”ADVANCES IN WATERBORNE RHEOLOGY MODIFIERS: IMPROVI NG THICKENING EFFICIENCY IN LOW TO ZERO VOC ARCHITECTU RAL PAINT FORMULATIONS” By Dr. Mihai Polverejan, Group Leader, Construction and Yaw Aidoo, Group Leader, Decorative Coatings; Elementis Specialties Inc. East Windsor, NJ.

The impact of rheology modifiers on paint and coatings formulations has been, and continues to be immeasurable. This is especially true in architectural coatings as the choice of rheology modifier in most cases, determines the paint and film properties. Rheology modifiers used in the architectural paints include cellulose-based (water soluble polymers - HEC), poly-acrylic-based (ASE and HASE) and ether-urethane polymer/polyether-based (HEUR/PEPO).

Cellulose-based additives have been used to thicken paints and coatings for well over five decades. This class of rheology modifiers is relatively easy to formulate with without creating stability issues observed in the other classes of rheology modifiers. The thickening mechanism is by volume exclusion, resulting in the occurrence of flocculation – both pigment and latex - of the paint system. This may result in poor wet and dry hide film properties, as well as affect other paint film characteristics. However, the paint does not exhibit viscosity loss on tinting and color stability issues as is observed with the other type of thickeners.

The poly-acrylic thickener was an attempt to provide the paint manufacturer with a liquid alternative to the cellulose-based rheology modifiers. The initial iteration was the alkali soluble emulsion, ASE, which was supplied as a low pH liquid to be incorporated as a dilute solution (1:1 with water) into the letdown phase of the paint batch making process. The thickening mechanism was similar to that of HEC. Their main advantages were ease of handling as well as the elimination of dust. Application properties such as spatter resistance, leveling, etc. were observed to be similar to, if not better than, paints thickened with HEC.

Modifying the ASE thickeners with hydrophobes resulted in thickeners – hydrophobically modified alkali soluble emulsion, HASE - that possess the dual thickening mechanism of both hydrophobe association and volume exclusion. This class of thickeners was observed to improve paint film properties such as wet and dry hide, as well as improve application properties such as spatter resistance, flow and leveling, etc. versus cellulosic thickened paints.

Another class of thickeners referred to as nonionic synthetic associative thickeners – NiSATs – are based on an ethylene oxide chain backbone end-capped with hydrophobic functionalities. The hydrophobes of the associative thickener adsorbs onto the surface of the hydrophobic particles present in the paint (latex, some pigments, etc.) to form a network structure. This network stabilizes the paint and eventually provides the desired rheology. Associative thickeners play a crucial role in defining the rheology of waterborne latex paints. In comparison to water soluble thickeners such as cellulose or acrylic co-polymers (ASE), paints made with associative thickeners exhibit better performance in sag and leveling, moisture resistance, spatter resistance and coverage. However viscosity stability on colorant addition, along with color stability, are a few of the issues that a formulator has to deal with in formulating with NiSATs. The formulator also has the flexibility of using a combination of both associative and non-associative thickeners to tailor the needed rheological profile to provide superior paint performance. The diagram below (Figure 1) shows the impact the different class of thickeners has on different paint properties.

Fig.1: Comparison of properties for different thickeners

In a paint system, the hydrophobic entities of the thickener associate with the hydrophobic components of the system including surfactants, latex particles, pigments etc. The forces holding the network together are rather weak and do not require much energy to be disrupted. The system is very dynamic with the hydrophobe adsorbing and desorbing from surfaces competing with other surface active agents. The resulting network will impart the paint system a certain level of rigidity.

The diagram below illustrates the formation of the network.

Fig 2: Illustration of a fully networked associative thickening mechanism

Factors Affecting Thickener Efficiency

A paint formulation comprises a mixture of different components held in equilibrium with each other by the interaction – physically or chemically – of these components. These components can be categorized into different classes of raw materials. These include the dispersant, surfactant, pigments (primary and extender), latex and biocides. The thickening efficiency of the associative thickeners is impacted by the choice of some of these raw materials.

