Composite film structure, method and apparatus capable of inkless color printing with ultrafast laser

Abstract

The application discloses a composite film structure capable of realizing color inkless printing by using ultrafast laser, and a printing method and equipment.The dielectric surface of a metal / dielectric composite film is irradiated by focused ultrafast laser pulses, so that an oxidation reaction is induced on the dielectric film surface to form a transparent oxide film, and finally a three-layer composite film of metal / dielectric / oxide is formed from bottom to top.The thickness of the oxide film at the corresponding position is controlled by changing the total energy density of irradiation, so as to change the color of the composite film surface at the corresponding position.The method for realizing color inkless printing by using ultrafast laser has a resolution of 20000 dpi.The composite film structure can form double-resonance absorption in the visible light band, so that the color gamut formed can cover more than 85% sRGB.The printing method does not involve any organic matter and toxic substances, and is environment-friendly.

Description

Technical Field

[0001] This invention belongs to the industrial application field of ultrafast laser advanced manufacturing, specifically relating to a composite film structure, method, and equipment that can achieve inkless color printing using ultrafast lasers. Background Technology

[0002] Color printing has become commonplace in homes, with nearly 150 million printers sold worldwide annually. However, printers are a significant source of environmental pollution because widely used inkjet or laser color printers require large amounts of ink or toner. These materials cause substantial environmental pollution. First, inks contain concentrations of volatile harmful substances and elements such as lead, cadmium, mercury, and polybrominated biphenyls (PBBBs). Second, toner releases large amounts of microparticles that can be absorbed by the human body during printer operation. Current research indicates that in a closed room, the number of airborne particulates is five times higher when a printer is running. When inhaled, these particles can penetrate the lungs, causing various respiratory inflammations in mild cases and cardiovascular diseases or even cancer in severe cases.

[0003] Therefore, developing inkless printing technology is not only of significant environmental importance but also has substantial commercial value. In 2016, Delft University of Technology in the Netherlands invented an inkless printing technology. Its working principle involves focusing infrared light through a specific lens to "burn" the paper, a process known as carbonization. However, the content printed using this technology will fade over time, and it can only achieve monochrome printing, making it difficult to print color images.

[0004] To address the inability of traditional inkless printing to produce colored patterns, recent years have seen the development of solutions utilizing ultrafast lasers to fabricate micro- and nano-structures on material surfaces to generate structural colors. Currently, ultrafast laser color printing technology mainly falls into three categories: 1) laser-induced self-organized nanogratings; 2) laser-induced self-organization of metal surfaces to generate nanoparticles with localized plasmon resonance; and 3) laser-induced formation of oxide films on stainless steel surfaces. Nanogratings produce iridescent colors, which have some application value in anti-counterfeiting, but cannot produce patterns of specific colors. Metal nanoparticles, due to localized surface plasmon resonance absorption, can form colors that do not change with the viewing angle, but their color gamut is very narrow, covering only 15% of the standard RGB color gamut, and can only be produced on noble metal surfaces, thus limiting their application. The last solution is based on Fabry-Perot interference of transparent oxide films formed on metal surfaces, such as stainless steel—similar to the principle of soap bubbles producing color. Therefore, its color varies significantly with the viewing angle, and its color gamut is also narrow, generally covering only 30% of the standard RGB color gamut. Therefore, the main problem we face is how to broaden the color gamut of ultrafast laser color printing while ensuring that the color does not change with the viewing angle. Summary of the Invention

[0005] This invention provides a composite film structure that can achieve color inkless printing using ultrafast lasers.

[0006] This invention also provides a method for achieving wide color gamut color printing on the surface of a high-absorption metal thin film and a high-absorption dielectric thin film using ultrafast lasers. This dual-layer composite film has a total thickness of <150 nanometers and can be deposited on almost any substrate material.

[0007] The present invention also provides a device for achieving color inkless printing using ultrafast lasers.

