This article was originally published in 2013 and updated in 2023.
The basic concept of a tinting system is that the selected color shade can be formulated by dispensing colorants into the can with a prefilled base paint under set conditions and at a ratio according to the specific formulation. Excellent compatibility between the main components is essential to be able to reach the predicted color and reproduce it at any time.
One of the key issues in implementing a tinting system is making sure compatibility requirements will be met under all relevant tinting processing conditions.
Compatibility checks start with performing standard compatibility tests between the paint bases and colorants. Measurements are made within the range of dosages and procedures prescribed for the system. The main issues to be checked are related to achieving uniform and optimal color development.
Let's explore the methods to check the degree of color development and the role of compatibilizers to enhance paints quality.
Color Development is the Key
Good color development implies that the
color appears in a uniform manner and at the expected strength.
1 The term "color development" is used for tinted paint to describe the degree of color quality and color uniformity.
A practical method for determining the degree of color development is called the "
rub-up test," which involves
rubbing the drying, tacky paint film. Any color separation in the drying film is clearly detected and measured as a color difference between the touched and the untouched film. There are also modified versions of this method, such as:
-
the brush-out and
- spray-out tests.2
Figue 1: Rub-up Test
The main causes of poor color development are
improper compatibility between colorants and paint, resulting in pigment separation, as well as pigment flocculation
during film formation.
Color Compatibility Tests: Find Your Best Match
Compatibility tests are carried out by incorporating the following steps:
- Adding 1% (for the pastel base) or 10% (for the transparent base) colorant to the base paint,
- Mixing for 2 or 10 minutes on the paint shaker,
- Applying the paint, and
- Comparing the 2- and 10-minute sample colors and rub it.
Any color difference between the samples indicates poor color development, and some correction of the base will be needed.
Universal colorants are designed for use in both water-borne and solvent-borne systems. The same colorant is expected to demonstrate good compatibility with both paint categories in the colorant database. This remarkable characteristic feature of universal colorants is enabled by applying specific amphiphilic surfactant compounds, showing well-balanced ratios between hydrophilic and lipophilic moieties.
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Figure 2: Checking compatibility of all colorants with each base paint
However, this design does not guarantee optimal compatibility with any water-borne or solvent-borne paint formulation. In a few cases, the paint system chosen for inclusion as part of the tinting system requires some correction to create the conditions for good compatibility. Because the actual solvent in the main universal colorants is water (it used to be glycol for the first generations of colorants),
solvent-borne paints require the most frequent compatibility adjustments.
Typically, this is noticed in the above-mentioned compatibility test as poor compatibility (a strong rub) after 2 minutes of shaking time but a less severe rub after 10 minutes of shaking. Correction of the original paint formulation with some "
compatibilizer" usually enables the user to reach acceptable compatibility (Figure 3).
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The main contribution of the compatibilizer is supporting the distribution (emulsification) of the colorant in the solvent-borne paint.
In the case of water-borne paint, compatibility issues are mainly demonstrated by reaching good color development after 2 minutes of shaking but poor color development after 10 minutes, a performance indicating poor compatibility and poor color reproducibility.
Figure 3: Compatibility test: 2 minutes shaking test
(Left: Initial; Right: Including 0.4% Compatibilizer in base paint)
The Role of Compatibilizers
The following two options are available for the adjustment of the poor color development between a base paint and colorants:
- adjustment of the base paint and
- adjustment of the colorants
As the same colorants are used in many systems and bases, modification of the colorants would mean all well-performing bases would have to be checked as well. Usually, the modification of the base paint (option 1), which shows poor color development, is considered a viable option.
A most frequently noticed color development problem in water-borne paints is that color development is ok after 2 minutes of shaking but poor after 10 minutes of mixing. The colorants do not show any indication of flocculation. Combining both clearly shows rub-up.
The effect is explained by the desorption of stabilizer or dispersant from the colored pigment particle and the adsorption of this onto the
titanium dioxide and/or
extenders in the white base paint. Therefore, the colorant pigment remains unprotected, tends to flocculate, and will show poor color development (Figure 4).
Figure 4: No rub after 2 minutes shaking time (L); Poor color development and strong rub, after 10 minutes shaking (R)
The solution for the described color development is to adjust the base paint by adding a compatibilizer (Figure 5). The compatibilizer occupies the adsorptive sites on the pigment or extender, thus, preventing a loss of stabilizer from the colored pigment after it is added to the base paint and, hence the color stability is retained.
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Figure 5: Scheme of desorption/adsorption of dispersant, moving from color pigment to base paint pigment. The role of the compatibilizer is to furnish additional stabilizer to the system.
Basic Features of Products That Make Good Compatibilizers
The following characteristics are shared by the main products that have demonstrated successful performance in adjusting compatibility between base paints and aqueous universal colorants:
- surfactant properties,
- hydrophilic,
- excellent compatibility with complete colorant series, and
- multi-functional adsorption properties.
Conclusions
Color development in tinting systems is corrected by using compatibilizers in the base paints. The selection of the compatibilizer is related to the characteristic properties of the colorants and the base paints. Hydrophilic compatibilizers show the best performance in the case of using hydrophilic colorants; this is valid for both water-borne and solvent-borne paints.
Suitable Compatibilizers in Coatings Industry
View a wide range of
compatibilizers available in the market today, analyze technical data of each product, get technical assistance or request samples.