TECHNICAL INFORMATIONRHEOLOGY ADDITIVES FOR AQUEOUS
WOOD & FURNITURE COATINGS
L-TI 802

Rheology additives for aqueous wood & furniture coatings

Contents
15	
RHEOBYK associative thickeners –product differentiation

03

Introduction

04

Rheology of coatings

06

Shear rate

16	Influence of cosolvents onrheological properties

09

Rheology additives in wood coatings

17

Selection guide for associative thickeners

10	
RHEOBYK associative thickeners – products
and applications

18

RHEOBYK liquid thixotropes

20

Natural and synthetic clays

23

LAPONITE and OPTIGEL – advantages

24

Producing perfect hydroclay gels

11

Structure of RHEOBYK associative thickeners

13	
RHEOBYK associative thickeners for tinting
paste systems
14	
RHEOBYK associative thickeners – productoverview

03

Introduction
Flow behavior is one of the most important characteristics of aliquid coating. To a great extent, flow behavior determines thehandling and application properties of the coating.
A key factor in describing flow behavior is viscosity (η). However,for most coating systems, viscosity is not a constant; it is dependent
on a variety of parameters. In addition to its dependence on
temperature, another primary parameter is the coating’s response
to mechanical stress, as this can influence application properties.

Note
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Rheology additives for aqueous wood & furniture coatings

Rheology of coatings
Rheology is the complex interrelationship between viscosity
and shear forces. The rheology of a coating system isdetermined primarily by the:• binder (chemistry, molecular weight)• solvent content and resin solubility• pigmentation level
It can also be influenced by wetting and dispersing
additives. Deflocculating additives (e.g. DISPERBYK-2015,
DISPERBYK-190) reduce the viscosity, while controlled
flocculating additives (such as ANTI-TERRA-250) increase
the viscosity and thixotropy. These wetting and dispersing
additives are primarily used for pigment stabilization, while
their rheological impact is a desirable side effect (see ebook,Wetting and Dispersing Additives).

Rheology additives
Consequently, special rheology additives are required for
optimum adjustment of rheological properties. In mostcases, these additives are used to improve anti-settlingproperties during storage and sag resistance during
application. In addition, improved flow behavior controls theuniform orientation of matting agents as well as effectpigments (aluminium and pearlescent pigments) and factors
such as image sharpness in printing inks. Numerous
products designed to control the rheology of coating
systems are already on the market and their mechanisms
are essentially the same: In the liquid phase, these additives
form three-dimensional networks (typically by hydrogenbonding). These lattice structures are temporarily destroyedby shear, and recover after shear is discontinued to give thecoating its pseudoplastic or thixotropic flow properties.

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Rheology additives for aqueous wood & furniture coatings / Rheology of coatings

Sedimentation, sagging
During storage, pigments and ﬁllers in a coating can settle
and form sediments that are difficult to reincorporate(G. 01). During application on inclined and vertical surfaces,
runs and sags frequently occur at higher film thicknesses(G. 02). Higher viscosity at low shear in combination with ayield point can substantially reduce both sedimentation andsagging. This results in longer shelf life with less settlingand better sag resistance during application.

Sedimentation and settling

However, the rheological properties described above may
also have undesirable effects on the deaeration/defoaming
and leveling properties of the coating: air bubbles rise to
the coating surface more slowly and surface levelingis impaired. Clearly the “right” flow behavior is always acompromise partly governed by the application parameters
for each particular application.

G. 01

Sagging

G. 02

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Rheology additives for aqueous wood & furniture coatings

Shear rate
The dependence of viscosity on shear rate is of practicalimportance. In practice, a relatively large shear range must
be considered (G. 03). During production (dispersing,blending, and filling) and application (rolling, brushingor spraying), coatings are exposed to high shear rates(> 1000 s -1); during storage and in the interval between
application and hardening, shear rates are relatively low(< 1 s -1). Rheological characterization over the entire shear
range is best obtained with rotational viscometers. In all
instruments of this type, the liquid to be tested is sheared
between a stationary surface and a moving surface.

Important rheology parameters
Parameter

Definition

Shear stress 

Force

Unit
N/m2 = Pa (Pascal)
Formerly: dyne/cm2
1 dyne/cm2 = 0.1 Pa

Area
Shear rate(m/s)/m = 1/s = s -1

Velocity
Distance

Viscosity 

Pa·s
Formerly: P (Poise)
1 cP = 1 mPa·s

Shear stress
Shear rate

A known rotational force is applied and the resulting rotation
speed, dependent on the liquid’s resistance to flow (viscosity),
is measured. From the measured shear rate (proportional to
the rotation speed) and shear stress  (proportional to theforce applied), the viscosity  may be calculated and charted
in a viscosity curve diagram (G. 03).

T. 01

Formula for calculating
shear stress

Formula for calculating
shear rate

F
= 
A

v
=
d

Formula for calculating
viscosity



= 

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Rheology additives for aqueous wood & furniture coatings / Shear rate

Typical shear ranges
Viscosity η (Pa·s)
Low shear forces

Medium shear forcesHigh shear forces

100

Transportation

Storage

Leveling

Production
Can viscosity under stirring

Settling

Application

Sagging
Rheometer
Brookfield
Flow cup 4 mm
Krebs-Stormer

ICI cone/plate

Control
0.01
0.001

0.01

0.1

1

10

100

1,000

10,000
Shear rate(s -1)
G. 03

Low-shear conditions are typically experienced by thecoating while it is stored in the can and immediately after
it has been applied to the substrate. During these phases,
low shear viscosity is needed to resist pigment settling andfilm sag while providing the required leveling of the applied
coating film. Low shear viscosity is often measured usinga Brookfield viscometer.

