How to use starting point formulations for easier formulating of acrylic waterborne paints

Well-developed starting point formulations are an extremely valuable tool that shows which raw materials are stable with each other, especially in relation to the raw material of a given supplier who presents such a formulation, as well as in comparison to the competition, because starting point formulations in combination with comparisons of competing raw materials can be interesting material for competitive advantage.

Use of starting point formulations

At the beginning of the 1990s, but also after 2000, where access to technical materials on raw materials was very limited due to the lack of access to the Internet and the lack of many technical materials on the Internet, very basic starting formulations were required, whereby novice formulators needed basic knowledge about what should be in the formulation at all. Therefore, the starting point formulations developed in those years were extremely simple, but they provided the necessary knowledge about what type of main raw materials should build a given type of latex paint formulation. An example of such a formulation (without showing the trade names of the raw materials) is shown in Table 1. This formulation is based on very basic ingredients used to achieve class 2 wet-scrub resistance classified by EN 13300 (5 to 20µm thickness loss after 200 cycles tested by ISO 11998).

Table 1. Example of a simple starting point formulation
Ingredients		Weight, kg
Water Dispersing agent In-can preservative Defoamer Neutralising agent Titanium dioxide Calcium carbonate filler Polymer emulsion HEC thickener HEUR thickener Total		298.1 19.5 4.6 11.4 0.2 271.3 271.3 116.4 3.0 4.2 1000 kg
PVC Solid content EN 13300 class	approx. 76 % approx. 62 % 2

This simple formulation allows extremely novice formulators to know where to start by providing the basic formulation constants (PVC, solid content) and the quantities of raw materials to prepare the paint in the laboratory and further test and modify it. Often, however, such formulations are not enough, especially for demanding projects and more experienced formulators. It is true that the presented formulation has been prepared practically and from the raw materials used in it actually reaches class 2, but it lacks many important data and more advanced raw materials or lab-scale production processes that are used in practice.

The role of such a simple and basic starting formulation is to prepare a laboratory sample from it for self-development of formulation modification skills, replacement of ingredients and observations based on how the properties change. For newcomers, such formulations are of great educational importance, but from a business perspective, for which undoubtedly starting point formulations are being developed today, such simple formulas are not very attractive.

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Also by Artur Palasz – Application studies and transfer of starting point formulations to the R&D stage and full-scale production

Advanced starting point formulations

For more advanced formulators and R&D departments, extensive starting point formulations containing much more data are prepared. Such formulations are often referred to as core formulations, as they are the basis for slight modifications and adaptations to your own needs, e.g. with thickeners, but initially they are already a well-developed paint formulation for a specific application. The core-starting point formulations are followed by a list of raw materials with trade names and suppliers, however, for the purpose of this article, they have been hidden so as not to advertise.

Table 2. Wood & trim gloss acrylic paint formulation
Ingredients		Weight, lbs		Weight, kg		Function
TiO2 slurry – grinding by cowles dissolver, 15 minutes at 20-26 fps (6-8 m/s) Lab-scale vessel must be equipped with a cooling-jacket
Tap water1 Dispersant Defoamer Biocide Titanium dioxide Low-shear HEUR thickener Total		268.2 13.2 5.9 2.3 881.8 4.3 1,175 lbs		365.0 18.0 8.0 3.2 1,200.0 5.8 1,600 kg		Carrier, solvent Dispersing agent Defoaming In-can preservative White pigment Stabilisation
Let-down (10 minutes agitation by anchor mixer)
Acrylic polymer emulsion TiO2 slurry (75 % solids) Biocide Fungicide Coalescing agent Flash rust inhibitor Attapulgite 20% suspension Tap water1 High-shear HEUR thickener Substrate wetting agent Newtonian HEUR thickener Total		558.0 359.6 2.1 19.6 16.7 2.1 52.3 49.3 1.9 6.8 13.3 1,080 lbs		680.0 440.0 2.6 24.0 27.2 2.6 64.0 54.0 2.3 8.4 16.3 1,300 kg		Film forming Opacity In-can preservative Film preservative Film forming aid Metal cans protection Low-shear thickener Solvent Improving spraying Substrate wetting Improving leveling
1 Water hardness up to 3.0 mmol Ca2+ (17.55 °a / 30 °f)
Quality control:			Test results and method
Viscosity at 77 °F (25 °C): ·      Initial ·      Overnight			90 KU 96 KU				ASTM D562
Fineness of grind by Hegman gage:			> 7				ASTM D1210
Opacity (drawdown 7 mils gap applicator):			> 98.5 %				Reflectometer 45/0
Gloss @60° (drawdown as above):			> 72.0 %				ASTM D523
pH			8.0 – 8.3				ASTM E70
Formulation constants:
PVC:	18.7 %		Solids:		43.5 % by volume
PVC–additives:	21.5 %				56.7 % by weight
CPVC:	62.5 %		VOC:		UE: 0 g/L
Q (PVC/CPVC):	0.30				US: 0.37 g/L
(P+F)/B:	0.97				US–water: 0.42 g/L
Weight per US gallon:	10.8 lbs/gal		Density:		1.29 g/cm3

