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Solvent-Based Carbon Black Dispersions

Comparing new novel dispersants with competitors samples


In this technical work, we looked at solvent-based systems typically used in industrial coatings using carbon black (Pigment Black 7) and a standard resin, Laropal A81. We compared two of our newly developed mobile complex dispersing agents with two industry-standard grades.


These newly launched products are Lansperse SL58 and Lansperse SL66 which complement our offerings for novel dispersing agents for solvent-based systems.


Carbon black is one of the most used pigments in the coatings industry ranging from exterior automotive coatings to printing inks.


Pigment Black 7 is made up of aggregates of primary particles which are fused. The primary particles are around 10 - 80nm in diameter with the aggregates being around 200 nm in diameter. These aggregates associate together through van der Waals forces to form agglomerates. These tend to be 50 - 300nm in diameter.


The requirement for optimum colour performance is excellent pigment dispersion and stabilisation.


During this process, the importance of the primary particle size is noted in affecting the optical density and colour shade of the ink/coating. The primary particle size also influences the rheology.


Primary praticle size

Decrease in optimal density, bluish hue - Increase in optimal density, brownish hue


Lower viscosity - Higher viscosity



Other important areas to consider in carbon black dispersions are structure, porosity and surface chemistry. Structure is usually defined as the fusion and branching of primary particles into aggregates. One way to measure the structure is the oil absorption number (OAN).


An increase in structure (increasing oil absorption) causes an increase in viscosity, and an improvement in dispersibility but a reduction in jetness.

Porosity is a comparison of the carbon black’s surface area measured in two ways, the BET surface area and the STSA surface area. The BET surface area is the total surface area whilst the STSA surface area is the external surface area. There is an increase in viscosity with higher porosity i.e. higher ratio of BET/STSA.


The surface chemistry of the carbon blacks can play a major factor. These are mainly oxygen-containing groups. These oxidised surfaces tend to improve wetting, dispersion and rheology. However, increasing this level of surface oxidation makes the pigment more hydrophilic and lowers the pH.


Formulations used


Table 1



SBK - Competitor 1

SBK - Competitor 2

SBK - Lansperse SL58

SBK - Lansperse SL66

Laropal A81 (60% in PMA)

25 

25 

25 

25 

PMA

40 

30.8 

40 

40 

Competitor 1

10 

 

 

 

Competitor 2

 

19.2 

 

 

Lansperse SL58 

 

 

10 

 

Lansperse SL66 

 

 

 

10 

Elftex 430 

25 

25 

25 

25 

Total

100 

100 

100 

100 


Laropal A81 – Standard aldehyde resin for dispersing pigments, with excellent solubility and compatibility.

PMA – Propylene glycol monomethyl ether acetate.

Competitor 1 - 100% active complex amine-based dispersant.

Competitor 2 - Around 50% active in PMA and is a block co-polymer type dispersant.

Lansperse SL58 - 100% active new complex dispersant with improved fluidity.

Lansperse SL66 - 100% active new complex dispersant with improved fluidity.

The difference between the Lansperse SL58 and Lansperse SL66 is in the ratio of some of the raw materials.

Elftex 430 – Ex. Cabot Corporation is a universal regular colour carbon black with low structure and typically lower viscosity dispersions.


The formulations were dispersed on an Eiger bead mill with 1.5mm zirconia beads for 30 minutes to a Hegmann < 7 (< 10 microns).


Dispersions were coated onto LENETA cards and coated at 25-micron wet film thickness using a TQC automatic applicator running at 50mm/sec.


Gloss was measured using a standard 20/60/85 gloss meter on these drawdowns and viscosity/rheology measurements were undertaken over a period using a DIN 6 flow cup.


Viscosity 


Table 2 - Viscosity over time, seconds

No of days 

Competitor 1

Competitor 2 

Lansperse SL58

Lansperse SL66

4 

10 

11 

8 

25 

11 

13 

12 

12 

27 

21 

18 

15 

14 

30 

28 

19 

17 

17 

32 

78 

26 

24 

24 

42 

Viscosity over time


Drawdowns and gloss readings


For this part of the investigation we only used the Lansperse SL58 versus the two competitors' products as the Lansperse SL66 was not suitable in the viscosity tests.


Drawdowns of the dispersions were coated onto a LENETA card at 24 microns (wet film).


Figure 1 shows the black dispersions prepared in Table 1.


Figure 1



Gloss readings


Lansperse SL58 

Competitor 1 

Competitor 2 

Gloss at 20° 

116 

84 

96 


The black dispersions were then mixed 5% with our solvent white dispersion based on Lansperse SL58 and then coated onto the opacity sheets. 

 

These are shown below in figure 2.


Figure 2



Gloss readings


Lansperse SL58 

Competitor 1 

Competitor 2 

Gloss at 20° 

78 

64 

0.4 


The results are interesting in that the Lansperse SL58 appears to be better than the competitors in dispersing this carbon black in a Laropal A81 system. Its viscosity is comparable to the standards and the drawdowns show that it gives a more glossy coating and its appearance looks a deeper black. In the tinted ones, there is a big difference between the Lansperse SL58 and Competitor 2.


Further investigation on the colour formation may pick up more differences. 

 

Further work 


Several different carbon blacks with varying surface areas will be evaluated along with different binder systems for solvent-based systems, especially for solvent-based decorative coatings.


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