Seminar on

Effect of Anilox Profiles on Flexo Print

 Quality 

By

Mr. Shyam Santosh Laturiya

Under the Guidance of

Prof. Dr. Akshay V. Joshi

 

Pune Vidyarthi Griha’s College of Engineering and Technology & G. K. Pate (Wani) Institute of Management, Pune, India 

Academic Year 2020-21

Flexography printing is a roll-feed web printing process. Anilox roller the heart of the flexography printing. An engraved metal or ceramic roller utilized in flexographic printing presses to transfer ink from the fountain roller to the printing plate. A flexographic inking system is also known as an anilox system. The purpose of the anilox roller is to pick up ink from the fountain roller and deliver a predetermined, metered, uniform amount of ink to the rubber printing plate. The anilox roller is additionally called a metering roller, a knurled roller, and an engraved roller. It is used for the transfer of a precisely specified quantity of ink onto the printing plate. Therefore, the quality of the anilox roll has a tremendous influence on printing quality. It is a special transfer roller for flexographic printing presses. The surface is made up of numerous recesses of the same size, shape, and depth. These recesses are called cells or ink holes. The cell can store ink, through the irregular shape, size, and depth of the anilox roller, the quantity of ink will be controlled to attain the specified thickness of the ink layer. The anilox roller plays a vital role in flexographic printing [1].

    Anilox Line Per Inch (LPI) Line count or screen count refers to the amount of cells per inch/centimeter as measured along the engraving angle because that's where the cells line up in closest proximity to each other. L/cm stands for lines per centimeter L/in stands for lines per inch, this refers to the number of cells per inch L/cm. Line count is the number of cells per linear inch, at the angle of engraving, typically 30°, 45° or 60° about the axis of the anilox roll. Once engraved, anilox cell count does not change. Lower anilox line counts accommodate higher volumes for solid coverage and coatings. A Line Screen is that the measure of what percentage halftone lines are printed during a linear inch [2]

Fig 1: Anilox Line Per Inch

Anilox Cell Structure are typically one among five types- Trihelices, Pyramid, Quadrangular, Hexagonal or Hexagonal Channel Screen. A Trihelices screen could be a line engraved at a 45-degree angle. These are primarily utilized in coating applications of viscous fluids. A Pyramid cell essentially an inverted pyramid. This engraving is incredibly commonly utilized in the industry. They are typically utilized in metered roll systems that don't require a doctor blade. The ink transferred may be a vital function within the printing. A quad engraving is very similar to a pyramid engraving, it’s just cut short, these have more versatile and more positive release characteristics, this engraving type most commonly appears with a doctor blade system. Finally, we have the hexagonal cell. Hexagonal cells have superb release qualities and may be utilized in both chrome and ceramic engravings. Each cell is linked together be a shallow channel. Due to the spectrum line, it will be utilized with a range of inks, adhesives, etc. Hexagonal cells typically hold more ink than a quad engraved pattern and generate a more even and predictable flow throughout the printing. The 60 degrees hexagonal pattern allows for more cells to be compacted in a locality and provides the most efficient distribution of volume. There is less wasted space if compared to diamond shape patterns. This is the explanation, the most uniform distribution of ink of the 60-degree hexagonal engraving became the norm in flexo printing [3].

Fig 2: Anilox Cell Structure

Image copywrite © Label & Narrow Web. All Rights Reserved.

Cell volume means the capacity of the engraved surface per square inch, expressed in billions of cubic microns (BCM). Higher volume translates to higher solid ink density, more colour, or a heavier coating thickness. Lower volumes apply thinner ink films directly related to higher print quality and process efficiency. Anilox cell volume changes over time, because of wear, plugging and cleaning procedures. Dirty or plugged cells are temporary and may be corrected to revive cell volume and colour. Wear is irreversible and permanent, resulting in weaker or less colour due to lower volume [4].

Fig 3: Anilox Cell Volume

Image copywrite © KompoZite.COM. All Rights Reserved.

Anilox screen angle the 60° hex pattern is usually recommended for many flexo printing applications for the subsequent reasons: Cells will be nested more tightly together, permitting approximately 15% more cells in each area. Post areas are eliminated because of the position of the cells during laser engraving. Cells will be shallower while still releasing a similar amount of ink because more cells fit into a sq in area. Channeling is avoided (as compared to the 30°) because the straight side of the cell wall isn't positioned horizontally. The 60° hex pattern is most easily reproducible from a producing standpoint. 45° and 30° patterns could also be preferable in non-printing flexo applications (such as coatings, laminations, and specialty printing), but ordinarily don't seem to be recommended for general flexo printing applications [5].

