Dominant Factors of Dominant Factors of Gloss Control in Gloss Control in

Radiation Curable Radiation Curable CoatingsCoatings

By By

Suresh K. DevisettiSuresh K. DevisettiLoyd J. BurchamLoyd J. Burcham

Richard C. MacQueenRichard C. MacQueenCongoleum Corporation, Mercerville, Congoleum Corporation, Mercerville,

NJ-08619NJ-08619RadTech e5|2008 Technical ConferenceMay 4-7, 2008 ; Chicago, IL

OutlineOutline BackgroundBackground Experimental MethodsExperimental Methods

Formulation, Application, UV-Cure Formulation, Application, UV-Cure ConditionsConditions

ResultsResults Gloss change with Irradiance – PI %Gloss change with Irradiance – PI % Gloss Change with UV Energy – PI %Gloss Change with UV Energy – PI %

DiscussionDiscussion Gloss Change with Uncured Surface Gloss Change with Uncured Surface

ThicknessThickness Gloss as a function of Absorbed Light Gloss as a function of Absorbed Light

IntensityIntensity ConclusionsConclusions AcknowledgmentsAcknowledgments

IntroductionIntroduction Control of gloss – especially low-gloss – is important for achieving Control of gloss – especially low-gloss – is important for achieving

desired aesthetics in UV coatings.desired aesthetics in UV coatings. A low gloss surface is created by fine surface roughness which A low gloss surface is created by fine surface roughness which

reflects incidental light in a diffusive manner.reflects incidental light in a diffusive manner. Typically, surface gloss is measured at 60Typically, surface gloss is measured at 6000 angles. angles.

Low Gloss (Matte) < 20 Low Gloss (Matte) < 20 Satin : 20-40Satin : 20-40

Semi-Gloss : 45-65Semi-Gloss : 45-65 High Gloss > 80 High Gloss > 80

Desirable in many industrial coating Desirable in many industrial coating applications. applications.

Provides an elegant and natural look.Provides an elegant and natural look. Camouflages any minor imperfections.Camouflages any minor imperfections.

Why Low Gloss?Why Low Gloss?

Usage of appropriate Matting Agents.Usage of appropriate Matting Agents. Usage of “incompatible” Components.Usage of “incompatible” Components. Dual – Cure Process ( Air + Air).Dual – Cure Process ( Air + Air). Dual – Cure Process (Air + Nitrogen).Dual – Cure Process (Air + Nitrogen).

How to Matte UV Coatings?How to Matte UV Coatings?

Factors that Influence UV Factors that Influence UV Gloss in Dual – Cure Gloss in Dual – Cure

MechanismMechanism Matting Agent (Type, Size, Treatment & Level).Matting Agent (Type, Size, Treatment & Level). Process (Intensity, Energy, Temp., Lamp type).Process (Intensity, Energy, Temp., Lamp type). Coating (Viscosity, Reactivity, Functionality, PI Coating (Viscosity, Reactivity, Functionality, PI

%).%). Thickness, Oxygen Inhibition, Substrate.Thickness, Oxygen Inhibition, Substrate.

ObjectiveObjective

To investigate the influence of To investigate the influence of various parameters as a group on the various parameters as a group on the gloss and to determine the dominant gloss and to determine the dominant factors that influence the gloss factors that influence the gloss control in UV coatings.control in UV coatings.

ExperimentalExperimental FormulationFormulation

NoNo ComponentComponent Wt%Wt% PropertiesProperties

11 Urethane Acrylate Urethane Acrylate Oligomer Oligomer

40.040.0 Difunctional Difunctional

22 Monomer Monomer 40.840.8 Difunctional Difunctional

33 Matting AgentMatting Agent 15.015.0 Polyamide; 5µPolyamide; 5µ

44 PhotoinitiatorPhotoinitiator 0.07-0.07-0.60%0.60%

Type 1 Type 1 (cleavage) (cleavage) ApplicationApplication

Air-knife Coater Coating Thickness - 30µ Plasticized PVC Substrate

Curing ProcessCuring Process ““Dual-Cure" Process.Dual-Cure" Process. 11stst Stage – Stage –

1. Curing in Air Atmosphere.1. Curing in Air Atmosphere. 2. Light Hammer™ UV processor2. Light Hammer™ UV processor ((Fusion UV Fusion UV

systemssystems).).

