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Ink Film Splitting Acoustics in Offset Printing
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
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: urn:nbn:se:kth:diva-3869ISBN: 91-7178-261-3 (print)OAI: oai:DiVA.org:kth-3869DiVA: diva2:9805
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
List of papers
1. Acoustic investigation of cavitation noise from offset ink film splitting
Open this publication in new window or tab >>Acoustic investigation of cavitation noise from offset ink film splitting
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2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 3, 314-322 p.Article in journal (Refereed) Published
Abstract [en]

The acoustic signal from the nip during film splitting between inked rollers and on ink transfer to paper was investigated on laboratory scale, using two sheet-fed offset inks (based on mineral oil and vegetable oil) and two coated fine papers (glossy and matte). Film splitting emits a broad noise-like acoustic spectrum in the range 5-50 kHz, from which the two simplest measures of average power and average frequency were derived. Using these two measures, four characteristic regimes of film splitting on the rollers could be distinguished as a function of ink load. Moreover, for intermediate amounts, average power was found to be accurately predicted by a simplistic model of sound produced by cavity expansion due to the under-pressure in the nip exit, thus providing a physical interpretation of the nip noise emission. For printing, the average power was higher for the glossy paper than the matte, presumably due to a more efficient sealing of the nip, or onset of ink setting. The vegetable oil-based ink gave higher power than its mineral oil counterpart. These results were found to be consistent with longer-time measurements of tack evolution from the Ink Surface Interaction Tester. This correlation and the verified theory thus provide support to practical applications of acoustic emission as an on-press monitoring tool.

Keyword
film splitting, printing, ink tack, cavitation noise
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5436 (URN)000241531500005 ()
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
2. Acoustic emission and tack of heat-set inks during setting on MWCpapers and fountain solution emulsification
Open this publication in new window or tab >>Acoustic emission and tack of heat-set inks during setting on MWCpapers and fountain solution emulsification
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 4, 432-440 p.Article in journal (Refereed) Published
Abstract [en]

To investigate the relationship between ink film splitting noise and ink tack, two tack-measuring devices were monitored by a microphone. The first of these was the Deltack(R) (Prufbau), to study tack build on paper, and the second was the Hydroscope(R) (Testprint), measuring ink tack change with fountain solution level. Three medium weight coated (MWC) papers and two heat-set inks of differing tack and emulsion capacity were analysed. It was concluded that acoustic average power is a consequence of cavitation and flow mechanisms, and not necessarily linked linearly to tack. The Hydroscope measurements usually gave decreasing tack, average power and average frequency with increasing fountain solution concentration; however fountain solution droplets can also act as an extra sound source. A relation between average frequency and droplet size was postulated. The results demonstrate the sensitivity of the acoustic method and support its implementation for further studies in the field.

Keyword
film splitting, printing, ink tack, cavitation noise, fountain solution, water-in-ink emulsion
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5437 (URN)000252298100005 ()
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
3. Acoustic characterisation of film splitting in a HSWO printing nip
Open this publication in new window or tab >>Acoustic characterisation of film splitting in a HSWO printing nip
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2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 4, 424-431 p.Article in journal (Refereed) Published
Abstract [en]

An acoustic technique for investigation of ink film splitting was further developed and applied to monitor printing of light weight coated (LWC) papers on a heat-set web offset (HSWO) press. The acoustic average power from the nip exit was found to decrease with decreasing ink amount and ink tack and increasing fountain solution amount. When printing on the lower side, the average power increased with surface pore area of the LWC papers, presumably connected to tack build during the extended contact time with the blanket. The method is non-destructive, statistical, and readily automatable, with applications both as on-line sensor and research tool for probing dynamic interactions during ink transfer.

Keyword
film splitting, ink, tack, HSWO, fountain solution, LWC, acoustic emission
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5438 (URN)000252298100004 ()
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
4. Use of an on-press acoustic sensor to monitor coldset offset printing of newspaper
Open this publication in new window or tab >>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.

Keyword
coldset printing, cavitation, film splitting, optical density, acoustic emission
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5439 (URN)000241531500006 ()
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
5. New technique for monitoring ink-water balance on an offset press
Open this publication in new window or tab >>New technique for monitoring ink-water balance on an offset press
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2007 (English)In: Appita journal, ISSN 1038-6807, Vol. 60, no 2, 120-128 p.Article in journal (Refereed) Published
Abstract [en]

An acoustic technique, with microphone placed near the print nip exit on a. sheet-fed offset press during trial printing of newsprint, was used to provide information relating to splitting of the ink-fountain solution film. The average acoustic power increased with tack of the ink used and with target optical density. Further, average power decreased during each run, reasonably strongly correlated to increase in fountain solution consumption. This indicates that average power is primarily sensitive to instantaneous tack of the ink-fountain solution film, and can be used to monitor tack and indirectly infer ink-water balance in the nip. Laboratory experiments were also performed using the Hydroscope instrument to simultaneously measure tack and average acoustic power of the splitting of inked rollers during fountain solution titration and evaporation. While these two measured parameters were not directly correlated over all conditions of emulsification, both decreased in tandem over intermediate amounts of fountain solution.

Keyword
offset printing, ink tack, ink-water, balance, fountain solution, newsprint, linting, acoustic emission, lithography
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5440 (URN)000247921900006 ()
Note
Uppdaterad från submitted till published: 20100928. QC 20100928Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved

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