Painting & Coating Industry (PCI) logo Powder coating summit logo
search
cart
facebook twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
Painting & Coating Industry (PCI) logo Powder coating summit logo
  • NEWS
    • Latest News
    • Market Trends & Reports
    • Price Alerts
    • Subscribe to eNewsletters
    • Global Top 10/ PCI 25
    • Weekly Featured Article
    • COATLE Word Game
  • PRODUCTS
    • Product News
    • Must See Products and Services
  • MATERIALS
    • Additives
    • Resins/Polymers
    • Pigments
    • Equipment
    • Distributors
  • TECHNOLOGIES
    • Adhesives
    • Architectural Coatings
    • Industrial Coatings
    • Nanotechnology
    • Powder Coatings
    • Solventborne
    • Special Purpose Coatings
    • Sustainability
    • UV Coatings
    • Waterborne
    • FINISHING
      • Finishing News
      • Finishing Technologies
      • Finishing Equipment
    • RESOURCES
      • Columns
        • Ask Joe Powder
        • Did you know?
        • Distribution Dive
        • Focus on Canada
        • Formulating With Mike
        • Innovation Insights
        • Moody's Coatings Conundrums
        • Powder Coating Perspectives
        • Target the Market
        • TiO2 Insider
      • Blogs
        • Editor's Viewpoint
        • Industry Insights
      • Coatings Supplier Handbook
      • Podcasts and Videos
        • COAT-IT! Podcast
        • Videos/PCI TV
      • PCI Store
      • eBooks
      • Sponsor Insights
      • White Papers
      • COATLE Word Game
    • EVENTS
      • Coatings Trends & Technologies Summit
      • Paint and Coatings Academy
      • Webinars
      • Calendar of Events
      • Lifetime Achievement Award
    • DIRECTORIES
      • Buyer's Guide
      • Equipment Directory
      • Materials Directory
    • EMAGAZINE
      • Current Issue
      • eMagazine Archive
      • China Issue Archive
      • Editorial Advisory Board
    • CONTACT
      • Contact Us
      • Advertise
      • Subscribe to eMagazine
      • Subscribe to eNewsletters
    Paint and Coating EquipmentUV CoatingsUV/EB Curing Equipment

    The Impact of Different Intensities on the Performance of LED-Cured Coatings

    By David Ivarsson
    pci0321-Efsen-1145626155-900.jpg
    wacomka/iStock / Getty Images Plus via Getty images
    March 16, 2021

    UV-LED technology provides a number of great advantages, such as energy savings, long lifetime, low heat, no ozone and no mercury. With LED technology, we rely on thousands of small LEDs to sufficiently cure a coating. What if there is a deviation along the width of the lamp? If a segment goes out, if some of the optics get damaged or dirty, how does this impact the curing, and the final coating properties?

    This study aims to determine what level of deviation causes problems with insufficient cure. To prevent problems with insufficient cure, EFSEN has developed a proprietary technology called ICAD® to continuously monitor the output of a UV lamp during production. Not only does this show us the complete picture of the UV output along the width of the lamp, it is also able to use the extracted information to adjust the power level of any segments that do not conform to the specification (Figures 1 and 2). This will provide assurance, in real time, that all segments perform according to the specifications, and also lets users know directly when there is damage, dirt or other issues preventing a segment from performing to standard.

    A measurement of five pcs AC8300-395 UV LED heads.
    FIGURE 1 » A measurement of five pcs AC8300-395 UV LED heads.
    A measurement of five pcs AC8300-395 UV LED heads after “calibration” of heads.
    FIGURE 2 » A measurement of five pcs AC8300-395 UV LED heads after “calibration” of heads.

     

    What is the Required Illumination to Sufficiently Cure the Reactive Material?

