Other Auxiliary Chemicals

As padded fabric dries, liquor moves toward the surface and carries the dye with it. The result is two-sidedness and shade variation across the width. A migration inhibitor restricts that movement. Derin Kimya's other auxiliaries category holds one product for this job.

What is migration and when does it happen?

When padded fabric enters the dryer, the water evaporates. Evaporation happens at the surface, so liquor from inside the cloth moves outward by capillary action and carries dissolved dye with it. By the end of drying, part of the dye sits on the outer face rather than through the cross-section.

This shows up in two ways. The two faces of the cloth come out at different depths, which is two-sidedness. And where the temperature distribution inside the stenter or dryer is uneven, a colour difference appears across the width or along the length between the fast-drying and slow-drying zones.

Migration is worst in pad-dry processes, on heavy fabrics and at high drying temperatures. The same mechanism operates in pigment printing and in coating.

How does a migration inhibitor work?

Migration inhibitors restrict how freely the liquor can move. They do it in one of two ways: by raising the viscosity of the liquor so capillary flow slows, or by binding the dye temporarily so it cannot travel to the surface during drying. After drying, the product either washes out or stays in the finish, depending on the formulation.

In practice the dosage is held within a narrow band. Too little does not stop the migration; too much thickens the liquor and produces uneven squeeze at the padder along with a stiffer handle.

Where dye migration starts at the padder and in the stenter, and where an inhibitor earns its dosage, is covered in the anti-migration agent guide.

Is migration a chemical problem only?

No. The chemical is one of three measures.

1. Pick-up. The less liquor left on the cloth, the less water there is to travel. Raising the padder pressure lowers migration directly.
2. Drying profile. Running the first zone hot to skin-dry the surface leaves an early dry layer that reduces the flow coming from inside. The opposite approach, slow and even drying throughout, works better on some recipes; which one applies is settled by trial on that fabric.
3. Migration inhibitor. This comes in where the two settings above are not enough.

Trying to cover a machine setting with a chemical leads to a dosage that keeps climbing and a handle that keeps getting worse.

Where does a migration inhibitor come up?

On pad-dry and pad-dry-pad-steam ranges the cloth enters the dryer wet, and migration is a standard risk item on both. The same movement occurs in the first drying zone of a thermosol range running disperse dyes.

In pigment printing and coating the mechanism is similar, except that what travels is pigment and binder rather than dye. Binder collecting at the surface during drying changes both the colour yield and the adhesion.

Exhaust dyeing does not carry this risk: the cloth is dyed in the bath and no free dye is left on it to travel during drying.

What is in this category?

Derin Kimya's other auxiliaries category holds one product: DK COATIN MPR, a migration inhibitor. Per-product dosage, application method and compatibility are given on the product page: pending from the client.