JPH1123381A - Temperature detecting element and temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element which can be used repeatedly for detecting the temperature or temperature distribution over a wide range by adding at least two kinds of liquid crystal having different N/S transition points and at least two kinds of dichroic coloring matter having different colors to a liquid crystal/polymer compound film. SOLUTION: An appropriate quantity, e.g. 1-10 pts.wt., of azo based and perylene based dichroic coloring matters, for example, are mixed with 100 pts.wt. of smectic liquid crystal having different transition points between nematic phase (N) and smectic phase (S) and microcapsulated. The dichroic coloring matter for detecting the temperature based on the color at the time of coloring (color development) changes the colors to be combined depending on the N/S transition point of liquid crystal. The dispersion liquids of two kinds or more of microcapsulated liquid crystal thus produced are mixed by same weight and applied onto a PET conductive substrate. It is then dried to form a composite film of liquid crystal/polymer (PDLC) of about 10 μm thick which is then applied with a protective film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a temperature detecting element and a temperature detecting sensor comprising a liquid crystal / polymer composite film.

[0002]

2. Description of the Related Art The use of a color change (thermochromism) of a thermochromic substance as a means for detecting temperature has been conventionally performed in various fields. For example,
As a method using irreversible color change (color formation), a method using a thermosensitive dye, cobalt, chromium, nickel,
A method (thermal coating) using a salt or an organic complex of magnesium, iron or the like is known. This method has a wide temperature detection range, but has a drawback that it cannot be used repeatedly because it is irreversible. As a method utilizing reversible discoloration, there are ethylene derivatives substituted with condensed aromatic rings such as spiropyrans, bianthrone, and dixanthylene. There is a method utilizing the fact that the color develops when melted and turns colorless when solidified. However, in this method, the temperature detection range is limited.

[0003] Further, temperature and temperature distribution are also detected using liquid crystal. Cholesteric liquid crystals have a helical structure, and the helical pitch changes significantly depending on the temperature, and accordingly, the color of the liquid crystal also changes significantly. A liquid crystal temperature detecting device that detects a temperature or a temperature distribution utilizing such an effect is used. This temperature detection device using cholesteric liquid crystal has the advantages of being inexpensive, mass-produced, and easy to use, but may exhibit a hysteresis phenomenon in which different temperatures appear when the temperature rises and falls, resulting in measurement accuracy. , Reproducibility and stability.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to detect a temperature and a temperature distribution over a wide range, and to use the apparatus repeatedly. It is an object of the present invention to provide a novel temperature detecting method using a liquid crystal according to a principle different from the prior art.

[0005]

The above object is achieved by the present invention described below. That is, the present invention comprises a liquid crystal / polymer composite film in which liquid crystal particles are dispersed in a polymer matrix, a sheet in which a conductive substrate or a protective layer is sandwiched between two conductive substrates, and a composite film. Are a temperature detection element and a temperature detection sensor, characterized by containing at least two types of liquid crystals having different N / S transition temperatures and at least two types of dichroic dyes having different colors.

According to the present invention, the temperature to be detected is determined by detecting the temperature or temperature distribution of a device which is in a colorless and transparent state by applying a voltage to a liquid crystal particle / polymer composite film containing a dichroic dye. When exposed to an atmosphere in which the liquid crystal has a temperature lower than the temperature of the atmosphere, a liquid crystal having a transition temperature of N (nematic layer) / S (smectic layer) undergoes a phase transition. Color (coloring) with the dichroic dye, the temperature and temperature distribution of the atmosphere can be detected from the color of the coloring.

[0007]

Next, the present invention will be described in more detail with reference to preferred embodiments. A feature of the present invention is a liquid crystal / polymer composite film (PDLC film: Polymer Dispersed Liquid Crystal) in which liquid crystal particles are dispersed in a polymer matrix.
In the film, at least two kinds of liquid crystal materials having different N / S transition temperatures and at least two kinds of dichroic dyes having different colors are contained.

