Printing and environmental sustainability

Ivana Bolanča Mirković, Igor Majnarić, Sandra Mustač 1, Zdenka Bolanča

University of Zagreb, Faculty of Graphic ArtsGetaldićeva 2, 10000 Zagreb, CroatiaE-mail: ivana.bolanca@grf.hr, igor.majnaric@grf.hr,zdenka.bolanca@grf.hr 1Bsc student, University of Zagreb, Faculty of Graphic ArtsGetaldićeva 2, 10000 Zagreb, CroatiaE-mail:sandra.mustac@gmail.com

Abstract

The impact of the printing process on the environment is significant. This paper explores the voltage of reverse roller in indirect electrophotography printing in the field of 0V to -250 V on the life end of the printed products through the efficiency of recycling. In addition, the quality of color reproduction is discussed. For the printing is used: uncoated woodfree paper, double-sided coated paper and Soho coated paper.

Characteristic of the results of image analysis handsheets made from recycled fibers prints obtained by changing the voltage of reverse rollers from 0 to -200V is reduced in the total dirt spot number and increasing in the dirt spot area. The efficiency of recycling is the highest for printing on uncoated paper, then on Soho coated paper, and the worst on double-sided coated paper. The quality of fullcolored prints observed through the volume gamut of prints gives reverse results.

This is just part of a comprehensive study involving all six separate stages of electrophotography printing synchronal performed. In this study the use of experimental design and creation of statistical models in the direction of optimization process and environmental sustainability follows.

Keywords: environmental sustainability, digital printing, voltage of reverse roller, quality of prints, recycling

1. Introduction

The concept of environmental sustainability refers to the systematic conditions that should not be disturbed by human activities either at a global or regional level more than the planet allows. At the same time all the natural resources must not be depleted, and have to be sufficient for the next generations. These two requirements should be in balance with the third one regarding sustainability which refers to the principle of ethics and fairness.

Ecological flexibility is the capacity of an eco-system to overcome certain disruptions without irreversible losses to conditions of its balance. Ecological space is the amount of energy, resources and territory which can be used in environmentally sustainable way, and ecological footprint points this out. Environmentally more sustainable product system and demands of sustainable conditions will result in production and consumption that are in the system of contemporarily industrial society and sustainability. The term of sustainability is significant for the development, and it includes energy and material flows, closed loop systems, clean technologies, economical and social factors, implementation of society values and quality. Therefore, the switching to sustainability is large and complex process of technological, economical and society innovation in which many differences have to adjust and find their place.

Environmental awareness, health and safety factor have an important role in identification of printing technologies for the future. In order to increase effectiveness of resource usage and effectiveness of environmental management system, life cycle assessment of the product has to be considered and included in planning and projecting, starting from early stage of design.

The level of environmental awareness is present in printing industry, which enables making the right choices. Significance of making the right choice is in the field of printing substrates (substrates with high content of secondary raw material, substrates made from total chlorine-free process), inks (lower solvent content level biodegradable inks, formulation with more renewable raw material), printing (clean technologies, preparation of printing forms with no wastewater which contains chemicals from the process, cleaning agents for machine elements which are based on renewable resource) and postpress finishing (binding process can be specified to enable full recycling of paper content without glue contamination.

The main component of the waste is paper used in the preparation of the printing process. Due to preparatory process for offset printing machine overall paper consumption is by 3.7 times higher for smaller editions in relation to a digital offset printing machine [Kadam S.R., Evans M.E., Rothenberg S. 2009]. The offset printing inks are present with the amount of about 2.7g per one print at smaller editions, and are decreased as the edition increases. The amount of ink that goes to waste is less in digital offset printing than in conventional process.

Shown results are a part of an extensive research of the relevant factors in technological process of digital electrophotography printing, simply defined by the terms of tamping, exposure and developing. In this paper, the influence of changing the voltage of the reverse rollers in relation to reproduction quality, and in relation to the last phase of the lifecycle and properties of recycled fibers are discussed.

