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WO2018206524A1 - Procédé de fabrication d'un affichage à cristaux liquides stabilisé par polymère - Google Patents

Procédé de fabrication d'un affichage à cristaux liquides stabilisé par polymère Download PDF

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Publication number
WO2018206524A1
WO2018206524A1 PCT/EP2018/061765 EP2018061765W WO2018206524A1 WO 2018206524 A1 WO2018206524 A1 WO 2018206524A1 EP 2018061765 W EP2018061765 W EP 2018061765W WO 2018206524 A1 WO2018206524 A1 WO 2018206524A1
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Prior art keywords
medium
substrate
polymerisable
compounds
light source
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Application number
PCT/EP2018/061765
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English (en)
Inventor
Steffen GNAUCK
Thorsten RACHOR
Sven Schuepfer
Dmitry USHAKOV
Leo WEEGELS
Original Assignee
Merck Patent Gmbh
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Application filed by Merck Patent Gmbh filed Critical Merck Patent Gmbh
Priority to CN201880030554.2A priority Critical patent/CN110612476A/zh
Priority to KR1020197036452A priority patent/KR20200004403A/ko
Publication of WO2018206524A1 publication Critical patent/WO2018206524A1/fr

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    • 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
    • G02F1/137—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • 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
    • G02F1/137—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/13775—Polymer-stabilized liquid crystal layers
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K2019/0444—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit characterized by a linking chain between rings or ring systems, a bridging chain between extensive mesogenic moieties or an end chain group
    • C09K2019/0448—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit characterized by a linking chain between rings or ring systems, a bridging chain between extensive mesogenic moieties or an end chain group the end chain group being a polymerizable end group, e.g. -Sp-P or acrylate
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/10—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings
    • C09K19/12—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings at least two benzene rings directly linked, e.g. biphenyls
    • C09K2019/121—Compounds containing phenylene-1,4-diyl (-Ph-)
    • C09K2019/122—Ph-Ph
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/10—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings
    • C09K19/12—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings at least two benzene rings directly linked, e.g. biphenyls
    • C09K2019/121—Compounds containing phenylene-1,4-diyl (-Ph-)
    • C09K2019/123—Ph-Ph-Ph
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/10—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings
    • C09K19/12—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing at least two benzene rings at least two benzene rings directly linked, e.g. biphenyls
    • C09K2019/121—Compounds containing phenylene-1,4-diyl (-Ph-)
    • C09K2019/124—Ph-Ph-Ph-Ph
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/30—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing saturated or unsaturated non-aromatic rings, e.g. cyclohexane rings
    • C09K19/3001—Cyclohexane rings
    • C09K19/3003—Compounds containing at least two rings in which the different rings are directly linked (covalent bond)
    • C09K2019/3004—Cy-Cy
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/30—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing saturated or unsaturated non-aromatic rings, e.g. cyclohexane rings
    • C09K19/3001—Cyclohexane rings
    • C09K19/3003—Compounds containing at least two rings in which the different rings are directly linked (covalent bond)
    • C09K2019/3009—Cy-Ph
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/30—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing saturated or unsaturated non-aromatic rings, e.g. cyclohexane rings
    • C09K19/3001—Cyclohexane rings
    • C09K19/3003—Compounds containing at least two rings in which the different rings are directly linked (covalent bond)
    • C09K2019/301—Cy-Cy-Ph
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/08—Non-steroidal liquid crystal compounds containing at least two non-condensed rings
    • C09K19/30—Non-steroidal liquid crystal compounds containing at least two non-condensed rings containing saturated or unsaturated non-aromatic rings, e.g. cyclohexane rings
    • C09K19/3001—Cyclohexane rings
    • C09K19/3003—Compounds containing at least two rings in which the different rings are directly linked (covalent bond)
    • C09K2019/3016—Cy-Ph-Ph

Definitions

  • the present invention relates to a method of manufacturing a liquid crystal (LC) display of the polymer sustained alignment (PSA) type, using an LC medium containing a photopolymerisable monomer, and using a radiation source having a narrow emission peak for photopolymerisation of the monomer.
  • LC liquid crystal
  • PSA polymer sustained alignment
  • a liquid crystal (LC) display mode which has meanwhile found widespread interest and commercial use is the so-called “polymer sustained” (PS) or “polymer sustained alignment” (PSA) mode, for which the term “polymer stabilised” is also occasionally used.
  • PS polymer sustained
  • PSA polymer sustained alignment
  • host mixture (hereinafter also referred to as "host mixture”) and further contains a small amount, typically ⁇ 1 % by weight, for example 0.2 to 0.4% by weight, of one or more polymerisable compounds, which are typically selected from polymer- isable mesogenic or LC compounds, also known as “reactive mesogens” or RMs.
  • the LC medium containing the polymerisable compound(s) is contained between two substrates.
  • Each substrate is equipped with an electrode structure, or alternatively two electrode structures are provided on only one of the substrates.
  • one or both substrates may contain an alignment layer which is provided on the substrate or (if present) the electrode structure such that it is in contact with the LC medium, to induce initial alignment of the LC molecules.
  • the polymerisable compounds or RMs are polymerised or crosslinked in situ, usually by UV photopolymerisation, typically while a voltage is applied to the electrodes of the display.
  • the polymerisation is carried out at a temperature where the LC medium exhibits an LC phase, usually at room temperature.
  • the polymerised or crosslinked RMs phase-separate from the LC medium and form a polymer layer on the substrate surfaces, where they induce and stabilise a pretilt angle of the LC molecules relative to the substrates.
  • the pretilt angle generation and polymer stabilisation effects have proven to achieve inter alia a significant reduction of the response times.
  • the PS(A) mode is meanwhile used in various LC display modes.
  • PS-VA vertically aligned
  • PS-OCB optically compensated bend
  • PS-IPS in-plane switching
  • PS-FFS far-field switching
  • PS-UB-FFS Ultra Brightness FFS
  • PS-TN twisted nematic
  • PS-posi-VA mode positive VA
  • an LC medium with negative dielectric anisotropy is contained between two substrates each of which is equipped with an electrode structure and optionally with an alignment layer, for example of rubbed polyimide.
  • an alignment layer for example of rubbed polyimide.
  • PS-VA homeotropic
  • LC molecules realign parallel to the substrates.
  • a standard multidomain VA (MVA) or patterned VA (PVA) pixel and electrode structure layout can be used. It is also possible to use only one structured electrode without protrusions, which significantly simplifies production and improves contrast and transparency.
  • PS-FFS displays two electrodes are provided on only one of the two substrates. One of the electrodes is structured in a comb-shaped manner and the other is unstructured.
  • FFS displays have a low viewing-angle dependence of the contrast.
  • FFS displays usually contain an LC medium with positive dielectric anisotropy, and an alignment layer, usually of polyimide, which induces planar (i.e. horizontal or parallel) alignment of the LC molecules in the non-addressed state.
  • PS-FFS displays which comprise a layer of an LC medium with negative dielectric anisotropy instead of an LC medium with positive dielectric anisotropy.
