Influence of the plastificated digital printed sheets on the graphic products quality.

Babic, Darko ; Jurecic, Denis ; Tomas, Ante 等

Abstract: The digital printing found the application in printing smaller runs with the aim to get cheaper product. Today's aspects of application and development of the digital printing are directed primarily to the printing quality. Surface finishing of printed products by plastific coating is used on different products (show cards, leaflets, invitation cards ...) or parts of products such as (cover, book jacket, cover for boxes ...) and the finishing processes which are used are cutting, gluing, bending, creasing, back rounding etc. As different from papers printed with the classical printing processes, paper printed with the digital printing techniques and additionally coated with plastic implement the disadvantages as the problem of interactions visible only in the finishing process which results in non acceptance (ugliness) of the final printed products(most often hard cover books). By investigation of the chosen parameters of the digital printing process and finishing of the printed surface by plastic coating, the interventions on the standardized processes are defined.

Key words: digital printing, sheet, coating with plastic, finishing

1. Introduction

The digital printing found the application in printing smaller runs with the aim to get cheaper product. Today's aspects of application and development of the digital printing are directed primarily to the printing quality. Surface finishing of printed products by plastific coating is used on different products (show cards, leaflets, invitation cards) or parts of products such as (cover, book jacket, cover for boxes) and the finishing processes which are used are cutting, gluing, bending, creasing, back rounding etc. As different from papers printed with the classical printing processes, paper printed with the digital printing techniques and additionally coated with plastic implement the disadvantages as the problem of interactions visible only in the finishing process which results in non acceptance (ugliness) of the final printed products(most often hard cover books). By investigation of the chosen parameters of the digital printing process and finsihing of the printed surface by plastic coating, the interventions on the standarized processes are defined. The name "digital printing" originates from the fact that the computer gives the basic support in this process. Digital print-ing is the printing techniques in which the pressure is not essen-tial as in the convetional printing techniques where the printing ink is transferred on the printing forms by means of pressure. It can be said for the conventional (basic) printing techniques that they belong to the type of multiplying of text and images with the common name "Impact Printing". Because in the alternative printing techniques the pressure is not essential, they are called "Non Impact Printing" or shortened form NIP. There are several different processe of digital printing. Electro-photography is the most often used process. It is used for laser printers and in production office copies by means of the proofs on single colour or multi colour digital printing machines. Elec-trography (ionography) is most often used in plotters, and the variant ionography in so called intelligent printers. Plotters work in the principle with the coated papers while ionographic systems work with normally used papers. Thermotransfer process found the broad application in the area of facsimile transfer. Thermotransfer printers with the printing ink which melts by heat are used in multicolour reproduction and in the most demanding phase for experimental digital printing. Ink-jet works on the principle of spraying the fine droplets ink on the absorbend paper. The spreying is perfromed by special nozzles aided by the computer. The system works without the mechanical contact and without the printing form. Its application is manifold from the common outpu on A4 from, till the printing of huge posters, giantography, till the elaboration of the secti-ons of scenery for theatres. Rarely used NIP processes are magnetography, photoelectrophoresis and eceltrosensitive proc-esses. In this work, the sheet of papers printed on E-Print 1000+ machine were used for investigation (figure 1). The total pre-press is done "on-lina" by means of computer. This excludes the usage of film, as the mediator in transferring information on the printing form. Printing form is not necessary at all and num-eorus operations of its preparation, layout and justification are omitted.

[FIGURE 1 OMITTED]

Plate cylinder mantle serves as the information carrier, that is as the printing form. It is made of the photo conductive organica material on which the laser head writes the digitalized elements of the image with differentiated properties of the sur-face. They can be conditionally called printing elements and non printing elements. There are no mechanical destroying or chemical changes on the mantle of the plate cylinder, only the distribution of the electric charge which will bound the polari-zed molecules of the liquid ink by electrostatic forces. The image on the mantle of the plate cylinder is generated again with each its revolution. This gives numerous possibilities of colour change as well as other interventions during the printing process. With the printing unit the inking system is added consising of six containers which are connected by pressure pipeline system up to the nozzles aided by the computer. Dur-ing each revolution of the plate cylinder, each nozzle spreys its ink for each separation. After the electrostatic ink applying, the image separation which is now visible is transferred by adhe-sion from the mantle onto the rubber blanket of the offset cylinder.

