Influence of Printing Substrate on Quality of Line and Text Reproduction in Flexography

This study characterizes and compares the parameters of the quality reproduction of fine elements in flexography on coated and uncoated paper as well as on OPP film (oriented polypropylene). A monochrome test form was created and printed using cyan UV ink. The analysis of results confirms the importance of interaction between the printing substrate and ink; it also indicates identical line and text deformations on the print. Quality reproduction on coated paper is higher in relation to OPP film for all the research parameters. The ink penetrates significantly more and with more irregularity into the pores and throats of the uncoated paper, which results in less homogeneous elements, and in such way that it loses its original shape. In coated paper and OPP film, the ink spreads more on the substrate area which gives it a significantly more homogeneous shape. However, due to the surface spread of the ink, the biggest changes in the size of fine elements are noticeable in the OPP film. The scientific contribution of this paper is based on the comparison of print quality parameters of fine elements, which can contribute to the optimization of the production process and quality of the final graphical product.

Chitosan/Montmorillonite Coatings for the Fabrication of Food-Safe Greaseproof Paper

Here, we report a non-toxic method for improving the oil-resistant performance of chitosan coated paper by coating the mixture of chitosan and montmorillonite (MMT) instead of coating chitosan solution only. Through combining MMT into the chitosan coatings, the coated paper exhibited a lower air permeability and enhanced oil resistance under a lower coating load. For coated papers C2.5 and C3 by coating 2.5% (w/v) and 3% (w/v) chitosan without adding MMT in the chitosan coating, the coating load was 3.76 g/m2 and 3.99 g/m2, respectively, and the kit rating values were only 7–8/12. Regarding the sample C2M0.1 coated by the mixed solution containing 2% (w/v) chitosan and 0.1% (w/v) MMT, its coating load was only 3.65 g/m2, the paper permeability after coating was reduced to 0.00507 μm/Pa·s, owing to the filling of MMT into the cellulosic fibers network, and the kit rating reached 9/12. Moreover, C2M0.1 showed improved mechanical properties, whereby its tearing resistance was 5.2% and 6.6% higher than that of the uncoated paper in the machine direction and the cross direction, respectively.

Application of Polyvinyl Acetate/Lignin Copolymer as Bio-Based Coating Material and Its Effects on Paper Properties

In this work, lignin-vinyl acetate copolymers containing different fractions of lignin were synthesized by the copolymerization technique. The synthesized copolymer was successfully applied to coat the paper for enhancing its properties and performance. The effects of the lignin-vinyl acetate copolymer on the physicochemical, air permeability and mechanical properties of paper were investigated. The mechanical strength, hydrophilic, and air permeability properties of coated paper were improved with the increasing content of the lignin. Lignin-vinyl acetate copolymer containing 15% lignin coated paper exhibited a 1.86 times increase in the tensile index, 45 times increase in the water contact angle, and a 41.1% reduction in the air permeability compared with uncoated paper. Scanning electron microscopy was applied to study the morphology of the coated and uncoated paper. The results showed that paper surface porosity structure was decreased, while the surface smoothness was enhanced considerably with increasing lignin fraction in the copolymer. Therefore, the successful fabrication of such an enchanting coated paper may afford new potential and great applications in the packaging paper.

Colour quality testing of CYAN offset prints depending on pigment concentration and different CTP screening mode

One of the problems in the offset printing technique is the picking of uncoated paper, which occurs due to the activity of pressure cylinder and sticky offset inks. To reduce offset ink stickiness, it is possible to add cheaper ink filler that will indirectly reduce the concentration of pigment. However, there is also a reduction in the colour tones and quality of reproduction. In this experiment we used: standard cyan offset ink (Sun Lit Express ink which consists of phthalocyanine based pigment) and high-quality gloss coated cardboard (250 g/m2 Euroart plus gloss). This paper aims to show how the CTP screening type (AM/FM mode) and the CTP line screening (80, 100, 120 line/cm and 10 μm, 20 μm 25 μm diameter of print elements) manifest on the reproduction quality of a standard gradation wedge. This research will create the possibility of correlating the factors of user reduction of pigment concentration and reproduction quality of cyan colour separation. By using the AM screenings and adding different concentrations of ink filler, more stable cyan prints are achieved.

The influence of PCL-ZnO coating composition on coated offset cardboard prints

The most significant printing branch in these days is packaging printing. Packaging must primarily preserve the product from damaging, but at the same time must attract the consumers to be picked up from the shelf in the store. To ensure protective and aesthetic role of the packaging the prints are commonly coated with varnishes which will improve visual, mechanical, surface, and optical properties. In this paper a coating composed of polycaprolactone (PCL) and nanoscale ZnO was used to coat the offset prints on the cardboard. The coatings were prepared by adding various weight amounts of the ZnO nanoparticles (weight ratios of 0.1, 0.5 and 1%) into the mixture of PCL and ethyl-acetate. The coatings were applied onto prepared offset prints. The prints were evaluated before and after coating process by determining colour coordinates, print gloss, water vapour permeability and by calculating colour difference. The results showed that on the uncoated paper coating with prepared OVPs did not affect the colour reproduction outside acceptable tolerance levels, except for magenta coated with w(ZnO) = 0.5 and 1%. The coating with prepared coatings caused almost none change of print gloss on uncoated paper, but increased the print gloss on coated paper. The water-vapor permeability was lowered on both investigated paper types but on the uncoated paper the addition of ZnO nanoparticles decreased barrier properties in comparison to the coating composed of only PCL. Increasing the mass of added ZnO increases barrier properties of the print on both investigated cardboards. To conclude, this research has proved applicability of the PCL-ZnO coatings as a OVP on cardboard offset prints as it did not highly influenced colour reproduction but had decreased water vapour transmission rate. On the coated paper/cardboard one must take into account the increased colour difference of magenta and chose the ink to be closer to the target values at the beginning. In addition, to further investigate applicability in the packaging printing, further research should include investigation of resistance to ink fading in the ageing process, bending tests, adhesion etc.

