Method for producing halftone contract proofs using plotter printed proofs with a combination of hybrid and non-hybrid screens for subsequent flexographic printing

Abstract

The present invention relates to a method for producing halftone contract proofs using plotter-printed proofs with a combination of hybrid and non-hybrid screens for subsequent flexographic printing. This allows AM, FM, and XM screens to be combined in the proof without distortion, and allows the parameters defining plotter printing to be automatically incorporated into different machines capable of performing such printing. The method consists of 15 steps, in which specific hybrid screens are generated for halftone plotter proofs using correction curves and minimum values ​​different from those used for flexographic cliché printing, and the information required for automating the process is incorporated in files and databases in a standardized manner by modifying the dot gain settings on the color profile.

Description

[Technical Field]

[0001] The present invention is in the field of the graphic arts industry, and in particular in the field of flexographic printing and related processes. [Background technology]

[0002] Flexography is a direct printing system in which ink is transferred to a substrate by a high-relief flexible plate (also known as a stencil) that is attached to a roller.

[0003] Flexography is a technology that allows for high speed and low cost printing, the main advantage of which is the ability to print on a wide variety of substrates. Flexography is present in a wide variety of markets and is today the most widely used printing system in the packaging industry, where it is used on all types of materials, including plastic, cardboard, and paper.

[0004] Flexography allows for the use of a wide variety of inks, including water-based, solvent-based or UV-curable inks. In addition to its versatility in materials and inks and speed, flexography also allows for a high degree of automation and requires little machine maintenance.

[0005] The printing of ink through the printing plate onto the substrate is carried out using a printing screen (i.e., a series of dots whose density and size determine the color strength). There are three types of screens: - Traditional Amplitude Modulation or AM frame: When producing different tones, the size of the dots varies, but the distance between them always remains constant. Stochastic frequency modulation frames or FM frames: When generating different tones, the size of the dots is always kept the same, but the distance between the dots is varied. Hybrid cross-modulation frame or XM frame: a combination of an AM frame and an FM frame.

[0006] AM screens are defined by lineature, or line density per centimeter (lpc), or line density per inch (lpi), which is the measurement of the dot grid. Different sized dots that provide an equivalent percentage of ink are called dot percentages. Smaller dots provide lighter color intensity, while larger dots provide darker color intensity, resulting in a point where the dots touch each other to form a continuous area as the dot size increases. Dots are also characterized by the angle or direction at which they line up within the raster.

[0007] In FM frames, the size of the dots is defined by the diameter of the dot or the number of pixels, and the number of dots per unit area is called the dot percentage.

[0008] While AM ​​screens are typically used, FM screens are used to achieve smooth transitions in color density in gradations, to tone down specific areas, and to reproduce fine details in highlights. The dispersion and randomness of the dots in the applied areas creates a more gradual transition from the white area to the printed area.

[0009] For most FM frames, they only work at dot percentages below halftone, and where they start to work depends on the ruling and dot size of the FM frame. At higher percentages (midtones and hightones), AM frames are always used. Thus, a frame set can consist of only AM frames, or a combination of AM and FM frames, or a combination of AM, XM, and FM frames.

[0010] The dots used in a hybrid or XM screen are controlled according to the FM screening method but aligned according to the AM screen angle set at midtone. This allows for a transition between AM and FM screens without noticeable crossover or gradation defects between the two. Various solutions for the transition from AM to FM raster are available from various manufacturers.

[0011] In practice, dots on a flexographic printing press are printed larger than dots on a cliche (printing plate). This increase is known as dot gain. To correct this dot gain for the desired target curve of tone values, so-called correction curves are applied during the creation of the cliche.

[0012] Because of the high investment required to produce printing plates, printing tests are often carried out on inkjet plotters (known as "halftone contract proofs") before production. In these tests, parameters (e.g., color, ruling, trapping (overlap of adjacent inks to avoid misregistration during machine movement, plate production and mounting) and angles) are simulated to assess whether the printed result of the cliche is as desired according to the graphic design.

[0013] Since inkjet printing technology in plotters is different from flexographic printing, printing film files (1-bit tiff files used to create the cliches) in a plotter requires software to recreate this simulation so that the test print resembles the flexographic printing result using the cliches.

[0014] When starting up a new flexographic press, the usual procedure for running a test print is as follows:

[0015] 1. Design a so-called "mechanical" color test design and obtain a PDF file containing information such as the number of lines, angle, dot shape, screen type, etc. This file does not include the correction curve.

[0016] 2. Raster file generation, or rasterization in a RIP (Raster Image Processor) application. In this process, the pdf file is converted into a 1-bit tiff file with as many colors as there are in the original file.

