Color designs are developed on fabrics by printing with dyes and pigments in paste form with specially designed machines. Printing is used to apply coloring localized areas only. Printed fabrics usually have clear-cut edges in the printed portions on the face of the fabric. Printing allows for great design flexibility and relatively inexpensive patterned fabric
DIFFERENCE BETWEEN DYEING AND PRINTING
- Mono color application
- Dyes are applied in liquid form
- Salt is needed
- Temperature is used for better penetration during dyeing
- Water plays an important role in dyeing
- Percentage shade is calculated on the weight of material
- Time is allowed for better penetration
- Half bleached fabric is used for dyeing
- The fabric is handled either in open width or in rope form
- The fabric may be in wet/dry condition during dyeing
- Uniform color application on both the faces of fabrics
- Machinery requirement is comparatively simple (tanks, winches, jiggers, soft flow, padding mangle etc)
- Cost of dyeing/meter is lower
- The process of dyeing consumes more time
- Dyeing consumes more water
- Mono or multi color application
- Dyes are applied in paste form
- Salt is not needed
- Temperature is not used during printing.
- Thickening agent plays an important role
- Percentage shade is calculated on the weight of paste
- Time is not required since color is applied on the surface of the fabric only
- Full-bleached fabric is used for printing
- The fabric is handled only in open width form
- The fabric is to be in dry condition only during printing
- Due to single face printing, printed face will be darker and other face will be paler
- Machine requirement is complex by way of design, screen preparation, printing machines and after process machineries
- Cost of printing/meter is higher
- The process of printing consumes short time
- Printing consumes less water
Preparation of Print paste
- Dye stuff or Pigment used as a coloring matter depending on the nature of the fiber.
- Lumps are broken by using a wetting agent and a smooth paste is obtained.
- Selected on the basis of cost, fastness & shade requirement.
2. Thickener Prevents the spreading of the color on the cloth by capillary action.
- Choice of a thickener depends upon the class of dye to be printed and the style of printing.
- Eg. CMC, British gum, Sodium Alginate, Emulsion thickener etc.
3. Wetting agent is used to obtain a smooth paste of the dyestuff without formation of any lumps
- Lumps if allowed to remain get deposited on the cloth during printing produce dark spots.
- For insoluble dyestuffs like vats & Napthols, wetting agents are used to facilitate -wetting of the dyestuff
- For direct, acid, basic & reactive dyes, which are water soluble , a wetting agent is not normally required.
4. Dispersing agents are used to prevent precipitation of dye particles as the concentration of the dyestuff in the printing paste is high.
- Di-ethylene glycol
- Sodium benzyl sulphenalilate .
5. Anti foaming agent are used to reduce frothing in the printing paste
- Dyestuffs have a tendency to froth during color preparation and printing because of
- -the presence of wetting agents
- -continuous agitation by the printing roller and brush finisher.
- Due to frothing
– the paste overflows on the floor or into other color box.
-the print also becomes specky and lighter in shade.
6. Fixation accelerators are Used to improve dyestuff fixation in printing as well as to shorten fixation time.( swelling compounds)
- Also effective in preventing fixation unevenness that may be caused by fluctuation of conditions for dyestuff fixation such as time, temp, humidity etc.
- P- phenyl phenol is applied for polyester,
- Thio urea is applied for polyamide,
- Resorcinal is applied for polyamide , cotton, acrylic fibers.
7. Hygroscopic Agents used to take up sufficient amounts of water during steaming to give mobility to the dye molecules to enable them to transfer to the fiber.
eg. Urea, Glycerine, Diethylene glycol
8. Oxidizing agents are required for printing certain classes of dyes & also in discharge & resist printing.
- Most commonly used oxidizing agents:
- -chromates and dichromates
- -nitrates and nitrites of sodium
- -potassium ferro cyanide
9. Reducing Agents They are required for discharge and resist printing as a discharge chemicals
- Sodium sulphoxilate formaldehyde
- Zinc sulphoxilate formaldehyde
- Potassium sulphite
- Ferrous sulphate, stannous chliride, thio urea.,etc
Best method for low yardage samples exclusive limited quality designs; Large repeat sizes (up to 120” possible); Wet-on dry prints effect possible; Better color definition than roller prints due to heavier lay-on of color; Acceptable to all woven & knitted fabrics; Rapid preparation of screens and rapid pattern changes over possible; Ability to print cut garment parts and small items (towels, scarves etc.)
Limitations; –Half tone designs not possible; Fine-line paisley prints not possible; Lengthwise stripe designs not possible; Slow production; uneconomical for large production yardage.
