KR101881621B1 - Method and apparatus for reliably laser marking articles - Google Patents

Abstract

The present invention is a method and apparatus for producing a color and optical density selectable visibility mark (102) on an anodized aluminum specimen (100). The method includes providing a laser marking system having a laser (10), a laser optics (14) and a controller (20) operatively connected to the laser (10) to control and store laser pulse parameters. The controller 20 selects a stored laser pulse parameter associated with the desired color and optical density and includes a picosecond temporal pulse width greater than about 1 and less than about 1000 to strike the anodized aluminum 18 Directs the laser marking system to produce laser pulses 12 having laser pulse parameters associated with the desired color and optical density.

Description

[0001] METHOD AND APPARATUS FOR RELIABLY LASER MARKING ARTICLES [0002]

The present invention relates to laser marking of anodized aluminum articles. More particularly, it relates to marking anodized aluminum with a laser processing system. More particularly, the present invention relates to marking anodized aluminum in a durable and commercially desirable manner with laser processing systems. In particular, the present invention relates to characterizing the interaction between anodized aluminum and visible and infrared wavelength picosecond laser pulses to reliably and repeatably produce durable marks with desired color and optical density.

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. The appearance refers to the ability to render marks reliably and repeatably with a selected shape, color and optical density. Durability remains unchanged despite wear on the marked surface. Ease of application refers to the cost of materials, time and resources that produce the mark, including programmability. Programmability refers to the ability to program a marking device with a new pattern to be marked by changing the software, as opposed to changing hardware such as a screen or a mask.

Anodized aluminum, which is lightweight, rigid, easily shaped, and has a durable surface finish, has many applications in industrial and commercial products. Anodizing is 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 resistance to corrosion or abrasion, and for cosmetic purposes . These surface layers can be painted or dyed virtually in any color, creating a permanent, colorless, durable surface on the metal. Many of these metals can advantageously be marked using embodiments of the present invention. In addition, metals such as stainless steel that resist corrosion can be marked in this manner. Many articles made from such metals have the need for permanent, visible, and commercially desirable markings. Anodized aluminum is an exemplary material having such a need. Marking the anodized aluminum with laser pulses produced by the laser processing system can quickly produce durable marks at an extremely low cost per mark in a programmable manner.

It has been known for years to produce color changes on the surface of anodized aluminum with laser pulses. Appl. Phys. P. Maja, M. Autric, P. Delaporte, P. Alloncle (COLA'99 - 5th International Conference on Laser Ablation, July), published in A 69 [Suppl.], S343-S346 (1999), pp S43- 19-23, 1999, Göttingen, Germany) describes the removal of anodization from an aluminum surface, but requires the removal of the anodic oxide from the surface The following color changes are noted in the laser energy.

Our mechanism to explain the change in color or optical density of metal surfaces is the creation of laser-induced periodic surface structures (LIPSS). The femtosecond laser pulses are used to generate a laser beam on a metal such as aluminum or aluminum using a femtosecond laser pulse. Describes the various colors that can be created. This paper describes the creation of black or gray marks on metal and the creation of gold color on metal. Some other colors are mentioned, but there is no further explanation. LIPSS is only a suggested explanation for the creation of marks on metal surfaces. Also, only laser pulses with a temporal pulse width of 65 femtoseconds are being taught or suggested to generate these structures. Additionally, there is no mention as to whether the aluminum sample is anodized or the surface is cleaned before laser processing. 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. The temporal pulse shape can range from simple Gaussian pulses to more complex shapes depending on the task. Exemplary non-Gaussian laser pulses useful for certain types of processes are described in U.S. Patent No. 7,126,746 (inventor: Sun et al., Entitled "GENERATING SETS OF TAILORED LASER PULSES"), And is incorporated herein by reference. This patent discloses a method and apparatus for generating a laser pulse having a varying temporal profile from a typical Gaussian temporal profile computed by a diode pumped solid state (DPSS) laser. These non-Gaussian pulses are so-called "tailored " pulses because their temporal profiles are corrected from the typical Gaussian profile by combining more pulses to create and / or generate a single pulse and electronically optically modulate the pulse . This often includes one or more power peaks whose instantaneous power increases to a value that is greater than the average power of the pulse for a fraction of the pulse duration, thereby producing a pulse whose pulse energy varies as a function of time. This type of customized pulse can be effective in treating the material at high rates without causing debris problems or excessive heating of the surrounding material. 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, the Gaussian pulse duration is measured using a full width at half maximum (FWHM) measurement. In contrast, using the integral square method as described in U.S. Patent No. 6,058,739 (inventor Morton et al., Entitled "LONG LIFE FUSED SILICA ULTRAVIOLET OPTICAL ELEMENTS"), complex pulse temporal shapes Can be measured and compared in a more meaningful manner. In this patent, the 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 having 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 is an impairment to the anodic oxide , Which is sufficient to cause unwanted outcomes. "Dark" or "Bright" or color names are relative terms. A standard method of quantifying color is referenced to the colorimetric CIE system. This system is described in "CIE Fundamentals for Color Measurements ", Ohno, Y., IS & T NIP 16 Conf, Vancouver, CN, Oct. 16-20, 2000, pp 540-545. In such a measurement system, achieving a commercially desirable black mark requires a parameter less than or equal to L * = 40, a * = 5, and b * = 10. This results in a visibility gray or a black mark of neutral color without color. In U.S. Patent No. 6,777,098, entitled "MARKING OF AN ANALYZED LAYER OF ALUMINUM OBJECT ", inventor Keng Kit Yeo arises from a layer between aluminum and an anodic oxide so that the anodized surface is anodically oxidized, Describes a method of marking an aluminum article. The markers described there are described using infrared laser pulses in the nanosecond range, where the hue is dark gray or black and somewhat less luminous than the unmarked portion. Additionally, aluminum needs to be cleaned from all surface particles, e.g., particles remaining after polishing before anodizing. Marking by the method claimed in this patent is disadvantageous for two reasons: first, generating a commercially desirable black mark with a pulse in the nanosecond range tends to cause destruction of the oxide layer, and secondly, Or other treatments followed by cleaning of the aluminum may add another step that is associated with the process at an associated cost and may interfere with the desired surface finish by further processing.