So far, the process of recycling is studied a lot. The domain of influential process factors is being researched: the kind and the amount of chemicals used in various process stages, pH values and fiber suspension consistency, temperature of suspension, the time of disintegration, hydrodynamic flotation factors [Thender K., Pugh R.J.,2004; Zhao Y. et al. 2004; Azevedo M.A.D. et al., 1999, Luo Q. 2003]. Machildon and co-authors and Magda have researched the efficiency of the flotation in relation to size, shape and surface characteristics of dispersed particles of printing dye, the volume of the air and the size of the air bubbles [Machildon L. et. al. 1999; Magda J.J. 1999]. In the described issues the most of the studies were dedicated to hydrodynamic factors of recycling process, the influence of chemical and physical system conditions to the process efficiency, while the influence of printing techniques and graphic materials were less studied [Carre B., Magnin L., 2004; Manning A., Fricker A., Thompson R,. 2006; Bolanca Mirkovic I., Bolanca Z., 2005; Schiller A. 2008].

According to gained results the contribution of this paper is determining the influence of the conditions in digital indirect printing based on electrophotography using liquid toner ElectroInk on the quality of the prints and characteristics of recycled fibers, which presents the contribution to determinants for further development within the meaning of sustainability in that area.

2. Experimental

For the printing HP Indigo TurboStream machine based on indirect electrophotography is used. The printing form contains following elements: standard CMYK RGB wedge in the

range from 10-100 screen value, textual positive and negative microelements, standard wedge for production of ICC profile and 3D gamut, and standard ISO illustration for visual control. The prints are made on paper with Soho coat for digital printing, both side coated and uncoated paper for conventional offset printing. The bases of the papers have the same chemical composition of the paper raw materials and the difference is in the coating.

After the calibration of the machine, the printing is followed, with the correction of the voltage of reverse roller, for the next voltages: 0V, -50V, -125V, -200V and -250V.

Figure 1. Indirect electrophotography printing

Tamping of photoconductor is the initial phase of electrophotography process. The next phase is exposing, which is carried out with the laser head which forms four light rays at once. The third stage in the indirect electrophotography is developing. It is conducted in three separate parts: the development with the processing drum, developing with reverse rollers and fixing with squeegee roller. All these aforementioned distinct phases are performed synchronized and they are the subject contented of our project, within which are researches presented in this paper.

This is followed by spectrophotometric analysis made with X-Rite SwatchBook and ColorShop 2,6 application. From ICC profile with the use of MONACO Platinum programe the gamut of prints is established. In the paper the curve of reproduction, ΔE CIE Lab and 2D and 3D gamut of the reproduction are shown.

Figure 2. Workflow

For recycling of the prints alkaline chemical deinking flotation is used. In the process the next chemicals are used: sodium hydroxide 1%, hydrogen peroxide 1%, sodium silicate 2%, DTPA 0,2%, and surface active substance 0,4%. Consistency of the suspension in the phase of disintegration is 10%, while in the flotation phase the consistency is 0,6%. The time of the disintegration is 10 minutes, and the time of the flotation is 8 minutes [Bolanča Mirkovic I., Bolanča Z. 2005].

After the disintegration and flotation laboratory handsheets are made with the use of standard sheet former Rapid- Köthen, according to INGEDE Method 1 and ISO 5269-2[ ISO 5269_2]. On this laboratory handsheets using spectrophotometer Technidyne Color Touch 2 model ISO, before and after flotation brightness [ISO 2470] and effective residual ink concentration are measured [TAPPI T 567 pm-97].

