Printing

Textile Printing

- Methods & Styles

- Ingredients of Printing paste

- Printing paste preparation

- Fixation & after-treatment process

May, 2016

Dr. RAMESH DURAISAMY

Asso.Professor, Dept. of Chemistry

College of Natural Sciences, Arba Minch University

Arba Minch, Ethiopia (East Africa)

Printing• Printing is the process of applying color to fabric in defined areas to obtain

the desired pattern.

• In properly printed fabrics the color is bonded with the fiber, so as to resist

washing and friction.

• Textile printing is related to dyeing but, where as in dyeing proper the whole

fabric is uniformly covered with one color, in printing one or more colors

are applied in certain

parts only.

• Textile printing is one of the procedures of textile decoration. Textile

printing requires the correct coordination between the printing machinery

support and the human skill for producing the best of the results.

• In printing, wooden blocks, stencils, engraved plates, rollers, or silk screens

are used to place colors on the fabric.

• Pigment dyes and reactive dyes are used in the company.

There are broadly categorized into four types of printing:

(i) Direct printing

(ii) Mordant printing

(iii) Resist printing

(iv) Discharge printing

Direct printing, in which colorants containing dyes, thickeners, and the

mordant or substances necessary for fixing the colour on the cloth are

printed in the desired pattern.

Printing of a mordant in the desired pattern prior to dyeing cloth; the

colour adheres only where the mordant was printed.

Types / Styles of Printing

Resist printing, in which a wax or other substance is printed onto

fabric which is subsequently dyed. The waxed areas do not accept the

dye, leaving uncoloured patterns against a coloured ground.

Discharge printing, in which a bleaching agent is printed onto

previously dyed fabrics to remove some or the entire colour.

Printing is carried out with different instruments. Different methods are use

to produce impression on fabric. Methods of printing differ on the demand

of user. Also, it depends on the materials type and type of purpose of end

product use. The following methods can be applied for textile printing

operation. They are as follows:

1. Block printing 10. Photo printing

2. Burn-out printing 11. Rotary Screen printing

3. Blotch printing 12. Screen printing

4. Digital printing 13. Stencil printing

5. Duplex printing 14. Jet spray printing

6. Engraved roller printing 16. Transfer printing

7. Electrostatic printing 17. Warp printing

8. Flock printing 18. Spray printing

9. Ink-jet printing 19. Tie and Batik dyeing (special method)

Methods of Printing

Printing Machine

Machine Name Type

1 Ichinose Rotary Screen Printing Machine

1 Baby Screen Printing Machine Rotary Screen Printing Machine

1 Strike Off Manual flat-bed screen printing

Manual Flat-bed

Screen Printing M/C

Rotary Screen

Printing M/C

Hand Screen Printing

Screen Printing consists of three elements :

Mesh Stencils Squeeze

PurposeSampling Process Check the out come

Hand screen printing

• Printing process involves following steps:

The print paste is prepared using binder, water and dyestuff.1 kg

binder is used for every 10 g of color.

The table top is a sandwich of a rubber blanket, a cotton fabric and a

resin coated screen.

The fabric is glued on to the table top & the screen is placed over the

fabric; the print paste is poured over it and spread on the fabric

manually by a wooden squeegee.

Rotary Sample Printing Machine

• Sampling Machine

• To check the fabric in garment form.

Machine used

–

Baby Rotary screen printing

Machine Parts -

• Transporting Roller

• Crease Removing Roller

• 14 Printing Rollers

• Nickel Screen

ROTARY SCREEN PRINTING

• Name of the machine – Ichinose

• Used for the bulk production.

• Average speed of m/c - 16 m/min.

• Average productivity – 8000-10,000 m/shift

• Maximum no. of screen possible – 14

• Speed : complexity of design increases –

speed of the production decreases.

• Average speed - 16 m/min

Steps in Printing Process

A typical Printing process involves:

Preparation of print paste

Printing of fabric

Drying

Fixation of dyestuff

Washing-off

1. Preparation of printing paste: Type of specific formulation used

depends on the fibre, the colorant system used and to some extent the

type of printing machine.

2. Printing of fabric: Dye or pigment paste is applied to the

substrate using different techniques.

3. Fixation (Drying): Immediate after printing, the fabric is dried and

then the prints are fixed mainly with steam or hot air (for pigments).

Note that intermediate drying is not carried out when printing carpets

(too much energy needed for removing the highly viscous liquor).

4. After-treatment (Washing)

This final operation consists in washing and drying the fabric (it is not

necessary when printing with pigments or with other particular

techniques such as transfer printing).

Cont..

DYE USED RECIPE TREATMENT COMMENTS

Pigment Dyes

Pigment + binder +

thickener + softener +

surfactant + urea

(hygroscopic agent) + anti

choking agent (if required).

