DE102018216221B4 - Process for producing a structured surface on an object - Google Patents

Abstract

Method for producing a structured surface on an object, in which the total area of the structured surface is divided into partial areas (1, 2, 3, ...., n) and in the individual partial areas (1, 2, 3, ...., n) structure elements formed with laser radiation each form a periodic structure with a structure period Λ (d), so that from one observation position (P) several partial areas (1, 2, 3, ...., n), which are at different distances and Angles to the observation position (P) are arranged discretely to one another, each an image with the same color impression with the same wavelength λ can be detected or recognized when the structured surface is irradiated with white light, and the structure period Λ (d) of the individual partial surfaces (1, 2 , 3, ...., n) is determined according to the equation, where θi is the angle of incidence of the white light on the structured surface; λi the respective predetermined wavelength of the respective color of the color impression of the respective partial area (1, 2, 3, ...., n), θobsn (d = 0) the angle starting from the observation position (P) to the respective partial area (n) , which is calculated according to the equation, where L is the distance of the respective partial area (1, 2, 3, .... or n) in the horizontal direction to the observation position (P) and h is the distance of the respective partial area (1, 2, 3, .... or n) in the vertical direction to the observation position (P).

Description

The invention relates to a method for producing a structured surface on an object. A structured surface is to be designed in such a way that defined color effects due to refraction effects can be produced when the surface is irradiated.

In the recent past, new laser structuring methods have been put into practice with which structures which also have an optical effect and are visually recorded can be formed on large areas with high productivity and in a short time.

On the one hand, this applies to the process of laser-induced periodic surface structures, in which polarized laser radiation is used to form structural elements (LIPSS). Methods of direct laser interference structuring (DLIP) are even more suitable because they can achieve even greater productivity and diversity in the formation of periodic structural elements.

With structural elements corresponding to surfaces, refractive effects of electromagnetic radiation, depending on the angle of incidence and the angle in relation to an observation position, can produce different color impressions on a correspondingly structured surface.

In particular, due to the respective observation position and the size of the observed or recorded correspondingly structured area size, the effect occurs that, due to the different angular relationships, no larger area areas produce the same color impression with the same color with a certain wavelength. The respective color changes accordingly with the viewing angle θ, for example from red to orange to yellow, although the structure elements have been designed with a period structure Λ for a red wavelength.

As a rule, several colors are always broken and reflected on a surface, so that a rainbow effect can be seen. The color white cannot be achieved with the known structures.

However, for certain applications, for example for product labeling, it is desirable that certain larger, correspondingly structured surface areas, starting from an observation position, produce the same color impression and electromagnetic radiation from this or more surface areas structured in this way with the same wavelength or in the same color are reflected in the direction of the observation position in the direction of the observation position should. So far, however, this has not been achieved to a sufficient extent.

So are out DE 10 2016 104 300 A1 a security element and a manufacturing method therefor are known.

CH 659 433 A5 relates to a document with a diffractive optical security element.

An optically variable security element is in DE 10 2016 214 407 A1 described.

It is therefore an object of the invention to provide possibilities with which larger surface areas of a surface of an object provided with periodically arranged structural elements produce the same color impression in the same color when viewing or imaging from or at an observation position.

According to the invention, this object is achieved with a method which has the features of claim 1. Advantageous refinements and developments of the invention can be realized with features designated in the subordinate claims.

In the method for producing a structured surface, the total area of the structured surface is divided into partial areas on an object.

In the individual partial areas, structure elements formed by means of laser radiation each have a periodic structure with a structure period A (d) formed so that from one observation position several partial areas, which are arranged discretely to one another at different distances and angles to the observation position, each have an image with the same color impression with the same wavelength λ when the structured surface is irradiated with white light.

bestimmt.The structure period Λ (d) of the individual partial areas according to the equation $$\mathrm{\Lambda }\left(\text{d}\right)=m\lambda /(\text{sin}\left(\mathrm{\theta }i\right)-\text{sin}\left(\mathrm{\theta }\text{obsn}\left(d\right)\right)$$

certainly.

berechnet.It is θi the angle of incidence of white light on the textured surface; λi the respective predetermined wavelength of the respective color of the Color impression of the respective partial area, θobsn (d = 0) the angle starting from the observation position to the respective partial area n, which is based on the equation $$\mathrm{\theta }\text{obsn}\left(\text{d}=0\right)=\text{arctan}\left(\text{L}/\text{H}\right)$$

calculated.

