System and method for forming an image on a substrate

Abstract

A scanning laser having a wavelength compatible with a coating binder so as to cure it as the laser scans and irradiates the coating on a moving web. A system and method for curing flakes by providing a scanning laser which scans across a moving coated substrate in a magnetic field allows images to be formed as magnetically aligned flakes are cured into a fixed position. The images have regions of cured aligned flakes. The scanning laser cures the magnetically aligned flakes within it region it irradiates. Alternatively an array of lasers can be used wherein individual lasers can be switched on and off to fix irradiated coating as a moving web is moved at a high speed.

Claims

1. A method comprising: moving a substrate along a path, wherein a first region of the substrate includes a coating of flakes within a binder and at least some of the flakes are alignable when a stationary magnetic field is applied, and wherein the stationary magnetic field is created using at least a first magnetic assembly on a first side of the substrate and a second magnetic assembly on a second side of the substrate; applying the stationary magnetic field so as to orient at least some of the flakes within the coating; and while applying the stationary magnetic field and while the substrate is moving along the path relative to the stationary magnetic field, selectively curing, using a laser, a first sub-region of the first region so as to cure the binder and maintain alignment of flakes within the first sub-region, wherein a beam of the laser is directed at the first sub-region while the first sub-region is located between the first magnetic assembly and the second magnetic assembly.

2. The method of claim 1, wherein the substrate moves at a speed of at least 7.62 m/s (25 ft/s) along the path.

3. The method of claim 1, wherein curing the first sub-region results in curing the coating in a predetermined pattern.

4. The method of claim 1, further comprising: after selectively curing the first sub-region, curing a second sub-region of the first region, wherein the second sub-region includes at least a portion of flakes outside of the first sub-region.

5. The method of claim 4, wherein curing the second sub-region occurs farther in a direction the substrate is moving than where curing the first sub-region occurs.

6. The method of claim 4, wherein curing the first sub-region and curing the second sub-region result in two distinct, visible regions of aligned flakes.

7. The method of claim 4, wherein, after curing the first sub-region and curing the second sub-region, the alignment of the flakes within the first subregion is different than an alignment of flakes within the second sub-region.

8. The method of claim 4, further comprising: prior to curing the second sub-region, aligning flakes within the second sub-region by applying a second magnetic field or a second electric field.

9. The method of claim 4, wherein the first sub-region is adjacent to the second sub-region.

10. The method of claim 4, wherein the first sub-region is cured at a first curing station, and wherein the second sub-region is cured at a second curing station.

11. The method of claim 10, wherein the second curing station is downstream, in a direction of movement of the substrate along the path, from the first curing station.

12. The method of claim 4, wherein the second sub-region is cured using a UV lamp.

13. The method of claim 4, wherein curing the second sub-region results in curing the coating in a predetermined pattern.

14. The method of claim 1, further comprising: applying the coating of the flakes within the binder to the first region.

15. The method of claim 1, wherein the substrate bends around a magnetic cylinder.

16. A method of forming an image on a substrate comprising: moving the substrate at a speed of at least 25 ft/min and applying a stationary magnetic field to align at least two of a plurality of flakes disposed within a binder on the substrate, wherein the stationary magnetic field is created using at least a first magnet on a first side of the substrate and a second magnet on a second side of the substrate; and irradiating, using a laser and while applying the stationary magnetic field and while the substrate is moving in a first downstream direction relative to the stationary magnetic field, one or more sub-regions of the plurality of flakes so as to cure the binder and maintain a magnetic or electrical alignment of flakes within the one or more sub-regions and to form one of at least two contrasting regions of magnetically or electrically alignable flakes, wherein a beam of the laser is directed at the one or more sub-regions while the one or more sub-regions are located between the first magnet and the second magnet.

17. The method of claim 16, wherein the plurality of flakes are magnetically alignable flakes and the stationary magnetic field is applied.

18. The method of claim 16, wherein irradiating the one or more sub-regions results in curing of a coating in a predetermined pattern.

19. The method of claim 16, wherein the beam of the laser is moved in a direction perpendicular to the first downstream direction.

