KR20140008521A - Method and apparatus for reliably laser marking articles - Google Patents

Abstract

A method is disclosed for creating a mark 152 with desired attributes on the mark 152 itself and on the anodized specimen 150. The method comprises providing a laser marking system 10, 12, 14, 16, 18, 20, 22 having controllable laser pulse parameters, determining a laser pulse parameter associated with a desired attribute, selected laser pulse parameters Directing the laser marking system 10, 12, 14, 16, 18, 20, 22 to mark the article 18 using. The laser mark 162 so made has optical density, white color, texture indistinguishable from surrounding articles, and durable and substantially intact anodized oxide 160 ranging from transparent to opaque. Anodic oxide 120 may also be dyed and optionally bleached to produce other colors 136 and 144.

Description

METHOD AND APPARATUS FOR RELIABLY LASER MARKING ARTICLES}

This application is a continuation of part of application 12 / 704,293, filed February 11, 2010.

The present invention relates to laser marking of anodized articles. In particular, the present invention relates to marking anodized articles in a durable and commercially desirable manner with a laser processing system. In particular, the present invention relates to characterizing the interaction between anodized articles and ultraviolet, visible and infrared wavelength laser lasers to reliably and repeatably produce durable and commercially desirable white marks on anodized articles. will be.

Marketed products often require some type of marking on the product for commercial, regulatory, cosmetic or functional purposes. Preferred attributes for marking include consistent appearance, durability and ease of application. Appearance refers to the ability to render a mark reliably and repeatably at a selected shape, color and optical density. Durability is the quality that remains unchanged despite the wear of the marked surface. Ease of application refers to costs in materials, time and resources to produce the mark, including programmability. Programmability refers to the ability to program a marking device with a new pattern to be marked by changing software, unlike changing hardware such as a screen or mask.

Lightweight, rigid, easily molded, and durable surface finishes anodized metal articles have many applications in industrial and commercial goods. Anodic oxidation describes one of a number of electrolytic passivation processes that increase the natural oxide layer on metals such as aluminum, titanium, zinc, magnesium, niobium or tantalum for increased corrosion or wear resistance and for cosmetic purposes. . These surface layers can be colored or dyed in virtually any color, creating a permanent, uncolored and durable surface on the metal. Many of these metals can advantageously be marked using aspects of the present invention. In addition, metals such as stainless steel that resist corrosion can be marked in this way. Many articles made from metals such as these need a permanent, visible and commercially desirable marking. Anodized aluminum is an exemplary material with such a need.

It has been known for many years to produce color changes on the surface of anodized aluminum articles with laser pulses. Appl. Phys. A 69 [Suppl.], S343-S346 (1999), pp S43-S346], P. Maja, M. Autric, P. Delaporte, P. Alloncle, COLA'99-5th International Conference on Laser Ablation, July A paper entitled "Dry laser cleaning of anodized aluminum" by 19-23, 1999, Göttingen, Germany describes the removal of anodization from an aluminum surface, but underneath Of note is the color change that occurs at the laser energy.

Our mechanism that has attempted to account for changes in color or optical density of metal surfaces is the generation of laser-induced periodic surface structures (LIPSS). The paper, "Colorizing metals with femtosecond laser pulses" by AY Vorobyev and Chunlei Guo, Applied Physics Letters 92, (041914) 2008, pp 41914-1 to 141914-3, uses femtosecond laser pulses to generate on metals such as aluminum or aluminum. It describes the different colors that can be made. This paper describes the creation of black or gray marks on metal and the gold color on metal. Several other colors are mentioned but no further explanation. LIPSS is only a suggested description for the generation of marks on metal surfaces. In addition, only laser pulses with a temporal pulse width of 65 femtoseconds are taught or suggested to produce these structures. In addition, there is no mention as to whether the aluminum sample is anodized or the surface is cleaned before the laser process. In addition, this paper does not discuss possible damage to the oxide layer.

When discussing the laser pulse duration, a method of measuring the pulse duration should be defined. Temporal pulse shapes can range from simple Gaussian pulses to more complex shapes depending on the task. Exemplary non-Gaussian laser pulses that are beneficial for certain types of processes are described in US Pat. No. 7,126,746 (inventor: Sun et al., Titled “GENERATING SETS OF TAILORED LASER PULSES”), which is an assignee of the present invention. And is incorporated herein by reference. This patent discloses a method and apparatus for generating a laser pulse having a temporal profile that changes from a typical Gaussian temporal profile produced by a diode pumped solid state (DPSS) laser. These non-Gaussian pulses are so-called "tailored" pulses because their temporal profile is fixed from a typical Gaussian profile by generating a single pulse and / or combining more than one pulse to electro-optically modulate the pulse. This often includes one or more power peaks where the instantaneous power increases to a value greater than the average power of the pulse during one fraction of the pulse duration, resulting in a pulse in which the pulse energy changes as a function of time. Tailored pulses of this type can be effective in treating materials at high rates without causing debris problems or excessive heating of surrounding materials. The problem is that measuring the duration of complex pulses such as those using standard methods typically applied to Gaussian pulses can produce anomalous results. Typically Gaussian pulse duration is measured using full width at half maximum (FWHM) measurements. In contrast, using the integral square method, as described in US Pat. No. 6,058,739 (Inventor Morton et al., Entitled “LONG LIFE FUSED SILICA ULTRAVIOLET OPTICAL ELEMENTS”), complex pulse temporal shapes can be obtained. It can be measured and compared in a more meaningful manner. In this patent, pulse duration is measured using the following equation.

