acav ultra high shear presentation

ACAV Viscometers by1

ACAV

Coating ColorRunnabilityAnalyzers

Picture: Voith

ACAV Viscometers by

Viscosity Measurement

Coating colors are rheologically complex materials:

Their viscosity is strongly dependent on shear rate

Viscosity is dependent on shearing time

They are viscoelastic

They may have significant extensional viscosity and/or normal stresses

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ACAV Viscometers by


Viscosity Ranges of Viscometers

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ACAV Viscometers by


Shear Rates of Modern Coaters

Real shear rates are higher because part of the coating is already in the paper pores and the paper surface is not even!

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Coat weight g/m2 10 10 8

Color solids % 62 62 62

Machine speed m/min 1000 1500 2000

Color density kg/m3 1500 1500 1500

Coating thickness under blade µm 21,5 21,5 17,2

Average shear rate Million 1/s 1,4 2,3 3,7

Shear

Rate =Speed of coater

Film thickness

ACAV Viscometers by


Shearing History of Coating Color

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Applicator NipPumping

Mixing

Blade

Screens

Rod

0 102 103 104 106105 107

Curtain hitting point

ACAV Viscometers

Coating Color Circulation

Conventional

viscometers measure

ONLY low shear

rates!

Share Rate (1/s)

= Conventional viscometers

ACAV Viscometers by


Why Full Shear Rate Range Measurement?

Measure the full range of shear rates to check the Impact of different factors on the viscosity

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Chemical factors

- Van der Waals

- Electrostatic Repulsion/Attraction

- Steric Factors

Hydrodynamic factors

- Particle size

- Distribution of Particle size

- Shape of Particles

- Viscosity of Water Phase

- Solid Fraction

PCC-Slurry

0.0 2.0x105 4.0x105 6.0x105 8.0x1050

500

1000

1500

2000

Vis

cosity

(mP

as)

Shear rate (1/s)

= Conventional viscometers

ACAV Viscometers by


Dominating Factors at Different Shear Rates

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SURFACE CHEMISTRY AT LOW SHEAR• Solids content

• Electric attraction/repulsion

• Van der Waals attraction

• Steric repulsion

• Viscosity of water phase

HYDRODYNAMICS AT ULTRA HIGH SHEAR

• Solids content (i.e. volume fraction of particles)

• Particles size

• Shape of the particles

• Particle size distribution

• Viscosity of water phase

Brookfield,

rotational

and capillary

viscometers

Capillary and

SLIT viscometers

ACAV Viscometers by


Shear Rate Ranges of Viscometers

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ACAV Viscometers by


Additional Notes on Shear Rate Because viscosity is often strongly dependent on shear rate, it is

necessary to know what is the actual shear rate in the process. If shear rate is not known, it doesn’t make sense to compare viscosity of samples

to their performance during the process.

Usually it doesn’t matter is shear rate 50 000 1/s or 60 000 1/s.

it matters is shear rate 10 000 or 100 000 1/s.

Often it is enough to know order of magnitude of shear rate.

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ACAV Viscometers by


Viscometers & Shear Rate

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Rheological Properties of Starch Latex Dispersions and Starch Latex-Containing Coating Colors

1Jae Y. Shin, 2Nathan Jones, 1,3Do Ik Lee, 1Paul D. Fleming, 1Margaret K. Joyce, 3Ralph DeJong,

and 3Steven Bloembergen*.

The unique characteristics and properties of internally crosslinked starch latex binders for paper

coating were presented. While low shear Brookfield and Hercules rheograms are commonly used in

the industry to assess the runnability of coatings, these results demonstrate that such low shear

techniques can be extremely misleading when it comes to the prediction of coating performance on

high speed metered size press, rod and blade coaters. The use of more specialized “ultra-high” shear

equipment such as the ACAV might be needed to better understand the rheological performance under

commercial coating conditions.

PaperCon 2012 http://www.tappi.org/Downloads/Conference-Papers/2012/12PAPERCON/12PAP11.aspx

http://www.tappi.org/Downloads/Conference-Papers/2012/12PAPERCON/12PAP11.aspx

ACAV Viscometers by

Coating optimization

Effect of Particle Size Distribution on Ultra High Shear Viscosity

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Narrow distribution, 67%

Wide distribution, 67%

Narrow distribution, 65% solids

Wide distribution, 65% solids

= Measurement range of Conventional viscometers

Curves are

identical below

200 000 1/s

ACAV Viscometers by


Runnability of new cheaper co-binder system is same as earlier. Production of the grade was 60 000 t/a

Paper mill wanted to save money,

because of lowered paper prices.

