news

Color paste can be divided into water-based paste, solvent based paste, and universal paste. It is preferred to match your coating system, and then consider: pigment type, solid content, color development, weather resistance/acid and alkali resistance, compatibility, viscosity, ionicity, and additive system; Many problems such as sedimentation, floating color, discoloration, coagulation, layering, loss of luster, and color migration are rooted in the wrong selection of colorants.

You mainly produce water-based coatings (styrene acrylic, silicone acrylic, water-based 2KPU), with a focus on water-based coatings and solvent based coatings.

1、 Distinguish between the two types of colorants first

1. Inorganic pigments (iron red, iron yellow, iron black, titanium dioxide, chromium based, composite inorganic pigment CICP)

✅ Advantages: high density, strong weather resistance, good heat resistance, acid and alkali resistance, high coverage, not easy to fade, moderate cost ❌ Disadvantage: High density! Very easy to settle and press hard cake; Some iron series are prone to flash rust; The particle size is too large and the fineness is not good, which makes it easy to become rough

2. Organic colorants (phthalocyanine blue/green, perpetual red, benzidine yellow, pyrrole red DPP, etc.)

✅ Advantages: Strong coloring power, bright colors, fine particle size, low density, and much lower sedimentation risk than inorganic materials ❌ Disadvantages: Poor coverage, weak weather resistance in many varieties, poor solvent resistance, easy to float and flower, some may migrate, expensive price

Important reminder: Charcoal black slurry is quite unique, with a huge specific surface area and high difficulty in wetting and dispersing. It is prone to coarsening, flocculation, and black hair gray. Therefore, it is necessary to choose a specialized high dispersion charcoal black slurry.

2、 How to choose color paste (by priority)

① System matching (first principle, if wrong, it will lead to a crash)

· Waterborne paint (styrene acrylic, pure acrylic, silicon acrylic, water-based PU): water-based color paste, do not mix solvent color paste in casually → demulsification, particles, gel, lusterless water-based interior subdivision:

· Anionic color paste: most styrene acrylic and pure acrylic lotion (most lotion are anionic), with the best compatibility and mainstream

· Non ionic color paste: suitable for ion sensitive systems (partial cationic lotion, 2K water-based PU, formula containing multivalent metal ions, zinc rich), not easy to flocculate; Disadvantages: Slightly low coloring power and high price

· Cationic color paste: very few, only cationic system, directly agglomerates with anionic lotion

Solvent based and oil-based paints: solvent pigments (alcohol soluble, ester soluble)

Do not blindly believe in “universal colorants”: Universal colorants are compromise products, and their stability, medium resistance, and color development will be compromised. Industrial formulas should be avoided as much as possible

② Select weather resistance level according to the usage environment

Interior wall: Ordinary organic/inorganic color paste is sufficient

Exterior walls and outdoor workpieces: ✅ Priority: Iron oxide, composite inorganic CICP, phthalocyanine blue-green, DPP red, quinacridone ❌ Avoid low weather resistant organic compounds such as benzidine yellow and sun resistant bright red, which may fade or discolor after several months

Corrosion prevention, contact with acid and alkali, water immersion: avoid organic pigments that are not resistant to hydrolysis; Inorganic iron oxide is relatively stable

③ Check the indicators of the color paste itself (procurement/inspection should ask the supplier)

1. Pigment solid content: Same color, high solid content=less added amount, less water/additives introduced, less impact on the rheological and stability of the original paint (very critical! Adding too much low solid color paste is equivalent to adding a large amount of water, directly diluting the yield value and inducing settlement and delamination)

2. Dispersant system: The color paste comes with its own dispersant! This is the incompatibility between the dispersant, thickener and lotion in your base paint and the dispersant in the invisible pit color paste → dispersant exchange and desorption → pigment flocculation, color floating, thickening and sedimentation

For example, the color paste uses small molecule anionic dispersants, while your paint is a polymer dispersant system, which can easily cause dispersant displacement and pigment instability after mixing

three

4. Fineness: generally ≤ 5 μ m, and it is best for the topcoat to be ≤ 3 μ m; Poor fineness, rough paint film, poor coverage, and faster settling

5. Thermal storage stability: Store separately at 50 ℃ for 7 days to check for layering, thickening, and discoloration; Many colorants sink naturally when stored, and adding them to paint will only make it worse

