UNIT – 4 PRINTING Structure Overview Learning Objectives 4.1. Definition 4.2. Styles of Printing 4.3. Methods of Printing 4.4. Fully Automatic Hydratex Flat Bed Printing Machine 4.5. Rotary Screen Printing Machine 4.6. Transfer Printing 4.7. Fixation and After Treatment 4.8. Printing of Blended Fabrics 4.9. Print Paste Formulation 4.10. Other Types of Printing Let Us Sum Up Answer to Learning Activity OVERVIEW On reading this Unit the students can learn about the Definition of Printing, Styles of Printing, Methods of Printing, Fully Automatic Hydratex Flat Bed Printing Machine, Rotary Screen Printing Machine, Transfer Printing, Fixation and After Treatment, Printing of Blended Fabrics, Print Paste Formulation and Other Types of Printing like Pigment Printing, Batik Printing, Khadi Printing etc. LEARNING OBJECTIVE 148
Transcript
UNIT – 4PRINTING
Structure
OverviewLearning Objectives4.1. Definition4.2. Styles of Printing4.3. Methods of Printing4.4. Fully Automatic Hydratex Flat Bed Printing Machine4.5. Rotary Screen Printing Machine4.6. Transfer Printing4.7. Fixation and After Treatment4.8. Printing of Blended Fabrics4.9. Print Paste Formulation4.10. Other Types of PrintingLet Us Sum UpAnswer to Learning Activity
OVERVIEW
On reading this Unit the students can learn about the Definition of Printing, Styles of Printing, Methods of Printing, Fully Automatic Hydratex Flat Bed Printing Machine, Rotary Screen Printing Machine, Transfer Printing, Fixation and After Treatment, Printing of Blended Fabrics, Print Paste Formulation and Other Types of Printing like Pigment Printing, Batik Printing, Khadi Printing etc.
LEARNING OBJECTIVEAfter completion of this Unit the student will learn about:
Definition of Printing
Styles and Methods of Printing
148
Fully Automatic Hydratex Flat Bed Printing Machine
Rotary Screen Printing Machine
Transfer Printing
Fixation and After Treatment
Printing of Blended Fabrics
Print Paste Formulation
Other Types of Printing like Pigment Printing, Batik
Printing, Khadi Printing etc
4.1. DEFINITION
Printing is the process of transfer of a design (or) art work on to textile materials, providing a decorative look. Printing can also conceal many of the fabric defects. The chemical principles are generally the same (viz. dye - fibre fixation mechanism, medium etc.,) for printing and dyeing. Excepting for the method of application, printing can be called as a localized dyeing. This is achieved by controlled application of colors to the respective areas as per design [single colour or multicolor] by the use of thickened printing paste. The application method may be by manual, block, stencil, screen (or) transfer printing and the styles could be of direct, discharge, resist (or) other styles. The fabric is generally dried after printing, followed by dye- fibre colour fixation by steaming (or) dry heat as per fibre class and dyes. The fixation treatment is followed by washing in order to remove unfixed colors, gums and other residues from the substrate.
a) Difference between Dyeing and Printing:
1. The purpose of printing is to produce multicolored designs on textile fabric. On the other hand, the purpose of dyeing is to produce, solid, all over, single color.
2. In printing, a fairly concentrated dyestuff solution is used contrast to dilute dyes stuff solutions used dyeing.
3. In general, printing processes are more complicated than the concerned with dyeing, and the machinery employed is
149
much word elaborates and demands a higher capital outlay.
4. Because of the basic difference existing between and printing techniques, different types of machines are used in these two processes of textiles, color action, whereas jiggers, winches and padding mangles as well as been dyeing machines are commonly used in dyeing, block screens, stencils and rollers are used as the instruments of printing followed generally by steaming of the printed fabrics to effect the transfer into the fabric.
4.2. STYLES OF PRINTING
The term Style of printing deals with the chemical aspects of printing viz., recipe formulation, motives and ground colour application, fixation and washing methods, with respect to style of printing it is classified into three types as follows:
1. direct style
2. discharge style and
3. resist style
Discharge and resist style printing
Discharge and resist possible effects
150
1. Direct style of printing:
In direct style of printing, the required class of dye along with suitable thickener and other fixation additives are directly applied to the fabric by suitable means. The printing can be all colours application by screens (blotch printing) or over print on dyed ground. Generally a light colour overlap on dark/medium colour is to be given in order to prevent out fitting. This style is direct, simple and reproducible. Examples of direct styles are pigment printing, Azoic printing, Disperse printing, Reactive printing, Vat printing etc. The printed cloth is dried, colours are fixed by steaming (or) dry heat and washed if necessary.
a) Advantages:
Simple, Direct &ease of reproducibility
Number of operations is less. All colors are applied & fixed simultaneously.
b) Disadvantages:
More paste consumption.
Contact colours give over lap & mixed tone on printing.
Sharp features by wet on wet printing lose clarity
Excess overlap gives smudged printing.
Clarity and distinct look of motives are less attained.
Risk of tinting of ground colour in washing.
2. Discharge Style of Printing:
In discharge style of printing the ground colour is applied by dyeing or padding with dischargeable dyes. The motifs are printed with discharging agent (reducing type) which destroys the ground dye chromophore during steaming. Thus a white discharge is formed. By incorporating a dye unspoiled by the discharging agent in the printing paste, a colour discharge is formed. Vat discharge printing on reactive ground, disperse
151
discharge etc. In colour discharge the ground colour is discharged and replaced by a new colour in the printed area.
It is the production of a printed pattern on a pre-dyed cloth, with a paste containing a suitable reducing agent, which destroys (strips) the ground colour dye during subsequent steaming at the printed portions. Thus discharge style is nothing but a localized stripping.
a) White Discharge:
If the ground colour on the printed area is destroyed by the reducing agent, leaving a white pattern on the printed area it is called as white discharge printing.
b) Colour Discharge:
A colour discharge is the one in which a new colour unspoilt by the reducing agent, is printed on a dischargeable dyed ground. During steaming the ground colour is destroyed, whereas the non-dischargeable colour in the printed portion is developed at the same time, giving a coloured pattern on the pre – dyed cloth. The discharge resistant dye added to the print paste is also called as an illuminating dye. Thus colour discharge is the process in which the pre – dyed ground colour is destroyed and replaced by a new colour.
c) Advantages:
It enables light, brighter colours to be obtained on a dark ground.
Very sharp features like fine outlines, dots, raster etc., can be produced with total clarity, without any smudging (due to overlapping of contact colours) or outfitting problems normally faced by direct style of printing.
Tinting of white pattern on coloured ground (In case of direct style) is avoided by discharge printing.
The effect, clarity, distinction, richness and aesthetic appeal obtained add value for discharge printing.
152
Level ground shades are best obtained by dyeing than blotch printing.
Open ground (flat screen printing) joint marks can be eliminated by discharge printing.
d) Disadvantages:
It is an expensive process.
Two stage application involved in dyeing or padding and discharge printing.
