Study of inkjet prints properties.

Sindic, Igor ; Dobric, Eugen ; Bolanca, Mirkovic Ivana 等

Abstract: Ink Jet is the printing technology which uses droplets of ink without any contact with the printing substrate. The droplets are sprayed through the nozzles on the substrate to create the image. In this work the research results of the influence of different Ink Jet printing technologies (thermal one, piezoelectric technique) on the characteristics and the durability of the prints have been presented. The dyes and pigment dispersion have been used and the matt paper as the printing substrate as well. The research results show increased dot values on prints obtained by using the pigment dispersion in relation to the dye with the application of the mentioned substrates. The presentation of the two dimensional and three dimensional model gamut of the observed samples in CIE [L.sup.*][a.sup.*][b.sup.*] colour space confirms the previously mentioned supposition. The durability of prints in the controlled environmental conditions has also been discussed.

Key words: Ink Jet, pigment based ink, dye based ink, mat substrate, screen value, colour gamut, durability

1. Introduction

Ink jet technology is the printing technology using the ink droplets without the contact with the printing form. The ink droplets are sprayed through the nozzles on the substrate to obtain the image. The principle of this technology is the directing of small ink droplets on the printing substrate through the nozzles [Thompson, 2004].

The system of droplets formation includes the application of the controlled pressure on the liquid ink in the container, which enters into the pipes for ink supply and passes through the nozzles in the printing head in which the liquid is transformed into droplets. There are different ways of achieving this effect, depending on technology.

There are two main technologies applied to ink jet printers, continuous ink jet and drop on demand (Bruno, 1999). Continuous ink jet technology include: the single jet, multiple jet and hertz technology. In the drop on demand technology, there are: valve jet, piezoelectric, thermal or bubble jet and hotmelt or phase-change ink jet technology.

In continuous jet technology, a continuous stream of ink is produced by forcing it through a narrow nozzle at a pressure of about 3x10-5Pa. The number and size of the produced droplets depends on the surface tension of the liquid ink, the applied pressure, and the nozzle diameter [Pond, 2000]. Single jets are used for in-line coding and addressing systems. They can print at web speeds of 5 ms-1. Multiple jet technology uses an array of closely spaced nozzles. The image forming droplets are not charged. The unwanted droplets are charged and deflected into gutter. Hertz technology uses extremely small nozzles and produce very small droplets.

Piezoelectric ink jet is one of the simplest ways of droplets formation, electronically on demand. In this case, the piezoelectric effect is used in which small electronic impulses delivered to suitable crystalline materials cause them to expand [Berger, 2003]. Droplets are generated intermittently according to the electronic signals received. In this technology, the usual structure is composed of the array of nozzles, each of which has its piezoelectric crystal. There are different possibilities of geometrical configurations for setting these nozzles based on these materials. The ink coating on the substrate can be influenced exclusively by the increase of the vibration frequency of piezocrystal which contributes to the increase of droplets number on the substrate surface. In this case, there is no need for the deflection system of droplets as in the continuous ink jet. The system is very simple and cheep.

The principle of the thermal or bubble ink jet technology is on warming up a small quantity of ink present in each nozzle, by means of the heating element actuated by the digital data stream [Mao et al. 2003]. The liquid ink boils creating a bubble which forces an equivalent volume of ink droplet trough the nozzle and onto the substrate.

By increasing or shortening the duration of the electrical signal the size of the bubbles is influenced, which results in spraying greater ink quantity onto the substrate surface.

Hot melt or phase-change ink jet technology is extension of the bubble jet principle in that an impulse heater is used to create the droplets on demand. The ink is a hot melt formulation. The ink is in a form of solid sticks of coloured wax, one for each printing colour. The wax is melted into a reservoir where it is kept fluid by the heating element. The hot liquid ink is pumped trough a nozzle and the ink solidifies on the substrate surface.

The difference between the continuous and drop on demand ink jet technology is in the fact that the applied pressure on the reservoir is not continuous, because it is used only when the droplet is needed. The pressure is applied in response to digital electronic signals from the imaging computer.

