PAPER COLORATION

October 2008

Water & Paper Treatment

Topics
1. Ciba Product Ranges

2. Dyestuffs (Colorants):
A) Classes of Dyes
B) Factors affecting Dyeing processes
3. Application of Dyes:
A) Paper Coloration Methods
B) Handling and Storage
4. Ciba Direct Dyes
5. Fixing

Water & Paper Treatment

Ciba Color Product Range

®
• FWA (OBA)

®
• Dyes

®
• Pigments

• Colorformers ®

Water & Paper Treatment

Classes of Colorants Use for Dyeing Paper
• Acid Dyes
• Basic Dyes
• Anionic Direct Dyes (ADDs)
• Cationic Direct Dyes (CDDs)
• Colored Pigments
• Fiber Reactive Dyes

Water & Paper Treatment

Factors that Influence Dyeing

• Furnish (Pulps) • Chlorine

• Degree of Refining • Points of Addition
– Thin Stock
• pH – Thick Stock
• Contact Time • Broke Addition
• Order of Addition • Machine Conditions:
• Water Hardness – Wire Design
– Table Design
• Chemical Additives: – Size Press
– Starches – Drying process
– Retention Aids
– Wet Strength • Fillers (Type and Quantity
– Dye Fixative Used)
– Coagulants
– Alum • White Water System
– Biocides • Moisture of paper web.
– Sizing
• Temperature

Water & Paper Treatment

Pulps
• The fiber that is used has great impact on the final
shade of the paper and the performance of the
colorants.

• Hardwood & Softwood Blend:

• length of fiber
• Degree of Refining:
• more of the fiber exposed
• dyeing sights increased
• more opaque (less voids, areas for light transmission)
• Brightness:
• High brightness results in brighter shades
• Low brightness results in duller shades

Water & Paper Treatment

Fillers
• The use of fillers, such as clays, calcium carbonates,
and titanium dioxides will have a considerable effect
on the final shade of the paper :
• Clays, Carbonates, TiO2, ATH, etc.
• shade/brightness of the filler
• receptivity to colorant
• surface area effect
• An increase in the amount of filler in the sheet will
require an increase in the amount of dye in order to
maintain the same depth of shade.
• The fillers, which are not dyed as readily as the fiber,
have a masking effect on the colorants.
• Effect on Colored Two-sidedness.

Water & Paper Treatment

Chemical Additives
•Retention Aids:
> can help retain colorants as well as fiber, filler, and fines
> impact depth, and shade
•Dyestuff Fixatives:
> used to improve bleed-fastness
> can assist in exhaustion of less substantive dyestuffs onto
the fiber
> effect on shade.

Water & Paper Treatment

Chemical Additives

–Alum
> aids in retention of less substantive dyestuffs
(acid sized system)
> point of addition
> impact on shade
–Biocides & Defoamers
> compatibility issues
> oxidation of colorants

Water & Paper Treatment

Order of Addition
• Key for Color Performance
• relation to other chemical additives
• depth, shade, two-sidedness, bleed-fastness
• Finite Number of Points of Addition
• agitation, space for totes, pumps, etc.
• Find What Works
• and stay with it for consistency from run to run

Water & Paper Treatment

Point of Addition
• Agitation is Essential
• inlet to stock transfer pump
• beater chest (with good mixing ability)
• Contact Time (Between Colorant & Fiber)
• for consistent color performance, the contact
time must be consistent
• might be a challenge for batch addition

Water & Paper Treatment

pH

• The pH of a paper machine system will have

a definite impact on both the shade and the
retention of the colorants used.
• Sensitivity of shade to pH
• most dyes to some degree
• Direct Yellow 4 - classic case
bright, green shade of yellow when it is used at an acidic pH.
However, when the pH rises to an alkaline level, the shade changes
to a very dull red shade of yellow

• Consistent pH is key for consistent color.

Water & Paper Treatment

Water

– Water hardness can be a hindrance as well as help in

the application of dyestuffs on a paper machine
– Color
– Seasonal
– Hardness: (Natural hardness, Artificial hardness)
• Helpful for color production.
• Hindrance in make down systems.
Salts can be added to raise the water hardness levels
and increase dye retention. This will result in deeper,
brighter shades, and more efficient dye usage.

