Print Mottle Research Articles

Evaluation of print mottle of double coated paper by octave band filtering technique

The effects of the pre-coating color formulation, dwell time, and coat weights of pre- and top- coating layers on print mottle of double-coated paper were investigated using an octave band filtering image processing technique. To investigate the effect of pre-coating color formulations, six types of coating colors were used. Mottle index and coefficient of variance (COV) of double-coated paper increased as the size of pre-coating pigment particles decreased, which was attributed to the reduction in relative pore size of the pre-coating layer. Decreasing the dwell time decreased transfer time from the coating head to dryer of a Maiyoh coater. As the transfer time to dryer decreased, the mottle index and COV increased because of uneven distribution of latex within the coating layer. Pre-coat weight was found to have a greater impact on print mottle than the top-coat weight.

Textile Sublimation Printing: GLCM Print Mottle Assessment of Black Printed Fabric

The white fabric was printed with different printing temperatures and pressing times using the sublimation printing process in solid-tone black color with a 100 % total ink limiting level. Non-uniformity of the print was examined through print mottle determined by grey level co-occurrence matrix (GLCM) image processing method. Color strength of print was also determined by reflectance spectrophotometry. The print with the lower print mottle was obtained at a printing temperature of 190 °C at a longer pressing time of 120 s or at an increased printing temperature of up to 210 °C at the reduced pressing time of 60 s. The print with the lower print mottle had the lowest entropy, contrast, and correlation and the highest energy and homogeneity. The print with a higher color strength was accompanied by decreased print mottle. Choosing a suitable printing temperature and pressing time for sublimation printing is helpful in achieving print with low print mottle and high color strength and balancing cost, price, and price.

Optimization of flexo process parameters to reduce the overall manufacturing cost

The flexo process parameters play an important role in ink transfer and will lead to wastage of inks, substrate, solvents and printed stocks if not monitored and controlled. The work focuses on optimizing the flexo process parameters for 40 microns 3-layer polyethylene (PE) film with Blue Nitrocellulose (NC) ink to reduce overall manufacturing cost while maintaining the print quality for diaper application. An experimental design was conducted for the response Ink GSM (grams per square meter), ?E and Print Mottle with factors such as ink viscosity, anilox volume, plate dot shape and substrate opacity. The data was analyzed through Main Effect, Interaction Plot and Analysis of Variance (ANOVA). The regression models were developed for the response to validate the predictive ability of model. The process optimization resulted in reduction of Ink GSM, ?E and Print Mottle by 18%, 52% and 1% respectively. The ink consumption reduced by 18.26% with minimized print defects, thereby reducing the overall manufacturing cost.

Matrica ko-pojavljanja nivoa sivog (GLCM) za analizu štampe na tekstilu

Print mottle is a print defect. This print defect has great attention in print quality assessment. Print mottle is determined by the grey level co-occurrence matrix (GLCM). An important parameter in the GLCM processing is the direction angle of pixels in the digitalized print image. This research aimed to investigate the influence of the direction angle, which is an important input parameter in GLCM processing, on the output parameters, such as entropy, energy, contrast, correlation, and homogeneity. Hence, prints were generated in four different colors (cyan, magenta, yellow and black) on white polyester elastase fabric by sublimation printing. The non-uniformity of the print for each color was processed at different direction angles, such as 0° (horizontal), 90° (vertical), 45° (right-diagonal), and 135° (left-diagonal). Values for GLCM parameters obtained at different direction angles were slightly different regardless of print color. The choice of direction angle influenced the values of GLCM parameters. The average of all four directional angle values obtained for each GLCM parameter was taken. The GLCM processing method can be used for prints of different colors, patterns, and different quality levels to evaluate their print uniformity.

Back-trap mottle: A review of mechanisms and possible solutions

Print mottle is a serious and common uneven printing defect that occurs when printing coated paper by the offset multicolor printing process. It is characterized by a non-uniform appearance in terms of brightness, gloss, or color density that appears mostly in solid printed areas. Back-trap print mottle and water-interference print mottle occur when the quality of the paper substrate, especially the coating layer quality, is not satisfactory. To cope with this quality problem of coated papers, the understanding of the offset printing process, the requirements of coated-paper quality, and the reasons for this problem should be addressed. In this review, the basic process of offset printing and the mechanisms of print mottles were explored, the importance of coating uniformity in both the coating structure and process was reviewed, and the approaches to cope with print mottle were introduced.

