Technical Articles

Technical Comparison of New Gravure Cylinder Technology

February 21, 2020

A Comparison of Conventional and New Technology Gravure Cylinders in Terms of Density, Lightness and Chroma, Color Gamut, and Quality of Dot, Gradients and ISO Images

Chandramohan Seetharamiah Srinivasaraju
M.S. Candidate, Rochester Institute of Technology

Summary

Gravure is losing package printing market share to Flexo in North America. Closing the cost gap between flexo and gravure is a prerequisite to regaining market share. This could be accomplished by adopting new cylinder technologies that reduce the cost of cylinder preparation and the size of cylinder inventories. This study examined one such technology, RotoHybrid Cylinders. RotoHybrid is new to the gravure industry and has just entered beta testing. Gravure printers would like to understand how RotoHybrid and Conventional Chrome cylinders compare in terms of ability to print images. This research assessed image quality differences between conventional Chrome cylinders and RotoHybrid cylinders (HCR Type 1) when cylinders are new. For this research, image quality was assessed on the basis of density, dot surface area, lightness and chroma, gamut volume and the visual quality of gradients and ISO images.

The print trial used Chrome and HCR Type 1 cylinders (electromechanically engraved copper on a steel base protected by a Hybrid Chrome Replacement coating). The result of the trial demonstrated that RotoHybrid cylinders outperform conventional Chrome cylinders in terms of density, dot quality, chroma and gamut volume. Based on these results, RotoHybrid cylinders could create an opportunity for gravure printers to regain market share in package printing.

Background Introduction

The Gravure industry in North America has been declining and losing market share to Flexo in package printing for several decades (Gravure & Its Markets, 2018). It is understood from Karl Bardin’s statement (Kozak, 2004), a significant factor affecting this decline is the cost difference between preparing and engraving cylinders versus making and mounting flexo plates. Today, leading flexo printers prepare and mount flexo plates in their printing plants where cost is reduced by using shared resources. In contrast, gravure cylinder preparation and engraving is commonly outsourced to a third-party supplier. Hence, gravure has to bear the added burden of the supplier’s infrastructure cost, transport cost, and profit margin (Luman, 2017; Ellis, 2017).

Current technology gravure cylinders have two layers of metal on a steel base: soft engravable copper and hard protective chrome. The protective functionality of chrome is required to achieve an economically acceptable print life and high quality reproduction of images (Gravure Association of America, & Gravure Education Foundation, 2003, pp. 204-205). However, the chrome bath used in electroplating is toxic and environmentally hazardous to earth soil, air and water (Health Effects Notebook for Hazardous Air Pollutants, 2017; National Institute for Occupational Safety and Health, 1975; Chromic Acid, n.d.). The chrome electroplating process is not banned by the government, but it is heavily regulated (Environmental Protection Agency, 2012; Chromium Electroplating: National Emission Standards for Hazardous Air Pollutants, 2016; United States Department of Labor, n.d.). Printers are reluctant to accept this regulatory burden because it makes it difficult to run their plants efficiently. This regulatory burden is heavy enough to convince most printers not to bring current technology cylinder preparation and engraving in-house (Friedman, 1998).

Closing the cost gap between flexo and gravure depends on adopting in-plant cylinder production. Eliminating the need for chrome in gravure cylinder preparation requires new technology. Such technology would reduce the burden of environmental regulation and clears the path for printers to bring the cylinder production
into the plant.

Today, chromeless gravure cylinders are being developed by RotoHybrid (a research company developing new gravure cylinder technology). RotoHybrid’s chromeless cylinders are new to the gravure industry and have just entered beta testing. Gravure printers would like to understand difference between the RotoHybrid Cylinders and Conventional gravure cylinders in terms of image quality.

Theoretical Basis

In this research, printed ink density and dot surface area are used as quantitative measure of image quality. For precise density measurement of ink alone, the density of the substrate has to be subtracted from the combined density of the ink and paper. This can be accomplished by calculating relative density as shown in Equation 1 (Williams, 2007).

D_rel = D_{i+p (abs)} – D_{p (abs)}

where D_rel =Relative Density
D_{i+p (abs)} = Absolute density of ink and paper
D_{p (abs)} = Absolute density of paper

Dot surface area is calculated in square microns (μm²). Average dot area (in pixels) and pixels per micron square are the metrics used in calculating the dot surface area. The formula for calculating the dot surface area is given by Equation 2.

Literature Review

Hybrid Chrome Replacement (HCR) technology was developed by RotoHybrid to replace chrome plating. The Hybrid Chrome Replacement (HCR) coating process has its foundation in Diamond-Like Carbon (DLC) formed from a material containing carbon atoms as a major constituent and a trace amount of hydrogen atoms (RotoHybrid Coatings, n.d; HybridCylinders, 2017, para. 5; U.S. Patent No. 8,691,386, 2014). DLC combines the properties of graphite and diamond. DLC films made with a high concentration of sp2 bonded carbon atoms behave more like graphite during tribological (friction) tests. DLC films made with high concentrations of sp3 bonded carbon atoms behave are more like diamond, are super hard, and perform impressively in tribological environments (Erdemir & Donnet, 2006). Prior research indicates that Plasma Enhanced Chemical Vapor Deposition (PECVD) is commonly used (Vetter, 2014; Singh & Jatti, 2015) for coating DLC on the metal surfaces.

