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WO1998016865A1 - Cellule electro-optique a 'mode inverse' constituee de cristaux liquides encapsules dans une couche polymere et procede de fabrication de celle-ci - Google Patents

Cellule electro-optique a 'mode inverse' constituee de cristaux liquides encapsules dans une couche polymere et procede de fabrication de celle-ci Download PDF

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Publication number
WO1998016865A1
WO1998016865A1 PCT/EP1997/005599 EP9705599W WO9816865A1 WO 1998016865 A1 WO1998016865 A1 WO 1998016865A1 EP 9705599 W EP9705599 W EP 9705599W WO 9816865 A1 WO9816865 A1 WO 9816865A1
Authority
WO
WIPO (PCT)
Prior art keywords
liquid crystal
electro
optical cell
cell according
organic medium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP1997/005599
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English (en)
Inventor
Giuseppe Chidichimo
Giovanni De Filpo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SPS SpA
Original Assignee
SPS SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by SPS SpA filed Critical SPS SpA
Priority to AU49467/97A priority Critical patent/AU4946797A/en
Publication of WO1998016865A1 publication Critical patent/WO1998016865A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G02F1/13347—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals working in reverse mode, i.e. clear in the off-state and scattering in the on-state

Definitions

  • the present invention relates to a "reverse-mode" electro-optical cell made of liquid crystals encapsulated in a polymeric layer, which constitutes the supporting matrix, and to a method for manufacturing it.
  • a polymeric layer which constitutes the supporting matrix
  • Many conventional composite materials constituted by polymers and liquid crystals are used in electro-optical applications such as the production of displays and variable-transmission devices having large surfaces.
  • Liquid crystals per se are in fact not suitable materials for these applications.
  • control of optical transmission through liquid-crystal layers requires the use of polarizing layers which, by allowing only light components polarized in very specific directions to pass through them, drastically reduce overall light transmission.
  • Encapsulated liquid crystals their method of use in electro-optical devices and a method for manufacturing them are the subject of US patent 4,435,047 of 1984, in the name of J.L. FERGASON.
  • an encapsulated liquid crystal is constituted by discrete microdroplets of liquid crystals having dieletric positive anisotropy ⁇ e contained in an encapsulating medium.
  • the example provided in the FERGASON patent relates to an encapsulated liquid crystal confined within polyvinyl alcohol (PVA).
  • PVA polyvinyl alcohol
  • the encapsulated liquid crystal is of the ⁇ e- positive kind.
  • the FERGASON process uses an emulsion in which the e ulsifier is water, which must be removed after a certain amount of polyvinyl alcohol, by being arranged at the interface between the water and the liquid crystal, has encapsulated the microdroplets of the latter in the emulsion.
  • part of the water remains trapped within the material, causing an undesirable high conductivity and plasticity of the active material, with consequent poor adhesion to supports.
  • the method consisted in mixing a polymer (or prepoly er) and a (nematic) with positive dieletric anisotropy ⁇ e liquid crystal to provide a single-phase solution.
  • the liquid crystal is of the ⁇ e-positive kind.
  • liquid-crystal droplets were thus formed by phase separation by means of:
  • the orientation of the liquid crystal is not uniform inside the microdroplets and also varies in its overall distribution from droplet to droplet.
  • This configuration is highly opaque.
  • the orientation of the liquid crystal becomes uniform in the entire material in the presence of an electrical field, owing to the positive dieletric anisotropy of the liquid crystal.
  • This configuration allows light to pass and the cell appears to be transparent.
  • liquid crystal dispersed in the matrix acts as a plasticizer, worsening the structural characteristics of the device.
  • the magnetic field produces its orientating effects only after phase separation has already started; accordingly, the degree of alignment of the liquid crystals along the field is limited.
  • Said device is a polarizing filter.
  • LCG Liquid Crystal Gel
  • This apparatus has a reverse-mode electro-optical operating mode, since it is transparent in the absence of an electrical field but assumes an opaque state when the field is applied.
  • the presence of the surfactant generates microdroplets in which the liquid crystal molecules are orientated at right angles to the polymeric parts.
  • This effect has been used to obtain a display known as RNPDLC by using a mix of prepolymers which UV-crosslink and a liquid crystal which is orientated at low frequency during the photopolymerization of the polymers.
  • the aim of the present invention is to solve and overcome the problems observed in currently available products as described above.
  • a first object of the present invention is to provide an electro-optical cell having reverse-mode operation.
  • a second object in combination with the first one, is to provide an electro-optical cell having a high optical contrast.
  • a third object of the present invention is to provide an electro-optical cell formed on a glass or plastic support .
  • a fourth object of the present invention is to provide a cell in which the material comprised between the supports adheres strongly to the supports themselves.
  • a fifth object of the present invention is to provide a cell having high structural rigidity characteristics.
  • an electro-optical liquid crystal cell in a polymeric layer characterized in that it comprises a uniform dispersion of microspheres or microagglomerates of molecules of nematic liquid crystal, with uniformly aligned molecules, in a polymeric matrix which is self-adherent to electrically conducting glass or plastic, rigid or flexible supports, said matrix being able to maintain indefinitely the alignment of the molecules of said liquid crystal set during the preparation of the cell by an external magnetic field (or by other force fields), said molecules being able to rotate in a spontaneously reversible manner by means of an electrical field applied across the conducting supports, the two states determining transparency (spontaneous orientation) or opacity (orientation forced by the electrical field) of the cell (reverse-mode operation).
