JPH0546060A - Volume hologram optical film and production thereof and window formed by using this film - Google Patents

Abstract

PURPOSE:To obtain the volume hologram optical film which can be photopolymerized by a long wavelength region of visible light or near IR light. CONSTITUTION:The volume hologram optical film having a layer structure of the refractive index changing periodically with a photopolymn. is obtd. by using a photopolymerized compsn. contg. a photo-radical polymn. initiator consisting of a quaternary ammonium cation and borate anion and radically polymerizable org. compd. and a liquid crystal. The hologram characteristics are more improved particularly if an external field, such as electric field, is impressed to the film at the time of the photopolymn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volume hologram optical film using a photopolymerizable compound, a method for producing the same, and a window using the same.

[0002]

2. Description of the Related Art A volume hologram optical film is known in which layers having different refractive indexes are laminated in layers in a resin film. This is manufactured, for example, by irradiating a light-curing resin with light rays whose phases are aligned from two directions which are not on a straight line to cause interference, and layers having different refractive indexes are laminated in layers.

[Problems to be Solved by the Invention]

In this case, a combination of bisimidazoles and cyclopentanone-2,5-bismethylenes is known as a photopolymerization initiator, but the heat resistance and the light resistance of the obtained volume hologram optical film are not always required. The sex is not excellent. Although conventional photopolymerization initiators have good sensitivity to blue to green light, they have low sensitivity to red to near-infrared light, and volume hologram optical films in these wavelength regions have recently been in increasing demand. Was not suitable for the production of.

[0004]

The present invention has been made to solve the above-mentioned problems, and is capable of radical polymerization with a photo-radical polymerization initiator comprising a quaternary ammonium cation and a borate anion. A photopolymerizable composition containing an organic compound and a liquid crystal as essential components is irradiated with light rays whose phases are aligned from two directions that are not on a straight line, and the photopolymerizable composition is cured by utilizing the interference effect of these two light rays. And a volume hologram optical film characterized by having a layered structure in which the refractive index changes periodically, and by sandwiching the volume hologram optical film between electrodes, a hologram of the hologram can be formed by applying an electric field between the electrodes. A volume hologram optical film with electrodes having variable characteristics, and the use of the volume hologram optical film or the volume hologram optical film with electrodes It is to provide a window to the butterflies.

Further, a photopolymerization composition containing a photoradical polymerization initiator composed of a quaternary ammonium cation and a borate anion, an organic compound capable of radical polymerization and a liquid crystal as essential components is used from two directions not in a straight line. Applying light rays having the same phase, curing the photopolymerizable composition into a layer by utilizing the interference effect of these two light rays, and then completing the curing of the whole, and the refractive index changes periodically. A method for producing a volume hologram film having a layered structure and a liquid crystal and a polymer by applying different external fields in the two curing steps, in which the refractive index is periodic. The present invention provides a method for producing a volume hologram optical film, which comprises producing a volume hologram optical film having a layer structure that changes to the above.

The volume hologram optical film of the present invention comprises
A layer having a high refractive index and a layer having a low refractive index are repeatedly laminated. Of course, the layer having a high refractive index and the layer having a low refractive index may be completely separated, but usually the refractive index gradually changes.

In the present invention, a photoradical polymerization initiator comprising a quaternary ammonium cation and a borate anion is used as the photopolymerization initiator. The quaternary ammonium cation may have absorption from visible light to near infrared. In this case, visible light to near-infrared light enables polymerization. Four
Examples of the quaternary ammonium cation include cyanine aminium and immonium dyes. Specific cations include the following cations.

[0008]

[Chemical 1]

The borate anion is represented by the following general formula (1). In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently an alkyl group, aryl group, alkylarylene group, arylalkylene group, allyl group, alkenyl group, alkynyl group, alicyclic and saturated or Represents an unsaturated heterocyclic group, wherein at least one of R ₁ , R ₂ , R ₃ and R ₄ has a carbon number
It is an alkyl group having 1 to 8 or an aryl alkylene having 7 to 16 carbon atoms.