Table 2 shows an example of a starting point formulation called core formulation, which is an advanced presentation of the method of preparing the initial formulation for testing raw materials dedicated to wood & trim paints based on acrylic polymer emulsion. This formulation is divided into two stages of preparation. First, slurry preparation involves making a suspension of pigment, in this case titanium dioxide, stable for storage and use in various formulations. This process, referred to as grinding, consists in high-speed grinding of aggregates and agglomerates of titanium dioxide with surfactants and stabilising the particles for their use as a premix in the production of latex paints. The formulation contains guidelines for the preparation of the slurry and its use in paint, where it is combined with the polymer dispersion and other ingredients in the let-down process. Such a production process, where only the slurry is produced in the cowles dissolver, and then combined with the polymer dispersion and other components, is a process typically used in the USA by paint manufacturers and its use does not shock the surfactants responsible for stabilising the slurry and polymer dispersion at their connecting.

In addition, the process of adding the slurry to the polymer dispersion, and not vice versa, makes mixing easier and is self-supported by the difference in slurry density (heavier than the polymer dispersion, slurry density > 2.6g/cm³) and the polymer dispersion. As you can see, all data is expressed in units understood in Europe (SI units) and in USC (US customary units), thanks to which the formulation is fully understood by both US and European formulators.

The formulation also contains basic data on quality parameters, such as viscosity, fineness of grind, opacity, gloss and pH. These data are needed for the formulator to know what parameters to reconstruct during further R&D work and modification of the formulation for its own needs. Using such data in conjunction with other test results provided with the formulation (case studies, ladder studies) allows for easy understanding of how changes in the obtained parameters come from specific raw materials.

Indication of water hardness is the next stage of formulation advancement, showing what to pay attention to when further reformulating your own samples. Water hardness is usually related to the effectiveness of the defoamers in the formulation, or as in the case of the attapulgite thickener formulation, which, depending on water hardness, allows for varying viscosity and stability (see Figure 1). The graph shows how the viscosity of the same formulation – prepared paint samples changes depending on the water in which it was prepared (use of water for mill-base, let-down and preparation of attapulgite slurry). The tap water used in the tests had a hardness of 3.0 mmol Ca²⁺ (significant hardness), and demineralised water had a conductivity of <5 µS/cm.

Figure 1. Influence of the water used to prepare paints with the test thickener attapulgite on the viscosity

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Also by Artur Palasz – Focus on protective: Flash rust inhibitors in waterborne paints for architectural and wood applications

The presented differences in viscosity are not drastic, but significant enough that a formulator who tries to repeat the obtained results and adapt them to his own formulation may encounter a discrepancy in the results and rejection of the formulation. The advanced starting formulation in this case consists in providing additionally clearly marked information in the form of a comparison of the viscosity building effectiveness, which in the case of the attapulgite used is clearly water-dependent (the composition of the water affects the penetration between the layers of the thickener and its hydration).

