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A comparative study between conventional rotary screen printing and digital all over printing

Abstract

Due to the ever increasing interest and developments in digital all over printing in the textile printing arena, a study has been made to explore the advantages that can be reaped from this mode of printing in terms of quality, time, cost and environmental aspects in comparison with the conventional rotary screen printing.

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Figure 1: AOP Printing machines. (a) MS LaRio and (b) Conventional roatry screen printing machine.

Necessary parameters for comparison have been explored under the scope of the machines available in the AOP floors of Robintex Group, a Germany-Bangladesh joint venture, representing conventional and digital AOP printing respectively.

The study outlines the advantages and disadvantages of each type of printing technology (ie. Digital and conventional) and gives a comparative analysis for making better decision in choosing each technology according to the needs.

Keywords: Digital AOP printing, Conventional AOP printing, Rotary screen printing, Digital vs conventional rotary screen printing.

Introduction

Luigi Milini, the founder of MS Printing Solutions introduced the world with a whole new concept of single-pass printing. At the end of 90s, this Italian visionary began to develop a novel printing idea. For his endeavor, MS LaRio came into the textile printing arena as the first ever single-pass digital machine in the world which debuted in 2010.

Surpassing the limitations of its predecessors, this machine is faster, more accurate and hassle free, an extreme example of digital AOP printing technology, offering similar production performance as a traditional rotary screen printing machine with its 70m/minute printing speed.

Needing no screens, in single pass digital printers like MS LaRio, direct inkjet sampling cuts out long, expensive and complex industrial processes followed in the conventional rotary screen printing machines.

While going with digital printing, preparation of colour-separated positives or screens, and printing of fabrics in huge print rooms is no longer necessary. Style changes can be prepared while the machine is still producing. There are nearly no limitations in quantities of colors and complexity of designs.

As many steps are cut down in digital printing, it is more environmentally sustainable than rotary printing.

Taking into consideration the pure print cost, digital textile printing in most cases is more expensive than the traditional counterpart. The real cost advantage is limited to the fact that, with digital textile printing no screens are needed.

As the length of textile print runs decreases, and the demand for short-run production and just-in-time delivery increases, digital printing is cost-effective. In this case, rotary screen printing is still very relevant. As digital print technologies improve, offering faster production and larger cost-effective print runs, digital printing has the potential to become the technology that provides the majority of the world’s printed textiles.

Project methodology

The project had both qualitative and quantitative parts.

The scope of our project mainly encircles the following machines used in Robintex’s AOP printing floors:

Name of the machine Type Origin
MS LaRio Digital Printing Italy
Zimmer Rotary Screen Printing Austria
MHMS Rotary Screen Printing Austria

The project is prepared by:

  1. Observation: I observed the whole process of both kinds of digital and conventional printing machines based on the machine manuals and experience with the machines, process, products and the workers. By observing and interviewing, I collected data of different parameters, scenarios and found out the comparative points, each of the machine’s strengths and limitations and how the other available technologies can support for solutions.
  2. Interviewing: As curiosity to know, opens up a wealth of knowledge, I never stopped asking different people related to the factory which include: the Vice President, Junior Vice President, operator, helper, technicians, assistants, and other employees. I asked the questions and verified the answers with my existing knowledge, books, online sources, etc.
  3. Following different books, resources and seminars: I have read different books, followed different resources and seminars. A noteworthy webinar is AOPTB’s (All Over Printing Technologists of Bangladesh) ‘Future prospect and barriers of digital AOP in Bangladesh’ held on 6 August 2021.

Key outcomes/result or discussion

As Digital printers don’t operate with screens, this fundamental difference opens up a great deal of comparative discussion between digital printing and traditional rotary printing. So, what are the advantages we get from Digital printing for not having any screen? Are there any cons? Let us delve through our analysis.

No screen, so plug design and play!

Speed

Nowadays speed is a paramount factor; and in digital printing, this is a positive catalyst as no screens have to be taken into account to engrave. As an aftermath, lead times can be cut and shortened considerably. A digital file of a design can be loaded into the digital printing machine in a matter of minutes after which it can directly be printed on fabric.

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Figure 2: Design is being inserted with Match Print software which enables us to print on the supported printers without investing any time for preprocessing on most file formats. Photo courtesy: Author.

This enables printers to keep up with fast-fashion demands for shorter lead times and acceleration of the time-to-market.

