February 2008
By Chris Smith
In September of 2005, International Paper announced a new standard in brightness and optical properties in all of its office papers. This announcement and acceptance by the marketplace not only changed International Paper's grade mix towards a mix of higher brightness papers, more importantly it drove a new industry standard for brightness and whiteness within the industry.
What occurred after this announcement, at least in North America, was that instead of standard office papers being 84 TAPPI brightness, a new standard was established at 92 brightness with increased demand not only for 92 brightness paper but also for 96 and 98 brightness. In addition to the new brightness standard, the well-established European measure of CIE whiteness was also adopted with a minimum range of 145 CIE whiteness set as a new standard.
To achieve these new standard optical properties, many papermakers had to increase their overall cost of production by incorporating more fluorescent whitening agents (FWA) into their furnish mixes by increasing bleaching of incoming pulp or by purchasing higher brightness market pulp. These methods not only caused an increase in cash production costs, but many times also had a negative effect on machine efficiency and in some cases the overall environmental footprint of the papermaking operation.
As the trend towards higher brightness continued, many mills found that the costs of making the new grades were higher than they anticipated. The direct costs from increased use of FWAs and bleaching were significant; equally important were the secondary costs associated with these methods including their impact on other chemical additives, machine efficiency, fiber mix and bleach plants.
Unfortunately, these direct and indirect costs were making the production of these grades not economically feasible for many mills. While some companies had developed proprietary methods to make the new higher brightness grades, many could not make them consistently, or even worse could not make them at all. At the same time this was occurring, the FWA market started to tighten up and the price of FWAs started to rise, making these grades even more expensive to make. Mill management, in many cases, was hesitant to add these grades that their marketing departments were demanding to their production mix for the fear that the new additions would hurt their overall operational efficiencies.
Around this time, a number of customers approached Nalco and asked for assistance and consultation in making these new grades. There was a particular concern what effect the drive towards higher brightness would have on other wet end additives, particularly retention aid chemistries and internal sizes. Many of the inquiries involved providing additional understanding of what changes would be recommended, or what implications would be seen as production was shifted to these new grades. Some organizations said that they would not be able to meet the new optical targets and inquired about technology that Nalco may have in development to assist in this effort.
Nalco was already in the process of developing technology to reduce thermal reversion within the papermaking process. Although this technology was primarily aimed at wood-containing grades, it showed activity in the laboratory in woodfree grades. As Nalco moved forward in development, it was discovered that the technology had a synergistic effect with FWAs, as was evidenced by the technology, not only helping to reduce thermal reversion, but an "activation" of certain FWAs as realized by an increased florescence value at an equal FWA dose.
Nalco continued through its formal commercialization process with the requisite beta trials and discovered that this technology could potentially allow the papermaker to make these grades cost efficiently by significantly reducing the amount of FWAs that they use or reducing the short-term elevated bleaching levels needed for incoming pulp when these short grade runs would occur.
More importantly, Nalco's customers found that they could achieve these improved optical properties and could do so with an optimal furnish mix including furnish mixes with low brightness or wood-containing pulp. Because of the success that had been recognized in the field, the technology was formally commercialized in the Americas on November 10, 2006, as EXTRA WHITE™ Brightness Technology and later in early 2007 in Europe and Asia Pacific.
Nalco's new patent pending Extra White technology is the first in a series of advancements that form the foundation of SMART Solutions for opticals management. Extra White Brightness Technology enables the paper industry to raise the whiteness and brightness standards of their grades while positively affecting uniformity of shade for high-bright grades manufacture.
This new technology delivers cost-effective brightness and whiteness development in an environmentally friendly and safe manner while having a positive affect on operational efficiency when compared with traditional brightness development methods.
Benefits
The benefits of Extra White technology are derived primarily from the ability of the technology to reduce thermal reversion throughout the papermaking operation and activate optical brightening agents (OBAs). This allows papermakers to recognize up to a one point increase in ISO brightness while simultaneously reducing OBA consumption by up to 50%. This creates value to the papermaker by providing an alternative method of manufacture to increasing brightness specifications while delivering a significant reduction in many of the inherent negative effects associated with excessive OBA use of other alternative brightness development methods.
Theory
Extra White Brightness Technology has been engineered and commercially proven to prevent paper web brightness loss across the paper machine due to exposure to heat and moisture (sometimes known as thermal reversion) and has been proven to activate optical brighteners.