Medium-shear conditions are created during coating stirring,pouring, and some types of pumping. During these phases,
medium shear viscosity helps to facilitate good in-can
appearance and handling properties and may also affectspattering. Medium shear viscosity is often measured using a
Krebs-Stormer viscometer and a Brookfield viscometer at highrpm. Krebs-Stormer viscosity is expressed in Krebs Units (KU),
and rheology additives are often referred to in “KU builders”
or “medium-shear builders.”

High-shear processes include brushing, certain aspects ofrolling, and spraying. High shear viscosity influences brushand roller drag, as well as film building and hiding power.
High shear viscosity is often measured using a cone-plateviscometer including the standard ICI viscometer. Therefore,rheology additives that offer a good high shear viscosity areoften referred to as “ICI builders” or “high-shear builders.”

Rheology additives for aqueous wood & furniture coatings / Shear rate

Thixotropic flow behavior

Viscosity η

Pseudoplastic flow behavior

Viscosity η

Newtonian flow behavior

Shear rate

Viscosity η

08Shear rate

Shear rate

G. 04

G. 05

G. 06

Newtonian flow behavior
The simplest form of flow behavior occurs if viscosity is independentof shear rate. This behavior, also known as Newtonian flow, only
occurs in ideal liquids and can be observed in water, pure solvents,and mineral oils, for example. Since viscosity does not dependon shear rate, it can be measured at any shear rate (single-point
measurement) to obtain a complete rheological description of
the system. In coating systems, however, Newtonian flow behavior
is not typical and actually undesirable (other than in some stain
formulations): the slightest shear stress (gravity) induces flow,
resulting in sagging after application. Such formulations also exhibit
rapid settling.

Pseudoplastic flow behavior
More typical flow behavior seen in coating systems is
pseudoplasticity, also known as “shear thinning.” Here, viscosity
is inversely proportional to shear rate: Viscosity decreases as shear
increases, i.e. the coating material becomes thinner. Frequently,
such liquids also exhibit a yield point: it does not flow at low
shear; flow only begins after the yield point has been reachedor exceeded. In terms of application properties, this type of flow
behavior has some advantages: The coating has a low viscosity
when subjected to high shear, simplifying handling during
production and application. At lower shear rates, for example
during storage, the coating’s viscosity is higher, thus effectively
eliminating pigment sedimentation. At the same time, sag
resistance following application on vertical surfaces is substantially
improved. However, higher viscosity at lower shear rates may beundesirable for surface flow and deaeration of the freshly applied
wet paint ﬁlm. A stated viscosity for any pseudoplastic material
is only meaningful if the corresponding shear rate is also indicated.
Hence, a single-point measurement for such materials is of little
value; the rheological behavior of the material can only be
represented by the entire viscosity curve.

Thixotropic flow behavior
Thixotropy describes viscosity behaviors that are both timedependent and shear-dependent. A pseudoplastic substance
exhibits different viscosities as a function of changing shear rates,
but these viscosities are independent of time. When a thixotropic
substance is sheared at a constant rate, viscosity decreases as shear(time) duration increases. Once the shear is discontinued (= 0),
viscosity returns to the original value. The viscosity curve ofthixotropic liquids typically shows a “hysteresis loop," i.e. viscosity
recovery after shear does not replicate the initial shear thinningfrom the equilibrium curve. Recovery viscosity is lower than theshear down viscosity at every shear rate. This clearly shows that it
is not possible to attribute a unique viscosity value at a given shear
rate for a thixotropic material; the viscosity measured depends on
the sample’s prior shear history.

Pseudoplasticity and thixotropy
With regard to sedimentation behavior, pseudoplastic andthixotropic materials demonstrate very similar performance:high viscosity at low shear rates reduces settling. The
differences between pseudoplastic and thixotropic liquids
become more obvious when focusing on sagging and sag
resistance: Pseudoplastic materials allow application of fairly
thick films without sagging because viscosity recovery occurs
very quickly following application. Thixotropic materials also
display increased sag resistance, however, the effect is lesspronounced because the process of viscosity recovery isslower. On the other hand, this can be beneficial regarding
deaeration and leveling.

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Rheology additives for aqueous wood & furniture coatings

Rheology additives in wood coatings
Wood coatings are applied in different ways and eachapplication method requires a different viscosity profile.
Therefore the choice of additive also changes dependingon whether the film is applied by roller, curtain coater or
if it is sprayed by HVLP or airless/airmix. In addition to
the application method, both the geometry and position(vertical or horizontal) of the coated object are also
important when choosing flow properties.

Coatings applied by spraying require some pseudoplasticity
so that their viscosity is low enough to pass through thenozzle, yet high enough not to sag once they hit thesubstrate.

BYK offers a full product range to cover and fulfill all ofthese different requirements.