On the contrary, for printing in rotary screen printing machine, the designers need to separate the colours and give instructions to prepare screens accordingly.

This is limited to the number of screen positions that the rotary printer has. Although there are 24-color rotary machines (eg. Zimmer’ Rotascreen), most customers are limited to 12 colors but often reduce to 6 to 8 colors to save costs of screens. After the separation process, a separate screen has to be created for each color. An intermediary department is the strike off department which prepare strike off samples to ensure if the desired colou and shade is matched with the buyers’ demand.

Preparing well-made color separation films is both costly and time consuming. Logistics are also involved.

From interviewing it is found that, it takes a minimum of 10 days to get from artwork to color-separated film ready for screen engraving.

With multiple designs being made ready for sampling with a deadline ahead, changing of ideas at the last minute is a logistics nightmare.

After a minimum of 10 days when the screens are engraved, they have to be installed and registered in the rotary printing machine so all colors match up perfectly. Because of these additional steps, the rotary screen printing cycle — from design until finalized product — takes up three to six weeks.

Extra departments and steps in rotary screen printing:

As screens have to be made, extra departments or sections are needed for rotary screen printing.

Engraving

Engraving is an extra step in rotary screen printing and it consists of sub-steps which demand attention and skilled workers. A slight indifference to any step results in the quality degradation of printing.

Here it can be seen that screen engraving requires highly skilled technicians and, although the turnaround times from positive colour-separated film can be as short as one working day, the fact that multiple designs, each with several screens, being prepared at the same time for the same deadline can clog up the process.

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Figure 3: Some extra machines and elements used in engraving section which are not needed for Digital printing. (a) screen, (b) endring setting machine, (c) end rings, (d) endring catalyst. Photo courtesy: Auhtor.

Ensuring special environment for engraving and failing adds to the cost

The screen is to be coated in a light yellow light room as excessive light dissipates the heat of the emulsion. To keep the temperature of the emulsion perfect, often ACs are installed in the screen preparation room. If the emulsion contains any tiny sand particles or any other dirt or dust during screen coating, those sand particles can form a pinhole on the screen or appear  which degrades the printing quality. As a result, these well kept rooms add extra cost along with the cost for the skilled personnels taking care of the room.

Design materials cost (640 mm repeat)

An estimated cost for preparing screen is given below for 640 mm repeat which clearly does not take into account for digital printing as no screen is needed there.

Item Cost
Screen 195 mesh 7880/- (Screen colour miller)
Photo emulsion 476/-
Endring 640 repeat 437/- (2 pieces)
Endring glue 90/- (2 pieces)
Chromic acid 19/-
Degreaser 14/-
Total cost 8916/-

 

Item Cost
Screen 165 mesh 6840/- (Screen colour miller)
Photo emulsion 476/-
Endring 640 repeat 437/- (2 pieces)
Endring glue 90/- (2 pieces)
Chromic acid 19/-
Degreaser 14/-
Total cost 7876/-

 

Item Cost
Screen 135 mesh 5800/- (Screen colour miller)
Photo emulsion 476/-
Endring 640 repeat 437/- (2 pieces)
Endring glue 90/- (2 pieces)
Chromic acid 19/-
Degreaser 14/-
Total cost 6836/-

Source: Estimated cost from Robintex Group’s screen engraving section.

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Figure 4: Some extra machines and elements used in engraving section which are not needed for Digital printing. (a) Coating machine, (b) Laser engraving machine, (c) Laser stripping machine. Photo courtesy: Auhtor.

So, for each screen in rotary screen printing, we have to spend money, time and effort. For each color, the number of screens increases, cost and complexity also increases. But for higher order, the cost gets compensated which is a beauty and the most vital advantage of rotary screen printing. Moreover, these screens can be reused by stripping.

Nickel test failure

Rotary screens are made of nickel. So, while doing pigment printing with rotary screen, a friction takes place with the screen and the pigment. As a result, nickel particles get into the printed fabric which ultimately causes nickel test failure or RSL failure which is very common in rotary screen printing.

After printing, each screen and squeegee has to be washed with a lot of water for further use. The activities related to this:

  • Is a waste of a lot of water
  • Increases load in the ETP
  • Can be hazardous if they are not treated
  • Labour and time intensive. Needs at least one or two persons to clean each squeegee properly

Moreover, for the same design with different colorway, the squeegee and the screen have to be changed or washed which is time consuming. On the other hand, the change in colorway is just a push of some buttons in Digital AOP printing.