According to the recycling process phases image analysis is made with the use of SpecScan® Apogee System software in accordance with TAPPI standard method [TAPPI T 563 pm-97]

3. Results and discussion

Figure 3 shows the results of image analysis from handsheets made of fibers from different phases of recycling prints obtained by varying the voltage of reverse rollers in indirect electrophotography printing with HP Indigo TurboStream.

a) Sample for the recycling on double sided b) Sample for the recycling on Soho coated paper coated paper

c) Sample for the recycling on uncoated paper

Figure 3. Total dirt spot count versus voltage of reverse rollers and types of the printing substrate

The common characteristic found in results is the reduced of total dirt spot number by variation of voltage reverse rollers from 0 V to -200 V. The results are dependent on the substrate characteristics. In used printing substrates there is no difference in the chemical composition of the raw paper, but in the finishing process in relation to the coating. For double-sided coated paper prints, standard for offset printing, efficiency of the deinking flotation procedure ranges from 10-26% depending on the voltage of reverse rollers in the recycling samples printing process. Slightly higher recycling efficiency (33-47%) is achieved by using the paper with Soho coating which is specially adjusted for indirect electrophotographic printing. The best efficiency of recycling (75-84%) is achieved by using woodless uncoated offset paper.

The coating of paper is a significant factor of the recycling process effectiveness. The fact must be acknowledged that the coating process assists in dispersing the fillers in the coating. In recycling process dispersants are at time surface active and together with alkali can lead to acceptable ink detachment from the coated paper. These species can hydrophilise ink containing agglomerates and hinder flotation efficiency as well as contribute to unwanted foam generation and/or stability.

The coating of paper is a significant factor of the recycling process effectiveness. The fact must be acknowledged that the coating process assists in dispersing the fillers in the coating. In a recycling process at time, dispersants are surface active and together with alkali can lead to acceptable ink detachment from the coated paper. On uncoated paper the adhesion of printing ink to paper depends on paper properties such as surface structure, fibre type, ash content and drying mechanism of the chosen printing process.

These species can hydrophilise ink containing agglomerates and hinder flotation efficiency as well as contribute to unwanted foam generation and stability. On the uncoated paper, the adhesion of printing ink to paper depends on paper properties such as surface structure, fiber type, ash content and drying mechanism of the chosen printing process.

The results show the opposite relationship between the voltage of reverse rollers in indirect electrophotographic printing of samples for recycling and dirt spot area (Fig. 4)

a) Sample for recycling on double sided coated b) Sample for the recycling on Soho paper coated paper

c) Sample for the recycling on uncoated paper

Figure 4. Total dirt spot area versus voltage of reverse rollers and printing substrate types

With increasing of the negative voltage of reverse rollers in the printing, the total dirt spot area on the handsheets made from recycled fibers is increased. In this case the impact of the printing substrate on recycling is also proven. Thus, recycling of prints made with the -250V voltage of reverse rollers, efficiency to reduce dirt spot area of the substrate with a Soho coating is 48%, for the surface with double-sided coating designed for offset printing is 75% and for uncoated woodfree paper is about 90%. Reduce of total dirt spot number with increase of total dirt spot area indicates the increase in the size of individual particles. For better monitoring and interpretation of the deinking flotation mechanism, Figure 5 shows the dirt spot histograms for dirt spot size from 0001-0006 to >=5 mm2.

After flotation Before flotationa) Sample for recycling on double sided coated paper

Before flotation After flotationb) Sample for the recycling on Soho coated paper

After flotation Before flotation

c) Sample for the recycling on uncoated paper

Figure 5. Dirt content histograms for handsheets made from recycled print fibers with the reverse rollers voltage of -200V

The research results show that the larger negative voltage of the reverse roller formed larger flat dirt spot areas, sometimes larger than 5 mm2. Handsheets made from the fibers after the disintegration of prints on uncoated woodfree paper have the greatest number of such spots (141-199) depending on the voltage of the transmission drum, while such spots can be at least expected if the double-sided coated paper prints are used for recycling. On the prints made on woodfree uncoated paper and Soho coated paper the efficiency of recycling process in comparing the total dirt spot area in the total of >= 0.04 mm2, and the total of <0.04 mm2 is almost equal. For prints on uncoated woodfree paper recycling efficiency is around 90%, while for the prints on Soho coated paper efficiency is about 42%. Recycling specifics of prints in the described experimental conditions are significant for prints on the double-sided coated paper for offset printing, referring to the good efficiency of about 82% for the recycling when it comes to spots in the 0.04 - >= 5.000 mm2 for prints made at reverse roller voltage of -200 V and a very inefficient flotation efficiency for spots in the class size of 0.001-0.04 mm2

should be pointed out. Given that this is the efficiency of removing the spots below 1%, this is probably due to fragmentation of large particles and the inability of flotation methods for their removal as well.