In addition to the application method, the formulation
itself also plays a key role: Matted and pigmented systems
require a certain elastic flow to prevent settling.

BYK rheology additives for wood coatings
Organic

Inorganic

RHEOBYK

Chemical base

LAPONITE

OPTIGEL

Brand name

Associative thickeners

Liquid thixotropes

Synthetic clay

Natural clay

Product type

Mostly pseudoplastic to Newtonian

Thixotropic

Thixotropic to pseudoplastic,
depending on dosage

Thixotropic

Flow characteristics

Easy to incorporate

Easy to incorporate (while stirring)

Easy dispersible in DI waterHigh shear force needed

Incorporation characteristics

Post-addition possible

Post-addition possible

Pre-dispersion recommended

In the grind or pre-gel

Incorporation stage

For pigmented and clear systems

For pigmented and clear systems

For pigmented and clear systems

For pigmented systems

Usage area

Flow & leveling,anti-sagging, anti-settling

Anti-sagging, anti-settling

Anti-sagging, anti-settling

Anti-settling

Purpose

G. 07

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Rheology additives for aqueous wood & furniture coatings

RHEOBYK associative thickeners – products and applications
RHEOBYK associative thickeners have been designed tooffer formulators broad formulating latitude in paints,
coatings, inks, sealants, caulks, and adhesives while
alleviating many of the problems often encountered withconventional urethane-based thickeners. RHEOBYK
associative thickeners impart excellent flow and leveling,high film build, excellent stability, and unsurpassed
resistance to blister, spatter, and syneresis when used witha broad variety of latex binders, including large and small
particle size acrylics, vinyl acrylics, styrene acrylics, andethylene vinyl acetates (EVAs). While the use of RHEOBYK
associative thickeners can eliminate or reduce the needfor cellulosics, these products are more compatible withcellulosics than urethane-based thickeners, leading to
reduced paint syneresis and curtain sagging.

RHEOBYK associative thickeners technology
in paints and coatings:• Increased resistance(to water, alcohol, liquid cleansers, etc.)• Improved barrier effect• Improved viscosity stability with tinting pastes• Increased stability with respect to pH fluctuations• No syneresis and improved storage stability• No reduction in gloss• Haze-free• VOC-free• Tin-free

Rheological effects
Different associative thickeners can be used to adjust various
effects in the three different shear ranges: low, medium, andhigh shear. Low-shear thickeners lead to an improved storage
stability and sag resistance. Medium-shear thickeners are used
to improve in-can viscosity and high shear thickeners increasebrush drag and improve the spatter resistance.
HEUR – Hydrophobic ethoxylated urethane• Non-ionic and emulsifier-free• Typical HEUR odor and clarity• Designed for high shear viscosity range for PU
and acrylic dispersions, as well as vinyl, EVA,
and low-responsive systems• Suitable for exterior coatings

Structure of HEUR

HEUR
Hydrophobic ethoxylated urethaneHydrophobic groups   

Connecting groups   

Compatibility providing units

G. 08

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Rheology additives for aqueous wood & furniture coatings

Structure of RHEOBYK associative thickeners
RHEOBYK associative thickeners are water-soluble, associative
polymer thickeners. They primarily consist of water-soluble
polyalkylene glycol, onto which a few non-water-soluble(hydrophobic) groups have been added. In aqueous solution,these hydrophobic groups either group together to form
micelles or associate with other hydrophobic components,
such as latex particles. The long polyalkylene oxide backbone
remains dissolved in water, where it links micelles and latex
particles into a network – this is what causes the rheologicaleffect. The greater the amount of (finely divided) latex
particles present that can associate with the hydrophobicgroups, the greater the rheological effect. Hence the term
“associative” thickening (G. 09).

Associative thickening
mechanism

Latex particles   

Polyalkylene glycol   Hydrophobic groups

G. 09

Rheology additives for aqueous wood & furniture coatings / Structure of RHEOBYK associative thickeners

How it works
When the interactions described above form a threedimensional network, associative thickeners greatly increase
viscosity, especially under high-shear conditions. This
strengthens the internal structure and thickens the material
to a honey-like consistency, a process also described asbrush drag. The number and chemical nature of thehydrophobic groups in the thickener molecule determine
whether the increase in viscosity that can be achieved willproduce a Newtonian or thixotropic/pseudoplastic behavior.
Unlike systems utilizing laminar silicates (OPTIGEL) to
produce a thixotropic behavior, systems thickened withRHEOBYK associative thickeners have no yield point, which
ensures superior paint flow and leveling (G. 10).

Associative thickener vs. a laminar silicate

Viscosity η

12Brush drag = reduced spattering

Shear rateRHEOBYK   

G. 10

OPTIGEL

Impact of structure on performance

Impact of hydrophobic chain length

Viscosity η

The size of the hydrophobic groups influences the additive's
performance. These hydrophobic groups are mostly aliphatichydrocarbon chains with a chain length of 6 –16 C atoms.
With longer chains the flow behavior will be morepseudoplastic and the viscosity at low shear will be high.
These additives are called low-shear thickeners.
Shorter hydrophobic chains will result in a more Newtonian
flow: instead of providing high viscosity at low shear,
they provide higher viscosity at higher shear rates. These
products are called high-shear thickeners (G. 11).

