CN1399729A - Fabrication of aligned liquid crystal cell/film by simultaneous alignment and phase separation - Google Patents

Abstract

Disclosed is a method capable of simultaneously producing a phase-separated organic film and a microstructure with desired alignment liquid crystals. The steps of the method include preparing a mixture of liquid crystal material, prepolymer and polarization sensitive material. The mixture is coated on a substrate and treated with combined ultraviolet or visible light or heat, which simultaneously induces phase separation so that a properly aligned layer or microstructure of liquid crystal material is formed adjacent to the substrate.

Description

Fabrication of Aligned Liquid Crystal Cells/Films by Simultaneous Alignment and Phase Separation

field of invention

The invention belongs to the field of light modulation devices made of composite organic materials using self-aligned alignment layers. Specifically, the present invention combines two processes, one for in-situ photoalignment using polarized ultraviolet radiation, and the other for phase-separated composite organic film (PSCOF) technology using a one-step or multi-step process Anisotropic phase separation is achieved to prepare aligned liquid crystal films adjacent to the polymer layer with or without pretilt angle. In particular, this method enables the preparation of aligned liquid crystal cells without the need to previously fabricate two alignment layers, each on its substrate.

Background technique

The PSCOF method was recently invented and used at Kent State University to prepare contiguous layers of polymer and liquid crystal that are parallel to each other. This method is disclosed in US Patent 5,949,508, incorporated herein by reference. The PSCOF method involves a process similar to that used in the manufacture of polymer dispersed liquid crystal films. Polymers and liquid crystals mixed in predetermined ratios are placed between two substrates with strictly defined thicknesses or overlaid on one substrate. When a beam of ultraviolet light is incident on one side, the phase separation process begins. The rate of polymerization (and phase separation) is faster due to the higher light intensity near the UV radiation source. As phase separation begins, the organic or liquid crystal material is expelled from the polymerized portion and begins to migrate away from the UV radiation source. As a result, a uniform polymer film is obtained on one side of the cell, while a substantially uniform liquid crystal layer is formed on the opposite side of the cell further from the UV source. The separation of liquid crystals from polymers on such substrates further away from the UV source can be facilitated by the use of pre-applied layers of aligned and readily wettable liquid crystal materials. In this manner, an aligned liquid crystal film can be formed.

Alignment layers are typically constructed of long chain polymeric materials which are usually later subjected to processes such as mechanical rubbing or UV radiation to alter their surface properties. There are several generally accepted techniques for forming an alignment layer on a liquid crystal device substrate. Commonly used methods are rubbing or photo-alignment of organic/polymer films and evaporation of inorganic materials. While each method is capable of aligning liquid crystal materials, each method has specific drawbacks.

The most common method of forming an alignment layer is the rubbing technique. In this method, for example, polyamic acid is spin-coated or deposited on a substrate. Two heat treatments, soft bake and vigorous bake, were performed on the polyamic acid to form a polyimide (PI) film. After a period of proper cooling, rub the PI film with a cloth such as velvet in a consistent single direction. Later, when the liquid crystal contacts the rubbing surface, the liquid crystal is aligned along the rubbing direction. Unfortunately, this method will cause mechanical damage and generate electrostatic charges, both of which are not conducive to liquid crystal displays, especially for liquid crystal displays using thin film transistors. This rubbing method also generates dust from the cloth and PI, which may contaminate the liquid crystal material.

Another method of forming an alignment layer involves growing a PI film on a substrate as described above. Linearly polarized UV light is projected onto the surface of the PI film to create the desired molecular alignment. UV radiation anisotropically photodissociates photosensitive chemical bonds in PI, including those on the imide ring. This selectively reduces the polarizability of PI molecules and changes their surface properties and morphology. Unfortunately, the anchoring between the alignment layer and the liquid crystal produced by this method is very weak and has poor thermal and chemical stability. Furthermore, this method requires an expensive multi-step process. Yet another drawback of this approach is that it only offers limited charge retention and lower thermal stability compared to tribotechnology.

A similar method of preparing alignment layers using photopolymers is also known. For example, films of photosensitive polymers such as poly(vinyl) 4-methoxycinnamate (PVMC), poly(vinyl)cinnamate (PVC), and polysiloxane cinnamate can be used to make liquid crystal materials sensitive to Quasi-arrangement. When these materials are exposed to linearly polarized ultraviolet light (LPUV), photoreactions are initiated after solvent evaporation. This approach results in both cross-linking (bonding) of side chain molecules and product orientation in a single direction, the direction determined by the direction of linear polarization. However, these methods cannot chemically fix the orientation of the molecules, which lose their alignment when exposed to normally present, unpolarized ultraviolet light. Also, over time, the chemical makeup of these materials is lost. Accordingly, the alignment layer thus produced cannot contribute to a fixed, stable orientation of the liquid crystal material.

