transition temperature is lower than that of the compensating film and the carrier layer.

[0045] The pressing tool according to the invention can also be used to produce surface structures in an embossing process. For example, CLI (changeable laser image) structures can be created in this way. Such structures are characterized, for example, by microlenses arranged in a matrix. For this purpose, the pressing tool can have the aforementioned surface structures in a negative. The embossing process can take place during a lamination process or independently in a separate process step, for example, after a lamination process. In the embossing process, the plastic body to be embossed, together with the pressing tool, is also exposed to increased pressure and elevated temperature.

[0046] The present invention is explained in more detail below with reference to figures, whereby the illustrated examples are merely exemplary and do not represent a limitation with regard to the scope of the described invention. They show in detail: Fig. 1: Schematic representations of a pressing tool according to the invention in a first embodiment, in a first variant in the form of a laminated sheet with a ceramic foil applied thereto; A) top view; B) cross-sectional view; and in a second variant in the form of a self-supporting ceramic foil; C) cross-sectional view; Fig. 2: Schematic representations of a pressing tool according to the invention in a second embodiment in the form of a self-supporting ceramic foil; A) top view; B) cross-sectional view; Fig. 3: Schematic representations of a pressing tool according to the invention in a third embodiment; A) top view; B) cross-sectional view; C) polymer film stack to be pressed therewith; Fig. 4 Schematic representation of the steps of the process for producing the ceramic film; A) Preparation of a TZP dispersion; B) Pouring the dispersion onto a substrate; C) Drying the formed layer; D) Peeling the dried layer from the substrate; E) Sintering the peeled layer; Fig. 5 Scanning electron microscopy (SEM) image of a sintered TZP ceramic with a ReAl 11 O 18 -platelet phase in a first embodiment of the invention (Example 1); Fig. 6 Scanning electron microscopy (SEM) image of a sintered TZP ceramic with a ReAl 11 O 18 -platelet phase in a second embodiment of the invention (Example 2); Fig. 7 Scanning electron microscopy (SEM) image of a sintered TZP ceramic with a ReAl 11 O 18 -platelet phase in a third embodiment of the invention (Example 3); Fig. 8 Scanning electron micrograph (SEM) of a sintered TZP ceramic without platelet phase in a fourth embodiment of the invention (Example 4).

[0047] In the figures, like reference symbols denote elements with the same function or the same elements.

[0048] Fig. 1A, Fig. 1B show a pressing tool 100 according to the invention in the form of a rectangular flat product. In this embodiment, the pressing tool, in a first variant, is formed by a conventional stainless steel laminating sheet (press sheet) 120 and a ceramic foil 110 bonded to this laminating sheet using a transfer adhesive tape (not shown). The thickness ratios of the steel laminating sheet and the ceramic foil do not correspond to the actual ratios: The laminating sheet can, for example, have a thickness of 0.5 mm. The ceramic foil has, for example, a thickness of 0.3 mm. Fig. Figure 1A shows a top view of the laminating sheet with the ceramic foil on top. Fig. Figure 1B shows a cross-section through the pressing tool, whereby the adhesive located between the lamination sheet and the ceramic foil is not shown. In a further embodiment, the pressing tool is formed by a self-supporting ceramic foil 110 ( Fig. 1C: Cross-sectional view).

[0049] Fig. Figure 2 shows a pressing tool 100 according to the invention in the form of a self-contained band. In this embodiment, the pressing tool is formed by a self-contained band of ceramic foil 110. Here, too, the thickness ratios of the steel laminating band and the ceramic foil do not correspond to the actual ratios: The laminating band can, for example, have a thickness of 0.5 mm. The ceramic foil has a thickness of 0.3 mm, for example. Fig. 2A shows a top view of the band-shaped pressing tool. Fig. Figure 2B shows a cross-section through the band-shaped pressing tool. Alternatively, this pressing tool can also be designed in the form of a sandwich consisting of a ceramic foil bonded to a self-contained band of steel laminating tape (not shown).

[0050] Fig. Figure 3 shows a pressing tool 100 according to the invention in the form of a rectangular flat product. In this embodiment, the pressing tool is formed by a stainless steel laminating sheet (press sheet) 120 and ceramic foils 110 bonded to this laminating sheet using a transfer adhesive tape (not shown). The thickness ratios of the steel laminating sheet and the ceramic foils do not correspond to the actual ratios: The laminating sheet can, for example, have a thickness of 0.5 mm. The ceramic foils have a thickness of 0.3 mm, for example. Fig. Figure 3A shows a top view of the lamination sheet with the ceramic foil on top. Fig. Figure 3B shows a cross-section through the pressing tool, whereby the adhesive located between the laminating sheet and the ceramic foil is not shown.

[0051] The laminating sheet 120 has edge regions 101, 102 that are thicker than the central region 105. A ceramic film is applied to one side of each of the edge regions 101, 102 and the central region 105. The increased thickness in the edge regions can be achieved, for example, by metal deposition by welding. The edge thickness increase compared to the thickness of the central region is, for example, 0.1 mm. By using such pressing tools 100 during lamination, laminates (plastic bodies) can be produced from polymer films of different sizes. These laminates are thicker in the middle because several polymer films are welded together there, while only one or a few polymer films are present in the edge regions. A laminate (plastic body) 200 produced in this way is Fig. 3C, when both sides of the Fig. 3A, Fig. 3B are used. In the example shown, a central polymer film 250, which can form a personalization side, is flanked by two smaller outer polymer films 230, 240, the latter leaving the central polymer film free in the edge regions 201, 202, while the films form a stack in the central region 205. The finished laminate is finally cut along line 260 to produce two pieces suitable for sewing into a passport document.