Limited choice of ground and motif colours.
Requires rigid process care that any default will lead to damages
3. Resist Style of Printing:
Resist style involves pre-printing the fabric with paste containing the resisting agent and non-resistant dye and padding with resistible ground colour. During steaming the ground colour is resisted in the printed areas leaving white & colour resist printed motifs. (E.g.) Reactive resist with pigment, Aniline black resist with vat, Indigo sol etc. In white resist print the padded ground is resisted to white and in colour resist the ground colour is resisted giving way for a new colour, on the printed areas. In both discharge & resist styles, we get sharp, clear &distinct motifs on dark grounds. This effect is not attained by direct style of printing. Overlaps and Joint marks are avoided in discharge & resist style of printing. Direct style of printing on cellulosics, silk, wool, synthetics like nylon, polyester and acrylics and printing on blends are discussed exclusively in the specific paper being presented next.
a) White Resist:
If the ground colour is resisted from fixation by the printed resist, the out come being white printed pattern on a colour ground, it is called as white resist.
b) Colour Resist:
153
By incorporating a colour class, which is not affected by the resisting agent, after printing, drying and ground colour application the ground colour is resisted at the printed portions during fixation. The outcome being coloured motifs, which are clearly seen on a coloured ground. This is called colour resist.
c) Resisting Agents:
Resisting agents can be basically classified into (1) Chemical resist (2) Mechanical resist.
Chemical resisting agents can be acid, alkali, various salts, oxidizing agents or reducing agents. For example the printed resist with acid can prevent the fixation of alkali reactive ground by neutralizing effect. They prevent fixation or development of the ground colour by chemically reactive with the dye or with the reagents necessary for its fixation.
Difference between Discharge and Resist styles of Printing
Discharge Resist
In this method the ground colour is applied first, followed by discharge printing.
In this method the resist is printed first, followed by ground colour application
Mostly reducing type-discharging agents are used.
Acids, Alkalies, Oxidising agents. Reducing agents, Wax, Thickening gums, Resins, Finishing agents can be used.
Discharge prints are normally sharper and brighter.
Resist prints are subdued and lack brightness and sharpness.
Colour choice for ground, illumination colours is limited. Colour mixings are more difficult.
Colour choice is more and mixing is relatively easier.
Cost of discharge printing is higher. Cost of resist printing is lower.
154
Reproducibility is difficult. Reproducibility is better.
Percentage rejection is more (setting problem etc)
Percentage rejection is less (being printed on white grounds)
Work procedure is relatively simple. Work procedure is relatively complex.
Requires stronger chemical action. Require milder chemical action.
Consumes less time. Numbers of operations are less.
Consumers more time. Numbers of operations are more.
Printing problems like mesh chock-up etc., are much less.
Because of insoluble resisting agent, chock-up problems, are faced.
Chances of less ground contamination.
Chances of more ground contamination.
More pollution load. Less pollution load.
Simple chemical principle (usually reduction)
Chemical principles are complex and varied.
4.3. METHODS OF PRINTING
The term method of printing refers to mechanical means of application of printing paste to the substrate via block printing, stencil printing, screen-printing (rotary/flat), roller printing, Transfer printing (or) Manual application.
(i) Application by Hand:
This method is actually the manual application of design and colour on substrate directly. Few of the ways are hand painting, watery effect designs, spray work, marbling, combined and special effects.
155
Hand block printing is the oldest method of printing in which wooden blocks with a raised design (i.e. in relief) like rubber stamp are used. In use the block is placed on a colour pad which contains the necessary printing paste. In this way the raised design in transferred onto the fabric, after the block becomes uniformly charged with the paste by colour pad. The block is then placed on the cloth to be printed and is smartly tapped on the fabric.
For producing multi coloured print effect may blocks depending on the number of colours being used are employed. In case of stencil printing the design is carved as a cut opening on the metal plate or sheet and placed on fabric. Required colour paste is applied manually by squeegee / soft sponge material.
(ii) Roller Printing Machine:
Engraved rollers are hollow steel cylinders, electroplated with a layer of copper into which the engravings are etched. The engravings are really a serried of parallel channels, approximately 7 /1000 to 8/1000 of an inch deep & there are between 35 -50 of these channels to the Inch. Finally the roller is chromium plated, to prevent damage by scratching and to prolong its printing life.
156
The most common type of roller machine consists of a large hollow metal pressure cylinder, around which the printing rollers are arranged. Each printing roller is individually driven can be adjusted vertically & laterally to ensure correct register of the pattern, and is pressed into the pressure bowl. The printing roller is fed with colour from a colour box by a second brush like roller. A sharp stainless steel blade scrapes the roller surface immediately before printing, leaving the colour only in the engraved areas from where it can be transferred to the fabric as roller & fabric pass in contact with each other. The fabric to be printed is fed on to the pressure cylinder on top of an endless rubber printing blanket to which it is stuck, so preventing any sideways movement & loss of register in printing. In this passage around the cylinder the fabric is printed by every roller in turn, each applying its colour & part of the design. Finally, after leaving the cylinder the cloth is dried, often by passage through a hot – air dryer & then over steam heated cylinder.
(iii) Screen Printing :
Table Printing Machine (Flat Screen)
In case of flat screens, since the screen is made of filament fabric, generally squeeze tips are made of rubber material. The various profiles and hardness of Rubber are decisive factors for suitability on type of motifs (Fine patterns, large motifs, flatness of design etc.,) few systems make use of solid metal rod squeegees, pressured by mechanical, pneumatic or magnetic means. Principle of flat screen is same for table and machine printing. The design to be printed is present as open perforated area on a stretched fabric base (bolting cloth) held by frame. The screen frame is placed on the spread fabric and colour is applied / transferred from screen to fabric by squeegee made of rubber or metal manually and mechanically. This is a discontinuous process.
157
The printing table is simple equipment used for manual printing. The printing base is made of asbestos sheet (or) plywood supported by wooden legs at a height of 90cm. Placed above the base are
1. One (or) two layers of felt cloth.
2. One (or) two layers of cotton (or) p/c poplin fabric.
3. A rubber blanket (or) rexin sheet.
All the above layers are stretched in all directions and are properly fixed to the table sides. The table is generally given an inclination in order to have easy workability and draining of washed liquor. Placed at the lower end, a vertical setting rail extends through out the length of the table. Movable stoppers (guttas) are placed on the rail, which are set according to the repeat pattern of the screen. A projection from the screen rests on the stoppers during printing, which helps as reference mark for successive repeats. Two hexagonal screws from either side of screen bottom prevent any archial movement of screen during printing. Generally, length of table varies from 2m – 40m or 100m; width varies from 1.2m –1.8m.
158
a) Operation sequence:
Adhesive application using rubber squeezee blade. PVA solution or thermoplastic adhesive can be used.
Fixing of cloth without creases in a straight fashion.
Repeat setting using standard gauge (or) vernier.
