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Putting INK to PAPER


January 1, 2001
By Pulp & Paper Canada

For paper makers, the Internet is the best thing that has happened since sliced bread. Okay, perhaps that is an exaggeration, but contrary to the doom and gloom forecast in the early 90s, the informat…

For paper makers, the Internet is the best thing that has happened since sliced bread. Okay, perhaps that is an exaggeration, but contrary to the doom and gloom forecast in the early 90s, the information super highway has not threatened the viability of paper. Rather, paper complements Internet uses. “The electronic media is providing new opportunities for print,” said Bob Brown, Heidelberg Web Systems.

Brown gave the keynote address at the 2000 International Printing & Graphic Arts conference, held October 1 to 4 in Savannah, GA. Thirty-seven presentations were given over three days, looking at concerns of and advances made in printing.

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According to a survey done by Heidelberg, print consumption will increase 4% per year while electronic media consumption will grow by 8 to 10% annually. As the overall electronic media consumption increases, so will the print media. Brown said that print that has been done for the Internet far outweighs print that has been replaced by the Internet. “The Internet is breathing more life into print and creating more demand,” said Brown.

Readers appreciate e-media for its speed. It provides high value, but print media still delivers the message most effectively, said Brown.

Print researchers can contribute to continued growth of print use by introducing equipment and expertise to have better performing paper at all grades. Technical innovation will improve quality and reduce waste, and is a critical element, said Brown, to increasing print’s use. “Its time to shed our technology inferiority complex.”

Brown described some of the improvements in his area of expertise — offset printing. Paper waste has been lowered. Productivity has increased substantially. To illustrate this point, Brown noted that in 1994 the production time for a 64-page Time magazine issue was 18 hours. This year a 96-page issue has a print run of 12 hours. Heidelberg, said Brown, is investing in new technology.

Print researchers will face challenges and among them, according to Brown, is integration of technology, training of personnel to use this technology and interaction and performance of consumables.

The medium is the message

Score another point for paper. Jali Heilmann, VTT Information Technology, did a study that compared e-books, and printed books. When e-books were first launched in the market in 1998, VTT sought to evaluate the technical and commercial potential of the electronic book as compared to the conventionally printed book.

Electronic publishing offers several advantages. Delivery and printing expenses can be drastically reduced, as they make up, with marketing expenses, approximately 50% of the price of a printed book. Without printing expenses, very small editions can be published profitably. For the consumer, an entire library can be carried in a lightweight form. E-books and magazines are cheaper and are easy and fast to purchase.

Nevertheless, the study found that people preferred to read a conventional book or newspaper. Not even the information technology professionals preferred the electronic form.

Participants of the study found the e-book to be harder to read, too heavy (they weighed 500 grams) and were afraid they might break it (thought to be too fragile).

The researchers concluded that e-books:

strained eyes;

took too long to read;

are too heavy;

had too short a battery operating life;

are too expensive; and

are not as user-friendly as a conventional book.

However, said Heilmann, in an age where a hand held computer like the PalmPilot is so successful, it seems inevitable that alternate technical solutions will be introduced to make e-books more acceptable. He is not sure when e-books will truly become competition but he said, “Electronic books are here to stay.”

On the surface

Optical properties and models of paper surfaces were discussed in the first session. Christine Barratte, cole Franaise de Papeterie, developed an ink transfer model, designed to lead to a greater understanding of ink transfer to paper. The paper characteristics, ink parameters, ink spreading, and ink absorption co-efficient are taken into account. The study presents a sequence of ink transfer. It also presented ideas for the understanding of transfer but can also look at print density, take into account optical phenomena, adjust coefficient, according to the printing process. All of the work was done with uncoated papers.

Toshi Enomae, University of Tokyo, looked at the mechanisms of print gloss development in nip printings, such as coating composition and structure, printing and ink conditions, and printing direction of paper.

Coating materials affected print gloss. Higher contents of acrylonitrile groups, higher gel content and higher latex content provided higher print gloss. In terms of coating structure, lower pore volume provided higher print gloss. For printing conditions, a lower speed and a higher nip pressure provided higher print gloss.

Richard Hainzl, ACREO AB, presented a light scattering model. The goal was to develop one that is better than ones commonly used. Ultimately, such a device could help to reduce the development cost of newspaper and optimize paper product use.

The research tested the light scattering model using five different paper samples. The model was used to measure light scattering, simulate fluorescence of coatings, simulate gloss variation, and simulate paper samples with an ink film added on the top surface. The simulation results show very good agreement with measured values of the properties that researchers tried to simulate.

Jean-Phillipe Berni presented a new technique to predict print quality using the components of formation of unprinted paper. With the measurement of surface uniformity (MSU) index the intensity of local nonuniformity of formation is partitioned as a function of scale of formation over a wide range of scale. This technique shows that properties are typically controlled by formation components over a limited range of scale of formation, specific to the paper grade/ paper property combination.

This method has been extended to predicting print quality from the formation of the unprinted paper.

Dow Chemical Company developed a robust digital image analysis method for counting missing dots in gravure printing. Dave Smith said that the robust missing dot counting technique is a machine vision algorithm that adapts to printing parameters (dot size and frequency) as well as to lighting conditions, and then yields an accurate, reproducible result across a wide set of image characteristics.

He said that some of the causes of missing dots are plugged cells due to poor engraving, inefficient electrostatic assist, and pinpoint roughness. This system counts more accurately than humans, said Smith.