[0010]

[Chemical 2]

Of these, preferred borate anions are:
It is decomposed by light into triallylboron and alkyl radicals or arylalkyl radicals. These include, for example, triphenylbutylborate anion, trianisylbutylborate anion, and the like.

These photo-radical polymerization initiators may be used in combination with N, N-dialkylaniline capable of absorbing oxygen in the radical polymerization process, ammonium salts of organic boron,
For example, tetrabutylammonium butyl triphosphate or the like may be used in combination to accelerate the decomposition.

The radically polymerizable organic compound used in the present invention may be a conventional radically polymerizable ethylenically unsaturated compound. A typical compound is an acrylic photopolymerizable compound. For example, various acrylate monomers and acrylate oligomers are mixed and used.

The liquid crystal used in the present invention is a nematic liquid crystal,
A smectic liquid crystal or the like can be used, and any liquid crystal having a different refractive index in a different alignment state can be used. Further, usually, several kinds of liquid crystal materials and non-liquid crystal materials having a liquid crystal-like structure are mixed to obtain a desired refractive index anisotropy, dielectric anisotropy, temperature range exhibiting liquid crystallinity, threshold voltage, etc. Used as a composition.

When an electric field is applied by being sandwiched between substrates with electrodes, a combination of a nematic liquid crystal having a positive dielectric anisotropy and a radical-polymerizable organic compound (monomer, oligomer, etc.) is particularly preferable. The refractive index (n _p ) of the polymer (including other solid substances described later) is the ordinary refractive index (n _o ) or extraordinary optical refraction of the liquid crystal used. It is preferable that the rate (n _e ) is substantially the same. In particular, it is preferable that the refractive index (n _o ) of the liquid crystal is approximately the same.

In the present invention, in order to further facilitate the formation of holograms, a polymeric binder soluble in a mixed liquid of a heat-polymerizable monomer and an uncured product may be used together. Examples of the polymeric binder include polyvinyl acetate, polyvinyl butyral, polyacrylic acid ester and the like. In addition to this, viscosity modifier, colorant,
You may add additives, such as a pigment.

In the present invention, the liquid crystal is usually 10 wt% in the total composition.
~ 75wt% This is because if it is less than 10 wt%, the advantage of mixing liquid crystal is not fully utilized, and if it exceeds 75 wt%, it becomes difficult to maintain the film shape. More preferably, 20 wt%
~ 70wt%

In the present invention, a photopolymerization composition containing the photoradical polymerization initiator, the radically polymerizable organic compound and liquid crystal as essential components is used. As a first step, 1
Light rays whose phases are aligned from two directions which are not on a straight line are applied, and the photopolymerization composition is cured into a layer by utilizing the interference effect of these two light rays. Then, as a second step, the entire curing is completed by light or heat. As a result, a volume hologram optical film having a layered structure whose refractive index changes periodically is manufactured.

In the present invention, it is preferable to apply an external field such as an electric field or a magnetic field for aligning the liquid crystal in a specific direction during any one of the two curing steps. Of course, an external field that produces different orientations may be applied to both steps.
This makes it possible to manufacture a volume hologram optical film having a layer structure composed of a liquid crystal and a polymer and having a refractive index periodically changed therein.

The volume hologram optical film produced in this manner can have a larger difference in refractive index between layers than the volume hologram optical film produced without applying an external field. Liquid crystal molecules are aligned in a specific direction by applying an external field. The liquid crystal molecules forcibly oriented by this external field have some influence on the interface during polymerization of the polymer, and try to maintain the same orientation even if the external field is removed. It seems to give a change to. Normally, the external field may be applied only in one of the steps, but different external fields may be applied to both of the two steps so that different alignment states are obtained.

When the photopolymerizable composition is cured by the interference of light in the first step, the radically polymerizable organic compound is deposited by the polymerization. At that time, in the layer where polymerization has occurred, the remaining composition becomes liquid crystal excess, and the force to homogenize with the photopolymerization composition of the surrounding layer where polymerization does not occur works, and the polymer is relatively polymerized. Tends to have many layers. vice versa,
The remaining layer, which is cured when the whole is cured in the second step, tends to be a layer having a relatively small amount of polymer. This allows
It seems that the difference in refractive index between the layers becomes large.