    This is one of the most basic questions to ask with radiation curing processes. While this might seem like a simple question, it can actually be quite complicated in reality. And if our curing system is under dimensioned, or if the output has fallen due to damage, dirt, aging or lack of maintenance, then problems occur. The curing issue might result in lacking properties of the final product such as adhesion failure, and low scratch and chemical resistance. With some luck, the deviation can be discovered quickly to halt production and rework whichever pieces have been produced with insufficient cure.

    However, if the problem is not identified there might be huge claims, as unfit products reach the consumer. Even worse are the cases were neither the producer nor the consumer realize that the product is unfit, as the performance seems to be acceptable. The consumer can then be exposed to residual monomers, initiators or other harmful components without even realizing it.

    Setting and fulfilling curing requirements is key to preventing this and ensuring a safe, durable product for the consumer. There are many things to consider. Does the light source provide the optimal spectral distribution? Is the intensity high enough to ensure an efficient reaction? Is there enough dose for the cure speed required?

     

    Transitioning to Industry 4.0 – Accurate Curing Requirements

    In essence, Industry 4.0 is about optimizing production, using technology to eliminate errors and maximize flexibility. For UV curing, a transition into Industry 4.0 requires that we are able to set accurate curing requirements and that we have the right means to ensure that those requirements are fulfilled at all times. We have to establish an accurate process window and ensure we do not drift outside of this window.

    How far we have come to monitoring and controlling UV systems differs from industry to industry. Implementing sensors or measuring procedures for frequent controls with radiometers are used in many processes. When it comes to conveyor-based production systems, it has become the industry standard to measure with a radiometer at the start of (or a few times during) each shift. If done correctly, this will help confirm that an arc or microwave UV lamp is performing as it should.

    The emerging LED technology that is already proved and implemented to some extent works quite differently in comparison with conventional curing units. A conventional lamp typically uses one bulb to cover the whole line width, thus a measurement at one point of this lamp will give a good idea of how the lamp performs throughout the whole width, with a reduction towards the edges. This is not the case with an LED light source. An LED unit consists of several light sources, thus measuring in one spot will not give you the full picture of how the unit behaves (Figure 3).

    The difference between a conventional lamp (left side) and LED (right side).
    FIGURE 3 » The difference between a conventional lamp (left side) and LED (right side).

     

    The Choice of Wavelength

    There have been LED units in commercial production for quite some time, despite the previous lack of sufficient cure control. This study aims to establish how critical cure control is to understand if there is an urgency for implementing control systems for LED lamps, or if catching the deviations in our light source is not critical. In order to find the answer, there are a couple of things to consider. An operating window must be established for our process, and we have to look into how changes along the LED lamp affect the output in each point along the width. To establish a process window, a test is set up to identify the breaking point – the minimum amount of light that cures the coating enough to reach the requirements.

    Before proceeding to pinpoint the dose required, it is important to ensure we are using a light source with the optimal spectral output. For LEDs, this is basically selecting the optimal wavelength. The choice of wavelength is mainly governed by the following factors:

    · Which wavelength offers the best match to the absorption of the initiators in the coating. · Which wavelength will have the best penetration properties (for deep curing applications) or the best way of overcoming oxygen inhibition (for surface curing applications) (Figure 4).

    Then it is of course important to take into account what output and long-term performance we can expect from a system at the chosen wavelength.

    LED systems at 365, 385, 395 and 405 nm are available at high output with decent price performance and life length. While lower-wavelength LEDs would be attractive to fill the surface curing role, they are not commercially feasible quite yet.

    Shorter wavelengths release their energy at the very surface. Longer wavelengths have increased penetration, thus release energy throughout the film.
    FIGURE 4 » Shorter wavelengths release their energy at the very surface. Longer wavelengths have increased penetration, thus release energy throughout the film.

    For this article, the LED curing of white base coats was selected as the process step to evaluate. This is a common product, produced in large quantities in the wood coatings market. When evaluating a base coat, the primary focus is the deep curing, as surface curing is generally not required. The longer wavelengths will excel; thus 395 or 405 nm should be selected. Looking at the absorption of Irgacure 819, a common initiator for pigmented coatings, the 395 nm LED is a slightly better match than 405 nm.

