Overview
ISO 4621:1986, published by the International Organization for Standardization (ISO), specifies the requirements and testing methods for chrome oxide green pigments. These pigments, composed essentially of chromium(III) oxide (Cr2O3) in dry powder form, are widely used in general applications such as paints and varnishes. The standard outlines three distinct grades, each defined by strict limits on particle residue size and composition, ensuring consistency and high quality in industrial uses. Adherence to this standard ensures that pigments are pure, free from extenders, and exhibit reliable color and performance properties.
Key Topics
- Pigment Grades: The standard defines three purity grades based on the residue content after sieving:
- Grade 1: Maximum 0.01% (m/m) residue passing a 45 μm sieve.
- Grade 2: More than 0.01% and up to 0.1% (m/m) residue.
- Grade 3: More than 0.1% and up to 0.5% (m/m) residue.
- Purity Requirements: Chrome oxide green pigments must not be blended with other colorants or extenders.
- Testing Methods: ISO 4621 details the procedures for evaluating pigment characteristics, including:
- Total chromium content
- Soluble chromium content
- Matter volatile at 105°C
- Loss on ignition at 1000°C
- Water-soluble matter (hot extraction method)
- Color matching and pH of aqueous suspensions using referenced ISO methods
- Quality Assurance: Pigments must match agreed color references and comply with maximum tolerances for impurity residues.
Applications
Chrome oxide green pigments standardized by ISO 4621:1986 are crucial where consistent color, stability, and safety are required. Key application areas include:
- Paints and Coatings: Used for coloring paints, ensuring stable, non-fading pigment in architectural, automotive, and industrial finishes.
- Varnishes: Imparting durable green coloration to protective coating systems.
- Plastics and Construction Materials: Suitable for colorants in resins, plastics, and cementitious products owing to their chemical stability and resistance to weathering.
- Ceramics and Glass: Used in high-temperature applications due to pigment robustness.
Utilizing ISO-compliant chrome oxide green pigment ensures compatibility in international markets, reliable production quality, and adherence to industry safety and environmental regulations.
Related Standards
Several ISO standards complement or reference ISO 4621:1986 to define additional aspects of pigment testing and quality:
- ISO 707: General methods for testing pigments and extenders
- ISO 842: Sampling methods for raw materials in paints and varnishes
- ISO 1042: Volumetric laboratory glassware specifications
- ISO 3696: Water quality for laboratory use
- ISO 3876/6: Methods for determining soluble metal content in paints
- ISO 6713: Preparation of acid extracts from paints
- ISO 385/1: Laboratory glassware - burettes requirements
- ISO 787 Parts 1, 2, 3, 5, 7, 9, 16, 20: A series detailing various pigment testing methods including color, volatile matter, water solubility, oil absorption, residue on sieve, pH, tinting strength, and ease of dispersion
By adhering to ISO 4621:1986, pigment manufacturers and users can ensure consistent quality, meet regulatory demands, and optimize product performance in numerous applications requiring high-quality chrome oxide green pigment.