ES2425615T5 - Method to orient the magnetic flakes - Google Patents

Description

DESCRIPTION

Method to orient the magnetic flakes

Background of the invention

This invention relates generally to optically variable pigments, films, devices and images, and more particularly to aligning or orienting magnetic flakes, such as during a painting or printing process, to obtain an illusory optical effect.

Optically variable devices are used in a wide variety of applications, both decorative and utilitarian. Optically variable devices can be manufactured in various ways to achieve a variety of effects. Examples of optically variable devices include holograms printed on credit cards and authentic software documentation, color-changing images printed on banknotes and enhancing the surface appearance of items such as motorcycle helmets and wheel covers.

Optically variable devices can be manufactured as a film or sheet that is pressed, stamped, glued, or otherwise affixed to an object, and can also be manufactured using optically variable pigments. One type of optically variable pigment is commonly referred to as a color-changing pigment because the apparent color of properly printed images changes with such pigments as the viewing angle and / or illumination is tilted. A common example is the "20" printed with color-changing pigment in the lower right corner of a twenty US dollar bill, which serves as an anti-counterfeiting device.

Some anti-counterfeiting devices are covered, while others are meant to get noticed. Unfortunately, some optically variable devices that are meant to be noticed are not widely known because the optically variable appearance of the device is not drastic enough. For example, the color change of an image printed with color-changing pigment may not be noticeable under uniform fluorescent overhead lights, but may be more noticeable in direct sunlight or under single-point lighting. This may make it easier for a counterfeiter to pass counterfeit notes without the optically variable characteristic because the recipient may not be aware of the optically variable characteristic, or because the counterfeit note may appear substantially similar to the authentic note under certain conditions.

Optically variable devices can also be made with magnetic pigments that align with a magnetic field after applying the pigment (typically in a carrier such as an ink vehicle or a paint vehicle) to a surface. However, magnetic pigment paint has been used primarily for decorative purposes. For example, the use of magnetic pigments to produce wheels with a painted cover that have a decorative feature that appears as a three-dimensional shape has been described. A pattern was formed in the painted product by applying a magnetic field to the product while the paint medium was still in a liquid state. The paint medium had scattered non-spherical magnetic particles aligned along the magnetic field lines. The field had two regions. The first region contained lines of a magnetic force that were oriented parallel to the surface and arranged in the shape of a desired pattern. The second region contained lines that were not parallel to the surface of the painted product and were arranged around the pattern. To form the pattern, permanent magnets or electromagnets shaped corresponding to the desired pattern shape were arranged under the painted product to orient non-spherical magnetic particles dispersed in the paint in the magnetic field while the paint was still wet. When the paint dried, the pattern was visible on the surface of the painted product as the light rays incident on the paint layer were influenced differently by the oriented magnetic particles.

Similarly, a process for producing a pattern of flaky magnetic particles in a fluoropolymer matrix has been described. After covering a product with a composition in liquid form, a magnet with the desirable shape was disposed at the bottom of the substrate. Magnetic flakes dispersed in a liquid organic medium are oriented parallel to the magnetic field lines, tilting from the original planar orientation. This inclination ranged from perpendicular to the surface of a substrate to the original orientation, which included flakes essentially parallel to the surface of the product. The flat oriented flakes reflected incident light towards the observer of the card, while the reoriented flakes did not, providing the appearance of a three-dimensional pattern on the coating.

While these approaches describe methods and apparatus for layering paint three-dimensional type, they are not suitable for high speed printing processes because they are essentially batch processes. It is desirable to provide methods and apparatus for high speed in-line printing and painting that redirects magnetic pigment flakes. Furthermore, it is desirable to create more perceptible optically variable security features in financial documents and other products.

Document subsequently published to WO 02/090002 A2 describes multilayer magnetic flakes that can be oriented using a magnet arranged adjacent to a substrate, for example a magnet in the shape of a character. In some examples in this document, the portions adjacent to the magnet appear black when viewed under a 90 degree angle of view.

EP 0556449 A1 describes pattern formation by bringing adjacent magnets to substrates covered with a paint layer containing non-spherical magnetic particles, which causes an alignment of the particles according to a magnetic field caused by the magnet. Some portions of the aligned particles may be arc-shaped. With the method described in this document, characters can be formed that appear white, while the surrounding area appears black.

US 3,853,676 A discloses arranging magnetic pigments in a curved shape near very close reference points to a film using curved magnetic fields to create an illusion of depth.