They used a large amount (1,2) of

expensive co-binder and a small

amount of cheap co-binder (0,35).

After testing several co-binder

combinations Color A was best with

only 0,4 parts of expensive binder and

0,55 parts of cheap binder.

Runnability and water retention of Color

A is exactly same as earlier.

Runnability of Color B is not as good as

in Reference.

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Coating cost saving: 153 000 EUR/year!

ACAV Viscometers by


More fibers in coating circulation caused streaking problems

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Conventional

viscometers

measure ONLY

low share rates!

ACAV Viscometers by


Runnability and Particle Size Distribution

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POOR RUNNABILITY, wrong

particle size distribution

GOOD RUNNABILITY, right

particle size distribution

Curves are identical below 0.25 million 1/s

Less Breaks with

high speed and

reduced blade

pressure

ACAV Viscometers by


Temperature Effects

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60ºC

50ºC

30ºCCoating shear rates

Logical behaviour

below 100 000 1/s


Increase of coating color

temperature destroys the

surface active ingredient

of the latex.

ACAV Viscometers by


New coating recipe provided higher solid content at lower ultra high shear viscosity level

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Precoat old, 62 % Solids

Precoat new, 68 % Solids

BENEFITS:

• Coating costs reduced 10 %

• Saved drying energy 50 kWh/t

• Speed increase 33 % from 900 to

1200 m/min!

Results provided by: Rohm & Haas and Burgo Ardennes

ACAV Viscometers by

ACAV Viscometers

ACAV Viscometers are the most powerful tools for runnabilityanalysis of coating colors and pigment slurries.

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A2 A4

ACAV Viscometers by

ACAV Viscometers

Blade versus Slit Geometry

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BLADE

0.5 mm

SLIT

Coating Color~ 0.5 mm

~ 2

0 µ

m

Base paper8

0 µ

m

Similar Velocity Profiles

with Blade and Slit

ACAV Viscometers by

ACAV Viscometers

ACAV Slit

Best correlation to blade load

Best correlation to formation of agglomerates

Best correlation to scratch count

Enables analysis of most viscous pigment slurries

Enables analysis of highest shear rates and simulation of fastest blade

coaters

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ACAV Viscometers by

ACAV Viscometers

Slit Assembly

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ACAV Viscometers by

ACAV Viscometers

SLIT Viscosity versus Blade Load

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Pilot coater speed 1200 mpm

Blade pressure needed to

achieve 12 g/m2 coat weight

Aalto University

ACAV Viscometers by

ACAV Viscometers

ACAV SLIT Viscosity vs Scratch Counts

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Amount of dispersant added

is given as a percentage

1,60 %

1,60 %

0,80 % 0,80 %

0,40 %

0,40 %

1,60 %1,60 %

Results: TAPPI, 2001 Coating and Graphics Arts Conference and Trade Fair, pages 77 -86

Dr. Rajan R. Iyer, Ray Hollingsworth, Dr. David R. Skuse, Imerys, Sandersville,USA

ACAV Viscometers by

ACAV Viscometers

Possible formation of Agglomerates / SLIT Some pigment and/or chemical combinations cause agglomeration behavior, when

the color is under a high shear. The pigment and the chemical combinations can form

big blocks (agglomerates), which cause problems in coating machines and for

example in screens.

The possible formation of the agglomerates can be measured by the SLIT. With the

agglomerate measurement, we use same pressure during the whole measurement

and we measure the flow. If there is the formation of the agglomerates, they block the

SLIT and the flow will decrease or even stop, if there is a strong formation.

If the SLIT is blocked, a customer can open the SLIT and take a sample of the block

and use chemical analyzers (IR, AAS, etc.) to find out the reason (pigment or/and

chemical) , which caused the problem.

23

ACAV Viscometers by

ACAV Viscometers

Stability Test with SLIT/Agglomerates

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Coating colors with strong

structures are more likely to form

agglomerates. Therefore dry

bleeding and scratching are more

probable.

Formation of agglomerates, Extrusion Pressure is Constant

ACAV Viscometers by

ACAV Viscometers

Runnability on High-Speed Blade Coating

Evaluation of the temperature change of coating (TCH) under high-

shear rate viscosity with a SLIT die in laboratory experiments is one of

the best ways to simulate coating fluidity under the blade.

Water retention, high shear rate viscosity with a SLIT die, and

properties of the base paper are needed to predict blade coating

runnability.