Fig 4: Anilox Screen Angle

The ink transfer ratio to the upper plate for different contact angle (30°,50°,70°,90°), while the contact angle of the trapezoidal groove is 70° and the contact angle of the upper plate is increases, the ink transfer rate decreases. The wetted area of the trapezoidal groove is the same but, with the contact angle increasing, the upper plate wetted area decreases, so the rate of ink transfer is reduced. Ink transfer ratio to the trapezoidal groove for different contact angle (30°,50°,70°,90°), and the contact angle of the upper plate is 70°, it will see that the trapezoidal groove contact angle increases, the ink transfer rate increases. The increasing contact angle of the trapezoidal groove, the adhesion of upper plate is reduced and the other parts unchanged, so that the transfer rate is increases. The contact angle of the trapezoidal groove remains constant 70°, and with the increase of the contact angle of the upper plate, the adhesion of upper plate reduces, so that the transfer rate decreases. Changing in the aspect ratio of trapezoidal groove, less ink is transferred with the increasing of aspect ratio, that is to say trapezoidal groove with large open width transferred more ink. If ink is transferred out from anilox, it is not only by adhesive forced from the upper plate and trapezoidal groove, but also by capillary force which block printing ink transferred. Because of the anilox roller mesh point size is small, the capillary force is inversely proportional to the opening width. The larger the opening width, the smaller the capillary force, the greater the ink transfer rate [6].

The flexography inking system of high-line screen engraving technologies is anilox rollers, this delivers the accuracy and consistent amount of ink during the process of flexography, making it possible to produce the high-resolution print quality. The cell clogging of anilox roller five level of cell clogging from which the first level of cell clogging and the bottom of all cells is almost uniform in shape and depth and there is no sign of clogging, in second level bottom of less than half of cells is narrow and the depths of less than half of cells is reduces (slightly red, widening yellow outline) and average ink transfer reduces, in the third level shape of the bottom of about half of cells is change. Half of cell depths decrease (red is almost invisible, yellow predominates), and the average ink transfer reduces, in the fourth level more than half of cell bottoms is narrow and no longer visible, more than half of the cell depths decrease (red is no longer visible), and average ink transfer reduces, and in the fifth level bottom of almost all cells is narrowed and no longer visible, depths of almost all cells reduces (yellow and green predominate) and average ink transfer reduces. The higher the level of clogging, the higher the minimum line screen of the anilox rollers. This means the rollers of the lowest liners are more difficult to clog. The engraving line screen increases, the average cell depth to opening ratio also increases. The line screen distribution of anilox rollers engraved at angle of only 60° by the level of clogging as the level of pollution increases, the average line screen also increases [7].

The specification of the cell engravings of the anilox roll provide the largest influence on the amount of ink deposited on to the substrate, and hence on the optical density and halftone reproduction. The density of the halftone dot structures shows that there is an interaction between the line ruling on the plate and the cell volume of the anilox roll. The rate of density increase for increasing anilox volume is greater at higher line rulings than for lower line rulings. This is attributed to a greater perimeter of the dots at the higher ruling, per unit area on the plate. The anilox cell volume is the dominant factor on the print quality, but other aspects such as the cell shape also have an effect. Cells of similar volume, but of different line rulings, produces different results on the printed image in terms of the volume of ink transfer. The roughness of a printed ink film is dependent on the volume of ink carried by the anilox roll. The cell pitch of the anilox roll does not affect the printed ink roughness. The cell volume changed, the anilox engraving with the highest cell volume produces the highest optical density. The anilox specifications have the large overall effect on the optical density [8].

Vibration and sound signals were analysed for patterns relating to cell wear on anilox rolls used in flexo printing. The major defect of the anilox roll is the cell wear. The surface engraving cell of an anilox roller determines the ink film thickness. The depth and angle (volume) of each cell determine the amount of ink transfer, cell wear makes the walls lower, and the amount of ink carried by the worn spots will increase reducing the uniformity and quality of print. Using new, lightly used, and heavily used rollers, the cells show more rough and rounded surfaces (walls), some pitting, chipping, and fracture of cell surfaces. If the wear of the roll cells is increased, the spikes number and amplitudes decreases, and the location shift along the frequency axis occurs. Cell wear symptoms is clearly revealed to the short time frequency transform (STFT). The vibration signals do not lead to any consistent results relativity to cell wear. The power spectral density (PSD) patterns reveal to the number of high-energy spikes and their magnitudes decrease as cell wear increases. The spikes spread out with cell wear. Great potential for designing an on-line anilox roll testing and evaluation system that will optimize its useful life and enhance the print quality [9].

There are so many process parameters involved in flexography that effect on the print quality. The printing quality is usually defined by the line width, thickness and ink transferred. The print quality is determined by anilox cell geometry and volume, printing plate properties, nip pressure, printing angle, printing speed, doctor blade, contact angle, ink type and viscosity. Dot dipping is a printing defect where the dot enters the anilox cell, leading to bad printing results, anilox volume plays a significant role in ink release, an increases in anilox volume shows result in an overall increases in cross-sectional area, reducing sheet resistance and improving the conductivity of the printing network. Increases in anilox and printing forces leads to more ink transfer onto the anilox roller, that produces a thicker printed line width. Increasing the anilox speed cause a decrease in average printed line width, this is due to the amount of ink picked up by the anilox roller, at a lower speed, more ink is picked up by the anilox, as there is more time for the ink to enter the anilox cells, with more ink in anilox cells, the ink transfer over to the flexographic printing plate and substrate is more is result in higher line width due to more ink spreading. Increasing the anilox also increases the average printed line width as the anilox force is increases, the nip pressure between the printing plate and anilox roller is increases. A higher nip pressure increases the ink transfer onto the printing plate, as more ink is push out of the anilox cells, so that it is resulting in a higher line width due to more ink spreading. This increases in line width is due to the increase in ink transfer, a higher anilox volume is made possible by having larger anilox cells. Anilox volume and printing force have a dominant effect on the printed line width; printing speed and relief depth have a mild effect on printed line width; anilox speed and anilox force have an almost negligible influence on the printed line width, the trend with anilox force is different. Anilox volume and printing force are the primary factors, while printing speed and relief depth are secondary factors affecting the printed line width and the print quality [10].

References

1. Anilox Roller. Retrieved from http://printwiki.org/Anilox_Roller#:~:text=A%20flexographic%20inking%20system%20is,to%20the%20rubber%20printing%20plate
2. MAIN PARAMETERS OF LASER ENGRAVED CERAMIC ANILOX ROLLERS. Retrieved from https://cheshireanilox.co.uk/wp-content/uploads/2017/09/anilox-parameters.pdf
3. Anilox Roll Specifications: Line Count or Volume? Retrieved from https://www.labelandnarrowweb.com/issues/2008-07/view_features/anilox-roll-specifications/
4. Effect of Anilox Cell Geometries to Print Quality Flexographic Printing Technology. Retrieved from https://www.materials-academy.co.uk/dwnlds/seminar/posters/Foulston.pdf
5.  ANILOX ROLL. Retrieved from https://fdocuments.in/document/anilox-roll.html
6.  Chen J., Tang Z., Wang S., and Miao B. (2015). Simulation of Ink Transfer Characteristics for the anilox. Applied Mechanics and Materials Vols 713-715 pp 2859-2863. Retrieved from https://www.scientific.net/AMM.713-715.2859
7.  Eugenijus J. (2020). Investigation of anilox roller cell clogging. Journal of Graphic Engineering and Design, Volume 11 (2). Retrieved from https://www.researchgate.net/publication/347741073_Investigation_of_anilox_roller_cell_clogging.
8. Bould D., Hamblyn S., Gethin D., and Claypole T. (2010). Effect of impression pressure and anilox specification on solid and halftone density. Journal of Engineering Manufacture. Retrieved from https://www.semanticscholar.org/paper/Effect-of-impression-pressure-and-anilox-on-solid-Bould-Hamblyn/2fe464fc596106ef233675256f4f493555b89c2f
9. Uwe T., and Issam A. (2007). Using sound and vibration signals to monitor cell wear on anilox rolls. Nondestructive Testing and Evaluation. Retrieved from https://www.tandfonline.com/doi/abs/10.1080/10589750412331290596
10. Zhong Z., Ee J., Chen S., and Shan X. (2020.). Parametric investigation of flexographic printing processes for R2R printed electronics. Materials and manufacturing processes. Retrieved from https://www.tandfonline.com/doi/abs/10.1080/10426914.2020.1732411?journalCode=lmmp20.

Seminar on

Parameters Affecting Gray Balance in G7 Caibration

By

Mr. Aditya Deepak Hugay

 

Under the Guidance of

Prof. Dr. Akshay V. Joshi

 

Pune Vidyarthi Griha’s College of Engineering and Technology & G. K. Pate (Wani) Institute of Management, Pune, India 

Academic Year 2020-21

Digital printing is a printing process in which digital-based images directly printed onto a variety of substrates. Unlike offset printing there is no need for plate in the case of digital printing. Digital files such as PDFs files can be sent directly to the digital printing press to print on paper and other substrates. One of the problems faced by the industry is that of correct color reproduction on different machines and on various printing processes. To solve this problem Idealliance® developed a specification called the G7 which defined a universal appearance of B&W imagery or a printed grey scale and also how to calibrate and control any printing and proofing system to achieve that appearance. G7 defines a* and b* target values for each step of the combined three process colors grey scale. G7 stands for greyscale plus seven colors (RGBCMYK). This method is used in many printing processes such as gravure, offset and flexo. It’s been recently introduced into digital printing (Fig. 1).

Fig.1 G7 Calibration

     Image copywrite © Idealliance. All Rights Reserved.

G7 defined grey balance as a standardized scale of CMY percentages that should appear neutral to the eye and defined the a* and b* for each scale step. G7grey balance is “paper-relative” meaning that images printed on different-colored substrates appear slightly different when viewed side byside [1]. Unlike offset printing there is no need for plate in the case of digital printing. Digital printing is certainly more expensive per page than other conventional however digital printing does not need manufacturing of plates, so the overall cost comes down(Fig.2) [2].

            Fig.2 Ink-jet printer

               Image copywrite © Encyclopedia Britannica. All Rights Reserved.

