To locally improve radar transmittance and / or light transmittance, the surface of metallic effect pigments is laser-treated.

Abstract

This invention relates to a method and / or fine patterning method for marking and / or finely patterning objects containing effect pigments or metal-containing particles, such as vehicle body parts or cosmetic containers, or layers, such as paint layers or printing ink layers, using energy input (e.g., heat input, preferably by laser). This results in a persistent reduction in the opacity of the metal-containing pigment flakes or metal-containing particles due to changes in their shape factor. In the treated surface, this change in shape factor leads to a persistent, localized increase in transparency, translucency, or transmittance against electromagnetic waves, particularly radar wave transmittance, radio wave transmittance, and / or light wave transmittance, and / or a localized decrease in reflectivity, for example, in the manufacture of painted radomes. The method differs from conventional laser marking in that the transmittance against electromagnetic waves of normally reflective metallic effect pigment surfaces or metal-containing particles is persistently increased due to changes in the shape factor caused by the laser beam, wherein the pigment flakes or particles are changed by direct melting and / or triggering of auxiliary chemical reactions, causing at least partial melting of their metallic core, and, if necessary, chemical changes and / or destruction.

Description

Technical Field

[0001] This invention relates to marking and / or fine patterning methods for metallic effect pigment surfaces, interference metallic effect pigment surfaces, and pigment-containing objects, said marking and / or fine patterning methods for persistently and locally improving transparency, light transmittance, or transmissivity to electromagnetic waves, especially radar waves, radio waves, and / or light waves, and / or locally reducing reflectivity.

[0002] The present invention also relates to products of the method, such as plastic body parts coated with metallic effect pigments that are more transparent to radar waves, and cosmetic bottles or motor vehicle operating components and mobile phones that are subsequently marked with transparent, translucent or backlit signs.

[0003] Similarly, the present invention relates to implementing the method by applying suitable metallic effect pigments or metal-containing particles with a thin metal layer, as well as printing inks, varnishes, masterbatches, and interference metallic effect pigments. The invention also relates to objects comprising such suitable particles or pigments and optimized for the application of the method, or objects configured for applying the method, for example by using suitable laser-sensitive filler materials to promote the chemical reaction or physical deformation of the metallic component of the pigment or metal-containing particles. Background Technology

[0004] Radar sensors are increasingly being used in vehicles within the automotive industry. To achieve autonomous driving in the future, radar sensors must be installed around the vehicle. Therefore, these radar sensors must be mounted behind plastic body parts coated with vehicle paint. Metallic effect paints are widely used as a component of primers in automotive painting, and there is significant customer demand.

[0005] However, these metallic effect paints cause both radar beam reflection and safety-related changes to the directional characteristics of radar antennas. In particular, the position of obstacles can be severely distorted as the antenna's radiation angle is altered by the paint layer. This distortion also depends on the vehicle's color and the metal content in the coating. There are significant problems, especially when repairing original painted automotive parts after paint damage, because the (primarily manual) repair process only allows for insufficient control over the paint thickness parameter, which is crucial for radar transmission.

[0006] For a long time, people have tried to find a solution to this problem, but so far there has been virtually no success.

[0007] These issues are fully elaborated in the literature DE 102014222837 A1, and quantified in F. Pfeiffer's 2010 paper "Analysis and Optimization of Radomes for Automobile Radarsensoren" at the Technical University of Munich.

[0008] The paper measures, and for example, illustrates in Table 4.5 on page 46, the effects of different metallic pigment primers on millimeter-wave radar beams in the frequency range of approximately 75 GHz. Metal content plays a crucial role here.

[0009] In particular, when the primer of curved body parts has a high metal content (such as light silver metal), it can cause high reflection of the radar beam, resulting in severe distortion, attenuation and distortion of the antenna's directional characteristics and radiation angle.

[0010] Table 4.5: Study on the metal content and relative permittivity of the primer coating

[0011] Table 4.5:Metal content and relative permittivity of the basecoatsinvestigated

[0012]

[0013] LM:soIvent baseα / not specmeα:water basea

[0014] color basecoat = Name of colored base coat

[0015] weight - % = weight percentage

[0016] metal content = metal content

[0017] rel.permitivity = relative permittivity

[0018] LM: solvent based = LM: solvent based

[0019] not specified:water based=Not specified:water based

[0020] The author's proposed solution is to add an inductive or capacitive device that at least partially compensates for the reflection of electromagnetic radiation (5) from the radar sensor caused by the paint layer. This solution has been patented by EP 2151889 A1 (Audi AG).

[0021] However, this solution in the prior art (similar to an oscillating circuit) must be carefully adapted according to the paint and layer thickness.

[0022] The double-painting method even requires the thickness of the bumper to depend on the paint used, which has created problems in the automotive industry.

[0023] Furthermore, the bandwidth of this solution is insufficient, making it almost unsuitable for the wider field of view of radar.

[0024] Another drawback of existing technological solutions for the automotive industry is that they must be optimized based on the pigment / paint system and paint thickness. Therefore, manufacturing issues are pre-programmed according to the vehicle's color.

[0025] For example, repainting after scratches appear in the radome area is difficult and requires extensive re-optimization through modeling, taking into account the shape of the body parts that house the radome. Overall, this presents a challenge for automakers seeking a universal solution.

[0026] Therefore, some radar manufacturers have attempted to use radar equipment that is compatible with a wide variety of metallic pigment paints. However, in many cases, especially when the primer has a high metal content, reliable compatibility is nearly impossible.

[0027] According to documents DE 102014222837 A1 or DE 102016001310 A1, there was no attempt to change or reduce the effect of the paint. Instead, the problems of attenuation, reflection, antenna directional characteristics, and distortion were adaptively solved through compensatory control of electronic devices.

[0028] Other documents, such as EP 1462817 A1, teach the use of absorbing materials to reinterfere with the directional characteristics of an antenna that are distorted due to undesirable reflections. However, this does not produce a paint-independent solution, as the distortion of directional characteristics and undesirable reflections are paint-dependent. The required absorbing solvent is also paint-dependent.

[0029] As known from documents DE 19819709 A1, DE 10026454 C1, and DE 102007059758 A1, after covering radar equipment with a metal layer, this metal layer is so thin that although it reflects light, it remains transparent to radar waves and can be used as an radome. The design of this metal layer in front of the radar antenna is completely free, as long as the metal layer is thin enough (in fact, significantly thinner than the "skin depth" of radar waves, but significantly thicker than the "skin depth" for human visible wavelengths). For example, a 100nm thin Daimler logo in the middle of the heat sink grille in front of radar equipment.

[0030] Electromagnetic waves approaching a uniform metal surface perpendicularly are usually almost completely reflected, partly because if the surface is perfectly conductive, it is, in principle, equipotential. The electric field E in the metal is canceled out by its conductivity, as if there were waves interacting with a field vector opposite to the electric field vector.

[0031] However, in reality, the incident wave does not attenuate directly at the surface because the conductivity of metals is not infinite; therefore, the electric field component E of the electromagnetic wave is not immediately canceled out at the surface. Instead, the electric field component E travels deeper into the conductive material with the wave, and there it attenuates exponentially with increasing depth. The penetration depth of electromagnetic waves in homogeneous metals depends on the reciprocal of the root of the wave frequency. At a depth of 300 nm in aluminum, only 37% of the incident 76 GHz radar wave remains. An exponential attenuation is also observed in dielectric varnish layers containing aluminum sheets that are insulated from each other, but to a lesser extent.