Where T (t) is a function representing the temporal shape of the laser pulse.

Another problem with reliable and repeatable calculation of marks with the desired color and optical density in anodized aluminum is that the energy required to produce very dark marks with readily available nanosecond pulse width solid-state lasers damages the anodization. In other words, it is sufficient to cause unwanted results. "Dark" or "bright" or color name is a relative term. Standard methods for quantifying color refer to the CIE system of colorimetric methods. This system is described in CIE Fundamentals for Color Measurements, Ohno, Y., IS & T NIP16 Conf, Vancouver, CN, Oct. 16-20, 2000, pp 540-545. In such a measurement system, achieving commercially desirable black marks requires parameters less than or equal to L * = 40, a * = 5, and b * = 10. This results in black marks of visible gray or neutral color without color. In US Pat. No. 6,777,098 (named “MARKING OF AN ANODIZED LAYER OF AN ALUMINIUM OBJECT”), inventor Keng Kit Yeo takes place in a layer between aluminum and anodized oxide and is thus anodized with a black mark that is as durable as the anodized surface. A method of marking an aluminum article is described. The marks described there are described using infrared laser pulses in the nanosecond range, with shades of dark gray or black and somewhat less shiny than unmarked portions. In addition, aluminum needs to be cleaned on all surface particles, such as those remaining after polishing before anodization. Marking by the method claimed in this patent is disadvantageous for two reasons: firstly, producing commercially desirable black marks with pulses in the nanosecond range tends to cause the destruction of the oxide layer, and secondly, polishing Alternatively, the cleaning of aluminum following other treatments adds another costly step in the process, which is likely to interfere with the desired surface finish by further processing.

What is desired but not disclosed in this field is anodizing to black, white or intermediate gray levels or to color, which does not require expensive femtosecond lasers, obstruct the oxide layer in the process, or require cleaning following surface preparation. It is a reliable and repeatable method of making a mark on wrought aluminum. In addition, no information is provided on how to repeatedly produce various colors on the anodized aluminum surface, and no effects of damage or bleaching on the anodization layer have been thoroughly investigated. Thus, a mark having the desired optical density or grayscale and color on anodized aluminum using a lower cost laser without causing unwanted damage to the underlying oxide or requiring cleaning prior to anodization. There is a need for a method for generating reliably and repeatably.

One aspect of the invention marks anodized aluminum articles with visible white marks of various optical densities. These marks have a durable and commercially desirable appearance. This is accomplished by using a laser marking system to produce a mark. These marks are created in or under the oxide layer and are thus protected by the oxide. The laser pulses make the marks durable by producing commercially desirable marks without causing substantial damage to the oxide layer. Durable, commercially desirable marks are created on anodized aluminum by controlling laser parameters that generate and direct laser pulses. In one aspect of the invention, the laser processing system is adapted to produce laser pulses with appropriate parameters in a programmable manner.

Exemplary laser pulse parameters that may be selected to improve the reliability and repeatability of laser marking anodized aluminum include laser type, wavelength, pulse duration, pulse repetition rate, number of pulses, pulse energy, pulse temporal shape, pulse spatial Shape and focal size and shape. Additional laser pulse parameters include specifying the location of the focal point relative to the surface of the article and directing the speed of relative movement of the laser pulse relative to the article.

Aspects of the present invention are durable and commercially desirable marks by whitening an oxide layer on top of a metal article with optical densities ranging from barely detectable to the naked eye to bright white depending on the specific laser pulse parameters employed. Create Another aspect of the invention creates durable and commercially desirable marks on anodized aluminum by bleaching or partially bleaching dyed or colored anodized oxides with or without marking the underlying aluminum. Another aspect of the present invention is directed to an anodization layer that scatters light without removing all of the anodic oxide, creating a mark that changes appearance from a light “frosted” or diffuse appearance to an opaque, bright, white appearance. Generate a micro-scale modification for the

