scholarly journals Causes of back-trap mottle in lithographic offset prints on coated papers

TAPPI Journal ◽  
2016 ◽  
Vol 15 (2) ◽  
pp. 91-101 ◽  
Author(s):  
Gunnar ENGSTRÖM
Keyword(s):  
Mass Distribution ◽  
Evaporation Rate ◽  
Critical Concentration ◽  
Relaxation Times ◽  
Print Quality ◽  
Surface Porosity ◽  
Nonuniform Surface ◽  
Coating Surface ◽  
Coated Papers ◽  
Coating Mass

Back-trap mottle is a common and serious print quality problem in lithographic offset printing of coated papers. It is caused by nonuniform ink retransfer from an already printed surface when it passes through a subsequent printing nip with the print in contact with the rubber blanket in that nip. A nonuniform surface porosity gives rise to mottle. A key parameter in mottling contexts is the coating mass distribution, which must be uniform. Good relationships between mottle and mass distribution have also been reported; the mottle pattern coincides with that of the coating mass distribution. High blade pressures, compressible base papers, and high water pick-up between application and metering, which plasticizes the paper, yield uniform mass distributions, but these parameters might have a detrimental effect on the runnability in blade coating in terms of web breaks. The general opinion has been that nonuniform surface porosity is caused by binder migration and enrichment of binder in the coating surface, more in the high coat weight areas and less in the low coat weight areas. Recent research has suggested that a more probable mechanism is depletion of binder in the coating surface. Nonuniform shrinkage of the pigment matrix (filter cake) formed during the consolidation between the first critical concentration (FCC) and the second critical concentration (SCC) is another possible mechanism. Relevant relaxation times for latex and the time scales for consolidation show that the high coat weight areas shrink more than the low coat weight areas in the coating layer. A recent pilot-scale experiment has shown that the drying strategy did not affect the differences in shrinkage between high and low coat weight areas. The drying strategy has a pronounced impact on mottle. A high evaporation rate at the beginning of the evaporation results in less mottle than a low evaporation rate. The least mottle is obtained if the drying is performed with a gap in the course of evaporation between the FCC and the SCC.

Flexographic ink-coating interactions: effects of latex variations in coating layers

TAPPI Journal ◽  
2016 ◽  
Vol 15 (4) ◽  
pp. 253-262 ◽  
Author(s):  
ERIK BOHLIN ◽  
CAISA JOHANNSON ◽  
MAGNUS LESTELIUS
Keyword(s):  
Contact Angles ◽  
High Ratio ◽  
Print Quality ◽  
Particle Sizes ◽  
Mixed Composition ◽  
Coating Surface ◽  
Covered Area ◽  
Surface Optical ◽  
Flexographic Printing ◽  
Coating Formulation

The effect of coating structure variations on flexographic print quality was studied using pilot-coated paperboard samples with different latex content and latex particle sizes. Two latexes, with particle sizes of 120 nm and 160 nm, were added at either 12 parts per hundred (pph) or 18 pph to the coating formulation. The samples were printed with full tone areas at print forces of 25 N and 50 N in a laboratory flexographic printing press using a waterbased ink. A high ratio of uncovered areas (UCAs) could be detected for the samples that contained 18 pph latex printed at a print force of 25 N. UCAs decreased with increased print force and with decreased amounts of latex in the coating formulation. The fraction of latex covered area on the coating surface was estimated to be 0.35–0.40 for the 12 pph, and 0.70–0.75 for the 18 pph samples. The ink penetration depth into the coating layer could be linked to the fraction of latex-free areas on the coating surface. Optical cross section microscopy indicated that a higher printing force did not increase the depth of penetrated ink to any greater extent. Higher printing force did increase contact between plate and substrate, leading to an improved distribution of the ink. This, in turn, increased print density and decreased UCAs. On closer inspection, the UCAs could be categorized as being induced by steep topographic changes. When appearing at other locations, they were more likely to be caused by poor wetting of the surface. To understand the wetting behavior of the coating surface, observed contact angles were compared with calculated contact angles on surfaces of mixed composition.