[0032] The thickness of metallic pigment primers commonly used in the automotive industry depends on the hue and is approximately 15 micrometers. Due to the unavoidable parasitic capacitance between partially overlapping metallic pigment flakes, they behave almost like a uniform, conductive metallization structure against radar waves. This metallization structure is almost two orders of magnitude thicker than the maximum metallization thickness recommended based on the teachings above.

[0033] This parasitic capacitance between individual pigment flakes can also be explained as interfacial polarization.

[0034] According to the guidelines in document DE 19644164 A1 (Bosch), thicker metal elements in the microwave path are not allowed to be wider than lambda / 10 (lambda = wavelength, i.e., 4 mm for 76 GHz radar waves), thus making these metal elements practically transparent to thinner ones. For 76 GHz radar waves, the width of any possible metal element in front of the antenna must not exceed 0.4 mm.

[0035] However, this condition is only met when the metallic effect pigment flakes are sufficiently far apart. This is not the case with conventional metallic effect paints, because the density of metallic pigments in the primer matrix must be high enough to provide sufficient hiding power and allow for pigment overlap. However, parasitic resistance and interfacial polarization increase with the frequency of pigment overlap. As pigment density increases, the paint behaves more and more like a uniform metallic layer because at such high frequencies, the pigments appear to be electrically connected to each other due to stray capacitance.

[0036] Because radar issues increase with the pigment content in automotive paint, attempts have been made to simulate metallic effects using low-metallic pigment blends. In these blends, a larger proportion of pearlescent pigments is added to a smaller proportion of metallic effect pigments. Pearlescent pigments generally do not pose a radar problem because they are built on a dielectric, light-transmitting core. However, this blend inevitably makes the overall visual impression of the painted parts appear less metallic than traditional body panels, which is not necessarily desirable.

[0037] While these documents indicate that the problems with metallic paint are known, they do not disclose paint-independent solutions for full metallic effect paints.

[0038] The automotive industry urgently needs a solution that is paint-independent and virtually invisible to radar waves, compatible with both all-metal effect pigment paints and a variety of traditional coating processes (spraying, dipping, electrostatics, etc.). Summary of the Invention

[0039] Therefore, the first technical problem to be solved by the present invention relates to a method for increasing the transmission of radar waves in a vehicle body part coated with metallic effect pigments or containing metal particles, wherein interfering metallic effect pigments or containing metal particles in front of the radar sensor are eliminated in the radar beam path of the painted vehicle body part, preferably without marking or damaging the pigment-containing paint layer that can be distinguished by the human eye.

[0040] Surprisingly, the increased radar wave transmission achievable by the method according to the invention also results in increased light wave transmission as a side effect. In other words, the treated metallic-effect colored surface, or the surface with interference metallic-effect colored surface, or the surface typically provided with metallic particles, can become transparent or translucent, enabling other applications, such as retrospectively marking transparent signs or patterns on backlit control elements, reflective objects, or decorative surfaces.

[0041] This raises a second surprising but equally important technical problem with the method according to the invention: how to make the reflective metallic effect pigments or metallic particles essentially transparent, translucent, or invisible and almost no longer reflective by means of laser processing.

[0042] Since the area processed by the method becomes almost transparent, a third technical problem is raised: how to reduce the area involved in the processing and make it so thin that it is imperceptible or almost imperceptible to the naked eye, and yet improve the transmission of radar waves.

[0043] A suitable Y-shaped opening pattern is known from patent document US 3975738 (U.S. Air Force, 1976, Slotted radome for fighter jets), which should be transparent to any polarization of radar waves.

[0044] Although the disclosure does not involve metallic paint, but only a uniform metallic surface that must be transparent to radar waves, the teachings derived from the slotted antenna area still seem to be applicable as a partial solution, and the applicability of this partial solution to laser-patterned metallic effect paint has been experimentally confirmed.

[0045] The optimized dimensions of the Y-groove, which depend on the wavelength, are given very precisely in numerical terms, especially the width of the line that should be transparent.

[0046] The gap width disclosed in document US 3975738 is 0.0175λ, which corresponds to a line width of 70 micrometers at a wavelength of 4 millimeters, which is invisible to the naked eye on paint.

[0047] These dimensions are the result of very careful optimization work for scanning attack radar, in which the incidence of radar waves on the radome is constantly changing, which is also necessary for advanced radar technology in automobiles.

[0048] The technical problem to be solved by the present invention is solved by a reprocessing method for improving the radar wave transmittance of painted vehicle body parts, the method comprising the following steps:

[0049] - Provides painted vehicle body parts, said vehicle body parts comprising metallic effect pigments, interference metallic effect pigments, or metal-containing particles that have at least partially a thin, bonded metallic component in the form of metal.

[0050] -Introducing lasers,

[0051] The laser is designed to at least trigger the melting of the metallic component of the pigment or particles in metallic form, thereby changing the shape factor of the pigment or particles and thereby improving the transmission of radar waves without damaging the coating and / or impairing the optical properties of the coating. The pigment, heated by the laser, melts and loses its flat shape factor due to the surface tension of the liquid metal, shrinking into a spherical droplet. The surface tension of the liquid metal forces a significant change in the shape factor of the pigment.

[0052] The technical problem to be solved by the present invention is also solved by a body part or paint layer, the body part or paint layer containing at least one pigment or metal-containing particles converted according to the aforementioned method, without damaging the paint layer and / or impairing the optical properties of the paint layer at that location.

[0053] The technical problem to be solved by the present invention is also solved by a convertible particle, such as a flake, preferably a metallic effect pigment flake, wherein the convertible particle is used in the aforementioned method, and wherein the particle comprises at least:

[0054] - The first metal in metallic form; and

[0055] - (with or without an intermediate layer) the first oxide that encapsulates the first metal.

[0056] According to a preferred embodiment of the invention, certain areas of a vehicle body component are selectively protected from or exempted from laser input (patterns), for example, by selective laser scanning or by using a mask.

[0057] According to a preferred embodiment of the invention, multiple localized laser inputs generate patterns in painted vehicle body parts, the patterns consisting of areas with altered pigments and areas without altered pigments.

[0058] According to a preferred embodiment of the invention, the pattern is used to improve only the transmittance or transmission characteristics for radar waves.

[0059] According to a preferred embodiment of the invention, the selected pattern is used as a frequency selective surface, which is used, for example, to manufacture radar absorbing material (RAM).

[0060] According to a preferred embodiment of the present invention, the pattern is designed such that the paint layer constitutes an electromagnetic functional component of a slot antenna, radome, array antenna, or wavelength-selective absorption surface.

[0061] According to a preferred embodiment of the invention, improved radio wave transmission, radar wave transmission, or millimeter wave transmission is achieved in a desired area of ​​the vehicle body component by forming a slotted radome pattern or slotted pattern in the paint layer through laser processing.

[0062] According to a preferred embodiment of the present invention, since the width of the line formed by laser processing of the slot radome pattern is less than one-tenth of a millimeter, the pattern formed by laser processing in the paint layer is imperceptible or almost imperceptible to the human eye.

[0063] According to a preferred embodiment of the invention, the thin binder metal component of the pigment (in metallic form) is designed to be so thin that the metal component is partially transparent to the laser used in the method having a wavelength between 10600 nm (CO2 laser) and 266 nm (four times the frequency of Nd-Yag laser), preferably between 1064 nm and 355 nm; that is, the metal component is designed to be so thin that at least 0.2% of the laser is transmitted through the metal component at at least one wavelength in the wavelength range.

[0064] According to a preferred embodiment of the invention, the initial sheet or thin metal component is at least partially liquefied and resolidified in a spherical shape.

[0065] According to a preferred embodiment of the invention, the metallic component of the pigment reacts with other components of the pigment and / or with the laser-sensitive filler material of the matrix through an exothermic chemical reaction by means of synergistic action or by partially absorbing light input, thereby embedding the pigment into the matrix.

