LEP vs. LEPx: When the Substrate Changes the Rules

Ronen Dolev | 2026

Industrial Printing, Materials, Applications & Color Science

Introduction - One Substrate, Two Imaging Architectures. Will the Product Behave the Same?

Imagine two digital presses with a maximum web width of 340 mm. One uses conventional LEP architecture; the other uses LEPx. Both are designed to produce labels, both rely on indirect thermal image transfer, and both support a range of substrates including papers and polymer films.

Suppose the same image is printed on the same BOPP film using both presses, following suitable surface preparation and using the inks and primers approved for each system.

Will the printed ink layer exhibit the same adhesion? Will registration remain stable throughout the run? Will white-ink opacity be equivalent? Will the samples behave identically after lamination?

You cannot infer this solely because both platforms belong to the same technology family.

The transition from LEP to LEPx introduced a substantial change in image-formation architecture. Instead of a single imaging engine generating color separations sequentially, LEPx uses multiple imaging engines operating in parallel and a common blanket belt.

In both systems, however, the completed image is still transferred to the substrate through an intermediate surface.

This distinction makes it necessary to separate what happens inside the press during image construction from what happens at the ink–substrate interface during transfer and throughout the finished product's life. That is the starting point for this article.

1. A Substrate Is More Than the Surface We Print On

In industrial printing, substrates are often described by broad names: paper, PET, BOPP, or PE. But the polymer name alone tells only part of the story.

Two BOPP films can differ in layer composition, degree of orientation, surface roughness, coefficient of friction, surface-treatment history, and additives present in their outermost layers. These differences can affect printing performance even when the materials are commercially described as the same type of film.

The same applies to paper. Two coated papers of comparable grammage may behave differently because of variations in coating composition, porosity, topography, and chemical functionality at the surface.

Assessing a substrate for LEP or LEPx therefore requires attention to at least three levels of material properties.

The first concerns bulk behavior: thickness, elastic modulus, elongation, shrinkage, and thermal response.

The second concerns surface properties: surface energy, polarity, roughness, additive migration, and the composition of the outermost layer.

The third concerns the product's industrial construction, which may include coating, primer, ink, varnish, adhesive, and lamination layers.

A press's ability to transport a web does not establish that all three levels meet the requirements of the intended application.

2. What Actually Changes from LEP to LEPx?

The central difference lies in imaging architecture, not in the basic principle of transferring an ink film to the substrate.

In conventional LEP, a shared imaging engine images color separations sequentially and, in relevant one-shot configurations, accumulates them on an intermediate blanket before transferring them to the substrate.

In LEPx, as implemented in the HP Indigo V12, six imaging engines can create separations in parallel. The separations are accumulated on a blanket belt, from which the multicolor image is transferred to the substrate.

The fundamental principle of indirect thermal transfer is therefore retained in both architectures.

A key feature of this approach is that much of the ink-layer preparation for transfer occurs on the blanket rather than by drying a large amount of liquid ink directly on the substrate.

This does not mean the substrate experiences no heat, pressure, or mechanical stress. The final transfer occurs through physical contact, and the production line may also include surface treatment and inline priming with associated drying operations.

A change in blanket architecture, by itself, therefore does not prove a change in the thermal conditions experienced by the substrate. Such a conclusion requires measurement of both process conditions and printed results.

3. LEP and LEPx - Published Substrate Capabilities

For a practical comparison, consider two presses from the same nominal web-width category: the HP Indigo 6K+ as a conventional LEP representative, and the HP Indigo V12 as an LEPx representative.

These ranges are published product specifications, not comparative experimental results.

It would be incorrect to conclude that the 6K+'s ability to handle a thinner film results solely from its imaging-engine structure, or that the V12's upper thickness limit is an inherent constraint of LEPx physics.

Approved substrate windows depend on web handling, tension control, press architecture, surface-treatment configuration, and application requirements.

Similarly, thickness compatibility alone does not establish printability. A substrate must also meet operational, print-quality, and end-use performance requirements.

4. Surface Energy - Why Dyne Level Is Not an Adhesion Test

Many polymer films, particularly PE and PP, exhibit relatively low surface energy and may require suitable preparation for printing or coating. Corona treatment is a common way to modify their surface properties.