Methodology

The methodology consists of the steps required to generate samples for measurement followed by the steps required to analyze these samples and draw conclusions. The methodology is divided in to nine steps which are outlined in the flowchart shown below (see Figure 1).

Process color test layout designed for the print test include a Tone Step Wedge, Control Strip, ECI2002 Random i1iO Single and Two page chart, Continuous Gradients and ISO Images. This layout was identically engraved on Chrome and HCR Type 1 cylinders. These cylinders are used on the Mondi Production Press to print on a plastic substrate at a standard press conditions using solvent based ink. The print samples collected were measured for density, lightness and chroma data using a Spectro Dens device, dot surface area using BetaFlex³Pro device, gamut volume using ColorThinkPro and Esko Color Engine software.

Results

This section discusses the analysis of Density data, Dot surface area data, Lightness and Chroma data, Gamut Volume data, Image Quality of gradients and ISO images. It first discusses the quantitative density data generated by measurement of the print samples. The second, third and fourth section presents and discusses quantitative Dot area data, Lightness and Chroma data, and Gamut volume data respectively. The fifth section presents and discusses qualitative data generated from a visual assessment of Continuous Gradients and ISO images.

Quantitative Density Data. Figures 2 compares Chrome and HCR Type 1 print density data measured on production press prints.

For each print, the data source used is a Tone Wedge. Examination of Figure 2 shows that the HCR Type 1 print densities using black, yellow, magenta, and cyan data ink are higher than the corresponding Chrome print densities. Consistently higher HCR Type 1 print densities observed (compared to Chrome) warrant statistical analysis to investigate the significance of this observation. Statistical analysis of black, yellow, magenta and cyan density data from press prints of Chrome and HCR Type 1 Cylinders are shown in Tables A1 to A4 of Appendix A. The results reveal that the difference is significant at p < 0.001 for all tone percentages.

Quantitative Dot area (μm2) data. Dot Area (μm2) data was generated by measuring the tone step wedges using BetaFlex³Pro device and software. Bar charts for measured Dot Area were prepared to summarize Chrome and HCR Type1 results.

Examination of Figure 3 leads to observation that HCR Type 1 print Dot Area values are higher than Chrome print Dot Area values. Chrome and HCR Type 1 values for Black 2% dots are missing because neither cylinder could reproduce these dots. Whereas both HCR Type 1 and Chrome cylinders could reproduce Yellow 2% dots. In the 2% Magenta and Cyan tone areas, HCR Type 1 cylinders were able to reproduce dots on the production press whereas Chrome cylinders could not reproduce the same dots. See Figure A1 and A2 in Appendix A.

Quantitative Lightness L* and Chroma C* Data of KYMC. L*C*h data is generated by measuring the control strip patches in a gravure production press printed samples of conventional and HCR Type1 cylinders. The resultant average data of the L*C* are presented in the line charts with Chrome and HCR in side by side format in Figure A5 and A6 in Appendix A. Figure A5 and A6 show higher Chroma values and low Lightness values for black, yellow, magenta and cyan tones % in gravure production print sheets printed using HCR Type 1 cylinders (compared to Chrome). This is a result of increased density values of HCR Type1 and it warrant gamut analysis to investigate the significance of this observation on the gamut volume. HCR black Chroma value at 100% tone is less than that of Chrome. The reason could be higher ink film thickness transferred by HCR causing lower Chroma value especially in 100% tones.

Gamut Volume Data. Density and Chroma analysis shows that small increase in ink density results in the increase in Chroma values. The sensitivity of chroma values in relation to ink density values warrant gamut volume analysis. Gamut Volume data is generated by measuring the ECI2002 Random i1iO two page chart sample sheets printed on the gravure production press using conventional gravure and new technology gravure cylinders. The charts were measured using i1Profiler software connected to i1iO device to generate ICC profiles of Chrome and HCR Type1 cylinders. The resultant ICC profile is used in ColorThinkPro application to visually present the gamut boundary and compare both the cylinder gamut. It is observed from Figure 6 that the gamut boundary of gravure production press with HCR Type1 cylinders is noticeably bigger than that of gravure production press with Chrome cylinders.

The gamut volume analysis done in Esko Color Engine Pilot application using Gamut Volume tool revealed that the HCR Type1 cylinder gamut volume in Cubic dE is higher than the Chrome counterpart. This shows the gamut sensitivity to small differences in ink density, so higher ink density values of HCR Type 1 cylinders resulted in increased Chroma and reduced Lightness values and hence marginal increase in the output gamut volume by HCR Type1. Further, the gamut volumes of Chrome and HCR are compared with the other industry standard press ICC profile downloaded from Adobe website. The comparisons revealed that the gamut volume of HCR Type 1 is higher than the other standard ICC profiles. See Figure 6.

Reproduction of Pantone spot colors by Chrome and HCR Type1 ICC profiles based on the gamut volume is assessed in Esko Color Engine Pilot application using Gamut Check tool. Assessment revealed that the HCR Type1 cylinder could reproduce 1% to 5 % more Pantone spot colors than conventional Chrome cylinders. See Table A5 and A6 in Appendix A.