  • the LC medium with negative dielectric ansiotropy shows a more favourable director orientation that has less tilt and more twist orientation compared to the LC medium with positive dielectric anisotropy, as a result of which these displays have a higher transmission.
  • PS-posi-VA mode displays the initial orientation of the LC molecules in the non-addressed state is homeotropic like in PS-VA displays, however, the LC medium has positive dielectric anisotropy.
  • two electrodes in posi-VA displays are provided on only one of the two substrates and preferably exhibit intermeshed, comb-shaped (interdigital) structures. Upon application of a voltage to the electrodes an electrical field is created in a direction substantially parallel to the layer of the LC medium, and the LC molecules realign substantially parallel to the substrates.
  • the PSA display typically contains an alignment layer, for example of polyimide, that provides the initial alignment of the LC molecules before the polymer stabilisation step.
  • Rubbed polyimide layers have been used for a long time as alignment layers.
  • the rubbing process causes a number of problems, like mura, contamination, problems with static discharge, debris, etc. Therefore instead of rubbed polyimide layers it was proposed to use polyimide layers prepared by photoalignment, utilizing a light-induced orientational ordering of the alignment surface. This can be achieved through photodecomposition, photodimerisation or photoisomerisation by means of polarised light.
  • a suitably derivatised polyimide layer is required that comprises the photoreactive group.
  • treatment of the poylimide and improvement with bumps or polymer layers are relatively great.
  • a self alignment agent or additive to the LC medium that induces the desired alignment, for example homeotropic or planar alignment, in situ by a self assembling mechanism.
  • the alignment layer can be omitted on one or both of the substrates.
  • SA self-aligned
  • SA self-aligning
  • a self-aligning additive is added to the LC medium.
  • Suitable self-aligning additives are for example compounds having an organic core group and attached thereto one or more polar anchor groups, which are capable of interacting with the substrate surface, causing the additives on the substrate surface to align and induce the desired alignment also in the LC molecules.
  • Preferred self- aligning additives comprise for example a mesogenic group and a straight- chain or branched alkyl side chain that is terminated with one or more polar anchor groups, for example selected from hydroxy, carboxy, amino or thiol groups.
  • the self-aligning additives may also contain one or more
  • polymerisable groups that can be polymerised under similar conditions as the RMs used in the PSA process.
  • the SA mode can also be used in combination with the PSA mode.
  • An LC medium for use in a display of such a combined mode thus contains both one or more RMs and one or more self-aligning additives.
  • PSA displays can be operated as either active-matrix (AM) or passive-matrix (PM) displays.
  • AM active-matrix
  • PM passive-matrix
  • optimisation of the response times, but also of the contrast and luminance (and thus transmission) of the LC display is still desired.
  • the PSA method can provide significant advantages.
  • a shortening of the response times, which correlate with a measurable pretilt angle in test cells can be achieved without significant adverse effects on other parameters.
  • a preferred method to apply an LC medium to an AM type PSA display is the so-called “one drop filling" (ODF) method, which is exemplarily and
  • a droplet or an array of droplets (2) of the LC medium is dispensed on a first substrate (1 ).
  • a sealant material is provided in the region (3) between the LC droplets and the edges of the substrate (1 ).
  • a second substrate (4) is coupled and fixed to the first substrate (1 ), thus forcing the LC droplets (2) to spread and form a continuous layer between the two substrates (1 . 4).
  • the polymerisable compounds contained in the LC medium are polymerised or crosslinked in situ, usually by UV photopolymerisation which is achieved by exposing the LC medium to UV radiation, preferably while a voltage is applied to the electrode structures.
  • the polymerisation is carried out at a temperature where the LC medium exhibits an LC phase, usually at room temperature.
  • the polymerised or crosslinked RMs phase-separate from the LC medium and form a polymer layer on the substrate surfaces, where they induce a pretilt angle of the LC molecules relative to the substrates.
  • Polymerisation of the RMs preferably takes place with an applied voltage for example in case of PS-VA, PS-OCB, PS-FFS, PS-UB-FFS, PS-TN displays, and with or without, preferably without, an applied voltage in case of PS-IPS displays.
  • PS-OCB displays it is possible for the bend structure to be stabilised so that an offset voltage is unnecessary or can be reduced.
  • PS-VA displays the pretilt has a positive effect on the response times.
  • LC host mixture and RM(s) are suitable for use in PSA displays because, for example, only inadequate tilt angles or no tilt angles at all could be generated or because, for example, the voltage holding ratio (VHR) is inadequate for TFT display applications.
  • VHR voltage holding ratio
  • the LC mixtures and RMs known from prior art still have some disadvantages when used in PSA displays.
  • RMs of prior art do often have high melting points, and do only show limited solubility in many commonly used LC mixtures. As a result the RMs tend to spontaneously crystallise out of the LC mixture.
  • the risk of spon- taneous polymerisation prevents that the LC host mixture can be warmed in order to better dissolve the RMs, so that a high solubility even at room temperature is required.
  • there is a risk of phase separation for example when filling the LC medium into the LC display (chromatography effect), which may greatly impair the homogeneity of the display. This is further aggravated by the fact that the LC media are usually filled in the display at low temperatures in order to reduce the risk of spontaneous polymerisation (see above), which in turn has an adverse effect on the solubility.
  • RM which is soluble in the LC host mixture
  • the choice of suitable RMs becomes even smaller if UV photopolymerisation without the addition of photoinitiators is desired, which is advantageous for certain applications.
  • the selected combination of LC host mixture/RM should have a low rotational viscosity, good electrical properties and in particular a high VHR.
  • a high VHR after irradiation with UV light is particularly important, because UV exposure does not only occur as normal exposure during operation of the finished display, but is also a necessary part of the display production process.
  • An LC medium for use in PSA displays should also enable the generation of a small pretilt angle.
  • Suitable and preferred materials are those which, compared to prior art materials, can generate a lower pretilt angle after the same exposure time, and/or can generate at least the same pretilt angle after a shorter exposure time. This would allow to reduce the display production time, also known as "tact time", and production costs.
  • a further problem in the production of PSA displays is the presence and removal of residual amounts of unpolymerised RMs after the
  • Unreacted RMs may adversely affect the properties of the display, for example by polymerising in an uncontrolled manner during display operation. This can cause defects like the so-called "image sticking" in the display.
  • image burn means that the image produced in the display by temporary addressing of individual pixels does still remain visible even after the electric field in these pixels has been switched off, or after other pixels have been addressed.
  • image sticking can be caused by the presence of unpolymerised RMs.
  • Uncontrolled polymerisation of the residual RMs is initiated by UV light from the environment or the backlight. In the addressed display areas, this changes the tilt angle after a number of addressing cycles. As a result, a change in transmission in the addressed areas may occur, while it remains unchanged in the non-addressed areas.
  • Image sticking can also occur for example if an LC medium having a low VHR is used in the PSA display.
  • the UV component of daylight or of the backlighting can cause undesired decomposition reactions of the LC molecules and thus initiate the production of ionic or free-radical impurities. These can accumulate in particular at the electrodes or the alignment layers, where they reduce the effective applied voltage.
  • LC media with negative dielectric anisotropy as used for example in PS-VA or PS-FFS displays, do often exhibit reduced reliability compared to LC media with positive dielectric anisotropy.