Print-dry-cure (at

150˚C, for 5-6 min)

Low cost + Time

Saving

Reactive Dyes

Sodium Alginate +

NaHCO3 (fixing agent) +

Hexa Metaphosphate (water

softener) + Soda Ash

(Oxidation) + urea

(hygroscopic agent)

Print-dry-ageing (i.e.

steam 102˚C)- wash-

saturated steam

Nil

Discharge Printing

Binder + Urea (hygroscopic

agent) + thickener (HEF) +

Softener + Pigment

Print-dry-ageing (i.e.

steam 102˚C)- wash-

saturated steam

Rangolite SE (for

discharge)

PRINT PASTE INGREDIENTS

Essential Ingredients of Printing paste

The ingredients found in paste formulations includes:

Dyes or pigments, thickeners, sequestering agents, dispersing or

suspending agents (surfactants), water-retaining agents (humectants),

defoamers, catalysts, and hand modifiers.

• In addition to the ingredients, pigments require a binder or resin

system to fix the pigment and may include adhesion promoters

• For blended fabrics pigments are used, which are not dyes but are

colored particles glued to the surface of the fabrics.

Printing pastes are made up of four main components:

The coloring matter used (dyes or pigments)

The binding agent

The solvent

The auxiliaries

Coloring matter: Either dyestuffs or pigments. Dyes are in solution and

become chemically or physically incorporated into the individual fibers.

The dyes used for printing mostly include vat, reactive, naphthol and

disperse colours which have good fastness properties.

Pigments are largely insoluble, so often organic solvents are used

(such as benzene or toluene).

The pigmented printing paste must physically bind with the fabric, so

must contain a resin, which holds the pigment in place on top of the

fabric.

Cont..

Binder: Responsible for the fastness of the pigment prints during use.

The most important fastnesses are wash fastness, chemical cleaning

fastness and friction fastness.

Binders are “self-crosslinking polymers” mainly on acrylates,

butadiene and vinyl acetate, with solid contents of approx.. 40 - 50%.

Binders made of natural wood resin, wax stand linseed or safflower

oils and chitosan , when using chitosan as a binder, and no solvent is

necessary.

Solvents: Usually added in the formulation of the thickeners.

Type of paste (emulsion or plastisol) and thickening agent determines

the type of solvent needed.

White spirit is commonly used organic solvent.

The organic solvent concentration in print pastes may vary from

0 - 60% , with no consistent ration of organic solvent to water.

Cont..

Generally, the auxiliaries used for printing are the same as those used in

dyeing with a dye bath. These types of auxiliaries include:

Thickener: To make viscous paste of dyes in water, a thickener is used.

Thickeners used depends on the printing technique and fabric and

dyestuff used.

Thickening agents are starch derivatives, flour, gum Senegal and gum

arabic and albumin and sodium alginate.

Starch used to be the most preferred of all the thickenings, but

nowadays gums or alginates derived from seaweed is preferred as they

allow better penetration of color and are easier to wash out.

Wetting agent: It helps in obtaining a smooth paste of dyes without any

lumps, for example: TRO and ethylene oxide condensator.

Cont..

Defoaming agent: Formation of foam during print paste preparation and

application is quite common but should be avoided. Foam may produce

specky dyeing. The antifoaming agents help in foam generation.

E.g. Silicon compounds, organic & inorganic esters, aliphatic esters, etc.

Acid or alkali: Depending on the types of dyes used in printing, acid or

alkali is used in the print paste. An acid liberating salt is commonly used,

For example ammonium chloride and diammonium hydrogen phosphate.

For reactive printing on cotton, sodium carbonate or sodium bicarbonate

are used.

Cont..

Oxidizing or reducing agent: They are used in printing with solubilized

vat colors and also in discharge and resist printing. Discharging agents

such as sodium sulphoxylate formaldehyde are used in the discharge

printing. E.g. m-nitrobene sulphonate, sodium chlorate, H2O2, sodium

dithionite, formaldehyde sulphoxylates, thiourea dioxide, tin (II) chloride

Hygroscopic agents: The function of hygroscopic agents is to take up

sufficient amount of water (moisture) during steaming to give mobility to

the dyes to move into the fibre. Eg. Urea and Glycerin.

Cont..

Dispersing agent: Dispersing agents are necessary in the print paste to

prevent aggregation of the dyestuff in the highly concentrated pastes.

E.g. Diethylene glycol.

Preservatives: Used to prevent the action of bacteria and fungus to make

it dilute. E.g. Salicylic acid.

Carriers: Cresotinic acid methyl ester, trichlorobenzene, n-butyl

phthalimide in combination with other phthalimides, methylnaphthalene)

Retarders: Derivatives of quaternary amines, leveling agents

Resist agents: zinc oxide, alkalis, amines, complexing agents

Metal complexes : copper or nickel salts of sarcosine or

hydroxyethylsarcosine)

Cont..

