PRINTING OF NYLON FABRIC

•      Nylon was the first synthetic fibre produced in commercially significant quantities.
•    The development of knitting machinery led to the production of warp knitted nylon fabric which could be heat set and dyed or printed to give material with good easy care properties.
•    Both nylon 6,6 made  by condensation of hexamethylene diamine and adipic acid and nylon 6 made from caprolactum are used in substantial quantities.
•    Nylon 11, made from aminoundecanoic acid is of much lesser interest.
•    Nylon is a compact synthetic fibre and is hydrophobic in nature.
•   It has terminal amino groups (-NH₂), terminal carboxyl groups (-COOH) and amide groups (-CONH-) along the chain.
•    Therefore, it has affinity for anionic dyes like acid dyes.
•    In acidic medium the dye-fibre forms salt formation link.
•   Acid dyes, metal complex dyes, reactive dyes and disperse dyes are used for printing of nylon fabrics.
•   The fabric is well prepared before printing so that absorbency, smooth and flat surface and whiteness can give quality prints.
•    The fabric is heat set normally in grey state at about 160°C by hot air for 30-40 seconds. Then it is scoured, bleached and optical whitened.

Selection of dyes for printing:

            Acid dyes are usually sodium salt of suphonic acid from azo / TPM / cyanine/ acrydile / xanthenes / AQ etc dye groups. It has very good affinity for nylon and gives bright prints with good fastness properties. Although, washing fastness is satisfactory. For better results metal complex acid dyes are preferred. But they do not produce brilliant prints.

            Disperse dyes can be used for printing of nylon but it give poor washing fastness, therefore, seldom used. Reactive dyes particularly Ramazol class are used to some extent. Some of the selected basic and direct dyes can also be printed on nylon.

Printing of nylon fabric with acid or metal complex dyes:

Selection of printing ingredients:

1. Acid dye is soluble in water but the addition of urea and acetic acid assists the dissolution of dye.
2. As nylon is hydrophobic in nature, takes up very little amount of water or paste, swelling agents are used for better penetration of printing paste. For this purpose carbolic acid or thidiethylene glycol is used.
3. For high colour yield it is essential to include an acid or acid liberating agent, and both. Acid liberating agents like ammonium tartarate, ammonium sulphate or sodium acetate are used. Combination of ammonium sulphate and citric acid gives good result.
4. Glycerine or pine oil can be added as lubricating agent as well as antifoaming agent.
5. The choice of thickening agent must be made from products stable at low pH and providing satisfactory adhesion and film elasticity. Modified natural products based on guar gum and locust bean gum are widely used for sharp prints and better colour value.

Printing paste recipe:

X parts	Acid dye or Metal complex dye
3 parts	Urea
3 parts	Acetic acid
20 parts	Boiling water
5  parts	Ammonium sulphate
1 parts	Thiodiethylene glycol or Carbolic acid
1 parts	Glycerine or Pine oil
Y parts	Thickening paste
100 parts	Total

Fixation Process:

            The above printing paste is well mixed, filtered and printed on well prepared fabric by suitable method and dry it.

            The printed fabric is steamed in a star ager at 10-15 lbs/inc² i.e. 110-115°C for 15-20 minutes.

After treatment process:

            Acid dyes have very good affinity towards nylon with satisfactory washing fastness, so that unfixed dye can stain white unprinted portion of the fabric. To preserve whiteness of the unprinted area and to get good quality prints, especial reserving agent treatment is given. First printed fabric is treated with 1-2 gpl reserving agent i.e. Levocol NW at room temperature. It forms complex with the unfixed dye molecules and does not allow staining.

            The treatment is followed by cold wash and soaping with 1-2 gpl NID and 1-2 gpl reserving agent at 50-60°C for 10-15 minutes. Finally rinse with hot and cold water and dry the fabric.

Printing of nylon fabric with reactive dyes and disperse reactive dyes:

Reactive dyes form true chemical bonds with NH or NH2 groups in the polyamide chain, in acid media between pH value 3 – 5. Selected reactive dyes particularly Ramazol class (Vinyl sulphone group) are preferred, which produce prints of good fastness and brilliant colours. Procinyl dyes, a disperse reactive dyes, introduced by I.C.I. also used and give prints of good washing fastness on nylon.

The thickening agent use is sodium alginate, modified locust bean gum or guar gum. Sodium alginate is widely preferred for good print paste stability and sharp prints with good colour yield.

Sodium chlorate is added with procinyl dyes in printing paste to prevent the reduction of the dye during steaming.

Printing paste recipe:

X parts	Ramazol dyes or procinyl dyes
2 - 3 parts	Urea
1 parts	Acetic acid / Formic acid
20 parts	Water
1  parts	Sodium chlorate
1 parts	Glycerine or Pine oil
Y parts	Thickening paste
100 parts	Total

Well prepare fabric is printed by above printing paste by suitable method and dried. The printed fabric is steamed at 7 – 10 lbs/inch2 i.e. 105°C for 15 to 20 minutes in s star ager.

Wash the fabric with cold water and soaped with 1 – 2 gpl NID at 60°C for 10 minutes followed by rinsing and drying.

Printing of nylon fabric with disperse dyes:

Disperse dyes have limited application in printing of nylon. They do not give prints of satisfactory fastness to washing particularly in heavy shades and the prints produced are dull. They are commonly used for printing nylon with light and medium shades.

Printing paste recipe:

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	Glycerine or Pine oil
Y parts	Thickening paste
100 parts	Total

Well prepare fabric is printed by above printing paste by suitable method and dried. The printed fabric is steamed in a pressure ager at 25 lbs/inch2 for 20 minutes or in a loop ager at 160 – 170°C for 6 – 7 minutes.

It is then rinsed with water, soaped for 10 minutes at 60°C with NID, rinsed again and dried.

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PRINTING OF POLYESTER FABRIC

CLASSROOM PRESENTATION ON 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.