This treatment can introduce polar functional groups and change surface wetting behavior. Yet three different concepts must be kept separate: wetting, interfacial interaction, and adhesion.

Wetting tension measures how test liquids behave on a surface. Adhesion results from interfacial interactions, along with mechanical and structural factors. They are not equivalent.

ASTM D2578 and ISO 8296 describe procedures for assessing wetting tension; neither a wetting-tension result nor a single dyne value should be treated as conclusive evidence that an ink, varnish, or adhesive will achieve satisfactory bonding.

The implication for LEP versus LEPx is straightforward. Even if the same substrate exhibits an equal dyne level in both tests, that does not prove identical mechanical durability of the printed ink layer.

Conversely, if a difference in adhesion is observed, it should not automatically be attributed to imaging architecture before examining substrate preparation, surface composition, and primer behavior.

Qualification must include the treatment-and-primer process, not only the imaging engine.

The publicly listed V12 inline priming unit is relevant to print qualification because the resulting surface available for ink-film transfer may be a dried primer rather than the untreated polymer. The material comparison should capture the incoming substrate condition, whether treatment was refreshed, the applied primer system, drying state, and any topcoat already present on the stock. Merely noting that both presses printed BOPP is inadequate.

Do not imply that the presence of inline priming makes every self-adhesive label stock printable without verification. Surface-tension tests reflect wetting characteristics; primer compatibility and ink adhesion remain separate outcome measurements. A standardized failure-location assessment is essential before linking a difference to the LEP-to-LEPx architecture.

5. BOPP - Where Surface Chemistry Meets Dimensional Stability

Biaxially Oriented Polypropylene (BOPP) is a major material in label production. It offers low weight, a variety of optical appearances, useful moisture resistance, and versatility across label and packaging constructions.

However, not all BOPP grades are interchangeable. Differences in orientation, layer architecture, and additives may influence dimensional stability and surface behavior.

Aging of corona treatment

Studies of corona-treated BOPP indicate that surface characteristics can change during storage. Mechanisms discussed in the literature include reorientation of chemical groups within the polymer and changes in the near-surface state.

A dyne value measured shortly after film manufacture may therefore differ from the value obtained after storage. This reflects the material's condition at the time of printing, not necessarily a press-related problem.

Does LEPx change BOPP performance?

The published material examined for this article does not establish that LEPx provides better adhesion to BOPP than conventional LEP.

The proper question is whether the two systems, operated with approved inks, surface treatments, and process conditions, produce ink layers with equivalent performance on the same BOPP grade.

Such an assessment should address not only successful ink transfer but also image uniformity, dimensional stability, and post-conversion performance.

6. PE - The Mechanics of a Flexible Film

Polyethylene (PE) often exhibits greater flexibility and elongation than some PET and BOPP film grades used in printing. These properties depend strongly on the polymer grade, film structure, and manufacturing method.

In roll-to-roll printing, a flexible film may be especially sensitive to web tension, temperature, and transport conditions.

Why it matters

Behavior in the machine direction (MD) and cross direction (CD) influences dimensional stability and the geometry of the printed result.

In relevant label-printing modes, a common architectural advantage of LEP and LEPx is one-shot transfer of the multicolor image to the substrate. The substrate is not required to pass separate transfer stations for each individual color separation.

Nevertheless, it must still travel through web-handling, tension-control, and auxiliary units.

A change in tension between the web's entry and exit points can affect the dimensions of the complete image even when the internal registration between the color separations is satisfactory.

An LEP-versus-LEPx comparison on PE should therefore measure two separate outcomes: registration among color separations and the full image's geometric stability relative to the substrate. These are different performance metrics.

7. PET - Why the Grade Matters More Than the Material Name

Polyethylene Terephthalate (PET) is available in a wide range of constructions and grades. An oriented, heat-set PET film will not necessarily behave like amorphous PET.

A 2012 paper in the Journal of Industrial and Engineering Chemistry examined the dimensional stability of PET and BOPP substrates in roll-to-roll printing processes. Among the tested materials, PET engineered for printing showed better thermal and dimensional stability than the BOPP and commercial amorphous PET samples.