Shear rateRHEOBYK-H (low-shear thickener)   

RHEOBYK-M (medium-shear thickener)   

RHEOBYK-T & RHEOBYK-L (high-shear thickeners)   

Unthickened resin

G. 11

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Rheology additives for aqueous wood & furniture coatings

RHEOBYK associative thickeners for tinting paste systems
Associative thickeners are often sensitive to the addition of
surfactants, dispersing agents, wetting agents, and solvents.
These additives reduce the associative interactions between
the latex particles and the hydrophobic groups of the
thickener, thereby reducing viscosity. This problem primarily
arises when adding pigment concentrates that contain large
amounts of interfering agents, such as dispersants andsurfactants. (G. 12)

Conclusions
Over the years, the paint and coatings industry has adopted
environmental regulations to lower VOC emissions inarchitectural coatings. As a result, paint manufacturers are
moving from traditional oil-based paint systems to aqueous
paint systems. The challenge for the paint manufacturer
is to maintain performance properties such as brushability,
stain removal, and durability.

RHEOBYK-7600 leads to a considerable increase in viscosity
in the low shear range, stabilizes viscosity when colorant is
added, and improves color paste acceptance.

The RHEOBYK associative thickeners system introduced in
1997 was designed for the paint manufacturer for use in

The rheological properties are comparable with those of
HEAT technology. The new additive also offers significantly
better leveling properties. In addition to being VOC-, APEO-,
and tin-free, RHEOBYK-7600 is also liquid, which facilitates
incorporation and handling. Due to its composition, it ishighly compatible in many aqueous systems. Both sagging
tendency and storage stability are improved. It is notnecessary to adjust the pH value or control the temperatureduring incorporation.

RHEOBYK-7600 – theoretical consideration of viscosity stability
after tinting

Base paint withpolymer thickeners

Base paint withRHEOBYK-7600

Typical reduction
in viscosity

Viscosity ηProcessability is optimized by combining with rheology
additives that are effective in the high shear range.
Benefits• Very good viscosity stability after tinting• Balanced ratio of anti-sagging and leveling – improved
leveling properties• Improved colorant acceptance• Improved anti-settling and anti-sagging properties• Good compatibility with different systems• Easy handling and incorporation due to the viscosityof the additive• VOC-, APEO-, and tin-freelatex or aqueous paints to provide a smooth and creamy
paint consistency with butter-like brush feel while
preventing roller spatter (splashing that can occur from thepaint roller). In addition, a patented technology allows all
RHEOBYK associative thickeners to be supplied VOC-free.
This technology, known as RHEOBYK associative thickeners
VF technology, will also further enhance paint quality inareas such as color uniformity and paint consistency (Iessseparation).

Basic paintnot tinted+ 10 % pigment
concentrate

Basic paintnot tinted+ 10 % pigment
concentrate
G. 12

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Rheology additives for aqueous wood & furniture coatings

RHEOBYK associative thickeners – product overview

VOC-free

SVOC (g/l)

Formaldehyde-free

APEO-free

Organotin-free

Typical usage (%)

Remarks

Ratio P:N*1

Chemistry

Actives (%)

Product

RHEOBYK-L 1400 VF

HEUR

20.0

2.0 : 4.5

1.5 - 5.0



0.8 - 2.0

Highly efficient ICI builder suited for acrylic and styrene-acrylic systems

RHEOBYK-M 2600 VF

HEUR

20.0

3.0 : 3.0

5.0 - 10.0







0.8 - 2.0

Designed for lower response resin systems and offers “balanced rheology” in thesesystemsRHEOBYK-T 1000 VF

HEUR

22.5

1.0 : 5.0



< 1.5







0.8 - 2.0

ICI Driver with minimal impact on KU response

RHEOBYK-T 1010 VF

HEUR

22.5

1.5 : 4.5



< 1.5







0.8 - 2.0

Improved Newtonian/ICI Driver and resistance to syneresis

RHEOBYK-425*2

HEUR

50.0

4.0 : 1.0

1.5 - 5.0



RHEOBYK-7610

HEUR

20.0

5.0 : 0.0



< 1.5







0.2 - 2.0

Excellent leveling properties while providing good sag-resistance, for airless application

RHEOBYK-H 3300 VF

HEUR

17.5

4.0 : 2.0



< 1.5







0.5 - 2.5

Most universal associative thickener with balanced properties. Good starting point forevaluations

RHEOBYK-H 6500 VF

HEUR

20.0

5.0 : 2.0

5.0 - 10.0







0.5 - 2.5

RHEOBYK-H 7500 VF

HEUR

17.5

5.0 : 1.0

5.0 - 10.0







0.5 - 2.5

Developed for a variety of hard-to-thicken latexes

RHEOBYK-H 7625 VF

HEUR

20.0

4.0 : 0.0



< 1.5







0.1 - 1.5

cPs/KU Driver for low binder systems, ideal for spray applied contractor brands

Excellent viscosity stability during tinting

High- & medium-shear thickeners

Low-shear thickeners
0.1 - 2.0

Specialty rheology modifiers
RHEOBYK-7600

HEUR

15.0

5.0 : 0.0









0.1 - 1.5

RHEOBYK-HV 80

HASE

30.0

7.0 : 1.0









0.5 - 2.5

Yes  *1 P = pseudoplastic, N = Newtonian, 1 = weak, 7 = strong  *2 Contains organotin  

T. 02

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Rheology additives for aqueous wood & furniture coatings

RHEOBYK associative thickeners – product differentiation
The typical rheology profile of associative thickeners is causedby the differently pronounced interactions between the acrylic
copolymer dispersion and the associative thickener.
All associative thickeners demonstrate pseudoplasticity.
After shear stress is stopped the viscosity will recover
immediately.
The greater the pseudoplasticity, the greater the increase inviscosity in the low shear area. Conversely, the lower thepseudoplasticity, the lower the shear thinning effect, and themore Newtonian the viscosity profile, respectively (G. 13).

