Talc for Wall Paint_wallpaint

Talc for Class 2 Wall Paint – How Choosing the Right Talc Promotesit to a Higher Class

Technical Bulletin 1204

1. Summary2. Introduction

3. Description of trialsDifferences between talc grades testedExperimental

4. Results and discussionsWet scrub resistance according to ISO11998Optical propertiesMud-crackingSheenViscosity

5. Conclusions

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1. Summary

The most important property that characterises thedurability of an interior decorative paint is the wetscrub resistance (WSR). The European standard, EN 13300, divides interior wall and ceiling paints into fivedifferent classes depending on the wet scrub resistancedetermined according to ISO 11 998. The purpose ofthis study was to investigate the effect of talc type onthe WSR. Of course the other important decorativepaint properties were also evaluated. The performanceof the following talc types were evaluated:

➤ pure macro-crystalline talcs - FINNTALC M15, M20SLand PLUSTALC C700

➤ micro-crystalline talc with a small amount of chloriteand magnesite (MgCO3)

➤ macro-crystalline chlorite (Mg-Al-silicate) containingtalc

FINNTALC M15 and M20SL showed the best overallperformance, resulting in excellent wet scrub resi-stance. The paints containing the FINNTALC gradesreached the wet scrub class 2, but those with chlorite-rich talc dropped to class 3. The very hydrophobic sur-face of FINNTALCs explains the superior WSR comparedto the other types.

Paints containing the FINNTALC grades also had thebest combination of optical properties, i.e. the highesthiding power and whiteness at sheen values below 5.

Contents

The pure macro-crystalline FINNTALC grades had alsothe viscosity profile that is normally desired for deco-rative paints - easy to apply without sagging or sedi-mentation problems.

The key points for the success of FINNTALC gradesare the macro-crystalline fine structure and high andconstant purity. The macro-crystallinity is a propertyof the raw material, but the purity is achieved by flo-tation, which means that impurities are removed by awet process. This ensures the high and constant purity,that is essential for reliable raw material supplies topaint producers in the long term.

2. Introduction

Talc is, after calcium carbonate, the second mostwidely used extender in interior decorative paints. It isnot used to cheapen the paint formulation, but toimprove the performance. Talc is a special extender;its surface is hydrophobic and the particle form islamellar. These two properties are typical for pure talc(steatite). But not all talc grades on the market are thesame. Each talc deposit has its own characteristics, likefingerprints. The talc can be more or less lamellar(macro- or micro-crystalline) and contain differentsecondary minerals, often chlorite (Mg-Al-silicate),magnesite (MgCO3) or dolomite. These differenceshave marked effects on the properties of interior

EN 13 300, divides interior wall and ceiling paints intofive different classes according to their wet scrub resi-stance, measured according to the ISO 11 998 stan-dard. The wet scrub resistance in this ISO standard isdetermined as the loss of paint film thickness in µm. The classes are the following:

paints. The purpose of this study was to clarify theeffect of different types and fineness of talc on themost important interior paint properties.

The durability of the paint film is largely defined bythe wet scrub resistance. A new European standard,

2 3Mondo Minerals OY . Technical Bulletin 1204 Mondo Minerals OY . Technical Bulletin 1204

FINNTALC SL grades are additionally purified by aelectro magnetic separator that removes nearly all themagnetic impurities. This improves the quality of theFINNTALC SL grades still further.

The other type of MONDO MINERALS talc in thisstudy was PLUSTALC. This group of products is basedon pure Asian macro-crystalline raw material. The rawmaterial for PLUSTALC grades is naturally so pure thatit does not need flotation.

3. Description of Trials

Differences between Talc Grades TestedIn this study, the typical paint talc grades of MONDOMINERALS were compared with commonly used com-petitive products. The talc grades tested varied in theirmineralogical base, in morphology (macro- vs. micro-crystalline), in particle size and in brightness. So all theimportant talc properties were varied to determinetheir impact on the paint performance.

