Wednesday, June 26, 2019

Quality Control in Flexo Platemaking

Flexographic printing is continuously evolving, and the platemaking process is seeing this exponentially. Platemaking is evolving not only in the development of new and innovative materials but also in the technological improvements of imaging and processing equipment. Together these make a more efficient and consistent workflow to deliver high-quality plate that can consistently reproduce the information of a digital file in its finished structure. All of us have been familiarizing ourselves with terms such as high definition, high resolution, surface screening pattern, and flat-top dot, among others. The reality is that ALL suppliers in this field have achieved a synergy, bringing about a complete revolution making the flexo printing process more competitive compared to other technologies such as rotogravure and offset. However, in an environment that tends to become more automated, there are still uncertainties in the manufacture of the plates and even returns of the finished product. In this post, we will review the procedures, tools, and criteria that can be used to maintain an adequate environment in ​​digital platemaking based on the golden rule...“What cannot be measured cannot be controlled". What to measure? How to measure it? How often? Are some of the questions that will serve as a starting point to deliver a finished product that meets the user's expectations.

Quality Control
Broadly speaking, quality control includes a combination of procedures designed to monitor and validate effective "acceptance/rejection" criteria in key stages of a process:
  1. First, identify the variables that have the greatest impact on the process or workflow. These will then become the key control points for the process.
    • By finding the key control points we can ensure quality at critical stages in the workflow and reduce the opportunity for defects downstream in the process.
  2. Define standards to use "acceptance / rejection" criteria.
    • Due to the physical limitations of the process involved, tolerances must be established for these standards.
  3. Measurements are taken at these key control points to verify the process and conformity of the product to these standards.
A benefit of establishing measurement standards is the increased opportunity for a consistent and successful process or product. In addition, the key control points ensure that any defective product is identified in the earliest stages of the workflow.

Key Control Points
Image 1. Digital Plate Construction
A digital plate is processed without the use of a negative film. On the surface of the sheet material is a thin carbon layer that is removed using a laser ablation technique in conjunction with a 1-Bit TIFF file. After ablation, the carbon layer acts as a negative or mask, blocking ultraviolet light during the exposure process. The processing stages of a digital plate are back exposure, image ablation, main exposure, processing (solvent or thermal), drying (solvent), and post-exposure/finished plate which can be grouped into three key control points:
  1. Ripped Digital File
  2. Imaging (mask ablation)
  3. Processed/Finished Plate
Ripped Digital file
Once the digital file is ripped, it becomes the digital negative and cannot be manipulated. All information of the image, tone curve, and metadata is contained within the file and is used directly by the imaging device. Therefore, when reviewing this type of file, it is important to consider:
  • Image resolution
  • Orientation of the image (right reading/wrong reading)
  • Linescreen, angle, and dot shape
  • Screen configuration (halftones and solids)
  • Compensation (bump and printing curves)
  • Dimensional accuracy (distortion)
  • Registration marks or guides
All elements of the ripped file must be verified and certified that they correctly adapt to the standards defined by both: the basic workflow and those unique to the job. The use of an application, such as a bit-map viewer software (Image 2), for the visualization of this type of file is an excellent process control tool.


Image 2. Esko Grapholas visualization tool

Imaging (mask ablation)
The quality of the image ablation on the carbon mask of the plate is a function of the raw material and the adjustments of the imaging device and its condition. The plate manufacturer must ensure a uniform and consistent application of this layer to avoid problems during ablation and/or exposure. Before and after ablation, the mask should be checked for visible marks, scratches or abrasions. Remember, at this stage, the plate is more susceptible to damage because it has yet to be cured.

Measurements must be obtained during this stage by a transmission densitometer, the following apply:
  1. Fidelity of the image (focus adjustment)
  2. Density of the mask from 3.5 to 4.3
  3. Stain level of the plate after the device removes carbon mask (Dmin) <0.07
  4. 50% Density on 0.30 +/- 0.02
It is important to maintain a consistent ablation on any digital imaging device with any digital plate. Ensure the laser is properly focused on the carbon mask to concentrate its energy in the smallest possible area and achieve a clean removal. Defects due to poor focus are seen as visual lines in areas that have been removed or malformed dots (Image 3).


