First of all you have to know that an iron oxide black pigment show a magnetic structure. A wetting and dispersing additive for sure can help during grinding, but for the stabilization the magnetic structure of the iron oxide black pigment is stronger compared to the steric hindrance of the wetting and dispersing additive. There are other inorganic black pigments on the market, which will give similar color compared to iron oxide black pigments but are easier to stabilization. Besides the inorganic black pigments a coarse carbon black is an alternative to the iron oxide black pigment.
Very efficient wetting and dispersing additives for the stabilization in co-grind formulation are DISPERBYK-2013, DISPERBYK-2055 and DISPERBYK-2205 for solvent-borne systems and DISPREBYK-2055 or DISPERBYK-2012 for water-borne systems.
Defoamer can have hydrophobic particles and/or foam destroying polymers in its formulation, therefore it is necessary to homogenize the additive before incorporation, normally a pictogram is pritnted on the label of the additive. Another possibility could be that the shear force differ during production process, here a stronger incorporation, either higher shear force or longer incorporation time, is needed.
If the foam only occurs in the yellow pigment concentrate there is a high chance that exchanging the yellow pigment would be the best choice. You might use a pigment which is partly soluble in the solvent you are using for example a PY 74.
PY 74 can be easily used in pigment concentrates with white spirit or water as a solvent, but if you use stronger solvents (Esters, Ketones or aromatic solvents) this pigment show strong foam development. Besides the foam formation the grinding often show flooding and floating or low gloss. A wetting and dispersing additive cannot help in this case, because parts of the pigments will be soluble in the solvent and then a wetting and dispersing additive cannot adsorb onto the pigment surface and stabilize it. Only an exchange of pigment would be helpful.
If you use a solvent stable yellow pigment, it might be helpful to adjust the dosage of the wetting and dispersing additive or to use BYK-052 N, BYK-061 or BYK-066 N as a defoamer in the formulation.
Rheology behavior can have a huge influence on leveling, if the coating has strong pseudoplastic behavior with a high viscosity in the low shear range it can show a negative effect on the leveling as well. Important for leveling is the right surface tension to get the substrate wetting with the well-balanced viscosity. In our test systems, we achieved perfect balance with a combination of RHEOBYK-H 7625 VF (0.05-0.20% active substance) and RHEOBYK-L 1400VF (0.3-1.0% active substance).
Air-less or air-assisted airless (air-mix) application tend to show strong foam development during application. Typically, this foam is micro foam, micro foam is much harder to defoam compared to marco foam. For sure a defoamer like BYK-1790, BYK-052N (or aromatic free BYK-1752) or BYK-054 are perfect for this applications. Besides the defoamers we found that surface additives can have an huge influence, positive or negative, on foam development or defoaming properties. BYK-310 and BYK-3760 showed the lowest influences on foam development in a solvent-borne high solids coatings when it comes to surface tension reduction for good substrate wetting or anti-cratering properties. BYK-392 and BYK-354 shows good leveling and defoaming properties when combined with a defoamer.
Some additives as example defoamer need higher shear forces to be incorporated well into the coating. Often the dimensions of container to stirring blade differ from laboratory equipment to production equipment, therefore energy input will be different. In this case, a higher velocity or a longer incorporation of the additive can solve the problem.
Craters occur if there is a surface tension problem. It might be that a particle with a lower surface tension falls into the fresh coating and after drying a crater is visible.
In water-borne systems it is common to use defoamer, if the defoamer is too strong or not well incorporated this can lead to crater as well.
In any case the surface tension of the coating needs to be reduced. Products like BYK-302 (BYK-3752 cyclic silicone amount <0.1%), BYK-378 (BYK-3764 cyclic silicone amount <0.1%) or BYK-3760 (cyclic silicone amount <0.1%) are the right products to test.
If the craters are caused by the defoamer, a better incorporation can solve the problem. It is recommended to stir the paint longer with a high speed mixer.
Besides the good deflocculation and stabilization of the carbon black, it is important to use the right grade. To achieve jetness or deep blue black a very fine particle sized carbon black is required, usually here a primary particle below 0.015µm is used. Pigments with such small particle size have a very huge surface. To stabilize these pigments it is important to have the right wetting and dispersing additive and the right amount, because a perfect stabilization means a complete coverage of the pigment surface with the wetting and dispersing additive. In each case the wetting and dispersing additive needs to be compatible with the resin system.