In ink jet technology a series of inks are used which can be grouped as follows: inks based on water, inks based on solvents, inks in which the phase change appears, UV inks and two component inks. Colorants are made of organic dye, politer dye and pigment inks [Braddock, 2002; Savastano 2002; Kobayashi et al. 2003, Usui et al. 2002].

Inks based on water are usually used in small office ink jet printers. They are suitable for thermal ink jet inks based on solvent are often used in industrial marketing or in coating applications where the print is made on non-porous surface such as plastic, metal or glass. As there is no penetration or absorption, the output is based on quick evaporation of solvent in ink in order to fix it on the surface. Important development in ink jet technology are successful implementation and commercialization of ink based on pigment in coloured printing.

No matter which ink jet technology is used, the fluidity of ink is very important factor. On one hand the inks must be fluid in order not to block the nozzles of the printing head, on the other hand the fluidity must not be too great in order not to cause the spilling the ink on paper causing the weak output resolution. Good ink for ink jet is the one which is fluid enough to pass through the nozzles and which dries slowly enough to prevent solidifying at the nozzle opening.

The development result in this area are the systems based in water with great resistance to water (Desie et al. 2003; Esumi, 2001). Dye molecules are dispersed in a water-based resin system, the solubility of which is pH dependent. This principle of differential solubility applied to dye molecules relies on the presence of functional groups which give the dye molecule solubility in dependence of pH value.

The ink jet printing technique has been presented in the last years as an almost ideal solution for business reports, digital photographs, and pages for website or results of scientific works.

Image quality, durability and permanence are the major attributes of ink jet prints that attract the attention of scientists [Miller, 2002; Miller & Rolly, 2004].

The term impression quality defines as how an image looks immediately after it has been printed, including the aspects of colour accuracy and outer parameters which include the reproduction quality [Kabalnov, 2004]. The durability depends on the physical and mechanical characteristic of the raw materials, the effect of light, heat and humidity. The permanence of impression depends on the chemical resistance of its components and on the influence of external factors.

The aim of this work is to determine the output characteristics of ink jet drop on demand technology using the dye based inks and pigment based inks in relation to the printing substrate and the output stability. Except the scientific contribution, the results of these researches are essential in the application, because just this ink jet technology becomes one of the most spread printing technologies for business and personal applications. Because of its spread application, high demands are set for ink jet output technology in the greatest product spectrum. High output quality with the resistance to outer influences are necessary and just this work can be the contribution in this segment.

2. Experimental

The prints obtained by piezoelectric and thermal ink jet or bubble jet technology was used in the researches.

The following printers were used for sample preparations: Seiko ColorPaiter 64S, Encad NovaJet 1000i i Epson 7000. The devices Seiko ColorPaiter 64S and Epson use piezoelectric technology and Encad NovaJet 1000i uses the thermal one.

The test form is designed so, to contain ISO and ECI templates, as it can be seen in figure 2.

[FIGURE 2 OMITTED]

The part containing the ECI measuring form consists of 336 patches of different colour values combinations of subtractive synthesis. It is intended for the spectrometric analysis. The information quantity obtained by this measurement enables the construction of 2D and 3D gamut in perceptual uniform colour space.

Except that, there is one standard ISO template on the test form intended for the visual control. Seiko ColorPaiter 64S is the printer of newer generation and it uses the determined pigment based ink. Ink based on solvent has approximately the same formulation as follows: propyleneglycolmonomethylester acetate, ethyleneglycolmonobutilester acetate and cyclohexanon. It is printed with six print heads with CMYK +[C.sub.L] + [M.sub.L].

Encad NovaJet 1000i printer uses pigment based ink, and prints with six print heads with CMYK + [C.sub.L] + [M.sub.L]. In this case it is aqueous ink jet ink.

