MPMA One Day Seminar Water Based Paints An...

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MPMA One Day SeminarWater Based Paints An Overview

Part 3:ALL YOU NEVER WANTED TO

KNOW ABOUT CPVC!!!!

Philip Green

September 15 2015


INTRODUCTION

After over 30 years of being involved in theTechnical side of the Coatings industry, I find thatCPVC is probably one of the most over utilized andmisunderstood terms that is used.

The aim of this short talk is not only to de-mystify thesubject but also give you some very practical ideasof how CPVC affects and is used in the formulationof paints.


DefinitionCPVC = Critical Pigment Volume Concentration

Below CPVC there is a lot more binder thanpigment/extender i.e. the paint is well bound.

Above CPVC there is less binder than pigment/extenderi.e. the paint is Under Bound.

At CPVC there is justenough binder to satisfyall the pigment/extender.

Many paint propertieschange dramaticallyat/about CPVC.


Properties affected by CPVC (1)

Wet/dry opacity and colour

a) Well bound paint (below CPVC)

High latex level so in the wet state the paintwill be lighter/whiter in colour, higher inopacity.

In dry state latex is clear socolour will be darker, lesswhite, have a lower opacity.


Properties affected by CPVC (1) cont

b) Under bound paint (above CPVC) the latex level willbe lower so the wet opacity will be lower and thecolour will be darker.

On drying there will be air voids left in the film by theabsence of latex, these voids will act as lightscattering sites.

So the dry film will be ,lighter, whiter and higher inOpacity than the wet film.



c) At or just above CPVC the loss in dry opacity due tothe latex drying, going clear is roughly balanced bythe increase in dry opacity due to the air voids. Sothe colour/opacity stay about the same when goingfrom wet to dry.

Of course use of Microvoid opacifiers can affect theabove 3 situations but by closely watching a paintdry an experienced paint chemist can normallyjudge whether the product is below, above or nearCPVC.



d) One question that I am often asked is why are deepand clear tint bases not made at PVC’s that areabove CPVC?

Well the answer is that such a tint base will vary inopacity and depth of colour considerably not onlyfrom batch to batch of paint (as the componentscause slight variations in PVC and CPVC) but alsofrom colour to colour tinted either due to the amountand/or type of pigment used.

I.e. Colour reproducibility is a nightmare.



Change in porosity, stain resistance

As most people are aware as PVC increases,approaches and exceeds CPVC there is a dramaticchange, (Downgrading) in stain resistance.

At first glance this is puzzling but if one thinks interms of porosity it begins to make sense.

A well-bound film has few voids or surface porosityinto which stains can soak into the film. Andtherefore the stains stay on the surface and areeasy to remove.



However as the PVC gets closer and exceedsCPVC the amount of binder drops and the potentialfor air voids increases and therefore the surfaceporosity and places where the stains can soak intothe film increases dramatically, the stains can soakin and are very difficult to remove.



Of course CPVC/PVC are not the only formulationfactors that effect surface porosity and stainresistance. The following can also have positiveand negative effects:

a) Dispersant/dispersant level

b) Pigment/extender type and level

c) Latex type/level

d) Defoamer type and level

I.e. formulating for good stain resistance is acomplex and tricky balancing act.



Scrubs, Washability and abrasion resistance

All of these properties change, downgrade at orabout CPVC – when one considers that all theseproperties will be positively influenced by increasedbinder being present and negatively influenced byincreased air voids being present you can quicklyunderstand that washability, Scrubs/abrasionresistance will decrease dramatically as oneapproaches or exceeds CPVC.



• However there are lots of technologiesavailable, which can be used to positivelyinfluence these properties cost effectively.By the way although we can safely saythat these properties are downgraded asPVC is increased the change is actuallyquite gradual until you get quite close toCPVC.



Change in Exterior Durability

This property like the 2 just described isdirectly/indirectly controlled by the amount ofbinder that is present or how many air voids arepresent so like the others Durability doesdowngrade on or about CPVC. However thechange is subtly different:

Up to CPVC the change is gradual

Around, just above CPVC the change is quitedramatic.



• The change is actually quite gradualuntil you get quite close to CPVC. Butas the PVC increases (circa 85%) thefall off becomes gradual again

• Again like the other propertiesdiscussed there are technologiesavailable to positively influencedurability so obtaining 2-3 yearsdurability. At a PVC of 75-85% in nowalmost the norm.


