Before jumping into disperse dye, you have to understand the disperse dye definition. From the disperse dye definition, you will get to know about some basics of this dye. Then it will be easier for you to better understand the dye structure as well as properties.
Disperse dyes are one of the major classes of dye that are non-ionic in nature and having substantivity for hydrophobic fibers especially polyester, nylon etc.
They are insoluble in water at room temperature and slightly soluble only at higher temperature. Disperse dyes have overall good to excellent light and wet fastness properties. Diffusion number of Disperse dye is measured with polyester fiber.
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Disperse Dye Definition
The Society of Dyers and Colorists (UK) provides Disperse dye definition as “a substantially water insoluble dye having substantivity for one or more hydrophobic fibers, e.g. cellulose acetate or polyester and usually applied from fine aqueous dispersion.”
As their name implies, these dyes are present in the dye bath as a fine aqueous suspension in the presence of a dispersing agent. These dyes contain micro-fine dye particles with a diameter below 1 µm as well as varying amount of dispersing agent. Disperse dye dispersion is carried out with dispersing agent.
The water dissolves a small amount of the dye in monomolecular form. The hydrophobic fibers then absorb the dye from the solution. Because these dyes are non-ionic organic compounds of relatively low molecular weight, many sublime on heating and dyeing by absorption of the dye vapor is also possible.
Fig: Partial chemical structure of lignosulphonate & alkylsulphonate and dispersing agent
Image Source: Textile Preparation & Dyeing
Already got the basic idea about its property from the above disperse dye definition, right? Let’s know detailed properties of it…..
Properties of Disperse dye:
Disperse dyes are not soluble in water.
For dyeing with disperse dye, dispersing agent is a must.
This is an organic substance that is free from ionizing group.
Overall light and wet fastness is good to excellent.
Acidic medium is used for the application of disperse dye. In strong alkaline medium, some azo disperse dye undergoes degradation and thus decreases the percent exhaustion.
These dyes are highly used for synthetic fiber dyeing like polyester, nylon, tri-acetate, di-acetate etc.
These dyes exhibit smaller molecular size than the other dyes.
Dyeing with disperse dye is carried out in high temperature. As, these dyes are mostly insoluble in water but have limited solubility only at higher temperature.
These are derivatives of azo, anthraquinone, nitro and quinine groups.
Melting temperature of this dye is 122-150℃ and they are in crystalline, powder and paste form.
Variety shades of color is possible.
On the application of heat, color will be fade.
Trade names or commercial names of Disperse dye
Classification Of Disperse Dye
Disperse dyes are classified into 5 groups. Here’s the list:
>Dyes with no suffix: They are suitable for acetates and nylon. Example: C.I Disperse Yellow 13
>Class-A dyes: These dyes have low fastness to heat treatment. These are also suitable for acetates and nylon but they are of some use of polyester. Example: C.I. Disperse Violet 1
>Class-B dyes: These dye class exhibits excellent dyeing behavior for polyester. A good coverage of physically variations as in textured yarn is also possible. The dyed materials have moderate heat fastness. These dye class is suitable for acetates and nylon. Example: C.I. Disperse Blue 56
>Class-C dyes: These dyes giver better heat fastness than class B dyes. No matter what process is chosen for dyeing polyester such as carrier method, high temperature method and pad-thermosol method, these dyes are all-round suitable. Example: C.I Disperse Orange 30.
>Class-D dyes: These dyes have maximum heat fastness including resin finishing. They are intended for particularly polyester dyeing. It is recommended to use high temperature or pad thermosol method for dyeing polyester. They are not suitable for carrier method. Nylon can also be dyed with these dyes.
Chemical Structure Of Disperse Dye
Various structures are found in disperse dye. These are:
Azo dyes are the largest and most important group covering yellow, orange and red hues. These are cheap dyes. Don’t need numerous intermediate process while manufacturing.
Where, R1 = electrophilic group
R2 and R3 = H or electrophilic groups
R4 and R5 = H or neucleophilic groups
R6 and R7 = H or alkyl or substituted alkyl groups
>C.I Disperse Orange 5
> C.I Disperse Red 19
>C.I Disperse Orange 30
> C.I Disperse Blue 183
> C.I Disperse Red 73
A small dye class covering just yellow and orange hues. Lower cost, ease of manufacturing, very good fastness to light and ability to produce green color with blue antraquinone dyes makes this dye class special.
Example: C.I Disperse Yellow 42
Large and important dye class of disperse dyes. From greenish yellow to bluish green, all colors can be covered by this dye class.
>C.I Disperse Yellow 77
> C.I Disperse Orange 5, 6
> C.I Disperse Red 86
> C.I Disperse Blue 73
>Methine (Styryl Dyes)
This is a small dye group. This is specially intended for producing greenish yellow.
These dyes are particularly used for producing bright colors. These dyes possess a good color build up property, good fastness to light along with high degree of stability like anthraquinone dyes.
>C.I Disperse Yellow 54
> C.I Disperse Yellow 206
Image Source: Textile Preparation & Dyeing
Diffusion number of Disperse dye
A polyester film is wrapped around a glass rod and dyed with disperse dyes under simulated conditions. At the end of dyeing the number of layers dyed is counted and designed as diffusion number of the dye. These number provide a basis of selection of dyes for producing combination shades.
To Wrap Up!
Disperse dyes are an important dye class for hydrophobic fibers. Nowadays, the popularity for synthetic fibers like polyester increases the popularity of Disperse dye also. In our industry, polyester is now widely dyed with disperse dye.
Salma Hasin Shila, the author of this site completed her BSc. in Textile Engineering (Wet Processing Engineering) from www.butex.edu.bd (BUTEX). She has a passion for textile technology and loves to write about it. She wants to share her knowledge to help the students in their studies and businessman & entrepreneurs in their business in making wise decisions fast.