Yet another method for forming an alignment layer on a substrate is by deposition of an inorganic material at a qualitatively different angle of incidence on the surface of the substrate. This forms an alignment layer whose structure determines the orientation of the liquid crystal. Inorganic materials that have been used include silicon oxides and magnesium oxides. This deposition method has proven to be cumbersome and difficult to use during fabrication.

Another method of forming an alignment layer developed by Kent State University is in situ ultraviolet irradiation. This method is disclosed in US Patent 5,936,691, incorporated herein by reference. This in situ irradiation method is similar to the conventional method of exposing PI films to polarized UV light. However, this in situ irradiation method is to irradiate the polyimide (PI) film with UV light while it is being softly and vigorously baked. Compared with the conventional UV irradiation technique, the alignment layer obtained in this way has higher anchoring energy and better thermal stability. For example, cells fabricated by conventional methods lose their alignment after being held at 100°C for 12 hours, while cells made by the in situ irradiation method show no signs of degradation when held at 300°C for 12 hours. This in situ irradiation method of forming the alignment layer avoids many of the disadvantages of other methods known in the art, while requiring fewer and simpler processing steps.

While this in situ irradiation method has proven effective, it still requires that the alignment film must also be properly coated and processed. Furthermore, as with all of the above-discussed alignment methods, the alignment layer can be damaged if care is not taken when transferring such substrates between manufacturing sites. Theoretically, it is also considered that the currently known alignment layer can only directly affect the liquid crystal material adjacent to it.

From the foregoing, it is apparent that there is a need in the art for a light modulating device comprising a phase-separated composite organic film and a method of making such a film, which is uniformly aligned during its formation and does not require separate preparation and handling. Alignment layers with different properties.

Contents of the invention

According to the above, a first aspect of the present invention is to provide a light modulation device comprising a phase-separated composite organic film or a microstructure and a method of manufacturing such a device, wherein the device aligns liquid crystal materials uniformly without the need for Two independent alignment layers.

Another aspect of the present invention is to provide a self-aligned phase-separated composite organic film, which is manufactured by a one-step or multi-step process of simultaneously performing phase separation and photo-alignment.

Still another aspect of the present invention is to provide an anisotropic film or microstructure produced by simultaneous photoalignment and photopolymerization.

Yet another aspect of the present invention is to provide an anisotropic film or microstructure produced by simultaneous photoalignment and solvent-induced phase separation, wherein the alignment of liquid crystals is at all internal polymer interfaces of the microstructure obtained from (the wall).

Yet another aspect of the present invention is to provide a film or microstructure fabricated by simultaneous photoalignment and thermally induced polymerization.

Still another aspect of the present invention is to provide an anisotropic film or microstructure comprising two or more layers prepared by a multi-step process, wherein layers of liquid crystal material are individually aligned on each film surface and may have properties different orientations.

Another aspect of the invention is a method for making an anisotropic film comprising the steps of: spin coating a photocrosslinkable polyimide on a substrate, spin coating a reactive polyimide on the polyimide For the liquid crystal monomer, applying polarized light causes the crosslinking of polyamic acid and the photoalignment and polymerization of the reactive monomer to occur simultaneously. The UV light causes an appropriate morphology to form at the polyimide/liquid crystal interface, which then determines the orientation of the liquid crystal material.

Yet another aspect of the present invention is a method for producing an anisotropic film comprising the steps of: spin coating a liquid crystal polymer (LCP) on a substrate, spin coating a reactive monomer on the LCP, applying The polarized light allows simultaneous photoalignment of the LCPs and photoalignment and polymerization of the reactive monomers.

Still another aspect of the present invention is a method for producing an anisotropic film comprising the steps of: preparing a mixture of a liquid crystal material, a polymer and a solvent, coating the mixture on a substrate, evaporating the solvent, applying polarized light Photoalignment and phase separation of the liquid crystal material occur simultaneously.

Still another aspect of the present invention is a method for producing an anisotropic film comprising the steps of: preparing a mixture of a liquid crystal material and a thermally polymerizable monomer, applying the mixture to a substrate, and subjecting it to heat treatment to polymerize the monomer , applying polarized light to photoalign the liquid crystal material.