  • the term "reliability” as used hereinafter means the quality of the performance of the LC medium and the LC display during time and with different stress loads, such as light load, temperature, humidity, voltage, and comprises display effects such as image sticking (area and line image sticking), mura, yogore etc. which are known to the skilled person in the field of LC displays.
  • a standard parameter for categorising the reliability is the voltage holding ration (VHR) value, which is a measure for maintaining a constant electrical voltage in a test display. The higher the VHR value, the better the reliability of the LC medium or display.
  • VHR voltage holding ration
  • RMs and LC host mixtures are required which enable or support quick and complete polymerisation of the RMs.
  • a controlled reaction of the residual RM amounts is desirable. This could be achieved by providing improved RMs that polymerise quicker and more effectively than the RMs of prior art.
  • a further problem observed in PSA displays of prior art is a limited stability of the pretilt angle.
  • the pretilt angle which is generated during display manufacture by polymerising the RMs, does not remain constant but can deteriorate after the display was subjected to voltage stress during display operation. This can negatively affect the display performance, e.g. by increasing the black state transmission and hence lowering the contrast.
  • mura Another problem observed in prior art is that the use of conventional LC media in PSA displays often leads to the occurrence of various types of non- uniformity in brightness in the display, also known as "mura".
  • mura can sometimes be observed as an identifier of the LC dispensing and assembly process. This phenomenon is also known as "ODF mura” or "ODF drop mura”.
  • the display mode is a VA type mode, like MVA, PVA or PS-VA
  • the imprint of the droplets is often visible after fabrication because the droplets are not spreading evenly over the entire display area.
  • VA modes like for example MVA or PVA
  • the non-uniformity generally disappears with time passing.
  • PSA displays however, the non-uniformity remains, and the droplet imprint is "fixed" by the polymerisation process.
  • the present invention has the object to provide improved PSA displays and methods for their production which do not have the drawbacks of prior art as described above, or do so only to a reduced extent, and which provide one or more of the above-mentioned desired advantageous effects and properties.
  • UV1 step the LC medium is exposed to UV radiation emitted by a radiation source (hereinafter also referred to as “light source”), while applying a voltage to the electrode structures, to generate a pretilt angle.
  • UV2 step the LC medium is exposed to UV irradiation without a voltage, in order to ensure complete polymerisation of any residual RM molecules that did not polymerise in UV1 step.
  • a complete polymerisation is important because residual unreacted RM molecules can lead to undesired effects like reduced reliability, reduced tilt angle stability or image sticking in the display.
  • UV photopolymerisation process including UV1 step and UV2 step is hereinafter also shortly referred to as "PSA process”.
  • UV1 step usually a metal halide lamp is used as UV radiation source, with an emitted UV intensity in the UV-A range (310-380 nm) that is typically between 75 and 125 mW/cm 2 .
  • the irradiation time is typically in the range of 60-180 seconds, but depends on the desired extent of the generated pretilt angle.
  • different lamp types can be used, for example a metal halide lamp, or a UV fluorescent lamp which does also have a suitable emission spectrum in the UV-A range.
  • the UV lamps and the RM should be selected such that the RM has maximum absorption in the wavelength range of the UV lamp emission spectrum, so as to ensure effective and complete polymerisation.
  • a typical RM that is used in prior art for the production of PSA displays is biphenyl diacrylate or biphenyl dimethacrylate, which may also be fluorinated.
  • Biphenyl dimethacrylate has an absorption spectrum with strong absorption at the short end of the UV spectrum, especially at wavelengths below 300nm.
  • the UV lamp should therefore be selected such that its emission spectrum shows sufficient overlap with the absorption spectrum of the RM to enable sufficient polymerisation in the PSA process.
  • the PSA process as currently used has some drawbacks which can negatively influence display performance and operation.
  • the metal halide lamp in the UV1 and UV2 steps with a specific UV-cut off filter that cuts off and absorbs radiation at the short wavelength end of the lamp emission spectrum, especially at wavelengths below 300nm, to protect especially the organic materials in the display from exposure to shorter UV wavelengths.
  • the tact time is preferably clearly shorter than
  • UV intensity in UV2 step should be reduced compared to UV1 , to avoid or reduce negative effects like reduced reliability or image sticking.
  • UV exposure of the LC medium to shorter wavelengths and/or over a longer time period can cause degradation of LC compounds or RMs.
  • LC compounds with a terphenyl group which are often used in PSA LC media to enhance polymerisation, have an absorption spectrum that overlaps with the UV lamp emission spectrum, and are therefore prone to degradation especially when exposed to shorter UV wavelengths.
  • degradation can cause ionic impurities, which reduce the reliability and VHR and lead to image sticking.
  • Such terphenyl compounds can therefore only be used in PSA displays with strong limitations related to the UV photopolymerisation conditions, and may require the use of cut-off filters.
  • UV exposure can also cause degradation of other organic materials in the display panel which have an absorption peak in the wavelength range of the UV lamp emission spectrum, like the material of the colour filter or the polyimide alignment layer. As these materials are in contact with the LC medium their degradation can also lead to an interaction with the LC molecules thereby generating ionic impurities which can lead to image sticking as explained above.
  • the problems observed with short UV wavelengths are also aggreviated by the fact that many conventionally used RMs, like biphenyl dimethacrylate as discussed above, require irradiation at shorter wavelengths to ensure efficient photopolymerisation. However, the choice of suitable RMs with absorption at higher wavelengths is still limited.
  • metal halide lamps Another drawback of metal halide lamps is their limited life time, typically about 750-1000 working hours. Also, their UV intensity is stable only within 15-20 min after start, leading to a longer tact time. Besides, as explained above for their use in the PSA process a UV cut-off filter between 300-320 nm is needed. Additionally a so called “cold mirror" is needed to reduce the thermal stress caused by the specific spectrum of the lamp type (high IR intensity). In case of UV-fluorescent lamps the use of UV-cut off filter and a cold mirror is not necessary due to the specific lamp spectrum. However, their life time is also limited, typically to about 2000 working hours. Their UV intensity is stable within 1 minute after start. Another drawback is that both metal halide lamps and UV fluorescent lamps need for their function mercury as an emitting material. However, the use of mercury is disadvantageous for environmental reasons and is often strongly limited by local law. It was now surprisingly found that significant improvements in the
  • photopolymerisation process as part of the PSA display production process could be achieved by using a lamp with a narrow emission peak in the UV wavelength range, especially an LED (light emitting diode) lamp.
  • a lamp with a narrow emission peak in the UV wavelength range especially an LED (light emitting diode) lamp.
  • LED light emitting diode
  • the invention relates to a method of manufacturing an LC display of the PSA mode, which comprises a) providing a first substrate and a second substrate, wherein each substrate is equipped with an electrode structure, or one of the substrates is equipped with two electrode structures and the other substrate is not equipped with an electrode,
  • the invention further relates to a method of manufacturing an LC display of the PSA mode, which comprises steps a), b) and c) as described above, wherein the light source used in step c) is an LED lamp.
  • the invention furthermore relates to an LC display of the PSA type obtained from a process as described above and below.
