Deliverable 4.5 ML² Multi Layer Micro Lab D4.5 - Report on product range for UV curing lacquers, validated for ML² devices 1. Introduction... 2 2. UV embossing lacquer chemistry... 2 2.1. The main components in UV embossing lacquer composition... 2 2.2. UV Curing Polymerization Process... 3 3. UV cured polymer materials properties... 4 3.1. UV Curing Lacquer: Primary Properties... 4 3.2. UV Curing Lacquer: Secondary Properties... 4 4. UV lacquer testing method... 5 4.1. Coating adhesion test... 5 5. UV curing embossing lacquer evaluation mould template... 8 6. The lacquer trials on pilot UV embossing machine... 10 7. The evaluation results of embossing lacquer developed... 11
1. Introduction UV embossing technology is able to replicate nano and micro structure precisely on the substrate surface. The process can fabricate the structure with depths from as small as few nanometers to several hundred microns. The principle can be further applied indirectly and directly to produce optical components, including microfluidic channels of lab-on chips. Roll to roll UV embossing replication is a continuous manufacturing method which is able to produce large volume high quality nano and micro surface structure at relatively low cost. Direct embossing is another way to produce nano, micro and smooth flat surface on to the optical components. The advantages of the technology are including that refractive index matching, super transparency, higher Tg and low birefringence. The properties required by the optical application can be achieved by formulating UV curing lacquer. This report will cover the key elements of UV curing lacquer materials and substrates, also mould tooling, and embossing process. The discussion will be focused on primary and secondary material property requirements, and also the application examples. 2. UV embossing lacquer chemistry There are two main category of UV curable lacquer, one is based on the free radical acrylate polymerization and another is cationic epoxy/acrylate hybrid polymerization. Since the cationic polymerization is relative slower chain reaction, it is not suited for a roll to roll embossing process. Contrast to cationic polymerization, free radical polymerization is fast which provided possibility to have the roll to roll process line spend to maintain at speed up to 30-50 meter per minute. 2.1. The main components in UV embossing lacquer composition The main components in a free radical acrylate lacquer composition: Oligomer Monomer Pigment Additives Photo initiator The main components in a cationic epoxy/acrylate hybrid lacquer composition: Epoxy Polyol Oligomer Monomer Pigment Additives Photo initiator
Some commonly used monomers and oligomers in the formulation: 2.2. UV Curing Polymerization Process The free radical acrylate polymerization is started from a free radical which is generated by a photo initiator exposed to the UV light.
3. UV cured polymer materials properties The UV curing technology was widely used in verity industry, coating, printing, imprint, microelectronic,.. Depending on the applications, especially for the roll to roll microfluidic channels application, we define them as primary properties which are required in general all the application, and secondary properties which are special required for special application. 3.1. UV Curing Lacquer: Primary Properties Good adhesion to substrate surface Good peeling from mould surface High transparency, low haze, low colour High Tg Good anti-scratch Refractive index RI= 1.50-1.56 Low birefringency Good surface wetting Right viscosity Shrinkage control Curing speed Chemical resistant: alcohols, acid, bases, polar solvent Halogen free 3.2. UV Curing Lacquer: Secondary Properties Antistatic Conductive Super - hydrophilic Super - hydrophobic
Good weathering stability Good metallization adhesion Refractive index RI <1.50, RI >1.56 Food contact applicable High purity, low extractable Biocompatible Biodegradable Low odour Colour 4. UV lacquer testing method 4.1. Coating adhesion test The cross hatch adhesion test was used to evaluate the coating adhesion on the substrate. This test method follows American standard test method (ASTM) D3002 and D3359.This test is fast and simple to perform with an inexpensive cross-hatch cutter test kit. A lattice pattern is cut into the finish film down to the substrate using a cross-hatch cutter. The test area is then brushed diagonally five times in each direction to remove any loose film finish particles. A special tape for testing adhesion is then firmly applied over the crosshatch test area and removed quickly by pulling the tape back off of the test area to reveal the amount of coating lifted off by the test tape. The cross-hatched test area is then visually compared to ASTM standards D3002 and D3359. In the standard list, there are five charts with visual diagrams of varying degrees of film pull-off. ASTM class 5B illustrates no film pull-off, representing the highest level of adhesion. ASTM class 1B illustrates between 35% and 65% of the film removed, representing the poorest adhesion. Class 2B-4B represent varying degrees of adhesion properties that fall between class 1B and 5B. (See illustration provided.) By the nature of this visual comparison, the results are sometimes somewhat subjective and not always definitive with a numerical value associated with this test. Complete test methods may be found on ASTM website (www.astm.org).