    However, when taking into account the harsh absorption of titanium dioxide, 405 nm becomes the most attractive choice, as seen in Figure 5.

    Absorption of rutile titanium dioxide in the 300 to 500 nm range. The table shows the transparency at common LED wavelengths. Absorption of rutile titanium dioxide in the 300 to 500 nm range. The table shows the transparency at common LED wavelengths.
    FIGURE 5 » Absorption of rutile titanium dioxide in the 300 to 500 nm range. The table shows the transparency at common LED wavelengths.

    Due to the fact that the transparency changes drastically with a wavelength shift of only 10 nm, it could be useful to know the actual peak wavelength of the chosen light source. The peak wavelength of an LED is generally +/- 5 nm, which essentially means that a 405 nm unit could really be close to 400 nm in the case of low-bin diodes, or close to 410 nm in the case of high-bin diodes. The impact of this wavelength shift is complicated to establish, as it depends on many different factors that are different for different applications. It might very well be of significance.

     

    Test Setup and Execution – Dose and Peak Requirements

    With the wavelength specified, the dose and peak requirements can be established. The evaluation performed for this article looked at a varying output at constant speed. The focus was on the dose as the main limiting factor, as LED units provide a high intensity (1,000+ mJ/cm² L405 in a narrow wavelength band, a factor much higher than arc lamps would provide).

    A commercial LED curing base coat was selected for evaluation. The conditions of a factory running this product were replicated, but with varied LED power level (Figure 6). The purpose was to learn which level of deviation would be acceptable and to identify the breaking point at which the curing was insufficient. The product of choice was an intermediate coating, a base coat, which is applied after sealing of the surface.

    The wood coating line at Freda, Lithuania. The test uses the same base coat with the same settings as the three base coat positions cured with 405 nm.
    FIGURE 6 » The wood coating line at Freda, Lithuania. The test uses the same base coat with the same settings as the three base coat positions cured with 405 nm.

    The main purpose of this base coat is to build up the opacity and color of wood furniture. It is typically applied in three layers, each at about 10-micron film weight, and featuring a high pigment load, about 40% titanium dioxide. In case of insufficient curing, the deep curing will suffer, causing adhesion failure. The selected test methods to evaluate the adhesion was tape, crosscut + tape and finally Hamberger Hobel. Hamberger Hobel is a refined version of the classic coin-test, where the coin is replaced with a cutting head that is pushed down to the surface with a constant pressure. A decent result with a Hamberger Hobel is to withstand at the very least 10 Nm of pressure; the highest IKEA standard requires 20 N (this is only for certain premium surfaces).

    The first thing evaluated was with the same level of curing on all three basecoat layers. The dose indicated by the coating supplier was selected as starting point, progressively reducing the dose until adhesion failed. A dose level higher than the indicated curing requirement was also evaluated to see if there would be a benefit with an even higher dose. Surprisingly, it was observed that the adhesion was still acceptable when the dose was reduced to 50% of the curing specification. Curing with a higher dose than specified provided no advantage (Figure 7).

    Adhesion and Hamberger results at descending power output. Note that the 40% power level passed the adhesion test but is just barely on the right side of the breaking point. The coating supplier dose specification is 230 mJ/cm² L405.
    FIGURE 7 » Adhesion and Hamberger results at descending power output. Note that the 40% power level passed the adhesion test but is just barely on the right side of the breaking point. The coating supplier dose specification is 230 mJ/cm² L405.

     

    The Importance of Monitoring the Full Width of an LED Array

    It could be argued that the coating supplier selected a far too high dose specification. However, there are many LED systems today running without control systems thoroughly implemented, making it reasonable to include a substantial safety margin in order to ensure sufficient curing even if the LED array would suffer from malfunctioning segments, or damaged/dirty lenses. This reasoning does result in a significantly higher energy consumption (100% higher than required in this particular case). Furthermore, running LEDs at high output has a significant impact on the lifetime.

