Print Paste Ingredients and Fabric Dyeing


Printing

Printing is the process of applying color to fabric in definite patterns or designs. Printing can also be defined as localized area of dyeing.

So, textile printing is related to dyeing but in dyeing, the whole fabric is uniformly covered with one color, whereas in printing one or more colors are applied to a certain part only.
Usually color is applied on the fabric using colorants and chemicals in a paste form in a predetermined design.

Printing paste

The printing paste is a mixture of colorants and thickener along with some auxiliaries 
chemicals such as acid or alkali, hygroscopic agent, surface active agent etc.

The purpose of print paste is to produce a medium for the dye or pigment, so that it can be easily applied on fabric or garments as per design or requirements.

Printing ingredients

The essential ingredients of a printing paste are selected from the following chemicals –
1. Colorant (dyestuffs or pigment),
2. Thickener,
3. Wetting agent
4. Solvent.
5. Dispersing agent for printing with disperse dye.
6. Hygroscopic agent
7. Acid or alkali,
8. Reducing chemicals,
9. Oxidizing agents,
10. anti-foaming agent.
11. Mild oxidizing agent (Resist salt).

Functions of the ingredients

The print paste ingredients are used for the following purposes –

1.Colorant (Dyes/ Pigment)

Dyestuff or pigment is used to produce required shade i.e. color effect on fabric. Direct dye, reactive dye, pigment color etc. are used to produce particular shade and color effect on the fabric. Details of the dyes and pigment will be discussed later.Dye-stuff is selected on the basis of the following factors –

  • The shade and color effect to be produced.
  • The quality and nature of the fabric.
  • The end use of the fabric.
  • The cost of the fabric.
  • The fastness properties of dyes.

Example: Direct dye, reactive dye,pigment,color etc.

2.Thickener

Thickener is the main ingredient of printing paste. It is a thick, viscose substance which imparts stickiness to the print paste. The main functions and objects of a thickener are –

  • To maintain a sharp outline of printed design.
  • To prevent bleeding or spreading of color effect.
  • To prevent the premature reactions among the chemicals of the print paste.
  • To hold the ingredients of the print paste on the surface of fabric and in the print paste.

Example: Na-alginate, fine gum, starch tragacanth, British gum, C.M.C, PVA etc.

3.Acid and Alkalis

Acid or alkali is used to maintain required pH and fix the dye molecule with the fiber. If acidic condition is required during steaming or curing, an acid liberating agent is used. 
And a suitable alkali is used, if alkaline condition is needed.
Acid: Organic acid such as; CH3-COOH, ammonium salts of mineral acids
Alkali: Sodium carbonate, Sodium hydroxide, Sodium bi-carbonate etc.

4.Wetting agent

Wetting agent is a surface-active agent, which reduces surface tension of water and allows all the materials to wet very easily.

If wetting agent is not used in print paste the light dye particles will float on the solution and the heavy particles will be stored and create a layer underneath. The functions of wetting agent are –

  • To reduce the surface tension of water.
  • To make the print paste smooth.
  • To dissolve the dye stuff in the paste.
  • To help the dye molecules to penetrate inside the fibers easily.

Example: Glycerine, Turkey red oil, olive oil, lethofene.

5.Solvents or solution aids or dispersing agents

Solvents are used to prevent aggregation of dye stuff molecules in the highly concentrated dye paste i.e. to disperse the dye molecule uniformly. The functions of a solvent are –

  • To increase solubility of dye.
  • To spread the dye molecules evenly in print paste.
  • To create a medium.

Example: Hot water, solution salt B, methylated spirit, diethylene glycol.

6.Dispersing agent

In case of printing with disperse dyes, we have to use dispersing agent. As the disperse dyes are insoluble in water they are dispersed in the thickening emulsion evenly by the help of dispersing agent. So in case of printing with disperse dye, dispersing agent act as a solvent.

7.Hygroscopic agent

After print paste application on fabric, steaming is carried out to fix dye molecules with fiber. In this steaming process, steam is absorbed by the print paste and this absorption is increased by using hygroscopic agents.

So, hygroscopic agent helps to penetrate the dye paste into fiber polymer system during steaming.
Example: Urea, glycerine etc.

Role of urea during fixation of dye with fiber

  1. Water is evaporated during drying of printed fabric
  2. So, no water is present at the time of fixation (i.e. steaming) at 140 to 150oC
  3. No ionization of dye and cellulosic fiber
  4. No dye fixation will occur
  5. Urea melts at 132oC
  6. Provide molten bath in printed fabric at fixation temperature
  7. Dye dissolution and fiber swelling in presence of urea
  8. Finally, dye fixation is occurred with fiber

8.Oxidizing or reducing agent

Oxidizing agents develop final color in steaming or in the subsequent after treatment, assist in color fixation. Reducing agents destroy color from the fiber i.e. fabric. 
Moreover, in case of insoluble vat and sulphur dyes reducing agents are used to make them soluble.
Example: NaClO3, KClO3, NaNO3 are oxidizing agents. Rongalite-C, stannous chloride,sodium hydro-sulphite, sodium sulphide are reducing agents.