Water & Paper Treatment

Residual Chlorine
• Carryover from Water Treatment
• Carryover from Pulp Mill
• Residual from biocide control
• Carryover from Pulper bleaching of broke or
recycled fiber.
> will oxidize-bleach dyestuffs
> variation in residual chlorine level will lead to variation in shade
> target <1ppm

Water & Paper Treatment

Effect of Residual Chlorine
% Strength
100

90

80

70

60

50
0 1 2 3 4
Residual Chlorine, ppm
Direct Blue 290
Water & Paper Treatment
 Effect of Residual Chlorine
% Strength
120

100

80

60

40

20

0
0 1 2 3 4
Residual Chlorine, ppm
Direct Red 254

Water & Paper Treatment

 Effect of Residual Chlorine

% Strength
100
90
80
70
60
50
40
30
20
10
0
0 1 2 3 4
Residual Chlorine, ppm

Water & Paper Treatment

Direct Yellow 127
Residual Chlorine
• Use of anti-chlor (to neutralize excess chlorine);
• sodium bisulfite (reducing agent)
• anti-chlors can impact the shade and strength of colorants.
• suggested use - just enough to neutralize excess chlorine.

Water & Paper Treatment

Broke/Recycled Fiber
The effective management of broke is critical in running
consistent color on a paper machine, especially a machine
that makes colored paper.
– Shade (colored broke)
– Fluorescence (recycled fiber/high bright broke)
– Filled or Unfilled
– Lowers freeness (more fines)
– Anionic Trash
• Broke should be pulped separately
• Broke chest with consistency control and flow control.
• Only broke, made with the same dyes.
• Broke should be added into Machine Chest at controlled consistency
and flow.

Water & Paper Treatment

White Water System
• The presence of fines, fillers, and colorants in the white
water of a paper machine will affect the final shade of the
paper.

• “Coming to Equilibrium” on a Colored Production Run.

• Grade Changes

• Colored Fines & Filler/Consistent Retention

Water & Paper Treatment

Temperature & Moisture

Thermo-chromatic Colorants - shade sensitive to heat.

Sample off paper machine should be allowed to settle to
room temperature before measurement.

 Moisture - gives appearance of depth.

Generally, the more moisture a sheet contains, the deeper
or stronger the shade looks.
the moisture profile should be as uniform as possible before
making any serious evaluation of color. The sample should
be conditioned to standard moisture.

Water & Paper Treatment

Classes of Colorants Use for Dyeing Paper
• Acid Dyes
• Basic Dyes
• Anionic Direct Dyes (ADDs)
• Cationic Direct Dyes (CDDs)
• Colored Pigments
• Fiber Reactive Dyes

Water & Paper Treatment

Pigments
Advantages: Disadvantages:

 Good - Excellent Light-fastness  No Affinity for Cellulose

 High Bleed-fastness  Poor Build-up Properties

N N N
 Good Chemical Resistance  Sensitive to Retention
(Only as good as retention system)
N Cu N
 Brighter than ADDs:  Two-sidedness Tendency
 1.0 to 2.5 points brighter
 Reduced FWA Usage
N N  Handling
N / Housekeeping

Water & Paper Treatment

Indanthrene Pigment
Anionic Direct Dyes (ADDs)
Advantages: Disadvantages:

 Good affinity for bleached

cellulose.  Duller Shades than Acid Dyes,
Basic Dyes, or Pigment.
 Useful for un-sized paper grades.
 Good Light-fastness.  Increased Alum usage causes
duller Shades and Reduces
HGood
2N OH CH3O
Bleed-fastness. OCH3
Light-fastness.
HO NH2
 Increased dye retention with
higher temperature or salt  Poor Bleed-fastness in deep
addition. N=N shades. N=N
 Less two-sided than Acid or Basic  Some products sensitive to pH
Dyes. conditions.
SO3Available as stable
SO3 liquid SO3
formulations. SO3

Water & Paper Treatment

Cationic Direct Dyes (CDDs)
Advantages: Disadvantages:

 High affinity for bleached and  Sensitive to anionic trash (loss of

semi-bleached cellulose.
strength).
 Higher affinity for most fillers
 Some products sensitive to ph
 No fixative required. (mottling effects).
 Not affected by water hardness.  Higher dyeing costs.
 Generally produce clear
backwater.  May “granite”
 Effectively control two-sidedness  Incompatible with acid and direct
in combination with anionic dyes. dyes.
 Compatible with cationic
polymers (wet strength, retention,
drainage)

Water & Paper Treatment

Basic Dyes
Advantages: Disadvantages:

 High affinity
(CHfor
3)2N
bleached and  Sensitive
N(CH to anionic
3)
trash (loss of
strength). 2
semi-bleached cellulose.
 Excellent affinity for unbleached  Poor affinity for bleached
C cellulose (Fixative
cellulose (lignins/tannins). required)
 Brilliant colors  Poor light-fastness
 High tinctorial value  Poor alcohol bleed-fastness
 Economical  “Graniting” effect
 Incompatible with acid and direct
NH2 dyes
_
CH2+} Cl

Methyl Violet

Water & Paper Treatment

Acid Dyes
Advantages: Disadvantages:

 High affinity for bleached and  Little or no affinity for cellulose

semi-bleached cellulose.  Fixation necessary
(alum/cationic fixative)
 Excellent water solubility
 Effluent problems (colored
 Bright shades backwater/deep shades)
 Do NaO
not “granite”
3S  Poor bleed-fastness
 Moderate-good light-fastness  Generally top-sided (exception:
acid red 137)
N N  NH under certain
Color migration
drying conditions.

CI Acid Yellow 36 (13065)

Water & Paper Treatment

Reactive Dyes
Advantages: Disadvantages:

 True chemical bonding with  Hydrolysis of dye

cellulose possible (colored backwater)
 Excellent water solubility  Dye - fiber fixation time
 Bright shades (comparable requirements.
to acid dyes)
 High bleed-fastness
 Available as liquid
formulations.

Water & Paper Treatment

 What is the best dyeing
method?

Water & Paper Treatment

Dyes Application (Colouring) Methods

 Wet End Application:

• Batch Dyeing:
• Dyes Added to Beater or Pulper.
• Continuous Dyeing:
• Dyes Added to Stock Flow.
• Split Dyeing:
• Dyes Added to Pulper.
• Shade Controlled as Continuous.

 Surface Coloration:
• Size Press
• Calendar
• Coating

Water & Paper Treatment

 Batch Dyeing Process
Fixing agent
Filler
• Sequence here is only a guide
Dyestuff
(recipe dependant)
• In some cases, a split addition of fixing Size
agent before and after the colorant Alum
addition is preferred.
• Avoid direct contact of anionic colorants
and pigments with cationic agents in
the Pulper.
• The process of chemical addition could
be fully automated.
• Batch dyeing still in use in many paper
mills.

Water & Paper Treatment

Batch Dyeing Process
Advantages: Disadvantages:

 Good for deep shades.  Longer time for grade

 Optimized order of addition. change.
 Longer Contact Time.  Very limited shade control.
 Better Dye yield
 Better Light fastness
 Batch to batch Shade
 Better Bleed differences.
 Brighter Shades
 No shade correction.
 No addition of several
products at the same time.  Entire Stock Preparation is
colored.
 Cost efficient.
 Broke management issues.
 Low flexibility

Water & Paper Treatment

Continuous Dyeing Process
Advantages: Disadvantages:

 Late Dye Addition  Order of addition is limited.

 Less Color contamination of  Short contact time.
the stock preparation.  Back-water coloration.
 Quick shade changes.  Difficult to produce deep
 Quick shade corrections. shades.
 Reduced worker exposure to  More of an effect on Charge
dyes. Demand.
 Easier shade control.  More two-sidedness (top).
 Less broke.  Higher dyeing costs on deep
 Closed loop control possible shades.

Water & Paper Treatment

Split Dyeing Process
 70 to 80% of the dyes added to the Pulper.
 The rest of the dyes dosed to;
 Suction side of machine-chest stock pump, or
 Drop-leg from level-box, or
 Suction side of 1st stage cleaners pump, or
 Suction Side of Fan Pump.
 Achieve advantages of Batch Addition with shade control
advantages of Continuous Addition.

 Split dyeing can also be split between the

wet end and size-press.

