Micro-structure having optical effects

Abstract

The invention relates to a micro-structure having partial structures which differ in shape, wherein each of the partial structures has an optically active surface and can be provided by a method comprising the step in which a surface element, which has a straight base line and an upper-side line which is non-parallel with the base line, is rotated about a rotational axis which, in the plane of the surface element, is perpendicular to the base line, as a result of which a circular sector is formed from the base line, and the optically active surface is formed from the upper-side line. The invention also relates to a method for producing a micro-structure, to an optical element carrying the micro-structure, and to the use of the optical element.

Description

Microstructure with optical effects Field of the invention The present invention relates to a microstructure with optical effects, a method for producing a microstructure, an optical element with the microstructure and the use of the optical element. State of the art WO 2009 / 013000 A2 discloses a security element for value documents with an optically variable structure, which comprises a first embossed structure composed of first embossed elements. The embossed structure is designed such that at least partial areas of the coating are visible when viewed from a first viewing angle and are at least partially concealed when viewed from a second viewing angle. Tilting the security element about a first axis thus creates a first tilting effect. The structure has a second embossed structure, which is arranged within the first embossed structure and generates a second tilting effect in addition to the first tilting effect. WO 2013 / 045056 A1 discloses a security element with an optically variable structure containing a raised embossed element, preferably in the shape of a cone or a spherical segment. The embossed element has a partial cutout, preferably in the shape of an arcuate partial segment, with the remaining conical or spherical segment portion forming an embossed element that exhibits desired optical effects, such as tilt effects, depending on the viewing angle. Problems to be solved by the invention However, the state of the art does not disclose structures that show high variability in the encoding of optical effects in surfaces of microstructures and can be easily manufactured. Therefore, it is the object of the present invention to provide optically variable structures with a high number of achievable optical effects when rotating and tilting. Summary of the invention The problem was solved by providing a microstructure with a circular base, where circular sectors of different structure have optically effective surfaces. The subject matter of the present invention includes in particular the following aspects: [1] Microstructure with substructures which differ from one another in their shape, wherein each of the substructures has an optically effective surface and can be represented by a method which comprises the step in which a surface element which has a straight base line and an upper side line which is non-parallel and non-perpendicular to the base line is rotated about an axis of rotation which is perpendicular to the base line in the plane of the surface element, whereby a circular sector is formed from the base line and the optically effective surface is formed from the upper side line, wherein the substructures can be represented by rotating about the same axis of rotation and differ from one another in their surface profile and in the angle of the upper side line to the base line. [1 -1] Microstructure according to aspect [1], wherein the microstructure has a height of less than 100 pm, preferably less than 20 pm, more preferably less than 10 pm. [1 -2] Microstructure according to one of the preceding aspects, consisting of (i) partial structures which can be produced by said method, or (ii) partial structures which can be produced by said method and structures which cannot be produced by said method. [1 -3] Microstructure according to one of the preceding aspects, wherein the partial structures that can be produced by said method additionally differ from one another in their shape in that they differ from one another in the curvature of the top line, the number of top lines, the distance of the top line from the base line and / or the radius of the circular sector. [1-4] A microstructure according to any one of the preceding aspects, wherein the top line (i) represents a single line, which may be straight or curved, or (ii) is a profile line of a profile composed of a plurality of independently selected profile lines. [1 -5] Microstructure according to any one of the preceding aspects, wherein the optically effective surface is a light-reflecting surface. [1 -6] Microstructure according to one of the preceding aspects, wherein the axis of rotation is located at the center or at an end point of the base line. [2] Microstructure according to aspect [1], wherein all substructures