JP2019020433A - Dimming film - Google Patents

Abstract

To provide a dimming film using a reverse type liquid crystal element, in which practically enough adhesive strength is ensured from the viewpoint of handling stability during manufacturing or during use of a product.SOLUTION: A dimming film has a dimming layer (liquid crystal layer) capable of switching among two or more levels of haze depending on an applied voltage, held between two transparent substrates having a transparent conductive layer and an alignment layer formed thereon. The alignment layer facing the dimming layer is divided into regions to form a pattern, and the dimming layer (liquid crystal layer) is adhered to the transparent conductive layer that is partially exposed.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a light control film using as a light control layer a liquid crystal element capable of switching the haze to two or more steps according to an applied voltage, and in particular, a transmission scattering type that becomes transparent when no voltage is applied and becomes scattered when voltage is applied. The present invention relates to a light control film using the liquid crystal element as a light control layer.

  As a liquid crystal element using a liquid crystal material, a TN (Twisted Nematic) mode has been put into practical use. In this mode, light is switched by utilizing the optical rotation characteristics of the liquid crystal, and when used as a liquid crystal element, it is necessary to use a polarizing plate. However, the use efficiency of light becomes low by using a polarizing plate. As a liquid crystal element with high light utilization efficiency without using a polarizing plate, there is a liquid crystal element that performs switching between a liquid crystal transmission state (also referred to as a transparent state) and a scattering state. As the liquid crystal element, generally, a polymer dispersed liquid crystal (PDLC) in which liquid crystal molecules are dispersed in a polymer, or a polymer network made of a resin formed in a three-dimensional network. There is known one using a polymer network type liquid crystal (PNLC) having liquid crystal molecules arranged in voids formed in the substrate. In both PDLC and PNLC, part or all of the liquid crystal composition containing a polymerizable compound that is polymerized by ultraviolet rays exhibits liquid crystallinity. And both PDLC and PNLC are manufactured through the process of hardening the said liquid-crystal composition by ultraviolet irradiation, and forming the hardened | cured material composite body of a liquid crystal and a polymeric compound.

  As a technique for switching between a transmission state and a scattering state by a liquid crystal layer, a polymer dispersion type liquid crystal display device in which liquid crystal is dispersed in a polymer is known (for example, Patent Documents 1 and 2). In such a polymer dispersion type liquid crystal display device, by utilizing the difference in refractive index between the liquid crystal and the polymer, the liquid crystal is aligned in the electric field direction (transmission state) and the liquid crystal molecules are in a random direction. (Scattering state) is switched.

  Two types of normal mode and reverse mode are known for the light control film using the liquid crystal element as a light control layer, depending on its usage. The normal mode is a mode in which a transmission state is obtained by applying a voltage and a scattering state is obtained by removing an electric field. The reverse mode is a mode in which a transmission state is obtained when no voltage is applied and a scattering state is obtained when a voltage is applied. As reverse type liquid crystal elements, for example, configurations described in Patent Documents 3 to 5 are known.

  A liquid crystal element having a liquid crystal layer which is a reverse type liquid crystal element and has a liquid crystal layer cured by irradiating ultraviolet rays with an ultraviolet irradiation device, and at least one of the substrates aligns the liquid crystal vertically, for example, It is disclosed in Patent Document 6.

Japanese Patent Laid-Open No. 10-36317 JP 2013-76956 A Japanese Patent No. 2885116 Japanese Patent No. 4132424 Japanese Patent No. 6103108 International Publication No. 2015/022980

  In a reverse type device using PNLC or PDLC, since the liquid crystal must be vertically aligned, a liquid crystal alignment layer (vertical liquid crystal alignment layer) that aligns the liquid crystal vertically is used. Since the vertical liquid crystal alignment layer is a highly hydrophobic film, the adhesion between the liquid crystal layer and the liquid crystal alignment layer is lowered. For this reason, countermeasures have been taken to introduce a large amount of a curing agent for enhancing the adhesion between the liquid crystal layer and the liquid crystal alignment layer in the liquid crystal composition used in the reverse type element. However, when a large amount of curing agent is introduced, the vertical alignment of the liquid crystal is hindered, and the transparency when no voltage is applied and the scattering characteristics when a voltage is applied are greatly reduced. Therefore, when a large amount of the curing agent is introduced, the liquid crystal alignment layer needs to have a high liquid crystal vertical alignment property.

