According to a dictionary Tupperware is a company name and refers to their products.
In the daily conversation the word is used also for other company's plastic container? Or just for their products?
As a native English speaker, I use "Tupperware" for general plastic containers, not just for specifically Tupperware's products. In the same way, many people use "Kleenex" instead of "tissue" even though Kleenex is a brand name.
Tupperware
is an example of a generic trademark there are many other examples: Kleenex, Xerox, Thermos, Zamboni, Chap Stick, where the trademarked name is used to refer to the functional object.
Tupperware is usually used to refer to plastic containers with formed sides and snap close lids for carrying leftover food. Similar foodstock containers are made by Rubbermaid, Hefty, and Ziploc, and they are often generically referred to as "Tupperware".