METHODS OF AND DEVICES FOR PRINTING

TECHNICAL FIELD

[0001] The present application generally relates to methods of and devices for printing a material on a substrate.

BACKGROUND

[0002] Signs are commonly used along roadways to display information to motor vehicle drivers and pedestrians. One type of sign, a highway sign, typically includes reflective or retroreflective sheeting that has characters printed or placed thereon. The characters provide information that is of interest to the motor vehicle drivers or pedestrians, and the retroreflective sheeting allows the information to be vividly displayed at nighttime. Retroreflective sheeting has the ability to return a substantial portion of incident light in the direction from which the light originated. Light from motor vehicle headlamps is retroreflected by the signs, allowing the information to be read more easily by passing motorists and pedestrians.

[0003] Many types of signs, including highway signs, tend to be fairly large in size to accommodate large characters. The characters are typically applied to the signs by screen printing or using cut-out characters. In screen printing, a positive or negative image of the characters is first provided on a screen. This often is accomplished by exposing non- masked portions of a photosensitive screen to light and removing the un-sensitized, masked regions by scrubbing. Ink is then forced through the openings in the screen where the photosensitive material was removed onto the retroreflective sheeting. Screen printing is the method of choice for making the more common street signs, such as "stop" and "yield" signs. However, screen printing custom or unique signs (such as, for example, highway and road signs) is costly and inefficient because a separate screen needs to be made for each individual sign.

[0004] When a custom or unique sign is needed, the cut-out character method is frequently used. Cut-out characters are made by die cutting each character or by electronically cutting the characters from a stock material such as, for example, Scotchcal™ ElectroCut™ Graphic Films manufactured by 3M Company of St. Paul, Minnesota. The cut-out characters typically are secured to the underlying retroreflective

sheeting by use of an adhesive. Although the screen printing and cut-out character methods provide suitable ways of placing characters on highway signs, these methods tend to be time-consuming and somewhat cumbersome.

[0005] Thermal printing has become a popular and commercially successful technique for forming characters on a substrate. Also referred to as thermal transfer printing, nonimpact printing, thermal graphic printing, and thermography, thermal printing is a process by which a colorant is transferred with the aid of heat from a carrier to a thermal print receptive substrate. Thermal printing is more rapid than screen printing or using cut-out characters, and it is less cumbersome and relatively simple to practice. [0006] U.S. Patent No. 5,972,111 (assigned to the assignee of the present application) describes a digital printer in which a pigmented material, such as, for example, paint, is deposited in metered amounts onto a print medium. The digital printer includes a wheel rotatable by a shaft of a motor, an idler disposed in a paint reservoir, and a cable disposed around the wheel and the idler. Rotation of the wheel and thus movement of the cable may be selectively controlled. As the wheel rotates, paint contained within the paint reservoir coats the cable and is thus drawn by the cable in front of an air stream. The air stream directs the paint from the cable onto the print medium. By employing a plurality of such paint injectors in a single print head, each containing a different color of paint, and securing the paint injectors to a computer controlled, movable carriage positioned over the print medium, a digital image can be created on the print medium. [0007] U.S. Patent No. 6,786,971 (assigned to the assignee of the present application) describes a printing device for digital printing on a print medium. The printing device includes a wheel rotatable by a motor, a liquid dispenser for depositing a quantity of liquid (e.g., paint) on the wheel along the outer edge, and an air jet positioned adjacent the outer edge for removing the liquid from the outer edge and directing the liquid toward the print medium as the wheel rotates through the air jet. In at least some embodiments, the outer edge of the wheel includes a plurality of teeth that transport the liquid from the liquid dispenser to the air jet. An electronically controlled motor may be used to selectively rotate the wheel through the air jet thereby causing a desired amount of liquid to be removed from the wheel. The liquid is transported by the air jet toward and onto the print medium. By employing a plurality of such printing devices, a full color digital image can be reproduced on any print medium.

SUMMARY

[0008] There is a continuing need to improve the performance, reduce the cost, and/or to simplify the manufacture of signs.

[0009] The present application is directed to methods of printing various types of signage, including highway signs and license plates. The methods are more efficient and/or cost- effective than prior art methods of printing signs. The present application is also directed to various types of signage printed using these methods and to various types of apparatuses for printing these types of signage.