The highly pseudoplastic RHEOBYK-H additives are used inairless and airmix spray applications, especially in vertical
spray. Here it is also useful to combine a pseudoplastic
associative thickener such as RHEOBYK-H 7500 VF withLAPONITE products to prevent the sagging effect.

The more Newtonian additives are used for roller or curtain
coater applications. They will also improve the brushability
and prevent spattering due to their strong performance in thehigh shear area. In combination with LAPONITE, they will also
provide the typical alkyd feeling during brush application.

Medium pseudoplastic additives RHEOBYK-M 2600 VF or
RHEOBYK-H 3300 VF will build in-can viscosity and are
generally a good starting point for evaluation of RHEOBYK
associative thickeners.

All products
High- & medium-shear thickeners
Viscosity (mPa·s)

Viscosity (mPa·s)

6,000

450

Test system: Aqueous
acrylic systems
Dosage: 0.1 % active
substance
Measurement: byko-visc
Advanced EX, Spindle R3,
Shear rate 5/50/5 rpm
Measurement time:
1 min. for each step

400
5,000
350
300

4,000

250
3,000
200
150

2,000

100
1,000

50
0

0
5 rpm

50 rpmRHEOBYK-T 1000 VF

RHEOBYK-T 1010 VF

RHEOBYK-L 1400 VF

RHEOBYK-H 7625 VF

RHEOBYK-H 7500 VF

RHEOBYK-7600

5 rpm

RHEOBYK-M 2600 VF

Shear

RHEOBYK-H 3300 VF

5 rpm

RHEOBYK-H 6500 VF

50 rpm

5 rpm

Shear

G. 13

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Rheology additives for aqueous wood & furniture coatings

Influence of cosolvents on rheological properties
Impact of cosolvents on associative
thickener performance

Time dependency caused by watersoluble cosolvents

Immediate viscosity build by usageof water insoluble cosolvents

Viscosity η (Pa·s)

Flow time (s)Flow time (s)

1.0

50

60
55
50
45
40
35
30
25

45
40

0.5

35
30

0.0

25

1

10

1,000

100

1h

3h

5h

Without additional cosolvent and RHEOBYK-H 3300 VF
Butyl glycol (BG)  
Butyl diglycol

G. 14

24 h

1h

3h

2.0 % RHEOBYK-T 1000 VF

G. 15

1.0 % RHEOBYK-T 1000 VF
0.75 % RHEOBYK-L 1400 VF

Dipropylene glycol methyl ether (DPIM)

0.6 % RHEOBYK-M 2600 VF

0.3 % RHEOBYK-M 2600 VF

Dipropylene glycol n-butyl ether (DPnB)

0.4 % RHEOBYK-H 3300 VF
0.4 % RHEOBYK-H 6500 VF

0.2 % RHEOBYK-H 3300 VF
0.15 % RHEOBYK-H 6500 VF

Test system: aqueous floor coating based on urethane hybrid
dispersion; viscosity measurement: 1 day after incorporation,
Anton-Paar Rheometer; RHEOPLUS/32 V3.62, CP25-1/1 – 1,000 s-1

The efficiency of the associative thickeners strongly depends on thecosolvents used. As the water solubility of the solvent increases, theperformance of the rheology additive decreases, particularly in the
low shear range.
In parallel to the cosolvent, the emulsifier, the particle size of thebinder emulsion and the solid content also have a strong impact on
the performance of the rheology additive.
Water insoluble cosolvent have a positive effect on the viscosity build
up in the low shear range because they cause the emulsion particle
to swell and might also participate in the hydrophobic interactions.

24 h
Time

1.5 % RHEOBYK-L 1400 VF

Ethyl diglycol (EDG)

5h

Time

Shear rate (s -1)

Test system: aqueous acrylic system, cosolvent BG,

Test system: aqueous acrylic system, cosolvent DPnB,

viscosity measurement with DIN 4 cup

viscosity measurement with DIN 4 cup

When using highly water-soluble cosolvents, a significant timedependency can be observed in the performance of the associative
thickeners. Therefore, special attention must be paid to viscosity
development during storage so that it can be adapted to the final
application conditions.

Cosolvents with a limited solubility in water lead to a faster or
instantaneous viscosity build.

G. 16

However, this typical behavior might not be observed in all cases.
Interactions of individual components will remain unpredictable andwill need to be verified through laboratory testing.