Visual Assessment of ISO Images and Continuous Gradients. The ISO 12640-1 “Wine and Tableware” (N4) and ISO 12640-1 “Bicycle” (N5) SCID images (See Figure A3 and A4 in Appendix A) printed using Chrome and HCR Type 1 cylinders on production presses were visually evaluated for legibility, smoothness, sharpness, image detail, and print defects to award ratings. The ratings awarded to Press prints are summarized in Table 1.

In Press prints, HCR Type 1 cylinders continued to demonstrate superior ability to print the ISO Bicycle fine lines. In addition, the number of missing dots in highlight areas was noticeably reduced when using HCR Type 1 cylinders compared to Chrome. Finally, the use of HCR Type 1 (vs Chrome) cylinders enhanced edge sharpness. Images printed with HCR Type 1 cylinders had darker, sharper edges due to the superior ability of these cylinders to print fine black dots. Based on these findings, Chrome Press prints were awarded an overall rating of Good while the HCR Type 1 Press prints were awarded a rating of Excellent.

Gravure production press prints of cyan, magenta, yellow, and black continuous gradients were visually evaluated for gradient smoothness and print defects to award ratings. The ratings awarded to press prints are summarized in Table 2.

Examination of Table 2 leads to two observations. 1) On a production press, HCR Type 1 cylinders produced higher quality gradients than Chrome cylinders. 2) The quality of black gradients printed using HCR Type 1 cylinders is much better than the quality of black gradients printed using Chrome cylinders. HCR’s superior ability to print small dots is a major factor contributing to this improvement.

Summary and Conclusions

In terms of density, HCR solids exhibit superior density compared to Chrome solids. The density values obtained for Chrome samples were typical of conventional gravure printing; the densities achieved in HCR samples were exceptional and impressive. Visual analysis revealed that HCR’s higher black densities resulted in increased sharpness in the highlight and shadow areas. These results strongly support the conclusion that HCR densities outperform Chrome densities for samples printed using the same screens, engraving methods, ink formulations, and press conditions.

Based on the results just discussed, HCR can achieve higher relative density, chroma values compared to Chrome for identically engraved cylinders printed using identical print conditions. This means fully formulated ink could be mixed with extender to match Chrome solid ink densities when printing with HCR cylinders. Extender is significantly less expensive than fully formulated ink, so adding extender simultaneously lowers ink cost. The resulting cost reduction would further improve the overall competitiveness of gravure printing compare to flexographic printing. Higher Chroma (C*) values achieved by HCR cylinders increased the gamut volume on the press resulting marginal Pantone spot color reproduction thus reducing some of the expensive spot color ink cost. Using specially formulated high Chroma process inks the gamut volume could be further increased and thus allowing more number of expensive Pantone spot colors and brand color reproduction at a lower ink cost.

The dot surface area analysis compared identically engraved Chrome and HCR cylinders, the results show that the larger dots were purely a function of the difference in coating thickness. In conventional Chrome cylinders, chrome coating is electroplated using process conditions that create microcracks in the chrome surface. Wet ink in these cracks lubricates the doctor blade/cylinder interface and greatly reduces frictional heating. With HCR cylinders, the coefficient of friction between the doctor blade and cylinder is reduced to 0.1. This means that the doctor blade/cylinder interface no longer requires lubrication to prevent excessive heat buildup and the need for microcracks is eliminated. Since drying conditions are no longer constrained by the need to dry ink in microcracks, the distance between the doctor blade and impression nip can be reduced. This enables ink in small cells to remain wet and printable, thus enabling smaller dots to be printed reliably. Improving the ability of Gravure to print smaller dots would improve its image quality.

Governments, especially in Europe, have been tightening regulatory requirements associated with the use of chrome. This trend is expected to continue and could result in a ban on using chrome to plate gravure cylinders. Because HCR coating is an environmentally friendly process which is not regulated, it provides a viable option for engravers, trade houses, and printers to replace Chrome. The results of this research demonstrate that in terms of image quality, HCR is a better option than Chrome and this could potentially accelerate the adoption of HCR.

Density and dot quality results strongly support the conclusion that HCR Type 1 Cylinder enhanced the quality of image detail and outperform Chrome using the same screens, engraving methods, ink formulations, and press conditions. The adoption of environment-friendly HCR could make in-house cylinder making possible, potentially reduce the cost of cylinder, and accelerate the growth of the gravure industry.

