Preparation method of mica paper pulp calcining chemical pulping

The separated mica is calcined at a high temperature to remove part of the crystal water in the mica structure, so that the mica flakes will expand in the direction perpendicular to the cleavage surface, and the texture will become soft, and then chemically treated to make the mica flakes full The ground separation is split, and then it is washed and classified into a slurry. The mica paper that is pulped and made by this method is called powder mica paper.

a. Sorting and drying of mica raw materials

The raw materials used in natural mica paper are mainly scraps of natural crushed mica and flake mica processing. The purpose of sorting is mainly to remove the adhesive flakes, biotite, green mica, and other impurities and foreign impurities that are not suitable for making mica paper. In order to ensure the calcining quality of mica, thick mica flakes with a thickness greater than 1.2mm must be removed. The sorted mica is cleaned by adding water in a cylindrical screen or vibrating screen to remove impurities such as sand and sand in the mica material and sieve out fine materials that are too small to purify the mica material. The purified mica contains 20%~25% of water, which must be removed to reduce the content of attached water to less than 2%. Drying is carried out on a special belt dryer, using steam as the heat source.

b. Calcination of mica

Put the mica into a specific electric furnace, heat it to 700~800℃, and keep it for 50~80min to remove the crystal water in the mica crystals, and obtain high-quality mica material for pulping. The calcination of mica currently mostly uses indirect heating rotary kilns. The calcined mica clinker needs to be screened to remove the silt, combustible ash and mica fragments with a diameter of less than 6mm that were originally sandwiched between the mica layers. The calcining quality of mica will affect the electrical properties, flexibility, folding resistance, tensile strength and pulping rate of mica paper.

c. Preparation of powder mica slurry

The calcined mica (clinker) is chemically treated to make it into a scaly slurry that can be dispersed in water and suspended uniformly, and the water-soluble impurities are removed by washing to meet the requirements of the papermaking process.