Sheet materials and articles including TIO2 and laser marking

Abstract

A material sheet marked with a pulsed laser, having an outer edge and an inner edge separated by a core. The distance from the outer edge to the inner edge is the sheet thickness. The material sheet has a total TiO2 concentration of less than approximately 1.00%. There is an outer layer that starts from the outer edge and extends into the core, with a thickness of approximately 10.00% to approximately 40.00% of the sheet thickness, and the outer layer has an average TiO2 concentration of approximately 2.50% to approximately 10.00%.

Description

Technical Field

[0001] The present invention relates to laser-marked articles of sheet material, and articles comprising such sheet material and laser marking.

Background Art

[0002] Short pulse laser decoration utilizes energy from nano, pico, and femto short pulse lasers over a variety of wavelengths and energies to mark decorative patterns on articles such as products and / or packages. Any and all other decoration techniques that can be applied to products and / or packages (i.e., labels, screen printing, digital printing, etc.) can be used in conjunction with laser marking to achieve various decorative and functional effects. The laser technology used for short pulse laser marking is, importantly, a high throughput technology that uses a fixed laser source where the laser beam is directed at the product or package to be marked by electronically / mechanically controlled mirrors (i.e., “galvo” sets) and lenses (i.e., F theta and similar lenses). These mirrors and lenses steer the laser beam across the surface of the article (this steering is also referred to as “scanning”) so that the laser can impart an image such as a digital image (e.g., from a computer file such as a PDF file) onto the surface of the package or product. This approach has the further advantage over other decoration techniques in that the use of digital images allows for customization and personalization of the decoration.

[0003] There is considerable interest in the possibilities presented by laser-marked articles, such as those made using short-pulse laser marking. For example, replacing adhesive labels on polymer containers is not only economically beneficial but also ecologically beneficial. Removing adhesive labels from polymer containers reduces the total weight of the packaging material, which in turn reduces the amount of petroleum-derived material per package, thus reducing the weight of the packaging and thus requiring less fuel for transportation. Furthermore, since adhesive labels often need to be removed before recycling due to potential impurities that may be introduced into the recycling process, the absence of adhesive labels makes it easier to recycle polymer containers.

[0004] Recent recycling regulations for plastics limit the amount of colorants and other chemicals that can be added to recycled plastics. Unfortunately, many chemical additives help laser marking to ensure crisp and precise markings on plastics. Removing or limiting these chemical additives could be detrimental to the laser marking process. Ironically, removing certain chemical additives to facilitate plastic recycling could restrict laser marking, which is itself an environmentally friendly process.

[0005] Laser marking of small items (i.e., golf balls, etc.) and / or small areas on items (i.e., date codes, address labels on finished packages) is known. Lasers are improving, and newer lasers have a variety of energies and wavelengths, but these marking processes can still be slow and expensive. Furthermore, they lack the ability to mark small characters requiring high precision, such as small font text consisting of alphanumeric characters (i.e., instructions for use, ingredient lists). For example, date codes are marked on packages by relatively simple lasers, but these use single lines of large, inaccurate, or unevenly spaced spots (ranging from 250 μm to over 800 μm in diameter) and relatively large font characters. This is equivalent to printing stick figures that are suitable for some purposes but are difficult for consumers to read and almost impossible for machines to read. More specifically, large, inaccurate, or unevenly spaced single lines cannot currently be used to mark high-precision small font text or machine-readable graphics, such as UPC or QR codes, on articles.

[0006] The current state of laser marking apparatus and processes generally includes a laser that generates a laser beam and a scanner that directs the beam to the surface of the article to be marked. The scanner may use a set of mirrors directed at the article surface by a Garbo set, or a polygon scanner may be used. Apparatus utilizing a Garbo set includes "raster" marking processes and "vector" marking processes. These are either high-speed but low precision and resolution, or low-speed but high precision and resolution. A combination of high speed and high precision does not exist in the prior art. This problem is particularly evident when marking large areas on an article, such as when using laser marking as a complete replacement for other decorative techniques, where all text and / or graphics (many of which are required for regulatory purposes) to be provided on at least one face of the article are provided via laser marking. While marking large areas can be facilitated by polygon scanners, these lack flexibility in terms of modifying the image.

[0007] The raster laser marking process places individual laser marks in a grid, and the image is marked row by row, point by point by the laser. Each pulse is "gate-controlled" so that the pulse is emitted only to dark pixels in the image and not to bright pixels (or vice versa). Each pulse is individually gate-controlled, and the pulse energy of each pulse can be varied to produce a grayscale. State-of-the-art raster marking processes are virtually limited to lasers with a repetition rate of about 100 kHz, considering the practical limit of the update rate of about 10 uS when signaling the on / off function of the laser (i.e., "gating"), and can only be made faster by increasing the pulse interval, which may come at the expense of fine detail such as that required to mark small font text and graphics.

[0008] The vector marking process can run at frequencies above 100 kHz because the pulse is typically gate-open while the laser beam is "directed" (by a mirror) to the shape of the vector line to be marked. Vector-marked items, including text, are often recognizable because the marked line is typically one pulse width (unless filled in), and the pulses converge near corners where the surface velocity of the laser beam slows down as it bends the corner. However, it has been found that the accuracy of mark placement by vector marking is compromised when the surface velocity of the laser beam is very high.

[0009] High-speed laser marking can be achieved using polygon scanners (for example, the High Throughput Raster Processing Polygon scanner system from Next Scan Technology (Evergem, Belgium)), which can be optimized for high speed and high accuracy. Polygon scanner systems use rotating polygon mirrors for column scanning. These scanners are typically used for full-surface processing of regular patterns. Specifically, the field of view is typically square, which is relatively large depending on the printing standard, and repeating patterns are marked repeatedly on subsequent items. The square field of view configuration of these scanners may not be suitable for accurate marking of small letters, alphanumeric characters, logos, pictures, etc.

[0010] While high speed is important for high throughput, high precision is crucial for the legibility of laser-marked patterns, which is important when marking text (i.e., for human readability) and when marking machine-readable codes such as barcodes, UPC codes, and QR codes (i.e., for machine readability). The quality of the laser marks and the precision of their position on the object are both important for the legibility of the laser-marked patterns. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] Therefore, there is still a need for materials such as sheet materials containing low levels (e.g., <1%) of TiO2, and articles containing such materials, that can be laser-marked using high-speed laser marking processes. [Means for solving the problem]

[0012] The present invention provides solutions to one or more of the drawbacks of the prior art, as well as other advantages. This specification, claims, and drawings describe various features and embodiments of the present invention, including a material sheet which may be a polymer, marked with a pulsed laser, the material sheet having an outer and inner edge separated by a core. The distance from the outer edge to the inner edge is the sheet thickness. The material sheet has an average TiO2 concentration of less than about 1.00%, preferably less than about 0.95%, more preferably less than about 0.90%, and even more preferably less than about 0.80%. Furthermore, there is an outer layer that starts from the outer edge and extends into the core, the thickness of which the outer layer is about 10.00% to about 40.00% of the sheet thickness, preferably about 9.00% to about 35.00%, more preferably about 8.00% to about 32.00%, and even more preferably about 7.00% to about 30.00%, and the outer layer has an average TiO2 concentration of about 2.50% to about 10.00%, preferably about 2.75% to about 9.50%, more preferably about 3.00% to about 9.25%, and even more preferably about 3.25% to about 9.00%. Laser markings on material sheets may include UPC, QR, data matrix, or other machine-readable symbols or codes, the machine-readable symbols or codes having an overall symbol grade of 1.5 or higher according to ISO / IEC 15416-1 (for verification of one-dimensional barcodes) or an overall symbol grade of 1 or higher according to ISO / IEC 15415 (for verification of two-dimensional barcodes).

[0013] In another embodiment of the present invention, the material sheet forms an article, which may be a garbage bag, bottle, pouch, tube, film, laminate, bag, wrap, drum, jar, cup, or cap.

[0014] In one embodiment, the laser marks include a predetermined pattern which is a line or a curve, and the spacing between adjacent laser marks varies within the line or curve.

[0015] In another embodiment, the laser mark includes a predetermined pattern which is a grid of positions, each containing a mark or gap in the grid pattern. The grid pattern has a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any one of the two or more rows being separated by an X distance, and each adjacent pair in the two or more rows being separated by a Y distance, where the X distance and the Y distance are equal.