2. Experimental

The device for thermal plastic coating of sheets, on which the plasticized samples were prepared, consists of automatic feeder, calender machine, plastic coating device, separator and delivery table. The prepared sheet are transported by vacuum head on the table with the transport belt for carrying the sheets from the feeder to the calender machine (chromium roller with thick walls with polished surface with the forced circulation of dia-thermic oil) which is heated to the temperature of 105-112 [degrees]C. Over the calender machine there is a coil of thermal foil which is used for sheet coating. In the described principle of plastic coating it is possible to regulate the speed of flow, the tension of foil and the temperature of the calender machine. By plastic coating of the papers printed in the digital printing, it was seen that the set problem of finishing processes on the mentioned plastic coated sheets was not solved by the mentioned regula-tions. The investigation was done on three samples of differnet grammage coated with glossy plastic by means of the described method under standard conditions. The finishing processes for finding and testing the values of the supposed deformations are cutting of sheets and creaing of cover in the form of hard cover. The investigation se interaction of time, that is of period, after the printing of sheets by digital printing techniques for 8, 32, 56 and 80 hours, as the time for drying or surface stablization befor the plastic cotaing process.

[FIGURE 2 OMITTED]

It is visible from the table that the stabilization time of the sheet surface printed with the digital printing techniques as well as the possibility of sheet drying separately is very important for decreasing and removing the deformations Sheets (covers) were cut on high speed guillotine POLAR, the cover was produced by hand and after setting the book block the product was creased on the machine under the roller temperature of 40[degrees]C.

2.1. Classification of paper coated

Table 2. gives an overview of the classification of paper coated on both sides for sheet fed offset printing, for web offset and rotogravure printing (the terms correspond generally to common technical everyday language; official or standardized definitions are not available). The paper thickness can be derived approximately from the paper grammage normally given: 100 g/[m.sup.2] corresponds approximately to 0.1 mm thickness.

3. Results and discussion

The functions of the dependence of the defrometions during cutting in relation to the function of time for plastic coating after printing are visible in the table. As sample, the sheets of fine art papers were observed. They had the grammage of 200, 250 and 300 g/m2, they were printed with multicolours in several tones in digital printing technique, on one side, and they were thermally plastic coated with the glossy plastic. In the table, there are deformations in mm in the sense of drawing the print with plastic coating foil from the edges of the printing substrate for the cutting in the direction of plastic and cross direction in the chosen periods from the time of printing. It is visible from the table that longer time was needed for stabilization the printed surface in the sense of increasing the interaction bond between the print (pigment and mineral oil) and the printing substrate.

4. Conclusions

The aheets of paper printed in the digital printing techniques after plastic coating dhow certain weaknes whcih is visible in the finishing processes of materila separation (cutting, punching) and deformations of the form (bending, back rounding). Pigment and mineral oil are burden for the paper surface which is observed as the interlayer between the paper and the plastic foil. During the thermal processing of such paper, by plastic coating of the glossy or matt plastic, the interlayer is glued on plastic because of the reaction of the thermal leading the inter-layer and its separating from the printing substrate (paper). The printing substrate is glued into the plastic foil, the primary contact with paper weakens and during cutting of such three-layer material, it separates together with plastic from the printing substrate. Mineral oil which is contained in a certain percentage with pigment on the printing substrate dries longer time. Its thermal sensitivity is decreased in longer drying period and it decreases the interaction of the whole print with the plastic foil. In finishing processes it implements the stability of the three-layer component.

5. References

Hesse, F., Tenzer H. J.: Grundlagen der Papierveearbeitung, VEB Fachbuchverlag, Leipzig, 1966.

Kipphan, H.: Handbook of Printing Media, Springer, Berlin, 2001, 962-964

Kipphan, H.: Status and Trends in Digital Multicolor Printing, Conference on Digital Printing Springfield (VA) 1994. Technologies (Proceedings). The Society for Imaging Science and Technology (IS&T), Springfield (VA) 1997, pp. 11-19.

