DE102012110048B3 - Producing molding comprises providing composite of substrate and workpiece, coating with metallic conductive layer, embossing other structures in existing structures of workpiece by metallic conductive mold insert and cooling mold insert - Google Patents

Abstract

Producing a molding comprises: (a) providing a composite (11) of a substrate (10) and an workpiece (20) applied to it and made from a thermoplastic; (b) coating at least one of the structures of the workpiece with a metallic conductive layer (40), which is connected to a conductive metal surge arrester; (c) embossing the other structures in the existing structures of the workpiece by a metallic conductive mold insert having cavities; and (d) cooling the mold insert below glass transition temperature and then demolding the composite of the substrate and modified work piece. Producing a molding comprises: (a) providing a composite (11) of a substrate (10) and an workpiece (20) applied to it and made from a thermoplastic, whose structures protrude a height above the workpiece; (b) coating at least one of the structures of the workpiece with a metallic conductive layer (40), which is connected to a conductive metal surge arrester; (c) embossing the other structures in the existing structures of the workpiece by a metallic conductive mold insert having cavities, whose average diameter corresponds to more than half the average width of the existing structures, at a temperature above the glass transition temperature of the thermoplastic material of the workpiece; and (d) cooling the mold insert below glass transition temperature and then demolding the composite of the substrate and modified work piece located on it out of the mold insert. The surge arrester is electrically connected to the mold insert via a device for determining the electrical resistance and the mold insert is approximated to the existing structures, after the electric resistance has dropped below a limit value, when the mold insert has contacted the metallic conductive layer. An independent claim is also included for a device for manufacturing a molding, comprising a system with a mold insert for hot stamping, and for receiving a composite of a substrate and a deformable workpiece on one side and the mold insert on opposite side, where means for determining the electrical resistance is provided for an electrically conductive mold insert which has a device for receiving an electrically conductive connection with an electrically conductive arrester.

Description

The invention relates to a method and a device for producing a shaped body, in particular a shaped body, which has at least two hierarchically arranged structural planes. Hierarchical is understood to be a structure of a structure in which at least one hierarchical level follows a preceding hierarchical level in such a way that the structures of the preceding hierarchical level in each case form the substrate for the structures of the subsequent hierarchy level.

The physical cause why geckos can walk on vertical walls and even on ceilings has been studied extensively in recent years, see K. Autumn, How Gecko's Toes Stick, American Scientist 94, p. 124, 2006. It is now known that the toes of geckos consist of small, very fine hairs, the so-called Setae, which adhere to any surface due to the van der Waals forces. In order for a gecko weighing several hundred grams to adhere to the ceiling, the setae, which are considered as the first hierarchical level, each have a multiplicity of nanostructured hairs called spatulas applied as the second hierarchical level (see E. Arzt, p. Gorb and R. Spolenak, From Micro to Nano Contacts in Biological Attachment Devices, PNAS 100, p. 10603, 2003).

The nature of the structure of the hierarchies is crucial for the function of the setae: Since the liability of the geckos mainly on the so-called Van der Waals forces, d. H. comparatively low and short-range forces, the hairs must adapt perfectly to rough surfaces in order to obtain a high contact surface with the ground. The setae, however, consist of β-keratin, d. H. a stiff fiber protein with a modulus of elasticity between 1 and 4 GPa. To ensure the necessary adaptability despite this stiff material, the hairs must be hierarchical. In fact, due to their hierarchical structure, the effective modulus of elasticity of the setae is only 100 kPa, 4 orders of magnitude less than the unstructured β-keratin. As a result, the Setae are very cuddly, which causes a high actual contact surface with almost any surface.

From the DE 10 2008 053 619 A1 For example, a method for producing a technical molding having hierarchical structures is known. For this purpose, a layer of a thermosetting plastic between two parallel, thermally conductive plates are introduced, a pressing pressure applied between the two plates and the two plates heated so that the layer is heated to a temperature above the glass transition point of the plastic. The two plates differ in that they have on their surface a different adhesive force or roughness or they are heated to two different temperatures.

Subsequently, the two plates are pulled apart while maintaining the temperature, whereby the layer adheres to one of the two plates, while forming on the other plate a plurality of first threads. After curing of the plastic, a substrate, on which a plurality of first threads is applied, obtained and introduced between two parallel, thermally conductive plates. After applying a pressing pressure and heating the two plates to a temperature above the glass point, the two plates are pulled apart while maintaining the temperature, whereby the substrate adheres to one of the two plates, while at the other of the two plates a plurality of second threads , whose undersides are each firmly connected to the surface of each first thread forms.

