Monday, May 9, 2011

Heat Setting

This operation is crucial for fabrics made of synthetic fibres (PE, PA, elastomers), for triacetate, and partly for PAC fibres (setting), since it grants excellent dimensional stabilization and crease proof properties, maintained till the fabric is exposed (by air blowing) to temperatures exceeding the heat setting one (after being treated with water at a temperature above the second order glass transition temperature, i.e. 80-85°C for acrylics).


 

Heat setting is carried out on gray fabrics (scarcely applied), on scoured fabrics (frequently applied) and on dyed fabrics (scarcely applied).


 

The process grants excellent dimensional stability and good crease-proof properties.

As far as operating conditions are concerned, the fabric must be treated in accurately controlled moisture and temperature conditions.


 

Fibre

Min T. °C

Max. T. °C

Time (in seconds)

Polyester (PE)

170

210

15-50

Polyamide (PA) 6.6

170

210

15-40

Polyamide (PA) 6

160

180

15-40

Triacetate

160

180

15-40

Acrylic (PAC)

160

180-200

15-40

Elastomers

170

180-200

15-40


 

Machines used: stenters.


 

Fluctuating temperatures inside the stenter cause a consistent variation of crystallinity in the fibre structure, which leads to different affinity for dyes.


 

The moisture in the fibre produces soft hand, but variable moisture percentages in the different fabric sections create the above mentioned defect (variable crystallinity).


 

Too low temperatures do not allow a good setting while too high temperatures and too long setting times cause yellowing (PA and elastic fibres), stiff hand (acrylics), and loss of elasticity (elastic fibres).


 

The presence of combustion gas (NOx) produces a yellowing of the elastomers.


 

The heat setting process carried out before scouring could fix the stains on the fabric or make the scouring process more difficult due to the modification of the lubricating products (cracking with emission of polluting gas).


 

Heat setting after dyeing could lead to the sublimation of disperse dyes (if not accurately selected).

Friday, May 6, 2011

Testing of Vinyl sulphone/ Mono-chlorotriazine Dyestuffs by print strike off method

Although a comparative exhaust dyeing method is always recommended for comparing two samples of dyestuffs, people in printing industry prefer to make strike off prints to compare the standard and sample.

Print Paste preparation for strike off:

Materials used

Vinyl Sulphone dyes

H/P type of dyes

Dyestuff

40 grams

40 grams

3-4% Sodium Alginate gel

720 grams

720 grams

Sodium Bicarbonate

30 grams

20 grams

Soda Ash

---

15 grams

Resist Salt

10 grams

10 grams

Urea

100 grams

100 grams

Water

100 grams

95 grams

Total

1000 grams

1000 grams


 

Method of printing:

On a well mounted RFD fabric on printing table, using the above paste prepared separately for standard and sample, two strikes off would be printed with the test screens.

After the print, gets dried properly, the fabric will be passed through saturated steam chamber (in a Star Ager) at 1050C for 10-15 minutes or dry curing chamber at 1500C for 4 to 5 minutes. This is followed by hot wash, cold wash, neutralization with acetic acid 2gpl and 2 soaping, hot and cold washes.

Final pH is set at 6 by doing an acetic acid treatment at the end of all washings.