Image 3. Out of focus ablated image 

A weekly ablation test should be carried out to monitor that both the device and the material do not vary from their original setting parameters. Using a transmission densitometer (Image 4), standardized targets are measured; these consist of 100% and 50% removed areas which are compared to the material with the mask removed manually. (NOTE: Calibrate the transmission densitometer with the control strip supplied by the manufacturer to confirm the correct amount of transmitted light is consistent with the amount transmitted when the unit was manufactured.) If the readings are below recommended targets, then there is too much energy being applied by the laser and the physical size of the dots will be larger than desired. On the contrary, if they are higher, then very little energy is acting on the plate to remove the carbon mask, resulting in lines present in solid areas and smaller than the desirable dot size affecting the applied bump curve. In either case, the energy (mJ/cm2) applied to the plate must be adjusted by modifying the RPM or power.


Image 4. Transmission densitometer

Finished plate
After the plate is processed, it is necessary to carry out measurements to ensure specification compliance. These results are dependent on the condition of the platemaking equipment and adequate monitoring of the processing conditions found during optimization. You should consider the following control points:
  • Caliber
  • Relief
  • Dot formation
  • Tackiness
  • Cleaning

Caliber
Both the caliper and the relief can be measured with an analog or digital reading micrometer
Image 5: Micrometer
(Image 5). (NOTE: Calibrate a micrometer using a precision block placed between the surface to ensure the readings are accurate.) The test area must be at least 1" x 1", and multiple measurements throughout the plate are necessary to determine uniformity. The caliper of the plate is one of the most important factors when controlling the impression setting on the press machine; any low spot will not print or will cause overprinting for the remainder of the printing plate. All areas must be at full print height including solids and halftones. Flexographic Image Reproduction Specifications & Tolerances (FIRST) specifies variations for raw material thickness of digitally-imaged photopolymer plates and sleeves as follows:

        Within the same plate: +/- 0.0005" (0.0127 mm)
        Within a set of plates:  +/- 0.001" (0.0025 mm)

The flatness of the finished plate depends on the platemaking process; however, any variation will be accumulated with those of other variables, so the lower the better.

Relief
The relief specifications must be defined and confirmed depending on the caliper, the graphic details, press machine requirements, and other variables. Target relief specifications should be confirmed with the printer.

Dot Formation
The accuracy of the dot and the formation of the minimum dot is inspected with a microscope (100X) and a flexo plate analyzer. Specific characteristics are evaluated and verified to confirm a successful minimum dot; this method ensures that, although the minimum dot is small, it can be used as an effective control point. This may or may not be the dot percentage used in the production job (Image 6).


Image 6: MinDot test with two different screen configurations (stochastic and circular)

Once the smallest stable dot has been determined, the objective in the production of plates is to maintain this stable value by type of plate. Considerable changes in processing conditions can lead to considerable deviations (e.g. changes in UVA light emission intensity, etc.).

Additionally, a control strip must be recorded and processed with each plate for immediate verification of the consistency, not only of the platemaking but also of the compensation curves applied (Image 7). The use of a constant objective provides a single set of standards and tolerances to meet.


Image 7. Prepress scale where the values that must be measured on the plate for each tone are labeled. Source: FIRST

To verify the tonal accuracy of the finished plate, tools such as flexographic plate analyzers are used to measure the size of the halftones. Utilizing this tool improves process control, production efficiency and consistency of print quality. We recommend the BetaFlex Pro and the Plate to Print to create a record of the data collection verifying the specifications of the plate have been met. In any case, whatever the device used, calibration procedures and the process of taking measurements must be clearly documented along with the approval/rejection criteria.

