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