[0010] Some embodiments of the present application relate to a method of digitally printing an image on a signage, comprising: filling one or more holes in a disc with a pigmented material; positioning the disc in proximity to a substrate; and directing a fluid stream at the one or more filled holes in the disc such that at least a portion of the pigmented material is removed from the one or more holes in the disc and is deposited onto the substrate.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Fig. 1 is a front view of one embodiment of a fluid delivery system of the present application.

[0012] Fig. 2 is a cross-sectional rear view of the fluid delivery system of Fig. 1.

[0013] Fig. 3 is a perspective view of the fluid delivery system of Figs. 1 and 2.

[0014] Fig. 4 is a schematic drawing of the fluid delivery system of Figs. 1-3 in operation.

DETAILED DESCRIPTION

[0015] Various embodiments will be described in detail. These embodiments should not be construed as limiting the scope of the present application in any manner, and changes and modifications may be made without departing from the spirit and scope of the inventions.

[0016] As used herein, the term "pigmented material" is meant to include all colored (or non-colored) inks, dyes, paints, or combinations or variations thereof.

[0017] As used herein, the term "print medium" and "substrate" are used interchangeably and are meant to include any print medium or substrate known in the art, including but not

limited to paper, plastic, polymer, synthetic paper, metal foil, vinyl, non-woven materials, cloth, glass, wood, cement, metal, films, optical sheeting, and combinations or variations thereof. The print medium or substrate can be, for example, a rigid, pliable, or flexible material.

[0018] As used herein, the term "signage" is meant to include signs, including, but not limited to, outdoor signs (e.g., highway signs, street signs, etc); indoor signs, for example, building interior signing (e.g., fire exit signage, fire extinguisher signage, and the like); off-street signs (e.g. , parking lot signage, no parking signs, fire lane signs, and the like); license plates; billboards; and truck siding.

[0019] As used herein, the terms "fluid delivery system," "printer," "paint injector," or variations or combinations thereof are used interchangeably.

[0020] The printers described in U.S. Patent Nos. 5,972,111 and 6,786,971 can exhibit overspray. This is typically caused by the air nozzles blowing ink off of the wire and onto the print medium without sufficient precision. Additionally, the printers described in U.S. Patent Nos. 5,972,111 and 6,786,971 have some limitations with respect to the viscosity of the ink that they can accurately and precisely deposit onto a print medium. The printers and methods described herein improve upon some of the features of these prior art printers.

[0021] One embodiment of an improved fluid delivery system is shown in Figs. 1-4. Figs. 1, 2, 3, and 4 are respective front, back, perspective, and side views of an improved fluid delivery system, generally indicated at 10. An elongate reservoir of ink 20 (shown in cross-section in Figs. 1 and 2) is attached to plate 22. More specifically, the distal end of reservoir 20 is attached to an elongate reservoir retaining member 24 that is fastened to reservoir 20 by means of a fastening mechanism 26, such as, for example, a threaded nut that is threaded onto a threaded shaft. Elongate reservoir of ink 20 is also attached to a wiper 28 that is positioned closely adjacent to a disc 30.

[0022] Disc 30 is fixed to plate 22 by a bolt 32 such that disc 30 may rotate in a counterclockwise direction about a central axis. At all times, a portion of disc 30 is submerged in elongate reservoir of ink 20. Disc 30 includes multiple holes 34 of the same or varying diameter. During rotation of disc 30 through reservoir 20, ink 33 fills holes 34. As disc 30 rotates out of reservoir 20, wiper 28 removes excess ink from disc 30. Wiper 28 also removes ink from the back surface of disc 30. Wiper 28 is shown as wiping only

the back surface of disc 30, but wiper 28 may be implemented to wipe both the front and rear surfaces of disc 30 such that the only ink adhering to disc 30 is contained within holes 34.

[0023] After disc 30 rotates past wiper 28, disc 30 rotates past a nozzle 40 (shown in cross-section in Fig. 2). A gas emitted by nozzle 40 contacts the rear side of disc 30 causing ink in holes 34 to be dislodged and to be carried through the air by the gas stream and to be deposited onto a print medium 42 (shown in Fig. 4) positioned adjacent to fluid delivery system 10. A gas supply hose 44 supplies gas to nozzle 40. Bolt 32 holds disc 30 in relative position to nozzle 40 so that gas passing onto disc 30 and/or through holes 34 does not substantially move disc 30 from in front of nozzle 40 or cause disc 30 to substantially vibrate or wobble.