Water & Paper Treatment

 Wet-End Dyes Applications
Possible Dosing Points
Pulp Mill
Level-Box Cleaners

H.D. Additives 2 3
1
Tower
Refined
Chest-1
Refiner

V.Screen
2 3
Refined Mixing Machine
Chest-2 Chest Rejects
Chest
Refiner
To
Pulp Bales
H/Box
Broke

Pulper Fan Pump

Pressure Screen
Dump Broke
White Water from
Chest Chest 1
PM Wire Pit (Silo)
Water & Paper Treatment
Surface/ Size-Press Coloration
Advantages: Disadvantages:

 Economical  Reduced Bleed-fastness.

 Can use most classes of  Reduced Light-fastness.
dyes.  Sensitive to sheet quality and
 Can achieve deep shades. imperfection.
 Can achieve brighter shades.  Deep shades have a
 Can correct two-sidedness. tendency to mottle.
 Ecologically more sound.  Sensitive to:
 Moisture variations
 Entire Stock-Preparation &  Liquid pick-up variations
wet-end not contaminated  Degree of sizing
with dyes.  Caliper profile

Water & Paper Treatment

Size-Press Dyes Application
Addition Points
Paper Roll Paper Guide Roll

Spray Bars

Soft Hard
Roll Roll
Paper
web
Starch
Overflow

Fresh make up
Starch Banana Roll

Chrome
Plated

After Dryers
Service Tank
Water & Paper Treatment
 Size Press Variables
 Entering sheet moisture 5-15%
 After SP moisture up to 45%
 SP nip has three zones
 The main parameter affecting Solution Paper
the Pick-up is absorption.
 Factors controlling absorption: Absorption
 Porosity of the sheet
 Internal sizing
 Moisture content Roll Roll Shear zone
 Starch viscosity and temp.
 PM speed Hydrodynamic
 Pond size (height) Metering
 Roll hardness
 Roll diameter
 Rolls nip pressure
 Entering and lead out angles
Water & Paper Treatment
 How to use dyes?

Water & Paper Treatment

Preparing of Dye Stock-Solutions
Preparation of stock solutions
• Only with soft water (condensate)
• Prepare low concentration dilutions ( 0.5 -10%)
• With hard water use a sequestrant to avoid precipitation by
calcium or magnesium salts.
• Prepare only what you really need.
• Clean the tank before you prepare a new solution
Risk of contamination with bacteria, fungi (sludge, slime ->
filter blocking)

Water & Paper Treatment

Preparing of Dye Stock-Solutions
• For continuous dyeing
• Dilution with fresh water (constant pressure)
• For batch dyeing
• Dilution/ dissolution not always necessary
• Dilution to transport the dyes using computerized pump systems
(fresh water)
• Dilution with fresh water (reduces risk of mottling)
• Preparing of stock solutions
• Only with soft water (condensate water)
• Check stability in the laboratory.

Water & Paper Treatment

Miscibility of Dyestuffs
• Cationic dyes (CDD) can, as a general rule, be mixed
together (cationic charged)
But
• Don’t make stock solutions
• Only for continuous feeding
• Only for fast use
• The compatibility should be tested in the lab
• Incompatibilities are possible:
• By different formulations
• Strong differences in pH - value

Water & Paper Treatment

Miscibility of Dyestuffs
• Anionic dyes should never be mixed with cationic
products (including dyes)
• Fixing agents (Tinofix WSP or ECON)
• Retention aids (cationic)
• Aluminum sulphate
• Cationic starches or sizes.

• Cationic dyes should never be mixed with anionic

products
Precipitation

Water & Paper Treatment

Cleaning

• Tank systems should be cleaned before each refill process

• Contamination with micro-organisms
• Pump systems (continuous) should be cleaned with water
during shade-changes
• Check the filter-basket
• With batch systems check the filter baskets regularly
• Irgasol (or similar) can be used to aid the cleaning process
• Pipes, tanks, pumps, etc
• Regular system cleaning ( 2-3 monthly intervals)

Water & Paper Treatment

Storage of Dyestuffs
• Don't expose to sunlight
• Not at high temperature
• Not below 0°C
• If stored below 0°C (and product has frozen)
• Bring it to room temp (thawing process), gentle stirring.
• Store powder dyes in dry rooms
• Keep lids on containers (minimize drying out esp.
Pigments).

