JPH0792438A - Liquid crystal composite optical element - Google Patents

Abstract

PURPOSE:To constitute a light controllable element, display element, recording element, etc., having novel performance by imparting a memory characteristic capable of maintaining a light scattering characteristic of light even after removal of an electric field or magnetic field to the liquid crystal composite optical element which is formed by dispersing liquid crystals into a resin matrix and is changed in the scattering characteristic described above by electricity, magnetism, heat, etc., and changing the light scattering characteristic of the light. CONSTITUTION:Writing and erasing, etc., are executed with this element by utilizing the memory effect of liquid crystal molecule orientation at the boundary between the resin matrix and the liquid crystals by a phase transition to a liquid crystal phase from a temp. higher than the temp. at which the liquid crystals cause the phase transition to an isotropic liquid in the state of applying an electric field or magnetic field thereto and by utilizing the effect that the memory effect is erased by heating to a temp. higher than the temp. at which the liquid crystals the phase transition to the isotropic liquid after the electric field or the magnetic field is removed. The light controllable element, etc., having the transmission characteristic only in the diagonal direction are possible as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composite optical element in which a liquid crystal is dispersed in a resin matrix and the transmission / scattering characteristics of light can be changed by electricity, magnetism, heat or the like. The present invention relates to a dimming element, a display element, and a recording element, which have memory characteristics capable of retaining characteristics and have the purpose of changing the transmission and scattering characteristics of light.

[0002]

2. Description of the Related Art Heretofore, a composite element of liquid crystal and resin in which liquid crystal is dispersed in a resin matrix has been disclosed as a display device or a light control device. This composite element of liquid crystal and resin has a structure in which a large number of nematic liquid crystal droplets having a refractive index corresponding to the ordinary ray component of the liquid crystal close to the refractive index of the resin are dispersed in the resin matrix, or likewise a mesh resin. It has a structure in which a material containing liquid crystal in a matrix is sandwiched between a plastic film or a glass plate having a transparent electrode. In the composite element in which liquid crystal is dispersed in this resin matrix, the alignment direction of the liquid crystal molecules is irregular when no electric field is applied, so the effective refractive index of the liquid crystal part and the refractive index of the resin part differ, and the interface The light is scattered and appears cloudy, but when an electric field higher than the threshold electric field is applied, the alignment direction of the liquid crystal molecules is aligned with the electric field direction, and the effective refractive index of the liquid crystal part is close to that of the resin part. Therefore, the light scattering effect is reduced and the light transmission state is achieved. In particular, a display device or dimmer using a composite element in which a liquid crystal is dispersed in a resin matrix using a plastic film with a transparent electrode can easily have a large area, and can be flexibly and freely bent. It has the characteristic of having flexibility that allows

However, in the liquid crystal element of the composite element in which the liquid crystal is dispersed in the above resin matrix, the light transmission state can be maintained only while the electric field is applied,
When the electric field is removed, it returns to the initial light-scattering state, so it does not exhibit a memory effect of maintaining the light-transmitting state even after the electric field is removed. There is a problem that recording, displaying, and erasing cannot be performed. As a solution to this problem, in a liquid crystal element including a composite element in which liquid crystal is dispersed in a resin matrix, a memory effect in which a light transmission state is maintained even after removal of an applied electric field is, for example, the 37th Applied Physics Association. Lecture Proceedings Collection 30aB
1 (March 1990) and Japanese Journal
al of Applied Physics Vo
l. 30, No. 4, p. 616 (April 1991)
Etc.

Further, a liquid crystal element for applying an electric field and thermally writing, displaying and erasing is also known. These liquid crystal elements include those that utilize the cholesteric-nematic phase transition effect, those that utilize the supercooling phenomenon in nematic liquid crystals, and those that use smectic liquid crystals, all of which are used in ordinary liquid crystal display elements. Similar to the liquid crystal cell, it has a structure in which a liquid crystal material is sandwiched between glass plates provided with matrix-shaped or segment-shaped transparent electrodes.

On the other hand, those which perform writing or recording thermally have a coloring or discoloring action due to thermal decomposition or sublimation, or react with a reagent or the like to change their optical absorptivity or reflectance. Thermal paper is used in which the surface of the paper is coated with a substance that is used.There is a method in which the surface of the thermal paper is locally heated by a thermal head or the like to generate color or change its hue, and it is widely used. ing.

[0006]

However, there is a problem that a sufficient light transmission state cannot be obtained by the memory effect simply by applying an electric field or a magnetic field to the composite element of the liquid crystal and the resin matrix made of the liquid crystal and the resin material. there were.
Further, in the light control element including the liquid crystal and the resin matrix composite element, only by switching the light scattering and the transmission state such as white turbidity in the direction perpendicular to the element, the element has the light control function in the oblique direction. There is a problem that it is difficult to construct such a thing.