[0024] Rotation of disc 30 may be controlled by a controller, generally indicated at 57. Any type of controller may be used. In one embodiment, the controller includes circuitry that receives signals from a signal generating device, such as a microprocessor or another device that can supply discrete signals to instruct selective rotation of disc 30. [0025] In operation, ink 33 contained in reservoir 20 is picked up by holes 34 in disc 30 and is advanced by rotation of disc 30, indicated by the counterclockwise arrow, past wiper 28 (where excess ink is removed) and then in front of nozzle 40. Gas (e.g., compressed air, nitrogen, etc.) that is blown through nozzle 40 disperses or directs the ink 33 from disc 30 toward the print medium 42. Depending on many factors, including the viscosity of the ink in reservoir 20, the diameter of holes 34, and the speed at which disc 30 is rotating, a relatively precise amount of ink can be deposited onto print medium 42. Further, because the ink to be deposited does not pass through a nozzle, the percent solids and/or the viscosity of the ink can be greater than prior art printers permitted. [0026] The fluid delivery system of the present application facilitates the use of higher viscosity inks. This results in more flexibility in selecting the ink to be used in a specific application. Further, the fluid delivery system of the present application reduces the incidence of overspray. The use of a hole as an ink carrier results in delivery of a more precise or exact volume of ink with little overspray. Additionally, the spray pattern may be controlled by the shape and size of the hole, providing greater precision printing of high viscosity fluids.

[0027] The fluid delivery system of the present application sprays one "dot" at a time, much like an ink jet printer. However, one advantage that the fluid delivery system of the present invention offers over an ink jet printer is the ability to vary the amount or volume of ink and the viscosity of the ink. The volume of ink deposited onto the print medium may be controlled by, for example, hole size, number of holes, disc speed, disc thickness, and hole shape.

[0028] Disc 30 can be made of any material known to those of skill in the art, including, but not limited to, aluminum, stainless steel, brass, plastic, or the like. Figs. 1-4 show a disc 30 having two different sizes of holes 34. This is only exemplary, as disc 30 could contain more or fewer holes, more or fewer differently sized holes, and/or smaller or larger diameter holes. One advantage of having different sized holes on a single disc is that one size hole (typically the smaller diameter hole) can be used for fine detailed work and the other size hole (typically the larger diameter hole) can be used for filling in objects.

[0029] Exemplary wiper materials include rubber and foam, but any material known to those of skill in the art can be used.

[0030] The fluid delivery system of the present application is uniquely qualified to print high viscosity inks or inks that have a high percent solids due to the fact that, among other things, the ink does not pass through an orifice. In particular, the fluid delivery system can print inks that have a viscosity too low for conventional screen printing and a viscosity too high for conventional ink jet printing. In addition, the fluid delivery system can print inks that have a particle size that is too great for both conventional ink jet printing or screen printing. The maximum viscosity of an ink for ink jet printing is typically 20 centipoise (cP) (0.02 pascal-second (Pa-s)) at approximately 25 degrees Celsius, and the maximum particle size for ink jet ink printing is typically 1-2 microns. Screen print inks typically require a viscosity greater than 800 cP (0.8 Pa-s) at approximately 25 degrees Celsius, and screen printing can typically print inks with particle sizes up to 125 microns. In comparison, the fluid delivery system can print inks having a viscosity between 1 cP (0.001 Pa-s) and 2000 cP (2 Pa-s) at ambient or room temperature, in addition to having the capability to print inks having a particle size between about 0 microns and about 600 microns.

[0031] A list of exemplary commercially available inks that fall within this range includes: 3M Process Color Series 700, 3M Process Color Series 880-00, 3M Process Color Series 880i, 3M Process Color Series 990, 3M Scotchlite Transparent Screen Printing Ink Series 2900, 3M Screen Printing Ink Series 1900, 3M Screen Printing Ink Series 9700UV, Nazdar 3500 Series UV Vinex Screen Ink, Avery Dennison Series 4930 Series Inks (10 year-1 Component Solvent Ink*), Sericol UVTS Series Ink, Nazdar UVTS Series Ink, Avery Dennison® UVTS-Sericol Ultraviolet Curable Printing Inks, Avery Dennison® UVTS-NazDar Ultraviolet Curable Printing Inks, Kiwalite KT Series Screen Process Ink, Avery Dennison® IOTS SeriesTwo-Component Printing Inks For Traffic Sign Products, Sericol Sinvacure UV Curable Screen Ink, Avery Dennison® 7TS Series Inks One Component Solvent Ink System For Traffic Sign Products, and Ink Dezyne VP- 000 Series Vinyl Plus Screen Ink.