  At present, a liquid crystal alignment layer mainly used industrially uses an organic film made of a polyimide polymer that is excellent in durability and suitable for controlling the pretilt angle of liquid crystal. As the polyimide polymer, polyamic acid which is a polyimide precursor, polyimide obtained by imidizing polyamic acid, or the like is used. The liquid crystal alignment layer is produced from a liquid crystal alignment treatment agent using these polymers.

  Here, the liquid crystal composition, particularly the polymerizable compound in the liquid crystal composition, has a role of forming a polymer network and obtaining desired optical characteristics. However, this polymerizable compound also has a role as the curing agent, and there is a need for improvement in order to increase the adhesion with the vertical liquid crystal alignment layer more efficiently even with a small introduction amount.

  The present invention provides a light control film using a reverse type liquid crystal element, which has a practically satisfactory adhesion strength in terms of handling stability at the time of manufacture and use of the product. With the goal.

In order to solve the above problems, the light control film according to the present invention is:
In the light control film formed by sandwiching a light control layer capable of switching the haze in two or more stages according to the applied voltage between the two transparent substrates formed with the transparent conductive layer and the alignment layer,
The alignment layer is divided so that an alignment region and a non-alignment region are formed, and the light control layer is polymerized and bonded to the transparent conductive layer partially exposed through the non-alignment region. And

With the light control film using the reverse type liquid crystal element according to the present invention, it is possible to provide a light control film that has a practically satisfactory adhesion strength in terms of handling stability during manufacturing and product use Is done.
That is, the adhesion strength between the light control layer (PNLC or PDLC), the transparent conductive layer, and the transparent film substrate with the alignment layer is sufficiently high without causing deterioration of the transparency when no voltage is applied and the scattering characteristics when the voltage is applied. Provided is a light-controlling film which is secured and has an adhesion which is practically satisfactory in terms of handling stability during production and use of the product.

It is sectional drawing which shows the principal part of the light control film of embodiment of this invention. It is a conceptual diagram which shows the example of patterning of the orientation layer of the light control film of embodiment of this invention. It is a conceptual diagram which shows the example of patterning of the orientation layer of the light control film of embodiment of this invention. It is a conceptual diagram which shows the modification of the patterning of the orientation layer of the light control film of embodiment of this invention. It is a conceptual diagram which shows the modification of the patterning of the orientation layer of the light control film of embodiment of this invention.

Hereinafter, the light control film of the embodiment of the present invention will be described taking the case of PNLC as an example. However, the light control film which concerns on this invention is not limited by the following description. For example, the present invention can be similarly applied to PDLC. For convenience of explanation, there is a case where it is exaggerated and illustrated in a size different from the actual scale.
In the PNLC, when the liquid crystal molecules are irregularly arranged along the network polymer fibers inside the liquid crystal layer, the display becomes opaque (scattering state), and when the liquid crystal molecules are aligned perpendicular to the display surface, The display becomes transparent (transparent state).
In PDLC, a liquid crystal material containing liquid crystal molecules (liquid or capsule-like) is provided in each polymer formed from a cured resin material in a polymer matrix. As the refractive index difference from the polymer matrix changes according to the orientation state, the scattering state / transmission state is modulated.

  The production of a light control film comprising a light control layer by reverse PNLC is generally performed as follows. That is, first, a mixture of a liquid crystal and a photopolymerizable compound (monomer) is sandwiched between a pair of transparent substrates (laminated with a transparent electrode and an alignment layer). Next, the photopolymerizable compound in the liquid crystal is changed into a polymer by photopolymerization by irradiating ultraviolet rays under a certain condition. By photopolymerization and cross-linking, a polymer network having innumerable fine domains (polymer voids) is formed in the liquid crystal.

