DE102015120535A1 - Apparatus and method for producing a double-sided microstructured film - Google Patents

Abstract

The invention relates to a device and a method for producing a film microstructured on both sides (13) as well as a film microstructured on both sides produced by the method (13). The device comprises:
- A coating unit (20) with which a UV-curable material (21) can be applied to both sides of a film;
- a rotatable first roll body (4) having a microstructure on its roll surface (2), the first roll body (4) being arranged so that the roll surface (2) can impress the microstructure on a first sheet side of the coated sheet (12);
- A rotatable second roller body (5) having a microstructure on its roll surface (2), wherein the second roller body (5) is arranged so that the roller surface (2) can impart the microstructure on a second film side of the coated film (12); and
- At least one of the roller bodies (4,5) associated with UV radiation source (3).

Description

The invention relates to a device and a method for producing a film microstructured on both sides as well as a film produced by the process.

Technological background

Controlling the surfaces of flexible substrates with fine, defined structures is of great importance in many technological applications, such as in flexible electronics, microfluidics, in electronic circuits or in the production of flexible displays. The scale on which these surfaces are to be produced precisely extends to the micro-scale. Then one speaks of microstructures. A special task is to produce flexible substrates on both sides with high coverage accuracy.

In Kang et al., Sci. Rep. 4, 5387 (2014) the printing of RFID components is investigated and different layers applied on one side. The accuracy of the functional layers significantly determines the functionality of the overall component. In addition to the dimensions of the patterns in the individual layers, the accuracy of overlaying the patterns is another important feature. The coverage accuracy achieved between the individual layers is in the range of ± 30 μm. In this case, the production of the structured elements was carried out sequentially at several stations, whereby various inaccuracies with respect to the exact location and thus the coverage accuracy can be expected. The determination of overlay accuracy at different positions shows that issues of substrate stability also play an important role.

Current applications requiring high coverage accuracy in roll-to-roll production include: manufacturing flexible displays, flexible-carrier electronic circuits, and flexible electronics.

Current methods for achieving high registration accuracy include fixing a film to a rigid substrate with subsequent processing and release of the film prior to use (display).

In DE 10 2013 106827 A1 describes the problem of congruent production (registration accuracy) of photomasks, which can also be caused by the distortion of the substrate. In this case, a high accuracy despite marks in the edge area is not accessible over the entire surface. The proposed solution is based on the application of an inherent mask, which is subsequently transferred into different functional layers. The disadvantage here is that this inherent masking layer remains permanently in the product; In addition, only one-sided registration is possible.

Well-known techniques for the production of surface structures by exposure are known in CH 697447 discussed. The UV exposure for the microstructuring of curable photoresists in several steps on planar substrates is in GB 20090001958 shown. In this case, different masks, pattern surfaces and methods can be used to copy surface microstructures or locally dissolve the photopolymer deposited on the surface and thus obtain a diverse structured surface.

Basic methods of microstructuring using photohardenable materials and planar or cylindrical masks are in US 5,259,926 shown. Here, in a multi-step process, a certain substrate surface is provided with microstructures.

The production of a coverage accuracy in UV curing of photopolymers with UV light is described in US 2002/098426 represented and used for this purpose separate structures in the mask.

The commonly practiced procedure of curing photohardenable materials over a UV transparent substrate during contact with a microstructured metal cylinder is exemplified in US Pat WO 2008/086116 A1 listed. Here one side of the strip material is coated by UV drying of photohardenable materials but no overlay accuracy is produced.

In DE 69618929 T2 describes a glass roller with internal UV lamp, which serve for the production of coatings by curing a photocurable material. However, the glass roller carries no defined structures to be transferred to the substrate. The glass roller serves to press and forward the UV light of the UV lamp mounted therein. Consequently, there are no demands on high accuracy or registration accuracy nor on microstructuring of the surface by use of the glass roll.

