New High-Performance Associative Thickeners in Modern Coating Formulations

Nonionic Synthetic Associative Thickeners (NiSATs), along with their contribution to mid-shear viscosity, can be characterized by "which high shear stresses achieve which high viscosities." A wide variety of associative thickeners are available on the market, and all affect viscosity differently. In selecting the appropriate product, the desired specific performance criteria are decisive. In addition, increasingly stringent environmental regulations and costs now play an important role. To meet these demands (for example, for environmental labeling such as ecolabel), the German "Blauer Engel" and similar formulations require appropriate adaptation, and therefore also for the relevant raw materials. In principle, numerous rheological additives can be used to control the rheological properties of latex paints (for example, application and performance criteria). Polymer-based additives are the most frequently used product group in this context. These are subdivided into three categories: Modified Celluloses, Alkali-Swellable Acrylics, and Nonionic Synthetic Associative Thickeners (NiSATs) (see Figure 1).

Figure 1. Thickener Classification

Polymer-based rheological additives perform their thickening functions through volume exclusion (molecular weight/hydrodynamic volume) and/or an associative mechanism. In this associative mechanism, a structure (see Figure 2) is obtained as a result of interaction between latex particles and, to a lesser extent, pigment volume extenders. Since this structure can only be maintained at low shear stress and will break down reversibly under high stress, it is referred to as a "transient network." In general, in products showing the property of "creating high viscosity at low shear stress," the associative characteristic in the thickening mechanisms is more predominant, along with the flow property of "shear thinning under stress to a degree." In products showing more pronounced Newtonian flow characteristics, "volume exclusion" is a large part of the active factor for viscosity formation under high shear stress. Due to these properties, these products must be used at proportionally higher concentrations to achieve the same effect compared to shear-thinning thickeners. As a result, this product group always constitutes a large part of thickener combinations, and this situation plays a determining role in costs. The new RHEOLATE® HX 6008 and RHEOLATE® HX 6050 additives, which are the subject of this article, are the product of intensive research and development work aimed at efficiency optimization, particularly at high shear stress. Additionally, these additives also contribute to mid-shear viscosity to a certain extent.

Figure 2. Network structure in paint thickened with NiSAT

NiSAT thickeners, due to the properties they carry, are of decisive importance for systems requiring good flow and optimum leveling along with good film-forming effect (coverage). Beyond this, in exterior paints that require high resistance to moisture, weather conditions, light, and chalking, a high-efficiency thickener can also provide a positive effect. However, it was found that RHEOLATE® HX 6008 is particularly suitable for aqueous acrylic and alkyd systems (in other words, solutions with finer particle size and larger surface areas). On the other hand, RHEOLATE® HX 6050 exhibits its strong properties in vinyl acetate-ethylene (VAE) and also vina-veova-based solution systems with coarser particles and smaller active surface areas. Both show equal performance in styrene-acrylic binder systems. This is clearly shown below in Section 1 of this study. The particle sizes of these binder solutions are at mid-level. Furthermore, both RHEOLATE® HX 6008 and RHEOLATE® HX 6050 can serve as a functionally equivalent alternative instead of a combination of a mid/low-shear thickener and a high-shear thickener. This provides the opportunity to significantly simplify paint formulations. Detailed information on "Complexity Reduction" is provided in Section 2. As previously described, additives used to obtain Newtonian characteristics (high-shear thickeners) generally form the dominant part of a thickener combination; they also benefit from any effect that increases efficiency. These products combine excellent leveling properties with good film formation without over-concentrating the "in-can" protective viscosity. Higher efficiency means usability at lower concentrations. This reduces formulation costs. In general, these qualities are associated with better film properties (hardness, water resistance, abrasion resistance, etc.). For more information on this topic, see Section 3 in this study.

Section 1: Efficiency Evaluation among Different Binder Systems

In this section, two additives serving as binders, RHEOLATE® HX 6008 and RHEOLATE® HX 6050, are present at equal concentrations in all related formulations. The paint system used for this purpose is purely acrylic-based, and the pigment volume concentration (PVC) is 30%. Another paint system with a PVC percentage of 50% was also additionally used. The binder used in this alternatively prepared formulation is based on styrene-acrylic, vina-veova, and vinyl acetate-ethylene (VAE) (see Tables 6 and 7). The graphs below also show viscosities at high shear rate (ICI) 1,000 s-1, and Krebs-Stormer viscosities are also given in table form. ICI viscosities are not shown in these graphs because the shear stress measurement range ends at 1,000 s-1. In some cases, it will be necessary to set these limits because the torque range of the measuring device will be exceeded. The unit of high shear viscosity is taken as Poise (P), and 10 P = 1 Pascal.