17

Rheology additives for aqueous wood & furniture coatings

Selection guide for associative thickeners
RHEOBYK-H 3300 VF is the starting point for all aqueous
wood and furniture coatings. It generally performs well
for all kind of application methods, but in some cases,
depending on the emulsifier or cosolvent, for example, it
might be necessary to switch to a different product. The
testing order is shown in the following chart.

For spray applications, the flow should be adjusted to be
more pseudoplastic, while roller applications require a more
Newtonian viscosity profile.
Sometimes it is also useful to try combinations of two or
more rheology additives, especially a combination of highand low-shear thickeners.

Selection guideLow-shear thickeners (“H grades”)
Pseudoplastic

Starting pointRHEOBYK-H 3300 VF

Spray application

High-shear thickeners (“L/T grades”)
NewtonianRoller application

RHEOBYK-M 2600 VF
In combination or as stand-alonerheology modifier

Adjustment of “in-can” viscosity(“body”) at low additive dosage

RHEOBYK-H 6500 VF
RHEOBYK-H 7500 VF
RHEOBYK-H 7625 VF
Improvement of anti-settling and anti-sagging properties
Prevention of picture framing
Elimination of insufficient edge coverageFirst recommendation   

Second recommendation

A combination might be helpful

RHEOBYK-L 1400 VF
A combination might be helpful

RHEOBYK-T 1000 VF
RHEOBYK-T 1010 VF
Improvement of leveling
Adjustment of “brushability”

G. 17

18

Rheology additives for aqueous wood & furniture coatings

RHEOBYK liquid thixotropes
RHEOBYK-420 is a liquid rheology additive that creates strong
thixotropic flow behavior in coatings and printing inks. This
product is a solution of a modiﬁed urea in N-methyl pyrrolidone(N-methyl pyrrolidone-free versions are also available). Theirfunctional mechanism is based on the fact that the active
substances in these additives are insoluble in common coating
solvents and/or blends: properly incorporated into coating
systems, the additive separates in a controlled manner, forming
very ﬁne, needle-like microcrystals, which in turn, form a threedimensional lattice structure via hydrogen bonds. The initialformation of this structure may take up to several hours.
Hydrogen bonding between the urea groups of the individual
molecules leads to the formation of the network structure.
During application of such a modiﬁed coating system, very low
shear forces are sufﬁcient to destroy these lattice structures,
giving the coating the desired low application viscosity. Following
application, the structure reforms in a delayed manner that ischaracteristic of thixotropic materials and the viscosity of theapplied wet coating layer increases again.

Chemical structures

RHEOBYK-420 (and its derivates) is also rheologically activein pure water and does not require the presence of resins.
Nevertheless, the presence of cosolvents can improvecompatibility and lead to easier incorporation.

NMP = N-methyl pyrrolidone, DMSO = Dimethyl sulfoxide

RHEOBYK-420

Urea groups   Modifying groups:

high polar  G. 18

medium polar

Modified urea products
Product

Active content

Carrier

RHEOBYK-420

52 %

NMP

RHEOBYK-D 420

52 %

DMSO

RHEOBYK-7420 CA

52 %Cyclic amide

RHEOBYK-7420 ET

42 %Amide ether

Label

RemarkCrystallizes below 5 °C

T. 03

Network formation via hydrogen bonding

G. 19

19

Rheology additives for aqueous wood & furniture coatings / RHEOBYK liquid thixotropes

Compatibility check and improvement

1. Incorporation
The first step to check compatibility is to add the liquid thixotrope to the non-pigmented formulation.
It should be incorporated homogeneously while vigorously stirring.

2 % RHEOBYK-420
in water/BG/
DISPERBYK-192
94/5/1

2. Compatibility test
Next, compatibility must be assessed following incorporation. This can be done visually. It might be helpful todraw the system down onto a glass plate. It might take a few minutes for the rheological effect to build up.

Homogeneous

Inhomogeneous• Excellent thickening• No particles• No or only weak rheological effect• Particles visible in the coating or application

Recommended cosolvents• Polypropylene glycol (PPG 600)
• Butyl glycol (BG)
• Dipropylene glycol dimethyl ether

If seeding is observed, acompatibility improvement isrequired, which can be achievedby using different cosolvents andwetting & dispersing additives.

2 % RHEOBYK-420
in pure water

No particles/no seeds anda good rheological effect:
Compatibility is good and noformulation changes arenecessary.
G. 20

20

Rheology additives for aqueous wood & furniture coatings

Natural and synthetic clays
Mode of action
LAPONITE and OPTIGEL products from BYK are smectitebased rheology additives for aqueous systems. Smectites area group of layered silicate minerals that occur naturally, butwhich can also be produced synthetically. Smectites have aplatelet structure; the platelets are very thin, about 1 nm.
The platelet diameter is about 500-1000 nm (1 μm) for
natural smectites (OPTIGEL products) and 25-50 nm forsynthetic smectites (LAPONITE products). These platelet
stacks then separate into their individual platelets when
added to water and dispersed under high shear conditions.

House-of-cards structure
The surfaces of individual LAPONITE/OPTIGEL platelets
are negatively charged, but their edges are either neutralor positively charged. Because their overall charge ispredominantly negative, the platelets repel each other inthe suspension, a process that distributes them evenly
throughout the solution.