Also, M.P. Murphy, S. Kim, M. Sitti, Enhanced Adhesion by Gecko-Inspired Hierarchical Fibrillar Adhesives, ACS Appl. Materials & Interfaces 1, 849, 2009, the production of a technical molding with hierarchical structures. In this case, the curing of pourable two-component polyurethanes is initiated by means of initiators. The production of the first hierarchical level takes place with the aid of etched silicon wafers, which are usually destroyed for demolding. The second hierarchical level is produced by a so-called inking process, in which the ends of the first level are immersed in uncured polyurethane, after which the ends are placed on an etched silicon wafer. The still liquid polyurethane on the ends of the first structure is now drawn by capillary action into the cavities of the mold insert and cures there after some time. In order to demould the hierarchical level, the silicon wafer has to be destroyed again. The smallest structures shown have only a diameter of 3 microns.

Proceeding from this, it is the object of the present invention to propose a method and a device suitable for this purpose for producing a shaped body, in particular a shaped body having at least two hierarchically arranged structural levels, which do not have the aforementioned disadvantages and limitations.

In particular, a method is to be provided with which a structure of at least two hierarchically arranged structural levels can be technically produced in the simplest possible way, thereby achieving high actuality Contact surfaces with almost any surface can be achieved that the smallest structures have diameters in the range of 50 nm to 5 .mu.m, in particular from 100 nm to 1 micron.

Furthermore, a device is to be provided which is particularly suitable for carrying out this method.

This object is achieved with respect to the method by the steps of claim 1 and with respect to the device by the features of claim 9. The subclaims each describe advantageous embodiments of the invention.

The at least two hierarchically arranged structural levels are built up in succession by a modified hot stamping process. For this purpose, the method according to the invention has the method steps a) to d).

According to step a), first of all a composite is provided which has a substrate and a workpiece applied thereon made of a thermoplastic, which also includes thermoplastic elastomers and shape memory polymers. The workpiece here has structures that protrude a height h ₁ over the workpiece. Particularly suitable for the process of the invention are the thermoplastics polycarbonate, polystyrene, methyl methacrylate / acrylonitrile / butadiene / styrene polymer (MABS polymers), cyclo-olefin copolymers, polymethyl methacrylate, polylactides, and polytetrafluoroethylene.

In a preferred embodiment, a first mold insert, which has first cavities, which are preferably introduced into the first mold insert in the form of microstructures, is hot-stamped into the workpiece with a first mold insert. It is crucial that the hot embossing at a temperature above the glass transition temperature T _{g of} the thermoplastic material and the subsequent cooling of the first mold insert below T _g occur before the composite is finally removed from the first mold insert.

The reproducible production of structures produced according to the invention having at least two, preferably at least three levels of hierarchy requires exact contacting with the already existing structures during embossing. Since the structures are sometimes only a few micrometers high, the accuracy of the attack must be in the submicrometer range. The unpredictable temperature expansion of the machine and the component and the manufacturing tolerances (residual layer thickness) require a very flexible, and independent of the height of the structures detection method. These requirements fulfill neither optical nor force-based detection methods with reasonable effort.

Optical measuring devices would have to be constantly aligned with the structure, a procedure that is not effective for micro- and nanostructures. In addition, such measuring devices would have to withstand temperatures of at least 450 ° C.

In contrast, a force-based measuring device would have to have a resolution in the range of a few μN and be located directly behind the mold insert in order to measure as few disturbing variables as possible. Nevertheless, the estimated disturbances are still too large to detect the contact between the mold insert and the structure. At the same time, forces of up to 1000 kN act during the stamping process. These enormous forces would simply destroy such a measuring device.

According to the invention, the reproducible production of hierarchically arranged microstructures and nanostructures takes place by means of an electrical resistance measurement. For this purpose, according to step b), individual, already existing, microstructures having a metallically conductive layer, preferably a gold layer, having a thickness of 1 nm to 200 nm, preferably from 5 nm to 100 nm, particularly preferably from 10 nm to 25 nm coated (gilded), which is enough to make them electrically conductive. During the process, the electrical resistance between the respectively used metallically conductive mold insert and the gold-plated microstructures (reference structures) is preferably measured continuously, but at least during step c) and, if this is carried out, also during step e). For this purpose, the metallically conductive layer must be connected to an electrically conductive arrester, which allows electrical contact with the mold insert used. If the mold insert touches the structures during the approach, the electrical resistance drops abruptly. The embossing is then carried out for a certain time after the electrical resistance has dropped below a predefined limit, during which time the mold insert imprints new structures into the already existing structures heated above T _g .