[0008] A composite film structure capable of color inkless printing using ultrafast lasers is a metal / dielectric composite film structure that satisfies the following: when a focused ultrafast laser pulse irradiates the dielectric surface of the metal / dielectric composite film, an oxidation reaction is induced on the dielectric film surface to form a transparent oxide film, ultimately forming a three-layer composite film consisting of metal / dielectric / oxide layers from bottom to top. The color of the corresponding position on the composite film surface can be changed by controlling the thickness of the oxide film at the corresponding position by changing the total energy density of the irradiation.

[0009] Preferably, the lower layer of the metal / dielectric composite film is a metal material with high absorption in the optical band (the real part of the metal's dielectric constant is negative at the laser wavelength, and its absolute value is close to its imaginary part, such as titanium nitride, titanium, chromium nitride, platinum, etc.); the upper layer is a dielectric film with high absorption in the visible light band, such as silicon, germanium, titanium aluminum nitride, etc. After depositing the high-absorption dielectric film on the high-absorption metal surface, ultrafast laser is used to induce oxidation on the dielectric film surface, thereby achieving wide color gamut color printing.

[0010] Preferably, the lower layer of the metal / dielectric composite film is one or more of titanium nitride, titanium, chromium nitride, and platinum; the lower layer is one or more of silicon, germanium, and titanium aluminum nitride.

[0011] In this invention, the lower layer of the composite film is a metal film, and the upper layer is a dielectric film. The thickness of the metal film is not limited, but generally it is >50 nanometers. However, preferably, its thickness is between 20-50 nanometers, which saves material while ensuring the formation of a complete metal film. The thickness of the dielectric film is between 30-100 nanometers. Preferably, the thickness of the dielectric film is between 50-100 nanometers. Dielectric films within this thickness range can form structural colors with the widest color gamut.

[0012] A method for achieving color inkless printing using ultrafast lasers includes: irradiating the dielectric surface of the metal / dielectric composite film described in any of the above technical solutions with a focused ultrafast laser pulse, inducing an oxidation reaction on the surface of the dielectric film to form a transparent oxide film, ultimately forming a three-layer composite film consisting of metal / dielectric / oxide layers from bottom to top; and changing the thickness of the oxide film at corresponding positions by changing the total energy density of the irradiation to change the color (and reflection spectrum) at corresponding positions on the surface of the composite film.

[0013] The composite thin film of this invention can be deposited on any substrate material, all of which are free of any organic components. The substrate material can be a planar substrate or object surface, a surface structure with a specific structure, or even an arbitrary curved surface. Preferably, this invention can deposit a metal thin film (or other suitable material) on an optically flat substrate such as glass, sapphire, or silicon wafer using vacuum magnetron sputtering (or other existing methods), followed by a dielectric thin film. Alternatively, the film can be deposited on a substrate with a certain degree of roughness, such as an unpolished single-crystal silicon surface.

[0014] The metal / dielectric two-layer composite thin film material of this invention replaces traditional paper, and its base color can be changed by altering the thickness of the dielectric film. The film can be coated on any smooth or somewhat rough (such as unpolished silicon wafers) hard or flexible (such as aluminum foil and steel foil) substrate.

[0015] This invention enables the on-site fabrication of the aforementioned bilayer composite film. Specifically, it involves coating a highly absorbent dielectric film (such as silicon, germanium, or titanium aluminum nitride) with a highly absorbent dielectric film (such as titanium nitride, titanium, or platinum) in the visible light band, forming a two-layer composite film. This composite film material can be prepared via magnetron sputtering or electron beam evaporation. Alternatively, readily available composite film products can be used.

[0016] In this invention, the metal material in the composite thin film is selected as a high-loss metal material in the optical band, so as to form a nontrivial phase shift at the interface between the metal material and the dielectric material, thereby reducing the thickness of the thin film and improving the material utilization efficiency. Preferably, titanium nitride is used as the metal material because titanium nitride has advantages such as high hardness and wear resistance, which can effectively extend the service life.