Mode of action – house-of-cards structure

The difference in charge between their edges and theirsurfaces then generates a slight edge-to-face attraction
between the platelets. Small amounts of divalent cations,such as Ca2+ or Mg2+, can further contribute to thisinteraction. These produce a house-of-cards structure,
which results in a gel formation.

Mode of action in motion and at rest
In motion

G. 21

At rest

G. 22

21

Rheology additives for aqueous wood & furniture coatings / Natural and synthetic clays

Yield point and thixotropy
The stability of the gel reflects the bonding strength
between platelets. When external forces (such as a stirrer,
paint brush or roller) act on the gel, the house-of-cards
structure collapses and the gel returns to its fluid state.
Once the external force is reduced, the structure reforms
and the liquid again behaves like a gel. LAPONITE andOPTIGEL produce what is known as a yield point. Thismeans, a minimum force is required before a substancestarts to flow.

Yield point and thixotropy
Viscosity η

RHEOBYK

Additionally, the gel exhibits a thixotropic behavior. The
greater the stirring force acting on the gel, the more
completely the house-of-cards structure will collapse, i.e.
the thinner the liquid will become. After stirring, the houseof-cards structure will reform within a short period of time
and the viscosity will return to its original level.

OPTIGEL/LAPONITE

Shear rate
G. 23

On the other hand, the associative/Newtonian thickeners in
the RHEOBYK associative thickeners product line behave
differently, exhibiting virtually no yield point and remaining
highly viscous, even when vigorously stirred.

Thixotropic and pseudoplastic
Viscosity
3,000
2,500
2,000
1,500
1,000
500
0
5 rpm
0.5 % RHEOBYK-T 1010 VF/RHEOBYK-H 7500 VF
0.5 % LAPONITE-SL 25

50 rpm
0.5 % OPTIGEL-WX

5 rpm

Shear

0.5 % LAPONITE-RDS

G. 24

22

Rheology additives for aqueous wood & furniture coatings / Natural and synthetic clays

OPTIGEL/LAPONITE – major applications
Product

FeaturesLAPONITE-RDS and LAPONITE-S 482
pre-mixes can be added at any stage ofthe manufacturing process.

LAPONITE-EP

Modified; for adjustment of in-can viscosity

LAPONITE-RD

General purpose grade; highest gel strength; pseudoplastic flow; high elasticity performance

LAPONITE-RDS

Easier to disperse; longer processing period; higher Ca2+/Mg2+ tolerance

LAPONITE-S 482

Powder grade for intermediate sole grade preparation; for higher dosage levels; for post-addition and post-correction

LAPONITE-SL 25

Ready-to-use version; for post-addition and post-correction

OPTIGEL-CK

Universal, thixotropic thickener for water-soluble systems; stabilizer for latex paints, ceramics

OPTIGEL-CL

Thixotropic anti-settling agent/stabilizer for paints, ceramics

OPTIGEL-CG

Economical, thixotropic thickener for paints and building chemicals

OPTIGEL-CMO

Thixotropic thickener and stabilizer for paints and technical applications; compatible with large amounts of electrolytes

OPTIGEL-LX

Highly effective thickener for flat and semi-gloss latex paints, silicon resin paints, and adhesives

OPTIGEL-WA

Effective thickener for flat and semi-gloss latex paints, water-soluble paints, additive for the building industry and cleansers

OPTIGEL-WM

Highly effective, universal thickener for semi-gloss latex paints, water-soluble paints, adhesives, and textile auxiliaries

OPTIGEL-WX

Effective thickener for flat and semi-gloss latex paints, water-soluble paints, silicate paints, and printing inks

OPTIGEL-W 724

Highly effective thickener for semi-gloss and high PVC latex paints, water-soluble coatings, and anti-corrosion primers (i.e. 2-pack PUR, 2-pack epoxy)

LAPONITE-SL 25 is ready to use at any
stage of the manufacturing process

T. 04

23

Rheology additives for aqueous wood & furniture coatings

LAPONITE and OPTIGEL – advantages
Benefits of the yield point
The formation of a yield point reduces sagging. This makes it
possible to apply thick coats of paint in a single application
without negative side effects such as beading, dripping or
sagging. This is achieved thanks to the stabilizing effect of
the OPTIGEL house-of-cards structure, which rebuilds
completely shortly after the paint is applied. The yield point
significantly improves storage stability, keeping pigments andfillers in suspension and preventing heavier pigments fromsettling and lighter pigments from floating up to the surface.
Thixotropic behavior alone would not have this effect; it may
slow down the settling process, but does not prevent it. The
system must also have a yield point, which also reduces liquid
separation (syneresis).

Advantages
For your product:• Easy handling• No sagging• No dripping• Excellent storage stability• No settling

For your production processes:• Easy to meter• Easy to disperse• Universally applicable

LAPONITE products
LAPONITE-RD is a fully synthetic, inorganic product witha precisely controlled chemical composition. It has apowerful stabilizing effect. Other outstanding features are
its superior whiteness and its ability to form transparent
gels. LAPONITE-RDS and LAPONITE-S 482 have been
modified in a way that makes these powdered products
particularly easy to disperse. LAPONITE-SL 25 is a readyfor-use aqueous dispersion at 25 % solid content.

