Controlling Rheology In Low to Zero VOC Waterborne Architectural Coatings: Improving

Thickening Efficiency in Low to Zero VOC Waterborne Coatings

By Mr. Yaw Aidoo, Group Leader, Decorative Coatings, Dr. Mihai Polverejan, Group Leader, Construction and Dr. Tom Lynch, Principal Scientist R&D; Elementis Specialties Inc. East Windsor, NJ.

The continued legislation and regulation of volatile organic compounds, VOC, in waterborne architectural coatings over the last couple of decades has consistently challenged the paint formulators and manufacturers in the choice and use of traditional rheology modifiers to provide the needed viscosity and rheological profiles, as well as application properties for a given paint. To meet these regulations, they eliminated the coalescing solvents and other co-solvents, which generally improved the efficiency of rheology modifiers. Raw material suppliers – especially latex manufacturers – have developed low to zero VOC capable latex binders that have become difficult to thicken with traditional nonionic synthetic associative thickeners, NiSATs, due to latex surfactant stabilization and particle morphology. The rheology modifiers typically used in architectural coatings fall into different categories and are suited for a required type of application. These categories are summarized in Table 1 below. Table 1: Main types of rheology modifier categories used in waterborne architectural coatings, the type of thickening mechanism they employ and type of paint systems they are mostly used in.

Thickening Mechanism Application

Cellulosic Thickeners/Modified

Volume Exclusion /

Associative Mostly High PVC

Anionic Acrylic Thickeners/Modified

Volume Exclusion /

Associative High PVC/DIY

Nonionic Synthetic Associative

Thickeners Associative High End DIY

Historically, cellulosic thickeners, also referred to as hydroxyethyl cellulose (HEC) were used as the most efficient way of thickening waterborne paints. The development of the anionic acrylic thickeners, also known as alkali-swellable emulsions (ASE), followed suite in an effort to provide paint formulators and manufacturers the convenience and the ease of use of a liquid alternative to cellulosic thickeners. These acrylic thickeners are low in pH as well as active content however, unlike the cellulosics they do not create dust. The thickening mechanisms are similar with both having hydrophobic modified versions; hydrophobically-modified HEC (HMHEC) and hydrophobically-modified alkali swellable emulsion (HASE). Generally, the viscosity profile achieved with these thickeners is highly shear-thinning exhibiting a quick recovery and a relatively poor sag/leveling balance. They are mostly used in high PVC paint formulations that are typically spray applied. The class of rheology modifiers referred to as nonionic synthetic associative thickeners, NiSATs, were developed to provide improved application properties such as flow and leveling, spatter resistance, film build, etc. that are usually associated with high end paint formulations targeted for the do-it-yourself (DIY) market segment. However, they are observed to be relatively inefficient for thickening compared to the HECs and acrylic thickeners. This class of thickeners possesses a unique thickening mechanism, where their hydrophobic entities

associate with other hydrophobic moieties in the paint system i.e. latex particles, hydrophobes from surfactants and to a lesser extent pigments, to develop a transient structured network. Figure 1 below illustrates the formation of a fully associated network of a NiSAT in a paint system. This structured network is responsible for providing the paint system with viscosity.

Fig 1: Illustration of a fully networked associative thickening mechanism

The main downside to this type of thickening mechanism is the fact that the associations are easily disrupted in the presence of other hydrophobes as found, for example, in colorants. When colorants are added to paint systems thickened solely with traditional NiSATs a drastic viscosity drop is observed. This problem was somewhat resolved by increasing the initial viscosity of the paint base, which unfortunately further results into manufacturing issues such as an increase in the amount of time necessary to fill paint cans. Despite all of these issues, paint formulators and manufacturers still possess the desire to introduce products that are differentiated enough from their competition. These formulators look to their raw material suppliers to provide products that will assist them in achieving these differentiations, and at the same time meeting the regulatory specifications legislated by the government. To this end, the Next Generation NiSATs discussed in this paper have been developed to provide formulators with;

Improved thickening efficiency

Improved Viscosity retention upon tinting

Improved color stability

Improved flow and sag balance while maintaining all other paint and film properties. These newly developed NiSATs affect both the low/mid shear and high shear viscosities of the paint system, and provide the paint formulator the flexibility of formulating their products with the needed differentiation. Figure 2 below is a spider chart that compares positives and negatives of some of the main properties the different classes of thickeners are observed to affect in a paint system.

