Fremgangsmate for fremstilling av magnesiumhydroksidpartikler

Provided are magnesium hydroxide particles having a hexagonal crystal form and having an aspect ratio (H) which satisfies the following expression (I), (wherein H is an aspect ratio, A is an average secondary particle diameter ( mu m) of all of the particles measured by a laser diffraction scattering method and B is a specific surface area (m /g) of all of the particles measured by a BET method), a flame-retardant comprising the particles, a flame-retardant resin composition comprising 100 parts by weight of a synthetic resin and a 5 to 300 parts by weight of the magnesium hydroxide particles, and a molded article therefrom. The magnesium hydroxide particles are hexagonal single crystals, the hexagonal form thereof are not necessarily required to be regular hexagonal, and the size thereof are not necessarily constant. However, the aspect ratio thereof has a specific value in relation to the specific surface area and the average particle diameter, and the magnesium hydroxide particles have excellent properties as a flame retardant for synthetic resins.