Finally, it is important to consider the following frequency of operations to maintain stable conditions:
  1. Measure and record the lot number, relief, caliper, minimum dot percentage and halftone percentage of at least one color of each job. 
  2. Conduct a weekly "MinDot finder" test when there is a lot change of the photopolymer plate. This weekly test will help establish an appropriate main and back exposure.
  3. Perform a daily "focus test" and a weekly "stain test" every time there is a lot change This testing will confirm adequate mask ablation. Maintenance for cleaning lens optics and changing parts must be programmed with the manufacturer.
  4. Conduct a bi-monthly audit of the intensity of the UV exposure lamps. It is recommended to change lamps when the readings fall below 80% of their original power especially for jobs that incorporate special effects in the highlights or solids.
  5. Weekly measure the Brix degrees or density of the processing solvent and adjust according to the manufacturer's recommendations.
  6. Review the back exposure at each lot change and adjust accordingly.
  7. Only back expose plates that will be used in less than half an hour.
There are many more initiatives that can be incorporated, but a quality control process must aim for continuous improvement based on the customer's needs. The process should detect any defects in the early stages of the manufacturing process where the cost is much lower than having a defective product in the machine. It should also be noted that a quality control program involves raw materials duly certified by the manufacturers. The goal is to reduce waste, decrease reprocessing, and increase consistency.

The return on investment in these types of programs is easily justifiable when packaging is produced consistently, downtime costs are reduced, margins are improved, and time-to-market is reduced. At MacDermid Graphics Solutions, we not only offer quality products under the tightest tolerances, but we also have a team of specialists willing to help you implement this type of initiative to increase your competitiveness.

To learn more contact MacDermid Graphics Solutions. Email us today.




Written By: Ivan Rozo, Business Development Manager, MGS Latin America

Ivan Rozo is the Business Development Manager for Latin America. Ivan is a Chemical Engineer with a Master Degree in Business Administration with an emphasis in marketing. He has more than ten years of experience in the Flexographic industry working in roles of sales and technical support in which he has led optimization projects. Ivan's is responsible for attracting new business and consolidating strategic accounts at MacDermid in Latin America.






Tuesday, May 28, 2019

An EPIC® Journey
Bryce Benson’s introduction to EPIC plate technology


In May 2017, during my first year with MacDermid Graphics Solutions, I visited Miller Graphics in Sunne, Sweden.  While waiting for my meeting, I ran into Jan Viberg, then with Esko, and now the Managing Director of Marvaco Sweden.  Never one to shy away from good conversation, Viberg asked quite frankly, “When’s MacDermid going to bring back the EPIC plate? That was a great plate.” As I replied to many questions in that first year, I simply said, “I don’t know, but I can find out.” First, I had to learn a bit about the EPIC plate, so I called our headquarters in Atlanta, Georgia.
EPIC’s journey began in the early nineties. Flexible film printing struggled to attain a balance of low dot gain with good solid ink density and coverage --- capped plate technology was the solution. For the people who think “baseball cap” when you hear “cap”, the cap we are referring to here is a micro-rough layer on a photopolymer printing plate that aids in the transfer of ink to the substrate. Think of it as something like sandpaper - with peaks, valleys, and crevasses that allow more ink to be picked up by the plate. The cap allows the best of both worlds - a hard plate that gives you good dot reproduction WITH good ink transfer. EPIC quickly became the plate of choice within the label market due to its image reproduction and its excellent ink coverage. BUT ink coverage didn’t limit the plate to labels; it also became widely popular for flexible packaging and pre-print corrugated applications.

EPIC’s appearance was unique, featuring a translucent white non-image area and a capped, green image area – very different from MacDermid’s pink plates. This contrast gave it great quality control properties and made it very simple for plate mounting before the days of camera mounting systems and analog platemaking...oh the things we take for granted. Next came magnificent surface screening technologies, allowing you to build the microcells in the image file, becoming favorable over capped plates. While prepress screening technologies are great, they require a high degree of process control on press. The skills required, combined with the decrease in prepress specialists, made the simplicity of cap technology desirable. 

So now…The Cap is Back! The introduction of new capped plates with inherent flat-top dots (AHEM…our LUX® ITP EPIC®plate) provides the print consistency and high solid ink density needed to produce the finest detail graphics on flexible film. LUX ITP EPIC helps you achieve high solid ink density, excellent ink transfer, superior print consistency, and faster imaging. It’s the photopolymer plate that combines a revolutionary capped surface with award-winning flat-top dot technology…could it get any better? Oh…AND you can eliminate the need for surface screening! Yes, you read that correctly. Say farewell to surface screening.