The screen is placed above the cloth and two persons standing on either side of the table print the colour with rubber squeezes manually. Generally, for each colour alternate blocks are printed in order to avoid squeezee and frame marks.
After printing each colour, the print is dried.
The drying can be done either by bottom steam pipes (or) over heated hot air blower.
After completion of printing, the fabric is dried well, rolled on a cylindrical shaft and removed.
The blanket is thoroughly washed with fresh water, brush scrubbing, scrapping, and soap washing followed by final water wash. Any residual water on blanket is wiped off.
b) Advantages:
1. Very simple equipment.
2. Easy to install & less maintenance.
3. Cost is low.
4. Best suited for economical printing of small lots.
5. Operation is simple. .
6. Damages can be easily controlled.
7. The power requirement is low.
8. Unlimited colours can be printed.
c) Disadvantages:
1. Laborious working – all operations are done manually.
159
2. Time consumption will be more.
3. Low productivity.
4. Selvedge to selvedge variation, within & between repeat variations due to manual operation.
5. Discontinuous process.
6. No scope for simultaneous printing of all colours.
7. Large piece lengths cannot be handled.
8. Registration is comparatively difficult.
9. Scope of lot to lot variation.
10.Joint mark problem.
Note: Semi automatic and computerized printing carriages are available, in which the printing operation and the trolley movement are automatic (programmable). One man can control operations and colour feeding.
d) Mechanized Printing Table:
Mechanization of printing table gives the advantage of improved productivity, quality and ease of working. The following types of table printing machines are available.
1. Moving Trolley Printing Table:
In this system the screen is fixed on a trolley unit, which moves on rail on both sides blanket. The squeeze movement is supported by chain drive. Using a handle the squeeze movement can be enhanced manually. Pressure can also be adjusted. Forward movement of trolley is facilitated by lever lock, which fits in stopper blocks. [E.g. PANON table – (Spain)]
2. Automatic Printing Head Table:
In this system the screen holder trolley operates automatically for printing. As well the forward and reverse movement of printing head also is automatic. By mechanical sensors the unit stops at every repeat stopper &squeezee
160
pressure is pneumatically applied. [E.g. GALLI printing tables – (Spain)]
e) Computerized Printing Carriage:
This is more advanced version of mechanized printing table. The pressure unit comprise of squeeze drive unit. The pressure is applied pneumatically. Printing pressure, speed, no/: of strokes, lowering and lifting of squeezes &screens can be programmed in computer PLC. The forward and reverse movement and the speed of the printing trolley is also programmed as per repeat without any need for stopper setting. This system entirely works on programmable computer PLC, is capable of delivering good results.
f) Turning Table:
Small lot printing is enhanced by turnable blanket loop. The fabric is struck to the turning blanket table. As per computer program, the blanket moves and stops based on set repeat. The printing takes place from stationary printing head / heads. After printing the blanket moves forward to set repeat distance. The printed fabric is dried by a subsequent drier unit. After the end of printing and drying the fabric is removed and blanket can be washed from the detachable washing unit. This system can accommodate rotary screen also. The printing unit and blanket drive unit are driven by PLC.
g) Method of preparing the screen:
Photo chemical method is most widely used for preparing the screen. This is based on the principle that when a coating of a solution of ammonium-dichromate gelatine is dried and exposed
161
to light, insolubilities takes place. The photo sensitive coating may be given to the boiling cloth fixed to the screen frame, dried and exposed to light after keeping in contact with a positive film (design drawn paper) and after insolubilities of the exposed portion, the unexposed photo sensitive coating is washed out, leading to the blocking of the intersites of the cloth at the exposed portion and keeping them open for the forcing of the printing paste later while printing at the unexposed portions.
The required design is drawn on a tracing paper with Indian ink.
Synostosing solution may be prepared as follows:
Chrome-Gelatine Solution
Solution A Solution B
200 g pure gelatin 70 g Ammonium Dicarbonate
500 g boiling water 150 g Soiling water
80 g Liquor Ammonia
700 g Total 300 g Total
Solution A and Solution B are mixed in a dark room. After applying the solutions to the screen cloth, they are dried in the dark, at room temperature.
The design paper is placed on a lass-topped table and then on the dry photo sensitive screen. The exposure is stored from under the glass table using mercury vapour lamps or tubes with uniform intensity of light all over the screen. The light is allowed to pass through the design paper and then come into contact with the emulsion coated screen cloth. The lights are switched on for a definite length of time. After that the lights are switched off. The exposed screen is then washed with certain chemicals, when the portions of the emulsion sealed from the light by the Indian ink on the drawing gets washed off.
162
The other portions where contact was made between light and emulsion, the materials remain. In the screen cloth, empty spaces are produced according to the design. The coating of the screen with photographic emulsion, it’s drying, exposure and washing must all be done in a dark room. After touching to correct minor defects, the screen is ready to use.
4.4. FULLY AUTOMATIC HYDRATEX FLAT BED PRINTING MACHINE
The fully automatic hydratex flat bed-printing machine consists of three units fabric Feeding unit, printing unit, drying unit with plaiter.
Fully Auto Hydratex Printing Machine
1. Batch Roll, 2. Gumming unit, 3. Tension bar, 4. Vertical feeding unit,
roll, 9. Washing unit, 10.Photo-cell control, 11.Circulation fan,
12. Plaiter, 13. Open trolley
(i) 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.
(ii) 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
163
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. Most of the movements in this machine are controlled hydraulically by central high-pressure hydraulic pump. 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.
(iii) 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.
(iv) 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.
Adhesive application System: Permanent adhesives like thermoplast can be coated by coating squeezee. Otherwise, PVA application unit can also be operated.
(v) 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. An A.C. motor enhances the forward & reverse movement of squeezee. Adjustable pressure knobs are available to control required squeezee pressure. The speed & stroke length of the squeezee are also controllable.
164
(vi) Screen Holder:
Two sets of screen holders on each side of blanket are normally placed at the centre of printing station. Both the printing stations & holders are movable on rail.
(vii) Intermediate Dryer:
Optional intermediate driers are available to dry the fabric during printing.
(viii) Programmer:
In case of printing of cross border sarees or garment engineering designs, the various components of design can be simultaneously printed. According to the number of repeats of the respective designs, the individual printing units can be automatically operated by pre – setting commands from the programmer.
(ix) Drier Unit:
This unit consists of an endless open mesh conveyer made of synthetic material, which supports and carries the printed fabric through the dryer. The fabric after drying leaves to the plaiter unit and the conveyer runs back to the start position. In the drier chamber, the circulation fans transport hot air through radiators and splash through duct holes on fabric. Dried up
165
gaseous matter is evacuated by exhaust fan system. According to the speed of printing, sets of photo – cells coordinate the with drawl of printed cloth from blanket on to the conveyer.
(x) 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. Powder print is taken to verify joints and settings.
As per motifs, flood & printing squeezes are selected & kept attached to the printing unit. 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. When cross border designs are being printed, the programmer unit can be used. The colour is fed manually to the screens. According to the repeat size & squeezee speed, the machine can operate up to eighteen strokes per minute.
