RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018

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1 RADIATION CURINGEUROPEAN COATINGS JOURNA
RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018 “Rate of polymerisation was higher.“ Dr Richard PlenderleithLambson Ltd.richard.plenderleith@lambson.com3 questions to Richard PlenderleithBAPO is well-known as an efficient photoinitiator for free-radical radiation curing. Can you explain why you chose to use it instead as a comparison product in cationic curing BAPO is well known as a free radical photinitiator but can also be used in cationic polymerisation as an “activator“ for onium salts. This occurs via ‘Free Radical Promoted Cationic Polymerisation’ which is described in the literature. As BAPO has a relatively strong absorption in the LED relevant region (365-405 nm) and is the most active of the commercially available phosphine oxide photoinitiators, it was selected as the control. Added benefits of this system are that, the photobleaching of BAPO means it can be used to cure thick sections without blocking the light and preventing depth cure. This will be important in the curing of composites. How long does it take the UV coating to harden after application at different thicknesses The hardness of the coating has not been evaluated as part of this work but it can be assumed that this is related to the degree of conversion. The degree of conversion in resin formulations polymerised with the G1 based system was typically higher than the degree of conversion in the control (BAPO based) system. What’s more, the initial rate of polymerisation in the G1 based system was typically higher than the initial rate of polymerisation in control (BAPO based) system. This data is shown in the report. Absolute values for the time taken to reach hardness would tionality of resins, concentrations of initiators, thickness of coatings and additives used. Usually more catalyst is added to the UV coating mixture than consumed for curing. What impact does it have on the performance of the coated parts and the person in close con The performance of coated parts will be dependent upon the resin system which is tor would be required compared to the G1 based system. This is because the light absorbing, G1, component is regenerated by the catalytic process so can be used at low concentrations. The degree of conversion in the G1 based systems was typically higher than the degree of conversion in the control (BAPO based) systems which would likely give improved mechanical properties to a coating. Reducing exposure scenarios to workers is clearly very important, as are the toxicological effects of all molecules in question. The relevant toxicological tests are currently being performed on G1. Radiation curing search results for radiation curing!Find out more: www.european-coatings.com/360     Dietliker K., A compilation of photoinitiators: commercially available for UV today, SITA Technology Ltd., Edinburgh, 2002., 2002.    Davidson R.S., Exploring the Science, Technology and Applications of U.V. and E.B. Curing, Sita Technology Ltd, 1999., 1999.    Crivello J.V., Dietliker K., Photoinitiators for Free Radical Cationic & Anionic Photopolymerisation, 2nd Edition, Wiley, Chichester & New York, Vol. 3,

2 1999.. 3, 1999.  
1999.. 3, 1999.    Green W.A., Industrial Photoinitiators: A Technical Guide, CRC Press, 2010., 2010.    Fouassier J.-P., Lalevée J., in Photoinitiators for Polymer Synthesis, Wiley-VCH Verlag GmbH & Co. KGaA, 2012, pp 367–397.p 367–397.    Kahveci M.U., Yilmaz A.G., Yagci Y., in Photochemistry and Photophysics of Polymer Materials, ed. N. S. Allen, John Wiley & EUROPEAN COATINGS JOURNAL 03 – 2018RADIATION CURING EUROPEANC OATINGS dossier PRESENTED BY 22 EFFECT PIGMENTS  FORMULATION TRAINING \r\f \n\n \n\t\b\n\t\n\b\t\t\n\n \f\f \n\t\t\n\b\n\n\n\r\n\n \r\r\r\n\t\n\t  dossier    PRESENTED BY FORMULATION TRAINING PIGMENTS PIGMENTS \b\t\t\n\n \f \b\t\t\n\n \f \b\t\t\n\n \f \b\t\t\n\n \f \b\t\t\n\n \f \b\t\t\n\n \f \f \n\t\t\n\b \f \n\t\t\n&#

