Natural latex is a liquid compound harvested from the rubber tree (Hevea Brasiliensis), an important crop in Southeast Asia. When collected from the rubber tree the liquid is mixed with ammonia and TMTD/ZnO to maintain its properties. Standard rubber latex (low ammonia content) is used as a raw material for the manufacture of balloons, gloves, sanitary ware, etc., but also for foamed rubber products such as pillows and mattresses.
The production process of latex pillows
Origin of the DUNLOP process
In 1887 John Boyd Dunlop (1840–1921) was born in Scotland. He invented the first inflatable tire for his son’s tricycle based on the thermal vulcanization of natural rubber. It was then patented on December 7, 1888. However, two years later, the patent was officially canceled because another Scottish inventor, Robert William Thomson (1822-1873), patented the technology. The same was done in Great Britain, France (1846), and in the United States (1847). However, the process was named after Dunlop and became the primary system for vulcanized rubber and foam latex products.
There are two standard industrial processes used to produce foam rubber: DUNLOP and TALALAY production processes.
The Talalay process, was invented in late 1940, is more time-consuming and more complex than the Dunlop process. It is used by a few manufacturers worldwide and has a small market share. The base material in both systems is natural latex (NL) or SBR-latex (styrene-butadiene rubber), or a combination of both.
Dunlop foam process
In the case of pure natural latex, the latex “or latex milk” will be mixed with the necessary chemicals. When cured for the specified time, the latex compound will be foamed with a foam mixer. A gelling agent was then added to accelerate the formation of a stable foam structure (in the case of SBR, SBR-latex can foam without curing), then added to the metal mold. The molds are placed in a steam oven or tunnel to vulcanize or ripen. Because foam products are good heat insulators, the mold is therefore equipped with a number of pins to transfer heat to the foam body. When the vulcanization is complete, the pillow or mattress is removed from the mold, washed, dried, and finally ready for sale.
Talalay foam process
In the Talalay process, there are 3 different pre-vulcanization or ripening steps than the Dunlop process.
1) Only 40-60% of the foam latex compound is added to the mold, then closed and inflated to create a vacuum to inflate the foam to the full volume of the mold.
2) The foam is frozen at -20°C to keep the structure stable.
3) CO2 is injected through the valve into the mold to make the foam gel or maintain its shape.
The rest of the processes follow the same steps of the Dunlop process: vulcanization, mold removal, washing and drying.
Dunlop’s original vulcanization process uses steam as a heat medium to catalyze the polymer chain bonding reaction. Foams with many micro bubbles are naturally a bad conductor of heat. Therefore, allowing heat to seep into thick mattress cores or pillow molds is a slow and inefficient process. In fact, expensive heavy metal molds equipped with many pins are used to try to speed up the process. But it still takes a lot of time and energy.