The use of Light-emitting diode (LED) technology has become popular in many technical applications, such as the field of curing photopolymer printing plates, in which LEDs displace fluorescent tubes. LEDs are a desirable radiation source for curing photopolymer printing plates because of their excellent short-term and good long-term stability.
Various systems and processes for curing printing plates by exposure to a functional energy source are known, including methods for providing curing radiation using LEDs, such as is described in U.S. Pat. No. 9,315,009, titled EXPOSING PRINTING PLATES USING LIGHT EMITTING DIODES and U.S. Pat. No. 8,578,854, titled CURING OF PHOTO-CURABLE PRINTING PLATES USING A LIGHT TUNNEL OF
MIRRORED WALLS AND HAVING A POLYGONAL CROSS-SECTION LIKE A KALEIDOSCOPE, both of which are owned by the Applicant of this invention and are incorporated herein by reference in their entireties.
LEDs are typically characterized by reference to their center emission wavelength. U.S. Pat. No. 9315009 describes the use of arrays in which LEDs of different center wavelengths, all in the ultraviolet (UV) spectrum, are used for curing sheet photopolymers. Using an array of UV LEDs of different wavelengths in curing a printing plate may produce flexographic printing dots having desirable geometric characteristics. Using an array of UV LEDs of different wavelengths may have advantages not only for exposure of the front, image-containing side of the plate that receives ink for transferring a printed image to a substrate, but also for exposure of the non-printing, back side of the plate. Accordingly, there remains a need in the art to provide an array of discrete LEDs having multiple center emission wavelengths that provides for stable, reproducible exposure of photopolymer plates.
Exemplary embodiments of the invention include an apparatus for irradiating a printing plate having a photosensitive polymer. The apparatus includes a plurality of light-emitting diodes arranged in an array of columns and rows, such as in a chip on board (COB) configuration comprising each LED in the form of an integrated (IC) circuit chip mounted on a printed circuit board (PCB), or a surface mount design (SMD) LED, in which LEDs in discrete housings are surface mounted on a substrate. Each LED has an emission pattern, and the plurality of LEDs includes one or more members of at least a first species of LED having a first center emission wavelength, one or more members of a second species of LED having at least a second center emission wavelength and, in some embodiments, one or more members of a third species of LED having at least a third center emission wavelength. The second center emission wavelength is different than the first center emission wavelength, and the third center emission wavelength different than the first and second center emission wavelengths. The array is configured with the respective species of LEDs disposed adjacent one another in a repeating sequence of the first species, the second species and the third species (in embodiments having at least three species). The apparatus also includes at least one controller connected to the LED array. A controller is configured to independently control each species and to activate the LED array to cause all species of LEDs to emit radiation toward the printing plate simultaneously with emissions patterns of adjacent members of the different species of LED overlapping with one another on the plate.
In one embodiment, the apparatus is positioned to expose a back, non-printing side of the printing plate.
In another embodiment, the apparatus is positioned to expose a front, printing side of the printing plate.
In a further embodiment, a system including a first apparatus as described herein is positioned to expose a back, non-printing side of the printing plate and a second apparatus as described herein, positioned to expose a front, printing side of the printing plate.
In some embodiments, the array may comprise a unit configured to irradiate less than a full first dimension and less than a full second dimension of the plate. A plurality of units may be arranged to form a linear source configured to irradiate the full first dimension of the plate simultaneously but less than the full second dimension of the plate simultaneously, with the exposure system further comprising means for providing relative movement between the plate and the linear source along the second direction. In other embodiments, a plurality of units may be arranged to form a source configured to irradiate the full first dimension of the plate and the full second dimension of the plate simultaneously. The units may be configurable to permit one unit to emit a different emission characteristic than another unit simultaneously, to permit the same unit to emit different emission characteristics during different portions of an exposure duration, or a combination thereof. The different radiation characteristic may include, for example, a different collective emission intensity or a different blend of relative emission intensities from the respective species. Methods for exposing a printing plate using such exposure systems may include controlling at least one unit to provide a different radiation characteristic than at least one other unit simultaneously, or to provide a first radiation characteristic in a first portion of an exposure duration, such as a first portion of relative motion or in a first step of a multi-step exposure, and a second radiation characteristic in a second portion of the exposure duration.
