PIGMENT BLUE 28/ Cobalt Aluminate blue 6028B
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Technical Information
What Is PB28 / Cobalt Aluminate blue 6028B
CAS 1345-16-0, CI 77346, PB28 / Cobalt Aluminate blue 6028B is a cobalt aluminate (CoAl2O4) inorganic pigment with a spinel crystal structure. It delivers a distinctive reddish-blue shade with heat resistance exceeding 1000°C, surviving conditions that destroy any organic pigment. This grade offers excellent lightfastness and chemical resistance, is non-migrating, and completely inert. While it has lower tinting strength than organic blues, its unmatched durability makes it ideal for extreme environments.
Why Choose Cobalt Aluminate blue 6028B
This specific 6028B grade is tailored for plastics applications where thermal and chemical stability are critical. It withstands high processing temperatures in engineering plastics without degrading, migrating, or bleeding. Its inert nature ensures consistent coloration even in aggressive polymer matrices or repeated heat cycles. Unlike ultramarine or phthalo blue, which fail above 300°C or in harsh chemical environments, 6028B remains stable in demanding compounding and molding processes. While it costs more, its durability eliminates rework and color shift risks in high-performance plastics. This grade has no siblings, making it the singular choice for applications requiring a non-toxic, fully inert blue that retains its reddish hue under extreme thermal stress.
Key Features
- Heat resistant above 1000°C, far exceeding the limits of any organic or conventional inorganic blue pigment.
- Reddish-blue spinel structure providing exceptional lightfastness and weatherability in outdoor plastics.
- Completely non-migrating and chemically inert, preventing blooming or reaction with plasticizers in engineering polymers.
- Maintains color stability through repeated high-temperature processing cycles with zero degradation.
- Unmatched durability for critical applications where organic blues fade or ultramarine decomposes.
C.I.NO.: PB28
Advantage:
Main Application Recommended: Plastics
Product Description – PB28
Cobalt Aluminate blue 6028B (PIGMENT BLUE 28) is a high-temperature calcined blue pigment known for its excellent chemical resistance, outdoor durability, lightfastness, thermal stability, non-bleeding, and non-migrating properties. It is widely used in applications requiring high heat resistance, weather resistance, and lightfastness, and is compatible with most resins or polymers. It features a reddish undertone, fine particle size, and easy dispersibility, along with high tinting strength and good opacity.
Recommended Application
Coatings: solvent based paints, water based paints, auto paints, industrial coatings, powder coatings, wood coatings, coil coatings
Plastics: PE, PP, PBT, PVC, PET, EVA, ABS
Technical Data
| Product Information | ||||
| Chemical Type | Co-Al-O | CAS NO. | 1345-16-0 | |
| C. I. Name | Pigment Blue 28 | EINECS / ELINCS NO. | 310-193-6 | |
| C. I. Constitution No. | 77346 | Chemical Formula | ||
| Technical Performance | ||||
| Full Shade | Tint | |||
| Weather Resistance | 5 | 5 | Heat Stability °C | 800°C |
| Light Fastness | 8 | 8 | ||
| Physical Properties | ||||
| Physical Form | Powder | Resistance to Acid | 5 | |
| Specific Density (g/cm3): | ~4.2 | Resistance to Alkali | 5 | |
| Moisture Content | < 1.0 | |||
| Water soluble salt | < 1.0 | |||
| Oil Absorption g/100g | 16-26 | |||
| PH | 7.5~9.5 | |||
| Packaging | ||||
| 25kgs/bag 800kgs/Pallet | ||||
| Storage | Shelf Life | 5 years | ||
| Should be stored in cool, dry and ventilate place. | ||||
| TRANSPORTATION | ||||
| Avoid inversion, sunlight, moisture and crash. Avoid damage the package. | ||||
- Light fastness: Light fastness rating is assessed on 1 to 8 Blue Wool scale where 1 = ‘Poor’ and 8 = ‘Excellent’.
- Heat Stability : Heat stability values given indicate the maximum temperature at which the pigment can be stoved for 10 min. on the full shade and in reductions without undergoing any significant change in shade.
- Oil absorption: The oil absorption is determined on the basis of EN ISO 787-5 and given in g linseed oil per 100 gm. pigment.
- Solvent bleeding: The bleeding in solvents is tested using the powder grades and the visual rating given on 1 to 5 Grey scale
where 1 = ‘Heavy bleeding’ and 5 = ‘No bleeding”
Technical Note — The data and recommendations provided are based on HONOR Pigment’s internal testing and manufacturing experience. They are offered in good faith to assist customers in evaluating product suitability for their specific applications. As processing conditions, formulations, and end-use requirements vary widely, customers should conduct their own validation under actual use conditions. HONOR Pigment makes no warranties, express or implied, regarding the accuracy of this information or its fitness for any particular purpose. Nothing herein shall be construed as a license or recommendation to infringe any patent. HONOR Pigment’s standard terms and conditions of sale apply.oduct contains particles < 0.1 μm. Any user of this product is responsible for determining the suitability of Honor Pigments’s products for its particular application & to ensure that any proprietary rights & existing laws & legislation are observed.