Figure 2. Comparison of properties for various types of thickeners.

From the spider chart in figure 2 above the next generation (New Technology) of thickeners is

based on the urethane chemistry and was observed to provide an improvement in properties

that were lacking in the older versions of the same chemistry. Further discussions in this paper

will show the extent to which these properties are improved.

Experimental

The next generation rheology modifiers – both KU and ICI builders - were evaluated versus

competitive traditional/commercial rheology modifiers to show their efficiencies in a series of

paint formulas based on different latex chemistries. The evaluations were performed to target

Stormer and ICI viscosities, followed by paint and film properties testing. For the purpose of this

paper, two thickeners evaluated will be discussed.

Case Study #1: Low/Mid Shear-Effective (KU Builder) Nonionic Synthetic Associative

Thickener (NiSAT) In a 30 PVC 34 % NVV

Table 2: Acrylic Semi-Gloss Medium Base Formulation

Raw Material Wt%

Water 17.00

Ammonia, 28% 0.10

Biocide 0.05

Defoamer, Silicone 0.10

Dispersant 0.40

Surfactant 0.20

TiO2 21.50

3.00

Propylene Glycol 1.00

Latex Resin 46.70

Coalescent 1.00

Defoamer, Silicone 0.10

Water 3.70

Water +Thickener 6.00

Total 100.00

Paint Properties

Pounds/Gallon 10.70

Weight Solids, % 50

Volume Solids, % 35

PVC, % 30

VOC, (g/L)

These low shear-effective benchmarks are listed in Table 3 below. The viscosity target range of

105 KU to 115 KU for Stormer viscosity was set for the evaluation. The mid shear-effective

thickeners were combined with high shear-effective thickeners listed in table 4 below. The

paints were then tested and the data is shown below.

Table 3: Low/mid shear-effective thickeners used in the KU thickener evaluation

Type Active, NVM, lb APEO-Free VOC

NextGen LS 1 NiSAT 15 Yes 0

NextGen LS 2 NiSAT 15 Yes 0

Comp LS 1 NiSAT 20 Yes 0

Table 4: High shear-effective thickeners used in combination with KU - Case Study 1

Type Active, NVM, lb APEO-Free VOC

Conv. HS 1 NiSAT 20 Yes 0

Conv. HS 2 NiSAT 21 Yes 0

NextGen HS 2 NiSAT 21 Yes 0

Fig. 3: Mid shear-effective thickener active concentration

Low shear-effective thickener concentration for NextGen LS 2 is observed to be up to 60% more efficient than NextGen LS 1 and up to 50% more efficient than the competitive commercial benchmark, Comp LS 1.

Conv HS 1 Conv HS 2 NextGen HS 2

NextGen LS 1 2.40 2.40 2.10

Comp LS 1 1.88 1.88 1.41

NextGen LS 2 0.90 0.90 0.75

0.00

0.50

1.00

1.50

2.00

2.50

3.00

CO

NC

, NV

M, L

BS/

10

0 G

ALS

Thickener Use Levels

Fig 4: Stormer viscosity

The Stormer viscosity generated with all nine combinations is relatively similar, with NextGen LS

2 showing to be the most efficient.

Fig 5: Viscosity loss on tinting – 8 oz./gallon of Phthalocyanine Blue

Viscosity retention has been related to overall thickener concentration in the paint system; the

more the thickener concentration the better the viscosity retention on tinting. This relation is

virtually ‘debunked’ as in the case of NextGen LS 2. As a result of its thickening efficiency, it

was observed the overall concentration of the NextGen LS 2 was lower than all other

combinations, as shown in Figure 3, but showed the most improved viscosity retention versus

the other KU builders, as shown in Figure 5.

Conv HS 1 Conv HS 2 NextGen HS 2

NextGen LS 1 112 119 115

Comp LS 1 108 116 106

NextGen LS 2 113 120 109

95

100

105

110

115

120

125

STO

RM

ER, K

UStormer Viscosity

Conv HS 1 Conv HS 2 NextGen HS 2

NextGen LS 1 -20 -22 -23

Comp LS 1 -14 -15 -18

NextGen LS 2 -7 -9 -9

-25

-20

-15

-10

-5

0

ST

OR

ME

R, Δ

KU

Viscosity Change on Tinting

Figure 6: Sag Resistance

Sag resistance performance of paint systems thickened with the NextGen LS 2 thickener were

observed to be similar to the paint systems thickened with the commercial benchmark, as well

as the first generation thickener, NextGen LS 1.