[0066] According to a preferred embodiment of the present invention, the metal component in metallic form is a vacuum-metallized pigment, or has a vacuum-metallized core or layer, wherein the metal component preferably has a metal core of maximum thickness or a layer of less than 80 nm, more preferably less than 32 nm, more preferably less than 27 nm, further preferably less than 25 nm, and most preferably a layer between 8 nm and 17 nm.

[0067] According to a preferred embodiment of the invention, the method is used to reduce the light reflectance or albedo perpendicular to the pigment surface by at least 6 dB, preferably 10 dB, more preferably 12 dB, and most preferably 20 dB, wherein “light wave” here also includes infrared or ultraviolet waves, provided that the measured light wavelength is smaller than the diameter of the untreated pigment.

[0068] According to a preferred embodiment of the invention, the radio wave reflectivity, radar wave reflectivity, reflection scattering parameter, or albedo perpendicular to the pigment surface is reduced by at least 6 dB, preferably 10 dB, further preferably 12 dB, and most preferably 20 dB by using the method described above.

[0069] According to a preferred embodiment of the invention, the radio wave transmittance, radar wave transmittance, or millimeter wave transmittance of the colored surface of the treated object is increased by at least 6 dB, preferably 10 dB, further preferably 12 dB, and most preferably 20 dB for at least one wavelength of infrared, visible, or ultraviolet light by using the method.

[0070] According to a preferred embodiment of the invention, the metallic component in the metallic form is composed of a metal or alloy having a relatively low melting point, preferably tin, zinc, lead, silver, or copper, or particularly preferably aluminum, indium, or a tin-indium alloy.

[0071] According to a preferred embodiment of the invention, a portion of the metal component in the form of the metal undergoes an exothermic reaction with the metal oxide layer containing metal particles or the metal oxide layer of the pigment, and the metal component is at least partially oxidized (aluminothermic reaction).

[0072] According to a preferred embodiment of the invention, the light input directly or indirectly causes the outer surface area of ​​at least one pigment or metal-containing particle to decrease by a factor of 10, preferably 20, further preferably 30, or even more advantageously 60, through surface tension, thereby resulting in a corresponding reduction in the opacity of the pigment, which increases transparency and radio wave transmittance.

[0073] According to a preferred embodiment of the invention, the layer / matrix containing the pigment / particles includes polyimide, polystyrene, polyethylene, fluoropolymers such as polytetrafluoroethylene, and more preferably polymethacrylamide or mixtures thereof.

[0074] The technical solution of the present invention is particularly a method for solving the above-mentioned technical problems, wherein an object containing a thin metal sheet or metal particles is reprocessed by light or heat input, preferably by laser, especially a pulsed Nd-YAG laser used for laser marking, to produce a subsequent physical or chemical change in the metal sheet or metal particles in a dielectric matrix, thereby permanently and significantly reducing the covering power of the metal sheet or metal particles, and increasing the transmission of the object to electromagnetic waves (light waves, radar waves, radio waves). The metal sheet can be a metallic effect pigment, an interference metallic effect pigment, or metal particles. Attached Figure Description

[0075] Figure 1 This paper illustrates how interfacial polarization and parasitic capacitance between metallic pigments in the primer negatively affect radar wave transmission (F. Pfeiffer's paper, "Analysis and Optimization of Radars for Automobile Radar Sensors", Technical University of Munich, 2010).

[0076] Figure 2 The diagram shows the omnipolar slot arrangement and slot dimensions for a metal radome for a fighter jet, as recommended in U.S. Patent 3,975,738 (Prior Art, U.S. Air Force, 1976).

[0077] Figure 3 Examples of the main features and effects of different traditional laser marking methods are shown in Surface Technology. The existing technology in the book, by Dr. Feist;

[0078] Figure 4 This illustrates the reprocessing of a metallic pigment layer according to the present invention to improve transparency;

[0079] Figure 5 A view showing the shape change of a pigment subjected to laser treatment according to the present invention;

[0080] Figure 6 This illustrates the effect of decomposition on the filler material used to produce Figure 5 The transformation and pigment residue of the filler material

[0081] Figure 7 This demonstrates how interference metallic effect pigments with thin cores are relatively refractory.

[0082] Figure 8 This demonstrates how to determine the preferred Nd-YAG laser parameters from the test area;

[0083] Figure 9 The metallic effect pigments are generally no longer visible in the laser-marked areas, and specifically, not only are they not visible directly on the surface;

[0084] Figure 10 The test matrix used to further determine the laser parameters of the present invention is shown, along with some test results at different pulse intervals in dark, low-dose "Chromos" metallic effect pigments with a particularly thin aluminum core and a silica protective layer.

[0085] Figure 11This demonstrates how to use a network analysis apparatus to measure the scattering parameters, particularly the input reflectance S, of a laser-treated paint sample as a function of frequency, by experimentally comparing it with an untreated paint sample. 11 and the forward transmittance S when necessary 21 ;

[0086] Figure 12 This demonstrates how to use a network analysis apparatus to measure the scattering parameters, particularly the free-space input reflectivity S, of a metallic paint slotted radome prototype as a function of frequency, through experimental comparison with an untreated paint sample. 11 and, if necessary, free space forward transmittance S 21 ;

[0087] Figure 13 Details of a prototype slotted radome made of "Zenexo Golden Shine" laser-interference metallic effect pigment, featuring a Y-shaped slot outline on a plastic body component;

[0088] Figure 14 An example of an antenna radome using silver aluminum pigment AluStar is shown, wherein the primer is laser-treated with a 40-micron clear coat;

[0089] Figure 15 Showing according to Figure 14 The reflectivity S11 and transmittance S21 of the radome design were measured experimentally. Detailed Implementation

[0090] The present invention relates to a method for reprocessing and / or fine patterning of objects containing metallic pigments, such as vehicle body parts or cosmetic containers or layers, such as paint layers or printing ink layers, wherein the opacity of the metallic pigment flakes is persistently reduced by means of heat input by altering the shape factor of the opacity-containing pigment flakes, such as metallic effect pigments or interference metallic effect pigments.

[0091] This invention is important for the future of autonomous driving because the application of effect pigments containing metals can interfere with radar reception. For example... Figure 1 As shown, the two overlapping metallic pigments in the varnish form a capacitor and thus appear to be electrically connected to each other at GHz frequencies. For this reason, a solution that makes the varnish permeable to radar waves is important.

[0092] In the treated surface, this change in shape factor results in a persistent, localized increase in the transparency, translucency, or transmittance of electromagnetic waves, especially radar waves, radio waves, and / or light waves, and / or a localized decrease in reflectivity, for example, in the manufacture of radomes coated with metallic effect paint in an inconspicuous automotive color for radar sensors (millimeter waves).

[0093] The treated surface is also used to manufacture backlighting operating elements for the cockpits of vehicles used in the telecommunications industry, to manufacture 5G transponders with transparent metallic coatings that allow radio waves to pass through, and in the cosmetics industry to manufacture finely engraved transparent markings on expensive packaging or to create inconspicuous micromarks as security, anti-copying, provenance, or authenticity guarantees for objects such as bank notes.

[0094] Figure 4 An advantageous embodiment of a method for generating thermal input using a conventional laser unit 1 (e.g., an Nd-YAG laser unit) suitable for laser marking is shown.

[0095] The laser unit 1 generates a laser beam 2 that irradiates the dielectric substrate 3, and can move / scan relative to the dielectric substrate 3. The substrate 3 may be, for example, a laser-permeable primer of metallized automotive paint, or a material of a cosmetic container, preferably made of transparent or translucent polypropylene or polyethylene.