On the other hand, in a liquid crystal device for applying an electric field and thermally writing, displaying, and erasing using a cholesteric-nematic phase transition liquid crystal, a nematic liquid crystal, a smectic liquid crystal, or the like, the thickness of a liquid crystal layer, that is, a glass having a transparent electrode attached thereto. The distance between the plates or plastic plates must be kept constant at all times, and if stress or strain is applied to the glass plate or plastic plate with transparent electrodes, the alignment state of liquid crystal molecules will change and the characteristics will deteriorate. Moreover, there is a problem that it cannot be bent freely like paper.

Further, the thermal paper on which writing and recording are performed cannot be used only once because it is not possible to erase what has been written and recorded once, or to erase a part and then write again. There was a problem.

The present invention has been made to solve the above problems, and has a memory characteristic capable of retaining the characteristic even after the external field is removed, and writing, recording, displaying, and erasing can be performed any number of times. An object of the present invention is to obtain a liquid crystal composite optical element that can be repeatedly performed and a light control element having a function of adjusting light in an oblique direction.

[0010]

A liquid crystal composite optical element according to the present invention is an element in which a liquid crystal is dispersed in a resin matrix, and the liquid crystal undergoes a phase transition to an isotropic liquid under an electric field or magnetic field. It is characterized by utilizing a memory effect of liquid crystal molecule alignment at an interface between a resin matrix and liquid crystal by causing a phase transition from a temperature higher than a temperature to a liquid crystal phase, wherein the liquid crystal is isotropic after removing an electric field or a magnetic field. At least writing and erasing or at least one of writing and erasing can be performed by utilizing the effect that the memory effect is erased by heating at a temperature higher than the temperature at which the liquid crystal undergoes a phase transition. It is also possible to sandwich an optical element, and a transparent conductive film can be attached to the plastic film described above, and the transparent conductive film can be attached to the liquid crystal composite optical element. It is also possible to utilize the memory effect of the liquid crystal molecular alignment while applying an electric field or magnetic field is inclined from the vertical direction Te.

[0011]

According to the present invention, in a composite element including a liquid crystal material and a resin material, a phase transition from a temperature equal to or higher than the phase transition temperature of liquid crystal to an isotropic liquid to a liquid crystal phase while applying an electric field or a magnetic field causes an external field By utilizing the memory effect of the liquid crystal molecule orientation and the memory erasing effect at the interface between the polymer resin material and the liquid crystal material, which can maintain its characteristics even after removing the light, the liquid crystal resin matrix composite element has a dimming function, and Writing, recording, displaying, and erasing are performed.

[0012]

EXAMPLE An element is formed by sandwiching a liquid crystal and a resin matrix composite element, which is composed of a liquid crystal material and a resin material and has liquid crystal dispersed in a resin matrix, between a plastic film or a glass plate having a transparent electrode. For example, an epoxy resin, a curing material, and a nematic liquid crystal E7 are mixed in a weight ratio of 1: 1: 1, and sandwiched between glass plates provided with ITO transparent electrodes using a spacer having a thickness of 20 μm to produce an element. As shown in FIG. 2, when the electric field larger than the threshold value is not applied, the orientation direction of the liquid crystal molecules is irregular, so that the refractive index of the liquid crystal part and the refractive index of the resin matrix part are different. Since light is scattered at the interface, the light transmittance is low and it looks cloudy,
When an electric field that is sufficiently higher than the threshold electric field is applied, the alignment direction of the liquid crystal molecules is aligned with the electric field direction, and the effective refractive index of the liquid crystal part becomes a value close to that of the resin matrix part, so the light scattering effect decreases. It becomes a light transmission state.

By the way, in such a composite element of liquid crystal and resin matrix, by selecting a combination of liquid crystal and resin matrix material, the light transmission state can be maintained even after the electric field is removed as shown in FIG. This electroless light transmission state can be returned to the original light scattering state by heating above the phase transition temperature from the liquid crystal state to the isotropic liquid. That is, when the liquid crystal and the resin matrix composite element are heated once and then returned to room temperature, the whole becomes cloudy, and then writing, recording, and the like can be performed by applying an electric field only to a portion to be displayed. . In this case, it can be erased by heating again. On the other hand, it is also possible to apply an electric field evenly to the element to bring it into a light transmitting state and then locally heat only the portion to be displayed so that it becomes clouded for writing and recording. In this case, it is possible to erase from the recorded and displayed state by applying an electric field.
Since the written / recorded or erased state is maintained for a long time without applying an electric field, display can be performed. A similar memory effect can be obtained by applying a magnetic field instead of an electric field.