of the microstructure can be represented by the said method, wherein rotation is carried out around the same axis of rotation, whereby the base lines of the substructures together form a circular base area of ​​the microstructure. [3] Microstructure according to any one of the preceding aspects, in particular according to aspect [2], wherein the method comprises cutting out a part of the microstructure, whereby a base surface other than a circular base surface is formed from the base surface of the microstructure. [3-1] Microstructure according to aspect [3], wherein the base area formed by the cutting out is an angular structure, for example a square or hexagon. [3-2] Microstructure according to aspect [3] or [3-1], wherein the axis of rotation is located on a non-edge point, preferably on the center of the base area formed by the cutting out. [3-3] Microstructure according to one of the aspects [3] to [3-2], wherein the base surface formed by the cutting out is formed point-symmetrically around the intersection point with the rotation axis. [3-4] Microstructure according to one of the aspects [3] to [3-3], wherein the cutting creates cutting surfaces perpendicular to the base surface. [4] Microstructure according to one of the preceding aspects, wherein the top line of the surface element is a first line and the surface element has a second top line from which an optically effective surface is formed, wherein the first line and the second line are inclined upwards towards the rotation axis and the second line differs from the second line in the inclination towards the rotation axis. [4-1] Microstructure according to aspect [4], wherein the first line is further away from the axis of rotation than the second line. [4-2] Microstructure according to aspect [4] or [4-1], wherein the end point of the first line touches the end point of the second line. [5] Microstructure according to aspect [4], wherein the first line and the second line are profile lines of a top profile with multiple peaks and valleys. [5-1] Microstructure according to aspect [5], wherein the height of the profile is 1 to 50 pm. [5-2] Microstructure according to aspect [5] or [5-1], wherein at least one of the low points lies on the baseline. [6] Microstructure according to aspect [5], wherein the profile has a plurality of first profile lines and a plurality of second profile lines, wherein the first profile lines have the same or different angle of inclination to the axis of rotation and the second profile lines have the same or different angle of inclination to the axis of rotation and wherein first and second profile lines alternate and are preferably arranged directly one after the other. [6-1] Microstructure according to aspect [6], wherein the inclination angles of the first profile lines are equal and the inclination angles of the second profile lines are equal. [6-2] Microstructure according to aspect [6] or [6-1], wherein the first and second profile lines are straight. [6-3] Microstructure according to any one of aspects [6] to [6-2], wherein the upper endpoints of the first and second profile lines represent the high points of the profile and the lower endpoints of the first and second profile lines represent the low points of the profile. [6-4] Microstructure according to any one of aspects [6] to [6-3], wherein the first and second profile lines form a sawtooth-like profile. [6-5] Microstructure according to any one of aspects [6] to [6-4], wherein the rotation axis is perpendicular to one end point of the baseline and the profile extends from the other end point of the baseline to a point on the rotation axis. [7] Microstructure according to aspect [6], wherein the high points of several of the profile lines lie on a straight line perpendicular to the rotation axis and / or the low points of the profile lines lie on a straight line perpendicular to the rotation axis. [7-1] Microstructure according to aspect [7], wherein all peaks of the profile lines lie on a straight line perpendicular to the rotation axis. [7-2] Microstructure according to aspect [7] or [7-1], wherein the straight line on which the low points lie is the base line of the surface element. [8] A microstructure according to any one of the preceding aspects, which is or contains an embossed and cured polymer structure. [8-1] Microstructure according to aspect [8], wherein the optically active surface is a surface of the polymer structure. [9] Microstructure according to any one of the preceding aspects, wherein the optically effective surface is the surface of a coating of an embossed and cured polymer structure. [9-1] Microstructure according to aspect [9], wherein the coating comprises an optically effective coating, for example a colored or reflective metal-containing coating. [9-2] Microstructure according to aspect [9] or [9-1], wherein the coating comprises a protective layer. [9-3] Microstructure according to any one of aspects [9] to [9-2], wherein the coating comprises an optically effective coating and a protective layer applied thereto.