[0017] In this invention, the upper dielectric film of the composite thin film undergoes an oxidation reaction under ultrafast laser irradiation, forming a transparent oxide film. Preferably, aluminum titanium nitride is used as the dielectric film. First, aluminum titanium nitride exhibits high absorption in the visible light band. Second, under laser irradiation, aluminum titanium nitride forms transparent aluminum oxide and titanium oxide, effectively forming a three-layer composite thin film of metal / dielectric / oxide. Furthermore, both aluminum titanium nitride and aluminum oxide possess advantages such as wear resistance, high temperature resistance, and corrosion resistance, thus allowing the resulting structural color to be preserved for a long time. Simultaneously, when using aluminum titanium nitride, the composite thin film material can be rapidly prepared using mature processes such as magnetron sputtering or electron beam evaporation.

[0018] In this invention, the surface area of ​​the oxide film depends on the laser-affected area. The printed color can be controlled by adjusting the incident laser energy density, scanning speed, and number of repeated scans. The aforementioned ultrafast laser amplification can be combined with a controllable three-dimensional translation stage and a micromirror. The three-dimensional translation stage is used to adjust the laser energy density acting on the film surface and broaden the laser writing field range. The micromirror is used to change the laser beam irradiation position to achieve patterning.

[0019] This invention focuses an ultrafast laser pulse onto a two-layer composite film composed of a high-absorption metal and a high-absorption dielectric. The laser beam induces an oxidation reaction on the surface of the dielectric material, forming a transparent oxide film. A dual resonant absorption occurs between the metal, the dielectric, and the laser-induced oxide film. By controlling the thickness of the oxide film, the absorption spectrum in the visible light band can be tunable, thereby achieving structural colors with an ultrawide color gamut.

[0020] This invention requires an atmospheric or pure oxygen environment. The bilayer composite film is irradiated with an ultrafast laser, inducing an oxidation reaction in the surface dielectric material to form a transparent oxide layer in the laser-irradiated area, thereby forming a metal / dielectric / oxide three-layer composite film with dual resonant absorption in the visible light band.

[0021] In this invention, preferably, the laser used is a picosecond pulsed laser with a flat-topped energy distribution. The ultrafast laser pulse has a pulse width of less than 10 picoseconds, circular polarization, and no restrictions on repetition frequency or center wavelength (e.g., wavelength 600 nm-1500 nm). The energy density at the focal point reaches the oxidation threshold of the desired dielectric material but is below the ablation threshold.

[0022] Preferably, the energy density at the focal point is between 0.01 and 0.05 J / cm². 2 Between these processes, the laser is focused onto the sample surface to induce an oxidation reaction. The power density after focusing is much lower than the ablation threshold of the thin film. For example, the multi-pulse ablation threshold of silicon is 0.2 J / cm². 2 .

[0023] In this invention, the laser scanning path is arbitrary. In actual processing, a more optimized scanning path can be designed as needed.

[0024] In this invention, changing the printing color can be achieved by changing the laser energy or scanning speed alone, or by changing both simultaneously, or by repeating scanning, etc. Its essence is to change the total energy density of the irradiation per unit area.

[0025] For ease of processing, it is preferable to focus the ultrafast laser onto the sample to achieve a sufficiently high power density to cause oxidation on the dielectric surface.

[0026] Preferably, ultrafast lasers use circular polarization. This prevents the formation of periodic ripples on the material surface due to interference between surface electromagnetic waves and the incident laser in linear polarization mode, which would otherwise result in iridescent colors. Therefore, the polarization mode of the laser spot must be determined before irradiating the thin film. The polarization state of the laser is determined using a half-wave plate and a polarizing beam splitter, combined with a spot analyzer.

[0027] An apparatus for achieving color inkless printing using ultrafast lasers, comprising:

[0028] Ultrafast laser emitter, used to provide the required ultrafast pulsed laser;

[0029] Light intensity regulating element to adjust the energy of the input laser;

[0030] Polarization adjustment optical elements adjust the polarization of the incident laser to the desired polarization state;

[0031] A focusing optical element is used to focus the laser, after adjusting the light intensity and polarization direction, onto the two composite films.

[0032] The scanning direction adjustment element is used to adjust the scanning direction of the focused laser along the x and y axes.

[0033] When the polarization direction of the incident laser is already determined and meets the processing requirements, i.e., when the polarization of the incident laser is circularly polarized, the aforementioned polarization adjustment optical element can be omitted.

