Process of 3-layer co-extruded biaxial oriented polypropylene (BOPP) synthetic paper
Process of 3-layer co-extruded biaxial oriented polypropylene (BOPP) synthetic paper

The inorganic filler for the paper surface layer of the present invention is selected from one of the group consisting of calcium carbonate, diatomite, clay, titanium dioxide and barium sulphate or a mixture thereof with a granule diameter of 0.5-5 μ, and the quantity used thereof may be 2-4% depending on the required writing quality and printability.

The major action of inorganic filler for the present invention is to let PP synthetic paper make use of the irregular configuration of said filler extending to form some fine holes during biaxial orientation, to lower the specific gravity of synthetic paper considerably below 0.75 without additive frothing agent, and to equip the synthetic paper with the best opacity. In consideration of the dispersibility of the inorganic filler, the resin composite of synthetic paper also may use the pre-formed master batch of inorganic filler and PP resin.

The inorganic filler for the intermediate layer of the present invention is a mixture of calcium carbonate or diatomite or clay and titanium dioxide, the using quantity thereof is 15-22% weight, and the said titanium dioxide is essentially red schorl of which the major action is to adjust the shadowing of pp synthetic paper and the whiteness of paper surface and to resist against ultraviolet.

The static resistant agent for the synthetic paper of the present invention may be that for the current BOPP in general, and it is essentially the Grade 3 amine of which the charge translation can eliminate the static effect resulted from processing friction, and the quantity used is 1-3% weight.

In order to prevent the mutual adhesion between the paper surface from happening during rolling the synthetic paper of the present invention, the adhesion resistant agent is required and it may be the current silicon dioxide in general for BOPP so as to upgrade the stretching and flattening of the synthetic paper, and quantity 0.05-0.15% weight is used.

In order to prolong the usable life of the synthetic paper of the present invention and to prevent the said paper subject to the UV action from ageing and decomposing, the UV absorbent is used in a quantity of 0.05-0.15% weight.

The specific gravity of PP synthetic paper product of the present invention may be below 0.75, and adjusted through changing the formula of composition thereof and is lower than 0.79 which is the specific gravity of Toko Kaihai s Japanese Patent 3-87225 so that the consumers can use more area further economically even though the unit weight is the same.

The present invention adopts the synthetic paper with 3-layer structure consisting of paper surface layer/intermediate layer/paper surface layer, wherein the extrudate of PP resin composite from one primary extruder and the extrudate of resin composite from two secondary extruder are co-flow to the same one T-type die for extrusion to form a sheet with 3-layer structure and then result in a synthetic paper through cooling/shaping, biaxial orientation, corona discharge treatment and rolling, and if the synthetic paper thickness over 100μ is required, it will be laminated. Such a synthetic paper through the foregoing process and processing is closely related to its physical property, productivity, equipment and operation. The BOPP product in general is a transparent product with filler. However, in the imitation process, a large quantity of inorganic filler is required to be added to the raw material formula of the PP synthetic paper of the present invention, so the productivity of biaxial orientation, the dispersibility of inorganic filler and the quality stability of product are subject to an ordeal. http://www.szsanxin.cn/en-us/products05.html