Preparation of Synthetic Fabrics for Printing

ð  The importance of knowing which fibre or fibres are present in a fabric has already been stressed. Because the many fibres available differ in their chemical and physical properties the method used to prepare fabrics made from them for printing also vary.

ð  Depending on the origin of their component fibres, fabrics may contain impurities. The nature of these impurities varies with different fibres, and so do the methods adopted to remove them.

ð  Such impurity-removal operations are known as Scouring treatments and they are often followed by bleaching.

ð  It is important to distinguish between chemical bleaching done with sodium hypochlorite or hydrogen peroxide, and optical bleaching.

ð  It is generally advisable to have the material supplied scoured and bleached where appropriate, ready for printing.

Polyester

ð  It is necessary to remove size from polyester fabric in order to obtain maximum colour yield. Starch is removed by enzyme desizing. When water soluble PVA is used as sizing agent non-ionic surfactant is used as desizing agent and when polyacrylic sizing agent is used non-ionic surfactant and soda ash is used as desizing agent.

ð  A simple scour to remove lubricants is given. The material is treated as below:

Lissapol D                   :           1.5  parts

Soda ash                      :           2.0  parts

Total liquor                  :    1000.0  parts

Temperature                :           70 ˚C

Time                            :           30  minutes     

ð  The bleaching carried out by treating the fabric in a bath containing

                        Sodium chlorite           :           2-3 parts

                        Formic acid                 :           2    parts for pH = 3

                        Sodium nitrate             :           1    parts

                        At boil for 1 hour.

ð  The fabric is heat-set by exposing it to a temperature of 220˚ to 230˚C for a few seconds in a stenter or curing chamber with hot air or radiant heat produced by infrared burners.

Nylon

ð  Nylon material is heat-set by dry heat at 210˚C to prevent the formation of permanent wrinkles during processing and to make it dimensional stable.

ð  Desizing and scouring is done by batch and continuous process.

Batch process              Continuous process

            Soda ash                                      1-3 gpl                                 ---

            Sodium pyrophosphate                  ---                                3-6 gpl

            Anionic surfactant                      1-2 gpl                            1-2 gpl

            Non-ionic surfactant                   2-3 gpl                            2-3 gpl

            Temperature / Time              70 ˚C /20-30 mi           90 ˚C /10-20 min

ð  Bleaching of nylon is necessary and therefore material is treated in a bath containing

Wetting agent                                     :           2 gpl

Sodium chlorite (80%)                      :           2 gpl

Sodium nitrate                                   :           2 gpl

Time / Temperature                           :           30 min / 85 ˚C

Acetic acid for maintain pH 3.5 – 4

ð  After bleaching, it is washed well and treated with Sodium bi-sulphite liquor to remove chlorine and washed.

Acrylic

ð  The fabric is scoured with Non-ionic detergent                      :           1-2 gpl

        Wetting agent                  :           2   gpl

        Formic acid (85%)          :           2   ml/l           

        Temperature / Time         :           75 ˚C / 1 hour

ð  Bleaching is carried out with

Sodium chlorite (80%)            :           2.5 gpl

Sodium nitrate                         :           3    gpl

Noigen HC                              :           1    gpl

Conc. Sulphuric acid               :           1.5 gpl (pH 3-3.5)

Temperature / Time                 :           95 ˚C / 30 min

The fabric is washed and then given an anti-chlor treatment with 2 gpl sodium thiosulphate solution at 60 ˚C for 20 mins, washed and dried.