Printing produces colourful effect on the fabrics Printing is application of colour in the form of a design. Printing can be done by hand or machine. The dyes used in printing are in the form of pastes.
A) Hand printing B) Machine printing
� Block Printing : Block printing was practiced by Chinese and Indians some two thousand years ago. Blocks are made of wood or wood and lino. The design is carved on line which is generally cut to a thickness of � inch. This cut piece of lino is struck to wooden piece of the same size. Many printers use only wooden blocks on which the design has been carved. These blocks are dipped in paste of colour and then pressed on the fabric, so that coloured pattern is produced on the fabric. First a block carrying the paste of one colour is stamped on the fabric and allowed to dry. Then another block carrying the paste of different colour is stamped over it to form the multi-coloured patterns. The process is repeated over the entire fabric surface to be printed.
It is a slow and costly process, uniform pressure is needed to transfer the colour. The intensity of colour cannot be uniform throughout.
� Stencil Printing : Stencil printing originated in Japan. Its high cost limits its use and importance. In this, printing, the design must be first cut in cardboard, wood or metal. The stencil may have a fine delicate design, or there may be large spaces through which a great amount of colour may be applied. A stencil design is usually limited to the application of one or two colours and generally used for narrow width of fabric like block printing. This method is very slow.
� Screen Printing : Originally, this technique was referred to as silk screen printing because the screens were made of fine, strong silk thread. Today they are also made of nylon, polyester, vinyl and metal. Screen printing is done with the use of either flat or cylindrical screens.
Each screen design may be drawn by hand and a coating of lacquer or other impermeable substance applied to all parts of the screen that are not part of its design. Today the design is photographed and a negative is used for each sensitized screen to opaque or block out, those areas not part of the screen's colour design. Each screen is then fitted into a wooden or metal frame.
The printing paste or dye is poured on the screen and forced through its unblocked areas onto the fabric with a rubber-edged squeeze. The frame is then raised and placed on the next section of the fabric and the operation is repeated until the entire length of the cloth is printed with that particular colour. This process must be repeated for each colour to be used in the design.
The hand screen printing is time-consuming and limited to relatively short lengths of 60 yards (58m) of fabric. Electronically controlled automatic machines can screen print long lengths of cloth at rates of upto 450 yards (400m) per hour.
Machine printing includes Direct Roller printing, Duplex printing, discharge printing, resist printing, pigment printing, transfer printing, photo printing and flock printing.
� Direct Roller Printing : Roller printing was developed in 1785. Thousands of yards of coloured designed fabrics are produced in an hour by this method of printing.
In this printing, several copper cylinders or rollers are engraved with design. Engraving the designs on the rollers is a hard and careful work lasting many days, but actual printing by this method takes very little time.
The roller is as wide as the cloth. The numbers of rollers required depends on the number of colours used in the design. One roller prints one colour only.
The roller printing machine comprises of a large central cylinder around which passes the fabric to be printed, this cylinder rotates with the moving fabric. Number of colour printing rollers, carrying different colours, press against the fabric and the central cylinder. Thus if there are five colours in the design there are five colour printing rollers. Each of these rollers is made of copper and engraved with the respective design. Furnished rollers which move at intervals, containing the colour or dye are placed close to the design rollers. The dye is absorbed by the brush like surface and transferred to the design engraved rollers.
Next to the design roller is a big iron cylinder or roller around which the cloth is drawn as it is printed. The cloth to be printed needs a rubberized blanket (for padding) and grey cloth pass between the engraved rollers and the cylinder. The blanket gives a good surface for sharp printing and the grey cloth protects the blanket besides absorbing the excess dye.
Printing machines of this kind can be provided with upto fourteen rollers, as they are able to produce patterns in fourteen colours. The roller printing machine prints only on one side of the fabric.
� Duplex Printing : In Duplex printing, the printing is done on both the sides. The fabric may be passed through the roller printing machine in separate operations. This printing forms clear outline on both sides of fabric.