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Figure 5: Screens and squeegees are being washed manually with a lot of water. Photo courtesy: Author.

Adjusting squeegees and screens to the machine

Adjusting squeegees and screens is labour and time intensive. Accuracy is very important here. The engraved screens have to be installed and registered in the rotary printing machine so all colors match up perfectly.

Strike off

There is a separate section named strike off for preparing the screens and samples by making hand screens for each separate colors and print pastes to find out the best recipe for matching with the desired artwork or swatch given by the buyers. Here also money is spent for hand screen preparation, various chemicals and skilled personnels are needed.

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Figure 6: Adjusting squeegees in the machine. Photo courtesy: Author.

Color kitchen

This is often a messy room where different types of chemicals are mixed to prepare different print pastes. There are always different types of orders and designs for which different colored pastes have to be prepared. As a result, there are many trial and errors, waste of print pastes and other chemicals. Humans come close contact with those chemicals like reactive dyes, pigments, urea, etc. and this can get them into jeopardy as these chemicals can be hazardous if not proper PPEs and precautions are maintained. Moreover, chemicals can increase the ETP load or get released to the environment which can bring in a lot of health and environmental problems.

There are additional machines used in the colour kitchen like: mixing tank, pumps, fiters, etc. which consume electricity and need maintenance.

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Figure 7: Color kitchen. Photo courtesy: Author.

Digital AOP printing replaces all the above steps by using print heads

On the other hand, due to no screen is used, digital printing is clean, energy, water saving and sustainable for the environment.

In MS LaRio there are 6 bars, each bar having 34 printheads, resulting in an array of 204 heads, all ready to work according to the need of the design. MS Printing Solutions uses robust Kyocera printheads which are designed for high speed textile printing.

Figure 8: Kyocera printhead of MS LaRio. (2 pieces)

The charm of this single-pass technology is, it enables faster printing since the fabric moves at a constant speed through the printer and the total image is created in just one pass.

That is why, where a multi-pass printer can print more than a few linear meters per minute, Robintex’s MS LaRio, the monster printer, prints an astonishing 70 meter per minute, allowing flexibility, quick response and short production timing which is a revolution in terms of speed of a digital printer as it is quite close to the speed of rotary screen printers.

No limitation of repeats

Repeat calculation is a very significant factor in rotary screen printing as the designs must be in repeats of certain measurement for rotary screens as the rotary screens are manufactured in certain sizes. But in Digital printing there is no limitation of that. Design of any repeat size or even no repeat can be printed here without any hassle.

No limitation of mesh count

In rotary screen printing, the mesh count is also a significant factor which has to be selected as per the complexity of the design which is cost and time intensive and needs an expert eye for proper selection. On the contrary, in Digital printing mesh selection is not necessary.

Belt washing is automatic

There is a built in washer which is always automatically commanded. The belt washing is done with the use of least energy and resources in an environmentally friendly way.

Heads can be cleaned automatically

In the ‘Cleaning’ panel it is possible to select the colors on which cleaning procedures can be performed.

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Figure 9: Cleaning in MS LaRio.

There are three options for three different cleaning cycles for different colored heads. ‘Soft cleaning’ executes a fill-up of the heads using a limited amount of ink and then removes the liquid in excess.

‘Cleaning’ option performs the normal cleaning using pressurized ink and then removes the liquid in excess.

But there are some challenges with the heads too

Each head is extremely sensitive and expensive.

Moreover if only one of the nozzles stop jetting, there will be a line mark created on the fabric which is a clear defect.

The whole machine along with the heads need an optimum operating environment. The printer is designed to work with an environment temperature within 20 and 30 degrees with a relative humidity within 45 and 65 %. Outside these parameters, it is not possible to ensure the right performance of the inks. Even more, without the right kind of environment, the expensive print heads can severely get damaged.

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Figure 10: Dehumidifier along with AC are needed for maintaining proper condition for the printing machine.

It is also necessary to check the belt adhesive status before starting to print, warming it up if necessary. The fabric detachment during the printing process can cause damages on the heads carriage not covered by the warranty.

Achieving grey color is difficult

According to the interview with the factory personnels, it has been seen that achieving grey colour is quite difficult in MS LaRio unless ready made grey inks are used in the print heads.

