| Transfer Printing Essay, Research Paper
Transfer Printing
Man s urge to decorate his clothing and fabrics of his environment, by means of
printing, dates back to the earliest of times. Over the ages and even more now it is
desirable to have designs on our fabrics. There are many ways of getting these designs
onto our clothing and fabric. One way of doing this is printing on fabric. Printing is the
localized coloration of textiles(Mock). It is characterized by use of delivery systems that
apply precise amounts of colorant to locations on the fabric. There are several printing
methods such as roller printing, screen printing, ink jet printing, and transfer printing.
This paper will focus on the method of transfer printing.
One of the latest and most interesting developments in the field of textile printing
is the process known as transfer, or Sublistatic , printing. Transfer printing is a term
used to describe any process by which a colored design may be transferred without image
distortion from a print on paper to a textile or polymeric material. It is simply a heat
transfer method of patterning synthetic fabrics. The pattern is first printed on to a paper
web. This is done with special inks that contain dispersed dyestuffs which sublime at a
temperature between 160 and 220 degrees Fahrenheit. Sublimation is the process in
chemistry whereby a solid is converted into a vapor by heat and back again into a solid on
cooling(Storey). At this temperature the dyestuffs have little affinity for the paper carrier,
but a high affinity for the fabric to be printed and thus the image is transferred from the
paper to the fabric. There are many advantages of transfer printing.
The majority of polyester, acrylic, acetate and triacetate fibers are suitable for the
transfer process. Fabrics woven or knitted with up to thirty percent natural fiber mixtures
also react well to transfer printing. It is also easy to print continuous fabric, cut pieces of
fully fashioned garments, or even the made-up garments themselves, with a rotary or flat
press calendering machine. More advantages include flexibility, quality, and the fact that
bonded fabric can be printed after the bonding has taken place. To run a transfer print
order entails the setting up of a calender, which is a quick operation. All that has to be
done is turning the dial to the correct temperature and proper speed. The paper and fabric
is put through the calender and printing begins. All the steaming and washing necessary
for wet printing produces fabric shrinkage of only 8-12 percent. Seconds created by
misprints, smearing, or other problems run 5-8 percent(Printing guide). Waste through
checking sampling and handling runs less than 1%(Printing guide). These numbers are
all significantly low. Quality is only natural to transfer printing. Paper is easier to print
than fabric, and gravure printing gives better results than screen printing. One serious
drawback to the printing of this type of cloth used to be the amount of distortion that
resulted. Now, stripes, checks, and other geometric patterns are all easily attainable by
the transfer process. Obviously transfer printing did not mysteriously appear out of the
blue without any forerunners. Transfer prints on textiles have been produced in various
forms for atleast a century.
Development
In 1953, an Italian process, The Star transfer printing process was introduced by
Stampa Tessuti Artistici of Milan(Miles). This was a direct and true forerunner of
transfer printing as we know it today. The paper was all photogravure printed and mainly
transferred onto natural silk and extremely fine quality cotton. The transfer paper was at
first in cut sheets. It was passed between pressure rollers at varying temperatures. The
big disadvantage of the Star method was that a normal fixing process was also necessary
after transference, and this made it very expensive and non-competitive. Today we have
more modern technologies.
Transfer Techniques
In 1960, Noel Deplasse started experimenting and in 1965 Filatures Masurel
registered the name Sublistatic when referring to the products of other firms. Deplasse
became Director of Society Sublistatic and it took about four years before the company
reached its full commercial peak. In 1970, Bemrose, an old British photogravure printing
firm, decided to go into the transfer business with their own patents. The two highly
secret aspects of the process, and those which differ slightly from firm to firm, are the
composition of the disperse print paste and the depth of the engraving on the
rollers(Miles). Transfer paper can be printed by four different methods: photogravure,
flexography, lithography, and screen printing. The first two processes are by the far the
most widely used. Photogravure at first led the field possibly only because the French
firm, Provoust Masurel, had the machinery. However, in the early 1970s flexography
made great strides into the transfer business, and in fact could produce 90 percent of the
designs being used(Storey). Lithographic printing from flat plates is only suitable for
non-continuous designs. Screen printing also accounts for very little of the market.
There are basically two groups of advantages in the transfer process, those affecting
design and those for industry.
Since the design is first printed on paper, one does not have to rely on the ability
of the cloth surface to accept certain effects. With all other methods of printing the cloth
structure is very important. Now though, the design needs only to be something which
can be printed on paper, therefore giving few limitations. This gives freedom to the
designer. It is possible now to get detailed printing from trichromatic photographically
separated positives and to produce an infinite number of tonal and color effects in this
way(Storey). Also interesting and valuable from the design viewpoint is the fact that
exact fitting of colors is achieved at the paper stage. The photogravure printing machines
employ electronic color registers which control registration. This means that some of the
best work produced by the transfer method can have the fine detail and precision of color
fit associated with the work seen in many of the old nineteenth-century pattern
books(Storey).