[0010] Method for producing a microstructure, comprising the following steps: (i) producing a partial structure representation by a method comprising the step of rotating a surface element having a straight base line and a top line non-parallel to the base line about an axis of rotation perpendicular to the base line in the plane of the surface element, whereby a circular sector is formed from the base line and the optically effective surface is formed from the top line; (11) producing a microstructure representation which comprises the partial structure representation obtained according to step (i) and at least one partial structure representation which is different in shape therefrom; and (iii) producing the microstructure based on the microstructure representation obtained in step (ii). [10-1] The method according to aspect

[0010] , wherein in step (iii) a microstructure according to any one of claims 1 to 9 is produced.

[0011] Method according to aspect

[0010] , wherein step (iii) comprises the following steps: (iii-1) producing an embossing tool as a negative of the microstructure representation obtained in step (ii); (iii-2) pressing the embossing tool obtained in step (iii-1) onto an uncured substrate to form an embossed substrate; and (iii-3) curing the embossed substrate obtained in step (iii-2) to form the microstructure. [11-1] The method according to aspect

[0011] , wherein the method is a nanoimprint lithography method. [11-2] The method of aspect

[0011] or [11-1], wherein the method comprises roll-to-roll embossing of a plurality of the microstructures.

[0012] A method according to aspect

[0010] or

[0011] , which comprises applying a coating to the optically active surface.

[0013] Microstructure obtainable according to a method according to any one of aspects

[0010] to

[0012] ,

[0014] Optical element with a carrier and a plurality of microstructures arranged on the carrier according to one of the aspects [1] to [9] or

[0013] , [14-1] Optical element according to aspect

[0014] , wherein the carrier is a polymer film.

