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The selection of raw materials for the formulation of latex paint is a kind of maze in which the formulator not only has to find mutually compatible raw materials, but also balance the quality of the resulting formulation with the price. Here, Artur Palasz Ph.D., Spektrochem, explores this topic with a comprehensive overview of how formulators should select raw materials
To be able to calculate the cost of the raw material’s share in the recipe, you need to know which one you will take into account in the tests; what the dose and percentage in the formulation will be; and how it will affect the quality parameters assumed at the beginning of the project compared to competing raw materials. We should also not forget about issues related to the impact of the raw material on VOC, product labeling (GHS, NFPA704, HMIS) and the impact on the environment (carbon footprint, sustainability, transport costs, legal regulations, etc.).
It’s all a real mess that needs to be sorted out and systematised, especially for beginner formulators who don’t have much of this type of knowledge handed to them on a plate.
To start selecting raw materials, we need to prepare assumptions about what type of paint we should formulate and what liquid parameters and coating properties it should have. Will it be a flat paint (matte), or with a higher gloss, or maybe an intermediate gloss (velvet-like, satin-like, eggshell, etc.)? What are the durability parameters of the coatings, what areas of application should it be adapted to (indoors, outdoors), whether resistance to water, disinfectants, stain resistance, etc. is required? A whole range of properties and parameters must be defined that will constitute the acceptance criteria for the formulation, e.g. specific properties (e.g. spattering rating min. 8 when painting with a roller, scrub resistance min. 1,200 cycles to failure, whiteness index min. 85, etc.).
The next step is to build the formulation and select raw materials for testing that will meet these criteria. It is a complex process that requires experience and a professional consultant in the selection of raw materials, and the next step is to calculate the price of raw materials in relation to performance in a formulation that ensures specific parameters. But how to interpret the parameters of raw materials, how to read their case study results and how to select samples for testing at the R&D stage? This article is a starter guide for novices, as well as a reminder for advanced formulators, created by a laboratory dedicated to building knowledge about the effectiveness of raw materials in latex paint formulations as a knowledge pill.
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First of all…
If we have already defined what type of latex paint we want to formulate in terms of liquid and coating parameters, the first step in selecting the raw material should be to review its SDS and additional documents describing its classification in the light of various legal regulations. The growing market awareness of sustainability means that more and more raw materials contain some bio-based components or are 100% bio-based. Such information is also useful when choosing a raw material, so you should pay attention to it.
When reviewing Safety Data Sheets (SDS), first of all, pay attention to the labeling of the raw material and the hazards it poses, both as the material itself and whether it requires labeling when used in a given concentration in the formulation. In the case of latex paints, marking with GHS pictograms is undesirable in many markets. This type of testing usually involves biocides, but also sometimes polymer dispersions and additives, e.g. coalescents. It is very important to pay attention to the content of SVHC (Substances of Very High Concern) ingredients, as well as the hazards and hazards posed by the ingredient, for example, the GHS 08 pictogram with the phrase H350 – May cause cancer if inhaled (Figure 1), in contact with skin and if swallowed. Conscious choice of raw material with unfavourable labeling does not have to influence the labeling of the final paint, because everything depends on the concentration and participation in the formulation. However, a conscious approach to accepting such a raw material for testing is necessary, as working with it in the laboratory will require appropriate personal protective equipment, as well as ensuring the safety of the paint production process, storage, further use of the paint with the need to recommend specific safety standards, etc.
Figure 1. Example from SDS with the designation GHS 08 and the phrase H350
If the raw material comes from, for example, outside our country, it is necessary to check whether it is registered in REACH (or the equivalent of such registration in a given country). Otherwise, there will be a problem with the possibility of purchasing and importing such raw material to our country. It is equally important to familiarise yourself with local regulations regarding waste disposal, fire hazards if the raw material poses such, and any other local regulations regarding the use of the raw material. In some applications where contact with food will be required, it is also necessary to check whether the manufacturer has a document called Food Contact Information (or another similar document) specifying whether a given raw material can be used to formulate coatings for contact with food, and if so, in what concentration ( e.g. in mg/m2 of coating) and what criteria it meets, e.g. American FDA 21 CFR 175.105, FDA 21 CFR 175.300, etc.