As the liquid crystal material used in the present invention, any of conventionally known nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, discotic liquid crystal and polymer liquid crystal can be used. A preferred liquid crystal is a smectic liquid crystal, and any smectic liquid crystal having a different transition temperature (N / S transition temperature) between the nematic phase (N) and the smectic phase (S) can be used. These smectic liquid crystals preferably have a wide temperature range showing a nematic phase, and in the present invention,
By using a smectic liquid crystal material having a nematic phase in a temperature range of 1 ° C. or more, the driving voltage required to make the liquid crystal / polymer composite film transparent can be reduced.

In order to detect the temperature with the color at the time of coloring (coloring), a dichroic dye is added to the smectic liquid crystal in an appropriate amount.
For example, 1 to 1 per 100 parts by weight of smectic liquid crystal
0 parts by weight are mixed. In that case, the dichroic dye contained in the liquid crystal is not particularly limited,
Any of azo type, perylene type, anthraquinone type and the like can be used. The point is to change the color of the dichroic dye to be combined according to the N / S transition temperature of the liquid crystal. That is, for example, a liquid crystal having an N / S transition temperature of 60 ° C. is combined with a yellow dichroic dye, and a liquid crystal having an N / S transition temperature of 70 ° C. is combined with a red dichroic dye.

As the polymer material forming the polymer matrix in which the liquid crystal particles are dispersed, any polymer material which is not compatible with the liquid crystal and which has excellent transparency and film-forming ability can be used. Specifically, an appropriate polymer material, for example, a polyvinyl alcohol resin, an epoxy resin, a fumarate resin, an acrylic resin, a polycarbonate resin, a UV-curable resin of polythiol, or the like is used according to the method of forming the composite film.

The liquid crystal containing a dichroic dye (hereinafter simply referred to as liquid crystal) is preferably used after being microencapsulated. Preferred examples of the microencapsulation include the following methods. That is,
A liquid crystal is emulsified and dispersed in an aqueous medium with a radical-reactive surfactant, a water-soluble protective colloid, or a radical-reactive protective colloid or a mixture of two or more of these, and a radical initiator is dissolved in water or the liquid crystal. Is dissolved or dispersed, and the temperature is raised to the decomposition temperature of the initiator, whereby a capsule wall film surrounding the liquid crystal particles can be produced.

Further, a liquid crystal in which a radical-reactive monomer is dissolved in an aqueous medium is emulsified and dispersed with a water-soluble protective colloid, and a radical initiator is dissolved or dispersed in water or in the liquid crystal. By raising the temperature to such a value, a capsule wall film surrounding the liquid crystal particles can be produced.

As the radical reactive surfactant, a commercially available ionic or nonionic reactive surfactant can be used. For example, sodium styrenesulfonate, polyethylene glycol diacrylate, polyprolene glycol polytetramethylene glycol and the like can be mentioned. Preferably, a bifunctional or more functional surfactant is mixed. Examples of the water-soluble protective colloid include partially saponified polyvinyl alcohol, hydroxyethyl cellulose, polyethylene glycol and the like.

The radical-reactive protective colloid is obtained by introducing a radical-reactive group into a side chain of a polymer having a hydrophilic group and a hydrophobic group, for example, an acryloyl group is added to a hydroxyl group of (partially saponified) polyvinyl alcohol. Any one having an addition-polymerizable double bond such as the introduced one can be used. As the radical polymerizable monomer to be dissolved in the liquid crystal, one having compatibility with the liquid crystal such as styrene, vinyl acetate, and (meth) acrylate can be used. Preferably, a mixture of two or more functional monomers is preferred.

As the polymerization initiator, any of water-soluble, oil-soluble and the like can be used. When raising the polymerization temperature does not hinder, a redox polymerization initiator may be used. It is also possible to initiate polymerization using ionizing radiation such as gamma rays or electron beams.

In the microencapsulated liquid crystal having the above structure, the polymer material used as a wall material is preferably used in a range of 5 to 25 parts by weight per 100 parts by weight of the core material smectic liquid crystal. If the amount of the wall material used is less than the above range, the problem of liquid crystal seeping out or the like cannot be sufficiently solved because the wall thickness is thin. On the other hand, if the amount used exceeds the above range, the wall thickness will be large,
Since the amount of dichroic dye incorporated into the wall increases and the wall is colored, it is not preferable in that the reflection density at the time of applying a voltage is not sufficiently low. The thickness of the wall in the encapsulated state varies depending on the liquid crystal material, the polymer material, the encapsulation method, and the like to be used.
It is about 0 nm.