(xi) Printing Cycle:
1. Printing station up, forward blanket movement and flood stroke.
2. Blanket stop, printing station down.
3. Printing stroke on. Then the cycle continues.
166
4.5. ROTARY SCREEN PRINTING MACHINE
(i) 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. The brush roll tweezes loose threads and fibrous matters, which are removed by suction. Fabric heater unit is provided with electrical heating coils inside, which preheats the fabric.
(ii) Printing Unit:
The printing unit comprise of endless rubber blanket, printing heads, squeeze support systems, colour feed pumps to individual squeezes and auto levelers, pressure application systems to squeezes, pre washer, blanket washing unit, gluing unit for PVA adhesive application & infra red lamps for blanket heating. Both the blanket and screen drive heads are driven by D.C motor drive at uniform surface speed. The blanket after printing gets pre washed by water spray & sponge gets second wash in the washing unit.
(iii) 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. A blanket guider prevents shifting of blanket during movement. The infra – red lamps heat washed blanket.
(iv) Printing Head:
The printing heads provide support at both ends to the end ring glued rotary screen. It also encompasses squeeze support cradle at both sides. The squeeze 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 squeeze. The color level inside screen can be controlled manually (or) by auto leveler units.
In this system the squeezing is done by S.S. Metal blade (0.1 – 0.2 mm thick) of varying widths (40, 45, 50 mm etc.,) according to the type of motifs. The squeeze unit with blade is lowered during printing by pneumatic means.
S.S Rod & Magnet System
In this system, the squeezing is enhanced by S.S rods which are pulled downwards by electromagnets placed beneath
168
the blanket. By changing the voltage, squeezing pressure can be varied.
According to the type of motifs, various rod sizes (4, 6,8,10,12,16,20 (or) 30mm dia) can be selected.
(vi) 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.
According to the printing speed, compensator roll 1 (at feed) and compensator roll 2 (at delivery) synchronizes the movement of fabric.
(vii) Working:
The respective screens are mounted on the rotary heads. Selected squeezes 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 squeegee pressure is also set accordingly. The printed fabric is conveyed through dryer and plaited. The speed of printing is possible up to 80 meters /min depending upon the substrate. Since the speed of printing is very high, strict vigilance is required during printing.
169
(viii) Advantages:
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
(ix) Disadvantages:
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
The value of continuous rotary screen printing first became apparent in the 1960’s. The yellow screens, each applying the appropriate motif, are arranged sequentially as in roller printing, but they are aligned over a moving horizontal blanket that carries the fabric between the two. As the fabric moves forward the screens rotate and colour is applied on fabric. One arrangement for the delivery of print paste is shown in figure.
The squeegee blade is flexible to accommodate any variation in pressure required to force the paste evenly through the mesh of the screen across the width of the fabric. In some
170
models the squeegee is replaced by a metal rod held in position by a magnetic field. This more suited to heavier fabrics, since the mechanism imposes higher limit on the minimum amount of paste that can be delivered.
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 rate is low
Machine cost is high Machine cost is low
It is best suited for larger lotsIt is best suited for smaller lots
No joint marksJoint 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 printedOverall & cross border designs are printed
171
Uniform printing results are achieved
Less uniformity (block to block, edge to edge variation)
Colour consumption and wastage more
Colour consumption & wastage are less
4.6. TRANSFER PRINTING
Transfer printing involves the transfer of colour from one surface to another surface, generally from a paper to a textile material. It makes possible to express delicate designs which were difficult to reproduce by the conventional printing technique on fabrics. Here, in 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 sec at around 200C.
a) 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. There are basically four techniques available for transfer printing.
Types of Transfer Printing
1. Wet – transfer printing
2. Film – release transfer printing
3. Sublimation – transfer printing
4. Melt transfer printing
1. Wet –transfer printing:
In this water soluble dyes printed on paper migrate to fabric having fixing chemicals, which is fed in wet condition. This process was developed by Trans prints Ltd. for transfer printing of nylon and acrylic. It uses transfer paper printed with acid dye or cationic dye. In transfer printing, cloth to be printed is first padded
172
with the treating liquor. Then transfer paper is fed along with wet state fabric, both are sandwiched in between a cylinder of large caliber & an endless blanket for transfer printing at 100 – 120 c and the printed cloth is washed.
2. Film – release transfer printing:
In this method, the film layer-containing colour from the paper is transferred completely to the textile substrate by the application of heat & pressure. The adhesion forces between film layer and fabric being stronger than the adhesion between film & paper.
Since, STP process is only suited for disperse & PET system, other class of dyes, which cannot be sublimed, can be printed by film – release method. In this system, the paper is printed with highly flexible polymeric film containing dyes & dye fixing gents. The fabric and papers are passed through the nip of a heated calendar at 60 c –150 c with a pressure of 25 kg /cm2. The coloring matter & the thermoplastic binder are transferred to the fabric under heat & pressure. After the release of the film, paper is removed when the design is completely transferred to the fabric. The prints are then fixed by steaming (or) dry – heat treatment. The polymeric film breaks up during these treatments. Generally, washing of the print is not necessary. How ever, for certain dyes such as reactive dyes, which do not give 100% fixation, washing off is required to remove the unfixed dye.
173
3. Sublimation transfer printing:
The vapour phase transfer takes place by heating under pressure at 180–220 C for 20 seconds. The dye sublimes under heat from the paper and is absorbed by thermoplastic substrates (PET).
4. Melt transfer printing:
Here, the paper is printed with printing ink containing wax and thickener. When the printed design is placed down on the fabric and pressed by hot iron. The wax melts and the impression is transferred to the fabric.
b) Flat-Bed Press Transfer Printing Machine (STP process):
In this machine, the fabric or garment is placed on the press bed and the pre- printed release paper is placed on it. It is then hot pressed between 180– 220 c for 20 –30 seconds. Thus the pattern on the printed-paper is transferred on to the fabric or garment, which is then removed, from the machines.
174
Continuous Calendar Transfer Printing Machine (STP Process)
In this machine, the fabric and the pre – printed release paper pass in close contact with each other round a large cylinder or drum (0.5 to 2 m diameter). The two are held in contact by means of an endless blanket under tension. The cylinder is heated electrically to 180 -220 c and the fabric in firm contact with the paper is passed over it for 15 – 20 seconds. Thus the pattern on the paper is transferred on to the fabric by sublimation. The operation is continuous. The output is 15m per minute.
1. Advantages:
a. The open of transfer printing is simple and it does not require expensive machinery.
b. There is no after treatment is required ( STP process)
c. As it is simple operation, no skilled labour is required
175
d. Here, the faults do not occur. Because, the defects are rectified at the stage of paper printing itself
e. It requires less space
f. There is no need to store printing goods. The goods can be printed when required in the required quantity.
g. It is possible to print knitted goods and garments as well as grey fabric
2. Disadvantages:
a. The STP process is mainly applicable to PET material. This process is not applicable to natural fibres like cotton / silk as they are not thermoplastic and do not posses any affinity.
b. The number of dyes used for printing is limited
c. The cost of printed paper is high
d. It is uneconomical for shorter printing rums
e. There is a risk of trend change
f. Only surface printing is done
g. Disposal problem of printed paper.