After accepting all hazardous ingredients, labeling, legal regulations, VOC content, green-labeling (e.g. EU Ecolabel) and many others from the regulatory side, you can proceed to laboratory tests and check the functionality of the raw material in the formulations. It is not a good idea to replace this stage with an analysis of the price per kg of raw material purchase, because in many cases (especially additives), a higher price per kg does not mean an increase in the price of the paint, because a given additive may be so effective that its dosage will be low level, which will have a minimal impact on the price of the final paint. Often, before selecting raw materials for testing, the purchasing department intervenes and compares prices per kg without knowing their effectiveness.
Figure 2 shows an example of comparing the effectiveness of clay thickeners (phyllosilicates) in terms of building viscosity in the mid-shear area (KU viscosity) to the desired level of 90-110 KU on average. The chart shows the KU viscosity obtained in the PVC 34 latex paint formulation for various levels of thickeners dosage (active substances in total formulation), ensuring viscosity in the desired range. This was compared to the purchase price per kg and the impact on the price of a liter of paint by calculating the required dosage level to achieve a given viscosity.
Figure 2. Comparison of the performance of phyllosilicate thickeners with their purchase price and impact on the price of paint
Analysing the chart presented in Figure 2, it can be noticed that one of the thickeners (#5) is very expensive to purchase and costs US$50/kg. Its effectiveness at a dose of 0.15% of active ingredients per formulation allowed to obtain the desired viscosity, thus affecting the price of the paint by US$0.11/L, while compared to thickener #2, which costs US$15/kg, the viscosity was also achieved in the desired range for a dosage of 0.50%. which gave the same effect on the price of a litre of paint. Thickener #3 looks even more interesting, it costs US$20/kg, and it was possible to obtain the desired viscosity only when dosing 1.18% of active ingredients in the formulation, which resulted in a cost per litre of paint of US$0.34, therefore three times greater than thickener #5 costing US$50/kg. These examples show that it is not the purchase price that should determine the choice of raw material for testing, but the assessment of its effectiveness in the formulation. Therefore, this should be the next step before analysing the purchase price.
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Raw materials technical data
When assessing the functionality and performance of raw materials in formulations, you should start by reviewing their Technical Data Sheets (TDS). Depending on the type of raw material, the data contained in TDS is more or less extensive. They provide basic data about the ingredient we want to use for the formulation. Let’s analyse some examples to discuss how to correctly interpret the data contained in the TDS:
The characteristics of polymer dispersions are usually repeated regardless of the manufacturer and include dates regarding:
- Type of polymer dispersion (acrylic, styrene-acrylic, vinyl-acrylic)
- Solid content (e.g. 48% by weight)
- Surfactant/stabilization/emulsifying system: (anionic, non-ionic, anionic/non-ionic, protective colloid – usually for vinyl acetate copolymers, APEO-free surfactants)
- Minimum Film Forming Temperature (e.g. MFFT 73 °F / 23 °C)
- Glass transition temperature (e.g. Tg 79 °F / 26 °C)
- Viscosity: (e.g. range of viscosity 800 – 1,800 mPa · s, or > 300 mPa · s, measured typically by Brookfield viscometer)
- Density (usually 8.5 – 8.8 lbs/US gal / 1.02 – 1.06 g/cm3)
- Average particle size (e.g. 50 nm – for fine particles, 80 – 150 nm for typical acrylic/styrene-acrylic latex dispersions, 0.2 – 2.0 µm for vinyl acetate copolymers)
- pH (4.5 – 8.0 for vinyl acetate copolymers, 6.5 – 8.5 for styrene-acrylic or acrylic copolymers)
Not all of these data are often provided, but they constitute typical characteristics of polymer dispersions, allowing for a first understanding of the basic parameters. Additional characteristics that can be found in TDS for polymer dispersions include, for example:
- Mechanical stability – resistance of the polymer dispersion to destabilizsation by high shear forces, usually expressed as excellent resistance or no resistance. The parameter is usually tested according to on-house guidelines using devices generating high shear forces, e.g. Ultra-Turrax or Silverson, causing potential coagulation resulting from the destruction of surfactants. Measuring this resistance involves analyzing the degree of coagulation visually or on a sieve. The information provides data for the potential use of polymer dispersions in a one-pot production process for paints where grinding and let-down are carried out in a dissolver. Polymer dispersions with poor mechanical stability should be used in a let-down process carried out in a separate equaliser, not in a dissolver.