  • the LC display is preferably a PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB- FFS, PS-posi-VA, PS-TN, SA-VA or SA-FFS display.
  • Fig. 1 exemplarily illustrates the one drop filling (ODF) method.
  • Fig. 2 shows the emission spectrum of an UV LED lamp according to a preferred embodiment of the present invention.
  • full width half maximum or “FWHM” means the width of a spectrum curve measured between those points on the y-axis which are half the maximum amplitude.
  • the polymerisable compounds are preferably selected from achiral compounds.
  • electrode structure includes an electrode layer which may be a continuous layer, or a patterned electrode or pixel electrode, or an array of electrodes, patterned electrodes or pixel electrodes.
  • the terms “active layer” and “switchable layer” mean a layer in an electrooptical display, for example an LC display, that comprises one or more molecules having structural and optical anisotropy, like for example LC molecules, which realign and thereby change their orientation upon an external stimulus like an electric or magnetic field, resulting in a change of the transmission of the layer for polarized or unpolarized light.
  • the terms “tilt” and “tilt angle” will be understood to mean a tilted alignment of the LC molecules of an LC medium relative to the surfaces of the cell in an LC display (here preferably a PSA display).
  • pretilt and “pretilt angle” will be understood to mean the initial tilt angle of the LC molecules in the non-addressed display cell, which is generated by the PSA process including polymerisation of the polymerisable component of the LC medium.
  • the (pre)tilt angle here denotes the average angle ( ⁇ 90°) between the longitudinal molecular axes of the LC molecules (LC director) and the surface of the substrates which form the LC cell. In curved displays, the (pre)tilt angle is given relative to the tangent on the respective substrate.
  • a low (pre)tilt angle value (i.e. a large deviation from 90°) corresponds to a large (pre)tilt and indicates a strong (pre)tilt angle generation
  • a high (pre)tilt angle value (i.e. a small deviation from 90°) corresponds to a small (pre)tilt and indicates a weak tilt angle generation.
  • a suitable method for measurement of the (pre)tilt angle is given in the examples. Unless indicated otherwise, (pre)tilt angle values disclosed above and below relate to this measurement method.
  • the terms “homeotropic alignment” and “vertical alignment” will be understood to mean alignment of the LC molecules with their molecular long axes substantially perpendicular relative to the substrates.
  • planar alignment and “horizontal alignment” will be understood to mean alignment of the LC molecules with their molecular long axes substantially parallel relative to the substrates.
  • reactive mesogen and "RM” will be understood to mean a compound containing a mesogenic or liquid crystalline skeleton, and one or more functional groups attached thereto which are suitable for polymerisation and are also referred to as “polymerisable group” or "P".
  • polymerisable compound as used herein will be understood to mean a polymerisable monomeric compound.
  • unpolymerisable compound will be understood to mean a compound that does not contain a functional group that is suitable for polymerisation under the conditions usually applied for the polymerisation of the RMs.
  • mesogenic group as used herein is known to the person skilled in the art and described in the literature, and means a group which, due to the anisotropy of its attracting and repelling interactions, essentially contributes to causing a liquid-crystal (LC) phase in low-molecular-weight or polymeric substances.
  • Compounds containing mesogenic groups do not necessarily have to have an LC phase themselves. It is also possible for mesogenic compounds to exhibit LC phase behaviour only after mixing with other compounds and/or after polymerisation. Typical mesogenic groups are, for example, rigid rod- or disc-shaped units.
  • spacer group hereinafter also referred to as "Sp”, as used herein is known to the person skilled in the art and is described in the literature, see, for example, Pure Appl. Chem. 2001 , 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 1 16, 6340-6368.
  • spacer group or “spacer” mean a flexible group, for example an alkylene group, which connects the mesogenic group and the polymerisable group(s) in a polymerisable mesogenic compound.
  • One advantage is that, when using a UV lamp with only one narrow emission peak, especially an LED lamp, the optical energy transfer to the polymerisable compounds or RMs in the LC medium is more effective. This allows to reduce the UV intensity and/or the UV irradiation time , thus enabling a reduced tact time and savings in energy and production costs.
  • Another advantage is that the narrow emission spectrum of the lamp allows an easier selection of the appropriate wavelength for photopolymerisation.
  • Both a reduction of the UV radiation intensity and a shift to longer UV wavelengths help to protect the organic materials in the display against damage that may be caused by the UV light. This does also allow a more flexible choice, and extends the range, of suitable and available organic materials for use in the display, like the LC compounds or polymerisable compounds/RMs in the LC medium, or the organic materials used for example in the alignment layer or the colour filter.
  • alkenyl compounds can now more freely be used in the LC medium without the risk of degradation or interaction with the polyimide of the alignment layer.
  • RMs with absorption at the long wavelength side of the UV spectrum can now be used and polymerised more effectively. As a consequence reliability and VHR values can be improved.
  • an LED lamp is especially suitable for achieving the above- mentioned advantageous effects, because an LED lamp has a narrow emission spectrum. Moreover, an LED lamp has significantly higher lifetime and lower energy consumption than a metal halide lamp. Also, an LED lamp does not contain mercury which is beneficial for the environment.
  • the process according to the present invention thus enables advantageous effects like quick and complete polymerisation of the RMs, quick and controlled generation of a low pretilt angle, and enables short response times, high stability of the pretilt especially after UV exposure, reduced image sticking and reduced ODF mura.
  • it provides benefits related to the display manufacturing process, like a reduced tact time, savings in process costs, equipment and energy, and is also beneficial under environmental aspects.
  • the LC display produced using the process according to the present invention is preferably a PS-VA, PS-OCB, PS-IPS, PS-FFS, PS-UB-FFS, PS- posi-VA, PS-TN, SA-VA or SA-FFS display.
  • the structure of the displays according to the invention corresponds to the usual geometry for PSA or SA displays as described in prior art.
  • a first and a second substrate are provided which form the LC display cell, wherein each substrate is equipped with an electrode structure, or one of the substrates is equipped with two electrode structures and the other substrate is not equipped with an electrode.
  • the first and second substrates are preferably selected from glass or quartz substrates. At least one substrate should be transmissive for the photoradiation used for polymerising the polymerisable component of the LC medium.
  • At least one substrate should be transmissive for the photoradiation used for photopolymerisation or
  • the substrates are selected from plastic substrates, for example comprising or being made from polyester such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polyvinylalcohol (PVA), polycarbonate (PC) or
  • PET polyethylene terephthalate
  • PEN polyethylene naphthalate
  • PVA polyvinylalcohol
  • PC polycarbonate
  • TAC triacetylcellulose
  • the display according to the invention further comprises two electrode structures, preferably in the shape of transparent layers, which are applied onto one or both of the two substrates.
  • the electrode structures can be designed by the skilled person depending on the individual display type based on methods and materials known from common general knowledge or from the literature.
  • a multi-domain orientation of the LC molecules can be induced by providing electrodes having slits and/or bumps or protrusions in order to create two, four or more different tilt alignment directions.
  • Geometries without protrusions are preferred, in particular those in which, in addition, the electrode on the colour filter side is unstructured and only the electrode on the TFT side has slots.