Properties affected by CPVC (5)Breath ability/allowance of water vapour to leave thesubstrate by permeating through the dry paint film tothe Atmosphere. Logically/from what is said it canbe seen that a coatings ability to breath is directlylinked to PVC:

Ultra low 15-30% no water vapour permeabilityLow 30-65 some water vapour permeabilityHigh 65-high liquid water permeability



• One property that is indirectly linked to acoatings ability to allow water vapor to permeatethrough it is Fungus/Algae resistance. Asremoval of water vapor from a damp substrate isa must if you want really good fungus/algaeresistance.

• Of course this property can also be adversely orpositively affected by other formulation factorsnot just PVC/CPVC.


How to Positively Effect CPVC• Many experienced Paint Chemists use a whole

range of different technologies to manipulateCPVC to positively influence Dry Opacity, Stainresistance and Durability without downgradingother properties. Examples are:

• Fine Particle Sized Calcium Carbonates• China Clay, Calcined Clays, Structured Calcined

Clays• Talc• Kaolanites (Pyrofil)


Fine Calcium Carbonates• A 2 Micron CaCO3 will not only space the TiO2

so that that we get less crowding. So BetterTiO2 utilization it also closes up the film andgives better water resistance, Higher Sheen andbetter utilization without downgrade scrubssignificantly

• Some people also use 1 Micron calciumCarbonates


China Clay• Is the oldest filler used in the Paint Industry –it

was used in Cave Paintings 30-40000 Yearsago

• It’s a TiO2 spacer, sheen improver, Helps toreduce settling

• Imported grades dominate –expensive, so usehas died off in some markets

• Some people still use cheap grades in Low CostPaints (G1/G3) but they are very variable

• Clays love water so add them to the mill base asone of the first Pigments/Extenders


Calcined Clays 1• After America, The Far East was one of the first

Regions to see the benefit of using CalcinedClays in Paint

• Calcined Clays are water washed fine particlesized ( Sub 0.5 Micron) Aluminum Silicates thatare Calcined at 800-1200 Deg C in large RotaryCalciners

• The Calcining process drives off water,increases particle size, refractive index , traps airvoids (sintering) and increases Oil absorption


Calcined Clay 2• These changes increase the products Mohs

Hard from 2.5-3.0 to 6-7 , which in reality isprobably a 100 Fold increase

• We can use the particle size, refractive index, airvoids to allow us to Reduce TiO2 levels by 15-20% in Medium PVC Products

• The higher Mohs hardness allows to also reduceLatex levels whilst Maintaining Scrubs/Durability

• The higher OA lets us Manipulate/reduce theCPVC so we can obtain better dry hiding, whilstagain not adversely affecting scrubs/durabilitygreatly


Structured/Flash Calcined Clays

• Started to appear 10-15 Years ago andare basically higher efficacy versions ofStandard Calcined clays that allow us tosave even more TiO2 (10-15%) but likeStandard grades to achieve the benefitsyou need to reformulate –can be a trickybut rewarding process with some pitfalls


Talc 1

• In some European Markets they took adifferent approach to CPVC management-they didn’t manipulate the CPVC downwards they used the hydrophobic plateletsof fine Talc to effectively close off the filmto stains, make it less water sensitive andthus give better scrubs

• This then allowed them to increase PVC ,maintain scrubs but in increase dry opacity


Talc 2

• With the introduction of local fine whiteTalc a few years ago this “tool” wasadded to our local formulating “armory”

• Initially the use was more focused onimproving stain resistance of premiumsheens/ matt, but also improving mediumPVC water resistance and Breathability


Talc 3

• Recently we have begun to see Talc beingused in combination with Calcined Claysto good effect –as the imparted bluenesshelps to combat the imparted yellownessof Calcined Clays especially in Tint bases

• Talc is also used with MicrovoidTechnologies to optimize stain and polishresistance


Kaolanites 1

• Also known as Pyrofilite s –it has takenover the place in the formulators tool boxin some markets that used to be filled byKaolin in medium to high PVC productswhere a similar (lower) effect as CalcinedClays was required at a lower price with agreater adverse effect on scrubs


Inter mixing of Technologies

• In the past people tended to be CalcinedClay or Talc or Kaolanite or MicrovoidOpacifier “Fans” now with the currentpressure on costs more and more peopleare using the technologies together to givebenefits but users must also be aware thatproblems such as syneresis can ensue butsuch problems are easily overcome


Conclusion/Measurement

As can be seen from above CPVC is quite a complex issuewhich both positively and adversely affects coating propertiesand a lot of people say why can’t we measure/determine itaccurately – well we can for the simplest system, but not forthe very complex systems we tend to use as commercialpaints.

However from 30 years of involvement with CPVC baringextreme cases I can say that most commercial latex basedcoating systems have a CPVC in the range 55-60% PVC (50-55 and 60-65%) being the extreme cases)

MPMA One Day Seminar Water Based Paints An...

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