Referring now to the figures,
In some embodiments, exposure unit 105 may cover less than the full width of the plate on the drum and may raster back and forth in the longitudinal direction. In other embodiments, exposure unit 105 is configured to cover the full width of the plate mounting area of the drum, and remains stationary. Although shown with the plate mounted on a drum in
In one embodiment, the light exposure unit 105 includes a plurality of LEDs arranged in an LED array, such as in one of the exemplary arrays 130A-130E depicted in
In the embodiment depicted in
The output intensity of an LED may be controlled by changing the drive current supplied to the LEDs. In one embodiment, the intensities of the different species of wavelengths of the UV LED light assemblies are varied to produce relief printing dots having the desired geometric characteristics as described in U.S. Pat. No. 8,227,769, owned by the Applicant of the present invention and incorporated herein by reference. Beyond the advantages described in U.S. Pat. No. 8,227,769 for imaging the front (printing) side of a plate with a mix of wavelengths and intensities, there are also certain advantages to being able to provide a mix of wavelengths with variable intensity for exposing the back (non-printing) side of a plate. Various factors during production of the LED influence the center wavelength, and therefore the center wavelength of LEDs may vary from one batch to another. Similarly, attributes of printing plates may also vary from batch to batch. Thus, providing a plurality of LED wavelengths with variable intensity may permit optimized control of the LED wavelength and intensity to compensate for variation in particular batches of arrays or plates so that, for example, a shop running multiple lines can optimize efficiency and provide repeatability from line to line, and shops with single or multiple lines can achieve batch-to-batch repeatability for different batches of plates. Applicants have found that the ability to optimize and tune for efficiency and repeatability may have significant benefits both with respect to front (printing) side exposure as well as back (non-printing) side (floor) exposure.
For example, the ability to control intensity of one species of LED different from the corresponding intensity of another species of LED, enables a user to tune relative intensities of the respective species of LEDs to compensate for a detected difference between one batch of plates versus another batch of plates. Thus, the relative intensities may be tuned so that operation at a same set of operating conditions but for the differences in relative intensity produce results within a desired degree of deviation for different batches of plates, despite detected differences in sensitivity to actinic radiation in the different batches of plates, which sensitivity may be wavelength specific, may be caused by any aspect of the plate construction, and may impart commercially significant sensitivity with respect to a front side exposure, a back side exposure, or both. The ability to tune relative intensities of the respective species of LEDs in a plurality of exposure systems may allow users to compensate for detected differences between the respective exposure systems, such that the exposure systems as tuned can produce results within a desired degree of deviation at identical operating conditions except for the compensating differences in the relative intensities.
As illustrated in
In a the arrays 130C and 130D, shown respectively in
The exemplary array depicted in
The array of LEDs as described herein may comprise a plurality of subarrays or units, such as 7×4 subarray 145 depicted in
Wiring connections among the LEDs of the same species may be realized with a metal core PCB or insulated metal substrate PCB, such as BERGQUIST® THERMAL CLAD Insulated Metal Substrates (TCLAD®) made by Henkel, comprising a multilayer construction.
