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Characterisation of paper surfaces for improved printing paper grades

Project information

Grant agreement ID: E32

  • Start date

    10 October 2002

  • End date

    Not Available

Funded under:

IC-COST

Coordinated by:

N/A

Objective

A. BACKGROUND

Competition from other information media and increasing demands from customers force the pulp and paper industry to increase its know-how and improve its competitive edge. To meet these challenges the quality of paper as an information carrier, must be further developed.

Paper - an important information carrier

Paper has long been the most important material for the dissemination of information. It is cheap and environmentally friendly in compliance with sustainable development. For the reproduction of letters and pictures, the paper surface is the critical part. As the paper is composed of fibres, fines and mineral fillers, the surface as well as the structural characteristics of these components will critically determine the properties of the paper surface. The surface chemistry of paper is strongly influenced by raw materials and additives used in the papermaking process. The paper surface will also be strongly influenced by the papermaking unit operations such as forming, pressing, drying, calendering and coating. The quality of the printed image will depend on the level and the uniformity of the paper surface topography and chemistry, as well as the printing variables.

The influence of raw materials on the paper surface topography

Wood fibres used for papermaking have a width comparable to the smallest printed halftone dots, 50 æm. The wall thickness of the fibres may further give local height differences in the paper surface and may exceed 10 æm for some grades. Considering that the thickness of the applied ink layer may be less than 1 æm, it is easily understood that the local topography will

have a strong influence on the quality of the printed details. Different wood raw materials, plant fibres and recovered fibres treated by different pulping processes will strongly influence the dimensions, chemical and physical properties of the fibres and thus both the topography and chemistry of the paper surface.

The influence of papermaking unit processes on surface topography

The unit operations of the papermaking will influence the paper surface in many ways, some effects on purpose, others as not wanted side effects. A well-known effect is wire and felt marks as the forming fabric and the felts in the forming and press sections of the paper machine may impose a structural pattern in the paper surface. During drying the paper is held firmly on to heated steel cylinders. This procedure will result in a fairly smooth surface. More important, however, is the machine or super calendering at the end or after the paper machine. Here the paper is treated in nips between heated cylinders to reduce surface roughness and even out local thickness differences. Some paper grades are also coated with a mix of ground minerals and binders to further smoothen and even out the structure of the paper surface.

Paper surface chemistry and structure determine print quality

The surface chemistry of paper will influence the spreading and absorption rate of inks and dampening water applied in the printing process. The surface chemistry should be uniform even on micro-scale to allow uniform reproduction of each halftone dot. However, the local mix of fibres, fines and chemical additives will determine the local surface chemistry. We further know that in multicolour printing, the applied ink and dampening water in the first printing nip may change the chemistry and thus the transfer and absorption in the next printing nip only fractions of a second later.

The expanding use of recycled raw materials for papermaking experienced over recent years means that the chemical composition of many paper grades has become more complex than ever before.

A European perspective

Europe currently enjoys a fairly good volume balance in paper production and consumption. It can be safely stated that for most grades the quality demands in the West European market are equivalent or superior to the products offered in any other market. The threat to European printing paper comes from electronic media and industrial expansion in tropical countries. At short sight the threat from electronic media like TV and Internet is the competition for advertisement. In the long run it will be changing information acquisition habits, leading to decreased paper consumption. The main industrial threat for the European paper industry is probably large production units in tropical countries based on fast growing hardwood (mainly eucalyptus and acacia) with tailored and uniform fibre properties. The low production cost and good paper quality obtained by these competitors is a threat particularly to the European fine paper industry.

The COST Action

In the paper science communities around Europe, there is currently a strong interest in paper surfaces and print quality. This may be illustrated by the selected theme of the "2002 Ekmandagarna conference" in Stockholm, January 2002, which was "The printed paper surface". The conference attracted some 300 delegates, which is very high for this kind event.

Several new tools have been developed for paper surface topography measurements on the micro- scale. The tools include laser profilometry, white light interferometry and light gradient integration. Common for all methods is that they yield surface maps that may be further analysed with image analysis tools. On the surface chemistry side there are also good available characterisation methods like ESCA and surface energy measurements. The challenge seems to be to assess the development in surface energy during the first second after the paper surface has been moistened in the first printing nip and to measure the evenness in surface chemistry from point to point. For surface topography the main challenges seem to be how different structures in the surface will influence the distribution of ink pigments on the paper surface for different printing processes.

The community of papermakers and scientists will be stimulated by and benefit from a co-operation in a COST Action.

The planned activities are pre-competitive, allowing the co-operation to the common good. The emphasis will be on methods of characterisation, in order for the European paper industry to combine its efforts to find means for improved analysis of paper surfaces, to better modify the papermaking processes and develop new and better functional properties of paper.

B. OBJECTIVES AND BENEFITS

The main objective of the action is to develop and improve methods for analysis of printing paper surfaces in order to improve print quality. Further, it is also of interest to develop methods that can measure ink distribution on printed surfaces and correlate this to the local topography and chemistry.

The specific objectives are:

-to create a platform for interaction between scientists and papermakers in Europe to provide a good transfer of knowledge

-to define present knowledge of the influence of paper structure and chemistry on the obtainable print quality for different printing processes

-to identify knowledge gaps and suggest relevant research.

The expected benefits to the European paper industry will be:

-improved understanding of how raw materials and process conditions affect the paper surface

-identification of optimal surface structures for different printing methods

-quantification of the importance of uniformity in surface chemistry and topography on the print quality

-development of analysis methods that may better predict the print quality attainable on a certain paper surface

-improved understanding of how the paper surface is changed chemically and topographically as a result of the printing.