When applying this external field, specifically, there is a method in which the photopolymerizable composition is sandwiched between substrates with electrodes and irradiated with light rays to be cured. More specifically, the photopolymerizable composition is supplied onto a substrate with electrodes, and another substrate with electrodes is stacked on it, or the periphery of a pair of substrates with electrodes is sealed to form a cell. There is a method of forming and injecting a photopolymerizable composition into the composition to sandwich and cure the composition. An electric field as an external field is applied using this electrode.

The volume hologram optical film with electrodes can usually change its hologram characteristics by applying an electric field between the electrodes during use after manufacture. In the case where the electric field is not applied during use, the volume hologram optical film may be sandwiched between the electrodes only when it is manufactured.

As the substrate with electrodes, ITO (In ₂ O ₃ -Sn
Transparent substrates such as glass with a transparent electrode such as O ₂ ), SnO ₂ and plastics can be used. As a matter of course, an active element such as a thin film transistor (TFT), a thin film diode, a metal insulator metal non-linear resistance element (MIM) is provided for each pixel electrode, or an opaque electrode such as a metal line is formed on the substrate. It may be a matrix substrate. Further, in applications such as a mirror, one electrode may be a reflective electrode, and the substrate may be an opaque substrate.

This volume hologram optical film diffracts by layers having different refractive indexes. In the present invention, when a quaternary ammonium cation having absorption from visible light to near infrared, which is conventionally difficult to initiate photopolymerization, is used, photopolymerization can be initiated at a wavelength from visible light to near infrared. For this reason, the pitch of the layers having different refractive indexes can be made large, so that the hologram characteristic can be generated in the wavelength range from visible light to near infrared.

In the present invention, the layers having different refractive indexes are laminated in this way. Ideally, this refractive index difference is such that the refractive index n ₁ rapidly changes to n ₂ between the two layers, but in an actual volume hologram optical film, the refractive index usually changes gradually. Therefore, the maximum value in the high refractive index layer is n ₁ , the minimum value in the low refractive index layer is n ₂ ,
The refractive index difference Δn is represented by Δn = n ₁ −n ₂ . In the present invention, this refractive index difference Δn is related to the diffraction efficiency and the half-value width of the diffracted light.
It is 0.02 or more, preferably 0.05 or more.

The number of the layers is determined by the desired diffraction efficiency, but is about 10 to 100 with a pitch (a layer having a high refractive index and a layer having a low refractive index are set as one pitch). When the refractive index difference Δn is about 0.2, the diffraction efficiency exceeds almost 90% by stacking 30 pitches. Refractive index difference Δ
When n is about 0.1, it is necessary to stack about 60 pitches in order to obtain the same diffraction efficiency.

In the present invention, this layer structure may be parallel to the film surface or may be inclined at a specific angle with respect to the film surface. When it is close to the film surface, it is a reflection type volume hologram, and when it is close to the film surface, it is a transmission type volume hologram.

This volume hologram optical film can reflect or transmit light in a specific wavelength range.
As one of the uses, there is a window in which the volume hologram optical film is attached to a glass plate or a plastic plate or is sandwiched between them. In particular, the volume hologram optical film of the present invention can also control the reflection and transmission of light in the long wavelength region of visible light and near infrared light. So, for example,
A window that reflects near-infrared light and transmits visible light can also be provided.

By using a volume hologram optical film with electrodes in which a volume hologram optical film is sandwiched between substrates with electrodes, light in a specific wavelength range is reflected or transmitted, and its reflection characteristic is determined by an electric field. Can be changed by. If this is used, it becomes a window that can change the reflection / transmission characteristics of light. Specifically, the electric field enables control such that near infrared light is reflected in summer but near infrared light is transmitted in winter.