White color printing is not possible

White color print is not possible but if we take optical white fabric, we can compensate white printing with negative printing space thus allowing us to get impression of white print. Again the result is much better than conventional printing.

A few problems remain. Colorant type is still limited compared to screen printing. Inkjet printers cannot use flocks, glitters techniques yet. Fabric variety is still quite limited.

Pre- and post-treatment

Successful digital textile printing still asks for an industrial environment with access to wet and dry finishing equipment for the pre- and post-treatment. Processes cannot yet be standardized since treatments depend on type of substrates, type of inks, print penetration and type use of the final product.

A process sequence for pre- and post-reatment of Grey fabric for digital reactive printing is given below:

Batching – Heat setting (if lycra) — Gas singeing – Scouring – Bleaching/OBA – Drying – Chemical padding (with gumming and cutting of selvedge) – Digital reactive printing – Steaming (loop steamer machine) – Washing – Drying and chemical finishing (stenter machine) – Compacting finishing – Inspection and quality checking – Ready for delivery.

But these pre-and post-treat requirements are getting mitigated and new innovations are coming.  Today we have pre and post treatment free digital printing processes in pigment digital printing.

Area of difference Rotary MS LaRio
Production

speed

120 meters/minute 70 meters/minute
Screen cost Screen is a costly factor Zero cost for screen
Cost associated with

the number of colors

For each color a  screen is needed. So cost increases. No screen is needed.  Any number of color is possible. No extra cost.
Color cost Cheaper than digital inks Ink is slighlty costlier
Repeat size Repeat size needs to be calculated. No need to calculate repeat size
Mesh count Mesh count needs to be taken into account while preparing screens. No need to think about mesh counts.
Color limitation Though there are 24 color capacity, more than 12 colors is not feasible for most of the cases. Unlimited colors can be achieved
Cost associated with

the engraving

department

There is a cost for engraving department including the machines related to engraving, maintaining the room conditions and the manpower behind it. No engraving department is needed.  Hence, no cost.
Style change (design, color) Slow. Fast. With nearly no installation time.
ETP cost ETP is needed and so the money to run it is also needed. No need of any ETP.
Stripping process To reuse the screen, stripping is done, for which a lot of water and electricity are needed. No hassle of stripping as there is no screen.
Nickel issue Nickel found in rotary printed fabrics is very common. No nickel issue. So, no compliance issues.
Need of sampling

machine

Separate machine is needed for making samples. MS LaRio itself can make samples.
Manpower More manpower needed

than LaRio.

Less manpower needed than rotary screen printing.
Water consumption Consumes much water Water consumption can be reduced by 70%
Electricity

consumption

Consumes more electricity Electricity consumption can be reduced by 30%
Machine price: 5 x Rotary = 1 x MS Lario
Though MS LaRio machine price is at least 5 times higher than the rotary screen printing machine, considering all the aspects that came in our comparison including the environmental aspects, MS LaRio is a great long-term investment.

Print cost calculation

There are actually many parameters that need to be taken into account and so it is difficult to come to a definitive conclusion for the cost of each type of printing.

For our study, we will divide the costs into two parts: 1. Direct cost and 2. Indirect cost.

For cost calculatiom, we will utilize  “From conventional to digital: the three core investment reasons of digital textile printing“- an independent Gherzi study for print cost calculation.

 

Direct cost

Number of colors

For a cost comparison between rotary screen and digital printing, the number of colors in use in rotary is paramount. For each extra color in rotary, a new screen has to be engraved. So, the more colors used in a particular design, the higher the cost.

Here the more meters we print with a particular set of screens, the lower the costs of screens per printed meter gets. Moreover, if we print more color ways with the same set of screens, the costs are divided over more printed meters.

In digital printing, however, the print heads are able to produce any possible color without additional adjustments. This means that when printing a design that consists of more colors, no additional costs are made. Changing colors to make another colorway can happen instantly, where in conventional, we need to clean out the printing paste in each screen and replace it for the new color. For that reason, digital textile printing can be a more cost-friendly option for the companies that produce very colorful designs and many color ways per design.

Taking into consideration the pure print cost, digital textile printing in most cases is more expensive than traditional textile printing. The real cost advantage is limited to the fact that, with digital textile printing no screens are needed. Since for every color in use, one screen is needed with traditional textile printing, more colors are used, more attractive the digital printing is in direct comparison with traditional.