3. Various Irradiances3. Various Irradiances** and Energies and Energies**.. 22ndnd Stage - Stage -

1. Curing in Nitrogen Atmosphere.1. Curing in Nitrogen Atmosphere.

2. Aetek Processor (2. Aetek Processor (American Ultraviolet CompanyAmerican Ultraviolet Company).).

3. Dose: 350 mJ/cm3. Dose: 350 mJ/cm2 2 and Irradiance: 950 and Irradiance: 950 mW/cmmW/cm22..

* - Measured using a PowerMap™ Radiometer (EIT, Inc.)

Parameters Parameters

Studied:Studied: Gloss vs. Air-Cure Irradiance Gloss vs. Air-Cure Irradiance (200 to 840 (200 to 840

mW/cmmW/cm22).).

Gloss vs. Irradiance at different PI % Gloss vs. Irradiance at different PI % (0.07 to (0.07 to 0.60%).0.60%).

Gloss vs. Irradiance Gloss vs. Irradiance (80 to 320 mJ/cm(80 to 320 mJ/cm22)) at at different UV Energies for Various PI%.different UV Energies for Various PI%.

Gloss vs. Irradiance at different Gloss vs. Irradiance at different Temperatures Temperatures (80 to 100(80 to 10000F).F).

A BYK Gardener Glossmeter was used to measure the 60 degree gloss.

RESULTSRESULTS

Gloss after 1Gloss after 1stst Stage Stage vs.vs. Gloss after Gloss after 22nd nd StageStage

PI = 0.07%UV Energy Dose =

80mJ/cm2

The gloss after 2nd stage follows the same trend as the gloss after 1st stage.

The final gloss is strongly dependent on the gloss obtained in the 1st stage .

Gloss Gloss vs.vs. Irradiance at Irradiance at different PI %different PI %

At low PI %, the gloss decreases as the irradiance increases.At low PI %, the gloss decreases as the irradiance increases. Irradiance effect on the gloss is reduced as the PI % isIrradiance effect on the gloss is reduced as the PI % is

increased.

Gloss Gloss vs.vs. Irradiance at Irradiance at different PI %different PI %

At the optimum PI %, gloss is insensitive to UV Irradiance.

Optimum PI% produces the minimum glossOptimum PI% produces the minimum gloss.

Gloss Gloss vs.vs. Irradiance at Irradiance at different PI %different PI %

Beyond the optimum PI %, gloss increases as irradiance increases.

This trend is completely opposite to the trend This trend is completely opposite to the trend that is observed with lower PI%that is observed with lower PI% .

Gloss values drop to varying degrees as the total Gloss values drop to varying degrees as the total UV energy delivered to the UV coating increasesUV energy delivered to the UV coating increases .

At Low PI%, UV energy is more influential at lower irradiance than at high irradiance

10

20

30

40

50

100 200 300 400 500 600 700 800 900

80 mJ/ cm2160 mJ/ cm2320 mJ/ cm2

Irradiance (mW/ cm2) during Air Cure

600 G

loss

Low Photo Initiator Levels(0.07%)

Impact of UV energy on Gloss vs. Impact of UV energy on Gloss vs. IrradianceIrradiance

At optimum PI level, the drop in gloss with increased energy dose does not vary with irradiance.

(0.20%)

Impact of UV energy on Gloss vs. Impact of UV energy on Gloss vs. IrradianceIrradiance

At high PI level, increased total energy is again seen to lower the gloss, so gloss reduction with increased total energy occurs at all PI levels.

At high PI levels, UV energy is more influential at higher irradiance than at lower irradiance.

