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Use of an on-press acoustic sensor to monitor coldset offset printing of newspaper
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 3, 323-327 p.Article in journal (Refereed) Published
Abstract [en]

A newly developed acoustic emission on-line monitoring technique (Voltaire J. et al. 2004) provides insight into the dynamic interactions occurring between paper, ink-fount emulsion, and rubber blanket in offset printing. The technique uses a microphone placed in the vicinity of the exit of the paper-blanket nip. Through digital signal processing of the measured sound pressure it is possible to distinguish between machinery sound and that caused by the tacky ink splitting. In this study, printing of coldset inks on newsprint was carried out on a two-unit sheet-fed offset press. In line with earlier results, an increase in print density was found to correspond to increased sound pressure at the nip exit for higher frequencies (above 15 kHz). Depending on the status of the press at start-up, i.e. ink and fount condition and temperature, an increase or decrease towards a more stable value of the sound pressure was detected during the early running of the press, and in both cases this correlated well with the evolution in print density to its target value. This and related results can prove useful for monitoring, and adjusting by feedback, the initial press equilibration before the print-ready stage. Moreover, the acoustic emission can directly reveal destabilised conditions at longer running times that by other means would not be detected until later.

Place, publisher, year, edition, pages
2006. Vol. 21, no 3, 323-327 p.
Keyword [en]
coldset printing, cavitation, film splitting, optical density, acoustic emission
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5439ISI: 000241531500006OAI: oai:DiVA.org:kth-5439DiVA: diva2:9803
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Ink Film Splitting Acoustics in Offset Printing
Open this publication in new window or tab >>Ink Film Splitting Acoustics in Offset Printing
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis claims a relationship between the film splitting sound emission from the printing press nip and the dynamic interaction occurring there between ink, fountain solution and substrate in offset lithography. The film splitting sound derives from the cavitation formed by the pressure drop in the second half of the print nip flow passage. As the ink film is strained, the cavities expand and eventually implode into breaking filaments at the nip exit, while emitting a partly audible, broadband, high frequency, noisy sound. A free-field microphone, A/D-converter and laptop computer were used to record pressure signals in the frequency range of 10 Hz to 50 kHz emitted by a variety of printing instruments and presses for a range of offset ink and paper types. After signal acquisition and filtering two signal averages of power and frequency were estimated.

This average power increased with increasing loads of sheet-fed offset ink on an ink distributor, in accordance with a mass-conservation model developed. The behaviour of average frequency and power over different ink load ranges indicated transitions between different flow regimes. A glossy fine-coated paper gave higher average power than a corresponding matte paper during printing with such inks on a laboratory device, possibly due to an air sealing effect. The sound from tack measurements with the Deltack instrument during setting of heat-set offset inks printed on MWC papers showed a relation between the measured tack rise and average power, reflecting changes in splitting mechanism during the course of setting. With the Hydroscope instrument the interaction between these heat-set inks and fountain solution was studied, with the measured tack and sound emission displaying a clear, but non-linear, correlation. A heat-set offset pilot trial showed that the acoustic response from the printing nip sensitively and systematically detected changes in (LWC) paper type, optical density, ink-fount balance, and press stability. Pilot trials of cold-set offset inks on newsprint by sheet-fed presses indicated a strong correlation between evolution in average power, optical density and fountain solution consumption during the first thousand sheets normally needed for stabilisation.

Acoustic measurements of ink film splitting have, aside from the laboratory studies performed by one Japanese group, previously received little attention, with the current study showing that a great deal of information useful to the printer can be accessed from this sound emission. Although the detailed mechanisms for ink film splitting have to be further studied and supported by mathematical simulation, the sensitivity of the acoustic method recommends its implementation for monitoring and control of offset printing.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. vii, 54 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0604
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-3869 (URN)91-7178-261-3 (ISBN)
Public defence
2006-03-17, Sal E2, Lindstedtsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2010-09-28Bibliographically approved

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