[0032] The image that can be formed on a substrate to form signage can be any type of image, including, for example, words, letters, symbols, pictures, schematics, numbers, a pattern, and combinations or variations thereof. The images can be clear, transparent, or opaque, and the pigmented material can thus also be clear, transparent, or opaque. Further, the substrate and image may be colorless, comprise a solid color, or comprise a pattern of colors. Additionally, the substrate and image may be transmissive, reflective, non-reflective, or retroreflective.

[0033] Objects and advantages of the present application are further illustrated by the following examples, but the particular materials and amounts thereof recited in the examples, as well as other conditions and details, should not be construed to unduly limit the application. All parts, percentages and ratios herein are by weight unless otherwise specified.

EXAMPLE 1

[0034] An aluminum disc having a diameter of 3.5 inches (8.9 cm) and a thickness of 0.30 inch (0.76 cm) was attached to a variable speed mixing motor such that the disc could rotate counterclockwise around the attachment mechanism but was fixed along its Z axis. The motor was set so that the disc rotated at 10 RPMS. The disc included 24 holes each having a diameter of 0.05 inch (0.13 cm). The center point of each hole was 3 inches (7.6 cm) from the center of the disc and 0.25 inch (0.63 cm) from the edge of the disc. The

holes were formed in the disc in the pattern that is generally shown in Figs. 1-3 (a hole every 15 degrees along the circumference of the disc) and were spaced approximately 0.375 inch (0.95 cm) from an adjacent hole. An air nozzle that sprayed compressed air at a rate of 10 psi (68.9 MPa) was positioned to be rearwardly adjacent to the rotating disc such that the air nozzle directed a continuous stream of compressed air onto the rotating disc. On the opposite side of the disc as the air nozzle was positioned a sheet of 3M retroreflective sheeting including an overlay (retroreflective sheeting Model No. 3990 and/or 4090 manufactured by 3M Company of St. Paul, MN). An ink reservoir was filled with black 880i screen printable ink manufactured by 3M Company of St. Paul, Minnesota that was thinned to about 140 cP (0.14 Pa-s) using 891 ink thinner manufactured by 3M Company of St. Paul, Minnesota. The ink reservoir was then positioned adjacent to the disc such that at least a portion of the disc was in the reservoir at all times and such that when the motor was turned on, the disc rotated through the ink reservoir and ink from the reservoir adhered to or filled the holes in the disc. After the disc rotated through the ink reservoir, a foam wiper removed excess ink from the disc. The disc then passed by the air nozzle described above. The compressed air emitted by the air nozzle was controlled to selectively dislodge the ink from the holes in the disc resulting in a pattern (a straight line) being formed on the retroreflective sheeting. The shape, thickness, etc. of the pattern (straight line) was a function of the disc speed and web size. However, the average straight line had a thickness of 0.125 inch (0.32 cm) and was 4 feet (1.2m) long. The results of the test of Example I are reported in Table I below.

EXAMPLE 2

[0035] The process described above with respect to EXAMPLE 1 was followed except that the disc had a thickness of 0.080 inch (0.20 cm) and the holes in the disc had a diameter of 0.025 inch (0.06 cm). The results of the test of EXAMPLE 2 are reported in Table I below.

EXAMPLE 3

[0036] The process described above with respect to EXAMPLE 2 was followed except that the holes in the disc had a diameter of 0.0135 inch (0.03 cm). The results of the test of EXAMPLE 3 are reported in Table I below.

[0037] Table I. Dot Size Results for EXAMPLES 1-3

[0038] Based on the tests run as described in EXAMPLES 1-3, the inventor of the present application determined that smaller dot size (and thus greater accuracy and precision in printing) is achieved by using a disc with smaller holes. Further, the inventor was able to determine that the thicker disc provided better dot size control and less of a splatter pattern than the thinner disc. This may have been, in part, because the compressed air incident on the disc traveled through a longer "tunnel" when passing through the hole in the disc. Use of the thicker disc also reduced flexation of the disc during wiping and at the air nozzle as compared to use of the thinner disc.

[0039] Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments and implementations without departing from the underlying principles thereof. The scope of the present application should, therefore, be determined only by the following claims. Various modifications and alterations of the present invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention.