<p>Flexographic printing is a process that employs a flexible printing form and low viscous ink, often water-based. The flexible printing form is favourable for printing on rough surfaces, but the high surface tension of the ink may cause printability problems.</p><p>This work has focused on the interaction between paper/paperboard coating and water-based flexographic ink, aimed at increasing the knowledge about the printing process in form of physical/chemical parameters that are important for ink setting. The effects of printing conditions on print quality, such as printing pressure and temperature, have also been in focus.</p><p>The work has shown that fluids of different polarities, i.e. different dipole moments, behave differently when being absorbed by a coating layer. Due to their chemical compatibility to the coating layer, fluids with large dipole moment fill the pore matrix of the coating to a lesser extent but penetrate further into the coating than fluids with small dipole moments. On the other hand, polarity of the coating layer also affects the print. When printing on coatings with different polarities, higher print densities was obtained on the more polar substrates. As a tentative explanation, it is proposed that the ink builds different layer structures during drying depending on the coating polarity.</p><p>Print gloss is related to the ink setting which, in turn, is affected by the solvent retaining capacity of the ink. Large water holding capacity allows the ink components to smoothen out before the structure is set, resulting in a higher print gloss. The rheology of inks is affected by temperature; at a higher temperature the viscosity is reduced. The reduction in ink viscosity at higher temperature has been shown to affect the print quality, e.g., print density and dot gain. It is suggested that a thicker layer is immobilised during impression due to the lower viscosity and that it is an explanation of the higher print density at a higher printing temperature.</p><p>The influence of impression pressure on dot gain has been experimentally evaluated and mathematically modelled with good agreement. The dot gain is shown to respond non-linearly to the applied printing pressure.</p><p>Studies based on pilot coated and printed paperboards is also reported, and it is shown that the print quality, e.g. print density, print gloss and dot gain, is largely dependent on the type of ink chosen and on the coating characteristics. Higher clay content in the coating resulted in increased dot gain and a decreased mottling.</p>

Halftoning methods can be divided into two main categories, namely AM (Amplitude Modulated) and FM (Frequency Modulated). Some printing methods, such as Flexography, are not able to produce dots small enough to handle the highlights and the shadows of the original image by just using AM halftoning method. To overcome this problem FM method is used in the highlights (and the shadows) and an AM method in rest of the image. Hybrid halftoning (combination of AM and FM) technique for grayscale images has already be presented showing the best way to place FM and AM dots in the resulting binary image. This thesis work is and extension of that and presents hybrid technique for color images. In color images, besides the problem of transition area between AM and FM, a number of other factors needs to be addressed. One of such factors is to define the starting point of FM technique in different color channels. In this work all the possibilities of combining AM and FM in different color channels have been investigated and then the best approach for hybrid color halftoning is proposed. This approach not only uses the best solution for starting point of FM halftoning in each channel but also places the different color dots in the highlights, as homogenously as possible.

Flexographic printing is a process that employs a flexible printing form and low viscous ink, often water-based. The flexible printing form is favourable for printing on rough surfaces, but the high surface tension of the ink may cause printability problems. This work has focused on the interaction between paper/paperboard coating and water-based flexographic ink, aimed at increasing the knowledge about the printing process in form of physical/chemical parameters that are important for ink setting. The effects of printing conditions on print quality, such as printing pressure and temperature, have also been in focus. The work has shown that fluids of different polarities, i.e. different dipole moments, behave differently when being absorbed by a coating layer. Due to their chemical compatibility to the coating layer, fluids with large dipole moment fill the pore matrix of the coating to a lesser extent but penetrate further into the coating than fluids with small dipole moments. On the other hand, polarity of the coating layer also affects the print. When printing on coatings with different polarities, higher print densities was obtained on the more polar substrates. As a tentative explanation, it is proposed that the ink builds different layer structures during drying depending on the coating polarity. Print gloss is related to the ink setting which, in turn, is affected by the solvent retaining capacity of the ink. Large water holding capacity allows the ink components to smoothen out before the structure is set, resulting in a higher print gloss. The rheology of inks is affected by temperature; at a higher temperature the viscosity is reduced. The reduction in ink viscosity at higher temperature has been shown to affect the print quality, e.g., print density and dot gain. It is suggested that a thicker layer is immobilised during impression due to the lower viscosity and that it is an explanation of the higher print density at a higher printing temperature. The influence of impression pressure on dot gain has been experimentally evaluated and mathematically modelled with good agreement. The dot gain is shown to respond non-linearly to the applied printing pressure. Studies based on pilot coated and printed paperboards is also reported, and it is shown that the print quality, e.g. print density, print gloss and dot gain, is largely dependent on the type of ink chosen and on the coating characteristics. Higher clay content in the coating resulted in increased dot gain and a decreased mottling.

