brightness whiteness crable engineering llc

7/21/2019 Brightness Whiteness Crable Engineering Llc

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International Paper - Papermaking

Process Solutions

Brightness (3 Types) &

Whiteness (2 Types):

Full Disclosure CRABLE ENGINEERING LLC



Informing our Customers:

CRABLE ENGINEERING LLC

“Marketing psychologists state that a

last ing impression is made wi th in n inety

second s and that c o l o r accoun ts for 60%

of the acceptance or reject ion of an object ,

person, place, or circum stance. Because

co lor imp ress ions are both quick and long

last ing , decis ion s about colo r are cr i t icalfactors in the success o f 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.



Definition & Origin of Brightness

It is the measure of light reflected from asample at 457 nanometers +/- 44 nm.

Brightness represents the diffuse blue

reflectance of a sample, and thewavelengths indicated above were chosen

on a somewhat arbitrary basis.

It was introduced as a visual aid forassessing and controlling the degree of

pulp bleaching.





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.






Process Solutions

Pulp Bleaching Impact



Origin & Evolution of BrightnessThe need to simplify and standardize

bleaching assessment of pulp led to the firstinstruments 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 illuminatedwith an incandescent lamp at a 45o angleand reflectance is measured perpendicularlyor at a 0o angle of observation.





Evolution and Use of Brightness

As there was no comparable instrumentavailable for the papermaking process, theGE brightness meter (now referred to asDirectional or TAPPI T452 Brightness)

moved to the paper mill.Prior to the introduction of fluorescent

whitening agents, and as a consequence ofits purpose in describing the degree of bleaching, brightness over time becamesynonymous with how white the paperappeared (or simply whiteness).





Types of Brightness

There are two basic types of brightnessmeasurement: Directional and Diffuse.

Directional brightness (TAPPI brightness – TAPPI 452) employs the 450/00 geometry of

the original GE-Phovolt instrument. It has been the standard in the U.S. and Japan.

Diffuse brightness employs a D/00 geometrywhere D indicates diffuse illumination froma sphere, making it insensitive to sampleorientation. Diffuse brightness is thestandard in much of the rest of the world.





Illustration of Instruments

Directional

Diffuse

Sample

Photodetector

Light source

Sample

Photodetector

Light source





Types of Brightness

Two types of Diffuse brightness are commonlydiscussed, and a standard exists for both of them.

ISO C Brightness (ISO 2470-1, TAPPI 525) usesIlluminant C level of UV energy. It was selected as

the best approximation of normal office lightingconditions.

ISO D65 Brightness uses Illuminant D65(daylight). Control of D65 level of UV energy is

not good from instrument to instrument, but stillthere is now a standard for D65 Brightness (ISO2470-2).






Process Solutions

Differences Between D65 and C



Comparison of Brightness Types

TAPPI (450/00) , or Directional and Diffuse(D/00) Brightness (C or D65) cannot becorrelated. This is due to the fact that

multiple reflections which occur betweenthe sphere and sample make unpredictablechanges in Diffuse Brightness as comparedto Directional (TAPPI) Brightness.

The following two slides show brightnesscomparisons on a number of white papers.





Brightness Comparisons

Technidyne Technidyne

Sample D65 Brightness ISO Brightness TAPPI R457 C S-4M

A 98.92 91.78 89.9 6.93 5.2

B 95.34 88.99 87.3 6.14 4.7

C 105.58 95.08 91.8 10.58 7.9

D 111.20 99.83 96.5 11.48 8.5

E 110.61 98.94 95.5 11.90 9.2

F 112.25 100.43 96.0 12.58 9.5

G 113.46 100.89 96.4 13.45 10.3

H 110.11 98.68 94.7 11.73 8.8

I 112.28 100.15 95.9 12.97 9.8

J 93.00 88.64 90.0 5.44 4.3

K 102.01 92.52 90.6 9.56 8.0

L 110.12 99.05 95.0 12.08 9.1

M 110.14 99.48 96.1 10.97 8.4

N 107.24 96.68 94.1 10.66 8.1

O 106.90 96.28 93.0 10.61 7.9P 110.31 99.21 96.1 11.51 8.9

Q 109.57 99.03 96.1 10.90 8.2

R 113.86 101.50 97.4 13.25 10.3

S 111.55 99.29 95.0 12.80 9.6

T 85.48 85.43 87.6 0.02 0.0

Elrepho

Brightness

Elrepho

Fluorescence

Informing our Customers:CRABLE ENGINEERING LLC



Comparison: TAPPI vs ISO Brightness

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

86.0 87.0 88.0 89.0 90.0 91.0 92.0 93.0 94.0 95.0 96.0 97.0 98.0 I n c r e a

s e d I S O V

a l u e s

TAPPI Directional Brightness

Delta Brightness Comparisons - Real Data


S f



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




Problems and Limitations of Use Directional (TAPPI) brightness, first, has an issue in

that it is highly sensitive to fiber angle. Indeed, onecan impact directional brightness with changes inRush/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. Themeasurement is not suitable for paper or paperboardcontaining coloring matter (such as yellow or greendyestuff) which appreciably absorbs light in that part

of the spectrum extending from 400 to 500 nm.Colored papers must be measuredspectrophotometrically or colorimetrically in orderto obtain meaningful results.”




Problems and Limitations of Use

The biggest issue with use of brightness as a papermetric, though, is that it measures reflectance in aVERY narrow (blue) band of the reflectancespectrum. 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 visualimpact than a change from 90 to 96 brightness.

The higher the brightness of the paper (broughtabout through the use of FWA), the quicker the

paper will fade.




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, TiO2, or ATH tohide 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.




Ways to Avoid Lower BrightnessUse 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” mayoccur.

Use minimum amounts of dye for shade

control. Informing our Customers:CRABLE ENGINEERING LLC



CIE Whiteness

Whiteness is a visual perception thatinvolves the entire visible spectrum from

400 nm to 700 nm.

It was developed, specifically, as a singlemetric to describe the appearance and appealof 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.




CIE WhitenessMost import papers are shade formulated to

take advantage of the increase in Whitenesswith blue and red (or violet) tinting of the paper.

Whiteness can be less expensive to achieve

than Brightness: a small addition of tintingdye (low cost) can significantly improveWhiteness. [Tinting dye use can generallyonly lower Brightness.]

Change in the shade of paper with lightexposure is generally less severe than loss ofBrightness with FWA fade.

Informing our Customers:GREENVILLE COLORANTS LLC



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.)




International Paper - PapermakingProcess Solutions

Brightness, Whiteness, and L*



Brightness Conclusions

Either brightness or whiteness can be moreexpensive to achieve depending upon theshade of the paper and its „brilliance‟.

As one goes to very high brightness levels,

production costs rise ever more quickly, andthe visual impact becomes smaller.

ISO Brightness values are generally higher(as much as 1.5 to 4.5 points) and lessvariable than TAPPI Brightness values.

Whiteness often correlates better with visualappeal than does Brightness.




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 beenexhausted.

The only way to continue to increase CIEWhiteness, then, is to make the paper bluer.

Often, however, the product begins to look dulland grayish at the highest CIE Whiteness levels.

We need to refine the CIE Whiteness equations to prevent overuse of tinting dyestuff to artificiallyinflate the numerical value while actually makingthe paper look duller.




Whiteness Conclusions Although much of the rest of the world makes

and sells paper according to CIE Whitenesslevel (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:

brightness whiteness crable engineering llc

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