Mondo TB1206

Low Oil Absorption Talc for High Solids Coatings

Technical Bulletin 1206

Contents

2 Mondo Minerals B.V. . Technical Bulletin 1206

Abstract

High solids coatings are one solution of the paint

industry to solve the emission problem of volatile

organic compounds (VOC) in the paint formulations.

A lot of attention has been given to develop new

binder systems that have low solvent emissions (VOC)

with good application and protection properties. New

generation binders are low molecular weight and

low viscosity resins with low pigment binding power

and so they set new requirements for pigments and

extenders.

Traditionally talc is the preferred extender in protective

coatings due to its’ good barrier and anti-corrosion

properties. The high oil absorption value of a conven-

tional type of talc makes it difficult to get low enough

VOC-content in modern protective coatings. New, low

oil absorption, talc extender with controlled top size

has been developed in response to this challenge. This

new talc product is based on pure, macro-crystalline

talc ore which means good barrier and corrosion

protection due to high platyness and hydrophobic

character of the talc. What is unique is the optimized

particle size distribution for high solid coatings. The

coarse fraction is sharpened is such a way that the

fineness of grind requirements are met. The fines con-

tent is also reduced to lower the resin demand to the

level that enables the production of VOC-compliance

coatings. This paper demonstrates how the solid

content and pigment volume concentration (PVC) in

the solvent based protective coating can be increased

without increasing the viscosity and at the same time

anti-corrosion properties of coating are also improved.

Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Talc.as.mineral.filler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Talc.grades.used.in.the.study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Description.of.experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Results.and.discussions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

First.test.series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Second.test.series.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3Mondo Minerals B.V. . Technical Bulletin 1206

Introduction

One of the most important development targets in the

paint and coating industry for many years has been

to reduce the volatile organic compounds (VOC) in

the formulations. The development of high solids and

water based coatings has been an attempt to reduce

VOC emissions. In the movement towards low VOC

solvent borne coatings, little attention has been given

to pigmentation. With a new generation of polymer

binders adequate pigmentation is absolutely necessa-

ry to provide a paint film with necessary optical and

protective properties. In these new developments

extenders became more specific and more functio-

nal than before. In the sectors of metal protection,

maintenance and marine coatings, all developments

tendencies are towards low VOC systems. However,

official international VOC limits for the products for

such applications are absent [1]. The European Unions

(EU) paint product directive, 2004/42/EC, concerns

decorative paints, varnish, wood stains and vehicle

repair paints, but not other industrial coatings. The

current VOC-legislation that controls the VOC emissi-

ons of industrial protective coatings is a solvent emis-

sion directive 1993/13/EC, that concerns the manuf-

acturing plants and work using the coatings, but not

directly the coating products themselves.

The talc is the preferred extender in traditional protec-

tive coatings due to its good barrier and anti-corrosion

properties. However the high oil absorption value of

pure and platy talc with conventional particle size dis-

tribution (PSD) makes it difficult to get sufficiently low

enough VOC-content in modern high solid coatings.

A new, low oil absorption, talc with specially designed

PSD has been developed to response this challenge.

This new type of talc product, Plustalc D30E, is based

on pure, macro-crystalline talc ore, however the both

ends of PSD curve is cut. The coarse fraction is shar-

pened is such a way that the fineness of grind requi-

rements are met. The fines content is also reduced to

lower the resin demand to the level that enables the

production of VOC-compliance coatings.

The purpose of this study was to compare the per-

formance of the new low oil absorption talc, Plustalc

D30E, with the performance of three other commonly

used talc types. The talc grades were tested in a com-

mercial solvent based 2 pack epoxy primer whose pig-

ment volume concentration (PVC) and solid content

were relatively high.

Talc.as.mineral.filler

Talc is a natural mineral that is mined from the earth’s

crust. Talc stones are often referred to as soapstone.