[0017] 3. Test printing on a flexographic press. Print the finished product to check the printing characteristics of the machine (specifically the appropriate ruling, dot gain for calculation of the correction curve, and FM screen appropriate for the printing run).

[0018] 4. Generate the color design (using the four process colors cyan, magenta, yellow and black, or if an extended gamut is used, red, blue and green can be added). Rasterize this file to obtain a 1-bit / color file with the characteristics obtained from the mechanical tests (appropriate linearization, correction curves, etc.).

[0019] 5. Print a fingerprint on a flexographic printing machine using a specific cliche to obtain the printing color conditions. This proof consists of a color chart for reading the color gamut, a series of images for optimizing the color profile and checking the correct correction curves, and other elements.

[0020] 6. The color chart obtained in this test is measured by specific software, which calculates a so-called color profile, a file that numerically simulates the characteristics and printing conditions and thus indicates the range of colors used in the fingerprint.

[0021] 7. The color chart is printed on an inkjet plotter using 1-bit tiff files that are rasterized (or "ripped") in a RIP application under the same conditions as when the fingerprint cliches were created.

[0022] 8. The calculated color profile allows the measurement of the color difference (ΔE) between a fingerprint (target value) or a color chart printed on a flexographic printing press and a color chart printed on a plotter (actual value). For example, document ES2834100T3 describes a method for measuring printed colors, allowing the identification of the resulting color homogeneity by threshold value, using an automatic process that eliminates the need to rely on operator evaluation.

[0023] 9. If the result is not satisfactory, the color profile is recalculated and the color chart is reprinted in the plotter until the result is as close as possible to the result printed on the fingerprint.

[0024] 10. The color fingerprint design is printed on an inkjet plotter using a 1-bit tiff file that is rasterized (or "ripped") in a RIP application under the same conditions as when the fingerprint cliche was created.

[0025] 11. Visually compare the dot gain of the resulting printed proof with the flexographic print. If differences are found, make the necessary adjustments using the tools available in the software. This step is necessary because the color chart is only a part of the print result, and tolerances in the printing process can cause color differences across the fingerprint.

[0026] Currently, after this process, flexographic printing software packages (e.g., Kodak Colorflow, StudioRIP, or Agfa Sublima) handle the screen combinations, but existing softproofing software tools (e.g., GMG Color) do not allow a combination of AM, FM, and XM type screens in the same proof color profile and can only express the dot percentage of the screens. As a result, the flexographic results of the contract proof will be distorted on the AM screens if an FM screen is used in the profile, and on the FM screens if an AM screen is used in the profile.

[0027] Therefore, if it is important to the design to use an FM screen in one color and an AM screen in another color, or to use FM on one object and AM on another object in the same color, current procedures and applications make it impossible to do this without distortion in the plotter contract test, because the same dot percentage correction would have to be performed in the plotter print test using two different values.

[0028] However, traditionally, operators manually input printing characteristics and conditions into the RIP application and then perform tests on the plotter, a process that is time-consuming and prone to human error.

[0029] For all these reasons, there is a need in the market for a new procedure for producing plotter print proofs, which allows AM, FM and XM screens to be combined without distortion for subsequent flexographic printing, and which allows the parameters defining the printing on the plotter to be automatically incorporated into the different flexographic printing machines capable of carrying out such printing.

[0030] Description of the Invention The object of the present invention is to obtain a procedure for producing halftone contract proofs using plotter print proofs that allows for the distortion-free combination of AM, FM and XM screens for subsequent flexographic printing, and allows the parameters defining the plotter print to be automatically incorporated into the various flexographic printing machines capable of carrying out such printing.

[0031] Starting from a design requiring a combination of AM, FM and XM frames, the procedure of the present invention follows the following steps:

[0032] 1. Design a so-called mechanical color test design and obtain a PDF file containing information such as the number of lines, angle, dot shape, screen type, etc. This file does not include the correction curve.

[0033] 2. Creating a raster file, or rasterizing through a RIP (Raster Image Processor) application. In this process, the pdf file is converted into a 1-bit tiff file with as many colors as there are in the file.

[0034] 3. Test printing on a flexographic press. Print the finished product to check the printing characteristics of the machine (specifically the appropriate ruling, dot gain for calculation of the correction curve, and FM screen appropriate for the printing run).

[0035] 4. Generate the color design (using the four process colors cyan, magenta, yellow and black, or if you have an extended gamut, red, blue and green can be added). Rasterize this file to get a 1-bit / color file with the characteristics obtained from the mechanical tests (appropriate linearization, correction curves, etc.).