As a method for forming and dispersing the liquid crystal particles in the polymer matrix, any conventionally known methods such as a phase separation method and an emulsion method can be used, but the most useful method is the emulsion method. The emulsion method will be described below as a typical example. However, the present invention is not limited to the emulsion method. In the emulsion method, the liquid crystal is emulsified and dispersed in a medium mainly composed of water containing a surfactant or a protective colloid as necessary, and polyvinyl alcohol, gelatin, an acrylic acid copolymer, a water-soluble alkyd resin A method of applying a water-soluble or water-dispersible polymer material such as, for example, on a suitable substrate and drying to form a film having a suitable thickness. A liquid crystal / polymer film in which liquid crystal particles are uniformly dispersed is formed.

As a method of emulsifying and dispersing the liquid crystal in an aqueous solution or aqueous dispersion of the molecular matrix, a mixing method using various stirring devices such as an ultrasonic dispersion method and a mechanical dispersion method, and a film emulsification method [Tadao Nakajima, Masataka Shimizu, PHARMTEC
H JAPAN Vol. 4, No. 10, No. (1988)] is effective. The particle diameter of the obtained liquid crystal emulsion particles is 1 μm in volume distribution so that the liquid crystal molecules are easily aligned in the matrix or the capsule.
It is desirable that the ratio of liquid crystal particles of m or less is 10% or less in all the particles. For example, when an O / W emulsion of liquid crystal is obtained by a porous glass (MPG) membrane emulsification system, the average pore diameter of the MPG used is 0.3 μm (diameter).
With the above, the volume distribution of the liquid crystal particles to be emulsified and dispersed can be set in the above range.

Further, a liquid crystal emulsion containing liquid crystal particles having a volume distribution within the above range can be obtained by using a mechanical dispersion method. For example, a liquid crystal emulsion containing liquid crystal particles having a volume distribution within the above range can be obtained by setting the mechanical dispersion conditions to 1,000 rpm and 1 minute or more.

From the liquid crystal particle dispersion thus obtained, P
As a method for forming a DLC film, a method of applying and drying the liquid crystal particle dispersion on a substrate is preferable. Examples of an application method include electrodeposition, screen coating, blade coating, knife coating, slide coating, and intrusion coating. And fountain coating. The thickness of the PDLC film thus obtained is preferably about 3 to 23 μm.

If the film thickness is too thin, scattering (turbidity) during heating
Is insufficient, and if the film thickness is too large, a large driving voltage is required. Therefore, the above film thickness range is preferable. Usually, the amount of the liquid crystal used is desirably a mixture ratio (weight ratio) of polymer matrix forming material / liquid crystal of 55/45 to 35/65. If the amount of the liquid crystal used is too small, not only is the transparency at the time of voltage application insufficient, but also a point that a large voltage is required to make the film transparent, and the liquid crystal is insufficient. If too much is used, not only is scattering (turbidity) at the time of temperature detection insufficient, but also the strength of the membrane is undesirably reduced.

The PDLC film of the present invention includes the following three types. (1) One layer of PDLC film formed from a mixture of liquid crystal and microcapsules containing dichroic dyes in different combinations and a polymer matrix forming material (see FIG. 1). Depending on the temperature range to be measured, the temperature interval, etc., or according to the purpose of use of the temperature detecting element such as detection of temperature unevenness,
It is preferable to appropriately increase the types of liquid crystals having different N / S transition temperatures. (2) At least two layers of PDLC film are laminated, and each PDL
The C film contains only a combination of liquid crystals having different N / S transition temperatures and dichroic dyes having different colors (for example, the first layer has an N / S transition temperature of 50 ° C.).
Only the microcapsules containing the liquid crystal and the dichroic dye emitting green color are contained, and the second layer contains only the liquid crystal having the N / S transition temperature of 60 ° C. and the microcapsules containing the dichroic dye emitting yellow color. As shown in FIG. 2, a PDLC film is sequentially laminated. It is preferable that the number of PDLC films to be laminated is appropriately increased according to the temperature range to be measured, the temperature interval, the purpose of use of the temperature detecting element, and the like. (3) Although the PDLC composite film is a single layer, the film surface is divided into a plurality of regions by patterning, and the composite film is formed such that each region contains liquid crystals having different N / S transition temperatures (FIG. 3). reference). In this case, the dichroic dyes contained in each region may be of the same color or of different colors. The temperature is detected from which region is colored or the color of the color. The number of regions is not particularly limited, and it is preferable to appropriately set the number, size, arrangement, and the like of the regions according to the purpose of use of the temperature detecting element such as detection of temperature unevenness.