The structure transfer by curing a photohardenable material to produce patterns on flat substrates is shown in FIG EP 0 623 440 A1 shown. The used glass roller made of ULE is provided on the surface with patterns that transfer to a flat substrate by UV irradiation of a photocurable material become. The fabricated structures provide a pattern of high accuracy, but without the need for overlay accuracy.

In DE 60 007 535 T2 For example, a photocurable material which is in contact with a smooth surface of a roll body or a film is hardened by a UV radiation source. The film produced in this way has special properties for displays which are described by a certain thickness, high transparency and low scattering. A liquid display was made of this.

Current technological advances focus on transferring production processes to flexible substrates to save costs, simplify products, and ensure flexibility of use. First of all, the standard processes such as layer deposition, etching and structure definition have to be transferred to flexible substrates. The standard solution of thin-film technology, the combination of layer deposition, photolithography and etching already poses considerable challenges for roll-to-roll operation.

Particular challenges are placed on the structure definition, which is characterized not only by the resolution but also by the overlap accuracy.

In DE 10 2013 203 829 A1 describes an apparatus and an injection molding process for producing double-sided microstructured composite films exhibiting different plastic-elastic behavior on the top and bottom. The composite film, which consists of at least two film layers or layers, has locally defined sections with hydrophobic and / or hydrophilic properties on the surface. The device comprises a two-part molding tool which has a male part and a die which are arranged relative to one another such that an adjustable gap with a width of 10 μm to at least 500 μm is adjustable between them. The male part has surface formations between 1 and 100 μm on the side directed towards the gap as a negative for desired different microstructures. The matrix is permeable to UV radiation and also has recesses on the side directed toward the gap in coordination with the surface formations of the male part.

The usually sequential successive microstructuring by copying techniques such as printing, lithography or embossing requires a reorientation of substrate and copy master z. B. at each structuring step. Here, the consideration of changes in the carrier, such as the film is required; Dimensional changes of the carrier cause changes in the position of the reference or functional structure and thus have a significant influence on the functionality.

These changes of the wearer can u. a. caused by mechanical or thermal influences, as you experience during embossing.

Summary of the invention

• – eine Beschichtungseinheit, mit der ein UV-aushärtbares Material beidseitig auf eine Folie auftragbar ist;
• – einen drehbaren ersten Walzenkörper mit einer Mikrostruktur auf seiner Walzenoberfläche, wobei der erste Walzenkörper so angeordnet ist, dass die Walzenoberfläche die Mikrostruktur auf einer ersten Folienseite der beschichteten Folie aufprägen kann;
• – einen drehbaren zweiten Walzenkörper mit einer Mikrostruktur auf seiner Walzenoberfläche, wobei der zweite Walzenkörper so angeordnet ist, dass die Walzenoberfläche die Mikrostruktur auf einer zweiten Folienseite der beschichteten Folie aufprägen kann; und
• – zumindest eine den Walzenkörpern zugeordnete UV-Strahlungsquelle.

One or more of the described disadvantages of the prior art are achieved or at least mitigated with the aid of the device according to the invention for producing a film microstructured on both sides. For this purpose, the device comprises:

• A coating unit with which a UV-curable material can be applied to a film on both sides;
• A rotatable first roll body having a microstructure on its roll surface, wherein the first roll body is arranged so that the roll surface can impress the microstructure on a first sheet side of the coated sheet;
• A rotatable second roll body having a microstructure on its roll surface, wherein the second roll body is arranged so that the roll surface can impart the microstructure on a second sheet side of the coated sheet; and
• - At least one roller bodies associated with the UV radiation source.

The invention is based on the finding that the front and back of a coated film can be prepared simultaneously with microstructures with high coverage accuracy from a UV-curable material, if two roll bodies are provided with respective predetermined microstructures on the roll surface. The microstructures produced are hardened immediately after their formation by means of UV light.