- Freeze-thaw stability – parameter indicating whether the polymer dispersion shows coagulations or other failures as a result of cyclic freeze-thaw action, usually expressed briefly in the number of cycles, e.g. passed five cycles. Such information is usually too limited because it does not specify the course of the cycle or the temperatures to which the sample was frozen, although the default may be ASTM D2243 at –18 °C, but this information is usually not included in the TDS. It should be remembered that this is only a technical data for visual assessment of the lack of destruction of the sample after freeze-thaw cycles, which does not mean that the dispersion still has its properties.
- Elongation at break – how much the formed polymer dispersion film stretches without breaking, expressed in %, e.g. 600%, which means that the film elongates six times to its original length without destruction.
In addition to the above data, the TDS of a polymer dispersion usually also contains characteristics for which applications the manufacturer recommends a given type of binder, e.g. wall paints, wood paints, primers, direct to metal paints, etc., along with a short description of storage data (shelf life, storage temperature). In some TDSs, a certain amount of performance characteristics can be found in formulations with recommended examples, e.g. coalescents, well co-operating dispersants, defoamers, etc. – however, this happens in most cases when the manufacturer of polymer dispersions also offers this type of additives.
Titanium dioxide pigments
Titanium dioxide is the most expensive raw material in the formulation of latex paints. Its use is usually optimised first by the necessary use of the amount required to provide hiding power, as well as extending with the use of functional fillers, extending pigments, etc. In the case of titanium dioxide pigments, there is particularly no room for accidental or ineffective use. However, it is helpful to use the data contained in the TDS of these pigments.
The titanium dioxide TDS contains information about the type of titanium dioxide (rutile or anatase), of which the most widely used are the rutile varieties, obtained in the chloride or sulphate process, and this information is usually also included in the TDS. There is also data such as median particle size, oil absorption, specific resistance, bulk gravity, but also titanium dioxide content and classification according to ASTM D476 (and usually ISO 591-1, although this is not very useful). In the case of the ASTM D476 classification, it can be used to accurately select titanium dioxide suitable for testing in the final application and for a specific type of formulation. Table 1 summarises the classifications with associated end-use applications listed in ASTM D476.
|Table 1. End-use application classification of titanium dioxide ASTM D476
|TiO2 content, min.
|White exterior house paint and interior use
|Exterior coatings requiring excellent durability
|Exterior coatings requiring excellent durability with high gloss
|Interior and exterior coatings, medium-high PVC
|Interior and exterior coatings, low-high PVC
|Exterior colored coatings and polymers requiring IR-reflectance with excellent durability
Not all TDS of titanium dioxide pigments show the ASTM D476 classification, however, the vast majority of them can be found. The type of pigment determines, as seen in Table 1, the scope of application, which can significantly assist in the selection of a white pigment for testing in a specific formulation. For example, if we have to develop a cheap paint formulation with high PVC, the best solution will be highly surface treated type III (TiO2 content of at least 80% indicates that the rest is a high content of surface treatment). This type of titanium dioxide results in better dispersion and binding of a small amount of dispersion binder in PVC > 80%, and good physical spacing in a crowded system (highly filled).
In turn, for high-gloss enamel formulations with low PVC, type II should be used for application tests, as a second choice type VII, and for high-durable exterior coatings – type V. In this way, the ASTM D476 classification is extremely helpful for the formulator when choosing the right type of pigment. For a titanium dioxide manufacturer, having such a classification in the TDS and prepared on the basis of tests in individual types of formulations is an extremely important tool for technical marketing and recommendations for the use of a wide range of manufactured titanium dioxides.
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Performance in formulations
In order to use raw materials to formulate latex paint, a series of tests must be carried out to determine whether the individual ingredients in the composition meet the assumptions set out at the beginning. Selecting samples for testing from different suppliers is not easy and additional technical materials called case studies, guidelines, or application data sheets can help in making the decision and properly preparing the formulator. These are additional studies, much more extensive than TDS, which contain the results of application tests of individual raw materials, showing how to effectively use individual ingredients and how to efficiently work with a given raw material.
