Sunday, 17 February 2013

Why some prints smell of Kerosene

This smell is normally observed in pigment printing. 

In pigment printing, thickener is used. Two types of thickeners are common. One is emulsion thickener, which has zero solid content in it. This is obtained by emulsification of two immiscible liquids with the help of the emulsifier. Generally Oil-in-water emulsions are used.

A typical recipe of pigment contains 100 parts of binder, 100-150 parts of water, 20-parts emulsifier,  Kerosene or Mineral Turpentine Oil ( MTO) is used which is 750-800 parts. Apart from this 20 parts Urea is added  as hygroscopic agent and 4-6% paste of CMC (10 parts ) is added which acts as a protective colloid. The recipe is ideal for pigment printing. However it suffers from demerits such as inflammable fire hazards, air pollution, high costs and most important of all is the smell of the fabric which is due to residual Kerosene Oil or MTO. To counter these synthetic thickeners are used. These are high weight copolymers of acrylic or methacrylic acid. They come in acid or neutralized form. They do not suffer from drawbacks of the emulsion thickeners, however, they suffer from dull prints and harsh fabric feel.  Also the drying time is longer.  

There are some printers who feel that with synthetic thickeners, there is always a concern of colors spilling over when working with very fine intricate designs and they prefer to use MTO or kerosene. 

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