[0096] Importantly for this invention, the substrate 3 comprises a metallic effect pigment flake 4 having such a thin metallic core or layer in good condition that the metallic core or layer is preferably partially transmissive to laser light.

[0097] For this purpose, it is preferable to use pigments based on vacuum metallized flakes (VMPs) with a thin metal layer or metal core having a thickness of less than 40 nm, wherein the thin metal layer or metal core has a thickness of less than 30 nm for better convertibility, and more advantageously less than 20 nm.

[0098] These pigments may have other layers, preferably laser-transparent layers, such as protective layers made of alumina or silica, thicker interference layers made of iron oxide or chalcogenides, and / or layers that improve the adhesion or bonding ability of the sheet to the substrate, such as layers made of silanes, preferably alkylsilanes.

[0099] However, it has been shown that the other layers are not necessarily necessary for the method.

[0100] The heat input through the laser beam 2 into the laser-permeable metal layer or core of the pigment flake causes the metallic components of the pigment to melt and shrink in the liquid state, possibly due to high surface tension. This surface tension may also cause the more or less spherical residue 5 of the flake 4 to solidify in a much more compact form than the original flake. Figure 1Unlike the problem shown in the previous example, the residues have almost no longer any covering ability or parasitic resistance between them, and therefore almost no longer reflect light and microwaves, because the pigment-containing matrix in the laser-treated area no longer behaves like a metallic mirror, but rather like a transparent dielectric.

[0101] Figure 8 The magnified view of the laser-treated area according to the invention shows that although the silver / reflective pigment appears intact outside the area, the pigment appears to have disappeared in the treated area, and also appears to have disappeared below the surface in the right-hand view, because the pigment is made almost spherical by the method according to the invention and the pigment has almost completely lost its covering power.

[0102] Nd-YAG near-infrared (NIR) laser radiation at 1064 nm has proven particularly advantageous for the method because the absorption of the laser by the thin metal layer, A = 1 - RT, is particularly high at this wavelength. However, for a given colored or NIR-absorbing matrix material or a pigment coating that absorbs a given NIR, the absorption at this wavelength may be excessive. Double-frequency (532 nm, green laser beam) or triple-frequency (355 nm, ultraviolet laser beam) lasers have proven more advantageous in particular cases because the thin metal layer of the pigment, which is important for this invention, can absorb the laser beam energy at this shorter wavelength almost as well. Fiber lasers (e.g., short-pulse, Q-switched) or electronic flash tubes (e.g., xenon) can also be used as another form of energy input.

[0103] The matrix materials that can be used include: ABS (acrylonitrile butadiene styrene), ASA, PS, San (styrene polymer), thermosetting plastics, fluoropolymers, PA (polyamide), PBT (polybutylene terephthalate), PC (polycarbonate), PE (polyethylene), PET (polyethylene terephthalate), PETG (polyethylene terephthalate), PMMA (polymethyl methacrylate), POM (polyacetal), PP (polypropylene), silicone resin, TPE (thermoplastic elastomer), and TPU (thermoplastic elastomer).

[0104] Depending on the chemical composition of the pigment structure and the chemical properties of the matrix components, exothermic chemical reactions additionally occur in the method. For example, the filler material calcium carbonate decomposes under laser irradiation and releases carbon dioxide, which advantageously reacts with liquid metal. While the generation of these chemical reactions, indirectly triggered by laser irradiation, is not necessarily necessary to solve the technical problem of the invention, it is particularly advantageous for the method according to the invention, depending on the structure of the pigment, because the laser beam may not need to be so strong, and therefore the negative impact on the matrix is ​​less, since some of the melting energy is provided by the reaction. The temperatures generated by these reactions can advantageously liquefy other, more heat-resistant pigment components, such as a protective layer made of silica or an iron oxide interference layer.

[0105] Surprisingly, the liquid residues of the other, more heat-resistant pigment components were also able to contract compactly due to surface tension and trigger the desired aluminothermic reaction, which residuelessly converts the reflective metallic components of the metallic effect pigments into transparent oxides, such as aluminum oxide. Figure 5 The details shown on the right illustrate how the method according to the invention enables all layers of pigment to mix and react together in a more compact paste containing small air bubbles.

[0106] Figure 5 An enlarged cross-section is shown of a vehicle primer treated with a multilayer pigment having a thin aluminum core, according to the present invention. Figure 5 On the left side, only partially converted pigments can be seen in cross-section, which makes it possible to see its original layered structure.

[0107] Below this is a particularly heat-resistant silica protective layer, which is melted according to the method of the present invention and chemically reacts with the thin aluminum core during the aluminothermic reaction.

[0108] Very high temperatures are required to trigger the aluminothermic reaction with liquefied aluminum, which is extremely difficult to ignite.

[0109] X-ray analysis of the re-solidified pigment residue, similar to the paste, surprisingly revealed a considerable number of calcium atoms, as if these calcium atoms had reacted together. Since the pigment initially contained no calcium, it is largely speculated that the calcium atoms may be a component of common filler materials in the plastic matrix, and that these fillers may have chemically reacted with the pigment components (primarily a thin aluminum core encapsulated with silica), especially since one of the most commonly used fillers is calcium carbonate / calcite / kreide, which is known to decompose into quicklime and carbon dioxide under laser light.

[0110] Although the exact possible chemical interactions have not yet been definitively elucidated, Figure 6 The diagram illustrates how filler materials in one design scheme can help generate very high reaction temperatures with pigments.

[0111] However, it is important to recognize that the metal core is melted by selecting a suitable energy input, and the shape factor of the pigment / particles is changed by surface tension. Neither pigment coatings nor additional filler materials in the paint or matrix are prerequisites for the method, and are even, according to some design schemes, not intended / desired, in order to, for example, reduce foaming of pigment residues due to inherent chemical reactions.

[0112] By selectively altering the pigment in one (local) area (pattern) of a body component while keeping the pigment unchanged in another (local) area, it is possible to provide radar-transparent areas in the paint, while simultaneously providing design flexibility to achieve desired conditions ranging from partial transparency in the visible area to optically invisible structured areas. Therefore, according to a preferred embodiment of the invention, decoupling is achieved between the desired transparency for radar waves produced by patterning / structuring (by inputting energy into selected areas of the body component—e.g., through selective laser scanning or by using a mask) and the transparency in the visible area for an optically visible effect (design).

[0113] The light-transmittant matrix 19 comprises pigment flakes having a thin metal layer or metal core 16. The matrix 19 may, if necessary, contain conventional heat-sensitive filler particles 17, such as CaCO3 (calcite / chalcedony / calcium carbonate), which statistically may be located adjacent to the metal core. The use of CaCO3 in plastics to improve laser-markable properties is known in itself. For example, US 5075195, published in 1991, discloses a laser-marking filler material based on aluminum-effect pigments (with a metal oxide protective layer on the metal core) in a polypropylene matrix using chalk / calcite (=CaCO3) as filler.

[0114] According to the present invention, a laser beam 11 irradiates through a substrate to liquefy a thin metal layer or a partially transparent metal core 16 by partially absorbing the energy of the laser beam A, wherein the energy share A of the beam absorbed can be calculated as the difference A = 1 - RT between the energy reaching the sheet and the energy shares of the reflected (R) and transmitted (T) portions.

[0115] It is hypothesized that the surface tension of the liquid metal, causing it to contract into spherical droplets, forces a significant change in the shape factor of the pigment. After cooling and solidifying, these droplets cover an area much smaller than the original core. The significantly reduced opacity of the re-solidified residue of the original metal core of the pigment flake in the laser-irradiated area not only leads to increased transparency or translucency but also greatly improves microwave transmission due to the reduction in parasitic capacitance caused by the overlapping of the flakes.