  • the present invention also relates to a method for producing an electro-optical cell made of liquid crystal encapsulated in a polymeric layer, characterized in that it comprises the following operating steps: a) preparing an organic microemulsion of nematic liquid crystal in a polymerizable organic medium; b) spreading said microemulsion on glass or plastic supports which have been rendered electrically conducting beforehand on the inner faces; c) creating a sandwich which contains the fluid microemulsion; d) applying, to said sandwich, a magnetic field or another force field whose intensity and direction is such that it orientates the molecules of the liquid crystal; e) polymerizing the emulsifying organic medium, maintaining the magnetic field until said polymerization ends.
  • figures la-lb and 2a-2b are views of two operating modes of the cell; figure 3 is a photomicrograph, taken in a cross- polarizing microscope, of the liquid crystal emulsion in the organic medium before polymerization.
  • Said cell is composed of microspheres 1 made of nematic liquid crystal with uniformly aligned molecules dispersed in a polymeric matrix 2 which is self-adherent to conducting supports 3 and 4 which can conveniently be of the glass or plastic, rigid or flexible type.
  • Said first cell has a geometry which includes mesogenic molecules which are "spontaneously” orientated at right angles to the surface of the layer.
  • the index of refraction "n” of the polymer is matched to the index of refraction "n 0 " of the liquid crystal, which must have negative dielectric anisotropy.
  • the light that passes through the cell is scattered in all directions, rendering the device opaque.
  • FIG. 2a A second type of cell, which operates according to the same principle, is shown in figures 2a and 2b.
  • the index of refraction "n p " of the polymer is matched to the index of refraction "n e " of the liquid crystal, which must have a positive dielectric anisotropy.
  • the application of the electrical field causes the mesogenic molecules to become parallel to said field, making the cell assume an opaque state owing to the mismatch between the index of refraction of the polymer "n " and the index of refraction "n " of the liquid crystal.
  • the process that allows to obtain a cell of this kind is composed of a sequence of steps which can be described briefly as the preparation of an organic emulsion of nematic liquid crystal in a monomer or in a mix of monomers which can be polymerized by means of any conventional process, for example by using ultraviolet radiation or by using heat.
  • This emulsion is spread on two glass or plastic, rigid or flexible supports which have been treated beforehand so as to become conducting on the contact faces, thus forming a sandwich.
  • This sandwich which contains the fluid emulsion, is subjected to a magnetic field: at the same time, polymerization is performed by irradiation with ultraviolet radiation or, as an alternative, by thermal treatment.
  • the application of the magnetic field or of other fields in this context uniformly orientates the separate mesogenic molecules in microdroplets, but also orientates those of the fluid organic medium which are present at the interface or otherwise located in a more or less wide neighborhood of the mesogenic microdroplets.
  • the subsequent process for polymerizing the organic monomer produces a polymeric matrix which, in a more or less wide neighborhood of the polymer/liquid crystal interface. acquires a structure which preserves, by molecular interaction, the orientation of the mesogenic molecules confined in the microdroplets even in the absence of external fields.
  • the composite film obtained after polymerization of the organic monomer can appear perfectly transparent when the indices of refraction of the components are matched.
  • the mesogenic molecules that are uniformly aligned in their natural state in all the microdroplets that are present inside the film can be rotated at right angles by an electric field applied across the conducting supports, causing said film to become opaque owing to the mismatch of the indices of refraction.
  • liquid crystal is insoluble in the monomeric organic part, it is used in the amount strictly necessary to determine the electro- optical operation of the cell.
  • the size of the spheres of the liquid crystal can be better adjusted by using ultrasound methods and also by adjusting concentrations and temperatures.
  • the monomer has adhesive characteristics, so that it fixes itself well to the glass or plastic, rigid or flexible support.
  • EXAMPLE 1 In this example, an electro-optical cell was produced which had mesogenic molecules orientated at right angles to the surface of the electro-optical cell.
  • the liquid crystal used was a ZLI 4788-000 by MERCK, which was mixed with hydroxypropyl methacrylate in a 1:1 ratio (50% liquid crystal and 50% hydroxypropyl methacrylate) .
  • Said emulsion was deposited in the form of a thin layer on metallized glass with the addition of a small amount of inert spacers with a 10-micron diameter.
  • the cell was then placed in a magnetic field with a strength of approximately 3 tesla at right angles thereto, and after a few seconds it was irradiated with UV light generated by a PHILIPS HPK 125 125-watt lamp.
  • the cell appeared perfectly transparent in its natural state and became opaque by applying external electrical fields.
  • the l iquid crystal E 7 by MERCK was mixed with hydroxypropyl methacrylate in a 1:1 ratio and 1% of the radical initiator UV IRGACURE 651 by CIBA-GEIGY was added to the mix.
  • the mix was processed as in Example 1, but the magnetic field was arranged parallel to the cell.
  • the electro-optically active cell with naturally-aligned nematic spheres has been manufactured through the polymerization of an organic emulsion of nematic liquid crystal in a mix of acrylic monomers.
  • This method differs from conventional ones in that the liquid crystal microspheres are already present in the fluid phase when suitably selected organic monomers are mixed with the liquid crystal.
  • This process offers the advantage of great simplicity and furthermore eliminate the severe drawback of contamination on the part of water molecules, which worsen the electro-optical functionality of the film, drastically reducing its resistivity.
  • liquid crystal Since the liquid crystal is insoluble in the monomeric organic part, it is used in the amount that is strictly necessary to determine the electro-optical operation of the cell.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Nonlinear Science (AREA)
  • Dispersion Chemistry (AREA)
  • Mathematical Physics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Liquid Crystal (AREA)