Impact of UV Energy on Gloss vs. Impact of UV Energy on Gloss vs. IrradianceIrradiance

Gloss vs. Irradiance at different Gloss vs. Irradiance at different

Temp.Temp.

Increased thermal energy causes the gloss curves to offset to lower values in a trend similar to increasing total air-cure UV energy.

Gloss reduction with increased thermal energy also

occurs at higher PI levels.

Summary of the ResultsSummary of the Results

Defines three different curing regimesDefines three different curing regimes Low PI – Gloss Decreases with Irradiance.Low PI – Gloss Decreases with Irradiance. High PI – Gloss increases with Irradiance.High PI – Gloss increases with Irradiance. Optimum PI – No change in gloss with Optimum PI – No change in gloss with

irradiance.irradiance.

Change in UV energy doesn’t change Change in UV energy doesn’t change these trends, but offsets the curves.these trends, but offsets the curves.

DISCUSSIONDISCUSSION

2

Uncured Coating Surface Thickness

Optimum PIAll Irradiances

Low IrradianceLow PI

High PIHigh Irrad

1 3GLOSS

uncuredcured

uncuredcured

cured

Low gloss is obtained when the uncured layer is at its optimum thickness.

If the uncured layer thickness is more or less than its optimum thickness, the resulting gloss will be high.

Relating Gloss Phenomenon to Relating Gloss Phenomenon to Uncured Coating Thickness at the Uncured Coating Thickness at the

surfacesurface

Determined by the effectiveness of oxygen inhibition during the 1st stage

Absorbed Light IntensityAbsorbed Light Intensity PIIKI a 0

PIIKIa 0 - - Absorbed Light Intensity of the film [[M] . Absorbed Light Intensity of the film [[M] .

W/cm2].W/cm2].

- - UV intensity at the surface of the filmUV intensity at the surface of the film [ W/cm[ W/cm22]]

PI PI - Photo initiator % in the coating [molarity (M)] - Photo initiator % in the coating [molarity (M)]

K K - Constant - Constant

aI

0I

Premise: The bulk absorbed light intensity in the coating controls the thickness of the uncured surface layer after air-cure .

Values have been calculated at different irradiances and PI% .

aI

Gloss vs. Absorbed Light Gloss vs. Absorbed Light IntensityIntensity

The lowest gloss is obtained at a certain range of optimum absorbed light intensity.

The Gloss will be high if the absorbed light intensity is out of this optimum range.

Optimum Ia

Ia values are relative since K is unknown.

Gloss vs. Absorbed Light Gloss vs. Absorbed Light Intensity at different UV doseIntensity at different UV dose

Trend is the same at different total energies, except that higher total energies offset the curve to lower gloss .

ConclusionsConclusions

The most determining factor to achieve low The most determining factor to achieve low gloss - gloss - uncured coating thicknessuncured coating thickness at the at the surface after 1surface after 1stst stage air cure. stage air cure.

Air-cure UV irradiance and energy have an Air-cure UV irradiance and energy have an impact on the gloss, but this influence impact on the gloss, but this influence depends on PI% in the coating.depends on PI% in the coating.

When the photo initiator level is optimized, When the photo initiator level is optimized, the gloss is independent of irradiance and the gloss is independent of irradiance and the process control can be effectively the process control can be effectively managed with total energy dose alone.managed with total energy dose alone.

ConclusionsConclusions

A parameter called “A parameter called “Absorbed Light Absorbed Light IntensityIntensity” is used to explain the ” is used to explain the compounding effects of ‘Irradiance’ and compounding effects of ‘Irradiance’ and ‘PI %’ on the gloss.‘PI %’ on the gloss.

The lowest gloss is obtained at a certain range of optimum absorbed light intensity.

AcknowledgementsAcknowledgements

Matthew Jarosz Matthew Jarosz

Questions?Questions?

Thank you very muchThank you very much

RadTech e5|2008 Technical ConferenceMay 4-7, 2008 ; Chicago, IL