What is desired but not disclosed in this field is the use of anodized aluminum, either black, gray or color, that requires expensive femtosecond lasers, does not interfere with the oxide layer in the process, It is a reliable and repeatable way of making marks on the board. In addition, no information is provided as to how to repeatedly produce various colors on the anodized aluminum surface and no effect of damage or bleaching on the anodized layer has been thoroughly investigated. Thus, the use of lower cost lasers, without causing unwanted damage to the overlying oxide or requiring cleaning prior to anodization, allows the marking with the desired optical density or gray scale and color on the anodized aluminum Lt; RTI ID = 0.0 > reliable < / RTI >

An aspect of the present invention is to mark anodized aluminum articles with various optical density or gray scale and color visibility marks. These marks must have a durable and commercially desirable appearance. This is accomplished by using picosecond laser pulses to generate marks. These marks are produced on the surface of the aluminum under the oxide layer and thus protected by the oxide. The picosecond laser pulse makes the mark durable by producing a commercially desirable mark without causing significant damage to the oxide layer. A durable, commercially desirable mark is generated on the anodized aluminum by controlling the laser parameters that produce and direct the picosecond laser pulse. In one aspect of the invention, a 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 enhance the reliability and repeatability of laser marking of the anodized aluminum include laser type, wavelength, pulse duration, pulse repetition rate, pulse number, pulse energy, pulse temporal shape, Shape and focal size and shape. The additional laser pulse parameter includes specifying the position of the focus relative to the surface of the article and directing the relative movement of the laser pulse to the article.

An aspect of the present invention creates a durable, commercially desirable mark by darkening the surface of the anodized aluminum with optical density ranging from that which can hardly be detected by the naked eye to the black, depending on the particular laser pulse parameter employed. do. Another aspect of the invention likewise produces color with varying optical densities in tan or gold shades depending on the particular laser pulse parameters employed. Another aspect of the present invention produces a durable and commercially desirable mark on anodized aluminum by bleaching or partially bleaching dyed or colored anodic oxides without marking or marking the underlying aluminum.