That investigation concerned gravure printing for flexible electronic applications, not an LEP-versus-LEPx trial. It supports the importance of film properties but does not demonstrate a performance advantage for either LEP architecture.

Implications for label production

When comparing two printing systems, matching the generic material name is not sufficient. Film grade, thickness, treatment, orientation, and dimensional-stability data should be documented.

Using two different PET films could produce a false conclusion about the relative performance of the presses. The same principle applies to converting requirements and to choosing surface printing versus reverse printing.

8. Coated Papers - The Chemistry Between Ink and Coating

Coated paper is more complex than it appears. Its coating may contain mineral pigments, binders, and additives that influence roughness, gloss, optical properties, and interactions with the printed ink layer.

Two papers with similar basis weight and apparent shade can therefore behave differently in terms of adhesion and visual appearance.

Research presented at an IS&T conference in 2009 investigated adhesion mechanisms between LEP ink and paper. The work considered relationships between surface polarity and interactions at the ink–paper interface, alongside spectroscopic evaluation of the materials.

Its significance is that LEP adhesion cannot be understood exclusively as mechanical anchoring: interfacial chemistry also matters. However, the study did not provide direct comparative data for newer LEPx systems.

Engineering implications

When evaluating coated paper on LEP and LEPx, it is useful to measure whether image uniformity, gloss, color, and adhesion differ.

If a failure appears, the investigation must determine whether it occurs within the ink layer, between ink and coating, or within the coating itself. Separation of a printed layer is not automatically evidence of a transfer defect originating in the press.

9. Paper-Based Labels - From Facestock to Finished Pressure-Sensitive Construction

Paper-based labels deserve a separate materials-engineering discussion. The print surface may be coated paper, uncoated paper, or a textured specialty grade, but the commercial product is often a multilayer pressure-sensitive construction rather than an isolated paper web. Published paper-label portfolios distinguish coated, uncoated, wet-strength, and thermal grades, each engineered for a different balance of image reproduction, converting, moisture exposure, and end use. [11, 12]

A paper label is more than a paper facestock

A conventional self-adhesive paper label comprises a printable facestock, a pressure-sensitive adhesive, and a release liner bearing a release coating. The facestock provides the printable surface and much of the visible appearance; the adhesive determines application and removal behavior; and the liner supports handling, die-cutting, matrix stripping, dispensing, and transport through converting. Not every paper label uses this construction: wet-glue labels do not require a permanent pressure-sensitive adhesive or a release liner.

For LEP–LEPx comparisons, the same facestock alone is not enough to control the material variables. Adhesive type, liner grade, release behavior, combined laminate caliper, web tension, and roll conditioning must also be documented. A nominally identical paper face can behave differently if mounted on different liners or adhesives. In particular, the specified press thickness window must be interpreted using the manufacturer's applicable guidance for the actual construction, rather than assuming that facestock grammage describes total web thickness.

Semi-gloss and coated label papers

Semi-gloss coated-one-side (C1S) facestocks are widely used where print sharpness, contrast, and a consistent optical background matter. The coating can reduce the visible effect of the underlying fiber topography and improve ink holdout compared with many uncoated papers. UPM, for example, publicly describes LabelCoat as a semi-gloss C1S face paper intended for several printing technologies, including HP Indigo. Such a published product-category statement does not prove compatibility with every individual LEP or LEPx model and press setup. [12]

An appropriate cross-platform study should quantify white-point variation, surface roughness, solid-area uniformity, minimum printable detail, highlight and shadow reproduction, registration, ink adhesion, and post-finishing appearance. On coated paper, a separation at the ink–coating interface must be distinguished from cohesive failure within the paper coating or fiber structure; visual inspection of a tape-test result alone may not provide that distinction.

Uncoated, textured, and premium paper labels

Uncoated and textured facestocks may be selected intentionally for tactile appearance, lower surface gloss, or a natural paper aesthetic. Their topography and surface chemistry can differ markedly from those of semi-gloss grades. Although the LEP image is developed on an intermediate blanket, print uniformity and fine-detail reproduction can still depend on how the transferred ink layer contacts the actual paper surface. The consequences must be assessed on printed samples; it would be incorrect to assume either a universal advantage or disadvantage for LEPx.