From the talc range of MONDO MINERALS, two pro-ducts from Finland, FINNTALC M15 and FINNTALCM20SL, and one based on Chinese raw material,PLUSTALC C700, were selected for this study. FINN-TALC grades are macro-crystalline and purified by flo-tation. Flotation is a wet process involving severalsteps to separate the talc (steatite) from the otherminerals present in the basic rock. First, the raw materialis milled to separate the different minerals into dis-crete particles. This is fed together with water andcertain chemicals into a tank. Air is blown into thebottom of this tank. The talc particles accumulate onthe surface of the air bubbles which then carry themto the top of the tank. The froth (see Fig.1), which contains most of the talcis scraped off and collected. The other minerals sinkto the bottom of the tank. This process is repeatedthree times. The purified mineral is then milled to thefinal particle size.

Figure 1:

Photo of the

Flotation Tank

a very cost efficient way. The wet scrub resistance wasmeasured according to ISO 11998.

This bulletin describes how the choice of suitableextenders enables a class 2 paint to be formulated in


were also tested to see how the particle size affectedthe optical and other paint properties.

There was also one so-called micro-crystalline (lowaspect ratio) talc in the comparison to demonstratethe effect of particle form on paint properties. Theimpact of talc’s brightness on the paint properties wasalso studied. The brightness of the grades testedvaried from 75 % to 93 %.The properties of medium fine (d50= 5 µm) and coarse(d50= 10 µm) talc grades used are given in appendix 1.

The other talc grades tested in this study were chlorite-rich talcs. Chlorite is a magnesium aluminium silicate(Mg-Al-silicate) and has a hydrophilic surface. Thechlorite content of the talc grades used varied from10 to 55 % wt. The content of the other minerals wasfairly constant. Each talc grade contained only a fewpercent of carbonate minerals.

The talc grades were selected so that the particle sizeand size distribution were fairly similar in all cases. Theaverage particle size was around 5 µm. Coarser grades

Table 1:

Paint Properties

Measured and the

Target Values

Graph 1:

Wet Scrub Resistance

according to

ISO11998 for

Different Types of

Talc at Various

Pigment Volume

Concentrations

Graph 2:


of Different Types of

Talc at PVC of 70%

ExperimentalFirst two talc grades were tested in paints at different pig-ment volume concentrations (PVC) to see how the wetscrub resistance was affected by the PVC. Then, paintswere prepared with a PVC of 70%, containing the varioustalcs being tested. The WSR of each paint was determined.Depending on whether the paint formulation was classi-fied as class 2 or 3 indicated the most suitable products.The basic paint formulation is given below:

The same basic formulation was used in the trial toinvestigate the effects of different PVCs by merelyadjusting the binder content as necessary.

The paint properties determined with their target valuesare given in table 1.

4. Results and Discussions

The detailed analyses of the different talcs used arepresented in appendix 1. The results of the paint testsare given in tabular form in appendix 2.

Wet Scrub ResistanceIn graph 1, the wet scrub resistance results at differentPVCs are shown. Graph 2 shows the scrub resistance ofpaints containing different types of talc at constant PVC.

Graph 1 shows that pure macro-crystalline talc givesbetter wet scrub resistance values than chlorite-richtalc in the whole PVC range tested. The hydrophobicsurface of pure talc results in the superior wet scrubresistance in comparison to chlorite-rich talc.

Graph 2 shows clearly that the presence of chlorite inthe talc worsens the wet scrub resistance; the higherthe chlorite content, the worse the scrub resistance.On the other hand pure talcs give excellent wet scrubresistance.

The fineness of talc has a small effect on the wetscrub resistance, as shown in graph 3. The coarsergrades give slightly higher values than the finer grades.