Patent US 6,103,361 A describes the orientation of the magnetic flakes in such a way that in a first part and in a second part they are essentially parallel to a substrate, and between the first and second parts the flakes are perpendicular to the substrate. To orient the flakes, magnetizable matrices can be used.

GB 1,131,038 A describes the production of a pattern of particles in a polytetrafluoroethylene matrix using magnets to create an illusion of depth. The particles can be oriented inclined in this way relative to a substrate. For example, a star-shaped magnet can be used.

US 2,570,856 A describes a method in which a film containing magnetic particles is subjected to a magnetic field, for example, it is made to rotate within a magnetic field. After hardening, the film can be removed from the magnetic field.

GB 1,107,395 A describes devices and methods for printing characters on a sheet using ink containing magnetizable particles and using magnets to move the ink containing the particles onto the sheet. Some of the used magnets may be arranged on a roller.

Document WO 88/07214 A describes the orientation of preferably spherical particles, preferably a hemisphere of them is covered by a light reflecting material having magnetic or electrical properties. The particles can be brought into the desired orientation relative to a substrate using a magnetic or electric field, for example, so that the light reflecting material faces the substrate, in a continuous process in which the substrate is moved along. along a magnetic device. The magnetic device can include a series of permanent bar magnets that are disposed end-to-end and extend transversely to the substrate.

Patent EP 0325237 A2 describes a method and apparatus for producing a magnetic recording medium in which a substrate is moved in a direction of field lines of a magnetic field.

Compendium of the invention

The present invention provides a method as defined in claim 1.

Brief description of the drawings

Figure 1A is a simplified cross section of a printed image called a "flip-flop".

Figure 1B is a simplified plan view of the image printed on a document at a first selected viewing angle.

Figure 1C is a simplified plan view of the printed image at a second selected viewing angle, obtained by tilting the image relative to the point of view.

Figure 2A is a simplified cross section of a printed image that is called a "rolling bar" for analysis purposes.

Figure 2B is a simplified plan view of the rolling bar image at a first selected viewing angle.

Figure 2C is a simplified plan view of the rolling bar image at a second selected viewing angle.

Figure 12A is a schematic simplified side view of a lamination printing apparatus not in accordance with the claimed invention.

Figure 12B is a schematic simplified side view of a lamination printing apparatus according to the claimed description.

Figure 12C is a simplified perspective of a rolling drum with magnetic assemblies according to the apparatus illustrated in Figures 12A and 12B.

Figure 12D is a simplified perspective view of a portion of a laminating drum with a magnetically patterned surface.

Figure 12E is a simplified side view of the magnetic assembly for printing illusory three-dimensional images.

Figure 12F is a simplified side view of a magnet for printing illusory three-dimensional images.

Figure 13B is a simplified flow diagram of a method for printing an image according to another embodiment of the present invention.

Detailed description of the invention

introduction

The present invention in its various embodiments solves the problem of the predetermined orientation of the optically variable magnetic ink flakes in a high speed printing process. Typically, optically variable pigment particles dispersed in a liquid paint or ink vehicle are generally oriented parallel to the surface when printed or painted on a surface. The orientation parallel to the surface provides high reflectance of incident light from the covered surface. Magnetic flakes can be tilted while in the liquid medium by applying a magnetic field. The flakes are generally aligned in such a way that the longest diagonal of a flake follows a magnetic field line. Depending on the position and strength of the magnet, the magnetic field lines can penetrate the substrate at different angles, tilting the magnetic flakes at these angles. An inclined flake reflects incident light differently than a flake parallel to the surface of the printed substrate. Reflectance and hue may be different at different tilt angles. Slanted scales generally appear darker and have a different color than scales parallel to the surface at a normal viewing angle.

The orientation of magnetic flakes in printed images poses several problems. Many modern printing processes are high-speed over the batch process that applies a magnet against a static (non-moving) covered item and holds the magnet in position while the paint or ink dries. In some printers, the paper substrate is moved at speeds of 100 to 160 meters per minute. Sheets of paper are stacked after one print operation and fed into another. The inks used in such operations typically dry within milliseconds. Conventional processes are not suitable for such applications.

