发明内容：
[0001]The present invention relates to a process for the functionalization of a workpiece surface, comprising the steps of: a) provision of a workpiece; b) provision of a film; c) functionalization at least of one film side by locationally selective application of a functionalization composition comprising a polymeric material by means of a 3D printing process in one or more layers onto a portion of the film side; d) bringing the film into contact with at least one portion of the workpiece surface for development of a coherent or interlocking connection between the workpiece surface and the film functionalized in step c), the coherent or interlocking connection to the workpiece surface being achieved with a functionalized film side. The invention further relates to workpieces with a surface functionalized according to the invention.
[0002]The advantages of mass production in relation to quality and costs can in particular be utilized when large numbers of units of components of identical design are manufactured. However, this concept has the disadvantage that individualization of said components within the existing process can be achieved only at high technical cost. The literature therefore discusses many approaches to maximizing of efficiency in achievement of different designs which by way of example have different functionalities or decorative effects, in a manner based on a single production standard and within separate process steps. This approach combines the advantages of basic mass production with the desired component-flexibility, and is in particular attractive for modifications of workpiece surfaces, because changes to the underlying structure of the component are understandably significantly more complicated.
[0003]By way of example, it is known that decorative or functional elements can be combined with plastics components in that film plies with such elements are included into injection moldings. Within the process, a film ply is inserted into an injection mold and fixed in said mold. A plastics composition is then injected into the injection mold, where it bonds to the film ply and hardens. Such processes are termed in-mold decoration (IMD) processes. However, this procedure has the disadvantage that the high temperatures and pressures required for injection molding restrict the selection of possible materials that can be used. In particular it is not possible to use heat-sensitive electronic functional elements or decorative effects, because these would suffer irrevocable damage under the conditions of injection molding. Alongside high production costs for the injection molding, the above processes also lack flexibility, because injection molding can usually be carried out only with a composition that is to some extent homogeneous.
[0004]The patent literature also reveals possibilities for altering surface properties of consumer goods.
[0005]EP 011 87 96 A2 discloses an interior cladding component in particular for vehicles with a support which has film-laminated sections on the visible side and has at least one adjacent region covered with fabric or leather or a similar material, with, at the boundary between film and fabric, a groove is configured in the support, into which groove the edges of the film and of the fabric have been inserted and held there by adhesive bonding and/or by gripping.
[0006]DE 198 149 56 A1 describes a process for the production of motor-vehicle-interior claddings with a support which, on the side that is visible in the installed position, has been covered with a film, where polyurethane foam backing has been inserted in at least some sections between the film and the support, where the process comprises: 1) production of the film with over-dimensioning inclusive of an overwrap at the edges by thermoforming or the like; 2) trimming of the film to the desired final dimensions; 3) insertion of the air-permeable support into the film inclusive of insertion under pressure into the overwrapped edges; 4) insertion of this composite into the lower portion of a foaming mold and fixing by vacuum; 5) moving the upper portion of the foaming mold into place and thereby complete overwrapping of the edges of the film to the desired final shape; 6) introduction of the polyurethane into the closed mold to produce the foam backing and adhesive bonding of the film to the support in regions including the curved edges.
[0007]A very wide variety of processes in the additive manufacturing sector have also been described.
[0008]WO 2010 049 696 A2 discloses by way of example a device for the formation of a three-dimensional article by layer-by-layer addition of a construction material having a supportive structure for the support of the article during the shaping procedure and a removable underlying metallic layer which takes the form of a mesh, a foil, a foil or a foil. The base layer is fixed removably on the construction support.
[0009]DE 10 2014 104 321 A1 moreover describes a process for the production of a molding with the steps of: a) provision of a film ply; b) application of a plastics composition in a prescribed three-dimensional shape to the film ply by means of a three-dimensional printing process.
[0010]Despite the processes already known in the field of functionalization of workpiece surfaces, there continues to be increased interest in processes which can provide a very wide variety of functionally modified surfaces at high production speeds.
[0011]Therefore the object of the present invention is to provide a flexible and inexpensive process for the production of functionalized workpiece surfaces.