Here is again L the distance of the respective partial area in the horizontal direction to the observation position and h the distance of the respective partial area in the vertical direction to the observation position.

The observation position is determined either by the eyes of a person or by the location of a camera in relation to the partial areas. The directions horizontal and vertical can also lie in other axes if the respective surface structured according to the invention is not aligned parallel to the horizontal.

If the observation position in relation to the structured surface is changed by a movement, preferably a successive movement, the detectable or perceptible color impression also changes. For example, a surface area previously formed with appropriately structured partial areas can change from yellow to orange and from orange to red.

An object can be, for example, a product that can be labeled with the structured surface produced according to the invention or that can also be used, for example, for advertising purposes.

The respective structural period Λ (d) partial areas is determined by the spacing of structural elements arranged next to one another. The structure period Λ (d) should be kept constant in each partial area. Small variations in the structure period Λ (d) within a partial area, however, can be tolerated. This is particularly true if the angle difference from the observation position to the front and rear distances of the respective partial area has been taken into account.

ist und dabei ist d der Abstand zwischen der zur Beobachtungsposition am weitesten und der am nächsten in horizontaler Richtung angeordneten Teilfläche.For the production of a structured surface area in which a plurality of partial areas which are arranged at different distances from the observation position in the horizontal direction and a color impression with the same color with the same wavelength λ should cause the angle θobs2 starting from the observation position to the most distant partial surface so that $$\mathrm{\theta }\text{obs2}\left(\text{d}\right)=\text{arctan}\left(\left(\text{L}-\text{d}\right)/\text{H}\right)$$

is and d is the distance between the farthest to the observation position and the closest in the horizontal direction.

The partial areas should be structured with a diameter or a length of the area diagonal in the range 0.0003 mm to 1.0000 mm.

The subareas should be formed with structural elements that result from a material removal, a remelting process or a modification of the material of the object or a coating formed on the surface, which are arranged in a locally defined manner. A volume change in the area irradiated with laser radiation can be achieved in a remelting process. By remelting or also modifying the material in the surface area irradiated with laser radiation, a change in the optical refractive index, the transparency and / or the reflectivity can also be achieved in the structural elements obtained in this way.

There is also the possibility of increasing the size of the partial areas with a greater distance from the observation position and / or the structure period A (d) to reduce with a smaller distance to the observation position.

Partial areas which produce a red, green and blue color impression can advantageously be formed directly next to one another, so that a surface area designed in this way, when irradiated with white light, produces a homogeneous, in particular a white color impression in this surface area which deviates from the colors red, green and blue. The sub-areas that produce the different color impressions green, blue and red should be arranged next to each other in a regular arrangement.

It can also have an influence on an achievable color impression or the intensity of the color impression, in that partial areas that have a constant structural period Λ (d) have, but differ in height or depth with which the structural elements were formed in corresponding partial areas.

Partial areas can be partially overlapping. The same structuring should be formed within partial areas that are arranged at least almost the same distance from the observation position. Overlapping training is possible at a small distance from the respective observation position.

If the distance is greater, distances between sub-areas arranged next to one another can also be selected.

Laser structuring can be used, for example, to form linear, punctiform, cross-shaped or columnar structural elements. Structural elements of non-linear design should preferably be formed in a row arrangement.

Partial surfaces with different sizes and / or structural elements with different orientations of the respective structural elements can be formed on a structured surface formed on an object.

Structural elements should be formed in the partial surfaces that are as homogeneous as possible, for example in terms of depth or height and the extent in at least one axial direction.

As already indicated at the beginning, laser structuring methods, such as the LIPSS and in particular the DLIP, are also suitable with their embodiments.

With the DLIP method, the respective structural period can Λ (d) through a suitable choice of the angles of incidence, the interfering laser partial beams are influenced. With two partial beams, the structure period Λ results from the equation $$\mathrm{\Lambda \; =\; \lambda }/\mathrm{2nd}\text{sin}\left(\mathrm{\theta }\right).$$

It is λ the wavelength of the laser radiation and θ half the angle between the incident partial beams. In this way, structures can be formed which are as small as half the laser beam wavelength used to form structural elements.

Technical solutions as in DE 10 2016 215 160 A1 or DE 10 2013 004 869 B4 are particularly suitable. Their full disclosure content should be referred to here.