Combination of Starch and Nano‐Chitin Whiskers for Surface Treatment of Cellulosic Paper

AbstractNano‐chitin whiskers (NWs) are a group of renewable materials that have attracted wide interest. As surface sizing agents, the relevant research has been mainly concentrated on barrier properties since they are considered to be potential plastic alternatives. Nevertheless, it is likewise important to explore their potential to improve print quality. Herein, different dosages of NWs are added into cassava starch (CS) to explore their influence on the surface sizing and printing process. With the addition of NWs, the rheological behavior and film‐forming ability of composite pastes are improved. CS‐6 wt% NWs film with a sizing weight of 2.5 g m−2 can fully cover the pores of the base paper. Compared with CS sized paper with a similar loading weight, contact angle and printing surface strength are increased by 60.0% and 78.6%, respectively. Besides, CS‐6 wt% NWs sized paper show less print mottle on the surface than CS sized paper.

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

AbstractPrint 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.

Regression modeling of solid mottle in coated papers

The print industry has observed an exponential growth over the last decade. A shift from plastics to paper has been observed in the packaging industry due to its sustainability. The gravure process dominates the packaging industry because of long runs and high print precision. This work focuses on the effect of gravure process parameters on print mottle for 50 GSM (gram/square meters) and 65 GSM (gram/square meters) C1S (coated-one-side) paper. Solid mottle refers to unevenness in print density and occurs due to variations in substrate, ink, and process parameters degrading the print quality, thereby resulting in printed wastage and loss to an organization. The intricate mechanism of ink transfer in the gravure process needs to be studied in depth so as to deliver higher yield and lower print waste. The Stochastic Frequency Distribution Analysis (SFDA) algorithm was used to measure the print mottle. The design of experiments (DOE) was run for gravure process parameters such as line screen, viscosity, press speed, electrostatic assist (ESA) voltage, and air gap (distance between impression roller and charge bar) at varying levels. The experimental data were analyzed through analysis of variance (ANOVA), main plot, and interaction plot. The analysis revealed significance of all process parameters for minimization of solid mottle. The optimized settings showed reduction in solid mottle by 64.68% and 67.78% for 50 GSM and 65 GSM, respectively. A stepwise regression model was developed to predict the print mottle that showed correlation coefficient of 0.912 and 0.938 for 50 GSM and 65 GSM C1S papers. This work could serve as a framework to maintain operating levels of gravure process for minimization of solid mottle.

The influence of printing substrate on macro non-uniformity and line reproduction quality of imprints printed with electrophotographic process

Print quality is very important for every printing technique. It depends on many different quality attributes. This research included analysis of macro non-uniformities and line reproduction. 16 different paper substrates printed by electrophotographic process were analyzed. They were separated in two groups: coated and uncoated papers. Analysis of macro non-uniformity showed that print mottle has lower values when printed on coated papers than on uncoated papers. Line reproduction analysis showed that the toner spreaded, during melting and fixation, on line edges for both types of paper. According to these results it can be concluded that paper substrate affects the macro non-uniformity and line reproduction, thus overall print quality.

Analysis and Evaluation Model for Print Mottle using Wavelet Image Denoising Method

Print mottle is problematic in the print and paper industry. In this report, a mathematical evaluation model of print mottle was generated after analyzing several methods. The print mottle images can be evaluated by the model based on the theory of wavelet image denoising analyses that use the wavelet multi-scale fast algorithm. The model was then applied to analyze print mottle on four business papers (inkjet papers, newsprint papers, art papers, and double-coated offset printing papers). The correlation between the results of this method and the human visual evaluation system (HVS) was calculated and evaluated. Experimental results showed that the model predictions agreed with HVS results. The correlation between the printed newsprint papers and the eight different wavelet base functions was over 0.76 (such as haar, sym4, bior3.7, etc.) and decomposed at the first, second, and third levels. The results of the three other papers were better matched with the analysis by human eyes, but the correlation of the art paper and visual model were not as strong as the others. The optimal parameters for the print mottle model were presented in the four kinds of papers presented.

Washing treatment impact on print quality of screen printed knitted fabrics

The surface of textile materials is highly textured, commonly in non-uniform ways. Because of this texture effect, textile surface appears rougher and more porous than other printing substrates, which can cause excessive ink penetration during printing process. Next, washing process is very important factor because it influences ink characteristics on printed samples as well as structural changes of the textile substrate. The aim of this paper is to determine the influences of washing process and different mesh tread count used for printing on print quality. This will be obtained by using spectrophotometric analysis, and GLCM image processing method for print mottle estimation. The results of this research show that increasing number of washing processes leads to higher color differences reproduction color in comparison to printed materials before washing. It also shows that textile surface texture has a great influence on print mottle as well as that number of washing treatment series can generate variations of solid-tone print uniformity.