Fig 7: Leneta Leveling

Paint systems thickened with NextGen LS 2 exhibited similar Leneta Leveling to the other competitive thickener. Overall the sag/leveling balance is observed to be excellent with NGL 2, while exhibiting improved thickening efficiency.

Conv HS 1 Conv HS 2 NextGen HS 2

NextGen LS 1 10 12 12

Comp LS 1 16 16 14

NextGen LS 2 14 18 12

0

4

8

12

16

20Sa

g, m

ilsSag Resistance

Conv HS 1 Conv HS 2 NextGen HS 2

NextGen LS 1 10 10 10

Comp LS 1 10 9 10

NextGen LS 2 10 10 10

02468

1012

AX

IS T

ITLE

Leneta Leveling

Case Study 2: High Shear-Effective (ICI Builder) Nonionic Synthetic Associative

Thickener (NiSAT) In a 0 VOC VAE-based Satin White Base

The next generation high shear-effective thickener, NGH 1, was evaluated versus commercially

available competitive ICI builders displayed in Table 5, in a VAE-based Satin White paint. The

formula is presented in Table 6. The competitive ICI thickeners are labeled as CBH 1, CBH 2 and

CBH 3. A polyether urethane polyurea type KU builder was used in combination with all the ICI

builders tested.

The KU builder, a nonionic synthetic associative thickener, was used at an equal active concentration in combination with the ICI builders. The ICI builders were used at equal concentration to the competitive control, CBH 1. The viscosity target range of 95 KU to 100 KU for Stormer viscosity and 1.0 P to 1.3 P for ICI was set for the evaluation. The paint bases were then tinted with the Evonik 808-series universal colorants at a level of 2 oz. per gallon. The colorants evaluated were lamp black, phthalocyanine blue and red iron oxide.

Table 5: High Shear-effective Thickeners used for Evaluation in Case Study 2

Type Active, NVM, lb APEO-Free VOC

NextGen HS 1 NiSAT 20 Yes 0

Conv HS 1 NiSAT 21 Yes 0

Conv HS 2 NiSAT 20 Yes 0

Conv HS 3 NiSAT 20 Yes 0

Table 6: 0 VOC Interior Satin VAE White Base

Raw Materials LB/100 Gal Weight %

Water 100.00 9.22

Dispersant 7.70 0.71

Surfactant 2.50 0.23

In-Can Preservative 1.50 0.14

Defoamer 3.00 0.28

Amine 2.00 0.18

Titanium Dioxide 200.00 18.44

Clay (Extender) 40.00 3.69

Calcium Carbonate 70.00 6.45

Letdown Opaque Polymer 44.90 4.14

Defoamer 3.00 0.28 Density 10.85

VAE Polymer (55%) 387.60 35.73 % NVW 51

Water 140.00 12.90 % NVV 36

Subtotal 1002.20 92.38 % PVC 32

Water + Thickener 82.66 7.62 VOC lb/gal 0.0

Total 1084.86 100.00 VOC g/L 0.0

Thickener levels as shown in Table 7 below indicate up to a 40% less concentration for NGH 1

thickener compared to the commercially available competitive thickeners to achieve target

viscosity. Conv HS 2 showed to be relatively inefficient compared to the other thickeners.

Table 7: Thickener Use Levels In 0 VOC Interior Satin VAE White Base

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

KU Builder, NVM lb/100 gal 1.3 1.3 1.3 1.3

ICI Builder, NVM lb/100 gal 5.5 3.3 5.2 5.2

Total 6.8 4.6 6.5 6.5

Viscosity generated from the thickener concentrations shows the combination with NextGen HS

1 to exhibit improved thickening efficiency as shown in Table 8 below. The paint thickened with

Conv HS 2 was shown to exhibit low viscosity response, resulting in the worst sag/leveling

balance.