The invention will be explained by way of example below.

• 1 die Abhängigkeit der erforderlichen Strukturperiode A(d) von Teilflächen von der jeweiligen Beobachtungsposition in schematischer Form;
• 2 die Abhängigkeit der erforderlichen Strukturperiode A(d) von Teilflächen vom jeweiligen Abstand zur jeweiligen Beobachtungsposition in schematischer Form;
• 3 bis 8 mögliche Beispiele für Strukturierungen von Teilflächen;
• 9 mit mehreren nebeneinander angeordneten Teilflächen, die auf unterschiedliche Farbeindrücke strukturiert sind, erreichbare Farbeffekte und
• 10 erreichbare Farbeffekte bei einer herkömmlichen und einer erfindungsgemäß hergestellten Strukturierung.

Show:

• 1 the dependence of the required structural period A (d) of partial areas from the respective observation position in schematic form;
• 2nd the dependence of the required structural period A (d) of partial areas from the respective distance to the respective observation position in schematic form;
• 3rd to 8th possible examples of structuring of partial areas;
• 9 with several partial areas arranged side by side, which are structured on different color impressions, achievable color effects and
• 10th achievable color effects with a conventional and a structuring according to the invention.

With 1 is to clarify the influence of an observation position P to the required structural period Λ (d) of partial areas, if of several or all partial areas from an observation position P at the same time the same color impression with the same wavelength if possible λ should be recorded or recognized.

It becomes clear that the distance L in the horizontal direction and the height h in the vertical direction, i.e. the direction perpendicular to the distance L have a significant impact. This also applies to the angle of incidence θi of the white light that was selected at 0 ° in this example.

The color impression that can be detected by the observation position with respect to the recognizable color (s) can also be changed by rotating or taking a different angular position in relation to the observation position.

Taking into account the in 1 equations shown can be the structure period Λ (d) are calculated for each individual partial area and are then taken into account in the laser structuring of the respective partial areas, if with several partial areas the same color impression from an observation position P should be achieved.

You can also take into account the respective field of view or detection that can be captured by a person, as shown, or by a camera. This is indicated by the angles θobs1 and θobs2.

The change in the structural period A (d) depending on the distance d from partial areas 1 , 2nd , 3rd , .... n is in the left representation of 2nd clarified one-dimensionally and two-dimensionally in the right representation.

One can see that the structural period A (d) enlarged with increasing distance d from the observation position. The individual structural elements then have smaller distances from one another as the distance increases.

In the right representation of 2nd you can see how structural periods Λ (d) should change if the observation position is not arranged centrally in front of the structured total area which was formed with the partial areas 1, 2, 3. By changing the respective observation position P the color impression of partial areas can change.

The right representation of 2nd you can also see the possibility of changing structural periods Λ (d) on partial areas 1 , 2nd , 3rd , ...., n in the vertical and vertical direction in relation to the respective observation position P , ie can be structured accordingly in two perpendicular axial directions.

This illustration also shows that partial surfaces 1, 2, 3... Can be formed on a structured surface formed on an object with different sizes.

The dependence of the respective structural period Λ (d) from the distance d of the partial areas 1 , 2nd and 3rd to the respective observation position P you can also in 3rd detect. Here are the partial areas 1 , 2nd and 3rd were each provided with linear structural elements, the distance between them in the individual sub-areas 1 , 2nd and 3rd the structural period Λ (d) certainly. Here are the patches 1 , 2nd and 3rd circular and arranged immediately next to each other.

In the 4th partial areas shown 1 , 2nd and 3rd are spaced apart.

In the 5 became partial areas 1 , 2nd and 3rd partially overlapping. Partial areas overlap 1 , 2nd and 3rd each the same structure period Λ (d) exhibit.

In 6 is shown that partial areas 1 , 2nd and 3rd can be formed, which are arranged offset from one another.

The 7 shows the possibility of partial areas 1 , 2nd and 3rd offset to each other and can be formed partially overlapping.

In the in the 3rd to 7 Surface areas of the structured surface shown could be arranged with the corresponding arrangements of sub-areas 1 , 2nd and 3rd in compliance with the respective structural periods Λ (d) Depending on the distance to the observation position, it can be achieved that from there the same color impression can be recognized or recorded when the structured surface is irradiated.