3 28;\b
28;\b \f \n\t\t\n\b \n\n\n\r\n \n\n\n\r\n \n\n\n\r\n \n  ­€‚     PRESENTED BY BEST OF EC JOURNAL ON PIGMENTS www.european-coatings.com/pigments-dossier No matter if you require brilliant effects, weather and chemical resistance, corrosion protection or specific colour tones – pigments can do the job! Learn more about these all-rounders: in our new EC Dossier, we have compiled all technical papers, market reports, and product overviews on pigments from EC Journal. FORMULATION TRAINING \r\f \n\n \n\t\b\n\t\n FORMULATION TRAINING FREE DOWNLOAD! Anz-EC-Dossier-Pigments_101x297_23-01-18_RZ.indd 6 23.01.18 11:53 these phenomena will allow a retardation of the oxygen inhibition effect. A good performance for the IPN approach compared to pure cationic polymerisation would represent POTENTIAL VALUE IN FORMATION The main advantages of composite materials are their high strength, relatively low weight and corrosion resistance. As G1 has shown a high efficiency in cationic polymerisation and IPN synthesis, the following section focuses on its use in impregnation resins. Glass fibre is introduced to the resin which is then irradiated using UV curing (mercury-Fe doped lamp). This study aims to prepare formulations characterised by better curing than the reference (e.g. BAPO). As , effective polymerisation was observed using G1, where one pass is enough for the surface to become tack-free, and then a few passes are needed for the bottom of the sample using one or two layers of glass fibre. In contrast, the performance was significantly reduced using BAPO, where several passes are , when TMPTA is added to the model resin, the polymerisation rate increased (tack-free surfaces were reached after one pass when using one layer, and a few haviour demonstrates the benefits of the G1 based initiator system using the IPN approach The highest rates of polymerisation were achieved using a low G1 content (0.2% wt) with the introduction of TMPTA monomer A VERSATILE COMPOUND G1 was proposed as a photoinitiator with outstanding reactivity/efficiency compared to the well-known ref

4 erence (BAPO). The copper photoredox cat
erence (BAPO). The copper photoredox catalyst exhibits a high reactivity under ‘soft’ irradiation conditions (near-UV or ings, the production of thick glass/fibre composites as well as the synthesis of IPNs have been demonstrated. Reducing the G1 content in the resins shows its excellent efficiency as a catalyst, which is beneficial for The authors wish to thank the SATT Conectus Alsace for the funding of the project LED_catalyst. The authors also thank Dr. Jérémie Fournier from SATT Conectus Alsace for various scientific discussions. RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018 EUROPEAN COATINGS JOURNAL 03 – 2018 Table 2: Polymer properties and final epoxy function conversion (in %) obtained in air upon exposure to different light sources in the presence of G1 or BAPO/Iod/NVK (Iod: 5 wt%, NVK: 1 wt% in the formulations).Table 3: Number of passes to reach tack-free state for impregnated glass fibres with the model resin, using a UV conveyor (Mercury-Fe lamp), belt speed 2 m/min. CompositionAt the surfaceOn the bottomOne layer of glass fibre (2 mm thick)1.8% BAPO + 5% Iod + 1% NVK4 passes23 passes0.12% G1 + 4.7% Iod + 1% NVK1 pass9 passes0.22% G1 + 5% Iod + 1% NVK1 pass8 passes0.84% G1 + 4.5% Iod + 1% NVK1 pass7 passes1.7% G1 + 4.6% Iod + 1% NVK1 pass9 passesTwo layers of glass fibre (4mm thick)1.8% BAPO + 5% Iod + 1% NVK4 passes37 passes remains tacky0.12% G1 + 4.7% Iod + 1% NVK1 pass17 passes0.22% G1 + 5% Iod + 1% NVK1 pass20 passes0.84% G1 + 4.5% Iod + 1% NVK1 pass30 passes LED at 405 nm (I ca. 230 mW/cmLED at 375 nm (I ca. 40 mW/cmLED at 395 nm (I ca. 50 mW/cmHalogen lamp (I ca. 12 mW/cm1.8% BAPO1.8% BAPO1.8% BAPO1.8% BAPOThin sample (ca. 25µm)Final conversionPolymer propertiestackytackfreetackytackfreetackytackfreegeltackyThick sample (ca. 1.4mm)Final conversionPolymer propertiestackytackfreeSurface: tackyBottom: liquidSurface: tackfreeBottom: tackySurface: tackyBottom: gelSurface: tackfreeBottom: tacky 800s of irradiation, 400s of irradiationof G1 in the resin is also of great concern. After approximately seven months of storage in the absence of light at room temperature, ity in the model resin. Only a 3% change of pared to the fresh formulation. The good pot life of G1 containing formulations will prove HYDROLYTIC STABILITY OF The polymers based on G1 or BAPO were examined and characterised by their hydrolytic stability. The pieces of cured material were shows that the G1 cured materials exhibit better resistance than BAPO materials. The cured polymers produced with BAPO lose a larger percentage of their mass and lose structural integrity after 56 hours. The resins produced with G1 exhibited good remaining mechaniMECHANICS AND ADVANTAGES lows interpenetrated polymer networks (IPNs) to be formed through a simultaneous cationic/radical polymerisation of the model resin/TMPTA blend in a one-step hybrid cure process. This approach displays many desirable characteristics combining the advantages sation, as both radical and cationic species can be polymerised in one step by the same The polymerisation process was evaluated in air and in laminate conditions under 405 nm LED exposure for thin and thick samples. High monomer conversions were obtained for both epoxy and acrylate function of t