As embodied and broadly described herein, a method of producing color and optical density selectable visibility marks on anodized aluminum specimens to achieve the above with these and other aspects in accordance with the purposes of the present invention and Disclosed herein is an apparatus adapted to perform the method. Aspects of the present invention produce a visible mark having a selectable color and optical density on anodized aluminum article. The method includes providing a laser marking system having a controller operatively coupled to the laser to control a laser, laser optics and laser pulse parameters, wherein the controller having stored laser pulse parameters is stored associated with a desired color and optical density. Select a laser pulse parameter, and the laser pulse parameter associated with the desired color and optical density, including a temporal pulse width or continuous wave (CW) greater than about 1 picosecond and less than about 1000 nanoseconds to impinge on the anodized aluminum. Direct the laser marking system to yield a laser pulse having

1 shows a laser processing system;
2 shows a mark made of prior art nanosecond pulses;
3 is a mark made of picosecond pulses
4 shows a beam waist;
5 shows grayscale marks on anodized aluminum;
6 shows a mark on anodized aluminum;
7 shows dyed, visible marked anodized aluminum;
8 shows dyed, IR marked anodized aluminum;
9 is a graph showing the visibility laser pulse threshold;
10 is a graph showing an IR laser pulse threshold;
11 shows image data converted into laser parameters;
12A-12I illustrate color anodization applied to an aluminum article;
13 shows a white mark;
FIG. 14 shows grayscale marks on anodized aluminum. FIG.

Embodiments of the present invention mark anodized aluminum articles with visible marks of various optical densities and colors that are durable, selectable, predictable and repeatable. It is advantageous for these marks to appear on or near the surface of aluminum or within the anodic oxide and to protect both the surface and the mark by leaving the anodization layer substantially intact. Marks made in this way are referred to as interlayer marks as they are made on or on the surface of the aluminum underneath the oxide layer forming the anodic oxide or in the oxide itself. Embodiments of the present invention leave the surface of the oxide substantially undamaged after marking to protect the mark and provide a mechanically adjacent surface between the marked and non-marked regions of the neighborhood. Typically the texture of these marks is indistinguishable from the surrounding unmarked anodic oxide in the human hand. In addition, these marks must be able to be reliably and repeatably calculated, provided that a mark with a particular color and optical density is desired, the laser parameters that will produce the desired results when anodized aluminum is processed by the laser processing system. Means that the set of is known. In addition, in some cases it is contemplated that the white marks produced by the laser processing system by modifying the anodization layer are further processed by adding fluorescent or phosphorescent dyes to the anodic oxide before or after the laser treatment.

One embodiment of the present invention uses a laser processing system adapted for marking anodized aluminum articles. An exemplary laser processing system that may be adapted to mark anodized aluminum articles is an ESI MM5330 micromachining system manufactured by Electro Scientific Industries, Inc., 97229 Portland, Oregon. This system is documented in the October 2009 ESI publication "Model 5330ns Service Guide" ESI P / N 178987a, which is incorporated by reference in its entirety. The system is a micromachining system that employs a diode-pumped Q-switched solid state laser with an average power of 5.7W at a 30KHz pulse repetition rate and a second harmonic doubled to 532nm wavelength. Another exemplary laser processing system that may be adapted to mark anodized aluminum articles is also an ESI ML5900 micromachining system manufactured by Electro Scientific Industries, Inc., 97229 Portland, Oregon. The system is documented in the October 2009 ESI publication "Model 5900 Service Guide" ESI P / N 178472A, which is incorporated by reference in its entirety. The system employs a solid-state diode-pumped laser that can be configured to emit wavelengths from about 355 nm (UV) to about 1064 nm (IR) at pulse repetition rates up to 5 MHz. Either system can be adapted by the addition of suitable lasers, laser optics, part handling equipment and control software to reliably and repeatably produce marks on anodized aluminum surfaces in accordance with the methods disclosed herein. These modifications result in a laser having the laser parameters appropriate for the desired location on the anodized aluminum article properly positioned and maintained at the desired rate and pitch to allow the laser processing system to produce the desired mark with the desired color and optical density. Allow to direct the pulse.

1 illustrates an illustration of an ESI MM5330 micromachining system adapted to mark an article in accordance with one embodiment of the present invention. An adaptation is, in one embodiment of the invention, a laser of model Rapid, a diode pumped Nd: YVO ₄ solid state laser operating at 1064 nm wavelength, manufactured by Lumera Laser GmbH, Kaiserslautern, Germany. It includes. Optionally, these lasers use a solid harmonic frequency generator to reduce the wavelength to 532 nm, doubling the frequency, or doubling to about 355 nm, respectively, producing visible (green) or ultraviolet (UV) laser pulses. This laser 10 is rated to yield 6 watts of continuous power and has a maximum pulse repetition rate of 1000 KHz. The laser 10 cooperates with the controller 20 to produce a laser pulse 12 having a duration of 1 picosecond to 1,000 nanoseconds. These laser pulses 12 may be Gaussian or may be specially shaped or tailored by the laser optics 14 to allow for the desired marking. The laser optical system 14, in cooperation with the controller 20, directs the laser pulse 12 to form a laser spot 16 on or near the article 18. The article 18 is fixed on a stage 22 that includes a motion control element that cooperates with the controller 20 and the laser optics 14 to provide composite beam positioning capabilities. Composite beam positioning is achieved by causing the controller 20 to direct the steering element in the laser optics 14 to compensate for the relative movement induced by the movement of the stage 22, the laser spot 16, or both. The ability to mark the shape on the article 18 while 18 is moving relative to the laser spot 16.