A method for generating color and optical density selectable visibility marks on an anodized aluminum specimen to achieve these and other aspects of the invention in accordance with the purpose of the present invention, as embodied and broadly described herein, and An apparatus adapted to perform the method is disclosed herein. The present invention is a method and apparatus for generating color and optical density selectable visibility marks on anodized aluminum specimens. The method includes providing a laser marking system having a laser, a laser optics, and a controller operatively coupled to the laser to control a laser pulse parameter, wherein the controller having the stored laser pulse parameters is configured to control the laser pulse parameters associated with the desired color and optical density Selecting a stored laser pulse parameter and generating a laser pulse having a laser pulse parameter associated with a desired color and optical density, including a picosecond temporal pulse width greater than about 1 and less than about 1000 to impinge on the anodized aluminum And directs the laser marking system to calculate.
A method of generating marks on an anodized aluminum article according to one aspect includes providing a laser marking system having a laser, a laser optics, a stage, and a controller operatively connected to the laser and laser optics and the stage, The laser emits laser pulses directed at the anodized aluminum article by the laser optics in cooperation with the stage under the direction of the controller, and the laser marking system emits laser pulse parameters that characterize the interaction between the laser pulse and the anodized aluminum article Further comprising: providing a laser marking system; Determining a particular laser pulse parameter associated with generating the mark; Making a particular laser pulse parameter available to the controller; Controlling the laser in cooperation with the controller, the laser optics and the stage to produce a laser pulse having a specific laser pulse parameter; And generating a mark by directing the laser pulse to strike onto the anodized aluminum article. Here, the attributes of the mark may include size, shape, position, color, and optical density.
The laser pulse parameters may also include pulse width, wavelength, number of pulses, pulse temporal shape, pulse fluence, spot size, spot shape, and focus. Wherein the pulse width ranges from about 1 picosecond to about 1000 picoseconds and the wavelength ranges from about 1.5 microns to about 255 nanometers; The number of pulses ranging from 1 to about 10,000 pulses; The pulse temporal shape is one of Gaussian or tailored; The pulsed fluence ranges from 1.0 x ^10-6 J / cm2 to 1.0 J / cm2; Wherein the spot size ranges from about 10 microns to about 100 microns; The spot shape can be either Gaussian or shaped. In addition, the focal point can be focused either on the surface of the anodized aluminum article, on the surface or under the surface.
On the other hand, the optical density of the mark may be less than or equal to about L * = 40, a * = 5 and b * = 10, and the color of the mark may be one of black, transparent, gray, tan or gold.
The mark may also be produced by dyeing and optionally bleaching the anodized aluminum article.
The laser parameters can also be selected to produce a plurality of marks on the anodized aluminum article in a desired pattern with optical density varying to form an image. Here, a colored image can be produced by selectively removing and dying the photoresist layer to expose the anodic oxide, and applying the anodic oxide painted over the image by optionally bleaching the exposed and dyed anodic oxide.
On the other hand, the anodic aluminum article comprises a dyed anodic oxide, and the step of creating a mark comprises bleaching the dye with a laser pulse, wherein the laser pulse is higher than the critical fluence, Lt; RTI ID = 0.0 > fluence. ≪ / RTI >
On the other hand, the laser pulse parameter includes a wavelength, and the wavelength may be a wavelength smaller than the wavelength of infrared (IR). Further, the laser pulse parameter may include a wavelength, and the wavelength may be a wavelength that is larger than the wavelength of the ultraviolet (UV) light. Further, the laser pulse parameter may include a wavelength and the wavelength may be a wavelength of visible light. On the other hand, the wavelength may include a green light wavelength.
In addition, the step of generating the mark may further include the step of generating the intermediate layer mark under the anodic oxide.
In addition, the step of generating the mark may further include the step of generating the intermediate layer mark in the region corresponding to the position where the bleaching of the dye is performed.
On the other hand, the mark can have a uniform appearance over a wide range of viewing angles.
In addition, a method of producing a mark on an anodized aluminum article, wherein the anodized aluminum article has an anodized layer having an aluminum substrate and an anodized layer surface, wherein the mark is adjacent to the unmarked region of the anodized aluminum article And the top surface of the anodized layer may be mechanically adjacent between the adjacent marked areas and the non-marked areas.
In addition, a method of producing a mark on an anodized aluminum article, wherein the anodized aluminum article has an aluminum substrate and an anodized layer having an anodized layer surface, wherein the laser pulse has a focus, Lt; / RTI >
In addition, the method of forming a mark on an anodized aluminum article, wherein the anodized aluminum article has the form of an anodized layer on the upper surface of the aluminum substrate and the aluminum substrate, wherein the laser pulse has a focus, It can be located at a distance.
Also, in a method of producing a mark on an anodized aluminum article, the mark is invisible under ambient view conditions, and the mark may be visible under at least one non-ambient view condition. Here, the at least one non-ambient condition may comprise UV light.
Further, in the method of producing a mark on an anodized aluminum article, the mark can not be visually distinguished from the unmarked area when the mark is illuminated by the broad spectral visible light, It may be visible to the naked eye.
The method of producing a mark on an anodized aluminum article also includes an anodized aluminum article having an aluminum substrate and an anodized layer having an anodized layer surface, wherein the mark is produced under an anodized layer surface.
A laser marking apparatus adapted to produce a mark having a desired property on an anodized aluminum article according to another aspect comprises: a laser operative to produce a laser pulse; A laser optical system operative to correct and direct a laser pulse; A stage operative to hold and position an anodized aluminum article; And accessing a predetermined laser pulse parameter and generating and directing a laser pulse in accordance with a predetermined laser pulse parameter in cooperation with the laser, the laser optical system and the stage to strike an anodized aluminum article, And may include a controller operative to fabricate on the anodized aluminum article.
Here, the mark can be produced by dyeing and optionally bleaching the anodized aluminum article. The laser parameters can also be selected to produce marks on the anodized aluminum article in a desired pattern with optical density varying to form an image.