Automatic Flat bed screen printing
The fully automatic hydrate flat bed-printing machine consists of three units.
- Fabric Feeding unit
- Printing unit
- Drying unit with plaiter
- Fabric Feeding Unit: The cloth from the batch roll is taken through guide rolls, tension bars, and fabric guider and is pressed to the blanket by means of a feed roll. This feed roll is also provided with internal electric heaters.
- Printing Unit: This unit consists of an endless synthetic rubber blanket, which supports the fabric during printing & returns to feed position after washing. The forward movement of the blanket is facilitated by series of electromagnetic grippers, placed at both sides of the blanket. The gripper unit is operated forward and backward, according to the design repeat by means of hydraulic piston. During start, the magnets grip the blanket, move forward according to the repeat & release after stopping and return back to start position in open state. Thus the intermittent forward movement of blanket is enhanced.
Continuous Feeding : In order to avoid feed roll marks, this system is provided with a special continuous cloth feeding arrangement, which is achieved by two sets of dancing rolls; one at feeding end and the other at delivery end (D1 & D2). During printing, the upper layer of blanket is stationary. The bottom layer continuously moves to facilitate continuous feeding of fabric. The extraction unit at the bottom ensures this continuous movement of the blanket.
Washing Unit: This unit consists of series of water spray nozzles, brush rolls and rubber scrappers. A metal scrapper achieves a final cleaning of residues on blanket.
Printing Station: According to the capacity of the machine, eight to sixteen colour-printing stations are available. The printing station consists of squeeze holder drive brackets at each side. Adjustable pressure knobs are available to control required squeezee pressure. The speed & stroke length of the squeezee are also controllable.
Working: Before the start of printing, the hydraulic pump is switched on to develop the required pressure. The required design repeat is set and verified by measuring the movement of the blanket. The printing stations and screens are positioned according to the repeat and order of printing. The cloth is fed and printing stations are switched on. It gets printed sequentially at the various printing units & leaves to the dryer unit, gets dried & plaited on trolleys.
- Printing station up, forward blanket movement and flood stroke.
- Blanket stop, printing station down.
- Printing stroke on. Then the cycle continues.
Important Features: –Large repeat size (up to 60”) possible; Better color definition than roller prints; equal to hand screen; Adaptable to all woven & knits; Rapid changeover of designs possible; Best machine registration.
Limitations: – Cost of screen preparation and special mountings more costly than hand screen; Not adaptable to low yardage; Half-tone designs not possible; Fine-line paisley prints not possible; Lengthwise stripes not possible.
Rotary screen printing
Rotary printing M/c consists of
- Feeding Unit
- Printing Unit
- Drier & Plaiter Unit
Feeding unit : The feeding unit comprise of a feed pressure drive roll (lowered or lifted pneumatically), tension bars, brush rolls, compensator roll, Guiders, Curved fabric heater plates & the fabric is fed to the printing blanket by feed pressure roll. Fabric heater unit is provided with electrical heating coils inside, which preheats the fabric.
Printing Unit: The printing unit comprise of endless rubber blanket, printing heads, squeeze support systems, colours feed pumps to individual squeezes & auto levelers, pressure application systems to squeezes, pre washer, blanket washing unit, gluing unit for PVA adhesive application & infra red lamps for blanket heating. The blanket after printing gets pre washed by water spray & sponge gets second wash in the washing unit. The washing unit comprises series of water spray nozzles, brush rolls (or) sponge beds, rubber Scrappers. Metal scrapper enhances the final scrapping of residual water. It also encompasses squeezee support cradle at both sides. The squeezee is basically a long metal tube provided with series of small holes for discharge of colour paste. The colour pumps feed colour under pressure through the squeezee. The colour level inside screen can be controlled manually (or) by auto leveler units.
Dryer Unit: The fabric after printing is carried to the drier unit with the help of an endless conveyer. The conveyer is made of open mesh, temperature stable synthetic polymer. Drying is enhanced by hot air circulation through radiators by circulation fans. Gaseous dried up matter is evacuated by exhaust fan. The dried fabric leaves the drier unit and is plaited on open trolley.
Working: The respective screens are mounted on the rotary heads. Selected squeezees are inserted and connected to the respective colour pumps. The fabric to be printed is fed to the blanket and gets printed by the respective screens in a continuous fashion. With respect to required setting, individual screens are set axially and laterally and the squeezee pressure is also set accordingly. The printed fabric is conveyed through dryer and plaited. The speed of printing is possible up to 80 mtr/min depending upon the substrate. Since the speed of printing is very high, strict vigilance is required during printing.