6. Resistance to migration and color penetration: It is necessary to test for topcoat, recoating, and soft coating, otherwise the upper topcoat will be stained by the lower color paste

7. Heavy metals and ROHS: Export workpieces need to be confirmed in advance

④ Key points for selecting colorants based on your concern about settlement stratification

When using high-density colorants such as iron red, iron yellow, and composite inorganic in large quantities:

Prioritize the use of high solids, stable fineness, and fully dispersed coating colorants, and do not choose cheap colorants that are thin and prone to self sinking

Same hue, compare two color pastes: same amount added, observe the hardness and hardness of the sediment after thermal storage

2. Do not add high-density inorganic colorants in large proportions at once; The order of color paste addition and stirring speed should also be controlled

3. After the introduction of inorganic colorants, the low shear yield value/thixotropic structure of the base paint must be reinforced (such as polyurea, polyamide wax, bentonite, and silicone), otherwise even the best colorants will sink

3、 Precautions for the use of colorants (formula&process high-frequency stepping points)

1. Compatibility pre experiment (mandatory, before formal production)

Simple testing method: 1) Basic paint+predetermined amount of color paste, stir well at low speed. 2) Preparation: Hot storage at 50 ℃ for 7 days, room temperature for 30 days, freeze-thaw cycle. 3) Observation: whether there is water separation, settling hard cake, floating color and flower, loss of gloss, particle, color change. 4) Scraper: brush and spray, observe color development, leveling, color difference, and floating color (color wiping experiment: lightly wipe the wet film with fingers to observe color difference)

Floating color=pigment is enriched in the surface layer; Blossoming=Local striped and mottled, mostly due to density differences between pigments and mismatched dispersants

2. Order of addition and feeding method

✅ Correct: First adjust the pH, rheology, and dispersion stability of the base paint → slowly add the color paste under low-speed stirring → fully disperse after adding (do not vigorously beat at high speed! High speed cutting will damage the original dispersion and coating of the color paste, causing pigment flocculation) ❌ Error: Add color paste first and then thicken; High speed long-term sanding of color paste (the finished color paste has already been ground, but secondary grinding may cause it to break and disperse)

Color paste is usually added later! Industrial colorants are pre dispersed and not used for sanding with fillers (unless they are pigment powders, not finished colorants)

3. Add quantity control

There is a limit to the amount of color paste added!

Organic color paste: The recommended total addition amount is generally ≤ 3-5% (some high coloring carbon black is even lower)

Inorganic colorants: can be higher, but high addition levels will drastically change the system density, rheology, and PVC. Exceeding the upper limit: colorants come with too many additives, disrupting the balance of the original formula, and increasing the risk of water separation, settling, and loss of gloss

4. Risks of mixing different colorants

Do not mix different manufacturers and series of color pastes randomly: A factory’s iron red paste (small molecule dispersant)+B factory’s phthalocyanine blue paste (polymer dispersant), the two dispersants compete with each other for the surface of the pigment, which is prone to flocculation and coarsening. Same brand and series color paste

5. pH impact (water-based focus)

Most anionic water-based colorants have a stable pH range of 7.5-9.5; If the pH of your paint is low (<7), many anionic colorants will coagulate, discolor, and precipitate; The pH of the 2K water-based PU system is often weak and neutral, so a non-ionic color paste suitable for neutral environments should be selected.

6. Conflict with additives

Some defoamers and surfactants may interact with color paste dispersants, inducing float color

Multi valent metal ions (zinc powder, aluminum powder, calcium chloride, drying agent)+anionic color paste → flocculation precipitation, which is very common in anti-corrosion paints! Zinc rich systems should avoid anionic colorants as much as possible

HEUR binding thickening system: Some free surfactants in the color paste will “dissociate”, directly causing water separation and viscosity drop

7. Storage and management of color paste itself

Check the condition of the bucket upon arrival: reject the color paste that has been layered, hard cake, or cannot be stirred; If the color paste bucket is left to stand for a long time, it will also sink. Before use, the color paste bucket must be thoroughly stirred before adding it to the large tank. Otherwise, the upper layer of clear liquid will be added first, followed by thick color paste, resulting in a huge color difference.