In 8th six examples of possible formations of structural elements on partial surfaces are shown. The three partial areas shown in the upper row have linear structural elements with different angular orientations.

In the lower left illustration, linear structural elements with different orientations, in this example perpendicular orientations to one another, have been formed in a partial area. The two examples of partial areas shown next to it in the lower row have different punctiform structural elements, the spacing of which from one another is the respective structural period Λ (d) determine.

With 9 It should be clarified how surface areas of a surface structured according to the invention with partial areas, which depend on the respective observation position with structure periods Λ (d) structured for red, green and blue light and arranged in correspondence to one another, which each produce the same homogeneous color impressions. In the example shown, these are the colors red, yellow, green, blue, cyan, magenta and white.

10th shows a comparison of a conventionally structured surface, in which rainbow-shaped color impressions occur in the left representation. The right illustration shows how to adjust structure periods A (d) the same color impressions can be obtained in partial areas, taking into account the respective observation position.

Claims (9)

Method for producing a structured surface on an object, in which the total area of the structured surface is divided into partial areas (1, 2, 3, ...., n) and in the individual partial areas (1, 2, 3, .... , n) Structural elements formed with laser radiation each form a periodic structure with a structural period Λ (d), so that from one observation position (P) a plurality of partial areas (1, 2, 3, ...., n) are arranged at different distances and angles to the observation position (P) are arranged discretely to one another, in each case an image with the same color impression with the same wavelength λ can be detected or recognized when the structured surface is irradiated with white light and the structure period Λ (d) of the individual partial areas (1, 2, 3, ...., n) according to the equation $$\mathrm{\Lambda }\left(\text{d}\right)=m\lambda /(\text{sin}\left(\mathrm{\theta }i\right)-\text{sin}\left(\mathrm{\theta }\text{obs}\left(d\right)\right)$$

is determined, where θi is the angle of incidence of the white light on the structured surface; λi the respective predetermined wavelength of the respective color of the color impression of the respective partial area (1, 2, 3, ...., n), θobsn (d = 0) the angle starting from the observation position (P) to the respective partial area (n) that follows the equation $$\mathrm{\theta }\text{obsn}\left(\text{d}=0\right)=\text{arctan}\left(\text{L}/\text{H}\right)$$

is calculated, where L is the distance of the respective partial area (1, 2, 3, .... or n) in the horizontal direction to the observation position (P) and h is the distance of the respective partial area (1, 2, 3, ... or n) is in the vertical direction to the observation position (P). Procedure according to Claim 1 , characterized in that for the production of a structured surface area in which a plurality of partial surfaces (1, 2, 3, ...., n), which are arranged at different distances from the observation position (P) in the horizontal direction and a color impression with the same color of the same wavelength λ, the angle θobs1 from the observation position (P) to the most distant partial area is taken into account such that θobs2 (d) = arctan ((L - d) / h) and d is the distance between the to the observation position (P) is the furthest and the partial area (1, 2, 3, ..., n) arranged in the horizontal direction. Method according to one of the preceding claims, characterized in that the partial surfaces (1, 2, 3, ...., n) are structured with a diameter or a length of the surface diagonal in the range 0.0003 mm to 1.0000 mm. Method according to one of the preceding claims, characterized in that the partial surfaces (1, 2, 3, ...., n) with structural elements which are formed as a result of material removal, a remelting process or a modification of the material of the object or one formed on the surface Coating, which are arranged locally defined, are formed. Method according to one of the preceding claims, characterized in that the size of the partial areas (1, 2, 3, ...., n) increases with a greater distance from the observation position (P) and / or the structure period Λ (d) with a smaller distance is reduced to the observation position. Method according to one of the preceding claims, characterized in that partial areas (1, 2, 3, ...., n) which produce a red, green and blue color impression are formed directly next to one another, so that a surface area formed in this way is irradiated with white light produces a homogeneous, in particular a white color impression in this surface area that deviates from the colors red, green and blue. Method according to one of the preceding claims, characterized in that partial surfaces (1, 2, 3, ...., n) are partially overlapping. Method according to one of the preceding claims, characterized in that linear, punctiform, cruciform or columnar structural elements are formed. Method according to one of the preceding claims, characterized in that partial surfaces (1, 2, 3, ...., n) with different sizes and / or structural elements with different orientations of the respective structural elements are formed on a structured surface formed on an object.

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