[0034] Preferably, the scanning direction adjustment element is a micro-mirror assembly;

[0035] Preferably, the intensity regulating element is a combination of an optical half-wave plate and an optical analyzer, or an attenuator that can adjust the energy level to adjust the laser intensity to obtain the laser with the desired energy.

[0036] Preferably, the polarization adjustment optical element is an optical waveplate; the focusing optical element is a lens.

[0037] As a preferred option, a three-dimensional displacement stage that can be used in conjunction with a scanning direction adjustment element to achieve large-area printing is also included.

[0038] Preferably, it also includes one or more of the following elements:

[0039] A laser spot analyzer is used to observe the desired laser spot pattern.

[0040] An industrial camera is used to adjust the spatial position of the laser spot on the surface of the composite film and to acquire images of the laser action process.

[0041] The computer controls the light intensity adjustment element to adjust the light intensity, and controls the scanning direction adjustment element to adjust the scanning direction.

[0042] As a preferred method, during the laser irradiation of the thin film, an industrial camera is used to observe the material surface in the laser-affected area, enabling real-time monitoring of the entire processing process.

[0043] When the processing conditions (scanning speed, laser energy, working distance, etc.) are predetermined, the spot analyzer can be omitted.

[0044] During the manufacturing process, laser light is emitted from a laser source, its mode is adjusted by polarization-adjusting optical elements, and then focused onto the sample by a lens. During laser irradiation, the color of the thin film surface changes with varying scanning speed and laser energy density.

[0045] Before actual printing, several experiments can be conducted on the selected composite film material to obtain a database or curve showing the relationship between scanning speed and color for that material. Using a computer or other known software, the correspondence between the color data of the document to be printed and the scanning speed can be established, and the laser can be automatically controlled for scanning and printing.

[0046] The composite thin film structure used in this invention readily undergoes an oxidation reaction on its surface under laser irradiation, forming a transparent oxide. The structural colors generated by the interference of the three-layer metal-dielectric-oxide thin film formed after the laser-induced oxidation reaction remain largely unchanged with the viewing angle, and the color gamut is significantly wider than that of the two-layer metal-dielectric thin film.

[0047] This invention utilizes an ultrafast laser to achieve color inkless printing with a resolution of up to 20,000 dpi, exceeding that of ink-based printers currently on the market.

[0048] The composite film structure of the present invention can achieve color inkless printing using ultrafast lasers, and will form double resonant absorption in the visible light band, thereby resulting in a color gamut that can cover more than 87% of sRGB.

[0049] The printing method of this invention does not involve any organic matter or toxic substances, and is environmentally friendly. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the material system and ultrafast laser inkless printing equipment involved in the present invention.

[0051] Figure 2 The reflection spectrum and corresponding CIE color gamut of the multilayer thin film (each layer in the corresponding film structure of (a) to (c) of the present invention is 50 nanometers thick) involved in this invention.

[0052] Figure 3 (a) is the color plate generated on the surface of a 50 nm titanium nitride and a 50 nm aluminum titanium nitride thin film using ultrafast laser in this invention, and its corresponding color gamut in the CIE1931 color coordinate system (b).

[0053] Figure 4 These are the reflection spectra of the laser-colored material in this invention at different incident angles in the visible light band.

[0054] Figure 5 A photo of the "Westlake University Yung Valley Campus Academic Ring" created by depositing 50-nanometer titanium nitride and 50-nanometer aluminum titanium nitride onto a polished 4-inch single-crystal silicon wafer and then coloring it with an ultrafast laser.

[0055] Figure 6 A photo of the "Westlake University Yung Valley Campus Academic Ring" created by depositing 50-nanometer titanium nitride and 50-nanometer aluminum titanium nitride onto the rough surface of an unpolished 4-inch single-crystal silicon wafer and then coloring it with an ultrafast laser.

[0056] Figure 7 A colored copy of the "Preface to the Poems Composed at the Orchid Pavilion" was created by coating 50 nanometers of titanium nitride and 50 nanometers of aluminum titanium nitride onto a 10-micrometer-thick steel foil and then writing it with an ultrafast laser. The artwork was then rolled up on a soda can. Detailed Implementation

[0057] The invention will now be further described with reference to the accompanying drawings.