An additional aspect of the present invention is a method for producing anisotropic films and/or microstructures comprising two or more layers or microstructures, the method comprising the steps of sequentially performing the above two or more methods, whereby a multilayer alignment material is prepared in which the liquid crystals are individually and individually aligned at each interface/surface.

The above and other objects of the present invention will become apparent as the detailed description unfolds, which is a method for obtaining an organic film capable of simultaneously forming alignment and phase separation, the method comprising: preparing liquid crystals, prepolymers and a mixture of polarization-sensitive materials, coating the mixture on the substrate, using a light source to apply polarized light induction to simultaneously perform phase separation of the mixture and alignment of phase-separated liquid crystals, thereby forming a uniformly aligned liquid crystal material layer, the The layer is adjacent to the layer of polymer and polarization sensitive material on the substrate.

Another aspect of the present invention is to obtain a method of manufacturing a liquid crystal device with alignment properties, the method comprising: providing a substrate, providing a first mixture comprising at least a first polarization sensitizer and a prepolymer, providing a second mixture, which at least includes a second polarization sensitizer and a prepolymer, adding liquid crystals to the first or second mixture, coating the first mixture on a substrate, and applying the second mixture Coated on the first mixture, using a method selected from at least including visible light polarization, ultraviolet polarization, thermal induction, chemical induction and solvent induction, starting the treatment process for the first mixture: using a method selected from at least including visible light polarization, ultraviolet light Polarization, heat-induced, chemical-induced and solvent-induced methods, which initiate the process of processing the second mixture, carry out alignment of liquid crystals.

Yet another object of the present invention is to obtain a unit with alignment properties comprising at least a substrate and a mixture coated on the substrate, the mixture comprising at least a liquid crystal material, a prepolymer material and a polarization sensitive A material in which simultaneous polymerization and application of polarized light results in phase separation and photoalignment of the mixture, thereby forming a polymeric microstructure which imparts alignment properties to liquid crystal materials.

These and other objects of the present invention and its advantages over prior forms of art, which will become apparent in the ensuing description, are achieved by the improvements set forth below and claimed in the claims.

Brief description of the drawings

In order to fully understand the purpose, technology and structure of the present invention, reference should be made to the following detailed description and accompanying drawings, wherein:

1 is an enlarged schematic view of a partial cross-section of an optical modulation device prototype (before polymerization and alignment) according to the present invention;

2 is an enlarged schematic view of a partial section of an optical modulation device (after performing alignment and polymerization in one step simultaneously) according to the present invention;

Figure 3 is an enlarged schematic view of a partial section of a device obtained after completing the multi-step process according to the present invention; and

Fig. 4 is the enlarged schematic view of the partial section of the microstructure device obtained after completing the multi-step method according to the present invention;

Best Mode for Carrying Out the Invention

Referring now to FIG. 1, there can be seen a prototype light modulating device, generally designated by the numeral 10, fabricated in accordance with the present invention. It will be apparent that the light modulation device prototype 10 does not comprise (although one could be provided) a separate alignment layer of a different nature. The light modulating device of the present invention can be fabricated in a manner that does not require a separate spin-coating step for depositing alignment layer precursor materials on the substrate. The method also does not require soft baking and/or hard baking to align the alignment layers. Furthermore, the method does not require rubbing or structurally contacting the alignment layer to impart its properties that will subsequently act on the liquid crystal material.

Figure 1 shows a light modulating device prototype comprising a pair of opposing optically transparent substrates 12, which may be glass, plastic, or other materials generally known in the art. Advantageously, the device does not need to be subjected to the temperatures necessary to imidize the alignment layer of the prior art. As will be apparent, temperature sensitive materials which heretofore were unsuitable as substrates can be used in the present invention. In other words, flexible substrate materials such as plastic or polymer sheets can now be applied to liquid crystal devices because these devices do not need to withstand the high temperatures commonly used in the methods of vigorous baking and soft baking to create the alignment layer.

Polarizers 14 may be disposed on the outer surface of each substrate 12 in order to improve the optical properties of the transmitted light to provide an element operating in a transmissive mode. Electrodes 18 may be disposed on the inner surface of each substrate 12 . In the preferred embodiment, each electrode 18 is an indium tin oxide material. Alternatively, to provide a device operating in reflective mode, mirrors or light diverging sheets may be placed on the outside of the substrate opposite the light source.