  • Particularly suitable and preferred electrode structures for PS-VA displays are described, for example, in US 2006/0066793 A1 .
  • the first substrate is equipped with a first electrode structure and the second substrate is equipped with a second electrode structure.
  • one of the first and second substrates is equipped with a first and a second electrode structure, and the other of the first and second substrates is not equipped with an electrode structure
  • one of the first and second electrodes is a pixel electrode defining pixel areas, the pixel electrode being connected to a switching element disposed in each pixel area and optionally including a micro-slit pattern, and the other of the first and second electrodes is a common electrode layer, which may be disposed on the entire portion of the substrate facing the other substrate.
  • the display according to the invention preferably comprises an alignment layer on one or both of the first and second substrate, which induces initial alignment of the LC molecules.
  • the alignment layer is usually applied on the electrodes (in case electrodes are present) such that it contacts the LC medium.
  • the alignment layers control the alignment direction of the LC molecules of the LC layer.
  • the alignment layers are selected such that they induce homeotropic alignment or tilted homeotropic alignment of the LC molecules.
  • a suitable and preferred alignment layer for inducing homeotropic alignment or tilted homeotropic alignment comprises or consist of, for example, a polyimide, which may also be rubbed or prepared by a photoalignment method.
  • Suitable polyimide alignment layer materials for homeotropic alignment are commercially available, like for example AL60702 (from JSR).
  • Solution processable alignment layer materials are preferred. These are preferably processed from solution in a solvent, preferably an organic solvent, like for example N-methylpyrrolidone, 2-butoxyethanol or ⁇ -butyrolactone.
  • a solvent preferably an organic solvent, like for example N-methylpyrrolidone, 2-butoxyethanol or ⁇ -butyrolactone.
  • the alignment layer is formed by depositing a solution of an alignment layer material like for example polyimide, or a precursor thereof like for example a polyimide precursor, on the substrate, and optionally curing the alignment layer material or its precursor by exposure to heat and/or actinic radiation, for example UV radiation.
  • an alignment layer material like for example polyimide, or a precursor thereof like for example a polyimide precursor
  • the alignment layer material can be deposited on the substrate for example by coating or printing methods.
  • Preferred deposition techniques include, without limitation, dip coating, spin coating, ink jet printing, nozzle printing, letter-press printing, screen printing, gravure printing, doctor blade coating, roller printing, reverse-roller printing, offset lithography printing, dry offset lithography printing, flexographic printing, web printing, spray coating, curtain coating, brush coating, slot dye coating or pad printing.
  • area printing methods compatible with flexible substrates are preferred, for example slot dye coating, spray coating and the like.
  • a solvent is used for deposition of the alignment layer material, it is preferably dried off or evaporated off after deposition. Solvent evaporation can be supported for example by applying heat and/or reduced pressure.
  • Preferred methods for curing the alignment layer are thermal curing and photocuring, very preferably photocuring. Photocuring is for example carried out by exposure to UV radiation.
  • Suitable curing conditions can be selected by the skilled person depending on the precusor material used, based on his common knowledge and as described in the literature. In case of commercially available materials suitable processing and/or curing conditions are often provided together with the sales or sampling of the material.
  • the LC medium contains a self-aligning (SA) additive, preferably in a concentration of 0.1 to 2.5 %.
  • SA self-aligning
  • Preferred displays according to this preferred embodiment are SA-VA and SA- FFS displays.
  • Preferred SA additives for use in this preferred embodiment are selected from compounds comprising a mesogenic group and a straight-chain or branched alkyl side chain that is terminated with one or more polar anchor groups selected from hydroxy, carboxy, amino or thiol groups. Further preferred SA additives contain one or more polymerisable groups which are attached, optionally via spacer groups, to the mesogenic group. These polymerisable SA additives can be polymerised in the LC medium under similar conditions as applied for the RMs in the PSA process.
  • Suitable SA additives to induce homeotropic alignment are disclosed for example in US 2013/0182202 A1 , US 2014/0838581 A1 , US 2015/0166890 A1 and US 2015/0252265 A1 .
  • step b) of the process according to the present invention an LC medium comprising one or more polymerisable compounds that are polymerisable by photopolymerisation is interposed between the first and the second substrate
  • step b) is preferably interposed between the two substrates by the ODF method.
  • step b) comprises the following steps
  • the sealant material preferably deposited onto the first substrate before deposition of the LC medium onto said first substrate .
  • the sealant material is then preferably cured after deposition of the LC medium onto said first substrate, but before photopolymerisation of the polymerisable compounds contained in the LC medium.
  • the sealant material is by exposure to heat and/or photoradiation. In case the sealant material is cured by exposure to photoradiation, preferably
  • the photoradiation is selected such that it does not cause polymerisation of the polymerisable compound in the LC medium, and/or
  • the LC medium is protected from the photoradiation used for curing the sealant material.
  • the LC medium is protected from the photoradiation used for curing the sealant material by a photomask.
  • the sealant material is cured by exposure to light of the same light source as used for photopolymerisation of the polymerisable compounds in the LC medium as described above and below.
  • the PSA display may comprise further elements, like colour filters, a black matrix, a passivation layer, optical retardation layers, transistor elements for addressing the individual pixels, etc., all of which are well known to the person skilled in the art and can be employed without inventive skill.
  • step c) of the process according to the present invention the LC medium comprising the polymerisable compounds is exposed to light emitted from a light source, causing photopolymerisation of the polymerisable compounds, wherein the light source emits light having an emission peak with a peak wavelength in the range from 280 to 420 nm and a full width half maximum (FWHM) of 30 nm or less.
  • a light source emits light having an emission peak with a peak wavelength in the range from 280 to 420 nm and a full width half maximum (FWHM) of 30 nm or less.
  • FWHM full width half maximum
  • the light emitted by the light source used in step c) has an emission peak with a peak wavelength in the range from 350 to 400 nm.
  • the light emitted by the light source used in step c) has an emission peak with a peak wavelength in the range from 360 to 385 nm.
  • the light emitted by the light source used in step c) has an emission peak with a FWHM of 20 nm or less.
  • the light emitted by the light source used in step c) emits a light spectrum having a single emission peak.
  • the light source used in step c) emits a UV light with a radiation energy from 0.1 to 50 J/cm 2 .
  • the light source used in step c) is an LED lamp.
  • the light source in step b) is an LED lamp with an emission peak at 365 nm.
  • LED lamps are known to the skilled person and are commercially available.
  • Suitable and preferred LED lamps include, without limitation, those comprising or consisting of semiconductor LEDs (p-n junction type diodes), semiconductor laser diodes (LDs, another type of p-n junction diodes), also known as injection laser diodes (ILDs), and Organic Light Emitting Diodes (OLEDs).
  • semiconductor LEDs p-n junction type diodes
  • LDs semiconductor laser diodes
  • ILDs injection laser diodes
  • OLEDs Organic Light Emitting Diodes
  • Preferred laser diodes include double heterostructure (DH) lasers, quantum well lasers (QWLs), quantum cascade lasers (QCLs), interband cascade lasers (ICLs), distributed Bragg reflector lasers (DBRs), distributed feedback lasers (DFLs), vertical-cavity surface-emitting lasers (VCSELs), vertical external-cavity surface-emitting lasers (VECSELs), and external cavity diode lasers (EDLs).