Surfactants: Anionic and nonionic surfactants are the most commonly used surfactants in architectural coatings formulations. Both play a significant role in contributing to the overall stability of the paint system as a whole. Nonionic surfactants are usually identified by their HLB value. The higher the HLB, the more the surfactant will lower the thickening efficiency of the associative thickener.

Universal colorants are another source of surfactants that could affect the efficiency of associative thickeners. In order to form stable dispersions of the color pigments a considerable amount of surfactants and glycols are used. Introducing these colorants into a paint system thickened with associative thickeners results in a disruption of the associative network formed, as hydrophobes from the surfactants compete with the hydrophobes from the thickeners for the finite associative sites. This diruption usually results in a significant drop in viscosity of the paint system.

Fig 3: Illustration of the disruption of the associative network (as shown in Fig. 2) by the introducion of excess surfactants from colorant introduction.

Latex: The hydrophobes of the associative thickener associates with the latex particle to form a network resulting in viscosity build. The choice of latex used in a paint formulation could have an impact on the thickening efficiency of associative thickeners. There are different classes of latexes used in paint formulation. These can generally be classified as Styrene Acrylic, Acrylic, VA Veova, Vinyl Acetate Ethylene (VAE) and Poly Vinyl Acetate (PVA).

Fig 4: Diagram showing latex effect on thickener efficiency

As shown in the diagram (Figure 4) above, hydrophobicity of the latex decreases from the Styrene Acrylic to the Vinyl Acrylic latex. The mean particle size of the latex increases from the Styrene Acrylic latex to the Vinyl Acrylic latex. Latexes with smaller particle size and therefore higher surface area will possess a larger number of association sites available to NiSATs.

Solvent: The choice of solvent is observed to have an impact on thickening efficiency. The more hydrophilic the solvent, the more of an impact it has in reducing the thickening efficiency of the associative thickener.

As previously mentioned above, thickeners have an important role in determining, for the most part, the rheological properties of the paint system in which they are used. This may contribute to film and application properties, as well as in-can properties of the paint.

ENVIRONMENTAL REGULATIONS

Due to the ongoing legislation of environmental regulations targeted at reducing the emission of Volatile Organic Content (VOC) into the atmosphere, raw material suppliers, and as a consequence coatings formulators, have to formulate products that are lower in VOC than traditionally known. Thanks to innovative marketing these low to zero VOC products are being marketed to consumers as being ‘environmentally friendly’ or ‘Green’, creating a frenzied demand for these green products by environmentally conscious consumers. In order to achieve the VOC targets set by the environmental regulations in coatings formulations, the formulators have had to drastically reduce or completely eliminate solvents from these formulations. These solvents have played an integral part in providing paint and film properties important to the durability of the paint film during and after application. For example, in latex film formation Texanol, an architectural coatings industry standard coalescing solvent, is needed to aid in the coalescing of the latex particles during the process of drying resulting in proper paint film formation. However Texanol is 100% VOC. Similarly Ethylene and Propylene Glycol play a very important role of providing coating formulations with the much needed property of open time. This open time allows for painters to be able to apply the paint over a reasonable time period and be able to work into the already applied paint to provide an aesthetically good looking paint job. Open time also allows for a nice balance between the sag resistance and flow and leveling of the paint after application. Again these glycols are 100% VOC.

Raw material manufacturers have had to provide their customers with products to assist them in achieving their goal of formulating products the meet the legislated VOC targets. For instance, latex manufacturers are developing low and zero-VOC capable latex systems to be used in coatings formulations. However the morphology and stabilization of these latexes have resulted in systems that have an adverse effect on thickening efficiency of associative thickeners. A marked increase in the level of these associative thickeners is required to achieve the target viscosity specifications. To this end, Elementis Specialties has been and continues to develop associative thickeners, both nonionic and anionic, that are unique in architecture providing the coatings formulator with flexibility and solution to thickening inefficiency.