A power source 20 is connected to the electrode 18 via a switch 22 . Switch 22 may be used to connect a power source, short circuit two electrodes, or disconnect electrodes to store charge on them. The liquid crystal or organic material placed between the substrates is induced to produce an optical switching action using an electric or electromagnetic field or other external force. The operation of switch 22 may be controlled by a suitably designed electronic driver. The use of electronic drive circuits opened up specific fields of matrix cell devices, which in turn varied widely between these fields. The cell gap width between electrodes is determined by dimension 26 as shown in FIG. 1 .

Composite organic material 28 includes at least the following components: an organic or liquid crystal material, a prepolymer, and an alignment agent such as low temperature curable polyimide, which are sandwiched between substrates 12 . To obtain material 28, liquid crystal material is combined with prepolymer and polyimide in solution and filled between substrates 12 by capillary action. Of course, other known filling methods can be used. The edges of the substrate are sealed using known methods. Alternatively, material 28 may be spin-coated on a single substrate.

Referring now to FIG. 2, it can be seen that a light modulating element, indicated generally at numeral 30, is fabricated according to the present invention by simultaneous phase separation and alignment in a one-step process.

Generally, a "one-step process" is one in which a layer of material comprising at least an organic or liquid crystal material, a prepolymer, and a polarization-sensitive alignment agent such as a chromophore is applied by a method such as spin coating On the substrate, the coated substrate is treated by a method selected from the group consisting of polarized visible radiation, or polarized ultraviolet radiation and some type of phase separation. The one-step method is characterized in that all components will be subjected to the same treatment at the same time so that the phase-separated liquid crystal material components are evenly aligned.

A light source 32 , such as ultraviolet or visible light, is positioned adjacently below the linear polarizer 36 . After the light source 32 is excited, the ray 34 is emitted into the linear polarizer 36 , and the linear polarizer guides the linearly polarized ray 38 to pass through the substrate 12 and enter the cell gap 26 . Polymerization of the prepolymer material previously mixed with the alignment agent is induced by light or other means as will be described. As the polymerization reaction progresses, phase separation occurs between the liquid crystal material and the polymer/alignment agent. This is known as polymerization-induced phase separation. In particular, a light transmissive curable polymer layer 40 is formed on the electrode 18 on the substrate 12 adjacent to the light source 32 . On the opposite substrate 12, adjacent to the other electrode 18, a liquid crystal film layer 42 is formed. While phase separation occurs, linearly polarized radiation 38 breaks photosensitive chemical bonds in the prepolymer/polyimide layer and aligns polymer segments in a direction perpendicular to the polarization direction of the linearly polarized radiation. Additionally, depending on the chemical nature of the material, the rays 38 can direct polymer segments parallel or perpendicular to the substrate, or crosslink the polymer material in a specific direction parallel to the substrate. This promotes alignment of the liquid crystal film layer 42 at the interface 44 between the polymer layer 40 and the liquid crystal layer 42 . At interface 44, the liquid crystal appears to characterize the compatibilizing anchors in an aligned state during phase separation. It is also believed that only a very small amount of polyimide material is capable of adhering to the opposing substrate and mimicking the aligned orientation of interface 44 . A separate and distinct alignment layer may be provided on the substrate opposite interface 44, if desired.

As shown in FIG. 2 , the thickness of the polymer layer is represented by dimension 52 and the thickness of the liquid crystal layer is represented by dimension 54 . The physical parameters of the liquid crystal film, such as thickness, alignment state and liquid crystal material, can be selected according to the desired target by adjusting the composition and by fixing the cell gap by adopting an appropriate distance. Uniformly aligned elements employing nematic liquid crystals have been produced by the method of the present invention. In addition, ferroelectric and antiferroelectric liquid crystals are found in this structure with gray scale and even bistability. These cells have a much lower threshold voltage, have little light scattering (no haze), and are mechanically and electrically stable. Certain liquid crystal materials show improved electro-optical (E0) properties in phase-separated composite organic films. Optically controllable birefringent devices can also be generated using this approach. This approach makes it possible to fabricate uniform, very thin liquid crystal films. Several uniform films of thickness comparable to the wavelength of red light have been produced using this method of the invention.

Those skilled in the art will appreciate that phase separation can be accomplished in the practice of the present invention through the use of thermally induced, chemically induced or solvent induced techniques. Either of these techniques can be used in conjunction with irradiation to allow simultaneous phase separation and photoalignment. While not wishing to be bound by theory, it is believed that polarized light plays a decisive role in aligning the liquid crystal material at interfaces 44 and 46 in a uniform manner.