Epson 7000 uses dye based inks, and prints with six piezoelectric ink jet print heads. Instrumental analysis comprises measurements by spectrophotometer, static data processing obtained by measuring each of 336 patches. Except that, the conversions of CIEXYZ into CIE [L.sup.*][a.sup.*][b.sup.*] is made in order to enable the presentation of gamut sample in three dimensional unified colour space.

Part of the sample in the chamber was under the influence of ozone in the concentration of 3,5 ppm, at temperature of 23[degrees]C and relative humidity of 50%. From the results before and after the exposition of sample to ozone activity [DELTA].E is determined based on the differences of [L.sup.*][a.sup.*][b.sup.*] values.

3. Results and discussion

Some of the ways which enable the monitoring of quality reproduction is the relation of the inking density of prints and the screen value of the original by the screen value of the print and the original and by determining the relative printing contrast. In figure 3, the dependences of the screen value of the original and the screen values of the print for previously described systems have been presented.

[FIGURE 3 OMITTED]

It is visible from the result presentation that the best print quality can be obtained by Epson 7000 printer and the worst one by Encad NovaJet 1000i in the frame of previously mentioned experimental conditions. The print obtained by Epson printer has the smallest dot gain and it is nearest to the ideal one. The relation of the screen values of that print in the whole area is similar to the one which is characteristic for offset printing, which is then the sign of good reproduction. In the area of higher screen values (97-100%) there probably filling appears which is the characteristic of offset printing. For prints obtained by the devices Seiko and Encad higher dot gain is obtained. When for example the corrections in prepress were used for the device Encad, the qualitative reproduction in the area of low screen values could not be obtained in the frame of the presented experimental conditions.

In other words, lower quality of print is connected to ink jet technologies piezoelectric and thermal ones which use the pigment based ink in relation to the dye based ink.

Pigment based inks consist of small pigment particles dispersed in liquid phase. They are insoluble in water and there is a small interaction with the substrate coatings. On micro porous coating systems the pigment particles partially are better absorbed into the surface pores of the substrate. At modified pigments the charged groups are chemically attached to the surface of the pigment particles. This gives the possibility of dispersion in water and the interactions with the medium. Further modifications of the pigment surface include the polymers with hydrophilic/hydrophobic groups which encapsulate the pigment.

In order to present visually the differences and to determine the correlations among the particular gamut samples the comparative presentations of gamut are given in CIE [L.sup.*][a.sup.*][b.sup.*] colour space with regard to the [a.sup.*][b.sup.*] coordinates, for lightness [L.sup.*]50% (figure 4a). However, in order to obtain the more complete picture the three dimensional presentations are given (figure 4b).

[FIGURE 4 OMITTED]

The research results show that the greatest gamut surface is with Epson printer in relation to Encad and Seiko. These results point as well at the differences in relation to the used pigment and dye based inks. Greater gamut is obtained in the case of dye based ink. Except that it is visible that the print obtained by Encad printer which uses pigment ink on water base has greater gamut surface in relation to the print obtained by Seiko printer which uses pigment ink on solvent base. Pigment dispersions based on solvent dry quicker than those based on water and the pigment particles stay fixed on the application places.

Because except the print quality its stability is very important, the ozone stability was researched for the presented systems and the results are presented in figure 5.

[FIGURE 5 OMITTED]

The comparison of ozone stability of the print with dye and pigment inks in the frame of previously mentioned experimental conditions shows better durability of the pigment based inks in relation to dye. Generally speaking, the affinity to paper substrate is characteristic for dye which originates from the hydrogen bond Van der Waals and the dipole interaction on the substrate surface and d...d interaction among the dye molecules by forming the dye aggregates within the substrate.

4. Conclusion

On the basis of the research results, the following could be concluded:

--the greatest dot gain has the print obtained by thermal ink jet technology and pigment dispersion based on water in the described experimental conditions

--somewhat better results are obtained by using the piezoelectric ink jet technology and pigment ink based on solvent

--the smallest dot gain has the print obtained by using the piezoelectric technology and dye

--greater gamut is obtained in the case of dye based ink.