PCL-TiO2 nanocomposite to improve ageing of offset prints

UV radiation or sunlight can affect the printed sample by fading the ink surface and therefore the product losses it's decorative purpose and becomes less desirable to the customer. To create the efficient protective coating, titanium dioxide (TiO2) will be used as a well-known compound that should lower the effects of UV radiation. TiO2 should lower the colour fade after UV radiation and this will be determined by densitometric and colorimetric (CIE L*a*b*) measurements. In addition, measurement of print gloss will also be conducted to evaluate visual appearance of the sample. Biopolymer Polycaprolactone (PCL) was the base of the PCL-TiO2 composite in which TiO2 nano sized. To determine influence of the amount of TiO2, three composites were prepared by adding different weight ratio of the TiO2. The prepared nanocomposites were then applied onto the offset prints on gloss art print paper and on the uncoated paper. The results have shown that TiO2 coating does affect ink’s density, colorimetric properties and print gloss after initial coating. The change in chroma due to the accelerated ageing is most visible on yellow ink, cyan and magenta proved to be the more stable. Accelerated ageing caused change in the L* of black. On all colours, increase of the TiO2 weight ratio improved resistance of colour to change. Coated gloss paper was more resistant to density change where uncoated had lower change in chroma. It could be concluded that TiO2 has the ability to protect the prints in the measured time interval but it has to be noted that concentration of the TiO2 particles also causes colour difference and must be observed when defining composure of the nanocomposite.

OPTICAL DENSITY OF YELLOW PRINTS AT COATED AND UNCOATED PAPER

Optical Density is one of the important parameters used to control print quality. Optical density in print materials is form of interaction of ink with paper. This research is oriented to the investigation of optical density value of Yellow printing ink on coated and uncoated paper. The main purpose of this study is to analyze the effect of printing ink thickness on optimal density value. The optical density value of yellow prints obtained using densitometer measurement, printed using IGT method on coated and uncoated paper. Ink thickness variations are applied (0.8 - 9.6 μm). Density values was found to increase as the ink layer thickness increased to a certain point called the optimal density (2.4 μm ink thickness on coated paper and 4.5 μm on uncoated paper). Optical density of yellow printing ink on coated paper is higher uncoated paper, which relates to porosity on paper

Evaluation of the Sheet Resistance of Inkjet-Printed Ag-Layers on Flexible, Uncoated Paper Substrates Using Van-der-Pauw’s Method

With the growing significance of printed sensors on the electronics market, new demands on quality and reproducibility have arisen. While most printing processes on standard substrates (e.g., Polyethylene terephthalate (PET)) are well-defined, the printing on substrates with rather porous, fibrous and rough surfaces (e.g., uncoated paper) contains new challenges. Especially in the case of inkjet-printing and other deposition techniques that require low-viscous nanoparticle inks the solvents and deposition materials might be absorbed, inhibiting the formation of homogeneous conductive layers. As part of this work, the sheet resistance of sintered inkjet-printed conductive silver (Ag-) nanoparticle cross structures on two different, commercially available, uncoated paper substrates using Van-der-Pauw’s method is evaluated. The results are compared to the conductivity of well-studied, white heat stabilised and treated PET foil. While the sheet resistance on PET substrate is highly reproducible and the variations are solely process-dependent, the sheet resistance on uncoated paper depends more on the substrate properties themselves. The results indicate that the achievable conductivity as well as the reproducibility decrease with increasing substrate porosity and fibrousness.

Analysis of Printing Pressure Using Density Measurements of Printed Ink.

In process-color lithographic sheet-fed offset printing the uniformity of printing pressure is critical in achieving consistent print quality. The variations in printing pressure at blanket and impression cylinder nip affect the resultant print density of process colors. The variations in printing pressure are observed not only within the print run but also in the print area of the sheet. The printing pressure is the function of machine engineering, blanket cylinder covering material, substrate, and thickness of image carrier, packing materials used in packing of blanket and plate cylinder. Many printers, even today, use a feeler gauge to judge the level of printing pressure at two or three places along with the blanket and impression cylinder nip. The conventional feeler gauge method yields qualitative information and considers a very smaller portion of the print area. In this experimental work, the densitometry is used to devise an alternative subjective method to give information about the levels of printing pressure across the print area. The image equalling print area is divided into uniformly spaced small patches and one thousand sheets uncoated paper are printed with cyan color on large format offset printing machine. Three sheets, 101th, 501th, and 901th, representing the start, middle and the end of the print run are selected. Out of each identified sheets, three patches are selected from left middle and right columns giving a total nine locations from across the print area. The reflection densities, of nine cyan patches uniformly covering the print area, are measured using electronic densitometer for each of the sheets and tabulated. This approach, involving statistics, is aimed at providing a quantitative tool to analyze printing pressure variation across the print area and within the print run.