Liquid crystal cells – elements and systems – Particular structure – Interconnection of plural cells in series
Reexamination Certificate
2002-08-09
2004-09-07
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Interconnection of plural cells in series
C349S092000, C349S093000, C349S158000, C349S183000
Reexamination Certificate
active
06788360
ABSTRACT:
The invention relates to a stacked liquid cell, such as a stacked liquid crystal cell for use in a stacked display device, in particular a liquid crystal display device.
The invention further relates to a method of manufacturing a liquid cell, in particular a stacked liquid cell.
Stacked liquid cells, in particular stacked liquid crystal cells, and displays comprising such cells are as such known in the art. A stacked liquid cell generally comprises a plurality of cells (sub-cells) stacked one on top of the other. Each (sub-)cell comprises a liquid layer dispersed between substrate layers which serve to separate and confine the liquid layers during use and/or manufacture. The sub-cells together form a stack of liquid layers dispersed between substrate liquid layers, in which substrate layers may be shared between (sub-)cells. In a stacked liquid crystal cell at least one but typically all liquid layers are electro-optically active liquid crystal layers.
Such stacked LC cells may have advantages compared to single liquid layer devices. For example, in multi-color or full color display devices use of a stacked liquid cell may increase the active display area available per color by as much as a factor of three. A cholesteric display having a stack of cholesteric liquid crystal layers the pitch of which is selected such that R G and B is reflected in different layers is an exmaple. As another example, a first liquid layer may be a liquid crystal layer and a second liquid layer may serve as a temperature compensated compensation layer for the first liquid crystal layer.
However, on the down side, stacked liquid crystal cells are relatively thick and the distance between the liquid layers is relatively large. Such a large thickness is generally undesirable. Furthermore, in stacked liquid cells where the liquid layers are partitioned to form individually addressable pixels the large thickness may lead to substantial parallax effects. The thickness of the stacked liquid cell and the distance between the liquid layers is, to a large extent, caused by the relatively thick substrates between which the liquid layers are dispersed.
It is an object of the invention, inter alia, to alleviate these drawbacks and provide a stacked liquid cell having a relatively small thickness. More in particular, for example in case of a pixelated stacked display cell, the stacked liquid cell is to have a structure which allows parallax effects to be reduced. Furthermore, the stacked liquid cell is to allow facile and cost effective manufacture. In particular, the stacked liquid cell, or at least a substantial part thereof, is to be such as to be capable of being manufactured in a continuous process, or even a roll-to-roll process.
This object is, in accordance with the invention, achieved by a stacked liquid cell comprising a stack of liquid layers and substrate layers, wherein each liquid layer is dispersed between substrate layers, and wherein a liquid layer and a substrate layer adjacent thereto are replaced with a liquid layer and a polymeric layer of a stratified-phase-separated composite.
The stacked liquid cell comprises a stack of liquid layers and substrate layers, the liquid layers being dispersed between the substrate layers. In accordance with the invention, at least one liquid layer and adjacent substrate layer are replaced with a liquid layer and a polymeric layer of a stratified-phase-separated composite.
A stratified-phase-separated composite is obtainable by stratification of a stratified-phase-separable composition into a polymeric layer and a liquid layer. The polymeric layer and the liquid layer are separate, continuous layers arranged adjacent to each other sharing a common interface, the interface being sufficiently smooth to render the composite suitable for optical applications such as displays. The stratification is a controlled form of phase separation, more particularly referred to as stratified-phase-separation.
Conventional substrate layers have a thickness in the millimeter range, that is at least a thickness of 0.2 to 0.5 mm, typically even larger to ease handling. Conventional substrates need to have such a minimum thickness because of the manner conventional (stacked) cells are manufactured. Conventionally, a cell is manufactured by gluing together along their edges two opposite substrate layers to form an empty cell which is then filled with liquid to form the liquid cell. Such a method generally requires both substrate layers to be self-supporting. Moreover, if a constant liquid layer thickness is to attained throughout the cell the substrate layers need to be sufficiently rigid which also adds to the thickness.
Because the layer from which the stratified-phase-separated composite is obtained may be formed using conventional thin film forming methods, and the polymeric layer of the stratified-phase-separated composite is formed in situ—at the same time as the liquid layer—, a thin stratified-phase-separated composite, more particular a thin, at least relative to the thickness of a conventional substrate layer, polymeric layer can be made in an easy and cost effective manner.
The thickness of the polymeric layer is in the micrometer range. Typically, the thickness of the polymeric layer may be less than about 100, 50, 20 or 10 &mgr;m. Using conventional thin film forming methods, in particular coating and printing methods such as spin-coating, web-coating, ink-jet printing screen printing and the like, even thinner polymeric layers are readily available such as those having a thickness in the range 0.1 to 10 &mgr;m.
Therefore, in accordance with the invention, replacing a conventional substrate layer with a polymeric layer of a stratified-phase-separated composite reduces the thickness of the stacked liquid cell and, if the polymeric substrate layer is an interior layer of the stack the distance between liquid layers is reduced which, in turn reduces parallax. Parallax is of particular importance in non-emissive optical applications such as displays.
From the viewpoint of reducing thickness and parallax effects, the thickness of the polymeric layer is to be as small as possible. However, being a substrate layer the polymeric layer needs to provide the required support, ruggedness and mechanical integrity. It may need to serve as a substrate for the stacking of further layers such as a further stratified-phase-separated composite or the stacking of a conventional cell. Such requirements set a minimum on the polymeric layer, the specific value of which is to be determined on case-by-case basis. A minimum polymeric layer thickness would be typically 0.1 &mgr;m, or 0.5 &mgr;m or even larger 1 &mgr;m. If for example the polymeric layer is an exterior layer of the stack it needs to protect the stack during its operational lifetime which requires a larger, say 5 &mgr;m or more.
As will be described further hereinbelow in respect of the single substrate method, a stratified-phase-separated composite is obtainable by stratifying a stratified-phase-separable composition. Stratification is brought about by phase-separation. Suitable methods of phase-separation include polymerization-induced phase-separation, solvent-induced phase-separation or temperature-induced phase-separation such phase-separation methods being known in the art as such.
To obtain stratification, that is phase-separation in a stratified manner, use may be made of differential wetting. In one embodiment of differential wetting, the layer of stratified-phase-separable composition is provided on a substrate which has a better wettability for the liquid than for the polymer of the polymeric layer or the monomer(s) from which the polymer is obtained. In another, the stratified-phase-separable material is dispersed between a first and second substrate, the first substrate being well-wettable for the liquid and the second being well-wettable for the polymer/monomer from which the polymeric layer is obtained.
In an alternative method to obtain phase-separation in a stratified manner, a method which is preferably used in c
Broer Dirk Jan
Penterman Roel
Kim Robert H.
Koninklijke Philips Electronics , N.V.
Schechter Andrew
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