NEXT GENERATION ASSOCIATIVE THICKENERS

The introduction of latex systems to aid in achieving low to zero coating VOC targets has resulted in significant thickening inefficiencies. Basically, to achieve viscosity targets the newly developed latexes require drastically higher concentrations of the ‘traditional’ associative thickeners..

With a solid background and understanding in designing hydrophobes and their interactions, as well as a great deal of experience in urethane and polyether chemistry, Elementis has been able to and continues to develop associative thickeners that provides coatings formulators with the needed tools to overcome the challenges of thickener inefficiency across a broad range of binder systems with differing chemistries. These next generation thickeners also provide improved application properties such as sag/leveling balance and reduced impact on open time. One property that has eluded coatings formulators is viscosity retention on tinting. This is due to the high concentration of glycols and surfactants associated with pigment dispersions. These new thickeners have been observed to reduce or eliminate this viscosity loss compared to the traditional thickeners.

Elementis has also developed acrylic thickener (HASE) technology that is able to replace nonionic low shear effective thickeners at a reduced concentration maintaining film and application properties, as well as improved color stability.

APPLICATION DATA

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: High Shear-Effective (ICI Builder) N onionic 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 in a VAE-based Satin White paint. The formula is presented in Table 1. The competitive ICI thickeners will be labeled as COM 1, COM 2 and COM 3. A polyether urethane poly urea type KU builder was used in combination with all the ICI builders tested.

The KU builder 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, COM 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 concentration of 2 oz. per gallon. The colorants evaluated were lamp black, phthalo blue and red iron oxide.

Table 1: 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 2 below indicate up to a 40% less concentration for NGH 1 thickener compared to the commercially available competitive thickeners to achieve target viscosity. COM 2 showed to be relatively inefficient compared to the other thickeners.

Table 2: Thickener Use Levels In 0 VOC Interior Sat in VAE White Base

COM 1 NGH 1 COM 2 COM 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 NGH 1 to exhibit improved thickening efficiency as shown in Table 3 below. The paint thickened with the combination with COM 2 was shown to exhibit low viscosity response, resulting in the worst sag/leveling balance.

Table 3: Paint Property Response to Thickener Evalu ation

The application properties of the paints showed to be similar for all systems. (Table 4)

Table 4: Application Data For Thickener Evaluation In 0 VOC Interior VAE Satin White Base

COM 1 NGH 1 COM 2 COM 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. Figure 5 below shows the ratings data generated for the block resistance measurements from the evaluations.

COM 1 NGH 1 COM 2 COM 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 5: 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 (COM 1) control and better than the other commercially available thickeners.

Fig 6: Viscosity Change on Tinting

However, the paint containing the NGH 1 thickener exhibits a better color acceptance than the other paints (Figure 7).

COM 1 NGH 1 COM 2 COM 3

∆KU, B colorant 5 3 -5 1

∆KU, F colorant 7 -4 -3 -2

∆KU, E colorant 3 1 -4 -3

-6

-4

-2

0

2

4

6

8

VLT

, ∆

KU

Viscosity Change on Tinting

COM 1 NGH 1 COM 2 COM 3

1 Day RT 7 6 3 4

1 Day 120°F 0 0 0 0

7 Day RT 8 8 7 7

7 Day 120°F 0 5 0 0

0

2

4

6

8

10

Blo

ck R

esis

tanc

e R

atin

g

Block Resistance

Fig 7: Color Acceptance

The data generated from the evaluation of NGH 1 in the 0 VOC Interior Satin White Base shows that NGH 1 is a highly efficient high shear rheological additive that provides improved thickening efficiency and color stability versus the commercially available competitive thickeners, while maintaining paint film and application properties.

Case Study #2: Next Generation Hydrophobic-modified Alkali Soluble Emulsion (HASE)

NHT 1 is a solvent-free, APEO-free hydrophobically-modified alkali soluble emulsion (HASE) that can be used as an alternative to highly priced low shear-effective nonionic synthetic associative thickeners, NiSATs, for high end low to zero VOC interior waterborne paints. NHT 1 is an efficient Stormer viscosity builder and provides a balance of properties not typically seen with typical HASE thickeners. It provides an excellent sag/leveling balance as well as improved color stability.