Prepolymers suitable for the practice of the present invention are photopolymerizable monomers which are sensitive to the polarization direction of ultraviolet light such that when they are irradiated with ultraviolet light, there is directional polymerization of the monomer and macroscopic alignment of the polymer Simultaneously. If eg a chromophore component is added, it is possible to use prepolymers which are generally insensitive to polarized UV light. Thus, suitable prepolymers include, but are not limited to, NOA65 (available from Norland Products), vinyl ethers, acrylates, epoxies, diacetylenes, polyethylenes, and the like. As the chromophore, materials such as azobenzene, stilbene, cinnamate, chalcone, coumarin, bismaleimide and the like can be used. Usable polyimides are homo- or co-polyimides with side chains having low absorbance, and include SE1180, 610 (commercially available from Nissan Chemical Ind.) and having a chromophore incorporated therein functional groups.

Depending on the type of light modulating device required, the choice of liquid crystal material can be made. Suitable liquid crystal materials include, but are not limited to, nematic, ferroelectric, antiferroelectric, cholesteric and related liquid crystal materials.

As described above, by using the method of the present invention, it is possible to prepare polymer films parallel to each other and aligned liquid crystal films in one cell or on one substrate. Referring now to FIG. 3 , it can be seen that means for carrying out the one-step or multi-step process of the present invention are indicated generally at 60 . When thermally induced polymerization is used, the device may be sealed within heat source 62 . Heat from light source 32 may also be used, if appropriate.

In one embodiment of the one-step process as described above, a mixture of reactive liquid crystalline monomers, photosensitive monomers and low temperature curing polyimides is formulated for the preparation of anisotropic films. Reactive liquid crystal monomers may be selected from nematic diacrylate monomers and chiral diacrylate dopants having acrylate polymerizable groups. Photosensitive monomers such as NOA-65 and low temperature curing polyimides such as SE-1180 are mixed with reactive liquid crystal monomers to form photosensitive materials. This mixture was spin coated onto a substrate. As shown in FIG. 2 , light 34 emitted by an ultraviolet source 32 passes through a linear polarizer 36 . Linearly polarized light 38 passes through substrate 12 and electrode 18 and irradiates the coating mixture. UV light polarized at the interface 44 induces a simultaneous phase separation and alignment of the reactive liquid crystal monomers. The one-step process of the present invention produces alignment of the liquid crystal without a separate alignment layer at interface 46, thus eliminating the need for additional spin-coating and rubbing steps.

Likewise, the reactive liquid crystal monomer may be selected from nematic diepoxy monomers and chiral diepoxy dopants having epoxy polymerizable groups. Photosensitive monomers, photoinitiators and low-temperature curing polyimides are mixed with reactive epoxy-type monomers. This mixture was spin coated on a substrate and irradiated as described above. Polarized UV irradiation leads to simultaneous phase separation and photoalignment.

The one-step process discussed above is believed to be the most effective and efficient at forming uniformly aligned liquid crystal devices without separate and distinct alignment layers. Other methods described above, such as those using light radiation, heat, and/or solvent evaporation, can be implemented based on the above and also achieve substantially the same results.

In another example of the one-step process, a photocrosslinkable polyimide containing functional pendant groups such as cinnamate or coumarin was prepared and spin-coated on a substrate. Then reactive liquid crystal monomers, such as liquid crystal diacrylate, divinyl ether, diepoxy, liquid crystal diacetylene or other monomers with difunctionality or more, and photoinitiators are spin-coated on the polyamide imine film. Subsequent polarized UV radiation results in simultaneous photoalignment and photopolymerization. Spin-coating reactive liquid crystal monomers on the polyimide layer before the polyimide has cured may make the surface slightly non-uniform, but does not interfere with the alignment of the liquid crystal material.

Multiple steps may be used when multiple alignments of liquid crystal materials are desired. "Multi-step process" refers to a process in which a substrate is coated and treated in a single step to produce an aligned layer and/or layer/microstructure of liquid crystal material, which is then re-spun on a previously applied layer. Apply several coats and reprocess with one or more steps of treatment as described above, for example visible or ultraviolet radiation, radiation combined with heat treatment or radiation combined with solvent evaporation. The multi-step method includes the sequential application of at least two material application steps, wherein at least one type of material is applied during each step. More specifically, by using the multi-step method of the present invention, a single aligned liquid crystal material interface of different layers or microstructures can be obtained. Additionally, a mask 70 with appropriate openings as shown in FIG. 4 can be placed between the polarizer and the substrate, and can be repositioned at various stages to assist in the creation of aligned and electrically controllable microstructures 72 .