1 shows a laser processing system;
FIG. 2 is a diagram showing a mark made of a nanosecond pulse of the prior art; FIG.
FIG. 3 is a graph showing the relationship between the mark
4 shows a beam waist;
Figure 5 shows a grayscale mark on an anodized aluminum;
Figure 6 shows marks on anodized aluminum;
Figure 7 shows dyed, visibly marked anodized aluminum;
Figure 8 shows a dyed, IR-marked anodized aluminum;
9 is a graph showing the visibility laser pulse threshold;
10 is a graph showing the IR laser pulse threshold;
11 is a view showing image data converted into laser parameters; And
Figures 12a-i illustrate color anodization applied to an aluminum article.

It is an object of the present invention to mark anodized aluminum articles as durable, selectable, predictable, repeatable and with various optical density and color visibility marks. These marks are beneficial to appear on or near the surface of aluminum and to leave the anodized layer substantially intact to protect both the surface and the mark. The marks made in this way are referred to as interlayer marks since they are made on or on the surface of the aluminum below the oxide layer forming the anodic oxide. Ideally, the oxide remains intact following the marking to protect the mark and provide a mechanically adjacent surface between the adjacent marked and non-marked areas. In addition, these marks should be reliable and repeatable, and if a mark with a particular color and optical density is desired, then the laser parameters to produce the desired result when the anodized aluminum is processed by the laser processing system ≪ / RTI > is known. It also takes into account that such marks generated by the laser processing system are visibility. In this aspect, the laser processing system produces a mark that is not visible under conventional viewing conditions, but under other conditions, e.g., visible when illuminated by ultraviolet light. These marks may be used to provide anti-theft marking or other special marks.

One embodiment of the present invention employs 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 the ESI MM 5330 micromachining system manufactured by Electro Scientific Industries, Inc. of Portland, Oregon 97229. The system is a micromachining system employing 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 at a 532nm wavelength. Another exemplary laser processing system that can be adapted to mark anodized aluminum articles is the ESI ML5900 micromachining system manufactured by Electro Scientific Industries, Inc. of Portland, Ore. 97229. 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. Any of the systems can be adapted by the addition of suitable lasers, laser optics, part handling equipment, and control software to reliably and repeatably produce marks on the anodized aluminum surface in accordance with the methods disclosed herein. These modifications allow the laser processing system to provide a laser with an appropriate laser parameter at the desired location on the anodized aluminum article properly positioned and held at the desired rate and pitch to produce the desired mark with the desired color and optical density Allowing the pulse to be directed. An illustration of such an adapted system is shown in FIG.

Figure 1 illustrates an illustration of an ESI MM 5330 micromachining system adapted to mark an article in accordance with one embodiment of the present invention. In an embodiment of the invention, the diode pump type Nd: YVO ₄ solid state laser operating at 1064 nm wavelength is a laser 10, model Rapid, manufactured by Lumera Laser GmbH of Kaiserslautern, Germany, . Optionally, such lasers can be either doubled in frequency or tripled to about 355 nm using a solid harmonic frequency generator to reduce the wavelength to 532 nm, thereby producing visible (green) or ultraviolet (UV) laser pulses, respectively. This laser 10 is rated to produce a continuous power of 6 watts and has a maximum pulse repetition rate of 1000 KHz. The laser 10, in cooperation with the controller 20, produces a laser pulse 12 having a duration of 1 to 1,000 picoseconds. These laser pulses 12 may be Gaussian or may be specially shaped or customized by the laser optics 14 to allow for desired marking. The laser optics 14 cooperate with the controller 20 to direct the laser pulses 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 laser optics 14 to provide composite beam positioning capability. Composite beam positioning can be achieved by the controller 20 directing the steering element at the laser optics 14 to compensate for the relative motion induced by the movement of the stage 22, the laser spot 16, Is the ability to mark the shape on the article 18 while the substrate 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 direct the spatial shape of the laser pulses 12 that can be Gaussian or specially shaped. For example, a "top hat" spatial profile may be used that delivers laser pulses 12 with uniform dose of radiation across the impacting spot of the article to be marked. Such a specially shaped spatial profile can be created using a diffractive optical element. The laser pulse 12 may also be opened or closed or directed by the electro-optical element, the steerable mirror element or the galvanometer element of the laser optics 14.