The G7 method uses colorimetric concepts for press calibration and control. Instead of controlling solid ink density (SID) and tone value increase (TVI), this method controls the press by colorimetric values of gray to achieve a better visual match. G7 can be applied to any color reproduction irrespective of printing methods. With the results from the press calibration, the G7 method demonstrates its ability in calibrating a printing press other than offset printing. The improvement in gray balance proved that colorimetric control can achieve a better visual match. The G7 method was developed from offset printing using standard inks and paper defined in ISO 12647-2 (1997). Compared to commercial offset printing, the difference in ink colorants resulted in different densities at different tone values and different densities of solid process colors when printed with liquid inks. Using the curves created by offset data, the calibration may not be as definite as for offset printing. There is less control in digital press in adjusting solid ink density during printing, which means control the press by colorimetric value alone may not be sufficient. It affects the accuracy of using gray balance control in controlling press calibration and proofing. The concept of gray balance control is valid for different ink and substrates combination [3].

            G7 technology is a new calibration method developed to dominate the printing qualities, which uses colorimetric values to control the zone of neutral gray balance areas on printing sheets. It matches visual effects between originals and printings in process of the ink transfer, with the new three parameters introduced to, G7 technology can achieve the ideal same appearances with multiple devices to each other at least in neutral gray tones. But in lack of an appropriate tolerance among manufacturers, there still are some confines in subsequent productions. It is known that, G7 technology parameters are identical with the traditional ways of control from the research of G7 technology standard parameters. They are both have the concentrate on light, middle and shadow tones, G7 technology control the printing quality by commanding three parameters of HC, HR, SC as to make the tone control more accurate and easier. G7 technology relies more on the integrated effects of CMY ink and the neutral gray balance. G7 technology can predigest the complexity of the process largely, and improves the operations compared with the domination of four-color dot increase curves. How to achieve the neutral gray balance stability is the key, and is the most prominent feature of G7 technology. G7 technology is still relatively of new, there is no generally consensus of the tolerance. The results show G7 technology has a positive effect on controlling and can apply to the realistic production for better [4].

        Along with more and more attention focus on the digital printing, and ink-jet technology’s own superiority, ink-jet printing industry has gradually developed into a single flower. Therefore, it has important significance to realize the color accurate representation and get high quality print of ink-jet printing. However, the most effective way to achieve this goal is to control the gray balance of the printing process. G7 is a new method of control gray balance. It is based on GRACoL 7 standard to formulate a set of new calibration method, and it is established on the image of CTP (Computer to Plate) digital publishing and spectrophotometer detection. Generally, speak, controlling the gray balance in traditional printing is first to monitor the density of monochromatic, then based on the determined density of each monochromatic to chase the gray balance of CMY overprinting. However, the introduction of G7 has broken the traditional control method. G7 control the gray balance first, then, adjusting the density of monochromatic based on getting good representation of gray balance.G7 also introduced the parameters of HC (Highlight Contrast), HR (Highlight Range), SC (Shade Contrast) and the curve of NPDC to replace traditional TVI (Tone Value Increase), K value, etc. This method can greatly strengthen the accuracy of the color transfer processing of the digital ink jet printing. Therefore, we can say G7 puts the detection of gray balance onto a significant position [5].

  Gray balance is the critical control parameter in color reproduction which balance that correlates material characteristics and process control parameters. The paper chromaticity is measured using CIE L* a* b* three-dimensional space coordinate system to determine the characteristics of paper in ISO12647 standard. A slight deviation in chromaticity can have an impact on gray balance in process color printing. The experiment conducted for three paper grades viz. #1 (91.3L* 0.5a* 3.61b*), #2 (91.09L* 0.52a* -1.8b*) and #3 (91.21L* 2.24a* -5b*) showed chromaticity of paper #2 close to ISO 1 (95L* 0a* -2b*) standard followed by paper #1 and paper #3. The gray balance achieved by Cyan, Magenta and Yellow ideally has maximum amount of Cyan and equal amount of Magenta and Yellow. All the paper grades had higher proportion of Cyan than Magenta and Yellow. The paper #1 having slope towards yellow resulted in higher proportion of Yellow than Magenta while paper #3 with slope towards cyan resulted in higher proportion of Magenta than Yellow to achieve the gray balance. The proportion of Magenta and Yellow will differ according the deviation in chromaticity of paper. The gray balance curve will coincide with theoretical ideal value if the ink and paper property coincide with ISO standard. The gray balance varies due to different color characteristics of papers and will not be identical even under the same printing conditions. Therefore to achieve consistent color reproduction for a particular paper, the printer should re-calibrated for gray balance [6-7].

