Zinc borate

Zinc borate is characterized by good stability, small particle size, low water solubility, low specific gravity, good shell-forming properties, and good dispersibility. Its CAS number is 1332-07-6, and its molecular formula is 2ZnO.3B2O3.3.5H2O. It can be used as a flame retardant, partially replacing antimony trioxide (Sb2O3), and has wide applications in industries such as plastics, cables, rubber, synthetic fibers, coatings, paints, and unsaturated resins. Zinc borate can be compounded with halogenated flame retardants and halogen-free phosphorus-nitrogen flame retardants to achieve synergistic flame-retardant effects.

I. Basic Information

English Name: Zinc borate; ZB

CAS NO: 1332-07-6

Molecular Weight: 125.2261

ECN NO: 215-566-6

Specific Gravity: 2.36

Refractive Index: 1.580-1.599

Appearance: White powder

II. Product Features

1. It has halogen-free flame retardant, synergistic flame retardant, smoke suppression, and smoke elimination effects.

2. It can be compounded with various other halogen or halogen-free flame retardants for synergistic flame retardancy.

3. Zinc borate has good dispersibility and thermal stability, is insoluble in water, and can partially replace antimony trioxide (Sb2O3).

4. It has excellent resistance to precipitation, is odorless, non-toxic, and non-corrosive.

5. It is resistant to high temperatures and suitable for high-temperature processing.

6. It has good flame retardant effect on polymer charring.

III.ProductSpecifications

Content≥99%

Whiteness≥95%

Moisture%≤0.5%

ParticleSize(D50):3-5μm

ZincOxide:36.5-39.5%

BorneOxide:46.0-49.0%

LossonIgnition:13.0-15.5%

Residueon325Mesh≤0.5%

HeavyMetalPb≤15ppm

SpecificGravity:2.67g/cm³

MeltingPoint:980℃

RefractoryIndex:1.58

III. Mechanism of Flame Retardant and Antibacterial Action

1. Zinc borate has a certain char-forming effect, forming an inorganic expansion coating layer on the material surface, isolating combustible gas exchange and preventing heat transfer.

2. At temperatures above 300℃, zinc borate dehydrates, absorbing a large amount of heat from the surrounding material, lowering the temperature of the material environment, and also foaming, diluting combustible gases.

3. At high temperatures, zinc borate decomposes to generate B₂O₃ (and ZnX₂ or ZnOX if the material contains chlorine or bromine; X is Cl or Br), forming a coating layer on the polymer surface. This coating layer inhibits the generation of flammable gases and prevents oxidation and thermal decomposition. Furthermore, in halogen-containing materials, BX₃ is generated during combustion. BX₃ reacts with water in the gas phase to generate HX, producing halogen free radicals in the flame. These free radicals can inhibit the chain reaction of hydroxyl free radicals, thus acting as flame retardants.

4. It inhibits and interrupts the continuous reaction of flammable free radicals.

5. Zinc borate is toxic to cells and is also an enzyme inhibitor. It inhibits fungal growth by inhibiting enzyme activity in the cell, and has a wide range of effects on organisms that damage wood fibers, such as white-rot and brown-rot fungi, as well as termites and other insects that damage wood panels.

IV. Uses

1. It can be used as a corrosion inhibitor in coatings, and can be used as a rust inhibitor in coatings using organic or water-based solvents. Zinc borate offers better cost-effectiveness than adding chromium, lead, or barium pigments. In coating formulations, zinc borate is a better weight-based substitute for zinc chromate. When used in combination with zinc phosphate, barium metaphosphate, and other corrosion inhibitors, it exhibits excellent synergistic effects. Its water of crystallization only begins to decompose and release at 300°C, making it suitable for certain high-temperature baking systems. The typical addition ratio is 0.03-0.3 g/ml.

2. Zinc borate also performs well as a flame retardant. In rigid PVC, it achieves good flame retardant properties when used alone. In flexible PVC, PP, rubber, and other polymers, it is mainly used as a synergist in combination with inorganic flame retardants such as antimony trioxide, aluminum hydroxide, and magnesium hydroxide, or organic flame retardants such as brominated flame retardants. It has excellent smoke suppression and charring promotion effects, and plays a role in adjusting the flame retardant, physical, and electrical properties of the product. Major applications include wires and cables, engineering plastics, bakelite, conveyor belts, rubber tires, and artificial leather. The common addition amount is 1-10%.

3. In the chemical, steel, and coal industries, it is mainly used to manufacture various flame-retardant tapes (pipes), flame-retardant cables, etc. It can replace antimony trioxide, has good flame retardancy for halogenated polymers, can completely replace antimony trioxide in unsaturated polyesters, and can partially replace antimony trioxide in flexible polyvinyl chloride resins. It is suitable for high-temperature processing. It also has a good synergistic effect when used in combination with halogenated flame retardants. It is suitable for flame retardant applications in unsaturated polyesters, polyvinyl chloride, epoxy resins, polyolefins, polycarbonates, polyurethanes, ABS resins, and other plastics. It is also suitable as a flame retardant additive for fiber fabrics and wood coatings. Furthermore, zinc borate is an effective flame retardant; in unsaturated polyesters, rigid PVC, epoxy compounds, polyphenylene ethers, etc., zinc borate alone can achieve a flame-retardant effect. In other systems, such as flexible PVC products, the flame-retardant effect of zinc borate is poor; to obtain better results, it is used in combination with antimony trioxide.

4. It has good antibacterial effects on wood and plastic materials. Zinc borate can be used as an antibacterial agent to protect above-ground wood or wood-plastic composites from decay. It is added to the raw materials during the mixing stage, ensuring even distribution throughout the wood-plastic system. It inhibits the growth of decay fungi, such as white rot fungi and *Cladosporium glomeratum*, and also prevents insect infestation. The resistance of wood-plastic products to fungi depends on the type of wood, the type of resin, other additives used, and the processing method. The applicable proportion should not exceed 8%. When the content exceeds 1.5%, the amount of binder needs to be appropriately increased to enhance strength.

5. It can be used in agricultural fertilizers, micronutrient fertilizers, hydroponics nutrient solution additives, ceramic glazes, and also in medicine as a bactericide, mildew inhibitor, preservative, and rust-preventing pigment. It is also used in far-infrared absorption and insect- and fungicide treatment of wood.

V. Packaging Specifications and Storage Conditions

25KG, 500KG, and 1000KG packaging bags, etc.; Store in a cool, dry, and well-ventilated warehouse. Shelf life is 12 months.

The main production processes for zinc borate include the boric acid method and the borax method. The commonly used form is the 3,5-hydrate compound, but anhydrous and monohydrate versions are also available. Its main characteristics are halogen-free, substitutive, synergistic, flame-retardant, antibacterial, antifungal, and insect-repellent properties.