When a voltage is applied to a sheet in which the PDLC film in the temperature sensing element of the present invention is sandwiched between two conductive substrates or a conductive substrate and a protective layer, the liquid crystal is oriented to become light transmissive, It becomes a transparent and colorless state. When the transparent and colorless temperature detecting element is exposed to an atmosphere for measuring the temperature, a liquid crystal having an N / S transition temperature below the temperature of the atmosphere undergoes a phase transition, and a portion of the PDLC film where this liquid crystal exists is present. Alternatively, the region or the layer in the laminated film develops a specific color tone (however, when the same dichroic dye is used, a specific region develops in the region). The temperature of the atmosphere is detected from the color tone or the coloration location. In the above (1) and (3), if the area of the temperature detecting element is increased, it is possible to detect temperature unevenness in the atmosphere. When a voltage is applied to the temperature detection element after the temperature detection, the liquid crystal is oriented again, and the element returns to a transparent and non-colored state and can be reused. The voltage application is performed using corona charging when there is only one upper and lower electrode substrate or one conductive substrate.

The conductive substrate on which the PDLC film is applied is a substrate generally used in a conventionally known liquid crystal display device, and is, for example, a transparent conductive material such as ITO, SnO ₂ , and ZnO. On a transparent substrate such as a polymer film such as PET (polyethylene terephthalate). On the other hand, in the case of an opaque conductive substrate, the electrode is also required to function as a reflector, and for example, a substrate provided with an aluminum reflective electrode is preferable. The substrate itself may be a polymer film or other. Also, a transparent conductive material such as ITO, SnO ₂ or ZnO may be attached to a reflection plate such as a white PET (polyethylene terephthalate) film. Also, Al ₂ O ₃ , on the surface of the transparent conductive substrate opposite to the liquid crystal / polymer composite film,
A reflection plate formed by forming a reflection layer made of TiO ₂ , ZnO, or the like on glass or a polymer film may be bonded.

P formed on a transparent or reflective conductive substrate
When the DLC film is sandwiched between conductive substrates, the DLC film is generally used for a conventionally known liquid crystal display device. For example, a transparent conductive material such as ITO, SnO ₂ , ZnO is made of PET. And an electrode substrate attached to a transparent substrate such as a polymer film.

P formed on a transparent or reflective conductive substrate
When the protective layer is formed on the surface of the DLC film, the polymer material for forming the protective layer has excellent adhesiveness to the PDLC film and can form a transparent film, and has a refractive index of Any polymer material can be used as long as the difference is 0.05 or less as compared with the refractive index of the matrix forming polymer material of the PDLC film. For example, when polyvinyl alcohol is used as the matrix-forming polymer material, a preferable protective layer-forming polymer material is
A crosslinked polymer composed of a polyfunctional monomer such as trimethylolpropane tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and pentaerythritol tetra (meth) acrylate is exemplified. These monomers can be used alone or as a mixture of two or more kinds, and further mixed with other monomers.

P formed on a transparent or reflective conductive substrate
As the protective layer formed on the surface of the DLC film, it is desirable that the surface of the protective layer is smooth and the difference between the refractive index of the protective layer and the refractive index of the polymer matrix is 0.05 or less. If the difference exceeds 0.05, the difference between the refractive index of the liquid crystal and the refractive index between the liquid crystal and the protective layer when a voltage is applied becomes large, so that light scattering is increased and the contrast is reduced. Furthermore, it is preferably 0.03 or less. Further, the average roughness (Ra) of the obtained protective layer is preferably less than 0.1 μm. When the average roughness is 0.1 μm or more,
Light is scattered on the surface of the protective layer, and the contrast is reduced.