� Discharge Printing : This type of printing is suitable for fabrics with dark backgrounds. The fabric is first dyed. A discharge paste which contains chemicals to remove the colour is then printed on the fabric, to produce a white pattern on a ground colour. This print is done on materials like cotton and rayon.
Resist Printing : This is just the opposite of discharge printing. In this type of printing, resist paste is printed first on the white fabric, and the fabric is then piece dyed. The resist materials used are resins, or clay or gum. It is put in a patterned form on fabric and is subsequently immersed in dye. The dye will affect only the parts that are not covered by the resist paste. The places where resist material has been put remain undyed. After fabric has been passed through subsequent dyeing processes, the resist paste is removed, leaving a pattern on dark background.
Pigment Printing : In this, dyes used are insoluble in water and very fast to light. These pigments are made into colour printing paste, using various ingredients especially resin to act as binder and the pigment to the printed fabric.
� Transfer Printing : In this process, certain substances can be made to pass from a solid state directly to a vapour state when heated and return directly to a solid when cooled. The design is printed to a paper, which is fed into a machine. This is brought into contact with heat zone, which vapourizes the dye on the paper. Thus the dye is absorbed by the fabric.
� Photo Printing : In this type, the fabric is coated with a chemical that is sensitive to light. The negative of the design is put against the fabric surface and the light is made to fall on it. The design on the negative gets printed on the fabric. The fabric is then washed. Black and white designs and coloured designs can be printed on the fabric.
� Flock Printing : This is a technique of adhering minute pieces of fibre, called flock, to form design on fabrics. Using a suitable adhesive, a design is roller printed onto the fabric. Then flock of cotton, wool, viscose rayon, nylon or acrylic are applied to the fabric in a manner that causes it to adhere in an upright position and produce a pile like, velvet - textured design.
Thus dyeing and printing methods are adopted to enhance the beauty of the textile materials.
Uchapishaji hutoa athari ya rangi kwenye vitambaa Uchapishaji ni matumizi ya rangi katika fomu ya muundo. Uchapishaji waweza kufanywa kwa mkono au kwa mashine. Rangi zinazotumiwa katika uchapishaji ni za aina ya pastes. Uchapishaji wa mikono na mashine: Uchapishaji wa mikono na mashine ulijulikana kwa miaka elfu mbili iliyopita. Vipande vya mawe hutengenezwa kwa mbao au mbao na lino. Muundo ni kuchongwa juu ya mstari ambayo kwa ujumla kukatwa kwa unene wa inchi. Kipande hiki kilichokatwa cha lino hupigwa kwenye kipande cha mbao cha ukubwa uleule. Wachapishaji wengi hutumia tu vipande vya mbao ambavyo muundo huo umechongwa. Vipande hivyo hutiwa rangi na kisha kuingizwa kwenye kitambaa ili kutokeza rangi. Kwanza, kipande cha kitambaa chenye rangi moja hutiwa muhuri kwenye kitambaa hicho na kuruhusiwa kukauka. Kisha kipande kingine chenye mchanganyiko wa rangi tofauti hutiwa muhuri juu yake ili kutokeza michoro yenye rangi nyingi. Utaratibu huo hurudiwa juu ya uso wote wa kitambaa