Impact of non-uniform water absorption on water-interference print mottle in offset printing

2018 ◽  
Vol 33 (1) ◽  
pp. 150-163 ◽  
Author(s):  
Sofia Thorman ◽  
Göran Ström ◽  
Patrick A. C. Gane
Keyword(s):  
Moisture Absorption ◽  
Staining Technique ◽  
Relevant Information ◽  
Print Quality ◽  
Surface Adhesion ◽  
Offset Printing ◽  
Surface Moisture ◽  
Coated Papers ◽  
Burn Out ◽  
Lift Off

Abstract Print mottle is a serious and yet common print defect in offset printing. An imbalance between the feed of fountain solution and the ability of the paper substrate to absorb and transport this water away from the surface can cause moisture/water interference problems. In the study presented here, we have investigated the uniformity of aqueous absorption and coating structure of pilot-coated papers with different types and dosages of dispersants and linked this to print mottle and uncovered areas (UCA). In earlier studies, the print quality of these papers indicated that a moderate addition of excess dispersant caused ink refusal, ink-lift-off (ink-surface adhesion failure) and water-interference mottle when printing at elevated fountain feed. In the present study, we have shown that a majority of the samples with uneven water/moisture absorption and an uneven burn-out reflectance tended to have more severe printing problems related to surface-moisture/water.An aqueous staining technique was used to characterise the absorption non-uniformities. This method has been developed previously with focus on absorption of flexographic water-based inks but can clearly give relevant information also for offset printing, when it comes to moisture/water interference mottle.

The Inter-Relationship Between Paper Structure and Print Quality in Ink Jet Printing

1990 ◽  
Vol 197 ◽  
Author(s):  
John F. Oliver ◽  
A. Y. Jones
Keyword(s):  
Quality Evaluation ◽  
Capillary Absorption ◽  
Print Quality ◽  
Paper Properties ◽  
Coated Papers ◽  
Ink Jet ◽  
The Future ◽  
Jet Printing ◽  
Paper Structure ◽  
Potential Opportunity

ABSTRACTThis article describes a print quality evaluation of laboratory designed ink jet papers prepared on a dynamic former. A comparison with various plain and coated papers serves to illustrate the potential opportunity for papermakers to exploit novel types of paper structures in the future. The article will also briefly focus on some of the fundamental issues and key paper properties which perturb print quality and govern the capillary absorption of aqueous inks.

Dynamic Material Functions and the Structure of Asphalts

1996 ◽  
Vol 1535 (1) ◽  
pp. 3-9 ◽  
Author(s):  
J. Stastna ◽  
L. Zanzotto ◽  
G. Kennepohl
Keyword(s):  
Simple Model ◽  
Molecular Mass ◽  
Discrete Spectrum ◽  
Mass Distribution ◽  
Linear Response ◽  
Molecular Mass Distribution ◽  
Complex Modulus ◽  
Relaxation Times ◽  
Maxwell Model ◽  
Material Functions

A simple model of the complex modulus, based on the general principles for a linear response function, is presented. The model represents a generalization of the Maxwell model and it is indicated that the model well describes a relatively broad group of regular and modified asphalts. A discrete spectrum of no more than 10 relaxation times is obtained for all the asphalts studied. The spectra of modified asphalts indicate the presence of several relaxation times that can be related to the interface interactions of the base asphalt and the polymers used. It is indicated that the phase angle of the complex modulus contains valuable information about the structure of asphalts. An attempt to use this information for calculations of the molecular mass distribution is presented. A possibility to characterize asphalts by the so-called pseudospectra is also discussed.