4.7. FIXATION AND AFTER TREATMENT
(i) Ageing:
After the cloth is printed and dried, the dyestuffs and chemicals are present in the dry thickener film deposited on the cloth surfaces and the dye is not yet transferred to the cloth. This is done by either ageing or steaming. This is a critical step in printing, and unless this is done properly, loss of colour value, spreading of the color beyond the boundaries of the designs, appearance of specks etc. may results.
Ageing consists of exposing printing goods to more or less prolonged action of steam at atmospheric pressure to assist in
176
the diffusion and fixation of the dyes. This can be done in various ways:
(a) By hanging the goods in large ageing or hanging rooms.
(b) By passing them through an ageing chamber continuously where the required conditions of temperature and humidity are maintained, and
(c) By a short steaming in a continuous steam ager in the presence of moist or superheated steam.
The ageing rooms may be 25 to 40 feet in length and the printed cloth may be hung in long loops from a series of wooden bars. The floor may be of wood, stone or iron grating. The heat is supplied from live steam pipes arranged at the base of the walls. By using wet and dry bulb thermometers and adjusting the steam supply, the required humidity can be maintained in the ager. Goods may be kept in the ager for 1 to 6 days.
Where the production is large the ageing has to be done in a short time. This consists of an iron chamber inside which top and bottom guide rollers are provided.
A wooden hood is provided at the top of the chamber, arranged to carry off the fumes produced during ageing. A steam pipe runs into this hood. The cloth to be aged enters and leaves the ager through the same aperture, which is provided with two steam-heated pipes fixed parallel to the weft yarns of the fabric being aged. These prevent the formation of water drops from steam and falling on the cloth. The ager is supplied with low pressure steam through a perforated pipe placed beneath the lower series of guide rollers. The condensed water formed runs down the sides of the chamber and collects on the floor from where it is siphoned out from time to time.
The cloth is aged in the Rapid Ager at 650 C to 950C depending on the class of dye and style of printing employed. The cloth may be run at a speed of about 60 yards/min. and ageing may be done for about 3 min.
177
There are certain disadvantages of ageing. For example this is an expensive operation as the steam consumption is high and so are capital outlay and floor space requirements. Another factor is the time needed to start up to establish satisfactory conditions. Because of the large volume, long heating up times is needed and time is needed to fill the empty ager. Since there will be a large amount of cloth in the ager, spoilt yardages can run high in the case of accident, power shut off etc.
a) The Rapid Ager:
The Rapid ager consists of small iron chamber with the guide rollers at the top and bottom. A wooden hood is provided at the top of the chamber to carry off fumes during steaming.
The printed cloth enters and leaves the ager through the same apenture. Two heated pipes parallel to the weft thread of the cloth. The steam is supplied from perforated pipes fixed at the bottom of the ager. The condensed water formed from the steam runs down the sides of the chamber collects on the floor and is cleaned of from time to time. Goods printed with Vat dyes, vat resists Rapidogen resists etc., are steamed in the ager for 5 to 10 minutes at 100 to 102oC. The operation of steam in this ager is very high and therefore, the operation is expensive. Rapid ages
178
are not suitable for light weight goods because of the stress extended on the fabric.
(ii) Steaming:
Printed dyes are usually fixed by steaming process, the steam providing the moisture and rapid heating that brings about the transfer of dye molecule from the thickener film to the fabric within a reasonable time. The terms ‘ageing’ and ‘steaming’ refer to the same process of fixation. The time and conditions required for fixation in steam vary with the properties of the dyes and fibres used ranging from 10 seconds to 60 minutes in steam at 200 to 100oC. Technical and economic factors have encouraged the use of higher temperature and shorter time.
a) Batch Steamers:
For expensive fabric and small quantity there are obvious advantages in using steamers of low capacity, that can be quickly raised to walking temperature and that produce no creasing stretching and other damage to fabric. Batch steamers also show advantages when color yields are improved by steaming at above atmosphere pressure for example in the case of deep colors on polyester fabrics.
The following are the various dye fixation processes after printing of polyester fabrics.
1. Atmospheric Steaming:
This method does not require a pressure vessel, but in order to obtain moderate good yields of dye a ‘Carrier’ must be added to the print paste. Steaming for upto 1 hour is carried out at atmospheric pressure.
2. Pressure Steaming:
A steaming treatment of 20 – 30 min at a pressure of 2.0 x 105 – 1.4 x 105 N/n2 (30 – 20 lbs/in2) is given. In this method no carriers are necessary but the steamer must be capable of operating safely at much pressures.
179
3. High temperature Steaming:
The ICI High temperature steamer uses superheated steam to obtain accelerated dye fixation. The print paste contains an addition of urea, which aids dye transfer to the polyester fiber. High temperature steaming is a continuous process and no pressure seals are necessary. For ‘Terylene’ or polyester fabrics, temperature upto 180oC are usually employed with a treatment time of 1 Min.
4. Dry Head (Baking) Fixation:
An addition of 100 parts of urea per print paste and the use of an emulsion thickening is recommended. This method operates at the highest temperature range 180oC – 200oC and at times of 120 – 30 seconds respectively.
b) Thermo fixation process (curing or baking):
In case of pigment printing only when the printed fabric has been raised to an adequate temperature in the binder given enough energy to form a continuous film that incorporate the pigment particles and achieves satisfactory adhere to the fibre surface. At the same time, Cross-linking of binder molecules is achieved if suitable monometers or agents have been used, and the required pH and the temperature achieved.
The equipment for this purpose is the roller baker or “curing over” as shown in figure is an arrangement for carrying woven fabric through recirculated hot air, with as many fabric transport rollers as are required to provide the exposure time and fabric speed desired, times of 3 to 5 minutes at temperatures of the range 160 to 140oC are generally preferred.
c) Continuous Steamers:
For steaming large quantity of printed fabric continuous steamers such as “festoon steamers” can be used. Long loops are formed on-rods touching only the unprinted face to avoid marking off which are moved slowly along a track near the top of a steam chamber, constructed in brick or steel. The rods may be
180
slowly rotated to avoid bar marks. In its loops (Festoon) of upto 5 meters in length, long steaming time or high throughout speeds can be achieved without tension and mark-off problem. A fabric content of 800 meters allow an over all speed of 80 meters/min with a tem minute steaming time.
4.8. PRINTING OF BLENDED FABRICS
Nowadays blended fabrics are becoming more familiar than Synthetic and natural fibres because inorder to overcome the discomfortability caused by synthetic fabrics during wearing that is their hydrophobic nature and also the wrinkled effect caused by the natural fabrics finds the way for usage of blended fabrics like PET/Cellulosics, PET/COT, PET/WOOL, etc.