These stones are crushed, refined and fine milled

to PSD that is suitable for various paint and coating

applications. The fine structure of the talc is presented

on the Figure 1 [2]. Chemically, talc is a magnesium

silicate, Mg3Si4O10(OH)2, with a sandwich type of crys-

tal structure. Its’ theoretical chemical composition is

31,88 % MgO, 63,37 % SiO2 and 4,75 % H2O.

Figure.1:.

The.fine.

structure..

of.talc ..

Si+4

O-2

OH-

Mg+2


In nature talc does not exist in its’ theoretical form

or purity, but a small fraction of Mg and Si atoms

can be replaced by iron (Fe), aluminium (Al) or nickel

(Ni). Typically, the colour of talc stones is pale green

or white, but the colour can vary from pinkish to dark

green. The surface of talc stone has slippery feeling

and pearly lustre.

The unique fine structure of talc makes it ideal filler for

protective coatings:

➤ Talc’s surface is electrically neutral, which makes talc

highly hydrophobic, thus water.repellent.

➤ Talc’s particle form is platy, which is important for

an optimum filler packing in the paint film. The

platy particles also create a. good. barrier against

unwanted substances such as water, CO2 and O2.

The platyness helps also to design the right structu-

ral viscosity for the paint to reduce.the.settling.of.solid. particles,. improve. application. properties.(sprayability.and.brushablity).and.improve.the.sag/levelling.balance. The platy particle form of

talc reduces the shrinkage of binder system during

curing and so promotes. the. adhesion of paint

film to substrate.

➤ Talc is softest known mineral. The softness comes

from the platy structure. The talc plates slide across

each other when the plate pack is stressed by the

force, for instance when shearing the talc powder

between the fingers. The slippery feeling comes also

from this phenomena. The softness together with

the platy particle form improve.the.sandablity of

primers and improve.the.flexibility of paint film.

➤ Talc is highly inert. The talc does not dissolve in

acids or in bases, which is very important property

for the filler in many paint applications.

The particle form of talc is not always platy; it can be

also blocky. Blocky talcs are also called as a micro-

crystalline. The oil absorption of micro-crystalline talc

is lower than that of macro-crystalline (platy) talc at

the same Hegman fineness, even if the specific surface

area as measured by nitrogen adsorption is higher

with micro-crystalline talc.

There is no ideally pure talc deposit existing in the

nature, but the mineralogical composition of commer-

cial talc grades varies widely. The typical by-minerals

for the talc are carbonates like calcium carbonate,

dolomite or magnesite. The other typical by-minerals

are chlorite (Mg-Al-silicate) and mica. To be able to

utilise the protective functionality properties of talc

it should be pure and platy. The purity secures the

good water repellency and the platyness good barrier

properties.

Talc.grades.used.in.the.study.

The properties of talc grades used in this study are

given in table 1. All the talc grades had the same

fineness of grind (Hegman fineness), but they varied

in mineralogical composition and shape of PSD curve.

The oil absorption value of the talc used in protective

coating is very important. The oil absorption of talc is

effected by its’ mineralogical composition, morpho-

logy and PSD. Pure and platy talc has quite high oil

absorption at a given fineness. When talc contains

by-minerals such as magnesite (MgCO3), dolomite

(Ca,Mg-carbonate) or chlorite (Al-Mg-silicate) its’ oil

absorption is lowered. The platyness of talc varies

from deposit to deposit and it has big impact on the

oil absorption value. The talc grades that consist of

small plates have lower oil absorption than the talcs

with big plates. The less platyness is beneficial for oil

absorption point of view, but the protective properties

are reduced compared with platy talc. The best protec-

tion is therefore achieved by pure platy talc whose oil

absorption value is reduced by modifying its’ PSD. The

figure 2 shows how the PSD and mineralogical com-

position affect the oil absorption value of talc product

at the constant fineness of grind.