References

1. Science of G7. Retrieved from- https://connect.idealliance.org/g7/about/scienceofg7
2. A Step-by-Step Guide to the Digital Printing Process. Retrieved from- https://cgsasp.com/digital-printing-process/.
3. Xlaoylng R. (2008) G7 method for Indigo Press Calibration and Proofing. NIP24and Digital Fabrication (2008). Retrieved from- https://www.researchgate.net/publication/48909446
4. Li K., Sun H., Jiang W, (2012) The Standard Parameters Research in Digital Printing by G7 Technology. Applied Mechanics and Materials Vols 182-183 pp 348-351 Retrieved from- https://www.scientific.net/AMM.182-183.348
5. Zhenrong W. and Wanyou T. (2013) Research on the grey balance of ink-jet printing based on G7. Applied Mechanics and Materials Vol. 329 pp 429-433 Retrieved from- https://www.scientific.net/AMM.329.429
6. Wang H., Chen G.,Cui X. (2012)  Effect on Grey Balance caused by Slight Chromaticity Deviation of Paper in Image Reproduction.Applied Mechanics and Materials Vols. 236-237 pp 459-463Retrieved from- https://www.scientific.net/AMM.236-237.459
7. Li M., Chen G.(2015) Research on Grey Balance in Ink-Jet printing based on Paper Color Characteristics. Applied Mechanics and Materials Vol 731 pp 308-311 Retrieved from-https://www.scientific.net/AMM.731.308

 

 

Seminar on

Impact of Varying Plate Screening 

Techniques on Print Quality

 in Flexography

By

Ms. Gargi Sachin Shah

Under the Guidance of

Prof. Dr. Akshay V. Joshi

 

Pune Vidyarthi Griha’s College of Engineering and Technology & G. K. Pate (Wani) Institute of Management, Pune, India 

Academic Year 2020-21

In flexographic printing flexible printing plate is used. The image on the inked plate is in raised form and  non-image area is in recess form. They   rotate at high speeds to transfer the ink from the anilox roll to the substrate (paper). Each color requires a different printing plate (Fig.1). Now-  a-days continuous-tone images are reproduced in two stages. Firstly, the image must be digitized using a scanner or other digitizing device and care must be taken to capture enough data to provide sufficient resolution for the size of image to be printed, and also its halftone screen resolution. Then the scanned image is placed onto a page in a page-layout program. When the completed result is output to a printer, the page-layout program converts the digitized image to halftone dots. The process of screening is also referred as halftoning, and the resulting image is a halftone. After printing, the image will totally resemble the original image, with the smaller dots producing light shades or highlight areas and the larger dots making the dark shades or shadow areas [1].  An important factor in the improvement of flexographic print quality is advances in screening technologies. These screening technologies when combined with plate technologies and cure technologies, are of great advantage in the screening world: highlight dots and surface screening. Screening is converting the continuous tone image to the printable image comprised of dots of various shapes and sizes. The faithfully image reproduced and how much of the original contrast, saturation, and detail is preserved depends on how we screen an image. The different screening technologies are at the heart of flexo platemaking which are AM (Amplitude Modulated) Screening, FM (Frequency Modulated) Screening and Hybrid screening. Surface screening has brought better results to the issue related to the ink transfer and solid ink coverage helping those vibrant and saturated brand colors to become more consistent. Printer choosing and curing a plate is important, similarly screening selection is a vital element in implementing high-quality flexo. Screening selection will depend on your process and must be optimized for each process [2].

Fig 1: Flexographic Process

AM Screening

The basic working is that in an AM screening half tone dots are equally spaced and arranged on a grid and the number of dots on the orthogonal grid is fixed (fig. 2). Amplitude modulated (also known as conventional screening) is dependent on the size (“amplitude”) of the dots. In AM screening, the size of the dots is modulated or altered on a grid to create the illusion of different tones. Issues that come along with conventional screening, including loss of detail, subject moiré, screening moiré, rosette visibility and the optical bump [3]. The dots are equally spaced in AM screening, so this tends to create rosettes patterns along with moirés is clearly visible to the naked eye. To minimize the moirés effect, dots are designed to be placed at certain angles for a CMYK 4 color process that are C (75°), M (15°), Y (0°), K (45°) [4]. 

Fig 2: AM Screening Dot Placement

Image copyright ©2021 Phillips Printing. All Rights Reserved, Phillips Printing Co.

FM Screening

In frequency modulated (FM) screening, the size of the dot is constant, but the number (“frequency”) varies. In FM screening the dots are pseudo randomly placed  and not aligned along fixed screen angles to avoid causing artifacts (fig. 3). FM has  pseudo-random arrangement of the dots that is no direction to the screen, and therefore no screen angle. The result is that FM screening can overcome many of the reproduction problems associated with AM screening. With second order FM screens (the latest advancement in FM), FM-spaced dots are designed to grow in size through the tone scale in a fashion similar to AM dot structure. Flat tint reproduction can have a grainy appearance. Smooth transitions from mid-tone to shadow can be difficult to maintain. One advantage of stochastic screening is its ability to remain stable during the run [3].

Fig 3: FM Screening Dot Placement

Image copyright ©2021 Phillips Printing. All Rights Reserved, Phillips Printing Co.

XM (Cross Modulated) / Hybrid Screening

Screenings that don’t resemble AM or FM methodology are generally referred to as a “hybrid” technology. Hybrids are of two types - second order FM screens and hybrid AM screens. These technologies take advantage of both FM and AM screening, combining them together to produce the desired result [5]. XM makes use of FM screen in the highlighted and shadow areas and AM screen in the mid-tones (fig. 4). XM allows the smooth transition from one screen to the other. XM screens combine the best characteristic features of both AM and FM [4]. Hybrid AM/XM screening  helps to recover the lost part of the tone range by varying the size of highlight and shadow dots so they never get smaller than a size that can be considered for the printing process. Hybrid AM/XM screens are so called because they leverage a technique borrowed from FM screening [5].