Bibliography

Chromic Acid. (n.d.). Retrieved January 13, 2018, from https://pubchem.ncbi.nlm.nih.gov/compound/chromic_acid#datasheet=lcss§ion=Top
Chromium Electroplating: National Emission Standards for Hazardous Air Pollutants. (2016, June 30). Retrieved January 13, 2018, from https://www.epa.gov/stationary-sources-airpollution/chromium-electroplating-national-emission-standards-hazardous-air
Ellis, R. (2017, June 15). Color Ad Packaging: First North American Gravure G7 Master Printer. Retrieved November 11, 2018, from http://connect.idealliance.org/viewdocument/g7- case-study-color-ad
Environmental Protection Agency, Rules and Regulations, Vol. 77, Fed. Reg. 58219 § 182 (Wednesday, September 19, 2012).
Erdemir, A., & Donnet, C. (2006). Tribology of diamond-like carbon films: Recent progress and future prospects. Journal of Physics D: Applied Physics, 39(18), R311-R327. doi:10.1088/0022-3727/39/18/R01
Friedman, S. (1998). In the groove. Package Printing and Converting, 45(9), 42. Retrieved from http://search.proquest.com.ezproxy.rit.edu/docview/224547547?accountid=108
Gravure & Its Markets. (n.d.). Retrieved January 13, 2018, from http://www.era.eu.org/03/packaging_s1.html
Gravure Association of America, & Gravure Education Foundation. (2003). Gravure: Process and technology. Rochester, NY: Gravure Association of America, Gravure Education Foundation.
Health Effects Notebook for Hazardous Air Pollutants. (February 09, 2017). Chromium Compounds: Hazard Summary. Retrieved January 13, 2018, from https://www.epa.gov/sites/production/files/2016-09/documents/chromiumcompounds.pdf
Hybrid-Cylinders. (2017, February 21). Hybrid Cylinders Update and Outlook for 2017 [Press release]. Retrieved March 17, 2018, from http://www.hybridcylinders.com/hybridcylinders-update-and-outlook-for-2017/
Kozak, N., (February, 2004). Gravure Cylinders: Meeting The Challenge. Retrieved on June 7, 2018 from http://www.gaa.org/tech-articles/gravure-cylinders-meeting-challenge
Luman, T., (October, 2017). In-House Cylinder Engraving, GAAmericas Technical Forum Proceedings. Clearwater, Florida. Retrieved from http://www.gaa.org/2017-technicalforum-proceedings
National Institute for Occupational Safety and Health. (1975). Occupational exposure to chromium (VI). ( No. no. 76-129.;no. (NIOSH) 76-129.;). Washington, D.C;Cincinnati, Ohio;: Dept. of Health, Education, andWelfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health.
RotoHybrid Coatings. (n.d.). Retrieved March 17, 2018, from http://www.rotohybrid.com/rotohybrid-coatings/
Singh, T., & Jatti, V. (2015). Optimization of the deposition parameters of DLC coatings with the IC-PECVD method. Particulate Science and Technology, 33(2), 119-123. doi:10.1080/02726351.2014.943380
United States Department of Labor. (n.d.). Retrieved January 13, 2018, from https://www.osha.gov/Publications/OSHA_FS-3648_Electroplating.html
Vetter, J. (2014). 60 years of DLC coatings: Historical highlights and technical review of cathodic arc processes to synthesize various DLC types, and their evolution for industrial applications. Surface & Coatings Technology, 257, 213-240. 10.1016/j.surfcoat.2014.08.017
Williams, A. (2007). Inter-Instrument Agreement in Colour and Density Measurement. IFRA Special Report. Retrieved July 5, 2018, from http://www.wanifra.org/reports/2007/05/30/inter-instrument-agreement-in-colour-and-densitymeasurement
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Appendix A

Density data is statistically analyzed using T-tests for equality of means.

Note. This material is reproduced from ISO 12640-1:1997 with permission of the American National Standards Institute (ANSI) on behalf of the International Organization for Standardization (ISO). No part of this material may be copied or reproduced in any form, electronic retrieval system or otherwise or made available on the Internet, a public network, by satellite or otherwise without the prior written consent of the ANSI. Copies of this standard may be purchased from the ANSI, 25 West 43rd Street, New York, NY 10036, (212) 642-4900, https://webstore.ansi.org

Cylinder Smarts – A Comprehensive Guide to Essential Gravure Technology

February 21, 2020

Lead Author: Philip Pimlott

As Gravure Presses have embraced technology, becoming faster, more economical and less labor intensive, the Gravure Cylinder has endeavored to keep pace.

“Overpriced, long lead-time, outdated technology and cumbersome, resulting in the demise of Gravure and the rise of Flexography”.

Statements like this one are some of the most common criticisms leveled at the Gravure cylinder — but what are the facts and what are the options? When it comes to understanding the inherent strengths and benefits of gravure printing, it is important to examine three main characteristics of the gravure cylinder:

Let’s start with the Cylinder Base. This is an easy target for detractors of gravure to attack since it has not changed much since its inception. Cylinder bases are the machine parts made to fit the Press and support the engraving layer of copper at the appropriate circumference.

Bases can be made from various materials and are manufactured to specific circumference sizes.

Ordering new bases for a print job adds considerable cost. However, in fairness, these costs can be amortized across multiple press runs and subsequent jobs at the same, or similar repeats. The more a specific cylinder base is used, the less it actually costs over time. In other words, cylinder bases are an investment, so it’s important to know the different material types available as well as the advantages and disadvantages of each.

Steel Bases, for example are extremely durable and stable. A disadvantage is that they can only be used for a very limited range of circumferences and they are relatively heavy.

Steel bases are typically constructed by attaching (via shrink fit, or welding) shafts and heads to a steel tube. The constructed piece is then machined to the appropriate circumference and the correct shaft configuration for the intended press.

Shaftless cylinder bases are made in the same way, with the obvious exception of shafts. It is vital that the bases are constructed to precise tolerances for run-out, size, finish, and balance.

Run-out, or TIR is a measurement of the relative accuracy between all the diametrical planes of the base.

Size of the base is determined to accommodate the amount of copper that the Engraver requires for their process, typically between 0.012” and 0.020” in diameter.

Finish of the base body needs to be suitable for the copper plating process.