[0116] If the thermally decomposable filler particles 17 are located near the pigment, it is also presumed that the liquefied metal will undergo an exothermic reaction with the decomposition products of the filler particles, and at least partially transform into a transparent and dielectric metal oxide, which further enhances the transparency of the irradiated area. For example, very finely ground calcium carbonate particles are commonly used as fillers in primers and masterbatches. Under laser irradiation, the essentially thermally unstable calcium carbonate decomposes into quicklime and carbon dioxide. The latter then undergoes a strong exothermic reaction with the surface 18 of the liquid metal, in which a translucent metal / metal oxide sponge with CO bubbles is formed, as... Figure 5 As shown in the upper right corner, and as explained on page 173 of DC. Curran's paper ("Aluminium Foam Production using Calcium Carbonate as a Foaming Agent", Cambridge University, 2004).

[0117] Due to reaction kinetics, the bubbles contained in the spongy pigment residue are surrounded by a 40-100 nm thick (and transparent) metal oxide film.

[0118] This aluminum-carbon dioxide reaction, 2Al + 3CO₂ → Al₂O₃ + 3CO, which can be used in rocket engines for Mars spacecraft (Rossi et al., "Combustion of Aluminum Particles in Carbon Dioxide", Combustion Science and Technology, Vol. 164, pp. 209-237, 2001), is known to generate very high temperatures (>3000°C), especially through liquid aluminum. Such high temperatures are sufficient to ignite the aluminothermic reaction between the silica protective layer and the aluminum core, which can then potentially convert the remaining aluminum into transparent aluminum dioxide.

[0119] If the core of the metallic effect pigment is alternatively or additionally surrounded by other layers, such as a high-refractive-index chalcogenide layer, such as iron oxide, to achieve an interference color effect, the aluminum-carbon dioxide reaction driven by calcite decomposition can also ignite the aluminothermic reaction between the aluminum core and the chalcogenide layer, thereby completely transforming the thin aluminum core into a transparent oxide. This permanently alters the interference color effect in the laser-irradiated area and creates better radar wave transparency.

[0120] In the existing technology, metallic effect pigment manufacturers generally have technical and safety biases, believing that the thermite reaction poses a fire hazard and is a serious drawback that must be suppressed in any way.

[0121] Figure 7 The charts quantitatively show that the free enthalpy of the pigments according to the invention, having a thin core, preferably a VMP core, is so low that there is virtually no fire hazard and the pigments can be stored and transported more safely and dryly without special fire safety requirements.

[0122] The UTP (ultrathin pigment) of this invention, preferably having a chalcogenide interference layer (e.g., Fe₂O₃) when necessary, has a VMP (velocity permeable) aluminum core. This VMP core achieves better fire safety than classic interference pigments, which, due to their thicker aluminum cores, pose a high risk of aluminothermic reactions and therefore require stoichiometric color restrictions for safety reasons. This lower risk of UTP allows for a wider range of interference colors, which can also be better and more cost-effectively marked as transparent and / or microwave-transparent using laser marking.

[0123] The present invention also relates to products of the method, such as objects painted with metallic effect pigments, such as plastic body parts with higher radar wave transmittance, such as cosmetic bottles, banknotes, or motor vehicle operating components, which are subsequently marked or have micro-marks with transparent, translucent, or backlit markings (in a mirror coating) that are transparent to radar waves and / or light waves.

[0124] Similarly, the present invention relates to metallic effect pigments, interference metallic effect pigments, uses of metal-containing particles suitable for this method, and printing inks, varnishes, masterbatches, and articles containing such suitable particles or pigments, and is optimized for application to the process. Optimization is also achieved, for example, by using suitable laser-sensitive filler materials that promote the chemical reaction or physical deformation of the pigment or the metal content of the metal-containing particles.

[0125] This process differs from traditional laser marking in that the electromagnetic wave transmission of the normally reflective metallic effect pigment surface is persistently enhanced by pigment contraction induced by the laser beam. This is achieved by altering the pigment flakes through direct melting and / or by triggering auxiliary chemical reactions, causing the metallic core of the pigment flakes to at least partially melt, undergo chemical changes, and / or be destroyed. The treated surface can thus become more transparent or translucent.

[0126] For comparison, see Dr. Feist's "Surface Technology". The book Figure 3 (Prior art) illustrates the purpose of conventional laser marking methods.

[0127] Although these techniques have been known for decades as being able to mark pigment paint at the depth (specifically through localized carbonization, vaporization, or chemical changes in the primer substrate) without damaging the preceding clear coat or plastic layer, laser marking methods aimed at physically or chemically altering the metallic effect pigment itself so that it no longer interferes with microwave radiation without unduly impairing the paint's protective properties and / or optical characteristics are not known to date.

[0128] Unlike this invention, processes known from the prior art (engraving, color alteration and carbonization, foaming and layer removal) do not result in physical or chemical pigment transformations. Instead, conventional laser marking methods are based on transformations of the polymer matrix. The technical solutions of conventional laser marking methods neither reduce the opacity of individual pigments nor increase electromagnetic wave projection.

[0129] However, in order to achieve the best results, the method according to the present invention requires a vacuum metal pigment with a thin metal core or layer, or an interference metal effect pigment, preferably a core of a low-melting-point metal, such as tin, aluminum, indium, tin-indium alloy, zinc, lead, silver, copper, etc.

[0130] More preferably, the core can be so thin that it is partially transparent to the laser, thereby allowing the energy of the laser beam to be optimally absorbed within the core even after partial reflections, wherein the amount of metal that must be deformed or transformed remains sufficiently small. In any case, the core must be thin enough that the applied energy is sufficient to melt it.

[0131] However, the desired optical impression of the metallized coating is naturally the primary factor in choosing the optimal core thickness: a thinner aluminum core reflects less light (lower R values ​​in the table below) and therefore appears darker, while a thicker aluminum core (starting at approximately 320 angstroms / 32 nanometers in thickness, where over 90% of the light is reflected) appears as a brighter silver metal.

[0132] Table IV. Reflectance and transmittance of dehydrated Al films on transparent substrates with n=1.5 under optimal conditions at different wavelengths as a function of film thickness. (For film thicknesses > 100 Å, the calculated values ​​are consistent with direct measurements; backside antireflective.)

[0133] T ABLE IV.Calculated reflectance and transmittance of A1 filmsevaporated under optimum conditions onto transparent substrates of n=1.5 forvarious wavelengths as a function of film thickness.(Calculated values ​​agreewith directly measured ones for film thicknesses>100A; back surfaceantireflected.)

[0134]

[0135] Film thickness

[0136] Wavelength = wavelength

[0137] Table IV, from the Optical Society of America Journal, G. Hass and J.E. Waylonis, July 1961, Vol. 51 no. 7, "Optical Constants and Reflectance and Transmittance of Evaporated Aluminium in the Visible and Ultraviolet Spectra," presents the reflectance and transmittance of thin aluminum films at different wavelengths. Although optical absorption is important for quantifying the heating of the core by the laser beam, it is not explicitly given in the table; however, the absorption of a thin aluminum layer or core can be determined from the table using the formula A = 1 - RT. In the thickness range of 8 to 32 nm, absorption of 10% or higher is relatively advantageous. In the thickness range of 8–16 nm, depending on the wavelength, absorption exceeding 15% is sometimes most advantageous, providing relatively strong heating of the aluminum core with relatively low laser energy.