The laser pulses 12 are also shaped by the laser optics 14 in cooperation with the controller 20 as they are directed to form a laser spot 16 on or near the article 18. The laser optics 14 directs the spatial shape of the laser pulses 12, which may be Gaussian or specially shaped. For example, a "top hat" spatial profile may be used that delivers a laser pulse 12 having an even dose of radiation across the spot that impinges the article being marked. Such specially shaped spatial profiles can be generated using diffractive optical elements. The laser pulse 12 can also be opened or closed by an electro-optical element, a steerable mirror element or a galvanometer element of the laser optics 14.

The laser spot 16 refers to the focus of the laser beam formed by the laser pulse 12. As mentioned above, the distribution of laser energy in the laser spot 16 depends on the laser optics 14. In addition, the laser optics 14 controls the depth of focus of the laser spot 16, or how quickly the spot goes out of focus as the plane of measurement moves away from the focal plane. By controlling the depth of focus, the controller 20 directs the laser optics 14 and the stage 22 to position the laser spot 16 at or near the surface of the article 18 with high precision and repeatability. You can. Marking by positioning the focal point above or below the surface of the article allows the laser beam to defocus by a specified amount, thereby increasing the area illuminated by the laser pulses and reducing the laser fluence at the surface. Since the geometry of the beam waist is known, precise positioning of the focus above or below the actual surface of the article will provide additional precise control over the spot size and fluence.

FIG. 2 is a microphotograph showing marks produced on anodized aluminum 30 using prior art lasers with> 1 nanosecond pulses. Anodic oxides have shown undesired, undesired sign of cracking 32 in mark region 34. 3 shows the same color and optical density marks 38 on the same type of anodized aluminum 36 made with picosecond lasers that do not exhibit cracking. Picosecond lasers mark anodized aluminum articles in a commercially desirable black color without causing damage to the oxide layer. Commercially acceptable black is defined as a mark having a CIE chromaticity of L * = 40, a * = 5 and b * = 10 or less. Another advantage of using picosecond lasers is that they are much less expensive than prior art femtosecond lasers, require very little maintenance, and typically have a much longer operating life. In addition, aspects of the present invention do not require cleaning of the aluminum surface prior to anodizing to produce commercially desirable marks.

One embodiment of the invention performs marking on anodized aluminum under anodization. In order for interlayer marking to occur without damage to the anode oxide, laser fluence is defined by:

F = E / s

Where E is the laser pulse energy and s is the laser spot area, and

Fu <F <Fs

Where Fu is the laser modification threshold of the substrate, in this case aluminum, and Fs is the damage threshold for the surface layer or anode oxide. Fu and Fs were obtained experimentally and represent the fluence of selected lasers where the substrate and surface layer began to be damaged. For 10 ms pulses, our experiments show that Fu for Al is ~ 0.13 J / cm 2 for green and? 0.2 J / cm 2 for IR, Fs is 0.18 J / cm 2 for green and It is about 1 J / cm 2. Changing the laser fluence between these values produces marks of varying color and optical density. Different pulse durations and laser wavelengths will have corresponding values of Fu and Fs, respectively. The actual threshold for a given set of laser parameters is determined experimentally.

One embodiment of the present invention precisely controls laser fluence at the surface of an aluminum article by adjusting the position of the laser spot to be positioned precisely above or below the surface of the aluminum from being on the surface of the aluminum article. 4 shows a diagram of the laser pulse focus 40 and its near beam waist. The beam waist is represented by the surface 42 which is the diameter of the spatial energy distribution of the laser pulse as measured by the FWHM method on the optical axis 44 along which the laser pulse travels along. The diameter 48 represents the laser pulse spot size on the surface of the aluminum when the laser processing system focuses the laser pulse at an on-surface distance A-O. The diameter 46 represents the laser pulse spot size on the surface of aluminum when the laser processing system focuses the laser pulse at sub-surface distance O-B.

In addition to commercially preferred black, it is also useful to mark articles in grayscale values. 5 and 6 illustrate a series of grayscale marks made on anodized aluminum made by one embodiment of the present invention. The optical density of the mark ranges from almost indistinguishable from the background to full black. According to aspects of the present invention, each grayscale mark can be identified by a unique triple CIE colorimetric value. L *, a * and b *. Aspects of the present invention associate each desired grayscale value with a set of laser parameters that reliably and repeatably yield the desired grayscale value mark on the anodized aluminum upon command. Note also that a mark that may seem indistinguishable with the naked eye may become visible when illuminated with, for example, ultraviolet light other than broad spectrum visible light.

