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

Table 7.1 The summary of the UV embossing lacquer developed for the microstructure replication.

UV lacquer

No.

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 High refractive index UV

embossing lacquer 850 >120 1.576 Good

5 MIL587-3 High refractive index UV

embossing lacquer 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

Table 7.2 The evaluation results of the UV embossing lacquer developed for the microstructure replication.

UV lacquer

No.

UV lacquer products

Structure replication Other properties

1 Lentex 50 Suited for nano and

sub-micron structures

2 Lentex 700 Suited for replication of structure from 1 micro

to 500 microns. The lacquer has very good weathering stability.

3 AntiK 51 Suited for replication of structure from 1 micro

to 500 microns. A hydrophilic UV lacquer.

4 MIL587 Suited for replication of structure from 1 micro to 500 microns.

High refractive index

5 MIL587-3 Suited for replication of structure from 1 micro to 500 microns.

High refractive index

6 YKLJ-A Suited for replication of structure from 1 micro

to 500 microns.

A good adhesion UV lacquer for replicating micro structure on PMMA surface.

7 YKLJ-B Suited for replication of structure from 1 micro

to 500 microns.

A good adhesion UV lacquer for replicating micro structure on PMMA surface.

8 MIL1390

Suited for replication of structure from 1 nano meter to 500 microns.

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.