Fabric printing process:
This process is a part of wet processing. The main objective of the fabric printing process is to achieve the decorative surface of the fabric. The fabric printing process can be defined as a process of applying colours to the fabric surface according to the given design. The decorated fabric surface results after the fabric printing process. It is more economical than a design created during weaving by a jacquard loom.
Various fabric printing techniques:
The important fabric printing techniques getting used in the textile industry are given below:
1- Block printing.
2- Roller printing.
3- Stencil printing
4-Table screen printing.
5- Rotary screen printing.
6- Ink-jet or digital textile printing
7- Sublimation printing
8- Film release transfer printing
· This was the first printing method which was used to print fabric.
· In this method, a block with raised printing surface is used.
· The raised printing surface is inked with the desired colour first.
· The inked printing surface is pressed on the fabric surface.
· The desired design is completed after the repetition of a single block according to the design.
· In ancient ages, the blocks were made of terracotta.
· Now, the blocks are made of carved wood.
· The typical hand block print had no large, uniform areas of colour
· It was skilfully built up from many small coloured areas because wooden surfaces larger than about 10 mm in width would not give an even print.
· This had the advantage that a motif such as a flower would have an effect of light shade obtained from three or four blocks, each printing a different depth of the same colour or shade.
· The bleached or dyed fabric is fixed upon the printing table first with the help of pins.
· Now, the block is inked and then the inked block is placed on the fabric surface and pressed to make a colour impression on the fabric surface.
· The number of blocks getting used depends upon the number of colours present in the design.
· The design is engraved on the metal surface.
· Copper is used for engraved metal rollers.
· Copper could be incised by hand with a sharp steel tool. This is the reason why copper is used to engrave a design in roller printing.
· It is the first continuous fabric printing method.
· One engraved copper roller is used for each colour.
· Very sharp outlines are obtained in the roller printing method.
· The design rollers are mounted against the large main cylinder.
· The fabric travels together with a resilient blanket and a protective back grey around this large main cylinder.
· The paste of colour used for printing is placed in a colour paste trough.
· The transfer roller rotates partly immersed in the paste and touches with the engraved roller.
· All of the paste except for that contained in the engraving area is scraped away by the doctor blade.
· Any lint picked up from the fabric on the other side is scraped away on the other side by the cleaning blade.
· The pressure of the engraved copper roller against the fabric prints the design on the fabric.
· Any excess paste which is squeezed through the fabric is taken up by the back grey.
· This protects the blanket and prevents the design from being stained.
· The roller cost is very high.
· It has very high design costs as well.
· Design change is very difficult due to the high roller engraving costs.
· The effort required for hand engraving was soon reduced by application to the plate of a thin coating of blackened wax, which is easily scratched through to allow a controlled etching of the copper in an acid bath.
· Tonal effects are obtained by recoating with wax, except for the areas for dark tones, which are then etched to a greater depth.
· The stencil printing method initially was used for simple patterns on walls and for lettering.
· This printing method later on developed into a complicated craft for fabric printing in Japan.
· First of all, the desired design is drawn on suitable paper.
· There are many types of papers available for stencils.
· Fabicryl paper is one option for making a stencil.
· Transparent flexible plastic sheet is also used for stencil preparation.
· The portion of stencil paper is removed by a sharp blade where colour has to be printed.
· The fabric is fixed upon the table and then the stencil is fixed upon the table with the help of a cello tape.
· The desired colours are prepared in the colour tray.
· Fabicryl fabric colours are used for this purpose.
· The colour is applied to the open space with the help of a sponge.
· Separate sponge is used for each colour.
· The stencil is lifted up carefully.
· Now the fabric is removed from the printing table.
· The printed fabric is dried well before use.
· This is a very economical method of printing fabrics.
· In the year 1850 in Lyons, the first use of silk gauze as a supporting stencil base was employed.
· This technique soon became known as screen printing.
Stencil printed design:
· The screen printing method is the upgraded version of the stencil printing method.
· This design cost is very low in comparison to the roller printing method.
· The productivity is also high.
A filament polyester fabric is used for flat screens. The perforated nickel rollers are used for rotary screen preparation. First of all, the tracings of each colour are prepared either manually or by computerised machine. A transparent plastic sheet is used for tracing. The black portion in the tracing means a portion where the colour has to be printed. The screen for each colour is prepared separately. The polyester fabric is mounted tightly on the square iron frame with the help of strong adhesive in the case of flat screen printing. Now, the polyester fabric screen or nickel screen is coated with photo emulsion and dried well. the tracing is placed over exposing table and the screen is placed upon the tracing. Now the UV light of the exposing table is switched on for a fixed time. The area of the screen coming out to exposure to UV light gets hardened. Now the exposed screens are washed with the help of pressurised water. The unexposed area of photo emulsion on the screen is removed during washing. Finally, the screen is dried. The screen is checked manually for any defect. Now our screen is ready for printing. The nickel screen is exposed with the help of an exposing machine. The other process like washing and checking are similar to the flat screen exposing.
Table screen printing:
· As the name of the process implies, the screen printing process is carried out on the table then it is called table screen printing.
· A gum or wax-coated table is used for the table screen printing process.
· Sometimes, the printing table is covered with a thick layer of fabric.
· The fabric is spread over the printing table.
· The fabric is then mounted on the table in a straight line as per the design to be printed.
· In the case of a gum or wax table, the fabric is stuck on the table and gets stable on the table.
· Now, the screen of a design is placed on the fabric.