5 shows black marks 60, 62, 64, 66 made on anodized aluminum 70 according to one embodiment of the present invention. These marks 60, 62, 64, 66 have CIE chromaticities ranging from less than L * = 40, a * = 5 and b * = 10 to wholly transparent which makes them a commercially desirable mark. Another feature of these marks is that they have a uniform appearance over a wide range of viewing angles because they are under intact anodic oxide. Marks made using prior art methods tend to have wide variations in appearance depending on the viewing angle due to damage to the anodization layer. Specifically, when marking with prior art nanosecond pulses, applying sufficient laser pulse energy to the surface to create a dark mark causes damage to the anode oxide causing the appearance of the mark to change with viewing angle. The mark made by one aspect of the present invention does not damage the anode oxide, and its appearance does not change with the viewing angle, regardless of how dark the mark is. These improved marks are made with the following laser parameters.

Marks 60, 62, 64, 66 range from virtually invisible 60 to full black 62 as compared to unmarked aluminum in optical density. Grayscale optical densities 64 and 66 between the two extremes are created by moving the focus closer to the article, increasing the fluence to produce darker marks. The height of the focus on the surface of aluminum varies from zero for the darkest optical density mark 62, increasing in 500 micron increments for each mark 64, 66 from right to left in FIG. End at 5 mm above the surface. Note that the mark 64 created with a focus located 4.5-1.5 mm above the surface of aluminum represents tan or gold and the marks 62, 66 created with a focus at 1 mm or less show gray or black. Maintaining this precise control of the laser focal length from the working surface in addition to maintaining other laser parameters in the normal laser process tolerance results in the creation of laser marks with the desired color and optical density on the anodized aluminum. In addition, the darkest marks exhibit CIE chromaticities of less than L * = 40, a * = 5 and b * = 10, making them commercially desirable black marks.

Another aspect of the invention determines the relationship between picosecond laser pulse parameters and marks having colors other than grayscale. Colors other than grayscale can be calculated in two different ways on anodized aluminum. First, gold tones can be calculated with a range of optical densities. This color is produced by changes made at the interface between aluminum and oxide coatings. Careful selection of laser pulse parameters will yield the desired gold color without damaging the oxide coating. 5 also shows various shades of tan or gold produced by one aspect of the present invention.

Laser marking of anodized aluminum can also be accomplished by one aspect of the invention using IR wavelength laser pulses to mark aluminum. This aspect produces a mark of varying grayscale density by changing the laser fluence at the surface of aluminum in two different ways. As discussed above, grayscale can be achieved by varying the fluence at the surface by positioning the focal point above or below the surface of aluminum. The second way of controlling grayscale is to change the total dose at the surface of the aluminum by changing the bite size or line pitch when marking the desired pattern. Changing the bite size refers to adjusting the rate at which the laser pulse beam is moved relative to the surface of aluminum or to changing the pulse repetition rate, or both, as a result of changing the distance between successive laser pulse impact sites on the aluminum. Brings about. Changing the line pitch refers to adjusting the distance between marked lines to achieve various overlapping degrees. 6 shows an aluminum article 74 having an array of marks 72. These marks 72 are arranged in an array of six columns and four rows. The six columns represent the six Z-heights of the focal point on the surface of the aluminum and range from 0 (top row) to 5 mm (bottom row). Four rows represent the pitch of 5, 10, 20 and 50 micron scale values from left to right. As can be seen from FIG. 6, changing the Z-height of the focus and the pitch of the laser pulses can be of any desired, from less than CIE L * = 40, a * = 5, and b * = 10 to almost transparent. Gray levels of optical density can be calculated predictably, thereby yielding commercially desirable marks on anodized aluminum.

A second type of marking that can be applied to anodized aluminum using picosecond or nanosecond laser pulses is a modification in color contrast caused by bleaching of dyed anodized oxides. In general, the anodic oxide is porous and will readily accept many types of dyes. Referring again to FIG. 3, this micrograph of anodized aluminum shows the porous nature of the surface. The laser pulse used to mark the dyed anodized aluminum bleaches the dye depending on the wavelength and pulse energy as it marks the aluminum, revealing the mark on the underlying aluminum by making the anode oxide transparent. With higher fluences, it is possible to simultaneously mark and dye bleach the aluminum under the anodization layer in black, grayscale or the colors shown in the previous section. Less energy pulses can partially color the underlying aluminum mark by partially bleaching the anodic oxide dye and rendering it translucent. Finally, longer wavelength pulses can mark aluminum in a commercially desirable black or grayscale color without bleaching the anode oxide. FIG. 7 shows a dyed anodized aluminum article having marks made with visible (532 nm) laser pulses. Note that the dye in the anodic oxide is bleached in the areas subjected to laser pulses. 8 shows the same type of dyed anodized aluminum article having marks made with IR (1064 nm) laser pulses. Note that the anode oxide is not bleached by the IR laser pulses and thus does not reveal the underlying aluminum color beyond the translucency of the original oxide.