The device comprises a coating unit with which a UV-curable material can be applied to a film on both sides. The coating unit thus has the task of applying the UV-curable material on the front and back of the film. For this purpose, the film is preferably pretreated to ensure better adhesion of the material to be applied to their surfaces. The pretreatment may include, for example, a cleaning and activation of the surfaces by corona discharge.

For this purpose, the coating unit comprises, for example, two rollers which are connected to the wetted material are wetted. The position of the two rollers is chosen so that the upper and lower side of the film can each be coated by a roller. Depending on the task or requirement for the end product, both sides of the film can be wetted with different coating materials. In addition, the thickness of the coating can be adjusted via the coating unit and can be adapted accordingly to the dimensions of the structures to be applied. Optionally, the layer thickness on both sides of the film may be different.

For example, the foil may be formed from a flexible plastic material and provided wound up on a roll.

The coating material contains a UV-curable component and so-called photoinitiators. The coating material may further contain additives, fillers, pigments, etc.

Suitable UV-curable components are, in particular, organic monomers and oligomers which have a functionality suitable for free-radical or cationic polymerization. UV irradiation initiates the polymerization reaction to high molecular weight polymer systems.

As a polymerization mechanism, both the free radical polymerization and the cationic polymerization is suitable.

For the radiation-initiated (photoinitiated) free radical polymerization, compounds which are assigned to the class of acrylates, methacrylates, acrylamides, methacrylamides, vinyl compounds or styrene compounds are preferably used as UV-curable (low molecular weight) components. The low molecular weight compounds are characterized in that they have at least one free-radically polymerizable group in the molecule. Crosslinkers are components having at least two polymerizable groups in the molecule. In addition, the components carry at least one other property-determining functionality. For the specific case of the acrylates with the general structure CH ₂ = CH-COOR and methacrylates with the general structure CH ₂ = CH (CH ₃ ) -COOR, the nature of the radical R is characteristic of properties. They may, for example, belong to the following commercially available classes: aliphatic and aromatic urethane acrylates, polyether acrylates, polyester acrylates, epoxy acrylates, acrylic acrylates, mono-, bi-, tri- or multifunctional acrylates.

The photoinitiators, which may typically be added to a formulation up to a level of 10%, include in the case of free radical polymerization, among others. the following classes: type I photoinitiators (eg benzoin derivatives, acetophenone derivatives, benzil ketals, alpha-hydroxyalkylphenones and alpha-aminoalkylphenones, O-acyl-alpha-oximinoketones, acylphosphine oxides and acylphosphonates, peroxy compounds) and type II photoinitiators (eg benzophenones, xanthones and thioxanthones , alpha-ketocoumarine, aromatic 1,2-diketones, phenylglyoxylates).

Components of the formulations for the photo-initiated cationic polymerization are compounds from the class of cycloaliphatic epoxides (eg 3,4-epoxycyclohexylmethyl-3 ', 4'-epoxycyclohexanecarboxylate), epoxides, epoxidized compounds such as epoxidized linseed oil, vinyl ethers, polyols, oxetanes, hydroxy compounds, Ether compounds and siloxanes. These have at least one cationic polymerizable group. Analogously to the free-radical polymerization, crosslinking agents are components which have at least two polymerizable groups.

The photoinitiators include in the case of cationic photopolymerization u.a. the following classes of compounds: onium salts (aryldiazonium salts, diaryliodonium and triarylsulfonium salts, phenacylsulfonium and 4-hydroxyphenylsulfonium salts, sulfoxonium salts) and mixed ligand-arene-cyclopentadienyl metal salts. Cationic and free radical polymerization can compete in hybrid systems.

The apparatus further comprises (i) a rotatable first roll body having a microstructure on its roll surface, wherein the first roll body is arranged so that the roll surface can impress the microstructure on a first sheet side of the coated sheet, and (ii) a rotatable second roll body a microstructure on its roll surface, wherein the second roll body is arranged so that the roll surface can impart the microstructure on a second sheet side of the coated film. In other words, the film is passed through the device such that the two roll surfaces come into contact with the applied coating material and thereby impress the microstructure in the not yet cured material.