It has been discovered that one way to obtain improved optical effects on the painted / printed image is by orienting the magnetic flakes perpendicular to the direction of the moving substrate. In other words, the painted or printed liquid paint or ink medium with scattered flakes on the substrate moves perpendicular to the magnetic lines of the field to cause reorientation of the flakes. This type of orientation can provide noticeable illusory optical effects on the printed image. One type of optical effect is called a kinematic optical effect for analysis purposes. An illusory kinematic optical effect generally provides an illusion of movement in the printed image when the image is tilted relative to the viewing angle, assuming a stationary light source. Another illusory optical effect provides virtual depth to a printed two-dimensional image. Some images can provide both movement and virtual depth. Another type of illusory optical effect changes the appearance of a printed field, for example by alternating between bright and dark colors when the image is tilted back and forth.

II. Examples of illusory images printed

Figure 1A is a simplified cross-section of a printed image 20 that is referred to as an optical "switch" effect, or "flip-flop", for analysis purposes. The flip-flop includes a first printed portion 22 and a second printed portion 24, separated by a transition 25. The pigment flakes 26 surrounded by the carrier 28, such as an ink vehicle or a paint vehicle, have been aligned parallel to a first plane in the first portion and the pigment flakes 26 'of the second portion have been aligned parallel to a second plane. The scales are shown as short lines in the cross-sectional view. Flakes are magnetic flakes, that is, pigment flakes that can be aligned by a magnetic field. They may or may not retain remanent magnetization. Not all of the flakes in each portion are exactly parallel to each other or to the respective alignment plane, but the overall effect is essentially as illustrated. Figures are not drawn to scale. A typical flake may be twenty microns wide and about one micron thick, so the Figures are merely illustrative. The image is printed or painted on a substrate 29, such as paper, plastic film, laminate, cardboard, or other surface. For ease of analysis, the term "printed" is used to generally describe the application of pigments in a carrier to a surface, which may include other techniques, including techniques that others may refer to as "painting."

Generally, scales seen normal to the plane of the scale appear bright, while scales seen along the edge of the plane appear dark. For example, light from an illumination source 30 is reflected off the flakes in the first viewing region 32. If the image is tilted in the direction indicated by an arrow 34, the flakes in the first region 22 are visible. vertically, while light is reflected off the scales in the second region 24. Thus, in the first viewing position, the first region appears light and the second region appears dark, while in the second viewing position the fields change with each other, the first region becomes dark and the second region becomes light. This provides a very striking visual effect. Similarly, if the pigment flakes change color, one portion may appear to be one first color and the other portion another color.

The carrier is usually transparent, clear, or tinted, and the scales are usually quite reflective. For example, the carrier may be tinted green and the flakes may include a metallic layer, such as a thin film of aluminum, gold, nickel, platinum, or metal alloy, or be a metal flake, such as a nickel flake. or alloy. Light reflected off one layer of metal through the green-stained carrier may appear bright green, while another portion with flakes on the end may appear dark green or another color. If the flakes are simply metallic flakes on a transparent carrier, then one portion of the image may appear shiny metallic, while another appears dark. Alternatively, the metallic flakes may be covered with a tinted layer, or the flakes may include an optical interference structure, such as an absorbent-spacer-reflective Fabry-Perot type structure.

Figure 1B is a simplified plan view of the printed image 20 on the substrate 29, which may be a document, such as a banknote or stock certificate, in a first selected viewing angle. The printed image can act as a security and / or authentication feature because the illusory image is not photocopied and cannot be produced using conventional printing techniques. The first portion 22 appears bright and the second portion 24 appears dark. A section line 40 indicates the cross section shown in Figure 1A. The transition 25 between the first and second portions is relatively steep. The document can be a banknote, stock certificate, or other high-value printed material, for example.

Figure 1C is a simplified plan view of the printed image 20 on the substrate 29 at a second selected viewing angle, obtained by tilting the image relative to the point of view. The first portion 22 now appears dark, while the second portion 24 appears light. The angle of inclination at which the image changes depends on the angle between the alignment planes of the scales in the different portions of the image. In one sample, the image went from light to dark when tilted about 15 degrees.

Figure 2A is a simplified cross section of a printed image 42 of a kinematic optical device which is referred to as a "rolling bar" for analysis purposes. The image includes pigment flakes 26 surrounded by transparent carrier 28 printed on substrate 29. The pigment flakes are curved aligned. As with the flip-flop, the region (s) of the rolling bar that reflect light from the faces of the pigment flakes appear lighter to the viewer than the areas that do not reflect light directly to the viewer. This image provides a band (s) of light or bar (s) that appear to move ("roll") through the image when the image is tilted from the viewing angle (assuming one source (s) ) fixed lighting (s).