Another aspect of the invention relates to laser marking anodized aluminum with colored anodized oxide using picosecond or nanosecond lasers. Anodic oxidation typically forms a porous surface, so dyes can be introduced that modify the appearance of aluminum. These dyes may be opaque or translucent and cause varying amounts of incident light to reach aluminum and reflect back through the anodic oxide. FIG. 7 illustrates an anodized aluminum article 80 with an array of marks 82 and pink dye in anodization, calculated according to one aspect of the present invention. Color is produced by bleaching the dye in the oxide layer as the underlying aluminum shows a range of laser-marked colors from shades of tan to gray and finally black. These shades are produced by changing the fluence of the laser pulses on the surface of aluminum. Four rows represent laser pulse pitch variations of 10 to 50 microns and columns represent varying focal lengths from the surface by 0.0 to 5.0 mm. In all cases, these laser parameters cause the dye on the aluminum to bleach through the bleaching of the dye over the aluminum. Laser mark optical densities range from transparent to CIE chromaticities of less than L * = 40, a * = 5, and b * = 10. The laser parameters used to generate these marks are given in Table 3.

Bleaching of anodizing dyes is frequency dependent. As shown in FIG. 7, the 532 nm laser pulse bleaches the anodizing dye even at the lowest applied fluence. IR laser wavelengths, on the other hand, produce marks on dyed anodized aluminum without bleaching the dye for most translucent dye colors. 8 shows anodized aluminum article 100 with a pink dye having a mark 102 made of IR laser pulses. Marks were made by fixing the laser fluence, ranging from translucent to black, changing the distance from the focus to the surface, and also the pitch. Six columns represent changing the distance between the surface of aluminum and the focal point of the laser pulse from 5.5 mm (right) to zero (left). Four rows represent changing the laser pulse pitch from 10 to 50 microns. The laser parameters used to generate these marks are shown in Table 4.

The relationship between bleaching anodizing dyes, marking aluminum and causing surface ablation for a 532 nm (green) laser wavelength is shown in FIG. 9. For 532 nm (green) laser pulses having parameters in those given in Tables 1, 2 and 3, FIG. 9 shows anodic oxide bleaching (Fb), marking aluminum under anodization (Fu) and surface ablation ( The fluence threshold for Fs) is shown in J / cm 2. For one aspect of the invention a 532 nm laser pulse yields Fb = 0.1 J / cm 2, Fu = 0.13 J / cm 2, and Fs = 0.18 J / cm 2. FIG. 10 shows the fluence threshold in J / cm 2 for 1064 nm (IR) laser pulses with parameters in those given in Tables 1, 2 and 3. FIG. For one aspect of the present invention, the fluence threshold for a 1064 nm laser pulse is Fu = 0.2 J / cm 2 and Fs = 1.0 J / cm 2 at J / cm 2. Note that the threshold for anode oxide bleaching is not available because the IR wavelength laser pulses do not begin to bleach the anode oxide until the laser fluence is large enough to cause damage to the underlying anode oxide. Note that the exact values for Fb, Fu and Fs will depend on the specific laser and optics used. They must be determined experimentally for certain process setups and articles to be marked and stored in the controller for later use.

In another embodiment of the present invention, the programmable nature of the adapted laser processing system allows for the marking of anodized aluminum articles with commercially preferred marks in a pattern. As shown in FIG. 11, in this aspect, the pattern 110 is converted into a digital representation 112 and decomposed into a list 114, in which case each entry 116 in the list 114 is a respective one. Contains a representation of a singular or plural position having color and optical density associated with the position of. The list 114 is stored in the controller 20. The controller 20 associates the laser parameters with each entry 116 in the list 114 so that when the laser parameters are sent to the laser 10, the optical system 14 and the motion control stage 22 as commands, It will cause the laser 10 to generate one or more laser pulses 12 that strike the aluminum article 18 at or near the surface 16. These pulses will produce a mark with the desired color and optical density. By moving the laser pulse 12 relative to the aluminum article 18 according to the position stored in the list when the mark is being generated, marks of the desired range of color and optical density are in a desired pattern on the anodized aluminum surface. Is made.