In the case studies discussed for this paper, NHT 1 was used in combination with a nonionic synthetic associative high shear-effective thickener. Two (2) paint systems will be discussed to show the versatility of the HASE thickener in paints based on different latex chemistries.

Case Study 2A: Next Generation HASE (NHT 1) In < 50 g/L VOC Acrylic Flat White Base

In the first case study, NHT 1 is evaluated versus a nonionic synthetic associative low shear-effective thickener, LSE 1 and a traditional HASE low shear-effective thickener, CHT 1. These were combined with a nonionic synthetic associative high shear-effective thickener, HSE 1 to achieve a Stormer KU viscosity of 105 KU +/-5, and an ICI of 1.2P to 1.5 P. The main properties of the evaluated thickeners are illustrated in Table 5.

Table 5: Typical Properties of Associative Thickene rs Used In Evaluation

Type Active, NVM, lb APEO-Free VOC

LSE 1 NiSAT 15 Yes < 0.01

NHT 1 HASE 30 Yes 0

CHT 1 HASE 30 Yes 0

COM 1 NGH 1 COM 2 COM 3

∆E, B colorant 1,3 0,7 0,6 1,0

∆E, F colorant 3,7 1,7 4,1 2,4

∆E, E colorant 1,7 0,7 0,6 1,5

0,0

1,0

2,0

3,0

4,0

5,0

Ru

b u

p,

∆E

Color Acceptance - Rub up

The thickener evaluation was performed in an acrylic paint system based on the formulation shown in Table 6 below.

Table 6: < 50 g/L VOC Acrylic Flat White Base

Ingredients Pounds Wt % GRIND Water 150.00 12.99 HMHEC 1.00 0.09 Amine 1.00 0.09 Ethylene Glycol 10.00 0.87 Defoamer 3.00 0.26 Dispersant 7.10 0.61 In-Can Preservative 3.00 0.26 Surfactant 3.00 0.26 Titanium Dioxide 220.00 19.06 Nepheline Syenite 150.00 12.99 Calcined Clay 50.00 4.33 Diatomaceous Earth 25.00 2.17 Attapulgite Clay 4.00 0.35 LETDOWN

Acrylic Latex (50%) 330.00 28.58

Defoamer 3.00 0.26 Density 11.55

Water 89.41 7.74 % NVW 55.94

Coalescent 5.00 0.43 % NVV 38.93

Subtotal 1054.51 91.34 % PVC 50.20

Water + Thickener 100.00 8.66 VOC lb/gal 0.39

Total 1154.51 100.00 VOC g/L 46.17

As shown in Table 7 below, a significant reduction in thickener use level is achieved by substituting for the NiSAT low shear-effective thickener, LSE 1, with NHT 1. Only 25% of the low shear-effective NHT 1 is needed to achieve similar Stormer viscosity versus the NiSAT low shear thickener, LSE 1. The efficiency of NHT 1 combined with its lower price provides the opportunity to significantly reduce raw material cost.

Table 7: Low Shear Thickener Use Levels

NVM, lb/100 gal Viscosity

Brush Leveling Sag

KU ICI

NHT 1 1.0 108 1.3 5 18

LSE 1 3.9 103 1.3 5 14

CHT 1 1.0 108 1.3 3 22

The paints were tinted with Lamp Black, Phthalo Blue and Red Iron Oxide, part of the UTSF low VOC line of colorants from Elementis Specialties. Viscosity loss on tinting as well as application

properties including brush leveling and sag resistance were evaluated, as shown in Figures 8, 9a and 9b,

Fig 8: Graph for viscosity loss on tinting

The paints were tinted at 4 oz. per gallon with each colorant. Figure 8 shows that NHT 1 provides excellent viscosity retention on colorant addition versus the NiSAT, LSE 1 and CHT 1. Excellent sag resistance and leveling balance is also achieved when LSE 1 is substituted for with NHT 1, (Figures 9a and 9b ).