- The printing is continuous.
- High production rate.
- No joint marks are faced.
- Best suited for overall designs, stripe & check patterns.
- Due to short contact time, sharpness is better.
- Less man power.
- Give more uniform printing results.
- Very high machine cost
- Uneconomical for short runs
- Penetration is difficult for thick fabrics.
- Cross border prints cannot be printed.
- At high printing speeds damage control becomes difficult.
- Due to mesh number constraint, reproduction of original art work is difficult.
- Design repeat is limited (64cm).
- High nickel screen cost.
- Colour consumption & wastage is higher.
Important Features: – Up to 40-inch repeat size are possible and larger than roller printing, but smaller than flat bed screen; Lengthwise stripe effect possible; Fall-on designs possible; Adaptable to all woven & knits; Cleaner and brighter colors than roller print; Excellent color definitions, but less than flat bed screen prints; Rapid change over of designs possible; Efficient for long runs and moderately small (1000 yards) runs.
Limitations: – Fine-line paisley prints not possible; Half tone designs not as effective as in roller printing.
Comparison of Rotary & Flat Bed Printing M/c
|Rotary Printing||Flat – Bed Printing|
|It is a continuous process||It is an intermittent process|
|Production rate is high||Production rat is low|
|Machine cost is high||Machine cost is low|
|It is best suited for larger lots||It is best suited for smaller lots|
|No joint marks||Jonit marks are faced (gap/over lap)|
|It is suited for all designs||Stripes, straight joint designs cannot be printed|
|Requires less man power||Requires more man power|
|Colour feeding is automatic||Colour feeding is manual|
|Repeat is limited to 64 cm, 72cm, 91.6cm etc.||Repeat is unlimited|
|Damage control is difficult||Damage control is easier|
|Less penetration of prints||Good penetration of prints|
|Reproducibility of original art work is less achieved||Better reproduction of original art work|
|Overall designs are printed||Overall & cross border designs are printed|
|Uniform printing results are achieved||Less uniformity (block to block, edge to edge variation)|
|Colour consumption and wastage more||Colour consumption & wastage are less|
Heat Transfer Printing
Transfer printing involves the transfer of colour from one surface to another surface, generally from paper to a textile material. It makes possible to express delicate designs which are difficult to reproduce by the conventional printing technique on fabrics. Here the transfer paper on which the patterns are printed with printing ink made of dyestuff having suitability for dry heat drying. They are treated for 15-40 seconds at around 2000 c.
Transfer Printing Paper : The required design with suitable dye inks in solvent are printed on a glazed non-fibrous strong paper coated with china clay and alginate, by using any one of the techniques viz. gravure (or) flexography (or) litho graphy (or) rotary printing. Then it is coated with an adhesive resin to have better tack with fabric.
Sublimation transfer printing : In this method, the vapour phase transfer takes place by heating under pressure at 180 – 2200 c for 20 seconds. The dye sublimes under heat from the paper and is absorbed by thermoplastic substrates (PET).
Important features: – Produces bright, sharp, clear fine-line designs; Ability to print cut garment parts and small items; Adaptable to long and short yardage runs; Rapid pattern changeover possible; Simple, low-investment installation steamers, washers, dryers, dryers etc not required; Fewest seconds of all printing processes; Heat setting also accomplished.
Limitation: – Lead-time for paper preparation can cause problems in high fashion markets; Fiber content in fabric should be minimum 50% synthetic Fiber. Cellulose’s & protein fibers cannot be printed; over print only on pastels or else will not completely cover the original color.
Computer Aided Design & Printing system
Computer aided designing offers innumerous benefits to the printer by way design generation, preview, colour separation etc., done in an automatic way. The configuration of CAD system is shown above. The hardware part involves central processing unit (CPU), colour monitor, keyboard, mouse & lighter pen. This can be interfaced with flat scanner or rotary drum scanner cum plotter, film plotter, laser engraving, wax jet engraving, ink jet engraving or to fabric ink jet printers.
System Scopes :
- Design generation in computer using drawing tools (pen, Bruch, air brush, texture / patterns, filling etc.).
- Tools for making lines, curves and geometrics.
- Colour selection using colour pallets.
- Resolution discretion.
- Design modification.
- Image rotation mirror work etc.,
- Cut, paste, edit, cloning etc.,
- Size modification (magnification or reduction).
- Fabric or sketch scanning.
- CMYK/RGB mode function.
- Colour separation selection, colour reduction.
- Repeat selection.
- Repeat stepping to the required manner.
- Cleaning, modification works.
- Masking function.