Graph 3:

Effect of Fineness

of Talc on the


(ISO11998) at a

PVC of 70%

Optical Properties – Hiding Power, Whiteness and GlossThe optical properties are the most important fordecorative paints. The paint film must hide the sub-strate to which it is applied. The whiteness and glossmust also lie within the target ranges. The formula-tion used in this study was a dead-matt interior paint,so the target sheen value had to be below 5. Manypaint producers require a minimum value of 85 % forpaint film whiteness. So the best talc is the one thatgives a paint whose optical performance complieswith these whiteness and gloss limits and also givesthe highest hiding power (contrast ratio at spreadingrate of 7.5 m2/l).

Only one type of extender in the formulation waschanged in each paint, so the brightness and particlesize distribution of that extender were the only factorscausing variations in the contrast ratio and the white-ness of the paint film. The hiding power and white-ness of a paint film are, to a certain extent, opposingproperties: the darker the paint film, the higher is thehiding power and vice versa. These two propertieshave to be balanced so that both are at acceptablelevels whilst maintaining the right gloss level. In graph4, the effect of talc type on these important opticalproperties is demonstrated.

FINNTALC M20SL showed the best balance of the opticalproperties. Also FINNTALC M15, micro-crystalline talcand PLUSTALC C700 gave acceptable results. Therewere small differences in the optical properties of thesetalc grades, which were mainly caused by the differencein the brightness of the various talc grades.

The particle size and size distribution clearly affect theoptical properties. The effect of the fineness of talc onthe optical properties of paint film and the whitenessof the talc itself are shown in graph 5. To assess theeffect of the fineness, talc grades were chosen thathad the same mineralogical base to eliminate differencesarising from other factors such as the purity. FINNTALCgrades made from standard talc raw material wereselected. As can be seen from graph 5, the effect islinear; the coarser the extender, the lower is thehiding power and whiteness of the paint film. Thebrightness of the extender decreases as the particlesize increases.

Graph 4:

The Effect of

Talc Type on the

Optical Properties of

the Paint Film at a

PVC of 70 % and

Contrast Ratio at SR

of 7.5 m2/l

Graph 5:

Optical Properties

of Paint Film and

Talc vs. the Average

Particle Size of Talc.

The Grades Used

Were FINNTALC

Standard Grades.


Mud-CrackingThe tension that develops in the film-forming processis responsible for the occurrence of mud-cracking inemulsion paint films. The film tension develops moreor less spontaneously and can vary greatly. The completeelimination of cracking is only possible when anextender with a reinforcing effect such as one with alamellar structure like macro-crystalline talc is used.The talc reduces the shrinkage of binders during dryingand so reduces the film tension. The lower shrinkageimproves the mud-cracking resistance and also adhesion

to the substrate. So the lamellar particle form is thekey to improving mud-cracking resistance. This propertyis given as the maximum dry film thickness where nocracks develop. The effect of talc type on mud-crackresistance is presented in graph 6.

FINNTALC M20SL that is very platy and pure resulted inthe best mud-cracking resistance. Micro-crystalline talc,that is less platy (lower aspect ratio) than macro-crystallinetalcs, resulted in the lowest mud-crack resistance.

Graph 6:

Effect of Talc on

Mud-Cracking

Resistance

Sheen (Gloss at an Angle of 85°)One important role of extenders in paints is glossregulation. The coarser the extender, the lower is thegloss; that is always the case. In this study, the paintswere matt, so the sheen (gloss at 85° angle) wasmeasured. Interior emulsion paints should exhibit aslow a sheen as possible, because experience hasshown that when this exceeds 5%, the unevennessof the substrate, brush marks, etc. become visibledue to irregularities in the gloss. The sheen value canbe eliminated or at least reduced to a tolerable levelby coarse lamellar extenders.

In graph 7, the sheen values for different types of talcare given. The effect of the fineness of the talc on thesheen value is shown in the graph 8.

Graph 7 shows that gloss depends on the fines contentof talc. The only exception to this can be seen in thetwo chlorite-rich talc grades that have somewhat highersheen values than would be expected from the finescontents. In graph 8, the sheen values of talc gradeswith the same mineralogical base, but of differentfineness are shown. This illustrates clearly how very sen-sitive the gloss is to the fineness of the extender. Whenthe fine fraction of the talc is reduced so is the gloss.

