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International Paper - Papermaking Process Solutions Brightness (3 Types) & Whiteness (2 Types): Full Disclosure CRABLE ENGINEERING LLC.

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Presentation on theme: "International Paper - Papermaking Process Solutions Brightness (3 Types) & Whiteness (2 Types): Full Disclosure CRABLE ENGINEERING LLC."— Presentation transcript:

1 International Paper - Papermaking Process Solutions Brightness (3 Types) & Whiteness (2 Types): Full Disclosure CRABLE ENGINEERING LLC

2 Informing our Customers: CRABLE ENGINEERING LLC Marketing psychologists state that a lasting impression is made within ninety seconds and that color accounts for 60% of the acceptance or rejection of an object, person, place, or circumstance. Because color impressions are both quick and long lasting, decisions about color are critical factors in the success of any visual experience. - About Color The fields of shade (or color) and appearance are critical to the acceptance of paper and board products, yet these product attributes are often overlooked. Or, systems to support them are often an afterthought in the design of papermachine processes.

3 Definition & Origin of Brightness It is the measure of light reflected from a sample at 457 nanometers +/- 44 nm. Brightness represents the diffuse blue reflectance of a sample, and the wavelengths indicated above were chosen on a somewhat arbitrary basis. It was introduced as a visual aid for assessing and controlling the degree of pulp bleaching. Informing our Customers: CRABLE ENGINEERING LLC

4 Origin & Evolution of Brightness Originally, brightness was assessed by observing a pulp sample through a blue- stained glass. The more the pulp is bleached, the more lignin is removed, and the higher the blue reflectance becomes. The reason for focusing on the blue-yellow axis is that the pulp starts out dark brown, changes to light brown, then to tan, and to diluted yellow as bleaching progresses. Informing our Customers: CRABLE ENGINEERING LLC

5 International Paper - Papermaking Process Solutions Pulp Bleaching Impact

6 Origin & Evolution of Brightness The need to simplify and standardize bleaching assessment of pulp led to the first instruments such as the GE-Photovolt. General Electric has long since sold this instrument business, but the term GE brightness remains. (Technidyne currently produces the instruments to measure it.) In this instrument, samples are illuminated with an incandescent lamp at a 45 o angle and reflectance is measured perpendicularly or at a 0 o angle of observation. Informing our Customers: CRABLE ENGINEERING LLC

7 Evolution and Use of Brightness As there was no comparable instrument available for the papermaking process, the GE brightness meter (now referred to as Directional or TAPPI T452 Brightness) moved to the paper mill. Prior to the introduction of fluorescent whitening agents, and as a consequence of its purpose in describing the degree of bleaching, brightness over time became synonymous with how white the paper appeared (or simply whiteness). Informing our Customers: CRABLE ENGINEERING LLC

8 Types of Brightness There are two basic types of brightness measurement: Directional and Diffuse. Directional brightness (TAPPI brightness – TAPPI 452) employs the 45 0 /0 0 geometry of the original GE-Phovolt instrument. It has been the standard in the U.S. and Japan. Diffuse brightness employs a D/0 0 geometry where D indicates diffuse illumination from a sphere, making it insensitive to sample orientation. Diffuse brightness is the standard in much of the rest of the world. Informing our Customers: CRABLE ENGINEERING LLC

9 Illustration of Instruments Directional Diffuse Sample Photodetector Light source Sample Photodetector Light source Informing our Customers: CRABLE ENGINEERING LLC

10 Types of Brightness Two types of Diffuse brightness are commonly discussed, and a standard exists for both of them. ISO C Brightness (ISO , TAPPI 525) uses Illuminant C level of UV energy. It was selected as the best approximation of normal office lighting conditions. ISO D65 Brightness uses Illuminant D65 (daylight). Control of D65 level of UV energy is not good from instrument to instrument, but still there is now a standard for D65 Brightness (ISO ). Informing our Customers: CRABLE ENGINEERING LLC

11 International Paper - Papermaking Process Solutions Differences Between D65 and C

12 Comparison of Brightness Types TAPPI (45 0 /0 0 ), or Directional and Diffuse (D/0 0 ) Brightness (C or D65) cannot be correlated. This is due to the fact that multiple reflections which occur between the sphere and sample make unpredictable changes in Diffuse Brightness as compared to Directional (TAPPI) Brightness. The following two slides show brightness comparisons on a number of white papers. Informing our Customers: CRABLE ENGINEERING LLC

13 Brightness Comparisons Informing our Customers: CRABLE ENGINEERING LLC

14 Comparison: TAPPI vs ISO Brightness Informing our Customers: CRABLE ENGINEERING LLC

15 The Scattering Properties of Glossy and Matt Samples GLOSSY SURFACE MATT SURFACE The surface properties of a sample influence the quality and quantity of light that reaches our eye; influencing the way an object appears. In fact, we sometimes calender samples to get the right look. Specular Reflection Diffuse Reflection Informing our Customers: CRABLE ENGINEERING LLC