Proper placement of the reference structures also enables process monitoring. On large areas, even the smallest wedge errors between the mold insert used in each case and the existing structure can lead to an uneven embossing result on the associated hierarchical level. This is because portions do not come in contact while others are crushed. By means of three Reference structures, which are preferably arranged as uniformly as possible circularly around the center of the workpiece, such errors can be easily detect and correct.

According to step c), following step b) with a metallic mold insert having cavities whose average diameter is smaller by at least a factor of 2, in special cases also by a factor of 100 or higher, compared to the already formed structures in the workpiece, another hierarchical level is impressed on the already existing structures of the preceding hierarchy level in the workpiece. As a result, the structures of the preceding hierarchical level are flattened at the end, resulting in a characteristic mushroom-shaped structure, which has a positive effect on the adhesion, by leading to an increase in the surface and allows a homogenized force application.

According to step d), the mold insert is subsequently cooled to a temperature below T _g following step c), and then the composite of the substrate and the modified workpiece, which is located on the substrate, is removed from the mold insert.

In a particular embodiment, steps c) and d) are repeated in order to produce a further hierarchical level in this way. For this purpose, it may be necessary in individual cases to renew the reference structures on the workpiece in each case beforehand. In general, when using gold-plated microstructures, however, a single application is sufficient for several hierarchical levels.

In a particular embodiment, the desired shaped body is provided with a particular last level of hierarchy by applying a drawing method following step d) according to steps e) and f). For this purpose, a special metallic conductive mold insert is used which is provided with nanostructures at least at those points where the structures of the preceding hierarchical level are located.

According to step e) is analogous to step c) is impressed, the nanostructure of the nanostructured form used in the previous level of the hierarchy: However, it is in the final step f) of the composite from the substrate and which then finally disposed modified workpiece above the T _g of the nano-structured mold insert smallest threads pulled out of the previously embossed structures.

The method according to the invention is suitable for the production of hierarchical microstructures and nanostructures, in particular for optical elements, integrated fluidic chips, resonators, as well as for the production of hierarchical gecko structures which can serve as adhesion devices, in particular as adhesive tapes or patches.

It has been shown that without the high-precision probing of micro- and nanostructures during the replication process hierarchical micro- and nanostructures are simply irreproducible to produce. The inventive method also allows a process control by a constant check of the wedge error between mold insert and structure. Finally, the method according to the invention is scalable, cost-effective and thus mass-suitable.

The invention is explained in more detail below with reference to exemplary embodiments and the figures. Show it:

1 Schematic representation of a first embodiment of the invention;

2 Schematic representation of the first steps of another embodiment of the invention;

3 Resistance signal and position when probing a gold pin with a flat steel plate;

4 Resistance signal and position when probing six gold pins of different height with a flat steel plate.

In 1 schematically a first embodiment of the invention is shown. 1a) and 1b) show the preparation of the composite 11 by impressing structures 211 . 212 . 213 in an unmodified workpiece 20 by approaching a first mold insert 31 , the cavities 311 . 312 . 313 whose diameter corresponds to the width of the structures to be produced 211 . 212 . 213 correspond, at a temperature above the glass transition temperature T _{g of} the thermoplastic material to the unmodified workpiece 20 , This is followed by the first mold insert 31 cooled to below T _g and finally the composite 11 from the first mold insert 31 removed from the mold.

In 1c) is shown as in step b) a structure 211 of the provided after step a) workpiece 20 ' with a gold layer 40 is provided. To make an electrical connection to the gold layer 40 to enable the gold layer 40 For this purpose with a metallic conductive arrester 41 , here a gold wire, connected.

1d) and 1e) show the impress of other structures 211 ' . 212 ' . 213 ' in the existing structures 211 . 212 . 213 of the workpiece 20 ' , This process is carried out by approximation of a metallically conductive mold insert 32 , the cavities 321 . 322 . 323 whose average diameter is at most half the average width of the existing structures 211 . 212 . 213 correspond, at a temperature above the glass transition temperature T _{g of} the thermoplastic polycarbonate, from which the workpiece 20 ' consists.

During the embossing process, the gold layer 40 over the arrester 41 and via a device for determining the electrical resistance electrically conductive with the metallic conductive mold insert 32 connected. For this purpose, the known so-called. Four-point method is used, the four wires 41 . 42 . 43 . 44 for the measurement, namely two wires 41 . 42 for the voltage measurement 45 and two more wires 43 . 44 for the power source 46 , needed. This method has the advantage that the resistance of the supply line does not falsify the measurement. An analog input module also serves as a power source 46 as and voltmeter 45 for determining the voltage V and is connected to the electrically conductive mold insert 32 and the gold layer 40 wired.