[0058] like Figure 1 As shown, titanium nitride 3 and aluminum titanium nitride 4 are continuously deposited on substrate 2 to form a double-layer metal / dielectric composite film. The substrate is placed on a three-dimensional electric displacement stage 1. The ultrafast laser pulse 12 passes through the energy control element 11 (in this embodiment, a combination of a half-wave plate and an optical analyzer is used; an attenuator capable of adjusting the energy level can also be used), the polarization adjustment element 10 (in this embodiment, a half-wave plate and a polarizing beam splitter are used), the x-axis micromirror 8, and the y-axis micromirror 9, and is then focused onto the surface of the aluminum titanium nitride film 4 by the lens 7.

[0059] In this example, the laser's center wavelength is 1030 nm, the pulse width is 10 picoseconds, and the repetition frequency is 5 kHz. Under laser pulse 12, aluminum titanium nitride 4 reacts with oxygen molecules 6 in the air to form a transparent oxide film 5 composed of aluminum oxide and titanium oxide. Figure 1 The black arrows in the diagram illustrate the optical path of incident light after reflection and refraction at the interface of the multilayer thin films. The thickness of the oxide film 5 is controlled by adjusting the laser energy and the total number of irradiation pulses; the energy density at the focal point is between 0.01 and 0.05 J / cm². 2 The reflectance spectrum of the composite film can be changed to form different colors. An industrial camera 13 is used to monitor the color formed on the sample surface. A computer 14 is used to adjust the scanning speed of the laser energy control element 11, the x-axis micro mirror 8, and the y-axis micro mirror 9 in a timely manner based on the color recorded by the industrial camera 13, forming a feedback system to ensure that the printing process is precise and controllable.

[0060] Figure 2 This invention relates to the composite thin film reflectance spectrum and color gamut in the CIE 1931 color coordinates. For example... Figure 2 As shown in (a), the monolayer aluminum nitride titanium film II and the dielectric aluminum nitride film III exhibit a broad-band reflection spectrum in the visible light band, and therefore lack a specific color. However, when an aluminum nitride film is deposited on top of an aluminum nitride titanium film, a nontrivial phase shift between the two films leads to resonant absorption, such as... Figure 2 The numerical simulation in (a) and the experimentally measured spectra in the inset (a reduced-down version of (a)) are shown. Resonant absorption caused by the nontrivial phase shift results in film structural colors that are largely independent of the observation angle. Similarly, when titanium aluminum nitride II is deposited on a titanium nitride I film, resonant absorption also occurs, as... Figure 2 As shown in (b). Therefore, after titanium nitride I, titanium aluminum nitride II, and transparent dielectric aluminum nitride III form a three-layer composite film, a dual resonant absorption is achieved, resulting in the film exhibiting a green color, as shown in [the diagram]. Figure 2 The measured reflectance spectrum is shown in (c). Dual resonance absorption can effectively broaden the color gamut. For example, to form a green reflectance spectrum, absorption must be formed in both the red and blue light bands. However, the single resonance of the two thin films can only absorb one of the bands, making it difficult to form green. Figure 2 (a) and (b) are the reflectance spectra from the numerical simulation. Figure 2 (c) is the experimentally measured reflectance spectrum. Figure 2 (d) illustrates the color gamut of titanium nitride I with aluminum titanium nitride II of varying thicknesses (as indicated by the gray arrows, where the thickness of aluminum titanium nitride I increases uniformly from 10 nm to 50 nm). Adding a 40 nm or 50 nm thick layer of transparent dielectric aluminum nitride to titanium nitride I and aluminum titanium nitride II effectively broadens the color gamut (e.g., ...). Figure 2As indicated by the black arrow in d, where t1 represents the thickness of the top transparent dielectric film. It should be noted that in this example, aluminum nitride is used as the top transparent dielectric for ease of deposition. However, in the structural color produced by laser-induced oxidation, the top layer consists of transparent aluminum oxide and titanium oxide.