Figure 3. Efficiency of RHEOLATE® HX 6008 and 6050 in pure acrylic paint (PVC 30)

The strongest Newtonian flow characteristics and highest ICI viscosity values were obtained with RHEOLATE® HX 6008 (see Figure 5). The flow characteristics obtained with RHEOLATE® HX 6050 show distinctly pronounced shear thinning under high shear. This is demonstrated by the quite high KU viscosities obtained with RHEOLATE® HX 6050 and noticeably lower high shear viscosity values.

Figure 4. Efficiency of RHEOLATE® HX 6008 and 6050 in pure acrylic paint (PVC 50)

Comparable flow characteristics are obtained with both rheological additives, but we can classify the paint formulated with RHEOLATE® HX 6008 as slightly more Newtonian in its properties. Generally speaking, the formulation containing RHEOLATE® HX 6008 exhibits somewhat higher viscosity values at all shear stress values. (See Figure 6)

Figure 5. Efficiency of RHEOLATE® HX 6008 and 6050 in Vina-Veova (PVC 50) based emulsion paint

Compared to RHEOLATE® HX 6008, RHEOLATE® HX 6050 provides higher mid-shear and high-shear viscosity contribution in Vina-Veova (Figure 7) and VAE (Figure 8) based paints.

Figure 6. Efficiency of RHEOLATE® HX 6008 and 6050 in Vinyl Acetate-Ethylene (PVC 50) based emulsion paint

The strongest Newtonian flow characteristics at high shear stresses and the highest viscosities at high shear stresses were achieved by RHEOLATE® HX 6008 used in pure acrylic systems. RHEOLATE® HX 6050 was dominant in vina-veova and VAE binder-based paints. RHEOLATE® HX 6008 and RHEOLATE® HX 6050 achieved similar results in styrene-acrylic paints and coatings. In the mid-shear stress range, RHEOLATE® HX 6050 produces higher viscosity structure in all systems. This is particularly true in acrylic-based systems and (to a somewhat lesser extent) in styrene-acrylic systems as well. At first glance, this appears to be an advantage. However, this also means that even very small additions of RHEOLATE® HX 6050 can lead to unwanted magnitude of viscosity increase at mid-shear stresses.

Section 2: Complexity Reduction

As mentioned above, in many formulations in practice, special thickener combinations are used for high, low, and mid-shear stresses. RHEOLATE® HX 6008 and RHEOLATE® HX 6050, however, have demonstrated that it is possible to achieve all desired properties using a single product. Reducing the number of raw materials leads to lower storage costs and also provides the formulator with the opportunity to reduce costs. To demonstrate these properties of RHEOLATE® HX 6008 and RHEOLATE® HX 6050, in Section 1 of this study they were tested in paint systems where they were proven to be dominant in character. For RHEOLATE® HX 6008, pure acrylic paint with a PVC percentage of 30% was selected. RHEOLATE® HX 6050 was tested in a VAE-based paint system with a PVC percentage of 50%. Rheological additive combinations sold on the market were used as reference products. In all paints, the reference viscosity was set to the same Krebs-Stormer viscosities (KU/mid-shear stress range) and ICI viscosities (high shear stress range 10,000 s-1). For RHEOLATE® HX 6008, the high shear stress values were 118 KU (± 1) and 3 Poise (± 0.2). For RHEOLATE® HX 6050, the pre-set values were 105 KU (± 1) and ICI viscosity of 1.5 Poise (± 0.2).

Table 1. Concentration of additive combinations

Both RHEOLATE® HX 6008 and RHEOLATE® HX 6050 can be used in place of thickener combinations sold on the market at mid and high shear stresses; reducing total concentration by significant amounts. The concentrations required to achieve reference viscosities are similarly significantly reduced.