The analog input module outputs a known current pulse I via the current source during the measurement 46 in the circuit; the resistance V is with the voltmeter 45 according to the ohmic formula R = V / I calculated. If the resistance R thus determined falls below a previously defined limit, this indicates that the electrically conductive mold insert 32 with the gold layer 40 is electrically connected and thus the embossing process starts. From the start time, the mold insert 32 for a time to the existing structures 211 . 212 . 213 approximated. In this way it is ensured that the impression of the other structures 211 ' . 212 ' . 213 ' actually takes place where the existing structures 211 . 212 . 213 are located.

In 1f) is schematically the introduction of last structures 211 ' ' 212 '' . 213 '' into the previously embossed structures 211 ' . 212 ' . 213 ' of the modified workpiece 20 '' according to step e) by approaching a metallically conductive nanostructured mold insert 33 shown at a temperature above T _g . Again, during the imprinting process, the gold layer 40 over the arrester 41 and the four-point measurement electrically conductive with the metallically conductive nanostructured mold insert 33 connected. If the value for the resistance thus determined also falls below a previously defined limit value, the embossing process is started and the nanostructured mold insert 33 for a time to the previously imprinted structures 211 ' . 212 ' . 213 ' approximated. In this way, it is also ensured here that the impressions of the last structures 211 '' . 212 '' . 213 '' actually takes place where the previously embossed structures 211 ' . 212 ' . 213 ' are located.

1g) shows the drawing process according to step e). This is the composite 11 from the substrate 10 and the last modified workpiece located thereon 20 ''' namely - in contrast to step d) and to 1e) Above (!) The glass transition temperature T _{g of} the thermoplastic from the nanostructured mold insert 33 drawn. This succeeds in the surfaces of the previously imprinted structures 211 ' . 212 ' . 213 ' with threads 221 to provide.

Finally shows 1h) as during step b) with a metallic conductive layer 40 providing structures 211 '' following step f) in 1g) from the rest of the modified composite 11 '' were separated, so that finally the desired shaped body, which in this case has three levels of hierarchy, was obtained.

In 2 The first steps of a further method for producing a shaped article according to the invention are shown schematically. 2a ) shows - in contrast to 1a) - as before the impressions of the structures 211 . 212 . 213 the first hierarchical level an electrically insulating layer 50 Kapton between a part of the unmodified workpiece 20 and the substrate 10 is inserted. At the same time here is on the unmodified workpiece 20 a later than arrester 41 Serving wire piece of gold.

Both the electrically insulating layer 50 as well as the later as arrester 41 serving wire piece are then, as in 2 B ), together with the unmodified piece of work 20 through the mold insert 31 accordingly in the composite 11 imprinted with. This saves you in step b), as a trap 41 Serving wire piece with the thin gold layer 40 to have to contact. In addition, the electrically insulating layer prevents 50 that a short circuit between the substrate 10 , which is usually also made of metal, and the gold layer 40 occurs.

3 shows the resistance (solid line) and the position (dashed line) during the probing of a gold-plated pin which has been touched with a flat steel plate. While no increase in force could be observed with the embossing plant, the resistance signal fell sharply during contact between the electrically conductive insert and the gold layer, since now flows through the contact, a current.

4 shows six, each with a gold layer provided pins of different height, which were touched with a flat steel plate. The resistance signal (solid line) shows every single contact. The dashed line shows the respective position of the steel plate. In further experiments probing accuracies of up to 50 nm could be determined.

The 3 and 4 prove the above-mentioned fact that without the high-precision probing of micro- and nanostructures during the replication process hierarchical micro- and nanostructures are simply not reproducible to produce.

LIST OF REFERENCE NUMBERS

10

substratum

11, 11 ', 11' '

composite

20, 20 ', 20' ', 20' ''

workpiece

211, 212, 213 etc.

Structures on the workpiece

221

threads

31, 32

(microstructured) mold inserts

311, 312, 313, 321 etc.