The laser spot 16 refers to the focal point of the laser beam formed by the laser pulse 12. As mentioned above, the distribution of the laser energy in the laser spot 12 depends on the laser optical system 14. In addition, the laser optical system 14 controls the depth of focus of the laser spot 12, or controls how quickly the spot goes out of focus as the plane of measurement moves away from the focus 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. . Marking by locating the focus above or below the surface of the article causes the laser beam to defocus by a specified amount thereby increasing the area illuminated by the laser pulse and reducing 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 fine control over spot size and fluence.

A picosecond laser that produces a laser pulse width in the range of 1 to 1,000 picoseconds is the preferred laser to produce reliable, repeatable marks on anodized aluminum. FIG. 2 is a microphotograph showing marks created on anodized aluminum 30 using a prior art laser with pulses greater than 1 nanosecond. The anodic oxide exhibits a distinct sign of cracking (32) in the mark area (34), which is undesirable. Figure 3 shows the same color and optical density mark 38 on the same type of anodized aluminum 36 made from a picosecond laser that does not exhibit cracking. The picosecond laser marks the anodized aluminum article in commercially desirable black 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 the prior art femtosecond lasers, require very little maintenance, and typically have a much longer operating life. Additionally, aspects of the present invention do not require cleaning of the aluminum surface prior to anodization to produce a commercially desirable mark.

One embodiment of the present invention performs marking on anodized aluminum under an anodic oxide. For interlayer marking to occur, the laser fluence is defined by:

F = E / s

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

Fu <F <Fs where Fu is the laser correction threshold of the substrate, in this case aluminum, and Fs is the damage threshold for the surface layer or anodic oxide. Fu and Fs represent the fluence of the selected laser, which was obtained by experiment and in which the substrate and surface layer begin to be damaged. For 10 ps pulses, our experiments show that Fu for Al is ~ 0.13 J / cm 2 for ps green and ~ 0.2 J / cm 2 for ps IR, ~ 0.18 J / cm 2 for ps green and ps IR Lt; -1 &gt; J / cm &lt; 2 &gt; Changing the laser fluence between these values produces a varying color and optical density mark. The 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.

The laser parameters associated with a particular color or optical density may also be determined by methods other than demonstration. For example, the laser parameters may be determined by performing a computer simulation of the laser / material interaction. Other sources of information about the laser / material interaction, such as textbooks, laser manuals or other descriptors, may be accessed and from there, suitable laser parameters may be determined by extrapolation. By directing the laser processing system to produce laser pulses with appropriate laser parameters and precisely controlling the laser fluence, marks of the desired color and optical density can be reliably and repeatably produced on the anodized aluminum article .

One embodiment of the present invention precisely controls the laser fluence at the surface of the aluminum article by adjusting the position of the laser spot by being located at a precise distance above or below the surface of the aluminum from the surface of the aluminum article. Fig. 4 shows an illustration of the laser pulse focus 40 and its vicinity beam waist. The beam waist is represented by the surface 42, which is the diameter of the spatial energy distribution of the laser pulse when measured by the FWHM method on the optical axis 44 traveling along the laser pulse. Diameter 48 represents the laser pulse spot size on the surface of aluminum when the laser processing system is focusing the laser pulse at a distance above the surface (A-O). Diameter 46 represents the laser pulse spot size on the surface of aluminum when the laser processing system is focusing laser pulses at a sub-surface distance (O-B).

In addition to commercially preferred black, it is also useful to mark the article with a gray scale value. Figures 5 and 6 illustrate a series of gray scale marks made on anodized aluminum made in accordance with one embodiment of the present invention. The optical density of a mark ranges from being almost indistinguishable from the background to completely black. According to an aspect of the present invention, each gray scale mark can be identified by a unique triple CIE colorimetric value. L *, a * and b *. Aspects of the present invention relate each desired gray scale value to a set of laser parameters that reliably and repeatably yields a desired gray scale value mark on anodized aluminum in an instruction. Note also that the mark, which may appear to be indistinguishable to the naked eye, may become visible, for example, when illuminated with ultraviolet light other than broad spectral visible light.