Figure 2B is a simplified plan view of image 42 of the rolling bar at a first selected viewing angle. A bright bar 44 appears in a first position in the image between two contrasting fields 46, 48. Figure 2C is a simplified plan view of the image of the rolling bar at a second selected viewing angle. The bright bar 44 'appears to have "moved" to a second position in the image, and the sizes of the contrasting fields 46', 48 'have changed. The alignment of the pigment flakes creates the illusion of a bar "rolling" down the image as the image is tilted (at a fixed angle of view and fixed lighting). Tilting the image in the other direction makes the bar appear to roll in the opposite direction (up).

The bar may also appear to have depth, even though it is printed on a plane. The virtual depth can appear to be much greater than the physical thickness of the printed image. Tilting the scales in a selected pattern reflects light to provide the illusion of depth or "3D" as it is commonly known. A three-dimensional effect can be obtained by arranging a shaped magnet behind the paper or other substrate with magnetic pigment flakes printed on the substrate in a fluid carrier. The flakes align along the magnetic field lines and create the 3D image after setting the carrier (eg, drying or curing). The image often appears to move as it is tilted, so cinematic 3D images can be formed.

Flip-flops and rolling bars can be printed with magnetic pigment flakes, ie. pigment flakes that can be aligned by a magnetic field. A printed flip-flop image provides an optically variable device with two distinct fields that can be obtained with a single printing pass and using a single ink formulation. A rolling bar type image provides an optically variable device that has a contrast band that appears to move as the image is tilted, similar to the semi-precious stone known as a tiger's eye. These printed images are quite conspicuous and the illusory aspects are not photocopied. Said images can be applied to banknotes, stock certificates, software documentation, security seals and similar objects such as authentication and / or anti-counterfeiting devices. They are particularly desirable for high-volume printed documents, such as banknotes, packaging, and labels, because they can be printed in a high-speed printing operation.

III. Rotating magnet printing.

FIG. 12A is a schematic simplified side view of a portion of a nonconforming recording apparatus 200. with the claimed invention. Magnets 202, 204, 206, 208 are located within a print roller 210, forming a pattern that corresponds to a printed image. The substrate 212, such as a web of paper, plastic film, or laminate, moves between the impression cylinder 214 and the impression roller 210 at high speed. The impression cylinder takes a relatively thick layer 212 of liquid paint or ink 215 containing magnetic pigment from a source container 216. The paint or ink is spread to the desired thickness on the impression cylinder with a blade 218. During printing of an image between the impression cylinder and the impression roller, the magnets of the impression roller orient (that is, selectively align) the magnetic pigment flakes in at least a portion of the printed image 220. A tensioning device 222 is used typically to maintain the desired tension of the substrate as it exits the printing roller and the printing cylinder, and the image on the substrate is dried with a dryer 224. The dryer can be a heater, for example, or the ink or paint can be UVA curable and set with a UVA lamp.

Figure 12B is a schematic simplified side view of a portion of a recording apparatus 200 'according to the present invention. Magnets 202 ', 204', 206 ', 208' are installed on tensioning device 222 'or other roller. Magnets orient magnetic pigment flakes in printed images before the fluid carrier of ink or paint dries or sets. A field 219 exits the printing roller 210 'and the flake impression cylinder 214 with an unselected orientation, and a wet image 220' is oriented by a magnet 206 'of the tensioning device 222' before the flakes are attached. Dryer 224 accelerates or completes the drying or curing process.

FIG. 12C is a simplified perspective view of a magnetic roller 232 in accordance with one embodiment of the present invention. The roller may be a printing cylinder or a tensioning device, as described in conjunction with Figures 12A and 12B, or another roller of a printing system that contacts the printing substrate before the ink or paint is set. . Magnetic assemblies 234, 236, 238, 240, 241 are attached to the roller with screws 242, allowing the magnetic assemblies to be changed without removing the roller from the printer. The magnetic assemblies can be configured to produce flip-flop 234, 236 or rolling bar 238 images, or they can be patterned magnetic material 240, 241 that produces a patterned image on the printed substrate, or other selected magnetic configuration. The magnetic structures of the roller are aligned with the sheet or roller to provide the desired magnetic field pattern to the fields printed on the substrate with magnetic pigment flakes. The illustrated patterns represent flat patterns that follow the curve of the roll circumference. Alternatively, the magnetic structure can be built into the roll, or a roll can be magnetized with a suitable surface material following selected guidelines.