Table 8: Paint Property Response to Thickener Evaluation

The application properties of the paints showed to be similar for all systems. (Table 9)

Table 9: Application Data For Thickener Evaluation In 0 VOC Interior VAE Satin White

Base

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

Adhesion - Aged Alkyd (1 Week) 3B 2B 2B 3B

Early Moisture Resistance (24H) 9D 9F 9D 9D

Stain Resistance (ASTM 4828) 5.7 5.9 6.0 5.9

Block resistance of the paint films were tested at both room temperature and elevated

temperature (120°F) for paint films cured overnight and after 7 days respectively. The ratings

data generated for the block resistance measurements from the evaluations (Figure 8)

illustrates that NextGen HS 1 imparts an improved blocking resistance to the coating especially

at elevated temperature.

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

KU, initial 95 98 82 97

KU, O/N 97 103 85 100

ICI, P 0.9 1.3 0.6 0.9

Sag Resistance, mils 8 12 4 8

Leveling 9 7 9 9

Fig 8: Block Resistance

The paint samples were tinted with low VOC universal colorants for testing for color stability.

The colors used were Lamp Black, Phthalo Blue and Red Iron Oxide. The colorant loading was

2 oz. per gallon. The viscosity change associated with the introduction of universal colorants in

waterborne paint systems is observed to be similar to the Control (Conv HS 1) and better than

the other commercially available thickeners.

Fig 9: Viscosity Change on Tinting

However, the paint containing the NextGen HS 1 thickener exhibits a better color acceptance

than the other paints with the competitive high shear thickeners (Figure 10).

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

1 Day RT 7 6 3 4

1 Day 120F 0 0 0 0

7 Days RT 8 8 7 7

7 Days 120F 0 5 0 0

0

2

4

6

8

10

RA

TIN

G

Block Resistance

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

∆KU, B colorant 5 3 -5 1

∆KU, E colorant 3 1 -4 -3

∆KU, F colorant 7 -4 -3 -2

-6

-4

-2

0

2

4

6

8

Sto

rme

r V

isco

sity

, Δ

KU

Viscosity Change on Tinting

Fig 10: Color Acceptance

Overall, it is observed that NextGen HS 1 shows to be a highly efficient high shear-effective

thickener that provides improved thickening efficiency in the 0 VOC Interior Satin White base

formulation as well as improved block resistance and color stability versus the competitive high

shear-effective thickeners, while maintaining other paint and film properties at a minimum.

Summary

In the two case studies above, it is observed that the next generation thickeners NextGen LS 2 and NextGen HS 1 provide the coatings formulator with improved thickening efficiency, viscosity retention on tinting and improved film properties as shown in the data generated. These improvements allow for flexibility in formulating differentiated paint products to be introduced in the market place with no negative impact(s) generally observed with the ‘traditional’, less efficient rheology modifiers. As paint manufacturers continue their quest of providing products that are unique in performance and differentiated from their competitors, there will always be a reliance on the raw material manufacturer to assist the formulators achieve their goals. These raw material suppliers will continue to be challenged to research and develop the next best raw material. In the case of additives, these will have to provide the needed efficiencies, both performance-wise and concentrations, with minimal to no effect on the coating properties. The latex manufacturer will have to continue providing binders that are zero VOC capable with improvements in block resistance, stain resistance, adhesion properties, etc. Specialty additive companies like Elementis will continue to develop the next generation rheology modifiers, dispersants, surfactants for these new latex resins. The new additives will provide the formulator with the much needed flexibility to formulate better and more differentiated coatings.

Conv HS 1 NextGen HS 1 Conv HS 2 Conv HS 3

∆E, B colorant 1.3 0.7 0.6 1.0

∆E, E colorant 1.7 0.7 0.6 1.5

∆E, F colorant 3.7 1.7 4.1 2.4

0.0

1.0

2.0

3.0

4.0

5.0

RU

B U

P, Δ

EColor Acceptance, Rub Up

References Lynch, Tom, Aidoo, Yaw, Buford, Nancy, Beaupre, Joseph, “New Nonionic Synthetic Associative Thickeners’, October, 2014 Polverejan, Mihai, Aidoo, Yaw, “Advances In Rheology Modifiers, Improving Thickening Efficiency In Low to Zero VOC Architectural Paint Formulations”, August, 2013