For these materials, qualification should include controlled visual examination of mottle, line breaks, fine type, contrast, and gloss at representative viewing angles. When comparing two presses, use the same paper lot and humidity-conditioning procedure to avoid confusing a substrate effect with an architectural effect.

Moisture-resistant and wet-strength papers are not interchangeable.

Two frequently confused properties are resistance to moisture uptake and retention of mechanical integrity while wet. Moisture-resistant coatings, internal sizing, and wet-strength chemistry address different failure mechanisms. A paper label on a chilled beverage bottle may encounter condensation, immersion, swelling, curl, wrinkling, fiber disruption, or loss of adhesion to the container. A suitable qualification must reflect the actual service conditions; a facestock marketed as moisture-resistant is not automatically equivalent to a wet-strength facestock. Published label-material guidance explicitly differentiates the categories. [11, 13]

This distinction is particularly relevant to an LEP-versus-LEPx study because a failure after refrigeration or immersion may originate in the paper, adhesive, or container interface rather than in the printed ink. Test the complete applied label, not simply the printed face material.

Paper moisture, curl, liner behavior, and registration

Paper is hygroscopic: its moisture content can change with ambient relative humidity, affecting dimensional stability, curl, stiffness, and coated-surface behavior. In a pressure-sensitive construction, the facestock and liner may respond differently to environmental changes. Their combined behavior can alter web flatness, winding characteristics, tracking, die-cutting performance, and dispensing reliability.

Both LEP and LEPx use an indirect image-transfer process in the relevant label configurations, so any difference in paper-web stability cannot responsibly be attributed to the blanket architecture alone. A meaningful comparison should record ambient conditions, equilibration time, MD/CD dimensional changes, web tension, total construction thickness, curl or lay-flat behavior, and registration over the run.

Paper white, optical brighteners, and color matching

Paper is part of the optical color-reproduction system. Facestock shade, opacity, coating gloss, and optical brightening agents (OBAs) can change measured and perceived color even when the digital file and nominal ink set are unchanged. In paper-grade comparisons, therefore, specify spectral data, sample backing, and measurement conditions. Fogra identifies M0, M1, and M2 measurements, paper-white Lab values, and optical-brightener characterization among relevant paper-testing methods. [14]

For an LEP–LEPx color comparison, use a consistent ISO 13655 measurement condition-commonly M1, where the assessment and optical-brightener content make it appropriate-and document the backing and illumination. Measure unprinted paper white as well as printed color patches. A Delta E difference without control of paper grade, backing, and measurement mode cannot establish a press-architecture effect.

Direct-thermal and thermal-transfer papers require separate approval

Thermal paper should not be treated as a generic alternative to semi-gloss label stock. Direct-thermal paper uses a heat-sensitive imaging layer, whereas a paper intended for thermal-transfer coding may rely on a different coating construction. Elevated process temperatures and contact with inks, varnishes, or coatings can affect some heat-sensitive grades. Although HP lists textured thermal among V12 substrate categories, this does not establish that every direct-thermal or thermal-transfer paper is approved for every configuration. Each grade requires specific compatibility and final-coding tests. [2, 11]

Qualification criteria for paper labels

A credible comparison should therefore test paper-based labels as finished constructions: evaluate coated semi-gloss and uncoated grades separately, and add wet-strength or thermal materials only when the intended application justifies them. Include the same facestock lot, adhesive and liner construction, conditioning environment, substrate-treatment or primer configuration approved for each system, print targets, measurement method, converting process, and end-use simulation.

The success criterion is not simply whether the press can image the paper. It is whether the produced label can be printed, converted, dispensed, applied, and used while meeting its specified requirements for visual quality, color, adhesion, readability, dimensional stability, and appearance after exposure.

Build the paper-label comparison around a complete construction.

Define coated semi-gloss and uncoated paper separately, then specify the adhesive chemistry, coat weight (where known), release coating, liner material, total caliper, stiffness, curl, and the roll's storage/conditioning history. For the same face-paper grade, a glassine liner and a PET liner can produce different web-handling and converting behavior because their moisture and mechanical responses differ.

In paper-label production, a difference in paper whiteness can be mistaken for a press-color deviation, while a difference in liner release force or matrix stripping can be mistaken for a printing-related production limitation. Include separate stages for print appearance, die strike, waste-matrix stripping, dispensing, and performance after application to the final container.

