Cotton Printing Types & Techniques

Flatbed Screen Printing

Flatbed screen printing can be considered an automated version of the older hand-operated silkscreen printing process used on t-shirts, sweatshirts, and other printed items. For each color in the print design, a separate screen must be constructed or engraved. If the design has four colors, then four separate screens must be engraved.

The modern flatbed screen printing machine consists of an infeed device, a glue trough, a rotating continuous flat rubber blanket, flat bed print table harness to lift and lower the flat screens, and a squeegee.

The infeed device allows for precise straight feeding of the fabric onto the rubber blanket, as the cloth is fed to the machine it is lightly glued to the blanket to prevent any shifting of the fabric or distortion during the printing process. The blanket carries the fabric under the screens which are in the raised position.

Once under the screens, the fabric stops. The screens are lowered and then the automatic squeegee moves across each screen pushing print paste through the design or open areas through the screens. The screens are raised, the blanket precisely moves the fabric to the next color and the process is repeated. Once each color has been applied the fabric is removed from the blanket. The fabric moves through the required fixation process. The rubber blanket is continuously washed, dried, and rotated back to the fabric infeed area.

The flatbed screen process is a semi-continuous, start-stop operation. From a productivity standpoint, the process is slow with production speeds in the range of 15-25 yards per minute. Flatbed screen printing also has design limits. The design repeat size is limited to the width and length dimensions of the flat screen, no continuous patterns such as linear stripes are possible with this method.

However, flatbed printing offers a number of advantages. Very wide machines can be constructed to accommodate fabrics such as sheets, blankets flags, carpets, or upholstery. Flatbed printing also allows multiple passes or strokes of the squeegee so that large amounts of print paste can be applied to penetrate pile fabrics such as blankets or towels.

Rotary Screen Printing

Due to the production and pattern limitations of flat bed screen printing, inventive machinery manufacturers developed rotary screen printing in 1963. Imagine taking a flat screen and shaping it into a roll by sealing the ends together and you have a rotary screen. This simple modification converts the semi-continuous process of flatbed printing to a continuous one.

The basic operations of rotary screen and flat screen printing machines are very similar. Both use the same type of infeed device, glue trough, rotating blanket or print table, dryer, and fixation equipment.

The first step in rotary screen printing is feeding the fabric onto a rubber blanket. The fabric then travels under the rotary screens one screen for every color in the design. The screens rotate as the fabric passes underneath. Print paste is continuously fed to the interior of the screen through a color bar or pipe. As the screen rotates, the squeegee device pushes print paste through the design areas of the screen onto the fabric.

By converting the screen printing process from semi-continuous to continuous, higher production speeds are obtained. Typical speeds are from 30–60 yards per minute or 27–54 meters per minute. Some patterns, depending upon design complexity and fabric construction, can be printed at even higher speeds.

Rotary screen machines are more compact than flat screen machines, therefore they use less plant floor space. The size of the design repeat is dependent upon the circumference of the rotary screen. This was initially seen as a disadvantage because the first rotary screens were small in diameter. Today’s screens are available in a wide range of sizes.

Modern rotary screen machines are highly productive. They have few design limitations and can be used for both continuous and discontinuous patterns. It is estimated that approximately 65% of the worldwide printed fabric market utilizes the rotary screen technique.

The principal disadvantage of rotary screen printing is the high cost of the equipment. Rotary screen printing is generally not profitable for printing small orders because of the time required to change screens and perform the necessary cleaning operations.

There are several common print defects associated with screen printing. These include machine stops, out of registration where the pattern is out of fit, glue streaks from the rubber blanket, color smear, color out from the lack of print paste, creased fabric, seam marks, lint on the fabric causing pick off, and lint of the screen causing stick in.

Machine stops count for as much as 40% of all defects. Remember with print designs, print application must be correct the first time because printing defects cannot be repaired. There have been many new and exciting improvements in screen printing in recent years, especially in the case of rotary screen machines. The use of microprocessor control systems has allowed for printing that is more accurate with reduced print defects and increased productivity. New techniques for recovery and reuse of unused print paste have reduced dye and chemical costs as well as the pollution load on wastewater treatment systems. Overall, these improvements have produced machines capable of better quality printing at higher productivity levels with fewer defects and reduced environmental impact. This having been said, it is still the fabric and the handling of the fabric in the printing process that accounts for many of the listed defects.