Stevenson, D.: Hendbook of Printing Processes, GATF Pittsburg, 1994

Stricevic, M.: Suvremena ambalaza 1, Skolska knjiga, Zagreb, 1981, 102-105

Stricevic, M.: Suvremena ambalaza 2, Skolska knjiga, Zagreb, 1983, 102-105

This Publication has to be referred as: Babic, D.; Jurecic, D. & Tomas, A. (2006). Influence of the Plastificated Digital Printed Sheets on the Graphic Products Quality, Chapter 01 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.2006.01

Authors' data: Assoc. Prof. Dr. Babic D.[arko] *, M. Sc. Jurecic D.[enis] *, B.Sc. Tomas A.[nte] **, * Faculty of Graphic Arts, University of Zagreb, Getaldiceva 2, 10000 Zagreb, Croatia, ** Slobodna Dalmacija d.d., Split, Croatia, babic@grf.hr, denis@grf.hr, ante.tomas@slobodnadalmacija.hr

Table 1. Characteristics of the device TECNOMAC/TC 500

TECNOMAC/TC 500

Device for plastic coating of paper

Characteristics of the device Unit Size

Minimal paper size mm 200 x 200

Maximal paper size mm 520 x 720

Min-maximal paper weight g/[m.sup.2] 80-350

Power supply -- 380V - 3F + N

Installed force Kw 15

Air consumption (6 bar) [dm.sup.3]/min 300

Max. speed (speed for plastic m/min 35
coating depend on the paper kind
and the used foil kind)

Table 2. Papers coated on both sides which are suitable for sheet-fed,
web-fed offset and web gravure printing--general properties and
application

Designation General quality characteristics and application

Cast-coated paper Paper with a mirror or glossy finish surface
 and large volume. Mainly white on one side and
 colored. Used especially for labels, envelopes,
 and high-quality folding boxes. Grammage 70-400
 g/[m.sup.2].

Cast-coated paper Paper with a mirror or glossy finish surface
 and large volume. Mainly white on one side and
 colored. Used especially for labels, envelopes,
 and high-quality folding boxes. Grammage 70-400
 g/[m.sup.2].

Original coated art Best quality coated paper. Thick coating layer
paper gives high degree of uniformity. Excellent
 printability and pressroom runnability.

Specially coated Coated paper for demanding and high-quality
illustration printing printing jobs. Glossy, half matte, or matte on
paper both sides. Quality is very consistent. Best
 printability and pressroom runnability.

Standard illustration Good quality paper coated on both sides.
printing paper

Ordinary illustration Paper coated on both sides for simple printing
printing paper work, limited quality with regard to gloss and
 evenness of the print image.

MWC/HWC paper Medium Weight Coated Paper/Heavy Weight Coated
 Paper Paper containing wood with grammage range
 of 80-130 g/[m.sup.2].

LWC paper Light Weight Coated Paper. Paper widely used
 for mass print runs in web offset printing. LWC
 paper range goes up to 72 g/[m.sup.2].

LLWC/ULWC paper Light Light Weight Coated Paper Ultra Low
 Weight Coated Paper Ultralight coated paper
 below 45 g/[m.sup.2], used in particular in
 web offset printing and gravure for printing
 international magazines and mail-order
 catalogs.

FC paper Film Coated Papers. Paper which is coated or
 pigmented on both sides in a super size press
 (film press) within the paper machine with a
 coating volume metered on rollers, thus
 avoiding swamping.

Table 3. Result presentation of the investigated paper samples
Kunstdruck 200 g/[m.sup.2]

Time
interval (h) 8 16 24 32 40 48 72

Cut in the 1,75 1,75 1,5 1 0,75 0,5 0,25
direction
of plastic
coating

Cot vertical 2,0 2,0 1,75 1,75 1,5 1,25 0,5
to the
direction
of plastic
coating

Table 4. Result presentation of the investigated paper samples
Kunstdruck 250 g/[m.sup.2]

Time
interval (h) 8 16 24 32 40 48 72

Cut in the 2,0 1,75 1,5 1 0,75 0,5 0
direction
of plastic
coating

Cot vertical 2,5 2,5 2,0 1,75 1,5 1,25 0,5
to the
direction
of plastic
coating

Table 5. Result presentation of the investigated paper samples
Kunstdruck 300 g/[m.sup.2 ]

Time
interval (h) 8 16 24 32 40 48 72

Cut in the 2,25 1,75 1,5 1 0,75 0,5 0,25
direction
of plastic
coating

Cot vertical 2,5 2,25 2,0 2,0 1,5 1,0 0,25
to the
direction
of plastic
coating