 

Fig 4: XM Screening 

Image copyright ©2007 Rujna, XM SCREENING TECHNOLOGY. All Rights Reserved.

 

AM screening technique proves itself to be a method with great print stability and less dot gain in mid tone areas due to the factors (fixed screen angle, screen ruling and screen shape) that affects the representation of darker and lighter parts to be inadequate. AM-FM screening is also referred to as transitional screening and it produces best output and grants a better dot gain curve. The advantages of this method is that rich details are achieved in highlight and shadow area, the graininess of the mid tones decreases, in flexography printing highlight break is avoided and tone break effect is reduced, it helps in achieving the optimum dot size and, also as there is no requirement of applying bump curves during the plate making process, so time required is less in prepress. AM/FM hybrid screening helped to improve the image details and smoother gradients also the highlight areas are produced more faithfully. Hybrid screening had random distribution of dots and AM had regular distribution. Hybrid screening gives more dot gain as compared to AM screening due to no use of bump up curve in hybrid screening. For effective results the prepress operator should make combination with FM and AM dots and to avoid problems during printing, a minimum dot-size should be previously specified [6]

Advantages of stochastic screening over conventional screening are there is no chance of apparent moire patterns and there are no screen angles involved in overlapping halftone screens with stochastic screening which makes it easy to print four color over each other with forming any moire patterns. There are no patterns formed by the randomly placed dots. Secondly slight misregistration errors on press can cause color shift issues, but with stochastic screening misregistration did not cause any color deviation. Stochastic screening also helps to improve image quality as it has ability to increase ink densities, which in turn helps tonal range and contrast to get better. Lastly, the overall sharpness and detail of images are the result of the small dots used in stochastic screens. The print contrast was result of stochastic screenings which enhanced image quality by improving overall tonal range and contrast. The graininess issue and benefit of reproducing sharp images is solved by small minimum dot-size held. Stochastic screening creates a larger gamut as a result of its application to the expanded gamut process. Tonal Value Increase is the issue when using stochastic screening with the flexographic printing process. It is possible the single stochastic screen would be sufficient to avoid the moire and perhaps reduce the TVI issues [7].

XM screening technology obtains unchanged high-screen frequencies where there is no loss of detail and with no extra problems on press because in most hybrid techniques, the intersection between AM and FM is clearly visible to the naked eye, and the complicated screening algorithms can slow the pre-press process. The true benefits and potential of computer-to-plate workflow is understood by using XM screening. In XM screening to capture fine details FM screening is applied in highlights and shadows, and to achieve smooth gradations AM screening in mid-tones. The main principle of XM methodology states that the press is part of the imaging system. XM more over is same as AM screening. The stability of AM is decreased in highlights and shadows (the line ruling increases) and FM behaves opposite to AM.  Hence XM screens combine the best performance characteristics of both, enabling a wide range of stability on press. For a smooth transition from one screen to the other without visibility XM uses FM screens in the highlight and shadow areas and AM in the mid-tones. AM dots become smaller when rendering highlights until the minimum reproducible dot size on press is reached but from that point on, dots are withdrawn from the grid – providing the desired tone. Likewise, in the shadows, the screen smoothly evolves from one screening type to the other without visibility to naked eye. The shadows and highlights may look stochastic, but this is not true stochastic screening. even if FM  uses smaller dots controlled in FM mode, they are aligned as a continuation of the AM screen angles established in the mid-tones. The result is an entirely new order of screening, called XM or cross-modulated screening. All the three methods AM, FM and XM screening are good, especially at rendering details. Screening is somewhere a determining factor in print quality [8].

Solid screening with Microcell technology can solve the density deficiency as well as the evenness of the color block is improved in the flexographic printing. The density value of the solid screening is not constant when PE is adopted as the carrier for printing. In addition, with the same exposure parameters and screening modes, the effect of the solid screening and value of solid density for coated paper were better than that of PE film. The Microcell technology, under different laser booster values and substrates, effectively improved the solid density and uniformity in the solid area and the solid screening with PE as the substrate effectively improved the uniformity and value of solid density for the flexographic printing. The Microcell technology will not only increase the investment of technology, but also the cost of production [9]. 