[0016] In yet another embodiment, the laser marking pulse laser includes a predetermined pattern of positions including marks or gaps within a grid pattern that form alphanumeric characters in the form of text, each having a font size in the range of 6pt to 10pt. The grid pattern may have a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, and each adjacent pair of positions along any one of the two or more rows being separated by an X distance, and each adjacent pair in the two or more rows being separated by a Y distance, where the Y distance is at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the X distance. Alternatively, the text may have a font size in the range of 11pt to 16pt, and the Y distance is at least 2 times, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times, the X distance.

[0017] In another embodiment of the present invention, in addition to the outer layer, there are two or more inner layers within the core, each inner layer having a different concentration of TiO2.

[0018] The present invention offers many advantages over the prior art. This is because laser marking can be, for example, an alternative visual communication method that can mark an article without the need for alphanumeric characters, text, paragraphs, and conventional labels that can be read by consumers. Specifically, the sheet material and article of the present invention can be marked with ingredient lists, instructions for use, UPC codes, etc. in a fast and cost-effective manner without using labels and adhesives. This reduces costs, is environmentally friendly (less waste stickers on the package), and allows for instantaneous changes to the message communicated to the consumer. For example, when an ingredient is changed in a formulation, as soon as the change can be made in the computer instructions to the laser device, a new ingredient label can be marked on the article. No new labels are required. Further, the present invention provides a method and process for laser marking a polymer material containing a small amount of laser marking additive TiO2.

Brief Description of the Drawings

[0019] [Figure 1] An article according to the present invention in which alphanumeric characters are marked in a checkerboard pattern. [Figure 2] A schematic diagram of a raising device according to the present disclosure. [Figure 3] A checkerboard according to the present disclosure, where the positions of adjacent parallel columns are stacked. [Figure 4] A checkerboard according to the present disclosure, where the positions in adjacent parallel columns are offset. [Figure 5] Alphanumeric characters marked in a checkerboard pattern according to the present invention. [Figure 6A] Alphanumeric characters in a checkerboard pattern marked according to the present invention. [Figure 6B] Alphanumeric characters in a checkerboard pattern marked according to the prior art process. [Figure 7] A schematic diagram of a two-layer sheet material according to the present invention. [Figure 8] A schematic diagram of a multi-layer material sheet of a material according to the present invention. [Figure 9] It is a graph showing the concentration of TiO2 in the material sheet of the present invention. [Figure 10] It is a revised version of FIG. 5 for showing mis-marked % calculations.

Mode for Carrying Out the Invention

[0020] Article As used herein, "article" refers to an individual object such as an object for consumer use, such as a container suitable for containing a material or composition. An article can be a container, and non-limiting examples thereof include bottles, tubes, pouches, films, laminates, bags, wraps, drums, jars, cups, caps, and the like. The compositions contained in such containers can be any of a variety of compositions including, but not limited to, detergents (e.g., laundry detergents, fabric softeners, dishwashing, skin care, and hair care), beverages, powders, paper (e.g., tissues, wipes), diapers, beauty care compositions (e.g., cosmetics, lotions), pharmaceuticals, oral care (e.g., toothpastes, mouthwashes), and the like. The container can be used to store, transport, and / or dispense the material and / or composition contained therein. Articles can be made of any of a variety of common materials including PET, PETG, HDPE, PP, PVOH, LDPE, LLDPE, steel, glass, aluminum, cellulose, pulp, paper, and the like.

[0021] As used herein, "sheet material" refers to any high aspect ratio structure having a thickness substantially less than its length and width. Sheet materials include flexible sheet materials such as films and laminates, as well as rigid materials such as bottle walls that can be formed by blow molding a preform or parison. Films and laminates may be wound up to form tubes or other containers.

[0022] As used herein, “layer” refers to a striped region within a sheet material, including at least a portion substantially parallel to the outer surface of the sheet material. Exemplary embodiments of sheet materials include co-extruded materials for forming films, co-blown materials such as parisons used in forming bottles, co-injection materials used in forming bottle preforms, and layered materials for bottle manufacturing such as overmolded preforms. As used herein, “layer” does not include painted, ink-printed, or coated materials or labels, including in-mold labels.

[0023] Figure 1 shows an article 10 having a predetermined feature 17 laser-marked as a grid 16. The predetermined feature 17 can be consumer-readable, machine-readable, or both. The predetermined feature 17 can be, for example, alphanumeric characters, a company logo, a drawing, artwork, a UPC, or a QR code. In this example, the marked position 12 constitutes the alphanumeric character 14, which in this case is the digit 2, "2". The unmarked positions 11 in the grid 16 are shown for illustrative purposes only and do not appear on the final marked article 10. The article 10 is shown as a container and has an opening 11 and a neck 13 that provides access to an internal space 15.

[0024] Articles according to the present invention may be formed from a single thermoplastic material or resin, or, in one or more embodiments, from two or more materials that are different from each other. The two or more materials may constitute layers within the article. The materials constituting each layer may be the same as or different from the other layers. For example, in addition to an outer layer containing TiO2, the article may contain polyethylene terephthalate (PET), polyethylene terephthalate glycol (PETG), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene naphthalate (PEN), polycyclohexylenedimethylene terephthalate (PCT), glycol-modified PCT copolymer (PCTG), copolyester of cyclohexanedimethanol and terephthalic acid (PCTA), polybutylene terephthalate (PBCT), acrylonitrile styrene (AS), and styrene butadiene copolymer. It may include one or more layers of thermoplastic resin selected from the group consisting of copolymers (SBC), or polyolefins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLPDE), high-density polyethylene (HDPE), propylene (PP), and combinations thereof.

[0025] For example, recycled thermoplastics and / or cellulosic materials such as polyethylene terephthalate (PCRPET), high-density polyethylene (PCRHDPE), low-density polyethylene (PCRLDPE), polyethylene terephthalate (PIRPET), high-density polyethylene (PIRHDPE), and low-density polyethylene (PIRLDPE), as well as post-consumer recycled (PCR) materials, post-industrial recycled (PIR) materials, and regrinded materials may also be used.

[0026] Thermoplastic materials may include monomers derived from renewable resources and / or monomers derived from non-renewable resources (e.g., petroleum) or combinations thereof. For example, thermoplastic resins may include polymers made entirely from bio-derived monomers, or polymers made partly from bio-derived monomers and partly from petroleum-derived monomers.

[0027] Additional pigments, colorants, and laser absorption additives may be added to the sheet material and article material of the present invention. A suitable selection of laser wavelengths in combination with the pigments / colorants / additives can provide suitable marking of the article. If the contrast or speed of the marking is insufficient, these pigments / colorants / additives can promote the absorption of laser energy and thereby function as laser absorption additives.

[0028] In embodiments of the present invention, the additive that facilitates laser marking is titanium dioxide (TiO2), and the amount of TiO2 incorporated into the plastic is 1% or less. Unfortunately, at this low level, TiO2 is not easily marked, especially in high-speed marking processes. While not bound by theory, it is thought that low-speed laser marking processes, such as those using a continuous laser that can be gate-open for a long time, or those using a pulsed laser that can impose multiple pulses (i.e., overlapping pulses) on a single area of ​​the material to be marked, can successfully mark materials incorporating 1% or less of TiO2. However, these processes are slow and require long cycle times to laser mark articles containing the material.

[0029] Many laser-absorbing additives, including TiO2, can have detrimental effects on the recycling of plastics and other polymer materials. Therefore, it may be beneficial to reduce the concentration of laser-absorbing additives in materials to be laser-marked. One such solution is to reduce the amount of laser-absorbing additives in the material as a whole while retaining sufficient additives on the surface to obtain good, clear, and concise markings on the material. Figure 7 shows a two-layer sheet material 126 having an outer edge 122 and an inner edge 123 defining a core 124. The distance from the outer edge 122 to the inner edge 123 is the sheet thickness. The sheet thickness may be about 10.0 microns to about 2.00 mm, preferably about 20.0 microns to about 1.50 mm, and more preferably about 50 microns to about 750 mm. The core 124 has an outer layer 120 and an inner layer 121. The outer layer is at least about 10.00% of the sheet thickness and less than about 40% of the sheet thickness. The outer layer 120 has a TiO2 concentration of approximately 2.50% to 10.00%, while the entire sheet has a TiO2 concentration of less than 1%. Those skilled in the art will understand the simple mathematical relationship between the TiO2 concentrations of the outer and inner layers. For example, if the outer layer has approximately 5.00% TiO2 and is 10.00% of the sheet thickness, and the inner layer has 0.0% TiO2, then the total TiO2 concentration in the sheet material is 0.50%, well below 1.00%.