Graph 7:

Gloss at 85° Angle

(Sheen) for Different

Types of Talc at PVC

of 70 %.

The Amount of

Particles Smaller

than 2 µm is

also Given.

Graph 8:

The Sheen of

FINNTALC Grades

with Different

Fineness at a

PVC of 70 %


Graph 9:

Viscosity Performance

of Different Talc

Grades in the Paints

at a PVC of 70 %

ViscosityExtenders also affect the applicational properties ofpaints. In this study, the viscosity of the paints was notadjusted; it varied with each of the talcs. Two differentviscosity values were measured: Brookfield 100 rpmand 1 rpm. The higher shear rate viscosity indicatesthe applicational properties and the lower shear ratethe stability and anti-sagging behaviour of the paint.The ideal viscosity profile would be a very low viscosityat a high shear rate and a very high viscosity at a lowshear rate. The shear thinning index or pseudo-plasticityindex (PSI) was calculated as follows:

PSI = Br1/ Br 100

The higher this ratio is, the better is the stability andresistance to sagging. In addition, the applicationalviscosity (Br100) should be as low as possible to givethe most desirable viscosity profile.

Graph 9 shows the viscosity performance of differenttalc types.

As one can see from graph 9, FINNTALC M20SL gavethe best viscosity performance - the lowest applicationalviscosity, but highest pseudo-plasticity index(Br1/B100). The micro-crystalline talc gave quite highviscosities, which is caused by the large content ofsmall particles that are not platy. Micro-crystalline talcgrinds very easily, which results in a high fines content.High fines content means high surface area of solidparticles and so higher viscosity. For platy talc, the truefines content cannot be seen from the particle sizedistribution curve determined using a Sedigraphbecause in this method the particle size is given as thediameter of round particles that sediment in water atthe same rate as the particles measured. More platyparticles precipitate more slowly, which means thatthe Sedigraph method gives too high a fines content.So if two different talc grades are compared, onebeing more platy than the other and they both havethe same percentage of fines as determined using aSedigraph, the product that is less platy actually containsmore fines than the more platy material.

5. Conclusions

The effect of different talc types on the most importantinterior decorative paint properties was evaluated.The main interest was to see the impact of talc typeon wet scrub resistance according to the ISO 11 998standard. The wet scrub resistance is a very importantproperty because it is used as a classification criteriafor interior and ceiling paints (EN 13300).

The pure, platy and floated FINNTALC grades, FINNTALCM15 and M20SL, gave the best overall performances.Paints containing them showed excellent wet scrubresistance. The paints containing the FINNTALC gradescomplied with wet scrub class 2 according to the classi-fication of EN 13 300. When the paint formulation

contained impure talc grades, (chlorite-rich talc), the classification dropped to class 3. The particle size oftalc affected the WSR somewhat – the coarser theproduct the better was the WSR.

FINNTALC grades had also the best combination ofoptical properties, which means that they had thehighest hiding power and paint film whiteness atsheen values below 5. The pure macro-crystallineFINNTALC grades had the viscosity profile that is nor-mally desired for decorative paints - easy to apply, butno sagging or sedimentation of solid particles. The performance of different type of talcs tested canbe summarised as follows:

++ positive impact + small positive impact 0 no effect - negative impact


Table 1.1:

Properties of

Medium Fine

Talc Grades

Table 1.2:

Properties of

Coarse Talc Grades


Table 2.1:

Paint Results of

Medium Fine

Talc Grades

Table 2.2:

Paint Results for

Coarse Talc Grades

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 orin 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 thecompleteness 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 mustexercise 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.

MONDO MINERALS OY . www.mondominerals.comKasarmikatu 22 . FI-00130 Helsinki . Phone +358 105 6211 . Fax +358 105 621 440 . E-Mail: [email protected]

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