Water & Paper Treatment

Pergasol Yellow 6G Liquid

An anionic direct dye in the bright greenish yellow segment

Uses DHTPTS intermediate : 60% - 80% variable costs
Used in printings, writings & copying papers.
For bright yellow and green shades with ADD or CDD
Turquoise dyes
Characterized by:
• Bright greenish yellow shade : hue angles 98-102,
moderate affinity sized, poor affinity unsized, good light
fastness
• Good bleachability (oxidative).
• Even to wire-sided.
• Good to excellent filler affinity.
Water & Paper Treatment
Pergasol Yellow F-6G Liquid

• A very bright fluorescent greenish yellow

• High affinity
• Suitable for wood containing printing papers (poor light
fastness)
• On wood-free, chalk filled papers (with pre addition of
Tinofix ECON) this product offers a very cost efficient
dyeing performance and achieving moderate (3) light
fastness
• Can be promoted against the competition Canary Yellow
dyes under AKD/ Chalk filled conditions and achieving a
much lower dyeing cost
• Very sensitive to anionic trash - redder shades

Water & Paper Treatment

Pergasol Yellow GA Liquid

• An anionic direct dye in the medium yellow segment

• Used in printing, writing & copying papers when
good light fastness is NOT required.
• Because of its good fiber affinity and economics is
very suitable for tissue dyeing and viscose film.
• The product is alum/ pH sensitive and gives a redder
shade especially in soft water.

Water & Paper Treatment

Pergasol Yellow GA Liquid
Characterized by:
• Excellent bleachability (NOT peroxide)
• Poor moderate light fastness
• Excellent fibre affinity, good filler affinity
• Wire - sided tendency
• Alum/ pH sensitive
• Fluorescent
• Dilutions stable in soft water, unstable in hard water

Water & Paper Treatment

Pergasol Yellow S Liquid

• An anionic direct dye in the reddish yellow segment.

• Economical dye for printing, copying, waste based
packaging papers & even deep dyed tissue.
• Based on stilbene chemistry-produced at McIntosh USA.
Characterized By:
• Dull reddish yellow shade, hue angles 75-78
• Lower affinity for cellulose - especially unsized moderate
light fastness (fades redder)
• Poor bleachability (better with reductive methods)
• Slightly to strong top – sided
• Poor fastness to alkali
• Good to excellent filler affinity (sized)
• Can interfere with fines retention.
Water & Paper Treatment
Pergasol Yellow S Liquid

• Stable as dilutions in soft water. Only stable in hard water

for relatively short periods.

Water & Paper Treatment

Pergasol Yellow G Liquid
• Anionic direct in the medium yellow segment.
• High affinity and good light fastness being suitable for use
in a wide range of papers.
• Used where non-fluorescence is required.
• Dyed paper tends to drift redder in shade (acid/ unsized)
Characterized by:
• High fibre and filler affinity.
• Good light fastness.
• Moderate hypochlorite bleachabilty
• Wire-sided tendency, non-fluorescent.
• Dilutions stable in soft water, unstable in hard water

Water & Paper Treatment

Pergasol Yellow RN Liquid
• Anionic direct in the medium yellow segment.
• Selected when good light fastness is required but tends to
be less economical than other Ciba medium shade
products.
• Used in printing, writing, and copying type papers.

Characterized by:
• Bright medium shade yellow, hue angle range 85-87, poor
bleachability, non-fluorescent, good fibre affinity, excellent
filler affinity. Wire-sided tendency.
• In some shades can exhibit photochromism.

Water & Paper Treatment

Pergasol Yellow 3GN Liquid

• Anionic direct in the medium yellow segment.

• Based on DHTPTS intermediate - made at Grenzach.
Excellent bleachability and good light fastness. An all
purpose economical dye for pale/ medium shades in
business papers and even tissue.
Characterized by:
• Bright greenish medium yellow, Excellent bleachability,
good light fastness, fluorescent, wire-sided tendency.