kinachotengenezwa. Ni mchakato wa polepole na wa gharama kubwa, shinikizo la usawa linahitajika kuhamisha rangi. Nguvu ya rangi haiwezi kuwa sawa katika sehemu zote. Uchapishaji wa Stencil: Uchapishaji wa Stencil ulitokana na Japani. Gharama yake ya juu hupunguza matumizi na umuhimu wake. Katika hii, uchapishaji, muundo lazima kwanza kukatwa katika makaratasi, mbao au chuma. Stensili inaweza kuwa na muundo mzuri, au kunaweza kuwa na nafasi kubwa ambazo kiasi kikubwa cha rangi inaweza kutumika. Stensili ni kawaida kuunganishwa na matumizi ya rangi moja au mbili na kwa ujumla kutumika kwa upana mwembamba wa kitambaa kama block uchapishaji. Mbinu hii ni polepole sana. "Kwanza, mbinu hiyo iliitwa ""silk screen printing"" kwa sababu ilitengenezwa kwa nyuzi nyembamba zenye nguvu." Leo pia hutengenezwa kwa nailoni, polyester, vinyl na chuma. Screen uchapishaji ni kufanyika kwa kutumia ama gorofa au silinda skrini. Kila muundo wa skrini unaweza kuchorwa kwa mkono na kufunikwa kwa lacquer au dutu nyingine isiyo na maji inayotumika kwa sehemu zote za skrini ambazo sio sehemu ya muundo wake. Leo, muundo huo huchukuliwa picha na negative hutumiwa kwa kila skrini iliyoathiriwa ili kuzuia au kuzuia maeneo hayo ambayo si sehemu ya muundo wa rangi ya skrini. Kisha kila kiwambo huwekwa kwenye fremu ya mbao au ya chuma. Pasta ya kuchapisha au rangi hutiwa kwenye skrini na kulazimishwa kupitia maeneo yake yasiyofungwa kwenye kitambaa kwa kushinikiza kwa makali ya mpira. Kisha frame huinuliwa na kuwekwa kwenye sehemu inayofuata ya kitambaa na operesheni hiyo inarudiwa hadi urefu wote wa kitambaa huchapishwa na rangi hiyo maalum. Utaratibu huu lazima urudiwe kwa kila rangi itakayotumiwa katika muundo. Uchapishaji wa mkono wa skrini ni wa muda mrefu na umepunguzwa kwa urefu mfupi wa 60m (58m) ya kitambaa. Mashine za kielektroniki zinazoongozwa na umeme zinaweza kuchapisha vipande virefu vya nguo kwa kasi ya hadi mita 450 kwa saa. Mashine ya uchapishaji inajumuisha uchapishaji wa Roller ya moja kwa moja, uchapishaji wa Duplex, uchapishaji wa kutolewa, kuchapisha kukabiliana, uchapishaji wa rangi, uchapishaji wa uhamisho, uchapishaji wa picha na uchapishaji wa kundi. Uchapishaji wa moja kwa moja wa roller: Uchapishaji wa roller ulibuniwa mnamo 1785. Maelfu ya yadi za vitambaa vyenye rangi hutengenezwa kwa saa moja kwa njia hii ya kuchapisha. Katika uchapishaji huu, silinda au magurudumu kadhaa ya shaba huchongwa na muundo. Kuchonga michoro kwenye magurudumu ni kazi ngumu na ya uangalifu inayodumu siku nyingi, lakini kuchapisha kwa njia hii huchukua muda mdogo sana. Roller ni pana kama kitambaa. Idadi ya rollers zinahitajika inategemea idadi ya rangi kutumika katika kubuni. Roller moja huchapisha rangi moja tu. Roller kuchapisha mashine inajumuisha kubwa ya kati silinda ambayo hupita kitambaa kuchapishwa, silinda hii inazunguka na kitambaa kusonga. Nambari ya rangi ya kuchapisha rollers, kubeba rangi tofauti, bonyeza dhidi ya kitambaa na silinda ya kati. Hivyo kama kuna rangi tano katika kubuni kuna rangi tano kuchapisha rollers. Kila moja ya magurudumu haya ni yaliyotengenezwa kwa shaba na kuchongwa na muundo husika. Furnished rollers ambayo hoja katika vipindi, zenye rangi au dye ni kuwekwa karibu na rollers kubuni. Rangi ni kufyonzwa na brush kama uso na kuhamishwa kwa kubuni engraved