For microstructuring the coated film, two roll bodies are used, which typically have a cylindrical shape. The impressed microstructure is located on the lateral surfaces of the cylinder.

The microstructuring of metallic roller bodies themselves can be taken from the prior art, see in particular DE 10 2012 010 635 A1 , Here is one with a Concentrating lens with 60 mm focal length focused ultra-short pulse laser controlled guided over the roll body surfaces while material removed. The leading speed and number of passes determines the removal on the surface to be prepared. With a control unit, precisely defined surface structures are generated in a controlled manner. The roughness of the surface structures generated by the laser can, for example, be smoothed with a microwave-excited noble gas plasma jet, which is guided in a computer-controlled manner over the structured surface.

The microstructures on both roll bodies may be the same or different. Microstructures include in particular microscopically fine structures that can only be identified with optical aids.

The device further comprises at least one UV radiation source associated with the roller bodies. In particular, a UV radiation source is arranged in such a way that the contact area between the roll body surface and the coated film is irradiated by the UV light field. At typical wavelengths of 250 to 370 nm, the irradiance in the contact region can be, for example, 10 W / cm ² . The UV radiation source serves to provide the UV light needed to initialize the curing polymerization reaction. Due to the UV curing, a very fast impression is possible, as is necessary for the microstructuring of films. Furthermore, the energy input for the curing of non-thermal type, so that the microstructuring can be done at room temperature. As a result, advantageously no delay due to thermally induced displacements is required, nor is the distortion of the structure due to thermally induced deformations in the support of the structures to be expected.

The two roller bodies are preferably arranged relative to one another in such a way that the two roller surfaces face each other mirror-symmetrically with respect to the film extending between the roller bodies. In other words, in the contact area, each point of the film is equidistant from the centers of the roller bodies. As a result, the microstructures on both sides of the film with the highest precision at the same time impress. It is further preferred if at least one roller body is made of a UV-transparent material. In particular, quartz glass can be used as the UV-transparent material. Furthermore, the roll body consisting of UV-transparent material can have a UV radiation source arranged within this roll body. As a result, the UV light necessary for curing can be conducted directly to the contact area of the roller bodies with the coating material on the film. The microstructures produced are thus cured directly after their formation. It is therefore preferred if the UV radiation source is oriented so that the UV radiation is directed to a point of the shortest distance to both roll surfaces.

In the case of roll bodies consisting of quartz glass, the structuring of the surface can likewise be carried out with the aid of layer-removing ultrashort pulse lasers. Other methods of microstructuring such as printing and / or water or sandblasting or Ultraschallabtragverfahren and surface smoothing, z. As laser irradiation, chemical etching or flame polishing are applicable.

• a) Bereitstellen einer Vorrichtung der vorab geschilderten Ausführung;
• b) Beidseitiges Beschichten der Folie mit einem UV-aushärtbaren Material;
• c) Aufprägen einer Mikrostruktur auf einer ersten Folienseite mittels des ersten Walzenkörpers;
• d) Aufprägen einer Mikrostruktur auf einer zweiten Folienseite mittels des zweiten Walzenkörpers; und
• e) Aushärten der mikrostrukturierten Folie durch UV-Bestrahlung.

Another aspect of the invention relates to a method for producing a double-sided microstructured film. The method comprises the steps:

• a) providing a device of the above-described embodiment;
• b) coating the film with a UV-curable material on both sides;
• c) impressing a microstructure on a first side of the film by means of the first roll body;
• d) impressing a microstructure on a second side of the film by means of the second roller body; and
• e) curing of the microstructured film by UV irradiation.

In step a), therefore, the above-described device according to the invention for producing a film microstructured on both sides is provided.

The (optionally pre-prepared) film is fed in step b) a coating unit, which, as already stated above, may consist of two pairs of rotatable rollers with which the coating material is applied to both sides of the film.