Figure 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 and 66 have a CIE chromaticity ranging from L * = 40, a * = 5 and b * = less than 10 to wholly transparent to make commercially desirable markings. Another feature of these marks is that they are below the undamaged anodic oxide so that they have a uniform appearance over a wide range of viewing angles. The marks made using the methods of the prior art tend to have wide variations in appearance depending on the viewing angle due to damage to the anodized layer. Specifically, when marking with the nanosecond pulse of the prior art, applying sufficient laser pulse energy to the surface to produce a dark mark causes damage to the anodic oxide, which causes the appearance of the mark to vary with the viewing angle. The mark made by an embodiment of the present invention does not damage the anodic oxide regardless of how dark the mark is, nor does the appearance change with the viewing angle. These improved marks are made with the following laser parameters.

The marks 60, 62, 64, and 66 have optical densities ranging from virtually invisible 60 to completely black 62 relative to unmarked aluminum. The gray scale optical density 64, 66 between the two extremes is created by moving the focus closer to the article while increasing fluence to produce a darker mark. The height of the focal point on the surface of aluminum varies from zero for the darkest optical density mark 62 to increase by 500 microns for each of the marks 64 and 66 from the right to left side of Figure 4, 60). &Lt; / RTI &gt; Note that marks 64 produced with focus located at 4.5 to 1.5 mm above the surface of aluminum represent yellowish brown or gold, and marks 62 and 66 produced with focus at 1 mm or less indicate gray or black. Maintaining this precise control over the laser focal distance from the work surface in addition to maintaining other laser parameters within the regular laser process tolerance allows laser marks with desired color and optical density to be produced on the anodized aluminum. Additionally, the darkest mark shows a CIE chromaticity of less than L * = 40, a * = 5, and b * = 10, making it a commercially desirable black marker.

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

Laser marking of anodized aluminum can also be achieved by one aspect of the present invention using IR wavelength laser pulses to mark aluminum. This embodiment produces a varying gray scale density mark by changing laser fluence at the surface of aluminum in two different ways. As discussed above, gray scale can be achieved by changing the fluence at the surface by locating the focus above or below the aluminum surface. A second way to control grayscale is to change the total dose at the surface of aluminum by changing the byte size or line pitch when marking the desired pattern. Changing the byte size refers to adjusting the rate at which the laser pulse beam is moved relative to the surface of aluminum, or changing the pulse repetition rate, or both, as a result of changing the distance between consecutive laser pulse impingement sites on aluminum . Changing the line pitch refers to adjusting the distance between the marked lines to achieve various overlapping degrees. 6 shows an aluminum article 74 having an array of marks 72. As shown in Fig. These marks 72 are arranged in an array of six columns and four rows. Six columns represent the six Z-elevations of the focal point on the surface of the aluminum and range from 0 (top row) to 5 mm (bottom row). The four rows represent the pitch of the 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 changing the pitch of the laser pulses can be achieved by varying the CIE L * = 40, a * = 5, and b * A gray level of optical density can be predictably calculated, thereby producing a commercially desirable mark on the anodized aluminum.

A second type of marking that can be applied to anodized aluminum using picosecond laser pulses is modification in color contrast caused by bleaching of the dyed anodic oxide. On a microscopic scale, the anodic oxide is porous and readily accepts many types of dyes. Referring again to Fig. 3, this micrograph of the 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 underlying aluminum markings by making the anodic oxide transparent. For higher fluences, marking of aluminum under the anodized layer and dye bleaching are possible simultaneously with black, gray scale, or the color shown in the previous section. The less energy pulses can partially color the underlying aluminum mark by partially bleaching the anodic dye and rendering it semi-transparently. Finally, longer wavelength pulses can mark aluminum in commercially desirable black or gray scale colors without bleaching the anodic oxide. Figure 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 area where the laser pulse is received. Figure 8 shows a dyed anodized aluminum article of the same type having marks made with IR (1064 nm) laser pulses. Note that the anodic oxide is not bleached by the IR laser pulse 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 of anodized aluminum having anodized color using a picosecond laser. Typically, anodization forms a porous surface, so that dyes that modify the appearance of aluminum can be introduced. These dyes may be opaque or translucent and cause varying amounts of incident light to reach the aluminum and be reflected back through the anodic oxide. Figure 7 shows an anodized aluminum article 80 having an array of marks 82 and a pink dye in the anodic oxide, calculated according to an aspect of the present invention. Color is produced by bleaching the dye in the oxide layer as the underlying aluminum shows the original color (silver) in a range of laser-marked colors from yellowish shades to gray and finally black. These shadows are created by changing the fluence of the laser pulse at the surface of aluminum. The four rows represent the laser pulse pitch change of 10 to 50 microns and the column represents the focal distance from the surface of 0.0 to 5.0 mm. In all cases these laser parameters bleach the dyes from the oxides on the aluminum to make them visible through the marks on the aluminum. The laser mark optical density ranges from transparent to L * = 40, a * = 5, and b * = CIE chromaticity of less than 10. The laser parameters used to generate these marks are given in Table 3.

