A New Approach to Measuring ERIC in Deinked Papers David Vahey, - - PowerPoint PPT Presentation

A New Approach to Measuring ERIC in Deinked Papers

David Vahey, J.Y. Zhu and Carl Houtman USDA, Forest Products Laboratory Madison, WI

Effective Residual Ink Conc. (ERIC)

200 400 600 800 1000 1200 Wavelength (nm) Absorbance

Paper (x100) Ink

950 nm

Assumption: At 950 nm any absorbance is due to ink

ERIC Uses Near Infrared (950 nm) to Emphasize Ink Absorbers

= Visible Light = Near Infrared (NIR) Ink Dye Lignin NIR Absorption depends mostly on ink concentration

ERIC Measurement

Ro R∞

Single sheet

• ver a black

cavity Stack of similar sheets

Reflectance at 950 nm using d/0º

Advantages of ERIC Measurement

• Rapid, commercially available
• Suitable precision for control actions
• An improvement over brightness

measurement

– More sensitive to ink – Less sensitive to dyes and lignin

Disadvantages of ERIC Measurement

• When Ro and R∞ are close, the errors increase
• Some samples exhibit such low reproducibility

that results become meaningless

• Sample must be repositioned to take the two

measurements

Goals of the Study

• Explore the sources of inconsistency in

ERIC measurements

• Determine the impact of using a different

wavelength and/or geometry (e.g. 750 nm with a UV/Vis spectrophotometer)

• Develop a preliminary error analysis

Light-Paper Interaction Theory

A* T = % Transmission R = % Reflection A = % Absorption I = 100%, Incident Illumination Conservation of Energy→ 100% = R + T + A

Approximate ERIC calculation

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − − × ≈ ) ( 1 100 (ppm) ERIC

2

m kg w T R

w = Basis Weight R = Reflectance fraction T = Transmittance fraction

Standard ERIC Measurement Approach

A* R0 Single Sheet R∞ Thick Stack T = 0 T>0

Kubelka-Munk Theory

I J

x In differential form: dI = -(K+S) I dx + S J dx dJ = -S I dx + (K+S) J dx Gain from scattering I Loss

• f

J

a bit of mathematics….

Standard ERIC calculations

( )

∞ ∞

− × = R R S ERIC 2 1 100

2

( )

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − − ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − =

∞ ∞ ∞ ∞

R R R R R w R S

2

1 1 ln 1

Problem: ERIC→∞ as Ro/R∞→1

w = basis weight, in kg/m2

ERIC Measurement Problem with Opaque Papers

A* R0 Single Sheet R0/R∞ ≈ 1-R0T2 Thick Stack T ≈ 0

*

~R0T2 ~R0T

R∞

High Opacity Paper

• With opacity > 97%, Ro and R∞ are very

close, thus the estimate of S is very poor.

• One possible solution is to use an estimated

value for Savg (near 50 m2/kg for TMP).

• Another is to base ERIC on R and T

measurements instead of Ro and R∞.

The R and T Method for ERIC

* T = Transmission R = Reflection I = 1, Incident Illumination ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ − + − − + − ⋅ − − =

− 2 2 2 2 1 2 2 2 2 2 2

4 ) 1 ( 2 1 sinh 4 ) 1 ( ) 1 ( x 100 R R T T R R T w T R ERIC

Experimental Setup for ERIC by the R and T method

Lamp Chopper Aperture Paper Aperture Moveable Detector for Transmission (T) and Reflection (R) Lens T R Amplifier Oscilloscope

Experimental Samples

• TMP: 65 g/m2 handsheets from pulp samples with

varying degrees of residual ink.

• Kraft: 65 g/m2 handsheets from pulp samples with

residual ink from laser printing.

• Newsprint: 50 g/m2 page from a directory.

Summary of Results

ERIC, by method Opacity Sample 792 693 558 702 96.1 TMP 2 1238 1100 939 1106 98.7 TMP 3 602 504 417 519 94.6 TMP 1 158 149 189 83.2 Kraft 140 127 181 81.7 News Commercial SavgR∞ R0R∞ RT

ERIC Results by Three Different Methods

News Kraft Trial 1 Trial 2 Trial 3 280 560 840 1120 1400 20 40 60 80 100

• ERIC (ppm)

Opacity ERIC RT RoR sR sR :Technidyne

Sample

Opacity (%)

Typical ERIC values

• ERIC ≈ 1000 ppm, for newsprint at the start
• f deinking
• ERIC ≈ 200-300 ppm for commercial

recycled newsprint

ERIC Error Analysis

200 400 600 800 1000 1200 10 100

RT R0R sR S 50 40 Data

ERIC (ppm) ERIC COV (%)

• 6

20

• 40

70

Conclusions

• ERIC values greater than 800 ppm are prone to

errors with standard RoR∞ method.

• Use of an estimated scattering coefficient S make

comparisons between different papers difficult.

• ERIC measurement using R and T

– Requires no assumptions about S. – Becomes increasingly accurate at high ERIC