[0030] Figure 8 shows a multilayer sheet material 136 having an outer edge 137 and an inner edge 138 defining a core 135. The sheet material 136 is shown together with an optional protective layer 134, which may be, for example, a varnish. The protective layer 134 may be added to the sheet material 136 either before or after laser marking of the sheet material 136. The sheet material 136 comprises an outer layer 130 and two inner layers 131 and 132, which may have the same or different concentrations of TiO2. It is understood that there may be three or more inner layers. Two or more inner layers may be made of different materials but have the same concentration of TiO2, or multiple inner layers may be made of the same material but have different concentrations of TiO2, or a combination thereof.

[0031] Figure 9 is a graphical representation of the potential concentration profile across the sheet material. The dashed line 145 represents the approximate separation between the outer layer 140 and the inner layer 141. The X-axis represents the layer thickness as a percentage of the total thickness. The outer layer shown in Figure 9 is approximately 14.00% of the total sheet thickness. The Y-axis represents the concentration of TiO2 in layers 140 and 141. Line 142 represents a scenario where the concentration of TiO2 in the outer layer 140 is constant at approximately 4.00% and the concentration of TiO2 in the inner layer 141 is 0.00%. This results in a total concentration of approximately 0.56% in the sheet material. In contrast, line 143 shows varying concentrations of TiO2 across the layers, with the concentration of TiO2 starting at approximately 6.00% and decreasing to approximately 4.00% in the outer layer 140, which again is approximately 14.00% of the total sheet thickness. Within the inner layer 141, the TiO2 concentration starts at 4.00% and decreases to 0.00% at approximately 30.00% of the total sheet thickness. This results in an overall concentration of approximately 0.90% of TiO2 in the sheet material. Those skilled in the art will understand that there are countless ways to reduce the total TiO2 concentration in the sheet material to less than approximately 1.00%, while simultaneously reducing the TiO2 concentration in the outer layer to approximately 2.50% to 10.00%, i.e., at least approximately 10.00% and less than approximately 40.00% of the total sheet thickness.

[0032] Laser and Raising Equipment To mark articles according to the present invention, pulsed lasers, such as short-pulse lasers, may be used. Lasers for use in the present invention are commercially available and include nanosecond, picosecond, and femtosecond lasers. These short-pulse lasers can emit pulses applied at high energy density and high repetition rates, and the high energy and high repetition rate are important to enable laser marking of articles at high speed. The laser marks themselves include marks made on articles such as products or packages by oxidation, reduction, ablation, etching, foaming, and carbonization.

[0033] Any suitable laser can be used to mark article 10. Figure 2 shows an embodiment of a lathing apparatus 200 equipped with a laser 20 useful for marking articles according to the present invention. The lathing apparatus 200 includes a laser 20 which can be any laser capable of generating sufficient energy to mark an article, such as a UV laser having an output in the range of 1W to 60W and a laser wavelength of 355 nanometers, or an IR marking laser having an output in the range of 1W to 300W, and even 500W, and a laser wavelength of 1064 nanometers. Such lasers are available from various suppliers, including the IPG ULPN-355-10-1-3-M marker or YLPN-1-1x350-50-3M MOPA module available from IPG Photonics (Oxford, MA, United States). Other forms and types of lasers are also possible, and different output ranges and settings may be used. The raising device may include an optical system that can be used, if necessary, to direct the laser beam and / or modify the laser beam by changing the energy density and / or spot size of the laser beam 28.

[0034] Frequency, or repetition rate, measured in Hz, is the number of laser pulses a single laser can deliver per second. For example, a 1 MHz laser delivers 1,000,000 pulses / second, and a laser with a repetition rate of 100 kHz delivers 100,000 pulses / second. The repetition rate can be important for processing certain lazing jobs (i.e., high-speed laser marking) in a short amount of time. More pulses available per unit time correlate almost linearly (inversely) to the time required to mark a given column for a particular job.

[0035] Pulse energy is the amount of energy contained in a single laser pulse and is typically measured in μJ or mJ. Typically, pulse energy is in the range of 5 μJ to 2000 μJ (2 mJ), preferably 7 μJ to 1000 μJ, and more preferably 10 μJ to 300 μJ. The average output of the laser is then given as pulse energy × repetition rate. Average power = pulse energy (J) * Repeat rate (Hz or 1 / second).

[0036] The peak power is equal to the pulse energy divided by the pulse duration, which can be less than 100 nanoseconds, less than 50 nanoseconds, less than 20 nanoseconds, less than 10 nanoseconds, or less than 1 nanosecond. Therefore, the pulse energy and pulse duration are linearly related to the peak power. Shorter pulse durations achievable with nanosecond, picosecond, and femtosecond lasers enable very high peak power, which is useful for marking objects.

[0037] In the lathing apparatus 200 depicted in Figure 2, the laser 20 projects a laser beam 28 onto an X-mirror 22 rotated by an X-Garbo 21. The X-mirror 22 and X-Garbo 21 collectively form an X-Garbo set. The laser beam 28 is then projected onto a Y-mirror 24 rotated by a Y-Garbo 23. The Y-mirror 24 and Y-Garbo 23 collectively form a Y-Garbo set. The X-mirror 22 and Y-mirror 24 cooperate to direct the laser beam 28 to a position on the article 27 where a desired mark 29 should be marked. The laser beam 28 typically passes through a lens 26 before reaching the article 27. The distance from the lens 26 to the article 27 is the focal length 25.

[0038] The combined optical system of a laising device may function to sweep a laser beam across the surface of an article in a series of passes. The laser beam may sweep across the article along a first row of a grid in the X direction, directed by an X-mirror while emitting (or omitting) pulses. The combination of the sweeping speed of the laser beam across the surface of the article, also called the surface velocity of the laser beam, and the repetition rate of the laser pulses determines the spacing of the marks along the X direction. X interval * Repetition rate = surface velocity

[0039] The laser may emit one or more pulses while sweeping across the article at a given position, thereby resulting in marked positions (or more), or the laser may omit pulses while sweeping across the article at a given position, thereby resulting in unmarked positions (i.e., voids). The laser beam may sweep across the article at a constant surface velocity while emitting and / or omitting pulses. The surface velocity or sweep velocity is defined above. The laser beam may then sweep across the article along a second row of the grid (such as a row adjacent to the first row) while emitting (or omitting) pulses. The laser beam may sweep across the first and second rows in the same or opposite directions. For example, the laser beam may sweep across the first row "from left to right" and then sweep across the subsequent / adjacent row "from right to left".

[0040] Those skilled in the art will understand that for an article to be marked, the laser energy must be absorbed by the material of the article. For example, a pulsed laser using 355 nm (UV) can be absorbed by TiO2 added to the article. Other combinations of laser wavelengths and the substrate or laser-absorbing additives of the article exist and are intended herein.

[0041] Laser marking Articles of the present invention are typically marked by a reduction or oxidation process. The term "translucent," as used herein, means that the material, layer, article, or part of an article being measured has a total luminous transmittance greater than 0% and less than or equal to 90%. The term "opaque," as used herein, means that the material, layer, article, or part of an article being measured has a total luminous transmittance of about 0%. Total luminous transmittance is measured according to ASTM D1003.

[0042] Reduction and oxidation involve laser energy altering the oxidation state of at least one component of an article, such as a laser-absorbing additive or opacifying pigment, resulting in a discoloration or color change that is visible as a mark. For example, though not bound by theory, the energy imparted from a UV laser could accelerate the reduction of TiO2 to form titanium dioxide, where the oxidation state of titanium is reduced to less than +4, thereby resulting in a color change from white / colorless to blue, and from dark blue to black.