- Individual colour film formation (black / transparencies)
- Films stacking and preview.
- Over lap adjustments.
- Colours ways selection and preview.
- Digital rasterisation.
Advantages of CAD Systems.
- Ease out manual labour.
- Quick process time.
- Reduces space & material by electronic data.
- Preview scope prior to final output – image
- Colour ways, fitting overlaps etc.,
- Convenience in data storage, transmission.
- Can eliminate films or even Screens for fabric printing.
- Faster communication scope.
- Image rectification and alteration scope prior to bulk production.
- Best quality of final printing ensured.
- High cost of installation.
- Manual spontaneity cannot be matched.
Digital Ink Jet Printing
Ink jet printing machine was primarily evolved for image printing on paper. The same system is now developed for printing on textile substrates. Typical fabric ink jet printing machine consists of a fabric feeding system form roll form, cloth guider system, and moving ink jet printing heads and take up roll system. Printing inks are based on CMYK (cyan, magenta, yellow and black) 4 colour system. Current printing systems offer scope to print acid, reactive, disperse and pigment colours. The prepared cloth is fed to the machine in open width in creaseless form. As per printing command the design image can be directly plotted on fabric using fast improving ink jet heads which are fed with individual colour inks. After each traverse movement of the ink jet head, the fabric is slowly advanced. Various ink jet release technologies are available viz.
- Continuous ink jet
- Drop on demand ( Bubble jet or piezo electrical impulse etc.,)
The current printing speeds vary from 15 meters to 200 meters per hour. This system poses promising scope for future in the following aspects. The applied colour can be fixed and after treated by suitable machinery.
- Direct image / design printing on fabric from CAD.
- Elimination of colour separation / films and screens (major savings)
- Design change can be done spontaneously.
- Quick response system for sample presentation.
- Direct printing of design colour ways on fabric.
- Saves time, labour, material and lead – time.
- Convenience of data handling ( Internet, CD, floppy etc.,)
- Eco friendly and clean technology.
- Low energy consumption
- Ensures better fastness, fixation and less water for washing.
- Total absence of gums.
- Reduced pollution potential.
- Very minimum manpower requirement.
- Best quality, reproduction and versatility in designs handling.
- Minimum basic colours can be used(CMYK)
- Low productivity.
- High equipment cost.
- Not suitable for all class of dyes.
- Useful for plain surface fabrics only.
- Penetration prints no possible.
Styles of prints
Also called an application print; most popular print types; Design is printed directly onto a white cloth or over a previously dyed fabric; the printed is considerably darker than the dyed backgrounds.
Identification of Direct prints: –
- The background is white, or has large portions of white background.
- The printed design is lighter in shade on back of the fabric than on the face. This may not be evident on lightweight fabrics because of the strike-through of the print paste.
If the fabric is over print.
- If the background color is the same shade on the face and back (piece dyed), and the print design are substantially darker than the background.
Fabrics that are dyed a solid color prior to printing; the design is applied by screen or roller with a chemical (sodium sulphoxylate formaldehyde, a reducing agent)
“White discharge print” White polka dot on a blue back ground can be made by first dyeing the fabric blue, then printing appropriate dots with the chemical which removes the blue color.
The colour-destroying chemical does not affect “Color discharge Print” Vat dyes; these two substances (the color removing chemical, and vat dye) may be mixed together in the same print paste.
When printing with this mixture, the color-removing chemical removes the previously dyed background color while the vat dye color is simultaneously printed.
A yellow polka dot on a blue background can be made by first dyeing the fabric “Blue” then printing with a yellow vat dye mixed with the removing-removing chemical
Discharge print can be made roller & screen methods, but not by heat transfer printing.
Discharge Prints are not widely used:
Production is more costly than direct print because fabric is to be dyed prior to printing.
Very careful and precise process control is required.
Developments of automatic & rotary screen-printing, high quality blotch prints, which can produce the same effect at lower lost.
Identification of discharge prints: –
The background removing is the same shade on the face and back of the fabric (piece dyed).
Print design area is white or a different removing or shade than background.
Back of the print design reveals traces of the background removing.
Involve 2 steps
- Printing a pattern design on a white fabric with a chemical (wax-like resinous substance) that will prevent or resist the penetration of dyes.
- Piece – dyeing the fabric.
Not popular type fabric; Used where background removing in a fabric can not be discharged; Performed as craft or hand printing rather than on production basis; Batik prints, tie-dye prints and ikat prints.
Pigment Prints: –
Pigment prints are direct prints made with pigments called dry printing.