Improving printability by designing a multi-layered coating structure (Ⅰ) : The effect of binder properties in the pre-coating layer on the characteristics of the top-coating layer

This study was carried out in order to investigate the effect of binder properties in pre-coating layer on the characteristics of top-coating layer and print mottle of coated paper. Four different latices were used as a binder in pre-coating layer, and coating color prepared with a same formulation was applied for top-coating. The properties and print mottle of coated paper were evaluated. It was found that glass transition temperature (Tg) was the important factor to control the properties of pre- and top-coating layer. PPS roughness of coated paper was decreased and paper gloss was increased with applying binder which has lower Tg. Properties of top-coating layer were affected by the binder used in pre-coating layer. Print mottle of coated paper was improved with using binder which has lower Tg in pre-coating layer. These results indicate that final printability and properties of top-coating layer can be improved with using suitable binder in pre-coating layer.

Investigation on electrostatic assist and gravure process parameters on solid mottle reduction for shrink films

Gravure is a high throughput printing process, normally associated with speed, quality, and long print runs. It is widely used for printing on shrink films and other substrates. The shrink films, in particular, polyvinyl chloride (PVC) and glycol-modified polyethylene terephthalate (PET-G), are two dominant substrates widely consumed and printed by gravure process. The PVC and PET-G offer different properties which greatly influence the printability. The surface energy of the substrate determines the adhesion and wettability of ink, while electrical properties such as surface and volume resistivity impact electrostatic assist (ESA) performance. The introduction of ESA in gravure further improved the print quality by eliminating dot skips with reduced impression pressure. However, print defects such as print mottle is inevitable. Print mottle occurs due to a discrepancy between substrate, ink, and process parameters which degrade the print quality. These complexities need to be addressed to deliver higher productivity with less print waste. Therefore, the study investigates the effect of process parameters, i.e., substrate type, line screen, air gap (distance between charge bar and impression roller), viscosity, voltage, and speed, and aims to quantify their effect numerically on defect minimization. The Design of Experiments (DOE) was generated for the above-mentioned parameters and analyzed to extract the best combination of process parameters. The optimized setting showed a reduction in solid mottle by 54% and 57% for PET-G and PVC, respectively.

Comparative study of different methods for the assessment of print mottle

AbstractPrint mottle is a print defect that occurs more or less on prints and has a negative influence on the evenness in print. Several methods to assess print mottle have been proposed. In this article, we analyzed three methods for print mottle evaluation: Histogram Mottle Macro, Gray level co‐occurrence matrix (GLCM) and M‐score. The aim was to compare them and to determine their relation to perceived non‐uniformity obtained by visual assessment. In the experimental part, we printed four different substrates with different optical properties with digital printing machine based on electrophotographic process. The surface of papers was characterized by measuring optical paper properties. The results obtained in this study suggest that GLCM method should be used for print mottle assessment. This method has the strongest correlation with the visual experience of print mottle. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 493–499, 2016

The influence of heat treatment on print mottle of screen printed textile knitted fabrics

Printed fabric is widely used, and it is exposed to various influences. One unavoidable impact is heat treatment during subsequent maintenance – ironing. Hence, many printed textile materials are exposed to different temperatures. Textile can be printed with conventional (screen) and digital (Inkjet) print technologies. In this paper, we analyzed screen printed textile and its sustainability after heat treatment. Heat can not only change the reproduced colour, but also affects the print uniformity (print mottle). The goal of this paper was to find what could be controlled and changed in order to get long-lasting printed textile. We used one natural textile material – cotton that was printed with screen print technology. Constant parameter during the experiment was a time of heat treatment. Ironing temperature and screen mesh count were varied. Results showed that samples printed with smaller screen mesh count maintain print uniformity after heat treatment.

