applied and intrinsic hiding for a one coat...

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Applied and Intrinsic Hiding for a One Coat System

Luz Adriana Gómez O., Ana Beatriz Araujo, Heidi V. Salinas, Dan Saucy.

The Dow Chemical Company –Dow Coatings Materials Business

ABSTRACT

The hiding power or opacity of a film remains one key property that every formulator

studies; but it is typically determined without considering the application methodology

used in the field. The current measurements performed in laboratories are usually

limited to the variables delineated by Kubelka-Munk theory, including film thickness,

measured on a film applied by the typical draw-down bar. While this approach

characterizes the opacity of the paint itself (Intrinsic Hiding), it is not sufficient to

characterize the visual opacity of a field-applied film (Applied Hiding). To connect

these two hiding concepts, a comprehensive consideration of additional factors in the

determination of film opacity has been addressed in this work. Specifically, we will

describe how the paint rheology affects the film thickness and roller pattern on the wall

and, ultimately, how that impacts the Applied Hiding of the real-world paint film. This

impact is especially important in the design of new “One Coat” hide products,

challenged to be competitive with current and well-known 2-coat products. The hiding

performance of these non-diluted, one-coat systems is highly dependent on the

application technique and not just the amount of TiO2 or other factors. The successful

understanding and control of the key variables leading to improved Applied Hiding

enables enhanced coating efficiency and cost reductions for sustainable coatings.

INTRODUCTION

The factors involved in the hiding power improvement of an applied one coat paint

system can be divided in two main groups, intrinsic properties related with the design of

the paint and the properties determined by the application of that paint to the wall.

INTRINSIC HIDING

Much effort has been expended to create “One Coat” systems. The main focus in such

efforts is the optimization of the paint pigment (TiO2). This optimization has been based

from the beginning in the simple Kubelka-Munk theoryi that describes the performance

of a white coat system using a two flux theory and parameterizes the system with the

thickness (h) and the scattering (S) and the absorption (K) coefficients of the media. In

Figure 1, the Kubelka-Munk reflectance at infinite thickness is shown.

Figure 1. Solution of the Kubelka-Munk theoryover a black substrate at infinite film thickness.

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Many studies have focused

almost no absorption and no

and opaque polymer has been

properly spacing the TiO2 pigment crystals to

minimum and thus maximize the back

been possible to completely eliminate this dependent scatteri

In the last 5 yearsii, a new technology has

performance by properly spacing the pigment crystals

eliminate dependent scattering, and therefore achieve the maximum possible

scattering from the TiO2. This technology forms

the binder particles and the TiO2 pigment

film in the dry paint that surrounds

TiO2 crystals and eliminate

patented and widely distributed in not just architectural coating

coatings.

Figure 2. Visual representationmechanism and SEM pictures in 3D of a TiO

APPLIED HIDING

The factors that determine hiding of a paint film are the level of TiO

the TiO2 scattering, the whiteness of the paint, and the film thickness

first three of these factors are determined by the formulation and are what we refer to

as “Intrinsic” properties of the paint.

ed on getting the maximum performance in system

no dependent scattering. For more than 20 years, extenders

has been extensively used to reduce the TiO2 requirement,

pigment crystals to reduce dependant scattering to a

and thus maximize the back-scattering. However, until recently

been possible to completely eliminate this dependent scattering.

, a new technology has been born that can improve the TiO

performance by properly spacing the pigment crystals in the dry paint to virtually


. This technology forms a composite in the wet paint between

the binder particles and the TiO2 pigment, which then produces a continuous

surrounds every single crystal with binder and thus

eliminate dependent scattering (Figure 2). This technolog

patented and widely distributed in not just architectural coatings but also in indus

epresentation of EVOQUE™ Precomposite Polymermechanism and SEM pictures in 3D of a TiO2-Evoque system.

The factors that determine hiding of a paint film are the level of TiO2, the efficiency of

scattering, the whiteness of the paint, and the film thickness (Figure 3


as “Intrinsic” properties of the paint.

systems with

0 years, extenders

requirement, by

dependant scattering to a

until recently, it has not

born that can improve the TiO2 optical

to virtually


a composite in the wet paint between

produces a continuous binder

thus spacing the

technology is

but also in industrial

EVOQUE™ Precomposite PolymerEvoque system.

