Transfer Printing Process:
By a simple heat process, a design printed on a piece of paper is transferred to the fabric. The dyes used are capable of vaporizing under the heat conditions of the process, and therefore they have a high affinity for the fibers of the fabric. Transfer printing has long been used on polyester and polyamide.
Printing by transfer onto textiles was one of first methods of accessing “print-ondemand,” printing textiles only as they are needed rather than to stockpile, and “print engineering,” printing on the textile only in the area needed for the final item. Transfer printing involves an intermediary paper substrate, increasingly printed by ink jet, with sublimating or other dyestuffs. Heat during transfer either sublimates that dye from the paper onto primarily polyester cloth, or traps the dyestuff under a “film” onto cloth of other fiber types.
Transfer printing in the textile industry usually means the sublimation of thermally stable dyes from a colored design on paper at high temperature followed by absorption of the dye vapors by synthetic fibers in the fabric. The paper presses against the fabric and dye transfer occurs without any distortion of the pattern. This type of vapor transfer printing was developed in the 1960s for printing fabrics made of synthetic fibers. To date, there are no commercial methods for transfer printing fabrics made from natural fibers.
Transfer printing is the term used to describe textile and related printing processes in which the design is first printed on to a flexible nontextile substrate and later transferred by a separate process to a textile. Transfer printing predates printing with sublimation dyestuffs. It may be asked why this devious route should be chosen instead of directly printing the fabric. The reasons are largely commercial but, on occasion, technical as well and are based on the following considerations.
- Designs may be printed and stored on a relatively cheap and nonbulky substrate such as paper, and printed on to the more expensive textile with rapid response to sales demand.
- The production of short-run repeat orders is much easier by transfer processes than it is by direct printing.
- The design may be applied to the textile with relatively low skill input and low reject rates.
- Stock volume and storage costs are lower when designs are held on paper rather than on printed textiles.
- Certain designs and effects can be produced only by the use of transfers (particularly on garments or garment panels).
- Many complex designs can be produced more easily and accurately on paper than on textiles.
- Most transfer-printing processes enable textile printing to be carried out using simple, relatively inexpensive equipment with modest space requirements, without effluent production or any need for washing-off.
Against these advantages may be set the relative lack of flexibility inherent in transfer printing: no single transfer-printing method is universally applicable to a wide range of textile fibers. While a printer with a conventional rotary-screen printing set-up can proceed to print cotton, polyester, blends and so forth without doing a great deal beyond changing the printing ink used, the transfer printer hoping to have the same flexibility would need to have available a range of equipment suited to the variety of systems that have to be used for different dyes and substrates using transfer technology.
In addition factors such as stock costs, response time and so on do not always apply and unlike dyers, most printers are able to operate without steaming or washing by using pigment-printing methods. Thus a balance exists which not only permits but even requires the coexistence of direct and transfer printing. The relative importance of the two methods consequently varies with fluctuations of the market, fashion and fibre preference.
Methods / Types of Transfer Printing:
A great many methods of producing textile transfer prints have been described in the literature. Many of them exist only in patent specifications but several have been developed to production potential. They may be summarized most conveniently as below.
This method depends on the use of a volatile dye in the printed design. When the paper is heated the dye is preferentially adsorbed from the vapour phase by the textile material with which the heated paper is held in contact. This is commercially the most important of the transfer-printing methods.
Heat Transfer Printing:
Heat transfer printing (HTP) is based on the ability of certain disperse dyes to sublime from a printed paper at temperatures of 180–200◦C and is the very essence of simplicity. It is therefore no wonder that it was once regarded as something of a philosopher’s stone.
This method has been used since the 19th century to transfer embroidery designs to fabric. The design is printed on paper using a waxy ink, and a hot iron applied to its reverse face presses the paper against the fabric. The ink melts on to the fabric in contact with it. This was the basis of the first commercially successful transfer process, known as Star printing, developed in Italy in the late 1940s. It is used in the so-called ‘hot-split’ transfer papers extensively used today in garment decoration.
This method is similar to melt transfer with the difference that the design is held in an ink layer which is transferred completely to the textile from a release paper using heat and pressure. Adhesion forces are developed between the film and the textile which are stronger than those between the film and the paper. The method has been developed for the printing of both continuous web and garment panel units, but is used almost exclusively for the latter purpose. In commercial importance it is comparable with sublimation transfer printing.
The concept of wet transfer printing was first introduced by Dawson International in the late 1960s, and was the subject of several patents and publications. It was based on the use of transfer papers printed with Lanasol reactive (α-bromoacrylamido) dyes, which were brought into contact with the substrate, prepadded with a thickened acid liquor. Through the application of heat and pressure, transfer (or ‘migration’) and fixation of the dyes took place, and a wash-off completed the process. The original Fastran process was based on the printing of garments, and radio-frequency (RF) heating was employed to enable a stack of garments to be printed simultaneously.
Water-soluble dyes are incorporated into a printing ink which is used to produce a design on paper. The design is transferred to a moistened textile using carefully regulated contact pressure. The dye transfers by diffusion through the aqueous medium. The method is not used to any significant extent at the present time.
These different methods are considered separately in this chapter since they introduce different scientific and technical factors, and their use is best discussed in the context of the rather different commercial environments.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.