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Results: TAPPI Coating Conf. 2002, Dr. Koji Okomori, Masato Yamaguchi,

Masahito Suzuki and Hirokazu Morii, R&D Division, Nippon Paper, Tokyo

ACAV Viscometers by

ACAV Viscometers

Guidelines for Interpreting Graphs

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Viscosity

(mPas)

100

1000

Optimum

Rheology

Behaviour High viscosity at ultra high shear rates:

1. Blade bleeding and streaking

2. Problems in maintaining target coat weight

3. Web breaks, scratches, agglomerates

Low viscosity at ultra high shear

rates: uneven coat weight

High viscosity at low shear rates:

pumping and start-up problems

High viscosity at high shear rates:

problems in screens, rod, jet and

applicators

110

2 3 4 5 6 710 10 10 10 10 10 Shear Rate 1/s

Low viscosity at

all shear rates:

water retention

problem

ACAV Viscometers by

ACAV Viscometers

Operational Limits of Blade Load

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Desired coat weight (c.w.) =

Blade load

Co

at w

eig

ht Operational area

Suitable viscosity:

even coating and no breaks.

Too low viscosity: c.w. is

not achieved due to uneven

coat weight.

Too high viscosity: c.w. is

not achieved due to web

breaks.

Web

breaks

Uneven

coat weight

Color viscosity must

be suitable for each

coat weight and

base paper

ACAV Viscometers by

ACAV Viscometers

Blade Pressure Correlation

“The blade run-in’s were compared to coating viscosity measurements

at various shear rates to confirm the validity of using ultra high shear

viscometer as a predictive tool in runnability”

“Ultra high shear viscosity, obtained by the capillary viscometer (ACAV

A2), showed GOOD CORRELATION to the blade pressures required to

obtain a target coat weight, even though the colors studied had

significantly different pigments (e.g. delaminated or chemically

engineered).”

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By ECCI, TAPPI Coating ´98

By Imerys, TAPPI Coating´01

ACAV Viscometers by

Pigment Slurry Analysis

Maximum viscosity range up to 12 000 mPas (Capillary)

Viscosity range up to 30 000 mPas (SLIT)

Shear rates from 100 1/s up to millions 1/s

Solids up to 76 %

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ACAV Viscometers by


Kaolin with Wide Particle Size Distribution

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ACAV Viscometers by


Kaolin with Narrow Particle Size Distribution

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ACAV Viscometers by


Dispersion Tests of Slurries of New Engineered Kaolin Pigment

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High viscosity and shear thickening

region cause screening problems.

Ultra high shear viscosity showed

good correlation to screening

The new kaolin pigment has a special

particle size distribution (the smallest

particles had been cut off)

0,22 %0,24 %

0,28 %

0,26 %


ACAV Viscometers by


Dispersion Tests of Slurries of Engineered Kaolin Pigment

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ACAV Viscometers by


Dosage of Dispersing Agent was deficient

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ACAV Viscometers by

Analysis of Coating Color Formulations

Different thickeners cause different viscosities at different shear rate ranges different behaviour in screens and applicators

different blade loads

Particle size of thickeners has an important impact on particle size distribution of coating colors

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ACAV Viscometers by


Viscosity Curves of “Typical” Coating Colors and Coating Colors

with Narrow Particle Size Distribution.

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Wide particle size

distribution

& traditional latexNarrow particle

size distribution

& traditional latex

Reproduced from R. Knappich et al.

ACAV Viscometers by


Viscosity Curves of Coating Color with Narrow Particle Size Distribution and Latex A/B

37

Narrow particle

size distribution

Ultra high shear

viscosity correlates

directly on blade

loads.

Reproduced from R. Knappich et al.

ACAV Viscometers by


Effect of Medium Co-binder Addition

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KAOLIN BASED COATING

PVOH

Starch

Latex A

Latex B

CMC

ACAV Viscometers by


Effect of Particle Size of Latex

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ACAV Viscometers by


Thickeners – Example of Shear Rate Effect

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Same coating color, five

different thickeners.

Pigment is mostly clay.

(Data: Sandås, Salminen)

• Note logarithmic scale.

• No correlation between low

and high shear rates.

• E.g. PVOH: low viscosity at

low shear rates, high viscosity

at high shear rates.

ACAV Viscometers by


Comparison and Effect of Thickeners

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Property No thickener CMC StarchDewatering rate 118 g/m2 49 g/m2 43 g/m2

Storage modulus 1.55 Pa 101 Pa 36 Pa

Visc. of water phase 1 mPas 3.5 mPas 8.3 mPas

Brookfield viscosity 100 mPas 1200 mPas 750 mPas

High shear viscosity 12 mPas 40 mPas 55 mPas

High de-watering rate = poor water retention

High storage modulus = high elasticity

Starch has relatively low formational structure -> low

elasticity and low viscosity at low shear rate. Thickens

water phase -> high viscosity at high shear rates.