Figures 7 and 8. Flow characteristics of RHEOLATE® HX 6008 and 6050 compared with reference thickener combinations

Compared with test paints containing additive combinations, paint modified with RHEOLATE® HX 6008 has demonstrated to be more Newtonian (See Figure 9). At approximately 100 s-1 shear stress, all formulations intersect with each other. At this shear stress, all viscosity values coincide with the pre-set KU viscosity. In VAE-based paint, compared with the reference thickener combinations tested, RHEOLATE® HX 6050 causes shear thinning flow characteristics at much lower shear stresses (See Figure 10). Both samples show very similar viscosity values at approximately 100 s-1 shear stress.

Table 2. Application results – RHEOLATE® HX 6008 pure acrylic paint, PVC 30

Table 3. Application results – RHEOLATE® HX 6050 VAE-based paint, PVC 50

It is evident that RHEOLATE® HX 6008 and RHEOLATE® HX 6050 can essentially be used in place of traditional thickener combinations with comparable properties. Paint formulations containing RHEOLATE® HX 6008 can maintain high quality properties during the process. With RHEOLATE® HX 6050, some remarkable differences, which can be classified as quite positive, particularly in terms of leveling, have been observed. The roller spatter resistance of both products is equally positive compared with additive combinations.

Section 3: Effect of RHEOLATE® HX 6008 on Dried Coating Film Properties

The performance parameters of the cured coating (gloss, hardness, etc.) are generally very critical and can sometimes be affected by minor changes in the formulation. Therefore, in addition to flow characteristics, the main focus of this section was on the effect of RHEOLATE® HX 6008 compared with rheological additives sold on the market on certain paint parameters after application and curing. The test system is acrylic-based lacquer. The system was set to a DIN 4 flow cup viscosity of 100 seconds for the tests described below. The reference value for the blank sample is 14 seconds.

Figure 9. Flow characteristics of RHEOLATE® HX 6008 in acrylic wood coating

RHEOLATE® HX 6008, compared with the standard thickener on the market, requires significantly lower concentrations to achieve the same flow times (See Figure 1). Both formulations show equal high viscosities at high shear stresses (ICI; 10,000 s-1). Looking at the rheograms, RHEOLATE® HX 6008, compared with the market reference sample, shows higher viscosities at low and high shear stresses. Both formulations show comparable viscosity values at mid-shear stresses.

Table 4. RHEOLATE® HX 6008 in Acrylic Wood Coating – Application properties

The coating containing RHEOLATE® HX 6008, due to lower additive loading levels, records notable progress at all test times. This is particularly evident when compared with the coating containing the market reference product, and is related to considerably shorter drying time, visibly high gloss, and higher film hardness (See Table 4).

Conclusion

The RHEOLATE® HX series is a recently developed, high-efficiency generation of associative thickeners (NiSATs) for aqueous systems and has the following characteristics: • Excellent viscosity structure at high shear stresses (ICI), with additional mid-shear viscosity contribution, • Compared with products available on the market, high efficiency offers significant material savings, • Simplified paint and coating formulations through reduced complexity, • Lower impact on paint film properties (for example, gloss and hardness due to lower loading levels). The flow characteristics achieved with the RHEOLATE® HX series are Newtonian in type (along with strong viscosity increase under high shear stresses). In all test systems, additional viscosity increase was observed at mid-shear stresses (KI). The effect described here on the rheological properties of aqueous coating formulations is characteristic for both products in the RHEOLATE® HX series and therefore clearly distinguishes them from thickeners currently available on the market. Both RHEOLATE® HX 6008 and RHEOLATE® HX 6050 can be used in numerous binder chemistries. However, the two products presented show their strong properties in the following binder systems (See Table 5).

Table 5. Binder designation

Key environmental data information for both products are available upon request.

Formulations

PVC30 and PVC50 formulations and acrylic wood coating formulations are available upon request.

Reference Text

Reference: Lynch, T., Mangnus, E., Buford, N., Beaupre, J., Aidoo, Y. (2015). New Nonionic Synthetic Associative Thickeners. Presentation at the European Coatings Congress 2015, Nuremberg.

Acknowledgements

We would like to express our special thanks to Laboratory Director Elke Piron and the team consisting of Sebastian Heinz, Wolfgang Fuchs, Anja Wingerath, Parwis Adli, Jörg Bungarten and Lisa Hoppe. The presented data would not have been possible without their contribution. Carlos Feito Technical Director Elementis     Frank Abschlag Technical Sales Manager Elementis     Dilşat Şahin Technical Manager Fuchs     Udo Schonhoff Technical Sales Manager – Coatings Fuchs