OPTIGEL-C products
OPTIGEL-C products are natural smectites and can be stored
as a powder or as a pre-gel. They produce a high yield point
in aqueous and water-soluble systems. This is why OPTIGEL-C
products significantly improve the stabilization of systems andhelp to prevent settling and sagging without raising theapparent viscosity.
Modified OPTIGEL products
OPTIGEL-LX, OPTIGEL-WA, OPTIGEL-WM, OPTIGEL-WX, and
OPTIGEL-W 724 are organically modified. They increase theviscosity and give aqueous and water-soluble systems athixotropic behavior. All OPTIGEL products are easy todisperse and are excellent stabilizers and anti-sagging agents.

LAPONITE and OPTIGEL

with OPTIGEL

Reducessagging

without OPTIGEL

Reducessettling
andsyneresis
G. 25

24

Rheology additives for aqueous wood & furniture coatings

Producing perfect hydroclay gels
Organoclays (bentonites, hectorites) are widely used as
thickeners in coating formulations to create or enhance
pseudoplastic flow behavior and thixotropy in order tocounteract settling and sagging. These materials come inpowder form and must be properly dispersed in the coating
system to achieve the desired results. Preparing organoclay
pastes in solvents (organoclay gels) as a masterbatch isoften found to be very convenient because these pastes
can then be easily introduced into various coating systems.

Theory...
Dry organoclay powder consists of particles where many
clay platelets are stacked together (G. 26). Solvents
penetrate the space between the platelets and the stacks
swell up. High shear forces are necessary to completely
separate the platelets from each other. Water is used as
chemical activator to create the organoclay gel: small
amounts of water are sufficient to form links between
several platelets via hydrogen bonds resulting in a three-dimensional network (G. 26). This network, which is
destroyed under shear and rebuilds when shear forces are
removed, is the reason for the pseudoplastic and thixotropic
flow behavior.

Well-dispersed organoclay
Dry stack oforganoclay platelets

Solvent swells
organoclay

Well-dispersed
organoclay platelets

Formation of three-dimensional network:
pseudoplastic and thixotropic flow behavior;
excellent anti-sagging and anti-settling properties

G. 26

25

Rheology additives for aqueous wood & furniture coatings / Producing perfect hydroclay gels…and practiceIn practice, it has been found that it is not possible toachieve good dispersion of the clay platelets with high shear
forces alone (G. 27). Incomplete dispersion yields a highly
viscous paste and a significantly reduced rheological effect:
insufficient anti-settling and anti-sagging properties. It
is common practice to use suitable wetting and dispersing
additives to guarantee complete dispersion of the clay
platelets. The resulting paste has a lower viscosity,
but demonstrates excellent anti-settling and anti-sagging
performance when incorporated into a coating system.

Poorly dispersed organoclay
Incomplete dispersion of organoclay platelets

ImportantHigh viscous paste,
reduced rheologicaleffectivity, reduced
transparency

G. 27

LAPONITE
Handling instructions – incorporation
into water pre-mix preparation• Preparation of water pre-mixtures(preferably DI water)• Rapid and homogenous incorporation
under agitation• Stirring period of approx. 30 min. for full activation• Pre-mix processing period depends on water
hardness and dosage (high water hardness
cause pre-mix processing reduction)• Pre-mixes should be processed as long as
they are liquid (no visible structure)01/2022
L-TI 8BYK-Chemie GmbH
P.O. Box 10 02 45
46462 Wesel
GermanyTel +49 281 670-0
Fax +49 281 65735

ADD-MAX®, ADD-VANCE®, ADJUST®, ADVITROL®, ANTI-TERRA®, AQUACER®, AQUAMAT®, AQUATIX®, BENTOLITE®, BYK®, BYK®-DYNWET®,
BYK®-MAX®, BYK®-SILCLEAN®, BYKANOL®, BYKETOL®, BYKJET®, BYKO2BLOCK®, BYKOPLAST®, BYKUMEN®, CARBOBYK®, CERACOL®, CERAFAK®,CERAFLOUR®, CERAMAT®, CERATIX®, CLAYTONE®, CLOISITE®, DISPERBYK®, DISPERPLAST®, FULACOLOR®, FULCAT®, GARAMITE®, GELWHITE®,
HORDAMER®, LACTIMON®, LAPONITE®, MINERAL COLLOID®, MINERPOL®, NANOBYK®, OPTIBENT®, OPTIFLO®, OPTIGEL®, POLYAD®, PRIEX®,
PURE THIX®, RECYCLOBLEND®, RECYCLOBYK®, RECYCLOSSORB®, RECYCLOSTAB®, RHEOBYK®, RHEOCIN®, RHEOTIX®, SCONA®, SILBYK®,TIXOGEL®, VISCOBYK® and Y 25® are registered trademarks of the BYK group.

info@byk.com
www.byk.com

The information herein is based on our present knowledge and experience. The information merely describes the properties of our products but noguarantee of properties in the legal sense shall be implied. We recommend testing our products as to their suitability for your envisaged purpose
prior to use. No warranties of any kind, either express or implied, including warranties of merchantability or fitness for a particular purpose, are maderegarding any products mentioned herein and data or information set forth, or that such products, data or information may be used without infringing
intellectual property rights of third parties. We reserve the right to make any changes according to technological progress or further developments.
This issue replaces all previous versions.