[0012]The following are therefore proposed: a process for the functionalization of workpiece surfaces as claimed in claim 1, and workpieces as claimed in claim 14, functionalized by said process. Advantageous further developments are stated in the dependent claims. They can be combined in any desired manner, unless the opposite is clearly apparent from the context.
[0013]The invention provides a process for the functionalization of a workpiece surface, where the process comprises at least the following steps:
[0014]a) provision of a workpiece;
[0015]b) provision of a film with at least two film sides, preferably with precisely two film sides;
[0016]c) functionalization of at least one film side by location-selective application of a functionalization composition comprising a polymeric material by means of a 3D printing process in one or more layers onto at least one portion of the at least one film side;
[0017]d) bringing the film into contact with at least one portion of the workpiece surface for development of a coherent or interlocking connection between at least one portion of the workpiece surface and the film functionalized in step c), the coherent or interlocking connection to the workpiece surface being achieved here with a functionalized film side.
[0018]It has been found that by means of the process of the invention it is possible to provide a very wide variety of functions to a large number of different workpiece surfaces. The process is not restricted here to specific geometries of the workpieces, and the process of the invention can also apply sensitive mechanical or electrical functions to complex surface geometries. The applied functionalities are advantageously located between the workpiece surface and the film, and these are therefore shielded by the film from undesired environmental effects. The film therefore provides mechanical protection which increases the durability of the applied functionalities. This is in particular advantageous in comparison with the prior art which to some extent recommends the application of functional elements to the uppermost surface of the workpiece. In such cases the film disadvantageously provides no mechanical protection. Another advantage is that the functionalization procedure can be decoupled from the production of the workpiece. It is therefore possible to continue use of existing standard production processes for the workpiece. The functionalization becomes chronologically independent of the manufacture of the workpiece, and it is possible to provide individual and varying functionalities as desired by customers. This reduces costs, accelerates production and avoids unnecessary holding of inventory of prefabricated components.
[0019]By means of the process of the invention it is possible to achieve functionalization of a workpiece surface. Workpiece surfaces here are the surfaces of any desired workpieces, where the workpieces can be composed of various materials such as plastic, glass, ceramic, thermoplastic polymers, thermoplastic elastomers, crosslinked rubber materials, thermoset materials, composite substances, composites, wood, metal, carbon, cork or paper. No limits are imposed on use in various workpiece sectors, and the workpieces can therefore derive from vehicle construction, from aerospace technology, from the consumer goods sector or from safety or security engineering, etc. Examples of suitable workpieces are workpieces with a surface area greater than 1 cm2, preferably greater than 10 cm2, and moreover preferably workpieces with a surface area greater than 50 cm2. Examples of suitable workpieces are dashboards for automobile engineering, electronics items such as radios, remote controls, lamps, smartphones, small electrical items such as toothbrushes, shavers, etc., and also non-electronic items such as book spines, razors, mechanical toothbrushes, other brushes or combinations of least two thereof.
[0020]The functionalization of the workpiece surface comprises the addition of further or additional elements which are perceptible by haptic or optical means to a user and which alter the perceived haptic, tactile or optical properties of the workpiece surface, or which are externally initially not perceptible, but provide new possible uses to the workpiece. Application of a 3D-printed film by lamination can by way of example alter the geometric design of a workpiece in a controlled manner (printed shaping). Application of a 3D-printed film by lamination can alter the haptic properties of a workpiece surface in a controlled manner (printed textures/printed pads/foams). Application of the 3D-printed film can alter the mechanical properties of a workpiece, for example the mechanical stiffness, or the flexibility. Application of a 3D-printed film by lamination can alter the electrical properties of a workpiece in a controlled manner. (printed conductors/circuit boards, antenna structures, electrical or electronic components, sensors, inductive or capacitive touch sensors, chips, display elements, in particular LED display elements or OLED display elements or LCD display elements). Application of a 3D-printed film by lamination can alter the optical properties of a workpiece in a controlled manner. (printed lenses, optical elements, inscription, decorative effects, safety or security features). The process of the invention can be used for additional provision of one or all of these examples of functionalities to a standard component.