Dynamic Balancing ensures that the finished cylinder will run smoothly in the press at speed and also run true (and without vibration) in some of the production equipment used in the Engraving Process.

Steel bases can practically last forever, even when given the bare minimum of attention. It is for this reason, there are massive inventories of steel bases stored and shipped between Printers and Engravers.

Cylinder base manufacturers have honed their craft over the years and have developed supply chains and production systems that can deliver cylinder bases within a few days at a reasonable cost. The same can be said for the Engravers, where production efficiencies have led to a much lower price point, bringing focus to the proportion of the base cost to the overall price of a new Engraved Cylinder.

Why Steel?

Several characteristics of steel need to be recognized and considered:

Steel is dimensionally stable, has a known coefficient of expansion.
Steel is relatively cheap, available and recyclable.
Steel is relatively easy to machine and being conductive, readily processes though the Galvanic lines at the Engraver.
Steel construction has a known deflection rate.
Steel construction tends to be relatively heavy, requiring the use of cranes throughout the processing and Print production phases.
The appropriate size tubing for a particular size may not be available when required, leading to a much more expensive material purchase and machining time at the Base manufacturer.
There is a defined limit to the amount that a base can be resized for a different repeat.

What’s the Alternative?

Many attempts have been and still are being made to replace the traditional cylinder base with a more viable alternative. Major Base manufacturers and third party suppliers have attempted to utilize alternative materials to produce replacement cylinder bases, or repurpose existing stock bases. Rigid foam materials, with conductive coatings, extruded elastomers (both conductive and non-conductive) and, more recently, injection molding of conductive material.

Market acceptance for these replacement technologies was challenged by the lack of confidence in the bond between the base material and the copper plating. The differential in Coefficient of Linear Thermal Expansion between copper and the replacement material caused delamination when the cylinder was exposed to extremely high temperatures during machining without sufficient coolant. Copper is an extremely good conductor and the non-metallic base materials were typically very poor conductors, as noted in the following examples.

Material	Coefficient of Linear Thermal Expansion
Metals
Steel	12.0
Aluminum	22.2
Copper	16.6
Nickel	9.6
Zinc	29.7
Non-metallic
Polyester – glass fiber-reinforced	25
ABS - glass fiber-reinforced	30.4
Polypropylene - glass fiber-reinforced	32
Polyurethane (PUR), rigid	57.6
Hard Rubber	77
Polyvinylidene fluoride (PVDF)	127.8

At present, the best candidates seem to be glass reinforced ABS Polyester, and Polypropylene. Without the glass fiber reinforcement, the Thermal coefficient number increases by a factor of up to 5 (e.g. Polyester – 123.5 / Polyester – glass fiberreinforced – 25). This would suggest that glass fiber-reinforced materials would be suitable for any Steel base replacement technology being considered.

Understanding that price, weight, transportation, limited resizing potential, availability of raw material, and delivery times are all real issues with steel bases, what solutions have been offered, and how do they stack up to steel?

Aluminum Bases

Aluminum has been considered a lighter-weight solution for the past 50 years or so. The challenge has always centered around creating a strong bond between the aluminum base and the copper required for engraving. There is a substantial difference between the Coefficient of Thermal Expansion of Aluminum and Copper. However, they are both good conductors and therefore react to temperature changes more rapidly than the non-metallic alternatives.

In recent years the use of Combustion Powder Spray/Thermal Spray Coating type technology has offered a solution to this problem. In this process, the basic principle is that metal powders are fed through a flame and propelled by high velocity Oxygen or air onto a substrate. Refinements to this principal and the development of alloys have led to a Copper plating replacement process and the possibility of removing the need for Chromium plating.

Price — About 1.5 times the price of Steel by volume.
Weight — About 55% the weight of Steel for an equivalent strength.
Transportation — You can put more on a truck before reaching maximum weight tolerances.
Limited resizing potential — Same as Steel.
Delivery times — Same as Steel.
Availability of raw material — Readily available in many more size options than Steel.

Note: Some years ago, a method of spraying an initial layer of Zinc onto a fiberglass core was patented. The concept relied upon the relatively low melting point of Zinc and the ability to coat that layer with Copper. Cold Spray technology has also been explored as an option; here the high velocity of the spray creates the bond.

Nickel Sleeves

Electroformed Nickel sleeves are used in conjunction with air-mandrels as a lightweight substitute for the traditional steel base. In essence, the steel base element of the cylinder stays at the Engraver and the printer and the nickel sleeve is transported between them.

The nickel sleeve can be copper-plated and processed through the Engraver using the airmandrels and existing equipment. On press, it’s the same story; the nickel sleeves are mounted onto the air-mandrels and are loaded into the press as normal, or mounted onto cantilevered mandrels.

Particular care has to be taken in cleaning both the components prior to assembly, as the slightest inclusion can show up on the printed piece. Ink can penetrate between the sleeve and the mandrel, making them difficult to remove without damage.

Each sleeve can only be used for one size and typically, due to economics, only one time. Any application where a user has the same, or limited repeats to deal with (some label work, gift- wrap, decorative and product) may find this technology appropriate to their needs.