[0036] 5. On a flexographic printing press using specific clichés toA fingerprint is printed to obtain the printing color conditions. The proof consists of a color chart for reading the color gamut, a series of images for optimizing the color profile and checking the correct correction curves, and other elements.

[0037] 6. The color chart obtained in this test is measured by specific software, which calculates a so-called color profile, a file that numerically simulates the characteristics and printing conditions and thus indicates the range of colors used in the fingerprint.

[0038] 7. The color chart is printed on an inkjet plotter using 1-bit tiff files rasterized (or "ripped") in a RIP application under the same conditions as when the fingerprint cliche was created, except for the correction curve and minimum dot.

[0039] 8. The color difference (ΔE) between the fingerprint (target value) or color chart printed on the flexographic printing press and the color chart printed on the plotter (actual value) is measured by the calculated color profile.

[0040] 9. If the result is not satisfactory, the color profile is recalculated and the color chart is reprinted on the plotter until a suitable result is obtained (i.e., as close as possible to the result printed on the fingerprint based on the criteria of ΔE average value < 1 and ΔE individual value < 5).

[0041] 10. To check the dot gain, print a control strip on the inkjet plotter, which consists of various dot percentages and AM and FM screens, where the AM screen is equalized according to the ruling and curve of the best fingerprint result so that the transition point is the same as in flexographic printing, and also simulate the dot size taking into account the dot gain in flexographic printing.

[0042] 11. The generation of rasterized (or "ripped") 1-bit tiff files in the RIP application is performed with the same angles and linearity as when the fingerprint cliches were created, but with a linear dot gain curve, introducing a minimum dot of 5% for FM frames and 0.1% for AM frames, and selecting XM frames.

[0043] 12. In the gain section of the color profile generation software, the minimum values ​​are adjusted: 0.1% dot percentage sets the dot gain of the AM screen, and 5% dot percentage sets the dot gain of the FM screen calculated from the fingerprint.

[0044] 13. The dot gain of the printed test results is measured against the printed results. If there are differences, necessary adjustments are made using the tools available in the software.

[0045] 14. The color fingerprint design is printed on an inkjet plotter using the rasterized (or "ripped") 1-bit tiff file in a RIP application, using the fingerprint ruling and angle and remaining parameters as in step 11.

[0046] 15. Visually compare the printed proof with the printout. If differences are found, make the necessary adjustments using the tools available in the program. This step is necessary because the color chart is only a portion of the printout, and tolerances in the printing process can result in color variations across the fingerprint print.

[0047] To support this procedure, the raster tiff files are modified so that the following parameters are included in the ripped pdf file in a standardized way: minimum AM points, minimum FM points, lpi, angle, AM raster, FM raster. The RIP application takes these parameters from the pdf file and the correction curves from the production program.

[0048] In addition, tables have been created in which the percentages corresponding to the transition points used in plotter printing tests and flexographic printing are normalized according to the ruling, FM screen dot size and dot gain curve, and these tables, along with parameters defining different flexographic devices, are incorporated into a database, making it possible to automatically incorporate this information into ripped tiff files.

[0049] All of the above makes it possible to generate plotter print proofs that can be combined without distortion with the AM, FM and XM screens for subsequent flexographic printing, and to automatically incorporate the parameters defining the plotter print into the different flexographic printing machines capable of carrying out such printing.

[0050] Throughout this specification and claims, the word "comprises" and variations thereof are not intended to exclude other technical features, components, or steps. Other objects, advantages, and features of the present invention will become apparent to those skilled in the art in part from the present invention and in part from the practice of the present invention. The following examples and drawings are provided for illustrative purposes and are not intended to limit the present invention. Furthermore, the present invention covers all possible combinations of the specific and preferred embodiments described herein. [Brief explanation of the drawings]

[0051] To complement the description herein and to aid in a better understanding of the features of the present invention, a set of drawings are attached hereto as an integral part of the description, in which the following are shown by way of example and not limitation:

[0052] [Figure 1] 1 shows a flow chart of a preferred embodiment of the subject of the present invention, a method for producing a halftone contract proof using a plotter printed proof using a combination of hybrid and non-hybrid screens for subsequent flexographic printing. DETAILED DESCRIPTION OF THE INVENTION

[0053] The numbering employed in Figure 1 of this document is used to identify the steps comprising the method of using a plotter printed proof with a combination of hybrid and non-hybrid screens to create a halftone contract proof for subsequent flexographic printing that is the subject of this invention. A description of these steps is provided for a preferred embodiment of the invention.