[0021]In step a) a workpiece is provided. The manner of provision of the workpiece here can be such that at least the surface of the workpiece is freely accessible. Before or during provision, the workpiece surface can moreover be prepared for the further steps by other process steps such as cleaning, electrostatic discharging or demagnetizing, or temperature-adjustment.
[0022]In step b) a film is provided. In the context of the invention, the word “film” means a semifinished product which has a substantially greater extent in two spatial directions than in the third spatial direction. In the context of the invention, the word “film” also means areal semifinished products which are otherwise frequently termed textiles, woven fabrics, laid scrims, braided fabrics, meshes, knitted fabrics, foams, and also polymer films. It is essential to the invention that the film has a modulus-to-film-thickness ratio which allows the film to be wound around a core of diameter 10 cm without fracture of the material. The modulus of the films is determined here as modulus of elasticity in the tensile test on a 2*10 cm sample with a certain thickness, and according to the invention is in a range from 10 MPa to 10 GPa, where the film thickness is in a range from 0.01 to 2 mm. The product of film thickness and film modulus of the film is preferably in the form of thickness [mm]*modulus [MPa]<5000, preferably <3000, particularly preferably <2000 mm MPa, and the elongation at break of the film in the tensile test is preferably >5%, preferably >10% and particularly preferably >20%, measuring in accordance with DIN EN ISO 527-2:2012-06. The film here can have one or more layers made of one, or of a composite of different, film material(s). The film material is an entirely areal material, optionally also with cutouts, or takes the form of laid scrim, mesh, or woven fabric. The material is preferably selected from the group consisting of leather, polymers, composite materials, metals, wood, or combinations of at least two thereof. The film material is preferably selected from the group consisting of polyurethane, polycarbonate, polyester, polyamide, polyetherimide, polyetherketone, polyimide, polyoxymethylene, polysilicone, thermoplastic elastomer, rubber, polyvinyl chloride, polyethylene, polypropylene, fiber-composite materials with continuous fibers, or mixtures of at least two thereof or layer structures made of at least two thereof. The film material can be continuous, but can also have cutouts. The provision of the film preferably likewise comprises preparative steps such as cleaning, conditioning via application of further substances such as lacquers, electrostatic treatment steps, temperature-adjustment, etc. The film can be partially transparent or colored, or can have a printed decorative effect.
[0023]In step c) at least one film side is functionalized by locationally selective application of a functionalization composition comprising a polymeric material by means of a 3D printing process in one or more layers onto a portion of the film side.
[0024]The present invention thus also comprises, in parts, a process for the production of functionalization by means of additive manufacturing on a film. The functionalization to be produced is not in principle subject to any restriction here. In particular, additive manufacturing permits, in an effective manner, production of a very wide variety of functionalizations for a very wide variety of applications with unrestricted geometries. Correspondingly, the functionalization to be produced is also not subject to any restriction; instead, the process step described here can in principle serve to create any functionalization that can be produced by an additive process. However, the process described here is particularly preferably intended for those functionalizations that require high stability and, respectively, homogeneous mechanical properties.
[0025]3D printing processes comprise in particular additive processes. In principle it is possible for the purpose of this process step to use any additive process.
[0026]The expression “additive manufacturing processes” denotes those processes that construct articles layer-by-layer. They therefore differ significantly from other processes for the production of articles, for example milling or drilling. In the latter processes, an article is subjected to operations in which its final geometry results from removal of material.
[0027]Additive manufacturing processes utilize various materials and process techniques for layer-by-layer construction of articles. In what is known as fused deposition modeling (FDM) by way of example, a thermoplastic wire is liquefied and, with the aid of a nozzle, is deposited layer-by-layer on a movable construction platform. Solidification produces a solid article. Control of the nozzle and/or on the film to be printed is achieved on the basis of a CAD drawing of the article. If the geometry of the functionalization is complex, for example with geometric undercuts, supportive materials must be additionally concomitantly printed, and in turn removed after completion of the functionalization.