  • DH double heterostructure
  • QWLs quantum well lasers
  • QWLs quantum cascade lasers
  • ICLs interband cascade lasers
  • DBRs distributed Bragg reflector lasers
  • DFLs distributed feedback lasers
  • VCSELs vertical-cavity surface-emitting lasers
  • VECSELs vertical external-cavity surface-emitting lasers
  • EDLs external cavity diode lasers
  • Preferred OLEDs include, depending on the emitting material, polymer light emitting diodes (PLEDs) and small molecule OLEDs (SM-OLEDs), and, depending on the addressing scheme, passive-matrix OLEDs (PMOLEDs) and active-matrix OLEDs (AMOLEDs).
  • PLEDs polymer light emitting diodes
  • SM-OLEDs small molecule OLEDs
  • PMOLEDs passive-matrix OLEDs
  • AMOLEDs active-matrix OLEDs
  • LED lamps emitting UV light are commercially available for example from Dr. Hoenle AG UV Technologie.
  • the emission spectrum of such a UV lamp with an emission peak at 365 nm is shown in Fig. 2.
  • the polymerisable compounds in the LC medium form a polymer or crosslinked polymer, which generates a pretilt angle of the LC molecules in the LC medium.
  • at least a part of the crosslinked polymer, which is formed by the polymerisable compounds will phase-separate or precipitate from the LC medium and form a polymer layer on the substrates or electrodes, or the alignment layer provided thereon.
  • Microscopic measurement data like SEM and AFM have confirmed that at least a part of the formed polymer accumulates at the LC/substrate interface.
  • Photopolymerisation of the polymerisable compounds in the LC medium can be carried out in one step.
  • photopolymerisation of the polymerisable compounds in the LC medium is carried out in two steps, a first polymerisation step, preferably with an applied voltage, for generating a pretilt angle, and a second polymerisation step, preferably without an applied voltage, for polymerising the compounds which did not, or not completely, react in the first step ("end curing").
  • step c) comprises the following steps
  • c1 exposing the LC medium comprising the polymerisable compounds to light emitted from a light source causing photopolymerisation of the polymerisable compounds, while a voltage is applied to the electrodes
  • c2) exposing the LC medium comprising the photopolymerised polymerisable compounds and any remaining unpolymerised polymerisable compounds to light emitted from a light source, causing photopolymerisation of the remaining unpolymerised polymerisable compounds, while no voltage is applied to the electrodes, wherein in one or both of steps c1 ) and c2), preferably in at least in step c1 ), very preferably both in step c1 ) and step c2), the light source is as defined above and below.
  • the same light source is used in steps c1 ) and c2).
  • the light source used in step c1 ) has a radiation intensity from 5 to 500 mW/cm 2 , very preferably from 25 to 125 mW/cm 2 .
  • the time for which the LC medium comprising the polymerisable compound is exposed to light is from 5 to 600 s, very preferably from 30 to 240 s.
  • the light source used in step c2) has a radiation intensity from 5 to 500 mW/cm 2 .
  • the time for which the LC medium comprising the polymerisable compound is exposed to light is from 10to 150 min.
  • the light source used in in steps c), c1 ) and c2) has an emission peak in the wavelength range where the photopolymerisable compounds show absorption.
  • a voltage is applied to the electrodes during polymerisation of the polymerisable compounds in the LC medium.
  • the LC medium contains a photoinitiator which initiates photopolymerisation of the polymerisable compounds in the LC medium.
  • Suitable photoinitiators are described in the literature and can be easily selected by the skilled person depending on the polymerisable compound and the desired polymerisation method.
  • Suitable photoinitiators for free-radical polymerisation are, for example, the commercially available photoinitiators of the the Irgacure® or Darocure® series (Ciba AG), like for example Irgacure651®, Irgacure184®,
  • a photoinitiator is added to the LC medium, its proportion, based on the total amount of polymerisable compounds in the LC medium, is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 3% by weight. If a photoinitiator is added to the LC medium, its proportion, based on the total solid contents of the LC medium (not including solvents), is preferably from 1 to 10,000 ppm, very preferably from 10 to 500 ppm.
  • polymerisable compounds used in the polymerisable are preferably the polymerisable compounds used in the polymerisable
  • component of the LC medium are selected such that they can be
  • the LC medium a polymerisation inhibitor or stabiliser which inhibits photopolymerisation of the polymerisable compounds in the LC medium.
  • a polymerisation inhibitor or stabiliser which inhibits photopolymerisation of the polymerisable compounds in the LC medium.
  • Suitable types and amounts of inhibitors and stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076 or
  • lrganox®1010 Further suitable and preferred inhibitors are those selected from Table D below.
  • an inhibitor or stabiliser is added to the LC medium, its proportion, based on the total amount of polymerisable compounds in the LC medium (not including solvents), is preferably 10-500,000 ppm, particularly preferably 50- 50,000 ppm.
  • the LC medium preferably comprises a polymerisable component A) comprising, preferably consisting of, one or more polymerisable compounds, and a liquid-crystalline component B) comprising, preferably consisting of, one or more mesogenic or liquid-crystalline compounds.
  • the liquid-crystalline component B) of an LC medium according to the present invention is hereinafter also referred to as "LC host mixture", and preferably contains only LC compounds that are selected from low-molecular-weight compounds which are unpolymerisable, and optionally contains additives like polymerisation initiators, inhibitors etc.
  • the proportion of the entire polymerisable component in the LC medium is preferably from > 0 to ⁇ 5%, very preferably from > 0 to ⁇ 1 %, most preferably from 0.05 to 0.5%.
  • the polymerisable compounds in component A) have an absorption maxium at longer UV wavelengths, preferably 340 nm or more, to avoid short UV light exposure in the PSA process.
  • B 1 and B 2 an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted, or mono- or
  • R° and R 00 each, independently of one another, denote H or alkyl having 1 to
  • Y 1 denotes halogen
  • R x denotes P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, CI, P or P-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or hetero- aryloxy group having 2 to 40 C atoms.
  • Preferred compounds of formula I are those in which B 1 and B 2 each, independently of one another, denote 1 ,4-phenylene, 1 ,3-phenylene, naphthalene-1 ,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, 9,10- dihydro-phenanthrene-2,7-diyl, anthracene-2,7-diyl, fluorene-2,7-diyl, coumarine, flavone, where, in addition, one or more CH groups in these groups may be replaced by N, cyclohexane-1 ,4-diyl, in which, in addition, one or more non-adjacent CH 2 groups may be replaced by O and/or S, 1 ,4- cyclohexenylene, bicycle[1 .1 .1 ]pentane-1 ,3-diyl, bicyclo[2.2.2]o
  • Very preferred compounds of formula I are those in which B 1 and B 2 each, independently of one another, denote 1 ,4-phenylene, 1 ,3-phenylene, naphthalene-1 ,4-diyl or naphthalene-2,6-diyl.