Fig 9a: Graph for Sag Resistance Fig 9b: Graph for Brush leveling

Case Study 2B: Next Generation HASE (NHT 1) In < 0 g/L VOC PVA Sat in White Base In this second case study, NHT 1 is used to substitute for LSE 1 in a paint base based on a PVA latex system. The formulation on which the paint used in the evaluation is shown in Table 8 . The evaluation is performed versus the same thickeners as in Case Study 2A above – LSE 1 and CHT 1 in a PVA based Satin White paints. The paint formula is presented in Table 9.

Table 8: Low Shear Thickener Use Levels

NVM, lb/100 gal Viscosity

Brush Leveling Sag, mils

KU ICI

NHT 1 4.2 96 1.3 8 14

-10

-5

0

5

10

Blue Black Red Oxide

NHT 1

LSE 1

CHT 1

NHT 1

LSE 1

CHT 1

LSE 1 5.5 91 1.6 8 16

CHT 1 3.9 91 1.5 4 18

Table 9: 0 g/L VOC 32 PVC Interior PVA Satin White Base Formula

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 PVA 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

As shown in Table 8, approximately 24% less NHT 1 thickener versus LSE 1 is used to achieve similar viscosity, while maintaining similar application properties such as sag resistance and brush leveling. The paints were tinted with three colorants – Lamp Black, Phthalo Blue and Red Iron Oxide – from the Elementis Specialties’ UTSF line at a dosage of 4 oz. per gallon. Viscosity loss on tinting as well as sag resistance and leveling were evaluated as shown in Figures 10, 11a and 11b.

Fig 10: Graph showing Viscosity Loss on Tinting Dat a

It was observed that NHT 1 provided good viscosity stability on color addition to the paint base (Figure 10). It was also noticed that NHT 1 maintained an excellent balance of sag resistance and leveling similar to that of the NiSAT, LSE 1 paint system as displayed in Figures 11a and 11b.

-2

0

2

4

6

Blue Black Red Oxide

NHT 1

LSE 1

CHT 1

Fig11a: Graph for Sag Resistance Fig 11b: Graph for Leveling

Overall, NHT 1 provides improved thickening efficiency, while maintaining an excellent balance of sag and leveling across different latex chemistries. It is also able to successfully replace NiSAT type thickeners retaining similar viscosity stability on colorant addition. With its unique architecture, NHT 1 has the possibility of being used as a cost effective and efficient Stormer viscosity builder, mostly in Interior architectural paint systems.

SUMMARY

There is continued research and development of additives to complement the low to zero VOC latex systems being recently introduced by the latex manufacturers. Rheological additives are continuously improved to provide the paint formulator with thickening efficiency complementing the newly introduced latex systems. This enables the formulator to have the flexibility of formulating to achieve the required paint, film and application properties.. NHG 1 and NHT 1 are examples of the next generation of associative thickeners taylored to fit these needs. The case studies discussed above prove their high efficiency together with their ability to provide the paint system with the desired balance of properties. They are also proven to be compatible in systems based on different latex chemistries.

REFERENCES

1. Skeist Incorporated, Coatings, VII “Cellulose Ethers”, October, 2004 2. Blake, Donald M. “Thickeners for Waterborne Coatings”, Handbook of Coatings

Additives, 1984 3. Padget, John C, “ Additives for Water-based Coatings”, pp.1-11, 1988 4. Elementis Specialties, “Rheology Handbook: 30th Edition”, pp.14-21, 2008 5. Holmberg, K, “Introductions to Surfactants”, Surfactants and Aqueous Polymers in

Aqueous Solution”, 2003 6. Paczkowski, Mark and Wehrens, Hersjel, Associative Thickeners and Point of Sale

Colorants: Can They Get Along?” Paint and coatings Industry, Vol. 23, April, 2007

NHT 1

LSE 1

CHT 1