    Another interesting question is to what degree neighboring LED segments contribute to the curing, whether they can compensate for blocked or inactive LED segments. This is done by measuring the output level along an LED head with inactive or underperforming segments (Figure 8).

    The graph shows a measurement of the UV dose deviation from a 395 nm LED array with the 2nd, 6th and 9th segment disabled. The straight line indicates the specified minimum dose requirement (122 mJ/cm²). The data was collected with an LEDCure 395, at 35 mm height, 40 m/min, 80% power level.
    FIGURE 8 » The graph shows a measurement of the UV dose deviation from a 395 nm LED array with the 2nd, 6th and 9th segment disabled. The straight line indicates the specified minimum dose requirement (122 mJ/cm²). The data was collected with an LEDCure 395, at 35 mm height, 40 m/min, 80% power level.

    It is clear to see that neighboring LEDs do contribute, but even for an LED array with a lot of margin, neighboring LEDs struggle to keep the curing on the edge of the operating window. In reality, this deviation would surely result in adhesion failure in the case mentioned previously in this article where base coat cure requirements were evaluated. This speaks to the importance of monitoring the full width of an LED array in order to maintain the cure required for desired coating performance. Continuous monitoring would also open up for reducing the cure requirement, as any LED deviation would be identified immediately.

    To successfully measure each segment of an LED array manually with radiometers would require a measurement every 2-5 cm, depending on the accuracy desired. In the applications discussed in this article, this would translate to roughly 50 measurements per array for high accuracy, or at least 20 measurements to be able to catch deviations. In addition to this, documenting and checking the data would also be required. Such a procedure would be far too time consuming to perform manually on a regular basis.

     

    Inline Continuous Automated Dynamic UV Monitoring

    EFSEN has developed ICAD, a proprietary in-line sensor that travels under the LED array during production to continuously monitor each LED segment (Figure 9).

    A picture of ICAD in action, measuring an LED array.
    FIGURE 9 » A picture of ICAD in action, measuring an LED array.

    This also allows for collecting curing history for efficient documentation of cure data. Any deviations are automatically detected and adjusted to the right level where possible. Alarms or automatic line stops can be set to trigger whenever the minimum output level cannot be reached.

    For more information, email david@efsen.dk.

    All photos and illustrations are made by EFSEN.

     

    KEYWORDS: Curing Equipment

    Share This Story

    Looking for a reprint of this article?
    From high-res PDFs to custom plaques, order your copy today!

    David Ivarsson, Application Engineer; EFSEN UV & EB Technology, Holte, Denmark

    Recommended Content

    JOIN TODAY
    to unlock your recommendations.

    Already have an account? Sign In

    • PCI-0724-Global10-Feature-1440.png

      2024 Global Top 10: Top Paint and Coatings Companies

      Who ranks on top? PCI’s annual ranking of the top 10...
      Paint and Coating Market Reports
      By: Courtney Bassett
    • PCI-0724-PCI25-Feature-1440.png

      2024 PCI 25: Top Paint and Coatings Companies

      PCI's annual ranking of the top 25 North American paint...
      Global Top 10 and PCI 25
      By: Courtney Bassett
    • pci1022-Kinaltek-Lead-1170.jpg

      A Novel Pigment Production Technology

      Following an extensive R&D program that demonstrated...
      Paint and Coating Pigments
      By: Jawad Haidar and Nitin Soni
    You must login or register in order to post a comment.
    Unable to fetch comments.