Property Unit MethodPure,.platy,.standard.

talc

Magnesite.rich.talc

Chlorite.rich.talc

Plustalc.D30E

Composition:

Talc %

XRD + LOI + Acid solubles

97 63 50 94

MgCO3 % 1,5 37

Chlorite % 1,5 50 6

Dolomite %

Loss.on.Ignition % 1000 °C/0,5 h 5,8 20,6 8,2 7,3

Acid.solubles % 1 M HCL, 100 °C 3,0 36,9 6,7 7,0

Particle.size:

Hegman fineness ASTM D 1210-79 4 4 4 4

Average PS, D50 µm Sedigraph 5100 4,5 4,5 5,2 9,8

Top cut, D98 µm Sedigraph 5100 20 20 20 22

Oil.absorption g/100g ISO 787/5 43 36 29 28

Specific.Surface.Area m2/g BET, ISO 4652 6,1 6,6 4,2 5,1

Whiteness,.Ry % DIN 53163 83 77 82 90

Table.1:..

The.properties..

of.talc.grades..

used.in.the.study .

100

90

80

70

60

50

40

30

20

10

0

100 10 1 0,1

PSD

by

Sedi

grap

h 51

00

OA = 43g/100g

OA = 36g/100g

OA = 28g/100gOA = 29g/100g

Conventional talc Plustalc D30E

Magnesite rich talc Chlorite rich talc

Figure.2:..

Particle.size..

distribution.of.

traditional.types.

of.talcs.and.low.

oil.absorption.

talc.at.the.same.

fineness.of.grind.

(Hegman.4) .

Figure 2 shows very clearly that if the talc contains

by-minerals like magnesite (MgCO3) and/or chlorite

(Al-Mg-silicate) the oil absorption value is lowered at

certain fineness of grind. Figure 2 shows also how the

reduction of fines of pure, platy talc reduces the oil

absorption value. The oil absorption can be reduced

from 43 to 28 g/100 g when the finest fraction of

talc particles is removed. This permits a remarkable

reduction in resin and solvent amounts in the coating

formulations.


3,0

2,5

2,0

1,5

1,0

0,5

0,0

0 50 100 150

ICI-v

isco

sity

of

talc

s te

sted

Talc

mix

ed in

100

g o

f lin

seed

oil

Talc load in g‘s

Pure, platy, standard talc Magnesite rich talc

Chlorite rich talc Plustalc D30E

When the oil absorption of the talc is reduced, it is

possible to optimise the filler loading in a coating.

Figure 3 illustrates the viscosity profiles of the talc

grades used in this study. The viscosity was measured

by ICI-viscometer after the talc was dispersed gradu-

ally increasing amounts in a linseed oil. As figure 3

shows the viscosity of standard type of talc increases

exponentially while the low oil absorption talc (Plustalc

D30E) demonstrates clearly moderate viscosity build

up.

Figure.3:..

The.viscosity..

profiles.of..

different..

talc.grades.in..

linseed.oil .


Description.of.experiments

The paint formulation used was solvent based 2 pack

epoxy primer that was based on solid epoxy resin and

a polyamide hardener. The components were mixed

in the stoichiometric ratio 4:1 by volume. The starting

formulation was the commercial general purpose anti-

corrosion primer for steel protection.

Two series of paints were evaluated. In the first series

each talc grade was milled to the PVC and solid

content that had the same application viscosity as

the starting formulation where pure, platy standard

talc was used. The target viscosity was 3000-4000 cP

measured by Brookfield RVDV-II+ viscometer (spindle

6, 50 rpm). In practise the amount of talc and solvent

content were changed in the formulations.

In the second series the PVC was kept constant (PVC=

51 v%) and the solids content was changed in such a

way that the same application viscosity was achieved

as in the first test series. In this series the amount of

solvent was changed and other components in the

formulation were kept constant. The magnesite rich

talc was not used in the second test series because it

had worse loadability than the standard talc.