Knitting
The are many advantages of transfer printing in industry, notably in the knitting
industry. Knitted fabrics nearly always present the printer with a problem. Good care has
to be taken not to extend the cloth before gumming it down and also to gum down
securely. It is difficult to get exact color registration owing to a tendency of the cloth to
advance along the print table during printing. With the transfer method all the colors are
printed at one operation, giving a sharply defined and accurate print. This advantage
applies to woven cloth as well. From the point of running a textile concern there are
several points in favor of using the transfer process. No special skills are needed to
operate either the rotary or the flat calenders used in printing off the cloth. Both types of
calender are inexpensive pieces of equipment. Add to these qualities the fact that the
transfer method needs no auxiliary printing equipment, and that no stocks of dyes or any
other chemicals are needed. It is also an extremely clean process mainly due to it being a
dry technique. To the knitted garment industry, the transfer process has the added merit
not only of being able to print the back and front of a garment at the same time, but being
able to heat set at the same time as well. Orders can usually be met in a short time. It is
these qualities of speed and adaptability which are among the most sought after in this
competitive era.
Photogravure
The method used for making the gravure rollers varies very little from that of the
production of the photographically engraved machine. The main differences are that the
cylinders are often of silver rather than copper. Silver is the best metal for giving a fine
surface. The positives are all photographed through extremely fine screens, so producing
rollers capable of printing all the subtleties of tone and color associated with modern
photogravure work. Conventional gravure rollers have all the cells or dots of the same
size but varying depths, and so can produce all the varying tones from one
color(Symposium). It has been found that for use in transfer printing the hard dot
method is better, the cells are of differing widths but of the same depth(Symposium).
This type of engraving not only makes a good end product, but means that the cylinders
can be etched automatically. They are rotated in a closed tank of acid for a measured
time and brought out etched to a correctly controlled depth. It is very important that the
etching is not too deep because this would mean that too much color would be transferred
to the cloth, with a possible loss of fastness. When all the cylinders are completed, they
are fitted in position in the gravure printing machine. This is unlike the textile roller
printing machine in that the cylinders are not arranged round a central pressure bowl, but
one after the other in a horizontal line. Each color must be dried before the next is
printed because there is a great deal of close color work and paper is not absorbent as
cloth is. Each roller is supplied with ink, has the surplus scrapped off by the doctor blade
and prints the paper, which then goes up vertically to be dried before coming down again
to be printed with the next color(Storey). When printed, the colors on the paper do not
even remotely resemble the eventual cloth and so it is obvious that the transfer printer
must be skilled at matching and sampling. This difficulty is being overcome by the
assembling of a growing range of standard shades. After being checked for flaws the
paper is then wound up. Another interesting feature worth mentioning is that single-color
cloths can be produced from paper printed by means of a specially engraved cylinder.
This paper gives to the cloth a solid shade dyeing effect. The correct matching of printed
and plain cloths can be found. Anyone who has experienced the difficulties of getting a
piece dyed shade to match a printed fabric will readily appreciated the significance of
this(Miles).
Limitations
There are some limitations to the transfer method. One of these being that it is
only really successful on polyester, polyamide and acrylic fibers or blends, and on acetate
and triacetate(Storey). There has been some criticism of the fastness properties on nylon
6-6 and triacetates and it is often felt that they are better if steamed afterwards. The
transfer paper is fairly costly and yardage printing does not become economic until after
ten thousand yards. A number of firms ran a commission printing service for the paper,
as well as developing their own collection for sale. Transfer printing as a method has
certainly not lived up to expectations and many companies became bankrupt. This was
partly due to the disenchantment with double knit polyester and the move back to rayon
and cotton(Symposium). Experiments in transferring onto these fibers continue.
Flexographic Printing
The idea of cutting relief images in rubber has been used of many years for the
printing of corrugated paper and packing cases. It is only in the last ten years or so that it
has begun to be used in cylinder form for Duplex printing of furnishing fabrics. Gobden
Chadwick Limited produced a machine for wallpaper work and transfer printing. In the
transfer printing field it shares almost equal popularity with photogravure work. It was
the advent of polyethyne in the packaging industry that first aroused interest in this type
of machine. Probably the two main reasons for the sudden increase in the use and
development of the method are the advances both in rubber technology, and in molding
techniques(Robinson). Aside from these reasons, transfer printing itself is becoming so
much more popular than was anticipated. It has provided a big outlet and incentive for
development.
For whichever industry they are intended, the patterned cylinders are made in one
of two ways. The pattern can be cut directly into the surface of the rubber roller. Several
rubber stereos are made and fixed with adhesive onto the surface of a rubber cylinder.
Some designs need a combination of the two types of cylinder.
When making a cylinder by direct cutting, the full size positive is first wrapped
round the rubber cylinder, which has been coated with photographic emulsion, and the
pattern is photographed onto this cylinder(Storey). The cylinder is then placed on a
mandrel and the cutter moves away the outer limits of the shapes to be cut away, and then
removes the background to a depth considered sufficient for the use to which the
particular roller will be put. It is important that the walls of the relief shapes should be
cut sloping out at an angle instead of vertically, to ensure sufficient support at the base.