[0015] Use of an optical element according to aspect

[0014] or [14-1] as a security element on valuable documents or as a decorative element. Advantages of the invention The present invention enables the encoding of a large number of different images in surfaces of microstructures. The microstructures can be used to create optical elements that create movement effects and / or 3D effects of the motif when tilted and rotated. The optical elements can be used as security elements on valuable documents or as decorative elements. The optical security features on valuable documents can be easily verified without any tools and are difficult to copy. Description of the characters In the figures, the arrow labeled H_max indicates the height of the microstructure and, in some embodiments, also represents the rotation axis. Alpha 1 and Alpha 2, or ai and 2, indicate the inclination angles of profile lines of the surface element. H_facet denotes the height of a profile line above the baseline. L_max-Sector denotes the length of the baseline of a surface element or a part thereof. If L_max-Sector denotes the total length of the baseline, it indicates the radius of the circular sector of the partial structure. Figures 1A and 1B show examples of equidistant rp-angle sectorization of square pixels in 4 (Figure 1A) and 8 images (Figure 1B). Figures 2A to 2C show surface elements for illustrating microstructures according to the invention according to embodiment 1. Figures 3A to 3C show surface elements for illustrating microstructures according to the invention according to embodiment 2. Figures 4A to 4C show surface elements for illustrating microstructures according to the invention according to embodiment 3. Figures 5A to 5C show surface elements for illustrating microstructures according to the invention according to embodiment 4. Figure 6 shows a microstructure according to the invention in plan view. Figure ? shows an example of an optical element according to the invention with a plurality of microstructures according to the invention. Embodiments of the invention The microstructure according to the invention is a three-dimensional structure, i.e., a microbody. Hereinafter, the microstructure according to the invention may be referred to simply as "the microstructure." The straight baseline may be referred to as "the baseline," and the top line non-parallel to the baseline may be referred to as "the top line." The microstructure preferably has dimensions below the millimeter range, i.e. in the micrometer range and below. The length and width or diameter is 10 pm to 2000 pm, preferably 20 pm to less than 1000 pm. The height can be 1 pm to 2000 pm, preferably less than 1000 pm. Thus, in embodiments, the microstructures can be designed so that they can be detected by touch. Preferably, however, the microstructure is very flat, with a microstructure height of 1 pm to 50 pm (cf. embodiments 2 to 4). Preferred is a shape with a length and width or diameter of 50 pm to less than 1000 pm and a height of 1 to 20 pm. The height of the profile is preferably 1 to 50 pm, more preferably 1 to 20 pm.Herein, the height of the microstructure refers to the distance between the baseline and the highest peak of the profile viewed in the rotation axis direction, while the height of the profile refers to the distance between the lowest trough and the highest peak of the profile viewed in the rotation axis direction. The microstructure according to the invention has substructures that differ from one another in their shape, each of these substructures being representable by the method defined herein, which can also be referred to as a rotation method. This means that the microstructure contains at least two such substructures. Each of these substructures is a partial solid of revolution and, in plan view, a circular sector. The other structures of the microstructure can be structures that cannot be represented by the rotation method. If all substructures of the microstructure can be represented by the rotation method, the microstructure as a whole is a solid of revolution. The partial structures differ from one another in their surface profile. This means that the top profile of a surface element which, when rotated, results in one of the partial structures differs from the top profile of a surface element which, when rotated, results in another of the partial structures. It follows that the microstructure has regions in which concentric lines around the axis of rotation show a height offset. According to the invention, the partial structure is defined by the expression that it “can be represented by a method which comprises the step in which a surface element which has a straight base line and a top line which is not parallel to the base line is rotated around a rotation axis which, in the plane of the surface element, is perpendicular to the base line is rotated, whereby a circular sector is formed from the base line and the optically effective surface is formed from the top line." With this expression, the shape of the partial structure is clearly defined by the representation method. An alternative to this is an exclusively structural definition, so that the above expression is interchangeable with the definition according to which a partial structure "represents a section of a solid body such that the base surface of the partial structure has the shape of a circular sector made up of two circular radii and a circular arc, wherein in the partial structure each section surface is perpendicular to the base surface and the intersection line of each section surface with the base surface represents a base line which is a circular radius of the circular sector, and wherein the section surface has a top line which is non-parallel to the base line and which is a profile line of the profile of the optically effective surface."The cutout areas correspond to the cutting areas when cutting out a piece of cake from a cake. The microstructure has optically effective surfaces. Visibility by the observer is a prerequisite for optical effectiveness. An optical surface can be visible when viewed from a first viewing angle and