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Engström, Gunnar
Publications (10 of 35) Show all publications
Engström, G. (2016). Causes of back-trap mottle in lithographic offset prints on coated papers. TAPPI Journal, 15(2), 91-101
Open this publication in new window or tab >>Causes of back-trap mottle in lithographic offset prints on coated papers
2016 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 15, no 2, p. 91-101Article in journal (Refereed) Published
Abstract [en]

Back-trap mottle is a common and serious print quality problem in lithographic offset printing of coated papers. It is caused by nonuniform ink retransfer from an already printed surface when it passes through a subsequent printing nip with the print in contact with the rubber blanket in that nip. A nonuniform surface porosity gives rise to mottle. A key parameter in mottling contexts is the coating mass distribution, which must be uniform. Good relationships between mottle and mass distribution have also been reported; the mottle pattern coincides with that of the coating mass distribution. High blade pressures, compressible base papers, and high water pick-up between application and metering, which plasticizes the paper, yield uniform mass distributions, but these parameters might have a detrimental effect on the runnability in blade coating in terms of web breaks. The general opinion has been that nonuniform surface porosity is caused by binder migration and enrichment of binder in the coating surface, more in the high coat weight areas and less in the low coat weight areas. Recent research has suggested that a more probable mechanism is depletion of binder in the coating surface. Nonuniform shrinkage of the pigment matrix (filter cake) formed during the consolidation between the first critical concentration (FCC) and the second critical concentration (SCC) is another possible mechanism. Relevant relaxation times for latex and the time scales for consolidation show that the high coat weight areas shrink more than the low coat weight areas in the coating layer. A recent pilot-scale experiment has shown that the drying strategy did not affect the differences in shrinkage between high and low coat weight areas. The drying strategy has a pronounced impact on mottle. A high evaporation rate at the beginning of the evaporation results in less mottle than a low evaporation rate. The least mottle is obtained if the drying is performed with a gap in the course of evaporation between the FCC and the SCC.

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-41680 (URN)000371621000004 ()
Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2019-06-10Bibliographically approved
Ragnarsson, M., Engström, G. & Järnström, L. (2013). Porosity Variations in Coating Layers - Impact on Back-trap Mottle. Nordic Pulp & Paper Research Journal, 28(2), 257-263
Open this publication in new window or tab >>Porosity Variations in Coating Layers - Impact on Back-trap Mottle
2013 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 2, p. 257-263Article in journal (Other academic) Published
Abstract [en]

A pilot coating trial was performed to study 1) whether the drying strategy introduces porosity variations in the coating layer and 2) whether porosity variations caused by the subsequent supercalendering are linked to back-trap mottle in offset prints. The porosity variations and the mean porosity were indirectly measured using a burn-out test. Coating colours were compared with three different binder systems 1) carboxy methyl cellulose (CMC)/SB-latex, 2) dextrin/SB-latex and 3) oxidized starch/SB-latex. The results showed that neither the mean porosity nor the porosity variations were affected by the drying strategies studied. During calendering the coating with the CMC/SB-latex binder system was compressed the most, but the porosity variations were nevertheless small. Both the compression and the porosity variations were influenced by the drying strategy, which shows that the strategy had an impact on the mechanical properties of the dry coating layer. With CMC/SB-latex and dextrin/SB-latex, the mottle increased when the porosity variations introduced by the calendering increased. In the case of the oxidized starch/SB-latex, the opposite was true. It was concluded that with CMC/SB-latex and dextrin/SB-latex, print mottle is caused by calendering and with oxidized starch/SB-latex by non-uniformities introduced during dewatering and drying, possibly binder migration.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2013
Keywords
coated papers, porosity variations, binders, back trap mottle
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-14407 (URN)000321291900010 ()
Note

Part of the thesis: Variations Related to Print Mottle in Starch-Containing Paper Coatings, http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-14409

Available from: 2012-07-30 Created: 2012-07-30 Last updated: 2019-07-11Bibliographically approved
Ragnarsson, M., Engström, G. & Järnström, L. (2008). Effects of the Partial Replacement of SB latex with Dextrin Starch on the Thickness Distribution of Coating Layers. In: Tappi 2008 Advanced Coatings Fundementals Symposium Proceedings: . Paper presented at Tappi Advanced Coating Fundamentals, Montreal, Canada (pp. 154-163). Atlanta: Tappi press
Open this publication in new window or tab >>Effects of the Partial Replacement of SB latex with Dextrin Starch on the Thickness Distribution of Coating Layers
2008 (English)In: Tappi 2008 Advanced Coatings Fundementals Symposium Proceedings, Atlanta: Tappi press , 2008, p. 154-163Conference paper, Published paper (Refereed)
Abstract [en]

A pilot coating trial has been carried out where the synthetic binder in the coating colour was partially replaced with dextrin starch. The coating thickness and the coating thickness distribution were investigated by means of burnout tests and mercury porosity measurements. The coating thickness distribution is governed by the surface profile of the base paper underneath the blade; this surface profile is controlled by the compressibility of the base paper and the blade pressure. Dewatering of the coating colours plasticises the paper and increases its compressibility; a linear relationship between dewatering and the standard deviation in the coating thickness was found for a given blade pressure. The characterization of the coating layers showed a small but measurable increase in the thickness variation for increasing starch content, which was caused by the higher water retention of the starch colours. The surface profile of the uncoated and coated paper was investigated with an optical profilometer. The data from those measurements and the coating thickness distribution investigation were used analytically to calculate the roughness change of the base paper during coating. The roughness change was found to be inversely proportional to the original base paper roughness, indicating that the rougher base paper was more compressible.