Water & Paper Treatment

Pergasol Red N Liquid
• An anionic bright red direct dye
• Intermediate in shade between Red 3B and Red 2G
Liquids
• Good affinity
• Moderate to good light fastness (2-3)
• Stable as a dilution in hard water

Water & Paper Treatment

Pergasol Red 2G Liquid

• Anionic direct in the scarlet/ yellowish red segment.

• Used in a wide range of papers where poor-moderate light
fastness can be accepted. Suitable for unsized papers
due to its very high fibre affinity.
Characterized by :
• Scarlet shade, hue angle range 17-21
• High fibre/ filler affinity, poor-moderate light fastness, wire-
sided tendency, good bleachability.
• Stable as dilutions in hard & soft water.

Water & Paper Treatment

Pergasol Red 3B Liquid New

• Anionic dye in the bluish red segment. Used in a wide range

of papers including tissue. Has good light fastness, bleed
fastness & fibre affinity.
Characterized By:
• Bluish red shade, hue angle range 9-12.
• Good light fastness.
• Good fibre affinity.
• Good oxidative bleachability.
• Even-wire sided tendency.
• Stable as dilutions in soft water, 10% min in hard water.

Water & Paper Treatment

Pergasol Red 2B Liquid
• Anionic direct in the bluish red segment.
• Bluer/ brighter than Red 3B Liquid New.
• For general use where lower cost is needed without
any bleed or light fastness requirements.
• Used in a wide range of paper including tissue, waste
based packaging and viscose film

Water & Paper Treatment

Pergasol Red 2B Liquid

Characterized By:
• Bright, bluish red shade, hue angle 5-7.
• Low light fastness, bleed fastness & affinity.
• Good cost performance/ low filler affinity.
• Good bleachability/ strong wire-sided (filled papers)
• Stable as dilutions in soft & hard water

Water & Paper Treatment

Pergasol Blue 2R Liquid

• Anionic dye in the reddish blue segment.

• A coppered light fast direct blue with a dullish shade &
moderate affinity. Used in business papers and tissue.
Especially in fine paper & cover papers where high
light fastness in required.

Water & Paper Treatment

Pergasol Blue 2R Liquid

Characterized By:
• Dull reddish blue, hue angles 256-261, moderate fibre &
good filler affinity.
• High light fastness
• Moderate bleachability
• Even-wire sided
• Stable as dilutions in soft and hard waters

Water & Paper Treatment

 Pergasol Blue R Liquid

• Anionic direct in the reddish blue segment.

Slightly greener and duller than Blue 2R Liquid,
• Non Coppered and has poor light fastness but
lower dyeing costs.
• Used in tissue and waste based packaging.

Water & Paper Treatment

 Pergasol Blue R Liquid

Characterized By:
• Dull reddish blue, hue angles 252-256.
• Poor light fastness/ moderate bleachability.
• Good fibre & moderate filler affinity.
• Even-wire-sided.
• Stable as dilutions in soft and hard waters.

Water & Paper Treatment

 Pergasol Blue GD Liquid

• An anionic blue dyestuff

• Copper free
• Moderate light fastness (2)
• Brighter in shade compared to Pergasol Blue R
Liquid & Blue 2R Liquid
• Good affinity
• Higher dyeing cost than Pergasol Blue R Liquid
but lower than Blue 2R Liquid.

Water & Paper Treatment

 Pergasol Blue DK Liquid

• A bright reddish blue shade for tinting whites and

business type papers
• Copper Free
• Good light fastness properties (3-4)
• Sensitive to alum/ cationic products (redder
shade)
• High pH formulation (12-13) labeled as corrosive

Water & Paper Treatment

Pergasol Turquoise F-2GE Liquid
• A cationic direct (CDD) Turquoise.
• Used in tissue/ fine papers for bright greenish blue/
turquoise and green shades.

Water & Paper Treatment

Pergasol Turquoise F-2GE Liquid
Characterized by:
• Bright turquoise shade, high light fastness & fibre affinity.
• Topsided (less than ADD), poor bleachability,
• Stable as dilutions in soft water

Water & Paper Treatment

Pergasol Turquoise R Liquid
• An anionic (ADD) direct turquoise. All ADD copper
phthalocyanines have very low affinity for cellulose which
means they need to be used with a cationic fixing agent or
alum depending upon the sizing system. This product is
made at Grenzach and Ciba are extremely competitive in
this area.

