EP-4735263-A1 - MICRO-STRUCTURE HAVING OPTICAL EFFECTS

EP4735263A1EP 4735263 A1EP4735263 A1EP 4735263A1EP-4735263-A1

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.

Inventors

Leiner, Claude
SOMMER, CHRISTIAN

Assignees

Joanneum Research Forschungsgesellschaft mbH

Dates

Publication Date: 20260506
Application Date: 20240627

Claims (15)

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.
2. Microstructure according to claim 1, wherein all partial structures of the microstructure can be represented by said method, wherein the rotation takes place about the same axis of rotation, whereby the partial structures obtained together result in 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 area of the microstructure other than a circular base area.
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 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.
7. Microstructure according to claim 6, wherein the high points of several of the profile lines lie on a straight line perpendicular to the axis of rotation and/or the low points of the profile lines lie on a straight line perpendicular to the axis of rotation.
8. A microstructure according to any preceding claim, 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 an upper side line not parallel to the base line 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; (ii) producing a microstructure representation which comprises the partial structure representation obtained according to step (i) and at least one partial structure representation which differs in shape therefrom; and (iii) producing the microstructure based on the microstructure representation obtained in step (ii).
11. The method of 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. Optical element with 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.

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 that has a first embossed structure made up 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 range and are at least partially concealed when viewed from a second viewing angle range. When the security element is tilted about a first axis, a first tilting effect is created. The structure has a second embossed structure that is arranged within the first embossed structure and creates a second tilting effect in addition to the first tilting effect. WO 2013/045056 A1 discloses a security element with an optically variable structure that contains a raised embossed element preferably in the form of a cone or a spherical segment. The embossed element has a partial cutout preferably in the form of an arcuate partial segment, wherein the remaining conical remainder or spherical segment remainder forms an embossed element that exhibits desired optical effects such as tilting 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 task was solved by providing a microstructure with a circular base, whereby 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 of rotating 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 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 which can be produced by the said method additionally differ from one another in their shape in that they differ from one another in the curvature of the upper-side line, the number of upper-side lines, the distance of the upper-side line from the base line and/or the radius of the circular sector. [1-4] A microstructure according to any preceding aspect, 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 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 takes place about 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 one of the preceding aspects, in particular according to aspect [2], wherein the method comprises cutting out a part of the microstructure, thereby forming a base area other than a circular base area from the base area of the microstructure. [3-1] Microstructure according to aspect [3], wherein the base area formed by the cutting is an angular structure, for example a square or hexagon. [3-2] Microstructure according to aspect [3] or [3-1], wherein t