In another embodiment of the present invention, the colored anodic oxide is patterned over previously patterned marks to present additional color and optical density. In this aspect, a grayscale pattern is created on the anodized aluminum article. The article is then coated with a photoresist coating that can be developed by exposure to laser pulses. The grayscale patterned, photoresist coated article is placed and aligned in a laser processing system such that the system can apply laser pulses to a pattern already applied to the article. The photoresist used is of a type known as "negative" photoresist, in which case the areas exposed to laser radiation will be removed and the unexposed areas will remain on the article following the subsequent process. The remaining photoresist will protect the surface of the article from the introduction of the dye, while the areas of the anode oxide that have been exposed and subsequently removed will be dyed in the desired color. This anodic oxide layer is designed to be translucent to produce a color pattern with a selected color and optical density to allow light to pass through the anodic oxide to the pattern below and reflect back through the anodic oxide. Such color anodic oxides can also be bleached if necessary using the techniques disclosed by the other aspects of the invention to produce the desired color with the desired transparency. Such colors may be applied over an area of the base pattern or applied on a point-to-point basis, typically in the range of 10 to 400 microns up to the limit of resolution of the laser system. This operation may be repeated to create multiple color overlays. In one aspect of the invention, anodized color overlay is applied to a multicolor overlay grid, such as a Bayer pattern. By designing a grayscale pattern to work with a color overlay grid, a durable and commercially desirable full color image can be created on anodized aluminum article.

12A-12I show a sequence of steps used to create this color overlay for two colors. In FIG. 12A, aluminum article 118 has a transparent anodization layer 120 and a mark 122 previously applied in accordance with another aspect of the present invention. The negative photoresist 124 is applied to the surface of the transparent anodic oxide 120. In FIG. 12B, laser pulse 126 exposes regions 128 and 130 of photoresist 124. In FIG. 12C, the unexposed resist 134 remains after the resist process, but the exposed resist has been removed leaving a void 132 in the treated resist layer 134. FIG. 12D shows the base anodization layer 120 having a section 136 where the anodic oxide is colored in color under the void 132 in the treated resist layer 134. Undamaged processed resist 134 prevents the anode oxide from obtaining color anywhere except where processed resist 134 is removed 132. 12E shows an article 118 having a base anodized oxide 120 having a colored portion 136 of anodized oxide in relation to the mark 122 previously applied after removal of the treated resist.

12F shows an article 118 having a base anodic oxide 120 including a second resist layer 138 and a colored portion 136. 12G shows this second resist layer 138 impinged by laser pulse 142 such that region 140 causes exposure. FIG. 12H shows an article 118 having a process of dyeing the anodic oxide under the removed resist 140 and the base anodic oxide 120 after removal of the remaining resist 138. This leaves an undamaged base anodization layer with colored regions 136 and 144 over previously marked region 122. FIG. 12I optionally illustrates a subsequent laser pulse 146 being used to bleach a portion of a previously anodized and dyed portion of an aluminum article to produce additional desired color or optical density. The process described by this aspect of the invention results in a colored pattern that is overlaid on the grayscale pattern, producing a mark with a wide range of durable and commercially desirable color and optical densities in a programmable pattern.

In another embodiment of the present invention, color anodized oxide can be produced on anodized aluminum articles in a particular pattern that yields the appearance of a full color image when viewed. In this aspect, the pattern representing the image is applied to the surface using the techniques described herein. Color dyes are introduced in the manner illustrated in FIGS. 12A-12I, except that the patterns into which these dyes are introduced into the base layer of the anode oxide are designed to convert grayscale representations to full color. An example of such a pattern is a Bayer filter (not shown), in which the red, green, and blue elements are perceived by fusing the red, green, and blue elements into a single color with an optical density associated with the grayscale mark under the color anodization filter. By juxtaposing the blue filter elements, the appearance of a full color image or pattern is produced. The resist may be a negative or positive resist, and the pattern exposing the resist may be generated by a mask, such as used in circuit or semiconductor applications, directly by electronic means, or directly deposited by a technique such as inkjet, or It can be abbreviated directly by the laser.

In another embodiment of the present invention, bright, white marks can be applied to anodized aluminum articles using a laser marking system as adapted herein. In this embodiment, the laser parameters are chosen to very simply exceed the damage threshold for the anodization layer without causing ablation. As shown in FIG. 13, this embodiment marks the anodized aluminum article by creating low level damage in the anodization layer without causing the anodic oxide to be ablated or otherwise removed from the surface. 13 shows anodized article 150 with white marks 152 created in this manner by one embodiment of the present invention. Low level damage involves many small "micro" cracks in the anodic oxide that diffract light of all wavelengths, giving the surface a "frosted" or matte white appearance. Since the anode oxide is not structurally damaged or cracked macroscopically, the surface retains its durability and there is no obvious change in texture. The laser parameters used to produce bright, white marks on anodized aluminum provide a laser fluence slightly above the damage threshold for anodization. The laser fluence is chosen to be large enough to create micro cracks in the anode oxide but not large enough to cause sufficient damage to change the durability or perceptible texture of the article. Table 5 contains the laser parameters used to produce bright, white marks on anodized aluminum articles as shown in FIG. 13.

By varying the laser fluence used within an indication range close to the damage threshold for certain anode oxides and articles, the appearance of the mark can range from slightly frosted to completely opaque, bright white. Additionally, this embodiment may combine this effect with colored anodized oxides to produce marks with varying degrees of saturation. As the laser fluence increases, the dyed anodization layer will first appear to be unsaturated, meaning that the color appears to be mixed with white. As the laser fluence increases, the colored anodic oxides are bleached and the marks have a bright, white appearance that is not colored.