Price — Major investment in an array of airmandrels at the Engraver and the Printer; the sleeves themselves are not cheap either.
Weight — a tiny fraction of the weight of the equivalent steel base.
Transportation — in Cardboard tubes, or boxes via your shipper of choice.
Limited resizing potential — one size only, that goes for the sleeve and the mandrel!
Availability of raw material — No shortage.
Delivery times — Repeat sizes should be available within a week.

“Polymer and Elastomer” Bases

Another lightweight solution comes in the form of a rigid Polyurethane Foam body that is molded onto a standard tubular steel axle and is subsequently coated with conductive material to enable copper plating.

Price – About 75% of the steel equivalent with the potential to rent, rather than purchase, bases.
Weight – 70% lighter than the steel equivalent.
Transportation – More to a truckload and less reliance on cranes.
Resizing Potential — Can be utilized for any future circumference.
Availability of Raw Material — Not restricted by material size availability.
Delivery Times — Usually supplied copper plated to size, but still similar to Steel Base.

Utilizing the same technology as the Lightweight Cylinder, existing stock cylinders can be reused for different circumferences (larger).

Although there are obviously limited weight advantages, the other attributes and limitations associated with polymer-based cylinders apply.

Note: As well as molding build-up material onto the cylinder, there are options to wind extruded material spirally around the cylinder, or by injection molding; both conductive and non- conductive materials are applied by these methods.

Repurposing:
Lightweight Build-Up System

Courtesy of Cylicron™

Traditional Resizing Methods

Steel sleeves can be added to steel based cylinders, effectively utilizing the old cylinder construction to attain a new (larger) size.

Price — almost as much as a new base.
Weight — can double the weight.
Transportation — Less per load.
Limited resizing potential — Swings & Roundabouts.
Availability of raw material — as with Steel
Delivery times — same as a new Steel base.

Note: Adding copper through plating, or reducing the steel body in a lathe achieves relatively small changes in circumference. Thicker layers of copper can also be applied through metal spraying processes.

ATTRIBUTES AS COMPARED TO STEEL BASES

	Aluminum	Nickel Sleeves	Polymer	Polymer Re-sizing	Traditional Re-sizing
Price
Weight
Transportation
Limited Resizing Potential
Availability of Raw Material
Delivery Times

+ Better — Worse = Equal

Looking at the table above, one would think that the adoption of Polymer cylinders would have been an ideal candidate for success.

However, for the reasons stated earlier, they were never commercially acceptable in North America.

To see why, one would also have to compare Polymer cylinders against Traditional steel base attributes:

Steel is dimensionally stable, has a known coefficient of expansion (COE).
Steel is relatively cheap, available and recyclable.
Steel is relatively easy to machine and being conductive, readily process though the Galvanic lines at the Engraver
Steel construction has a known deflection rate.

Versus:

Polymer cylinders are dimensionally unstable, with a COE at odds with other component materials.
Polymer cylinders use oil-based material that cannot be recycled.
Polymer cylinders are easily resized but are not inherently conductive and difficult to process through Galvanic lines.
Polymer cylinders have a deflection rate that has to be modified through engineered steel components.

Note: The caveat to some of these conclusions is the possibility of engraving directly into a polymer surface and coating the engraved surface via vacuum applied amorphous carbon. (Chrome surface replacement has been studied and successfully trialed to determine ink transfer and the ability to wipe non image areas cleanly.)

Cylinder Preparation

Beyond the materials that make up the cylinder, another key component of gravure performance is the way cylinders are prepared for engraving. Like bases, preparation methods vary in their ability to address specific printing concerns or desired outcomes as well as the necessities of maintenance, down time, and other operational aspects unique to each individual Printer.

Copper Plating

Copper has long been the preferred (and original) substrate for engraving, readily available and readily recyclable. Intelligent use of copper can be very economical.

Copper will only adhere to a clean (oxide and grease free) surface, so chemicals are used to degrease and deoxidize the surface to be plated.

For a steel base, an intermediate layer has to be plated onto the steel surface prior to copper plating in the acidic solutions used. Cyanide plating fell out of favor some years ago because of health concerns. It has since been replaced by nickel or alkaline copper.

These deposits are usually only a few microns thick and are designed to protect the steel from erosion caused by the Sulfuric acid used in the final plating process, which would result in the plate not adhering properly. With the advent of Electromechanical Engraving, the character of the plated copper had to be adjusted. It is vital that the diamond stylus of the engraving machine cuts through the copper cleanly, leaving a smooth cut and no burr on the surface.

To accommodate this, additives were developed that gave the copper plate the close-grained characteristics required, sometimes referred to as “Hard Copper”.

The copper-plated cylinder needs to be blemish free and dimensionally correct. The more accurate and smooth the copper plated surface is, the less machining required. Levelers and brighteners are added to the plating solution to help the process; however, much is dependent on the surface of the cylinder, prior to plating.

Most plated cylinders are machined on some combination of a lathe and a grinding process, although there are many cylindrical milling machines (polishmasters) still in service.

The criteria for a machined copper plated cylinder are that: the copper metal is appropriate for the desired engraving process, the circumference is exact, and the cylinder is round and runs true to the shaft bearing surface.

The surface finish needs to be fine enough that it will not retain pigment in the surface texture, but has sufficient roughness to help lubricate the doctor blade in the press; a typical standard surface roughness measurement would be 0.04Ra. Over the years, copper plating has evolved into a precise science, using automated equipment supported by sophisticated control systems; a long way from the Dickensian death traps of old.