In general, Figure 3 shows an example of a structure obtained by using the multi-step process of the present invention. It can be seen that the electrode layer 18 can be arranged adjacent to the substrate 12, with layers of alignment-inducing polymers with liquid crystal material, as described in the one-step process, placed on the electrode layer.

A multi-step approach can be used when it is desired to provide liquid crystal orientation with different properties at the interface between the liquid crystal material and adjoining layers or microstructures of different materials, such as polymer layers or configurations doped with polyimide, Substrate or equivalent membrane. Alternatively, an anisotropic film can be formed using a multi-step process in which a material forming an alignment layer is first coated on a substrate and another material comprising a liquid crystal material, a prepolymer, and an alignment agent is coated. on the former material. These materials are then phase separated and photoaligned to form an anisotropic film. At a minimum, the end result of the multi-step process provides at least one aligned interface layer 63 adjacent to the substrate 12 and a liquid crystal layer 66 adjacent to the interface layer 63 . In addition, a second alignment interface layer 68 adjacent to the liquid crystal layer 66 may also be formed. The multi-step process enables the second alignment interface layer to impart a different orientation to the liquid crystal layer 66 than the first alignment interface layer 63 . It is envisioned that the multi-step approach will be extremely useful in constructing twisted nematic devices, super twisted nematic devices, optically or electrically controllable birefringent devices, or any device in which the orientation of the liquid crystal material needs to be changed. The materials making up layers 63, 66 and 68 can be applied or formed in various combinations depending on the ultimate needs. It will also be appreciated that multi-step methods can be used to form anisotropic films that cannot be formed by other methods. The advantage of this method is that the film can be formed without having to spin coat the material twice. Typically, the prototype of the device is subjected to a treatment selected from the group consisting of using qualitatively different polarized wavelengths of ultraviolet light, using qualitatively different polarized wavelengths of visible light, using polarized ultraviolet light and polarized visible light, simultaneous visible radiation and heating, simultaneous UV radiation and solvent evaporation, and UV radiation. Various examples of the multi-step method and devices obtained therefrom will now be discussed.

In one example of a multi-step process, an azobenzene liquid crystal polymer (LCP) is spin-coated on a substrate. Reactive monomers such as liquid crystal diacrylate, divinyl ether, diepoxy, liquid crystal diacetylene or other monomers with difunctionality or more functionality and suitable photoinitiators are coated on the azobenzene LCP film of the top. Subsequent use of polarized ultraviolet radiation results in simultaneous photoalignment and photopolymerization to form layers 63 and 66 . The second spin coating may make the surface of the first film slightly uneven, but it will not cause alignment problems.

In another example of a multi-step process, a photosensitive monomer such as NOA65 and a polyimide containing a chromophore material are mixed and coated on a substrate. Irradiation of the coated substrate with linearly polarized ultraviolet light causes periodic undulations of the polymer surface to form layer 63 . A reactive liquid crystal monomer is spin-coated on the polymer surface and polymerized by UV irradiation. An anisotropic film was obtained as a result.

In another example of a multi-step process, a first mixture comprising vinyl ether, photoinitiator, and polyimide with a chromophore component is spin-coated Microns of linearly polarized UV irradiation. A second mixture comprising an acrylate, a photoinitiator, and a polyimide with a chromophore is spin-coated on the first coating and irradiated with linearly polarized ultraviolet light having a wavelength, eg, greater than or equal to about 350 nanometers. It will be appreciated that either the first or the second mixture may be added to the desired liquid crystal material. In addition, the orientation of linear polarizer 36 after the first exposure of the first material can be changed as desired to obtain the desired second orientation. Also, the choice of light wavelength depends on the chosen chromophore/photoalignment material. Depending on which mixture contains liquid crystal material, the position of the light source 32 can be adjusted accordingly. The result is a multi-layer anisotropic film in which each layer is oriented separately and uniformly, which is useful for optical compensation and display devices requiring a change of orientation at substrate surfaces of different properties. Those skilled in the art will know that these mixtures can be applied and processed in reverse order. In other words, the layers can be applied successively and irradiated with ultraviolet light. Alternatively, a single layer can be applied, using UV radiation, and then a second layer can be applied using UV radiation.

