Textile printing

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As textile printing are printing methods referred to which textiles are printed. Printing on textile fabric is more complex than printing on paper, as the different print media (such as cotton or polyester ) require special colors and forms of treatment.

Older processes were referred to as stuff printing .

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Printing processes for textile end products (e.g. T-shirts)

Flex and flock film transfer printing

Flex foil print with a characteristic smooth surface
Flock film print with a characteristic velvety surface

With flex and flock film transfer printing, the print motif is cut from special, single-colored plastic films and then transferred to the fabric. In addition to cotton fabrics, polyester, nylon , viscose and mixed fabrics can also be printed. The surface of flex films is smooth to matt / soft, while that of flock films is velvety.

Since this printing technique can only be used to print vector graphics without color gradients , it is particularly suitable for printing lettering, pictograms , logos and similar motifs. Multi-colored prints are possible (and quite common), but since all work steps have to be carried out for each color, the costs increase relatively sharply with each additional printing color.

A major advantage over other textile printing techniques is the high color fastness of the prints, as well as (especially compared to screen printing ) the quick and inexpensive possibility of producing individual items or small editions. However, since the same amount of work is required for each individual copy in contrast to screen printing (and therefore the costs per piece remain almost constant), this printing technique is less suitable for the production of long runs.

Structure of flex and flock films

Illustration of the three layers of flex and flock films (with the knife of a cutting plotter)

Flex and flock films consist of three layers:

The usually self-adhesive or “back-adhesive” carrier foils offer the possibility of repositioning accidentally lifted elements of the print motif - compared to non-self-adhesive carrier foils, weeding (see below) takes more time.
  • Paint layer
In the case of the most frequently used flex foils , the color layer is a polyurethane or (more rarely) polyvinyl chloride foil between 0.05 and 0.1 millimeters thick ; For special flexible films with special optical properties ( luminescent or reflective films, etc.) with a thickness between 0.06 and 0.35 millimeters - depending on the desired effect - other materials are also used (metals, mineral particles, etc.).
The color layer of flock films (thickness between 0.6 and 1 millimeter) consists - as the name suggests - of viscose flock fibers.
This adhesive is solid at room temperature and is activated by heat when the motif is pressed onto the textile.

Printing process

1. Plotting
Cutting plotter with drag knife when cutting white flex foil

With the help of a cutting plotter , the contours of the motif are scratched into the color and top layer of the film, the carrier film remains undamaged (see video).

2. Weeding

In the second step - so-called weeding - all those parts of the color and top layer that do not belong to the motif are manually lifted off the carrier film. Especially with small motifs, it is very helpful if the carrier film is self-adhesive so that parts of the color and top layer that have accidentally lifted off can be reattached.

One of the main disadvantages of flex and flock film transfer printing compared to most other textile printing techniques is that the complexity of the motifs plays an important role in the printing costs, as the amount of work involved in weeding varies greatly depending on the motif: large motifs can be basically without problems can also be produced cost-effectively in large runs, while weeding a very small motif can sometimes take more than 20 minutes.

3. Transfer to the tissue

After weeding and the subsequent positioning of the carrier film on the textile, the motif is transferred to the fabric with the help of a transfer press under pressure and heat. As soon as the adhesive of the top layer has cooled down again, the carrier film can finally be peeled off - the color layer (and thus the motif) remains on the fabric.

Digiflex printing

With Digiflex printing, a printable flex film is printed using solvent or eco-solvent ink. As with flex printing, the printed film is cut out using a cutting plotter. Then the motif is applied to a transfer film and transferred to the textile with a transfer press under pressure and heat. This process is economical even for very small print runs and has an extremely high quality compared to conventional transfer foils.

Flock printing

With direct flock, a special adhesive is applied through the open honeycomb of a screen. Then the flakes are shot into the still damp glue by means of an electrostat. Due to the charge, the flakes are arranged vertically and next to each other along the electromagnetic field. The finished flock is then dried in the oven. Finally, the flakes that have fallen next to the adhesive surfaces are vacuumed off.

Screen printing / stencil printing

A screen has to be made for each color, which causes comparatively high fixed costs. In principle, you can print with any color; to reduce the number of colors, color gradations can also be generated by screening . In this way, photo-like print templates with color gradients can also be implemented using screen printing. The basic colors cyan , magenta , yellow and black ( CMYK ) are used in the form of non-opaque (translucent) textile colors that are printed on top of each other. For this, the print motif has to be color-separated beforehand, i.e. broken down into the four basic colors.

