Paliocolor LC 242 and LC 756 - elecs-korea.com

1 Technical Information September 2002 PaliocolorLC 242 and LC value to our customersPPAALLIIOOCCOOLLOORR LLCC 224422 AANNDD PPAALLIIOOCCOOLLOORR LLCC 775566 AARREE TTWWOO PPOOWWDDEERRSS,, WWHHIICCHH,, WWHHEENNCCOOMMBBIINNEEDD,, PPRROODDUUCCEE AANN IINNTTEERRFFEERREENNCCEE CCOOLLOOUURR,, TTHHEE WWAAVVEELLEENNGGTTHH OOFF WWHHIICCHH IISSDDEETTEERRMMIINNEEDD BBYY TTHHEE RRAATTIIOO OOFF TTHHEE TTWWOO TTHHEESSEE MMAATTEERRIIAALLSS FFOORRMM AACCHHOOLLEESSTTEERRIICC LLIIQQUUIIDD CCRRYYSSTTAALL PPHHAASSEE,, WWHHIICCHH CCHHAARRAACCTTEERRIISSTTIICCAALLLLYY EEXXHHIIBBIITTSS HHIIGGHH AANNGGUULLAARRDDEEPPEENNDDEENNCCEE AANNDD VVEERRYY BBRRIIGGHHTT AA CCOOAATTEEDD CCHHOOLLEESSTTEERRIICC LLIIQQUUIIDD CCRRYYSSTTAALLLLAAYYEERR,, WWHHIICCHH HHAASS NNOO AABBSSOORRPPTTIIOONN,, AAPPPPEEAARRSS BBRRIIGGHHTTLLYY CCOOLLOOUURREEDD OONNLLYY TTHHRROOUUGGHH TTHHEEIINNTTEERRAACCTTIIOONN OOFF TTHHEESSEE MMAATTEERRIIAALLSS WWIITTHH BBAACCKKGGRROOUUNNDD TTHHEE CCOOLLOOUURRIIMMPPRREESSSSIIOONN CCAANN BBEE FFIIXXEEDD EEXXCCLLUUSSIIVVEELLYY VVIIAA UUVV--CCUURRIINNGG ((OORR EEBB--CCUURRIINNGG)).

2 The cholesteric liquid crystalline phase is characterised by a helical superstructure, aconsequence of which is the periodical change in the refraction index along the helicaldirection. This property gives rise to interference effects, reflecting light, the wavelengthof which is proportional to the size of the helix. When adding other, non-liquid crystallinematerials to this system, as in a formulation, the helix is widened, resulting in aweakening of the superstructure. This produces a colour shift and a reduction in thephase range, or processing window. Therefore in order to maintain an optimalprocessing window and colour purity, formulation has been kept to a 1: Structure of a cholesteric layerPaliocolor LC 242 is our nematic liquid crystal; Paliocolor LC 756 is our chiral Liquid Crystalrod-likemoleculesbirefringent helical superstructure change of refractive index from "layer to layer" multiple interferenceCholesterolNematic LCChiral dopantOOOMeOR'R' Paliocolor LC 242 / 756 Paliocolor LC 242 Paliocolor LC 756 Phase ( C)cr 63-70 n 120-125 icr >100 iHelical twisting power ( m-1)ca.

3 76(in combination with Paliocolor LC 242)Refraction index / / g/cm3 Colour settingAll pure spectral colours can be generated through the mixing of the two componentsLC242 and LC756 via melting or dissolving procedures. The essential ingredient isPaliocolor LC 756, which, depending on the quantity of this compound, defines the finalreflection wavelength of the coating. The following table lists some ratios of PaliocolorLC 242 and LC 756 together with the corresponding resulting reflection wavelengths (atface angle).Table 1 : ratios of Paliocolor LC 242/756 and corresponding reflection wavelengths(Indication; values depend on the helical twisting power of LC 756) Paliocolor LC 242(weight %) Paliocolor LC 756(weight %)Reflection wavelength(nm, before polymerisation) 2: Colour variations by mixing different ratios of Paliocolor LC 242 andLC 756 (coated on black PET) shifts by additives and polymerisation shrinkageAs described, the mixing of Paliocolor LC 242 with LC 756 produces a defined principle, these colours are now influenced by three main factors:- temperature- initiators- polymerisation shrinkageThe combination of Paliocolor LC 242 / 756 has been designed to be relativelytemperature stable.