The use of wetting agents is beneficial in dissolving dyestuff. For example, Turkey red oil (TRO) is the commonly used wetting agents for napthal and vat dyes, sodium salts of sulphated and animal oils and ethylene oxide condensates are examples of wetting agents.
Wetting agents are used to avoid the lump formation during due dissolution. They are anionic or non-ionic.
(ii) Dispersing agent:
They are included in the print paste to maintain the dye in dispersed form. To avoid precipitation or cluster formation of dyes. Some of the dispersing agents are Glycerin, Diethylene glycol, Dithioglycol.
182
(iii) Hygroscopic agents:
These agents absorb water from the steam and helps in the penetration of the dye into the fibre. Mostly used agents are Urea, glycerin.
(iv) Antifoaming agents:
This is included in the paste to avoid formation of foams. Benzene, pyridine & turpentine are the mostly used agents.
(v) Acids:
To maintain the pH of the printing paste acids are added in the printing paste. The mostly used acids are organic acids.
(vi) Oxidizing agents and Reducing agents:
They are mostly used in the discharge style of printing. Mostly reducing agents are used. Stannous chloride, zinc sulphoxylate formaldehyde, sodium sulphoxylate formaldehyde.
(vii) Thickening agents:
Selection of thickeners depends on the type of dye used and fabric to be printed. The quantity of thickening in the recipes is not rigid but may be increased or decreased because thickening agents may become thicker or thinner on standing and the compensating adjustment should be made to the water content only, so that other chemicals concentration remains constant.
a) Preparation of selected thickening Agents:
1. Sodium Alginate:
This is used for printing procion dyestuffs and direct dye.
Recipe:
12.5 parts - Sodium hexameta phosphates
dissolved
137.5 parts - water at 60oC &
800.0 parts - cold water are added
183
50.0 parts - thickening sprinkled on the solution
and stirring is Continued for 5-10 min
to break down any Lumps, finally, the
mixture is bulked to
-----------------------
1000 parts
-----------------------
After standing overnight it is used.
2. Synthetic Thickener:
These are poly acids which are in coiled form. They will give straight chain polymers when they are neutralized with alkalis which will increase the viscosity of the system.
1 part - Synthetic thickener
1 part - NH3 solution
0.5 parts - Emulsifier
95.0 parts - Water and stir well
------------------
1000 parts
------------------
* No electrolyte should be used in the case of synthetic thickener.
(viii) Selection criteria of Dyes:
For Synthetic blended fabric dyes that are mostly used are combination of two classes of dyes whose molecular size is very small is mostly used. Only those dyes can penetrate into the high crystalline nature of the synthetic fiber is used for PET component& also those which fix in easily in the natural fibre is also selected and used as a combination. So mostly used dyes are disperse dyes & Reactive dyes OR disperse dyes and vat
184
dyes. Pigments are also used since they go for surface deposition only.
(ix) Single dye application on Blended fabrics- Fixation techniques and after treatment:
Single fixation can be brought on blended textile by the usage of pigments for any kind of blend ratio. But only disperse dyes/ reactive dyes can be used for printing blends if the blend ration contain large amount of polyester or cotton portion.
(x) Direct style of printing using Pigment dyes on PET/Blends using single stage fixation Method:
a) Principle:
Insoluble pigments are deposited on textile material by forming a film of polymer layer (binder) on the surface of textile material. No after treatments is the very good advantage of this method i.e., printing and packing. For the cross linking of binder acidic and hot conditions are required. Liberation of NH3 from the thickener brings the acidic condition. Curing is done at 150oC for 10 minutes.
b) Recipe:
Pigment Paste
Pigment Emulsion – x gm requires 8 g +(3/2)x gm of binder
Stock thickening
Start with Water - 96.4 parts
Softener - 1.0 parts
Emulsifier - 0.4 parts
Stir in and Synthetic thickener (0.5%) - 0.7 parts
Mix well Ammonia - 0.5 ml
Cross-linking agent - 1.0 part
----------------------
100 parts
185
Note: Mix the two paste and stir well before printing.
c) Shop floor Practice:
Print
Dry
Cure (Hot ironing or treatment in curing chamber at 150oC for 5 minutes)
d) Fixation Techniques and after treatments:
The treatments done after printing are to fix the dye or pigments are called as after treatments. Different after-treatments are available which varies according to textiles and dyes which has been used for printing.
Curing:
Curing is a polymerization process in which some cross-linking reactions takes places. Normally acidic and high temperature conditions are required for curing. Various curing methods are available like hot ironing, exposing to sunlight for 3 days and by using curing chamber.
The curing chamber consist two rails for the feeding of fabric. High temperature condition is created using two fans and electrical heater which will supply the hot air. With the available curing chamber we can maintain temperature from 100 to 180oC. Usually curing is done at 150oC for 5 mts.
e) Problems & Remedies:
While printing the Blended material gets spoiled or damaged due to various problems faced by the technicians. Some problems & their remedies are listed below.
1. Splashes of printing paste at the time of printing:
Precautions should be taken to get printable viscosity of printing paste, selection of gums and chemicals. The splashes on
186
the white fabrics occur at the time of screen lifting because of vibration of bolting cloth. Addition of proper auxiliary will avoid the above problem.
2. Yellowing and uneven prints of the printed fabric cloth:
The fabric should be free from auxiliaries like size, conning oil, non-ionic emulsifiers and cotton impurities. The above problem can be avoided by proper pretreatment process.
f) Process and Quality control:
1. Bleeding at the time of printing and steaming:
This problem arises if excess dosage of axillaries like urea or similar products is present, which will absorb moisture from steam and air, resulting in the bleeding. The above problem can be avoided by proper addition of the above chemicals and also proper maintenance of thickening viscosity.
2. Mark off / hallowing because of sublimation:
This defect can be removed by- Selection of proper dyes and Good quality wrapper for pressure aging.
Low sublime disperse dyes convert into volatile form and deposit on the unprinted portion of the fabric, creating stains, similarly terry cotton wrapper will cause stains.
g) Ecological Aspects:
In any process of textile wet processing ecological consideration is of much importance.
1. By the discharge of printing paste into the effluent it is found the BOD of the effluent is found to be increased.
2. This can be minimized by using thickening agents like synthetic thickeners instead of natural thickeners.
3. The use of acidic pH also increases the pH value of the print paste effluent but this can be overcome during the process of neutralization in the treatment plant.
187
4. The use of discharging agent like stannous chloride in the print paste increases the metal content in the effluent load. This is avoided by going for the other discharging agents like rangolite-C
h) Development of Carbonized Style and details of Printing on P/C Blend:
1. Principle:
Fine-count 100% Polyester printed sarees are manufactured from PET/COT blend fabric by removing the cotton component by a treatment of 70% Sulphuric acid after printing with suitable disperse dyes. This process of removing the cellulosic component with sulphuric acid is called carbonization.