, the efficiency of

(Figure 3). The


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.

Figure 3. Main factors affecting the opacity of a paint film and

comparison between a regular paint and an Evoque system.

In the standard testing methods the film thickness is both predetermined and uniform

because it is created with a drawdown bar. Thus, the hiding that we measure in this

way is called the “Intrinsic Hiding” of the paint. This hiding defines the ability of the

paint to hide, and when optimized, defines the best that the paint can do.

In real-world application, the film thickness is not uniform and at a pre-determined

thickness. Rather it has a pattern determined by the application procedure. In this case,

we use the term “Applied Hiding” to indicate that it is the opacity of a real-world applied

paint film that we are studying. The Applied Hidingiii of a paint system is the result of

the Intrinsic Hiding modified by the film build and pattern uniformity created by the

application method over a specific substrate. These last factors are mainly influenced

by the rheology of the paint rather than the TiO2 content (Figure 4).

Figure 4. Definition of Applied Hiding

Figure 4 shows the non-uniform pattern that can beobtained by a roller application using a polyester nap.

≈

Influenced by rheology

APPLIEDHIDING

IntrinsicHiding

Film BuildPattern

Uniformity

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Figure 5.Detail of the paint patt

From an image such as Figure 5

which is, in fact, the “roller pattern”. In m

Normal distribution, such as

between opacity and film thickness is n

the roller pattern will always be less tha

same average thickness. Thus, the rea

opacity than the lab measurement beca

and smooth like the lab measurement.

Figure 6. Gaussian distribu

with a media

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.00

Re

lati

veA

rea

Frac

tio

n

Roller Patt

Detail of the paint patt

From an image such as Figure 5, we ca


Normal distribution, such as shown in F

hickness is n


same average thickness. Thus, the rea

opacity than the lab measurement beca

and smooth like the lab measurement.

. Gaussian distribu

with a median value

0.50

Roller Patt

m

, we ca



. Gaussian distribu

2 c

ern obtained

any cases, we obtain an approximately

ot linear (Figure 7

n the opacity from a uniform, smooth film of the

l applied film w

use the real

ti

ern Distribution

ern obtained with a polyester nap roller.

n evaluate the distribution of film thickness,


igure 6. However, because the relationship

ot linear (Figure 7), the average opacity from


l applied film will almost always have less

use the real-world application is not uniform

ti

(

1.

ern Distribution

with a polyester nap roller.

n evaluate the distribution of film thickness,


because the relationship

), the average opacity from


ill almost always have less

world application is not uniform

ti
on for the roller pattern distributionon for the roller pattern distribution
) ~ 1.1 mils (27.94 microns)

00 1.50 2.00

DFT (mils)

on for the roller pattern distribution

2.50

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Figure 7. Reflectance over black substrate as a function of

was used at 18 PVC

Because the net effect of the lack of film uniformity is so costly in

the efforts spent to optimize the paint system should consider that to maximize the

applied hiding of a paint, one must

minimizing the texture of the film. Minimizing the texture comes from minimizing the

initial texture pattern and maximizing the flow after the initial creation

(Figure 8). In addition, maximi

increase the opacity.

Figure 8. Comparison of the flow and sag performance for

new rheology modifiers for the HEUR type family.

0.84

0.86

0.88

0.9

0.92

0.94

0.96

10 15

R0

Reflectance over black substrate as a function of thickness. The

PVC of Rutile TiO2, and a resin index of refraction of 1.55.

Because the net effect of the lack of film uniformity is so costly in the hiding property,


one must maximize the smoothness of the film while also


initial texture pattern and maximizing the flow after the initial creation of the pattern

(Figure 8). In addition, maximizing the average film thickness will, of course, also

Comparison of the flow and sag performance for

new rheology modifiers for the HEUR type family.