The net effect of suppressing thermal darkening, chemically modifying pulp and activating optical brighteners often noticeably exceeds compensation of thermal darkening alone, thus allowing a more cost-effective and operationally efficient method for achieving increased brightness or whiteness specifications.
The new technology delivers:
- Up to a 50% reduction in OBA consumption
- Ability to achieve higher brightness targets
- Improvements of up to one point in brightness
- Opportunity to incorporate lower brightness or mechanical fiber into the furnish mix
In most cases the application of Extra White technology reduces the demand for OBAs by 40-50% at equivalent or improved brightness levels. By reducing the amount of OBAs required to achieve brightness specifications, the papermaker can either increase the amount of OBA use to reach even higher brightness levels without the fear of "greening" or other adverse effects, or simply take advantage of the many benefits of reduced OBA use.
A reduction in OBA use has many benefits, not the least of which is a lower total spend on OBAs, but also includes many operational benefits due to an overall reduction in cationic demand within the process. This normally includes other benefits in terms of additive efficacy in retention, drainage and sizing programs as well as improved process stability resulting in machine efficiency improvements.
In addition, reducing OBA consumption delivers a more natural whiteness development in the finished sheet that allows for improved shade control and metamerism. Normally, this results in a reduction in overall dye consumption for color correction and provides for improvements in proof matching.
Extra White Brightness Technology delivers such gains in a manner that is consistent with environmental sustainability initiatives. The ability of Extra White technology to lower the reliance on bleaching and the use of OBAs, thus, the stability of the wet end can be improved resulting in both improved filler performance and loadings. This results in higher fiber yields, lower fiber content and in many cases a reduction in the release of volatile organic compounds (VOCs) associated with the use of aromatic hydrocarbon-based OBAs.
Technology
The product is an aqueous solution that has been designed to be compatible with all traditional size press and wet end additives. As a result, any mill that has a size press can take advantage of the technology. Ideal candidates for the technology will be producing the highest brightness grades of paper (> 92% ISO brightness) and currently using more than 18 lb (8 kg) per ton of OBAs in either the wet end or at the size press. Other characteristics that may make the technology appealing include the following:
- Sites having trouble cost effectively achieving brightness targets or achieving brightness targets at the expense of runnability
- Sites that desire to increase the utilization of mechanical or other lower brightness fiber
- Sites that have problems consistently achieving brightness targets
- Sites particularly susceptible to brightness loss throughout the papermaking process that is due to high temperature, moisture or dwell times
- Sites experiencing high levels of process instability that can be attributed to large swings in cationic demand
- Sites where the last point of bleaching exceeds $6.50 per point
Case Studies
Machine type: Central American UCFS (50-92 g/m2 basis weight) mill producing copy paper at 92-96 GE Brightness, 490 m/min operating speed, 3,450 mm wire width, kraft, DIP & CTMP furnish, 40,000 tons/yr production.
Background: The mill was not able to produce hi-brightness grades (96 GE brightness) from a cost efficiency and technical position due to the high amounts of OBA required to achieve brightness targets.
Extra White Brightness Technology application: The technology was applied to the size press at a rate of 2 kg/ton with the goal of achieving production of a 96 GE brightness sheet without recognizing "greening" or operational efficiency issues attributed to excessive OBA usage.
Results: Achieved 96 GE Brightness sheet for the first time, 60% reduction of OBAs in 92 GE Brightness grades, improved process stability.
Machine type: North American UCFS (75-220 g/m2 basis weight) mill producing offset, 600 m/min operating speed, 6,000 mm wire width, DIP, Kraft and PCC furnish, 123,000 tons/yr production.
Background: The mill was challenged to produce hi-bright grades (98 brightness) from both a cost and production efficiency position due to the large amounts of OBA required to achieve brightness specifications which resulted in "greening" and required large amounts of colorants to correct the shade. In addition, the bleach plant was not able to keep up with the demands for the high bleached pulp.
Extra White Brightness Technology application: The technology was applied to the size press at a rate of 1.5 kg/ton with the goal of reducing OBA consumption significantly without negatively affecting optical or printing properties.
Results: A 1.0 increase in ISO brightness coupled with a 40% reduction in OBA consumption, Fig. 3, improved shade control, 10% reduction in ASA demand, 15% reduction in long-term brightness reversion, equal offset printing characteristics.
Chris Smith is Global Program Manager, Graphic Papers, Nalco Company
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