9.Carriers and swelling Agents

Carriers accelerate the rate of dye penetration into the fiber polymer, swell the fiber and reduce crystallinity. It is used in case of polyester fabric dyeing.
Swelling agents: Resorcinol, phenol, polyethylene glycol etc.
Carrier: Diphenyl

10.De-foaming agents or anti-foaming agents

The anti-foaming or de-foaming agent is used to prevent the formation of foam during continuous agitation of paste. If any foam creates dyeing will be uneven.
Examples: silicon defoamers, emulsified pine oil.

11.Mild oxidizing agent

Mild oxidizing agents prevent the reduction of dyes (e.g. azo dyes) during steaming. 
They also protect the strength of textiles.
Examples: resist salt-L, sodium chlorate.

Steps or stages of printing

Printing is carried out in various stages such as –
1. Preparation of the fabric.
a) Singeing b) desizing c) scouring d) bleaching e) mercerizing.
 ↓
2. Preparation of the printing paste.
 ↓
3. Application of print paste on the fabric (as per buyer requirement)
 ↓ (Using different types of style and method)
4. Drying of the printed fabric (800
to 1000
c by dryer for 3 to 5 minutes)
 ↓
5. Steaming or curing of the printed fabric (for the fixation of dye and fiber)
 ↓ 140-1500
c for 30 to 90 seconds 
6. After-treatment
a) Washing (Soap or detergent wash).
 ↓
7. Finishing (e.g. Softener application)

Styles of printing

Style refers to the manner by which a particular action is performed. Styles of printing mean the manner in which a printed effect is produced. 

The different styles of printing are–

1. Direct style of printing
2. Discharge style of printing.
3. Resist style of printing.
 
In broad sense the styles of printing are classified as below–
Printing style

Direct style

Discharge style 
a)White discharge 
b)Colour discharge.
Resist style 
a) White resist 
b)Colour resist.

1.Direct style of printing

In this style, the dyes are applied directly at the required places on the fabric, leaving the other portions white, by any printing method like block printing, screen printing etc. So,this style is called direct style of printing.
After printing, fabric is dried and steamed to allow the dye molecules to penetrate inside the fiber polymer and make a bond between dye and fiber polymer. 

Then the thickening agent and other chemicals are removed by washing, rinsing, soaping etc.
Direct dyes, vat dyes, reactive dyes etc are used in direct style of printing.

2.Discharge style of printing

Discharge means removal and discharging style means the process which can produce a white or coloured effect on a previously dyed ground.
This discharging of colour from previously dyed ground is carried out by a discharging agent, which is actually an oxidizing or reducing agent capable of destroying colour by oxidation or reduction.

This discharging agent is added in the print paste.
So it is carried out two steps

First step:

Dyeing – the fabric is dyed firstly with an easily reducible dye.

Second step:

Print Paste Ingredients and Fabric Dyeing
Discharge style of printing


Printing – the fabric is printed with a thickened solution of discharging agent. This discharging paste destroys the colour at the printed areas and leaves the dye of unprinted areas unaffected.

At the same time if any dye is present in the thickened solution of discharging agent, which is not affected by its discharging action can also be deposited and fixed on the ground.
There are two types of discharge style of printing.

1.White discharge

After dyeing and printing, the discharging agent discharges the dye of printed areas and leaves the dye of unprinted areas unaffected. So, a white design is produced on the coloured ground.

2.Colour discharge

Dyestuffs which are strongly resistant to discharging agent are included in the printing paste along with discharging agent. The discharging agent of print paste discharges the colour at the printed area. At the same time the dyestuff of print paste deposits and fixes itself on the ground. As a result, a colour discharge effect is obtained. In this way one or more colours may be applied.

Discharging agents may be 

a) Oxidizing agent – Potassium chlorate, Na-chlorate.
b) Reducing agent – Rongalite –c,stanneous chloride.

3. Resist style of printing

Resist means to hinder. In this process, a chemical is applied to the fabric with the help of print paste that will prevent the fixation of any color employed afterwards on that area. 

The style consists of two steps –

First step

Printing – at first the fabric is printed with a resist salt.

Second step

Print Paste Ingredients and Fabric Dyeing
Resist style of printing

Dyeing – then the fabric is dyed with a suitable dye.
As a result the area covered by the resist salt will not be dyed and the other portions will be dyed. So a printed effect is obtained. The resisting agent used depends on the class of dye to be employed afterwards.
There are two types of resist style of printing

1.White resist

If no colour is added in the print paste solution along with resist salt, after dyeing the printed area remains white. This is called white resist.

2.Colour resist

If any colouring material is added in the print paste along with resist salt, after dyeing the printed areas show no change of color while unprinted areas get color effect from dye solution. As a result coloured resist effect is obtained.

Differences between discharge and resist style of printing:

Discharge style 

  • In discharge style of printing, discharging print paste is applied on the fabric after it has been dyed. This agent destroys the dye in printed areas.
  • At first fabric is dyed. Then discharging occurs.
  • More wastage of dye occurs.
  • Relatively low chemical stability and low fastness property of printed fabric.

Resist style

  • In resist style of printing the resisting agent is mixed with the print paste and the thickened solution is printed on a white ground. Then the fabric is dyed.
  • At first with resisting print paste the fabric is printed. Then the fabric is dyed.
  • Less wastage of dye occurs.
  • Printed fabric has great chemical stability and better fastness properties.
Textile Academy is a Professional textile education Platform. Here we will provide you only interesting content, which you will like very much. For further Information and question contact us via email. 

Leave a Comment