[0061] The color produced after laser-induced oxidation of aluminum titanium nitride thin film to form oxide film is mainly related to the single pulse energy and the scanning speed of x-axis micromirror 8 and y-axis micromirror 9. Figure 3 The color swatches created in this example are shown, achieving over 85% of the sRGB and CMYK color gamuts in CIE 1931. From Figure 3 As shown in (b), compared to the structural color of the aluminum nitride / titanium aluminum nitride bilayer film—that is, the primary color of the composite film—the color gamut of the three-layer composite film formed after laser-induced oxidation is significantly broadened (laser coloring). In this example, the shape of the reflectance spectral lines of the three-layer composite film formed after laser-induced oxidation does not change significantly with the change of the observation angle, such as... Figure 4 As shown, the structural color formed using this material and method is therefore independent of the viewing angle.

[0062] The ultrafast laser processing structural color method of this invention offers high flexibility. Composite thin films can be deposited on smooth substrates, such as... Figure 5 As shown, it can also be plated on a rough substrate, such as... Figure 6 As shown, it can even be deposited on non-planar substrates, such as... Figure 7 As shown.

Claims

1. A method for achieving color inkless printing using ultrafast lasers, characterized in that, include: By irradiating the dielectric surface of a metal / dielectric composite film with a focused ultrafast laser pulse, an oxidation reaction is induced on the dielectric film surface to form a transparent oxide film. Finally, a three-layer composite film consisting of metal / dielectric / oxide layers is formed from bottom to top. The color of the corresponding position on the surface of the composite film is controlled by changing the total energy density of the irradiation. The metal / dielectric composite film has a metal / dielectric composite film structure. The lower layer of the metal / dielectric composite thin film is a metal material with high absorption in the optical band; the upper layer is a dielectric thin film with high absorption in the visible light band. The lower layer of the metal / dielectric composite film is one or more of titanium nitride, titanium, chromium nitride, and platinum; the upper layer is one or more of silicon, germanium, and titanium aluminum nitride.

2. The method for achieving color inkless printing using ultrafast lasers according to claim 1, characterized in that, The ultrafast laser pulse has a pulse width of less than 10 picoseconds, is circularly polarized, and has an energy density at the focal point that reaches the oxidation threshold of the required dielectric material but is below the ablation threshold.

3. The method for achieving color inkless printing using ultrafast lasers according to claim 1, characterized in that, In the metal / dielectric composite thin film, the thickness of the metal thin film is >50 nanometers, and the thickness of the dielectric thin film is between 30 and 100 nanometers.

4. The method for achieving color inkless printing using ultrafast lasers according to claim 1, characterized in that, Titanium nitride is used for metallic materials; titanium aluminum nitride is used for dielectric thin films.

5. An apparatus for achieving color inkless printing using an ultrafast laser, implementing the method of any one of claims 1 to 4, characterized in that, include: Ultrafast laser emitter, used to provide the required ultrafast pulsed laser; Light intensity regulating element to adjust the energy of the input laser; Polarization adjustment optical elements adjust the polarization of the incident laser to the desired polarization state; A focusing optical element is used to focus the laser, after adjusting the light intensity and polarization direction, onto the metal / dielectric composite film. The scanning direction adjustment element is used to adjust the scanning direction of the focused laser along the x and y axes.

6. The device for achieving color inkless printing using ultrafast lasers according to claim 5, characterized in that, The scanning direction adjustment element is a micro-mirror assembly; the light intensity adjustment element is a combination of an optical half-wave plate and an optical analyzer, or an attenuator capable of adjusting the energy level; the focusing optical element is a lens.

7. The apparatus for achieving color inkless printing using an ultrafast laser according to claim 5 or 6, characterized in that, It also includes a three-dimensional displacement stage that, in conjunction with scanning direction adjustment elements, enables large-area printing.

8. The device for achieving color inkless printing using ultrafast lasers according to claim 5, characterized in that, It also includes one or more of the following elements: A laser spot analyzer is used to observe the desired laser spot pattern. An industrial camera is used to adjust the spatial position of the laser spot on the surface of the composite film and to acquire images of the laser action process. The computer controls the light intensity adjustment element to adjust the light intensity, and controls the scanning direction adjustment element to adjust the scanning direction.

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