References

1. What is Flexographic Printing? Retrieved from https://www.printmatics.com/flexographic-printing
2. Flexo Plates: It’s all about the dots. Retrieved from https://www.flexpackmag.com/articles/90160-flexo-plates-its-all-about-the-dot
3. AM, FM & In Between Tuning Your Screening Dial Retrieved from https://idealliance.org/files/2006-3tech2.pdf
4. AM Screening v/s FM Screening. Retrieved from https://www.flexoglobal.com/blog-articles/2019/kymc-01-am-screening-vs-fm-screening.html
5. Hybrid AM Screening/XM Screening. Retrieved from https://www.flexoglobal.com/flexomag/09-May/flexomag-Pritchard.htm
6. Youssef K. (2015). The Impact of FM-AM Hybrid Screening and Am Screening on Flexographic Printing Quality. International Design Journal, Volume 5, Issue 4, pp 1471-1476. Retrieved from https://journals.ekb.eg/article_93687.htm
7. Trey R.  (2013). Stochastic Screening for Flexography and Its Application to Expanded Gamut Printing. TAGA Proceedings. 142-154.  Retrieved from https://www.printing.org/taga-abstracts/t130142
8.  Valdec D., Vusic D. and Tomisa M. (2007). XM Screening Technology. rujna, Zadar, Hrvatska, 26-29.  Retrieved from https://bib.irb.hr/datoteka/317114.XM_SCREENING_TECHNOLOGY.pdf
9. Enyin F. and Jinghuan G.  (2017). Research in the Solid Microcell Technology in the Flexographic Printing. Advances in Graphic Communication. Retrieved from https://doi.org/10.1007/978-981-13-3663-8_74

Seminar on

Evaluation of Spot Color Reproduction in Digital Process

By

Ms. Gauri Raju Adhalrao

Under the Guidance of

Prof. Dr. Akshay V. Joshi

 

Pune Vidyarthi Griha’s College of Engineering and Technology,Pune 

Academic Year 2020-21

Printing industry is increasingly adopting digital technologies to complement or replace analogy ones. In last few years there is a quite fast move from conventional to digital proofing systems because of the introduction of computer to plate (CTP) systems. As CTP systems do not use film anymore in the plate making process so digital color separations is use to make proofs.As the proofing workflow is moving from the traditional proofs based on films to a complete digital printing approach. Although, digital color separations is already in use in the graphic arts market for some time, their use in proofing is not widely accepted until recently. A proof is used as the main quality check in print runs , color accuracy,color consistency and quality of a digital proofing workflow is to be as good. In today’s print environment where it is able to calibrate color output between offset and digital presses to achieve consistent print results, maximize productivity and manufacturing flexibility is absolutely essential. Digital printing machine proofing in the Western printing industry is become the mainstream mode of production. [1] The primary goal of proofing is a tool for customer to check that the entire job is accurate. The digital proof is  also called as color proof which provides the color-reliable and true color reproduction of the contents of the file intended for printing. The quality of Digital proofing is improving continuously due to revolution of digital proofing device and color measuring device. To maintain color consistency and appropriate color matching digital proofing and printing is needed. [2]

Digital Proofing

      The purpose of digital proofing is to provide standard stimulated reference for printing as the main purpose of a proofing system is to simulate a given printing process so that the quality of the proofing device can be directly determined by measuring its ability to reproduce the standards of printing process. The digital proof is of centrally important for digital imaging printing systems the separations of an image to be reproduced are exchanged digitally. While using digital systems for proofing the proofer needs to be color calibrated to maintain color accuracy and color bars should be used on every proof. Digital proofing system  composed of high precision inkjet  color printer or  laser  color printer through the color printing and simulation printing proofing color with tthe original data to check proofs. [3]

Fig.1: Digital Proofing

Image copyright © 2021 Agfa-Gevaert Group. All rights reserved.

Digital Printing 

       Collecting reference values by performing test printings are really the same as using the stored values in the profile, since they too are measured from a printed sheet once(fig.2). The main advantage of printing a printing is that the data will be more up to date.  There will be no difference but since the printing process is affected by such a large number of factors. Making actual test printings also gives a possibility to collect data that is specific to certain conditions. To achieve accurate color matching in the job printing helps to find out difference between the printed work and the digital work to see whether the color has printed exactly the same way. The measurements can then be used to verify the colour proofs of the edition. For digital printing the proof printers are used and then the proofs are measured and compared in terms of press proofs and color accuracy and others parameters are checked. [4]

Fig.2: Digital Printing

©Image copyright © 2021 Abbott Communications Group

      