· The colour paste is dropped on the screen.
· The colour paste is wiped from one side of the screen to the other side of the screen with the help of a striper.
· Now, the screen is lifted up manually.
· This process is repeated continuously.
Rotary screen printing:
· The rotary screen printing process is a continuous printing technique.
· A fabric batch roller is placed at the feeding side.
· The fabric guider helps to minimise the chances of creasing in the fabric.
· There is a trough in the Machine in which PVA solution is filled.
· A padding roller partially immerses in the PVA solution there.
· The padding roller applies a thin film of PAV on the blanket.
· This blanket rotates in the clockwise direction continuously.
· When the fabric enters the machine, it is stuck on the blanket and gets stable there.
· The rotary screens are mounted on the printing heads as per design.
· The colour paste is filled into the screen partially either by the colour feeding pump or manually.
· The electromagnet is mounted under each printing head.
· A squeeze rod is inserted into each rotary screen roller.
· The placement of the screen roller is adjusted to find the perfect design fitting.
· When the machine runs, the colour comes out of open areas of the screen rollers and is applied to the fabric surface.
· Since the electromagnet attracts the squeeze rod, therefore, squeeze rod squeezes extra colour from the fabric.
· After the printing, the fabric is entered into the drying chamber.
· A conveyer blanket carries the fabric into the drying chamber.
· The fabric comes into contact with the hot air and gets dried there.
· Now, the fabric comes out of the drying chamber and passes through a plaiter
· Finally, the fabric falls into the cloth trolley.
· The water spray helps to clean the colour of the blanket and a water wiping system makes the blanket dry there.
· Transfer printing involves a number of processes in which designs are first usually printed onto paper and then in a later and separate process transferred to a textile.
· The most commercially important transfer-printing methods are
· Sublimation transfer process
· Film release process
Sublimation transfer printing:
· The design being printed is chosen first.
· Now, the design is printed on special paper by a sublimation printer.
· The printed design paper is placed on the fabric.
· In the non-commercial production, the design is then printed onto the fabric, by either using a heat press or by applying pressure and putting it into the oven.
· You will have to use a transfer paper (usually sublimation paper) so that the design transfers onto the fabric.
· Bringing the ink and the fabric together, the ink is embedded and therefore will remain more vibrant for longer (in comparison to other printing processes).
· The heat in the press or the oven opens the fabric’s pores up, whilst the pressure that’s put onto the fabric cools the ink down – turning it into a solid form.
· The press can then be released and the paper gently taken off of the shirt or mug (or whatever object that you have used).
Film release transfer printing:
· The film-release printing method relies on adhesion by using a film which will become viscous on heating and requires some pressure to make contact.· Instead of weakening the printed film by melting so that it can be partly pulled off the paper, the film-release systems employ a relatively strong film and a coated paper to facilitate the film's release.
· · Thus transfer is virtually complete and above a relatively low application pressure, it is independent of the contacting pressure used.
· It can be seen that in the film release transfer method the transfer itself does not depend upon some property of the dye such as volatility or solubility.
· · Thus dyes of all kinds or indeed any solid matter, i.e. pigments, metal powders, etc. can, in principle, be incorporated into the transfer medium.
· · This creates a much greater potential utility than is the case with the vapour-phase transfer, although the exploitation of this potential is not without its problems.
· · The fixation of the dyes or pigments transferred by the film-release systems depends upon the normal binding modes associated with the dyes and the substrates, i.e. disperse dyes may be fixed by thermofixation or high pressure steaming; acid dyes may be fixed on nylon or wool fibres by steaming in the presence of acid assistants; reactive dyes may be fixed to cellulosic fibres by steaming in the presence of alkali, etc.
· Dye fixation procedures may be divided conveniently into those based on wet fixation after transfer and dry fixation after transfer.
Inkjet or digital textile printing:
· Inkjet or digital printing is very different from previous printing methods, as it is neither a stamp nor a stencil method:
· · it is a spray. In many ways, it minimizes the intermediary step between the designer and the cloth.
· · Multiple jets spray out the image onto the cloth, and the image is limited by the width and length of the roll of cloth, rather than the usually much smaller size of the screen.
· · Colours are mixed by a “process” method; that is, not premixed but mixed as required from combinations of at least four colours of ink.
· · This CMYK (cyan/magenta/yellow/black) process allows a far greater range of colours within a single printed image as well as gradients of shade within a colour or between several.
· · The production of screens, stamps, or stencils generates economies of scale and mass production, with sweatshop labour and the risk of a design “monoculture” among the environmentally and socially challenging downsides to mass production and consumption.
· · Ink jet printing does not have these costs, so economies of scale are less significant. It could offer an increasingly viable, alternative, “on-demand” model to mass production, even bringing some steps back onshore.
· · As a “print-on-demand” system, designs could be scaled as suitable for a single finished item or engineered to suit a particular pattern piece.
· · Print engineering is still problematic, as textiles tend to shrink and thus distort the print even with careful calculations.
· · Inkjet printing can reduce waste at least by pattern pieces planned together in an economical print/cut layout, and printing just on the area of the pattern piece with a buffer for shrinkage.
· · The sensitivity of the ink jet textile printer is a great asset, but also a great challenge. Inkjet printing remains a compliment, but not yet a replacement for screen-based printing.
· · Many speciality inks are not yet produced in formulations that can be sprayed through tiny ink jet nozzles.
· · Designing for inkjet as if for screen-based printing is useful in certain contexts such as sampling, but also limiting for both methods.
Post a Comment