[0043] Spot size relates to the focal region where the laser beam contacts an object. "Spot size" is the diameter of a circular spot. While the spot is circular, it is possible to achieve an elliptical spot by controlling the laser beam optics relative to the object. Spot size can be modified by focusing or defocusing the laser beam, but the "fluence" (energy per unit area) within the spot decreases as the spot is expanded or defocused. Theoretically, the minimum spot size achievable with any laser is the wavelength of the laser itself. In practice, the minimum spot size achievable with a pulsed laser is about 7–20 μm. Spot sizes can range from about 10 μm to about 150 μm, preferably about 20 μm to about 100 μm, more preferably about 30 μm to about 80 μm, and even more preferably about 40 μm to about 60 μm. As discussed in the background art, the spot size for conventional laser marking (e.g., using a CO2 laser), such as date codes, is at least 250 μm and can exceed 800 μm. Another way to think about spot size in the context of marking is to compare it to the size of a paintbrush a painter uses to create a picture. Smaller spot sizes are used when very fine detail is desired. Larger areas to be covered may prefer larger spot sizes. However, laser marking mechanisms require a minimum fluence to achieve the desired mark, and therefore, a balance between pulse energy, pulse duration, pulse overlap, and spot size is crucial.

[0044] The geometric shape of the mark spacing can contribute to the cycle time and fluence (or energy per unit area) provided to the article. For example, the spacing between marks may be such that the marks do not overlap at all, or have 0% overlap. With 0% overlap, each individual laser pulse contributes to the energy provided to mark the article. If the laser does not have sufficient pulse energy or peak power to achieve the desired marks (e.g., if the concentration of the laser-absorbing additive is too low), the pulse spacing can be reduced to a point where the spots overlap in either the X or Y direction, or both. Overlapping the spots involves providing two or more laser pulses to the area of ​​the article where the spots overlap, which provides a higher fluence or energy per unit area to that part of the article. However, overlapping pulses are undesirable for high-throughput laser marking, as the pulse spacing is a major lever of cycle time. If the laser has a fixed repetition rate or pulse frequency, it is desirable to spread the pulses as much as possible while still achieving the desired mark type and mark contrast in order to achieve the lowest possible process time (also called cycle time). In one embodiment of the present invention, the pulses do not overlap.

[0045] Pulse duration is the length of time a pulse continuously remains above half its maximum value. Shorter pulses can produce higher peak power at a typical average power output. This is because average power = pulse energy (J). * This is because the repetition rate is (Hz or 1 / second). The peak power is equal to the pulse energy divided by the pulse duration. Therefore, if the pulse duration is significantly shorter, the resulting peak pulse power will be significantly higher. This peak power enables improved carbonization, foaming, oxidation, reduction, etc., on the target being marked. Short-pulse lasers utilize this phenomenon to mark articles, enabling marking mechanisms that are typically not found with longer-pulse lasers.

[0046] Go board pattern The articles of the present invention do not need to be marked in a grid pattern, however, a grid pattern can enable features that further provide reduced cycle time / high throughput. As used herein, “grid” or “bitmap grid” is interpreted to mean a regular, periodic array of positions which may contain multiple marks. The periodicity of the array includes periodicity in both the X and Y directions. Multiple marks in the grid may or may not be present at each of the positions in the grid. That is, marks may or may not be formed at a position in the grid (i.e., voids). As mentioned, the lathing apparatus sweeps a laser beam across the article while either laser pulses are being emitted from the laser or no pulses are being emitted. Marked positions occur when the laser is emitting pulses at a given position, and unmarked positions occur when the laser is not emitting pulses at a given position. A laser beam can be swept across an article at a constant surface velocity while the laser repetition rate is constant. Therefore, the periodicity of position will be regular (i.e., X-distance) in the direction the laser beam is swept across the article (i.e., the X-direction), even if the marked positions are not spaced equally, considering the possibility of unmarked positions. For unmarked positions, the distance between any marked positions along the same direction (i.e., the X-direction) can be an integer of the minimum distance measured between marks in that direction (i.e., 2x, 3x, or more).

[0047] A laser beam can be swept across articles in subsequent rows. The laser beam can be swept from left to right or right to left, and as it moves from row to row, it can be swept in the same direction (e.g., like a carriage return on a typewriter in a raster process), or it can be swept in alternating directions as it moves from row to row. A major contributing factor to reducing cycle time is sweeping the laser beam in alternating directions as it moves from row to row. Rows can be approximately parallel to each other. The distance between adjacent rows is the Y distance. The positions of adjacent rows can be directly above / below each other, or offset relative to each other. An offset equal to the X distance is understood to result in a realignment of the positions between rows.

[0048] Alphanumeric characters are letters or numbers; for example, in English, letters are A-Z, including uppercase and lowercase letters, and universal numbers are 0-9 and combinations thereof. Alphanumeric characters are not limited to any particular style or font. Chinese, Japanese (e.g., kanji, katakana), Russian, Arabic, and other languages ​​have different alphanumeric characters that can be used for marking.

[0049] Those skilled in the art will understand that the size of printed, or in this case, marked, alphanumeric characters is measured by their font. The smallest font generally accepted as consumer-readable on a marked article is about 6pt. Font sizes can be increased to very large sizes, but when marking the faces of consumer packaging, fonts larger than 20, for example, are impractical as a few characters may fill the entire package. The “faces” of consumer packaging are typically the front or back of the package, and these faces typically have different markings. For example, the product name and general product description (shampoo, conditioner, soap, etc.) are typically found on the front, while the ingredient list, UPC code, and instructions for use are usually found on the back. In the case of cylindrical packaging, a virtual vertical face can be drawn downwards from the bottle, with the front on one side of the virtual face and the back on the opposite side.

[0050] As discussed earlier, laser marks may not overlap to reduce the time required to mark a given pattern (i.e., "time to mark"). Time to mark can be further reduced by spacing the marks in either or both the X and / or Y directions, although increasing this spacing may lead to poor legibility of any alphanumeric characters constituting a given pattern. For example, increasing the X distance allows for a faster surface velocity of the laser beam across the surface of the article when marking a given row (at a constant repetition rate). Increasing the Y distance allows for fewer reversals in the process of marking a given pattern.

[0051] For certain predetermined patterns, increasing the Y distance (fewer inversions) may have a greater impact on reducing the time to marking than increasing the X distance (faster surface velocity). Conventional raster marking processes include equal X and Y spacing, but the Y distance is greater than the X distance. The X distance is preferably in the range of about 0.005 mm to about 0.500 mm, more preferably about 0.010 mm to about 0.100 mm, and even more preferably about 0.040 mm to about 0.075 mm. The Y distance is preferably in the range of about 0.010 mm to about 2.0 mm, more preferably about 0.050 mm to about 0.150 mm, and even more preferably about 0.060 mm to about 0.075 mm.

[0052] If the predetermined alphanumeric characters have a font size in the range of 6pt to 10pt, the Y distance may be at least 1.2 times, preferably 1.5 times, more preferably 1.7 times, and even more preferably 2 times, the X distance. If the predetermined alphanumeric feature part has a font size in the range of 11pt to 16pt, the Y distance is at least 2 times, preferably 2.5 times, more preferably 3 times, and even more preferably 4 times, the X distance.

[0053] Figures 3, 4, and 5 all show various depictions of a grid. More specifically, Figure 3 is a grid 39 illustrating the X direction 30, Y direction 32, X distance 31, and Y distance 33. Potential marking positions 36 are depicted by empty circles that make up the grid. Furthermore, in Figure 3, positions 36 between parallel columns 38 are "stacked" when the angle 35 between the position in the adjacent column 34 drawn in the Y direction between two potential marking positions and the X direction 30 is approximately 90 degrees. In other words, when using vectors to connect adjacent marks from an array to form a parallelogram (i.e., a unit cell), positions are stacked when the interior angles of the parallelogram are approximately 90 degrees. If the interior angles of the parallelogram are different from 90 degrees (i.e., 120 degrees and 60 degrees), the positions are offset. The X distance is measured from the center of one position to the center of an adjacent position in the X direction.

[0054] Those skilled in the art will understand that a grid of unit cells has four axes of symmetry: horizontal, vertical, and two diagonals. The laser marking considered herein can be performed along any of these four axes. For simplicity, the vertical and horizontal directions shown in Figure 5 will be described. Figure 5 can be rotated 45 degrees so that the diagonals are vertical and horizontal. Again, as shown in Figure 5, laser marking occurs across one row, and then the laser moves up or down to the row above or below, marking in the opposite direction.

[0055] Figure 4 shows another grid 49, illustrating an offset 44 with an offset distance 47 between adjacent parallel columns 48. The offset 44 is defined by an angle 45 between a position 46 in one column 48 and the nearest position 46 in the adjacent column 48, and the offset 44 exists when the angle 45 is greater than or less than 90 degrees. Figure 4 further shows the X direction 40, the X distance 41, the Y direction 42, and the Y distance 43.