As a method of forming the protective layer, a film is formed by polymerization in the same manner as the formation of the PDLC film as a solution in which the polymer material for forming the protective layer is dissolved in a solvent that does not dissolve the PDLC film or as an emulsion of a suitable medium. After applying the monomer to the PDLC film as described above, the monomer is converted into a polymer and cured by appropriate means (heating, electron beam irradiation, etc.). Separately, a method of forming a protective layer or a monomer layer, and transferring and laminating the protective layer or the monomer layer on the surface of the PDLC film (in the case of a monomer layer, polymerizing and curing at the time of transfer or after transfer) and the like can be mentioned. The thickness of the formed protective layer is preferably in the range of 1 to 5 μm.

The temperature detecting sensor according to the present invention comprises the temperature detecting element obtained as described above as a temperature detecting portion, and may have any structure as long as it can visually confirm the color or coloration of the color. Is not particularly limited. The temperature detection sensor can be used for temperature detection, temperature unevenness detection, and the like.

[0030]

Next, the present invention will be described more specifically with reference to examples. Example 1 (Production Example of Laminated PDLC Film) (1) 100 parts of smectic liquid crystal: 17215 (manufactured by Merck Japan, N / S phase transition temperature: 82 ° C.), dichroic dye: SI486 (yellow color / transparent) 2 parts) (manufactured by Mitsui Toatsu Chemicals) and stirred at a temperature of 120 ° C. for 30 minutes. To this mixed solution was added methyl methacrylate 11.6.
And 2,2'-azobisisobutyronitrile were added, and the mixture was stirred at room temperature for 4 hours. To this mixed solution, 252.8 parts of a 5% by weight aqueous solution of polyvinyl alcohol: EG-05 (manufactured by Nippon Synthetic Chemical Industry, degree of polymerization: 500, degree of saponification: 86.5 to 89.0) was added, and the pore diameter was 1.10 μm ( diameter)
Was dispersed by a membrane emulsification method using a porous glass membrane tube (manufactured by Ise Chemical Industry Co., Ltd.). Then, the mixture was left standing and polymerized at 70 ° C. for 6 hours under a nitrogen atmosphere to microencapsulate the liquid crystal.

In the same manner, (2) Smectic liquid crystal: S-5 (manufactured by Merck Japan, N / S phase transition temperature:
55 ° C.) / Dichroic dye: M86 (manufactured by Mitsui Toatsu Chemicals, red color / transparent dichroism), (3) smectic liquid crystal: 1
7855 (manufactured by Merck Japan, N / S phase transition temperature: 6
A dispersion of two types of liquid crystal microcapsules of 5 ° C.) / Dichroic dye M483 (manufactured by Mitsui Toatsu Chemicals, blue color / transparent dichroism) was prepared.

PVA: KH-20 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., polymerization degree: 2,000, saponification degree: 78.5 to 81.) as a thickener in each microencapsulated liquid crystal dispersion.
5) is calculated as follows: liquid crystal / (KP-06 + KH-20) = 50/5
0 (w / w) and stirred. Each of these dispersions (1) to (3) was applied in turn using a doctor blade on an ITO surface of an ITO-deposited white polyethylene terephthalate film (manufactured by Toray), dried, and a three-layer PDLC film was laminated. A film was formed. The thickness of each PDLC film was set to about 5 μm.

Release film made of polyethylene terephthalate: MC-19 (manufactured by Reiko Co., Ltd.) using a doctor blade to trimethylolpropane triacrylate: EXG-
40-8 (manufactured by Dainichi Seika), dried and dried
m was formed. After laminating this film surface with the composite film surface facing each other, irradiating it with 4 Mrad electron beam to polymerize and dry the acrylate, and then peeling off the release film, the film was smooth (average roughness: Ra). = 0.
01 μm).