Creating the Screen Engraving

The process of putting designs to be printed on both rotary and flat screens is known as screen engraving. The most widely used technique for screen engraving is known as the lacquer method.

This process begins with the creation of a print design. Once the design is finalized, a textile artist separates the design into its individual colors. A nickel-plated screen with approximately 12,000 holes per square inch is mounted in the coding station. The screen is then coated with a liquid color soluble photo-sensitive resin. The coated screen is carefully moved to a drying oven. It is then stored in a controlled environment for up to 48 hours prior to engraving.

At the engraving stage, the film with the opaque design is secured to the screen. A high-intensity light is then directed onto the screen, where ever the light hits the screen, it hardens the resin and forms a water-soluble barrier. Where light is prevented from hitting the screen due to the presence of the unique design, the resin remains water soluble.

After the proper amount of light exposure time, determined by the choice of resin, the screen is washed and dried. The design areas of the screen are opened and print paste is allowed to flow freely through, but the non-design areas are closed. The screen is cured in an oven to make the lacquer permanent. The lacquer engraving technique is used for nearly all flat screens.

For rotary screens, the most modern method of screen making is known as laser engraving. A skilled textile designer separates each color of the design into a digital file using a CAD or Computer Aided Design system. Concurrently, rotary screens are coated with resin using the same process employed with the lacquer technique. However, in this case, the resin is cured prior to laser engraving so it has a longer shelf life. The coated screen is loaded on a mandrel which is part of the laser engraving machine. The laser engraves the screen using the digitized CAD print design data. As with the lacquer technique, only one color per screen is possible. The laser vaporizes the resin without damaging the screen material which is nickel mesh.

Once the screen has been engraved, the motif on the screen is carefully inspected to ensure an accurate match to the color separation file derived from the original design. Laser engraving has greatly expanded the design possibilities for rotary screen printing.

There is also a technique known as the Galvano method for creating screens using nickel electroplating technology. The Galvano method allows for gradients of color as the screen can be constructed with different-sized cells. Intricately designed screens are possible with this technique.

To create a Galvano screen, a photo-sensitive chemical is first sprayed onto the base. Next, a negative of the image is placed on the base and an intense UV light cures the photo-sensitive chemical in areas not protected by the negative image. The unexposed chemical is washed away. The base is then placed in a nickel plating solution. The nickel is attracted to and plates the areas of the base that do not contain the photo-sensitive solution. This process forms the Galvano screen. The screen is then carefully removed from the mandrel.

Engraved Roller Printing

Engraved roller printing is a continuous printing process developed in the late 18th and early 19th centuries. Until the development of rotary screen printing, it was the only continuous fabric printing technique available. In this method, a heavy copper cylinder is engraved with the print design. Copper is soft, so once the design is engraved the roller is electroplated with chrome for durability.

The print design process and color separation are identical to that used for screen printing. Once each roller is engraved, it’s loaded on the printing machine. There is one roller per color in the design. Each roller is fed print paste by a furnish roller rotating in a color box full of print paste.

As print paste is applied to the print roller a stationary doctor blade scrapes away excess surface print paste leaving only that which is embedded in the design etchings. The print cloth is fed into the machine backed by a greige fabric to absorb print paste flow through. A cushioning print blanket backs the greige fabric. The greige fabric and the print blanket are washed, dried, and reused. Printing occurs as the fabric swipes print paste from the print roller as it passes through the pinch point between the roller and the main cylinder.

The high fixed cost of copper rollers, the expense of the engraving process, and the possible distortion of fabric during printing have led to its reduced use, now being less than 5% of the worldwide textile printing market. The primary advantage of this technique is the fine design detail.

Digital Inkjet Printing

Of the various methods of textile printing, digital printing provides a world of possibilities for the design of cotton fabrics. Currently, screen printing is the most common type of printing technique, but it has some limitations when compared to digital printing. Rotary screen printing accounts for approximately 65% of printed goods, while flat-bed screen printing accounts for about 17% of the market. Both methods require fairly high development time and costs because a screen must be prepared for each color in the print design.