15 20 25 30 35 40

Thickness (micrometers)

R0 vs film thickness

thicknessmean value

. The K-M theory

, and a resin index of refraction of 1.55.

the hiding property,


maximize the smoothness of the film while also


of the pattern

zing the average film thickness will, of course, also

Comparison of the flow and sag performance for

45

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FORMULATING PARAMETERS FOR A “ONE COAT” SYSTEM

The optimization of the intrinsic hiding properties is best represented in Figure 9 where

the EVOQUE™ technology and the proper selection of the TiO2 concentration are

combined to obtain a 98.0% of contrast ratio (CR) at 3 milsiv. In order to improve the

applied film thickness, the % volume solids (VS) was increased by 1/3 as compared

with the common 2-coat paints (30% VS).

Figure 9. Design of intrinsic properties for a “One Coat” paint.

As discussed above, to optimize the Applied Hiding, we need to maximize the

smoothness of the film. To this end, some studies of the pattern obtained with different

roller naps where carried out as shown in Figure 10.

Figure 10. Snapshots of the roller pattern generated just after covering the substrate.

BINDER

• EVOQUEplatform

RheologyModifiers

• New HEURgeneration

TiO2 PVC

• 18% - 22%

TotalVolumeSolids

• 38% - 42%

Lamb’s wool

Polyester Nylon

Microfiber

Stippled

Smooth

Rollercover

Substrate

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In this study, selected roller was microfiber.

The maximization of the flow after the initial creation of the pattern was produced using

the new HEUR rheology modifiers like ACRYSOL RM-400 or ACRYSOL RM-995v that

offer a great equilibrium between flow and sag resistance.

In order to increase the average film thickness, other than increasing the VS in the

formula, an increase in the ICI viscosity is needed. Products like ACRYSOL RM-

2020NPR and ACRYSOL RM-3000 among other ICI builder additives were tested.

RESULTS AND DISCUSSION OF RESULTS

The results shown below include the comparison of our systems with the commercial

products from the US market which have a main claim of “One Coat”. The Dow

proposals were formulated using acrylic binders below the CPVC. The system with the

conventional acrylic binder was formulated according to the intrinsic parameters define

for EVOQUE™ binder. All the systems studied were flat paints with a gloss below 5

units.

In Figure 11, the results for intrinsic opacity and whiteness obtained for the commercial

products (blue) and the Dow systems (green) are shown.

Figure 11. Intrinsic optical properties measured at 3 wet mils over black/white chart.

66

68

70

72

74

76

78

80

82

84

94.5

95

95.5

96

96.5

97

97.5

98

98.5

99

WI

Op

acit

y,C

Rat

3m

ils

Intrinsic Optical Properties

Intrinsic Opacity Whiteness Index, WI

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From Figure 11, we conclude that the optical effect in the hiding for the commercial

systems US1, US2 and US4 depends not just in the scattering efficiency but also

absorption to get better opacity. Dow systems do not sacrifice the whiteness to deliver

the opacity expected.

A comparison between the intrinsic and the applied hiding obtained using a microfoam

roller is included in the Figure 12.

Figure 12. Comparison between Applied and Intrinsic Opacity

for commercial and Dow´s “One Coat” systems.

US1 : Since the intrinsic hiding is good but the applied opacity is not, it is concluded

that there was an optimization in the intrinsic properties but no effort was made to

obtain a rheology profile that gives a good roller pattern. A lot of spattering was

observed.

US2 : Both intrinsic and applied hiding are good, the optimization of all the factors

previously discussed were balanced.

US3 : Excellent rheology design. Adequate whiteness (Figure 11) and applied opacity

(Figure 12).

US4 – Poor performance was observed for intrinsic and applied hiding.

Dow EVOQUE™ binder – Good and balanced performance between intrinsic and

applied opacity. This balance is the results of the composite formation with EVOQUE™

binder.

Dow AA – Better applied hiding than intrinsic. Excellent rheology profile was design for

this application.