[0031]

【Example】

Example 1 Acrylic photopolymerizable monomer and oligomer and the following formula (2)
A radical photoinitiator composed of a quaternary ammonium cation and a borate anion represented by N, N-dimethylaniline, polyvinyl butyral, N-vinylcarbazole,
2-Phenoxyethyl acrylate, tetrahydrofuran, and a nematic liquid crystal having a positive dielectric anisotropy with a refractive index anisotropy of 0.26 as a liquid crystal were mixed to obtain an uncured photopolymerized composition mixture. The ordinary refractive index (n _o ) of this liquid crystal was almost equal to the refractive index of the polymer after curing, and its mixing ratio was 40 wt% with respect to the whole. This mixed solution was cast on a glass plate.

[0032]

[Chemical 3]

As a light source for exposure, a near infrared semiconductor laser (wavelength 830 nm) was used as a light source, a beam expander was used to make parallel rays, and the rays were made into two rays using a mirror. The uncured liquid mixture cast on the glass plate was irradiated. Then, the whole was exposed to a halogen lamp light to complete the curing, and a volume hologram optical film was manufactured.

This volume hologram film had a reflectivity in the vicinity of 850 nm. When this volume hologram optical film was sandwiched between a pair of glass plates to form a window, it became a window that reflected near infrared rays and transmitted visible light.

Example 2 The mixed solution of Example 1 was cast on a glass plate with ITO,
Tetrahydrofuran evaporates and then another IT
Glass plates with O were superposed, and at the time of irradiation with a near infrared semiconductor laser, AC100V was applied between the electrodes to cure.

This volume hologram film had a reflectivity in the vicinity of 850 nm, and its reflection efficiency was slightly higher than that of Example 1. When this volume hologram optical film with electrodes was sandwiched between a pair of glass plates to form a window, it became a window that reflected near infrared rays and transmitted visible light. When AC100V was applied between the electrodes, the reflection ability of near infrared rays was significantly reduced.

[0037]

According to the present invention, the volume hologram film obtained is excellent in heat resistance and light resistance, and also has high sensitivity to red to near infrared light, and thus these demands have increased in recent years. It is suitable for the production of volume hologram films in the wavelength region of.

Further, since the liquid crystal is used together, reflection and transmission characteristics as a hologram can be improved by applying an external field such as an electric field in any of the curing steps.

Further, by using a volume hologram film with electrodes, depending on the state of application of an electric field between the electrodes,
It also has an advantage that the hologram characteristics can be changed.

The present invention can be applied in various ways within a range that does not impair the effects of the present invention.

Claims (5)

[Claims] 1. A photopolymerization composition comprising a photoradical polymerization initiator composed of a quaternary ammonium cation and a borate anion, an organic compound capable of radical polymerization and a liquid crystal as essential components, from two directions which are not in a straight line. A volume hologram optical film characterized by having a layer structure in which a light beam having a uniform phase is applied and a photopolymerization composition is cured by utilizing an interference effect of the two light beams, and a refractive index changes periodically. .. 2. A photopolymerizable composition comprising a photoradical polymerization initiator composed of a quaternary ammonium cation and a borate anion, an organic compound capable of radical polymerization and a liquid crystal as essential components from two directions which are not in a straight line. Applying light rays having the same phase, curing the photopolymerizable composition into a layer by utilizing the interference effect of these two light rays, and then completing the curing of the whole, and the refractive index changes periodically. A method for producing a volume hologram film having a layered structure. 3. The volume hologram optics according to claim 2, which has a layered structure composed of a liquid crystal and a polymer by applying different external fields in two curing steps, and the refractive index of which changes periodically within the liquid crystal and the polymer. A method for producing a volume hologram optical film, which comprises producing a film. 4. A volume hologram optical film with electrodes, wherein the volume hologram optical film according to claim 1 is sandwiched between electrodes, and the hologram characteristics are made variable by the applied state of an electric field between the electrodes. 5. A window characterized by using the volume hologram optical film according to claim 1 or the volume hologram optical film with an electrode according to claim 4.