Digital printing is used to rapidly produce trial prints for sale or evaluation. Many industry leaders believe digital printing has the potential to become the textile printing technique of the future. The current top digital printing speeds are substantially lower than those of a rotary screen machine. However, this comparison does not take into account the production downtime required for screen change and clean-up necessary in rotary screen printing. The limiting factor of digital printing speed is related to print head technology. Reports indicate that these production speeds will not increase until there is a breakthrough in the mechanics of the printing heads. Current research in this area is focusing on increasing the current color depth and color fastness of the dye systems now available. Generally, the fabric to be printed must be pretreated with a material such as sodium alginate and alkali so the printed dye will not bleed or smear before fixation.

Regardless of the technical limitations, digital inkjet printing is a viable commercial alternative technique for small runs, 50 yards and under, of highly styled, premium fabrics as are used in scarves and ties.

Resist Printing

In resist printing, the fabric is first printed in a design with a chemical that resists dye. The fabric is then dyed. The resist chemistry will leave the fabric white or a lighter version of the base color in the printed areas. One of the advantages of this method is that dyes with very high colorfastness can be used. Resist printing can be performed on cotton fabrics that will subsequently be dyed with reactive, vat or naphthol dyes. This combination of printing and dyeing is very similar to the ancient method of batik.

Discharge Printing

With discharge printing, the fabric is first dyed to the desired ground color, usually a dark shade. Next, the fabric is then printed with a chemical that selectively destroys the dye. This leaves a white discharge design in the ground color. As an alternative, a combination of the discharging agent and a dye is printed onto the fabric. The discharge agent destroys the ground color and the dye replaces the ground color in the design. The dye used must be unaffected by the discharge agent. This yields special color effects of a color discharge design surrounded by a stable ground color. Using this method, it is possible to surround delicate colors and intricate colors with deep ground colors.

Discharge printing has higher production costs than normal printing techniques. Designs not easily achieved with other printing methods can be produced by discharge printing. Care must be taken to choose ground colors that can be selectively destroyed without extraordinary means and without damaging the textile fabric.

Transfer Printing

Transfer printing involves the transfer of color from one surface, usually paper, to a second surface. The most common method is heat transfer printing, where the design is first printed on paper and then transferred onto a garment or fabric. For cotton, the only widely used commercial process involves printing release paper with pigments for logo printing onto t-shirts and other garments.

The first step in this process is to place the garment onto the bed of the press. The printed transfer paper is then placed on the garment and the press is closed applying both heat and pressure.

The heat softens and releases the pigment binder from the paper and adheres the logo to the garment. The release temperature is usually around 375 degrees Fahrenheit or 190 degrees Celsius. Garments printed using this process must be treated with caution when ironed or exposed to excessive heat. Additionally, these prints will exhibit all the characteristics of pigment prints, both good and bad. For fabrics, transfer print patterns can also be applied using dyestuff that is normally used in dyeing and wet printing. Cotton fabrics must be pre-treated to allow for fixation of the dyes. The desired pattern, in reverse mode, is printed onto the transfer paper. This paper is then placed onto the pre-treated fabric under heat and pressure and the dyes are transferred.

Transfer printing continues to grow in popularity because the process is efficient and a wide variety of colors and patterns can be applied with great clarity and definition. In addition, labor requirements and floor space are less at the print house and less water and other chemistries are used. However, this system requires longer runs to be profitable since the patterns must be printed onto the paper and rotary printing is normally used. In a typical application, a service company would make the pattern paper.

Cotton Printing Techniques

Modern textile printing incorporates a wide variety of colorants and technologies to produce a diverse array of printed textile products at various stages in the product development process.

Today, rotary screen printing accounts for the majority of cotton-printed clothing. However, newer printing technologies such as digital printing and cool transfer printing are attracting attention because of their reduced environmental footprint, and seemingly limitless color and design capabilities.

Technique Comparison

Cool Transfer Printing

A process that transfers a print design from paper to fabric. A special coated paper is printed with the desired pattern which is then transferred to the fabric under ambient conditions.