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Frequently Asked Questions About PB28
What specific plastic applications is Cobalt Aluminate blue 6028B best suited for?
PB28 / Cobalt Aluminate blue 6028B is specifically engineered for high-temperature engineering plastics, including polycarbonate (PC), polyamide (PA), polybutylene terephthalate (PBT), and polysulfone (PSU). Its robust crystal structure allows processing up to 300°C without degradation, making it ideal for automotive components, electrical housings, and outdoor signage requiring deep, heat-stable blue tones. It also excels in masterbatch formulations where precise color consistency is critical under repeated thermal cycles. However, due to its high opacity and tinting strength, it is less recommended for transparent or translucent polyolefin films unless dispersion equipment can handle fine particle agglomerates. For food-contact applications, always verify current regulatory compliance, as cobalt compounds may have migration limits in various jurisdictions.
Does PB28 have any performance limitations regarding lightfastness or chemical resistance?
While PB28 offers excellent lightfastness (typically 7-8 on the Blue Wool scale) and outstanding weather resistance, it has two notable limitations. First, it is sensitive to strong acidic environments (pH below 3), where cobalt ions may leach, causing color shift toward greenish-blue and reducing structural integrity. Second, in very high-loading scenarios (above 5% weight), the pigment can act as a catalyst that accelerates polymer degradation under prolonged UV exposure, particularly in polyolefins. It is also not recommended for applications requiring transparent red-shade blues, as its inherent greenish-blue hue is difficult to compensate with red pigments. For chemical resistance in automotive coolants or brake fluids, always conduct immersion tests, as polar solvents can cause slight surface dulling over time.
How does PB28 compare to its “sibling” pigment, PB29 (Ultramarine Blue), for plastic use?
PB28 and PB29 serve very different performance profiles. PB28 (Cobalt Aluminate) offers superior heat stability (up to 300°C vs. 250°C for PB29) and much stronger chemical resistance, especially against acids and alkalis. PB29, however, provides a brighter, more reddish-blue hue and is significantly more cost-effective. For plastics processing, PB28 is the choice for demanding engineering applications requiring durability, while PB29 is better suited for general-purpose polyolefins where processing temperatures remain below 230°C. A key differentiator is that PB28 does not require any dispersing aids and resists plate-out, whereas PB29 can be prone to agglomeration, causing surface defects. PB28 also excels in niche applications like laser marking, where its crystal structure produces a distinct contrast, while PB29 does not.
What are the critical processing parameters to avoid defects with Cobalt Aluminate blue 6028B?
To achieve optimal dispersion and void defects, maintain a melt temperature below 290°C for most polymers—exceeding this can cause the pigment to aggregate into visible specks. Use a shear-intensive screw design (e.g., double-flighted with mixing elements) at a compression ratio of 2.5:1 to 3:1 to break down any clumps. For masterbatch, pre-dry the pigment at 110°C for 2 hours to remove adsorbed moisture, which can cause splay marks in injection molding. Avoid combining PB28 with polymer additives containing free sulfur, as cobalt can react to form discolored cobalt sulfide specks. If you observe flow lines, increase back pressure by 10-15 bar to improve homogenization. For thin-wall parts (under 1.5 mm), use a nozzle diameter under 2 mm to minimize shear-induced pigment flocculation.
What is a suitable substitution or storage plan if PB28 is unavailable or needs long-term storage?
For emergency substitution, the closest match in performance and hue is CI Pigment Blue 36 (Cobalt Chromite Blue), which offers similar heat stability and greenish shade but may have slightly lower tinting strength. Do not replace PB28 with organic blue pigments (e.g., PB15:3) above 240°C, as they will degrade. For long-term storage, store PB28 in sealed, moisture-proof drums below 40°C (104°F) in a dry, dark environment—cobalt aluminate is hygroscopic and can form hard aggregates if exposed to humidity above 60% RH for extended periods. Shelf life is indefinite if containers remain unopened; after two years, conduct a 30-minute dispersion test at 200°C (392°F) to check for lumps. Always label stock with the original manufacturing date, and rotate older inventory first. For small batches, consider portable vacuum dryers to refresh material before use.
**Cobalt Aluminate blue 6028B takeaway:** This pigment delivers unrivaled heat stability and chemical resistance for engineering plastics, but requires careful control of processing temperature and acidity to unlock its full performance potential in demanding applications.
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