  FIG. 1 is a cross-sectional view showing a main part of a light control film 1 according to an embodiment of the present invention. The light control film 1 has a light control layer 2. The light control layer 2 is a PNLC type having a polymer network and liquid crystal molecules. A pair of alignment layers 7 a and 7 b are laminated on each surface of the light control layer 2. Transparent conductive films 3a and 3b are laminated on the surface of each alignment layer 7a and 7b located opposite to the light control layer side.

  The light control layer 2 has a behavior in which there is almost no unreacted component in the phase separation, and the polymer network and the liquid crystal region are clearly separated with high purity. In addition, an ideal alignment state can be realized without performing a pretilt alignment process by rubbing the substrate (conductive film), and the liquid crystal molecules are aligned almost uniformly in each domain divided by the polymer network. It will be.

The size of the PNLC domain is as fine as about 1 μm for fine particles (approximately 2 to 10 μm in diameter) in the light diffusion sheet and nematic liquid crystal droplets (generally several μm in diameter) dispersed in PDLC, and Rayleigh scattering. (Wavelength selective scattering) is not incurred, and scattering in a wide wavelength region including at least a visible light region wavelength (400 to 780 nm) is efficiently generated.

  The driving voltage of PNLC generally depends on the structural characteristics of the polymer network (domain size and shape, film thickness of the polymer network, etc.). The structure of the polymer network and the degree of light transmission and scattering obtained In relation, the drive voltage is determined. In order to construct a PNLC in which a sufficient degree of light transmission and scattering can be obtained in a voltage region of 100 V or less, each domain is uniform in size and uniform in size. Thus, it is necessary to form a polymer network. In the present invention, the domain size depending on the polymer network structure is controlled to be 3 μm or less, preferably 2 μm or less, and more preferably about 1 μm.

  The details of the manufacturing method are described in Japanese Patent No. 4387931 by Kyushu Nanotech Optical Co., Ltd. In the embodiment of the present invention, the liquid crystal element (PNLC) to be the light control layer is manufactured in accordance with the process according to the above patent. Is adopted. This process is very effective in designing and manufacturing the above-described “network structure in which the size and the like are controlled”.

  For the transparent substrate 5 constituting the transparent conductive films 3a and 3b, a polyethylene terephthalate (PET) film, a polyethylene (PE) film, a polycarbonate (PC) film, or the like can be used. By using such a resin film as the transparent base material 5, it is rich in flexibility and flexibility. Therefore, there is an advantage that the degree of freedom in handling is high, such as application to a curved surface shape and winding and storing, in addition to use by laminating on flat glass. In the present embodiment, the thickness of the transparent substrate 5 is set to about 50 to 200 μm. Generally, a metal oxide such as ITO is used for the transparent conductive layer 6. However, it is also possible to adopt a low resistance conductive polymer instead of ITO. As the conductive polymer, it is preferable to use a material containing a polyanion doped in a π-conjugated conductive polymer exemplified by PEDOT and PSS.

  The alignment layers 7a and 7b are vertical alignment layers. When no voltage is applied to the light control layer 2, the liquid crystal molecules are aligned so that the longitudinal direction of the liquid crystal molecules is along the normal direction of the alignment layers 7a and 7b. Orient. For this reason, the reverse type light control layer 2 is in a low haze state when no voltage is applied, and the transparency is increased.

  The alignment layers 7a and 7b, which are one of the main features of the present invention, will be described. The alignment layer of the present embodiment is assumed to be an organic film made of a polyimide polymer. Therefore, as described above, the reverse type light control film may cause a decrease in reliability due to low adhesion between the alignment layer and the light control layer. Therefore, in the light control film 1 of the present embodiment, the orientation layers 7a and 7b are patterned as described below, in other words, by selectively removing a part of the region, the adhesion is improved and the reliability is improved. Yes.