This method has been proven to work on a wide variety of printing patterns and also with a wide variety of printing problems.

Roy Rosenberger, Verity IA, presented a color image analysis system. The apparatus is a 200-dpi scanner designed to accumulate large images. The ink jet and print mottle methodologies reduce print evaluation to numeric data. This method of determining the performance of ink jet papers, according to the study, provides the mill quality control lab and research scientist an uncomplicated way of reporting results and accumulating data.

In another presentation, Jukka Perento, Tapio Technologies, spoke about the Tapio Paper Machine Analyzer (PMA). The machine measures the paper variability/quality with high resolution, according to Perento. The analyzer comes in two different sizes and samples can be machine direction or cross direction

In black and white

Four papers were presented in the session on ink setting. Sanna Rousu, bo Akademi University, studied the measure of ink adhesion as it transfers to paper coating layer. The ink surface interaction tester (ISIT) was used to detect the tack force development of the inks and varnishes on the model coatings as a function of time. This method provides an analysis of the tack behavior from the initial tack ris
e caused by the ink fluid phase absorption into the structure, until the final consolidation of the ink layer.

Addition of ink pigment was found to increase tack. Linseed oil and resin increased tack. For coating, it was found that overall capillary absorption was faster than diffusion.

Joachim Schoelkopf, University of Plymouth, looked at coating absorption rate studies of offset inks. This work focused on the offset or lithographic print process. In his conclusions, the author writes that “It is possible to use simple tack measurements based on the pull-off technique, as used by the ISIT tester, to determine a model for the viscosity and solids content of an offset ink as the ink begins to set on a paper surface. Under these conditions, the separation force is related predominantly to the viscous properties of the cohesive ink layer. This technique is proven to maintain the cohesion between the wet mobile ink layer and the immobilising interface, and between the ink and paper surface.”

Goran Strm, Stora Enso Research, looked at the absorption of inks into the coating of various substrates after offset printing. He tested this by timing the ink setting, and at different points, scraping the ink from the coated surface with a razor blade. “It sounds quite crude but it is really quite effective,” he said. The mass of the removed ink and extraction of the ink is weighed out, and a chemical analysis is performed on the ink extract.

About 50% of the oils have left the ink film at setting time, said Strm. The content of oil decreases due to absorption, but binder, pigment and other additives increase.

In his conclusion he said that oils are absorbed by the coatings; at setting time about half the oil is absorbed; the oil absorption is strongly dependent on the structure of the coating; porosity and pore size determine the rate of absorption.

Janet Preston, Imerys Minerals, used secondary ion mass spectrometry (SIMS) to study the distribution of ink components on paper samples. Distribution maps of constituent molecular groups were obtained from cross-sectioned printed and coated papers. Ion beam etching SIMS was also carried out on some of the samples to give higher resolution data on the depth distribution of components.

SIMS was found to give high resolution maps and its results agreed with other studies which had recently been carried out on the same printed samples, the research noted.

Cytec uses image analysis to evaluate its sizing chemicals. For the work presented at this conference, protocols were designed to measure ink-jet print targets and toner crease test sheets, using a scanner to acquire the image regions of interests. “The scanner is a versatile instrument and allows automation of the analysis process,” said Lesley Barker, Cytec Industries.

The locator on the scanner helps the image analysis program know exactly what it needs to measure. Small areas must be scanned for good precision at high resolution. Task automation was found to be important for efficiency.

Internal and surface sizing of inkjet printing papers was studied at Lappeenranta University of Technology. Tuija Kilpelinen said that this work was part of a larger study in which internal sizing and alkenyl succinic anhydride (ASA) were looked at. In this work different formulations of internal sizing agents were tested at different degrees of sizing. The results were evaluated with two commercial printers.

Press performance

In a session on on-press performance, Don Roworth, Colour Valid Group Ltd., described a video-based system able to monitor the color of selected areas of a print at full press speed. On-press color monitoring can be an effective tool for color management. According to Roworth, each color can be brought on line more quickly, ink wastage can be reduced, and the press can be run faster, for longer runs.

Douglas Bousfield, University of Maine, presented a “very academic talk” as he described it, about the rupture and stability of thin fluid layers. A model is developed to describe the rupture of a thin water film on a flat surface composed of different materials.

Linda Kim-Habermehl presented two studies, one on coated paper stiffness, and the second on the printability of light-weight coated rotogravure. The study on coated paper stiffness provided a practical overview, discussing the trends, such as cost-reduction efforts, that affect stiffness, and critical issues associated with stiffness performance. The study regarding rotogravure discussed key aspects associated with the printability of LWC rotogravure papers, such as the effect of latex as well as other coating components. Highlights include the following: LWC rotogravure printability is highly basestock-driven; the choice of latex in LWC rotogravure coating formulations can significantly impact printability. Rotogravure print performance can be more sensitive to pressure than temperature during finishing.

Yang Xiang, University of Maine, looked at the influence of ink coating interaction on final print density in multicolor offset. A laboratory print technique is proposed to screen samples for backtrap mottle problem and to study backtrap ink transfer. The results of this study showed that the final print density after backtrap increases with increasing ink setting rate.

The final paper presented at the conference looked at lightweight coated #5 publication grade print. The study was an overview of how papermakers are meeting demands for #5 LWC offset grades.


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