[0054] In a preferred embodiment of the invention, starting from a design requiring a combination of AM, FM and XM frames, the inventive procedure comprises the following steps:

[0055] i. First step (1): Create a color test design called a mechanical test and obtain a PDF file containing information such as the number of lines, angle, dot shape, and screen type. This file does not include the correction curve.

[0056] ii. Second step (2): Raster file generation, or rasterization by a RIP (Raster Image Processor) application. In this process, the pdf file is converted into a 1-bit tiff file with as many colors as there are in the file.

[0057] iii. Third step (3): Test printing on a flexographic printing press. The finished product is printed to check the printing characteristics of the machine (specifically, the appropriate ruling, dot gain for calculation of the correction curve, and FM screen appropriate for the printing run).

[0058] iv. Fourth step (4): Generate the color design (using the four process colors cyan, magenta, yellow and black, or red, blue and green can be added if an extended gamut is used). This file is rasterized to obtain a 1-bit / color file with the characteristics obtained from the mechanical test (appropriate linearization, correction curves, etc.).

[0059] v. Fifth step (5): A fingerprint is printed on the flexographic printing press using a specific cliche to obtain the printing color conditions. This proof consists of a color chart for reading the color gamut, a series of images for optimizing the color profile and checking the correct correction curves, and other elements.

[0060] vi. Sixth step (6): The color chart obtained in this test is measured by specific software, which calculates a so-called color profile. A color profile is a file that numerically simulates the printing characteristics and conditions, thereby indicating the color gamut used in the fingerprint.

[0061] vii. Seventh step (7): The color chart is printed on an inkjet plotter using 1-bit tiff files rasterized (or "ripped") in a RIP application under the same conditions as when the fingerprint cliche was created, except for the correction curve and minimum dot.

[0062] viii. Eighth step (8): The color difference (ΔE) between the fingerprint (target value) or the color chart printed on the flexographic printing press and the color chart printed on the plotter (actual value) is measured by the calculated color profile.

[0063] ix. Ninth step (9): If the result is not satisfactory, the color profile is recalculated and the color chart is reprinted on the plotter until a suitable result is obtained (i.e., as close as possible to the result printed on the fingerprint based on the criteria of ΔE average value < 1 and ΔE individual value < 5).

[0064] x. Tenth step (10): To check the dot gain, print a control strip on the inkjet plotter. This strip consists of various dot percentages and AM and FM screens, where the AM screen is equalized according to the ruling and curve of the best fingerprint result so that the transition point is the same as that of flexographic printing, and also simulate the dot size taking into account the dot gain in flexographic printing.

[0065] xi. Eleventh step (11): A rasterized (or "ripped") 1-bit tiff file is generated in the RIP application with the same angle and line count as when the fingerprint cliche was created, but with a linear dot gain curve, introducing a minimum dot of 5% for FM frames and 0.1% for AM frames, and selecting XM frames.

[0066] xii. Twelfth step (12): In the gain section of the color profile generation software, the minimum value is adjusted. A dot percentage of 0.1% sets the dot gain of the AM screen, and a dot percentage of 5% sets the dot gain of the FM screen calculated from the fingerprint.

[0067] xiii. Thirteenth step (13): The dot gain of the printed test results is measured against the printed results. If any differences are found, the necessary adjustments are made using the tools available in the software.

[0068] xiv. Fourteenth step (14): The color fingerprint design is printed on an inkjet plotter using the rasterized (or "ripped") 1-bit tiff file in a RIP application, using the same fingerprint ruling and angle and all other parameters as in step 11.

[0069] xv. Fifteenth Step (15): Visually compare the printed proof with the printed result. If any discrepancies are found, make the necessary adjustments using the tools available in the program. This step is necessary because the color chart is only a portion of the print, and color variations may occur across the fingerprint print due to tolerances in the printing process.

[0070] To support this procedure, in a preferred embodiment, the raster tiff files are modified so that the following parameters are incorporated in a standardized way into the pdf file to be ripped: minimum AM points, minimum FM points, lpi, angle, AM raster, FM raster. The RIP application imports these parameters from the pdf file and the correction curves from the production program.

[0071] In addition, tables have been created in which the percentages corresponding to the transition points used in plotter printing tests and flexographic printing are normalized according to the ruling, FM screen dot size and dot gain curve, and these tables, along with parameters defining different flexographic devices, are incorporated into a database, making it possible to automatically incorporate this information into ripped tiff files.

