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Thursday, 9 June 2016

PRINTING OF POLYESTER FABRIC


Printing of polyester with disperse dye:


Polyester is a hydrophobic fibre, compact in structure and non-polar fibre so water soluble or ionic dyes cannot be applied on polyester. Special dyes called disperse dyes, which are insoluble in water, are the most suitable dyes for printing polyester. Commercially available disperse dyes are coralene, foron etc. They give good colour value with good fastness properties under acidic pH. Excellent wet fastness properties are obtained, provided that the fixation and after treatment processes are correctly carried out.

The selection of the thickening agent depends on fabric structure, printing method, solid content of thickener and fixation method. High solid content thickeners like crystal gum or british gum give optimum sharpness of outlines, but form brittle films that crack and scatter dye by ‘dusting off’. The lower solids content thickeners such as alginates and locust bean (modified), form elastic films and are easily washed out. As they are costly than high solid content thickeners, often mixture of both or mixture with starch ethers is used.

Now-a-day, TKP is widely used as thickener in printing of polyester due to cost factor and ease of availability. TKP also give good sharpness but colour value as compared to guar gum is little less. A combination of guar gum and TKP gum is also used for better result.

Emulsion thickening paste is used in case of prints to be fixed by thermofixation method. Now a day use of synthetic thickeners is increases day by day due to ease of availability and constant quality.

Disperse dyes on polyester applied in an acidic pH for that non-volatile organic acid like tartaric acid or citric acid or acid liberating agent like sodium acetate, ammonium sulphate or ammonium tartarate is used to maintain pH 4.5-5.5.

A mild oxidizing agent like sodium chlorate is used to prevent reduction of the dye during steaming.

Swelling agent like Noigen EL-40 is added in print paste where print is going to fix by pressure steaming.

Glycerin or PEG 400 is added as lubricating agent in paste.

Printing paste recipe:

The content of the print paste will depend on the fixation method to be employed.

X parts
Disperse dyes
1 - 2 parts
Dispersing agent
20 parts
Boiling water
1 – 2 parts
Tartaric acid or Citric acid
1  parts
Sodium chlorate
1 parts
Non ionic swelling cum penetrating agent
1 parts
Glycerin or PEG 400
Y parts
Thickening paste
100 parts
Total

For fixation in super heated steaming or thermofixation, dyes fast to sublimation are preferred. In case of fixation by super heated steam, fixation accelerator like Levocol HTS is added in pace of swelling agent. Fixation accelerator accelerates the rate of dye fixation during short period at high temperature steaming. In case of fixation by thermofix method, fixation accelerator along with hygroscopic agent like urea is used.


The well prepared polyester fabric is printed by suitable method using above printing paste and dried. The fixation of disperse prints on polyester can be carried out by following methods.

1. High Pressure Steaming
Pressure: 25 lbs/inch2 or 2.5-3 kg/cm2
Temperature: 125-130°C
Duration: 30 minutes
Machine: pressure ager or star ager
Outcome: give full colour value

2. Super  Heated Steaming
Pressure: atmospheric pressure
Temperature: 160-175°C
Duration: 8 minutes
Machine: loop ager
Outcome: give very bright prints

3. Thermofixation
Pressure: hot air
Temperature: 200-210°C
Duration: 1 minutes
Machine: curing, polymerizer or stenter
Outcome: little dull shades produced with 10-15% less colour value

After treatment:

The fabric is then rinsed first with cold water, then reduction clearing treatment is given at 60°C for 15 minutes in a bath containing 2 gpl hydros, 2 gpl sodium hydroxide and 2 gpl NID to improve washing and rubbing fastness of the prints. The process is followed by rinse with hot water first and then with cold water and finally with cold acidic water to neutralize printed fabric.




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