UPM's openly published paper-label portfolio differentiates coated, uncoated, wet-strength and thermal grades. Its LabelCoat description gives a commercial example of semi-gloss C1S face paper suitable for several printing technologies, but it does not prove suitability for every particular LEP or LEPx configuration.

10. Metallic and Transparent Substrates - When the Substrate Changes the Color

Transparent and metallic materials require the printed result to be evaluated optically as well as mechanically.

An ink layer on white paper will not necessarily look the same on transparent film or a highly specular metallic surface.

On transparent materials, some of the incident light may pass through the construction. On metallic materials, reflected light can change substantially with illumination and viewing angle.

Where white ink is used, its opacity affects the background's contribution to the appearance of the colors printed above it.

Does LEPx produce a more opaque white?

A change in imaging architecture alone does not demonstrate that it does.

Opacity depends on factors including ink formulation, deposited quantity, layer structure, and the substrate underneath. An objective comparison requires appropriate measurements on the same material, with a defined coverage target and consistent test conditions.

Metallic substrates are particularly susceptible to misleading conclusions from a single Lab measurement. Angle-dependent appearance may require further instrumental and visual assessment.

Do not confuse printable film thickness with finished label construction thickness.

For pressure-sensitive labels, a stated press gauge may require interpretation using the press maker's definition of substrate thickness. Document whether the number describes the facestock or the whole web construction, and record the adhesive and liner. For unsupported PE/BOPP/PET film, document film gauge and roll properties separately. This distinction can change apparent comparability even when both press datasheets use the same unit: micrometers.

Published specifications describe individual machine envelopes, not a universal physical limit of LEP or LEPx. For example, public HP documents give a wider nominal gauge range for selected conventional 6K-family configurations than for V12. Such data support only a model-level comparison; they do not isolate an imaging-architecture effect.

11. Primer - The Interface Layer That Cannot Be Ignored

Primers play an important role in many printing systems, but they should not become the default explanation for every failure.

A primer may modify the surface chemistry and provide a more suitable interface for an ink layer. At the same time, it adds another layer and another interface that may fail.

In a substrate–primer–ink construction, separation may occur at the substrate–primer boundary, at the primer–ink boundary, or cohesively within one of the layers.

Compatibility with one system is not automatic compatibility with another

A primer approved for a particular LEP system is not automatically approved for LEPx.

Even where the ink family is similar, industrial compatibility must be evaluated for the specific press and application conditions. The V12 includes a publicly documented inline-priming configuration.

Its availability does not mean that every substrate requires the same primer, or that a primer used successfully on an earlier press will necessarily perform identically on the new platform.

Why this matters to comparative research

If the two systems use different primers, a difference in adhesion may arise from the primer rather than from imaging architecture.

Conversely, using the same primer on two platforms without appropriate approval may be an unsuitable experiment from a safety or compatibility standpoint.

A comparison of approved production configurations must therefore be distinguished from an experiment designed specifically to isolate an imaging-architecture variable. These are two different research objectives.

12. Why Finished-Product Testing Matters

A common error in evaluating printing technologies is to infer successful application performance from the appearance of the sheet or web immediately after printing.

For pressure-sensitive paper labels, finished-product testing must also assess die-cutting, matrix removal, liner release, dispensing, and adhesion to the final container. A label that prints correctly but curls excessively, loses fibers under moisture, or fails to dispense consistently has not passed application qualification. The complete paper–adhesive–liner system must be considered.

A printed ink layer can look excellent and pass an initial adhesion check, yet behave differently after lamination, varnishing, die-cutting, creasing, or exposure to service conditions.

Lamination creates a multilayer structure in which bond performance depends on additional interfaces.

An inadequate laminate bond does not necessarily indicate a defect in the printed ink layer. Its origin may lie in the laminating adhesive, the second film surface, process conditions, or other material factors.

An LEP-versus-LEPx comparison after lamination therefore has to assess the failure location as well as the measured peel force.

When peel testing flexible structures, film thickness and bending resistance can also affect the recorded force. Direct comparison between dissimilar constructions may be misleading unless an appropriate method and analysis are used.