The quality analysis and control method for color management of EPSON 7600 color printer is done by following step. First step is equipment calibration and linearization and second step is to characterize the printer and get the profiles. Then after this the final step is the profile of printer and press should be embedded in the digital proofing to complete the color conversion and for obtaining accurate digital proofs a practical solution is that were the profiles of printer is edited and optimized properly after this the transfer of ICC profiles in color management process is printed the test charts. Again to compare the outputs of the printer color management before and after .We should established the evaluation model of color management and profile in which it should include the subjective and objective evaluations. From this it is illustrated that the quality analysis of printed matter requires a comprehensive analysis of combining subjective and objective evaluation. For subjective evaluation a compare the  digital proofs and traditional print proofs by gray balance and test charts where it is found that the digital proofs have bright color, high saturation and excellent reduction of tone and Color reproduction of digital proofing is good and objective evaluation included the contrast of solid density, dot gain, gray balance, color difference and color gamut and then measure and compare it with offset printing. Through subjective and objective evaluation it seems that digital proof can match the national standard of offset through the editing and optimizing of profiles in standardized color management process. [5]
      The accurate color matching can be achieved for spot colors by digital proofing in commercial prepress system by illustrating the problems and reasons while outputting the spot colors. For that firstly select 18 basic color codes for maps in that some are spot colors and some are process color then open this  patches in Photoshop and set  their L*A*B values and then transfer it to CMYK color mode using default color setting and save in tiff file. The colorimetric values of the original is transformed in the custom color settings and the almost the same result is found in which the average color difference is very less and another reasons is that the only device settings of output plan template in the software is needed rest parameters are kept as default settings and several proofing correction are accurate in matching. [6]
        The reproduction error in a different color gamut based on digital image color through different color gamut mapping method image processing software can be done by obtaining the corresponding image effect in which 4 gamut mapping ways is selected in Photoshop respectively corresponding to the color space conversion and then print the output. So for handling photos the most suitable way is Equal ratio compression and Relative chromaticity then Absolute chromaticity is use in color theme for allowing the loss of local color and saturation priority is only suitable for a chart lines of graphic design work. For different color gamut chromatism which includes chromatism calculation in this we have to do calibration of two sample color according to L, a, b values and calculate the difference between Chromatism and individual by the formulas. The color information of digital image has minimum loses in different color gamut space but it shows the best color effect. [7]
          Monitor Calibration and Characterization is done to resolve the color consistency of computer displays and digital printing. Calibrating the display under standard condition to display colors, color management software is used. In this white point setting and adjustment and Contrast and brightness adjustment is done then for different display the calibration and characterizations display is separate. The display profile as RGB color mode to achieve color consistency of different displays for the same RGB mode image is used. And again for digital press calibration and characterization is done using hardware and software. So according to color management mechanism the paper made a use of instrument for display calibration and characteristic for ensuring the color display in the standard condition. For the Bizhub pro C6501 digital press calibration and characteristic using of ICC profile for display and digital press in RGB and CMYK mode of prepress software, and then convert color space of the original manuscript into CMYK mode. So, the color became dim and the correct image color is accepted and printed. After printing, the difference between the actual output color and the original display color under the digital press color gamut space is identified. So from this it provides an effective solution for the color consistency. [8]
          The color reproduction in terms of color difference and color consistency using the software and then check the effect of this software and proofing substrate on proof quality. Two types of custom semigloss art proofing paper is compare with two commercially available proofing software. After this combination of different substrate and proofing module should be tested with profile modules with the device that is profiled as CMYK device with charts of different module then calibration setup is created with two proofing device. And then generate the values and load it in proofing module to achieve better reproduction of color. The selected spot colors shows different behaviour when different combination is used and in digital proofing with custom proofing media color reproduction is mainly affected by proofing module. So without using manufacturer recommended proofing papers the appropriate module which reduces the costing of the proof is achieved with the results and Consistent Proof quality for spot colors is only achieved by standardizing a proofing process. [9]

References

1.  Introduction Quality managed proofing International IARIGAI Research Conference, September 8-11, Retrieved from  https://www.color.org/proofing.pdf

2. Introduction 2002 Switserland, Guangdong Jinfuyuan textile printing machinery company limited http://gd-jfy.com/en/NewsShow.asp?id=160

3.  What is Digital proofing of Spot color And Digital Proofs? China Grand Rise Packing  Printing Co.,LTD Retrieved from https://www.lxpack.com/en/new/new-92-464.html

4.  What is Digital Printing of spot color?  Introduction to Digital Printing Technology by Vince Cahill,Owner The Colorworks Retrieved from https://docplayer.net/14399669-Introduction-to-digital-printing-technology.html

5.  Hong S., Kai L., En Y., Hong C.  (2012) Study on Color Management of Digital Proofing. Applied Mechanics and Materials, Vols 182-183, Trans Tech Publications, Switzerland, PP 352-356. Retrieved from https://www.scientific.net/AMM.182-183.352 

6.  Liu S., Sun Q., Wei B., Chen W.  (2008) The Research of Map Spot Colors Digital Proofing in Commercial Prepress System. Society for Imaging Science and Technology, Retrieved from http://www.imaging.org/site 

7.  Wenge C.  (2012). Study on Reproduction of Color Information of digital image Based on different color gamut Advanced Mechanics and Materials, Vols  430-432, PP 838-841, Trans Tech Publications, Switzerland, Retrieved from https://www.scientific.net/AMR.430-432.838 

8.  Zhao Y.  (2015) Color Measurement and Analysis Based on the Konica Minolta Bizhub Pro C6501 Digital Press. Applied Mechanics and Materials Vol. 731, PP 62-67, Trans Tech Publications, Switzerland, Retrieved from https://www.scientific.net/AMM.731.62 

9. Abhijit L.  (2013) Attributal Standard Establishment For Spot Colors Accomplished Through Digital Proofing. IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) ISSN: 2278-1676 Volume 4, Issue 2, PP 38-40. Retrieved from http://iosrjournals.org/iosr-jeee/Papers/Vol4-issue2/F0423840.pdf