Place, publisher, year, edition, pages
Atlanta: Tappi press, 2008
Keywords
mottling, mass distribution, coating thickness, blade coating, starch, dewatering, surface profiling, compressibility
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-14403 (URN)1-59510-174-8 (ISBN)
Conference
Tappi Advanced Coating Fundamentals, Montreal, Canada
Funder
Swedish Research Council
Note

Part of the thesis: Variations Related to Print Mottle in Starch-Containing Paper Coatings, http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-14409

Available from: 2012-07-30 Created: 2012-07-30 Last updated: 2019-07-11Bibliographically approved
Kjellgren, H. & Engström, G. (2008). Influence of paper structure on barrier properties of starch-coated greaseproof paper. Nordic Pulp & Paper Research Journal, 23(1), 87-90
Open this publication in new window or tab >>Influence of paper structure on barrier properties of starch-coated greaseproof paper
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 87-90Article in journal (Refereed) Published
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-1932 (URN)10.3183/NPPRJ-2008-23-01-p087-090 (DOI)
Available from: 2007-11-09 Created: 2007-11-09 Last updated: 2017-12-07Bibliographically approved
Kjellgren, H. & Engström, G. (2008). Oxygen permeability of polyethylene-extrusion-coated greaseproof paper. Nordic Pulp & Paper Research Journal, 23(3), 272-276
Open this publication in new window or tab >>Oxygen permeability of polyethylene-extrusion-coated greaseproof paper
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 3, p. 272-276Article in journal (Refereed) Published
Abstract [en]

Polyethylene-extrusion-coated greaseproof paper exhibited significantly lower oxygen permeability than predicted from the oxygen permeability of polyethylene and greaseproof paper itself. Two mechanisms proposed for the superior oxygen permeability of polyethylene-extrusion-coated greaseproof paper were compared. 

National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-1933 (URN)10.3183/NPPRJ-2008-23-03-p272-276 (DOI)
Available from: 2007-11-09 Created: 2007-11-09 Last updated: 2017-12-07Bibliographically approved
Mesic, B., Engström, G. & Lestelius, M. (2008). Water-Borne and Solvent-Based Flexographic Inks Influence on Uncovered Area and Ink Leveling on PEcoated Paperboard. TAGA Journal Vol 4 2008
Open this publication in new window or tab >>Water-Borne and Solvent-Based Flexographic Inks Influence on Uncovered Area and Ink Leveling on PEcoated Paperboard
2008 (English)In: TAGA Journal Vol 4 2008Article in journal (Refereed)
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-25688 (URN)
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2019-07-09
Larsson, M., Vidal, D., Zou, X. & Engström, G. (2007). Impact of calendering on coating structures. NORDIC PULP AND PAPER RESEARCH JOURNAL 22(2): 267-274
Open this publication in new window or tab >>Impact of calendering on coating structures
2007 (English)In: NORDIC PULP AND PAPER RESEARCH JOURNAL 22(2): 267-274Article in journal (Refereed)
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-20195 (URN)
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-01-21
Larsson, M., Vidal, D., Zou, X. & Engström, G. (2007). Paper coating properties as affected by pigment blendning and calendering study. TAPPI JOURNAL 6(8): 16-22
Open this publication in new window or tab >>Paper coating properties as affected by pigment blendning and calendering study
2007 (English)In: TAPPI JOURNAL 6(8): 16-22Article in journal (Refereed)
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-22232 (URN)
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-01-21
Kjellgren, H., Gällstedt, M., Engström, G. & Järnström, L. (2006). Barrier and Surface Properties of Chitosan-Coated Greaseproof Paper. Carbohydrate Polymers, 65(4) 453-460 (2006)
Open this publication in new window or tab >>Barrier and Surface Properties of Chitosan-Coated Greaseproof Paper
2006 (English)In: Carbohydrate Polymers, 65(4) 453-460 (2006)Article in journal (Refereed)
Keywords
Greaseproof papers, Air permeance, Coatings, Chitosan, Oxygen Barrier properties
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-17294 (URN)
Projects
Barrier coatings for greaseproof paper
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2019-07-11
Mesic, B., Lestelius, M. & Engström, G. (2006). Convertability Effects on Printability of Low-Density Polyethylene-Coated Packaging Material. Paper presented at Proc. For Printing Technology SPb´06 P, Saint Petersburg, Russia. Paper presented at Proc. For Printing Technology SPb´06 P, Saint Petersburg, Russia.
Open this publication in new window or tab >>Convertability Effects on Printability of Low-Density Polyethylene-Coated Packaging Material
2006 (English)Conference paper, Published paper (Refereed)
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-17874 (URN)
Conference
Proc. For Printing Technology SPb´06 P, Saint Petersburg, Russia
Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2019-07-09
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