[0056] Figure 5 shows alphanumeric characters 52 marked on a grid 50. The alphanumeric character is the number "2," and is marked by the laser-marked position 54, in contrast to the unmarked position 56. When multiple alphanumeric characters, such as words, sentences, or paragraphs, are printed, characters that share the same column of text will also share the same horizontal column 53 of laser marking. That is, the laser device moves across a column, marking the necessary positions for each alphanumeric character, and then leaving the necessary number of unmarked positions between the characters, thereby forming a column where the markings are associated with multiple characters within that column. In this way, words, sentences, and paragraphs can be marked and are clearly legible to consumers or machines.

[0057] Horizontal columns 53 and vertical columns 55 define the grid 50. The distance between a marked position 54 and an unmarked position 56 in the horizontal column 53 defines the X distance 51. Furthermore, the distance between a marked position 54 and an unmarked position 56 in the vertical column 55 defines the Y distance 57. It is important to note that the X distance 51 and the Y distance 57 are defined with respect to the horizontal orientation (53) and vertical orientation (55), respectively, of the marked indicia, in this case the number "2". However, the marked position 54 can be marked in the horizontal direction 59 or the vertical direction 58. More specifically, when marking in the horizontal direction 59, the laser moves across the horizontal column 53, either marking each position (54 and 56, respectively) or leaving them unmarked. Next, the laser moves down or up by one Y distance and begins to travel across another column above or below the previously marked column. Similarly, when marking in the vertical direction 58, the laser moves up or down the vertical column 55, either marking or leaving each position (54 and 56, respectively) unmarked. The laser then moves across one X distance and begins to travel up or down the vertical column adjacent to the previously marked vertical column.

[0058] The aspect ratio of a number or letter is the ratio of its height to its width. The aspect ratio of the number "2" shown in Figure 5 is greater than 1 because its height is greater than its width. It is easy to see that marking the number "2" vertically 58 requires fewer inversions than marking it horizontally 59. This means that marking these indicia can be faster when sweeping the laser beam while marking vertically 58. Many considerations are made when deciding whether to mark horizontally or vertically. However, when considering the relative spacing and font size of alphanumeric characters, the X distance 51 and Y distance 57 are always defined horizontally and vertically, respectively, with respect to the indicia being marked.

[0059] The periodicity of the positions constituting the grid includes periodicity in the X direction and periodicity in the Y direction. The X and Y directions can be approximately orthogonal to each other. As depicted in Figures 3 and 4, the grid 39 and 49 can take the form of being evenly spaced along consecutive parallel rows, respectively. The direction parallel to consecutive parallel rows is denoted as the X direction (30, 40), and the direction approximately perpendicular to the X direction is denoted as the Y direction (32, 42). The distance between adjacent positions along any parallel row (e.g., in the X direction) is considered the X distance (31, 41), and the distance between adjacent parallel rows is considered the Y distance (33, 43).

[0060] The grid 39 can be a stacked grid as depicted in Figure 3. In a stacked grid, the positions where a mark can be placed along the first column are directly above the positions along the second column that are directly below the first column. In other words, the angle 35 formed between the column segment connecting the first position along the first column to an adjacent position along the first column and the column segment connecting the first position to its nearest position along the second column is 90°. In a stacked grid, the distance between adjacent positions along the X axis is equal to the X distance 31, and the shortest distance between adjacent positions along the X axis is the Y distance 33.

[0061] The grid can be an offset grid as depicted in Figure 4. In an offset grid 49, the positions where marks can be placed along the first X-axis are not directly above the positions along the second X-axis that are directly below the first X-axis. In other words, the angle 45 formed between the column segment connecting the first position along the first X-axis to an adjacent position along the first X-axis and the column segment connecting the first position to its nearest position along the second X-axis is greater than or less than 90°.

[0062] Those skilled in the art will understand that the X and Y directions can be selected to some extent arbitrarily for a given pattern. For example, Figure 6B depicts an embodiment of "2" produced by laser marking, where the X direction is perpendicular to the marked "2" 61. Those skilled in the art will understand that the X direction can easily be horizontal to the marked "2" 61.

[0063] Those skilled in the art will understand that the grid pattern (e.g., 39 and 49) and the regular spacing between adjacent positions assume a flat surface of the article. If the surface of the article is curved, the spacing may change with the curvature of the surface.

[0064] The X distance can be the same across all parallel rows that make up a grid. That is, the X distance does not change along the X direction of a given row, nor does it change between rows of a grid containing a given pattern. Alternatively, a given pattern may contain multiple regions where the X spacing within each region is the same but differs between regions. For example, one X distance may be used consistently when marking alphanumeric characters, while different X distances may be used when marking machine-readable codes such as UPC codes. Similarly, the Y distance may not change within a given pattern, or it may change between regions within a given pattern. The surface velocity of the laser beam and / or the marking direction (i.e., up / down or left / right) may also differ between regions. For example, it should be noted that articles laser-marked using a vector marking process generally exhibit variable position / mark spacing along one of their marked directions as the laser accelerates (moving marks further apart) and / or decelerates (moving marks closer together) along the process of marking the article. Laser marking can be performed at a constant speed while the laser is marking. The laser beam moves, stopping after completing one row along the X direction, then moving up or down along the Y direction to the next row, and then starting to mark the new row at a constant speed. This speed can also be the same throughout the entire marking of a given pattern. Articles marked with a CV bitmap grid marking process can be distinguished from articles marked with a vector marking process by the regular periodicity of the marks and, in many cases, by the absence of contours or "boundaries" defining the marked areas (see, for example, boundary 63 in Figure 6B).

[0065] Figures 6A and 6B illustrate the difference between laser marking via bitmap grid marking using the CV bitmap process 6A of the present invention and the prior vector marking process 6B, in which the alphanumeric characters 60 and 61 (i.e., the digit "2") are laser marked. The alphanumeric character 60 has clean, sharp edges and is substantially better defined with very little stray marking. Figure 6B is very contrasting, with mostly undefined edges and a considerable number of stray markings 62 outside the boundary of the alphanumeric character 61. Both characters 60 and 61 were marked in approximately the same amount of time.

[0066] High-speed laser marking of human / machine-readable text, symbols, and codes. As described above, the present invention enables laser marking of human- and machine-readable text, symbols, and codes. Furthermore, the present invention makes it possible to perform laser marking of text, symbols, codes, etc., even at high speeds. Existing raster processes are slow but accurate. Vector laser marking processes are faster and more accurate at low speeds, but inaccurate at high speeds, potentially resulting in illegible markings that are difficult for consumers or machines to read. Laser marking methods such as polygon scanners and CV bitmap scanning can offer higher speeds with better precision compared to other marking processes. As mentioned above, polygon scanners may be undesirable for flexibility reasons.

[0067] Figure 6B illustrates the potential effects of performing a vector-type process at high speed when marking text containing alphanumeric characters, including misplacement of marks within a column. This figure shows many rows that are misaligned, and if the marking starts either too early or too late, the outlines of the alphanumeric characters may become jagged, the overall appearance blurred, and potentially illegible (for example, it may be impossible to distinguish an "8" from a "0"). In contrast, the process created by a constant surface velocity (CV) bitmap path and the resulting pattern are shown in Figure 6A.

[0068] The surface velocity of the laser beam across the surface of an article in CV bitmaps can be faster than that achievable with other laser marking processes. Raster and vector processes are typical examples of surface velocities on the order of 1-2 m / s or less. CV bitmap processes can provide surface velocities exceeding 8 m / s, and even 10 m / s, 15 m / s, 18 m / s, 22.5 m / s, 32.5 m / s, 45 m / s, 60 m / s and above, and even 90 m / s and above.

[0069] The sweep path of the laser beam across the surface of the object can also contribute to reducing cycle time. Conventional raster laser marking processes sweep the laser beam across the rows in either a right-to-left or left-to-right direction, also known as unidirectional, and then "jump" the laser beam back (like a typewriter's carriage return) after marking each row to start the subsequent rows. In this way, subsequent rows can be easily aligned (i.e., stacked) and the grid positions can be aligned based on this identical starting point. To eliminate the jump distance and reduce the time between each marked row, the CV bitmap process may use a "bidirectional" process in which marking can be performed alternately in both directions (i.e., marking is performed from left to right in the first row and from right to left in the subsequent rows).