The starting formulation:

Raw.material w%

Solid epoxy 19,47

Auxiliary resin 1,80

Acrosolv PM 3,00

Thickener 0,93

Wetting agent 1 0,26

Wetting agent 2 0,26

Talc, pure, platy standard type 24,88

BaSO4 18,93

TiO2 7,03

Pigment 1,08

Xylene 15,68

Iso-butanol 6,71

Total, w%

100

PVCtot, v% 51

Solid content by weight, w% 68,9

Solid content by volume, v% 45,1

Density, g/ml 1,514

VOC, g/l 471

The anticorrosion properties of the paints were stu-

died according to ISO-standards:

➤ continuous neutral salt spray, 381 h (ISO 7253)➤ water condensation, 240 h (ISO 6270).

The paints were applied on sand blasted steel panels

(Sa 21/2) by using high pressure airless spray gun. The

panels were 150 x 75 x 2 mm in size. The dry film

thickness was 80-90 µm. After the application the

panels were left to be dried at room temperature for

one week before the start of tests. Three parallel test

panels were prepared for each paint.

The visible defects on the test panels (degree of

rusting and blistering) were evaluated immediately

after end of the test according to ISO 4628 standard.

The adhesion tests were carried out according ISO

4624 standard by using hydraulic pull-off tester. The

diameter of the pull-off button was 20 mm.


Results.and.discussions

First.test.series

The anticorrosion performance of different the talc

grade in the first test series is given in table 2 and

figure 4. In this series PVC and solids content were

adjusted to give the same application viscosity as the

reference paint had by differing the talc and solvent

loads. These types of adjustments were done to be

able to have the truly comparable formulation on each

talc type.

There were no surface defects (blistering or rust dots)

in any of the paints after humidity test for 240 hours.

The adhesion was also good for all the paints after the

humidity test. However the drop of adhesion was least

with Plustalc D30E.

After the salt spray test (381 h) the blisters with the

size of class 2 and some rust dots appeared on all

test panels. The rusting degree is classified from 0

(best= no rusting) to 5 (worst= 40-50 % of coated

area was rusted) according to the ISO 4628 standard.

The reference talc and magnesite talc had a few small

rust dots all over the panels, and the rusting class of

these talc grades was between 0 and 1. The reference

talc had also a few blisters all over the panels. Other

panels contained a few blisters and some rust dots

only at the scratch site. The amount of rust dots and

blisters were lowest with Plustalc D30E.

It must be noted that the paint with Plustalc D30E had

very high PVC (56 v%) and yet anti-corrosion proper-

ties were better than the reference paint of lower PVC

(PVC= 51 v%). Also the solids content was 4 v%-units

higher with Plustalc D30E than in the reference paints.

So the anti-corrosion properties can be improved with

increased PVC by using low oil absorption talc. The

anti-corrosion properties were improved until approa-

ching the critical PVC, after which the coating film

becomes too porous and the anti-corrosion properties

collapse.

Pure,.platy,.stan-dard.talc.=.Ref .

Magnesite..rich.talc

Chlorite..rich.talc

Plustalc.D30E

PVCtot,.v% 51 50 53 56

Solids.by.volume,.v% 45,1 44,3 46,9 49,3

Solids.by.weight,.w% 68,9 68,0 70,6 72,7

Talc.content,.w% 24,9 22,8 27,3 31,2

Density.of.paint,.g/ml 1,514 1,495 1,547 1,595

VOC,.g/l 471 478 455 435

Adhesion.(ISO.4624).before.tests..in.MPa.and.type.of.breakage

5,6 (100 % B) 5,6 (100 % B) 6,5 (100 % B) 6,0 (100 % B)

Condensation.(ISO.6270,.240.h):

Visible surface defects (ISO 4628) – – – –

Adhesion after test, MPa 4,8 (100 % B) 4,8 (100 % B) 6,3 (100 % B) 6,5 (100 % B)

Salt.spray.test.(ISO.7253,.381.h):

Degree of rusting (ISO 4628)Ri = 0-1;

a few rust dots all over the panel.

