Improvement of printability by the new designe of the multi-layered coating structure (II) : The effect of pigment blending in pre-coating layer on characteristics of top-coating layer
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This study was carried out in order to investigate the effect of pigment properties in a pre-coating layer on the characteristics of a top-coating layer and the print mottle of the coated paper. Five different pigments were applied for this study as raw materials for the pre-coating layer. The properties and print mottle of the coated paper samples were evaluated according to the coating color formulation. Type of pigments appliied in a pre-coating layer was one of the most important factor to control the properties of pre and top coating layer. Surface properties of pre and top coated paper were improved by blending GCC which had smaller particle size, with clay. Properties of a top-coating layer was affected by the pigment properties used in the pre-coating layer. It was found that print mottle of coated paper can be improved by replacing part of GCC with smaller particle size GCC or clay in pre-coating layer.Keywords:
Mottle
Coated paper
Layer by layer
Effects of latex Tg, starch level in color recipe and interval time between coating and drying on offset print mottle were studied. Coating colors were coated by a SDTA pilot coater. Coated samples were printed by RI print tester and commercial sheet-fed offset press and print mottle tendencies were evaluated. Starch and latex contents at coated surface were measured and relationships between print mottle and the surface binder contents were discussed. Temperature at the coated surface during drying process was measured and the influence of latex film formability on print mottle was also discussed.
Mottle
Offset printing
Coated paper
Grease
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Mottling is the uneven appearance of print, particularly in solid areas, small dark and light areas appearing in the surface of paper or paper board. Print mottle is influenced by many parameters, but the most important one is the type of paper which is used for printing. Variations in the surface characteristics such as absorption and smoothness play an important role while analysis of the mottle. Print mottle can occur in sheet-fed offset due to several reasons related to both the paper and its coating and the printing press. The aim of the research work was to improve our knowledge of the influence on mottle related to the different paper surfaces (both coated and un-coated paper) in single colour sheet fed offset press. Both the coated and un-coated papers were used with different gram mage for printing with the help of a specially designed test form. The results from the print trials show that fountain solution from the previous printing unit can cause a decreased print density and dot gain. The structure of the paper coating, uneven porosity distribution has high influence oil water induced mottle while the effect of the surface chemistry is low.
Mottle
Offset printing
Coated paper
Printing press
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Printed mottle of coated paper is one of the most common but the most difficult problem in offset printing. Printed mottle is caused by an uneven penetration of Ink into the paper, binder migration, etc. For a high quality printing, development of new paper coating technologies to prevent print mottle is required. So for, the study of solving printed mottle is coated paper absorption controlled by base paper sizing and coating layer binder migration control. As a results, printed mottle has improved in coated paper. But printing is worked by interaction of printing ink, coated paper and printing pressure, then we need to understand of interaction printing work and coated paper. This research focused on a way of improving printed mottle by investigating various printing conditions such as ink dispersion, nip condition and amount of ink transfer using IGT printability tester.
Mottle
Offset printing
Coated paper
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The principal reasons for applying a pigment coating to paper are to improve appearance and printability. The pigment coating provides a surface that is more uniform and more receptive to printing ink than are the uncoated fibers and, in turn, both facilitates the printing process and enhances the graphic reproduction. The improvement in print quality is readily apparent, especially in image areas or when multiple colors are involved. Although pigment coating of paper is to improve the printability, coated paper is not completely free from printing defects. Actually there are a number printing defects that are observed only with the coated papers. Among the printing defects that are commonly observed for coated papers, print mottle during multi-color offset printing is one of the most concerned defects, and it appears not only on solid tone area but also half dot print area. There are four main causes of print mottle ranging from printing inks, dampening solution, paper, and printing press or its operation. These indicates that almost every factors associated with lithographic printing can cause print mottle. Among these variation of paper quality influences most significantly on print mottle problems in multicolor offset printing, and this indicates that paper is most often to be blamed for its product deficiency as far as print mottle problems are concerned. Furthermore, most of the print mottle problems associated with paper is observed when coated papers are printed. Uncoated papers rarely show mottling problems. This indicates that print mottle is the most serious quality problems of coated paper products. Overcoming the print mottle is becoming more difficult because the operating speeds of coating and printing machines are increasing, coating weights are decreasing, and the demands on high-quality printing are increasing. Print mottle in offset printing is caused by (a) nonuniform back trap of ink caused by a nonuniform rate of ink drying, referred as “back trap mottle, and (b) nonuniform absorption of the dampening solution. Furthermore, both forms of print mottle have some relationship to the structure of the coated layer. The surest way of eliminating ink mottling is to eliminate unevenness in the base paper. Coating solutions, often easier to put into practice, should, however, be considered. In this paper the principal factors influencing print mottle of coated papers will be discussed. Especially the importance of base paper roughness, binder migration, even consolidation of coating layers, control of the drying rate, types of binders, etc. will be described.