Results of image analysis are further tracked and verified through the measurement of effective residual ink concentration and brightness. The highest brightness have handsheets made from recycled fibers prints on Soho coated paper (Brightness102) and the value is slightly increased by increasing the negative voltage values of the transfer roller in printing the recycling samples. Handsheets made from recycled fibers of prints on double-sided coated paper have a slightly lower brightness (brightness around 85) which is almost changed compared to the voltage of recycling samples. Effective residual ink concentration decreases for handsheets after flotation in comparison to those before flotation. Correlation between effective residual ink concentration and brightness is determined.

Given that the purpose of this paper is establishing links between the end of life of the printed product, the quality of prints with the ultimate goal of process optimization in the domain of suitable environment is shown below. As indicators of reproduction quality of a certain stage in the process of indirect electrophotography process, two dimensional and three-dimensional reproduction Gamut are shown.

Print on uncoated paper

Print on double sided coated paper

Print on Soho coated paper

Figure 6. Gamut of print, obtained by using the voltage of reverse roller of 0 V, -125 V and - 250 V on Soho coated paper

Table 1 Volumes of gamut V CIE L * a * b * CCU

Sample Voltage 0 Voltage -125 V Voltage -250 VUncoated paper 382.434 517.113 546.834Double-sided coated paper 551.702 730.174 762.139Soho coated paper 424.572 581.387 618.448

The largest reproduction gamut is achieved at a voltage of the reverse rollers - 250 V on the double-sided coated substrate. For this substrate is specific that the central part of gamut body at a voltage of 0 V has the best reproduction of green and blue tones. Increasing the voltage leads to a smaller reduction in reproduction of blue, and increase in the reproduction of magenta, red, yellow and green. In relation to the research, the minimum reproduction gamut is achieved at uncoated substrate, In the typical cross-sections there is a change in magenta, red, yellow and light green, increasing the voltage from 0V to -125 V. Voltage from -250V causes the change in tones containing a higher percentage of the yellow.

Gamuts obtained by reproduction on Soho coated paper are very similar in characteristic cross- sections to those on uncoated paper. The difference is noticed in light and dark shades, because the ink is better accepted on Soho coated surface.

4. Conclusion

Based on the results of image analysis a reduction in total dirt spot number and increasing the dirt spot area for voltage change of reverse rollers from 0 to -250 V for indirect electrophotography on recycled print samples is proven. This general trend show prints on all used substrates.Flotation deinking efficiency is dependent on the voltage of reverse rollers (0V-250V) in indirect electrophotography printing of samples and on the characteristics of the substrate as follows: double-sided coated paper 10-26%, Soho coated paper 33-47% and uncoated woodfree paper 75-84%.

The largest brightness have handsheets made from recycled fibers of prints on Soho coated paper. The research results in the context of reproduction quality indicators of the observed phase of indirect electrophotography process are as follows: the largest gamut is realized with printing on double-sided coated paper, followed by reproduction gamut on the Soho coated paper and the smallest gamut is achieved with reproduction on uncoated paper.

Given that the indirect electrophotography printing is complex process, with six separate, synchronous phases, the needs and characteristics of graphic material, along with a number of factors in the field of chemical deinking flotation (if the life end of printed products is followed) should be considered. In the further research experimental design will be used and statistical models will be created to obtain information about optimizing in the direction of environmental sustainability in this area.

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