The arrangements depicted in
For embodiments having n different wavelengths, the number of LEDs in the direction of relative movement between the light source 105 and the polymer plate 103 (i.e. rows of LEDs) is preferably a multiple of n. Likewise, the number of LEDs across the width of the array in the configurations depicted in
Referring back to
In some embodiments, controller 107 may also encompass the drivers 570 that independently control each LED species 500 as depicted in
In operation, controller 107 activates the LED array, causes all LED species to emit radiation towards the plate 103 simultaneously. This simultaneous emission results in emission patterns of adjacent members of, e.g., the first, second and the third species of LEDs 132, 134 and 136 respectively to overlap with one another on the plate 103, as illustrated in
In general, in a preferred arrangement, the plurality of LEDs are relatively evenly distributed so as to be evenly spaced from neighboring LEDs, with the total number of LEDs dictated by (a) the required power per surface unit to create the desired degree of exposure for the polymer, (b) the maximum power emitted by each LED, (c) the distance the of LEDs to the surface, and (d) the geometry of the radiation cone, in order to provide an acceptably homogeneous illumination of the surface. An arrangement that produces a homogenous illumination by each species is preferred. The arrays of LED sources may be mounted in a location at or near one end of a light tunnel or kaleidoscope, such as is described in U.S. Pat. No. 8,578,854. The use of such a light tunnel or kaleidoscope is known to create a generally acceptable level of homogeneity for the light sources.
While not limited to any particular size of the array or the LEDs, the multi-species LED arrangement may be implemented using LEDs in an arrangement similar to that currently used for single wavelength LEDs, which implementations are also known to provide a suitable degree of homogeneity of illumination. For example, in one exemplary system, an array of approximately 600 SMD LEDs are deployed in an area measuring approximately 1300×78 mm. Each SMD LED source may itself comprise an array of single-wavelength LEDs. The array in the 1300 mm dimension covers a full dimension of a plate to be exposed in the relevant dimension, and the 78 mm dimension is moved relative to a fixed plate. In that arrangement, each LED may be spaced approximately 13 mm apart, resulting in an array of 100×6 (600) LEDs. Such an array with the foregoing dimensions may be suitable for a 2 species system (in which 300 of each species are provided) without adjustment. Preferably, each number of rows and columns is evenly divisible by the number of LED species to produce an integer. Accordingly, for example, a three species system with approximately the same footprint as set forth above may have an array of 99×6 (or 102×6) SMD LEDs, in which case the overall dimensions or the relative spacing of the illumination area may be adjusted accordingly. Likewise, suitable arrays for a four species system may be 100×8, for a five species system may be 100×5, and so on. The invention is not limited, however, to any particular sizes or dimensions of the array, or number or size of LEDs. Although, preferably, the larger of the two numbers in the array corresponds to the number of columns of LEDs and the smaller of the two numbers corresponds to rows, the invention is not so limited. However, in embodiments in which each row is a different species, an arrangement with a smaller number of rows may have an advantage of requiring less complex wiring to provide independent control of each species. Although described above in connection with an SMD LED embodiment, it should be understood that each array may also be composed of COB LED sources, in which case each discrete LED source as described herein as being arranged in the array may comprise a COB LED, which COB LED itself comprises an array of tiny LEDs that are all the same wavelength.
In embodiments such as the arrays depicted in
The plate 103 has a length and a width. In one embodiment, the LED array has a width that irradiates full width of the plate simultaneously, but not the full length of the plate in which case relative motion between the array and the plate in the lengthwise direction provides the desired full exposure over time. In other embodiments, the LED array irradiates less than a full width and less than a full length of the plate 103 simultaneously, and additional relative movement between the array and the plate in the longitudinal direction is necessary to provide full exposure over time. In still other embodiments, the LED array irradiates full width and length of the plate 103 simultaneously. In some embodiments, it may be desirable to provide the full calculated exposure in fractional amounts over multiple passes or irradiation steps to minimize overheating of the LEDs or the printing plate or for finer control of the exposure process.