Cavities in the mold inserts

33

nanostructured mold insert

40

metallic conductive layer (gold layer)

41, 42

arrester; Conductor wires for voltage measurement

43, 44

Wires for the power source

45

Device for voltage measurement

46

power source

50

insulating layer (Kapton)

Claims (10)

Process for producing a shaped article comprising the steps of a) providing a composite ( 11 ) from a substrate ( 10 ) and a workpiece applied thereto ( 20 ' ) of a thermoplastic material containing structures ( 211 . 212 . 213 ) having a height above the workpiece ( 20 ' b) coating at least one of the structures ( 211 ) of the workpiece ( 20 ' ) with a metallic conductive layer ( 40 ), the layer ( 40 ) with a metallic conductive arrester ( 41 c) Imprinting further structures into the existing structures ( 211 . 212 . 213 ) of the workpiece ( 20 ' ) by approach of a metallic conductive mold insert ( 32 ), the cavities ( 321 . 322 . 323 ) whose average diameter is at most half the average width of the existing structures ( 211 . 212 . 213 ), at a temperature above the glass transition temperature T _{g of} the thermoplastic material to the workpiece, wherein the arrester ( 41 ) on a facility ( 45 ) for determining the electrical resistance electrically conductive with the mold insert ( 32 ) and the mold insert ( 32 ) to the existing structures ( 211 . 212 . 213 ) is approached after the electrical resistance has dropped below a threshold value when the mold insert ( 32 ) the metallically conductive layer ( 40 ), d) cooling the mold insert ( 32 ) below T _g and subsequent demolding of the composite ( 11 ) from the substrate ( 10 ) and the modified workpiece located thereon ( 20 '' ) from the mold insert ( 32 ). The method of claim 1, wherein the composite ( 11 ) is produced by impressing the structures ( 211 . 212 . 213 ) in an unmodified workpiece ( 20 ) by approximation of a first mold insert ( 31 ), the cavities ( 311 . 312 . 313 ) whose diameter corresponds to the width of the structures ( 211 . 212 . 213 ) at a temperature above T _g to the unmodified workpiece ( 20 ), followed by cooling of the first mold insert ( 31 ) below T _g and final demolding of the composite ( 11 ) from the first mold insert ( 31 ). Method according to claim 2, wherein prior to impressing the structures ( 211 . 212 . 213 ) at least partially an electrically insulating layer ( 50 ) between the unmodified workpiece ( 20 ) and the substrate ( 10 ) and / or on the unmodified workpiece ( 20 ) of arresters ( 41 ) is launched. Method according to one of claims 1 to 3, wherein the steps c) and d) are carried out in this order at least twice in succession with the proviso that the last embossed structures apply as the existing structures, in which the other structures whose mean width be imprinted at most half the mean width of the existing structures. Method according to one of Claims 1 to 4, the following steps being carried out following step d): e) introduction of last structures ( 211 '' . 212 '' . 213 '' ) into the previously imprinted structures ( 211 ' . 212 ' . 213 ' ) of the modified workpiece ( 20 '' ) by approaching a metallically conductive nanostructured mold insert ( 33 ) at a temperature above T _g , the arrester ( 41 ) on the institution ( 45 ) for determining the electrical resistance in an electrically conductive manner with the nanostructured mold insert ( 33 ) and the nanostructured mold insert ( 33 ) to the existing structures ( 211 ' . 212 ' . 213 ' ) is approached after the electrical resistance has dropped below a threshold value when the mold insert ( 32 ) the metallically conductive layer ( 40 f) pulling the composite ( 11 ) from the substrate ( 10 ) and the last modified workpiece ( 20 ''' ) Above T _g of the nano-structured mold insert ( 33 ), whereby the surfaces of the previously imprinted structures ( 211 ' . 212 ' . 213 ' ) now threads ( 221 ) exhibit. Method according to claim 4 or 5, wherein the at least one of the structures ( 211 ) of the workpiece ( 20 ' ) before carrying out another step again with a metallic conductive layer ( 40 ). Method according to one of claims 1 to 6, wherein during step b) at least three structures, which are located at different locations of the workpiece, each with a metallically conductive layer ( 40 ). Method according to one of claims 1 to 7, wherein the during step b) with a metallically conductive layer ( 40 ) structures ( 211 ) following step d) or subsequent to step f) from the rest of the modified composite ( 11 '' ) are separated. Device for producing a shaped article according to the method according to one of claims 1 to 8, comprising a system with a mold insert ( 31 . 32 . 33 ) for hot stamping and for receiving a composite ( 11 ) from a substrate ( 10 ) and a deformable workpiece located thereon ( 20 . 20 ' . 20 '' ) on one side, and the mold insert ( 31 . 32 . 33 ) on the opposite side, characterized in that a device ( 45 ) is provided for determining the electrical resistance, on the one hand electrically conductive with the mold insert ( 31 . 32 . 33 ) and the other means for receiving an electrically conductive connection with an electrically conductive arrester ( 41 ), which connects to electrically conductive areas on the deformable workpiece ( 20 . 20 ' . 20 '' ). Apparatus according to claim 9, characterized in that there are further provided means for timing the hot stamping process, including a limit value for the electrical resistance.

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