However, simply applying an electric field or a magnetic field in the liquid crystal state does not provide a sufficient memory effect of molecular orientation, and thus it is difficult to obtain a memory state having a high light transmittance. Therefore, in the element in which the liquid crystal is dispersed in the resin matrix, the memory effect can be obtained by causing the liquid crystal phase to change from a temperature higher than the temperature at which the liquid crystal changes to the isotropic liquid in the state where an electric field or a magnetic field is applied. By utilizing the effect of being more prominent, a memory state having a higher light transmittance than that obtained by simply applying an electric field or a magnetic field can be obtained. This memory state can be similarly erased by heating to a temperature higher than the temperature at which the liquid crystal undergoes a phase transition to an isotropic liquid after removing the electric field or magnetic field.

Embodiments of the present invention will be described below. The UV curable resin material INC-90 and the nematic liquid crystal E7 are mixed at a weight ratio of 1: 1 and sandwiched between glass plates or plastic films with transparent electrodes ITO using spacers having a thickness of about 20 microns. Ultraviolet rays were irradiated to polymerize the resin material to prepare a liquid crystal and resin matrix composite element. In this liquid crystal / resin matrix composite element, when no voltage is applied, the light transmittance is about 1%, and most of the light is scattered, so that the liquid crystal appears opaque, but the temperature at which the liquid crystal E7 undergoes a phase transition to an isotropic liquid By applying a phase transition to a liquid crystal phase at a high temperature, for example, a voltage of about 80 ° C. to a voltage higher than about 30 V is applied, the temperature of FIG.
As shown in FIG. 5, a light transmittance of about 40% can be obtained. This transmittance is about twice as high as the light transmittance of 20% in the memory state when a voltage of about 150 V is applied in the nematic liquid crystal state shown in FIG. 3, which is necessary for the memory. Lower voltages are also sufficient. In addition, the light transmission state after removing the voltage of about 40%, that is, the memory state, returns to the original light scattering state by heating the element to a temperature higher than the phase transition temperature of the liquid crystal, for example, higher than about 80 ° C. Such repetition can be performed.

A liquid crystal and a resin matrix composite element having such a memory effect are sandwiched between two plastic films having a transparent electrode such as ITO inside to form a sheet-like element, and a threshold value is applied between the transparent electrodes. When a sufficiently large voltage, for example, a voltage of 50 V is applied to the liquid crystal phase, the temperature of the phase transition to an isotropic liquid, for example, a temperature of about 80 ° C., is changed to a liquid crystal phase. Next, after the voltage is removed, the liquid crystal is locally heated to a temperature not lower than the phase transition temperature of the liquid crystal, for example, 80 ° C. or higher by a thermal head used in a device such as a general-purpose thermal transfer printer or a thermal printer. (Eg room temperature)
When it is set to "0", only the heated area becomes cloudy, and writing can be performed. Since the written state is maintained as it is, recording and display can be performed. In order to erase the recorded and displayed states, a voltage higher than the threshold electric field may be applied between the transparent electrodes to heat the liquid crystal to a temperature at which the liquid crystal is in an isotropic liquid state.

It is also possible to use a sheet-shaped element by sandwiching the liquid crystal and the resin matrix composite element by using two plastic films having no transparent electrode such as ITO. In this case, erasing can be performed by applying an electric field from the outside through a plastic film and heating to a liquid crystal state so that a sufficiently large electric field is effectively applied to the layers of the liquid crystal and the resin matrix composite element.
Also, after heating the sheet-shaped element once to a temperature at which it becomes an isotropic liquid state or more and then cooling it to a light-scattering state, a plastic film is formed using a needle-shaped electrode and a heating device capable of locally heating. While locally heating the liquid crystal and resin matrix composite element from the outside of the device, a voltage is applied to the device so that an electric field above the threshold value is applied, and only the required area is written as a light-transmitting state for writing and displaying. It is also possible to do so. In order to erase the element which has been written, recorded or displayed by heat or an electric field, it can be easily carried out by heating the element to the phase transition temperature or higher. Incidentally, it is of course possible to perform these erasing operations not only over the entire area of the element but also for only a necessary part.

Further, as a heating method, a thermal head used in a general-purpose thermal transfer type printer or a thermal type printer device can be used, but an infrared lamp or an infrared lamp is used for uniform erasing. A heating roller or the like can also be used. Furthermore, it is also possible to perform writing, recording, display, etc. by heating with laser light. When a laser beam is used, the diameter of the light beam can be extremely narrowed, so that high-definition writing can be performed and high-speed writing can also be performed.