[0138] The aluminum core, for example, is partially transparent to light from an Nd-YAG laser (1064 nm, doubled at 532 nm or tripled at 355 nm) at a thickness of about 40 nm (according to the table, transmittance > 0.2% at a thickness of 40 nm), and is best suited for absorbing laser light at a thickness of 8 to 32 nm, preferably 10 to 20 nm, and is particularly suitable for the method of the present invention within this thickness range.

[0139] Although the absorption of laser energy remains almost constant at 10% when the aluminum core thickness exceeds 40 nm, it is clear that larger cores heat up more slowly with the same energy absorption. Therefore, thicker cores are less conducive to potential physical melting effects or chemical reactions. Furthermore, with thicker cores, the multiple reflections of the laser beam within the pigment have a smaller effect on overall heating compared to when the core is thinner.

[0140] For these reasons, it is speculated, and experiments have confirmed, that a thicker core is not well suited to the method of the present invention, because a thicker core reflects the laser back into the substrate with low loss, and due to its larger volume, it will not heat up quickly anyway.

[0141] When an exothermic chemical reaction, such as an aluminothermic reaction, is triggered in the pigment according to the present invention (e.g., by laser ignition of an interferometric metallic pigment having an aluminum core and an iron oxide coating), a thicker metallic core reacts more violently and dangerously due to the larger amount of metal, thereby increasing the risk of fire. With a thinner aluminum core, the ignited aluminothermic reaction no longer propagates uncontrollably between pigments.

[0142] Based on the current biases regarding fire hazard safety technologies for aluminum nanoparticle-based pigments, aluminum nanoparticles, especially when in contact with specific metal oxides, such as stoichiometric amounts of iron oxide or titanium oxide, should be classified as potentially hazardous materials. (As evidence of these biases, see in particular Eckart's WO 2005 / 049739, according to which the achievable color gamut is limited due to fire hazard; see also Schlenk's EP3283573B1, according to which the aluminothermic reaction can be suppressed when the ratio of aluminum to the remaining substances is determined.) These limitations no longer apply to thin aluminum cores. Therefore, interference metallic effect pigments with thin cores suitable for the method according to the invention are more advantageous in at least two ways: a significantly wider color gamut and higher fire safety, as can be seen in… Figure 5 .

[0143] Although a range of possible physical and chemical explanations for the production of transparency through laser irradiation have been speculated for different pigment structure types, it has not yet been definitively determined which are the most important.

[0144] For pigments consisting only of a thin layer of aluminum metal, requiring an even thinner protective layer, it is speculated that the pigment is heated by a laser or simply melted (aluminum melting point 660°C), and due to the surface tension of liquid aluminum, it essentially loses its very flat shape factor, and as... Figure 4 Re-solidify into an approximate spherical shape as schematically shown, or according to Figure 5 The reaction shown involves a chemical reaction between the laser-sensitive filler material (calcite / chalk, CaCO3) in the plastic matrix and the filler material at approximately 800°C, and as... Figure 6 As shown on the right, it re-solidifies in a sponge-like and approximately spherical manner into aluminum / alumina / quicklime / CO2 / CO, wherein the aluminum is at least partially converted into alumina. In an improved design, it is suggested that MgCO3 / dolomite replace calcite / chalk as the filler material in the coating layer / plastic.

[0145] Therefore, the significant improvement in light and microwave transmission of the treated surface is not only due to Figure 4 Chinese suggestion Figure 8 The experiment showed a decrease in the hiding power of metallic effect pigments (in...). Figure 8 In the treated area, most of the pigment shrinks, leaving only a few pigments visible. This is not only because alumina, as a core transformation product, is essentially translucent, but also because quicklime is white, and because these reaction products can no longer reflect microwaves. This is partly due to the fact that these reaction products are no longer conductive, and partly because the absence of conductive flake components makes... Figure 1 The interface polarization phenomenon illustrated in the diagram will no longer exist, thus almost completely eliminating the parasitic resistance effect that is detrimental to microwave transmission.

[0146] exist Figure 5 The left side shows partially melted pigment that appears to have no chemical reaction characteristics (almost no mixing of layers).

[0147] On the other hand, Figure 5The right side shows clearly foamed pigment residue, which has multiple bubbles like a sponge, as if aluminum had reacted with plastic fillers known to be commonly used as foaming agents, such as calcium carbonate. This aluminum foam reaction is described in Aboraia et al., “production of aluminum foam and the effect of calcium carbonate as a foaming agent,” in the Journal of Engineering Science, Vol. 39, No. 2, March 2011, and in Dr. DC Curran’s 2004 Cambridge University dissertation, “Aluminium foam production using calcium carbonate as a foaming agent” https: / / www.repository.cam.ac.uk / handle / 1810 / 252945; in particular, see the paragraph on “Foaming mechanisms,” pp. 173-174, which relates to carbon dioxide.

[0148] In the two phenomena consistent with the observed experimental results, namely physical melting and / or chemical reactions, the shape factor of the original pigment flakes shrinks sharply, and thus the interfacial polarization and parasitic capacitance caused by pigment overlap also decrease sharply.

[0149] As a computational example, a vacuum-metallized pigment with a diameter of 8 micrometers (corresponding to a covering power of approximately 50 square micrometers) and a thickness of 12 nanometers is described, its metallic core being, for example, made of aluminum or an aluminum alloy in metallic form. The purity of the metal is relatively unimportant to this invention. The pigment is melted by a laser, and as... Figure 5 The detailed view in the upper left corner shows, through experiments, that the pigment, due to surface tension, re-contracts from its liquid state into droplets and then solidifies again in an approximately spherical form. The volume of the pigment remains constant at 0.603 cubic micrometers in both its original flake and droplet forms, which corresponds to a sphere with a diameter of approximately 1.04 micrometers, one of which is only 0.85 square micrometers.

[0150] The opacity of the pigment treated in this way is about 60 times less than that of the original pigment. Therefore, there is now far less pigment overlap against radar waves in the laser-treated area, or almost no overlap between the shrunken pigment residues. Furthermore, the pigment's transparency is much higher because the opacity is reduced by a factor of 60, since the now strongly shrunken pigment areas can hardly cover the background anymore. This transparency is also enhanced by two other phenomena: first, a more pronounced translucency is produced by stronger scattering around the smaller particles; second, the possible chemical reactions (usually oxidation) between the liquid metal core and its surroundings generally produce more transparent reaction products that make the core residues more translucent.

[0151] right Figure 5 The details shown on the right illustrate how multiple bubbles are generated in the paste-like substance of pigment residue after laser irradiation. The pigment residue, apart from these bubbles, is substantially homogeneous, providing a basis for several hypotheses and conclusions regarding the pigment conversion process. Firstly, very high temperatures are likely to be reached, as even the laser-transparent silica (melting point 1710°C) protecting the envelope structure completely melts.

[0152] Secondly, the bubbles in the pigment residue can only be explained by a chemical reaction that involves not only pure physical melting but also the generation of a considerable amount of gas. Since the main components of the pigment (aluminum and silica) can only react with each other via an aluminothermic reaction, and since this reaction cannot produce gas, the observed bubbles can be considered significant evidence. Therefore, other chemical reactions, either directly or indirectly, must occur, which can generate numerous bubbles within the pigment residue during the reaction process. It is known that common filler materials in plastic matrices, such as calcium carbonate, decompose into carbon dioxide and quicklime due to temperature, acting as a foaming agent for liquid aluminum. Furthermore, the combustion of liquid aluminum in carbon dioxide achieves extremely high combustion temperatures, up to 3000°C, which can completely liquefy silica and trigger an aluminothermic reaction between silica and aluminum. This fact makes it possible to explain the bubbles in the pigment residue. Figure 6 The hypothesis that calcium carbonate is considered a reagent and that the bubbles may contain a mixture of unreacted carbon dioxide and carbon monoxide becomes possible.