Claims

1. 1. A method for producing halftone contract proofs using plotter printed proofs together with a combination of hybrid and non-hybrid screens for subsequent flexographic printing of designs requiring amplitude modulation screens or AM screens, frequency modulation screens or FM screens, and hybrid or XM screens, comprising: i. First step (1): creating a so-called mechanical color test design and obtaining a PDF file containing information such as the number of lines, angle, dot shape, and screen type, but not including a correction curve; ii. A second step (2): A process of generating a raster file or rasterizing by a RIP (Raster Image Processor) application, in which the pdf file is converted into a 1-bit tiff file with the same number of colors as there are in the file; iii. Third step (3): Printing a test on a flexographic printing press, printing a finished product to check the printing characteristics of the machine (specifically, the appropriate ruling, dot gain for calculation of the correction curve, and FM screen suitable for the printing run); iv. Fourth step (4): Generation of color design (i.e., using four process colors: cyan, magenta, yellow, and black, or if it is an extended gamut, red, blue, and green can be added) by rasterizing the file to obtain a 1-bit / color file with characteristics obtained from mechanical testing (appropriate linearity, correction curves, etc.); v. A fifth step (5): printing a fingerprint on the flexographic printing machine using a specific cliche to obtain printing color conditions, the test consisting of a color chart for reading the color gamut, a series of images for optimizing the color profile and checking the correctness of the correction curves, and other elements; vi. A sixth step (6): the color chart obtained in this test is measured by specific software, which calculates a so-called color profile, which is a file that numerically simulates the printing characteristics and printing conditions and thus indicates the range of colors used in the fingerprint; vii. Seventh step (7): A color chart is printed on an inkjet plotter using a 1-bit tiff file rasterized (or "ripped") in the RIP application under the same conditions as when the fingerprint cliche was created, except for the correction curve and minimum point; viii. Eighth step (8): The color difference (ΔE) between the fingerprint (target value) or the color chart printed on the flexographic printing machine and the color chart (actual value) printed on the plotter is measured by the calculated color profile; ix. ninth step (9): if the result is not satisfactory, the color profile is recalculated and the color chart is reprinted on the plotter until a suitable result is obtained (i.e., as close as possible to the result printed on the fingerprint based on the criteria of ΔE average value < 1 and ΔE individual value < 5); x. Tenth step (10): Printing a control strip on the inkjet plotter to check the dot gain, the strip consisting of various dot percentages and AM and FM screens, the AM screen being equalized according to the ruling and curve of the best fingerprint result so that the transition point is the same as the flexographic print, and simulating the dot size taking into account the dot gain in the flexographic print; xi. An eleventh step (11): A rasterized (or "ripped") 1-bit tiff file is generated in the RIP application with the same angle and ruling as when the fingerprint cliche was created, but with a linear dot gain curve, introducing a minimum dot of 5% for FM frames and 0.1% for AM frames, and selecting XM frames; xii. Twelfth step (12): In the gain section of the color profile generation software, the minimum value is adjusted, and at a dot percentage of 0.1%, the dot gain of the AM screen is set, and at a dot percentage of 5%, the dot gain of the FM screen calculated from the fingerprint is set; xiii. A thirteenth step (13): The dot gain of the printed test results is measured against the printed results, and if any differences are found, necessary adjustments are made using tools available in the software; xiv. Fourteenth step (14): The color fingerprint design is printed on the inkjet plotter using the rasterized (or "ripped") 1-bit tiff file in the RIP application, using the same fingerprint ruling and angle and all other parameters as in step 11; xv. A fifteenth step (15): visually comparing the printed proof with the printout and, if there are any discrepancies, making the necessary adjustments using the tools available in the program; this step is necessary because the color chart is only a part of the printout and color variations may occur throughout the fingerprint print due to printing process tolerances; A method comprising:

2. 10. A method for producing a halftone contract proof using a plotter printed proof with a combination of hybrid and non-hybrid screens for subsequent flexographic printing as described in claim 1, wherein the raster tiff file is modified to incorporate the following parameters in a standardized manner into the pdf file to be ripped: minimum AM dot, minimum FM dot, lpi, angle, AM screen, FM screen, and correction curve, and the RIP application imports these parameters from the pdf file and the correction curve from a production program.

3. 3. A method for producing a halftone contract proof using a plotter printed proof together with a combination of hybrid and non-hybrid screens for subsequent flexographic printing as described in claim 2, wherein a table is created in which percentages corresponding to transition points in the plotter printed proof and the flexographic printing are normalized according to the ruling and dot size of the FM screen used and the correction curve, and these tables and parameters defining different flexographic equipment are incorporated into a database, thereby allowing this information to be automatically incorporated into the tiff file via the RIP.

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