LUX ITP EPIC is the newest addition to the award-winning technology from MacDermid with the convenience of flat-top dots right out of the box. No additional platemaking steps or equipment are needed to take advantage of the print quality and consistency that LUX flat-top dots provide.
LUX ITP EPIC offers a unique micro-rough surface for excellent ink transfer for challenging flexo printing applications or unique ink requirements. The innovative cap layer, specifically developed for the ITP chemistry, ensures that the plate provides the best tonal range possible. LUX ITP EPIC offers near 1:1 mask-to-plate imaging capability, thus minimizing the need for a bump curve. By reducing the bump curve, printers can expand the available color gamut and print a smaller dot creating…VIVID IMAGES! LUX ITP EPIC is a durable and extremely low tack plate, which is perfectly suited for long and clean running print jobs. Get the same quality from job 1,000 as you do with job 1, no surface screening required. And did I mention it is a 2-in-1 plate designed to be processed in either solvent or LAVA® thermal systems!

So, Jan, I have something EPIC ready for you…LUX ITP EPIC that is!


By: Bryce Benson, Territory Sales Manager - Nordics, Baltics, CIS MacDermid Graphics Solutions 

Thursday, March 7, 2019

UV LED & PHOTOPOLYMER TECHNOLOGY

Who's ready for some technical talk?! I hope you have your flexo dictionary handy...


As photopolymer plate formulators, manufacturers and suppliers, we often get asked about emerging technologies and their impact on flexographic printing plate development. Sustainability, printed electronics, 3D Printing are just a few “buzzwords” we hear a lot about, BUT…UV LED technology may be the most “emerged” technology that we come across today. We’d like to take a few minutes to discuss how we, from the plate development and supply side of the fence, see this technology playing out and where we see ourselves standing in this growing field.

UV LED Technology in Flexo Platemaking
While the most common application of UV LED in flexographic printing today is often seen as the “on press” or print application area, the use of UV LED for curing flexographic plates has been around for longer than one may think. The use of UV LEDs has been most successfully applied via Esko in their “Inline” technology that combined plate ablation systems with UV LED curing technology - in this case, the plate could be ablated and cured on the same unit. While the combination brought about an advancement in equipment consolidation, along with solid print performance that was sustained over a period of years, a separate back exposure step was still required and the additional curing step resulted in a productivity bottleneck in this technology.

An additional application surfaced within the last few years, in which UV LED light sources were used in concert with standard fluorescent bulks to produce a “flat-top dot” printing plate without the need for tying up your imager…GAMER CHANGER! The UV LEDs main function, in this case, were to “outrun” oxygen during the curing step, allowing for the formation of a flat dot surface, while the fluorescent bulbs completed the bulk curing process in the printing plate. While it did isolate the curing step back to a separate exposure frame and away from the imager, a modified exposure unit was required, along with the need for multiple curing steps- thus, the productivity and expense of such a unit may not have been ideal for certain segments of the market. With productivity at the top of everyone’s minds these days, we knew this was not going to be the end game.

The most recent addition to UV LED curing is a full LED-based, standalone exposure system.  Several of these have been publicized within the past 2-3 years, with one system receiving dominant praise in the industry to date, drumroll please…the Esko XPS Crystal system. This system allows for simultaneous, UV-LED based curing on the back and front side of the printing plate, in a manner that is consistent in its application pass to pass, and plate to plate. This technology has also allowed for the introduction of a “platform” approach to platemaking automation, in which ablation to exposure, or further into plate processing - can be aligned together within a one, single production system…now that’s what we were waiting for.
Eskso XPS Cyrstal in our Atlanta Innovation Center

UV LED Advantages
At this point, we need to take a step back into the “so what” question – why are we even interested in UV LED curing to begin with? The answers relative to flexographic platemaking are short and simple:

1)      Consistency
Photopolymers are not moody nor highly intelligent autonomous creatures. They are a mixture of chemicals designed with a class of behaviors and performance characteristics in mind, targeting a finished print application. Some could refer to them as high maintenance, as they require many other technologies to be successful- exposure, washout, on press components, etc. Any variation of these components can lead to variation in the application of said photopolymer materials, and this includes plate exposure technology. The more widely variable the exposure technology, the more variation one can expect from your photopolymer plate, seems logical enough. This is where UV LED technology holds a distinct advantage- an unparalleled uniformity of light intensity across the width of the exposure device, which translates into more uniformity of the finished printing plate itself. More uniformity means more consistency, and more consistency lends itself to more repeatable and predictable finished results. This, was the missing piece our industry was looking for all along.

There are additional areas of benefit relative to how UV curing is applied to the printing plate. In addition to supplying consistent and predictable amounts of UV energy to the plate, applying this in a consistent manner is also important. The ability to cure each plate the same way- meaning no differences relative to temperature, energy or even the time between the front side and back side exposures- lead to greater and greater consistency. And with consistency, comes standardization and predictability…and ultimately, SUCCESS!

2) Automation
UV LEDs are extremely powerful for their size, but it’s the size itself that brings the most flexibility into the platemaking arena. UV LEDs are most aptly integrated into smaller arrays that can be applied as a “light bar” for platemaking in which the bar itself, or the plate, moves under the irradiation source. This allows for a streamlined design, albeit one that is still highly, highly complex in its application despite the simplicity of the appearance.

This streamlined approach has enabled several integrations of UV LED designs to date. One such integration is the “connection” of ablation to exposure, wherein the plate is automatically transferred from one unit to the other. Additionally, several examples of exposure to processor integrations have been implemented and currently can be found within the industry today, but have been limited to solvent processing only.

The ultimate consolidation is the full combination: ablation - exposure - processing. How well can thermal or water wash systems integrate into this technology of the future? We’ll have to wait and see.

3) Future considerations
While the automation function is certainly a “future consideration” when evaluating UV LED technology, the other areas of consideration are related to productivity and environmental considerations. Productivity and sustainability - this won't be the last time you hear about this. 

For productivity purposes, we merely point to the expanding trends of “inherently flat top” formulations that have integrated into the market within the past few years, which was pioneered by, ahem…MacDermid. These formulations have changed the way we view formulation possibilities, and have increased the platemaking speed and efficiency as a result. Therefore, our “new normal” has changed - speed is here, and UV LED can help to enhance the control of these types of formulations during platemaking even further.

Additionally, a long-term consideration of UV LEDs when compared to existing fluorescent systems is the...c’mon you know the answer…environmental aspect and the elimination of mercury-based components. While not an active element in regulations today for flexographic platemaking systems, the regulations have slowly started to evolve in the areas of household lights, and the elimination of incandescent lighting within some regions. There will come a time in which mercury-based light sources may well be highly regulated or even banned in the future, and we as an industry must prepare for that eventuality.

Photopolymer Interaction
Now that the stage has been set for the importance of UV LED technology and its growing impact, how do we as formulators deal with this technology? The ink formulators have borne the brunt of this emergence thus far - being forced to contend with reformulation efforts, new raw materials, functional differences, etc. On the platemaking side, there are essentially two possibilities we are forced to face:  how do our current formulations interact with UV LED curing systems, and how do we modify or develop new formulations that take advantage of these light sources? Let’s discuss…

SPOILER ALERT - it's about to get technical...

While the existing UV LED platemaking systems do target the same peak wavelength for curing (365 nm) UV LEDs are inherently near-monochromatic (See Figure 1), i.e. a very narrow wavelength distribution, when compared to fluorescent bulbs (See Figure 2). 


Figure 1: Spectral Output of LED Exposure Unit
Figure 2: Spectral Output of Fluorescent Exposure Unit

As a result, photopolymer formulations that were developed with broad band bulbs in mind can quite possibly behave differently, and unpredictably with these new systems despite their wavelength target similarities. To date, there are many formulations that have become “qualified” in these systems, so it’s safe to say we, as the plate developers, have had a bit of serendipity with respect to the interactions between plates and light sources. There are, however, things that we have learned about along the way that will help guide us on where to go next.