C. SCIENTIFIC PROGRAMME

Types of activities

The Action will be in compliance with the general rules of COST and will include:

-workshops, conferences and seminars

-exchange of experts, scientists and graduate students for training

-exchange of reports, publications and experimental procedures

-state-of-the-art conferences and workshops

-joint projects in specific areas by two or more of the participants.

Scientific areas

The scientific areas in consideration will be those focusing on methods for characterisation of paper surfaces and the influence on paper surface properties on print quality. Some examples are:

-surface energetics and wetting of the paper surface components
- chemical characterisation of the components
-distribution of structural components (fibre, fines, fillers) in the paper surface
-micro- and macro-pores in the paper surface, and their distribution
-topographical characterisation
-topography analysis using image analysis techniques
-effects of chemical and mechanical treatment of the surface
-effects on the listed characteristics by changes in moisture and other printing environment variables.

Experimental techniques

Surface topography maps

Techniques for making surface topography maps on a micro scale have been developed in recent years and are beginning to gain popularity in the paper industry. It is to be expected that such methods can yield better characterisation parameters of the printability of a surface than the "air leakage"-based instruments like Parker Print Surf (PPS).

Image analysis

The use of image analysis in pulp and paper research is increasing rapidly and a set of useful tools has been produced in recent years. A topography map of a surface is essentially an image and methods developed to e.g. analyse SEM images may be applied to the surface topography data sets. Methods allowing the simultaneous measurement of ink distribution and local topography seem especially promising.

Surface chemistry

The surface chemistry of paper will determine spreading and absorption of printing ink and dampening water used in the printing process. Halftone dots in printing images may be as small as 50 æm in diameter and thus comparable to the characteristic dimension of a fibre
(fibre width = 30-40 æm). The chemistry of the paper surface will therefore change from halftone point to halftone point depending on whether the point hits a chemical pulp fibre, a mechanical pulp fibre, fines or fillers. The surface chemistry depends on the moisture content and the chemical additives. The main challenges in methodological development lies in describing how surface chemistry varies from point to point and changes as a function of time after the first moisture has been applied in the first printing nip - thus defining the properties of the surface that hits the next printing nips.

D. ORGANISATION AND TIMETABLE

Action structure

The MC will manage the Action in accordance with the existing COST regulations and establish its course of action in the first formal meeting. The MC will organise bi-annual meetings to monitor the progress of the COST Action.

Two Working Groups are proposed. Each will be headed by an elected leader and they will assist the Chairperson and the Vice-Chairperson in ensuring that the groups progress as stated in the MoU and to a high standard. The WG will hold separate meetings, once or twice per year. Wherever possible, the MC, WG and other meetings associated with COST will be held at the same time and venue.

The following Working Groups for the Action proposal are proposed:

WG 1:The influence of surface chemistry and topography on the obtainable print quality for uncoated paper qualities.

WG 2:The influence of surface chemistry and topography on the obtainable print quality for coated paper qualities.

Short Term Scientific Missions (STSM)

The Action would encourage the exchange of scientists between the participating research laboratories and from one field to another, as between paper science and material science through short-term scientific missions.

The COST activity will be carried out in co-operation with existing research programmes within the area, such as those carried out by the main pulp and paper research laboratories in Europe, the main suppliers of pulp and papermaking equipment, as well as suppliers of chemical additives. Scientists from other fields are encouraged to take part in the Action in order to provide input of outside ideas. The COST Action will build on results from COST E11 "Characterisation methods for fibres and paper" where several characterisation methods where described and looked into.

A website for the Action will be created and maintained by the Norwegian Pulp and Paper Research Institute (PFI) to enhance the communication within the Action and inform the external scientific community.

Timetable

The Action will run over a period of four years. Meetings and seminars in the working groups are planned to be held according to the plan below. The seminars will be common for the two working groups. The MC meetings and the seminars will be held at the same time.

E. ECONOMIC DIMENSION

The following COST countries have actively participated in the preparation of the Action or otherwise indicated their interest:

Finland
France
Germany
Hungary
Italy
Netherlands
Norway
Slovenia
Sweden
UK

On the basis of the national estimates provided by the representatives of these countries, the economic dimension of the activities to be carried out under the Action has been estimated, in 2002 prices, at roughly Euro 18 million.

The estimate is valid under the assumption that all the countries mentioned above but no other countries will participate in the Action. Any departure from this will change the total costs accordingly.

F. DISSEMINATION OF RESULTS

The most important results from this Action will be improved characterisation methods for paper surfaces. A main target group for dissemination of information of such results is the paper industry. The participating partners (mainly national research institutes and universities) will distribute reports and presentations from the COST Action to the national industry. It is planned to invite industry people to the seminars.

It is further of high value to standardise methods that characterise paper surfaces. The ISO/EN standardisation groups working with physical and chemical properties of paper will be informed of any progress towards a possible improved standard for paper surface characterisation.

The general scientific community will be informed through participation in conferences, through publications and through the Action website.

The MC will also maintain an active contact to the COST Forestry and Forest Products Technical Committee by:

- Attendance of the chairman or his representative at the meetings of the Forestry Sector Group
- Establishing close contact with the Technical Committee through its appointed liaison officer
- Submitting annual progress report to Forestry Sector Group
- Contributing to the COST Forestry and Forest products Technical Committee Activity report.

Coordinator

N/A

Address

Project information

Grant agreement ID: E32

  • Start date

    10 October 2002

  • End date

    Not Available

Funded under:

IC-COST

Coordinated by:

N/A