Stone paper, an eco-friendly and free-tree papers

FIGURE 1.
Layer schematic picture of stone paper [14] 
D
D
030010-4

---

FIGURE 2.
Flow chart of single-layered stone paper manufacturing process [14] 
After being processed in a series of mixing steps, all materials of stone paper in the form of granules are fed into 
an extruder (10) to be melted before being formed into sheets. The temperature of extruder is set above melting 
point of granules, in the range of 150
o
C up to 220
o
C. The melted granules are forced by two rotating screws in the 
extruder to the inlet of forming mold (1) having an o-shape gate, and then molded to a paper film through a paper 
film tube (3) having also a hollow o-shape. The paper film tube (3) has temperature as high as 150-220
o
C, so it is 
cooled down by cooling wind provided by cooling means (2) to about 80
o
C up to 120
o
C. The paper film tube (3) is 
then inflated by pressured air through a passage in the forming mold (1) and the initially molded paper film tube is 
drawn by leading roll (6). The purpose of inflation and drawing is to simultaneously stretch the paper film (3) in two 
directions, latitudinally and longitudinally, resulting in a paper (4) having a structure with two dimensional strength. 
After that, the paper film is drawn into folding means (5) and folded symmetrically to folded flat paper and then cut 
using cutting means (7) into two sheets of paper. The two resulting sheets of paper are each subjected to double-
sided surface treatment (8) to provide micro voids on the two surfaces of paper, and then wound into a roll (9). 
The rotation speed of leading roll (6), the amount of material extruded (10), and the required thickness of paper 
film tube are precisely controlled so that the paper film tube (3) can be inflated three to eight times at a distance of 
about 200 mm to about 700 mm from the forming mold gate (1). During inflation, the density of paper film (4) is 
reduced from 2 g/cm
3
of the raw materials to about 0.5 g/cm
3
. This saves the amount of volume by about 40% 
compared to the pulp density of about 0.7-0.9 g/cm
3
. The range of thickness, width, and density of stone paper 
produced can be arranged about 30-150 µm, 0.2-3.2 m, and 0.4-1 g/cm
3
respectively. [14]