For solvent-borne systems, we recommend to test DISPERBYK-161, DISPERBYK-2013, DISPERBYK-2200, BYK-9077 or BYK-9076.
For water-borne coatings there are two possibilities to grind the pigments, resin-free or in a shear stable resin. DISPERBYK-2012 and DISPERBYK-2014 can be used for both grinding methods, while the DISPERBYK-190 is recommended mainly for resin-free grindings.
There are different possible reason why flooding and floating occur.
One reason could be that the tinting paste (pigment concentrate) is not compatible with the base paint, another reason could be that the pigment or extender in the base paint is not well deflocculated and stabilized. The third reason could be that the pigment in the pigment concentrate is not well stabilized.
If you buy the tinting paste, we recommend to test the iron oxide red concentrate in a clear coating and perform a rub-out test. Iron oxide red has the characteristic of flooding and floating by itself, if it is not stabilized. This is described in our brochure [L-TI1] Additives for Pigment Concentrates (bitte als Link einfügen). You can try to improve the compatibility by a post addition of a wetting and dispersing additive like BYK-P 104 S, DISPERBYK-2155, DISPERBYK-2150, DISPERBYK-110 or DISPERBYK-2055.
In this brochure you will find as well information regarding raw material selection and a guideline for formulating pigment concentrates which is helpful for own evaluation of pigment concentrates. For solvent-borne resin-containing pigment concentrates we recommend to test following wetting and dispersing additives: DISPERBYK-2013, DISERBYK-2055, DISPERBYK-2150 and DISPERBYK-2155. You can find starting point formulation of pigment concentrates for different areas here.
Flooding and floating arise when one or more pigments are not well stabilized. There are two different ways of stabilization, controlled flocculation and deflocculation. Controlled flocculating additives are an excellent choice for formulations with only inorganic pigments, fillers where a high pigment load or a high film thickness is needed and gloss is less important. Besides the good stabilization of the pigments, controlled flocculating wetting and dispersing additive (for example ANTI-TERRA-204 or BYK-P 104) provide also anti-settling properties.
Deflocculating wetting and dispersing additives are the perfect match when it comes to high gloss systems and when organic pigments are involved.
Important for the selection is that the wetting and dispersing additive is compatible with the resin.
Deflocculating additives like DISPERBYK-2150, DISPERBYK-2155 or DISPERBYK-2055 are very compatible with many different resins and therefore very versatile. Especially in 2 pack epoxide systems the storage stability is quite important, for this application we developed the DISPERBYK-2152.
If there is only minor flooding and floating or a formation of Benard’ cells a small amount of a surface additive based on silicone chemistry will improve.
We recommend to test BYK-310, BYK-327 or BYK-3550.
DISPERBYK-2152 has a unique hyperbranched structure. The product provides excellent stabilization of inorganic and organic pigments, avoids flooding and floating and does not influence the storage stability.
NANOBYK-3620 uses nano hybrid technology to provide outstanding surface protection of aqueous coatings. This additive is especially recommended for high gloss systems and has no influence on transparency. The VOC-free aqueous dispersion improves scratch and abrasion resistance.
Wax based additives can improve the mechanical resistance, for water-borne high gloss coatings, AQUACER products are recommended.
As there are many different types of titanium dioxide which have a different treatment they have a more basic, acidic or neutral surface area. Typically, they have a Al2O3, SiO2, ZrO and sometimes an organic treatment. It is important to select the wetting and dispersing additive that is compatible with the resin and that the pigment affinic groups interacts with the surface treatment. If different grades / producers are used we recommend to use titanium dioxide with similar treatment for one coating.
Titanium dioxides which are mainly treated with Al2O3 need a product like DISPERBYK-110 while titanium dioxides with SiO2 treatment need products like DISPERBYK-2155 or DISPERBYK-2013.
All mentioned products will deflocculate and stabilize the titanium dioxide and the tendency of settling will be increased, therefore it is utmost important to use an anti-settling additive (for example GARAMITE-7305 powder or CLAYTONE-40 pre-gel) during the grinding.