A similar memory effect can be obtained by using a magnetic field instead of an electric field. For example, the above resin IN
A composite element consisting of C-90 and nematic liquid crystal E7
A memory state exhibiting a transmittance of about 20% can be obtained by causing a phase transition to a liquid crystal state while applying a magnetic field of 20000 Gauss from ℃. On the other hand, nematic liquid crystal ZLI4758 with negative dielectric anisotropy is mixed in a weight ratio of 1: 1 and sandwiched between glass plates or plastic films with transparent electrode ITO attached using spacers of about 20 microns and irradiated with ultraviolet rays. Then, the resin material was polymerized to fabricate a liquid crystal and resin matrix composite element. In this liquid crystal / resin matrix composite element, when no voltage is applied, the light transmittance is about 1%, and most of the light is scattered so that the liquid crystal appears cloudy, but it is more than the temperature at which the liquid crystal ZLI4758 undergoes a phase transition to an isotropic liquid. High temperature, for example, from 90 ℃ to 200
A memory state exhibiting a transmittance of about 25% can be obtained by causing a phase transition to a liquid crystal state while applying a magnetic field of 00 Gauss. Here, comparing the effect of the magnetic field with the effect of the electric field, a magnetic field of 1000 gauss corresponds to an electric field of about 300 volts per cm. Since the liquid crystal ZLI4758 has a negative dielectric anisotropy,
By applying a voltage of about V, the transmissivity from the transparent state is 3% contrary to the conventional liquid crystal resin matrix composite element.
It can be changed to a light scattering state that is cloudy to a certain degree.
Furthermore, when a magnetic field is applied in a direction inclined to the liquid crystal composite element, the element exhibits a transparent characteristic in an oblique direction, and by applying a voltage to this element, a dimming function in an oblique direction with respect to the element. It can also be an optical element having.

[0020]

According to the present invention described above, a thin and light-weight flexible liquid crystal and resin matrix composite element that can be freely bent is used to easily write and record by heating and applying an electric field or a magnetic field. Since operations such as display and erase can be performed and these operations can be repeated any number of times by using the same element, it is extremely economically advantageous and extremely effective in saving resources. is there.
Also, writing, recording, and displaying can be performed using a thermal head, laser, etc. in a general-purpose thermal transfer printer or thermal printer, and can also be used for display devices in word processors, personal computers, facsimiles, etc. Therefore, it is possible to construct a device that records and displays an arbitrary shape, that is, characters, numbers, symbols, images, etc., very easily. Further, it has an unprecedented excellent effect that it can be easily removed after recording or displaying and can be handled like an ordinary printed matter.

Further, it exerts an excellent effect that a transparent state can be changed from a transparent state to a cloudy light scattering state by applying a voltage, and a dimmer element having a transmission characteristic only in an oblique direction can be constructed. To do.

[Brief description of drawings]

FIG. 1 shows the memory effect of the present invention, that is, the state of light transmission changes from an isotropic liquid state to a liquid crystal phase when an electric field is applied to change the state from a light scattering state to a light transmitting state. A graph showing the relationship between the applied voltage and the transmittance in the memory state of the liquid crystal and the resin matrix composite element changing from the light scattering state to the light scattering state, and the transmittance in the memory state by applying and then removing the voltage in the liquid crystal state. 2 is a graph showing the relationship between the applied voltage and the transmittance in the liquid crystal and the resin matrix composite element which does not show the memory effect, and FIG. 3 shows the liquid crystal and the resin matrix composite element which shows the memory effect in which the electric field is gradually applied in the liquid crystal state. 6 is a graph showing the relationship between applied voltage and transmittance when the electric field is gradually removed.

Claims (5)

[Claims] 1. A composite element in which a liquid crystal is dispersed in a resin matrix, wherein a phase transition from a temperature higher than a temperature at which the liquid crystal undergoes a phase transition to an isotropic liquid to a liquid crystal phase under an electric field or magnetic field is applied. A liquid crystal composite optical element characterized by utilizing a memory effect of liquid crystal molecule alignment at an interface between a resin matrix and liquid crystal. 2. The liquid crystal composite optical element according to claim 1, wherein the memory state is erased by heating the liquid crystal to a temperature higher than a temperature at which the liquid crystal undergoes a phase transition to an isotropic liquid after the electric field or the magnetic field is removed. The liquid crystal composite optical element according to claim 1, wherein at least writing and erasing or writing or erasing is performed by utilizing the effect. 3. The liquid crystal composite optical element according to claim 1, wherein a liquid crystal composite optical element in which liquid crystal is dispersed in a resin matrix is sandwiched between plastic films. 4. A liquid crystal composite optical element, comprising a transparent conductive film attached to the plastic film according to claim 3. 5. An electric field or a magnetic field is applied at an angle to the vertical direction of the liquid crystal composite optical element in which liquid crystal is dispersed in a resin matrix, and the electric field or magnetic field is applied. The liquid crystal composite optical element according to claim 4.