93.36

97.91 98.23

95.45

98.18 97.96

90

91

92

93

94

95

96

97

98

99

100

Op

acit

y,C

R

Intrinsic and applied hiding

Intrinsic Opacity Applied Opacity

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According to these results, the systems that offer 98.0% Contrast Ratio applied at one

hand are the US-3, with good whiteness, and the US-2. On the other hand, Dow

proposals balance the intrinsic factors and the applied performance with very good

whiteness.

In Figure 13 we present the data for the paint yield of One Coat systems versus a two

coat system. The reference used (MEX1) as the two coat system was applied using

10%v dilution with water in order to promote the creation of a smooth pattern according

to the manufacturer recommendation. The yield was calculated using the real amount

of paint applied, eliminating the value of water added.

Figure 13. Data of the yield according to ASTM D5150 & ASTM D 344vi

All the One Coat systems do have a higher applied yield than the two coat system.

However, the total cost per square meter is higher for the One Coat systems. For the

Dow systems, since the yield is improved, the cost per square meter considering the

same price as US-2 and US-3, becomes competitive with the two coat system.

Finally, a general formula for the Dow proposals is shown in figure 14.

0

10

20

30

40

50

60

70

80

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

Pri

ce,U

SD/g

al

Yie

ld,m

2/L

Yield and price for One Coat Paints

Yield, m2/L Price USD/gal

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Figure 14. One Coat Type Formula.

CONCLUSIONS

A good selection of the rheology modifiers to create a desirable profile is not just a very

important factor to consider, it is also capable to compensate for a small lack of intrinsic

properties of the system. In some cases, it may be more economical to spend a little

more on rheology modifier and save cost by using less TiO2 in the paint. In the other

hand, the absence of a rheological profile design can easily waste the effort and cost

invested in the design of the intrinsic properties for paints in the final use.

For the Dow proposals, the use of EVOQUE™ binder maximizes the performance of

the intrinsic properties. This fact together with a good rheological design, converge in a

competitive One Coat paint versus a two coat system.

The possibility to create a rheological profile that covers the need for a One Coat

system comes from a combination of a broad portfolio of products and the expertise to

formulate profiles with a design rheology.

The use of EVOQUE™ binder and Opaque Polymer is a powerful combination to

maximize the intrinsic hiding of the paint.

One Coat Type Formula

Type of Raw Material % w

Solvent 10 - 15

Dispersant 2.0

Wetting agent 0.3

Co-solvent 2.0

Defoamer 0.3

Pigment 22 - 24

Extenders 15 - 17

Preservative 0.2

Emulsion 35 - 38

Opaque Polymer 6 - 8

Coalescent 1 - 2

pH agent 1

RM (KU builder) 1 - 2

RM (ICI builder) 0.4 - 0.6

PVC 40 -47

VS, % 40 - 45

WS, % 55 - 62

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ACKNOWLEDGMENTS

The Dow´s experts in Collegeville, which knowledge they are always sharing.

The Queretaro Team, who always accept the challenges with energy and enthusiasm.

Thank her husband, from who her learnt some useful Physics.

BIBLIOGRAPHIC REFERENCES

i. BARRON, V.; TORRENT, J. Use of the Kubelka—Munk theory to study the influenceof iron oxides on soil colour. Journal of Soil Science, 1986, vol. 37, no 4, p. 499-510.

ii. FASANO, D; ADAMSON, L. Advancements in TiO2 Composite Technology. PCIMagazine; August 2012.

iii. CONLEY, T.; FASANO, D. Intrinsic versus Applied Hiding: A new equation foroptimum performance – Part 1; PCI Magazine; April, 2014. CONLEY, T.; FASANO, D.Intrinsic versus Applied Hiding: A new equation for optimum performance – Part 2; PCIMagazine; May, 2014.

iv. ASTM D-2805-11. Standard Test Method for Hiding Power of Paints byReflectometry.

v. Brochure. Dow Coating Materials. ACRYSOL™ RM-400/RM-995 RheologyModifiers. A Breakthrough in Sag-Flow Rheology. 2014.

vi. ASTM D5150. Standard Test Method for Hiding Power of Architectural PaintsApplied by Roller. ASTM D 344 and Standard Test Method for Relative Hiding Powerof Paints by the Visual Evaluation of Brushouts.

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