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T E C H N I C A L PA P E RA D D I T I V E S1 8

PAINTING A MORE STABLE PICTUREImproving pigment dispersion and paint performance with versatile amino alcohols. By Dr Romain Severac and Yoann Fernandes, Angus Chemical Company,

Alkanolamines, such as 2-amino-2-methyl-1-propanol (AMP) and 2-amino-2-ethyl-1,3-propanediol (AEPD), are commonly used as key stabilising agents in a wide range of water-borne paint formu-lations. Not all alkanolamines are equivalent but AMP and AEPD can be used to improve the pigment particle size distribution and exploit synergistic effects with common dispersing agents. Opti-mising the formulation in this way has the potential to reduce raw material costs while improving paint performance.

O ne the most crucial steps in paint manufacturing is the disper-sion of pigments, which drastically impacts almost all perfor-

mance aspects of both the coating and dry film. The selection of a reg-ular dispersing agent mixture usually depends on the composition of the pigment blend [1]. This is due to the variety of pigments and their chemical compositions, as well as the development of a wide range of surface treatments [2]. With the presence of the amine function and the alcohol group, alkanolamines can form both ionic and hydrogen bonds with the surface of pigments [3], which drives both the wetta-bility of pigment agglomerates and the reduction of attractive forces between the particles resulting in the breakdown of pigment agglom-erates. In addition, AMP or AEPD interacts with conventional anionic dispersing agents such as polyacrylic surfactants or polyphosphates. Modifying the nature of the counter ion of these polymeric species ad-justs affinities with pigment surface. The combination of these specific synergies leads to an improved particle size distribution of pigments.

AMP ADSORPTION LINKED TO PARTICLE SURFACE

As shown in Figure 1, the adsorption ratio of AMP at the surface of sev-eral pigments was measured. The protocol used in this investigation is based on the preparation of slurries of each individual pigment at about 60 wt% solids content, with a disperser at high shear (20 min at 1700 rpm) in the presence of several concentrations of AMP. After this dis-persing step, slurries are centrifuged (min. 2h30 at 4500 rpm) until the dispersed pigments are fully settled, and the unabsorbed amount of AMP, free in the filtrate, is determined by a straightforward titration with a strong acid. All raw materials were used as supplied.The adsorption of AMP is significant in all cases (Figure 1) and this is important evidence of the strong affinity driving this phenomenon. The adsorption reaches a plateau that corresponds to the saturation of the surface.The quantity of adsorbed products appears to be linked to the par-ticle diameter. Given equivalent porosity, smaller particles have a higher surface area that can adsorb a higher concentration of AMP.By using the same protocol, five slurries of titanium dioxides were prepared with a wide range of surface treatments (0.1% to 10.3% of SiO2, 2.1% to 4.0% Al2O3, 0.0% to 0.5% ZrO2, and up to 0.25% organic treatment). The adsorption of amino alcohols was standardised by dividing the molar adsorption by the TiO2 surface areas. The versatil-ity of the adsorption is confirmed as adsorption occurs whatever the TiO2 treatment (Figure 2). The differences shown between the level of

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1 9T E C H N I C A L PA P E R

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RESULTS AT A GLANCE

ű Alkanolamines, such as 2-amino-2-methyl-1-propanol (AMP) and 2-amino-2-ethyl-1,3-propanediol (AEPD), are commonly used as stabilisers in water-borne paint formula-tions.

ű Depending on the chemical structure, agglomerates and particle size distribution can be optimised by exploiting specific amino alcohols and their interaction with pigments and dispersing agents.

ű Formulators can use amino alcohols to minimise unde-sirable side effects and improve overall pigment efficiency and potentially reduce costs.

ű Wet abrasion resistance is one example where amino alcohols and their synergy with common dispersing agents can improve paint performance.

the saturation plateau are close to the accuracy of the methodology and are insignificant.

IMPROVING TIO2 DISPERSION FOR BEST LIGHT SCATTERING EFFICIENCY

In parallel, means of particle size (PS) have been determined using a laser scattering technique. The evolution of the PS means as a func-tion of both AMP and AEPD concentrations is shown in Figure 3. The correlation between the concentration of both amino alcohols and the improvement in the TiO2 dispersion applies to almost all TiO2 types. This correlation is not visible with TiO2 “Kronos 2043” or TiO2 “Ti-Pure 706” as even at the lowest dosage (0.25 wt% of alkanolamines per pig-ment weight), the particle size is at the plateau. Further investigation

Figure 1: Adsorption of AMP at the surface of several pigments.