Usually, in contrast to offset printing, screen printing cannot print such a fine grid due to the coarse surface of textiles . In addition, the use of only 4 translucent colors and white for printing what are known as 4c halftone screen templates on dark textiles is not always sufficient. In order to be able to print dark textiles with full-color motifs such as photos, 6 to 18 colors are used in addition to white, depending on the separation effort and the hardware available.

The essential feature of the screen printing process in textile printing: The fabric is printed directly with the color or color paste. Depending on the type of textile dye, the opacity of the colors and the handle of the finished print vary. With pigment printing, the ink coverage is high, but the handle is hard. An additional increase in opacity can be achieved with pigment printing if you z. B. with dark fabrics first in white and then in the desired color, this is uneconomical due to the additional work step, since you can easily increase the composition of the printing paste. This printing method is cheapest for large quantities. In addition, depending on the textile color used (pigment, acid, reactive, vat and direct dyes), the print is the most resistant. Post-treatment is only required for pigments, otherwise it varies from simple washing to washing with various chemicals.

Dye sublimation printing

The fabric is printed indirectly, the motif is printed either with four-color coated sublimation color ribbons or with sublimation inkjet inks. The prints are transferred to polyester fabrics using transfer presses at 170 ° C-200 ° C. The colors sublimate in gaseous form into the hot polyester fiber, so the motif is hardly noticeable. The wash resistance of the print is higher than that of the processed textile. The number of colors is not limited, photo printing is possible. Only special types of textile can be printed.

Depending on the ink and printing software, the prints are either intensely color-correct or dull. The color space does not correspond one to one to the color space of normal inkjet inks. A special printer driver is therefore required for satisfactory results. In most cases, an ICC profile is not sufficient. White intermediate carriers are used for printing on dark fabrics.

Advantages: Photo printing is possible, color gradients can be displayed, different colored motifs can be pressed at once.

Disadvantages: there are relatively high color deviations, certain colors cannot be displayed on certain textiles, e.g. B. Blue on a yellow vest turns green. Thermal sublimation printing can only be carried out on light-colored textiles. The color white cannot be displayed.

Main area of ​​application safety vests with multi-colored printing.

Transfer film

Here the image is first printed on a carrier film, which is then completely transferred to the fabric with a transfer press. The transfer film can be printed in a similar way to paper, so normal PC printers can be used with all colors and screening methods. Accordingly, there are do-it-yourself sets ( iron-on film ) for this printing process . However, a transfer press is required for the transfer, as a normal iron does not exert the constant pressure that is necessary. The film makes the fabric a bit stiff: Since it is not as stretchy as the fabric, it tears easily, which is noticeable in larger areas of color.

Textile direct printing / DTG

"DTG" is the abbreviation for "Direct To Garment". With an inkjet printer connected to the PC, special (mostly water-based) pigment inks are printed directly on the textile and then permanently fixed with heat. The print is pleasantly soft to the touch and has good wash resistance, bright colors and a high level of detail. In contrast to sublimation printing, textiles made of 100% cotton and mixed fabrics are particularly suitable (depending on the ink with up to 50% polyester). Printing on light textile inks is usually unproblematic as no “under white” is required. For dark textiles - similar to screen printing - a white background must be used. With most of the printers currently on the market, this under-white is somewhat problematic, as it is very maintenance-intensive and complex to process and the textiles also have to be pretreated. The advantage of textile direct printing (DTG) is, on the one hand, the flexibility to customize textiles e.g. B. to print with individual names etc. within a motif, but also the high level of detail in photo-realistic prints.

Printing process for yard goods

The high total ink application - which is necessary to completely penetrate the fabric - still represents a challenge. Research has been carried out on digital printing processes since 1995 , but rotary film is still the most common way of printing.

Screen printing or film printing

Rotary screen printing

The rotary stencils of this continuous, rotary screen printing process are seamless hollow rollers that are covered with a fine-meshed plastic fabric (screen). The print subject is transferred photographically to the light-sensitive layer of the screen (exposure). When the screen is developed (washed out), the unexposed parts of the photo layer are exposed and thus become permeable for the printing ink. The printing ink is pumped from a storage container into the hollow roller, distributed there by a roller squeegee and pressed onto the fabric with continuous squeegee pressure through the exposed areas of the printing screen. A separate screen (printing form) is used for each color.

Flat film printing

Like rotary film printing, this printing technique is also used for continuous film printing. The print pattern is transferred photometrically to a frame with fabric (also called gauze , mostly made of polyester) and printed on the fabric with a squeegee (roller, doctor blade). A sieve is also required for each color.

With both methods there is the possibility of reducing the colors by means of raster printing . 4c printing (cyan, magenta, yellow, black) is particularly common here, and 6c printing (cyan, magenta, yellow, green, orange, black) as an alternative.

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