Pigment Black 7 - A comparison of Lansperse LT87 against a traditional dispersing agent
As part of the ongoing work we are undertaking on the new BioLoop dispersants, we have looked at a number of traditional pigments for water-based systems. In this blog, we are looking at Pigment Black 7. For this work, we used Elftex 430 from Cabot. This pigment has a low structure which can give lower viscosity at higher pigment loadings. The new BioLoop dispersing agents have many advantages over the synthetic counter-types in terms of better eco-profiling, hazard labelling and biodegradability. Lansperse DS200W has been our traditional dispersing agent for aqueous systems for many years and has a very good track history in terms of performance. Any new dispersing agents need to have a similar performance.
Preparation of dispersions
The mill-base formulations below were prepared using a high-speed stirrer with a saw tooth blade. The pigment is added to all the other components over a 10 minute period at a speed of 1000 rpm. The mill base is then mixed for a further 5 minutes. After this, the mill bases are processed on a laboratory-sized bead mill (we used an Eiger Torrance at 2000rpm for 60 minutes).
Viscosity and Stability of Dispersions
An effective way of determining dispersion quality is to assess the initial viscosity, and then over a period of time. Any major changes could indicate some form of destabilisation.
The viscosity analysis can be carried out using a combination of methods depending on the initial viscosity. For dispersions that have very low viscosities then DIN flow cups are the most suitable, we used either DIN4 or DIN6. For dispersions that have medium viscosity then a Brookfield cone and plate viscometer was used. Samples of dispersion were stored at room temperature and then the viscosities measured at regular intervals during prolonged storage.
Lansperse LT87 gave a dispersion of lower viscosity over the whole test period and suggests that higher pigment levels are achievable with this product.
Although in some instances it may be possible to produce a successful pigment dispersion, you may find that the pigment strength has been affected in some way. Comparable pigment strength against known standards or controls is essential to ensure that pigment addition levels don’t need to be adjusted. Comparable strength against industry standards is good but an increase in strength can be a bonus.
Each dispersion was incorporated into a Styrene/Butyl acrylate emulsion. Styrene/Butyl acrylate emulsions are the main polymer-forming component in most paint formulations. Using just the emulsion and pigment dispersion helped to prevent any other additive interference.
2.5g of dispersion was added to 100g of emulsion and then mixed thoroughly. The solution was then drawdown on a card and allowed to dry. The colour was then measured using a Konica-Minolta CM-5 to assess the CIELAB colour. The CIELAB colour space (also known as CIE L*a*b* or sometimes abbreviated as simply "Lab" colour space) is a colour space defined by the International Commission on Illumination (CIE) in 1976. It expresses colour as three values: L* for the lightness from black (0) to white (100), a* from green (−) to red (+), and b* from blue (−) to yellow (+). CIELAB was designed so that the same amount of numerical change in these values corresponds to roughly the same amount of visually perceived change.
Colour Analysis of Dispersions
As mentioned above the dispersion was mixed with a styrene / butyl acrylate emulsion and then coated onto Leneta card using a TQC automatic applicator. The coating conditions were Speed 30 mm/s and 24 micron thickness.
Both Lansperse DS200W and LT87 gave comparable colour performance.
A known weight of each dispersion is added to a low-quality paint and the rub-out test is performed to assess the level of flocculation.
The test is performed to determine whether there is pigment flocculation or flooding in the wet paint. The paint is applied to a test card and after a short drying time (flash-off) rub-out test is carried out by rubbing the paint film with a finger while it is still damp but already starting to dry. The instability or stability of the pigment dispersion is shown by the degree of colour difference evident between the rubbed area and the surrounding coating material.
The example shows a poor rub out and the pigment has probably flocculated.
The drawdowns below show the assessment on Lansperse DS200W and Lansperse LT87 tested at 2% level in an acrylic paint.
Lansperse DS200W Lansperse LT87
The results show that there are low levels of flocculation in both of the samples.
Particle Size Analysis
An important characteristic of a good dispersion is the particle size distribution curve.
Typically, a low particle size distribution is beneficial along with a good binomial curve that contains no higher particle size peaks. Any separate higher particle size peaks can indicate poor dispersion quality and a good chance of destabilisation over time.
Each dispersion was tested for particle size distribution by using a Mastersizer 3000.
Lansperse DS200W : D90 = 0.177um Lansperse LT87 : D90 = 0.132um
The particle size analysis indicates that dispersions based on Lansperse LT87 seem to have a lower particle size, but the differences are minor.
The new BioLoop dispersing agent Lansperse LT87 compares favourably with the traditional product Lansperse DS200W
If you require a product that has a good eco profile than the Lansperse LT87 is the product of choice.
To summarise, Lansperse LT87 is:
No Hazard labels