In-process paper behavior versus end-use moisture performance

For paper labels, distinguish moisture-related process variation from end-use durability. During printing, temperature and relative humidity influence web flatness, curl, coating response, and registration; after application, condensation, soak exposure, or wet-strength loss can originate in the face paper, adhesive, liner-removal process, or substrate-to-container bond. Use tests appropriate to the finished label rather than assigning any post-application defect to thermal image transfer.

A practical paper-label matrix should include semi-gloss C1S, uncoated textured stock and an application-specific wet-strength grade only where relevant. Each grade needs a consistent paper-white check and controlled conditioning before color or dimensional data can fairly compare the two press platforms.

13. How to Design a Credible Qualification Program

To determine whether LEPx genuinely affects substrate behavior, the investigation should be divided into two levels.

Level one - Commercial-product comparison

At this stage, each press should operate under the conditions approved for its configuration. The purpose is to determine whether both production systems can manufacture a product that meets the same end-use requirements.

Substrates should come from the same production lot wherever possible. Acceptance criteria should be established before testing, according to the intended application.

A test form should include solids, photographic images, fine lines, color targets, and features for assessing dimensional stability. Samples should be collected at multiple points during the production run.

Level two - Experimental isolation of variables

This stage addresses a more difficult question: whether the differences observed in the printed product arise from the substrate, primer, ink system, or transfer mechanism.

A structured experimental design is needed to isolate variables as far as practical.

If the two systems cannot use identical, approved auxiliary materials, the distinction must be documented. The result should not be presented as evidence that imaging architecture alone caused the difference.

Suggested test matrix

Adhesion and peel testing

In the labeling sector, the FINAT Test Methods Handbook includes FTM 21 and FTM 22 to evaluate ink adhesion under defined conditions.

The appropriate method must be chosen for the substrate and ink system, and the result should be interpreted together with a visual or instrumental assessment of the failure mode.

For flexible laminated constructions, methods such as ASTM D1876 (T-peel) may be useful when the specimen and test objective fall within their applicable scope.

A peel-force value does not replace identification of the precise layer or interface where failure occurred.

14. What Can We Actually Conclude Today?

The reviewed public specifications and research clearly separate established facts from open questions.

A result showing no statistically or practically meaningful difference would itself be an important engineering finding.

The purpose is not to force a distinction between technology generations. It is to establish whether an architectural change produces any measurable difference relevant to the substrate and the finished application.

Distinguish the press operating envelope from materials qualification.

The formal technical-specifications table on HP's V12 product page gives 40–300 µm, whereas some marketing FAQ text on the same family of web pages uses a different upper bound. In a formal comparative article, the technical-specifications table should be cited as the controlling public statement, with configuration-specific changes verified directly rather than inferred.

For paper facestocks and polymer films, printability should be reported as an outcome under a named construction and process, not as a universal claim about the polymer family. The measurable result is an accepted, converted, and applied label, including the adhesive and liner stages where relevant.

Table 4. Additional qualification conditions for pressure-sensitive paper labels

15. Does LEPx Require a New Approach to Materials Engineering?

At a fundamental level, materials engineering principles remain unchanged.

Surface properties, interfacial chemistry, ink-layer characteristics, and the substrate's mechanical and thermal behavior must still be understood.

A new press architecture, however, requires verifying that the complete product remains compatible with its specific production process.

This does not mean every substrate previously approved for LEP will fail on LEPx, nor does it mean every substrate requires a full qualification exercise from the beginning.

Material history, production experience, published manufacturer guidance, and similarity of process conditions can all provide valuable evidence.

Where durability or end-use performance is critical, however, similar technology names are not enough. The finished product must be shown to meet the relevant requirements.

Conclusions - The Real Difference Is Found at the Interface

The transition from LEP to LEPx represents a major development in digital printing architecture. Yet from a materials-engineering perspective, discussing six imaging engines, a blanket belt, and increased production speed is not enough.

The decisive question is what happens to the ink layer after transfer to the substrate, and how the product behaves throughout manufacturing and use.

BOPP may change surface properties during storage. PE film may respond to tension according to its structure and transport conditions. PET dimensional stability depends on orientation and thermal history. Coated paper can exhibit different chemical interactions with an ink layer. A metallic substrate can fundamentally change the perceived appearance of the same color.