[0070] The inversion of the laser beam after completing the row can also contribute to reducing cycle time. The inversion can be symmetrical or asymmetrical. An asymmetrical inversion may be preferable when the laser beam is sweeping across the surface of the article at high speeds.

[0071] The choice of marking direction can affect job cycle time, especially when marking features with high (or low) aspect ratios. The aspect ratio of a feature is generally considered to be the ratio of its height to its width. When the height and width are nearly equal, the aspect ratio is close to 1, and the impact of choosing the marking direction relative to the feature dimensions (on job cycle time) may be minimal. However, for features with high aspect ratios (e.g., height >> width) or low aspect ratios (e.g., width >> height), job cycle time can be reduced by choosing the marking direction relative to the feature dimensions. For example, the marking direction may be chosen to be approximately parallel to the longer dimension of the feature (i.e., the major axis), or it may be chosen to be approximately parallel to the shorter dimension of the feature (i.e., the minor axis) (see Figure 5 again). While many factors affect job cycle time, aligning the marking direction with the major axis of the feature is thought to reduce the number of inversions required when marking the feature, thereby reducing job cycle time.

[0072] The choice of marking direction can also affect job cycle time at very high surface velocities. At very high surface velocities, reversal time can increase to a point where it dominates job cycle time. By selecting the marking direction to be approximately parallel to the longer dimension of the feature, reversal can be minimized, thereby reducing job cycle time. As discussed earlier, the X and Y distances can differ, and this difference can contribute to reducing the job cycle. Loss of image clarity in feature areas such as alphanumeric characters can be compensated for by decreasing the X distance while increasing the Y distance.

[0073] Accuracy metrics As described above, the precision of laser mark placement can contribute to both the human readability of the marked text or image and the machine readability of the marked code. Numerous precision metrics can be used to characterize the precision of laser mark placement, which are detailed below.

[0074] Precision metrics generally depend on determining the arrangement of marked positions. The precision of laser marks can be determined relative to a given pattern, a grid, or relative to each other. While the arrangement of marks can be determined using image analysis, those skilled in the art will understand that any means of determining the arrangement (e.g., pencils and graph paper) can be used.

[0075] Microscopy Images for image analysis can be generated by microscopy. Stereoscopic microscopes such as the motorized Zeiss SteREO Discovery.V20 (Carl Zeiss Microscopy, LLC, Thornwood, NY) equipped with a color camera such as the Axiocam 305 (5-megapixel CMOS, Carl Zeiss Microscopy, LLC, Thornwood, NY) are used to image the target letters, digits, and images of the sample using reflected light illumination achieved by LED ring lights and light sources such as the Cold-light source CL 6000 LED lamp (Carl Zeiss Microscopy, LLC, Thornwood, NY). Typical light intensities of 80-100% of the maximum light intensity are used. Individual laser markings combined to form the target letters, digits, or images are resolved using a suitable magnification, combined with a zoom magnification such as 10x-345x, using an objective lens such as the Achromat S 1.5x FWD 28mm (Carl Zeiss Microscopy, LLC, Thornwood, NY). As an example, for characters, numbers, or images with a font size of 10pt, the total magnification is approximately 40x. After the target character enters the camera's field of view, the character, number, or image is focused using manual skill, or preferably using an autofocus module via a user interface platform (Zen V2.6 Blue Edition or higher with Zen Autofocus module, Carl Zeiss Microscopy, LLC, Thornwood, NY, etc.). Before collecting the image of the character, number, or image, the imaging settings are optimized by using the automatic exposure option from the user interface platform along with the lamp intensity. The image is collected in the highest possible resolution format, such as ZVI, and then exported as a TIFF file with a resolution of approximately 2464 × 2056 pixels. Furthermore, the marked columns of the character, number, or artwork should be approximately parallel to the horizontal boundary of the image.If necessary, multiple images taken at higher magnification can be precisely stitched together to encompass the entire area of ​​letters, numbers, or images.

[0076] Image analysis Images from the microscope appear gray, but are captured in color. The images are converted to grayscale using the NTSC protocol. Suitable image analysis software is required to perform this step and several other image processing steps. Analysis functions implemented in MATLAB, available from The Mathworks, Inc. (Natick, MA), are referenced in this description of the method.

[0077] Microscopy and subsequent image analysis may be performed on one or more predetermined patterns, parts of predetermined patterns, or individual images within a predetermined pattern, such as graphics or alphanumeric characters. If image analysis is performed on a part of a predetermined pattern, that part (such as individual graphics or alphanumeric characters) must be isolated from any surrounding images, characters, or artwork before analysis. A mask may be drawn around the character or image in the predetermined pattern. The mask isolates the character or image from other partial characters, numbers, barcodes, artwork, smudges, or other defects that may occur in the image.

[0078] Image analysis first relies on identifying the laser marks that make up the image. Laser marks can be identified by any reasonable means, for example, by repeatedly thresholding a grayscale image from a microscope. The starting threshold is set to capture only a few pixels that fall within some of the markings. The threshold then gradually changes to capture the continuously increasing area of ​​the markings. Progressive thresholding continues from the starting threshold to the stopping threshold. The stopping threshold can be determined automatically, for example, by using MATLAB's "multithresh" function (i.e., Otsu's method). Progressive thresholding can be advantageous in analysis because areas of the markings may overlap and / or merge, and the background may not be perfectly uniform. The direction of threshold progression (i.e., light to dark, or dark to light) can be used to identify dark markings against a relatively light background, or light markings against a relatively dark background. In the presented embodiment, dark marks against a relatively light background are identified.

[0079] Next, when the region reaches a certain size, connected components can be used to identify individual marks. The connected component algorithm is executed with each new threshold to group contact pixels into blobs. When a blob reaches 50% of the mark's area, it is identified as a mark. The center coordinates of a mark are found using the centroid method, which is implemented in MATLAB's "regionprops" function. The center is then used to determine the spacing between adjacent marks in a column (e.g., X distance) and the spacing between adjacent columns of a mark (e.g., Y distance) (see below).

[0080] Determine the observed X and Y distances and their standard deviations. Means of representing the precision of marked text, images, or codes within a grid pattern are the observed X and Y distances of the grid, and their standard deviations. While these parameters can be determined using image analysis, those skilled in the art will understand that any means of determining these distances and standard deviations may be used. One means of determining these values ​​by image analysis involves the use of "Delaunay triangles." In the Delaunay triangulation method, the center coordinates of the marks are passed to MATLAB's "Delaunay Triangulation" function, which creates a triangulation based on their center points. The edges of the Delaunay triangulation never intersect, and the center points are connected by their nearest neighbors.

[0081] The X-distance is taken as the distance between adjacent marked positions along a given column in a grid. Adjacent marked positions along a given column result in horizontal edges in the Delaunay triangulation data structure. These horizontal edges can be separated from other edges in the triangulation by calculating the angle of the edges. Horizontal edges in a grid column are within + / - 10 degrees of the horizontal edges of the image. Since the grid consists of periodic intervals of positions along the columns, the X-intervals should be relatively consistent (e.g., have a low standard deviation). In this analysis, horizontal edges with a length greater than twice the programmed distance can be excluded from consideration as indicating non-adjacent positions. The observed X-distance determined when analyzing images such as alphanumeric characters is taken as the average length of the horizontal edges between adjacent marks for all marks / columns in a given image or character. The X-distance for multiple characters in a macroscopic image can then be further averaged to provide the average X-distance for a given marking condition and a given image or given pattern.

[0082] The Y-distance can be determined as the vertical distance between adjacent columns. In a Delaunay triangulation, a horizontal edge can be part of two adjacent triangles. Each base edge gives each triangle two vertices, and a third vertex is the nearest neighbor mark in either the adjacent column above or below the base edge.

[0083] For each base edge, the vertical distance to the nearest mark above and below the base edge is determined. Only the minimum of these two distances (i.e., the closest) is recorded. Using only the minimum distance helps ensure that columns are adjacent and helps prevent double counting of columns. The mean and standard deviation of these vertical distances across a given image are then taken as the mean Y distance and standard deviation of the image. The top and bottom columns of letters / numbers are not used as the base of the measured triangle because they have only one adjacent column. The Y distances of multiple images in a given pattern or part thereof can then be further averaged to provide the mean Y distance and standard deviation of a given given pattern or part thereof (e.g., a given alphanumeric string).