Ri = 0-1; a few rust dots

all over the panel.


at scratch.


at scratch.

Blistering (ISO 4628)2 (S2); blister all over the panel.

2 (S2); blisters at scratch.

1 (S2-3); a few blisters at scratch.

1 (S2); a few blisters at scratch.

Adhesion after test, MPa 4,8 (100 % B) 6,9 (100 % B) 6,2 (100 % B) 5,8 (100 % B)

Overall.performance Adequate Adequate Good Very good

B = cohesion type breakage of coating film.

Table.2:.

Anti-corrosion..

properties.of..

different.talc..

types.in.solvent.

based.2.pack..

epoxy.primer.at.

constant.appli-.

cation.viscosity.

(3000-4000.cP..

by.Brookfield.

RvDV-II) .


Figure.4:

Adhesion.of.diffe-

rent.talc.types.after.

water.condensation.

(ISO.6270,.240.h).

and.neutral.salt.

spray.tests.(ISO.

7253,.381).in.sol-

vent.based.2.pack.

epoxy.primer.at.

constant.application.

viscosity.(3000-4000.

cP.by.Brookfield.

RvDV-II) .

7

6

5

4

3

2

1

0

Pure, platy, standard talc=

Ref.

Magnestic rich talc

Chlorite rich talc

Plustalc D30E

Adh

esio

n by

Pul

l-Off

Tes

t

Beforere tests After water condensation test After salt water test

PVC= 51 v%Solids= 45,1 v%



PVC= 50 v%aSolids= 44,3 v%

Second.test.series.

Anti-corrosion performance of different talc grades

in the second test series is given in table 3 and figure

5. In this series the PVC was kept constant and the

amount of solvents was reduced to get the same

application viscosity as the reference paint had.

The highest solid content was achieved by Plustalc

D30E; 51,1 v % (reference had 45,1 v %). The VOC-

content could be reduced from 471 g/l of the

reference paints to 420 g/l with Plustalc D30E.

There were no visible surface defects on the paints

films after the humidity test (ISO 6270, 240 h). The

reduction in adhesion was lowest with Plustalc D30E

after humidity testing.

A few blisters with size of class 2 and some small rust

dots appeared on the scratches of chlorite rich talc

and Plustalc D30E panels and the rusting degree (Ri)

was 0. The reference panels contained blisters and

rust dots all over the panels (Ri=0-1). The adhesion

after the salt spray test was best with Plustalc D30E.


Pure,.platy,..standard.talc.=.Ref .

Chlorite...rich.talc

Plustalc.D30E

PVCtot,.v% 51 51 51

Volume.based.solids,.v% 45,1 49,0 51,1

Mass.based.solids,.w% 68,9 72,2 73,8

Talc.content,.w% 24,9 26,1 26,7

Density.of.paint,.g/ml 1,514 1,575 1,603

VOC,.g/l 471 438 420

Adhesion.(ISO.4624).before.tests..in.MPa.and.type.of.breakage

5,6 (100 % B) 6,6 (100 % B) 6,9 (100 % B)

Condensation.(ISO.6270,.240.h):

Visible surface defects (ISO 4628) – – –

Adhesion after test, MPa 4,8 (100 % B) 5,5 (100 % B) 7,1 (100 % B)

Salt.spray.test.(ISO.7253,.381.h):

Degree of rusting (ISO 4628)Ri = 1;

a few rust dots all over the panel.

Ri = 0; a few rust dots at and below scratch.

Ri = 0; a few rust dots

at scratch.

Blistering (ISO 4628)2 (S2);

blister all over the panel.2 (S2);

blisters at scratch.1 (S2);

a few blisters at scratch.

Adhesion after test, MPa 4,8 (100 % B) 6,4 (100 % B) 7,0 (100 % B)

Overall.performance Adequate Good Very good

B = cohesion type breakage of coating film.