2. Recipe:
Sulphuric acid - 70%
Temperature - 10oC
Urea - 10 gpl
3. Shop Floor Practice:
First the PET/Cotton is printed with disperse dye using carrier method. Then the fabric is padded with Sulphuric acid solution. Padded fabric is batched for 2 hours at room temperature.
4. After treatments:
Fabric is then washed thoroughly by using hot and cold water. Bleaching by using peroxide can also be done to remove the yellowness.
4.10. OTHER TYPES OF PRINTING
(i) Pigment Printing:
a) Printing of cotton fabric with pigments colors:
Compositions of pigments printing paste besides the pigment, the pigment printing paste contains a binder for fixation
188
of the pigment, a suitable thickening agent to facilitate the printing process cross linking agents to improve fastness properties, catalysts to accelerate the cross linking of the binder, softening agents to improve the handle of the fabric, auxiliaries to prevent formation of rust and drying out of the printing paste and dispersing agents to stabilize the pigment emulsion and binder dispersion.
Pigments are supplied as dispersion called emulsion or pigment paste containing surface active agents to keep them in staple dispersion. The binder is the most important ingredient in the printing paste. It is a film forming material of high molecular weight. A thickener used must have no effect on handle of the fabric and it must be removed easily after curing.
A dispersion of one liquor into another in which it is immiscible. There are two types of emulsion viz water-in-oil (w/o) and oil-in-water (o/w) type, in system containing 25% water usually from 2/o type of emulsion where as these as containing 31% water from o/w emulsion.
Catalysts are acid liberating suite to accelerate the cross linking of binder and to facilitate the reaction between the binder and the substrate. Diammonium phosphate is the most commonly used catalyst.
Dimethly urea and dimethylol urea are examples of cross linking agents, which are not self reacting.
Dispersing agents and polyalcohols are usually incorporated in the paste to stabilize the emulsion and prevent it from drying.
1. The Process:
The sequence is PRINT-DRY-CURE. In this process a binder emulsion (usually 20%) is first prepared and is mixed with pigment dispersion; this paste is used then for printing.
2. Preparation of Binder Emulsion:
200 parts Aramine SLN Binder
189
5 parts Emulsifier
50 parts Urea (Hygroscopic agent)
30 parts Diammonium phosphate(1:3) (Acid liberating agent)
(Catalyst)
50 parts Water
665 parts Kerosene mixed under high-speed stirrer
1000 parts (Total)
3. Printing Recipe Preparation:
50 parts Acramine pigment (Dispersion)
40 parts Binder emulsion
10 parts Fixer CCL
100 parts (Total)
The Binder content can be increased if required. The fabric printed with the above recipe suitable method (screen, roller or rotary screen) and it is dried at 90oC to 100oC until free from kerosene and then curing chamber at 140oC for 5 minutes.
The advantage of using pigments in printing are as follows:
1. Application to all kinds of fibres especially to fibre mixtures and blends.
2. High production of prints due to elimination of after treatment.
3. Greater degree of certainty as regards color matching.
4. High fastness properties
5. Non-staining of white ground
6. Availability of complete range of colors.
The disadvantages of pigment printing are the use of costly and hazarders kerosene and the lack of fastness to rubbing and dry-cleaning. The present trend, however, is to
190
replace partially or fully kerosene is the print by the use of monomer products of synthetic origin such as acrylic thickeners.
(ii) Khadi Printing:
Khadi printing is usually carried out on a dyed fabric with a paste containing a white paste pigment like titanium-dioxide thus producing white effect on colored ground.
A typical recipe is,
300 parts TO2
300 parts Binder SLN
100 parts polyvinyl acetate emulsion (Acrylic thickener)
20 parts Fixer CCL
5 parts Optical whitener (Ranipal)
275 parts Emulsion thicker
1000 parts after printing, the fabric is dried and cured
(iii) Hand block printing:
Hand block printing is the simplest of all methods of printing, and generally considered to be the most artistic, the hand-block printing is used in the cottage industry.
For this method of printing the accessories required are the block containing the design, a printing pad that can be suitably and comfortably accommodate the block and a printing table of convenient size having a resilient surface usually by laying a few layers of a thick of cloth.
For producing multi-colored designs many blocks (as many as the number of colors used) are employed, each of them providing a part of the final designs. Each block is used for printing one color of the design. Naturally each color of the design requires separate pads.
For making a block for printing a wooden block is selected. It should be noted that the surface of the block should have no knots. The surface is made even and smooth. It should have
191
length and breath sufficient to hold the design comfortable in it. It is usually to provide four nail points at the four corners. In a multi colored design, these four nail points will be in exactly the same position in all the blocks. The design is transferred into the surface of the block usually by means if carbon paper. The unwanted portions are then neatly carded away so that only the design portion projects from the surface of the block.
This projection should be limited to a maximum ¼“. It is very difficult to curve fine lines because they easily break. In such circumstances it is usual to metal strips to form this line. Now the block is ready for use.
Printing is generally carried out on very heavy built tables, preferably with stone or concrete tops. The printer may work in a standing position; the height of stone table varies accordingly. The printing table used is not of any definite size but it is better to have width more than the width of a normal cloth usually being printed and length suitable to the convenience. It is usual to cover the rigid surface with a resilient material. First several thick nesses of blanket are carefully laid on the table, and the whole is then covered with a sheet of water proof fabric. The cloth to be printed is spread out on the table and kept in place either by pinning it on to a back grey (black cloth) or by gumming it down directly on to the water proof cover. It is essential that no movement of the cloth occur during the printing operation. The cloth is wound round a wooden tube, called a shell. Some British gum or gum Senegal paste is then placed at the table end spread along it in as thin a film as possible, using a rubber squeegee. The roll of cloth is unrolled along the table so gummed, and lightly pressed into place either by hand or by careful ironing.
The printing pad is charged with the color paste so that spreads evenly throughout the pad. It should be noted that the pad should not contain too much color. If too much color is contained in the pad then excessive color to be taken up by design parts of the block and while printing this might flow down, thus spreading the design beyond the limit and a sharp edge will
192
not be obtained. The block is placed on the pad with the design touching the color 2 to 3 times so that every part of the design gets on even charge of the color. Now the lock is placed on its respective position on the cloth.
Holding the block firmly with the left hand and the block is tapped on its top once or twice with the right hand or income cases a wooden hammer. The cloth is held with one hand and with other hand the block is lifted. Care should be taken to see that the cloth is not lifted along with the block. The block is again placed on the color pad and placed on the cloth at the next repeat so that the two repeat conclude correctly. The success of the block printing is how correctly the reports can be made so that the repeats cannot be easily detected. After printing the block be immediately washed.
1. Printing of multi coloured design using block printing:
For producing multi-coloured prints many block (as many as the number of color used) are employed each of them providing a part of the final design. The first block has traced upon it all those parts of the pattern (design), which are to be printed with the same color or first color. Those parts of the block not used for the block not used for this pattern are cut away so as to leave the pattern standing out in relief. This block is pressed upon a colored pad or smeared with colour paste so as to leave the desired colored impression. In the same way another block is prepared of the parts of the pattern to be printed in a second color and this is impressed on the fabric to cover the same area as the first block. While printing a multicolored design it is better to print the whole cloth with one color first and print with the second color, then with the third color so on. This can be repeated using as many blocks as there are colors in the pattern and thus a multi-colored pattern may be fully up on the fabric.