20. The method of claim 16, further comprising: after applying the stationary magnetic field and after irradiating the one or more sub-regions, applying a different stationary magnetic field to the substrate, wherein the different stationary magnetic field is created using at least a third magnet, and wherein the third magnet is different from the first magnet and the second magnet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention will now be described in conjunction with the drawings in which:

(2) FIG. 1 is an isometric drawing of a high-speed system for aligning and curing flakes coated on a web having two alignment stations and two curing stations;

(3) FIG. 2 is illustrates the path of a scanning laser that is used for curing flakes on a moving web

(4) FIG. 3 shows an image formed by using the scanning laser programmed to scan across a moving substrate to create an apple logo;

(5) FIG. 4 depicts an alternative embodiment wherein a roller having magnets therein align flakes while a laser writes/cures flakes forming the apple logo.

(6) FIG. 5 is a diagram showing two magnets on either side of the substrate with a laser directed at an angle irradiating the substrate so as to cure the coating there upon.

(7) FIG. 6 is a diagram showing an alternative embodiment of the invention where an optic is used to convert a spot beam to a line across the substrate for curing coating on a moving web.

(8) FIGS. 7 and 8 illustrate irradiating a beam in a restricted region of the substrate using a laser beam.

(9) FIG. 9 is an illustration of a system wherein an nm array of lasers provide a linear array of beams for irradiating regions on the moving substrate wherein the lasers can be controllably be switched on selectively.

(10) FIG. 10 is an illustration of a printed label using the lasers to fix magnetically aligned flakes in a predetermined pattern.

DETAILED DESCRIPTION

(11) This invention provides a high-speed system and method for applying field-alignable flakes in ink or paint to a substrate in a plurality of regions and for aligning flakes within a region, and in-situ, while the flakes are aligned within an applied field such as a magnetic field, freezing those flakes in their magnetically aligned position by writing an image in the wet magnetic ink with an ultra-violet (UV) laser beam. Ink that is not exposed to the UV beam is not cured and flakes within this ink are not fixed in their aligned position and only flakes that have been written or cured in their clear or tinted ink or paint carrier with the UV beam are cured and fixed in their aligned position as UV curing binder solidifies. This system and method provides selective curing of locations within the wet ink as the substrate passes through the magnetic field at speeds of 25 ft/min and even up to speeds of 400 ft/min or greater.

(12) There are several aspects, which make this system a significant advance in the field of coating images. It offers selective curing of particular regions of flakes in binder as the coated substrate is moving at high speed through a magnetic field. It offers the benefit of freezing flakes in their aligned position before the flakes exit the magnetic field; by way of example, a fine laser beam can be directed to a wet coated region between at least a pair of magnets so as to freeze aligned flakes in their position by curing the binder they are in. This is important as aligned flakes in uncured binder exiting an applied field often become disoriented and lose their intended alignment. Furthermore the invention provides a scanning laser that writes a UV beam across the substrate. Because the laser beam moves in a different direction along a path nearly orthogonal to the direction the substrate is travelling, this allows virtually any design to be created and the aligned flakes within that design cured within the binder or carrier are frozen in place. Yet still further, this system allows flakes that were not cured outside of a the region written by the UV laser, to be realigned by a second different magnetic field down stream and subsequently cured in different alignment, providing a contrast between the first aligned cured flakes and the second aligned cured flakes. Aspects of the invention will now be described in greater detail.