4 Up to processing temperatures of 65 C, the reflection band ofPaliocolor LC 242/756 is almost temperature independent, whilst between 65 and 100 C, only a linear dependence is observed, a fact which the user can easily take intoaccount during coating and mixingFigure 3: Temperature dependence of reflection wavelength of a Paliocolor LC242/756mixture (non-polymerised)40045050055060065070020 30405060708090100 Temperature [ C]Temperature dependence of a non-polymerisedmixture of Paliocolor LC242 / LC 756 WAVELENGTH[nm]The addition of initiators generally results in a minor shift of the reflection colour towardslonger wavelengths (around 10 nm / weight % of initiator).Also of importance for the resulting reflection wavelength is the shrinkage of the coatedlayer observed after polymerisation.

5 This causes a shortening of the helix. Hence, a shiftof the reflection wavelength to shorter wavelengths occurs (10-30 nm depending on thewavelength).When using 2 weight % initiator, these two effects usually compensate each ProcedurePaliocolor LC 242 and Paliocolor LC 756 can be mixed together using either solventsor by heating into the isotropic phase. The former preparation procedure is the methodof choice in terms of handling and avoiding unintended the Paliocolors consist of a very reactive acrylate group, only small amounts ofinitiators are sufficient to achieve good curing. Our recommendation lies in the region of2 3 %.Coating ConditionsCoating conditions as well as the properties of the substrate are critical for the opticalqualities of the coating, effecting the supramolecular structure (helix) and hence theangle dependence of the types of roll- or reverse roll coaters as well as knife coater and krrc (knife reverse rollcoater) can be utilised for the coating.

6 However, essential for good coating is the use ofhigh shear , Paliocolor LC 242 and Paliocolor LC 756 will be prepared according to thesolution procedure mentioned above. After coating the solvent must be completelyremoved in a drying tunnel (up to 100 C), prior to curing. Good orientation of the liquidcrystalline molecules has been acheived with a drying time of 15-20 seconds within thedrying tunnel. The air flow should be laminar and turbulence avoided. Should this occur,cloudy areas can appear on the substrate and scattering is particularly good substrate for coating is PET, especially that of video tape quality. It isimportant to ensure that the coated surface is free of any chemicals (release-coatings,adhesives etc.)

7 , static charges or inhomogenity, all of which badly influence ahomogenous colour effect. Similar results can be obtained by coating onto EffectsWhen coating Paliocolor onto a transparent foil, the optical effect is almost impossibleto recognise. An observer will see only an irisdescent colour effect when lookingthrough the foil. In this case the CLC-layer selectively reflects a pre-defined wavelengthand allows the rest of the spectrum to be transmitted. To observe the special coloureffect of the material, this transmitted light must be removed. In other words, thebackground colour is of primary choosing a black surface, all the transmitted light is absorbed and the observer onlysees the reflected pure colour with strong angular the surface has been chosen to be white, the transmitted light is unselectivelyreflected and thus interferes with the pre-defined selectively reflected light.

8 In this case,the observer only sees a pearlescent coloured pigments are used in the background, the overall effect is far morecomplex. The scattered light from the pigments interferes with the selectively reflectedlight of the CLC-layer. However by careful choice of colour combinations, one canobtain numerous new colour variations; for example, from a pastel-green-pastel-lightblue flop (green-blue Paliocolor -mixture on green surface), via a yellow-milkywhite-yellow flop (blue-violet Paliocolor -mixture on yellow surface) and a magenta-red flop(blue-violet Paliocolor -mixture on red surface) to a magenta-blue-violet flop (red-greenPaliocolor-mixture on blue surface).By using just two Paliocolor components every user can create its own flipflop effect togives its product a unique feature.

9 The choice of dramatic effects like the change from ared colour to become a green one or mild changes when using coloured pigments forthe background colour are all possible.