Abstract

L'invention concerne une cellule composée d'une couche polymère encapsulant un cristal liquide nématique, qui auto-adhère à un support électriquement conducteur de type sandwich en verre ou en plastique. Cette cellule est transparente dans son état naturel, et devient opaque par application d'un champ électrique (en mode fonctionnement inverse). Le procédé permettant de fabriquer une cellule conforme à la présente invention consiste à disperser, dans un milieu organique polymérisable, des microsphères d'un cristal liquide nématique pour former une émulsion fluide. Cette émulsion est placée entre deux supports en verre ou en plastique, rigides ou flexibles, qui sont rendus électriquement conducteurs; puis, au moyen de l'action d'un champ magnétique (ou d'un autre champ de force), on oriente les molécules de cristaux liquides; cela provoque également une impression, à l'interface des sphères de cristaux liquides orientées, dans le milieu organique de dispersion. Dans ces conditions, en présence d'un champ magnétique ou d'un autre champ de force, le milieu organique est polymérisé par exemple par rayonnement ultraviolet ou par échauffement. Une fois que la polymérisation s'est produite, et après retrait du champ magnétique, les molécules de cristaux liquides gardent leur orientation, laquelle peut être changée de façon réversible par application d'un champ électrique sur le support conducteur. Le mode de fonctionnement est de type 'inverse' à contraste optique élevé.
PCT/EP1997/005599 1996-10-14 1997-10-10 Cellule electro-optique a 'mode inverse' constituee de cristaux liquides encapsules dans une couche polymere et procede de fabrication de celle-ci Ceased WO1998016865A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU49467/97A AU4946797A (en) 1996-10-14 1997-10-10 "reverse-mode" electro-optical cell made of liquid crystals encapsulated in a polymeric layer and method for manufacturing it