Batch length

In addition to the number of colors in use, the batch length to be printed is the second cost parameter to be taken into consideration for a direct cost comparison of digital textile printing with rotary screen printing.

Following graph of the Gherzi study shows that the break even for a one color print is at about 200 m, for a two color print at about 700 m, for a three color print at about 1200 m and for a four color print at about 2000 m.

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Figure 11:Picture 6: Digital textile printing break even cost calculation. Source: Gherzi research.

Besides the above factors, there are some other parameters identified by Gherzi which are difficult to quantify directly in monetary values but have direct correlation with digital textile printing.

Indirect cost

According to Gherzi, there are  4 different fields consisting of totally 37 indirect cost parameters which influence the digital textile printing activities. These are:

  • Sustainability
  • Speed
  • Flexibility
  • New business models

Positioning the parameters in a grid with the relative awareness of textile printing companies against the relative impact on total cost of ownership, a table is made according to interviews by Gherzi.

Sustainability

Though sustainability issues are not perceived as the main driver criteria for digital textile printing among the most printers, low dye consumption and the reduced waste of printed fabric are significant points. However, facts as reduced fresh water consumption and waste water charge, reduced consumption of chemicals and reduced consumption of energy compared to classical textile printing technologies are a fact even if carbon footprint and green image are no issue for the majority of textile printers. But in Robintex’s case there is a great awareness of green image and sustainability which made them invest in digital printing.

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Figure 12: Digital textile printing indirect cost drivers. Source: Gherzi interviews.

Speed

Speed related parameters are the main positive drivers in favor of digital textile printing. The advantage of no need for screens results in shortened lead times from defined design to printed fabric. A style installation on machine is basically a software issue since a graphic file is fed directly to the printing machine. Sampling activities are accelerated as the quality of printed samples are equal to the production quality as long as it is printed on the same type of machine. The ongoing trend for fast fashion in combination with more collections and shorter lots also favor the digital textile printing technology.

Flexibility

Digital textile printing is a very flexible production process. It allows more collections, more colors, more design features (even different ones than traditional textile printing) and very easy color variations. Warehousing is nearly not required. Production quality can be expected similar to sample quality. Further the production even of short lots became much more attractive.

New business models

The digital textile printing technology offers the potential of a variety of new business models. The direct interaction via web opens new possibilities of communication and interaction between involved parties (brands, designers, retail, printers, consumers), the single pass machines further allow unique opportunities of large production lots in very short time after order.

Conclusion

There are a huge number of potential customers around the world who has demand for digital printing. The main challenge is selling the added value of digital which are as of now still in hindsight for many.

There is a positive intention to get greener, but ditect cost is also important where Rotary screen printing comes into play with less investment and lower cost in terms of bigger work orders.

As the length of textile print runs decreases, and the demand for short-run production and just-in-time delivery increases, digital printing is providing the cost-effective solutions. As digital printing technologies improve, offering faster production and larger cost-effective print runs, digital printing has the potential to replace an important part of installed rotary screen printing capacity.

 

Acknowledgment

This paper and the project would not be possible without the extraordinary support of Sakhawat Abu Khair Mohammed, the Managing Director and Robin Razon Sakhawat, the Director of Robintex Group. I strongly acknowledge your utmost support for giving me the full access and opportunity  to learn and gain first hand experience from the machines and responsible personnels of Robintex Group.

The project got its maturity  for the exceptional support of my industry expert, Mr. Ashraful Alam Tipu, Founder and President of Benevolent Textile Services. Thank you for giving us your precious time to interview you.

I express my gratitude to my industry supervisor, Md. Shariful Islam, Senior Vice President, Dyeing and Printing, Robintex Group for his guidance for the project.

I strongly acknowledge my gratitude to Md. Nasimuzzaman Nasim, Junior Vice President, Digital Printing-MSL Unit, Md. Ariful Islam, MG Morshed Mukul,  Md. Nayon Hossain and all the employees working in the AOP floor of the company who helped me with valuable lessons.

I am also thankful to all the members of Textile Today including my project coordinator Sanjoy Saha, Manager, Industry Engagement & Sub-Editor, and Abu Hasnat Kakon, Manager, Textile Today for their incredible patience, constant inspiration and push towards excellence. Without you, it would never be possible.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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