Pigments: Pigments are insoluble colouring matters. They can be classified into organic and inorganic pigments. Inorganic pigments are carbon black, Titanium dioxide, metal oxides like Chromium, iron, lead, cadmium, etc. Because of higher particle size, excepting carbon black & TiO2 others are not used for printing.
Binders: Binders are transparent, film forming polymeric substances made of poly acrylic monomers. For improved properties co-polymerisation with vinylchloride. Acrylic acid, methacrylic acid, styrene (or) butadiene is normally done. The Binder can be self cross-linking type (forms three-dimentsional network) or applied along with a suitable cross – linking agent. A good binder should offer transparency of film, good film strength, abrasion resistance, flexibility, soft feel, inert to additives, dyes and offer good fastness.
Thickeners : Since the thickener should leave the printed complex on drying, no solid content thickener can be used. Best – used thickeners are,
- Kerosene emulsion paste
- MTO emulsion paste
Cross – linking agents : If the binder is not of self – cross linking type, external cross linking agent like melamine formaldehyde resin is incorporated in the printing paste to improve wet fastness of prints.
Acid-liberating agents : The polymerization & cross linking of the binder takes place in acidic medium. Direct addition of acid to printing paste leads to pre – mature polymerization in the paste itself. To avoid this, ammonium salts of acids are used. (E.g.) Diammonium phosphate. During drying & curing, ammonia is evaporated and phosphoric acid is liberated at 1500c.
Other additives: Silicon softener can be used to impart softness & hygroscopic agents like urea can be used to prevent screen choking.
Identification: – Comparing the differences in fabric stiffness between a designs printed portion and a non-printed portion of the same fabric. The pigment print area will be slightly stiffer and a bit thicker than the non-print area. Deep shades are stiffer than light shades pigment prints are least costly. Because, Simple to apply; Lease amount of processing; No after treatments (steaming & Washing).
Pigments produces bright, rich colors; Applied to all fibers; Good to excellent fastness to light and dry cleaning; Widely used for drapery and curtain fabrics; Excellent lot-to-lot shades matching attainable; Loose gradually and become more faded with each laundering; Poor fastness to crocking (rubbing) especially in dark colors.
Background” has been obtained by printing; Direct Print; The print and pattern design color are printed on to a white fabric in one printing operation; Imitates discharge or resist print effects.
Identification: – The blotch print background color is lighter on backside of the fabric.
Possibilities of large background color areas of the print are not covered with full depth of colors; Precious control is necessary; If pigment prints, fabrics very often result in objectionable stiff hand.
Tiny particles of fibers (1/10” – 1/4”) are made to adhere to a fabric surface in according to a particular design; printing the design with adhesive; exposing the fibre flock to the fabric.
The fibre flock is shifted on to the fabric while the fabric is passing in open width through flocking chamber; Mechanical beaters cause fabrics to vibrate become sticks on fabric.
Flock particles are given electrostatic charges – rests, all fibers being oriented in an upright position when they adhere to fabric; slower and more costly; rayon’s and nylon fibers most popular; fibers are dyed prior to flocking; The ability of flocked fabric to with stand dry cleaning and washing depends quality & characteristics of adhesive.
Printing with chemical substance (sulfuric Acid) that will destroy the fibre in the pattern design print area; Fabrics are used in low-cost summer blouses and cotton lingerie; Interesting designs can be created with blends.
Fabrics in which both sides of the fabric have been printed; Imitate Jacquard & Dobby woven design fabric; Very expensive printing
Prints that have two or more distinct designs, each located in separate areas of the fabric, and each designed to become a specific part of the garment; printed by hand screen or heat transfer methods.
Warp Prints involve printing the warp yarns of a fabric before it is placed on the loom for weaving, then, the fabric is woven with a solid color weft usually white or contrast color.
The result is a soft, shadowy design on the fabric; Producing warp prints require careful and skilled labor; these prints are found almost exclusively on high quantity and expensive fabrics.
Printed fabric defects
The imperfections or defects may results from
- Improper printing procedure
- Improper preparation of fabric prior to printing
- Imperfections in the material
- Color drag
Color of the print smudges from rubbing against an object before it becomes dry
2. Color splatter
The print paste instead of being placed on the fabric is thrown or splatters on tot he fabric surface.
3. Fuzzy pattern: –
The edges of the pattern are not sharp or clear lines; caused by improper singeing or inadequate viscosity of print paste.
Printing rolls, or screens improperly aligned so, patterns do not aligned properly.
5. Stop mark
Color streak across the fabric due to stopping and restarting of the machine.
6. Tender spots
Weakened areas in the print design, due to excessive chemicals