Diss. Karlstad : Karlstads universitet, 2007.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 55-57).

Thesis (M.S.)--Rochester Institute of Technology, 2005. / Typescript. Includes bibliographical references (leaves 89-94).

The objective of this thesis is to prepare a business plan on establish a new company focused on technology low-volume printing self adhesive labels and other flexible materials with methods of UV flexo and digital printing. The author's method of digital printing holds a protected utility design (Úřad průmyslového vlastnictví, registration number 11001, dated March 19, 2001)

Magistro studijų baigiamajame darbe išanalizuoti fleksografinių spausdinimo formų gamybos procesai, išnagrinėti ir atskleisti vaizdų rastravimo ypatumai, detaliai aprašyta originalo (projekto) paruošimo spausdinimui eiga ir spausdinimo formų gamyba. Eksperimentiškai ištirta rastravimo proceso režimų įtaka spausdinimo formų kokybei naudojant skirtingas skaitmenines plokštes. Nustatytos geriausios rastravimo programų versijos atskiriems atvejams. / In the MS thesis are analyzed procedures of the flexographic printing plates manufacturing. The peculiarities of the screening processes are revealed. The details of the workflow of the preparation of the originals (projects) for printing and the process of printing plates manufacturing are described. Experimentally is investigated the influence of the screening regimes on the quality of the printing plates using different photopolymeric plates. The best versions of the screening program for the particular cases were determined.

There are high demands on flexographic print quality to be sufficiently high and consistent in order to create a competitive packaging. At the same time the production efficiency need to be high. Printers thus need to achieve the same quality every time and quickly start-up new printing jobs. To accomplish this, one needs to gain a thorough understanding of how the liquid packaging board interacts with the ink and impacts the print quality. This thesis focuses on water-based ink absorption of liquid packaging boards and particularly on a) how uniformity of ink absorption can be measured and b) to what extent the absorption characteristics contribute to print mottle in flexographic printing. The work encompasses two parts. First, an absorption non-uniformity test method has been developed using a staining technique. This method is unique as it measures how unevenly an aqueous solution is absorbed, in a short time period and without impact from surface roughness. Moreover, the contributions from white-top mottle and absorption non-uniformity can be quantified simultaneously from one single measurement. Second, a method to independently study the effects of absorption non-uniformity on print quality has been established. This is achieved by introducing artificial absorption non-uniformities with well-controlled barrier patterns. A barrier pattern may modify local pore structure and/or surface energy, hence lead to lateral absorption variations. By these means, it is possible to produce a substrate property-matrix; encompassing absorption non-uniformity and for example surface roughness. It was demonstrated that non-uniform absorption indeed has a negative impact on print quality, both on smoother and rougher boards. Low absorption made print density decrease and uneven absorption caused print mottle. This was the case when other properties of the samples were kept within a narrow range; otherwise surface roughness appeared to determine print mottle ranking.

Thesis (Ph.D.)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Hsieh, Jeffery; Committee Member: Breedveld, Victor; Committee Member: Empie, Jeff; Committee Member: Forney, Larry; Committee Member: Singh, Preet