The coated film is fed to the two roller bodies in step c) or step d) and thus brought into contact with the roller surfaces, so that the predetermined structure is impressed on the coated film.

For permanent preservation of the microstructure, the surface contour of the film is cured by photoinduced polymerization in step e).

The method is arranged in chronological order so that the step e) of curing preferably takes place immediately after or at the same time as the impressing of the microstructures in step c) or step d). This will ensure that from the roll surfaces imprinted microstructure does not or only minimally alters its shape before curing.

Film speeds in the range from 10 ^-3 m / s to 2 m / s are preferably specified for passing through the roll body surfaces of the coated film. This speed range is suitable to ensure a defined microstructuring.

The rotational speeds of the two roller bodies are synchronized with each other. The synchronous movement of the two roller bodies can be achieved by an electronic control of the two roller drives. The rotational speed of the roll surfaces can be controlled by local speed measurement on the roll surfaces and it can be carried out at present speed differences, a readjustment. The rotational movement is adjusted to the film speed so that the web speed of the roll surfaces coincides with the film speed. By fine adjustment of position and speed of the roll surfaces, a high overlap accuracy of top and bottom is achieved. Further, the two-sided patterning process of films is not limited to the microscale, but may be extended to mesoscale structures, for example, with even finer textured roll surfaces. Furthermore, auxiliary structures on the roller bodies are conceivable, which ensure the synchronous movement.

Finally, the invention relates to a double-sided microstructured film produced by the process described above. The double-sided microstructured film is characterized by a high coverage accuracy of the top and bottom. Together with the flexibility of the carrier material, this product is predestined for applications in the field of flexible electronics, microfluidics, electronic circuits or the manufacture of flexible displays.

Further preferred embodiments of the invention will become apparent from the other claims and the following description.

Brief description of the figures

The invention will be explained in more detail with reference to an embodiment and associated drawings. The figures show:

1 Schematic representation of the device according to the invention and the method for producing a double-sided microstructured film with a UV radiation source according to a first embodiment

2 Schematic representation of the device according to the invention and the method for producing a double-sided microstructured film with two UV radiation sources according to a second embodiment

Detailed description of the invention

1 shows a schematic device for producing a double-sided microstructured film 13 , The device is viewed in perspective in cross section. Statically, the device comprises a coating unit 20 and a structuring unit 30 ,

The coating unit 20 is exemplified by two pairs of rollers 22 realized, which are represented in this cross-sectional perspective as a circle. The rollers 20 are with the UV-curable material 21 wetted, which is represented by a thin circular ring. The coating unit 20 may alternatively consist of other rollers to a modified film guide and another order of the UV-curable material 21 to enable. Alternatively, other coating methods may be used, such as spraying, misting, slot die application, etc.

The structuring unit 30 comprises a first roller body 4 and a second roll body 5 , which are arranged opposite each other in pairs and are also shown as circles. The edge of both roll body 4 . 5 each represents a microstructured roll surface 2 represents.

The first roll body 4 consists of UV-opaque material 16 and is characterized by a lower transparency of the circle interior. The second roll body 5 consists of a UV-transparent material 15 , here quartz glass, and is characterized in the figure by a high transparency of the interior of the circle as such. In the interior of the second roller body 5 There is a UV radiation source 3 , the UV radiation 31 in the first roll body 4 and second roll body 5 emitted intermediate space emitted.

Dynamic is in 1 the following method is shown. A slide 10 is via a feeder 11 indicated by an arrow, the coating unit 20 fed. By contact of the film 10 with the UV-curable material 21 wetted surfaces of the rotatable rollers 22 creates the coating unit 20 as starting material one on both sides with UV-curable material 21 coated film 12 ,

Then the film coated on both sides 12 the structuring unit 30 supplied so that the double-coated film 12 at the same time in Contact with the roll surfaces 2 of the first roll body 4 and the second roller body 5 comes. Due to the synchronous rotation of the two roller bodies 4 . 5 becomes the microstructure of the coated film 12 embossed on both sides and by the UV radiation source 3 hardened. The discharge takes place 14 of the final product, a double-sided microstructured film 13 , The high coverage accuracy between the top and bottom of the double-sided microstructured film 13 is schematically characterized by triangular profiles on both sides, which are arranged mirror-symmetrically with respect to the film.

