David Bland
Over the past couple of years we have all noticed that in order to reduce costs, paper manufacturers have changed the coating formulation of all grades of coated paper and increased the volume of coating applied.
Long passed are the days when you could build a house out of 300gsm board as the modern coated stocks, with up to 25 % of their thickness now made up from fillers and coating instead of fibre, are sadly all soft and flexible with no "crackle" to them.
The stealthy migration from china clay to calcium carbonate has resulted in two major problems for printers, one of which in my opinion has reached unacceptable levels.
Firstly, calcium migrating from the sheets during printing into the fount and inking system causes contamination of both rollers and fount. New calcium removing founts are now being introduced by some chemistry suppliers in an effort to counter this problem.
This contamination, however, adversely affects the dot-gain characteristics of a press and therefore necessitates regular de-glazing of rollers and flushing of water systems. This inevitably increases printer's overheads due to the downtime on press and the ever-increasing costs of waste disposal.
I have recently become even more concerned, however, by the speed at which all modern coated papers discolour, literally overnight, from bright white to yellow and I encourage all printers to judge this for themselves by simply looking at the colour of the top sheet on any stack of work, compared to the sheets below.
The use of calcium requires the addition of optical brighteners in order to improve the whiteness of the paper to a sellable level. It is these optical brighteners that are discolouring so very quickly (a quite barmy fact).
Until recently, when raised with merchants, the yellowing has been attributed to discolouration of the sealer or coating used by so many printers today but I fear that, while we all accept that these sealers discolour, this is really diverting focus away from the real issue, which is clearly visible on unprinted or unsealed material.
I recently visited a French mill and raised this yellowing with their technical staff only to be met with looks of surprise and claims of "that is the first time that it has been raised as an issue." However, upon continuing the tour into the sheeting plant the yellowing was visible on all new pallets of paper and the man preparing the pallets for shrink-wrapping was removing every top sheet! Sacre bleu!
A comment was made to me by a merchant representative recently in that, if I want a paper that does not go yellow, I must buy yellow in the first place as it does not contain any optical brighteners.
Having spoken to a major chemical supplier I am informed that as with most things, optical brighteners come in many grades and that the speed of discolouration implies the use of very poor quality materials.
I have carried out my own simple tests on a range of papers, boards, greeting card board, and folding box boards produced in France, Germany, Finland, Holland and Sweden and bought through four different UK merchants and I have to report that all show the same discolouration over a very short period of time.
So marked is this discolouration problem that I have to question both the environmental and archival credentials of the papers available on the market today.
I am sure that this is a simple oversight by the UK merchants and their parent mills, but as a purchaser of some 6 million of paper per year, our group has yet to receive one detailed information sheet advising of changes to the make-up of the paper or to the environmental or archival credentials of any sheet on the market.
Surely the time has now come for a new standard to be researched and published that would grade all coated papers by their light fastness so that printers and paper specifiers can advise their clients as to the most suitable material for any job.
Perhaps the quality of the optical brighteners should be listed and maybe there would be a case for a price differential for papers that can be proven to hold their original colour?
Indeed, I challenge the UK merchants in that if any can offer me a competitively priced, mid-range, coated sheet that does not discolour then I will buy it.
I am not expecting many calls!
David Bland
Operations Director
Alderson Brothers Printers
The paper industry responds
Firstly I would like to say that coated papers have always been subject to fade this is not a new phenomenon.
Yes, perhaps coating levels have increased in recent years, but this does not necessarily mean more fade. In the past, the aim of the marketing people was to achieve stiffness for faster runnability on press, but requirements change and the development work moved in the direction of print quality, particularly ink gloss or ink lift. Coating levels can help achieve this but it is more related to the content of the coating formulation.
Coating formulations have always been a mix of clay and calcium carbonate, and in the 1980s and '90s, a higher proportion of clay was used compared to calcium carbonate. However, the calcium carbonate producers significantly developed the pigment in the '90s, producing a much finer calcium carbonate pigment that gave excellent paper gloss and print gloss characteristics. The increased use of calcium carbonate not only helped achieve a much better print result, particularly for the medium coated sector, but also allowed a much more natural whiteness to be achieved. Calcium carbonate is a much more naturally white pigment than the "yellow" clay that used to dominate old coating formulations. Moving to a more natural white pigment has actually led to less use of optical brightening agents (OBA's) as old clay dominated papers were loaded with OBA to counteract the yellow look of the sheet with the blue reflectance of the OBA.
Yes, OBA's have always been subject to fade, but with less present, the more natural white sheet should fade less. David's letter says that calcium carbonate (CaCO3) requires OBA to improve whiteness, which is untrue. Calcium Carbonate is a naturally white, bright pigment and negates the need for high OBA usage. Perhaps with much higher brightness levels being achieved, the perceived change in paper shade may appear more over time as the starting point is higher, but calcium carbonate will help achieve higher whiteness levels and allow lower OBA additions for a given shade.
Different OBA products are on the market but all will fade with time and UV exposure. I am unaware of mills selecting poorer quality OBA products. The move has been away from hexa-OBA's to tetra-OBA's. Tetra-OBA will not achieve the same brightness levels but with increased use of calcium carbonate, there is no need to use the higher brightness products. Less addition now means less fade compared to the old clay-dominated formulations.