[0028]Alongside the above there are additive manufacturing processes which utilize thermoplastic powders in order to construct the desired functionalizations layer-by-layer. These use what is known as a “coater” to apply thin powder layers, which are then selectively melted by means of an energy source. The surrounding powder here supports the geometry of the component. This method is more cost-effective than the FDM process described above for manufacture of complex functionalizations. It is moreover possible to arrange and, respectively, manufacture various functionalizations in close-packed format in what is known as the powder bed. By virtue of these advantages, powder-based additive manufacturing processes are the most cost-effective additive production processes available in the market. Industrial users therefore mainly use these processes. Examples of powder-based additive manufacturing processes are what is known as laser sintering (SLS, selective laser sintering) and high-speed sintering (HSS). These differ from one another in the method used to introduce the selective-melting energy into the plastic. In the case of the laser sintering process, the energy is introduced by way of a deflected laser beam. In the case of what is known as the high-speed sintering (HSS) process, for example as described in EP 1 648 686, the energy is introduced by way of infrared (IR) radiant sources in combination with an IR absorber selectively printed into the powder bed. The method known as selective heat sintering (SHS) utilizes the printing unit of a conventional thermal printer for selective melting of thermoplastic powders.
[0029]Direct powder methods/powder bed systems are known in the form of laser melting processes, for example selective laser melting (SLM), laserCUSING and direct metal laser sintering (DMLS). The single exception from this process principle is the electron beam melting process (EBM), in which an electron beam is used under high vacuum.
[0030]Another system that uses a powder bed is the Höganäs digital metal process. This system uses a precision inkjet to deposit a specific “ink” on a layer of thickness 45 μm made of metal powder. A further 45-micrometer powder layer is applied, and the printing step is repeated until the component has been completed. The component is then released and sintered to obtain the final size and strength. One of the advantages of this system is that construction is achieved at room temperature without the partial melting that occurs when laser technology or electron beam technology is used. In principle, there is also no need for any supportive structures during the construction procedure, because these are supported by the powder bed.
[0031]Although systems with powder supply use the same starting material, there is a considerable difference in the manner of layer-by-layer addition of the material. The powder flows through a nozzle, whereupon it is melted by a beam directly on the surface of the treated component.
[0032]Systems with powder supply are also termed laser cladding, directed energy deposition and laser metal deposition. The process is very precise, and is based on automated deposition of a layer of material with a thickness between 0.1 mm and a number of centimeters. Some of the features of this process are the metallurgical bonding of the coating material to the base material and the absence of undercuts. The process differs from other welding techniques in the small extent to which the heat introduced penetrates into the film. Highly heat-sensitive films can therefore also be processed.
[0033]A development of this technology is the laser engineered net shaping (LENS) powder supply system. This method permits addition of material to an existing component on the film.
[0034]It is also possible to use ADAM (atomic diffusion additive manufacturing) with various metal powders. For this, the powder is shaped layer-by-layer in plastics binder. After the printing procedure, the functionalization is sintered together with the film in an oven which burns the binder off and consolidates the powder to give a final, fully consolidated metal component.
[0035]In summary, additive processes that can be used for the purpose of this process step comprise by way of example those described above. Suitable examples are therefore high-speed sintering, selective laser melting, selective laser sintering, selective heat sintering, binder jetting, electron beam melting, fused deposition modeling, fused filament fabrication, cladding, friction stir welding, wax deposition modeling, contour crafting, metal-powder application processes, cold gas spraying, electron beam melting, stereolithography, 3D screen printing processes, light-controlled electrophoretic deposition, printing of highly metal-powder-filled thermoplastics by the FDM process, nanoscale metal powder in the inkjet process, DLP (direct light processing), inkjetting, and continuous light interface processing (CLIP). These processes can be used for the application of the functionalization composition in step c).
[0036]It is also possible to use areal processes for the application of the functionalization composition. In these, just as in the stereolithography process, a photopolymer solution is photoirradiated. Here, however, the photoirradiation is not spot-photoirradiation by way of a laser beam, but instead is areal photoirradiation. For this, a photoirradiation matrix is projected onto the respective layer in order to harden the material at these sites.
[0037]In the case of the DLP process (digital light processing), a dot pattern is projected from above onto the photopolymer area, and the construction platform drops layer-by-layer into the solution. This process has the advantage that it is also possible to use different intensities of photoirradiation to vary the hardening. It is thus possible by way of example to achieve easier removal of supportive structures, if these have been hardened to a lesser extent.