5 he �model resin and TMPTA (FC 80
he �model resin and TMPTA (FC 80% for thin tent was observed on the epoxide function However, the presence of TMPTA ensures a faster polymerisation rate at the initial stage (0-100 s) compared to the pure cationic poly). The decreasing inhibition time when using the IPN approach may have several explanations: for example, the radicals that are formed can As the reaction proceeds, the build-up of the glassy epoxy network will result in a viscosity increase. This will induce a delay of the radical termination reactions with a consequent increase in propagation rate; in addition, the viscosity increase can slow down the diffusion of atmospheric oxygen into the sample. Both RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018ceeds (Figure 2). This behaviour may be attributed to the longer lifetimes of the initiating species in the G1-based system (G1 radical cations may be involved in initiating cationic polymerisation as will be shown in The remaining activity of the G1-based system after the light source is turned off allows higher conversions and can be an advantage PHOTOINITIATION COMPARED UNDER Under 405 nm LED exposure, G1 appears to be an excellent photoinitiator for cationic polymerisation. According to the results in The cationic polymerisation of 25 µm thick versions (FCs): the change of FC with various concentration of G1 is insignificant: ca. 2-6%. In the case of thick samples (1.4 mm thick), the final conversion of epoxide functionality This is attributed to the strong absorption of light in the G1 system. Owing to the catalytic behaviour of G1, a reduced G1 content (30-fold less compared to BAPO content) leads to a higher practical efficiency than BAPO in the photopolymerisation of a coating. Tack-free trations and thickness of a G1-based system.These results highlight the efficiency of G1 as a photocatalyst at very low concentrations. This suggests applications in low migration systems, which may be very important for G1 is also effective under various irradiation conditions - near-UV or visible LEDs as well as polychromatic light from halogen lamps. G1 exhibits a high efficiency at 375, 395, and 405nm, or with the halogen lamp: FC � 80% using thin samples (25 µm thick) with good polymer properties, except for the halogen lamp exposure due to its low light intensity (I In the case of thick samples, very high FC (ca. 99%) and tack-free coatings are obtained on both sides using 405 nm LEDs for G1. This is ation source. These results demonstrate the effectiveness of this approach with UV-visible G1 has demonstrated high efficiency in photopolymerisation reactions, but the stability Figure 4: Photopolymerisation profiles of epoxy function conversion vs. irradiation time for IPN synthesis in the presence of G1/Iod/NVK in the model resin/TMPTA blend in air, using thick samples (1.4 mm) under 405 nm LED exposure. : Enlargement of the photopolymerisation profiles for the first 100 s irradiation. Conversion in %Time in s 1008040200 Conversion in %Time in s Zoom: 0 – 100s Model resin / TMPTA (90/10 % w/w) Model resin / TMPTA (80/20 % w/w) Model resin / TMPTA (70/30 % w/w) Model resinFigure 5: Number of passes to be tack-free for impregnated glass fibres with IPNs, using a U

6 V conveyor (Mercury-Fe lamp), belt speed
V conveyor (Mercury-Fe lamp), belt speed 2 m/min. 108642020105 Numer of passesNumer of passesModel resin / TMPTA blendModel resin / TMPTA blend 1 pass1 pass1 pass8 passes20 passespassespassespassesOne layerTwo layers RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018tion of G1 accompanied by the formation of The NVK-based cations (formed here in the hibit a high efficiency toward the initiation of the cationic polymerisation process. The regeneration of G1 is a key step for efficient initiation; therefore the catalytic cycle does not create coloured photoproducts and almethylolpropane triacrylate, TMPTA) and the epoxide group content of the model tem under irradiation with different lights were studied. The model resin used was clohexyl)methyl) adipate (“UviCure S128”), 7-oxabicyclo[4,1,0]hept-3-ylmethyl 7-ox7-ox(“-Cure S105”) and the dendritic polyol “BolThe epoxide group content of the model resin and the double bond content of TMPTA were followed continuously by real-time mulations were deposited on a BaF2 pellet The composite samples were cured using a Dymax UV conveyor with mercury-Fe lamp. PERFORMANCE OF G1 The newly developed photoinitiating system (G1/Iod/NVK 1.7/4.6/1.0 %w/w) displayed higher polymerisation efficiency compared to toinitiators currently in the market (BAPO/Iod/NVK 1.8/5/1 %w/w). Higher polymerisation rates (Rp) and higher final epoxy function For a similar weight content, the BAPO-based system is much less efficient, which could be attributed to the better light absorption cients: ε for BAPO at 405 nm). For comparison, G1 created tack-free surfaces for the coatings while tacky polymers were obtained with Under the same conditions (PI content and LED exposure), G1 exhibits better residual catalytic activity when irradiation is stopped and the ‘dark polymerisation process’ proFigure 2: Photopolymerisation profiles of epoxy functions of the model resin in air with G1/Iod/NVK (1.7/4.6/1 %w/w/w) and BAPO/Iod/NVK (1.8/5/1 %w/w/w) under 405 nm LED exposure. 806040200 Conversion in %Time in s 1.7% BAPOLight switched off OPCu N NPPhPhPhPh OOOP Figure 3: Weight loss vs. heating time at ca. 75 °C for the resins produced with G1/Iod/NVK (0.22/5/1 %w/w/w) and BAPO/Iod/NVK (1.8/5/1 %w/w/w). 12108420 Weight loss in %Heating time in hours BAPO250 hours atBAPO56 hours at Table 1: Final epoxy function conversion (in %) obtained in air under 405 nm LED exposure in the presence of [G1] or BAPO/ Iod/NVK (Iod: 5 wt%, NVK: 1 wt% in the formulations). BAPO1.7% 1.22% 0.84% 0.44% 0.22% Thin samples (25µm thick) Thick samples (1.4mm thick) 800s of irradiation, 400s of irradiation RADIATION CURINGEUROPEAN COATINGS JOURNAL 03 – 2018 RESULTS AT A GLANCERadiation curing provides fast and efficient cure of high-performance coatings, but in the interests of energy efvelop photoinitiating systems that will operate under the longer wavelengths A novel photoinitiating system makes use of a copper photoredox catalyst (G1) used in combination with an iodonium salt and N-vinylcarbazole. This three-component system provided efficient cationic polymerisation when using LEDs at 375, 395, 405 nm or a halogen lamp. For comparison purposes, G1 was shown to be much more efficient than As