Influence of the surface roughness of coated and uncoated papers on the digital print mottle

Many factors influence the occurrence of print mottle in prints. In printing process three main components are involved: printing press, substrate and toner. They can be considered as separate components, but in most cases their interaction influences the quality of the print.The goal of this work was to examine the influence of surface roughness of different types of paper (coated and uncoated on print mottle of electro-photographic digital prints. We set up a hypothesis that print mottle will be more apparent on rougher surfaces. In the experimental part we printed four different substrates with different surface properties on electrophotographic printing press. Morphology of the papers surface was analysed using atomic force microscopy (AFM) from which surface properties were calculated. For print mottle characterization Gray level co-occurrence matrix (GLCM) method was used. Based on the measurements and results we can conclude, contrary to the initial hypothesis, that uncoated papers with rougher surfaces produce smaller print mottle values.

GLCM Print Mottle Assessment of Ink Jet Printed Billboard Materials

Print mottle is a common print defect, so the evaluation of this print parameter is vital in print quality assessment. The aim of this research is print mottle estimation, i.e. solid-tone surface uniformity assessment of different billboard materials, printed using ink jet technology. A GLCM image processing method was used as a tool for print mottle determination, as it proved to be good surface roughness as well as print mottle estimator. The main idea was to apply GLCM image processing method on ink jet printed samples that possess print mottle defects, and to test if this method can produce reliable estimations of this negative print effects. After obtaining quantitative results of print mottle level for each sample, all of them, according to appropriate color, were subsequently visually compared, in order to gain qualitative information about its solid-tone uniformity and establish which substrate material is superior in terms of solid-tone surface uniformity, as well as to verify previously obtained quantitative results and conclusions.

Effect of ink transfer on print mottle in shrink films

The gravure printing process is considered a pioneer in long run package printing jobs, offering exceptional print quality teamed with high quantities. Shrink films, primarily polyvinyl chloride (PVC) and polyethylene terephthalate-glycol modified (PET-G) are extensively printed using the rotogravure printing process. The intricacies of the printing process and the complex nature of the interactions between the substrate, ink, and printing press, if not studied and controlled, can contribute to unnecessary variation and degradation in print quality. Printability not only can be approximated in the dimensions of densitometry and spectrophotometry, but can also be gauged by print defects such as mottle. This study investigates the effect of process parameters, viz., line screen, ink viscosity, printing speed, and impression roller hardness on print mottle, and explores a way to minimize the same. Design of experiments were generated and analyzed through analysis of variance, main and interaction effects. Furthermore, a regression model was generated to predict the print mottle. The predicted values from the model were in close agreement with the press results. The optimization of process parameters resulted in reduction of print mottle in solid printed areas by 34% and 51% on PET-G and PVC, respectively.

Influence of the Variation of the Coating Color Composition and Characteristics of Inks on the Printability of the Coated Paper

ABSTRACT In this study, the influence of the physical properties of ink such as ink dispersity and emulsified amount on the printability of a coated paper was investigated with seven kinds of cyan inks. In addition, two kinds of coating formulations were tested to evaluate the effect of coating structure on the coated paper printability. It was found that the cyan ink with 2 pigment size had the best dispersibility and hence the ink showed a best ink density on the two kinds of coated papers. When the emulsified ink A with IPA 20 wt% had a lower viscosity than emulsified ink B with IPA 10 wt%, the emulsified ink A showed relatively high value of the ink transfer rate in comparison with emulsified ink B. Despite the high value of ink transfer rate, the coated paper did not show a good printability because those inks with low vis-cosity due to a strong emulsification were easy to make print mottle on the coated paper. Keywords: Printability, ink dispersibility, emulsified ink, printed mottle, coated paper

An evaluation method for print mottle using wavelet denoising and image grey level intensity gradient

Abstract Print mottle is observed as an unevenness of printed tone across an image area. There are many causes of mottle on typical print media, i.e. printing and writing papers, packaging and board, as well as foils and polymer surfaces amongst others, in both applications of traditional printing techniques, such as offset and flexography as well as digital methods, including inkjet and electrophotography. Causes range from inhomogeneous surface chemistry and absorption characteristics to instability factors on the printing press. Since the phenomenon is both physical and aesthetical, providing an evaluation for comparison purposes is challenging, frequently requiring panels of observers to provide a visual ranking. A new evaluation method is proposed using wavelet denoising and grey level gradient analysis of the print image. The index of print mottle is built on the bases of the average of grey level gradient and its distribution standard deviation. The method was tested for print mottle evaluation on paper in specific situations under different image basis functions and decomposition level. The results show that the method is in good agreement with visual assessment, and is also less time consuming both in the process and in statistical analysis, with correlation coefficient (r2) of at least 0.79 and as high as 0.88 with every function basis (level 2 or 3).