  2 and 3 are diagrams showing an example of patterning of the alignment layers 7a and 7b of the present embodiment. Each figure (a) shows alignment layer 7a, and (b) shows alignment layer 7b. The same applies to FIGS. 4 and 5. In each figure, the filled area indicates the oriented area 71 and the blank area indicates the non-oriented area 72. Here, the alignment region 71 refers to a region having a function of positively imparting an alignment effect to the light control layer in the alignment layer. In other words, it can be said that the conventional alignment layer is occupied by the alignment region 71 over the entire area. The non-oriented region 72 is a region where the transparent electrode is exposed in the oriented layer. That is, it can be said that the non-alignment region 72 is a region having less alignment effect on the light control layer than the alignment region 71. For example, the non-orientation region 72 may have a configuration without any orientation effect. As shown in each drawing, in the alignment layer, the alignment regions 71 and the non-alignment regions 72 are alternately arranged continuously with a certain regularity.

  In the above configuration, the light control layer 2 directly contacts the transparent electrode 6 in the non-oriented region 72. In general, the dimming layer 2 has a higher adhesion strength in the relationship with the transparent electrode 6 than in the relationship with the alignment layers 7a and 7b. Therefore, by providing the non-orientation region 72, the light control layer 2 is firmly bonded to the transparent electrode 6 through the orientation layers 7a and 7b. In addition, proper alignment control is performed by the alignment region 71, and normal operation of the liquid crystal is also guaranteed. Here, the adhesion strength and the orientation regulating force are in a trade-off relationship. In the present embodiment, attention is paid to the balance between the adhesion strength and the orientation regulating force. Therefore, as shown in FIGS. 2 and 3, the area ratio of the alignment region 71 and the non-alignment region 72 is approximately 50:50, in other words, the ratio of the non-alignment region 72 per unit area in the alignment layer is 50%. The alignment layers 7a and 7b are designed.

  FIG. 2 shows alignment layers 7a and 7b patterned in a stripe shape. FIG. 3 shows alignment layers 7a and 7b patterned in a checkered pattern. As shown in FIGS. 2A and 2B and FIGS. 3A and 3B, in each alignment layer, the other non-alignment region 72 is formed at a position corresponding to one alignment region 71. . By arranging in this way, the alignment control of the liquid crystal is appropriately secured while achieving reliable adhesion between the respective layers. Here, it is necessary to appropriately design the balance between the alignment regulating force of the liquid crystal molecules having a trade-off relationship and the adhesion strength of the light control film by patterning (selective removal) of the alignment layer. This design is preferably performed from the viewpoints of handling stability and safety at the time of manufacture, construction, and further use of the product.

  As a patterning technique for the alignment layer, a technique exemplified in JP-A-2000-47219 can be employed. Specifically, a resist is formed in a predetermined alignment layer pattern shape, and ashing is performed by irradiating the entire surface of the substrate with ultraviolet rays. Thereafter, by washing the substrate with an alkaline resist stripping solution or the like, the ashed alignment layer and the resist are removed, and the alignment layer is patterned. The above method is merely an example. For example, as a patterning method, a transfer printing method using a printing plate can be employed.

  The above is the embodiment of the present invention. According to the light control film of the embodiment, it is possible to increase the adhesion strength of the light control layer without changing the configuration of the liquid crystal composition by injecting a curing agent or the like into the light control layer. In addition, this invention is not limited to the said embodiment, A deformation | transformation is possible in the range which does not deviate from the main point of this invention.