--print obtained by pigment ink on water base has greater gamut surface in relation to the print which uses pigment ink on solvent base

--ozone stability of print with dye and pigment inks have reverse trend in relation to the gamut surface, and the durability of the pigment based inks is better in relation to dye.

Except the contribution to explanation of screen values, gamut size and the durability of different Ink Jet prints in relation to the principles of the Ink Jet technology, characteristics of the materials and the interactions on the phase surfaces in the scientific sense, research results are interesting in the sense of application. The obtained results justify further researches and by using the experimental design and statistic methods the domain of print durability in relation to the new materials will specially be treated.

5. References

Thompson, B.; (2004). Printing Materials, Science and Technology, Pira International, ISBN 185802150, Surrey

Bruno, M.; (1999). Printing in a Digital world, Graphic Arts Technical Foundation, Rochester Pond, S. F.; (2000). Inkjet Technology and Product Development Strategie, Torrey Pines Research

Berger, S.S.; (2003). Development of an Improved Model for Piezoelectric Driven Ink Jets, Proceedings of International Conference on Digital Printing Technologies, Ioannidis, A. (Ed.) 323-327, ISBN 0-89208-247-X New Orleans, Lousiana, October, 2003. The Society for Imaging Science and Technology, Springfield

Mao C. Y.; Yang J. C.; Wu C.L.; Chiu C.L.; & Chenc.J.; (2003). Application of Micro-Fuel Injection System by Thermal Bubble Inkjet Technology, Proceedings of International Conference on Digital Printing Technologies, Ioannidis, A. (Ed.) 338-342, ISBN 0-89208-247-X New Orleans, Lousiana, October, 2003. The Society for Imaging Science and Technology, Springfield

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Usui M.; Hayashi H,; Hara K.; & Kitahara T.; (2002). The Development of Pigment Ink for Plain Paper, Proceedings of International Conference on Digital Printing Technologies, Ioannidis, A. (Ed.) 369- 373, San Diego, California, October, 2002. The Society for Imaging Science and Technology, Springfield

Desie, G.; Pascual, O.; Pataki, T; de Almeida, P.; Mertens, P.; Allaman, S.;Soucemarianadin A.; ( 2003). Imbibition of Dye and Pigment -based Aqueous Inks into Porous Substrates, Proceedings of International Conference on Digital Printing Technologies, Ioannidis, A. (Ed.), ISBN 0-89208-247-X New Orleans, Lousiana, October, 2003. The Society for Imaging Science and Technology, Springfield

Esumi K.; (2001) Interaction between surfactants and Particles: Dispersion, Surface Modifications, and Adsolubisation, Journal of Colloid and Interface Science, 241, 1-17 Miller N., HP Ink Jet Photo Prints, http:// www.Hp.com/ product/ img/lightfastness. pdf 2002

Miller N., Rolly L., HP Ink Jet Technology, Designing Inks for photo printing, http://www.hp.com/hpinfo/newsroom/press-kits/2004/pma/fs-ink- tech.pdf 2004 Kabalnov J.; Dupuy C.; Gondek J.; Lee J.H.; Bhaskar R.; Berfanger D.; (2004).

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Authors' data: BSc. Sindic I.[gor] *, BSc. Dobric E.[ugen] *, MSc. Bolanca Mirkovic I.[vana]**, PhD. Prof. Bolanca Z.[denka] **, Europapress Holding *, Faculty of Graphic Arts, University of Zagreb **, Croatia, igors@metro.com.hr , e_dobric@yahoo.com, grfibolanca@yahoo.com, zbolanca@yahoo.com

This Publication has to be referred as: Sindic, I.; Dobric, E.; Bolanca Mirkovic, I. & Bolanca, Z. (2006). Study of Inkjet Prints Properties, Chapter 45 in DAAAM International Scientific Book 2006, B. Katalinic (Ed.), Published by DAAAM International, ISBN 3-901509-47-X, ISSN 1726-9687, Vienna, Austria

DOI: 10.2507/daaam.scibook.2006.45