The degree of perfection in the printed pattern will depend on the accurate registration of each block, so that there is no over lapping of the color boundaries and also on the general levelness
193
of the color impression. It is usual to give some after treatments to the cloth after printing. These after treatments will vary according to the group of color being applied. Steaming is one after treatment, which is generally applied to almost all printing.
This method is a laborious and time-consuming, since a very number of impressions have to be made to print the whole design on the entire cloth.
As a result the Production is low; however, no special printing machines are required in block printing.
(iv) Batik sytle printing:
“BATIK” is an Indonesia word describing a form of RESIST printing which, although known and practiced as a native craft in southeast India, Europe and parts of Africa has achieved an unrivalled degree of craftsmanship in the Island of JAVA.
In this printing, the RESIST is obtained by applying WAX to both sides of the fabric. Dyeing is then carried out in the cold and avoid melting the wax, thus confining the coloration to the unwaxed area. Selective further waxing and redyeing allows a variety of colorings of increasing depth to be built up additively.
The designs are usually drawn by hand using a special type of pen made of bamboo. As an alternative hand blocks containing the required designs may also be used. The hand blocks are partially dipped in molten wax and then printed on the cloth with the molten wax. There are quite a wide range of designs that can be produced by this type of printing. The only draw is that in most cases one design cannot be reproduced exactly afterwards.
Batik printing involves the following
1. Preparation of cloth for batik printing
2. Wax printing of the cloth
3. Dyeing of the cloth (Cold dyeing using Napthal color)
4. Drying of the cloth
194
5. Further waxing and re-dyeing of the cloth
6. Removal of wax from the printed cloth
1. Preparation of cloth for batik printing:
The cloth to be printed is first treated with a thin starch solution and iron this preliminary process improves the results and tends to prevent undye penetration of the wax into the cloth. Usually the wax is printed on both the face and back of the fabric, and the results are better if the wax is not allowed to penetrate the cloth but rather to form LAYERS ON THE TWO SURFACES. In this way the edge of the objects shaper in the final result.
2. Wax printing of the cloth:
The cloth to be printed with the wax is stretched out on a table covered with layers of cloth, to prevent the hot wax from smoking into them the tablecloth is sprinkled with an even layer of china clay or fine sand. In java, banana leaved previously soaked in dilute caustic acid are used, as the wax neither adhere to these not penetrate into them.
The wax is applied from a special form of printing block. The wax is kept molten in a simple waxing vessel, which is a shallow dish of sufficient size into hold the block. A piece of felt is placed in the bottom of this vessel, wax is poured over the felt and the whole is kept heated throughout the printing operation by a small kerosene lame. The metal block, which retains its heat throughout the printing operation, is furnished as required from the surface of the felt saturated worth molten wax.
3. Dye stuffs suitable for use in batik printing:
Dyestuff suitable for this work must be capable of being applied from a cold dye bath, since a heated dye bath would remove was resist.
The following classes of dyes are of interest.
1. Indigo and other cold-dyeing vat dyestuff
2. Azioc ‘Brenthol’ dyestuffs
195
3. ‘Procion’ dyestuffs-cold brand (M.brand)
4. ‘Soledon’ dyestuffs – Soubise vat dyes
5. Batiks are dyes in shallow float thoughts of suitable size to accommodate the fabric. The fabric is placed in the through and dye liquor poured over it, and then it is rubbed gently by hand to aid penetration. When thoroughly moistened the fabric is removed and either placed flat in another similar through or allowed to over a bamboo rod then dried.
In a multi colored design, the cloth is first coated with wax in places where white patches are required. The clothes then dyes with the lightest color of the design using azoic dyestuffs (naphthal colors) under no circumstances the cloth should be heated with the wax coating. After drying in shade, the cloth is gain coated with wax wherever this color becomes part of the design. The cloth is dyed with the next deeper color. The cloth is given further coating of wax as before and dyes with a deeper shade. In this manner the cloth is given wax coating and then dyes with deeper and deeper shade. After the complete designs have been formed the cloth is boiled in water for removing the wax.
4. Removal of wax from the printed fabric:
The final operation in the batik printing is the complete removal of the wax used as the resisting agent. This is carried out, after the drying operation have been completed, by immersing the cloth in a bath of very hot or boiling water to remove as much as possible of the surface-held wax followed by a treatment in a hot solution of soda to remove the remaining. The wax that is removed by the hot water is skimmer off, collected recast into blocks of suitable size and used again.
196
Learning Activity
1. What are the advantages of Direct Style of Printing?
_________________________________________________
_________________________________________________
_________________________________________________
2. Explain about Moving Trolley mechanized Printing table.
_________________________________________________
_________________________________________________
_________________________________________________
3. Explain about Ageing.
_________________________________________________
_________________________________________________
_________________________________________________
4. What are the accessories needed for Hand Block Printing?
_________________________________________________
_________________________________________________
_________________________________________________
LET US SUM UP
In this unit you have studied about the Definition of Printing, Styles of Printing, Methods of Printing, Fully Automatic Hydratex Flat Bed Printing Machine, Rotary Screen Printing Machine, Transfer Printing, Fixation and After Treatment, Printing of Blended Fabrics, Print Paste Formulation and Other Types of Printing like Pigment Printing, Batik Printing, Khadi Printing etc.
197
ANSWER TO LEARNING ACTIVITY
Learning Activity
1. Advantages:
Simple, Direct &ease of reproducibility
Number of operations is less. All colors are applied & fixed simultaneously.
2. In this system the screen is fixed on a trolley unit, which moves on rail on both sides blanket. The squeeze movement is supported by chain drive. Using a handle the squeeze movement can be enhanced manually. Pressure can also be adjusted. Forward movement of trolley is facilitated by lever lock, which fits in stopper blocks.
3. Ageing consists of exposing printing goods to more or less prolonged action of steam at atmospheric pressure to assist in the diffusion and fixation of the dyes. This can be done in various ways:
(a) By hanging the goods in large ageing or hanging rooms.
(b) By passing them through an ageing chamber continuously where the required conditions of temperature and humidity are maintained, and
(c) By a short steaming in a continuous steam ager in the presence of moist or superheated steam.
4. For this method of printing the accessories required are the block containing the design, a printing pad that can be suitably and comfortably accommodate the block and a printing table of convenient size having a resilient surface usually by laying a few layers of a thick of cloth.
![Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 ... 5 - Formatted.pdf · Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 ... and Scatterplots] Unit 5 – Inequalities and Scatterplots](https://static.documents.pub/doc/80x56/5b76ea0a7f8b9a4c438c05a9/unit-1-unit-2-unit-3-unit-4-unit-5-unit-6-unit-7-unit-8-5-formattedpdf.jpg)
