Printing Effulent

8/6/2019 Printing Effulent

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Printing Process & its role in Effluent

Printing processes

colour paste preparation

printing

fixation

after-treatment

Different printing techniques

Printing with pigments: can be used on almost all types of textilePaste Content:

o Pigment

o thickening agent

o binder

o fixing agents,

o plasticizers,

o defoamers

Pigment paste (3040% pigment content) - x gBinder (approx. 40% solid content) - 80 g + 3x/2 g

Application of printing paste dried Pigment fixation with hot air.

Advantage of pigment printing: No subsequent washing

Printing with dyes

Compared to pigment printing, the composition of the pastes is more complexand variable, being determined not by the dye used, but by the printingTechnique, the substrate, the application and the fixation methods applied.

Paste Content:o Dye

o Thickening Agent

o oxidizing agents (e.g. m-nitrobenzenesulphonate, sodium chlorate,

hydrogen peroxide)o reducing agents (e.g. sodium dithionite, formaldehyde

sulphoxylates, thiourea dioxide)o discharging agents for discharge printing (e.g. anthraquinone)

o substances with a hydrotropic effect, like urea

o dye solubilisers, which are polar organic solvents like glycerine,

ethylen glycol, butyl glycol, thiodiglycol, etc.o resists for reactive resist printing (e.g. sulphonated alkanes)

o defoamers, (e.g. silicon compounds, organic and inorganic esters,

aliphatic esters, etc.).


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Thickening stock solution:alginate-based thickening agent: 700 goxidising agent: 50 gcomplexing agent: 3 gpreserving agent: 0.5 - 1 gwater: x gTotal: 1000 g

Printing paste:thickener stock solution: 800 greactive dyestuff: x gwater: y gTotal: 1000 g

Paste Application:o direct printing (which also includes digital and transfer printing)

o discharge printing

o resist printing.

Direct Printing: dye is applied to specific areas of a pretreated textilesubstrate, which can be white or pre-dyed (in light colours)

Discharge Printing

Resist Printing


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Fixation:

Fixation with steam. Water vapour condenses on the printed material, swellsup the thickener, heats the print and provides the necessary transport mediumfor the diffusion of the dye.The distribution of the dye between fibre and thickener is an important factor indetermining the fixation degree of the dye, which is called the "retaining power"

of the thickener. The thickener, in fact, is often composed of polysaccharides andtherefore competes with cellulose in retaining the dye. This is the main reasonwhy the fixation rate of a given dye is 10 % lower in printing than in dyeing.

After Treatment: Washing, Soaping & Drying

Printing technology

Flat-screen printing

Rotary-screen printing

Roller printing

Jet printing

Environmental issues

Emission sources typical of printing processes are:

printing paste residues

waste water from wash-off and cleaning operations

volatile organic compounds from drying and fixing.

. Printing paste residues

2.5 4 kg for conventional squeegees (depending on diameter and length of thesqueegee)2.5 kg from pipes and the pumps1 - 2 kg from the screens6.5 8.5 kg Total

2. Waste water from wash-off and cleaning operations

Typical values for water consumption are as follows:

350 l per pump and pipes for one printing paste supply system 35 l per squeegee (modern washing equipment)

90 l per screen (modern washing equipment).

Urea consumption levels in reactive printing pastes: Urea from reactiveprinting pastes is the main source of NH3 and NH4

+ in the waste water fromprinting housesUrea content in reactive printing paste can be up to 150 g/kg paste. Urea is alsoused in printing pastes for vat dyes, but in much lower concentration (about 25g/kg paste). Urea is applied to:


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increase the solubility of dyestuffs with low water solubility

increase the formation of condensate, which is necessary for allowingmigration of the dyestuff from the paste to the textile fibre

form condensates with a higher boiling point (115C) which means thatrequirements for constant operating conditions are lower (non-constantoperating conditions can negatively affect reproducibility if urea is notused).

3. Volatile organic compounds from drying and fixing

aliphatic hydrocarbons (C10-C20) from binders

monomers such as acrylates, vinylacetates, styrene, acrylonitrile,acrylamide, butadiene

methanol from fixation agents

other alcohols, esters, polyglycols from emulsifiers

formaldehyde from fixation agents


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ammonia (from urea decomposition and from ammonia present, forexample, in pigment printing pastes)

N-methylpyrrolidone from emulsifiers

phosphoric acid esters

phenylcyclohexene from thickeners and binders

Printing auxiliaries

Thickening agents for Dye PrintingThickening agents are essential components of printing pastes. They areresponsible for preventing capillary flow between the threads of the fabric, thus

inhibiting dye diffusion. Oil/water emulsions, used in the past as thickeners, havenow been largely replaced by formulations similar to those used for warp sizes.Standard components of modern thickeners include natural polysaccharides,both unmodified and chemically modified (e.g. seed derivatives, starchdegradation products, alginates) and fully synthetic polymers (mainly based onpolyacrylic acid). Thanks to the improvements made in the characteristics of thestarting materials, thickening agents are now supplied almost exclusively in cold-soluble form.

Auxiliaries for pigment printingThickening agents


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Water-in-oil emulsions were widely used in the past as thickeners. Theycontained up to 70 % of white spirit (mixture of aliphatic hydrocarbons with C12-C50 chain length), which resulted in emissions of volatile organic carbon in theexhaust air from drying and curing ovens. Halfemulsion printing pastes (oil inwater) are only occasionally employed today. Nevertheless, modern thickenerscan still contain approximately 10 % of mineral oils, which are ultimately found inexhaust air. New generation thickeners have been developed which do notcontain any volatile solvents. They are supplied in the form of non-dusting

granules [64, BASF, 1994].BindersThe pigment has no affinity for the fibre. Therefore, in order to coat the pigmentand protect it from mechanical abrasion, a binder is added to the printing paste.Binders are in general selfcross- linking polymers which reticulate during thefixation step. They are supplied as aqueous polymer dispersions, based mainlyon acrylates and less commonly on butadiene and vinyl acetate.Fixing agentsAdditional fixing agents are sometimes necessary to enhance the level of wet-fastness, especially with smooth fibres such as PES. Melamine-formaldehydecondensates are used for this purpose. In order to reduce the consequent

formaldehyde emissions, modified compounds of the same chemical type, butwith a low formaldehyde content, are now common.PlasticisersPlasticisers are mainly silicones or fatty acid esters, which are used to improvethe dry rubbing fastness and give a smooth dry handle to the fabric.EmulsifiersIn high- and low solvent pigment printing pastes, the emulsifiers serve to stabilisethe solvent (white spirit). In solvent-free pigment printing they are used to preventagglomeration of the pigment, screen blocking and separation of components ofthe print paste [186, Ullmann's, 2000]. Non-ionic surfactants such as aryl- andalkyl polyglycol ethers are the most commonly used for this purpose.

Printing Effulent

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