Being that it is very easy for a positive to twist out of position slightly when it is wound
around the cylinder, subsequent color rollers have their patterns printed onto them. This
ensures that if there is a flaw, each cylinder will still match up with the others in the set.
To make a cylinder built up from a series of rubber stereos, each color separation
is photographed on to a zinc plate and acid-etched. Bakelite powder is dusted over the
mold before placing it in the press in order to maximize the depth of the finished stereo.
A piece of unvulcanized rubber of the correct size is then placed in the press in contact
with the mold and then heat and pressure vulcanize and form the rubber(Miles). From
there it has to be cured. All the stereos are then placed into correct repeat positions
around a rubber roller and fixed with an adhesive. The rollers then have to be cut deeply
by hand. When the design is finished with, the rubber can be turned off and the roller can
be used again.
As far as transfer printing is concerned, most of the flexographic printing
machines are suitable for six colors, and are of the single impression cylinder type. This
impression cylinder is of steel and is very heavy. It is finely surfaced and measured as to
be very exact in diameter. A rubber roller rotates in the color trough and then transfers its
color to an anilox cylinder which in turn supplies a controlled amount of color to the
pattern roller. The anilox roller has a steel core lined with copper. When the machine
runs at about 200 feet per minute, it is unnecessary to air dry between colors. If the
machine is to be run around 300 feet per minute it is essential to have a warm air drier
unit installed between each color station. The amount of color can be varied simply by
changing the speed of the rubber inking roller. An important point to note in flexographic
transfer printing is the quality of paper needed. It is too absorbent it will not give up
sufficient dyestuff on subliming. If the surface is too hard it will cause a pressing out of
color, leading to subsequent shadowing in the print on cloth(Miles). Flexography has a
part to play in Durex direct fabric printing as well as transfer work. Flexographic
cylinders are used in the English Calico machine. This machine was constructed by the
Stalwart Engineering Company and was later sold. Only three machines were built. The
printing cylinders are arranged in a vertical form, so the running of the machine is simple.
Although very accurate registration of colors is impossible with this arrangement, it is
considerably better than the ordinary Duplex, and has the advantage that when pigments
are used the amount of color deposited on the cloth is less than from the Alijaba machine,
which means that the cloth is much less stiff(Storey). Flexography was slow to take off
in the United States, but now computerized laser cutting is being used for the production
of the cylinders.
Machinery
There are three basic types of machinery available for the transfer printing of
textile materials. They are: flat-bed presses, continuous high production machines, and
vacuum transfer machines. Flat-bed presses range from very simple units to the more
comply highly productive models having conveyor or rotary supply stations. In the
simple machines a top metal plate is maintained at a certain temperature and is lowered to
press the paper into good contact with the garment. Transfer of the print is obtained in
less than a minute. Uniformity of temperature and pressure are important, and different
manufacturers have used several systems to achieve these requirements. Continuous
transfer printing machines are available in several forms. The most common is the type
where the paper and fabric pass face to face around a heated cylinder or calender while
contact between the paper and the heated surface is maintained by controlled pressure
from and endless blanket. Production rates up to 1300 meters per hour are possible,
depending upon the path length of the fabric in contact with the heated cylinder. An
essential element in printing by this method is an even temperature distribution over the
heated cylinder surface to avoid changes in color across the cloth width. Both flat-bed
presses and cylinder machines can be made to operate under conditions of partial or
complete vacuum. By using a finely perforated cylinder which can be maintained at an
internal pressure lower than atmospheric pressure, air can be made to flow through the
print paper and fabric(Miles). This enhances the dye transfer rate and improves fabric
penetration. The fabric is held against the cylinder surface and the pressure difference
ensures contact with the paper without the use of a backing blanket. With the
Kannegiesser Vacumat machine, heat is supplied externally through infrared heaters
placed around the cylinder. The main advantages of this method are the absence of fabric
compression and glazing and the better penetration of thick fabric and low pile material.
For high pile fabrics there may be some creep or movement of the paper relative to the
fabric, with loss of design definition. Production rates are of the order of 200 meters per
hour(Miles).
Into the Future
Recently, immense changes and developments have taken place in the field of
textile printing. These changes are almost all related to computerization. The speed,
accuracy and flexibility which can result from these automated systems are highly
desirable qualities, particularly at this time. Quick response, the phrase used to indicate a
system which allows the producer to respond immediately to the demands of the
consumer of client, has become the watchword. Printing was and still is a very important
element of producing a fabric. With new techniques being discovered all the time, it will
be continued for a long time.
References
1. Robinson, P. Exploring Fabric Printing , 1970, Mills and Boon Limited.
2. Symposium on Transfer Printing , March 24-25, 1976, New Jersey,Textile Research
Institute.
3. A Transfer Printing Guide , 1979, Yves Mahe.
4. Storey, J. Manual of Textile Printing , 1992, New York, Thames and Hudson.
5. Miles, L. Textile Printing , 1981, England, The Dyers Company Publications Trust
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