ACAV Viscometers by

Comparison of shear rates

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ViscometerShear Rate

1/sComparison to process

Brookfield 10 Shear rate 200,000 times lower

Rotational 40,000 Shear rate 50 times lower

Capillary

ACAV A4500,000

Shear rate comparable to most real

processes

Capillary

ACAV A22,000,000

Shear rate same as in high speed

coating process

ACAV SLIT 10,000,000Possibility to simulate even highest

shear rates

ACAV Viscometers by

Comparison of Shearing Times

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Viscometer Shearing Time Compared to process

Brookfield 1 s Tens of thousand times

Rotational 1 s Tens of thousand times

ACAV Capillar 1 ms About 30 times longer

ACAV SLIT 30 µs Same as under blade

ACAV Viscometers by

Service of ACAV A2

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Hydraulic oil

& oil filter,

every 2nd

year

Piston seal,

300-500

analyses

Door safety switches,

once a year

ACAV Viscometers by

Extensional Viscosity

Accelerating Flow and Extensional Viscosity

Extensional viscosity (EXTV) is a color’s

resistance to accelerating flow.

Coating colors contain polymeric thickeners,

which have considerable effect on extensional

viscosity.

Without velocity gradient, polymer chains are

random coils. When flow speed increases (arrows

are representing flow velocity), the accelerating

flow field stretches and orientates these coils.

This causes resistance to accelerating flow, i.e.

extensional viscosity.

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ACAV Viscometers by


Advantages of EXTV Option Of ACAV A2

Excellent repeatability

Easy to use and calibrate

Method based on the well-known Euler number

The Euler number can be measured at different shear rates to examine

possible changes in extensional viscosity versus shear rate.

The higher the Euler number, the higher the extensional viscosity of the

sample.

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ACAV Viscometers by


Extensional viscosity measurement (EXTV) option.

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EXTV

ACAV Viscometers by


Extensional Viscosity vs. Shear Rate

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Coating colors under

development for

curtain coater

LWC coating color

Water

ACAV Viscometers by


Influence of Thickener on EXTV

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Source: IMERYS TECHNICAL GUIDE

ACAV Viscometers by

Curtain Coating

Shear rate

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ACAV Viscometers by

Curtain Coating

Nozzle is 0.3 mm, solids content 10 g/min, target coating thickness 10 µm and if coater

speed is 1,200 m/min => it is necessary to feed coating color 0.2 l/s every meter of the web.

The flow rate of the coating color is about 0.7 m/s, so the shear rate inside the nozzle is

about 13,000 /s.

At the moment when the coating color hits the web the shear rates can be >1,000,000 /s.

If the ultra high shear viscosity is too high or there is a lack of extensional viscosity in the

coating color, it could cause uncoated areas on the base paper.

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Alleborn, N., Südderhauf, H., Raszillier, H.

High-Speed curtain coating of paper

PTS 20. Streicherei-Symposium 2001

ACAV Viscometers by

Curtain Coating

Curtain Coaters and ACAV EXTV

ACAV’s EXTV option was found to be capable of measuring extensional viscosity.

Based on the measurement data, special thickeners, dosage of special thickeners

and solids content of the coating colour all effect the extensional viscosity of the

coating colour which was the expected result.

Surfactants or other normally used thickeners did not increase extensional viscosity

which was expected, based on the runnability of the curtain coater. Pigment system

had no measureable influence on extensional viscosity.

Lower coating colour viscosity enables lower flow rates in extensional viscosity

measurement, so extensional viscosity can be measured at lower shear rates. Lower

flow rates can also be obtained by using an orifice with a larger hole.

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Conclusions of PTS 2007 article of Curtain Coaters:

M.Ojanen / Kemira; T.Sinkko and L.Kunnas / UPM

ACAV Viscometers by

Curtain Coating

Curtain Coaters and ACAV EXTV (continues)

“Based on the measurement data and experience with a pilot curtain coater, the Euler

number of the coating colour should be >5 at shear rate of 20,000 1/s. If the Euler

number is < 5, there is a strong likelihood that problems caused by lack of extensional

viscosity might occur.”

“To ensure a reliable measurement, ACA EXTV device should be cleaned and

washed carefully after each measurement. Even tiny impurities can cause errors. This

can be seen as instability in the graph, especially at low flow rates. Otherwise taking a

measurement is quick and easy: the measurement accuracy is only dependant on the

solids content of coating colour.”