  • P 1 , P 2 , P 3 a vinyloxy, acrylate, methacrylate, fluoroacrylate, chloro- acrylate, oxetane or epoxy group,
  • Sp 1 , Sp 2 , Sp 3 a single bond or a spacer group as defined for Sp
  • one or more of the radicals P 1 -Sp 1 -, P 1 -Sp 2 - and P 3 - Sp 3 - may denote R aa , with the proviso that at least one of the radicals P 1 -Sp 1 -, P 2 -Sp 2 and P 3 -Sp 3 - present is different from
  • H, F, CI, CN or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH 2 groups may each be replaced, independently of one another, by (R°) C(R 00 )-, -C ⁇ C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, CI, CN or P 1 -Sp 1 -, particularly preferably straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having
  • R y and R z H, F, CH 3 or CF 3 ,
  • -OCO-CH CH-, or a single bond, where n is 2, 3 or 4, and at least one of Z 2 and Z 3 is not a single bond, L F, CI, CN, P 1 -Sp 1 - or straight-chain or branched, optionally mono- or polyfluorinated, alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or
  • L on each occurrence identically or differently, has one of the meanings given above or below, and is preferably F, CI, CN, NO2, CH3, C2H5, C(CH 3 ) 3 , CH(CH 3 ) 2 , CH 2 CH(CH3)C 2 H5, OCH 3 , OC2H5, COCH3, COC2H5, COOCH3, COOC2H5, CF 3 , OCF3, OCHF2, OC2F5 or P-Sp-, very preferably F, CI, CN, CH3, C2H5, OCH3, COCH3, OCF3 or P-Sp-, more preferably F, CI, CH3, OCH3, COCH3 Oder OCF 3 , especially F or CH 3 .
  • Preferred compounds of formulae M1 to M31 are those wherein P 1 , P 2 and P 3 denote an acrylate, methacrylate, oxetane or epoxy group, very preferably an acrylate or methacrylate group. Further preferred compounds of formulae M1 to M31 are those wherein Sp 1 , Sp 2 and Sp 3 are a single bond.
  • Further preferred compounds of formulae M1 to M31 are those wherein one of Sp 1 , Sp 2 and Sp 3 is a single bond and another one of Sp 1 , Sp 2 and Sp 3 is different from a single bond.
  • Further preferred compounds of formulae M1 to M31 are those wherein those groups Sp 1 , Sp 2 and Sp 3 that are different from a single bond denote - (CH2)si-X"-, wherein s1 is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X" is X" is the linkage to the benzene ring and is -O-, -O-CO-, -CO-O, -O-CO- O- or a single bond.
  • Further preferred polymerisable compounds and RMs are those selected from Table E below. Particular preference is given to LC media comprising one, two or three polymerisable compounds of formula I.
  • the proportion of compounds of formula I in the LC medium is from 0.01 to 5%, very preferably from 0.05 to 1 %, most preferably from 0.1 to 0.5%.
  • the polymerisable component A) medium comprises, very preferably consists of, one or more polymerisable compounds of the preferred embodiments as described above.
  • the LC medium contains an LC component B), or LC host mixture, comprising one or more, preferably two or more LC compounds which are selected from low-molecular- weight compounds that are unpolymerisable. These LC compounds are selected such that they stable and/or unreactive to a polymerisation reaction under the conditions applied to the polymerisation of the polymerisable compounds.
  • the proportion of the LC component B) in the LC medium is preferably from 95 to ⁇ 100%, very preferably from 99 to ⁇ 100%.
  • LC media in which the LC component B), or the LC host mixture has a nematic LC phase, and preferably has no chiral liquid crystal phase.
  • the LC component B), or LC host mixture is preferably a nematic LC mixture.
  • the LC medium contains an LC component B), or LC host mixture, based on compounds with negative dielectric anisotropy.
  • LC media are especially suitable for use in PS-VA, SA-VA and PS-UB- FFS displays.
  • Preferred compounds for use in an LC host mixture with negative dielectric anisotropy according to this first preferred embodiment are selected from Table A below.
  • the LC medium contains an LC component B), or LC host mixture, based on compounds with positive dielectric
  • Such LC media are especially suitable for use in PS-OCB, PS-TN, PS-Posi-VA, PS-IPS, PS-FFS or SA-FFS displays.
  • Preferred compounds for use in an LC host mixture with positive dielectric anisotropy according to this second embodiment are selected from Table B below.
  • the LC media and LC host mixtures for use in a display of the present invention preferably have a nematic phase range of at least 80 K, particularly preferably at least 100 K, and a rotational viscosity ⁇ 250 mPa s, preferably ⁇ 200 mPa s, at 20°C.
  • LC media based on compounds with negative dielectric anisotropy according to the first preferred embodiment in particular for use in PS-VA and PS-UB- FFS displays, have a negative dielectric anisotropy ⁇ , preferably from -0.5 to -10, in particular from -2.5 to -7.5, at 20°C and 1 kHz.
  • LC media based on compounds with negative dielectric anisotropy according to the first preferred embodiment in particular for use in PS-VA and PS-UB- FFS displays, preferably have a birefringence ⁇ below 0.16, particularly preferably from 0.06 to 0.14, very particularly preferably from 0.07 to 0.12.
  • LC media based on compounds with positive dielectric anisotropy according to the second preferred embodiment in particular for use in PS-OCB, PS-TN, PS-IPS, PS-posi-VA, PS-FFS and SA-FFS displays, have a positive dielectric anisotropy ⁇ , preferably from +2 to +30, very preferably from +3 to +20, most preferably from +4 to +17 at 20°C and 1 kHz.
  • LC media based on compounds with positive dielectric anisotropy preferably have a birefringence ⁇ from 0.14 to 0.22, very preferably from 0.16 to 0.22.
  • LC media based on compounds with positive dielectric anisotropy preferably have a birefringence ⁇ from 0.07 to 0.15, very preferably from 0.08 to 0.13.
  • LC media according to the invention based on compounds with positive dielectric anisotropy according to the second preferred embodiment, for use in displays of the PS-TN-, PS-posi-VA-, PS-IPS- Oder PS-FFS-type, preferably have a positive dielectric anisotropy ⁇ from +2 to +30, particularly preferably from +3 to +20, at 20°C and 1 kHz.
  • the LC medium according to the present invention does essentially consist of a polymerisable component A) and an LC component B) (or LC host mixture) as described above and below.
  • the LC medium additionally comprises one or more further components or additives, preferably selected from the list including but not limited to co-monomers, chiral dopants, polymerisation initiators, inhibitors, stabilisers, surfactants, wetting agents, lubricating agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.
  • further components or additives preferably selected from the list including but not limited to co-monomers, chiral dopants, polymerisation initiators, inhibitors, stabilisers, surfactants, wetting agents, lubricating agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.
  • additives may be polymerisable or non-polymerisable.
  • Polymerisable additives are accordingly ascribed to the polymerisable component or component A).
  • Non-polymerisable additives are accordingly ascribed to the non-polymerisable component or component B).
  • the LC medium contains one or more chiral dopants, preferably in a concentration from 0.01 to 1 %, very preferably from 0.05 to 0.5%.