Water & Paper Treatment

Anionic Direct Dyes (ADDs)
Both ADDs and cellulose are negatively charged, and are
therefore naturally subject to repulsive forces. In order for the
dyes to be fixed to the fibre, these forces need to be overcome.
This is generally achieved by mixing ADDs with cellulose in thick
suspension (eg 3% or higher) so bringing the dyes and fibres
close enough to overcome the electrostatic barrier. This is
otherwise assisted by the presence of electrolyte in the water
either naturally occurring (hard water), or by the addition of alum,
fixing agent, or other highly charged cationic material.
Repulsion
- Energy Barrier

Distance
Dyestuff/Fiber

Attraction
+
Water & Paper Treatment
Cationic Direct Dyes (CDDs)
The natural attraction between the cationic dyes and anionic cellulose
fiber allows the dye to overcome the energy barrier for bonding to be
overcome very easily, which leads to much faster fixation rates, and
generally higher levels of exhaustion.

Repulsion

-
Distance
Dyestuff/Fibre

Attraction
+
Water & Paper Treatment
 ANIONIC AND CATIONIC
DYESTUFF

ADD

Repulsion
WATER

Cellulose

WATER
Attraction

NOTATION : ADD Anionic Direct Dye

CDD Cationic Direct Dye
+ CDD +
Water & Paper Treatment
Influence of Water Hardness on ADDs and
CDDs

The electrolyte in hard water, which is a mixture of cations and

anions, surrounds the anionic surfaces of both cellulose and the
ADD, creating electrically neutral surface, which reduces the
repulsion between the two, and therefore allows the dye and
fibres to approach each other, and bonding to take place. In soft
water, where no electrolyte is present, dye exhaustion tends to
be lower than in hard water for ADDs. CDDs are not affected by
the water hardness.
Energy Barrier In Soft Water

Repulsion
Energy Barrier In Hard Water
-

Distance
Dyestuff/Fibre

Attraction
Water & Paper Treatment +
 ADD
Shelter Effect by Electrolytes

Undisturbed Repulsion

Cellulose fiber

NOTATION A R
R : Repulsion
A : Attraction A ADD
ADD : Anionic Direct Dye
CDD : Cationic Direct Dye R
A

Water & Paper Treatment

 Influence of Fixing Agent
on ADDs and CDDs

Highly charged low molecular weight polymers are often used instead of
electrolyte to assist the fixation of dyestuffs to cellulose.

Anionic Direct Dyes

When used with ADDs, the fixing agent can be added to the fibre before the
addition of dyes, which neutralizes the anionic charge on the fibre surface,
allowing the ADD to approach so that bonding can take place. Fixing
agent can also be added after the addition of dye, when it will form
precipitate with the ADD remaining in the system, which is then
mechanically retained on the fiber surface.
Cationic Direct Dyes
CDDs tend to fix more intensely to fines and anionic trash present in the
paper making system, causing mottled dyeing. In this situation,
the fixing agent is added to the fibre before the dyestuff, this
will neutralize the anionic trash, so that even dyeing will take place.

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FIXING AGENT
TINOFIX
ADD

Cellulose fiber

Filtration

Pigment ADD

Notation : ADD Anionic Direct Dye

CDD Cationic Direct Dye
Cationic Fixing Agent ( Tinofix WSP )

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Influence of Alum or Fixing Agent on ADD’s
- In most cases only part of the anionic direct dye really
behaves like a dye, being adsorbed on thefibresurface and
then diffusing into thefibre. Depending on:-
- Affinity of the dye
- Shade intensity
- Addition point of fixing agent or alum etc…
- There is nearly always one part of the anionic direct dye
which is precipitated and, more or less loosely retained on
thefibre

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Topics
1. Silurian Fiber

2. Metamerism

3. Two Sidedness

4. Lightfastness

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Silurian Fibres
• Causes
– Adding neat dyes (especially CDD turquoises) at a point of
poor mixing
– Adding basic dyes to mixed waste furnishes

• Corrective action
– In line, dilute the dyes and add on the suction side of a pump
to give immediate mixing

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Metamerism
• Occurs when two objects looks the same color when
viewed under one light source, but looks different when
view under a different light… different spectral response
due illumination and the amount of light absorbed.