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Ground calcium car bonate Rutile T iO2 Delaminated clay

Kaolin clay, medium par ticle size

Kaolin clay, ultr a-fine par ticle size

will be performed at lower concentrations of these dispersing agents. In Figure 2, these two examples correspond to pigments with the high-est affinity with AMP and AEPD (the adsorbed amount is the highest).Confirmation of the fundamental difference between a neutraliser, such as sodium hydroxide, and stabilisers, such as AMP or AEPD, may be seen in Figure 4. According to this experiment, showing the evolu-tion of the TiO2 particle size, shown as a function of dispersion time (66 wt% TiO2, 1.5% of neutraliser, disc diameter 4 cm, can diameter 7 cm, speed 1600 rpm), either AMP or AEPD are able to wet and support the dispersion of TiO2 which makes it possible to recover the expected optimum particle size and results in the best light scattering efficiency. At the opposite end of the spectrum, a simple neutraliser such as sodium hydroxide, even after a long dispersion time, is not able to significantly support this process.

AEPD REDUCES THE NEED FOR DISPERSING AGENTS

In addition to the natural dispersing property of both AMP and AEPD, the interaction with regular dispersing agents commonly used in the industry was evaluated [4]. Table 1 presents a select list of dispersing agents containing polyphosphate and either a hydrophilic or hydro-phobic, neutralised copolymer of maleic anhydride. Samples of co-polymers were classified from the most hydrophilic (Sample 1) to the most hydrophobic (Sample 5). Dispersing agents have been engaged in dispersing agent demand curves (evolution of Krebs viscosities with dispersant concentrations) either alone or combined with AEPD. This common procedure consists of determining the minimum concentra-tion of dispersing agent required to produce the optimum wetting point. This point corresponds to the concentration at which the vis-cosity no longer decreases. Figure 5 sums up all comparative examples, and the impact of the pres-ence of 0.3 wt% AEPD on these dispersing agents is significant. The sys-tematic improvement of the dispersing agent shows the universality and versatility of AEPD. It means that the use of AEPD enables the reduction in primary dispersing agents in water-based formulated products, mini-mising drawbacks of these hydrophilic anionic species [5, 6].

LOW CONCENTRATIONS MINIMISE COMMON SIDE EFFECTS

In addition to the ability of minimising the overall dispersing agent concentrations to reduce the dry-film hydrophilicity, the strong inter-

Figure 2: Adsorption average of AMP and AEPD at the surface of several TiO2 particles.

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Figure 3: Evolution of the particle size means of TiO2 slurr ies containing AMP and AEPD.

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Figure 4: Evolution of particle size of TiO2 Kronos 2190 slurr ies as a function of the dispersing time with difference neutralisers.

NaOH AMP AEPD

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Figure 5: Dispersant demand cur ves with several dispersing agents and TiO2 D with and without 0.3 wt% AEPD.

“Calgon N new” (sol 25%) with 0.3% AEPD 1000/tit “Calgon N new” (sol 25%) “Orot an C A2500” with 0.3% AEPD 1000/tit

“Orot an C A2500” “Orot an 681” with 0.3% AEPD 1000/tit “Orot an 681” “Orot an QR1124” with 0.3% AEPD 1000/tit

“Orot an QR1124” “Orot an 731” with 0.3% AEPD 1000/tit “Orot an 731”

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action between AMP and AEPD with an acrylic dispersing agent can improve its intrinsic property. A set of satin water-based coatings with low volatile organic compounds, were taken through a design of ex-periment methodology (4 concentrations of TiO2 from 12% to 18%; three neutralisers including AMP, AEPD and NaOH; and three concen-trations of polyacrylic dispersing agents). Wet scrub resistance tests, based on the ISO 11998:2006 standard, were performed under harsh conditions (1500 cycles, 4 weeks of dry film drying, 200 µm applied on a panel, 4 repeated tests). Figure 6 shows the statistical analysis in a box plot representation. Despite the lower concentrations of these additives, in the range of 0.1 wt% to 0.3 wt% loaded at the dispersion

step, this experiment provides a good illustration of the result of the interaction provided by these amino alcohols. This effect could be also linked to the initial adsorption mechanism disclosed in this paper. As amino alcohols such as AMP or AEPD are adsorbed to a large extent on both pigments and fillers surface, and linked to dispersing agents, this reduces the remaining free amino alcohols in the binder matrix, minimising the well-known usual effect of highly polar compounds in a dry paint film. This effect becomes especially significant when consid-ering the current reformulation trends for titanium dioxide optimisa-tion, which leads to an increase of filler concentration that negatively affects this parameter if not properly adjusted.

2 1T E C H N I C A L PA P E R

AMINO ALCOHOLS BOOST PIGMENT EFFICIENCY

Alkanolamines such as 2-amino-2-methyl-1-propanol (AMP) and 2-ami-no-2-ethyl-1,3-propanediol (AEPD), are commonly used as key stabilising agents in a wide range of water-borne paint formulations. Due to the strong interaction between specific amino alcohols and both pigments and dispersing agents, the level of agglomerates and the overall particle size distribution of pigments can be improved in paint formulations. Not all alkanolamines are equivalent, and these effects strongly depend on the chemical structure of the product. In addition to the natural dispers-ing ability of these molecules, synergistic effects have been identified with regular dispersing agents, such as polyphosphates and neutralised copolymers of maleic anhydride. The versatility of 2-amino-2-methyl-1-propanol and 2-amino-2-ethyl-1,3-propanediol can be used to re-duce both numbers and levels of some commonly used paint additives through the optimisation of paint formulations, potentially lowering raw material costs while improving paint performance. Formulators are able to unleash the potential boosting effect of amino alcohols to significantly minimise the undesirable “side effects” of regular additives, and improve the overall pigment efficiency. In particular, the improvement of wet abrasion resistance can be enhanced by the presence of amino alcohols and thanks to synergistic effects with common dispersing agents.