  • the chiral dopants are preferably selected from the group consisting of compounds from Table B below, very preferably from the group consisting of R- or S-101 1 , R- or S-201 1 , R- or S-301 1 , R- or S-401 1 , and R- or S-501 1 .
  • the LC medium contains a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph. Furthermore, it is possible to add to the LC medium, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl- ammonium tetraphenylborate or complex salts of crown ethers for improving the conductivity, or agents for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases, for example as described in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281 , 24 50 088, 26 37 430 and 28 53 728.
  • conductive salts preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, t
  • LC compounds for use in component B) of the LC medium are either known or methods for the preparation thereof can readily be derived from the prior art by the person skilled in the relevant art, since they are based on standard methods described in the literature, for example in EP-A-0 364 538, DE-A-26 36 684 and DE-A-33 21 373.
  • the LC medium used in accordance with the invention can be prepared in a manner conventional per se, for example by mixing one or more of the above-mentioned compounds with one or more polymerisable compounds as defined above, and optionally with further LC compounds and/or additives. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent,
  • the LC medium as used in the present may also comprise compounds in which, for example, H, N, O, CI, F have been replaced by the corresponding isotopes like deuterium etc.
  • Tables A-E show suitable and preferred components of the LC medium as used in the present invention. Suitable compounds for use in an LC host mixture with negative dielectric anisotropy are listed in Table A. Suitable compounds for use in an LC host mixture with positive dielectric anisotropy are listed in Table B. Suitable compounds for use as chiral dopants are listed in Table C. Suitable compounds for use as stabilisers are listed in Table D. Suitable compounds for use as RMs are listed in Table E.
  • the LC medium according to the invention comprises one or more compounds selected from the group consisting of compounds from Table A.
  • the LC medium according to the invention comprises one or more compounds selected from the group consisting of compounds from Table B.
  • Table C shows possible chiral dopants which can be added to the LC medium according to the invention.
  • the LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, of dopants.
  • the LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table C.
  • Table D shows possible stabilisers which can be added to the LC limbann according to the invention.
  • n here denotes an integer from 1 to 12, preferably 1 , 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are not shown).
  • the LC medium preferably comprises 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1 % by weight, of stabilisers.
  • the LC media preferably comprise one or more stabilisers selected from the group consisting of compounds from Table D.
  • Table E shows illustrative reactive mesogenic compounds which can be used in the LC media in accordance with the present invention.
  • the mixtures according to the invention comprises one or more polymerisable compounds selected from the groups of the compounds of Table E.
  • compounds RM-1 , RM-4, RM-8, RM- 17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41 , RM-48, RM-52, RM-54, RM-57, RM-64, RM-74, RM-76, RM-88, RM-102, RM-103, RM-109, RM-1 17, RM-120, RM-121 and RM-122 are particularly preferred.
  • threshold voltage for the present invention relates to the capa- citive threshold (Vo), also known as the Freedericks threshold, unless explicitly indicated otherwise.
  • the optical threshold may also, as generally usual, be quoted for 10% relative contrast (Vio).
  • the process of polymerising the polymerisable compounds in the PSA displays as described above and below is carried out at a temperature where the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably is carried out at room temperature.
  • the nematic LC host mixture N1 is formulated as follows.
  • Polymerisable mixtures are prepared by adding, in each case, one of the reactive mesogens (RM) shown below to one of the a nematic LC host mixtures N1 -N3, respectively, at a concentration of 0.3% by weight.
  • RM reactive mesogens
  • the display used for measurement of the voltage holding ratio consists of two plane-parallel glass outer plates at a separation of 6 ⁇ , each of which has on the inside an electrode layer and an unrubbed VA-polyimide alignment layer (JSR-PI2) on top, which effect a homeotropic edge alignment of the liquid-crystal molecules.
  • Polymerisable mixtures according to the invention are introduced into the display or test cell and the polymerisable compounds are polymerised by irradiation with UV light of defined intensity. Two UV irradiation steps are carried out, the first step hereinafter named “UV 1 " and the second step hereinafter name "UV 2".
  • step UV 1 irradiation time is 5 minutes, with a voltage simultaneously being applied to the display (usually 40 V pp square wave, 200 Hz).
  • step UV 2 irradiation time is 60 minutes without applied voltage.
  • the above-mentioned 365nm LED lamp from Hoenle with an intensity of 85 mW/cm 2 and having an emission spectrum as shown in Fig. 2 is used for polymerisation in both UV steps.
  • the UV intensity is measured using a standard UVA meter (Hoenle UV-meter high end with UVA sensor).
  • test cells are irradiated for UV 1 and UV 2 using a current standard UV lamp instead of an LED lamp.
  • a Metall-Halide lamp from Hoenle with an intensity of 100 mW/cm 2 plus a 320 nm cut off filter is used for polymerisation.
  • a UV fluorescence lamp with an intensity of 3.5 mW/cm 2 without any cut off filter is used for polymerisation.
  • the irradiation times are the same as for the LED processing.
  • the UV intensity is measured using a standard UVA meter (Hoenle UV-meter high end with UVA sensor) without the cut off filter.
  • the VHR value is determined before and after UV exposure at 1 V, 60 Hz, 64 s pulse, 100°C (measuring instrument: Autronic-Melchers VHRM-105).
  • VHR values are shown in Table 2.
  • the PS-VA display test cell used for measurement of the tilt angles consists of two plane-parallel glass outer plates at a separation of 4 ⁇ , each of which has on the inside a electrode layer with dashed gaps and an unrubbed VA-polyimide alignment layer (JSR-PI2) on top, which effect a homeotropic edge alignment of the LC molecules.
  • the electrodes of the top and the bottom glass are parallel but shifted.
  • the top glass has an additional resin black mask to cover areas of misalignment.
  • Polymerisable mixtures according to the invention are introduced into the test cells, and the polymerisable compounds are polymerised by irradiation with UV light for 2 minutes unless stated otherwise, with a voltage simultaneously being applied to the display (usually 40 V pp square wave, 200 Hz).
  • a voltage simultaneously being applied to the display usually 40 V pp square wave, 200 Hz.
  • the previous mentioned 365nm LED lamp from Hoenle with an intensity of 85 mW/cm 2 is used for polymerisation.
  • the UV intensity is measured using a standard UVA meter (Hoenle UV-meter high end with UVA sensor).
  • the pretilt angle is determined after UV irradiation and polymerisation of the polymerisable compounds under the conditions as described above.
  • the tilt angle is determined by Axo-Scan (Axometrics, Inc.).
  • a high value i.e. a large deviation from the 90° angle corresponds to a large tilt here.
  • the pretilt angles are shown in Table 3.

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

Abstract

La présente invention concerne un procédé de fabrication d'un affichage à cristaux liquides (LCs) de l'alignement soutenu par polymère (PSA) à l'aide d'un milieu LCs contenant un monomère photopolymérisable, et à utiliser une source de lumière ayant un pic d'émission étroit pour la photopolymérisation du monomère.
PCT/EP2018/061765 2017-05-11 2018-05-08 Procédé de fabrication d'un affichage à cristaux liquides stabilisé par polymère WO2018206524A1 (fr)

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