Likewise, by selecting the appropriate combination of ingredients, several coated substrates can be fabricated using the multi-step process of the present invention, in which one layer comprises vinyl ether, photoinitiator and polyimide with chromophore and as discussed above treated with ultraviolet radiation in the same manner, while the second layer comprises acrylate and polyimide with chromophores and is treated with visible radiation. In order for a material to polymerize and align, it should be sensitive to visible light, so a sufficient amount of at least about 1% maleimide is added to the mixture. As a result, the mixture is irradiated with visible light having a wavelength, for example, greater than or equal to 410 nanometers. As above, the liquid crystal material can be either in the first mixture or in the second mixture. Of course, the polarization direction can be changed to change the orientation of the liquid crystal material as needed. This multi-step process has been used to fabricate retardation films as well as other electro-optic elements.

In another embodiment of the multi-step process of the present invention, a first layer comprising epoxy monomer and curing agent is coated on a substrate and heat treated to induce polymerization. A second layer comprising UV-curable monomers, a photoinitiator, and polyimide for photo-alignment is coated on the first layer and irradiated with linearly polarized UV rays. These layers can be applied in reverse order if desired. If so, polyimide with chromophores will be included in the layer formed by heat treatment. As above, the liquid crystal material may be included in the mixture of the first layer or in the mixture of the second layer. These devices provide qualitatively different liquid crystal orientations for optical retardation, optical compensation, and adjustable optical retardation.

In yet another embodiment, a first layer comprising a reactive liquid crystal monomer, a photoinitiator, and a polyimide is coated on a substrate and irradiated with linearly polarized visible light as described above. A second layer comprising epoxy resin and curing agent is coated over the first layer and heating as described above induces solvent-induced phase separation of the second layer. The layers can also be operated on in reverse order if desired.

Likewise, thermally induced phase separation can be used in the multi-step process of the present invention. The layer comprising polymethyl methacrylate (PMMA) and reactive liquid crystal monomers can be deposited before or after irradiation of the layer with ultraviolet or visible light. If UV light is used, prepolymers such as polymethyl methacrylate or polyimide are used together with reactive monomers, UV photoinitiators and liquid crystal materials. If visible light is used, the UV initiator is replaced by a visible light initiator.

Those skilled in the art will appreciate that the advantages of the present invention are numerous. First, the light modulating device of the present invention can be used in optically and electrically controllable devices. The disclosed method to manufacture an alignment liquid crystal device without a separately formed alignment layer in a single ultraviolet irradiation step is simpler and more cost-effective, and can be used in place of known methods for the manufacture of any Currently, liquid crystal devices using alignment layers are used. Elimination of the rubbing process reduces damage to the device and increases manufacturing yield. Elimination of the high temperature baking process used in the prior art allows the use of plastic substrates.

The method of the present invention is very flexible and can be used with nematic, ferroelectric, antiferroelectric and cholesteric liquid crystal materials, just to name a few. The method of the present invention can be used to make multilayer anisotropic films in which each layer has a separate and unique orientation. By adjusting the angle of incidence of the radiation, a molecular pretilt can be obtained in the liquid crystal layer. Patterned microstructures using a mask during application of UV or visible light can be used to fabricate active devices or any device that can be switched optically, electrically, or that is sensitive to external mechanical forces. Furthermore, the methods described by this disclosure are applicable to any liquid crystal device requiring alignment.

Thus, it can be seen that the structures and methods of use presented above have achieved the objects of the present invention. While only the best mode and preferred embodiments have been shown and described in detail in accordance with the patent statutes, it is to be understood that the invention is not limited thereto and is not thereby limited. For that reason, reference should be made to the following claims for an appreciation of the true scope and breadth of the present invention.

Claims (29)

