Description: 521 synthetic resins or natural rubbers -- part of the class 520 series / 521 synthetic resins or natural rubbers -- part of the class 520 series/() synthetic resins (class 520, subclass 1) (50) cellular products or processes of preparing a cellular product, e.g., foams, pores, channels, etc. (56) particle which is expandible, process of preparing an expandible particle, or process of expanding a particle to form a cellular product (57) including step of surface coating a particle or process of expanding a surface coated particle
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