Ballard Shells

Simply put, a Ballard Shell is a layer of Copper plated onto a polished copper surface that has nickel oxide present, enabling the layer to be removed when the engraving needs to be changed. The trick is in having enough adhesion to retain a good bond during processing and printing, but not so much as to make removal difficult.

Ballard shells are routinely used in publication, where standard repeats and frequent copy change make the technique ideal. Any base can be used for Ballard Shell production, in fact the technique can negate some of the risks associated with Polyurethane bases and Nickel sleeves.

Zinc Plating

Primarily used for Direct Laser Engraving, Zinc was chosen for its tendency to readily melt (melting point of Zinc is 420°C [as opposed to 1,100°C for Copper] and it has a boiling point of 900°C), zinc vaporizes under the extreme heat of the laser light.

Zinc has also been found to be excellent for Electromechanically engraving, as it cuts very cleanly due to its crystalline structure. These engravings must be Chromium plated to protect the relatively soft zinc surface but cannot be refurbished by de-chrome / re-chrome, as with copper surfaced cylinders.

Epoxy Resins & Polymer Coatings

Laser Engraved Epoxy Resin and urethane/acetyl polymer coatings were developed and trialed in the early 1980s. These trials were abandoned due to unpredictable surface wear and performance on press. The criteria for the trials were demanding. The expectation was to replace traditional engravings for the high-volume magazine press runs of the day.

Since that time, different attempts have been made to resurrect this type of product, taking advantage of the progress made in material science. The future of Laser Engraved Polymer/Resin is still uncertain, and also brings the questions about using traditional bases and processing prior to coatings along with it.

Ceramic Coating

Ceramic Cylinders are fairly new to Gravure, but are finding their niche in the industry. The thermal spray coating on these cylinders is actually Chromium Oxide, which produces a hardness of 1150 Vickers and a porosity of <3%.

The laser engraved cells resemble those found on anilox rolls, from which the technology was developed. Advantages include 10 – 20 times the life of a traditional copper and chrome cylinder and good ink transfer from very fine screen rulings. Currently used for coatings, adhesives and primers, some “product” gravure is produced from these cylinders.

Engravable Nickel

Developed and marketed initially for use with Nickel Sleeves, this promised to offer a surface that could be engraved using standard equipment and print reasonable run lengths without the need for Chromium plating.

Development ceased in North America and Europe; there were options to apply the engravable Nickel to alternative carriers other than the original Nickel Sleeve. Press trials have shown that this technology certainly had the potential to succeed, either as a stand-alone product, or in conjunction with another innovation.

Engraving

There are three main Engraving methodologies in general use today:

Electromechanical Engraving (AKA Electronic Engraving)

First introduced in the 1960s, electronic engraving became popular for packaging in the 1970s. The technology brought consistency and predictability to the gravure process for the first time.

Prior to electronic engraving there was indirect exposing of a screen and a positive to a gelatin coated paper (carbon tissue), or direct exposure of screened images onto a photosensitive coating on the copper cylinder.

The etching process for carbon tissue depended on a series of dilutions of ferric chloride that would etch progressive tone values to differing depths. For direct exposure, spray etching with a constant dilution of ferric chloride was utilized. Although direct exposure increased predictability, there remained risk of uneven etching and therefore subsequent revision of the cylinder.

Electronic engraving relies on a constant engraving head frequency and variable surface speeds and traverse speeds to deliver the desired line screens and angles.

The frequency (speed) of Engraving Heads increased over the years and, currently, engraving speeds of 24 kHz are achievable. Along with this development came more refined techniques that improved the fidelity of the engravings.

It is true to say that the results achieved by the latest electromechanical engraving machines bear no resemblance to the early models.

Advances in electromechanical engraving technology have addressed the issue of “sawtooth” edges on text, which has been used as a criticism of the gravure industry over the past forty years. Different stylus angles, which are measured at the cutting tip deliver differing cell depths for any given cell width, so a fine screen that is selected for detail can be made to deliver the cell volume required for color density by selecting a more acute engraving stylus angle.

Common angles are 115° to 140°. For some specialized engraving, stylus angles below 90° may be utilized, in these cases the very tip of the stylus may be ground to a “chisel” edge to provide strength and engrave a larger, but shallower highlight cell. To avoid moiré patterns in the printed product, pseudo-screen angles are achieved by adjusting the elongation and compression of the engraved cells along with the screen ruling.

Elongation and compression are achieved by altering the surface speed of the cylinder against the constant frequency of the engraving head.

The pitch (screen ruling, or lines per linear inch) of the engraving track determines the potential size, or width of the engraved cell. If you can imagine a screw cut thread, the relative coarseness of the thread is dependent on the traverse speed, the faster the traverse speed the courser the thread, which in turn allows the tool to cut deeper.

Now if you imagine that the tool can also track in and out, in relation to the centerline, you can visualize how the cell shape is formed.

Indirect Laser Imaging

This process improved on the original direct exposure technology by utilizing more substantial coatings and laser ablation. The laser head can be controlled to deliver very precise shapes that conform to the outline of the desired image, therefore creating extremely fine detail in small font text, for example. Because this technology ablates the coating very rapidly, line screens of 2,000 lines per centimeter may be achieved within reasonable process times.