2 shows a schematic device for producing a double-sided microstructured film 13 according to a second embodiment. In contrast to 1 exist both roll body 4 . 5 made of UV-transparent material 15 and each have one within the roller body 4 . 5 arranged UV radiation source 3 , The UV radiation sources 3 are symmetrical with respect to the coated film 12 arranged and thus irradiate both sides of the film with UV radiation 31 , The advantage of this arrangement is that even for coated films 12 that are non-transparent to UV radiation 31 are, a two-sided curing of the through the roller body 4 . 5 is ensured impressed microstructures.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013106827 A1 [0006]
• CH 697447 [0007]
• GB 20090001958 [0007]
• US 5259926 [0008]
• US 2002/098426 [0009]
• WO 2008/086116 A1 [0010]
• DE 69618929 T2 [0011]
• EP 0623440 A1 [0012]
• DE 60007535 T2 [0013]
• DE 102013203829 A1 [0016]
• DE 102012010635 A1 [0033]

Cited non-patent literature

• Kang et al., Sci. Rep. 4, 5387 (2014) [0003]

Claims (10)

Device for producing a double-sided microstructured film ( 13 ), comprising - a coating unit ( 20 ), with which a UV-curable material ( 21 ) on both sides of a film ( 10 ) is orderable; A rotatable first roll body ( 4 ) with a microstructure on its roll surface ( 2 ), wherein the first roll body ( 4 ) is arranged so that the roll surface ( 2 ) the microstructure on a first film side of the coated film ( 12 ) can imprint; A rotatable second roller body ( 5 ) with a microstructure on its roll surface ( 2 ), wherein the second roll body ( 5 ) is arranged so that the roll surface ( 2 ) the microstructure on a second film side of the coated film ( 12 ) can imprint; and - at least one of the roller bodies ( 4 . 5 ) associated UV radiation source ( 3 ). Device according to Claim 1, in which the two roller bodies ( 4 . 5 ) are arranged to one another such that the two roll surfaces ( 2 ) mirror-symmetric with respect to the between the roll bodies ( 4 . 5 ) coated film ( 12 ) are opposite. Apparatus according to claim 1 or 2, wherein at least one roll body, ( 4 ) or ( 5 ), of a UV-transparent material ( 15 ) is made. Device according to claim 3, wherein the layer of UV-transparent material ( 15 ) existing roll body arranged within this roller body UV radiation source ( 3 ) owns. Device according to Claim 4, in which the UV radiation source ( 3 ) is oriented so that the UV radiation ( 31 ) to a point of the shortest distance to both roll surfaces ( 4 . 5 ). Process for producing a double-sided microstructured film ( 13 ), comprising the steps of: a) providing a device according to one of the preceding claims; b) Double-sided coating of the film ( 10 ) with a UV-curable material ( 21 ); c) imprinting a microstructure on a first side of the film by means of the first roll body ( 4 ); d) impressing a microstructure on a second side of the film by means of the second roller body ( 5 ); and e) curing the microstructured film by UV irradiation ( 31 ). The method of claim 6, wherein the step e) of curing takes place immediately after or simultaneously with the imprinting of the microstructures in step c) or step d). The method of claim 6 or 7, wherein a film speed is in the range of 10 ^-3 m / s to 2m / s. Method according to one of Claims 6 to 8, in which a rotational speed of the two roller bodies ( 4 . 5 ) is synchronized. Double-sided microstructured foil ( 13 ) prepared by a process according to any one of claims 6 to 9.

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