It should also be noted that the formulation constants given in the start point formulations (Table 2) such as PVC, CPVC, Q, etc. are not indicated for information, but are used for further reformulation to obtain the desired properties of the paint and coating, similar to those determined on the basis of tests of the paint prepared from the subject start point formulations. Formulating your own recipe from the raw materials used in case studies allows you to obtain similar results when building a recipe based on the behaviour of the formulation constants indicated in the materials provided with the raw material sample. Please note that PVC and other formulation constants are used to build the formulation and are not to be calculated after development.

It may seem that examples of using the right water and paying attention to PVC, CPVC and other solids are not very advanced when it comes to starter formulations. Nothing could be more wrong. It is such small ingredients that are responsible for many further failures when formulating your own recipes. Providing them with properly shown case studies not only provide the necessary knowledge for the formulator from the R&D department of the paint manufacturer, but also clearly show the direction in which to go to achieve the appropriate results established in the laboratory developing starting point formulations.

Replacement of ingredients in the starting formulation

When using a starting point formulation, the standard procedure of the paint manufacturer’s R&D department is to substitute raw materials for testing whether the production raw materials used by them will be suitable for use in the formulation. We will discuss an example of such a swap and its potential failures using the formulation shown in Table 2 (wood & trim acrylic paint).

In the discussed example, the acrylic binder will be changed, which in the case of the discussed formulation must be characterised by ensuring high resistance to blocking. The start point formulation uses a self-crosslinking acrylic emulsion core-shell with a core Tg 70°C and a shell Tg 15°C (acrylic emulsion No. 1). The tests showed what happens when the acrylic emulsion is changed to other acrylic binders with a uniform morphology – acrylic emulsion No. 2 (Tg 35°C) and acrylic emulsion No. 3 (Tg 50°C). As can be seen from the Tg, the binders have different hardnesses and therefore should represent a different effect on coating hardness and blocking. All binders contained the same solid content and were substituted in the same amount into the formulations of Table 2. The test results are shown in Table 3 and graphically in the pictures of the blocking resistance tests.

Figure 2. Consequences of replacing the acrylic binder in the formulation of Table 2 and effect on blocking

The results of the blocking resistance tests show how drastic deterioration can be achieved when the binder originally used in the start point formulations is changed. It’s not about not trying to change this binder when necessary, but to do this change in a way supported by research. That is why it is so important to provide start point formulations with recommendations as to the binders that provide the desired properties.

The example shown shows another extremely important feature of the substitution of binders based on data from technical data sheets of polymer emulsions. Interchanged polymer dispersions do not represent hardness that goes hand in hand with blocking resistance. The hardness of the coating, and thus the Tg, cannot be considered as an indicator of good or poor blocking resistance – see the results in Table 3. Especially in the case of the core-shell dispersion, which apparently is much softer and obtained the best blocking resistance result.

Table 3. Coating test results after changing binders
Wood & trim formulation	Pendulum hardness ASTM D4366	Blocking resistance ASTM D4946
		Rating	Type of separation	Performance
Acrylic emulsion No. 1 Acrylic emulsion No. 2 Acrylic emulsion No. 3	81 s 108 s 165 s	10 4 6	No tack 0 (75-100% tack) 1 (50-75% tack)	Perfect Very poor Very poor

This case is just an example. Such case studies discussing what will happen when we replace the raw material A with B are extremely valuable knowledge for the formulator, and not only from the educational point of view, but also for faster obtaining results, faster and easier development of the final formulation, and even earlier for easier decision-making about testing a given product.

Summary

Providing starting point formulations is a standard procedure aimed at educating and bringing novice formulators closer to the world of paints and raw materials, but above all it is a technical marketing tool. Nowadays, it can no longer be just a short list of raw materials from which paint can be made, but knowledge coming from research, case studies, ladder dose tests showing how to use a given raw material in the best way, and in which cases its best efficiency is achieved. Having been building such recipes for over 16 years on the European, Americas and Pacific markets, I know perfectly well how valuable this knowledge is even for advanced formulators. It allows you to take a sample for testing and walk through it without walking in the dark.

Author: Artur Palasz, Ph.D.

SPEKTROCHEM – Technical Center of Raw Materials for Architectural Paints, Poland

e-mail: [email protected]