The Thermal Behavior Analysis of a Human Eye Subjected to Laser Radiation Under the Non-Fourier Law of Heat Conduction

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Najat A. Alghamdi ◽  
Hamdy M. Youssef
Keyword(s):  
Heat Conduction ◽  
Laser Irradiation ◽  
Power Density ◽  
Evaporation Rate ◽  
Relaxation Times ◽  
Blood Perfusion ◽  
Absolute Temperature ◽  
Ambient Temperatures ◽  
Human Eye ◽  
Fourier Heat Conduction

Abstract Purpose: The physiological conditions and environment have vital roles in the heat transfer in the human tissues, such as the multilayered human-eye. In this paper, a mathematical model of the human eye subjected to an exponential laser beam concerning the change in blood perfusion, porosity, evaporation rate, and ambient temperatures has been constructed based on non-Fourier heat conduction law. Methods: The human eye has been divided into six layers. Appropriate boundary and interface conditions have been considered. A separable function has been assumed, and the twelve equations have been formulated in matrix form. The solutions have been calculated by using maple 17 software. Results: The results have been shown in figures with different cases. The absolute temperature distribution based on various values of the power density of laser irradiation and relaxation times parameters have been discussed first. The effect of the blood perfusion, porosity, evaporation rate, time, and ambient temperatures have also been discussed. Conclusions: The power density of laser irradiation, blood perfusion, porosity, evaporation rate, time, and ambient temperatures significantly affects the value of the temperature passing through the human eye layers.

Study on the Effect of Calender on Coating surface structure and Printability of Coated Paper

2014 ◽  
Vol 904 ◽  
pp. 46-49 ◽  
Author(s):  
Jian Guo Li ◽  
Ying Li
Keyword(s):  
Surface Structure ◽  
Visual Analysis ◽  
Coating Layer ◽  
Mercury Porosimetry ◽  
Lower Amount ◽  
Print Quality ◽  
Coated Paper ◽  
Paper Surface ◽  
Coating Surface ◽  
Printing Quality

The structure of the coating layer has a strong influence on the optical and physical properties of paper as well as on the print quality. Ink is transferred and sets onto the paper surface in the printing process, which affect printing quality and usage of ink. The objective of this experiment was to investigate the influence of calender on coating surface structure and Printability. The surface structure was explored in the method of numerical and visual analysis using mercury porosimetry measurement and scanning electron microscopy (SEM). The findings indicated that the calender treatment affected the pore size, depth and distribution of the coated paper surface. It could be concluded that Calender could increase the smoothness, gloss and paper surface efficiency of coated paper, which resulted in lower amount of ink usage, lower amount of ink absorption and higher print density.

scholarly journals Activity and stability of RuO2-coated titanium anodes prepared via the alkoxide route

2006 ◽  
Vol 71 (11) ◽  
pp. 1173-1186 ◽  
Author(s):  
Vladimir Panic ◽  
Aleksandar Dekanski ◽  
Slobodan Milonjic ◽  
Vesna Miskovic-Stankovic ◽  
Branislav Nikolic
Keyword(s):  
Degradation Mechanism ◽  
Sol Gel ◽  
Active Material ◽  
Coating Surface ◽  
Coating Mass ◽  
Voltammetric Behavior ◽  
Forced Hydrolysis ◽  
The Stability ◽  
Hydrolysis Of ◽  
Alkoxide Route