[0038]In the 3D printing method termed LCM (lithography-based ceramic manufacturing), the photopolymer bath is photoirradiated from below, rather than from above. This process is specifically used for photoirradiation of a mixture made of solid constituents (ceramic) and a photopolymer solution. The resultant green body is sintered after the 3D printing procedure, and the binder is burnt out. This 3D printing process has the advantage of the possibility to use a variety of granulates.
[0039]With CLIP (continuous liquid interface production) technology it is possible to produce objects without visible layers. The photopolymerization of the liquid resin is controlled by means of balancing of UV light (hardening) and oxygen (which prevents hardening). The base of the resin tank consists of a light- and air-permeable material, similar to that of contact lenses. It is thus possible in the undermost layer, by means of oxygen, to produce what is known as a “dead zone”, which permits the further construction of the object that is drawn continuously upward out of the tank.
[0040]In the case of stereolithography (SLA process), a plastic that hardens on exposure to light and is also termed photopolymer is hardened in thin layers by a laser. The process takes place in a melt bath comprising the monomers on which the light-sensitive (photosensitive) plastic is based. After each step, the workpiece is lowered a few millimeters into the bath and retracted to a position that is below the previous position by the amount corresponding to one layer thickness.
[0041]The 3D printing process utilized in this step for the production of a functionalization by means of additive manufacturing comprises firstly a step in which the functionalization is produced by repeated spatially selective arrangement, layer-by-layer and in accordance with a cross section of the functionalization, in particular application and/or melting and/or polymerization and/or adhesive bonding, of at least one functionalization composition on the film.
[0042]In particular, a process that operates by means of inkjet technology can be used as additive process. An example that can be mentioned here is binder jetting.
[0043]Any material that can be processed by means of an additive process can moreover in principle be used as functionalization composition. The material used can therefore by way of example be any material that can be melted under suitable conditions and that resolidifies. It is moreover possible to use only one functionalization composition or to use a mixture of materials, or to use a plurality of functionalization compositions. If a plurality of functionalization compositions are used, these can be arranged in different layers or else in the same layers.
[0044]In principle, the functionalization composition can be present in powder form on the film, or else can already be in molten form when it is applied to the film.
[0045]The expression “coherent or interlocking connection” between the workpiece surface and the surface of the film functionalized in step c) means, according to the invention, a connection between the two surfaces which is such that the two surfaces preferably cannot be separated from one another without use of considerable forces. Specifically, the expression “coherent connection” means either a coherent chemical connection or a coherent physical connection. The expression “interlocking connection” means a connection between the surfaces with dovetailing of the surfaces. It is preferable that the dovetailing is achieved by subjecting the surfaces to a forming procedure. The strength of a bond between the two surfaces is preferably ≥0.1 N/mm, preferably ≥0.3 N/mm, preferably ≥0.5 N/mm, measured in accordance with DIN ISO 55529:2012-09.
[0046]In an advantageous embodiment of the process of the invention, at least a portion of the functionalized composition comprises a fusible polymer. It is preferable that the entire functionalization composition comprises a fusible polymer. It is moreover preferable that the fusible polymer is in particulate form, where at least 90% by weight of the particles have a particle diameter that is ≤0.25 mm, preferably ≤0.2 mm, particularly preferably ≤0.15 mm. The particles comprising the fusible polymer can by way of example have homogeneous structures such that no further fusible polymers are present in the particles.
[0047]Suitable functionalization compositions can be produced by way of various familiar processes, for example grinding processes, cryogrinding, precipitation processes, spray-drying processes, and others.
[0048]The functionalization composition preferably also comprises, alongside the fusible polymer, other additives such as fillers, stabilizers and the like, and also other polymers. The total content of additives in the particles can by way of example be ≥0.1% by weight to ≤60% by weight, preferably ≥1% by weight to ≤40% by weight.
[0049]In a preferred embodiment, the functionalization composition comprises a fusible polymer selected from: polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyetherketoneketone (PEKK), polyethersulfones, polyimide, polyetherimide, polyesters, polyamides, polycarbonates, polyurethanes, polyvinyl chloride, polyoxymethylene, polyvinyl acetate, polyacrylates, polymethacrylates, TPE (thermoplastic elastomers), thermoplastics such as polyethylene, polypropylene, polylactide, ABS (acrylonitrile-butadiene-styrene copolymers), PETG (a glycol-modified polyethylene terephthalate), or else polystyrene, polyethylene, polypropylene, and blends and/or alloys of at least two of the polymers mentioned.