Figure 4.1 Cross hatch addesion testing kits
Figure 4.2 Cross hatch addesion testing failure illustration patterns.
5. UV curing embossing lacquer evaluation mould template In order to evaulate the UV lacquer embossing replication properties, two types of mould template was designed, first template is the sub micro dimention which has the size between 2-200 microns, and second template has a size dimention between 0.2 to 4mm. The sub micro size template was originated by the method of Reactive Ion Etching on Si waffer, second template was made by laser engraving on stainless steel sheet. Both templates used for evaluation were Nickle shims replicated from the original structure. Figure 5.1 The sub micro structure microfluidic template. The numbers show the channel width in microns. Figure 5.2 The detail sub micro structure from microfluidic template.
Figure 5.3 The micro structure microfluidic template. The numbers show the channel width in millimetre and the channel size is about 0.2mm.
6. The lacquer trials on pilot UV embossing machine Some of the evaluations was carried out on the pilot UV embossing machine shown in Fig 6.1. Figure 6.1 The UV precision embossing pilot machine The pilot machine Web width: 500 mm Coating width: 400-450 mm Roll face width: 500 mm Coating speed: 1.5-15 m/min Unwind and rewind OD: 600mm (2500m @100um) Machine speed: 18m/min Coating film substrate: PET, PMMA, PC, BOPP, TPU, TAC, PEN, Base film thickness: 12-500 microns Viscosity: 300-3000 cps Coating weight: 10-50 g/m2
7. The evaluation results of embossing lacquer developed UV lacquer No. Table 7.1 The summary of the UV embossing lacquer developed for the microstructure replication. UV lacquer products Lacquer property Viscosity mpa.s@25 C Tg C Refractive Index @25 C Adhesion to substrate PET or PMMA 1 Lentex 50 general purpose 45-70 100 N/A Good 2 Lentex 700 general purpose 650-800 110 1.478 Good 3 AntiK 51 hydrophilic UV lacquer 440 N/A 1.48 Good 4 MIL587 5 MIL587-3 High refractive index UV embossing lacquer High refractive index UV embossing lacquer 850 >120 1.576 Good 2700 >120 1.562 Good 6 YKLJ-A PMMA UV embossing lacquer 2600 N/A N/A Good 7 YKLJ-B PMMA UV embossing lacquer N/A N/A Good 8 MIL1390 Low refractive index UV embossing lacquer 45-65 N/A 1.390 Good
UV lacquer No. Table 7.2 The evaluation results of the UV embossing lacquer developed for the microstructure replication. UV lacquer products 1 Lentex 50 2 Lentex 700 3 AntiK 51 4 MIL587 5 MIL587-3 6 YKLJ-A 7 YKLJ-B 8 MIL1390 Structure replication Suited for nano and sub-micron structures structure from 1 micro to 500 microns. structure from 1 micro to 500 microns. structure from 1 micro to 500 microns. structure from 1 micro to 500 microns. structure from 1 micro to 500 microns. structure from 1 micro to 500 microns. structure from 1 nano meter to 500 microns. Other properties The lacquer has very good weathering stability. A hydrophilic UV lacquer. High refractive index High refractive index A good adhesion UV lacquer for replicating micro structure on PMMA surface. A good adhesion UV lacquer for replicating micro structure on PMMA surface. A low refractive index UV embossing lacquer used for reduced surface reflectivity surface and suited to blend with higher refractive index lacquer to prepare refractive index matching surface.