Titanium anodes with an active RuO2 coating of two different thicknesses were prepared from the oxide suspended in ethanol ("ink" method), while the oxide itself was synthesized by the hydrolysis of ruthenium ethoxide in an ethanolic solution (alkoxide route). The morphology of prepared oxide was examined by scanning electron microscopy. The electrochemical properties of the prepared Ti/RuO2 anodes, involving their cyclic voltammetric behavior in H2SO4 and NaCl solutions, activity in the chlorine and oxygen evolution reaction, impedance behavior in H2SO4, and stability during electrolysis in dilute chloride solutions, were investigated. The performances of the anodes are compared to those of a Ti/RuO2 anode prepared by the sol-gel procedure from an oxide sol obtained by the forced hydrolysis of ruthenium chloride in acid solution. The anodes prepared via the alkoxide route showed a higher capacitance and activity for the chlorine evolution reaction than the anode prepared by the inorganic sol-gel procedure. The results of the stability test showed that the utilization of the coating active material is better when the anodes were prepared via the alkoxide route than via the inorganic sol-gel procedure, particularly for anodes with a smaller mass of coating. The different rates of loss of activity indicate a degradation mechanism for the anodes prepared via the alkoxide route in which electrochemical dissolution of RuO2 from the coating surface prevails over the growth of an insulating TiO2 layer in the coating/Ti substrate interphase. The effect of RuO2 dissolution from the coating surface increases with increasing coating mass.

Effects of coating formulation on coating thermal properties and coated paper print quality in xerography

2012 ◽  
Vol 27 (2) ◽  
pp. 451-458 ◽  
Author(s):  
Ning Yan ◽  
Chong Liang ◽  
David Vidal ◽  
Xuejun Zou
Keyword(s):  
Thermal Conductivity ◽  
Geometric Mean ◽  
Thermal Characteristics ◽  
Print Quality ◽  
Coated Papers ◽  
Coating Layers ◽  
Visual Ranking ◽  
Coating Formulation ◽  
Styrene Butadiene ◽  
Bulk Thermal Conductivity

Abstract The effects of coating formulation on thermal characteristics of coating layers (namely thermal diffusivity, specific heat capacity and heat conductivity) were systematically studied and their impact on xerography print quality was evaluated. Model coatings were prepared using ground calcium carbonate or kaolin pigment mixed with styrene butadiene latex binder in various proportions (from 6 to 25 pph). As expected, porosity was shown to be a key parameter for thermal conductivity of the coating layers, and is mainly determined by the latex concentration. Particle size distribution (PSD) and pigment morphology also affected the thermal characteristics of the coating layers. It was found that the bulk thermal conductivity of the coating layers can be accurately predicted by a geometric mean model based on the pigment, latex and air contents. Print quality on model coated papers was evaluated in terms of print gloss, toner adhesion and pairwise visual ranking. It was demonstrated that print gloss is improved by decreasing the bulk thermal conductivity of the coatings. The coating formulated with the pigments with the steepest PSD and 10 pph of latex had a relatively low thermal conductivity and the best print quality.

scholarly journals Experimental Analysis of the Extensional Flow of Very Weakly Viscoelastic Polymer Solutions

Materials ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 192
Author(s):  
Manuel Rubio ◽  
Alberto Ponce-Torres ◽  
Emilio José Vega ◽  
José María Montanero
Keyword(s):  
Polyethylene Oxide ◽  
High Speed ◽  
Polymer Solutions ◽  
Critical Concentration ◽  
Extensional Flow ◽  
Relaxation Times ◽  
High Speed Imaging ◽  
High Reproducibility ◽  
Molecular Weights ◽  
Viscoelastic Polymer

We study with ultra-high-speed imaging the thinning of the filament formed during the breakup of a pendant droplet of very weakly viscoelastic polymer solutions of polyvinylpyrrolidone (PVP) and polyethylene oxide (PEO). In the latter case, we consider two molecular weights: 10 5 g/mol (PEO100K) and 2 × 10 6 g/mol (PEO2M). The results allow us to measure with high reproducibility extensional relaxation times of the order of 10 μ s. Despite the noticeable differences between PVP and PEO100K, very similar values are obtained for the range of concentrations where the linear elasto-capillary is established. For PEO2M, the extensional relaxation time depends on the concentration even for values significantly smaller than the overlap one. The prediction c low for the concentration below which the linear elasto-capillary regime cannot be reached qualitatively agrees with the results for PVP and PEO2M, while it underestimates the critical concentration for PEO100K. The results for PEO2M are consistent with those reported in the literature for higher concentrations.

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