7 G1 functions as a catalyst, it can be ef
G1 functions as a catalyst, it can be effective at very low concentrations. Adding a free-radical curing material (TMPTA) produced faster overall cure onic and free-radical polymer network. Effective cure of thick composites was Figure 1: Photoredox catalytic cycle for the three-component G1/Iod/NVK system. Ph-NVK· Electron transfer reactionOxidative pathwayReductive pathwayNear UV-visible light: LEDOxidised structureExcellent initiating species for the ring opening polymerisation G1* G1 G1 ter content, stability of the formulation and The G1/Iod/NVK system is compared to a trimethylbenzoyl)-phenylphosphine oxide). As will be shown below, the development of photoredox catalysts such as G1 is a way of creating a new photoinitiating system with PHOTOCATALYTIC After irradiation, the copper complex G1 generates initiating species upon interaction with iodonium salt as an oxidising agent through an electron transfer reaction ). The phenyl radicals produced interact with the NVK additive that acts as a reducing agent, leading to the regenera EUROPEAN COATINGS JOURNAL 03 – 2018RADIATION CURING Copper photo-redox catalyst is efficient with near-UV and visible LEDs. By H. Mokbel, C. Dietlin, F. Morlet-Savary, J.-P. Fouassier, and J. Lalevée (Institut de Science des Matériaux de Mulhouse IS2M); D. Anderson and R. Plenderleith (Lambson Ltd); F. Dumur and D. Gigmes (Aix Marseille University).A novel photoinitiating system uses a copper photoredox catalyst (G1) in combination with an iodonium salt and ficient cationic polymerisation when using LEDs or a halogen lamp. As G1 is a catalyst, it can be effective at very low sation process is considered to be a ‘green’ -tivity, low energy requirements and little vola-tile release. In current academic/industrial ap-proaches, photoinitiating systems are still often operated using high light intensity and energy in the UV-vis range, which gives rise to efficiency To overcome these drawbacks, photosensitive systems that can operate at safer (longer) waveing systems should be adapted to the use of lowing reduced energy consumption, improved Visible light has much less energy than UV light toinitiating systems. Most of the compatible systems already present in the market exhibit low quantum yields for the production of reactive Thus, there is an urgent need to introduce new photoinitiators or photoinitiating systems with absorption profiles matching LED emissions. However, there are at present only a limited CONCEPT AND ADVANTAGES OF THE A novel photoinitiating system operating lated to the development of a photoredox catalyst. Very few families of photocatalysts (PCs) usable in photoinduced polymerisation reactions have been developed and none are currently on the market due to low reactivity, high process cost and potential toxicity problems. The copper complex referred to below as G1, disclosed in [11], toinitiator active upon near-UV or visible light exposure. The cationic polymerisation ing Polymer Networks (IPN) (polymerisation ture of thick epoxy/glass fibre composites The efficiency of G1 based photoinitiating -carbazole [NVK]) is evaluated. The effects of the light source (LEDs at 375, 395, 405 nm and halogen lamp), G1 concentration, Source: Bits and Splits - Stock