Cool Transfer Print – FABRICAST™ SK-1871-14CT

Digital Printing

A process that applies small drops of color through print heads onto a fabric. There is virtually no limit to the number of colors or size of the request.

Digital Print – FABRICAST™ DK-2810-2A

Rotary Screen Printing

A continuous method of printing in which a perforated cylindrical screen is used to apply color. Color is forced from the interior of the screen onto the fabric.

Rotary Screen Print – FABRICAST™ SK-1923-4P (Puff)

Cool Transfer Printing

Market interest in transfer printing on cotton fabrics has been strong for many years; however, standard heat transfer printing was achievable only for polyester and nylon fabrics, and the transfer prints available for cotton offered poor hand and were limited in terms of inks available. Today, cool transfer printing technology makes it possible to transfer digital quality prints to a cotton fabric under ambient conditions.

Key Features

Transfer print design from paper to fabric
No heat required
Typical speeds: 20 to 40 yards per minute
Best for: High-quality cotton fabrics, photo-realistic images, brilliant colors, soft and drapeable fabrics

Advantages

Ability to produce photo-realistic images
Comparable speeds to rotary screen printing
Maintains soft, drapeable feel
Increased image brightness
Reduced water, dye, and energy consumption, less waste
High dye transfer and colorfastness

Disadvantages

Newest technology
More expensive than rotary printing, but typically less expensive than digital printing on per yard basis
No raised surface special effects, e.g., glitter, mother of pearl, metallic flakes, puff

Color Rich & Cost Competitive

Cool transfer printing provides the flexibility to print on a variety of fabrics, the photo-realistic print quality of digital printing, and production rates comparable to rotary screen printing. Even with the overprinting technique, cool transfer printed products maintain the soft, natural feel of the cotton fiber. A recent innovation to the cool transfer printing technology is the capability to print on both sides of the fabric during one pass on a duplex printing machine. The technology allows for an easy diversification of pattern design and coloring, and the achievement of multiple print/dye effects on a single fabric. Although dye selection is the ultimate determinant of fabric colorfastness, in testing, cool transfer printing has exhibited better colorfastness compared to digitally printed textiles, due to better penetration of the dye into the fiber.

Environmental Advantage

Fewer process steps combined with lower consumption and output of WECs (water, energy, and chemicals) make cool transfer printing a compelling environmentally friendly alternative to other cotton print methods. A key difference between traditional transfer printing and cool transfer printing is the elimination of heat in the process. Cool transfer printing is executed at room temperature, therefore not requiring heat. Unlike other methods of printing, up to 90% dye transfer is achievable with cool transfer printing. With greater dye utilization, there is less dye lost in the printing process, and therefore no need for extensive removal of unfixed dye. The reduction of steps in the printing process provides both a cost-effective and environmentally friendly alternative to digital and rotary screen printing due to minimized water usage. Cool transfer print rolls can also be used multiple times, and used printed transfer paper can be repurposed for other applications such as packaging.

Ready to Compete

Although cool transfer printing offers many advantages for printed cotton fabrics, the technology is relatively new. Therefore cost and performance are key barriers to adoption into widespread production. While cool transfer printing cannot replace the special effect printing possible with rotary screen printing (e.g., glitter or puff), its speed, limited WEC footprint, strong color depth and colorfastness, and image quality make it a strong competitor.

Cool Transfer Print – FABRICAST™ SK-1987-2A3 (97% Cotton/3% Spandex, Jersey)

Digital Inkjet Printing

Digital printing is the fastest-growing segment of the printed textiles market. From a technical standpoint, digital printing is identical to the technology used in a household inkjet printer, though larger to accommodate fabrics that are up to 126 inches wide. The digital print heads deposit ink droplets onto fabric based on a predetermined pattern from the digital file. This non-contact printing technology eliminates the need to produce screens that are required for traditional printing methods.²Digital printing has been used in conjunction with body scan data to produce printed fabrics that are custom-fitted for the individual. It has also been used to rapidly produce trial prints for sale or evaluation.