[0084] displacement Another way to parameterize the precision of laser marking when using a grid is by percentage displacement. As shown in Figure 6B, an inaccurate laser marking process can result in substantial displacement or overhang of marks or gaps within a row, leading to blurry images (such as alphanumeric characters) with jagged contours. Displacement within a row can be represented using any of a number of means, including simple visual inspection. For example, such means may include simply observing a character (or other element of a given pattern) and assessing whether it is legible given prior knowledge of the intended marked pattern (e.g., alphanumeric characters). Displacement can also be quantified. Importantly, human- and machine-readable patterns generally have a "smooth" contour (as opposed to the jagged contour shown in Figure 6B). In other words, for user-readable and machine-readable patterns, the leftmost and rightmost marked positions within a given column (or marked portion of a column) are generally not substantially displaced (in the X direction) with respect to the X distance from the leftmost and rightmost marked positions (each) within the adjacent columns (above and below).

[0085] In this displacement quantification, the starting point of each marked portion within a column (of a given character or pattern element) is considered the leftmost mark, and the ending point of each marked portion within a column is considered the rightmost mark. The starting and ending points for each marked portion within a column are determined relative to the corresponding starting and ending points (each) of the adjacent columns above and below it. A column under consideration is determined to be "displaced" to the left of the character / pattern element if the starting points of both the column above and below it are to the left of the starting point of the measured column, and a column under consideration is determined to be "displaced" to the right if the ending points of both the column above and below it are to the right of the ending point of the measured column. The horizontal distance from the starting (and ending) point of the column to the starting (and ending) points of the column above and below is determined, and the displacement is taken as the shorter of these two distances. Leftward displacement is the displacement determined by the starting point, and rightward displacement is the displacement determined by the ending point. A marked portion within a column may contain no displacement, contain leftward or rightward displacement, or contain both leftward and rightward displacement. The top and bottom rows containing the images to be analyzed (i.e., alphanumeric characters) are omitted from the analysis because they do not have two adjacent rows. One means of identifying the start and end points of each row is to use the aforementioned Delaunay triangulation analysis to determine the X distance, Y distance, and standard deviation.

[0086] For a given image such as alphanumeric characters, the "% displacement" is the sum of the displacements for the columns containing the characters, divided by the number of columns that make up the characters (each displaced mark is counted as one displacement). % displacement = (total displacement within the character) / (number of columns within the character) * 100

[0087] For a given pattern containing multiple alphanumeric characters as text, the "A%D" or average % displacement is simply the sum of the % displacements for each character in the sample set divided by the number of characters in the sample, "n".

[0088] mismarked percentage Another way to quantify the precision of laser marking when a grid pattern is used is by the percentage of mismarked positions, i.e., "mismarked %". Referring here to Figure 10, which is a modified version of Figure 5 for illustrative purposes, Figure 5 shows the alphanumeric character "2" marked with a grid pattern. There are approximately 130 marked positions 54. In Figure 10, there are 8 gaps 101 where a marking position should be. Furthermore, there are 4 marked positions 100 where a gap should be. As is clear, both the gaps where a marking position should be and the marked positions where a gap should be are mismarked misses, and therefore they are added together and compared to the number of marked positions. In the example in Figure 10, there are 12 (8+4) misses out of a total of 130 desired marked positions. Mismarked % = number of misses divided by the number of desired marked positions and multiplied by 100, ((12 / 130) * 100) = 9.23%. Figure 6B shows the significantly mismarked alphanumeric characters ("2") where the mismarked percentage exceeds 20%.

[0089] The "average percentage of mismarks" for a given pattern containing text is simply the sum of the percentages of mismarks for each alphanumeric character divided by the number of alphanumeric characters. To achieve the desired readability of text composed of alphanumeric characters, the average percentage of mismarks for alphanumeric characters is less than about 20%, preferably less than about 15%, more preferably less than about 10%, and even more preferably less than about 5%.

[0090] Method for determining the total amount of %TiO2 in an article A series of thermoplastic resin chips containing suitable grades of pigment TiO2 are prepared using a single-screw or twin-screw extruder at concentrations of 0.5, 0.75, 1, 1.5, 2, 3, 5, 7.5, and 10%. Flat parts such as plaques or chips are manufactured using injection molding machines, such as those available from BOY Machines, Inc. (Exton, PA 19341 USA). Pigment TiO2 is best selected from grades that include coatings to enable compatibility with the resin and ensure good dispersibility and homogeneity throughout the part. Examples of pigment TiO2 intended for use with polyolefins include TIOXIDE® TR48 (Venator, Wynyard Park, UK) and Ti-Pure® R-103 (The Chemours Company FC LLC, Wilmington, Delaware USA). Since many examples of pigment TiO2 have surface coatings, the percentage of powder added in the extrusion process may differ slightly from what is expected. For this reason, the %TiO2 content of the chip is confirmed by inductively coupled plasma emission spectroscopy (ICP-OES), and the measured values ​​are used for Raman spectroscopy as described herein.

[0091] Samples from 0.5, 0.75, 1, 1.5, 2, 3, 5, 7.5, and 10% TiO2 standard tips are cut into smaller pieces using ceramic scissors and a knife. The scissors and knife are washed between samplings. Blank resin samples (the same resin used for the TiO2 standard) and TiO2 standard samples are prepared (n=1 to n=3). Approximately 0.05 to 0.1 g of sample is transferred to a pre-washed 15 mL TFM UltraWAVE tube (Milestone Srl, Bergamo, Italy) and weighed. Each sample is combined with a digesting agent such as nitric acid, hydrochloric acid, and fluoroboric acid. The sample is then completely digested by heating to a final temperature of 250 to 260°C using an UltraWAVE Microwave Digestion System. The sample is then transferred to a 50 mL polypropylene tube, combined with an internal standard, and diluted to 50 mL with deionized water. The resulting test solution is visually checked to confirm complete digestion of the sample, ensuring that the solution yields a clear solution free of particulate matter. The clear solution is analyzed for Ti by ICP-OES. Working standards are prepared by combining appropriately diluted reference standards (Inorganic Ventures, Christiansburg, Virginia, USA) covering the target concentration range (45 ppm to 145 ppm Ti) with a selected internal standard (Y). The final composition of these working standards is matched to the prepared sample in terms of acid content for matrix matching purposes. The analytical results of these working standards provide the data necessary to create calibration curves for titanium quantification. The prepared standards and test samples are analyzed using an ICP-OES analyzer such as the Agilent 5110 ICP-OES (Agilent Technologies, Inc., Santa Clara, CA, USA) using multiple wavelengths to demonstrate appropriate selectivity using one wavelength selected for reporting purposes (Ti 336 nm) and yttrium (Y 371 nm) used as the internal standard.

[0092] Method for determining %TiO2 within a specific layer Standards of thermoplastic resins with varying amounts of TiO2 are analyzed by Raman spectroscopy using a Raman microscope such as the Renishaw Virsa® Raman analyzer (Renishaw plc., Gloucestershire, United Kingdom), which is equipped with a continuous 785 nm laser, a fiber-optic coupled probe including an electric x / y / z stage, a live video camera, a halogen or LED light source for white light sample observation, and a 20x / 0.40 NA LE Plan Nikon microscope objective lens. The sample surface is localized using live white light video images before data acquisition. Spectrum acquisition is achieved by two-dimensional (2D) mapping by scanning the sample in x and y directions relative to the incident laser beam, or by scanning a standard line in the x or y direction. 300 μm 2 A minimum of 300 Raman spectra covering the above area are obtained for each calibration standard. For each collected spectrum, the area of ​​the intrinsic TiO2 Raman peak that does not interfere with the Raman peak from the host resin is determined, and the obtained value is divided by the area of ​​the intrinsic Raman peak from the host resin. For HDPE, as an example, for each collected spectrum, %TiO2 is determined by calculating the area of ​​the TiO2 Raman peak centered at approximately 417 cm⁻¹¹ and dividing it by the spectral signature area of ​​HDPE between 1390 and 1504 cm⁻¹¹. The calibration curve is generated by calculating the average value of all normalized TiO2 and plotting the result against the %TiO2 determined from the ICP-OES method. This calibration formula is used to determine the %TiO2 in a particular layer of the article.