(13) Turning now to FIG. 1 a system is shown having a flexible substrate 1 moving in a direction 2 at a controlled speed of approximately 25 ft/min to 400 ft/min. The speed can be increased or decreased. Of course if the substrate is moving at too great a speed, the UV laser will not be able to fully cure flakes within a desire region defining the letter A on the substrate. Writing or curing occurs by a curing of the UV-curable ink vehicle by the scanning beam of the ultra violet laser 8. The beam 9 is moved in the direction perpendicular to the direction 2 of the continuously moving substrate as shown. The region 3 on the web is coated in a printer press (not shown in this figure) with UV-curable magnetic ink containing platelets of a magnetic pigment. The pigment can be any magnetic pigment including metallic, color-shifting or micro-structured pigments. The ink vehicle can be clear or dyed. When the printed region 3 is advanced to location 4 between two permanent magnets 5 and 6, magnetic platelets of the pigment become oriented along magnetic lines 7 of the field. The UV-laser 8 generates the beam 9 of light. The beam scans forth-and-back the region 10 in the direction across the substrate. The amplitude of the scan depends on the graphics of an image. The ink vehicle cures in the places where the beam 9 illuminates it. Magnetic platelets are fixed in their positions with respect to the surface of the coated insignia 3. The scanning of the beam is controlled by a computer (not shown in FIG. 1) linked to the printing press. The computer provides writing of a predetermined image 10 of A in the coated area 4 and the registration of this image in the margins of the coated area 4 by controlling the speed of the substrate and the amplitude of scanning. Thus, the computer provides the function of a controller.

(14) The insignia A coated on the substrate is formed by continuously moving substrate 1 downstream to the position 11 into the magnetic field of different configuration while the laser beam irradiates and cures the clear or tinted ink or paint while scanning. Of course the laser 8 can be preprogrammed to sweep in any number of ways so as to generate virtually any image. The second magnetic field 14 is created by the magnet 12 of the polarity 13. The magnet 12 generates a field with magnetic lines 14. Magnetic platelets dispersed in the remaining layer of non-cured wet ink align themselves in a direction forming a linear convex Fresnel array reflector.

(15) After the insignia is formed and cured by the laser 8, it is moved downstream in a later moment in time to the position 15 where the wet ink about the A becomes cured by rays 16 of UV light coming from the UV lamp 17. The image now consists of the bright image 18 of the letter A illusively floating on the top of a dynamic background 19 having appearance of a cylindrical surface as a result of the second magnetic field 14.

(16) Further details of the scanning/writing process will now be described. The Laser beam 9 scans or sweeps the layer of wet ink with the frequency determined by the speed of the substrate and the amplitude determined by the graphics of the image as illustrated in FIGS. 2 and 3. The laser beam (not shown in FIG. 2), scanning from the left to the right with the variable amplitude 202 perpendicularly to the layer of wet ink 201 is moved at a high speed in the direction 203 in the plane of the page. The scanning light of the laser 8 locally cured the ink creating the snake-like or tight zigzag path of the beam 204 at the particular speed of the substrate. Reduction of the speed of the substrate changes the path creating an image of an apple at the same amplitude of the beam scanning across the wet ink 201 as is illustrated in FIG. 3. This zigzag path is essentially transverse to the direction in which the substrate moves.

(17) In FIG. 2 each scanned line has a predetermined length, determined by the laser's scan back and forth. For the purposes of understanding this invention, the continuous zigzag snake-like line consistent with the path 204 taken by the laser, in effect provides nine successive lines, wherein the length of some of these lines vary to create a visible pattern or logo. Therefore the laser is programmed to scan across the moving substrate and cure lines of flakes, one after another, successively to form the zigzag pattern shown. The lines formed across the moving substrate are at an angle and the steepness of the angle is dependent upon the speed at which the substrate is moving. Thus, locations across the substrate in a direction across the downstream direction are cured in this manner.

(18) Referring to FIG. 3 an image of an apple 300 is shown formed by a laser having a beam directed in a predetermined zigzag pattern in a manner as shown in FIG. 2.

(19) Although scanning or sweeping of the laser beam is shown to be done in a single continuous sweep back and forth, the laser can be switched on and off during a single sweep across so as to create a broken line or even a dashed line, by pulsing the laser accordingly.

(20) Direct writing with the laser beam is particularly advantageous for the substrate moving around a cylinder containing embedded magnets for a formation of a magnetic field as shown in FIG. 4. The layer 31 of wet ink is coated onto the substrate 32 moving in the direction 33. The substrate is wrapped around the cylinder 34 containing imbedded or engraved magnets not shown in FIG. 4. Laser beam 35 scans the layer of the ink with the frequency determined by the speed of the substrate and the amplitude determined by the graphics of the image.