Bleaching of anodizing dyes is frequency dependent. As shown in Figure 7, the 532 nm laser pulse bleaches the anodizing dye even at the lowest fluence. On the other hand, the IR laser wavelength produces marks on the dyed anodized aluminum without bleaching the dye for most translucent dye colors. Figure 8 shows an anodized aluminum article 100 having a pink dye with a mark 102 made of an IR laser pulse. The mark was made by adjusting the laser fluence by changing the distance from the focus to the surface, ranging from translucent to black, and changing the pitch. The six columns represent the distance between the surface of the aluminum and the focus of the laser pulse from 5.5 mm (right) to zero (left). The 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 of the anodic oxidation dye for 532 nm (green) laser wavelength, marking aluminum and causing ablation is shown in FIG. For a 532 nm (green) laser pulse with parameters in the given parameters in Tables 1, 2 and 3, FIG. 8 shows anodic oxide bleaching (Fb), aluminum under anodic oxide (Fu) and surface ablation Fs) is represented by J / cm &lt; 2 &gt;. For an embodiment of the present invention, the 532 nm laser pulse yields values of Fb = 0.1 J / cm2, Fu = 0.13 J / cm2, and Fs = 0.18 J / cm2. Figure 10 shows the fluence threshold in J / cm &lt; 2 &gt; for a 1064 nm (IR) laser pulse with parameters within those given in Tables 1, 2 and 3. For one embodiment of the present invention, the fluence threshold for 1064 nm laser pulses is Fu = 0.2 J / cm2 and Fs = 1.0 J / cm2 at J / cm2. Note that the threshold for the anodic oxide bleaching is not available since the IR wavelength laser pulse does not begin to bleach the anodic oxide until the laser fluence is high enough to cause damage to the deposited anodic oxide. Note that the exact values for Fb, Fu, and Fs will depend on the particular laser and optical system used. They must be determined experimentally for a given process setup and article 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 the marking of anodized aluminum articles that are commercially desirable as a pattern. 11, the pattern 110 is transformed into a digital representation 112 and decomposed into a list 114, in which case each entry 116 in the list 114 is assigned Lt; RTI ID = 0.0 &gt; and / or &lt; / RTI &gt; 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 commanded to the laser 10, the optical system 14 and the motion control stage 22, The laser 10 will cause one or more laser pulses 12 to strike the aluminum article 18 at or near the surface 16. [ These pulses will produce marks 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 while the mark is being generated, a desired range of color and optical density marks can be formed on the anodized aluminum surface in a desired pattern Is made.

In yet another embodiment of the present invention, the colored anodic oxide is patterned over a previously patterned mark to present additional color and optical density. In this aspect, a gray scale 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 aligned and placed within the laser processing system so that the system can apply a laser pulse in alignment with the pattern already applied to the article. The photoresist used is a type known as a "negative" photoresist, in which case the area exposed to the laser radiation will be removed and the unexposed area 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 exposed areas of the anodic oxide that have been removed will be dyed in the desired color. This anodization layer is designed to be translucent so as to allow light to pass through the anodic oxide and go back to the underlying pattern and be reflected back through the anodic oxide to produce a color pattern with a selected color and optical density. These color anodic oxides can also be bleached if desired using techniques disclosed by other aspects of the present invention to produce the desired color with the desired transparency. These colors can be applied over the area of the base pattern or on a point-by-point basis, typically ranging from 10 to 400 microns, to the limit of the resolution of the laser system. This operation can be repeated to create a multi-color overlay. In one aspect of the invention, the anodizing color overlay is applied to a multiple color overlay grid, such as a Bayer pattern. By designing the gray scale pattern to work with the color overlay grid, a durable and commercially desirable full color image can be created on the anodized aluminum article.

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

Figure 12f illustrates an article 118 having a base anodic oxide 120 that includes a second resist layer 138 and a colored portion 136. [ 12G shows this second resist layer 138 bombarded by the laser pulse 142 to cause the region 140 to be exposed. Figure 12G shows the process 118 of dyeing the anodic oxide under the removed resist 140 and the product 118 having the base anodic oxide 120 after removal of the remaining resist 138. [ This leaves an undamaged base anodized layer with colored areas 136, 144 over the previously marked areas 122. [ Figure 12i illustrates a subsequent laser pulse 146 that is optionally used to bleach a portion of the previously anodized and dyed portion of the aluminum article to produce an additional desired color or optical density. The process described by this aspect of the present invention results in a colored pattern overlaid on the gray scale pattern, producing a mark with a wide range of durable, commercially desirable color and optical density in a programmable pattern.