53

Conclusions of PTS 2007 article of Curtain Coaters:

M.Ojanen / Kemira; T.Sinkko and L.Kunnas / UPM

ACAV Viscometers by

Film Coating

54

Premetering

rod

Paper

web

Backing

roll

Transfer

roll

Application

Nip

Shear rate

about 1 000 000 1/s

Coated

paper

Film

split

Transfer

nip

Normally a film coating

is dual-sided,

simultaneously

Shear Rate

~ 1 000 000 1/s

ACAV Viscometers by

Film Coating

Requirements

The shear rate of a coating color in the application nip is about same as

the shear rate under the blade in a blade coating process: both the

coating film thickness and speed gradients are about same, if both

coaters run the same speed.

The relevant area to measure viscosity is around 1 million 1/s in both

cases.

Rod pressure has operational limits, and therefore ultra high shear rate

viscosity has to be suitable for achieving desired coat weight.

Too high viscosity or solids content, on the other hand, leads to misting

and spitting of coating color at the nip outlet.

55

ACAV Viscometers by

Film Coating

Rod misting phenomenon is comparable to

blade bleeding in blade coating process.

Rod misting may be reduced by:

Reducing high shear rate viscosity

Reducing solids content

Reducing amount of plate-like particles (clay)

Extensional viscosity may also be important,

as there is a converging flow field at the

entrance of the application nip.

56

Picture: Voith

ACAV Viscometers by

Film Coating

It is believed that high extensional viscosity is bad for

runnability: filaments elongate more before they break up, and

therefore misting is more problematic.

According to experience, misting may be reduced by:

Lowering high shear rate viscosity

Reducing amount of blocky pigment particles (GCC)

Increasing solids content

Splitting of coating film seems to be more regular and smooth,

when the solids content of the coating color is high.

In addition, relatively high viscosity at high shear rate range

has a positive effect on orange peel formation.

57

ACAV Viscometers by

Air Content Measurement

Air Content Measurement Option of ACAV

58

ACAV Viscometers by


59

Coating MethodCritical Air content

[%]

Blade & Roll

Application6 - 8

Film 8 - 12

Jet & Blade 2

Curtain 0,2 - 0,5

ACAV Viscometers by


Repeatability of ACM Option of ACAV

60

Two samples were taken

from the same coating

color. Air content of both

samples was measured

10 times.

ACAV Viscometers by

Spray Nozzle Option

‘Viscosity’ and flow resistance of spray nozzle

ACAV equipped with Spray Nozzle Option can be used as coating head for laboratory coaters (Helicoater, CLC, …)

61

ACAV Viscometers by

Spray Nozzle Option

62

Spray NozzleSame geometry and

flow as in process

version

Quick Connector

ACAV Viscometers by

Comparison of ACAV A2 and A4

ACAV Viscometers

Shear rates 100 - 10 000 000 1/s

Viscosity range - 30 000 mPas

Over 120 units sold since 1997

Best correlation to blade loads

Best correlation to runnability

problems

Capillary, SLIT, Spray, DWR, Air

Content and EXTV technologies

63

ACAV Viscometers by


Unique Measurement Method

ACAV is the only unit which can forecast the probable occurrence of the

following runnability problems:

too high blade loads

formation of agglomerates

number of scratches

blade bleeding

blade streaking

problems in maintaining target coat weight

blocks in screens

other problems in coaters and applicators

64

ACAV Viscometers by


ACAV A4

Shear Rates up to 4,000,000 1/s

Capillary, SLIT and Spray Nozzle options

Dynamic Water Retention (DWR)

Best correlation to blade load

65

ACAV Viscometers by


66

ACAV Viscometers by


67

ACAV Viscometers by

Customer Opinions

“Coating formulations frequently used for specialty paper application are of exceptional character and often very demanding from the rheological point of view.”

“Comprehension of the flow characteristics at realistic shear rates is of paramount importance for formulating of new advanced specialty coatings.”

“The ACAV 2 viscometer was our natural choice as we found it by far the most suitable for our purposes. In addition we have also had a very good earlier experience from ACAV 2 at another Ahlstrom site.”

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Erkki Laiti, PhD, Manager of R&D Services at Ahlstrom Research Corporate Center

ACAV Viscometers by

Customer Opinions

Experience of Slurry Measurements

“According to our experiences in screening problems caused by special

slurries, we can see the difference between slurries, which flow easily

through the screens compared to slurries, which block them. The

difference can be seen from shear thickening behaviour at high shear

rates by using the ACAV2.”

69

Matti Lindeman, Group Leader, UPM, R&D laboratory, Lappeenranta, Finland

ACAV Viscometers by

Slow Speed – No Runnability Problems

70In past the runnability wasn’t a problem.

ACAV Viscometers by

High Speed – Need for Latest Technology

71

Nowadays we do need the latest technology to

prevent and to solve runnability problems.