There are two main types of paste used:

1. Pigmented emulsions: Pigmented emulsions are suitable for all fiber

types, they are able to dry by evaporation at room temperature and are

able to be cured at 320F for 2 - 3 minutes, which achieves washing and

dry cleaning fastness. A typical formulation of a pigment emulsion

printing paste is:COMPONENTS RATIO

Water 10%

Emulsifier 1%

Thickener 4%

White spirit 62%

Catalyst solution 3%

Binder 15%

Pigment dispersion 5%

Pastes which are entirely

water-based are obtained

by replacing the white

spirit with water.

Types of printing paste

2. Plastisol printing pastes: Based on a vinyl resin dispersed in

plasticizer; characterized by virtually 100% non-volatility (no solvent is

present); used frequently for printing on dark or dark-colored

fabrics. Components of plastisol printing pastes consist of

PVC homopolymer (i.e., a vinyl resin) dispersed in phthalate

plasticizer;

liquid plasticizer (i.e., dialkyl phthalate or di-iso-octyl phthalate);

heat and light stabilisers (i.e., liquid barium/cadmium/zinc

combined with epoxy plasticizer);

high proportion of extender to improve wet-on-wet properties.

Cont..

Printing paste preparation

All the necessary ingredients for the paste are metered (dosed) and

mixed together in a mixing station.

Since between 5 and 10 different printing pastes are usually necessary

to print a single pattern.

In order to reduce losses, due to incorrect measurement, the

preparation of the pastes is done in automatic stations.

In modern plants, with the help of special devices, the exact amount of

printing paste required is determined and prepared in continuous mode

for each printing position, thus reducing leftovers at the end of the run.

Fixation processes After printing, the fabric is dried. Water evaporation leads to an

increase in dye concentration and at the same time prevents the

colours from smearing when the fabric is transported over the guide

rollers. At this stage the dye is not yet fixed.

The aim of the subsequent fixation step is to transport as much as

possible of the dye, which is retained by the thickener, into the fibres.

This is especially important with dyes, such as vat dyes, for example,

that are printed in the insoluble form and are converted into the

corresponding soluble state only after reaction with the reducing

agents during the fixation process.

Fixation Methods

1. Atmospheric steam

Treatment at 2120F with saturated steam.

Used with direct dyes, vat dyes, napthol dyes, acid dyes, cationic

dyes, reactive dyes.

Festoon steamer most common equipment

Acid agar for acid dyes.

2. Pressure steam

Treatment at 2300F under pressure

Used with disperse dyes

Turbo-autoclave most common equipment.

3. High temperature steam

Treatment with superheated steam at temperature up to 4200F.

Used with disperse dyes and pigments

Can also be used as an atmospheric steamer.

4. Dry heat

Treatment with dry heat at temperature up to 4200F.

Used with disperse dyes and reactive dyes.

Cont..

Fixation Methods after Printing with Disperse Dyes

After printing with disperse dyes the dyes is fixed on the

fabric by one of the following dye- fixation methods,

1. Thermo fixation

2. Super Heated Steaming

3. High Pressure Steaming

The features of this method of dye fixation are:

1. No steam is used.

2. Dye is fixed by subjecting the print to hot air at 2100C for 1 minute.

3. The fixation is carried out in a backing oven or in a stenter where heat

setting can also be done simultaneously.

4. The process productivity is high.

5. The dye which have good sublimation fastness are subjected to this

thermofixation process.

6. There is 10-15% loss of colour in thermofixation, so the shade

becomes dull.

7. It is a continuous process of dye fixation which gives high production.

Thermofixation

Super Heated Steaming

The features of this method of dye fixation are:

1. It is a continuous process of dye fixation.

2. This method is the best of the three methods.

3. Dye is fixed at 1000-1800C for 2-1 minutes by radiators.

4. Higher productivity.

5. No loss of color.

6. Dyes with medium sublimation fastness can be applied.

7. The fabric handle is very soft.

High Pressure Steaming

The features of this method of dye fixation are :

1. Discontinuous process of dye fixation

2. Low productivity.

3. Dye fixation is done by high pressure steam.

4. Low production so costly process.

5. Dyes with low sublimation fastness can be applied.

6. It gives good Colour yield and bright print & smoothness.

The Essential Requirements in all Print Fixation Processes

The pick-up of enough water to swell the thickener film, but not so

much as to cause the print to spread.

Dispersion and solution of the dye, and production of a liquid medium

through which the dye can diffuse to the fibre surface.

Absorption of water by fibres such as cotton, nylon and wool, which

must be swollen to allow penetration of dye.

Raising the temperature to a level that accelerates the processes of

diffusion, especially into the fibre.

In some cases steam can satisfy all the requirements but, as in all

coloration processes, auxiliary chemicals may be introduced to assist dye

solution and diffusion, or to make the process less critically dependent on

the maintenance of ideal conditions.

Printing defects

Some of the printing defects are:

Improper positioning of print

Fluff

Sharpness/blurr

Joint marks