  For example, in the above-described embodiment, it has been described that the alignment layers 7a and 7b are designed so that the ratio of the non-alignment region 72 per unit area in the alignment layer is 50%. The present invention is not limited to this. The area ratio can be freely changed according to the intended use of the light control film according to the present invention and the specifications required for the adopted product. For example, in a reverse type liquid crystal element, transparency at OFF (no electric field application) is often important. Therefore, the case where priority is given to securing the alignment regulating force (vertical alignment of liquid crystal molecules) by the alignment layer is also assumed. In that case, the area ratio of the alignment region 71 and the non-alignment region 72 in each alignment layer can be set so that the former is higher than the latter. FIG. 4 is a conceptual diagram showing each alignment layer according to a modification in which the area ratio of the non-alignment region to the alignment region is set to be small. Each alignment layer according to the modification shown in FIG. 4 is provided with non-alignment regions 72 that are extremely narrow and intermittent compared to the other examples. In this modification, the ratio of the non-oriented region per unit area is set to about 5%.

  The inventor has a light control film (normal type) that does not have a vertical liquid crystal alignment layer and the liquid crystal is in contact with a transparent electrode, and a light control film that has a vertical liquid crystal alignment layer on the entire surface (conventional reverse type). And tested (peeling test) and evaluated. As a result, with respect to the adhesion strength (unit: N / 25 mm) after the production of the light control film, measurement data is obtained that the latter has about 50 times the strength with respect to the former.

  When the adhesion strength of the light control film 1 of the modification shown in FIG. 4 was measured, measurement data indicating that the strength was about 20 times that of the conventional reverse type adhesion strength was obtained. That is, even in the modification shown in FIG. 4, it was confirmed that the adhesion strength was improved more reliably than the conventional reverse type light control film. However, if the ratio of the non-oriented region per unit area is less than 1%, it is difficult to obtain an effective numerical value as compared with the conventional reverse-type adhesion strength.

  Therefore, as described above, it is preferable to design based on the configuration of the above-described embodiment if the balance between the adhesion strength and the alignment regulating force is conscious and the viewpoint of reducing the burden of manufacturing the alignment film is emphasized. On the other hand, a design based on a modification as shown in FIG.

  Further, in the above-described embodiment, the alignment layer subjected to regular patterning has been described. The light control film according to the present invention is not necessarily a regular alignment layer. For example, as shown in FIG. 5, it is sufficient that at least oriented regions and non-oriented regions are formed alternately. Further, in the light control film according to the present invention, each alignment layer is not necessarily required to have the other non-alignment region 72 formed at a position corresponding to one alignment region 71. For example, as shown in FIG. 5, the other alignment region 71 may be formed at a position corresponding to one alignment region 71.

  The patterning described in the above embodiment is merely an example, and the continuous pattern of the alignment region and the non-alignment region is not limited to these. The boundary line of each region does not need to be linear. As a method for imparting an alignment function to the alignment region of the alignment layer, various well-known techniques can be employed in addition to rubbing and photo-alignment.

DESCRIPTION OF SYMBOLS 1 Light control film 2 Light control layer 3a, 3b Transparent conductive film 5 Transparent base material 6 Transparent electrode 7 Orientation layer

Claims (5)

In the light control film formed by sandwiching a light control layer capable of switching the haze in two or more stages according to the applied voltage between the two transparent substrates formed with the transparent conductive layer and the alignment layer,
The alignment layer is divided so that an alignment region and a non-alignment region are formed, and the light control layer is polymerized and bonded to the transparent conductive layer partially exposed through the non-alignment region. A light control film.   The light control film according to claim 1, wherein the alignment layer has the alignment region and the non-alignment region patterned continuously and alternately.   The light control film according to claim 1, wherein the alignment layer is formed in a striped pattern or a checkered pattern.   The light control film according to any one of claims 1 to 3, wherein a ratio of the non-oriented region per unit area in the oriented layer is 1% or more and 50% or less.   In the light control layer, liquid crystal molecules are arranged in voids of a polymer network formed in a three-dimensional network by photopolymerizing the monomer by irradiating ultraviolet light to a liquid crystal and monomer mixture. The light control film according to any one of claims 1 to 4, wherein the light control film has a structure in which liquid crystal molecules are dispersedly disposed in a polymer matrix.