Key Features

Digital image transferred to fabric
Nozzles eject ink droplets directly onto fabric
Non-contact process
Photo-realistic and complex images
Full CAD integration
Typical speeds: 30 to 40 yards per hour for traversing head machines. Some newer machines claim linear throughput speeds up to 100 yards per minute.
Best for: Sampling, small runs <500 yards

Advantages

No limit to number of colors
Instant registration
Capable of large repeat sizes
High speed for prototyping
On-demand printing, less printed inventory needed
Sampling and production done on the same printer
Lower water and power consumption, and chemical waste

Disadvantages

High cost
Poorer colorfastness
Fabric may require special preparation and pre-treatment to improve absorption and keep colorant from smearing
Digital print heads are easily damaged and costly to replace
No raised surface special effects, e.g., glitter, mother of pearl, metallic flakes, puff

Endless Design Capabilities

One of the key advantages of digital textile printing is its endless design capabilities. Digital printing offers photo-realistic and fine-detail image quality, unlimited colors, repeat size, and the ability to change from one design to another without any waste of printed fabric. The on-demand nature of digital printing also accommodates customized designs and reduces lead times. Digital printers can print on fabric yardage and whole garments, and allow for printing on dark colors. Direct-to-garment t-shirt printing is the newest and fastest-growing digital printing method for garment printing. This technology employs a digital inkjet printer and a form (platen) which is used to hold the garment in the correct position during the printing process. This technology is also used to print directly on socks, hats, and even shoes.

Quality & Speed

Because the digital print design is communicated with a digital image file, greater image quality and color control may be achieved. The types of colorants used will determine the need for and type of pre- and post-fabric treatment. Reactive dyes (high saturation, vivid colors) always require both pre- and post-treatment to ensure that the dye chemically bonds with the fiber, and to remove excess dyes from the printed fabric. For pigments, washing may be required when a pretreatment is used. Otherwise, it is not needed. Post-treatment is always required.

While digital printing can achieve incredible photo-realistic quality, colorfastness can be an issue compared to other cotton print methods. Although colorfastness primarily depends on dye selection, less dye penetrates the fiber because digital printing is a non-contact process. New research in digital printing is focused on increasing color depth and colorfastness.

Although digital printing is more costly than rotary screen printing, industry experts argue that digital printing’s efficiencies ultimately make it a more cost-effective option on shorter runs. Because digital printing eliminates the need for a screen likes the ones that are created for rotary screen printing, downtime for screen changing and cleanup is eliminated, and print registration issues are reduced.³ While not a replacement for rotary screen printing, today digital inkjet printing is a viable commercial alternative for small runs (<50 yards) of highly styled premium fabrics.

Poised for Production

Today, digital printing accounts for an estimated 2% of the world’s printed textiles; however, the global market for digital textile printing is expected to grow 17.9% from 2016 to 2022,⁴ primarily driven by clothing and home textiles.⁵ While recent innovations in print head design and expansion of digital printing inks and color control processes have helped expand demand, compared to other cotton printing methods, the digitally printed textile market is limited by the complexity of the process and the ability to address the volume needs of a broader market.^3,6,7 Additionally, the pre- and post-treatments required for digital printing also demand dedicated equipment and technical expertise based on the specific ink technologies being used.⁸

Digital Print – FABRICAST™ SK-1951-5A1 (Reactive)

Rotary Screen Printing

This is the most commonly used print method and accounts for approximately 65% of the printed fabric market worldwide. This continuous method of printing applies color through a perforated cylindrical screen. As the screen rotates, a squeegee device inside of the screen pushes the print medium through the screen and onto the fabric.

Key Features

Continuous printing method
Color is applied through a perforated cylindrical rotating screen
Typical speeds: 50 to 120 yards per minute
Best for: Long runs of the same pattern, complex patterns, surface treatments such as glitter, adhesives, sequins, pearlescent, metallic, 3D particles

Advantages

Fastest printing method
Quick changeover of patterns
Versatile design and special effect options
Cost-effective for long production runs

Disadvantages

Not profitable for short yardages
Sampling and production may look different
Some color limitations, prints only spot colors
Not suitable for fine detail
Higher speed printing can cause registration problems
Cannot print in garment form