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT96PD000249A IT1287963B1 (it) 1996-10-14 1996-10-14 Cella elettroottica di cristallo liquido inglobato in uno strato polimerico con funzionamento reverse mode e procedimento per la
ITPD96A000249 1996-10-14

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Publication Number Publication Date
WO1998016865A1 true WO1998016865A1 (fr) 1998-04-23

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Country Status (3)

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AU (1) AU4946797A (fr)
IT (1) IT1287963B1 (fr)
WO (1) WO1998016865A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6383577B1 (en) 1997-06-27 2002-05-07 Consorzio Per Le Tecnologie Biomediche Avanzate - Tebaid Reverse mode electro-optical film composed of one mutual dispersion of polymers and liquid crystals
EP1213601A4 (fr) * 1999-06-23 2005-06-08 Citizen Watch Co Ltd Afficheur a cristaux liquides
CN103197459A (zh) * 2013-04-19 2013-07-10 南京晶多新材料科技有限公司 一种反式电控调光玻璃及其制造方法和应用
US8830423B2 (en) 2007-11-30 2014-09-09 Merck Patent Gmbh Liquid crystal device and method of manufacture thereof

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0275999A2 (fr) * 1987-01-22 1988-07-27 Asahi Glass Company Ltd. Dispositif optique à cristal liquide et procédé de fabrication
WO1989009807A1 (fr) * 1988-04-11 1989-10-19 Kent State University Materiaux modulant la lumiere comprenant des micro-gouttelettes de cristaux liquides dispersees dans une matrice polymere birefringente
JPH04136814A (ja) * 1990-09-28 1992-05-11 Toppan Printing Co Ltd 調光フィルムおよびその製造方法
EP0488116A2 (fr) * 1990-11-26 1992-06-03 Seiko Epson Corporation Elément pour afficheur à cristal liquide dispersé dans un polymère et procédé de fabrication

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0275999A2 (fr) * 1987-01-22 1988-07-27 Asahi Glass Company Ltd. Dispositif optique à cristal liquide et procédé de fabrication
WO1989009807A1 (fr) * 1988-04-11 1989-10-19 Kent State University Materiaux modulant la lumiere comprenant des micro-gouttelettes de cristaux liquides dispersees dans une matrice polymere birefringente
JPH04136814A (ja) * 1990-09-28 1992-05-11 Toppan Printing Co Ltd 調光フィルムおよびその製造方法
EP0488116A2 (fr) * 1990-11-26 1992-06-03 Seiko Epson Corporation Elément pour afficheur à cristal liquide dispersé dans un polymère et procédé de fabrication

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
NOLAN P ET AL: "Reverse mode polymer dispersed liquid crystal display incorporating a dual frequency addressable liquid crystal mixture", MOLECULAR CRYSTALS AND LIQUID CRYSTALS LETTERS SECTION, 1991, UK, vol. 8, no. 4, ISSN 0140-6566, pages 75 - 83, XP000241840 *
PATENT ABSTRACTS OF JAPAN vol. 16, no. 407 (P - 1411) *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6383577B1 (en) 1997-06-27 2002-05-07 Consorzio Per Le Tecnologie Biomediche Avanzate - Tebaid Reverse mode electro-optical film composed of one mutual dispersion of polymers and liquid crystals
EP1213601A4 (fr) * 1999-06-23 2005-06-08 Citizen Watch Co Ltd Afficheur a cristaux liquides
US8830423B2 (en) 2007-11-30 2014-09-09 Merck Patent Gmbh Liquid crystal device and method of manufacture thereof
CN103197459A (zh) * 2013-04-19 2013-07-10 南京晶多新材料科技有限公司 一种反式电控调光玻璃及其制造方法和应用

Also Published As

Publication number Publication date
ITPD960249A0 (it) 1996-10-14
ITPD960249A1 (it) 1998-04-14
AU4946797A (en) 1998-05-11
IT1287963B1 (it) 1998-09-10

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