[0093] To determine the %TiO2 in a specific layer of an article, a properly flat cross-section of the sample for viewing the internal structure of a potentially layered article is prepared by a method known to those skilled in the art of microscopy. Preferred methods include slicing parallel to the layer using a sharp single-edge razor blade (cutting perpendicular to the thickness direction of the layer is unacceptable), cryogenic fracture of the article (removing a small area, clamping it with forceps, placing it in a liquid nitrogen bath, and fracturing it if brittle), and / or low-energy broad-beam cryogenic ion milling, such as using a Hitachi IM4000Plus Ion Milling System (Hitachi High-Tech America, Inc., Dallas, Texas). The cross-section of the sample is visualized in real time using a white-light video camera. Two-dimensional (2D) chemical mapping of the cross-section is obtained by scanning the cross-section in the thickness direction by focusing a laser beam on or below the cross-sectional surface and collecting data points every 5 μm, preferably every 1 μm, with a detector exposure time of a maximum of 10 seconds and a laser power of 20 mW or less on the sample, appropriately adjusted to maximize the Raman signal while preventing detector saturation or sample burning. In this way, spectral data is collected over a region having a width of approximately half the total cross-sectional thickness dimension (i.e., if the film thickness is 200 μm, the region to be analyzed should be 200 μm in the thickness direction × 100 μm in the orthogonal direction, as observed through a microscope). Full Raman spectral data at each pixel in the dataset is corrected against cosmic rays and a baseline corrected before image generation. Hyperspectral Raman images highlighting the TiO2 distribution from spectral features inherent to the host resin, such as TiO2HDPE, are generated using suitable software such as Renishaw WiRE® 5 software. The layers and layer thicknesses are determined by techniques known to those skilled in the art. The concentration of %TiO2 in different layers of the article is obtained by selecting at least 300 Raman spectra from evenly spaced intrinsic positions within a square / rectangle across each interface of the cross-section containing TiO2.For HDPE, as an example, for each collected spectrum, %TiO2 is determined by calculating the area of ​​the TiO2 peak centered at approximately 417 cm⁻¹ and dividing it by the spectral signature area of ​​HDPE in the range of 1390–1504 cm⁻¹. A calibration curve is used to obtain the average %TiO2 within individual layers of the article.

[0094] Method for determining the overall grade of barcode symbols For the verification of one-dimensional barcodes, seven verification parameters specified by ISO / IEC 15416-1 (decoding, symbol contrast, minimum reflectance, minimum edge contrast, modulation, defects, and decodeability) are measured using an ISO / IEC compliant barcode verifier such as the Axicon 15500 (Axicon Auto ID Limited, Oxfordshire, UK). "Barcode" is synonymous with the term "symbol" as defined in ISO / IEC 15416-1. Each of these parameters is assigned a grade from 0 to 4 according to ISO / IEC 15416-1, where 0 represents failure and 4 represents the highest quality. At least 10 scans collecting reflectance profiles across the full width of the barcode are measured using an ISO / IEC compliant barcode verifier. The scan reflectance profile grade for each scan reflectance profile shall be the lowest grade of any parameter evaluated for that profile. The overall grade of the barcode symbol is calculated by the arithmetic mean of each grade in the scan reflectance profile. The overall grade of a barcode symbol is reported to the nearest tenth of a digit. For one-dimensional barcode symbols, the measurement can be performed using any combination of aperture diameter, wavelength of light, and angle of incident light as recommended by ISO / IEC.

[0095] For the verification of two-dimensional barcode symbols, including two-dimensional multi-line barcode symbols and two-dimensional matrix symbols, grading is performed according to ISO / IEC 15415 using an ISO / IEC compliant 2D barcode symbol verifier such as the Axicon 15500 (Axicon Auto ID Limited, Oxfordshire, UK). Each parameter receives a grade from 0 to 4, where 0 represents failure and 4 represents the highest quality. The parameter with the lowest grade becomes the overall grade of the 2D symbol. For two-dimensional barcode symbols, measurements can be performed using any combination of aperture diameter, wavelength of light, and angle of incident light recommended by ISO / IEC.

[0096] Unless otherwise specified, all percentages are weight percentages based on the weight of the composition. Unless specifically stated otherwise, all ratios are weight ratios. All numerical ranges include narrower ranges, and the upper and lower range limits are interchangeable in creating further ranges that are not explicitly defined. The number of significant figures does not limit the indicated quantity or the precision of the measurement. All measurements are understood to be taken at approximately 25°C and under ambient conditions, where “ambient conditions” means conditions at approximately 1 atmosphere and approximately 50% relative humidity.

[0097] The dimensions and values ​​disclosed herein should not be understood as being strictly limited to the exact numerical values ​​listed. Instead, unless otherwise specified, each such dimension is intended to mean both the listed value and the functionally equivalent range encompassing that value. For example, a dimension disclosed as "40 mm" is intended to mean "approximately 40 mm."

[0098] All documents referenced herein, including any patents or patent applications that are cross-referenced or related, and any patent applications or patents for which this application claims priority or benefit thereof, are incorporated herein by reference in their entirety unless expressly excluded or particularly limited. No citation of any document shall be deemed prior art to any invention disclosed or claimed herein, nor shall it be deemed to teach, suggest or disclose any such invention, either alone or in combination with any one or more other references. Furthermore, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in any document incorporated by reference, the meaning or definition given to that term in this document shall prevail.

[0099] While specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications within the scope of the invention be covered in the appended claims.

Claims

1. A material sheet marked with a pulsed laser, comprising an outer edge and an inner edge separated by a core, wherein the distance from the outer edge to the inner edge is the sheet thickness, and the material sheet contains less than 1.00% TiO ２ It has a total concentration of TiO, and has an outer layer that starts from the outer edge and extends into the core, the thickness of the outer layer is about 10.00% to about 40.00% of the sheet thickness, and the outer layer is about 2.50% to about 10.00% TiO ２ A material sheet having an average concentration of [a certain value].

2. The material sheet according to claim 1, wherein the material sheet is a polymer.

3. The material sheet according to claim 1 or 2, wherein the laser marking on the material sheet is a UPC, QR, data matrix, or other machine-readable code or symbol.

4. The material sheet according to claim 3, wherein the machine-readable symbol is a one-dimensional barcode symbol and has an overall symbol grade of 1.5 or higher based on verification in accordance with ISO / IEC 15416 (2016).

5. The material sheet according to claim 3, wherein the machine-readable code is a two-dimensional barcode symbol and has one or more grades based on verification in accordance with ISO / IEC 15415 (2011).

6. The material sheet according to any one of claims 1 to 5, wherein the material sheet forms an article selected from the group consisting of garbage bags, bottles, pouches, tubes, films, laminates, bags, wraps, drums, jars, cups, or caps.

7. The material sheet according to any one of claims 1 to 6, wherein the material sheet has a thickness of approximately 10.0 microns to approximately 2.00 mm.

8. The pulse laser markings each include the positions of a predetermined pattern that includes marks or gaps in a grid pattern, The predetermined pattern includes alphanumeric characters in the form of text with a font size in the range of 6pt to 10pt. The grid pattern includes a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y. The Y distance is at least 1.2 times the X distance. A material sheet according to any one of claims 1 to 7.

9. The pulse laser markings each include the positions of a predetermined pattern that includes marks or gaps in a grid pattern, The predetermined pattern includes alphanumeric characters in the form of text with a font size in the range of 11pt to 16pt. The grid pattern includes a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y. The Y distance is at least twice the X distance. A material sheet according to any one of claims 1 to 8.

10. In addition to the outer layer, the core has two or more inner layers, each inner layer having a different concentration of TiO ２ A material sheet according to any one of claims 1 to 9, having the following characteristics.

11. The material sheet according to any one of claims 1 to 10, wherein most of the pulsed laser markings do not overlap with adjacent markings.

12. The laser marking pulse lasers each include the positions of a predetermined pattern, which includes marks or gaps within a grid pattern. The grid pattern includes a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y. Most of the marks in the X direction do not overlap. A material sheet according to any one of claims 1 to 11.

13. The laser mark includes a predetermined pattern which is a line or a curve. The material sheet according to any one of claims 1 to 12, wherein the spacing between adjacent laser marks varies within the line or curve.

14. The laser marking pulse lasers each include the positions of a predetermined pattern, which includes marks or gaps within a grid pattern. The grid pattern includes a plurality of positions positioned in two or more rows, the two or more rows being substantially parallel, each adjacent pair of positions along any of the two or more rows being separated by a distance X, and each adjacent pair in the two or more rows being separated by a distance Y. The Y distance is equal to the X distance, A material sheet according to any one of claims 1 to 13.

Images