Pure, platy, standard talc=

Ref.

Chlorite rich talc Plustalc D30E

8

7

6

5

4

3

2

1

0

Adh

esio

n by

Pul

l-Off

Tes

t

Beforere tests After water condensation test After salt water test


PVC= 56 v%Solids= 49,3 v%PVC= 51 v%

Solids= 41,0 v%

Figure.5:

Adhesion.of.dif-

ferent.talc.types.

after.water.con-

densation.(ISO.

6279,.240.h).and.

neutral.salt.spray.

tests.(ISO.7253,.

381).in.solvent.

based.epoxy.coa-

tings.at.constant.

PVC.(51.v%).and.

at.constant.appli-

cation.viscosity.

(3000-4000.cP..

by.Brookfield.

RvDV-II) .

Table.3:..

Anti-corrosion.pro-

perties.of.different.

talc.types.in.solvent.

based.epoxy.primer.

at.constant.PVC..

(51.v%).and.at.con-

stant.application.

viscosity.(3000-4000.

cP.by.Brookfield.

RvDV-II) .


Conclusions

The anti-corrosion performance of new low oil absorp-

tion talc (Plustalc D30E) was compared with three

other commercial talc types in solvent borne general

purpose epoxy primer. The formulation was based on

solid epoxy resin and a polyamide hardener. The com-

ponents were mixed in the stoichiometric ratio 4:1 by

volume. The starting formulation had high pigment

volume concentration (PVC= 51 v%) and relatively

high solid content also (solids by volume= 45,1 v%).

The talc types tested were:

➤ pure, platy standard talc (reference)➤ magnesite rich talc➤ chlorite rich talc➤ pure, platy, low oil absorption talc (Plustalc D30E)

All the talc grades had the same top cut: Hegman

fineness 4.

The study showed that by pure, platy and low oil

absorption talc (Plustalc D30E) the solid content

and PVC in the paint formulations can be increased

without increasing the viscosity compared with tradi-

tional high solvent containing formulations and at the

same time the anti-corrosion properties are improved.

This means that Plustalc D30E-type talc helps to deve-

lop VOC-complaint paints with reduced formulation

costs and with improved coating performance. The

benefits of low resin and diluent demand of Plustalc

D30E can be utilised in all the paint and coating

systems were an increased solids content is desired.

The performance of different talc types can be sum-

marised as follows:

Water..repellency

Anti-corrosion.properties.(blistering.&.rusting)

Adhesion Load-.ability

Viscosity Solids.content

Reduction.of.VOC

Pure, platy standard talc ++ + + 0 0 0 0

Magnesite talc 0 + + – – – –

Chlorite talc – + + + + + +

Pure, platy low oil absorption talc (Plustalc D30E)

++ ++ + ++ ++ ++ ++

– negative impact0 no effect+ positive impact++ very positive impact.

References

[1]. CEPE Presentation “Proposal for Inclusion of PC into Product Directive 2004/42/EC”, December 2007.

[2]. http://www.ima-eu.org/en/talcwhat.html, 24.2.2004.

MONDO MINERALS B.V. . www.mondominerals.comKajuitweg 8 . NL -1041 AR Amsterdam . Phone +31 20 448 7 448 . Fax +31 20 448 7 437 . E-Mail: [email protected]

The information contained in this Technical Bulletin relates only to the specific tests designated herein and does not relate to the use of products in combination with any other material or in any process. The information provided herein is based on technical data that Mondo Minerals believes to be reliable, however Mondo Minerals makes no representation or warranty as to the completeness or accuracy thereof and Mondo Minerals assumes no liability resulting from its use for any claims, losses, or damages of any third party. Recipients using this information must exercise their own judgement as to the appropriateness of its use, and it is the user‘s responsibility to assess the materials suitability (including safety) for a particular purpose prior to such use.

Documents

Mondo TB1206