rollers. Karibu na roll ya kubuni kuna silinda kubwa ya chuma au roll ambayo kitambaa huchorwa wakati kinapochapishwa. Kitambaa cha kuchapishwa kinahitaji blanket ya mpira (kwa padding) na kitambaa cha kijivu kupita kati ya rollers engraved na silinda. Kitambaa hicho hutoa uso mzuri wa kuchapisha kwa uangalifu na kitambaa hicho cha kijivu hulinda kitambaa hicho pamoja na kunyonya rangi iliyozidiwa. Mashine za uchapishaji za aina hii zinaweza kutolewa na rollers kumi na nne, kama wao ni uwezo wa kuzalisha mifumo katika rangi kumi na nne. Mashine ya kuchapisha kwa rolls huchapisha upande mmoja tu wa kitambaa. Duplex Printing: Katika Duplex uchapishaji, uchapishaji ni kufanyika juu ya pande zote mbili. Kitambaa inaweza kupita kupitia mashine ya kuchapisha roller katika shughuli tofauti. Uchapishaji huo hufanyiza umbo wazi pande zote mbili za kitambaa. Uchapishaji wa kutolewa: Aina hii ya uchapishaji inafaa kwa vitambaa vyenye mandhari nyeusi. Kwanza kitambaa hicho hutiwa rangi. Pasta ya kutolewa ambayo ina kemikali za kuondoa rangi huchapishwa kwenye kitambaa, ili kutengeneza muundo mweupe kwenye rangi ya msingi. Uchapishaji huu hufanywa kwenye vifaa kama pamba na rayon. Kupinga Uchapishaji: Hii ni kinyume tu cha uchapishaji wa kutolewa. Katika aina hii ya uchapishaji, pastha ya kukabiliana huchapishwa kwanza kwenye kitambaa cheupe, na kitambaa kisha hutiwa rangi ya kipande. Vifaa vya kukabiliana vinavyotumiwa ni resini, au udongo au gundi. Inatengenezwa kwa muundo kwenye kitambaa na kisha hutiwa rangi. Rangi itaathiri tu sehemu ambazo hazijafunikwa na pastha ya kukabiliana. Maeneo ambapo nyenzo ya kukabiliana imewekwa hubaki bila kupakwa rangi. Baada ya kitambaa kupita kupitia michakato ya baadaye ya rangi, mchanganyiko wa kukabiliana huondolewa, ukiacha muundo kwenye msingi mweusi. Uchapishaji wa rangi: Katika hii, rangi zinazotumiwa hazitoweki katika maji na zinaangaza haraka sana. Pigmenti hizi hutengenezwa kuwa mchanganyiko wa uchapishaji wa rangi, kwa kutumia viungo mbalimbali, hasa resini, kufanya kazi kama kiunganishi na rangi kwa kitambaa kilichochapishwa. Uchapishaji wa uhamisho: Katika mchakato huu, vitu fulani vinaweza kufanywa kupita kutoka hali ngumu moja kwa moja kwa hali ya mvuke wakati wa kupasha joto na kurudi moja kwa moja kwa hali ngumu wakati wa baridi. Muundo huo huchapishwa kwenye karatasi, ambayo huingizwa ndani ya mashine. Hii huletwa katika kuwasiliana na eneo la joto, ambayo vaporizes rangi juu ya karatasi. Hivyo rangi hiyo huingizwa katika kitambaa. Uchapishaji wa picha: Katika aina hii, kitambaa hufunikwa kwa kemikali ambayo ni nyeti kwa nuru. Nakala ya hasi ya muundo huo huwekwa juu ya kitambaa na nuru huangushwa juu yake. Muundo ulio kwenye picha hasi huchapishwa kwenye kitambaa. Kisha kitambaa hicho huoshwa. Michoro nyeusi na nyeupe na michoro ya rangi inaweza kuchapishwa kwenye kitambaa. Flock Printing: Hii ni mbinu ya kushikamana vipande vidogo vya nyuzi, aitwaye kundi, kuunda muundo juu ya vitambaa. Kwa kutumia kamba inayofaa, muundo huchapishwa kwenye kitambaa hicho. Kisha, nyuzi za pamba, sufu, viscose rayon, nylon au akriliki hutumiwa kwenye kitambaa kwa njia ambayo husababisha kushikamana katika nafasi ya wima na kutokeza mchanganyiko kama wa velvet. Hivyo, mbinu za kupaka rangi na kuchapisha hutumiwa ili kuboresha uzuri wa vitambaa.