The main driver for the move to finer calcium carbonate pigments is that of print quality. As the CaCO3 pigments became finer, this allowed high solids coating, increased particle packing, resulting in higher gloss levels and improved ink holdout. Ink lift is better, but also much work is carried out in relation to ink setting rates calcium carbonate particles are less tortuous than the old clay particles, allowing faster ink vehicle absorption, and a faster ink setting rate which can be very beneficial, especially given the increased use of eight-, 10- and 12-colour perfecting presses. Print quality benefits from recent coating developments.
Yes, calcium carbonate is alkaline and will react more with acidic fount solutions, increasing the risk of dusting on press and the effect on print quality. However, if fount quality and pH level is controlled and not allowed to become too acidic, then the reaction and resultant dust can be controlled and minimised. Indeed, founts have developed accordingly and neutral founts are being used more, together with founts in the traditional operating range of 5.0 -5.5 pH which have been developed not to attack the calcium carbonate coating as readily. As long as fount acidity and surface tension are controlled, the printer keeps damping on press to a minimum and the papermaker selects the correct coating binder and insolubiliser in the coating formulation, then dusting should not be an issue.
The above is just related to coating formulations. Over the years, CaCO3 has replaced clay as a filler in the base paper since the development of neutral papermaking sizing systems. CaCO3 could not be used previously in acidic papermaking systems but once neutral systems were developed, this allowed the use of CaCO3 bringing with it a whiter, brighter, cheaper pigment than clay whilst providing improved opacity, ink setting and drying, print evenness and contrast, longevity and strength. Strength improved as less CaCO3 filler could be used for a given opacity and longevity improved as the neutral sizing meant less paper degradation over time.
David's letter also refers to testing on folding box boards and greeting card boards. These products nearly always use mechanical pulp for improved stiffness. Mechanical pulp yellows over time, so with these type of board products, yellowing will occur. With woodfree (chemical pulp) products, lignin has been removed from the pulp and will therefore not yellow over time like mechanical-containing grades. The pulp is much whiter brighter with no lignin present.
All papers will fade to certain extents over time, but calcium carbonate brings many print quality benefits and a more naturally white sheet, allowing less use of OBA's and less resultant fade. The use of calcium carbonate as a filler with neutral sizing prevents paper degradation over time which occurred with the old acid sizing system, and the use of chemical pulp in woodfree grades produces less fade over time. As long as fount quality is controlled and pH levels not allowed to drop below 5.0, dusting on press should not be an issue. Medium sector coated papers, through coating development and the use of finer calcium carbonate pigments, have improved their print quality and natural brightness levels significantly over the past ten years, encroaching on the print quality of the real art market to the extent that the cost difference between medium and real art is no longer justified.
Chris Venables
Technical services manager
Antalis
In response to the concerns of Mr Bland
Having checked our records, Premier Paper has not raised discolouration as an issue with any of our paper suppliers in the last two years. It is, of course, possible for paper to discolour if left in sunlight for a prolonged period, but good housekeeping will prevent this from occurring.
Calcium carbonate occurs naturally in water, in differing levels depending on location, and also in some inks, particularly Magenta. As these two elements of Litho printing, ie water and ink, form a major part of the process, so it is possible that any calcium build up on rollers and blankets may arise from other sources, not just the paper. A more thorough investigation of all the factors relating to a specific problem would need to be conducted in order to draw a conclusion on its origin.
Ron Brindley
Technical services
Premier Paper
Having spoken to Terry Parker, commercial services manager at Smurfit Townsend Hook and Mike Brewer, quality manager at Coated Papers, Smurfit Townsend Hook, we formulated the following reply to David Bland's open letter.
Over the years there has been a call for smoother coated papers, hence more coating. Calcium carbonate is a major component of coated papers across Europe.
There are different types of carbonate, including marble, ground and precipitated, marble being a whiter, smoother and finer mineral than English china clay and used predominately in matt and silk coated grades.
Calcium carbonate, due to its "blocky" structure, tends to "open up" the surface, offering better ink setting and drying characteristics and reduced mottle tendency.
Due to its inherent whiteness it requires less OBA's to achieve a target brightness, and we choose brighteners that offer the least fade possible for our paper grades.
We also use pigmented colorants to achieve our shade specification, which offer better light fastness than dyes.
In the past we have conducted light fastness tests on various coated grades compared with our own products, exposing sheets to north daylight under controlled conditions, and we have found our products to be within the top 20% of the ranking achieved. So, of course, we would not be against contributing towards a working standard for light fastness.
As regards "coating deposit" build-up on blankets and rollers, we very rarely encounter any adverse comments but at one printer where it was more of a problem it was overcome simply by a change of fount.
It should be stressed, however, that calcium deposits are not always solely related to paper coatings. Water sources from "hard water" areas contain calcium and magnesium salts and the inks themselves can contain chalk "extenders". The overall press chemistry and press settings can also play a contributory role.
Scott Barclay
Managing director
Hale Paper