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Metamerism
• Causes
– Use of different colorants in the production sample compared
to the standard. The pair will match under D65 illumination
but would be a mis-match under other light sources
– Presence of FWA or fluorescent dyes.
• Corrective action
– Establish standards with a low level of fluorescence to
accommodate production changes off white grades to colored
grades

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Structural Two-Sidedness
• Papers produced on single wire machines are structurally
two-sided due to the dewatering of the stock suspension on
the wire
• Fines are washed out from the wire side and build up
mainly on the top (felt) side
• Color two-sidedness is caused by structural two-sidedness
in the sheet
• This can be minimized/ eliminated by careful selection of
colorants and/ or by changing addition points or orders of
addition of wet end products

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Structural Two-Sidedness

Top Side
Wire Side

Conc”
of Fines

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Selection of Colorants
• Anionic direct dyes vary in color two-sidedness behaviour
• Certain products eg. Pergasol Turquoise R Liquid/ Pergasol
Yellow S-Z Liquid are top sided
• Under acidic rosin/ alum conditions most ADD’s tend to be top
sided to varying degrees due to possible alum-dye complexes
behaving more like a pigment
• Pigments, due to the washing out effect from the wire-side, are
top-sided colorants. This can be useful in the correction of very
wire-sided dye formulations
• The affinity of colorant for filler has a big impact on two-sidedness
behaviour. e.g. Top sided dye with low filler affinity becomes
increasingly wire-sided as sheet filler content increases

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Order of Addition
• The order of addition of fixing agents and alum with ADD’s
can influence two-sidedness. Dyes sensitive to pre
addition of alum or cationic agents tend to complex and
behave more like a pigment – topsided

• The order of addition of filler with respect to the colorants

can influence the final result. e.g. A strongly top sided
shade can become more even sided by adding the filler
after the colorants in the system

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Method of Dyeing
• Continuous addition normally can lead to increased color
two-sidedness

• This is due to the addition to lower consistency stock (fines

concentration - in some cases) and much shorter dye-fibre
contact times, leading to lower absorption onto the “longs”
and increased absorption onto the “fines”

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Sizing Method
• A change from rosin/ alum sizing to AKD sizing with chalk
will increase the wire-sided tendency of direct dyes. In
many cases reformulation is required

• This is due mainly to the removal of alum from the system

and reduced affinity (ADD's) at the higher pH with chalk
filled papers

• Higher cationic AKD sizes tend to move dyes more towards

the top (felt) side

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Fixing Agents
• Fixing agents can often be used to increase the top sided
tendency of ADD's

• This is particularly useful when trying to correct a wire-

sided recipe under AKD/ chalk filled conditions.

• Pre or post addition will be determined by the fractionation

test method

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Retention Systems
• Any loss of retention (fines) can influence color two-
sidedness. This is normally a move towards more top-
sidedness

• Mills changing retention systems should be made aware

that color two-sidedness may be affected. From
experience this can only be determined on machine trials

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Dye Migration
• It is essential to establish if the color two-sidedness is due
to structural two-sidedness or due to dye migration during
the drying process

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Machine Parameters
• Increased dewatering/ vacuum

• Increased machine speed

• Increased refining (more fines)

• Stock temperature (dewatering)

• Different pulp types (affinity issue)

• Wet-end chemistry/ charge

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Light Fastness
Xenon Lamp:
Samples are exposed in a Xenon lamp until a fade is seen on
paper under test. Samples are then compared for fade against
the Blue Wool Standards (1-8), for equivalent degree of fade.

1 Poor light fastness - Tissues/ disposables

2-3 Medium light fastness - Printings/ writings
4-5 Good light fastness - Cover papers
6-8 Excellent light fastness - Laminates

Daylight tubes:
Considerably less fade potential compared to Xenon Arc
lamps. Used for low light fastness papers such as imaged
carbonless copy papers.

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Light Fastness

Correlation Between Xenon and Daylight Exposure

Blue Wool Scale Xenon Daylight

Light fastness rating Arc Exposure

3 3-4 hours 30-40 hours

4 6-8 hours 70-100 hours
6 30-40 hours 240-280 hours

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