    Report Abusive Comment

    Subscribe For Free!
    • eMagazine
    • eNewsletter
    • Online Registration
    • Subscription Customer Service

    More Videos

    Sponsored Content

    Sponsored Content is a special paid section where industry companies provide high quality, objective, non-commercial content around topics of interest to the PCI audience. All Sponsored Content is supplied by the advertising company and any opinions expressed in this article are those of the author and not necessarily reflect the views of PCI or its parent company, BNP Media. Interested in participating in our Sponsored Content section? Contact your local rep!

    close
    • Modern arapartment complex painted in bright colors.
      Sponsored byEPS - Engineered Polymer Solutions

      Architectural Polymers Leading the Way in Coatings Innovation

    • paint sprayer in a workshop
      Sponsored byallnex

      Enabling Performance and Compliance: allnex Introduces a New Line of VOC Exempt Solvent-Borne Resins

    Popular Stories

    No. 3 AkzoNobel

    AkzoNobel to Close Two Manufacturing Sites

    A collage of products using non-PFAS

    A Surge in Non-PFAS Releases

    Default Aerospace Image

    PPG Plans Major Aerospace Facility



    PCI Buyers Guide

    Submit a Request for Proposal (RFP) to suppliers of your choice with details on what you need with a click of a button

    Start your RFP

    Browse our Buyers Guide for manufacturers and distributors of all types of coatings products and much more!

    Find Suppliers

    Events

    September 3, 2025

    Coatings Trends & Technologies Summit

    The Coatings Trends & Technologies (CTT) Summit is an annual conference for both liquid and powder coatings formulators and manufacturers to discuss innovations in coatings technology. This event combines high-quality technical presentations, a resource-rich exhibit hall, and dedicated networking opportunities to connect scientific minds, foster innovation, and cultivate game-changing new ideas!

    January 1, 2030

    Webinar Sponsorship Information

    For webinar sponsorship information, visit www.bnpevents.com/webinars or email webinars@bnpmedia.com.

    View All Submit An Event

    Poll

    Longest-running laboratory experiment

    What is the longest-running laboratory experiment?
    View Results Poll Archive

    Products

    CTT Summit Short Courses (Live 9/3/25)

    Coatings Trends & Technologies Summit is expanding its offerings with four short courses. These short courses will offer an extensive day of interactive learning.

    See More Products
    pci  webinar april 2025

    PCI CASE EBOOK

    Related Articles

    • The Effects of Different Curing Methods on Tack-Free Curing

      The Effects of Different Curing Methods on Tack-Free Curing

      See More
    • Digital Tool Predicts the Impact of Fouling Control Coatings on Ship Efficiency

      Digital Tool Predicts the Impact of Fouling Control Coatings on Ship Efficiency

      See More
    • pci1117-Vencorex-157396257-900.jpg

      How the Design of (Poly)isocyanate Hardeners Can Impact the Properties of Aliphatic Polyurea Coatings

      See More

    Related Products

    See More Products
    • failiure-analysis-of-paints

      Failure Analysis of Paints and Coatings, Revised Edition

    • auto-paints-and-coatings

      Automotive Paints and Coatings, 2nd Edition

    • organic coatings.jpg

      Organic Coatings: Science and Technology, 4th Edition

    See More Products
    ×

    Keep the info flowing with our eNewsletters!

    Get the latest industry updates tailored your way.

    JOIN TODAY!
    • RESOURCES
      • Advertise
      • Contact Us
      • Directories
      • Store
      • Want More
    • SIGN UP TODAY
      • Create Account
      • eMagazine
      • eNewsletters
      • Customer Service
      • Manage Preferences
    • SERVICES
      • Marketing Services
      • Reprints
      • Market Research
      • List Rental
      • Survey & Sample
    • STAY CONNECTED
      • LinkedIn
      • Facebook
      • Youtube
      • X (Twitter)
    • PRIVACY
      • PRIVACY POLICY
      • TERMS & CONDITIONS
      • DO NOT SELL MY PERSONAL INFORMATION
      • PRIVACY REQUEST
      • ACCESSIBILITY

    Copyright ©2025. All Rights Reserved BNP Media.

    Design, CMS, Hosting & Web Development :: ePublishing