In another embodiment of the present invention, the color anodic oxide may be produced on the anodized aluminum article in a specific pattern that gives 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 Figures 12A-12I, except that the pattern in which these dyes are introduced into the base layer of the anodic oxide is designed to convert the gray scale representation to full color. An example of such a pattern is a Bayer filter (not shown), in which the red, green, and blue elements of the eye are fused in a single color having an optical density associated with a gray scale mark under the color anodic oxide filter, By juxtapositioning the blue filter elements, the appearance of a full color image or pattern is created. 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 a circuit or semiconductor application or may be directly written by electronic means or deposited directly by a technique such as an ink jet, And can be directly ablated by a laser.

It will be apparent to those skilled in the art that many modifications may be made to the details of the embodiments of the present invention without departing from the underlying principles of the invention. Accordingly, the scope of the invention should be determined only by the following claims.

Claims (34)

CLAIMS What is claimed is: 1. A method for generating a mark on a metal substrate and an article comprising a metal oxide layer on the substrate,
Directing a beam of laser pulses onto the substrate through the metal oxide layer to produce a mark below the surface of the metal oxide layer,
Wherein the beam of laser pulses is characterized by a depth of focus located in the article and wherein the laser pulse is greater than a laser modification threshold of the substrate at the article, Wherein the mark has a laser fluence less than the damage threshold of the mark. The method of claim 1, wherein the laser pulse has a wavelength in the range of 1.5 microns to 255 nanometers. 3. The method of claim 2, wherein the wavelength comprises a green light wavelength. The method of claim 1, wherein the laser pulse has a pulse width in the range of 1 to 1000 picoseconds. 3. The method of claim 2, wherein the wavelength comprises an ultraviolet (UV) wavelength. 3. The method of claim 2, wherein the wavelength comprises an infrared (IR) wavelength. The method of claim 1, wherein the laser pulse has a pulse fluorescence in the range of 1.0 x ^10-6 J / cm2 to 1.0 J / cm2. The method of claim 1, wherein the laser pulse has a spot size in the range of 10 microns to 100 microns. The method of claim 1, wherein the metal oxide layer is an anodic oxide layer having pores formed therein, the article further comprising a dye in the pores. 10. The method of claim 9 wherein the beam of laser pulses is characterized by a depth of focus located within the article such that the laser pulses cause the laser pulses in the article to have a wavelength that bleaches the dye in the pores, Gt; a &lt; / RTI &gt; mark. The method of claim 1, wherein the mark has a CIE chromaticity less than or equal to L * = 40, a * = 5, and b * = 10. delete The method of claim 1, wherein the laser pulse is characterized by a laser pulse parameter that causes the mark to be generated beneath the surface of the metal oxide layer without causing ablation of the metal oxide layer. . 2. The method of claim 1, wherein the laser pulse is characterized by a laser pulse parameter that causes the mark to be generated beneath the surface of the metal oxide layer without cracking the metal oxide layer. A method of producing a mark on an anodized metal article, the anodized metal article comprising a metal substrate and an anodic oxide layer formed on a surface of the metal substrate, wherein the anodic oxide layer has a plurality of pores formed therein And a dye in the plurality of pores, the method comprising:
Bleaching the dye by directing a laser pulse to be applied to the anodized metal article,
Wherein the laser pulse has a laser fluence less than the damage threshold fluence and the anodic oxide layer can be damaged if the damage pulse threshold is greater than the damage threshold fluence. delete delete The method of claim 1, wherein directing a beam of laser pulses through the metal oxide layer onto the substrate comprises directing the laser pulse such that a focal spot of the laser pulse is within the metal oxide layer / RTI &gt; The method of claim 1, The method of claim 1, wherein directing a beam of laser pulses through the metal oxide layer onto the substrate directs the laser pulse such that the focus of the laser pulse is outside the metal oxide layer / RTI &gt; wherein the mark comprises at least one of the following: delete delete delete delete A laser marking apparatus adapted to produce a mark on a metal substrate and an article having a metal oxide layer on the metal substrate,
A laser operative to produce a laser pulse;
A laser optics operative to modify and direct the laser pulse; And
A controller cooperating with the laser and the laser optics to generate and direct a beam of laser pulses to be applied onto the metal substrate through the metal oxide layer,
Wherein the beam of laser pulses is characterized by a depth of focus located in the article, the laser pulse being greater than a laser modification threshold of the metal substrate in the article, And has a laser fluence less than the damage threshold of the layer.
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