TDS does not provide key information on recommended use in sample formulations. Therefore, it is crucial to use the next stage of selecting raw material, which is the analysis of case studies, application guidelines and other technical documents showing how binders, additives or fillers works effectively. Examples of such data for polymer dispersions include:
- In the full range of PVC and the result is scrub resistance
- What binding capabilities does it have in a formulation with fillers with high oil absorption (e.g. kaolin)
- What gloss level is obtained in low PVC formulations (e.g. PVC 15), how does it affect blocking and hardness depending on the use of various coalescents
- Ladder studies characterizing MFFT for various coalescent doses and further LFFT (Low Film Forming Temperature) for paints prepared with these coalescent doses in relation to forming a coating on an absorbent/non-absorbent substrate at low temperature
- How it affects whiteness and yellowness after exposure in weathering chambers, how its gloss changes after aging in the case of low PVC coatings
For fillers, performance data in formulations may include:
- Recommended wetting and dispersing additives, dosage levels and obtained mill-base parameters (viscosity, stability, settling, etc.)
- Impact on key coating parameters:
- in the case of standard fillers, e.g. volume solids, whiteness/yellowness, opacity in various PVC ranges, impact of filler share and its oil absorption on Q ratio control (PVC/CPVC), Impact on opacity in high PVC, dirt pick-up, etc.
- in the case of functional fillers, depending on the type of fillers and intentional impact on parameters, e.g. gloss/sheen reduction curve for a specific range of PVC, effect on enhancing scrubbability, lowering the specific gravity of the coating, increasing hardness, effect on opacity, extending titanium dioxide pigments, etc.
For defoamers, providing the necessary application data is crucial for their ease of use, operational efficiency and avoidance of potential defects. This is related to the characteristics of individual types of defoamers and the necessary application guidelines for these additives should include:
- Type of chemical-base (silicone-based or silicone-free, mineral oil-based, polymer-based, etc.)
- Point of addition (100% dosing at grind stage, 2/3 at grind stage + 1/3 at let-down stage, adding with separate assist defoamer, etc.)
- Shear forces needed for incorporation (related to the above point of addition, but also equipment requirements if production is to take place on a dissolver with a low-power engine)
- Duration of incorporation
- Recommended dosage level in specific PVC
- Effect on gloss (in low-PVC high gloss coatings)
- Foam collapse effectiveness, e.g. stir test, roller test, repeated after stoprage stability test checking the effectiveness of defoamer over time
- Impact on coatings defects, suitability for use in clear varnish formulations
- Recommendations for specific polymer dispersions
For each raw material, comparisons with competitive raw materials should be prepared, as well as efficiency assessments in different formulations, e.g. different types of paints (interior, exterior, wood & trim paints, roof paints, cabinet enamels, parquet varnishes, etc.), different formulating practices, e.g. US/Canada and EU with different raw materials used, available on the local market, different PVC ranges for prepared paints, etc. Such technical materials allow formulators to more easily select raw materials for testing and learn about its effectiveness through analysis in case studies and translate it into their formulations.
Preparing a formulator for the independent selection of raw materials is a long-term process requiring learning theory and practice. In terms of theory, you also need to know legal and environmental regulations, formulation habits prevailing on the market, consumer expectations, and in the case of practice, it is necessary to constantly build experience based on tests, consultations, case study analyses, participation in webinars and technical conferences to constantly deepen knowledge from specialists building recommendations on the effective use of raw materials in latex paint formulations.
Mastering the free navigation of technical data and the ability to analytically interpret test results is facilitated when the formulator is provided with clearly understandable application studies, developed on the basis of real-life formulations that are understandable to him and which use methods used by the paint industry to determine specific types of parameters of liquid paints and paints. coatings.
This is an inherent element of the process of introducing raw materials to the market and consciously using them, especially in times of so important optimisation of resource management and price optimisation of the final product, such as latex paints.
Author: Artur Palasz, Ph.D., Spektrochem – Technical Center of Raw Materials for Architectural Paints, Poland
e-mail: [email protected]