(21) For security applications, images may be produced by a UV laser whose beam has passed through an interchangeable beam shaping optic. This optic transforms the existing laser beam into various patterns. Theses patterns will then locally cure the UV curable binder in which the magnetic pigment is encapsulated. These patterns may be in the form of line boarders, lines within images, dot matrix's, wordage, or any type of image. The benefit is that the patterns can be imprinted at high speeds and in high definition. The beam shaping optic can be rotated and or translated to create highly complex patterns that creating the effect of having an even greater depth of field. Patterns can be printed before, during or, to a lesser degree, after the magnetic flakes have been affected by magnets.

(22) A UV laser may be used to create complex patterns or patterns comprising of different resolvable feature. In addition, laser light creates an additional degree of freedom by enabling multiple alignments of the magnetic flakes for each printing process. This is achieved by changing the magnetic pigment orientation between each UV laser exposure to the laser writing process or between exposures between the laser writing process and the conventional curing that can take place subsequent to the laser writing as is shown in FIG. 1. This extra degree of freedom created by multiple flake orientation technique may create highly diverse and unique security image features.

(23) Using a laser to cure flakes within a binder has numerous advantages as described above. It allows selective curing while a substrate is moving through a magnetic field. However there are further advantages. Magnetic devices currently being developed for the alignment of magnetic particles are becoming more and more complicated. In some instances the magnetic assembly may consist of two or more housings containing magnetic assemblies and located on one or both sides of a fast moving paper or plastic substrate with very tight spaces between these housings. As was mentioned heretofore, it is desired to cure flakes subjected to a magnetic field while the flakes are still within the field, for example between the magnets. Notwithstanding, this is often very difficult, and at times impossible to cure the flakes in the binder using a conventional arc or ultraviolet LED lamp through a very narrow gap between the magnetic assemblies. Only narrow focused and long distance directing of a laser beam is able to cure the ink in such tight spaces. Thus it is desirable to have a sweeping laser beam or multiple beams for creating a variable length line for some applications.

(24) However in other instances a very narrow window in the form of a line is available and scanning along the line as the substrate is moving at a high speed is not possible.

(25) FIGS. 5 and 6 illustrate an embodiment of the invention wherein a UV laser beam is converted to a line of light that is focused within a very narrow window corresponding to the width of the substrate available to irradiate the moving substrate and cure the ink while still in the magnetic field. Turning now to FIG. 5 a magnetic assembly 1 is shown on either side of the substrate 50, which moves in a direction of the arrow shown. A laser 52 provides a beam 53 which is directed so as to irradiate the coated substrate while a coating between the magnets is in the magnetic field, not shown. FIG. 5 is illustrative of the fact that by using a narrow laser beam the substrate can be cured while in the magnetic field, where in the past a large UV lamp would have been used after the coating exited the magnetic field. By using a narrow width beam it is possible it launch and direct the beam into a very narrow available window in which to cure the coating.

(26) Turning now to FIG. 6, a magnetic cylinder 41, containing embedded magnets for aligning of magnetic particles, was mounted on the printing press. In operation, the flexible substrate 42 moves in the direction 43. The substrate 42 has regions 44 of wet ink on its surface printed with magnetic ink at the print station of the press, not shown in the figure. The flexible substrate 42 bends around the magnetic cylinder 41 contacting one quadrant 45 of its surface. The printed regions 44 on the substrate are registered with the magnets of the cylinder 41 aligning magnetic particles and forming the rolling bar feature 46, disclosed in for example U.S. Pat. No. 7,604,855. Alignment of platelets occurs in the margins of the quadrant 45. If magnetic ink with aligned magnetic particles is not cured in the margins of the quadrant 45, they begin to re-align and lose the rolling bar effect in the location 46 where the web 42 starts to separate from cylinder 41. Such unwanted re-alignment occurs because magnetic particles follow direction of magnetic field that continues to change with the growth of a distance between the substrate 42 and the cylinder 41 in the margins of the angle 47. It would make sense to let the particles become aligned along the region 48 of the substrate 42 over the quadrant 45 where they could be aligned properly, and cured in the portion 49 of the substrate that is close to the end of the quadrant.