[0052] To produce the ceramic film, the starting materials (e.g. TZP, Al2O3, La2O3) are mixed together with a dispersant, e.g. toluene, and a binder, e.g. polyvinyl acetate, to form a dispersion D ( Fig. 4A: Process step a). This dispersion is then poured onto a substrate U, for example a Mylar film (trademark of DuPont), and removed with a metering blade (not shown) ( Fig. 4B: Process step b). The formed layer is then dried, whereby the dispersant evaporates. A compacted layer (K) of the inorganic particles in the binder remains ( Fig. 4C: Process step c). The dried layer is then peeled off the substrate ( Fig. 4D: Process step d). Finally, the peeled layer is sintered in a furnace to obtain a ceramic foil ( Fig. 4E: Process step e). Examples 1 to 4:

[0053] The compositions listed in Table 1, where ZrO2, optionally Y2O3, and optionally CeO2 were converted to a tetragonally stabilized zirconium dioxide using a coating process, and the stabilized zirconium dioxide was mixed with Al2O3 and optionally La2O3, were each dispersed in water, the dispersions deagglomerated, and homogenized in a grinding step. After separation from the grinding beads, the mixture was dispersed in toluene together with polyvinyl acetate. The dispersion was then poured onto a Mylar film (DuPont) and removed using a metering doctor blade. The resulting layer was dried, peeled off the substrate after drying, and the peeled layer was sintered in a furnace (without applying pressure). The sintering conditions for these ceramic materials were as follows: Ceramic material according to Example 1: 1480 to 1500°C, 3 to 5 hours; Ceramic material according to Example 2: 1350 to 1480°C, 3 to 5 hours; Ceramic material according to Example 3: 1420 to 1500°C, 3 to 5 hours; Ceramic material according to Example 4: 1350 to 1480°C, 3 to 5 hours.

[0054] The thickness of the sintered samples (ceramic foils) was approximately 0.5 mm. Scanning electron micrographs (SEM) of the resulting ceramic foils were taken. These are shown in Fig. 5 to 8. These are tetragonally stabilized ZrO2 (TZP) with or without an embedded platelet phase.

[0055] When investigating the mechanical properties of the sintered ceramic materials, the results given in Table 2 were found.

[0056] The SEM images show a platelet-like phase α in the form of elongated dark areas, the tetragonally stabilized ZrO2-(TZP) phase β in the form of bright, almost circular areas, and unreacted globular Al2O3 particles γ in the form of small black spots. However, the material of Example 4 / Fig. 8 no platelet-like phase, since no ReA 11 O 18 has been formed. Table 1 (data in wt.%): Beisp. 1 / Fig. 5 Beisp. 2 / Fig. 6 Beisp. 3 / Fig. 7 Beisp. 4 / Fig. 8 ZrO2 75,6 85,7 84,5 95,0 Y2O3 0 4,3 1,9 4,8 CeO2 14,4 0 8,6 0 Al2O3 7,5 8,3 4,5 0,2 La2O3 2,5 1,7 0,5 0 Table 2 - mechanical properties: Beisp. 1 / Fig. 5 Beisp. 2 / Fig. 6 Beisp. 3 / Fig. 7 Beisp. 4 / Fig. 8 Density ϱE[g / cm3] 5,95 5,75 5,96 5,98 E-Modul [GPa] 210 220 210 220 Flexural strength σ 3B [MPa] 950 1250 1150 1350 Vickers hardness HV 0,5 1200 1420 1350 1400 Vickers hardness HV 10 1100 1250 1200 1250 Fracture toughness K lc [MPa√m] 10,8 7,5 8,5 8,2 List of reference symbols: 100 pressing tools 101, 102 marginal area 105 central area 110 ceramic foil 120 Press sheet, laminating sheet 200 plastic bodies, laminate 201, 202 marginal area 205 midrange 230, 240 (outer) polymer films 250 (center) polymer film 260 cutting line D Dispersion K unsintered ceramic layer U pad α platelet-shaped phase β TZP phase γ Al2O3

Claims

[1] Press tool (100) formed by a self-supporting ceramic foil (110) or by a press plate (120) coated on one or both sides with a ceramic foil (110), wherein the ceramic foil (110) is formed from a ceramic material containing zirconium dioxide. [2] Press tool (100) according to claim 1, characterized by that the ceramic material contains tetragonally stabilized zirconium dioxide. [3] Press tool (100) according to claim 2, characterized by that the tetragonally stabilized zirconium dioxide is stabilized with yttrium oxide and / or cerium oxide. [4] Press tool (100) according to one of the preceding claims, characterized by that the ceramic material additionally contains an aluminate of at least one rare earth metal. [5] Press tool (100) according to claim 4, characterized by that the ceramic material contains hexagonal platelets. [6] Press tool (100) according to one of the preceding claims, characterized bythat the at least one ceramic foil (110) is connected to the press plate (120) by means of an adhesive. [7] Press tool (100) according to one of the preceding claims, characterized by that the self-supporting ceramic foil (110) or the press sheet (120) coated with the at least one ceramic foil (110) is designed in the form of a rectangular flat product or a self-contained strip. [8] Press tool (100) according to claim 7, characterized by that the rectangular flat product is thickened at least on one side in two opposite edge regions (101, 102). [9] Use of a ceramic foil (110) containing zirconium dioxide as a pressing tool (100) in a lamination process.

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