16 Problems and Limitations of Use Directional (TAPPI) brightness, first, has an issue in that it is highly sensitive to fiber angle. Indeed, one can impact directional brightness with changes in Rush/Drag ratio. Per TAPPI method T 452, section 1.2: This procedure is applicable to all naturally-colored pulps, and papers and board made therefrom. The measurement is not suitable for paper or paperboard containing coloring matter (such as yellow or green dyestuff) which appreciably absorbs light in that part of the spectrum extending from 400 to 500 nm. Colored papers must be measured spectrophotometrically or colorimetrically in order to obtain meaningful results. Informing our Customers: CRABLE ENGINEERING LLC

17 Problems and Limitations of Use The biggest issue with use of brightness as a paper metric, though, is that it measures reflectance in a VERY narrow (blue) band of the reflectance spectrum. This does not correlate well with the perception of whiteness or visual appeal. Also, brightness is not a linear function. A change from 84 to 90 brightness has much more visual impact than a change from 90 to 96 brightness. The higher the brightness of the paper (brought about through the use of FWA), the quicker the paper will fade. Informing our Customers: CRABLE ENGINEERING LLC

18 Ways to Increase Brightness Start with brighter pulp. This could involve additional bleaching or washing of the pulp or even purchase of High Brightness pulp. Cover the fiber with fillers of higher brightness. E.g. use very bright clay, PCC, TiO 2, or ATH to hide the yellower fiber. Use Fluorescent Whitening Agents (FWA) to boost the blue reflectance measured as brightness. Keep the FWA on the surface of the sheet using good film formers such as PVOH or PEG. Use the cleanest, brightest coatings (starch or PVOH in uncoated paper) possible. Informing our Customers: CRABLE ENGINEERING LLC

19 Ways to Avoid Lower Brightness Use no post-consumer fiber (contains more fines and contaminants) which dull the paper. Avoid heavy metal ions (such as copper, manganese, and iron) in the process. Use a chelant to control them if necessary. Treat very hard water to prevent precipitation of the FWA. Do not overuse FWA or green-over may occur. Use minimum amounts of dye for shade control. Informing our Customers: CRABLE ENGINEERING LLC

20 CIE Whiteness Whiteness is a visual perception that involves the entire visible spectrum from 400 nm to 700 nm. It was developed, specifically, as a single metric to describe the appearance and appeal of white papers. Values of Whiteness increase as the paper becomes bluer and slightly redder. Whiteness can be increased both through use of FWA and tinting dyes. Informing our Customers: CRABLE ENGINEERING LLC

21 CIE Whiteness Most import papers are shade formulated to take advantage of the increase in Whiteness with blue and red (or violet) tinting of the paper. Whiteness can be less expensive to achieve than Brightness: a small addition of tinting dye (low cost) can significantly improve Whiteness. [Tinting dye use can generally only lower Brightness.] Change in the shade of paper with light exposure is generally less severe than loss of Brightness with FWA fade. Informing our Customers: GREENVILLE COLORANTS LLC

22 CIE Whiteness There are two types of CIE Whiteness. First is outdoor CIE Whiteness (per ISO 11475). It yields the higher value due to the higher UV energy level of Illuminant D65. It came first and is the only one commonly used. Second is indoor CIE Whiteness (per ISO 11476). It yields lower values but is more representative of office lighting conditions, using the UV energy level of Illuminant C. CIE Whiteness should ONLY be used for near- white papers. (And this is becoming an issue.) Informing our Customers: CRABLE ENGINEERING LLC

23 International Paper - Papermaking Process Solutions Brightness, Whiteness, and L*

24 Brightness Conclusions Either brightness or whiteness can be more expensive to achieve depending upon the shade of the paper and its brilliance. As one goes to very high brightness levels, production costs rise ever more quickly, and the visual impact becomes smaller. ISO Brightness values are generally higher (as much as 1.5 to 4.5 points) and less variable than TAPPI Brightness values. Whiteness often correlates better with visual appeal than does Brightness. Informing our Customers: CRABLE ENGINEERING LLC

25 Whiteness Conclusions The uppermost Whiteness values have now been pushed beyond their practical limits for true white papers. As one goes to very high whiteness levels, the positive impacts of FWA on the paper have been exhausted. The only way to continue to increase CIE Whiteness, then, is to make the paper bluer. Often, however, the product begins to look dull and grayish at the highest CIE Whiteness levels. We need to refine the CIE Whiteness equations to prevent overuse of tinting dyestuff to artificially inflate the numerical value while actually making the paper look duller. Informing our Customers: CRABLE ENGINEERING LLC

26 Whiteness Conclusions Although much of the rest of the world makes and sells paper according to CIE Whiteness level (which is not printed on packaging) the attempt to introduce whiteness into the U.S. market was not well received. Much of the reason for this is that major U.S. customers are familiar with brightness (mostly TAPPI T452 brightness) and are unwilling to give up this metric. Brightness is still printed on the ream wrap and, oddly, is used to distinguish between quality levels. Informing our Customers: CRABLE ENGINEERING LLC


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