Dispersing Agents
Disperse dye does not dissolve; it sits in the bath as solid particles. The job of a dispersing agent is to keep those particles apart and stop them coalescing through a cycle that runs to 130 °C.
What does a dispersing agent do?
Disperse dye is a milled solid that does not dissolve in water. During dyeing, individual dye molecules leave the particle surface and diffuse into the polyester fibre. The particles left in the bath are the reservoir feeding that flow.
Particles tend to join up. They agglomerate to lower their surface energy, and the coarse aggregates that result cannot enter the fibre. The dispersing agent adsorbs onto the particle surface and keeps that from happening.
What happens through the HT cycle?
Polyester dyeing runs around 130 °C, and that is where the dispersion is under most strain. As temperature rises the dispersing agent's hold on the particle surface weakens, while the particles collide more often.
Cooling brings a separate risk. Dye molecules that were in solution at high temperature come out again as the bath cools and grow onto existing particles. Fast, uncontrolled cooling is a common cause of the specks found at the end of a dyeing.
How does agglomeration show on the cloth?
Two faults are typical.
The first is specking. Coarse aggregates settle mechanically on the fabric surface and read as dark flecks. Reduction clearing takes out some of them; the ones that have seated deeply stay.
The second is a filtration mark, seen in package, fibre and beam dyeing. As the liquor passes through the package, aggregates are filtered out; the outer layer dyes dark and the inner layer pale. In package dyeing the dispersing agent is therefore the first thing checked.
What is the link with oligomer?
Oligomer is the polyester's own low molecular weight fraction, which migrates out of the fibre into the bath at HT temperature. As the bath cools it loses solubility and leaves a white deposit on the fabric and on machine surfaces.
Some dispersing agents for disperse dyeing are formulated to hold oligomer in suspension as well. That function feeds straight through to how often the machine has to be cleaned. Oligomer performance for the Derin Kimya products is given on the product pages: pending from the client.
What sets the dosage?
Dosage is judged together with depth of shade and liquor ratio. On dark shades the solids load in the bath is high and the demand on the dispersing agent rises with it. In short-liquor machines the same quantity of dye sits in a smaller volume, so concentration rises and stability is under more strain. The product range is on the product page: pending from the client.
Product comparison
Comparison
| Product | Description | Suitable process | Dosage | Temperature stability | Oligomer dispersion |
|---|---|---|---|---|---|
| DK EG 111 | Dispersing agent for polyester dyeing | awaiting data | awaiting data | awaiting data | awaiting data |
| DK EG 111 PLUS | Speciality dispersing agent for polyester dyeing | awaiting data | awaiting data | awaiting data | awaiting data |
Products
- DK EG 111
Dispersing agent for polyester dyeing that keeps disperse dye particles apart through the HT cycle.
- DK EG 111 PLUS
Speciality polyester dispersing agent that holds dispersion stability high on dark shades and package dyeing.
Common questions
Is a dispersing agent the same as a levelling agent?
No. A dispersing agent keeps the dye distributed as a solid in the bath. A levelling agent controls how fast dye goes onto the fibre. Some products do both, but the faults they address differ: specking in one case, unlevelness in the other.
Doesn't the dye already contain a dispersing agent?
Commercial disperse dyes are milled with a dispersing agent. That amount is enough to get the powder into water; the full HT cycle and the mechanical load in the machine call for additional dispersing agent in the bath.
Where do you look first when specks appear?
Cooling rate, dispersing agent dosage and bath pH. If those are sound, check the machine surfaces for old dye and oligomer build-up; the source is often the machine rather than the bath.
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We develop custom formulations. Tell us your process, machine type and the result you are after, and the lab will set up a trial and send a sample.