Paper labels introduce an equally important set of variables: coated or uncoated facestock, paper-white and optical-brightener behavior, humidity response, coating strength, adhesive and liner construction, and converting performance. Their suitability cannot be inferred from print appearance or paper thickness alone.

None of these phenomena, by itself, demonstrates an advantage or disadvantage of LEPx over LEP.

The engineering task is to separate the effects of the substrate, surface preparation, ink-layer properties, and press architecture.

A press can transfer ink successfully and still produce an article that is unsuitable for its intended application.

Qualification of a material for digital printing does not end with its acceptance on the press. It ends only when the converted, finished product satisfies the performance requirements established for its intended use.

That principle should guide every credible LEP-versus-LEPx materials comparison.

Technical and Scientific References

1. HP Indigo, The HP Indigo LEP / LEPx Technology & The Future of Digital Printing. Public white paper (2020).
2. HP Indigo V12 Digital Press. Official published specifications for substrate thickness, web width, architecture, and inline priming.
3. HP Indigo 6K+ Digital Press. Published technical specifications and substrate capabilities.
4. ASTM D2578-23. Standard Test Method for Wetting Tension of Polyethylene and Polypropylene Films.
5. ISO 8296:2003. Plastics-Film and sheeting-Determination of wetting tension.
6. Bhattacharyya, M. K., et al. Investigation of Ink-Substrate Adhesion in LEP Printing. IS&T NIP & Digital Fabrication Conference (2009).
7. Lee, J.-W., and Yoo, Y.-T. A Comparative Study on Dimensional Stability of PET and BOPP Substrates for Fabrication of Flexible Electric/Electronic Devices Through Roll-to-Roll Printing. Journal of Industrial and Engineering Chemistry (2012).
8. Surface Modification of Biaxially Oriented Polypropylene Film Using Acrylic Acid-Corona Treatment: Part II-Long-Term Aging Surface Properties. Surface and Coatings Technology (2013).
9. ASTM D1876-08(2023). Standard Test Method for Peel Resistance of Adhesives (T-Peel Test).
10. FINAT. Technical Handbook-FTM 21 and FTM 22, Ink Adhesion Testing.
11. UPM Adhesive Materials. Paper labels: coated, uncoated, wet-strength and thermal constructions, with adhesives and liners.
12. UPM Specialty Materials. UPM LabelCoat: public example of a semi-gloss C1S label face paper with HP Indigo among the listed printing methods.
13. UPM Specialty Materials. UPM LabelCoat Moistproof: moisture-resistant label face paper and published converting/printing uses.
14. Fogra. Paper testing and specifications: paper white, optical brighteners, gloss and ISO 13655 measurement conditions.

2026 revision - independently accessible source checks

HP V12 public press and substrate data. https://www.hp.com/us-en/industrial-printers/indigo-digital-presses/labels-flexible-packaging-digital-presses/v12-printing-press.html

HP Indigo 6K-family public technical specifications. https://h20195.www2.hp.com/v2/GetPDF.aspx/4AA8-0016ENW.pdf

UPM public paper-label construction guide. https://www.adhesivematerials.upm.com/label-solutions/label-types/paper-labels/

UPM LabelCoat commercial C1S paper example. https://www.upmspecialtymaterials.com/products/paper-catalogue/categories/face-papers/upm-labelcoat/

FINAT Technical Handbook test method overview. https://finat.com/documents/540/technical-handbook-2019-folder-low.pdf

ASTM D2578 wetting tension standard. https://store.astm.org/d2578-23.html

Publication boundary: This revised article uses general printing science, independently published material, and publicly accessible manufacturer specifications. Customer notes, internal technical updates, restricted training, and confidential maintenance instructions were not used as evidence for any new externally publishable assertion. Product or software capabilities may depend on configuration and release; absence of a publicly verified feature must not be interpreted as proof of its availability.

Research and intellectual-property note. Independent technical analysis based on public documentation, scientific research, and recognized standards. Brand names identify products only. No confidential service data, proprietary ink formulations, or unpublished internal results were used. No physical LEP–LEPx comparison was performed. Findings from other printing processes are not presented as proof of LEPx performance.