The temperature detecting element thus obtained (FIG. 2)
To produce a sheet-shaped temperature detection sensor. When a voltage was applied to the temperature detection sensor by corona charging to make it transparent and no color was formed, and the temperature detection sensor was exposed to an atmosphere at 60 ° C., the laminated film emitted red light. After the temperature measurement, an electric field was applied again to return the temperature detection sensor to a transparent and colorless state. This time, when the temperature detection sensor was exposed to an atmosphere of 70 ° C., the laminated film developed a purple color.

Example 2 (One layer of PDLC film: mixing microencapsulated liquid crystal) The dispersions of the three kinds of microencapsulated liquid crystals obtained in Example 1 were mixed with the same weight, and this mixed liquid was used in Example. Apply and dry on a PET conductive substrate in the same manner as in Step 1 to obtain a film thickness of about 10 μm.
Was formed, and a protective layer was formed on the film surface. The temperature sensing element thus obtained (see FIG. 1)
Was used to prepare a sheet-shaped temperature detection sensor, and the temperature was measured in an atmosphere of 60 ° C. in the same manner as in Example 1.
A red color was formed in a spot-like manner, and the result of Example 1 was reproduced. After further applying an electric field, the atmosphere (70
When the temperature was measured at (° C.), a purple color was formed in spots.

Example 3 (One-layer PDLC film: patterning) The dispersion liquid of three kinds of microencapsulated liquid crystals obtained in Example 1 was used to form a pattern as shown in FIG. 3 on the PET conductive substrate of Example 1. Pattern printing was performed. After an electric field was applied to the temperature detection sensor to make it transparent and colorless, the temperature was measured in an atmosphere of 60 ° C. in the same manner as in Example 1. Only the layer (3) in FIG. Emit red light. Further, after applying an electric field, the temperature was measured in an atmosphere (70 ° C.) different from the above. As a result, the (2) layer portion in FIG. 3 was colored blue and the (3) layer portion was colored red.

Further, as shown in FIG. 4, unevenness in temperature was detected on the heating element by using the sheet-shaped temperature detecting sensors prepared in Examples 1 and 2. In the case of using any of the temperature detection sensors of Examples 1 and 2, as shown in FIG.
The part at 65 ° C. or higher developed purple color.

[0038]

According to the present invention as described above, the temperature to be measured is detected by the color of the liquid crystal in the PDLC film accompanying the N / S transition. In a temperature detecting element composed of a single PDLC film, a large number of microcapsules having different combinations of N / S transition temperatures and dichroic dyes are randomly dispersed in the film surface, or patterning is performed. By making it fine and random, temperature unevenness in the measurement atmosphere can be detected.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a temperature detection sensor used in a second embodiment.

FIG. 2 is a diagram illustrating a temperature detection sensor used in the first embodiment.

FIG. 3 is a diagram illustrating a temperature detection sensor used in a third embodiment.

FIG. 4 is a diagram illustrating an example of detecting temperature unevenness of the temperature detection sensor according to the present invention.

Claims (7)

[Claims] 1. A liquid crystal / polymer composite film in which liquid crystal particles are dispersed in a polymer matrix, comprising two conductive substrates or a sheet sandwiched between a conductive substrate and a protective layer,
A temperature detecting element, wherein the composite film contains at least two types of liquid crystals having different N / S transition temperatures and at least two types of dichroic dyes having different colors. 2. The composite film is a laminated film of at least two layers,
The temperature detecting element according to claim 1, wherein each of the composite films includes a liquid crystal having a different N / S transition temperature and a dichroic dye having a different color. 3. The temperature detecting element according to claim 1, wherein the composite film is patterned into at least two regions, and each region contains a liquid crystal having a different N / S transition temperature and a dichroic dye having a different color. 4. The temperature detecting element according to claim 3, wherein dichroic dyes of the same color tone are used instead of dichroic dyes of different colors. 5. The liquid crystal according to claim 1, wherein the liquid crystal is a smectic liquid crystal.
The temperature detection element according to any one of claims 1 to 4. 6. The temperature detecting element according to claim 1, wherein the liquid crystal particles are microencapsulated together with a dichroic dye. 7. A temperature detection sensor comprising the temperature detection element according to claim 1 as a temperature detection section.