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1、 Fundamental essential differences

Inorganic pigments: metal oxides, salts (titanium dioxide, iron oxide red/yellow, chromium based, cobalt blue, ultramarine), crystalline inorganic substances, chemically stable bonds, insoluble in resins/solvents.

Organic pigments: Aromatic conjugated macromolecules (azo, phthalocyanine, quinacridone, DPP, etc.) that develop color through conjugated chromophores; Molecules are organic covalent structures that are easily degraded by UV light, oxygen, and thermal attacks.

2、 Brightness/chroma, hue characteristics

Inorganic pigments

✅ Features: Low saturation, dark, heavy, and steady color tone

Advantage colors: yellow brown, red brown, black, white (iron oxide, titanium dioxide);

Shortcomings of bright color schemes: It is difficult to produce bright and vibrant colors such as bright red, bright orange, bright purple, and bright green; Cobalt blue is relatively bright, but the cost is high;

Low coloring power, requiring a higher amount of addition to achieve the same color depth;

The color tone is mostly earthy.

organic pigment

✅ Features: Conjugated color system, high color saturation, bright and transparent color, with a wide range of chromatography that can produce high gloss bright red, bright orange, rose red, bright purple, bright blue, and bright green; The coloring power is much higher than inorganic, and a small amount of addition can achieve very deep colors.

For example, DPP red, quinacridone red, phthalocyanine blue/green have a much higher brightness than iron oxide red and ultramarine.

⚠️ Subdivision: There is a huge gap within organic pigments

Ordinary low-grade azo: high brightness, but poor weather resistance;

High performance organic pigment HPP (DPP, quinacridone, isoindoline, phthalocyanine): retains brightness, greatly improves weather resistance, and is expensive.

3、 Weather resistance (UV+oxygen+rainwater, outdoor aging, the most critical indicator of coatings)

Inorganic pigments

✅ The weather resistance is generally excellent, and the crystal structure is stable. UV irradiation is not easy to damage the lattice; Not easily photodegradable.

Rutile titanium dioxide and iron oxide series: excellent color retention under long-term outdoor exposure;

Disadvantages: Some inorganic materials have photoactivity (such as titanium dioxide, which can catalyze resin degradation and cannot be used outdoors); Chromium yellow is prone to sulfurization and blackening.

Aging failure mode: rarely fades on its own; More often than not, it involves powdering (weathering of the pigment surface lattice), migration, and discoloration due to sulfurization contamination.

organic pigment

❌ Poor weather resistance of ordinary organic pigments: UV light breaks the conjugated chromophore structure, causing direct fading and discoloration. Light aging mechanism: UV energy destroys the aromatic conjugated chain, the chromophore group breaks, and the color becomes lighter/discolored; At the same time, free radicals will be generated, which will accelerate the aging of the resin.

classification:

1. Ordinary azo (such as benzidine yellow): Poor weather resistance, limited to indoor inks and plastics, strictly prohibited for outdoor coatings

2. High performance HPP organic pigments (DPP, quinacridone, phthalocyanine, isoindoline): significantly improved weather resistance, can be used as outdoor topcoats, but still weaker than iron oxide and rutile titanium dioxide; The weather resistance performance under high concentration is better than that of thin coloring.

Organic pigment aging characteristics: Thin coating causes more severe fading (light is easier to penetrate); The higher the amount added, the better the weather resistance (pigment protection effect)

Performance Inorganic Pigments Organic Pigments

High covering power (high refractive index of crystals), mostly transparent/semi transparent; A few high coverage organic pigments

Excellent heat resistance, high temperature stability, poor heat resistance of ordinary organic materials; HPP has good heat resistance

Excellent solvent resistance/migration resistance, does not migrate. Low end organic compounds are prone to migration and color bleeding; HPP improvement

High density, easy to settle, low density, better suspension stability

There is a large difference in oil absorption values, and iron oxide generally has a higher oil absorption. Some high color organic pigments have a higher oil absorption value, which affects the viscosity of the formula

Most of the cost is low (iron-based, titanium dioxide), and HPP high-performance organic pigments are expensive

5、 Selection and judgment logic (paint/ink)

1. Indoors, bright colors and high saturation are required → Priority should be given to organic pigments (phthalocyanine, azo, etc.)

2. Outdoor, long-term weather resistant color retention, color does not need to be particularly bright → Priority is given to inorganic pigments (iron oxide, rutile titanium dioxide, cobalt based)

3. Outdoor high gloss color topcoat (such as bright red and bright orange): Only HPP high-performance organic pigments can be used, combined with UV absorbers/hindered amine HALS, and PVC with increased pigment volume concentration to enhance color retention; The cost has significantly increased.

6、 Common Misconceptions

one ❌ All organic pigments are weather resistant: HPP high-performance organic pigments can be used outdoors, but their color retention ability is not as good as iron-based inorganic pigments;

two ❌ Inorganic pigments will not fade: anatase titanium white will catalyze resin pulverization; Chromium yellow turns black when encountering sulfides;

three ❌ Bright=good weather resistance: On the contrary, the stronger the conjugated structure and the more vibrant the color of ordinary organic pigments, the higher the risk of photodegradation.