Figure 12D is a simplified perspective section of a portion of a roll 232 'with a magnetic assembly 244 embedded in the roll. The magnetic assembly has a star-shaped cross section, and its surface 244 'is essentially abutting the surface of the roller. The magnetic assembly may be in the form of permanently magnetized material, as illustrated in Figure 12F, or have a tip section of SUPERMALLOY, MU-METAL, or similar material, as illustrated below in Figure 12E. The roller rotates in the direction of the first arrow 246 and a substrate or paper film 248 is moved in the direction of the second arrow 250. A field 252 including magnetic pigment flakes has been printed on the substrate. The field was on the surface of the star-shaped magnetic assembly when the roller was close to the substrate, and an illusory optical feature 254 in the shape of a star has formed in the field. The magnetic pigment flakes are fixed while the magnetic assembly is in contact with the substrate.

The illusory optical effect 254 is a star with an apparent depth much greater than the physical thickness of the printed field. It has been found that the type of carrier used with the magnetic pigment flakes can affect the final result. For example, a solvent-based (including water-based) carrier tends to reduce in volume as the solvent evaporates. This can cause additional alignment, such as tilting the partially sloped flakes toward the plane of the substrate. UVA curable carriers tend not to shrink, and the alignment of the magnetic pigment flakes after contact with the magnetic field pattern tends to be more precisely preserved. Whether it is desired to preserve alignment or improve alignment by evaporation of the solvent in the carrier depends on the intended application.

Figure 12E is a simplified side view of a magnetic assembly 256 with a permanent magnet 258 that provides the magnetic field that is directed to the substrate 248 by a patterned tip 260 of SUPERMALLOY or other high permeability material. The patterned magnetic field lines 262 are shown for illustrative purposes only. Some "supermagnet" materials are hard, brittle, and generally difficult to machine into intricate shapes. SUPERMALLOY is much easier to machine than NdFeB magnets, for example, and thus can provide an intricate magnetic field pattern with sufficient magnetic field strength to align the magnetic pigment flakes in the desired pattern. The low remanent magnetization of SUPERMALLOY and similar alloys also makes them easier to machine.

Figure 12F is a simplified side view of a magnetic assembly 264 with a shaped permanent magnet 258 '. It is not necessary to shape the entire length of the magnet, but only the portion that produces the desired field pattern on the substrate 248. Although some materials that are commonly used to form permanent magnets are difficult to machine, simple patterns can be formed. at least in the tip section. Other materials that form permanent magnets can be machinable and can provide sufficient strength magnetic to produce the desired illusory optical effect. Similarly, magnetic alloys can be cast or formed into relatively complex shapes using powder metallurgy techniques.

IV. Illustrative methods

Figure 13B is a simplified flow diagram of a method 310 for printing an image on a moving substrate. A substrate is moved by passing a rotating roller with embedded magnets (step 312) to align the magnetic pigment flakes (step 314) that have been applied to the substrate in a fluid carrier. The magnetic pigment flakes are then fixed (step 316) to obtain an optically variable image resulting from the alignment of the pigment flakes. The magnetic pigment flakes are aligned by magnets in a tensioning device. After lining up the flakes, the ink or paint dries or cures to fix the image.

Various magnetic structures can be incorporated into the rollers or roller, including magnetic structures to form flip-flop or rolling bar images. Other magnetic structures, such as magnets with one face having a selected shape, can be incorporated into the rollers to provide high speed printing of optically variable images. For example, a magnet that has a ring shape on its face (the roller face) can produce a "fisheye" effect in a field printed with magnetic pigment flakes. The magnets on the rollers or roller can be modeled in other shapes, such as a star, a $ sign, or an € sign, for example. Arranging the magnets on the tensioner or other roller near the dryer can prevent image problems in magnetic pigment flakes from degrading as the image leaves the trailing edge of the magnet face.

Claims (1)

1. A method of forming an image on a substrate, the method comprising: (a) Printing fields of the substrate (219) of the substrate with magnetic pigment flakes dispersed in a fluid carrier with an unselected orientation on the substrate using a printing roller (210 ') and a printing cylinder (214) while the substrate is moved between the printing cylinder (214) and the printing roller (210 ') at high speed, the substrate is tensioned by a roller of the tensioning device (222') that makes contact with the substrate comprising magnets (202 ' , 204 ', 206', 208 ') that provide a desired magnetic field pattern, (b) orienting a wet image (220 ') in one of the fields (219) by means of one of the magnets (206') installed in the roller of the tensioning device (222 ') before the flakes are fixed, and (c) fixing the flakes using a drier (224) while the field (219) is in contact with the magnet (206 ').