hidden when viewed from a second viewing angle. Optically effective surfaces are those that are visible from at least one viewing angle. The simplest optically effective surface has no coating and consists of the material of the microstructure. For example, the microstructure can contain a polymer whose surface reflects light and is therefore optically effective. However, optical effectiveness can also be imparted or modified by coating the surface. The optically effective surfaces on the microstructure result in optical effects when rotated and tilted, i.e. from different viewing angles (0, μp).Here, cp denotes a horizontal angle on the circular surface created by rotating the baseline around the rotation axis, and 0 denotes a vertical angle relative to this circular surface. Rotating the microstructure changes the viewing angle cp, while tilting or inclining changes the viewing angle 0. In the surface element, the orientation of the top line relative to the baseline is also denoted by the angle 0. The spatial orientation of the unit consisting of the surface element and the rotation axis is, of course, not restricted. However, for clarity, the following spatial orientation is assumed: The rotation axis and the surface element are vertical, defining "top" and "bottom," with the base line being the lower side and the upper line being part of the upper side of the surface element. The rotation occurs horizontally, so that the base line creates a horizontally positioned circular sector as the base area. The three-dimensional basic shape of the microstructure is not restricted and can be, for example, a tetrahedron, a spherical segment, a truncated pyramid, a cone, a truncated cone, a cylindrical segment, or a pyramid, or it can be composed of parts of the aforementioned basic shapes. Thus, the base area of ​​the microstructure is not limited to a circular shape either. The base area of ​​the microstructure can be composed of circular sector-shaped substructures and structures of other geometries. The method for representing the microstructure can also comprise, for example, cutting out part of the microstructure, thereby forming a non-circular base area from the circular base area, e.g., a square. However, the circular base area can also be part of the overall base area of ​​the microstructure, whereby the other part can be configured arbitrarily, resulting in an overall non-circular base area.Rectangular or square overall surfaces allow the microstructures to be arranged next to each other over a wide area. The microstructure according to the invention enables the encoding of a number of different images directly into the optically effective surfaces. This results in optical features that become visible at specific viewing angles relative to the surface and relative to the light source. By carefully selecting the images, an image sequence can be created that, when the surface is tilted and / or rotated, creates motion effects of the subject, similar to a film. The surface element A partial structure can be represented by rotating a surface element that has a base line and a top line that is non-parallel and non-perpendicular to the base line, around a rotation axis. Non-parallel means that a line is curved or that a straight line is perpendicular or inclined upwards or downwards towards the rotation axis. In the simplest case, the top line is a line that connects the base line to the rotation axis. This line is either straight, so that the surface element is a right-angled triangle, or curved. When rotated, the non-parallel top line creates an optically active surface. However, it is not impossible for a parallel profile line to also create an optically active surface. The surface element used in the rotation process corresponds to the cutout surface described above. The top surface can have any number of lines that are independently non-parallel to the base line. In addition, it can have any number of parallel lines. A top surface with several different lines is referred to herein as a profile. A profile can consist of several profile lines that are straight or curved and / or differ from one another in their length and / or their angle or orientation to the base line and thus also differ from the rotation axis. The profile can also be a combination of straight and curved profile lines, so that a profile has high points and low points connected by straight and / or curved profile lines. The high points can lie on one or several straight lines perpendicular to the rotation axis. The same applies to the low points. It is preferred that all high points lie on a first straight line and all low points lie on a second straight line parallel to the first straight line. The second straight line can lie on the baseline. The height of the surface element, i.e. the distance between the baseline and the profile, can be arbitrary. It may be preferred that the distance between the baseline and the lowest point of the profile is small, e.g. 50 nm to 1 pm, or even zero. An example of a top side is sawtooth-shaped, wherein in embodiments the individual sawteeth lie on the baseline and do not touch each other or only touch each other at one point. By rotating the profile around the axis of rotation, a solid body is formed which has elevations with high points and indentations with low points, as well as flanks between the high points and low points. The flanks are created by rotating the profile lines around the axis of rotation and result in the optically effective surfaces of the image element. The structure of the upper side of the surface element can be selected depending on the desired intensity values ​​of the optically active surfaces. The relative intensity values ​​of the individual substructures and microstructures from the respective 0,rp viewing angles can be calculated. The base area of ​​a circular microstructure can be divided into rp sectors, i.e., circular sector-shaped base areas of the substructures. Each sector of each microstructure is assigned an intensity value between 0 and maximum intensity, depending on the previously calculated intensity values ​​of the microstructure in