As depicted in
The back side of a plate may also be exposed in a drum configuration, in accordance with the arrangement depicted in
In the embodiment 700 depicted in
In the embodiment depicted in
The overall mechanism for creating the exposure may comprise a table having an outer frame 1110 that holds a transparent (e.g. glass) inner portion 1112. The upper 1120 and lower 1122 linear radiation sources (e.g. arrays of LEDs as described herein) are mounted on a gantry system or carriage 1130. The radiation sources are connected to a power source, such as an electrical power cord having sufficient slack to extend the full range of motion of the carriage. Tracks (not shown) disposed on the outer frame portion provide a defined path for the gantry system or carriage to traverse. The carriage may be moved on the tracks by any drive mechanism known in the art (also coupled to the power supply and the controller), including a chain drive, a spindle drive, gear drive, or the like. The drive mechanism for the carriage may comprise one or more components mounted within the carriage, one or more components fixed to the table, or a combination thereof. A position sensor (not shown) is preferably coupled to the carriage to provide feedback to the controller regarding the precise location of the carriage at any given time. The control signal output from the controller for operating the radiation sources and for controlling motion of the carriage may be supplied via a wired or wireless connection. The controller may be mounted in a fixed location, such as connected to the table with a control signal cable attached to the sources similar to the power cable, or may be mounted in or on the carriage. The control system and drive mechanism cooperate to cause back/forth relative motion in a transverse direction between the light from the radiation sources and the plate. If should be understood that other embodiments may be devised in which the drive mechanism is configured to move the portion of the table containing the plate past stationary upper and lower linear radiation sources, as well as embodiments in which the radiation sources cover less than the full width of the plate and are movable in both the transverse and longitudinal direction to provide total plate coverage (or the plate is movable in both directions, or the plate is movable in one of the two directions and the sources are movable in the other direction to provides the full range of motion required to cover the entire plate). In one work flow configuration, the table for conducting the exposure step (i.e. exposure table) as described above may be positioned to automatically receive an imaged plate from an imager. For example, an imager may be positioned so that the imaged plate expelled therefrom lands in a first location, and a robotic handling device may be configured to automatically pick up and move the imaged plate from the first location to a processing location on the exposure table, where the exposure process as described herein is then performed using transverse linear sources attached to a carriage that traverses the plate longitudinally.
In the exemplary embodiment 800 depicted in
One exemplary control pattern may activate the radiation subsources in a sequence that causes relative motion between the radiation field and the plate, such as a movement that essentially mimics the same light patterns that would be provided by main and back linear sources attached to a carriage, but with the advantage of having no moving parts. The illumination pattern may be configured to illuminate multiple portions of the front and back simultaneously (e.g. such as in a pattern that mimics multiple carriages—one starting at one end of the plate, and one starting in the middle). The illumination pattern in such a configuration is not constrained to patterns that mimic one or more carriages, however, and may be implemented in any pattern that provides the desired time delay, overall exposure, and lack of simultaneous exposure from front and back for any particular cross sectional coordinate of the plate. The pattern may also comprise illuminating the entire back at once and then the entire front, either in a single exposure for each side, or in fractional exposures of the full required exposure for each side, with the desired time delay applied between each front and back exposure. Furthermore, although shown in a flat configuration, it should be understood that systems in which both the plate and the sources are stationary may also be arranged in a cylindrical configuration.
It should be noted that the arrays as described herein may be configured for use in connection with exposure of printing plates in connection with any method or apparatus known in the art, and methods and apparatus of use are not limited to those described herein as examples. Additionally, the methods and apparatus as described herein may be combined in a workflow. For example, the front side of a plate may be exposed using a drum system such as is depicted schematically in
Note that when a method is described that includes several steps, no ordering of such steps is implied, unless specifically stated.
It will also be understood that embodiments of the present invention are not limited to any particular implementation and that the invention may be implemented using any appropriate techniques for implementing the functionality described herein. Furthermore, embodiments are not limited to any particular operating system.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill skilled in the art from this disclosure, in one or more embodiments.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
As used herein, unless otherwise specified, the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being !imitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting of only elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.
Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being !imitative to direct connections only. The terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein device A is directly connected to device B. It means that there exists a path between the device A and the device B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.
Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.
This application claims priority from U.S. Provisional Application Ser. No. 62/839,171, filed Apr. 26, 2020, titled APPARATUS AND METHOD FOR EXPOSING PRINTING PLATES USING LIGHT EMITTING DIODES, incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/061556 | 4/24/2020 | WO | 00 |
Number | Date | Country | |
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62839171 | Apr 2019 | US |