Versatile Designs

Today’s rotary screen machines are highly productive, allow for the quick changeover of patterns, have few design limitations, and can be used for both continuous and discontinuous patterns. Although the size of the design repeat is dependent upon the circumference of the screens, the standard circumference of production screens measures 25.75”, 32”, or 36” and there are also many custom screens available. On average, rotary screen printing machines operate between 12 and 24 screens, which allow for between 13 and 25 colors respectively (+1 color for the fabric color). Rotary screen printing can accommodate both reactive dyes and pigments. Reactive dyes form a bond with the fiber, and therefore the finished product performs more like a dyed fabric, with high colorfastness and soft hand. To properly fix the reactive dye, steaming the fabric is necessary. In contrast, pigments are attached to the surface of the fabric. After printing, the fabric goes through a tenter to dry and cure the print onto the fabric. The print can be felt on the surface of the fabric. While versatile in terms of design and special printing effects, rotary screen printing, unlike digital printing, does not allow for printing in garment form.

Fast & Efficient

Rotary screen printing is the fastest printing method for cotton with typical speeds ranging from 50 to 120 yards per minute depending upon design complexity and fabric construction. While cool transfer printing and digital inkjet printing can claim lower WEC inputs and outputs, rotary screen printing’s environmental advantage is efficiency due to its fast speeds and high yields. Rotary screen printing can accommodate long fabric lengths and provides a continuous and economical process.1 Due to high screen engraving costs and machine downtime needed to change patterns, rotary screen printing machines are generally not profitable for short yardages of widely varying patterns.¹

Future of Rotary Screen Printing

While rotary screen printing is not one of the newest printing technologies, it still accounts for the majority of today’s printed textiles. Innovations in this area are focused on automation, efficiency, and sustainability. New developments include laser-assisted screen alignment systems to reduce registration issues and new systems that recapture and reuse print paste or wastewater. Other developments are focused on improving print paste flow from the screens to the fabrics.

Resist Printing

In resist printing, the fabric is first printed in a design with a chemical that resists dye. The fabric is then dyed. The resist chemistry will leave the fabric white or a lighter version of the base color in the printed areas. One of the advantages of this method is that dyes with very high colorfastness can be used. Resist printing can be performed on cotton fabrics that will subsequently be dyed with reactive, vat or naphthol dyes. This combination of printing and dyeing is very similar to the ancient method of batik.

Discharge Printing

With discharge printing, the fabric is first dyed to the desired ground color, usually a dark shade. Next, the fabric is then printed with a chemical that selectively destroys the dye. This leaves a white discharge design in the ground color. As an alternative, a combination of the discharging agent and a dye is printed onto the fabric. The discharge agent destroys the ground color and the dye replaces the ground color in the design. The dye used must be unaffected by the discharge agent. This yields special color effects of a color discharge design surrounded by a stable ground color. Using this method, it is possible to surround delicate colors and intricate colors with deep ground colors.

Transfer Printing

Transfer printing involves the transfer of color from one surface, usually paper, to a second surface. The most common method is heat transfer printing, where the design is first printed on paper and then transferred onto a garment or fabric. For cotton, the only widely used commercial process involves printing release paper with pigments for logo printing onto t-shirts and other garments.

The first step in this process is to place the garment onto the bed of the press. The printed transfer paper is then placed on the garment and the press is closed applying both heat and pressure.

The heat softens and releases the pigment binder from the paper and adheres the logo to the garment. The release temperature is usually around 375 degrees Fahrenheit or 190 degrees Celsius. Garments printed using this process must be treated with caution when ironed or exposed to excessive heat. Additionally, these prints will exhibit all the characteristics of pigment prints, both good and bad. For fabrics, transfer print patterns can also be applied using dyestuff that is normally used in dyeing and wet printing. Cotton fabrics must be pre-treated to allow for fixation of the dyes. The desired pattern, in reverse mode, is printed onto the transfer paper. This paper is then placed onto the pre-treated fabric under heat and pressure and the dyes are transferred.

Transfer printing continues to grow in popularity because the process is efficient and a wide variety of colors and patterns can be applied with great clarity and definition. In addition, labor requirements and floor space are less at the print house and less water and other chemistries are used. However, this system requires longer runs to be profitable since the patterns must be printed onto the paper and rotary printing is normally used. In a typical application, a service company would make the pattern paper.