EP3626476A1 - Method for producing a structured surface on an object - Google Patents

Abstract

In the method, the total area of the structured surface is divided into partial areas (1, 2, 3, ..., n) and there, in each case a periodic structure with a structure period A (d) is formed with laser elements, so that a Observation position (P) a plurality of partial areas (1, 2, 3, ...., n), which are arranged discretely at different distances and angles to the observation position (P), each an image with the same color impression with the same wavelength λ during irradiation the structured surface can be detected or recognized with white light. The structure period Λ (d) of the individual partial areas (1, 2, 3, ...., n) is determined according to the equation Λd = mλ / (sinθi − sinθobsd.

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 can be caused as a result of refraction effects when the surface is irradiated.

In the recent past, new laser structuring methods have been put into practice with which structures that 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 are even more suitable (DLIP), because it enables 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 no larger area areas cause the same color impression with the same color with a certain wavelength due to the different angular relationships. 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.

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 have the same color impression in the same color when viewing or imaging from or at an observation position to evoke.

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 on an object is divided into partial areas.

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

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

certainly.

berechnet.Here θi is the angle of incidence of white light on the structured 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 $$\mathrm{\theta obsn}\left(\mathrm{d}=0\right)=\arctan \left(\mathrm{L}/\mathrm{H}\right)$$

calculated.

Here again L is the distance of the respective partial area in the horizontal direction to the observation position and h is 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 can also be used, for example, for advertising purposes.

The respective structural period Λ (d) of partial areas is predetermined 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 of the structure period Λ (d) within a partial area can, however, 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 several partial surfaces, which are arranged at different distances from the observation position in the horizontal direction and are intended to produce a color impression with the same color with the same wavelength λ, the angle 0obs2 should start from the observation position to the most distant partial surface be taken into account that $$\mathrm{\theta obs}\mathrm{2nd}\left(\mathrm{d}\right)=\arctan \left(\left(\mathrm{L}-\mathrm{d}\right)/\mathrm{H}\right)$$

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 region 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 reducing the structure period Λ (d) with a smaller distance from 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.

An influence on an achievable color impression or the intensity of the color impression can also be achieved by partial areas which have a constant structure period Λ (d), but have been formed in height or depth with the structure elements in corresponding partial areas , differentiate.

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.

In the case of a larger distance, distances between partial areas arranged next to one another can also be selected.

Laser structuring can be used, for example, to form linear, punctiform, cruciform 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.

In the DLIP method, the respective structure period Λ (d) can be influenced by a suitable choice of the angle of incidence, of the partial laser beams interfering with one another. With two partial beams, the structure period Λ results from the equation $$\mathrm{\Lambda }=\mathrm{\lambda }/\mathrm{2nd}\sin \left(\mathrm{\theta }\right)\mathrm{.}$$

Here λ is the wavelength of the laser radiation and θ is half the angle between the incident partial beams. So 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.

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

Show:

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

With Figure 1 It should be clarified what influence an observation position P has on the respective required structural period Λ (d) of partial areas, if from several or all partial areas from one observation position P the same color impression with the same wavelength λ should be detected or recognized at the same time.

It is clear that the distance L in the horizontal direction and the height h in the vertical direction, that is to say the direction perpendicular to the distance L, have a considerable influence. This also applies to the angle of incidence θi of the white light, which was chosen at 0 ° in this example.

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

Taking into account the in Figure 1 The equations shown can be used to calculate the structure period Λ (d) for each individual partial area and then take it into account in the laser structuring of the respective partial areas if the same color impression from an observation position P is to be achieved with several partial areas.

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 structure period Λ (d) as a function of the distance d from partial areas 1, 2, 3, .... n is in the left-hand illustration of Figure 2 clarified one-dimensionally and two-dimensionally in the right representation.

It can be seen that the structure period Λ (d) increases 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 Figure 2 it can be seen how structural periods Λ (d) should change if the observation position is not arranged in the center in front of the structured total area that 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 Figure 2 one can also use the possibility of changing structural periods Λ (d) on partial surfaces 1, 2, 3, ...., n which can be structured accordingly in the vertical and vertical direction with respect to the respective observation position P, i.e. in two perpendicular axial directions .

This illustration also shows that one is on an object trained structured surface also partial areas 1, 2, 3 .... Can be formed with different sizes.

The dependence of the respective structural period Λ (d) on the distance d of the partial areas 1, 2 and 3 from the respective observation position P can also be seen in Figure 3 detect. The partial areas 1, 2 and 3 have each been provided with linear structural elements, the spacing of which from one another in the individual partial areas 1, 2 and 3 determines the structural period Λ (d). Here, the partial areas 1, 2 and 3 have a circular design and are arranged directly next to one another.

In the Figure 4 Subareas 1, 2 and 3 shown are spaced apart.

In the Figure 5 partial areas 1, 2 and 3 were partially overlapping. Partial areas 1, 2 and 3 overlap, each having the same structural period Λ (d).

In Figure 6 it is shown that partial areas 1, 2 and 3 can also be formed which are arranged offset to one another.

The Figure 7 shows the possibility that partial areas 1, 2 and 3 can be offset from one another and partially overlapping.

In the in the Figures 3 to 7 The surface areas of the structured surface shown could be achieved with the corresponding arrangements of partial areas 1, 2 and 3 while observing the respective structural periods Λ (d) depending on the distance to the observation position, so that the irradiation of the structured surface can be seen or the same color impression from there can capture.

In Figure 8 six examples of possible formation of structural elements on partial areas 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 subareas shown next to it in the lower row have different punctiform structural elements, the distances between which determine the respective structural period Λ (d).

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

Figure 10 shows a comparison of a conventionally structured surface, in which rainbow-shaped color impressions occur in the left representation. The illustration on the right shows how the same color impressions can be obtained by adapting structural periods Λ (d) 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
A periodic structure with a structure period Λ (d) is formed in the individual sub-areas (1, 2, 3, ..., n) with structural elements formed with laser radiation, so that from one observation position (P) several sub-areas (1, 2 , 3, ...., n), which are arranged discretely at different distances and angles to the observation position (P),
one 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) the equation $$\mathrm{\Lambda }\left(\mathrm{d}\right)=\mathit{m\lambda }/\left(\sin \left(\mathrm{\theta }i\right)-\sin \left(\mathrm{\theta obs}\left(d\right)\right)\right)$$

is determined, whereby
θ i the angle of incidence of 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 $$\mathrm{\theta obsn}\left(\mathrm{d}=\mathrm{0}\right)=\arctan \left(\mathrm{L}/\mathrm{H}\right)$$

calculated is
where L is the distance of the respective partial area (1, 2, 3, .... or n) in 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). A method according to claim 1, characterized in that for producing 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 with the same wavelength λ,
the angle θobs1 from the observation position (P) to the most distant partial surface is taken into account in such a way that
θ obs2 (d) = arctan ((L - d) / h) and where d is the distance between the part surface furthest to the observation position (P) and the closest one in the horizontal direction (1, 2, 3, ... ., n) is. 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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