(27) To prevent the loss of the desired magnetic alignment effect, magnetic particles should be cured in the field. If conventional mercury lamps or UV LED light sources illuminate the cylinder 1, they have to illuminate large area of it to cure or pre-cure the ink because they cannot cure the ink instantaneously. Reduction of the area where the web is contacting the magnetic cylinder 42 reduces a time required for a proper alignment of magnetic flakes. In accordance with an embodiment of this invention, we found, that it was beneficial to use a high power UV laser so as to illuminate the narrow region on the end of the quadrant of the magnetic cylinder. In this regard, the laser 50 is provided to produce the light beam 51 to the quartz cylindrical lens 52 installed across the substrate 42. The lens converges the laser beam and generates the cross-web light flow 53 falling on the web 52 as the narrow line 54 of an intense UV light for curing the magnetic ink without distortion of the rolling bar effect. The rolling bar in this instance is merely exemplary. Providing a curing narrow line laser light, for example, a line having width of less than one inch and a width of many times greater, conveniently positioned to irradiate the moving substrate though a narrow line or window opening would allow curing within the magnetic field other magnetically alignments of flakes produce by other magnetic arrangements.

(28) For practical applications using UV curable binder commercially available we suggest using a laser in the wavelength range of 325 nm to 425 nm, and preferably in the range of 355 nm to 405 nm and wherein said laser has a power in the range of 100 mW to 2000 mW.

(29) The power of the laser depends very much upon the speed at which the substrate is moving and the distance the laser is from the substrate. For example, if the substrate is moving more slowly, less power is required from the laser as the region being irradiated with experience the beam for a longer duration. Lasers in the wavelength ranges of 355 nm/349 nm and 405 nm are commercially available. We have also found re-focusable lasers to be very useful for curing wherein the lasers can be adjusted so that they do not provide a small dot, but rather a spot or line of 0.0625 to 0.375.

(30) Referring to FIG. 7 a cylinder 71 is shown irradiated with a beam 73 of a laser 70. The grey magnetic region is shown to be 3 inches in width and the curing region adjacent the laser beam 71 is 1 in width. In FIG. 8 a substrate 81 is shown having a magnet 85 below having a width of 3 and a curing laser bar 80 above having a width of 1. The width is determined by the area of the contact of the substrate with the surface of the apparatus bearing embedded magnets. The curing region has to be not larger than one third of that area. In general the last of the contact zone is preferably where curing occurs.

(31) Referring now to FIG. 9, an alternative embodiment of the invention is shown wherein a ln linear array of lasers or nn array 93 (as shown) of laser beams are provided which, when all switched on, irradiate locations forming a line across the substrate 95. Advantageously, the line is not a zigzag but is a straight line, and as the substrate moves; the lasers are controlled so as to be switched on, and off in a desired manner, an image is formed in the aligned flakes as the coating is cured to fix the flakes in the pattern. A dynamic, line-by-line curing is achieved as the substrate moves and the beams change their irradiating pattern by switching the laser within the array, dynamically. An example of an image 100 produced by the using a laser array is demonstrated in FIG. 10.

(32) In alternative but related embodiment, a suitably programmed controller (not shown) controls the switching on and off of particular lasers within the array, so as to be able to change the image being frozen within the binder. For example if all of the flakes within a region are upstanding, and the array shown is programmed to irradiate a particular sub-region defining a desired image, a next label to be printed can have a different image by switching on and off different lasers in the array. This provides the ability to, for example cure flakes with an image of a serial number, and on a subsequent label cure a different serial number, such that individual labels can be printed with unique serial numbers, by varying the region of flakes to be cured accordingly. At a subsequent curing stage, the remaining flakes in the uncured binder can be oriented to be flat upon the substrate to provide contrast to the cured upstanding flakes. Heretofore, it was not possible to magnetize and cure images in this manner in a high-speed process.

(33) Although some or all adjacent labels may have different visible images as a result of curing different regions of flakes or areas within the coated label region, the alignment of flakes and curing of flakes by the first laser curing station that corresponds to a same region on another label on moving web or substrate will have a same alignment.

(34) In embodiments of this invention a UV laser has been used to cure flakes in a UV curable binder. Of course other laser wavelengths that are compatible with curing a particular binder having flakes therein can be used.