Future Developments
Future developments aren’t just “because” we can develop them; there are distinct benefits that are targeted specific to UV LED technology now that these light sources have become more readily available to test on and learn from. These benefits include:

1) Productivity…back again!
The current class of polymers in the market today have shown distinct differences in their behavior under UV LED conditions. Generically speaking, the “inherently flat-top dot” chemistries cure much faster under UV LED conditions, like their behavior under bank light conditions. With the benefits gleaned from the ability to control intensity with said systems, in combination with the uniformity of the intensity, there is new ability to focus on formulation speed without fear of losing control of the plate consistency. Future iterations of UV LED products can therefore be developed to best optimize the utilization and efficiency of these systems without harming final quality. When combined with the automation aspect, this has intriguing possibilities for the platemaking facilities of the future. Stay tuned…

2) Optimized cure/performance

In addition to the monochromatic wavelength structure of UV LED systems, the other main difference in UV LED systems is the overall lamp intensity- i.e. it is WAY higher than typical bank light systems.  As a result, the curing mechanism itself can radically change. This has been observed with two main defects on the finished printing plate: inconsistent or unpredictable dot gain, and dot cupping.  While certainly addressable via optimization of process/curing conditions, the goal of new plate developments is to widen the platemaking window, allowing for a broader range of optimum conditions that aren’t impacted by slight changes in graphics, relief targets, print applications, etc…you know, the usual plethora of conditions the industry deals with.

MacDermid Graphics Solutions' (MGS) Technology Strategy
Within the MGS development & support team, our aim is to fully support UV LED technology as we truly believe this represents the future pathway of flexo platemaking. The reasons for this are articulated above, but we also feel this technology brings out the best in our photopolymer formulations, MGS is always striving for better! Similarly, we feel we can continue to evolve our development programs to further expand the capabilities of flexographic printing in combination with the benefits previously outlined. To summarize, the gateway to UV LED will continue to drive forward because of three main elements:

  • The outstanding uniformity of consistency of photopolymer plates derived from UV LED platemaking, and the print benefits obtained therefrom.
  • The ability to automate platemaking.
  • The increasing environmental pressures that will ultimately impact mercury-based light sources that are found in the existing bank light systems on the market today.

Productivity and sustainability…last time - we promise!
It is a key plate technology strategy for MacDermid to be prepared for this technological emergence and adoption, rather than waiting for it happen – we don’t elevate your print by sitting on the sidelines. By working very closely with the suppliers of UV LED technologies, our platform strategy is focused on two key areas of strength:

  • High quality formulations that exist TODAY, qualified and proven to work in UV LED systems. These include resins such as Digital RAVE and LUX ITP 60.
  • Newer technology platforms that are developed to be “tuned” to UV LED light sources, providing even greater productivity and wider performance latitude than plate technologies that currently exist.

By combining our formulation expertise with outstanding collaborative partnerships, we can help propel this technology not only to full adoption, but to greater and greater capabilities for our industry and customer base. Improved quality, productivity and efficiency- areas that will drive more market share towards flexo and away from our competing technologies- while continuing to maximize profit along the way.

To elevate your print to the next level with UV LED technology, contact MacDermid.




Based on article, UV LED & Photopolymer Technology” by: 

Ryan Vest, Global Director of Innovation - MacDermid Graphics Solutions

Ryan Vest, Global Director of Innovation, has been key in the development of industry-changing technologies such as LAVA® thermal plate processing and the LUX® Flat Top Dot technologies. He is widely known in the industry for his expertise in liquid photopolymer and corrugated plate technologies. Vest earned his Bachelor of Science in Chemistry from Berry College in 1995 and his Master of Science (M.S.) in Chemistry from North Carolina State University in 1998, joining MacDermid that very same year.




Quality Control in Flexo Platemaking

Flexographic printing is continuously evolving, and the platemaking process is seeing this exponentially. Platemaking is evolving not only ...