ACKNOWLEDGEMENTS

The authors would like to thank Kronos and Chemours for providing both materials and valuable feedback throughout this investigation. In addition,

Table 1: Selected dispersing agents.

Dispersing agents Technology Neutralisation

“Calgon N*” polyphosphate sodium salt

“Orotan QR 1124*”hydrophobic copolymer of anhydride maleic

ammonium salt

“Orotan 731*”hydrophobic copolymer of anhydride maleic

sodium salt

“Orotan 681*”hydrophobic copolymer of anhydride maleic

ammonium salt

“Orotan CA2500*”hydrophobic copolymer of anhydride maleic

sodium salt

* Registered trademark of a third party

Mirodur S.p.A.Via delle Scienze, 3 - 04011 Aprilia (LT) ItalyTel. +39 06 9281746 Fax +39 06 9280644www.turbomill.com - info@turbomill.com

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T E C H N I C A L PA P E RADDIT IVES2 2

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“Formulators can minimise several negative side effects.“

Dr Romain SeveracANGUS Chemical CompanyRSever ac@angus.com

3 questions to Dr Romain Severac

Concerning the cost reduction: what would be your estimate in a standard formulation for a premium indoor paint? We’ve seen in a number of formulations how the functional versatili-ty of our amino alcohols can help formulators reduce both the number and levels of commonly used paint additives. For example, as demonstrated in this investigation, the highly effective co-dispersion properties of AMP or AEPD can enable the reduction of primary dispersing agents used in the grind phase. At the same time, the hiding and gloss performance of AMP and AEPD also imply a potential for reducing the use of both pigments and binders. The unique nature of our amino alcohols can enhance the long-term stabilisation of the coating system, which is primarily based on the pH buff-ering effect combined with the enhancement of regular dispersing agents (such as polyacrylates), improving the robustness, the reproducibility, and the shelf life of the formulated product. In addi-tion, numerous studies demonstrate a potential synergistic effect between both AMP and AEPD and certain approved biocides in many formulation types across multiple applications. This synergistic effect can provide enhanced syneresis control and improved in-can stability, while helping formula-tors optimise their use of approved biocides, depending on the individual formulation.

Which side-effect is minimised the best by using AMP and AEPD? Because the versatility of AMP and AEPD may enable the significant reduction of commonly used primary dispersing agents, formulators can also minimise several negative side effects of these additives, such as water resist-ance or wet scrub resistance. In the case of reducing polyphosphates concentrations, the optimisa-tion of these wetting agents helps to improve the overall rheology profile of the formulation. It is also important to stress that, as is with all dispersing agents, the optimum performance can be achieved by finding the right balance between the use of different dispersing agents.

How can AMP and AEPD be implemented into an established formulation? This is strongly driven by what individual performance improvements or attributes are being targeted with the for-mulation. To start, AMP or AEPD can be loaded, even partially, to enhance dispersion during the grind phase, especially when prepared as a solution of pre-neutralised blend of dispersing agents. This will enable AMP or AEPD to interact with the dispersing agent and, as a result, enhance the synergistic effect. Then, step by step, dispersing agents can be reduced until all desired critical perfor-mance properties are maintained.

thanks go to Farah Shaik Dawood and Marianne Riffault who performed laboratory work during their student internship at ANGUS Chemical Company.

REFERENCES

[1] Tiarks F., Frechen T., Kirsch S., Leuninger J., Melan M., Pfau A., Richter F., Schuler B., Zhao C.-L., Formulation effects on the distribution of pigment particles in paints, Progress in Organic Coatings 48 (2003) pp 140–152

[2] Winkler J., Dispersing Pigments and Fillers, (Hanover: Vincentz Net work, 2012), p. 35.

[3] Müller B., Poth U., Coatings Formulation, 2nd revised Edition (Hanover: Vin-centz Net work, 2011), p. 172.

[4] Clayton J., Pigment/Dispersant Interactions in Water-based coatings, Surface Coatings International 9 (1997) pp 414-420

[5] Verkholantsev V. V., Multifunctional aids, European Coatings Journal, 5 (2000) pp 42–50

[6] Muth M., Freytag A., Conrad M., Maintaining protection: how dispersants affect corrosion resistance of waterborne paints, European Coatings Journal, 1 (2016) pp 30-33

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