1. A method for manufacturing an organic membrane that simultaneously completes phase separation and alignment, comprising: Preparation of mixtures of liquid crystals, prepolymers and polarization sensitive materials; applying said mixture to a substrate; and Application of polarized light by the light source causes simultaneous phase separation of the mixture and alignment of the phase-separated liquid crystals, thereby forming a uniformly aligned layer of liquid crystal material that is compatible with the polymer on the substrate and The layers of polarization sensitive material are contiguous. 2. The method according to claim 1, further comprising: A second substrate is applied over said layer. 3. The method according to claim 1, wherein said step of applying radiation causes at least a major portion of said polarization sensitive material to be mixed with said prepolymer, said polarization sensitive material imparting to said liquid crystal material quasi-arrangement properties. 4. The method according to claim 1, further comprising: A polarizer is interposed between the light source and the substrate to impart the desired alignment to the liquid crystal material. 5. The method according to claim 4, further comprising: An ultraviolet light source is provided on a side adjacent to the substrate and opposite to the side on which the mixture is applied. 6. The method according to claim 4, further comprising: A visible light source is provided on a side adjacent to the substrate opposite to the side on which the mixture is applied. 7. The method according to claim 1, further comprising: preparing an initial mixture of an initial prepolymer and an initial polarization sensitive material; and The initial mixture is coated on the substrate prior to the coating step. 8. A method according to claim 7, wherein said initial polarization sensitive material is sensitive to a different wavelength of light than said polarization sensitive material. 9. The method according to claim 8, further comprising: Initially polarized light is applied to said initial mixture prior to said coating step to impart an aligned orientation thereto. 10. The method according to claim 8, further comprising: Initially polarized light is applied to said initial mixture after said coating step to impart an aligned orientation thereto. 11. The method according to claim 10, further comprising: A mask and a polarizer are placed between the light source and the substrate prior to the step of applying irradiation to form the liquid crystal layer with microstructures. 12. The method according to claim 11, further comprising: Another mask is placed between the light source and the substrate after the initial irradiation step. 13. The method of claim 7, wherein said initial polarization sensitive material and said polarizing material are activated by ultraviolet or visible light. 14. The method according to claim 1, further comprising: preparing said mixture with at least a heat-activated prepolymer; and The mixture is thermally activated to induce phase separation and to impart an aligned orientation to the liquid crystals. 15. The method according to claim 14, wherein said polarized light is visible light or ultraviolet light. 16. The method according to claim 1, further comprising: preparing said mixture with epoxy and resin; and The mixture is subjected to phase separation to induce phase separation of the mixture and to impart an aligned orientation to the liquid crystals. 17. The method according to claim 16, wherein said polarized light is visible light or ultraviolet light. 18. The method according to claim 1, further comprising: A mask and a polarizer are placed between the light source and the substrate prior to the step of applying irradiation to form the liquid crystal layer with microstructures. 19. A method of manufacturing a liquid crystal device with alignment properties, comprising: provide a base; providing a first mixture comprising at least a first polarization sensitizer and a prepolymer; providing a second mixture comprising at least a second polarization sensitizer and a prepolymer; mixing liquid crystals into the first mixture or the second mixture; coating said first mixture on said substrate; coating said second mixture on top of said first mixture; Initiating a process on said first mixture by a method selected from at least including visible light polarization, ultraviolet polarization, thermal induction, chemical induction and solvent induction; Initiating a process on said second mixture by a method selected from the group consisting of at least visible light polarization, ultraviolet polarization, thermal induction, chemical induction, and solvent induction; and The process imparts a directional alignment to the liquid crystals. 20. The method according to claim 19, wherein at least one of said initiating steps comprises simultaneously using a kind of said polarization method and a kind of said induction method so as to phase-separate said prepolymer from said prepolymer. the liquid crystal described above. 21. The method according to claim 19, further comprising: The first and second mixtures are sandwiched between the second substrate and the first substrate, so that the second substrate is fixed to the first substrate. 22. The method according to claim 19, wherein said polarization method comprises: positioning a light source proximate to said substrate; and A polarizer is placed between the base and the light source. 23. The method according to claim 19, further comprising: Repositioning of said polarizers after said first activation step wherein said polarization sensitizers impart alignment of different orientations at their respective interfaces with said liquid crystals. 24. The method according to claim 17, wherein said inducing process phase separates said prepolymer and said polarization sensitizer from said liquid crystal. 25. A unit with aligned properties comprising: at least one substrate; and a mixture coated on said substrate, said mixture comprising at least a liquid crystal material, a prepolymer material and a polarization-sensitive material, wherein simultaneous polymerization and application of polarized light cause phase separation and optical alignment of said mixture, The polymeric microstructure that imparts the alignment properties to the liquid crystal material is thus formed. 26. The unit according to claim 25, further comprising: Before applying said first mixture, a second mixture is coated on said substrate, said second mixture comprising at least a second polarization-sensitive material, wherein application of polarized light imparts said The liquid crystal material having the alignment property of said second mixture undergoes optical alignment. 27. A cell according to claim 26, wherein between said liquid crystal material and said polymeric microstructure and said polarization sensitive material and between said liquid crystal material and said second polarization sensitive material Different and independent interfaces are formed between them. 28. A device according to claim 27, wherein said interface aligns said liquid crystal material in qualitatively different orientations. 29. A device according to claim 28, wherein said liquid crystal material forms a microstructure.

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