Laser parameters for generating these bright, white marks include the use of a 355 nm wavelength third harmonic diode-pumped solid Nd: YVO ₄ laser, which is a high power pulsed laser emission energy in the range of 266 to 532 nm. The laser operates at 4KW and is in the range of 1KW to 100KW or more preferably 1KW to 12KW. Laser fluences range from about 0.1 × 10 ⁻⁶ J / cm 2 to 100.0 J / cm 2 or more specifically 1.0 × 10 ⁻⁶ J / cm 2 to 10.0 J / cm 2. Pulse durations range from 1 ms to 1000 ms or more preferably from 1 ms to 200 ms. The laser repetition rate is in the range of 1 KHz to 100 MHz or more preferably 10 KHz to 1 MHz. The speed at which the laser beam travels with respect to the article being marked ranges from 1 mm / s to 10 m / s or more preferably from 100 mm / s to 1 m / s. The pitch or spacing between adjacent rows of laser pulses on the surface of the article ranges from 1 micron to 1000 microns or more preferably from 10 microns to 100 microns. The spot size of the laser pulses measured at the surface of the article ranges from 10 microns to 1000 microns or more preferably from 50 microns to 500 microns. The position of the focal point of the laser pulse relative to the surface of the article ranges from -10 mm to +10 mm or more specifically 0 to +5 mm.

FIG. 14 shows a clear anodized aluminum article 160 having three rows of six marks 162 each applied to a surface using laser parameters as listed in Table 5, in the leftmost column. The spot size varies from 200 microns of to 60 microns in each row to 500 microns in the rightmost column. The neighboring interline distance or pitch of the laser pulses increases from 10 microns in the top row to 20 microns for the middle row and from 50 microns in the bottom row. As the power increases, the brightness of the white mark increases and the transparency decreases.

Embodiments of the present invention mark an article with an infrared laser pulse comprising a CO ₂ laser. The laser parameters used to successfully mark anodized articles with white marks made by retrofitting in the anodization layer are listed in Table 6.

Laser parameters for generating these bright, white marks include the use of 10.6 micron wavelength CO ₂ lasers. The laser operates at 75 KW and is in the range of 1 KW to 500 KW or more preferably 50 KW to 150 KW. Laser fluences range from about 1.0 × 10 ⁻⁶ J / cm 2 to 100.0 J / cm 2 or more specifically 1.0 × 10 ⁻⁶ J / cm 2 to 10.0 J / cm 2. The pulse duration ranges from 1 ms to continuous wave operation or more preferably from 100 ms to 100 ms. The laser repetition rate is in the range of 1 KHz to 1 MHz or more preferably 10 KHz to 250 KHz. The speed at which the laser beam travels with respect to the article being marked ranges from 1 mm / s to 10 m / s or more preferably from 100 mm / s to 1 m / s. The pitch or spacing between adjacent rows of laser pulses on the surface of the article ranges from 1 micron to 1000 microns or more preferably from 10 microns to 100 microns. The spot size of the laser pulses measured at the surface of the article ranges from 10 microns to 1000 microns or more preferably from 50 microns to 500 microns.

It will be apparent to those skilled in the art that many changes can be made in the details of the above embodiments of the invention without departing from the underlying principles of the invention. Accordingly, the scope of the invention should be determined only by the claims that follow.

Claims (10)

A method for producing a mark on an anodized article having a desired property including optical density, color, texture and durability,
Providing a laser marking system having a laser with controllable laser fluence;
Determining the laser fluence associated with generating the mark with the desired attributes; And
Directing the laser marking system to mark the anodized specimen using the determined laser fluence, thereby providing optical density ranging from transparent to opaque, white color, texture indistinguishable from ambient unmarked texture, And producing the mark with a durable and substantially intact anodized oxide. The method of claim 1, wherein the sample comprises a metal. The method of claim 2, wherein the metal comprises aluminum. The method of claim 1, wherein the anodic oxide is dyed in addition to laser processing to produce the mark with additional color. The method of claim 4, wherein the dyed anodic oxide is additionally laser bleached. Laser-marked marks on anodized specimens with optical densities ranging from transparent to opaque, white color, textures that are substantially indistinguishable from the surrounding unmarked textures, and durable and substantially intact anodic oxides Wherein the appearance of the mark is a result of laser-induced damage causing scattering of light in the anodization layer. The mark made with a laser on an anodized sample according to claim 6, wherein the sample comprises a metal. 8. The mark of claim 7, wherein the metal comprises aluminum. The mark made with a laser on an anodized sample according to claim 6, wherein the anodic oxide is dyed in addition to laser treatment to produce the mark with additional color. The mark made with a laser on an anodized specimen according to claim 9, wherein the dyed anodized oxide is additionally laser bleached.

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