the image of the optical element to be encoded. Suitable surface elements are calculated based on these intensity values ​​of the sectors, and the substructures of the microstructure are then represented from these. These substructures are then combined to form the shape of the microstructure. A partial structure produced by the rotation process forms a circular sector in plan view. The profile of a surface element for representing a partial structure or sector is calculated such that, in the microstructure, certain surface parts [A_ref] of the resulting total surface [A_ges] reflect incident light in at least one desired 0-viewing direction, and other surface parts [A_aus] block incident light from the desired viewing direction (e.g., by reflection in a different viewing direction or in a non-viewable direction). The proportion of these surface parts depends on the intensity value of the sector of the image to be encoded. [I_sector] and the maximum achievable intensity value [l_max] of the sector and is determined by the following formulas: A_ref / A_ges=l_sector / I_max (Formula 1) A_out=A_total-A_ref (Formula 2) This creates a brightness impression of the microstructure for the viewer in the desired 0-viewing direction that corresponds to the encoded images. According to the encoded brightness impression of the neighboring images, the brightness impression changes due to the different shapes of the substructures while maintaining the 0-viewing direction and simultaneously changing the rp-viewing direction, i.e., when rotating. The high number of optical effects of the microstructure results from the combination of sectors and the profiles of the sectors. The optical element The optical element (Figure 7) contains a plurality of microstructures according to the invention, which are arranged on a carrier and represent the pixels of the motif of the optical element. The optical element can, for example, be a security feature on a valuable document. Any carrier can be used, for example paper or a film. Materials for the film can be plastics, in particular PC (polycarbonate), PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate), PP (polypropylene), PA (polyamide) or PE (polyethylene), or biaxially oriented polypropylene (BOPP). The film can be translucent. The entire surface of the optical element is divided into individual microstructures with any base area (e.g. square, rectangular, hexagonal or generally a combination thereof), whereby geometries that cover the entire surface when arranged next to one another are preferred. Depending on the number of images to be encoded, the surface area of ​​the microstructures is divided into sectors (Figures 1A and 1B). The surface area of ​​the images to be encoded is also divided into the same microstructures, whereby the relative intensity values ​​of the individual microstructures of the images are calculated. The inventive approach enables the encoding of any number of different images directly into the structures of the surface of the optical security features, which become visible at specific viewing angles relative to the surface and relative to the light source. By a sensible selection of the images, this In this way, a sequence of images can be created which, similar to a film, creates the effect of movement in the subject when the surface is tilted and / or rotated. The number of images is fundamentally arbitrary; however, the maximum intensity and distinguishability of the images decrease with increasing numbers depending on the light source under which the images are viewed. Strongly parallel light, such as sunlight, allows for greater distinguishability, while more diffuse light, such as ambient light, permits less distinguishability. Therefore, in practical terms, there is a maximum number of images depending on the task and the subject. Production The partial structures can be manufactured based on the structures obtained by the imaging process. Known microstructuring methods can be used to create the microstructures, e.g., embossing processes such as nanoimprint lithography (NIL). Known methods can be used in which thermoplastic films or films coated with radiation-curing lacquers are embossed. Microstructures that contain or consist of polymers are preferred, enabling production by embossing processes, e.g., roll-to-roll processes. Alternatively, known molding processes such as injection molding or extrusion, which inject molten material into a negative mold to create the desired shape, can be used to create the microstructures. Microstructures can be obtained by using suitable inserts containing the negative of the surface relief of the microstructure. The embossing tool has the negative of the surface relief of the microstructure and can be manufactured by known processes such as photolithography, electron beam lithography or laser beam lithography. Coating A reflective or reflection-enhancing coating, in particular a metallic or high-refractive-index coating, can be applied to at least some of the optically active surfaces. This coating can be a metallic coating, for example, vapor-deposited to a thickness of 50 nm. Aluminum, gold, silver, copper, palladium, chromium, nickel, and / or tungsten, as well as their alloys, can be used as the coating material. Alternatively, the reflective or reflection-enhancing coating can be formed by a coating with a material with a high refractive index. The optically effective surfaces of the microstructures can be metallized after embossing and curing of an embossing lacquer on a carrier foil. To prevent copying of the security feature by molding the structures, it is possible to seal the coated structures with another polymer. A further layer of lacquer can also be applied as a protective lacquer or adhesive. Four embodiments for constructing surface elements with profiles are described below as examples. Embodiments 3 and 4 may be preferred, as they allow more degrees of freedom. Embodiment 1 (Figures 2A to 20 A structural angle ai is calculated according to the desired 0-viewing direction, so that incoming rays from a light source are reflected by the optically effective surfaces (2) in the direction of the 0-viewing angle. For surface portions intended to block the light, a line (3) parallel to the baseline is used. Depending on the required intensity value (0 to l_max) of the microstructure sector, the following profile lines result: (i) For the case intensity = 0 (Fig. 2A), no structure is observed; the volume of the sector consists only of the base area (or the surface of the carrier). (ii) For the case intensity = l_max (Fig. 2B), a straight line with slope = ai results; the volume of the sector corresponds to a cone sector with H = H_max. (iii) For the case intensity = l_sector (Fig. 2C) in the range between 0 and l_max, a combination of the two functions results, whereby the proportion of the straight line is calculated according to the required area ratio from formula 1. The volume body of the sector corresponds to a truncated cone sector with H = H_facet. A disadvantage of this embodiment compared to the particularly preferred embodiments is that the filtered light is not controlled, which can result in stray images near the desired zero viewing direction, which can also disrupt the image sequence of the subject when rotating or tilting. Furthermore, the desired zero viewing direction, the maximum height of the structures, and the base area of ​​the pixels cannot be selected independently of one another. Only two of these parameters can be freely selected, while the third parameter is derived from the other two parameters. Embodiment 2 (Figures 3A to 30 According to the desired 0-viewing direction, an angle ai is calculated so that incoming rays from a light source are reflected in the direction of the ©-viewing angle. In addition, a second 0-viewing direction with a corresponding angle 2 is selected, under which a negative image of the image to be encoded is to appear. For areas that are to block the light, a straight line with a gradient of 2 is used. used to direct the masked light into the 0 viewing direction of the negative image. Depending on the required intensity value of the pixel sector, the following profile lines result: (i) For the case of intensity = 0 (Fig. 3A), a straight line with slope = 2 and a straight line with slope = 0 are obtained to fill the sector. The solid corresponds to a conical sector with H = H_Max, which does not completely cover the base area. (ii) For the case intensity = l_max (Fig. 3B), a straight line with slope = ai results. The volume of the sector corresponds to a cone sector with H = H_max. (iii) For the case of intensity = l_sector (Fig. 3C) in the range between 0 and l_max, a combination of the two lines results, with their contribution to the profile calculated according to the required area ratio from Formula 1. Additionally, a straight line with slope = 0 is used to connect the two straight lines. The solid body of the sector corresponds to a truncated cone sector with a conical sector superimposed. An advantage of this embodiment is that the filtered light is used to generate another image (a negative image of the encoded image) under a different zero-viewing direction. However, flat sections remain, which can lead to noise. A disadvantage is that the desired zero-viewing direction, the maximum height of the structures, and the base area of ​​the microstructure cannot be selected independently. Only two of these parameters can be freely selected, while the third parameter is derived from the other two parameters. Fabricated microstructures can be measured using a Keyence laser scanning microscope. Embodiment 3 (Figures 4A to 4C) According to the desired 0-viewing direction, an angle ai is calculated so that incoming rays from a light source are reflected in the direction of the ©-viewing angle. Additionally, a second 0-viewing direction with a corresponding angle α2 is selected, under which a negative image of the image to be encoded is to appear. For surface portions that are to mask the light, a curve with a gradient of α2 is used to direct the masked light into the 0-viewing direction of the negative image. Additionally, this approach subdivides straight lines if they exceed H_max. This allows for decoupling of the three parameters—the 0-viewing direction, the maximum height of the structures, and the base area of ​​the microstructure—and avoids straight lines with a gradient of 0. Depending on the required intensity value (0 - l_max) of the microstructure sector, the following profiles result: (i) For the case of intensity = 0 (Fig. 4A), several straight lines with slope = «2 are obtained, which are subdivided by other straight lines, resulting in a sawtooth-like profile. (ii) For the case intensity = l_max (Fig. 4B), several straight lines with slope = ai result, which are subdivided by other straight lines, also resulting in a sawtooth-like profile. (iii) For the case intensity = l_sector (Fig. 4C) in the range between 0 and l_max, a combination of the two ranges results, whereby their share in the profile is calculated according to the required area ratio from formula 1. Embodiment 4 (Figures 5A to 50 Based on embodiment 3, a structural angle of 2 = 45° is chosen for the masking surfaces and their subdivisions. The combination of two surfaces perpendicular to each other enables an effect similar to that of a retroreflective structure, which reflects incident light back toward the source. This reflects the portion of the light to be masked in a direction different from the viewing direction, preventing unwanted negative images from being created. Examples Various microstructures according to the invention were produced using the method according to the invention. 1. Circle_V2: Profile according to embodiment 3; h_max = 2.5 pm; base area 80 x 80 pm; ai = 14°; ai = 28° 2. Qube_V1: Profile according to embodiment 3; h_max = 2.5 pm; base area 100 x 100 pm; ai = 14° 3. Qube_V1: Profile according to embodiment 4; h_max = 5 pm; base area 100 x 100 pm, ai = 14° In all three experiments, microstructures with the desired motifs and effects could be produced when the viewing angle changed. List of reference symbols (1) Baseline (2) Profile line (non-parallel top line) (3) Profile line (4) Rotation axis