The etching process can be ferric chloride, or electrolytic etching using saline solutions. For linework, this process is well established and accepted for the delivery of high-fidelity printing. Due to the etching process, concerns remain regarding the method’s ability to deliver consistent cell volumes and cell walls across areas of line work. As a result, technology for half-tone work under this method continues to evolve.

Direct Laser Engraving

Originally developed for the Publication industry, the benefits of this method further increased consistency against the multi-ribbon (multi-head) Helio-Klischograph Engraving machines and the etching processes that were typically used to balance color from page to page.

Subsequently, Max Daetwyler Corporation developed a system that successfully engraved into zinc-plated cylinders using laser technology.

Speeds were increased to 70 kHz and developed to engrave into copper; there remains the possibility of laser engraving into many substrates. The possibility still exists that the industry may return to a non-metallic substrate, just as was originally intended in the creation of the process.

The laser engraved cell has several advantages over Electronic Engraving. Because of the “bucket” shaped cell, as opposed to the inverted pyramid delivered by a diamond stylus, Laser has the ability to deliver ink in a more uniform and economical fashion.

The industry has chosen half-autotypical screens which alter both the area and depth of cells to describe tonal values, whereas “conventional” laser engraving used cells of a relatively consistent area and differing depths (more like the carbon tissue of old).

This produced an almost photographic quality (continuous tone) to illustrations, but with the advent of faster solvents, was challenging to print in the highlight areas.

Because of the mechanical restrictions of the engraving and exposing machines, they are limited to a finite number of “screen angles” by altering the traverse, rotation and head frequency.

By combining screens and angles, illustrations can be printed without the risk of Moiré patterns, or color shift. In the case of direct laser engraving, only two angles are available. The exception is “conventional laser,” because each cell is relatively the same size and 100% coverage at differing ink thicknesses, there is no fear of screen clash and therefore, no need for different screen angles.

The choice of screen rulings, that is the number of rows of cells per linear inch, or centimeter, is determined by the type of work to be printed along with the ink, or coating and the substrate. The more rows, or lines per inch/cm, the higher the resolution of the printed image.

In electromechanical engraving, ensuring that the correct amount of ink is transferred to achieve the color densities requires different stylus geometry.

The more acute the angle of the diamond stylus tip, the deeper the engraved cell for a given area. For indirect laser, the depth of the cell is controlled by the etching time.

Direct laser determines cell depth by altering the power of the laser light. As the available power of lasers increase, newer machines are successfully engraving directly into copper, bringing a new level of resolution to conventional processing lines.

Not bad for a process that has supposedly not changed in fifty years!

Where Does Gravure Go From Here?

The processes that are currently in daily use are capable of delivering a fine product for a reasonable cost. In the future, challenges and opportunities will include new applications for gravure and shorter press runs, requiring faster changeovers.

Further development using current methods and materials will continue, will create value and should be recognized. However, if the industry is to experience a game-change, new methodologies and materials will most likely be required. Encouraging innovation and embracing opportunities presented by economical, portable, high performance replacement image carriers could bring significant benefits to the industry as a whole.

One such example would be industry-led technology developments that can deliver more economical solutions for press-side engraving that perform well on press, without the requirement for chrome – an advancement that would represent a giant leap forward.

Plasma Substrate Treatment

July 30, 2019

By ELISE M. SANDERS
February 2006

Abstract

As a venue to improve the wettability of inks in the print industry, printers utilize surface-treatment technologies. These technologies allow adhesion of inks to plastics, polymers, films, and flexible packaging. Many treatment processes occur before substrates leave the factory, but further processing becomes a necessity due to a combination of uneven surface treatment and the limited longevity of the initial treatment. Popular processes today include corona, atmospheric plasma, cold gas plasma, and plasma-grafting treatments. How do these different treatments compare, what seems to be the best, and what is the future moving towards?

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Gravure & Its Role In Printed Electronics

July 30, 2019

By RYAN HILL
February 2006

Introduction

Conventional printing processes, such as gravure, may be able to revolutionize the way electronics are manufactured. The trend in the electronics industry is towards smaller products, lower prices, and more reliable products (Pudas, 2004). Traditional semiconductor electronics require a circuit board in order to function. To date, most circuit boards have chips, transistors, and other components that are soldered to a sheet of fiberglass.

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Digital Proofing Of Gravure Spot-Color Printing

July 30, 2019

By YU-JU WU
February 2006

Summary

Spot color is widely used in gravure printing to obtain a colorful appearance. With new developments in printers, inks, and media, an inkjet printer can be treated as a digital proofer for gravure printing, providing significant time and cost savings compared to conventional procedures for job approvals. The implementation of digital proofing is integrally related to color management. In the digital proofing process, a third-party RIP can be employed to interpret raster and vector data files for a specific printer, distributing the right amount of ink on

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Color Management Investigations For Rotogravure

July 30, 2019

By CHRISTINE WHEATLEY
February 2005

Abstract

In the gravure industry, having a proofing press that is used to simulate the visual characteristics of a finished product has become common practice. It is often difficult to achieve accurate color on the proof press since it may use different substrates, inks, and run different speeds than the final press. The proofing press also introduces delays in the cylinder delivery process, typically adding half a day to the production cycle. One way to reduce the necessity of using the proofing press is to use color management to provide off-line, color-accurate proofs.

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