Mottle
Offset printing
Coated paper
Screen printing
Digital printing
Printing press
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Print mottle, as a printing defect, is becoming a serious concern for papermakers and printers, due to the increasing demand for high quality printing, to the increase of coating and printing speeds, and to the decrease of coating weight. The intention of this study is to evaluate quantitatively the relationship between print mottle and chemical distribution in the coated paper by the use of image analysis and ESCA analysis. The results are summarized as follows : 1. A method of obtaining the surface profile of the binder distribution was developed using ESCA with an analyzer slit of 2 mm diameter of effective area.2. A quantitative evaluation method for print mottle by image analysis was developed.3. Print mottle caused by non-uniform absorption of dampening solution corresponds directly with the non-uniformity of the surface distribution of binders and pigments. And both print mottle and non-uniformity of binder distribution at the coated surface have a scale of 1-3 mm diameter.4. Depth profiles of the coated layer show uneven distribution not only of the binder but also the pigments. Also, starch and latex show different distributions in the coated layer.5. No clear relationship between z-direction distribution of chemical components and print mottle was detected, and thus, print mottle seems to be independent of the z-directional coating composition.
Mottle
Coated paper
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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.
Mottle
Offset printing
Coated paper
Gloss (optics)
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Development of the paper coating technologies to prevent print mottle is needed to obtain high quality printing. Printing mottle is recognized as the most common printing problems in using coated paper and which is one of the most difficult problems to solve in offset printing. Print mottle is one of the most important quality properties of printed products and manufacturers strive to improve the paper surface to gain higher and more even print mottle. The prevention of printed mottle requires of coating color formation, especially the minimum of binder migration. The results the uniformity of liquid absorption by paper at very short contact time between paper and testing printing liquids.
Mottle
Offset printing
Coated paper
Screen printing
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Printed mottle of coated paper is one of the most common but the most difficult problem in offset printing. Printed mottle is caused by an uneven penetration of ink into the paper, binder migration, etc. For a high quality printing, development of new paper coating technologies to prevent print mottle is required. So for, the study of solving printed mottle is coated paper absorption controlled by base paper sizing and coating layer binder migration control. As a results, printed mottle has improved in coated paper. But printing is worked by interaction of printing ink, coated paper and printing pressure, then we need to understand of interaction printing work and coated paper. This research focused on a way of improving printed mottle by investigating various printing conditions such as ink dispersion, nip condition and amount of ink transfer using IGT printability tester.
Mottle
Offset printing
Coated paper
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Uneven print density, print mottle or mottle, call cause severe print quality problems and is a frequent problem for printers. Print mottle can occur ill sheet-fed offset due to several reasons related to both the paper and its coating and the printing press. The aim of the project was therefore to improve our knowledge of the influence on mottle related to the fountain solution which dampens the paper surface, water induced mottle. Pilot coated papers were produced and printed in a full-scale 4-colour sheet-fed offset printing press. During printing a specially designed test form was used. This must be used together with a blanket which has cut-out areas corresponding to the areas oil the test form. In this way it is possible to create a number of different printing situations oil the same printed paper sheet. The results from the print trials show that fountain solution from the previous printing unit can cause a decreased print density and dot gain. Water induced print mottle is Caused by the fountain solution from the previous printing unit. Back-trap from the following print units Will have a smoothing effect and will decrease the mottle. The results are based oil a hypothesis test at the 5% level. Water induced mottle can be related to both the printing process and the paper. The structure of the paper coating, Uneven porosity distribution, has a high influence oil water induced mottle while the effect of the Surface chemistry is low. The paper with high SB latex content showed the most uneven porosity distribution.
Mottle
Offset printing
Coated paper
Fountain
Printing press
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The relationship of coating micropore, optical properties and print mottle were studied. Coated papers with various micropore size distribution were prepared on a pilot SDTA coater and were printed on a 4 color sheet-fed offset press. The print mottle was evaluated both visually and with an image analyzer. The micropore of the coating, unevenness of the coating and optical properties of the coated paper such as whiteness were measured. Then the relationship between print mottle and these measured factors was studied.The results are summarized as follows ;(1) There is no mutal relationship between print mottle and micropore of coating.(2) Uneven whiteness of non-printed areas affects the print mottle. Sometimes it increases print mottle and sometimes it decreases print mottle.(3) Such uneven whiteness is caused by uneven opacity of the paper.
Mottle
Opacity
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