Grafica News - June 2016
Heat Transfers And Growing Relevance In Our Times
Heat Transfer printing is generally used to describe printing processes related to textile decoration in which normally the design is first printed onto what is referred to as transfer media (normally paper or film which is a non textile substrate) and later the design is transferred onto a textile material by a separate process.
The relevance and necessity for such an extraordinary option may be rightly questioned, but 'mercifully' the reasons are largely logical based on commercial and technical considerations as may be delineated below:
- The convenience of printing designs and storing them on relatively economical and non bulky media like paper and transferring onto more expensive textile materials as and when sales demands arise - merely attach the transfer to garment.
- The ease of executing short run repeat orders by transfer process due to sheer inability to do so by direct printing.
- The ability to apply the design onto the textile materials with a relatively low skill labour force and with the almost zero rejection rate which is difficult to achieve in direct printing.
- The advantage of reduced inventory costs since stocking paper with the imprinted design is lower than on printed textiles.
- The limitations of certain designs which are too challenging to produce by direct printing and so easily executed by transfer process on garments and garment panels
- The case of complex designs where the ease of achieving accuracy is more on transfer media like paper/film than on the garment.
- The comparatively lower space and inexpensive equipment required for transfer printing activity makes it the ideal choice in addition to the low effluents and almost non-existent washing off generated wastes as compared to direct printing units handling more effluent generating products /chemicals, lower cost of time, inventory, transport, space is a big attraction.
- Superior durability and washability as compared to direct printing
After delineating all the above advantages, it is also fair to mention the relative lack of flexibility inherent in transfer printing.
There is no single solution in transfer printing to cope with the needs of the wide range of textile fibres, while a direct printer can print on all fibres (cotton, poly cotton blends, jute, canvas, nylons, etc) by conventional rotary /screen printing set-up, merely by changing the printing ink used. The transfer printer hoping to have the same efficiency and flexibility would require a range of equipment suited to the variety of systems that have to be used for different substrates and inks using the transfer technology.
Further, the factors of stock – costs, response time and so on do not always apply and unlike dyers, most printers are able to operate without expensive steaming and washing equipment 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 the fluctuations of the market, fashion and fibre requirements.
So, What Makes It Most Popular Even Today?
- Easy to decorate smooth and textured uneven fabrics which are a challenge for direct printing
- Exact reproduction of customers design
- No misprints
- No undesirable marks and stains on fabrics
- Soft handle as compared to direct prints in hot splits
- Enables multi color designs with greater ease and embellishments like glitters
- Photo prints achieved with ease
Several methods of transfer printing on textiles have been mentioned in patent literature but few have resulted into methods of production potential and are as summarized below:
Dye Sublimation Transfer: This method is most suited for 100% polyester fabrics and depends on the use of volatile dyes to print designs on paper by methods ranging from rotogravure and lithographic to digital processes in our times. Heating the printed paper under conditions of time temperature and pressure vaporizes the dye which is then adsorbed from the vapour phase by the textile material held in contact with the paper. This is one of the most widely used and important transfer printing process today.
Fusible Melt Transfer: This method has been used since 100 years to transfers designs to fabrics. The design is printed with wax based inks printed on paper and a hot iron applied to its reverse face pressing paper to fabric. The ink melts onto the fabric in contact with it. This was the basis of the first commercially successful transfer printing process known as STAR printing, Developed in Italy in the 1940s, it is used in the so-called hot-split transfer widely used in garment decoration even today.
Film Release: It is similar to melt transfer but different in that the design is held in an ink layer which is transferred completely to the textile from a release media paper using heat and pressure. The principle is of adhesion forces developed between the print matter on the film and the receptive textile which is stronger than that between the print matter on the transfer media –film/paper. Methods are established for printing of both continuous web and garment panel units but mainly used for the latter application. Commercially it rivals the sublimation transfer printing.
Over the years, there has been a growing demand for heat transfer option instead of direct to garment printing. So, a wide gamut of heat transfer inks and chemicals are being developed to cover the most wide range of substrates including flexible and rigid, natural and synthetic ranging from cotton, poly cotton blends, acrylics, polyamide fibre based nylons, water repellant fabrics, EVA and PU footwear materials, school bags, umbrellas, PVC rainwear, windcheaters, garments, undergarments, plastics like abs, HDPE, PP, and a range of rubber materials. As a result, there is also a need for a suitable transfer film and paper.