How Stone Paper is Made
Stone paper‘s manufacturing process is fundamentally different to tree-based paper, and much more difficult than traditional plastic manufacturing. It’s also an art that not many people get the chance to see, as there are only a handful of manufacturers around the world. Pebble is the first company to take you on a personal tour of a stone paper plant and explain the innovative process behind it.
The 5 Steps to Making Stone Paper
There are five key steps to producing stone paper which will be highlighted in this article. From beginning to end, these steps are:
- Raw Materials
- Pellet Making
- Surface Handling
1. Raw Materials
Stone paper starts out as calcium carbonate rocks, which are usually sourced as waste from marble quarries. These stones are gathered in a large deposit on-site. The inside of these stones is what is necessary for the main component of stone paper, as it is a pure, natural white.
The rocks are taken from the on-site deposit into a grinding mill, where the impure outer layer of the stones is carved away, and the inner core is ground into a powder finer than flour. This powder is collected in bags in a neighboring warehouse in a supply enough for the production requirements. The grinding mill is deactivated completely when not in use.
3. Pellet Making
This is where the main ingredient for stone paper production is created. A small amount of high-density polyethylene is mixed with the calcium carbonate powder to create pellets that have the complete composition of stone paper. At this step, the difficulties with material ratios begin.
After pellets leave the pellet making process, they are melted into a malleable consistency that resembles the same process as plastic foil manufacturing. Only this step is far more difficult than traditional plastic, because stone paper has such a large component of calcium carbonate. At this step, the temperature and extrusion speed must be closely controlled to ensure high quality. This is why extrusion machine is calibrated for one specific paper thickness.
5. Surface Handling
After step 4, the paper is actually usable if it’s not being printed. Some packaging applications use raw stone paper for example. But if it needs to be decorated, the surface must be coated to make it receptive to printing inks. This last step is where the double surface handling takes place, turning the raw material into paper and board series, named accordingly as RPD and RBD.
Finally, the the paper is weighed, packaged, and shipped out to the customer. The leftover waste from this process is also recycled back into stone paper for the next batch.