Claims

Patent claims 1. Microstructure with substructures that differ from one another in their shape, wherein each of the substructures has an optically effective surface and can be represented by a method that comprises the step of rotating a surface element that has a straight base line and an upper side line that is non-parallel and non-perpendicular to the base line about an axis of rotation that is perpendicular to the base line in the plane of the surface element, whereby a circular sector is formed from the base line and the optically effective surface is formed from the upper side line, wherein the substructures can be represented by rotating about the same axis of rotation and differ from one another in their surface profile and in the angle of the upper side line to the base line.

2. Microstructure according to claim 1, wherein all partial structures of the microstructure can be represented by said method, wherein the rotation takes place around the same axis of rotation, whereby the partial structures obtained together form a circular base area of ​​the microstructure.

3. A microstructure according to claim 1 or 2, wherein the method comprises cutting out a portion of the microstructure, thereby forming a base surface of the microstructure other than a circular base surface.

4. Microstructure according to one of the preceding claims, wherein the top line of the surface element is a first line and the surface element has a second top line from which an optically effective surface is formed, wherein the first line and the second line are inclined upwards towards the axis of rotation and the second line differs from the second line in the inclination towards the axis of rotation.

5. The microstructure of claim 4, wherein the first line and the second line are profile lines of a top-side profile having multiple peaks and troughs.

6. Microstructure according to claim 5, wherein the profile has a plurality of first profile lines and a plurality of second profile lines, wherein the first profile lines have the same or different angle of inclination to the axis of rotation and the second profile lines have the same or different angle of inclination to the axis of rotation and wherein first and second profile lines alternate with one another.

7. Microstructure according to claim 6, wherein the high points of several of the profile lines lie on a straight line perpendicular to the rotation axis and / or the low points of the profile lines lie on a straight line perpendicular to the rotation axis.

8. A microstructure according to any one of the preceding claims, which is or contains an embossed and cured polymer structure.

9. Microstructure according to one of the preceding claims, wherein the optically active surface is the surface of a coating of an embossed and cured polymer structure.

10. A method for producing a microstructure, comprising the following steps: (i) producing a partial structure representation by a method comprising the step of rotating a surface element having a straight base line and a top line not parallel to the base line about an axis of rotation perpendicular to the base line in the plane of the surface element, whereby a circular sector is formed from the base line and the optically effective surface is formed from the top line; (ii) producing a microstructure representation comprising the partial structure representation obtained according to step (i) and at least one partial structure representation different in shape therefrom; and (iii) producing the microstructure based on the microstructure representation obtained in step (ii).

11. The method according to claim 10, wherein step (iii) comprises the following steps: (iii-1) producing an embossing tool as a negative of the microstructure representation obtained in step (ii); (iii-2) pressing the embossing tool obtained in step (iii-1) onto an uncured substrate to form an embossed substrate; and (iii-3) curing the embossed substrate obtained in step (iii-2) to form the microstructure.

12. A method according to claim 10 or 11, which comprises applying a coating to the optically active surface.

13. Microstructure obtainable according to a process according to any one of claims 10 to 12.

14. An optical element comprising a carrier and a plurality of microstructures arranged on the carrier according to one of claims 1 to 9 or 13.

15. Use of an optical element according to claim 14 as a security element on valuable documents or as a decorative element.

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