[0050]The functionalization composition preferably comprises a polyurethane obtainable at least partly from the reaction of aromatic and/or aliphatic polyisocyanates with suitable (poly)alcohols and/or (poly)amines or blends thereof. At least a proportion of the (poly)alcohols used preferably comprises those from the group consisting of: linear polyester polyols, polyether polyols, polycarbonate polyols, polyacrylate polyols, and a combination of at least two of these. In a preferred embodiment, these (poly)alcohols or (poly)amines bear terminal alcohol and/or amine functionalities. In another preferred embodiment, the molar mass of the (poly)alcohols and/or (poly)amines is 52 to 10 000 g/mol. It is preferable that these (poly)alcohols or (poly)amines as starting materials have a melting point in the range from 5 to 150° C. Preferred polyisocyanates, at least a proportion of which can be used for the production of the fusable polyurethanes, are TDI, MDI, HDI, PDI, H12MDI, IPDI, TODI, XDI, NDI and decane diisocyanate. Particularly preferred polyisocyanates are HDI, PDI, H12MDI, MDI and TDI.
[0051]It is likewise preferable that the functionalization composition comprises a polycarbonate based on bisphenol A and/or on bisphenol TMC.
[0052]Alternatively it is possible that the functionalization composition is a metal. In this embodiment, the application sectors of the functionalized workpieces can be in medical technology, in the air travel sector, in the automotive sector or in the jewelry production sector. Suitable metals for the functionalization composition comprise, for example, tool steels, maraging steels or martensite-hardening steels, stainless steel, aluminum or aluminum alloys, cobalt-chromium alloys, nickel-based alloys, for instance superalloys, titanium and titanium alloys, for example in commercial purity, copper and copper alloys, or precious metals, for instance gold, platinum, palladium, silver. The functionalization is constructed layer-by-layer in the process of the invention. If the number of repetitions for application and irradiation is sufficiently small, the article that is to be constructed can also be described as two-dimensional. This type of two-dimensional article can also be characterized as a coating. By way of example, the number of repetitions carried out for application and irradiation for construction thereof can be ≥2 to ≤20.
[0053]A process for the production of a functionalization on a film preferably comprises by way of example the steps of:
[0054]I) deposition, on the film, of a resin that crosslinks by a free-radical route, thus obtaining a layer of a build material connected to the film;
[0055]II) deposition, onto a previously applied layer of the build material, of a resin that crosslinks by a free-radical route, thus obtaining a further build material layer connected to the previously applied layer;
[0056]III) repetition of step II) until the functionalization has been formed;
[0057]where the deposition, at least in step II), of a resin that crosslinks by a free-radical route is achieved by photoirradiation and/or other irradiation of a selected region of a resin that can be crosslinked by a free-radical route, in accordance with the respectively selected cross section of the functionalization.
[0058]In this embodiment it is moreover optionally possible after step III) to carry out a further step IV):
[0059]IV) treatment of the functionalization obtained after step III) under conditions sufficient to obtain, by exposure to further high-energy radiation and/or by thermally induced post-curing, postcrosslinking in the resin crosslinked by a free-radical route.
[0060]In this embodiment, therefore, the functionalization is obtained in two production phases. The first production phase can be regarded as the construction phase. This construction phase can be realized by means of photoradiative additive manufacturing processes such as the inkjet process, stereolithography or the DLP (digital light processing) process, and is provided by the steps I), II) and III). The second production phase can be regarded as curing phase and is provided by the step IV). Here, the functionalization obtained after the construction phase is converted to a more mechanically durable article without further alteration of its shape.
[0061]In step I) of the embodiment, a resin crosslinked by a free-radical route is deposited on the film. This is usually the first step in inkjet, stereolithography and DLP processes. A layer of a build material connected to the film is thus obtained and corresponds to a first selected cross section of the precursor.
[0062]In step III), step II) is rep