[0153] Test equipment, test samples, and test results.

[0154] A conventional computer-controlled desktop laser marking device is used as the near-infrared laser source. It has a pulsed Nd-YAG laser with a fixed pulse frequency of 15 kHz at 1064 nm. The desktop laser marking device is equipped with a suitable scanning unit, adjustment unit and sample holding device.

[0155] The device is capable of outputting virtually arbitrary 2D patterns onto test samples with variable pulse intervals (typically using pulse intervals of 6 to 36 micrometers) and specified beam power attenuation from 6 watts to about one-tenth of a watt.

[0156] Since the appropriate pulse interval and pulse power depend largely on the pigment and matrix, the appropriate laser parameters must be determined on a case-by-case basis.

[0157] The test sample was made of a flat polypropylene sheet and equipped with different metallic effect pigments and interference metallic effect pigments having a thin aluminum core according to the invention.

[0158] Polypropylene plates with various concentrations of different metallic effect pigments were provided as test subjects. These pigments were applied directly to the plastic or to the primer, as is common in the automotive industry. Additionally, some samples were coated with a clear coat over the primer, as is common in automotive coatings.

[0159] As a comparative example, non-inventory pigments, such as pearlescent pigments and metallic effect pigments with thicker metal cores, were tested, which confirmed that a thin metal core is indeed important for the method according to the invention.

[0160] For pigments not included in this invention, such as pearlescent pigments from Kuncai, no laser parameters were found to produce any transparency: no transparency was produced, and the matrix was burned when the laser beam was too strong.

[0161] In most of the samples according to the invention, achieving transparency through laser irradiation with a clear varnish proved more difficult, likely due to laser loss in the varnish. This consequently only partially produced the desired transparency result.

[0162] Figure 8 This demonstrates how suitable Nd-YAG laser parameters for each pigment / matrix / substrate combination can be determined by experimental regions with different marking velocities (pulse spacing), laser power, and wait times after each polygon sequence.

[0163] Choose concentrically arranged rings as the track. When power is high and marking speed is low, in Figure 8 In the view on the left, the bright foam of the substrate can be seen on the test sample, and in addition to the achieved transparency, it can also be felt by touch.

[0164] This additional tactile effect may be advantageous or desirable in situations such as creating backlit, laser-treated signs on operating elements made of metallic-effect colored plastic, particularly for control elements with laser-treated signs that must operate at night in car, ship, or aircraft cockpits, computer keyboards, or mobile phones, as well as operating elements that must be both visible and tactile for safety reasons.

[0165] These experiments confirm that when using metallic effect pigments with a thin metallic core, the laser-treated areas become transparent or translucent, and the mirror-like effect within the laser-treated areas is destroyed. This is especially true in... Figure 9 The pair in the right view Figure 8 In a highly magnified detail view of the area, the individual metallic effect pigments become visible due to magnification.

[0166] It has been shown that, in most cases, a beam power of 0.25 watts at 15 kHz is sufficient to produce the transparent / semi-transparent effect and the corresponding reduction in reflectivity of the present invention.

[0167] At higher power levels, it may be as follows Figure 9 As shown individually, it produces more carbonization of the matrix.

[0168] When higher concentrations of foaming agents (such as calcium carbonate decomposed under laser) are used in a targeted manner or when stronger laser irradiation is applied, in addition to localized transparency, the irradiated area can also be given a perceptible tactile effect.

[0169] Figure 9 An enlarged view of the metallic effect colored surface of the test object after laser treatment is shown. The left view focuses on the surface, and the right view focuses on below the surface. The enlarged view shows that in the laser-treated area, the reflective pigment is almost no longer visible, except for some carbonization caused by the laser, and is also almost no longer visible below the surface, because the pigment shrinks under laser irradiation due to the surface tension of the melting and liquid core, so that the covering power of the pigment is effectively eliminated.

[0170] Similarly, due to the shrinkage of the laser-treated pigment, the pigment overlap and parasitic capacitance that cause problems with microwave transmission virtually disappear, resulting in a high reflectivity in the untreated area. Therefore, the laser-treated area does not reflect light or microwaves, which can be achieved by... Figure 11 The network analysis-testing device was validated.

[0171] Figure 10A more mature experimental test matrix with a square-shaped scanned test area is shown at a laser power of 0.25W, a pulse repetition frequency of 15kHz, and a wavelength of 1064nm, and is based on... Figure 8 The principle, parameters, and results of optimizing laser parameters are explained.

[0172] The pulse spacing for the six test areas was 6, 12, 18, 24, 30, and 36 micrometers, with the achieved transparency decreasing accordingly (the illuminated area obviously darkens as the laser pulse spacing increases). The writing speed increased. In the case of 36 micrometers, grid lines and individual irradiation points became visible. Five pigment types and concentrations were tested.

[0173] Results are shown for a low-concentration sample (Chromos pigment, manufacturer Schlenk), which appears particularly dark and almost non-reflective even in areas not treated with lasers, due to the pigment's characteristic of a particularly thin metallic core composed of aluminum (pigment content: 0.16%).

[0174] Five samples were successfully tested, including Schlenk's pure aluminum Decomet pigment, which lacks a silicon protective layer, meaning it does not possess the additional heat of reaction required for the aluminothermic reaction. All samples exhibited similar levels of optical transparency.

[0175] With the help of Figure 11 The waveguide material characterization kit (MCK) shown determines the microwave reflection characteristics of a test sample by measuring the reflection coefficient of the test sample between two waveguides, each connected to a vector network analysis device (VNA).

[0176] For a laser-patterned paint sample made of the interference metallic effect pigment Zenexo Golden Shine according to the present invention (pigment structure: a thin aluminum metal layer, enveloped by a silicon dioxide protective layer, followed by an interference layer composed of iron oxide, with a golden interference color), after laser irradiation with a relatively large and noticeable laser pulse spacing of about 0.1 mm, the reflectance coefficient decreased as expected from -5 dB in the untreated state to -15 dB.

[0177] Transmission characteristics can also be determined by measuring the reflection coefficient. The reflection coefficient (S0.05) is -15 dB. 11 This means that only a very small amount of microwave energy is reflected by the laser-treated paint on the test object, while almost all radar energy is transmitted through the test object without obstruction.

[0178] When performing waveguide measurements, it is possible to quantitatively measure how laser treatment improves the transmissibility of a painted surface to radar waves, and to what extent laser irradiation suppresses unwanted reflections on the paint.

[0179] exist Figure 13 The image shows the characteristics of the radome slot profile (a Y-shaped slot matrix radome, laser-transparent to resemble an object coated with Zenexo Golden Shine pigment).

[0180] exist Figure 14 The image shows the characteristics of a Y-shaped slot matrix radome, which is laser-treated through a 40-micron clear varnish to become an object coated with silver pigment Alustar.

[0181] Figure 12 This illustration shows the measurement of the free-space reflectance coefficient of a test sample, such as a metallic-painted car body component, using a Vector Network Analysis Device (VNA) and a Free-Space Material Characterization Kit (MCK). Illustration source: Michel Joussemet, “novel devices and Material Characterization at mm-wave and Teraherz,” Agilent Technologies, available via the internet at https: / / www.keysight.com / upload / cmc_upload / All / noveldevices.pdf.

[0182] Figure 13 and Figure 14 The Y-shaped slot radome outline shown is derived from the teachings of slot antenna theory, which clearly applies to slots in a uniform, well-conducting metal plate. Of course, the slot radome is not the only possible application of this invention in the microwave, radar, or 5G telecommunications fields.

[0183] The invention also includes manufacturing transmitting or receiving antennas or antenna elements on plastics using laser-treated metallic effect pigment paint, and manufacturing relatively inexpensive radar-absorbing structures for flying objects.

[0184] When using VMP pigments and suitable, particularly low-loss dielectric substrates, the overall teachings of antenna theory and radiation absorption structures can be extrapolated, especially in the microwave range, to metallic effect colored surfaces, because these pigments are particularly smooth and have good overlap properties from the manufacturing process.

[0185] Figure 13 and Figure 14The Y-shaped slit and the circular radome outline shown were laser-processed and then experimentally measured under a millimeter beam (at a frequency range of approximately 76 GHz, corresponding to a wavelength of 4 mm).

[0186] according to Figure 15 Measurements of the painted polycarbonate sheet were compared with those of the untreated metallic-effect colored surface.

[0187] These measurements indicate that, for pigmented materials (tests 38-1 to 38-7, aluminum thickness not exceeding 80 nm), laser treatment has a considerable impact on the reflection and transmission of millimeter waves. Particularly for structure 3 (a complete circle treated with laser), the test results are almost as good as those for the unpigmented polycarbonate sheet.

[0188] Other important aspects of the present invention can be described as follows: The technical solution of the present invention is to provide a method for persistently improving the transparency, translucency, or transmittance of a substantially dielectric object or layer comprising a sheet containing metal or particles coated with metal to electromagnetic waves or other electromagnetic radiation, characterized in that the metal component of the sheet or particles is preferably at most 80 nm thick, more preferably at most 30 nm thick, and an energy input (light input or heat input, etc.) achieved, for example by laser, is sufficient to achieve a persistent shape change of the metal component and / or trigger a chemical reaction of the metal component, said shape change or chemical reaction significantly improving the transparency, translucency, or transmittance of the object or layer to electromagnetic waves.

[0189] However, preferably, it does not cause damage to the dielectric layer or the object itself.

[0190] The technical solution of the present invention also lies in any product of a method for improving the transparency, translucency, or transmission of an object with respect to electromagnetic waves.

Claims

1. A reprocessing method for improving radar wave transmittance in painted vehicle body parts, the method comprising the following steps: - Provides painted vehicle body parts, said vehicle body parts comprising metallic effect pigments, interference metallic effect pigments, or metal-containing particles that at least partially have a thin, bonded metallic component in the form of metal. -Introducing lasers, The laser is characterized in that it is designed to at least trigger the melting of the metallic component of the pigment or particles in metallic form, thereby changing the shape factor of the pigment or particles and thereby improving the transmission of radar waves without damaging the coating and / or impairing the optical properties of the coating. The pigment, heated by the laser, melts and loses its flat shape factor due to the surface tension of the liquid metal, shrinking into spherical droplets. The surface tension of the liquid metal forces a significant change in the shape factor of the pigment.

2. The reprocessing method according to claim 1, wherein, By selectively scanning with lasers or by using masks, certain areas of the vehicle body can be selectively protected from or exempted from laser input.

3. The reprocessing method according to claim 1, characterized in that, Multiple localized laser inputs create patterns in painted vehicle body parts, the patterns consisting of areas with altered pigments and areas without altered pigments.

4. The reprocessing method according to claim 3, characterized in that, The pattern improves only the transmittance or transmission characteristics for radar waves.

5. The reprocessing method according to claim 3, wherein, The selected pattern is used as a frequency selective surface, which is used to manufacture radar-absorbing materials.

6. The reprocessing method according to claim 3, wherein, The pattern design is such that the paint layer formed by the painting constitutes an electromagnetic functional component of a surface that selectively absorbs wavelengths.

7. The reprocessing method according to claim 6, wherein, The pattern design is such that the paint layer constitutes an electromagnetic functional component of a slot antenna, radome, or array antenna.

8. The reprocessing method according to claim 1, characterized in that, Improved radio wave transmission, radar wave transmission, or millimeter wave transmission is achieved in desired areas of the vehicle body components by forming slit patterns in the paint layer formed by laser processing.

9. The reprocessing method according to claim 8, characterized in that, A slotted radome pattern is formed in the paint layer by laser processing.

10. The reprocessing method according to claim 9, characterized in that, Because the width of the lines formed by laser processing in the slotted radome pattern is less than one-tenth of a millimeter, the pattern formed by laser processing in the paint layer is imperceptible to the human eye.

11. The reprocessing method according to claim 1, characterized in that, The thin binder metal component of the pigment in metallic form is designed to be so thin that it is partially transparent to the laser used in the method with wavelengths between 10600 nm and 266 nm; that is, the metal component is designed to be so thin that at least 0.2% of the laser light is transmitted through it at at least one wavelength in the wavelength range.

12. The reprocessing method according to claim 1, characterized in that, The initial sheet or thin metal component is at least partially liquefied and resolidified in a spherical shape.

13. The reprocessing method according to claim 1, characterized in that, The metallic component of the pigment reacts with other components of the pigment and / or with the laser-sensitive filler material of the matrix through an exothermic chemical reaction, either by synergy or by partially absorbing the laser input, and the pigment is embedded in the matrix.

14. The reprocessing method according to claim 1, characterized in that, The metallic component is a vacuum-metallized pigment, or has a vacuum-metallized core or layer, wherein the metallic component has a metallic core of maximum thickness or a layer of less than 80 nm.

15. The reprocessing method according to claim 1, characterized in that, The method described herein reduces the reflectivity or albedo of light waves perpendicular to the pigment surface by at least 6 dB, wherein "light waves" here also includes infrared or ultraviolet waves, provided that the measured wavelength of light is smaller than the diameter of the untreated pigment.

16. The reprocessing method according to claim 1, characterized in that, The radio wave reflectivity, radar wave reflectivity, reflection scattering parameter, or albedo perpendicular to the pigment surface is reduced by at least 6 dB using the method described above.

17. The reprocessing method according to claim 1, characterized in that, By using the method, the radio wave transmittance, radar wave transmittance, or millimeter wave transmittance of the colored surface of the treated object is increased by at least 6 dB for at least one of the following light wavelengths: infrared, visible light, or ultraviolet light.

18. The reprocessing method according to claim 1, wherein, The metallic component in the form of metal is composed of metals or alloys with relatively low melting points.

19. The reprocessing method according to claim 1, wherein, A portion of the metallic component in the form of metal undergoes an exothermic reaction with a metal oxide layer containing metal particles or a metal oxide layer of pigment, and the metallic component is at least partially oxidized.

20. The reprocessing method according to claim 2 or 3, wherein, The laser input directly or indirectly causes the outer surface area of ​​at least one pigment or metal-containing particle to decrease by a factor of 10 through surface tension, thereby resulting in a corresponding reduction in the pigment's covering power, which in turn increases transparency and radio wave transmittance.

21. A painted vehicle body component or paint layer comprising at least one pigment or metal-containing particles converted by a reprocessing method according to any one of claims 1 to 20, without damaging the paint layer and / or impairing its optical properties at that location.

22. The painted vehicle body component or paint layer according to claim 21, wherein, The layer / matrix containing the pigment / particles includes polyimide, polystyrene, polyethylene, fluoropolymers, or mixtures thereof.

23. The painted vehicle body component or paint layer according to claim 22, wherein, The layer / matrix containing the pigment / particles is polymethacrylimide.

24. A convertible particle, said convertible particle being used in the reprocessing method according to claim 1, wherein, The particles contain at least: - The first metal in metallic form; and - A first oxide that encapsulates the first metal, with or without an intermediate layer.

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